Abstract:
A discharge liquid agitating mechanism, and an inkjet recording apparatus having the discharge liquid agitating mechanism, are provided which are simple in construction, and are yet capable of preventing sedimentation of particles and the like contained in a discharge liquid. 
     A discharge liquid agitating mechanism in an inkjet recording apparatus which discharges a discharge liquid to a recording medium while moving the recording medium and inkjet heads  100  relative to each other, includes a main tank  80  formed of a flexible material, a support table  81  for supporting the main tank  80 , a nozzle  83  for introducing a compressed gas between the main tank  80  and support table  81 , a plurality of subtanks  90  formed of the flexible material, a plurality of plate-like objects  91  for supporting the subtanks  90 , nozzles  93  for introducing the compressed gas between the subtanks  90  and plate-like objects  91 , a pipeline  86  for connecting the main tank  80  and subtanks  90 , and pipelines  96  for connecting the subtanks  90  and inkjet heads  100.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to a discharge liquid agitating mechanism in an inkjet recording apparatus which records images on a recording medium in an inkjet mode, and to an inkjet recording apparatus having the discharge liquid agitating mechanism. 
         [0003]    2. Description of the Related Art 
         [0004]    In such an inkjet recording apparatus, pigment ink, or UV (Ultraviolet) ink mixed with a curing accelerator or a UV curable resin, is used as a discharge liquid for recording images on a recording medium. The UV ink is cured by being irradiated with ultraviolet light from a UV lamp immediately after the ink is discharged to the recording medium. Therefore, by using such UV ink, it is possible to perform proper printing not only on ordinary paper but also on a film made of a resin which does not absorb ink. 
         [0005]    Such UV ink has a problem that pigments acting as a coloring material, metal particles for giving a special gloss and other contained particles settle in the interiors of ink tanks and ink supply routes. An uneven concentration distribution of these particles inside the ink tanks not only causes a reduction in printing accuracy, but can also cause an unsatisfactory discharge performance of inkjet heads when the inkjet recording apparatus is not used for a certain period of time. 
         [0006]    Under the circumstances, an inkjet recording apparatus described in Japanese Unexamined Patent Publication No. 2006-327048 has main tanks and subtanks, and uses a pump to circulate ink through pipelines extending between the tanks, thereby to prevent sedimentation of particles and the like contained in the ink. 
         [0007]    However, UV curable resin contained in the UV ink, generally, is highly corrosive. Therefore, where the construction described in Japanese Unexamined Patent Publication No. 2006-327048 is employed, it is necessary to use an expensive, corrosion-resistant pump, which poses a problem that the entire apparatus becomes expensive. 
       SUMMARY OF THE INVENTION 
       [0008]    The object of this invention, therefore, is to provide a discharge liquid agitating mechanism, and an inkjet recording apparatus having the discharge liquid agitating mechanism, which are simple in construction, and are yet capable of preventing sedimentation of particles and the like contained in a discharge liquid, without circulating the discharge liquid. 
         [0009]    The above object is fulfilled, according to this invention, by a discharge liquid agitating mechanism in an inkjet recording apparatus which discharges a discharge liquid to a recording medium while moving the recording medium and inkjet heads relative to each other, comprising a flexible discharge liquid container; a support member for supporting the discharge liquid container; and a gas supply device for introducing a compressed gas between the discharge liquid container and the support member; wherein currents of the compressed gas supplied from the gas supply device vibrate the discharge liquid container to agitate the discharge liquid. 
         [0010]    With such discharge liquid agitating mechanism, currents of the compressed gas supplied from the gas supply device vibrate the discharge liquid container. Consequently, although simple in construction, the discharge liquid stored in the container can be agitated. 
         [0011]    In a preferred embodiment, the discharge liquid agitating mechanism supplies the compressed gas intermittently when discharge of the discharge liquid from the inkjet heads is stopped. This can prevent the vibration of the discharge liquid container, when supplying the compressed gas, from influencing the inkjet heads, thereby to maintain high printing accuracy. 
         [0012]    In another aspect of this invention, a discharge liquid agitating mechanism in an inkjet recording apparatus which discharges a discharge liquid to a recording medium while moving the recording medium and inkjet heads relative to each other, comprises a main tank formed of a flexible material; a first support member for supporting the main tank; a first gas supply device for introducing a compressed gas between the main tank and the first support member; a plurality of subtanks formed of the flexible material; a plurality of second support members for supporting the subtanks; a second gas supply device for introducing the compressed gas between the subtanks and the second support members; a first pipeline for connecting the main tank and the subtanks; and second pipelines for connecting the subtanks and the inkjet heads; wherein, by supplying the compressed gas to the main tank and the subtanks, respectively, the first gas supply device and the second gas supply device are arranged to vibrate the main tank and the subtanks, respectively, to agitate the discharge liquid. 
         [0013]    With such discharge liquid agitating mechanism, since the main tank and subtanks are provided, liquid volume variations in the main tank impart little influence, to maintain the discharge constant. It is also possible to change the main tank, thereby allowing the discharge liquid to be replenished cleanly and easily. 
         [0014]    In a further aspect of this invention, there is provided an inkjet recording apparatus which discharges a discharge liquid to a recording medium while moving the recording medium and inkjet heads relative to each other, comprising a discharge liquid agitating mechanism, the discharge liquid agitating mechanism including a flexible discharge liquid container; a support member for supporting the discharge liquid container; and a gas supply device for introducing a compressed gas between the discharge liquid container and the support member; wherein currents of the compressed gas supplied from the gas supply device vibrate the discharge liquid container to agitate the discharge liquid. 
         [0015]    Other features and advantages of the invention will be apparent from the following detailed description of the embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    For the purpose of illustrating the invention, there are shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangement and instrumentalities shown. 
           [0017]      FIG. 1  is a schematic side view of an inkjet recording apparatus according to this invention; 
           [0018]      FIG. 2  is an explanatory view illustrating an outline of a discharge liquid agitating mechanism; 
           [0019]      FIG. 3A  is an explanatory view illustrating a state of feeding compressed air to a main tank  80 ; 
           [0020]      FIG. 3B  is an explanatory view illustrating a state of feeding compressed air to the main tank  80 ; 
           [0021]      FIG. 4A  is an explanatory view illustrating a state of feeding compressed air to a subtank  90 ; 
           [0022]      FIG. 4B  is an explanatory view illustrating a state of feeding compressed air to the subtank  90 ; and 
           [0023]      FIG. 5  is a block diagram showing a principal electrical structure of the inkjet recording apparatus according to this invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    An embodiment of this invention will be described hereinafter with reference to the drawings. The construction of an inkjet recording apparatus according to this invention will be described first.  FIG. 1  is a schematic side view of the image recording apparatus according to this invention. 
         [0025]    The inkjet recording apparatus is constructed to record images on printing paper serving as a recording medium held on tables  1  by suction. The apparatus includes a paper feeder  2 , a paper discharger  4 , a table moving mechanism  5  for moving ten tables  1  arranged at regular intervals along a circulating track, an image recorder  3  for recording images on the printing paper on the tables  1  moved by the table moving mechanism  5 , a GUI (Graphical User Interface)  6  having a touch-panel input and output unit, and a temperature sensor  10  for measuring the surface temperature of tables  1  in movement. 
         [0026]    The paper feeder  2  includes a stocker unit  40  and a feed section  50 . The stocker unit  40  holds the printing paper on an upper portion thereof, and feeds the printing paper, one sheet at a time, to the feed section  50 . The feed section  50  feeds the printing paper received from the stocker unit  40  to the tables  1  moving along the circulating track. 
         [0027]    The image recorder  3  records images in an inkjet mode on the printing paper held by suction on the upper surfaces of tables  1  moved in one direction by the table moving mechanism  5 . This image recorder  3  includes a pretreatment agent coating head  21 , four recording heads  22 ,  23 ,  24  and  25 , five heaters  26 ,  28 ,  29 ,  30  and  31 , and a scanner  32 . A discharge liquid agitating mechanism to be described hereinafter is disposed in this image recorder  3 . 
         [0028]    The pretreatment agent coating head  21  applies a transparent pretreatment agent to the printing paper before the four recording heads  22 ,  23 ,  24  and  25  record images. As this pretreatment agent, an anchor coat is used for improving adhesion of ink to the printing paper when, for example, glossy printing paper or grazed printing paper is used. 
         [0029]    The four recording heads consist of a recording head  22  for black ink, a recording head  23  for cyan ink, a recording head  24  for magenta ink, and a recording head  25  for yellow ink. The recording heads  22 ,  23 ,  24  and  25  are arranged above the tables  1  movable in one direction. Each of these recording heads  22 ,  23 ,  24  and  25  includes a plurality of inkjet heads having numerous inkjet nozzles arranged in a direction perpendicular to the moving direction of the tables  1 , and discharge the inks from the inkjet nozzles onto the printing paper to record images thereon. 
         [0030]    The five heaters consist of a preheating heater  26 , intermediate heaters  28 ,  29  and  30 , and a main heater  31 . These heaters  26 ,  28 ,  29 ,  30  and  31  are constructed to blow hot air to the printing paper. The scanner  32  has a linear CCD camera for measuring the density of entire images and/or patches recorded. 
         [0031]    A suction fan  55  is disposed under the moving track of tables  1 . The tables  1  have a hollow structure, and have suction bores formed in the surfaces thereof to communicate with the inner spaces. Thus, by exhausting air from the suction fan  55 , the printing paper supplied to the surfaces of tables  1  are held on the tables  1  by suction through the suction bores. 
         [0032]    The paper discharger  4  includes a paper discharge cylinder  77  for wrapping the printing paper peripherally thereof to separate the printing paper from each table  1 . This paper discharger  4  is constructed for switching transport of the printing paper received from the paper discharge cylinder  77  between two directions, one through a transport path provided by a first conveyor  73  and a second conveyor  76 , and the other through a transport path provided by a third conveyor  74  and a fourth conveyor  75 . 
         [0033]    Next, the discharge liquid agitating mechanism will be described.  FIG. 2  is an explanatory view illustrating an outline of the discharge liquid agitating mechanism. 
         [0034]    This discharge liquid agitating mechanism includes, as discharge liquid containers, a bag-like main tank  80  formed of a flexible material, and four bag-like subtanks  90  also formed of the flexible material. The main tank  80  and subtanks  90  are arranged above each of the pretreatment agent coating head  21  and four recording heads  22 ,  23 ,  24  and  25  of the image recorder  3  shown in  FIG. 1 .  FIG. 2  shows, by way of example, the discharge liquid agitating mechanism disposed above the recording head  22  which has eight inkjet heads  100 . 
         [0035]    The main tank  80  is placed on a support table  81  which is substantially horizontal, and their entirety is housed in a casing  82 . The support table  81  has a bore  84  formed in a bottom surface thereof, where a nozzle  83  acting as a compressed gas supply device is connected for blowing in compressed air acting as a compressed gas. A compressor  87  is connected to the nozzle  83  for delivering the compressed air. A pressurization adjusting unit  88  is connected to the casing  82  for adjusting pressure in the casing  82  to a predetermined pressure in order to feed the ink from the main tank  80  to the subtanks  90 . Pressure piping of plant facilities may be branched for use with these compressor  87  and pressurization adjusting unit  88 . 
         [0036]    The subtanks  90  have a smaller capacity than the main tank  80 . In this embodiment, four subtanks  90  with a capacity of about 100 ml are provided for one main tank  80  with a capacity of about 2 to 3 L. The four subtanks  90  are connected to the main tank  80  through a pipeline  85 . The ink is fed from the four subtanks  90  to the inkjet heads  100  in the recording head  22  through pipelines  96 , respectively. 
         [0037]    The main tank  80  and subtanks  90 , which are bag-like containers formed of a flexible material, are deformable with variations in the quantity of the pretreating agent or ink stored therein. If the discharge liquid containers were not deformable, layers of air would be formed in the discharge liquid containers, and variations in the internal pressure due to a reduction in the quantity of the pretreating agent or ink stored therein would cause a phenomenon of air flowing back from the inkjet nozzles, thereby causing an unsatisfactory discharge performance of the inkjet nozzles. Therefore, the main tank  80  and subtanks  90  are formed of a flexible material, to be deformable in liquid-tight state in response to internal liquid quantity, thereby preventing the unsatisfactory discharge performance of the inkjet nozzles due to the air in the main tank  80  and subtanks  90 . 
         [0038]      FIGS. 3A and 3B  are explanatory views illustrating a state of directing compressed air to the main tank  80 .  FIG. 3A  shows how the compressed air is blown to the main tank  80 .  FIG. 3B  shows in enlargement how the compressed air is blown to the main tank  80 . 
         [0039]    The main tank  80  is placed on the support table  81  to have an ink outlet port  89  facing sideways. With the main tank  80  placed in this way, a large area of contact between the bag-shaped external surface of the main tank  80  and the upper surface of the support table  81  can be secured. The support table  81  has the bore  84  formed in a position close to the ink outlet port  89  of the main tank  80 . As shown in  FIG. 3A , through this bore  84  the nozzle  83  blows compressed air from obliquely below the support table  81  to the main tank  80 , to form air currents flowing in one direction away from the outlet port  89  of the main tank  80 . When the compressed air is blown to the main tank  80 , a gap between the main tank  80  and support table  81  is decompressed, whereby the flexible main tank  80  temporarily sticks to the upper surface of the support table  81 . When the compressed air is further blown thereafter, as shown in  FIG. 3B , the external surface of the flexible main tank  80  will vibrate slightly in an undulating manner. By vibrating the main tank  80  in this way, the discharge liquid in the main tank  80  can be agitated uniformly. 
         [0040]    In order to vibrate the main tank  80  and agitate the discharge liquid effectively, the bore  84  of the support table  81  and the nozzle  83  need to be arranged in such a positional relationship that currents of the compressed air are formed between the support table  81  and main tank  80 , to flow in one direction which is the longitudinal direction of the main tank  80 . It is therefore preferred that the position of the bore  84  in the support table  81  is close to the outlet port  89 , and a bore may be formed in a side plate of the support table  81  located under the outlet port  89 . 
         [0041]      FIGS. 4A and 4B  are explanatory views illustrating a state of directing compressed air to each subtank  90 .  FIG. 4A  is a front view of the subtank  90  and adjacent components.  FIG. 4B  is a side view of the subtank  90  and adjacent components. 
         [0042]    Each subtank  90  has an inlet port  98  for receiving the ink flowing through the pipeline  85  from the main tank  80 , and an outlet port  99  for discharging the ink to the pipeline  96  connecting the subtank  90  and inkjet heads  100 . The subtank  90  is stuck to a plate-like object  91  acting as support member extending substantially vertically, to have the inlet port  98  and outlet port  99  facing sideways. As shown in  FIG. 4B , the plate-like object  91  is L-shaped in a side view. The subtank  90  is partially stuck to the plate-like object  91  using double-stick tape, so as to form a gap between the subtank  90  and plate-like object  91  where the compressed air from a nozzle  93  can flow in. Although not shown in  FIG. 2 , the nozzles  93  constituting the compressed gas supply device for supplying compressed air to the subtanks  90  are connected to the compressor  87  as is the nozzle  83  noted above. 
         [0043]    As shown in  FIGS. 4A and 4B , the nozzle  93  directs the compressed air to the subtank  90 , to form horizontal gas currents flowing from a lateral position toward a gap between a portion of the plate-like object  91  located below the subtank  90  and an external surface of the subtank  90 . Consequently, the subtank  90  vibrates in the same way as the main tank  80  described above, to agitate the discharge liquid in the subtank  90  uniformly. 
         [0044]      FIG. 5  is a block diagram showing a principal electrical structure of the above inkjet recording apparatus. This inkjet recording apparatus includes a controller  190  having a RAM  191  for temporarily storing data and the like at times of control, a ROM  192  for storing operating programs required for control of the apparatus, and a CPU  193  for performing logical operations. This controller  190  is connected through an interface  195  to the GUI  6  noted hereinbefore and to a driver  86  for driving various components of the inkjet recording apparatus. The controller  190  is connected also to the compressor  87  and pressurization adjusting unit  88  noted hereinbefore. This controller  190  controls various types of operation of the inkjet recording apparatus. 
         [0045]    In the inkjet recording apparatus having the above construction, the supply of compressed air from the compressor  87  is stopped at normal image recording times. In this state, while the tables  1  holding the printing paper by suction are moved along the circulating track, the inks are discharged from the inkjet nozzles by the action of piezoelectric elements arranged in the inkjet heads. 
         [0046]    The interior of the casing  82  in which the main tank  80  is mounted is pressurized to a fixed pressure (0.02 MPa in this embodiment) by the pressurization adjusting unit  88 . At this time, the discharge liquid is continuously fed from the main tank  80  to the subtanks  90  in this inkjet recording apparatus, to maintain the discharge liquid volume in the subtanks  90  at about 50 to 70% of the capacity of the subtanks  90 . 
         [0047]    Compressed air is supplied from the nozzles  83  and  93  to the main tank  80  and subtanks  90  when an image recording is not carried out, such as when preparations are made for an image recording or when an image recording is suspended. That is, the compressor  87  is driven when the discharge liquid is not discharged from the inkjet heads  100 . Compressed air is supplied to the main tank  80  and subtanks  90  when an image recording is not carried out as noted above, in order to prevent a situation where imaging accuracy is impaired by the vibrations applied to the main tank  80  and subtanks  90  and transmitted to the recording heads  22 ,  23 ,  24  and  25 . 
         [0048]    Where the discharge liquid is a common water-soluble pigment ink, the compressed air may be supplied to the main tank  80  and subtanks  90  intermittently at a frequency of about once every hour. In this case, the time for supplying the compressed air may be about 10 seconds for compressed air of about 0.5 MPa used in factory piping, which can fully agitate the discharge liquid and maintain uniformity of the discharge liquid. 
         [0049]    Therefore, this inkjet recording apparatus controls the driving of the compressor  87  to supply the compressed air to the main tank  80  and subtanks  90  intermittently when the discharge liquid is not discharged from the inkjet heads  100 . 
         [0050]    When compressed air piping which is part of plant facilities is branched for use as a source of compressed air, instead of the compressor  87 , a switch valve mounted on the piping may be controlled to adjust the supply time, supply intervals and supply timing of compressed air to the main tank  80  and subtanks  90 . 
         [0051]    In this inkjet recording apparatus, the supply time, supply intervals and supply timing of compressed air can also be varied as appropriate according to the behavior of the discharge liquid used for image recording. The supply of compressed air may be carried out manually, instead of relying on a recording apparatus operating program stored in the ROM  192  of the controller  190 . 
         [0052]    This invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention. 
         [0053]    This application claims priority benefit under 35 U.S.C. Section 119 of Japanese Patent Application No. 2009-220518 filed in the Japanese Patent Office on Sep. 25, 2009, the entire disclosure of which is incorporated herein by reference.