JPH03213355A - Ink jet print head - Google Patents

Abstract

PURPOSE:To accomplish gradation recording by changing dot diameters by providing a plurality of irregular openings over a beating resistor provided in an ink passage. CONSTITUTION:A heating resistor 2 provided on a base board 1 is energized and heated by a common electrode 3 and selective electrode 4. The resistor 2 is covered with a protection film 5, over which a pit layer 6 is formed. A plurality of openings are provided in the layer 6 so that each of them is positioned over each resistor 2 and divided into a plurality of openings by partition walls 63, 64. With such arrangement, when impressed voltage is not so high, a bubble (a) is produced only in each opening. When said voltage is higher, a bubble (a) is produced in an opening 73, whereas bubbles produced in openings 71, 72 are formed into one large bubble (b). When voltage is made still higher, all bubbles produced in the openings 71, 72, 73 are formed into one bubble, causing a large change in volume of bubble. As a result, the size of a drop of ink can be precisely controlled, so that gradation recording can be accomplished by changing diameters of dots.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a print head in an inkjet printer, particularly a thermal inkjet printer.

(Prior art) Conventionally, in inkjet printers using thermal inkjet heads, it is difficult to change the size of the ink drop itself, so it is difficult to express the gradation of an image. A matrix is formed and gradations are expressed in a pseudo manner by the distribution of dots within the matrix. However, this method requires a 4x4 matrix to express 16 gradations, and has the disadvantage that the actual resolution is reduced to 1/4. Therefore, attempts have been made to find ways to express gradations without sacrificing resolution.

The amount of ink droplet ejected depends on the size of the bubble generated when the physical properties of the ink are constant, and the size of this bubble depends on the temperature of the heater-ink interface.

Furthermore, this temperature increase depends on the amount of heat generated by the heater, that is, the applied voltage or pulse width. Therefore, gradation is expressed by changing the amount of ink drop by changing the amount of heat applied to the heater.

The gradation setting circuit described in Japanese Utility Model Application Publication No. 57-141043 uses a voltage dividing circuit to change the voltage value and set the density gradation. In this method of modulating the amount of ink drop by changing the voltage value of the drive pulse applied to the heater to generate vapor bubbles, the range of the amount of ink drop that can be modulated is narrow, and it is difficult to reach a sufficient gradation level. I couldn't get it.

JP-A-55-132258 and JP-A-63-428
The liquid jet recording method described in Japanese Patent No. 68 uses a gradient in the resistance value distribution of a heater and performs gradation recording by utilizing the heat generation gradient generated by an applied voltage. Although this method can modulate the volume of the ink drop over a wide range, it is difficult to maintain a constant relationship between the applied voltage and the amount of ink drop, and the problem is that the volume of the bubble cannot be controlled accurately. have.

Utility Model Publication No. 60-105148 and Japanese Patent Application Publication No. 622614
The method described in Japanese Patent No. 53 disposes a plurality of heating resistors in one nozzle, but has the disadvantage that the number of selection electrodes increases and the circuit configuration becomes complicated.

Therefore, none of the conventional gradation expression methods can be said to be appropriate.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned problems.The present invention has been made in order to solve the above-mentioned problems. The object of the present invention is to provide an inkjet print head that enables gradation expression through modulation of .

(Means for Solving the Problems) The present invention provides an inkjet print head that includes an ink channel holding ink and an ink discharge port communicating with the ink channel, and that discharges ink from the ink discharge port. , a heat generating resistor is provided inside the ink flow path, and a plurality of unequal openings are provided on the heat generating resistor.

The plurality of apertures may have different areas, or the height, width, shape, etc. of the partition walls of the apertures may be varied. Moreover, these may be combined, and the point is that the conditions for coalescence of bubbles generated in adjacent openings may be made different.

(Function) The present invention provides an inkjet print head that includes an ink flow path holding ink and an ink ejection port communicating with the ink flow path, and that ejects ink from the ink flow path. By having a heating resistor inside and having a plurality of uneven openings on the heating resistor, the growth area of bubbles generated in each opening is limited, and due to the difference in the growth area, adjacent The conditions for the bubbles to coalesce and grow differ depending on the opening. Therefore, depending on the applied voltage, bubbles may grow only within each aperture, or bubbles generated in adjacent apertures may coalesce into one, and larger bubbles may grow. By controlling the bubbles that coalesce according to this, the bubble volume can be accurately controlled, and the dot diameter can be accurately modulated.

(Example) Fig. 3 is for explaining the outline of a thermal inkjet head to which the present invention is applied. FIG. 3 is a cross-sectional view of the vicinity of the tip of the nozzle taken in the drop injection direction. In the figure, 1 is a substrate, 2 is a heating resistor, 3 is a common electrode, 4 is a selection electrode, 5 is a protective layer, 6 is a bit layer, 7 is an opening, 8 is a groove, 9 is a groove plate member, and 10 is a It is an adhesive layer. The heating resistor 2 is disposed on the substrate 1 and heated by electricity from the common electrode 3 and the selection electrode 4. The heating resistor 2 is covered with a protective film 5, and a bit layer 6 is formed on the protective film 5.

A plurality of openings 7 are provided in the bit layer 6, and each opening 7 is positioned above each heating resistor 2, and as is clear from FIG. It is partitioned by an opening. The substrate 1 on which the above-mentioned bit layer has been formed and the groove plate member 9 on which the grooves 8 have been formed are adhered with an adhesive layer 10, and the grooves 8 constitute an ink flow path, the tip of which is a point where an ink drop is ejected. It becomes an exit.

When ink is introduced into the ink flow path and the heating resistor 2 is energized to heat the ink, bubbles are generated and ink drops corresponding to the increase in volume are ejected. At this time, the presence of the openings 7 in the bit layer 6 restricts the growth of bubbles in the horizontal direction, so that bubbles are generated stably.

The above is an outline of a thermal inkjet head having a bit layer, and in this embodiment, a plurality of apertures are arranged in the aperture 7 of the bit.

FIG. 1 shows an example in which three openings are provided. In the figure, 6 is a bit layer, 71, 72, 73 are openings, and 2 is a heating resistor disposed at the bottom of the bit layer 6.

The heating resistor 2 is exposed to the openings 71, 72, 73,
Its surface is usually covered with the above-mentioned protective film.

FIG. 2(A) shows a cross section taken along line II--II in FIG. 1, and the same parts as in FIG. 1 are given the same reference numerals and their explanations are omitted. In the figure, 63 is the partition wall between the openings 71 and 72, 64 is the dark partition wall between the openings 72 and 73, and 61.62
indicates the bit layer 6 in FIG. In this embodiment, a bit layer is provided, but it is not necessarily necessary to provide a bit layer, and if this is not provided, 61, 62
is provided as a partition wall. Here, the heights of the partition walls are equal, for example, 61.62, the highest, and 64.62.
63.

In such a thermal inkjet head,
When the applied voltage is not very high, bubbles a + a and a are generated only within each opening, as shown in FIG. 3(B). If the temperature is higher than that, bubbles a are generated within the aperture 73, as shown in FIG.
The bubbles generated within the openings 71 and 72 are combined as shown in b to form a larger bubble. If the applied voltage is even higher, the openings 71, 72.7, as shown in FIG.
All the bubbles generated in step 3 come together and a large volume change occurs. By providing a plurality of apertures on the heating resistor in this manner, the size of the ink drop can be accurately controlled and gradation recording can be performed by modulating the dot diameter.

In addition, in the above embodiment, the heights of the partition walls of the openings were made to be different, but the invention is not limited to this, and the area, shape, depth, etc. of the openings may be changed, or they may be combined. . The size, number, etc. of the openings can be determined as appropriate.

FIGS. 4 and 5 are process diagrams for explaining the outline of the method for manufacturing the thermal inkjet head having the apertures described in the above embodiment.

In FIG. 4, bit 7 explained in FIG. 3 is provided. First, a heating resistor 2. is placed on a substrate 1. A common electrode 35 and a selection electrode 4 are formed by sputtering or the like, and a protective film 5 is deposited thereon (Figure (A)). On top of that, photosensitive polyimide is applied and patterned using a photolithography process to form a bit layer 6 in which bits 7 are formed ((B)
figure). Next, apply photosensitive polyimide thinner than above,
Similarly, patterning is performed using a photolithography process to form partition walls 64 (Figure (C)), and photosensitive polyimide is further applied thinner than the above, and patterning is performed using a similar photolithography process to form partition walls 64.
is formed to constitute a substrate member (Figure (D)). and,
The groove plate member explained in FIG. 3 is adhered.

FIG. 5 shows a case where partition walls 61 and 62 are formed separately. The process shown in FIG. 4(A) is the same, and the process shown in FIG.
), the partition wall 61 is formed, and the partition wall 63 is similarly formed.
(B)), and then the partition walls 64 are formed (Figure B).
Furthermore, partition walls 62 are formed to constitute a substrate member (see (D)). Then, the groove plate member is bonded in the same manner as described with reference to FIG.

(Effects of the Invention) As is clear from the above description, according to the present invention, by providing a plurality of unequal openings on the heating resistor provided inside the ink flow path, the volume of the bubble can be accurately determined. This has the effect of providing a thermal ink jet head capable of performing gradation recording by dot diameter modulation.

[Brief explanation of drawings]

FIG. 1 is a plan view of the vicinity of a heating resistor of a thermal inkjet head for explaining one embodiment of the present invention, and FIG.
The drawings are a sectional view taken along line II-II of FIG. 1 for explaining the operation, FIG. 3 is a schematic explanatory diagram of a thermal inkjet head to which the present invention is applied, and FIGS. FIG. 3 is an explanatory diagram of the manufacturing process of the thermal inkjet head of the example. DESCRIPTION OF SYMBOLS 1...Substrate, 2...Heating resistor, 3...Common electrode, 4...Selection electrode, 5...Protective layer, 6...Bit layer, 71°72.73... Opening hole, 8...Groove, 9...
-Groove plate member, 10...adhesive layer.

Claims (1)

[Scope of Claims] An inkjet print head comprising an ink channel holding ink and an ink discharge port communicating with the ink channel, and discharging ink from the ink discharge port, comprising: An inkjet printhead comprising a heat generating resistor and a plurality of non-uniform apertures provided on the heat generating resistor.