Patent Publication Number: US-2013249995-A1

Title: Coating apparatus and inkjet recording apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a coating apparatus, and more particularly to a coating apparatus which is incorporated in an inkjet recording apparatus and coats paper with a prescribed treatment liquid. 
     2. Description of the Related Art 
     An inkjet recording apparatus is known which can be used with generic printing paper (general paper used in general offset printing, and the like (namely, paper having cellulose as a main component, such as top grade paper, coated paper, art paper, etc.), rather than special inkjet paper) by coating the paper with a prescribed treatment liquid before printing. An inkjet recording apparatus of this kind is provided with a coating apparatus which applies the prescribed treatment liquid to the paper before printing. 
     The coating apparatus can use various methods, such as a method of applying the liquid by spraying (spray application method), a method of applying the liquid using an inkjet head (inkjet application method), and the like, and a method of applying the liquid by using a coating roller (roller application method) is relatively common. 
     In general, with the roller application method, a supply roller takes up a treatment liquid stored in a coating liquid receptacle, and supplies the treatment liquid to the coating roller. However, with this method, the treatment liquid collects in the form of rings in both end portions of each roller, and can be scattered by the rotation of the rollers or can drip from the rollers. 
     Therefore, Japanese Patent Application Publication No. 2011-062831 proposes that a supply roller is formed to have the width greater than the width of a coating roller, and furthermore, the coating liquid receptacle is formed to extend to both end portions of the coating roller, thereby preventing the treatment liquid from scattering and dripping. 
     However, the composition of Japanese Patent Application Publication No. 2011-062831 has a drawback in that, although scattering and dripping of the treatment liquid from the supply roller can be prevented, scattering and dripping of the treatment liquid from the coating roller cannot be prevented. That is, collections of the treatment liquid also occur on the coating roller, as well as the supply roller, but since the coating liquid receptacle is not disposed below either end of the coating roller, then there is a drawback in that scattering and dripping of the treatment liquid which occur from the coating roller cannot be captured in the coating liquid receptacle. 
     Furthermore, generally, the ring-shaped collections of the liquid which occur in both end portions of the coating roller become especially marked when the supply roller is rotated continuously, or when the supply roller is rotated at high speed. Then, the composition described in Japanese Patent Application Publication No. 2011-062831 also has a drawback in not being able to respond to cases where the processing is carried out continuously over a long period of time, or where the processing is carried out at high speed. 
     SUMMARY OF THE INVENTION 
     The present invention has been contrived in view of these circumstances, an object thereof being to provide a coating apparatus and an inkjet recording apparatus which are capable of preventing the occurrence of collections of liquid in both end portions of a coating roller. 
     In order to attain the aforementioned object, the present invention is directed to a coating apparatus, comprising: a coating roller which is configured to apply a coating liquid to an object to be coated; a supply roller which is configured to abut on the coating roller and supply the coating liquid to the coating roller, wherein: the supply roller has a circumferential surface of which a width is larger than a width of a circumferential surface of the coating roller, the circumferential surface of the supply roller has a contact region configured to make contact with the coating roller and non-contact regions configured not to make contact with the coating roller, the non-contact regions are arranged respectively in both end portions of the circumferential surface of the supply roller in a widthwise direction thereof, the contact region has a surface state different from a surface state of each of the non-contact regions such that a flow velocity of the coating liquid flowing on each of the non-contact regions is faster than a flow velocity of the coating liquid flowing on the contact region; and a coating liquid supply device which is configured to supply the coating liquid to the supply roller. 
     According to this aspect of the present invention, the width of the circumferential surface of the supply roller is formed to be larger than the width of the circumferential surface of the coating roller, so as to form the non-contact regions that do not make contact with the coating roller in both end portions of the circumferential surface of the supply roller. The supply roller is formed to differentiate the surface state between the contact region which makes contact with the coating roller and the non-contact regions which do not make contact with the coating roller, in such a manner that the flow velocity of the coating liquid flowing on the non-contact regions is faster than the flow velocity of the coating liquid flowing on the contact region. More specifically, the coating liquid is made to flow more readily on the non-contact regions than on the contact region. Thus, it is possible to prevent the occurrence of ring-shaped collections of the coating liquid at both ends of the coating roller, and scattering of the coating liquid from the coating roller and the occurrence of dripping of the coating liquid can be prevented. 
     Surface tension acts on the coating liquid so as to reduce the surface area thereof. In the contact region, a film of the coating liquid is formed between the coating roller and the supply roller, and therefore a force causing the coating liquid to flow in the axial direction is obtained due to the surface tension when the volume of the coating liquid increases. On the other hand, in the non-contact regions, the coating roller is not present and therefore the force moving the coating liquid in the axial direction does not exist. As a result of this, the flow of the coating liquid stagnates in the end portions of the coating roller and ring-shaped collections of the coating liquid occur in the end portions of the coating roller. By making the coating liquid flow more readily in the non-contact regions, as in the present invention, it is possible to suppress the occurrence of collections of the coating liquid in the end portions of the coating roller and the occurrence of ring-shaped collections of the coating liquid can be prevented in the end portions of the coating roller. Furthermore, since the occurrence of collections of the coating liquid can be prevented even when the coating roller is rotated at high speed, then it is possible to increase the speed of the coating process. 
     In order to attain the aforementioned object, the present invention is also directed to a coating apparatus, comprising: a coating roller which is configured to apply a coating liquid to an object to be coated; multi-stage supply rollers which are arranged to sequentially abut to each other, wherein: a final one of the supply rollers which is at a final stage of the multi-stage supply rollers is configured to abut on the coating roller and supply the coating liquid to the coating roller, the final one of the supply rollers has a circumferential surface of which a width is larger than a width of a circumferential surface of the coating roller, the circumferential surface of the final one of the supply rollers has a contact region configured to make contact with the coating roller and non-contact regions configured not to make contact with the coating roller, and the non-contact regions are arranged respectively in both end portions of the circumferential surface of the final one of the supply rollers in a widthwise direction thereof, in each pair of the supply rollers constituted of a first one of the pair and a second one of the pair which abuts on the first one of the pair and is nearer to the coating roller than the first one of the pair, the first one of the pair has a circumferential surface of which a width is larger than a width of a circumferential surface of the second one of the pair, the circumferential surface of the first one of the pair has a contact region configured to make contact with the second one of the pair and non-contact regions configured not to make contact with the second one of the pair, and the non-contact regions are arranged respectively in both end portions of the circumferential surface of the first one of the pair in a widthwise direction thereof, and in each of the supply rollers, the contact region has a surface state different from a surface state of each of the non-contact regions such that a flow velocity of the coating liquid flowing on each of the non-contact regions is faster than a flow velocity of the coating liquid flowing on the contact region; and a coating liquid supply device which is configured to supply the coating liquid to an initial one of the supply rollers which is at an initial stage of the multi-stage supply rollers. 
     According to this aspect of the present invention, the coating liquid is supplied to the coating roller by the multi-stage supply rollers constituted of the plurality of supply rollers. The supply rollers constituting the multi-stage supply rollers are formed in such a manner that, in each pair of the supply rollers, the width of the circumferential surface of a first one of the pair of the supply rollers at a preceding stage is larger than the width of the circumferential surface of a second one of the pair of the supply rollers at a subsequent stage, and there are the regions which are not contact with the second supply roller at the subsequent stage in both end portions in the widthwise direction of the circumferential surface of the first supply roller at the preceding stage. Furthermore, the circumferential surface of a final one of the supply rollers at the final stage is formed to have the width larger than the width of the circumferential surface of the coating roller, and there are the regions which do not make contact with the coating roller in both end portions in the widthwise direction of the circumferential surface of the supply roller at the final stage. Each of the supply rollers is formed by differentiating the surface state between the contact region and the non-contact regions, in such a manner that the flow velocity of the coating liquid flowing on the non-contact regions is faster than the flow velocity of the coating liquid flowing on the contact region. Consequently, it is possible to prevent the occurrence of ring-shaped collections of the coating liquid at both ends of each of the coating roller and the supply rollers. 
     Preferably, the surface state of the contact region is different from the surface state of each of the non-contact regions such that a contact angle of the coating liquid to each of the non-contact regions is smaller than a contact angle of the coating liquid to the contact region. 
     According to this aspect of the present invention, the surface state of each of the non-contact regions is differentiated from the surface state of the contact region such that the contact angle of the coating liquid to each of the non-contact regions is smaller than the contact angle of the coating liquid to the contact region. In other words, the hydrophilic properties of the non-contact regions are increased compared to the contact region. Thereby, the flow velocity of the coating liquid flowing on the non-contact regions is made faster than the flow velocity of the coating liquid flowing on the contact region, and the coating liquid can be made to flow more readily on the non-contact regions than on the contact region. 
     Preferably, a material constituting the contact region is different from a material constituting each of the non-contact regions such that the contact angle of the coating liquid to each of the non-contact regions is smaller than the contact angle of the coating liquid to the contact region. 
     According to this aspect of the present invention, the material which constitutes the contact region and the material which constitutes the non-contact regions are differentiated in such a manner that the contact angle of the coating liquid to the non-contact regions is smaller than the contact angle of the coating liquid to the contact region. Thereby, the flow velocity of the coating liquid flowing on the non-contact regions is made faster than the flow velocity of the coating liquid flowing on the contact region, and the coating liquid can be made to flow more readily on the non-contact regions. For example, when the supply roller is made of rubber material, then the contact region is made from rubber having high hydrophobic properties (for example, fluoric rubber), and the non-contact regions are made from rubber having high hydrophilic properties (for example, nitrile butadiene rubber (NBR)). For example, when the supply roller is made from a metal material, then the contact region is made from a metal having hydrophobic properties (for example, aluminum, stainless steel, or the like), and the non-contact regions are made from a metal having hydrophilic properties (for example, titanium, or the like). Consequently, it is possible to make the contact angle of the coating liquid to the non-contact regions smaller than the contact angle of the coating liquid to the contact region. In other words, it is possible to increase the hydrophilic properties of the non-contact regions compared to the contact region. 
     Preferably, the contact region is made from a hydrophobic material and each of the non-contact regions is made from a hydrophilic material. 
     According to this aspect of the present invention, the contact region is made from the material having hydrophobic properties and the non-contact regions are made from the material having hydrophilic properties. For example, as described above, when the supply roller is made of rubber material, then the contact region is made from rubber having high hydrophobic properties (for example, fluoric rubber), and the non-contact regions are made from rubber having high hydrophilic properties (for example, NBR). For example, when the supply roller is made from the metal material, then the contact region is made from a metal having hydrophobic properties (for example, aluminum, stainless steel, or the like), and the non-contact regions are made from a metal having hydrophilic properties (for example, titanium, or the like). Consequently, it is possible to make the contact angle of the coating liquid to the non-contact regions smaller than the contact angle of the coating liquid to the contact region. In other words, it is possible to increase the hydrophilic properties of the non-contact regions compared to the contact region. 
     It is also preferable that at least one of the contact region and each of the non-contact regions is coated with a thin film such that the contact angle of the coating liquid to each of the non-contact regions is smaller than the contact angle of the coating liquid to the contact region. 
     According to this aspect of the present invention, at least one of the contact region and the non-contact regions are coated with a thin film in such a manner that the contact angle of the coating liquid to the non-contact regions is smaller than the contact angle of the coating liquid to the contact region. For example, the contact region is coated with a hydrophobic film of PTFE (polytetrafluoroethylene (tetrafluoride)), PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer polytetrafluoroethylene), or the like. Furthermore, the non-contact regions are coated with a hydrophilic film of silica particles, or the like. Consequently, it is possible to make the contact angle of the coating liquid to the non-contact regions smaller than the contact angle of the coating liquid to the contact region. In other words, it is possible to increase the hydrophilic properties of the non-contact regions compared to the contact region. 
     Preferably, the contact region is coated with a hydrophobic film and each of the non-contact regions are coated with a hydrophilic film. 
     According to this aspect of the present invention, the contact region is coated with the hydrophobic film and the non-contact regions are coated with the hydrophilic film. For example, as described above, the contact region is coated with the hydrophobic film, such as PTFE, PFA, or the like, and the non-contact regions are coated with the hydrophilic film of silica particles, or the like. Consequently, it is possible to make the contact angle of the coating liquid to the non-contact regions smaller than the contact angle of the coating liquid to the contact region. 
     It is also preferable that a surface roughness of the contact region is different from a surface roughness of each of the non-contact regions such that the contact angle of the coating liquid to each of the non-contact regions is smaller than the contact angle of the coating liquid to the contact region. 
     According to this aspect of the present invention, the surface roughness of the contact region and the surface roughness of the non-contact regions are differentiated in such a manner that the contact angle of the coating liquid to the non-contact regions is smaller than the contact angle of the coating liquid to the contact region. In other words, the value of the surface roughness of the non-contact regions is made greater than the contact region. Consequently, it is possible to make the contact angle of the coating liquid to the non-contact regions smaller than the contact angle of the coating liquid to the contact region. In other words, it is possible to increase the hydrophilic properties of the non-contact regions compared to the contact region. 
     Preferably, each of the non-contact regions has grooves which are arranged in a uniform pitch in a circumferential direction of the supply roller and are parallel to an axis of the supply roller. 
     According to this aspect of the present invention, the grooves parallel to the axis of the supply roller are formed at the uniform pitch in the circumferential direction, in the non-contact regions. Hence, a force causing the coating liquid to flow along the grooves acts due to the effects of the surface tension, and the flow velocity of the coating liquid flowing on the non-contact regions can be made faster than the flow velocity of the coating liquid flowing on the contact region. In other words, the coating liquid can be made to flow more readily in the axial direction, in the non-contact regions. Therefore, it is possible to prevent the occurrence of ring-shaped collections of the coating liquid at both ends of the coating roller, and scattering of the coating liquid from the coating roller and the occurrence of dripping of the coating liquid can be prevented. 
     Preferably, the supply roller has flange sections in both ends thereof. 
     According to this aspect of the present invention, the flange sections are arranged at both ends of the supply roller. In other words, a return portion is formed in each end portion of the supply roller. Thus, it is possible to prevent the coating liquid from adhering to the edges of the supply roller and scattering in the axial direction. 
     In order to attain the aforementioned object, the present invention is also directed to an inkjet recording apparatus, comprising: the coating apparatus as defined in claim  1  which is configured to apply a prescribed coating liquid to a surface of paper; and an inkjet head which is configured to form an image by ejecting and depositing ink droplets onto the surface of the paper that has been coated with the coating liquid. 
     According to this aspect of the present invention, the prescribed coating liquid is applied to the paper before printing, by the coating apparatus according to the present invention described above. An image is recorded on the paper by ejecting and deposing ink droplets from the inkjet head onto the paper which has been coated with the coating liquid by the coating apparatus. Since the coating apparatus does not scatter the coating liquid, it is possible to carry out the coating process without soiling the peripheral area. Furthermore, since the coating process can be performed at high speed, then compatibility with high-speed printing can be achieved. 
     According to the present invention, it is possible to prevent the occurrence of collections of the coating liquid in both end portions of the coating roller. Consequently, scattering or dripping of the coating liquid from the coating roller can be prevented. Furthermore, even when the coating roller is rotated at high speed, it is possible to prevent scattering and dripping of the coating liquid from the coating roller, and therefore it is possible to increase the speed of the coating process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein: 
         FIG. 1  is a general schematic drawing of an inkjet recording apparatus including a coating apparatus; 
         FIG. 2  is a block diagram showing the schematic composition of a control system of the inkjet recording apparatus; 
         FIG. 3  is a side view diagram showing the schematic composition of the coating apparatus; 
         FIG. 4  is a plan diagram showing the schematic composition of the coating apparatus; 
         FIG. 5  is a perspective diagram showing the schematic composition of the coating apparatus; 
         FIG. 6  is a perspective diagram showing the schematic composition of a modification of the coating apparatus; 
         FIG. 7  is a perspective diagram showing the schematic composition of the modification of the coating apparatus; 
         FIG. 8  is a side view diagram showing the schematic composition of a coating apparatus of a type which supplies treatment liquid to a coating roller through two supply rollers (two-stage supply rollers); and 
         FIG. 9  is a plan diagram showing the schematic composition of the coating apparatus shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     General Composition of Inkjet Recording Apparatus 
       FIG. 1  is a general schematic drawing of an inkjet recording apparatus including a coating apparatus. 
     The inkjet recording apparatus  10  is configured to record an image by an inkjet method on generic printing paper (cut sheets of paper) using aqueous ink (ink containing water as solvent). When an image is recorded by the inkjet method using the aqueous ink on the generic printing paper without any treatment, it is not possible to record the image of high quality due to the occurrence of feathering, bleeding, and the like. Therefore, in the inkjet recording apparatus of this kind, the image recording is carried out after coating the paper with a prescribed treatment liquid. More specifically, the image recording is carried out after applying a liquid having a function of aggregating a coloring material component in the ink, onto the paper. The inkjet recording apparatus is provided with the coating apparatus for this purpose. The composition of the inkjet recording apparatus  10  according to the present embodiment is described in detail below. 
     As shown in  FIG. 1 , the inkjet recording apparatus  10  in the present embodiment includes: a paper supply unit  20 , which carries out a supply process of sheets of paper P; a treatment liquid application unit  30 , which carries out a treatment liquid application process; an image recording unit  40 , which carries out an image recording process; an ink drying unit  50 , which carries out a drying process; a fixing unit  60 , which carries out an image fixing process; and a recovery unit  70 , which carries out a recovery process of the sheets of paper P. 
     The treatment liquid application unit  30 , the image recording unit  40 , the ink drying unit  50  and the fixing unit  60  are provided with conveyance drums  31 ,  41 ,  51  and  61 , respectively, as conveyance devices for the sheets of paper P. The sheets of paper P are conveyed through the treatment liquid application unit  30 , the image recording unit  40 , the ink drying unit  50  and the fixing unit  60 , by means of the conveyance drums  31 ,  41 ,  51  and  61 . 
     Each of the conveyance drums  31 ,  41 ,  51  and  61  is formed in a cylindrical shape, which corresponds to the width of the sheet of paper P, and rotates by being driven by a motor (not shown) (in  FIG. 1 , the conveyance drums  31 ,  41 ,  51  and  61  rotate in the counter-clockwise direction). Each of the conveyance drums  31 ,  41 ,  51  and  61  is provided with grippers disposed on the circumferential surface thereof. The sheet of paper P is conveyed with the leading end portion thereof being gripped by the gripper. In the present embodiment, each of the conveyance drums  31 ,  41 ,  51  and  61  has the grippers disposed in two locations on the circumferential surface thereof, and it is thereby possible to convey two sheets of paper P in one revolution. 
     The circumferential surface of each of the conveyance drums  31 ,  41 ,  51  and  61  is formed with a plurality of suction holes. The sheet of paper P is held on the outer circumferential surface of each of the conveyance drums  31 ,  41 ,  51  and  61 , due to the rear surface of the sheet of paper P being vacuum suctioned through the suction holes. In the present embodiment, the sheets of paper P are held by vacuum suction; however, it is also possible to adopt a composition which holds the sheets of paper P by electrostatic attraction. 
     Transfer drums  80 ,  90  and  100  are disposed respectively between the treatment liquid application unit  30  and the image recording unit  40 , between the image recording unit  40  and the ink drying unit  50 , and between the ink drying unit  50  and the fixing unit  60 . The sheets of paper P are conveyed between the respective units by means of the transfer drums  80 ,  90  and  100 . 
     Each of the transfer drums  80 ,  90  and  100  is composed as a cylindrical frame, which corresponds to the width of the sheet of paper P, and rotates by being driven by a motor (not shown) (in  FIG. 1 , the transfer drums  80 ,  90  and  100  rotate in the clockwise direction). Each of the transfer drums  80 ,  90  and  100  is provided with grippers disposed on the circumferential surface thereof. The sheet of paper P is conveyed with the leading end portion thereof being gripped by the gripper. In the present embodiment, each of the transfer drums  80 ,  90  and  100  has the grippers disposed in two locations on the circumferential surface thereof, and it is thereby possible to convey two sheets of paper P in one revolution. 
     Circular arc-shaped guide plates  82 ,  92  and  102  are disposed along the conveyance path of the sheets of paper P, below the transfer drums  80 ,  90  and  100 , respectively. The sheets of paper P which are conveyed by the transfer drums  80 ,  90  and  100  are conveyed while the rear surfaces of the sheets of paper P (the surfaces reverse to the printing surfaces) are guided by the guide plates  82 ,  92  and  102 . 
     The transfer drums  80 ,  90  and  100  are provided with driers  84 ,  94  and  104 , which are disposed inside the transfer drums  80 ,  90  and  100  and blow warm air flows toward the sheets of paper P conveyed by the transfer drums  80 ,  90  and  100 , respectively (in the present embodiment, three driers are disposed along the conveyance path of the sheets of paper P). The warm air flows blown out from the driers  84 ,  94  and  104  during the conveyance process strike the printing surfaces of the sheets of paper P conveyed by the transfer drums  80 ,  90  and  100 . 
     The driers  84 ,  94  and  104  can be composed so as to heat the sheets of paper P by radiating heat from infrared heaters, or the like, (so-called heating by radiation), rather than the composition where the sheets of paper P are heated by being blown with the warm air flows. 
     The sheets of paper P supplied from the paper supply unit  20  are conveyed successively to the conveyance drum  31 , the transfer drum  80 , the conveyance drum  41 , the transfer drum  90 , the conveyance drum  51 , the transfer drum  100  and the conveyance drum  61 , and are finally recovered by the recovery unit  70 . From the supply at the paper supply unit  20  until the recovery at the recovery unit  70 , the sheets of paper P are subjected to prescribed processing and images are recorded on the printing surfaces of the sheets of paper P. 
     The compositions of the respective units of the inkjet recording apparatus  10  according to the present embodiment are described in detail below. 
     &lt;Paper Supply Unit&gt; 
     The paper supply unit  20  carries out the paper supply process of the sheets of paper P. In particular, the inkjet recording apparatus  10  in the present embodiment successively supplies the cut sheets of paper P, one sheet at a time. The paper supply unit  20  includes a paper supply device  21 , a paper supply tray  22  and a transfer drum  23 . 
     The paper supply device  21  supplies the sheets of paper P stacked in a magazine (not shown), one sheet at a time from the upper side, successively to the paper supply tray  22 . 
     The paper supply tray  22  outputs the sheet of paper P supplied from the paper supply apparatus  21 , to the transfer drum  23 . 
     The transfer drum  23  receives the sheet of paper P output from the paper supply tray  22 , and rotates so as to transfer the sheet of paper P to the conveyance drum  31  of the treatment liquid application unit  30 . 
     As described above, when an image is recorded by the inkjet method using the aqueous ink on a generic printing paper with no treatment, it is not possible to record an image of high quality due to the occurrence of feathering, bleeding, and the like. Therefore, in order to prevent these problems, the prescribed treatment liquid is applied to the sheet of paper P by the treatment liquid application unit  30 , which is described below. 
     &lt;Treatment Liquid Application Unit&gt; 
     The treatment liquid application unit  30  applies the prescribed treatment liquid to the printing surface of the sheet of paper P (an object to be coated) P. The treatment liquid application unit  30  includes: a conveyance drum (hereinafter referred to as the “treatment liquid application drum”)  31 , which conveys the sheet of paper P; and a coating apparatus  32 , which coats the printing surface of the sheet of paper P conveyed by the treatment liquid application drum  31  with the prescribed treatment liquid. 
     The treatment liquid application drum  31  receives the sheet of paper P from the transfer drum  23  of the paper supply unit  20  (by gripping the leading end of the sheet of paper P with the gripper), and conveys the sheet of paper P along a prescribed conveyance path by rotating. 
     The coating apparatus  32  applies the prescribed treatment liquid by means of a roller to the printing surface of the sheet of paper P which is conveyed by the treatment liquid application drum  31 . The composition of the coating apparatus  32  is described in detail later. 
     The treatment liquid applied by the coating apparatus  32  is constituted of a liquid which contains an aggregating agent that aggregates components in the ink composition. 
     The aggregating agent used can be a compound capable of changing the pH of the ink composition, or a multivalent metal salt, or a polyallyl amine. 
     Desirable examples of the compound capable of lowering the pH of the ink composition are acidic substances having high water solubility (such as phosphoric acid, nitric acid, malonic acid, citric acid, or derivatives or salts of these compounds, or the like). It is possible to use either one type only, or a combination of two or more types, of the acid substances. By this means, the aggregating properties are raised and the whole of the ink can be solidified. 
     Moreover, it is desirable that the pH (at 25° C.) of the ink composition is not less than 8.0, and the pH (at 25° C.) of the treatment liquid is in the range of 0.5 to 4. Consequently, it is possible to achieve good image density and resolution and high speed inkjet recording. 
     It is possible to include additives in the treatment liquid. For example, the treatment liquid can contain commonly known additives, such as an anti-drying agent (humectant agent), an anti-fading agent, an emulsion stabilizer, a permeation promoter, an ultraviolet light absorber, an antibacterial agent, an antiseptic agent, a pH adjuster, a surface tension adjuster, an antifoaming agent, a viscosity adjuster, a dispersant, a dispersion stabilizer, an anti-rusting agent, a chelating agent, or the like. 
     By applying a treatment liquid of this kind to the printing surface of the sheet of paper P in advance of printing, the occurrence of feathering and bleeding, or the like, can be prevented, and printing of high quality can be performed, even if using general printing paper. 
     In the treatment liquid application unit  30  having the composition described above, the sheet of paper P is held on the treatment liquid application drum  31  and is conveyed along the prescribed conveyance path. During this conveyance process, the printing surface of the sheet of paper P is coated with the treatment liquid by the coating apparatus  32 . 
     The sheet of paper P of which the printing surface has been coated with the treatment liquid is then transferred from the treatment liquid application drum  31  onto the transfer drum  80  at a prescribed position. Thereupon, the sheet of paper P is conveyed along the prescribed conveyance path by the transfer drum  80  and is transferred onto the conveyance drum  41  of the image recording unit  40 . 
     As described above, the drier  84  is disposed inside the transfer drum  80  and blows a warm air flow toward the guide plate  82 . The warm air flow is blown onto the printing surface of the sheet of paper P during the conveyance process from the treatment liquid application unit  30  to the image recording unit  40  by the transfer drum  80 , and thereby the treatment liquid that has been applied to the printing surface of the sheet of paper P is dried (i.e., the solvent component in the treatment liquid is evaporated). 
     &lt;Image Recording Unit&gt; 
     The image recording unit  40  forms a color image on the printing surface of the sheet of paper P by ejecting and depositing droplets of inks of colors of cyan (C), magenta (M), yellow (Y) and black (K) onto the printing surface of the sheet of paper P. The image recording unit  40  includes: a conveyance drum (hereinafter referred to as the “image recording drum”)  41 , which conveys the sheet of paper P; a paper pressing roller  42 , which presses the printing surface of the sheet of paper P and causes the rear surface of the sheet of paper P to make tight contact with the outer circumferential surface of the image recording drum  41 ; a paper floating detection sensor  43 , which detects floating of the sheet of paper P; and inkjet heads  44 C,  44 M,  44 Y and  44 K, which form an image by ejecting and depositing ink droplets of the respective colors of C, M, Y and K onto the printing surface of the sheet of paper P. 
     The image recording drum  41  receives the sheet of paper P from the transfer drum  80  (by gripping the leading end of the sheet of paper P with the gripper), and conveys the sheet of paper P along a prescribed conveyance path by rotating. 
     The paper pressing roller  42  is constituted of a rubber roller, which corresponds to the width of the sheet of paper P, and is disposed in the vicinity of the paper receiving position of the image recording drum  41  (the position where the sheet of paper P is received from the transfer drum  80 ). The sheet of paper P transferred from the transfer drum  80  onto the image recording drum  41  is nipped by the paper pressing roller  42 , thereby causing the rear surface of the sheet of paper P to make tight contact with the outer circumferential surface of the image recording drum  41 . 
     The paper floating detection sensor  43  detects floating of the sheet of paper P passing the paper pressing roller  42  (a prescribed amount of floating or more from the outer circumferential surface of the image recording drum  41 ). The paper floating detection sensor  43  is constituted of a laser emitter and a laser receiver, for example. The laser emitter emits laser light parallel to the axis of the image recording drum  41 , from one end of the image recording drum  41  toward the other end thereof, at a position a prescribed height above the outer circumferential surface of the image recording drum  41 . The laser receiver is disposed so as to oppose the laser emitter on the other end of the image recording drum  41 , and receives the laser light emitted by the laser emitter. If floating of the sheet of paper P occurs to a certain extent or more as the sheet of paper P passes the paper pressing roller  42 , then the laser light emitted from the laser emitter is obstructed by the sheet of paper P and cannot be received by the laser receiver. The paper floating detection sensor  43  detects the floating of the sheet of paper P by determining the presence or absence of the received laser light in the laser receiver. 
     The four inkjet heads  44 C,  44 M,  44 Y and  44 K are disposed after the paper floating detection sensor  43  and are disposed at uniform intervals along the conveyance path of the sheet of paper P. The inkjet heads  44 C,  44 M,  44 Y and  44 K are constituted of line heads, which correspond to the width of the sheet of paper P. Each of the inkjet heads  44 C,  44 M,  44 Y and  44 K ejects droplets of the ink of the corresponding color toward the image recording drum  41 , from a row of nozzles formed in a nozzle surface thereof. 
     The ink used in the inkjet recording apparatus  10  according to the present embodiment is an aqueous ultraviolet-curable ink, which contains a pigment, polymer particles and a water-soluble polymerizable compound which can be polymerized by an active energy beam. The aqueous ultraviolet-curable ink can be cured by being irradiated with ultraviolet light, and has properties such as excellent weatherproofing and high film strength. 
     The pigment used is a water-dispersible pigment in which at least a portion of the surface of each pigment particle is coated with a polymer dispersant. 
     The polymer dispersant employs a polymer dispersant having an acid value of 25 to 1000 (KOH mg/g). In this case, self-dispersion stability is good and aggregating properties upon contact with the treatment liquid are good. 
     The polymer particles use self-dispersing polymer particles having an acid value of 20 to 50 (KOH mg/g). In this case, self-dispersion stability is good and aggregating properties upon contact with the treatment liquid are good. 
     It is desirable that the polymerizable compound is an anionic or cationic polymerizable compound from the viewpoint of not disturbing the reaction between the aggregating agent, the pigment and the polymer particles, and has a solubility of not less than 10 wt % (and more desirably, not less than 15 wt %) with respect to water 
     The ink contains a polymerization initiator which starts polymerization of the polymerizable compound by the active energy beam. The initiator can include a suitably selected compound which is capable of starting the polymerization reaction upon irradiation with the active energy beam; for example, it is possible to use an initiator (for example, a photopolymerization initiator) which creates active species (radical, acid, base, or the like) upon irradiation with a beam of radiation, light or an electron beam. The polymerization initiator can also be contained in the treatment liquid, and it is sufficient that the polymerization initiator is contained in at least one of the ink and the treatment liquid. 
     Moreover, the ink contains 50 to 70 wt % of water. Further, it is possible to include additives in the ink. For example, the ink can contain commonly known additives, such as a water-soluble organic solvent or an anti-drying agent (humectant agent), an anti-fading agent, an emulsion stabilizer, a permeation promoter, an ultraviolet light absorber, an antibacterial agent, an antiseptic agent, a pH adjuster, a surface tension adjuster, an antifoaming agent, a viscosity adjuster, a dispersant, a dispersion stabilizer, an anti-rusting agent, a chelating agent, or the like. 
     In the image recording unit  40  having the composition described above, the sheet of paper P is conveyed along the prescribed conveyance path by the image recording drum  41 . The sheet of paper P transferred from the transfer drum  80  onto the image recording drum  41  is firstly nipped by the paper pressing roller  42 , and is thereby caused to make tight contact with the outer circumferential surface of the image recording drum  41 . Thereupon, the presence or absence of floating is determined by the paper floating detection sensor  43 , whereupon ink droplets of the colors of C, M, Y and K are ejected and deposited onto the printing surface of the sheet of paper P from the respective inkjet heads  44 C,  44 M,  44 Y and  44 K, thereby forming a color image on the printing surface of the sheet of paper P. 
     When the paper floating detection sensor  43  detects the sheet of paper P floating from the outer circumferential surface of the image recording drum  41 , the conveyance of the sheet of paper P is halted. Thus, the floating sheet of paper P can be prevented from making contact to the nozzle surfaces of the inkjet heads  44 C,  44 M,  44 Y and  44 K. 
     As described above, in the inkjet recording apparatus  10  according to the present embodiment, the aqueous ink is used for each of the colors. Even if using the aqueous ink of this kind, since the printing surface of the sheet of paper P has been coated with the treatment liquid as described above, then it is possible to carry out printing of high quality even if using generic printing paper. 
     The sheet of paper P on which the image has been printed is transferred from the image recording drum  41  onto the transfer drum  90 . Thereupon, the sheet of paper P is conveyed along the prescribed conveyance path by the transfer drum  90  and is transferred onto the conveyance drum  51  of the image drying unit  50 . 
     As described above, the drier  94  is disposed inside the transfer drum  90  and blows a warm air flow toward the guide plate  92 . The sheet of paper P thereby undergoes a drying process during the conveyance by the transfer drum  90 , although an ink drying process is carried out in the ink drying unit  50  at a later stage. 
     Although not shown in the drawings, the image recording unit  40  is provided with a maintenance unit which performs maintenance of the inkjet heads  44 C,  44 M,  44 Y and  44 K, and the inkjet heads  44 C,  44 M,  44 Y and  44 K are moved to the maintenance unit as and when necessary so as to be able to receive required maintenance. 
     &lt;Ink Drying Unit&gt; 
     The ink drying unit  50  dries the liquid component remaining on the sheet of paper P after the image recording. The ink drying unit  50  includes: a conveyance drum (hereinafter referred to as the “ink drying drum”)  51 , which conveys the sheet of paper P; and an ink drying device  52 , which carries out the drying process on the sheet of paper P conveyed by the ink drying drum  51 . 
     The ink drying drum  51  receives the sheet of paper P from the transfer drum  90  (by gripping the leading end of the sheet of paper P with the gripper), and conveys the sheet of paper P along a prescribed conveyance path by rotating. 
     The ink drying device  52  is constituted of a drier (in the present embodiment, three driers disposed along the conveyance path of the sheet of paper P) for example, and blows a warm air flow (at 80° C., for example) toward the sheet of paper P which is conveyed by the ink drying drum  51 . 
     In the ink drying unit  50  having the composition described above, the sheet of paper P is conveyed along the prescribed conveyance path by the ink drying drum  51 . During this conveyance process, a warm air flow is blown from the ink drying device  52  onto the printing surface of the sheet of paper P, and the ink that has been deposited on the printing surface is dried (i.e., the solvent component of the ink is evaporated). 
     The sheet of paper P which has passed through the ink drying device  52  is then transferred from the ink drying drum  51  onto the transfer drum  100  at a prescribed position. Thereupon, the sheet of paper P is conveyed along the prescribed conveyance path by the transfer drum  100  and is transferred onto the conveyance drum  61  of the fixing unit  60 . 
     As described above, the drier  104  is disposed inside the transfer drum  100  and blows a warm air flow toward the guide plate  102 . The sheet of paper P thereby undergoes a drying process during the conveyance by the transfer drum  100 . 
     &lt;Fixing Unit&gt; 
     The fixing unit  60  fixes the image that has been recorded on the printing surface of the sheet of paper P, by applying heat and pressure to the sheet of paper P. The fixing unit  60  includes: a conveyance drum (hereinafter referred to as the “fixing drum”)  61 , which conveys the sheet of paper P; an ultraviolet light source  62 , which applies ultraviolet light onto the printing surface of the sheet of paper P; and an in-line sensor  64 , which captures a printed image as well as determining a temperature and humidity, and the like, of the sheet of paper P after the printing. 
     The fixing drum  61  receives the sheet of paper P from the transfer drum  100  (by gripping the leading end of the sheet of paper P with the gripper), and conveys the sheet of paper P along a prescribed conveyance path by rotating. During this conveyance, the ultraviolet light source  62  applies ultraviolet light to the printing surface of the sheet of the paper P, on which the aggregate of the treatment liquid and the ink is thereby irradiated with ultraviolet light and solidified. 
     The in-line sensor  64  includes a temperature meter, a humidity meter, and a CCD line sensor, and the like, and determines the temperature and humidity, and the like, of the sheet of paper P conveyed by the fixing drum  61 , as well as reading the image printed on the sheet of paper P. Abnormalities of the inkjet recording apparatus  10  and head ejection defects, and the like, are checked on the basis of the determination results of the in-line sensor  64 . 
     In the fixing unit  60  having the composition described above, the sheet of paper P is conveyed along the prescribed conveyance path by the fixing drum  61 . During this conveyance process, the printing surface of the sheet of paper P is irradiated with ultraviolet light by the ultraviolet light source  62 , and the aggregate of the treatment liquid and the ink is solidified. 
     The sheet of paper P which has undergone the fixing process is transferred from the fixing drum  61  to the recovery unit  70  at a prescribed position. 
     &lt;Recovery Unit&gt; 
     The recovery unit  70  recovers the sheets of paper P which have undergone the series of printing processes, in a stacked fashion in a stacker  71 . The recovery unit  70  includes: the stacker  71 , which recovers the sheets of paper P; and a paper output conveyor  72 , which receives the sheet of paper P that has undergone the fixing process in the fixing unit  60  from the fixing drum  61 , conveys the sheet of paper P along a prescribed conveyance path, and outputs the sheet of paper P to the stacker  71 . 
     The sheet of paper P that has undergone the fixing process in the fixing unit  60  is transferred from the fixing drum  61  onto the paper output conveyor  72 , conveyed by the paper output conveyor  72  to the stacker  71 , and then recovered in the stacker  71 . 
     Control System 
       FIG. 2  is a block diagram showing the schematic composition of a control system of the inkjet recording apparatus  10  according to the present embodiment. 
     As shown in  FIG. 2 , the inkjet recording apparatus  10  includes a system controller  200 , a communication unit  201 , an image memory  202 , a conveyance control unit  203 , a paper supply control unit  204 , a treatment liquid application control unit  205 , an image recording control unit  206 , an ink drying control unit  207 , a fixing control unit  208 , a recovery control unit  209 , an operating unit  210 , a display unit  211 , and the like. 
     The system controller  200  functions as a control device which performs overall control of the respective units of the inkjet recording apparatus  10 , and also functions as a calculation device which performs various calculation processes. The system controller  200  includes a CPU, ROM, RAM, and the like, and operates in accordance with a prescribed control program. Control programs executed by the system controller  200  and various data necessary for control purposes are stored in the ROM. 
     The communication unit  201  includes a prescribed communication interface, and sends and receives data between the communication interface and a connected host computer. 
     The image memory  202  functions as a temporary storage device for various data including image data, and data is read from and written to the memory through the system controller  200 . Image data which has been read in from the host computer through the communication unit  201  is stored in the image memory  202 . 
     The conveyance control unit  203  controls the driving of the conveyance drums  31 ,  41 ,  51  and  61  and the transfer drums  80 ,  90  and  100 , which are the conveyance devices of the sheets of paper P in the treatment liquid application unit  30 , the image recording unit  40 , the ink drying unit  50  and the fixing unit  60 . 
     More specifically, the conveyance control unit  203  controls the driving of the motors which drive the conveyance drums  31 ,  41 ,  51  and  61 , and also controls the opening and closing of the grippers which are disposed on the conveyance drums  31 ,  41 ,  51  and  61 . 
     Similarly, the conveyance control unit  203  controls the driving of the motors which drive the transfer drums  80 ,  90  and  100 , and also controls the opening and closing of the grippers which are disposed on the transfer drums  80 ,  90  and  100 . 
     Further, since the conveyance drums  31 ,  41 ,  51  and  61  are provided with the mechanisms for holding the sheets of paper P by attraction on the circumferential surfaces thereof, then the conveyance control unit  203  also controls the driving of the attraction holding mechanisms (in the present embodiment, since the sheets of paper P are held by vacuum suction, then the conveyance control unit  203  controls the driving of vacuum pumps functioning as negative pressure generating devices). 
     Furthermore, since the transfer drums  80 ,  90  and  100  are provided with the driers  84 ,  94  and  104 , then the conveyance control unit  203  also controls the driving (amount of heating, and air flow volume) of the driers  84 ,  94  and  104 . 
     The driving of the conveyance drums  31 ,  41 ,  51  and  61  and the transfer drums  80 ,  90  and  100  is controlled in accordance with instructions from the system controller  200 . 
     The paper supply control unit  204  controls the driving of the respective sections (the paper supply device  21 , the transfer drum  23 , and the like) which constitute the paper supply unit  20 , in accordance with instructions from the system controller  200 . 
     The treatment liquid application control unit  205  controls the driving of the respective sections (the coating apparatus  32 , and the like) which constitute the treatment liquid application unit  30 , in accordance with instructions from the system controller  200 . 
     The image recording control unit  206  controls the driving of the respective sections (the paper pressing roller  42 , the inkjet heads  44 C,  44 M,  44 Y and  44 K, and the like) which constitute the image recording unit  40 , in accordance with instructions from the system controller  200 . 
     The ink drying control unit  207  controls the driving of the respective sections (the ink drying apparatus  52 , and the like) which constitute the ink drying unit  50 , in accordance with instructions from the system controller  200 . 
     The fixing control unit  208  controls the driving of the respective sections (the ultraviolet light source  62 , the in-line sensor  64 , and the like) which constitute the fixing unit  60 , in accordance with instructions from the system controller  200 . 
     The recovery control unit  209  controls the driving of the respective sections (the paper output conveyer  72 , and the like) which constitute the recovery unit  70 , in accordance with instructions from the system controller  200 . 
     The operating unit  210  includes prescribed operating devices (for example, operating buttons, a keyboard, a touch panel, or the like), and outputs operational information input from the operating device to the system controller  200 . The system controller  200  executes various processing in accordance with the operational information input from the operating section  210 . 
     The display unit  211  includes a prescribed display device (for example, an LCD panel, or the like), and causes prescribed information to be displayed on the display device in accordance with instructions from the system controller  200 . 
     As described above, the image data to be recorded on the sheet of paper is read into the inkjet recording apparatus  10  from the host computer through the communication unit  201  and is stored in the image memory  202 . The system controller  200  generates dot data by carrying out prescribed signal processing on the image data stored in the image memory  202 , and records an image represented by the image data by controlling the driving of the inkjet heads of the image recording unit  40  in accordance with the generated dot data. 
     In general, the dot data is generated by subjecting the image data to color conversion processing and halftone processing. The color conversion processing is processing for converting image data represented by sRB, or the like (RB 8-bit image data, for example) into ink volume data for each color of ink used by the inkjet recording apparatus  10  (in the present embodiment, ink volume data for the respective colors of C, M, Y and K). The halftone processing is processing for converting the ink volume data of the respective colors generated by the color conversion processing into dot data of the respective colors by error diffusion processing, or the like. 
     The system controller  200  generates the dot data of the respective colors by applying the color conversion processing and the halftone processing to the image data. The image represented by the image data is recorded on the sheet of paper by controlling the driving of the corresponding inkjet heads in accordance with the dot data for the respective colors thus generated. 
     Image Recording Process 
     Next, an image recording operation of the inkjet recording apparatus  10  according to the present embodiment is explained. 
     When the system controller  200  outputs a paper supply instruction to the paper supply device  21 , a sheet of paper P is supplied from the paper supply device  21  to the paper supply tray  22 . The sheet of paper P supplied to the paper supply tray  22  is transferred onto the treatment liquid application drum  31  of the treatment liquid application unit  30  through the transfer drum  23 . 
     The sheet of paper P transferred on the treatment liquid application drum  31  is conveyed along the prescribed conveyance path by the treatment liquid application drum  31 , and during this conveyance process, the treatment liquid is applied onto the printing surface of the sheet of paper P by the coating apparatus  32 . 
     The sheet of paper P of which the printing surface has been coated with the treatment liquid is transferred from the treatment liquid application drum  31  onto the transfer drum  80 . Thereupon, the sheet of paper P is conveyed along the prescribed conveyance path by the transfer drum  80  and is transferred onto the image recording drum  41  of the image recording unit  40 . During the conveyance of the sheet of paper P by the transfer drum  80 , the warm air flow is blown onto the printing surface of the sheet of paper P from the drier  84  disposed inside the transfer drum  80 , and the treatment liquid that has been applied to the printing surface is dried. 
     The sheet of paper P transferred from the transfer drum  80  to the image recording drum  41  is firstly nipped by the paper pressing roller  42  and the rear surface of the sheet of paper P is caused to make tight contact with the outer circumferential surface of the image recording drum  41 . 
     The presence or absence of floating in the sheet of paper P that has passed the paper pressing roller  42  is then determined by the paper floating detection sensor  43 . If floating of the sheet of paper P is detected, the conveyance of the sheet of paper P is halted. On the other hand, if no floating is detected, then the sheet of paper P is continued to be conveyed to the inkjet heads  44 C,  44 M,  44 Y and  44 K. Thereupon, when the sheet of paper P passes below the inkjet heads  44 C,  44 M,  44 Y and  44 K, ink droplets of the respective colors of C, M, Y and K are ejected and deposited onto the printing surface of the sheet of paper P by the inkjet heads  44 C,  44 M,  44 Y and  44 K, and a color image is thereby formed on the printing surface. 
     The sheet of paper P on which the image has been formed is transferred from the image recording drum  41  onto the transfer drum  90 . Thereupon, the sheet of paper P is conveyed along the prescribed conveyance path by the transfer drum  90  and is transferred onto the ink drying drum  51  of the image drying unit  50 . During the conveyance of the sheet of paper P by the transfer drum  90 , the warm air flow is blown onto the printing surface of the sheet of paper P from the drier  94  disposed inside the transfer drum  90 , and the ink that has been deposited on the printing surface is dried. 
     The sheet of paper P transferred to the ink drying drum  51  is conveyed along the prescribed conveyance path by the ink drying drum  51 . During this conveyance, the warm air flow is blown from the ink drying apparatus  52  onto the printing surface of the sheet of paper P and the liquid component remaining on the printing surface is dried. 
     The sheet of paper P that has undergone the drying process is transferred from the ink drying drum  51  onto the transfer drum  100 . The sheet of paper P is conveyed on the prescribed conveyance path by the transfer drum  100  and is transferred onto the fixing drum  61  of the fixing unit  60 . During the conveyance of the sheet of paper P by the transfer drum  100 , the warm air flow is blown onto the printing surface of the sheet of paper P from the drier  104  disposed inside the transfer drum  100 , and the ink that has been deposited on the printing surface is dried further. 
     The sheet of paper P transferred to the fixing drum  61  is conveyed along the prescribed conveyance path by the fixing drum  61 . During this conveyance, the printing surface of the sheet of paper P is irradiated with ultraviolet light, and the image formed on the printing surface is fixed. The sheet of paper P is then transferred from the fixing drum  61  onto the paper output conveyor  72  of the recovery unit  70 , conveyed by the paper output conveyor  72  to the stacker  71 , and then output to the stacker  71 . 
     As described above, in the inkjet recording apparatus  10  according to the present embodiment, the sheet of paper P is conveyed on the drums and during the course of conveyance, the respective processes of the application and drying of the treatment liquid, the deposition and drying of the ink droplets, and the fixing, are carried out on the sheet of paper P, thereby recording the prescribed image on the sheet of paper P. 
     Coating Apparatus 
     Next, the coating apparatus  32 , which is incorporated in the inkjet recording apparatus  10  according to the present embodiment, is described. 
     &lt;Basic Composition of Coating Apparatus&gt; 
     Firstly, the basic composition of the coating apparatus  32  is described. 
     As described above, the coating apparatus  32  applies the treatment liquid (i.e., a coating liquid) to the surface (i.e., a surface to be coated) of the sheet of paper (i.e., an object to be coated) P, which is conveyed by the treatment liquid application drum (i.e., a conveyance device of the object to be coated)  31 . 
       FIGS. 3 ,  4  and  5  are a side view diagram, a plan diagram and a perspective diagram, respectively, showing the schematic composition of the coating apparatus  32 . 
     As shown in  FIGS. 3 to 5 , the coating apparatus  32  includes: a coating roller  302 , which is configured to abut on the surface of the sheet of paper P to apply the treatment liquid to the surface of the sheet of paper P; a supply roller  304 , which is configured to supply the treatment liquid to the circumferential surface of the coating roller  302 ; and a treatment liquid receptacle (i.e., a coating liquid supply device)  306 , which supplies the treatment liquid to the circumferential surface of the supply roller  304 . The coating apparatus  32  is disposed in the conveyance path of the sheet of paper P that is conveyed by the treatment liquid application drum  31 . 
     The coating roller  302  applies the treatment liquid to the surface of the sheet of paper P, by making the circumferential surface thereof in contact with and pressed against the surface of the sheet of paper P, which is conveyed by the treatment liquid application drum  31 . 
     The coating roller  302  has the circumferential surface of which a width (the dimension in the axial direction of the coating roller  302 ) is larger than a width (the dimension in the axial direction of the treatment liquid application drum  31 ) of the circumferential surface of the treatment liquid application drum  31 . The coating roller  302  is disposed in parallel with the treatment liquid application drum  31 , while axle portions at both ends of the coating roller  302  are rotatably supported by a coating roller supporting arm (not shown). The coating roller  302  is disposed in such a manner that the center of the circumferential surface thereof in the widthwise direction substantially coincides with the center of the circumferential surface of the treatment liquid application drum  31  in the widthwise direction. 
     The coating roller supporting arm is arranged on a coating apparatus main body frame (not shown). The coating roller supporting arm is arranged swingably about the position of the axis of rotation of the supply roller  304  when the supply roller  302  is situated in a prescribed supply position (described later). 
     A coating roller supporting arm swinging device (for example, a cylinder, or the like) which causes the coating roller supporting arm to swing is arranged on the coating apparatus main body frame. The coating roller supporting arm is caused to swing and move between a coating roller abutting position and a coating roller separating position, by the coating roller supporting arm swinging device. The coating roller  302  moves to a prescribed application position due to the coating roller supporting arm moving to the coating roller abutting position. Furthermore, by moving the coating roller supporting arm to the coating roller separating position, the coating roller  302  is moved to a prescribed withdrawn position. When the coating roller  302  moves to the application position, the circumferential surface of the coating roller  302  is in contact with and pressed against the circumferential surface of the treatment liquid application drum  31 . When the coating roller  302  moves to the withdrawn position, the circumferential surface of the coating roller  302  is separated from the circumferential surface of the treatment liquid application drum  31 . 
     A coating roller rotation drive device (for example, a motor) (not shown) is arranged on the coating roller supporting arm in order to rotate the coating roller  302 . The coating roller  302  is rotated at a prescribed speed of rotation due to being driven by the coating roller rotation drive device. The direction of rotation of the coating roller  302  is an opposite direction to the direction of rotation of the treatment liquid application drum  31 . 
     The supply roller  304  supplies the treatment liquid to the circumferential surface of the coating roller  302 , by making the circumferential surface of the supply roller  304  in contact with the circumferential surface of the coating roller  302 . 
     The supply roller  304  has the circumferential surface of which a width (the dimension in the axial direction of the supply roller  304 ) W 1  is larger than the width (the dimension in the axial direction of the coating roller  302 ) W 2  of the circumferential surface of the coating roller  302 , so as to be able to supply the treatment liquid to the whole of the widthwise direction of the coating roller  302 . The supply roller  304  is disposed in parallel with the coating roller  302 , while axle portions at both ends of the supply roller  304  are rotatably supported by a supply roller supporting arm (not shown). The supply roller  304  is disposed in such a manner that the center of the circumferential surface thereof in the widthwise direction substantially coincides with the center of the circumferential surface of the supply roller  302  in the widthwise direction. 
     As described above, the supply roller  304  has the circumferential surface of which the width is larger than the width of the circumferential surface of the coating roller  302 . Then, there are regions (non-contact regions) N which do not make contact with the circumferential surface of the coating roller  302  in both end portions of the circumferential surface of the supply roller  304  (in  FIG. 4 , the non-contact regions N are indicated by undulating lines at both ends of the supply roller  304 ). Each of the non-contact regions N has a surface state that is different from a surface state of a region (contact region) M which makes contact with the circumferential surface of the coating roller  302 . More specifically, the non-contact regions N are formed so as to have increased wettability (hydrophilic properties) and the treatment liquid is more liable to flow thereon than in the contact region M. In this way, by making the treatment liquid more liable to flow in the non-contact regions N, it is possible to prevent ring-shaped collections of the treatment liquid due to the treatment liquid stagnating in both end portions of the coating roller  302 . More specifically, it is possible to prevent the occurrence of ring-shaped collections of the treatment liquid in both end portions of the coating roller  302 . This point is described in detail below. 
     The supply roller supporting arm is arranged on the coating apparatus main body frame. The supply roller supporting arm is arranged swingably about a swinging axis. 
     A supply roller supporting arm swinging device (for example, a cylinder, or the like) which causes the supply roller supporting arm to swing is arranged on the coating apparatus main body frame. The supply roller supporting arm is caused to swing and move between a supply roller abutting position and a supply roller separating position, by the supply roller supporting arm swinging device. The supply roller  304  moves to a prescribed supply position due to the supply roller supporting arm moving to the supply roller abutting position. Furthermore, by moving the supply roller supporting arm to the supply roller separating position, the supply roller  304  is moved to a prescribed supply halt position. When the supply roller  304  moves to the supply position, the circumferential surface of the supply roller  304  is in contact with and pressed against the circumferential surface of the coating roller  302 . When the supply roller  304  moves to the supply halt position, the circumferential surface of the supply roller  304  is separated from the circumferential surface of the coating roller  302 . 
     A supply roller rotation drive device (for example, a motor) (not shown) is arranged on the supply roller supporting arm in order to rotate the supply roller  304 . The supply roller  304  is rotated at a prescribed speed of rotation due to being driven by the supply roller rotation drive device. The direction of rotation of the supply roller  304  is an opposite direction to the direction of rotation of the coating roller  302 . 
     The treatment liquid receptacle  306  stores the treatment liquid and supplies the treatment liquid to the circumferential surface of the supply roller  304 . 
     The treatment liquid receptacle  306  is formed in a dish shape having an open upper part. The treatment liquid receptacle  306  is arranged horizontally on the coating apparatus main body frame. The treatment liquid is stored in the treatment liquid receptacle  306 . A part (lower part) of the supply roller  304  is immersed in the treatment liquid stored in the treatment liquid receptacle  306 . By rotating the supply roller  304 , the treatment liquid is taken up and is supplied to the circumferential surface of the coating roller  302 , which abuts on the circumferential surface of the supply roller  304 . 
     The treatment liquid is circulated and supplied to the treatment liquid receptacle  306  by a treatment liquid supply unit (not shown). The treatment liquid supply unit monitors a height of the surface of the treatment liquid stored in the treatment liquid receptacle  306 , and circulates and supplies the treatment liquid so as to keep this height uniform. 
     The basic composition of the coating apparatus  32  is as described above. 
     &lt;Coating Operation&gt; 
     Next, the basic operations of coating are described. 
     In an initial state, the coating roller  302  is situated at the standby position, and the supply roller  304  is situated in the separated position. Consequently, in the initial state, the coating roller  302  is separated from the treatment liquid application drum  31 , and the supply roller  304  is separated from the coating roller  302 . 
     Firstly, the coating roller  302  and the supply roller  304  are driven to rotate. By rotating the supply roller  304 , the treatment liquid is supplied to the circumferential surface of the supply roller  304 . 
     Next, the supply roller  304  is moved to the supply position. Thereby, the treatment liquid is supplied to the circumferential surface of the coating roller  302 , due to the circumferential surface of the supply roller  304  abutting to the circumferential surface of the coating roller  302 . In other words, due to the circumferential surface of the supply roller  304  abutting to the circumferential surface of the coating roller  302 , the treatment liquid that has been deposited on the circumferential surface of the supply roller  304  is transferred onto the circumferential surface of the coating roller  302 , whereby the treatment liquid is supplied to the circumferential surface of the coating roller  302 . With this, the preparations for coating are completed. By moving the coating roller  302  to the application position in this state, it is possible to apply the treatment liquid to the surface of the sheet of paper P which is conveyed by the treatment liquid application drum  31 . 
     Here, the movement of the coating roller  302  is controlled in synchronism with the conveyance of the sheet of paper P. More specifically, at the timing that the leading end of the sheet of paper P arrives at the position where the coating roller  302  is disposed, the coating roller  302  is controlled so as to move from the withdrawn position to the application position, and furthermore, at the timing that the trailing end of the sheet of paper P arrives at the position where the coating roller  302  is disposed, the coating roller  302  is controlled so as to move the coating roller  302  from the application position to the withdrawn position. Thus, the coating roller  302  is moved to the application position in synchronism with the timing at which the sheet of paper P passes, whereby the treatment liquid is applied to the surface of the sheet of paper P. 
     In this way, by moving the coating roller  302  which has received a supply of the treatment liquid on the circumferential surface thereof, in accordance with the conveyance of the sheets of paper P, the treatment liquid is applied to the surfaces of the sheets of paper P which are conveyed successively. 
     When the coating process has been completed, firstly, the rotations of the coating roller  302  and the supply roller  304  are halted in the state where the coating roller  302  is situated in the withdrawn position. Thereupon, the supply roller  304  is moved to the standby position. Thereby, the coating roller  302  is halted in the state of being separated from the treatment liquid application drum  31 , and the supply roller  304  is halted in the state of being separated from the coating roller  302 . 
     &lt;Detailed Structure of Coating Apparatus&gt; 
     As described above, in the coating apparatus  32  according to the present embodiment, in order to be able to supply the treatment liquid to the whole region of the coating roller  302  in the widthwise direction, the width (the dimension in the axial direction) of the circumferential surface of the supply roller  304  is formed to be larger than the width (the dimension in the axial direction) of the circumferential surface of the coating roller  302 . Hence, there are the regions (non-contact regions) N which do not make contact with the coating roller  302  in both end portions of the circumferential surface of the supply roller  304 . 
     When the treatment liquid is supplied to the coating roller  302  by using the supply roller  304  having the circumferential surface of which the width is larger than the width of the circumferential surface of the coating roller  302  as described above, ring-shaped collections of the treatment liquid occur in both end portions of the coating roller  302 . The reason for this is as follows. Surface tension acts on the treatment liquid so as to reduce the surface area thereof. In the region (contact region) where the coating roller  302  makes contact with the supply roller  304 , there is a film of the treatment liquid and therefore a force causing the treatment liquid to flow in the axial direction due to the surface tension is obtained when the volume of the treatment liquid increases. On the other hand, in the non-contact region, the coating roller  302  is no longer present and therefore the force moving the treatment liquid in the axial direction does not exist. Hence, the flow of the treatment liquid (the flow in the axial direction) stagnates at the end portions of the coating roller  302  and ring-shaped collections of the treatment liquid are produced at the end portions of the coating roller  302 . In this way, the ring-shaped collections of the treatment liquid that are produced in the end portions of the coating roller  302  occur due to the stagnation of the flow of the treatment liquid in the end portions of the coating roller  302 . 
     Consequently, by preventing the stagnation of the flow of the treatment liquid in the end portions of the coating roller  302 , it is possible to prevent the occurrence of ring-shaped collections of the treatment liquid in the end portions of the coating roller  302 . 
     Therefore, in the coating apparatus  32  according to the present embodiment, the treatment liquid is prevented from forming ring-shaped collections at both end portions of the coating roller  302  by differentiating the surface state of the non-contact regions N so as to make the treatment liquid flow more readily on the non-contact regions N (flow more readily in the axial direction). This point is described in detail below. 
     &lt;Structure for Preventing Occurrence of Collections of Treatment Liquid&gt; 
     As described above, by preventing the stagnation of the flow of the treatment liquid in the end portions of the coating roller  302 , the occurrence of ring-shaped collections of the treatment liquid in the end portions of the coating roller  302  can be prevented. Therefore, the treatment liquid is made to flow more readily in the non-contact regions N of the supply roller  304 . More specifically, the supply roller  304  is formed in such a manner that when the treatment liquid flows on the supply roller  304  alone, the flow velocity VN of the treatment liquid flowing on each of the non-contact regions N is faster than the flow velocity VM of the treatment liquid flowing on the contact region M (i.e., VN&gt;VM), then it is possible to prevent the occurrence of ring-shaped collections of the treatment liquid in the end portions of the coating roller  302 . 
     In order to make the flow velocity VN of the treatment liquid flowing on each of the non-contact regions N faster than the flow velocity VM of the treatment liquid flowing on the contact region M, the surface state of the non-contact regions N is differentiated so as to increase the wettability (hydrophilic properties). More specifically, provided that the wettability of the non-contact regions N is raised, it is possible to make the treatment liquid flow more readily in the non-contact regions N and the flow velocity VN of the treatment liquid flowing on each of the non-contact regions N can be made faster than the flow velocity VM of the treatment liquid flowing on the contact region M (i.e., VN&gt;VM). 
     &lt;Processing for Increasing the Wettability of the Non-Contact Regions&gt; 
     In order to increase the wettability of the non-contact regions N, the supply roller  304  is formed in such a manner that the contact angle θN of the treatment liquid to the non-contact regions N is smaller than the contact angle θM of the treatment liquid to the contact region M (i.e., θN&lt;θM). 
     It is possible to form the supply roller  304  in the following ways, in order to differentiate the contact angle θM of the treatment liquid from the contact region M and the contact angle θN of the treatment liquid to the non-contact regions N. 
     &lt;&lt;First Mode: Method Based on Changing Material&gt;&gt; 
     It is possible to differentiate the contact angle θM of the treatment liquid to the contact region M from the contact angle θN of the treatment liquid to the non-contact regions N, by differentiating the material used to compose the contact region M from the material used to compose the non-contact regions N. 
     For example, when the supply roller  304  is made of rubber, the contact region M is made from rubber having high hydrophobic properties (for example, fluoric rubber), and the non-contact regions N are made from rubber having high hydrophilic properties (for example, nitrile butadiene rubber (NBR)). 
     For example, when the supply roller  304  is made of metal, the contact region M is made from a metal having hydrophobic properties (for example, aluminum, stainless steel, or the like), and the non-contact regions N are made of a metal having hydrophilic properties (for example, titanium, or the like). 
     Thereby, it is possible to make the contact angle θN of the treatment liquid to the non-contact regions N smaller than the contact angle θM of the treatment liquid to the contact region M. In other words, it is possible to increase the hydrophilic properties of the non-contact regions N compared to the contact region M. Then, it is possible to make the treatment liquid flow more readily in the non-contact regions N, and stagnation of the flow of the treatment liquid can be prevented in the end portions of the coating roller  302 . Consequently, it is possible to prevent the occurrence of ring-shaped collections of the treatment liquid in the end portions of the coating roller  302 . 
     &lt;&lt;Second Mode: Method Based on Coating&gt;&gt; 
     By applying a coating treatment to the contact region M and/or the non-contact regions N, it is possible to differentiate the contact angle θM of the treatment liquid to the contact region M and the contact angle θN of the treatment liquid to the non-contact regions N. 
     For example, the contact region M is coated with a hydrophobic film of PTFE (polytetrafluoroethylene (tetrafluoride)), PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer polytetrafluoroethylene), or the like. Furthermore, the non-contact regions N are coated with a hydrophilic film of silica particles, or the like. 
     Thereby, it is possible to increase the hydrophilic properties of the non-contact regions N compared to the contact region M, and the treatment liquid can be made to flow more readily in the non-contact regions N. Then, it is possible to prevent stagnation of the flow of the treatment liquid in the end portions of the coating roller  302 . Consequently, it is possible to prevent the occurrence of ring-shaped collections of the treatment liquid in the end portions of the coating roller  302 . 
     Provided that the hydrophilic properties of the non-contact regions N can be increased, it is not necessarily required to apply the coating treatment to both the contact region M and the non-contact regions N. In other words, it is possible to apply the coating treatment to the non-contact regions N only, so as to increase the hydrophilic properties thereof compared to the contact region M. 
     &lt;&lt;Third Mode: Method Based on Changing Surface Roughness&gt;&gt; 
     By differentiating the surface roughness in the contact region M and in the non-contact regions N, it is possible to differentiate the contact angle θM of the treatment liquid to the contact region M and the contact angle θN of the treatment liquid to the non-contact regions N. 
     In other words, the value of the surface roughness of the non-contact regions N is made greater than the contact region M. More specifically, a process for roughening the surface is applied to the non-contact regions N. 
     Thereby, it is possible to make the contact angle θN of the treatment liquid to the non-contact regions N smaller than the contact angle θM of the treatment liquid to the contact region M. Then, it is possible to make the treatment liquid flow more readily in the non-contact regions N, and stagnation of the flow of the treatment liquid can be prevented in the end portions of the coating roller  302 . Consequently, it is possible to prevent the occurrence of ring-shaped collections of the treatment liquid in the end portions of the coating roller  302 . 
     As described above, by forming the supply roller  304  as to make the contact angle θN of the treatment liquid to the non-contact regions N smaller than the contact angle θM of the treatment liquid to the contact region M(θN&lt;θM), it is possible to prevent stagnation of the flow of the treatment liquid in the end portions of the coating roller  302 , whereby the occurrence of ring-shaped collections of the treatment liquid in the end portions of the coating roller  302  can be prevented. 
     In any of these modes, it is desirable that the contact angles (θM and θN) are not larger than 90°. If the contact angle is larger than 90°, then the treatment liquid becomes liable to pass around onto the end faces of the rollers, and the treatment liquid becomes liable to collect on the end faces of the rollers. 
     &lt;Other Methods&gt; 
     As described above, it is possible to prevent the occurrence of ring-shaped collections of the treatment liquid in the end portions of the coating roller  302 , by making the treatment liquid flow more readily in the axial direction, in the non-contact regions N of the supply roller  304 . 
     The treatment liquid can be made to flow more readily in the axial direction in the non-contact regions N, by forming linear grooves in the non-contact regions N. More specifically, as shown in  FIG. 6 , a plurality of grooves  308  parallel to the axis of the supply roller  304  are formed at a uniform pitch apart in the circumferential direction of the supply roller  304 , in the non-contact regions N at both ends of the supply roller  304 . 
     By forming the grooves  308  of this kind in the circumferential surface of the supply roller  304 , a force acts so as to cause the treatment liquid to flow along the grooves  308  due to the action of the surface tension, and the treatment liquid can be made to flow more readily in the axial direction in the non-contact regions N (the flow velocity VN of the treatment liquid flowing on the non-contact regions N can be made faster than the flow velocity VM of the treatment liquid flowing on the contact region M). Consequently, it is possible to prevent the occurrence of ring-shaped collections of the treatment liquid at both ends of the coating roller  302 . 
     It is preferable to form the plurality of fine grooves in the non-contact regions N, in order to be able to make the force causing the treatment liquid to flow in the axial direction act effectively on the treatment liquid due to the surface tension. More specifically, the contact surface area is secured by forming the plurality of fine grooves. For example, the grooves having the depth of 1 mm and the width of 0.5 mm are formed at intervals of 1 mm apart. 
     &lt;Structure for Preventing Scattering of Treatment Liquid in Axial Direction&gt; 
     As described above, according to the coating apparatus  32  of the present embodiment, the non-contact regions N at both ends of the supply roller  304  are composed in such a manner that the treatment liquid flows more readily in the axial direction. In this case, it is possible that the treatment liquid that has flowed to the end portions of the supply roller  304  adheres to the edges of the end faces of the supply roller  304  and scatters in the axial direction. 
     Therefore, in order to prevent this, as shown in  FIG. 7 , flange sections (portions having increased diameter)  310  are arranged at both end portions of the supply roller  304 . In other words, a return portion is formed in each end portion of the supply roller  304 . 
     Consequently, it is possible to prevent scattering, in the axial direction, of the treatment liquid that flows in the axial direction in the non-contact regions N. 
     Other Embodiments 
     In the embodiment described above, there is one supply roller; however, it is also possible to adopt a composition in which the treatment liquid (i.e., the coating liquid) is supplied to the coating roller  302  by means of a plurality of supply rollers (so-called multi-stage supply rollers). In this case, a composition is adopted which satisfies the aforementioned relationship between the rollers. 
     More specifically, the supply rollers constituting the multi-stage supply rollers are formed in such a manner that, in each pair of the supply rollers, the width of the circumferential surface of a first one of the pair of the supply rollers at a preceding stage (the supply roller nearer to the treatment liquid receptacle) is larger than the width of the circumferential surface of a second one of the pair of the supply rollers at a subsequent stage (the supply roller nearer to the coating roller), and there are the regions which are not contact with the second supply roller at the subsequent stage in both end portions in the widthwise direction of the circumferential surface of the first supply roller at the preceding stage. Furthermore, the circumferential surface of a final one of the supply rollers at the final stage (the supply roller that abuts on the coating roller) is formed to have the width larger than the width of the circumferential surface of the coating roller, and there are the regions which do not make contact with the coating roller in both end portions in the widthwise direction of the circumferential surface of the supply roller at the final stage. Each of the supply rollers is formed by differentiating the surface state between the contact region and the non-contact regions, in such a manner that the flow velocity of the treatment liquid flowing on the non-contact regions is faster than the flow velocity of the treatment liquid flowing on the contact region. 
       FIGS. 8 and 9  are a side view diagram and a plan diagram, respectively, showing a schematic composition of the coating apparatus of the type that supplies the treatment liquid to the coating roller through two supply rollers (two-stage supply rollers). 
     As shown in  FIGS. 8 and 9 , the coating apparatus  32  includes: the coating roller  302 ; a second supply roller  304 B, which supplies the treatment liquid to the circumferential surface of the coating roller  302 ; a first supply roller  304 A, which supplies the treatment liquid to the circumferential surface of the second supply roller  304 B; and the treatment liquid receptacle  306 , which supplies the treatment liquid to the circumferential surface of the first supply roller  304 A. 
     The first supply roller  304 A has the circumferential surface of which the width WA is larger than the width WB of the circumferential surface of the second supply roller  304 B (i.e., WA&gt;WB). Consequently, there are the regions (non-contact regions) which do not make contact with the second supply roller  304 B in both end portions in the widthwise direction of the circumferential surface of the first supply roller  304 A. 
     Furthermore, the second supply roller  304 B has the circumferential surface of which the width WB is larger than the width WC of the circumferential surface of the coating roller  302  (i.e., WB&gt;WC). Consequently, there are the regions (non-contact regions) which do not make contact with the coating roller  302  in both end portions in the widthwise direction of the circumferential surface of the second supply roller  304 B. 
     Similarly to the embodiments described above, each of the supply rollers (the first supply roller  304 A and the second supply roller  304 B) is formed in such a manner that the flow velocity of the treatment liquid flowing on the non-contact regions is faster than the flow velocity of the treatment liquid flowing on the contact region. More specifically, the surface state of the non-contact regions is differentiated so as to increase the wettability (hydrophilic properties) and make the treatment liquid flow more readily in the non-contact regions. 
     Consequently, it is possible to prevent the occurrence of ring-shaped collections of the treatment liquid in both end portions of each roller. 
     In the embodiment described above, the supply rollers are constituted of the two rollers; however, it is also possible to compose multi-stage supply rollers using a greater number of supply rollers. 
     Furthermore, in the embodiments described above, the case where the present invention is applied to the coating apparatus for applying the prescribed treatment liquid to the paper in the inkjet recording apparatus has been described; however, the application of the present invention is not limited to this. It is also possible to apply the present invention in general to a coating apparatus which applies a coating liquid by means of rollers to an object to be coated. 
     It should be understood that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.