JP2013116571A - Liquid droplet discharging head and recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid droplet discharging head and recording apparatus capable of suppressing variation in speed due to crosstalk even when using low-viscosity ink, reducing the overflow of the ink from a nozzle, and achieving stable discharge.SOLUTION: Multiple ink flow paths 18 to which ink is supplied and multiple partitions 17 are alternatively arranged in parallel. The partition 17 between the adjacent ink flow paths 18 includes an actuator which deforms corresponding to impressed voltage applied to electrodes on a surface of the partition 17. In the liquid droplet discharging head, the ink in the ink flow path 18 is discharged from the nozzle by deformation of the partition 17. The ink flow path 18 has a cross section in a parallel arrangement direction of the partition 17 formed in a rectangular shape. When the depth direction parallel to the surface of the partition 17 is the height h, the parallel arrangement direction of the partition orthogonal to the depth direction is the width w, the longitudinal/lateral ratio (height h/width w) of the cross section of the ink flow path 18 formed in the rectangular shape is 5.00 or more and less than 7.75, and the resonance frequency of the partition 17 is 1.5 MHz or more.

Description

  The present invention relates to a droplet discharge head and a recording apparatus. More specifically, even when a low-viscosity ink is used, stable discharge can be performed without causing overflow of ink due to crosstalk between adjacent ink flow paths. The present invention relates to a liquid droplet ejection head and a recording apparatus equipped with the same.

  As a liquid droplet ejection head for ejecting ink from a nozzle, a large number of ink flow paths and a large number of partition walls are alternately arranged in parallel, and the partition walls between adjacent ink flow paths are applied to electrodes formed on the surface of the partition walls. 2. Description of the Related Art There is known a shear mode type droplet discharge head that includes an actuator that deforms in response to an applied voltage and discharges ink in an ink flow path from a nozzle by a deformation operation of a partition wall.

  FIG. 1 shows an example of a shear mode type droplet discharge head. (A) is a general-view perspective view, (b) is a sectional view.

  In the droplet discharge head 1 shown in the figure, 11 is an ink tube, 12 is a nozzle forming member, 13 is a nozzle, 14 is an upper substrate, 15 is an ink supply port, 16 is a lower substrate, and 17 is a partition. An ink flow path 18 is formed by the partition wall 17, the upper substrate 14, and the lower substrate 16.

  Each partition wall 17 is formed by an upper wall portion 17a and a lower wall portion 17b made of a piezoelectric material such as PZT whose polarization directions are opposite to each other. However, the piezoelectric material may be only a portion indicated by reference numeral 17a, for example. It suffices if it is at least part of the partition wall 17. The partition walls 17 are alternately arranged in parallel with the ink flow paths 18, so that one partition wall 17 is shared by the ink flow paths 18 and 18 on both sides thereof. One end of each ink flow path 18 is connected to a nozzle 13 provided at a position corresponding to each ink flow path 18 in the nozzle forming member 12, and the other end passes through an ink supply port 15, and ink (not shown) is connected to the ink tube 11. Connected to the tank.

  An electrode (not shown) is formed on the surface of the partition wall 17 facing the ink flow path 18, and a predetermined drive voltage is applied to the electrode to cause the partition wall 17 to be deformed into a U-shape so that an ink tube is formed. A pressure for ejection is applied to the ink supplied into the ink flow path 18 via 11, and the ink in the ink flow path 18 is ejected as droplets from the nozzle 13.

  FIG. 2 is a diagram illustrating the operation of the droplet discharge head 1 during ink discharge. Here, three ink flow paths 18A, 18B, and 18C separated by the partition walls 17A, 17B, 17C, and 17D among the multiple partition walls 17 and the multiple ink flow paths 18 are illustrated. Electrodes 19A, 19B, 19C are formed on the surface of the partition wall 17 in each ink flow path 18, and each electrode 19A, 19B, 19C is a drive for driving the partition wall 17 to discharge ink in the ink flow path 18. It is connected to a drive signal generator 100 that supplies signals.

  First, when no drive signal is applied to any of the electrodes 19A, 19B, and 19C, none of the partition walls 17A, 17B, and 17C is deformed (FIG. 2A). In this state, when the electrodes 19A and 19C are grounded and a drive signal is applied to the electrode 19B, an electric field in a direction perpendicular to the polarization direction of the piezoelectric material constituting the partition walls 17B and 17C is generated, and each of the partition walls 17B and 17C is The joint surface of the upper wall portion 17a and the lower wall portion 17b is deformed, and the partition walls 17B and 17C are deformed toward the outside, and the volume of the ink flow path 18B is enlarged to cause negative flow in the ink flow path 18B. Pressure is generated and ink flows (FIG. 2B).

  Further, when the potential is returned to 0 from this state, the partition walls 17B and 17C return from the expanded position shown in FIG. 2B to the neutral position shown in FIG. 2A, and high pressure is applied to the ink in the ink flow path 18B. It takes.

  Next, when a drive signal is applied to deform the partition walls 17B and 17C in the opposite directions to reduce the volume of the ink flow path 18B, a positive pressure is generated in the ink flow path 18B (FIG. 2C). ).

  As a result, the meniscus in the nozzle due to a part of the ink filling the ink flow path 18B is pushed out and moved in the direction pushed out from the nozzle, and protrudes out of the nozzle to form a liquid column of ink. After that, while maintaining this state (FIG. 2C) for a predetermined period, the positive pressure in the ink flow path 18B is eventually reversed to become negative pressure. In the process of changing from positive pressure to negative pressure, the meniscus is changed. A force is applied to pull the ink into the ink flow path 18B, tearing the liquid column of ink in the vicinity of the nozzle, and the ejected ink is ejected as droplets and flies. Here, after the pressure in the ink flow path 18B becomes a negative pressure, when the partition walls 17B and 17C are returned again to the neutral position shown in FIG. A negative pressure is applied to the ink in the flow path 18B, and the pressure of the ink in the ink flow path 18B that is going to change from negative pressure to positive pressure by the inversion as described above is canceled, and the meniscus is changed. Damping to suppress vibration due to the reverberation pressure of the meniscus.

  Thus, when driving the droplet discharge head 1 having a plurality of ink flow paths 18 separated by the partition walls 17 at least partially made of a piezoelectric material, when the partition walls of one ink flow path perform a discharge operation, Since the adjacent ink flow path is affected by the operation of the partition wall, normally, among the plurality of ink flow paths 18, one ink flow path 18 that is separated from each other with one or more ink flow paths 18 in between is combined. The plurality of ink flow paths are divided into two or more groups so as to form a group, and the drive control is performed so that the droplet discharge operation is sequentially performed in time division for each group. For example, when all the ink channels 18 are driven to output a solid image, so-called three-cycle driving is performed in which the ink channels 18 are selected every two ink channels and ejected in three phases.

  This three-cycle driving operation will be further described with reference to FIG. In the example shown in FIG. 3, the droplet discharge head will be described on the assumption that the ink flow path is composed of nine ink flow paths 18 of A1, B1, C1, A2, B2, C2, A3, B3, and C3. In addition, FIG. 4 shows a timing chart of pulse waveforms applied to the respective ink flow paths 18 of A, B, and C at this time.

  When droplets are ejected, first, a voltage is applied to the electrodes of each ink flow path of the A group (A1, A2, A3), and the electrodes of the ink flow paths adjacent to both are grounded. For example, when a drive signal composed of a rectangular wave of 1 AL width positive voltage + Von is applied to the A set of ink flow paths, the partition walls of the A set of ink flow paths to be ejected are deformed to the outside, and a negative pressure is generated in the ink flow path 18. Will occur. Due to this negative pressure, ink flows from the ink tank into the A set of ink flow paths 18 (Draw).

  If this state is maintained for 1 AL, the pressure is reversed to a positive pressure. Therefore, when the electrode is grounded at this timing, the deformation of the partition wall is restored, and a high pressure is applied to the ink in the A set of ink flow paths 18 (Release ). Furthermore, when a rectangular wave of negative voltage −Voff is applied to the electrodes of each ink flow path of the A set at the same timing, the partition wall is deformed inward, and a higher pressure is applied to the ink (Reinforce), and the ink column is pushed out from the nozzle. It is. After 1AL, the pressure is reversed and the inside of the ink flow path 18 becomes a negative pressure. When 1AL further passes, the pressure in the ink flow path 18 is reversed and becomes a positive pressure, so at this timing (after 2AL has passed) When the ground is grounded, the deformation of the partition wall is restored and the remaining pressure wave can be canceled.

  Here, the voltage of this drive signal is | Von | ≧ | Voff |.

  Subsequently, the operation is performed in the same manner as described above for each ink flow path 18 of the B group (B1, B2, B3) and further to each ink flow path 18 of the C group (C1, C2, C3).

  Note that AL (Acoustic Length) is ½ of the acoustic resonance period of the ink flow path. This AL applied a rectangular wave voltage pulse to the partition, which is an electromechanical conversion means, measured the speed of the ejected droplet, and changed the rectangular wave pulse width while keeping the rectangular wave voltage value constant. Sometimes it is determined as the pulse width that maximizes the flying speed of the droplet. A pulse is a rectangular wave having a constant voltage peak value. When 0V is 0% and a peak voltage is 100%, the pulse width is 10% of the voltage from 0V and the peak voltage. It is defined as the time between 10% of the falling edge. Furthermore, the rectangular wave here refers to a waveform in which both the rise time and fall time between 10% and 90% of the voltage are within ½ of AL, preferably within ¼. .

  By the way, the pressure applied to eject the ink remains in the ink flow path and vibrates even after the ink is ejected, so that the ink pressure in the nozzle fluctuates and the meniscus vibrates. When positive pressure is applied to the ink in the nozzle due to the pressure fluctuation at this time, the meniscus moves in a direction protruding from the nozzle. The meniscus protruding from the nozzle may be drawn into the nozzle with the next negative pressure after the positive pressure is reversed. This vibration is repeated several times, and the movement of the meniscus is gradually attenuated and the next discharge becomes possible.

  However, especially when ink is ejected continuously, the meniscus may jump out too much. Such protrusion of the meniscus is not a problem when the ink has a high viscosity. However, when a low-viscosity ink, particularly a low-viscosity ink of less than 6 cp, is used, the ink largely protrudes from the nozzle due to meniscus vibration. As a result, the discharge may become unstable.

  As a result of intensive analysis on the causes of ink overflow and ejection instability caused by meniscus protrusion in such a shear mode type liquid droplet ejection head, the present inventor has found that there are two causes.

  First, the viscosity resistance is insufficient for discharging low-viscosity ink, and the conventional technique cannot sufficiently suppress the overflow of ink. Since the viscosity resistance is proportional to the inverse of the square of the ink viscosity and the cross-sectional area of the flow path, when the viscosity is halved, the viscosity resistance is halved. For this reason, the meniscus vibration at the time of ejection becomes large, the meniscus protrudes greatly from the nozzle, and the ink overflows.

  Secondly, in a shear mode type liquid droplet ejection head, normally, two adjacent ink flow paths cannot be driven at the same time with one partition interposed therebetween. However, when three-cycle driving is performed as described above, for example, The ink flow path is continuously driven. Therefore, for example, in the example of FIG. 2, when the ink flow path 18B is driven for ejection, the movement of the partition walls 17B and 17C at that time is interlocked with the adjacent ink flow paths 18A and 18C. As a result, half of the vibration is transmitted to the adjacent ink flow paths 18A and 18C only by driving the ink flow path 18B, and meniscus vibration is also generated in the nozzles of these ink flow paths 18A and 18C. As the adjacent ink flow paths are continuously driven, these meniscus vibrations propagate through the entire head and generate complicated pressure waves that are folded and overlapped. As a result of taking into account this complex pressure wave, the pressure applied in the ink flow path fluctuates depending on whether or not the adjacent ink flow paths are continuously driven, the speed changes, and the ejection becomes unstable. .

In order to suppress the overflow of ink due to the protrusion of the meniscus, it is considered that the viscosity resistance should be increased. In order to increase the viscous resistance, the cross-sectional area may be reduced according to the equation of motion of the flow path shown in the following equation. However, if the cross-sectional area is simply reduced, the amount of droplets that can be ejected is also reduced in proportion, and the design is not appropriate for a droplet ejection head.

  As a result of diligent investigation focusing on the shape factor of the viscous resistance in the above formula, the present inventor has found that the ink flow path structure having a rectangular cross section has a longitudinal direction parallel to the partition wall surface in the cross sectional shape, and this depth direction. When the vertical direction of the partition walls perpendicular to each other is horizontal, increasing the vertical length and increasing the vertical / horizontal ratio calculated from the vertical ÷ horizontal width to make it distorted can reduce the absolute value of the cross-sectional area so much. It was discovered that viscous resistance can be increased. That is, it has been found that the viscosity resistance can be increased without reducing the droplet amount at the expense, and the ink can be prevented from overflowing even with low-viscosity ink, and a droplet discharge head capable of stable discharge can be obtained. .

  The following reasons are conceivable. That is, it is known that the viscosity of the ink has a shear rate dependency, which is lower than the static viscosity in a high shear region during actual ejection. In the shear mode type droplet discharge head, the high shear region in the ink flow path that is in contact with ink and actually vibrates at a high speed is a partition portion including a piezoelectric material. Therefore, the partition portion corresponds to a non-shear region. This is presumably because the viscosity resistance is more greatly affected than the ceiling wall and bottom wall portions. That is, it has been found that the effect of the partition wall influences more than the effect of simply reducing the cross-sectional area in the cross-sectional shape of the ink flow path.

  On the other hand, as a result of intensive studies on the aspect ratio of the cross-sectional shape of the ink flow path, it has been found that an adverse effect is seen when trying to obtain the effect of viscous resistance + α. As described above, when the aspect ratio is increased, the effect of increasing the viscous resistance can be obtained without sacrificing the amount of droplets. However, the crosstalk between the adjacent ink flow paths becomes very large by itself. That is, it cannot be put into practical use as it is.

  This is because as the aspect ratio is increased without changing the thickness of the partition wall, that is, as the partition wall is increased, the structure of the ink flow path becomes softer, so that the primary resonance occurs and the pressure fluctuation becomes too large. It is thought to be the cause. As a result of intensive studies by the inventor, it has been found that such a problem can be reduced by the hardness of the partition wall, specifically, the hardness of the partition wall having a certain resonance frequency or higher. Invented.

  Conventionally, in order to solve the problem of ink overflow when such low-viscosity ink is used, there has been no technology focusing on the aspect ratio of the ink flow path structure and the characteristics of hardness required for the partition walls.

  For example, as shown in FIG. 9, Patent Document 1 includes an ink flow path serving as an ink flow path, which includes a fired ink flow path 501 having a nozzle 505 and a non-fired ink flow path 502 having no nozzle 505. By alternately shifting these in the ink discharge direction orthogonal to the length direction and the column direction of the ink flow path, the fired ink flow path 501 is replaced with a wide ink flow path area 501a having an inactive side wall 503, and It is disclosed that the influence of crosstalk between adjacent ink flow paths is reduced by forming a T-shaped cross section including a narrow ink flow path area 501b having an operating side wall 504.

  Here, it is described that the aspect ratio of the narrow ink flow path region 501b having the working side wall 504 is about 5 or more, but the hardness of the working side wall 504, which is a partition, is described. In addition, there is no disclosure of suppressing ink overflow due to meniscus protrusion when low-viscosity ink is used.

  In fact, according to the present inventors, when the low-viscosity ink in which the cross-sectional shape of the ink flow path region 501a sandwiched between the non-operational side walls 503 is too wide and the viscosity resistance is too small and less than 6 cp is used. The ink overflowed and could not be used. In addition, since the structure is complicated, the cost is high and it cannot be practically used.

  Further, Patent Document 2 describes the resonance frequency of the partition walls constituting the droplet discharge head. However, this technique measures the impedance of the partition wall and determines the frequency at which the impedance is minimized and determines the frequency of the resonance, thereby testing the part. Crosstalk is performed focusing on the resonance frequency of the partition wall. There has been no mention of reduction, and furthermore, reduction of ink overflow due to meniscus protrusion, and the problem has not been solved.

  Further, Patent Document 3 describes the aspect ratio and resonance frequency of the partition walls constituting the droplet discharge head. However, this technique has the problem that the pressure performance of the ink becomes non-uniform due to the variation in rigidity due to the manufacturing process such as the variation in the thickness of the adhesive layer to which the partition is bonded. In addition to defining the aspect ratio, the resonance frequency of the partition walls, the density of the piezoelectric ceramics, and the Young's modulus of the piezoelectric ceramics satisfy the specified relationship, and the rigidity of all the partition walls is aligned within a range suitable for discharge. It is to homogenize the performance. By specifying the aspect ratio of the ink flow path structure and the resonance frequency of the partition wall, it is possible to reduce crosstalk when using low viscosity ink and to reduce ink overflow. No mention was made and the problem was not solved.

Special table 2009-500209 Japanese Patent No. 2632061 JP 2003-246064 A

  The present invention provides a shear mode type droplet discharge in which a large number of ink flow paths and a large number of partition walls are alternately arranged in parallel, and ink in the ink flow paths is discharged from the nozzles by a deformation operation of the partition walls between adjacent ink flow paths. In the head, by defining the ink flow path structure and the resonance frequency of the partition wall, even if low viscosity ink is used, speed fluctuation due to crosstalk can be suppressed, and overflow of ink from the nozzle can be reduced, It is an object of the present invention to provide a droplet discharge head capable of performing stable discharge and a recording apparatus using the same.

  Other problems of the present invention will become apparent from the following description.

  The above problems are solved by the following inventions.

The invention according to claim 1 is an electrode in which a large number of ink flow paths and a large number of partition walls to which ink is supplied are alternately arranged, and the partition walls between adjacent ink flow paths are formed on the surface of the partition walls. In a liquid droplet ejection head that is configured by an actuator that deforms in response to an applied voltage applied to the ink, and that ejects the ink in the ink flow path from a nozzle that communicates with the ink flow path by a deformation operation of the partition wall,
The ink flow path is formed in a rectangular cross-sectional shape in the direction in which the partition walls are arranged, and has a depth direction parallel to the partition surface and a direction in which the partition walls are orthogonal to the depth direction. When it is horizontal, the aspect ratio (vertical / horizontal) in the cross-sectional shape of the ink flow path formed in the rectangular shape is 5.00 or more and less than 7.75,
In the liquid droplet ejection head, the partition wall has a resonance frequency of 1.5 MHz or more.

  The invention according to claim 2 is the droplet discharge head according to claim 1, wherein the aspect ratio of the ink flow path is 6.00 or more and 7.00 or less.

  A third aspect of the present invention is the droplet discharge head according to the first or second aspect, wherein the ink flow path has a lateral width between the adjacent partition walls of 40 μm or more and 60 μm or less.

  The invention according to claim 4 is characterized in that an insulating protective film made of an organic material is formed on the surface of the electrode of the partition wall facing the ink flow path. It is a droplet discharge head of description.

  A fifth aspect of the present invention is the droplet discharge head according to any one of the first to fifth aspects, wherein the ink has a viscosity of less than 6 cp.

  According to a sixth aspect of the present invention, the liquid droplet ejection head according to any one of the first to fifth aspects is provided, and recording is performed by landing ink ejected from the nozzles on a recording material. It is a recording device.

  According to the present invention, a shear mode type liquid in which a large number of ink flow paths and a large number of partition walls are alternately arranged, and ink in the ink flow paths is ejected from the nozzles by a deformation operation of the partition walls between adjacent ink flow paths. Even if a low-viscosity ink (for example, an ink having a viscosity of less than 6 cp) is used in the droplet ejection head, speed fluctuation due to crosstalk can be suppressed, and overflow of ink from the nozzles can be reduced and stable ejection can be performed. It is possible to provide a droplet discharge head and a recording apparatus that can perform the above-described process.

(A) is a schematic perspective view showing an example of a shear mode type droplet discharge head, and (b) is a sectional view. The figure which shows the action | operation at the time of the ink discharge of the droplet discharge head shown in FIG. The figure explaining the 3-cycle drive operation | movement of the droplet discharge head shown in FIG. The figure which shows an example of the drive signal at the time of 3 cycle drive operation | movement Sectional drawing which follows the (v)-(v) line | wire of Fig.1 (a) which shows the longitudinal cross-sectional shape of an ink flow path Diagram explaining resonance frequency Perspective view partially broken away showing another example of a droplet discharge head The figure which shows schematic structure of a recording device Sectional drawing which shows the ink flow path structure of the conventional droplet discharge head

  In the liquid droplet ejection head according to the present invention, a large number of ink flow paths and a large number of partition walls are alternately arranged in parallel, and the partition walls between adjacent ink flow paths are applied to an applied voltage applied to an electrode formed on the surface of the partition walls. It is composed of an actuator that responds and deforms. Such a droplet discharge head is a so-called shear mode type droplet discharge head made of a piezoelectric material such as PZT whose actuator is polarized and deformed in response to an applied voltage. Pressure is applied to the ink in the ink flow path by the deformation operation, and the ink is ejected as droplets from the nozzle communicating with the ink flow path.

  In the present invention, as an example of the ink, a low-viscosity ink having a meniscus that protrudes greatly in a shear mode type liquid droplet ejection head and is likely to cause a problem of overflow (viscosity at an ink temperature used for ejection) is an object. This low-viscosity ink is supplied and filled in the ink flow path for discharging.

  The viscosity of the ink is usually a normal temperature (25 ° C.), but it is known that the viscosity of the ink is temperature-dependent. In some cases, the ink supply means or the discharge head may have a heating device. In some cases, the ink temperature is increased to lower the viscosity. In this case, the viscosity of the ink is a viscosity measured at the set temperature at which the ink used for ejection is heated.

  FIG. 5 is a cross-sectional view taken along line (v)-(v) in FIG. 1B, which is along the depth direction parallel to the surface of the partition walls 17 and in the direction in which the partition walls 17 are juxtaposed. The longitudinal cross-sectional shape at the time of cut | disconnecting along is shown. The structure of the ink flow path 18 according to the present invention will be described with reference to the drawing. The ink flow path 18 according to the present invention has a vertical direction h in the depth direction parallel to the surface of the partition wall 17 and the partition wall 17 orthogonal to the depth direction. When the side-by-side direction is defined as the width w, the vertical cross-sectional shape of the partition wall 17 in the side-by-side direction is formed in a rectangular shape, and the aspect ratio (vertical h / width w) in the vertical cross-sectional shape is 5.00 or more and Less than .75.

  Here, the horizontal length (w) of the ink flow path is the horizontal width of the region filled with ink. That is, it means the lateral width of the final flow path that is made usable by forming an electrode on the surface of the partition wall after forming the ink flow path. This horizontal width is observed along the depth direction parallel to the surface of the partition walls and the longitudinal cross-sectional shape when the ink flow path is cut along the parallel direction of the partition walls using an observation device such as a microscope. Can be obtained.

  When at least one of the vertical length (h) and the horizontal length (w) varies in one ink flow path, measurement is performed at a plurality of positions in the length direction of the ink flow path, and the average is obtained. It is preferable to take.

  When the aspect ratio of the ink flow path is within the above range, the viscosity resistance can be increased without reducing the cross-sectional area of the ink flow path and reducing the droplet amount. Thereby, overflow of ink can be suppressed.

  If this aspect ratio is less than 5.00, the proportion of the partition wall region that vibrates at high speed becomes small, and even if the cross-sectional area is the same, the viscous resistance is small and the overflow of ink is suppressed. It becomes difficult. On the other hand, when it is 7.75 or more, the ink flow path becomes too long and becomes a soft flow path structure, and it becomes difficult to suppress the primary resonance only by defining the resonance frequency of the partition wall described later. Will become bigger. More preferably, it is 6.00 or more and 7.00 or less.

  In general, the ink flow path is formed by grinding a groove having a predetermined depth to be an ink flow path on the substrate surface in parallel by a grinding blade such as a rotating grindstone. Therefore, the ink flow path in which the aspect ratio satisfies the above range can be formed by appropriately selecting or adjusting the thickness and the grinding depth of such a grinding blade.

  In the liquid droplet ejection head according to the present invention, as shown in FIG. 1, the ink flow path 18 has a shallow groove portion 18a whose depth gradually decreases on the side opposite to the nozzle end where the nozzle 13 is disposed. Ink formed in a straight shape from the nozzle end to the opposite end as shown in FIG. 7 is not limited to the structure in which the ink is supplied from the direction crossing the length direction of the ink flow path 18 (upward in FIG. 1). The flow path 18 may be supplied along the length direction of the ink flow path 18 from the opposite end. In FIG. 7, the same reference numerals as those in FIG. 1 denote the same components.

  In the case of a droplet discharge head having a shallow groove portion 18a in the ink flow path 18 as shown in FIG. 1, the aspect ratio of the ink flow path 18 is an effective driving length with a constant depth shown in FIG. (L length).

  In this ink flow path, the horizontal width (w) of the flow path between the adjacent partition walls is preferably 40 μm or more and 60 μm or less. By setting this range, it is possible to obtain a sufficient viscosity resistance even with a low viscosity ink of 6 cp or less, and to stably discharge the ink. If the thickness is less than 40 μm, the viscosity resistance may be too high and the amount of liquid may be insufficient. If the thickness exceeds 60 μm, the viscosity resistance may be insufficient and 6 cp of ink may not be stably ejected.

  The partition wall in the present invention has a resonance frequency of 1.5 MHz or more. Since the partition wall has a resonance frequency equal to or higher than this value, the partition wall has so-called hardness, so that primary resonance can be effectively suppressed and crosstalk can be reduced. If it is less than 1.5 MHz, it will be difficult to suppress the primary resonance of the partition walls, and it will be difficult to reduce crosstalk.

  Here, the resonance frequency of the partition wall is measured by a measuring device such as an impedance analyzer, a network analyzer, or an impedance / LCR meter by applying a variable frequency voltage to the electrode on the partition wall surface to deform the partition wall. This is the primary resonance frequency (primary resonance) of the partition wall (FIG. 6). The measurement is performed for all the partition walls of the droplet discharge head, and is calculated as an average value of the measurement results.

  The resonant frequency of the partition can be adjusted by the shape of the partition and the characteristics of the material of the piezoelectric material used. For example, when the vertical / horizontal ratio of the piezoelectric material in the partition wall portion is increased (for example, the height of the partition wall is increased), the resonance frequency is lowered because the rigidity of the partition wall is decreased. On the other hand, when the aspect ratio of the piezoelectric material in the partition wall portion is reduced (for example, the thickness of the partition wall is increased), the rigidity of the partition wall is increased, so that the resonance frequency is increased. Therefore, in order to form the partition so that the resonance frequency of the partition satisfies the above value or more, it can be adjusted by decreasing the vertical / horizontal ratio of the piezoelectric material in the partition (for example, increasing the thickness of the partition). Further, by using a piezoelectric element having a high Young's modulus or a small compliance, the rigidity can be increased and the resonance frequency can be increased.

  In addition, when the electrode provided on the side surface of the partition wall is provided by plating, the rigidity of the partition wall can be increased by increasing the thickness of the plating, and the resonance frequency can be increased, and these are appropriately combined within the scope of the present invention. Can be adjusted.

  In the present invention, an insulating protective film made of an organic material can be further formed on the electrode surface of the partition wall facing the ink flow path so as to prevent the electrode from coming into direct contact with the ink. Such an insulating protective film is preferably a film formed by vapor deposition such as chemical vapor deposition, and a film made of polyparaxylylene or a derivative thereof is particularly suitable.

  The horizontal length (w) of the ink flow path in the present invention is the width of the final flow path after the formation of the protective film when such an insulating protective film is formed on the electrode surface. .

  The droplet discharge head according to the present invention is not limited to the one in which the nozzle 13 is disposed at the end portion in the length direction of the ink flow path 18 as shown in FIGS. The upper substrate 14 may be opened at a portion.

  In the present invention, the low-viscosity ink of less than 6 cp may be a generic term for liquid materials that can be ejected from the nozzles of a shear mode type droplet ejection head. For example, in addition to ink for image formation, color filters for liquid crystal panels, Examples thereof include functional liquids used for various industrial applications such as semiconductor device manufacturing apparatuses.

  Next, an example of a recording apparatus according to the present invention is shown in FIG.

  FIG. 8 is a diagram illustrating a schematic configuration of a recording apparatus that forms an image on a recording material. In the recording apparatus 200, the recording material P is sandwiched between a pair of conveyance rollers 201 and is further rotated by a conveyance motor 202. It is conveyed in the Y direction in the figure by a driven conveyance roller 203.

  The droplet discharge head 1 is provided between the transport roller 203 and the transport roller pair 201 so as to face the recording surface PS of the recording material P. The droplet discharge head 1 is substantially the same as the conveyance direction (sub-scanning direction) of the recording material P by a driving unit (not shown) along the guide rail 204 spanned across the width direction of the recording material P. The nozzle 205 is mounted on a carriage 205 provided so as to be able to reciprocate along the XX ′ direction (main scanning direction) orthogonal to the recording surface PS of the recording material P. The drive signal generator 100 (see FIG. 2) is electrically connected via the flexible cable 206.

  The droplet discharge head 1 scans and moves the recording surface PS of the recording material P in the XX ′ direction as the carriage 205 moves in the main scanning direction, and discharges droplets from the nozzles during the scanning movement. By doing so, a desired inkjet image is formed.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

(Examples 1-5, Comparative Examples 1-11)
A piezoelectric material substrate made of two PZTs (H8H manufactured by Sumitomo Metal Electrodevice Co., Ltd.) and a lower substrate, each of which is polarized, are joined together with an adhesive with different polarization directions of each piezoelectric material substrate, and then the piezoelectric material Parallel so that a plurality of groove-like ink flow paths with a certain depth from one end to the other end of the substrate at a depth crossing the bonding surface using a rotating grindstone from the surface of the substrate and the partition walls therebetween are alternated. In addition, after forming an electrode and a parylene protective film on the side surface of each partition wall, the upper surface of each ink flow path is covered with an upper substrate, and each ink flow path has a straight shape as shown in FIG. A droplet discharge head was formed.

  All the droplet discharge heads were set to 180 dpi, and the length of the ink flow path was set to 5 mm.

  In addition, each droplet discharge head varies the aspect ratio of the ink flow path as shown in Table 1 by changing the thickness and the grinding depth of the rotary grindstone, and the thickness of the partition is shown in Table 1. Thus, the resonance frequency of the partition walls was varied as shown in Table 1.

  The resonance frequency is measured by applying a variable frequency voltage to each electrode to drive the partition wall, measuring the resonance frequency of the primary resonance using an impedance analyzer (FRA1260 manufactured by Toyo Corporation), and calculating the average value of all the partition walls. This was done by calculating

The piezoelectric material had a density of 8.02 g / cm ³ and a Young's modulus of 109.9 GPa.

(Evaluation)
Each droplet ejection head was evaluated for ejection stability, presence or absence of ink overflow, and crosstalk ratio.

Discharge stability Ink is discharged from each ink flow path by using the water-based ink (surface tension: 41 dyn / cm) having a viscosity of 5.7 cp and performing the 3-cycle driving shown in FIG. 3 at 7.2 kHz. Discontinue discharge from time to time, measure the amount of discharged droplets using a precision balance, find the average amount of discharged droplets per droplet, and show the fluctuations in the amount of droplets when the droplet speed is changed: It was evaluated according to the criteria. The results are shown in Table 1.
○: Even when the discharge speed is 6 to 10 m / sec or more, the fluctuation of the liquid amount during discharge is within 10%.
(Triangle | delta): The liquid volume fluctuation | variation at the time of discharge is less than 10% until discharge speed is -8m / sec, and if it exceeds 8 m / sec, liquid volume fluctuation | variation will exceed 10%.
X: The liquid amount fluctuation | variation at the time of discharge exceeds 10% when discharge speed is less than-8m / sec.

Presence / absence of ink overflow Continuous discharge was performed for 10 minutes from 128 nozzles, which is 1/2 or more of all nozzles, and observation was made as to whether or not nozzles were missing due to ink overflow, and evaluation was performed according to the following criteria: . Nozzle missing was marked as x when even one nozzle occurred. The results are shown in Table 1.
○: No overflow occurred. ×: Nozzle missing due to overflow.

A crosstalk rate is discharged from one ink flow path at a discharge speed of 6 m / sec, and the ink flow paths on both sides or adjacent ones are sequentially driven for a total of 60 ink flow paths, and the difference in droplet discharge speed is calculated. Measured and evaluated according to the following criteria. The results are shown in Table 1.
○: Speed difference is less than 15% △: Speed difference is 15% or more and less than 20% ×: Speed difference is 20% or more (not practical)

(Examples 6 and 7, Comparative Examples 12 to 14)
As shown in Table 2, the droplet discharge heads are 300 dpi, and the length of the ink flow path is 2 mm, except that the aspect ratio of the ink flow path and the resonance frequency of the partition walls are different. Similarly, each droplet discharge head was evaluated for discharge stability, presence or absence of ink overflow, and crosstalk ratio. The results are shown in Table 2.

  As shown in Tables 1 and 2, in Examples 1 to 7, satisfactory results were obtained for all three items of ejection stability, ink overflow, and crosstalk ratio, whereas Comparative Example 1 was obtained. In -14, at least any item cannot be satisfied, and the effect of the present invention is not obtained.

  In particular, in Comparative Examples 9 and 12, ink refill shortage to the ink flow path occurred, and it was not practical.

  In addition, the cross-sectional area of the ink flow path is, for example, 285 × 50 = 1425 μm in Example 2 and 200 × 70 = 14000 μm in Comparative Example 1, which is almost the same cross-sectional area, but in Example 2, three items are good. On the other hand, in Comparative Example 1, both the ejection stability and the overflow of the ink are bad, and it can be seen that the shape effect on the viscous resistance appears.

  Further, it can be seen from Comparative Examples 10 and 11 that the resonance frequency needs to be 1.5 MHz or more, and Comparative Examples 7 and 12 show that the aspect ratio needs to be 5.00 or more.

1: Droplet ejection head 11: Ink tube 12: Nozzle forming member 13: Nozzle 14: Upper substrate 15: Ink supply port 16: Lower substrate 17: Partition 17a: Upper wall portion 17b: Lower wall portion 18: Ink flow path 19A -19C: Electrode 100: Drive signal generating unit 200: Recording apparatus 201: Conveying roller pair 202: Conveying motor 203: Conveying roller 204: Guide rail 205: Carriage 206: Flexible cable P: Recording material PS: Recording surface

Claims (6)

A large number of ink flow paths and a large number of partition walls are alternately arranged in parallel, and the partition walls between the adjacent ink flow paths are responsive to an applied voltage applied to an electrode formed on the partition wall surface. A liquid droplet ejection head configured to eject the ink in the ink flow path from a nozzle communicating with the ink flow path by a deformation operation of the partition wall.
The ink flow path is formed in a rectangular cross-sectional shape in the direction in which the partition walls are arranged, and has a depth direction parallel to the partition surface and a direction in which the partition walls are orthogonal to the depth direction. When it is horizontal, the aspect ratio (vertical / horizontal) in the cross-sectional shape of the ink flow path formed in the rectangular shape is 5.00 or more and less than 7.75,
A liquid droplet ejection head, wherein the partition wall has a resonance frequency of 1.5 MHz or more.   The droplet discharge head according to claim 1, wherein an aspect ratio of the ink flow path is 6.00 or more and 7.00 or less.   3. The droplet discharge head according to claim 1, wherein the ink flow path has a lateral width between the adjacent partition walls of 40 μm or more and 60 μm or less.   4. The droplet discharge head according to claim 1, wherein an insulating protective film made of an organic material is coated on the electrode surface of the partition wall facing the ink flow path.   The droplet discharge head according to claim 1, wherein the ink has a viscosity of less than 6 cp. A recording apparatus comprising the droplet discharge head according to claim 1, wherein recording is performed by landing ink discharged from the nozzle on a recording material.

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