Patent Publication Number: US-9844948-B2

Title: Printing apparatus with ink circulation flow path

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a printing apparatus which is provided with an ink circulation flow path which is configured to include an ink ejecting head. 
     2. Related Art 
     In the related art, a printer is known which is provided with a head unit, a sub-tank, an ink circulation flow path, and a filter. The head unit ejects an ink, the sub-tank reserves the ink, the ink circulation flow path includes a circulation outgoing path in which the ink which is supplied from the sub-tank to the head flows and a circulation return path in which the ink which returns to the sub-tank from the head unit flows, and the filter is provided in the circulation outgoing path. In this printer, foreign matter in the ink is prevented from flowing into each head of the head unit by filtering the ink using the filter (refer to JP-A-2013-240980). 
     The present inventor discovered the following problems. 
     In a printing apparatus which is provided with an ink circulation flow path configured to include an ink ejecting head, when a circulation return path is removed from an ink reservoir section in order to exchange the ink ejecting head, during the cleaning of the ink ejecting head, and the like, there is a case in which the ink flows backward to the ink ejecting head in the circulation return path. There is a concern that foreign matter contained in the ink will flow into the ink ejecting head together with the backward flow of the ink to the ink ejecting head in the circulation return path. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a printing apparatus capable of suppressing the flowing of foreign matter into the ink ejecting head together with the backward flow of the ink to the ink ejecting head in the circulation return path. 
     According to an aspect of the invention, there is provided a printing apparatus which includes an ink ejecting head which ejects an ink, an ink reservoir section which reserves the ink, an ink circulation flow path which includes a circulation outgoing path in which the ink which is supplied to the ink ejecting head from the ink reservoir section flows and a circulation return path in which the ink which returns to the ink reservoir section from the ink ejecting head flows, and an open-close section which is provided in the circulation return path and is capable of opening and closing the circulation return path, in which the circulation return path is opened by the open-close section when the ink flows in the circulation return path in a forward direction, and the circulation return path is closed by the open-close section when the ink flows in the circulation return path in a reverse direction. 
     In this case, when the ink flows in the circulation return path in the reverse direction, the ink is prevented from flowing into the ink ejecting head. Accordingly, foreign objects contained in the ink which flows backward flowing into the ink ejecting head is suppressed. Therefore, in the printing apparatus, it is possible to suppress the flowing of foreign matter into the ink ejecting heads together with the backward flow of the ink to the ink ejecting head in the circulation return path. 
     In this case, the open-close section preferably includes a check valve. 
     In this case, the check valve opens the circulation return path when the ink flows in the circulation return path in the forward direction, and the check valve closes the circulation return path when the ink flows in the circulation return path in the reverse direction. Therefore, it is possible to increase the reliability as an open-close section. 
     The printing apparatus preferably includes a plurality of the ink ejecting heads, in which the circulation return path preferably contains a plurality of branch paths, one end portion of each being joined to the corresponding ink ejecting head, and a root path at which the plurality of branch paths merge at another end portion side of the branch paths, and in which the open-close section is preferably provided in the root path. 
     In this case, even if the open-close section is not provided in each of the branch paths, it is possible to suppress the flowing of foreign matter into the plurality of ink ejecting heads together with the backward flow of the ink to the plurality of ink ejecting heads in the circulation return path. Therefore, in this case, it is possible to reduce the number of open-close sections in comparison to a case in which the open-close section is provided in each of the branch paths. 
     The printing apparatus preferably includes a plurality of the ink ejecting heads, and a plurality of the open-close sections, in which the circulation return path preferably contains a plurality of branch paths, one end portion of each being joined to the corresponding ink ejecting head, and the open-close section is preferably provided in each of the branch paths. 
     In this case, in comparison to a case in which the open-close section is provided in the root path at which the plurality of branch paths merge, it is possible to more reliably suppress the flowing of foreign matter into the ink ejecting heads together with the backward flow of the ink to the ink ejecting heads in the circulation return path. 
     The printing apparatus preferably further includes a filter which is provided in the circulation outgoing path and filters the ink. 
     In this case, foreign matter contained in the ink which flows to the ink ejecting head in the circulation outgoing path is captured in the filter. Therefore, foreign matter contained in the ink which flows to the ink ejecting head in the circulation outgoing path flowing into the ink ejecting head is suppressed. 
     In the printing apparatus, a back pressure within a predetermined range is preferably applied to the ink inside the ink ejecting head based on a differential head between the ink ejecting head and the ink reservoir section and a pressure loss of the ink in the circulation return path. 
     In this case, the pressure loss of the ink in the circulation return path is reduced. Therefore, it is not necessary to increase a differential head of the negative pressure on the ink ejecting head in order to retain the head back pressure within a predetermined range. Therefore, even when the circulation of the ink in the ink circulation flow path is stopped, a great reduction in the head back pressure is suppressed. Therefore, in this case, even when the circulation of the ink in the ink circulation flow path is stopped, it is possible to suppress the entry of bubbles from the nozzles of the ink ejecting heads. 
     The printing apparatus preferably further includes a circulation pump which is provided in the ink circulation flow path and causes the ink to circulate within the ink circulation flow path. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a schematic configuration diagram of a printing apparatus according to an embodiment of the invention. 
         FIG. 2  is a piping flow diagram illustrating an ink supply section which is provided in the printing apparatus illustrated in  FIG. 1 . 
         FIG. 3  is a piping flow diagram illustrating an ink supply section according to a modification example. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, description will be given of a printing apparatus  1  according to the embodiment of the invention with reference to the accompanying drawings. 
     Description will be given of the overall configuration of the printing apparatus  1  with reference to  FIG. 1 . The printing apparatus  1  performs printing on a printing medium  100  which is set therein by ejecting an ultraviolet curing ink (hereinafter referred to as “a UV ink”). The printing medium  100  is a belt-shaped continuous paper sheet. Note that, the material of the printing medium  100  is not particularly limited, and various materials such as paper-based materials and film-based materials may be used. 
     The printing apparatus  1  is provided with a feed section  2 , an ink ejecting section  3 , and an irradiating section  4 . Although omitted from the drawing in  FIG. 1 , the printing apparatus  1  is provided with an ink supply section  5  (refer to  FIG. 2 ) which supplies a UV ink to the ink ejecting section  3 . 
     The feed section  2  is a roll-to-roll system and feeds the printing medium  100 . The feed section  2  is provided with a feed-out reel  6 , a winding reel  7 , a rotating drum  8 , and a plurality of rollers  9 . The printing medium  100  which is fed out from the feed-out reel  6  passes the rotating drum  8  and the plurality of rollers  9  and is wound onto the winding reel  7 . The rotating drum  8  is a cylindrical drum which is supported by a supporting mechanism (not shown) to be capable of rotating. When the printing medium  100  is fed along the circumferential surface of the rotating drum  8 , the rotating drum  8  is passively rotated due to the friction force between the circumferential surface and the printing medium  100 . The rotating drum  8  functions as a platen in relation to the ink ejecting section  3 . 
     The ink ejecting section  3  is provided with a plurality of head units  11 . The plurality of head units  11  is provided to line up along the circumferential surface of the rotating drum  8 . The plurality of head units  11  correspond, one-for-one, with a plurality of types of UV ink (for example, the four colors CYMK). Each of the head units  11  is provided with a plurality of ink ejecting heads  12  (refer to  FIG. 2 ) which eject UV ink using an ink jet system. The head units  11  eject the UV inks onto the printing medium  100  which is supported on the circumferential surface of the rotating drum  8 . Accordingly, a color image is formed on the printing medium  100 . 
     The irradiating section  4  is provided with a plurality of temporary curing irradiators  13  and a real curing irradiator  14 . The plurality of temporary curing irradiators  13  is provided to line up along the circumferential surface of the rotating drum  8  alternately, one for each of the plurality of head units  11 . The temporary curing irradiators  13  are provided on the downstream side of the feed path of the printing medium  100  in relation to the corresponding head units  11 . The temporary curing irradiators  13  irradiate the printing medium  100  onto which the UV ink is ejected with ultraviolet rays. Accordingly, the UV ink is temporarily cured straight after landing on the printing medium  100 , and spreading of the dots and mixing of the colors are suppressed. The real curing irradiator  14  is provided closer to the downstream side than the temporary curing irradiator  13  which is provided closest to the downstream side in the feed path. The real curing irradiator  14  irradiates the printing medium  100  which is subjected to the ejection of the UV inks and the temporary curing with ultraviolet rays of a greater integral light quantity than the temporary curing irradiators  13 . Accordingly, the UV ink which lands on the printing medium  100  is completely cured and is fixed to the printing medium  100 . 
     Note that, it is possible to use, for example, a light emitting diode (LED) lamp, a high pressure mercury lamp, or the like which radiates ultraviolet rays in the temporary curing irradiators  13  and the real curing irradiator  14 . 
     Description will be given of the ink supply section  5  with reference to  FIG. 2 . The ink supply section  5  is provided with an ink cartridge  21 , a supply flow path  22 , an open-close valve  23 , a supply pump  24 , a sub-tank  25 , a liquid level sensor  26 , a compressing-decompressing section  27 , an ink circulation flow path  28 , an outgoing path filter  30 , a heating section  31 , a degassing section  32 , and a check valve  33 . 
     The UV ink is stored in the ink cartridge  21 . The ink cartridge  21  is mounted in a holder  34 . The upstream end of the supply flow path  22  is inserted into the ink cartridge  21  which is mounted in the holder  34 , and the downstream end of the supply flow path  22  is inserted into the sub-tank  25 . In order from the upstream side, the open-close valve  23  and the supply pump  24  are provided in the supply flow path  22 . The open-close valve  23  opens and closes the supply flow path  22 . It is possible to use a magnetic operation valve, for example, as the open-close valve  23 . The supply pump  24  supplies the UV ink which is stored in the ink cartridge  21  to the sub-tank  25  via the supply flow path  22 . 
     The sub-tank  25  temporarily reserves the UV ink which is pumped from the ink cartridge  21 . The sub-tank  25  is an open system tank. The liquid level sensor  26  detects whether or not the liquid level of the UV ink in the sub-tank  25  is greater than or equal to a first liquid level L 1 , and detects whether or not greater than or equal to a second liquid level L 2  which is greater than the first liquid level L 1 . When the liquid level sensor  26  detects that the liquid level of the UV ink in the sub-tank  25  is less than the first liquid level L 1 , the UV ink is supplied from the ink cartridge  21  to the sub-tank  25 . When the liquid level sensor  26  detects that the liquid level of the UV ink in the sub-tank  25  is greater than or equal to the second liquid level L 2 , the supply of the UV ink from the ink cartridge  21  to the sub-tank  25  is stopped. Accordingly, the liquid level of the sub-tank  25  is maintained between the first liquid level L 1  and the second liquid level L 2 . Therefore, a differential head ΔH between the nozzle surface of the ink ejecting head  12  and the liquid surface of the sub-tank  25  is maintained within a predetermined range. Accordingly, the back pressure (hereinafter referred to as “head back pressure”) of the UV ink inside the ink ejecting head  12  is maintained within a predetermined range (for example, −400 Pa to 3000 Pa), and a good meniscus is formed in the nozzles of the ink ejecting head  12 . 
     The compressing-decompressing section  27  compresses or decompresses the inside of the sub-tank  25  by supplying air into the sub-tank  25  or discharging the air in the sub-tank  25  via an air flow path  35 . For example, the compressing-decompressing section  27  compresses the sub-tank  25  during the initial filling of the first circulation flow path  28  with the UV ink, during the cleaning of the ink ejecting heads  12 , or the like. 
     The ink circulation flow path  28  is the flow path of the UV ink which passes from the sub-tank  25 , through the ink ejecting heads  12 , and returns to the sub-tank  25 . The ink circulation flow path  28  is provided with a circulation outgoing path  36  and a circulation return path  37 . 
     The UV ink which is supplied to the ink ejecting heads  12  from the sub-tank  25  flows in the circulation outgoing path  36 . The circulation outgoing path  36  is provided with an outgoing path side root path  36   a  and a plurality of outgoing path side branch paths  36   b  which branch from the outgoing path side root path  36   a . The upstream end of the outgoing path side root path  36   a  is inserted into the sub-tank  25 . In order from the upstream side, the outgoing path side root path  36   a  is provided with a circulation pump  29 , the outgoing path filter  30 , the heating section  31 , and the degassing section  32 . One of the outgoing path side branch paths  36   b  is provided for one of the ink ejecting heads  12 . The downstream end of the outgoing path side branch path  36   b  is connected to the ink ejecting head  12 . 
     The UV ink which returns to the sub-tank  25  from the ink ejecting head  12  flows in the circulation return path  37 . In other words, of the UV ink which is supplied from the sub-tank  25  to the ink ejecting head  12  via the circulation outgoing path  36 , the UV ink which is not ejected from the ink ejecting heads  12  returns to the sub-tank  25  via the circulation return path  37 . The circulation return path  37  is provided with a plurality of return path side branch paths  37   b , and a return path side root path  37   a  at which the plurality of return path side branch paths  37   b  meet n the downstream side thereof. One of the return path side branch paths  37   b  is provided for one of the ink ejecting heads  12 . The upstream end of the return path side branch path  37   b  is connected to the ink ejecting head  12 . The downstream end of the return path side root path  37   a  is inserted into the sub-tank  25 . The check valve  33  is provided in the return path side root path  37   a.    
     The circulation pump  29  pumps the UV ink which is reserved in the sub-tank  25  toward the ink ejecting head  12  side. Therefore, when the circulation pump  29  operates, the UV ink circulates within the ink circulation flow path  28 . It is possible to favorably use a gear pump as the circulation pump  29  because it is possible to suppress pulsation and there is little fluctuation in the flow rate with the passage of time. 
     The outgoing path filter  30  removes foreign matter in the UV ink by filtering the UV ink which flows in the circulation outgoing path  36 . Examples of the foreign matter include a polymer of the UV ink caused by friction heat which is generated by the circulation pump  29  which is a gear pump, dust and bubbles which are mixed in when the upstream end of the supply flow path  22  is inserted into the ink cartridge  21 , and the like. Note that, although head filters  38  which filter the UV ink are also provided on the inlet side of the ink ejecting heads  12 , it is possible to cause the head filters  38  which are difficult to exchange to last a long time by providing the outgoing path filter  30  in the circulation outgoing path  36 . 
     The heating section  31  heats the UV ink which flows in the ink circulation flow path  28  to a predetermined temperature (for example 35° C. to 40° C.) The predetermined temperature is a temperature at which the UV ink which is supplied to the ink ejecting heads  12  reaches a viscosity which is appropriate for ejection from the ink ejecting heads  12 . During the start-up of the printing apparatus  1 , the printing apparatus  1  starts the printing operation after heating the UV ink which has a lower temperature than the predetermined temperature to the predetermined temperature using the heating section  31 . 
     The heating section  31  is provided with a hot water tank  41  including a heater, a hot water circulation flow path  42 , a hot water pump  43 , and a heat exchanger  44 . The hot water tank  41  reserves hot water which is adjusted to fall within a predetermined temperature range. The hot water circulation flow path  42  is a flow path running from the hot water tank  41 , through the heat exchanger  44 , and returns to the hot water tank  41 . The hot water pump  43  causes the hot water to circulate within the hot water circulation flow path  42 . The heat exchanger  44  performs heat exchanging between the hot water which flows in the hot water circulation flow path  42  and the UV ink which flows in the ink circulation flow path  28 . 
     The degassing section  32  degasses the UV ink which flows in the ink circulation flow path  28 . Accordingly, the supplying of the UV ink containing bubbles to the ink ejecting heads  12  is prevented. The degassing section  32  is provided with a degassing module  45  and a negative pressure pump  46 . The degassing module  45  is provided with a plurality of hollow fiber membranes, for example. The negative pressure pump  46  reduces the pressure outside of the hollow fiber membranes. Accordingly, the UV ink which flows in the hollow fiber membranes is degassed. 
     Incidentally, in the circulation return path  37 , there is a case in which the UV ink flows backward to the ink ejecting head  12  side. For example, a case in which the circulation return path  37  is removed from the sub-tank  25  in order to exchange a portion of the ink ejecting heads  12 , or a case in which, during the cleaning of the ink ejecting head  12  which is performed by causing the UV ink to circulate within the ink circulation flow path  28  using the circulation pump  29  while compressing the sub-tank  25  using the compressing-decompressing section  27 , the circulation pump  29  stops due to a malfunction or the like. In these cases, as described above, when foreign matter is contained in the UV ink which flows in the circulation return path  37 , there is a concern that foreign matter contained in the UV ink will flow into the ink ejecting heads  12  together with the backward flow of the UV ink to the ink ejecting head  12  side in the circulation return path  37 . 
     In order to prevent the flowing of foreign matter into the ink ejecting heads  12  together with the backward flow of the UV ink to the ink ejecting head  12  side in the circulation return path  37 , in the printing apparatus  1  of the present embodiment, the check valve  33  is provided in the return path side root path  37   a  of the circulation return path  37 . The check valve  33  allows the flowing of the UV ink from the ink ejecting head  12  side to the sub-tank  25  side in the circulation return path  37  (a forward direction), and prevents the backward flowing of the UV ink from the sub-tank  25  side to the ink ejecting head  12  side (a reverse direction). In other words, the circulation return path  37  is opened by the check valve  33  when the UV ink flows in the forward direction in the circulation return path  37 , and the circulation return path  37  is closed by the check valve  33  when the UV ink flows in the reverse direction in the circulation return path  37 . Therefore, the flowing of foreign matter contained in the UV ink which flows backward into the ink ejecting heads  12  is suppressed. Therefore, according to the printing apparatus  1  of the present embodiment, it is possible to suppress the flowing of foreign matter into the ink ejecting heads  12  together with the backward flow of the UV ink to the ink ejecting head  12  side in the circulation return path  37 . It is possible to use, as appropriate, a well known system such as a sliding system, a lift system, or a disc system for the check valve  33 . 
     In the check valve  33 , the pressure loss is extremely small (for example, approximately 200 Pa), and the influence of the pressure loss by the check valve  33  on the head back pressure is small. Therefore, in order to retain the head back pressure within a predetermined range, it is not necessary to increase a differential head ΔH of the negative pressure on the ink ejecting heads  12 . Therefore, it is possible to reduce restrictions to the layout of the sub-tank  25 . In addition, even when the circulation of the UV ink in the ink circulation flow path  28  is stopped, a great reduction in the head back pressure is suppressed. Therefore, according to the printing apparatus  1  of the present embodiment, even when the circulation of the UV ink in the ink circulation flow path  28  is stopped, the entry of bubbles from the nozzles of the ink ejecting heads  12  is suppressed. The check valve  33  is beneficial since the replacement thereof is substantially unnecessary. 
     Since the check valve  33  is provided in the return path side root path  37   a , even if the check valve  33  is not provided in each of the return path side branch paths  37   b , it is possible to suppress the flowing of foreign matter into the plurality of ink ejecting heads  12  together with the backward flow of the UV ink to side of the plurality of ink ejecting heads  12  in the circulation return path  37 . Therefore, according to the printing apparatus  1  of the present embodiment, it is possible to reduce the number of the check valves  33  in comparison to a case in which the check valve  33  is provided for each of the return path side branch paths  37   b.    
     Note that, the sub-tank  25  is an example of “an ink reservoir section”. The check valve  33  is an example of “an open-close section”. 
     In order to prevent the flowing of foreign matter into the ink ejecting heads  12  together with the backward flow of the UV ink to the ink ejecting head  12  side in the circulation return path  37 , it is conceivable to also provide a filter in the circulation return path  37  in the same manner as the outgoing path filter  30  is provided in the circulation outgoing path  36  instead of providing the check valve  33  in the circulation return path  37 . However, since it is necessary to exchange the filter for a new filter when the filter is used to a certain extent, costs are increased. While the head back pressure is applied based on the differential head ΔH and the pressure loss of the UV ink in the circulation return path  37 , when a filter is provided in the circulation return path  37 , the pressure loss of the UV ink in the circulation return path  37  increases by approximately 10 kPa, for example. Therefore, in order to retain the head back pressure within a predetermined range, the differential head ΔH of the negative pressure on the ink ejecting heads  12  should be increased in response to the increase in the pressure loss. In other words, the sub-tank  25  should be provided further below the ink ejecting heads  12 . Therefore, the layout of the sub-tank  25  is restricted. In addition, in this case, when the circulation of the UV ink in the ink circulation flow path  28  is stopped during the stopping of the operation of the printing apparatus  1  or the like, since, of the differential head ΔH and the pressure loss, only the differential head ΔH of the increased negative pressure affects the head back pressure, the head back pressure is greatly reduced. Therefore, there is a concern that bubbles will enter from the nozzles of the ink ejecting heads  12 . Therefore, in order to prevent the flowing of foreign matter into the ink ejecting heads  12  together with the backward flow of the UV ink to the ink ejecting head  12  side in the circulation return path  37 , it is more preferable to provide the check valve  33  in the circulation return path  37  than the filter. 
     The invention is not limited to the embodiment described above, and it goes without saying that various configurations may be adopted within a scope that does not depart from the gist of the invention. For example, the present embodiment may be modified to the forms described below. 
     As illustrated in  FIG. 3 , the check valves  33  may be provided in each of the return path side branch paths  37   b  instead of providing the check valve  33  in the return path side root path  37   a . In this case, in comparison with the case in which the check valve  33  is provided in the return path side root path  37   a , it is possible to more reliably suppress the entry of foreign matter to the ink ejecting heads  12  together with the backward flow of the UV ink to the ink ejecting head  12  side in the circulation return path  37 . Naturally, the check valves  33  may be provided in each of the return path side root path  37   a  and the return path side branch paths  37   b.    
     The open-close section which is provided in the circulation return path  37  is not limited to the check valve  33 . For example, it is possible to use a magnetic operation valve which opens the circulation return path  37  when the UV ink flows to the sub-tank  25  in the circulation return path  37  and closes the circulation return path  37  when the UV ink flows to the ink ejecting heads  12  in the circulation return path  37 , or a manual operation valve. Note that, when using the check valve  33  as the open-close section, it is not necessary to open and close the circulation return path  37  by electrical control or by the operation of an operator, and it is possible to increase the reliability as an open-close section. 
     The ink which is used in the printing apparatus  1  is not limited to the UV ink, and, for example, may be an aqueous ink, an oil-based ink, a solvent ink, or a volatile ink. 
     The entire disclosure of Japanese Patent Application No. 2015-055790, filed Mar. 19, 2015 is expressly incorporated by reference herein.