Ink jet head

An ink-jet head includes a base member provided with a plurality of channel grooves separated from each other by channel walls and connecting front and rear ends together, a cover member arranged in contact with the base member and opposed to a surface provided with the plurality of channel grooves of the base member, an electrode arranged as a drive electrode on at least a part of inner surfaces of the channel grooves, and conductive resin arranged at the rear end to fill inner spaces of the channel grooves and electrically connected to the drive electrode. The rear end of the channel groove is shallower than the front end of the channel groove.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink-jet head for use in a printer or the like, and particularly to an ink-jet head, in which an ink chamber is defined by walls containing a piezoelectric member, and a voltage is applied to the piezoelectric member to cause deformation and thereby to cause pressure vibrations in the ink chamber so that an ink accumulated in the ink chamber is ejected therefrom.

2. Description of the Related Art

In recent years, non-impact printing devices, e.g., of an ink-jet type, which can be easily configured to perform color printing and multilevel gradation, have been rapidly spreading instead of impact printing devices. As an ink-jet head used as an ink ejecting unit in the non-impact printing device, attention has been given particularly to a drop-on-demand type, which can eject only ink droplets required for the printing, in view of high ejection efficiency and easy reduction of cost. A Kyser type and a thermal jet type are mainstream of the drop-on-demand type.

However, the Kyser type does not allow easy reduction in size, and thus is not suitable for a high-density structure. The thermal jet type is suitable for a high-density structure, but requires ink having appropriate heat resistance because it uses a heater for heating the ink to generate bubbles, and ejects the ink by using energy of the bubbles. Also, it is difficult to provide a long-life heater. Further, an energy efficiency is low, and therefore power consumption is large.

An ink-jet type utilizing a shear mode of a piezoelectric material has been disclosed as a type overcoming problems of the foregoing types. In the ink-jet type, electrodes are formed on opposite side surfaces of a wall (which will be referred to as a “channel wall” hereinafter) of an ink channel made of a piezoelectric material, and an electric field perpendicular to a direction of polarization of the piezoelectric material is produced by using these electrodes so that the channel wall is deformed in a shear mode, and pressure wave variations caused thereby are utilized to eject ink droplets. This type is suitable to high-density arrangement of nozzles, low power consumption and high drive frequency.

Referring toFIG. 14, description will now be given on a structure of an ink-jet head utilizing the shear mode. This ink-jet head includes a base member1, which is made of a piezoelectric material subjected to polarization processing in a vertical direction ofFIG. 14, and is provided with a plurality of channel grooves4, a cover member2provided with an ink supply port21and a manifold space24, and a nozzle plate9having nozzle holes or orifices10. Base member1, cover member2and nozzle plate9are fixed together to form an ink channel. The “ink channel” is a portion of a pressure chamber formed by utilizing an inner space of channel grooves4. On only an upper half of a channel wall3, electrodes5are formed for applying an electric field. In the following description, the side, on which nozzle plate9is present, will be referred to as the front side, and the opposite side will be referred to as the rear side. In this ink channel, the rear end portion of each channel groove4is worked into a round or curved form corresponding to a diameter of a dicing blade used for forming the groove. Further, a shallow groove portion6is also formed by the dicing blade to provide an electrode leading portion for external electrical connection. The electrode formed in shallow groove portion6is connected at its rear end, e.g., to an external electrode8of a flexible printed board11by a bonding wire7. In the ink-jet head of the above structure, the ink is supplied from manifold space24through the region of the round form. However, the pressure required for the ejection is to be generated in the region, where the upper portions of channel walls3of base member1are joined and fixed to cover member2. Thus, the region of the round form is not required for such pressure generation, and becomes a cause of increase in electrostatic capacitance.

Japanese Patent Laying-Open No. 9-94954 has disclosed a structure of the ink-jet head, which is not provided with a round-shaped region and thereby can reduce the electrostatic capacitance. In the ink-jet head disclosed in this publication, however, connection is performed on a bottom surface of a base board for externally pulling out an electrode from a channel wall so that complicated steps are required for forming the electrode for connection.

As a structure, which can reduce an electrostatic capacitance of an ink-jet head and allows easy pull-out of an electrode from a channel wall, a structure shown inFIGS. 15 and 16is already disclosed.FIG. 15is a perspective exploded view of the ink-jet head with certain parts cut away.FIG. 16is a cross section of an assembly of the ink-jet head. This ink-jet head has a feature that channel grooves4extend longitudinally throughout base member1with uniform depth. This structure can eliminate a round-shaped region, and can reduce an electrostatic capacitance. Also, it is possible to reduce a used amount of a piezoelectric material. Channel grooves4are sealed in the vicinity of their rear ends by electrically conductive resin26so that electrical connection is established to keep the same potential at electrodes5on the opposite sides of each channel groove4. Conductive resin26reaches the rear ends of channel grooves4, and the rear end of base member1is connected to flexible printed board11with anisotropic conductive film (which will be referred to as an “ACF” hereinafter)12therebetween. External electrode8on the surface of flexible printed board11and conductive resin26are pressed together in a direction of thickness of ACF12interposed therebetween, and thereby are electrically connected together. However, each ink channel is electrically independent of the others owing to characteristics of ACF12.

In a conventional ink-jet head, conductive resin26in a liquid state is applied to the vicinity of the rear end of channel grooves4, and then is cured. Therefore, a crack may occur between conductive resin26and channel wall3due to cure shrinkage of conductive resin26. Conductive resin26is cured at a raised temperature, but conductive resin26has a larger coefficient of linear expansion than the piezoelectric material of base member1. Therefore, thermal shrinkage, which occurs due to cooling after the curing, may cause a crack between conductive resin26and channel wall3.FIG. 17shows an example of a crack caused by the above reason. A crack16is present between conductive resin26and channel wall3. This crack may cause a failure in electrical connection between electrode5and external electrode8.

SUMMARY OF THE INVENTION

The invention provides an ink-jet head, which can prevent occurrence of a crack between conductive resin and a channel wall.

The ink-jet head according to the invention includes a base member having front and rear ends, and provided with a plurality of channel grooves separated from each other by a channel wall(s) including a piezoelectric material, and connecting the front and rear ends together; a cover member arranged in contact with the base member and opposed to a surface provided with the plurality of channel grooves of the base member; a drive electrode arranged on at least a part of inner surfaces of the channel grooves; and conductive resin arranged at the rear end to fill inner spaces of the channel grooves and electrically connected to the drive electrode. The rear end of the channel groove is shallower than the front end of the channel groove. According to the above structure, sufficient shear-mode deformation of the channel wall can be ensured in the vicinity of the front end, and further a required volume of the conductive resin can be reduced at the rear end. Accordingly, it is possible to reduce a stress, which occurs on an interface between the conductive resin and the channel wall due to cure shrinkage or thermal shrinkage of the conductive resin, and therefore occurrence of a crack can be prevented.

Preferably, the depth of the channel groove continuously decreases as the position moves from the front end toward the rear end. According to this structure, the ink can flow smoothly from a manifold space to an ink channel, and can be ejected stably.

Preferably, the channel groove includes a front region starting from the front end, and extending in a longitudinal direction of the channel groove, and has a uniform depth in the front region, and the depth of the channel groove at the rear end is smaller than the depth of the channel groove in the front region. According to this structure, the channel groove in the portion, which is particularly significantly related to ink ejection, has the uniform depth so that the efficiency of the shear-mode deformation of the channel wall can be increased, and the ink can be ejected efficiently.

Preferably, a region from the front end to a middle portion in the longitudinal direction of the channel groove includes a wall-fixed region having an upper end of the channel wall fixed to the cover member, and the wall-fixed region has a shorter length in the longitudinal direction of the channel groove than the front region. According to this structure, the channel groove has the uniform depth throughout the wall-fixed region so that the efficiency of the shear-mode deformation can be high throughout the wall-fixed region.

Preferably, the channel groove has a rear region starting from the rear end and extending in the longitudinal direction of the channel groove, and has a uniform depth in the rear region, and the depth of the channel groove in the rear region is smaller than the depth of the channel groove at the front end. This structure can prevent unintended forward flow of the conductive resin along the channel groove before curing. Therefore, an efficiency of application of the conductive resin can be improved, and a used amount of the conductive resin can be reduced.

Preferably, the ink-jet head includes an external electrode fixed to the rear end of the base member, the external electrode and the conductive resin are electrically connected together via an anisotropic conductive film interposed therebetween, and the channel groove has a sectional area of 2300 μm2or more at the rear end. According to this structure, the conductive resin can have at least a required minimum area for contact and connection to the external electrode via the anisotropic conductive film, and therefore the electrical connection can be ensured.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIGS. 1 to 3, description will now be given on a structure of an ink-jet head according to a first embodiment of the invention. As shown inFIGS. 1 and 2, the ink-jet head has a front end, to which a nozzle plate9is attached, and a rear end opposite to the front end, and includes a base member1and a cover member2similarly to the structure shown inFIGS. 15 and 16.FIG. 1is an exploded view showing structures with certain parts cut away for illustration.FIG. 2is a cross section of the ink-jet head taken along line extending through a center of a channel groove4in a longitudinal direction of channel groove4.

Base member1is made of a piezoelectric material, and is provided with the plurality of parallel channel grooves4extending between the front and rear ends. Channel grooves4are separated from each other by channel walls3, which are a part of base member1. On a substantially upper half of each side surface of channel wall3, i.e., inner surface of channel groove4, a thin electrode5is formed as a drive electrode for causing shear-mode deformation of channel wall3. The rear end of channel groove4is filled with conductive resin26so that conductive resin26is electrically connected to electrode5. Conductive resin26is electrically connected to an external electrode8on a surface of a flexible printed board11via an ACF12.

Cover member2is provided with a concave portion forming a manifold space24b. A manifold member20internally has a manifold space24a. Manifold member20has an open front side, and is provided on its rear side with an ink supply port21. Base member1and cover member2are joined together to form an assembly. Flexible printed board11is arranged on the rear end of the assembly thus formed, and manifold member20is attached thereto to close the rear end so that manifold spaces24aand24bare connected together to form a continuous manifold space24.

The foregoing structures are substantially the same as those of the conventional ink-jet head shown inFIGS. 15 and 16. However, the ink-jet head of the embodiment differs from the conventional ink-jet head in that the rear end of channel groove4is shallower than the front end of channel groove4. The structure, in which the rear end of channel groove4is shallower than the front end thereof, is a basic feature of the invention, and the mere feature that the rear end is shallower than the front end can achieve an effect to a certain extent. However, it is preferable that the depth of channel groove4continuously decreases as the position moves from the front end toward the rear end, as shown inFIG. 2. This structure having the “continuously” decreasing depth does not eliminate a structure, which partially includes a flat portion having a uniform depth, but eliminates only a structure having a portion, in which the depth of channel groove4increases as the position moves toward the rear end.

FIG. 3shows a rear view of the ink-jet head with manifold member20removed for illustration. Since channel grooves4are shallow at the rear end, exposed rear end portions of conductive resin26have a smaller total area than front end portions thereof represented by broken line.

Various portions of the ink-jet head have following specific sizes, and are manufactured as follows. Channel groove4has a depth of 300 μm, a width of 77 μm and a pitch of 169 μm. Referring toFIG. 2, a region A, in which base member1is in contact with cover member2, has a length of 1.1 mm, and a region B, in which manifold space24bis formed above channel grooves4, has a length of 2.4 mm. The “lengths” related to the various regions are sizes in the longitudinal direction of channel grooves4unless otherwise specified.

Electrode5is made of aluminum, is formed by oblique vapor deposition and has a thickness of 1.0 μm. Instead of aluminum, electrode5may be made of an electrically conductive material such as copper, nickel or titanium.

Nozzle plate9is formed of a polyimide film of 50 μm in thickness, and nozzle holes10are formed by excimer laser processing. Nozzle plate9may be formed of a macromolecular resin film containing polyethylene instead of the polyimide film. Nozzle holes10may be formed in a metal plate such as a stainless steel plate by punching.

Cover member2is formed of an unpolarized piezoelectric substrate, and manifold space24bis formed by sand-blasting. Cover member2may be formed of a ceramic substrate. Manifold space24bmay be formed by milling or molding.

A rear end portion of each channel groove4is filled with electrically conductive resin26, and ACF (Anisotropic Conductive Film)12is used for connection between external electrode8and conductive resin26.

The following manner is employed for manufacturing the ink-jet head, in which channel groove4becomes shallower as the position moves from the front end toward the rear end.

First, as shown inFIG. 4, a dicing blade15is lowered vertically toward a piezoelectric substrate30, which is a material of base member1, to form an arc-shaped portion or recess. Oblique vapor deposition with aluminum is effected to form electrode5on the upper half of each of side surfaces of channel walls3, i.e., inner surfaces of channel grooves4thus formed, as shown inFIG. 5.

As shown inFIG. 6, conductive resin26is supplied from a dispenser (not shown) into opposite ends of channel groove4, and is cured. As shown inFIG. 7, polishing is effected on the upper surface to remove a portion of conductive resin26overflowed from channel groove4. Consequently, conductive resin26in each channel groove4is separated and electrically isolated from conductive resin26in neighboring groove(s)4. As shown inFIG. 8, piezoelectric substrate30is cut off to provide pieces forming base members1. In the above manner, working and processing can be performed symmetrically so that two base members1can be simultaneously produced.

It is assumed that dicing blade15has a radius of 25.4 mm, and provides a depth of 300 μm at a position forming the front end of the ink-jet head. In this case, the substrate can be cut at a position spaced by 3.5 mm from the front end so that channel groove4can have a depth of about 60 μm at the rear end.

According to the ink-jet head of the embodiment, the rear end of channel groove4has a smaller depth than the front end. Therefore, sufficient shear-mode deformation of channel walls3can be ensured in the vicinity of the front end owing to sufficiently deep channel grooves4, and at the same time, it is possible to reduce a required volume of conductive resin26owing to the small depth of channel grooves4at the rear end. Therefore, it is possible to reduce a stress occurring on the interface between conductive resin26and channel wall3due to cure shrinkage or thermal shrinkage of conductive resin26, and thus it is possible to prevent a crack between conductive resin26and channel wall3. Owing to the prevention of the crack, reliable electrical connection can be ensured between electrode5and external electrode8.

In the structure having the channel groove, of which depth continuously decreases as the position moves from the front end toward the rear end, the ink can smoothly flow from manifold space24into the ink channels so that the ink can be stably ejected.

In this embodiment, channel groove4has a depth of 60 μm at the rear end. It is preferable to reduce the depth at the rear end in view of reduction of the volume of conductive resin26. However, excessively small depth causes such a situation that conductive resin26is connected to external electrode8via ACF12only through an excessively small contact area, and thus sufficient electrical connection is impossible. Thus, a certain area or more is required. For example, if channel groove4has a width of about 77 μm, the depth of 30 μm or more can ensure the sufficient electrical connection. This is owing to the fact that channel groove4has a sectional area of 2300 μm2or more at the rear end. Thus, an area of 2300 μm2or more is required for contact with conductive resin26for ensuring the sufficient electrical connection.

Referring toFIG. 9, description will now be given on a structure of an ink-jet head according to a second embodiment of the invention. This ink-jet head is similar to that of the first embodiment of the invention except for that channel groove4has a portion of a uniform depth in a region C of a predetermined length starting from the front end. This region is referred to as a “front region”. In a region D following region C, the depth of channel groove4continuously decreases as the position moves toward the rear end.

Various portions of the above ink-jet head have following specific sizes, and are manufactured as follows. Region A has a length of 1.1 mm, and region B has a length of 3.1 mm. Region C has a length of 1 mm. At the rear end, channel groove4has a depth of 100 μm. For forming region C, as shown inFIG. 10, dicing blade15is lowered vertically toward piezoelectric substrate30, which is a material of base member1, and then is horizontally moved in the longitudinal direction of channel groove4so that a structure shown inFIG. 11can be easily formed. In this embodiment, channel groove4has a depth of 300 μm at the front end, and region C has a length of 1 mm so that the structure can be formed by horizontally moving dicing blade15kept at a cutting depth of 300 μm for a distance of 1 mm. In the example ofFIGS. 10 and 11, only one region C is formed. However, symmetrical two base members1can be produced at the same time as shown inFIGS. 7 and 8by horizontally moving dicing blade15for a distance equal to a sum of double the length of region C and a cut thickness.

Region A is a wall-fixed region, in which an upper end of channel wall3is fixed to cover member2. In region A, shear-mode deformation of channel wall3occurs to generate a pressure required for ink ejection. Region C having channel groove4of the uniform depth substantially overlaps with region A, and therefore the efficiency of shear-mode deformation of channel wall3can be increased, in addition to the effect similar to that of the first embodiment already described. Therefore, the ink can be ejected efficiently.

In the example already described with reference toFIG. 9, region C (front region) has a smaller length than the wall-fixed region (region A). However, it is preferable that the length of region C is equal to or larger than that of region A as shown inFIG. 12. In this structure, channel groove4has a uniform depth throughout region A so that the efficiency of shear-mode deformation can be high throughout region A. Therefore, the above structure is preferable.

Referring toFIG. 13, a structure of an ink-jet head according to a third embodiment of the invention will now be described. This ink-jet head is basically similar to that of the first embodiment except for that channel groove4has a portion of a uniform depth in a region F of a predetermined length starting from the rear end. This region is referred to as a “rear region”. In a region E preceding region F, the depth of channel groove4continuously decreases as the position moves toward the rear end.

Various portions of the above ink-jet head have following specific sizes, and are manufactured as follows. Region A has a length of 1.1 mm, and region B has a length of 2.4 mm. Region F has a length of 0.5 mm. In region F, channel groove4has a depth of 60 μm. Region F can be easily formed by horizontally moving dicing blade15when processing the piezoelectric substrate.

According to the ink-jet head of the third embodiment, region F including channel groove4of the uniform depth is present in the region near the rear end, where conductive resin26is arranged. Therefore, such an undesired situation can be prevented that uncured conductive resin26flows forward along channel groove4when conductive resin26is supplied from a dispenser. Consequently, an efficiency of application of conductive resin26can be increased, in addition to the effect similar to that of the first embodiment already described. Increase in application efficiency results in decrease in used amount of conductive resin26.

According to the invention, the shear-mode deformation of the channel wall can be sufficiently ensured in the vicinity of the front end, and further the volume of the conductive resin can be reduced at the rear end. Therefore, it is possible to reduce the stress occurring on the interface between the conductive resin and the channel wall due to cure shrinkage or thermal shrinkage of the conductive resin, and occurrence of a crack between the conductive resin and the channel wall can be prevented.

INDUSTRIAL APPLICABILITY

The invention can be applied to the ink-jet heads arranged in printers or the like of the ink-jet type.