Method of manufacturing nozzle plate, liquid droplet ejection head and image forming apparatus

The method of manufacturing a nozzle plate formed with nozzles which eject liquid droplets, the method comprises the steps of: forming and patterning an opaque metal film onto a transparent substrate; forming photosensitive resin over the opaque metal film and the transparent substrate; exposing the photosensitive resin to light from a side adjacent to the transparent substrate; developing the photosensitive resin which has been exposed to the light; forming a metal layer on the opaque metal film after the developing step; and separating at least the transparent substrate from the metal layer, wherein the nozzle plate comprises at least the metal layer, and a liquid droplet ejection surface of the nozzle plate is on a side where the transparent substrate has been separated in the separating step.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing a nozzle plate, a liquid droplet ejection head and an image forming apparatus, and more particularly to a method of manufacturing a nozzle plate in which nozzles for ejecting droplets of liquid are formed.

2. Description of the Related Art

The print head of an inkjet type image forming apparatus has a plurality of nozzles formed in a nozzle plate, which constitutes an ejection surface that opposes the recording medium. The shape of the nozzles which eject ink droplets onto the recording medium readily affects the size and the ejection speed, and the like, of the ink droplets, and therefore, the nozzles must be processed to a high degree of accuracy.

A processing method using electroforming (hereinafter referred to as “electroforming method”) is known as a method of manufacturing a nozzle plate of this kind. A characteristic feature of the electroforming method is that it allows nozzle plates to be manufactured at low cost, compared to a processing method using a laser beam or a processing method using a press.

FIGS. 11A to 11Cshow a first related method of manufacturing a nozzle plate based on an electroforming method in the related art. Firstly, as shown inFIG. 11A, a photosensitive resin (hereinafter referred to as “resist”)202which is photocurable is formed and patterned on a metal substrate200. The plan shape of the resist202is circular, and the center thereof substantially coincides with the center of a nozzle to be formed. Next, as shown inFIG. 11B, a metal layer204of nickel plating, or the like, for example, is grown and formed on the metal substrate200by means of an electroforming method. When the thickness of the metal layer204exceeds the thickness of the resist202, the metal layer204is grown in such a manner that the metal layer204gradually covers the resist202from the periphery thereof. Then, a recess portion206having an internal wall with a curved cross-sectional shape is formed. In other words, the metal layer204is formed to overhang the resist202. Finally, as shown inFIG. 11C, the metal substrate200and the resist202are peeled away from the metal layer204, and the metal layer204corresponding to a nozzle plate260is thus obtained. Nozzles (through holes)251each having a curved cross-section corresponding to the recess portions206inFIG. 11Bare formed in the nozzle plate260.

FIGS. 12A and 12Bshow a second related method of manufacturing a nozzle plate based on an electroforming method in the related art. Firstly, a patterned resist302is formed in a substantially circular cylinder shape on a metal substrate300, and a metal layer304is grown on the metal substrate300to a height lower than the height of the resist302, as shown inFIG. 12A. Then, the metal substrate300and the resist302are peeled away from the metal layer304, and the metal layer304corresponding to a nozzle plate360is thus obtained, as shown inFIG. 12B. Nozzles351each having an inner wall with a substantially linear shaped cross-section (straight shape) are formed in the nozzle plate360.

Japanese Patent Application Publication No. 10-296982 discloses a third related method of manufacturing a nozzle plate based on an electroforming method. Firstly, an opaque metal film is patterned onto a transparent substrate, and a photosensitive resist layer having a thickness of 100 μm made of a photocurable resin is formed on the opaque metal film. Thereupon, the resist layer is exposed to light via the opaque metal film from the side of the transparent substrate. In this exposure process, the amount of exposure light received by the resist layer is adjusted in such a manner that a strong exposure is achieved on the transparent substrate side, and the amount of exposure light declines as it moves toward the opposite side from the transparent substrate. The development processing is carried out subsequently, and a sharp end-shaped (tapered) resist which narrows in the direction of irradiation is formed. Then, a metal layer is formed on the opaque metal film and the metal layer is then separated from the transparent substrate and the resist, and the metal layer corresponding to a nozzle plate is thus obtained. The surface of the nozzle plate corresponding to the ink droplet ejection side (ink ejection surface) is the surface of the metal layer opposite to the transparent substrate.

However, there are the following problems in the methods of manufacturing the nozzle plate based on the electroforming method in the related art.

In the first related method of manufacture, as shown inFIG. 11C, the nozzles251having a curved cross-section on the inner walls have to be arranged at a certain interval with respect to the adjacent nozzles in accordance with their shape, and hence there are limitations on the degree to which the density of the nozzles can be raised. Furthermore, the diameter W of the nozzles251is uneven due to variation in the metal layer204formed to a thickness greater than that of the resist202by electroforming, and there is a problem in that this unevenness is liable to affect the size and flight characteristics, such as the ejection speed, of the ink droplets ejected from the nozzles251.

In the second related method of manufacture, when the patterned resist302is formed on the metal substrate300, as shown inFIG. 13A, an unpatterned resist layer306is formed on the metal substrate300and the resist layer306is then exposed to light from the upper side. More specifically, ultraviolet light310is irradiated onto the resist layer306via a mask308formed with apertures308acorresponding to the prescribed nozzle shape. In this exposure process, a portion of the ultraviolet light310irradiated onto the resist layer306may be dispersed, and it may be reflected by the metal substrate300on the under side of the resist layer306. When the developing process is carried out in this case, a resist306aon the side adjacent to the metal substrate300assumes a broadened shape as shown inFIG. 13B, rather than a straight shape such as the resist302shown inFIG. 12A. There is a decline in the dimensional accuracy of the nozzles formed in this case, and the flight characteristics of the ink droplets ejected from the nozzles deteriorate.

In the third related method of manufacture, light exposure is carried out by adjusting the amount of light irradiated onto a 100 μm-thick resist layer, in such a manner that the light intensity is lower on the side opposite to the transparent substrate than it is on the side adjacent to the transparent substrate. Hence, there is slight variation in the amount of exposure light, as well as slight variation during developing, which adversely affect the dimensional accuracy of the resist formed into a tapered shape, leading to poor accuracy in the overall dimensions of the nozzles.

Furthermore, the dimensional accuracy of the resist is generally good on the base side; however, in the third related method of manufacture, the surface forming the ink droplet ejection surface of the nozzle plate is the surface on the opposite side to the transparent substrate, which corresponds to the base. Thus, the ink droplet ejection sides of the nozzles are formed on the basis of the resist shape that has inferior dimensional accuracy compared to the opposite side (the side of the transparent substrate). Therefore, there is a problem in that the dimensional accuracy of the nozzles on the ink droplet ejection side is not good, and this poor accuracy is liable to affect the ejection volume and the flight characteristics, such as the ejection speed, of the ink droplets ejected from the nozzles.

SUMMARY OF THE INVENTION

The present invention has been contrived in view of the foregoing circumstances, and provides a method of manufacturing a nozzle plate, a liquid droplet ejection head, and an image forming apparatus which improve the dimensional accuracy of the nozzles on the droplet ejection side.

In order to attain the aforementioned object, the present invention is directed to a method of manufacturing a nozzle plate formed with nozzles which eject liquid droplets, the method comprises the steps of: forming and patterning an opaque metal film onto a transparent substrate; forming photosensitive resin over the opaque metal film and the transparent substrate; exposing the photosensitive resin to light from a side adjacent to the transparent substrate; developing the photosensitive resin which has been exposed to the light; forming a metal layer on the opaque metal film after the developing step; and separating at least the transparent substrate from the metal layer, wherein the nozzle plate comprises at least the metal layer, and a liquid droplet ejection surface of the nozzle plate is on a side where the transparent substrate has been separated in the separating step.

According to the present invention, the liquid droplet ejection surface of the nozzle plate is the surface from which the transparent substrate has been separated in the separating step, and corresponds to the side where the exposure light is incident on the photosensitive resin in the exposing step. Therefore, the dimensional accuracy of the nozzles is improved on the liquid droplet ejection side thereof, compared to a case where the liquid droplet ejection surface is on the opposite side. Accordingly, the flight characteristics, such as the ejection volume and ejection speed, of the liquid droplets ejected from the nozzles are improved.

Preferably, the exposing step comprises the step of controlling at least one of a wavelength range of the light, an amount of the light and an irradiation angle of the light to the photosensitive resin, in such a manner that the light divergently travels through the photosensitive resin. According to this, it is possible to form nozzle shapes which produce good flight characteristics, by adopting a tapered shape which narrow toward the end.

Preferably, the photosensitive resin is of 10 μm through 50 μm in thickness. If the thickness of the photosensitive resin is 10 μm through 50 μm, then the dimensional accuracy of the photosensitive resin is good on the side that is not adjacent to the transparent substrate. If the thickness of the photosensitive resin is 50 μm, then the dimensional accuracy is ±5 μm or less, and if the thickness of the photosensitive resin is 10 μm, then the dimensional accuracy is ±1 μm or less.

Preferably, the opaque metal film has liquid repellency. According to this, it is not necessary to carry out a separate liquid repelling treatment on the liquid droplet ejection surface of the nozzle plate.

Preferably, the opaque metal film is of not less than 1 μm and not more than 5 μm in thickness. According to this, straight portions are formed in the nozzles on the liquid droplet ejection side thereof, and therefore the ejection direction is stabilized.

In order to attain the aforementioned object, the present invention is also directed to a liquid droplet ejection head, comprising the nozzle plate manufactured by the above-described method.

In order to attain the aforementioned object, the present invention is also directed to an image forming apparatus, comprising the above-described liquid droplet ejection head.

According to the present invention, the liquid droplet ejection surface of the nozzle plate is the surface on the side where the transparent substrate is separated from the metal layer in the separation step, and corresponds to the side where the exposure light is incident on the photosensitive resin in the light exposure step. Therefore, the dimensional accuracy of the nozzles is improved on the liquid droplet ejection side thereof, compared to a case where the liquid droplet ejection surface is on the opposite side. Accordingly, the flight characteristics, such as the ejection volume and ejection speed, of the liquid droplets ejected from the nozzles are improved.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

General Composition of Inkjet Recording Apparatus

FIG. 1is a general schematic drawing of an inkjet recording apparatus corresponding to an image forming apparatus according to an embodiment of the present invention. As shown inFIG. 1, the inkjet recording apparatus10comprises: a printing unit12having a plurality of print heads12K,12C,12M, and12Y for ink colors of black (K), cyan (C), magenta (M), and yellow (Y), respectively; an ink storing and loading unit14for storing inks of K, C, M and Y to be supplied to the print heads12K,12C,12M, and12Y; a paper supply unit18for supplying recording paper16; a decurling unit20for removing curl in the recording paper16; a suction belt conveyance unit22disposed facing the nozzle face (ink-droplet ejection face) of the print unit12, for conveying the recording paper16while keeping the recording paper16flat; a print determination unit24for reading the printed result produced by the printing unit12; and a paper output unit26for outputting image-printed recording paper (printed matter) to the exterior.

InFIG. 1, a magazine for rolled paper (continuous paper) is shown as an example of the paper supply unit18; however, more magazines with paper differences such as paper width and quality may be jointly provided. Moreover, papers may be supplied with cassettes that contain cut papers loaded in layers and that are used jointly or in lieu of the magazine for rolled paper.

In the case of a configuration in which roll paper is used, a cutter28is provided as shown inFIG. 1, and the roll paper is cut to a desired size by the cutter28. The cutter28has a stationary blade28A, whose length is not less than the width of the conveyor pathway of the recording paper16, and a round blade28B, which moves along the stationary blade28A. The stationary blade28A is disposed on the reverse side of the printed surface of the recording paper16, and the round blade28B is disposed on the printed surface side across the conveyance path. When cut paper is used, the cutter28is not required.

The recording paper16delivered from the paper supply unit18retains curl due to having been loaded in the magazine. In order to remove the curl, heat is applied to the recording paper16in the decurling unit20by a heating drum30in the direction opposite from the curl direction in the magazine. The heating temperature at this time is preferably controlled so that the recording paper16has a curl in which the surface on which the print is to be made is slightly round outward.

The decurled and cut recording paper16is delivered to the suction belt conveyance unit22. The suction belt conveyance unit22has a configuration in which an endless belt33is set around rollers31and32so that the portion of the endless belt33facing at least the nozzle face of the printing unit12and the sensor face of the print determination unit24forms a plane.

The belt33has a width that is greater than the width of the recording paper16, and a plurality of suction apertures (not shown) are formed on the belt surface. A suction chamber34is disposed in a position facing the sensor surface of the print determination unit24and the nozzle surface of the printing unit12on the interior side of the belt33, which is set around the rollers31and32, as shown inFIG. 1. The suction chamber34provides suction with a fan35to generate a negative pressure, and the recording paper16on the belt33is held by suction.

The belt33is driven in the clockwise direction inFIG. 1by the motive force of a motor (not shown) being transmitted to at least one of the rollers31and32, which the belt33is set around, and the recording paper16held on the belt33is conveyed from left to right inFIG. 1.

Since ink adheres to the belt33when a marginless print job or the like is performed, a belt-cleaning unit36is disposed in a predetermined position (a suitable position outside the printing area) on the exterior side of the belt33. Although the details of the configuration of the belt-cleaning unit36are not shown, examples thereof include a configuration in which the belt33is nipped with cleaning rollers such as a brush roller and a water absorbent roller, an air blow configuration in which clean air is blown onto the belt33, or a combination of these. In the case of the configuration in which the belt33is nipped with the cleaning rollers, it is preferable to make the line velocity of the cleaning rollers different than that of the belt33to improve the cleaning effect.

The inkjet recording apparatus10can comprise a roller nip conveyance mechanism, in which the recording paper16is pinched and conveyed with nip rollers, instead of the suction belt conveyance unit22. However, there is a drawback in the roller nip conveyance mechanism that the print tends to be smeared when the printing area is conveyed by the roller nip action because the nip roller makes contact with the printed surface of the paper immediately after printing. Therefore, the suction belt conveyance in which nothing comes into contact with the image surface in the printing area is preferable.

A heating fan40is disposed on the upstream side of the printing unit12in the conveyance pathway formed by the suction belt conveyance unit22. The heating fan40blows heated air onto the recording paper16to heat the recording paper16immediately before printing so that the ink deposited on the recording paper16dries more easily.

The print unit12is a so-called “full line head” in which a line head having a length corresponding to the maximum paper width is arranged in a direction (main scanning direction) that is perpendicular to the paper conveyance direction (sub-scanning direction) (seeFIG. 2).

As shown inFIG. 2, the print heads12K,12C,12M and12Y which constitute the print unit12each comprise line heads in which a plurality of ink ejection ports (nozzles) are arranged through a length exceeding at least one edge of the maximum size recording paper16intended for use with the inkjet recording apparatus10.

The print heads12K,12C,12M, and12Y are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side (left side inFIG. 1), along the conveyance direction of the recording paper16(paper conveyance direction). A color image can be formed on the recording paper16by ejecting the inks from the print heads12K,12C,12M, and12Y, respectively, onto the recording paper16while conveying the recording paper16.

The print unit12, in which the full-line heads covering the entire width of the paper are thus provided for the respective ink colors, can record an image over the entire surface of the recording paper16by performing the action of moving the recording paper16and the print unit12relatively to each other in the paper conveyance direction (sub-scanning direction) just once (in other words, by means of a single sub-scan). Higher-speed printing is thereby made possible and productivity can be improved in comparison with a shuttle type head configuration in which a print head moves reciprocally in a direction (main scanning direction) which is perpendicular to the paper conveyance direction.

Although a configuration with four standard colors, K M C and Y, is described in the present embodiment, the combinations of the ink colors and the number of colors are not limited to these, and light and/or dark inks can be added as required. For example, a configuration is possible in which print heads for ejecting light-colored inks such as light cyan and light magenta are added.

As shown inFIG. 1, the ink storing and loading unit14has ink tanks for storing the inks of the colors corresponding to the respective print heads12K,12C,12M, and12Y, and the respective tanks are connected to the print heads12K,12C,12M, and12Y by means of channels (not shown). The ink storing and loading unit14has a warning device (for example, a display device or an alarm sound generator) for warning when the remaining amount of any ink is low, and has a mechanism for preventing loading errors among the colors.

The print determination unit24has an image sensor (line sensor and the like) for capturing an image of the ink-droplet deposition result of the printing unit12, and functions as a device to check for ejection defects such as clogs of the nozzles in the printing unit12from the ink-droplet deposition results evaluated by the image sensor.

The print determination unit24of the present embodiment is configured with at least a line sensor having rows of photoelectric transducing elements with a width that is greater than the ink-droplet ejection width (image recording width) of the print heads12K,12C,12M, and12Y This line sensor has a color separation line CCD sensor including a red (R) sensor row composed of photoelectric transducing elements (pixels) arranged in a line provided with an R filter, a green (G) sensor row with a G filter, and a blue (B) sensor row with a B filter. Instead of a line sensor, it is possible to use an area sensor composed of photoelectric transducing elements which are arranged two-dimensionally.

The print determination unit24reads a test pattern image printed by the print heads12K,12C,12M, and12Y for the respective colors, and the ejection of each head is determined. The ejection determination includes the presence of the ejection, measurement of the dot size, and measurement of the dot deposition position.

A post-drying unit42is disposed following the print determination unit24. The post-drying unit42is a device to dry the printed image surface, and includes a heating fan, for example. It is preferable to avoid contact with the printed surface until the printed ink dries, and a device that blows heated air onto the printed surface is preferable.

In cases in which printing is performed with dye-based ink on porous paper, blocking the pores of the paper by the application of pressure prevents the ink from coming contact with ozone and other substance that cause dye molecules to break down, and has the effect of increasing the durability of the print.

A heating/pressurizing unit44is disposed following the post-drying unit42. The heating/pressurizing unit44is a device to control the glossiness of the image surface, and the image surface is pressed with a pressure roller45having a predetermined uneven surface shape while the image surface is heated, and the uneven shape is transferred to the image surface.

The printed matter generated in this manner is outputted from the paper output unit26. The target print (i.e., the result of printing the target image) and the test print are preferably outputted separately. In the inkjet recording apparatus10, a sorting device (not shown) is provided for switching the outputting pathways in order to sort the printed matter with the target print and the printed matter with the test print, and to send them to paper output units26A and26B, respectively. When the target print and the test print are simultaneously formed in parallel on the same large sheet of paper, the test print portion is cut and separated by a cutter (second cutter)48. The cutter48is disposed directly in front of the paper output unit26, and is used for cutting the test print portion from the target print portion when a test print has been performed in the blank portion of the target print. The structure of the cutter48is the same as the first cutter28described above, and has a stationary blade48A and a round blade48B.

Although not shown, the paper output unit26A for the target prints is provided with a sorter for collecting prints according to print orders.

Structure of the Print Head

Next, the structure of the print head will be described. The print heads12K,12M,12C and12Y of the respective ink colors have the same structure, and a reference numeral50is hereinafter designated to any of the print heads.

FIG. 2is a plan view perspective diagram showing an example of the structure of the print head50.FIG. 3is a cross-sectional diagram (along line3-3in theFIG. 2) showing the three-dimensional composition of one of liquid droplet ejection elements (an ink chamber unit corresponding to one nozzle51).

The nozzle pitch in the print head50should be minimized in order to maximize the density of the dots printed on the surface of the recording paper. As shown inFIG. 2, the print head50according to the present embodiment has a structure in which a plurality of ink chamber units (droplet ejection elements)53, each comprising a nozzle51forming an ink droplet ejection port, a pressure chamber52corresponding to the nozzle51, and the like, are disposed two-dimensionally in the form of a staggered matrix, and hence the effective nozzle interval (the projected nozzle pitch) as projected in the lengthwise direction of the print head (the direction perpendicular to the paper conveyance direction) is reduced and high nozzle density is achieved.

As shown inFIG. 2, the planar shape of the pressure chamber52provided for each nozzle51is substantially a square, and the nozzle51and an inlet of supplied ink (supply port)54are disposed in both corners on a diagonal line of the square.

As shown inFIG. 3, the nozzle plate60according to the present embodiment is provided on the nozzle surface (ink ejection surface)50A of the print head50. The nozzles51are formed in the nozzle plate60. The method of manufacturing the nozzle plate60is described later.

Furthermore, each pressure chamber52is connected via a supply opening54to a common flow passage55. The common flow channel55is connected to an ink tank (not shown), which is a base tank that supplies ink, and the ink supplied from the ink tank is delivered through the common flow channel55to the pressure chambers52.

An actuator58provided with an individual electrode57is joined to a pressure plate (common electrode)56which forms the upper face of each pressure chamber52, and the actuator58is deformed when a drive voltage is applied to the individual electrode57and common electrode56so that the volume of the pressure chamber52is changed, thereby causing ink to be ejected from the nozzle51. A piezoelectric element is suitable as the actuator58. When ink is ejected, new ink is supplied to the pressure chamber52from the common flow channel55through the supply port54.

As shown inFIG. 4, the plurality of ink chamber units53having this structure are composed in a lattice arrangement, based on a fixed arrangement pattern having a row direction which coincides with the main scanning direction, and a column direction which, rather than being perpendicular to the main scanning direction, is inclined at a fixed angle of θ with respect to the main scanning direction. By adopting a structure in which a plurality of ink chamber units53are arranged at a uniform pitch d in a direction having an angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to align in the main scanning direction is d×cos θ.

More specifically, the arrangement can be treated equivalently to one in which the nozzles51are arranged in a linear fashion at uniform pitch P, in the main scanning direction. By means of this composition, it is possible to achieve a nozzle composition of high density, in which the nozzle columns projected to align in the main scanning direction reach a total of 2,400 per inch (2,400 nozzles per inch).

In a full-line head comprising rows of nozzles that have a length corresponding to the entire width of the image recordable width, the “main scanning” is defined as printing one line or one strip in the width direction of the recording paper (the direction perpendicular to the conveyance direction of the recording paper) by driving the nozzles in one of the following ways: (1) simultaneously driving all the nozzles; (2) sequentially driving the nozzles from one side toward the other; and (3) dividing the nozzles into blocks and sequentially driving the nozzles from one side toward the other in each of the blocks.

In particular, when the nozzles51arranged in a matrix such as that shown inFIG. 4are driven, the main scanning according to the above-described (3) is preferred. More specifically, the nozzles51-11,51-12,51-13,51-14,51-15and51-16are treated as a block (additionally; the nozzles51-21, . . . ,51-26are treated as another block; the nozzles51-31, . . . ,51-36are treated as another block; . . . ); and one line is printed in the width direction of the recording paper20by sequentially driving the nozzles51-11,51-12, . . . ,51-16in accordance with the conveyance velocity of the recording paper20.

On the other hand, “sub-scanning” is defined as to repeatedly perform printing of one line (a line formed of a row of dots, or a line formed of a plurality of rows of dots) formed by the main scanning, while moving the full-line head and the recording paper relatively to each other.

In implementing the present invention, the arrangement of the nozzles is not limited to that of the example illustrated. Moreover, in the present embodiment, a method is employed wherein an ink droplet is ejected by means of the deformation of the actuator58, which is, typically, a piezoelectric element, but in implementing the present invention, the method used for ejecting ink is not limited in particular, and instead of a piezo jet method, it is also possible to apply various other types of methods, such as a thermal jet method, wherein the ink is heated and bubbles are caused to form therein, by means of a heat generating body, such as a heater, ink droplets being ejected by means of the pressure of these bubbles.

Method for Manufacturing Nozzle Plate

Next, a method of manufacturing the nozzle plate according to an embodiment of the present invention will be described.

FIGS. 5A to 5Fare illustrative diagrams showing steps of manufacturing a nozzle plate60according to the first embodiment. Firstly, in a step of forming an opaque metal film, as shown inFIG. 5A, an opaque metal film102which is impenetrable to ultraviolet light is formed and patterned in accordance with the nozzle shapes and the nozzle arrangement, onto a transparent substrate100which transmits ultraviolet light, such as a glass substrate. For the patterning method of the opaque metal film102, a commonly known technique, such as photolithography, is used. The opaque metal film102is thin, having a thickness of approximately 1 μm or lower, and a dimensional accuracy of around ±0.1 μm or less.

Next, in a resist layer forming step, a photosensitive and photocurable resin layer (resist layer)104is formed over the surface of the transparent substrate100on which the opaque metal film102has been formed as shown inFIG. 5B. In the present embodiment, the thickness of the resist layer104is approximately 10 μm through 50 μm.

Next, in a light exposure step, as shown inFIG. 5C, ultraviolet light108is irradiated through a diffusion plate106onto the side of the transparent substrate100opposite to the side where the opaque metal film102is formed (namely, the transparent substrate side). The diffusion plate106has the function of converting the transmitted light into diffused light, and it comprises, for example, a combination of ground glass, and a lens system, and the like. Consequently, the ultraviolet light108atransmitted by the diffusion plate106becomes diffused light, and travels through the transparent substrate100. The patterned opaque metal film102on the transparent substrate100functions as a mask, and partially intercepts the ultraviolet light108ain accordance with the shape of the patterning. On the other hand, the ultraviolet light108awhich is transmitted rather than being intercepted by the opaque metal film102is diffused light, and divergently travels through the resist layer104.

Next, in a developing step, a development process of the resist layer104is carried out. Since the exposed portion of the resist layer104on which the ultraviolet light108ahas been irradiated in the light exposure step produces a curing reaction, then when the development process is carried out, the unexposed portion of the resist layer104is removed. In other words, in the development process, as shown inFIG. 5D, a resist104ahaving an inversely tapered shape which is narrower at the transparent substrate100side and broader at the opposite side thereof is formed on the transparent substrate100.

Next, in a metal layer forming step, a metal layer110is formed on the opaque metal film102, as shown inFIG. 5E. The metal layer110is formed by using a commonly known electroforming method, and is made of nickel, or the like, for example.

Next, in a separating step, as shown inFIG. 5F, the metal layer110and the opaque metal film102are separated from the transparent substrate100and the resist104a. In the present embodiment, since the shape of the resist104ais the inversely tapered shape (seeFIG. 5E), the transparent substrate100is separated after the resist104ais separated. Thus, it is possible to obtain a nozzle plate60having the metal layer110and the opaque metal film102. Through holes (nozzles)51corresponding to the shapes of the inversely tapered resist104aare formed in the nozzle plate60.

There are no particular restrictions on the separation sequence of the transparent substrate100and the resist104a, and it may be changed appropriately in accordance with the shape of the resist104a, and the like. If the resist104ahas a substantially cylindrical shape with hardly any taper, then it is possible to separate the transparent substrate100and the resist104afrom the metal layer110and the opaque metal film102in a single action.

Moreover, according to requirements, it is also possible to remove the opaque metal film102from the metal layer110and to obtain a nozzle plate60consisting of the metal layer110.

In general, in the resist layer forming step shown inFIG. 5B, the dimensional accuracy of the resist layer104formed on the transparent substrate100tends to decline as the resist layer becomes thicker. In the above-described third related method of manufacture, the thickness of the resist layer is 100 μm, and a dimensional accuracy in the resist layer of approximately ±10 μm is expected on the side that is not adjacent to the transparent substrate; whereas in the present embodiment, since the resist layer104has a small thickness of approximately 10 μm through 50 μm, then the dimensional accuracy in the resist layer104on the side that is not adjacent to the transparent substrate100will be approximately ±5 μm or less when the thickness of the resist layer104is 50 μm, and ±1 μm or less when the thickness of the resist layer104is 10 μm. In this way, in the present embodiment, it is possible to manufacture the nozzle plate60having excellent dimensional accuracy.

Further, the resist layer104has better dimensional accuracy at the side adjacent to the transparent substrate100, compared to the side opposite from the transparent substrate100. In the present embodiment, the surface of the opaque metal film102of the nozzle plate60, in other words, the surface which makes contact with the transparent substrate100inFIG. 5E, is the surface of the nozzle plate60on the ink droplet ejection side (ink ejection surface)60A, and this is a characteristic feature of the present embodiment. In this way, the dimensional accuracy of the nozzles51on the ink droplet ejection side is good, compared to the third related method of manufacture in which the surface on the opposite side to the transparent substrate forms the ink ejection surface.

Furthermore, in the present embodiment, the patterned opaque metal film102on the transparent substrate100functions as the mask in the light exposure step, and it has good dimensional accuracy, then the dimensional accuracy of the nozzles51formed through the subsequent developing step, metal layer forming step and separation step, is good.

In the present embodiment, since the ink ejection surface60A of the nozzle plate60is made of the opaque metal film102, it is then preferable that the opaque metal film102has liquid-repelling properties. Thereby, when ink mist generated as ink droplets are ejected from the nozzles51has adhered to the ink ejection surface60A, then it can be removed readily by means of a blade or the like (not illustrated), and therefore, it is possible to prevent ejection errors in the nozzles51caused by ink mist adhering to the ink ejection surface60A.

FIG. 6is an illustrative diagram showing the characteristic portion of a light exposure step in the method of manufacturing a nozzle according to a second embodiment of the present invention.FIG. 7is a modification example ofFIG. 6. The steps apart from the light exposure step are similar to those of the first embodiment and are therefore omitted from the drawings.

In the present embodiment, as shown inFIG. 6, the transparent substrate100and so on are disposed in a substantially perpendicular direction with respect to the direction of irradiation from a light source112. The light source112emits the ultraviolet light108as parallel light, and is controlled by a control device114. The control device114adjusts the wavelength range and light quantity of the ultraviolet light108emitted by the light source112, and also adjusts the angle of irradiation, in accordance with the material of the resist layer104, and the like. Accordingly, it is possible to form nozzles51having a desired tapered angle.

The control device114may control the resist layer104side in such a manner that the transparent substrate100forms a prescribed angle of a with respect to the direction of irradiation of the light source112, as shown inFIG. 7. In this case also, it is possible to achieve similar beneficial effects to the case shown inFIG. 6.

FIG. 8is a side view cross-sectional diagram showing a nozzle plate according to a third embodiment of the present invention.FIG. 9is a modification example ofFIG. 8.

In the present embodiment, as shown inFIG. 8, a liquid-repelling film116having liquid repellency is provided on the ink ejection surface60A of the nozzle plate60. The method of manufacturing the nozzle plate60is carried out similarly to the first embodiment shown inFIGS. 5A to 5F, and after completing the separation step (seeFIG. 5F), the liquid-repelling film116is formed on the surface of the opaque metal film102.

It is also possible to form the liquid-repelling film116on the surface of the metal layer104as shown inFIG. 9, after removing the opaque metal film102and the metal substrate100in the separation step shown inFIG. 5F.

By means of the liquid-repelling film116formed on the ink ejection surface60A of the nozzle plate60, even if the ink mist generated as ink is ejected becomes attached to the ink ejection surface60A, this ink mist can be removed readily by means of a blade, or the like, and therefore it is possible to prevent ejection errors in the nozzles51caused by soiling, or the like, on the ink ejection surface60A.

Although not shown in the drawings, it is also possible to compose the opaque metal film102in such a manner that it has liquid repellency, and in this case, the step of forming the liquid-repelling film114shown inFIGS. 8 and 9can be omitted, and the efficiency of the manufacture can be improved.

FIGS. 10A to 10Fare illustrative diagrams showing steps of manufacturing a nozzle plate according to the fourth embodiment. The fourth embodiment is a mode in which the thickness of the opaque metal film102formed on the transparent substrate100in the step shown inFIG. 10Ais not less than 1 μm and not more than 5 μm. In the nozzle plate60manufactured by using the opaque metal film102of this kind, straight portions51A of a height (depth) corresponding to the thickness of the opaque metal film102are formed in the nozzles51on the side adjacent to the ink ejection surface60A as shown inFIG. 10F, and therefore the ejection direction is stabilized.

If the thickness of the opaque metal film102is smaller than 1 μm, as in the first embodiment, then the straight portions51A cannot function and there is little contribution to the stability of the ejection direction. On the other hand, if the thickness of the opaque metal film102is greater than 5 μm, then there is significant dimensional variation during patterning, which will have an adverse effect on the ink ejection volume and the ejection speed at the nozzles51. Moreover, if the height (depth) of the straight portions51A is large, then the fluid resistance increases, and hence ejection efficiency declines. Consequently, it is desirable that the thickness of the opaque metal film102is equal to or greater than 1 μm and equal to or less than 5 μm, as in the present embodiment.

The resist layer104in the present embodiment has the same thickness with the first embodiment (approximately 10 μm through 50 μm). Furthermore, as in the third embodiment, it is also possible to form a liquid-repelling film on the surface of the opaque metal film102after the step inFIG. 10F. Since the remaining steps are common to those of the first embodiment (seeFIGS. 5A to 5F), then the same reference numerals are applied and description thereof is omitted here.