Ink jet printer head.

0001The present invention relates to a printing head of an ink jet printer used in office automation (OA) equipment, etc.

0002As a means of recording graphics, characters, etc. clearly on paper, a printer employing an ink jet head which jets ink from a very small nozzle at a high speed in accordance with an electric signal is used. There are two ink jetting methods now available. One of them jets ink by means of a heating element and the other jets ink by means of a piezoelectric vibrating plate.

0003Figs. 3 and 4 show a principle of an ink jetting method which uses a heating element. In this method, a conductor 2, a heating element 3 and a drive circuit 4 are provided on a substrate 1 made of ceramics or the like, and an ink chamber 8 enclosed by a flat plate 5, resin material 6 and sealing material 7 is formed.

0004The flat plate 5 is provided with a nozzle 9, and a projection 10 to form an orifice for easy jetting of ink from the nozzle 9 by bubbles is also provided halfway in the ink passage to the nozzle 9. Numeral 11 is an ink tank, which is connected to the ink chamber 8 by means of an ink feed pipe 12 so that ink 13 of the ink tank 11 provided at an upper position is filled in the ink chamber.

0005Fig. 4(a) through (c) are partially enlarged views of Fig. 3, showing how ink particles are generated by the heating element 3. Fig. 4(a) illustrates how ink is filled into the ink chamber 8 from the ink tank 11.

0006When an electric signal is sent to the drive circuit 4 and the heating element 3 is thereby heated, a bubble 14 expands on the heating element 3, as shown in Fig. 4(b) and the pressure caused by this bubble is blocked by the projection 10 and is directed to the edge of the nozzle 9. Ink is thereby projected from the nozzle 9, in the form of an ink particle 15, onto recording paper 16, thus forming a dot thereupon.

0007If the drive circuit 4 is blocked the moment the ink particle 15 jets out, the heating element 3 is quickly cooled by the ink, and the bubble is shrunk, thereby causing ink to flow into the ink chamber 8 from the ink tank 11. Repeating the processes illustrated in Figs. 4(a), (b) and (c) allows characters, graphics, etc. to be drawn on the recording paper 16.

0008This method has a shortcoming in that since ink is jetted out by means of bumping, pressure inside the ink chamber becomes uneven in the process illustrated in Fig. 4(b), thereby causing unnecessary fine ink particles to be scattered, and making it difficult to form a beautifully round print dot. Furthermore, there is also another shortcoming in that containment of residual bubbles inside the ink chamber makes the pressure in the ink chamber unstable.

0009The object of the present invention is to provide an ink jet printer head which draws characters and graphics with high accuracy.

0010The present invention is an ink jet printer head which prints by jetting out ink from a nozzle, comprising a heating element, a first ink chamber on the heating element, a second ink chamber with the nozzle on the first ink chamber, a partition plate which separates the first and the second ink chambers, and at least two holes in the partition plate which allow ink to pass therethrough, at least one of the two holes and the nozzle being provided substantially coaxially with the center of the heating element.

0011While this construction can be used alone independently, a plurality of such printer heads can be used in a single printer.

0012According to this invention, by circulating the ink in the ink chambers and removing residual bubbles, the bad effect of such bubbles on the ink particles can be lessened. Furthermore, circulating the ink allows the ink to be slow in caking and makes its quality uniform. Furthermore, by making the discharge pressure uniform, uniform ink particles can be stably obtained. Ink particles from an ink jet head according to the present invention are very fine, normally, several ten thousands of dots per second, and smaller than residual bubbles present in the ink chambers.

0013A preferred embodiment of an ink jet printer head according to the present invention will now be described with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="none"><li>Fig. 1 illustrates the principle of the present invention, and</li><li>Figs. 2(a) through (d) are partially enlarged views of Fig. 1, illustrating the generating processes of ink particles.</li></ul>

0014In order to make a contrast with the aforementioned prior art shown in Figs. 3 and 4(a) through (c), the same parts are given the same numerals, while the elements unique to the present invention are given new numerals starting with 20.

0015Similarly to the prior art, in the present invention too there are provided a conductor 2, a heating element 3 and a drive circuit 4 on a substrate 1 made of ceramic or the like, and a first ink chamber 8 enclosed by a first flat plate 5, resin 6 and sealing material 7, is formed so that it encloses the heating element 3.

0016In the present invention, a second ink chamber 23 enclosed by a second flat plate 20, resin 21 and sealing material 22 is formed on the first ink chamber 8. Therefore, the first flat plate 5 serves as a partition plate separating the two ink layers chambers 8, 23.

0017The first and second flat plates 5, 20 are provided with a first hole 9 and a second hole 24, respectively, at the positions which substantially correspond to the center of the heating element 3, with the second hole 24 serving as a nozzle. The first flat plate 5 is provided with a third hole 25 which allows circulation of ink through each ink chambers 8, 23.

0018Ink 13 inside an ink tank 11 is pressurized by an ink pump 26 and is sent into the first ink chamber 8 through the ink feed pipe 27, the second ink chamber 23 and the second hole 25. It passes through the ink discharge pipe 28, and flows out from the outlet 29 provided at a position lower than the head and then returns to the ink tank 11.

0019Fig. 2(a) illustrates ink flow in a static condition, in which ink in the second hole (nozzle) 24 is normally in the retracted state towards the second ink chamber 23.

0020Fig. 2(b) illustrates the state in which a first bubble 14 is being generated by the heat of the heating element 3. Pressure caused by this bubble 14 is directed towards the first hole 9 of the first flat plate 5, and the second hole (nozzle) 24, as indicated by arrows, jetting out ink by the second hole (nozzle) 24 and, at the same time, increasing the jetting power of ink from the second hole 24 by blocking and reversing the ink flow through the third hole 25.

0021Fig. 2(c) illustrates the condition in which a first bubble 14 and a second bubble 30 further expand, causing the ink of the second hole (nozzle) 24 to be correspondingly projected.

0022Fig. 2(d) illustrates the condition in which the ink at the edge of the second hole (nozzle) 24 has jetted out in the form of an ink particle 15, and also shows the ink flow, by arrows, obtained when the first bubble 14 is made smaller due to the blocking of the heating element by the drive circuit 4.

0023By repeating the processes in Figs. 2 (a) through (d), characters and graphics are drawn on the recording paper 16.

0024While this construction can be used alone independently, a plurality of such printer heads may be installed together.