Patent Publication Number: US-8540337-B2

Title: Image forming apparatus and foam application device

Description:
TECHNICAL FIELD 
     The present invention relates to an image forming apparatus and a foam application device. 
     BACKGROUND ART 
     Conventionally, an inkjet recording device has been known as an image forming apparatus such as a printer, a facsimile machine, a copier, and a multifunctional peripheral having those functions, the image forming apparatus employing the liquid-ejection recording method in which, for example, a recording head ejecting ink droplets is used. The image forming apparatus employing the liquid-ejection recording method is capable of ejecting droplets from its recording head onto a fed sheet (or an OHP sheet or any medium on which ink droplets or other liquid can be applied, and may be referred to as a recording medium, a recording paper, a recording sheet, or the like) to form (the terms “form”, “record”, “type”, “image”, and “print” may be regarded as synonymous with each other) an image on the fed sheet. The image forming apparatuses employing the liquid-ejection recording method include a serial-type image forming apparatus in which its recording head moves in the main scanning direction and ejects droplets to form an image, and a line-type image forming apparatus in which its recording head ejects droplets to form an image without moving. 
     In this description, the term “image forming apparatus” employing the liquid ejection recording method refers to an apparatus capable of forming an image by ejecting a fluid onto a medium such as a piece of paper, strings, fibers, silk fabric, metal, plastics, glass, wood, and ceramics. Further, the term “image forming” refers not only to forming an image having significant information such as letters or figures onto a medium but also to forming an image having no significant meaning such as patterns onto a medium (including a case where ink droplets are just discharged onto a medium). Further, the term “ink” is not limited to a material generally called ink but refers to any material which becomes a fluid upon being ejected such as DNA samples, resists, and pattern materials. 
     In such an image forming apparatus employing the liquid ejection recording method, ink droplets are formed out of ink including coloring material. Because of this feature, such image forming apparatus may have a drawback causing problems such as the feathering in which dots formed by droplets have an irregular (beard) shape, and color bleeding in which when ink droplets having different colors are applied adjacent to each other on a sheet, the ink droplets having different colors are mixed on the boundary between the droplets, thereby blurring the color on the boundary. In addition, there is another problem that it takes time to dry the droplets after being applied to the sheet. 
     To overcome the problems, according to, for example, Patent Document 1, a heating unit is provided for heating before or after the printing to control ink bleeding and dry the ink droplets quickly after being applied to the sheet. According to Patent Document 2, a pretreatment fluid is applied to the sheet by using an application roller so that the pretreatment fluid reacts with the ink droplets to control ink bleeding. According to Patent Document 3, a pretreatment fluid is ejected in a mist form from a fluid ejection head, and according to Patent Document 4, a treatment fluid is applied before or after printing to improve ink fixing performance. 
     [Patent Document 1] Japanese Laid-Open Patent Application No. H8-323977 
     [Patent Document 2] Japanese Laid-Open Patent Application No. 2002-137378 
     [Patent Document 3] Japanese Laid-Open Patent Application No. 2005-138502 
     [Patent Document 4] Japanese Laid-Open Patent Application No. 2003-205673 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     However, when a heating unit is added as described in Patent Document 1, energy consumption may be increased. Further, when the pretreatment fluid is applied by using the application roller or the fluid ejection head, the fluid may not be uniformly applied. In addition, since the fluid is additionally applied, it may become more difficult to quickly dry the sheet after the fluid reacts with the ink droplets on the sheet, and the sheet may be more likely to be curled or bent, which may cause problems such as jamming. 
     The present invention is made in light of the above circumstances and may provide an image forming apparatus in which a foam-like fluid, gel, or fluid and gel may be uniformly applied and the supply amount of the foam may be easily adjusted to maintain the quality of the foam to be applied. In addition, the inventors of the present invention have found a new problem that when a treatment fluid is foamed to prepare the treatment fluid in foam form and then the treatment fluid in foam form is applied, not all the treatment fluid in foam form may be applied. Namely, there is generated a residual treatment fluid in foam form (extra foam). In this case, when the extra foam is not applied to a process, the extra foam may be dried, and the dried component of the treatment fluid may be adhered. As a result, there may be some problems which may deteriorate the performance of applying the foam-like fluid (gel) (the fluid (gel) may not be uniformly applied) and the performance of a driving system. 
     The present invention is made in light of the above problems as well and may provide an image forming apparatus capable of solving the problems and maintaining the quality of the foam to be applied. 
     Means for Solving the Problems 
     According to an aspect of the present invention, an image forming apparatus includes an image forming unit forming an image on a recording medium; and a foam application unit applying foam to the recording medium or an intermediate member for applying the foam to the recording medium, the foam being prepared by forming at least one of a liquid and a gel. The foam application unit includes a foam forming unit forming the foam; an application unit applying the foam to the recording medium or the intermediate member; and a supplying unit introducing the foam from the foam forming unit and supplying the foam to the application unit through a supply opening. In this configuration, the supplying unit includes a discharge opening through which the foam that has not been supplied to the application unit is discharged, and the amount of foam introduced into the supplying unit is greater than that of foam supplied to the application unit. 
     Further, the fluid resistance of the foam at the discharge opening on the supplying unit when the foam is being discharged may be greater than the fluid resistance of the foam at the supply opening on the supplying unit when the foam is being supplied. 
     Further, the image forming apparatus may further includes a unit for varying a fluid resistance of the foam at the discharge opening on the supplying unit when the foam is being discharged. 
     Further, the image forming apparatus may further include a unit for varying the fluid resistance of the foam at the supply opening on the supplying unit when the foam is being supplied. 
     Further, the discharge opening may be positioned lower than the supply opening. 
     Further, the discharge opening may be disposed outside the application unit with respect to the width direction of the recording medium or the intermediate member. 
     According to another aspect of the present invention, an image forming apparatus includes an image forming unit forming an image on a recording medium; and a foam application unit applying foam to the recording medium or an intermediate member for applying the foam to the recording medium, the foam being prepared by forming a treatment liquid which is in at least one of a liquid form and a gel form. The foam application unit includes an application unit applying the foam; a channel collecting extra foam remaining without having been applied; and a heat unit heating the extra foam on the channel to return the extra foam to a liquid form. 
     Further, the heat unit may be in first-mode or second-mode operations; the heat unit heats the extra foam in the first-mode and the heat unit does not heat the extra foam in the second-mode. 
     Further, the image forming apparatus may further include a foam forming unit forming the foam out of the treatment liquid; and a treatment liquid container containing the treatment liquid to be supplied to the foam forming unit, or a waste liquid container. In this configuration, the channel may be in communication with the foam forming unit and the treatment liquid container or the waste liquid container. 
     Further, the heating unit may include plural surfaces each in contact with the extra foam. 
     Further, the extra foam refers to the foam that has not been supplied to the application unit. 
     According to another aspect of the present invention, a foam application device applies foam to a target application member, the foam being prepared by foaming at least one of a fluid or a gel. The foam application device includes a foam forming unit forming the foam; an application unit applying the foam to the target application member; and a supplying unit introducing the foam from the foam forming unit and supplying the foam to the application unit through a supply opening. In this configuration, the supplying unit includes a discharge opening through which the foam that has not been supplied to the application unit is discharged, and the amount of foam introduced into the supplying unit is greater than that of foam supplied to the application unit. 
     According to another aspect of the present invention, a foam application device applies foam to a target application member, the foam being prepared by foaming at least one of a fluid or a gel. The foam application device includes an application unit applying the foam; a channel collecting extra foam remaining without the foam having been applied; and a heat unit heating the extra foam on the channel to return the extra foam to a liquid form. 
     It should be noted that in the description, the term “foam” (may be also referred to as “foam-like fluid”, or “foam-like gel”) may refer to a fluid or a gel in foam form in which a large number of air bubbles are dispersed in the fluid or the gel so as to form the fluid or the gel with compressibility (aggregation of micro-bubbles) when the foam is being applied. In other words, the term “foam” may refer to a fluid or a gel bubble having a round shape and containing gas such as air inside the round shape, and is formed due to the surface tension of the fluid or the gel containing the gas inside so that a cubic (three-dimensional) shape of the foam can be sustained for a certain period of time. It should be noted that to sustain the cubic shape for the certain period of time, preferably, the foam has a bulk density equal to or less than 0.05 g/cm 3 , the distribution range of the foam bubble diameters is between 10 μm and 1 mm, and an average foam bubble diameters is equal to or less than 100 μm. Further, the shape of a foam bubble is spherical when the foam bubble independently exists. However, when plural foam bubbles are aggregated together, each shape of the foam bubbles may become polyhedral due to their surface tensions. Further, the term “gel” refers to a semi-consolidated material having a net or honeycomb shape in which colloidal solution and high-molecular components dispersed in a disperse medium lose their independent mobility due to their mutual interactions and the particles of the material are in contact with each other. 
     EFFECTS OF THE PRESENT INVENTION 
     In an image forming apparatus and a foam application device according to an embodiment of the present invention, a discharge opening is formed on the supplying unit supplying the foam through the supply opening to the application unit applying foam to the target application member; and the amount of foam introduced into the supplying unit is greater than the amount of foam supplied to the application unit. By having these features, it may become possible to uniformly apply a fluid, a gel, or a fluid and a gel so as to form a film having a substantially even thickness, control the supply amount easily, and maintain the quality of the foam to be applied at a certain level. 
     Further, an image forming apparatus and a foam application device according to an embodiment of the present invention include the application unit applying the foam; the channel collecting extra foam remaining without having been applied; and the heat unit heating the extra foam on the channel to return the extra foam to a liquid form. By having these features, it may become possible to uniformly apply a fluid, a gel, or a fluid and a gel so as to form a film having a substantially even thickness, collect the extra foam, and waste the collected extra foam when necessary to maintain the quality of the foam to be applied at a certain level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing an exemplary configuration of an image forming apparatus including a foam application device according to an embodiment of the present invention; 
         FIG. 2  is a view showing another exemplary configuration of an image forming apparatus including a foam application device according to an embodiment of the present invention; 
         FIG. 3  is a view showing still another exemplary configuration of an image forming apparatus including a foam application device according to an embodiment of the present invention; 
         FIG. 4  is a view showing still another exemplary configuration of an image forming apparatus including a foam application device according to an embodiment of the present invention; 
         FIG. 5  is a schematic view showing an example of a foam forming section of the foam application device; 
         FIG. 6  is a schematic perspective view showing a first example of a reservoir section of the foam application device; 
         FIG. 7  is a schematic perspective view showing an example of an application amount/application area adjusting section of the foam application device; 
         FIG. 8  is a schematic perspective view showing another example of the application amount/application area adjusting section of the foam application device; 
         FIG. 9  is a view illustrating the adjustment of an application film thickness in the foam application device; 
         FIG. 10  is a schematic perspective view showing a second example of the reservoir section of the foam application device; 
         FIG. 11  is a schematic perspective view showing a third example of the reservoir section of the foam application device; 
         FIG. 12  is a schematic perspective view showing a fourth example of the reservoir section of the foam application device; 
         FIG. 13  is a perspective view showing an example of a heating device; 
         FIG. 14  is a perspective view showing another example of the heating device; 
         FIG. 15  is a perspective view showing still another example of the heating device; 
         FIG. 16  is a schematic view showing where extra foam bubbles are collected in the foam forming section in an image forming apparatus in  FIG. 4 ; 
         FIG. 17  is a schematic view showing a foam collection and cleaning operation in the foam forming section in an image forming apparatus in  FIG. 4 ; 
         FIG. 18  is a flowchart showing a process of the operations (a first mode operation) during the foam application; 
         FIG. 19  is a flowchart showing a process of the operations (a second mode operation) during the foam collection and cleaning operation; 
         FIG. 20  is a schematic block diagram of a control section of the image forming apparatus; 
         FIG. 21  is a flowchart showing an exemplary printing process by the control section; 
         FIG. 22  is a flowchart showing a process following the process in  FIG. 21 ; 
         FIG. 23  is a flowchart showing a process following the process in  FIG. 21 ; 
         FIGS. 24A and 24B  are partially enlarged views showing parts where the application surface of an application roller is in contact with unfixed resin fine particles when a relatively high pressure is applied on the contact surface between the application roller and a recording medium in a case where the foam application device is applied to an electrophotographic-type image forming apparatus; and 
         FIGS. 25A and 25B  are partially enlarged views showing parts where the application surface of an application roller is in contact with unfixed resin fine particles when a relatively low pressure is applied on the contact surface between the application roller and a recording medium in a case where the foam application device is applied to an electrophotographic-type image forming apparatus. 
     
    
    
     DESCRIPTION OF THE REFERENCE NUMERALS 
     
         
         
           
               100 : RECORDING TARGET MEDIUM (SHEET) 
               101 : RECORDING HEAD UNIT 
               102 : FEEDING BELT 
               103 : SHEET FEED TRAY 
               200 : FOAM APPLICATION DEVICE 
               201 : TREATMENT FLUID (A FLUID, A GEL, OR A FLUID AND GEL TO BE FOAMED) 
               205 : FOAM FORMING SECTION 
               210 : FOAM BUBBLES 
               211 : RESERVOIR SECTION 
               212 : APPLICATION ROLLER 
               231 : INTRODUCING OPENING 
               232 : SUPPLY OPENING 
               233 : APPLICATION AMOUNT/APPLICATION AREA ADJUSTING SECTION 
               234 : DISCHARGE OPENING 
               401 : DISCHARGE CHANNEL 
               402 : DISCHARGING PUMP 
               501 : HEATING DEVICE 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     In the following, embodiments of the present invention are described with reference to the accompanying drawings. First, an example of an image forming apparatus having a foam application device according to a first embodiment of the present invention is described with reference to  FIG. 1 .  FIG. 1  is a schematic diagram showing an exemplary configuration of the image forming apparatus. As shown in  FIG. 1 , the image forming apparatus includes a recording head unit  101 , a feeding belt  102 , a sheet feed tray  103 , and a foam application device  200  (a device for applying foam bubbles to an application target member) according to an embodiment of the present invention. The recording head unit  101  serves as an image forming unit by ejecting droplets onto a sheet  100  as a recording medium to be recorded to form an image on the sheet  100 . The sheets  100  are stacked in the sheet feed tray  103 . The feeding belt  102  feeds the sheet  100 . The foam application device  200  is provided on the upstream side of the recording head unit  101  and applies a foam-like liquid to the sheet  100  which is an application target member. 
     The recording head unit  101  has the line-type fluid ejection heads for ejecting droplets. Each of the line-type fluid ejection heads has plural nozzles arranged along the width direction of the sheet  100 . Namely, the recording head unit  101  includes recording heads  101   y ,  101   m ,  101   c , and  101   k  for ejecting yellow (Y), magenta (M), cyan (C), and black (K) ink-droplets, respectively. It should be noted that the recording heads may be mounted on a carriage as the serial-type image forming apparatus. 
     The feeding belt  102  is an endless belt extended between a feeding roller  121  and a tension roller  122  to rotate between the rollers. The sheet  100  may held to the feeding belt  102  by using electrostatic attraction, vacuum suction, or other known holding means. 
     The sheets  100  stacked in the sheet feed tray  103  are picked up one by one by a pickup roller  131 , and fed through a feeding path  135  and held onto the feeding belt  102  by a feeding roller pair  132  and another feed roller pair not shown). 
     Next, in the foam application device  200 , foam bubbles  210  are applied to the sheet (hereinafter may be also referred to as a “recording target medium”)  100  as the application target member fed on the feeding belt  102 . The foam bubbles  210  applied to the sheet  100  are rapidly dried, and the droplets of each color are ejected from the recording head unit  101  to form an image on the sheet  100 . Then, the sheet  100  is discharged to a discharge tray (not shown). 
     On the other hand, as shown in  FIG. 1 , the foam application device  200  includes a container  202 , a pump  203 , a foam forming section  205 , a reservoir section (or a “foam supplying section”)  211  and an application roller (or an “application member”)  212 . The container  202  contains a fluid, a gel, or a fluid and gel (hereinafter collectively referred to as a “treatment fluid” or a “set agent”)  201  that can be changed to a foam form. The pump  203  pumps the treatment fluid  201  from the container  202 . The foam forming section  205  forms the foam bubbles  210  from the treatment fluid  201  supplied from the pump  203  through a supply channel  204 , each foam bubbles  210  having a short diameter so as to be adapted to the application of the foam bubbles  210 . The foam bubbles  210  formed in the foam forming section  205  are introduced into the reservoir section  211  through a supply channel  206  and an introducing opening  231 . In the reservoir section  211 , the foam bubbles  210  are elongated and developed in the width direction of the recording target medium  100  (or may be an intermediate medium). The elongated and developed foam bubbles  210  are applied to the outer surface of the application roller  212  so that the application roller  212  serves as an applying unit applying the foam bubbles  210  to the recording target medium  100 . 
     Further, the reservoir section  211  may adjust the amount of the foam bubbles  210  to be supplied to the application roller  212  (accordingly, an amount of the foam bubbles  210  applied from the application roller  212  to the recording target medium  100 ) by varying the fluid resistance of the foam bubbles  210  at a supply opening  232  (shown in  FIG. 1 ). The reservoir section  211  further includes an application amount/application area adjusting section  233  and a discharge opening  234 . The application amount/application area adjusting section  233  determines a supply area on the application roller  212  to which the foam bubbles  210  are supplied (namely, an application area defined by the application roller  212 ) by varying the size and the area of the supply opening  232  determined by the degree of opening/closing of the application amount/application area adjusting section  233 . The foam bubbles  210  that have not been supplied to the application roller  212  (extra foam bubbles  210 ) are discharged through the discharge opening  234 . 
     Further, in the foam application device  200 , there is provided a discharge channel  401  by which there is communication between the discharge opening  234  and the container  202 . An adjusting valve  403  and a discharging pump  402  are provided on the discharge channel  401 . The adjusting valve  403  controls the amount of foam bubbles  210  to be discharged through the discharge opening  234  by varying the fluid resistance of the foam bubbles  210  at the discharge opening  234 . The discharging pump  402  not only assists the discharge of the foam bubbles  210  from the discharge opening  234  to the container  202  but also defoams the foam bubbles  210  by compressing the foam bubbles  210 . It should be noted that the foam bubbles  210  may be discharged to another tank such as a waste tank. 
     The foam application device  200  further includes a thickness control section  214  and a cleaning member  215 . The thickness control section  214  controls the film thickness (application film thickness) of the foam bubbles  210  applied to the outer surface of the application roller  212 . The cleaning member  215  removes the applied foam bubbles  210  remaining on the outer surface of the application roller  212 . 
     Herein, the treatment fluid  201  that is formable may be a reforming agent reforming the surface of the sheet  100  upon being applied to the surface. For example, by uniformly applying the foam (fluid)  210  to the sheet  100  (not limited to paper as a material, as described), it becomes possible to promote the penetration of the water component of the ink, thicken the ink color components, and accelerate the drying of the ink, thereby serving as a fixing agent (a setting agent) capable of avoiding blurs (such as feathering and bleeding) and strike-through and improving the productivity (increasing the number of output sheets per unit time). 
     The treatment fluid  201  may be a solution including as components a surface active agent (one of anionic, cationic, and nonionic agents, or any combination thereof), a cellulose derivative (such as hydroxypropylcellulose) promoting the penetration of water, and a base such as talc particles. Fine particles may be added to the treatment fluid  201 . 
     Preferably, as the foam content, the foam bubbles  210  have a bulk density of from about 0.01 g/cm 3  to about 0.1 g/cm 3 . 
     By applying the foam bubbles  210  including a large amount of air to the sheet  100  as described above, it becomes possible to uniformly apply a small amount of fluid, that dries quickly, and obtain a high-quality image without causing blur, strike-through, uneven density, and the like. 
     Namely, when compared with a case where a treatment fluid in a fluid or mist form is applied, the application of the foamed treatment fluid may have the following advantages (effects): 
     (1): Foam includes a large amount of air. Therefore, applying only a small amount of fluid may be enough. 
     (2): Characteristics of foam are similar to those of solid materials. Therefore, the film thickness of applied foam may be easily controlled by, for example, cutting off the foam bubbles that have been applied. Further, when the foam bubbles are applied from an applying section to a sheet, the foam bubbles exhibit an excellent detachability from the applying section. Therefore, the foam can be uniformly applied. 
     (3) The water component of the applied foam hardly penetrates into the fibers of the sheet. Therefore, a wrinkle or a curl of the sheet may hardly occur. 
     Such advantages of applying foam may be commonly observed when any type of treatment fluid is used. Preferably, the treatment fluid  201  may further have the effects of controlling the generation of paper powder from the sheet  100  and changing the background color of the sheet  100 . 
     On the other hand, in order to uniformly apply foam along the width direction with respect to the recording target medium (or may be an intermediate medium for further applying the applied foam to its recording target medium), it is necessary to sufficiently elongate and develop the foam bubbles in the above direction before the foam bubbles are applied. However, as described above, the characteristics of the foam bubbles are similar to those of solid materials. Therefore, it may not be easy to elongate and develop the foam bubbles along the width direction of the recording target medium or the intermediate medium. In addition, it may be difficult to control the amount of foam bubbles to be supplied to the applying section and to substantially maintain the bulk density, the foam density, and the diameters of the foam bubbles at certain target levels. 
     To overcome the difficulties, according to an embodiment of the present invention, in the foam supplying section supplying foam bubbles to the applying section through the supply opening so that the foam bubbles can be supplied from the applying section to the target application member, the discharge opening is formed to discharge the foam bubbles that have not been applied to the applying section, so that a larger number of foam bubbles than is necessary to be supplied to the applying section are introduced into the foam supplying section. By having this configuration, it becomes possible to allow the treatment fluid to be uniformly applied to form a film of the applied foam bubbles having a substantially even thickness, easily control the amount of foam bubbles to be applied, and maintain the quality of the foam bubbles to be applied at a certain level, thereby enabling improving the quality of the images formed on the sheet. 
     First, an exemplary configuration of the foam forming section  205  in the foam application device  200  is described with reference to  FIG. 5 . As shown in  FIG. 5 , the foam forming section  205  includes a container  221  containing the treatment fluid  201  pumped from container  202  by the pump  203 , a porous member  222  having a cylindrical shape disposed in the container  221 , and a gas supplying section  223  supplying gas inside the porous member  222 . The gas supplying section  223  may have a fan and a duct to blow air inside the porous member  222 . Further, one end of the supply channel  206  surrounds the porous member  222  so that the treatment fluid  201  to be foamed is sufficiently supplied to the porous member  222 , and first slits  224  and second slits  225  are provided at the inlet section of the supply channel  206  (in the vicinity of the porous member  222 ) so that the formed foam bubbles  210  do not randomly spread around inside the container  221 . 
     In this foam forming section  205 , the foam bubbles  210  are formed out of the treatment fluid  201  by supplying air inside the porous member  222 . While gas is being supplied, the formed foam bubbles  210  move (are fed) inside the supply channel  206  due to their own driving power (kinetic energy) to the reservoir section  211 . When the air supply is stopped, the formation of the foam bubbles  210  is stopped, and accordingly, the movement of the foam bubbles  210  is stopped. As is described above, foam bubbles  210  move due to their own driving power. Therefore, the foam bubbles  210  can be moved and stopped without any additional moving means for moving foam bubbles. 
     Next, an exemplary configuration of the reservoir section  211  in the foam application device  200  is described with reference to  FIG. 6 .  FIG. 6  is a schematic perspective view of the reservoir section  211 . 
     As shown in  FIG. 6 , the reservoir section  211  includes a foam reservoir container  300  and the application amount/application area adjusting section  233 . In the foam reservoir container  300 , there are provided an introduction opening  231  through which the foam bubbles  210  are supplied from the foam forming section  205  through the supply channel  206 , the supply opening  232  through which the foam bubbles  210  are supplied to the application roller  212 , and the discharge opening  234  through which the extra foam bubbles  210  are discharged. The application amount/application area adjusting section  233  is for varying the area of the supply opening  232 . 
     In the reservoir section  211 , the foam bubbles  210  supplied from the foam forming section  205  through the introduction opening  231  into the foam reservoir container  300  are pushed toward the side of the application roller  212  through the supply opening  232 . When the adjusting valve  403  is closed and the foam bubbles  210  are supplied to the reservoir section  211 , pressure is generated by the supply of the foam bubbles  210 . Due to the pressure, the foam bubbles  210  in the reservoir section  211  are elongated and developed along the width direction of the sheet  100 . In this case, the adjusting valve  403  is controlled to adjust the pressure so that the foam bubbles  210  be distributed throughout the reservoir section  211 . 
     Then, at a prescribed timing, the adjusting valve  403  is open, so that while more foam bubbles  210  than is necessary to be supplied to the application roller  212  are being introduced (supplied) into the inside of the foam reservoir container  300 , the extra foam bubbles  210  are discharged to the discharge channel  401  through the discharge opening  234 . By doing this, it becomes possible to sufficiently apply the foam bubbles  210  along the prescribed width direction of the sheet  100 . It should be noted that by controlling the adjusting valve  403 , it becomes possible to vary the fluid resistance of the foam bubbles  210  at the discharge opening  234  so that the foam bubbles  210  in the reservoir section  211  be preferentially supplied to the application roller  212 . 
     The application amount/application area adjusting section  233  may include an adjustment plate  233   a  moving in the vertical direction to open/close the supply opening  232  as shown in  FIG. 7 . Otherwise, the application amount/application area adjusting section  233  may include not only the adjustment plate  233   a  moving in the vertical direction but also another adjustment plate  233   b  moving in the lateral direction (corresponding to the width direction of the sheet  100 ) to open/close the supply opening  232  as shown in  FIGS. 6 and 8 . 
     In the case of  FIG. 7  where the application amount/application area adjusting section  233  includes only the adjustment plate  233   a , the fluid resistance of the foam bubbles  210  at the supply opening  232  may be adjusted by varying the size of the supply opening  232  defined by moving the adjustment plate  233   a  in the vertical direction. By doing this, it becomes possible to adjust the application area on the application roller  212  with respect to the rotational direction of the application roller  212 , thereby enabling controlling the application area on the sheet  100  with respect to the feeding direction of the sheet  100 . On the other hand, in the case of  FIG. 8  where the application amount/application area adjusting section  233  includes not only the adjustment plate  233   a  but also the adjustment plate  233   b , the fluid resistance of the foam bubbles  210  at the supply opening  232  may be adjusted by varying the size of the supply opening  232  defined by moving the adjustment plate  233   a  in the vertical direction and moving the adjustment plate  233   b  in the lateral direction. By doing these things, it becomes possible to adjust the application area on the application roller  212  with respect to the rotational and the lateral directions of the application roller  212 , thereby enabling controlling the application area on the sheet  100  with respect to the feeding and the width (orthogonal to feeding) directions of the sheet  100 . In  FIG. 8 , the adjustment plate  233   b  is provided on one side of the supply opening  232 . However, two adjustment plates  233   b  may be provided one on each side of the supply opening  232  so that the center with respect to the width direction of the sheet  100  becomes the center reference point when the sheet  100  is fed the feeding direction. 
     Further, the thickness control section  214  provided as shown in  FIG. 9  optimally controls the film thickness of the foam bubbles  210  applied on the outer surface of the application roller  212  by adjusting the distance from the thickness control section  214  to the application roller  212 . Further, for example, by performing a prescribed operation on a display operations section of an image forming apparatus, it becomes possible to move the thickness control section  214  by using driving means (not shown) in the tangential or normal direction with respect to the circumferential surface of the application roller  212 . By doing this, it becomes possible to set an optimal application film thickness of the applied foam bubbles. 
     Next, other examples of an image forming apparatus having a foam application device according to other embodiments of the present invention are described with reference to  FIGS. 2 through 4 . In the figures, the same reference numerals are used for the same components in  FIG. 1  and the descriptions thereof are herein omitted. As shown in  FIG. 2 , on the discharge channel  401  providing communication between the discharge opening  234  and the container  202 , a heating device  501  is provided on the downstream side of the discharging pump  402 . The heating device  501  heats the extra foam bubbles discharged through the discharge channel  401  and returns the discharged foam bubbles to a liquid form. 
     When the foam bubbles are heated by the heating device  501 , the films of the foam bubbles are dried and the thickness of the films becomes thinner. In addition, the internal part of the foam bubbles is thermally expanded and accordingly the internal pressure of the foam bubbles is increased. As a result, the thickness of the films becomes further thinner, thereby sufficiently defoaming the foam. After being defoamed, the foam bubbles becomes a discharge liquid (herein referred to as a “reduction treatment liquid”). This reduction treatment liquid may be collected in the container  202  to be used as the foam again. 
     In this example, the discharge channel  401  is in communication with the container  202  which is a treatment liquid containing section for containing the treatment fluid  201 . However, as shown in  FIG. 3 , the discharge channel  401  may be in communication with a waste tank  503  which is a waste liquid containing section. Otherwise, as shown in  FIG. 4 , the discharge channel  401  may be in communication with the foam forming section  205  so that the discharged foam can be foamed in the foam forming section  205  to be used again. 
     As described above, the foam bubbles  210  is a fluid or a gel having a round shape and containing gas such as air inside the round shape, and is formed due to the surface tension of the fluid or the gel containing the gas inside so that a cubic (three-dimensional) shape of the foam can be maintained for a certain period of time. Preferably, the foam has a bulk density equal to or less than 0.05 g/cm 3 , the distribution range of the foam bubble diameter is between 10 μm and 1 mm, and an average foam bubble diameter is equal to or less than 100 μm. Further, the shape of a foam bubble is spherical when the foam bubble exists alone. However, when plural foam bubbles are aggregated together, each shape of the foam bubbles becomes polyhedral due to their surface tensions. 
     Next, another example of an image forming apparatus having a foam application device according to a second embodiment of the present invention is described with reference to  FIG. 10 .  FIG. 10  is a schematic diagram showing an exemplary configuration of the reservoir section in the foam application device. As shown in  FIG. 10 , the reservoir section  211  includes a foam reservoir container  700  having a cylindrical shape. The introduction opening  231  is formed on one end side in the axis direction of the foam reservoir container  700 . The discharge opening  234  is formed on the other end side in the axis direction of the foam reservoir container  700 . Further, in the foam reservoir container  700 , a feeding agitation member  701  having a screw shape is disposed along the axis direction of the foam reservoir container  700 , so that the foam bubbles  210  can swiftly and uniformly spread around the supply opening  232  as the feeding agitation member  701  rotates. By having this structure, it becomes possible to feed the foam bubbles  210  from the introduction opening  231  to the discharge opening  234  in a short period. 
     Further, as shown in  FIG. 10 , the introduction opening  231  and the discharge opening  234  may be formed on the upper and lower sides of the reservoir container  700 , respectively. By doing this, it may become possible to effectively collect the foam which is lacking uniformity due to defoaming of the foam bubbles  210 . This is because defoamed foam bubbles are likely to be sunk due to their greater specific gravity. Therefore, preferably, the discharge opening  234  is formed lower than the introduction opening  231 . More preferably, the discharge opening  234  is formed at the lowest part of reservoir container  700 . 
     Next, still another example of an image forming apparatus having a foam application device according to a third embodiment of the present invention is described with reference to  FIG. 11 .  FIG. 11  is a schematic plan view showing an exemplary configuration of the reservoir section in the foam application device. As shown in  FIG. 11 , a channel  711  provides communication between the introduction opening  231  and the discharge opening  234 , and the width of the channel  711  becomes narrower as the foam approaches the discharge opening  234 . The supply opening  232  is formed along the direction from the introduction opening  231  to the discharge opening  234  (parallel to the axis direction of the application roller  212 ). By having this structure, a supply pressure of the foam bubbles  210  becomes constant along the longitudinal direction of the supply opening  232  and a time period required to fill the entire reservoir section  211  with the foam bubbles  210  may be reduced because the width of the channel  711  is gradually reduced. 
     Next, still another example of an image forming apparatus having a foam application device according to a fourth embodiment of the present invention is described with reference to  FIG. 12 .  FIG. 12  is a schematic plan view showing an exemplary configuration of the reservoir section in the foam application device. As shown in  FIG. 12 , the discharge openings  234  are formed one on each side of the reservoir container  700 , and the introduction opening  231  is formed between the discharge openings  234 . The supply opening  232  is formed along the arranging direction of the discharge opening  234 , the supply opening  232 , and the other discharge opening  234  (parallel to the axis direction of the application roller  212 ). By having this structure, the foam bubbles  210  introduced through the introduction opening  231  are spread toward both side ends simultaneously and the distance necessary for the foam bubbles  210  to be spread throughout the reservoir container  700  becomes shorter. Therefore, the foam bubbles  210  may fill the reservoir section  211  in a shorter time period. Further, the distance between the supply opening  232  and each of the discharge openings  234  becomes shorter. Therefore, the supply pressure of the foam bubbles  210  along the longitudinal direction of the supply opening  232  may become substantially constant more accurately. 
     Preferably, each of the discharge openings  234  is disposed outside the application roller  212  (outside of the supply opening  232 ) with respect to the width direction of the sheet  100 . By having this structure, residual foam bubbles  210  may be avoided and the defoamed foam lacking uniformity may be discharged more easily. 
     Next, exemplary configurations of the heating device  501  are described with reference to  FIGS. 13 through 15 . Each of the heating devices  501  is provided on the discharge channel  401 , and as is described above, defoams the extra foam bubbles discharged in the discharge channel  401  (returns the discharged foam bubbles to a liquid form) by heating the extra foam bubbles. The heating device  501  shown in  FIG. 13  includes a heat transfer section  505  and a heating section  504  transferring heat to the heat transfer section  505 . 
     As shown in  FIG. 13 , the heat transfer section  505  may have plural holes (through holes)  505   a  formed along the direction parallel to the discharge direction of the foam bubbles to increase the area for contacting the foam bubbles. However, the shape or the configuration of the heat transfer section  505  is not limited to this. The similar effect to that in  FIG. 13  may be obtained when the heat transfer section  505  has comb-shaped fins  505   b  like a heatsink as shown in  FIG. 14  or has a net filter as shown in  FIG. 15 . Namely, preferably, the heat transfer section  505  has a structure having as many surface areas to contact the extra foam bubbles discharged through the discharge channel  401  as possible. Further, the heat transfer section  505  may be made of aluminum having excellent heat conductivity and corrosion resistance. However, the material of the heat transfer section  505  is not limited to aluminum. For example, the heat transfer section  505  may be formed of a copper alloy, a metal such as an SUS, or a plastic having excellent heat conductivity. 
     In the example of  FIG. 13 , the heating section  504  is formed so as to cover the circumference of the heat transfer section  505 . However, the heating method or the heat transfer method are not limited to those described above. For example, the heat transfer method may be based on any of conduction, convention, and radiation, and the heating method may be microwave heating, electromagnetic induction heating, radiant heating, resistance heating, or the like. 
     Next, an example (in  FIG. 4 ) where the reduction treatment liquid is collected into the foam forming section  205  is described with reference to  FIGS. 16 and 17 . 
     The discharging pump  402  is provided on the upstream side of the heating device  501 , so that the extra foam bubbles are discharged toward the downstream side. On the downstream side of the discharging pump  402 , the extra foam bubbles are heated by the heating device  501  to be defoamed and returned to a liquid form. 
     Further, on the downstream side of the heating device  501 , the discharge channel  401  is divided into two channels  506  and  508 , and valves  505  and  507  are provided on the channels  506  and  508 , respectively. On the downstream side of the valve  505 , the channel  506  is in communication with the inside of the porous member  222  having a cylindrical shape. On the downstream sides of the valve  507 , the channel  508  is provided to the inside of the container  221 , so that the channel  508  is in communication with the atmosphere above the liquid surface or the inside of the treatment fluid  201  in the container (foam foaming container)  221 . Further, an atmosphere communication channel  510  is provided to cause communication between the inside of the container  221  and the atmosphere outside the container  221 . On the atmosphere communication channel  510 , an atmosphere open valve  509  for opening/closing the atmosphere communication channel  510  is provided so that the air inside of the container  221  is released to outside the container  221 . 
     Next, in the example where the reduction treatment liquid is collected into the foam forming section  205 , an operation controlled by a foam controlling section described below during the foam application is described with reference to a flowchart of  FIG. 18 . 
     In this operation during the foam application, the atmosphere open valve  509  for the foam foaming container  221  is closed; the discharging pump  402  is activated to operate; the valve  507  is closed, the valve  505  is open; and the heating device  501  is deactivated. 
     Namely, during the foam application, the foam bubbles  210  foamed in the foam forming section  205  are fed to the reservoir section  211  and applied to the application roller  212  for the foam application. Then, the extra foam bubbles remaining in the reservoir section  211  without being applied to the application roller  212  are fed toward the foam forming section  205  by the discharging pump  402  through the discharge channel  401 . Then, since the valve  507  on the channel  508  is closed and the valve  505  on the channel  506  is open, the extra foam bubbles are fed to the inside of the porous member  222  having a cylindrical shape through the channels  506  so that the extra foam bubbles may be used for another foam forming. 
     Then, during the foam application, since the extra foam bubbles are used for another foam forming, it is not necessary to defoam the extra foam bubbles. Therefore, the heating device  501  is deactivated. Namely, the extra foam bubbles are fed and collected in the foam forming section  205  without being heated by the heating device  501  to be returned to a liquid form. Further, the atmosphere open valve  509  is closed to maintain the pressure in the container  221  substantially constant. In this description, the operation during the foam application is referred to as a first mode operation. 
     Next, a control in a case where the process of the foam application is finished and the extra foam bubbles are collected and cleaned is described with reference to a flowchart of  FIG. 19 . 
     In the foam collection and cleaning operation, the atmosphere open valve  509  for the foam foaming container  221  is open, the pump  203  is reversely rotated so that the treatment fluid  201  is fed toward the container  202  from the foam foaming container  221 . After the surface height of the treatment fluid  201  in the foam foaming container  221  is lowered to a prescribed level, the heating device  501  is activated for heating; the discharging pump  402  is activated for pumping; the valve  505  is closed; and the valve  507  is open. 
     Namely, to collect the extra foam bubbles, the atmosphere open valve  509  is open to maintain the atmosphere pressure in the foam foaming container  221  substantially equal to the atmosphere outside the foam foaming container  221 , the treatment fluid  201  in the foam foaming container  221  is fed into the container  202  to lower the surface height of the treatment fluid  201  in the foam foaming container  221  to the level where foam bubbles cannot be formed (lower than that of the first slits  224 ). In this state, by operating the discharging pump  402 , a negative pressure is generated in the supply channel  206 , and gas is introduced into the supply channel  206  through the first slits  224 , so that the foam bubbles in the entire supply channel  206  may be substantially fully pushed out to the reservoir section  211 . 
     Then, the heating device  501  is activated and the discharging pump  402  is operated. By doing this, the extra foam bubbles are discharged from the reservoir section  211  to the discharge channel  401 . and the discharged extra foam bubbles are heated by the heating device  501 , so that the extra foam bubbles are exploded and separated into fluid and gas. During this process, the valve  505  is closed and the valve  507  is open. Therefore, a liquid defoamed from the foam bubbles (reduction treatment liquid) is discharged to the fluid surface of the treatment fluid  201  in the foam foaming container  221  from the upper side of the foam foaming container  221  through the channel  508 . In this description, this foam collection and cleaning operation is referred to as a second mode operation. 
     In this case, a mixture of gas and liquid is discharged from the outlet of the divided channel  508 . If the mixture is discharged from the outlet of the divided channel  508  directly in the treatment fluid  201 , the treatment fluid  201  may be foamed again when the gas rises in the treatment fluid  201  from the outlet of the divided channel  508 . To avoid the foaming of the treatment fluid  201  again, as described above, the liquid surface of the treatment fluid  201  in the container  221  is lowered and the mixture is discharged above the liquid surface of the treatment fluid  201 . 
     Next, the control section of the above image forming apparatus is briefly described with reference to the block diagram of  FIG. 20   
     As shown in  FIG. 20 , the control section may include a CPU  801 , a ROM  802 , a RAM  803 , an operations display section  804 , various sensors  805 , various motors  806 , an I/O control section  807 , an image reading device (scanner)  808 , a reading control section  809 , a plotter section (print mechanism section)  810 , a print control section  811 , a network control device  812 , a communication control section  813 , and a foam application control section  814 . The CPU  801  performs system control of the image forming apparatus. The ROM  802  stores, for example, programs to be executed by the CPU  801 . The RAM  803  is used as a working area. An operator can perform various settings on the operations display section  804 . The various sensors  805  detect size of the sheet, jams, and the like. The I/O control section  807  transmits and receives control signals to and from the various sensors  805  and the various motors  806 . The reading control section  809  controls the image reading device (scanner)  808 . The print control section  811  controls the plotter section (print mechanism section)  810 . The communication control section  813  controls the network control device  812  performing I/F control for a telephone line and various facsimile communications, and the like. The foam application control section  814  controls the foam application device  200 . 
     In this case, the various sensors  805  include a liquid end detector detecting whether the treatment fluid  201  is present in the container  202 ; the various motors  806  include motors for driving the pump  203 , the application amount/application area adjusting section  233 , and the thickness control section  214 , and rotating the application roller  212 , the feeding roller  121 , the feeding roller pair  132 , the pickup roller  131 , and the like. 
     Further, in addition to the control of the foam application, the foam application control section  814  performs other controls during the foam application and the control of the foam collection and cleaning operation as described with reference to  FIGS. 18 and 19 . 
     An exemplary printing operation in the image forming apparatus is described with reference to the flowcharts in  FIGS. 21 through 23 . 
     Referring to  FIG. 21 , when an image output request is received, it is determined whether the treatment fluid (setting agent) application function is activated. Then, when it is determined that the treatment fluid application function is activated, it is further determined whether at least a prescribed amount of the treatment fluid  201  is present in the container  221  of the foam forming section  205 . When it is determined that less than the prescribed amount of the treatment fluid  201  is present in the container  221 , the pump  203  is operated to supply the treatment fluid  201  from the container  202  to the container  221  of the foam forming section  205 . On the other hand, when it is determined that at least the prescribed amount of the treatment fluid  201  is present in the container  221 , gas is supplied to the foam forming section  205  to form the foam bubbles  210  without supplying additional treatment fluid  201  to the container  221 . By doing this, as described above, the foam bubbles  210  are supplied to the reservoir section  211  and elongated and developed in the reservoir section  211 , and the extra foam bubbles  210  are discharged through the discharge opening  234  and the discharge channel  401 . 
     Then, as shown in  FIG. 22 , the discharge channel  401  and the feeding belt  102  are driven to start the operations, and the application amount/application area adjusting section  233  moves to open the supply opening  232  at a prescribed timing to start applying the foam bubbles  210  to the surface of the application roller  212 . By doing this, the foam bubbles  210  are applied to the surface of the application roller  212  and thickness control section  214  controls the thickness of the applied foam bubbles  210  so that the foam bubbles  210  have a prescribed thickness, and the applied foam bubbles  210  are transferred to the feeding belt  102 . 
     Then, the recording target medium (sheet)  100  is fed from the sheet feed section (sheet feed tray  103 ) to the feeding belt  102 . The foam bubbles  210  are applied to the fed recording target medium  100  by the application roller  212 , and a printing operation starts when the recording section of the recording target medium  100  reaches the recording head unit  101 . On the other hand, when the amount of the foam bubbles  210  applied to the application roller  212  reaches the necessary amount for the printing area of the sheet  100 , the supply opening  232  is closed by the movement of the amount/application area adjusting section  233  of the reservoir section  211  to stop the supply of the foam bubbles  210  to the application roller  212 . 
     After the printed recording target medium  100  is discharged, the same process from feeding the sheet is repeated until all necessary sheets are printed. When the all necessary sheets are printed, the supply of the gas to the foam forming section  205  is stopped to stop forming the foam bubbles. Then, the operations of the feeding roller  121  and the feeding roller pair  132  are stopped. Then, after a prescribed time period necessary for the successful completion of the cleaning operation, the feeding belt  102  and the application roller  212  are stopped. 
     On the other hand, in the process of  FIG. 21 , when it is not necessary to apply the foam bubbles  210  of the treatment fluid  201  because, for example, a special type of the recording target medium  100  is used, the treatment fluid application function should be deactivated. When the treatment fluid application function is not activated, the process goes to the process shown in  FIG. 23 . In the process, the feeding belt  102  and the application roller  212  are operated, and the recording target medium  100  is fed from the sheet feed section, printed by the recording head unit  101 , and discharged. Then, when all the necessary media are printed, the operations of the feeding roller  121  and the feeding roller pair  132  are stopped. Then, after a prescribed time period, the feeding belt  102  and the application roller  212  are stopped. 
     In this process, the application roller  212  is being rotated. This is because the maximum gap between the application roller  212  and the feeding belt  102  is narrower than the of total thickness of the thickness of the sheet  100  and the thickness of the foamed setting agent (foam)  210 . Therefore, application roller  212  is rotated so as not to obstruct the feeding of the recording target medium  100 . 
     It should be noted that in the above embodiment, the foam application device  200  applies foam bubbles to the sheet on which an image is to be formed. However, for example, the foam application device  200  may be disposed on the downstream side of the recording head unit so that the foam bubbles are applied to the sheet on which an image has been formed already. Further, in the above embodiment, the foam bubbles are formed of a liquid that can be foamed. However, for example, the present invention may also be applied to a device capable of applying the foam bubbles to an application member, the foam bubbles being formed of a gel that can be foamed, and an image forming apparatus including the device. 
     Further, in the above embodiment, a case is described where the extra foam bubbles that have not been supplied to the application member (application means such as the application roller) are collected. However, the foam bubbles remaining on the application member may be scraped off and cleaned by a cleaning member, so that the foam bubbles scraped off by the cleaning member are collected through a channel, and a heating device may be provided on the channel. 
     Further, the foam application device according to an embodiment of the present invention may be applied to an electrophotographic-type image forming apparatus, and a fixing method, a fixing device, an image forming method, and an image forming apparatus using a foam-like fixing liquid for fixing resin fine particles to a medium by applying a small amount of the foam-like fixing liquid to the medium without leaving residual oil on the applied medium, the foam-like fixing liquid being capable of being rapidly fixed to the medium on which resin fine particles are adhered after being applied to the medium without disturbing the fine particles including resin such as toner on the medium such as a sheet. 
     Therefore, as an example, a case is described where the present invention is applied to an electrophotographic-type image forming apparatus with reference to  FIGS. 24A through 25B .  FIGS. 24A through 25B  are partially enlarged views showing a part where an application surface of a roller (roller application means) is in contact with unfixed resin fine particles.  FIGS. 24A and 24B  show cases where a relatively high pressure is applied on the contact surface between an application roller  1011  and a recording medium  1010 . On the other hand,  FIGS. 25A and 25B  show cases where a relatively low pressure is applied on the contact surface between the application roller  1011  and the recording medium  1010 . In the figures, it is assumed that the application roller  1011  rotates and the recording medium  1010  is fed in the corresponding directions designated by arrows in the figures. 
     First, the case is described where the relatively high pressure is applied on the contact surface between the application roller  1011  and the recording medium  1010 .  FIG. 24A  shows a case where a foam-like fixing liquid  1012  forming a single layer of bubbles  1013  is applied to the application surface of the application roller  1011 . It should be noted that the diameters of the bubbles shown in  FIGS. 24A through 25B  are substantially the same as each other. Therefore, a layer thickness of the foam-like fixing liquid  1012  may be thinner than that in the case of  FIG. 24B  or  25 B. However, in the case of  FIG. 24A , the single layer of bubbles  1013  is formed. In this case, the bubbles  1013  are likely to be adhered to the application surface of the application roller  1011 . Therefore, the foam-like fixing liquid  1012  may not be uniformly applied to the unfixed resin fine particles (unfixed toner)  1015  on the recording medium  1010  and as a result, the unfixed resin fine particles  1015  may be adhered to the bubbles  1013  and offset to the application surface of the application roller  1011  (toner offset). 
     On the other hand,  FIG. 248  shows a case where a foam-like fixing liquid  1012  forming plural layers of bubbles  1013  is applied to the application surface of the application roller  1011 . In this case, the bubbles  1013  may be easily adhered to the uneven surface of the unfixed resin fine particles  1015 ; the foam-like fixing liquid  1012  forming a layer of bubbles  1013  are likely to be separated from each other; and the foam-like fixing liquid  1012  may be uniformly applied to the toner layer on the recording medium  1010 . Therefore, it becomes possible to reliably prevent the toner offset. 
     Because of the feature, in the case where a relatively high pressure is applied on the contact surface between the application roller  1011  and the recording medium  1010 , it may become possible to reliably prevent the toner offset in which the unfixed resin fine particles  1015  are adhered to the application surface of the application roller  1011 , by measuring the average size of the bubbles  1013  in advance and controlling the film thickness of the layer of the foam-like fixing liquid  1012  formed on the application surface of the application roller  1011  so that the film thickness of the layer of the foam-like fixing liquid  1012  is equal to plural times of the thickness of a single layer of the bubbles  1013 . 
     Next, the case is described where the relatively low pressure is applied on the contact surface between the application roller  1011  and the recording medium  1010 .  FIG. 25A  shows a case where a foam-like fixing liquid  1012  forming a single layer of bubbles  1013  is applied to the application surface of the application roller  1011 . In this case, the bubbles  1013  may be easily adhered to the uneven surface of the unfixed toner  1015 ; a layer of bubbles is likely to be separated from the surface of the application roller  1011 ; and the foam-like fixing liquid  1012  may be applied to the surface of the unfixed toner  1015 . 
     On the other hand,  FIG. 25B  shows a case where the foam-like fixing liquid  1012  forming plural layers of bubbles  1013  is applied to the application surface of the application roller  1011 . In this case, the bubbles  1013  are more likely to bind to each other. Therefore, the bubbles  1013  are likely to remain on the surface of the application roller  1011 . Unfortunately, the unfixed toner  1015  may be adhered to the bubbles  1013  and as a result, adhered (offset) to the surface of the application roller  1011 . 
     Therefore, the toner offset in a case where a relatively low pressure is applied on the contact surface between the application roller  1011  and the recording medium  1010  (under a low-pressure condition) may be reliably prevented by measuring the average size of the bubbles  1013  in advance and controlling the film thickness of the layer of the foam-like fixing liquid  1012  formed on the application surface of the application roller  1011  so that the film thickness of the layer of the foam-like fixing liquid  1012  is equal to the thickness of a single layer of the bubbles  1013 . However, when the thickness of the layer of the bubbles  1013  on the application surface of the application roller  1011  is too thick, the bubbles  1013  are likely to move in the area between the application roller  1011  and the recording medium  1010 , thereby causing the accompanying movement of the toner particles. As a result, the image may be moved. Therefore, it is preferable to adequately control the film thickness of the layer of the foam-like fixing liquid  1012  so that the toner offset and the movement of the image can be prevented. 
     As described above, by controlling the film thickness of the layer of the foam-like fixing liquid in accordance with the size of the bubbles included in the foam-like fixing liquid and the applied pressure, it may become possible to prevent the toner offset to contact application means such as the application roller and the movement of the image and fix the unfixed resin fine particles (unfixed toner) to the recording medium with a small amount of application of the foam-like fixing liquid. 
     Namely, according to an embodiment of the present invention, a method is provided in which resin fine particles on a recording medium are fixed to the recording medium by applying a fixing liquid to the resin fine particles by using contact application means, the resin fine particles having been softened with a softener for dissolving or swelling at least a part of the resin fine particles. In this case, the fixing liquid is in foam form including bubbles when the fixing liquid is applied to and in contact with the resin fine particles. Further, by controlling the film thickness of the layer of the fixing liquid in accordance with the applied pressure, it may become possible to prevent the toner offset to contact application means such as the application roller and the movement of the image and fix the unfixed resin fine particles (unfixed toner) to the recording medium with a small amount of application of the fixing liquid. Further, the method may be effective for resin fine particles such as toner fine particles used in an electrophotographic technique. Further, by controlling the film thickness of the layer of the foam-like fixing liquid in accordance with the film thickness of the layer of the resin fine particles, it may become possible to prevent toner offset and the movement of the image. 
     The present application is based on and claims the benefit of priority of Japanese Patent Application Nos. 2007-320952, filed on Dec. 12, 2007 and 2008-229693, filed on Sep. 8, 2008, the entire contents of which are hereby incorporated herein by reference.