Patent Publication Number: US-9904247-B2

Title: Cooling device and image forming apparatus incorporating the cooling device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application Nos. 2015-214108, filed on Oct. 30, 2015, 2015-214109, filed on Oct. 30, 2015, 2016-058390, filed on Mar. 23, 2016, and 2016-058394, filed on Mar. 23, 2016, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     This disclosure relates to a cooling device to cool a recording medium and an image forming apparatus incorporating the cooling device. 
     Related Art 
     Image forming apparatuses are known to include a cooling device to cool a heated recording medium with a cooling unit using, for example, a heat pipe or a heat sink. Further, a cooling device is also known to have multiple cooling units disposed on both sides of a recording medium in order to cool both sides of the recording medium effectively. In this case, the multiple cooling units are located shifted to each other in a sheet conveying direction. 
     When multiple cooling units are employed in an image forming apparatus, the multiple cooling units have the same cooling method. 
     Depending on a cooling method, however, a cooling device needs a specified space to be installed. Therefore, it may be difficult to dispose multiple cooling units employing the same cooling method or multiple cooling units with the same cooling method may not be installed due to a space requirement. 
     More specifically, when a cooling device employs a heat pipe roller, the heat pipe roller includes a roller and a radiation fin, and the diameter of the radiation fin is greater than the diameter of the roller. Due to this configuration, in a case in which multiple heat pipe rollers are aligned, the radiation fin of one heat pipe roller of the multiple heat pipe rollers interferes movement of the radiation fin of another heat pipe roller disposed adjacent to the one heat pipe roller. Even when respective positions of the multiple heat pipe rollers are shifted to have wider space therebetween in order to prevent the multiple heat pipe rollers from interfering with each other, the cooling device increases in size in a sheet conveying direction. In addition, a gap between two adjacent heat pipe rollers increases, resulting in deterioration of the cooling performance to a recording medium to be conveyed. 
     By contrast, when a cooling device employs a heat sink, the heat sink includes a fin extending in a vertical direction that interferes with a sheet conveying direction in which a recording medium is conveyed. Accordingly, when a heat sink is provided above and below the recording medium in the sheet conveying direction, the cooling device is extended in a vertical direction, and therefore the size of the cooling device increases. 
     Further, the cooling units having the same cooling method include respective heat absorbing surfaces having the same shape. Therefore, the cooling units have a sheet entry direction of the recording medium toward the cooling device and a sheet discharging direction of the recording medium from the cooling device, which is the same direction as the sheet entry direction. 
     Accordingly, a guiding member is provided to guide the recording medium after passing the cooling device toward a sheet discharging unit that is disposed at a position different from a sheet ejecting direction. 
     In addition, the cooling device may need to provide a belt disposed facing the recording medium to hold and convey the recording medium, and further respective belt drive units for the cooling units disposed at the upstream side and the downstream side in the sheet conveying direction. 
     Accordingly, a large section in which the recording medium is not cooled is provided between a cooling unit disposed at the upstream side and another cooling unit disposed at the downstream side. As a result, the image forming apparatus increase in size, and therefore the cooling efficiency deteriorates. 
     SUMMARY 
     At least one aspect of this disclosure provides a cooling device including a first cooler configured to cool a first face of a recording medium and a second cooler configured to cool a second face of the recording medium. The first cooler includes a first heat absorbing face and a first liquid flowing passage. The first heat absorbing face is configured to contact an inner circumferential surface of a belt to face the first face of the recording medium. The second cooler includes a second heat absorbing face and a second liquid flowing passage. The second heat absorbing face is disposed facing the second face of the recording medium. 
     Further, at least one aspect of this disclosure provides an image forming apparatus including a heating device configured to fix a toner image to the recording medium, and the above-described cooling device configured to cool the recording medium conveyed from the heating device. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating an image forming apparatus according to an embodiment of this disclosure; 
         FIG. 2A  is a side view illustrating a cooling device included in the image forming apparatus of  FIG. 1 , viewed from a front of the image forming apparatus; 
         FIG. 2B  is a plan view illustrating the cooling device of  FIG. 2A , viewed from a top of the image forming apparatus; 
         FIG. 3  is a diagram illustrating a comparative cooling device to the cooling device of  FIG. 2 ; 
         FIG. 4A  is a side view illustrating a cooling device provided with a liquid cooling jacket in a first cooler, viewed from the front of the image forming apparatus; 
         FIG. 4B  is a plan view illustrating the cooling device of  FIG. 4A , viewed from the top of the image forming apparatus; 
         FIG. 5  is a schematic view illustrating a cooling device provided with a liquid cooling roller in a second cooler; 
         FIG. 6  is a schematic view illustrating a cooling device provided with a first cooler above a recording media conveying passage and a second cooler below the recording media conveying passage; 
         FIG. 7  is a schematic view illustrating a cooling device provided with a first cooler below a downstream side of the recording media conveying passage in the sheet conveying direction and a second cooler above an upstream side of the recording media conveying passage in the sheet conveying direction; 
         FIG. 8  is a schematic view illustrating a cooling device provided with a first cooler above the downstream side of the recording media conveying passage in the sheet conveying direction and a second cooler below the upstream side of the recording media conveying passage in the sheet conveying direction; 
         FIG. 9  is a schematic view illustrating a cooling device provided with a first cooler below the recording media conveying passage and a second cooler above the recording media conveying passage; 
         FIG. 10  is a schematic view illustrating a cooling device provided with a first cooler above the recording media conveying passage and a second cooler below the recording media conveying passage; 
         FIG. 11A  is a side view illustrating a variation of the cooling device of  FIG. 1  and  FIG. 2 , viewed from the front of the image forming apparatus; 
         FIG. 11B  is a plan view of the cooling device of  FIG. 11A , viewed from the top of the image forming apparatus; 
         FIG. 12A  is a side view illustrating a cooling device provided with a first cooler and a second cooler both employing a liquid cooling method, viewed from a front of the image forming apparatus; 
         FIG. 12B  is a plan view illustrating the cooling device of  FIG. 12A , viewed from the top of the image forming apparatus; 
         FIG. 13  is a partial enlarged view illustrating the cooling device of  FIG. 11A ; 
         FIG. 14  is a schematic view illustrating the cooling device and a support roller of  FIG. 13 ; 
         FIG. 15  is a partial enlarged view illustrating the cooling device of  FIG. 14 ; 
         FIG. 16  is a schematic plan view illustrating a sheet transfer guide; 
         FIG. 17A  is a side view illustrating a variation of the sheet transfer guide; 
         FIG. 17B  is a side view illustrating the sheet transfer guide attached to a base; 
         FIG. 17C  is a top view illustrating the sheet transfer guide partly attached to the base; 
         FIG. 18  is a schematic view illustrating a variation of the support roller; 
         FIG. 19  is a diagram illustrating a case in which a single drive motor drives a drive roller that functions as a belt driving body and a different drive roller that functions as a rotary body; 
         FIG. 20  is a schematic view illustrating a variation of the cooling device of  FIG. 13  and  FIG. 14 ; 
         FIG. 21  is an enlarged view illustrating a downstream side end of a first heat absorbing surface of the first cooler and a lower part of the second cooler; 
         FIG. 22  is a schematic view illustrating a variation of the cooling device of  FIG. 11 ; 
         FIG. 23  is a perspective view illustrating a heat pipe roller included in the second cooler; 
         FIG. 24  is an enlarged view illustrating a downstream side of the first heat absorbing surface of the first cooler in the sheet conveying direction; 
         FIG. 25  is a partial enlarged view illustrating the cooling device of  FIG. 13 ; 
         FIG. 26  is a schematic view illustrating of a variation of the cooling device of  FIG. 11 ; 
         FIG. 27  is a schematic view illustrating of a variation of the cooling device of  FIG. 2 ; 
         FIG. 28A  is a side view illustrating a front of a comparative cooling device to the cooling device of  FIG. 11 , viewed from the front of the image forming apparatus; 
         FIG. 28B  is a top view illustrating the comparative cooling device of  FIG. 28A , viewed from the top of the image forming apparatus; 
         FIG. 29  is a schematic view illustrating an image forming apparatus employing an inkjet recording method with a first belt; and 
         FIG. 30  is a schematic view illustrating an image forming apparatus employing an inkjet recording method with the first belt and a second belt. 
     
    
    
     DETAILED DESCRIPTION 
     It will be understood that if an element or layer is referred to as being “on”, “against”, “connected to” or “coupled to” another element or layer, then it can be directly on, against, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, if an element is referred to as being “directly on”, “directly connected to” or “directly coupled to” another element or layer, then there are no intervening elements or layers present. Like numbers referred to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     Spatially relative terms, such as “beneath”, “below”, “lower”, “above”, “upper” and the like may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements describes as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, term such as “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors herein interpreted accordingly. 
     Although the terms first, second, etc. may be used herein to describe various elements, components, regions, layers and/or sections, it should be understood that these elements, components, regions, layer and/or sections should not be limited by these terms. These terms are used to distinguish one element, component, region, layer or section from another region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present disclosure. 
     The terminology used herein is for describing particular embodiments and examples and is not intended to be limiting of exemplary embodiments of this disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes” and/or “including”, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     Descriptions are given, with reference to the accompanying drawings, of examples, exemplary embodiments, modification of exemplary embodiments, etc., of an image forming apparatus according to exemplary embodiments of this disclosure. Elements having the same functions and shapes are denoted by the same reference numerals throughout the specification and redundant descriptions are omitted. Elements that do not demand descriptions may be omitted from the drawings as a matter of convenience. Reference numerals of elements extracted from the patent publications are in parentheses so as to be distinguished from those of exemplary embodiments of this disclosure. 
     This disclosure is applicable to any image forming apparatus, and is implemented in the most effective manner in an electrophotographic image forming apparatus. 
     In describing preferred embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this disclosure is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes any and all technical equivalents that have the same function, operate in a similar manner, and achieve a similar result. 
     Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, preferred embodiments of this disclosure are described. 
     Now, a description is given of a color image forming apparatus  1000  according to an embodiment of this disclosure with reference to the drawings. 
     It is to be noted that identical parts are given identical reference numerals and redundant descriptions are summarized or omitted accordingly. 
     The image forming apparatus  1000  may be a copier, a facsimile machine, a printer, a multifunction peripheral or a multifunction printer (MFP) having at least one of copying, printing, scanning, facsimile, and plotter functions, or the like. According to the present example, the image forming apparatus  1000  is an electrophotographic copier that forms toner images on recording media by electrophotography. 
     It is to be noted in the following examples that: the term “image forming apparatus” indicates an apparatus in which an image is formed on a recording medium such as paper, OHP (overhead projector) transparencies, OHP film sheet, thread, fiber, fabric, leather, metal, plastic, glass, wood, and/or ceramic by attracting developer or ink thereto; the term “image formation” indicates an action for providing (i.e., printing) not only an image having meanings such as texts and figures on a recording medium but also an image having no meaning such as patterns on a recording medium; and the term “sheet” is not limited to indicate a paper material but also includes the above-described plastic material (e.g., a OHP sheet), a fabric sheet and so forth, and is used to which the developer or ink is attracted. In addition, the “sheet” is not limited to a flexible sheet but is applicable to a rigid plate-shaped sheet and a relatively thick sheet. 
     Further, size (dimension), material, shape, and relative positions used to describe each of the components and units are examples, and the scope of this disclosure is not limited thereto unless otherwise specified. 
     Further, it is to be noted in the following examples that: the term “sheet conveying direction” indicates a direction in which a recording medium travels from an upstream side of a sheet conveying path to a downstream side thereof; the term “width direction” indicates a direction basically perpendicular to the sheet conveying direction. 
       FIG. 1  is a schematic diagram illustrating a color image forming apparatus  1000  according to an embodiment of this disclosure. 
     As illustrated in  FIG. 1 , the image forming apparatus  1000  has a housing  200  that includes a tandem-type image forming part  150 , an exposure device  6 , a transfer device  7 , and four primary transfer rollers  11 Y,  11 C,  11 M, and  11 K. 
     The tandem-type image forming part  150  includes four process units  1 Y,  1 C,  1 M, and  1 K functioning as image forming units aligned in tandem. Suffixes, which are Y, C, M, and K, are used to indicate respective colors of toners (e.g., yellow, cyan, magenta, and black toners) for the process units. The process units  1 Y,  1 C,  1 M, and  1 K have substantially the same configuration except for containing different color toners of yellow (Y), cyan (C), magenta (M), and black (K) corresponding to color separation components of a color image. The process units  1 Y,  1 C,  1 M, and  1 K are detachably attachable to the housing  200  of the image forming apparatus  1000 . 
     The four process units  1 Y,  1 C,  1 M, and  1 K form respective single color toner images of yellow (Y), cyan (C), magenta (M), and black (K) on photoconductors  2 Y,  2 C,  2 M, and  2 K, respectively. The exposure device  6  is disposed above the process units  1 Y,  1 C,  1 M, and  1 K and exposes respective surfaces of the photoconductors  2 Y,  2 C,  2 M, and  2 K, respectively, to form respective electrostatic latent images thereon. 
     It is to be noted that  FIG. 1  illustrates the four process units  1 Y,  1 C,  1 M, and  1 K having the identical configuration and functions to each other except toner colors, which are yellow (Y), magenta (M), cyan (C), and black (K). Each process unit  1  includes the photoconductor  2  (i.e., photoconductors  2 Y,  2 C,  2 M, and  2 K) and an image forming components disposed around the photoconductor  2  in a counterclockwise direction in the drawing. Specifically, the image forming components are a charging roller  3  (i.e., charging rollers  3 Y,  3 C,  3 M, and  3 K) that is disposed substantially upward from a rotation center of the photoconductor  2 , a developing device  4  (i.e., developing devices  4 Y,  4 C,  4 M, and  4 K), and a photoconductor cleaning blade  5  (i.e., photoconductor cleaning blades  5 Y,  5 C,  5 M, and  5 K). 
     Specifically, the photoconductor  2  has a drum shape and functions as a latent image bearer. The charging roller  3  serves as a charger to charge a surface of the photoconductor  2 . The developing device  4  forms a toner image on the surface of the photoconductor  2 . The photoconductor cleaning blade  5  serves as a cleaner to clean the surface of the photoconductor  2 . 
     In  FIG. 1 , the exposure device  6  is disposed above the respective surfaces of the process units  1 Y,  1 C,  1 M, and  1 K. The exposing device  6  includes, e.g., a light source, polygon mirrors, f-θ lenses, and reflection lenses to irradiate a laser beam onto the surface of the photoconductor  2 . 
     The transfer device  7  is disposed below the process units  1 Y,  1 C,  1 M, and  1 K. The transfer device  7  includes an intermediate transfer belt  10  including an endless belt that functions as a transfer body. The intermediate transfer belt  10  is stretched over multiple of rollers  21  through  24  functioning as supports. One of the rollers  21  through  24  is rotated as a driving roller to circulate (rotate) the intermediate transfer belt  10  in a direction indicated by arrow DD in  FIG. 1 . 
     Four primary transfer rollers  11 Y,  11 C,  11 M, and  11 K functioning as primary transfer units are disposed at positions at which the primary transfer rollers  11 Y,  11 C,  11 M, and  11 K face the respective photoconductors  2 Y,  2 C,  2 M, and  2 K. At the respective positions, the primary transfer rollers  11 Y,  11 C,  11 M, and  11 K are pressed against an inner circumferential surface of the intermediate transfer belt  10 . Thus, primary transfer nip regions are formed at positions at which the photoconductors  2 Y,  2 C,  2 M, and  2 K contact pressed portions of the intermediate transfer belt  10 . Each of the primary transfer rollers  11 Y,  11 C,  11 M, and  11 K is connected to a power source, and a given direct current (DC) voltage and/or an alternating current (AC) voltage are supplied to the primary transfer rollers  11 Y,  11 C,  11 M, and  11 K. 
     A secondary transfer roller  12  that functions as a second transfer unit is disposed at a position at which the secondary transfer roller  12  faces the roller  24  that is one of the rollers over which the intermediate transfer belt  10  is stretched. The secondary transfer roller  12  is pressed against an outer circumferential surface of the intermediate transfer belt  10 . Thus, a secondary transfer nip region is formed at a position at which the secondary transfer roller  12  and the intermediate transfer belt  10  contact each other. Similar to the primary transfer rollers  11 Y,  11 C,  11 M, and  11 K, the secondary transfer roller  12  is connected to a power source, and a given direct current (DC) voltage and/or an alternating current (AC) voltage are supplied to the secondary transfer roller  12 . 
     Multiple sheet trays  13  are disposed below the housing  200  to accommodate sheet-type recording medium P, such as sheets of paper or overhead projector (OHP) sheets. Multiple sheet trays  13  are disposed below the housing  200  to accommodate sheet-type recording medium P, such as sheets of paper or overhead projector (OHP) sheets. Each sheet tray  13  is provided with a feed roller  14  to feed the recording media P stored therein. An output tray  20  that functions as a sheet output unit is mounted on an outer circumferential surface of the housing  200  at the left side in  FIG. 1  to stack recording medium P discharged to an outside of the housing  200 . 
     The housing  200  includes a recording medium conveying passage R to transport a recording medium P from the sheet trays  13  to the output tray  20  through the secondary transfer nip region. On the recording medium conveying passage R, registration rollers  15  are disposed upstream from the secondary transfer roller  12  in a conveying direction of a recording medium (hereinafter, referred to as a “sheet conveying direction”). A fixing device  8 , a recording medium cooling device  9 , and a pair of output rollers  16  are disposed in turn at positions downstream from the secondary transfer roller  12  in the sheet conveying direction. The fixing device  8  that functions as a heating device includes a fixing roller  17  and a pressure roller  18 . The fixing roller  17  functions as a fixing member including an internal heater (a heat source). The pressure roller  18  that functions as a pressing member to press the fixing roller  17 . A fixing nip region is formed at a position at which the fixing roller  17  and the pressing roller  18  contact each other. It is to be noted that the configuration of the fixing device  8  is not limited to a roller-type fixing device as described above. For example, a belt-type fixing device can be applied to this disclosure. 
     Next, a description is given of a basic operation of the image forming apparatus  1000  with reference to  FIG. 1 . 
     It is to be noted that the components and units having the identical configuration or structure except for toner color are occasionally described without suffixes. For example, the photoconductors  2 Y,  2 C,  2 M, and  2 K are hereinafter also referred to in a singular form as the photoconductor  2 . 
     When imaging operation is started, the photoconductor  2  (i.e., the photoconductors  2 Y,  2 C,  2 M, and  2 K) of the process unit  1  (i.e., the process units  1 Y,  1 C,  1 M, and  1 K) is rotated counterclockwise in  FIG. 1 , and the charging roller  3  (i.e., the charging rollers  3 Y,  3 C,  3 M, and  3 K) uniformly charges the surface of the photoconductor  2  with a given polarity. Based on image information of a document read by a reading device  100  or print information instructed by an external device, the exposing device  6  irradiates laser light onto the charged surface of the photoconductor  2  to form an electrostatic latent image on the surface of the photoconductor  2 . At this time, image information exposed to each photoconductor  2  is single-color image information obtained by separating a desired full-color image into single-color information on yellow, cyan, magenta, and black. The developing device  4  (i.e., the developing devices  4 Y,  4 C,  4 M, and  4 K) supplies toner onto the electrostatic latent image formed on the photoconductor  2 , thus making the electrostatic latent images a visible image as a toner image. 
     One of the rollers  21  through  24  over which the intermediate transfer belt  10  is stretched is driven to rotate the rollers  21  through  24  to circulate the intermediate transfer belt in the direction indicated by arrow DD in  FIG. 1 . A voltage having a polarity opposite a charged polarity of toner and subjected to constant voltage or current control is supplied to the primary transfer roller  11  (i.e., the primary transfer roller  11 Y,  11 C,  11 M, and  11 K). As a result, a transfer electric field is formed at the primary transfer nip region between each primary transfer roller  11  and the opposing photoconductor  2 . Toner images of respective colors on the photoconductors  2  are transferred one on another onto the intermediate transfer belt  10  by the transfer electric fields formed at the primary transfer nip regions. Thus, the intermediate transfer belt  10  bears a full-color toner image on the surface of the intermediate transfer belt  10 . Residual toner remaining on each photoconductor  2  without being transferred onto the intermediate transfer belt  10  is removed with the cleaning blade  5 . 
     With rotation of the feed roller  14 , a recording medium P is fed from the corresponding sheet tray  13 . The recording medium P passes through the registration rollers to be sent to the secondary transfer nip region between the secondary transfer roller  12  and the intermediate transfer belt  10  by the registration rollers  15  so as to synchronize with the full-color toner image on the intermediate transfer belt  10 . At this time, a transfer voltage of the polarity opposite the charged polarity of toner of the toner image on the intermediate transfer belt  10  is supplied to the secondary transfer roller  12 . As a result, a transfer electric field is formed at the secondary transfer nip region. By the transfer electric field formed at the secondary transfer nip region, the toner image on the intermediate transfer belt  10  is collectively transferred onto the recording medium P. Then, the recording medium P is sent into the fixing device  8 , and the fixing roller  17  and the pressing roller  18  apply heat and pressure to fix the toner image on the recording medium P. After the recording medium P is cooled with the recording medium cooling device  9 , the pair of output rollers  16  output the recording medium P onto the output tray  20 . 
     When performing a duplex printing job, the cooled recording medium P is guided to a reversing path  26  by switching separation pawls  25   a  and  25   b . Then, a separation pawl  27  is switched and a roller  28  is rotated in a reverse direction, so that the reversed recording medium P is conveyed to the registration rollers  15  via a reversing path  29 . Thus, the recording medium P is reversed. 
     At this time, a toner image that is an image to be printed on a back face of the recording medium P is formed on the intermediate transfer belt  10 . After being transferred onto the back face of the recording medium P, this toner image is fixed to the recording medium P by the fixing device  8  and the recording medium P is cooled by the cooling device  9 . Then, the recording medium P is conveyed by the pair of output rollers  16  onto the output tray  20 . 
     The above description relates to image forming operation for forming a full color image on a recording medium. In other image forming operation, a single color image can be formed by any one of the process units  1 Y,  1 C,  1 M, and  1 K, or a composite color image of two or three colors can be formed by two or three of the process units  1 Y,  1 C,  1 M, and  1 K. 
     Next, a description is given of a configuration of the cooling device  9  according to an embodiment of this disclosure. 
       FIG. 2A  is a side view illustrating the cooling device  9  included in the image forming apparatus  1000  of  FIG. 1 , viewed from a front of the image forming apparatus  1000 .  FIG. 2B  is a plan view illustrating the cooling device  9  of  FIG. 2A , viewed from a top of the image forming apparatus  1000 . 
     The cooling device  9  includes a first cooler  30  and a second cooler  40 . The first cooler  30  cools a back face side of the recording medium P (i.e., a non-image forming face or a face on which no image is formed in a single-side printing job) and the second cooler  40  cools a front face side of the recording medium P (i.e., an image forming face or a face on which an image is formed in the single-side printing job). Specifically, the first cooler  30  includes a first heat absorbing face  32  that contacts the recording medium P via a first conveying belt  51  that functions as a first belt. The second cooler  40  includes a second heat absorbing face  41  that directly contacts the recording medium P and has a cooling structure different from the cooling structure of the first cooler  30 . In addition, both the first cooler  30  and the second cooler  40  include a liquid flowing passage. 
     The above-described configuration can use the merits in the layout of the first cooler  30  and the second cooler  40 , and therefore can achieve a space-saving and efficient layout of the cooling device  9 . In addition, the configuration can achieve a reduction in size of the cooling device  9  and the image forming apparatus  1000 . 
     Specifically, the first cooler  30  that is a heat sink includes the first heat absorbing face  32  having a flat heat absorbing surface having a width extending in the sheet conveying direction in which a recording medium is conveyed. The first heat absorbing face  32  is disposed upstream from the second cooler  40  in the sheet conveying direction. The first cooler  30  (for example, a heat sink) includes fins  31  and fan  33 . The fins  31  function as multiple heat dissipating bodies extending from the first heat absorbing face  32  in a direction separating from a recording media conveying passage and perpendicular to the sheet conveying direction. The fan  33  functions as an airflow generator to generate airflow that passes through the liquid flowing passage  34  between the fins  31 . The first heat absorbing face  32  and the fins  31  include metal material. Heat received by the first heat absorbing face  32  is dissipated via the fins  31 . 
     As illustrated in  FIG. 2B , the fins  31  are disposed immediately below the first conveying belt  51 . That is, the fins  31  are disposed facing the width of the first conveying belt  51  perpendicular to the sheet conveying direction. 
     The fans  33  are disposed at the front side of the first cooler  30 , e.g., a heat sink (the front side of the image forming apparatus  1000 ) and the back side of the first cooler  30  (the back side of the image forming apparatus  1000 ). As illustrated in  FIG. 2B , the fan  33  at the front side blows, that is, exhausts air toward the fins  31 . The fan  33  at the back side intakes air inside the fins  31  and exhausts the air out the image forming apparatus  1000 . Alternatively, the fan  33  at the front side can be disposed at the front side of the first cooler  30  (the heat sink) while no fan  33  is disposed at the back side. It is to be noted that air flow can flow in an opposite direction to the above-described air flow. 
     In  FIG. 2A , the fins  31  form the liquid flowing passage  34  through which air flow passes in the vertical direction in the drawing sheet. The liquid flowing passage  34  in the first cooler  30  is formed in a direction intersecting the sheet conveying direction. 
     The recording medium P passes through the fixing device  8  that is disposed upstream from the cooling device  9  in the sheet conveying direction. Then, as illustrated in  FIG. 2A , the recording medium P travels in a sheet conveying passage formed between sheet conveying rollers  65  and  66  and the first heat absorbing face  32  of the first cooler  30  in the cooling device  9 . By so doing, the heat of the recording medium P is taken by the first heat absorbing face  32 . Consequently, the heat of the first heat absorbing face  32  is dissipated via the fins  31  and exhausted by the fan  33 . It is to be noted that the sheet conveying rollers  65  and  66  are not depicted in  FIG. 2B . 
     The first cooler  30  includes the first conveying belt  51  that conveys the recording medium P. The first conveying belt  51  is wound around a drive roller  52  and driven rollers  53 ,  54 , and  55  to form an endless belt having a loop. An inner circumferential surface of the first conveying belt  51  is in contact with the first heat absorbing face  32  of the first cooler  30 . The drive roller  52  is driven by a driving motor to rotate in a counterclockwise direction, so as to rotate the first conveying belt  51 . 
     The second cooler  40  includes a rotatable cylindrical heat pipe roller. The second cooler  40  employing a heat pipe roller configuration includes a second heat absorbing face  41  that has a shape to change a sheet conveying direction of the recording medium P after passing the first heat absorbing face  32 . The second cooler  40  can wind a recording medium, and therefore can change the sheet conveying direction while cooling the recording medium. A combination of a heat pipe roller and a heat sink can provide high cooling performance. A face of a recording medium having a toner image faces (contacts) the second cooler  40 . However, since the second cooler  40  is disposed at a downstream side in the sheet conveying direction, an angle of conveyance of the recording medium can be changed while restraining a mechanical stress to the toner image on the recording medium. 
     A heat pipe roller (i.e., the second cooler  40 ) is a pipe-shaped roller having an inner pipe part  42  in which a refrigerant is inserted. The heat pipe roller (i.e., the second cooler  40 ) includes a second heat absorbing face  41 , the inner pipe part  42 , and a fin  43 . The second heat absorbing face  41  includes a rotary body. The inner pipe part  42  functions as a liquid flowing passage and a container to contain the refrigerant inside the rotary body. The fin  43  functions as a heat dissipating body in which the refrigerant evaporated by heat of the recording medium and stored in the container is liquefied due to thermal exchange. 
     As illustrated in  FIG. 2B , the fin  43  is disposed at one longitudinal end (a far side) of the heat pipe roller (i.e., the second cooler  40 ), so as to dissipate heat of the refrigerant. As illustrated in  FIG. 2B , the fin  43  that functions as a second heat dissipating body is disposed outside the first conveying belt  51 , and therefore the fin  43  is located at a different position from the fin  31  that functions as a first heat dissipating body. While contacting a front face side of the recording medium P during conveyance of the recording medium P (an image forming face when performing a single-side printing job), an outer circumference of the heat pipe roller (i.e., the second cooler  40 ) is rotated with movement of a second conveying belt  58  in a clockwise direction. 
     The outer circumference of the heat pipe roller (i.e., the second cooler  40 ) includes a second heat absorbing face  41  that contacts the recording medium P, so that heat of the recording medium P is taken by the second heat absorbing face  41 . The second heat absorbing face  41  has a circular cross section, which is different from the shape of the first heat absorbing face  32 . The liquid refrigerant of the inner pipe part  42  that has received the heat from the recording medium P vaporizes on the second heat absorbing face  41 . The vaporized heat (steam) moves through a center passage of the inner pipe part  42  (i.e., a fluid passage) toward the far side of the cooling device  9  where the fin  43  is disposed, as illustrated in  FIG. 2B . The (vaporized) refrigerant contacts an inner wall of the fin  43  that is cooled by airflow blowing from the fan  44 . Due to the contact of the refrigerant with the cooled inner wall of the fin  43 , heat exchange occurs to condense the refrigerant into a liquid form, as illustrated in  FIG. 2B . Consequently, the refrigerant passes through the center passage of the inner pipe part  42  back to the heat receiving part at the near side of the cooling device  9 , where the refrigerant is vaporized again due the heat exchange. The above-described cycle is repeated. 
     In  FIG. 2A , the inner pipe part  42  includes and functions as a fluid passage through which fluid (e.g., liquid refrigerant, vaporized gas) passes in a vertical direction to the drawing sheet. By contrast, in  FIG. 2B , the fluid passage extends in a direction intersecting the sheet conveying direction. 
     The second cooler  40  includes the second conveying belt  58  that functions as a second belt and conveys the recording medium P. The second conveying belt  58  includes an inner circumferential surface and is wound around the drive roller  57  and the driven roller  56  in contact with the inner circumferential surface to form an endless belt having a loop. The second conveying belt  58  also includes an outer circumferential surface disposed facing the second heat absorbing face  41  of the heat pipe roller (i.e., the second cooler  40 ). The outer circumferential surface of the second conveying belt  58  is biased by the heat pipe roller. Accordingly, the second conveying belt  58  is inwardly curved along with the outer circumferential surface of the heat pipe roller (i.e., the second cooler  40 ). The drive roller  52  is driven by a driving motor to rotate in the counterclockwise direction, so as to rotate the second conveying belt  58  in the counterclockwise direction. 
     The first conveying belt  51  and the second conveying belt  58  use different drive sources, and therefore the first conveying belt  51  of the first cooler  30  and the second conveying belt  58  of the second cooler  40  are controlled separately. By having different drive sources, the load to the first conveying belt  51  and the load to the second conveying belt  58  can be reduced. 
     The first cooler  30  and the second cooler  40  are not disposed facing each other in a direction intersecting each other but are shifted from each other in the sheet conveying direction. Since the heat absorbing surface of the first cooler  30  and the heat absorbing surface of the second cooler  40  have different shapes from each other, when the first cooler  30  and the second cooler  40  are disposed facing each other, it is difficult to secure a good contact area with respect to the recording medium P. Therefore, by disposing multiple coolers shifted from each other in the sheet conveying direction, the contact area can be optimized according to the shape of each heat absorbing surface, and therefore the contact area with the recording medium P can be secured sufficiently. 
     Further, the first cooler  30  is disposed upstream from the fixing device  8  in the sheet conveying direction and the second cooler  40  is disposed downstream from the fixing device  8  in the sheet conveying direction. A starting point of the nip region between the first heat absorbing face  32  and the sheet conveying rollers  65  and  66  is located at a substantially same height as a starting point of a nip region between the second heat absorbing face  41  and the first conveying belt  51 . Therefore, the recording medium P can be conveyed smoothly from the first cooler  30  to the second cooler  40 . The second cooler  40  winds the recording medium P around the outer circumference, and therefore can change the sheet conveying direction according to a winding angle of the recording medium P (a transport angle) while cooling the recording medium P. 
     However, when the recording medium P is cooled by the second cooler  40  for the first time, the second cooler  40  applies a load of curvature of the recording medium P and cools the recording medium P after the recording medium P is heated by the fixing device  8 . As a result, the second cooler  40  applies a peculiar winding (curl) in a winding direction to the recording medium P. 
     By contrast, the first cooler  30  has the width extending in the sheet conveying direction and has a smaller load of curvature of the recording medium P. Therefore, by cooling the recording medium P after heated by the fixing device  8 , the peculiar winding of the recording medium P is prevented. Accordingly, the recording medium P is guided to the second cooler  40  in a cooled and stable state. 
     Further, the first cooler  30  is disposed on the opposite side of the recording medium P to which a toner image is fixed in the fixing device  8  and the second cooler  40  is disposed on the opposite side of the first cooler  30  across the recording media conveying passage. According to this positional relation, a space can be secured above the first cooler  30 . Therefore, when the recording medium P is jammed between the fixing device  8  and the second cooler  40 , good visibility and sheet removing performance can be enhanced when a user removes the jammed sheet from the image forming apparatus  1000 . 
     In the present embodiment, the first cooler  30  (the heat sink) includes the first heat absorbing face  32  having the width extending in the sheet conveying direction. However, the configuration of the first cooler  30  is not limited thereto. For example, a liquid type cooling device that includes the first heat absorbing face  32  having the width extending in the sheet conveying direction and a liquid flowing passage  63  through which the liquid flows (see  FIG. 4 ) can be applied to the first cooler  30  of this disclosure. 
     Further, the configuration of the second cooler  40  is not limited to the above-described rotatable heat pipe roller. For example, a liquid type rotary cooling device that includes the liquid flowing passage  63  through which a roller is disposed for the liquid to flow for heat transport (see  FIG. 5 ) can be employed to the second cooler  40  of this disclosure. 
       FIG. 3  is a diagram illustrating a comparative cooling device  9 A to the cooling device  9  of  FIG. 2 . 
     The comparative cooling device  9 A illustrated in  FIG. 3  includes a first cooler  30 A and a second cooler  40 A, both include respective heat pipe rollers. The first cooler  30 A (i.e., the heat pipe roller) includes a heat absorbing surface  41  and a fin  43   a , and the second cooler  40 A (i.e., the heat pipe roller) includes a heat absorbing surfaces  41   a  and the fin  43 . The heat absorbing surfaces  41  and  41   a  have an identical shape to each other. The outer diameter of the fin  43  is greater than the outer diameter of the heat pipe roller (i.e., the second cooler  40 ) having the heat absorbing surface  41 . 
     Further, the fin  43   a  of the first cooler  30 A and the fin  43  of the second cooler  40 A are disposed at the far side of the cooling device  9 A (the far side on the drawing sheet) from the second conveying belt  58  and adjacent to each other in the sheet conveying direction. As a result, the fin  43  of the second cooler  40 A interferes with the fin  43   a  of the first cooler  30 . Therefore, the heat absorbing surfaces  41  and  41   a  cannot be disposed facing each other such that a nip region is formed between the heat absorbing surfaces  41  and  41   a  or adjacent to each other at upstream and downstream positions in the sheet conveying direction. 
     In order to avoid interference of the fins  43  and  47   a  with each other, the heat absorbing surface  41  and the heat absorbing surface  41   a  are disposed shifted from each other in the sheet conveying direction, as illustrated in  FIG. 3 . However, as the fin  43  and the fin  43   a  are shifted from each other, the cooling device  9 A increases in size. Further, shifting the positions of the fin  43  and the fin  43   a  creates a non-contact region A 1  where the second conveying belt  58  and the heat absorbing surfaces  41  and  41   a  do not contact with each other between the heat absorbing surface  41  and the heat absorbing surface  41   a . As a result, the cooling performance deteriorates. 
     By contrast, the cooling device  9  according to the present embodiment of this disclosure as illustrated in  FIGS. 2A and 2B , the first cooler  30  does not have a fin at the far side of the cooling device  9  intersecting the sheet conveying direction. Accordingly, as illustrated in  FIG. 2B , the fin  43  of the second cooler  40  does not interfere with the first cooler  30 . 
     Therefore, as illustrated in  FIG. 2A , the fin  31  or the first conveying belt  51  of the first cooler  30  can be inserted to an inner circumference area of the fin  43  of the second cooler  40 . As a result, when compared with the configuration of the cooling device  9 A illustrated in  FIG. 3 , the configuration of the cooling device  9  according to the present embodiment can restrain an increase in size in the sheet conveying direction. Further, when compared with the configuration of the cooling device  9 A, the cooling device  9  according to the present embodiment can make the distance from a left end portion (a downstream end in the sheet conveying direction) of the first heat absorbing face  32  illustrated in  FIG. 2A  to a starting point of a nip region that corresponds to a contact face between the second heat absorbing face  41  and the first conveying belt  51  (a region of the sheet conveying passage where the recording medium P does not contact a cooling portion). Accordingly, the cooling device  9  of  FIGS. 2A and 2B  has a higher cooling performance compared to the comparative cooling device  9 A of  FIG. 3 . 
     There is a case of a comparative cooling device in which the heat sink employed in the first cooler  30  illustrated in  FIG. 2A  is also applied to the second cooler  40 . In this case, since the fin extends in a direction vertically intersecting the recording media conveying passage (that is, in a vertical direction), the size of the cooling device increases in height. 
     By contrast, the cooling device  9  of  FIG. 2A  has a configuration in which the diameter of the heat pipe roller (i.e., the second cooler  40 ) having the second heat absorbing face  41  is smaller than the height of the fin  31 . By so doing, the cooling device  9  can be lower in height when compared with the configuration of the above-described comparative cooling device having a heat sink in both the first cooler and the second cooler. 
     Further, a combination of a heat sink having a substantially linear sheet conveying direction and a heat pipe roller having a roller shape can change an ejecting direction of the recording medium P in the cooling device  9  according to the winding angle of the heat pipe roller (i.e., the second cooler  40 ) with respect to an entering direction of the recording medium P. Accordingly, the layout performance of the image forming apparatus  1000  can be enhanced. 
     As described above, a reduction in size of the cooling device  9  and the image forming apparatus  1000  can be achieved by including the first cooler  30  and the second cooler having different cooling types or configurations from each other. 
     It is to be noted that the configuration of the first cooler  30  and the configuration of the second cooler  40  are not limited to  FIGS. 2A and 2B . For example, a liquid type cooler can be employed as illustrated in  FIG. 4 . 
       FIG. 4A  is a side view illustrating the cooling device  9  provided with a liquid cooling jacket  67  in the first cooler  30 , viewed from the front of the image forming apparatus  1000 .  FIG. 4B  is a plan view illustrating the cooling device  9  of  FIG. 4A , viewed from the top of the image forming apparatus  1000 . 
       FIG. 4A  is a side view illustrating the cooling device  9  provided with a liquid cooling jacket  67  in the first cooler  30 , viewed from the front of the image forming apparatus  1000 .  FIG. 4B  is a plan view illustrating the cooling device  9  of  FIG. 4A , viewed from the top of the image forming apparatus  1000 . As cooled fluid (liquid) flows in the liquid flowing passage  63  inside the liquid cooling jacket  67 , the first heat absorbing face  32  is cooled to cool the recording medium P after a toner image is fixed to the recording medium P. By contrast, the heat pipe roller (i.e., the second cooler  40 ) of  FIG. 4A  has the same configuration as the second cooler  40  illustrated in  FIG. 2A . Thus, a combination of a heat pipe roller and a liquid cooling jacket can provide high cooling performance. 
     As illustrated in  FIG. 4B , the liquid heated by heat of the recording medium P received from the first heat absorbing face  32  passes through a tank  61  to store liquid and a pump  62  to circulate cooling liquid. Thereafter, the liquid is cooled in a radiator  60  that functions as a heat dissipating part. The radiator  60  includes fans  60   a  and  60   b . Airflow blown from the fans  60   a  and  60   b  passes inside the radiator  60 . Then, the liquid flows in the liquid flowing passage  63  inside the liquid cooling jacket  67 . 
     The liquid (cooling liquid) is, for example, a liquid that contains water as main component and an antifreeze (e.g., propylene glycol or ethylene glycol) to reduce the freezing point, and an antirust (e.g., phosphate medium Phosphoric acid potassium salt, or inorganic potassium salt) as additives. 
     It is to be noted that the air flow direction of the fans  60   a  and  60   b  intersects a direction in which the fan  44  blows air. 
     The cooling device  9  includes the first cooler  30  and the second cooler  40 . The first cooler  30  cools the back face side of the recording medium P (i.e., the non-image forming face in the single-side printing job) and the second cooler  40  cools the front face side of the recording medium P (i.e., the image forming face in the single-side printing job). Specifically, the first cooler  30  includes the first heat absorbing face  32  that contacts the recording medium P via the first conveying belt  51  that functions as a first belt. The second cooler  40  includes the second heat absorbing face  41  that directly contacts the recording medium P and has a cooling structure different from the cooling structure of the first cooler  30 . 
     In addition, both the first cooler  30  and the second cooler  40  include a fluid passage through which fluid (liquid) flows. The fluid passages in the first cooler  30  and the second cooler  40  in the first cooler  30  are formed in the direction intersecting the sheet conveying direction. 
       FIG. 5  is a schematic view illustrating the cooling device  9  provided with a liquid cooling roller in the second cooler  40 . 
     As illustrated in  FIG. 5 , a liquid type rotary cooling device that includes the liquid flowing passage  63  inside the roller can be employed instead of the heat pipe roller (i.e., the second cooler  40 ) of  FIG. 2A . In the case of this cooling device  9  of  FIG. 5 , respective fluid passages are disposed inside and outside the liquid flowing passage  63 . That is, liquid flows in the inside fluid passage and the outside fluid passage. After passing through the roller, the liquid passes through a tank to store liquid and a pump to circulate cooling liquid. Thereafter, the liquid is cooled in a radiator that functions as a heat dissipating part. By employing the above-described liquid type rotary cooling device for the second cooler  40  and combining with the first cooler  30  including a heat sink configuration, a reduction in size of the cooling device  9  and the image forming apparatus  1000  can also be achieved. 
     The cooling device  9  includes at least the first cooler  30  and the second cooler  40 . The first cooler  30  cools the back face side of the recording medium P (i.e., the non-image forming face in the single-side printing job) and the second cooler  40  cools the front face side of the recording medium P (i.e., the image forming face in the single-side printing job). Specifically, the first cooler  30  includes the first heat absorbing face  32  that contacts the recording medium P via the first conveying belt  51  that functions as a first belt. The second cooler  40  includes a second heat absorbing face  64  that directly contacts the recording medium P when conveying the recording medium P and has a cooling structure different from the cooling structure of the first cooler  30 . 
     In addition, both the first cooler  30  and the second cooler  40  include the liquid flowing passage  34  and the liquid flowing passage  63 . The liquid flowing passage  34  in the first cooler  30  and the liquid flowing passage  63  in the second cooler  40  are formed in the direction intersecting the sheet conveying direction. 
       FIG. 6  is a schematic view illustrating the cooling device  9  provided with the first cooler  30  above the recording media conveying passage and the second cooler  40  below the recording media conveying passage. 
     In the cooling device  9  of  FIG. 6 , the first cooler  30  is disposed on the same side as a toner image side of the recording medium P to which a toner image is fixed in the fixing device  8  and the second cooler  40  is disposed on the opposite side of the first cooler  30  across the recording media conveying passage. According to this positional relation, the toner image side of the recording medium P that is ejected from the fixing device  8  is cooled by the first cooler  30  having the width extending in the sheet conveying direction, and then the opposite side of the recording medium P is cooled by the second cooler  40 . 
     The temperature of the first heat absorbing face  32  of the first cooler  30  and the temperature of the second heat absorbing face  41  of the second cooler  40  are constantly maintained to a room temperature. Specifically, the temperature falls within a range of from 20 degree Celsius through 30 degree Celsius. The first heat absorbing face  32  of the first cooler  30  is greater in a contact width to the recording medium P than the second heat absorbing face  41  of the second cooler  40 . Therefore, a contact area to the recording medium P can be secured easily. As a result, the cooling device  9  can provide a higher cooling performance. The first heat absorbing face  32  of the first cooler  30  is greater in a contact width to the recording medium P than the second heat absorbing face dispose of the second cooler  40 . Therefore, a first cooler  30  to the recording medium P can be secured easily. As a result, the cooling device  9  can provide a higher cooling performance. The first heat absorbing face  32  of the first cooler  30  is disposed near and downstream from the fixing device  8 . By so doing, a higher cooling effect can be provided by utilizing a temperature difference between the heated recording medium P and the first cooler  30 . 
     Further, in the cooling device  9  of  FIG. 6 , the first cooler  30  having a higher cooling effect is disposed on the same side of the toner image side of the recording medium P. By so doing, when passing the recording medium P in the single-side printing job, toner adhering to the recording medium P is cooled and condensed. Accordingly, image failures during conveyance such as abrasion between the toner image surface and a sheet transfer guide before the recording medium P is ejected from the cooling device  9  and uneven gloss due to a sheet conveying roller can be prevented. 
     The cooling device  9  includes the first cooler  30  and the second cooler  40 . The first cooler  30  cools the front face side of the recording medium P (i.e., the image forming face in the single-side printing job) and the second cooler  40  cools the back face side of the recording medium P (i.e., the non-image forming face in the single-side printing job). Specifically, the first cooler  30  includes the first heat absorbing face  32  that contacts the recording medium P via the first conveying belt  51  that functions as a first belt. The second cooler  40  includes the second heat absorbing face  41  that directly contacts the recording medium P and has a cooling structure different from the cooling structure of the first cooler  30 . In addition, both the first cooler  30  and the second cooler  40  include the liquid flowing passage  34  and the liquid flowing passage  63 . The liquid flowing passage  34  in the first cooler  30  and the liquid flowing passage  63  in the second cooler  40  are formed in the direction intersecting the sheet conveying direction. 
       FIG. 7  is a schematic view illustrating the cooling device  9  provided with the first cooler  30  below a downstream side of the recording media conveying passage in the sheet conveying direction and the second cooler  40  above an upstream side of the recording media conveying passage in the sheet conveying direction. 
     In the cooling device  9  of  FIG. 7 , the second cooler  40  is disposed opposite to the first cooler  30  across the sheet conveying direction and upstream of the first cooler  30  in the sheet conveying direction. In addition, the second cooler  40  is disposed on the toner image side of the recording medium P to be fixed in the fixing device  8 , that is, disposed above the recording media conveying passage. 
     By contrast, the first cooler  30  is disposed downstream from the second cooler  40  in the sheet conveying direction and opposite to the toner image side of the recording medium P, that is, disposed below the recording media conveying passage. 
     Generally, an angle of conveyance is changed to a predetermined angle depending on the shape of the sheet transfer guide. However, if the sheet transfer guide is bent or curved, the recording medium P is conveyed while sliding along the shape of the sheet transfer guide, and therefore image failures during conveyance such as damage or scratch onto the image are likely to occur. However, according to the layout of the configuration according to the present embodiment, the cooling device  9  without the sheet transfer guide can cool the recording medium P while the second cooler  40  changes the angle of conveyance of the recording medium P heated by the fixing device  8 . Accordingly, the image failures during conveyance due to the movement of the recording medium P sliding along the sheet transfer guide can be prevented. 
     Further, according to this positional relation, even when the recording medium P is jammed between the second cooler  40  and the pair of output rollers  16  that is disposed at the downstream side of the recording media conveying passage, a space for removing recording media is secured above the first cooler  30 . Therefore, good visibility and sheet removing performance can be enhanced when a user removes the jammed sheet from the image forming apparatus  1000 . 
     The cooling device  9  of  FIG. 7  includes at least the first cooler  30  and the second cooler  40 . The first cooler  30  cools the back face side of the recording medium P (i.e., the non-image forming face in the single-side printing job) and the second cooler  40  cools the front face side of the recording medium P (i.e., the image forming face in the single-side printing job). Specifically, the first cooler  30  includes the first heat absorbing face  32  that contacts the recording medium P via the first conveying belt  51  that functions as a first belt. The second cooler  40  includes the second heat absorbing face  41  that directly contacts the recording medium P and has a cooling structure different from the cooling structure of the first cooler  30 . 
     In addition, both the first cooler  30  and the second cooler  40  include a fluid passage through which fluid (liquid) flows. The fluid passage in the first cooler  30  and the fluid passage in the second cooler  40  are formed in the direction intersecting the sheet conveying direction. 
     Further, the second heat absorbing face  41  of the heat pipe roller (i.e., the second cooler  40 ) has a shape to change the sheet conveying direction of the recording medium P toward the first heat absorbing face  32  that is disposed in a direction different from the entering direction of the recording medium P. 
       FIG. 8  is a schematic view illustrating the cooling device  9  provided with the first cooler  30  above the downstream side of the recording media conveying passage in the sheet conveying direction and the second cooler  40  below the upstream side of the recording media conveying passage in the sheet conveying direction. 
     In the cooling device  9  of  FIG. 8 , the second cooler  40  is disposed upstream from the first cooler  30  in the recording media conveying passage and opposite to the toner image side of the recording medium P to be fixed in the fixing device  8 , that is, disposed below the recording media conveying passage. 
     By contrast, the first cooler  30  is disposed downstream from the second cooler  40  across the recording media conveying passage and on the same side as the toner image side of the recording medium P in the fixing device  8 , that is, disposed above the recording media conveying passage. 
     Generally, an angle of conveyance is changed to a predetermined angle depending on the shape of the sheet transfer guide. However, if the sheet transfer guide is bent or curved, the recording medium P is conveyed while sliding along the shape of the sheet transfer guide, and therefore image failures during conveyance such as damage or scratch onto the image are likely to occur. However, according to the layout of the configuration according to the present embodiment, the cooling device  9  without the sheet transfer guide can cool the recording medium P while the second cooler  40  changes the angle of conveyance of the recording medium P heated by the fixing device  8 . Accordingly, the image failures during conveyance due to the movement of the recording medium P sliding along the sheet transfer guide can be prevented. 
     Further, according to the above-described layout of the configuration according to present embodiment, the first cooler  30  having a large contact area with the recording medium P and a higher cooling effect is disposed on the same side of the toner image side of the recording medium P. By so doing, when passing the recording medium P in the single-side printing job, toner adhering to the recording medium P is cooled and condensed. Accordingly, image failures during conveyance such as abrasion between the toner image surface and the sheet transfer guide before the recording medium P is rejected from the cooling device  9  and uneven gloss due to the sheet conveying roller can be prevented. 
     The cooling device  9  of  FIG. 8  includes at least the first cooler  30  and the second cooler  40 . The first cooler  30  cools the back face side of the recording medium P (i.e., the non-image forming face in the single-side printing job) and the second cooler  40  cools the front face side of the recording medium P (i.e., the image forming face in the single-side printing job). Specifically, the first cooler  30  includes the first heat absorbing face  32  that contacts the recording medium P via the first conveying belt  51  that functions as a first belt. The second cooler  40  includes the second heat absorbing face  41  that directly contacts the recording medium P and has a cooling structure different from the cooling structure of the first cooler  30 . 
     In addition, both the first cooler  30  and the second cooler  40  include a fluid passage through which fluid (liquid) flows. The fluid passage in the first cooler  30  and the fluid passage in the second cooler  40  are formed in the direction intersecting the sheet conveying direction. 
     Further, the second heat absorbing face  41  of the heat pipe roller (i.e., the second cooler  40 ) has a shape to change the sheet conveying direction of the recording medium P toward the first heat absorbing face  32  that is disposed in a direction different from the entering direction of the recording medium P. 
     In the cooling device  9  of  FIGS. 2 and 4A through 8 , the first conveying belt  51  of the first cooler  30  and the second conveying belt  58  of the second cooler  40  are disposed separately. Specifically, the cooling device  9  includes a first belt conveying device that contacts the first cooler  30  while conveying the recording medium P and a second belt conveying device that contacts the second cooler  40  while conveying the recording medium P. The first belt conveying device includes the first conveying belt  51 , the drive roller  52 , and the driven rollers  53 ,  54 , and  55 . The second belt conveying device includes the driven roller  56 , the drive roller  57 , and the second conveying belt  58 . By providing the first belt conveying device to the first cooler  30  and the second belt conveying device to the second cooler  40 , both the first conveying belt  51  and the second conveying belt  58  can be driven by different drive sources. Therefore, the load on the drive sources can be reduced. By disposing two small drive sources, an installation space of the image forming apparatus  1000  can be more saved. 
       FIG. 9  is a schematic view illustrating the cooling device  9  provided with the first cooler  30  below the recording media conveying passage and the second cooler  40  above the recording media conveying passage. 
     In the cooling device  9  of  FIG. 9 , the first heat absorbing face  32  of the first cooler and the heat absorbing surface  41  of the second cooler  40  are disposed facing each other across the recording media conveying passage. Specifically, the first cooler  30  employing a heat sink and the second cooler  40  employing a heat pipe roller are disposed facing in the vertical direction. The heat sink (i.e., the first cooler  30 ) is disposed below the heat pipe roller (i.e., the second cooler  40 ). Further, part of the first cooler  30  (such as the fin  31 ) is disposed closer toward a shaft center of the fin  43  of the second cooler  40  from the outer circumferential surface of the fin  43  of the second cooler  40 . When compared with the configuration in which the first cooler  30  and the second cooler  40  are disposed shifted in the sheet conveying direction as illustrated in  FIGS. 2A and 2B , the cooling device  9  of  FIG. 9  according to the present embodiment can be reduced in size. 
     The inner circumferential surface of the first conveying belt  51  is in contact with the first heat absorbing face  32  of the first cooler  30 . The inner circumferential surface of the first conveying belt  51  is in contact with the first heat absorbing face  32  of the first cooler  30 . 
     The first heat absorbing face  32  of the first cooler  30  has a shape to change the sheet conveying direction of the recording medium P cooperating together with the second heat absorbing face  41  of the second cooler  40  or a shape to change the sheet conveying direction of the recording medium P in a direction different from the entering direction of the recording medium P. Specifically, the first heat absorbing face  32  of the heat sink (i.e., the first cooler  30 ) is inclined slightly downward toward the center at the upstream side of the sheet conveying direction. The first heat absorbing face  32  is inclined upward from the center at the downstream side of the sheet conveying direction. 
     Further, the second heat absorbing face  41  is disposed facing the first heat absorbing face  32 . Where the first heat absorbing face  32  faces the second heat absorbing face  41  has a curved shape curved along an outline of the second heat absorbing face  41 . The curved shape of the first heat absorbing face  32  contacts the outer circumferential surface of the second heat absorbing face  41 . The sheet conveying rollers  65  and  66  are disposed facing the heat sink (i.e., the first cooler  30 ) with the first conveying belt  51  interposed therebetween. Therefore, the recording medium P is pressed by the sheet conveying roller  65  against the heat sink (i.e., the first cooler  30 ), so that the recording medium P is cooled. As indicated by a dotted line in  FIG. 9 , the ejecting direction of the recording medium P is changed such that the recording medium P is ejected in an upwardly inclined direction after the recording medium P has passed the nip region between the first cooler  30  and the second cooler  40  of the cooling device  9 . While the second cooler  40  winds a recording medium to change the sheet conveying direction while cooling the recording medium, the first heat absorbing face  32  of the first cooler  30  upstream and downstream from the center and the nip region between the first cooler  30  and the second cooler  40  so as to contact the recording medium. By so doing, a contact range of the first heat absorbing face  32  of the first cooler  30  and the recording medium is increased, thereby achieving a high cooling performance. By bending the first heat absorbing face  32  of the heat sink (i.e., the first cooler  30 ) into a shape along the recording media conveying passage in the sheet conveying direction, when compared with the configuration in which the first heat absorbing face  32  has a flat shape, the contact area of the first heat absorbing face  32  with the recording medium P increases. Accordingly, a high cooling performance can be achieved. 
     Further, since the recording medium P is cooled by the sheet conveying roller  65  and the heat sink (i.e., the first cooler  30 ) before the recording medium P enters into the nip region between the heat pipe roller (i.e., the second cooler  40 ) and the first conveying belt  51 , curling of the recording medium P is restrained, and therefore the recording medium P can enter the nip region easily. Further, after the recording medium P is ejected from the nip region, the load of the recording medium P is received by the heat sink (i.e., the first cooler  30 ) and the recording medium P is cooled by the sheet conveying roller  66  and the heat sink (i.e., the first cooler  30 ). Therefore, curling of the recording medium P is restrained and the recording medium P is conveyed toward the pair of output rollers  16  disposed downstream in the sheet conveying direction. Further, by disposing the heat sink (i.e., the first cooler  30 ) below the heat pipe roller (i.e., the second cooler  40 ), the load of the recording medium P is received by the first heat absorbing face  32  of the heat sink (i.e., the first cooler  30 ). Accordingly, the recording medium can closely contact with the first heat absorbing face  32  of the heat sink (i.e., the first cooler  30 ) without sagging, and therefore the cooling performance can be enhanced. 
     In  FIG. 9 , the fan  33  that is disposed at the near side of the image forming apparatus  1000  and before the heat sink (i.e., the first cooler  30 ) blows and generates airflow. The airflow flows in the liquid flowing passage  34  between the fins  31  of the heat sink (i.e., the first cooler  30 ) from the near side to the far side. The airflow is sucked by another fan disposed on the back side face of the heat sink (i.e., the first cooler  30 ). 
     The cooling device  9  of  FIG. 9  includes at least the first cooler  30  and the second cooler  40 . The first cooler  30  cools the back face side of the recording medium P (i.e., the non-image forming face in the single-side printing job) and the second cooler  40  cools the front face side of the recording medium P (i.e., the image forming face in the single-side printing job). Specifically, the first cooler  30  includes the first heat absorbing face  32  that contacts the recording medium P via the first conveying belt  51  that functions as a first belt. The second cooler  40  includes the second heat absorbing face  41  that directly contacts the recording medium P and has a cooling structure different from the cooling structure of the first cooler  30 . 
     In addition, both the first cooler  30  and the second cooler  40  include the liquid flowing passage  34  and the fluid passage  42 , respectively. The liquid flowing passage  34  in the first cooler  30  and the fluid passage  42  in the second cooler  40  are formed in the direction intersecting the sheet conveying direction. 
     Further, the first conveying belt  51  functions as a common conveying belt having an inner circumferential surface that slides on the first heat absorbing face  32  and an outer circumferential surface that holds and conveys the recording medium together with the second heat absorbing face  41 . 
       FIG. 10  is a schematic view illustrating the cooling device  9  provided with the first cooler  30  above the recording media conveying passage and the second cooler  40  below the recording media conveying passage. It is to be noted that parts and components of the cooling device  9  of  FIG. 10  are identical to the parts and components of the cooling device  9  of  FIG. 9 . Therefore, the same reference numerals are used and a detailed description according to this examples is omitted. 
     When compared with the configuration of the cooling device  9  in which the first cooler  30  and the second cooler  40  are disposed shifted in the sheet conveying direction as illustrated in  FIGS. 2A and 2B , the cooling device  9  of  FIG. 10  according to the present embodiment can be reduced in size. 
     The cooling device  9  includes the first cooler  30  and the second cooler  40 . The first cooler  30  cools the back face side of the recording medium P (i.e., the non-image forming face in the single-side printing job) and the second cooler  40  cools the front face side of the recording medium P (i.e., the image forming face in the single-side printing job). 
     The sheet conveying rollers  65  and  66  are disposed facing the first cooler  30  (the heat sink) with the first conveying belt  51  interposed therebetween. Therefore, the recording medium P is pressed by the sheet conveying roller  65  against the first cooler  30  (the heat sink), so that the recording medium P is cooled. As indicated by a dotted line in  FIG. 10 , the ejecting direction of the recording medium P is changed such that the recording medium P is ejected in a downwardly inclined direction after the recording medium P has passed the nip region between the first cooler  30  and the second cooler  40  of the cooling device  9 . By bending the first heat absorbing face  32  of the first cooler  30  (the heat sink) into a shape along the recording media conveying passage in the sheet conveying direction, when compared with the configuration in which the first heat absorbing face  32  has a flat shape, the contact area of the first heat absorbing face  32  with the recording medium P increases. Accordingly, a high cooling performance can be achieved. 
     Further, since the recording medium P is cooled by the sheet conveying roller  65  and the first cooler  30  (the heat sink) before the recording medium P enters into the nip region between the second cooler  40  (the heat pipe roller) and the first conveying belt  51 , curling of the recording medium P is restrained, and therefore the recording medium P can enter the nip region easily. Further, by disposing the first cooler  30  (the heat sink) above the second cooler  40  (the heat pipe roller), the heat moved via the first heat absorbing face  32  of the first cooler  30  (the heat sink) can easily be released from a leading end releasing portion of the fin via the fin of the heat sink (i.e., the first cooler  30 ) or by passing a space between the fins. Accordingly, when compared with the configuration in which the heat sink (i.e., the first cooler  30 ) is disposed below the heat pipe roller (i.e., the second cooler  40 ), the cooling performance can be enhanced. 
       FIG. 11A  is a side view illustrating a cooling device  9 B of a variation of the cooling device  9  of  FIG. 1  and  FIG. 2 , viewed from the front of the image forming apparatus  1000 .  FIG. 11B  is a plan view of the cooling device  9 B of  FIG. 11A , viewed from the top of the image forming apparatus  1000 . 
     In the cooling device  9  of  FIGS. 1, 2, and 4A through 8 , the first cooler  30  and the second cooler  40  include separate conveying belt, which are the first conveying belt  51  and the second conveying belt  58 , respectively, so as to convey the recording medium P. By contrast, the cooling device  9 B in  FIGS. 11A and 11B  includes a single common conveying belt, which is the first conveying belt  51 . Accordingly, in the configuration of  FIGS. 11A and 11B , the first conveying belt  51  functions as a common conveying belt. 
     The cooling device  9 B of  FIGS. 11A and 11B  includes the first cooler  30 , the second cooler  40 , and a sheet conveying device  50 . The first cooler  30  cools the back face side of the recording medium P (i.e., the non-image forming face in the single-side printing job) and the second cooler  40  cools the front face side of the recording medium P (i.e., the image forming face in the single-side printing job). The sheet conveying device  50  conveys the recording medium P. 
     The first cooler  30  includes a heat sink that includes the first heat absorbing face  32  having a width extending in the sheet conveying direction. The first cooler  30  is disposed upstream from the second cooler  40  in the sheet conveying direction. The configuration of the first cooler  30  other than the above-described structure is identical to the configuration of the first cooler  30  illustrated in  FIGS. 2A and 2B . 
     The second cooler  40  includes a rotatable cylindrical heat pipe roller. A heat pipe roller is a pipe-shaped roller having the inner pipe part  42  in which a refrigerant is inserted. 
     As illustrated in  FIG. 11B , the fin  43  is disposed at one longitudinal end (a far side) of the heat pipe roller (i.e., the second cooler  40 ), so as to dissipate heat of the refrigerant. While contacting the front face side of the recording medium P during conveyance of the recording medium P (i.e., the image forming face in the single-side printing job), the outer circumference of the heat pipe roller (i.e., the second cooler  40 ) is rotated with movement of the first conveying belt  51  in the clockwise direction. 
     The configuration of the second cooler  40  other than the above-described structure is identical to the configuration of the second cooler  40  illustrated in  FIGS. 2A and 2B . 
     The sheet conveying device  50  includes the first conveying belt  51  that forms an endless belt having a loop, the drive roller  52 , the driven rollers  53 ,  54 , and  55 , and the sheet conveying rollers  65  and  66 . The drive roller  52  is driven by the driving motor to rotate in the counterclockwise direction, so as to rotate the first conveying belt  51 . The first conveying belt  51  moves from right to left in  FIGS. 11A and 11B  to convey the recording medium P. The entering direction of the recording medium P to the cooling device  9 B is different from the ejecting direction of the recording medium P from the cooling device  9 B. In the cooling device  9 B, the position of exit from the nip region between the first conveying belt  51  and the second heat absorbing face  41  is set in the direction of the pair of output rollers  16 . By so doing, the sheet transfer guide to change the direction of the recording medium P ejected from the cooling device  9 B to the pair of output rollers  16  is not used, thereby reducing the number of sheet transfer guides. 
     As illustrated in  FIGS. 11A and 11B , the cooling device  9 B includes the first conveying belt  51  and the drive roller  52 . The first conveying belt  51  has the inner circumferential surface that slides on the first heat absorbing face  32  and the outer circumferential surface that contacts the second heat absorbing face  41 . The drive roller  52  functions as a belt driving body to drive the first conveying belt  51 . 
     Further, the first conveying belt  51  functions as a common conveying belt that contacts both the first heat absorbing face  32  and the second heat absorbing face  41  and that holds and conveys the recording medium P together with the sheet conveying rollers  65  and  66  and the second heat absorbing face  41 . This function can also be applied to the configurations of the cooling device  9  of  FIGS. 9 and 10 . It is to be noted that the shapes of respective heat absorbing surfaces of the first cooler  30  and the second cooler  40  are not limited to the above-described shapes. For example, the first cooler  30  has a roller shape and the second cooler  40  has a shape (for example, a curved shape) different from the roller shape of the first cooler  30 . 
     In addition, the first conveying belt  51  does not contact the fixing device  8 . 
     Accordingly, even when the recording medium P is ejected from the fixing device  8  in the direction as illustrated in  FIG. 11A  (i.e., left and right directions or a horizontal direction in  FIG. 11A ), the ejecting direction of the recording medium P from the cooling device  9 B can be changed so that the recording medium P is ejected from the cooling device  9 B in a different direction, as illustrated in  FIG. 11A  (i.e., upward and downward directions or a vertical direction in  FIG. 11A ). Since the upstream and downstream belts and the drive roller  52  can be used in common by the first cooler  30  and the second cooler  40 , an increase in size of the image forming apparatus  1000  can be restrained. Therefore, the cooling efficiency is enhanced. 
     Further, when one of the first cooler  30  and the second cooler  40  includes a cooling method using a heat pipe roller and the other includes a cooling device employing a cooling method different from the cooling method using a heat pipe roller, the first cooler  30  and the second cooler  40  can be disposed closer to each other in the sheet conveying direction, compared to a configuration in which the first cooler  30  and the second cooler  40  employ the heat pipe cooling method. That is, the outer circumferential surface of the fin  43  of the second cooler  40  is located farther toward a shaft center of the second absorbing face  41  than the outer circumferential surface of the second heat absorbing face  41  and part of the first cooler  30  (such as the fin  31 ) is disposed closer toward a shaft center of the fin  43  of the second cooler  40  from the outer circumferential surface of the fin  43  of the second cooler  40 . Accordingly, a non cooling area between the first cooler  30  and the second cooler  40  can be reduced in length in the sheet conveying direction, and therefore the cooling efficiency can be enhanced. 
     Further, since both the front side face and the back side face of the recording medium P are cooled, a higher cooling effect can be provided. 
     Further, since the heat sink (i.e., the first cooler  30 ) can be located closer to the heat pipe roller (i.e., the second cooler  40 ), the cooling device and the image forming apparatus can be reduced in size. 
     Further, a distance D 1  between the inner circumferential surface of the first conveying belt  51  and the leading end of the fin  31  is smaller than a radius D 2  of the driven roller  55  (or of the driven roller  54 ). In addition, the axial center of the driven roller  55  or the driven roller  54  is located at a position to separate from the fin  31  relative to the inner circumferential surface of the first conveying belt  51  stretched between the driven rollers  54  and  55 . 
     Further, the leading ends of the fins  31  are disposed facing the inner circumferential surface of the first conveying belt  51 , and the distance D 1  between the leading end of each fin  31  and the inner circumferential surface of the first conveying belt  51  is identical to the multiple fins  31 . In other words, a direction in which the leading ends of the multiple fins  31  is parallel to a moving direction of the first conveying belt  51 . 
     Accordingly, since the inner circumferential surface of the first conveying belt  51  is disposed close to the leading end of each fin  31 , the cooling device  9 B can reduce in size in a direction intersecting the sheet conveying direction. 
     It is to be noted that the first conveying belt  51  that functions as a common conveying belt can be applied to the configurations of the cooling device  9  illustrated in  FIGS. 4 through 8 . 
     The configurations according to the above-described embodiments include the first cooler  30  and the second cooler  40  having different cooling types from each other but are not limited thereto. 
       FIG. 12A  is a side view illustrating a cooling device  9 L provided with the first cooler and the second cooler  40  both employing a liquid cooling method, viewed from a front of the image forming apparatus  1000 .  FIG. 12B  is a plan view illustrating the cooling device  9 L of  FIG. 12A , viewed from the top of the image forming apparatus  1000 . 
     For example, the heat pipe roller (i.e., the second cooler  40 ) illustrated in  FIG. 4A  may be replaced with the liquid type rotary cooling device illustrated in  FIG. 5 , as illustrated in  FIGS. 12A and 12B . 
     As illustrated in  FIG. 12A , liquid that is cooled by the radiator  60  flows through an inner passage of the liquid flowing passage  63  of the second cooler  40  that is disposed at the downstream side of the sheet conveying direction. Then, the cooled liquid flows through an outer passage of the liquid flowing passage  63  to be discharged to an outside the second cooler  40 . The discharged liquid enters the liquid flowing passage  63  of the first cooler  30  disposed at the upstream side of the sheet conveying direction. At this time, the liquid enters from the extreme downstream inlet port in the sheet conveying direction of the liquid flowing passage  63 . Then, the liquid is discharged from the extreme upstream outlet port in the sheet conveying direction of the liquid flowing passage  63 . Thereafter, the liquid passes through the tank  61  and the pump  62 , and eventually reaches the radiator  60  in which the liquid is cooled. 
     The first cooler  30  includes the first heat absorbing face  32  having a shape that is different from the shape of a second heat absorbing face  64  of the second cooler  40 . When conveying the recording medium P, the second heat absorbing face  64  directly contacts the recording medium P. 
     In the configuration of  FIGS. 12A and 12B , the ejecting direction of the recording medium P from the cooling device  9 L can be changed so that the recording medium is ejected from the cooling device  9 L in a different direction from the entering direction. In addition, the upstream and downstream belts and the drive roller can be used in common by the first cooler  30  and the second cooler  40 , an increase in size of the image forming apparatus  1000  can be restrained. Therefore, the cooling efficiency is enhanced. 
     The cooling device  9 L of  FIGS. 12A and 12B  includes the first cooler  30 , the second cooler  40 , the first conveying belt  51 , and the drive roller  52 . Specifically, the first cooler  30  includes the first heat absorbing face  32  that cools the back face side of the recording medium P (i.e., the non-image forming face in the single-side printing job). The second cooler  40  is disposed downstream from the first cooler  30  in the sheet conveying direction and includes the second heat absorbing face  64  that cools the front face side of the recording medium P (i.e., the image forming face in the single-side printing job). The first heat absorbing face  32  of the first cooler  30  and the second heat absorbing face  64  of the second cooler  40  have different shapes from each other. The first conveying belt  51  has the inner circumferential surface that contacts and slides on the first heat absorbing face  32  of the first cooler  30  and the outer circumferential surface that contacts the second heat absorbing face  64  to hold and convey the recording medium P together. The drive roller  52  functions as a belt driving body to drive the first conveying belt  51 . In addition, both the first cooler  30  and the second cooler  40  include the liquid flowing passages  63  through which fluid (liquid) flows. The liquid flowing passage  63  in the first cooler  30  and the liquid flowing passage  63  in the second cooler  40  are formed in the direction intersecting the sheet conveying direction. 
     Further, the configuration of the cooling device  9 L is not limited to the configurations according to the above-described embodiments. 
     For example, the position of the first cooler  30  and the position of the second cooler  40  in the sheet conveying direction (i.e., in the horizontal direction) may be switched, like the configuration illustrated in  FIG. 7 . Further, the position of the first cooler  30  and the position of the second cooler  40  in the vertical direction may be switched, like the configuration illustrated in  FIG. 8 . 
       FIG. 13  is a partial enlarged view illustrating the cooling device  9 B of  FIG. 11A .  FIG. 14  is a schematic view illustrating the cooling device  9 B and a support roller  70  of  FIG. 13 . 
     As illustrated in  FIG. 13 , the first heat absorbing face  32  of the first cooler  30  includes a width W extending in the sheet conveying direction. The first heat absorbing face  32  has a curved shape having a center projecting upwardly by a height H relative to an upstream end (a right end in  FIG. 13 ) thereof and a downstream end (a left end in  FIG. 13 ) thereof in the sheet conveying direction. Further, a contact start position HP 1  of the first conveying belt  51  and the second heat absorbing face  41  of the second cooler  40  is located on an extension of a virtual line (a two-dot chain line in  FIG. 13 ) connecting the upstream end and the downstream end of the first heat absorbing face  32  in the sheet conveying direction. 
     The upstream end and the downstream end of the first heat absorbing face  32  are projecting start positions of the first heat absorbing face  32 . Alternatively, as illustrated in  FIG. 14 , the support roller  70  is disposed between the fixing device  8  and the cooling device  9 B to convey the recording medium P. In this configuration, the upstream end and the downstream end of the first heat absorbing face  32  may be located at respective positions intersecting a virtual line connecting a nip region of the support roller  70  and the contact start position HP 1  on the second cooler  40 . At this time, the contact start position HP 1  on the second cooler  40  is located upstream from the extreme downstream position of the second cooler  40  in the direction of rotation of the second cooler  40 . 
     As a result, a contact width of the first heat absorbing face  32  and the first conveying belt  51  can be increased and the recording medium P can contact the first heat absorbing face  32  reliably. Therefore, the recording medium P can be cooled more efficiently. 
     A sheet transfer guide  71   a  is disposed between the sheet conveying rollers  65  and  66 . A lower end of the sheet transfer guide  71   a  includes an inclined surface  71   a   1  that inclines downward from the upstream side to the downstream side of the sheet conveying direction. In other words, the inclined surface  71   a   1  has a shape of which a distance between the first heat absorbing face  32  and the sheet transfer guide  71   a  is reduced from the upstream side to the downstream side of the sheet conveying direction. Since the upstream end of the first heat absorbing face  32  is projected, when the leading end of the recording medium P enters the nip region of the sheet conveying roller  65  and the first heat absorbing face  32 , an upward force is applied to the leading end of the recording medium P. Therefore, it is likely that, depending on a type of the recording medium P, the leading end of the recording medium P is likely to be lifted by the stiffness of the recording medium P after the recording medium P has passed the sheet conveying roller  65 . However, due to the shape of the lower end of the sheet transfer guide  71   a , the leading end of the recording medium P can be guided to the nip region of the sheet conveying roller  66  and the first heat absorbing face  32 . 
     A sheet transfer guide  71   b  is disposed between the sheet conveying rollers  66  and the second heat absorbing face  41 . A lower end of the sheet transfer guide  71   b  includes a substantially horizontal face from the upstream side to the downstream side of the sheet conveying direction. Further, the downstream end of the sheet transfer guide  71   b  in the sheet conveying direction is located closer toward a shaft center of the fin  43  of the second cooler  40  from the outer circumferential surface of the fin  43  of the second cooler  40 . Accordingly, the downstream end of the sheet transfer guide  71   b  in the sheet conveying direction can be positioned closer to the second heat absorbing face  41 , and therefore the leading end of the recording medium P can be guided to the contact start position HP 1  reliably. 
     It is to be noted that the sheet transfer guides  71   a  and  71   b  may be included in the cooling devices  9  having the configurations illustrated in  FIGS. 2 and 4 through 8  and having respective configurations described below. 
     Further, the second cooler  40  includes a heat pipe roller. Therefore, the first conveying belt  51  can slidably move along the outer circumferential surface of the second cooler  40 , following the shape of the downstream side of the first heat absorbing face  32  of the first cooler  30  in the sheet conveying direction. Therefore, the first heat absorbing face  32  of the first cooler  30  can contact the first conveying belt  51  in the sheet conveying direction. Consequently, the recording medium P can be cooled more efficiently. 
     In  FIG. 14 , the support roller  70  is disposed upstream from the first cooler  30  in the sheet conveying direction. The support roller  70  functions as a sheet conveying body having a rotary body to hold and convey the recording medium P after the recording medium P has passed the fixing device  8 . The rotary body of the support roller  70  includes a drive roller  70   a  and a driven roller  70   b . The drive roller  70   a  is driven by a drive source that is different from the drive source that drives the drive roller  52  of the cooling device  9 B. 
     A speed of rotation of the second cooler  40  that is rotated by movement of the first conveying belt  51  is greater than a speed of rotation of the drive roller  70   a . Accordingly, the recording medium P is conveyed between the second cooler  40  and the support roller  70  with tension, and therefore can contact the first cooler  30  more reliably. 
     Thus, by providing a rotary body driving device that is different from a rotary body driving device for driving a belt driving body, fine control can be performed. For example, a magnitude relation of a linear velocity of the drive roller  70   a  and a linear velocity of the first conveying belt  51  can be changed according to a type of the recording medium P. 
     By contrast, the drive roller  70   a  and the drive roller  52  of the cooling device  9 B may be driven by a common driving method. A detailed description of a case in which the drive roller  70   a  and the drive roller  52  of the cooling device  9 B are driven by a single common drive source and a case in which the drive roller  70   a  and the drive roller  52  of the cooling device  9 B are driven by different drive sources is given below. 
     As described above, the speed of rotation of the second cooler  40  that is rotated by movement of the first conveying belt  51  is greater than the speed of rotation of the drive roller  70   a . Further, a speed of movement of the first conveying belt  51  is substantially same as the speed of rotation of the second cooler  40 . Accordingly, this configuration can prevent the leading end of the recording medium P from bending when the leading end of the recording medium P enters the second cooler  40 . 
     Further, the smallest gap of 2 mm or greater is preferably provided between the second heat absorbing face  41  and the first heat absorbing face  32 . Accordingly, this configuration can prevent the leading end of the recording medium P from bending when the leading end of the recording medium P enters the second cooler  40  even if a downstream end of the first heat absorbing face  32  and the second cooler  40  are positioned in the relation as illustrated in  FIG. 21 . 
       FIG. 15  is a partial enlarged view illustrating the cooling device  9 B of  FIG. 14 . 
     A sheet transfer guide  80  is disposed between the support roller  70  and the first cooler  30  so as to guide the recording medium P from the support roller  70  to the first cooler  30 . The sheet transfer guide  80  includes guide portions  80   a  and  80   b . The guide portion  80   a  is substantially flat. The guide portion  80   b  includes a guide face that is inclined upwardly from the upstream side to the downstream side in the sheet conveying direction. The sheet transfer guide  80  is positioned below the sheet conveying direction to guide the back face side of the recording medium to the first cooler  30 . 
     Further, as illustrated in  FIG. 16  that is a schematic plan view of the sheet transfer guide  80 , there are multiple drive rollers  70   a  disposed separated at predetermined intervals in an axial direction. The upstream end of the guide portion  80   b  in the sheet conveying direction extends toward a shaft  70   a   2  between adjacent drive rollers  70   a . Accordingly, even when the recording medium P that has passed the support roller  70  is curled downwardly, the sheet transfer guide  80  can guide the leading end of the recording medium P to the first cooler  30  reliably. 
     In addition, the sheet transfer guide  80  in  FIG. 15  is disposed so as not to project over a virtual line (a two-dot chain line in  FIG. 15 ) connecting the nip region of the support roller  70  and the contact start position HP 1  on the second cooler  40 . Accordingly, this configuration can prevent the back face side of the recording medium P from sliding and abrading with the sheet transfer guide  80  and resulting in damage or scratch on the image of the recording medium P. 
     It is to be noted that a sheet transfer guide  120  is disposed above the virtual line (the two-dot chain line in  FIG. 15 ). An upstream end of the sheet transfer guide  120  in the sheet conveying direction includes an inclined surface  120   a  that is inclined downwardly to guide the leading end of the recording medium P to the downstream side of the sheet conveying direction. A lower end  120   b  that is a rest of the upstream end of the sheet transfer guide  120  in the sheet conveying direction has a substantially horizontal face. 
     Further, the sheet transfer guide  80  is not limited to the above-described shape. For example, as illustrated in  FIG. 17A , the sheet transfer guide  80  may be linearly be inclined entirely from the upstream side to the downstream side in the sheet conveying direction. 
       FIG. 17A  is a side view illustrating a variation of the conveyance guide  80 .  FIG. 17B  is a side view illustrating the conveying guide  80  attached to a base  80   d .  FIG. 17C  is a top view illustrating the conveying guide  80  partly attached to the base  80   d.    
     According to this configuration, the downstream end of the sheet transfer guide  80  in the sheet conveying direction can be located closer to the driven roller  53 . Accordingly, the leading end of the recording medium P can be guided to upwards over the driven roller  53 . 
     Further, as illustrated in  FIG. 17B , the sheet transfer guide  80  may include a guide part  80   e  and the base  80   d  on which the guide part  80   c  is mounted. According to this configuration, when the guide part  80   c  is stained or deteriorated, the guide part  80   c  can be replaced without removing the base  80   d.    
     By contrast, as illustrated in  FIG. 17C , multiple guide parts  80   c  can be disposed partly in the direction intersecting the sheet conveying direction. Each guide part  80   e  extends in the sheet conveying direction and includes a material different from the base  80   d . For example, the guide part  80   c  preferably includes a material to which a smaller amount of toner adheres. 
     When compared with the configuration illustrated in  FIG. 16 , the drive roller  70   a  illustrated in  FIG. 17C  has a smaller width in the axial direction. According to this configuration, a contact area in which the recording medium P after the fixing device  8  contacts the support roller  70  or the guide part  80   c  of the sheet transfer guide  80  may be smaller than the contact area described above. Accordingly, the image formed on the recording medium P can be less scratched or stained. 
     It is to be noted that the guide part  80   c  may expand outwardly to the center in the width direction that intersects with the sheet conveying direction. 
       FIG. 18  is a schematic view illustrating a variation of the support roller  70 . 
     As illustrated in  FIG. 18 , the center of rotation of the driven roller  70   b  may be disposed shifted from the center of rotation of the drive roller  70   a  to the upstream side of the sheet conveying direction. Specifically, the cooling device  9  includes the support roller  70  that functions as a conveyance body including the drive roller  70   a  that functions as a first rotary body and the driven roller  70   b  that functions as a second rotary body. The drive roller  70   a  and driven roller  70   b  are disposed upstream from the first cooler  30  in the sheet conveying direction to hold and convey the recording medium P that has passed through the fixing device  8 . The drive roller  70   a  is disposed near the first cooler  30  to the recording media conveying passage. The driven roller  70   b  is disposed near the second cooler  40  to the recording media conveying passage. The center of rotation of the driven roller  70   b  is shifted from the center of rotation of the drive roller  70   a  to the upstream side of the sheet conveying direction. Accordingly, the recording medium P is ejected from the nip region of the support roller  70  with the printed face up, and therefore can be conveyed to the first heat absorbing face  32  of the first cooler  30  more reliably. 
     Next, a detailed description is given of a case in which a single drive source drives both the drive roller  52  that functions as a belt driving body and the drive roller  70   a  that functions as a rotary body, with reference to  FIG. 19 . 
     When a driving force that is generated by a drive source is transmitted to the first conveying belt  51 , the first conveying belt  51  is moved in the sheet conveying direction along with rotation of the drive roller  52  in the counterclockwise direction in  FIG. 19 . Further, the driving force is transmitted from a pulley  86  that is coaxially mounted on the drive roller  52  to a pulley  87  that is coaxially mounted on the drive roller  70   a  via a timing belt  91 , a pulley  88 , and a pulley  89 . By so doing, the drive roller  70   a  is rotated in a direction to eject the recording medium P, that is, in the counterclockwise direction. Since the pulleys  88  and  89  are disposed above the sheet conveying rollers  65  and  66 , the timing belt  91  is wound around the rollers to bypass an air flow passage to the fan  33  and the fins  31  of the first cooler  30 . 
     By contrast, the second cooler  40  that includes a heat pipe roller is in contact with the first conveying belt  51  and is rotated in the clockwise direction by a frictional force generated between the first conveying belt  51  and the second heat absorbing face  41  of the second cooler  40 . The recording medium P discharged from the fixing device  8  is conveyed by the drive roller  70   a  and the driven roller  70   b  to the downstream side in the sheet conveying direction. Then, the recording medium P is held and conveyed by the second cooler  40  and the first conveying belt  51  to be conveyed to a further downstream side in the sheet conveying direction. 
     The surface speed of the first conveying belt  51  is determined based on at least the diameter of the drive roller  52 , the thickness of the first conveying belt  51 , and the number of rotations of the drive roller  52 . 
     Further, the surface speed of the drive roller  70   a  is determined based on at least the diameter of the drive roller  70   a  and the number of rotations of the drive roller  70   a . The number of rotations of the drive roller  70   a  is determined based on the number of rotations of the drive roller  52  and a ratio of teeth of the pulley  86  and teeth of the pulley  87 . 
     Consequently, by taking slippage due to friction when the heat absorbing surface  41  contacts the surface of the first conveying belt  51  into consideration, the surface speed (i.e., the speed of the surface of the heat absorbing surface  41 ) of the second cooler  40  is substantially same as the surface speed of the first conveying belt  51 . 
     In the configuration illustrated in  FIG. 19 , when the surface speed of the drive roller  70   a  is greater than the surface speed of the first conveying belt  51 , the recording medium P that is held and conveyed by the drive roller  70   a  and the driven roller  70   b  is bent (curved like waves) within a section from a holding position of the sheet conveying rollers  65  and  66  and the first conveying belt  51  to the drive roller  70   a . This might reduce the contact area of the recording medium P to the first cooler  30 . 
     In order to restrain the bending of the recording medium P in that section, the surface speed of the drive roller  70   a  is preferably set to be smaller than the surface speed of the first conveying belt  51 . 
     For example, when a sum of the diameter of the drive roller  52  and the thickness of the first conveying belt  51  is the same as the diameter of the drive roller  70   a , the (reduction) ratio of the number of teeth of the pulley  87  and the number of teeth of the pulley  86  is set to be greater than 1. 
     Alternatively, when the (reduction) ratio of the number of teeth of the pulley  86  and the number of teeth of the pulley  87  is set to 1, the sum of the diameter of the drive roller  52  and the thickness of the first conveying belt  51  is set to be greater than the diameter of the drive roller  70   a.    
     Alternatively, when the sum of the diameter of the drive roller  52  and the thickness of the first conveying belt  51  is set to be smaller than the diameter of the drive roller  70   a , the number of teeth of the pulley  87  is set to be greater than the number of teeth of the pulley  86  so that the surface speed of the drive roller  70   a  is smaller than the surface speed of the first conveying belt  51 . 
     According to the above-described driving methods, the number of parts are reduced and the size of the image forming apparatus  1000  or the cooling device  9  can be reduced. 
     Next, a detailed description is given of a case in which the drive roller  70   a  that functions as a belt driving body and the drive roller  70   a  that functions as a rotary body are driven by different drive sources. This case can be applied to the configurations of the embodiments with reference to  FIGS. 2A, 2B, 9, 11A, and 11B . 
     In this case, the cooling device  9  includes the support roller  70  that functions as a sheet conveying body in addition to the drive roller  52  that functions as a belt driving body. The support roller  70  in this case is disposed upstream from the first cooler  30  in the sheet conveying direction and includes the drive roller  70   a  that functions as a rotary body and a rotary body driving device to rotate the drive roller  70   a . The drive roller  70   a  holds and conveys the recording medium P after the recording medium P has passed the fixing device  8 . This configuration does not include the pulleys  86 ,  87 ,  88 , and  89  and the timing belt  91  illustrated in  FIG. 19 . 
     The surface speed of the first conveying belt  51  is determined based on at least the diameter of the drive roller  52 , the thickness of the first conveying belt  51 , and the number of rotations of the drive roller  52 . The surface speed of the drive roller  70   a  is determined based on at least the diameter of the drive roller  70   a  and the number of rotations of the drive roller  70   a.    
     According to this configuration, the surface speed of the drive roller  70   a  can be set to be smaller than the surface speed of the first conveying belt  51  as follows. 
     For example, when the sum of the diameter of the drive roller  52  and the thickness of the first conveying belt  51  equals to the diameter of the drive roller  70   a , the number of rotations of the drive roller  70   a  is set to be smaller than the number of rotations of the drive roller  52 . 
     Further, when the number of rotations of the drive roller  52  equals to the number of rotations of the drive roller  70   a , the sum of the diameter of the drive roller  52  and the thickness of the first conveying belt  51  is set to be greater than the diameter of the drive roller  70   a.    
     Alternatively, when the sum of the diameter of the drive roller  52  and the thickness of the first conveying belt  51  is smaller than the diameter of the drive roller  70   a , the number of rotations of the drive roller  70   a  is set to be smaller than the number of rotations of the drive roller  52  so that the surface speed of the drive roller  70   a  is smaller than the surface speed of the first conveying belt  51 . 
     Thus, by providing different rotary body driving devices to perform the above-described driving operations, the number of rotations of the drive roller  52  and the number of rotations of the drive roller  70   a  can be controlled by the fine control. For example, a magnitude relation of a linear velocity of the drive roller  70   a  and a linear velocity of the first conveying belt  51  can be changed according to a type of the recording medium P. 
       FIG. 20  is a schematic view illustrating a cooling device  9 C as a variation of the cooling device  9 B of  FIGS. 13 and 14 . 
     As illustrated in  FIG. 20 , the center of an upper face of the first heat absorbing face  32  of the first cooler  30  may be flat-shaped, so that the upper face of the first heat absorbing face  32  may be located on a virtual line (a dashed line in  FIG. 20 ) connecting a nip position of the support roller  70  and the contact start position HP 1  of the second cooler  40  to the first conveying belt  51 . At this time, the contact start position HP 1  is located at a lowest point of the second cooler  40 . The lowest position indicates, for example, an intersection of a vertical line extending downwardly from the center of rotation of the second heat absorbing face  41  and an outer circumference of the second heat absorbing face  41 . Accordingly, a drive torque to drive the first conveying belt  51  is reduced and the belt durability is enhanced since the back face side of the first conveying belt  51  is not pressed hard against the first heat absorbing face  32 . 
       FIG. 21  is an enlarged view illustrating a downstream end  32   a  of the first heat absorbing surface  32  of the first cooler  30  and the lower part of the second cooler  40 . 
     When a direction from an upstream end to the downstream end  32   a  of the first heat absorbing face  32  in the sheet conveying direction represents a width direction (that is, a horizontal direction in the drawing), the downstream end  32   a  of the first heat absorbing face  32  is located within the width of the second cooler  40  in the width direction (the horizontal direction in the drawing). In other words, the downstream end  32   a  of the first heat absorbing face  32  is located downstream from an extreme upstream position HR of the second cooler  40  in the sheet conveying direction. To be more specific, the downstream end  32   a  of the first heat absorbing face  32  is located closer to the center of the axis of the second cooler  40  than the outer circumferential surface of the fin  43  of the second cooler  40 . 
     According to this configuration, the first cooler  30  and the second cooler  40  can be located relatively closer to each other in the sheet conveying direction. Therefore, a reduction in size of the cooling device and a higher cooling effect can be achieved simultaneously. 
       FIG. 22  is a schematic view illustrating a cooling device  9 D as a variation of the cooling device  9 B of  FIGS. 11A and 11B . 
     In the cooling device  9 D, the second cooler  40  functions as a rotary body that is rotated with movement of the first conveying belt  51  and that conveys the recording medium P while holding between the second heat absorbing face  41  and the first conveying belt  51 . The second cooler  40  can move in the same direction as a through-thickness direction of the first conveying belt  51 . 
     The image forming apparatus  1000  according to an embodiment of this disclosure is capable of conveying recording media of any thickness of from thin paper to thick paper. However, when the downstream end of the first cooler  30  is located significantly close to the second cooler  40 , a distance between the first cooler  30  and the second cooler  40  is reduced. Therefore, it is likely that the recording medium P is rubbed between the first cooler  30  and the second cooler  40 . 
     In order to address this inconvenience, the cooling device  9 D can move in the same direction as the through-thickness direction of the first conveying belt  51  on the first heat absorbing face  32 , as illustrated in  FIG. 22 . By so doing, the second cooler  40  can move according to the thickness of the recording medium P. Accordingly, a mechanical stress to the recording medium P is reduced, and therefore a belt driving load can be restrained. 
     Specifically, the image forming apparatus  1000  includes a sheet metal  85 , a bearing  81 , a bearing holder  82 , a spring  84 . The sheet metal  85  has a guide opening  83  and is secured to the image forming apparatus  1000 . The bearing  81  supports a shaft end of the heat pipe roller, i.e., the second cooler  40 . The bearing holder  82  holds the bearing  81 . The bearing holder  82  is biased by the spring  84  to be movable in the guide opening  83 . One end of the spring  84  is secured to the guide opening  83  and the opposite end of the spring  84  is secured to the bearing holder  82 . According to this configuration, when the second cooler receives a force greater than the biasing force of the spring  84  from the recording medium P, the second cooler  40  can move in a longitudinal direction of the guide opening  83  or in a direction indicated by arrow in  FIG. 22 . 
       FIG. 23  is a perspective view illustrating the heat pipe roller, that is, the second cooler  40 . 
     The second cooler  40  is a rotary body that is rotated with movement of the first conveying belt  51  and that holds and conveys the recording medium P together with the second heat absorbing face  41  and the first conveying belt  51 . An outer surface of the second heat absorbing face  41  of the second cooler  40  includes a coat layer  90 . 
     As illustrated in  FIG. 23 , the outer surface of the second heat absorbing face  41  of the second cooler  40  includes a coat layer  90 . A region Lcoat of the coat layer  90  is formed greater than a width of conveyance of the recording medium P and a greater region than the region Lcoat is unwanted. Further, the coat layer  90  includes a material to which toner does not easily adhere, for example, high-release glass coating agent (SiO2). When the heat pipe roller (i.e., the second cooler  40 ) is disposed facing a toner image formed on the recording medium P, the second cooler  40  contacts the surface of the recording medium P on which a half melted toner image is formed. However, by providing the coat layer  90  on the outer surface of the second heat absorbing face  41  of the second cooler  40 , the coat layer  90  can prevent the half melted toner image from adhering to the second cooler  40 . It is to be noted that the heat pipe roller (i.e., the second cooler  40 ) may be provided to the front face side of the recording medium P (the image forming face in the single-side printing job) or to the back face side of the recording medium P (the non-image forming face in the single-side printing job). When the heat pipe roller (i.e., the second cooler  40 ) is mounted on the front face side of the recording medium P (the image forming face in the single-side printing job), the coat layer  90  contacts the toner image formed on the recording medium P even in the single-side printing job. Further, when the heat pipe roller (i.e., the second cooler  40 ) is mounted on the back face side of the recording medium P (the non-image forming face in the single-side printing job), the coat layer  90  contacts the toner image formed on the recording medium P in a duplex printing job. 
     The first conveying belt  51  includes a thin film resin material such as polyimide. Further, in order to restrain uneven gloss on the back face side of the recording medium P, the arithmetic average roughness (Ra) on the front face side of the first conveying belt  51  is set to be in a range of from 0.4 μm through 3.2 μm, more preferably, in a range of from 0.6 μm through 1.9 μm. 
     Due to the relation of the coat layer  90  and the first conveying belt  51 , even when the recording medium P is not held by the second heat absorbing face  41  and the first conveying belt  51 , the second heat absorbing face  41  can be prevented from adhering to the first conveying belt  51 . 
     Alternative to the coat layer  90 , the surface treatment may be applied to the second heat absorbing face  41  of the second cooler  40 . For example, a fluorinated tube may be shrunk by heat shrink to be attached to the outer circumference of the second heat absorbing face  41 . This configuration can also obtain the same effect as the above-described configuration with the coat layer  90 . 
       FIG. 24  is an enlarged view illustrating a downstream side of the first heat absorbing surface  32  of the first cooler  30  in the sheet conveying direction. 
     As illustrated in  FIG. 24 , the first heat absorbing face  32  includes a main cooling face  32   d  and an auxiliary cooling face  32   c . Both the upstream end and the downstream end of the first heat absorbing face  32  in the sheet conveying direction have respective curved surfaces. The main cooling face  32   d  includes a face having a radius of curvature R 1  centered on a virtual center O 1  and the auxiliary cooling face  32   c  includes a face having a radius of curvature R 2  centered on a virtual center O 2  (R 1 &gt;R 2 ). For example, the radius of curvature R 1  equals to 754.8 mm and the radius of curvature R 2  equals to 2 mm. 
     By providing the auxiliary cooling face  32   c , the first conveying belt  51  is tensioned downwardly hard so that a relatively large tension force applied by the first conveying belt  51  is maintained. Further, the first conveying belt  51  can contact the auxiliary cooling face  32   c . Since the auxiliary cooling face  32   c  has a curved surface, rapid wear of the first conveying belt  51  caused when both ends of the main cooling face  32   d  have sharp corners can be prevented. Further, scratch or damage to the back face side of the first conveying belt  51  due to stress concentration to the upstream end and the downstream end of the first heat absorbing face  32  can be prevented. 
     Further, by effectively using the entire region of the main cooling face  32   d  in the sheet conveying direction, a higher cooling effect can be provided. 
       FIG. 25  is a partial enlarged view illustrating the cooling device  9 B of  FIG. 13 . 
     As illustrated in  FIG. 25 , the width W in the sheet conveying direction where the first heat absorbing face  32  and the first conveying belt  51  contact to each other is greater than a contact width  41   b  where the second heat absorbing face  41  and the first conveying belt  51  contact to each other. 
     Accordingly, the cooling effect on the first heat absorbing face  32  increases, adhesion of toner to the second heat absorbing face  41  when the recording medium P enters the contact start position HP 1  is restrained, and scratch or damage to the image can be prevented. 
       FIG. 26  is a schematic view illustrating of a cooling device  9 E as a variation of the cooling device  9 B of  FIGS. 11A and 11B . 
     In the cooling device  9 B of  FIGS. 11A and 11B , the second heat absorbing face  41  of the second cooler  40  directly contacts the recording medium P. By contrast, in the cooling device  9 E according to the present embodiment, the second heat absorbing face  41  of the second cooler  40  contacts the recording medium P via a sheet conveying belt  69 . The second cooler  40  includes the sheet conveying belt  69  that conveys the recording medium P. The sheet conveying belt  69  includes an inner circumferential surface that is wound around the heat pipe roller (i.e., the second cooler  40 ), a drive roller  68 , and the sheet conveying rollers  65  and  66 . The sheet conveying rollers  65  and  66  are rotated with rotation of the drive roller  68 . The drive roller  68  is driven by a driving motor to rotate in the clockwise direction, so as to rotate the sheet conveying belt  69  in the clockwise direction. 
     Alternatively, the drive motor used to drive the drive roller  52  of the first conveying belt  51  may also be the drive source of the drive roller  68 . For example, the sheet conveying belt  69  may be rotated along with movement of the first conveying belt  51 . 
     Alternatively, a gear is mounted on the shaft of the drive roller  52 , so that the drive roller  52  can be linked to the gear mounted on the drive roller  68  via the gear train. 
     Accordingly, in addition to the above-described effect, the configuration in which the first conveying belt  51  and the sheet conveying belt  69  hold and convey the recording medium P can reduce abrasion to the toner image on the recording medium P. 
       FIG. 27  is a schematic view illustrating of a cooling device  9 F as a variation of the cooling device  9 B of  FIGS. 11A and 11B . 
     In the cooling device  9 B of  FIGS. 11A and 11B , the leading end of each fin  31  of the first cooler  30  is uncovered. By contrast, in the cooling device  9 F according to the present embodiment, an opening of the leading end of each fin  31  is covered by a cover  35 . The cover  35  is disposed across the heat sink (i.e., the first cooler  30 ) from the front side to the rear side. The fin  31  is surrounded by the cover  35 , the heat receiving part  32 , and the adjacent fins  31  disposed at both ends of the fin  31  in the sheet conveying direction. Thus, by surrounding the fin  31  by the above-described members, the liquid flowing passage  34  is formed to cause airflow to pass along the fins  31 . 
     Further, the distance D 1  between the inner circumferential surface of the first conveying belt  51  and the outer face of the cover  35  is smaller than the radius D 2  of the driven roller  55  (or of the driven roller  54 ). In addition, the axial center of the driven roller  55  or the driven roller  54  is located at a position to separate from the cover  35  relative to the inner circumferential surface of the first conveying belt  51  stretched between the driven rollers  54  and  55 . Further, the cover  35  is arranged parallel to the inner circumferential surface of the first conveying belt  51  that faces the cover  35 . Accordingly, since the inner circumferential surface of the first conveying belt  51  is disposed close to the cover  35 , the cooling device  9 F can reduce in size in the direction intersecting the sheet conveying direction. Further, the outer face of the cover  35  is flat or curved, and therefore the inner circumferential surface of the first conveying belt  51  can be disposed closer to the cover  35  when compared with the configuration of the cooling device  9 B illustrated in  FIGS. 11A and 11B . 
     It is to be noted that the cover  35  can be applied to the heat sink (e.g., the first cooler  30 ) according to each of the above-described embodiments. 
       FIG. 28A  is a side view illustrating a front of a comparative cooling device  9 G to the cooling device  9  of  FIGS. 2A and 2B , viewed from the front of the image forming apparatus  1000 .  FIG. 28B  is a top view illustrating the comparative cooling device  9 G of  FIG. 28A , viewed from the top of the image forming apparatus  1000 . 
     The cooling device  9 G of  FIGS. 28A and 28B  includes at least a first cooler  30 G and a second cooler  40 G. The first cooler  30 G cools the back face side of the recording medium P (i.e., the non-image forming face in the single-side printing job) and the second cooler  40 G cools the front face side of the recording medium P (i.e., the image forming face in the single-side printing job). The first cooler  30 G having the first heat absorbing surface  41   a  and the second cooler  40 G having the second heat absorbing face  41  are heat pipe rollers having the same shape. Specifically, the first cooler  30  includes the first heat absorbing surface  41   a  that contacts the recording medium P via the first conveying belt  51  that functions as a first belt. The second cooler  400  includes the second heat absorbing face  41  that directly contacts the recording medium P. 
     In addition, both the first cooler  300  and the second cooler  40 G include a fluid passage through which fluid (liquid) flows. 
     In the comparative cooling device  9 A in  FIG. 3 , the fin  43  and the fin  43   a  are disposed at the far side of the cooling device  9 A (the far side on the drawing sheet) from the second conveying belt  58  and adjacent to each other in the sheet conveying direction. Therefore, as the heat absorbing surface  41  and the heat absorbing surface  41   a  are disposed closer to each other in the sheet conveying direction, the fin  43  and the fin  43   a  interfere each other. 
     By contrast, as illustrated in  FIG. 28B , while the second cooler  40 G is disposed to cause the fin  43  to be disposed the far side of the image forming apparatus  1000 , the first cooler  300  is disposed to cause the fin  43   a  to be disposed to the near side of the image forming apparatus  1000 . Therefore, when compared with the comparative cooling device  9 A illustrated in  FIG. 3 , the cooling device  9 G illustrated in  FIGS. 28A and 28B  can locate the first heat absorbing surface  41   a  and the second heat absorbing face  41  closer to each other without causing the fin  43  of the second cooler  40 G and the fin  43   a  of the first cooler  30 G to interfere with each other. 
     However, as illustrated in  FIG. 28B , the fin  43  and the fin  43   a  are disposed the front and back of the cooling device  9 G across the first conveying belt  51 , and therefore the size of the cooling device  9 G increases in a direction from the front to the back of the cooling device  9 G. Further, the fin  43  has a diameter greater than respective diameters of the heat absorbing surfaces  41  and  41   a . Therefore, the operability of the cooling device  9 G may be degraded when the heat absorbing surfaces  41  and  41   a  are supported by the frame. For example, the heat absorbing surface  41  is inserted into a supporting hole of the frame downwardly from the upper part in  FIG. 28B  and is fixed to the frame. The heat absorbing surface  41   a  is inserted into a supporting hole of the frame upwardly from the lower part in  FIG. 28B  and is fixed to the frame. Accordingly, the direction to fix the heat absorbing surface  41  and the direction to fix the heat absorbing surface  41   a  are opposite to each other. 
     By contrast, as the above-described embodiments of the cooling devices  9 ,  9 B through  9 F, and  9 L, the cooling methods are different between the first cooler  30  and the second cooler  40 . Therefore, not only the size from the front side to the rear side of each of the cooling devices  9 ,  9 B through  9 F, and  9 L or the housing  200  of the image forming apparatus  1000  but also the size in the horizontal direction (i.e., the size in the sheet conveying direction) can be reduced. 
     The recording medium P is not limited to a recording medium used in an electrophotographic image forming apparatus. For example, a recording medium used in an inkjet image forming apparatus (that is, a sheet-type recording medium or a roll-type recording medium) can be applied to this disclosure. 
       FIG. 29  is a schematic view illustrating an image forming apparatus  1000 A employing an inkjet recording method. 
     In the image forming apparatus  1000 A, as the recording medium P is conveyed by a sheet conveying body  110 , liquid is sprayed from an inkjet head  113  onto the recording medium P, so that an image is formed. A heating body  111  such as an electric heater is disposed below an exposure glass  112  onto which the recording medium P is guided. The heating body  111  heats the recording medium P via the exposure glass  112 . The heating body  111  forcedly heats solvent ink drops landed on the surface of the recording medium P and causes highly permeable organic solvents included in the solvent ink drops to quickly evaporate. Then, the recording medium P is cooled by a cooling device  9 J 1  that corresponds to any of the cooling devices  9 ,  9 B through  9 F, and  9 L according to the above-described embodiments. It is to be noted that the heating body may be disposed downstream to the inkjet head  113  in the sheet conveying direction. 
     Same as the configuration illustrated in  FIG. 29 , the recording medium P is not limited to a recording medium used in an electrophotographic image forming apparatus. For example, a recording medium used in an inkjet image forming apparatus illustrated in  FIG. 30  (that is, a sheet-type recording medium or a roll-type recording medium) can be applied to this disclosure. 
       FIG. 30  is a schematic view illustrating an image forming apparatus  1000 B employing an inkjet recording method. 
     The elements or devices of the image forming apparatus  1000 B illustrated in  FIG. 30  are similar in structure and functions to the elements or devices of the image forming apparatus  1000 A, except the image forming apparatus  1000 A employs two belts (the first conveying belt  51  and the second conveying belt  58 ) included in the cooling device  9 J 1  that corresponds to any of the cooling devices  9 ,  9 B through  9 F, and  9 L while the image forming apparatus  1000 B employs one belt (the first conveying belt  51 ) in a cooling device  9 J 2  that corresponds to any of the cooling devices  9 ,  9 B through  9 F, and  9 L. Therefore, the elements or devices of the image forming apparatus  1000 B may be denoted by the same reference numerals as those of the image forming apparatus  1000 A and the descriptions thereof are omitted or summarized. 
     Further, the recording medium is not limited to be conveyed in the image forming apparatus. For example, this disclosure can apply a recording medium that is conveyed in any device employing cooling processes to perform after the recording medium is heated (for example, an electronic substrate or a printed circuit board). 
     The above-described embodiments are illustrative and do not limit this disclosure. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements at least one of features of different illustrative and exemplary embodiments herein may be combined with each other at least one of substituted for each other within the scope of this disclosure and appended claims. Further, features of components of the embodiments, such as the number, the position, and the shape are not limited the embodiments and thus may be preferably set. It is therefore to be understood that within the scope of the appended claims, the disclosure of this disclosure may be practiced otherwise than as specifically described herein.