JPH01235652A - Liquid jet recording - Google Patents

Abstract

PURPOSE:To allow gradation recording to be performed and printing speed to be set at the same level as when gradation recording is not performed in a normal operation mode by entering an independent energy-level signal in at least two independent areas and permitting a single bubble to generate by a combination of said signals and its size to change. CONSTITUTION:A heat-generating element section is, for instance, divided in two elements 19a, 19b, and these are allowed to drive independently by means of their respective control electrodes. Signals E1, E2 are so timed as to enter the two heat-generating elements 19a, 19b almost simultaneously to generate a single bubble. It is possible to generate bubbles of different sizes by combining the values of E1 and E2. Accordingly, the size of ink droplets to be discharged changes and the diameter of pixels can be changed to enable gradation recording. Both heat-generating elements are caused to drive concurrently, so that bubble production time can be shortened and discharge response speed be increased. At the same time, the gradation recording can be achieved at almost the same speed as the non-gradation recording.

Description

[Detailed description of the invention] Technical field The present invention relates to a liquid jet recording method, and more particularly, to a liquid jet recording method.

The present invention relates to a method of driving a thermal energy application section of a bubble jet type inkjet recording head.

The Asahi elephant skin non-impact recording method has recently attracted attention because the noise generated during recording is so small that it can be ignored. Among them, high-speed recording is possible,
Moreover, 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 and improvements have been made to date. Some have been commercialized, and efforts are still being made to put them into practical use.

In this type of inkjet recording method, recording is performed by causing droplets of a recording liquid called ink to fly and adhere to a recording member. There are several types of methods depending on the control method used to control the flight direction of the generated recording liquid droplets.

First, the first method is the one disclosed in USP 3060429 (Tele type method), in which tJs droplets of recording liquid are generated electrostatically, and the generated recording liquid droplets are used as a recording signal. Recording is performed by controlling the electric field in accordance with the temperature and selectively depositing recording liquid droplets on the 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 described, for example, in USP 3596275, U
The method disclosed in SP 3298030 etc. (Swe
et method), in which droplets of recording liquid with a controlled amount of charge are generated by a continuous vibration generation method, and a --like electric field is applied to the generated droplets with a controlled amount of charge. Recording is performed on a recording member by flying between deflection electrodes.

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, charges are electrostatically induced in the recording liquid droplet discharged by the charging electrode, and the droplet is charged with an amount of charge corresponding to the recording signal. (2) When a small 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 added, and the small droplet that carries the recording signal Only drops can be deposited on the recording member.

The third method is, for example, the method disclosed in U.S. Pat. No. 3,416,153 (Llertz method), in which an electric field is applied between a nozzle and a ring-shaped charging electrode, and small droplets of recording liquid are generated and misted by a continuous vibration generation method. This is a method of converting and recording. That is, in this method, the atomization state of small droplets is controlled by varying the electric field strength 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 US Pat. No. 3,747,120 (Stemme 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, this Stemme 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 Stemme 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. According to the mechanical vibration, small droplets of recording liquid are ejected from the ejection port and attached to the recording member, thereby performing recording.

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. Second, it is not necessary to collect droplets that are not needed to record an image, and unlike the first and second methods, there is no need to use a conductive recording liquid, and the material of the recording liquid is It has great advantages such as a high degree of freedom. On the other hand, it is difficult to make the recording head multi-nozzle because there are problems in processing the recording head, and it is extremely difficult to miniaturize the piezoelectric vibrating element having the desired resonance number. This method has drawbacks such as that it is not suitable for high-speed recording because the recording liquid droplets are ejected and ejected in 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-mentioned US P3
No. 747120) discloses, as a modification, the use of thermal energy instead of the mechanical vibration energy provided by means such as the piezo vibration element.

That is, the above-mentioned publication describes the use of a heating coil that directly heats a liquid as a pressure increasing means in place of the piezo vibrating element in order to generate steam that causes a pressure increase.

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, it is not clear 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.

Furthermore, Japanese Patent Application Laid-open No. 55-132259 discloses that in a bubble jet type inkjet recording head, two or more heating elements are provided and the timing of input signals for heating these heating elements is shifted to perform gradation recording. As proposed by Tsutsumi, if you do this, by inputting the signal twice (or more) at different timings,
Two (or more) bubbles are generated. Therefore, the generation of bubbles~
As the ink column grows and contracts, the time required for ink column growth, ejection, and meniscus recovery (in other words, ink replenishment from the supply side) at the orifice portion becomes longer, and the printing speed decreases.

Purpose The present invention was made in view of the above-mentioned circumstances.
In particular, it was developed with the aim of providing a recording method that performs gradation recording using a bubble jet type inkjet recording head and makes the printing speed equivalent to that of normal gradation recording. It is.

Structure In order to achieve the above-mentioned object, the present invention provides a thermal energy application unit that accommodates the recording liquid introduced, generates bubbles in the recording liquid by heat, and generates an acting force as the volume of the bubbles increases. an orifice connected to the flow path for ejecting the recording liquid as droplets by the acting force; and an orifice connected to the flow path for introducing the recording liquid into the flow path. In a liquid jet recording head comprising a liquid chamber and a means for introducing the recording liquid into the liquid chamber, the thermal energy acting section comprises at least two independent regions, each of which has an independently variable energy level. The present invention is characterized in that the signals are input, and the combination of the signals generates one bubble and changes its size to eject the droplet. Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a block diagram of main parts for explaining an embodiment of the present invention, FIG. 2 is a diagram showing an example of a heating element drive signal for explaining the operation of the present invention, and FIG. 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. 4 is a perspective view showing an example of a bubble jet head, and FIG. FIG. 6 is a perspective view of the head when it is disassembled into the lid substrate (FIG. 5(a)) and the heating element substrate (FIG. 5(b)).
This is a perspective view of the lid substrate shown in FIG. 5(a) seen from the back side.
In the figure, 11 is a lid substrate, 12 is a heating element substrate, 13 is a recording liquid inlet, 14 is an orifice, 15 is a channel, 16 is a region for forming a liquid chamber, 17 is an individual (independent) electrode, 18
is a common electrode, 19 is a heating element (heater), and 20 is a recording liquid (
21 is a bubble, and 22 is a flying ink droplet.

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.

(C) shows a state in which adjacent ink layers that are rapidly heated over the entire surface of the heater 19 are instantaneously vaporized 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. At the tip of the ink column, it moves forward while maintaining the extruded speed, and at the rear end, the ink flows backward from the orifice surface into the nozzle due to the decrease in nozzle internal pressure as the bubbles contract, 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.

In (g), the air bubbles have completely disappeared in the process of refilling the orifice with ink by capillary action and returning to the state of (a).

The present invention performs gradation recording in the bubble jet type inkjet recording head as described above.

In addition, the printing speed is made to be the same as when normal gradation recording is not performed.In the present invention, the heating element section 19 is separated into two parts, for example, 19a and 19b, and each The control electrodes 17a and 17b can each be driven independently. However, in the present invention, only one bubble is generated even if the heating element is separated into two (or more) parts.

FIG. 2 is a diagram showing an example of a signal for driving the heating elements 19a, 19b. In the present invention, two heating elements 19a, 19
The timings of the signals E, , E2 inputted to the terminals b are simultaneous as shown in FIG. 2, and are not changed as in the technique described in Japanese Patent Application Laid-Open No. 55-132259. Therefore, two nearby
The two heating elements are heated at the same time, and only one bubble is generated. just.

Even if the timing is not changed, if you look at the rising edges of two signals over a very short period of time, they will never show exactly the same rising edge, so of course there will be this slight difference. In short, the present invention is based on JP-A-55-132
Rather than generating two bubbles by intentionally changing the timing as in the invention described in Japanese Patent No. 259, the timing of the signals is almost the same and one bubble is generated.

Fig. 2 explains a method of applying energy to the first and second heating elements almost simultaneously to change the pixel diameter, where E is the energy applied to the first heating element 19a, and E2 is the energy applied to the second heating element 19a. In the present invention, by combining the values of E and E2, it is possible to generate bubbles of various sizes.

Therefore, the size of the ejected ink droplet changes accordingly, and the pixel diameter can be changed, making it possible to perform one-tone recording. Add energy, for example.

The pulse ', can be varied by changing the pressure, the pulse 11] or the flowing current, and in FIG. Compared to E2 in b), this is recorded on paper a and the size of the pixel 3o is made smaller.

The advantage of using multiple heating elements to generate one bubble is that by changing the input energy level with one heating element, the bubble diameter can be changed, making it possible to express gradations. However, there is a limit to the gradation level (range) that can be expressed. It is clear that if one heating element is provided on two sides, for example, the gradation level that can be expressed will be doubled by simple calculation.
In the invention described in No. 132259, No. 7
As shown in the figure, the energy E1 applied to the two heating elements
．． The timing of E2 is changed, and it takes t2 hours to drive the heating element, but in the present invention, the surface heating element is driven at the same time, so tx (tx< tz) time, and the bubble generation time to discharge response speed can be increased.

Effects As is clear from the above description, according to the present invention, gradation printing can be performed at approximately the same speed as non-gradation printing in bubble jet type inkjet 1 to printing.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of the main part (heat generating part) for explaining one embodiment of the present invention, FIG. 2 is a waveform diagram of a driving signal of a heating element 1 for explaining the operation of the present invention, and FIG. The figure 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. 4 is a perspective view showing an example of a bubble jet head, and FIG. 5 is an exploded perspective view. , FIG. 6 is a diagram of the lid substrate viewed from the back side, and FIG. 7 is a diagram for explaining an example of the prior art. 11...Lid substrate, 12...Heating element substrate, 17.17a
. 17b, 18-・electrode, 19, l9a, 1
9 b - heating element, 20 - recording liquid, 21... air bubbles,
22... Flying droplet, 30 recording pixels.

Claims (1)

[Claims] 1. A flow path that accommodates the recording liquid to be 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 in communication with which the recording liquid is ejected as a droplet by the acting force; a liquid chamber in communication with the flow path and with which the recording liquid is introduced into the flow path; In a liquid jet recording head comprising a means for introducing thermal energy, the thermal energy applying section comprises at least two independent regions, signals with variable energy levels are inputted to these regions independently, and a combination of the signals causes the thermal energy to be applied. A liquid jet recording method characterized in that the droplet is ejected by generating one bubble and changing its size.