Droplet discharging head and droplet discharging device

A droplet discharging head includes: a nozzle portion that discharges a liquid material; a liquid chamber that is in communication with the nozzle portion and supplies the liquid material to the nozzle portion in receiving a pressure from outside; and a reservoir that is in communication with a plurality of the liquid chamber through a plurality of ink supply passages and supplies the liquid material fed from outside via a material inlet to the plurality of liquid chambers. In the droplet discharging head, assuming that: a direction running from the material inlet toward the liquid chamber is a first direction; a direction perpendicular to the first direction is a second direction; a straight line passing through the material inlet in the first direction is a first reference line; and a straight line passing through the material inlet in the second direction is a second reference line, the longer a distance from the second reference line is for a liquid chamber, the shorter a distance from the first reference line is for the liquid chamber.

BACKGROUND

1. Field of the Invention

Several aspects of the present invention relate to a droplet discharging head and a droplet discharging device.

2. Related Art

It is required that droplet discharging heads employed in droplet discharging devices including inkjet recorders discharges more minute droplets.

In order to have an discharged droplet more minute, it is necessary to reduce the period of vibration in the cavity that supplies a liquid material to the nozzle in receiving pressures from outside through oscillation. In order, in turn, to reduce the period of vibration in the cavity, it is required that the entire flow path of a liquid material be made smaller. Such flow path includes the nozzle, the cavity and the reservoir that stores a liquid material to be supplied to the cavity.

However, if the reservoir is made smaller, resistance increases in the reservoir against the flow of the liquid material, thereby reducing the efficiency in supply of the liquid material to the cavity. This may cause some nozzles to eject droplets without sufficient supply of the material.

JP-A-2003-211644 is an example of related art, disclosing a technology that concerns supply of ink in inkjet recorders.

SUMMARY

An advantage of the invention is to reduce variation in supply of a material to each nozzle in a droplet discharging head.

A droplet discharging head according to a first aspect of the invention includes: a nozzle portion that discharges a liquid material; a liquid chamber that is in communication with the nozzle portion and supplies the liquid material to the nozzle portion in receiving pressures from outside; and a reservoir that is in communication with a plurality of the liquid chamber through a plurality of ink supply passages and supplies the liquid material, having been supplied from outside via a material inlet, to the plurality of liquid chambers. In the droplet discharging head, assuming that: a direction running from the material inlet toward the liquid chamber is a first direction; a direction running perpendicular to the first direction is a second direction; a straight line passing through the material inlet in the first direction is a first reference line; and a straight line passing through the material inlet in the second direction is a second reference line, the longer the distance from the second reference line is for a liquid chamber, the shorter the distance from the first reference line is for the liquid chamber.

A droplet discharging head according to a second aspect of the invention includes: a reservoir having a material inlet; a plurality of ink supply passages connected to the reservoir; a plurality of liquid chambers connected respectively to each of the plurality of ink supply passages; and a plurality of nozzle portions connected respectively to each of the plurality of liquid chambers. In the droplet discharging head, a normal line made from the outer circumference of the reservoir to the connection between a first of the plurality of liquid chambers and a first of the plurality of ink supply passages is shorter in length than the first ink supply passage.

A droplet discharging head according to a third aspect of the invention includes: a reservoir having a material inlet; a plurality of ink supply passages connected to the reservoir; a plurality of liquid chambers connected respectively to each of the plurality of ink supply passages; and a plurality of nozzle portions connected respectively to each of the plurality of liquid chambers. In the droplet discharging head, a normal line made from the outer circumference of the reservoir to the connection between a first of the plurality of liquid chambers and a first of the plurality of ink supply passages is different in length from a normal line made from the outer circumference of the reservoir to the connection between a second of the plurality of liquid chambers and a second of the plurality of ink supply passages.

This alleviates the difference in time for the liquid material to reach each of the liquid chambers and realizes a nearly uniform efficiency in supply of the liquid material to each liquid chamber. Consequently variation in supply of the material to each nozzle can be reduced.

In the above droplet discharging head, it is preferable that the normal line made from the outer circumference of the reservoir to the connection between the first of the plurality of liquid chambers and the first of the plurality of ink supply passages be shorter in length than the first ink supply passage.

In the above droplet discharging head, it is preferable that the plurality of ink supply passages are each different in length.

In the above droplet discharging head, it is preferable that: the reservoir have a plurality of connections connecting to the plurality of supply passages; the reservoir have a side surface that is at least partly a curved face; and the plurality of connections be formed on the curved face.

In the above droplet discharging head, it is preferable that: the reservoir have a plurality of connections connecting to the plurality of supply passages; the reservoir have a polygonal bottom face; the side surface of the reservoir be composed of a plurality of faces; and a first of the plurality of connections be formed on one of the plurality of faces while a second of the plurality of connection be formed on another of the plurality of faces.

It is preferable that the above droplet discharging head include a plurality of the reservoir.

In the above droplet discharging head, it is preferable that the plurality of reservoirs be disposed to form a zigzag shape. This allows a highly dense disposition of the reservoirs and the nozzles.

A droplet discharging device according to a fourth aspect of the invention includes the above droplet discharging head.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Embodiments of the invention will be described.

In the embodiments of the present invention, “interval” refers to “length” and is used in a wider sense than “distance” that is used to represent the length of a line segment connecting two points as orthographically projected on a plumb line.

First Embodiment

As shown inFIGS. 1A and 1B, a droplet discharging head10according to a first embodiment of the invention includes a nozzle plate11, a flow path substrate12, a diaphragm13, piezoelectric elements14, support substrates15, a head case16and electrodes19. Nozzle portions100are formed in the nozzle plate11and reservoirs18, cavities (liquid chambers)103and ink supply passages102communicating the reservoirs18and the cavities are formed between the flow path substrate12and the diaphragm13.

The structure of the droplet discharging head is not limited to one described above but may also be one in which the nozzle plate11and the flow path substrate12are integrally formed if the structure allows application of the relationship between the reservoirs18, the cavities103and the ink supply passages102to be described below. Also, the nozzle portions100may be provided on the borderline between the flow path substrate12and the diaphragm13.

The droplet discharging head10is installed in a head unit portion (represented by A) of a droplet discharging device shown, for example, inFIG. 2. Droplet discharging devices include film forming devices employed for industrial use, in addition to image forming devices. A film forming device refers to a device that forms a functional film such as a color filter or a metal wiring through discharging of a liquid material that includes an organic substance such as a high-polymer material or an inorganic substance such as metallic particles, onto a substrate.

Having been taken into the droplet discharging head10from an external supply unit via ink inlets17, a liquid material fills the space that forms the reservoirs18, the cavities103and the nozzle portions100. Subsequently, electric signals transmitted from the electrodes19to the piezoelectric elements14generate a flexure in the piezoelectric elements14and the diaphragm13, increasing the pressure inside the cavities103for a moment, thereby causing droplets to be discharged from the nozzle portions100.

InFIGS. 3A and 3B, a plurality of cavities103are connected to one reservoir18through a plurality of ink supply passages101. The droplet discharging head10includes at least one such reservoir18thus connected with a plurality of cavities103.

The material inlet17is located on a circumferential edge part on the farther side of the reservoir18from the cavities103. This is for facilitating escape of bubbles in the reservoir18.

In the first embodiment, the reservoir18has an oval shape and the cavities103are each connected to the reservoir along an arc of the oval.

As shown inFIG. 3A, the longer the interval between a cavity103and the material inlet17is in Direction1(a first direction), the shorter the interval therebetween is in Direction2(a second direction). In other words, the endmost cavities103are both located with a longer interval from the material inlet17in Direction2, but with a shorter interval therefrom in Direction1, as compared to the cavity103in the center.

Namely, assuming that a straight line passing through the material inlet17in the first direction is a first reference line and a straight line passing through the material inlet17in the second direction is a second reference line, the following relationship is established for a first cavity103aand a second cavity103bof the plurality of cavities103. In the case where a first distance in the first direction (L1a), which is the distance between the second reference line and the first cavity103a, is larger than a second distance in the first direction (L1b), which is the distance between the second reference line and the second cavity103b, a first distance in the second direction (L2a), which is the distance between the first reference line and the first cavity103a, is smaller than a second distance in the second direction (L2b), which is the distance between the first reference line and the second cavity103b.

Furthermore, the positional relationship between the plurality of cavities103may also be described as follows.

Namely, inFIG. 3B, a first normal line made from the outer circumference of the reservoir18to the connection between the first cavity103aand a first ink supply passage101ais shorter in length than the first ink supply passage101a. Also, a second normal line made from the outer circumference of the reservoir18to the connection between the second cavity103band a second ink supply passage101bis shorter in length than the first normal line. That means, even if the first ink supply passage101aand the second ink supply passage101bare equal in length, the first normal line and the second normal line are different in length.

A normal line here refers to a straight line perpendicular to a line that is tangent to the outer circumference of the reservoir18.

Provided here that the first ink supply passage101aand the first normal line are equal in length and the second ink supply passage101band the second normal line are equal in length, the difference between the lengths of the ink supply passages surface in the form of a difference between their capabilities to supply the liquid material to the respective cavities. A problem of this kind, as well, can be resolved by the features of the droplet discharging head shown inFIG. 3B.

In contrast, in a comparative example shown inFIG. 4, the reservoir18has a semicircular shape and all the cavities103are connected to the side of the chord in its shape.

Therefore, the cavities103are located with an equal interval from the material inlet17in Direction1(the first direction), irrespective of their interval from the material inlet17in Direction2(the second direction) perpendicular to Direction1that runs from the material inlet17toward the cavities103. Namely, the endmost cavities103are both located with a longer interval from the material inlet17in Direction2as compared to the central cavity103, but with respect to Direction1all the cavities103are located at an equal interval from the material inlet17.

Supply of ink into the reservoir18via the material inlet17generates a straight flow of ink, flowing from the material inlet17toward the chord to which the cavities103are connected, as well as flows of ink branching from the straight flow.FIG. 5Aindicates the major flows of ink in the reservoir of the droplet discharging head according to the comparative example, andFIG. 5Bindicates the major flows of ink in the reservoir18of the droplet discharging head10according to the first embodiment, respectively by arrows.

As shown inFIG. 5A, in the comparative example, the nearer a cavity103is to the respective ends of the group of cavities, i.e. the longer the interval in Direction2from the material inlet17is for the cavity103, the longer it takes for the ink to reach the cavity103and, thus, the worse the supply efficiency is for the cavity103. Consequently, cavities103near the respective ends of the group of cavities may not be fed with sufficient ink at times.

In the droplet discharging head10according to the embodiment of the invention, as shown inFIG. 5B, the longer the interval in Direction2from the material inlet17is for a cavity103, the shorter the interval in Direction1from the material inlet17is for the cavity103. Thus, the difference in time it takes for the ink to reach each of the cavities103is reduced and the supply efficiency is maintained nearly uniform.

The reservoir18according to the first embodiment can be formed by electroforming using a metal such as nickel, cobalt or manganese or an alloy of those metals. Alternatively, it may be integrally formed together with the cavity103by implementing photolithography onto a silicon substrate.

As shown inFIGS. 6A through 6E, the reservoir18may be of any shape if it allows the ink to reach each of the cavities103with little time difference. For example, the shape may be circular as shown inFIG. 6Aor polygonal as shown inFIGS. 6B and 6C. Or, it may be curved on the side to which the cavities are connected, as shown inFIGS. 6D and 6E.

As described above, in the droplet discharging head10according to the first embodiment, the longer the interval from the material inlet17is for a cavity103in Direction2perpendicular to Direction1, the shorter the interval from the material inlet17is for the cavity in Direction1.

Consequently, the difference in time for the ink to reach each of the cavities103is reduced and the efficiency in supply of ink is kept nearly uniform for each of the cavities103. This reduces variation in the supply of material to each nozzle.

In particular, in order to make discharged droplets more minute, it is necessary to reduce the size of the entire flow path of ink, including the reservoir18. However, reduction in the size of the reservoir18increases resistance against the flow of ink in the reservoir18, thereby deteriorating the efficiency in supply of ink to the cavities103. In the meantime, application of the droplet discharging head10according to the first embodiment improves the efficiency in supply of ink to each nozzle.

Second Embodiment

In a second embodiment, as shown inFIGS. 7A and 7B, a plurality of reservoirs18are disposed to form a zigzag shape. Since the reservoirs18are disposed in such a manner that they back against each other's material inlets17, the cavities103are disposed on both the right and the left sides of the reservoirs18.

In the second embodiment, as in the first embodiment, the longer the interval from the material inlet17is for a cavity103in Direction2perpendicular to Direction1that runs from the material inlet17toward the cavities103, the shorter the interval from the material inlet17is for the cavity103in Direction1.

In the same way as in the first embodiment, the droplet discharging head10according to the second embodiment of the invention allows the efficiency in supply of ink to each of the cavities103to be kept nearly uniform, thereby reducing variation in the supply of a material to each nozzle. In addition, the reservoirs18can be disposed with a high density since they are disposed to form a zigzag shape in backing against each other's material inlets17.

The entire disclosure of Japanese Patent Application Nos: 2006-064777, filed Mar. 9, 2006 is expressly incorporated by reference herein.