Patent Publication Number: US-11040529-B2

Title: Liquid ejecting apparatus and liquid ejecting method

Description:
The present application is based on, and claims priority from, JP Application Serial Number 2018-120388, filed Jun. 26, 2018, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a liquid ejecting apparatus and a liquid ejecting method. 
     2. Related Art 
     Various studies are being made to apply an ink jet technology to, for example, formation of electrodes, direct formation of various electrical components, formation of light emitting bodies and filters used for displays, and formation of microlenses. The increasing range of uses for the ink jet technology increases the variety of types of liquid to be ejected from nozzles. For example, JP-A-2010-110968 discloses a method of ejecting liquid with a high viscosity from a nozzle. 
     With the liquid ejecting method of JP-A-2010-110968, the range of the viscosity of the liquid within which the liquid can be stably ejected from the nozzle is limited. The inventors of the present application have studied on this point. Consequently, the inventors have determined that a phenomenon in which when the viscosity of the liquid increases, the resistance at the boundary between the inner wall surface of the nozzle and the liquid to be ejected increases and the loss of energy of the liquid required for the ejection due to friction or the like increases leads to poor stability of the ejection. The inventors have found a problem that the poor stability of the ejection becomes more noticeable as the viscosity of the liquid is higher. 
     SUMMARY 
     According to an aspect of the present disclosure, a liquid ejecting apparatus is provided. The liquid ejecting apparatus includes a nozzle that ejects liquid with a viscosity of 50 mPa·s or higher; a pressure chamber communicating with the nozzle; a pressure change portion that changes a pressure of the liquid in the pressure chamber; and a controller that controls the pressure change portion. The controller, by driving the pressure change portion, executes first control of decreasing the pressure of the liquid in the pressure chamber, hence pulling a center portion of a meniscus of the liquid in the nozzle toward the pressure chamber, and forming a liquid membrane with the liquid at an inner wall surface of the nozzle; and second control of, in a state in which the liquid membrane is formed at the inner wall surface, increasing the pressure of the liquid in the pressure chamber, hence inverting a shape of the center portion of the meniscus to a protruding shape protruding toward an opening of the nozzle on a side opposite to the pressure chamber and forming a liquid column, and further, ejecting the liquid column from the center portion of the meniscus having the protruding shape toward the opening so as not to contact the liquid membrane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an explanatory view illustrating an outline configuration of a liquid ejecting apparatus according to a first embodiment. 
         FIG. 2  is an explanatory view illustrating an outline configuration of a head according to the first embodiment. 
         FIG. 3  is an explanatory view illustrating an example of a waveform of a drive voltage to be supplied to a piezoelectric element. 
         FIG. 4  is an explanatory view schematically illustrating a state of a meniscus in a nozzle in an initial state. 
         FIG. 5  is an explanatory view schematically illustrating a state of the meniscus in the nozzle in a first step. 
         FIG. 6  is an explanatory view schematically illustrating a state of the meniscus in the nozzle in a second step. 
         FIG. 7  is an explanatory view schematically illustrating a state of the meniscus in the nozzle in a third step. 
         FIG. 8  is an explanatory view schematically illustrating a state of the meniscus in the nozzle after liquid ejection. 
         FIG. 9  is an explanatory view illustrating a test result for the relationship between the number of capillaries and the pseudo nozzle diameter. 
         FIG. 10  is another explanatory view schematically illustrating a state of the meniscus in the nozzle in the first step. 
         FIG. 11  is still another explanatory view schematically illustrating a state of the meniscus in the nozzle in the first step. 
         FIG. 12  is an explanatory view illustrating an outline configuration of a head having a circulation channel. 
         FIG. 13  is an explanatory view illustrating an outline configuration of a head having a plurality of nozzles. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     A. First Embodiment 
       FIG. 1  is an explanatory view illustrating an outline configuration of a liquid ejecting apparatus  100  according to a first embodiment. The liquid ejecting apparatus  100  includes a tank  10 , a pressure pump  20 , a supply pipe  30 , a head  40 , and a controller  90 . 
     The tank  10  houses liquid. The liquid in the tank  10  is compressed by the pressure pump  20  and is supplied to the head  40  through the supply pipe  30 . The pressure pump  20  according to this embodiment is a metering pump capable of supplying liquid at a constant flow rate. As the metering pump, a gear pump with less pulsing may be employed. Alternatively, for example, a buffer tank for absorbing pulsing may be provided at a portion of the supply pipe  30 , and one of various metering pumps of diaphragm type and plunger type may be used. 
     The liquid supplied to the head  40  through the supply pipe  30  is ejected by the head  40 . The operation of the head  40  is controlled by the controller  90 . The controller  90  can be realized by, for example, a computer including a processor such as a central processing unit (CPU), a main memory, and a non-volatile memory. The non-volatile memory in the controller  90  stores a computer program for controlling the head  40 . The controller  90  realizes ejection of the liquid by the head  40 , the ejection of the liquid including a first step, a second step, and a third step which will be described later, by executing the computer program. 
     In this embodiment, the liquid to be ejected by the head  40  has a viscosity of 50 mPa·s or higher. The viscosity of the liquid is desirably within a range of from 50 to 10000 mPa·s. The liquid may be a material in a state in which a substance is in a liquid phase. The liquid includes a material in a liquid state, such as a sol or a gel. The liquid is not limited to liquid as one state of a substance, and includes liquid that particles of a functional material made of a solid substance, such as a pigment or metal particles, are dissolved, dispersed, or mixed in a solvent. A representative example of the liquid may be an ink or a liquid crystal emulsifier. The ink includes various types of liquid-state compositions, such as general water-base ink, oil-base ink, gel ink, and hot-melt ink. 
     The metal particles may be, for example, a Sn—Pb-based material, a Sn—Ag-based material, a Sn—Ag—Cu-based material, a Sn—Bi-based material, a Sn—Cu-based material, a Sn—Cu—Ni-based material, a Sn—Ag—Bi-based material, a Sn—Ag—Bi—In-based material, a Sn—Ag—Bi—Cu-based material, a Sn—Zn-based material, or a Sn—Zn—Bi-based material. 
     The solvent may be, for example, straight-chain or branched-chain aliphatic hydrocarbon, alicyclic hydrocarbon, or aromatic hydrocarbon; a halogen substituent of one of these hydrocarbons; or silicone oil, as a desirable example. For example, the solvent may be one or a mixture of at least two of hexane, heptane, octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, toluene, xylene, mesitylene, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M (Isopar: trade name of Exxon Mobil Corporation), Shellsol 70, Shellsol 71 (Shellsol: trade name of Shell Oil Company), a solvent of Amsco OMS or Amsco 460 (Amsco: trade name of American Mineral Spirits Company), and KF-96L (Shin-Etsu Chemical Co., Ltd.). 
     The particles are particulate substances each having a desirable shape, such as a spherical shape, a spheroidal shape, or an indefinite shape. The particle diameter is a dimension of a particle obtained based on an assumption that the particle has a spherical shape, and may be represented by a mean particle diameter of particulate materials including particles. The particle-diameter distribution of the particulate materials, which are a set of particles, can be obtained by laser diffracting and scattering method, and for example, can be obtained by Microtrac FRA (manufactured by Nikkiso Co., Ltd.). The mean particle diameter of particles is a volume mean particle diameter obtained by using the particle-diameter distribution of the thus obtained particulate material. 
       FIG. 2  is an explanatory view illustrating an outline configuration of the head  40  according to the first embodiment. The head  40  includes a nozzle  60  that ejects liquid, a pressure chamber  43  that communicates with the nozzle  60 , and a pressure change portion  44  that changes the pressure of the liquid in the pressure chamber  43 . The pressure change portion  44  is controlled by the controller  90 . 
     The liquid supplied from the tank  10  to the head  40  flows to the pressure chamber  43  through a supply channel  42 . The liquid in the pressure chamber  43  is compressed by the pressure change portion  44 , and hence is ejected from the nozzle  60 . In this embodiment, the nozzle  60  includes a straight portion  61  and a tapered portion  62 . The straight portion  61  is a portion of the nozzle  60 . The straight portion  61  has a nozzle opening  64  at an end portion of the straight portion  61  on the side opposite to the pressure chamber  43 , and has an angle of smaller than 5 degrees between a center axis CL of the nozzle  60  and an inner wall surface  63  of the nozzle  60 . The inner diameter of the straight portion  61  is set within a range of from 50 to 1000 μm. The angle between the center axis CL of the nozzle  60  and the inner wall surface  63  of the nozzle  60  is calculated in a state in which the surface roughness of the inner wall surface  63  of the nozzle  60  and irregularities due to processing marks in an etching process thereof are averaged. The tapered portion  62  is a portion of the nozzle  60 . The tapered portion  62  is provided nearer to the pressure chamber  43  than the straight portion  61 , and has an angle of equal to or larger than 5 degrees between the center axis CL of the nozzle  60  and the inner wall surface  63  of the nozzle  60 . The inner diameter of the nozzle  60  in the tapered portion  62  increases toward the pressure chamber  43 . The angle between the tangential line of the inner wall surface  63  in the tapered portion  62  and the center axis CL of the nozzle  60  is desirably equal to or smaller than 45 degrees. The tapered portion  62  may be straight or curved in a cross section including the center axis CL of the nozzle  60 . The nozzle  60  may not include the tapered portion  62 . In this case, the straight portion  61  directly communicates with the pressure chamber  43 . 
     The pressure change portion  44  according to this embodiment includes a piezoelectric element  45  and a displacement amplifying mechanism  50 . The displacement amplifying mechanism  50  includes a first partition wall  51 , a first elastic member  52 , a housing chamber  53 , a second partition wall  54 , and a second elastic member  55 . The piezoelectric element  45  expands and contracts in accordance with the voltage to be applied by the controller  90 . One end portion in an expansion/contraction direction of the piezoelectric element  45  is fixed to a casing  41  of the head  40 . The other end portion in the expansion/contraction direction of the piezoelectric element  45  is fixed to the first partition wall  51 . The outer peripheral edge of the first partition wall  51  is supported by the casing  41  via the first elastic member  52 . The housing chamber  53  is provided on the side opposite to the piezoelectric element  45  with the first partition wall  51  interposed between the housing chamber  53  and the piezoelectric element  45 . A working fluid is sealed in the housing chamber  53 . The working fluid according to this embodiment is a liquid containing a filler dispersed therein and having a predetermined viscosity. The second partition wall  54  is provided on the side opposite to the first partition wall  51  of the housing chamber  53 . The outer peripheral edge of the second partition wall  54  is supported by the casing  41  via the second elastic member  55 . The area by which the first partition wall  51  contacts the working fluid is larger than the area by which the second partition wall  54  contacts the working fluid. The working fluid is not limited to the liquid, and may be a material having fluidity when the working fluid receives a pressure from the outside and is deformed, and exhibits a fluid-like characteristic that can transmit a pressure in all directions like liquid. For example, the working fluid may be one of various types of rubber materials such as silicon rubber, or may be a gel body having both fluidity and elasticity. 
     When the piezoelectric element  45  is displaced in accordance with the voltage applied by the controller  90 , the piezoelectric element  45  displaces the first partition wall  51  toward the housing chamber  53 . The first partition wall  51  displaced toward the housing chamber  53  displaces the second partition wall  54  toward the pressure chamber  43  via the working fluid sealed in the housing chamber  53 . The second partition wall  54  displaced toward the pressure chamber  43  changes the capacity of the pressure chamber  43 . The displacement amount of the second partition wall  54  at this time is larger than the displacement amount of the first partition wall  51  because the displacement amount of the second partition wall  54  is increased according to the Pascal&#39;s law. That is, the displacement amount of the second partition wall  54  is larger than the displacement amount of the piezoelectric element  45 . Thus, the change in the capacity of the pressure chamber  43  is larger than that of an aspect without the displacement amplifying mechanism  50 . When the capacity of the pressure chamber  43  is decreased, the liquid in the pressure chamber  43  is compressed. In contrast, when the capacity of the pressure chamber  43  is increased, the liquid in the pressure chamber  43  is decompressed. The displacement amplifying mechanism  50  is not limited to the above-described aspect, and may employ one of various types of aspects. For example, the capacity of the pressure chamber  43  may be changed by increasing the displacement of the piezoelectric element  45  using a lever, and deforming a vibrating plate that constitutes a wall surface of the pressure chamber  43  using a lever. 
       FIG. 3  is an explanatory view illustrating an example of a waveform of a drive voltage to be supplied to the piezoelectric element  45  by the controller  90 .  FIG. 3  illustrates a drive waveform for performing one cycle of ejecting liquid from the nozzle  60 . The drive waveform includes a pull waveform portion W 1  for decompressing the liquid in the pressure chamber  43 , and a push waveform portion W 2  for compressing the liquid in the pressure chamber  43 . First, the controller  90  supplies the pull waveform portion W 1  to the piezoelectric element  45 . When the pull waveform portion W 1  is supplied, the piezoelectric element  45  is displaced in the contraction direction, the capacity of the pressure chamber  43  is increased, and the liquid in the pressure chamber  43  is decompressed. Then, the controller  90  supplies the push waveform portion W 2  to the piezoelectric element  45 . When the push waveform portion W 2  is supplied, the piezoelectric element  45  is displaced in the expansion direction, the capacity of the pressure chamber  43  is decreased, the liquid in the pressure chamber  43  is compressed, and the liquid is ejected from the nozzle  60 . 
       FIGS. 4 through 8  are explanatory views each schematically illustrating a motion of a meniscus in the nozzle  60  when the liquid is ejected from the nozzle  60  according to this embodiment.  FIGS. 4 through 8  each illustrate the inside state of the nozzle  60  in the form of a cross section including the center axis CL of the nozzle  60 .  FIG. 4  illustrates a state of the meniscus in the nozzle  60  in an initial state. In the initial state, the pressure of the liquid in the pressure chamber  43  is not changed. Thus, the outer peripheral edge of the meniscus is located at the nozzle opening  64 , and a center portion M of the meniscus is located nearer to the pressure chamber  43  than the nozzle opening  64  in the nozzle  60  due to the surface tension. 
       FIG. 5  illustrates a state of the meniscus in the nozzle  60  in a first step. First, in the first step, the controller  90  supplies the pull waveform portion W 1  to the piezoelectric element  45  to decrease the pressure of the liquid in the pressure chamber  43 . Thus, the center portion M of the meniscus is pulled toward the pressure chamber  43  so that a liquid membrane  71  defined by the liquid remains at the inner wall surface  63  of the nozzle  60 . In  FIG. 5 , the center portion M of the meniscus is pulled to the inside of the straight portion  61 . Since the liquid membrane  71  is formed at the inner wall surface  63  of the nozzle  60 , it can be considered that a quasi-nozzle defined by the liquid membrane  71  is formed in the nozzle  60 . In this specification, the quasi-nozzle defined by the liquid membrane  71  is also referred to as pseudo nozzle. A pseudo nozzle diameter Dp is equal to or smaller than a diameter obtained by subtracting a value that is twice a thickness tm of the liquid membrane  71  formed at the inner wall surface  63  of the nozzle  60  from a nozzle diameter D. The pseudo nozzle diameter Dp is a diameter that is equal to or smaller than two-thirds of the nozzle diameter D. The method of calculating the thickness tm of the liquid membrane  71  formed at the inner wall surface  63  of the nozzle  60  is described later. In this specification, the control on the piezoelectric element  45  by the controller  90  to perform the first step is also referred to as first control. 
       FIG. 6  illustrates a state of the meniscus in the nozzle  60  in a second step. In the second step, the controller  90  supplies the push waveform portion W 2  to the piezoelectric element  45  in the state in which the liquid membrane  71  is formed at the inner wall surface  63  of the nozzle  60 , that is, in the state in which the pseudo nozzle is formed. The piezoelectric element  45  increases the pressure of the liquid in the pressure chamber  43 , and hence inverts the shape of the center portion M of the meniscus to a protruding shape protruding toward the nozzle opening  64 . The magnitude and speed of the change in pressure, which are required for the inversion and are to be applied to the liquid in the pressure chamber  43 , are substantially equivalent to the magnitude and speed of the change in pressure, which are required for ejecting the liquid from the nozzle  60  without formation of the above-described pseudo nozzle. The center portion M of the meniscus has a smaller resistance than the resistance of the liquid that contacts the inner wall surface  63  of the nozzle  60 . Thus, when the shape of the center portion M of the meniscus is inverted to the protruding shape protruding toward the nozzle opening  64 , the compressed liquid starts concentrating toward the center portion M of the meniscus having the protruding shape. 
       FIG. 7  illustrates a state of the meniscus in the nozzle  60  in a third step. In the third step, the controller  90  continues to supply the push waveform portion W 2  to the piezoelectric element  45  in the state in which the center portion M of the meniscus has the protruding shape protruding toward the nozzle opening  64 . The piezoelectric element  45  increases the pressure of the liquid in the pressure chamber  43 , hence a liquid column  72  is formed at the center portion M of the meniscus having the protruding shape toward the nozzle opening  64 , and the liquid column  72  is ejected from the nozzle  60  so as not to contact the liquid membrane  71 . The center portion M of the meniscus has a smaller resistance than the resistance of the liquid that contacts the inner wall surface  63  of the nozzle  60 . Thus, the speed at which the liquid in the liquid membrane  71  formed at the inner wall surface  63  of the nozzle  60  moves toward the nozzle opening  64  is higher than the speed at which the center portion M of the meniscus of the liquid column  72  moves toward the nozzle opening  64 . The liquid column  72  is pushed out so as not to contact the liquid membrane  71 , and hence, when the liquid column  72  passes through the nozzle opening  64 , the diameter of the ejected liquid column  72  in the radial direction of the nozzle  60  becomes smaller than two-thirds of the inner diameter of the nozzle  60 . In this specification, the control on the piezoelectric element  45  by the controller  90  to perform the second step and the third step is also referred to as second control. 
       FIG. 8  illustrates a state of the meniscus in the nozzle  60  after the third step. After the third step, the liquid column  72  ejected outside the nozzle  60  flies as a liquid droplet  73 . Thereafter, the state of the meniscus of the liquid remaining in the nozzle  60  returns to the initial state. In this case, the liquid column  72  may become the liquid droplet  73  in the nozzle  60  and the liquid droplet  73  may be ejected outside the nozzle  60 , or the liquid column  72  ejected outside the nozzle  60  may fly as the liquid column  72  without becoming the liquid droplet  73 . After the liquid column  72  is ejected from the nozzle  60 , the controller  90  may supply the pull waveform portion W 1  to the piezoelectric element  45  and decrease the pressure of the liquid in the pressure chamber  43  to cut the tail of the ejected liquid column  72 . 
     In the first step, the speed at which the center portion M of the meniscus moves toward the pressure chamber  43  is desirably about a speed that the liquid membrane  71  is formed at the inner wall surface  63  of the nozzle  60  and a cavity formation phenomenon does not occur in the liquid in the nozzle  60 . The cavity formation phenomenon is also referred to as cavitation. In the first step, the speed at which the center portion M of the meniscus is pulled can be set in accordance with the type of the liquid to be ejected, the nozzle diameter D, and so forth. For example, in the third step, the speed at which the center portion M of the meniscus is pulled can be 2 to 100 times lower than the speed at which the liquid to be ejected moves toward the nozzle opening  64 . 
     The speed at which the center portion M of the meniscus moves toward the pressure chamber  43  in the first step is obtained by image capturing the situation in which the center portion M of the pulled meniscus moves by a stroboscope from a lateral side of the nozzle  60  on a predetermined cycle, using a plurality of obtained images, and calculating a mean speed in a period immediately after the center portion M of the meniscus starts moving along the center axis CL of the nozzle  60  to immediately before the center portion M stops moving. The speed at which the liquid to be ejected moves toward the nozzle opening  64  in the third step is obtained by image capturing the situation in which the center portion M of the meniscus of the liquid column  72  or a tip end M 1  of the liquid droplet  73  pushed out from the center portion M of the meniscus having the protruding shape moves by a stroboscope from the lateral side of the nozzle  60  on a predetermined cycle, using a plurality of obtained images, and calculating a mean speed in a period immediately after the center portion M of the meniscus of the liquid column  72  or the tip end M 1  of the liquid droplet  73  starts moving along the center axis CL of the nozzle  60  to immediately before the center portion M of the meniscus of the liquid column  72  or the tip end M 1  of the liquid droplet  73  passes through the nozzle opening  64 . 
     The speed at which the liquid ejected outside the nozzle  60  flies in the third step is obtained by image capturing the situation in which the center portion M of the meniscus of the liquid column  72  or the tip end M 1  of the liquid droplet  73  pushed out from the center portion M of the meniscus having the protruding shape moves by a stroboscope from the lateral side of the nozzle  60  on a predetermined cycle, using a plurality of obtained images, and calculating a mean speed in a period immediately after the center portion M of the meniscus of the liquid column  72  or the tip end M 1  of the liquid droplet  73  appears outside the nozzle  60  to immediately after the center portion M of the meniscus of the liquid column  72  or the tip end M 1  of the liquid droplet  73  has moved by a distance of 0.5 mm from the nozzle opening  64  along the center axis CL of the nozzle  60 . However, images obtained after the center portion M of the meniscus of the liquid column  72  or the tip end M 1  of the liquid droplet  73  has moved by a distance of 1.0 mm or larger from the nozzle opening  64  along the center axis CL of the nozzle  60  is not used for calculating the mean speed. 
     As illustrated in  FIG. 5 , the thickness tm of the liquid membrane  71  formed at the inner wall surface  63  of the nozzle  60  is an average thickness that is obtained by the following method. First, the state of the liquid in the nozzle  60  is image captured by a stroboscope from the lateral side of the nozzle  60 , and in an obtained two-dimensional image, a curve portion that satisfies one of conditions (A) to (C) is obtained from the curve expressed by the meniscus. (A) The center of curvature of the meniscus is located on the inner wall surface  63  side of the nozzle  60  with respect to the meniscus. (B) The curvature of the meniscus is infinite. In this case, being infinite represents that the radius of curvature of the meniscus is 100 times or larger that of the nozzle diameter D. (C) The center of curvature of the meniscus is located on the center axis CL side of the nozzle  60  with respect to the meniscus, and the radius of curvature of the meniscus is larger than the maximum radius of the nozzle  60 . When the nozzle  60  has the straight portion  61  and the tapered portion  62 , the maximum radius of the nozzle  60  is the maximum value of the radius of the tapered portion  62 . It is assumed that an end portion of the curve portion thus obtained near the nozzle opening  64  is a point A, and an end portion of the curve portion near the pressure chamber  43  is a point B. Then, an area S is obtained. The area S is a region defined by a perpendicular line of the center axis CL passing through the point A, a perpendicular line of the center axis CL passing through the point B, the inner wall surface  63  of the nozzle  60 , and the meniscus. The area S of the region is divided by a distance L between the point A and the point B in the direction along the center axis CL of the nozzle  60 . The obtained value is the thickness tm of the liquid membrane  71 . In addition, as illustrated in  FIG. 6 , the minimum diameter of the pseudo nozzle between the center portion M of the meniscus having the protruding shape and the point A in the direction along the center axis CL of the nozzle  60  is the pseudo nozzle diameter Dp. 
     In the first step, the thickness tm of the liquid membrane  71  formed at the inner wall surface  63  of the nozzle  60  may have any percentage with respect to the nozzle diameter D within a range that the liquid column  72  does not contact the liquid membrane  71  in the second step and the third step. In the first step, the thickness tm of the liquid membrane  71  formed at the inner wall surface  63  of the nozzle  60  is desirably 20% or less with respect to the nozzle diameter D. 
     The diameter of the ejected liquid column  72  or the ejected liquid droplet  73  in the radial direction of the nozzle  60  when the liquid column  72  or the liquid droplet  73  passes through the nozzle opening  64  can be obtained by image capturing the situation in which the liquid column  72  or the liquid droplet  73  pushed out from the center portion M of the meniscus having the protruding shape by a stroboscope from the lateral side of the nozzle  60  on a predetermined cycle, using a plurality of obtained images, and measuring the maximum diameter of the liquid column  72  or the liquid droplet  73  that passes through the nozzle opening  64 . 
       FIG. 9  is a graph illustrating a test result obtained for the relationship between the number of capillaries Ca and the ratio of the pseudo nozzle diameter Dp to the nozzle diameter D. In this test, the state of the liquid in the nozzle  60  while the above-described first step, second step, and third step were performed was image captured by a stroboscope from the lateral side of the nozzle  60  on a predetermined cycle, and the thickness tm of the liquid membrane  71  was calculated by using obtained images. The diameter obtained by subtracting a value that is twice the calculated thickness tm of the liquid membrane  71  from the nozzle diameter D was assumed as the pseudo nozzle diameter Dp. In this test, a liquid ejecting apparatus  100  including a nozzle  60  made of transparent acrylic resin was used such that the state of the liquid in the nozzle  60  can be image captured by a stroboscope. The test was performed at an ordinary temperature of 25° C. As the liquid, glycerin having a viscosity of 800 mPa·s at the ordinary temperature was used. The number of capillaries Ca was obtained through the following Expression (1) by using a viscosity η of the liquid, a speed V at which the center portion M of the meniscus is pulled, and a surface tension σ of the liquid.
 
 Ca=η×V/σ   (1)
 
     In  FIG. 9 , a point P 1  indicated by a circle mark represents a test result when the nozzle diameter D is 160 μm. A point P 2  indicated by a triangle mark represents a test result when the nozzle diameter D is 210 μm. A point P 3  indicated by a rhombus mark represents a test result when the nozzle diameter D is 310 μm. In addition,  FIG. 9  illustrates the relationship between the number of capillaries Ca and the ratio of the pseudo nozzle diameter Dp to the nozzle diameter D in a curve when the thickness tm of the liquid membrane  71  is calculated by using the following Expression (2). In this curve, the diameter obtained by subtracting a value that is twice the thickness tm of the liquid membrane  71  calculated by using the following Expression (2) from the nozzle diameter D was assumed as the pseudo nozzle diameter Dp. The thickness tm of the liquid membrane  71  obtained through the test is substantially based on the following Expression (2).
 
 tm= 1.34× Ca   2/3 /(1+1.34×2.5× Ca   2/3 )  (2)
 
With the test result, the pseudo nozzle diameter Dp decreases as the number of capillaries Ca increases. In a range in which the number of capillaries Ca is two or more, the pseudo nozzle diameter Dp becomes a diameter that is equal to or smaller than two-thirds of the nozzle diameter D while being almost not affected by the size of the nozzle diameter D.
 
     With the liquid ejecting apparatus  100  according to the above-described embodiment, the pseudo nozzle defined by the liquid membrane  71  is formed in the nozzle  60 , and the pseudo nozzle ejects liquid. Since the resistance in the pseudo nozzle is smaller than that near the inner wall surface  63  of the nozzle  60 , the energy loss of the liquid to be ejected can be decreased, and the diameter of the liquid to be ejected in the radial direction of the nozzle  60  can be smaller than the pseudo nozzle diameter Dp. Accordingly, liquid with a high viscosity and a small diameter can be stably ejected. 
     In addition, in this embodiment, since the liquid is ejected such that the liquid column  72  is ejected from the pseudo nozzle so as not to contact the liquid membrane  71 , the energy loss of the liquid to be ejected can be decreased. Accordingly, the flying speed of the liquid to be ejected can be increased. 
     In addition, in this embodiment, since the liquid is ejected from the pseudo nozzle defined by the liquid membrane  71 , even when liquid including a material with large particle diameters is ejected, clogging of the nozzle  60  can be suppressed. 
     In addition, in this embodiment, the pseudo nozzle diameter Dp is equal to or smaller than two-thirds of the nozzle diameter D and the liquid is ejected from the pseudo nozzle so as not to contact the liquid membrane  71  that forms the pseudo nozzle. Accordingly, the liquid with a diameter smaller than two-thirds of the nozzle diameter D can be ejected. 
     In addition, in this embodiment, the speed at which the center portion M of the meniscus moves toward the pressure chamber  43  in the first step is set to be lower than the speed at which the liquid to be ejected moves toward the nozzle opening  64  in the third step. Accordingly, when the center portion M of the meniscus is pulled, occurrence of cavitation in the liquid can be suppressed, and an ejection failure of the liquid from the nozzle  60  can be suppressed. 
     In addition, in this embodiment, the length by which the center portion M of the meniscus is pulled in the first step is set such that the center portion M is located within the straight portion  61 . Accordingly, the change in pressure in the pressure chamber  43  which is required when the center portion M of the meniscus is pulled can be decreased, and the pressure change portion  44  can be decreased in size. In addition, when the center portion M of the meniscus is pulled, mixing of an air bubble into the pressure chamber  43  can be suppressed. 
     In addition, in this embodiment, since the pressure change portion  44  includes the displacement amplifying mechanism  50 , a further large change in pressure can be generated in the liquid in the pressure chamber  43 . Accordingly, the center portion M of the meniscus can be largely pulled, and the compressed liquid can be further concentrated at the center portion M of the meniscus having the protruding shape. 
     B. Other Embodiments 
     (B-1) In the liquid ejecting apparatus  100  of the above-described first embodiment, the pressure change portion  44  includes the displacement amplifying mechanism  50 . Alternatively, the pressure change portion  44  may not include the displacement amplifying mechanism  50 . In this case, the pressure change portion  44  according to an aspect may include, for example, the piezoelectric element  45  and a vibrating plate that defines a wall surface of the pressure chamber  43 . With this aspect, the capacity of the pressure chamber  43  can be changed by expansion and contraction of the piezoelectric element  45  fixed to the vibrating plate. Note that the aspect of compressing the liquid in the pressure chamber  43  is not limited to the above-described piezoelectric system, and may be thermal system of generating air bubbles in the pressure chamber  43  and compressing the liquid, or valve system of compressing the inside of the pressure chamber  43  using a solenoid and a valve and ejecting the liquid. 
     (B-2) In the liquid ejecting apparatus  100  of the above-described first embodiment, as illustrated in  FIG. 5 , the controller  90  pulls the center portion M of the meniscus into the straight portion  61  such that the thickness of the liquid membrane  71  gradually increases from the point A toward the point B in the first step. Alternatively, as illustrated in  FIG. 10 , the controller  90  may pull the center portion M of the meniscus into the straight portion  61  such that the liquid membrane  71  near the point B is thinner than the liquid membrane  71  between the point A and the point B in the first step. Still alternatively, as illustrated in  FIG. 11 , the controller  90  may pull the center portion M of the meniscus into the tapered portion  62  beyond the straight portion  61  in the first step. In this case, the liquid near the tapered portion  62  can be stirred, and hence an increase in the viscosity of the liquid near the tapered portion  62  can be suppressed. In addition, the distance by which the liquid is accelerated by the compression increases from the second step to the third step, and hence the liquid can be ejected at a high speed. The position to which the center portion M of the meniscus is pulled in the first step may be a position at which the second step and the third step can be performed. The inversion of the center portion M of the meniscus in the second step may be performed in the tapered portion  62  or in the straight portion  61  if the center portion M of the meniscus is pulled into the tapered portion  62  in the first step. 
     (B-3) In the liquid ejecting apparatus  100  of the above-described first embodiment, the liquid to be ejected from the nozzle  60  may contain a filler. Contraction of the volume of the liquid is suppressed in accordance with the type of the filler contained in the liquid, and an advantageous effect of realizing good color reproduction can be obtained. The content of the filler in the liquid may be, for example, 50% by weight or higher. 
     (B-4) As illustrated in  FIG. 12 , in the liquid ejecting apparatus  100  of the above-described first embodiment, the head  40  may include a circulation channel  46  that communicates with the tapered portion  62  of the nozzle  60 . The liquid flowing to the circulation channel  46  without being ejected from the nozzle  60  circulates from the supply channel  42  into the pressure chamber  43  by the pressure of a pump or the like. In this case, a flow of the liquid from the pressure chamber  43  to the circulation channel  46  can be generated, and hence an increase in the viscosity of the liquid can be suppressed from the inside of the pressure chamber  43  to the nozzle  60 . The thickness tm of the liquid membrane  71  is measured not on the side provided with the opening of the circulation channel  46 , but desirably on the side not provided with the opening of the circulation channel  46 . The liquid flowing to the circulation channel  46  may be discharged to a waste liquid tank or the like without circulating into the pressure chamber  43 . The circulation channel  46  may communicate with the pressure chamber  43  or the straight portion  61  of the nozzle  60 . 
     (B-5) In the liquid ejecting apparatus  100  of the above-described first embodiment, the head  40  includes a set of the nozzle  60 , the pressure chamber  43 , and the pressure change portion  44 . Alternatively, as illustrated in  FIG. 13 , the head  40  may include a plurality of sets of nozzles  60   a ,  60   b , and  60   c , pressure chambers  43   a ,  43   b , and  43   c , and pressure change portions  44   a ,  44   b , and  44   c . In this case, liquid with a high viscosity and a small diameter can be stably ejected from the plurality of nozzles  60   a ,  60   b , and  60   c.    
     (B-6) In the above-described first embodiment, the state of the liquid in the nozzle  60  and outside the nozzle  60  is image captured by a stroboscope from the lateral side of the nozzle  60 . However, image capturing may be performed in a direction along the center axis CL of the nozzle  60 . In addition, image capturing and measurement may be performed by using, for example, a high-speed camera and a laser displacement gauge. 
     C. Other Aspects 
     The present disclosure is not limited to the above-described embodiments, and may be implemented in various aspects within the scope of the disclosure. For example, the present disclosure can be implemented according to the following aspects. The technical features in the above-described embodiments corresponding to the technical features of the aspects described below can be appropriately replaced with one another or combined with one another to address part or the entirety of the problems of the present disclosure or to attain part or the entirety of the advantageous effects of the present disclosure. In addition, a technical feature may be appropriately omitted unless otherwise the technical feature is described as being essential in this specification. 
     (1) According to an aspect of the present disclosure, a liquid ejecting apparatus is provided. A liquid ejecting apparatus includes a nozzle that ejects liquid with a viscosity of 50 mPa·s or higher; a pressure chamber communicating with the nozzle; a pressure change portion that changes a pressure of the liquid in the pressure chamber; and a controller that controls the pressure change portion. The controller, by driving the pressure change portion, executes first control of decreasing the pressure of the liquid in the pressure chamber, hence pulling a center portion of a meniscus of the liquid in the nozzle toward the pressure chamber, and forming a liquid membrane with the liquid at an inner wall surface of the nozzle; and second control of, in a state in which the liquid membrane is formed at the inner wall surface, increasing the pressure of the liquid in the pressure chamber, hence inverting a shape of the center portion of the meniscus to a protruding shape protruding toward an opening of the nozzle on a side opposite to the pressure chamber and forming a liquid column, and further, ejecting the liquid column from the center portion of the meniscus having the protruding shape toward the opening so as not to contact the liquid membrane. 
     With the liquid ejecting apparatus according to the aspect, since the resistance on the inner side of the liquid membrane in the nozzle is smaller than that near the inner wall surface of the nozzle, the energy loss of the liquid to be ejected can be decreased, and the diameter of the liquid to be ejected in the radial direction of the nozzle can be smaller than the diameter on the inner side of the liquid membrane. Accordingly, liquid with a high viscosity and a small diameter can be stably ejected. 
     (2) In the liquid ejecting apparatus according to the aspect, a diameter of the ejected liquid column in a radial direction of the nozzle may be smaller than two-thirds of an inner diameter of the nozzle when the liquid column passes through an end surface of the nozzle near the opening. 
     With the liquid ejecting apparatus according to the aspect, since the diameter on the inner side of the liquid membrane formed in the nozzle is the diameter that is two-thirds of the inner diameter of the nozzle, the liquid with a diameter smaller than two-thirds of the inner diameter of the nozzle can be ejected. 
     (3) In the liquid ejecting apparatus according to the aspect, a speed at which the center portion of the meniscus moves toward the pressure chamber in the first control may be lower than a speed at which the liquid column to be ejected moves toward the opening of the nozzle in the second control. 
     With the liquid ejecting apparatus according to the aspect, when the meniscus is pulled, occurrence of cavitation in the liquid can be suppressed, and an ejection failure of the liquid from the nozzle can be suppressed. 
     (4) In the liquid ejecting apparatus according to the aspect, the nozzle may have a straight portion and a tapered portion provided nearer to the pressure chamber than the straight portion, a diameter of the nozzle in the tapered portion may increase toward the pressure chamber, and the center portion of the meniscus may be pulled into the straight portion in the first control. 
     With the liquid ejecting apparatus according to the aspect, the change in pressure in the pressure chamber which is required when the meniscus is pulled can be decreased, and the pressure change portion can be decreased in size. In addition, when the meniscus is pulled, mixing of an air bubble into the pressure chamber can be suppressed. 
     (5) In the liquid ejecting apparatus according to the aspect, the nozzle may have a straight portion and a tapered portion provided nearer to the pressure chamber than the straight portion, a diameter of the nozzle in the tapered portion may increase toward the pressure chamber, and the center portion of the meniscus may be pulled into the tapered portion in the first control. 
     With the liquid ejecting apparatus according to the aspect, the liquid near the tapered portion can be stirred, and hence an increase in the viscosity of the liquid near the tapered portion can be suppressed. In addition, the distance by which the liquid is accelerated by the compression increases, and hence the liquid can be ejected at a high speed. 
     (6) In the liquid ejecting apparatus according to the aspect, the liquid may contain a filler. 
     With the liquid ejecting apparatus according to the aspect, contraction of the volume of the liquid is suppressed in accordance with the type of the filler contained in the liquid, and an advantageous effect of realizing good color reproduction can be obtained. 
     (7) The liquid ejecting apparatus according to the aspect may further include a circulation channel that communicates with the pressure chamber and that circulates the liquid to the pressure chamber. 
     With the liquid ejecting apparatus according to the aspect, a flow of the liquid from the pressure chamber to the circulation channel can be generated, and hence an increase in the viscosity of the liquid can be suppressed from the inside of the pressure chamber to the nozzle. 
     (8) In the liquid ejecting apparatus according to the aspect, the pressure change portion may include a piezoelectric element and a displacement amplifying mechanism that increases a displacement amount of the piezoelectric element. 
     With the liquid ejecting apparatus according to the aspect, a further large change in pressure can be generated in the pressure chamber. Accordingly, the center portion of the meniscus can be largely pulled, and the flow of the compressed liquid can be further concentrated at the center portion of the meniscus having the protruding shape. 
     (9) In the liquid ejecting apparatus according to the aspect, the nozzle, the pressure chamber, and the pressure change portion may form a set and a plurality of the sets may be provided; and the controller may control each of the pressure change portions. 
     With the liquid ejecting apparatus according to the aspect, liquid with a high viscosity and a small diameter can be stably ejected from the plurality of nozzles. 
     The present disclosure can be implemented according to various aspects other than the liquid ejecting apparatus. For example, the present disclosure can be implemented according to any aspect of a liquid ejecting method, a liquid ejecting head, a computer program that provides a method of controlling liquid ejection, and a non-transitory storage medium storing the computer program.