Patent Publication Number: US-7896966-B2

Title: Liquid applying apparatus and ink-jet printing apparatus

Description:
This application is a continuation of Internatonal Application No. PCT/JP/2006/315960, filed on Aug. 11, 2006. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a liquid applying apparatus and an ink-jet printing apparatus, and more specifically to a liquid applying apparatus for applying a liquid with a predetermined purpose such as accelerating aggregation of a pigment at printing with an ink having the pigment as a color material. Particularly, the present invention relates to control of an applying amount of the liquid to a medium. 
     BACKGROUND ART 
     As this type of applying apparatus, an apparatus is known with which a liquid to be applied is supplied to an applying member such as a roller, which applies the supplied liquid to a medium. Among the applying apparatuses using such type of an applying member, a construction to seal a portion which supplies or applies an applying liquid to a roller is described in Patent Document 1. The applying mechanism described in the document is a mechanism for applying an ink to a roller with a pattern of a printing plate formed on the surface thereof in a gravure printing device. In this mechanism, an ink chamber which has doctor blades extending in the longitudinal direction of the roller at positions corresponding to upper and lower two locations along the circumferential surface of the roller as well as elastic members provided on both sides of these two doctor blades, respectively, is used. By bringing this chamber into contact with the circumferential surface of the roller, a liquid chamber is defined by the chamber and the roller. And when the roller rotates, the applying liquid in this liquid chamber is supplied or applied to the roller. 
     This construction to supply a liquid while the chamber holding the liquid is brought into contact with the roller, has an advantage such as preventing leakage of the liquid. Particularly, in an ink-jet printing apparatus such as a printer provided with an applying mechanism, leakage of the applying liquid caused by attitude change during transportation can be prevented, and a printer that can be adapted to transportation can be realized. 
     The patent document 1: Japanese Patent Application Laid-open No. 08-58069 
     DISCLOSURE OF THE INVENTION 
     The applying mechanism disclosed in Patent Document 1 is a mechanism in which the chamber holding the liquid is brought into contact with the roller, and at that contact portion the liquid adheres onto the roller, is transported thereon and transferred to a medium with rotation of the roller. Therefore, the adhesion amount on the roller might change depending on the state of the above contact with the liquid or the state of the contact portion. 
     For example, when the viscosity of the liquid is changed, the state of the flow (movement) of the liquid at the contact portion is changed, so that the amount of the liquid which can adhere to the roller and go out of the above contact portion is changed. As described above, if factors are caused which changes the contact state between the liquid holding member such as the chamber and the applying member such as the roller, the amount of liquid adhering to the applying member and going out of this contact portion is changed and the amount to be finally transferred (applied) to the medium is also changed. It is preferable that such unintended change of applying amount is reduced as mach as possible. 
     The present invention was made in view of the above points and has a purpose to provide a liquid applying apparatus and an ink-jet printing apparatus which can reduce an unintended change of an applying amount. 
     To achieve the above object, there is provided a liquid applying apparatus comprising: liquid applying means that includes an applying member for applying a liquid to an applying medium and a liquid holding member which contacts with said applying member to form a liquid holding space for holding the liquid in the liquid holding space, and that moves said applying member relatively to the applying medium to apply the liquid in the liquid holding space to the applying medium through said applying member; and control means for controlling an amount of the liquid applied by said liquid applying means. 
     In another aspect of the present invention, there is provided a liquid applying apparatus comprising: a liquid applying unit that includes an applying roller for applying a liquid to an applying medium and a liquid holding member which contacts with said applying roller to form a liquid holding space for holding the liquid in the liquid holding space, and that rotates said applying roller to apply the liquid in the liquid holding space to the applying medium through said applying roller; and control means for changing a speed of a liquid flow in the liquid holding space to control an amount of the liquid applied through said liquid applying roller. 
     In further aspect of the present invention, there is provided a liquid applying apparatus comprising: a liquid applying unit that includes an applying member for applying a liquid to an applying medium and a liquid holding member which contacts with said applying member to form a liquid holding space for holding the liquid in the liquid holding space, and that moves said applying member relatively to the applying medium to apply the liquid in the liquid holding space to the applying medium through said applying member; and control means for changing pressure in the liquid holding space to control an amount of the liquid applied through said liquid applying member. 
     In still further aspect of the present invention, there is provided a liquid applying apparatus comprising: a liquid applying unit that includes an applying roller for applying a liquid to an applying medium and a liquid holding member which contacts with said applying roller to form a liquid holding space for holding the liquid in the liquid holding space, and that rotates said applying roller to apply the liquid in the liquid holding space to the applying medium through said applying roller; and control means for changing a rotational speed of said applying roller to control an amount of the liquid applied through said liquid applying roller. 
     In still further aspect of the present invention, there is provided a liquid applying apparatus comprising: a liquid applying unit that includes an applying member for applying a liquid to an applying medium and a liquid holding member which contacts with said applying member to form a liquid holding space for holding the liquid in the liquid holding space, and that moves said applying member relatively to the applying medium to apply the liquid in the liquid holding space to the applying medium through said applying member; a storage portion for storing the liquid; a supply path for supplying the liquid from said storage portion to the liquid holding space; a recovery path for recovering the liquid from the liquid holding space to said storage portion; circulation means for circulating the liquid in a flow path including said storage portion, said supply path, the liquid holding space and said recovery path; and control means for changing a circulation speed of the liquid circulated by said circulation means to control an amount of the liquid applied. 
     In still further aspect of the present invention, there is provided a liquid applying apparatus comprising: a liquid applying unit that includes an applying roller for applying a liquid to an applying medium and a liquid holding member which contacts with said applying roller to form a liquid holding space for holding the liquid in the liquid holding space, and that rotates said applying roller to apply the liquid in the liquid holding space to the applying medium through said applying roller; and control means for changing a contact force between said applying roller and said liquid holding member to control an amount of the liquid applied through said liquid applying roller. 
     Furthermore, there is provided an ink jet printing apparatus comprising: any one of liquid applying apparatuses stated above; and printing means for printing an image on the medium by ejecting ink to the medium, to which the liquid is applied in said liquid applying apparatus. 
     According to the above construction, when applying a liquid in a liquid holding space to an applying medium through an applying member (for example, applying roller), the amount of the liquid to be applied to the applying medium can be controlled. For example, pressure of the liquid or a flow velocity of the liquid in the liquid holding space is changed so as to adjust the applying amount. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an outline construction of a liquid applying apparatus in an embodiment of the present invention; 
         FIG. 2  is a longitudinal sectional side view showing an example of arrangement of an applying roller, a counter roller, a liquid holding member and the like shown in  FIG. 1 ; 
         FIG. 3  is a front view of the liquid holding member shown in  FIGS. 1 and 2 ; 
         FIG. 4  is an end face view showing an end face where the liquid holding member shown in  FIG. 3  is cut at IV-IV line; 
         FIG. 5  is an end face view showing an end face where the liquid holding member shown in  FIG. 3  is cut at V-V line; 
         FIG. 6  is a plan view of the liquid holding member shown in  FIG. 3 ; 
         FIG. 7  is a left side view showing a state where a contact portion of the liquid applying member shown in  FIG. 3  is brought into contact with a liquid applying roller; 
         FIG. 8  is a right side view showing a state where a contact portion of the liquid applying member shown in  FIG. 3  is brought into contact with a liquid applying roller; 
         FIG. 9  is a longitudinal sectional view showing a state where an applying liquid is filled in a liquid holding space defined by the liquid holding member and the applying roller and the liquid is applied to an applying medium by rotation of the applying roller; 
         FIG. 10  is a longitudinal sectional view showing a state where an applying liquid is filled in a liquid holding space defined by a liquid holding member and an applying roller and the applying roller is rotated while an applying medium does not exist in an embodiment of the present invention; 
         FIG. 11  shows a flow path construction of a liquid applying apparatus according to an embodiment of the present invention; 
         FIG. 12  is a block diagram showing an outline construction of a control system of a liquid applying apparatus according to an embodiment of the present invention; 
         FIG. 13  is a flowchart showing a sequence of a liquid applying operation according to an embodiment of the present invention; 
         FIG. 14  is a graph showing a pressure in a liquid holding space in the above liquid applying apparatus, corresponding to a flow rate of a circulation flow; 
         FIG. 15  is a graph showing a relation between the applying amount and the flow rate of the above circulation flow; 
         FIG. 16  is a graph for explaining temperature dependence of viscosity of an applying liquid; 
         FIG. 17  is a graph for explaining viscosity dependence of an applying amount; 
         FIG. 18  is a graph for explaining a relation between an applying speed and an applying amount; 
         FIG. 19  is a table used for circulation speed decision processing according to an embodiment of the present invention; 
         FIG. 20  is a longitudinal sectional side view showing an outline construction of an ink-jet printing apparatus according to another embodiment of the present invention; 
         FIG. 21  is a perspective view showing an essential part of the ink-jet printing apparatus shown in  FIG. 20 ; 
         FIG. 22  is a block diagram showing an outline construction of a control system of the ink-jet printing apparatus shown in  FIG. 20 ; and 
         FIG. 23  is a flowchart showing a sequence of a liquid applying operation and a printing operation executed in the ink-jet printing apparatus shown in  FIG. 20 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described in detail referring to the drawings. 
     First Embodiment 
       FIG. 1  is a perspective view showing an entire configuration of an embodiment of a liquid applying apparatus  100  according to the present invention. The liquid applying apparatus  100  shown herein is roughly configured to have a liquid applying mechanism for applying a predetermined applying liquid (also referred to as applying liquid hereinafter) to an applying medium (also referred to as applying medium hereinafter) and a liquid supplying mechanism for supplying the applying liquid to the liquid applying mechanism. 
     The liquid applying mechanism has a cylindrical applying roller (also referred to as applying roller hereinafter)  1001 , a cylindrical counter roller (medium support member)  1002  arranged opposite to the applying roller  1001 , and a roller driving mechanism  1003  for driving the applying roller  1001 , or the like. The roller driving mechanism  1003  is composed of a roller driving motor  1004  and a power transmission mechanism  1005  having a gear train for transmitting a driving force of this roller driving motor  1004  to the applying roller  1001 . 
     Moreover, the liquid supplying mechanism is configured by having a liquid holding member  2001  for holding an applying liquid between itself and the circumferential surface of the applying roller  1001 , and a liquid flow path  3000  (not shown in  FIG. 1 ), which will be described later, for supplying the liquid to the liquid holding member  2001 . The applying roller  1001  and the counter roller  1002  are rotatably supported by shafts in parallel with each other, which respective both ends are rotatably mounted to a frame, not shown. Moreover, the liquid holding member  2001  extends over substantially the whole length of the applying roller  1001  in the longitudinal direction and is movably mounted to the above frame via a mechanism capable of approach/separation with respect to the circumferential surface of the applying roller  1001 . 
     The liquid applying apparatus of the embodiment is further provided with an applying medium supplying mechanism  1006  composed of a pickup roller and the like for conveying the applying medium to a nip portion between the applying roller  1001  and the counter roller  1002 . Moreover, in a conveying path of the applying medium, a paper discharge mechanism  1007  composed of a paper discharge roller and the like for conveying the applying medium on which the applying liquid has been applied to a paper discharge portion (not shown) is provided on the down stream side of the applying roller  1001  and the counter roller  1002 . These paper feed mechanism and paper discharge mechanism are operated by a driving force of the driving motor  1004  transmitted via the power transmission mechanism  1005  as well as the applying roller or the like. 
     The applying liquid used in the embodiment is a liquid for promoting an aggregation of a pigment when printing is performed with ink having the pigment as color material. An example of components of the applying liquid is described below:
         Calcium nitrate tetrahydrate: 10%   Glycerin: 42%   Surfactant: 1%   Water: remaining amount       

     The viscosity of the above applying liquid is  5  to 6 cP (centipoise) at 25° C. 
     It is needless to say that the applying liquid in application of the present invention is not limited to the above. For example, a liquid containing a component to insolubilize or coagulate a dye can be used as another applying liquid. Alternatively, a liquid containing a component to suppress curl (phenomenon that the medium is brought into a curved shape) of the applying medium can also be used as another applying liquid. 
     When water is used in a liquid to be applied, slidability between the applying roller and the contact portion of the liquid holding member is made better by adding a component to lower surface tension to the liquid. In the above example of components of the applying liquid, glycerin and surfactant are components to lower the surface tension of water. 
     Next, components of each portion configuring the liquid applying apparatus roughly described above will be explained in detail. 
       FIG. 2  is a side sectional view showing a detail arrangement of the applying roller  1001 , the counter roller  1002  and the liquid holding member  2001 . The counter roller  1002  is biased toward the circumferential surface of the applying roller  1001  by a biasing mechanism, not shown, configured by having a spring or the like. By rotating the applying roller  1001  clockwise in this state in the figure, a printing medium P to which the applying liquid is to be applied can be held between the both rollers and can be conveyed in the arrow direction in the figure. In this embodiment, the material of the applying roller  1001  is a silicon having rubber hardness of 40 degrees, with the surface roughness of Ra 1.6 um and the diameter of 23.169 mm. The material of the counter roller  1002  is a steel material with a diameter of 14 mm. 
     When the liquid holding is biased toward the circumferential surface of the applying roller  1001  by the biasing force of the spring (pressing means)  2006 , to be brought into contact with the applying roller, a long liquid holding space S extending over the whole liquid applying area by the applying roller  1001  is formed. In this liquid holding space S, the applying liquid is supplied from a liquid flow path  3000 , which will be described later, via the supply port of the liquid holding member  2001 . In this case, since the liquid holding member  2001  is configured as follows, unintentional leakage of the applying liquid from the liquid holding space S to the outside can be prevented or decreased while the applying roller  1001  is stopped. 
     A configuration of the liquid holding member  2001  is shown in  FIGS. 3 to 8 . As shown in  FIG. 3 , the liquid holding member  2001  is configured to have the space forming member  2002  and the annular contact member  2009  provided on the surface of the space forming member  2002 . In the space forming member  2002 , a recess portion  2003  cross section profile of which has an arc is formed along the longitudinal direction at the center. The contact member  2009  has straight portions  2010 ,  2011  which are fixed along the respective straight edge portions of the recess portion  2003 , and circumference portions  2012 ,  2013  which are fixed in a state that each of the portions  2012 ,  2013  extends from upper one of the edge portions through the recess portion to the similar straight edge portion on the opposite side. By this configuration, when the contact potion  2009  of the liquid holding member  2001  is brought into contact with the applying roller  1001 , contact along the circumferential surface shape of the applying roller is made possible, which can realize contact with a uniform pressure. 
     As described above, the contact member  2009  of the liquid holding member in this embodiment is formed integrally without seams and thus is brought into contact with the outer circumferential surface of the applying roller  1001  continuously without a gap by the biasing force of the spring member  2006 . As a result, the liquid holding space S becomes a space substantially blocked by the contact member  2009 , one surface of the space forming member and the outer circumferential surface of the applying roller  1001  and the applying liquid is held in this space. In the state where rotation of the applying roller  1001  is stopped, the contact member  2009  and the outer circumferential surface of the applying roller  1001  maintain a liquid tight state, by which leakage of the liquid to the outside can be surely prevented. On the other hand, when the applying roller  1001  is rotated, as will be described later, the applying liquid passes between the outer circumferential surface of the applying roller  1001  and the contact member  2009  and adheres to the outer circumferential surface of the applying roller in a layered state. As described in  FIG. 13  or later, an embodiment of the present invention controls an amount of the applying liquid adhered to the outer circumferential surface of the applying roller. 
     Here, the close contact state between the outer circumferential surface and the contact member  2009  when the applying roller  1001  is stopped means that, as mentioned above, a liquid is prevented from passing between the inside and the outside of the above liquid holding space S. In this case, the contact state of the contact member  2009  is such that the contact member is in direct contact with the outer circumferential surface of the applying roller  1001  and also includes a state that the contact member is brought into contact with the above outer circumferential surface through a liquid film formed by a capillary force. 
     Moreover, both right and left side portions  2012 ,  2013  in the longitudinal direction of the contact member  2009  form a slowly curved shape seen from any direction of front ( FIG. 3 ), plane ( FIG. 6 ) and sides ( FIGS. 7 ,  8 ). Therefore, even if the contact member  2009  is brought into contact with the applying roller  1001  with a relatively large pressing force, the entire contact member  2009  is elastically deformed substantially uniformly, and a large local distortion is not generated. Therefore, the contact member  2009  is brought into contact with the outer circumferential surface of the applying roller  1001  continuously without a gap as shown in  FIGS. 6 to 8 , and the above substantially blocked space can be formed. 
     A liquid supply port  2004  and a liquid recovery port  2005  having a hole piercing the space forming member  2002 , respectively, are provided in an area surrounded by the contact member  2009  in the space forming member  2002  as shown in  FIGS. 3 to 5 . These ports communicate with cylindrical connection portions  20041 ,  20051  projected on the back surface side of the space forming member. These connection portions  20041 ,  20051  are connected to a liquid supply flow path  3000 , which will be described later. In this embodiment, the liquid supply port  2004  is formed in the vicinity of one end portion (left end portion in  FIG. 3 ) of the area surrounded by the contact member  2009 , while the liquid recovery port  2005  is provided in the vicinity of the other end portion (right end portion in  FIG. 3 ) of the same area. The liquid supply port  2004  supplies the applying liquid supplied from the liquid flow path  3000  to the above-mentioned liquid holding space S, while the liquid recovery port  2005  flows out the liquid in the liquid holding space S into the liquid flow path  3000 . By this supply/flow-out of the liquid, the applying liquid flows from the above-mentioned left end portion to the right end portion in the liquid holding space S. 
     (Applying Liquid Flow Path) 
       FIG. 11  is a diagram showing an outline construction of a liquid flow path  3000  connected to the liquid holding member  2001  for supplying an applying liquid to the liquid holding member and for recovering the applying liquid from the liquid holding member. 
     The liquid flow path  3000  is provided with a tube  3101  and a tube  3102  constituting a first flow path (supply flow path) connecting a liquid supply port  2004  of a space forming member  2002  constituting the liquid holding member  2001  to a buffer tank  3002  for storing the applying liquid. Moreover, the liquid flow path  3000  is provided with tubes  3103 ,  3104  and  3105  constituting a second flow path (recovery flow path) which connects a liquid recovery port  2005  of the space forming member  2002  to the buffer tank  3002 . And the buffer tank  3002  is provided with an atmospheric air communication port  3004 . 
     A first T-shaped flow path  3301  connecting three ports is provided between the tube  3101  and the tube  3102  constituting the first flow path. The first T-shaped flow path  3301  allows one of the connection port  3008  to communicate with the atmospheric air. Closer to the communicating port  3008  that communicates with the atmospheric air than the meeting point of the first T-shaped flow path  3301  connecting three ports, a first shut-off valve  3201  for switching communication/shutoff between the communication port  3008  and the first T-shaped flow path  3301  is provided. Moreover, the first T-shaped flow path  3301  connects to the buffer tank  3002  through the tube  3101 . Closer to the connection port that is connected to the tube  3101  than the meeting point of the first T-shaped flow path connecting the three ports, a second shut-off valve  3202  for switching communication/shutoff between the tube  3101  and the first T-shaped flow path  3301  is provided. Moreover, the first T-shaped flow path  3301  connects the remaining connection port to the liquid supply port  2004  through the tube  3102 . This construction of the first shut-off valve  3201 , the second shut-off valve  3202  and the first T-shaped flow path  3301  allows the tube  3102  to select its connection to either the atmospheric air or the buffer tank  3002  using the combination of communication/shutoff of the two shut-off valves. 
     Moreover, in the second flow path which includes the tube  3103 ,  3104  and  3105 , a pump  3007  is arranged for forcing the applying liquid and air to flow in the direction toward the buffer tank  3002  in this liquid flow path  3000 . To the side of the pump  3007  into which the applying liquid flows (also referred to as an “upstream side of pump” in this specification), the tube  3104  is connected. Conversely, to the side of the pump  3007  from which the applying liquid flows out (also referred to as a “downstream side of pump” in this specification), the tube  3105  is connected. This tube  3105  connects the buffer tank  3002  to the pump  3007 . The tube  3104  connects the pump  3007  to the second T-shaped flow path  3302  connecting the three ports while the tube  3103  connects the second T-shaped flow path  3302  to the liquid recovery port  2005 . 
     By connecting the buffer tank  3002  to the space forming member  2002  through these first and second flow paths, and by driving the pump  3007 , the applying liquid in the buffer tank  3002  can be supplied to the space forming member  2002  while being circulated. 
     Moreover, the liquid flow path  3000  is provided with a third flow path (replenishing flow path) that connects an replaceable tank  3001  for storing the applying liquid to the second flow path as well as a fourth flow path that connects the buffer tank  3002  to the replaceable tank  3001 . It is to be noted that the replaceable tank  3001  is a tank with capacity larger than that of the buffer tank  3002 . 
     A tube  3106  that is included in the third flow path is connected to the replaceable tank  3001  through a first connection port  3005  in the syringe-needle shape and a pedestal  3003  constituting a connection flow path. That is, by making the first connection port  3005  in the syringe-needle shape penetrate a rubber  3501  that is provided at the bottom portion of the replaceable tank  3001 , a tube  3106  connects to the replaceable tank  3001 . And the other port of the tube  3106  connects to the above second T-shaped flow path  3302 . In this embodiment, the tube  3106  is a replenishing flow path for supplying the applying liquid from the replaceable tank  3001  to the buffer tank  3002 . 
     The second T-shaped flow path  3302  is provided with a third shut-off valve  3203  capable of switching communication/shutoff between the tube  3103  and the second T-shaped flow path  3302  at a part closer to the tube  3103  than a meeting point connecting the three ports. Also, the second T-shaped flow path  3302  is provided with a fourth shut-off valve  3204  capable of switching communication/shutoff between the tube  3106  and the second T-shaped flow path  3302  at a part closer to the tube  3106  than the meeting point. With the construction of the third shutoff  3203 , the fourth shut-off valve  3204  and the second T-shaped flow path  3302 , the counterpart of connection with the tube  3104  can be selected from either the replaceable tank  3001  or the space forming member  2002  according to the combination of communication/shutoff of the two shut-off valves. 
     The fourth flow path includes tubes  3107  and  3108 . The tube  3108  included in the fourth flow path is connected to the replaceable tank  3001  through the second connection port  3006  in the syringe-needle shape and the pedestal  3003  constituting the connection flow path. That is, by making the second connection port  3006  in the syringe-needle shape penetrate a rubber  3502  that is provided at the bottom portion of the replaceable tank  3001 , the tube  3108  connects to the replaceable tank  3001 . The replaceable tank  3001  communicates with the buffer tank  3002  through a fifth shut-off valve  3205  capable of switching communication/shutoff between the tube  3107  and the tube  3108 . 
     It is to be noted that switching of the respective shut-off valves is carried out by a control signal from a control portion  4000 , which will be described later, and thereby filling, supply, recovery and the like of the applying liquid is carried out. 
     Also, the positions of the second T-shaped flow path and the third and fourth shut-off valves that make the tube  3103  for recovering the applying liquid and the tube  3106  merge and that also switch between these flow paths and the tube  3104  are as follows. These positions may be arranged anywhere as long as they are between the pump  3007  and the liquid recovery port  2005 . Also, as will be described later in another embodiment of the liquid flow path, the second T-shaped flow path and the third and fourth shut-off valves may be arranged between the liquid supply port  2004  and the buffer tank  3002 . That is, the second T-shaped flow path and the third and fourth shut-off valves may be arranged at any position as long as they are on the upstream side of the pump  3007 . 
     In this embodiment, on the upstream side of the pump  3007 , the recovery flow path and the replenishing flow path are merged, and also switching of the connection between a flow path leading to the pump  3007  and the recovery flow path and between the flow path leading to the pump  3007  and the replenishing flow path is made. In this switching, when the recovery flow path connects to the pump  3007 , the replenishing flow path does not connect to the pump  3007 . Thus, during this time, circulation can be carried out in the first flow path, liquid holding space S and second flow paths, or supply/recovery of the applying liquid to the liquid holding space S can be carried out, by the pump  3007 . On the other hand, when the replenishing flow path connects to the pump  3007  by the above switching, the recovery flow path does not connect to the pump  3007 . Therefore, during this time, the applying liquid can be replenished from the replaceable tank  3001  to the buffer tank  3002  through the third flow path. 
     In this way, in this embodiment, merging and switching of the recovery flow path and the replenishing flow path are carried out on the upstream side of the pump  3007 , and the flow path that is not in communication with the pump  3007  is shutoff from the pump  3007 . Therefore, the control for the flow paths having the buffer tank  3002  and the replaceable tank  3001  can be carried out using a single pump. 
     Moreover, by controlling driving of this pump  3007 , as will be described in  FIG. 13  and later, the applying liquid is circulated to and from the liquid holding member  2001 , and the flow velocity of the applying liquid flowing from the liquid supply port  2004  to the liquid recovery port  2005  in the liquid holding member  2001  is controlled. 
     (Control System) 
       FIG. 12  is a block diagram showing an outline construction of a control system in a liquid applying apparatus of this embodiment. In this figure, reference numeral  4000  denotes a control portion as a control means for controlling the entire liquid applying apparatus. The control portion  4000  has a CPU  4001  for executing processing operation such as various calculations, control and determination. Also, the control portion  4000  has a ROM  4002  for storing control programs, such as processing that will be described later in  FIG. 13 , executed by the CPU  4001  as well as a RAM  4003  for temporarily storing data which is under processing of the CPU  4001  and input data. Moreover, it has a timer for detecting use time or nonuse time of the apparatus that is referred to at the control of the flow velocity of the applying liquid as will be described later. 
     Moreover, to this control portion  4000  are connected an input operation portion  4004  including a keyboard for inputting a predetermined command or data or various switches and a display portion  4005  for making various displays including input/setting state of the liquid applying apparatus. It is also provided with a detection portion  4006  including a sensor for detecting a position of the applying medium and an operation state of each part. This detection portion has a temperature sensor  4061  for detecting an environment temperature to be referred to at the control of the flow velocity of the applying liquid, which will be described later. The roller driving motor  1004 , the pump driving motor  4009 , and the first to fifth shut-off valves are connected through driving circuits  4007 ,  4008  and  4010  to  4014 , respectively. 
     (Liquid Applying Operation Sequence) 
     The processing of the liquid applying executed by the above construction of the applying apparatus will be described below. This processing includes control of a circulation speed according to an embodiment of the present invention. That is, it includes controlling the speed of a flow (circulation flow) generated in the liquid holding member  2001  due to circulation caused by supply of the applying liquid to the liquid holding member  2001  and recovery of the applying liquid therefrom. 
       FIG. 13  is a flowchart showing a processing procedure of liquid applying in the liquid applying apparatus according to an embodiment of the present invention. Each process of the liquid applying will be described referring to this flowchart. 
     When the liquid applying apparatus is powered on, the control portion  4000  executes the following applying operation sequence according to the flowchart shown in  FIG. 13 . 
     The combinations of opening/closing of the respective shut-off valves shown in  FIG. 11  are made to four combinations: “standing”, “replenishing”, “circulation” and “recovery.” Moreover the control portion  4000  selects a combination suited to the state of the apparatus and sends a control signal to the respective shut-off valves to operate according to the selected combination. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 First 
                 Second 
                 Third 
                 Fourth 
                 Fifth 
               
               
                   
                 shut-off 
                 shut-off 
                 shut-off 
                 shut-off 
                 shut-off 
               
               
                   
                 valve 
                 valve 
                 valve 
                 valve 
                 valve 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Standing 
                 Open 
                 Close 
                 Close 
                 Close 
                 Close 
               
               
                 Replen- 
                 Close 
                 Close 
                 Close 
                 Open 
                 Open 
               
               
                 ishing 
               
               
                 Circula- 
                 Close 
                 Open 
                 Open 
                 Close 
                 Close 
               
               
                 tion 
               
               
                 Recovery 
                 Open 
                 Close 
                 Open 
                 Close 
                 Close 
               
               
                   
               
            
           
         
       
     
     Here, the “standing” shows a state of the respective shut-off valves while the apparatus is not in operation after the applying liquid has been recovered from the liquid holding space S. The “replenishing” shows a state of the respective shut-off valves where the applying liquid is being supplied from the replaceable tank to the buffer tank. The “circulation” shows a state of the respective shut-off valves where the applying liquid is circulated in the buffer tank, the first flow path, liquid holding space S and second flow path. The “recovery” shows a state of the respective shut-off valves where the applying liquid is recovered from the liquid holding space S to the buffer tank. 
     Filling Process 
     In  FIG. 13 , at Step S 1 , the filling process of the applying liquid to the liquid holding space S is executed. In this filling process, the respective shut-off valves are set to the opening/closing combination of “circulation” and the pump  3007  is driven for a certain period of time. This opening/closing combination allows the buffer tank  3002  to communicate with the liquid holding space S through the first and second flow paths. By this, if the applying liquid has not been filled in the liquid holding space S and the first and second flow paths, inside air is fed to the buffer tank  3002  by the pump and discharged to the atmospheric air through the atmospheric air communication port  3004 , as well as the applying liquid is filled into the respective portions. On the other hand, if the respective portions have been already filled with the applying liquid, the applying liquid in the respective portions flows and is supplied with the appropriate concentration and viscosity. By this initial operation, the applying liquid is supplied to the applying roller  1001 , enabling the applying medium to be applied. 
     Replenishing Process 
     At Step S 1 , if it is determined by a sensor or the like as the liquid-level control means for detecting the liquid level in the liquid holding space that the filling of the applying liquid in the buffer tank  3002  is insufficient, the respective shut-off valves are set to the “replenishing” opening/closing combination. At the same time, the pump  3007  is driven for a certain period of time. This opening/closing combination allows the buffer tank  3002  to communicate with the replaceable tank  3001  through the third and fourth flow paths. By this, the applying liquid is filled into the buffer tank  3002 . 
     Circulation Speed Decision Process 
     Next, when an applying start command is inputted (Step S 2 ), a circulation speed decision processing (Step S 3 ) is carried out before the pump  3007  is driven again. In this embodiment, pressure in the liquid holding space is controlled by controlling the speed of the circulation flow generated in the liquid holding space defined by the liquid holding member  2001  and the applying roller  1001  according to the decided circulation speed. It results in changing the flow (movement) of the applying liquid at the portion where the contact member  2009  of the liquid holding member  2001  is in contact with the applying roller  1001  (portion N shown in  FIG. 9 ), to control the amount of applying liquid which adheres to the applying roller  1001  and going out of the contact portion N. By this, the amount of the applying liquid transferred (applied) onto the applying medium P is controlled. 
       FIG. 14  is a diagram showing a pressure in the liquid holding space according to the flow rate of the circulation flow. Here, since the cross-sectional area of the flow in the liquid holding space is constant, the above flow rate corresponds to the flow velocity.  FIG. 14  shows an average pressure in the flow direction in the liquid holding space when the water head difference between the buffer tank  3002  and the liquid holding member  2001  in the flow path shown in  FIG. 11  is 0 cm. The pressure is also distributed according to the flow velocity distribution in the flow direction of the liquid holding space but it shows a pressure tendency shown in  FIG. 14  at any location. 
     As is obvious from  FIG. 14 , the faster the flow velocity is, the lower the pressure in the liquid holding space becomes, that is, the larger the negative pressure in the liquid holding space becomes. Then, the lower the pressure in the liquid holding space is, the smaller the applying amount becomes. That is, the larger the negative pressure in the liquid holding space is, the smaller the amount of the applying liquid going out of the liquid holding space becomes.  FIG. 15  is a graph showing a relation between the flow rate (thus, the flow velocity) of the circulation flow and the applying amount. As is obvious from this figure, the faster the flow velocity is, the smaller the applying amount becomes. 
     When the pressure in the liquid holding space is lowered, the contact pressure of the contact member  2009  against the applying roller  1001  is increased. As a result, the contact area of the contact portion N between the contact member  2009  and the applying roller  1001  is increased. Also, the state of meniscus of the applying liquid formed in a gap at the contact portion N is also changed. By changing the state of the contact portion N in this way, the amount of the applying liquid that can go out through the gap of the contact portion N from the liquid holding member  2001  can be changed. There can be other factors deciding the amount adhering to the applying roller and transported, but in any case, in this embodiment, when the pressure in the liquid applying member or the flow velocity of the circulation flow are used as parameters, the relation as shown in  FIG. 15  is obtained between this parameter and the applying amount. Then the applying amount is controlled based on that. 
     It should be noted that the contact portion N is formed of the contact member and the applying roller along the longitudinal direction of the liquid holding member  2001 , and as mentioned above, the pressure in the liquid holding space is distributed along the longitudinal direction. Thus, the amount of the applying liquid going out of the contact portion N might be different along the longitudinal direction of the liquid holding member. However, the difference in the amount is not so large that it can be recognized as uneven applying when applying the medium. In other words, there is a possibility that the uneven applying might occur in a construction, such as an elongated liquid holding member, where an extreme negative gradient pressure is formed. However, such a construction with an extreme negative pressure might cause another problem such as insufficient motor torque due to sticking of the liquid holding member. In addition, since there is a risk that the contact portion N causes leakage and air enters, such a construction is not practical. 
     In the circulation speed decision processing of this embodiment, the circulation speed that can correspond to the applying amount as mentioned above is decided according to the environment temperature, the type of paper to be used as the applying medium and the applying mode relating to the rotating speed of the applying roller. By this, even if the environment temperature, paper type or the rotating speed of the applying roller varies, the applying amount can be controlled to be constant. 
       FIG. 16  is a graph explaining the temperature dependence of the viscosity of the applying liquid. As is obvious from the figure, the higher the temperature rises, the lower the viscosity becomes in any of the applying liquid with compositions A, B, C and D.  FIG. 17  is a graph explaining the viscosity dependence of the applying amount. As is shown in this figure, the higher the viscosity is, the more the applying amount becomes. When the characteristics shown in  FIGS. 16 and 17  are put together, the higher the temperature is, the smaller the applying amount becomes. As a result, in the applying amount control of this embodiment, when the temperature is higher, the applying amount of the liquid is increased by lowering the circulation speed, so that the constant applying amount is maintained irrespective of the temperature change. 
     The amount transferred (applied) onto the applying medium is changed according to the irregularity of the surface of the applying medium such as paper. Generally, the rougher the surface is with the larger irregularity, the smaller the amount to be applied becomes. In this embodiment, such control is carried out that, by lowering the circulation speed so as to increase the applying amount for the applying medium with the rougher surface so that the applying amount is maintained constant irrespective of the type of the applying medium to be used. 
     Moreover, the applying amount is changed according to the applying speed of the applying member such as the applying roller to the applying medium.  FIG. 18  is a graph showing a relation between the applying speed and the applying amount. As is shown in this figure, the faster the applying speed (rotating speed of the applying roller in this embodiment) is, the larger the applying amount becomes. Therefore, in the applying amount control of this embodiment, in the mode where the rotating speed of the applying roller is faster, the applying amount of the liquid is decreased by increasing the circulation speed so that constant applying amount is maintained irrespective of the applying mode. If the rotation speed of the applying roller is changed, it is necessary to change the rotation speeds of the counter roller  1002 , the discharge roller  1007  and the like in accordance with the change of the rotation speeds of the counter roller  1002 . It is needless to say that changing the rotating speed of the applying roller cases the conveying speed of the applying medium to be changed. 
       FIG. 19  is a table used for circulation speed decision processing of this embodiment. In this figure, with regard to the “temperature” indicating the value of the environment temperature, if it is higher than a predetermined threshold temperature, it is “High”, while if it is not higher than the predetermined threshold temperature, it is “Low”. As for the “paper type” indicating the type of the applying medium, if the irregularity on the surface of the paper is rougher than a predetermined roughness, it is “Rough”, while if it is not rougher than the predetermined roughness, it is “Smooth”. Moreover, as for the “grade” corresponding to the applying speed, a mode where a rotating speed of the applying roller  1001  is slower than a predetermined rotating speed is “High”, while the mode where the speed is not slower than the predetermined rotating speed is “Low”. The mode with the slower rotating speed has the slower applying speed. In this case, applying with a higher noise grade with lower noise can be carried out. 
     In the table shown in  FIG. 19 , a “pump speed”, which is a driving speed of the pump, is decided based on the values of the above parameters: “temperature”, “paper type” and “grade”. The pump speed gets faster sequentially in order from A, B, C . . . G, H. If the temperature is “High” and the grade is “High”, for example, the pump speed is made faster when the paper type is “Smooth” than the case where it is “Rough” (A&lt;B). Also, if the temperature is “Low” and the grade is “High”, the pump speed is made faster than the above case, and the pump speed is also faster when the paper type is “Smooth” than the case where it is “Rough” (A&lt;B&lt;. . . &lt;E&lt;F). In this way, any of the pump speeds A to H is decided according to the “temperature”, “paper type” and “grade”. 
     With the decided pump speed, the pump is driven in the next applying process. In this embodiment, a driving voltage for achieving the decided pump speed is applied to the pump to be driven. As a result, the applying amount is maintained constant by controlling the speed of the circulation flow in the liquid holding member  2001 . 
     In this embodiment, the “temperature”, which is the environment temperature of the liquid applying apparatus, is detected by the temperature sensor  4061  shown in  FIG. 12 . And, the “paper type”, which is the type of the applying medium, can be detected by input set by a user through the input operation portion  4004 . It is needless to say that this paper type can be also detected with a well-known detection mechanism using an optical sensor. Moreover, the “grade” can be determined according to the liquid applying mode set by a user through the input operation portion  4004 . 
     It is needless to say that the parameters deciding the pump speed are not limited to the “temperature” and the like in the above example. For example, a standing time of an apparatus, which affects the viscosity of the applying liquid, can be used as a parameter. The longer the standing time becomes, the more evaporation is generated. It increases the viscosity of the applying liquid. If the standing time is used as a parameter, an elapsed time from the end of circulation of the applying liquid to the start of the next circulation may be measured with the timer  4015  shown in  FIG. 12 , for example and the pump speed may be controlled according to the time. Thus, any factor affecting the viscosity of the applying liquid can be used as a parameter in deciding the pump speed. 
     The applying amount might be changed according to the duration of use of the applying liquid or the applying roller. For example, when the applying liquid or the applying roller is deteriorated due to its use, the applying amount might be changed. Therefore, their durations of use can be used as parameters in deciding the pump speed. 
     Moreover, in the above embodiment, it was described that the applying amount depends on the surface state of the applying medium. The applying amount might be different depending on the thickness of the applying medium. Therefore, this thickness can be used as a parameter in deciding the pump speed. Also, the mode according to the rotating speed of the applying roller described in the above embodiment relates to the applying grade, but the mode is not limited to that. For example, if there is a mode such as a silent mode in which the applying roller rotates at a relatively low speed, the driving speed of the pump can be decided according to the rotating speed. 
     In addition, the control of the circulation speed described in the above-mentioned embodiment is to control the circulation speed in the liquid holding space when applying is being conducted to the applying medium while the applying medium is held between the applying roller and the counter roller. For example, if the pump is driven before the applying medium is fed to between the applying roller and the counter roller or if the pump is driven while the applying is not being conducted on the medium during post processing or the like, the circulation speed is not controlled but the pump is driven at a constant speed. 
     Applying Process 
     Referring to  FIG. 13 , again, when the above-mentioned circulation speed decision processing (Step S 3 ) is completed, the pump driving starts at the decided pump speed (Step S 4 ) and the applying roller  1001  starts to rotate clockwise as shown by an arrow in  FIG. 2  (Step S 5 ). By this rotation of the applying roller  1001 , the applying liquid L filled in the liquid holding space S passes through the contact portion N of the applying roller  1001  and the lower edge portion  2011  of the contact member  2009  against the pressing force of the contact member  2009  of the liquid holding member  2001  against the applying roller  1001 . And the applying liquid adheres to the outer circumference of the applying roller  1001  in a layered state. The applying liquid L adhering to the applying roller  1001  is fed to the contact portion of the applying roller  1001  and the counter roller  1002 . 
     Then, the applying medium is conveyed to a portion between the applying roller  1001  and the counter roller  1002  by an applying medium supply mechanism  1006 . With this, the applying medium is inserted between these rollers and conveyed to a paper discharge portion with rotation of the applying roller  1001  and the counter roller  1002  (Step S 6 ). During this conveyance, the applying liquid adhered to the outer circumferential surface of the applying roller  1001  is transferred to the applying medium P from the applying roller  1001  as shown in  FIG. 9 . The amount to be transferred is controlled to be constant by the above-mentioned control of the circulation speed. 
     It is needless to say that the means for supplying the applying medium to the portion between the applying roller  1001  and the counter roller  1002  is not limited to the above supply mechanism. For example, manual insertion using a predetermined guide member as a supplementary means may be used in combination with the above mechanism, manual insertion is used alone or any other mechanism may be used. 
     In  FIG. 9 , a portion expressed with crossing lines indicates the applying liquid L. Here, the thickness of the applying liquid layer on the applying roller  1001  and on the applying medium P is expressed in an exaggerated manner than an actual thickness for clear representation of the state of the applying liquid L at applying. 
     As mentioned above, the applied portion of the applying medium P is conveyed in the arrow direction by a conveying force of the applying roller  1001 . With this, an unapplied portion of the applying medium P is conveyed to the contact portion of the applying medium P and the applying roller  1001 , and the applying liquid is applied over the entire applying medium by carrying out this operation continuously or intermittently. 
       FIG. 9  shows an ideal applying state where all the applying liquid L which has passed through between the contact member  2009  and the applying roller  1001  and adhered to the roller is transferred to the applying medium P. However, in actuality, not all of the applying liquid L adhering to the applying roller  1001  is transferred to the applying medium P. That is, when the applying medium P to be conveyed is separated from the applying roller  1001 , the applying liquid L might adhere to the applying roller  1001  and remain on it. The applying liquid that remains on this applying roller  1001  passes between the applying roller  1001  and the upper edge portion  2010  of the contact member  2009  against the pressing force of the contact member  2009  of the liquid holding member  2001  against the applying roller  1001  and returns into the liquid holding space S. And it is mixed with the applying liquid filled in the space S. 
     In this embodiment, the circulation speed is controlled, considering the return amount of the applying liquid so that the amount finally to be transferred to the applying medium is maintained constant. 
     Moreover, this returning operation of the applying liquid is also carried out even if the applying roller  1001  rotates while the applying medium does not exist as shown in  FIG. 10 . That is, by rotating the applying roller  1001 , the applying liquid adhering to the outer circumference of the applying roller  1001  passes through the portion (nip portion) of the applying roller and the counter roller  1002 . After passing through it, the applying liquid is divided into the applying roller  1001  side and the counter roller  1002  side, and the applying liquid remains on the applying roller  1001 . And the applying liquid L adhering to the applying roller  1001  passes through between the upper edge portion  2010  of the contact member  2009  and the applying roller  1001  and enters into the liquid holding space S, where it is mixed with the applying liquid filled therein. 
     End Process 
     When the applying operation to the applying medium has been executed as mentioned above, determination is made if the applying process may be completed or not (Step S 7 ). If the applying process is not to be completed, the process returns to step S 6 , where the applying operation is repeated till the applying process is completed for all the portions requiring applying of the applying medium. When the applying process is completed, the applying roller  1001  is stopped (Step S 8 ), and moreover, driving of the pump  3007  is stopped (Step S 9 ). After that, the process goes on to Step S 2 , and if the applying start command has been inputted, the operation in the above Steps S 2  to S 8  is repeated. If the applying start command has not been inputted, on the other hand, post processing, such as recovery operation to recover the applying liquid in the holding space S and the liquid flow paths, is carried out (Step  10 ), and the processing relating to the applying is completed. 
     For the above recovery operation, the opening/closing combination of the respective shut-off valves is set to “recovery” and the pump  3007  is driven for a certain period of time. This opening/closing combination allows the liquid applying space S to communicate with the buffer tank  3002  through the second flow path and with the communication port  3008  that is the atmospheric air communication port through the first flow path. By this, the atmospheric air is supplied to the tubes  3102 , the liquid applying space S, the tubes  3103 ,  3104 , the pump  3007  and the tube  3105 , and the filled applying liquid is recovered to the buffer tank  3002 . By performing this recovery operation, evaporation of the applying liquid from the liquid holding space S can be fully prevented or reduced. 
     Also, after the recovery operation, the respective shut-off valves are set to the opening/closing combination of “standing”. With this opening/closing combination, the replaceable tank  3001 , the buffer tank  3002  and the liquid applying space S are shut off from each other. As a result, movement between the tanks or outflow to the outside of the applying liquid can be prevented or reduced even if the attitude of the apparatus is tilted during movement, transportation and the like. 
     According to the above described embodiments, driving of flowing liquid means (pump) for causing a liquid in the liquid holding space to flow is controlled so that the applying amount of the liquid can be adjusted. More specifically, controlling of driving the pump causes the flow speed of the liquid in the liquid holding space to change so that the pressure in the liquid holding space varies. Thereby, the contact force of the liquid holding member against the applying roller varies, and with this variation the amount of applying liquid which goes out of the contact portion varies. In this way, applying amount of the applying liquid can be adjusted. 
     (Embodiment of the Ink-Jet Printing Apparatus) 
       FIG. 20  shows an outline construction of an ink-jet printing apparatus provided with the applying mechanism having approximately the same construction as the above-mentioned liquid applying apparatus. In this ink-jet printing apparatus  1 , a feed tray on which a plurality of printing media P are loaded is provided, and a separation roller  3  of a semilunar shape separates the printing media P loaded on the feed tray one by one and feed it to a conveying path. In the conveying path, an applying roller  1001  and a counter roller  1002  that constitute the liquid applying means of the above liquid applying mechanism are arranged, and the printing medium P fed from the feed tray  2  is fed into between the both rollers  1001 ,  1002 . The applying roller  1001  rotates in the clockwise direction in  FIG. 20  by the rotation of the roller driving motor and applies the applying liquid on the printing surface of the printing medium P while conveying the printing medium P. The printing medium P applied with the applying liquid is fed into a portion between the conveying roller  4  and the pinch roller  5 , and by the counterclockwise rotation of the conveying roller  4  in the figure, the printing medium P is conveyed onto the platen  6  and moved to a position opposite to the printing head  7  constituting the printing means. The printing head  7  is an ink-jet printing head on which the predetermined number of nozzles for ink ejection are disposed, and while the printing head  7  makes scanning in the direction perpendicular to the paper surface of the figure, ink drips are ejected from the nozzles to the printing medium P according to printing data to carry out printing. By alternately repeating this printing operation and a predetermined amount of conveying operation by the conveying roller  4 , images are formed on the printing medium. With this image forming operation, the printing medium P is held between the paper discharge roller  8  and the paper discharge spur  9  provided on the down-stream side of the scanning area of the printing head in the conveying path of the printing medium and discharged onto the paper discharge tray  10  by rotation of the paper discharge roller  8 . 
     As a ink-jet printing apparatus, a so-called full-line type ink-jet printing apparatus, which performs printing operation using a lengthy printing head provided with nozzles for ejecting ink over the maximum width of the printing medium, may be constituted. 
     The applying liquid used in this embodiment is a processing liquid accelerating an aggregation of a pigment when performing printing with an ink having the pigment as a color material. In this embodiment, by using the processing liquid as the applying liquid, aggregation of the pigment is accelerated by making this processing liquid react with the pigment that is a color material of the ink to be ejected onto the printing medium applied with this processing liquid. And this insolubilization can improve the printing density. Moreover, it can reduce or prevent bleeding. It is needless to say that the applying liquid used in the ink-jet printing apparatus is not limited to the above example. 
       FIG. 21  is a perspective view showing an essential part of the above-mentioned ink-jet printing apparatus. As shown in this figure, an applying mechanism  100  is provided above one end of the feed tray  2 , and a printing mechanism with the printing head  7  is provided above the center of the feed tray  2  and the higher position than that of the applying mechanism. 
       FIG. 22  is a block diagram showing an outline construction of a control system of the above-mentioned ink-jet printing apparatus. In this figure, the roller driving mechanism  1004 , the pump driving motor  4009  and shut-off valves  3201 - 3205 , which are elements of the liquid applying mechanism, are the same elements as those described in the above-mentioned liquid applying apparatus. Similarly to the embodiment of the above applying apparatus, a detection portion  5006  has a temperature sensor  5011 , and a controller  5000  has a timer  5017 . 
     A CPU  5001  controls driving of each element of the applying mechanism according to the program of a processing procedure, which will be described later in  FIG. 23 . It also controls driving of an LF motor  5013  a CR motor  5015  and the printing head  7  of the printing mechanism through driving circuits  5012 ,  5014  and  5016  respectively. That is, the driving of the LF motor  5013  rotates the conveying roller  4  and the like, and the driving of the CR motor moves a carriage on which the printing head  7  is mounted. Moreover, control to eject ink from the nozzles of the printing head is carried out. 
       FIG. 23  is a flowchart showing a procedure of the liquid applying and printing operation involved in it in the ink-jet printing apparatus of this embodiment. 
     In this figure, the processing in Steps S 101 , S 103  to S 106  and Step S 109  to S 111  are the same as the processing in Steps S 1 , S 3  to S 6  and S 8  to S 10 , respectively. 
     As shown in  FIG. 23 , when a command to start printing is given (Step S 102 ), a series of liquid applying operations including circulation speed decision processing and a pump operation are carried out (Steps S 103  to S 106 ). Thereby the liquid is applied to portions of the printing medium that require liquid applying. 
     After this applying process, the printing operation is carried out for the printing medium on which the applying liquid has been applied to the portions as required (Step S 107 ). That is, the printing head  7  is made to scan the printing medium P conveyed by the conveying roller  4  by a predetermined amount and ink is ejected from the nozzles according to the printing data during this scanning to apply the ink to the printing medium and form dots on it. Since the applied ink reacts with the applying liquid, printing density can be improved and bleeding can be prevented. By repeating the above conveying of the printing medium and scanning with the printing head, printing is made on the printing medium P and the printed printing medium is discharged onto the paper discharge tray  10 . When it is determined that printing has been completed at Step S 108 , processing at Step S 109  and after is carried out and this whole processing is finished. 
     In this embodiment, with liquid applying to the printing medium, printing is performed sequentially to the portion where the applying has been finished. More specifically, the embodiment is the case that when the length of the conveying path from the applying roller to the printing head is shorter than the length of the printing medium, and when the portion of the printing medium on which the liquid has been applied reaches the scanning area by the printing head, applying is performed by the applying mechanism to another portion on the printing medium. That is, liquid applying and printing are performed sequentially on different portions of the printing medium per predetermined amount of conveyance of the printing medium. However, in another application of the present invention, printing may be performed after applying on one printing medium is completed. 
     Also, in the printing apparatus of the present invention, by applying a liquid including a fluorescent whitening agent by the liquid applying mechanism, whiteness of the medium can be improved. In this case, the printing means after the liquid applying is not limited to the ink-jet printing method but a printing method such as a thermal transfer method, an electronic photo method and the like can obtain the effect. Also, a photosensitizing agent may be applied before printing in a printing apparatus in a silver-halide photography method. 
     (Other Preferred Embodiments) 
     In the above embodiment, a control form to make the applying amount constant by controlling the circulation speed was described, but application of the present invention is not limited to this form. For example, if there is a mode that a larger amount of applying liquid than usual amount is preferable, the pump may be driven so that the circulation speed of the applying liquid in the liquid holding space is slowed in that mode. Conversely, if smaller amount of applying liquid than usual amount is preferable, the pump may be driven so that the circulation speed is increased. 
     As described above, the applying amount can be changed by changing the circulation speed or pressure in the liquid holding space. Therefore, the above described embodiments change the circulation speed or the pressure in the liquid holding space to control the applying amount. However, control method of the applying amount according to the present invention is not limited to the above methods. For example, the applying amount can be changed by changing rotating speed of the applying roller, as shown in  FIG. 18 . Accordingly, the applying amount may be controlled by changing rotating speed of the applying roller, instead of changing the circulation speed. In this case, when it is need to increase the applying amount of the applying liquid, the control is made to increase the rotating speed of the applying roller. Conversely, when it is need to decrease the applying amount of the applying liquid, the control is made to lower the rotating speed of the applying roller. 
     The present invention may include an embodiment in which the rotational speed of the applying roller is changed in accordance with temperature to maintain the applying amount constant. More specifically, the applying amount can be changed by temperature change, as shown in  FIGS. 16 and 17 . Accordingly, for controlling the applying amount to be constant regardless of the temperature, the control may be made to change the rotational speed of the applying roller according to the temperature. 
     Furthermore, as described above, when the contact force between the liquid holding member and the applying roller varies, the amount of the applying liquid going out of the liquid holding space. As a result, the applying amount varies. Therefore, the present invention may include a configuration that controls the applying amount of the applying liquid by employing a change in the contact force between the liquid holding member and the applying roller. For example, when it is need to increase the applying amount of the applying liquid, the control is made to decrease the contact force, and when it is need to decrease the applying amount of the applying liquid, the control is made to increase the contact force. In this manner, the present invention includes the control method as an embodiment which controls the applying amount by changing the contact force between the liquid holding member and the applying roller. In this case, it is no need to change the circulation speed and the rotational speed of the applying roller. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.