JPH02185446A - Ink jet printer - Google Patents

Abstract

PURPOSE:To allow ink discharge with a simple mechanism and high efficiency by permitting an electric current to run in ink to cause a thermal element to be heated. CONSTITUTION:When a voltage is applied to an area between a top electrode 1 and an electrode 3d, an electric current passes through the side of the electrode 3d a heat generating element 3c an electroconductor layer 3a to ink 2 the top electrode 1. The temperature rises in the heat generating element 3c with the highest electric resistance across the current path, and bubbles generate at a position with the highest temperature. Although the current does not pass through the bubbles 6, a current passage is ensured by providing an adequately large conductor layer 3a, considering the size of bubbles for ink discharge. Aa a result, the ink is pushed up and discharged. In order to ensure the ink passage, bubbles 6 are allowed to grow smoothly by providing a large area for the conductor layer 3a of a bottom electrode 3. In addition, the current is concentrated by minimizing the area of the heat generating element 3c to increase the efficiency of energy required for ink evaporation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus used in printers, facsimile machines, etc., and particularly to a printing mechanism using liquid ink.

[Conventional technology]

Conventional inkjet printers of this type include those that use piezoelectric elements to eject ink, and so-called bubble jet printers that eject ink by foaming it with the heat of heating elements.

[Problem to be solved by the invention]

The above-mentioned conventional inkjet printers have piezoelectric elements and heat generating elements, so the print head structure is complicated, and in order to form uniform dots, elements of the same quality must be formed. Therefore, the cost was high. Furthermore, there is a drawback that print quality is likely to deteriorate due to changes in the elements over time.

Additionally, with traditional bubble jet printers.

It was necessary to arrange the heating elements at a pitch equivalent to the printing density, and to make fine wiring in order to drive each heating element independently according to the printing signal.

An object of the present invention is to provide an inkjet printer that solves the above problems.

[Means to solve the problem]

To achieve the above object, the present invention provides an inkjet head having a nozzle that opens toward a recording medium, which has at least two electrodes facing each other with conductive ink interposed therebetween, and at least one of the electrodes has a heating element. By applying a voltage to the electrodes, the ink is energized and the heating element generates heat to foam the ink, thereby ejecting the ink from the nozzle.

〔Example〕

Next, one embodiment of the present invention will be explained with reference to the drawings.

FIG. 1 ω, (b) is a diagram showing an embodiment of the present invention,
Figure 1(a) is an external view showing the print head;
b) is a cross-sectional view of the same. The inside of the head is filled with ink 2, which is a coloring material, and its internal pressure forms a meniscus on the nozzle 5. Upper electrode 1 and lower electrode 3 face each other with ink 2 in between. The lower electrode 3 includes a conductive layer 3a and an insulating layer 3b.

It is constructed by laminating a heating element 3c and an electrode 3d. Further, the ink 2 contains conductive fine fibers mixed therein.1. O3/m
This is because it has a higher conductivity.

FIGS. 2(a) to 2(d) are diagrams showing the printing process according to the present invention. When a voltage is applied between the upper electrode 1 and the electrode 3d, a current flows in the order of the electrode 3d -> the heating element 3c -> the conductive layer 3a -> the ink 2 -> the upper electrode 1 as shown in FIG. 2(a). Heating element 3c with the highest electrical resistance among the current paths
The temperature rises, and a bubble 6 is generated at the highest temperature position. Although no current flows inside the bubble 6, by making the conductive layer 3a sufficiently large in consideration of the bubble size required for ink ejection, a current path is secured, and bubble growth due to heat generation is promoted. (Figure 2 (
b)) As a result, the ink is pushed up and ejected as shown in FIG. 2(c). After the ink has completely flowed out,
New ink is filled from the periphery as shown in Figure (d).

Eventually, a meniscus is formed again, returning to the state shown in FIG. 6 can be grown smoothly and by reducing the area of the heating element 3c, the current can be concentrated and the energy efficiency of vaporizing the ink can be increased.

According to calculations conducted under certain conditions, the heat of vaporization to eject ink for one pixel is 1 to 3 μJ, and the conductivity of the vaporized ink must be 10' to 10'S/■. However, since the conductivity of water-based ink is less than Is/m, in the present invention, a highly conductive substance is dispersed in the ink to obtain an ink with a predetermined conductivity. For example, it may be possible to disperse fine carbon fibers with a length of 100 mm or less, metal powder formed into fibers, or the like.

〔Effect of the invention〕

As described above, according to the present invention, ink can be ejected efficiently with a simple mechanism by causing a heating element to generate heat by passing a current through the ink. In addition, the print head requires only a return electrode on the nozzle side, so there is no need for a fine pattern, and only the lower electrodes need to be formed at the same pitch as the printing density, so it can be manufactured at low cost. have an effect.

[Brief explanation of the drawing]

FIG. 1(a) is an external view showing one embodiment of the present invention, and FIG. 1(b) is an external view showing an embodiment of the present invention.
is a cross-sectional view of the same, and FIGS. 2(a) to 2(c) are diagrams showing the printing operation of the printer according to the present invention. 1... Upper electrode 2... Ink 3a...
Conductive layer 3b... Insulating layer 3c... Heating element 3d... Electrode 5... Nozzle

Claims (1)

[Claims] (1) An inkjet head with a nozzle that opens toward the recording medium has at least two electrodes facing each other across conductive ink, at least one of which has a heating element, and a voltage is applied to the electrode. An inkjet printer characterized in that the ink is ejected from a nozzle by energizing the ink and causing the heating element to generate heat to foam the ink.