Method of manufacturing ink jet head

Abstract: A method of manufacturing an ink jet head comprising the steps of: laminating a dry film photoresist (51) on an inner surface of a nozzle plate (2), the dry film photoresist being a photohardening resin; exposing the photoresist (51) with such energy as to half-harden the photoresist while superposing thereon a photomask (M1) having a predetermined masking pattern; developing the thus exposed photoresist (51); laminating a photoresist (52); secondarily exposing the photoresists (51), (52) to form a partially hardened portion (51C); bonding an elastic plate on the portion (51C); and integrating the bonded plates while hardening them by heating.

Description: The invention relates to a method of manufacturing ink jet heads used in ink jet printers. A method of forming an ink jet head using a photohardening resin is disclosed in Japanese Examined Patent Publication No. 42670/1990. The head is used in a so-called ink jet printer in which ink portions contained in independently arranged ink chambers are selectively pressured to form ink droplets, which are then jetted out of corresponding nozzles. The disclosed method involves the steps of: exposing and developing a photohardening resin laminated on a substrate to form ink chambers and ink flow paths thereon; and then bonding a nozzle plate thereon through an adhesive so as to be integral therewith. However, uniform application of the adhesive on the bonding surface having the ink chambers and the ink flow paths is so difficult that some of the adhesive is forced out into the small ink flow paths to block the jetting of ink droplets. In addition, adhesion is not strong enough due to the adhesive not being applied thick enough, or pressure leaks occur to adjacent ink chambers. Prior art document US-A-4666823 discloses a method for producing an ink jet head, in which a photosensitive resin is used to form ink pathways on a substrate. The resin is exposed to light and the unexposed portion is removed. A covering is placed over the substrate and the remaining photosensitive resin, and the resin is then cured. From the description of the preferred embodiments it is evident that a dry film photoresist is fused to a thin layer. Then, a photomask is superposed on the dry film photoresist. After that, light exposure is applied from over the photomask. Subsequently, the unexposed portions are removed. Finally, a flat plate is covered over the ink pathways formed by the dry film photoresist. The covering is performed by aid of heat curing treatment. The invention has been made in view of the above circumstances. Accordingly, an object of the invention is to provide an improved method of manufacturing an ink jet head for an ink jet printer. This object is solved by the method of independent claim 1. Further advantageous features aspects and details of the invention are evident from the dependent claims, the description and the drawings. According to a specific aspect of the invention a method is disclosed wherein a cavity forming substrate is formed that has a reinforced portion and a bonding portion by the process of exposing and developing a photohardening resin. That is, a laminated film of a photohardening resin is first exposed on a substrate so as to be half hardened, and then developed to form predetermined ink chambers and ink flow paths thereon. Successively, the bonding surface of the thus processed substrate is subjected to secondary exposure to locally form a hardened portion. With the profile of the cavity forming layer maintained by this hardened portion, the other substrate is integrally bonded thereon by the half-hardened photohardening resin portion. Another aspect of the invention is to provide a method characterized as preventing leakage of ink and pressure from the ink chambers and the like. That is, a peripheral portion around each ink chamber and each ink flow path, the peripheral portion excluding a portion near them, is subjected to secondary exposure so that the peripheral portion can be hardened. While preventing deformation of the ink chamber and the ink flow path by the hardened portion, the peripheral portion around the ink chamber and the ink flow path is bonded surely by the half-hardened resin portion near them. Still another aspect of the invention is to provide a method characterized as forming a rigid wall by secondary exposure of the portion around each ink chamber and each ink flow path in order to improve the accuracy in forming the ink chamber and the ink flow path. Still another aspect of the invention is to provide a method characterized as achieving consistent bonding by eliminating partial inconsistency in the area of the bonding surface as well as deformation of the substrate which occurs during the forming process. Figures 1(a) to 1(g) are diagrams showing the steps of forming a part of the cavity forming layer on the side of a nozzle plate, which is an embodiment of the invention; Figures 2(a) to 2(g) are diagrams showing the steps of forming the other part of a cavity forming layer on the side of an elastic plate in the above embodiment; Figure 3 is a sectional view showing an integrally bonded cavity forming substrate; Figure 4 is a plan view showing a part of the bonding surface of an ink jet head in enlarged form; Figure 5 is a plan view showing the entire part of the bonding surface; Figure 6 is a plan view showing a part of a bonding surface of an ink jet head of another type in enlarged form; Figure 7 is a perspective view showing a part of a bonding surface of an ink jet head of still another type in enlarged form; Figures 8(a) and 8(b) are diagrams showing a part of a forming process, which is another embodiment of the invention; Figure 9 is a plan view showing a part of a bonding surface obtained by the process shown in Figures 8(a) and 8(b) in enlarged form; Figure 10 is a plan view showing a part of a bonded surface of an ink jet head of another type in enlarged form; Figure 11 is a plan view showing a part of a bonding surface of an ink jet head of still another type in enlarged form; Figure 12 is a perspective view showing a part of a bonding surface of an ink jet head of still another type in enlarge form; and Figure 13 is a diagram showing an example of an ink jet head having a cavity type substrate formed by a method of the invention. Embodiments of the invention will now be described with reference to the accompanying drawings. Figures 1 and 2 show a method of manufacturing a cavity forming substrate constituting a piezoelectric ink jet head, which is an embodiment of the invention. Figure 13 shows an ink jet head having a cavity forming substrate prepared by the above-mentioned manufacturing method. An ink jet head using this substrate will be described briefly with reference to Figure 13. A cavity forming substrate 1 includes: a nozzle plate 2 having a plurality of nozzles 21; a cavity forming layer 3 having a common reservoir 31 and individual ink chambers 32; and an elastic plate 4 elastically deforming so as to apply pressure to ink contained in each ink chamber 32. The cavity forming substrate 1 is bonded to the top surface of a head frame 6 in place. A top end of a piezoelectric vibrating element 7 is bonded to the elastic plate 4 with the base end thereof supported by a fixed plate 8. The piezoelectric vibrating element 7 is longitudinally contracted and expanded by an alternating electric field applied through a wiring pattern 81 and a lead frame 82, both mounted on the fixed plate 8, to deform the elastic plate 4. As a result, the ink contained in each ink chamber is pressured to be jetted out in the form of an ink droplet from the corresponding nozzle 21. The method of preparing the cavity forming substrate 1 will be described with reference to Figures 1 and 2. Figures 1(a) to 1(g) show the steps of preparing a part or substructure 23 of the cavity forming layer 3 formed on the side of the nozzle plate 2. A dry film photoresist 51 of, e.g., a negatively photosensitive epoxy acrylate is laminated on an inner surface, or a cavity forming surface, of the nozzle plate 2 shown in Figure 1(a), by heating and/or applying pressure. The dry film photoresist 51 is not fluid but adhesive, so that the dry film photoresist 51 can be bonded easily by merely applying a small external force to the nozzle plate 2 (Figure 1(b)). Then, a photomask M1 is positioned thereon so as to match either a not shown positioning pattern formed on the nozzle plate 2 or the nozzle 21. The photomask M1 has preformed opaque patterns a and b so that a flow path 33 and the reservoir 31 that communicates with the nozzle 21 will later be formed thereon as shown in Figure 3. As shown in Figure 1(c), when light is injected onto the dry film photoresist 51 from over the photomask M1 as parallel rays in such an amount as not to harden the photoresist, e.g., about 90 mJ/cm 2 , the flow path 33 and the reservoir 31 remain on the surface of the dry film photoresist 51 as unexposed portions 51A that correspond to the opaque portions a, b, whereas the other portions corresponding to transparent portions c of the mask are left half-hardened; i.e., the portions underlying portions c become half-hardened portions 51B that are insoluble to a solvent but are adhesive. In the above-mentioned embodiment, a light energy is used to provide the half-hardened portions. However, any other energy which activates a photosensitive resin such as an electron beam may be used instead of the light energy. A laminated body of a predetermined thickness having both the unexposed portions 51A and the half-hardened portions 51B is formed on the surface of the nozzle plate 2 by repeating such lamination of the dry film photoresist 51 and exposure (Figure 1(d)). Then, the unexposed portions 51A are removed from the laminated body made of films of dry film photoresist 51 using a solvent such as trichloroethane (Figure 1(e)). As a next step, a dry film photoresist 52 for forming an ink chamber 32 is laminated on the thus processed laminated body, and the ink chamber 32 is formed by the steps of similarly exposing the dry film photoresist 52 while positioning thereon a not shown transparent photomask having an opaque pattern corresponding to the ink chamber 32 and then removing the unexposed portion 52A (Figure 1(f)). As the last step, part of the laminated body having both dry film photoresists 51 and 52 is subjected to secondary exposure so that such part can be hardened. In this exposure, a photomask M3 having an opaque pattern d for masking a portion slightly larger than the unexposed portions 51A and 52A is used as shown in Figure 1(g). Light whose energy is large enough to harden the half-hardened dry film photoresist portions 51B, 51B, e.g., about 2J/cm 2 , or more preferably, 5J/cm 2 is injected from above the photomask M3 to form hardened portions 51C, so that the entire part of a wall forming portion that excludes a portion around the ink chamber 32, the reservoir 31, and an ink supply portion 34 connecting the ink chamber 32 to the reservoir 31 (Figures 3 and 4) is formed into a hardened portion 51C. The hardened portion is provided so that the cavity forming layer 3 is not deformed, or less deformed, by pressure applied at the time of bonding. A further part or substructure 43 of the cavity forming layer 3 and an insulating layer 42 are formed on the elastic plate 4 by a process shown in Figures 2(a) to 2(g). The elastic plate 4 used in this embodiment is a metal thin plate having a thickness of 5 µm or less prepared by nickel electroforming. A dry film photoresist 59 is first laminated on a surface of the elastic plate 4, i.e., a surface to which the end of the piezoelectric vibrating element 7 is bonded. The dry film photoresist 59 is of the same type as the dry film photoresists 51, 52 arranged on the side of the nozzle plate 2. A coating of a liquid photosensitive resin applied by a spinner method or a roll coating method may be used instead of the dry film photoresist. The dry film photoresist 59 is exposed with a photomask placed thereon, and then developed to form such an insulating layer 42 as shown in Figure 2(c). Although not shown, the photomask employed in this process has a ring-like opaque pattern slightly narrower than the ink chamber 32 but slightly larger than the section of the piezoelectric vibrating element 7. Accordingly, an island-like thick portion 44 is formed in the middle through a ring-like thin portion 45 on the surface of the elastic plate 4 from which the ring-like unexposed portion has been removed by the post-exposure developing process. The portion 44 comes in contact with the piezoelectric vibrating element 7. Then, a dry film photoresist 55 of the same type as the dry film photoresists 51 and 52 arranged on the nozzle plate 2 is laminated on the back of the elastic plate 4 while inverting the elastic plate 4. As shown in Figure 2(d), a photomask M5 having an opaque pattern f for forming an ink chamber 32, a reservoir 31, and an ink supply portion 34 is put in place, and light having energy large enough to harden the dry film photoresist 55, i.e., about 5J/cm 2 is irradiated thereto to form a hardened portion 55B on the dry film photoresist 55, the hardened portion being around these portions 32, 31 and 34. The dry film photoresist 55 which is on the unexposed portion 55A is removed by a solvent (Figure 2(e)); a dry film photoresist 56 is laminated thereon, and is exposed and developed using a not shown photomask having an opaque pattern which corresponds to the ink chamber 32 and the reservoir 31 and which excludes the ink supply portion 34 (Figure 2(f). And,as necessary, the entire part of the dry film photoresists 55 and 56 is subjected to secondary exposure and then heated so that the dry film photoresists 55 and 56 are hardened. The cavity forming part 23 of layer 3 on the side of the nozzle plate 2 and the cavity forming part 43 of layer 3 on the side of the elastic plate 4, which further carries insulating layer 42 and which have been formed in the above-mentioned processes, are bonded together by pressure. As shown in Figure 3 both are bonded integrally with each other, i.e., the cavity forming part 23 on the nozzle plate 2 side is bonded onto the surface of the cavity forming part 43 on the elastic plate 4 side, whereby as area 51C of Fig. 1 is not being deformed, or less deformed, portion 5C in Fig. 3 which is around the ink chamber is not being deformed either because it has been hardened by the secondary exposure, while portion 5B of part 23 in Fig. 3, corresponding to portion 51B in Fig. 1, remains half-hardened. This embodiment is characterized as bonding the cavity forming part 23 on the side of nozzle plate 2 to the cavity forming part 43 on the side of the elastic plate 4 while leaving the portion around the ink chamber 32 of the cavity forming part 23 not subjected to secondary exposure. As the gap between adjacent ink chambers is narrowed in order to arrange the nozzles in a higher density, preferably as shown in Fig. 5, columnar hardened portions 5C' are formed by subjecting portions near a relatively large bonding portion 35 around the reservoir 31, as well as the ink supply portion 34 and the like requiring high accuracy in profile to spot-like secondary exposure. These hardened portions 5C' are utilized to prevent the ink chambers 32 and the like from being deformed. In this embodiment, lightened portions 36 are formed in the relatively large bonding portion 35 that surrounds the reservoir 31, particularly, portions not affecting the function of the ink jet head, out of the cavity forming parts 23, 43 which are formed on the nozzle plate 2 and the elastic plate 4, respectively, as shown in Figure 5. Such lightened portions are provided to keep the bonding surface area from being partially inconsistent. This arrangement obviates inconveniences that the nozzle plate 2 and the elastic plate 4 are bent due to the soft dry film photoresist 5 on the half-hardened portion 5B inconsistently affecting part of the nozzle plate 2 and the elastic plate 4 or that the bonded surface is separated due to inconsistent heating at the time of bonding. Further, to form a so-called edge type cavity forming substrate in which the axis of a nozzle 21 runs in parallel to the plane of the substrate 1 as shown in Figure 6, a sidewall portion 37 of the nozzle 21 and of the ink supply portion 34 and a portion around such sidewall 37 are subjected to secondary exposure. Still further, to form a cavity forming substrate 1 such as shown in Figure 7, i.e., a cavity forming substrate of such a type that ink is supplied to an ink chamber 32 from a reservoir 31 arranged at both ends thereof through ink supply paths 34 having no constriction, the following steps will be taken. First a sidewall portion 37 defining the ink chamber 32 on the side of the elastic plate 4 is formed so as to be half-hardened. Then, a columnar hardened portion 5C' is formed by subjecting the sidewall portion 37 to spot-like secondary exposure. The thus formed sidewall portion 37 is further bonded by a half-hardened portion 5B to a not shown nozzle plate placed thereon and then heated for hardening. Still further, in the case of a cavity forming substrate having a heating element, an ink chamber and a nozzle which are half-hardened, are first formed on a substrate made of glass or silicon with the heating element mounted thereon. A sidewall portion excluding a portion around the ink chamber is then subjected to secondary exposure for hardening. Figure 8 shows another embodiment of the invention, particularly, the process of secondary exposure to be effected on the dry film photoresists 51 and 52 on the half-hardened portion 5B formed on the nozzle plate 2. In this embodiment, the description of the steps corresponding to those shown in Figures 1(a) to 1(f) will be omitted since they have been already described with reference to Figures 1(a) to 1(f). That is, these are the steps of forming the ink chamber 32, the reservoir 31, the flow path 33, and the like by repeating the process of laminating the dry film photoresists 51, 52 on the nozzle plate 2 and subjecting the laminated photoresists to such exposure as not to harden the photoresists and to development. The half-hardened portion 5B' corresponding to portion 51B of Fig. 1 out of the thus formed layers of dry film photoresists 51, 52 are then to be subjected to secondary exposure. To do so, a photomask M6 having an opaque pattern g' as a portion excluding a transparent portion f' that is slightly larger than the ink chamber 32 as shown in Figure 8(b) is used. This opaque pattern g' is positioned on the layers of dry film photoresists 51, 52. Then, parallel rays of light whose energy is sufficient for hardening, i.e., from 2J/cm 2 to 5J/cm 2 , are irradiated thereto. Accordingly, as shown in Figure 9 , the films of dry film photoresists 51 and 52 are processed so that only a sidewall portion 39 surrounding the ink chamber 32 and the ink supply portion 34 is formed into a hardened portion 5C'. Thus, by bonding this cavity forming part 23 to a not shown cavity forming part 43 on the elastic plate 4 by pressure, both parts 23 and 43 are bonded together by an adhesive force provided by the half-hardened portion 5B' with the boundaries of the ink chambers 32 and the ink supply portion 34 maintained by the sidewall portion 39. As the final step, the entire part of the bonded layers is subjected to a hardening process by heating so as to form an integral body. Figure 10 is an embodiment characterized as controlling deformation of the ink supply portion 34 that requires a particularly stringent accuracy in profile. Such control is accomplished by subjecting the sidewall portion 39 of the ink supply portion 34 to secondary exposure by the above-mentioned method so that such sidewall portion can be formed into a hardened portion 5C'. Figure 11 is an embodiment characterized as further reinforming the sidewall portion 39 by forming an indented hardened portion 5C' around both the ink chamber 32 and the ink supply portion 34 by the above-mentioned method. Further, with respect to a cavity forming substrate 1 such as shown in Figure 12, i.e., a cavity forming substrate 1 of such a type that ink is supplied to an ink chamber 32 from a reservoir 31 arranged at both ends thereof through ink supply portions 34 that have no constriction, a peripheral portion of a sidewall portion 37 that defines the ink chamber 32 and the ink supply portions 34 is hardened by the above-mentioned method in such a manner that such peripheral portion surrounds the sidewall portion 37. Still further, this last embodiment is applicable to a cavity forming substrate of a so-called edge type in which the axis of a nozzle runs in parallel to the plane of the substrate 1 or to a cavity forming substrate of a so-called bubble type in which a heating element is arranged in a flow path immediately before a nozzle, so that the sidewall of the ink chamber and of the nozzle can be hardened by secondary exposure.

Claims: A method of manufacturing an ink jet head, comprising the steps of: preparing a part or substructure (23) of a cavity forming layer (3) by laminating a photohardening resin on a substrate; first exposing and then developing said photohardening resin by activation energy rays having such energy as to half-harden said photohardening resin to form a cavity required for jetting ink; secondarily exposing only parts of said photohardening resin to locally form hardened portions by activation energy rays having energy necessary for hardening; and bonding a bonding surface of said photohardening resin of said part or substructure (23) to a further part or substructure (43) of said cavity forming layer (3) for integration. The method of manufacturing an ink jet head according to claim 1, wherein the step of first exposing and then developing said photohardening resin comprises using a mask (M1;M2) having such a pattern that the bonding surface of said photohardening resin is kept from being partially inconsistent from the bonding surface of said further part or substructure (43). The method of manufacturing an ink jet head according to claim 1 or 2, wherein the step of secondarily exposing comprises exposing a peripheral portion around an ink chamber (32) and an ink flow path (33), the peripheral portion excluding a portion immediately around the ink chamber (32) and the ink flow path (33) so that the peripheral portion is hardened. The method of manufacturing an ink jet head according to any one of claims 1 to 3, wherein the step of secondarily exposing comprises exposing at least a peripheral portion around an ink flow path (33) so that the peripheral portion is hardened. The method of manufacturing an ink jet head according to any one of the preceding claims, wherein the step of secondarily exposing comprises exposing a portion around an ink flow path (33) so that said portion is hardened in indented form. The method of manufacturing an ink jet head according to any one of the preceding claims, wherein the step of secondarily exposing comprises exposing a portion around an ink supply portion (34) connecting an ink reservoir (31) to an ink chamber (32) so that said portion is hardened. The method of manufacturing an ink jet head according to any one of the preceding claims, wherein the step of secondarily exposing comprises exposing a portion around a wall defining an ink flow path (33) so that said portion is hardened.

Inventors: KATAKURA TAKAHIRO, NAKA TAKAHIRO, NAKAMURA OSAMU, SONEHARA HIDEAKI, USUI MINORU, KATAKURA, TAKAHIRO, NAKA, TAKAHIRO, NAKAMURA, OSAMU, SONEHARA, HIDEAKI, USUI, MINORU, Katakura, Takahiro, c/o Seiko Epson Corporation, NAKA, TAKAHIRO, C/O SEIKO EPSON CORPORATION, Nakamura, Osamu, c/o SEIKO EPSON CORPORATION, Sonehara, Hideaki, c/o Seiko Epson Corporation, USUI, MINORU, C/O SEIKO EPSON CORPORATION
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1993
Main classification: B41J2
IPC codes: B41J2