JP3108955B2 - Droplet ejection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a droplet discharge apparatus, and more particularly, to an on-demand type multi-nozzle ink jet recording apparatus having a plurality of nozzles and ejecting ink droplets from each nozzle as required. The present invention relates to a droplet discharge device.

[0002]

2. Description of the Related Art At present, an on-demand type multi-nozzle ink jet recording apparatus uses a piezoelectric element to convert an electric signal into a mechanical displacement and apply pressure to ink in a flow path to eject ink droplets. There is a so-called bubble jet system in which ink droplets are ejected by applying heat to ink in a path and generating steam pressure.

US Pat. No. 3,683,212 discloses a cylindrical structure covering a flow path, and US Pat. No. 3,946,398 discloses a diaphragm structure using a piezoelectric element. Have been. Further, JP-A-55-
No. 65559 discloses a structure in which a bimorph element, which is a combination of a piezoelectric element and a diaphragm, which is generally called a Kaiser type, is attached to the upper part of each flow path. In a conventional inkjet head using these piezoelectric elements,
Since one piezoelectric element must correspond to one nozzle, and the piezoelectric element is large, it has been difficult to realize a high-density multi-nozzle head for achieving high printing quality. FIG. 7 shows a typical conventional example of a Kaiser type head. As described above, in the Kaiser type head, the vibration plate 22 serving as a cover is adhered to the substrate 21 on which the flow passage 20 is formed, and the piezoelectric element 23 is adhered to each flow passage portion on the vibration plate. As is clear from FIG.
Since the size of the piezoelectric element 23 is larger than the pitch, the flow path has a fan shape, and it is difficult to increase the nozzle density. Channel 2
The shapes of the ink droplets ejected from the respective flow paths are not constant because the shapes of the 0s are different from each other. Further, a large number of piezoelectric elements need to be attached to predetermined positions, and the manufacturing process becomes complicated.

Japanese Patent Publication No. 61-59911 discloses the principle of a so-called bubble jet system. In this method, the size of the heating element for heating the ink can be reduced, so that the above-mentioned problems, which are caused by the increase in the density and the number of nozzles, which are observed in the ink jet head using the conventional piezoelectric element, are small. However, the bubble jet method is extremely inefficient as compared with the piezoelectric element method, and it is necessary to give 10 times or more energy to eject one ink droplet. Further, since it is necessary to boil the ink, it is necessary to use an ink which has a relatively low boiling point and does not cause deterioration due to heat or form a deposit on the heating element. In addition, there is a problem in durability such that the heating element is damaged by cavitation generated when the vapor bubbles are generated and disappeared.

In order to overcome these problems, Japanese Patent Application Laid-Open
No. 247,051 discloses a method using a shear mode of a piezoelectric element. FIG. 8 shows a typical configuration. In this method, a flow path partition is constituted by a piezoelectric element 28 perpendicular to the substrates 25 and 26 and polarized in the height direction of the head 27, and electrodes formed on both sides of the partition. An electric field perpendicular to the polarization direction 29 is applied to deform the flow path partition wall of the piezoelectric element in a shearing mode, applying pressure to the ink in the flow path and ejecting ink droplets from the nozzles 30. In this method, the displacement amount of the flow path partition necessary for ejecting ink droplets can be secured by optimizing two dimensions, the height of the flow path partition perpendicular to the nozzle arrangement direction and the length of the flow path. The flow paths can be arranged at the same pitch as the nozzles, and an ink jet head having a large number of nozzles at high density can be configured.
In addition, any ink having good energy efficiency can be used as in the case of a conventional inkjet head using a piezoelectric element.

However, in the method using the shear mode,
Since the flow path partition is constituted by the piezoelectric element, 50 to 500 [μ
m], or a large number of very thin piezoelectric element plates must be combined, or a large number of channel partition walls having a height of several hundred μm or more must be formed on a rectangular parallelepiped piezoelectric element substrate by some method. As the piezoelectric material, PZT, quartz, lipeum niobate, etc. are known, but all are hard and brittle materials,
It is not suitable for forming a large number of flow path partition walls by machining. It is also conceivable to form the channel partition walls by a chemical method such as etching. However, these materials are not considered to have good workability, and it is very difficult to process them to a depth of several hundred μm. Therefore, in the configuration using the above-mentioned shear mode, the production cost becomes enormous and mass production is difficult.

[0007]

As described above, an ink jet recording apparatus using a conventional piezoelectric element has the advantages of being energy efficient and being able to use any ink, but has a high density for printing with high quality. It is not suitable for use with a large number of nozzles.

In addition, the bubble jet method has problems such as low energy efficiency, large restrictions on ink, and poor durability.

In order to solve these problems, an ink jet recording apparatus using a shear mode of a piezoelectric element has been disclosed. However, it is necessary to perform fine processing on a fragile piezoelectric material, and it is difficult to manufacture the piezoelectric material. Not suitable.

An object of the present invention is to provide a mass-produced and inexpensive droplet discharge device having a novel principle and configuration having a large number of nozzles arranged at high density, having high energy efficiency and high durability. is there.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a flow system having a plurality of partitions provided substantially perpendicular to a plane direction and a flow path defined by the partitions. And a cover plate formed of a piezoelectric element plate polarized in the thickness direction and fixed on an end surface of the partition wall.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the preferred embodiments shown in the accompanying drawings. FIG. 1 is a cross-sectional view of a flow path showing a basic configuration of a droplet discharge device according to the present invention. In the droplet discharge device according to the present invention, a plurality of partitions 1a, 1b, 1c, 1d are formed substantially at right angles to the plane direction.
a, 1b, 1c, 1d, the ink flow paths 2a, 2b, 2
and a drive electrode 4 on both surfaces.
a, 4b, 4c, and a cover plate 6 formed of a piezoelectric element plate formed with a ground electrode 5 and polarized in the thickness direction (the direction of arrow P), and not shown in FIG. And a nozzle plate provided.
Considering both the ease of deformation of the partition and the workability of the flow path and the partition, the flow paths 2a, 2b, 2c and the partitions 1a, 1
The cross sections of b, 1c and 1d are preferably rectangular.

FIG. 2 is a principle diagram for explaining the droplet discharging operation of the above-mentioned device. Here, an operation of ejecting a droplet from the flow channel 2b will be described. Driving electrode 4b corresponding to channel 2b among three driving electrodes 4a to 4c shown
Only in this case, a voltage is applied in the direction in which the piezoelectric element (cover plate 6) contracts in a plane. Channel 2 of cover plate 6
b only shrinks, so that the partition walls 1 on both sides of the flow path 2b
b and 1c are drawn, and the volume of the flow path 2b is reduced. For this reason, pressure is applied to the liquid in the flow path 2b, and a droplet is ejected from the nozzle. In addition, the non-selection channel 2a will be described. Since the piezoelectric element plate above the adjacent channel 2b shrinks,
The piezoelectric element portion above the flow path 2a and the partition wall 1a also
It is drawn in the direction and deformed. However, in this case, since the partition wall 1a is deformed in the same direction as the partition wall 1b, the volume of the flow path 2a does not change, and no pressure is applied to the ink in the flow path 2a. The same applies to the channel 2c. As described above, according to the present invention, it is possible to select only a specific flow path and eject droplets by using the cover plate 6 composed of a structurally integrated piezoelectric element plate.

Next, FIG. 3 is a perspective view of a multi-nozzle ink jet head using the present invention, and FIG. 4 is a sectional view thereof. A large number of channels 8 and partition walls 9 are formed in the channel substrate 7. The cross section of each flow path 8 and the partition 9 is substantially rectangular. Each channel 8 is independent on the nozzle plate 10 side and communicates with a common ink chamber 11 for supplying ink on the opposite side. Each flow path 8 and partition wall 9 extend in parallel from the nozzle portion to the common ink chamber portion, and correspond to the pitch of the nozzle 10a. Therefore, there is no need to adopt a fan-shaped channel arrangement as in the conventional inkjet head using a piezoelectric element, and it is possible to create a multi-nozzle inkjet head having an arbitrary number of nozzles. , Serial printers and line printers.

On the lower surface of the flow path substrate 7, a ground electrode 12 is provided.
A cover plate 14 made of a piezoelectric element plate on which a drive electrode 13 corresponding to each flow path is formed on the upper surface is mounted. The piezoelectric element plate serves as an actuator for deforming the flow path partition 9 and also functions as a flow path cover. Each drive electrode 13 has an electrode terminal 13a for supplying a signal from a flexible cable or the like. A nozzle plate 10 in which nozzles 10a corresponding to respective flow paths are formed is mounted on the front surface of the head.

In this structure, the flow path substrate 7 is a passive component whose partition 9 formed in a part thereof is deformed by the cover plate 14 made of a piezoelectric element plate. As compared with the conventional ink jet recording apparatus thus configured, the selection range of the material and the forming method of the flow path substrate 7 is very wide. For example, it is also possible to use a plastic member formed by injection molding suitable for mass production. In particular, when durability of the head is required, it is possible to use a photosensitive glass whose physical properties are changed by exposure to ultraviolet rays and which can be selectively etched by further applying a heat treatment. In the case of this configuration, since a relatively deep flow path needs to be formed, XeF and XeC which are ultraviolet light sources having excellent linearity are used as the exposure light source.
It is desirable to use an excimer laser using a gas such as 1, KrF, KrCl, or ArF.

Next, dimensions for designing a multi-nozzle ink jet head will be described. X [dp
i] (dots per inch) when realizing a print density of n channels, the adjacent channel pitch DN is: DN = 0.0254 × n / X [m] (1) Become. The dot diameter DD required at this time is as follows: DD = √2 × 0.0254 / X [m] (2) It is empirically known that a flying ink droplet becomes a dot having a diameter about twice when it adheres to paper, and the necessary ink droplet amount Qi is as follows. ^{Qi = π × DD 3/48} [m 3] ··· (3) By the way, the ink in the pressurized flow path in addition emitted as an ink droplet from a nozzle, also flowing back into the common ink chamber side. For this reason, the partition walls must give the flow path a volume reduction of about twice or more the required ink droplet amount. Therefore, the required flow volume change amount Qc is as follows: Qc ≧ 2 × Qi (4)

Next, the contraction amount ω of the piezoelectric element plate is obtained. The thickness of the piezoelectric element plate is T, and the width of the drive electrode is 0.8 of the flow path pitch.
When the applied voltage is V and the lateral piezoelectric constant is d, the amount of shrinkage ω is as follows. ω = d × V × 0.8 × DN / T (5) Since the partition wall is deformed substantially as shown in FIG. 2, the height of the partition wall is H and the length of the flow path is L. The flow path volume change amount dQ at this time is as follows: dQ = ω × H × L / 2 (6) At this time, it is assumed that the rigidity of the partition wall in the lateral direction is sufficiently smaller than that of the piezoelectric element plate.

Since the flow volume change amount Qc and dQ must be equal, from Equations 4 and 6, 2 × Qi ≦ ω × H0 × L0 / 2 (7) Here, when Qi is rewritten using equations (1) to (3) and equation (5) is substituted for ω, the following equation is obtained. 1.9 × 10 ⁻⁴ × π / X ² ≦ d × V × H × L × n / T (8) By transformation, H × L ≧ 1.9 × 10 ⁻⁴ × π × T / (X ² × d × V × n) (9) From this equation, it is possible to roughly estimate the relationship between the dimensions, material properties, and driving conditions of each part necessary to obtain an arbitrary nozzle density.

Here, the transverse piezoelectric strain constant d is set to 198 × 10 ^-12
[M / V], the drive voltage V is 200 [V], and the thickness T of the piezoelectric element plate is 10 ⁻⁴ [m], the required flow path length L for the heads with various nozzle densities FIG. 5 shows the relationship between the heights H of the partition walls. FIG. 5A shows the case where the flow path is formed in one row (n = 1), and FIG. 5B shows the case where the head is formed of two flow path rows shifted by a half pitch (n = 2). is there.
In FIG. 5, the relationship between the partition wall height and the flow path length must be at the upper right of the curve in order to produce a head of each print density. More specifically, referring to FIG. 5A, under the condition of a flow path length of 30 [mm] and a partition wall height of 0.4 [mm], since it is located at the upper right of the curve of 400 [dpi], 4
Although it can be applied to a 00 [dpi] head,
Since it is located at the lower left of the curve of 0 [dpi], it is impossible to obtain a sufficient amount of ink droplets for printing and cannot be applied to a 300 [dpi] head.

As described above, the lower limit of the flow path length and the height of the head partition wall for designing a head having desired specifications can be known by using the equation (9). On the other hand, there is an upper limit to the flow path length and the height of the partition wall in order to satisfy the requirements of reducing the material cost, realizing a small and light printing device, and reducing the height of the partition wall as much as possible in order to improve workability. The upper limit of these realistic dimensions is the channel length L ≦ 100 [mm] (10) Partition height H ≦ 2 [mm] (11) Therefore, in order to realize the recording apparatus based on the present invention, the flow path length and the partition wall height are determined by the equations (9), (10), and (1).
1) It must be within a range that satisfies the expression.

Another embodiment using the present invention is shown in FIG. In order to realize a printing device with a high printing density, it is necessary to apply fine processing to form the flow passages and the partition walls. Therefore, by forming the flow path 16 and the partition wall 17 on both sides of the flow path substrate 15 as shown in FIG. 6, the distance between the flow path and the partition wall on each of these surfaces can be doubled, and the workability is improved. Further, as is apparent from the equation (9), by forming two rows, the flow path length L and the flow path partition wall height H can be reduced, so that the processability can be improved and the printing apparatus can be downsized. it can.

In the droplet discharge device of the present invention, since the partition walls are deformed to apply pressure to the liquid in the flow path and eject droplets from the nozzle, the physical properties of the liquid are not limited at all, , Ink can also be used. Therefore, the present invention is not limited to a recording device as a computer terminal, but can be applied to a wide range of uses such as discharging various liquids, for example, an industrial printing device, a small amount of reagent discharge, and facsimile.

[0024]

As described above, according to the present invention, it is possible to inexpensively provide a droplet discharge device which has a large number of nozzles arranged at high density, has good energy efficiency, and has excellent durability. is there.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing the operation of the first embodiment.

FIG. 3 is a perspective view of a second embodiment.

FIG. 4 is a sectional view of a second embodiment.

FIG. 5 is a relationship diagram showing a relationship between a flow path length and a partition wall height.

FIG. 6 is a sectional view of a third embodiment.

FIG. 7 is a plan view and a cross-sectional view showing a first conventional example.

FIG. 8 is a plan sectional view and a front view showing a second conventional example.

[Explanation of symbols]

1a, 1b, 1c, 1d, 9, 17 Partition wall 2a, 2b, 2c, 8, 16 Channel 3, 7, 15 Channel substrate 4a, 4b, 4c, 13 Drive electrode 5, 12 Ground electrode 6, 14 Cover plate (Piezoelectric element plate) 10 Nozzle plate 10a Nozzle 11 Common ink chamber

Claims (10)

(57) [Claims] A substrate having a plurality of partition walls on a surface thereof;
A flow path substrate having the flow path is formed in a portion sandwiched between the partition wall and a cover plate that is secured to the front Symbol partition wall end face on the free
See, electrodes are formed on both surfaces of the cover plate, less the
The electrodes on one side are provided corresponding to the respective flow paths, and through the electrodes, a selected flow of the cover plate is selected.
By applying a voltage to the part corresponding to the road,
A droplet discharge device characterized by deforming partition walls on both sides of a road . 2. A portion according to claim 1, wherein the portion of the cover plate corresponds to an arbitrary selected flow path.
Voltage is applied in the direction in which the cover plate shrinks in the plane.
Droplet discharge device, characterized in that it is. 3. A part according to claim 1, wherein the portion of the cover plate corresponds to an arbitrary selected flow path.
By applying a voltage to the
A droplet discharge device characterized by being deformed so as to be deformed . 4. The claim 1-3, nozzles communicating with the flow path Yes and bored, to include a nozzle plate which is fixed to an end face of the channel substrate and the cover plate Characteristic droplet discharge device. 5. The common ink chamber according to claim 4 , wherein the plurality of flow paths are connected at one end to form a common ink chamber and the other end communicates with the nozzle. Characterized by having a constant cross-sectional area between them. 6. The claim 1-5, wherein the channel substrate, the said channel on both sides partition walls are formed respectively, wherein the pair mounted on opposite sides of the channel substrate A droplet discharge device comprising a cover plate and the nozzle plate having a plurality of nozzle rows. 7. The claim 1-6, the thickness of the cover plate T, the transverse piezoelectric constant d, the applied voltage V, and printing density was X [dpi], the flow path column of n columns In the case of forming a head, a droplet discharge device is characterized in that a flow path length L of the flow path and a height H of the flow path partition satisfy the following three equations. H × L ≧ 1.9 × 10 ⁻⁴ × π × T / (X ² × d × V × n) L ≦ 100 [mm] H ≦ 2 [mm] In any of 8. claims 1-7, wherein the flow channel substrate, the droplet discharge device, characterized in that the plastic member formed by injection molding. 9. The claim 1-7, characterized in that the flow channel substrate, exposing the channel shape on a photosensitive glass substrate, a member formed by performing an anisotropic selective etching Droplet discharge device. 10. The droplet discharge device according to claim 9 , wherein an excimer laser is used as the light source for exposure.