JP2009061614A - Ink jet head and method of manufacturing ink jet head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head improved in adhesiveness between a protecting film formed on a piezoelectric substrate and an adhesive which sticks a nozzle plate. <P>SOLUTION: The protecting film 26 which protects the piezoelectric substrate 18 is formed at the piezoelectric substrate 18 of the inkjet head 10. A patterned recess 62 is formed on the surface of the protecting film 26 of a face to which the nozzle plate 17 is adhered. The nozzle plate 17 is stuck by applying the adhesive 24 to the protecting film 26 surface having the recess 62. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inkjet head that ejects ink. The present invention also relates to a method for manufacturing the inkjet head.

  The ink jet head ejects a small amount of liquid droplets, and is composed of a head chip, a nozzle plate, and a head base. The head chip includes an actuator member provided with an ink flow path, and the ink flow path has a means for generating energy necessary for discharging droplets. The nozzle plate is a resin or metal plate provided with a plurality of nozzle holes, which are minute holes for discharging droplets. The cross-sectional area of the ink flow path is larger than the cross-sectional area of the nozzle hole. The nozzle holes are provided in the nozzle plate so that the central axis of the nozzle holes and the central axis of the cross section of the ink flow path substantially coincide. The head base includes a wiring board and a member for supporting the wiring board. An ink jet head is an assembly of a head chip, a nozzle plate, and a head base, and the components are often bonded together with adhesive, coated with each other, or both Has been made.

  The ink jet head has a problem that its durability is remarkably lowered due to the corrosive action of ink, temperature change, physical load and the like. In particular, the vicinity of the nozzle hole, which is an ink discharge portion, is always in a state of being immersed in ink and is easily affected by the corrosive action of the ink. When a problem occurs in the vicinity of the nozzle hole, the ejection characteristics of the inkjet head are greatly affected. For this reason, many efforts have been made to improve the durability of the single actuator member having the nozzle plate and the ink flow path, and to maintain a good adhesion state of these members.

  As a material for the nozzle plate, a metal such as a polyimide resin or stainless steel having high chemical resistance is usually used, which is not a big problem. On the other hand, lead zirconate titanate (PZT) is often used as an actuator member. However, PZT has low resistance to ink, and characteristic deterioration due to corrosion tends to occur in a liquid contact portion with ink. Therefore, Patent Document 1 discloses a method in which an inkjet head including a base member formed of PZT is coated with an organic insulating film having high chemical resistance. In the method disclosed in Patent Document 1, as an insulating film, an organic film mainly composed of parylene C excellent in permeation-preventing ability of various gases including water vapor, and parylene N excellent in water resistance as a main component. By laminating these using an organic film, deterioration of the protective film is prevented. Thereby, the insulation state between the electrode and the aqueous ink is maintained, and the deterioration of the actuator member and the electrode is prevented.

  However, the above method has a problem that it can cope with a specific ink but cannot cope with most inks. For example, the joint between the laminated parylene N film and the parylene C film has extremely low chemical resistance. Therefore, delamination occurs when ink enters between the parylene N film and the parylene C film. This does not necessarily occur in special inks, but also occurs when a general solvent such as isopropyl alcohol is used. For this reason, it is desirable to protect the inkjet head with a parylene monolayer film, but the parylene monolayer film has several problems.

  For example, when a parylene C single-layer film is formed, the adhesive force with the adhesive is reduced as compared with a laminated film of parylene C and parylene N. This is because the parylene C film is inferior to the parylene N film in adhesion. In order to evaluate the adhesive strength between the two, a peel test was performed in which an epoxy adhesive was used as the adhesive and the nozzle plate side was peeled off from the PZT substrate at an angle of 90 °. As a result, the adhesive strength was 1/10 or less in the case where the parylene C single layer film was formed as compared with the case where the laminated film of parylene C and parylene N was formed on PZT.

  Further, when a parylene N single layer film is formed, the parylene N single layer film is a porous material, so that the ink solvent reaches PZT and PZT is corroded.

  From the above results, in order to protect the inkjet head with the parylene single layer film, it is required to improve the adhesive strength between the parylene C film having high chemical resistance and the adhesive.

  As one of the methods for increasing the bonding strength between the parylene C film and the adhesive, it is possible to change the surface topography (shape) of the bonding surface of the parylene C film, and several surface treatment methods for this purpose are known. Yes. Many of such surface treatment methods are methods for roughening the surface of the adhesive surface, and examples include chemical etching, plasma and reactive etching, mechanical ablation, and sandblasting. These are all processing methods that can have some effect on the surface topography. It is also possible to change the surface topography of the adhesive surface by incorporating roughness into the surface of the adhesive surface mold.

  However, the conventional techniques for improving the adhesion by surface treatment have the following various problems.

  For example, plasma surface treatment must be performed in a non-standard environment such as a vacuum, which increases both production time and production costs. In addition, the surface treatment that improves the adhesion by chemically changing the surface by plasma, RIE (reactive ion etching), corona, etc. is unstable. Often must be combined. Therefore, there is a problem that the manufacturing process becomes complicated. Also, surface treatments such as mechanical ablation and sand blasting may introduce unwanted foreign matter into the manufacturing process and affect the yield and quality of the inkjet head. In addition, when the rough surface finish is performed by the above-described method, the strength of the joint may be increased, but the surface structure produced by such a method is not controlled and is not optimized for adhesion. . Furthermore, many of the types of surface treatment methods described above are not environmentally friendly. Further, in surface processing using a mold, it may be difficult to take out a part from the mold.

  Furthermore, surface treatments that produce the most effective surface for adhesion have the problems of reducing yield and increasing cost and production time. In addition, there is a problem that the manufacturing process is adversely affected by affecting the shape of each component. In addition, during the assembly of the inkjet head, it is desirable to surface-treat a specific part of the inkjet head component, but if other surfaces of the same component are processed, problems may occur. Masking areas that are not subjected to surface treatment in order to prevent the occurrence of defects can add considerable cost.

As a technique for solving the above-described problem, for example, Patent Document 2 discloses a technique for performing surface processing by laser irradiation. In the surface processing method described in Patent Document 2, an initiator for protecting a part of the substrate surface is applied to the substrate surface, and then laser irradiation is performed to polish the unprotected part to obtain a desired density and This is a method for forming a microstructure having a size.
JP 2004-74469 A (published March 11, 2004) JP 2003-268666 A (published on September 25, 2003)

  However, the technique disclosed in Patent Document 2 has a problem that fine particles contained in the initiator enter the ink flow path when the initiator is applied. Since the size of the fine particles is on the order of several hundred nanometers, a very small amount will not cause nozzle clogging. However, when several tens of pieces are aggregated, nozzle clogging may occur. Even when nozzle clogging does not occur, ink ejection bends occur when particles adhere to the vicinity of the nozzle holes and within the nozzle taper. Furthermore, there is a possibility that the fine particles are dissolved in the ink solvent. In this case, the ink performance is changed, which may cause a defect in the product itself.

  Therefore, the present invention has been made in view of the above problems, and its purpose is to improve chemical resistance by improving the adhesion between the protective film and the adhesive by performing surface treatment of the protective film. It is another object of the present invention to provide an inkjet head with improved reliability and a method for manufacturing the same.

  In order to solve the above problems, an inkjet head according to the present invention is an inkjet head including a nozzle plate having nozzle holes for ejecting ink and a piezoelectric substrate for ejecting ink from the nozzle holes. A protective film for protecting the piezoelectric substrate is formed on the surface of the piezoelectric substrate, the nozzle plate is bonded to the piezoelectric substrate and the protective film with an adhesive, and the nozzle plate is bonded. A patterned recess is formed on the surface of the protective film.

  According to the said structure, since the protective film is formed in the surface of a piezoelectric substrate, the tolerance with respect to the chemical | medical agent of a piezoelectric substrate is improving. Further, the surface shape of the protective film on the surface where the piezoelectric substrate and the nozzle plate are bonded is not flat, and patterned concave portions are formed. By providing the concave portion on the surface, the effective adhesion area between the protective film and the adhesive is increased, and the adhesive strength of the adhesive to the protective film is increased. Therefore, the nozzle plate bonded to the piezoelectric substrate via the adhesive is less likely to be displaced, and an ink jet head having a strong adhesive force between the components can be manufactured. Moreover, although the adhesive force of the adhesive agent with respect to the protective film varies depending on the formation density and shape of the concave portions formed in the protective film, the ink jet head of the present invention can be provided with concave portions having a desired density and shape. Therefore, it is possible to stably provide the concave portions having the density and shape optimal for the required adhesive force.

  Furthermore, in the ink jet head of the present invention, in addition to the above-described configuration, the surface of the protective film is preferably formed of an organic insulating film.

  According to the above configuration, contact between the conductive ink and the ink chamber electrode provided in the channel groove of the piezoelectric substrate can be avoided. Thereby, it is possible to prevent a leak current from flowing when a voltage is applied to the channel groove. Therefore, it is possible to prevent a discharge failure due to the inability to achieve normal channel wall shear mode deformation.

  Furthermore, in the ink jet head of the present invention, in addition to the above-described configuration, the material of the organic insulating film is preferably composed mainly of paraxylylene resin.

  According to the above configuration, since the protective film is a parylene film, the protective film is chemically stable and excellent in chemical resistance. Therefore, the chemical resistance of the inkjet head can be improved.

  Furthermore, in the ink jet head of the present invention, in addition to the above-described configuration, the paraxylylene resin is preferably polymonochloroparaxylylene.

  According to the said structure, the protective film which protects an inkjet head is comprised by the organic film which has the parylene C excellent in the permeation | transmission prevention power of various gas containing water vapor | steam as a main component. Therefore, even when ink is vaporized by heat in the inkjet head, it is possible to prevent the ink from passing through the protective film and reaching the piezoelectric substrate. Therefore, it is possible to prevent the ink jet head from being damaged due to the deterioration of the piezoelectric substrate due to the ink and the electrolytic corrosion of the electrode material.

  Furthermore, in the ink jet head of the present invention, in addition to the above-described configuration, the thickness of the protective film is preferably 1 μm or more and 10 μm or less.

  According to the above configuration, the surface of the piezoelectric substrate is covered with a protective film having a thickness of 1 μm or more, and the generation of pinholes in the protective film due to the unevenness of the surface of the piezoelectric substrate and the influence of dust adhering to the surface of the piezoelectric substrate is prevented. Can do. This prevents ink from reaching the piezoelectric substrate and further prevents deterioration of the piezoelectric substrate due to ink. Moreover, according to the said structure, the thickness of a protective film is 10 micrometers or less. Thereby, the time required for film formation can be shortened, and the cost of raw materials can be reduced.

  Furthermore, in the inkjet head of the present invention, in addition to the above-described configuration, the distance from the bottom of the recess to the surface of the protective film is 50 nm or more, and the distance from the bottom of the recess to the bottom of the protective film Is preferably 10 nm or more. The bottom surface of the protective film is a surface on the protective film side where the protective film and the piezoelectric substrate are in contact.

  According to the said structure, the distance from the bottom part of a recessed part to the protective film surface is 50 nm or more. In this case, the active surface of the protective film is exposed on the surface, and the adhesive strength between the protective film and the adhesive can be greatly improved. Accordingly, it is possible to prevent the separation of the nozzle plate that may occur when the ink attached to the nozzle surface is scraped off. Further, when the distance from the bottom of the recess to the bottom surface of the protective film is 10 nm or more, it is possible to prevent the influence of heat damage that occurs when forming the recess on the channel. As a result, the occurrence of cracks in the channel can be prevented. By preventing the occurrence of cracks, it is possible to prevent the inkjet head from causing fatigue failure based on the cracks.

  Further, in the ink jet head of the present invention, in addition to the above-described configuration, the shape of the concave portion on the surface of the protective film is a circle, and the diameter of the circle is preferably 50 μm or less.

  Furthermore, in the ink jet head of the present invention, in addition to the above-described configuration, the shape of the concave portion on the surface of the protective film is preferably a star shape.

  According to the said structure, the surface shape of a recessed part is a star shape. When the surface shape of the concave portion is a star shape, compared to the case where the surface shape of the concave portion is circular, the region that can exert the anchor effect of the protective film, that is, the effective contact area with the adhesive, Becomes larger. Therefore, by using a star pattern, the adhesive strength between the protective film and the adhesive can be increased as compared with the circular pattern, and the reliability of the ink jet head can be improved.

  Furthermore, in the ink jet head of the present invention, in addition to the above-described configuration, the cross-sectional shape of the concave portion on the surface orthogonal to the surface of the protective film is an inversely tapered shape whose width becomes narrower toward the surface of the protective film. It is preferable.

  According to the said structure, a recessed part is what is called a reverse taper shape, and can improve the adhesive strength with an adhesive agent rather than a normal taper shape.

  Further, in the ink jet head of the present invention, in addition to the above-described configuration, the total cross-sectional area of the opening of the concave portion on the surface of the protective film is 10% or more of the area of the region to which the nozzle plate adheres. Is preferred. Here, it is assumed that the area of the region where the nozzle plate adheres in the protective film includes the opening of the recess, but does not include the opening of the ink chamber.

  According to the said structure, the ratio which occupies for the adhesion surface of the recessed part formed is 10% or more. When the recess is formed, the effective contact area with the adhesive is increased as compared with the case where the surface is flat without being formed. Therefore, according to the said structure, adhesive strength can be raised more.

  Further, in the ink jet head of the present invention, in addition to the above-described configuration, the forming material of the nozzle plate is preferably polyimide.

  According to the said structure, the nozzle plate is formed with the polyimide excellent in chemical resistance. Therefore, the chemical resistance of the nozzle plate can be improved, and an ink jet head excellent in chemical resistance can be provided.

  Furthermore, in the ink jet head of the present invention, in addition to the above-described configuration, the adhesive is preferably an epoxy adhesive.

  According to the said structure, the piezoelectric substrate and the nozzle plate have adhere | attached with the epoxy-type adhesive agent excellent in chemical resistance. Accordingly, it is possible to prevent deterioration of the adhesive due to the ink and to keep the adhesion between the nozzle plate and the piezoelectric substrate strong.

  An ink jet head manufacturing method according to the present invention is the above ink jet head manufacturing method, characterized by including a processing step of forming the concave portion by laser irradiation.

  According to the method, the recess is formed by laser irradiation. By changing the laser irradiation conditions, a recess having a desired shape and size can be formed. Further, by using a laser, an ink jet head can be manufactured by a simple process at low cost.

  Furthermore, in the ink jet head manufacturing method of the present invention, the laser is preferably an excimer laser.

  According to the above method, since the excimer laser is used to form the recess, it is possible to reduce thermal damage to the protective film in the processing step. Therefore, the deterioration of the protective film can be prevented and an ink jet head with improved reliability can be manufactured. Further, the processing residue generated when forming the recess can be easily removed by excimer laser scanning. Therefore, an ink jet head can be manufactured by a low-cost and simple process without requiring a separate device for removing processing residues.

  As described above, in the ink jet head according to the present invention, the protective film for protecting the piezoelectric substrate is formed on the piezoelectric substrate, and the patterned concave portion is formed on the surface of the protective film to which the nozzle plate is bonded. The adhesive film is applied to the surface of the protective film where the recesses are formed and the nozzle plate is affixed. As a result, the adhesive strength between the protective film and the adhesive increases, and the piezoelectric substrate and the nozzle plate become stronger. Since they are bonded, the chemical resistance and reliability of the inkjet head can be improved.

  The method for manufacturing an inkjet head according to the present invention is a method for manufacturing an inkjet head in which a patterned recess is formed on the surface of a protective film formed on a piezoelectric substrate. Therefore, the inkjet head can be manufactured by a simple process with low cost.

  An embodiment of an ink jet head according to the present invention will be described below with reference to FIGS.

[Configuration of inkjet head]
First, the configuration of the ink jet head in the present embodiment will be described with reference to FIGS. 2, 3, 5, 7, 8, and 9.

  FIG. 2 is a perspective view illustrating a schematic configuration of the inkjet head 10. FIG. 3 is a diagram illustrating a surface of the head chip (piezoelectric substrate) 18 to be bonded to the nozzle plate 17.

  As shown in FIG. 2, the inkjet head 10 includes a head chip 18 having an actuator member 11 and a cover member 12 and a nozzle plate 17 having a nozzle hole 16.

  The actuator member 11 is manufactured by processing a piezoelectric material wafer such as lead zirconate titanate (PZT) having ferroelectricity, and has a thickness of 1 mm, a width of 6 mm, and a depth of 12 mm. Here, the thickness and the width are the length of the long side and the length of the short side of the surface having the nozzle plate bonding surface 15 of the actuator member 11, respectively. In the actuator member 11, a channel groove 13 serving as an ink chamber is formed with a channel wall 14 interposed therebetween. For convenience of explanation, in FIG. 2, the number of channel grooves is omitted.

  The channel groove 13 is a part of an ink chamber for discharging ink. The channel groove 13 is formed in the actuator member 11 by a cutting process in which a dicing blade of a dicer is driven while being cut halfway in the thickness direction of the actuator member 11. The channel groove 13 has a depth of 300 μm and a lateral width of 80 μm. Each channel groove 13 is formed in parallel to each other and at the same depth so as to penetrate from one end of the actuator member 11 to the other end. The channel wall 14 is a partition wall formed between the channel grooves 13.

  The cover member 12 is a member that seals the upper portion of the channel groove 13 and is obtained by processing a piezoelectric material wafer. An ink chamber 25 is formed by covering the upper portion of the channel groove 13. As the piezoelectric material of the cover member 12, PZT is used similarly to the actuator member 11 in order to improve the matching of the thermal expansion coefficient with the actuator member 11. Note that it is sufficient that the coefficient of thermal expansion is relatively close to that of the actuator member 11, and inexpensive alumina ceramic may be used. The cover member 12 is provided with a counterbore that becomes a common ink chamber when an ink jet head is configured, and a through-processing portion that becomes an ink supply port. The actuator member 11 and the cover member 12 are bonded by a commercially available adhesive.

  The nozzle plate 17 is a member having nozzle holes 16 for ejecting ink. The nozzle plate 17 is bonded to the ink ejection surface (nozzle plate bonding surface 15) of the head chip 18 so that the nozzle holes 16 are arranged at positions corresponding to the respective channel grooves 13. The material of the nozzle plate 17 may be any material as long as it can be laser processed as long as it does not require a very high discharge performance, such as a consumer printer. On the other hand, in the case of industrial inkjet printer applications, high accuracy is required especially in terms of ink landing accuracy and discharge volume, so that variations in nozzle diameter and nozzle taber shape are strictly controlled. There is a need to. Therefore, as a method for manufacturing a high-precision nozzle, a method of processing an excimer laser beam on a thin resin plate is used. In this case, the material of the nozzle plate 17 is preferably a material with high excimer laser processing ease, such as polyethylene, polypropylene, polyimide, and polyamideimide. Alternatively, it may be a metal nozzle plate 17 obtained by electroforming plating of Ni. The nozzle plate 17 in this embodiment uses polyimide as a material.

  FIG. 3 is a diagram showing the nozzle plate bonding surface 15 of the head chip 18. FIG. 3A shows a state before an organic insulating film (protective film) 26 is formed on the surface, and FIG. FIG. 6 is a diagram showing the head chip 18 after the organic insulating film 26 is formed thereon. FIG. 7 is a cross-sectional view of the inkjet head 10.

  As shown in FIGS. 3 and 7, the ink chamber 25 is formed by covering the channel groove 13 with the cover member 12. In the ink chamber 25, an ink chamber electrode 23 is provided on the upper portion of the channel wall 14 (on the side close to the cover member 12). When ink ejection is performed using the inkjet head 10, shear mode deformation is caused in the channel wall 14 by applying potentials having opposite phases to the ink chamber electrodes 23 facing each other across the channel wall 14. Let That is, by generating a potential difference between the ink chamber electrodes 23 on both sides of the channel wall 14, the upper half of the channel wall 14 where the ink chamber electrode 23 is provided and the ink chamber electrode 23 are not provided. The channel wall 14 is deformed at the boundary with the lower half. The volume change inside the ink chamber 25 due to this deformation applies pressure to the ink inside the ink chamber 25. Using this pressure, ink droplets are ejected from the nozzle holes 16 arranged at the tip of the ink chamber.

  The ink chamber electrode 23 is formed by depositing a metal as an electrode material from above the channel groove 13 and removing the metal film formed on the upper surface of the channel wall 14 before covering the actuator member with the cover member 12. . As the electrode material, metals such as Au, Al, and Cu are preferable. In this embodiment, Au is used, and the thickness of the ink chamber electrode 23 is 0.5 μm.

  As shown in FIG. 3B, an organic insulating film 26 is formed on the surface of the head chip 18, the surface of the ink chamber electrode 23, and the bottom surface and side surfaces of the ink chamber 25. The organic insulating film 26 is for isolating and protecting the members constituting the inkjet head 10, the ink chamber electrodes 23, and the adhesive from the ink.

  Examples of the organic insulating film 26 include resin materials such as polyethylene and epoxy, among which a parylene film is preferable. The parylene film is chemically stable and excellent in chemical resistance and insulation. Therefore, it is possible to prevent the inkjet head from being damaged due to the electrolytic corrosion of the electrode material. In addition, when using ink having conductivity such as water-based ink and ink containing metal particles, a leak current flows due to voltage application between the channels when the head is driven, and normal channel wall shear mode deformation is not achieved. A discharge failure may occur. However, the above-described ejection failure can be prevented by using a parylene film having excellent insulating properties. In addition, when an ink containing an organic solvent as a main component is used, the parylene film can be used to isolate the members and the adhesive constituting the inkjet head from the highly soluble organic solvent. Parylene is formed by vapor phase growth at room temperature. Therefore, the organic insulating film 26 can be formed without causing thermal damage to a member whose characteristics are deteriorated by heat. Further, the organic insulating film 26 can be uniformly formed even on a member having a complicated surface shape. In the inkjet head 10, polymonochloroparaxylylene (parylene C) is used. Parylene C is excellent in the permeation preventing power of various gases including water vapor. Therefore, even when the ink is vaporized by heat, it is possible to prevent the ink jet head constituent member from being deteriorated by the ink.

  The thickness of the organic insulating film 26 is preferably 1 μm or more. When the surface of the head chip 18 is covered with an organic insulating film 26 having a thickness of 1 μm or more, the pinholes of the organic insulating film 26 due to the unevenness of the surface of the head chip 18 and the influence of dust adhering to the surface of the head chip 18. Occurrence can be prevented. Accordingly, it is possible to prevent ink from reaching the head chip 18 and further prevent deterioration of the head chip 18 due to ink. On the other hand, the thickness of the organic insulating film 26 is preferably 10 μm or less from the viewpoint of shortening the film forming process time and reducing the raw material cost. In the inkjet head 10, the thickness of the organic insulating film 26 is 3.5 μm.

  FIGS. 5A and 5B are views showing the shape and pattern of the recess 62 provided on the nozzle plate bonding surface 15. The recess 62 is formed by laser processing described later. The recess 62 shown in FIG. 5A is a rectangular pattern formed parallel to the long side of the opening of the ink chamber 25, and the recess 62 shown in FIG. 5B is a circular pattern. The shape and pattern of the recess 62 can be changed to a desired shape and pattern by changing the mask used during laser processing. For example, the shape of the surface of the concave portion 62 can be processed into a star shape. When the surface shape of the concave portion 62 is a star shape, a region where the anchor effect of the organic insulating film 26 can be exerted, that is, an effective contact area with the adhesive, is larger than when the concave portion 62 is a circular shape. Therefore, by forming the concave portion 62 in a star pattern, the adhesive strength between the organic insulating film 26 and the adhesive can be increased as compared with the circular pattern, and the reliability of the inkjet head can be improved. In addition, the shape of the opening part of the recessed part 62 is not limited to the shape mentioned above.

  The cross-sectional shape of the surface of the recess 62 perpendicular to the surface of the organic insulating film 26 is a tapered shape. The tapered shape is such that the width on the bottom side is smaller than the width on the surface side. That is, the wall surface of the recess 62 is inclined from the surface to the bottom. Here, the inclination angle of the inclination is defined as a taper angle. More specifically, it is the angle at which the line drawn in the direction perpendicular to the surface intersects the wall surface. In this embodiment, the taper angle of the recess 62 is about 10 °. The taper angle can be adjusted to an arbitrary angle by processing while shifting the laser irradiation axis. Further, the recess 62 may have a so-called reverse taper shape in which the width on the bottom side is wider than the width on the surface side. By making the recessed part 62 into a reverse taper shape, compared with a normal taper shape, adhesive strength with an adhesive agent can be raised.

  FIG. 8 is a diagram illustrating the difference in adhesive strength depending on the formation conditions of the recess 62. Specifically, it is a diagram showing the adhesive strength with respect to the processing amount of the recess 62 (depth of the recess 62) and the adhesive strength with respect to the processing area ratio. The adhesive strength was evaluated by a 90 ° peel test. The processing area ratio is the area of the processing portion (the total cross-sectional area of the opening of the recess 62) with respect to the total area of the region to which the nozzle plate 17 adheres. Here, it is assumed that the total area includes the opening of the recess, but does not include the opening of the ink chamber.

  In the ink jet head, the ink adhering to the nozzle surface is scraped off by a rubber blade or the like, and therefore, when the adhesive strength is weak, the nozzle plate is peeled off when wiping with the rubber blade. Therefore, an adhesive strength of at least 20 g / mm is necessary to withstand wiping with a rubber blade.

  As shown in FIG. 8, when the processing amount of the recessed part 62 is smaller than 50 nm, it turns out that the adhesive strength exceeding 20 g / mm cannot be achieved even if the processing area ratio is controlled. On the other hand, when the processing amount is 50 nm, the adhesive strength can exceed 20 g / mm. From this result, the depth of the recess 62 from the surface of the organic insulating film 26 is preferably 50 nm or more. As conditions other than the depth of the recess 62 and the processing area ratio, the shape of the recess 62 is a circular pattern with a diameter of 50 μm, and the taper angle is 10 °.

  By the way, the depth of the concave portion 62 is not limited, and it is necessary to leave the organic insulating film on the bottom so that the thermal damage generated during processing does not affect the channel portion. FIG. 9 is a diagram showing a crack generated in the channel portion. If the distance from the bottom of the recess to the bottom of the organic insulating film (the thickness of the bottom of the recess) is shorter than 10 nm, a crack occurs in the channel portion (PZT) as shown in FIG. Cracks do not affect the characteristics of the initial ink jet head, but as time passes, fatigue cracks occur starting from that portion. Therefore, it is preferable that the film thickness of the bottom of the recess is 10 nm or more.

  Further, as shown in FIG. 8, when the processing area ratio is 5%, the adhesive strength is less than 20 g / mm regardless of the processing amount. On the other hand, when the processing area ratio is 10% or more, the adhesive strength can be 20 g / mm or more. As the processing area ratio increases, the adhesive strength also increases. From this result, it is preferable that the density of the recesses 62 is 10% or more as a processing area ratio.

[Adhesive strength in prior arts (1) and (2)]
On the other hand, as surface processing, the surface roughness is increased by operating the conventional technique (hereinafter referred to as the conventional technique (1)) in which only ashing is performed and the film formation conditions of the organic insulating film. The adhesive strength in the related art (hereinafter referred to as the prior art (2)) will be described with reference to FIG. 10 and FIG. In the prior art (1), in bonding the head chip and the nozzle plate, after ashing the nozzle plate bonding surface of the head chip and the bonding surface of the nozzle plate with the head chip, the adhesive is applied to the nozzle plate bonding surface of the head chip. This is a technique for performing adhesion by applying. The prior art (2) is a technique for performing adhesion by manipulating the film forming conditions of the parylene C film, which is an organic insulating film, to increase the surface roughness of the parylene C film surface.

  FIG. 10 is a graph showing a test result of adhesive strength in the prior art (1). Specifically, the change in the contact angle of the nozzle plate adhesion surface with respect to pure water and the change in the adhesion strength when the nozzle plate and the head chip are adhered to each other during each ashing time are shown. As ashing conditions, the output is 100 W, and the process gas is air. The adhesive strength is evaluated by a 90 ° peel test. As shown in FIG. 10, the contact angle of the nozzle plate adhesion surface is 10 ° or less by the ashing process for 3 minutes, but the adhesion strength with the nozzle plate is 10 g / mm or less even if the treatment time is increased. I know that there is. Therefore, it can be seen that the method using only the ashing process cannot secure a desired adhesive strength.

  FIG. 11 is a graph showing a test result of adhesive strength in the prior art (2). Specifically, the adhesive strength with respect to the surface roughness of the surface of the organic insulating film is shown. Conventionally, it is considered that if the surface roughness of the bonding surface is high, the bonding strength is increased by the so-called anchor effect. However, as shown in FIG. 11, it can be seen that even when the surface roughness of the parylene C film is increased to 50 nm, the adhesive strength is less than 10 g / mm.

[Inkjet head manufacturing method]
Next, an inkjet head manufacturing method will be described with reference to FIGS. 1, 4, 5, and 6 from the step of forming the organic insulating film 26 to the step of attaching the nozzle plate 17 to the head chip 18. To do.

  FIG. 4 is a diagram illustrating a part of the processing process of the manufacturing method of the inkjet head. First, in the film forming process, the organic insulating film 26 is formed by vapor deposition (step S1). After the film forming process, in the processing process, a laser is irradiated only to a place where it is desired to increase the adhesive strength with the adhesive, thereby forming a fine recess in the organic insulating film 26 (step S2). After the processing step, in the removal step, the entire laser irradiation region is irradiated with a low-power laser to remove by-products generated in the processing step (step S3). After the removing step, an adhesive is applied to the processed surface in the applying step (step S4). After the coating process, in the pasting process, the nozzle plate 17 is bonded and pasted to the surface coated with the adhesive (step S5).

  First, the processing step (step S2) for forming the recess 62 will be described with reference to FIGS.

  FIGS. 1A and 1B are cross-sectional views of the surface of the head chip 18 perpendicular to the depth direction of the ink chamber 25 (channel groove 13). FIG. 1A is a cross-sectional view during laser irradiation, and FIG. 1B is a cross-sectional view after laser irradiation. The laser 61 is irradiated from a position facing the surface to which the nozzle plate 17 is attached. As shown in FIG. 1A, when irradiating the laser 61, a mask (not shown) is used so that the laser 61 is not irradiated inside the ink chamber 25, and only the nozzle plate bonding surface 15 is selected. In particular, the laser 61 is irradiated. A laser irradiation apparatus that performs laser irradiation includes a mask for deforming the laser 61 into a desired shape and pattern, and a reduction projection lens for further reducing the laser 61 that has passed through the mask into a reduced pattern. . By providing this configuration, as shown in FIG. 1B and FIG. 5, a fine recess 62 having a desired shape and pattern can be formed in the organic insulating film 26.

  In this embodiment, an excimer laser (wavelength 248 nm) is used as the laser 61. By using an excimer laser, thermal damage to the organic insulating film 26 at the time of forming the recess can be reduced, and a processing residue described later can be removed. As the laser device, NovaLine 100 manufactured by Lambda Physic was used. Further, as laser excitation gas, halogen gas (fluorine and Ne mixed gas, fluorine concentration 5%) purity 99.9%, rare gas (Kr) purity 99.995%, buffer gas (Ne) purity 99.995%, In addition, an inert gas (He) purity of 99.995% was used.

  The recess 62 formed by normal laser processing tends to have a tapered shape in which the shape (lower shape) on the bottom side is smaller than the shape (upper shape) on the surface side of the processed material. The taper angle described above can be adjusted to an arbitrary angle by processing while shifting the laser irradiation axis. Furthermore, by processing while shifting the focus position of the laser 61, a so-called reverse taper shape in which the processing width on the inner side is wider than the processing width on the front surface side can be easily formed. By making the recessed part 62 into a reverse taper shape, compared with a normal taper shape, adhesive strength with an adhesive agent can be raised.

  Next, the removal process (step S3) for removing processing residues will be described.

  After processing by the laser 61, a minute processing residue is generated around the recess 62. This is considered that soot scattered by ablation adheres during processing with an excimer laser. Therefore, it is necessary to remove the processing residue before applying the adhesive 24 to the organic insulating film 26. However, the processing residue can be easily removed by scanning the entire surface of the laser processing region with a very low power excimer laser. Can be removed. Since the processing residue is a melt of the organic insulating film 26, when a laser other than an excimer laser is used, plasma processing (ashing) or wet processing must be performed to remove the processing residue. Therefore, a new device is required, and the processing becomes complicated.

  The processing step and the removal step are performed in a clean atmosphere such as a clean room.

  Next, the application process (step S4) for applying the adhesive 24 will be described.

  In order to bond the head chip 18 and the nozzle plate 17, an adhesive 24 is applied to the nozzle plate bonding surface 15 in the coating process. In order to uniformly bond the head chip 18 and the nozzle plate 17 over the entire surface, the adhesive 24 is preferably thin and has a uniform thickness. Therefore, after a uniform thin adhesive layer is formed on a sheet such as a polyimide film using a bar coater, a spin coater, or the like, the adhesive layer is transferred to the nozzle plate bonding surface 15 of the head chip 18. In the present embodiment, a uniform adhesive 24 layer having a thickness of 4 μm is formed on the polyimide film using a known bar coater. Thereafter, the nozzle plate adhesive surface 15 of the head chip 18 is pressed onto the polyimide film on which the adhesive 24 layer is formed, and the stamp is transferred. As a result, a uniform layer of adhesive 24 having a thickness of 2 μm is formed in a region other than the opening of the ink chamber 25 on the nozzle plate bonding surface 15.

  As the adhesive 24, a material excellent in chemical resistance is preferable, and an epoxy adhesive, a silicon cross-linking fluorine adhesive, and a polyimide amide are preferable, and an epoxy adhesive is more preferable.

  Next, an attaching process (step S5) for attaching the nozzle plate 17 to the head chip 18 will be described with reference to FIG.

  FIG. 6 is a schematic diagram showing a method of attaching the nozzle plate 17 to the head chip 18 by adjusting the position. As shown in FIG. 6, first, the nozzle plate 17 is disposed at a position facing the nozzle plate bonding surface 15 of the head chip 18. Next, an alignment camera 81 having built-in cameras on both the upper and lower sides is moved between the nozzle plate 17 and the head chip 18, and the central axes of all the nozzle holes 16 and the centers of the openings of the ink chambers 25 corresponding to the respective nozzle holes 16. Read the position information with respect to the axis. By processing the read information in an information processing unit (not shown), the amount of positional deviation in the rotational direction of the nozzle plate 17 and the positional deviation in the XY direction on a plane parallel to the nozzle plate 17 is calculated. Thereafter, based on the result, at least one of the nozzle plate 17 and the head chip 18 is set so that the central axis of all the nozzle holes 16 and the central axis of the opening of the corresponding ink chamber 25 coincide with each other. To adjust the alignment. Here, the X direction and the Y direction are a direction parallel to the long side and a direction parallel to the short side of the nozzle plate, respectively.

  Next, a tool (not shown) used to fix the nozzle plate 17 to the head chip 18 is gradually moved toward the head chip 18 to bring the nozzle plate 17 closer to the head chip 18, and finally the nozzle The bonding surface of the plate 17, that is, the surface (back surface) facing the head chip 18 of the nozzle plate 17 is brought into contact with the nozzle plate bonding surface 15 to which the adhesive 24 has been applied in advance. Thereafter, the adhesion between the head chip 18 and the nozzle plate 17 is completed by applying pressure and heating.

  In addition, this invention is not limited to embodiment mentioned above, A various change is possible in the range shown to the claim. In other words, embodiments obtained by combining technical means appropriately changed within the scope of the claims are also included in the technical scope of the present invention.

(Additional notes)
In addition, it can also be said that the inkjet head of the present invention has the following features. That is, in an inkjet head comprising: a piezoelectric substrate having a channel groove extending from an ink ejection surface; and a nozzle plate having a nozzle hole disposed on the ink ejection surface of the piezoelectric substrate so as to face one end of the channel groove. In other words, the protective film formed so as to cover the channel groove has an uneven portion formed by selectively subjecting the surface of the protective film to the nozzle plate to be surface-treated.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by the following example.

  The ejection performance of the inkjet head 10 in this embodiment and the inkjet head in the prior art were compared.

  As Example 1, the inkjet head 10 having the above-described configuration is used, the surface shape of the recess 62 is circular, the diameter is 30 μm, the taper angle is 10 °, and the thickness of the bottom of the recess is 10 nm. . As Comparative Example 1, an ink jet head in which a concave portion was not provided on the surface of the organic insulating film, only an ashing process was performed, an adhesive was applied, and a head chip and a nozzle plate were adhered to each other was used. Further, as Comparative Example 2, an ink jet head formed by processing fine concave portions on the surface of the organic insulating film until the thickness of the concave bottom portion became 10 nm was used. As Comparative Example 3, an ink jet head in which the surface of the organic insulating film has a circular surface shape and a recess having a diameter of 500 nm was used.

  Three each of the inkjet heads of Example 1 and Comparative Examples 1 to 3 were manufactured, and the number of nozzle holes that caused non-ejection of ink was compared for each inkjet head after continuous ejection for one month (test) 1). Also, after continuous discharge for one month, discharge voltages for obtaining a desired ink discharge speed (8 m / sec) were compared (Test 2).

  As a result, in Test 1, in Example 1, ink could be ejected from all the nozzle holes 16. On the other hand, in Comparative Example 1 and Comparative Example 3, non-ejection of ink occurred in 20 to 30 nozzle holes. In Test 2, Example 1 had almost no change at the beginning of the test and after one month. On the other hand, in Comparative Example 2, a voltage twice as high as that required at the beginning of the test was required in some channels. Then, when each inkjet head was observed with the microscope from the nozzle surface side, in the inkjet heads of Comparative Example 1 and Comparative Example 3, the locations where the adhesive was peeled (communication locations) were observed between the nozzle holes. Further, the nozzle plate of each inkjet head was peeled off, and the nozzle plate attachment portion of the head chip was observed with a microscope. As a result, in the inkjet head of Comparative Example 2, it was found that the channel wall was damaged. On the other hand, in the inkjet head 10 of the present embodiment of Example 1, the above-described problems were not found. In other words, the ink jet head 10 in this embodiment is an ink jet head having high ejection reliability, with no displacement between the nozzle hole and the cross section of the ink chamber of the head chip and no deformation of the nozzle plate.

  The ink jet head according to the present invention can be suitably used for an ink jet head to which a nozzle plate in which nozzle holes for discharging ink are formed is attached.

It is sectional drawing of the head chip which is a structural member of the inkjet head in embodiment of this invention. It is a perspective view showing the composition of the ink jet head in the embodiment of the present invention. It is a figure which shows the nozzle plate adhesion surface of the head chip which is a structural member of the inkjet head in embodiment of this invention. It is a figure which shows the manufacturing process of the inkjet head of this invention. It is a figure which shows the pattern of the recessed part of the inkjet head in embodiment of this invention. It is a figure which shows the alignment method of a nozzle plate and a head chip. It is sectional drawing of the inkjet head in embodiment of this invention. 4 is a graph showing a difference in adhesive strength depending on a recess processing pattern in an inkjet head according to an embodiment of the present invention. It is the figure which showed the crack which generate | occur | produced in the channel part. It is the graph which showed the difference in the adhesive strength by the ashing process time, and a contact angle of the surface processing method in a prior art. It is the graph which showed the difference in the adhesive strength by the surface roughness of the surface processing method in a prior art.

Explanation of symbols

10 Inkjet head 11 Actuator member (piezoelectric substrate)
12 Cover member (piezoelectric substrate)
13 Channel groove 14 Channel wall 15 Nozzle plate adhesion surface 16 Nozzle hole 17 Nozzle plate 18 Piezoelectric substrate 23 Ink chamber electrode 24 Adhesive 25 Ink chamber 26 Organic insulating film (protective film)
61 Laser 62 Concave part 81 Alignment camera X X direction Y Y direction

Claims (14)

In an inkjet head comprising a nozzle plate having nozzle holes for discharging ink, and a piezoelectric substrate for discharging ink from the nozzle holes,
A protective film for protecting the piezoelectric substrate is formed on the surface of the piezoelectric substrate,
The nozzle plate is bonded with an adhesive via the piezoelectric substrate and the protective film,
An ink jet head, wherein a patterned recess is formed on a surface of the protective film to which the nozzle plate is bonded.   The inkjet head according to claim 1, wherein the surface of the protective film is formed of an organic insulating film.   The inkjet head according to claim 2, wherein the material of the organic insulating film is mainly composed of paraxylylene resin.   The inkjet head according to claim 3, wherein the paraxylylene resin is polymonochloroparaxylylene.   5. The ink jet head according to claim 1, wherein the protective film has a thickness of 1 μm or more and 10 μm or less.   6. The distance from the bottom of the recess to the surface of the protective film is 50 nm or more, and the distance from the bottom of the recess to the bottom of the protective film is 10 nm or more. The inkjet head of any one of Claims.   The ink jet head according to claim 1, wherein a shape of the concave portion on the surface of the protective film is a circle, and a diameter of the circle is 50 μm or less.   The ink jet head according to claim 1, wherein a shape of the concave portion on the surface of the protective film is a star shape.   The cross-sectional shape of the concave portion on a surface orthogonal to the surface of the protective film is an inversely tapered shape whose width becomes narrower toward the surface of the protective film. The inkjet head as described.   The total cross-sectional area of the opening of the recess on the surface of the protective film is 10% or more of the area of the region to which the nozzle plate is bonded. Inkjet head.   The inkjet head according to any one of claims 1 to 10, wherein a material for forming the nozzle plate is polyimide.   The inkjet head according to claim 1, wherein the adhesive is an epoxy adhesive. It is a manufacturing method of the ink-jet head according to any one of claims 1 to 12,
The manufacturing method of the inkjet head characterized by including the process process which forms the said recessed part by laser irradiation.   The method of manufacturing an ink jet head according to claim 13, wherein the laser is an excimer laser.