# Patent

## Title
Head chip, liquid jet head, and liquid jet device

## Abstract

A head chip has an actuator plate having a plurality of grooves, a drive electrode formed on each of the side walls of the grooves, and a cover plate which has an introduction aperture. A nozzle plate is fixed to an end surface of the actuator plate through an adhesive and has a plurality of nozzles which communicate with respective ones of the grooves. A number of escape holes are formed between the nozzle plate and the actuator plate, corresponding in number to the number of nozzles, and each escape hole has a contour which surrounds a periphery of each nozzle with the contour being spaced apart from a contour of each nozzle by at least a given distance so that the adhesive remaining at the time of fixing the nozzle plate is accumulated in the escape holes.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a head chip that ejects liquid from a nozzle opening to record an image or a character on a recording medium, a liquid jet head including the head chip, and a liquid jet device including the liquid jet head.
2. Description of the Related Art
At present, as one example of a liquid jet device, there has been provided an ink jet type recording device that ejects ink (liquid) on a recording medium such as recording paper for recording an image, a character, or the like thereon. The recording device is, for example, a printer, a facsimile machine or the like. The recording device supplies ink to an ink jet head from an ink tank through an ink supply pipe, and ejects ink onto the recording medium from a nozzle opening of the ink jet head, thereby performing the recording.
In general, as illustrated in FIGS. 11 and 12, the ink jet head includes a head chip 100 including an actuator plate 101, a cover plate 102, a nozzle plate 103, and a support plate 104. In this example, the head chip 100 to which aqueous ink having an electrical conductivity is supplied is described.
The actuator plate 101 is a plate made of a piezoelectric material, and includes a plurality of grooves 111 each partitioned by side walls 110 therein. The grooves 111 function as channels into which ink flows to be accumulated. Plate-like drive electrodes (not shown) are formed on both side walls 110 of each groove 111 along the longitudinal direction thereof by vapor deposition or the like. A drive voltage is applied to the drive electrodes.
The cover plate 102 is stacked on the upper surface of the actuator plate 101, and blocks the plurality of grooves 111. An ink introduction aperture 102a into which ink is introduced is recessed in the cover plate 102. Further, slits 102b that communicate with the grooves 111 are formed in the ink introduction aperture 102a. In this situation, as illustrated in FIG. 13, the slits 102b alternately communicate with the grooves 111. As a result, the plurality of grooves 111 are in a state where grooves 111a to which ink is supplied and grooves 111b to which no ink is supplied are alternately arranged. The grooves 111a to which ink is supplied function as ejection channels, and the grooves 111b to which no ink is supplied function as dummy channels.
The actuator plate 101 and the cover plate 102 which are stacked on each other are supported by the support plate 104 in a state where those plates 101 and 102 are fitted into a fitting aperture 104a of the support plate 104 as illustrated in FIGS. 11 and 12. In this situation, an end surface of the support plate 104 is flush with end surfaces of the actuator plate 101 and the cover plate 102.
The nozzle plate 103 is in the form of a plate, and fixed to the end surfaces of the support plate 104, the actuator plate 101, and the cover plate 102 with an adhesive S. The adhesive S is omitted from FIGS. 11 and 12.
A plurality of nozzle openings 103a are formed at given intervals in the nozzle plate 103. In this situation, as illustrated in FIG. 13, the plurality of nozzle openings 103a are formed so as to communicate with the grooves 111a that function as the ejection channels. That is, the nozzle openings 103a are formed at the same intervals as those of the grooves 111a that function as the ejection channels.
When ink is ejected with the use of the ink jet head having the head chip 100 configured as described above, ink is first supplied to the inside of the grooves 111a that function as the ejection channels through the ink introduction aperture 102a and the slits 102b so that the grooves 111a are filled with the ink. Then, a drive voltage is applied to the drive electrodes. Then, due to the piezoelectric thickness-shear effect, the side walls 110 of the actuator plate 101 are so deformed as to project toward the grooves 111b being the dummy channels, and the volume of the grooves 111a being the ejection channels increases. With an increase in volume of the grooves 111a, ink is led to the grooves 111a from the ink introduction aperture 102a through the slits 102b. Then, after the ink has been led into the grooves 111a being the ejection channels, a drive voltage applied to the drive electrodes is set to zero, thereby returning the volume that has increased once to an original volume. Through the above-mentioned operation, a pressure inside of the grooves 111a being the ejection channels increases to pressurize ink.
As a result, a drop of ink, that is, an ink droplet can be ejected from the nozzle openings 103a. 
Incidentally, the nozzle plate 103 in which the plurality of nozzle openings 103a are formed is fixed with the adhesive S as described above. In general, in assembling the head chip 100, the nozzle plate 103 is attached onto the support plate 104, the actuator plate 101, and the cover plate 102 which are previously applied with the adhesive S. For that reason, in the attaching, the adhesive S is caused to flow into the nozzle openings 103a as illustrated in FIGS. 14 and 15, resulting in such a disadvantage that the nozzle openings 103a are partially infilled.
In particular, it is general that the nozzle openings 103a are each formed into a tapered configuration in cross section. For that reason, the inlet diameter of the nozzle openings 103a located on the grooves 111 side is larger than the outlet diameter thereof. Hence, the adhesive S is liable to flow into the nozzle openings 103a from the inlet side. When the inlet diameter of the nozzle openings 103a is larger than the horizontal width of the grooves 111, inflow of the adhesive S is particularly remarkable.
When a part of the nozzle openings 103a is thus blocked by inflow of the adhesive S, ejection failure in which, for example, ink cannot be normally ejected is induced. For that reason, it is desirable to take some countermeasures so as to prevent the above-mentioned disadvantages.
Under the circumstances, as one of the countermeasures, there is known a method of stepping the adhesive for adhesion of the nozzle plate (JP 05-330061 A). In the method, the nozzle openings are formed in the nozzle plate having an adhesive surface applied with the adhesive in advance. Then, the adhesive around the nozzle openings is concentrically removed with a diameter larger than the diameter of the nozzle openings.
As another countermeasure, there is known a method of forming a plurality of grooves for complementing a surplus of the adhesive around the nozzle openings when the nozzle openings are formed in the nozzle plate (JP 07-117230 A).
However, the conventional method still suffers from the following disadvantages.
First, according to the method of stepping the adhesive, it is conceivable to prevent the adhesive from flowing into the nozzle openings. However, it is difficult to find out a suitable adhesive for the stepping method. That is, the adhesive of this type is required to provide at least an adhesion property for firmly adhering to the nozzle plate, a shaping property for executing the stepping process, and ink resistance. However, it is difficult to actually find out the adhesive having those various properties, which makes the method unviable.
On the other hand, according to the method of forming a plurality of grooves for complementing a surplus of the adhesive around the nozzle openings, the surplus adhesive can be indeed pulled into the grooves. However, the adhesive applied at positions close to the nozzle openings is still caused to flow into the nozzle openings. Further, when the surplus adhesive fills the grooves, and the remaining surplus adhesive cannot be complemented by the grooves, the surplus adhesive is still caused to flow into the nozzle openings. For that reason, the amount of inflow adhesive may be indeed reduced, but inflow per se cannot be prevented. Accordingly, the possibility that the ejection failure is induced still remains.
Further, there is conceivable a technique in which, for the purpose of preventing the surplus adhesive from being contained, the adhesive having the amount smaller than the amount for sufficient adhesion is applied to allow the nozzle plate 103 to adhere to a joining body formed of the actuator plate 101 and the cover plate 102. However, when the above-mentioned technique is applied, there is the fear that the adhesion is insufficient. When the adhesion is insufficient, the following disadvantages may occur.
For example, in the case where the adhesion is insufficient, when the nozzle plate 103 is cleaned up by a cleaning member such as a wiper (not shown), there is a risk that the nozzle plate 103 may be peeled off from the above-mentioned joining body. Further, when the adhesion is insufficient, there is a risk that an unwanted gap may be formed between the nozzle plate 103 and the joining body, whereby the ink led to the ejecting groove 111 may leak out of the gap.
In this way, when the adhesive is insufficient, the fear may arise that the above-mentioned disadvantages occur. Therefore, it is essential to apply the sufficient amount of adhesive, and it is necessary to allow the nozzle plate 103 to surely adhere to the joining body. Accordingly, there arises the above-mentioned problem resulting from the adhesive
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned circumstances, and therefore an object of the present invention is to provide a head chip, a liquid jet head, and a liquid jet device with a high quality, which are capable of effectively preventing an adhesive from flowing into nozzle openings with a simple configuration, and cause no ejection failure.
The present invention provides the following means for solving the above-mentioned problem.
According to the present invention, a head chip for ejecting liquid toward a recording medium includes: an actuator plate having a plurality of grooves to be filled with the liquid, formed at given intervals in a horizontal width direction; a drive electrode which is formed on each side wall of each of the plurality of grooves, increases pressure within each of the plurality of grooves by deforming the side wall when a drive voltage is applied to the drive electrode, and causes the filled liquid to be ejected from an inside of each of the plurality of grooves; a cover plate which is stacked on the actuator plate, and has an introduction aperture from which the liquid is introduced into the plurality of grooves; a nozzle plate which is fixed to an end surface of the actuator plate through an adhesive, and has a plurality of nozzle openings which communicate with the plurality of grooves, respectively, and are each formed at a position facing corresponding one of the plurality of the grooves; and a number of escape holes which are formed between the nozzle plate and the actuator plate, the number corresponding to a number of the plurality of nozzle openings, in which each of the plurality of escape holes has a contour which surrounds a periphery of each of the plurality of nozzle openings with the contour being spaced apart from a contour of each of the plurality of nozzle openings by at least a given distance, and in which the adhesive remaining at a time of fixing the nozzle plate is accumulated in the plurality of escape holes.
In the head chip according to the present invention, liquid is filled into the plurality of grooves formed in the actuator plate through the introduction aperture formed in the cover plate. In this case, when a drive voltage is applied to the drive electrodes, the side walls of the grooves are deformed by the piezoelectric thickness-shear effect. As a result, the volume of the grooves is reduced to increase the pressure, and the filled liquid is ejected from the inside of the grooves. Then, the ejected liquid is ejected to the external after having passed through the nozzle openings formed in the nozzle plate. Moreover, when passing through the nozzle openings, the liquid is ejected in the form of a liquid drop, that is, a liquid droplet. As a result, a character, an image or the like can be recorded on the recording medium.
Incidentally, in assembling the head chip, it is necessary to fix the nozzle plate onto the end surface of the actuator plate with the adhesive. In this situation, a number of escape holes in which the surplus adhesive is escaped and accumulated are disposed between the nozzle plate and the actuator plate, the number corresponding to the number of nozzle openings. Moreover, each of the escape holes is so formed as to have the contour which surrounds the periphery of each of the nozzle openings with the contour being spaced apart from the contour of each of the nozzle openings by a given distance or more.
Accordingly, at the time of adhering the nozzle plate, even if the surplus adhesive is spread, the surplus adhesive can be allowed to enter the escape holes and be accumulated in the escape holes before arriving at the nozzle openings. For that reason, the adhesive is prevented from flowing into the nozzle openings to infill the nozzle openings, and hence the ejection failure can be prevented. In particular, each escape hole is formed such that the contour of the escape hole is spaced apart by at least a given distance from the contour of the nozzle opening irrespective of the shape of the nozzle opening, and hence the escaped adhesive can be surely accumulated in the escape hole. Hence, the ejection failure can be effectively prevented.
From the above-mentioned viewpoints, there can be provided the high-quality head chip that causes no ejection failure. Further, because of such a simple configuration in which only the escape holes are additionally provided, the head chip can be readily assembled, and the yield can be improved to reduce the costs. Further, there can be provided the highly viable head chip.
In the head chip according to the present invention, each of the plurality of nozzle openings is an opening having the contour forming a circle.
In the head chip according to the present invention, the nozzle openings are circularly formed, and hence liquid can be more straightly ejected in a state where the linearity of the liquid is improved. Accordingly, the quality of the head chip can be more enhanced.
In the head chip according to the present invention, each of the plurality of nozzle openings has a center that is located in the middle of each of the plurality of grooves in the horizontal width direction, and the contour having a diameter that is larger in size than a horizontal width of each of the plurality of grooves.
In the head chip according to the present invention, a center of the nozzle openings is located in the middle of the grooves in the horizontal width direction, and the diameter of the nozzle openings is set to be larger in size than the horizontal width of the grooves. Specifically, the diameter of the nozzle opening is so large as to extend across the side walls. Even in this case, because of the provision of the escape holes, no adhesive flows into the nozzle openings. Thus, the inflow of the adhesive does not need to be taken into consideration, and hence it is unnecessary that the diameter of the nozzle openings is reduced according to the horizontal width of the grooves. Accordingly, the horizontal width of the grooves can be made shorter than that in the related art, and the pitches of the head chip can be narrowed.
In the head chip according to the present invention, each of the plurality of escape holes is formed into a square having a center that is substantially coincident with a center of each of the plurality of nozzle openings.
In the head chip according to the present invention, the escape holes do not have a complicated configuration but have a simple square configuration, and hence the escape holes can be simply provided. Further, because of the square shape of the escape holes, when the nozzle openings are circular, larger space in which the adhesive is allowed to be accumulated can be ensured at four corners of the escape holes. Accordingly, the adhesive can be more surely prevented from flowing into the nozzle opening side.
In the head chip according to the present invention, the plurality of escape holes are formed in an adhesion plate that is interposed between the nozzle plate and the actuator plate, and fixed to both of the nozzle plate and the actuator plate through the adhesive.
In the head chip according to the present invention, the escape holes can be formed in the adhesion plate, and hence the escape holes with a desired size and shape can be surely obtained. In particular, the escape holes can be easily and surely positioned with respect to the plurality of nozzle openings with only interposition of the adhesion plate, and hence assembling is simpler.
In the head chip according to the present invention, the plurality of grooves have a part that functions as ejection channels which are filled with the liquid and a part that functions as dummy channels which are filled with no liquid, the part that functions as the ejection channels and the part that functions as the dummy channels being alternately arranged, the introduction aperture is formed with slits that introduce the liquid into only grooves in the part that functions as the ejection channels, and the plurality of nozzle openings are so formed as to communicate with only grooves in the part that functions as the ejection channels.
In the head chip according to the present invention, the slits are formed in the introduction aperture, and hence the liquid can be introduced into only the grooves that function as the ejection channel among the plurality of grooves. That is, the grooves that function as the dummy channels are alternately disposed among the plurality of grooves, and the liquid can be introduced into only the grooves that function as the ejection channels. Then, when a voltage is applied to the drive electrodes, the liquid with which the grooves that function as the ejection channel are filled can be ejected through the nozzle openings.
In particular, the plurality of grooves alternately function as the ejection channels, and hence even if liquid having conductivity is used, the drive electrodes formed on the side walls of the grooves that function as the ejection channels and the drive electrodes formed on the side walls of the grooves that function as the dummy channels can be selectively used in a state where those electrodes are electrically isolated from each other without being rendered conductive through the liquid. Accordingly, recording can be surely conducted with the use of an electrically conductive liquid. In addition, the range of choice of available liquid is widened, and hence more value can be added.
A liquid jet head according to the present invention includes: the above-mentioned head chip according to the present invention; supply means for supplying a given amount of the liquid to the introduction aperture; and control means for applying the drive voltage to the drive electrode.
In the liquid jet head according to the present invention, the supply means surely supplies a given amount of the liquid to the introduction aperture of the head chip. Then, the drive voltage is appropriately applied to the drive electrodes by the control means, thereby making it possible to eject liquid from the nozzle openings for recording as described above.
In particular, the high-quality head chip that causes no ejection failure is provided, and hence recording can be surely conducted, and higher quality can be achieved likewise.
A liquid jet device according to the present invention includes: the above-mentioned liquid jet head according to the present invention; conveying means for conveying the recording medium in a predetermined direction; and moving means for reciprocating the liquid jet head in a direction orthogonal to the predetermined direction in which the recording medium is conveyed.
In the liquid jet device according to the present invention, the moving means reciprocates the liquid jet head in the direction orthogonal to the predetermined direction in which the recording medium is conveyed while the conveying means conveys the recording medium in the predetermined direction. As a result, recording can be accurately performed in a desired range of the recording medium. In particular, the high-quality liquid jet head that causes no ejection failure is provided, and hence it is possible to provide higher quality of the liquid jet device per se likewise.
According to the head chip of the present invention, there can be provided a high-quality head chip that can effectively prevent the adhesive from flowing into the nozzle openings with a simple configuration, and causes no ejection failure.
According to the liquid jet head and the liquid jet device of the present invention, the above-mentioned head chip is provided, and hence ejection failure caused by inflow of the adhesive can be eliminated, and higher quality can be achieved.



BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a perspective view illustrating an ink jet printer which is one embodiment of a liquid jet device according to the present invention;
FIG. 2 is an external perspective view of an ink jet head configuring the ink jet printer illustrated in FIG. 1;
FIG. 3 is a perspective view of a head chip configuring the ink jet head illustrated in FIG. 2;
FIG. 4 is an exploded perspective view of the head chip illustrated in FIG. 3;
FIG. 5 is an enlarged view of the head chip illustrated in FIG. 4 in a state where an actuator plate and a cover plate are exploded;
FIG. 6 is a cross-sectional view of the head chip illustrated in FIG. 3, which illustrates a positional relationship between grooves and nozzle openings;
FIG. 7 is a view of the head chip illustrated in FIG. 3 viewed from a nozzle plate side;
FIG. 8 is an enlarged view of a nozzle opening periphery illustrated in FIG. 7, which illustrates a positional relationship between the nozzle openings and escape holes;
FIG. 9 is a cross-sectional view taken along an arrow A-A of FIG. 7;
FIG. 10 is a view illustrating a state where a drive voltage is applied to drive electrodes to deform side walls from a state illustrated in FIG. 6;
FIG. 11 is a perspective view illustrating an example of a conventional head chip;
FIG. 12 is an exploded perspective view of the head chip illustrated in FIG. 11;
FIG. 13 is a view of the head chip illustrated in FIG. 11 viewed from a nozzle plate side;
FIG. 14 is an enlarged view of a nozzle opening periphery illustrated in FIG. 13; and
FIG. 15 is a cross-sectional view taken along an arrow B-B of FIG. 13.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Hereinafter, an embodiment of the present invention is described with reference to FIGS. 1 to 10.
In this embodiment, as an example of a liquid jet device, an ink jet printer 1 that conducts recording by using a conductive and aqueous ink (liquid) W is described.
The ink jet printer 1 according to this embodiment includes, as illustrated in FIG. 1, a plurality of ink jet heads (liquid jet heads) 2 that eject the ink W, conveying means 3 for conveying recording paper (recording medium) P in a predetermined conveying direction L1, and moving means 4 for reciprocating the plurality of ink jet heads 2 in an orthogonal direction L2 orthogonal to the conveying direction L1.
That is, the ink jet printer 1 is a so-called shuttle type printer that records characters or images on the recording paper P by moving the ink jet heads 2 in the orthogonal direction L2 orthogonal to the conveying direction L1 while conveying the recording paper P in the conveying direction L1.
In this embodiment, a case in which four ink jet heads 2 that eject the ink W of respectively different colors (for example, black, cyan, magenta, and yellow) are provided is exemplified. Those four ink jet heads 2 are of the same configuration.
The four ink jet heads 2 are mounted on a carriage 6 incorporated into a substantially rectangular casing 5.
The carriage 6 includes a tabular base 6a on which the plurality of ink jet heads 2 are mounted, and a wall 6b erected vertically from the base 6a. The carriage 6 is reciprocatably supported by guide rails 7 arranged along the orthogonal direction L2. Further, the carriage 6 is coupled with a conveying belt 9 wound around a pair of pulleys 8 in a state where the carriage 6 is supported by the guide rails 7. One of the pair of pulleys 8 is coupled with an output shaft of a motor 10, and rotates upon receiving a rotary drive force from the motor 10. As a result, the carriage 6 can reciprocate in the orthogonal direction L2.
That is, the pair of guide rails 7, the pair of pulleys 8, the conveying belt 9, and the motor 10 function as the moving means 4.
Further, in the casing 5, a pair of carry-in rollers 15 and a pair of conveying rollers 16 are spaced from each other in parallel along the orthogonal direction L2 as in the case of the pair of guide rails 7. The pair of carry-in rollers 15 are disposed on a back side of the casing 5, and the pair of conveying rollers 16 are disposed on a front side of the casing 5. The pair of carry-in rollers 15 and the pair of conveying rollers 16 are rotated by a motor (not shown) while holding the recording paper P therebetween. As a result, the recording paper P can be conveyed along the conveying direction L1 from the back side toward the front side of the casing 5.
That is, the pair of carry-in rollers 15 and the pair of conveying rollers 16 function as the conveying means 3.
As illustrated in FIG. 2, each ink jet head 2 mainly includes a rectangular fixing plate 20 attached to the base 6a of the carriage 6 with a screw (not shown), a head chip 21 fixed on an upper surface of the fixing plate 20, supply means 22 for supplying the ink W to an ink introduction aperture 31a (described later) of the head chip 21, and control means 23 for applying a drive voltage to drive electrodes 37 described later.
The head chip 21 mainly includes, as illustrated in FIGS. 3 and 4, an actuator plate 30, a cover plate 31, a support plate 32, a nozzle plate 33, and an adhesion plate 34.
The actuator plate 30 is a plate made of a piezoelectric material such as a lead zirconate titanate (PZT). On an upper surface of the actuator plate 30 are formed a plurality of grooves 35 extending in a longitudinal direction (direction indicated by an arrow X), which are spaced at given intervals in a horizontal width direction (direction indicated by an arrow Y). That is, the plurality of grooves 35 are partitioned by side walls 36, respectively.
The plurality of grooves 35 are formed so as to open on the front end side of the actuator plate 30, and also formed so as to be gradually shallower toward the rear end surface. The rear end surface side of the grooves 35 is sealed with sealing means (not shown).
Further, among the plurality of grooves 35 according to this embodiment, the grooves 35a that function as ejection channels that are filled with the ink W and the grooves 35b that function as (un-filled) dummy channels that are filled with no ink W are alternately arranged.
As illustrated in FIGS. 5 and 6, the side walls 36 of the plurality of grooves 35 are formed with the drive electrodes 37 in the longitudinal direction by deposition or the like. The drive electrodes 37 are electrically joined together on the rear end side of the actuator plate 30 having a depth which becomes shallower within the respective grooves 35. Then, the joined grooves 35 are electrically connected to extraction electrodes 27a of a flexible substrate 27 described later.
When the drive voltage is applied to the drive electrodes 37, the drive electrodes 37 functions so that the side walls 36 are deformed by the piezoelectric thickness-shear effect to increase the pressure within the grooves 35a that function as ejection channels, and that the filled ink W is ejected from the inside of the grooves 35a. 
In this situation, the drive voltages different in polarity are applied to the drive electrodes 37 disposed within the grooves 35a that function as the ejection channels, and the drive electrodes 37 disposed within the grooves 35b that function as the dummy channels.
Returning to FIGS. 3 and 4, the cover plate 31 is stacked on the upper surface of the actuator plate 30 in a state where a part of the plurality of grooves 35 is exposed therefrom. Further, the cover plate 31 is formed with an ink introduction aperture 31a, to which the ink W is supplied, in the horizontal width direction. Further, the ink introduction aperture 31a is formed with a plurality of slits 31b that allow the supplied ink W to be introduced into the grooves 35a which function as the ejection channels. That is, the plurality of slits 31b are formed at positions facing the grooves 35a which function as the ejection channels. As a result, the grooves 35a that function as the ejection channels can be filled with the ink W.
The support plate 32 supports the actuator plate 30 and the cover plate 31 which have been stacked on each other, and also supports the nozzle plate 33 and the adhesion plate 34 at the same time. The support plate 32 is formed with a fitting hole 32a in the horizontal width direction, and supports both of the plates 30 and 31 in a state where the actuator plate 30 and the cover plate 31 which have been stacked on each other are fitted into the fitting hole 32a. In this situation, those plates 30, 31, and 32 are fitted together in such a manner that the end surface of the support plate is flush with the front end surfaces of both the plates 30 and 31.
Then, the nozzle plate 33 is fixedly adhered to the end surface of the support plate 32 and the front end surfaces of both the plates 30 and 31 with the adhesive S in a state where the adhesion plate is interposed therebetween. In FIGS. 3 and 4, the adhesive S is omitted.
The nozzle plate 33 is a sheet-like plate made of a film material such as polyimide, which is about 50 μm in thickness. The nozzle plate 33 has one surface being an adhesion surface adhered to the adhesion plate 34, and another surface being an opposed surface facing the recording paper P. The opposed surface is coated with a water repellent film having water repellency for preventing, for example, attachment of the ink W.
Further, the nozzle plate 33 is formed with the plurality of nozzle openings 33a at given intervals in the horizontal width direction. In this situation, the nozzle openings 33a are formed at positions that face the grooves 35a functioning as the ejection channels, and communicate with the grooves 35a. 
More specifically, as illustrated in FIGS. 6 and 7, the nozzle openings 33a are formed at the same intervals as the pitches of the grooves 35a so that the centers of the nozzle openings 33a are coincident with the horizontal width centers of the grooves 35a that function as the ejection channels.
Further, each nozzle opening 33a is circularly formed so that the contour thereof forms a circle. Moreover, as illustrated in FIG. 4, the nozzle opening 33a is tapered in cross section so that an inlet diameter D1 (diameter of contour of nozzle opening 33a) on the adhesion surface side is larger than an outlet diameter D2 on the opposed surface side. In particular, the inlet diameter D1 of the nozzle opening 33a is larger than the horizontal width of the groove 35a which functions as an ejection channel.
The nozzle openings 33a are formed by using an excimer laser device or the like.
As illustrated in FIGS. 3 and 4, the adhesion plate 34 is a plate formed with substantially the same thickness and the same size as those of the nozzle plate 33. The adhesion plate 34 is made of, for example, ceramic, polyimide, or the like, but material thereof may be freely selected as long as the material has resistance to the ink W. Further, it is preferable that a material of the adhesion plate 34 have substantially the same thermal deformation characteristic as that of a material used for the joining body of the actuator plate 30 and the cover plate 31 so that the mutual thermal deformation is substantially equal to each other because the adhesion plate 34 is to be adhered to the joining body.
The adhesive plate 34 is formed with the plurality of escape holes 34a at the same pitches as those of the nozzle openings 33a so that the escape holes 34a face the nozzle openings 33a. That is, the number of the escape holes 34a correspond to the number of the nozzle openings 33a. Moreover, as illustrated in FIGS. 8 and 9, the escape holes 34a are so formed as to surround the peripheries of the nozzle openings 33a in a state where the contour of the escape holes 34a are spaced apart from the contour of the nozzle openings 33a by at least a given distance H, and at the time of fixing the nozzle plate 33, the surplus adhesive S is escaped and accumulated in the escape holes 34a. 
Specifically, each escape hole 34a is formed into a square having a center coincident with the center of the nozzle opening 33a, and the length of one side thereof is [(inlet diameter D1 of nozzle openings 33a)+((above-mentioned given distance H)×2)]. The escape openings 34a do not communicate with the grooves 35b that function as the dummy channels.
As illustrated in FIG. 2, the head chip 21 thus configured is fixed to the upper surface of the fixing plate 20 as described above. To the upper surface of the fixing plate 20 are fixed a rectangular base plate 24 made of aluminum or the like in a vertically erecting state, and a passage member 22a that supplies the ink W to the ink introduction aperture 31a of the head chip 21. Above the passage member 22a, a pressure buffer 22b with a reservoir that reserves the ink W therein is so arranged as to be supported by the base plate 24. The pressure buffer 22b and the passage member 22a are coupled with each other through an ink connecting pipe 22c. Further, an upper portion of the upper buffer 22b is fitted with a supply tube 40 from which the ink W is supplied.
With the above-mentioned configuration, when the ink W is supplied to the pressure buffer 22b through the supply tube 40, the ink W is reserved in the reservoir within the pressure buffer 22b once. Then, the pressure buffer 22b supplies a given amount of ink W out of the reserved ink W to the ink introduction aperture 31a of the head chip 21 through the ink connecting pipe 22c and the passage member 22a. 
That is, the passage member 22a, the pressure buffer 22b, and the ink connecting pipe 22c function as the above-mentioned supply means 22.
As illustrated in FIG. 1, the supply tubes 40 are coupled with ink tanks 41 incorporated into the casing 5, respectively. With the configuration, the inks W different in color which are reserved in the ink tanks 41 are supplied to the four ink jet heads 2, respectively.
Further, as illustrated in FIG. 2, the base plate 24 is fixed with an IC substrate 26 including a driver circuit 25 such as an integrated circuit for driving the head chip 21. The driver circuit 25 and the drive electrodes 37 of the head chip 21 are electrically connected to each other through the flexible substrate 27 on which the plurality of extraction electrodes 27a are printed.
As illustrated in FIG. 5, the flexible substrate 27 is connected to the drive electrodes 37 so as to be fitted into the shallower portions of the respective grooves 35. Then, the driver circuit 25 applies the drive voltage to the drive electrodes 37 through the flexible substrate 27, whereby the ink W is ejected.
That is, the driver circuit 25 and the flexible substrate 27 function as the above-mentioned control means 23.
Next, a description is given hereinafter of a case in which a character, a graphic, or the like is recorded on the recording paper P by using the ink jet printer 1 configured as described above.
It is assumed that, in an initial state, the inks W different in color are sufficiently filled in the four ink tanks 41, respectively. Further, the ink W within the ink tank 41 is supplied to the pressure buffer 22b through the supply tube 40 due to a hydraulic head difference. For that reason, a given amount of ink W is supplied to the ink introduction aperture 31a of the head chip 21 through the ink connecting pipe 22c and the passage member 22a, and filled within the grooves 35a which function as ejection channels through the slits 31b. 
In the above-mentioned initial state, when the ink jet printer 1 is actuated, the pair of carry-in rollers 15 and the pair of conveying rollers 16 rotate and convey the recording paper P toward a conveying direction L1. Further, at the same time, the motor 10 rotates the pulleys 8 to move the conveying belt 9. As a result, the carriage 6 reciprocates in the orthogonal direction L2 while being guided by the guide rails 7. During the operation, the head chips 21 of the respective ink jet heads 2 allow the ink W of four colors to be appropriately ejected onto the recording paper P, thereby enabling a character, an image, or the like to be recorded. In particular, because of the shuttle system, recording can be accurately performed in a desired range of the recording paper P.
Now, the motion of the respective ink jet heads 2 is described in more detail below.
When reciprocation starts by the carriage 6, the driver circuit 25 applies the drive voltage to the drive electrodes 37 through the flexible substrate 27. In this situation, the drive electrodes 37 disposed within the grooves 35a that function as the ejection channels are grounded, and the drive voltage of (+) is applied to the drive electrodes 37 disposed within the grooves 35b that function as the dummy channels. More specifically, as illustrated in FIG. 10, the drive voltage of (+) is applied to the drive electrodes 37 disposed on the two side walls 36 that partition the grooves 35a, respectively, so that the two side walls 36 are deformed. That is, the two drive electrodes 37 disposed within the grooves 35b that function as the dummy channels function, individually, as electrodes for causing the ink W to be ejected from the inside of the adjacent grooves 35a, respectively.
In FIG. 10, a case in which the ink W is ejected from one groove 35a among the plurality of grooves 35a is exemplified.
When the drive voltage is applied, the side walls 36 are so deformed as to project toward the side of the grooves 35b that function as the dummy channels, due to the piezoelectric thickness-shear effect, and the volume of the grooves 35a that function as the ejection channels increases. With an increase in the volume of the grooves 35a, the ink W is led into the grooves 35a from the ink introduction aperture 31a through the slits 31b. Then, at timing when the ink W is led into the grooves 35a, the drive voltage applied to the drive electrode 37 becomes zero. As a result, the deformation of the side walls 36 returns to the original shape, and the volume of the grooves 35a which has been increased once is returned to the original volume. Through the above-mentioned operation, the pressure inside of the grooves 35a that function as the ejection channels increases, and the ink W is pressurized. As a result, the ink W is ejected from the inside of the grooves 35a. 
Then, the ejected ink W is ejected to the external after having passed through the nozzle openings 33a. Moreover, when passing through the nozzle openings 33a, the ink W is ejected in the form of a liquid drop, that is, an ink droplet. As a result, as described above, a character, an image, or the like can be recorded on the recording paper P.
In particular, the nozzle openings 33a according to this embodiment is tapered in cross section, and hence the ink droplet can be ejected straight at high speed with high linearity. Hence, recording can be performed with high image quality. Moreover, the plurality of grooves 35 alternately function as the ejection channels, and hence even with use of the aqueous ink W, the drive electrodes 37 disposed in the grooves 35a that function as the ejection channels, and the drive electrodes 37 disposed in the grooves 35b that function as the dummy channels can be selectively used so as to be electrically isolated from each other without being rendered conductive through the ink W. Accordingly, recording can be performed by using the aqueous ink W. Thus, the ink W having the electrical conductivity can be used without any problem, and hence more value can be added to the ink jet printer 1.
Subsequently, a description is given in brief of fixation of the nozzle plate 33 in assembling the head chip 21 configured as described above.
First, prior to the fixation, after the adhesive S has been applied on the front end surfaces of the actuator plate 30 and the cover plate 31, the adhesion plate 34 is brought into contact with the front end surfaces of both the plates 30 and 31 while executing positioning so that the grooves 35a which function as ejection channels face the escape holes 34a of the adhesion plate 34, and is then thermally cured. In this situation, it is preferable to use the epoxy-based adhesive S which is cured by heating. Then, after the adhesive S has been applied on the adhesion plate 34, the nozzle plate 33 is brought into contact with the adhesion plate 34 while executing positioning so that the escape holes 34a and the nozzle openings 33a face each other, and is then thermally cured. Finally, after the adhesive S has been applied on the end surface of the support plate 32, the support plate 32 is pushed against the rear surface of the nozzle plate 33 and then heated so as to be cured. As a result, the head chip 21 illustrated in FIG. 3 can be assembled.
In particular, even if the surplus adhesive S is spread at the time of adhering the nozzle plate 33, the adhesive S can be allowed to enter the escape holes 34a and be accumulated therein before arriving at the nozzle openings 33a as illustrated in FIGS. 8 and 9. For that reason, the adhesive S is prevented from flowing into the nozzle openings 33a to infill the nozzle openings 33a, and hence the ejection failure can be prevented. Moreover, the escape holes 34a are each formed with a size which enables keeping at least a given distance H from the contour of the nozzle openings 33a, and hence the escaped adhesive S can be surely accumulated therein. In addition, the escape holes 34a of this embodiment are square, and hence a large space in which the adhesive S can be accumulated is ensured at four corners of the square. Accordingly, the adhesive S can be surely prevented from flowing into the nozzle openings 33a side. As a result, the ejection failure caused by inflow of the adhesive S can be effectively prevented.
As a result, there can be provided the high-quality head chip 21 causing no ejection failure. Further, because of the simple configuration in which only the escape holes 34a are additionally provided, the head chip 21 can be readily assembled, and the low costs can be achieved with the improved yield, whereby the head chip 21 high in realizablity can be provided.
Moreover, the plurality of escape holes 34a are formed in the adhesion plate 34. Hence, the adhesion plate 34 and the nozzle plate 33 are merely stacked on each other, thereby enabling the escape holes 34a to be readily and surely positioned with respect to the plurality of nozzle openings 33a. Thus, the assembling is simple.
Further, with the existence of the escape holes 34a, it is unnecessary to take the inflow of the adhesive S into the nozzle openings 33a into consideration, and hence it is unnecessary to reduce the inlet diameter D1 of the nozzle openings 33a according to the horizontal width of the grooves 35. Accordingly, the horizontal width of the grooves 35 can be shortened more than that of the related art, and the pitches of the head chip 21 can be narrowed.
For example, in the conventional art, the horizontal width of the grooves 35 is 75 μm, the horizontal width of the side walls 36 is 66 μm, and the inlet diameter D1 of the nozzle openings 33a is 55 μm. On the other hand, according to this embodiment, even if the pitches are narrowed to the degree that the horizontal width of the grooves 35 is 40 μm, and the horizontal width of the side walls 36 is 30 μm, the inlet diameter D1 of the nozzle openings 33a can be kept to 55 μm. In this case, the size of the escape holes 34a may be about 70 μm in the length of one side.
Further, according to the ink jet head 2 and the ink jet printer 1 according to this embodiment, there is provided the high-quality head chip 21 having no ejection failure which is caused by inflow of the adhesive S, and hence the high quality can be achieved, likewise.
The technical scope of the present invention is not limited to the above-mentioned embodiment, and various modifications can be added without departing from the split of the present invention.
For example, in the above-mentioned embodiment, the ink jet printer 1 has been exemplified as the liquid jet device, but the liquid jet device is not limited to the printer. For example, the liquid jet device may be a facsimile device, an on-demand printing device, or the like.
Further, the configuration of the escape holes 34a is square, but is not limited to this configuration. The configuration of the escape holes 34a may be freely designed as long as the contour of the escape holes 34a surrounds the periphery of the nozzle openings 33a so as to be spaced apart from the contour of the nozzle openings 33a by at least the given distance H.
Further, the configuration of the nozzle openings 33a is not limited to circle. For example, the configuration thereof may be a polygonal shape such as triangle, oval shape, or a star shape. When the nozzle openings 33a are thus formed, the configuration of the escape holes 34a may be determined according to the configuration of the nozzle openings 33a. 
Further, a case of using the aqueous ink W has been described. However, for example, an oil-based ink having non-conductivity, a solvent ink, an oil ink, a UV ink, or the like may be used. In the case of using the oil-based ink, configuration may be made in such a manner that the slits 31b formed in the ink introduction aperture 31a are eliminated, and all of the plurality of grooves 35 are filled with the ink W. Then, the nozzle openings 33a may be formed to communicate with all of the grooves 35. Even in this case, the same advantageous operations and effects can be obtained.

## Claims

1. A head chip for ejecting liquid toward a recording medium, comprising:
an actuator plate having a plurality of grooves that are to be filled with the liquid and that are formed at given intervals in a horizontal width direction;
a drive electrode which is formed on each side wall of each of the plurality of grooves and which increases pressure within each of the plurality of grooves by deforming the side wall when a drive voltage is applied to the drive electrode to cause the filled liquid to be ejected from an inside of each of the plurality of grooves;
a cover plate which is stacked on the actuator plate and which has an introduction aperture from which the liquid is introduced into the plurality of grooves;
a nozzle plate fixed to an end surface of the actuator plate through an adhesive, the nozzle plate having a plurality of nozzle openings which communicate with the plurality of grooves, respectively, and which are each formed at a position facing a corresponding one of the plurality of the grooves; and
a number of escape holes formed between the nozzle plate and the actuator plate, the number corresponding to a number of the plurality of nozzle openings,
wherein each of the plurality of escape holes has a contour which surrounds a periphery of each of the plurality of nozzle openings with the contour being spaced apart from a contour of each of the plurality of nozzle openings by at least a given distance,
wherein each of the plurality of nozzle openings has a circular contour having a center that is located in the middle of each of the plurality of grooves in the horizontal width direction, and the circular contour has a diameter that is larger in size than a horizontal width of each of the plurality of grooves, and
wherein the adhesive remaining at a time of fixing the nozzle plate is accumulated in the plurality of escape holes.

2. A head chip according to claim 1, wherein each of the plurality of escape holes has a square shape having a center that is substantially coincident with a center of each of the plurality of nozzle openings.

3. A head chip according to claim 1, wherein the plurality of escape holes are formed in an adhesion plate that is interposed between the nozzle plate and the actuator plate, the adhesion plate being fixed to both of the nozzle plate and the actuator plate through the adhesive.

4. A head chip according to claim 1, wherein the plurality of grooves have a part that functions as ejection channels which are filled with the liquid and a part that functions as dummy channels which are not filled with liquid, the part that functions as the ejection channels and the part that functions as the dummy channels being alternately arranged,
wherein the introduction aperture is formed with slits that introduce the liquid into only grooves in the part that functions as the ejection channels, and
wherein the plurality of nozzle openings are so formed as to communicate with only grooves in the part that functions as the ejection channels.

5. A liquid jet head, comprising:
the head chip according to claim 1;
supply means for supplying a given amount of the liquid to the introduction aperture; and
control means for applying the drive voltage to the drive electrode.

6. A liquid jet device, comprising:
the liquid jet head according to claim 5;
conveying means for conveying the recording medium in a predetermined direction; and
moving means for reciprocating the liquid jet head in a direction orthogonal to the predetermined direction in which the recording medium is conveyed.

7. A head chip for ejecting liquid toward a recording medium, comprising:
an actuator plate having a plurality of grooves that are to be filled with the liquid and that are formed at given intervals in a horizontal width direction;
a drive electrode which is formed on each side wall of each of the plurality of grooves and which increases pressure within each of the plurality of grooves by deforming the side wall when a drive voltage is applied to the drive electrode to cause the filled liquid to be ejected from an inside of each of the plurality of grooves;
a cover plate which is stacked on the actuator plate and which has an introduction aperture from which the liquid is introduced into the plurality of grooves;
a nozzle plate fixed to an end surface of the actuator plate through an adhesive, the nozzle plate having a plurality of nozzle openings which communicate with the plurality of grooves, respectively, and which are each formed at a position facing a corresponding one of the plurality of the grooves; and
a number of escape holes formed between the nozzle plate and the actuator plate, the number corresponding to a number of the plurality of nozzle openings,
wherein each of the plurality of escape holes has a contour which surrounds a periphery of each of the plurality of nozzle openings with the contour being spaced apart from a contour of each of the plurality of nozzle openings by at least a given distance,
wherein the plurality of escape holes are formed in an adhesion plate that is interposed between the nozzle plate and the actuator plate, and the adhesion plate is fixed to both of the nozzle plate and the actuator plate through the adhesive, and
wherein the adhesive remaining at a time of fixing the nozzle plate is accumulated in the plurality of escape holes.

8. A head chip according to claim 7, wherein each of the plurality of escape holes is formed into a square having a center that is substantially coincident with a center of each of the plurality of nozzle openings.

9. A liquid jet head, comprising:
the head chip according to claim 7;
supply means for supplying a given amount of the liquid to the introduction aperture; and
control means for applying the drive voltage to the drive electrode.

10. A liquid jet device, comprising:
the liquid jet head according to claim 9;
conveying means for conveying the recording medium in a predetermined direction; and
moving means for reciprocating the liquid jet head in a direction orthogonal to the predetermined direction in which the recording medium is conveyed.