JPH02270556A - Ink jet printer - Google Patents

Abstract

PURPOSE:To obtain a low-cost ink jet printer of a simple structure which provides no change with time by providing a electrodes at opposed positions in a nozzle, high-conductivity ink supplied to an area between the electrodes and a voltage application device for applying a voltage between the electrodes. CONSTITUTION:A top electrode 1 and a bottom electrode 3 are installed in a head 7. The bottom electrode 3 is insulated from ink 4 using an insulation film 2. However, part of the bottom electrode 3 is exposed right under the opening of a nozzle 5. The top electrode 1 and the exposed part of the bottom electrode 3 are opposed to each other through the ink 4. If a voltage is applied to an area between the top electrode 1 and the bottom electrode 2 from a power supply, the ink 4 becomes energized. In this case, the ink 4 is of high conductivity. Consequently, the ink 4 is allowed to evaporate and spurt out, resulting in printing. The heat of evaporation which allows the ink equivalent to a single dot of print pixel is 1 to 3muJ and the conductivity of ink is 10<1> to 10<4>s/m. However, the generally used water ink has the conductivity of 1s/m or less. Therefore, it contains a dispersed high-conductivity material so that the conductivity is kept at a specified level.

Description

TECHNICAL FIELD The present invention relates to an inkjet printer, and more particularly to an inkjet printer that prints on a transfer material such as paper by foaming and ejecting ink inside a nozzle.

BACKGROUND OF THE INVENTION In general, inkjet printers include those that use a piezoelectric element to eject ink, and those that include a heat generating element and use the heat to generate bubbles and eject ink.

Such inkjet printers are not only used as output devices for computers and the like, but also applications of this method to facsimiles and the like are being considered.

However, since conventional inkjet printers use piezoelectric elements and heat generating elements, they have a disadvantage in that the structure of the print head section becomes complicated. Furthermore, in order to form uniform dots, it is necessary to use elements of the same quality, which also has the disadvantage of increasing costs.

Furthermore, there is also the drawback that print quality is likely to deteriorate due to changes in the element over time.

OBJECTS OF THE INVENTION An object of the present invention is to provide an inkjet printer that has a simpler structure, is not affected by changes over time, and is inexpensive.

Structure of the Invention An inkjet printer according to the present invention has a nozzle that opens toward a transfer material, and prints on the transfer material by foaming and ejecting ink inside the nozzle, wherein the nozzle It is characterized in that it has at least two opposing electrodes provided inside the device, high conductivity ink provided between these electrodes, and voltage application means for applying a voltage between the electrodes.

Example Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 2 is an external perspective view of a print head section of an embodiment of an inkjet printer according to the present invention. In the figure, the head section 7 is provided with a plurality of nozzles 5, and by ejecting ink from the nozzles 5, printing is performed on a transfer material (not shown).

The inside of this head section 7 is filled with ink 4, which is a coloring material, as shown in the cross-sectional view of the head in FIG. 1, and the internal pressure forms a meniscus at the nozzle 5. are doing. In addition, the first
The figure is a sectional view taken along the line AA of the head section 7 shown in FIG.

Also, inside the head part 7, an upper electrode 1 and a lower electrode 3 are provided.
is provided. Although the lower electrode 3 is insulated from the ink 4 by the insulating film 2, an exposed portion 8 of the lower electrode 3 is located directly below the opening of the nozzle 5.

In other words, the upper electrode 1 and the exposed portion 8 of the lower electrode 3 are opposed to each other with the ink 4 interposed therebetween.

As will be described later, ink 4 having high conductivity is used. Therefore, if a voltage is applied between the upper electrode 1 and the lower electrode 2 by a power source (not shown), a current flows through the ink 4. As a result, printing is performed by foaming and ejecting the ink 4.

Next, the printing process will be explained using FIG.

FIG. 3 is a cross-sectional view showing the printing process in the print head section of the inkjet printer according to this embodiment, and parts equivalent to those in FIG. 1 are designated by the same reference numerals.

First, when a voltage is applied between the upper electrode 1 and the lower electrode 3 by a power source (not shown), a current flows as shown by the dotted line in FIG. 3(a). Then, bubbles 6 are generated near the exposed portion 8, that is, the position where the current density is highest, as shown in FIG. 2(b). Since no current flows inside the bubble 6, current concentration occurs around the bubble, and bubble growth progresses due to heat generation. As a result, the ink is pushed up and ejected onto a transfer material (not shown) as shown in FIG. Printing is thereby performed. After the ink has completely flowed out, the same figure (d)
), new ink is filled from the surrounding area. Eventually, a meniscus is formed again and the state returns to the state shown in FIG.

In other words, in the present invention, current is passed through the ink itself, and the generated heat causes the ink to foam and eject the ink. Further, in this case, by limiting the exposed portion 8 of the lower electrode 3 to a small area as in this embodiment, the current is concentrated and the energy efficiency of vaporizing the ink is increased.

Next, ink will be explained. According to calculations performed by the inventor under certain conditions, the heat of vaporization to eject ink for one print pixel is 1 to 3 [μJ], and the electrical conductivity of the vaporized ink is 101 to 10. '(s/m). However, the conductivity of common water-based inks used in conventional inkjet printing is
1 [s/m) or less, in the present invention, a substance with high conductivity is dispersed in the ink in advance,
This gives the ink a predetermined electrical conductivity.

For example, if fine carbon fibers with a length of 100 μm or less or metal powder formed into fibers are dispersed in the ink, an ink having a desired electrical conductivity can be obtained. In addition, it is sufficient to use an ink having such conductivity that it can be effectively foamed by passing an electric current through it.

Further, in this embodiment, the electrodes are arranged as shown in FIG. 1, but the electrodes are not limited to such a position as long as the current is concentrated and the ink is easily foamed.

In other words, the present invention uses ink that effectively foams when a current is passed through it, and foams the ink by applying a voltage to the electrodes.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, the present invention has the advantage that ink can be ejected efficiently with a simple mechanism by passing an electric current through the ink itself to generate heat.

Further, according to the present invention, since the structure is simple in that opposing electrodes are provided within the nozzles of the print head, there is an advantage that it can be constructed at low cost without using piezoelectric elements or heating elements.

[Brief explanation of drawings]

Fig. 1 is an external view of the print head section of an inkjet printer according to an embodiment of the present invention, and Fig. 2 is an A-A in Fig. 1.
FIG. 3 is a cross-sectional view showing the printing process. Explanation of symbols of main parts 1... Upper electrode 2... Insulating film 3... Lower electrode 4... Ink 5... Nozzle 8...Exposed part

Claims (1)

[Claims] (1) An inkjet printer that has a nozzle that opens to a transfer material, and prints on the transfer material by foaming and ejecting ink inside the nozzle, the printer being provided inside the nozzle and facing the An inkjet printer comprising: at least two electrodes, highly conductive ink provided between these electrodes, and voltage application means for applying a voltage between the electrodes.