JP2793593B2 - Liquid jet recording head - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid jet recording head, and more particularly, to driving of a thermal energy action section of a bubble jet type ink jet recording head.

2. Description of the Related Art Non-impact recording methods have recently attracted attention in that the generation of noise during recording is extremely small to a negligible level. Among them, the so-called ink jet recording method, which can perform high-speed recording and can perform recording on so-called plain paper without requiring a special fixing process, is an extremely powerful recording method. Some have been proposed and commercialized with improvements, while others are still being put to practical use.

In such an ink jet recording method, recording is performed by flying droplets of a recording liquid called so-called ink and attaching the droplets to a recording member. The control method for controlling the flying direction of the generated recording liquid droplet is roughly classified into several types.

First, the first method is, for example, a method disclosed in US Pat. No. 3,060,429 (Tele type method), in which droplets of a recording liquid are generated by electrostatic absorption, and the generated droplets of the recording liquid are converted according to a recording signal. The electric field is controlled, and recording is performed by selectively adhering the recording liquid droplets onto the recording member.

More specifically, in more detail, an electric field is applied between the nozzle and the accelerating electrode to discharge a uniformly charged droplet of the recording liquid from the nozzle, and the discharged droplet of the recording liquid is converted into a recording signal. In accordance with this, recording is performed by causing the droplets to fly between the xy deflection electrodes configured so as to be electrically controllable and selectively adhering small droplets onto the recording member by a change in the intensity of the electric field.

The second method is a method (Sweet method) disclosed in, for example, US Pat. No. 3,596,275, US Pat. No. 3,298,030, in which a droplet of a recording liquid whose charge amount is controlled by a continuous vibration generation method is generated, and the generated charging is performed. The recording is performed on the recording member by causing the controlled amount of the droplet to fly between the deflection electrodes to which a uniform electric field is applied.

More specifically, a charging electrode configured so that a recording signal is applied in front of an orifice (ejection port) of a nozzle, which is a part of a recording head provided with a piezoelectric vibrating element, is separated by a predetermined distance. The piezoelectric vibrating element is mechanically vibrated by applying an electric signal of a constant frequency to the piezoelectric vibrating element, and a droplet of the recording liquid is discharged from the discharge 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 amount according to the recording signal. When the droplet of the recording liquid whose charge amount is controlled flies between the deflection electrodes to which a constant electric field is uniformly applied, the droplet is deflected according to the added charge amount and carries a recording signal. Only the recording material can be deposited on the recording member.

The third method is a method (Hertz method) disclosed in, for example, US Pat. No. 3,416,153, in which an electric field is applied between a nozzle and a ring-shaped charging electrode to generate and expose small droplets of a recording liquid by a continuous vibration generation method. This is the method of recording. That is, in this method, the intensity of the electric field applied between the nozzle and the charging electrode is modulated according to the recording signal to control the dewdrop state of the small droplet, and the gradation of the recorded image is obtained for recording.

The system shown in FIG. 4 is, for example, a system (Stemme system) disclosed in US Pat. No. 3,747,120. This system is fundamentally different from the above three systems in principle.

That is, in each of the three methods, the droplet of the recording liquid discharged from the nozzle is electrically controlled during the flight, and the droplet carrying the recording signal is selectively attached to the recording member. On the other hand, according to the Stemme method, recording is performed by ejecting a small droplet of recording liquid from an ejection port in accordance with a recording signal.

That is, in the Stemme method, the piezoelectric vibrating element attached to the recording head having the ejection port for ejecting the recording liquid includes:
Applying an electrical recording signal, converting the electrical recording signal into mechanical vibration of a piezo-vibrating element, and ejecting a droplet of the recording liquid from the ejection port in accordance with the mechanical vibration to cause the droplet to fly and adhere to the recording member. Is to record.

Each of these four conventional methods has its own features, but on the other hand, there are points that can be solved.

That is, in the first to third methods, the direct energy of the generation of the droplet of the recording liquid is electric energy,
Droplet deflection control is also electric field control. Therefore, the first method is simple in structure, but requires a high voltage to generate small droplets, and is not suitable for high-speed printing because it is difficult to use a multi-nozzle recording head.

The second method enables multi-nozzle recording heads and is suitable for high-speed recording. However, the method is complicated in structure, and the electrical control of small droplets of recording liquid is difficult and difficult. Are liable to occur.

The third method has a feature that an image with excellent gradation can be recorded by exposing a recording liquid droplet, but on the other hand, it is difficult to control the dew state, and fogging occurs in the recorded image. In addition, there are problems such as the fact that it is difficult to use a multi-nozzle recording head, and it is not suitable for high-speed recording.

The fourth scheme has relatively many advantages over the first to third schemes. That is, in order to perform recording by discharging the recording liquid from the discharge port of the nozzle on demand (on-demand), it is simple in terms of the configuration. It is not necessary to collect small droplets that are not required for recording an image, and there is no need to use a conductive recording liquid as in the first and second methods, and the recording liquid material Has a great advantage such as a large degree of freedom. However, on the other hand, it is difficult to form a multi-nozzle recording head because there are problems in processing the recording head and it is extremely difficult to reduce the size of the piezoelectric vibrating element having a desired resonance number. However, since the recording liquid droplets are ejected and fly by the mechanical energy of mechanical vibration of the piezo-vibration element, it is not suitable for high-speed recording.

Furthermore, Japanese Patent Application Laid-Open No. 48-9622 (corresponding to the above-mentioned US Pat. No. 3,747,120) describes, as a modification, the use of thermal energy instead of the mechanical vibration energy by means such as the piezo-vibration element. Have been.

That is, the above-mentioned publication describes that a heating coil that directly heats a liquid in order to generate a vapor that causes a pressure increase is used as a pressure increasing means instead of the piezoelectric vibrating element.

However, the above publication discloses that a heating coil serving as a pressure increasing means is energized to directly evaporate the liquid ink in a bag-shaped ink chamber (liquid chamber) having only one opening through which the liquid ink can enter and exit. However, there is no suggestion as to how to heat the liquid when the liquid is continuously and repeatedly discharged. In addition, since the position where the heating coil is provided is provided at the deepest part of the bag-shaped liquid chamber far from the supply path of the liquid ink, in addition to being complicated in terms of the head structure, continuous It is not suitable for repeated use.

Moreover, according to the technical contents described in the above-mentioned publication, it is not possible to quickly form a preparation state for the next liquid discharge after performing the liquid discharge with the generated heat which is practically important.

As described above, the conventional method has advantages and disadvantages in terms of configuration, high-speed recording, multi-nozzle recording head, generation of satellite dots and occurrence of fogging of a recorded image, etc. There was a restriction that only the application was possible.

Japanese Patent Application Laid-Open No. 55-132259 discloses that in a bubble jet ink jet recording head, two or more heating elements are provided, and gradation recording is performed by shifting the timing of an input signal for heating these heating elements. However, in this case, two (or more) bubbles are generated with a time lag by inputting a signal twice (or more) at a shifted timing. Accordingly, the time required for the growth of the ink column, the ejection, and the recovery of the meniscus (in other words, the replenishment of the ink from the supply side) becomes longer due to the generation, growth, and contraction of the air bubble, and the printing speed decreases. .

Object The present invention has been made in view of the above circumstances, and particularly, in recording using a bubble jet type ink jet recording head, performs gradation recording, and does not perform normal gradation recording with printing speed. The purpose is to provide a recording method equivalent to the case.

Configuration In order to achieve the above object, the present invention provides a thermal energy operating section that accommodates a recording liquid to be introduced, generates bubbles in the recording liquid by heat, and generates an action force accompanying an increase in the volume of the bubbles. A flow path provided with a orifice for communicating with the flow path and discharging the recording liquid as droplets by the action force, and an orifice for communicating with the flow path and introducing the recording liquid into the flow path. A liquid jet recording head comprising a liquid chamber and a means for introducing the recording liquid into the liquid chamber, wherein the thermal energy action section comprises two independent heating elements, and these heating elements are independently driven. In the liquid jet recording head to which a signal can be input,
When two heating elements are driven in cooperation with each other, two driving signals are input to the two heating elements at the same time, and one of the two independent heating elements is driven to be larger than a bubble formed. The method is characterized in that one bubble is generated and the droplet is discharged by the action force of the one large bubble. Hereinafter, a description will be given based on an example of the present invention.

FIG. 1 is a main part configuration diagram 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. FIG. 4 is a diagram for explaining the operation of a bubble jet head as an example of an ink jet 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 a diagram shown in FIG. FIG. 5A is a perspective view of the head substrate when disassembled into a lid substrate (FIG. 5A) and a heating element substrate (FIG. 5B). FIG. 6 is a lid substrate shown in FIG. 5A. 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 flow path, 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), 20 is a recording liquid (ink), 21 is a bubble, and 22 is a flying ink droplet.

First, the ink ejection by the bubble jet will be described with reference to FIG. 3. (a) is a steady state, in which the surface tension of the ink 20 and the external pressure are in an equilibrium state at the orifice surface.

3B shows a state in which the heater 19 is heated until the surface temperature of the heater 19 sharply rises and the adjacent ink layer is heated until boiling development occurs, and minute bubbles 21 are scattered.

(C) is a state in which the adjacent ink layer heated rapidly on the entire surface of the heater 19 is instantaneously vaporized to form a boiling film, and the bubbles 21 grow. At this time, the pressure in the nozzle rises by an amount corresponding to the growth of the bubble, the balance with the external pressure on the orifice surface is lost, and the ink column starts to grow from the orifice.

(B) shows a state in which the bubble has grown to the maximum, and the 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 applying the electric pulse.

(E) shows a state where the bubble 21 is cooled by ink or the like and starts to contract. At the front end of the ink column, the ink moves forward while maintaining the extruded speed, and at the rear end, the ink flows back from the orifice surface into the nozzle due to the decrease in the internal pressure of the nozzle due to the shrinkage of the bubble, causing the ink column to constrict. I have.

4F, the bubble 21 is further contracted, the ink comes into contact with the heater surface, and the heater surface is cooled more rapidly. At the orifice surface, the external pressure is higher than the internal pressure of the nozzle, so that the meniscus largely enters the nozzle. The tip of the ink column becomes a droplet and moves in the direction of the recording paper.
Flying at a speed of 10m / sec.

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

The present invention, in the bubble jet type ink jet recording head as described above, performs gradation recording, and, in order to make the printing speed equal to when normal gradation recording is not performed, in the present invention The heating element 19 is separated into two parts, for example, 19a and 19b, and can be driven independently by the control electrodes 17a and 17b. However, in the present invention, even if the heating element is separated into two (or more), only one bubble is generated.

FIG. 2 is a diagram showing an example of a signal for driving the heating elements 19a and 19b. In the present invention, the timings of the signals E ₁ and E ₂ input to the two heating elements 19a and 19b are shown in FIG. And at the same time, and do not change as in the technique described in JP-A-55-132259. Therefore, two adjacent heating elements are heated simultaneously, and only one bubble is generated. However, even if the timing is not changed, the rising of two signals does not show exactly the same rising in a very short time.
Not surprisingly, there are slight differences. In short, the present invention does not intentionally change the timing and generate two bubbles as in the invention described in JP-A-55-132259. To be generated.

Figure 2 is substantially the energy added simultaneously to the first and second heating element, intended to explain how to change the pixel size, E ₁ is the energy applied to the first heating element 19a, the E ₂ second Energy to be applied to the heating element 19b of
In the present invention, by combining the values of E ₁ and E _2,
Various large and small bubbles can be generated. Accordingly, the size of the ejected ink droplet changes in accordance with the change, the pixel diameter can be changed, and the gradation can be stored. The applied energy can be varied by changing, for example, a pulse voltage, a pulse width, or a flowing current. In FIG. 2A, the second heating element 19b is used.
To to reduce the voltage E ₂ addition is obtained (Figure 2 compared to E ₂ in (b)) is recorded on the recording paper to reduce the size of the pixels 30.

The advantage of having a plurality of heating elements to generate one bubble is that the bubble diameter can be changed by changing the input energy level with one heating element, and gradation expression is possible. However, there is a limit to the gradation level (range) that can be expressed. Thus, the heating element is, for example, 2
It is obvious that the number of gradation levels that can be expressed by simple calculation will be doubled if the number is provided.
In the invention described in JP-A-132259, as shown in FIG. 7, the timings of the energy E ₁ and E ₂ applied to the two heating elements are changed, and it takes t ₂ hours to drive the heating elements. However, in the present invention, since both heating elements are driven at the same time, t ₁ (t ₁ <
t ₂ ) The time may be sufficient, and the bubble generation time to the ejection response speed can be increased.

Effects As is clear from the above description, according to the present invention, in bubble jet ink jet recording, gradation recording can be performed at substantially the same speed as non-gradation recording.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part (heating unit) for explaining an embodiment of the present invention, FIG. 2 is a waveform diagram of a heating element drive signal for explaining an operation of the present invention, FIG. Is a view 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, FIG. 5 is an exploded perspective view, FIG. 6 is a view of the lid substrate viewed from the back side, and FIG.
FIG. 9 is a diagram for explaining an example of the related art. 11 ... lid substrate, 12 ... heating element substrate, 17, 17a, 17b, 18 ...
Electrodes, 19, 19a, 19b: heating element, 20: recording liquid, 21: air bubble, 22: flying droplet, 30: recording pixel.

Claims (1)

(57) [Claims] 1. A storage device for accommodating a recording liquid to be introduced,
A flow path attached to a thermal energy action section for generating air bubbles in the recording liquid by heat and generating an operation force accompanying an increase in the volume of the air bubbles; A liquid jet recording head comprising: an orifice for discharging droplets; a liquid chamber communicating with the flow path and introducing the recording liquid into the flow path; and a means for introducing the recording liquid into the liquid chamber. The heat energy operating section is composed of two independent heating elements, and the two heating elements are driven in cooperation in a liquid jet recording head to which a driving signal can be input independently. In this case, two driving signals are input to the two heating elements at the same time, and one of the two independent heating elements is driven to generate one bubble larger than a bubble formed. One Liquid jet recording head and performs droplet ejection by the action force of the bubbles.