Patent Publication Number: US-2023139189-A1

Title: Drying apparatus and image forming system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This patent application is based on and claims priority pursuant to 35 U.S.C. §119(a) to Japanese Patent Application No. 2021-179193, filed on Nov. 2, 2021, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a drying apparatus and an image forming system. 
     Related Art 
     Drying apparatuses are known in the related art for drying a recording medium on which an image is to be formed using a heated gas in a drying chamber. 
     For example, a drying apparatus including a drying furnace (drying chamber) configured such that a recording medium on which an image is printed by an image forming apparatus is dried with hot air blown from a hot air blower is known. The hot air is generated by heating outside air taken in by an intake fan with a heater. 
     SUMMARY 
     In one aspect, a drying apparatus includes a drying chamber to dry a drying-target medium with a gas maintained at a preset temperature, and the drying-target medium is a medium to be dried. The drying chamber takes in the gas from a suction chamber into which a gas is sucked in through an intake hole formed in a retaining face on which the drying-target medium is retained with the gas sucked into the suction chamber. 
     In another aspect, an image forming system includes an image forming apparatus and the drying apparatus described above. The image forming apparatus includes a medium retainer including the suction chamber and the retaining face; and an image forming engine to form an image on a recording medium being the drying-target medium. The drying apparatus dries the recording medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings, wherein: 
         FIG.  1    is a diagram illustrating the general arrangement of an image forming system according to a first embodiment of the present disclosure: 
         FIG.  2 A  is a schematic plan view of an example of four recording heads of an image forming unit in the image forming system according to the first embodiment; 
         FIG.  2 B  is a schematic plan view of one of four head units of a recording head for black (K) ink according to the first embodiment; 
         FIG.  3 A  is a schematic cross-sectional view of a portion of the head unit illustrated in  FIG.  2 B , taken in a longitudinal direction of a liquid chamber; 
         FIG.  3 B  is a schematic cross-sectional view of the portion of the head unit, taken along line SCI illustrated in  FIG.  3 A , that is, in a direction that is orthogonal to the longitudinal direction of the liquid chamber and that is a direction in which nozzles are arranged; 
         FIG.  4    is a diagram illustrating the schematic configuration of a post-treatment drying unit and the image forming unit in the image forming system according to the first embodiment; 
         FIG.  5    is a graph illustrating an overview of a flow of air from a suction chamber of the image forming unit to a drying chamber of the post-treatment drying unit and an overview of a change in temperature; 
         FIG.  6    is a perspective diagram illustrating the external appearance of an image forming system according to a second embodiment of the present disclosure; 
         FIG.  7    is a plan view of a carriage scanning mechanism in the image forming system according to the second embodiment; 
         FIG.  8    is a schematic diagram illustrating the internal configuration of the image forming system according to the second embodiment; 
         FIG.  9    is a diagram illustrating the schematic configuration of a post-treatment drying unit and an image forming unit of an image forming system according to a first modification of the present disclosure; and 
         FIG.  10    is a diagram illustrating the schematic configuration of a post-treatment drying unit and an image forming unit of an image forming system according to a second modification of the present disclosure. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views. 
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result. 
     Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     First Embodiment 
     An example of an image forming system including a drying apparatus according to a first embodiment of the present disclosure will be described hereinafter with reference to the drawings. 
     The image forming system according to the first embodiment includes, for example recording heads that discharge inks of four colors, namely, black (K), cyan (C), magenta (M), and yellow (Y), and form an image with the inks on a recording medium. However, the image forming system to which aspects of the present disclosure are applicable is not limited thereto. In one example, the image forming system further includes recording heads for inks of green (G), red (R), light cyan (LC), and/or other colors. In another example, the image forming system includes only a recording head for black (K) ink. In the following description, symbols with suffixes “K,” “C,” “M,” and “Y” correspond to black, cyan, magenta, and yellow, respectively. The image forming system may be based on another image forming method such as an electrophotographic method. 
     In the first embodiment, a continuous sheet wound on a roll (hereinafter referred to as “roll sheet Md”) is used as a recording medium. In some embodiments of the present disclosure, the image forming system forms an image on a recording medium other than a roll sheet. In an embodiment of the present disclosure, the image forming system may form an image on a cut sheet. In one or more embodiments of the present disclosure, the image forming system is used to form an image on a recording medium, examples of which include a sheet of plain paper, a sheet of high-quality paper, a sheet of thin paper, a sheet of thick paper, a sheet of recording paper, a roll sheet, an overhead projector (OHP) sheet, a synthetic resin film, a thin metal film, and any other recording medium having a surface on which an image is to be formed using ink, toner, or the like. As used herein, the term “roll sheet” refers to a continuous sheet (continuous form) having sets of perforations at predetermined intervals to cut the sheet into pieces along the sets of perforations. Each page of the roll sheet is, for example, an area defined between two sets of perforations formed at predetermined intervals. 
     As illustrated in  FIG.  1   , an image forming system  100  according to the first embodiment includes a loading unit  10  and a pre-treatment unit  20 . The loading unit  10  loads the roll sheet Md. The pre-treatment unit  20  applies pre-treatment to the loaded roll sheet Md. The image forming system  100  further includes an image forming unit  40 , a post-treatment unit  50 , and an unloading unit  60 . The image forming unit  40  is an image forming apparatus that forms an image on a surface of the roll sheet Md. The post-treatment unit  50  applies post-treatment to the roll sheet Md on which the image is formed. The unloading unit  60  unloads the roll sheet Md to which post-treatment is applied. The image forming system  100  further includes a pre-treatment drying unit  30  and a post-treatment drying unit  80 . The pre-treatment drying unit  30  dries the roll sheet Md to which pre-treatment is applied. The post-treatment drying unit  80  is a drying apparatus that dries the roll sheet Md after post-treatment is applied to the roll sheet Md. The image forming system  100  further includes a controller  70  that controls the operation of the image forming system  100 . The controller  70  is, for example, a general-purpose computer. 
     In the image forming system  100  according to the first embodiment, the roll sheet Md is loaded into the image forming system  100  by the loading unit  10 , and a surface of the roll sheet Md is subjected to pre-treatment and drying by the pre-treatment unit  20  and the pre-treatment drying unit  30 , respectively. In the image forming system  100 , the image forming unit  40  forms an image on the surface of the roll sheet Md that is subjected to pre-treatment and drying. In the image forming system  100 , furthermore, in the first embodiment, the roll sheet Md on which the image is formed is subjected to post-treatment and drying by the post-treatment unit  50  and the post-treatment drying unit  80 , respectively. In the image forming system  100 , then, the unloading unit  60  winds the roll sheet Md. 
     Next, the components of the image forming system  100  according to the first embodiment will be described in detail. 
     In one or more embodiments of the present disclosure, the image forming system  100  does not include one or more of the pre-treatment unit  20  and the like described below, depending on the type of a recording medium on which an image is to be formed. 
     The loading unit  10  conveys the recording medium to the pre-treatment unit  20  and the like. In the first embodiment, the loading unit  10  includes a sheet feeder  11 , a plurality of conveyance rollers  12 , and the like. The loading unit  10  loads the roll sheet Md wound around and held by a sheet feeding roll of the sheet feeder  11  by using the conveyance rollers  12  and the like and conveys the roll sheet Md to the pre-treatment unit  20  and the like described below. 
     The pre-treatment unit  20  applies treatment to the recording medium before an image is formed on the recording medium. In the first embodiment, the pre-treatment unit  20  applies pre-treatment to a surface of the roll sheet Md loaded by the loading unit  10  with a pre-treatment liquid. In the first embodiment, the pre-treatment is a treatment for uniformly applying a pre-treatment liquid described below, which has a function of aggregating ink, to the surface of the roll sheet Md (i.e., the recording medium). Through the treatment, in the formation of an image on paper dedicated to inkjet printers or a recording medium other than inkjet dedicated paper, in the image forming system  100 , a pre-treatment liquid having a function of aggregating ink can adhere to the surface of the recording medium using the pre-treatment unit  20  before an image is formed on the recording medium. As a result, the image forming system  100  can reduce quality degradation in an image to be formed, such as bleed-through, density degradation, tone degradation, and show-through, and also reduce issues related to waterfastness, weather-fastness, and other types of fastness of image. Accordingly, the quality of an image formed thereafter can be improved. 
     As illustrated in  FIG.  1   , the pre-treatment unit  20  uses a roll coating method to apply a stored pre-treatment liquid  20 L to the surface of the roll sheet Md loaded into the pre-treatment unit  20  by the loading unit  10 . More specifically, in the pre-treatment unit  20 , first, a stirring roller  21  and a thinning roller  22  are used to transfer the pre-treatment liquid  20 L onto a surface of an application roller  23  in a thin film form. The application roller  23  rotates while being pressed against a rotating platen roller  24 , and the roll sheet Md is conveyed into a gap between the application roller  23  and the platen roller  24  to apply the pre-treatment liquid  20 L to the surface of the roll sheet Md. 
     The pre-treatment unit  20  uses a pressure regulator  25  to control a nip pressure for applying the pre-treatment liquid  20 L. The nip pressure is a pressure acting on a position at which the application roller  23  and the platen roller  24  come into contact with each other. The pre-treatment unit  20  may control the rotational speeds of the application roller  23  and the platen roller  24 . As a result, the pre-treatment unit  20  can change the rotational speeds of the application roller  23  and the like, and can change the nip pressure using the pressure regulator  25 . In addition, the pre-treatment unit  20  can more accurately control the amount of application of the pre-treatment liquid  20 L (such as the film thickness, the amount of liquid, the amount of adhesion, or the amount of dry adhesion). This makes it possible to apply the pre-treatment liquid  20 L to the surface of the roll sheet Md (i.e., the recording medium) in an amount of application suitable for subsequent image formation and post-treatment. 
     The pre-treatment drying unit  30  dries the recording medium by heating or the like. More specifically, the pre-treatment drying unit  30  according to the first embodiment heats heat rollers  31   h  to, for example. 40° C. to 100° C., and conveys the roll sheet Md to which the pre-treatment liquid  20 L is applied while bringing the roll sheet Md into contact with the heat rollers  31   h . As a result, the pre-treatment drying unit  30  can evaporate the moisture of the pre-treatment liquid  20 L adhering to the roll sheet Md and dry (the pre-treatment liquid  20 L of) the roll sheet Md. 
     To increase the drying effect, as illustrated in  FIG.  1   , the pre-treatment drying unit  30  according to the first embodiment preferably includes a plurality of heat rollers  31   h  arranged in multiple stages. In this configuration, to weaken the drying strength, the heat roller temperature is decreased. For example, the heat roller temperature is set to about 40° C. to 80° C. In one example, some of the heat rollers  31   h  are heated while the other heat rollers  31   h  are not heated. To increase the drying strength, the number of heat rollers  31   h  used is increased, or the heat roller temperature is increased. As described above, the drying strength can be controlled by changing the temperature of the heat rollers  31   h  and/or the number of heat rollers  31   h  used. 
     The pre-treatment drying unit  30  may perform drying using a method other than using the heat rollers  31   h . 
     For example, the pre-treatment drying unit  30  may use infrared drying, microwave drying, hot-air drying, or any other drying method. Alternatively, the pre-treatment drying unit  30  may use a plurality of drying methods in combination. In one example, the pre-treatment drying unit  30  may heat the roll sheet Md (i.e., the recording medium) (preheating step) before the pre-treatment unit  20  applies the pre-treatment liquid  20 L to the roll sheet Md. Like the post-treatment drying unit  80  described below, the pre-treatment drying unit  30  may be a drying apparatus that dries the recording medium with a heated gas in a drying chamber. 
     The image forming unit  40  is an image forming apparatus that forms an image on a recording medium. In the first embodiment, the image forming unit  40  employs an inkjet recording method in which ink is discharged onto the roll sheet Md, which is dried by the pre-treatment drying unit  30 , to form an image on the surface of the roll sheet Md. 
       FIG.  2 A  is a schematic plan view of an example of four recording heads  40 K,  40 C,  40 M, and  40 Y of the image forming unit  40  according to the first embodiment.  FIG.  2 B  is a schematic plan view of one of four head units  40 K- 1 ,  40 K- 2 ,  40 K- 3 , and  40 K- 4  of the recording head  40 K for black (K) ink. 
     As illustrated in  FIG.  2 A . the image forming unit  40  includes an air-suction type sheet retainer  46  (a medium retainer) at a position facing the recording heads  40 K,  40 C,  40 M, and  40 Y with the roll sheet Md therebetween. The sheet retainer  46  includes a retaining face  46   a  having intake holes  46   b  (see  FIG.  4   ) and retains the roll sheet Md on the retaining face  46   a  with air sucked in from the intake holes  46   b . This prevents the roll sheet Md on which the inks discharged from the recording heads  40 K,  40 C,  40 M, and  40 Y land from floating from the retaining face  46   a  of the sheet retainer  46 . As a result, a high-quality image can be formed. 
     The image forming unit  40  may include a full-line recording head. In the image forming unit  40  according to the first embodiment, the four recording heads  40 K,  40 C,  40 M, and  40 Y, which correspond to black (K), cyan (C), magenta (M), and yellow (Y), respectively, are arranged in this order from the upstream side to the downstream side in a conveyance direction Xm of a recording medium. 
     The recording head  40 K for black (K) ink includes four head units  40 K- 1 ,  40 K- 2 ,  40 K- 3 , and  40 K- 4  arranged in a staggered manner in a direction orthogonal to the conveyance direction Xm of the roll sheet Md. This configuration allows the image forming unit  40  to form an image on an entire image forming area (print area) of the roll sheet Md (i.e., the recording medium) in its width direction (direction orthogonal to the conveyance direction Xm of the roll sheet Md). 
     As illustrated in  FIG.  2 B , the head unit  40 K- 1  includes a plurality of nozzles  40   n , which are discharge ports, in a nozzle surface (an outer face of a nozzle plate  43  illustrated in  FIG.  3 A  described below). The plurality of nozzles  40   n  are arranged in a line along the longitudinal direction of the head unit  40 K- 1  to form a nozzle row. The head unit  40 K- 1  may include a plurality of nozzle rows. 
       FIG.  3 A  is a schematic cross-sectional view of a portion of the head unit  40 K- 1 , taken in the longitudinal direction of liquid chambers  40   f .  FIG.  3 B  is a schematic cross-sectional view of a portion of the head unit  40 K- 1 , taken along line SC1 illustrated in  FIG.  3 A , that is, in a direction orthogonal to the longitudinal direction of the liquid chambers  40   f  (i.e., in the direction in which the nozzles  40   n  are arranged). 
     As illustrated in  FIG.  3 A , the head unit  40 K- 1  includes a channel substrate  41 , a diaphragm  42 , a nozzle plate  43 , and a frame member  44 . The channel substrate  41  forms a channel of ink to be discharged. The diaphragm  42  is joined to a lower surface of the channel substrate  41  in  FIG.  3 A  (an inner direction of the head unit  40 K- 1 ). The nozzle plate  43  is joined to an upper surface of the channel substrate  41  in  FIG.  3 A  (an outer direction of the head unit  40 K- 1 ). The frame member  44  holds the periphery of the diaphragm  42 . The head unit  40 K- 1  further includes a pressure generator  45  for deforming the diaphragm  42 . 
     In the head unit  40 K- 1  according to the first embodiment, the channel substrate  41 , the diaphragm  42 , and the nozzle plate  43  are stacked on one another to form a nozzle communication path  40   r  and a liquid chamber  40   f , which are channels communicating with a corresponding one of the nozzles  40   n . In the head unit  40 K- 1 , the frame member  44  is further stacked to form an ink inflow port  40   s  for supplying ink to the liquid chamber  40   f , a common liquid chamber  40   c  for supplying ink to the liquid chamber  40   f , a housing that accommodates the pressure generator  45 , and an ink supply port  40   i  for supplying ink from outside the head unit  40 K- 1  to the common liquid chamber  40   c , and the like. 
     The head unit  40 K- 1  can deform (flexurally deform) the diaphragm  42  using the pressure generator  45 . With this configuration, in the head unit  40 K- 1 , the volume of the liquid chamber  40   f  can be changed to change the pressure acting on the ink in the liquid chamber  40   f . As a result, the head unit  40 K- 1  can discharge ink from the corresponding one of the nozzles  40   n . 
     The pressure generator  45  may include an electromechanical transducer element. The pressure generator  45  includes piezoelectric elements  45   p , a base substrate  45   b  to which the piezoelectric elements  45   p  are bonded and secured, and pillars arranged in gaps between adjacent piezoelectric elements  45   p . In the first embodiment, each of the piezoelectric elements  45   p  is an electromechanical transducer element. The pressure generator  45  further includes flexible printed circuit (FPC) cables  45   c  for coupling the piezoelectric elements  45   p  to a drive circuit (drive integrated circuit (IC)), and the like. 
     As illustrated in  FIG.  3 B , each of the piezoelectric elements  45   p  may be a laminated piezoelectric element (lead zirconate titanate (PZT)) in which piezoelectric materials  45   pp  and internal electrodes  45   pe  are alternately stacked on one another. The internal electrodes  45   pe  include a plurality of individual electrodes  45   pei  and a plurality of common electrodes  45   pec . In the first embodiment, the internal electrodes  45   pe  are configured such that the individual electrodes  45   pei  or the common electrodes  45   pec  are alternately coupled to end faces of the piezoelectric materials  45   pp . 
     In the piezoelectric elements  45   p  according to the first embodiment,  d   33  direction is used as the piezoelectric direction of the piezoelectric materials  45   pp . Accordingly, the pressure generator  45  can pressurize or depressurize the ink in the liquid chambers  40   f  by using the piezoelectric effects (displacements in  d   33  direction) of the piezoelectric elements  45   p . The pressure generator  45  may pressurize or depressurize the ink in the liquid chambers  40   f  by using the displacements of the piezoelectric elements  45   p  in d31 direction. The pressure generator  45  may include one row of piezoelectric elements for each of the nozzles  40   n . The piezoelectric element members (the piezoelectric elements 45p) may be divided to form the pillars at the same time as the piezoelectric elements  45   p . That is, in the head unit  40 K- 1 , no voltage is applied to the piezoelectric elements  45   p  such that the piezoelectric element members can be used as the pillars. 
     The following describes a specific operation (pull-push discharge operation) of discharging ink from the nozzles  40   n . 
     First, the head unit  40 K- 1  reduces the voltage to be applied to the piezoelectric elements  45   p  (the pressure generator  45 ) from a reference potential to reduce the size of the piezoelectric elements  45   p  in the stacking direction thereof, and flexurally deforms the diaphragm  42 . As a result, the volume of the liquid chambers  40   f  increases (or expands), and ink flows into the liquid chambers  40   f  from the common liquid chambers  40   c . Then, the head unit  40 K- 1  increases the voltage to be applied to the piezoelectric elements  45   p  to expand the piezoelectric elements  45   p  in the stacking direction. As a result, the diaphragm  42  is deformed in the direction of the nozzles  40   n  to reduce (or shrink) the volume of the liquid chambers  40   f . Consequently, a pressure is applied to the ink in the liquid chambers  40   f , and the ink is discharged (ejected) from the nozzles  40   n . Then, the voltage to be applied to the piezoelectric elements  45   p  is returned to the reference potential to return (or restore) the diaphragm  42  to the initial position. The expansion of the liquid chambers  40   f  reduces the pressure in the liquid chambers  40   f , and the liquid chambers  40   f  are filled (or replenished) with ink from the common liquid chambers  40   c . After the vibration of the meniscus surface of each of the nozzles  40   n  is attenuated (or stabilized), the operation proceeds to the next operation for discharging ink, and the operation described above is repeatedly performed. 
     The method for driving the head unit  40 K- 1  is not limited to the example described above, namely, the pull-push discharge operation. That is, the recording head  40 K is driven in such a manner that a voltage (drive waveform) to be applied to the piezoelectric elements  45   p  is controlled to perform pull discharge, push discharge, or the like. 
     The pressure generator  45  is not limited to the example (the piezoelectric elements 45p) described above. That is, the pressure generator  45  may be of a type (so-called thermal type) in which ink in each of the liquid chambers  40   f  is heated using a heat element to generate a bubble (see, for example, Japanese Unexamined Patent Application Publication No. 61-59911). Alternatively, the pressure generator  45  may be of a type (so-called electrostatic type) in which a diaphragm and an electrode are arranged opposite to each other on the wall surface of each of the liquid chambers  40   f  and the diaphragm is deformed by an electrostatic force generated between the diaphragm and the electrode (see, for example, Japanese Unexamined Patent Application Publication No. 6-71882). 
     The configuration and operation of the other head units  40 K- 2 ,  40 K- 3 , and  40 K- 4  are similar to those of the head unit  40 K- 1  described above and will not be described herein. 
     The configuration and operation of the other recording heads  40 C,  40 M, and  40 Y are similar to those of the recording head  40 K for black (K) ink and will not be described herein. 
     With the configuration described above, the image forming system  100  according to the first embodiment can form a black-and-white or full-color image in an entire image forming area using the image forming unit  40  (the four recording heads  40 K,  40 C,  40 M, and 40Y) in a single conveyance operation of the recording medium (the roll sheet Md). 
     The post-treatment unit  50  applies treatment to the recording medium after an image is formed on the recording medium. In the first embodiment, the post-treatment unit  50  applies post-treatment to the surface of the roll sheet Md on which an image is formed by the image forming unit  40  with a post-treatment liquid. In the first embodiment, the post-treatment is a treatment for applying (discharging) a post-treatment liquid to the surface of the roll sheet Md (i.e., the recording medium). The post-treatment liquid is formed in a shape such as a spot shape or a stripe shape. As a result, the recording medium with an image formed thereon can have improved scratch resistance and gloss, and improved storage stability (such as waterfastness, lightfastness, and gasfastness) and the like. 
     The post-treatment liquid adheres to, in at least a portion of the recording medium on which an image is formed (a portion to which ink adheres), an area smaller than the area of the portion, and may or may not adhere to a portion of the recording medium on which no image is formed. 
     In the post-treatment method, it is preferable that the post-treatment liquid adhere to (or be deposited onto) a portion of the roll sheet Md on which an image is formed. It is more preferable that the post-treatment unit  50  change the amount of discharge (or the amount of adhesion) of the post-treatment liquid and the method of discharging the post-treatment liquid, based on the type, the permeability, the glossiness, and/or the resolution of the recording medium, and/or the amount of adhesion of the pre-treatment liquid (or the amount of liquid) applied by the pre-treatment unit  20 . 
     Further, the post-treatment unit  50  according to the first embodiment is configured to use a recording head similar to that of the image forming unit  40  to discharge the post-treatment liquid onto a target portion in a desired amount (in a desired spot shape or a desired stripe shape). Specifically, the post-treatment unit  50  is configured to select (1) discharging the post-treatment liquid onto an entire area of the roll sheet Md in which an image can be formed; (2) discharging the post-treatment liquid onto an area of the roll sheet Md where an image is formed, (3) discharging the post-treatment liquid onto an area of the roll sheet Md corresponding to an image forming portion (a dot discharge portion), or the like. Alternatively, the post-treatment unit  50  is configured to select (4) discharging the post-treatment liquid onto an area of the roll sheet Md (i.e., the recording medium) larger than the image forming portion. Examples of the area include an area larger than the outer edge of the image forming portion by +1 dot or  2  dots or more. Further, the post-treatment unit  50  is configured to discharge the post-treatment liquid to an area of n% (in a spot shape or a stripe shape) of a selected area to which the post-treatment liquid is to be discharged, where n% may be set to 5% to 50%. The value n may be determined in advance by experiment, numerical calculation, or the like. 
     The post-treatment unit  50  according to the first embodiment may select a method for discharging the post-treatment liquid, such as (1) discharging the post-treatment liquid based on a print duty, or (2) discharging the post-treatment liquid based on the number of droplets of the post-treatment liquid to be discharged. At this time, the post-treatment unit  50  may calculate a print duty or the number of droplets of the post-treatment liquid from input information (such as print image data) and determine a method for discharging the post-treatment liquid based on the calculated print duty or the like. Accordingly, in the image forming system  100  according to the first embodiment, as compared to the application (discharging) of the post-treatment liquid to the entire surface of the recording medium, the post-treatment unit  50  can be used to deposit (discharge) the post-treatment liquid only in a specific portion of an area where an image is formed. As a result, the time taken for the post-treatment, in particular, the time taken to dry the post-treatment liquid, can be shortened. In addition, the amount of the post-treatment liquid used for the post-treatment can be reduced, and the cost of the post-treatment can be reduced. 
     The post-treatment method of the post-treatment unit  50  is not limited to any specific method and may be selected as appropriate in accordance with the type of post-treatment liquid. The post-treatment method of the post-treatment unit  50  is more preferably similar to the method for discharging ink in the image forming unit  40 , from the viewpoint of a reduction in the size of the image forming apparatus and the storage stability of the post-treatment liquid. Like a recording head of the image forming unit  40 , the post-treatment unit  50  preferably includes a liquid discharge head having a plurality of nozzles  40   n  on a nozzle surface. 
     The post-treatment liquid to be discharged preferably contains an appropriate amount of water-soluble organic solvent (wetting agent), which is used in the method for discharging ink in the image forming unit  40 . In the post-treatment unit  50 , it is preferable that the amount of adhesion of the post-treatment liquid after drying be 0.5 g/m 2  to 10 g/m 2 . Examples of the post-treatment liquid include a treatment liquid containing a component that allows a transparent protective layer to be formed on the roll sheet Md (i.e., the recording medium). The treatment liquid containing a component that allows a transparent protective layer to be formed is a treatment liquid containing, for example, a water-dispersible resin, a water-soluble organic solvent (wetting agent), a penetrant, a surfactant, water, and/or other components, as appropriate. Alternatively, the post-treatment liquid may be a resin composition and/or a thermoplastic resin including a component that is polymerized by ultraviolet irradiation. Preferably, the post-treatment liquid is a thermoplastic resin emulsion for improving the glossiness and the fixability. As a result, the post-treatment unit  50  can increase the gloss of the surface of the roll sheet Md on which an image is formed or protect the surface of the roll sheet Md with a resin layer, depending on the method of discharge (application) of the post-treatment liquid. 
     As in the first embodiment, the use of the post-treatment unit  50  prevents an image (ink) from being peeled (or stripped) from the recording medium by rubbing the surface of the roll sheet Md on which the image is formed with another object (e.g., a roll sheet). That is, scratch resistance (abrasion resistance) can be improved. In addition, quality degradation in an image to be formed, such as bleed-through, density degradation, tone degradation, gloss degradation, and show-through, can be reduced, and issues related to waterfastness, weather-fastness, and other types of fastness of image can also be reduced. 
     The post-treatment drying unit  80  is a drying apparatus that dries the recording medium with a heated gas in a drying chamber. That is, the post-treatment drying unit  80  can evaporate the moisture of the post-treatment liquid adhering to the roll sheet Md and dry (the post-treatment liquid of) the roll sheet Md. In one example, in the image forming system  100  that does not include the post-treatment unit  50 , the post-treatment drying unit  80  is used to dry ink deposited on a recording medium by the image forming unit  40 . The details of the post-treatment drying unit  80  will be described below. 
     The unloading unit  60  unloads (or discharges) the recording medium on which an image is formed. As illustrated in  FIG.  1   , the unloading unit  60  includes a storage unit  61 , a plurality of conveyance rollers  62 , and the like. The unloading unit  60  winds the roll sheet Md with an image formed on a front side thereof around a storage roll of the storage unit  61   using the conveyance rollers  62  and the like and stores the roll sheet Md. In some cases, the pressure acting on the roll sheet Md to be wound around the storage roll of the storage unit  61  may be increased. To prevent another image from being transferred to the back side of the roll sheet Md, a drying unit may be disposed to further dry the roll sheet Md immediately before the roll sheet Md is wound. Like the post-treatment drying unit  80 , the drying unit may be a drying apparatus that dries the recording medium with a heated gas in a drying chamber. 
     Next, the configuration and operation of the post-treatment drying unit  80 , which is a feature of the present disclosure, will be described. 
       FIG.  4    is a diagram illustrating the schematic configuration of the post-treatment drying unit  80  and the image forming unit  40  according to the first embodiment. 
       FIG.  5    is a graph illustrating an overview of a flow of air from the sheet retainer  46  of the image forming unit  40  to a drying chamber  81  of the post-treatment drying unit  80  and an overview of a change in temperature. 
     While the post-treatment unit  50  is disposed between the image forming unit  40  and the post-treatment drying unit  80  in the conveyance direction Xm of the roll sheet Md, the post-treatment unit  50  is not illustrated in  FIG.  4    because the post-treatment unit  50  is not related to the drying configuration of the post-treatment drying unit  80 . 
     The post-treatment drying unit  80  heats the air in a heating chamber  83  to a target temperature using a heater  84 , and feeds the heated air (heated gas) into the drying chamber  81  to dry the roll sheet Md in the drying chamber  81 . For example, the target temperature (preset temperature) is preferably within a range of greater than or equal to 60° C. and less than or equal to 180° C., and more preferably within a range of greater than or equal to 60° C. and less than or equal to 80° C. In the first embodiment, the drying chamber  81  is provided with an adjustment heater  82  to adjust the temperature of the drying chamber  81  to be used for drying. The post-treatment drying unit  80  includes a blower fan  85  for blowing the air in the heating chamber  83  into the drying chamber  81  from an inlet  81   a  of the drying chamber  81 . The air fed into the drying chamber  81  by the blower fan  85  is blown onto the roll sheet Md. 
     In an existing drying apparatus, outside air (outside air of the drying apparatus or outside air of an image forming system including the drying apparatus) is taken into a drying chamber and heated by a heater in the drying chamber to obtain a heated gas whose temperature is increased to a temperature for drying a recording medium. If the temperature of the outside air is low, the heater consumes a large amount of energy to increase the temperature of the outside air to a temperature suitable as a heated gas. In the first embodiment, accordingly, a high-temperature gas (a gas having a higher temperature than the outside air) discharged from the image forming unit  40 , more specifically, a high-temperature gas discharged from a suction chamber  46   c  in the sheet retainer  46  of the image forming unit  40 , is fed into the drying chamber  81  to reduce the amount of energy to be consumed by the heater  84  in the heating chamber  83  or the adjustment heater  82  in the drying chamber  81 . 
     In the first embodiment, the sheet retainer  46  of the image forming unit  40  sucks and holds the roll sheet Md so as to prevent the landing positions of the inks discharged from the recording heads  40 K,  40 C,  40 M, and  40 Y from being displaced on the roll sheet Md (or prevent the roll sheet Md from floating from the retaining face  46   a  of the sheet retainer  46 ). As illustrated in  FIG.  4   , the suction chamber  46   c  of the sheet retainer  46  is coupled to the heating chamber  83  of the post-treatment drying unit  80  through a duct  48 . The heating chamber  83  heats the inside air to a target temperature using the heater  84 . The heating chamber  83  is in communication with the drying chamber  81  through a duct  86 . The duct  86  is provided with the blower fan  85 . The blower fan  85  sucks the air (the air heated to the target temperature) in the heating chamber  83  and feeds the sucked air into the drying chamber  81 . 
     The blower fan  85  sucks the air from the heating chamber  83  to create a negative pressure in the heating chamber  83 . Accordingly, the air in the suction chamber  46   c  of the sheet retainer  46 , which is in communication with the heating chamber  83  through the duct  48 , is sucked into the heating chamber  83  through the duct  48 . As a result, the inside of the suction chamber  46   c  is brought under a negative pressure, and a suction airflow is generated in the intake holes  46   b  formed in the retaining face  46   a  of the sheet retainer  46  such that external air is sucked into the suction chamber  46   c . The suction airflow allows the roll sheet Md to be sucked and held on the retaining face  46   a . 
     As illustrated in  FIG.  4   , the sheet retainer  46  according to the first embodiment includes a roll sheet heater  47  on the inner surface of the retaining face  46   a  (inside the suction chamber  46   c ). The roll sheet heater  47  heats the retaining face  46   a  of the sheet retainer  46 , and heats the roll sheet Md sucked and held on the retaining face  46   a . With the roll sheet heater  47 , the air in the suction chamber  46   c  is heated to a temperature higher than that of the outside air, as illustrated in  FIG.  5   . 
     In the first embodiment, the heated air (the gas having a higher temperature than the outside air) in the suction chamber  46   c  is fed into the heating chamber  83  of the post-treatment drying unit  80  through the duct  48 . Thus, the amount of energy consumed by the heater  84  in the heating chamber  83  and the adjustment heater  82  in the drying chamber  81  of the post-treatment drying unit  80  can be made smaller than that in a case where the outside air is fed into the drying chamber  81 . 
     In the related art, the high-temperature air in the sheet retainer  46  is exhausted to the outside of the image forming apparatus through an exhaust duct to prevent temperature rise of the image forming unit  40 . In the first embodiment, the high-temperature gas in the suction chamber  46   c , which is exhausted to the outside of the image forming apparatus in the related art, is used. The high-temperature gas is fed into the drying chamber  81  to reduce the energy consumption for increasing the temperature of the gas in the drying chamber  81  to a desired temperature. 
     In the first embodiment, the high-temperature gas from the sheet retainer  46  of the image forming unit  40  is not directly fed into the drying chamber  81 , but, as illustrated in  FIG.  4   , is heated by the heater  84  in the heating chamber  83  before being fed into the drying chamber  81 . This configuration allows air having a higher temperature to be fed into the drying chamber  81 , and can improve the drying function of the post-treatment drying unit  80 . 
     The heating chamber  83  is optional. If the high-temperature gas from the sheet retainer  46  of the image forming unit  40  has a sufficiently high temperature, the high-temperature gas from the sheet retainer  46  of the image forming unit  40  may be fed directly into the drying chamber  81 . 
     Examples of the heater  84  and the adjustment heater  82  in the post-treatment drying unit  80  include a gas heater, a nichrome wire heater, and a ceramic heater. 
     Second Embodiment 
     An example of an image forming system including a drying apparatus according to a second embodiment of the present disclosure will be described hereinafter with reference to the drawings. 
       FIG.  6    is a perspective diagram illustrating the external appearance of an image forming system  100  according to the second embodiment. The image forming system  100  according to the second embodiment includes a so-called inkjet image forming apparatus. The image forming system  100  according to the second embodiment is configured as a single apparatus (image forming apparatus) and does not have functions corresponding to the pretreatment unit  20  and the post-treatment unit  50  in the first embodiment described above. 
     In the image forming system  100 , a guide rod  3   a  and an auxiliary guide rail  3   b  are bridged between two side plates. A carriage  5  is held by the guide rod  3   a  and the auxiliary guide rail  3   b  so as to be movable in a direction indicated by an arrow A (a main-scanning direction). The carriage  5  is coupled to a timing belt  4   c  attached to a drive pulley  4   a  and a pressurization pulley  4   b . The timing belt  4   c  is driven by a main-scanning motor  4   d  through the drive pulley  4   a  such that the carriage  5  reciprocates in the main-scanning direction A. A tensile force is applied to the timing belt  4   c  by the pressurization pulley  4   b . As a result, the carriage  5  is driven without having a slack. 
       FIG.  7    is a plan view of a carriage scanning mechanism in the image forming system  100  according to the second embodiment. 
     In  FIG.  7   , the roll sheet Md is intermittently conveyed in a direction indicated by an arrow B (a sub-scanning direction) below the carriage  5  that is reciprocating. The recording heads  40 K,  40 C,  40 M, and  40 Y discharge ink from a plurality of nozzles onto the roll sheet Md. As a result, a predetermined image, character, or the like is printed on the roll sheet Md. The ink is an example of a liquid. Examples of the ink include, but are not limited to, aqueous ink, ultraviolet (UV) curable ink, electron beam curable ink, and solvent ink. 
     The image forming system  100  further includes a maintenance mechanism  6  and cartridges 7. The maintenance mechanism  6  performs maintenance of the recording heads  40 K,  40 C,  40 M, and  40 Y. The cartridges  7  supply ink to the recording heads  40 K,  40 C,  40 M, and  40 Y. The carriage  5  includes an encoder sensor  5   a . The encoder sensor  5   a  continuously reads an encoder sheet  5   b  held between the two side plates to detect the position of the carriage  5  in the main-scanning direction. The movement of the carriage  5  between the two side plates is controlled based on the position of the carriage  5  in the main-scanning direction, which is detected by the encoder sensor  5   a . The carriage  5  is provided with an imaging unit  5   c  that moves together with the carriage 5. The imaging unit  5   c  reads color patches of a reference chart and executes a color measurement process for each type of sheet. 
       FIG.  8    is a schematic diagram illustrating the internal configuration of the image forming system  100  according to the second embodiment. 
     In the image forming system  100  according to the second embodiment, the image forming unit  40  forms an image on a surface of the roll sheet Md fed by the loading unit  10 . In the image forming unit  40 , the recording heads  40 K,  40 C,  40 M and  40 Y mounted on the carriage  5  perform printing on the roll sheet Md sucked and held on the retaining face  46   a  of the sheet retainer  46 . After the roll sheet Md on which the image is formed is dried by a post-printing drying unit  80 ′, the unloading unit  60  winds the roll sheet Md. 
     The post-print drying unit  80 ′ according to the second embodiment has a configuration similar to that of the post-treatment drying unit  80  according to the first embodiment illustrated in  FIG.  4   . Also in the second embodiment, a high-temperature gas in the suction chamber  46   c  (see  FIG.  4   ) of the sheet retainer  46 , which is exhausted to the outside of the image forming apparatus in the related art, is used. The high-temperature gas is fed into a drying chamber of the post-printing drying unit  80 ′ to reduce the energy consumption for increasing the temperature of the gas in the drying chamber to a desired temperature. 
     First Modification 
     A modification of the image forming system  100  according to the first and second embodiments will be described hereinafter. This modification is hereinafter referred to as “first modification.” While the first modification will be described as a modification of the image forming system  100  according to the first embodiment described above, the first modification is also applicable to a modification of the image forming system  100  according to the second embodiment. 
     In response to completion of a printing operation of the image forming system  100 , the conveyance of the roll sheet Md is stopped, and the roll sheet Md present in the drying chamber  81  at this time remains in the drying chamber  81 . If the temperature in the drying chamber  81  remains high even after the completion of the printing operation, the roll sheet Md is exposed to a high temperature for a long time, and thermal damage (such as deformation) is caused to the roll sheet Md. To address the thermal damage, the first modification provides a configuration for rapidly cooling the temperature in the drying chamber  81  after the printing operation is completed. 
       FIG.  9    is a diagram illustrating the schematic configuration of a post-treatment drying unit  80  and an image forming unit  40  of the image forming system  100  according to the first modification. 
     The image forming system  100  according to the first modification has the same basic configuration as that of the first embodiment described above, except that, in the first modification, as illustrated in  FIG.  9   , the duct  86  of the post-treatment drying unit  80  includes branched two upstream portions (upstream branch paths  86 A and  86 B) on the upstream side in the airflow direction. 
     The upstream branch path  86 A of the duct  86  is in communication with the heating chamber  83 , as in the first embodiment described above. The upstream branch path  86 B of the duct  86  is in communication with an outside air duct  88  that takes in outside air. The branch portion of the duct  86  is provided with a flow path switch  87  (e.g., a switching valve). The flow path switch  87  is controlled by the controller  70  to switch whether the drying chamber  81  coupled to the duct  86  on the downstream side in the airflow direction is to communicate with the heating chamber  83  through the upstream branch path  86 A or to communicate with the outside air duct  88  through the upstream branch path  86 B. 
     The controller  70  controls the flow path switch  87  to cause the drying chamber  81  coupled to the duct  86  on the downstream side in the airflow direction to communicate with the heating chamber  83  through the upstream branch path  86 A during the printing operation. As a result, during the printing operation, the high-temperature gas in the suction chamber  46   c   of the sheet retainer  46  of the image forming unit  40  is fed into the heating chamber  83 , and the gas that is further heated in the heating chamber  83  is fed into the drying chamber  81  through the duct  86 . Accordingly, as in the first embodiment described above, the energy consumption can be reduced. 
     In response to the completion of the printing operation, the controller  70  stops the conveyance of the roll sheet Md and controls the flow path switch  87  to cause the drying chamber  81  coupled to the duct  86  on the downstream side in the airflow direction to communicate with the outside air duct  88  through the upstream branch path  86 B. As a result, after the completion of the printing operation, the outside air taken from the outside air duct  88  is fed into the drying chamber  81  through the duct  86 . Accordingly, the inside of the drying chamber  81  is rapidly cooled, which prevents thermal damage (such as deformation) from being caused to the roll sheet Md remaining in the drying chamber  81 . 
     Second Modification 
     Another modification of the image forming system  100  according to the first and second embodiments will be described hereinafter. This modification is hereinafter referred to as “second modification.” While the second modification will be described as a modification of the image forming system  100  according to the first embodiment described above, the second modification is also applicable to a modification of the image forming system  100  according to the second embodiment. 
       FIG.  10    is a diagram illustrating the schematic configuration of a post-treatment drying unit  80  and an image forming unit  40  of the image forming system  100  according to the second modification. 
     In the second modification, the image forming unit  40  includes a print chamber  49  serving as an image forming chamber. The print chamber  49  accommodates the recording heads  40 K,  40 C,  40 M, and  40 Y (image forming engines). The print chamber  49  includes a warm air fan  49   a  to blow warm air onto the roll sheet Md to heat the roll sheet Md. The warm air from the warm air fan  49   a  raises the temperature in the print chamber  49 . Like the air in the suction chamber  46   c  of the sheet retainer  46 , the air in the print chamber  49  has a higher temperature than the outside air. The air in the print chamber  49  is fed into the drying chamber  81  of the post-treatment drying unit  80 , which may contribute to reduction in energy consumption. 
     In the image forming system  100  according to the second modification, air having a higher temperature among the air in the print chamber  49  and the air in the suction chamber  46   c  of the image forming unit  40  is fed into the drying chamber  81  of the post-treatment drying unit  80  to further reduce the energy consumption. 
     The image forming system  100  according to the second modification has the same basic configuration as that of the first embodiment described above, except that, in the second modification, as illustrated in  FIG.  10   , the duct  48  coupled to the inlet of the heating chamber  83  of the post-treatment drying unit  80  includes two branched portions (upstream branch paths  48 A and 48B) on the upstream side in the airflow direction. 
     The upstream branch path  48 A of the duct  48  is in communication with the suction chamber  46   c  of the sheet retainer  46 , as in the first embodiment described above. The upstream branch path  48 B of the duct  48  is in communication with the print chamber  49 . The branch portion of the duct  48  is provided with a flow path switch  87 . The flow path switch  87  is controlled by the controller  70  to switch whether the heating chamber  83  coupled to the duct  48  on the downstream side in the airflow direction is to communicate with the suction chamber  46   c  through the upstream branch path  48 A or to communicate with the print chamber  49  through the upstream branch path  48 B. 
     The image forming system  100  according to the second modification further includes a print chamber temperature sensor  49   b  and a suction chamber temperature sensor  46   d . The print chamber temperature sensor  49   b  serves as a first temperature sensor for detecting the temperature in the print chamber  49 . The suction chamber temperature sensor  46   d  serves as a second temperature sensor for detecting the temperature in the suction chamber  46   c  of the sheet retainer  46 . The temperature detection results of the temperature sensors  49   b  and  46   d  are sent to the controller  70 . The controller  70  compares the temperature detection results of the temperature sensors  49   b  and  46   d  during the printing operation. For example, a switching condition is that the temperature of the chamber with which the heating chamber  83  is not in communication (e.g., the suction chamber  46   c ) is higher than the temperature of the chamber with which the heating chamber  83  is currently in communication (e.g., the print chamber  49 ) by a predetermined temperature (determined by, for example, the manufacturer or system administrator of the mage forming system  100 ) or higher. When the switching condition is satisfied, the controller  70  controls the flow path switch  87  to switch the flow path. In response to the flow path being switched to the upstream branch path  48 B in communication with the print chamber  49  by the flow path switch  87 , as illustrated in  FIG.  10   , the controller  70  operates a suction fan  48   a  to suck the air in the suction chamber  46   c  through a duct  48 C to maintain the suction chamber  46   c  at the negative pressure. 
     According to the second modification, air having a higher temperature among the air in the suction chamber  46   c  and the air in the print chamber  49  can be fed into the heating chamber  83  of the post-treatment drying unit  80 . The energy consumed by the post-treatment drying unit  80  can further be reduced. 
     The configurations described above are examples, and various aspects of the present disclosure provide, for example, the following effects, respectively. 
     First Aspect 
     A first aspect provides a drying apparatus including a drying chamber  81  configured to dry a drying-target medium (e.g., the roll sheet Md) with a gas maintained at a preset temperature (target temperature), the drying-target medium being a medium to be dried, the gas maintained at the preset temperature being a gas taken in with the drying-target medium being sucked and held by a sheet retainer  46  including an intake hole  46   b  and a suction chamber  46   c . 
     An existing drying apparatus heats taken-in outside air using a heater to obtain a gas (hot air) whose temperature is increased to a preset temperature for drying a drying-target medium to be dried. If the outside air has a low temperature, the amount of energy consumed to increase the temperature of the outside air to a preset temperature for use as warm air is increased. 
     Accordingly, this aspect employs a configuration in which a gas taken in with the drying-target medium being sucked and held by a medium retainer including an intake hole and a suction chamber is taken into a drying chamber and drying is performed in the drying chamber using the gas. The medium retainer sucks a gas in a medium conveyance path, which is typically higher in temperature than the outside air, and the gas sucked by the medium retainer and discharged from the medium retainer is usually higher in temperature than the outside air. In one example, the medium retainer includes a heater for heating the drying-target medium. Accordingly, in the related art, the gas discharged from the medium retainer is usually exhausted to the outside of the image forming apparatus through an exhaust duct to suppress the internal temperature rise of the image forming apparatus. According to this aspect, the high-temperature gas in the medium retainer, which is exhausted to the outside of the image forming apparatus in the related art, is taken into the drying chamber. This makes it possible to reduce the energy consumed by the heater to increase the temperature of the taken-in gas to a preset temperature for drying the drying-target medium. Alternatively, if the high-temperature gas in the medium retainer has reached the preset temperature for drying the drying-target medium, the heater may be omitted in the drying apparatus, which makes it possible to further reduce the energy consumption. 
     Second Aspect 
     A second aspect provides the drying apparatus according to the first aspect, in which the drying chamber has an inlet  81   a  through which the gas discharged from the suction chamber is taken in. 
     With this configuration, the high-temperature gas discharged from the suction chamber can be taken into the drying chamber. 
     Third Aspect 
     A third aspect provides the drying apparatus according to the first or second aspect, further including a heater (e.g., the heater  84  or the adjustment heater  82 ) configured to heat the gas discharged from the suction chamber. 
     With this configuration, the drying-target medium can be dried with a gas having a higher temperature. 
     Fourth Aspect 
     A fourth aspect provides the drying apparatus according to the third aspect, in which the heater (e.g., the heater  84 ) is configured to heat the gas before the gas is taken into the drying chamber (e.g., the drying chamber  81 ). For example, the heater  84  is in the heating chamber  83  disposed upstream from the drying chamber in the direction in which the gas is taken into the drying chamber. 
     With this configuration, the heated gas can be fed into the drying chamber, and the drying chamber has less temperature variation. A drying process that achieves uniform drying for the recording medium can be implemented. 
     Fifth Aspect 
     A fifth aspect provides the drying apparatus according to the third or fourth aspect, in which the heater is configured to perform heating using a gas heater, a nichrome wire heater, or a ceramic heater. 
     This configuration can implement an appropriate drying process for the recording medium. 
     Sixth Aspect 
     A sixth aspect provides the drying apparatus according to any one of the third to fifth aspects, in which the gas heated by the heater has a temperature in a range of greater than or equal to 60° C. and less than or equal to 80° C. 
     This configuration can implement an appropriate drying process for the recording medium. 
     Seventh Aspect 
     A seventh aspect provides an image forming system  100  including an image forming apparatus (e.g., the image forming unit  40 ) configured to form an image on a recording medium (e.g., the roll sheet Md), and a drying apparatus (e.g., the post-treatment drying unit 80) including a drying chamber  81  configured to dry the recording medium, in which the drying apparatus is the drying apparatus according to any one of the first to sixth aspects. 
     This configuration can implement an image forming system with low energy consumption. 
     Eighth Aspect 
     An eighth aspect provides the image forming system according to the seventh aspect, in which the drying chamber of the drying apparatus has an inlet  81   a  through which a gas discharged from an image forming chamber (e.g., the print chamber  49 ) included in the image forming apparatus and configured to form an image on the recording medium is taken in, and the image forming system further includes a first temperature sensor (e.g., the print chamber temperature sensor  49   b ) configured to detect a temperature in the image forming chamber, a second temperature sensor (e.g., the suction chamber temperature sensor  46   d ) configured to detect a temperature in the suction chamber, and a switching unit (e.g., the controller  70  and the flow path switch  87 ) configured to switch the gas to be taken into the drying chamber to a gas discharged from one of the image forming chamber and the suction chamber having a higher temperature, based on the temperature detected by the first temperature sensor and the temperature detected by the second temperature sensor. That is, the flow path switch  87  switches a source from which the gas is taken into the drying chamber between the image forming chamber and the suction chamber. 
     This configuration allows air having a higher temperature to be fed into the drying chamber, and can further reduce the energy consumed by the drying apparatus. 
     The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and/or features of different illustrative embodiments may be combined with each other and/or substituted for each other within the scope of the present invention. 
     The functionality of the elements disclosed herein may be implemented using circuitry or processing circuitry which includes general purpose processors, special purpose processors, integrated circuits, application specific integrated circuits (ASICs), digital signal processors (DSPs), field programmable gate arrays (FPGAs), conventional circuitry and/or combinations thereof which are configured or programmed to perform the disclosed functionality. Processors are considered processing circuitry or circuitry as they include transistors and other circuitry therein. In the disclosure, the circuitry, units, or means are hardware that carry out or are programmed to perform the recited functionality. The hardware may be any hardware disclosed herein or otherwise known which is programmed or configured to carry out the recited functionality. When the hardware is a processor which may be considered a type of circuitry, the circuitry, means, or units are a combination of hardware and software, the software being used to configure the hardware and/or processor.