JP5007766B2 - Inkjet head - Google Patents

Description

The present invention relates to a face-eject type ink jet head in which the flow lines in individual ink chambers and the angles of ink droplets ejected from ink nozzles are substantially perpendicular.

Conventionally, many ink jet heads have been proposed as represented by JP-B 53-12138 and JP-B 53-45698. The hole shape of the nozzle portion of these ink jet heads was a truncated cone or a cylinder as shown in FIG.

Japanese Patent Publication No.53-12138 Japanese Examined Patent Publication No. 53-45698

However, in these embodiments, for manufacturing reasons, an individual ink chamber is formed by anisotropic etching in silicon having a crystal plane orientation (110), and a nozzle portion is provided at a position facing an inclined surface constituting the individual ink chamber. When arranged, since the streamline reaches the vicinity of the nozzle portion along the inclined surface constituting the individual ink chamber, the streamline cannot be made perpendicular to the nozzle surface in the nozzle portion. As a result, there is a problem that the ink droplets are not ejected straight in the vertical direction with respect to the nozzle surface, and the desired print quality cannot be satisfied.

On the other hand, an individual ink chamber is created by anisotropic etching in silicon having a crystal plane orientation (110),
If the nozzle part is placed at a position that does not face the inclined surface that constitutes the individual ink chamber, bubbles flowing from the ink tank or the like will remain at the position of the tip of the inclined surface. I could not. Therefore, there is a problem that a sufficient pressure necessary for discharging in the individual ink chamber cannot be generated, and a desired print quality cannot be satisfied.

On the other hand, when the length of the nozzle portion is increased in order to discharge ink droplets straightly, the meniscus return speed decreases due to an increase in flow path resistance at the nozzle portion,
There is also a problem that the response frequency of the inkjet head is not improved.

In view of this point, an object of the present invention is to devise the structure of the nozzle portion to realize an ink jet head with good print quality and high response speed.

In order to solve the above-described problems, the present invention includes an ink nozzle, a second nozzle, and an individual ink chamber, and a streamline of the individual ink chamber due to a volume variation of the individual ink chamber is bent at a substantially right angle. An ink jet head that ejects ink droplets from ink nozzles is characterized in that the center of the ink nozzle relative to the center of the second nozzle is positioned relatively to the ink supply side.

The individual ink chamber is formed by anisotropic etching in silicon having a crystal plane orientation (110).

It is sectional drawing of the electrostatic drive type inkjet head to which this invention is applied. FIG. 2 is a partial top view and a partial cross-sectional view for explaining a nozzle portion and an individual ink chamber in FIG. 1. FIG. 2 is a partial cross-sectional view for explaining an ink droplet ejection direction in FIG. 1. It is explanatory drawing for showing another structural example of the nozzle part of FIG. The top view and sectional drawing of the nozzle part of the conventional inkjet recording device.

Hereinafter, an electrostatic drive type ink jet head to which the present invention is applied will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of the electrostatically driven inkjet head of this example. The inkjet head 1 has a three-layer structure in which a silicon nozzle substrate 3 is laminated on the upper side and a glass electrode substrate 4 is laminated on the lower side with a cavity substrate 2 interposed therebetween.

The central cavity substrate 2 is a silicon substrate having a crystal plane orientation (110), and by etching from the surface, a plurality of independent long individual ink chambers 5, one common ink chamber 6, and the common ink Grooves that function as a plurality of ink supply ports 7 that communicate the chambers 6 with the individual ink chambers 5 are formed. These grooves are closed by the nozzle substrate 3, and the portions 5, 6, and 7 are partitioned.

In addition, an ink intake port 12 is formed at a portion defining the lower surface of the common ink chamber 6. Ink is supplied from an external ink tank (not shown) through the ink intake port 12 to the common ink chamber 6, and from here through each ink supply port portion 7 to the independent individual ink chamber 5. The

On the nozzle substrate 3, nozzle portions 11 are formed at positions corresponding to the tip side portions of the individual ink chambers 5, that is, positions opposite to the ink supply port portions 7.
Communicates with the corresponding individual ink chamber 5. On the bottom surface of the individual ink chamber 5, there is formed a thin portion that functions as a diaphragm 51 that can be elastically displaced in the out-of-plane direction (vertical direction in the figure).

On the upper surface of the electrode substrate 4 that is bonded to the cavity substrate 2, a shallow etched recess 41 is formed at a position facing each diaphragm 51. On the bottom surface of the recess 41,
An individual electrode 10 facing the diaphragm 51 is formed. The individual electrode 10 has a segment electrode portion 10a made of ITO and an electrode terminal portion 10b exposed to the outside.

By bonding the electrode substrate 4 to the cavity substrate 2, the diaphragm 51 defining the bottom surface of each individual ink chamber 5 and the segment electrode portion 10a of the individual electrode 10 face each other with a very narrow gap. This gap is sealed with a sealant 60 and is in a sealed state.

A common electrode terminal 22 is formed on the cavity substrate 2, and a driving voltage is applied between the common electrode terminal 22 and each individual electrode 10 by the voltage applying means 21. Since the cavity substrate 2 is conductive, each diaphragm 51 functions as a common electrode.

When the diaphragm 51 is attracted to the individual electrode side by electrostatic force generated by applying a driving voltage between the diaphragm 51 which is a common electrode and the individual electrode 10, the diaphragm 51 is elastically deformed and the segment electrode 10a And is adsorbed to the surface of the segment electrode 10a. As a result, the volume of the individual ink chamber 5 increases and ink flows into the individual ink chamber 5 from the common ink chamber 6 side through the ink supply port 7.

When the electrostatic attraction force is released, the diaphragm 51 is moved to the segment electrode 10 by its elastic return force.
It leaves the surface of a and returns to the initial state. As a result, the volume of the individual ink chamber 5 is rapidly reduced. Due to the ink pressure vibration in the individual ink chamber generated at this time, a part of the ink in the individual ink chamber is ejected from the nozzle unit 11 as an ink droplet.

(Nozzle and individual ink chamber)
2A is a top view mainly showing the nozzle portion 11 in the nozzle substrate 3 and the individual ink chambers 5 in the cavity substrate 2, and FIG. 2B is a partial cross section of the portion cut along the line bb. FIG.

As shown in these drawings, the individual ink chamber 5 is partitioned and formed by a bottom surface 51a, a side wall surface 52, a side wall surface 53, an inclined surface 54, and an inclined surface 55. The bottom surface 51 a and the inclined surface 54 intersect at an entering corner 56, and the inclined surface 54 and the surface of the cavity substrate 2 intersect at an entering corner 57 and an entering corner 58. In single crystal silicon, as is well known, when etching is performed with an alkali such as an aqueous potassium hydroxide solution or hydrazine, anisotropic etching is possible because of a large difference in etching rate depending on crystal planes.

Specifically, since the etching rate of the (111) crystal plane is the lowest, a structure in which the (111) plane remains as a smooth surface with the progress of etching is obtained. Side wall surface 52, side wall surface 53,
The inclined surface 54 and the inclined surface 55 are (111) planes, and the side wall surface 52 and the side wall surface 53 are surfaces perpendicular to the surface of the cavity substrate 2, and the angle Θ 4 of the inclined surface 54 with respect to the cavity substrate 2. The angle Θ5 of the inclined surface 55 with respect to the cavity substrate 2 is 30 °. The angle Θ1 between the entering corner 57 and the side wall surface 52 and the angle Θ2 between the entering corner 56 and the side wall surface 52 are both about 1
The angle Θ3 between the entering corner 58 and the side wall surface 53 is about 109 °.

As shown by the dotted line in FIG. 2A, the entering corner 58 is extended to the side wall surface 52, thereby entering the entering corner 57.
In addition, the entering corner 57 can be eliminated by extending the entering corner 57 to the side wall surface 53.

On the nozzle substrate 3 side, a second nozzle 11b etched in a cylindrical shape is formed in a portion facing the inclined surface 54, and the center of the second nozzle 11b is formed with the entering corner 57 and the entering corner 5.
8, the side wall surface 52, and the side wall surface 53 are at substantially the same distance. The ink nozzle 11a has a cylindrical shape with a diameter smaller than that of the second nozzle, and the center of the ink nozzle 11a is formed at the position where ink is supplied to the center of the second nozzle (the ink supply port 7 side). is there.

Here, the flow of ink will be described with reference to FIG. Due to the elastic displacement of the vibration plate 51, a streamline of arrows as shown in the figure is generated in the ink chamber 5. This streamline becomes a streamline of about 15 ° along the inclined surface 54 (see Θ6 in the figure) and reaches the vicinity of the second nozzle 11b. In order for the ink droplets discharged from the ink nozzle 11a to be discharged straight in the vertical direction with respect to the nozzle surface 3a, the second nozzle 11b and the ink nozzle 11a have a streamline of about 15 ° along the inclined surface. It is necessary to make it perpendicular to the nozzle surface 3a in the same way as the discharge direction. That is, the second nozzle 11b and the ink nozzle 11a need to be 90 ° with respect to the streamline of the individual ink chamber.

FIG. 3 is a partial cross-sectional view centering on the ink nozzle 11a and the second nozzle 11b in FIG. 2B, and the amount of eccentricity is different between the center of the second nozzle 11b and the center of the ink nozzle 11a, respectively. With reference to FIG. 3, the eccentric amount and the ejection direction of the ink droplet 13 will be described.
FIG. 3A shows a case where the center of the ink nozzle 11a and the center of the second nozzle 11b are the same. In this case, the streamline along the inclined surface 54 constituting the individual ink chamber 5 is the second nozzle 11b.
Therefore, the streamlines at the second nozzle 11b and the ink nozzle 11a are as shown in the figure, and cannot be perpendicular to the nozzle surface 3a. Actually, according to the experiments by the present inventors, the diameter of the ink nozzle 11a is 25 μm, the length is 25 μm, and the second nozzle 11b.
The diameter of the nozzle is 66 μm, the length is 55 μm, the center of the second nozzle 11b and the ink nozzle 11a.
In this case, the ink droplets were ejected with an inclination of about 2 ° on the side opposite to the supply port 7 side with respect to the vertical direction of the nozzle surface 3a, as indicated by 13a.

FIG. 3B shows a case where the center of the ink nozzle 11a is decentered by 3 μm toward the supply port 7 with respect to the center of the second nozzle 11b. According to the experiments by the present inventors, for example, the diameter of the ink nozzle 11a is 25 μm, the length is 25 μm, the diameter of the second nozzle 11b is 66 μm, the length is 55 μm, and the ink is in the center of the second nozzle 11b. When the center of the nozzle 11a is decentered by 3 μm toward the supply port 7, the ink droplets appear on the nozzle surface 3 as indicated by 13b in FIG.
It was confirmed that the ink was discharged in the vertical direction a. In this way, the streamlines that reach the vicinity of the second nozzle 11b along the inclined surface 54 that constitutes the individual ink chamber 5 can be made perpendicular to the nozzle surface 3a by the second nozzle 11b and the ink nozzle 11a. did it.

In other words, as described above, the ejection direction of the ink droplet changes depending on the amount of eccentricity between the center of the second nozzle 11b and the center of the ink nozzle 11a, and the center of the ink nozzle 11a with respect to the center of the second nozzle 11b. It was confirmed by experiment that the case where the ink was eccentric 3 μm toward the ink supply port 7 side was suitable.

According to the experiments by the present inventors, for example, the diameter of the ink nozzle 11a is 25 μm and the length is 1.
When the diameter of the second nozzle 11b is 66 μm and the length is 55 μm, even if the center of the second nozzle 11b and the center of the ink nozzle 11a are the same, the ink droplets ejected from the ink nozzle 11a It was confirmed that the liquid was discharged straight in the vertical direction with respect to 3a. However, when the flow path resistance at the nozzle portion increases, the meniscus return speed decreases, and as a result, the response frequency of the inkjet head decreases, which is not suitable as an inkjet head.

According to the experiments by the present inventors, for example, the second nozzle 11b is located at a position facing the diaphragm 51.
When the center of the ink nozzle 11a is the center of the second nozzle 11b, it was confirmed that the ink droplets ejected from the ink nozzle 11a are ejected straight in the vertical direction with respect to the nozzle surface 3a. . However, since the air bubbles flowing in from the ink tank or the like remain in the vicinity of the entrance corner 57 and the entrance corner 58 (see FIG. 2A), the bubbles cannot be removed. As a result, it was not possible to generate a sufficient pressure necessary for discharging in the individual ink chamber, and the desired print quality could not be satisfied.

In the present embodiment, the center of the ink nozzle 11a is decentered by 3 μm toward the ink supply port 7 with respect to the center of the second nozzle 11b. However, the present invention is not limited to this. The length of the second nozzle, the depth of the individual ink chamber, and the like may be selected as appropriate according to the flow path dimensions. Moreover, although the cross-sectional shape of the ink nozzle 11a and the 2nd nozzle 11b was circular, it can select suitably polygons, such as a triangle and a square, and star shape, for example.

(Modification of nozzle part)
FIG. 4 shows another example of the nozzle portion 11. In FIG. 4A, the second nozzle 11b is formed in a truncated cone, and the ink nozzle 11a is formed in a cylindrical shape.

In FIG. 4B, the second nozzle 11b is formed in a truncated cone, and the ink nozzle 11a is formed in a truncated cone.

FIG. 4C is a partial plan view with the nozzle portion 11 as the center, and FIG. 4D is a partial cross-sectional view of the portion cut along the cc cross section. As shown in these drawings, the second nozzle 11b is formed in a quadrangular pyramid, and the ink nozzle 11a is formed in a cylindrical shape.

In addition, the shape of the ink nozzle 11a to be formed, the shape of the second nozzle 11b, the combination of the shapes of the ink nozzle 11a and the second nozzle 11b, and the like have properties that should be appropriately set according to individual inkjet heads. Therefore, the shape of the ink nozzle 11a, the second nozzle 11
The shape of b is not limited to a cylindrical shape, a truncated cone, and a truncated pyramid. For example, a polygonal shape such as a triangle, a hexagonal shape, a prismatic shape such as a star shape, a triangular shape such as a triangular shape, a hexagonal shape, etc. A pyramid such as a polygon or a star can be appropriately selected.

(Other embodiments)
Each of the above examples relates to an electrostatic drive type ink jet head, but the present invention can be similarly applied to a piezoelectric type ink jet head and an ink jet head using thermal energy.

(Effect of the invention)
As described above, in the ink jet head of the present invention, the center of the ink nozzle relative to the center of the second nozzle is formed at a position relatively to the ink supply side. In this way, even if the individual ink chambers are formed in silicon having a crystal plane orientation (110) by anisotropic etching, it is possible to realize an ink jet head with good print quality and high response speed.

1 inkjet head, 2 cavity substrate, 3 nozzle substrate, 4 electrode substrate, 5
Individual ink chamber, 6 common ink chambers, 7 ink supply port, 11 nozzle portion, 11a ink nozzle, 11b second nozzle, 51 diaphragm, 52, 53 side wall surface, 54, 55 inclined surface, 56, 57, 58 corner.

Claims (6)

A first nozzle;
A second nozzle that communicates with the first nozzle and has a shape in which a cross-sectional area of the flow path is larger than a cross-sectional area of the flow path of the first nozzle in a portion communicating with the first nozzle;
An ink chamber communicating with the second nozzle;
An inclined surface that forms part of the ink chamber and is inclined with respect to a central axis of the first nozzle;
An ink supply port located in a direction in which the ink chamber expands when viewed from the inclined surface;
With
The first nozzle is at a position overlapping the inclined surface when viewed from the central axis direction of the first nozzle,
The central axis of the first nozzle is provided at a position shifted from the central axis of the second nozzle toward the ink supply port,
The ink supplied from the ink supply port to the ink chamber is sent to the second nozzle and ejected as ink droplets from the first nozzle. A first nozzle;
A second nozzle that communicates with the first nozzle and has a shape in which a cross-sectional area of the flow path is larger than a cross-sectional area of the flow path of the first nozzle in a portion communicating with the first nozzle;
An ink chamber communicating with the second nozzle;
An inclined surface that forms part of the ink chamber and is inclined with respect to a central axis of the first nozzle;
An ink supply port that communicates with the ink chamber and is positioned in a direction in which ink flows toward the inclined surface;
With
The first nozzle is at a position overlapping the inclined surface when viewed from the central axis direction of the first nozzle,
The central axis of the first nozzle is provided at a position shifted from the central axis of the second nozzle toward the ink supply port,
The ink supplied from the ink supply port to the ink chamber is sent to the second nozzle and ejected as ink droplets from the first nozzle. In claim 1 or 2,
The ink jet head according to claim 1, wherein the first nozzle is formed in a truncated cone shape. In claim 1 or 2,
The inkjet head is characterized in that the first nozzle is formed in a cylindrical shape, and the second nozzle is formed in a truncated cone shape. In claim 1 or 2,
The inkjet head is characterized in that the first nozzle is formed in a truncated cone shape, and the second nozzle is formed in a truncated cone shape larger than the truncated cone shape of the first nozzle. In claim 1 or 2,
The inkjet head is characterized in that the second nozzle is formed in a polygonal shape.

Images