Ink ejection method

Abstract

Provided are an ink ejection method and an inkjet head capable of stably ejecting ink while securing the width between the ejection surface and the landing surface. The ink ejection method is performed by an inkjet head including a nozzle (N) and an ink flow path communicating with the nozzle (N), and the ink flow path includes a pressure chamber (12) that imparts pressure fluctuations to the ink inside. The inkjet head has an ink viscosity of 5.7 mPa·s, a density of 1080 kg / m 3 When the surface tension is 41 mN / m and the speed of sound is 1521 m / s, the Q value related to the pressure vibration of the ink in the pressure chamber (12) is 10 or more and 18 or less, the resonance period related to the meniscus vibration of the ink in the nozzle (N) is 1 to 6 times the resonance period related to the pressure vibration, the opening diameter of the nozzle (N) is 20 μm or more, and the width between the ink ejection surface and the ink landing surface of the inkjet head is 5.0 mm or more.

Description

Technical Field

[0001] The present disclosure relates to an ink ejection method to the law .

Background Art

[0002] There is an inkjet head that ejects ink and lands it on a medium. An image, a film, or the like is formed on the medium by the landed ink. There are demands for higher precision and higher speed of formation. For higher precision and higher speed, stable ejection is required for the inkjet head. Patent Document 1 discloses a technique for stabilizing a meniscus. The meniscus is the ink liquid surface in the nozzle.

[0003] The inkjet head makes ink droplets fly and land on a medium. In this ink droplet, minute droplets may be generated in addition to the main droplet (main droplet). The minute droplets are called satellites. When the satellites adhere to a position different from that of the main droplet, the quality deteriorates.

[0004] There is a width between the ink ejection surface and the ink landing surface of the medium. If this width is wide, an image or the like can be recorded on a medium with unevenness. Also, when there are variations in the thickness, warpage, or bending of the medium, the wider the width, the lower the risk of the medium coming into contact with the ink ejection surface. Therefore, the ink ejection surface is less likely to be damaged.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, if the width between the ink ejection surface and the ink landing surface of the medium is wide, the attachment positions of the satellites are likely to vary. Further, if an attempt is made to reduce the satellites with the above width widened, the meniscus is difficult to stabilize.

[0007] An object of the present disclosure is to provide an ink ejection method capable of stably ejecting ink while securing the width between the ejection surface and the landing surface. the law This is to be provided.

Means for Solving the Problems

[0008] To achieve the above object, one aspect of the present disclosure is An inkjet head including a nozzle and an ink flow path communicating with the nozzle, the ink flow path including a pressure chamber that applies pressure fluctuations to the internal ink, and an ink ejection method using the inkjet head, The inkjet head is When the viscosity of the ejected ink is 5.7 mPa·s, the density is 1080 kg / m 3 , the surface tension is 41 mN / m, and the speed of sound is 1521 m / s, The Q value related to the pressure vibration of the ink in the pressure chamber is 10 or more and 18 or less, The resonance period related to the meniscus vibration of the ink in the nozzle is 1 time or more and 6 times or less of the resonance period related to the pressure vibration of the ink in the pressure chamber, The opening diameter of the nozzle or a diameter equivalent to the opening diameter is 20 μm or more, The width between the ink ejection surface and the ink landing surface of the inkjet head is set to 5.0 mm or more.

Advantages of the Invention

[0009] According to the present disclosure, there is an effect that ink can be stably ejected while securing the width between the ejection surface and the landing surface of the inkjet head.

Brief Description of the Drawings

[0010]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6A

Figure 6B

Figure 7A

Figure 7B

Figure 8A

Figure 8B

Figure 9A

Figure 9B

Figure 10A

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Figure 11A

Figure 11B

Figure 12A

Figure 12B

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments will be described with reference to the drawings. [First Embodiment] FIG. 1A is a cross-sectional view including a nozzle N of an inkjet head 1 according to the first embodiment. FIG. 1B is a diagram showing an equivalent circuit of the inkjet head 1 according to the first embodiment. As shown in the cross-sectional view of FIG. 1A, the inkjet head 1 discharges ink from the nozzle N. An ink flow path for supplying ink to the nozzle N communicates. The ink flow path includes a pressure chamber 12 and an upper communication path 13. Ink is sent from an ink tank to a common supply path (not shown). The ink in the common supply path is supplied to the pressure chamber 12 via the upper communication path 13. The upper communication path 13 may include a constriction where the opening diameter is partially narrowed to restrict the inflow amount of ink.

[0012] A diaphragm 16 faces the pressure chamber 12. Along the diaphragm 16, a piezoelectric element 15 is located. When the piezoelectric element 15 deforms in a bending mode, the diaphragm 16 vibrates. The pressure chamber 12 changes in size according to the vibration of the diaphragm 16. According to this size variation, pressure variation is applied to the ink. The piezoelectric element 15 is, for example, lead zirconate titanate (PZT) or the like.

[0013] As shown in the equivalent circuit of FIG. 1B, the nozzle N is represented by a combination of a capacitor Cn, a resistor element Rn, and an inductor Ln. The pressure chamber 12 is represented by a combination of resistor elements R1, R2 and inductors L1, L2. Also, the pressure chamber 12 has capacitors C1, Ce1 in parallel with the ground plane. The combination of circuit components is the same in the following embodiments.

[0014] The resistor elements R1, R2 represent the flow path resistance of the ink flow path. The resistor elements R1, R2 may be collectively represented by a single resistor element. The inductors L1, L2 represent the inertia of the ink flow path. The inductors L1, L2 may be collectively represented by a single inductor. The capacitor C1 represents the elastic compliance of the ink. The capacitor Ce1 represents the elastic compliance of the wall surface of the pressure chamber 12. The pressure chamber 12 has elasticity related to the deformation of the piezoelectric element 15 and the diaphragm 16. The compliance corresponding to this elasticity is the above capacitor Ce1. The pressure chamber 12 is, for example, rectangular parallelepiped in shape, but is not limited thereto. For example, the pressure chamber 12 may be a rectangular shape with rounded corners or rounded in a plan view of the pressure chamber 12 viewed from above, that is, in the direction from the top to the bottom of the figure.

[0015] The upper communication path 13 has a length and width (shape) different from those of the pressure chamber 12. Therefore, the upper communication path 13 is represented by a circuit component with parameters separate from those of the pressure chamber 12. The upper communication path 13 is represented by a combination of resistor elements R3, R4 and inductors L3, L4. The resistor elements R3, R4 may be collectively represented by a single resistor element. The inductors L3, L4 may be collectively represented by a single inductor. The upper communication path 13 has capacitors C3, Ce3 between it and the ground plane. Capacitor C3 is the elastic compliance of the ink. Capacitor Ce3 is the elastic compliance of the wall surface of the upper communication path 13. A thin-walled portion (compliance plate) for vibration pressure absorption may be located on the wall surface of the upper communication path 13. The compliance plate may be made of polyimide or various thin plates. The upper communication path 13 is, for example, in a circular cylindrical shape in a cross-sectional view perpendicular to the flow direction of the ink, i.e., the vertical direction in the figure, but is not limited thereto. Also, when the upper communication path 13 does not have a compliance plate, it may be regarded as a rigid body. That is, the capacitance of capacitor Ce3 is negligibly large and can be treated as substantially zero.

[0016] Among the circuit components representing the upper communication path 13, the circuit component representing the pressure chamber 12, and the circuit component representing the nozzle N, the resistor element and the inductor are connected in series. The capacitors are arranged in parallel between the series portion and the ground plane. The resonance period of this equivalent circuit includes a resonance period Tm corresponding to the volume fluctuation of the ink and a resonance period Tc corresponding to the pressure fluctuation of each ink flow path portion and the whole. The volume fluctuation of the ink corresponds to the fluctuation of the liquid surface (meniscus) position in the nozzle N. That is, the resonance period Tm is also the resonance period related to the meniscus vibration. The liquid surface position referred to here can be located not only inside the nozzle N but also temporarily outside the nozzle N as the ink is ejected.

[0017] To the piezoelectric element 15, for example, a drive signal including a drive pulse having a length of half the resonance period Tc is applied substantially in synchronization with the resonance period Tc of the pressure fluctuation in the pressure chamber 12. Residual vibrations occur in the pressure vibration of the ink in the pressure chamber 12 and the volume vibration of the ink in the ink flow path even after the application of the drive signal. In the case of the multi-drop method in which the drive pulse is applied a plurality of times within the drive period related to the recording of one dot, new pressure fluctuations are superimposed on the residual vibrations. Therefore, the amplitude corresponding to the second and subsequent times of the plurality of drive pulses increases compared to the amplitude of the first time.

[0018] In the actual volume vibration and pressure vibration, vibrations related to their respective resonances are mixed. Further, in the volume vibration and pressure vibration, vibration components corresponding to the resonance of the upper communication path 13 and the resonance of the entire ink flow path may also be mixed. The period of the volume vibration of the ink is different from the period of the pressure vibration. Here, the resonance period Tm of the volume vibration is longer than the resonance period Tc of the pressure vibration in the pressure chamber 12. Therefore, the position of the meniscus corresponding to the volume vibration is displaced from the position corresponding to the vibration at the resonance period Tc by the resonance period Tm. When the resonance period Tm becomes long, in the vicinity of the maximum of the vibration component due to the resonance period Tm, the ink liquid surface is maintained in a state of protruding greatly from the opening of the nozzle N for a long time. As a result, the ink overflows onto the nozzle opening surface (ink ejection surface). This overflow has an adverse effect on the ejection of the ink.

[0019] FIG. 2 is a diagram showing a calculation example by numerical simulation of the vibration pattern of the ink pressure in the pressure chamber 12 and its frequency spectrum. This FIG. 2 is an example at the time of ink ejection by a combination of an inkjet head and ink having a resonance period Tc = 5.36 μs, a resonance period Tm = 26.78 μs, a Q value Qc = 12.6, and a Q value Qm = 2.03. Qc and Qm will be described later. For the ink ejection, a multi-drop method is used in which droplets of about 3 pL per shot are continuously ejected eight times at intervals of the resonance period Tc related to the pressure vibration and landed at one pixel position (thin dotted line). Each drive pulse is a pull-in pulse having an amplitude of about 250 kPa with a half-cycle width of the resonance period Tc.

[0020] The pressure in the pressure chamber 12, i.e., the capacitor Ce, can be calculated as the amount of deformation of the piezoelectric element 15 accompanying the pressure fluctuation, i.e., the output voltage. A plurality of modes are further superimposed on the obtained waveform.

[0021] In FIG. 2A, the pressure vibration at the point Pc in FIG. 1B is indicated by a thick dotted line. This vibration is a damped vibration in which the amplitude of the sine wave vibration mainly corresponding to the resonance period Tc increases with the drive pulse and decays after the end of the drive pulse. As is well known, the damped vibration is represented by the product of the initial amplitude, the damping term, and the vibration component, and the damping becomes faster as the damping coefficient ζ of the damping term increases toward 1.

[0022] In the frequency spectrum shown in FIG. 2B, a peak clearly appears at the resonance frequency fc = 1 / Tc. The resonance period Tc is specified by the position of this peak. Also, a small peak appears at the resonance frequency fm = 1 / Tm. In FIG. 2B, the frequencies fcl and fch indicate the positions where the spectral intensity of the amplitude becomes 1 / √2 of the peak spectral intensity. That is, the distance between the frequencies fch and fcl indicates the half-value width of the vibration energy of the pressure vibration.

[0023] From the result of superimposing waves of the above plurality of modes, the component of the resonance frequency fc is extracted, thereby obtaining the characteristics of the vibration at the resonance frequency fc. For example, for the waveform shown by the thick dotted line in FIG. 2A, only the vibration near the resonance period Tc of interest may be extracted by a band-pass filter (BPF; Band Pass Filter) or the like. Alternatively, components outside the band including the resonance frequency fc, for example, components outside the range of the above half-value width, may be eliminated from the frequency spectrum obtained from the above result by Fourier transform. The frequency spectrum in which the vibration of the target frequency band is selectively extracted is inverse Fourier-transformed to obtain the time change of the pressure vibration of the specific target. In FIG. 2A, the vibration waveform due to the pressure vibration at the period Tc after such processing is shown by a solid line. Since the original vibration waveform mostly has components corresponding to the resonance period Tc, the vibration waveform is almost the same before and after applying the BPF. In the waveform after this BPF, the envelope line shown by the thin solid line represents the attenuation of the vibration at the resonance period Tc. The attenuation rate ζ will be described later. In addition, as a parameter representing the degree of attenuation in such damped vibration, in addition to the attenuation coefficient ζ, the Q value is known. Let Qc be the Q value indicating the degree of attenuation of the pressure vibration in the pressure chamber 12. It is expressed as ζ≒(1 / 2Qc). Therefore, the larger the value of Qc, the longer the reverberation remains.

[0024] On the other hand, the resonance frequency fm = 1 / Tm is the resonance frequency of the vibration of the meniscus, which is the liquid surface of the nozzle N. This resonance period Tm depends on the volume vibration of the liquid in the nozzle N (the entire individual flow path).

[0025] FIG. 3A is a diagram showing an example of the vibration pattern of the meniscus. FIG. 3B is a diagram showing a calculation example by numerical simulation of its frequency spectrum. The inkjet head related to ink ejection, ink characteristics, and the conditions of the ejection method are the same as the conditions in FIG. 2 above. In FIG. 3A, the meniscus vibration at the point Pm in FIG. 1 is shown by a thick dotted line. In this vibration, the center of the sine wave vibration corresponding to the resonance period Tc varies due to the vibration corresponding to the resonance period Tm. The superposition of the vibrations of these multiple modes causes both vibrations to increase as a whole along with the driving pulse and decay after the end of the driving pulse.

[0026] The frequency spectrum of the vibration of the meniscus shown by the broken line in FIG. 3B has the maximum peak at the frequency corresponding to the resonance period Tm. Also, a peak at the frequency corresponding to the resonance period Tc appears in this frequency spectrum. The frequencies fmh and fml shown in FIG. 3B indicate the half-value width of the vibration energy, that is, the position where the spectral intensity of the amplitude becomes 1 / √2 of the peak spectral intensity. By applying a BPF inside this half-value width, the vibration waveform shown by the solid line in FIG. 3A can be obtained. That is, this vibration waveform is a component of the vibration of the meniscus due to the resonance period Tm. In the waveform after this BPF, the envelope line shown by the thin solid line represents the decay of the vibration with the resonance period Tm. For such a damped vibration of the meniscus, the damping ratio ζ and the Q value are also determined. Also, let Qm be the Q value indicating the degree of attenuation of the meniscus vibration. The larger the value of Qm, the longer the reverberation remains. When the meniscus vibration is a positive value, the tip of the ink protrudes from the opening of the nozzle N. The timing Fm is the point where this protrusion is maximum. If such a long protrusion continues, that is, if the period Tm is long, a part of the ink that has not separated as a droplet may overflow from the nozzle opening surface without returning to the nozzle N.

[0027] When obtaining the characteristics of the vibration from measured values, the resonance period Tc and Qc are obtained, for example, from the amount of deformation of the piezoelectric element 15 accompanying the pressure fluctuation, that is, the output voltage. Also, the resonance period Tm and Qm are obtained, for example, by sequentially obtaining the moving speed of the meniscus at the nozzle N by irradiating a laser beam from the opening of the nozzle N and performing Doppler measurement of the reflected wave.

[0028] The damping coefficient ζ in an electric circuit such as an equivalent circuit is represented by the following mathematical formula (1). ζ = Rc / (2Lcωc) … (1) ωc is the angular velocity of the resonance period Tc, and ωc = 2π / Tc. Therefore, Qc is expressed by the following mathematical formula (2) according to the relationship with the above attenuation coefficient ζ. Qc = 2πLc / (RcTc) … (2) Note that the resonance period Tc is expressed by the following mathematical formula (3). Tc = 2π√(LcCc) 1 / 2 … (3)

[0029] Rc, Lc, and Cc represent the combined resistance, combined inductance, and combined capacitance in the pressure chamber 12, respectively. However, these are values that are difficult to obtain analytically. Therefore, the combined resistance Rc, combined inductance Lc, and combined capacitance Cc may be numerically obtained by numerical simulation. Well-known circuit simulation software such as LTspice may be used for the numerical simulation.

[0030] On the other hand, based on the resonance period Tm of the liquid surface vibration and various parameters, etc., Qm is expressed by the following mathematical formula (4). Qm = 2πLm / (RmTm) … (4) The resonance period Tm is expressed by the following mathematical formula (5). Tm = 2π√(LmCm) 1 / 2 … (5) The combined inductance Lm is the sum of the inductances of the upper connecting passage 13, pressure chamber 12, and nozzle N arranged in series. The combined resistance Rm is the sum of the resistance values of the upper connecting passage 13, pressure chamber 12, and nozzle N arranged in series. The combined capacitance Cm is approximately the capacitance of the capacitance Cn of the nozzle N and is expressed by the following mathematical formula (6). Cm = Cn = πφ 4 / (128σ) … (6) It should be noted that in the original text, the formula for Tc should be $Tc = 2\pi\sqrt{(LcCc)}$ to be more accurate. The above translation has been corrected accordingly.Here, φ is the diameter (nozzle diameter), i.e., the opening diameter, when the cross-section of the nozzle N is circular, and σ is the surface tension of the ink. When obtaining these analytically, they can be approximately calculated. Alternatively, some or all of the above values may be calculated by numerical simulation. Note that the cross-section of the nozzle N may not be circular. For example, when the cross-section is elliptical or rectangular, φe = 2·r1·r2 / (r1 + r2) can be used as a value equivalent to the nozzle diameter φ, i.e., the hydraulic diameter, for the long side r1 and the short side r2.

[0031] When each component is a rectangular parallelepiped, the resistance value R, inductance L, and capacitance C of the component are represented by the following mathematical formulas (7)-(9). R = 8η(a + b) 2 h / (a 3 b 3 ) … (7) L = ρh / (ab) … (8) C = abh / (ρv 2 ) … (9) Among the above, a and b are the lengths of the short side and the long side, respectively, of the cross-section perpendicular to the flow path direction of the rectangular parallelepiped. h is the length along the flow path of the rectangular parallelepiped. η is the ink viscosity, ρ is the ink density, and v is the speed of sound of the ink. η, ρ, v, and the above σ are constants according to the ink.

[0032] When the shape of each component is a frustum of a cone with diameters φ1 and φ2 at both ends, the resistance value R, inductance L, and capacitance C of the component are represented by the following mathematical formulas (10)-(12). R = 128η / (3π)(d / (φ2 - φ1)((1 / φ1) 3 -(1 / φ2) 3 )) … (10) L = 4ρ / π(d / (φ2 - φ1)((1 / φ1) - (1 / φ2))) … (11) C = πd / 12(φ1 2 + φ1φ2 + φ2 2 ) / (ρv 2 ) … (12)

[0033] The wall surfaces of each of the above-described flow paths are not limited to the diaphragm of the pressure chamber 12 and may be made of an elastic material. For example, each flow path configuration may have a thin portion (compliance plate) for vibration pressure absorption. The compliance plate may include, for example, polyimide in addition to the above-described PZT and diaphragm. The capacitance of the capacitor Ce1 related to this side wall is represented by the following formula (13). Ce1 = αb 4 (hb) / (2Ed 3 ) … (13) h and b are the vertical and horizontal lengths of the side wall, respectively. E is the Young's modulus of the side wall. d is the thickness of the side wall. α is a coefficient corresponding to (h / b). When h / b > 5, α = 0.0284. Note that the vertical width h of the side wall does not have to be the same as the length h along the flow path direction of each component having the rectangular parallelepiped shape described above. When the structure is complicated, such as when the wall surface is a laminated plate, it is difficult to analytically obtain the capacitance of the capacitor Ce1. In this case, it may be numerically obtained by using analysis software such as the finite element method. As the analysis software, for example, software of ANSYS Inc. (registered trademark), COMSOL Multiphysics of COMSOL Inc. (registered trademark), etc. may be used.

[0034] Qc, Qm, the resonance periods Tc, Tm according to the actual structure of the inkjet head and the characteristics of the ink can also be specified from the vibration waveforms of FIGS. 3A and 3B obtained by actual measurement or numerical simulation.

[0035] For example, a plurality of maximum points or minimum points in the above-described vibration waveform are extracted, and the damping ratio can be obtained from the ratio of these displacement amounts. The amplitude term in the vibration of the damping coefficient ζ is represented as A·exp(-ζω 0 t). Therefore, the ratio of the maximum pressure values P(n) and P(n + 1) in the pressure vibration periods n and n + 1 is represented by the following formula (14) based on formula (1). P(n + 1) / P(n) = exp(-RcTc / (2Lc)) … (14)

[0036] From this formula (14) and the above formula (2), the following approximate formula (15) can be obtained. Qc = -π / ln(P(n + 1) / P(n)) … (15) Similarly, take the ratio V(n + 1) / V(n) of the volume V at the maximum timing t1 of the period n and the maximum timing t1 + Tm of the next period n + 1 in the volume vibration. This value is represented by formula (16). V(n + 1) / V(n) = exp(-RmTm / (2Lm)) … (16) From this formula (16) and the above formula (2), the following formula (17) can be obtained. Qm = -π / ln(V(n + 1) / V(n)) … (17) The phases of the vibrations of the volume V and the pressure P can be regarded as the same.

[0037] Note that Qc and Qm obtained only from a single period n and period n + 1 are likely to have low accuracy due to the influence of noise and the like. Therefore, Qc and Qm can be obtained for each of a plurality of periods n = 1, 2…, and these can be simply averaged. That is, Qc is obtained as the average of N periods by the following formula (18). Qc = (-π / N)Σ n=1~N 1 / ln(P(n + 1) / P(n)) … (18) N is the number of periods to be referred to.

[0038] Similarly, Qm is obtained as the average of N periods by the following formula (19). Qm = (-π / N)Σ n=1~N 1 / ln(V(n + 1) / V(n)) … (19)

[0039] Note that when obtaining Qc from the results of experiments or simulations in this way, the number of periods N to be averaged may be determined within the range where the amplitude can be obtained accurately. That is, the faster the decay, the smaller the number of periods N may be.

[0040] Alternatively, Qc and Qm may be directly obtained from the spectral distribution. That is, Qc and Qm are obtained by the following mathematical formulas (20) and (21). Qc = fc / (fch - fcl) … (20) Qm = fm / (fmh - fml) … (21) The resonance frequencies fc and fm are the reciprocals of the resonance periods Tc and Tm, respectively. The upper limit frequencies fch and fmh are the frequencies at which the spectral intensity is 1 / √2 (about -3 dB) of the spectral intensity at the resonance frequencies fc and fm, respectively. The lower limit frequencies fcl and fml are the frequencies at which the spectral intensity is 1 / √2 (about -3 dB) of the spectral intensity at the resonance frequencies fc and fm, respectively. fch > fc > fcl and fmh > fm > fml.

[0041] In FIGS. 2B and 3B, the resonance frequencies fc and fm corresponding to the resonance periods Tc and Tm and their peak spectral intensities are specified, respectively. Also, the upper side frequencies fch and fmh and the lower side frequencies fcl and fml at which the spectral intensity becomes 1 / √2 (about -3 dB) with respect to the peak spectral intensity are specified. From these, Qc and Qm are obtained from the mathematical formulas (20) and (21).

[0042] The vibration of the ink during ink ejection, which is characterized as described above, affects the accuracy of the actually ejected ink droplets. In the present disclosure, using the above resonance periods Tc, Tm, and Qc, a structure capable of stably ejecting ink and a range of ink combinations are defined. In particular, in the present disclosure, considering image recording onto surfaces other than paper, a case where the width (gap) between the nozzle opening surface of the inkjet head 1 and the landing surface of the ejected ink is wide is assumed. In the present disclosure, for ink ejection with a wide width, the width is defined as 5.0 mm or more. Further, it is better that stable ejection is possible even when the width is about 10.0 mm or more. The ink droplets are decelerated by air resistance or the like during flight from the nozzle opening surface to the landing surface. Therefore, when the width is large, the deviation of the landing position corresponding to the deceleration cannot be ignored. When flying at a width of 10 mm at an ejection speed of 10 m / s, the landing position of the ink droplets decelerated by the ideal air resistance on the model has a variation of ±105 μm. In an image with 360 dpi (about 70 μm / pixel), this variation corresponds to ±1.5 pixels.

[0043] Also, when the width becomes wide, if satellites occur, the satellites are likely to land at positions different from the main liquid. Such variations in the landing position can lead not only to a decrease in the design quality but also to a decrease in practicality, for example, a decrease in the reading accuracy of barcodes, two-dimensional symbols, etc. Therefore, when performing an image recording operation in a state where the width is wide, higher stability of ink ejection is required.

[0044] That is, the required image quality can be determined as a level at which barcodes, two-dimensional symbols, etc. can be stably decoded. There are standards such as ISO / IEC 15415 and ISO / IEC 15416 for evaluating the printing quality of barcodes and two-dimensional symbols. In the present disclosure, in these standards, the overall C evaluation, that is, the printing quality at which the lowest of the evaluations according to the individual evaluation criteria is C or higher is stably decodable. It has been found by the inventors' experiments that a deviation of about 3 pixels can be tolerated in a 360 dpi image. That is, for example, for droplets with a discharge volume of about 20 - 30 pL per shot, the ink and the inkjet head are required to be able to stably discharge the ink at a discharge speed of 10 m / s or more while reducing the generation of satellites over a width of 10 mm.

[0045] Furthermore, in inkjet recording apparatuses mainly for industrial use, a high-speed recording operation is also required. In the present embodiment, stable discharge in the range where the driving frequency is 10 kHz or more, particularly up to about 11 kHz, is desired. A driving frequency of 10 kHz or more corresponds to a driving period of 100 μsec or less. A driving frequency of 11 kHz corresponds to a driving period of about 90 μsec (90.9 μsec).

[0046] For example, when Qc related to the pressure vibration of the pressure chamber 12 increases and the reverberation of the pressure vibration in the pressure chamber 12 becomes large, the meniscus cannot be maintained and is easily broken. On the other hand, if Qc for the pressure vibration in the pressure chamber 12 is too small, the rear end portion of the discharged ink droplet is likely to decelerate compared to the front end portion. As a result, the discharged ink is less likely to coalesce as a single droplet, and micro-droplets (satellites) are likely to be generated.

[0047] Figure 4 is a diagram experimentally obtaining the minimum speed of ink droplets that generate satellites for each nozzle shape with respect to Qc. In the experiment, ink was discharged while changing Qc for four types of nozzle shapes represented by different symbols. The specific nozzle shapes are omitted from the description as they are not relevant to the content of the present disclosure. The discharged ink has, as a reference value, a viscosity of 5.7 mPa·s at 25°C and a density of 1080 kg / m3 The surface tension is 41 mN / m and the speed of sound is 1521 m / s.

[0048] As described above, Qc is determined by the combination of the shape of the inkjet head and the properties of the ink. Here, the shape of the inkjet head and the type of ink are fixed. When the temperature of the ejected ink rises, the combined resistance Rc of the pressure chamber 12 relatively decreases. Utilizing this property, based on the above formula (2), other parameters can be generally maintained while changing Qc. If the nozzle shape is the same, the lower limit speed at which satellites occur increases as Qc increases. It has been shown that if Qc is 10 or more, satellites are less likely to occur at normal ink ejection speeds.

[0049] FIG. 5 is a chart showing the stability of ink ejection with respect to Qc. Here, two types of inks A and B are used in the experiment. For ink ejection, a multi-drop method is used in which droplets are ejected a plurality of times, here 8 consecutive droplets, at intervals of the resonance period Tc related to the pressure vibration and landed at one pixel position. The droplet volume per shot is 3 pL. Each drive pulse is a pull-in pulse with a half-cycle width of the resonance period Tc. In the multi-drop method, the volume of the ink per shot, especially the volume of the last droplet, is smaller than that of a single shot in the single-drop method, so satellites are less noticeable. Note that the drive pulses usually used for ink ejection include waveforms for reducing reverberation vibration and the like. Therefore, if it is within the range of the parameters obtained as follows with this waveform, ink ejection in actuality is more improved. As a result, when Qc is in the range of 10 or more and 18 or less (Examples 1 to 5), it is ejected appropriately, but when Qc exceeds 18 (Comparative Examples 1 and 3), large variations in speed according to the ejection frequency occur and a result of unstable ejection is obtained. Also, it can be seen that when Qc is less than 10, problems such as the ease of satellite generation occur (Comparative Example 2). It can be understood that by setting Qc to an appropriate value, the stability of ink ejection can be obtained even if the ink physical properties change.

[0050] FIG. 6A and FIG. 6B are diagrams for explaining the frequency stability in FIG. 5. FIG. 6A shows the experimental results of obtaining the change rate of the ejection speed with respect to 10 m / s for the driving period under the conditions of the left three columns in FIG. 5.

[0051] When the driving period is short, that is, when the driving frequency is high, the reverberation of the previous driving period is likely to remain. When Qc increases, this influence spreads to the side with a longer driving period, and the ejection speed of the ink tends to vary easily from the assumed speed. For image quality, the variation in the ejection speed that is allowed as a variation of about 3 pixels or less is, for example, about 10%. In FIG. 6A, it is shown that in each pattern where Qc is 18 or less, the variation in the assumed speed within the range where the driving frequency is 11 kHz or less is within 10%. From the above, as condition 1, in the range of 10 ≦ Qc ≦ 18, the result that the ink is stably ejected while reducing the generation of satellites is obtained.

[0052] FIG. 6B is a chart showing the results of obtaining the frequency stability while changing the surface tension under the conditions of ink X in FIG. 5 and a temperature of 40°C. By changing the surface tension, while maintaining Qc and the resonance period Tc, the resonance period Tm can be decreased, and accordingly Qm can be increased. That is, the ratio Tm / Tc of the resonance periods Tm and Tc changes.

[0053] As shown in FIG. 6B, it is shown that when Tm / Tc is large, the ejection speed tends to be unstable with respect to the driving frequency. When Tm / Tc becomes 6 or less, the ejection speed is stable within the above allowable range. Also, as described above, when the resonance period Tm becomes small, the overflow of the ink from the nozzle opening surface is reduced.

[0054] On the other hand, conventionally, it has been known that when Tm / Tc becomes small, the degree of satellite generation deteriorates (for example, International Publication No. 2009 / 107552). This is because the ink column protruding from the nozzle N at the resonance period Tc is likely to separate according to the short resonance period Tm. In the above, it is suggested that when φ≤10 μm of the nozzle diameter and Tm / Tc<1, the generation state of satellites deteriorates. This condition is considered effective also for the stable ejection of ink in the present disclosure. Thus, as Condition 2, in the range of 1≤Tm / Tc≤6, ink is stably ejected while reducing the generation of satellites. In other words, the resonance period Tm related to the meniscus vibration may be 1 to 6 times that of the resonance period Tc related to the pressure vibration in the pressure chamber 12.

[0055] When the width between the nozzle opening surface and the ink landing surface is wide and the amount of ink droplets to be flown is small, the flying direction of the ink is likely to vary due to the influence of ambient wind or the like. Since the amount of ink droplets depends on the nozzle diameter φ, the nozzle diameter φ is determined to be large to such an extent that the ink droplets can fly stably due to inertia. On the other hand, as shown in the above formulas (5) and (6), the resonance period Tm depends on the square of the nozzle diameter φ. That is, when the nozzle diameter φ is increased, Tm / Tc is likely to increase significantly. Further, when the resonance period Tc increases, the upper limit value of the driving speed decreases, that is, a high-speed image recording operation becomes impossible. Therefore, it is not suitable for use in an inkjet recording apparatus for industrial applications.

[0056] Therefore, the inkjet head preferably has a large cross-sectional area of the flow path other than the nozzle N and a short flow path length along the flow path. The nozzle diameter φ of the nozzle N is determined to be large within the range possible by adjusting such a structure. In a general flow path structure, when the nozzle diameter φ is about 20 μm or more, the above Conditions 1 and 2 are not satisfied. On the contrary, the inkjet head of the present disclosure adjusts the cross-sectional area and the flow path length as described above as Condition 3, and maintains stable flight of the ink with φ≥20 μm of the nozzle diameter.

[0057] Within the scope of compliance with the premises and conditions 1 to 3 defined above, the structure of the inkjet head may be variously deformed.

[0058] [Second Embodiment] The inkjet head 1a of the second embodiment will be described. Figs. 7A and 7B are diagrams showing a schematic cross-sectional view and an equivalent circuit of the inkjet head 1a. In the schematic cross-sectional view, although the ink flow path is located within the substrate, the drawing of the substrate other than the nozzle plate is omitted. As shown in Fig. 7A, the inkjet head 1a includes a lower communication passage 14 between the nozzle N and the pressure chamber 12. A recovery flow path 22 is connected to the lower communication passage 14 in addition to the nozzle N.

[0059] The recovery flow path 22 recovers the ink that stays near the nozzle N without being discharged from the opening of the nozzle N, and returns it to an ink tank or the like via a common discharge flow path 21 (common liquid chamber). If the ink stays for a long time, the components may separate, and air and dust that have entered from the opening of the nozzle N may be mixed into the ink. Due to these, the quality of the ink deteriorates. As a result, the ejection accuracy of the ink decreases, and / or the quality of an image or the like recorded by the landed ink deteriorates. The recovery flow path 22 returns such ink to the ink tank. The recovered ink is agitated again, and dust is removed from the ink by a filter. Ink of appropriate quality corresponding to the amount of ink ejected or recovered is supplied from the ink tank to the pressure chamber 12 via a common supply flow path 11 (common liquid chamber) and an upper communication passage 13.

[0060] The common supply flow path 11 and the common discharge flow path 21 communicate with the upper communication passage 13, the pressure chamber 12, the lower communication passage 14, and the recovery flow path 22, respectively, which are a plurality of individual flow paths each connected to a plurality of nozzles N.

[0061] As shown in FIG. 7B, the equivalent circuit of the inkjet head 1a includes electronic components corresponding to the lower communication passage 14 and the recovery passage 22, respectively. The lower communication passage 14 is represented by resistive elements R5, R6 and inductors L5, L6 arranged in series, and capacitors C5, Ce5 arranged in parallel between the ground plane. The recovery passage 22 is represented by resistive elements Rr1, Rr2 and inductors Lr1, Lr2 arranged in series, and capacitors Cr1, Cre arranged in parallel between the ground plane. The wall surfaces of the lower communication passage 14 and the recovery passage 22 may be regarded as rigid bodies. That is, the capacitances of the capacitors Ce5, Cre are negligibly large and can be treated as substantially zero.

[0062] The recovery passage 22 is designed so that the pressure vibration applied in the pressure chamber 12 is efficiently transmitted to the nozzle N. That is, the recovery passage 22 has a high impedance compared to the upper communication passage 13, the pressure chamber 12, the lower communication passage 14, and the nozzle N so that the pressure vibration is less likely to be transmitted to the recovery passage 22. Therefore, approximately, the recovery passage 22 may be ignored in the calculation / experiment of the pressure vibration and the volume vibration.

[0063] Since the common supply passage 11 and the common discharge passage 21 are sufficiently wide compared to the individual passages, they are treated as open ends, that is, ground planes.

[0064] That is, the combined inductance Lm of the ink passage is the sum of the inductances of the upper communication passage 13, the pressure chamber 12, the lower communication passage 14, and the nozzle N. The combined resistance Rm of the ink passage is the sum of the resistance values of the upper communication passage 13, the pressure chamber 12, the lower communication passage 14, and the nozzle N. As a result, in the calculation of the resonance periods Tc, Tm and Qc, Qm in the inkjet head 1a, values with the influence of the lower communication passage 14 added to the inkjet head 1 are obtained.

[0065] [Third and Fourth Embodiments] As described above, in order to increase Qc and decrease the resonance period Tm, it is preferable to shorten and widen the ink flow path. For this purpose, the upper communication path 13 and the lower communication path 14 may be omitted. The ink flow path is shortened by this amount. Also, the upper communication path 13 and the lower communication path 14 are thinner than the pressure chamber 12. Therefore, the combined resistance Rm is obtained by the sum of the resistance values of the pressure chamber 12 and the nozzle N. The combined inductance Lm is obtained by the sum of the inductances of the pressure chamber 12 and the nozzle N. As a result, in the inkjet head, the resonance period Tm becomes smaller. Qc can be increased.

[0066] FIG. 8A is a schematic cross-sectional view of the inkjet head 1b according to the third embodiment. FIG. 8B is an equivalent circuit diagram of the inkjet head 1b. In the schematic cross-sectional view shown in FIG. 8A, the pressure chamber 12 communicates with the common supply flow path 11 via a short upper communication path 13. The pressure chamber 12 communicates directly with the nozzle N. The piezoelectric element 15b located on the side surface of the pressure chamber 12 may be deformed in a shear mode instead of the above-described bending mode. The equivalent circuit diagram shown in FIG. 8B is the same as the equivalent circuit in the inkjet head 1 according to the first embodiment.

[0067] FIG. 9A is a schematic cross-sectional view of the inkjet head 1c according to the fourth embodiment. FIG. 9B is an equivalent circuit diagram of the inkjet head 1c. The schematic cross-sectional view shown in FIG. 9A further omits the upper communication path 13 from the cross-sectional structure of the inkjet head 1b according to the third embodiment shown in FIG. 8A. Therefore, the pressure chamber 12 communicates directly with the common supply flow path 11.

[0068] Accordingly, in the equivalent circuit diagram shown in FIG. 9B, the circuit components corresponding to the upper communication path 13 are deleted. By performing numerical simulation in the same procedure as above using this equivalent circuit, the resonance periods Tc, Tm and Qc, Qm can be obtained. In the inkjet heads 1 to 1c shown in the first to fourth embodiments, the ink to which pressure fluctuations are respectively applied in the pressure chambers 12 can be directly transmitted linearly to the nozzles N as they are. Such a structure is also called an end shooter.

[0069] [Fifth Embodiment] For the ink flow path having the above series structure, the ink flow path with respect to the nozzle N can be made substantially parallel. This also reduces the resonance period Tm. FIG. 10A is a schematic cross-sectional view of the inkjet head 1d according to the fifth embodiment. FIG. 10B is an equivalent circuit diagram of the inkjet head 1d.

[0070] As shown in FIG. 10A, the first pressure chamber 12a and the second pressure chamber 12b communicate with the lower communication path 14 connected to the nozzle N in parallel. The first pressure chamber 12a is connected to the common supply flow path 11 via the first upper communication path 13a. The second pressure chamber 12b is connected to the common discharge flow path 21 via the second upper communication path 13b. That is, as a whole, the ink is supplied from the common supply flow path 11 to the lower communication path 14 and the nozzle N via the first upper communication path 13a and the first pressure chamber 12a. The ink in the lower communication path 14 that is not ejected from the nozzle N is sent to the common discharge flow path 21 via the second pressure chamber 12b and the second upper communication path 13b. That is, the second pressure chamber 12b, the second upper communication path 13b, and the second lower communication path 14b on the right side of the nozzle N in the figure of the lower communication path 14 are the recovery flow path 22. That is, the lower communication path 14 is divided into a first lower communication path 14a on the side of the first pressure chamber 12a and a second lower communication path 14b on the side of the second pressure chamber 12b.

[0071] However, the ink that has flowed into the second pressure chamber 12b can be returned to the lower communication passage 14 and discharged from the nozzle N during ink discharge. The first pressure chamber 12a, the first upper communication passage 13a, the second pressure chamber 12b, the second upper communication passage 13b, and the lower communication passage 14 are symmetrically located with respect to the central axis of the nozzle N. That is, the first pressure chamber 12a and the second pressure chamber 12b apply pressure fluctuations to the ink to be discharged from the nozzle N in parallel. As a result, when viewed from the nozzle N, the cross-sectional area of the ink supply path during ink discharge is the sum of the cross-sectional area of the first pressure chamber 12a and the cross-sectional area of the second pressure chamber 12b. The pressure fluctuations applied to the ink in the first pressure chamber 12a and the second pressure chamber 12b are transmitted perpendicular to the extending direction of the nozzle N toward the connection position with the nozzle N in the lower communication passage 14. Therefore, this structure is also called a side shooter.

[0072] In the equivalent circuit shown in FIG. 10B, the lower communication passage 14 is divided into two at the connection position with the nozzle N as a boundary. The first upper communication passage 13a, the first pressure chamber 12a, and the first lower communication passage 14a are arranged in parallel with the second upper communication passage 13b, the second pressure chamber 12b, and the second lower communication passage 14b.

[0073] The first pressure chamber 12a is represented by resistor elements R11, R12, inductors L11, L12, and capacitors C11, Ce1. The first upper communication passage 13a is represented by resistor elements R13, R14, inductors L13, L14, and capacitors C13, Ce3. The first lower communication passage 14a is represented by resistor elements R15, R16, inductors L15, L16, and capacitors C15, Ce5. The second pressure chamber 12b is represented by resistor elements R21, R22, inductors L21, L22, and capacitors C21, Ce2. The second upper communication passage 13b is represented by resistor elements R23, R24, inductors L23, L24, and capacitors C23, Ce4. The second lower communication passage 14b is represented by resistor elements R25, R26, inductors L25, L26, and capacitors C25, Ce6.

[0074] Capacitors C11, C13, C15, C21, C23, and C25 represent the elastic compliance of the ink, respectively. Capacitors Ce1 and Ce2 represent the elastic compliance of the wall surfaces of the first pressure chamber 12a and the second pressure chamber 12b, respectively. Capacitors Ce3 and Ce4 represent the elastic compliance of the wall surfaces of the first upper communication passage 13a and the second upper communication passage 13b, respectively. Capacitors Ce5 and Ce6 represent the elastic compliance of the wall surfaces of the first lower communication passage 14a and the second lower communication passage 14b, respectively.

[0075] Resistance elements R11 to R16 and inductors L11 to L16 are connected in series. Capacitors C11, C13, C15, Ce1, Ce3, and Ce5 are connected in parallel between each part's resistance element and inductor and the ground surface, respectively. Resistance elements R21 to R26 and inductors L21 to L26 are connected in series. Capacitors C21, C23, C25, Ce2, Ce4, and Ce6 are connected in parallel between each part's resistance element and inductor and the ground surface, respectively. Therefore, the combined inductance Lm related to volume vibration is obtained by adding the inductance of inductor Ln to the reciprocal of the sum of the reciprocals of the total inductance values of inductors L11 to L16 and the total inductance values of inductors L21 to L26. The combined resistance Rm is obtained by adding the resistance value of resistance element Rn to the reciprocal of the sum of the reciprocals of the total resistance values of resistance elements R11 to R16 and the total resistance values of resistance elements R21 to R26.

[0076] The parameter values of the individual circuit components may be determined so that the resonance period Tc and Qm are within appropriate ranges as described above. On the side connected to the common supply channel 11 and the side connected to the common discharge channel 21, the parameters of the circuit components may or may not be the same. When these are the same, the combined inductance Lm is the sum of 1 / 2 of one combined inductance and the inductance of the inductor Ln. The combined resistance Rm is the sum of 1 / 2 of one combined resistance and the resistance value of the resistor element Rn. The combined inductance Lc and combined resistance Rc for the pressure vibration may be obtained by numerical simulation. The resonance periods Tm, Tc and Qm, Qc are obtained analytically according to the above equations (1) to (4) or numerically by equations (17), (18), etc.

[0077] Even in such an inkjet head 1d of the side shooter, by reducing the combined inductance Lm, the resonance period Tm can be reduced. That is, since the flow path cross-sectional area is large and the flow path length is small, it is easy to increase the nozzle diameter φ and the capacitance of the capacitor Cn. In particular, in the side shooter, the combined resistance and combined inductance other than the nozzle N can be made relatively small compared to the resistance value and inductance of the nozzle N. Therefore, it is easier to reduce the resonance frequency Tm and increase Qc than in the end shooter. Thus, this inkjet head 1d can easily incorporate a nozzle N with φ≧20 μm.

[0078] [Sixth Embodiment] FIG. 11A is a schematic cross-sectional view of an inkjet head 1e according to the sixth embodiment. FIG. 11B is an equivalent circuit diagram of the inkjet head 1e. As shown in FIG. 11A, in the inkjet head 1e, a first upper communication path 13a and a second upper communication path 13b are connected to both ends of the pressure chamber 12 connected to the nozzle N. The first upper communication path 13a connects the pressure chamber 12 and the common supply channel 11. The second upper communication path 13b connects the pressure chamber 12 and the common discharge channel 21. Along the wall surface of the pressure chamber 12, a piezoelectric element 15 and a diaphragm 16 that deform in a flexural mode are positioned.

[0079] That is, the first upper communication passage 13a and the second upper communication passage 13b are positioned in parallel with respect to the pressure chamber 12. In the equivalent circuit shown in FIG. 11B, the pressure chamber 12 is divided into a first pressure chamber 12a and a second pressure chamber 12b with the nozzle N as a boundary. The first pressure chamber 12a is connected to the first upper communication passage 13a, and the second pressure chamber 12b is connected to the second upper communication passage 13b. The circuit components of the first pressure chamber 12a and the first upper communication passage 13a are positioned in parallel with the circuit components of the second pressure chamber 12b and the second upper communication passage 13b.

[0080] Normally, in this inkjet head 1e, ink flows from the common supply passage 11 to the first upper communication passage 13a and the pressure chamber 12 (the first pressure chamber 12a). Among the ink in the pressure chamber 12, the ink not ejected from the nozzle N flows from the second pressure chamber 12b to the common discharge passage 21 through the second upper communication passage 13b. At the time of ink ejection, pressure fluctuations are also applied to the ink in the second pressure chamber 12b together with the ink in the first pressure chamber 12a, and a part of the ink is ejected from the nozzle N.

[0081] This inkjet head 1e does not have the first lower communication passage 14a and the second lower communication passage 14b. Therefore, the inductances of the inductors L15, L16, L25, L26 and the resistance values of the resistance elements R15, R16, R25, R26 are each zero. The combined resistance Rm and the combined inductance Lm are smaller than the values in the inkjet head 1d by the amounts of decrease in these inductances and resistance values.

[0082] [Seventh Embodiment] FIG. 12A is a cross-sectional view parallel to the nozzle opening surface of the inkjet head 1f according to the seventh embodiment. FIG. 12B is an equivalent circuit diagram of the inkjet head 1f. As shown in FIG. 12A, in this inkjet head 1f, the common supply passage 11 and the common discharge passage 21 are directly connected to both ends of the pressure chamber 12. Therefore, normally, ink flows from the common supply passage 11 through the pressure chamber 12 to the common discharge passage 21.

[0083] As shown in FIG. 12B, the pressure chamber 12 is divided into a first pressure chamber 12a and a second pressure chamber 12b with the nozzle N as a boundary. The ink that has flowed into the second pressure chamber 12b passing through the position of the nozzle N can also have pressure fluctuations applied thereto during ink ejection, and a part of the ink can be ejected from the nozzle N. The circuit components of the first pressure chamber 12a and the circuit components of the second pressure chamber 12b are positioned in parallel with respect to the circuit components of the nozzle N.

[0084] The inkjet head 1f further does not have a first upper communication passage 13a and a second upper communication passage 13b as compared with the inkjet head 1e. Therefore, in the combined resistance Rm, the resistance values of the resistance elements R13, R14, R23, and R24 are zero. In the combined inductance Lm, the inductances of the inductors L13, L14, L23, and L24 are zero. By these amounts, the combined resistance Rm and the combined inductance Lm are smaller than the values in the inkjet head 1e.

[0085] As described above, the ink ejection method of the present embodiment is by an inkjet head 1 including a nozzle N and an ink flow path communicating with the nozzle N, and the ink flow path includes a pressure chamber 12 that applies pressure fluctuations to the internal ink. This ink ejection method satisfies the following conditions when the viscosity of the ejected ink is 5.7 mPa·s, the density is 1080 kg / m 3 , the surface tension is 41 mN / m, and the speed of sound is 1521 m / s. (1) In the inkjet head 1, Qc related to the pressure vibration of the ink in the pressure chamber 12 is 10 or more and 18 or less. (2) The resonance period Tm related to the meniscus vibration of the ink in the nozzle N is 1 time or more and 6 times or less of the resonance period Tc related to the pressure vibration of the ink in the pressure chamber 12. (3) The nozzle diameter φ or the diameter φe equivalent to the nozzle diameter φ is 20 μm or more. (4) The width between the nozzle opening surface of the inkjet head 1 and the ink landing surface is 5.0 mm or more. According to this ink ejection method, regardless of the specific shape of the inkjet head 1, it is possible to reduce the breakage of the meniscus, the variation in the landing position, and the generation of satellites. Therefore, this ink ejection method can stably eject ink while ensuring the width between the ink ejection surface and the landing surface.

[0086] Further, this ink ejection method may eject ink by a multi-drop method in which a plurality of droplets are continuously ejected for one pixel. Since the droplet amount per drop, particularly the size of the droplet ejected last, can be made small with respect to the ink amount per pixel, satellites are likely to be reduced.

[0087] Also, in this ink ejection method, the width between the nozzle opening surface of the inkjet head 1 and the ink landing surface may be 10.0 mm or more. Under the above conditions, ink can be stably ejected when the width is up to 10 mm. If the distance between the nozzle opening surface and the ink landing surface is sufficiently separated in this way, images can be recorded on more diverse surfaces.

[0088] Also, the ejection volume from one nozzle may be 20 pL or more and 30 pL or less, and the drive cycle related to ink ejection may include a range of 90 μsec or more and 100 μsec or less. That is, in this ink ejection method, ink can be stably ejected with an ejection volume of 20 - 30 pL from one nozzle and a drive cycle of about 10 - 11 kHz. Therefore, this ink ejection method can quickly obtain a desired image with appropriate quality by the high-speed recording operation required for image recording operations in industrial applications and the like.

[0089] Also, the inkjet head 1 of the present embodiment satisfies the structural conditions related to the above ink ejection method.

[0090] In addition, the inkjet heads 1d to 1f may have a recovery channel 22 for recovering the ink that is not ejected from the nozzles N. In this case, the structure of the ink channel may be symmetric with respect to the central axis of the nozzle N. In this way, since the recovery channel side is also used for ink ejection, the cross-sectional area of the channel related to ink ejection apparently increases. Therefore, it is easy for this inkjet head 1 to reduce the resonance frequency Tm. Accordingly, the inkjet head 1 can easily increase the nozzle diameter φ to 20 μm or more.

[0091] Note that the content of the present disclosure is illustrative and various modifications are possible. For example, in the above description, it was described on the premise that the ejection volume from one nozzle is 20 - 30 pL and the driving is at about 10 - 11 kHz. However, the ejection volume and the driving frequency may be outside these ranges.

[0092] Also, the number of continuous injections in the multi-drop method does not have to be 8. It may be an appropriate number of injections. Further, in the ejection waveform, an appropriate waveform for reducing the reverberation vibration may be added. Alternatively, it does not have to be ink ejection in the multi-drop method.

[0093] Also, the ink recovered by the recovery channel does not necessarily have to be returned to the ink tank. It may be discarded as it is, or may be stored separately once and then subjected to some treatment.

[0094] Also, in the above-described embodiment of the side shooter, an ink channel symmetric with respect to the central axis of the nozzle N was shown, but it is not limited to this. The orientation, shape, and size of the ink channel may be different as long as they do not adversely affect ink ejection. In addition, the specific configurations, structures, setting contents, etc. shown in the above embodiments can be appropriately changed without departing from the spirit of the present disclosure. The scope of the present invention includes the scope of the invention described in the claims and its equivalent scope.

Industrial Applicability

[0095] The present disclosure can be used for an ink ejection method. to the law It can be utilized.

Explanation of Reference Numerals

[0096] 1, 1a to 1f Inkjet heads 11 Common supply channel 12 Pressure chamber 12a First pressure chamber 12b Second pressure chamber 13 Upper communication channel 13a First upper communication channel 13b Second upper communication channel 14 Lower communication channel 14a First lower communication channel 14b Second lower communication channel 15, 15b Piezoelectric elements 16 Diaphragm 21 Common discharge channel 22 Recovery channel N Nozzles

Claims

1. 1. A method for ejecting ink from an inkjet head, comprising: a nozzle; and an ink flow path communicating with the nozzle, the ink flow path including a pressure chamber that applies pressure fluctuation to ink therein, the method comprising: The inkjet head comprises: The viscosity of the ejected ink is 5.7 mPa·s and the density is 1080 kg / m ３ , surface tension is 41 mN / m, and sound speed is 1521 m / s, a Q value associated with pressure vibration of the ink in the pressure chamber is equal to or greater than 10 and equal to or less than 18, a resonance period associated with meniscus vibration of the ink in the nozzle is equal to or greater than 1 time and equal to or less than 6 times a resonance period associated with pressure vibration of the ink in the pressure chamber, The nozzle has an opening diameter or a diameter equivalent to the opening diameter of 20 μm or more, The width between the ink ejection surface and the ink landing surface of the inkjet head is 5.0 mm or more. Ink ejection method.

2. 2. The ink ejection method according to claim 1, wherein the ink is ejected by a multi-drop method in which a plurality of ink droplets are ejected continuously onto one pixel.

3. 2. The ink ejection method according to claim 1, wherein the distance between the ink ejection surface of the ink jet head and the ink landing surface is 10.0 mm or more.

4. 4. The ink ejection method according to claim 3, wherein the ejection volume from one nozzle is between 20 pL and 30 pL, and the drive period for ink ejection is within the range of between 90 [mu]sec and 100 [mu]sec.

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