JP2008149649A - Inkjet head and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head having a superior ink ejection performance and simple constitution, in which a shock absorbing member composed of a material equal to a piezoelectric board in the coefficient of linear expansion is arranged between a nozzle plate and the piezoelectric board. <P>SOLUTION: The inkjet head includes a piezoelectric board 31, a nozzle plate 10 and a spacer 20. A channel groove 32 is formed on the main surface of the piezoelectric board 31. The nozzle plate 10 has a nozzle hole 11, which is arranged on the ink ejection surface of the piezoelectric board 31 and is opposite to one end of the channel groove 32. The spacer 20 is arranged between the piezoelectric board 31 and the nozzle plate 10. The spacer 20 has a difference in the coefficient of linear expansion with regard to the piezoelectric board 31 smaller than that between the nozzle plate 10 and the piezoelectric board 31. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet head that discharges droplets from nozzle holes of a nozzle plate disposed at the tip of a channel groove provided in a piezoelectric substrate. Moreover, it is related with the manufacturing method of the inkjet head.

  In general, an ink jet head is used in an ink jet printer or the like to constitute a droplet discharge device. Such an ink jet head is configured by joining members such as a nozzle plate, a head chip, and a head base.

  The nozzle plate is made of a resin or metal plate material. A plurality of nozzle holes are formed in the nozzle plate. Each of the plurality of nozzle holes is a minute hole that ejects an ink droplet. The plurality of nozzle holes are arranged one-dimensionally or two-dimensionally. From a single or a plurality of nozzle holes arbitrarily selected from among the plurality of nozzle holes, ink droplets having an arbitrary number of drops are ejected.

  The head chip includes an actuator member such as a piezoelectric substrate. For example, when the actuator member is a piezoelectric substrate, a plurality of channel grooves serving as ink flow paths are formed in parallel on the main surface. The channel walls sandwiched between the channel grooves are provided with drive electrodes on both sides thereof. Each channel wall is deformed by applying a predetermined voltage to the drive electrode. The volume of each channel groove changes due to the deformation of the channel wall. Due to this volume change, the ink in the channel groove is ejected from the nozzle hole.

  The head base includes a drive circuit and outputs a voltage to be applied to the drive electrode. It also supports the head chip.

  The materials of the members constituting such an ink jet head are different from each other, and the linear expansion coefficients of the members are different. For this reason, thermal deformation occurs in each member due to a change in environmental temperature, particularly heating in the manufacturing process. Such thermal deformation causes various problems for the ink jet head.

  For example, when the ink ejected from the inkjet head is a solvent-based ink, the following problems occur. For joining the members of the inkjet head, it is necessary to use an adhesive that is difficult to dissolve in a solvent. Therefore, an epoxy adhesive is used as an adhesive for such applications. When an extremely high adhesive such as an epoxy adhesive is bonded to the piezoelectric substrate, thermal stress is generated in the adhesive due to a difference in linear expansion coefficient between the piezoelectric substrate and another member. This thermal stress acts directly on the piezoelectric substrate, and a large distortion occurs in the piezoelectric substrate. Due to the distortion of the piezoelectric substrate, for example, a crack occurs in the piezoelectric substrate, resulting in a product defect.

  For example, when the ink ejected from the ink jet head is a water-based ink, the following problems occur. When the drive electrode, which is a metal film, is in contact with the ink, a current flows in the ink by the voltage applied to the drive electrode. This current causes electrolytic corrosion of the drive electrode. Therefore, in general, in order to avoid contact between the drive electrode and the ink, an organic insulating film such as a polyparaxylene film (hereinafter referred to as a parylene film) is formed on the inner surface of the ink chamber and the adhesive surface with the nozzle plate. The However, since the adhesion between the organic insulating film and the piezoelectric substrate is not so strong, peeling of the organic insulating film occurs due to thermal deformation of each member.

  Therefore, in order to suppress the deformation of the piezoelectric substrate, an ink jet head provided with a slip support plate for supporting the nozzle plate on the outer periphery of the head chip is used (for example, see Patent Document 1). The nozzle plate is directly bonded to the piezoelectric substrate with an adhesive or the like. The nozzle support plate is bonded to the piezoelectric substrate with an adhesive or the like through a spacer formed of a member having a linear expansion coefficient substantially equal to that of the piezoelectric substrate.

  Further, for example, as the nozzle plate, it is common to use a resin material such as polyimide from the viewpoint of easiness of laser processing of the nozzle hole, but in this case, the following problems occur.

For example, the linear expansion coefficient of polyimide is 10 × 10 ^{−6 to} 20 × 10 ⁻⁶ (1 / ° C.). When the environmental temperature is set to 60 ° C., if the length of the piezoelectric substrate and the nozzle plate is 50 mm, a difference in deformation amount of about 50 μm occurs. Although it is possible to suppress thermal deformation by increasing the thickness of the nozzle plate and increasing its rigidity, in that case, the nozzle holes to be laser processed in the nozzle plate are molded while controlling the shape with submicron accuracy. It becomes difficult. In order to form a good nozzle hole shape by laser processing, the thickness of the nozzle plate is desirably 50 μm or less. However, in this case, the end of the nozzle plate where the piezoelectric substrate is bonded is curled. Furthermore, the center positions of the nozzle hole and the ink flow path cross section are shifted, making it difficult to perform high-precision alignment, and the yield of the inkjet head is significantly reduced.

Therefore, in order to suppress deformation of the nozzle plate, a rigid member that maintains the shape of the nozzle plate may be provided on the nozzle ejection surface side of the nozzle plate (see, for example, Patent Document 2).
JP 2003-182080 A JP 2002-52717 A

  However, the following problems occur in the prior art.

  In the technique of Patent Document 1, in the inkjet head manufacturing process, the nozzle plate is bonded to the piezoelectric substrate in a step subsequent to the step of bonding the piezoelectric substrate and the nozzle support plate. As the adhesive used in this step, a high-hardness adhesive is used from the viewpoint of ink resistance. In this case, the nozzle plate is bonded to both the piezoelectric substrate and the nozzle support plate. Therefore, a large thermal deformation occurs in the nozzle plate. Furthermore, the center positions of the nozzle hole and the ink channel cross section are shifted.

Specifically, lead zirconate titanate (PZT) is usually used as the piezoelectric substrate, and the linear expansion coefficient of PZT is 4 × 10 ^{−6 to} 9 × 10 ⁻⁶ (1 / ° C.). In contrast, the nozzle support plate is made of aluminum having a linear expansion coefficient of approximately 24 × 10 ⁻⁶ (1 / ° C.). Here, when the environmental temperature is 60 ° C. and the length of the piezoelectric substrate and the nozzle support plate is 50 mm, the difference in deformation amount between the piezoelectric substrate and the nozzle support plate due to thermal expansion and contraction is about 100 μm. Therefore, a large thermal stress is applied to the nozzle plate bonded over these members. As a result, the nozzle plate is greatly deformed, and in the worst case, the nozzle plate is destroyed.

  Thus, it is conceivable to employ the technique of Patent Document 2 in order to suppress the deformation of the nozzle plate.

In the technique of Patent Document 2, it is desirable to use a metal plate as a rigid member in order to suppress deformation of the nozzle plate. In order to align the nozzle hole of the nozzle plate and the hole of the metal plate with high accuracy, it is necessary to perform hole processing with the same high accuracy as the nozzle hole of the nozzle plate on the metal plate. The nozzle plate, which is a resin plate, can be ablated by excimer laser. However, the metal material is dissolved in the metal plate by ablation, and a desired accuracy cannot be realized. Therefore, it is necessary to perform other hole processing means such as a CO ₂ laser and cutting processing on the metal plate. However, processing methods other than ablation processing do not reach the processing accuracy of excimer laser on resin materials. If the size of the hole in the metal plate is made larger than the nozzle hole in the nozzle plate, alignment becomes easier, but in this case, ink aggregates and the like are generated at the step between the hole in the metal plate and the nozzle hole in the nozzle plate. In addition, there is a possibility that the ejection performance of the head is significantly deteriorated. Furthermore, the number of parts of the inkjet head increases, and the manufacturing cost of the inkjet head increases. Further, since the weight of the ink jet head increases, it becomes difficult to control the position of the ink jet head.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an ink jet head having a simple configuration excellent in ink discharge performance by providing a buffer member made of a material having a linear expansion coefficient equal to that of a piezoelectric substrate between a nozzle plate and a piezoelectric substrate. .

  An ink jet head according to the present invention includes a piezoelectric substrate, a nozzle plate, and a buffer member. A channel groove is formed on the main surface of the piezoelectric substrate. The nozzle plate is provided with a nozzle hole that is disposed on the ink ejection surface of the piezoelectric substrate and faces one end of the channel groove. A buffer member is disposed between the piezoelectric substrate and the nozzle plate. The buffer member has a smaller difference in linear expansion coefficient from the piezoelectric substrate than a difference in linear expansion coefficient between the nozzle plate and the piezoelectric substrate.

  In this configuration, thermal deformation due to the difference in linear expansion coefficient occurs between the piezoelectric substrate and the buffer member. However, the difference in linear expansion coefficient between the piezoelectric substrate and the buffer member is smaller than the difference in linear expansion coefficient between the nozzle plate and the piezoelectric substrate. Therefore, the thermal deformation generated in the piezoelectric substrate is reduced. Thereby, the landing accuracy of ink discharge in the inkjet head is increased.

  The buffer member may have a difference in linear expansion coefficient with the nozzle plate smaller than a difference between the linear expansion coefficient of the nozzle plate and the linear expansion coefficient of the piezoelectric substrate.

  In this configuration, thermal deformation due to a difference in linear expansion coefficient occurs between the nozzle plate and the buffer member. However, the difference in coefficient of linear expansion between the nozzle plate and the buffer member is smaller than the difference in coefficient of linear expansion between the nozzle plate and the piezoelectric substrate. Accordingly, thermal deformation that occurs in the nozzle plate is reduced.

  Thus, the thermal deformation of the nozzle plate is reduced compared to the conventional case. In addition, since a rigid member on the outer surface of the nozzle plate is not necessarily required, there is no step on the outer surface in the vicinity of the nozzle hole of the nozzle plate, and there is no possibility that ink aggregates or the like are generated on the step.

  The piezoelectric substrate may be provided with a protective film for preventing erosion by ink in the channel groove. If the piezoelectric substrate is configured in this way, the piezoelectric substrate of the ink jet head has a longer life against ink.

  The buffer member may be a spacer provided separately from the piezoelectric substrate and the nozzle plate. By configuring the buffer member in this way, it is possible to arbitrarily set the plate thickness of the spacer. Increasing the plate thickness increases the rigidity of the spacer and suppresses deformation of the nozzle plate. Further, by reducing the plate thickness, the spacer can be reduced in weight, and the weight of the entire inkjet head can be reduced.

  In addition, the spacer may include a protective film that prevents erosion by ink on the surface facing the piezoelectric substrate. If the spacer is configured in this manner, the life of the ink jet head spacer with respect to the ink is extended.

  The spacer may be a light-transmitting material. By configuring the spacer in this way, it is possible to check with a microscope whether there is any entrapment of bubbles or dust on the bonded surface after the spacer is bonded to the nozzle plate or the piezoelectric substrate.

  Further, the spacer may contain alumina or quartz as a main component. By configuring the spacer in this way, it becomes easy to make the linear expansion coefficient of the spacer appropriate and provide translucency.

  Moreover, you may provide the 1st adhesive agent which adhere | attaches a spacer and a nozzle plate, and the 2nd adhesive agent which adhere | attaches a spacer and a piezoelectric substrate. If these adhesives are adhesives that are sparingly soluble in the ink, the state of the pressure wave applied to the ink in the ink chamber is maintained even in the spacer portion, and the landing accuracy of ink ejection in the inkjet head can be maintained high. Also, the adhesive extends the life of the ink. As this adhesive, an epoxy-based adhesive is suitable.

  Further, the hardness after curing of the first adhesive may be smaller than the hardness after curing of the second adhesive. If it does in this way, it will become possible to absorb the deformation by the linear expansion coefficient between a spacer and a nozzle plate. As the second adhesive, a silicon cross-linking fluorine-based adhesive is suitable.

  The buffer member may be a buffer film formed on a nozzle plate or a piezoelectric substrate. If such a buffer film is used, the weight of the inkjet head can be reduced while suppressing deformation of the nozzle plate. In addition, if the buffer film is formed by vacuum deposition, the buffer member is provided by the same process as the other base treatment, and the manufacturing process is simplified. Moreover, such a buffer film is easy to form a hole. Further, if the main component of such a buffer film is quartz, it becomes easy to make the linear expansion coefficient of the spacer appropriate.

  Further, depending on the thickness of the buffer film, it is difficult to form the hole provided in the buffer film by laser processing, and it is necessary to form by a method other than laser processing such as metal mask processing. Therefore, in the manufacturing process of the inkjet head, a mask pattern that covers the nozzle hole formation position is formed on the surface of the nozzle plate facing the piezoelectric substrate, and then the nozzle plate is formed on the surface of the nozzle plate that is bonded to the piezoelectric substrate. A buffer film having a linear expansion coefficient that is smaller than the difference between the linear expansion coefficient of the piezoelectric substrate and the linear expansion coefficient of the piezoelectric substrate than the difference between the linear expansion coefficient of the plate and the piezoelectric substrate is formed. Next, if the mask pattern of the nozzle plate is removed and then the nozzle holes are laser-molded in the nozzle plate, the film can be easily formed even if the buffer film is thick. Stress caused by the difference in linear expansion coefficient can be suppressed.

  According to the present invention, it is possible to reduce the deformation of the nozzle plate and the deformation of the piezoelectric substrate due to the difference in the linear expansion coefficient of each member. Further, it is possible to reduce the deviation of the center position between the nozzle hole and the cross section of the ink flow path and the deviation of the center position between the nozzle hole and the hole of the buffer member when the adhesive is cured or the environmental temperature changes. In addition, the weight of the inkjet head can be reduced.

  First, a first embodiment of the present invention will be described.

  The ink jet head of this embodiment is used for an ink jet printer. This ink jet head ejects ink droplets with an arbitrary number of drops from any one selected from a plurality of nozzle holes.

  FIG. 1 is a partially exploded perspective view of the ink jet head. The front side of the inkjet head is the front side, the back side is the back side, and the left side is the left side. In the figure, the fourth ink chamber from the left side is shown, and the right side of the figure is a cross section of the inkjet head.

  The inkjet head includes a head chip 30, a spacer 20 disposed on the front side of the head chip 30, a nozzle plate 10 disposed on the front side of the spacer 20, and a head base (not shown) that is bonded to the bottom surface side of the head chip 30. And consist of: Here, as an adhesive for adhering the spacer 20 and the nozzle plate 10 and an adhesive for adhering the spacer 20 and the piezoelectric substrate 31, both of them are high hardness adhesives (epoxy type) from the viewpoint of chemical resistance. , Hardness at curing 60-80).

  The nozzle plate 10 is a thin resin plate material (polyimide sheet: manufactured by Ube Industries, Upilex) in the front-back direction. A plurality of nozzle holes 11 are formed in the nozzle plate 10. Each of the plurality of nozzle holes 11 is a minute hole that ejects an ink droplet. The plurality of nozzle holes 11 are arranged in a straight line.

The spacer 20 is a thin ceramic plate material (main component: alumina Al ₂ O ₃ ) in the front-back direction. The thickness of the spacer 20 is 20 μm. A plurality of spacer holes 21 are formed in the spacer 20. Each of the plurality of spacer holes 21 is arranged linearly so as to be coaxial with the nozzle holes 11 of the nozzle plate 10. As the ceramic plate material, a translucent material can be used. This is done by checking with a microscope whether there is a bubble or dust between the spacer 20 and the head chip 30 and between the nozzle plate 10 and the spacer 20 after the spacer 20 and the nozzle plate 10 are bonded together. It is to do.

  The head chip 30 includes a piezoelectric substrate 31 and a cover member 37. The piezoelectric substrate 31 and the cover member 37 are thin members in the top-bottom direction, respectively. The piezoelectric substrate 31 is mainly composed of lead zirconate titanate (PZT). A plurality of channel grooves 32 are formed in parallel from the front surface to the back surface of the piezoelectric substrate 31. The channel groove 32 is formed by applying a dicer to the upper surface of the piezoelectric material wafer polarized in the plate thickness direction and running it while being cut halfway in the dicing blade thickness direction. In this embodiment, the dimension from the front surface to the back surface of the head chip 30 is 12 mm, the wafer thickness of the piezoelectric material is 1 mm, the dimension from the left side surface to the right side surface is 6 mm, the depth of the channel groove 32 is 300 μm, and the channel groove 32 The width is 80 μm. The channel grooves 32 are linearly arranged so that the center of the cross section coincides with the central axis of the nozzle hole 11. A partition wall formed between the channel grooves 32 becomes the channel wall 33.

  The head chip 30 is formed by covering the piezoelectric substrate 31 with a cover member 37 from above and bonding it with an adhesive. The cover member 37 is obtained by processing a wafer made of a piezoelectric material in the same manner as the piezoelectric substrate 31, and is provided with a concave portion 38 and a penetrating portion 39 serving as a common ink chamber and an ink supply port. Here, the same piezoelectric material as that of the piezoelectric substrate 31 is used as the cover member 37. This is to improve the matching of the thermal expansion coefficients of the cover member 37 and the piezoelectric substrate 31.

  Since the spacer 20 is provided between the piezoelectric substrate 31 and the nozzle plate 10 as described above, the linear expansion coefficient is different between the piezoelectric substrate 31 and the spacer 20 and between the spacer 20 and the nozzle plate 10. Thermal deformation caused by

Here, the linear expansion coefficient of the piezoelectric substrate (here, PZT: about 4 × 10 ⁻⁶ (1 / ° C.)) and the linear expansion coefficient of the spacer 20 (here, alumina: about 4 × 10 ⁻⁶ (1 / C))) is substantially equal. The linear expansion coefficient of the nozzle plate 10 (here, polyimide: 10 × 10 ⁻⁶ (1 / ° C.)) is larger than that of the piezoelectric substrate and the spacer, and the linear expansion coefficient of the spacer 20 and the line of the piezoelectric substrate 31 The difference in expansion coefficient is smaller than the difference in linear expansion coefficient between the nozzle plate 10 and the piezoelectric substrate 31. Therefore, the thermal deformation generated in the piezoelectric substrate is reduced as compared with the case where the nozzle plate 10 and the piezoelectric substrate 31 are directly bonded.

  In addition, the material of the adhesive that bonds each member may be a material other than that of the present embodiment, but from the viewpoint of chemical resistance, both of them are epoxy-based adhesives (hardness upon curing). 60 to 80) and a low-hardness silicon cross-linked fluorine-based adhesive having high chemical resistance (hardness at curing 30 to 40) is preferably used. In particular, the adhesive disposed between the head chip 30 and the spacer 20 is more preferably a high-hardness adhesive from the viewpoint of maintaining the state of pressure waves applied to the ink in the ink chamber 40. On the other hand, as an adhesive disposed between the spacer 20 and the nozzle plate 10, the difference in deformation amount due to the linear expansion coefficient between the spacer 20 and the nozzle plate 10 is more preferable than the viewpoint of maintaining the pressure wave applied to the ink. From the viewpoint of absorbing water, a low-hardness adhesive is more desirable. Therefore, if the adhesive disposed between the head chip 30 and the spacer 20 is an epoxy adhesive and the adhesive disposed between the spacer 20 and the nozzle plate 10 is a silicon cross-linking fluorine adhesive, A high-performance inkjet head can be manufactured.

Further, the material of the cover member 37 may be any material other than the present embodiment, as long as the thermal expansion coefficient is relatively close to that of the piezoelectric substrate 31 (here, PZT). For example, an inexpensive ceramic mainly composed of alumina may be used. The linear expansion coefficient of alumina is about 4 × 10 ⁻⁶ (1 / ° C.).

  The material of the spacer 20 may be any material other than that of the present embodiment, as long as the thermal expansion coefficient is relatively close to that of the piezoelectric substrate 31 (here, PZT). For example, it is desirable to use quartz as the main component for ceramics and Ti as a main component for metals. However, the material of the spacer 20 is desirable if it has translucency, but may be light-shielding.

  Further, the material of the nozzle plate 10 may be a material other than the present embodiment. As long as the inkjet head is used for an application that does not require such a high discharge performance as a consumer printer, any material can be used for the nozzle plate 10 as long as laser processing is possible. On the other hand, if it is an inkjet head for industrial inkjet printers in which high accuracy is required for the ejection position and ejection volume, a material that can reduce nozzle diameter variation and nozzle taper variation in nozzle holes 11 is preferable. Specifically, as a method of manufacturing the nozzle with high accuracy, if a method of processing the nozzle plate 10 using excimer laser light is used, the material of the nozzle plate 10 is a material with high excimer laser processing ease. More desirable. Examples of materials with high excimer laser processing ease include thin resin materials such as polyethylene, polypropylene, and polyimide amide. In addition, as long as it is a method other than processing using an excimer laser beam, any material capable of forming a high-precision nozzle, such as a metal material obtained by electroforming plating such as nickel, may be used. Good.

  Next, the detailed configuration of the ink chamber will be described. FIG. 2 shows a cross-sectional view of the ink chamber as seen from the front side.

  As shown in FIG. 3A, the channel groove 33 surrounded by the cover member 37 and the piezoelectric substrate 31 constitutes the ink chamber 40. On the upper side surface of the channel wall 33, drive electrodes 41 are provided opposite to each other with the channel wall 33 interposed therebetween. The drive electrode 41 is formed by evaporating a metal serving as an electrode material such as Au, Al, or Cu on the channel wall 33 from above, and removing the metal film on the top surface of the channel wall 33 and the metal film on the bottom surface side of the channel groove 32. It is formed by. Here, Au having a thickness of 0.5 μm is used as the metal film. A drive electrode is also provided on the back surface of the piezoelectric substrate 31. The driving electrode on the back surface is wired by wire bonding and connected to a chip-based driving circuit. The drive electrode 41 may be formed by known means, and any means may be used.

  In the present embodiment, a parylene film that is chemically stable and has high chemical resistance and insulation is formed as an organic insulating film 42 in the ink chamber having the above-described configuration. FIG. 4B shows the state of the organic insulating film in the ink chamber 40.

  Here, the thickness of the organic insulating film 42 is set to 3.5 μm. The thickness of the organic insulating film is desirably 1 μm or more so that pinholes are not generated due to the unevenness of the base member or the influence of dust attached to the base member. On the other hand, the thickness of the organic insulating film 42 is desirably 10 μm or less from the viewpoint of shortening the time of the film forming process and reducing the raw material cost. Based on this, it is a more desirable condition that the film thickness of the organic insulating film 42 is between 1 μm and 10 μm.

  The drive electrode 41 is covered with the organic insulating film 42. Therefore, even if water-based ink or conductive ink including metal particles is stored in the ink chamber 40, the leak current does not flow due to the voltage applied to the drive electrode 41. This has the effect of preventing problems such as breakage of the ink-jet head due to electrolytic corrosion of the electrode material and ejection failure due to failure to achieve normal channel wall shear mode deformation. Further, even if a solvent-based ink containing an organic solvent as a main component is stored in the ink chamber 40, it is possible to isolate and protect members, adhesives, and the like constituting the inkjet head from a highly soluble organic solvent. . The parylene film is formed by vapor phase growth at room temperature, so it can be deposited almost uniformly without causing thermal damage to a substrate whose characteristics deteriorate due to heat or a substrate whose surface shape is complicated. There is also an advantage that it can be done.

  The parylene film includes polymonochloroparaxylylene (parylene C), polyparaxylylene (parylene N), and the like. It is also possible to use a method in which the film material is changed according to the characteristics of the material and the base member, or two or more kinds of materials are laminated.

  Although not shown, an organic insulating film is also formed on the front side surface of the piezoelectric substrate 31, that is, the bonding surface with the spacer 20. This organic insulating film is not an essential component of the present invention.

  Although not used in this embodiment, a parylene film as an organic insulating film may be formed on the adhesion surface of the spacer 20 to the head chip 30. As described above, by further providing a parylene film on the adhesion surface between the spacer 20 and the head chip 30, damage due to thermal stress on the parylene film formed on the adhesion surface between the piezoelectric substrate 31 and the spacer 20 can be further reduced. This organic insulating film is not an essential component of the present invention.

  Next, the shape of the nozzle hole 11 formed in the nozzle plate 10 will be described. FIG. 3 shows a cross-sectional view of the inkjet head viewed from the right side. In the figure, the organic insulating film and the adhesive are not shown.

  The nozzle hole 11 of the nozzle plate 10 has a conical shape having a diameter of about 40 μm on the back side (right side in the figure) into which ink flows and a diameter of about 20 μm on the front side (left side in the figure) from which ink is ejected. In this case, the taper angle is expressed by a descending angle on the back side of the nozzle hole with respect to the front side of the nozzle hole 11 and is about 11 °. Here, the hole diameter variation on the front side of the nozzle hole 11 is within a reference value ± 0.5 μm, and the taper angle variation is within a reference value ± 1.0 °. Further, a water repellent film is provided on the surface (ink ejection surface) opposite to the adhesion surface with the spacer 20 of the nozzle plate 10 from the viewpoint of ensuring straightness of the ejected ink and eliminating liquid droplets remaining on the ink ejection surface. (Not shown) is provided. In this embodiment, Optool DSX manufactured by Daikin Industries, Ltd. is used as the water repellent film.

  The spacer hole 21 provided in the spacer 20 is arranged coaxially with the nozzle hole 11. The diameter of the spacer hole 21 is substantially equal to the diameter of about 40 μm on the back side (right side in the figure) of the nozzle hole 11.

  When ink is ejected by this inkjet head, shear mode deformation is caused in the channel wall 33 by applying potentials having opposite phases to the drive electrodes 41 facing each other across the channel walls 33. That is, by generating a potential difference between the drive electrodes 41 on both sides of the channel wall 33, the boundary between the upper half of the channel wall 33 where the drive electrode 41 is formed and the lower half where the drive electrode 41 is not formed is broken. As an eye, the channel wall 33 is deformed into a "<" shape. The volume change in the ink chamber due to this deformation causes a pressure change in the ink in the ink chamber. Using this pressure change, ink droplets are ejected from the nozzle hole 11 and the spacer hole 21 arranged at the tip of the ink chamber.

  Next, the bonding process of the head chip 30, the spacer 20, and the nozzle plate 10 will be described with reference to FIG.

  As described above, when the head chip 30 and the nozzle plate 10 are bonded, it is necessary to align the positions of the nozzle holes 11 with high accuracy. Therefore, it is necessary to similarly bond the spacer 20 disposed between the head chip 30 and the nozzle plate 10.

  Here, the bonding process between the spacer 20 and the head chip 30 will be described in detail. First, alignment (adjustment) is performed by a dedicated device so that the central axis of the cross section of the ink chamber 40 and the central axis of the spacer hole 21 formed in the spacer 20 coincide with each other. Specifically, the alignment camera 55 with built-in cameras on both the upper and lower sides is moved between the spacer 20 and the head chip 30, and the central axis of all the spacer holes 21 formed in the spacer 20 and the central axis of the cross section of the ink chamber 40. , The positional deviation is calculated, the position is corrected by moving either the spacer 20 or the head chip 30, and the center axis of all the spacer holes 21 of the spacer 20 and the center of the cross section of all the ink chambers 40. Align so that the position with the axis matches. Next, the spacer bonding surface to which the adhesive is applied in advance in the plurality of ink chambers 40 of the head chip 30 and the spacer 20 are brought into close contact. Specifically, a jig (not shown) used for fixing the spacer 20 to the apparatus is gradually moved vertically downward toward the head chip 30, and the bonding surface (back side) of the spacer 20 is moved to the head chip 30. Contact the spacer adhesion surface. Here, a liquid adhesive is generally used for bonding the spacer 20 to the head chip 30. In order to bond the nozzle plate to the head with a thin and uniform adhesive, use a bar coater or spin coater to form a uniform and thin layer of adhesive on a sheet of polyimide film, etc. Is pressed against the spacer bonding surface of the head chip 30 to transfer the adhesive having a desired thickness to the spacer bonding surface.

  In this embodiment, as a method for applying the adhesive, a known bar coater device is used, a uniform adhesive layer having a thickness of 4 μm is formed on the polyimide film, and the head chip is formed on the polyimide film on which the adhesive layer is formed. A method of stamp transfer by pressing the adhesive surface with 30 was used. Accordingly, an adhesive layer having a uniform thickness (2 μm or more in the present embodiment) can be formed in a region other than the cross section of the ink chamber 40 on the front surface of the head chip 30.

  Thus, the center axis of the cross section of the plurality of ink chambers 40 of the head chip 30 to which the adhesive has been transferred and the center axis of the spacer hole 21 of the spacer 20 are aligned, and the spacer 20 and the head chip 30 are aligned. Is manufactured by pressurizing and heating to bond.

  After the bonding of the spacer 20 and the head chip 30 is completed, the nozzle plate 10 and the spacer 20 are further bonded using the same apparatus and means as shown in FIG. Manufactured.

  In addition, since the area of the adhesion surface with the spacer 20 of the head chip 30 and the area of the nozzle plate 10 are the same as the area of the head chip 30, the inkjet head of this embodiment does not necessarily require a nozzle support member. As long as the area of the nozzle plate 10 is larger than the area of the head chip 30, a nozzle support member may be provided.

  Next, an inkjet head according to a second embodiment of the present invention will be described.

  The ink jet head of this embodiment is the same as that of the first embodiment regarding the schematic configuration of the head chip and the configuration of the organic insulating film formed around the channel wall 33, but is characterized by a buffer member.

In the present embodiment, a SiO ₂ film is formed on the bonding surface of the nozzle plate with the head chip. Although the linear expansion coefficient of the SiO ₂ film is about 8 × 10 ⁻⁶ (1 / ° C.), which is larger than the linear expansion coefficient of PZT, which is a piezoelectric substrate, about 4 × 10 ⁻⁶ (1 / ° C.), the material of the nozzle plate It is smaller than the linear expansion coefficient 10 × 10 ^{−6 to} 20 × 10 ⁻⁶ (1 / ° C.) of polyimide, and has a linear expansion coefficient intermediate between PZT and polyimide. For this reason, it is an optimal material to arrange as a buffer member instead of the spacer.

Thus, the difference in the linear expansion coefficient between the SiO ₂ film and the piezoelectric substrate is smaller than the difference in the linear expansion coefficient between the nozzle plate and the piezoelectric substrate. Further, the difference in the linear expansion coefficient between the SiO ₂ film and the nozzle plate is smaller than the difference in the linear expansion coefficient between the nozzle plate and the piezoelectric substrate. Accordingly, the thermal deformation generated in the piezoelectric substrate and the thermal deformation generated in the nozzle plate are reduced as compared with the case where the nozzle plate and the piezoelectric substrate are directly bonded.

Incidentally, the SiO ₂ film in order to be suitable as an underlayer for various film formation, also forming a water repellent film on the ink ejection surface of the nozzle plate (the back surface of the adhesive surface), formed the SiO ₂ film In this case, it may be used as a base layer. In this case, the SiO ₂ film as a spacer, that a SiO ₂ film as an underlying layer can be simultaneously formed in the same vacuum (simplicity of the process), also a spacer as in the first embodiment There is an advantage over the case of the first embodiment in that it does not need to be used (reduction of member cost).

FIG. 5 shows a flow chart from the formation of the SiO ₂ film and the water repellent film on the nozzle plate to the nozzle hole processing on the nozzle plate, and FIG. 6 shows a sectional view of the nozzle plate of the process corresponding to FIG. .

FIG. 6A shows a state in which SiO ₂ films 61 and 62 are formed on the nozzle plate 60 as a base layer and a buffer film by the process of FIG. 5A. Here, as the nozzle plate 60, as in the first embodiment, a polyimide sheet having a thickness of 50 μm (manufactured by Ube Industries, Upilex) is used. The SiO ₂ films 61 and 62 can be formed by sputtering or vapor deposition, but in this embodiment, sputtering is used. The SiO ₂ film 61 serves as a buffer film that suppresses the generation of stress due to the difference in linear expansion coefficient between the nozzle plate 60 and the head chip, and the SiO ₂ film 62 serves as an underlayer for the water repellent film on the nozzle ejection surface. Is.

In the nozzle hole processing process of FIG. 6C, laser processing of the nozzle holes is performed. From the viewpoint of ensuring the processing accuracy at this time, the thickness of the SiO ₂ film 62 needs to be reduced. Therefore, it is a necessary condition that the thickness of the SiO ₂ film 62 is, for example, 30 nm or less. On the other hand, if the film thickness of the SiO ₂ film 61 is too thin, the stress due to the difference in linear expansion coefficient between the nozzle plate 60 and the piezoelectric substrate cannot be suppressed, and the film itself is destroyed. Therefore, it is necessary to have a certain film thickness. Therefore, the film thickness of the SiO ₂ film 61 needs to be 1 μm or more, for example. Here, the thickness of the SiO ₂ film 61 is 10 μm. Since the SiO ₂ film 61 having such a thickness is unsuitable for laser processing, in this embodiment, when forming the SiO ₂ film 61, a nozzle processing portion is previously shielded with a metal mask or the like, and the SiO ₂ film 61 is formed. _Two films were not formed.

If the adhesion between the material of the nozzle plate 60 and the SiO ₂ films 61 and 62 is poor, for example, a metal film such as Ta can be used as the underlayer. Furthermore, as another method for forming a concave shape, after forming a flat film, a photosensitive resist is applied, mask exposure is performed with an aligner or the like, patterning is performed, and a SiO ₂ film is formed by dry etching with a desired pattern. A processing method can also be used.

  In addition, as a method of forming the concave shape, for example, when a metal film such as Ni, Au, or Cu is used as the buffer film of the buffer member, there is a method by plating or the like in addition to sputtering. Specifically, a Ni (Au, Cu) thin film having a thickness of about 100 nm is formed as a seed layer on the nozzle plate material by a method such as vapor deposition, and a Ni (Au, Cu) film having a thickness of about 30 μm is formed thereon by plating. Is to form.

Next, a step of forming a water-repellent film shown in FIG. As shown in FIG. 6B, a water repellent film 63 is formed on the SiO ₂ film 62 on the nozzle discharge surface side of the nozzle plate 60. The water repellent film 63 can be formed by sputtering or vapor deposition, or by spin-coating a liquid agent and rinsing. In this embodiment, vapor deposition is used. Specifically, a solution obtained by diluting a water repellent film main agent with a fluorine-based solvent is allowed to flow into the chamber, and a vapor deposition process is performed at a temperature between 80 ° C. and room temperature (about 20 ° C.). A film was formed. Here, as in the first embodiment, Optool DSX manufactured by Daikin Industries, Ltd. was used as the water repellent film 63.

The SiO ₂ film 62 becomes an adhesion layer between the nozzle plate 60 and the water repellent film 63. If the thickness of the adhesion layer is increased from 15 nm to 30 nm, when the nozzle plate 60 is laser processed, the nozzles may be left behind depending on the laser processing conditions. For example, when reducing the nozzle shape or increasing the hole diameter ratio between the inlet side (ink inflow side) and the outlet side (ink ejection side) of the nozzle, the number of laser shots can be reduced, or the laser output Processing may be performed with reduced energy, but if processing is performed under such conditions, the remaining processing of the nozzle plate will be noticeable. Therefore, in order to form a uniform and stable nozzle under various laser processing conditions, it is desirable that the thickness of the adhesion layer be in the range of 15 nm or less. In the present embodiment, the thickness of the SiO ₂ film 62 is set to 10 nm.

  On the other hand, the thickness of the water repellent film 63 is controlled by the amount of liquid introduced into the vapor deposition apparatus, but in the case of 1.8 nm, which is thinner than 2 nm, the film thickness in the chamber when the film is formed by the vapor deposition process. Due to the variation, a portion in which a part of the water-repellent film is not bonded to the adhesion layer on the substrate is generated. For the above reasons, the thickness of the water repellent film is desirably 2 nm or more.

  In addition, when the thickness of the water repellent film exceeds 4 nm, the hydrophilic group for bonding with the adhesion layer is left, and the surplus part may come out on the water repellent film and reduce the water repellency. . For this reason, the more preferable thickness of the water-repellent film on the ink ejection side particularly requiring water repellency is 2 nm or more and 4 nm or less.

  The water repellent has high water repellency, and in the case of water-based ink, the liquid droplet moves by the inclination of the water repellent surface having a static contact angle of about 70 ° and a dynamic contact angle of about 20 °. Thus, the performance as a water repellent film is high. In this example, the thickness of the water repellent film 63 was set to 2.4 nm.

  Next, a step of processing nozzle holes in the nozzle plate 60 shown in FIG. FIG. 6C is a diagram showing the situation at this time. The arrows shown in the figure indicate the irradiation direction of the processing laser light. By irradiating the nozzle plate 60 with the processing laser light, a by-product 67 is generated when the nozzle hole 68 is processed. The by-product 67 is deposited as a material containing carbon when the resin is processed, for example, and is formed not only on the processing laser irradiation side but also on the opposite side (ink ejection side).

  In this embodiment, an excimer laser (wavelength 248 nm) is used as the processing laser. Note that NovaLine 100 manufactured by Lambda Physic Co. was used as the processing laser device, and the purity of the halogen gas (mixed gas of fluorine and Ne, fluorine concentration 5%) as the laser excitation gas was 99.9%, and the rare gas (Kr) purity was 99.995%. Buffer gas (Ne) 99.995% and inert gas (He) purity 99.995% were used.

  In the processing of the nozzle hole 68 according to the present embodiment, since the laser irradiation surface is focused, the laser intensity decreases as the processing proceeds (as the laser moves toward the ink ejection side), and the processing diameter on the laser irradiation side becomes smaller. It is large and has a tapered shape because the processing diameter is small on the ink ejection side. Here, the laser irradiation side of the nozzle hole is called an inlet side (ink inflow side), and the opposite side is called an outlet side (ink discharge side). Since the irradiated laser pattern is circular, the nozzle cross-sectional shape is also circular. In this example, the inlet-side nozzle hole diameter was set to 40 nm and the outlet-side nozzle hole diameter was set to 20 nm.

  Next, a step of cleaning the nozzle plate 60 shown in FIG. As shown in FIG. 6D, by-products generated during processing are removed. In particular, the by-product on the surface opposite to the surface on which the water-repellent film is formed is difficult to remove, and may be removed using a method such as ashing before performing a normal cleaning process. On the other hand, the by-product adhering to the surface on the water repellent film forming side can be easily removed by using a tape having relatively low adhesiveness.

  Next, a bonding process with the head chip shown in FIG. The nozzle plate 60 used in this step has a configuration shown in FIG. Before bonding the nozzle plate to the head chip, it is necessary to ash the bonding surface of the nozzle plate in order to increase the lyophilicity with the adhesive on the bonding surface of the nozzle plate. On the other hand, the surface on which the water repellent film is formed becomes the ink ejection surface of the inkjet head. The above process is performed in a clean atmosphere such as a clean room.

In order to compare the ink jet head according to the manufacturing method in the first embodiment and the second embodiment with the ink jet head according to the conventional manufacturing method, samples of three types of ink jet heads of type 1, type 2, and type 3 are prepared. did. Type 1 is an ink jet head manufactured by a conventional method (without a buffer member). Type 2 is an ink jet head in which alumina is disposed as a spacer between the nozzle plate and the head chip as described in the first embodiment. As described in the second embodiment, type 3 is an inkjet head in which a SiO ₂ film is formed as a buffer member on the bonding surface of the nozzle plate with the head chip. Three heads of each of these three types of samples were manufactured, and the number of non-ejection nozzles in continuous ejection for one month was compared for each head.

  As a result, in the inkjet head (type 2, type 3) of the present invention, ink could be ejected from all nozzle holes, but in the conventional inkjet head (type 1), ejection failure was observed with about 20 to 30 nozzles. Occurred. On the other hand, when the discharge voltage for obtaining a desired ink discharge speed (8 m / sec) was measured, there was almost no change in the ink jet heads of the present invention (type 2 and type 3), whereas the conventional ink jet head ( Type 1) required approximately twice as much voltage as the original. Then, when each inkjet head was observed with the microscope from the nozzle surface side, in the type 1 inkjet head, a location where the adhesive was peeled between the nozzles (communication location) was found. Further, the nozzles of each inkjet head were peeled off, and the nozzle bonding portion of the head chip was observed with a microscope. As a result, a part of the parylene film was peeled off in the type 1 inkjet head and found to be corroded by ink. It was. On the other hand, no defect was found in the ink jet head of the present invention.

  From this result, in the inkjet of the present invention, by providing a buffer member between the nozzle plate and the head chip, various problems (nozzle holes and ink chambers of the head chip) due to the difference in the linear expansion coefficient between the nozzle plate and the head chip. It can be said that an inkjet head with high ejection reliability can be manufactured without any deviation in the center position with respect to the cross section or deformation of the nozzle plate.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The present invention relates to an ink jet head used for an ink jet printer or the like, and more particularly to an ink jet head having a nozzle plate in which ejection openings are formed.

It is a partial exploded perspective view of the ink jet head concerning a 1st embodiment. It is sectional drawing of the ink chamber seen from the front of the said inkjet head. FIG. 2 is a cross-sectional view of an ink chamber as seen from the side surface of the inkjet head. It is a figure explaining the adhesion process of the head chip and spacer of the above-mentioned ink jet head. It is a flowchart of the manufacturing process of the nozzle plate of the inkjet head which concerns on 2nd Embodiment. It is nozzle plate sectional drawing in the manufacturing process of the nozzle plate of the said inkjet head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Nozzle plate 11 ... Nozzle hole 20 ... Spacer 21 ... Spacer hole 30 ... Head chip 31 ... Piezoelectric substrate 32 ... Channel groove 33 ... Channel wall 37 ... Cover member 38 ... Counterbore 39 ... Penetration part 40 ... Ink chamber 41 ... Drive electrode 42: organic insulating film 55 ... alignment camera 60 ... nozzle plate 61, 62 ... SiO ₂ film 63 ... water-repellent film 67 ... by-product 68 ... nozzle hole

Claims (15)

A piezoelectric substrate having a channel groove extending from the ink ejection surface;
In an inkjet head comprising: a nozzle plate having a nozzle hole facing one end of the channel groove by being disposed on the ink discharge surface of the piezoelectric substrate;
A buffer member disposed between the piezoelectric substrate and the nozzle plate;
An inkjet head, wherein a difference between a linear expansion coefficient of the buffer member and a linear expansion coefficient of the piezoelectric substrate is smaller than a difference between a linear expansion coefficient of the nozzle plate and a linear expansion coefficient of the piezoelectric substrate.   The difference between the linear expansion coefficient of the buffer member and the linear expansion coefficient of the nozzle plate is smaller than the difference between the linear expansion coefficient of the nozzle plate and the linear expansion coefficient of the piezoelectric substrate. The inkjet head as described.   The inkjet head according to claim 1, wherein the piezoelectric substrate includes a protective film for preventing erosion by ink in the channel groove.   The inkjet head according to claim 1, wherein the buffer member is a spacer provided separately from the piezoelectric substrate and the nozzle plate.   The inkjet head according to claim 4, wherein the spacer includes a protective film that prevents erosion by ink on a surface facing the piezoelectric substrate.   The inkjet head according to claim 4, wherein the spacer is made of a translucent material.   The inkjet head according to claim 6, wherein the spacer is mainly composed of alumina or quartz.   The inkjet head according to any one of claims 4 to 7, further comprising: a first adhesive that bonds the spacer and the nozzle plate; and a second adhesive that bonds the spacer and the piezoelectric substrate.   The inkjet head according to claim 8, wherein the first adhesive and the second adhesive are adhesives that are hardly soluble in ink.   The inkjet head according to claim 9, wherein the first adhesive and the second adhesive are epoxy adhesives.   The inkjet head according to claim 8 or 9, wherein the first adhesive has a hardness after curing smaller than a hardness after curing of the second adhesive.   The inkjet head according to claim 11, wherein the first adhesive is a silicon-crosslinking fluorine-based adhesive, and the second adhesive is an epoxy-based adhesive.   The inkjet head according to claim 1, wherein the buffer member is a buffer film formed on the nozzle plate or the piezoelectric substrate.   The inkjet head according to claim 13, wherein the buffer film is mainly composed of quartz. In a method for manufacturing an inkjet head in which nozzle holes are formed in a nozzle plate disposed on an ink discharge surface of a piezoelectric substrate,
Forming a mask pattern covering the nozzle hole formation position on the side of the nozzle plate facing the piezoelectric substrate;
The difference between the linear expansion coefficient of the piezoelectric substrate and the linear expansion coefficient of the piezoelectric substrate is larger than the difference between the linear expansion coefficient of the nozzle plate and the linear expansion coefficient of the piezoelectric substrate on the bonding surface side of the nozzle plate with the piezoelectric substrate, and the nozzle plate A step of depositing a buffer film having a linear expansion coefficient on the piezoelectric substrate having a small difference from the linear expansion coefficient of
Removing the mask pattern of the nozzle plate and the buffer film formed on the mask pattern;
And a step of laser forming the nozzle hole at the removal position of the mask pattern on the nozzle plate in this order.

Images