阅读说明：本技术 液体吐出装置及液体吐出方法 (Liquid discharge device and liquid discharge method ) 是由 须贝圭吾 于 2019-06-25 设计创作，主要内容包括：一种液体吐出装置及液体吐出方法,在液体吐出装置中能稳定吐出高粘度且小直径的液体。具备：喷嘴,吐出粘度为50mPa·s以上的液体；压力室,连通于喷嘴；压力变化部,使压力室内的液体的压力变化；控制部,控制压力变化部。控制部驱动压力变化部,执行：第一控制,通过使压力室内的液体的压力降低,将喷嘴内的液体的弯液面的中央部朝向压力室侧拉入,在喷嘴的内壁面形成液体产生的液膜；第二控制,在喷嘴的内壁面形成液膜的状态下,通过使压力室内的液体的压力上升,使弯液面的中央部的形状朝向压力室的相反侧的喷嘴的开口部侧反转为凸形状而形成液柱,进一步从凸形状的弯液面的中央部朝向喷嘴的开口部侧,使液柱以不接触液膜的方式吐出。(A liquid discharge device and a liquid discharge method are provided, which can discharge liquid with high viscosity and small diameter stably. The disclosed device is provided with: a nozzle for discharging a liquid having a viscosity of 50 mPas or more; a pressure chamber communicated with the nozzle; a pressure changing unit that changes a pressure of the liquid in the pressure chamber; and a control unit for controlling the pressure change unit. The control unit drives the pressure changing unit, and executes: a first control of drawing a central portion of a meniscus of the liquid in the nozzle toward the pressure chamber side by reducing a pressure of the liquid in the pressure chamber, and forming a liquid film generated by the liquid on an inner wall surface of the nozzle; and a second control step of raising the pressure of the liquid in the pressure chamber in a state where the liquid film is formed on the inner wall surface of the nozzle, inverting the shape of the central portion of the meniscus toward the opening portion side of the nozzle on the opposite side of the pressure chamber to a convex shape to form a liquid column, and discharging the liquid column from the central portion of the convex meniscus toward the opening portion side of the nozzle without contacting the liquid film.)

1. A liquid discharge device is characterized by comprising:

a nozzle for discharging a liquid having a viscosity of 50 mPas or more;

a pressure chamber in communication with the nozzle;

a pressure changing unit that changes a pressure of the liquid in the pressure chamber; and

a control section for controlling the pressure change section,

the control unit drives the pressure changing unit to execute the following control:

a first control of drawing a central portion of a meniscus of the liquid in the nozzle toward the pressure chamber side by reducing a pressure of the liquid in the pressure chamber, thereby forming a liquid film generated by the liquid on an inner wall surface of the nozzle; and

and a second control step of raising the pressure of the liquid in the pressure chamber in a state where the liquid film is formed on the inner wall surface, inverting the shape of the central portion of the meniscus toward the opening portion side of the nozzle on the opposite side of the pressure chamber to a convex shape to form a liquid column, and discharging the liquid column so as not to contact the liquid film from the central portion of the convex meniscus toward the opening portion side.

2. The liquid discharge apparatus according to claim 1,

the discharged liquid column has a diameter in the radial direction of the nozzle that is smaller than two-thirds of the inner diameter of the nozzle when passing through the end surface of the nozzle on the opening portion side.

3. The liquid discharge apparatus according to claim 1 or 2,

the speed at which the central portion of the meniscus moves toward the pressure chamber side in the first control is slower than the speed at which the liquid column discharged in the second control moves toward the nozzle opening portion side.

4. The liquid discharge apparatus according to claim 1 or 2,

the nozzle has a straight portion and a tapered portion provided on the pressure chamber side than the straight portion,

the nozzle in the tapered portion becomes larger in diameter toward the pressure chamber side,

in the first control, a central portion of the meniscus is drawn into the linear portion.

5. The liquid discharge apparatus according to claim 1 or 2,

the nozzle has a straight portion and a tapered portion provided on the pressure chamber side than the straight portion,

the nozzle in the tapered portion becomes larger in diameter toward the pressure chamber side,

in the first control, the central portion of the meniscus is pulled in until it enters the tapered portion.

6. The liquid discharge apparatus according to claim 1 or 2,

the liquid contains a filler.

7. The liquid discharge apparatus according to claim 1 or 2,

the liquid circulation device is provided with a circulation flow path which is communicated with the pressure chamber and circulates the liquid in the pressure chamber.

8. The liquid discharge apparatus according to claim 1 or 2,

the pressure changing unit includes a piezoelectric element and an expansion/displacement mechanism for expanding a displacement amount of the piezoelectric element.

9. The liquid discharge apparatus according to claim 1 or 2,

the nozzle, the pressure chamber and the pressure changing portion are provided with a plurality of sets,

the control unit controls each of the pressure varying units.

10. A liquid discharge method for discharging a liquid having a viscosity of 50 mPas or more from a nozzle, the liquid discharge method comprising:

a first step of drawing a central portion of a meniscus of the liquid in the nozzle toward the pressure chamber side by reducing the pressure of the liquid in a pressure chamber communicating with the nozzle by using a pressure changing portion that changes the pressure of the liquid in the pressure chamber, thereby forming a liquid film generated by the liquid on an inner wall surface of the nozzle;

a second step of increasing the pressure of the liquid in the pressure chamber by using the pressure changing section in a state where the liquid film is formed on the inner wall surface, and inverting the shape of the central portion of the meniscus to a convex shape toward the opening portion side of the nozzle on the opposite side of the pressure chamber to form a liquid column; and

a third step of raising the pressure of the liquid in the pressure chamber by using the pressure changing unit in a state where the center portion of the meniscus is formed in the convex shape toward the opening portion side of the nozzle, and discharging the liquid column from the center portion of the convex meniscus toward the opening portion side without contacting the liquid film.

Technical Field

The present invention relates to a liquid discharge device and a liquid discharge method.

Background

Various studies have been made to apply the ink jet technology to the formation of electrodes, the direct formation of various electrical components, the formation of light emitters and filters used in displays, the formation of microlenses, and the like. As the application of the ink jet technology expands, the kinds of liquid discharged from the nozzles also vary. For example, patent document 1 discloses a method of discharging a high-viscosity liquid from a nozzle.

Disclosure of Invention

According to an embodiment of the present invention, a liquid discharge device is provided. The liquid discharge device includes: a nozzle that discharges a liquid having a viscosity of 50 mPas or more; a pressure chamber in communication with the nozzle; a pressure changing unit that changes a pressure of the liquid in the pressure chamber; a control unit that controls the pressure change unit. The control unit drives the pressure changing unit to execute the following control: a first control of drawing a central portion of a meniscus of the liquid in the nozzle toward the pressure chamber side by reducing a pressure of the liquid in the pressure chamber, thereby forming a liquid film generated by the liquid on an inner wall surface of the nozzle; and a second control step of raising the pressure of the liquid in the pressure chamber in a state where the liquid film is formed on the inner wall surface, inverting the shape of the central portion of the meniscus toward the opening portion side of the nozzle on the opposite side of the pressure chamber to a convex shape to form a liquid column, and discharging the liquid column so as not to contact the liquid film from the central portion of the convex meniscus toward the opening portion side.

Drawings

Fig. 1 is an explanatory view showing a schematic configuration of a liquid discharge device according to a first embodiment.

Fig. 2 is an explanatory diagram showing a schematic configuration of the head portion in the first embodiment.

Fig. 3 is an explanatory diagram showing an example of a waveform of a driving voltage supplied to the piezoelectric element.

Fig. 4 is an explanatory view schematically showing a state of the meniscus in the nozzle in the initial state.

Fig. 5 is an explanatory view schematically showing a state of the meniscus in the nozzle in the first step.

Fig. 6 is an explanatory view schematically showing a state of the meniscus in the nozzle in the second step.

Fig. 7 is an explanatory view schematically showing a state of the meniscus in the nozzle in the third step.

Fig. 8 is an explanatory view schematically showing a state of the meniscus in the nozzle after the liquid is discharged.

Fig. 9 is an explanatory diagram showing the test results regarding the relationship between the number of capillaries and the virtual nozzle diameter.

Fig. 10 is another explanatory view schematically showing a state of the meniscus in the nozzle in the first step.

Fig. 11 is another explanatory view schematically showing a state of the meniscus in the nozzle in the first step.

Fig. 12 is an explanatory view showing a schematic configuration of a head having a circulation flow channel.

Fig. 13 is an explanatory view showing a schematic configuration of a head having a plurality of nozzles.

Description of the reference numerals

10 … storage tank; 20 … pressure pump; 30 … supply tube; 40 … head; 41 … a housing; 42 … supply flow path; 43. 43a, 43b, 43c … pressure chambers; 44. 44a, 44b, 44c … pressure change portions; 45 … piezoelectric element; 46 … circulation flow path; 50 … extended displacement mechanism; 51 … first partition wall; 52 … a first resilient member; 53 … accommodating chamber; 54 … second partition wall; 55 … a second elastic member; 60. 60a, 60b, 60c … nozzle; 61 … straight line portion; 62 … taper; 63 … inner wall surface; a 64 … nozzle opening; 71 … liquid film; 72 … liquid column; 73 … droplet; 90 … control section; 100 … liquid discharge device.

Detailed Description

A. The first embodiment:

fig. 1 is an explanatory diagram showing a schematic configuration of a liquid discharge device 100 according to a first embodiment. The liquid discharge device 100 includes a tank 10, a pressure pump 20, a supply pipe 30, a head 40, and a control unit 90.

The tank 10 contains a liquid. The liquid in the tank 10 is pressurized by the pressurizing pump 20 and supplied to the head 40 through the supply pipe 30. The pressurizing pump 20 in the present embodiment is a fixed displacement pump capable of supplying a liquid at a fixed flow rate. As the fixed displacement pump, a gear pump with less pulsation can be used. Further, for example, by providing a buffer tank for absorbing pulsation in a part of the supply pipe 30, various kinds of fixed displacement pumps of a diaphragm type or a plunger type can be used.

The liquid supplied to the head 40 through the supply pipe 30 is discharged through the head 40. The operation of the head 40 is controlled by the control unit 90. The control unit 90 can be realized by a computer including a processor such as a CPU, a main memory, and a nonvolatile memory, for example. A computer program for controlling the head 40 is stored in a nonvolatile memory in the control unit 90. The control unit 90 executes the computer program to realize the discharge of the liquid from the head unit 40 including the first step, the second step, and the third step, which will be described later.

In the present embodiment, the liquid discharged through the head 40 has a viscosity of 50mPa · s or more. The viscosity of the liquid is preferably in the range of 50 to 10000 mPas. The liquid may be a material in a state where the substance is in a liquid phase, and a liquid material such as a sol or a gel is also included in the liquid. In addition, not only a liquid as a state of a substance, but also a substance in which particles of a functional material composed of a solid material such as a pigment or metal particles are dissolved, dispersed, or mixed in a solvent, and the like are included in the liquid. Typical examples of the liquid include ink and liquid crystal emulsifier. The ink includes various liquid compositions such as general aqueous ink, oil-based ink, gel ink, and hot-melt ink.

Examples of the metal particles include Sn-Pb-based materials, Sn-Ag-Cu-based materials, Sn-Bi-based materials, Sn-Cu-Ni-based materials, Sn-Ag-Bi-In-based materials, Sn-Ag-Bi-Cu-based materials, Sn-Zn-based materials, and Sn-Zn-Bi-based materials.

Examples of the solvent include linear or branched aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons, halogen-substituted hydrocarbons thereof, and silicone oils. As an example, hexane, heptane, octane, isooctane, decane, isodecane, decahydronaphthalene, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, toluene, xylene, mesitylene, ISOPAR C, ISOPAR E, ISOPAR G, ISOPAR H, ISOPAR L, ISOPAR M (product name of ISOPAR: EXON Co.), SHELLSOL 70, SHELLSOL 71 (product name of SHELLSOL OIL Co.), AMSCO OMS, AMSCO 460 solvent (product name of AMSCO: SPIRITS Co.), KF-96L (product name of shin SILICON Co.) or the like may be used alone or in combination.

The particles are, for example, particles having any shape such as a spherical shape, a spheroid shape, or an irregular shape. The particle diameter refers to the size of particles obtained assuming that the particles have a spherical shape, and can be represented by the average particle diameter of the particulate material formed of the particles. The particle size distribution of the particulate material as the aggregate of particles can be obtained by a laser diffraction/scattering method, and can be obtained, for example, by using MICROTRAC FRA (manufactured by japan electronics corporation). The average particle diameter of the particles is a volume-average particle diameter determined from the particle diameter distribution of the particulate material thus obtained.

Fig. 2 is an explanatory diagram showing a schematic configuration of the head 40 in the first embodiment. The head 40 includes a nozzle 60 that discharges a liquid, a pressure chamber 43 that communicates with the nozzle 60, and a pressure changing portion 44 that changes the pressure of the liquid in the pressure chamber 43. The pressure changing portion 44 is controlled by the control portion 90.

The liquid supplied from the tank 10 to the head 40 flows into the pressure chamber 43 via the supply flow path 42. The liquid in the pressure chamber 43 is pressurized by the pressure changing portion 44 and discharged from the nozzle 60. In the present embodiment, the nozzle 60 includes a linear portion 61 and a tapered portion 62. The linear portion 61 has a nozzle opening 64 at an end opposite to the pressure chamber 43, and is a portion of the nozzle 60 where an angle between the central axis CL of the nozzle 60 and the inner wall surface 63 of the nozzle 60 is less than 5 degrees. The inner diameter of the linear part 61 is set within the range of 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 where the surface roughness of the inner wall surface 63 of the nozzle 60 and the irregularities generated by the machining traces processed at the time are averaged. The tapered portion 62 is a portion of the nozzle 60 that is provided on the pressure chamber 43 side of the linear portion 61 and in which the angle between the center axis CL of the nozzle 60 and the inner wall surface 63 of the nozzle 60 is 5 degrees or more. The inner diameter of the nozzle 60 in the tapered portion 62 increases toward the pressure chamber 43 side. The angle between the tangent to the inner wall surface 63 of the tapered portion 62 and the center axis CL of the nozzle 60 is preferably 45 degrees or less. The tapered portion 62 may be linear 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 linear portion 61 directly communicates with the pressure chamber 43.

The pressure changing unit 44 in the present embodiment includes a piezoelectric element 45 and an expanding displacement mechanism 50. The expanding and displacing mechanism 50 includes a first partition 51, a first elastic member 52, a housing chamber 53, a second partition 54, and a second elastic member 55. The piezoelectric element 45 expands and contracts in accordance with a voltage applied by the control unit 90. One end portion of the piezoelectric element 45 in the expansion and contraction direction is fixed to the case 41 of the head 40, and the other end portion of the piezoelectric element 45 in the expansion and contraction direction is fixed to the first partition 51. The outer peripheral edge of the first partition wall 51 is supported by the housing 41 via the first elastic member 52. A housing chamber 53 in which the working fluid is sealed is provided on the opposite side of the piezoelectric element 45 with the first partition wall 51 interposed therebetween. The working fluid in the present embodiment is a liquid having a predetermined viscosity in which a filler is dispersed. A second partition wall 54 is provided on the opposite side of the storage chamber 53 from the first partition wall 51. The outer peripheral edge of the second partition wall 54 is supported by the housing 41 via a second elastic member 55. The first partition wall 51 has a larger area in contact with the working fluid than the second partition wall 54. The working fluid is not limited to a liquid, and may be made of a material that exhibits fluidity when deformed by external pressure and exhibits the property of a fluid capable of transmitting pressure in all directions, such as a liquid. For example, the working fluid may be various rubber materials based on silicone rubber, or may be a gel having both fluidity and elasticity.

If the piezoelectric element 45 is displaced according to the voltage applied by the control unit 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 volume 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 is enlarged by the pascal principle. That is, the displacement amount of the second partition wall 54 is larger than the displacement amount of the first partition wall 51. Therefore, the change in the volume of the pressure chamber 43 is larger than in the case where the extended displacement mechanism 50 is not provided. The liquid in the pressure chamber 43 is pressurized by the reduction in volume of the pressure chamber 43. On the other hand, the liquid in the pressure chamber 43 is decompressed by the volume expansion of the pressure chamber 43. The expanding and displacing mechanism 50 is not limited to the above-described embodiment, and various embodiments can be adopted. For example, the displacement of the piezoelectric element 45 may be increased by a lever, and the volume of the pressure chamber 43 may be changed by deforming a vibration plate constituting a wall surface of the pressure chamber 43 by the lever.

Fig. 3 is an explanatory diagram showing an example of a waveform of the drive voltage supplied to the piezoelectric element 45 by the control unit 90. Fig. 3 shows a drive waveform for performing one cycle of discharge of the liquid from the nozzle 60. The drive waveform includes a pull-in waveform portion W1 for depressurizing the liquid in the pressure chamber 43 and a push-out waveform portion W2 for pressurizing the liquid in the pressure chamber 43. First, the control section 90 supplies the pull-in waveform portion W1 to the piezoelectric element 45. By supplying the pull-in waveform portion W1, the piezoelectric element 45 is displaced in the direction of shrinking, the volume of the pressure chamber 43 is expanded, and the liquid in the pressure chamber 43 is decompressed. Next, the control section 90 supplies the pushed-out waveform portion W2 to the piezoelectric element 45. By supplying the push-out waveform portion W2, the piezoelectric element 45 is displaced in the expansion direction, the volume of the pressure chamber 43 is reduced, the liquid in the pressure chamber 43 is pressurized, and the liquid is discharged from the nozzle 60.

Fig. 4 to 8 are explanatory views schematically showing the operation of the meniscus in the nozzle 60 when the liquid is discharged from the nozzle 60 in the present embodiment. In fig. 4 to 8, the inside of the nozzle 60 is shown as a cross-sectional view including the center axis CL of the nozzle 60. Fig. 4 shows a meniscus state in the nozzle 60 in an initial state. In the initial state, since no pressure change occurs in the liquid in the pressure chamber 43, the outer peripheral edge of the meniscus is positioned at the nozzle opening 64, and the central portion M of the meniscus is positioned closer to the pressure chamber 43 than the nozzle opening 64 in the nozzle 60 due to surface tension.

Fig. 5 shows a state of the meniscus in the nozzle 60 in the first step. First, in the first step, the control unit 90 supplies the pull-in waveform portion W1 to the piezoelectric element 45, and lowers the pressure of the liquid in the pressure chamber 43, thereby pulling the central portion M of the meniscus toward the pressure chamber 43 side and causing the liquid film 71 generated by the liquid to stay on the inner wall surface 63 of the nozzle 60. In fig. 5, the central portion M of the meniscus is drawn into the linear portion 61. By forming the liquid film 71 on the inner wall surface 63 of the nozzle 60, it is considered that a virtual nozzle generated by the liquid film 71 is formed in the nozzle 60. In the present specification, the virtual nozzle formed by the liquid film 71 is also referred to as a virtual nozzle. The virtual nozzle diameter Dp is equal to or smaller than the nozzle diameter D minus 2 times the thickness tm of the liquid film 71 formed on the inner wall surface 63 of the nozzle 60. As will be described later, the virtual nozzle diameter Dp is a diameter equal to or smaller than two-thirds of the nozzle diameter D. A method of calculating the thickness tm of the liquid film 71 formed on the inner wall surface 63 of the nozzle 60 will be described later. In this specification, the first step in which the control unit 90 controls the piezoelectric element 45 is also referred to as a first control.

Fig. 6 shows a state of the meniscus in the nozzle 60 in the second step. In the second step, the control unit 90 supplies the pushed waveform portion W2 to the piezoelectric element 45 in a state where the liquid film 71 is formed on the inner wall surface 63 of the nozzle 60, that is, in a state where a dummy nozzle is formed. The pressure of the liquid in the pressure chamber 43 is increased by the piezoelectric element 45, and the shape of the central portion M of the meniscus is inverted to a convex shape toward the nozzle opening 64 side. The magnitude and speed of the pressure change applied to the liquid in the pressure chamber 43 required at this time are substantially equal to the magnitude and speed of the pressure change required to discharge the liquid from the nozzle 60 without forming the dummy nozzle. Since the resistance of the central portion M of the meniscus is smaller than that of the liquid in contact with the inner wall surface 63 of the nozzle 60, if the shape of the central portion M of the meniscus is inverted to a convex shape toward the nozzle opening 64 side, the pressurized liquid starts to concentrate toward the central portion M of the convex meniscus.

Fig. 7 shows the meniscus state in the nozzle 60 in the third step. In the third step, the controller 90 continues to supply the waveform portion W2 to the piezoelectric element 45 in a state where the central portion M of the meniscus is convex toward the nozzle opening 64. The pressure of the liquid in the pressure chamber 43 is increased by the piezoelectric element 45, and a liquid column 72 is formed in the center portion M of the convex meniscus toward the nozzle opening 64, and the liquid column 72 is discharged from the nozzle 60 without contacting the liquid film 71. Since the resistance of the central portion M of the meniscus is smaller than that of the liquid in contact with the inner wall surface 63 of the nozzle 60, the speed of movement of the central portion M of the meniscus of the liquid column 72 toward the nozzle opening 64 side is faster than the speed of movement of the liquid in the liquid film 71 formed on the inner wall surface 63 of the nozzle 60 toward the nozzle opening 64 side. Since the liquid column 72 is pushed out so as not to contact the liquid film 71, the discharged liquid column 72 has a diameter smaller than two-thirds of the inner diameter of the nozzle 60 in the radial direction of the nozzle 60 when passing through the nozzle opening 64. In this specification, the second step and the third step performed by the control unit 90 controlling the piezoelectric element 45 are also referred to as second control.

Fig. 8 shows the meniscus state in the nozzle 60 after the third step. After the third step, the liquid column 72 discharged to the outside of the nozzle 60 flies as droplets 73. Thereafter, the meniscus state of the liquid remaining in the nozzle 60 returns to the initial state. The liquid column 72 may be formed into the droplets 73 in the nozzle 60 and the droplets 73 may be discharged to the outside of the nozzle 60, or the liquid column 72 discharged to the outside of the nozzle 60 may be formed into the droplets 73 and may fly in the form of the liquid column 72. After the liquid column 72 is discharged from the nozzle 60, the control unit 90 may supply the pull-in wavy portion W1 to the piezoelectric element 45, reduce the pressure of the liquid in the pressure chamber 43, and cut the discharged liquid column 72.

In the first step, the speed at which the central portion M of the meniscus moves toward the pressure chamber 43 is preferably such a speed that the liquid film 71 is formed on the inner wall surface 63 of the nozzle 60 and no cavitation occurs in the liquid in the nozzle 60. The cavitation phenomenon is also called cavitation. In the first step, the speed at which the central portion M of the meniscus is drawn in can be set according to the type of liquid to be discharged, the nozzle diameter D, and the like. For example, in the third step, the speed of the discharged liquid moving toward the nozzle opening 64 can be reduced by 2 to 100 times.

In the first step, the speed at which the central portion M of the meniscus moves toward the pressure chamber 43 is obtained by capturing an image of the movement of the central portion M of the meniscus drawn in from the side of the nozzle 60 in a predetermined period by a strobe, and using the plurality of images obtained, the speed is calculated from the average speed from the time when the central portion M of the meniscus starts moving along the center axis CL of the nozzle 60 to the time when the movement is stopped. In the third step, the speed at which the discharged liquid moves toward the nozzle opening 64 is obtained by capturing images of the movement of the center M of the meniscus of the liquid column 72 or the tip M1 of the liquid droplet 73 pushed out from the center M of the convex meniscus from the side of the nozzle 60 in a predetermined cycle by stroboscopic light, and using the plurality of obtained images, the average speed from the center M of the meniscus of the liquid column 72 or the tip M1 of the liquid droplet 73 to the center M of the meniscus of the liquid column 72 or the tip M1 of the liquid droplet 73 before the nozzle opening 64 starts moving along the center axis CL of the nozzle 60 is calculated.

In the third step, the flying speed of the liquid discharged to the outside of the nozzle 60 is obtained by taking an image of the movement of the center M of the meniscus of the liquid column 72 or the tip M1 of the droplet 73 pushed out from the center M of the convex meniscus from the side of the nozzle 60 in a predetermined cycle by a strobe, and using the obtained plurality of images, the flying speed is calculated from the average speed after the center M of the meniscus of the liquid column 72 or the tip M1 of the droplet 73 appears outside the nozzle 60 and after the droplet has moved from the nozzle opening 64 by a distance of 0.5mm along the center axis CL of the nozzle 60. However, the image in which the center M of the meniscus of the liquid column 72 or the tip M1 of the droplet 73 is moved from the nozzle opening 64 by a distance of 1.0mm or more along the center axis CL of the nozzle 60 is not used for calculating the average velocity.

As shown in fig. 5, the thickness tm of the liquid film 71 formed on the inner wall surface 63 of the nozzle 60 is an average thickness obtained by the following method. First, the state of the liquid in the nozzle 60 is photographed from the side of the nozzle 60 by a strobe, and a portion of a curve satisfying any of the following conditions (a) to (C) among curves indicated by the meniscus is obtained in the obtained two-dimensional image. (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. The term "infinite" as used herein means that the radius of curvature of the meniscus is 100 times or more 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. The maximum radius of the nozzle 60 is the maximum of the radius of the tapered portion 62 in the case where the nozzle 60 has the linear portion 61 and the tapered portion 62. In the portion of the curve thus obtained, the end on the nozzle opening 64 side is point a, and the end on the pressure chamber 43 side is point B. Next, the area S of the region surrounded by the perpendicular line passing through the center axis CL of the point a, the perpendicular line passing through the center axis CL of the point B, the inner wall surface 63 of the nozzle 60, and the meniscus is obtained. The thickness tm of the liquid film 71 is obtained by dividing the area S of this region by the distance L between the point a and the point B in the direction along the center axis CL of the nozzle 60. As shown in fig. 6, the minimum diameter of the virtual nozzle between the center M of the convex meniscus and the point a in the direction along the center axis CL of the nozzle 60 is the virtual nozzle diameter Dp.

In the first step, the thickness tm of the liquid film 71 formed on the inner wall surface 63 of the nozzle 60 may be any thickness with respect to the nozzle diameter D as long as the liquid column 72 does not contact the liquid film 71 in the second step and the third step. In the first step, the thickness tm of the liquid film 71 formed on the inner wall surface 63 of the nozzle 60 is preferably 20% or less with respect to the nozzle diameter D.

When passing through the nozzle opening 64, the diameter of the discharged liquid column 72 or liquid droplet 73 in the radial direction of the nozzle 60 can be examined by taking an image of the movement of the liquid column 72 or liquid droplet 73 pushed out from the center M of the convex meniscus from the side of the nozzle 60 in a predetermined period by means of stroboscopic light, and measuring the maximum diameter of the liquid column 72 or liquid droplet 73 passing through the nozzle opening 64 using a plurality of obtained images.

Fig. 9 is a graph showing the test results of examining the relationship between the capillary number Ca and the ratio of the virtual nozzle diameter Dp to the nozzle diameter D. In this test, the state of the liquid in the nozzle 60 during the first step, the second step, and the third step is photographed from the side of the nozzle 60 in a predetermined cycle by using a strobe, and the thickness tm of the liquid film 71 is calculated using the obtained images. The diameter obtained by subtracting 2 times the calculated thickness tm of the liquid film 71 from the nozzle diameter D is assumed as the virtual nozzle diameter Dp. In this test, the liquid discharge apparatus 100 in which the nozzle 60 is made of a transparent acrylic resin was used so that the state of the liquid in the nozzle 60 could be photographed by stroboscopic imaging. The test was carried out at ambient temperature of 25 ℃. As the liquid, glycerin having a viscosity of 800mPa · s at normal temperature was used. The capillary number Ca is determined by the following equation (1) using the viscosity η of the liquid, the speed V of drawing in the central portion M of the meniscus, and the surface tension σ of the liquid.

Ca＝η×V/σ…(1)

In fig. 9, a point P1 indicated by a circle mark indicates the test result in the case where the nozzle diameter D is 160 μm. The point P2 indicated by a triangular mark indicates the test result in the case where the nozzle diameter D is 210 μm. The point P3 marked by a diamond indicates the test results in the case where the nozzle diameter D was 310 μm. In fig. 9, the relationship between the capillary number Ca and the ratio of the virtual nozzle diameter Dp to the nozzle diameter D when the thickness tm of the liquid film 71 is calculated using the following expression (2) is shown by a curve. In this graph, a diameter obtained by subtracting a value obtained by multiplying 2 times the thickness tm of the liquid film 71 calculated by the following expression (2) from the nozzle diameter D is defined as the virtual nozzle diameter Dp. The thickness tm of the liquid film 71 obtained by the test approximately corresponds to the following formula (2).

tm＝1.34×Ca^2/3/(1+1.34×2.5×Ca^2/3)…(2)

According to the test results, the virtual nozzle diameter Dp becomes smaller as the capillary number Ca increases. In the range where the capillary number Ca is 2 or more, the virtual nozzle diameter Dp is a diameter of two thirds or less of the nozzle diameter D without being affected by the size of the nozzle diameter D.

According to the liquid discharge device 100 of the present embodiment described above, the virtual nozzle generated by the liquid film 71 is formed in the nozzle 60, and the liquid is discharged from the virtual nozzle. Since the resistance in the dummy nozzle is smaller than the vicinity of the inner wall surface 63 of the nozzle 60, the diameter of the nozzle 60 for discharging the liquid in the radial direction can be made smaller than the dummy nozzle diameter Dp while reducing the energy loss of the discharged liquid. Therefore, a liquid having a high viscosity and a small diameter can be stably discharged.

In the present embodiment, since the liquid column 72 discharges the liquid from the virtual nozzle without contacting the liquid film 71, energy loss of the discharged liquid can be reduced. Therefore, the flying speed of the discharged liquid can be increased.

In addition, in the present embodiment, since the liquid is discharged from the virtual nozzle formed by the liquid film 71, even when the liquid containing the material having a relatively large particle diameter is discharged, the clogging of the nozzle 60 can be suppressed.

In the present embodiment, the virtual nozzle diameter Dp is equal to or less than two thirds of the nozzle diameter D, and the liquid is discharged from the virtual nozzle without contacting the liquid film 71 forming the virtual nozzle. Therefore, it is possible to discharge a liquid having a diameter less than two thirds of the nozzle diameter D.

In the present embodiment, the speed at which the central portion M of the meniscus moves toward the pressure chamber 43 in the first step is set to be slower than the speed at which the liquid discharged in the third step moves toward the nozzle opening 64. Therefore, when the central portion M of the meniscus is pulled in, the occurrence of cavitation in the liquid can be suppressed, and discharge failure of the liquid from the nozzle 60 can be suppressed.

In the present embodiment, the length by which the central portion M of the meniscus is drawn in the first step is set within the linear portion 61. Therefore, the pressure change in the pressure chamber 43 required for drawing the central portion M of the meniscus can be reduced, and the pressure changing portion 44 can be downsized. Further, when the central portion M of the meniscus is pulled in, it is possible to suppress air bubbles from being mixed into the pressure chamber 43.

In the present embodiment, since the pressure changing unit 44 includes the expanding displacement mechanism 50, a larger pressure change can be generated with respect to the liquid in the pressure chamber 43. Therefore, the central portion M of the meniscus can be drawn more largely, and the pressurized liquid can be concentrated more on the central portion M of the convex meniscus.

B. Other embodiments are as follows:

(B-1) in the liquid discharge device 100 according to the first embodiment, the pressure changing unit 44 includes the expansion/displacement mechanism 50. In contrast, the pressure changing unit 44 may not include the expanding displacement mechanism 50. In this case, the pressure changing portion 44 may be a type of diaphragm including, for example, the piezoelectric element 45 and a wall surface constituting the pressure chamber 43. In this embodiment, the volume of the pressure chamber 43 can be changed by expansion and contraction of the piezoelectric element 45 fixed to the diaphragm. The method of pressurizing the liquid in the pressure chamber 43 is not limited to the piezoelectric method described above, and may be a thermal method of pressurizing the liquid by generating bubbles in the pressure chamber 43, or a valve method of pressurizing the pressure chamber 43 by an electromagnetic valve and a valve and discharging the liquid.

(B-2) in the liquid discharge apparatus 100 according to the first embodiment, as shown in FIG. 5, the controller 90 draws the central portion M of the meniscus into the linear portion 61 so that the liquid film 71 becomes thicker from the point A toward the point B in the first step. In contrast, as shown in fig. 10, the controller 90 may draw the central portion M of the meniscus into the linear portion 61 so that the liquid film 71 near the point B is thinner than the liquid film 71 between the point a and the point B in the first step. As shown in fig. 11, the control unit 90 may draw the central portion M of the meniscus beyond the linear portion 61 into the tapered portion 62 in the first step. In this case, since the liquid in the vicinity of the tapered portion 62 can be stirred, the liquid in the vicinity of the tapered portion 62 can be suppressed from thickening. Further, since the distance over which the liquid is accelerated by the pressurization is increased in the second step to the third step, the liquid can be discharged at a high speed. In the first step, the position to which the central portion M of the meniscus is drawn may be any position as long as the second step and the third step can be realized. The inversion of the central portion M of the meniscus in the second step may be performed in the tapered portion 62 or in the linear portion 61 when the central portion M of the meniscus is drawn into the tapered portion 62 in the first step.

(B-3) in the liquid discharge device 100 according to the first embodiment, the liquid discharged from the nozzle 60 may contain a filler. Depending on the kind of the filler contained in the liquid, an effect of achieving good color developability or the like can be obtained in addition to suppressing volume shrinkage of the liquid. The content of the filler in the liquid may be, for example, 50 mass% or more.

(B-4) As shown in FIG. 12, in the liquid discharge device 100 according to the first embodiment, the head 40 may be provided with the circulation channel 46 communicating with the tapered portion 62 of the nozzle 60. The liquid that flows into the circulation flow path 46 without being discharged from the nozzle 60 is circulated from the supply flow path 42 into the pressure chamber 43 by the pressure of a pump or the like. In this case, since the flow of the liquid from the pressure chamber 43 to the circulation flow path 46 can be generated, the thickening of the liquid from the inside of the pressure chamber 43 to the nozzle 60 can be suppressed. Preferably, the thickness tm of the liquid film 71 is measured not on the side of the circulation flow path 46 where the opening is provided, but on the side of the circulation flow path 46 where the opening is not provided. The liquid flowing into the circulation flow path 46 may be discharged to a waste liquid tank or the like without circulating in the pressure chamber 43. The circulation flow path 46 may communicate with the pressure chamber 43 and the linear portion 61 of the nozzle 60.

(B-5) As shown in FIG. 13, in the liquid discharge device 100 of the first embodiment, the head 40 includes a pair of nozzles 60, a pressure chamber 43, and a pressure changing portion 44. In contrast, the head 40 may be provided with a plurality of sets of the nozzles 60a, 60b, and 60c, the pressure chambers 43a, 43b, and 43c, and the pressure changing portions 44a, 44b, and 44 c. In this case, a liquid having a high viscosity and a small diameter can be stably discharged from the plurality of nozzles 60a, 60b, and 60 c.

(B-6) in the first embodiment, the state of the liquid inside the nozzle 60 and outside the nozzle 60 is photographed from the side of the nozzle 60 using a strobe, but the photographing may be performed from a direction along the center axis CL of the nozzle 60. Further, the image may be captured and measured by a high-speed camera or a laser displacement meter.

C. Other modes are as follows:

the present invention is not limited to the above-described embodiments, and can be implemented in various forms without departing from the spirit thereof. For example, the present invention can be realized in the following manner. Technical features in the above-described embodiments that correspond to technical features in the respective embodiments described below can be appropriately replaced or combined in order to solve part or all of the technical problems of the present invention or achieve part or all of the effects of the present invention. In addition, if this technical feature is not necessarily described in the present specification, deletion can be appropriately performed.

(1) According to an embodiment of the present invention, a liquid discharge device is provided. The liquid discharge device includes: a nozzle that discharges a liquid having a viscosity of 50 mPas or more; a pressure chamber in communication with the nozzle; a pressure changing unit that changes a pressure of the liquid in the pressure chamber; a control unit that controls the pressure change unit. The control unit drives the pressure changing unit to execute the following control: a first control of drawing a central portion of a meniscus of the liquid in the nozzle toward the pressure chamber side by reducing a pressure of the liquid in the pressure chamber, thereby forming a liquid film generated by the liquid on an inner wall surface of the nozzle; and a second control step of raising the pressure of the liquid in the pressure chamber in a state where the liquid film is formed on the inner wall surface, inverting the shape of the central portion of the meniscus toward the opening portion side of the nozzle on the opposite side of the pressure chamber to a convex shape to form a liquid column, and discharging the liquid column so as not to contact the liquid film from the central portion of the convex meniscus toward the opening portion side.

According to the liquid discharge device of this aspect, since the resistance inside the liquid film in the nozzle is smaller than the vicinity of the inner wall surface of the nozzle, the diameter of the liquid discharged in the radial direction of the nozzle can be made smaller than the diameter inside the liquid film while reducing the energy loss of the discharged liquid. Therefore, a liquid having a high viscosity and a small diameter can be stably discharged.

(2) In the liquid discharge device according to the above aspect, the diameter of the discharged liquid column in the radial direction of the nozzle may be smaller than two-thirds of the inner diameter of the nozzle when the liquid column passes through the end surface of the nozzle on the opening portion side.

According to the liquid discharge device of this aspect, since the inside diameter of the liquid film formed in the nozzle is two thirds of the inner diameter of the nozzle, it is possible to discharge the liquid having the diameter of two thirds of the inner diameter of the nozzle.

(3) In the liquid discharge apparatus of the above aspect, a speed at which the central portion of the meniscus moves toward the pressure chamber side in the first control may be slower than a speed at which the liquid column discharged in the second control moves toward the nozzle opening portion side.

According to the liquid discharge apparatus of this aspect, when the meniscus is drawn in, cavitation in the liquid can be suppressed, and therefore, a discharge failure of the liquid from the nozzle can be suppressed.

(4) In the liquid discharge apparatus according to the above aspect, the nozzle may have a straight portion and a tapered portion provided on the pressure chamber side with respect to the straight portion, and a diameter of the nozzle in the tapered portion may be larger toward the pressure chamber side.

According to the liquid discharge device of this aspect, since the pressure change in the pressure chamber required when drawing in the meniscus can be reduced, the pressure change portion can be made smaller. Further, when the meniscus is drawn in, it is possible to suppress the mixing of air bubbles into the pressure chamber.

(5) In the liquid discharge apparatus according to the above aspect, the nozzle may have a straight portion and a tapered portion provided on the pressure chamber side with respect to the straight portion, and a diameter of the nozzle in the tapered portion may be larger toward the pressure chamber side.

According to the liquid discharge device of this aspect, since the liquid in the vicinity of the tapered portion can be stirred, thickening of the liquid in the vicinity of the tapered portion can be suppressed. Further, since the distance over which the liquid is pressurized and accelerated becomes long, the liquid can be discharged at a high speed.

(6) In the liquid discharge device of the above aspect, the liquid may contain a filler.

According to the liquid discharge device of this aspect, depending on the type of the filler contained in the liquid, in addition to suppressing the volume shrinkage of the liquid, an effect of achieving good color developability or the like can be obtained.

(7) In the liquid discharge device according to the above aspect, a circulation flow path that communicates with the pressure chamber and circulates the liquid in the pressure chamber may be provided.

According to the liquid discharge device of this aspect, since the flow of the liquid from the pressure chamber to the circulation flow path can be generated, thickening of the liquid from the pressure chamber to the nozzle can be suppressed.

(8) In the liquid discharge device according to the above aspect, the pressure changing portion may include a piezoelectric element and an expansion/displacement mechanism that expands a displacement amount of the piezoelectric element.

According to the liquid discharge device of this aspect, since a pressure change larger than that in the pressure chamber can be generated, the liquid can be drawn more into the central portion of the meniscus, and the pressurized liquid can be concentrated more on the convex central portion of the meniscus.

(9) In the liquid discharge device according to the above aspect, the plurality of sets of the nozzles, the pressure chambers, and the pressure changing portions may be provided, and the control portion may control each of the pressure changing portions.

According to the liquid discharge device of this aspect, it is possible to stably discharge a liquid having a high viscosity and a small diameter from the plurality of nozzles.

The present invention can be realized by various means other than the liquid ejecting apparatus. For example, the present invention can be realized by a liquid discharge method, a liquid discharge head, a computer program for realizing the control method, a non-transitory recording medium for recording the computer program, and the like.