Patent Description:
Recent inkjet techniques not only form images of letters and pictures using usual inks, but are widely attempting to form patterns having special functions using inks containing particles or cells.

In the inkjet techniques, nozzle shapes for stabilizing discharging liquid droplets have been known because there is a need for discharging liquid droplets to accurate positions stably.

However, there has been a problem that existing nozzle shapes cannot maintain stable discharging when inks containing particles or cells adhere to the nozzle surface.

A reported inkjet recording head intended to stabilize discharging after a wiping operation includes a plurality of ink discharging holes through which an ink is discharged, orifices leading to the ink discharging holes, an orifice plate in which these orifices are formed, a liquid flow path, and a discharging pressure generating element used for discharging an ink and provided at a predetermined position of the liquid flow path, wherein the orifice plate includes grooves having upper ends at the same height as the discharging surface and having a depth smaller than or equal to the plate thickness of the orifice plate, wherein the grooves have a shape surrounding the discharging holes and are provided at positions apart from the discharging holes (for example, see <CIT>).

<CIT> discloses a liquid droplet discharging unit configured to discharge a liquid through an ejection orifice, in which a high-repellency region surrounds the orifice.

According to one aspect of the present disclosure, a liquid droplet discharging apparatus includes a liquid droplet discharging unit. The liquid droplet discharging unit includes a nozzle surface, and a nozzle having an edge and a nozzle hole is formed in the nozzle surface. The liquid droplet discharging unit is configured to discharge a liquid through the nozzle. A water contact angle of an adjoining region of the nozzle in the nozzle surface is greater than a water contact angle of any other region of the nozzle surface. The adjoining region has an inner rim and an outer rim and is a region present in a manner to surround the nozzle and in a manner to contact the edge of the nozzle or a region present at a distance of <NUM> micrometers or less from the edge of the nozzle. The distance between the inner rim and the outer rim of the adjoining region is greater than or equal to half the diameter of the nozzle hole but less than or equal to five times greater than the diameter of the nozzle hole.

A liquid droplet discharging apparatus of the present disclosure includes a liquid droplet discharging unit. The liquid droplet discharging unit includes a nozzle surface, and a nozzle is formed in the nozzle surface. The liquid droplet discharging unit is configured to discharge a liquid through the nozzle. A water contact angle of an adjoining region of the nozzle in the nozzle surface is greater than a water contact angle of any other region of the nozzle surface.

The present disclosure has an object to provide a liquid droplet discharging apparatus that can maintain stable discharging even when a liquid containing particles or cells adheres to a nozzle surface.

The present disclosure can provide a liquid droplet discharging apparatus that can maintain stable discharging even when a liquid containing particles or cells adhere to a nozzle surface.

The liquid droplet discharging apparatus of the present disclosure includes at least a liquid droplet discharging unit, and further includes other units as needed.

The liquid droplet discharging apparatus of the present disclosure includes a liquid droplet discharging unit. The liquid droplet discharging unit includes a nozzle surface, and a nozzle is formed in the nozzle surface. The liquid droplet discharging unit is configured to discharge a liquid through the nozzle. A water contact angle of an adjoining region of the nozzle in the nozzle surface is greater than a water contact angle of any other region of the nozzle surface.

The liquid droplet discharging apparatus of the present disclosure is based on the following problems found in the existing techniques. That is, in the existing inkjet recording head disclosed in <CIT>, the grooves formed around the discharging holes have a function of accommodating an ink, but there is a problem that the ink accommodated in the grooves and the ink in the discharging hole cannot be securely separated from each other. Accordingly, the existing inkjet recording head can stabilize discharging an ink by eliminating influences of any ink adhering to the nozzle surface, but when a liquid containing particles or cells is used, cannot maintain stable discharging if such a liquid overflows to the nozzle surface.

The liquid droplet discharging apparatus of the present disclosure can maintain stable discharging even when a liquid containing particles or cells adheres to the nozzle surface. Therefore, for example, when discharging liquid droplets of a liquid such as a cell suspension into a well plate (container) including a plurality of wells used for an assay, the liquid droplet discharging apparatus can discharge a liquid droplet of a constant amount to the accurate position of each well without being given adverse influences by any liquid adhering to the nozzle surface (e.g., disorder of the discharging direction, and changes of the amount of the liquid to be discharged). Accordingly, the liquid droplet discharging apparatus can stably maintain the accuracy of the discharging position of a liquid droplet and the amount of the liquid to be discharged.

The liquid droplet discharging unit is a liquid droplet discharging unit configured to discharge a liquid through a nozzle formed in a nozzle surface. Preferable examples of the liquid droplet discharging unit include a liquid droplet discharging head.

The liquid droplet discharging unit preferably includes a nozzle plate including a nozzle surface and nozzles formed in the nozzle surface, and further includes other members as needed.

The nozzle plate includes the nozzle surface as a surface at a side to which a liquid droplet of the liquid is discharged, and includes nozzles (hereinafter may also be referred to as "nozzle holes"), which are through-holes formed in the nozzle surface.

The nozzle plate is not particularly limited and a known nozzle plate may be appropriately selected depending on the intended purpose. A nozzle plate formed of silicon (Si) as a main component is preferable.

The content of silicon in the nozzle plate is preferably <NUM>% by mass or greater, more preferably <NUM>% by mass or greater, and yet more preferably <NUM>% by mass or greater.

It is preferable that the nozzle surface have a water repellent film.

The water contact angle of an adjoining region of the nozzle in the nozzle surface is greater than the water contact angle of any other region of the nozzle surface. When a region having a relatively high water contact angle is provided around the nozzle in the nozzle surface, it is possible to maintain stable discharging even when a liquid containing particles or cells adheres to the nozzle surface.

The "water contact angle" is a contact angle of pure water measured by the θ/<NUM> method.

The water contact angle θ<NUM> of the adjoining region is not particularly limited and may be appropriately selected depending on the intended purpose so long as the water contact angle θ<NUM> is relatively greater than the water contact angle θ<NUM> of the any other region, and is preferably <NUM> degrees or greater, more preferably <NUM> degrees or greater, and yet more preferably <NUM> degrees or greater. The difference (θ<NUM>-θ<NUM>) between the water contact angle θ<NUM> of the adjoining region and the water contact angle θ<NUM> of the any other region is preferably <NUM> degrees or more, more preferably <NUM> degrees or more, and yet more preferably <NUM> degrees or more.

The adjoining region is a region present in a manner to surround the nozzle, and has a water contact angle relatively greater than the water contact angle of any other region of the nozzle surface.

The adjoining region of the nozzle in the nozzle surface is not particularly limited so long as the adjoining region is a region present in a manner to surround the nozzle, and a region present at a distance of <NUM> micrometers or less from the edge of the nozzle (nozzle hole).

It is preferable that the distance between the edge of the nozzle and the adjoining region be constant all around the nozzle. The distance is preferably <NUM> micrometers or less.

It is preferable that the adjoining region have a circular shape concentric with the nozzle.

The size of the adjoining region, expressed by the distance between the inner rim and the outer rim of the adjoining region, is greater than or equal to half the diameter of the nozzle hole but less than or equal to five times greater than the diameter of the nozzle hole.

When the distance between the edge of the nozzle and the adjoining region is extremely long or when the size of the adjoining region is extremely small, there is a risk that stable discharging may not be achieved because any liquid overflowing to the nozzle surface cannot keep a distance enough not to influence the next discharging. When the size of the adjoining region is extremely large, there is a risk that any liquid overflowing to the nozzle surface may remain in the adjoining region, and the remaining liquid may influence discharging of the next liquid droplet.

The water contact angle is not particularly limited, may be appropriately adjusted by a known method depending on the intended purpose, may be adjusted by providing a water repellent film on the adjoining region, or may be adjusted by adjustment of the surface roughness of the adjoining region as described below.

The distribution of the water contact angle values may be uniform or may be varied in the adjoining region. When the distribution of the water contact angle values is varied, it is preferable that the water contact angle of the inner region within the adjoining region of the nozzle when seen in the radial direction about the nozzle be greater than the water contact angle of the outer region within the adjoining region.

It is preferable to provide the variation in a manner that the water contact angle at a side closer to the nozzle (inner side) is relatively greater, and the variation may be a monotonous variation, a variation in a logarithmic function manner, or a gradual variation.

It is preferable that the surface roughness of the adjoining region of the nozzle in the nozzle surface be greater than the surface roughness of the any other region of the nozzle surface. In this way, the water contact angle of the adjoining region may be greater than the water contact angle of the any other region due to the surface roughness of the adjoining region being greater (coarser) than the surface roughness of the any other region.

The surface roughness Ra can be measured according to JIS B060E2013, and can be measured with, for example, a confocal laser microscope (available from Keyence Corporation) or a stylus surface profilometer (DEKTAK <NUM>, available from Bruker AXS GmbH).

The surface roughness Ra<NUM> of the adjoining region is not particularly limited and may be appropriately selected depending on the intended purpose so long as the surface roughness Ra<NUM> is relatively greater than the surface roughness Ra<NUM> of the any other region, and is preferably from <NUM> through <NUM>, more preferably from <NUM> through <NUM>, and yet more preferably from <NUM> through <NUM>. The difference (Ra<NUM>-Ra<NUM>) between the surface roughness Ra<NUM> of the adjoining region and the surface roughens Ra<NUM> of the any other region is preferably from <NUM> through <NUM>, more preferably from <NUM> through <NUM>, and yet more preferably from <NUM> through <NUM>.

It is preferable that the nozzle surface include a concavity around the nozzle.

It is preferable that the adjoining region of the nozzle be present in the concavity.

The concavity in the nozzle surface is not particularly limited so long as the concavity is a region present in a manner to surround the nozzle, and may be a region present in a manner to contact the edge of the nozzle (nozzle hole) or may be a region present slightly apart from the edge of the nozzle (nozzle hole).

It is preferable that the distance between the edge of the nozzle and the concavity be constant all around the nozzle. The distance is preferably <NUM> micrometers or less, more preferably <NUM> micrometers or less, and yet more preferably <NUM> micrometers.

The depth of the concavity from the nozzle surface (reference surface) is preferably <NUM> micrometers or less and more preferably <NUM> micrometers or less.

It is preferable that the concavity have a circular shape concentric with the nozzle.

The size of the concavity, expressed by the distance between the inner rim and the outer rim of the concavity, is preferably greater than or equal to half the diameter of the nozzle hole but less than or equal to five times greater than the diameter of the nozzle hole.

When the distance between the edge of the nozzle and the concavity is extremely long or when the depth is extremely small or when the size of the concavity is extremely small, there is a risk that stable discharging may not be achieved because any liquid overflowing to the nozzle surface cannot keep a distance enough not to influence the next discharging. When the depth is extremely large or when the size of the concavity is extremely large, there is a risk that any liquid overflowing to the nozzle surface may remain in the concavity, and the remaining liquid may influence discharging of the next liquid droplet.

The liquid is not particularly limited and may be appropriately selected depending on the intended purpose, and preferably contains settleable particles. The liquid is not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the liquid include an ink composition and a cell suspension.

The settleable particles are not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the settleable particles include metal particles, inorganic particles, and cells.

The cells are not particularly limited and may be appropriately selected depending on the intended purpose. Examples of the cells include cells derived from humans and cells derived from animals.

An embodiment for carrying out the present disclosure will be described below with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and any redundant description will be skipped.

In <FIG>, the X axis, the Y axis, and the Z axis may represent directions. The X direction along the X axis represents a predetermined direction in a recording medium, or a predetermined direction in an array plane in which a plurality of wells (concavities) of a well plate (container) (used for, for example, an assay using cells) are arrayed. The Y direction along the Y axis represents a direction orthogonal to the X direction in the recording medium or the array plane. The Z direction along the Z axis represents a direction orthogonal to the array plane.

The orientation pointed to by the arrow representing the X direction is expressed as +X direction, and the orientation opposite to the +X direction is expressed as -X direction. The orientation pointed to by the arrow representing the Y direction is expressed as +Y direction, and the orientation opposite to the +Y direction is expressed as -Y direction. The orientation pointed to by the arrow representing the Z direction is expressed as +Z direction, and the orientation opposite to the +Z direction is expressed as -Z direction. In an embodiment, it is assumed that the liquid droplet discharging head is configured to discharge a liquid droplet in the -Z direction as an example.

<FIG> is a schematic view illustrating an example of a liquid droplet discharging head of the liquid droplet discharging apparatus of the present disclosure.

As illustrated in <FIG>, the liquid droplet discharging head <NUM> includes a chamber <NUM> and a wiring <NUM>.

The chamber <NUM> is an example of a liquid chamber configured to store a liquid <NUM>, and includes an atmospherically exposing portion <NUM>, a liquid chamber member <NUM>, an elastic member <NUM>, and a MEMS chip <NUM>. <FIG> illustrates an example case where the chamber <NUM> stores a liquid <NUM>, which is a particle suspension in which settleable particles <NUM> are suspended (or settleable particles <NUM> are dispersed). As the settleable particles <NUM>, for example, metal particles, inorganic particles, cells, or cells derived from humans can be assumed.

The size of the chamber <NUM> and the liquid amount of the liquid <NUM> that can be stored in the chamber <NUM> are not particularly limited and may be appropriately selected depending on the intended purpose. The liquid amount of the liquid <NUM> may be, for example, from <NUM> microliter through <NUM>. When the liquid <NUM> is, for example, a cell suspension in which cells are dispersed, the liquid amount of the liquid <NUM> may be from <NUM> microliter through <NUM> microliters. The liquid amount of the liquid <NUM> changes under control of a control unit serving as a factor contributing to the vibration characteristic of a membrane <NUM>. The liquid amount E illustrated in <FIG> represents the liquid amount of the liquid <NUM> filled in the chamber <NUM>.

The atmospherically exposing portion <NUM> is a portion that exposes the chamber <NUM> to the atmosphere. The chamber <NUM> includes the atmospherically exposing portion <NUM> at a side closer to the Z+ direction of the chamber <NUM>. Bubbles mixed in the liquid <NUM> can be emitted from the atmospherically exposing portion <NUM>.

The MEMS chip <NUM> is a device produced by microfabricating a silicon substrate through a semiconductor process using photolithography, and is an example of a vibration unit in which the membrane <NUM>, a piezoelectric element <NUM>, and a membrane support <NUM> are integrated.

The MEMS chip <NUM> is joined to an end of the liquid chamber member <NUM> extending along the direction in which a liquid droplet D is discharged (-Z direction in <FIG>). The chamber <NUM> stores the liquid <NUM> in a space formed by joining the liquid chamber member <NUM> and the MEMB chip <NUM> to each other via the elastic member <NUM>.

The substrate of the MEMS chip <NUM> is not limited to silicon, but other members formed of, for example, glass may be used. The method for producing the piezoelectric element <NUM> is not limited to a semiconductor process, but any other method than a semiconductor process may be used, such as a process of patterning a precursor liquid of a piezoelectric material by an inkjet method.

The membrane <NUM> is an example of a nozzle plate (a film-shaped member) secured to an end of the chamber <NUM> at a side closer to the -Z direction and formed integrally with the membrane support <NUM> of the MEMS chip <NUM>. The membrane <NUM> includes a nozzle hole <NUM>, which is a through hole, at approximately the center of the membrane <NUM>. The membrane support <NUM> is an example of a supporting member configured to support the membrane <NUM>.

It is preferable that the nozzle hole <NUM> be formed as a true-circular through hole at approximately the center of the membrane <NUM>. However, the nozzle hole <NUM> may have a polygonal planar shape. When the nozzle hole <NUM> has a circular shape, the diameter of the nozzle hole <NUM> is not particularly limited, but is preferably twice or more greater than the size of the settleable particle <NUM> in order to avoid the nozzle hole <NUM> being clogged with the settleable particle <NUM> and discharge a liquid droplet D stably. Specifically, because the size of an animal cell, or a human cell in particular is typically about from <NUM> micrometers through <NUM> micrometers, the diameter of the nozzle hole <NUM> is preferably from <NUM> micrometers through <NUM> micrometers or greater to match the cell used.

On the other hand, when the liquid droplet D has an extremely large size, it is difficult to achieve the object of forming a minute liquid droplet D. Therefore, the diameter of the nozzle hole <NUM> is preferably <NUM> micrometers or less. Accordingly, in the liquid droplet discharging head <NUM>, the diameter of the nozzle hole <NUM> is preferably from <NUM> micrometers through <NUM> micrometers.

The piezoelectric element <NUM> is an example of a vibration unit configured to vibrate the membrane <NUM>, and formed on the lower surface of the membrane <NUM> integrally with the MEMS chip. The shape of the piezoelectric element <NUM> can be designed to match the shape of the membrane <NUM>. For example, when the planar shape of the membrane <NUM> is a circular shape, it is preferable to form a piezoelectric element <NUM> having an annular (ring-like) planar shape around the nozzle hole <NUM>.

The piezoelectric element <NUM> includes a piezoelectric material <NUM>, a lower electrode <NUM> provided on the upper surface (the surface at a side closer to the +Z direction) of the piezoelectric material <NUM>, and an upper electrode <NUM> provided on the lower surface (the surface at a side closer to the -Z direction) of the piezoelectric material <NUM>.

By application of a drive waveform to the lower electrode <NUM> or the upper electrode <NUM> of the piezoelectric element <NUM>, the membrane <NUM> shrinks in the X direction and a shrinking stress is applied to enable the membrane <NUM> to vibrate along the Z direction. As the constituent material of the piezoelectric material, for example, lead zirconate titanate can be used. Other than this, various materials can be used, such as bismuth iron oxide, metal niobate, and barium titanate, and these materials additionally including metals or different oxides.

One end of the wiring <NUM> is coupled to a wiring coupling portion <NUM> of the MEMS chip <NUM> via a conductive adhesive <NUM>. The wiring <NUM> is led out to the external side surface of the liquid chamber member <NUM> and disposed along the external side surface, and the other end of the wiring <NUM> is coupled to a drive waveform generation source <NUM>.

The piezoelectric element <NUM> vibrates the membrane <NUM> in response to voltages applied respectively to the lower electrode <NUM> and the upper electrode <NUM> through the wiring <NUM> coupled to the piezoelectric element <NUM> via the conductive adhesive <NUM>. The conductive adhesive <NUM> is an adhesive having conductivity and formed of, for example, an epoxy resin-based material mixed with a conductive filler.

The elastic member <NUM> is a member formed by containing an elastic body that does not conduct the vibration generated by driving by the MEMS chip <NUM> to the liquid chamber member <NUM> as much as possible. The elastic member <NUM> also has a function of joining the liquid chamber member <NUM> and the MEMS chip <NUM> to each other. For example, such an elastic member <NUM> can be formed of an adhesive that bonds the MEMS chip <NUM> and the liquid chamber member <NUM> with each other. However, it is not indispensable to provide the elastic member <NUM> because the main function of the discharging head <NUM> can be realized even when the elastic member <NUM> is a hard material or when the liquid chamber member <NUM> and the MEMS chip <NUM> are directly joined to each other without the elastic member <NUM>.

A preferable material of the liquid chamber member <NUM> has a weak cytotoxicity, heat resistance, and a good fabrication property. Examples of such a material include polyether ether ketone (PEEK) and polycarbonate (PC), which are so-called engineering plastics. However, materials such as other plastics, metals, and ceramics can also be used. If the liquid chamber member <NUM> has heat resistance, it is easy to handle the liquid chamber member <NUM> because the liquid chamber member <NUM> having heat resistance can endure treatment in an autoclave (a high pressure, <NUM> degrees C) for sterilization. However, heat resistance is not an indispensable property because there are other available methods such as ethanol and UV irradiation.

The drive waveform generation source <NUM> is a signal generator configured to output a drive waveform as a drive signal to the piezoelectric element <NUM>. By outputting a drive waveform to the piezoelectric element <NUM>, the drive waveform generation source <NUM> can cause the membrane <NUM> to deform and discharge the liquid <NUM> stored in the chamber <NUM> in the form of a liquid droplet D. Moreover, by causing the membrane <NUM> to deform by a drive waveform set to a predetermined cycle, the drive waveform generation source <NUM> can cause the membrane <NUM> to resonantly vibrate and discharge the liquid.

It is preferable to install the MEMS chip <NUM> on a downstream side (a side closer to the -Z direction) of the liquid chamber member <NUM> in the discharging direction. In a process for locating a tissue, there may be a case where it is good to not simply locate a cell suspension but add a liquid or a gel constituting an organism or a liquid or a gel having biocompatibility before or after location of cells. This contributes to factors such as adhesiveness of a cell with the bottom of a well, the cell survival rate, and cell maturity.

<FIG> is a view illustrating an example of a structure around a nozzle of the liquid droplet discharging apparatus of <FIG>. In <FIG>, "a" and "b" exemplarily illustrate the portions enclosed within broken lines in an expanded size. "a" is an expanded view of the nozzle surface (not a concavity) and "b" is an expanded view of the bottom surface of a concavity in the nozzle surface.

In an embodiment of <FIG>, a concavity is formed around a nozzle hole in the nozzle surface. This concavity can be formed by dry etching using a photo mask during a process of fabricating the MEMS chip. The nozzle surface that is not a concavity has a surface roughness reflecting the mirror surface of a Si wafer (Ra<<NUM>). A fabricated surface including the bottom surface of the concavity fabricated by dry etching has a relatively rough surface (Ra of from <NUM> through <NUM>). However, the surface roughness values are reference values, and may be values in any other ranges so long as there is a difference in water contact angle.

In an embodiment of <FIG>, a same water repellent film is formed all over the nozzle surface. However, because of the effect of the asperity in the fabricated surface of the concavity (i.e., because of the relatively greater surface roughness), the water contact angle of the fabricated surface of the concavity is greater than the water contact angle of the nozzle surface other than the concavity. Hence, the concavity corresponds to the adjoining region. SiO<NUM> (denoted by the reference numeral <NUM>) for improving adhesiveness of a fluorine-based water repellent film is disposed between Si (denoted by the reference numeral <NUM>), which is the main component of the nozzle plate, and the water repellent film <NUM>.

<FIG> and <FIG> are schematic views illustrating another example of the structure around a nozzle of the liquid droplet discharging apparatus. In <FIG> and <FIG>, "a" and "b" exemplarily illustrate the portions enclosed within broken lines in an expanded size. "a" is an expanded view of the any other region and "b" is an expanded view of the adjoining region of the nozzle.

In the embodiment of <FIG>, a concavity is formed around the nozzle. However, it is not indispensable to form a concavity, but it is only needed that the adjoining region of the nozzle and the any other region have a contact angle difference as in the embodiment of <FIG> and <FIG>. The contact angles may be varied by an asperity structure of the surface (<FIG>), or may be varied by the difference between water repellent films on the surface (<FIG>).

In the embodiment of <FIG>, a same water repellent film is formed all over the nozzle surface. However, because of the effect of the asperity formed in the adjoining region of the nozzle (i.e., because of the relatively greater surface roughness), the water contact angle of the adjoining region of the nozzle is greater than the water contact angle of the any other region. SiO<NUM> (denoted by the reference numeral <NUM>) for improving adhesiveness of a fluorine-based water repellent film is disposed between Si (denoted by the reference numeral <NUM>), which is the main component of the nozzle plate, and the water repellent film <NUM>.

In the embodiment of <FIG>, a water repellent film 4b formed on the adjoining region of the nozzle and a water repellent film 4a formed on the any other region have different water contact angles from each other. The water contact angle of the water repellent film 4b on the adjoining region of the nozzle is greater than the water contact angle of the water repellent film 4a of the any other region. SiO<NUM> (denoted by the reference numeral <NUM>) for improving adhesiveness of a fluorine-based water repellent film is disposed between Si (denoted by the reference numeral <NUM>), which is the main component of the nozzle plate, and the water repellent film (denoted by the reference numeral 4a or 4b).

The configurations of the embodiments of <FIG> and <FIG> can both be produced using a MEMS process.

<FIG> illustrate structural patterns around the nozzle of the liquid droplet discharging apparatus illustrated in <FIG>. In each drawing, the upper view illustrates a cross-sectional view taken at a position transversing the nozzle in the Y axis direction like <FIG>, and the lower view illustrates a plan view of the nozzle and the nozzle surface seen from a side to which a liquid droplet is discharged.

<FIG> illustrates a structure of an existing typical nozzle shape without a concavity and an adjoining region around the nozzle hole. <FIG> illustrates the structure illustrated in <FIG>, where the concavity is present in a manner to surround the nozzle and contact the edge of the nozzle. In <FIG>, the concavity is present in a manner to surround the nozzle and be slightly apart from the edge of the nozzle. The bottom surface (denoted by the reference numeral <NUM>) of the concavity is an adjoining region having a relatively great surface roughness. It is preferable that the concavity have a concave shape concentric with the nozzle hole as in <FIG> and <FIG>, but the concavity needs not necessarily have a circular shape in order to achieve the effect. The size of the concavity, expressed by the distance between the inner rim and the outer rim of the concavity, is preferably at least greater than or equal to half the diameter of the nozzle hole but less than or equal to five times greater than the diameter of the nozzle hole. When the size of the concavity is extremely small, there is a risk that stable discharging may not be achieved because any liquid overflowing to the nozzle surface cannot keep a distance enough not to influence the next discharging. When the size of the concavity is extremely large, there is a risk that any liquid overflowing to the nozzle surface may remain also in the concavity, and the remaining liquid may influence discharging of the next liquid droplet.

<FIG> are schematic views illustrating phenomena when a liquid adheres to the nozzle surface in the structural patterns of <FIG> respectively.

<FIG> illustrates a phenomenon when a liquid <NUM> overflows to the nozzle surface in an existing typical nozzle hole shape. Any ink overflowing from the nozzle hole during discharging or maintenance couples to the ink in the nozzle hole, and forms a liquid pool coupled to the liquid in the liquid chamber as illustrated. If the next liquid droplet is discharged in this state, the flying direction of the liquid droplet is largely bent, or the liquid droplet is absorbed into the liquid pool and cannot fly.

In <FIG> according to the structural pattern of <FIG> (embodiment <NUM>), any liquid that may overflow to the nozzle surface is kept on the nozzle surface having a relatively small water contact angle, and no ink remains near the nozzle hole. In this state, the next liquid droplet can fly correctly.

Also in <FIG> according to the structural pattern of <FIG> (embodiment <NUM>), the same effect as the embodiment <NUM> works even when a nonconcave region is present around the nozzle hole. Any liquid may slightly remain at the nonconcave region, but is not so influential as to make discharging unstable.

Claim 1:
A liquid droplet discharging apparatus, comprising
a liquid droplet discharging unit,
wherein the liquid droplet discharging unit includes a nozzle surface (<NUM>), and a nozzle having an edge and a nozzle hole (<NUM>) being formed in the nozzle surface (<NUM>), the liquid droplet discharging unit being configured to discharge a liquid through the nozzle,
wherein
a water contact angle of an adjoining region of the nozzle in the nozzle surface (<NUM>) is greater than a water contact angle of any other region of the nozzle surface (<NUM>),
the adjoining region has an inner rim and an outer rim and is a region present apart from the edge of the nozzle at a distance of <NUM> micrometers or less from the edge of the nozzle, and
the distance between the inner rim and the outer rim of the adjoining region is greater than or equal to half the diameter of the nozzle hole but less than or equal to five times greater than the diameter of the nozzle hole (<NUM>).