JPH021312A - Liquid jet recording head - Google Patents

Abstract

PURPOSE:To achieve stable discharge of a jet liquid drop by generating bubbles in good stability by a method wherein a ratio of a radius of a projected circular figure on a passage containing a thermal energy operating part of a bubble to time is specified, and generating conditions of the bubble are controlled. CONSTITUTION:Recording liquid is stored and besides, a bubble is generated in this recording liquid by heat. A thermal energy operating part generating working force following increase of volume of the bubble 31 is annexed to the passage. An orifice for discharging the recording liquid as a liquid drop by this working force is interconnected by arrangement to the passage. When a radius of a projected circular figure to the passage containing the thermal energy operating part of this bubble 31 is taken as gamma to be taken as an ordinate and time (t) is taken as an abscissa, dr/dt is established to be larger than d(r+DELTAr)/d(t+DELTAt) from a point of time when the bubbles 31 reaches one half of a maximum volume just before reaching the maximum volume. However, DELTAr, and DELTAt are taken as positive increase. Consequently, the bubble is stably generated and a jet liquid drop is discharged in good stability from the orifice.

Description

DETAILED DESCRIPTION OF THE INVENTION Separation of Powers The present invention relates to a liquid jet recording head, and more particularly to a bubble jet type liquid jet recording head.

The conventional absorption non-impact recording method has recently attracted attention because the noise generated during recording is extremely small to the extent that it can be ignored. 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 B. Various methods have been proposed and improvements have been made to improve the quality of products. Some have been developed, and efforts are still being made to put them into practical use.

Such Infusiera I recording method involves flying small droplets of recording liquid called ink.
The method of generating droplets of the recording liquid and the generated recording (however, Δr
, Δ is an increment (>O)) There are several methods for controlling the flying direction of droplets.

First, the first method is the one disclosed in, for example, USP 3060429 (Tele type method), in which small droplets of recording material 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 elaborate more on this, what about the nozzle and acceleration? I! An xy deflection electrode configured to apply an electric field between the electrodes to eject a negatively charged recording liquid droplet from a nozzle, and to electrically control the ejected recording liquid droplet in accordance with a recording signal. Recording is performed by making the droplets fly between the recording members and selectively attach them to the recording member by changing the intensity of the electric field.

The second method is described, for example, in USP 3596275, U
The method disclosed in SP 3298030 etc. (Swe
et method), in which small droplets of recording liquid with a controlled amount of charge are generated by a continuous vibration generation method, and the generated droplets with a controlled amount of charge are deflected by a --like electric field. Recording is performed on a recording member by flying between 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. When a droplet of recording liquid whose Ip charge is controlled flies between deflection electrodes to which a constant electric field is applied, it is deflected according to the amount of charge applied, and plays a role in recording equalization. Only small droplets are allowed to deposit on the recording member.

The third method is, for example, USP:1416. L53 (Llertz method), which applies an electric field between a nozzle and a ring-shaped charging electrode and uses a continuous vibration generation method to generate and atomize small droplets of recording liquid for recording. . That is, in this method, the atomization state of small droplets is controlled by modulating the electric field strength applied between the nozzle and the charging electrode in accordance with the recording signal, and the 1lIff tonality of the recorded image is produced and recorded.

The fourth method is a method (Stemme method) disclosed in, for example, USP 3,747,120, and this method is fundamentally different in principle from the above three methods.

That is, in all three methods, the droplets of the recording liquid ejected from the nozzle are electrically controlled while they are in flight, and the droplets carrying the recording signal are selectively deposited on the recording member. In contrast, this Stcmme method records
Recording is performed by ejecting small droplets from the recording body in response to a recording signal.

In other words, the Stemme method uses piezo vibration;
An electrical recording signal is applied to the third element, the electrical recording signal is converted into mechanical vibration of the piezoelectric vibrating element, and a droplet of recording liquid is ejected from the ejection port according to the mechanical vibration to fly the recording member. Recording is done by attaching it to the surface.

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 is complicated in structure and the electrical control of the recording liquid droplets is sophisticated and difficult; 2! Satellite on the recording material!・There are problems such as dots being easily generated.

The third method has the advantage of being able to record images with excellent gradation by atomizing a small amount of recording liquid, but on the other hand, it is difficult to control the atomization state and fog occurs on the recorded image. And it is difficult to make the recording head multi-nozzle.
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 configuration is simple, and since recording is performed by ejecting the recording liquid from the ejection opening of the nozzle on-demand (on-de+aand), it is possible to eject small droplets that fly as in the first to third methods. Second, it is not necessary to collect droplets that are not needed for recording an image, and unlike the first and second methods, there is no need to use a conductive recording body, 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 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, the above-mentioned publication discloses that the liquid ink in the bag-shaped ink chamber (liquid chamber), which has only one opening through which liquid ink can enter and exit, is directly heated by energizing a heating coil as a pressure means. It is only described that the liquid is vaporized, and there is no suggestion as to how to heat the liquid when continuously and repeatedly discharging the liquid. 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. It is not suitable for repeated use.

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.

In this way, the conventional method has advantages and disadvantages in terms of structure, high-speed recording, multi-nozzle recording head, and satellite dots, and it should be applied only to applications that take advantage of these advantages1j)
There was a restriction that there was no

Furthermore, Japanese Patent Application Laid-Open No. 55-161665 discloses that in a bubble jet type liquid jet recording head, by recording in such a way that the average value of the volume change rate of bubbles is 5×103 sec1 or more, continuous long-term recording is possible. Also, a liquid jet recording method has been disclosed which is capable of always stably recording high-speed, high-resolution, and higher-quality images.

FIG. 6 is a diagram for explaining an example of the liquid jet recording head disclosed in the above-mentioned Japanese Patent Application Laid-open No. 56-161665, and FIG. 6(a) is a front view of the liquid jet recording head as seen from the orifice side. The partial view, FIG. 6(b), is a partial cross-sectional view of FIG. 6(a) taken along the section indicated by the dashed line XY. The orifice 5 is bonded so as to cover the surface of the substrate 3 on which the converter 2 is provided with a grooved plate 4 having a predetermined number of grooves with a predetermined linear density and a predetermined +j+ depth.
It has a structure in which a liquid discharge part 6 is formed. In the case of the recording head shown in the figure, a plurality of orifices 5 (51, 52,
5.), but of course application to a recording head with a single orifice is also possible.

The liquid ejection part 6 has an orifice 5 at its terminal end for ejecting liquid droplets, and an orifice 5 for ejecting liquid droplets. has a heat acting part 7 where the thermal energy generated by the low heat converter 2 acts on the liquid to generate bubbles and cause rapid changes in state due to expansion and contraction of the volume. The heat acting part 7 is located above the heat generating part 8 of the electrothermal converter 2, and has a heat acting part 9 that contacts the liquid of the heat generating part 8 as its bottom surface.

The heat generating section 8 includes a lower layer 10 provided on the substrate 3 and a heat generating resistor layer 11 provided on the lower layer 10, and the heat generating resistor RiJll includes the JFIJ for generating heat.
Electrodes 13, 14 for communicating with 11 are provided on its surface. The electrode 13 is an electrode common to the heat generating section of each liquid discharging section, and the electrode 14 is a selection electrode for selectively generating heat in the heat generating section of each liquid discharging section. It is located along the road.

The upper layer 12 isolates the heat generating resistor layer 11 from the liquid in the liquid discharge part 6 in order to chemically and physically protect the heat generating resistor layer 11 from the liquid used, and also provides r
Heat generating resistor layer 1 that prevents short circuit between B poles 13 and 14
It has 1 protective function. The upper part R1J12 has the above-mentioned function, but if the heating resistor 11 is liquid resistant and there is no possibility of electrical short circuit between the electrodes 13 and 14 through liquid, It is not necessarily necessary to provide this, and it may be designed as an electrothermal transducer having a structure in which the liquid comes into direct contact with the surface of the heat generating resistance layer 11.

The lower layer 10 mainly has a heat flow control function.

That is, when discharging droplets, the proportion of heat generated in the heat generating resistor layer 11 being conducted to the heat acting section 7 side is as high as possible, rather than being conducted to the substrate 3 side. , after the power to the heat generating resistor WJ11 is turned off, the heat acting part 7
This is provided so that the heat in the heat generating part 8 is quickly released to the substrate 3 side, and the liquid in the heat acting part 7 and the generated bubbles are rapidly cooled.

In this way, when discharging the liquid, the proportion of the heat flow toward the heat acting part 7 side is as large as possible, and when the power to the heat generating resistor layer 11 is turned off, the heat flow rate toward the substrate 3 side is increased as much as possible. By increasing the ratio as much as possible, we aim to improve the efficiency of liquid ejection energy, high thermal response, and continuous repeatable droplet ejection, improve the droplet ejection frequency, equalize the amount of ejected droplets, and eject droplets. In order to stabilize the direction, equalize the droplet ejection speed, stabilize the droplet ejection direction, equalize the droplet ejection speed, and improve the fidelity and reliability of the response to the recording signal,
In the bubble volume change curve, recording is performed such that the average value of the bubble volume change rate is 5×10 3 sec1. This point will be explained more specifically.

FIG. 7 is a diagram for explaining this point more specifically. When an electrical signal with a pulse waveform indicated by symbol p is input to the electrothermal transducer 2 provided in the recording head, the heat acting section 7 The temporal change in the volume of bubbles generated is shown.

Now, set the time to electrothermal converter 2. When a pulsed electrical signal p is inputted by turning on and off at time tf, bubbles are generated in the heat acting part 7 at time ti, and the volume Vv of this bubble starts to increase from the time point onward, until time I : The maximum field WtVvp is reached at p. When the electric signal P is turned off at time tf, the bubble volume V2 begins to decrease after time jp.

The speed at which the bubble volume Vv decreases when the electric signal (■) is turned off depends on the temporal rate of change in the bubble volume VV at time □. That is, by creating a bubble volume change curve such that the average value Vt (□/) dt Vvp of the temporal rate of change during heating is 5×103 sec1 or more, the bubble volume Vv when the electric signal p is turned off is It is possible to effectively make the tasting curve steeper without using any special cooling means, and the above-mentioned purpose can be more than achieved. So, in bubble jet technology.

The bubble growth conditions are the most important point.
Strictly regulating the constantly changing state of bubbles is
Although it is extremely important to obtain stable ejection performance, in JP-A-55-161665, it is simply defined in terms of average value. The average value perspective overlooks minute changes,
It's not appropriate.

In addition, in JP-A-55-161665, as stated in the specification, the size of the flow channel groove serving as the discharge port is approximately 80 μrn x 80 μm (length and width), and compared to It seems to be applied to inkjets with relatively large ejection ports, or in other words, ejection ports arranged in a relatively low density, and is not suitable for printers or copiers that require high-definition printing quality. Met.

In order to obtain high-definition printing quality, for example, the size of the ejection port is at most 30μrn x 30μm (900μIn” in cross-sectional area), preferably 25μrn
25 μrn or less is required. Also, its arrangement density is 16
Book/rn m or more is required. By the way, in order to obtain such high-definition printing quality, the heat generating parts are integrated at a very high density (16 heads/mm or more), just like the ejection ports, so there are problems caused by heat accumulation. Therefore, more strict regulations should be made on the conditions for temperature rise.
Defining the conditions in terms of a simple average value is as described in Japanese Patent Application Laid-Open No. 55-161665, where the size of the ejection port is about 80 μm x 80 μm, 1F! Even if it is sufficient for heads such as
It has nozzles arranged in 16 nozzles/m rn or more,
This was not sufficient for a head that performs recording with a product size of 411. In addition, in heads arranged at high density (16 lines/mm or more), it is necessary to form ink droplets that are several steps smaller than the head described in JP-A-55-161665. It is necessary to stably form finer bubbles with better reproducibility, and it is only by precisely regulating the state of the bubbles that change from moment to moment that high-vf fine printing using a high-density head is possible. It becomes.

The present invention was made in view of the above-mentioned circumstances.
In particular, this method was developed for the purpose of stably ejecting droplets in a bubble jet liquid jet recording head arranged at high density (16 droplets/mm or more).

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 acting force as the volume of the bubbles increases. an orifice connected to the flow path and configured to eject the recording liquid as a droplet by the acting force; a liquid chamber for introducing the recording liquid into the channel;
In a liquid jet recording head comprising means for introducing the recording liquid into the liquid chamber, the radius of a circular shape projected onto the flow path including the thermal energy acting portion of the bubble is taken as the vertical axis, and the horizontal axis is defined as r. If time is plotted on the axis, from the time when the bubble becomes 1/2 of its maximum volume until just before it reaches its maximum volume (where Δr and ΔL are the increases (>O))
) is characterized by satisfying the following relational expression. Hereinafter, the present invention will be explained based on examples.

The present invention strictly defines bubble generation conditions, which are one of the factors that most affect droplet ejection conditions, in bubble jet type limb ejection recording heads in order to more strictly determine stable ejection conditions. .

FIG. 1 is a diagram for explaining one embodiment of the present invention.
a) The figure shows the relationship between the projected figure radius of a bubble and time,
(b) is an enlarged view of the main part, (c) is a diagram showing conditions not included in the present invention, (d) is a diagram showing differences in drive pulses (energy), and FIG. 2 is a diagram showing conditions not included in the present invention. FIG. 3 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. - Figure 4 is a perspective view showing an example of the head when the head shown in Figure 3 is disassembled into the lid substrate (Figure 4 (a)) and the heating element substrate (Figure 4 (b)). FIG. 5 is a perspective view of the lid substrate shown in FIG. 4(a) seen from the back side, and in the figure, 21 is a lid substrate, 22 is a heating element substrate, 23 is a recording liquid inlet, 24 is an orifice, 25 is a flow path, 2G is a region for forming a liquid chamber, 27 is an individual (independent) electrode, 2
8 is a common electrode, 29 is a heating element (heater), 30 is ink, 31 is a bubble, and 32 is a flying ink droplet, and the present invention is applied to such a bubble jet type liquid jet recording head.

First, ink jetting into the bubble jet 1 will be described with reference to FIG. 2. (a) is a steady state, in which the surface tension of the ink 30 and the external pressure are in equilibrium on the orifice surface.

In (b), the heater 29 is heated until the surface temperature of the heater 29 rises rapidly and boiling IIja development occurs in the adjacent ink layer, and microbubbles 31 are scattered.

(C) shows a state in which adjacent ink layers that are rapidly heated over the entire surface of the heater 29 are instantaneously vaporized to form a boiling film, and the bubbles 31 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.

(, ]) indicates a state in which the bubble has grown to its maximum, and an amount of ink 3o corresponding to the volume of the bubble is pushed out from the orifice surface. At this time, no current is applied to the heater 29, and the surface temperature of the heater 29 is decreasing.

The maximum value of the volume of the bubble 31 is slightly delayed from the timing of electric pulse application.

(G) shows a state in which the bubbles 31 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 31 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 0 rn/see.

(g) is a process in which ink is refilled into the orifice due to the old canal phenomenon and returns to the state in (a).
The bubbles have completely disappeared.

FIG. 1(a) shows the relationship between the radius of the bubble projection figure (usually a circle) on the vertical axis and the time on the groove axis. What is defined in the present invention is the relationship between the bubble radius r and the time t from the time when the volume of the bubble becomes 1/2 of the maximum bubble until the time when the bubble becomes the maximum bubble. High density (16
In the bubble jet technology, which requires finer bubbles arranged in the order of 2 mm or more, in order to generate bubbles stably and with good reproducibility, the projected radius of the bubbles must increase smoothly. desirable.

The inventor has carefully determined that it is optimal for the bubble's projected figure radius and time from when the bubble becomes 1/2 of its maximum volume to just before reaching its maximum volume to satisfy the following conditions. This was discovered through repeated experiments.

(However, Δr and Δ are increments (>O)) What this equation means is that the curve lies smoothly, as shown in FIG. 1(a).

In order to obtain such a curve, various factors (pulse energy to be applied, material of the thermal energy acting part, dimensions, etc.) come into play.

Although the explanation is delayed, FIG. 1(b) shows the radius r of the projected figure (shaded area) of the bubble 31, and FIG. 1(c) shows the case under different conditions from the present invention. As shown in the figure, such a sudden rise is not desirable for stable bubble generation.

Next, to explain the difference between Figure 1(a) and Figure 1(c), in the case of Figure 1(a), the graph gradually falls off, whereas in the case of Figure 1(b), it gradually slows down. I'm going to stand up. Looking at this from the perspective of energy manpower, in the case of figure (a), it is sufficient to apply voltage for a short time as shown in figure (d) and (i), but in the case of figure (b), (d) Figure (ii)
As shown in (iii), it is necessary to manually supply energy over a long period of time or in a manner in which the voltage is gradually increased, which requires extra energy and is disadvantageous from a cost standpoint.

On the other hand, when considering the structural aspect of the thermal energy acting part, it is now possible to find that materials with high thermal conductivity such as alumina and silicon (on the contrary,
When considering a device in which a heat storage layer such as 5IO2 is provided and a heating resistor is placed on top of the heat storage layer, bubbles are generated when a voltage pulse is applied to the heating resistor, causing the heating resistor to generate heat. Heat is temporarily blocked by the heat storage layer (transferred to the ink without escaping to the substrate side) and generates bubbles. Thereafter, when the bubbles disappear, the heat blocked by the heat storage layer also quickly escapes to the substrate, which has high thermal conductivity, such as alumina or silicon. Now, if we try to make the graph as shown in Figure 1 (c), it not only requires a lot of energy, but also requires a thick heat storage layer to prevent heat from escaping. Alternatively, it is necessary to use a material with low thermal conductivity as the substrate.

This requires a lot of energy, and by storing the generated heat, a graph-like state is created for the first time. However, with this structure of the thermal energy acting part, when the head is driven continuously, there is no place for the heat to escape, and the head gradually becomes overheated, which not only prevents the response speed from increasing, but also deteriorates the physical properties of the ink. It gradually changes as the temperature rises, and stable bubble generation and ink droplet ejection are no longer performed. This problem is especially
It is serious in heads arranged in high density (more than 16 trees/m rn).

Table 1 shows an example of the experimental results. The arrangement density of the head used at this time was 16 wood/mm, and the size of the heating element was 24 μm x 120 l1rn. From this, it can be seen that driving can be performed at a higher response frequency, which is more advantageous.

Table 1 As is clear from the above description, according to the present invention, bubble generation is performed stably, thereby achieving stable discharge,
In addition, low energy driving is possible, resulting in low cost.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the present invention.
a) The figure shows the relationship between the radius of the bubble's projected figure and time;
(b) is an enlarged view of the main part, (c) is a diagram showing conditions not included in the present invention, (d) is a diagram showing the difference in driving pulse (energy), 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. 3 is a perspective view showing an example of the bubble jet head, FIG. 4 is an exploded perspective view,
FIG. 5 is a view of the lid substrate viewed from the back side, and FIGS. 6 and 7 are views for explaining an example of the conventional bubble die 1 to recording head. 27.28... Electrode, 29... Heating element, 3o... Ink, 31... Air bubble. Figure (C) Hunting j1 Time diagram Figure t Figure (dn (e) Bow == Oζ == 3rd Figure 1.36 Agony IQ) (b) Figure A

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, the radius of a circular figure projected onto the flow path including the thermal energy acting portion of the bubble is defined as r, and this is taken as the vertical axis; If time t is plotted on the horizontal axis, from the time when the bubble becomes 1/2 of its maximum volume until just before it reaches its maximum volume, dr/dt>d(r+Δr)/d(t+Δt) (where Δr, A liquid jet recording head characterized in that it satisfies the following relational expression: Δt is an increase (>0).