JPH0229341A - Liquid jet recording head - Google Patents

Abstract

PURPOSE:To prevent crosstalk in liquid passages and prevent ejection performance from bering varied between a central region and end parts by a construction wherein the ratio of the height of a passage provided with a thermal energy applying part to the height of a liquid chamber for introducing a recording liquid into the passage is adjusted to a specified value. CONSTITUTION:In order to prevent crosstalk between orifices, the height of a passage 16 and height of a passage 15 are set to satisfy a certain relationship, whereby it is ensured that a pressure wave which would generate crosstalk does not affect the adjacent passage. Namely, the height ha of the passage 15 and the height hb of the passage 16 are set to satisfy the relationship hb/ha>2, whereby crosstalk or insufficient liquid supply is prevented from occurring.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to liquid jet recording heads, and more particularly to dimensions of flow paths and liquid chambers of bubble jet heads.

The non-impact recording method has recently attracted attention because it generates negligible noise during recording. Among them, high-speed recording is possible,
However, the so-called inkjet recording method, which allows recording on plain paper without the need for special fixing treatment, is an extremely powerful recording method, and various methods have been proposed, improved, and commercialized. Some have been developed, and efforts are still being made to put them into practical use.

Such an inkjet recording method involves jetting droplets of a recording liquid called ink.

Recording is performed by attaching the recording liquid to a recording member, and it is roughly divided into several methods depending on the method of generating recording liquid droplets and the control method for controlling the flight direction of the generated recording liquid droplets. Ru.

The first method is, for example, the one disclosed in USP No. 3,060,429 (Tale type method), in which small droplets of recording liquid are generated by electrostatic attraction and the generated recording liquid droplets are Recording is performed by controlling an electric field in accordance with a recording signal to selectively attach recording liquid droplets onto a recording member.

To explain this in more detail, an electric field is applied between the nozzle and the accelerating electrode to eject a negatively charged recording liquid droplet from the nozzle, and the ejected recording liquid droplet is converted into a recording signal. Accordingly, the droplet is caused to fly between x and y deflection electrodes configured to be electrically controllable, and the droplet is selectively deposited on the recording member by changing the intensity of the electric field to perform recording.

The second method is a method (Sweet method) disclosed in, for example, USP No. 3,596,275, USP No. 3,298,030, etc., and is a method (Sweet method) in which the amount of charge is controlled by a continuous vibration generation method. Generate droplets and control the amount of charge generated.

Recording is performed on a recording member by flying the deflection electrode between deflection electrodes to which an electric field of - type is applied.

Specifically, the orifice (discharge port) of a nozzle, which is a part of the recording head to which the piezo vibrating element is attached.
A charged electrode configured to have a recording signal applied thereto is arranged at a predetermined distance in front of the piezo vibrating element, and an electric signal of a constant frequency is applied to the piezo vibrating element to mechanically vibrate the piezo vibrating element, A small droplet of recording liquid is ejected from the ejection port. At this time, a charge is electrostatically induced in the recording liquid droplet discharged by the charging electrode, and the droplet is charged with a charge according to the recording signal. When a droplet of recording liquid with a controlled amount of charge flies between deflection electrodes to which a constant electric field is uniformly applied, it is deflected according to the amount of charge applied.
A third system, in which only the droplets carrying the recording signal can be deposited on the recording member, is e.g.
The method (Hertz method) disclosed in the specification of No. 3 applies an electric field between a nozzle and a ring-shaped charging electrode,
This method uses a continuous vibration generation method to generate and atomize small droplets of recording liquid for recording. That is, in this method, the feeding state of the droplets is controlled by modulating the electric field intensity applied between the nozzle and the charging electrode in accordance with the recording signal, and the gradation of the recorded image is produced.

The fourth method is, for example, the method disclosed in USP No. 3,747,120 (Ste+u+e method), and this method is fundamentally different in principle from the above three methods.

That is, in all three methods, the droplets of recording liquid ejected from the nozzle are electrically controlled while they are in flight, and the droplets carrying the recording signal are selectively attached to the recording member. In contrast, in the Ste+ams method, recording is performed by ejecting small droplets of recording liquid from an ejection port in response to a recording signal.

In other words, the Steam method applies an electrical recording signal to a piezo vibrating element attached to a recording head that has an ejection port for discharging recording liquid, and converts this electrical recording signal into mechanical vibration of the piezo vibrating element. In this method, recording is performed by ejecting small droplets of recording liquid from the ejection opening according to the mechanical vibrations and adhering them to the recording member.

These four conventional methods each have their own advantages, but there are also points that can be solved in the other method.

That is, in the first to third methods, the direct energy for generating droplets of the recording liquid is electrical energy, and the deflection control of the droplets is also electric field control.

Therefore, although the first method is simple in structure, it requires a high voltage to generate droplets, and it is difficult to use a multi-nozzle recording head, making it unsuitable for high-speed recording.

The second method allows the recording head to have multiple nozzles and is suitable for high-speed recording, but it has a complicated structure, and the electrical control of recording liquid droplets is sophisticated and difficult, and satellite dots are placed on the recording member. There are problems such as easy occurrence of.

The third method has the advantage of being able to record images with excellent gradation by atomizing recording liquid droplets, but on the other hand, it is difficult to control the atomization state and fog occurs in the recorded image. In addition, it is difficult to create a multi-nozzle recording head.
There are various problems such as being unsuitable for high-speed recording.

The fourth method has relatively many advantages compared to the first to third methods. In other words, the structure is simple, and since recording is performed by ejecting recording liquid from the ejection opening of the nozzle on-demand, it is possible to reduce the number of small droplets that fly as in the first to third methods. Among them, it is unnecessary to collect droplets that are not needed for recording an image, and as in the first and second methods.

It has great advantages such as there is no need to use a conductive recording liquid and there is a large degree of freedom regarding the material of the recording liquid.

On the other hand, it is difficult to make a recording head with multiple nozzles due to problems in the processing of the recording head and the extremely difficult miniaturization of a piezoelectric vibrating element with a desired resonance number. This method has disadvantages such as that it is not suitable for high-speed recording because the recording liquid droplets are ejected into flight using the mechanical energy of the mechanical vibration of the piezoelectric vibrating element.

Furthermore, Japanese Patent Application Laid-Open No. 48-9622 (the above Usp No. 3)
No. 747120 (corresponding to the specification) discloses, as a modification, the use of thermal energy instead of the mechanical vibration energy provided by means such as the piezo vibrating element.

That is, the above-mentioned publication describes a so-called bubble jet liquid jet recording device that uses a heating coil that directly heats liquid as a pressure increasing means instead of a piezo vibrating element to generate steam that causes a pressure increase. There is.

However, in the above publication, the liquid ink in the bag-shaped ink chamber (liquid chamber), which has only one opening through which liquid ink can go in and out, is directly heated and vaporized by energizing the heating coil as a pressure increasing means. However, when discharging liquid continuously and repeatedly, there is no way to know how to heat it.
There is nothing to suggest. In addition, the heating coil is located at the deepest part of the bag-shaped liquid chamber far from the liquid ink supply path, which makes the head structure complicated and requires continuous high-speed printing. For repeated use,
It is not suitable.

Moreover, with the technical content described in the above-mentioned publication, it is not possible to quickly prepare for the next liquid discharge after discharging the liquid using the generated heat, which is important in practice.

As described above, conventional methods have advantages and disadvantages in terms of structure, high-speed recording, multi-nozzle recording heads, generation of satellite dots, and fogging of recorded images. There was a restriction that it could only be applied.

JP-A-55-132271 also discloses a predetermined number of working chambers connected to the discharge chamber 1 for discharging recording liquid, and a mechanism for supplying the recording liquid from its supply source to each working chamber. A communication port with the action chamber is provided on a wall that forms a part of the relay room and whose area is W, and the total area of these communication ports is S. When you do, W/
A liquid jet recording device has been proposed in which all the action chambers are connected to the relay chamber so that the value of S is 50 or more.

FIG. 19 is a sectional view of essential parts showing an example of an extreme case of the above-mentioned inkjet head. As shown in FIG. 19, the length of Q of the wall surface 1 of the relay chamber is increased to increase the area of W.
The ratio of the communication port 2 to the total area S is set to W/S≧50. In an inkjet head, the relationship between S and W is important as a factor that reduces the influence of crosstalk, but more precisely, the distance between the ejection orifices or the reflected pressure after ejecting a droplet is important. It should be specified based on the relationship with waves, etc. For example, although this is an extreme example, W/S≧50 can be satisfied even if the relationship between the arrangement of the communication ports 2 and the wall surface 1 of the relay room is determined as shown in FIG.

However, it is difficult to reduce crosstalk. The distance between ejection orifices, which is one of the factors for reducing crosstalk, is often determined based on specifications such as print speed or print density, and is rarely determined from the standpoint of crosstalk prevention. Therefore, it is desirable to take precautions against other factors, such as reflected pressure waves.

■--Fish The present invention was made in view of the above-mentioned circumstances.
In particular, this was done with the aim of eliminating crosstalk and making ejection performance uniform in a bubble jet type inkjet multi-nozzle array.

In order to achieve the above object, the present invention contains a recording liquid to be introduced, generates bubbles in the recording liquid by heat, and generates an action force as the volume of the bubbles increases. a flow path provided with an energy acting portion; an orifice connected to the flow path for ejecting the recording liquid as a droplet by the acting force;
In a liquid jet recording head comprising a liquid chamber for introducing the recording liquid into the flow path and a means for introducing the recording liquid into the liquid chamber, the height of the flow path is ha, and the height of the liquid chamber is It is characterized by satisfying the following relationship, where hb is hb.

Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a sectional view of a main part for explaining an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of a bubble jet head as an example of an inkjet head to which the present invention is applied, and FIG. The figure is a perspective view showing an example of a bubble jet head; FIG. 4 is a perspective view showing an example of a bubble jet head; )
FIG. 5 is a perspective view of the lid substrate shown in FIG. 4(a) seen from the back side. In the figure, 11 is the lid substrate, 12 is the heating element substrate, 1, 3 14 is a recording liquid inlet, 14 is an orifice, 15 is a channel, 1G is a region for forming a liquid chamber, 1.7 is an individual (independent) electrode, 18 is a common electrode, 1
9 is a heating element (heater), 20 is ink, 21 is a bubble, 2
2 is a flying ink droplet, and the present invention is.

This invention is applied to such a bubble jet type liquid jet recording head.

First, ink ejection by bubble jet will be explained with reference to FIG.

(a) is a steady state, in which the surface tension of the ink 20 and the external pressure are in equilibrium on the orifice surface.

In (b), the heater 19 is heated until the surface temperature of the heater 19 rises rapidly and boiling development occurs in the adjacent ink layer, and microbubbles 21 are scattered.

(Q) shows a state in which the adjacent ink layer that is rapidly heated on the entire surface of the heater 19 instantaneously vaporizes to form a boiling film, and the bubbles 21 grow. At this time, the pressure inside the nozzle increases by the amount of bubble growth, and the balance with the external pressure on the orifice surface is lost, causing an ink column to begin to grow from the orifice.

(d) shows a state in which the bubble has grown to its maximum, and ink 20 corresponding to the volume of the bubble is pushed out from the orifice surface. At this time, no current is flowing through the heater 19, and the surface temperature of the heater 19 is decreasing. The maximum value of the volume of the bubble 21 is slightly delayed from the timing of electric pulse application.

(e) shows a state in which the bubbles 21 are cooled by ink or the like and begin to contract.The tip of the ink column moves forward while maintaining the extruded speed, and the rear end of the ink column moves forward as the bubbles contract. Due to the decrease in internal pressure, ink flows back into the nozzle from the re-orifice surface, creating a constriction in the ink column.

In (f), the air bubbles 21 are further contracted, the ink comes into contact with the heater surface, and the heater surface is cooled even more rapidly. At the orifice surface, the external pressure is higher than the nozzle internal pressure, so the meniscus is largely moving into the nozzle. The tip of the ink column becomes a droplet and drops 5 to 1 droplets toward the recording paper.
It is flying at a speed of 0m/see.

(g) is a process in which ink is refilled (refilled) into the orifice by capillary action and the state returns to (a).
The bubbles have completely disappeared.

Therefore, the present invention is intended to prevent crosstalk between orifices in a multi-array type head in a bubble jet type inkjet as described above, and furthermore, to prevent the recording liquid from flowing from the liquid chamber to the flow path. Ink) is quickly replenished, and variations in the replenishment speed near the center of the multi-array and near both ends are reduced, thereby increasing the response frequency and reducing dispersion in ejection performance (ink near the center of the multi-array and near both ends). This is to reduce the difference between the two ends.

When putting the multi-array head as described above into practical use, as is well known, there is crosstalk between two orifices and variations in speed when replenishing recording liquid (ink) to each channel. Regarding crosstalk, for example, it can be almost solved by increasing the distance between adjacent orifices (flow paths), but in reality, the distance between adjacent orifices is often determined from the specifications of the printer itself, and crosstalk is not necessarily resolved. The distance may not be ideal for prevention. Therefore, a solution using another method is desired.

The present invention has been made in view of the second point mentioned above.If the height of the liquid chamber and the height of the flow path satisfy a certain relationship, the pressure waves that cause crosstalk will be transmitted to the flow path immediately adjacent to the liquid chamber. It was experimentally discovered that it has no effect on

On the other hand, a problem caused by variations in the speed of ink replenishment is that the replenishment speed is different near the center of the orifice and near both ends, resulting in variations in ejection performance and response frequency. To solve this problem, the liquid resistance from the walls (bottom and ceiling) of the liquid chamber to the ink moving inside the liquid chamber should be reduced. Experiments have shown that if you do this, the ink can move smoothly.

Although the above two points, that is, crosstalk and dispersion in ejection performance, are different problems, it can be seen that in order to solve them simultaneously, it is sufficient to set the height of the liquid chamber to a certain value.

FIG. 1 is a sectional view taken along the line I-X in FIG. 3, where the height of the flow path 15 is ha and the height of the liquid chamber 16 is bb.

By satisfying the relationship such that bb ha>2, the above two problems are solved.

Table 1 below shows experimental results using experimentally manufactured heads with different ha and hb dimensions.

Loss!・Without leakage or insufficient liquid supply,
It can be seen that good droplet ejection is performed at a high response frequency.

Further, in the present invention, the maximum response frequency becomes higher when the number of orifices is large and the arrangement density is high (for example, 16 orifices/1 m1 or more), and the present invention is especially effective for highly integrated heads.

FIG. 6 is a detailed diagram for explaining the structure of a bubble generating means using a heating resistor, and in FIG. 9, 31 is a heating resistor, 32
33 is an electrode, 33 is a protective layer, and 34 is a power supply device. Useful materials for forming the heating resistor 31 include, for example, a mixture of tantalum-3in, tantalum nitride, nichrome, a silver-palladium alloy, Silicon semiconductors, or hafnium, lanthanum, zirconium, titanium, tantalum, tungsten, molybdenum, niobium, and chromium.

Examples include borides of metals such as vanadium.

Among the materials constituting these heating resistors 31, metal borides are particularly excellent, and among them, hafnium boride has the best properties.
Next, zirconium boride.

The order is lanthanum boride, tantalum boride, vanadium boride, and niobium boride.

The heating resistor 31 can be formed using the above-mentioned materials using methods such as electron beam evaporation and sputtering. The film thickness of the heating resistor 31 is set so that the amount of heat generated per unit time is as desired.

It is determined according to its area, material, shape and size of the heat-acting part, as well as actual power consumption, etc., but in the normal case, it is o,oot~5μm, preferably 0.0μm.
It is assumed to be 1 to 1 μm.

As the material constituting the electrode 32, many commonly used electrode materials can be effectively used, and specifically,
For example, A Q p A g HA u HP te
Examples include Cu, and these materials are used to provide a predetermined size, shape, and thickness at a predetermined location by a method such as vapor deposition.

The characteristics required of the protective layer 33 are to protect the heat generating resistor 31 from the recording liquid without preventing the heat generated by the heat generating resistor 31 from being effectively transferred to the recording liquid. Examples of useful materials for forming the protective layer 33 include silicon oxide, silicon nitride, magnesium oxide, aluminum oxide, tantalum oxide, and zirconium oxide. It can be formed by The thickness of the protective layer 33 is usually 0.01 to 10 μm, preferably 0.1 to 5 μm, and most preferably 0.1 to 3 μm.

The recording head created as described above is supplied with recording liquid at a pressure such that the recording liquid will not be ejected from the ejection port when the heating resistor does not generate heat, and at the same time supplying the recording liquid in pulses to the electric/thermal converter according to the image signal. When a voltage was applied and recording was performed, a clear image was obtained.

FIG. 7 is a block diagram showing an example of the heating element drive circuit at that time. Reference numeral 41 denotes a known optical internal cuff sensor unit for reading, which is composed of a photodiode, etc. The image signal is processed by a processing circuit 42 consisting of a circuit such as a comparator, and then input to a drive circuit 43. The drive circuit 43 drives the recording head 44 by controlling the pulse width, pulse amplitude, repetition frequency, etc. according to the input signal.

For example, in the simplest recording, the input image signal is discriminated between black and white in the processing circuit 42 and input to the drive circuit 43. In the drive circuit 43, the pulse width and pulse amplitude for obtaining an appropriate droplet diameter and the repetition frequency for obtaining a desired recording droplet density are converted into controlled signals to drive the recording head 44.

In addition, as another recording method that takes gradation into consideration, one is to perform recording by changing the droplet diameter, and the other is to perform recording by changing the number of recording droplets as follows. You can also do it.

First, in the recording method for changing the droplet diameter, the image signal inputted by the optical cuff sensor section 41 is converted into an opening signal of pulse width and pulse amplitude of each level determined to obtain the desired droplet diameter. Drive circuit 4 having multiple output circuits
The processing circuit 42 determines which of the three signal levels should be used for outputting the signal and processes the signal. In addition, in the method of changing the number of recording droplets, the optical internal cuff sensor section 4
The input signal to 1 is A/D converted and outputted in the processing circuit 42, and according to the output signal, the drive circuit 43 controls the recording head so that recording is performed by changing the number of ejected droplets per one input signal. Outputs a signal to drive 44.

Alternatively, a similar device may be used to supply the recording liquid to the recording head 44 at a pressure higher than the pressure at which the recording liquid overflows from the ejection port without causing the heating resistor to generate heat, while performing electrothermal conversion. When recording was performed by applying a voltage to the body in the form of continuous repeated pulses, it was confirmed that droplets of a number corresponding to the applied frequency were ejected stably and with a uniform diameter.

From this point of view, it has been found that the recording head 44 is extremely effectively applied to continuous ejection at high frequencies.

In addition, since the recording head, which is the main part of the recording device, is minute, it is possible to easily line up multiple recording heads, allowing high-density Multi-Oi]
Fisted recording heads are possible.

FIG. 8 is a diagram for explaining another means for generating bubbles in the recording liquid. In the figure, 51 is a laser oscillator, 52 is an optical modulation drive circuit, 53 is an optical modulator, 54 is a scanner, and 55 is a condensing lens, and a laser beam generated by a laser oscillator 51 is pulse-modulated in an optical modulator 53 according to an image information signal that is input to an optical modulator drive circuit 52, electrically processed, and output. . The pulse-modulated laser beam passes through a scanner 54 and is focused by a condensing lens 55 on the outer wall of the thermal energy acting section, heating the outer wall 56 of the recording head and causing the inner recording liquid 57 to be heated. to generate air bubbles. Alternatively, the wall 56 of the thermal energy application section is made of a material that is transparent to the laser beam, and the laser beam is condensed by the condenser lens 55 so as to be focused on the recording liquid 57 inside, thereby directly heating the recording liquid. Bubbles may be generated by

FIG. 9 is a diagram for explaining an example of a printer using laser light as described above, in which the nozzle section 61 is arranged at a high density (for example, 8 nozzles/am).

An example is shown in which the stacks of paper 62 (for example, A4 width) are stacked so as to cover all of them.

Laser light emitted from the laser oscillator 51 is guided to the entrance aperture of the optical modulator 53. In the optical modulator 53, the laser beam undergoes intensity modulation according to the image information input signal to the optical modulator 53. The modulated laser beam passes through the reflecting mirror 5.
8 bends the optical path toward the beam expander 59 and enters the beam expander 59 . The zero-order laser beam whose beam diameter is expanded by the beam expander 59 while remaining parallel is as follows:
Rotating polygon that rotates at high speed and constant speed #! 0 rotation polygon incident on 6o! The laser beam swept by 1180 is imaged by the condenser lens 55 on the outer wall 56 of the thermal energy acting part of the drop generator or on the recording liquid inside.

As a result, bubbles are generated in each thermal energy applying portion, and recording droplets are ejected to perform recording on the recording paper 62.

FIG. 10 is a diagram showing still another bubble generating means. In this example, a pair of discharge electrodes 7o arranged on the inner wall side of the thermal energy application section receive a high voltage pulse from a discharge device 71, A discharge is caused in the recording liquid, and the heat generated by the discharge instantly forms bubbles.

11 to 18 are diagrams showing specific examples of the discharge electrode shown in FIG. 10, respectively.

In the example shown in FIG. 11, the electrode 70 is shaped like a needle to concentrate the electric field and cause an efficient discharge (with low energy).

In the example shown in FIG. 12, two flat plate electrodes are used so that air bubbles are stably generated between the electrodes. The position of generated bubbles is more stable than needle-shaped electrodes.

The example shown in FIG. 13 is one in which the electrode has a substantially coaxial hole. The holes in the two electrodes serve as guides, making the position of one generated bubble even more stable.

The example shown in FIG. 14 is a ring-shaped electrode, which is basically the same as the example shown in FIG. 14, and is a modified example thereof.

In the example shown in FIG. 15, one side is a ring-shaped electrode and the other side is a needle-shaped electrode. The ring-shaped electrode aims to stabilize the generated bubbles, and the needle-shaped electrode aims to improve efficiency by concentrating the electric field.

In the example shown in FIG. 16, one ring-shaped electrode is formed on the wall surface of the thermal energy application section. In addition to the effects of the example shown in FIG. 15, this is aimed at ease of manufacturing by forming electrodes in a two-dimensional manner on the substrate. A plurality of such planar electrodes can be easily manufactured with high density by vapor deposition (or sputtering) or photoetching techniques. Particularly effective for multi-arrays.

The example shown in FIG.

The ring-shaped electrode forming part of the example shown in Fig. 16 is placed on the outer periphery of the electrode and is raised one step higher than the surrounding area.This is also aimed at stabilizing the generated bubbles, and as shown in Fig. 15. Adding a three-dimensional guide to the one shown will make it more stable.

As is clear from the above explanation, according to the present invention, in a multi-nozzle array bubble jet liquid jet recording head, crosstalk between each flow path is eliminated, and the ejection performance is improved between the center area and the edge area. This has the advantage that there is no variation in the frequency, and the response frequency can be further increased.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of main parts for explaining an embodiment of the present invention, and FIG. 2 is a diagram for explaining the operation of a bubble jet head as an example of an inkjet head to which the present invention is applied. Fig. 3 is a perspective view showing an example of a bubble jet head, Fig. 4 is an exploded perspective view, Fig. 5 is a view of the lid substrate from the back side, and Fig. 6 is a bubble jet head using a heating resistor. FIG. 7 is a block diagram for explaining an example of a heating element drive circuit; FIG. 8 is a diagram for explaining an example of a bubble generating means using laser light. , FIG. 9 is a diagram for explaining an example of a printer, FIG. 10 is a diagram for explaining an example of a bubble generating means using electric discharge, and FIGS. 11 to 18 are diagrams for explaining an example of a printer. 611 is a diagram showing a specific example of the discharge electrode shown in FIG. 10, and FIG. 19 is a diagram for explaining an example of the prior art.
- Blue substrate, 1.2... Heating element substrate, 14... Orifice, 15... Channel, 16... Liquid chamber, 17.18.
...Electrode, J9...Heating element, 20...Recording liquid, 21
...bubbles. Figure 1 Bu 2 x Figure 3 Figure Figure Figure Figure

Claims (1)

[Claims] 1. A flow path that accommodates the recording liquid introduced and is provided with a thermal energy acting section that generates bubbles in the recording liquid by heat and generates an acting force as the volume of the bubbles increases. an orifice that communicates with the flow path and causes the recording liquid to be ejected as droplets by the acting force; and a liquid chamber that communicates with the flow path and introduces the recording liquid into the flow path. In a liquid jet recording head comprising means for introducing the recording liquid into the liquid chamber, when the height of the flow path is ha and the height of the liquid chamber is hb, [(hb)/
A liquid jet recording head characterized in that it satisfies the following relationship: (ha)]>2.