Image forming apparatus

Abstract

To set an appropriate fixing temperature according to a change in a plurality of toners to reduce a failure in fixing, even if an image is formed by layering the toners on a recording material.SOLUTION: An image forming apparatus P comprises: a plurality of developing devices 7 for forming toner images; primary transfer rollers 10 that sequentially transfer the toner images onto a recording material S, and forms toners on the recording material S in a layered manner; a fixing device F1 that applies heat and pressure to the recording material S to which the toner images are transferred to fix the toner images onto the recording material S; a memory 40 that stores use history values of the developing devices 7; and a control unit 31 that controls the fixing temperature of the fixing device F1. The control unit 31 determines the fixing temperature according to the difference ΔL between the use history values L stored in the memory 40.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, for example, an image forming apparatus provided with a fixing unit that fixes a toner image formed by an electrophotographic process onto a transfer material by a thermal fixing unit. [Background technology]

[0002] Conventionally, in an image forming apparatus using an electrophotographic process, a developing device is provided that supplies a developer to an electrostatic latent image formed on the surface of an image carrier by scanning and exposing the image carrier, and develops the electrostatic latent image into a developer image. The developing device is provided with a developer carrier that carries the developer, a developer container that contains the developer, and the like, and is configured to electrostatically supply the developer carried on the surface of the developer carrier to the surface of the image carrier. In recent years, it is often the case that the developing device is housed together with the image carrier and other process means (charging members, etc.) as a process cartridge.

[0003] The developer image developed on the image carrier is transferred onto a recording material, and then passes through a fixing device serving as an image heating device, whereby the toner image is fixed (bonded) onto the recording material. Contact-type heat fixing devices are widely used as fixing devices. For example, this type of fixing device forms a fixing nip section with a fixing member that is heated to a predetermined fixing temperature by a heating member, and a pressure member disposed opposite to the fixing member. The fixing device fixes the unfixed toner image formed on the recording material as a fixed image by applying heat and pressure in the fixing nip section.

[0004] When an image forming apparatus and a developing device are used, the toner characteristics in the developing container change due to thermal and mechanical stress. In addition, changes occur in the developability and the melting characteristics of the developing material, and the appropriate fixing temperature when fixing in the fixing device changes. Conventionally, as a means for dealing with changes in the developing material, it has been proposed to change the fixing temperature depending on the usage history of the developing device (for example, see Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 3246942 [Patent Document 2] JP 2011-203721 A [Patent Document 3] JP 2012-194447 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, an image forming apparatus that can form a full-color image with multiple toners on a sheet of paper is equipped with multiple developing devices, and the usage history of each developing device may differ. In addition, in the case of an image formed on a recording material in multiple layers, the appropriate fixing temperature is not simply determined in proportion to the usage history of the developing device. It is known that the appropriate fixing temperature also changes depending on the relative relationship between the toner characteristics of the upper and lower layers of toner superimposed on the recording material. Conventionally, it has not been possible to set a fixing temperature according to the change in the characteristics of each toner, taking into account the relationship between the top and bottom of the toners formed in multiple layers on the recording material.

[0007] The present invention has been made under these circumstances, and aims to reduce fixing defects by setting an appropriate fixing temperature in accordance with the changes in each toner, even in images in which multiple toners are multiplexed on a recording material. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0009] (1) An image forming apparatus comprising a plurality of developing means for forming a toner image, a transfer means for sequentially transferring the toner images onto a recording material and forming multiple layers of toner on the recording material, a fixing means for pressurizing and heating the recording material onto which the toner image has been transferred, thereby fixing the toner image onto the recording material, a storage medium for storing a usage history of the developing means, and a control means for controlling a fixing temperature of the fixing means, wherein the control means determines the fixing temperature in accordance with the difference between the usage history of one of the developing means and the usage history of the other of the developing means, which are stored in the storage medium. Effect of the Invention

[0010] According to the present invention, even in an image in which a plurality of toners are multiplexed and formed on a recording material, an appropriate fixing temperature can be set according to the changes in each toner, thereby reducing fixing defects. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram for explaining a schematic configuration of an image forming apparatus according to first to third embodiments; [Diagram 2] FIG. 1 is a diagram illustrating a cross-sectional configuration of a fixing device according to first to third embodiments; [Diagram 3] FIG. 1 is a diagram illustrating a memory and a communication unit of a process cartridge according to first to third embodiments. [Figure 4] FIG. 1 is a schematic diagram showing an example of a toner layer heated in a fixing nip portion in Example 1; [Diagram 5] Flowchart for explaining a fixing temperature determination method according to the first embodiment [Figure 6] FIG. 13 is a diagram for explaining an image processing unit according to the second embodiment. [Figure 7] 11 is a flowchart for explaining image data processing according to the second embodiment. [Figure 8] Flowchart for explaining a fixing temperature determination method according to the second embodiment [Figure 9] Flowchart for explaining a fixing temperature determination method according to the third embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. EXAMPLES

[0013] (Image forming device) An image forming apparatus according to a first embodiment will be described below. FIG. 1 shows an image forming apparatus P according to a first embodiment, which includes four image forming stations 3Y, 3M, 3C, and 3K arranged in a substantially straight line. Of the four image forming stations 3Y, 3M, 3C, and 3K, 3Y is an image forming station that forms a yellow (hereinafter abbreviated as Y) image. 3M is an image forming station that forms a magenta (hereinafter abbreviated as M) image. 3C is an image forming station that forms a cyan (hereinafter abbreviated as C) image. 3K is an image forming station that forms a black (hereinafter abbreviated as K) image.

[0014] Each of the image forming stations 3Y, 3M, 3C, and 3K has a drum-type electrophotographic photosensitive member (hereinafter referred to as photosensitive drum) 4Y, 4M, 4C, and 4K as an image carrier, and a charging roller 5Y, 5M, 5C, and 5K as a charging means. Each of the image forming stations 3Y, 3M, 3C, and 3K also has an exposure device 6 as an exposure means, a developing device 7Y, 7M, 7C, and 7K as a developing means, and a cleaning device 8Y, 8M, 8C, and 8K as a cleaning means. In the following description, when the description is common to each of the stations 3Y, 3M, 3C, and 3K, the notations Y, M, C, and K such as the photosensitive drum 4, the charging roller 5, and the developing device 7 will be omitted.

[0015] In the first embodiment, the photosensitive drum 4, the charging roller 5, and the developing device 7 are integrated as a process cartridge 2 (see FIG. 3), and are configured to be detachably attached to the main body of the image forming apparatus P (the portion of the image forming apparatus P excluding the process cartridge 2). However, the process cartridge 2 in the present invention may be one that includes at least the photosensitive drum 4 and the developing device 7, and is configured to be detachably attached to the main body of the apparatus as a whole. Also, the developing device 7 may be configured to be detachably attached to the main body of the apparatus or the process cartridge 2 by itself. Also, the photosensitive drum 4 and the developing device 7 may be fixed to the main body of the image forming apparatus, eliminating the need for replacement by the user.

[0016] The photosensitive drum 4 is a cylindrical photosensitive body that rotates around its axis in the counterclockwise direction of the arrow. The surface of the photosensitive drum 4 is uniformly charged by the charging roller 5. In the first embodiment, the charging roller 5 is a conductive roller having a conductive rubber layer on a metal core, and is disposed in parallel to the photosensitive drum 4 in contact with it at a predetermined pressure, and rotates in response to the rotation of the photosensitive drum 4.

[0017] In the first embodiment, the developing device 7 is a contact development type reversal developing device containing toner as a one-component developer having a normal negative charging polarity (charging polarity for developing an electrostatic latent image). The developing device 7 is provided with a developing roller 71 as a developer carrier (rotating body), a toner supply roller 72, and a regulating blade 73 as a developer regulating member. The toner supply roller 72 is an elastic sponge roller formed with a foam on the outer periphery of a conductive core metal. The toner supply roller 72 is disposed so as to come into contact with the developing roller 71 with a predetermined penetration amount.

[0018] (Image formation operation) Based on information received from an external device (not shown) such as a host computer, the video controller 30 performs processes such as bitmapping character codes and halftoning using dithering of halftone images. The video controller 30 transmits a print signal and image information to a control section (also a heating control section) 31 as a control means. When the image information is received, an image forming operation is started. When forming an image, the photosensitive drum 4Y is rotated in the direction of the arrow in the image forming station 3Y. First, the outer peripheral surface (surface) of the photosensitive drum 4Y is uniformly charged by a charging roller 5Y, and the charged surface of the photosensitive drum 4Y is exposed by irradiating it with laser light according to image data by an exposure device 6, forming an electrostatic latent image.

[0019] The developing device 7Y supplies toner to the electrostatic latent image on the photosensitive drum 4Y to visualize it as a toner image. The toner supplied by the toner supply roller 72Y and held on the developing roller 71Y is thinned by the regulating blade 73 and is used for development. The regulating blade 73Y has a function of regulating the thickness of the toner layer on the developing roller 71Y, and also has a function as a developer charging means that imparts a predetermined charge to the toner on the developing roller 71Y.

[0020] The developing roller 71Y is rotated in the direction of the arrow in FIG. 1, so that the surface of the developing roller 71Y moves in the same direction as the photosensitive drum 4Y. In the first embodiment, the developing roller 71Y is rotated at a speed where the surface of the developing roller 71Y moves at 140% of the surface of the photosensitive drum 4 in order to obtain an appropriate image density. The developing device 7Y is pressed against the photosensitive drum 4Y by a biasing means (not shown), and as a result, the developing roller 71Y is pressed against the photosensitive drum 4Y. This causes the surface of the developing roller 71Y to deform, forming a development nip portion, thereby enabling stable development in a stable contact state. In this way, the developing device 7Y forms a Y toner image on the surface of the photosensitive drum 4Y. The same image forming process is also performed in the image forming stations 3M, 3C, and 3K. As a result, an M toner image is formed on the surface of the photosensitive drum 4M, a C toner image is formed on the surface of the photosensitive drum 4C, and a K toner image is formed on the surface of the photosensitive drum 4K.

[0021] An endless intermediate transfer belt 9 is provided along the arrangement direction of the image forming stations 3Y, 3M, 3C, and 3K and is stretched around a drive roller 9a, a driven roller 9b, and a driven roller 9c. The drive roller 9a rotates in the direction of the arrow in Fig. 1. This causes the intermediate transfer belt 9 to rotate along each of the image forming stations 3Y, 3M, 3C, and 3K at a speed of 100 mm / sec.

[0022] Toner images of each color are transferred in sequence onto the outer circumferential surface (surface) of the intermediate transfer belt 9 by primary transfer rollers 10Y, 10M, 10C, and 10K as primary transfer means disposed opposite the photosensitive drums 4Y, 4M, 4C, and 4K with the intermediate transfer belt 9 in between. As a result, a full-color toner image of four colors is formed on the surface of the intermediate transfer belt 9.

[0023] Toner remaining on the surfaces of the photosensitive drums 4Y, 4M, 4C, and 4K after the primary transfer (hereinafter referred to as transfer residual toner) is removed by cleaning blades (not shown) provided in the cleaning devices 8Y, 8M, 8C, and 8K, thereby preparing the photosensitive drums 4Y, 4M, 4C, and 4K for the next image formation.

[0024] Meanwhile, recording materials S stored in a feed cassette 11 provided at the bottom of the main body of the image forming apparatus P are separated and fed one by one from the feed cassette 11 by a feed roller 12, and fed to a pair of registration rollers 13. The pair of registration rollers 13 sends the fed recording materials S to a transfer nip portion between the intermediate transfer belt 9 and a secondary transfer roller 14.

[0025] The secondary transfer roller 14 is disposed so as to face the driven roller 9b with the intermediate transfer belt 9 interposed therebetween. When the recording material S passes through the transfer nip portion, a voltage is applied to the secondary transfer roller 14 from a high voltage power source (not shown). As a result, a full-color toner image is secondarily transferred from the surface of the intermediate transfer belt 9 onto the recording material S passing through the transfer nip portion. Here, the above-mentioned photosensitive drum 4, intermediate transfer belt 9, secondary transfer roller 14, etc. constitute an image forming unit.

[0026] The recording material S carrying the toner image is then conveyed to a fixing device F1 as a fixing means. The recording material S is heated and pressurized as it passes through the fixing device F1, and the unfixed toner image is heat-fixed (fixed) onto the recording material S. The recording material S is then discharged from the fixing device F1 to a discharge tray 15 outside the image forming apparatus (printer) P. Residual toner remaining on the surface of the intermediate transfer belt 9 after the secondary transfer is removed by an intermediate transfer belt cleaning device 16. This prepares the intermediate transfer belt 9 for the next image formation.

[0027] (Fixing device (fixing section)) Next, the fixing device (fixing section) F1 that fixes the toner image will be described. In the following description, with respect to the fixing device F1 and the members that constitute the fixing device F1, the longitudinal direction is the direction perpendicular to the conveying direction Dr of the recording material S (see FIG. 2) on the surface of the recording material S. The transverse direction is the direction parallel to the conveying direction Dr of the recording material S on the surface of the recording material S. The width is the dimension in the transverse direction. With respect to the recording material S, the longitudinal width is the dimension in the direction perpendicular to the conveying direction Dr of the recording material S on the surface of the recording material S.

[0028] 2 is a schematic cross-sectional view of the fixing device F1. The fixing device F1 rotates and drives a pressure roller 21 as an opposing body (pressure body) that faces the fixing film 22 and forms a nip portion that sandwiches and conveys the recording material S together with the fixing film 22 under pressure, and rotates the fixing film 22 by the conveying force of the pressure roller 21. That is, the fixing device F1 is a so-called tensionless type device of a so-called film heating type and pressure roller driving type.

[0029] The fixing device F1 shown in the first embodiment includes a pressure roller (pressure member) 21, a fixing film (fixing member) 22, a heater (heating member) 23, a heater holder (heating member holding member) 24, and a rigid stay (rigid member) 25. The pressure roller 21, the fixing film 22, the heater 23, the heater holder 24, and the rigid stay 25 are all elongated members extending in the longitudinal direction.

[0030] The heater 23 has a ceramic substrate 231 that is elongated in the longitudinal direction and has heat resistance, insulating properties, and good thermal conductivity. A resistance heating element (not shown) is formed along the longitudinal direction at the center of the short side of the front side (the pressure roller 21 side) of the substrate 231. Power supply electrodes (not shown) for supplying power to the resistance heating element are provided on the inside of both ends in the longitudinal direction of the substrate 231. A heat-resistant overcoat layer 232 is provided on the front side of the substrate 231 so as to cover the surface of the resistance heating element (not shown).

[0031] The fixing film 22 is formed in a cylindrical shape from a flexible heat-resistant resin material. The peripheral length of the fixing film 22 is 57 mm. The fixing film 22 has a cylindrical base layer 221, which is a polyimide layer having a thickness of 50 microns, and an elastic layer 222 made of silicone rubber having a thickness of 200 microns on the outer periphery of the base layer 221. The elastic layer 222 has a release layer 223 made of fluorine resin having a thickness of 15 microns on the outer periphery, which provides non-adhesiveness to toner.

[0032] The inner circumferential length of the fixing film 22 is 3 mm larger than the outer circumferential length of the heater holder 24 that holds the heater 23. The fixing film 22 is loosely fitted onto the heater holder 24 that holds the heater 23 with some margin in the circumferential length. In other words, the fixing film 22 contains the heater 23. The rigid stay 25 is made of a rigid member having a downward U-shaped cross section. The rigid stay 25 is disposed in the center of the upper surface of the heater holder 24 in the short direction.

[0033] 2, the pressure roller 21 has a round shaft-shaped core 211, an elastic layer 212 made of silicone rubber formed concentrically around the outer periphery of the core 211, and a release layer 213 made of conductive fluororesin around the elastic layer 212. The outer periphery of the pressure roller 21 is 63 mm. The elastic layer 212 may be formed by foaming heat-resistant rubber such as fluororubber or silicone rubber. The release layer 213 may be made of insulating fluororesin.

[0034] The pressure roller 21 is disposed below and in parallel with the fixing film 22, and both longitudinal ends of the core metal 211 are rotatably held via bearing members. The core metal 211 and the rigid stay 25 of the pressure roller 21 are pressurized by a pressure spring (not shown) at both longitudinal ends so that the outer circumferential surface (surface) of the pressure roller 21 and the outer circumferential surface (surface) of the fixing film 22 come into contact with each other. The pressure brings the surface of the pressure roller 21 into contact with the surface of the fixing film 22, forming a fixing nip portion NF of a predetermined width between the surface of the pressure roller 21 and the surface of the fixing film 22, which sandwiches and conveys the recording material S. The total pressure of the pressure is 20 kgf.

[0035] The fixing operation of the fixing device F1 will be described with reference to Fig. 2 and parts of Figs. 1 and 3. In response to a print command, the pressure roller 21 is rotated in the direction of the arrow by a rotation control unit (drive control means) (not shown) at a predetermined process speed. The fixing film 22 is rotated in the direction of the arrow around the outer periphery of the heater holder 24 while the inner periphery of the fixing film 22 slides closely against the heater 23 due to frictional force with the surface of the pressure roller 21 at the fixing nip NF. In addition, the control unit 31 functioning as a power supply control means (temperature control unit, heating control unit) supplies power to the resistance heating element of the heater 23 in response to the print command. The heater 23 rises in temperature due to the power supply, and heats the fixing film 22.

[0036] The temperature of the heater 23 is detected by a temperature detection element 26 serving as a temperature detection means such as a thermistor provided on the rear side of a substrate 231 of the heater 23. The control unit 31 controls the power supply to the resistance heating element based on an output signal from the temperature detection element 26 so that the heater 23 maintains a predetermined temperature (heating temperature controlled by heating) T. This allows the fixing nip portion NF to be maintained at the predetermined temperature T.

[0037] The recording material S carrying the unfixed toner image t is introduced into the fixing nip portion NF through the fixing entrance guide 27, and is nipped and conveyed between the surface of the pressure roller 21 and the fixing film 22. During the conveying process, the heat and pressure of the fixing film 22 are applied to the recording material S, and the unfixed toner image t is heated and fixed to the surface of the recording material S.

[0038] As described above, the toner image t is formed in the order of Y, M, C, and K according to the arrangement order of the image forming stations 3, and is superimposed on the intermediate transfer belt 9 in the order of Y from the belt side, followed by M, C, and K. When the toner images t are transferred sequentially to the recording material S (secondary transfer), the toner images t secondarily transferred to the recording material S become an image formed by superimposing K, C, M, and Y from the recording material S side. When the image with all four colors superimposed is sent to the fixing device F1, the Y toner formed at the first image forming station is formed on the fixing film 22 side. Then, it comes into contact with the fixing film 22, and the K toner formed at the fourth image forming station is formed on the recording material S side and the pressure roller 21 side, and comes into contact with the recording material S.

[0039] (Process cartridge memory) 3 is a diagram for explaining the memory and communication unit of the process cartridge 2 in the first embodiment. Memories 40Y, 40M, 40C, and 40K serving as storage media are provided on the frame surfaces of the process cartridges 2Y, 2M, 2C, and 2K, respectively, Y, M, C, and K. Communication units 41Y, 41M, 41C, and 41K for transmitting and receiving signals to and from the memories 40Y, 40M, 40C, and 40K are provided on the main body side of the image forming apparatus P. Information can be written to and read from the memory 40 via the communication unit 41 from the control unit 31 provided in the image forming apparatus P.

[0040] In the first embodiment, "usage history values" LY, LM, LC, and LK, which change according to the use of the developing devices 7Y, 7M, 7C, and 7K from the initial use, are written and stored in the memories 40Y, 40M, 40C, and 40K as needed. In the first embodiment, the "usage history value" L is the total travel distance of the developing roller 71. The control unit 31 calculates the distance traveled by the surface of the developing roller 71 from the circumferential speed of the surface of the developing roller 71 and the rotation time, and calculates the total travel distance by integrating this from the initial use of the process cartridge 2 (when use began), and writes this into the memory 40. A "usage history value" of 1 is written per 1 meter of the total travel distance.

[0041] In the developing device 7 of the process cartridge 2, the toner supplied by the toner supply roller 72 and held on the developing roller 71 rubs against the regulating blade 73. In addition, since the surface of the developing roller 71 is rotated at a speed different from that of the surface of the photosensitive drum 4, the toner held on the developing roller 71 also rubs against the photosensitive drum 4. As the total travel distance of the developing roller 71 increases, the number of times and the distance over which the toner is subjected to mechanical stress due to rubbing increases.

[0042] The "usage history value" L may be, for example, an integrated value of the rotation time, number of rotations, and rotation distance of each unit such as the photosensitive drum 4 and the developing roller 71. It may also be the remaining amount of toner or the number of printed pages. Furthermore, it may be the temperature and humidity environment in which the process cartridge 2 operates, the resistance value of each member of the printer 1 that changes depending on the temperature and humidity, the remaining amount of toner (remaining amount of developer) contained in the developing device 7, etc.

[0043] Furthermore, these parameters may be combined, or specific parameters may be weighted and then combined. In other words, the type of the "usage history value" is not particularly limited as long as it is a parameter that can be read by control unit 31 via communication unit 41 and that changes depending on the use of developing device 7 from the initial use.

[0044] In addition, in the first embodiment, the developing device 7 is held in the process cartridge 2, but the present invention is an invention for a phenomenon that occurs when the developability changes with the change in the usage history value of the developing device 7. Therefore, the present invention can be applied to image forming apparatuses other than those using a process cartridge, and for example, even if the configuration is such that toner is replenished, it is possible to obtain the same effect as in the first embodiment as long as the configuration is such that the developability changes with the change in the usage history value of the developing device 7.

[0045] (toner) The toner in the first embodiment is configured such that the surface of a toner matrix made mainly of a thermoplastic resin is coated (adhered) with non-melting particles having a higher melting point than the thermoplastic resin on the outside of the toner. The toner matrix may contain coloring material, wax, charge control agent, etc. It may also contain magnetic material, etc.

[0046] The temperature of the toner on the recording material S in the fixing process is approximately 70° C. to 150° C. Here, in this temperature range, the part that exhibits adhesion is referred to as a meltable toner base, and the part that does not exhibit adhesion or has adhesion sufficiently lower than that of the toner base is referred to as a non-melt material.

[0047] The particles on the toner surface are provided as a means for improving fluidity, charging properties, and transferability. Means for attaching particles to the toner surface include attaching by shearing force in a post-process, chemically bonding, and forming as part of the surface layer. For convenience, all of the particles attached to the toner surface and formed particulate matter are referred to as external additives here. Non-melting substances such as silica and silicon compounds are often used as external additives, and non-melting substances affect fixing performance.

[0048] If the toner surface is covered with a large amount of non-melt material, the real contact area of ​​the toner matrix with the recording material S surface or the fixing film 22 surface in the fixing process is reduced. Here, the ratio of the toner surface covered with non-melt material is referred to as the coverage rate. The real contact area here refers to the contact area between the meltable toner matrix and the surface of a member such as the recording material S or the fixing film 22 in the fixing process, excluding the portion covered with non-melt material. If the real contact area is small, the toner matrix does not adhere to the surface of the mating member, and the adhesion and adhesive force are reduced. In the first embodiment, a method for determining an appropriate fixing temperature is provided for a toner having a configuration in which the surface of the toner matrix is ​​covered with an external additive containing a non-melt material, and the coverage rate of the non-melt material decreases as the use history of the process cartridge 2 increases.

[0049] In the case where the external additive is fixed and highly coated from the time of manufacture, the coverage rate tends to decrease as the history of use of the process cartridge 2 increases. For example, there are external additives in the form of hemispheres chemically formed on the surface of the toner matrix, external additives semi-embedded, and external additives chemically bonded. These external additives are difficult to embed in the surface of the matrix, but due to their large particle size, they are easily peeled off by mechanical stress in the developing container. In addition, these external additives have a high function of preventing contact with other members, so the impact of a decrease in coverage rate is large.

[0050] (Poor Fixation and Its Mechanism) In the fixing process, when the toner on the recording material S is heated and fixed in the fixing nip NF and discharged from the fixing nip NF, the adhesive force between the recording material S and the toner may be insufficient, and the adhesive force between the fixing film 22 and the toner may exceed the adhesive force. When this happens, the toner on the recording material S is transferred to the fixing film 22, causing a fixing failure. The adhesive force between the toner and the surface of the fixing film 22 and between the toner and the surface of the recording material S can be considered in terms of the following two factors. Overall adhesive force = adhesive force generated per unit contact area x actual contact area

[0051] The adhesive force generated per unit contact area is determined by the surface properties of the member surface material and the chemical releasability. The surface of the fixing film 22 in the first embodiment is made of a material that is smooth and has low non-adhesive surface energy. On the other hand, the recording material S is paper made of fibers and fillers, and is not non-adhesive and has large irregularities. Therefore, the adhesive force generated per unit contact area between the toner and the recording material S is larger than that of the fixing film 22.

[0052] The main parameters of the real contact area are the coverage of the non-melted matter on the toner, the viscoelastic temperature characteristics of the toner, and the temperature of the toner. The viscoelastic temperature characteristics of the toner are the degree to which the toner melts and its viscoelasticity changes depending on the temperature. If the coverage of the non-melted matter is low, the real contact area will be large, and if the toner base melts and deforms, it will be easier to adhere to the target object, and the real contact area will be large.

[0053] In a full-color image forming apparatus that forms a plurality of toners in multiple layers, two or more layers of toner are laminated on the recording material S, and in the fixing nip portion NF, the toner in contact with the fixing film 22 and the toner in contact with the recording material S may be different. Fig. 4(a) is a schematic diagram showing an example of a toner layer heated in the fixing nip portion NF. Due to the difference between the toner T22 (Tt) in contact with the fixing film 22 and the toner TS (Tt) in contact with the recording material S, the temperature difference, etc., a difference may occur between the real contact area between the fixing film 22 and the toner T22 and the real contact area between the recording material S and the toner TS.

[0054] The adhesive force generated per unit contact area between the fixing film 22 and the recording material S is small on the fixing film 22 side, but poor fixing occurs if there is a large difference in the actual contact area between the fixing film 22 and the recording material S. In such a case, it is necessary to increase the fixing temperature and increase the amount of melting and deformation of the toner.

[0055] When the fixing temperature is raised and more heat is applied to the toner, both the toner in contact with the fixing film 22 and the toner in contact with the recording material S melt and deform. However, the adhesive force on the recording material S side, which has a large adhesive force per unit contact area, increases significantly, but the increase in adhesive force on the fixing film 22 side, which has a small adhesive force per unit contact area, is small. In addition, since there is a geometric limit to the melt deformation, the toner tends to saturate after a certain deformation. At a certain temperature, the adhesive force on the recording material S side exceeds that on the fixing film 22 side, and fixing can be achieved without poor fixing.

[0056] However, if the conditions are such that the real contact area between the toner and the fixing film 22 is likely to be larger than the real contact area between the toner and the recording material S, the required fixing temperature will be higher. If the conditions are such that the real contact area between the toner and the fixing film 22 is unlikely to be larger than the real contact area between the toner and the recording material S, the required fixing temperature will be lower.

[0057] In a full-color image forming apparatus that forms multiple toner images, the toner in contact with the fixing film 22 and the toner in contact with the recording material S are different, and the coverage rate of the non-melted material and the viscoelastic temperature characteristics of the toner may differ. The coverage rate of the non-melted material also changes depending on the usage conditions of the process cartridge 2. This is because the stress applied to the toner in the developing device 7 causes non-melted material such as external additives to peel off, decreasing the coverage rate.

[0058] Since the amount of toner consumed by each image forming station 3 varies depending on the image to be output, the timing of replacement of each process cartridge 2 may also differ depending on the image forming station 3. The usage history of each process cartridge 2 also differs depending on the image forming station 3.

[0059] A decrease in the coverage of the non-melted toner leads to an increase in the actual contact area with the fixing film 22, which is a change that leads to poor fixing. A decrease in the coverage of the non-melted toner in contact with the recording material S leads to an increase in the actual contact area with the recording material S, which is a change that leads to suppression of poor fixing.

[0060] (Experiment 1) An experiment was conducted to confirm the change in the fixing temperature at which fixing can be performed without fixing failure, depending on the usage history value L of the process cartridge 2 that supplies the toner that comes into contact with the fixing film 22 side, and the usage history value L of the process cartridge 2 that supplies the toner that comes into contact with the recording material S side. The usage history value L is the total travel distance of the developing roller 71. The process speed of the image forming device used in the experiment was 100 mm / s, and the interval (paper interval) between the preceding recording material S and the next recording material S was 30 mm. The experiment was conducted with the image forming device set up in an environment with an environmental temperature of 23°C and a humidity of 50%. For the experiment, general LBP printing paper with a basis weight of 80 g / m was used. 2 ,LTR size paper (width 216mm length 279mm) was used.

[0061] The fixability evaluation image used in the evaluation is a secondary color solid image in which 100% Y toner is layered on 100% M toner. The M toner contacts the recording material S, and the Y toner contacts the fixing film 22. A process cartridge 2M containing M toner with a different usage history value LM and a process cartridge 2Y containing Y toner with a different usage history value LY are prepared, and an image is formed by combining each process cartridge. An experiment was conducted by changing the fixing temperature of the fixing device F1 to determine the minimum fixing temperature at which fixing can be performed without fixing failure. Starting from a condition where the detection temperature of the temperature detection element 26 of the heater 23 of the fixing device F1 is 23°C, 10 consecutive sheets are printed in a row, and the fifth print image is evaluated.

[0062] FIG. 4(b) is a graph summarizing the results of Experiment 1. The horizontal axis is the difference ΔL=LY-LM between the usage history value LY and the usage history value LM. The vertical axis is the fixing temperature (°C) at which fixing was possible without fixing failure. The required fixing temperature increased in proportion to the difference ΔL in the usage history values. When the difference between the usage history value LY of the process cartridge 2Y that supplies the Y toner in contact with the fixing film 22 side and the usage history value LM of the process cartridge 2M that supplies the M toner in contact with the recording material S side increased, the required fixing temperature increased. This is because the toner in contact with the fixing film 22 side has a longer usage history than the toner in contact with the recording material S side, and was subjected to a longer stress in the developing device 7, resulting in a decrease in the coverage rate of non-melted materials such as external additives.

[0063] (Method of Determining Fixing Temperature in Example 1) In the first embodiment, the fixing temperature is set according to the usage history of each station by referring to the usage history values ​​LY, LM, LC, and LK stored in the memories 40Y, 40M, 40C, and 40K of the process cartridge 2 of each image forming station. The method of determining the fixing temperature in the first embodiment is shown in the flowchart of FIG. 5. In step (hereinafter referred to as S) 10, the control unit 31 receives a print signal. In S11, the control unit 31 provisionally sets the fixing temperature T0 based on information other than the process cartridge 2, such as the print paper, image size, image forming device, usage history of the fixing device, and environmental temperature.

[0064] In S12, the control unit 31 acquires the usage history values ​​LY, LM, LC, and LK stored in the memories 40Y, 40M, 40C, and 40K of the process cartridges 2 of each image forming station. In S13, the control unit 31 obtains ΔL between each color, that is, performs the following six types of calculations. ΔL=LY-LM ΔL = LY - LC ΔL = LY - LK ΔL=LM-LC ΔL=LM-LK ΔL = LC - LK

[0065] In S14, the control unit 31 uses the largest ΔL among the ΔL calculated in S13, and calculates a correction value ΔT for the fixing temperature by the following formula. Fixing temperature correction value ΔT (℃) = correction coefficient × ΔL In the first embodiment, the correction coefficient was set to 0.002 (° C.). In S15, the control unit 31 adds the correction value ΔT determined in S14 to the fixing temperature T0 temporarily set in S11 (T0+ΔT) to reset the final fixing temperature.

[0066] Depending on the image, all four colors of toner may be combined. The toner in contact with the fixing film 22 side and the toner in contact with the recording material S side have a particularly large effect on fixability. Hereinafter, the toner in contact with the fixing film 22 side is referred to as the upper layer toner, and the toner in contact with the recording material S side is referred to as the lower layer toner. That is, in a toner image formed on the recording material S in a multiplicity of toner images, the toner in the toner image formed closest to the recording material S among the toners piled up on the recording material S is referred to as the lower layer toner, and the toner in the toner image formed farthest from the recording material S is referred to as the upper layer toner. In the first embodiment, ΔL is defined as "usage history value L of the upper layer toner - usage history value L of the lower layer toner".

[0067] When ΔL is a positive value, the usage history of the process cartridge 2 of the upper layer toner is longer than that of the lower layer toner. In other words, the upper layer toner is more stressed in the developing device 7 than the lower layer toner, and there is a high possibility that the coverage rate is lower. The upper layer toner is disadvantageous in fixability when the toners are stacked in a state where the actual contact area is likely to be larger than that of the lower layer toner, and the fixing temperature needs to be increased. On the other hand, when ΔL is a negative value, there is room to lower the fixing temperature.

[0068] (Calculation Example of Fixing Temperature Correction Value in Example 1) According to the method for determining the correction value of the fixing temperature in Example 1, the correction value of the fixing temperature was calculated for a set of process cartridges 2 having different usage history values ​​L. The usage history values ​​L of the process cartridges 2 used and the calculated correction value ΔT of the fixing temperature are shown in Table 1. [Table 1]

[0069] Set 1 in Example 1 is a case where all process cartridges 2 are brand new. In this case, the correction value ΔT of the fixing temperature is 0. Set 2 is a case where all process cartridges 2 are used equally. In this case, the correction value ΔT of the fixing temperature is 0.

[0070] Set 3 is the case where the K process cartridge 2K is replaced with a new one and the usage history value LK is reset to 0. The correction value ΔT of the fixing temperature is calculated to be +6°C. In this case (set 3), the coverage rate of the non-melted matter of the K toner is higher than that of the other toners. In an image using multiple color toners including the K toner, the K toner becomes the bottommost toner. Compared to the fixing film 22, the actual contact area with the recording material S is more likely to decrease, and a higher fixing temperature is required.

[0071] Set 4 is a case where the Y process cartridge 2Y is replaced with a new one and the usage history value LY is reset to 0. The correction value ΔT of the fixing temperature is calculated as 0° C. In this case (set 4), the coverage rate of the non-melted matter of the Y toner is higher than that of the other toners. In an image using toners of multiple colors including the Y toner, the Y toner becomes the toner of the uppermost layer. Compared to the recording material S, the actual contact area with the fixing film 22 is more likely to be reduced, and the fixing temperature can be lowered. However, in an image using toners of multiple colors not including the Y toner, the necessary fixing temperature does not change. Therefore, in set 4 of the embodiment 1, the fixing temperature is not changed.

[0072] Set 5 is a case where the lower layer toner supplying process cartridge has a longer usage history value L (LK>LC>LM>LY). The correction value ΔT of the fixing temperature is -2°C. In all toner combinations, the coverage rate of the non-melted matter of the lower layer toner is lower than that of the upper layer toner. This allows the fixing temperature to be lowered.

[0073] (Comparison with conventional examples) As a comparative study against Example 1, a case was considered in which the fixing temperature was determined according to a conventional fixing temperature determination method for a set of process cartridges 2 with different usage history values ​​L, the same as those calculated in Example 1. The usage history value L of the process cartridge used was the same as that in Table 1 of Example 1. In Conventional Example 1, the fixing temperature was not determined using the usage history value L in the memory 40 of the process cartridge, and the fixing temperature was always set at a fixing temperature that would not cause any problems even under the most unfavorable conditions. For example, the fixing temperature was always set at a fixing temperature correction value of +6°C. In this case, no fixing failure occurred in Set 3, but an excessive (high) fixing temperature was set in Sets 1, 2, 4, and 5.

[0074] In the conventional example 2, the process cartridge 2 with the largest usage history value L among the four colors is selected during the replacement life of the process cartridge 2, and the fixing temperature is determined. Sets 2, 3, 4, and 5 are all set to the same fixing temperature of 3000. In this case, it is not possible to set appropriate fixing temperatures for the set where the fixing temperature should be increased and the set where the fixing temperature should be decreased.

[0075] In conventional example 3, the one (0) with the smallest usage history value L is selected from the four colors, and the fixing temperature is determined. The same fixing temperature is set for sets 1, 3, 4, and 5. In this case, too, it is not possible to set appropriate fixing temperatures for the set whose fixing temperature should be increased and the set whose fixing temperature should be decreased.

[0076] (Modification of the first embodiment) The viscoelastic temperature characteristics of the toner matrix and the adhesive strength it exerts vary depending on the color materials and waxes used, so not all colors are the same. It is also known that Y is most likely to form in the uppermost layer, and K is most likely to form in the lowermost layer. By intentionally changing the viscoelastic temperature characteristics of the toner, it is also possible to limit combinations that have poor fixing properties.

[0077] In the first embodiment, the change in fixing temperature from the start of use was estimated and the fixing temperature correction value ΔT was determined on the assumption that the fixing properties were equal for all color combinations when the process cartridge 2 was first used. Even in the initial stage, if the fixing temperatures required for all color combinations are not the same and the most unfavorable combination is limited, the difference in the usage history values ​​of the process cartridge 2 may be calculated for only the limited combination, and the fixing temperature correction value ΔT may be determined.

[0078] For example, when the combination of Y and M and the combination of M and C are the most unfavorable configurations in terms of fixability, the following two calculations are performed, and the largest ΔL is used to determine the correction value ΔT of the fixing temperature. ΔL=LY-LM ΔL=LM-LC If the conditions are limited in this way, the cases in which the fixing temperature needs to be increased are limited, and the cases in which the fixing temperature can be decreased are increased.

[0079] (summary) As described above, the fixing temperature is determined using the difference between the usage history value of the process cartridge 2 that supplies the toner that contacts the fixing film 22 side and the usage history value of the process cartridge 2 that supplies the toner that contacts the recording material S side. This makes it possible to set an appropriate fixing temperature according to the change in toner even for an image formed by multiple toners.

[0080] In the first embodiment, the first image forming station is Y, followed by M, C, and K in that order, but the effect of the first embodiment is not limited to the color order. By determining the fixing temperature using the usage history value L of the process cartridge 2 that supplies the upper layer toner and the lower layer toner, it is possible to set an appropriate fixing temperature.

[0081] As described above, according to the first embodiment, even in an image in which a plurality of toners are multiplexed and formed on a recording material, an appropriate fixing temperature can be set according to the change in each toner, and fixing defects can be reduced. EXAMPLES

[0082] The image forming apparatus to which the present invention is applied is similar to that of the first embodiment, but the toner used for the image is identified by an image processing means, and the optimum fixing temperature is determined using the difference in the usage history value L of the process cartridge.

[0083] (Image processing unit) The video controller 30 as an image processing unit (image processing means) will be described with reference to Fig. 6. The video controller 30 includes devices such as a host computer interface (I / F) unit 302, an image forming device interface unit 303, a ROM 304, a RAM 305, and a CPU 306, which are interconnected via a CPU bus 301. The CPU bus 301 includes address, data, and control buses. The host computer I / F unit 302 has a function of bidirectionally connecting and communicating with a data transmitting device such as a host computer via a network. The image forming device I / F unit 303 has a function of bidirectionally connecting and communicating with an image forming device P.

[0084] The ROM 304 holds control program codes for executing image data processing (described later) and other processes. The RAM 305 is a memory for holding bitmap data and image density information resulting from rendering the image data received by the image forming apparatus I / F unit 303, and for holding a temporary buffer area and various processing statuses. The CPU 306 controls each device connected to the CPU bus 301 based on the control program codes held in the ROM 304. The video controller 30 of the second embodiment is an image processing unit (image processing unit) that generates an image signal for image formation from the received image data, and is also an image analysis unit (image analysis unit) that acquires density information of a toner image.

[0085] (Image data processing) 7 is a flow chart showing image data processing. In S20, the video controller 30 acquires data written in a page description language (PDL) that specifies image data and print conditions for the image data sent from the host computer. The video controller 30 converts the image data written in the PDL into image data for printing (bitmap data).

[0086] In S21, if the image data is related to a color image, the video controller 30 performs the following conversion process since the color information is in the form of RGB (red, green, blue) data. That is, the video controller 30 converts each color information by allocating it to device RGB data reproducible by the image forming apparatus P. In S22, the video controller 30 converts the color information of the image data from device RGB data to device YMCK (yellow, magenta, cyan, black) data. This YMCK data is defined as a ratio of the toner amount to the toner amount obtained on the recording material S when the lasers of each color image forming station are all turned on, and has a range of 0% to 100%. A data value of 0% is when all the lasers are turned off and the toner amount is 0.

[0087] Here, the exposure amount of each color of YMCK is calculated for the YMCK data using a gradation table that indicates the relationship between the exposure amount of each color and the amount of toner actually used. At S23, the video controller 30 functions as an image information acquisition means that acquires image information including density information of the toner image, thereby calculating the image density from the YMCK data. For example, if the image data for a pixel is Y=50%, M=30%, C=60%, and K=0%, the image density is 140% (=50+30+60+0).

[0088] (Relationship between density information and toner amount) The relationship between the density information and the amount of toner on the recording material S will be described. The density information is the density information of the pixel with the maximum exposure amount in each image information acquisition region. In the second embodiment, the minimum value of the density information is 0%, and the maximum density is 200%. The density information correlates with the actual amount of toner per unit area on the recording material S, and the amount of toner per unit area on the recording material S when the density information is 100% is, for example, 0.45 mg / cm. 2 In addition, the toner amount per unit area on the recording material S when the density information is 200% is, for example, 0.90 mg / cm 2 It is.

[0089] Returning to the flow chart, in S24, the video controller 30 calculates the pixel with the highest image density from among all pixels by image data processing, and determines the upper layer toner and the lower layer toner from the image data of Y, M, C, and K of the calculated pixel. For example, if the image data of the pixel with the highest image density is Y=70%, M=30%, C=60%, and K=0%, the upper layer toner is Y and the lower layer toner is C. The video controller 30 also functions as a determination means. Note that a lower limit threshold may be set for the image data of the toner to be determined. For example, the lower limit threshold is set to 30%, and the upper layer toner and the lower layer toner are determined from toners above the threshold. This is because toners with less image data have less effect on fixability. In this case, for example, if the image data of the pixel with the highest image density is Y=70%, M=30%, C=60%, and K=10%, K is excluded because it is below the threshold, and the upper layer toner and the lower layer toner are selected from Y, M, and C. The upper layer toner is Y, and the lower layer toner is C. Also, for example, if all of the toner levels are below 30%, the fixing temperature correction may not be performed.

[0090] In S25, the video controller 30 transmits information on the upper layer toner and the lower layer toner to the control unit 31. In parallel with the process of S25, the video controller 30 executes the processes of S26 and S27. In S26, the video controller 30 determines the exposure output according to the YMCK exposure pattern. In S26, the video controller 30 performs the exposure output. In the second embodiment, the usage history value L of the process cartridge 2 for the upper layer toner and the lower layer toner determined in S24 of FIG. 7 by the image data processing is used to calculate the correction value ΔT of the fixing temperature.

[0091] (Method of Determining Fixing Temperature in Example 2) The method of determining the fixing temperature in the second embodiment is shown in the flowchart of FIG. 8. Note that S30 to S32, S34, and S35 are the same processes as S10 to S12, S14, and S15 in FIG. 5, and therefore the description will be omitted. In the second embodiment, in S36, the control unit 31 causes the video controller 30 to execute the processes of S20 to S25 described in FIG. 7 in parallel with the processes of S31 and S32. Through this image data processing, the video controller 30 calculates the pixel with the highest image density, and determines the upper layer toner and the lower layer toner from the Y, M, C, and K image data of that pixel. The control unit 31 receives information on the upper layer toner and the lower layer toner from the video controller 30 in the process of S25 in FIG. 7.

[0092] In S33, the control unit 31 calculates a correction value for the fixing temperature using the usage history value L of the process cartridge 2 for the upper layer toner and the lower layer toner. For example, if the upper layer toner is Y and the lower layer toner is C in an image at a pixel with the highest image density, the control unit 31 calculates the correction value ΔT for the fixing temperature in the same manner as in the first embodiment by using the following formula. ΔL = LY - LC

[0093] In an image with a small amount of toner, even if the toner coverage is unfavorable, poor fixing is unlikely to occur. The greater the amount of toner, the more heat is required for fixing, and the difference in adhesive strength between the fixing film 22 and the recording material S becomes important. In the second embodiment, the upper layer toner and the lower layer toner in the image pixel with the largest amount of toner among the toners forming the image are determined, and the fixing temperature is determined from the information of the process cartridge 2 for the upper layer toner and the lower layer toner. This makes it possible to determine an appropriate fixing temperature for the image.

[0094] As described above, according to the second embodiment, even in an image in which a plurality of toners are multiplexed and formed on a recording material, an appropriate fixing temperature can be set according to the change in each toner, and fixing defects can be reduced. EXAMPLES

[0095] In the third embodiment, the surface of the toner matrix is ​​covered with an external additive containing a non-melt material, and a method for determining an appropriate fixing temperature is provided for a toner in which the substantial coverage rate of the non-melt material increases as the history of use of the process cartridge 2 increases. Some toners to which external additives are attached lose their adhesiveness and cohesiveness to the contact member as the history of use of the process cartridge 2 increases. The external additives attached to such toners are lightly attached to the toner surface at the time of manufacture, but as the history of use of the process cartridge 2 increases, they are embedded in the toner matrix and fixed. This makes it difficult for the additives to be removed before the fixing process, and it is believed that the substantial true contact area in the fixing process decreases. The method for determining the fixing temperature in the third embodiment is the same as that in the first embodiment, but the formula for calculating ΔL is different.

[0096] (Method of Determining Fixing Temperature in Example 3) A method for determining the fixing temperature in the third embodiment is shown in the flow chart of Fig. 9. S40 to S45 in Fig. 9 are similar to S10 to S15 in Fig. 5 in the first embodiment except for the calculation formula, so the description will be omitted.

[0097] In S43, the control unit 31 determines the correction value ΔT of the fixing temperature using the difference ΔL in the usage history value L of the process cartridge 2, as in the first embodiment, and performs the calculation using the following formula. The following six types of calculations are performed. ΔL=LM-LY ΔL = LC - LY ΔL = LK - LY ΔL=LC-LM ΔL=LK-LM ΔL=LK-LC

[0098] In S44, the control unit 31 uses the highest value LΔ among the calculated ΔL values ​​to calculate a correction value ΔT for the fixing temperature according to the following formula. Fixing temperature correction value ΔT (℃) = correction coefficient × ΔL In S45, the control unit 31 adds the fixing temperature correction value ΔT to the fixing temperature T0 to determine the final fixing temperature.

[0099] In the third embodiment, the difference ΔL is set to "usage history value of lower layer toner - usage history value L of upper layer toner". This is because the less the usage history, the smaller the actual true contact area, and is the opposite of the first embodiment (FIG. 5, S13). In the third embodiment, the fixing temperature is also determined using the difference between the usage history value of the process cartridge 2 that supplies the toner that contacts the fixing film 22 side and the usage history value of the process cartridge 2 that supplies the toner that contacts the recording material S side. This makes it possible to set an appropriate fixing temperature according to the change in toner, even for an image formed by multiple toners.

[0100] As described above, according to the third embodiment, even in an image in which a plurality of toners are multiplexed and formed on a recording material, proper fixing temperatures are set according to the changes in each toner, and fixing defects can be reduced.

[0101] The disclosure of this embodiment includes the following configuration. (Configuration 1) a plurality of developing means for forming toner images; a transfer means for sequentially transferring the toner images onto a recording material to form multiple toner images on the recording material; a fixing unit for applying pressure and heat to the recording material onto which the toner image has been transferred, thereby fixing the toner image onto the recording material; a storage medium for storing a usage history of the developing means; A control means for controlling a fixing temperature of the fixing means; An image forming apparatus comprising: The image forming apparatus, wherein the control means determines the fixing temperature in accordance with a difference between a usage history of one of the developing means and a usage history of the other developing means, the difference being stored in the storage medium. (Configuration 2) An image information acquisition means for acquiring image information, The image forming apparatus according to configuration 1, wherein the control means determines the fixing temperature in accordance with the image information acquired by the image information acquisition means and a difference in usage history of the plurality of developing means. (Configuration 3) In the toner image formed on the recording material in a multiplicity, when the toner of the toner image formed closest to the recording material among the toners overlapped on the recording material is defined as a lower layer toner, and the toner of the toner image formed farthest from the recording material is defined as an upper layer toner, The image forming apparatus according to configuration 1 or 2, characterized in that the control means determines the fixing temperature according to a difference between a usage history of a developing means for forming the upper layer toner and a usage history of a developing means for forming the lower layer toner. (Configuration 4) image information acquiring means for acquiring image information; a determining unit for determining which toner image has the largest amount of image data based on the image information acquired by the image information acquiring unit, from among the toner images multiplexed and formed on the recording material; Equipped with Among the toners forming the toner images determined by the determining means, the toner of the toner image formed closest to the recording material is defined as a lower layer toner, and the toner of the toner image formed farthest from the recording material is defined as an upper layer toner, The image forming apparatus according to configuration 1, characterized in that the control means determines the fixing temperature according to a difference between a usage history of a developing means for forming the upper layer toner and a usage history of a developing means for forming the lower layer toner. (Configuration 5) the toner is a toner containing a thermoplastic resin as a main material, and particles made of a material having a melting point higher than that of the thermoplastic resin are attached to the outside of the toner, The image forming apparatus according to configuration 3 or 4, wherein the control means determines the fixing temperature to be higher as the difference between the usage history of the developing means for forming the upper layer toner and the usage history of the developing means for forming the lower layer toner becomes larger. (Configuration 6) the developing means is a rotating body, 6. The image forming apparatus according to any one of configurations 1 to 5, wherein the usage history is a total travel distance of the rotating body. (Configuration 7) 7. The image forming apparatus according to configuration 6, wherein the total travel distance is based on a peripheral speed of the surface of the rotating body and a time taken for the rotating body to rotate. [Explanation of symbols]

[0102] 7. Developing device 10 Primary transfer roller 31 Control Unit 40 Memory F1 Fixing device

Claims

1. a plurality of developing means for forming toner images; a transfer means for sequentially transferring the toner images onto a recording material to form multiple toner images on the recording material; a fixing unit for applying pressure and heat to the recording material onto which the toner image has been transferred, thereby fixing the toner image onto the recording material; a storage medium for storing a usage history of the developing means; A control means for controlling a fixing temperature of the fixing means; An image forming apparatus comprising: The image forming apparatus, wherein the control means determines the fixing temperature in accordance with a difference between a usage history of one of the developing means and a usage history of another of the developing means, the difference being stored in the storage medium.

2. An image information acquisition means for acquiring image information, 2. The image forming apparatus according to claim 1, wherein the control unit determines the fixing temperature in accordance with the image information acquired by the image information acquisition unit and a difference in usage history of the plurality of developing units.

3. In the toner image formed on the recording material in a multiplicity, when the toner of the toner image formed closest to the recording material among the toners overlapped on the recording material is defined as a lower layer toner, and the toner of the toner image formed farthest from the recording material is defined as an upper layer toner, 2. The image forming apparatus according to claim 1, wherein the control means determines the fixing temperature in accordance with a difference between a usage history of a developing means for forming the upper layer toner and a usage history of a developing means for forming the lower layer toner.

4. image information acquiring means for acquiring image information; a determining unit for determining which toner image has the largest amount of image data based on the image information acquired by the image information acquiring unit, from among the toner images multiplexed and formed on the recording material; Equipped with Among the toners forming the toner images determined by the determining means, the toner of the toner image formed closest to the recording material is defined as a lower layer toner, and the toner of the toner image formed farthest from the recording material is defined as an upper layer toner, 2. The image forming apparatus according to claim 1, wherein the control means determines the fixing temperature in accordance with a difference between a usage history of a developing means for forming the upper layer toner and a usage history of a developing means for forming the lower layer toner.

5. the toner is a toner containing a thermoplastic resin as a main material, and particles made of a material having a melting point higher than that of the thermoplastic resin are attached to the outside of the toner, 5. The image forming apparatus according to claim 3, wherein the control unit determines the fixing temperature to be higher as the difference between the usage history of the developing unit that forms the upper layer toner and the usage history of the developing unit that forms the lower layer toner increases.

6. the developing means is a rotating body, 5. The image forming apparatus according to claim 1, wherein the usage history is a total travel distance of the rotating body.

7. 7. The image forming apparatus according to claim 6, wherein the total travel distance is based on a peripheral speed of the surface of the rotating body and a time taken for the rotating body to rotate.

Images