Image forming system

Abstract

To provide an image formation system with which it is possible to suppress occurrence of image defects to a varnish image that is formed on top of a toner image.SOLUTION: When a toner image is fixed to a varnish image forming screen (S3), a recording medium is reconveyed to a secondary transfer unit (S4, S5). A voltage larger than or equal to a discharge voltage is applied to a secondary transfer outer roller that forms the secondary transfer unit (S6). This causes a discharge to occur on the varnish image forming screen side, resulting in development of positive and negative ions to a toner, and a surface of the toner image is coated by a coating of these ions. For an aqueous varnish, adhesion of the toner image and the aqueous varnish can be reduced by formation of coating by positive ions, and the adhesion of the toner image and the aqueous varnish can be increased by formation of coating by negative ions. For an oily and a UV varnish, a voltage of the polarity that is opposite the aqueous varnish is applied so as to cause a discharge to occur. By performing such discharge processing, it is possible to suppress occurrence of image defects such as "bleeding" and "repelling" to the varnish image that is formed on top of the toner image.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to an image forming system including an image forming apparatus that forms a toner image on a recording material and a varnish coating apparatus that forms a varnish image on the recording material.

Background Art

[0002] Recently, in addition to a toner image formed on a recording material using a developer, a varnish image using a transparent varnish is formed on the recording material by overlapping it with the toner image or the like in order to decorate the surface of the recording material. As an apparatus for forming a varnish image, for example, an inkjet-type varnish coating apparatus (referred to as a varnish coater) is used. The varnish coater can partially apply a varnish to the recording material after the toner image is fixed to form a varnish image desired by the user (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, conventionally, when forming a varnish image over a toner image, there has been a risk that the varnish is repelled or the varnish bleeds due to the wettability of the toner. In this specification, the wettability of the toner indicates the affinity of the varnish for the toner surface, in other words, the ease of adhesion of the varnish. When the wettability of the toner is low, that is, when it is difficult to wet, the varnish is repelled and deviates from a predetermined landing position, and an image defect called so-called "repelling" may occur in the varnish image. On the contrary, when the wettability of the toner is high, that is, when it is easy to wet, the shape of the varnish in the form of droplets is not maintained and it spreads by wetting, and an image defect called so-called "bleeding" may occur in the varnish image.

[0005] In view of the above problems, the present invention aims to provide an image forming system that can suppress image defects in the varnish image caused by the wettability of the toner when forming a varnish image on top of a toner image on a recording material. [Means for solving the problem]

[0006] An image forming system according to one embodiment of the present invention comprises an image forming apparatus capable of forming a toner image on a recording material using a wax-containing toner, and a varnish coating apparatus capable of forming a varnish image on one side of a recording material using an aqueous varnish, the image forming system comprising: an endless image carrying belt that carries and rotates a toner image; a first rotating body that abuts against the inner circumferential surface of the image carrying belt; a second rotating body provided between the first rotating body and the image carrying belt, forming a transfer nip portion that transfers the toner image from the image carrying belt to the recording material while holding and transporting the recording material; a voltage applying means capable of applying a voltage to the second rotating body; a fixing means capable of heating the recording material at a plurality of fixing temperatures, which applies heat and pressure to the recording material on which the toner image has been formed to fix the toner image to the recording material; and through the fixing means The device comprises an inversion transport means capable of inverting the front and back sides of the passed recording material and transporting it to the transfer nip section, and a voltage application means and a control means for controlling the inversion transport means, wherein during single-sided printing on the recording material, the recording material is inverted by the inversion transport means and transported again to the transfer nip section after the toner image is transferred to the one side and the toner image is fixed by the fixing means, and as it passes through the transfer nip section with the one side facing the second rotating body side, the voltage application means applies a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and applies a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than the threshold, before being discharged to the varnish coating device so that a varnish image is formed on the one side.

[0007] An image forming system according to one embodiment of the present invention comprises an image forming apparatus capable of forming a toner image on a recording material using a wax-containing toner, and a varnish coating apparatus capable of forming a varnish image on one side of a recording material using an oil-based varnish or UV varnish, the image forming system comprising: an endless image carrying belt that carries and rotates a toner image; a first rotating body that abuts against the inner circumferential surface of the image carrying belt; a second rotating body provided between the first rotating body and the image carrying belt, forming a transfer nip portion that transfers the toner image from the image carrying belt to the recording material while holding and transporting the recording material; a voltage applying means capable of applying a voltage to the second rotating body; a fixing means capable of heating the recording material at multiple fixing temperatures, and fixing the toner image to the recording material by applying heat and pressure to the recording material on which the toner image has been formed; and the fixing means The device comprises an inversion transport means capable of inverting the front and back sides of the recording material that has passed through the step and transporting it to the transfer nip section, and a voltage application means and a control means for controlling the inversion transport means, wherein when printing on one side of the recording material, the recording material is inverted by the inversion transport means and transported again to the transfer nip section after the toner image is transferred to the one side and the toner image is fixed by the fixing means, and as it passes through the transfer nip section with the one side facing the second rotating body side, the voltage application means applies a voltage that is equal to or greater than the discharge start voltage and has negative polarity if the fixing temperature is below a threshold, and applies a voltage that is equal to or greater than the discharge start voltage and has positive polarity if the fixing temperature is greater than a threshold, and then discharges to the varnish coating device so that a varnish image is formed on the one side.

[0008] An image forming system according to one embodiment of the present invention comprises an image forming apparatus capable of forming a toner image on a recording material using a wax-containing toner, and a varnish coating apparatus capable of forming a varnish image on one side of a recording material using an aqueous varnish, the image forming system comprising: an endless image carrying belt that carries and rotates a toner image; a first rotating body that abuts against the inner circumferential surface of the image carrying belt; a second rotating body provided between the first rotating body and the image carrying belt, forming a transfer nip section that transfers the toner image from the image carrying belt to the recording material while holding and transporting the recording material; a voltage applying means capable of applying a voltage to the first rotating body; a fixing means capable of heating the recording material at multiple fixing temperatures and fixing the toner image to the recording material by applying heat and pressure to the recording material on which the toner image has been formed; and a reversing transport means capable of reversing the front and back sides of the recording material that has passed through the fixing means and transporting it to the transfer nip section, and the voltage applying means and The device comprises a control means for controlling a reversing transport means, and is characterized in that, when printing on one side of a recording material, the recording material is inverted by the reversing transport means and re-transported to the transfer nip section, passing through the transfer nip section with the one side facing the second rotating body and with no voltage applied by the voltage application means, and then being inverted by the reversing transport means and re-transported to the transfer nip section, and passing through the transfer nip section with the one side facing the first rotating body, the voltage application means applies a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and applies a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than a threshold, before being discharged to the varnish coating device so that a varnish image is formed on the one side.

[0009] An image forming system according to one embodiment of the present invention comprises an image forming apparatus capable of forming a toner image on a recording material using a wax-containing toner, and a varnish coating apparatus capable of forming a varnish image on one side of a recording material using an oil-based varnish or UV varnish, the image forming system comprising: an endless image carrying belt that carries and rotates a toner image; a first rotating body that abuts against the inner circumferential surface of the image carrying belt; a second rotating body provided between the first rotating body and the image carrying belt, forming a transfer nip section that transfers the toner image from the image carrying belt to the recording material while holding and transporting the recording material; a voltage applying means capable of applying a voltage to the first rotating body; a fixing means capable of heating the recording material at multiple fixing temperatures and fixing the toner image to the recording material by applying heat and pressure to the recording material on which the toner image has been formed; an inversion transport means capable of inverting the front and back sides of the recording material that has passed through the fixing means and transporting it to the transfer nip section; and the voltage applying means The device comprises a control means for controlling the inversion transport means, and is characterized in that, when printing on one side of a recording material, the recording material is inverted by the inversion transport means and transported again to the transfer nip section, passing through the transfer nip section with the one side facing the second rotating body and with no voltage applied by the voltage application means, and is further inverted by the inversion transport means and transported again to the transfer nip section, and when passing through the transfer nip section with the one side facing the first rotating body, the voltage application means applies a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and applies a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than a threshold, before being discharged to the varnish coating device so that a varnish image is formed on the one side. [Effects of the Invention]

[0010] According to the present invention, when forming a varnish image on top of a toner image on a recording material, it is possible to suppress image defects in the varnish image caused by the wettability of the toner. [Brief explanation of the drawing]

[0011] [Figure 1]A schematic diagram showing the configuration of the image forming system. [Figure 2] A graph showing the relationship between the control voltage and film thickness involved in the formation of the varnish image. [Figure 3] A block diagram showing the control configuration of an image forming system. [Figure 4] A flowchart illustrating the image formation process during single-sided printing in an external power supply system, where a toner image is formed on one side and varnish is applied to the same side. [Figure 5] This schematic diagram shows the transport flow of recording material to explain discharge control during single-sided printing using an external power supply system, and includes (a) the toner image formation on one side (one side) to the double-sided transport section, and (b) the transport section from the double-sided transport section through the secondary transfer section to the inversion discharge section. [Figure 6] A flowchart illustrating the image formation process during double-sided printing using an external power supply system, where toner images are formed on both sides and varnish is applied to one side. [Figure 7] This schematic diagram shows the transport flow of recording material to explain discharge control during double-sided printing using an external power supply system, and includes: (a) from toner image formation on both sides to the double-sided transport section, (b) from the double-sided transport section to the reversal ejection section via the secondary transfer section (without discharge), and (c) from the reversal ejection section to the reversal ejection section via the double-sided transport section and the secondary transfer section. [Figure 8] A graph showing the relationship between the voltage and current applied to the secondary transfer section. [Figure 9] A flowchart illustrating the image formation process during single-sided printing in an internal power supply system, where a toner image is formed on one side and varnish is applied to the same side. [Figure 10] This schematic diagram shows the transport flow of recording material to explain discharge control during single-sided printing using an internal power supply system, and includes: (a) from toner image formation on one side (one side) to the double-sided transport section, (b) from the double-sided transport section to the inversion discharge section via the secondary transfer section (without discharge), and (c) from the inversion discharge section to the inversion discharge section via the double-sided transport section and the secondary transfer section. [Figure 11] A flowchart illustrating the image formation process during double-sided printing using an internal power supply system, where toner images are formed on both sides and varnish is applied to one side. [Figure 12]It is a schematic diagram showing the conveyance flow of a recording material for explaining discharge control during double-sided printing in an internal power supply method, (a) from toner image formation on the double-sided side to the double-sided conveyance unit, and (b) from the double-sided conveyance unit to the reverse discharge unit via the secondary transfer unit.

Embodiments for Carrying out the Invention

[0012] [First Embodiment] First, the image forming system of this embodiment will be described using FIG. 1. The image forming system 1X shown in FIG. 1 includes an image forming apparatus 100 that forms a toner image on a recording material S, and a varnish coater 200 that forms a varnish image on the recording material S. The varnish coater 200 is a post-process unit that can be attached to the image forming apparatus 100 for function expansion, and the image forming apparatus 100 and the varnish coater 200 are connected so as to be able to transfer the recording material S. Further, the image forming apparatus 100 and the varnish coater 200 are connected by a data input / output interface (not shown) so as to be able to transmit and receive control signals, data, etc. between them. The recording material S on which a toner image is formed by the image forming apparatus 100 is conveyed to the varnish coater 200 for the purpose of improving the gloss, water resistance, abrasion resistance, etc. of the toner image formed on the recording material S, and a varnish image is formed on the recording material S by the varnish coater 200 separately from the toner image. The formation of the varnish image by the varnish coater 200 will be described later.

[0013] Note that although the illustration of the image forming system 1X is omitted, it may include other post-process units such as a relay device and a finisher device. The relay device is arranged between the image forming device 100 and the varnish coater 200, and reverses the recording material S conveyed from the image forming device 100 and sends it to the varnish coater 200, or temporarily stacks it and then sends it to the varnish coater 200. The finisher device performs, for example, a punching process of making holes in the recording material S or a stapling process of bundling a plurality of recording materials S and closing the needles, and discharges the punched recording material S or the bundle of the recording materials S with closed needles to the discharge tray. In addition to such post-process units, for example, a recording material supply device (not shown) capable of storing a large amount of recording materials S inside may be provided, and the recording material S may be supplied from the recording material supply device to the image forming device 100.

[0014] <Image forming device> The image forming device 100 will be described. The image forming device 100 is an electrophotographic tandem full-color printer. The image forming device 100 has image forming units Pa, Pb, Pc, and Pd that form yellow, magenta, cyan, and black images, respectively. The image forming device 100 forms a toner image on the recording material S based on, for example, image data sent from a document reading device (not shown) connected to the image forming device 100 or an external device 1000 such as a personal computer. Examples of the recording material S include sheet materials such as plain paper, thick paper, rough paper, embossed paper, and coated paper.

[0015] The image data has toner image data related to the toner image formed by the image forming device 100 and data related to the varnish image formed by the varnish coater 200. Similar to the toner image data, the varnish image data has individual varnish images associated with the coordinates of the image forming area on the recording material S for each page.

[0016] The transport process for the recording material S of the image forming apparatus 100 will now be described. The recording material S is stored in a cassette 10 and is fed out of the cassette 10 by a supply roller 13 in accordance with the image forming timing. The recording material S fed out by the supply roller 13 is transported to a registration roller 12 located in the middle of the transport path 114. After the registration roller 12 corrects the skewness and timing of the recording material S, the recording material S is sent to the secondary transfer section T2. ​​The secondary transfer section T2 is a transfer nip section formed by a secondary transfer inner roller 14 and a secondary transfer outer roller 11.

[0017] Next, we will explain the image formation process, which takes place at a similar timing to the transport process of the recording material S to the secondary transfer unit T2 described above. First, we will explain the image forming units. The image forming units Pa, Pb, Pc, Pd, and Pe for each color are configured almost identically, except that the toners used in the developing units 1a, 1b, 1c, and 1d are yellow (Y), magenta (M), cyan (C), and black (K). Therefore, in the following, we will explain the black image forming unit Pd as a representative example, and omit explanations for the other image forming units Pa, Pb, and Pc.

[0018] The image forming unit Pd mainly consists of a developing device 1d, a charging device 2d, a photosensitive drum 3d, a photosensitive drum cleaner 4d, and an exposure device 5d. The surface of the rotating photosensitive drum 3d is uniformly charged in advance by the charging device 2d, and then an electrostatic latent image is formed by the exposure device 5d, which is driven based on an image information signal. Next, the electrostatic latent image formed on the photosensitive drum 3d is developed into a toner image using a developer by the developing device 1d. Then, in response to the application of a primary transfer voltage to the primary transfer roller 6d, which is positioned between the image forming unit Pd and the intermediate transfer belt 80, the toner image formed on the photosensitive drum 3d is primary transferred onto the intermediate transfer belt 80. Any remaining primary transfer toner on the photosensitive drum 3d is collected by the photosensitive drum cleaner 4d.

[0019] The intermediate transfer belt 80, which serves as the image-carrying belt, is an endless belt member that is stretched by the secondary transfer internal roller 14 and tension rollers 15 and 16, and driven in the direction of arrow R2. In this embodiment, the tension roller 16 also serves as a drive roller for driving the intermediate transfer belt 80. The image formation process for each color, which is processed in parallel by the image forming units Pa to Pd, is performed at the timing of sequentially superimposing the upstream color toner image that has been primary transferred onto the intermediate transfer belt 80. As a result, a full-color toner image is ultimately formed on the intermediate transfer belt 80, and the toner image is transported to the secondary transfer unit T2 by the intermediate transfer belt 80 as it rotates carrying the toner image. After passing through the secondary transfer unit T2, any remaining secondary transfer toner is removed from the intermediate transfer belt 80 by the transfer cleaner 22.

[0020] A power supply 403 capable of applying variable polarity and voltage is connected to the secondary transfer outer roller 11, which acts as the second rotating body, while the secondary transfer inner roller 14, which acts as the first rotating body, is connected to ground potential (0V) (this is called the external power supply method). When a secondary transfer voltage with the opposite polarity to the charging polarity of the toner is applied to the secondary transfer outer roller 11 by the power supply 403, a transfer electric field is generated in the secondary transfer section T2, and the toner image supported on the intermediate transfer belt 80 is transferred to the recording material S. For example, when a secondary transfer voltage of "1 to 7 kV" is applied by the power supply 403, a current of "40 to 120 μA" flows through the secondary transfer section T2.

[0021] For example, the secondary transfer outer roller 11 has an elastic layer of, for example, ion-conductive foamed rubber (NBR rubber) on the outer circumference of the core metal, and its outer diameter is formed to be "20-25 mm". Also, the secondary transfer outer roller 11 has a resistance value of, for example, "1 × 10 5 ~1 × 10 8 It is set to Ω (ambient temperature "23℃", relative humidity "50%" RH, "2kV" applied).

[0022] As described above, the transport process and image forming process synchronize the timing of the recording material S and the full-color toner image in the secondary transfer section T2, and secondary transfer is performed. After that, the recording material S is transported to the fixing device 50. The fixing device 50 has a fixing roller 51 and a pressure roller 52, and a halogen heater 53 is arranged inside the fixing roller 51. The fixing roller 51, as a fixing rotating body, is heated by the halogen heater 53, which is a heating means. The halogen heater 53 can change its temperature to heat the fixing roller 51 by supplying power from a heater power supply 54, which is a power supply means. The pressure roller 52, as a pressure rotating body, is provided to be able to move toward and toward the fixing roller 51 by a contact / separation mechanism (not shown) so as to move between a pressurized position in which it contacts and pressurizes the fixing roller 51 and a separated position in which it does not contact the fixing roller 51. When the pressure roller 52 contacts the fixing roller 51, a fixing nip portion of a predetermined width is formed in the transport direction of the recording material S.

[0023] The fixing device 50, acting as a fixing means, grips and transports the recording material S on which the toner image has been formed in the fixing nip section formed by the fixing roller 51 and the pressure roller 52, and applies heat and pressure to the recording material S, thereby fixing the toner image to the recording material S. That is, the toner of the toner image formed on the recording material S is melted and mixed by heating and pressurizing, and fixed to the recording material S as a full-color image.

[0024] As will be described in detail later, in this embodiment, when printing on one side or both sides of the recording material S, the recording material S is sent to a switchback section 32 having a rotating roller (not shown) that can rotate in both forward and reverse directions after the toner image has been fixed to the "varnish image forming surface". The switchback section 32, as a switchback means, performs switchback transport to change the transport direction of the recording material S by swapping the front and rear ends of the recording material S in order to swap the front and back surfaces of the recording material S. The recording material S is selectively sent from the switchback section 32 to either the double-sided transport section 33 or the reversal discharge section 31. In this embodiment, the varnish coater 200 is capable of forming a varnish image on only one of the predetermined surfaces of the recording material S, and the surface on which the varnish image of the recording material S is formed is called the "varnish image forming surface".

[0025] When the recording material S is sent to the double-sided transport unit 33, it is transported again toward the secondary transfer unit T2 by the double-sided transport unit 33, which is a double-sided transport means having transport rollers (not shown). As the recording material S passes through the secondary transfer unit T2, it is transported one or more times by the switchback unit 32 and the double-sided transport unit 33 until the varnish image forming surface, on which the toner image has been formed, faces the secondary transfer outer roller 11 side (second rotating body side). On the other hand, when the recording material S is sent to the inversion discharge unit 31, which is an inversion discharge means, it is discharged to the varnish coater 200 by the inversion discharge unit 31. These inversion discharge unit 31, switchback unit 32, and double-sided transport unit 33 constitute an inversion transport means that can invert the front and back sides of the recording material S that has passed through the fixing device 50 and transport it to the secondary transfer unit T2.

[0026] In this embodiment, when the recording material S passes through the secondary transfer section T2 with the varnish image forming surface facing the secondary transfer outer roller 11, a predetermined voltage of a predetermined polarity is applied by the power supply 403. After that, the recording material S that has passed through the fixing device 50 is transported again if necessary, and discharged to the varnish coater 200 with the varnish image forming surface facing the position detection section 245, varnish discharge section 246, and varnish solidification section 247 of the varnish coater 200.

[0027] The intermediate transfer belt 80 has a volume resistivity of, for example, "5 × 10 8 ~1 × 10 14 The material has a hardness of Ω·cm (23℃, 50%RH) and a hardness of 60~85° (23℃, 50%RH) on the MD-1 hardness scale. The static friction coefficient is set to 0.15~0.6 (23℃, 50%RH). The intermediate transfer belt 80 is formed with a three-layer structure consisting of a base layer, an elastic layer, and a surface layer, starting from the back side where the secondary transfer inner roller 14 makes contact.

[0028] The base layer is made of materials such as polyimide or polycarbonate resins, or various types of rubber containing carbon black as an antistatic agent, and is formed to a thickness of 0.05 to 0.15 mm. The elastic layer is made of materials such as urethane rubber or silicone rubber containing an ionic conductive agent, and is formed to a thickness of 0.1 to 0.5 mm. The surface layer is made of resin materials such as fluororesin and is formed to a thickness of 0.0002 to 0.02 mm. For the surface layer, the base material is made of one type of material such as polyurethane, polyester, or epoxy resin, or two or more types of elastic materials such as elastic rubber, elastomer, or butyl rubber. To reduce surface energy and improve lubricity, the surface layer is formed by dispersing one or more types of powders or particles, such as fluororesin, or particles of different sizes, on this base material.

[0029] <Developer> In this embodiment, a two-component developer containing toner and a carrier is used. The toner contains a binder resin, a colorant, and a release agent. The binder resin can be any known resin. For example, vinyl copolymers such as styrene-(meth)acrylic copolymer, polyester resins, hybrid resins in which vinyl copolymers and polyesters are chemically bonded, epoxy resins, styrene-butadiene copolymers, etc., can be used. As for the colorants, known ones can be used for yellow (Y), magenta (M), cyan (C), and black (K).

[0030] Examples of release agents include aliphatic hydrocarbon waxes such as low molecular weight polyethylene wax, low molecular weight olefin copolymer wax, microcrystalline wax, Fischer-Tropsch wax, and paraffin wax, as well as oxides of aliphatic hydrocarbon waxes such as oxidized polyethylene wax, or block copolymers thereof; waxes mainly composed of fatty acid esters such as carnauba wax and montanic acid ester wax; ester waxes which are synthetic reaction products of higher fatty acids and higher alcohols such as behenyl behenate and behenyl stearate; and deoxidized fatty acid esters such as deoxidized carnauba wax, which may be partially or completely deoxidized.

[0031] <Varnish Coater> Next, the varnish coater 200 will be described using Figures 1 and 2. The varnish coater 200 is an inkjet-type varnish coating device that can form varnish images such as characters, line drawings, and figures desired by the user, separately from the toner image, by ejecting varnish onto the surface of the recording material S. In the inkjet method, a varnish image is formed by adhering the varnish to the recording material S by ejecting varnish droplets toward the recording material S. The varnish coater 200 can form a varnish image on the recording material S based on varnish image data contained in the image data.

[0032] The varnish coater 200 comprises a sheet transport unit 241, a position detection unit 245, a varnish discharge unit 246, and a varnish solidification unit 247. The sheet transport unit 241 transports the recording material S by adsorbing it onto the belt transport surface using an air suction device (not shown) through holes formed in the transport belt 242. Along the sheet transport path of the sheet transport unit 241, the position detection unit 245, the varnish discharge unit 246, and the varnish solidification unit 247 are arranged in order from the upstream side to the downstream side in the transport direction (arrow X direction) of the recording material S. The position detection unit 245 is a detection unit that uses, for example, a charge-coupled element (CCD), and detects the position of the leading end of the recording material S in the transport direction, the positions of both ends in the width direction intersecting the transport direction, and the position of the toner image on the recording material S, with respect to the recording material S that is adsorbed and transported on the belt transport surface. By detecting the position of the toner image with the position detection unit 245, the varnish coater 200 can overprint a varnish image on top of the toner image.

[0033] The varnish dispensing unit 246 forms a varnish image on the recording material S by dispensing varnish onto one side of the recording material S being transported by the sheet transport unit 241. The varnish dispensing unit 246 has multiple print heads (not shown). The print heads are, for example, line-type heads, and multiple dispensing ports (not shown) are arranged in a width direction intersecting the transport direction of the recording material S, covering a range that covers the maximum width of the recording material S on which an image can be formed by the varnish coater 200. The varnish dispensing method of the print heads may include a method using a heating element, a method using a piezoelectric element, a method using an electrostatic element, a method using a MEMS element, etc. Although not shown in the illustration, the varnish is supplied from the tank to the print heads via tubes.

[0034] The thickness of the varnish image depends on the amount of varnish applied per unit area to the recording material. The amount of varnish applied is varied by adjusting the amount of varnish ejected from the print head. For example, in the case of a system using a piezoelectric element, as shown in Figure 2, the amount of varnish ejected changes in accordance with the adjustment of the control voltage, and the thickness of the varnish image is adjusted in accordance with increasing or decreasing the amount of varnish ejected per unit area. In this embodiment, the thickness of the varnish image is adjusted to a range of, for example, "5 to 100 μm", preferably "10 to 70 μm".

[0035] Furthermore, the resolution of the varnish image that can be formed with the varnish coater 200 is, for example, "600 dpi," in which case the line width of the varnish image is adjusted in units of "600 dpi." Note that the range of varnish film thickness, the resolution of the varnish image, and the adjustment range of the line width of the varnish image described above may be changed as appropriate depending on the varnish ejection method of the print head in the varnish coater 200, the type of varnish, etc.

[0036] In this embodiment, water-based varnish or oil-based varnish can be used as the varnish. Water-based varnish, for example, mainly consists of a latex emulsion and contains water, amino alcohol, and a modifier. Examples of latex emulsions include styrene / acrylic emulsion, acrylic emulsion, and polyester emulsion. Amino alcohol is used to adjust the pH of the varnish and is mixed in the varnish composition to adjust the varnish to a pH of 8 to 10. Amino alcohol refers to compounds having an amino group (or group of amino groups) bonded to an alkyl alcohol or aryl alcohol, for example. Examples of modifiers include surfactants that adjust the surface tension of the varnish. Examples include anionic surfactants, nonionic surfactants, silicone surfactants, and fluorosurfactants. The content of each of these components is not particularly limited, but water-based varnish contains, for example, 40 to 95% by weight of latex emulsion, 5 to 30% of water, 1 to 5% by weight of ammonia, and 0.1 to 5% of a modifier. Examples of water-based varnishes include "Aqua Pack Varnish (product name)" (manufactured by T&K TOKA Corporation).

[0037] Oil-based varnishes primarily consist of resins, solvents, and drying oils. Examples of resins include rosin-modified phenolic resins and rosin-modified maleic acid resins. Examples of solvents include mineral oils such as diesel fuel and petroleum-based solvents such as paraffinic solvents. Examples of drying oils include vegetable oils such as linseed oil. Oil-based varnishes only need to contain one of these components, or they may contain two or more. The content of each component is not particularly limited, but an oil-based varnish typically contains, for example, 20-30% by mass of resin, 10-20% by mass of solvent, and 30-40% by mass of drying oil. Examples of oil-based varnishes that can be used include "Best Dry OP Varnish (product name)" and "Best One Matte OP Varnish (product name)" (manufactured by T&K TOKA Corporation).

[0038] Returning to Figure 1, the recording material S, on which a varnish image has been formed on one side by the varnish dispensing unit 246, is sent by the sheet transport unit 241 to the varnish solidification unit 247 downstream in the transport direction, where the varnish on the recording material S is solidified. The varnish solidification unit 247 solidifies the varnish image formed on the recording material S by irradiating it with infrared light of a wavelength corresponding to the varnish, for example, using an infrared lamp. Alternatively, the varnish solidification unit 247 solidifies the varnish image by drying the varnish by blowing hot air onto the recording material S. In this way, the varnish image can be overprinted on top of the toner image.

[0039] Next, the control configuration of the image forming system 1X will be explained using Figure 3 with reference to Figure 1. In this embodiment, an example is given in which the image forming apparatus 100 centrally manages and controls the operation commands to the varnish coater 200. Although various devices such as motors and power supplies are connected to the main control unit 101 and the varnish processing control unit 330, which will be described later, their illustration and explanation are omitted here as they are not essential to the invention.

[0040] In the image forming system 1X of this embodiment, as shown in Figure 3, the varnish processing control unit 330 is connected to the main control unit 101, which serves as a control means, via communication units 501 and 502, enabling communication of operation commands and various data. The varnish processing control unit 330 operates the varnish coater 200 according to operation commands from the main control unit 101. That is, the main control unit 101 can control the entire image forming system 1X, including the varnish coater 200, by controlling the operation of the image forming apparatus 100 and transmitting operation commands and various data to the varnish coater 200.

[0041] The main control unit 101 and the varnish processing control unit 330 described above may have the same configuration. For example, each may have a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory).

[0042] The main control unit 101 includes a CPU 102, a ROM 103, and a RAM 104. The ROM 103 stores various programs, such as the "image formation processing" described later (see, for example, Figures 4 and 6). The RAM 104 stores various data, such as image data acquired from the operation unit 110 or an external device 1000 (see Figure 1). The RAM 104 can also temporarily store calculation results associated with the execution of various programs.

[0043] The image forming apparatus 100 includes, for example, an operation unit 110 having a liquid crystal display unit 111 (see Figure 1), and the operation unit 110 is connected to the main control unit 101. The operation unit 110 is, for example, a touch panel. The operation unit 110 can display various screens on the liquid crystal display unit 111 that present various programs and various data, and accepts inputs such as starting various programs and inputting various data in response to touch operations by the user on the screen. The touch panel displays a screen that includes various buttons and switches as software keys.

[0044] The user can input the start of various programs, such as image formation jobs, from the operation unit 110. At that time, the user can input the type of recording material S (plain paper, coated paper, etc.), size (A3 landscape, A4 portrait, etc.), and whether to perform single-sided or double-sided printing. When the user inputs the start of an image formation job, the CPU 102 executes the "image formation process (program)" stored in the ROM 103 (see Figures 4 and 6 below).

[0045] Furthermore, the main control unit 101 is connected to a power supply 403, a voltage detection sensor 403a that detects the output voltage of the power supply 403, and a current detection sensor 403b that detects the output current flowing between the power supply 403 and the secondary transfer outer roller 11. The main control unit 101 controls the power supply 403 according to the detection results of the voltage detection sensor 403a and the current detection sensor 403b during an image forming job. In addition, a heater power supply 54 is connected to the main control unit 101, and the main control unit 101 can control the heater power supply 54 so that the surface temperature of the fixing roller 51 reaches a desired temperature, for example, "140 to 190°C", which is the fixing temperature at which the toner image can be fixed to the recording material S. The fixing temperature is set to a predetermined temperature according to the basis weight of the recording material S in order to achieve both good toner fixation on the recording material S and gloss of the toner image after fixing. The main control unit 101 controls the heater power supply 54 to heat the recording material S at a fixing temperature based on the basis weight corresponding to the type of recording material S input from the operation unit 110, which is one of several fixing temperatures pre-stored in the ROM 103.

[0046] The varnish processing control unit 330 includes a CPU 331, a ROM 332, and a RAM 333. The CPU 331 operates the sheet transport unit 241, the position detection unit 245, the varnish discharge unit 246, and the varnish solidification unit 247 of the varnish coater 200 based on a control program stored in the ROM 332. When the varnish processing control unit 330 receives varnish image data from the main control unit 101, it stores the received varnish image data in the RAM 333 and controls the varnish coater 200 to form a varnish image on the recording material S based on this varnish image data.

[0047] As mentioned earlier, conventionally, when a varnish image is formed on top of a toner image on a recording material, there was a risk of image defects such as "repellency" or "bleeding" occurring in the varnish image. The occurrence of "repellency" or "bleeding" in the varnish image is due to the wettability of the toner on which the varnish image is superimposed. Generally, wettability indicates the ease (affinity) of a liquid (in this case, varnish) adhering to a solid surface (in this case, the toner surface), and is evaluated by the magnitude of the contact angle between the liquid and the recording material S.

[0048] The larger the contact angle, the lower the wettability and the more likely the varnish is to be repelled. Varnish "repelling" is a phenomenon that occurs when varnish is dispensed where wettability is low, i.e., where the contact angle is greater than 90 degrees, causing the varnish to deviate from its intended landing position (coordinate). Conversely, the smaller the contact angle, the higher the wettability and the more likely the varnish is to bleed. Varnish "bleeding" occurs when varnish is dispensed where wettability is high, i.e., where the contact angle is less than 90 degrees, causing the varnish to lose its shape as a droplet and collapse. As mentioned above, toner contains wax as a release agent, and the wax can precipitate on the toner surface due to the heat during fixing. The wettability of the toner can be lowered or raised depending on the degree of this wax precipitation.

[0049] <Image Formation Processing> Therefore, in this embodiment, the occurrence of image defects such as "repulsion" and "bleeding" in the varnish image is suppressed. First, the "image formation process" in the case of the external power supply method will be explained using Figures 4 to 8 with reference to Figures 1 and 3. Figure 4 is a flowchart of the image formation process during single-sided printing in the external power supply method, in which a toner image is formed on only one side and varnish is applied to the same side. The "image formation process" is started by the main control unit 101 when the start input of the image formation job is received and is repeated until the end of the image formation job. In the following, the case in which one side of the recording material S on which the toner image M1 is formed is the "varnish image formation surface" will be explained as an example.

[0050] As shown in Figure 4, when the image forming job starts, the main control unit 101 forms a toner image M1 on the intermediate transfer belt 80 based on the image data stored in the RAM 104 (S1) to be transferred to one side (one side) of the recording material S. The main control unit 101 then transfers the toner image M1 from the intermediate transfer belt 80 to the recording material S in the secondary transfer unit T2 (S2). When transferring the toner image M1 from the intermediate transfer belt 80 to the recording material S, the main control unit 101 uses the power supply 403 to apply a secondary transfer voltage with the opposite polarity to the charge polarity of the toner to the secondary transfer outer roller 11. For example, if the charge polarity of the toner is negative, a positive polarity secondary transfer voltage is applied to the secondary transfer outer roller 11.

[0051] The main control unit 101 applies heat and pressure to the recording material S using the fixing device 50 to fix the toner image M1 to one side of the recording material S (S3), and then transports the recording material S to the double-sided transport unit 33 via the switchback unit 32 (S4). Conventionally, after the toner image M1 is fixed, the recording material S is transferred to the varnish coater 200. In contrast, in this embodiment, after the toner image M1 is fixed, as shown in Figure 5(a), the recording material S is transported to the double-sided transport unit 33 via the switchback unit 32.

[0052] Then, the main control unit 101 re-transports the recording material S to the secondary transfer unit T2 via the double-sided transport unit 33 (S5). The recording material S is inverted by the switchback unit 32 and passes through the secondary transfer unit T2 with the side on which the toner image M1 is formed facing the secondary transfer outer roller 11, as shown in Figure 5(b). As the recording material S passes through the secondary transfer unit T2, the main control unit 101 applies a predetermined voltage to the secondary transfer outer roller 11 using the power supply 403 to perform a discharge treatment that generates a discharge between the secondary transfer outer roller 11 and the recording material S (S6). The discharge treatment is performed to form a film on the toner surface by discharge, changing the wettability of the toner, that is, changing the adhesion force between the toner surface and the varnish. The voltage applied for the discharge treatment will be described later (see Tables 1 and 2).

[0053] The main control unit 101 transports the discharged recording material S to the fixing device 50. In order to allow the discharged recording material S to pass through, the main control unit 101 separates the pressure roller 52 from the fixing roller 51 in the fixing device 50, creating a non-pressurized state (S7). In other words, the recording material S passes through the fixing device 50 without being subjected to heat or pressure. The main control unit 101 transports the recording material S that has passed through the fixing device 50 to the varnish coater 200 (S8). At this time, as shown in Figure 5(b), the recording material S is inverted by the switchback unit 32 and then handed over to the varnish coater 200 by the inversion discharge unit 31 so that the side with the fixed toner image M1 faces the position detection unit 245, varnish discharge unit 246, and varnish solidification unit 247 as it is transported inside the varnish coater 200.

[0054] Figure 6 is a flowchart showing the image formation process during double-sided printing in an external power supply system, where toner images are formed on both the front and back sides, and varnish is applied to the front side. To facilitate understanding, Figure 6 shows the process from fixing the toner image M1 to the front side of the recording material S, to forming the toner image M2 on the back side.

[0055] As shown in Figure 6, after fixing the toner image M1 on one side, the main control unit 101 forms a toner image M2 on the intermediate transfer belt 80 to be transferred to the second side of the recording material S (S11). The main control unit 101 then transfers the toner image M2 from the intermediate transfer belt 80 to the recording material S in the secondary transfer section T2 (S12). When transferring the toner image M2 from the intermediate transfer belt 80 to the recording material S, the main control unit 101 also applies a secondary transfer voltage with the opposite polarity to the charging polarity of the toner to the secondary transfer outer roller 11 using the power supply 403.

[0056] The main control unit 101 applies heat and pressure to the recording material S using the fixing device 50 to fix the toner image M2 to two sides of the recording material S (S13), and then transports the recording material S to the double-sided transport unit 33 via the switchback unit 32 (S14). In this embodiment, after the toner image M2 is fixed, the recording material S is transported to the double-sided transport unit 33 via the switchback unit 32, as shown in Figure 7(a).

[0057] Then, the main control unit 101 re-transports the recording material S to the secondary transfer unit T2 via the double-sided transport unit 33 (S15). The recording material S, with toner images (M1, M2) formed on both sides, passes through the secondary transfer unit T2 with the two sides where the toner image M2 is formed facing the secondary transfer outer roller 11, as shown in Figure 7(b). At this time, the main control unit 101 is in a non-applied state, not applying voltage to the secondary transfer outer roller 11 by the power supply 403 (S16). In other words, the discharge process described above is not performed. The main control unit 101 also sets the pressure roller 52 to a non-pressurized state by separating it from the fixing roller 51 so that the recording material S passes through the fixing device 50 without heat and pressure being applied (S17).

[0058] The main control unit 101 transports the recording material S that has passed through the fixing device 50 to the double-sided transport unit 33 via the switchback unit 32 (S18), and then the double-sided transport unit 33 transports it again to the secondary transfer unit T2 (S19). The reason for this second transport is to allow the recording material S to pass through the secondary transfer unit T2 with the side on which the toner image M1 has been formed facing the secondary transfer outer roller 11, as shown in Figure 7(c). When the recording material S passes through the secondary transfer unit T2, the main control unit 101 applies a predetermined voltage to the secondary transfer outer roller 11 using the power supply 403, performing a discharge process that generates a discharge between the secondary transfer outer roller 11 and the recording material S (S20).

[0059] The main control unit 101 transports the discharged recording material S to the fixing device 50 (S21). The main control unit 101 maintains the fixing device 50 in a non-pressurized state (S21) so that the recording material S after discharge is not subjected to heat or pressure when it passes through the fixing device 50, and transports the recording material S that has passed through the fixing device 50 to the varnish coater 200 (S22). At this time, as shown in Figure 7(c), the recording material S is inverted by the switchback unit 32 and then handed over to the varnish coater 200 by the inversion discharge unit 31 so that the side on which the toner image M1 is fixed faces the position detection unit 245, varnish discharge unit 246, and varnish solidification unit 247 when it is transported inside the varnish coater 200.

[0060] The polarity of the predetermined voltage applied to the secondary transfer outer roller 11 for the discharge treatment described above (see S6 in Figure 4 and S20 in Figure 6) is described below. In this embodiment, as shown in Table 1, the polarity of the voltage applied to the secondary transfer outer roller 11 by the power supply 403 is changed depending on whether "repellency" or "bleeding" is to be suppressed, depending on the type of varnish. [Table 1]

[0061] If the toner has low wettability, the water-based varnish may repel. To suppress this repulsion, a negative voltage is applied to the secondary transfer outer roller 11, and a discharge treatment is performed. This creates a negative ion film on the toner surface, increasing the toner's wettability compared to before the discharge treatment. In other words, the energy from the discharge generated by the application of a predetermined voltage acts on the toner, increasing its surface energy and activating the toner surface, making it radical. In this case, polar groups are generated on the toner surface, increasing the adhesion to the water-based varnish compared to before the discharge treatment.

[0062] On the other hand, if the toner has high wettability, the water-based varnish may "bleed." To suppress the "bleeding" of the water-based varnish, a positive voltage is applied to the secondary transfer outer roller 11 and a discharge treatment is performed. As a result, a film of positive ions is formed on the surface of the toner, suppressing radicals, and thus the wettability of the toner can be lowered compared to before the discharge treatment. In other words, the polar groups on the toner surface react due to the discharge, lowering the surface energy of the toner, thus lowering the wettability of the toner.

[0063] On the other hand, in the case of oil-based varnish, a voltage of the opposite polarity to that of water-based varnish is applied. That is, in order to suppress the "repellency" of oil-based varnish, a negative polarity voltage is applied to the secondary transfer outer roller 11, and in order to suppress the "bleeding" of oil-based varnish, a positive polarity voltage is applied to the secondary transfer outer roller 11.

[0064] Furthermore, the "repellency" and "bleeding" of water-based and oil-based varnishes are influenced by the wax contained in the toner. The wax may precipitate on the toner surface due to the heat from the fixing device 50, and the degree of this wax precipitation determines whether "bleeding" or "repellency" occurs. If the amount of wax precipitation is small, "bleeding" is more likely to occur with water-based varnishes, and "repellency" is more likely to occur with oil-based varnishes. Conversely, if the amount of wax precipitation is large, "repellency" is more likely to occur with water-based varnishes, and "bleeding" is more likely to occur with oil-based varnishes. This is because oil-based varnishes have properties (water repellency) similar to wax more than water-based varnishes.

[0065] The degree of wax deposition in these toners is determined by the fixing temperature at which the toner image is fixed. When the fixing temperature is below a threshold (for example, 140-190°C), the amount of wax deposition is small, and when the fixing temperature is above the threshold, the amount of wax deposition is large.

[0066] From the above perspective, in the case of water-based varnish, bleeding is likely to occur when the fixing temperature is below the threshold, so a positive voltage is applied to the secondary transfer outer roller 11 to suppress bleeding of the water-based varnish. Also, in the case of water-based varnish, repulsion is likely to occur when the fixing temperature is above the threshold, so a negative voltage is applied to the secondary transfer outer roller 11 to suppress repulsion of the water-based varnish.

[0067] On the other hand, in the case of oil-based varnish, "repellency" is more likely to occur when the fixing temperature is below the threshold, so a negative voltage is applied to the secondary transfer outer roller 11 to suppress "repellency" of the oil-based varnish. Also, in the case of oil-based varnish, "bleeding" is more likely to occur when the fixing temperature is above the threshold, so a positive voltage is applied to the secondary transfer outer roller 11 to suppress "bleeding" of the oil-based varnish.

[0068] Next, we will discuss the voltage applied to the secondary transfer outer roller 11 for the discharge process described above. Figure 8 shows the resistance value "5 × 10 6This shows the relationship between the applied voltage (V) of the power supply 403 detected by the voltage detection sensor 403a and the amount of current (μA) detected by the current detection sensor 403b when using the secondary transfer outer roller 11 of (Ω).

[0069] The inventors conducted experiments to determine whether "repellency" or "bleeding" occurred in the varnish image, separately for water-based varnish and oil-based varnish. In the experiment, a recording material S with a solid black toner image fixed to it was re-transported, and after passing through the secondary transfer section T2 with different voltages applied for discharge treatment, spot varnish processing with a spot diameter of "Φ1 mm" was performed on the toner image. The inventors then visually confirmed whether "repellency" or "bleeding" occurred in the varnish image. Table 2 shows the experimental results. The recording material S was A3 size "OK Top Coat + 127.9 g / m²" 2 ) (manufactured by Oji Paper Co., Ltd.) was used. [Table 2]

[0070] As shown in Table 2, both water-based and oil-based varnishes exhibited "repellency" and "bleeding" in the varnish image when no voltage was applied, i.e., when no discharge treatment was performed. In contrast, with water-based varnishes, no "repellency" occurred when a negative voltage of "-60 to -40 μA" was applied, and no "bleeding" occurred when a positive voltage of "40 to 60 μA" was applied. On the other hand, with oil-based varnishes, no "bleeding" occurred when a negative voltage of "-60 to -40 μA" was applied, and no "repellency" occurred when a positive voltage of "40 to 60 μA" was applied.

[0071] In light of the above experimental results, in this embodiment, when performing the discharge process described above, a voltage equal to or greater than the discharge start voltage that allows a current of 40 μA or more and 60 μA or less in absolute value to flow is applied by the power supply 403. The voltage value that allows a current of 40 μA or more and 60 μA or less in absolute value to flow is, for example, 2200 V or more and 2800 V or less in absolute value, as shown in Figure 8. By applying a voltage that allows a current of 40 μA or more in absolute value to flow, the wettability of the toner can be changed as described above, thereby suppressing the occurrence of "repellency" and "bleeding" in the varnish image. However, applying a voltage that allows a current greater than 60 μA in absolute value to flow is undesirable because the discharge may accelerate the deterioration of the secondary transfer outer roller 11, potentially shortening the lifespan of the secondary transfer outer roller 11.

[0072] As described above, in this embodiment, the recording material S on which the toner image is fixed to the varnish image forming surface where the varnish image is formed is re-transported to the secondary transfer section T2 to which a voltage equal to or greater than the discharge voltage is applied to the secondary transfer outer roller 11, thereby generating a discharge on the varnish image forming surface side on which the toner image is formed. In the toner image formed on the varnish image forming surface side, positive and negative ions appear in the toner due to the discharge, and the surface of the toner image is coated with a film of these ions. In the case of water-based varnish, if the fixing temperature is below the threshold and "bleeding" is likely to occur, a film of positive ions is generated to reduce the adhesion between the toner image and the water-based varnish. On the other hand, if the fixing temperature is above the threshold and "repellency" due to wax is likely to occur, a film of negative ions is generated to improve the adhesion between the toner image and the water-based varnish. In the case of oil-based varnish, a voltage of the opposite polarity to that of the water-based varnish described above is applied to generate a discharge on the varnish image forming surface side on which the toner image is formed. By performing this discharge process, it is possible to suppress image defects such as "bleeding" or "repellency" in the varnish image when the varnish image is superimposed on the toner image on the recording material.

[0073] [Second Embodiment] In the first embodiment described above, an external power supply method was explained as an example in which a secondary transfer voltage is applied to the secondary transfer outer roller 11 in order to form a transfer electric field in the secondary transfer section T2, but the invention is not limited to this. The embodiment described above may also be applied to a method (referred to as an internal power supply method) in which a secondary transfer voltage is applied to the secondary transfer inner roller 14 that contacts the inner circumferential surface of the intermediate transfer belt 80 in order to form a transfer electric field in the secondary transfer section T2. ​​Below, a second embodiment of the internal power supply method will be described, mainly in terms of the differences from the first embodiment described above.

[0074] First, a brief explanation of the internally powered image forming apparatus will be given. In the internally powered system, a power supply 403 with variable polarity and voltage is connected to the secondary transfer inner roller 14, and the secondary transfer outer roller 11 is connected to ground potential (0V) (see Figure 10(a) described later). When the power supply 403 applies a secondary transfer voltage with the same polarity as the charging polarity of the toner to the secondary transfer inner roller 14, a transfer electric field is generated in the secondary transfer section T2, and the toner image supported on the intermediate transfer belt 80 is transferred to the recording material S. The secondary transfer inner roller 14 may have the same configuration as the secondary transfer outer roller 11 described above. In addition, the main control unit 101 is connected to the power supply 403, a voltage detection sensor 403a that detects the output voltage of the power supply 403, and a current detection sensor 403b that detects the output current flowing between the power supply 403 and the secondary transfer inner roller 14.

[0075] Next, the "image formation process" in the internal power supply system will be explained using Figures 9 to 12(b) with reference to Figure 3. Figure 9 is a flowchart of the image formation process during double-sided printing in the internal power supply system, where toner images are formed on both the one-sided and two-sided surfaces, and varnish is applied to the one-sided surface. To make the explanation easier to understand, Figure 9 shows the process from fixing the toner image M1 to the one-sided surface of the recording material S, to forming the toner image M2 on the two-sided surface. Here again, the explanation will be given as an example where the one-sided surface of the recording material S on which the toner image M1 is formed is the "varnish image formation surface". In the image formation process of the second embodiment shown in Figure 9, the same steps as in the image formation process of the first embodiment described above (see Figure 6) are given the same step numbers, and the explanation is simplified or omitted.

[0076] As shown in Figure 9, the main control unit 101 forms a toner image M1 to be transferred to one side of the recording material S on the intermediate transfer belt 80 (S41). The main control unit 101 then transfers the toner image M1 from the intermediate transfer belt 80 to the recording material S in the secondary transfer unit T2 (S12). When transferring the toner image M1 from the intermediate transfer belt 80 to the recording material S, the main control unit 101 uses the power supply 403 to apply a secondary transfer voltage to the secondary transfer roller 14 that has the same polarity as the charge polarity of the toner.

[0077] The main control unit 101 applies heat and pressure to the recording material S using the fixing device 50 to fix the toner image M1 to one side of the recording material S (S13), and then transports the recording material S to the double-sided transport unit 33 via the switchback unit 32 (S14). In this embodiment, after the toner image M1 is fixed, the recording material S is transported to the double-sided transport unit 33 via the switchback unit 32, as shown in Figure 10(a).

[0078] Then, the main control unit 101 re-transports the recording material S to the secondary transfer unit T2 via the double-sided transport unit 33 (S15). As shown in Figure 10(b), the recording material S, on which the toner image M1 has been formed on the first surface, passes through the secondary transfer unit T2 with the side on which the toner image M1 has been formed facing the secondary transfer outer roller 11. At this time, the main control unit 101 is in a non-applied state, meaning that no voltage is applied to the secondary transfer inner roller 14 by the power supply 403 (S16). In other words, the discharge process described above is not performed. Furthermore, the main control unit 101 sets the pressure roller 52 to a non-pressurized state by separating it from the fixing roller 51 so that the recording material S passes through the fixing device 50 without heat and pressure being applied (S17).

[0079] The main control unit 101 transports the recording material S that has passed through the fixing device 50 to the double-sided transport unit 33 via the switchback unit 32 (S18), and then the double-sided transport unit 33 transports it again to the secondary transfer unit T2 (S19). As a result, as shown in Figure 10(c), the recording material S passes through the secondary transfer unit T2 with the side on which the toner image M1 is formed facing the secondary transfer roller 14. When the recording material S passes through the secondary transfer unit T2, the main control unit 101 applies a predetermined voltage to the secondary transfer roller 14 using the power supply 403, performing a discharge process that generates a discharge between the secondary transfer roller 14 and the recording material S (S20). The polarity of the predetermined voltage applied to the secondary transfer roller 14 by the power supply 403 is determined in the same way as in the first embodiment described above, based on whether the varnish is water-based or oil-based, and whether the fixing temperature is below or above a threshold, and the voltage value is the same as in the first embodiment described above.

[0080] The main control unit 101 transports the discharged recording material S to the fixing device 50 (S21). The main control unit 101 maintains the fixing device 50 in a non-pressurized state (S21) so that the recording material S after discharge is not subjected to heat or pressure when it passes through the fixing device 50, and transports the recording material S that has passed through the fixing device 50 to the varnish coater 200 (S22). In the case of the internal power supply system, as shown in Figure 10(c), the recording material S is transferred to the varnish coater 200 by the reversal discharge unit 31 without being reversed by the switchback unit 32. This is because, after the second retransport (see S19), the side on which the toner image M1 is fixed faces the position detection unit 245, varnish discharge unit 246, and varnish solidification unit 247.

[0081] Figure 11 is a flowchart showing the image formation process during double-sided printing in an internal power supply system, where toner images are formed on both the one-sided and two-sided surfaces, and varnish is applied to the one-sided surface. To facilitate understanding, Figure 11 shows the process from fixing the toner image M1 to the one-sided surface of the recording material S, to forming the toner image M2 on the two-sided surface.

[0082] As shown in Figure 11, after fixing the toner image M1 on one side, the main control unit 101 forms a toner image M2 on the intermediate transfer belt 80 to be transferred to the second side of the recording material S (S31). The main control unit 101 then performs a secondary transfer of the toner image M2 from the intermediate transfer belt 80 to the recording material S in the secondary transfer unit T2 (S2).

[0083] The main control unit 101 applies heat and pressure to the recording material S using the fixing device 50 to fix the toner image M2 to two sides of the recording material S (S3), and then transports the recording material S to the double-sided transport unit 33 via the switchback unit 32 (S4). After the toner image M2 is fixed, the recording material S is transported to the double-sided transport unit 33 via the switchback unit 32, as shown in Figure 12(a).

[0084] Then, the main control unit 101 re-transports the recording material S to the secondary transfer unit T2 using the double-sided transport unit 33 (S5). The recording material S, on which toner images (M1, M2) are formed on both sides, passes through the secondary transfer unit T2 with the side on which the toner image M1 is formed facing the secondary transfer roller 14, as shown in Figure 12(b). As the recording material S passes through the secondary transfer unit T2, the main control unit 101 applies a predetermined voltage to the secondary transfer roller 14 using the power supply 403, performing a discharge process to generate a discharge between the secondary transfer roller 14 and the recording material S (S6). The polarity of the predetermined voltage applied to the secondary transfer roller 14 by the power supply 403 is determined in the same way as in the first embodiment described above, based on whether the varnish is water-based or oil-based, and whether the fixing temperature is below or above a threshold, and the voltage value is the same as in the first embodiment described above.

[0085] The main control unit 101 transports the discharged recording material S to the fixing device 50. In order to allow the discharged recording material S to pass through, the main control unit 101 separates the pressure roller 52 from the fixing roller 51 in the fixing device 50 to a non-pressurized state (S7). The main control unit 101 transports the recording material S that has passed through the fixing device 50 to the varnish coater 200 (S8). In the case of the internal power supply system, as shown in Figure 12(b), the recording material S is transferred to the varnish coater 200 by the reversal discharge unit 31 without being reversed by the switchback unit 32. This is because, due to the above retransportation (see S5), the side on which the toner image M1 is fixed faces the position detection unit 245, varnish discharge unit 246, and varnish solidification unit 247.

[0086] As described above, in the case of the internal power supply method, the side on which the toner image M1 is formed must be directed toward the secondary transfer inner roller 14 side rather than the secondary transfer outer roller 11 side. Therefore, the re-transport procedure of the recording material S differs from that of the external power supply method described above. On the other hand, the discharge process associated with the voltage application by the power supply 403 is the same as in the case of the external power supply method. Therefore, even in the case of the internal power supply method, performing the discharge process in the same way as in the case of the external power supply method has the effect of suppressing image defects such as "bleeding" and "repulsion" in the varnish image.

[0087] [Other embodiments] In the first and second embodiments described above, the fixing device 50 was kept in a non-pressurized state when the recording material S was re-transported, but this is not limited to this. For example, the recording material S may be passed through in a non-heated state, that is, when the power supply to the halogen heater 53 by the heater power supply 54 is stopped, i.e., when the fixing roller 51 is not heated by the halogen heater 53. Although not shown in the figures, a retraction path that bypasses the fixing device 50 may be provided within the image forming apparatus 100, and the recording material S may be transported through this retraction path when it is re-transported.

[0088] In the first and second embodiments described above, the case where water-based varnish or oil-based varnish was used as the varnish was explained, but the varnish is not limited to these, and may be an ultraviolet-curing UV varnish. UV varnish mainly contains a photosensitive resin, a photosensitive monomer, a photoinitiator, and additives. Examples of photosensitive resins include acrylic resins having (meth)acryloyl groups. Examples of photosensitive monomers include monomers and oligomers having at least one (meth)acryloyl group in the molecule. Examples of photoinitiators include acetophenone, benzoin ethyl ether, and 1-hydroxycyclohexyl phenyl ketone. Examples of additives include waxes, plasticizers, leveling agents, solvents, polymerization inhibitors, anti-aging agents, photosensitizers, and defoamers. UV varnish may contain one of these, or two or more. The content of each component is not particularly limited, but it is preferable that the UV varnish contains, for example, 1-20% by mass of photosensitive resin, 30-70% by mass of photosensitive monomer, 5-15% by mass of photoinitiator, and 5% by mass or less of additives. Examples of UV varnishes that can be used include "UV L Carton OP Varnish (product name)", "UV L Gloss OP Varnish (product name)", and "UV Matte OP Varnish (product name)" (manufactured by T&K TOKA Corporation). When using such UV varnishes, in order to suppress image defects such as "repellency" and "bleeding" in the varnish image, a discharge treatment similar to that used when using the oil-based varnish described above should be performed on the toner image before applying the varnish. [Explanation of symbols]

[0089] 1X…Image forming system, 11…Second rotating body (secondary transfer outer roller), 14…First rotating body (secondary transfer inner roller), 31…Inversion transport means (inversion discharge means, inversion discharge section), 32…Inversion transport means (switchback means, switchback section), 33…Inversion transport means (double-sided transport means, double-sided transport section), 50…Fixing means (fixing device), 51…Fixing rotating body (fixing roller), 52…Pressurizing rotating body (pressure roller), 53…Heating means (halogen heater), 54…Power supply means (heater power supply), 80…Image carrying belt (intermediate transfer belt), 100…Image forming apparatus, 101…Control means (main control unit), 200…Varnish coating device (varnish coater), 403…Voltage application means (power supply), S…Recording material, T2…Transfer nip section (secondary transfer section)

Claims

1. An image forming system comprising an image forming apparatus capable of forming a toner image on a recording material using a wax-containing toner, and a varnish coating apparatus capable of forming a varnish image on one side of a recording material using an aqueous varnish, An endless image-carrying belt that carries and rotates the toner image, A first rotating body that contacts the inner circumferential surface of the image-carrying belt, A second rotating body is provided between the first rotating body and the image carrying belt, and forms a transfer nip section that transfers a toner image from the image carrying belt to the recording material while gripping and transporting the recording material. Voltage applying means capable of applying voltage to the second rotating body, A fixing means capable of heating the recording material at multiple fixing temperatures, which applies heat and pressure to the recording material on which a toner image has been formed to fix the toner image to the recording material, An inversion transport means capable of reversing the front and back sides of the recording material that has passed through the fixing means and transporting it to the transfer nip section, The system comprises a voltage application means and a control means for controlling the inverting transport means, During single-sided printing on a recording material, the recording material is inverted by the inversion transport means after the toner image is transferred to the one-sided side and fixed by the fixing means, and then transported again to the transfer nip section with the one-sided side facing the second rotating body side, and as it passes through the transfer nip section, the voltage application means applies a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and applies a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than a threshold, before being discharged to the varnish coating device so that a varnish image is formed on the one-sided side. An image forming system characterized by the following features.

2. The fixing means comprises a fixing rotating body and a pressing rotating body that is provided so as to be able to move toward and away from the fixing rotating body and forms a fixing nip portion that clamps and conveys the recording material while in contact with the fixing rotating body. The fixing means causes the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image is fixed to one side, to pass through the pressurized rotating body in an unpressurized state separated from the fixing rotating body. The image forming system according to claim 1.

3. The fixing means comprises a fixing rotating body, a pressurizing rotating body that forms a fixing nip portion for gripping and conveying the recording material while in contact with the fixing rotating body, and a heating means for heating the fixing rotating body. The heating means is provided with a power supply means that supplies power to the heating means to cause heating, The fixing means allows the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to one side, to pass through in a non-heated state with the power supply to the heating means by the power supply means stopped. The image forming system according to claim 1.

4. During double-sided printing on recording material, after the toner image is fixed to one side of the recording material, it is inverted by the inversion transport means and re-transported to the transfer nip section, at which point the toner image is transferred to the two sides opposite to the one side. After the toner image is fixed to the two sides, the material is inverted by the inversion transport means and re-transported to the transfer nip section, passing through the transfer nip section with the two sides facing the second rotating body and no voltage applied by the voltage application means, and then inverted again by the inversion transport means and re-transported to the transfer nip section, passing through the transfer nip section with one side facing the second rotating body, at which point the voltage application means applies a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and applies a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than a threshold, before being discharged to the varnish coating apparatus so that a varnish image is formed on the one side. The image forming system according to claim 1.

5. The fixing means comprises a fixing rotating body and a pressing rotating body that is provided so as to be able to move toward and away from the fixing rotating body and forms a fixing nip portion that clamps and conveys the recording material while in contact with the fixing rotating body. The fixing means causes the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to the two sides, to pass through the pressurized rotating body in an unpressurized state separated from the fixing rotating body. The image forming system according to feature 4.

6. The fixing means comprises a fixing rotating body, a pressurizing rotating body that forms a fixing nip portion for gripping and conveying the recording material while in contact with the fixing rotating body, and a heating means for heating the fixing rotating body. The heating means is provided with a power supply means that supplies power to the heating means to cause heating, The fixing means allows the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to the two sides, to pass through in a non-heated state with the power supply to the heating means by the power supply means stopped. The image forming system according to feature 4.

7. The inverted transport means includes a switchback means that changes the transport direction of the recording material by swapping the leading and trailing ends of the recording material that has passed through the fixing means, a double-sided transport means that transports the recording material from the switchback means to the transfer nip section, and an inverted discharge means that discharges the recording material in an inverted state from the switchback means to the varnish coating device. The recording material is discharged to the varnish coating device in an inverted state by the inversion discharge means. The image forming system according to any one of claims 1 to 6.

8. An image forming system comprising an image forming apparatus capable of forming a toner image on a recording material using a wax-containing toner, and a varnish coating apparatus capable of forming a varnish image on one side of a recording material using an oil-based varnish or UV varnish, An endless image-carrying belt that carries and rotates the toner image, A first rotating body that contacts the inner circumferential surface of the image-carrying belt, A second rotating body is provided between the first rotating body and the image carrying belt, and forms a transfer nip section that transfers a toner image from the image carrying belt to the recording material while gripping and transporting the recording material. Voltage applying means capable of applying voltage to the second rotating body, A fixing means capable of heating the recording material at multiple fixing temperatures, which applies heat and pressure to the recording material on which a toner image has been formed to fix the toner image to the recording material, An inversion transport means capable of reversing the front and back sides of the recording material that has passed through the fixing means and transporting it to the transfer nip section, The system comprises a voltage application means and a control means for controlling the inverting transport means, During single-sided printing on a recording material, the recording material is inverted by the inversion transport means after the toner image is transferred to the one-sided side and fixed by the fixing means, and then transported again to the transfer nip section with the one-sided side facing the second rotating body side. As the recording material passes through the transfer nip section, the voltage application means applies a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than a threshold, before being discharged to the varnish coating device so that a varnish image is formed on the one-sided side. An image forming system characterized by the following features.

9. The fixing means comprises a fixing rotating body and a pressing rotating body that is provided so as to be able to move toward and away from the fixing rotating body and forms a fixing nip portion that clamps and conveys the recording material while in contact with the fixing rotating body. The fixing means causes the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image is fixed to one side, to pass through the pressurized rotating body in an unpressurized state separated from the fixing rotating body. The image forming system according to claim 8.

10. The fixing means comprises a fixing rotating body, a pressurizing rotating body that forms a fixing nip portion for gripping and conveying the recording material while in contact with the fixing rotating body, and a heating means for heating the fixing rotating body. The heating means is provided with a power supply means that supplies power to the heating means to cause heating, The fixing means allows the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to one side, to pass through in a non-heated state with the power supply to the heating means by the power supply means stopped. The image forming system according to claim 8.

11. During double-sided printing on recording material, after the toner image is fixed to one side of the recording material, it is inverted by the inversion transport means and re-transported to the transfer nip section, at which point the toner image is transferred to the two sides opposite to the one side. After the toner image is fixed to the two sides, the material is inverted by the inversion transport means and re-transported to the transfer nip section, passing through the transfer nip section with the two sides facing the second rotating body and no voltage applied by the voltage application means, and then inverted again by the inversion transport means and re-transported to the transfer nip section, passing through the transfer nip section with one side facing the second rotating body, at which point the voltage application means applies a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than a threshold, before being discharged to the varnish coating apparatus so that a varnish image is formed on the one side. The image forming system according to claim 8.

12. The fixing means comprises a fixing rotating body and a pressing rotating body that is provided so as to be able to move toward and away from the fixing rotating body and forms a fixing nip portion that clamps and conveys the recording material while in contact with the fixing rotating body. The fixing means causes the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to the two sides, to pass through the pressurized rotating body in an unpressurized state separated from the fixing rotating body. The image forming system according to feature 11.

13. The fixing means comprises a fixing rotating body, a pressurizing rotating body that forms a fixing nip portion for gripping and conveying the recording material while in contact with the fixing rotating body, and a heating means for heating the fixing rotating body. The heating means is provided with a power supply means that supplies power to the heating means to cause heating, The fixing means allows the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to the two sides, to pass through in a non-heated state with the power supply to the heating means by the power supply means stopped. The image forming system according to feature 11.

14. The inverted transport means includes a switchback means that changes the transport direction of the recording material by swapping the leading and trailing ends of the recording material that has passed through the fixing means, a double-sided transport means that transports the recording material from the switchback means to the transfer nip section, and an inverted discharge means that discharges the recording material in an inverted state from the switchback means to the varnish coating device. The recording material is discharged to the varnish coating device in an inverted state by the inversion discharge means. The image forming system according to any one of claims 8 to 13, characterized by the features described herein.

15. An image forming system comprising an image forming apparatus capable of forming a toner image on a recording material using a wax-containing toner, and a varnish coating apparatus capable of forming a varnish image on one side of a recording material using an aqueous varnish, An endless image-carrying belt that carries and rotates the toner image, A first rotating body that contacts the inner circumferential surface of the image-carrying belt, A second rotating body is provided between the first rotating body and the image carrying belt, and forms a transfer nip section that transfers a toner image from the image carrying belt to the recording material while gripping and transporting the recording material. Voltage applying means capable of applying voltage to the first rotating body, A fixing means capable of heating the recording material at multiple fixing temperatures, which applies heat and pressure to the recording material on which a toner image has been formed to fix the toner image to the recording material, An inversion transport means capable of reversing the front and back sides of the recording material that has passed through the fixing means and transporting it to the transfer nip section, The system comprises a voltage application means and a control means for controlling the inverting transport means, During single-sided printing on a recording material, the recording material is inverted by the inversion transport means and re-transported to the transfer nip section, passing through the transfer nip section with the one-sided side facing the second rotating body and no voltage applied by the voltage application means. Furthermore, it is inverted by the inversion transport means and re-transported to the transfer nip section, and as it passes through the transfer nip section with the one-sided side facing the first rotating body, the voltage application means applies a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than a threshold, before being discharged to the varnish coating apparatus so that a varnish image is formed on the one-sided side. An image forming system characterized by the following features.

16. The fixing means comprises a fixing rotating body and a pressing rotating body that is provided so as to be able to move toward and away from the fixing rotating body and forms a fixing nip portion that clamps and conveys the recording material while in contact with the fixing rotating body. The fixing means causes the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image is fixed to one side, to pass through the pressurized rotating body in an unpressurized state separated from the fixing rotating body. The image forming system according to claim 15, characterized in that it is the same as described above.

17. The fixing means comprises a fixing rotating body, a pressurizing rotating body that forms a fixing nip portion for gripping and conveying the recording material while in contact with the fixing rotating body, and a heating means for heating the fixing rotating body. The heating means is provided with a power supply means that supplies power to the heating means to cause heating, The fixing means allows the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to one side, to pass through in a non-heated state with the power supply to the heating means by the power supply means stopped. The image forming system according to claim 15, characterized in that it is the same as described above.

18. During double-sided printing on recording material, after the toner image is fixed to one side of the recording material, it is inverted by the inversion transport means, and as it passes through the transfer nip section with the one side facing the second rotating body, a predetermined transfer voltage is applied by the voltage application means, thereby transferring the toner image to the two sides opposite to the one side. After the toner image is fixed to the two sides, the material is inverted by the inversion transport means and re-transported to the transfer nip section. As it passes through the transfer nip section with one side facing the first rotating body, the voltage application means applies a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than the threshold, before being discharged to the varnish coating apparatus so that a varnish image is formed on the one side. The image forming system according to claim 15, characterized in that it is the same as described above.

19. The fixing means comprises a fixing rotating body and a pressing rotating body that is provided so as to be able to move toward and away from the fixing rotating body and forms a fixing nip portion that clamps and conveys the recording material while in contact with the fixing rotating body. The fixing means causes the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to the two sides, to pass through the pressurized rotating body in an unpressurized state separated from the fixing rotating body. The image forming system according to claim 18.

20. The fixing means comprises a fixing rotating body, a pressurizing rotating body that forms a fixing nip portion for gripping and conveying the recording material while in contact with the fixing rotating body, and a heating means for heating the fixing rotating body. The heating means is provided with a power supply means that supplies power to the heating means to cause heating, The fixing means allows the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to the two sides, to pass through in a non-heated state with the power supply to the heating means by the power supply means stopped. The image forming system according to feature 18.

21. The inverted transport means includes a switchback means that changes the transport direction of the recording material by swapping the leading and trailing ends of the recording material that has passed through the fixing means, a double-sided transport means that transports the recording material from the switchback means to the transfer nip section, and an inverted discharge means that discharges the recording material in an inverted state from the switchback means to the varnish coating device. The recording material is discharged to the varnish coating device in an inverted state by the inversion discharge means. The image forming system according to any one of claims 15 to 20, characterized in that it is the same as described in the previous claim.

22. An image forming system comprising an image forming apparatus capable of forming a toner image on a recording material using a wax-containing toner, and a varnish coating apparatus capable of forming a varnish image on one side of a recording material using an oil-based varnish or UV varnish, An endless image-carrying belt that carries and rotates the toner image, A first rotating body that contacts the inner circumferential surface of the image-carrying belt, A second rotating body is provided between the first rotating body and the image carrying belt, and forms a transfer nip section that transfers a toner image from the image carrying belt to the recording material while gripping and transporting the recording material. Voltage applying means capable of applying voltage to the first rotating body, A fixing means capable of heating the recording material at multiple fixing temperatures, which applies heat and pressure to the recording material on which a toner image has been formed to fix the toner image to the recording material, An inversion transport means capable of reversing the front and back sides of the recording material that has passed through the fixing means and transporting it to the transfer nip section, The system comprises a voltage application means and a control means for controlling the inverting transport means, During single-sided printing on a recording material, the recording material is inverted by the inversion transport means and re-transported to the transfer nip section, passing through the transfer nip section with the one-sided side facing the second rotating body and no voltage applied by the voltage application means. Furthermore, it is inverted by the inversion transport means and re-transported to the transfer nip section, and as it passes through the transfer nip section with the one-sided side facing the first rotating body, the voltage application means applies a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than a threshold, before being discharged to the varnish coating apparatus so that a varnish image is formed on the one-sided side. An image forming system characterized by the following features.

23. The fixing means comprises a fixing rotating body and a pressing rotating body that is provided so as to be able to move toward and away from the fixing rotating body and forms a fixing nip portion that clamps and conveys the recording material while in contact with the fixing rotating body. The fixing means causes the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image is fixed to one side, to pass through the pressurized rotating body in an unpressurized state separated from the fixing rotating body. The image forming system according to claim 22, characterized in that it is as described above.

24. The fixing means comprises a fixing rotating body, a pressurizing rotating body that forms a fixing nip portion for gripping and conveying the recording material while in contact with the fixing rotating body, and a heating means for heating the fixing rotating body. The heating means is provided with a power supply means that supplies power to the heating means to cause heating, The fixing means allows the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to one side, to pass through in a non-heated state with the power supply to the heating means by the power supply means stopped. The image forming system according to claim 22, characterized in that it is as described above.

25. During double-sided printing on recording material, after the toner image is fixed to one side of the recording material, it is inverted by the inversion transport means, and as it passes through the transfer nip section with the one side facing the second rotating body, a predetermined transfer voltage is applied by the voltage application means, thereby transferring the toner image to the two sides opposite to the one side. After the toner image is fixed to the two sides, the toner is inverted by the inversion transport means and re-transported to the transfer nip section. As the toner passes through the transfer nip section with one side facing the first rotating body, the voltage application means applies a voltage of negative polarity that is equal to or greater than the discharge start voltage if the fixing temperature is below a threshold, and a voltage of positive polarity that is equal to or greater than the discharge start voltage if the fixing temperature is greater than the threshold, before the toner is discharged to the varnish coating apparatus so that a varnish image is formed on the one side. The image forming system according to claim 22, characterized in that it is as described above.

26. The fixing means comprises a fixing rotating body and a pressing rotating body that is provided so as to be able to move toward and away from the fixing rotating body and forms a fixing nip portion that clamps and conveys the recording material while in contact with the fixing rotating body. The fixing means causes the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to the two sides, to pass through the pressurized rotating body in an unpressurized state separated from the fixing rotating body. The image forming system according to claim 25, characterized in that it is as described above.

27. The fixing means comprises a fixing rotating body, a pressurizing rotating body that forms a fixing nip portion for gripping and conveying the recording material while in contact with the fixing rotating body, and a heating means for heating the fixing rotating body. The heating means is provided with a power supply means that supplies power to the heating means to cause heating, The fixing means allows the recording material, which is re-transported to the transfer nip section by the inversion transport means after the toner image has been fixed to the two sides, to pass through in a non-heated state with the power supply to the heating means by the power supply means stopped. The image forming system according to claim 25, characterized in that it is as described above.

28. The inverted transport means includes a switchback means that changes the transport direction of the recording material by swapping the leading and trailing ends of the recording material that has passed through the fixing means, a double-sided transport means that transports the recording material from the switchback means to the transfer nip section, and an inverted discharge means that discharges the recording material in an inverted state from the switchback means to the varnish coating device. The recording material is discharged to the varnish coating device in an inverted state by the inversion discharge means. The image forming system according to any one of claims 22 to 27.

Images