Patent Publication Number: US-2022221811-A1

Title: Image forming apparatus to which solvent cartridge that can accommodate therein solvent is detachably attachable independently of developing cartridge

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a by-pass continuation application of International Application No. PCT/JP2020/035454 filed Sep. 18, 2020 claiming priority from Japanese Patent Application No. 2019-180540 filed Sep. 30, 2019. The entire contents of the International Application and the priority application are incorporated herein by reference. 
    
    
     BACKGROUND 
     A conventional image forming apparatus includes a main casing, a photosensitive drum, a developing cartridge, a transfer unit, and an applicator. The developing cartridge supplies toner onto the photosensitive drum. The transfer unit transfers toner that has been supplied onto the photosensitive drum to a sheet. The applicator applies solvent to the toner that has been transferred to the sheet. 
     SUMMARY 
     In the conventional image forming apparatus described above, it is desired that a cartridge that can accommodate therein solvent is provided, or solvent is supplied into the main casing. 
     In view of the foregoing, it is an object of the present disclosure to provide: an image forming apparatus in which a solvent cartridge that can accommodate therein solvent can be replaced independently of a developing cartridge; an image forming apparatus in which solvent can be supplied into a main casing; a drum cartridge that can accommodate therein solvent; and a developing cartridge that can accommodate therein solvent. 
     In order to attain the above and other objects, according to one aspect, the present disclosure provides an image forming apparatus including: a main casing; a photosensitive drum; a developing cartridge; a transfer unit for transferring the toner that has been supplied onto the photosensitive drum to a sheet; a solvent cartridge; and an applicator. The photosensitive drum is rotatable about a drum axis extending in a first direction. The developing cartridge includes a toner casing that can accommodate therein toner. The developing cartridge supplies the toner onto the photosensitive drum. The developing cartridge is detachably attachable to the main casing. The solvent cartridge includes a solvent casing that can accommodate therein solvent for dissolving the toner. The solvent cartridge is detachably attachable to the main casing independently of the developing cartridge. The applicator applies the solvent to the toner that has been transferred to the sheet. The applicator is positioned at one end portion of the main casing in a second direction crossing the first direction. The main casing has an opening through which the developing cartridge and the solvent cartridge pass when the developing cartridge and the solvent cartridge are attached to the main casing, the opening being positioned at another end portion in the second direction of the main casing. The image forming apparatus further includes a cover positioned at the another end portion in the second direction of the main casing. The cover is movable between: a closed position where the cover closes the opening; and an open position where the opening is opened. The developing cartridge and the solvent cartridge are positioned between the applicator and the cover in the second direction, and the solvent cartridge is positioned closer to the applicator than the developing cartridge is to the applicator in a state where the developing cartridge and the solvent cartridge are attached to the main casing and the cover is at the closed position. 
     With this image forming apparatus, the solvent cartridge that can accommodate therein solvent can be replaced independently of the developing cartridge. 
     According to another aspect, the present disclosure also provides an image forming apparatus including: a main casing; a photosensitive drum; a developing cartridge; a transfer unit for transferring the toner that has been supplied onto the photosensitive drum to a sheet; a solvent cartridge; and an applicator. The photosensitive drum is rotatable about a drum axis extending in a first direction. The developing cartridge includes a toner casing that can accommodate therein toner. The developing cartridge supplies the toner onto the photosensitive drum. The developing cartridge is detachably attachable to the main casing. The solvent cartridge includes a solvent casing that can accommodate therein solvent for dissolving the toner. The solvent cartridge is detachably attachable to the main casing independently of the developing cartridge. The applicator applies the solvent to the toner that has been transferred to the sheet. The applicator is positioned at one end portion of the main casing in a second direction crossing the first direction. The main casing has an opening through which the developing cartridge and the solvent cartridge pass when the developing cartridge and the solvent cartridge are attached to the main casing. The opening is positioned above the developing cartridge and the solvent cartridge in a state where the developing cartridge and the solvent cartridge are attached to the main casing. The image forming apparatus further includes a cover positioned above the developing cartridge and the solvent cartridge in a state where the developing cartridge and the solvent cartridge are attached to the main casing. The cover is pivotally movable about a cover axis extending in the first direction. The cover is movable between: a closed position where the cover closes the opening; and an open position where the opening is opened. The solvent cartridge is positioned closer to the applicator than the developing cartridge is to the applicator in a state where the developing cartridge and the solvent cartridge are attached to the main casing and the cover is at the closed position. 
     Even with this image forming apparatus, the technical advantages described above can be exhibited. 
     According to still another aspect, the present disclosure also provides an image forming apparatus including: a main casing; a photosensitive drum; a developing cartridge; a transfer unit for transferring the toner that has been supplied onto the photosensitive drum to a sheet; and an applicator. The photosensitive drum is rotatable about a drum axis extending in a first direction. The developing cartridge includes a toner casing that can accommodate therein toner. The developing cartridge supplies the toner onto the photosensitive drum. The developing cartridge is detachably attachable to the main casing. The applicator applies solvent for dissolving toner to the toner that has been transferred to the sheet. The main casing has an inlet port allowing the solvent in a solvent cartridge to enter the main casing therethrough in a state where the solvent cartridge is connected to the main casing. The inlet port is positioned on an outer surface of the main casing. 
     With the image forming apparatus, solvent can be supplied to the main casing through the inlet port formed on the main casing. As a result, the solvent can be supplied to the applicator. This configuration can make the image forming apparatus compact in comparison with a case where a solvent cartridge is accommodated in the main casing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the embodiment(s) as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 2  is a perspective view of the image forming apparatus; 
         FIG. 3  is a front view of the image forming apparatus illustrated in  FIG. 2 ; 
         FIG. 4  is a perspective view of the image forming apparatus illustrated in  FIG. 2  as viewed from an angle different from that in  FIG. 2 , and illustrating a state where a solvent cartridge is detached from a main casing; 
         FIG. 5  is a cross-sectional view taken along a line V-V in  FIG. 3 ; 
         FIG. 6A  is a perspective view of the solvent cartridge; 
         FIG. 6B  is another perspective view of the solvent cartridge as viewed from an angle different from that in  FIG. 6A ; 
         FIG. 7  is an explanatory view of a positional relationship among a developing cartridge, the solvent cartridge, a first circuit board, and a second circuit board; 
         FIG. 8  is a perspective view of an image forming apparatus; 
         FIG. 9  is a perspective view of an image forming apparatus; 
         FIG. 10  is a perspective view of an image forming apparatus; 
         FIG. 11  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 12  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 13  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 14  is a perspective view of the image forming apparatus; 
         FIG. 15  is an explanatory view of a positional relationship among a developing cartridge, a drum cartridge, a solvent cartridge, an applicator, a first circuit board, and a second circuit board, and illustrating a state where a sheet cassette is detached from a main casing; 
         FIG. 16  is an explanatory view of a positional relationship among the solvent cartridge, a supply pipe, a pump, and the applicator; 
         FIG. 17  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 18  is a perspective view of the image forming apparatus illustrated in  FIG. 17 , and illustrating a state where a sheet cassette is pulled out of a main casing; 
         FIG. 19  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 20  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 21  illustrates the image forming apparatus illustrated in  FIG. 20 , and illustrating a state where a cover is at its open position; 
         FIG. 22  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 23  illustrates the image forming apparatus illustrated in  FIG. 22 , and illustrating a state where a cover is at its open position; 
         FIG. 24  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 25  is a perspective view of the image forming apparatus; 
         FIG. 26  is a perspective view of the image forming apparatus as viewed from an angle different from that in  FIG. 24 ; 
         FIG. 27  is an explanatory view of a state where a solvent cartridge is connected to an inlet port; 
         FIG. 28  is an explanatory view of a positional relationship among an applicator, a first circuit board, the solvent cartridge, a supply pipe, and a pump; 
         FIG. 29  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 30  is an explanatory view illustrating a state where a drum cartridge is detached from a main casing; 
         FIG. 31  is a perspective view of the drum cartridge; 
         FIG. 32  is a perspective view of the drum cartridge as viewed from an angle different from that in  FIG. 31 ; 
         FIG. 33  is an explanatory view of a positional relationship among the drum cartridge attached to the main casing, a first circuit board, and a second circuit board; 
         FIG. 34  is a schematic diagram illustrating a configuration of an image forming apparatus; 
         FIG. 35  is a perspective view of a developing cartridge and an applicator; 
         FIG. 36  is a perspective view of a developing cartridge and a drum cartridge; 
         FIG. 37  is a perspective view of a developing cartridge and a drum cartridge; and 
         FIG. 38  is a schematic diagram illustrating a configuration of an image forming apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     First Embodiment 
     1. Overview of Image Forming Apparatus  1   
     An overview of an image forming apparatus  1  will be described with reference to  FIG. 1 . 
     The image forming apparatus  1  includes a main casing  2 , a sheet cassette  3 , a photosensitive drum  4 , a charging unit  5 , an exposure unit  6 , a developing cartridge  7 , a transfer unit  8 , an applicator  9 , a heater  10 , and a discharge tray  11 . 
     1.1 Main Casing  2   
     The main casing  2  accommodates therein the sheet cassette  3 , the photosensitive drum  4 , the charging unit  5 , the exposure unit  6 , the developing cartridge  7 , the transfer unit  8 , the applicator  9 , and the heater  10 . 
     1.2 Sheet Cassette  3   
     The sheet cassette  3  can accommodate therein a sheet(s) S. The sheet S is, for example, a printing paper. The sheet(s) S accommodated in the sheet cassette  3  is transferred toward the photosensitive drum  4 . 
     1.3 Photosensitive Drum  4   
     The photosensitive drum  4  is rotatable about a drum axis A 1 . The drum axis A 1  extends in a first direction. The photosensitive drum  4  extends in the first direction. The photosensitive drum  4  has a hollow cylindrical shape. 
     1.4 Charging Unit  5   
     The charging unit  5  can charge a surface of the photosensitive drum  4 . Specifically, the charging unit  5  is a scorotron charger. However, a charge roller may be employed as the charging unit  5 . 
     1.5 Exposure Unit  6   
     The exposure unit  6  can expose the surface of the photosensitive drum  4  to light. The exposure unit  6  exposes the surface of the photosensitive drum  4  to light in a state where the surface of the photosensitive drum  4  is charged by the charging unit  5 , whereby an electrostatic latent image is formed on the surface of the photosensitive drum  4 . Specifically, the exposure unit  6  is a laser scan unit. note that an LED array may be used as the exposure unit  6 . 
     1.6 Developing Cartridge  7   
     The developing cartridge  7  is attachable to the main casing  2 . In other words, the developing cartridge  7  is attachable to the image forming apparatus  1 . The developing cartridge  7  supplies toner to the photosensitive drum  4 . Specifically, the developing cartridge  7  includes a toner casing  12 , and a developing roller  13 . 
     1.6.1 Toner Casing  12   
     The toner casing  12  can accommodate therein toner. In other words, the developing cartridge  7  can accommodate therein toner. The toner includes toner particles, and as needed, may contain external additive as needed. The toner particles contain binder resin, and may contain colorant, pigment dispersant, parting agent, magnetic material, and electrification control agent. The binder resin is a base of the toner particles. The binder resin binds together components contained in the toner particles. The colorant colors the toner particles with a desired color. The colorant is dispersed in the binder resin. The pigment dispersant improves dispersibility of the colorant. The electrification control agent provides electrostatic property to the toner particles. The electrostatic property may be either positive electrification or negative electrification. The external additive adjusts the electrostatic property, fluidity, and preservation stability of the toner particles. 
     1.6.2 Developing Roller  13   
     The developing roller  13  can supply toner accommodated in the toner casing  12  to the surface of the photosensitive drum  4 . The developing roller  13  makes contact with the photosensitive drum  4 . Note that the developing roller  13  may not make contact with the photosensitive drum  4 . The developing roller  13  extends in the first direction. The developing roller  13  has a solid cylindrical shape. The developing roller  13  is rotatable about a developing axis A 2 . The developing axis A 2  extends in the first direction. 
     1.7 Transfer Unit  8   
     The transfer unit  8  transfers the toner that has been supplied onto the photosensitive drum  4  to the sheet S. The transfer unit  8  makes contact with the photosensitive drum  4 . Note that the transfer unit  8  may not make contact with the photosensitive drum  4 . Specifically, the transfer unit  8  is a transfer roller. The transfer roller extends in the first direction. The transfer roller has a solid cylindrical shape. The transfer roller is rotatable about a transfer axis A 3 . The transfer axis A 3  extends in the first direction. The transfer unit  8  may be a transfer belt instead. 
     1.8 Applicator  9   
     The applicator  9  applies solvent to the toner that has been transferred to the sheet S in a state where the developing cartridge  7  is attached to the main casing  2 . The solvent can dissolve the toner. Specifically, the solvent can dissolve the binder resin in the toner. The solvent is, for example, Aliphatic monocarboxylate, aliphatic dicarboxylate, carbonic ester, and the like. 
     The applicator  9  is a spraying device of an electrostatic spraying type. The applicator  9  applies solvent to the toner by electrostatically spraying the solvent on the toner on the sheet S. Specifically, the applicator  9  includes an applicator casing  14 , and a plurality of nozzles  15 . The applicator casing  14  can accommodate therein the solvent. The plurality of nozzles  15  extends downward from the applicator casing  14 . The solvent accommodated in the applicator casing  14  is sprayed through the plurality of nozzles  15 . Note that the applicator  9  may a device of an inkjet type to apply solvent to the toner. Alternatively, the applicator  9  may apply solvent to the toner using a roller. 
     1.9 Heater  10   
     The heater  10  heats the sheet S that has moved past the applicator  9 . That is, the heater  10  heats the sheet S to which the solvent has been applied by the applicator  9 . Chemical reaction between the toner and the solvent applied to the toner is facilitated by the heat applied from the heater  10 . Hence, a time period required for solidifying the toner to which the solvent has been applied and fixing the toner to the sheet can be reduced. 
     1.10 Discharge Tray  11   
     The discharge tray  11  is positioned on an upper surface of the main casing  2 . In a state where the developing cartridge  7  is attached to the main casing  2 , the discharge tray  11  is positioned above the developing cartridge  7 . The sheet S that has moved past the heater  10  is discharged onto the discharge tray  11 . In other words, the sheet S that has moved past the applicator  9  is discharged onto the discharge tray  11 . 
     2. Details of Image Forming Apparatus  1   
     Next, details of the image forming apparatus  1  will be described with reference to  FIGS. 1 through 7 . 
     The image forming apparatus  1  further includes a first cover  21  (see  FIG. 2 ), a second cover  22  (see  FIG. 2 ), a drum cartridge  23  (see  FIG. 1 ), a solvent cartridge  24  (see  FIG. 2 ) a supply pipe  25  (see  FIG. 5 ), a pump  26  (see  FIG. 5 ), a first circuit board  27  (see  FIG. 7 ), a second circuit board  28  (see  FIG. 7 ), and an operation panel  29  (see  FIG. 2 ) in addition to the main casing (see  FIG. 2 ) described above. 
     2.1 Details of Main Casing  2   
     As illustrated in  FIGS. 2 and 3 , the main casing  2  has a first opening  2 A, a second opening  2 B, and a third opening  2 C. The main casing  2  includes a guide  2 D 1 , and a guide  2 D 2 . 
     2.1.1 First Opening  2 A 
     The first opening  2 A is positioned at one end portion E 1  in a second direction of the main casing  2 . The second direction crosses the first direction. The developing cartridge  7  passes through the first opening  2 A when the developing cartridge  7  is attached to the main casing  2 . Further, the drum cartridge  23  is also attachable to the main casing  2  through the first opening  2 A. The developing cartridge  7  and the drum cartridge  23  are attachable to the main casing  2  in the second direction. Note that the developing cartridge  7  and the drum cartridge  23  those attached to the main casing  2  are detachable from the main casing  2  through the first opening  2 A. 
     2.1.2 Second Opening  2 B 
     The second opening  2 B is positioned at the one end portion E 1  in the second direction of the main casing  2 . The second opening  2 B is positioned to be spaced apart from the first opening  2 A in the first direction. The solvent cartridge  24  passes through the second opening  2 B when the solvent cartridge  24  is attached to the main casing  2 . That is, the drum cartridge  23  and the developing cartridge  7  are attachable to the main casing  2  through the first opening  2 A whereas the solvent cartridge  24  is attachable to the main casing  2  through the second opening  2 B positioned away from the first opening  2 A. Accordingly, the solvent cartridge  24  is attachable to the main casing  2  independently of the drum cartridge  23  and the developing cartridge  7 . In other words, the drum cartridge  23  is attachable to the main casing  2  independently of the solvent cartridge  24 . The solvent cartridge  24  is attachable to the main casing  2  in the second direction. Further, the solvent cartridge  24  attached to the main casing  2  is detachable from the main casing  2  through the second opening  2 B. 
     2.1.3 Third Opening  2 C 
     The third opening  2 C is positioned at the one end portion E 1  in the second direction of the main casing  2 . The sheet cassette  3  is attachable to the main casing  2  through the third opening  2 C. The sheet cassette  3  is attachable to the main casing  2  in the second direction. Note that the sheet cassette  3  attached to the main casing  2  is detachable from the main casing  2  through the third opening  2 C. 
     The third opening  2 C is positioned to be spaced apart from the second opening  2 B in the first direction. Hence, the sheet cassette  3  is attachable to the main casing  2  independently of the solvent cartridge  24 . In other words, the solvent cartridge  24  is attachable to the main casing  2  independently of the sheet cassette  3 . 
     Further, the third opening  2 C is positioned downward of the first opening  2 A. Hence, the sheet cassette  3  is positioned below the developing cartridge  7  in a state where the sheet cassette  3  is attached to the main casing  2 . 
     The sheet cassette  3  includes a sheet handle  3 A. In a state where the sheet cassette  3  is attached to the main casing  2 , the sheet handle  3 A is positioned at the one end portion E 1  in the second direction of the main casing  2 . 
     2.1.4 Guide  2 D 1  and Guide  2 D 2   
     As illustrated in  FIG. 4 , the guide  2 D 1  is positioned inside the second opening  2 B. The guide  2 D 1  guides the solvent cartridge  24  (see  FIG. 2 ) when the solvent cartridge  24  is attached to the main casing  2 . The guide  2 D 1  extends in the second direction. The guide  2 D 1  is a rib protruding in an up-down direction. 
     The guide  2 D 2  is positioned inside the second opening  2 B. The guide  2 D 2  is positioned to be spaced apart from the guide  2 D 1  in the first direction. The guide  2 D 2  guides the solvent cartridge  24  (see  FIG. 2 ) when the solvent cartridge  24  is attached to the main casing  2 . The guide  2 D 2  extends in the second direction. The guide  2 D 2  is a rib protruding in the up-down direction. 
     2.2 First Cover  21   
     As illustrated in  FIG. 2 , the first cover  21  is positioned at the one end portion E 1  in the second direction of the main casing  2 . The first cover  21  is movable between a first closed position (see  FIG. 1 ) and a first open position (see  FIG. 2 ). The first cover  21  is pivotally movable about a first cover axis A 11 . The first cover axis A 11  extends in the first direction. 
     As illustrated in  FIG. 1 , in a state where the first cover  21  is at the first closed position, the first cover  21  extends in the up-down direction. The first cover  21  closes the first opening  2 A in a state where the first cover  21  is at the first closed position. 
     On the other hand, in a state where the first cover  21  is at the first open position, the first cover  21  extends in the second direction as illustrated in  FIG. 2 . The first opening  2 A is opened in a state where the first cover  21  is at the first open position. 
     2.3 Second Cover  22   
     The second cover  22  is positioned at the one end portion E 1  in the second direction of the main casing  2 . The second cover  22  is provided independently of the first cover  21 . 
     The second cover  22  is movable between a second closed position (see  FIG. 5 ) and a second open position (see  FIG. 2 ). The second cover  22  closes the second opening  2 B in a state where the second cover  22  is at the second closed position. The second opening  2 B is opened in a state where the second cover  22  is at the second open position. 
     The second cover  22  is pivotally movable about a second cover axis A 12 . The second cover axis A 12  extends in the first direction. The second cover axis A 12  is positioned away from the first cover axis A 11 . The second cover axis A 12  is positioned downward of the first cover axis A 11 . The second cover  22  includes a cover body  22 A, a guide  22 B 1 , and a guide  22 B 2 . 
     2.3.1 Cover Body  22 A 
     As illustrated in  FIG. 5 , the cover body  22 A extends in the up-down direction in a state where the second cover  22  is at the second closed position. The cover body  22 A closes the second opening  2 B when the second cover  22  is at the second closed position. 
     On the other hand, as illustrated in  FIG. 2 , the cover body  22 A extends in the second direction in a state where the cover body  22 A is at the second open position. The cover body  22 A has a flat plate-like shape. The cover body  22 A has a first surface S 1 , and a second surface S 2 . 
     In a state where the solvent cartridge  24  is attached to the main casing  2  and the second cover  22  is at the second closed position, the first surface S 1  makes contact with the solvent cartridge  24  as illustrated in  FIG. 5 . In other words, the second cover  22  makes contact with the solvent cartridge  24  in a state where the solvent cartridge  24  is attached to the main casing  2  and the second cover  22  is at the second closed position. Specifically, the second cover  22  makes contact with a first handle  24 B (described later) in a state where the solvent cartridge  24  is attached to the main casing  2  and the second cover  22  is at the second closed position. 
     In a state where the solvent cartridge  24  is attached to the main casing  2  and the second cover  22  is at the second closed position, the second surface S 2  is positioned on the opposite side of the first surface S 1  from the solvent cartridge  24 . 
     2.3.2 Guide  22 B 1  and Guide  22 B 2   
     As illustrated in  FIG. 2 , the guide  22 B 1  is positioned on the first surface S 1  of the second cover  22 . The guide  22 B 1  guides the solvent cartridge  24  in cooperation with the guide  2 D 1  of the main casing  2  when the solvent cartridge  24  is attached to the main casing  2  while the second cover  22  is at the second open position. The guide  22 B 1  is in line with the guide  2 D 1  in the second direction when the solvent cartridge  24  is attached to the main casing  2  while the second cover  22  is at the second open position. The guide  22 B 1  extends in the second direction. The guide  22 B 1  is a rib extending in the up-down direction. 
     The guide  22 B 2  is positioned on the first surface S 1  of the second cover  22 . The guide  22 B 2  is spaced apart from the guide  22 B 1  in the first direction. The guide  22 B 2  guides the solvent cartridge  24  in cooperation with the guide  2 D 2  of the main casing  2  when the solvent cartridge  24  is attached to the main casing  2  while the second cover  22  is at the second open position. The guide  22 B 2  is in line with the guide  2 D 2  in the second direction when the solvent cartridge  24  is attached to the main casing  2  while the second cover  22  is at the second open position. The guide  22 B 2  extends in the second direction. The guide  22 B 2  is a rib protruding in the up-down direction. 
     2.4 Drum Cartridge  23   
     As illustrated in  FIG. 1 , the drum cartridge  23  is attachable to the main casing  2 . In other words, the drum cartridge  23  is attachable to the image forming apparatus  1 . The drum cartridge  23  includes the photosensitive drum  4 , the charging unit  5 , and the transfer unit  8 . Note that the main casing  2  may include the transfer unit  8 . 
     Further, the developing cartridge  7  is detachably attachable to the drum cartridge  23 . The developing cartridge  7  is attachable to the main casing  2  in a state where the developing cartridge  7  is attached to the drum cartridge  23 . 
     2.5 Solvent Cartridge  24   
     As illustrated in  FIGS. 2 and 3 , the solvent cartridge  24  is positioned away from the developing cartridge  7  in the first direction in a state where the developing cartridge  7  and the solvent cartridge  24  are attached to the main casing  2 . With this positional relationship, increasing in size of the image forming apparatus  1  in the up-down direction can be restrained. 
     Further, the solvent cartridge  24  is positioned away from the sheet cassette  3  in the first direction in a state where the solvent cartridge  24  and the sheet cassette  3  are attached to the main casing  2 . The solvent cartridge  24  and the sheet cassette  3  are arranged in the first direction in a state where the solvent cartridge  24  and the sheet cassette  3  are attached to the main casing  2 . 
     Further, as illustrated in  FIG. 5 , the solvent cartridge  24  is positioned downward of the applicator  9  in a state where the solvent cartridge  24  is attached to the main casing  2 . 
     As illustrated in  FIGS. 6A and 6B , the solvent cartridge  24  includes a solvent casing  24 A, the first handle  24 B, a second handle  24 C, a cartridge guide  24 D 1 , and a cartridge guide  24 D 2 . 
     2.5.1 Solvent Casing  24 A 
     The solvent casing  24 A can accommodate therein solvent. In other words, the solvent cartridge  24  can accommodate therein solvent. The solvent dissolves toner. 
     As illustrated in  FIG. 5 , in a state where the solvent cartridge  24  is attached to the main casing  2 , the solvent casing  24 A extends in the second direction. The solvent casing  24 A has a discharge opening  24 E. 
     The discharge opening  24 E allows the solvent to be discharged therethrough from the solvent casing  24 A to the supply pipe  25 . The discharge opening  24 E is positioned at one end portion E 11  in the second direction of the solvent casing  24 A. 
     2.5.2 First Handle  24 B 
     The first handle  24 B is positioned at another end portion E 12  in the second direction of the solvent casing  24 A in a state where the solvent cartridge  24  is attached to the main casing  2 . The first handle  24 B is positioned closer to the second cover  22  than the discharge opening  24 E is to the second cover  22  in the second direction in a state where the solvent cartridge  24  is attached to the main casing  2 . In other words, in a state where the solvent cartridge  24  is attached to the main casing  2 , the first handle  24 B is positioned between the discharge opening  24 E and the second cover  22  in the second direction. A user moves the solvent cartridge  24  in the second direction during attachment of the solvent cartridge  24  to the main casing  2  and detachment of the solvent cartridge  24  from the main casing  2 . At this time, the first handle  24 B is grasped by the user. 
     2.5.3 Second Handle  24 C 
     As illustrated in  FIG. 6A , the second handle  24 C is positioned on an upper surface S 11  of the solvent casing  24 A. The second handle  24 C is grasped by the user when the user carries the solvent cartridge  24  that has been detached from the main casing  2 . 
     2.5.4 Cartridge Guide  24 D 1  and Cartridge Guide  24 D 2   
     As illustrated in  FIG. 6B , the cartridge guide  24 D 1  is positioned on a lower surface S 12  of the solvent casing  24 A. The cartridge guide  24 D 1  is in a form of a groove. When the solvent cartridge  24  is attached to the main casing  2  while the second cover  22  is at the second open position, the guide  22 B 1  (see  FIG. 4 ) of the second cover  22  and the guide  2 D 1  (see  FIG. 4 ) of the main casing  2  are fitted into the cartridge guide  24 D 1 . The cartridge guide  24 D 1  is guided by the guide  22 B 1  and the guide  2 D 1 . Hence, the solvent cartridge  24  is guided by the guide  22 B 1  and the guide  2 D 1  in the second direction. 
     The cartridge guide  24 D 2  is positioned on the lower surface S 12  of the solvent casing  24 A. The cartridge guide  24 D 2  is spaced apart from the cartridge guide  24 D 1  in the first direction. The cartridge guide  24 D 2  is in a form of a groove. When the solvent cartridge  24  is attached to the main casing  2  while the second cover  22  is at the second open position, the guide  22 B 2  (see  FIG. 4 ) of the second cover  22  and the guide  2 D 2  (see  FIG. 4 ) of the main casing  2  are fitted into the cartridge guide  24 D 2 . The cartridge guide  24 D 2  is guided by the guide  22 B 2  and the guide  2 D 2 . Accordingly, the solvent cartridge  24  is guided by the guide  22 B 2  and the guide  2 D 2  in the second direction. 
     2.6 Supply Pipe  25   
     As illustrated in  FIGS. 5 and 7 , the supply pipe  25  supplies solvent to the applicator  9 . The supply pipe  25  has one end portion  25 A, and another end portion  25 B. The one end portion  25 A is connected to the discharge opening  24 E of the solvent cartridge  24  in a state where the solvent cartridge  24  is attached to the main casing  2 . The other end portion  25 B is positioned away from the one end portion  25 A. The other end portion  25 B is connected to the applicator casing  14  of the applicator  9 . 
     2.7 Pump  26   
     As illustrated in  FIG. 5 , the pump  26  is positioned between the one end portion  25 A and the other end portion  25 B of the supply pipe  25 . The pump  26  pumps the solvent from the solvent cartridge  24  to the applicator  9 . When the pump  26  is driven in a state where the solvent cartridge  24  is attached to the main casing  2 , the solvent accommodated in the solvent cartridge  24  is introduced into the applicator casing  14  of the applicator  9  through the discharge opening  24 E and the supply pipe  25 . Specifically, the pump  26  is a gear pump. 
     2.8 First Circuit Board  27   
     As illustrated in  FIG. 7 , the first circuit board  27  and the solvent cartridge  24  are arranged in the second direction in a state where the solvent cartridge  24  is attached to the main casing  2 . The first circuit board  27  is positioned on the opposite side of the solvent cartridge  24  from the second cover  22  in the second direction in a state where the solvent cartridge  24  is attached to the main casing  2 . The first circuit board  27  is electrically connected to the pump  26 . Specifically, the first circuit board  27  is a control circuit board. The first circuit board  27  controls the pump  26 . 
     2.9 Second Circuit Board  28   
     The second circuit board  28  is positioned away from the first circuit board  27  in the first direction. The second circuit board  28  is positioned on the opposite side of the developing cartridge  7  from the first circuit board  27  in the first direction in a state where the developing cartridge  7  is attached to the main casing  2 . In other words, the developing cartridge  7  is positioned between the first circuit board  27  and the second circuit board  28  in the first direction. The second circuit board  28  is electrically connected to the charging unit  5  and the transfer unit  8 . The second circuit board  28  applies a voltage to the charging unit  5  and the transfer unit  8 . Further, the second circuit board  28  is electrically connected to the applicator  9 . The second circuit board  28  supplies electric power to the applicator  9 . Further, the second circuit board  28  is electrically connected to the developing cartridge  7 . The second circuit board  28  applies a voltage to the developing cartridge  7 . The second circuit board  28  is electrically connected to the developing roller  13 . The second circuit board  28  applies a voltage to the developing roller  13 . 
     2.10 Operation Panel  29   
     As illustrated in  FIG. 2 , the operation panel  29  is positioned on the upper surface of the main casing  2 . The operation panel  29  is positioned away from the discharge tray  11  in the first direction. The operation panel  29  is positioned above the solvent cartridge  24  in a state where the solvent cartridge  24  is attached to the main casing  2 . The operation panel  29  is electrically connected to the first circuit board  27 . The operation panel  29  is operated by the user. 
     3. Functions and Effects 
     (1) According to the image forming apparatus  1 , the solvent cartridge that can accommodate therein solvent can be replaced independently of the developing cartridge, as illustrated in  FIG. 2 . 
     Further, in a state where the developing cartridge  7  and the solvent cartridge  24  are attached to the main casing  2 , the solvent cartridge  24  is positioned away from the developing cartridge  7  in the first direction. 
     Accordingly, increasing in size of the image forming apparatus  1  in a direction crossing the first direction can be suppressed. 
     For example, increasing in size of the image forming apparatus  1  in the up-down direction can be restrained in comparison with a configuration in which the developing cartridge  7  and the solvent cartridge  24  are arranged in the up-down direction in a state where the developing cartridge  7  and the solvent cartridge  24  are attached to the main casing  2 . 
     (2) According to the image forming apparatus  1 , the first opening  2 A and the second opening  2 B are positioned at the one end portion E 1  in the second direction of the main casing  2 , as illustrated in  FIG. 2 . The developing cartridge  7  is attachable to the main casing  2  through the first opening  2 A in the second direction. The solvent cartridge  24  is attachable to the main casing  2  through the second opening  2 B in the second direction. 
     With this configuration, replacement of the developing cartridge  7  and the solvent cartridge  24  can be performed at one side in the second direction of the main casing  2 . In other words, the replacement of the solvent cartridge  24  can be performed at the one side of the main casing  2  which is the same as the side in which the replacement of the developing cartridge  7  is performed. 
     Accordingly, facilitated replacement of the developing cartridge  7  and the solvent cartridge  24  can be achieved. 
     (3) According to the image forming apparatus  1 , as illustrated in  FIG. 5 , the second cover  22  makes contact with the solvent cartridge  24  in a state where the solvent cartridge  24  is attached to the main casing  2  and the second cover  22  is at the second closed position. 
     Therefore, detachment of the solvent cartridge  24  from the main casing  2  can be suppressed by making use of the second cover  22 . As a result, release of the discharge opening  24 E of the solvent cartridge  24  from the one end portion  25 A of the supply pipe  25  in the main casing  2  can be restrained. 
     (4) According to the image forming apparatus  1 , the second cover  22  has the guide  22 B 1  and the guide  22 B 2  as illustrated in  FIG. 2 . The guide  22 B 1  and the guide  22 B 2  guide the solvent cartridge  24  when attaching the solvent cartridge  24  to the main casing  2  while the second cover  22  is at the second open position. 
     Accordingly, the solvent cartridge  24  can be guided toward the main casing  2  by making use of the second cover  22  positioned at the second open position. 
     As a result, the attachment of the solvent cartridge  24  to the main casing  2  can be performed easily. 
     (5) According to the image forming apparatus  1 , the main casing  2  has the guide  2 D 1  and the guide  2 D 2  as illustrated in  FIGS. 2 and 4 . The guide  2 D 1  and the guide  2 D 2  guide the solvent cartridge  24  during the attachment of the solvent cartridge  24  to the main casing  2 . 
     Hence, the solvent cartridge  24  can be guided inside the main casing  2 . 
     As a result, the attachment of the solvent cartridge  24  to the main casing  2  can be performed more easily. 
     (6) According to the image forming apparatus  1 , the sheet handle  3 A of the sheet cassette  3  is positioned at the one end portion E 1  in the second direction of the main casing  2  as illustrated in  FIG. 2 . 
     With this arrangement, replacement of the sheet cassette  3  can be performed at the one side of the main casing  2  in the second direction. In other words, the replacement of the sheet cassette  3  can be performed at the side the same as the side in which the replacement of the developing cartridge  7  and the solvent cartridge  24  is performed with respect to the main casing  2 . 
     As a result, the replacement of the developing cartridge  7 , the solvent cartridge  24 , and the sheet cassette  3  can be facilitated. 
     (7) According to the image forming apparatus  1 , the first circuit board  27  is electrically connected to the pump  26  that pumps the solvent from the solvent cartridge  24  to the applicator  9 , as illustrated in  FIG. 7 . 
     Here, the first circuit board  27  and the solvent cartridge  24  are arranged in the second direction in a state where the solvent cartridge  24  is attached to the main casing  2 . In other words, the first circuit board  27  is positioned close to the solvent cartridge  24  in the first direction. 
     Hence, a wiring for connecting the first circuit board  27  and the pump  26  to each other can be shortened. 
     (8) According to the image forming apparatus  1 , the developing cartridge  7  is positioned between the solvent cartridge  24  and the second circuit board  28  in the first direction, as illustrated in  FIG. 7 . In other words, the second circuit board  28  is positioned on the opposite side of the developing cartridge  7  from the solvent cartridge  24  in the first direction. 
     With the above positional relationship, the solvent cartridge  24  can be suppressed from being electrified due to electric power supplied from the second circuit board  28  to the charging unit  5  and the applicator  9 . 
     4. Modifications 
     (1) As illustrated in  FIG. 8 , the second opening  2 B may be positioned at one end portion in the first direction of the main casing  2 . In this case, the second cover  22  is pivotally movable about a second cover axis A 12  extending in the second direction. 
     The solvent cartridge  24  is attachable to the main casing  2  in a state where the solvent cartridge  24  is mounted on the second cover  22 . The solvent cartridge  24  is attachable to the main casing  2  in the first direction. 
     At least a portion of the solvent cartridge  24  is juxtaposed with the developing cartridge  7  in the first direction in a state where the developing cartridge  7  and the solvent cartridge  24  are attached to the main casing  2 . 
     Note that, even in this modification, the solvent cartridge  24  is positioned away from the developing cartridge  7  in the first direction in a state where the developing cartridge  7  and the solvent cartridge  24  are attached to the main casing  2 . 
     (2) As illustrated in  FIG. 9 , the second opening  2 B may be positioned at an upper end portion of the main casing. In this case, the solvent cartridge  24  is attachable to the main casing  2  in the up-down direction. 
     Incidentally, even in this modification, the solvent cartridge  24  is positioned away from the developing cartridge  7  in the first direction in a state where the developing cartridge  7  and the solvent cartridge  24  are attached to the main casing  2 . 
     (3) The image forming apparatus  1  may include a single cover  20  instead of the first cover  21  and the second cover  22  as illustrated in  FIG. 10 . The cover  20  is movable between a closed position (not illustrated) and an open position (see  FIG. 10 ). The cover  20  closes the first opening  2 A and the second opening  2 B in a state where the cover  20  is at the closed position. The first opening  2 A and the second opening  2 B are opened in a state where the cover  20  is at the open position. 
     According to this modification, since the first opening  2 A and the second opening  2 B can be opened and closed using the single cover  20 , the replacement of the developing cartridge  7  and the solvent cartridge  24  can be performed easily even in a case where the replacement of both the developing cartridge  7  and the solvent cartridge  24  is desired. 
     (4) As illustrated in  FIG. 11 , the solvent cartridge  24  may be positioned on the opposite side of the developing cartridge  7  from the first circuit board  27  in the first direction in a state where the developing cartridge  7  and solvent cartridge  24  are attached to the main casing  2 . 
     (5) As illustrated in  FIG. 12 , the second circuit board  28  may be positioned downward of the developing cartridge  7  in a state where the developing cartridge  7  and the solvent cartridge  24  are attached to the main casing  2 . 
     (6) The sheet cassette  3  may be installed in the main casing  2  so as not to be attachable to or detachable from the main casing  2 . In this case, the sheet cassette  3  includes a portion for accommodating therein the sheet S and movable through the third opening  2 C between an interior position in which the portion is positioned inside the main casing  2  and an exterior position in which the portion is positioned outside the main casing  2 . 
     (7) The guide  2 D 1  and the guide  2 D 2 , and the guide  22 B 1  and the guide  22 B 2  may be grooves. The cartridge guide  24 D 1  and the cartridge guide  24 D 2  may be ribs. 
     (8) The developing cartridge  7  and the drum cartridge  23  may be detachably attachable to the main casing  2  independently of each other. 
     (9) The developing cartridge  7  may be integral with the drum cartridge  23 . 
     Second Embodiment 
     Next, a second embodiment will be described with reference to  FIGS. 13 through 19 , wherein like parts and components are designated by the same reference numerals as those shown in the first embodiment to avoid duplicating description. 
     An image forming apparatus  1  according to the second embodiment includes a main casing  2  (see  FIG. 14 ), a cover  30  (see  FIG. 14 ), a drum cartridge  31  (see  FIG. 13 ), a solvent cartridge  32  (see  FIG. 13 ), a supply pipe  33  (see  FIG. 15 ), a pump  34  (see  FIG. 15 ), a first circuit board  39 A (see  FIG. 15 ), and a second circuit board  39 B (see  FIG. 15 ). 
     1. Details of Main Casing  2   
     As illustrated in  FIG. 14 , the main casing  2  has a first opening  35 , a second opening  36 , and a third opening  37 . The main casing  2  includes a guide  38 A (see  FIG. 15 ) and a guide  38 B (see  FIG. 15 ). 
     1.1 First Opening  35   
     The first opening  35  is positioned at one end portion E 1  in the second direction of the main casing  2 . The second direction crosses the first direction. The developing cartridge  7  passes through the first opening  35  when the developing cartridge  7  is attached to the main casing  2 . Further, the drum cartridge  31  (see  FIG. 13 ) is also attachable to the main casing  2  through the first opening  35 . The developing cartridge  7  and the drum cartridge  31  are attachable to the main casing  2  in the second direction. Note that the developing cartridge  7  and the drum cartridge  31  those attached to the main casing  2  are detachable from the main casing  2  through the first opening  35 . 
     1.2 Second Opening  36   
     The second opening  36  is positioned at the one end portion E 1  in the second direction of the main casing  2 . The second opening  36  is positioned downward and away from the first opening  35 . The second opening  36  is positioned on the opposite side of the third opening  37  from the first opening  35 . The solvent cartridge  32  passes through the second opening  36  when the solvent cartridge  32  is attached to the main casing  2 . That is, the drum cartridge  31  and the developing cartridge  7  are attached to the main casing  2  through the first opening  35  whereas the solvent cartridge  32  is attached to the main casing  2  through the second opening  36  positioned away from the first opening  35 . Hence, the solvent cartridge  32  is attachable to the main casing  2  independently of the drum cartridge  31  and the developing cartridge  7 . In other words, the drum cartridge  31  is attachable to the main casing  2  independently of the solvent cartridge  32 . The solvent cartridge  32  is attachable to the main casing  2  in the second direction. Note that the solvent cartridge  32  attached to the main casing  2  is detachable from the main casing  2  through the second opening  36 . 
     1.3 Third Opening  37   
     The third opening  37  is positioned at the one end portion E 1  in the second direction of the main casing  2 . The sheet cassette  3  is attachable to the main casing  2  through the third opening  37 . The sheet cassette  3  is attachable to the main casing  2  in the second direction. Note that the sheet cassette  3  attached to the main casing  2  is detachable from the main casing  2  through the third opening  37 . The sheet cassette  3  is detachably attachable to the main casing  2  independently of the solvent cartridge  32 . In other words, the solvent cartridge  32  is detachably attachable to the main casing  2  independently of the sheet cassette  3 . 
     The third opening  37  is positioned between the first opening  35  and the second opening  2 B in the up-down direction. Hence, the sheet cassette  3  is positioned below the developing cartridge  7  in a state where the sheet cassette  3  is attached to the main casing  2 . The sheet cassette  3  is positioned between the developing cartridge  7  and the solvent cartridge  32  in the up-down direction in a state where the developing cartridge  7 , the solvent cartridge  32 , and the sheet cassette  3  are attached to the main casing  2 . 
     Note that the sheet cassette  3  includes the sheet handle  3 A. The sheet handle  3 A is positioned at the one end portion E 1  in the second direction of the main casing  2  in a state where the sheet cassette  3  is attached to the main casing  2 . 
     1.4 Guide  38 A and Guide  38 B 
     As illustrated in  FIG. 15 , the guide  38 A is positioned inside the second opening  36 . The guide  38 A guides the solvent cartridge  32  when the solvent cartridge  32  is attached to the main casing  2 . The guide  38 A extends in the second direction. The guide  38 A is a rib extending in the first direction. 
     The guide  38 B is positioned inside the second opening  36 . The guide  38 B is positioned away from the guide  38 A in the first direction. The guide  38 B guides the solvent cartridge  32  when the solvent cartridge  32  is attached to the main casing  2 . The guide  38 B extends in the second direction. The guide  38 B is a rib extending in the first direction. 
     2. Cover  30   
     As illustrated in  FIG. 14 , the cover  30  is positioned at the one end portion E 1  in the second direction of the main casing  2 . The cover  30  is movable between a closed position (see  FIG. 13 ) and an open position (see  FIG. 14 ). The cover  30  is pivotally movable about a cover axis  30 A. The cover axis  30 A extends in the first direction. 
     As illustrated in  FIG. 13 , the cover  30  extends in the up-down direction in a state where the cover  30  is at the closed position. The cover  30  closes the first opening  35  in a state where the cover  30  is at the closed position. 
     On the other hand, as illustrated in  FIG. 14 , the cover  30  extends in the second direction in a state where the cover  30  is at the open position. The first opening  35  is opened when the cover  30  is at the open position. 
     3. Drum Cartridge  31   
     As illustrated in  FIG. 13 , the drum cartridge  31  is attachable to the main casing  2 . In other words, the drum cartridge  31  is attachable to the image forming apparatus  1 . The drum cartridge  31  includes the photosensitive drum  4 , the charging unit  5 , and the transfer unit  8 . Note that the main casing  2  may include the transfer unit  8 . 
     Further, the developing cartridge  7  is detachably attachable to the drum cartridge  31 . The developing cartridge  7  is attachable to the main casing  2  in a state where the developing cartridge  7  is attached to the drum cartridge  31 . 
     4. Solvent Cartridge  32   
     The solvent cartridge  32  is positioned below the developing cartridge  7  in a state where the developing cartridge  7  and the solvent cartridge  32  are attached to the main casing  2 . This arrangement can suppress increasing in size of the image forming apparatus  1  in the first direction. At least a portion of the exposure unit  6  is positioned upward of the developing cartridge  7  and the solvent cartridge  32  in a state where the developing cartridge  7  and the solvent cartridge  32  are attached to the main casing  2 . 
     Further, the solvent cartridge  32  is positioned below the sheet cassette  3  in a state where the solvent cartridge  32  and the sheet cassette  3  are attached to the main casing  2 . 
     Further, the solvent cartridge  32  is positioned downward of the applicator  9  in a state where the solvent cartridge  32  is attached to the main casing  2 . 
     As illustrated in  FIG. 14 , the solvent cartridge  32  includes a solvent casing  32 A, a cartridge handle  32 B, a cartridge guide  32 C, and a cartridge guide  32 D. 
     4.1 Solvent Casing  32 A 
     The solvent casing  32 A can accommodate therein solvent. In other words, the solvent cartridge  32  can accommodate therein solvent. The solvent dissolves toner. 
     As illustrated in  FIG. 16 , the solvent casing  32 A extends in the second direction in a state where the solvent cartridge  32  is attached to the main casing  2 . The solvent casing  32 A has a discharge opening  32 E. The discharge opening  32 E allows the solvent to be discharged therethrough from the solvent casing  32 A to the supply pipe  33 . The discharge opening  32 E is positioned at one end portion E 11  in the second direction of the solvent casing  32 A. 
     4.2 Cartridge Handle  32 B 
     The cartridge handle  32 B is positioned at another end portion E 12  in the second direction of the solvent casing  32 A in a state where the solvent cartridge  32  is attached to the main casing  2 . The user moves the solvent cartridge  32  in the second direction when attaching the solvent cartridge  32  to the main casing  2  and when detaching the solvent cartridge  32  from the main casing  2 . At this time, the cartridge handle  32 B is grasped by the user. 
     4.3 Cartridge Guide  32 C and Cartridge Guide  32 D 
     As illustrated in  FIG. 15 , the cartridge guide  32 C is positioned on a side surface  32 S 1  in the first direction of the solvent casing  32 A. The cartridge guide  32 C is in a form of a groove. The guide  38 A of the main casing  2  is fitted into the cartridge guide  32 C when the solvent cartridge  32  is attached to the main casing  2 . The cartridge guide  32 C is guided by the guide  38 A. Accordingly, the solvent cartridge  32  is guided by the guide  38 A in the second direction. 
     The cartridge guide  32 D is positioned on a side surface  32 S 2  in the first direction of the solvent casing  32 A. The side surface  32 S 2  is positioned away from the side surface  32 S 1  in the first direction. The cartridge guide  32 D is in a form of a groove. The guide  38 B of the main casing  2  is fitted into the cartridge guide  32 D when the solvent cartridge  32  is attached to the main casing  2 . The cartridge guide  32 D is guided by the guide  38 B. Hence, the solvent cartridge  32  is guided by the guide  38 B in the second direction. 
     5. Supply Pipe  33   
     As illustrated in  FIG. 16 , the supply pipe  33  has one end portion  33 A and another end portion  33 B. The one end portion  33 A is connected to the discharge opening  32 E of the solvent cartridge  32  in a state where the solvent cartridge  32  is attached to the main casing  2 . The other end portion  33 B is positioned away from the one end portion  33 A. The other end portion  33 B is connected to the applicator casing  14  of the applicator  9 . 
     6. Pump  34   
     The pump  34  is positioned between the one end portion  33 A and the other end portion  33 B of the supply pipe  33 . The pump  34  pumps the solvent from the solvent cartridge  32  to the applicator  9 . When the pump  34  is driven in a state where the solvent cartridge  32  is attached to the main casing  2 , the solvent accommodated in the solvent cartridge  32  is introduced into the applicator casing  14  of the applicator  9  through the discharge opening  32 E and the supply pipe  33 . Specifically, the pump  34  is a gear pump. 
     7. First Circuit Board  39 A 
     As illustrated in  FIG. 15 , the first circuit board  39 A is juxtaposed with the applicator  9  in the first direction. The first circuit board  39 A is electrically connected to the pump  34 . Specifically, the first circuit board  39 A is a control circuit board. The first circuit board  39 A controls the pump  34 . 
     8. Second Circuit Board  39 B 
     The second circuit board  39 B is positioned to be spaced apart from the first circuit board  39 A in the first direction. The second circuit board  39 B is positioned on the opposite side of the applicator  9  from the first circuit board  39 A in the first direction. In other words, the applicator  9  is positioned between the first circuit board  39 A and the second circuit board  39 B in the first direction. The second circuit board  39 B is electrically connected to the charging unit  5  and the transfer unit  8 . The second circuit board  39 B applies a voltage to the charging unit  5  and the transfer unit  8 . The second circuit board  39 B is electrically connected to the applicator  9 . The second circuit board  39 B supplies electric power to the applicator  9 . Further, the second circuit board  39 B is electrically connected to the developing cartridge  7 . The second circuit board  39 B applies a voltage to the developing cartridge  7 . The second circuit board  39 B is electrically connected to the developing roller  13 . The second circuit board  39 B applies a voltage to the developing roller  13 . 
     9. Functions and Effects 
     (1) According to the image forming apparatus  1 , as illustrated in  FIG. 14 , replacement of the solvent cartridge  32  that can accommodate therein the solvent can be performed independently of the developing cartridge  7 . 
     Further, the solvent cartridge  32  is positioned downward of the developing cartridge  7  in a state where the developing cartridge  7  and the solvent cartridge  32  are attached to the main casing  2 . 
     Accordingly, enlargement of the image forming apparatus  1  in the first direction can be restrained. 
     For example, enlargement of the image forming apparatus  1  in the first direction can be restrained in comparison with a configuration where the developing cartridge  7  and the solvent cartridge  32  are arranged in the first direction in a state where the developing cartridge  7  and the solvent cartridge  32  are attached to the main casing  2 . 
     (2) According to the image forming apparatus  1 , the first opening  35  and the second opening  36  are positioned at the one end portion E 1  in the second direction of the main casing  2 , as illustrated in  FIG. 14 . The developing cartridge  7  is attachable to the main casing  2  through the first opening  35  in the second direction. The solvent cartridge  32  is attachable to the main casing  2  through the second opening  36  in the second direction. 
     Hence, the replacement of the developing cartridge  7  and the solvent cartridge  32  can be performed at one side in the second direction of the main casing  2 . In other words, the replacement of the solvent cartridge  32  can be performed at the side of the main casing  2  which is the same as the side in which the replacement of the developing cartridge  7  is performed. 
     Accordingly, the developing cartridge  7  and the solvent cartridge  32  can be replaced easily. 
     (3) According to the image forming apparatus  1 , the sheet handle  3 A of the sheet cassette  3  is positioned at the one end portion E 1  in the second direction of the main casing  2  as illustrated in  FIG. 14 . Hence, replacement of the sheet cassette  3  can be performed at the one side of the main casing  2  in the second direction. In other words, the replacement of the sheet cassette  3  can be performed at the side the same as the side in which the replacement of the developing cartridge  7  and the solvent cartridge  32  is performed with respect to the main casing  2 . 
     As a result, the replacement of the developing cartridge  7 , the solvent cartridge  32 , and the sheet cassette  3  can be performed easily. 
     10. Modifications 
     (1) As illustrated in  FIG. 17 , the solvent cartridge  32  may be positioned inside the sheet cassette  3  in a state where the solvent cartridge  32  and the sheet cassette  3  are attached to the main casing  2 . 
     The solvent cartridge  32  is attachable to the main casing  2  while the solvent cartridge  32  is mounted on the sheet cassette  3 . The solvent cartridge  32  is attachable to the main casing  2  in the second direction. 
     Note that, even in this modification, the solvent cartridge  32  is positioned downward of the developing cartridge  7  in a state where the developing cartridge  7  and the solvent cartridge  32  are attached to the main casing  2 . Further, as illustrated in  FIG. 18 , the solvent cartridge  32  is detachable from the sheet cassette  3  in a state where the sheet cassette  3  is detached from the main casing  2 . 
     (2) The solvent cartridge  32  may be positioned between the developing cartridge  7  and the sheet cassette  3  in the up-down direction in a state where the developing cartridge  7 , the solvent cartridge  32 , and the sheet cassette  3  are attached to the main casing  2 . 
     (3) As illustrated in  FIG. 19 , the second circuit board  39 B may be positioned downward of the developing cartridge  7  in a state where the developing cartridge  7  and the solvent cartridge  32  are attached to the main casing  2 . The second circuit board  39 B may be positioned between the developing cartridge  7  and the solvent cartridge  32  in the up-down direction. 
     (4) The sheet cassette  3  may be installed in the main casing  2  so as not to be attachable to or detachable from the main casing  2 . In this case, the sheet cassette  3  may include a portion for accommodating therein the sheet S and movable through the third opening  37  between an interior position in which the portion is positioned inside the main casing  2  and an exterior position in which the portion is positioned outside the main casing  2 . 
     (5) The guide  38 A and the guide  38 B may be grooves. The cartridge guide  32 C and the cartridge guide  32 D may be ribs. 
     (6) The developing cartridge  7  and the drum cartridge  31  may be detachably attachable to the main casing  2  independently of each other. 
     (7) The developing cartridge  7  may be integral with the drum cartridge  31 . 
     Third Embodiment 
     Next, a third embodiment will be described with reference to  FIGS. 20 and 21 , wherein like parts and components are designated by the same reference numerals as those shown in the first embodiment to avoid duplicating description. 
     As illustrated in  FIG. 20 , an image forming apparatus  1  according to the third embodiment includes the main casing  2  described above, a cover  40 , a drum cartridge  41 , a solvent cartridge  42 , a supply pipe  43 , and a pump  44 . 
     1. Details of Main Casing  2   
     As illustrated in  FIGS. 20 and 21 , the main casing  2  has an opening  45 . The main casing  2  has one end portion  2 E 1  and another end portion  2 E 2  in the second direction. The second direction crosses the first direction. The other end portion  2 E 2  is spaced apart from the one end portion  2 E 1  in the second direction. The applicator  9  is positioned at the one end portion  2 E 1  of the main casing  2 . 
     1.1 Opening  45   
     The opening  45  is positioned at the other end portion  2 E 2  in the second direction of the main casing  2 . The developing cartridge  7  and the solvent cartridge  42  pass through the opening  45  when the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  2 . The developing cartridge  7  and the solvent cartridge  42  are attachable to the main casing  2  in the second direction. Note that the developing cartridge  7  and the solvent cartridge  42  those attached to the main casing  2  are detachable from the main casing  2  through the opening  45 . 
     2. Cover  40   
     The cover  40  is positioned at the other end portion  2 E 2  in the second direction of the main casing  2 . The cover  40  is movable between a closed position (see  FIG. 20 ) and an open position (see  FIG. 21 ). The cover  40  is pivotally movable about a cover axis  40 A. The cover axis  40 A extends in the first direction. 
     As illustrated in  FIG. 20 , the cover  40  extends in the up-down direction in a state where the cover  40  is at the closed position. The cover  40  closes the opening  45  in a state where the cover  40  is at the closed position. 
     On the other hand, as illustrated in  FIG. 21 , the cover  40  extends in the second direction in a state where the cover  40  is at the open position. The opening  45  is opened in a state where the cover  40  is at the open position. 
     3. Drum Cartridge  41   
     As illustrated in  FIGS. 20 and 21 , the drum cartridge  41  is movable in the second direction through the opening  45  between an interior position (see  FIG. 20 ) and an exterior position (see  FIG. 21 ). The drum cartridge  41  is positioned inside the main casing  2  (see  FIG. 20 ) in a state where the drum cartridge  41  is at the interior position. The drum cartridge  41  is positioned outside the main casing  2  (see  FIG. 21 ) in a state where the drum cartridge  41  is at the exterior position. 
     As illustrated in  FIG. 20 , the drum cartridge  41  includes the photosensitive drum  4 , the charging unit  5 , and a drum frame  41 A. The drum cartridge  41  may include the transfer unit  8 . In the present embodiment, the main casing  2  includes the transfer unit  8 . The transfer unit  8  can convey the sheet S in the second direction toward the applicator  9 . 
     The drum frame  41 A extends in the second direction. The drum frame  41 A supports the photosensitive drum  4 . The drum frame  41 A can support the developing cartridge  7  and the solvent cartridge  42 . The drum cartridge  41  is movable in a state where the drum frame  41 A supports the developing cartridge  7  and the solvent cartridge  42 . 
     The developing cartridge  7  is detachably attachable to the drum frame  41 A. A state where the developing cartridge  7  is attached to the drum frame  41 A denotes a state where the developing cartridge  7  is supported by a certain position of the drum frame  41 A. The developing cartridge  7  may be movable relative to the drum frame  41 A in a state where the developing cartridge  7  is attached to the drum frame  41 A. 
     The developing cartridge  7  is attached to the main casing  2  while the developing cartridge  7  is attached to the drum frame  41 A and the drum cartridge  41  is at the interior position. The developing cartridge  7  is detachable from the drum frame  41 A in a state where the drum cartridge  41  is at the exterior position, as indicated by an imaginary line in  FIG. 21 . 
     4. Solvent Cartridge  42   
     The solvent cartridge  42  is detachably attachable to the main casing  2  independently of the developing cartridge  7 . The solvent cartridge  42  is detachably attachable to the drum frame  41 A independently of the developing cartridge  7 . A state where the solvent cartridge  42  is attached to the drum frame  41 A denotes a state where the solvent cartridge  42  is supported by a specific position of the drum frame  41 A. The solvent cartridge  42  may be movable relative to the drum frame  41 A in a state where the solvent cartridge  42  is attached to the drum frame  41 A. 
     The solvent cartridge  42  is attached to the main casing  2  in a state where the solvent cartridge  42  is attached to the drum frame  41 A and the drum cartridge  41  is at the interior position. The solvent cartridge  42  is detachable from the drum frame  41 A in a state where the drum cartridge  41  is at the exterior position, as indicated by an imaginary line in  FIG. 21 . 
     As illustrated in  FIG. 20 , in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  2  and the cover  40  is at the closed position, the developing cartridge  7  and the solvent cartridge  42  are positioned between the applicator  9  and the cover  40  in the second direction, and the solvent cartridge  42  is positioned closer to the applicator  9  than the developing cartridge  7  is to the applicator  9 . By virtue of this positional relationship, the supply pipe  43  for connecting the solvent cartridge  42  to the applicator  9  can be shortened. Further, since the developing cartridge  7  is positioned closer to the cover  40  than the solvent cartridge  42  is to the cover  40  in the second direction in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  2 , the developing cartridge  7  can be replaced easily in a state where the cover  40  is at the open position (see  FIG. 21 ). Further, this configuration can restrain the user&#39;s hands from getting dirty with solvent adhered to the solvent cartridge  42  during a process of attachment and detachment of the developing cartridge  7 . 
     Further, the photosensitive drum  4  is positioned between the applicator  9  and the cover  40  in the second direction and the solvent cartridge  42  is positioned closer to the applicator  9  than the photosensitive drum  4  is to the applicator  9  in the second direction in a state where the developing cartridge  7 , the drum cartridge  41 , and the solvent cartridge  42  are attached to the main casing  2  and the cover  40  is at the closed position. 
     Further, the solvent cartridge  42  includes a solvent casing  42 A. 
     4.1 Solvent Casing  42 A 
     The solvent casing  42 A can accommodate therein solvent. In other words, the solvent cartridge  42  can accommodate therein solvent. The solvent dissolves toner. 
     The solvent casing  42 A extends in the second direction in a state where the solvent cartridge  42  is attached to the main casing  2 . The solvent casing  42 A has a discharge opening  42 B. The discharge opening  42 B allows the solvent to be discharged therethrough from the solvent casing  42 A to the supply pipe  43 . The discharge opening  42 B is positioned at one end portion E 11  in the second direction of the solvent casing  42 A. The solvent casing  42 A has another end portion E 12  positioned away from the one end portion E 11  in the second direction. The one end portion E 11  is positioned on the opposite side of the other end portion E 12  from the developing cartridge  7  in the second direction in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  2 . 
     5. Supply Pipe  43   
     The supply pipe  43  allows the solvent to be supplied from the solvent cartridge  42  to the applicator  9  therethrough. The supply pipe  43  is positioned between the applicator  9  and the solvent cartridge  42  in the second direction in a state where the solvent cartridge  42  is attached to the main casing  2 . 
     The supply pipe  43  has one end portion  43 A and another end portion  43 B. The one end portion  43 A is connected to the discharge opening  42 B of the solvent cartridge  42  in a state where the solvent cartridge  42  is attached to the main casing  2 . The other end portion  43 B is positioned away from the one end portion  43 A. The other end portion  43 B is connected to the applicator casing  14  of the applicator  9 . 
     6. Pump  44   
     The pump  44  is positioned between the one end portion  43 A and the other end portion  43 B of the supply pipe  43 . The pump  44  pumps the solvent from the solvent cartridge  42  to the applicator  9 . When the pump  44  is driven in a state where the solvent cartridge  42  is attached to the main casing  2 , the solvent accommodated in the solvent cartridge  42  enters the applicator casing  14  of the applicator  9  through the discharge opening  42 B and the supply pipe  43 . Specifically, the pump  44  is a gear pump. 
     7. Functions and Effects 
     (1) According to the image forming apparatus  1 , replacement of the solvent cartridge  42  that can accommodate therein the solvent can be performed independently of the developing cartridge  7  as illustrated in  FIG. 21 . 
     Further, as illustrated in  FIG. 20 , in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  2  and the cover  40  is at the closed position, the developing cartridge  7  and the solvent cartridge  42  are positioned between the applicator  9  and the cover  40  in the second direction, and the solvent cartridge  42  is positioned closer to the applicator  9  than the developing cartridge  7  is to the applicator  9 . 
     With this configuration, the supply pipe  43  for connecting the solvent cartridge  42  to the applicator  9  can be shortened. 
     Further, since the developing cartridge  7  is positioned closer to the cover  40  than the solvent cartridge  42  is to the cover  40  in the second direction, the developing cartridge  7  can be replaced easily in a state where the cover  40  is at the open position (see  FIG. 21 ). 
     Note that there may be a case where a timing for replacement of the developing cartridge  7  is different from a timing for replacement of the solvent cartridge  42 . For example, in a case where the solvent cartridge  42  (the solvent casing  42 A) has a size greater than that of the developing cartridge  7  (the toner casing  12 ), frequency of replacement for the developing cartridge  7  is assumed to be greater than that of frequency for the solvent cartridge  42 . Therefore, replacement of the developing cartridge  7  can be performed easily. 
     Further, the user&#39;s hands can be suppressed from getting dirty with the solvent adhered to the solvent cartridge  42  during a process of attachment and detachment of the developing cartridge  7 . 
     8. Modifications 
     The image forming apparatus  1  may include a drawer. The drawer is movable between an interior position and an exterior position. The drawer is positioned inside the main casing  2  in a state where the drawer is at the interior position. The drawer is positioned outside the main casing  2  when the drawer is at the exterior position. The drawer is not detachable from the main casing  2 . The developing cartridge  7  may be detachably attachable to the drawer in a state where the drawer is at the exterior position. The solvent cartridge  42  may be detachably attachable to the drawer independently of the developing cartridge  7  in a state where the drawer is at the exterior position. 
     Further, the developing cartridge  7  may include the photosensitive drum  4 . The photosensitive drum  4  may be positioned between the applicator  9  and the cover  40  in the second direction in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the drawer, the drawer is at the interior position, and the cover  40  is at the closed position. The solvent cartridge  42  may be positioned closer to the applicator  9  than the photosensitive drum  4  is to the applicator  9  in the second direction in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the drawer, the drawer is at the interior position, and the cover  40  is at the closed position. 
     Note that, even in this modification, the solvent cartridge  42  is positioned closer to the applicator  9  than the developing cartridge  7  is to the applicator  9  in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the drawer and the drawer is at the interior position. 
     Further, the drum cartridge including the photosensitive drum  4  may be detachably attachable to the drawer independently of the developing cartridge  7 . 
     Fourth Embodiment 
     Next, a fourth embodiment will be described with reference to  FIGS. 22 and 23 , wherein like parts and components are designated by the same reference numerals as those shown in the third embodiment to avoid duplicating description. 
     As illustrated in  FIGS. 22 and 23 , an image forming apparatus  1  according to the fourth embodiment includes a main casing  46 , a cover  47 , and a drum cartridge  48 . Note that the exposure unit  6  is an LED array in the fourth embodiment. 
     1. Details of Main Casing  46   
     The main casing  46  has an opening  46 A. The opening  46 A is positioned in an upper end portion of the main casing  46 . The developing cartridge  7  and the solvent cartridge  42  pass through the opening  46 A when the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  46  (see  FIG. 23 ). The opening  46 A is positioned above the developing cartridge  7  and the solvent cartridge  42  in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  46 . 
     The developing cartridge  7  and the solvent cartridge  42  are detachably attachable to the main casing  46  in a third direction. The third direction crosses the first direction and the second direction. Incidentally, the developing cartridge  7  and the solvent cartridge  42  those attached to the main casing  46  are detachable from the main casing  46  through the opening  46 A. 
     The main casing  46  has one end portion  46 E 1  and another end portion  46 E 2  in the second direction. The other end portion  46 E 2  is positioned away from the one end portion  46 E 1  in the second direction. The applicator  9  is positioned at the one end portion  46 E 1  in the second direction of the main casing  46 . 
     2. Cover  47   
     The cover  47  is positioned at the upper end portion of the main casing  46 . The cover  47  includes the discharge tray  11 . The cover  47  is positioned above the developing cartridge  7  and the solvent cartridge  42  in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  46 . The cover  47  is movable between a closed position (see  FIG. 22 ) and an open position (see  FIG. 23 ). The cover  47  is pivotally movable about a cover axis  47 A. The cover axis  47 A extends in the first direction. The cover axis  47 A is positioned at the one end portion  46 E 1  in the second direction of the main casing  46 . 
     As illustrated in  FIG. 22 , the cover  47  extends in the second direction in a state where the cover  30  is at the closed position. The cover  47  closes the opening  46 A in a state where the cover  47  is at the closed position. 
     On the other hand, as illustrated in  FIG. 23 , the cover  47  extends in the third direction in a state where the cover  47  is at the open position. The opening  46 A is opened in a state where the cover is at the open position. 
     3. Drum Cartridge  48   
     As illustrated in  FIGS. 22 and 23 , the drum cartridge  48  is detachably attachable to the main casing  46  in the third direction in a state where the cover  47  is at the open position. Note that the drum cartridge  48  attached to the main casing  46  is detachable from the main casing  46  through the opening  46 A. 
     The drum cartridge  48  includes the photosensitive drum  4  described above, the charging unit  5 , and a drum frame  48 A. 
     The drum frame  48 A supports the photosensitive drum  4 . The drum frame  48 A can support the developing cartridge  7 . The drum cartridge  48  is movable while the drum frame  48 A supports the developing cartridge  7 . 
     The developing cartridge  7  is detachably attachable to the drum frame  48 A. A state where the developing cartridge  7  is attached to the drum frame  48 A denotes a state where the developing cartridge  7  is supported by a certain position of the drum frame  48 A. The developing cartridge  7  may be movable relative to the drum frame  48 A in a state where the developing cartridge  7  is attached to the drum frame  48 A. 
     As illustrated in  FIG. 22 , the developing cartridge  7  is attached to the main casing  46  in a state where the developing cartridge  7  is attached to the drum frame  48 A and the drum cartridge  48  is attached to the main casing  46 . Further, the developing cartridge  7  is detachable from the drum frame  48 A in a state where the drum cartridge  48  is attached to the main casing  46  and the cover  47  is at the open position (see  FIG. 23 ). 
     Further, in a state where the drum cartridge  48  is detached from the main casing  46 , the developing cartridge  7  is detachable from the drum frame  48 A as indicated by an imaginary line in  FIG. 23 . 
     As illustrated in  FIG. 22 , the solvent cartridge  42  is detachably attachable to the main casing  46  independently of the developing cartridge  7 . The solvent cartridge  42  is detachably attachable to the main casing  46  independently of the drum cartridge  48 . The solvent cartridge  42  attached to the main casing  46  is detachable from the main casing  46  through the opening  46 A in a state where the cover  47  is at the open position (see  FIG. 23 ). 
     The solvent cartridge  42  is positioned closer to the applicator  9  than the developing cartridge  7  is to the applicator  9  in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  46  and the cover  47  is at the closed position. Accordingly, the supply pipe  43  for connecting the solvent cartridge  42  and the applicator  9  to each other can be shortened. 
     Further, the cover axis  47 A is positioned farther away from the solvent cartridge  42  than the applicator  9  is from the solvent cartridge  42  in the second direction in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  46 . With this configuration, the solvent cartridge  42  is positioned on the opposite side of the applicator  9  from the cover axis  47 A in the second direction in a state where the solvent cartridge  42  is attached to the main casing  46 . Hence, in a state where the cover  47  is at the open position (see  FIG. 23 ), the solvent cartridge  42  can be replaced easily. 
     4. Functions and Effects 
     According to the fourth embodiment, the solvent cartridge  42  that can accommodate therein the solvent can be replaced independently of the developing cartridge  7 , as illustrated in  FIG. 23 . 
     Further, as illustrated in  FIG. 22 , the solvent cartridge  42  is positioned closer to the applicator  9  than the developing cartridge  7  is to the applicator  9  in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  46  and in a state where the cover  47  is at the closed position. 
     This arrangement can shorten the supply pipe  43  for connecting the solvent cartridge  42  and the applicator  9  to each other. Further, the user&#39;s hands can be suppressed from getting dirty with the solvent adhered to the solvent cartridge  42  during a process of attachment and detachment of the developing cartridge  7  to and from the main casing  46 . 
     Further, the cover axis  47 A is positioned at the one end portion  46 E 1  in the second direction of the main casing  46 . The cover axis  47 A is positioned farther from the solvent cartridge  42  than the applicator  9  is from the solvent cartridge  42  in the second direction in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the main casing  46 . 
     Hence, the solvent cartridge  42  is positioned on the opposite side of the applicator  9  from the cover axis  47 A in the second direction in a state where the solvent cartridge  42  is attached to the main casing  46 . As a result, replacement of the solvent cartridge  42  can be performed easily in a state where the third opening  37  is at the open position. 
     5. Modifications 
     The image forming apparatus  1  may include a drawer. The drawer is movable between an interior position and an exterior position. The drawer is positioned inside the main casing  46  in a state where the drawer is at the interior position. The drawer is positioned outside the main casing  46  when the drawer is at the exterior position. The drawer is not detachable from the main casing  46 . The developing cartridge  7  may be detachably attachable to the drawer in a state where the drawer is at the exterior position. The solvent cartridge  42  may be detachably attachable to the drawer independently of the developing cartridge  7  in a state where the drawer is at the exterior position. 
     Further, the developing cartridge  7  may include the photosensitive drum  4 . The photosensitive drum  4  may be positioned between the applicator  9  and the cover  47  in the second direction in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the drawer, the drawer is at the interior position, and the cover  47  is at the closed position. The solvent cartridge  42  may be positioned closer to the applicator  9  than the photosensitive drum  4  is to the applicator  9  in the second direction in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the drawer, the drawer is at the interior position, and the cover  47  is at the closed position. 
     Note that, even in this modification, the solvent cartridge  42  is positioned closer to the applicator  9  than the developing cartridge  7  is to the applicator  9  in a state where the developing cartridge  7  and the solvent cartridge  42  are attached to the drawer and the drawer is at the interior position. 
     Further, the drum cartridge including the photosensitive drum  4  may be detachably attachable to the drawer independently of the developing cartridge  7 . 
     Fifth Embodiment 
     Next, a fifth embodiment will be described with reference to  FIGS. 24 through 28 , wherein like parts and components are designated by the same reference numerals as those shown in the first embodiment to avoid duplicating description. 
     As illustrated in  FIGS. 24 and 25 , an image forming apparatus  1  according to the fifth embodiment includes the main casing  2  described above, a cover  50 , a drum cartridge  51 , a supply pipe  53  (see  FIG. 28 ), a pump  54  (see  FIG. 28 ), and a first circuit board  56  (see  FIG. 28 ). 
     1. Details of Main Casing  2   
     As illustrated in  FIGS. 25 and 26 , the main casing  2  has an opening  59  and an inlet port  55 . 
     1.1 Opening  59   
     As illustrated in  FIG. 25 , the opening  59  is positioned at one end portion E 1  in the second direction of the main casing  2 . The second direction crosses the first direction. The developing cartridge  7  passes through the opening  59  when the developing cartridge  7  is attached to the main casing  2 . Further, the drum cartridge  51  is also attachable to the main casing  2  through the opening  59 . The developing cartridge  7  and the drum cartridge  51  are attachable to the main casing  2  in the second direction. Note that the developing cartridge  7  and the drum cartridge  51  those attached to the main casing  2  are detachable from the main casing  2  through the opening  59 . 
     1.2 Inlet Port  55   
     In a state where a solvent cartridge  52  is attached to the main casing  2 , the inlet port  55  allows solvent accommodated in the solvent cartridge  52  to be introduced into the main casing  2  therethrough. Specifically, the inlet port  55  allows the solvent accommodated in the solvent cartridge  52  to be introduced into the supply pipe  53  (see  FIG. 28 ) therethrough in a state where the solvent cartridge  52  is connected to the inlet port  55 . The inlet port  55  is in communication with an internal space of the supply pipe  53  (see  FIG. 28 ). 
     As illustrated in  FIG. 26 , the inlet port  55  is positioned on an outer surface of the main casing  2 . Specifically, the inlet port  55  is positioned on an upper surface of the main casing  2 . The inlet port  55  is positioned away from the discharge tray  11  in the first direction. Further, the inlet port  55  is positioned away from the developing cartridge  7  in the first direction. Further, the inlet port  55  is positioned away from the applicator  9  in the first direction. Further, the inlet port  55  is positioned on the opposite side of the first circuit board  56  from the developing cartridge  7  in the first direction. In other words, the first circuit board  56  is positioned between the developing cartridge  7  and the inlet port  55  in the first direction. 
     The inlet port  55  is positioned away from the one end portion E 1  of the main casing  2  in the second direction. The inlet port  55  is positioned on the opposite side of the developing cartridge  7  from the one end portion E 1  of the main casing  2  in the second direction. The inlet port  55  is positioned on the opposite side of the applicator  9  from the developing cartridge  7  in the second direction. 
     1.3 Protrusion  57   
     As illustrated in  FIG. 27 , the main casing  2  includes a protrusion  57 , and a second thread  58 . 
     The protrusion  57  extends through a lid  52 D in a state where the solvent cartridge  52  is connected to the inlet port  55 . The lid  52 D will be described later. The protrusion  57  is positioned within the inlet port  55 . The protrusion  57  extends in the up-down direction. The protrusion  57  is positioned to be spaced apart from an inner peripheral surface of the inlet port  55 . 
     1.4 Second Thread  58   
     The second thread  58  is in threading engagement with a first thread  52 C in a state where the solvent cartridge  52  is connected to the inlet port  55 . The first thread  52 C will be described later. The second thread  58  is positioned on the inner peripheral surface of the inlet port  55 . 
     2. Solvent Cartridge  52   
     The solvent cartridge  52  can be connected to the main casing  2 . The solvent cartridge  52  can be connected to the main casing  2  independently of the developing cartridge  7  (see  FIG. 24 ). The solvent cartridge  52  can be connected to the inlet port  55 . 
     The main casing  2  is replenished with the solvent in a state where the solvent cartridge  52  is connected to the main casing  2 . The solvent cartridge  52  is removed from the main casing  2  (see  FIG. 26 ) upon completion of replenishment of the main casing  2  with the solvent. The image forming apparatus  1  can perform printing operation in a state where the solvent cartridge  52  is removed from the main casing  2 . 
     The solvent cartridge  52  includes a solvent casing  52 A, a sleeve  52 B, the first thread  52 C, and the lid  52 D. 
     2.1 Solvent Casing  52 A 
     The solvent casing  52 A can accommodate therein solvent. In other words, the solvent is accommodated within the solvent cartridge  52 . The solvent dissolves toner. 
     The solvent casing  52 A is positioned outside the main casing  2  in a state where the solvent cartridge  52  is connected to the inlet port  55 . The solvent casing  52 A is positioned upward of the main casing  2  in a state where the solvent cartridge  52  is connected to the inlet port  55 . The solvent casing  52 A extends in the up-down direction in a state where the solvent cartridge  52  is connected to the inlet port  55 . The solvent casing  52 A has a discharge opening  52 E. The discharge opening  52 E allows the solvent to be discharged therethrough from the solvent casing  52 A to the supply pipe  53  (see  FIG. 28 ). The discharge opening  52 E is positioned at a lower end portion of the solvent casing  52 A in a state where the solvent cartridge  52  is connected to the inlet port  55 . 
     2.2 Sleeve  52 B 
     The sleeve  52 B is positioned at an outer periphery of the discharge opening  52 E. The sleeve  52 B is inserted into the inlet port  55  in a state where the solvent cartridge  52  is connected to the inlet port  55 . 
     2.3 First Thread  52 C 
     The first thread  52 C is in threading engagement with the second thread  58  in a state where the solvent cartridge  52  is connected to the inlet port  55 . With this threading engagement, displacement of the discharge opening  52 E of the solvent cartridge  52  relative to the inlet port  55  can be suppressed during replenishment for the solvent. As a result, stabilized replenishment of the main casing  2  with the solvent in the solvent cartridge  52  can be performed. The first thread  52 C is positioned on an outer peripheral surface of the sleeve  52 B. In other words, the sleeve  52 B has the first thread  52 C at the outer peripheral surface of the sleeve  52 B. 
     2.4 Lid  52 D 
     The lid  52 D is positioned inside the discharge opening  52 E. The lid  52 D closes the discharge opening  52 E as indicated by an imaginary line in  FIG. 27  in a state prior to connection of the solvent cartridge  52  to the inlet port  55 . The lid  52 D is torn by the protrusion  57  as indicated by a solid line in  FIG. 27  in a state where the solvent cartridge  52  is connected to the inlet port  55 , thereby allowing the discharge opening  52 E and the inlet port  55  to be in communication with each other. 
     3. Cover  50   
     As illustrated in  FIG. 25 , the cover  50  is positioned at one end portion E 1  in the second direction of the main casing  2 . The cover  50  is movable between a closed position (see  FIG. 24 ) and an open position (see  FIG. 25 ). The cover  50  is pivotally movable about a cover axis  50 A. The cover axis  50 A extends in the first direction. 
     As illustrated in  FIG. 24 , the cover  50  extends in the up-down direction in a state where the cover  50  is at the closed position. The cover  50  closes the opening  59  in a state where the cover  50  is at the closed position. 
     On the other hand, as illustrated in  FIG. 25 , the cover  50  extends in the second direction in a state where the cover  50  is at the open position. The opening  59  is opened when the cover  50  is at the open position. 
     4. Drum Cartridge  51   
     As illustrated in  FIG. 24 , the drum cartridge  51  is detachably attachable to the main casing  2 . In other words, the drum cartridge  51  is detachably attachable to the image forming apparatus  1 . The drum cartridge  51  includes the above-described photosensitive drum  4 , the above-described charging unit  5 , and the transfer unit  8 . Note that the main casing  2  may include the transfer unit  8 . 
     Further, the developing cartridge  7  is detachably attachable to the drum cartridge  51 . The developing cartridge  7  is attachable to the main casing  2  in a state where the developing cartridge  7  is attached to the drum cartridge  51 . 
     5. Supply Pipe  53   
     The supply pipe  53  is positioned inside the main casing  2  (see  FIG. 24 ), as illustrated in  FIG. 28 . The supply pipe  53  has one end portion  53 A and another end portion  53 B. The one end portion  53 A is connected to the inlet port  55  (see  FIG. 27 ) of the main casing  2 . The other end portion  53 B is positioned away from the one end portion  53 A. The other end portion  53 B is connected to the applicator casing  14  of the applicator  9 . 
     6. Pump  54   
     The pump  54  is positioned between the one end portion  53 A and the other end portion  53 B of the supply pipe  53 . The pump  54  pumps the solvent from the solvent cartridge  52  to the applicator  9 . When the pump  54  is driven in a state where the solvent cartridge  52  is connected to the main casing  2 , the solvent accommodated in the solvent cartridge  52  is introduced into the applicator casing  14  of the applicator  9  through the inlet port  55  and the supply pipe  53 . Specifically, the pump  54  is a gear pump. 
     7. First Circuit Board  56   
     The first circuit board  56  is positioned inside the main casing  2  (see  FIG. 24 ). The first circuit board  56  extends in the second direction. The first circuit board  56  is positioned juxtaposed with the applicator  9  in the first direction. The first circuit board  56  is electrically connected to the pump  54 . Specifically, the first circuit board  56  is a control circuit board. The first circuit board  56  controls the pump  54 . 
     8. Functions and Effects 
     According to the image forming apparatus  1 , as illustrated in  FIG. 25 , the solvent cartridge  52  is positioned outside the main casing  2  in a state where the solvent cartridge  52  is connected to the main casing  2 . Further, the inlet port  55  of the main casing  2  allows the solvent accommodated in the solvent cartridge  52  to enter the main casing  2  therethrough in a state where the solvent cartridge  52  is connected to the main casing  2 . 
     Accordingly, the replenishment of the main casing  2  with the solvent accommodated in the solvent cartridge  52  can be performed from an outside of the main casing  2  through the inlet port  55 . As a result, the applicator  9  can be replenished with the solvent (see  FIG. 28 ). Accordingly, the image forming apparatus  1  can be made compact in comparison with a configuration where the solvent cartridge  52  is accommodated inside the main casing  2 . 
     Further, the inlet port  55  is positioned on the upper surface of the main casing  2 . Hence, the solvent casing  52 A is positioned upward of the main casing  2  in a state where the solvent cartridge  52  is connected to the main casing  2 . As a result, the solvent can flow smoothly from the solvent cartridge  52  into the main casing  2  by making use of a gravitational force. 
     Further, the first thread  52 C of the solvent cartridge  52  is in threading engagement with the second thread  58  of the main casing  2  in a state where the solvent cartridge  52  is connected to the main casing  2 , as illustrated in  FIG. 17 . Therefore, displacement of the discharge opening  52 E of the solvent cartridge  52  from the inlet port  55  during the replenishment for the solvent can be suppressed. As a result, the replenishment of the main casing  2  with the solvent from the solvent cartridge  52  can be performed stably. 
     9. Modifications 
     (1) The image forming apparatus  1  may be able to perform printing operations while the solvent cartridge  52  is connected to the main casing  2 . 
     (2) The inlet port  55  may be positioned at a side surface of the main casing  2 . 
     Sixth Embodiment 
     Next, a sixth embodiment will be described with reference to  FIGS. 29 through 33 , wherein like parts and components are designated by the same reference numerals as those shown in the first embodiment to avoid duplicating description. 
     1. Drum Cartridge  60   
     As illustrated in  FIG. 29 , an image forming apparatus  1  according to the sixth embodiment includes a drum cartridge  60 . As illustrated in  FIGS. 29 and 30 . the drum cartridge  60  is detachably attachable to the main casing  2 . In other words, the drum cartridge  60  is detachably attachable to the image forming apparatus  1 . 
     The drum cartridge  60  includes the photosensitive drum  4 , the charging unit  5 , the transfer unit  8 , a drum frame  61  (see  FIG. 31 ), a charge electrode  62 A (see  FIG. 32 ), a charge electrode  62 B (see  FIG. 32 ), a transfer electrode  62 C (see  FIG. 33 ), and a sheet conveying roller  63  (see  FIG. 29 ). Note that the main casing  2  may include the transfer unit  8  and the sheet conveying roller  63 . 
     1.1 Drum Frame  61   
     The drum frame  61  illustrated in  FIG. 31  supports the photosensitive drum  4 , the charging unit  5 , and the transfer unit  8 . The developing cartridge  7  is detachably attachable to the drum frame  61 . In other words, the developing cartridge  7  is detachably attachable to the drum cartridge  60 . The developing cartridge  7  is attachable to the main casing  2  (see  FIG. 29 ) in a state where the developing cartridge  7  is attached to the drum cartridge  60 . That is, the applicator  9  (see  FIG. 29 ) described above applies solvent to toner that has been transferred to the sheet S in a state where the drum cartridge  60  and the developing cartridge  7  are attached to the main casing  2 . 
     The drum frame  61  extends in the first direction and the second direction. The second direction crosses the first direction. Preferably, the second direction is perpendicular to the first direction. More preferably, the second direction is perpendicular to both the first direction and the third direction in a state where the drum cartridge  60  is attached to the main casing  2 . The drum frame  61  has one end portion E 21  and another end portion E 22  in the first direction. The drum frame  61  has one end portion E 31  and another end portion E 32  in the second direction. The developing cartridge  7  is positioned at the other end portion E 32  in the second direction of the drum frame  61  in a state where the developing cartridge  7  is attached to the drum frame  61 . 
     The drum frame  61  includes a side plate  64 A, a side plate  64 B, a solvent casing  65 , a waste solvent casing  66 , and a tube  67 . In other words, the drum cartridge  60  includes the solvent casing  65 , the waste solvent casing  66 , and the tube  67 . 
     1.1.1 Side Plate  64 A and Side Plate  64 B 
     The side plate  64 A is positioned at the one end portion E 21  in the first direction of the drum frame  61 . The side plate  64 A extends in the second direction. 
     The side plate  64 B is positioned to be spaced apart from the side plate  64 A in the first direction. The side plate  64 B is positioned at the other end portion E 22  in the first direction of the drum frame  61 . As illustrated in  FIG. 32 , the side plate  64 B extends in the second direction. 
     1.1.2 Solvent Casing  65   
     As illustrated in  FIG. 29 , the solvent casing  65  is positioned at the one end portion E 31  in the second direction of the drum frame  61 . In a state where the developing cartridge  7  is attached to the drum frame  61 , at least a portion of the solvent casing  65  is positioned on the opposite side of the photosensitive drum  4  from the developing cartridge  7  in the second direction. In other words, in a state where the developing cartridge  7  is attached to the drum frame  61 , the photosensitive drum  4  is positioned between the solvent casing  65  and the developing cartridge  7  in the second direction. In a state where the drum cartridge  60  is attached to the main casing  2  of the image forming apparatus  1 , at least a portion of the solvent casing  65  is positioned between the photosensitive drum  4  and the applicator  9  in the second direction. 
     At least a portion of the solvent casing  65  is positioned on the opposite side of the photosensitive drum  4  from the transfer unit  8  in the third direction. The third direction crosses the first direction and the second direction. Preferably, the third direction is perpendicular to both the first direction and the second direction. Specifically, the third direction is a direction defined by connecting the drum axis A 1  and the transfer axis A 3  to each other. In the present embodiment, the third direction is inclined with respect to the up-down direction in a state where the drum cartridge  60  is attached to the main casing  2 . Note that the third direction may be parallel to the up-down direction in a state where the drum cartridge  60  is attached to the main casing  2 . At least a portion of the solvent casing  65  is spaced apart from the photosensitive drum  4  in the third direction. The charging unit  5  is positioned between at least a portion of the solvent casing  65  and the photosensitive drum  4  in the third direction. At least a portion of the solvent casing  65  is positioned upward of the photosensitive drum  4  in a state where the drum cartridge  60  is attached to the main casing  2 . 
     As illustrated in  FIG. 31 , the solvent casing  65  is positioned between the side plate  64 A and the side plate  64 B in the first direction. The solvent casing  65  extends in the first direction. The solvent casing  65  has one end portion in the first direction connected to the side plate  64 A. The solvent casing  65  has another end portion in the first direction connected to the side plate  64 B. The solvent casing  65  can accommodate therein solvent. The solvent casing  65  has a discharge opening  651 . 
     The discharge opening  651  is positioned at the one end portion in the first direction of the solvent casing  65 . The discharge opening  651  allows the solvent accommodated in the solvent casing  65  to be discharged therethrough. 
     1.1.3 Waste Solvent Casing  66   
     As illustrated in  FIG. 29 , the waste solvent casing  66  is positioned at the other end portion E 32  in the second direction of the drum frame  61 . The waste solvent casing  66  is positioned on the opposite side of the photosensitive drum  4  from the solvent casing  65  in the second direction. In other words, the photosensitive drum  4  is positioned between the solvent casing  65  and the waste solvent casing  66  in the second direction. 
     The waste solvent casing  66  is positioned on the opposite side of the photosensitive drum  4  from the charging unit  5  in the third direction. The waste solvent casing  66  is positioned downward of the developing cartridge  7  in a state where the developing cartridge  7  and the drum frame  61  are attached to the main casing  2 . The waste solvent casing  66  supports the developing cartridge  7  in a state where the developing cartridge  7  is attached to the drum frame  61 . 
     As illustrated in  FIG. 32 , the waste solvent casing  66  is positioned between the side plate  64 A and the side plate  64 B in the first direction. The waste solvent casing  66  extends in the first direction. The waste solvent casing  66  has one end portion in the first direction connected to the side plate  64 A. The waste solvent casing  66  has another end portion in the first direction connected to the side plate  64 B. The waste solvent casing  66  can accommodate therein waste solvent. The waste solvent will be described later. 
     1.1.4 Tube  67   
     As illustrated in  FIG. 31 , the tube  67  is positioned at the one end portion E 21  in the first direction of the drum frame  61 . The tube  67  extends in the second direction. The tube  67  has one end portion in the second direction connected to the waste solvent casing  66 . 
     1.2 Charge Electrode  62 A, Charge Electrode  62 B, and Transfer Electrode  62 C 
     As illustrated in  FIGS. 32 and 33 , the charge electrode  62 A, the charge electrode  62 B, and the transfer electrode  62 C are positioned at the other end portion E 22  in the first direction of the drum frame  61 . The charge electrode  62 A, the charge electrode  62 B, and the transfer electrode  62 C are positioned away from the tube  67  in the first direction. The charge electrode  62 A, the charge electrode  62 B, and the transfer electrode  62 C are positioned on the opposite side of the solvent casing  65  from the tube  67  in the first direction. In other words, the solvent casing  65  is positioned between the charge electrode  62 A, the charge electrode  62 B, and the transfer electrode  62 C, and the tube  67  in the first direction. The charge electrode  62 A, the charge electrode  62 B, and the transfer electrode  62 C are mounted on the side plate  64 B. The charge electrode  62 A and the charge electrode  62 B are electrically connected to the charging unit  5 . Specifically, the charging unit  5  includes a wire  5 A (see  FIG. 29 ), and a grid  5 B (see  FIG. 29 ). The charge electrode  62 A is electrically connected to the wire  5 A. The charge electrode  62 B is electrically connected to the grid  5 B. The transfer electrode  62 C is electrically connected to the transfer unit  8 . 
     1.3 Sheet Conveying Roller  63   
     As illustrated in  FIG. 29 , the sheet conveying roller  63  conveys the sheet S toward the photosensitive drum  4  and the transfer unit  8  in a state where the drum cartridge  60  is attached to the main casing  2 . Specifically, the sheet conveying roller  63  makes contact with a sheet conveying roller  70  of the main casing  2  in a state where the drum cartridge  60  is attached to the main casing  2 . The sheet conveying roller  70  of the main casing  2  will be described later. The sheet conveying roller  63  can convey the sheet S in cooperation with the sheet conveying roller  70  in a state where the drum cartridge  60  is attached to the main casing  2 . Note that the sheet conveying roller  63  is in separation from the sheet conveying roller  70  in a state where the drum cartridge  60  is detached from the main casing  2 , as illustrated in  FIG. 30 . The sheet conveying roller  63  extends in the first direction. The sheet conveying roller  63  is rotatable about a conveying axis A 4 . The conveying axis A 4  extends in the first direction. The sheet conveying roller  63  is mounted on the waste solvent casing  66 . In other words, the waste solvent casing  66  supports the sheet conveying roller  63 . The sheet conveying roller  63  is positioned on the opposite side of the waste solvent casing  66  from the developing cartridge  7  in the third direction in a state where the developing cartridge  7  is attached to the drum frame  61 . 
     2. Details of Main Casing  2   
     Details of the main casing  2  will next be described with reference to  FIGS. 29 and 33 . 
     The main casing  2  includes a supply pipe  68 A (see  FIG. 29 ), a pump  68 B (see  FIG. 29 ), a waste solvent tray  68 C (see  FIG. 29 ), a discharge pipe  68 D (see  FIG. 29 ), a first circuit board  69 A (see  FIG. 33 ), a second circuit board  69 B (see  FIG. 33 ), and the sheet conveying roller  70  (see  FIG. 29 ). 
     2.1 Supply Pipe  68 A 
     As illustrated in  FIG. 29 , the supply pipe  68 A supplies solvent to the applicator  9 . The supply pipe  68 A has one end portion and another end portion. The one end portion of the supply pipe  68 A is connected to the discharge opening  651  (see  FIG. 31 ) of the drum cartridge  60  in a state where the drum cartridge  60  is attached to the main casing  2 . The other end portion of the supply pipe  68 A is positioned away from the one end portion of the supply pipe  68 A. The other end portion of the supply pipe  68 A is connected to the applicator casing  14  of the applicator  9 . 
     2.2 Pump  68 B 
     The pump  68 B is positioned between the one end portion and the other end portion of the supply pipe  68 A. The pump  68 B pumps the solvent from the solvent casing  65  to the applicator  9 . When the pump  68 B is driven in a state where the drum cartridge  60  is attached to the main casing  2 , the solvent accommodated in the solvent casing  65  is introduced into the applicator casing  14  of the applicator  9  through the discharge opening  651  and the supply pipe  68 A. The solvent entered the applicator casing  14  is sprayed through the nozzles  15  onto the toner that has been transferred to the sheet S from the photosensitive drum  4 . The sprayed solvent dissolves the toner on the sheet S. Specifically, the pump  68 B is a gear pump. 
     2.3 Waste Solvent Tray  68 C 
     The waste solvent tray  68 C is positioned below the applicator  9 . The waste solvent tray  68 C is positioned to be spaced apart from the applicator  9 . The sheet S on which toner has been transferred passes through a space between the applicator  9  and the waste solvent tray  68 C. The waste solvent tray  68 C accommodates therein the waste solvent. The waste solvent is solvent discharged from the applicator  9  but not applied to the sheet S. For example, in a case where printing operations are continuously performed on a first sheet S and a second sheet S subsequent to the first sheet S, solvent discharged from the applicator  9  to an interval between the first sheet S and the second sheet S is not applied to either of the first sheet S and the second sheet S, but is accommodated in the waste solvent tray  68 C as the waste solvent. Further, in a case where a width in the first direction of the sheet S is smaller than a range in which the solvent is applied in the first direction, the solvent discharged from the applicator  9  is not applied to the sheet S but is accommodated in the waste solvent tray  68 C as the waste solvent. 
     2.4 Discharge Pipe  68 D 
     The discharge pipe  68 D discharges the waste solvent from the applicator  9 . The discharge pipe  68 D has one end portion and another end portion. In a state where the drum cartridge  60  is attached to the main casing  2 , the one end portion of the discharge pipe  68 D is connected to the other end portion in the second direction of the tube  67  (see  FIG. 31 ). The other end portion of the discharge pipe  68 D is positioned away from the one end portion of the discharge pipe  68 D. The other end portion of the discharge pipe  68 D is connected to the waste solvent tray  68 C. In a state where the drum cartridge  60  is attached to the main casing  2 , the waste solvent in the waste solvent tray  68 C enters the waste solvent casing  66  through the discharge pipe  68 D and the tube  67 . 
     2.5 First Circuit Board  69 A 
     As illustrated in  FIG. 33 , the first circuit board  69 A is positioned at one end portion in the first direction of the main casing  2 . In a state where the drum cartridge  60  is attached to the main casing  2 , the first circuit board  69 A is positioned to be spaced apart from the drum cartridge  60  in the first direction. In a state where the drum cartridge  60  is attached to the main casing  2 , the first circuit board  69 A is positioned on the opposite side of the one end portion E 21  of the drum frame  61  from the other end portion E 22  of the drum frame  61  in the first direction. The first circuit board  69 A is electrically connected to the pump  68 B (see  FIG. 29 ). Specifically, the first circuit board  69 A is a control circuit board. The first circuit board  69 A controls the pump  68 B. 
     2.6 Second Circuit Board  69 B 
     The second circuit board  69 B is positioned to be spaced apart from the first circuit board  69 A in the first direction. In a state where the drum cartridge  60  is attached to the main casing  2 , the second circuit board  69 B is positioned on the opposite side of the drum cartridge  60  from the first circuit board  69 A in the first direction. In other words, the drum cartridge  60  is positioned between the first circuit board  69 A and the second circuit board  69 B in the first direction. In a state where the drum cartridge  60  is attached to the main casing  2 , the second circuit board  69 B is electrically connected to the charge electrode  62 A, the charge electrode  62 B, and the transfer electrode  62 C. The second circuit board  69 B applies a voltage to the wire  5 A of the charging unit  5 , the grid  5 B of the charging unit  5 , and the transfer unit  8 . Further, the second circuit board  69 B is electrically connected to the applicator  9 . The second circuit board  69 B supplies electric power to the applicator  9 . 
     2.7 Sheet Conveying Roller  70   
     As illustrated in  FIG. 29 , the sheet conveying roller  70  is positioned below the sheet conveying roller  63  in a state where the drum cartridge  60  is attached to the main casing  2 . The sheet conveying roller  70  makes contact with the sheet conveying roller  63  in a state where the drum cartridge  60  is attached to the main casing  2 . The sheet conveying roller  70  can convey sheet S in cooperation with the sheet conveying roller  63  in a state where the drum cartridge  60  is attached to the main casing  2 . 
     3. Functions and Effects 
     (1) According to the drum cartridge  60 , as illustrated in  FIG. 29 , solvent can be accommodated in the solvent casing  65 . Accordingly, the solvent can be supplied when replacement of the drum cartridge  60  is performed. 
     (2) According to the drum cartridge  60 , as illustrated in  FIG. 29 , at least a portion of the solvent casing  65  is positioned between the photosensitive drum  4  and the applicator  9  in the second direction in a state where the drum cartridge  60  is attached to the main casing  2 . 
     With this arrangement, in a state where the drum cartridge  60  is attached to the main casing  2 , at least a portion of the solvent casing  65  is positioned close to the applicator  9 . 
     As a result, the supply pipe  68 A for supplying the solvent from the solvent casing  65  to the applicator  9  can be shortened, thereby restraining complication of a piping arrangement from the solvent casing  65  to the applicator  9 . 
     Further, enlargement of a capacity of the solvent casing  65  can be achieved by making use of a space between the photosensitive drum  4  and the applicator  9 . 
     (3) According to the drum cartridge  60 , as illustrated in  FIG. 29 , waste solvent can be accommodated in the waste solvent casing  66 . Accordingly, the waste solvent can be collected when the drum cartridge  60  is replaced. 
     (4) According to the drum cartridge  60 , as illustrated in  FIGS. 32 and 33 , the charge electrode  62 A is positioned on the opposite side of the solvent casing  65  in the first direction from the tube  67  (see  FIG. 31 ) through which the waste solvent flows. 
     Hence, the charge electrode  62 A can be restrained from getting dirty with the waste solvent even if leakage of the waste solvent from the tube  67  occurs. 
     (5) According to the drum cartridge  60 , as illustrated in  FIGS. 32 and 33 , the transfer electrode  62 C is positioned on the opposite side of the solvent casing  65  in the first direction from the tube  67  (see  FIG. 31 ) through which the waste solvent flows. 
     With this positional relationship, the transfer electrode  62 C can be restrained from getting dirty with the waste solvent even if leakage of the waste solvent from the tube  67  occurs. 
     Seventh Embodiment 
     Next, a seventh embodiment will be described with reference to  FIGS. 34 through 38 , wherein like parts and components are designated by the same reference numerals as those shown in the first embodiment to avoid duplicating description. 
     1. Details of Developing Cartridge  7   
     As illustrated in  FIG. 35 , a developing cartridge  7  according to the seventh embodiment extends in the first direction. The developing cartridge  7  has one end portion E 41  and another end portion E 42  in the first direction. 
     The developing cartridge  7  includes a casing  71 , an agitator  72  (see  FIG. 34 ), a developing electrode  73 , a storage medium  74 , and a plurality of electrical contact surfaces  75 . 
     1.1 Casing  71   
     The casing  71  extends in the first direction and the second direction. The second direction crosses the first direction. Preferably, the second direction is perpendicular to the first direction. Specifically, the second direction is a direction defined by connecting the developing axis A 2  (see  FIG. 34 ) and an agitator axis A 5  to each other. The agitator axis A 5  will be described later. 
     As illustrated in  FIG. 34 , the casing  71  has one end portion E 51  and another end portion E 52  in the second direction. The developing roller  13  is positioned at the one end portion E 51  in the second direction of the casing  71 . The casing  71  includes the toner casing  12  described above, a solvent casing  71 A, and a tube  71 B. 
     1.1.1 Toner Casing  12   
     At least a portion of the toner casing  12  is positioned between the developing roller  13  and the solvent casing  71 A in the second direction. In a state where the developing cartridge  7  is attached to the main casing  2 , the toner casing  12  is positioned on the opposite side of the developing roller  13  from the photosensitive drum  4  in the second direction. 
     1.1.2 Solvent Casing  71 A 
     The solvent casing  71 A is positioned at the other end portion E 52  in the second direction of the casing  71 . In a state where the developing cartridge  7  is attached to the main casing  2 , the solvent casing  71 A is positioned on the opposite side of the toner casing  12  from the developing roller  13  in the second direction. The solvent casing  71 A can accommodate therein solvent. 
     1.1.3 Tube  71 B 
     As illustrated in  FIG. 35 , the tube  71 B is positioned at one end portion in the first direction of the casing  71 . In other words, the tube  71 B is positioned at the one end portion E 41  in the first direction of the developing cartridge  7 . 
     As illustrated in  FIG. 34 , the tube  71 B is positioned at one end portion in the third direction of the casing  71 . The third direction crosses the first direction and the second direction. The third direction is parallel to the up-down direction in a state where the developing cartridge  7  is attached to the main casing  2 . The tube  71 B extends in the second direction. The tube  71 B has one end portion in the second direction in communication with the solvent casing  71 A. The tube  71 B has a discharge opening  71 C. 
     The discharge opening  71 C is positioned at another end portion in the second direction of the tube  71 B. The discharge opening  71 C is positioned at the one end portion E 51  in the second direction of the casing  71 . In other words, the discharge opening  71 C is positioned on the opposite side of the toner casing  12  from the solvent casing  71 A in the second direction. In a state where the developing cartridge  7  is attached to the main casing  2 , the discharge opening  71 C is positioned at a lower end portion of the casing  71 . The solvent accommodated in the solvent casing  71 A flows the tube  71 B and is discharged through the discharge opening  71 C. The discharge opening  71 C allows the solvent accommodated in the solvent casing  71 A to be discharged therethrough. 
     1.2 Agitator  72   
     The agitator  72  is positioned inside the toner casing  12 . The agitator  72  is positioned between the developing roller  13  and the solvent casing  71 A in the second direction. The agitator  72  is rotatable about the agitator axis A 5 . The agitator  72  makes rotations to agitate the toner in the toner casing  12 . The agitator axis A 5  extends in the first direction. 
     1.3 Developing Electrode  73   
     As illustrated in  FIG. 35 , the developing electrode  73  is positioned at the other end portion E 42  in the first direction of the developing cartridge  7 . The developing electrode  73  is mounted on the other end portion in the first direction of the casing  71 . The developing electrode  73  is positioned away from the tube  71 B and the discharge opening  71 C in the first direction. The developing electrode  73  is electrically connected to the developing roller  13 . 
     1.4 Storage Medium  74   
     The storage medium  74  is positioned at the other end portion E 42  in the first direction of the developing cartridge  7 . The storage medium  74  is mounted on the other end portion in the first direction of the casing  71 . The storage medium  74  is positioned away from the tube  71 B and the discharge opening  71 C in the first direction. The storage medium  74  is an IC chip. The storage medium  74  has a flat plate shape. The storage medium  74  stores therein information related to the developing cartridge  7 . Data related to the developing cartridge  7  is, for example, data indicative of whether the developing cartridge  7  is a new cartridge or an old cartridge, and data indicative of the number of sheets (or dot counts) printable using the developing cartridge  7 . 
     1.5 Plurality of Electrical Contact Surfaces  75   
     The plurality of electrical contact surfaces  75  are positioned on a surface of the storage medium  74 . In the present embodiment, the storage medium  74  has the electrical contact surfaces  75 . The plurality of electrical contact surfaces  75  are positioned at the other end portion E 42  in the first direction of the developing cartridge  7 . The plurality of electrical contact surfaces  75  are positioned away from the tube  71 B and the discharge opening  71 C in the first direction. The plurality of electrical contact surfaces  75  are electrically connected to the storage medium  74 . Note that the plurality of electrical contact surfaces  75  may be positioned away from the storage medium  74 . In a case where the plurality of electrical contact surfaces  75  are positioned away from the storage medium  74 , each of the electrical contact surfaces  75  is electrically connected to the storage medium  74  through a wiring. A single electrical contact surface  75  may be used. 
     2. Drum Cartridge  78   
     As illustrated in  FIG. 34 , the image forming apparatus  1  includes a drum cartridge  78 . The developing cartridge  7  is detachably attachable to the main casing  2  in a state where the developing cartridge  7  is attached to the drum cartridge  78 . The drum cartridge  78  will be described below. 
     The drum cartridge  78  is detachably attachable to the main casing  2 . In other words, the drum cartridge  78  is detachably attachable to the image forming apparatus  1 . The drum cartridge  78  includes the photosensitive drum  4  described above, the charging unit  5 , the transfer unit  8 , and a drum frame  78 A. 
     The drum frame  78 A supports the photosensitive drum  4 , the charging unit  5 , and the transfer unit  8 . The photosensitive drum  4  is positioned at one end portion in the second direction of the drum frame  78 A. The developing cartridge  7  is detachably attachable to the drum frame  78 A. In other words, the developing cartridge  7  is detachably attachable to the drum cartridge  78 . The developing cartridge  7  is positioned at another end portion in the second direction of the drum frame  78 A in a state where the developing cartridge  7  is attached to the drum frame  78 A. 
     3. Details of Main Casing  2   
     Next, details of the main casing  2  will be described with reference to  FIG. 34 . 
     The main casing  2  includes a supply pipe  76 , and a pump  77 . 
     3.1 Supply Pipe  76   
     The supply pipe  76  supplies the solvent to the applicator  9 . Specifically, the supply pipe  76  has one end portion and another end portion. In a state where the developing cartridge  7  is attached to the main casing  2 , the one end portion of the supply pipe  76  is connected to the tube  71 B of the developing cartridge  7 . In other words, in a state where the developing cartridge  7  is attached to the image forming apparatus  1 , the supply pipe  76  is connected to the tube  71 B positioned at the one end portion E 41  in the first direction of the developing cartridge  7 . Hence, in a state where the developing cartridge  7  is attached to the image forming apparatus  1 , the solvent casing  71 A is connected to the supply pipe  76  of the image forming apparatus  1  through the tube  71 B. The other end portion of the supply pipe  76  is positioned away from the one end portion of the supply pipe  76 . The other end portion of the supply pipe  76  is connected to the applicator casing  14  of the applicator  9 . 
     3.2 Pump  77   
     The pump  77  is positioned between the one end portion and the other end portion of the supply pipe  76 . The pump  77  pumps the solvent to the applicator  9 . When the pump  77  is driven in a state where the developing cartridge  7  is attached to the main casing  2 , the solvent accommodated in the developing cartridge  7  is introduced into the applicator casing  14  of the applicator  9  through the tube  71 B, the discharge opening  71 C, and the supply pipe  76 . The solvent entered the applicator casing  14  is sprayed through the nozzles  15  onto the toner that has been transferred to the sheet S from the photosensitive drum  4 . The sprayed solvent dissolves the toner on the sheet S. Specifically, the pump  77  is a gear pump. 
     4. Functions and Effects 
     (1) According to the developing cartridge  7 , the solvent casing  71 A can accommodate therein solvent, as illustrated in  FIG. 34 . Hence, the solvent can be supplied when the developing cartridge  7  is replaced. 
     (2) According to the developing cartridge  7 , in a state where the developing cartridge  7  is attached to the main casing  2 , the supply pipe  76  of the main casing  2  is connected to the tube  71 B positioned at the one end portion E 41  in the first direction of the developing cartridge  7 , as illustrated in  FIG. 35 . On the other hand, the developing electrode  73  is positioned at the other end portion E 42  in the first direction of the developing cartridge  7 . 
     With this configuration, the developing electrode  73  can be restrained from getting dirty with the solvent even if the solvent is leaked from the supply pipe  76 . 
     (3) According to the developing cartridge  7 , as illustrated in  FIG. 35 , the plurality of electrical contact surfaces  75  is also positioned at the other end portion E 42  in the first direction of the developing cartridge  7 . 
     With this configuration, the electrical contact surfaces  75  can be restrained from getting dirty with the solvent even if leakage of the solvent from the supply pipe  76  occurs. 
     5. Modifications 
     (1) As illustrated in  FIG. 36 , the drum cartridge  78  may include a supply pipe  78 B. 
     The supply pipe  78 B is positioned at one end portion in the first direction of the drum cartridge  78 . The drum frame  78 A supports the supply pipe  78 B. In a state where the drum cartridge  78  is attached to the main casing  2 , the supply pipe  78 B is positioned upward of the photosensitive drum  4 . In a state where the developing cartridge  7  is attached to the drum cartridge  78 , one end portion of the supply pipe  78 B is connected to the solvent casing  71 A. Hence, the solvent casing  71 A is connected to the supply pipe  78 B of the drum cartridge  78  in a state where the developing cartridge  7  to the drum cartridge  78 . Further, another end portion of the supply pipe  78 B is connected to the applicator casing  14  of the applicator  9  in a state where the drum cartridge  78  is attached to the main casing  2 , thereby allowing the solvent accommodated in the solvent casing  71 A to be supplied to the applicator  9  through the supply pipe  78 B. 
     Note that, as illustrated in  FIG. 37 , the supply pipe  78 B may be positioned downward of the photosensitive drum  4  in a state where the drum cartridge  78  is attached to the main casing  2 . 
     (2) The drum cartridge  78  may be dispensed with in the image forming apparatus  1 . In this case, the photosensitive drum  4 , the charging unit  5 , and the transfer unit  8  are fixed to the main casing  2 . The developing cartridge  7  is detachably attachable to the main casing  2 . 
     (3) As illustrated in  FIG. 38 , the image forming apparatus  1  may include a first circuit board  79 A and a second circuit board  79 B. 
     The first circuit board  79 A is positioned at one end portion in the first direction of the main casing  2 . In a state where the developing cartridge  7  is attached to the main casing  2 , the first circuit board  79 A is positioned to be spaced apart from the developing cartridge  7  in the first direction. In a state where the developing cartridge  7  is attached to the main casing  2 , the first circuit board  79 A is positioned on the opposite side of the one end portion E 41  of the developing cartridge  7  from the other end portion E 42  of the developing cartridge  7  in the first direction. The first circuit board  79 A is electrically connected to the pump  77  (see  FIG. 34 ). Specifically, the first circuit board  79 A is a control circuit board. The first circuit board  79 A controls the pump  77 . 
     The second circuit board  79 B is positioned to be spaced apart from the first circuit board  79 A in the first direction. In a state where the developing cartridge  7  is attached to the main casing  2 , the second circuit board  79 B is positioned on the opposite side of the developing cartridge  7  from the first circuit board  79 A in the first direction. In other words, the developing cartridge  7  is positioned between the first circuit board  79 A and the second circuit board  79 B in the first direction. In a state where the developing cartridge  7  is attached to the main casing  2 , the second circuit board  79 B is electrically connected to the developing electrode  73  (see  FIG. 35 ). The second circuit board  79 B applies a voltage to the developing roller  13 . Further, the second circuit board  79 B is electrically connected to an electrode (not illustrated) of the drum cartridge  78 . The second circuit board  79 B applies a voltage to the charging unit  5 . Further, the second circuit board  79 B is electrically connected to the applicator  9 . The second circuit board  79 B supplies electric power to the applicator  9 . Further, in a state where the developing cartridge  7  is attached to the main casing  2 , the second circuit board  79 B is electrically connected to the electrical contact surfaces  75  (see  FIG. 35 ). The second circuit board  79 B supplies electric power to the storage medium  74 . 
     While the description has been made in detail with reference to the embodiments and modifications thereof, it would be apparent to those skilled in the art that may variations and modifications may be made thereto. The parts and components appearing in the above-described embodiments and modifications may be combined arbitrary as long as any conflicting combination is avoided. 
     The present specification contains the following aspects. 
     (Aspect 1) According to aspect 1, an image forming apparatus includes: a main casing; a photosensitive drum; a developing cartridge; a transfer unit for transferring the toner that has been supplied onto the photosensitive drum to a sheet; a solvent cartridge; an applicator; and a heater. The photosensitive drum is rotatable about a drum axis extending in a first direction. The developing cartridge includes a toner casing that can accommodate therein toner. The developing cartridge supplies the toner onto the photosensitive drum. The developing cartridge is detachably attachable to the main casing. The solvent cartridge includes a solvent casing that can accommodate therein solvent for dissolving the toner. The solvent cartridge is detachably attachable to the main casing independently of the developing cartridge. The applicator applying the solvent to the toner that has been transferred to the sheet. The heater heats the sheet on which the solvent has been applied to the toner by the applicator. 
     (Aspect 2) In the image forming apparatus according to the aspect 1, the solvent cartridge is positioned away from the developing cartridge in the first direction in a state where the developing cartridge and the solvent cartridge are attached to the main casing. 
     (Aspect 3) In the image forming apparatus according to the aspect 2, the main casing has: a first opening through which the developing cartridge passes when the developing cartridge is attached to the main casing; and a second opening through which the solvent cartridge passes when the solvent cartridge is attached to the main casing. 
     (Aspect 4) The image forming apparatus according to the aspect 3 further includes: a first cover movable between: a first closed position where the first cover closes the first opening; and a first open position where the first opening is opened; and a second cover provided independently of the first cover, the second cover being movable between: a second closed position where the second cover closes the second opening; and a second open position where the second opening is opened. 
     (Aspect 5) In the image forming apparatus according to the aspect 4, the first opening and the second opening are positioned at one end portion of the main casing in a second direction crossing the first direction, and the developing cartridge and the solvent cartridge are attachable to the main casing in the second direction. 
     (Aspect 6) In the image forming apparatus according to the aspect 5, the solvent casing has a discharge opening allowing the solvent to be discharged therethrough, the discharge opening being positioned at one end portion in the second direction of the solvent casing, and the solvent cartridge includes a first handle positioned at another end portion in the second direction of the solvent casing, the first handle being positioned closer to the second cover than the discharge opening is to the second cover in the second direction. 
     (Aspect 7) In the image forming apparatus according to the aspect 6, the second cover makes contact with the solvent cartridge in a state where the solvent cartridge is attached to the main casing and the second cover is at the second closed position. 
     (Aspect 8) In the image forming apparatus according to the aspect 7, the second cover makes contact with the first handle in a state where the solvent cartridge is attached to the main casing and the second cover is at the second closed position. 
     (Aspect 9) In the image forming apparatus according to any one of the aspects 5 to 8, the first cover is pivotally movable about a first cover axis extending in the first direction, and the second cover is pivotally movable about a second cover axis extending in the first direction. 
     (Aspect 10) In the image forming apparatus according to any one of the aspects 5 to 9, the second cover includes a first guide guiding the solvent cartridge when the solvent cartridge is attached to the main casing in a state where the second cover is at the second open position. 
     (Aspect 11) In the image forming apparatus according to the aspect 10, the main casing includes a second guide guiding the solvent cartridge when the solvent cartridge is attached to the main casing. 
     (Aspect 12) In the image forming apparatus according to the aspect 11, the solvent cartridge includes a cartridge guide guided by the first guide and the second guide. 
     (Aspect 13) In the image forming apparatus according to the aspect 4, the first opening is positioned at one end portion of the main casing in a second direction crossing the first direction, the second opening is positioned at one end portion in the first direction of the main casing, the developing cartridge is attachable to the main casing in the second direction, and the solvent cartridge is attachable to the main casing in the first direction. 
     (Aspect 14) In the image forming apparatus according to the aspect 13, the first cover is pivotally movable about a first cover axis extending in the first direction, and the second cover is pivotally movable about a second cover axis extending in the second direction. 
     (Aspect 15) The image forming apparatus according to the aspect 3 further includes a cover movable between: a closed position where the cover closes the first opening and the second opening; and an open position where the first opening and the second opening are opened. 
     (Aspect 16) The image forming apparatus according to any one of the aspects 3 to 15 further includes a drum cartridge including the photosensitive drum, the drum cartridge being detachably attachable to the main casing independently of the solvent cartridge, the drum cartridge being detachably attachable to the main casing through the first opening. 
     (Aspect 17) In the image forming apparatus according to the aspect 16, the developing cartridge is detachably attachable to the drum cartridge. 
     (Aspect 18) The image forming apparatus according to any one of the aspects 2 to 17 further includes a sheet cassette that can accommodate therein the sheet, the sheet cassette being detachably attachable to the main casing independently of the solvent cartridge, the sheet cassette being positioned below the developing cartridge in a state where the sheet cassette is attached to the main casing. 
     (Aspect 19) In the image forming apparatus according to the aspect 18, the solvent cartridge is positioned away from the sheet cassette in the first direction in a state where the solvent cartridge and the sheet cassette are attached to the main casing. 
     (Aspect 20) In the image forming apparatus according to the aspect 19, the solvent cartridge is juxtaposed with the sheet cassette in the first direction in a state where the solvent cartridge and the sheet cassette are attached to the main casing. 
     (Aspect 21) In the image forming apparatus according to any one of the aspects 18 to 20, the sheet cassette includes a sheet handle, and the sheet handle is positioned at one end portion of the main casing in a second direction crossing the first direction in a state where the sheet cassette is attached to the main casing. 
     (Aspect 22) In the image forming apparatus according to any one of the aspects 2 to 21, the solvent cartridge is positioned downward of the applicator in a state where the solvent cartridge is attached to the main casing. 
     (Aspect 23) The image forming apparatus according to any one of the aspects 2 to 22 further includes a pump for pumping the solvent from the solvent cartridge to the applicator. 
     (Aspect 24) The image forming apparatus according to the aspect 23 further includes a first circuit board juxtaposed with the solvent cartridge in a second direction crossing the first direction in a state where the solvent cartridge is attached to the main casing. In this image forming apparatus, the first circuit board is electrically connected to the pump. 
     (Aspect 25) The image forming apparatus according to the aspect 24 further includes: a second circuit board positioned away from the first circuit board in the first direction; and a charging unit charging a surface of the photosensitive drum. In this image forming apparatus, the second circuit board applies a voltage to the charging unit. 
     (Aspect 26) In the image forming apparatus according to the aspect 25, the applicator is a spraying device of an electrostatic spraying type, and the second circuit board supplies electric power to the applicator. 
     (Aspect 27) In the image forming apparatus according to the aspect 25 or 26, the developing cartridge is positioned between the solvent cartridge and the second circuit board. 
     (Aspect 28) The image forming apparatus according to any one of the aspects 2 to 27 further includes a discharge tray onto which the sheet that has moved past the applicator is discharged. In this image forming apparatus, the discharge tray is positioned above the developing cartridge in a state where the developing cartridge is attached to the main casing. 
     (Aspect 29) The image forming apparatus according to the aspect 28 further includes an operation panel positioned away from the discharge tray in the first direction. In this image forming apparatus, the operation panel is positioned above the solvent cartridge in a state where the solvent cartridge is attached to the main casing. 
     (Aspect 30) In the image forming apparatus according to any one of the aspects 2 to 29, at least a portion of the solvent cartridge is juxtaposed with the developing cartridge in the first direction in a state where the developing cartridge and the solvent cartridge are attached to the main casing. 
     (Aspect 31) In the image forming apparatus according to the aspect 1, the solvent cartridge is positioned below the developing cartridge in a state where the developing cartridge and the solvent cartridge are attached to the main casing. 
     (Aspect 32) In the image forming apparatus according to the aspect 31, the main casing has: a first opening through which the developing cartridge passes when the developing cartridge is attached to the main casing; and a second opening through which the solvent cartridge passes when the solvent cartridge is attached to the main casing, and the first opening and the second opening are positioned at one end portion of the main casing in a second direction crossing the first direction. 
     (Aspect 33) In the image forming apparatus according to the aspect 32, the developing cartridge and the solvent cartridge are detachably attachable to the main casing in the second direction. 
     (Aspect 34) The image forming apparatus according to the aspect 33 further includes a sheet cassette that can accommodate therein the sheet, the sheet cassette being detachably attachable to the main casing, the sheet cassette being positioned below the developing cartridge in a state where the sheet cassette is attached to the main casing. 
     (Aspect 35) In the image forming apparatus according to the aspect 34, the sheet cassette is detachably attachable to the main casing in the second direction. 
     (Aspect 36) In the image forming apparatus according to the aspect 34 or 35, the solvent cartridge is positioned below the sheet cassette in a state where the solvent cartridge and the sheet cassette are attached to the main casing. 
     (Aspect 37) In the image forming apparatus according to the aspect 34 or 35, the solvent cartridge is positioned within the sheet cassette in a state where the solvent cartridge and the sheet cassette are attached to the main casing. 
     (Aspect 38) In the image forming apparatus according to any one of the aspects 34 to 37, the sheet cassette includes a sheet handle, and the sheet handle is positioned at the one end portion in the second direction of the main casing in a state where the sheet cassette is attached to the main casing. 
     (Aspect 39) The image forming apparatus according to any one of the aspects 31 to 38 further includes an exposure unit that can expose the photosensitive drum to light. In this image forming apparatus, at least a portion of the exposure unit is positioned upward of the developing cartridge and the solvent cartridge in a state where the developing cartridge and the solvent cartridge are attached to the main casing. 
     (Aspect 40) In the image forming apparatus according to any one of the aspects 31 to 39, the solvent cartridge is positioned downward of the applicator in a state where the solvent cartridge is attached to the main casing. 
     (Aspect 41) The image forming apparatus according to the aspect 1, the applicator is positioned at one end portion of the main casing in a second direction crossing the first direction, the main casing has an opening through which the developing cartridge and the solvent cartridge pass when the developing cartridge and the solvent cartridge are attached to the main casing, the opening being positioned at another end portion in the second direction of the main casing. the image forming apparatus further includes a cover positioned at the another end portion in the second direction of the main casing, the cover being movable between: a closed position where the cover closes the opening; and an open position where the opening is opened. In this image forming apparatus, the developing cartridge and the solvent cartridge are positioned between the applicator and the cover in the second direction, and the solvent cartridge is positioned closer to the applicator than the developing cartridge is to the applicator in a state where the developing cartridge and the solvent cartridge are attached to the main casing and the cover is at the closed position. 
     (Aspect 42) The image forming apparatus according to the aspect 41 further includes a drum cartridge including the photosensitive drum and a drum frame, the drum cartridge being movable in the second direction between: an interior position where the drum cartridge is positioned inside the main casing; and an exterior position where the drum cartridge is positioned outside the main casing. In this image forming apparatus, the developing cartridge is detachably attachable to the drum frame, and the solvent cartridge is detachably attachable to the drum frame independently of the developing cartridge. 
     (Aspect 43) In the image forming apparatus according to the aspect 42, the photosensitive drum is positioned between the solvent cartridge and the cover in the second direction in a state where the developing cartridge, the drum cartridge, and the solvent cartridge are attached to the main casing and the cover is at the closed position. 
     (Aspect 44) The image forming apparatus according to the aspect 41 further includes a drawer that is not detachable from the main casing, the drawer being movable between: an interior position where the drawer is positioned inside the main casing; and an exterior position where the drawer is positioned outside the main casing. In this image forming apparatus, in a state where the drawer is at the exterior position, the developing cartridge is detachably attachable to the drawer, and, in a state where the drawer is at the exterior position, the solvent cartridge is detachably attachable to the drawer independently of the developing cartridge. 
     (Aspect 45) In the image forming apparatus according to the aspect 44, the developing cartridge includes the photosensitive drum, and the photosensitive drum is positioned between the applicator and the cover in the second direction and the solvent cartridge is positioned closer to the applicator than the photosensitive drum is to the applicator in the second direction in a state where the developing cartridge and the solvent cartridge are attached to the drawer, the drawer is at the interior position, and the cover is at the closed position. 
     (Aspect 46) In the image forming apparatus according to the aspect 1, the applicator is positioned at one end portion of the main casing in a second direction crossing the first direction, the main casing has an opening through which the developing cartridge and the solvent cartridge pass when the developing cartridge and the solvent cartridge are attached to the main casing, the opening being positioned above the developing cartridge and the solvent cartridge in a state where the developing cartridge and the solvent cartridge are attached to the main casing. The image forming apparatus further includes a cover positioned above the developing cartridge and the solvent cartridge in a state where the developing cartridge and the solvent cartridge are attached to the main casing, the cover being pivotally movable about a cover axis extending in the first direction, the cover being movable between: a closed position where the cover closes the opening; and an open position where the opening is opened. In this image forming apparatus, the solvent cartridge is positioned closer to the applicator than the developing cartridge is to the applicator in a state where the developing cartridge and the solvent cartridge are attached to the main casing and the cover is at the closed position. 
     (Aspect 47) In the image forming apparatus according to the aspect 46, the cover axis is positioned at the one end portion in the second direction of the main casing, and the cover axis is positioned farther away from the solvent cartridge than the applicator is from the solvent cartridge in the second direction in a state where the developing cartridge and the solvent cartridge are attached to the main casing. 
     (Aspect 48) In the image forming apparatus according to the aspect 46 or 47, the developing cartridge and the solvent cartridge are detachably attachable to the main casing in a third direction crossing the first direction and the second direction. 
     (Aspect 49) The image forming apparatus according to the aspect 48 further includes a drum cartridge including the photosensitive drum and a drum frame to which the developing cartridge is detachably attachable. In this image forming apparatus, the drum cartridge is detachably attachable to the main casing in the third direction. 
     (Aspect 50) In the image forming apparatus according to any one of the aspects 41 to 49, the transfer unit can convey the sheet toward the applicator in the second direction. 
     (Aspect 51) The image forming apparatus according to any one of the aspects 41 to 50 further includes a supply pipe allowing the solvent to be supplied from the solvent cartridge to the applicator therethrough. In this image forming apparatus, the supply pipe is positioned between the applicator and the solvent cartridge in the second direction in a state where the solvent cartridge is attached to the main casing. 
     (Aspect 52) According to aspect 52, an image forming apparatus includes: a main casing; a photosensitive drum; a developing cartridge; a transfer unit for transferring the toner that has been supplied onto the photosensitive drum to a sheet; an applicator; and a heater. The photosensitive drum is rotatable about a drum axis extending in a first direction. The developing cartridge includes a toner casing that can accommodate therein toner. the developing cartridge supplies the toner onto the photosensitive drum, the developing cartridge being detachably attachable to the main casing. The applicator applies solvent for dissolving toner to the toner that has been transferred to the sheet. The heater heats the sheet on which the solvent has been applied to the toner by the applicator. In this image forming apparatus, the main casing has an inlet port allowing the solvent in a solvent cartridge to enter the main casing therethrough in a state where the solvent cartridge is connected to the main casing, the inlet port being positioned on an outer surface of the main casing. 
     (Aspect 53) In the image forming apparatus according to the aspect 52, the inlet port is positioned on an upper surface of the main casing. 
     (Aspect 54) In the image forming apparatus according to the aspect 52 or 53, the main casing includes a discharge tray positioned on an upper surface of the main casing, the sheet that has moved past the applicator being discharged onto the discharge tray, and the inlet port is positioned away from the discharge tray in the first direction. 
     (Aspect 55) In the image forming apparatus according to the aspect 54, the inlet port is positioned away from the developing cartridge in the first direction. 
     (Aspect 56) In the image forming apparatus according to the aspect 54 or 55, the inlet port is positioned away from the applicator in the first direction. 
     (Aspect 57) The image forming apparatus according to any one of the aspects 52 to 56 further includes a pump pumping the solvent to the applicator. 
     (Aspect 58) The image forming apparatus according to the aspect 57 further includes a first circuit board positioned between the developing cartridge and the inlet port in the first direction. In this image forming apparatus, the first circuit board is electrically connected to the pump. 
     (Aspect 59) In the image forming apparatus according to any one of the aspects 52 to 58, the solvent cartridge includes: a solvent casing that can accommodate therein the solvent, the solvent casing having a discharge opening allowing the solvent to be discharged from the solvent casing therethrough; and a lid closing the discharge opening, and the main casing includes a protrusion extending through the lid in a state where the solvent cartridge is connected to the inlet port. 
     (Aspect 60) In the image forming apparatus according to the aspect 59, the solvent cartridge includes a sleeve positioned on an outer periphery of the discharge opening, the sleeve being inserted into the inlet port in a state where the solvent cartridge is connected to the inlet port. 
     (Aspect 61) In the image forming apparatus according to the aspect 60, the sleeve includes a first thread at an outer peripheral surface of the sleeve, and the main casing includes a second thread in threading engagement with the first thread in a state where the solvent cartridge is connected with the inlet port. 
     (Aspect 62) According to aspect 62, a drum cartridge includes: a photosensitive drum; and a solvent casing that can accommodate therein solvent that dissolves toner. 
     (Aspect 63) The drum cartridge according to the aspect 62 further includes a drum frame to which a developing cartridge is detachably attachable, the developing cartridge including a toner casing that can accommodate therein toner. 
     (Aspect 64) In the drum cartridge according to the aspect 63, the photosensitive drum is rotatable about a drum axis extending in a first direction, the solvent casing is positioned at one end portion of the drum frame in a second direction crossing the first direction, the developing cartridge is positioned at another end portion in the second direction of the drum frame in a state where the developing cartridge is attached to the drum frame, and the photosensitive drum is positioned between the solvent casing and the developing cartridge in the second direction in a state where the developing cartridge is attached to the drum frame. 
     (Aspect 65) The drum cartridge according to the aspect 64 further includes a transfer unit transferring the toner that has been supplied onto the photosensitive drum to a sheet. 
     (Aspect 66) In the drum cartridge according to the aspect 65, the drum cartridge is detachably attachable to a main casing accommodating therein an applicator applying the solvent to the toner that has been transferred to the sheet. 
     (Aspect 67) In the drum cartridge according to the aspect 66, at least a portion of the solvent casing is positioned between the photosensitive drum and the applicator in the second direction in a state where the drum cartridge is attached to the main casing. 
     (Aspect 68) The drum cartridge according to the aspect 66 or 67 further includes a waste solvent casing that can accommodate therein waste solvent discharged from the applicator. 
     (Aspect 69) In the drum cartridge according to the aspect 68, the waste solvent casing is positioned on an opposite side of the photosensitive drum from the solvent casing in the second direction. 
     (Aspect 70) The drum cartridge according to the aspect 68 or 69 further includes a charging unit charging a surface of the photosensitive drum. In this drum cartridge, the waste solvent casing is positioned on an opposite side of the photosensitive drum from the charging unit in a third direction crossing both the first direction and the second direction. 
     (Aspect 71) The drum cartridge according to the aspect 70 further includes a charge electrode electrically connected to the charging unit; and a tube connected to the waste solvent casing. In this drum cartridge, the charge electrode is positioned on an opposite side of the solvent casing from the tube in the first direction. 
     (Aspect 72) The drum cartridge according to any one of the aspects 68 to 70 further includes: a transfer electrode electrically connected to the transfer unit; and a tube connected to the waste solvent casing. In this drum cartridge, the transfer electrode is positioned on an opposite side of the solvent casing from the tube in the first direction. 
     (Aspect 73) In the drum cartridge according to any one of the aspects 68 to 72, the waste solvent casing supports the developing cartridge in a state where the developing cartridge is attached to the drum frame. 
     (Aspect 74) The drum cartridge according to any one of the aspects 68 to 73 further includes a sheet conveying roller for conveying the sheet toward the photosensitive drum and the transfer unit, the sheet conveying roller being rotatable about a conveying axis extending in the first direction. 
     (Aspect 75) In the drum cartridge according to the aspect 74, the waste solvent casing supports the sheet conveying roller. 
     (Aspect 76) In the drum cartridge according to any one of the aspects 65 to 75, the transfer unit is a transfer roller rotatable about a transfer axis extending in the first direction. 
     (Aspect 77) In the drum cartridge according to any one of the aspects 62 to 76, the solvent is applied to toner that has been transferred from the photosensitive drum to a sheet to dissolve the toner on the sheet. 
     (Aspect 78) According to aspect 78, a developing cartridge includes: a developing roller; and a casing. The casing includes: a toner casing that can accommodate therein toner; and a solvent casing that can accommodate therein solvent that dissolves the toner. 
     (Aspect 79) In the developing cartridge according to the aspect 78, the developing roller is rotatable about a developing axis extending in a first direction and positioned at one end portion of the casing in a second direction crossing the first direction, the solvent casing is positioned at another end portion in the second direction of the casing, and at least a portion of the toner casing is positioned between the developing roller and the solvent casing in the second direction. 
     (Aspect 80) The developing cartridge according to the aspect 79 further includes an agitator agitating toner in the toner casing. In this developing cartridge, the agitator is positioned between the developing roller and the solvent casing in the second direction. 
     (Aspect 81) In the developing cartridge according to any one of the aspects 78 to 80, the developing cartridge is detachably attachable to a drum cartridge including a photosensitive drum. 
     (Aspect 82) In the developing cartridge according to the aspect 81, the developing cartridge is detachably attachable to a main casing to which the drum cartridge is detachably attachable in a state where the developing cartridge is attached to the drum cartridge, the main casing accommodating therein: a transfer unit transferring toner on the photosensitive drum to a sheet; and an applicator applying the solvent to the toner that has been transferred to the sheet. 
     (Aspect 83) In the developing cartridge according to the aspect 82, the solvent casing is connected to a supply pipe of the drum cartridge for supplying the solvent to the applicator in a state where the developing cartridge is attached to the drum cartridge. 
     (Aspect 84) In the developing cartridge according to the aspect 82, the solvent casing is connected to a supply pipe in the main casing for supplying the solvent to the applicator in a state where the developing cartridge is attached to the main casing. 
     (Aspect 85) The developing cartridge according to the aspect 84 further includes a developing electrode electrically connected to the developing roller. In this developing cartridge, the developing roller is rotatable about a developing axis extending in a first direction, the supply pipe is connected to one end portion in the first direction of the developing cartridge in a state where the developing cartridge is attached to the main casing, and the developing electrode is positioned at another end portion in the first direction of the developing cartridge. 
     (Aspect 86) The developing cartridge according to the aspect 84 or 85 further includes a storage medium having an electrical contact surface. In this developing cartridge, the developing roller is rotatable about a developing axis extending in a first direction, the supply pipe is connected to one end portion in the first direction of the developing cartridge in a state where the developing cartridge is attached to the main casing, and the electrical contact surface is positioned at another end portion in the first direction of the developing cartridge. 
     (Aspect 87) In the developing cartridge according to the aspect 86, the storage medium stores therein information related to the developing cartridge. 
     (Aspect 88) In the developing cartridge according to the aspect 86 or 87, the storage medium is positioned at the another end portion in the first direction of the developing cartridge. 
     (Aspect 89) In the developing cartridge according to any one of the aspects 78 to 88, the solvent is applied to toner that has been transferred to a sheet to dissolve the toner on the sheet.