Patent Publication Number: US-9889679-B2

Title: Application device and image forming system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority under 35 U.S.C. § 119 of Japanese Patent Application No. 2015-242574, filed on Dec. 11, 2015, the contents of which are incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to an application device and an image forming system. 
     2. Description of the Related Art 
     In inkjet recording systems, there is disclosed in the related art an example of a technique to apply a treatment liquid for aggregating ink immediately before ink droplets land on a sheet of paper of a recording medium in order to improve image quality. 
     There is also known in the related art another example of the technique to apply such a treatment liquid on an entire surface of a sheet using rollers.  FIG. 12  depicts a configuration example of an application unit as a treatment liquid application device (hereinafter also referred simply to as an “application device”) configured to apply a treatment liquid using such rollers. In  FIG. 12 , W indicates a recording medium such as paper,  90  represents an application unit,  91  represents a container, L represents a liquid such as a treatment liquid,  92  represents a squeeze roller,  93  represents an application roller, and  94  represents a pressure roller  94 . In this example, the treatment liquid is scooped by rotations of the squeeze roller  92  driven by a motor. The treatment liquid scooped by the squeeze roller  92  is partially scraped by a nip between the application roller  93  wrapped by an elastic member such as rubber and the squeeze roller  92 , and the remaining liquid is thinly and uniformly spread over the application roller  93 . The treatment liquid spread on the application roller  93  is transferred on a sheet sandwiched by an application nip formed between the pressure roller  94  and the application roller  93  (see Patent Document 1). 
     The elastic member wrapped around the application roller  93  may be quickly deteriorated when the application roller  93  retains in contact with the squeeze roller  92  or the pressure roller  94 . The positions of the application roller  93 , the squeeze roller  92  and the pressure roller  94  may be adjusted to allow the application roller  93  to be in contact with the squeeze, roller  92  and the pressure roller  94  only for applying the liquid, and be separated from the squeeze roller  92  and the pressure roller  94  while not applying the liquid. 
     RELATED-ART DOCUMENTS 
     Patent Documents 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014-024224 
         Patent Document 2: Japanese Unexamined Patent Application Publication No. 2014-058118 
       
    
     SUMMARY OF THE INVENTION 
     It is a general object in one embodiment of the present invention to provide an application device and an image forming system capable of preventing a recording medium from creasing while preventing deterioration of the application roller, when applying a treatment liquid to the recording medium having flexure in different width directions at a contact part between the application roller and the pressure roller. 
     According to an aspect of embodiments, there is provided an application device that includes a conveyer configured to convey a recording medium; an application roller configured to apply a treatment liquid to the recording medium; a pressure roller configured to sandwich the recording medium with the application roller to press the recording medium against the application roller; and a winding member disposed close to the pressure roller and configured to form a curved conveying path to have the recording medium curved with respect to a conveying direction to wind the recording medium around the pressure roller. In the application device, the pressure roller comes in contact with the application roller when applying the treatment liquid to the recording medium, and separates from the application roller when not applying the treatment liquid to the recording medium, and a predetermined positional relationship is provided between the pressure roller and the winding member in a period in which the pressure roller moves close to the application roller to be in contact with the application roller or in a period in which the pressure roller moves away from the application roller to be separated from the application roller. 
     Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a flow of an image forming system of an inkjet system according to an embodiment; 
         FIG. 2  is a schematic diagram illustrating an application device for use in the image forming system according to the embodiment; 
         FIGS. 3A and 3B  are diagrams illustrating an application mechanism included in a pretreatment liquid application device illustrated in  FIG. 2  when a pressure roller moves away from an application roller, where  FIG. 3A  is a schematic diagram illustrating an application mechanism in a pretreatment liquid spreading direction of the application roller, and  FIG. 3B  is a schematic diagram illustrating an application mechanism in a roller axis direction of the application roller; 
         FIGS. 4A and 4B  are diagrams illustrating the application mechanism illustrated in  FIG. 2  when the pressure roller is in contact with the application roller, where  FIG. 4A  is a schematic diagram illustrating the application mechanism in a pretreatment liquid spreading direction of the application roller, and  FIG. 4B  is a schematic diagram illustrating the application mechanism in a roller axis direction of the application roller; 
         FIG. 5  is a perspective diagram illustrating a moving mechanism of the pressure roller and the winding roller illustrated in  FIGS. 3A and 3B ; 
         FIGS. 6A and 6B  are partial configuration diagrams illustrating a positional relationship between a moving mechanism for the pressure roller and the winding roller, and an application roller when the winding angle is small, where  FIG. 6A  illustrates a separate status where the pressure roller separates from the application roller and  FIG. 6B  illustrates a contact status where the pressure roller is in contact with the application roller; 
         FIGS. 7A to 7D  are schematic diagrams illustrating positional relationships between the application roller, the squeeze roller, the pressure roller, and the winding roller illustrated in  FIGS. 6A and 6B ; 
         FIGS. 8A and 8B  are partial configuration diagrams illustrating a positional relationship between a moving mechanism for the pressure roller and the winding roller, and an application roller when the winding angle is large, where  FIG. 8A  illustrates a separate status where the pressure roller separates from the application roller and  FIG. 8B  illustrates a contact status where the pressure roller is in contact with the application roller; 
         FIGS. 9A to 9D  are schematic diagrams illustrating positional relationships between the application roller, the squeeze roller, the pressure roller, and the winding roller illustrated in  FIGS. 8A and 8B ; 
         FIG. 10  is a schematic configuration diagram illustrating an application mechanism having a rocking mechanism in a roller extending direction according to a second embodiment; 
         FIG. 11  is a schematic configuration diagram illustrating an application mechanism illustrated in  FIG. 10  in a roller axis direction; 
         FIG. 12  is a schematic diagram illustrating an example of a related art application unit; 
         FIG. 13  is a diagram illustrating creases formed in the application unit of  FIG. 12 ; and 
         FIG. 14  is a schematic diagram illustrating another example of a related art application unit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     When the related art treatment liquid application device for use in inkjet printers applies a treatment liquid to a continuous sheet such as a roll sheet, the flexure of the sheet (i.e., the recording medium W) may be formed in different width directions due to sheet properties or variability in thickness directions of the sheet. The recording medium W may become wavy by separating the application roller  93 , the squeeze roller  92 , and the pressure roller  94  for preventing deterioration of the elastic member covering the application roller  93 . 
     In  FIG. 13 , waves W 1  at upstream of the application nip N indicate appearance of a recording medium W such as a wavy sheet caused by properties of the sheet or variability in the thickness directions. When the waves W 1  formed in the recording medium W sandwiched between the application roller  93  and the pressure roller  94  reach the application nip N, the waves W 1  are flattened to form a crease W 2 . The creases W 2  in the recording medium W at downstream of the application nip N illustrate a result of the waves W 1  flattened by the application nip N. 
     In general, the waves W 1  caused by the flexure may be reduced by increasing tension of the recording medium when applying the liquid to the sheet. Hence, the sheet may be prevented from creasing by the tension of the sheet.  FIG. 14  depicts another example of a related art application unit  90 A (see Patent Document 2). In the application unit  90 A, the amount of liquid applied to the sheet is adjusted by having a winder  95  to wind the recording medium W around the application roller  93 . However, when the waves W 1  are formed in the recording medium W before reaching the application nip N in the application unit  90 A as illustrated in  FIG. 14 , the waves W 1  that have reached the application nip N are flattened by the application nip N to form additional creases W 2 . Thus, it appears that the creases are not completely removed by the configuration of the application unit  90 A. 
     The following describes embodiments of the present invention with reference to accompanying drawings.  FIG. 1  is a configuration diagram illustrating an embodiment of the present invention. More specifically,  FIG. 1  is a schematic diagram illustrating an inkjet image forming system (i.e., an inkjet printing system)  200  according to an embodiment. 
     In  FIG. 1 , a recording medium (recording medium or web) W of a continuous sheet rolled out of a roll paper feeder  210  is fed to a pretreatment device  220  including application mechanisms  331  and  332 . The pretreatment device  220  is configured to apply a treatment liquid (also called a “pretreatment liquid” or a “treatment liquid”) serving as a coating material having a property of aggregating ink droplets landing on an image forming surface of the recording medium W. The treatment liquid may be applied to one side or two sides of the recording medium W according to desired printed matter. 
     The recording medium W is subsequently transferred to first and second inkjet printers  230  and  250  (recording devices) at downstream of the pretreatment device  220  in a conveying direction of the recording medium W. The recording device having the first and second inkjet printers  230  and  250  ejects ink droplets on a surface of the recording medium W to which the treatment liquid is applied to form a desired image on the surface of the recording medium W. The recording device may further include a reversing device  240  in addition to the first and second inkjet printers  230  and  250 . To print two sides of the recording medium W, the first inkjet printer  230  forms an image on a first surface of the recording medium W, the reversing device  240  subsequently reverses the recording medium W to feed the reversed recording medium W to the second inkjet printer  250 , and the second inkjet printer  250  ejects ink droplets on a second surface (rear surface) of the recording medium W, thereby forming desired images. 
     The recording medium W on which the desired images are formed is conveyed to a posttreatment device  260  to apply a desired posttreatment to the recording medium W. After the posttreatment is applied, the recording medium W is rolled up by a roller  270  as illustrated in  FIG. 1 . The posttreatment may be folding or cutting instead of rolling up. 
       FIG. 2  is a schematic diagram illustrating the pretreatment device  220  for use in the image forming system  200  according to an embodiment. The pretreatment device  220  is configured to apply a pretreatment liquid L and evaporate the applied pretreatment liquid L. The pretreatment device  220  includes a pretreatment liquid L application unit (a pretreatment liquid L application device)  330  having the application mechanisms  331  and  332  configured to apply the pretreatment liquid L to the recording medium W. A heater unit (a recording medium heating device)  350  is disposed downstream of the pretreatment liquid L application unit  330  in a direction of conveying the recording medium W in order to evaporate the pretreatment liquid L applied to the recording medium W. 
     The pretreatment device  220  further includes an air loop unit  320 , a pretreatment liquid L supply unit  340 , and a dancer unit  380 . 
     The air loop unit  320  includes a rotationally supported guide roller  321 , and a feed-in (FI) roller  322  and FI nip roller  323  that sandwich the recording medium W to convey the recording medium W. The guide roller  321 , the rotationally driving FI roller  322 , and the rotationally driven FI nip roller  323  convey the recording medium W fed from a paper feeder  210  to allow the recording medium W to be drawn into the air loop unit  320 . At this moment, the rotation of the FI roller  322  is controlled by an optical sensor to form an air loop AL to allow the recording medium W to have uniform flexure. The recording medium W passing through the air loop AL that has tension applied by a tension shaft for stabilizing the conveyance is conveyed to the pretreatment liquid L application unit  330 . 
     The recording medium W via the air loop AL passes through two edge guides. The recording medium W passes through two path shafts  325  that have longitudinal directions orthogonal to a longitudinal direction (an arrow direction) of the recording medium W so that the recording medium W passes through the two path shafts in an S-shape. The recording medium W having passed the edge guides and the path shafts  325  has tension applied by the fixed tension shaft for stabilizing the conveyance. 
     The pretreatment liquid L application unit  330  includes a rotationally driven infeed roller  333 , a feed nip roller  334 , a rear surface application mechanism  331 , and a surface application mechanism  332 . The pretreatment liquid L application unit  330  further includes an application controller  81  (see  FIG. 10 ) configured to control the rear surface application mechanism  331  and the surface application mechanism  332 . A rotationally driving outfeed roller  335  and a feed nip roller  336  are disposed close to the pretreatment liquid L application unit  330 . 
     The feed nip roller  334  is configured to sandwich the recording medium W with the infeed roller  333 , and the feed nip roller  336  is configured to sandwich the recording medium W with the outfeed roller  335 . The infeed roller  333  and the feed nip roller  334  serve as a recording medium conveying unit. 
     The rear surface application mechanism  331  includes a squeeze roller  2   r , an application roller  3   r , a pressure roller  4   r , and a winding roller  5   r . The squeeze roller  2   r  is disposed inside a supply pan  1   r  containing the pretreatment liquid L so that the squeeze roller  2   r  applies the pretreatment liquid L to the application roller  3   r . Accordingly, the pretreatment liquid L is applied to one side (the rear surface) of recording medium W by the application roller  3   r  while the recording medium W is sandwiched and carried by the application roller  3   r  and the pressure roller  4   r . The recording medium W that passes through the rear surface application mechanism  331  is carried to the surface application mechanism  332 . 
     The surface application mechanism  332  includes a supply pan  1   f , a squeeze roller  2   f , an application roller  3   f , a pressure roller  4   f , and a winding roller  5   f  to apply the pretreatment liquid L to an outer surface (surface) of the recording medium W. The recording medium W that passes through the surface application mechanism  332  is carried by the outfeed roller  335  and the feed nip roller  336  to a heater unit  350  serving as a heater. 
     The rear surface application mechanism  331  and the surface application mechanism  332  are controlled to be selectively activated to selectively apply the pretreatment liquid L to one side or both sides of the recording medium W. 
     The pretreatment liquid L supply unit  340  pools the pretreatment liquid L in order to appropriately supply the pretreatment liquid L to the rear surface application mechanism  331  and the surface application mechanism  332 . 
     The heater unit  350  includes heating rollers  540   a ,  540   b ,  550   a ,  550   b ,  560   a  and  560   b  from upstream in the conveying direction of the recording medium W. The heater unit  350  further includes a discharge-specific conveyer roller  570  and a controller  580 . The controller  580  executes control processes to control heating (temperatures) of respective heaters  541   a  to  561   b  of the heating rollers  540   a  to  560   b.    
     The recording medium W conveyed by the outfeed roller  335  and the feed nip roller  336  is alternately conveyed via the heating rollers  540   a  to  560   b  to pass through the heater unit  350  by a feed roller  359  and a feed nip roller  360 . The heating rollers  540   a  to  560   b  are rotationally driven by the conveyed recording medium W while heating the conveyed recording medium W to evaporate the pretreatment liquid L applied to the recording medium W. 
     The recording medium W having the pretreatment liquid L evaporated in the heater unit  350  is sandwiched between the feed roller  359  and the feed nip roller  360  and transferred to the dancer unit  380 . 
     Note that the heater unit  350  may be excluded when the applied liquid or the recording medium has a fast-dry function or when an installation space for the pretreatment device  220  needs to be secured. In this configuration example, the recording medium W output from the rear surface application mechanism  331  and the surface application mechanism  332  is directly conveyed to the dancer unit  380 . 
     The dancer unit  380  includes two guide rollers  381  and  382 , a moving frame  384 , a position detector configured to detect the moving frame  384 , and two dancer rollers  385  and  386 . The moving frame  384  includes an anchor  383  at a lower part of the moving frame  384  to move the anchor  383  in directions of an arrow A together with the dancer rollers  385  and  386 . The recording medium W is bridged over the two guide rollers  381  and  382  and the two dancer rollers  385  and  386  in a W-shape. 
     The dancer unit  380  controls the conveyed amount of the feed roller  359  based on an output of the position detector to control a position in a vertical direction of the moving frame  384 . The position of the moving frame  384  is adjusted so as to provide a buffer for the recording medium W between the pretreatment device  220  and a posttreatment recording device  230 . 
     The recording medium W heated by the heater unit  350  is cooled by the dancer unit  380 , and subsequently conveyed to the posttreatment recording device  230 . 
     This configuration allows the pretreatment device  220  to apply the pretreatment liquid L to the recording medium W and transfer the recording medium W to the posttreatment recording device  230 . The pretreatment liquid L applied by the pretreatment device  220  to the recording medium W may improve the quality of images on the recording medium W by aiding the permeation and by preventing feathering, show-through, or bleed through of the ink due to ink density or color tone. 
     Application Mechanism of First Embodiment 
       FIGS. 3A and 3B  are diagrams illustrating the application mechanism  331  ( 332 ) included in the pretreatment device  220  illustrated in  FIG. 2  when the pressure roller  4  moves away from the application roller  3 .  FIG. 3A  is a schematic diagram illustrating the application mechanism  331  ( 332 ) in a roller extending direction of the application roller  3  and  FIG. 3B  is a schematic diagram illustrating the application mechanism  331  ( 332 ) in a roller axis direction of the application roller  3 . 
     Note that the rear surface application mechanism  331  and the surface application mechanism  332  illustrated in  FIG. 2  have the identical structural configurations, and an illustration below is thus given on the basis of the rear surface application mechanism  331 . Note that in the rear surface application mechanism  331  and the surface application mechanism  332  illustrated in  FIG. 2 , the supply pan  1   r  and supply pan  1   f  have identical structural configurations, the squeeze roller  2   r  and squeeze roller  2   f  have identical structural configurations, the application roller  3   r  and the application roller  3   f  have identical structural configurations, the pressure roller  4   r  and pressure roller  4   f  have identical structural configurations, and the winding roller  5   r  and winding roller  5   f  have identical structural configurations; and reference numerals of these components are partially omitted in the illustration given below. 
     The rear surface application mechanism  331  according to a first embodiment includes a squeeze roller mechanism  20  having a supply pan  1  and a squeeze roller  2 , an application roller mechanism  30  having the application roller  3 , and a pressure unit  40  (see  FIG. 5 ) having a pressure roller  4  and a winding roller  5 . 
     The pressure unit  40  may also be referred to as a lifting mechanism, a lifting mechanism, and a moving mechanism. The pressure unit  40  having the pressure roller  4  is removably fixed to a housing  6 . The supply pan  1  serving as a treatment liquid container contains a treatment liquid. The application roller  3  and the squeeze roller  2  are disposed inside the supply pan  1  and are rotationally fixed to the supply pan  1 . 
     The supply pan  1  of the rear surface application mechanism  331  is connected to the pretreatment liquid L supply unit  340  serving as a cartridge configured to supply the pretreatment liquid L. The supply pan  1  is disposed close to the rear surface application mechanism  331  and is connected to a pooling tank  11  configured to temporarily pool the pretreatment liquid L. The pretreatment liquid L fed from the pretreatment liquid L supply unit  340  and pooled in the pooling tank  11  is supplied to the supply pan  1  by a pump serving as an electrically driven liquid transfer unit such as a tubing pump or a diaphragm via a supply path  13  and a solenoid valve. 
     The pretreatment liquid L pooled in the supply pan  1  is scooped by the rotation of the squeeze roller  2  driven by an application adjusting motor  18   a  of a motor unit  18  (see a second embodiment in  FIG. 10 ) via a gear  18   b.    
     The amount of the pretreatment liquid L scooped by the squeeze roller  2  may be less affected by using an anilox roller or a wire bar having a dimpled surface when the viscosity of the pretreatment liquid L or a printing rate is changed. 
     The pretreatment liquid L scooped by the squeeze roller  2  is partially removed by a contact part (an application amount adjusting nip) between the application roller  3  covered with an elastic member such as rubber and the squeeze roller  2  such that the pretreatment liquid L remaining on the squeeze roller  2  is thinly and uniformly spread over the application roller  3 . 
     Two ends of the application roller  3  are supported by respective bearings  31  that are rotated with respect to the recording medium W or are driven by the conveyance of the recording medium W. 
     The pressure roller  4  is attached to the pressure unit  40  serving as the lifting mechanism to elastically press the pressure roller  4  to the application roller  3  for applying the pretreatment liquid L. 
     In the rear surface application mechanism  331 , the squeeze roller  2  is disposed at a lower part of the application roller  3  covered with an elastic member  3 E, and the pressure roller  4  is disposed at an upper part of the application roller  3 . The squeeze roller  2 , the application roller  3 , and the pressure roller  4  are moved in a vertical direction. 
       FIGS. 4A and 4B  are diagrams illustrating the application mechanism  331  ( 332 ) illustrated in  FIG. 2  when the pressure roller  4  is in contact with the application roller  3 .  FIG. 4A  is a schematic diagram illustrating the application mechanism  331  ( 332 ) in a roller extending direction of the application roller  3  and  FIG. 4B  is a schematic diagram illustrating the application mechanism  331  ( 332 ) in a roller axis direction of the application roller  3 . 
     The squeeze roller  2  and the pressure roller  4  are disposed to be in contact with the application roller  3  in an approximately vertical direction as illustrated in  FIG. 4B  when applying the pretreatment liquid L. 
     However, if the squeeze roller  2  or the pressure roller  4  is in contact with the application roller  3  that is not rotated, the elastic member  3 E of the application roller  3  may be slightly deformed. The slightly deformed elastic member  3 E of the application roller  3  may cause non-uniform application of the pretreatment liquid L. 
     In the rear surface application mechanism  331  according to the first embodiment, the squeeze roller  2  or the pressure roller  4  is separated from the application roller  3  when the pretreatment liquid L is not applied as illustrated in  FIGS. 3A and 3B . 
     As illustrated in  FIGS. 3B and 4B , the two ends of the squeeze roller  2  are provided with respective bearing members  21  such as bearings. The squeeze roller  2  is pressed up to the application roller  3  to form a nip or is pressed down to the application roller  3  via respective roller holders  22  supporting the bearing members  21  of the squeeze roller  2 . 
     Bar-shaped holder support members  23  are coupled to lower parts of the roller holders  22  at the two ends of the squeeze roller  2 . Washers  23   a  and  23   b  are attached at a middle position and a lower end of each of the holder support members  23 . A slightly compressed coil-shaped lifting spring  25  is attached between the washers  23   a  and  23   b.    
     The lower part of the lifting spring  25  is supported by an arm  27 . A squeeze cam  26  is disposed on a free end opposite to a point D of the arm  27 . The free end of the arm  27  is thus constantly in contact with the squeeze cam  26  by the elasticity of the lifting spring  25 . The arm  27  pivots on the point D as a pivotal fulcrum (pivots on the center of a circle along the arc) by the rotation of the squeeze cam  26 . The arm  27  is lifted to compress the lifting spring  25  by rotation of the squeeze cam  26 . The rotational axis of the squeeze cam  26  at this moment is located at a lower position. The spring load is propagated to the squeeze roller  2  via the holder support members  23 , the roller holders  22 , and the bearing members  21  to lift the squeeze roller  2  up to the application roller  3  to form a nip. 
     Note that the squeeze roller  2  is rotationally attached to (fitted in) a side frame of the supply pan  1 . The supply pan  1  is relatively supported with respect to the housing (frame)  6  of the rear surface application mechanism  331  to be lifted up or down along the frame. Accordingly, when the squeeze roller  2  is lifted up by the rotation of the squeeze cam  26 , the supply pan  1  is also lifted up so as to allow the squeeze roller  2  to be in contact with the application roller  3 . 
     The pretreatment liquid L is supplied by the pump  12  to the supply pan  1  from the pooling tank  11 . The squeeze roller  2  is partially immersed in the pretreatment liquid L even when the squeeze roller  2  is lifted toward the application roller  3 . 
     Pressure Lifting Unit 
       FIG. 5  is a perspective diagram illustrating a moving mechanism (a lifting mechanism) of the pressure roller  4  and the winding roller  5  illustrated in  FIGS. 3A and 3B . The pressure unit  40  includes supporting arms (pressure roller supporting members)  42  configured to support the pressure roller  4 . The supporting arms  42  are attached to respective ends of the pressure roller  4 . The supporting arms  42  partially form the lifting mechanism. The pressure unit  40  serving as the lifting mechanism of the pressure roller  4  includes a tension spring  43  connected to a ceiling of a housing  47  of the pressure unit  40  at an end opposite to a rotational shaft  46  of the supporting arms  42 . Eccentric cams (pressure roller eccentric cam)  44  are disposed near respective centers of the supporting arms  42 . 
     As illustrated in  FIGS. 3A to 5 , the two ends of the pressure roller  4  are rotationally supported by respective free ends of the supporting arms  42 . The supporting arms  42  are pulled by the tension springs  43  in a counter-clock direction on the rotational shaft  46  as the center. The tension springs  43  of the supporting arms  42  are provided with respective cams (eccentric cams)  44 . The pressure eccentric cams  44  are attached to a shaft  45 . 
     When applying the pretreatment liquid L, the pressure unit  40  serving as the lifting mechanism causes the pressure roller  4  to elastically press the application roller  3  by the rotation of the pressure eccentric cams  44  caused by the principle of the lever. 
     When not applying the pretreatment liquid L, the pressure unit  40  moves the pressure roller  4  upward to separate the application roller  3  from the pressure roller  4  to cancel the contact (the application nip N). In this case, the pressure roller  4  is moved away from the application roller  3  against the elastic force of the tension springs  43  by the rotation of the pressure eccentric cams  44  in contact with the respective supporting arms  42  disposed between the pressure roller  4  and the tension springs  43 . 
     In the pressure unit  40 , the pressure roller  4  elastically presses the application roller  3  when the pretreatment liquid L is being applied. When the pretreatment liquid L is not being applied, the pressure roller  4  is moved upward to cancel the contact between the application roller  3  and the pressure roller  4 . 
     When the supporting arms  42  pivot, the pressure roller  4  is lifted up or down relative to the application roller  3  at the application nip N, and the movement of the pressure roller  4  applies tension to the recording medium W in a width direction in accordance with the recording medium W being drawn by the application roller  3 . As a result, a part of the recording medium W to which tension is not applied may form flexure to be wavy. 
     When the recording medium W having the flexure is continuously conveyed by being sandwiched between the application roller  3  and the pressure roller  4 , the waves in the recording medium W are pressed and flattened to form creases at the application nip N serving as a contact part between the pressure roller  4  and the application roller  3 . 
     According to the first embodiment, q winding roller  5  collaboratively moving with the pressure roller  4  is disposed upstream of the application nip N in the recording medium W conveying direction to deflect the recording medium W conveying path, thereby preventing the recording medium W from creasing. 
     Winding Roller 
     In the application mechanism  331  ( 332 ) of the first embodiment, the pressure unit  40  includes the winding roller  5  of a winding unit  50  (see  FIG. 6A ) for winding the recording medium W around the pressure roller  4 . The winding roller  5  is disposed upstream in the recording medium W conveying direction of the pressure roller  4 . 
     The deflected conveying path is formed for the recording medium W to deflect with respect to the conveying direction when winding the recording medium W around the pressure roller  4  by disposing the winding roller  5  (the winding member) close to the pressure roller  4 . This configuration enables the recording medium W to pass through the winding roller  5  disposed upstream in the conveying direction to be wound around the pressure roller  4 , and then pass through the application nip N between the pressure roller  4  and the application roller  3  having the pretreatment liquid L applied. The pretreatment liquid L is applied to the recording medium W as a result. 
     In the winding unit  50  of the first embodiment, two ends of the winding roller  5  are fixed to respective arm-shaped supporting members (winding member supports)  52 . A fulcrum  56  serving as a rotational axis of each supporting member  52  is disposed at an end opposite to an end of the supporting member  52  to which the winding roller  5  is fixed, and an eccentric cam (eccentric cam for winding)  53  is disposed between the winding roller  5  and the fulcrum  56 . 
     As illustrated in  FIG. 3B , the fulcrum (the rotational axis)  56  is fixed to the supporting arm  42  of the pressure mechanism. The shaft (the eccentric shaft)  54  penetrates the supporting arms  42  at two ends of the pressure roller  4  to be fixed to the supporting arms  42 , and the lower surface of the pressure unit  40  is projected from an opening in a wall of the housing  47 . In this example, the eccentric shaft  54  of the eccentric cam  53  is rotationally fixed to the supporting arms  42  of the pressure mechanism. That is, the winding roller  5  is attached to the supporting arms  42  that support the pressure roller  4  and rotationally moving around the rotational shaft  46 . Note that a lower right corner (a lower right part of  FIG. 3B ) of the supporting arms  42  includes a cutout part so as not to interfere with moving operations of the winding roller  5 . 
     The eccentric shaft (core)  54  of the eccentric cam  53  projected from walls of the housing  47  of the pressure unit  40  is rotated manually or by using a winding adjustment motor M 2  (se  FIG. 5 ), which eccentrically rotates the eccentric cam  53  disposed in contact with the supporting member  52 . The supporting member  52  thus rotates around the fulcrum  56  as the center. 
     The positions of the winding roller  5  fixed to respective ends of the supporting members  52  become movable accordingly. As described above, since the supporting members  52  enable the adjustments of the positions of the winding roller  5  with respect to the pressure roller  4 , the supporting members  52  enable adjustment of a winding angle θ (see  FIG. 4B ) of the recording medium W with respect to the pressure roller  4 . 
     Note that the winding angle θ is adjusted by rotating the respective projected eccentric shafts (core)  54  of the eccentric cams  53  either manually or using the winding adjustment motor M 2  illustrated in  FIG. 5 . On the other hand, the pressure unit  40  is lifted up or down by rotating the respective shafts (cores)  45  of the projected eccentric cams  44  either manually or using a lifting adjustment motor M 1  (see  FIG. 5 ). 
     When the eccentric cams  44  or the eccentric cams  53  are rotated manually, space within the pretreatment device  220  is limited. Hence, it may be difficult to rotate these small and thin shafts (cores)  45  and  54  simultaneously within the limited space. 
     When the eccentric cams  44  and the eccentric cams  53  are eccentrically rotated by rotating the shaft  45  and the eccentric shaft  54  using the lifting adjustment motor M 1  and the winding adjustment motor M 2 , the lifting adjustment motor M 1  and the winding adjustment motor M 2  are controlled so as not to drive the lifting adjustment motor M 1  and the winding adjustment motor M 2  simultaneously but to selectively drive only one of the lifting adjustment motor M 1  and the winding adjustment motor M 2 . For example, the application controller  81  may include a selector function to selectively drive one of the lifting adjustment motor M 1  and the winding adjustment motor M 2 . 
     The adjustment of the winding angle of the pressure roller  4  and the winding roller  5  and the lifting adjustment of the pressure roller  4  are performed by separately rotating the shaft  45  and the eccentric shaft  54 . Thus, when the pressure roller  4  is moved by a lifting mechanism in a vertical direction, the winding angle remains unchanged. 
     One of the shaft  45  and the eccentric shaft  54  is manually rotated while the other is rotated by the corresponding motor. In this case, the shaft  45  and the eccentric shaft  54  are set so as not to rotate the shaft  45  and the eccentric shaft  54  simultaneously. 
     The necessary winding angle θ remains unchanged in a transient period when the pressure roller  4  is lowered down to the application roller  3  to start printing or when the pressure roller  4  is lifted up from the application roller  3  to stop printing. Thus, the stability of the recording medium W may be secured in a transient period when the pressure roller  4  comes in contact with the application roller  3  or when the pressure roller  4  separates from the application roller  3 . 
       FIGS. 6A and 6B  are partial configuration diagrams illustrating a positional relationship between the pressure unit  40  and the application roller  3  when a winding angle is small. Note that the pressure unit  40  serves as the moving mechanism for moving the pressure roller  4  and the winding roller  5 .  FIG. 6A  illustrates a status in which the pressure roller  4  separates from the application roller  3  at non-printing time (an application status is in a standby mode), and  FIG. 6B  illustrates a status in which the pressure roller  4  is in contact with the application roller  3  at printing time (an application status is in an operating mode). 
     The transition between the status of  FIG. 6A  and the status of  FIG. 6B  is achieved by rotating the eccentric cams  44  using a drive source such as the lifting adjustment motor M 1  or the like so as to pivotally turn the supporting arms  42  supporting the pressure roller  4  using the rotational shaft  46  as a pivotal fulcrum. 
     As illustrated in  FIGS. 6A and 6B , respective bearings  31  at opposite ends of the application roller  3  are attached to bearing holders  32 , and holder support members  34  are coupled to respective lower parts of the bearing holders  32 . A washer  33   a  is disposed at a middle of each holder support member  34  and a washer  33   b  is disposed at a lower end of the holder support member  34 . A coil-shaped lifting spring  35  is disposed between the washers  33   a  and  33   b  in a slightly compressed status. 
     As illustrated in  FIGS. 6A and 6B , a lower part of the lifting spring  35  is supported by a corresponding arm  37 . The arm  37  includes a point E as a fulcrum, and an application roller cam  36  is disposed at a free end of the arm  37 , that is, at an opposite end of the point E of the arm  37 . The arm  37  is pivotally moved based on the point E as a pivotal fulcrum along the rotations of the application roller cam  36 . The free end ( FIG. 6B ) of the arm  37  is constantly in contact with the application roller cam  36  by the elastic force of the lifting spring  35 . 
     The application roller cams  36  are rotationally driven by a drive source such as a motor, and rotational angles of the application roller cams  36  are controlled based on signals detected by a rotational angle detector such as&#39; an encoder. The rotations of the application roller cams  36  pivotally move the arms  37  based on respective points E as respective pivotal fulcrums, and the pivotally moved arms  37  compress the respective lifting springs  35  to propagate spring load to the application roller  3  via the holder support members  34 , the bearing holders  32 , and the bearings  31 . The force of the lifting spring  35  is determined by the pivotally moving angle of the pivotally moving arm  37 , and the pivotally moving angle of the pivotally moving arm  37  is determined by the rotational angle of the application roller cam  36 . 
     In a period where the pretreatment liquid L is applied to the recording medium W while the recording medium W is conveyed (statuses illustrated in  FIGS. 6B and 7C ), respective statuses of the lifting spring  35 , the arm  37 , and the application roller cam  36  are maintained as illustrated in  FIG. 6B , and the application roller  3  is located in an upward direction (toward the pressure roller  4 ). 
     In the statuses illustrated in  FIG. 7D  in which the recording medium W is stopped being conveyed, the squeeze cam  26  is rotated after the application roller cam  36  has been rotated to cause the application roller  3  to press against the pressure roller  4 . The rotations of the squeeze cam  26  moves the squeeze roller  2  in a downward direction to separate from the application roller  3  so as to stop the squeeze roller  2  from supplying the pretreatment liquid L to the application roller  3 . 
       FIGS. 7A to 7D  are schematic diagrams illustrating positional relationships (a contact status or a non-contact status between the squeeze roller  2 , the application roller  3 , the pressure roller  4 , and the winding roller  5 ) between the application roller  3 , the squeeze roller  2 , the pressure roller  4 , and the winding roller  5  illustrated in  FIGS. 3A and 3B , and  FIGS. 6A and 6B . The elastic member  3 E of the application roller  3  is controlled to be in contact with the squeeze roller  2  and the pressure roller  4  only while the squeeze roller  2  supplies the pretreatment liquid L to the application roller  3  by lifting operations of the squeeze roller  2 , the application roller  3  and the pressure roller  4  so as to prevent the elastic member  3 E from being degraded to increase the life of the elastic member  3 E. 
       FIG. 7A  illustrates a standby status before the pretreatment liquid L is applied. In  FIG. 7A , the squeeze roller  2  is located at a lower position, the application roller  3  is located at a lower position, and the pressure roller  4  is located at a higher position. The squeeze roller  2 , the application roller  3 , and the pressure roller  4  are separated from one another in manners similar to cases in  FIG. 3B  and  FIG. 6A . In this case, the application device as a whole is illustrated in  FIGS. 3A and 3B . 
     In this standby status, the recording medium W is stopped being conveyed, and the application roller  3  and the squeeze roller  2  are stopped being rotated. 
     When the standby status is changed to the application status, the squeeze cam  26  is rotated to move the squeeze roller  2  in an upward direction before the recording medium W is conveyed. Simultaneously, the application roller cam  36  is rotated to move the application roller  3  in an upward direction as illustrated in  FIG. 6B . Note that the moving amount of the squeeze roller  2  is greater than the moving amount of the application roller  3 , and the squeeze roller  2  is pressed in contact with the application roller  3 . 
     After the squeeze roller  2 , the application roller  3 , and the pressure roller  4  are in a status of  FIG. 7B , the squeeze roller  2  and the application roller  3  start rotating by a drive source such as a motor at low speeds in mutually opposite directions. The recording medium W starts being conveyed when the rotations of the squeeze roller  2  and the application roller  3  have become stable. 
     When the squeeze roller  2  and the application roller  3  have achieved a speed at which the application of the pretreatment liquid L from the squeeze roller  2  to the application roller  3  is secured, the pressure roller  4  is pressed against the application roller  3  to start applying the pretreatment liquid L at the application nip N. In this case, the conveying speed of the recording medium W and the circumferential speed of the application roller  3  are controlled to match the conveying speed of the recording medium W and the circumferential speed of the application roller  3 . 
     As illustrated in  FIGS. 7B and 7C , in a period where the pressure roller  4  approaches the application roller  3  and comes in contact with the application roller  3 , a predetermined positional relationship is maintained between the pressure roller  4  and the winding roller  5 . The recording medium W may be prevented from creasing along with lowering the pressure roller  4  by maintaining the predetermined positional relationship between the pressure roller  4  and the winding roller  5 . 
       FIGS. 7C and 6B  illustrate the application operations in which the pressure roller  4  presses against the application roller  3  by a predetermined amount. 
     In the application operations, the amount of the pretreatment liquid L to be removed is controlled by changing the load applied to the application amount adjusting nip between the application roller  3  and the squeeze roller  2  when the squeeze roller  2  scoops the pretreatment liquid L inside the supply pan  1 . 
     In addition, the amount of the pretreatment liquid L spread on the surface of the application roller  3  to form a thin film to be transferred to the recording medium W is adjusted by changing the load applied to the application amount adjusting nip between the application roller  3  and the squeeze roller  2 , and the pretreatment liquid L is thus applied (transferred and absorbed) to the recording medium W sandwiched between the pressure roller  4  and the application roller  3 . 
     The application controller  81  is coupled to the application mechanism  331  to appropriately adjust the pressing amount based on the application status, and the application controller  81  receives operating instructions associated with printing from the controller of the image forming system  200 . The application controller  81  adjusts the amount of the pretreatment liquid L applied by controlling the amount of the pretreatment liquid L supplied to the supply pan  1 , by controlling the nip pressure between the application roller  3  and the squeeze roller  2 , and by controlling the rotations of the eccentric cams  44  and the eccentric cam  53  (the nip pressure between the application roller  3  and the pressure roller  4 , etc.). 
     To end the application operations, the pretreatment liquid L is stopped being supplied to the application roller  3  by rotating the squeeze cam  26  to separate the squeeze roller  2  from the application roller  3  (see  FIG. 5B  and  FIG. 6B ) before the recording medium W stops being conveyed as illustrated in  FIG. 7D . 
     When the conveying speed of the recording medium W is decreased to stop conveying the recording medium W, the rotations of the application roller  3  and the squeeze roller  2  are also stopped. When the conveying speed of the recording medium W reaches a certain speed or lower, the pressure roller  4  is moved in a direction, which allows the pressure roller  4  to be separated from the application roller  3  to restore statuses illustrated in  FIGS. 7A and 3B  in order to prepare for the next application of the pretreatment liquid L. 
     Note that the eccentric cams  44  do not rotate simultaneously with the eccentric cams  53 . Accordingly, the pressure unit  40  may maintain a predetermined supported status of the winding unit  50  in a period where the pressure roller  4  approaches the application roller  3  to be in contact with the application roller  3 , or the pressure roller  4  is detached from the application roller  3  to move away from the application roller  3 . As illustrated in  FIGS. 7D and 7A , a predetermined distance between the winding roller  5  and the pressure roller  4  determines a predetermined winding angle when the pressure roller  4  is lifted up. 
     Since a change in the path length when to start printing or when to stop printing is small, a change in tension of the recording medium W or unstable behaviors of the recording medium W (twisting or flexure serving as factors of creasing) may be controlled to secure the stable status of the recording medium W. The recording medium W may be prevented from creasing, which is caused by lifting up or down of the squeeze roller  2 , the application roller  3 , and the pressure roller  4 . 
     Example if Winding Adjustment 
       FIGS. 8A and 8B  are partial configuration diagrams illustrating a positional relationship between the moving mechanism to which the pressure roller  4  and the winding roller  5  are attached and the application roller  3  when a winding angle is large.  FIG. 8A  illustrates a status in which the pressure roller  4  separates from the application roller  3  at non-printing time (an application status is in a standby mode), and  FIG. 8B  illustrates a status in which the pressure roller  4  is in contact with the application roller  3  at printing time (an application status is in an operating mode). 
     The transition between the status of  FIG. 6A  and the status of  FIG. 6B  is achieved by rotating the eccentric cams  44  using the lifting adjustment motor M 1  or the like so as to pivotally turn the supporting arms  42  supporting the pressure roller  4  using the rotational shaft  46  as a pivotal fulcrum. 
       FIGS. 8A and 8B  illustrate statuses in which a winding angle θB is greater than the winding angle θA illustrated in  FIG. 6B . In status transition illustrated in  FIGS. 6A and 6B  and  FIGS. 8A and 8B , the eccentric shaft (core)  54  of the eccentric cam  53  projected from the wall  57  is rotated manually (or by the winding adjustment motor M 2  illustrated in FIGS.  4 A and  4 B) to eccentrically rotate the eccentric cam  53  to move the supporting member  52  pivotally so as to move the position of the winding roller  5 . 
     As illustrated in  FIGS. 8A and 8B , when the winding angle θ is large, the winding roller  5  presses against the pressure roller  4  by the application of certain load. As the pressing mechanism, a compressed spring  55  is embedded in the eccentric cam  53 , and the winding roller  5  is pressed against the pressure roller  4  by pressing the compressed spring  55  against the supporting member  52  supporting the winding roller  5 . 
     The pressing load is set to be N 1 &gt;N 2  where N 1  represents a nip part between the pressure roller  4  and the application roller  3  at which a sheet on an output side of the pressure roller  4  is detached, and N 2  represents a nip part between the pressure roller  4  and the winding roller  5 . 
     In the configuration in which the winding roller  5  presses against the pressure roller  4 , the winding angle is increased, the recording medium W is capable of being sufficiently wound around the pressure roller  4  before the recording medium W reaches the application nip N between the application roller  3  and the pressure roller  4 , and the recording medium W is pressed by the winding roller  5  against the pressure roller  4 . The recording medium W being pressed against the pressure roller  4  is provided with predetermined tension to exhibit a higher stretching (straightening or smoothing) effect. 
     When thick paper is used as the recording medium W, the thick paper has rigidity and is hard to be wound around the pressure roller pressure roller  4  along the shape of the pressure roller  4 . Hence, the recording medium W may be conveyed with stability before entering into the application nip N 1  by providing a sufficiently large winding angle to secure a sufficiently long winding length. For example, when an application operation is performed, it may be preferable to dispose the winding roller  5  or adjust the winding roller  5  so as to allow the recording medium W to be wound around the pressure roller  4  by a winding angle of 45 degrees or above to obtain desired stability. 
     Note that the winding angle θ of winding the recording medium W sandwiched between the nip part N 1  and the nip part N 2  around the pressure roller  4  is the same angle θ when printing is performed and when printing is not performed. 
     Since the winding roller  5  is included in the supporting arms  42  configured to move the pressure roller  4  close to the application roller  3  or move the pressure roller  4  away from the application roller  3 , the winding angle remains unchanged while lifting the pressure roller  4  up or down. Thus, the winding roller  5  moves in collaboration with the supporting arms  42  configured to move the pressure roller  4 . 
     Compared to a configuration having a winding roller supporter independent from the supporting arms  42 , this configuration may reduce a change in the length of the conveying path of the recording medium W caused by movement of the pressure roller  4  close to or away from the application roller  3 . 
       FIGS. 9A to 9D  are schematic diagrams illustrating positional relationships between the application roller  3 , the squeeze roller  2 , the pressure roller  4 , and the winding roller  5 . 
     As illustrated in  FIGS. 9A to 9D , a predetermined winding angle is formed by maintaining a constant distance between the winding roller  5  and the pressure roller  4  when the pressure roller  4  is lifted up or down. The above configuration reduces a change in the length of the conveying path of the recording medium W by lifting up or down of the squeeze roller  2 , the application roller  3 , and the pressure roller  4  when starting printing or stopping printing. Thus, a change in tension or unstable behaviors (twist or flexure causing creases) of the recording medium W before entering the application nip N may be controlled, and the formation of creases in the recording medium W may be controlled. 
     Note that when the winding angle θ is large or when the winding roller  5  is brought in contact with the pressure roller  4 , a distance between the pressure roller  4  and the winding roller  5  is narrowed. Thus, it may be difficult to appropriately attach or replace the jammed recording medium W or the rolled recording medium W. 
     Accordingly, when the recording medium W is attached to the pressure roller  4  and the winding roller  5 , the winding angle (amount) is reduced so as to separate the winding roller  5  from the pressure roller  4  as illustrated in  FIGS. 6A and 6B . After, the recording medium W is attached, the positions of the supporting members  52  in the supporting arms  42  are adjusted manually or by using the winding adjustment motor M 2  by bringing the winding roller  5  in contact with the pressure roller  4  to increase the winding amount (angle) as illustrated in  FIGS. 8A and 8B . 
     In this case, the position of the winding roller  5  with respect to the pressure roller  4  is adjusted or the winding angle of winding the recording medium W around the pressure roller  4  is adjusted in a period in which a predetermined distance is maintained between the pressure roller  4  and the application roller  3 . The predetermined distance between the pressure roller  4  and the application roller  3  is maintained when the pressure roller  4  and the application roller  3  are not operated to move the pressure roller  4  and the application roller  3  close to each other or move the pressure roller  4  and the application roller  3  away from each other before the application operation starts or after the application operation ends. That is, the predetermined distance between the pressure roller  4  and the application roller  3  is maintained when the pressure roller  4  and the application roller  3  are separated for attaching the recording medium W, and also while the application operation is performed. 
     For example, while the application operation is performed, the positions of the supporting members  52  of the winding roller  5  may be adjusted with respect to the supporting arms  42  of the pressure unit  40 . As a result, the position of the winding roller  5  (the winding member) with respect to the pressure roller  4  may be adjusted in accordance with a desired amount of the pretreatment liquid L to be applied and a conveying speed of the recording medium W (and/or the rocking speed of the rocking unit). 
     As described above, when the winding angle illustrated in  FIGS. 6A and 6B  is small or when the winding angle illustrated in  FIGS. 8A and 8B  is large, the winding angle or the length of the recording medium W to be wound around the pressure roller  4  remains unchanged while printing is performed and while printing is not performed (other than when the recording medium W is attached). Thus, a stable status of the recording medium W may be secured. As a result, the recording medium W may be prevented from creasing along the lifting operations of the pressure roller  4  for preventing the elastic member  3 E of the application roller  3  from deteriorating. 
     The winding roller  5  according to the embodiment is installed upstream of the pressure roller  4  in a conveying direction of the recording medium W to have the conveying path of the recording medium W curved. Accordingly, even when the wave W 1  is formed in a sheet before entering the application nip N as illustrated in  FIG. 14  while the application operation is performed, waves may be reduced before the recording medium W reaches the application nip N by winding the recording medium W along the curved conveying path to press the recording medium W against the pressure roller  4 . Thus, the recording medium W may be prevented from creasing after the application nip N. 
     Note that a similar effect of preventing the recording medium W from creasing may be obtained by winding the recording medium W around the application roller  3 . In such a case; however, the winding amount of the recording medium W to be wound around the application roller  3  to which the pretreatment liquid L is applied is adjusted. Thus, the amount of the pretreatment liquid L to be applied to the application roller  3  is changed in accordance with the winding amount or the waves formed. In this configuration, it may be difficult to maintain a predetermined amount of the pretreatment liquid L to be applied to the application roller  3  as the application mechanism. Accordingly, it may be preferable to reduce the waves in the recording medium W by allowing the conveying path of the recording medium W to be curved immediately before the application of the pretreatment liquid L, as illustrated in the above embodiment. 
     Note that the winding roller  5  serving as the winding member may be a bar-shaped member instead of a roller-shaped member to exhibit the same effect; however, it is preferable to select the roller-shaped winding member because the recording medium W passes through better with the roller-shaped winding member. 
     In the illustration give above, the pressure unit  40  including the winding roller  5  is applied to the rear surface application mechanism  331  illustrated in  FIG. 2 ; however, a similar effect may be obtained when the pressure unit  40  including the winding roller  5   f  is applied to the surface application mechanism  332 . 
     Note that in order to prevent the application roller  3  and the pressure roller  4  from wearing or tearing due to the application roller  3  and the pressure roller  4  being in contact with each other at the edge of the recording medium W, the pressure unit  40  having the pressure roller  4  and the winding roller  5  may be rocked by the application unit  10  inside the application mechanism. 
     Application Mechanism of Second Embodiment 
       FIG. 10  is a schematic configuration diagram illustrating an application mechanism having a rocking mechanism in a roller extending direction according to a second embodiment.  FIG. 11  is a schematic configuration diagram illustrating the application mechanism illustrated in  FIG. 10  in a roller axis direction. 
     In an application mechanism  331 -A or  332 -A according to the second embodiment, an application unit  10  having an application roller  3  and a squeeze roller  2  is movably (swingably) disposed in a width direction of a recording medium W (a direction orthogonal to the recording medium W conveying direction) in a housing  60  of the application mechanism  331 -A or  332 -A. 
     A part of a moving mechanism  70 , an pressure unit (a pressure lifting mechanism)  40 , and the application unit  10  are disposed in the housing  60 . The application unit  10  is removably attached to the housing  60 . 
     In the second embodiment, the housing  60  has an opening  60   o  in a lower left part of the housing  60  in  FIG. 10 . To attach the application unit  10  to the rear surface application mechanism  331 , the application unit  10  is inserted from the opening  60   o  in a horizontal direction (see an arrow). As the application unit  10  is gradually inserted inside the housing  60 , two location pins  16 , one disposed upstream and the other downstream in an inserting direction are inserted in respective holes in location plates  67  of the housing  60 . As a result, the application unit  10  is located in a recording medium conveying direction (i.e., a depth direction in  FIG. 10 ). 
     Further, a latch  75  of the moving mechanism  70  is hooked on a latch pin (fitting member)  17  fixed to the application unit  10  to locate the application unit  10  in a width direction of the recording medium W (i.e., a horizontal direction in  FIG. 10 ). The moving mechanism  70  connected to the application unit  10  via the latch pin  17  causes the application unit  10  having a bottom surface with wheels (rollers)  15  to continuously or intermittently rock (linearly rock or reciprocate) in a direction orthogonal to the recording medium W conveying direction. The application unit  10  is moved by causing the wheels  15  to roll on a bottom surface (rails on the bottom surface) of the housing  60  in accordance with force of the moving mechanism  70 . 
     The moving mechanism  70  is indicated by a dash-dot line in  FIG. 10 . The moving mechanism  70  includes a slider  72 , the latch  75  disposed in the slider  72 , a location detecting target  74 , a screw shaft  73 , a frame  62  disposed on an inner wall of the housing  60 , and a motor  61  disposed on an outer wall of the housing  60 . A latch mechanism  71  is indicated by a circle in  FIG. 10 . The latch mechanism  71  includes the latch  75  and the like disposed in the slider  72  and in association with fitting of the latch pin  17  of the application unit  10 . 
     The motor (rocking motor)  61  fixed to the housing  60  drives the screw shaft  73 , to slide the slider  72  in a width direction of the recording medium W that is in a horizontal direction along the screw shaft  73 . The application unit  10  connected to the slider  72  via the latch pin  17  and the latch  75  may be rocked by reciprocating the slider  72  in the width direction. That is, the application unit  10  is moved in the housing  60  by moving the slider (a moving member)  72  connected to the application unit (a treatment liquid container)  10 , and the application roller  3  disposed in the application unit  10  rocks in the width direction of the recording medium W with respect to the pressure roller  4 . 
     A position sensor  63  is disposed near the moving mechanism  70 . The position sensor  63  having multiple sensors such as photo-interrupters detects a position of the moving mechanism  70  to detect two ends of a moving width of the moving mechanism  70  (the application unit  10 ). When the position sensor  63  senses one of the ends of the moving width to output a detected result, the moving mechanism  70  is controlled to reverse the moving direction. 
     The position sensor  63  senses a position of the location detecting target  74  in the moving mechanism  70  and outputs the detected position to an IC chip of a later-described recording medium when printing ends. The detected position is initially retrieved from the IC chip at a next printing and is used for the next printing. 
     The position sensor  63  includes multiple sensors along the moving direction of the moving mechanism  70 , and the sensors at two ends of the moving width of the moving mechanism  70  detect the position of the moving mechanism  70  has reached the two ends of the moving mechanism  70 . When printing ends, the position of the moving mechanism  70  is detected by detecting the sensor closest to the moving mechanism  70  or detecting the sensors between which the moving mechanism  70  is located. The moving mechanism  70  may also be provided with a location detecting target  74  for allowing the position sensor  63  to detect a position of the slider  72 . The example of the moving mechanism  70  has one location detecting target  74  but the moving mechanism  70  may have two location detecting targets  74 . 
     A rocking controller  82  connected to the moving mechanism  70  is connected to an application controller  81  or a controller of an image forming system  200 . The rocking controller  82  controls a moving direction, a moving rate and a driving time of the slider  72  of the moving mechanism  70  based on the amount of application determined based on the type of paper or the resolution, and information such as the printing rate or the position of the detected moving mechanism  70 . 
     The application unit  10  includes the IC chip to store the rocking position (the moving position) and the rocking direction (moving direction) of the application roller  3  at the end of the previous printing. Data of the rocking position and the rocking direction are read from the IC chip for next printing so that printing starts at the rocking position and the rocking direction stored at the end of the previous printing. The above operation may equalize abrasion wear within a range of rocking. 
     The pretreatment liquid L is applied from the rotating squeeze roller  2  to the application roller  3 . The pretreatment liquid L on the application roller  3  is applied to the recording medium W by allowing the recording medium W to pass between the pressure roller  4  and the application roller  3 . The recording medium W while being rocked has the pretreatment liquid L applied in the rear surface application mechanism  331 , and subsequently passes through the surface application mechanism  332  to reach the heater unit  350 . 
     When a large amount of the pretreatment liquid L is applied to result in low friction resistance between the recording medium W and the application roller  3  to allow the recording medium W to slip on the application roller  3 , the rocking mechanism may prevent abrasion of the surface of the application roller  3  at a position where the application roller  3  is in contact with the edge of the recording medium W. 
     In the application mechanism  331 -A, the elastic member  3 E of the application roller  3  is controlled to be in contact with the squeeze roller  2  and the pressure roller  4  only while the squeeze roller  2  supplies the pretreatment liquid L to the application roller  3  by lifting operations of the squeeze roller  2 , the application roller  3  and the pressure roller  4  so as to prevent the elastic member  3 E from being degraded to increase the life of the elastic member  3 E in a manner similar to the lifting, operations performed in the application mechanism  331  according to the first embodiment. The predetermined winding angle is formed by maintaining a constant distance between the winding roller  5  and the pressure roller  4  when the pressure roller  4  is lifted up or down. The above configuration reduces a change in the length of the path of the recording medium W by lifting up or down the squeeze roller  2 , the application roller  3 , and the pressure roller  4  at the start or the end of printing. Thus, a tension change or unstable behaviors (twist or flexure causing creases) of the recording medium W before entering the application nip N may be controlled, and the formation of creases in the recording medium W may be controlled. 
     When rocking operations are executed, the pressure roller  4  moves close to or moves away from the application roller  3  at the application nip N, and the movement of the application roller  3  applies tension to the recording medium W in a width direction (in reciprocating directions). As a result, a part of the recording medium W to which tension is not applied may form flexure to be wavy. 
     In accordance with the embodiments, the conveying path of the recording medium W is curved by disposing the winding roller  5  upstream of the application nip N in the conveying direction of the recording medium W. As a result, the recording medium W is pressed against the winding roller  5  to have predetermined tension, which divides various wavy deformations in the recording medium W caused by flexure at the conveyance by rocking, and stretches the sectioned wavy deformations to eliminate the deformations. Thus, the wavy deformations due to the flexure may be reduced so as to prevent the recording medium W from creasing. 
     The embodiments discussed above employ the pretreatment liquid L as an example of a treatment liquid; however, the treatment liquid may be a posttreatment liquid. 
     The embodiments discussed above provide a technology to apply pretreatment liquid L or a treatment liquid to a recording medium sandwiched between an application roller and a pressure roller at a position where the application roller is in contact with the pressure roller while preventing the recording medium having flexure in width directions from creasing. 
     A pretreatment liquid application device  330  includes a recording medium conveying unit (infeed roller)  333  configured to convey a recording medium W, an application roller  3  configured to apply a treatment liquid to the recording medium W, a pressure roller  4  configured to sandwich the recording medium W with the application roller  3  to form a contact part N in order to press the recording medium W for applying the treatment liquid to the recording medium W, and a winding roller  5  disposed close to the pressure roller  4  and configured to form a curved conveying path to have the recording medium W curved with respect to a direction of conveying the recording, medium W to wind the recording medium W around the pressure roller  4 . 
     The pretreatment liquid application device  330  enables the pressure roller  4  to come in contact with the application roller  3  while applying the treatment liquid to the recording medium W, and the pretreatment liquid application device  330  enables the pressure roller  4  to separate from the application roller  3  while not applying the treatment liquid to the recording medium W. The pretreatment liquid application device  330  provides a predetermined positional relationship between the pressure roller  4  and the winding roller  5  in a period in which the pressure roller  4  moves toward the application roller  3  to come in contact with the application roller  3  or in a period in which the pressure roller  4  moves away from the application roller  3 . 
     The embodiments discussed above are capable of applying a treatment liquid to a recording medium sandwiched between an application roller and a pressure roller at a position where the application roller is in contact with the pressure roller while preventing the recording medium having flexure in width directions from creasing. 
     The embodiments of the present invention are described above; however, the invention is not limited to those specifically described embodiments. Variations and modifications may be made without departing from the scope of the present invention, and the embodiments of the invention may appropriately be defined in a variety of applications. 
     The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.