Patent Publication Number: US-7588639-B2

Title: Liquid applying apparatus and ink jet printing apparatus

Description:
This application is a division of U.S. patent application Ser. No. 11/052,062, filed Feb. 8, 2005, now U.S. Pat. No. 7,395,778. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a liquid applying apparatus and an ink jet printing apparatus, and specifically, to a liquid applying apparatus that applies a liquid to a medium for a predetermined purpose, for example, for starting the coagulation of pigments earlier when printing is carried out using inks composed of the pigments as color materials. Likewise, the present invention relates to an ink jet printing apparatus comprising a mechanism that applies the liquid to a print medium used for ink jet printing, for a predetermined purpose, for example, for starting the coagulation of pigments earlier when printing is carried out using inks composed of the pigments as color materials. 
   2. Description of the Related Art 
   A spin coater, a roll coater, a bar coater, and a die coater are known as systems for applying a liquid or an aqueous material to various media. These applying systems are premised on continuous applying on relatively long applying media. Thus, for example, if applying media having a relatively small size and intermittently conveyed are to be applied the liquid to, paint beads may be disturbed at a position at which applying is started or ended. In this case, the coats obtained may be non-uniform among the applying media. 
   A known configuration that can solve this problem is described in Japanese Patent Application Laid-open No. 2001-070858. On the basis of the die coater system, this configuration uses a rotating rod bar and ejects a paint to the rod bar through an ejection slit to form a coat on the rod bar. The coat formed is contacted with and transferred to an applying medium as the rod bar rotates. In this case, when the coat formed on the rod bar is not transferred or applied to the applying medium, the paint is returned to a head by the rotation of the rod bar. The paint is then collected via a collecting slit. In other words, the rod bar continues to rotate even during non-applying, while the paint is being formed into a coat on the rod bar. This enables a uniform coat to be obtained even if applying media are intermittently supplied and applied the paint. 
   Even in the field of ink jet printing apparatuses, those using a liquid applying mechanism are known. Japanese Patent Application Laid-open No. 2002-517341 describes an apparatus which uses a doctor blade contacting with a roller and in which the application liquid is collected between the blade and the roller so that the application liquid is applied to the roller as the roller rotates. As the roller rotates, the application liquid applied to the roller is transferred and applied to a support conveyed between this roller and another roller. Japanese Patent Application Laid-open No. 08-072227 (1996) similarly discloses a mechanism in an ink jet printing apparatus which applies a treatment liquid before printing which liquid insolubilizes dyes. In Embodiment 1 of this document, the treatment liquid in a replenishing tank is pumped by being attached to the rotating roller. At the same time, the treatment liquid pumped is applied to print paper. 
   With the configurations described in the above patent documents, an application liquid is applied or supplied to the surface of the rod bar or roller. However, the part of the rod bar or roller to which the application liquid is applied or supplied is open to or in communication with the air. Thus, disadvantageously, the application liquid may be evaporated or for example, the application liquid may leak when the posture of the apparatus is changed. 
   In particular, with an ink jet printing apparatus such as a printer, in view of, for example, the leakage of the liquid caused by a change in the posture of the apparatus, it is difficult to apply the applying mechanism described in the above documents to the apparatus if its size has been reduced. 
   In contrast, Japanese Patent Application Laid-open No. 08-058069 (1996) discloses a configuration that seals a part that applies or supplies inks, that is, application liquids, to a roller. The applying mechanism described in this document operates in a gravure printing apparatus to apply inks to a roller (applying roller) having the surface of which is formed with a pattern of a printing plate. This mechanism uses an ink chamber having two doctor blades arranged at two vertical positions along a peripheral surface of the roller and extending in a longitudinal direction of the roller and elastic members provided at the opposite sides of the two doctor blades. The chamber is contacted with the peripheral surface of the roller to form a liquid chamber between the ink chamber and the roller. Then, the roller is rotated to apply or supply the application liquid from the liquid chamber to the roller. 
   However, the sealing arrangement disclosed in Japanese Patent Application Laid-open No. 08-058069 (1996) may provide an insufficient sealing property. That is, the doctor blades are separate from the elastic members provided at the opposite ends of each of the doctor blades through both doctor blades and elastic members are abutted against the roller for sealing. Thus, for example, the pressure exerted on the roller upon abutment may vary significantly between these members. In this case, the abutting pressure differs markedly between the junctions between the doctor blades and the elastic members and the other parts. Thus, the sealing may be insufficient in parts with a lower abutting pressure, resulting in the leakage of the liquid. If the abutting pressure itself is set at a large value in order to prevent the leakage of the liquid caused by the non-uniform abutting pressure, the application of inks to the roller may be unsatisfactory, which application is carried out by the blades and the roller in cooperation. 
   Moreover, in Japanese Patent Application Laid-open No. 08-058069 (1996), the ink chamber comprising the doctor blades and the elastic members is moved by engaging the ink chamber with a shaft in which a thread groove is formed and then rotating the shaft. The abutting pressure between the roller and the doctor blades and elastic members is exerted by simply fixing the position of the chamber. Thus, for example, if there are small concaves and convexes on the peripheral surface of the roller, the abutment does not conform to the concaves and convexes. This may degrade the sealing property to prevent inks from being favorably applied to the roller. 
   Further, Japanese Patent Application Laid-open No. 08-058069 (1996) describes the doctor blades provided to scrape extra inks adhering to the surface of the roller. Accordingly, this document does not disclose the configuration of blades or abutting portions which are preferred in association with the sealing property if the liquid is applied to the entire surface of a medium such as paper which has a certain thickness. 
   As described above, in association with the supply of the coating liquid to the roller, an arrangement is important which uses the abutting portion to appropriately seal the coating liquid chamber formed between the abutting portion and the roller. More specially, it is extremely important to provide the liquid holding space with a good sealing condition in order to keep a good quality of the applying liquid and enhance a handling ability of the applying apparatus in moving and transporting it. Accordingly, it is required to prevent the applying liquid from being evaporated and/or leaked while a roller remains stopped for a long time and when the posture of the applying apparatus happens to be tilted. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a liquid applying apparatus which can prevent an applying liquid from evaporating while an applying operation is at a stop and which can reliably prevent the liquid from leaking even when for example, the posture of the apparatus is tilted. 
   A first aspect of the present invention provides a liquid applying apparatus comprising a applying member which applies a liquid to a medium and which has a applying surface and a liquid holding member that abuts against the applying surface of the applying member to form a liquid holding space in which the liquid is held, the applying surface of the applying member being rotatively moved to apply the liquid supplied to the applying surface to the applying medium, the apparatus being characterized in that an abutting portion of the liquid holding member which abuts against the applying surface of the applying member is annularly formed of a single member. 
   Further, a second aspect of the present invention provides a printing apparatus characterized by comprising conveying means for conveying a print medium along a predetermined conveying path, printing means for printing the print medium, and a liquid applying mechanism that applies a liquid to the print medium conveyed along the conveying path, wherein the liquid applying mechanism comprises a applying member which applies a liquid to a medium and which has a applying surface and a liquid holding member that abuts against the applying surface of the applying member to form a liquid holding space in which the liquid is held, the applying surface of the applying member is rotatively moved to apply the liquid supplied to the applying surface to the applying medium, and an abutting portion of the liquid holding member which abuts against the applying surface of the applying member is annularly formed of a single member. 
   According to the present invention, a sufficient liquid-tight state can be established between the applying surface and the abutting portion. This makes it possible to prevent the applying liquid supplied to the liquid holding space from evaporating even if the apparatus is not used for a long period. Moreover, the present invention can prevent the applying liquid from leaking even if the whole apparatus is tiled during movement, transportation, or the like. 
   The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view generally showing the configuration of an embodiment according to a liquid applying apparatus of the present invention; 
       FIG. 2  is a vertical side view showing an example of the arrangement of a applying roller, a counter roller, a liquid holding member, and the like which are 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 view showing an end surface of the liquid holding member shown in  FIG. 3 , the view taken along line IV-IV in  FIG. 3 ; 
       FIG. 5  is an end view showing the end surface of the liquid holding member shown in  FIG. 3 , the view taken along line V-V in  FIG. 3 ; 
       FIG. 6  is a plan view of the liquid holding member shown in  FIG. 3 ; 
       FIG. 7  is a left side view showing how an abutting portion of the liquid applying member shown in  FIG. 3  is abutted against a liquid applying roller; 
       FIG. 8  is a right side view showing how the abutting portion of the liquid applying member shown in  FIG. 3  is abutted against the liquid applying roller; 
       FIG. 9  is a vertical sectional view showing how a applying liquid is filled into a liquid holding space formed by the liquid holding member and the applying roller and how a liquid is applied to a applying medium by the rotation of the applying roller; 
       FIG. 10  is a vertical sectional view showing how the applying liquid is filled into the liquid holding space formed by the liquid holding member and the applying roller and how the applying roller is rotated when no applying medium is present; 
       FIG. 11  is a diagram generally showing the configuration of a liquid channel in the liquid applying apparatus according to the embodiment of the present invention; 
       FIG. 12  is a block diagram generally showing the configuration of a control system according to the embodiment of the present invention; 
       FIG. 13  is a flowchart showing a liquid applying operation sequence according to the embodiment of the present invention; 
       FIG. 14  is a graph showing the relationship between a pressing force exerted by an abutting member on the applying roller and the amount of applying liquid applied to the applying medium according to a first embodiment of the present invention; 
       FIG. 15  is a vertical side view showing an essential part of a second embodiment of the present invention; 
       FIG. 16  is a vertical side view showing an essential part of a third embodiment of the present invention; 
       FIG. 17  is a vertical side view showing an essential part of a fourth embodiment of the present invention; 
       FIG. 18  is a partly cutaway front view of the liquid holding member shown in  FIG. 17 ; 
       FIG. 19  is a side view of the liquid holding member shown in  FIG. 18 ; 
       FIG. 20  is a vertical side view generally showing the configuration of an ink jet printing apparatus according to the 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 generally showing the configuration of a control system of the ink jet printing apparatus according to the present invention; 
       FIG. 23  is a flowchart showing the sequences of an applying operation and a printing operation according to another embodiment of the present invention; 
       FIG. 24  is a diagram illustrating a applying process executed on a surface of a medium and a applying surface upstream of a nip portion between the applying roller and a counter roller if the medium is ordinary paper according to the embodiments of the present invention; 
       FIG. 25  is a diagram showing the state of the surface of the ordinary paper and the applying surface of the applying roller, at the nip portion between the applying roller and the counter roller; 
       FIG. 26  is a diagram showing the state of the surface of the ordinary paper and the applying surface of the applying roller downstream of the nip portion between the applying roller and the counter roller; 
       FIG. 27  is a graph showing measured values of a load torque applied to a driving shaft of a motor when rotation is started, each value being measured with a condition that the applying roller is composed of a different material; 
       FIG. 28  is a graph showing measured values of the load torque applied to the driving shaft of the motor when rotation is started, each value being measured with a condition that the abutting member is composed of a different material; 
       FIG. 29  is a sectional view of the applying roller and the liquid holding member, in which the liquid holding member is brought into pressure contact with the applying roller from below in a vertical direction; 
       FIG. 30  is a sectional view showing the liquid holding member placed on a horizontal line passing through a rotational center of the applying roller; 
       FIG. 31  is a sectional view showing how the liquid holding member is placed so that a liquid applying space is partly located below the applying abutting surface; 
       FIG. 32  is a sectional view of the applying roller and the liquid holding member, showing an area effectively used as a position where the liquid holding member is brought into pressure contact with the applying roller; 
       FIG. 33  is a perspective view showing an applying roller and liquid applying means according to a fourth embodiment; 
       FIG. 34  is a sectional view of a liquid holding member shown in  FIG. 33 ; 
       FIG. 35  is a sectional view of the liquid holding member shown in  FIG. 33 ; 
       FIG. 36  is a side view of a liquid holding mechanism shown in  FIG. 33 ; and 
       FIG. 37  is a side view of the liquid holding mechanism shown in  FIG. 33 . 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 
   First Embodiment 
   According to the present embodiment, if the applying operation is not performed, a liquid is collected from a liquid holding space formed between an applying roller and a liquid holding member to hold the liquid. 
     FIG. 1  is a perspective view generally showing the configuration of an embodiment according to a liquid applying apparatus  100  of the present invention. The liquid applying apparatus shown in  FIG. 1  roughly has liquid applying means for applying a predetermined application liquid to a medium to which a liquid is to be applied (this medium will be referred to as a applying medium in the description below) and liquid supplying means for supplying a application liquid to the liquid applying means. 
   The liquid applying means has a cylindrical applying roller  1001 , a cylindrical counter roller (medium supporting member) placed opposite the applying roller  1001 , and a roller driving mechanism  1003  that drives the applying roller  1001 . The roller driving mechanism  1003  comprises a roller driving motor  1004  and a transmission mechanism  1005  which transmits the driving force of the roller driving motor  1004  to the applying roller  1001  and which has a gear train and the like. 
   The liquid supplying means has, for example, a liquid holding member  2001  that holds the application liquid between the liquid holding member  2001  and a peripheral surface of the applying roller  1001 , and a liquid channel  3000  (not shown in  FIG. 1 ) described later and through which the liquid is supplied to the liquid holding member  2001 . The applying roller  1001  and the counter roller  1002  are rotatively movably supported by respective shafts which are parallel to each other and each of which has opposite ends rotatively movably attached to a frame (not shown). Further, the liquid holding member  2001  extends almost all along the applying roller  1001  in a longitudinal direction. The liquid holding member  2001  is movably attached to the frame via a mechanism that enables the liquid holding member  2001  to contact with and separate from the peripheral surface of the applying roller  1001 . 
   The liquid applying apparatus according to the present embodiment further comprises an applying medium supplying mechanism  1006  which consists of a pickup roller or the like to convey an applying medium to a nip portion between the applying roller  1001  and the counter roller  1002 . Further, in a conveying path for applying media, a sheet discharging mechanism  1007  consisting of a sheet discharging roller or the like is provided downstream of the applying roller  1001  and the counter roller  1002  to convey a applying medium on which the application liquid has been applied, to a sheet discharging section (not shown). Like the applying roller and the like, the sheet supplying mechanism and the sheet discharging mechanism are operated under the driving force of the driving motor  1004  transmitted via the transmission mechanism  1005 . 
   The application liquid used in the present embodiment is intended to facilitate the coagulation of pigments when printing has been carried out using inks including the pigments as color materials. 
   An example of the components of the application liquid is shown below. 
   Tetrahydrate of calcium nitrate: 10% 
   Glycerin: 42% 
   Surface active agent: 1% 
   Water: remaining amount 
   The application liquid has a viscosity of 5 to 6 cp (centipoise) at 25° C. 
   In applications of the present invention, of course, the application liquid is not limited to the one described above. For example, a liquid including a component which insolubilizes or coagulate a dye may be used as another application liquid. 
   If water is used as a liquid to be applied, the slidability of the abutting portion between the applying roller and the liquid holding member according to the present invention is improved by containing a component that reduces surface tension in the liquid. In the above example of the components of the liquid to be applied, the glycerin and the surface active agent are components that reduce the surface tension. 
   Now, a detailed description will be given of the elements of the sections of the applying apparatus described above in brief. 
     FIG. 2  is a vertical sectional view illustrating an example of the arrangement of the applying roller  1001 , the counter roller  1002 , and the liquid holding member  2001 . 
   The counter roller  1002  is biased by biasing means (not shown) toward the peripheral surface of the applying roller  1001 . By rotating the applying roller  1001  clockwise in the figure, it is possible to sandwich an applying medium P on which the application liquid is to be applied, between the rollers, while conveying the applying medium P in the direction of an arrow in the figure. 
   According to the present embodiment, the applying roller is formed of silicon rubber and has a hardness of 40°, a surface roughness Ra of 1.6 μm, and a diameter of 23.169 mm. The counter roller  1002  is formed of iron and has a diameter of 14 mm. 
   Further, when urged and abutted against the peripheral surface of the applying roller  1001  under the biasing force of a spring member (pressing means)  2006 , the liquid holding member  2001  forms an elongate liquid holding space S extending all over an area applied the liquid by the applying roller  1001 . The application liquid from a liquid channel  3000 , described later, is supplied to the interior of the liquid holding space S via the liquid holding member  2001 . In this case, since the liquid holding member  2001  is configured as described below, the application liquid can be prevented from inadvertently leaking from the liquid holding space S to the exterior while the applying roller  1001  is stopped. 
     FIGS. 3 to 8  show the configuration of the liquid holding member  2001 . 
   As shown in  FIG. 3 , the liquid holding member  2001  has a space forming base material  2002  and an annular abutting member  2009  located on one surface of the space forming base material  2002 . A concave portion  2003  is formed in a central portion of the space forming base material  2002  along its longitudinal direction; a bottom portion of the concave portion  2003  has a circular cross section. The abutting member  2009  has linear portions fastened along the upper edges of the concave portion  2003  and circumferential portions fastened so as to extend from the upper edge through the bottom portion to the opposite upper edge. Thus, when the abutting member  2009  of the liquid holding member  2001  abuts against the applying roller  1001 , the abutment conforms to the shape of the peripheral surface of the applying roller. It is thus possible to achieve the abutment at a uniform pressure. 
   As described above, in the liquid holding member according to this embodiment, the abutting member  2009 , formed integrally and seamlessly, is continuously abutted without a gap against the outer peripheral surface of the applying roller  1001  under the biasing force of the spring member  2006 . As a result, the liquid holding space S is substantially closed by the abutting member  2009 , one surface of the space forming base material, and the outer peripheral surface of the applying roller  1001 . The liquid is held in this space. Then, when the rotation of the applying roller  1001  is stopped, the abutting member  2009  and the outer peripheral surface of the applying roller  1001  maintain a liquid tight state. The liquid can be reliably prevented from leaking to the exterior. On the other hand, when the applying roller  1001  rotates, the applying liquid flows slippery between the outer peripheral surface of the applying roller  1001  and the abutting member  2009 . The applying liquid then adheres to the outer peripheral surface of the applying roller in layers. In this case, when the applying roller  1001  is stopped and the liquid tight state is established between the outer peripheral surface of the applying roller  1001  and the abutting member  2009 , the liquid cannot flow out of the space as described above. In this case, the abutting state of the abutting member  2009  includes not only direct abutment against the outer peripheral surface of the applying roller  1001  but also abutment against the outer peripheral surface via a liquid film formed under a capillary force. 
   As shown in  FIGS. 3 to 8 , the longitudinally opposite sides of the abutting member  2009  are gently curved as viewed from its front ( FIG. 3 ), from above ( FIG. 6 ), or from its side ( FIGS. 7 and 8 ). Thus, even when the abutting member  2009  is abutted against the applying roller  1001  under a relatively high pressure, the whole abutting member  2009  is substantially uniformly elastically deformed. This prevents large distortions locally. Thus, as shown in  FIGS. 6 to 8 , the abutting member  2009  abuts tightly without the gap against the outer peripheral surface of the applying roller  1001 . As a result, a substantially closed space can be formed as described above. 
   On the other hand, as shown in  FIGS. 3 to 5 , a liquid supplying port  2004  and a liquid collecting port  2005  are formed in an area of the space forming base material  2002  which is surrounded by the abutting member  2009 ; the liquid supplying port  2004  and the liquid collecting port  2005  have holes penetrating the space forming base material  2002 . The liquid supplying port  2004  and the liquid collecting port  2005  are communicating with cylindrical connecting portions  20041  and  20051  projected from a back surface of the space forming base material. Further, the connecting portions  20041  and  20051  are connected to a liquid channel  3000  described later. In this embodiment, the liquid supplying port  2004  is formed near one end of an area surrounded by the abutting member  2009  (the left end in  FIG. 3 ), while the liquid collecting port  2005  is formed near the other end of the same area (the right end in  FIG. 3 ). The liquid supplying port  2004  is used to supply the application liquid provided through the liquid channel  3000 , to the liquid holding space S. The liquid collecting port  2005  is used to allow the liquid in the liquid holding space S to flow out to the liquid channel  3000 . The supply and flowout of the application liquid allows the liquid to flow from the left end to right end of the liquid holding space S. 
     FIGS. 29 to 32  are sectional views of the abutting portion between the applying roller  1001  and the liquid holding member  2001 . With reference to  FIGS. 29 to 32 , description will be given of a position where the liquid holding member  2001  is brought into pressure contact with the applying roller  1001 . The applying roller  1001  rotates in the directions of arrows in the figures to apply the liquid to the print medium. The abutting portion of the liquid holding member  2001  has an upper edge  2010  and a lower edge  2011  which extend in a direction crossing the one in which the applying roller  1001  is rotatively moved, and a left edge  2012  and a right edge  2013  which extend along the rotative moving direction of the applying roller  1001  (see  FIG. 3 ). For the surfaces of the right edge  2010  and lower edge  2011  which abut against the applying member  1001 , the abutting surface located downstream in the rotative moving direction of the applying member  1001  is called an abutting surface F 1 . The abutting surface located upstream in the rotative moving direction of the applying member  1001  is called an abutting surface F 2 . 
   If the liquid holding member  2001  is placed, in a vertical direction, below a horizontal line passing through a rotational center of the applying roller  1001  as shown in  FIG. 29 , the liquid holding space S is entered by an amount of air corresponding to the transfer to the applying roller  1001 . Consequently, bubbles are generated in the liquid holding space S. Thus, the bubbles remain on the applying abutting surface F 1 . Further, when the amount of liquid in the liquid holding space S decreases, the level may not reach the peripheral surface of the applying roller  1001 . As a result, stable applying cannot be achieved in this state. The bubbles also remain on the applying abutting surface F 1  if the applying abutting surface F 1  of liquid holding member  2001  is placed above its non-applying abutting surface F 2 . Therefore, when the applying abutting surface F 1  between the applying roller  1001  and the liquid holding member  2001  is placed below the non-applying abutting surface F 2 , the bubbles associated with the supply of the liquid are collected at the non-applying abutting surface F 2 . Stable applying is thus accomplished. 
   As described below, according to the present embodiment, when the apparatus is powered off or if for example, no print instruction has been transmitted for a specified time, a collecting operation is performed to collect the applying liquid from the liquid holding space S and liquid channel  3000 . 
   Now, consideration will be given of the case in which the liquid holding member  2001  is placed on the horizontal line passing through the rotational center of the applying roller  1001  as shown in  FIG. 30 . In this case, the applying abutting surface F 1  is located below the non-applying abutting surface F 2  in the vertical direction. Further, the liquid holding member  2001  is pressed against the applying roller  1001  in a horizontal direction. In this state, when the applying liquid is collected, the liquid remains in the applying abutting surface F 1  of the liquid holding member  2001 . When the apparatus is left in this liquid remaining state for a long time, the leakage of the liquid may occur while the apparatus is being transported. The liquid also remains in the applying abutting surface F 1  during the collecting operation even if the liquid holding member  2001  is placed, in the vertical direction, above the horizontal line passing through the rotational center of the applying roller  1001 . 
   Accordingly, as shown in  FIG. 31 , the liquid holding member  2001  is placed so that the liquid holding space S partly includes a space below the applying abutting surface F 1 . Thus, the liquid is gathered at a root C of the projecting portion of the liquid holding member  2001 . This reduces the amount of liquid remained at the applying abutting surface F 1  during collecting liquid to the storage tank. The above problem can thus be prevented. To allow the liquid to be gathered at the root C of the projecting portion, it is necessary to press the liquid holding member  2001  against the applying roller  1001  upward from the horizontal line. In this case, even in view of the tolerances of the parts, errors in mounting of the parts, errors in the flexure of the liquid holding member  2001  caused by the elasticity of its material, and the like, it is sufficient to mount the liquid holding member  2001  relative to the applying roller  1001  so that the pressing direction is inclined at at least 10° from the horizontal in a forward rotating direction. 
   As described above, the liquid holding member  2001  is desirably placed so that its applying abutting surface F 1  is below its non-applying abutting surface F 2  and that the liquid holding member  2001  is pressed against the applying roller  1001  in a direction inclined upward from the horizontal position in the vertical direction at least 10°. In other words, the liquid holding member  2001  is desirably placed in such an area as shown in  FIG. 32 , relative to the applying roller  1001 . This prevents bubbles from remaining at the applying abutting surface F 1  between the applying roller  1001  and the liquid holding member  2001  during the applying operation. Further, during the collecting operation, the amount of liquid remaining at the abutting surfaced F 1  decreases. 
   In the present embodiment, the applying abutting surface F 1  is set below that the non-applying abutting surface F 2 . The applying roller  1001  and the liquid holding member  2001  are arranged so that the midpoint between the upper edge  2010  and lower edge  2011  of the liquid holding member  2001  is on a straight line inclined, in the forward rotating direction, at 45° from the horizontal line passing through the rotational center of the applying roller  1001 . 
   (Application Liquid Channel) 
     FIG. 11  is a diagram generally illustrating the configuration of the liquid channel (supplying channel)  3000 , connected to the liquid holding member  2001  of the application liquid supplying means. 
   The liquid channel  3000  has a first channel  3001  that connects the liquid supplying port  2004  of the space forming base member  2002 , constituting the liquid holding member  2001 , to a storage tank  3003  that stores the application liquid, a second channel (collecting channel)  3002  that connects the liquid collecting port  2005  of the space forming base material  2002  to the storage tank  3003  together. An air communicating port  3004  is formed in the storage tank  3003 . The air communicating port  3004  is provided with an air communicating valve  3005  that selectively switches between a communicating state for the air and a closed state for the same. Further, the first channel  3001  is provided with a selector valve  3006 . The selector valve  3006  switches between a communicating state of the first channel  3001  with the air and a closed state of the same. Moreover, the second channel  3002  connects to a pump  3007  used to force the application liquid and air to flow through the liquid channel  3000  in a desired direction. In this embodiment, the pump generates a flow of the liquid in a direction from the first channel  3001  to the second channel  3002  via the liquid holding space S (as shown by an arrow in  FIG. 11 ). 
   In this embodiment, the first channel  3001  and the second channel  3002  are formed of cylindrical tubes. An opening formed at an end of each tube is placed at the bottom of the storage tank  3003  or close to the bottom. The position of the opening allows the application liquid in the storage tank  3003  to be completely consumed. 
   According to this embodiment, various types of the selector valves  3006  are applicable provided that they selectively enable and disable the communication between the first channel  3001  and the air. In this case, a three-way valve is used as shown in  FIG. 11 . The three-way valve  3006  has three ports that are in communication with one another. It is possible to allow two of the three ports to selectively communicate with any two of the storage tank tube  3011  in the first channel  3001 , liquid holding member tube  3012 , and air communicating port  3013 . The three-way valve  3006  is selectively switched between a connected state in which the tubes  3011  and  3012  are in communication with each other and a connected state in which the tube  3012  and the air communicating port  3013  are in communication with each other. This enables the application liquid in the storage tank  3003  or air obtained through the air communicating port  3013  to be selectively supplied to the space S formed by the liquid holding member  2001  and the applying roller  1001 . The switching of the three-way valve  3006  is carried out in accordance with a control signal from a control section  4000  described later. Thus, the application liquid is filled or supplied. 
   (Control System) 
     FIG. 12  is a block diagram generally showing the configuration of the control system in the liquid applying apparatus according to the present embodiment. 
   In  FIG. 12 , the control section  4000  operates as control means for controlling the whole liquid applying apparatus. The control section  4000  has a CPU  4001  that performs various process operations such as calculations, control, and determinations, a ROM  4002  that stores, for example, control programs for processes executed by the CPU  4001 , such as the one described later in  FIG. 13 , and a RAM  4003  that temporarily stores data used during process operations of the CPU  4001  as well as input data. 
   The control section  4000  connects to an input operation section  4004  including a keyboard, various switches, or the like with which predetermined instructions or data are input, a display section  4005  that provides various displays including inputs to and the set state of the liquid applying apparatus, and a detecting section  4006  including a sensor or the like which detects the position of a applying medium or the operational state of each section. The control section  4000  also connects to the roller driving motor  1004 , a pump driving motor  4009 , an air communicating valve  3005 , and the selector valve  3006 , via driving circuits  4007 ,  4008 ,  4010 , and  4011 . 
   (Liquid Applying Operation Sequence) 
     FIG. 13  is a flowchart showing a process procedure for applying a liquid in the liquid applying apparatus according to the present embodiment. The steps of liquid application will be described below with reference to this flowchart. 
   When the liquid applying apparatus is powered on, the control section  4000  executes an applying operation sequence described below, in accordance with the flowchart shown in  FIG. 13 . 
   Filling Step 
   In step S 1 , the liquid holding space S is filled with the application liquid. In this filling step, the air communicating valve  3005  of the storage tank  3003  is first opened to the air. The selector valve (three-way valve)  3006  is also switched as shown in  FIG. 19 . This allows the tubes  3011  and  3012  to communicate with each other to drive the pump  3007  for a specified time. Thus, air and/or the application liquid flows from the pump  3007  to the storage tank  3003 . Accordingly, if the liquid holding space S and the channels  3001  and  3002  have not been filled with the application liquid, the pump drives the air inside the space and channels out to the storage tank  3003 . The air is then discharged to the exterior of the apparatus. These portions are then filled with the application liquid. On the other hand, if these portions have already been filled with the application liquid, the application liquid in these portions starts to flow. These portions are thus supplied with an application liquid having an appropriate concentration and viscosity. This initial operation allows the application liquid to be supplied to the applying roller  1001 . It is thus possible to apply the application liquid to the applying medium. 
   Applying Step 
   Then, an applying start instruction is input (step S 2 ). Then, the pump  3007  restarts operation (step S 3 ). The applying roller starts rotating clockwise as shown by an arrow in  FIG. 1  (step S 4 ). The rotation of the applying roller  1001  causes the application liquid L filled into the liquid holding space S to slippery flow between the applying roller  1001  and a lower edge  2011  of the abutting member  2009  against the pushing force of the abutting member  2009  of the liquid holding member  2001 , which force acts on the applying roller  1001 . The application liquid adheres to the outer periphery of the applying roller  1001  in layer form. The application liquid L adhering to the applying roller  1001  is transferred to the abutting portion between the applying roller  1001  and the counter roller  1002 . 
   Then, an applying medium supplying mechanism  1006  conveys an applying medium to between the applying roller  1001  and the counter roller  1002 . The applying medium is inserted between these rollers and conveyed to a sheet discharging section as the applying roller  1001  and the counter roller  1002  rotate (step S 5 ). During this conveyance, the application liquid applied to the peripheral surface of the applying roller is transferred from the applying roller  1001  to the applying medium P as shown in  FIG. 9 . Of course, means for supplying an applying medium to between the applying roller  1001  and the counter roller  1002  is not limited to the above supplying mechanism. It is possible to use any means, for example, manual means which uses a predetermined guide member or which is solely used. 
   In  FIG. 9 , an area with crossing oblique lines denote the application liquid L. In this case, the application liquid on the applying roller  1001  and applying medium P is shown considerably thicker than the actual one in order to clearly illustrate how the application liquid L is applied. 
   As described above, an applied part of the applying medium P is conveyed in the direction of the arrow under the conveying force of the applying roller  1001 . Further, an unapplied part of the applying medium P is conveyed to the contact portion between the applying medium P and the applying roller  1001 . This operation is continuously or intermittently performed to apply the application liquid to the entire applying medium. 
     FIG. 9  shows the ideal applied state in which the all of the application liquid L adhering to the applying roller  1001  after slippery flowing out of the abutting member  2009  is transferred to the applying medium P. However, actually, not all of the application liquid L adhering to the applying roller  1001  is not transferred to the applying medium P. Specifically, when the applying medium P conveyed separates from the applying roller  1001 , the application liquid L often also adheres to and remains on the applying roller  1001 . The amount of application liquid L remaining on the applying roller  1001  varies depending on the material of the applying medium P or the state of fine concaves and convexes on the surface of the applying medium P. However, if the applying medium P is ordinary paper, the application liquid L remains on the peripheral surface of the applying roller  1001  after an applying operation. 
     FIGS. 24 ,  25 , and  26  are diagrams illustrating the process of applying between a surface of the medium P and an applying surface in the case where the medium is ordinary paper. In these figures, the liquid is painted over with black. 
     FIG. 24  shows the state of the upstream side of the nip portion between the applying roller  1001  and the counter roller  1002 . In this figure, the liquid adheres to the applying surf ace of the applying roller  1001  so as to slightly cover the fine concaves and convexes on the applying surf ace. 
     FIG. 25  shows the state of the surf ace of ordinary paper, the medium P, and the applying surf ace of the applying roller  1001 , at the nip portion between the applying roller  1001  and the counter roller  1002 . In this figure, the convexes on the surface of the ordinary paper, the medium P, contact with the applying surface of the applying roller  1001 . The liquid instantaneously permeates through or sticks to fibers in the surface of the ordinary paper, the medium P, through the contacting parts. The liquid adhering to those parts of the applying surface of the applying roller which do not contact with the convex portions on the surface of the ordinary paper remains on the applying surface. 
     FIG. 26  shows the state of the downstream side of the nip portion between the applying roller  1001  and the counter roller  1002 . In this figure, the medium has completely left the applying surface of the applying roller  1001 . The liquid adhering to those parts of the applying surface of the applying roller  1001  which do not contact with the convex portions on the surface of the ordinary paper remains on the applying surface. The liquid on the contacting parts also remains with very small amount on the applying surface. 
   The application liquid remaining on the applying roller  1001  slippery flows between the applying roller  1001  and the upper edge  2010  of the abutting member  2009  and returns to the liquid holding space S, against the pushing force of the abutting member  2009  of the liquid holding member  2001 , which force acts on the applying roller  1001 . The application liquid is then mixed with the application liquid filled into the space S. 
   The operation of returning the application liquid is similarly performed if the applying roller  1001  is rotated while no applying medium is present as shown in  FIG. 10 . That is, the application liquid adhering to the outer periphery of the applying roller  1001  as a result of the rotation of the applying roller  1001  slippery flows through the abutting portion between the applying roller  1001  and the counter roller  1002 . After flowing through the abutting portion, the application liquid is separated into two parts directed to the applying roller  1001  and the counter roller  1002 , respectively. The application liquid remains on the applying roller  1001 . Then, the application liquid adhering to the applying roller  1001  slippery flows between the upper edge  2010  of the abutting member  2009  and the applying roller  1001  to enter the liquid holding spaces. The application liquid is then mixed with the application liquid filled into the space S. 
   Ending Step 
   Once the operation of applying the liquid to the applying medium has been performed as described above, the apparatus determines whether or not to finish the applying step. If the applying step is not to be finished, the process returns to step S 5  to repeat the applying operation until the applying step is executed on the all the parts of the applying medium to which the liquid needs to be applied. When the applying step is finished, the applying roller  1001  is stopped (step S 7 ). Moreover, the driving of the pump  3007  is stopped (step S 8 ). Subsequently, the process shifts to step S 2  to repeat the operations from step S 2  to step S 8  unless an applying start instruction is input before a predetermined period elapses. Even after the predetermined period has elapsed, if the applying start instruction is not input, a postprocess is executed such as a collecting operation of collecting the application liquid from the liquid holding space S and liquid channels (step S 9 ). Then, the applying process is finished. 
   The collecting operation is performed by opening the air communicating valve  3005  and selector valve  3006  and driving the pump  3007  to cause the applying liquid in the applying liquid holding space S and second channel  3002  to flow into the liquid storing tank  3003 . The collecting operation makes it possible to prevent the applying liquid from evaporating from the liquid holding space S. Further, after the collecting operation, the air communicating valve  3005  is closed and the selector valve  3006  is switched to block the communication between the liquid storing tank  3003  and both first channel  3001  and air communicating port  3013 . The liquid storing tank  3003  is thus shut off from the air. Thus, the applying liquid can be prevented from evaporating from the liquid storing tank  3003 . The applying liquid can also be prevented from flowing out even if the posture of the apparatus is tilted during movement, transportation, or the like. 
   As described above, in the liquid applying apparatus according to this embodiment, the rotation of the applying roller  1001  causes the applying liquid filled into the liquid holding space S to flow slipperily out of the liquid holding space S against the pressing force of the lower edge  2011  of the abutting member  2009  exerted on the applying roller  1001 . The applying liquid is then supplied to the peripheral surface of the applying roller  1001  in layers. The thickness of the layers of the applying liquid, that is, the amount of applying liquid to be supplied to the applying roller  1001 , depends on the viscosity of the applying liquid, the relative speed between the outer peripheral surface of the applying roller and the applying medium, and the pressing force of the abutting member exerted on the outer peripheral surface of the applying roller  1001 . 
     FIG. 14  is a graph showing the measured amount of the above applying liquid applied to ordinary paper at 23° C. using the liquid applying apparatus according to this embodiment. In  FIG. 14 , the axis of abscissa indicates the total of forces of plural spring members  2006  used to allow the abutting member  2009  to exert the pressing force on the applying roller  1001 . The axis of ordinate indicates the amount of applying liquid applied. Measured values shown by white squares indicate the amount of applying liquid applied when relative movement speed is set at 114 mm/sec. A continuous line in the figure is obtaining by joining the averages of measured values together, the measured values being obtained by measuring the amount of applying liquid applied, three times for each pressing force under the above speed condition. On the other hand, measured values shown by blackened triangles indicate the amount of applying liquid applied when the relative movement speed is set at 35 mm/sec. A dot line in the figure indicates the amount of applying liquid applied when the relative movement speed is set at 35 mm/sec. The dot line is also obtaining by joining the averages of measured values together, the measured values being obtained by measuring the amount of applying liquid applied, three times for each pressing force under the above speed condition. 
   As is apparent from the above graph, the stronger the pressing force of the abutting member  2009  exerted on the outer peripheral surface of the applying roller  1001 , the smaller the thickness of the layer of the applying liquid flowing out slipperily from between the abutting member  2009  and the applying roller  1001 . As a result, the amount of applying liquid applied decreases. On the other hand, the higher the relative speed, the larger the thickness of the layer of the applying liquid flowing out slipperily from between the abutting portions. As a result, the amount of applying liquid applied increases. 
   In this embodiment, foreign matter such as paper dust or dirt may be caught in the nip portion between the applying roller  1001  and the lower edge  2011  of the abutting member  2009 , between the applying roller  1001  and the upper edge  2010  of the abutting member  2009 . According to the present embodiment, a frictional force exerted between the applying roller  1001  and the foreign matter is stronger than that exerted between the abutting member  2009  and the foreign matter. Thus, the foreign matter moves together with the applying roller  1001  instead of remaining between the applying roller  1001  and the abutting member  2009 . In contrast, if the frictional force exerted between the applying roller  1001  and the foreign matter is weaker than that exerted between the abutting member  2009  and the foreign matter, the foreign matter remains between the abutting member  2009  and the applying roller  1001 . This may result in, for example, the nonuniform application of the applying liquid or the entry of air into the liquid holding space. 
   To set the frictional force exerted between the applying roller  1001  and the foreign matter stronger than that exerted between the abutting member  2009  and the foreign matter as described above, this embodiment sets the hardness of the applying roller  1001  lower than that of the lower edge  2011  or the upper edge  2010 . Further, the abutting member  2009  is formed of a material that can slide more smoothly (that has a smaller coefficient of friction) than the applying roller  1001 . 
   While the applying means of the present embodiment is carrying out applying, the applying liquid permeates through the abutting portion between the applying roller  1001  and the abutting member  2009  to function as a lubricant. Thus, the applying roller  1001  can slide more smoothly when rotated without any applying liquid than while carrying out applying. Even if the applying liquid is held in the liquid holding member, when the standing-by applying roller  1001 , which is at a stop, is rotated, it can slide substantially as smoothly as when rotated without any applying liquid. The reason will be described below. Immediately after the applying roller  1001  has switched from the applying state to the stopped state, the applying liquid is present in the abutting portion between the applying roller  10014  and the abutting member  2009 . However, as the time elapses, the applying liquid present in the abutting portion between the applying roller  1001  and the abutting member  2009  is pushed out of the abutting portion. The resulting state is comparable to that observed when the applying roller  1001  is rotated without any applying liquid. 
   If the applying roller cannot slide smoothly when rotated as described above, loads on a motor that is the driving source of the applying roller  1001  increase. It is thus necessary to use a large-scale motor or increase power consumption. 
   It is therefore desirable to allow the applying roller  1001  to slide smoothly over the abutting member  2009  even without any applying liquid. Thus, the applying roller  1001  was experimentally made using the materials listed below. Experiments were made for the slidability of the applying roller  1001  on the abutting member  2009 . 
   Material  1 : EPDM of rubber hardness 30° 
   Material  2 : EPDM of rubber hardness 50° 
   Material  3 : EPDM of rubber hardness 70° 
   Material  4 : NBR (type A) of rubber hardness 30° (vulcanizing cross-linked) 
   Material  5 : NBR (type B) of rubber hardness 40° (peroxide cross-linked) 
   Material  6 : Silicon rubber (type A) of rubber hardness 40° 
   Material  7 : Silicon rubber (type A) of rubber hardness 70° 
   Material  8 : Silicon rubber (type B) of rubber hardness 50° 
   Material  9 : Silicon rubber (type B) of rubber hardness 70° 
   Both materials  4  and  5  are NBR but are formed of different rubber materials. All materials  6 ,  7 ,  8 , and  9  are silicon rubber but have different grades. 
     FIG. 27  shows measurements of a load torque applied to the driving shaft of the motor when it starts to rotate (starting torque); in this case, the abutting member  2009  was formed of EPDM of rubber hardness 35° and the applying roller  1001  was composed of each of the above materials. The abutting member  2009  was pressed against the applying roller  1001  at a total pressure of 600 gf. 
   In the graph in  FIG. 27 , the axis of abscissa indicates the measured values of the surface roughness of the applying surface of the applying roller  1001 . The axis of ordinate indicates the measured values of the load torque applied to the driving shaft of the motor when it starts to rotate. In the graph in  FIG. 27 , materials  1 ,  2 , and  3  are denoted by ∘, x, and □. Materials  4 ,  5 , and  6  are denoted by Δ, ⋄, and ●. Materials  7 ,  8 , and  9  are denoted by  , ▴, and ♦. 
     FIG. 27  indicates that a lower torque is applied to the applying rollers composed of materials  6  to  9  than to the applying rollers composed of materials  1  to  5  when they start to rotate. This indicates that silicon rubber is an appropriate material for the applying roller  1001 . 
     FIG. 28  shows measurements of the load torque applied to the driving shaft of the motor when it starts to rotate (starting torque); in this case, the abutting member  2009  was composed of material  1 ,  3 ,  4 , or  5 , which does not allow the applying roller  1001  to slide smoothly. Experiments were made by forming different abutting members  2009  using EPDM of rubber hardness 35° and silicon rubber of rubber hardness 30°. In this case, the abutting member  2009  was also pressed against the applying roller  1001  at a total pressure of 600 gf. 
   In the graph in  FIG. 28 , the axis of abscissa indicates the measured values of the surface roughness of the applying surface of the applying roller  1001 . The axis of ordinate indicates the measured values of the load torque applied to the driving shaft of the motor when it starts to rotate (starting torque). In the graph in  FIG. 28 , ∘, □, Δ, and ⋄ denote the measured values obtained when the abutting member  2009  was composed of EPDM of rubber hardness 35° and when the applying roller  1001  was formed of materials  1 ,  3 ,  4 , and  5 , respectively. Further, ●,  , ▴, and ♦ denote the measured values obtained when the abutting member  2009  was composed of silicon rubber of rubber hardness 30° and when the applying roller  1001  was formed of materials  1 ,  3 ,  4 , and  5 , respectively. 
     FIG. 28  indicates that a lower torque is applied to the applying roller when it starts to rotate if the abutting member  2009  is formed of silicon rubber than if the abutting member  2009  is formed of EPDM. 
   The above results indicate that the slidability of the applying roller  1001  upon rotation can be improved by forming at least one of the applying roller  1001  and abutting member  2009  using silicon rubber. 
   Second Embodiment 
   Now, with reference to  FIG. 15 , description will be given of an essential part of a second embodiment of the present invention. 
   According to the second embodiment, the applying member that applies the applying liquid to the applying medium is composed of the applying roller  1001 , the counter roller  1002 , and the intermediate roller  1006 . The abutting member  2009  of the liquid holding member  2001  configured as in the case of the first embodiment is abutted against the applying roller  1001  under the pressing force of the spring member  2006 . A liquid holding space S is thus formed between the intermediate roller  1006  and the applying member. 
   In this case, the applying roller  1001  and the counter roller  1002  are composed of a material similar to that used in the first embodiment. The intermediate roller  1006  is composed of the same material as that of the applying roller  1001  and has the same diameter as that of the roller  1001 . Further, the intermediate roller  1006  rotates in synchronism with the applying roller  1001  at the same rotation speed. The intermediate roller  1006  can be rotated using the driving force of the roller driving motor  1004  (see  FIG. 1 ), which rotates the applying roller  1001 . A motor dedicated for the intermediate roller  1006  can also be used. The remaining part of the configuration is similar to that of the above embodiment. In the relevant drawings, parts identical or corresponding to those of the first embodiment are denoted by the same reference numerals. 
   In the second embodiment configured as described above, the applying liquid from a liquid supplying channel  3000  (see  FIG. 11 ) connected to the liquid holding member  2001  is supplied to and filled into the liquid holding space S, formed between the liquid holding member  2001  and the intermediate roller  1006 . While the intermediate roller  1006  is at a stop, the liquid holding space S is kept liquid-tight to prevent leakage from it. 
   During an applying operation, the applying roller  1001  and the intermediate roller  1006  start to rotate in synchronism in opposite directions as shown by arrows in  FIG. 15 . The intermediate roller  1006  rotates to cause the applying liquid to flow slipperily out of the liquid holding space S against the pressing force of the abutting member  2009  exerted on the intermediate roller  1006 . The applying liquid is then supplied to the peripheral surface of the intermediate roller  1006  in layers. Subsequently, the applying liquid supplied to the intermediate roller  1006  is transferred to a position at which the intermediate roller  1001  abuts against the applying roller  1001 . At this position, the applying liquid adheres to the applying roller in layers. According to this embodiment, the applying roller  1001  and the intermediate roller  1006  are formed of the same material so as to have the same surface structure. Further, the surface energy of both rollers is set at substantially the same value. The applying liquid supplied to between the rollers is substantially uniformly divided to the applying roller  1001  and to the intermediate roller  1006 . That is, the applying roller  1001  is supplied with the applying liquid the amount of which is about half that of applying liquid supplied to the outer peripheral surface of the intermediate roller  1006  in layers. Then, the applying liquid supplied to the applying roller  1001  is applied to one surface of the applying medium P fed upward in the figure to between the applying roller  1001  and the counter roller  1002 . After passing through the abutting position between the applying roller and the intermediate roller, an amount of applying liquid remains on the intermediate roller. This applying amount is then returned to the liquid holding space S through the lower edge of the abutting member  2009 . 
   Thus, the applying liquid supplied to the applying roller  1001  is divided at the abutting position between the intermediate roller  1006  and the applying roller  1001 . This makes it possible to limit the amount of applying liquid supplied to the applying roller  1001 . In other words, it is possible to supply a reduced amount of applying liquid to the applying medium P compared to the direct applying, from the liquid holding space S, of the applying liquid to be applied to the applying roller  1001 . Therefore, the present embodiment is effective if a small amount of applying liquid is to be supplied to the applying medium. 
   Third Embodiment 
   Now, with reference to  FIG. 18 , description will be given of an essential part of a third embodiment of the present invention. 
   In the above description of the first and second embodiments, by way of example, the applying roller  1001  constitutes the applying member that applies the liquid to the applying medium. According to the third embodiment, the applying member is constructed by extending an endless belt  1009  around two rollers  1007  and  1008  instead of the applying roller  1001  and disposing a counter roller  1010  that sandwiches the belt  1009  between itself and the roller  1008 . 
   On the other hand, the liquid holding member  2001  is configured as shown in the above embodiments. The abutting member  2009  of the liquid holding member  2001  abuts against the roller  1007  under the pressing force of the spring member  2006  at a position where it is opposite the roller  1007 . An outer surface of the endless belt  1009  desirably has surface energy higher than that of the counter roller  1010 . Additionally, for example, the liquid channel through which the applying liquid is supplied to the liquid holding space S is similar to that of the above embodiments. 
   In the third embodiment, while the belt  1009  is at a stop, the liquid holding space S maintains a liquid-tight state between the abutting member  2009  and the endless belt  1009 . This prevents the liquid from leaking from the liquid holding space S. Further, during a liquid applying operation, the roller  1008  is rotated by the driving force of the motor or the like to circulate the endless belt  1009  in a direction shown by an arrow in the figure. The circulatory movement of the belt  1009  causes the applying liquid in the applying liquid holding space S to flow slipperily across the abutting position between the endless belt  1009  and the abutting member  2009 . The applying liquid then adheres, in layers, to the endless belt having passed through the liquid holding space S. 
   The applying liquid adhering to the endless belt  1009  reaches the abutting position between the endless belt  1009  and the counter roller  1010 . The applying liquid is then applied to one surface of the applying medium P fed downward in the figure to the abutting position. When the endless belt  1009  is separated from the applying medium P, an amount of applying liquid remains on the endless belt  1009 . This applying liquid is returned to the applying space S through between the endless belt  1009  and the lower edge  2011  of the abutting member  2009 . 
   As described above, according to the third embodiment, the belt  1009  is used to apply the applying liquid to the applying medium P. The third embodiment is thus effective if for example, it is necessary to set a large distance or spacing between the liquid holding member  2001  and a position where the applying member applies the liquid to the applying medium P. In other words, whatever distance or spacing there is between the liquid holding member  2001  and the path through which the applying medium is moved, the liquid can basically be applied using three members including the two rollers  1007  and  1008  and the endless belt  1009 . In addition to the two rollers, one or more idler rollers may be contacted with the endless belt  1009  so that its position is adjustable. Thus, even if the distance or spacing between the two rollers is set at various values, a constant tension can always be applied to the endless belt by adjusting the positions of the idlers rollers. 
   Fourth Embodiment 
   Now, with reference to  FIGS. 17 to 19 , description will be given of an essential part of a fourth embodiment of the present invention. 
   In the description of the first embodiment, by way of example, the liquid holding member  2001 , cooperating with the applying roller  1001  in forming the liquid holding space S, is constructed by fastening the abutting member  2009  to the space forming base material  2002  using an adhesive or the like, the abutting member  2009  being separate from the base material  2002 . In contrast, the elements of a liquid holding member  2020  according to the fourth embodiment are integrally formed of the same member. 
   Specifically, the liquid holding member  2020  is shaped by using a resin such as acrylic to integrally mold a space forming base material  2021  formed like a plate and having a rectangular front shape and an abutting portion  2022  formed like a rectangular ring and projecting along a peripheral portion of the space forming base material  2021  as shown in  FIG. 18 . Thus, the liquid holding member  2020  has a concave portion  2023  formed by the space forming base material  2012  and the abutting portion  2022  as shown in  FIG. 19 . The abutting portion  2022  has an upper edge  2024  extending along a direction parallel to that of a central axis of the applying roller  1001 , a lower edge  2025  parallel to the upper edge  2024 , and a left and right side edges  2026  and  2027  connecting the upper edge  2024  and the lower edge  2025  together. End surfaces of the upper edge  2024  and lower edge  2025 , that is, the surfaces abutting against the applying roller  1001 , are formed, from their outer edges to inner edges, like circular arcs conforming to the outer peripheral surface of the applying roller  1001  as shown in  FIG. 17 . Further, the side edges are also formed, from their upper edges to lower edges, like circular arcs conforming to the outer peripheral surface of the applying roller  1001  as shown in  FIG. 19 . 
   Moreover, a liquid supplying port  2028  and a liquid recovering port  2029  are formed near opposite ends of a concave portion  2023  in the space forming base material  2021 . Cylindrical connecting portions  2028  and  2029  are projected from the liquid supplying port  2028  and liquid recovering port  2029  for connection to the liquid channel. These connecting portions are integrally formed similarly to the other portions. The upper edge  2024 , the lower edge  2025 , and the left and right side edges  2026  and  2027  have their abutting surfaces roughened using file No. 500 so that the applying liquid permeates appropriately through the abutting surfaces. 
   On the other hand, desirably, the material and hardness of the applying roller  1001  are properly determined in accordance with the material of the liquid holding member  2020 . For example, if the liquid holding member  2020  is formed of acrylic, the applying roller  2001  may be formed of aluminum, while the counter roller  3001  may be formed of EPDM. Further, the EPDM has a rubber hardness of 50°. 
   By abutting the liquid holding member  2020  configured as described above, against the outer peripheral surface of the applying roller  1001  using the spring member  2006  as in the case of the first embodiment, it is possible to reliably prevent the liquid from leaking from the liquid holding space S as a result of the abutment between the applying roller  1001  and the abutting member  2009  while the applying roller  1001  is at a stop. On the other hand, while the applying roller  1001  is rotating, the applying liquid can be supplied to the peripheral surface of the applying roller  1001  in layers against the pressing force of the abutting member  2020  exerted on the applying roller  1001  as in the case of the first embodiment. Furthermore, in the fourth embodiment, the liquid holding member  2020  is integrally molded of the single member. Consequently, the fourth embodiment is expected to produce a liquid leakage prevention effect superior to that produced in the case of the sticking of the separate member. Further, manufacturing costs can be sharply reduced. 
   Description will be given below of a preprocess liquid supplying means according to the fourth embodiment of the present invention. 
     FIG. 33  is a perspective view showing an embodiment of the preprocess liquid supplying means according to the present invention. The applying liquid supplying means has a liquid holding mechanism  2030  that holds the applying liquid between itself and the peripheral surface of the cylindrical applying roller  1001  which is composed of an elastic member such as rubber and which applies the liquid to the medium and a liquid channel through which the liquid is supplied to the liquid holding mechanism  2030 . The liquid holding mechanism  2030  extends almost all over the applying roller  1001  in its longitudinal direction. The liquid holding mechanism  2030  is attached to the applying roller  1001  via a mechanism that enables it to be contacted with and separated from the peripheral surface of the applying roller  1001 . 
   The liquid holding mechanism  2030  will be described with reference to  FIGS. 33 to 37 .  FIGS. 34 and 35  are a sectional view and a perspective view, respectively, of the liquid holding mechanism  2031 .  FIGS. 36 and 37  are a side view and a sectional view of the liquid holding mechanism  2030 . 
   In  FIGS. 33 to 35 , reference numeral  2031  denotes a liquid holding member composed of an elastic member such as rubber and having two projecting portions  20311  along its longitudinal direction, a liquid holding space  20312  between the projecting portions, and a flange portion  20313 . The liquid holding portion  2031  is also characterized by being formed integrally and seamlessly. Reference numeral  2033  denotes a holding member that holds the liquid holding member  2031 . The holding member  2033  is composed of a flat surface  20331  on which the liquid holding member  2031  is held and a guide portion  20332  extending perpendicularly to the flat surface  20331 . Reference numeral  2032  denotes a stopper that stops the liquid holding member. As shown in  FIG. 35 , the liquid holding member  2031  is fixedly positioned on the flat surface  20331  of the holding member  2033 . In this case, the positioning is accomplished by fitting the projecting portions  20311  of the liquid holding member  2031  into holes  20321  in the stopper  2032 . Subsequently, the stopper  2032  is fixed to the holding member  2033  using screws. Reference numeral  2034  denotes guides that allow the liquid holding member  2031  to abut on a normal of the applying roller  1001 . The guide  2034  is fixed to opposite ends of the flat surface  20331  of the holding member  2033 . Reference numeral  2035  denotes a pedestal fixed to a fixing member such as a frame, parallel to the central axis of the applying roller. 
   This configuration allows the liquid holding member  2031 , the stopper  2032 , and the pedestal  2033  to operate integrally. The liquid holding member  2031 , the stopper  2032 , and the pedestal  2033  can be guided to guide holes  20352  formed in the right and left guides  2034  and in a positioning portion  20351  of the pedestal  2035 . The liquid holding member  2031 , the stopper  2032 , and the pedestal  2033  can then be slid in the normal direction of the applying roller  1001 . Reference numeral  2036  denotes a spring member mounted on the pedestal  2035  to urge the holding member  2033  from its rear surface to bring the holding member  2031  into pressure contact with the applying roller  1001 . 
   With the applying liquid holding mechanism  2030  according to the present embodiment, the liquid holding member  2031  abuts tightly against the outer peripheral surface of the applying roller along the upper edges  20311  of ribs of the liquid holding member  2031 . As a result, the liquid holding member  2031  forms an elongate liquid holding space S extending all over an area to which the applying liquid is applied by the applying roller  1001 . The applying liquid from the liquid supplying path, described later, is supplied to the interior of the liquid holding space S via the liquid holding member  2030 . 
   According to the present embodiment, the applying roller  1001  is formed of silicon and has a surface roughness Ra of 1.8 and a diameter of 23.169 mm. The liquid holding member  2031  is formed of EPDM having a rubber hardness of 50°. Further, according to the present embodiment, for the two projecting portions  20311  of the liquid holding member  2031 , the abutting surface located downstream of the applying roller  1001  is below the one located upstream of the applying roller  1001 . Furthermore, the applying roller  1001  and the liquid holding member  2031  are arranged at positions such that the midpoint between the two projecting portions of the liquid holding member  2031  lies on a straight line inclined at 45° from a horizontal line passing through the rotational center of the applying member. 
   When the liquid holding member  2031  according to the present embodiment was used and the pressing force exerted by the spring member  2036  on the liquid holding member was set at 2,000 gf, about 0.15 g of applying liquid was able to be applied to A4-sized ordinary paper. 
   Another Embodiment 
   In the above embodiments, the amount of liquid to be applied to the applying medium can be changed by changing the pressing force of the liquid holding member exerted on the coating roller, the pressing force changed by changing the magnitude of the elastic force of the spring member. 
   Moreover, the amount of liquid to be applied can be changed by changing the hardness of the liquid holding member and of the applying roller or a roller supporting the endless belt. 
   Further, in the above embodiments, the use of the coil spring serving as a spring member is shown as pressing means for pressing the liquid holding member against the applying roller. However, another spring, for example, a plate spring, can also be used. Moreover, an elastic member such as rubber can be used in place of the spring member. 
   According to the present invention, the positions where the liquid supplying port and the liquid collecting port are formed in the liquid holding member as well as the numbers of liquid supplying and collecting ports are not limited to those in the above embodiments. For example, it is possible to arrange the liquid supplying ports at the opposite ends of the liquid holding space, while forming one or more liquid collecting ports between these liquid supplying ports. Conversely, it is possible to arrange the liquid collecting ports at the opposite ends of the liquid holding space, while forming one or more liquid supplying ports between these liquid supplying ports. In short, the liquid held in the liquid supplying member has only to be able to flow through the liquid holding space. 
   In the above embodiments, the counter roller is provided opposite the applying roller or endless belt. However, a support member such as a plate material may be provided in place of the counter roller so that the applying member is sandwiched between the plate material and the applying roller. Then, the moving force of the applying roller or endless belt may be transmitted to the applying medium. In this case, a surface of the support member which contacts with the applying medium must have a small coefficient of friction and a low surface energy. 
   Embodiment of an Ink Jet Printing Apparatus 
     FIG. 20  is a diagram generally showing the configuration of an ink jet printing apparatus  1  comprising an applying mechanism having almost the same configuration as that of the above liquid applying apparatus. 
   The ink jet printing apparatus  1  is provided with a feeding tray  2  on which a plurality of print media P are stacked. A semicircular separating roller  3  separates each print medium P from the others stacked on the feeding tray and then feeds it to a conveying path. The applying roller  1001  and the counter roller  1002  are arranged in the conveying path; the applying roller  1001  and the counter roller  1002  constitute liquid applying means of the liquid applying mechanism. The print medium P fed by the feeding tray  2  is then fed to between the rollers  1001  and  1002 . The applying roller  1001  is rotated clockwise in  FIG. 20  by the rotation of a roller driving motor. The applying roller  1001  applies the application liquid to a print surface of the print medium P while conveying the print medium P. The print medium P to which the application liquid has been applied is fed to between a conveying roller  4  and a pinch roller  5 . Then, the conveying roller  4  is rotated counterclockwise in the figure to convey the print medium P on a platen  6 . The print medium P then moves to a position opposite to a print head  7  constituting printing means. The print head  7  is of an ink jet type in which a predetermined number of nozzles for ink ejection are disposed. While the print head  7  is being scanned in a direction perpendicular to the sheet of the drawing, printing is carried out by ejecting ink droplets from the nozzles to the print surface of the print medium P in accordance with print data. An image is formed on the print medium by alternately repeating a printing operation and a conveying operation performed by the conveying roller  4  to convey the print medium by a predetermined amount. Simultaneously with this image forming operation, the print medium P is sandwiched between a sheet discharging roller  8  and a sheet discharging spur  9  both provided downstream of the scan area of the print head in the conveying path for the print medium. The print medium P is then discharged onto a sheet discharging tray  10  by the rotation of the sheet discharging roller  8 . 
   As this ink jet printing apparatus, what is called a full line type can be constructed in which an elongate print head having nozzles from which inks are ejected and which are disposed over the maximum width of the print medium is used to perform a printing operation. 
   The application liquid used in the present embodiment is a treatment liquid that facilitates the coagulation of pigments when inks composed of the pigments as color materials are used for printing. 
   In the present embodiment, the treatment liquid is used as an application liquid to react with the pigments, which are the color materials of the inks ejected to the print medium to which the treatment liquid has been applied. This facilitates the coagulation of the pigments. The facilitation of the coagulation of the pigments improves the printing density. Moreover, it is possible to suppress or prevent bleeding. The application 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 ink jet printing apparatus. As shown in the figure, an applying mechanism  100  is provided above one end of the feeding tray  2 . A printing mechanism comprising the print head  7  and the like is provided above the applying mechanism  100  and above a central portion of the feeding tray  2 . 
     FIG. 22  is a block diagram showing a control arrangement for the above ink jet printing apparatus. In this figure, the roller driving motor  1004 , the pump driving motor  4009 , and the actuator  3005  for the air communicating valve, all of which are elements of the liquid applying mechanism, are similar to those descried for the liquid applying apparatus. 
   In accordance with a program of a process procedure described later in  FIG. 23 , a CPU  5001  controls the driving of the elements of the applying mechanism. The CPU  5001  also controls the driving of an LF motor  5013 , a CR motor  5015 , and the print head  7  which relate to the printing mechanism, via driving circuits  5012  and  5014  and a head driver  5016 . That is, driving by the LF motor  5013  rotates the conveying roller  4 . Driving by the CR motor moves a carriage on which the print head  7  is mounted. Moreover, the CPU  5001  performs control such that inks are ejected through the nozzles in the print head. 
     FIG. 23  is a flowchart showing the procedure of liquid application and an accompanying printing operation in the ink jet printing apparatus according to the present embodiment. In the figure, the processing during steps S 101 , during S 103  to S 105 , and during S 108  to S 110  is similar to that during step S 1 , during steps S 3  to S 5 , and during steps S 7  to S 9 , all the steps being shown in  FIG. 13 . 
   As shown in  FIG. 23 , in the present embodiment, a print start instruction is given (step S 102 ). Then, a series of liquid applying operations such as pump activation are performed (steps S 103  to S 105 ). 
   After this applying step, a printing operation is performed on a print medium having the application liquid applied to desired parts of the medium (step S 106 ). That is, the print head  7  is scanned over the print medium P conveyed by the conveying roller  4  by a predetermined amount at a time. During the scan, inks are ejected from the nozzles in accordance with print data so as to adhere to the print medium to form dots. The adhering inks react with the application liquid, thus improving the concentration and preventing bleeding. The conveyance of the print medium and the scanning of the print head are repeated to print the print medium P. The finished print medium is discharged onto the sheet discharging tray  10 . When the apparatus determines in step S 107  that the printing has been finished, the processing in step S 108  and the subsequent steps is executed to finish the present process. 
   In the present embodiment, as the liquid is applied to the print medium, printing is sequentially executed on parts of the print medium to which the liquid has already been applied. That is, the conveying path from the conveying roller to the print head is shorter than the print medium, and when a part of the print medium to which the liquid has already been applied reaches the scan area of the print head, the applying mechanism applies the liquid to another part of the print medium. Every time the print medium is conveyed by a predetermined amount, liquid application and printing are sequentially executed on different parts of the print medium. However, in an alternative form of application of the present invention, printing may be carried out after one print medium has been completely applied the application liquid to as described in Japanese Patent Application Laid-open No. 2002-096452. 
   In the above embodiments, by way of example, the liquid is applied in the ink jet printing-based printing apparatus. However, the present invention is applicable to printing apparatuses based on other systems. For example, the degree of whiteness of the medium can be improved by using a liquid containing a fluorescent whitening agent as an application liquid. A liquid containing components to restrain a curl (phenomenon in which a medium becomes curve shape) of the application medium may be used. The printing means after the liquid application is not limited to the ink jet printing system. Effects can be produced using a printing system such as a thermal transfer system or an electrophotographic system. In a silver salt-based printing apparatus, a photosensitive agent as the application liquid may be applied before printing. 
   The present invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and it is the intention, therefore, that the appended claims cover all such changes and modifications that fall within the true spirit of the invention. 
   This application claims priority from Japanese Patent Application Nos. 2004-035800 filed Feb. 12, 2004 and 2005-006773 filed Jan. 13, 2005, which are hereby incorporated by reference herein.