Droplet discharge head and droplet discharging unit incorporating the same

A droplet discharge head includes: a liquid reservoir which holds a liquid; a channel through which the liquid is guided to the liquid reservoir; and a driving element which changes the pressure in the liquid reservoir so as to discharge droplets of the liquid contained in the liquid reservoir through a nozzle, in which wall surfaces of the liquid reservoir and of the nozzle are arranged in a continuous line at a side opposite the channel with respect to the center of the nozzle as seen in a cross-sectional view through a central axis of the nozzle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a droplet discharge head and a droplet discharging unit incorporating the same, which may be included in a printer. Each of wall surfaces of a liquid reservoir and of a nozzle may be formed in a linear configuration as seen in a cross-sectional view or each of the wall surfaces may have a width narrowing toward an orifice so that, at a connecting portion of the liquid reservoir and the nozzle, the nozzle is wider than the liquid reservoir. With this configuration, the likelihood of malfunctions caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir may be reduced.

2. Description of the Related Art

Inkjet print heads discharge ink stored in an ink reservoir when a driving element changes the pressure in the ink reservoir. The driving element may include a piezoelectric element or a heater element.

A print head with a heater element as a driving element may be fabricated in the following manner. First, a drive circuit of the heater element, a heater element and other components may be sequentially mounted on a semiconductor substrate. Partition walls of ink reservoirs and of an ink channel may then be mounted on the semiconductor substrate by, for example, photolithography using photosensitive epoxy resin. A nozzle sheet, which is a sheet-like component on which nozzles are arranged, is provided on the semiconductor substrate. The ink reservoirs, the ink channel, the nozzles and other components may alternatively be integrated with one another.

Japanese Unexamined Patent Application Publication (JP-A) No. 5-77437 discloses, for example, a print head with a system for preventing nozzle clogging.

Printers suffer from a problem that defective printing may be caused by ingress of air bubbles, dust or other foreign matter into an ink reservoir. Recent printers have small nozzles for high quality and high resolution printing. Such fine nozzles may be a cause of defective printing.

In order to address this problem, a method disclosed in No. JP-A-5-77437 may be employed to periodically check defective printing. It is necessary, however, to frequently checking defective printing and the defective printing may not completely be eliminated. Defective printing may not be checked while a paper sheet is under going printing. Consequently, such a related art process is still impractical.

SUMMARY OF THE INVENTION

It is desirable to provide a droplet discharge head and a droplet discharging unit incorporating the same, which reduce the likelihood of malfunctions caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir.

According to a first embodiment of the invention, there is provided a droplet discharge head which includes: a liquid reservoir which holds a liquid; a channel through which the liquid is guided to the liquid reservoir; and a driving element which changes the pressure in the liquid reservoir so as to discharge droplets of the liquid contained in the liquid reservoir through a nozzle, in which wall surfaces of the liquid reservoir and of the nozzle are arranged in a continuous line at a side opposite the channel with respect to the center of the nozzle as seen in a cross-sectional view through a central axis of the nozzle.

According to a second embodiment of the invention, there is provided a droplet discharge head which includes: a liquid reservoir which holds a liquid; a channel through which the liquid is guided to the liquid reservoir; and a driving element which changes the pressure in the liquid reservoir so as to discharge droplets of the liquid contained in the liquid reservoir through a nozzle, wherein a wall surface of the liquid reservoir and a wall surface of the nozzle are linearly configured such that the width of the liquid reservoir and the width of the nozzle decrease toward a tip of the nozzle and that the width of the nozzle is wider at a connection portion of the liquid reservoir and the nozzle at a side opposite the channel with respect to the center of the nozzle as seen in a cross-sectional view through a central axis of the nozzle.

According to a third embodiment of the invention, there is provided a droplet discharging unit which includes a liquid discharging head for discharging desired droplets of a liquid, the liquid discharging head including: a liquid reservoir which holds the liquid; a channel through which the liquid is guided to the liquid reservoir; and a driving element which changes the pressure in the liquid reservoir so as to discharge the droplets through a nozzle, wherein wall surfaces of the liquid reservoir and of the nozzle are arranged in a continuous line at a side opposite the channel with respect to the center of the nozzle as seen in a cross-sectional view through a central axis of the nozzle.

According to a fourth embodiment of the invention, there is provided a droplet discharging unit which includes a liquid discharging head for discharging desired droplets of a liquid, the liquid discharging head including: a liquid reservoir which holds the liquid; a channel through which the liquid is guided to the liquid reservoir; and a driving element which changes the pressure in the liquid reservoir so as to discharge the droplets through a nozzle, wherein a wall surface of the liquid reservoir and a wall surface of the nozzle are linearly configured such that the width of the liquid reservoir and the width of the nozzle decrease toward a tip of the nozzle and that the width of the nozzle is wider at a connection portion of the liquid reservoir and the nozzle at a side opposite the channel with respect to the center of the nozzle as seen in a cross-sectional view through a central axis of the nozzle.

According to the configurations of the first and third embodiments of the invention, air bubbles, dust or other foreign matter coming into the liquid reservoir may hardly remain there and may easily be expelled through the nozzle. Malfunctions otherwise caused by the air bubbles, dust or other foreign matter existing in the liquid reservoir may be reduced.

According to the configurations of the second and fourth embodiments of the invention, by appropriately selecting an area having an increased width at the connecting portion, formation of projections that impede the ink flow may be prevented even if the components at the side of the nozzle are displaced with respect to the components of the partition of the ink reservoir. With these configurations, air bubbles, dust or other foreign matter coming into the liquid reservoir may hardly remain there and may easily be expelled through the nozzle. Malfunctions otherwise caused by the air bubbles, dust or other foreign matter existing in the liquid reservoir may be reduced.

According to the invention, malfunctions caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir may be reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, embodiments of the invention will be described in detail.

First Embodiment

1. Configuration of Embodiments

1-1. Overall Structure

FIG. 2is a perspective view of a printer1according to a first embodiment of the invention. The printer1is a line printer whose components are accommodated in a rectangular housing2. A sheet tray3is inserted in a tray port provided at the front of the housing2.

A paper sheet4on the sheet tray3is made to abut a feed roller6by means of a predetermined mechanism. Upon rotation of the feed roller6, the paper sheet4is transported toward the back side of the printer1as indicated by arrow A. A reverse roller7is provided downstream in the feeding direction of the paper sheet4. Upon rotation of the reverse roller7, the paper sheet4is transported toward the front side of the printer1as indicated by arrow B.

The paper sheet4moving in the reverse direction is then transported by a spur roller8across the sheet tray3and then discharged from a discharge port at the front side of the printer1as shown by arrow C. A print head cartridge10is removably provided between the spur roller8and the discharge port. The print head cartridge10may be set as shown in an arrow D.

The print head cartridge10includes a holder12of a predetermined configuration with a print head11disposed at a lower side thereof. The print head11discharges ink droplets of yellow (Y), magenta (M), cyan (C) and black (K). Ink cartridges for the colors of Y, M, C and K are disposed on the holder12. The printer1causes the print head11to discharge ink droplets onto the paper sheet4under transportation in order to print, for example, a desired image.

1-2. Print Head Configuration

FIG. 3is a plan view of the print head11seen from below. The print head11is constituted by multiple print head modules22fixed to a print head frame21with screws23. The print head frame21serves as a holder of the print head modules22. The print head frame21is formed of a metal plate having a predetermined thickness. The print head frame21has four elongated holes24extending perpendicularly to the direction in which the paper sheet is transported. The elongated holes24are arranged parallel to one another along the direction in which the paper sheet is transported. The arranged elongated holes24have a total length corresponding to the printing width of the print head11and have a certain width.

Each of the print head modules22is a unit constituted by integrated multiple print head chips25. In the present embodiment, each of the print head modules22is formed by integrated multiple print head chips25such that a single color of ink may be printed in half of a printing width of the print head11. Two print head modules22are provided in each elongated hole24in the print head frame21. Eight print head modules22in total are provided in the print head11so as to allow printing on a DIN A4-sized paper sheet4.

In particular, each of the print head modules22is fabricated in the following manner. The print head chips25are first mounted on a print head chip holder (not shown) disposed on the lower side of the head frame21. The print head chips25are connected to a flexible wiring board26. A main ink channel which guides the ink contained in the ink cartridges to the print head chips25is formed in the print head chip holder. The print head chips25are driven by the flexible wiring board26. The flexible wiring board26has rectangular openings26aat positions where the print head chips25are to be formed. A nozzle array provided in the print head chips25is exposed through the openings26a. The flexible wiring board26is connected to the print head chips25by electrodes disposed along the openings26a.

Each of the main ink channels is formed in the print head chip holder at the substantial center of the width of a corresponding one of the elongated holes24so as to extend along the longitudinal direction of the elongated hole24. The print head chips25are arranged in an alternating pattern with the main ink channels disposed therebetween.

1-3. Print Head Chip Configuration

FIG. 4is a detailed, partially cutaway perspective view of one of the print head chips25. The print head chip25includes a semiconductor substrate33on which heater elements31, a driving circuit for driving the heater elements31, electrodes32to which the flexible wiring board26is to be connected and other components are provided. The semiconductor substrate33also includes ink reservoirs34, an ink channel35and nozzles36.

The semiconductor substrate33includes multiple heater elements31which are continuously arranged at constant intervals along the main ink channel. Each heater element31includes the ink reservoir34.

The ink channel35is defined as a section of an ink channel which guides the ink supplied from the main ink channel to each ink reservoir34. The ink channel35corresponds to a certain range from an end surface of the main ink channel of the semiconductor substrate33. The ink channel35is a space having a certain width defined by the semiconductor substrate33and an opposite top plate39. The ink channel35includes circular columns37disposed in front of the ink reservoirs34for preventing interference between adjacent ink reservoirs34, the circular columns37providing and provide a space in the height direction of the ink channel35. Similarly, prismatic columns38are provided at the side of the main ink channel of the columns37to provide a space in the height direction of the ink channel35. Each of the columns38extends along the direction in which the ink flows such that a profile thereof seen from the ink reservoir34side is significantly smaller than that a profile seen from the perpendicular direction. With this configuration, the columns38prevent increase in channel resistance.

The ink reservoirs34are defined by a partition40disposed in an area other than the ink channel35and by a top plate39disposed on an upper surface of the partition40. The nozzles36are formed in the top plate39.

FIG. 1Ais a partially enlarged cross-sectional view, andFIGS. 1B and 1Care plan views of one of the ink reservoirs34.FIG. 1Bis a cross-sectional view taken along line IB-IB inFIG. 4.FIG. 1Cis a cross-sectional view taken along line IC-IC inFIG. 1A. The print head chip25is formed such that wall surfaces of the liquid reservoir34and of the nozzle36are arranged in a continuous line at a side opposite the ink channel35with respect to the center O of the nozzle36as seen in a cross-sectional view through a central axis of the nozzle as denoted by the reference letter F. In particular, each of the wall surfaces of the liquid reservoir34and of the nozzle36is formed in a linear configuration with each width narrowing toward an orifice from a bottom surface side of the ink reservoir34in the section denoted by F. Thus, each of wall surfaces of the liquid reservoir34and of the nozzle36is reversely tapered. With this configuration, the likelihood of malfunctions of the print head11caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir may be reduced by facilitating the ink flow at an opposite side of the ink channel35of the ink reservoir34where the air bubbles, dust or other foreign matter may often remain.

The print head chip25is reversely tapered toward the orifice from the bottom surface side at the wall surface of the ink reservoir34facing the ink channels35except for the area denoted by F. With this configuration, the print head chip25facilitates the ink flow to prevent malfunction of the nozzles caused by ingress of air bubbles, dust or other foreign matter.

1-4. Manufacturing Process of Print Head Chips

In the present embodiment, the semiconductor substrate33includes the semiconductor wafer on which the multiple print head chips25are collectively provided in a semiconductor manufacturing process. A sacrificial layer46is then formed to conform to the ink reservoir34and the ink channel35. A resin material is deposited to cover the sacrificial layer46so as to form the partition40and the top plate39. The sacrificial layer46is then removed to provide the ink reservoir34and the ink channel35. The partition40and the top plate39are thus integrally formed.

The wall surfaces of the ink reservoir34and of the nozzle36are formed in the above-described configuration when exposed to provide the sacrificial layer46. The print head chips25are then isolated by scribing.

FIG. 5is a cross-sectional view illustrating fabrication of the print head chip25corresponding toFIG. 1B. In the foregoing description, the print head chip25is provided by first collectively fabricating multiple print head chips and then isolating each chip. In the following drawings, however, a procedure of fabrication of the print head chip is shown for each semiconductor substrate33for ease of illustration.

Fabrication of the print head chip25may include formation of the heater elements31, the drive circuit for driving the heater elements31and other components on a semiconductor wafer to provide the semiconductor substrate33and then application of a positive photoresist45(e.g., PMER-LA900 manufactured by Tokyo Ohka Kogyo Co., Ltd.) on the semiconductor substrate33by spin coating. In the present embodiment, the positive photoresist45has a thickness of 10 micrometers. The heater elements31are fabricated from a tantalum layer.

The positive photoresist45is then exposed by using a stepper through a mask corresponding to the configuration of the ink reservoir34. The mask used herein is shown inFIG. 6in which a shielded area is hatched. The positive photoresist45is then exposed by using the stepper through a mask corresponding to the configuration of the ink channel35. The mask used herein is shown inFIG. 7in correspondence withFIG. 6. The ink channel35may be exposed prior to the ink reservoir34. Alternatively, the ink channel35and the ink reservoir34may alternatively be exposed at the same time through a single mask as shown inFIG. 8in correspondence withFIGS. 6 and 7.

In at least the process of exposing the ink reservoir34, a focusing position is shifted from the surface of the semiconductor substrate33toward the inside of the semiconductor substrate33. In this manner, the positive photoresist45is exposed in a tapered manner corresponding to the configuration of the wall surface of the ink reservoir34. InFIG. 5, unexposed areas are hatched. It is at least necessary to properly design the mask used for exposing the ink reservoir34according to the thickness of the positive photoresist45, the shift amount of the focusing position, the diameter and thickness of the nozzle36or other parameters so that the wall surfaces of the ink reservoir34and the nozzle36may be formed in a linear configuration.

In particular, the positive photoresist45is exposed using an i-line stepper NSR-2005i9C manufactured by Nikon Corporation at an irradiance level of 1200 mJ/cm2. The shift amount of the focusing position is 10 micrometers. Instead of the stepper, an aligner may be employed to expose the mask and the substrate in a superimposed manner. In this manner, the positive photoresist45may similarly be tapered with the mask disposed apart from the positive photoresist45by a certain distance.

The substrate is then subjected to paddle development for 3 minutes with a developing agent of 3% solution of hydroxylation tetramethyl ammonium (TMAH). The developed subject is then rinsed with pure water and spin dried. In this manner, a sacrificial layer46is provided to conform to the ink reservoir34and the ink channel35by the positive photoresist45as shown inFIG. 9.

Subsequently, a predetermined resin material is applied to the substrate to form a coating layer47and then the nozzle36is fabricated as shown inFIG. 10. In the present embodiment, the resin material is a light-curable negative photoresist. The negative photoresist is applied at a thickness of 10 micrometers by spin coating to form the coating layer47. The coating layer47is then exposed by using the stepper through a mask corresponding to the nozzle36and the coating layer47is exposed according to the configuration of the nozzle36. For the exposure, as in the exposure of the ink reservoir34, a focusing position is shifted such that the coating layer47is exposed in a tapered manner corresponding to the wall surface configuration of the nozzle36. The mask is properly designed according to the thickness of the coating layer47, the shift amount of the focusing position, the diameter and the thickness of the nozzle36or other parameters so that the wall surfaces of the ink reservoir34and the nozzle36may be formed in a linear configuration. The coating layer47is exposed using an i-line stepper NSR-2005i9C manufactured by Nikon Corporation at an irradiance level of 1200 mJ/cm2. The shift amount of the focusing position is 10 micrometers. InFIG. 10, the exposed area is hatched.

The coating layer47is then developed with a developing agent (OK73 thinner: manufactured by Tokyo Ohka Kogyo Co., Ltd.). The developed coating layer47is then rinsed with isopropyl alcohol to fabricate a nozzle36in the coating layer47.

Each of the print head chips25, after being isolated by scribing, is immersed in a predetermined solution so as to remove the sacrificial layer46. Any solution may be employed that may remove the sacrificial layer46. In the present embodiment, an organic solvent of propylene glycol monoethyl ether acetate (PGMEA) is used. The print head chip25is then subjected to supersonic vibration when immersed in the solution to remove the sacrificial layer46. The solution is replaced by isopropyl alcohol and the print head chip25is then dried. In this manner, the ink reservoir34and the ink channel35are fabricated.

2. Operation of Embodiment

In the thus-configured printer1(seeFIG. 2), the print head cartridge10is driven according to image data, text data or other data used for printing. The printer head11provided at the print head cartridge10discharges ink droplets, which will be deposited on the to-be-recorded paper sheet4while being transported by a predetermined mechanism. An image, text or the like is printed on the paper sheet4with the deposited ink droplets.

In the print head11(seeFIGS. 3 and 4), ink in the ink cartridges of Y, M, C and K is guided to the ink reservoirs34of the print head chips25. The pressure in the ink reservoirs34is changed by the heater element31disposed in each of the ink reservoirs34so that the ink in the ink reservoirs34is discharged as ink droplets from the nozzles36.

Air bubbles, dust or other foreign matter may often be included in the ink. Ingress of the air bubbles, dust or other foreign matter into the ink reservoirs34makes it difficult to stably discharge ink from the nozzles36which may lead to defective printing. In particular, in recent years, it has become a common demand to reduce the diameter of the ink droplets discharged from nozzles in order to obtain high resolution images. It is therefore necessary to reduce nozzle diameter. In order to reliably deposit ink droplets discharged from nozzles to a to-be-printed sheet, however, it is also necessary to provide a certain degree of discharge rate or discharging power.

Such a print head may have a profile such that the ink reservoir size is substantially larger the nozzle diameter, which may cause easy ingress of air bubbles, dust or other foreign matter in the ink reservoir.

In the printer1(seeFIG. 1), wall surfaces of the ink reservoir34and of the nozzle36are arranged in a continuous line at a side opposite the ink channel35with respect to the center O of the nozzle36as seen in a cross-sectional view through a central axis of the nozzle36. In particular, each of wall surfaces of the liquid reservoir34and of the nozzle36is formed in a linear configuration with each width narrowing toward an orifice from a bottom surface side of the ink reservoir34in this section. Thus, each of wall surfaces of the liquid reservoir34and of the nozzle36is reversely tapered.

With this configuration, the ink reservoir34has no recess or stepped portion that may otherwise facilitate ingress of air bubbles, dust or other foreign matter into the ink reservoir34and thus the air bubbles, dust or other foreign matter which entered the ink reservoir34may be expelled promptly from the nozzle36. The print head11according to the present embodiment may therefore include automatic restoration to the defective printing due to air bubbles, dust or other foreign matter. With this configuration, malfunctions caused by ingress of air bubbles, dust or other foreign matter into the ink reservoir34may be reduced.

Ingress of air bubbles, dust or other foreign matter may occur more frequently in a section at a side opposite the ink channel35with respect to the center O of the nozzle36than a section at the side of the ink channel35of the center O of the nozzle36. In the present embodiment, since wall surfaces of the liquid reservoir34and of the nozzle36are arranged in a linear configuration as seen in a cross section, malfunctions of the print head11caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir34may reliably be reduced.

The wall surfaces of the liquid reservoir34and of the nozzle36are formed to have the width narrowing, i.e., reversely tapered, toward the orifice from the bottom surface side of the ink reservoir34. With this configuration, obstacles that may prevent refilling operation may be eliminated.

In the present embodiment (seeFIGS. 5 to 9), corresponding to the configurations of the ink reservoir34and the nozzle36, the semiconductor substrate33on which the heater element31, the driving circuit for driving the heater element31and other components are formed is first fabricated. The positive photoresist45is then applied onto the semiconductor substrate33. The positive photoresist45is exposed and developed to provide the sacrificial layer46that conforms to the configurations of the ink reservoir34and the ink channel35. The configuration of the wall surface of the ink reservoir34is determined by the focusing set during exposure.

Subsequently, a light-curable negative photoresist is applied to form the coating layer47, which is then exposed and developed to provide the nozzle36(seeFIG. 10). The wall surface configuration of the nozzle36is determined by the setup of the mask and focusing during exposure. The print head chip25is then isolated and the sacrificial layer46is removed to provide the ink reservoir34and the ink channel35.

As described above, in the configuration in which the ink reservoir, the ink channel and the nozzle are fabricated through exposure and development using the sacrificial layer and a coating layer according to the present embodiment, malfunctions caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir34may be reduced by properly setting exposure conditions or other conditions. Accordingly, malfunctions caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir34may be reduced with a simple structure.

3. Effect of Embodiment

With the foregoing configuration, since the wall surfaces of the liquid reservoir and of the nozzle are arranged in a linear configuration as seen in a cross section, malfunctions caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir may be reduced.

Reversely tapered wall surfaces of the ink reservoir and of the nozzle may also reduce malfunctions caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir.

After the sacrificial layer which conforms to the configurations of the ink reservoir and the ink channel is provided, the coating layer is deposited which will then be exposed and developed to fabricate the nozzle. The sacrificial layer is then removed to provide the ink reservoir and the ink channel. Since the wall surfaces of the liquid reservoir and of the nozzle are arranged in a linear configuration as seen in a cross section with the focusing condition or other conditions during exposure being properly determined, malfunctions caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir may be reduced with the simple structure.

Second Embodiment

In the present embodiment, the print head chip is fabricated in the following manner. A partition of an ink reservoir, a column of an ink channel and other components are first formed on a semiconductor substrate. A nozzle sheet, which is a sheet-like component on which nozzles are arranged, is provided on the semiconductor substrate. A top plate39and the partition40in the present embodiment are provided separately. The printer according to the present embodiment is configured in the same manner as in the first embodiment except for the fabrication process of the print head chips. In the following description, similar components will be denoted by similar reference numerals as in the first embodiment.

As shown inFIG. 11A, a print head is fabricated in the following process. Negative resist51is first applied to a semiconductor substrate33by spin coating. Then, as shown inFIG. 11B, the negative resist51is exposed through a mask M which shields areas corresponding to an ink reservoir34and an ink channel35. The negative resist51may be photosensitive cyclized rubber. If necessary, a surface of the semiconductor substrate33may be treated or modified in order to improve adhesion intensity with the negative resist51. In the exposure process, a focusing position may be offset as in the first embodiment so that the print head is exposed in a reversely tapered manner to conform to the configuration of the wall surface of the ink reservoir.

The negative resist51is developed using a predetermined developing agent, solvent or other agent to remove unexposed areas as shown inFIG. 11C. In this manner, a partition of the ink reservoir34and columns37and38of the ink channel35are formed on the semiconductor substrate33, which may provide a partition40.

Subsequently, a separately prepared nozzle sheet53is aligned with and made to adhere onto the negative resist51as shown inFIG. 12. The nozzle sheet53is disposed through secondary adhesion of the negative resist51.

The nozzle sheet53is fabricated in the following manner. Negative resist52is applied to a certain thickness onto a substrate made of, for example, stainless steel having conductivity by spin coating. The negative resist52is exposed and developed through a mask corresponding to the configuration of the nozzle36. In this manner, a mold of the configuration of the nozzle36is formed on the substrate. In the exposure process for fabricating a nozzle plate, as in the fabrication of the sacrificial layer according to the first embodiment, a focusing position may be offset so that the print head is reversely tapered to conform to the configuration of the wall surface of the nozzle36. The wall surfaces of the ink reservoir34and of the nozzle36may be formed in a continuous linear configuration.

The substrate is then subjected to an electroforming process in a plating bath so as to form a nozzle sheet on the substrate. The nozzle sheet53is removed from the substrate, is subjected to a series of processing including washing, and then disposed on the print head chip25.

As described above, if the top plate39and the partition40are separately provided to form the print head chip, the same effect as that of the first embodiment may be obtained.

Third Embodiment

In fabrication of a print head chip according to the present embodiment, a nozzle configuration is determined by a sacrificial layer. A printer according to the present embodiment has the same configuration as that of the first embodiment except for the fabrication process of the print head chip. In the following description, similar components will be denoted by similar reference numerals as in the first embodiment.

As shown inFIG. 13, positive resist62is applied onto a semiconductor substrate33by spin coating. In the present embodiment, the positive resist62is applied to the thickness greater than the total thickness of the ink reservoir34and of the nozzle36.

The positive resist62is exposed through a mask M which shields areas corresponding to the ink reservoir34and the ink channel35as shown inFIG. 14A. In the present embodiment, a focusing position may be offset as in the first embodiment so that the print head is exposed in a reversely tapered manner to conform to the configuration of the wall surface of the ink reservoir.

The positive resist62is exposed through the mask M which shields areas corresponding to the nozzle36as shown inFIG. 14B. In this exposure process, as in the first embodiment, a focusing position may be offset so that the print head is exposed in a reversely tapered manner to conform to the configuration of the nozzle36. The mask M is selected such that the wall surfaces of the ink reservoir34and of the nozzle36may be formed in a continuous linear configuration.

The exposed area of the positive resist62is removed with a predetermined solvent to remove the sacrificial layer63which conforms to the configurations of the nozzle36, the ink reservoir34and the ink channel35as shown inFIG. 15A.

A coating layer64of UV-curable epoxy resin is applied to a predetermined thickness as shown inFIG. 15Band is then cured. The sacrificial layer63is subsequently removed to provide the nozzle36, the ink reservoir34and the ink channel35.

As described above, if the nozzle configuration is determined by the sacrificial layer, the same effect as that of the first embodiment may be obtained.

Fourth Embodiment

FIG. 16Ais a cross-sectional view andFIG. 16Bis a plan view of a print head chip incorporated in a printer according to a fourth embodiment of the invention corresponding toFIGS. 1A and 1B. A print head chip75according to the present embodiment has a round bottom surface of an ink reservoir34seen from a nozzle36side with a center O of the nozzle36at a side opposite to an ink channel35with respect to the center of the nozzle36. The print head chip75may therefore have uniformly inclined wall surfaces of the ink reservoir34and of the nozzle36at the opposite side of the ink channel35with respect to the center of the nozzle36. The print head chip75according to the present embodiment is the same as those of the foregoing embodiments except for the configurations of the nozzles36and the ink reservoir34. The configuration of the ink reservoir is not particularly limited to those described.

The same effects as those in the foregoing embodiments may be obtained in the present embodiment, even if the ink reservoir has a round configuration.

Fifth Embodiment

FIG. 17Ais a cross-sectional view andFIG. 17Bis a plan view of a print head chip incorporated in a printer according to a fifth embodiment of the invention corresponding toFIGS. 1A and 1B. In a print head chip85according to the present embodiment, a nozzle36is formed as an ellipse and an ink reservoir34is fabricated corresponding to the configuration of the nozzle36. The print head chip85according to the present embodiment is the same as those of the foregoing embodiments except for the configurations of the nozzle36and the ink reservoir34. The configuration of the nozzle36is not particularly limited to those described.

The same effects as those in the foregoing embodiments may be obtained in the present embodiment, even if the nozzle is formed as an ellipse.

Sixth Embodiment

In the foregoing embodiment, if the ink reservoir and the nozzle are exposed separately, a stepped portion may be formed between a top plate39and a partition40due to misalignment of the mask as shown inFIG. 18Bcorresponding toFIG. 1B. If a print head chip is fabricated with a nozzle sheet attached thereto, an attachment error of the nozzle sheet may cause a stepped portion between the top plate39and the partition40.

To address the problem of the stepped portion, in the present embodiment, a radius r1of the nozzle36is set greater than the distance r2from a center O of the nozzle36to the wall surface of the ink reservoir34in an end surface of the partition40at the side of the top plate39at a side opposite the ink channel35with respect to the center O of the nozzle36. In particular, the value (r1−r2) obtained by subtracting r2from r1is set greater than the maximum amount of displacement expected to occur between the top plate39and the partition40.

In the present embodiment, at a connecting portion of the ink reservoir and the nozzle, the nozzle is wider than the ink reservoir. With this configuration, formation of projections that impede the expelling of the air bubbles, dust or other foreign matter may be prevented even if the top plate39and the partition40are displaced from each other. In this manner, malfunctions caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir may be reduced.

As in the present embodiment, malfunctions caused by ingress of air bubbles, dust or other foreign matter into the liquid reservoir may be reduced also by setting the nozzle is wider than the ink reservoir at the connecting portion of the ink reservoir and the nozzle.

Seventh Embodiment

Although the tapered configuration of the wall surface of the ink reservoir or other components is determined by the focusing condition during exposure in the foregoing embodiments, the invention is not limited thereto. For example, the tapered configuration of the wall surface of the ink reservoir or other components may be determined by displacement of the mask during exposure.

Although the heater element is employed as the driving element in the foregoing embodiments, the invention is not limited thereto. Various driving elements including a piezoelectric element and an electrostatic actuator may also be used in the invention.

Although the foregoing description is given with reference to a line printer for color printing, the invention is not limited thereto. The invention may alternatively be applied to various printers including a line printer for black-and-white printing.

Although the foregoing description is given with reference to a printer, the invention is not limited thereto. The invention may also be applied to various devices including droplet discharging heads which discharges, for example, dyes or droplets of solution for forming a protective layer, a microdispenser which discharges droplets of test reagents, measuring devices, test equipment and pattern drawers.

The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP filed in the Japan Patent Office on Jul. 29, 2008, the entire content of which is hereby incorporated by reference.