JP2006035491A - Inkjet head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem of a conventional channel as bubbles tend to remain in the pressure chamber. <P>SOLUTION: In the inkjet head, each plate constituting a channel substrate is formed by etching a substrate comprising single crystal silicon, a part of a diaphragm opposes a part of a restrictor, and the diaphragm is recessed as compared with a diaphragm plate both on the side being bonded to a chamber plate and the side being bonded to a piezoelectric element. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet head with improved bubble elimination.

  Conventionally, an inkjet head formed with high accuracy by using a silicon single crystal substrate as a material for forming a flow path of the inkjet head and performing dry etching or anisotropic etching on the substrate is as follows. There is.

  A method is known in which a chamber substrate having a communication hole communicating with a nozzle opening is formed by forming a silicon oxide film on the single crystal silicon substrate and performing dry or anisotropic etching (for example, see Patent Document 1). .

  On the other hand, the restrictor that is the ink supply path from the common ink chamber and the nozzle opening that ejects ink droplets are very narrow, which causes clogging due to dust mixed in the ink, and prevents ink droplets from being ejected. In order to solve the problem, there is an ink jet head in which a foreign matter removing filter is built in the head (for example, see Patent Document 2).

  The head described in Patent Document 2 is an example in which a filter is disposed in a common ink chamber. This filter removes foreign matter adhering to the ink tank or the ink supply path before the narrow ink flow path in the head, thereby preventing problems such as non-ejection.

JP 2003-182077 A

JP 2003-127364 A

  However, as shown in Patent Document 2, when the built-in filter is arranged in the head by etching of silicon, it is the same surface as the diaphragm plate formed of silicon and is arranged by processing simultaneously in the common ink chamber. However, the filter is located immediately before the restrictor. Here, since the filter has a structure in which many holes smaller than the narrowest flow path diameter of the ink flow path in the head are opened, in the case of the structure of the above-mentioned Patent Document 2, bubbles are likely to remain when the ink is filled. . There is a possibility that bubbles remaining in the filter portion may enter the restrictor during the ejection of ink droplets.

  In order to solve this problem, it is conceivable to move the position of the filter disposed in the common ink chamber away from the position of the restrictor. As a result, when the plate is formed integrally with the diaphragm, the position of the filter is arranged higher than the entrance of the restrictor as shown in FIG.

  FIG. 9 is a plan view of FIG. 8 viewed from the diaphragm plate 3 side serving as a diaphragm. In such a configuration, the ink flow path rapidly expands at the outlet of the restrictor 14, that is, at the inlet of the pressure chamber 13. As a result, although it becomes easy to prevent bubbles from entering the pressure chamber by the filter, the flow path is rapidly expanded at the entrance from the restrictor to the pressure generating chamber.

  Furthermore, since it has a concave shape on the diaphragm side and the corner on the diaphragm side at the upper part of the restrictor outlet does not flow uniformly, it tends to stay, so that bubbles do not move easily. Therefore, there arises a problem that bubbles easily remain in the pressure chamber.

  In order to solve the above problems, in the present invention, a nozzle plate having a nozzle opening for discharging ink droplets, a communication hole communicating with the nozzle opening, a pressure generating chamber, and a common ink chamber are narrower than the width of the pressure generating chamber. A flow path substrate comprising a chamber plate having a restrictor as a flow path, a filter located in the common ink chamber, and a diaphragm plate having a thin vibration plate in a region sealing the pressure generating chamber, and the vibration In an ink jet recording head comprising a piezoelectric element in contact with a plate, each of the plates constituting the flow path substrate is formed by etching a substrate having single crystal silicon, and a part of the diaphragm A part of the restrictor is faced, and the diaphragm is joined to the side to be joined to the chamber plate and the piezoelectric element. Both sides, characterized in that it is concave in comparison with the diaphragm plate.

  The flow path resistance in the gap between the restrictor and the diaphragm sealed by the diaphragm is substantially the same as the flow path resistance at the outlet of the restrictor.

  Further, the bonding between the plates constituting the flow path substrate is anodic bonding.

  According to the present invention, the diaphragm plate in which the filter and the diaphragm are integrally formed is disposed so that the diaphragm covers a part of the restrictor in the region where the pressure generating chamber is sealed, and the position away from the restrictor. The diaphragm is disposed in the gap, and the gap between the restrictor and the diaphragm is made smaller than the depth of the ink flow path of the restrictor, so that it is possible to improve the bubble evacuation and provide an inkjet head with high ejection reliability.

  In the diaphragm in which the filter and diaphragm are integrally formed by dry etching processing of single crystal silicon, the filter is removed from the restrictor so that it is located in the common ink chamber for the purpose of enhancing bubble penetration and exclusion in the ink flow path in the head. It was configured to be far away and realized by arranging a thin diaphragm so as to cover a part of the restrictor in an area where the pressure generating chamber was sealed.

  FIG. 1 is a cross-sectional view showing a flow path configuration of an ink jet recording head according to the present invention.

  In order to facilitate understanding of the ink flow path, only the broken portion is shown. A chamber having an orifice plate 1 having a plurality of nozzles 11, a communication hole 12 communicating with the nozzles 11, a pressure chamber 13, and a narrow channel restrictor 14 for supplying ink from the common ink chamber 15 to the pressure chamber 13. The ink flow path substrate 10 is configured by the plate 2, the filter 17 for removing foreign matter in the common ink chamber 15, and the diaphragm plate 3 that is a diaphragm 16 that seals part of the pressure chamber 13 and the restrictor 14. Is done.

  As shown in FIG. 6, the restrictor 14 has a plurality of (in this example, two) flow paths, and is formed narrower by about 1/3 to 1/4 than the flow path width of the pressure chamber 13. . The diaphragm plate 3 is provided with a piezoelectric element 4 that expands and contracts in the major axis direction. The expansion and contraction of the piezoelectric element 4 changes the volume of the pressure chamber 13, and the pressure wave of the ink generated thereby communicates. An ink droplet is ejected from the nozzle 11 through the hole 12.

  Here, each of the above plates is made of the same kind of material, and specifically, each shape is formed using dry etching or anisotropic etching of single crystal silicon. In this technique, an inexpensive (100) wafer can be used which is a technique generally used for semiconductor parts.

  Next, an example of a method for manufacturing each plate will be described.

  FIG. 2 is a view showing a manufacturing example of the orifice plate 1. First, a silicon oxide film 30 is formed on the surface of the silicon substrate by a thermal oxidation method or the like, and matched with the shape of the nozzle 11 of the orifice plate 1, for example, the side having a two-stage shape (surface opposite to the orifice discharge surface). The silicon oxide film 30 is completely removed by patterning by a photolithography method (FIG. 2A).

  Thereafter, etching is performed to a necessary depth (FIG. 2B). Then, the processed surface was covered again with the silicon oxide film 30, and the side that became the orifice surface was patterned by the same photolithography method, and the silicon oxide film 30 other than the hole located at the nozzle diameter was removed and etched. Later, the silicon oxide film is completely removed (FIG. 2C).

  The removal of the silicon oxide film 30 is performed with a mixed solution of hydrofluoric acid and ammonium fluoride. Similarly, the chamber plate 2 can be easily formed by performing etching after masking portions other than the chamber plate 2 with a silicon oxide film.

  The diaphragm plate 3 can also be manufactured by the same method. First, the region to be the diaphragm 16 and the filter 17 is etched from one surface (FIG. 3A), and then the diaphragm is similarly fabricated from the other surface. 16 and the region to be the filter 17 are etched (FIG. 3B). Finally, an H-shaped diaphragm plate 3 is formed by forming a hole to be the filter 17 (FIG. 3C). Forming the ink flow path 10 using such a single crystal silicon substrate is that a complicated flow path can be easily formed by manufacturing a minimum number of plates. For example, if it is intended to form a similar diaphragm plate by etching a thin stainless steel plate, it is necessary to stack at least three plates, so that the method of this configuration leads to a reduction in material costs and assembly man-hours.

  Next, a method for ejecting ink droplets from the nozzle openings 11 will be described with reference to FIG. Although slightly different from the head structure of the present invention shown in FIG. 1, there is no problem in explaining the ejection of ink droplets, so an example close to the conventional inkjet head configuration will be described.

  First, ink filling into the ink flow path in the head is performed by supplying ink from the ink tank (not shown) to the common ink chamber 15 formed in the chamber plate 2 from the supply path provided in the flow path substrate fixing member 25. And the pressure chamber 13 is filled with ink via a restrictor 14 communicating with each nozzle opening 11. The filling method includes a pressure filling method in which pressure is applied from an ink tank, a negative pressure suction method in which suction is performed from the nozzle opening hole 11 of the ink jet head, and the like.

  FIG. 5 is a diagram illustrating an example of a driving pulse used for discharging a droplet from the nozzle opening 11.

  A voltage pulse is applied to the piezoelectric element with a predetermined potential difference as shown in FIG. 5, and a voltage is applied in a direction in which the piezoelectric element contracts (FIG. 5 (1)). As a result, the volume in the pressurizing chamber 13 expands, and the ink 20 flows from the common ink chamber 15 through the restrictor 14, and at the same time, the meniscus which is the interface between the air and the ink located in the nozzle opening 11 is also pressurized. It is drawn in to the chamber 13 side (FIG. 4B).

  If the voltage is held as it is (FIG. 5 (2)), the meniscus pull-in is completed and it tries to return to the opening 11 side again. At this point, a voltage is applied in a shorter time than in the contraction in the direction in which the piezoelectric element 4 expands (FIG. 5 (3)). Then, the ink accumulated in the pressure chamber 13 due to the expansion is compressed, and the pressure chamber 13 becomes a high pressure (FIG. 4C). At that time, the diaphragm 16 which is the diaphragm plate 3 around the piezoelectric element 4 has a shape that swells at one end as shown in FIG. 4C, and pressure is gradually applied to the ink as time passes. Using the energy, the ink droplet 50 is ejected as a droplet from the nozzle opening 11 (FIG. 4D).

  However, when the above operation is performed in the head, particularly in a state where the bubbles enter or remain in the pressure chamber 13, the pressure in the pressure chamber 13 generated by the contraction of the piezoelectric element 4 is inhibited by the bubbles to obtain a normal pressure. In the worst case, ink drops are not ejected.

  In the ink flow path structure of the ink jet head of the present invention, the filter 17 disposed in the common ink chamber 15 is disposed at a position far from the entrance to the restrictor 14. Since the hole of the filter 17 is smaller than the nozzle opening hole 11 and a very large number of holes are formed, bubbles are easily caught. Therefore, bubbles are prevented from moving due to repeated pressure changes due to ejection of ink droplets, and easily entering the restrictor 14. Further, the diaphragm 16 processed simultaneously with the filter 17 has a structure that is covered with a gap between the restrictor portion and the restrictor portion in the vicinity of the entrance to the pressure chamber 13. . FIG. 6 is a view showing a cross section AA of FIG.

  FIG. 7 shows a plan view of the head of the present invention viewed from the diaphragm plate 3 side.

  As shown in FIG. 1, the restrictor 14 is inserted into a part of the area of the diaphragm 16 (the shaded portion in FIG. 7), and the outlet from the restrictor 14 expands relatively slowly. Therefore, the ink flow rate when the ink 20 is filled is lowered. The amount of the restrictor 14 that enters the area of the diaphragm 16 may be even a little. Considering the deformation amount of the diaphragm 16 due to the displacement of the piezoelectric element 4 at the maximum, the piezoelectric material on the side bonded to the diaphragm 16 is used. The vicinity of the end of the element 4 on the side of the restrictor 14 (part B in FIG. 1) is good.

  In the case of the conventional structure, if there is a step at the exit portion, stagnation occurs and stagnation of bubbles occurs, but in the case of the present invention, the diaphragm plate 3 that is a thin plate of the diaphragm plate 3 extends to the vicinity of the exit portion of the restrictor 14. It is preferable that the flow path resistance in the gap Hd is substantially the same as the flow path resistance of the restrictor 14. As a result, the flow velocity at the upper corner of the restrictor 14 is almost the same as the flow velocity at the outlet of the restrictor 14, and a uniform flow is generated and bubbles can be prevented from staying. (FIG. 6). The gap Hd may be slightly larger than the deformation amount of the diaphragm 16. By narrowing the flow path in this way, the ink flow rate in that area becomes larger than the flow rate in the pressure chamber 13. In other words, it is possible to improve the bubble elimination by changing the flow rate of the ink 20 from the outlet of the restrictor 14 to the pressure chamber in a stepwise manner.

  In addition, it is desirable to join the flow path plates by anodic bonding. In anodic bonding, a glass thin film is formed on each flow path plate by sputtering or the like, and then each is connected to a positive electrode and a negative electrode. A voltage is applied between the plates while raising the temperature, and diffusion of Na + ions contained in the glass film occurs. At the beginning, anodic bonding between the plates is completed. Accordingly, it is possible to provide an ink jet head that can handle a wide range of inks, regardless of the type of solvent contained in the ejection ink.

  In this embodiment, as a means for ejecting ink droplets in the present invention, a piezo method using the distortion of a piezoelectric element has been described. However, even if the configuration is a thin film element, a plurality of piezoelectric materials and electrodes are used. A layered piezoelectric element may be used.

  In addition, it is natural that the same effect as that of the present invention can be obtained even when the driving method using the electrostatic method is used instead of the piezoelectric method used in this embodiment.

It is explanatory drawing which showed the implementation method of the inkjet head of this invention. (Example 1) It is explanatory drawing which showed the manufacturing process of the orifice plate of the inkjet head of this invention. It is explanatory drawing which showed the manufacturing process of the diaphragm plate of the inkjet head of this invention. It is a figure which shows the state figure of the ink droplet discharge of an inkjet head. It is one Example of the drive waveform of an inkjet head. It is AA sectional drawing shown in FIG. It is the top view seen from the diaphragm side of the ink jet head of the present invention. It is sectional drawing which showed the inkjet head of the prior art. It is the top view seen from the diaphragm side of the inkjet head of a prior art.

Explanation of symbols

1 is an orifice plate, 2 is a chamber plate, 3 is a diaphragm plate, 4 is a piezoelectric element, 10 is a flow path plate, 11 is a nozzle, 12 is a communication hole, 13 is a pressure chamber, 14 is a restrictor, 15 is a common ink chamber , 16 is a diaphragm, 17 is a filter, 18 is a restrictor partition, 30 is a thermal oxide film, and 50 is an ink droplet.

Claims (3)

A chamber plate having a nozzle plate having a nozzle opening for discharging ink droplets, a communication hole communicating with the nozzle opening, and a restrictor which is a flow path narrower than the pressure generating chamber from a common ink chamber with the pressure generating chamber A flow path substrate comprising a filter located in the common ink chamber and a diaphragm plate having a thin diaphragm in a region sealing the pressure generating chamber, and a piezoelectric element in contact with the diaphragm. In an ink jet recording head,
Each of the plates constituting the flow path substrate is formed by etching a substrate having single crystal silicon,
A part of the diaphragm and a part of the restrictor face each other, and the diaphragm has a concave shape on the side joined to the chamber plate and both sides joined to the piezoelectric element compared to the diaphragm plate. An ink jet head characterized by the above.   The flow path resistance in a gap between the restrictor and the diaphragm sealed by the diaphragm is set to be substantially the same as the flow path resistance at the restrictor outlet. Inkjet head. 2. The ink jet head according to claim 1, wherein bonding between the plates constituting the flow path substrate is anodic bonding.

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