JPH079681A - Ink jet head - Google Patents

Abstract

PURPOSE:To prevent insulation resistance of a piezoelectric substance from deterioration caused by penetration from a liquid chamber and permeation from an external environment in an ink jet head using the piezoelectric substance. CONSTITUTION:A part wherein a part of a thin film member 3 which is visible between a common liquid chamber 5 and a PCB 10 is cut off, and a rear end part of a piezoelectric substance 2 are exposed to the open air, and the exposed part is covered with a case body 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet head, and more particularly, to prevention of deterioration of insulation resistance of a piezoelectric material in an ink jet head of a type that ejects ink droplets by utilizing displacement of the piezoelectric material.

[0002]

2. Description of the Related Art FIG. 6 is a diagram showing a schematic structure of a conventional ink jet head, in which 1 is a substrate, 2 is a piezoelectric body, and 3 is a piezoelectric body.
Is a thin film member (passivation film), 4 is a flow path plate, 5 is an ink flow path, 6 is a common liquid chamber for supplying ink to each ink flow path 5, 7 is a reinforcing plate, 8 is a protection plate, and 9 is a nozzle plate. As is well known, 10 is a nozzle and 11 is an FPC (flexible printed circuit). By applying an electric field to the piezoelectric body 2, the piezoelectric body 2 is displaced in the thickness direction, and this displacement causes the flow path plate 4 to move. Ink flow path 5 provided in
The ink volume is changed and the ink droplets are ejected from the nozzles 10 of the nozzle plate 9.

In the ink jet head as described above, the piezoelectric body 2 is separated from the ink flow path 5 and the common liquid chamber 6 by the passivation film 3, but the piezoelectric body 2 is separated by the passivation film 6 or by the piezoelectric material. Due to the moisture permeation from the rear end portion 2'of the body 2, the piezoelectric body 2 is kept in a high humidity state, and the resistance value of the piezoelectric body 2 decreases. When the resistance value of the piezoelectric body 2 decreases, the prescribed electric field is not applied to the piezoelectric body 2, the displacement amount of the piezoelectric body 2 decreases, and the ink drop velocity becomes slow. Therefore, the ink droplets do not adhere to a predetermined position, which causes print disorder. When the resistance is further reduced, it becomes conductive and injection becomes impossible, and if current continues to be applied in that state, abnormal heat may be generated and an ignition phenomenon may occur. Therefore, it is desired that the piezoelectric body 2 is not in a high humidity state.

In order to solve such a problem, conventionally, a portion where the thin film member (passivation film) 3 is removed is formed in a portion which is not in contact with the ink, and the piezoelectric body 2 is opened to the outside by opening the portion to the outside air. The humidity is adapted to the environment so that the moisture does not stay inside the piezoelectric body and the humidity is constantly replaced with the external environment, and the humidity inside the piezoelectric body is prevented from gradually increasing.

[0005]

In the above-mentioned conventional technique, however, a part of the piezoelectric body is simply opened to the outside air environment. Water droplets adhere to the piezoelectric body of the open part, which causes a failure. Therefore, according to the present invention, water vapor that permeates from the thin film member 3 or the like above the piezoelectric body 2 is efficiently released to the outside without staying inside the piezoelectric body 2, and the piezoelectric body is always kept in a low humidity state. Aims to provide an ink jet head in which the piezoelectric body 2 is also protected from dirt.

[0006]

In order to solve the above problems, the present invention provides (1) a flow channel plate having a plurality of parallel flow channel grooves, and a convex portion corresponding to the flow channel grooves of the flow channel plate. By joining a piezoelectric body having a concave groove for forming, an ink flow path is formed by the flow path groove of the flow path plate and the convex portion of the piezoelectric body, and the piezoelectric body and the ink flow path are formed. In an inkjet head that has a thin film member at an interface and ejects ink in the ink flow path as an ink droplet from a nozzle provided in communication with the ink flow path by utilizing the piezoelectric effect of the piezoelectric body, An upper surface portion and / or a rear end portion of the body having an opening portion for opening the concave groove of the piezoelectric body, and the opening is covered by a casing; and (2) in (1) above,
The casing is integrally formed with a common liquid chamber for supplying an ink liquid to the ink flow path, and further, (3)
In the above (1) or (2), a part of the housing is formed of a member having high moisture permeability.

[0007]

In the ink jet head in which the flow path plate and the piezoelectric body are separated and joined by the thin film member, a part of the portion of the thin film member which is not in contact with the ink is cut off to make it open to the external environment. In order to prevent water vapor from accumulating in the housing, the housing is covered with a release part to protect the release part from dirt.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing the essential part of an embodiment of the present invention. In the figure, B is a release part without the thin film member 3, C is a release part with its rear end exposed to the atmosphere, The arrow indicates the direction of moisture permeability, 20
Is a case, and other parts having the same functions as those of the prior art shown in FIG. 6 are denoted by the same reference numerals as in FIG. Thus, in this embodiment, the common liquid chamber 6 and the FPC 11 are
And a part (B part) of the thin film member (passivation film) 3 between and and a surface (C part) opposite to the surface of the piezoelectric body 2 bonded to the nozzle plate 8 are released to the outside air. The open part is covered with a housing 20. As the material of the casing 20, cellulose (200 to 2000 g / m ² · day),
A material with high moisture permeability such as styrene (20-60g / m ² · day) is preferable.

FIG. 2 is a view showing a part of a cross section taken along the line AA of FIG. 1. In the drawing, 14 is a groove provided in the piezoelectric body 2, and as shown by an arrow in the drawing, ink From the flow path 5 to the thin film member 3
The water that has permeated the water stays in the concave groove portion 14 provided in the piezoelectric body 2 and increases the internal humidity.

3 and 4 are views showing the case where the housing 20 is integrated with the common liquid chamber 6, FIG. 3 shows an example in which the constituent members of the housing 20 are made thin to have moisture permeability, and FIG. Part of film material 20a
This is an example in which the is used to provide moisture permeability. By doing so, the number of parts and the manufacturing process can be reduced. But,
A new problem arises when the housing 20 and the common liquid chamber 6 are integrated. When a material having a high moisture permeability is used as the material of the common liquid chamber, the water content in the ink in the common liquid chamber 6 evaporates and the viscosity increases. Further, air permeates from the external environment, bubbles are mixed in the liquid chamber, and the ejection efficiency of the head is reduced. Therefore, when the housing 20 is formed integrally with the common liquid chamber 6, the thickness of the constituent members is reduced as shown in FIG. 3, or the notch is formed as shown in FIG. It is advisable to provide a film material 20a having a high water vapor transmission rate (such as cellulose or styrene described above) to the cutout portion to increase the water vapor transmission rate.

FIG. 5 is a diagram showing changes in humidity with time due to differences in the shape and material of the rear end portion of the piezoelectric body. In the case of a closed shape in which the rear end portion of the piezoelectric body is not exposed to the outside air, moisture is exposed to the outside. Since there is no place to release, as shown by curve A,
It gradually becomes 100% RH due to the moisture permeation from the liquid chamber. However, in the case of the open shape in which the high moisture permeable material is used and the water vapor is released to the outside, the humidity converges to slightly higher than the outside humidity as shown by the curve B. By providing a highly moisture-permeable member at the rear end of the piezoelectric body 2 or increasing the open area of the rear end, the humidity at the steady state can be kept constant at a lower value, but If the moisture permeability is higher (in extreme cases, the moisture permeable member is removed and there is no moisture permeable member at all), dust and water droplets tend to adhere as mentioned above, and the temperature change of the environment is also directly affected. It is easy to cause dew condensation. Therefore, it is desirable that the rear end sealing material is a member having as high moisture permeability as possible in terms of material and has a large area.

[0012]

【The invention's effect】

Effect corresponding to claim 1: By exposing a part of the piezoelectric body to the outside air, a high humidity component inside can be released, and by covering the outside air open portion with a housing, dust, water, etc. in the outside environment It also prevents the deterioration of the piezoelectric body due to the adherence of. Effect corresponding to claim 2: By integrating the housing and the common liquid quality, the number of parts and the number of steps can be reduced. Effect corresponding to claim 3: When the body and the common liquid chamber are integrated, a part of the body is made of a member having high humidity, so that the insulation deterioration of the piezoelectric body can be performed more effectively, and It is possible to prevent dust and water from adhering from the outside.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of essential parts for explaining an embodiment of the present invention.

FIG. 2 is a partial view of an enlarged cross section taken along line AA of FIG.

FIG. 3 is a cross-sectional configuration diagram of main parts for explaining another embodiment of the present invention.

FIG. 4 is a cross-sectional configuration diagram of essential parts for explaining another embodiment of the present invention.

FIG. 5 is a diagram showing changes in humidity inside an inkjet head of the present invention and a conventional example.

FIG. 6 is a schematic configuration diagram for explaining a conventional inkjet head.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Piezoelectric body, 3 ... Thin film member, 4 ... Flow path plate, 5
... Ink flow path, 6 ... Common liquid chamber, 7 ... Reinforcement plate, 8 ... Protective plate, 9 ... Nozzle plate, 10 ... Nozzle, 11 ... First FPC, 14 ... Groove, 20 ... Housing, 20a ... High moisture permeability Film material.

Claims (3)

[Claims] 1. A flow channel plate having a plurality of parallel flow channel grooves,
By joining a piezoelectric body having a concave groove for forming a convex portion corresponding to the flow channel of the flow channel plate, an ink flow is formed between the flow channel of the flow channel plate and the convex portion of the piezoelectric body. A thin film member is formed at the interface between the piezoelectric body and the ink flow path, and the ink in the ink flow path is provided to communicate with the ink flow path by utilizing the piezoelectric effect of the piezoelectric body. In an inkjet head that ejects ink droplets from a nozzle, an opening portion that opens the groove of the piezoelectric body is provided on the upper surface portion and / or the rear end portion of the piezoelectric body, and the opening portion is covered with a housing. An inkjet head characterized in that. 2. The ink jet head according to claim 1, wherein the casing is integrally formed with a common liquid chamber for supplying an ink liquid to the ink flow path. 3. The ink jet head according to claim 1, wherein a part of the housing is made of a material having high moisture permeability.