JPH05338149A - Ink jet head - Google Patents

Abstract

(57) [Abstract] [Purpose] For a drop-on-demand type ink jet head, an object thereof is to miniaturize a piezoelectric element so that ink mist and dot chipping do not occur and to manufacture at low cost. And A first substrate 1 in which a pressure chamber 3 and an ink supply path 4 are recessed from an inner surface, and a nozzle hole 7 for closely contacting the inner surface of the first substrate 1 and ejecting ink droplets.
The outer surface of the first substrate 1 for vibrating the outer wall of the pressure chamber 3 and the second substrate 2 in which the holes are formed to apply the discharge pressure to the ink liquid in the pressure chamber 3. And a piezoelectric element 8 disposed along the depth of the pressure chamber 3 is d [m
m], where the area of the piezoelectric element 8 is S [mm ² ],
It is configured so that 0.025 ≦ d ≦ S / 10 + 0.025 holds.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drop-on-demand type ink jet head for recording by applying an ejection pressure to an ink liquid in a pressure chamber and ejecting it as an ink droplet from a nozzle hole.

In this type of ink jet head, in order to maintain good recording quality due to ink droplets, it is necessary to prevent the occurrence of ink mist and the lack of dots during recording.

[0003]

2. Description of the Related Art FIGS. 12 and 13 show a conventional drop-on-demand type ink jet head.
2 is a plan sectional view, and FIG. 13 is a side sectional view.

In this structure, the energy of the strain of the piezoelectric element 91 generated in the pressure chamber 92 formed immediately below the piezoelectric element 91 causes ink droplets to be ejected from the nozzle holes 93 and fly to adhere to the recording paper. Then, the recording is performed.

[0005]

In order to manufacture an ink jet head at low cost, it is necessary to form a large number of substrates from one substrate material. For that purpose, a piezoelectric element that occupies the main part of the ink jet head is required. It is effective to make it small.

However, in the conventional ink jet head as described above, the piezoelectric element 91 generally has an area of 5
Since it is formed to have a size of about 10 mm ² and occupies a considerably large space, it is not possible to form a large number of substrates from one substrate material.

Therefore, if the area of the piezoelectric element is reduced to about 1.5 mm ² or less, a large number of substrates can be formed from one substrate material, and the manufacturing cost of the ink jet head can be considerably reduced. ..

However, if the piezoelectric element is made smaller, the pressure chamber becomes smaller and shorter accordingly. As a result, the distance between the nozzle hole and the pressure chamber is shortened, the fluid resistance is reduced, and the vibration in the head after ejecting the ink droplet is less likely to be attenuated. Then, due to the vibration that is not attenuated, fine ink droplets are ejected in the form of mist.

Further, when the piezoelectric element is made small, its vibration frequency becomes significantly high, and accordingly, it is necessary to cause the nozzle meniscus to move in response to this high frequency. Otherwise, dot missing will occur during recording. However, how far the movement of the ink surface can follow such high frequency vibration,
So far it has not been clarified.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an ink jet head which can be manufactured at a low cost by miniaturizing a piezoelectric element so that ink mist and dot chipping will not occur.

[0011]

In order to achieve the above object, the ink jet head of the present invention, as shown in FIG. 1 for explaining an embodiment, applies a discharge pressure to an ink liquid contained therein. Pressure chamber 3 for giving and the above pressure chamber 3
An ink supply path 4 for supplying an ink liquid to the first substrate 1 and a nozzle for ejecting ink droplets, which are in close contact with the first substrate 1 and the inner surface of the first substrate 1. A second substrate 2 having a hole 7 and the pressure chamber 3
A piezoelectric element 8 arranged along the outer surface side of the first substrate 1 for vibrating an outer wall portion of the first substrate 1 to apply a discharge pressure to the ink liquid in the pressure chamber 3. When the depth of 3 is d [mm] and the area of the piezoelectric element 8 is S [mm ² ], 0.025 ≦ d ≦ S / 10 + 0.025 is formed.

Further, the ink jet head of the present invention is
A first substrate 1 in which a pressure chamber 3 for applying a discharge pressure to the ink liquid contained therein and an ink supply passage 4 for supplying the ink liquid to the pressure chamber 3 are formed by recessing from the inner surface; The second substrate 2 which is in close contact with the inner surface of the first substrate 1 and has a nozzle hole 7 for ejecting ink droplets, and the outer wall of the pressure chamber 3 are vibrated. In order to apply a discharge pressure to the ink liquid in the pressure chamber 3, the first
And a piezoelectric element 8 arranged along the outer surface side of the substrate 1, and when the length of the nozzle hole 7 is L and the diameter thereof is D, 3 ≦ L / D ≦ 10 is satisfied. The nozzle hole 7
Is formed.

The piezoelectric element 8 has an area of 1.5 mm.
The pressure chamber 3 and the nozzle holes 7 are formed in large numbers in the first and second substrates 1 and ² with a size not exceeding ² .

[0014]

In order to suppress the generation of ink mist, it is considered effective to increase the fluid resistance. For that purpose, the ink viscosity should be increased or the cross-sectional area of the pressure chamber 3 should be decreased. ..

However, as the ink viscosity increases, the fixing time becomes longer, and moreover, the amount of water in the ink decreases, and a large amount of a solvent that is difficult to evaporate remains on the recording paper. As a result, the solvent moves along the fibers of the recording paper, and the shape of the recording dots deteriorates, leading to deterioration in printing quality, which is not a good method.

However, the cross-sectional area of the pressure chamber 3 can be reduced by making the depth of the pressure chamber 3 shallow, and the depth d of the pressure chamber 3 is 0.025 with respect to the area S of the piezoelectric element 8.
By setting ≦ d ≦ S / 10 + 0.025, ink droplets can be ejected without the occurrence of ink mist.

The ink jet head normally travels at a speed of about 0.5 m / s, and in order to suppress the influence of the surrounding wind, the ejection speed of the ink droplets should be one order lower than the head travel speed. It should be high.

That is, the ejection speed of the ink droplet is 5 m /
s or more is required, and in consideration of variations in characteristics between nozzles, speed fluctuations when the driving frequency is changed, and the like, it is possible for the head to stably eject ink droplets at 10 m / s, which is twice that. Is required.

If the ratio of the length L of the nozzle hole 7 to the diameter D is set to 3 ≦ L / D ≦ 10, an appropriate fluid resistance is generated, and the movement of the ink liquid surface causes the piezoelectric element 8 to move at a high frequency. Follows the vibration of and does not cause dot missing.

[0020]

Embodiments will be described with reference to the drawings. FIG. 1 is a perspective view showing a part of an inkjet head cut away, and FIG.
FIG.

The ink jet head is formed on first and second substrates 1 and 2 made of glass. The first substrate 1 has a thickness of, for example, 0.15 mm, a pressure chamber 3 for applying a discharge pressure to the ink liquid contained therein, and an ink supply path for supplying the ink liquid to the pressure chamber 3. Four
And are recessed from the inner surface. The depth d of the pressure chamber 3 is 0.05 mm.

The ink liquid is supplied from an ink cartridge (not shown) to the ink supply path 4 through the connecting pipe 5. The ink liquid has a viscosity of 2 centipoise (c
The liquid of P) is used.

The second substrate 2 is intimately bonded to the inner surface of the first substrate 1, that is, the surface on the side where the pressure chamber 3 and the like are recessed, and is a nozzle for ejecting ink droplets. The hole 7 is formed so as to penetrate the pressure chamber 3 at a position facing the tip portion of the pressure chamber 3. The nozzle hole 7 has a circular cross section,
The diameter D is 0.05 mm and the length L is 0.05 to 0.2 mm
Is.

The piezoelectric element 8 is provided along the outer surface of the first substrate 1.
When the voltage is applied to the piezoelectric element 8, the outer wall of the pressure chamber 3 vibrates, and a discharge pressure is applied to the ink liquid in the pressure chamber 3.

The piezoelectric element 8 is rectangular and its area is S
(Mm ² ) The pressure chamber 3 also has a shape along the piezoelectric element 8. However, so that the ink liquid flows smoothly,
Since the front and rear ends of the pressure chamber 3 are formed obliquely, the pressure chamber 3 is formed in a hexagonal shape as a whole. Reference numeral 9 is a circuit board on which a drive circuit for applying a voltage to the piezoelectric element 8 is formed.

The ink jet head is a multi-nozzle type in which a large number of nozzle holes 7 are arranged, and as shown in FIG. 3, the pressure chamber 3, the ink supply path 4 and the nozzle holes 7 are provided.
Are formed on one set of substrates 1 and 2 and communicated with the thick common ink supply path 6.

Next, an example of a method for manufacturing this ink jet head will be described. First, as shown in FIG. 4, first and second substrates 1 and 2 in which a pressure chamber 3, an ink supply path 4, a nozzle hole 7 and the like are formed by etching.
Is made of a photosensitive glass material. The nozzle holes 7 may be manufactured by an electroforming method or the like, and stainless steel or the like may be used as the material of the substrates 1 and 2.

Next, as shown in FIG. 5, the first and second
Substrates 1 and 2 are faced to each other and closely bonded. An anaerobic adhesive or the like can be used as the adhesive. Then, a silver paste is applied to the back surface of the first substrate 1 and baked at 160 ° C. for 1 hour, for example. This makes electrode 1
0 is formed. If stainless steel is used as the material of the first substrate 1, this electrode 10 is unnecessary.

Then, as shown in FIG. 6, a large piezoelectric element 8 of, for example, 15 × 10 mm is dried and hardened by an epoxy adhesive at, for example, 80 ° C. for 3 hours to be bonded, and then a dicing saw. The piezoelectric element 8 by
Cut into a predetermined size (1.5 mm ² or less) according to the position of the pressure chamber 3. Then, as shown in FIG.
The connection tube 5 is attached to the outer surface side of the substrate 1 and is connected to an ink cartridge (not shown).

Finally, as shown in FIG. 1, each piezoelectric element 8 is connected to the circuit board 9 on which the drive circuit for the piezoelectric element 8 is formed. In this way, the inkjet head is completed.

Next, the cross-sectional area of the pressure chamber 3 was changed by changing the depth d of the pressure chamber 3 and the relationship with the generation of ink mist was observed by experiments. The piezoelectric element is
By using a rectangular shape with a length of 1 mm and changing the width, the area S is changed in 0.5 mm ² units in the range of 0.5 to 2.0 mm ² , and the depth d of the pressure chamber 3 is 0.05. The value was changed by 0.05 mm in the range of up to 0.2 mm. The nozzle hole 7
Has a length L of 0.2 mm.

FIG. 8 shows the result of the experiment. In the figure, the mark ◯ shows the case where the ink droplets fly stably, and the mark X shows the case where the flying state of the ink droplets is unstable and a mist is generated. Shows.

As is clear from FIG. 8, as the depth d of the pressure chamber 3 is made deeper, the flying state of the ink droplet becomes unstable and the generation of mist becomes remarkable. Further, as the piezoelectric element 8 is larger, unstable flight occurs only when the depth d of the pressure chamber 3 is deep. That is, when the pressure chamber 3 is deep and the conduit resistance to the ink liquid is small, the vibration of the pressure chamber 3 generated by the piezoelectric element 8 is not attenuated and becomes unstable.

From these results, as shown by the straight line in FIG. 8, ink mist does not occur within the range of d ≦ S / 10 + 0.025.

However, d is 0.0 because of manufacturing limitations.
Since it is desirable that the distance is 25 mm or more, 0.025 ≦ d ≦ S / 10 + 0.025 should be satisfied after all.

Next, it was confirmed by an experiment how the ejection velocity v of the ink droplet changes by changing the dimension of the aspect ratio L / D of the nozzle hole 7. The diameter D of the nozzle hole 7 is 0.
The length L of the nozzle hole 7 was changed from 0.05 mm to 0.5 mm while keeping the value constant at 05 mm. The piezoelectric element 8 used has an area of 1.5 mm ² or less.

FIG. 9 shows the result of the experiment, and in order to make the ink drop velocity v which is guaranteed that the nozzle meniscus moves in response to the high frequency of the ink liquid to be 10 m / s or more, , 3 ≦ L / D ≦ 10.

The specific structure and manufacturing method of the ink jet head of the present invention are not limited to the above-mentioned embodiment, and for example, the entire arrangement is as shown in FIG. 10 or FIG. Various arrangements can be made on the substrates 1 and 2.

[0039]

According to the ink jet head of the present invention, even if the piezoelectric element is miniaturized, it is possible to prevent ink mist, dot dropout, etc. from occurring, and the piezoelectric element is miniaturized to, for example, 1.5 mm ² or less. In addition, it has an excellent effect that the inkjet head can be manufactured at a very low cost.

[Brief description of drawings]

FIG. 1 is a perspective view showing a cutaway part of an embodiment.

FIG. 2 is a side sectional view of an example.

FIG. 3 is an overall layout diagram of an embodiment.

FIG. 4 is a side sectional view showing a manufacturing process of an example.

FIG. 5 is a side sectional view showing a manufacturing process of an example.

FIG. 6 is a side sectional view showing a manufacturing process of an example.

FIG. 7 is a side sectional view showing a manufacturing process of an example.

FIG. 8 is a diagram showing an experimental result of an example.

FIG. 9 is a diagram showing an experimental result of an example.

FIG. 10 is an overall layout view of another embodiment.

FIG. 11 is an overall layout view of another embodiment.

FIG. 12 is a plan sectional view of a conventional example.

FIG. 13 is a side sectional view of a conventional example.

[Explanation of symbols]

 1 First Substrate 2 Second Substrate 3 Pressure Chamber 4 Ink Supply Channel 7 Nozzle Hole 8 Piezoelectric Element

Claims (4)

[Claims] 1. A pressure chamber (3) for applying a discharge pressure to the ink liquid contained therein and an ink supply passage (4) for supplying the ink liquid to the pressure chamber (3) are provided from the inner surface. A recessed first substrate (1) and a second substrate closely attached to the inner surface of the first substrate (1) and having a nozzle hole (7) for ejecting an ink droplet. (2) and the first wall for vibrating the outer wall of the pressure chamber (3) to apply a discharge pressure to the ink liquid in the pressure chamber (3).
And a piezoelectric element (8) arranged along the outer surface side of the substrate (1), the depth of the pressure chamber (3) is d [mm], and the area of the piezoelectric element (8) is S [ mm ² ], the ink jet head is characterized in that 0.025 ≦ d ≦ S / 10 + 0.025. 2. A pressure chamber (3) for applying a discharge pressure to the ink liquid contained inside and an ink supply passage (4) for supplying the ink liquid to the pressure chamber (3) are provided from the inner surface. A recessed first substrate (1) and a second substrate closely attached to the inner surface of the first substrate (1) and having a nozzle hole (7) for ejecting an ink droplet. (2) and the first wall for vibrating the outer wall of the pressure chamber (3) to apply a discharge pressure to the ink liquid in the pressure chamber (3).
And a piezoelectric element (8) arranged along the outer surface side of the substrate (1), and the length of the nozzle hole (7) is L and the diameter thereof is D, 3 ≦ L / D ≦ An ink jet head characterized in that the nozzle hole (7) is formed so that 10 is satisfied. 3. The piezoelectric element (8) has an area of 1.5 mm ²
The inkjet head according to claim 1 or 2, wherein the inkjet head is formed in a size not exceeding the above. 4. The ink jet head according to claim 1, 2 or 3, wherein a large number of the pressure chambers (3) and the nozzle holes (7) are formed in the first and second substrates (1, 2). ..