Liquid ejection head and image forming apparatus including same

A liquid ejection head includes a nozzle plate having a plurality of nozzles formed therein from which droplets are ejectable. The nozzle plate includes a nozzle substrate in which a plurality of nozzle holes each constituting a nozzle is formed, and a liquid-repellent film formed on a surface of the nozzle substrate on a droplet ejection side of the nozzle plate. A circumferential portion is formed around each nozzle on the droplet ejection side of the nozzle plate and is smoothly recessed toward an edge portion of the nozzle. The edge portion of the nozzle is smoothly continuous with an inner wall of the nozzle, and the liquid-repellent film having a uniform thickness is formed across the nozzle plate on the droplet ejection side of the nozzle plate to at least the edge portion of the nozzle.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2012-185951, filed on Aug. 25, 2012, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

1. Technical Field

Exemplary aspects of the present invention generally relate to a liquid ejection head and an image forming apparatus including the liquid ejection head.

2. Related Art

Like a printer, copier, plotter, facsimile machine, or multifunction device having two or more of these capabilities, an inkjet recording device employing a liquid ejection recording method is also a type of image forming apparatus.

Typically, the inkjet recording device includes a recording head constructed of a liquid ejection head that ejects droplets of a recording liquid such as ink onto a sheet of a recording medium to form an image on the sheet. The liquid ejection head has a nozzle face in which multiple nozzles, from which droplets are ejected, are formed. Ejection characteristics of the liquid ejection head, such as the volume and speed with which droplets are ejected from the nozzles, varies considerably depending on the shape and quality of each nozzle. It is also known that surface characteristics of a nozzle substrate, in which nozzle holes each forming the nozzle are formed, also considerably affects the ejection characteristics of the liquid ejection head. For example, adhesion of ink or the like to the area around the nozzle on the surface of the nozzle substrate may distort the trajectory of the droplets ejected from the nozzle.

To solve these problems, a liquid-repellent film is often formed on the surface of the nozzle substrate on a side from which droplets are ejected (hereinafter referred to as a droplet ejection side). As a result, the droplet ejection side of the nozzle substrate has a uniform surface across the surface of the nozzle substrate, thereby stabilizing the ejection characteristics of the liquid ejection head.

To further stabilize the ejection characteristics of the liquid ejection head, the nozzle face of the liquid ejection head is often wiped off and cleaned by an elastic blade such as a wiper formed of rubber or the like to remove liquid adhering to the portion around the nozzle during maintenance of the liquid ejection head.

However, repeated wiping of the nozzle face of the liquid ejection head abrades and wears away the liquid-repellent film around the nozzles, causing irregular ejection of the droplets from the liquid ejection head. In particular, because the wiper hits the edge of each nozzle relatively hard, the liquid-repellent film at the edge of the nozzle is easily abraded and worn away by such wiping.

To solve these problems, a concavity is often formed around the nozzle in the nozzle substrate on the droplet ejection side. However, formation of the concavity generates a step in the nozzle face, and an edge of the step is subjected to excessive load from the wiper that contacts the step, resulting in abrasion and wearing away of the liquid-repellent film at the step. In addition, it is difficult to remove viscous liquid accumulating within the concavity.

The concavity formed around the nozzle in the droplet ejection side of the nozzle substrate may be gradually tapered toward the bottom. However, although such a configuration reduces abrasion and wearing away of the liquid-repellent film at an outer circumferential part of the tapered concavity, the edge of the nozzle is still hit hard by the wiper. Consequently, durability of the liquid-repellent film at the edge of the nozzle deteriorates.

Alternatively, the thickness of the liquid-repellent film can be gradually reduced approaching the edge of each nozzle. However, such a configuration makes the liquid-repellent film excessively thin at the edge of each nozzle. Consequently, durability of the liquid-repellent film at the edge of the nozzle deteriorates, abetting abrasion and wearing away of the liquid-repellent film.

SUMMARY

In view of the foregoing, illustrative embodiments of the present invention provide a novel liquid ejection head with stable ejection characteristics and without abrasion and wearing away of a liquid-repellent film provided to the liquid ejection head, and an image forming apparatus including the liquid ejection head.

In one illustrative embodiment, a liquid ejection head includes a nozzle plate having a plurality of nozzles formed therein from which droplets are ejectable. The nozzle plate includes a nozzle substrate in which a plurality of nozzle holes each constituting a nozzle is formed, and a liquid-repellent film formed on a surface of the nozzle substrate on a droplet ejection side of the nozzle plate. A circumferential portion is formed around each nozzle on the droplet ejection side of the nozzle plate and is smoothly recessed toward an edge portion of the nozzle. The edge portion of the nozzle is smoothly continuous with an inner wall of the nozzle, and the liquid-repellent film having a uniform thickness is formed across the nozzle plate on the droplet ejection side of the nozzle plate to at least the edge portion of the nozzle.

In another illustrative embodiment, an image forming apparatus includes the liquid ejection head described above.

Additional features and advantages of the present disclosure will become more fully apparent from the following detailed description of illustrative embodiments, the accompanying drawings, and the associated claims.

DETAILED DESCRIPTION

In describing illustrative embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents that have substantially the same function, operate in a similar manner, and achieve a similar result.

Illustrative embodiments of the present invention are now described below with reference to the accompanying drawings. In a later-described comparative example, illustrative embodiment, and exemplary variation, for the sake of simplicity the same reference numerals will be given to identical constituent elements such as parts and materials having the same functions, and redundant descriptions thereof omitted unless otherwise required.

It is to be noted that a “sheet” of recording media is not limited to a sheet of paper but also includes any material onto which droplets including ink droplets adhere, such as an OHP sheet, cloth, glass, and a substrate.

Image forming apparatuses hereinafter described form an image on a recording medium, such as paper, string, fiber, cloth, lather, metal, plastics, glass, wood, and ceramics by ejecting droplets onto the recording medium. In this specification, an image refers to both signifying images such as characters and figures, as well as a non-signifying image such as patterns.

In addition, ink includes any material which is a liquid when ejected from the image forming apparatuses to form images on the recording medium, such as a DNA sample, a resist material, a pattern material, and resin.

Further, an image formed on the recording medium is not limited to a flat image, but also includes an image formed on a three-dimensional object, a three-dimensional image, and so forth.

A description is now given of an example of a configuration of a liquid ejection head411according to illustrative embodiments, with reference toFIGS. 1 and 2.FIG. 1is a vertical cross-sectional view illustrating an example of a configuration of the liquid ejection head411along a direction perpendicular to a direction of nozzle arrays (or a longitudinal direction of a liquid chamber6).FIG. 2is a vertical cross-sectional view of the liquid ejection head411in the direction of nozzle arrays (or a lateral direction of the liquid chamber6).

The liquid ejection head411includes a channel plate (or liquid chamber substrate)1, a vibration plate2bonded to a lower face of the channel plate1, and a nozzle plate3bonded to an upper face of the channel plate1.

The channel plate1, the vibration plate2, and the nozzle plate3together form multiple liquid chambers6communicating with, via channels5, respective nozzles4formed in the nozzle plate3to eject droplets therefrom, fluid resistors7that also function as supply paths to supply liquid such as ink to the liquid chambers6, and communication parts8that communicate with the liquid chambers6via the fluid resistors7. Ink is supplied from a common liquid chamber10formed in a frame member17, which is described in detail later, to the communication parts8via supply openings9formed in the vibration plate2.

The channel plate1is formed of a silicon substrate. The silicon substrate is etched to form grooves that constitute the channels5, the liquid chambers6, the fluid resistors7, and so forth. It is to be noted that, alternatively, the channel plate1may be formed by etching an SUS substrate using an acid etchant, or may be formed by machining such as press working.

The vibration plate2has vibrating portions (diaphragms)2acorresponding to the respective liquid chambers6to form a part of the walls of the liquid chambers6. Each of the vibrating portions2ahas a protrusion2bon an outer surface thereof opposite to the liquid chamber6. A drive element that deforms the vibrating portions2ato generate energy to eject droplets from the nozzles4, which, in the present illustrative embodiment, is a multi-layered piezoelectric member12, has columnar piezoelectric elements12A and12B (hereinafter also referred to as piezoelectric columns12A and12B), and upper surface of each of the piezoelectric columns12A and12B is bonded to the respective protrusions2b. A lower surface of the piezoelectric member12is bonded to a base member13.

The piezoelectric member12is constructed of piezoelectric layers21formed of lead zirconate titanete (PZT) or the like, and internal electrodes22aand22b, all of which are laminated alternately. Each of the internal electrodes22aand22bis drawn out to end faces of the piezoelectric member12and is connected to external electrodes23aand23bprovided to the respective end faces. A voltage is applied to each of the external electrodes23aand23bto displace the piezoelectric member12in a direction of lamination. Grooves are formed in the piezoelectric member12by half-cut dicing so that the piezoelectric member12has a predetermined number of the piezoelectric columns12A and12B positioned at predetermined intervals.

The piezoelectric columns12A and12B have the same basic configuration. A drive waveform is applied to the piezoelectric columns12A (hereinafter also referred to as drive columns12A) to drive the drive columns12A, and no drive waveform is applied to the piezoelectric columns12B (hereinafter also referred to as non-drive columns12B) so that the non-drive columns12B are used merely as columns. Either a bi-pitch configuration in which the drive columns12A and the non-drive columns12B are alternately used as illustrated inFIG. 2, or a normal-pitch configuration in which all the piezoelectric columns are used as the drive columns12A, is applicable to the present illustrative embodiment.

Two arrays of drive elements, each constructed of the multiple drive columns12A, are formed on the base member13.

Although the piezoelectric member12operates in the d33mode to pressurize liquid within the liquid chambers6in the present illustrative embodiment, alternatively, the piezoelectric member12may operate in the d31mode to pressurize the liquid within the liquid chambers6.

A flexible printed circuit (FPC)15for transmitting a drive signal is directly connected to the external electrodes23aof the drive columns12A. The FPC15implements a drive circuit16that selectively applies a drive waveform to the drive columns12A. It is to be noted that the external electrodes23bof all the drive columns12A, which are commonly and electrically connected to one another, are connected to a common wire of the FPC15.

The nozzle plate3is constructed of a nozzle substrate31and a liquid-repellent film32provided to the nozzle substrate31on a side from which droplets are ejected (hereinafter referred to as a droplet ejection side). Nozzle holes41, each forming the nozzle4having a diameter of from 10 μm to 35 μm, is formed, corresponding to the respective liquid chambers6, in the nozzle substrate31.

The frame member17formed by injection molding using, for example, epoxy resin or polyphenylene sulfide, is bonded to outer walls of a piezoelectric actuator unit constructed of the piezoelectric member12, to which the FPC15is connected, and the base member13. The common liquid chamber10and supply openings19, from which the liquid is supplied to the common liquid chamber10, are formed in the frame member17. The supply openings19are connected to a supply source such as a sub-tank or an ink cartridge, not shown.

In the liquid ejection head411having the above-described configuration, a voltage applied to the drive columns12A is reduced from a reference level to contract the drive columns12A so that the vibrating portions2A of the vibration plate2are lowered to expand the volume of each of the liquid chambers6, thereby forcing the liquid into the liquid chambers6. Thereafter, the voltage applied to the drive columns12A is increased to extend the drive columns12A in the direction of lamination so that the vibrating portions2aof the vibration plate2are deformed toward the nozzles4to contract the volume of each of the liquid chambers6. As a result, pressure is applied to the liquid within the liquid chambers6so that droplets are ejected from the nozzles4.

Then, the voltage applied to the drive columns12A is returned to the reference level to restore the vibrating portions2aof the vibration plate2to their initial positions so that the liquid chambers6are expanded, thereby generating negative pressure. As a result, the liquid flows from the common liquid chamber10to the liquid chambers6via the supply openings9, so that the liquid chambers6are filled with the liquid. After vibration of a meniscus formed in each of the nozzles4is damped, the next series of ejection is started.

It is to be noted that the method for driving the liquid ejection head411is not limited to the above-described example, and may be varied depending on the exact manner in which the driving waveform is applied.

A description is now given of an example of a structure of the nozzle plate3according to a first illustrative embodiment, with reference toFIG. 3.FIG. 3is an enlarged vertical cross-sectional view illustrating a portion around the nozzle4in the nozzle plate3.

As described above, the nozzle plate3includes the nozzle substrate31, in which the nozzle holes41, each forming the nozzle4, is formed. A base film33is formed on a surface31aof the nozzle substrate31on the droplet ejection side, and the liquid-repellent film32is formed on the base film33. In the present illustrative embodiment, the nozzle substrate31is formed of stainless steel.

The base film33improves adhesion between the nozzle substrate31and the liquid-repellent film32. However, alternatively, the base film33may not be provided in a case in which the nozzle substrate31and the liquid-repellent film32have good adhesion therebetween.

As illustrated inFIG. 3, a diameter of each nozzle4is gradually reduced toward an edge portion42of the nozzle4in a direction of ejection of the droplets. A circumferential portion43formed around each nozzle4on the droplet ejection side of the nozzle plate3is smoothly recessed toward the edge portion42in a cross-section along the direction of ejection of the droplets. The edge portion42is smoothly continuous with an inner wall of the nozzle4(or an inner circumferential surface of the nozzle hole41).

The liquid-repellent film32is of uniform thickness across the nozzle plate3to the edge portion42of each nozzle4. Accordingly, a surface of the liquid-repellent film32is also smoothly recessed at the circumferential portion43toward the edge portion42.

The thickness of the liquid-repellent film32from the edge portion42to the inner wall of the nozzle4(or the inner circumferential surface of the nozzle hole41) is gradually reduced.

A description is now given of a state of contact of a wiper51with the nozzle plate3, with reference toFIGS. 4A and 4B.FIG. 4Ais a vertical cross-sectional view illustrating the state of contact of the wiper51with the nozzle plate3viewed from the front.FIG. 4Bis a vertical cross-sectional view illustrating the state of contact of the wiper51with the nozzle plate3viewed from the lateral side.

As described above, in the nozzle plate3according to the first illustrative embodiment, the circumferential portion43is smoothly recessed toward the edge portion42. Such a configuration allows the wiper51to securely contact the circumferential portion43, which is smoothly recessed, without a gap therebetween, thereby reliably removing liquid from the surface of the nozzle plate3. In addition, because there is no step or edge at the circumferential portion43, the wiper51is protected from damage such as abrasion and scratches, thereby maintaining good cleaning performance over time.

To prevent deterioration in ejection performance caused by adhesion of liquid to the nozzle plate3, the surface of the nozzle plate3is wiped off by the wiper51formed of rubber or the like to remove residual liquid from the surface of the nozzle plate3. However, wiping of the surface of the nozzle plate3by the wiper51may abrade or tear off the liquid-repellent film32formed on the surface31aof the nozzle substrate31.

To prevent this problem, on the surface of the nozzle plate3, the circumferential portion43is smoothly recessed toward the edge portion42. Accordingly, the wiper51contacts the circumferential portion43with reduced pressure, thereby reducing damage to the circumferential portion43caused by wiping.

The edge portion42of the nozzle4is curved and smoothly continuous with both the inner wall of the nozzle4and the surface of the nozzle plate3. The liquid-repellent film32formed on the edge portion42, which is provided between and connects both the surface of the nozzle plate3and the inner wall of the nozzle4, tends to be damaged by the wiper51. However, as described above, the edge portion42is smoothly curved, thereby reducing damage such as abrasion and tearing off of the liquid-repellent film32caused by the wiper51.

In addition, the liquid-repellent film32is continuously formed from the edge portion42to the inner wall of the nozzle4, thereby preventing the liquid-repellent film32from tearing off by the wiper51.

Specifically, a part of each of the liquid-repellent film32and the base film33enters the nozzle hole41to be smoothly continuous with the inner wall of the nozzle4, so that the edge portion42of the nozzle4is covered with the liquid-repellent film32and the base film33and presents no open edge to the wiper51.

The liquid-repellent film32has a uniform thickness across the surface31aof the nozzle substrate31as described above. Accordingly, in the manufacture of the nozzle plate3using a method described later, the reaction of steam with air and thermal conductivity during heating are uniform on the surface31aof the nozzle substrate31, thereby providing the liquid-repellent film32with uniform repellency, durability, and adhesion to the surface31aof the nozzle substrate31.

In addition, the circumferential portion43formed on the droplet ejection side of the nozzle plate3is smoothly recessed toward the edge portion42of the nozzle4. Accordingly, damage to the wiper51is also reduced.

Specifically, an edge of the nozzle4or concavities in the surface of the nozzle plate3can abrade the wiper51at certain parts thereof, possibly causing irregular wiping of the surface of the nozzle plate3. Consequently, liquid remains adhered onto the nozzle plate3in a stripe pattern in a direction of movement of the wiper51.

As a result, such liquid, which becomes viscous and is fixed onto the surface of the nozzle plate3, is spread across the surface of the nozzle plate3by the wiping movement of the wiper51and may adhere around the nozzle4, causing irregular ejection of the droplets from the nozzle4.

To solve these problems, in the present illustrative embodiment, the circumferential portion43formed around the nozzle4is smoothly recessed toward the edge portion42of the nozzle4. As a result, abrasion of the wiper51is prevented, thereby preventing irregular ejection of the droplets from the nozzle4.

Further, even in a case in which sheet jam or the like causes the sheet to directly contact the nozzle face of the liquid ejection head411, the circumferential portion43, which is smoothly recessed toward the edge portion42of the nozzle4, hinders such sheet from directly hitting the area around the nozzle4.

A description is now given of a second illustrative embodiment, with reference toFIG. 5.FIG. 5is a vertical cross-sectional view illustrating an example of a structure of the nozzle base31according to the second illustrative embodiment.

In the second illustrative embodiment, the nozzle hole41formed in the nozzle substrate31further includes a linear portion44on the droplet ejection side of the nozzle plate3. The linear portion44is parallel to the direction of ejection of the droplets from the nozzle4. Although not shown inFIG. 5for ease of illustration, the liquid-repellent film32and the base film33are formed on the nozzle substrate31in a manner similar to the first illustrative embodiment.

It is known that the diameter of each nozzle considerably affects the ejection performance of the liquid ejection head. Uneven amount of recession in the circumferential portion43around each nozzle4and uneven size of the curve in the edge portion42of each nozzle4may vary the diameter of the nozzles4. Consequently, each nozzle4has a slightly different diameter, causing uneven ejection performance of the liquid ejection head411.

Provision of the linear portion44to the nozzle hole41fixes the diameter of the nozzle4even when the amount of recession in the circumferential portion43and the size of the curve in the edge portion42vary, thereby achieving uniform ejection performance of the liquid ejection head411.

A description is now given of an example of a method for manufacturing the nozzle plate3according to the second illustrative embodiment.FIGS. 6A to 6Hare schematic views illustrating steps in a process of manufacturing the nozzle plate3, respectively. It is to be noted that, the steps of manufacturing the nozzle plate3are substantially the same in both the first and second illustrative embodiments, differing only in a shape of a puncher used for press working.

First, a stainless steel plate320of a thickness of, for example, 50 μm, is prepared as illustrated inFIG. 6A. In the present example, stainless steel316is used for the plate320.

As illustrated inFIG. 6B, a puncher321having a tapered portion323and a linear portion324is used to form the nozzle4by press working.

A protrusion325formed by press working is polished away, such that the nozzle substrate31having the nozzle hole41is formed as illustrated inFIG. 6C. At this time, a circumference of the nozzle hole41on the droplet ejection side of the nozzle substrate31is smoothly recessed by polishing to form the circumferential portion43.

Next, for example, an SiO2layer333of 10 nm thickness, which forms the base film33of the liquid-repellent film32, is formed on the droplet ejection side of the nozzle substrate31by sputtering as illustrated inFIG. 6D.

The nozzle substrate31thus formed is then soaked for an hour in a solution in which fluorine-based solvent is mixed with 0.02 wt % modified perfluoropolyoxy-etane. Then, the nozzle substrate31is heated at 130° C. for 10 minutes. Thereafter, the nozzle substrate31is rinsed with fluorine-based solvent, so that an excess amount of the SiO2layer333, which is not bonded to the surface of the nozzle substrate31, is removed to form a fluorinated liquid-repellent layer332as illustrated inFIG. 6E. Modified perfluoropolyoxyetane reacts with steam in air to link with the surface of the SiO2layer333.

Next, a protective material314is bonded to the droplet ejection side of the nozzle substrate31as illustrated inFIG. 6F.

A liquid chamber side of the nozzle substrate31, which is opposite to the droplet ejection side and to which the protective material314is not bonded, is irradiated with O2plasma. As a result, the liquid-repellent layer332entering the liquid chamber side of the nozzle substrate31through the nozzle hole41is removed, so that the liquid-repellent film32and the base film33are formed on the droplet ejection side of the nozzle substrate31as illustrated inFIG. 6G.

Thereafter, the protective material314is removed to form the nozzle plate3as illustrated inFIG. 6H.

It is to be noted that chemical abrasive polishing is used in the step of polishing illustrated inFIG. 6C. In chemical abrasive polishing, chemical abrasion is used in addition to mechanical polishing, so that the nozzle substrate31is chemically etched to remove minute scratches and burrs therefrom, thereby improving smoothness of the nozzle substrate31.

In chemical abrasive polishing, an acute portion is particularly polished by chemical treatment and polishing pressure. As a result, the edge around the nozzle4is polished smoother than a flat portion. Therefore, the circumferential portion43around the nozzle4is smoothly recessed as described above. In addition, a corner between the surface of the nozzle plate3and the linear portion44of the nozzle4is chamfered by polishing. As a result, the surface of the nozzle plate3and the linear portion44are smoothly continuous with each other. Thus, manufacture of the nozzle plate3according to the second illustrative embodiment is facilitated.

Alternatively, the liquid-repellent layer332may be formed by vacuum deposition. It is to be noted that the liquid-repellent layer332still enters the nozzle hole41and the liquid chamber side of the nozzle substrate31in the vacuum deposition.

In the present illustrative embodiment, fluorinated liquid-repellent material is used as a liquid repellent. Although various materials are known as fluorinated (fluoroalkyl alkoxysilane) repellents, in the present illustrative embodiment, modified perfluoropolyoxyetane, perfluoropolyoxyetane variant, or a mixture of both (product name: OPTOOL DSX, manufactured by Daikin Industries, Ltd.; also known as terminal-modified alkoxysilane perfluoropolyether), is deposited with a thickness of between 5 nm and 20 nm to obtain the desired liquid repellency.

When the nozzle plate3is taken out of a deposition chamber after the deposition of the liquid-repellent layer332, the fluorinated repellent and the SiO2layer, that is, the base film33, are hydrolyzed by moisture in air and chemically linked with SiO2, so that the fluorinated liquid-repellent film32is formed.

A description is now given of a third illustrative embodiment, with reference toFIG. 7.

FIG. 7is an enlarged vertical cross-sectional view illustrating an example of a structure of the nozzle substrate31according to the third illustrative embodiment. In the third illustrative embodiment, a bulge45is formed on the surface31aof the nozzle substrate31toward the direction of ejection of the droplets around the nozzle4on the nozzle substrate31. A part of the bulge45is smoothly recessed to form the circumferential portion43around the nozzle4.

Although not shown inFIG. 7for ease of illustration, the liquid-repellent film32and the base film33are formed on the nozzle substrate31in a manner similar to the first illustrative embodiment.

In the third illustrative embodiment, an amount of polishing of the surface31aof the nozzle substrate31is controlled in the method for manufacturing the nozzle plate3described above in the second illustrative embodiment.

As a result, the wiper51securely contacts the circumferential portion43around the nozzle4even in a case in which the nozzle plate3is bent.

Specifically, during the manufacture or assembly of the liquid ejection head411, the nozzle plate3may be bent. Consequently, the bent nozzle plate3hinders secure contact between the surface of the nozzle plate3and the wiper51during the wiping, causing irregular wiping of the nozzle plate3. The irregular wiping around the nozzle4causes adherence of liquid around the nozzle4, resulting in irregular ejection of droplets from the nozzle4.

To solve these problems, in the third illustrative embodiment, the bulge45is provided around the nozzle4as illustrated inFIG. 7. Accordingly, the wiper51securely contacts the portion around the nozzle4during the wiping. A portion from the bulge45to the nozzle4is smoothly recessed to form the circumferential portion43. As a result, the load of wiping is reduced at the portion around the nozzle4, thereby increasing durability of the liquid-repellent film32around the nozzle4.

A description is now given of an example of a configuration and operation of the image forming apparatus401including the liquid ejection head411according to the foregoing illustrative embodiments, with reference toFIG. 8.FIG. 8is a schematic view illustrating an example of a configuration of a mechanical portion of the image forming apparatus401.

The image forming apparatus401is a line-type inkjet recording device and includes an image forming part402and a sheet tray404disposed in a lower part of the image forming apparatus401. The sheet tray404accommodates a stack of multiple sheets403.

The image forming part402forms images on the sheets403fed from the sheet tray404while the sheets403are being conveyed by a conveyance mechanism405. Thereafter, the sheets403having the images thereon are discharged from the image forming apparatus401to a discharge tray406provided to a lateral side of the image forming apparatus401.

The image forming apparatus401further includes a duplex unit407detachably attachable to the image forming apparatus401. During duplex image formation, the sheet403having the image on a front side thereof is conveyed backward by the conveyance mechanism405to the duplex unit407. The duplex unit407reverses and conveys the sheet403to the conveyance mechanism405such that an image is formed on a back side of the sheet403by the image forming part402. The sheet403having the images on both sides thereof is then discharged to the discharge tray406.

The image forming part402includes recording heads411k,411c,411m, and411y, each constituted of the full-line type liquid ejection head411according to the foregoing illustrative embodiments (hereinafter also collectively referred to as recording heads411). Each of the recording heads411ejects ink droplets of a specific color, that is, black (k), cyan (c), magenta (m), or yellow (y).

Each recording head411is attached to a head holder413such that the nozzle face of each recording head411having nozzle arrays, each constituted of the multiple nozzles4, faces downward. It is to be noted that, examples of the full-line type liquid ejection head include a configuration in which a single liquid ejection head is used to form a single line of an image, and a configuration in which multiple liquid ejection heads are arranged in a zigzag pattern to form a single line of an image.

Maintenance/recovery mechanisms412k,412c,412m, and412y(hereinafter collectively referred to as maintenance/recovery mechanisms412) that maintain the performance of the recording heads411are provided for the respective recording heads411.

During maintenance of the recording heads411such as purging and wiping, the maintenance/recovery mechanism412and the corresponding recording head411are moved relative to each other, so that a capping member and so forth included in each maintenance/recovery mechanism412face the nozzle face of the recording head411.

Although the recording heads411k,411c,411m, and411yare disposed, in that order, from upstream to downstream in a direction of conveyance of the sheet403in the example illustrated inFIG. 8, the arrangement of the recording heads411and the number of colors used are not limited thereto.

In addition, each recording head411may be formed either individually or together with a liquid cartridge, which supplies liquid to the recording head411, as a single integrated unit.

A sheet feed roller421and a separation pad, not shown, separate the sheets403in the sheet tray404one by one to feed each sheet403between a conveyance belt433of the conveyance mechanism405and a registration roller425along a first guide surface423aof a guide member423. Thereafter, the sheet403is conveyed to the conveyance belt433via a guide member426at a predetermined timing.

The guide member423also has a second guide surface423bthat guides the sheet403conveyed from the duplex unit407. The image forming apparatus401further includes a guide member427that guides the sheet403returned from the conveyance mechanism405to the duplex unit407during duplex image formation.

The conveyance mechanism405includes the endless conveyance belt433wound around a drive roller, that is, a conveyance roller431, and a driven roller432, a charging roller434that charges the conveyance belt433, a platen member435that flattens the conveyance belt433at a portion opposite the image forming part402, a pressing roller436that presses the sheet403conveyed by the conveyance belt433against the conveyance roller431, and a cleaning roller including a porous body, not shown, that removes liquid such as ink from the conveyance belt433.

A discharge roller438and a spur439, each of which discharges the sheet403having the image thereon to the discharge tray406, are provided downstream from the conveyance mechanism405.

The conveyance belt433rotated counterclockwise inFIG. 8is contacted and charged by the charging roller434, to which a high voltage is applied. As a result, the sheet403conveyed to the conveyance belt433thus charged is electrostatically attracted to the conveyance belt433. A curl and unevenness in the sheet403, which is strongly attracted to the conveyance belt433, are corrected to give a flatness to the sheet403.

The recording heads411eject the droplets onto the sheet403while the sheet403is moved as the conveyance belt433rotates. As a result, an image is formed on the sheet403. Thereafter, the sheet403having the image thereon is discharged to the discharge tray406by the discharge roller438.

Thus, the image forming apparatus401including the liquid ejection heads411according to the foregoing illustrative embodiments can securely provide higher-quality images at higher speed.

The foregoing illustrative embodiments are applicable to either serial-type image forming apparatuses or to the line-type image forming apparatuses.

The number of constituent elements and their locations, shapes, and so forth are not limited to any of the structure for performing the methodology illustrated in the drawings.