JPH06126955A - Electrostatic modified type ink jet head and recording method with same - Google Patents

Abstract

PURPOSE:To provide an ink jet head which can prevent evaporation of ink by independently providing nozzles and closing an ink discharge passage immediately before printing. CONSTITUTION:An ink jet head has an ink chamber 9 for filling ink therein and an orifice 6 for externally discharging the ink in the chamber, and comprises conductive elastic elements 3, 3 covered with insulating layers 4 and vertically oppositely disposed at the chamber side of the orifice 6 to form an ink discharge passage 9' therebetween. When a voltage is applied between the elements 3 and 3, the elements are elongated by an electrostatic attraction force to be applied to the elements to close the passage 9'. When both the elements are grounded, the elements are returned to original states to open the passage 9'.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ink jet system, and more particularly to an ink jet system in which an elastic body is extended by electrostatic attraction to close an orifice for ejecting ink during non-printing.

[0002]

2. Description of the Related Art In an ink jet recording apparatus, a bimorph type piezoelectric element expands and contracts an ink chamber by vibration to expand and contract the ink chamber to alternately eject and replenish ink, and a heater to generate bubbles in the ink liquid. Various methods such as a bubble jet method in which ink is ejected by the growth of bubbles are known.

A problem common to these various ink jet systems is that ink ejection is unstable. It is pointed out that the cause of this is that the water content of the ink evaporates and the viscosity of the ink increases, and that the evaporated and dried ink blocks the orifice.

To solve this problem, there is known a technique in which a cap is provided on the ink jet head, the cap is removed when printing is performed, and the cap is covered when printing is not performed to prevent ink evaporation. A device that automatically removes the cap is also proposed (see “Ja
pan Hardcopy'90 Proceedings P205-P208 ", June 1990, The Electrophotographic Society of Japan).

[0005]

However, this method is
The device for mechanically capping is complicated. Moreover, although an inkjet head is usually formed by arranging a large number of nozzles in parallel, if one of the nozzles is used for printing, the other nozzles are also opened and the ink may evaporate during that time. Become.

SUMMARY OF THE INVENTION The present invention is intended to solve the above problems, and an object thereof is to provide an ink jet head in which each nozzle independently closes the ink outflow path until just before printing, and can prevent ink evaporation. There is.

[0007]

In order to achieve the above-mentioned object, the present invention provides an ink chamber for filling ink therein,
In an inkjet head having an orifice for ejecting ink formed in the ink chamber, an ink outflow passage is formed on the ink chamber side of the orifice, and an electrode of which at least one is made of a conductive elastic body is opposed to the ink outflow passage. It is characterized by the configuration arranged.

Further, the method of the present invention is a recording method using an ink jet head having an ink chamber for filling ink therein and an orifice for ejecting ink formed in the ink chamber. An ink outflow path in which at least one electrode made of a conductive elastic body is arranged to face each other, and an electrostatic attractive force applied to the conductive elastic body when a voltage is applied between the conductive elastic body and the electrode. To extend the elastic body to close the ink outflow path,
The structure is characterized in that the conductive elastic body returns to its original state when the voltage is not applied to open the ink outflow path.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view of an ink jet head as an embodiment of the present invention. Although specific numbers are included, this is for the purpose of deepening understanding and is not limited to this. Further, although a nozzle is used as an example for description, the same applies to a slit.

Common electrodes 2 and 2 each made of a thin aluminum layer are formed on the opposing surfaces of the upper and lower substrates 1 and 1 having a thickness of 40 μm, and the thickness is 100 μm on the right side of the upper and lower substrates. Fix the conductive elastic body 3 with a thickness of 100 μm,
It is covered with an insulating layer 4 having a high dielectric constant of μm. Side plates 5 and 5 having a thickness of 40 μm are attached to the left and right sides of the substrates 1 and 1, an orifice 6 having a diameter of 30 μm is bored in the right side plate 5, and pressurized ink is supplied to the left side plate 5. The pipe line 7 to be connected is connected. The left side of the substrates 1 and 1 has a thickness of 0.
An ink chamber 9 is formed by covering a thin insulating layer 8 of 4 μm.

The ink chamber 9 is vertically sandwiched between the substrates 1 and 1 as shown in the drawing, and the front and rear sides thereof are partitioned by the side plates 5 and 5, but the direction perpendicular to the drawing is partitioned by a partition member (not shown). A large number of nozzles are formed in parallel in a direction perpendicular to the drawing.

The conductive elastic body 3 covered with the insulating layer 4 is
The top or bottom of the front, back, left, right, top, bottom is fixed to the top or bottom substrate 1,1 but the front, back, left, right, and bottom and the bottom (or top) are not fixed anywhere and are free. And an ink outflow passage 9'is formed between the upper and lower insulating layers 4 and 4. When a voltage is applied between the common electrodes 2 and 2, the ink outflow passage 9'is blocked by the electrostatic attraction acting on the conductive elastic bodies 3 and 3.

FIG. 2 is a diagram for explaining the operation of the ink jet head of FIG. (a) shows the standby state. + 400v is applied between the upper and lower common electrodes 2,2, and as a result, electrostatic attraction acting on the electric charges of opposite polarities charged in the conductive elastic bodies 3,3 causes the conductive elastic bodies 3,3 Closes the nozzle by extending in the direction of close contact.

(B) shows a printing state. If both electrodes are grounded immediately before printing, the charged electric charge disappears and the electrostatic attraction disappears, and both elastic bodies are restored to their original state by the elastic force, and the ink outflow passage 9'is formed. The ink outflow passage 9'is designed at the same position as the orifice 6 so that its opening is slightly wider than the orifice. In this embodiment, the diameter of the orifice 6 is 30 μm and the width of the ink outflow passage 9'is 35 μm.
It is μm.

(C) is an ink ejection state. If, for example, a well-known piezo device (not shown) is connected to the pipe line 7 and all the nozzles are pressurized at the same time, in the nozzle in which the ink outflow passage 9'is formed, the ink 10 is projected from the orifice 6 and the ink column Is formed. Of course, there is no ink ejection from the closed nozzle. In addition, without going through the pipeline 7,
The piezo device may be directly connected to the ink chamber 9.

(D) is a state in which the nozzle is closed again so that the next dot is not printed because it is part of the background. This is executed by applying + 1600v to the upper conductive elastic bodies 3 and 3 immediately after the ink is pressurized and ejected in (c). At this time, the ink column is cut to become the ink droplet 10a due to the surface tension, and continues to fly due to the inertial force. Of course, when the next dot is also printed subsequently, the nozzle is left open without applying a voltage. Finally, all nozzles are closed to complete printing.

Next, a quantitative explanation is supplemented to the above qualitative explanation. However, since the exact calculation becomes very complicated, it is an approximate calculation based on some assumptions.

When the nozzle is closed again, the electrostatic attractive force P acting on the upper conductive elastic body (this is referred to as "A").
Find (A). P (A) is P = σ × E (1) where σ is the charge density of holes charged in the conductive elastic body 3 and E is the electric field at that point.

This electric field is formed by the electrons (the charge density is -σ) of the lower conductive elastic body (this is "B"). This electric field is E = (− σ) / 2εoε2 (2) according to Gauss's theorem. Therefore, by substituting (2) into (1), P =-[sigma] 2/2 [epsilon] o [epsilon] ² (3) where [epsilon] o: dielectric constant of vacuum [epsilon] 2: relative dielectric constant of the high dielectric constant insulating layer.

Therefore, if the electron charge density −σ is obtained, the electrostatic attractive force P (A) can be calculated from the equation (3). Assuming that the ink outflow path 9'during the ink ejection of the electrostatic ink jet head is a parallel plate capacitor, its charge amount Q is calculated by the following equation. σ = C × V (4) where C is the capacitance and V is the applied voltage.

The charge density is obtained by dividing the charge amount Q by the area S. σ = Q / S (5) The electric capacitance C of the equation (4) is defined by the film thickness and relative permittivity of the ink layer and the high dielectric constant insulating layer 4, respectively.
If ε2, it can be calculated by the following equation (6). C = S × εo / (d2 / ε2 + d1 / ε1 + d2 / ε2) (6)

D1, ε1, d2 and ε2 are respectively 80 μ
m, 80, 20 μm, 40 If the area S is 1 m ² , C = 1 x 8.85 x 10 ^-12 / (20 x 10 ^-6 / 40 + 80 x 10 ^-6 / 80 + 20 x 10 ^-6 / 40) = 8.85 × 10 ^-6 / 2 = 4.43 (μF) (7) From (4), (5), and (7), the charge density σ is σ = 4.43 × 10 ^-6 × 1600 = 7.08 × 10 ^-3 (C / m ² ) (8)

By substituting this value into the equation (3), the electrostatic attractive forces P (A) and P (B) acting on the upper and lower conductive elastic bodies A and B can be obtained. P (A) = P (B ) = σ 2/2 εo ε2 (9) = (7.08 × 10 -3) 2 /2×40×8.85×10 -12 = 7.08 × 10 4 (N / m 2)

Next, the amount v of expansion (deformation) of the conductive elastic band is calculated. Generally, in the case of an elastic body, the length L before the force is applied
When a force acts on o and the length extends to L, the force and the elongation are directly proportional. At this time, a force equal to the force pulling the elastic body from the outside is generated inside the elastic body. This is called stress σ. A value obtained by dividing the extended length ΔL = L−Lo by the original length Lo is called strain ε, and a proportional constant of stress and strain is called elastic coefficient (elastic modulus, Young's modulus) E. σ = E × ε (10)

That is, the original length Lo and the applied pressure P
If (= σ) and the elastic modulus E are known, the extended length ΔL can be calculated from the following equation. ΔL = Lo × σ / E (11)

The elastic modulus E of soft rubber is 0.4 × 10 ⁶ N / m
² (= 0.4 MPa = 4 Kgf / cm ² ), in the case of the present invention, the original length Lo is 100 × 10 ⁻⁶ m and the electrostatic attractive force (= stress σ) as described above.
Is 1.77 × 10 ⁵ N / m ² . Put this value into Eq. (11) and calculate ΔL = (100 × 10 ⁶ × 7.08 × 10 ⁴ ) /0.4×10 ⁶ = 17.7 × 10 ^-6 (m) (12) and the extension distance of the conductive elastic body. Was asked. That is, in FIG. 2C, when +1600 v is applied to the upper conductive elastic body, the upper and lower conductive elastic bodies extend by 17.5 μm to close the ink outflow passage 9 ′.

Further, the electrostatic attractive force shown in the equation (9) is
Since the pressure of the ink is larger by one digit, the ink outflow passage 9'is not opened by the pressurization of the ink.

FIG. 3 is a diagram showing another embodiment of the present invention. In the embodiment shown in FIGS. 1 and 2, the conductive elastic body 3,
3 is provided and these are extended at the same time, the embodiment of FIG. 3 is of a type in which the conductive elastic body is used only on one side. The materials and manufacturing methods shown below are similarly applied to the embodiments shown in FIGS.

This ink jet head has an upper structure,
It is formed by dividing the lower structure and the side plate, and then pasting these three parts together.

The upper structure is a wall material 1 for separating each ink chamber.
1 are arranged in parallel at a pitch of 63.5 μm (in case of 400 DPI), and a rigid body in which aluminum is vapor-deposited uniformly as the common electrode 13 on the insulating substrate 12 or a rigid body coated with a conductive resin is placed on top of it. Adhesive, and each wall material 11
The conductive elastic body 14 covered with a thin insulating layer 15 is inserted between the two, and the conductive elastic body 14 is connected to the common electrode 13
It is fixed in the state of conducting to.

The wall material 11 preferably has a moderately soft surface in order to absorb shock waves, and is preferably made of a suitable oil-repellent resin. For example, insulating plastic such as polycarbonate (PC) is used. To do.

Similar to the embodiment shown in FIGS. 1 and 2, the conductive elastic body 14 has only the bottom surface fixed to the common electrode 13, and the upper surface and the four side surfaces, five surfaces in total, are the wall material 11 and the side plate described later. It is free from the above, and can be greatly deformed (expanded) with a small force. Then, the conductive elastic body 1
The film thickness of 4 is usually 200 μm and 235 μm when stretched,
Exactly twice the thickness of the embodiment of FIGS.

Referring to FIG. 4, a method of manufacturing the five-face-free conductive elastic body 14, which is a key point of this embodiment, will be described. First, an aluminum layer to be the common electrode 17 is uniformly formed on the insulating substrate 16 by a conventionally known method by a vapor deposition method or the like, and a wall surface separating the ink chamber is formed on the Teflon-based or silicone-based resin. Is formed by casting.

After adding an appropriate amount of acetylene black and a vulcanizing agent to chloroprene rubber and dispersing for a long time, toluene,
Conductive rubber solvent a with a solid concentration of 15 to 30 wt% by diluting with an appropriate solvent such as THF, cyclohexane, butanol
Is prepared and poured onto the above-mentioned substrate 16 placed on a horizontal table (FIG. 4 (a)).

Next, a metallic doctor blade b is squeezed to remove excess liquid (FIG. 4 (b)). Then, the wall material 1
Because 1 is oleophobic, the solution is slightly separated from the prism.
It looks like (c). When this is heated, a conductive rubber layer c having a thickness of about 10% and a thickness of about 20 μm is obtained (FIG. 4 (d)). By repeating this process, the conductive elastic body 14 having a predetermined thickness is completed (FIG. 4 (e)). At this time, the conductive elastic body 14 is not fixed to the wall member 11, and even if it is stuck, it can be easily peeled off by lightly moving it.

Next, a polyamide resin was added to methanol in an amount of 0.
Similarly, a 6 wt% dissolved solution d is poured and squeezed with a blade b (Fig. 4 (f)), and the insulating thin layer 15 is overcoated on the conductive elastic body 14 by heating to complete (Fig. 4 (g)). ).

For the insulating thin layer 15, it is preferable that the electric charge leaks in a proper time rather than a high resistance, and a polyamide resin having a volume resistivity of about 10 ¹⁰ Ωcm is suitable. Note that instead of the conductive rubber, an insulating rubber may be applied by the same method, and then the conductive resin and the insulating resin may be overcoated in this order.

As the conductive elastic body 14, known conductive rubber can be used. The conductive rubber is created by dispersing carbon black (acetylene black) in a rubber material. Thin insulating layer 15 to overcoat it
The thickness was about 0.4 μm.

The lower structure is formed by vapor-depositing aluminum on a suitable substrate 16 to form a common electrode 17, and applying an insulating layer 18 having a high dielectric constant thereon. The thickness is set so as to reach the lower part of the orifice, and in this embodiment, 80 μm.
And

The high dielectric constant insulating layer 18 is, for example, piezo rubber ("PR-30" manufactured by Nippon Special Ceramics Co., Ltd.).
2 ") is suitable. It is made by dispersing lead titanate (PbTiO3) in proloprene rubber. This insulator does not have to be rubber, but rubber is preferable in order to make close contact with the upper conductive elastic body 14 without a gap.

The side plate 19 is made of PET film having a thickness of 25 to 100 μm, with orifices 20 having a diameter of about 20 μm at 63.5 μm intervals.
Created by opening. Put the upper structure on the lower structure,
The ink jet head is completed by aligning the positions of the ink chamber and the orifice 20 formed thereby and fixing the side plate 19. At this time, an ink outflow passage is formed between the conductive elastic body 14 and the insulating layer 18 of the lower structure.

The operation of this embodiment is similar to that described with reference to FIGS. However, according to the embodiment of FIG.
Since the conductive elastic body 14 only needs to be formed in the upper structure, the structure is simple and easy to manufacture.

[0043]

As described above, according to the ink jet head of the present invention, since the conductive elastic body is used to open and close the ink outflow path, the nozzle is closed except during printing. Therefore, the evaporation of ink can be greatly reduced. Therefore, it is possible to prevent the evaporation of the ink from increasing the viscosity of the ink to clog the nozzles, the evaporation of the dried ink to block the orifice, and the like, and to achieve stable printing.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an inkjet head of the present invention.

2 (a) to (d) are views for explaining the operation of the inkjet head of FIG.

FIG. 3 is an exploded perspective view of another embodiment of the present invention.

4A to 4G are diagrams illustrating a method for forming a conductive elastic body.

[Explanation of symbols]

 1, 12, 16 Substrate 2, 13, 17 Common electrode 3, 14 Conductive elastic body 4, 15 Insulating layer 6, 20 Orifice 9 Ink chamber 9'Ink outflow path 10 Ink 10a Ink drop

Claims (5)

[Claims] 1. An ink jet head having an ink chamber for filling ink therein and an orifice for ejecting ink formed in the ink chamber, wherein an ink outflow passage is formed on the ink chamber side of the orifice,
An electrostatically-deformable inkjet head, characterized in that electrodes, at least one of which is made of a conductive elastic body, are arranged facing each other in the ink outflow path. 2. The electrostatic deformable ink jet head according to claim 1, wherein the conductive elastic body is fixed only on one surface, and the other five surfaces are not fixed and are free. 3. The electrostatic deformation type inkjet head according to claim 1, wherein the conductive elastic body is covered with an insulating layer. 4. A recording method using an inkjet head having an ink chamber for filling ink and an orifice for ejecting ink formed in the ink chamber, wherein at least one of the orifice and the ink chamber side is conductive. An ink outflow path is formed by arranging electrodes made of an elastic body so as to face each other, and the elastic body is elongated by an electrostatic attractive force applied to the conductive elastic body when a voltage is applied between the conductive elastic body and the electrode. A recording method using an electrostatically-deformable inkjet head, characterized in that the conductive elastic body returns to its original state and the ink outflow path is opened when the voltage is not applied. 5. The conductive elastic body is fixed only on one surface and the other five surfaces are not fixed, and the elastic body is freely expanded and contracted to open and close the ink outflow passage. A recording method using the electrostatic deformation type inkjet head described.