Patent Publication Number: US-2021162742-A1

Title: Liquid ejection unit and liquid ejection device

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a liquid ejection unit and a liquid ejection device. 
     Priority is claimed on Japanese Patent Application No. 2019-217527, filed Nov. 29, 2019, the content of which is incorporated herein by reference. 
     Description of Related Art 
     A liquid ejection device which ejects a liquid material (a liquid) such as ink to a desired position is known in the related art (for example, refer to Japanese Patent No. 5716213). In the liquid ejection device described in Japanese Patent No. 5716213, a piezoelectric element is provided in a part of a pipe provided in an ejection head. Such a liquid ejection device pushes out a liquid in the flow path while pressing the liquid and ejects the liquid by constricting and deforming a flow path using the piezoelectric element. 
     SUMMARY OF THE INVENTION 
     In the liquid ejection device as described in Japanese Patent No. 5716213, ejecting various liquids in place of ink used at the time of two-dimensional printing in the related art is required. For example, a liquid to be ejected may be a dispersion liquid as well as a solution. Examples of a dispersoid contained in the dispersion liquid include organic materials such as resin materials, inorganic materials such as metal particles and oxide particles, and biological materials such as cells and genes. 
     Such various liquids have various viscosities and many liquids have a higher viscosity than the ink used in the two-dimensional printing in the related art. The liquid ejection device described in Japanese Patent No. 5716213 deforms a flow path through the driving of the piezoelectric element and pushes out a liquid through the flow path. 
     However, if a liquid to be ejected has a high viscosity, even when pressure is applied from the piezoelectric element to the flow path, liquid droplets may be formed on an ejection port of the liquid ejection device while remaining attached to the ejection port and liquid droplets may not fly to an object to which a liquid is ejected in some cases. That is to say, since the liquid ejection device described in Japanese Patent No. 5716213 is not appropriate for ejecting a highly viscous liquid, there has been a demand for a liquid ejection device capable of ejecting a highly viscous liquid. 
     The present invention is made in view of such circumstances, and an object of the present invention is to provide a liquid ejection unit capable of appropriately ejecting a highly viscous liquid. Furthermore, another object of the present invention is to provide a liquid ejection device having such a liquid ejection unit and capable of appropriately ejecting a highly viscous liquid. 
     In order to achieve the above objects, one aspect of the present invention provides a liquid ejection unit which includes: a liquid holding section which has an ejection port through which a liquid is ejected and which holds the liquid; a pressure adjustment section which is configured to adjust a pressure of a liquid held in the liquid holding section; and a displacement member which is configured to displace at least a part of the liquid whose pressure is adjusted and eject the liquid from the liquid holding section. 
     According to the present invention, it is possible to provide a liquid ejection unit capable of appropriately ejecting a highly viscous liquid. Furthermore, it is possible to provide a liquid ejection device having such a liquid ejection unit and capable of appropriately ejecting a highly viscous liquid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view illustrating liquid ejection units and a liquid ejection device according to a first embodiment. 
         FIG. 2  is a schematic diagram illustrating a liquid ejection unit. 
         FIGS. 3A to 3D  are explanatory diagrams illustrating a state in which a liquid ejection unit ejects a liquid L. 
         FIG. 4  is an explanatory diagram of a liquid ejection unit and a liquid ejection device according to a second embodiment. 
         FIG. 5  is an explanatory diagram of a liquid ejection unit and a liquid ejection device according to a third embodiment. 
         FIG. 6  is an explanatory diagram of a liquid ejection unit and a liquid ejection device according to a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
     A liquid ejection unit and a liquid ejection device according to a first embodiment of the present invention will be described below with reference to  FIGS. 1 to 3 . In all the following drawings, in order to make the drawings easy to see, the dimensions, the ratios, and the like of the constituent elements may be appropriately changed. 
     In the following description, an xyz rectangular coordinate system is utilized and positional relationships between respective members will be described with reference to this xyz rectangular coordinate system. Here, a predetermined direction in a horizontal plane is assumed to be an x axis direction, a direction in the horizontal plane orthogonal to the x axis direction is assumed to be a y axis direction, and a direction (that is, a vertical direction) orthogonal to the x axis direction and the y axis direction is a z axis direction. 
     Also, an upward direction in the vertical direction is assumed to be a +z direction and a downward direction in the vertical direction is assumed to be a −z direction. Similarly, the words “above”, “upward” and “upper” are each assumed to mean the +z direction. The words “below”, “downward” and “lower” are each assumed to mean the −z direction. 
     Furthermore, in the following description, the expression “when viewed in a plan view” is assumed to be viewing an object from above and a “plan shape” is assumed to be a shape when the object is viewed from above. 
       FIG. 1  is a schematic perspective view illustrating liquid ejection units  101  and a liquid ejection device  1 . As illustrated in  FIG. 1 , the liquid ejection device  1  in this embodiment includes an ejection section  10  configured to hold a liquid and eject the held liquid, an attachment section  30  to which the ejected liquid droplets adhere, a placement section  40  on which the attachment section  30  is placed, and a control unit  50  configured to control an operation of each unit of the liquid ejection device  1 . 
     The liquid ejection device  1  ejects the liquid held in the ejection section  10  toward the attachment section  30 . The liquid ejected from the liquid ejection device  1  is not particularly limited and may be a dispersion liquid containing a dispersion medium in which particles are dispersed or a solution. 
     Examples of the particles dispersed in the dispersion medium include organic materials such as polymer particles and inorganic materials such as fine metal particles and inorganic oxide particles. Furthermore, cells can be used as the particles. 
     In this embodiment, a description will be provided assuming that the liquid ejected using the liquid ejection device  1  is a dispersion liquid having cells dispersed in a dispersion medium. In this case, as the dispersion medium, well-known buffer solutions such as a phosphate buffered saline and a Hank&#39;s balanced salt solution can be used. 
     &lt;Ejection Section&gt; 
     The ejection section  10  includes the plurality of (four in  FIG. 1 ) liquid ejection units  101  and a transport section  130  configured to transport each of the liquid ejection units  101 . 
     The plurality of liquid ejection units  101  may eject the same liquid L or may eject liquids L different from each other. In the following description, the liquid L ejected using the liquid ejection unit is a dispersion liquid having particles P dispersed therein. 
     (Liquid Ejection Unit) 
     The liquid ejection unit  101  includes a liquid ejection head  110  and a pressure adjustment section  120 A connected to the liquid ejection head  110 . 
     The details of the liquid ejection unit  101  will be described later. 
     (Transport Section) 
     The transport section  130  includes a support member  131  and a linear movement section  132 . 
     The support member  131  is a rectangular member when viewed in a plan view and supports a plurality of liquid ejection heads  110 . The plurality of liquid ejection heads  110  are supported by the support member  131  and arranged along an x axis. 
     The linear movement section  132  is a long member which extends in the y axis direction. The linear movement section  132  moves the support member  131  horizontally in the y axis direction. Both ends of the linear movement section  132  are supported by the support member (not shown). 
     The linear movement section  132  can adopt, for example, a known linear actuator including a stepping motor as a drive source. 
     The transport section  130  moves the support member  131  in the y axis direction, thereby moving a plurality of ejection units  11  supported by the support member  131  in the y axis direction which is a double-headed arrow direction indicated by a reference symbol D 1 . 
     &lt;Attachment Section&gt; 
     The attachment section  30  is arranged in an ejection direction of the liquid droplet L 1  ejected from the ejection section  10  and has the liquid droplet L 1  adhering thereto. Although the attachment section  30  may be of any type in accordance with a type of liquid L to be ejected, the purpose of ejection, and the like, in this embodiment, a Petri dish is used as the attachment section  30 . 
     Also, the attachment section  30  may be a so-called well plate in which a plurality of wells are arranged in a matrix form at equal intervals or may be a micro-electrode array (MEA) in which micro-electrodes are regularly arranged. 
     &lt;Placement Section&gt; 
     The placement section  40  includes an x stage  401 , a y stage  402 , and a base  403 . 
     The x stage  401  has the attachment section  30  placed thereon and supports and fixes the attachment section  30 . Furthermore, the x stage  401  moves the attachment section  30  horizontally in the x axis direction which is a double-headed arrow direction indicated by a reference symbol D 2 . 
     The y stage  402  moves the x stage  401  horizontally in the y axis direction which is a double-headed arrow direction indicated by a reference symbol D 3 . 
     The base  403  supports the y stage  402 . 
     The placement section  40  can adopt a known constitution as an xy stage. 
     The transport section  130  and the placement section  40  control relative positions of the liquid ejection unit  101  and the attachment section  30 . Thus, in the liquid ejection device  1 , it is possible to adhere the liquid ejected from the liquid ejection unit  101  to a desired position on the attachment section  30 . 
     &lt;Control Unit&gt; 
     The control unit  50  performs control to create a signal for operating each unit of the liquid ejection device  1  and supply the signal to each unit. 
     The control unit  50  controls an operation of each unit to create, for example, a drive signal to be supplied to the ejection section  10  and a drive signal to be supplied to the placement section  40 , and supply the signals to each unit. 
     &lt;Liquid Ejection Unit&gt; 
       FIG. 2  is a schematic diagram illustrating the liquid ejection unit  101 . 
     The liquid ejection head  110  includes a liquid holding section  111 , a support section  112 , a displacement member  113 , and a pipe  115 . 
     The pressure adjustment section  120 A includes a supply section  121  and a detection unit  122 . 
     &lt;Liquid Ejection Head&gt; 
     (Liquid Holding Section) 
     The liquid holding section  111  is a tubular member which extends substantially parallel to the z axis direction which is a liquid ejection direction. The liquid holding section  111  is formed of, for example, a material such as glass or a resin material. A wall surface of the liquid holding section  111  facing an inside  111   x  may be subjected to a liquid repellent treatment or a lyophilic treatment in accordance with the characteristics of a liquid L flowing through the inside. As a result, the liquid ejection head enables to eject the liquid appropriately according to the purpose of the present invention. 
     The liquid holding section  111  may be a tubular member or a plate-like member having a flow path formed therein. 
     It is desirable that the liquid holding section  111  have light transmissivity so that a state of the liquid L flowing through the inside can be checked. 
     The liquid holding section  111  has an inner diameter gradually decreasing in the −z direction. A lower end of the liquid holding section  111  is open as an ejection port  111   a.  For example, an outer diameter of the liquid holding section  111  is several mm. Furthermore, an inner diameter of the ejection port  111   a  is several tens of pm or more and several hundreds of pm or less. An upper end of the liquid holding section  111  is connected to the pipe  115 . 
     The liquid holding section  111  ejects the liquid L through the ejection port  111   a  in the −z direction. 
     (Support Section) 
     The support section  112  supports the liquid holding section  111  in an attachable or detachable manner. The support section  112  can adopt various commonly known constitutions as long as they can support the liquid holding section  111 . 
     The support section  112  includes a support main body  112   a  which supports the liquid holding section  111  and a screw  112   x  which fixes the liquid holding section  111  to the support main body  112   a.    
     In  FIG. 2 , the support main body  112   a  is shown as a rectangular parallelepiped member having an insertion section  112   b  into which the liquid holding section  111  is inserted. The screw  112   x  fixes the liquid holding section  111  inserted into the insertion section  112   b  in a screw manner. 
     (Displacement Member) 
     The displacement member  113  is a rectangular member when viewed in a plan view provided on an upper surface  112   s  of the support main body  112   a.  In  FIG. 1 , a shape of the displacement member  113  when viewed in a plan view is shown as a square. For example, the shape of the displacement member  113  when viewed in a plan view is a square of several mm×several mm. 
     The displacement member  113  is provided at a position in which the displacement member  113  and the liquid holding section  111  overlap when viewed in a plan view. The shape of the displacement member  113  when viewed in a plan view is larger than a shape of the liquid holding section  111  when viewed in a plan view. The shape of the displacement member  113  when viewed in a plan view is a square. A length of one side of the square is longer than the outer diameter of the liquid holding section  111 . 
     The displacement member  113  has a lower surface  113   a  adhered to the upper surface  112   s  of the support main body  112   a  and an upper surface  113   b  adhered to a lower surface  131   a  of the support member  131 . 
     Although a piezoelectric element, an actuator constituted of a magnet and a coil, and the like can be used as the displacement member  113 , it is desirable that a piezoelectric element be used. The piezoelectric element can have, for example, a structure in which electrodes for applying a voltage are provided on an upper surface and a lower surface of a piezoelectric material. In this case, the displacement member  113  applies a compressive stress in a lateral direction of the upper and lower electrodes by applying a voltage between the upper and lower electrodes of the displacement member  113  (the piezoelectric element) from the control unit  50 . Thus, the displacement member  113  vibrates in an upward/downward direction of a film surface (a double-headed arrow direction indicated by a reference symbol D 4  in the drawing). 
     The vibration direction of the displacement member  113  is the z axis direction and is set to be substantially parallel to the ejection direction of the liquid L. Here, the word “substantially” in the expression “substantially parallel” means that it is not required that the vibration direction of the displacement member  113  and the ejection direction of the liquid L be mathematically strictly parallel to the z axis. For example, the vibration direction of the displacement member  113  may be tilted within ±10° with respect to an z axis when the ejection direction of the liquid L (that is, the z axis direction) is 0°. 
     By performing the operation as described above, the displacement member  113  displaces the support section  112  substantially parallel to the ejection direction of the liquid L and further displaces at least a part of the liquid L held by the liquid holding section  111  and the liquid holding section  111  supported by the support section  112 . 
     In this specification, “displacement” refers to changing a position of a subject. In addition, in this embodiment, “displacement” means that a subject changes coordinates in the xyz rectangular coordinate system. In this meaning, the displacement of the liquid holding section  111  refers to changing coordinates of the liquid holding section  111  in the xyz rectangular coordinate system. In this embodiment, the liquid holding section  111  is displaced in the z axis direction due to the vibration of the displacement member  113 . 
     The piezoelectric material is not particularly limited and may be appropriately selected in accordance with the purpose thereof. In addition, examples thereof include lead zirconate titanate (PZT), bismuth iron oxide, metal niobate, barium titanate, and materials obtained by adding a metal or a different oxide to these materials. Among these, lead zirconate titanate (PZT) is preferable. 
     (Pipe) 
     The pipe  115  connects the liquid holding section  111  to the pressure adjustment section  120 A. The pipe  115  includes a first pipe  115   a,  a second pipe  115   b,  a third pipe  115   c,  and a branch pipe  115   d.    
     The first pipe  115   a,  the second pipe  115   b,  and the third pipe  115   c  are pipes formed of a soft resin material. Examples of the soft resin material include polyurethane, silicone rubber, fluororesin, and the like. 
     The branch pipe  115   d  is a three-way pipe (a three-way joint) and can adopt a commonly known constitution. 
     In the pipe  115 , one end of the first pipe  115   a  is connected to the upper end of the liquid holding section  111 . The other end of the first pipe  115   a  is connected to the branch pipe  115   d.    
     The second pipe  115   b  and the third pipe  115   c  are connected to the branch pipe  115   d.  The second pipe  115   b  has one end connected to the branch pipe  115   d  and the other end connected to the supply section  121 . The third pipe  115   c  has one end connected to the branch pipe  115   d  and the other end connected to the detection unit  122 . 
     &lt;Pressure Adjustment Section&gt; 
     (Supply Section) 
     The supply section  121  is connected via the liquid holding section  111  and the pipe  115  and supplies the liquid L to the liquid holding section  111  in a closed system. The supply section  121  may be any section as long as it can supply a liquid, may be, for example, a section which supplies the liquid L using the force of gravity or the like, and may be a section which can supply a liquid at a desired rate using a microvolume-pump such as a syringe pump, a tube pump, or a diaphragm pump. 
     Also, the supply section  121  may also have a function as an adjustment section which adjusts the pressure of the liquid L held in the liquid holding section  111 . To be specific, if the liquid L is supplied from the supply section  121  toward the liquid holding section  111 , the pressure of the liquid L increases. In addition, if the supply section  121  suctions the liquid L from the liquid holding section  111 , the pressure of the liquid L decreases. 
     (Detection Unit) 
     The detection unit  122  detects the pressures of the liquid L held in the liquid holding section  111 . For example, a semiconductor diaphragm type pressure sensor can be adopted for the detection unit  122 . 
       FIGS. 3A to 3D  are explanatory diagrams illustrating a state in which the liquid ejection unit  101  ejects the liquid L and are schematic diagrams illustrating a state in the vicinity of the ejection port  111   a  of the liquid holding section  111 . 
       FIG. 3A  illustrates the liquid holding section  111  in a state being left to stands still. 
     If the liquid L is supplied to the inside  111   x  of the liquid holding section  111 , a capillary phenomenon occurs in the liquid holding section  111  due to the surface tension of the liquid L. Thus, a force F 1  for pulling up the liquid L in the liquid holding section  111  in the +z direction is applied to the liquid L. 
     On the other hand, the force of gravity is applied to the liquid L in the −z direction. Furthermore, a force is applied to the liquid L in the vicinity of the ejection port  111   a  from the ejection port  111   a  toward the outside in accordance with the pressure of the liquid L. Thus, a force F 2  which pushes down the liquid L in the liquid holding section  111  in the −z direction is applied to the liquid L. 
     In the liquid holding section  111 , in a state in which the force F 2  is smaller than the force F 1 , even through the lower end of the liquid holding section  111  is open, the liquid L is held in the inside  111   x  of the liquid holding section  111  without being discharged through the ejection port  111   a.    
     Subsequently, as illustrated in  FIG. 3B , the liquid L is supplied from the supply section  121  to the liquid holding section  111 . In the liquid ejection unit  101 , the liquid holding section  111  to the pressure adjustment section  120 A are connected in a closed system. For this reason, if the liquid L is supplied from the supply section  121  to the liquid holding section  111 , in the liquid holding section  111 , the liquid Lis pressurized in accordance with a supply pressure of the liquid L. Thus, in the liquid holding section  111 , a force F 3  which pushes down the liquid L in the −z direction becomes larger than the force F 2  in  FIG. 3A . 
     At this time, if a state in which the force F 1  is larger than the force F 3  is provided, in the ejection port  111   a  of the liquid holding section  111 , the liquid L is held in the ejection port  111   a.  On the other hand, since the force F 3  is larger than the force F 2 , the liquid L in the ejection port  111   a  is pushed out in the −z direction, projects, and forms a meniscus LM. 
     Subsequently, as illustrated in  FIG. 3C , if the displacement member  113  displaces the liquid holding section  111 , an inertial force applied in the z direction is applied to the liquid L and the meniscus LM due to the vibration of the displacement member  113 . Thus, in the ejection port  111   a,  a force F 4  which pushes down the meniscus LM of the liquid L in the −z direction becomes larger than the force F 3  in  FIG. 3B . 
     If the force F 4  is larger than the force F 1 , a shape of the meniscus LM cannot be maintained in the ejection port  111   a.  In addition, as illustrated in  FIG. 3D , the meniscus LM is separated from the ejection port  111   a  and flies as a liquid droplet L 1 . 
     If the supply section  121  is continuously driven, as illustrated in  FIG. 3B , the liquid L is continuously supplied from the supply section  121  to the liquid holding section  111 . Furthermore, if the displacement member  113  is continuously driven, the liquid holding section  111  continuously vibrates in the z axis direction. For this reason, if the supply section  121  and the displacement member  113  are continuously driven, in the liquid holding section  111 , the phenomenon illustrated in  FIGS. 3B to 3D  repeatedly occurs and it is possible to continuously eject a liquid droplet L 1 . 
     Here, the detection unit  122  of the pressure adjustment section  120 A illustrated in  FIG. 2  detects the pressure of the liquid L pressurized using the supply section  121 . When the liquid ejection device  1  is used, it is advisable that a correspondence relationship between the pressure of the liquid L and the state of the liquid droplet L 1  to be ejected is checked in advance through a preliminary experiment. Thus, the pressure of the liquid L in which the liquid droplet L 1  is enabled to be appropriately ejected may be checked. 
     Examples of the “state of the liquid droplet L 1  to be ejected” include a volume of the liquid droplet L 1 , an adhering position of the liquid droplet L 1  in the attachment section  30 , and the like. 
     Also, an appropriate pressure of the liquid L is input to the control unit  50  in advance as the pressure of the liquid L when the liquid is ejected. The control unit  50  adjusts the pressure of the liquid L on the basis of the detection result of the detection unit  122  so that the pressure of the liquid L approaches a predetermined set value of the ejecting pressure of the liquid L. 
     That is to say, when the detection result of the detection unit  122  is higher than the set pressure, the control unit  50  controls the supply section  121  so that the amount of liquid L to be supplied from the supply section  121  is reduced. 
     Also, when the detection result of the detection unit  122  is lower than the set pressure, the control unit  50  controls the supply section  121  so that the amount of liquid L to be supplied from the supply section  121  is increased. 
     Thus, the liquid ejection unit  101  can appropriately adjust the pressure of the liquid L on the basis of the detection result of the detection unit  122  and eject the liquid droplet L 1 . 
     As described above, in the liquid ejection unit  101  in this embodiment, the pressure adjustment section  120 A which adjusts the pressure of the liquid L held in the liquid holding section  111  and the displacement member  113  which displaces the liquid holding section  111  are configured to have different constitutions. Thus, the following effects are achieved. 
     First, a case in which the liquid ejection unit does not have the constitution configured to adjust the pressure of the liquid Las described above is considered. In this case, the pressure of the liquid L in the ejection port  111   a  of the liquid holding section  111  is determined in accordance with a height (a depth) from a liquid surface of the liquid L in the liquid holding section  111  to the ejection port. In such a case, when a highly viscous liquid L is to be ejected, it may be necessary to increase a size of the liquid holding section  111  and increase the height from the liquid surface to the ejection port. 
     On the other hand, the liquid ejection unit  101  in this embodiment includes the pressure adjustment section  120 A configured to adjust the pressure of the liquid L held in the liquid holding section  111 . For this reason, also when the highly viscous liquid L is to be ejected, it is possible to appropriately adjust the pressure of the liquid L by adjusting the pressure applied to the liquid L of the liquid holding section  111  using the pressure adjustment section  120 A. Thus, in the liquid ejection unit  101  in this embodiment, it is possible to reduce a size of a device. 
     Also, when a constitution in which the supply section  121  configured to supply the liquid L to the liquid holding section  111  adjusts the pressure of the liquid Las in the liquid ejection unit  101 , it is also possible to utilize this constitution as a dispenser configured to continuously discharge the liquid L from the liquid ejection unit  101  by continuously supplying the liquid L from the supply section  121 . 
     Furthermore, for example, a constitution in which a part of a flow path through which a liquid flows is deformed, a part of a liquid held in the liquid holding section is displaced, and a liquid is ejected may be considered for the liquid ejection unit. hi this case, if a highly viscous liquid is to be ejected, it becomes necessary to deform a part of the flow path greatly or strongly. For example, if a piezoelectric element is adopted for a constitution in which the flow path is deformed, in order to greatly or strongly deform a part of the flow path, it may be necessary to increase a size of the piezoelectric element. 
     On the other hand, since the displacement member  113  and the pressure adjustment section  120 A are separate bodies in the liquid ejection unit  101 , it is possible to independently control an operation of the pressure adjustment section  120 A in the state of  FIG. 3B  and an operation of the displacement member  113  in the states of  FIGS. 3C and 3D . For this reason, for example, when liquids with different viscosities are ejected, when the driving conditions of the pressure adjustment section  120 A are adjusted in accordance with the viscosities of the liquids, it is possible to appropriately eject the liquids by simply driving the displacement member  113  under a constant driving condition. 
     Also, as illustrated in  FIGS. 3A to 3D , in the liquid ejection unit  101 , the displacement member  113  and the pressure adjustment section  120 A share a force applied to eject the liquid L from the liquid holding section  111  (a force applied to change the force F 2  to the force F 4 ). For this reason, even with the small displacement member  113 , it is possible to appropriately eject the liquid L. Thus, in the liquid ejection unit  101  in this embodiment, it is possible to reduce the size of a device. 
     According to the liquid ejection unit  101  having the above-described constitution, it is possible to provide a liquid ejection unit which can appropriately eject a highly viscous liquid. 
     Also, according to the liquid ejection device  1  having the above-described constitution, since the above-described liquid ejection unit is provided, it is possible to appropriately eject a highly viscous liquid. 
     Although the pressure adjustment section  120 A supplies the liquid L to the liquid holding section  111  using the supply section  121  and pressurizes the liquid Lin this embodiment, the pressure adjustment of the liquid L using the pressure adjustment section  120 A is not limited thereto. The pressure adjustment section  120 A may suction the liquid L from the liquid holding section  111  and adjust the pressure of the liquid L to be decreased. 
     In this case, for example, first, when the inside of the liquid holding section  111  is set to a negative pressure using the pressure adjustment section  120 A, the meniscus of the ejection port  111   a  is suctioned into the liquid holding section. After that, it is possible to eject a liquid droplet by displacing the displacement member  113  and displacing the liquid holding section  111  at a timing at which the meniscus naturally returns to the ejection port  111   a  or at a timing at which the inside of the liquid holding section  111  is set to a positive pressure by performing pressurizing using the pressure adjustment section  120 A. 
     If the liqudi L is ejected by driving the displacement member  113  in a state in which the pressure of the liquid L is reduced, a diameter of the generated liquid droplet L 1  tends to become smaller than a diameter of the liquid droplet L 1  of the liquid when the pressurized liquid L is ejected. 
     Also, although the liquid ejection device  1  in this embodiment has the plurality of liquid ejection units  101 , the present invention is not limited thereto. In addition, a constitution having only one liquid ejection unit  101  may be used. 
     Furthermore, although the displacement member  113  displaces the liquid L substantially parallel to the ejection direction of the liquid L in the liquid ejection unit  101  in this embodiment, the present invention is not limited thereto. Even if the displacement member  113  is configured to displace the liquid L in a direction intersecting the ejection direction of the liquid L, it is possible to appropriately eject a highly viscous liquid and it is possible to make a liquid ejection unit configured to solve the problems of the present invention. 
     Second Embodiment 
       FIG. 4  is an explanatory diagram of a liquid ejection unit and the liquid ejection device according to a second embodiment of the present invention and is a diagram corresponding to  FIG. 2 . A liquid ejection unit  102  in this embodiment is partially the same as the liquid ejection unit  101  in the first embodiment. Therefore, constituent elements in this embodiment that are the same as those of the first embodiment will be denoted by the same reference symbols and a detailed description thereof will be omitted. 
     The liquid ejection unit  102  includes a liquid ejection head  110  and a pressure adjustment section  120 B. 
     A liquid ejection device  2  in this embodiment has a constitution in which the liquid ejection unit  101  in the above-described liquid ejection device  1  is replaced with the liquid ejection unit  102 . 
     (Pressure Adjustment Section) 
     The pressure adjustment section  120 B includes a supply section  121  and a detection unit  123 . 
     The supply section  121  is connected via a liquid holding section  111  and a pipe  116 . The pipe  116  can have the same constitution as the above-described first pipe  115   a.    
     The detection unit  123  is an observation device configured to observe a state of a meniscus formed using an ejection port  111   a.  The “state of the meniscus” includes at least one selected from the group consisting of a shape and a volume of the meniscus and a formation position of the meniscus. Examples of the detection unit  123  include an imaging device configured to capture a meniscus and a laser measuring device configured to detect a position, a size, and a shape of a meniscus. 
     It is possible to detect a movement state of a meniscus by continuously detecting a position of the meniscus. The “movement state of the meniscus” includes an amplitude and a phase of the vibration of the meniscus by driving a displacement member. 
     When the liquid ejection device  2  including the liquid ejection unit  102  is used, a correspondence relationship between a state of the meniscus and a pressure of a liquid L is checked in advance using a preliminary experiment. 
     The state of the meniscus changes in accordance with the pressure of the liquid L. Thus, even if the pressure of the liquid L is not directly measured, the liquid ejection unit  102  can indirectly detect the pressure of the liquid L by checking the state of the meniscus using the detection unit  123 . 
     Also, the correspondence relationship between a pressure of the liquid L and a state of the liquid droplet L 1  to be ejected is checked in advance through a preliminary experiment. 
     An appropriate pressure of the liquid L is input to a control unit  50  in advance as the pressure of the liquid L when the liquid is ejected. Furthermore, the correspondence relationship between the state of the meniscus and the pressure of the liquid L is stored in advance in the control unit  50 . Such a control unit  50  indirectly detects the pressure of the liquid L from the state of the meniscus on the basis of the detection result of the detection unit  123  and adjusts the pressure of the liquid L to approach a predetermined set value of the ejecting pressure of the liquid L. 
     That is to say, when the pressure of the liquid L indirectly detected from the detection result of the detection unit  123  is higher than a set pressure, the control unit  50  controls the supply section  121  to reduce an amount of liquid L to be supplied from the supply section  121 . 
     Also, when the pressure of the liquid L indirectly detected from the detection result of the detection unit  123  is lower than the set pressure, the control unit  50  controls the supply section  121  to increase the amount of liquid L to be supplied from the supply section  121 . 
     Thus, the liquid ejection unit  102  can appropriately adjust the pressure of the liquid L on the basis of the detection result of the detection unit  123  and eject a liquid droplet L 1 . 
     Although the detection unit  123  detects the state of the meniscus formed in an ejection port in this embodiment, the present invention is not limited thereto. The detection unit  123  may observe a state of a liquid droplet L 1  ejected from the liquid holding section  111  when the liquid droplet L 1  flies. 
     The “state of the liquid droplet L 1  when the liquid droplet L 1  flies” includes at least one selected from the group consisting of a shape and a volume of a liquid droplet L 1 , a speed of the liquid droplet L 1 , and a flight position of the liquid droplet L 1 . Examples of the detection unit  123  include an imaging device configured to capture a liquid droplet L 1  and a laser measuring device configured to detect a size, a shape, and movement of the liquid droplet L 1 . 
     When the liquid ejection device  2  including the liquid ejection unit  102  is used, the correspondence relationship between a state of the liquid droplet L 1  and a pressure of the liquid L is checked in advance using a preliminary experiment. 
     The state of the liquid droplet L 1  changes in accordance with the pressure of the liquid L. Thus, even if the pressure of the liquid L is not directly measured, the liquid ejection unit  102  can indirectly detect the pressure of the liquid L by checking the state of the liquid droplet L 1  using the detection unit  123 . 
     Also, the correspondence relationship between a pressure of the liquid L and a state of the liquid droplet L 1  to be ejected is checked in advance using a preliminary experiment. 
     An appropriate pressure of the liquid L is input to the control unit  50  in advance as the pressure of the liquid L when the liquid is ejected. Furthermore, a correspondence relationship between a state of the meniscus and a pressure of the liquid L is stored in the control unit  50  in advance. Such a control unit  50  indirectly detects the pressure of the liquid L from the state of the liquid droplet L 1  on the basis of the detection result of the detection unit  123  and adjusts the pressure of the liquid L to approach a predetermined set value of the ejecting pressure of the liquid L. A pressure adjustment method of the liquid L may be the same as an adjustment method after the above-described state of the meniscus is detected. 
     Thus, the liquid ejection unit  102  can appropriately adjust the pressure of the liquid L on the basis of the detection result of the detection unit  123  and eject a liquid droplet L 1 . 
     With the liquid ejection unit  102  configured as described above, it is possible to provide a liquid ejection unit which can appropriately eject a highly viscous liquid. 
     With the liquid ejection device  2  configured as described above, since the above-described liquid ejection unit is provided, it is possible to appropriately eject a highly viscous liquid. 
     Although both a device configured to detect a state of a meniscus and a device configured to detect a state of a liquid droplet L 1  when the liquid droplet L 1  flies have been described as the detection unit  123 , the liquid ejection device may include both of these two types of detection units  123 . In this case, the control unit  50  may indirectly detect the pressure of the liquid L on the basis of the detection result of the two types of detection units  123  and control the pressure of the liquid L. 
     Third Embodiment 
       FIG. 5  is an explanatory diagram of a liquid ejection unit and a liquid ejection device according to a third embodiment of the present invention and is a diagram corresponding to  FIGS. 2 and 4 . A liquid ejection unit  103  in this embodiment is partially the same as the liquid ejection unit in the above-described embodiments. Therefore, constituent elements in this embodiment that are the same as those of the above-described embodiments will be denoted by the same reference symbols and a detailed description thereof will be omitted. 
     A liquid ejection unit  103  includes a liquid ejection head  160  and a pressure adjustment section  120 C. 
     A liquid ejection device  3  in this embodiment has a constitution in which the liquid ejection unit  101  in the above-described liquid ejection device  1  is replaced with the liquid ejection unit  103 . 
     The liquid ejection head  160  includes a liquid holding section  161 , a support section  162 , a displacement member  163 , and a pipe  116 . 
     A pressure adjustment section  120 A includes a supply section  121  and a detection unit  122 . 
     &lt;Liquid Ejection Head&gt; 
     (Liquid Holding Section) 
     The liquid holding section  161  can adopt the same constitution as the above-described liquid holding section  111 . 
     (Support Section) 
     The support section  162  supports the liquid holding section  161  in an attachable and detachable manner. The support section  162  can adopt various commonly known constitutions as long as they can support the liquid holding section  161 . 
     The support section  162  includes a support main body  162   a  configured to support the liquid holding section  161  and a screw  162   x  configured to fix the liquid holding section  161  to the support main body  162   a.    
     (Displacement Member) 
     The displacement member  163  can adopt the same constitution as the above-described displacement member  113 . 
     (Pipe) 
     The pipe  116  connects the liquid holding section  161  to the supply section  121 . 
     &lt;Pressure Adjustment Section&gt; 
     The pressure adjustment section  120 C includes a pressurizing section  125  and a detection unit  123 . 
     (Pressurizing Section) 
     The pressurizing section  125  includes a soft section  126  and a pressing section  127 . 
     The soft section  126  is a tubular member which is provided by connecting the liquid holding section  161  to the pipe  116  and is in communication with the liquid holding section  161  and the pipe  116 . The soft section  126  includes a soft resin material as a forming material. Examples of the soft resin material include polyurethane, silicone rubber, and fluororesin. 
     The soft section  126  may be formed integrally with the pipe  116  or may be a separate member. 
     The pressing section  127  is a member provided on the soft section  126  and configured to press the soft section  126  in accordance with an instruction from a control unit  50 . The pressing section  127  can adopt various known constitutions as long as they can press the soft section  126 . For example, the pressing section  127  can have the same piezoelectric element as the above-described displacement member  113 . 
     In the pressurizing section  125 , the soft section  126  having the pressing section  127  provided therein is pressurized and compressed by supplying electricity to the pressing section (a piezoelectric element)  127  and compressing the pressing section  127 . Thus, a liquid L inside the soft section  126  and the liquid holding section  161  is pressurized and a part of the liquid L is pushed out through an ejection port  161   x  of the liquid holding section  161 . 
     In the liquid ejection unit  103  as described above, first, when the liquid L in the liquid holding section  161  is pressurized in the pressurizing section  125 , in the ejection port  161   x  of the liquid holding section  161 , a part of the liquid L held in the liquid holding section  161  is pushed out and a meniscus is formed. 
     Subsequently, a liquid droplet is ejected in the same driving manner as in  FIG. 3  by driving the displacement member  163  and displacing the liquid holding section  161 . 
     With the liquid ejection unit  103  configured as described above, it is possible to provide a liquid ejection unit which can appropriately eject a highly viscous liquid. 
     In addition, with the liquid ejection device  3  configured as described above, since the above-described liquid ejection unit is provided, it is possible to appropriately eject a highly viscous liquid. 
     Fourth Embodiment 
       FIG. 6  is an explanatory diagram of a liquid ejection unit and a liquid ejection device according to a fourth embodiment of the present invention and is a diagram corresponding to  FIGS. 2, 4, and 5 . A liquid ejection unit  104  in this embodiment is partially the same as the liquid ejection unit in the above-described embodiment. Therefore, constituent elements in this embodiment that are the same as those of the above-described embodiment will be the same reference symbols and a detailed description thereof will be omitted. 
     The liquid ejection unit  104  includes a liquid ejection head  170  and a pressure adjustment section  120 B. 
     A liquid ejection device  4  in this embodiment has a constitution in which the liquid ejection unit  101  in the above-described liquid ejection device  1  is replaced with the liquid ejection unit  104 . 
     A liquid ejection head  170  includes a liquid holding section  171 , a nozzle plate  172 , a displacement member  173 , and a pipe  116 . 
     (Liquid Holding Section) 
     The liquid holding section  171  is a tubular member whose lower end in the z axis direction is open. A liquid L is held inside the liquid holding section  171 . Furthermore, an upper portion of the liquid holding section  171  is connected to the pipe  116 . 
     A lower end portion  171   x  of the liquid holding section  171  is closed by the nozzle plate  172  and the displacement member  173 . A liquid L is held in a space surrounded by the liquid holding section  171 , the nozzle plate  172 , and the displacement member  173 . 
     (Nozzle Plate) 
     The nozzle plate  172  is an annular member having an ejection port  172   x.  The nozzle plate  172  closes the lower end portion  171   x  of the liquid holding section  171 . The ejection port  172   x  communicates with the liquid holding section  171 . 
     A planar shape of the nozzle plate  172  and a size, a material, and a structure thereof when viewed in a plan view are not particularly limited and can be appropriately selected in accordance with the purpose. 
     Examples of a planar shape of an outer edge of the nozzle plate  172  include a circle, an ellipse, a rectangle, a square, and a rhombus. For example, when a shape of the outer edge of the nozzle plate  172  is circular, the nozzle plate  172  is an annular member. 
     An end portion of the nozzle plate  172  on the ejection port  172   x  side is not supported and can vibrate upward and downward. When the end portion of the nozzle plate  172  on the ejection port  172   x  side vibrates, a force is applied to the liquid L in the vicinity of the ejection port  172   x  downward and the liquid L is ejected through the ejection port  172   x  as a liquid droplet L 1 . 
     If a material of the nozzle plate  172  is too soft, the nozzle plate  172  easily vibrates. In addition, it is not easy to minimize the vibration immediately when ejecting is not performed. Thus, it is desirable to utilize a material having a certain degree of hardness. 
     Examples of the material of the nozzle plate  172  include metals, ceramics, polymer materials, and the like. Specific examples of the material of the nozzle plate  172  include stainless steel, nickel, aluminum, silicon dioxide, alumina, zirconia, and the like. 
     An opening shape of the ejection port  172   x  can be appropriately selected in accordance with the purpose. Examples of the opening shape of the ejection port  172   x  include a circle, an ellipse, a quadrangle, and the like. Among these, it is desirable that the opening shape of the ejection port  172   x  be circular. 
     An average opening diameter of the ejection port  172   x  is not particularly limited and can be appropriately selected in accordance with the purpose. When a liquid L to be ejected is a dispersion liquid, it is desirable that the opening shape of the ejection port  172   x  be twice or more a maximum diameter of a dispersoid such as cells dispersed in the liquid L to prevent clogging of the ejection port  172   x  with the dispersoid. 
     (Displacement Member) 
     The displacement member  173  vibrates the nozzle plate  172  to eject a liquid droplet L 1  through the ejection port  172   x.    
     The displacement member  173  is arranged between the lower end portion  171   x  of the liquid holding section  171  and the nozzle plate  172  and closes the lower end portion  171   x  of the liquid holding section  171 . 
     The shape, the size, the material, and the structure of the displacement member  173  are not particularly limited and can be appropriately selected in accordance with the purpose. 
     The shape and an arrangement of the displacement member  173  are not particularly limited as long as the effects of the present invention are not impaired and can be appropriately designed in accordance with the shape of the nozzle plate  172 . For example, when the planar shape of the nozzle plate  172  is a circular planar shape, it is desirable to provide the displacement member  173  concentrically around the ejection port  172   x.    
     It is desirable that a piezoelectric element be appropriately used as the displacement member  173 . As the piezoelectric element, a member having the same constitution as the piezoelectric element adopted for the displacement member  113  can be utilized. 
     In the liquid ejection unit  104  as described above, first, when a liquid L in the liquid holding section  171  is pressurized in the supply section  121 , in the ejection port  172   x  in the liquid holding section  171 , a part of the liquid L held in the liquid holding section  171  is pushed out and a meniscus is formed. 
     Subsequently, when a part of the liquid L held in the liquid holding section  171  is displaced by driving the displacement member  173 , a liquid droplet L 1  is ejected. 
     With the liquid ejection unit  104  configured as described above, it is possible to provide a liquid ejection unit which can appropriately eject a highly viscous liquid. 
     In addition, with the liquid ejection device  4  configured as described above, since the above-described liquid ejection unit is provided, it is possible to appropriately eject a highly viscous liquid. 
     Although the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the embodiments. The shapes, the combinations, and the like of the constituent elements illustrated in the above-described examples are merely examples and can be variously changed on the basis of design requirements and the like without departing from the gist of the present invention. 
     Among the constitutions of the liquid ejection unit and the liquid ejection device described in the above-described first to fourth embodiments, constitutions which achieve the same effects can be exchanged with each other as long as the effects of the present invention are not impaired. 
     For example, the liquid ejection device in the first embodiment may include the detection unit  123  included in the liquid ejection device described in the second to fourth embodiments instead of the detection unit  122 . 
     Similarly, the liquid ejection device described in the second to fourth embodiments may include the detection unit  122  included in the liquid ejection device in the first embodiment instead of the detection unit  123 . 
     Also, among the constitutions of the liquid ejection unit and the liquid ejection device described in the first to fourth embodiments, constitutions which achieve the same effects may be achieved may be repeatedly included as long as the effects of the present invention are not impaired. 
     For example, the liquid ejection device may include both of the detection unit  122  and the detection unit  123 . In this case, the control unit  50  may obtain the pressure of the liquid L on the basis of the detection result of both of the detection unit  122  and the detection unit  123  and control the pressure of the liquid L. 
     Also, when the liquid ejection device described in the first to fourth embodiments includes a plurality of liquid ejection units, all of the plurality of liquid ejection units have the same constitution and may have two or more types selected from the group consisting of the liquid ejection units  101  to  104  described above. 
     The present invention includes the following aspects. 
     [1] A liquid ejection unit includes: a liquid holding section having an ejection port through which a liquid is ejected and configured to hold the liquid; a pressure adjustment section configured to adjust a pressure of the liquid held in the liquid holding section; and a displacement member configured to displace at least a part of the liquid whose pressure is adjusted and eject the liquid from the liquid holding section. 
     [2] In the liquid ejection unit according to [1], the displacement member which is configured to displace the liquid holding section substantially parallel to an ejection direction of the liquid. 
     [3] In the liquid ejection unit according to [2], the liquid holding section is a tubular member extending substantially parallel to the ejection direction of the liquid, the liquid holding section and the displacement member are arranged to overlap when viewed in a plan view, and a shape of the liquid holding section when viewed in a plan view is smaller than a shape of the displacement member when viewed in a plan view. 
     [4] In the liquid ejection unit according to any one of [1] to [3], a supply section configured to supply the liquid to the liquid holding section is provided and the supply section is also configured to function as the pressure adjustment section. 
     [5] In the liquid ejection unit according to any one of [1] to [3], at least a part of the liquid holding section is formed of an elastic material and the pressure adjustment section is a unit provided in a place of the liquid holding section formed of the elastic material and configured to change a volume of the liquid holding section by deforming the liquid holding section. 
     [6] In the liquid ejection unit according to any one of [1] to [5], the pressure adjustment section includes a detection unit configured to directly or indirectly detect a pressure of the liquid which is held in the liquid holding section and whose pressure is adjusted. 
     [7] In the liquid ejection unit according to [6], the detection unit is configured to detect a pressure of the liquid which is held in the liquid holding section and whose pressure is adjusted and the pressure adjustment section is configured to adjust the pressure of the liquid to approach a predetermined set value of the ejecting pressure of the liquid on the basis of the detection result of the detection unit. 
     [8] In the liquid ejection unit according to [6], the detection unit is configured to observe a meniscus formed in the ejection port and the pressure adjustment section is configured to adjust the pressure of the liquid to approach a predetermined set value of the ejecting pressure of the liquid on the basis of at least one of a formation position of the meniscus or movement information of the meniscus. 
     [9] In the liquid ejection unit according to [6] or [8], the detection unit is configured to observe a liquid droplet ejected from the liquid holding section and the pressure adjustment section is configured to adjust the pressure of the liquid to approach a predetermined set value of the ejecting pressure of the liquid on the basis of at least one selected from the group consisting of the flight position of the liquid droplet, the shape of the liquid droplet, the volume of the liquid droplet, and the speed of the liquid droplet. 
     [10] In the liquid ejection unit according to [9], the detection unit is an imaging device or a laser measuring device. 
     [11] In the liquid ejection unit according to any one of [1] to [10], the liquid is a dispersion liquid containing particles and a dispersion medium having the particles dispersed therein. 
     [12] In the liquid ejection unit according to [11], the particles are cells. 
     [13] A liquid ejection device includes: the liquid ejection unit according to any one of [1] to [12]. 
     [14] In the liquid ejection device according to [13], a plurality of the liquid ejection units are provided and the plurality of liquid ejection units are arranged in a direction intersecting an ejection direction of the liquid. 
     According to the liquid ejection unit described in any one of [1] to [12] and the liquid ejection device described in [13] or [14], it is possible to achieve an object of the present invention by solving the problems in the related art. 
     EXPLANATION OF REFERENCES 
     
         
           1 ,  2 ,  3 ,  4  Liquid ejection device 
           50  Control unit 
           101 ,  102 ,  103 ,  104  Liquid ejection unit 
           110 ,  160 ,  170  Liquid ejection head 
           111 ,  161 ,  171  Liquid holding section 
           111   a,    161   x,    172   x  Ejection port 
           113 ,  163 ,  173  Displacement member 
           120 A,  120 B,  120 C Pressure adjustment section 
           121  Supply section 
           122 ,  123  Detection unit 
           127  Pressing section (piezoelectric element) 
         L Liquid 
         L 1  Liquid droplet 
         LM Meniscus