JPH01195050A - Liquid jet recording head - Google Patents

Abstract

PURPOSE:To stably emit a recording liquid, by making the ceiling in the vicinity of the heat energy acting part of a flow passage higher than the ceiling of a part other than said ceiling. CONSTITUTION:A lid plate member 21 constituting the side wall and ceiling of a flow passage is molded from plastic and a cavity 21a is formed to the part opposed to a heat energy acting part. By this constitution, since the flow passage is not blocked by an air bubble 31, stable emission is performed and high printing quality can be obtained.

Description

TECHNICAL FIELD The present invention relates to a liquid jet recording head, and more particularly to a bubble jet type liquid jet recording head.

The 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,
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.

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 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. (Sty
eet 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 that is 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 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.
Only the droplets carrying the recording signal are allowed to deposit on the recording member.

The third method is, for example, the method disclosed in U.S.P. 3416153 (Hertz method), in which an electric field is applied between a nozzle and a ring-shaped charged electrode, and small droplets of recording liquid are generated by a continuous vibration generation method. This method records by atomizing it. That is, in this method, the atomization state of 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 3,747,120 (Stemme method), and this method is fundamentally different in principle from the above-mentioned method.

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. 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 the recording liquid droplets is sophisticated and difficult. There are problems such as 1- is likely to occur.

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 in order to perform recording by ejecting the recording liquid from the ejection opening of the nozzle on-demand, the ejection flight is controlled as in the 6-1 to 3rd methods. There is no need to collect droplets that are not needed for recording an image, and there is no need to use a conductive recording liquid as in the first and second methods. It has great advantages such as a large degree of freedom in terms of liquid material. On the other hand, on the other hand, it is difficult to make a recording head with multiple nozzles due to problems in processing the recording head, and it is extremely difficult to miniaturize a piezoelectric vibrating element having 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-mentioned USP
No. 3,747,120) describes, 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 (7-) that directly heats the liquid as a pressure increasing means instead of a piezo vibrating element in order to generate steam that causes a pressure increase. Are listed.

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-like liquid chamber, far from the liquid ink supply path, which makes the spatula complex in structure and at high speed. It is not suitable for continuous 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.

As described above, conventional methods have advantages and disadvantages in terms of structure, high-speed recording, multi-nozzle recording head, generation of satellite draughts, and fogging of recorded images, etc. 5 Applications that take advantage of these advantages There was a restriction that it could only be applied to

Furthermore, in Japanese Patent Application Laid-Open No. 55-109670, a partition of a groove forming a part of a chamber (flow path) for storing recording liquid is formed on a substrate, and then the upper end of this partition is formed. A liquid jet recording head is disclosed in which the covers of the grooves are bonded together to form holes to serve as the chambers and orifices.

FIG. 7' is an exploded view for explaining an example of the liquid jet recording head disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 55-109670. In the figure, 1 is a heating element installation substrate (for example, an alumina substrate). , a heating element 2 is provided on the back surface thereof, that is, on the back surface in the figure. Further, as a material for the other substrate 3, glass ceramics, heat-resistant plastic, or the like is used, and a material having good water resistance, solvent resistance, heat resistance, and flatness is used. Next, the material that will become the groove wall 4 is a non-contact adhesive (for example, water glass) or a synthetic resin adhesive (for example, a thermosetting resin adhesive, or a thermosetting resin adhesive and a thermoplastic resin adhesive). Examples include composite adhesives (mixed adhesives), but this material only needs to meet the requirements of thermal stability, impact resistance, water resistance, and solvent resistance. The material that will become the groove walls 4 is laminated onto the substrate 3 by printing. After screen-printing the groove walls 4 on the substrate 3, the two substrates 1 and 3 are made to face each other as shown in the figure, aligned so that the heating element 2 and the groove 5 correspond to each other, and then bonded. The heating element mounting board 1 and the other board 3 are integrated.

FIG. 8 is a cross-sectional view of the head taken along one of the grooves 5, and the recording liquid 6 is supplied into the head as indicated by the arrow. Now, when a signal is input to the heating element 2 from the outside, the heating element 2 generates heat, and the liquid that receives thermal energy from the liquid 6 in the heat acting part 7 undergoes a change in state such as volumetric expansion or generation of bubbles. This causes a pressure change, and this pressure change is transmitted in the direction of the discharge orifice 8, and the liquid is discharged from the orifice 8 as a droplet 9.

FIG. 9 is an enlarged view showing how the liquid is ejected from the liquid jet recording head. When bubbles 10 are generated as described above, the bubbles reach the ceiling of the flow w+5 as shown in the figure. In this case, the flow path is temporarily blocked by air bubbles, and the next recording liquid is not sufficiently replenished, resulting in droplet ejection errors, reductions in ejection speed, or changes in the ejection direction. Disturbances etc. occur.

The invention described in JP-A-56-139970 is
This method solves the above-mentioned drawbacks, and generates and eliminates bubbles without blocking the liquid flow within the pores.

FIG. 10 is a diagram for explaining an example of a liquid jet recording head disclosed in Japanese Patent Application Laid-Open No. 139970/1985, in which an orifice 8, an ink chamber (flow path) 5, and a heating element 2 are shown. The ink 6 is supplied from the arrow P. The boundary surface (liquid level) between the ink 6 and the outside air is indicated by 11. Assuming that the number of bubbles generated on the heating element 2 is 10, the state before ejection is shown at to, and a driving pulse is applied to the heating element 2 between 1 and tl. The temperature rise of the heating element 2 starts at the same time as the driving pulse is applied. tl is a state in which the temperature of the heating element exceeds the vaporization temperature of the ink, and bubbles of 1° begin to form, and the liquid level 11 is lowered from the orifice surface by the bubbles 10.
It shows the state in which it swells in proportion to the amount of pressure applied to it. t2
Then, as the bubbles 10 grow further, the liquid level 11 swells further. At t3, the drive pulse falls, and when the temperature of the heating element 2 reaches almost the maximum, the liquid level 11 further expands. t
4, the temperature of the heating element has begun to fall, but the volume of the bubbles 10 has reached its highest level, and the liquid level 11 has further expanded. Note that at this time as well, the flow of ink 6 within ink chamber 5 is not blocked. At t5, the volume of the bubble 10 begins to shrink.

Therefore, the amount of ink 6 in the ink chamber 5 is increased by the amount that the air bubbles 10 contract with respect to the liquid level 11 that swells and comes out from the orifice 8.
On the contrary, it becomes a state where it is drawn in. As a result, the liquid level 11 is constricted at the portion indicated by the arrow Q. 10 more bubbles at t6
The contraction progresses, causing separation into the droplet and the liquid surface 11'.

At this point, the retreat of the ink 11 is suppressed by the pressure of the ink 6 supplied from the rear (arrow P).

At t7, the droplet 9 is ejected and flies, and the bubble 10 further contracts, but the pressure of the ink 6 supplied from the rear (arrow P) pushes back the bubble 11' to near the surface of the orifice 8.

At t8, the ink 6 is completely supplied and the process returns to t. Indicates that the state has returned to the same state as before.

As mentioned above, since the ink chamber 5 is already refilled with the ink 6 from the rear (arrow P) at the time t4, the degree of retreat of the liquid level 11' is reduced, and therefore, from then on, the ink chamber 5 is refilled from the rear (arrow P).
5 to t8, the ink 6 is completely supplied into the ink chamber 5, and the original t is quickly returned.

You can return to the state of

However, in the above-mentioned Japanese Patent Application Laid-Open No. 56-139970, "
It only states "to avoid blockage by air bubbles," but does not specify how to do so, which is very conceptual and difficult to implement.

Purpose The present invention was made in view of the above-mentioned circumstances.
In particular, in bubble jet type liquid jet recording,
This was done for the purpose of stably discharging the recording liquid.

Structure In order to achieve the above-mentioned object, the present invention includes a thermal energy acting part 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 causing the recording liquid to be ejected as droplets by the acting force; and an orifice for communicating with the flow path for 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, characterized in that the ceiling near the thermal energy acting part of the flow path is higher than the ceiling of other parts. It is something. Hereinafter, the present invention will be explained based on examples.

FIG. 1 is an enlarged sectional view of a main part for explaining one embodiment of the present invention, and FIGS. 2(a) and 2(b) are a perspective view of a main part and 3 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 the bubble jet head, and FIG. Lid substrate configuring the head shown in Figure 4 (Figure 5(a))
and heating element board (Fig. 5(b)). Fig. 6 is a perspective view of the lid board shown in Fig. 5(a) when viewed from the back side. 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 channel, 26 is a region for forming a liquid chamber, 27 is an individual (independent) electrode, 28 is a common electrode, 29 is a heating element (heater), 3
o 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 by a bubble jet will be described with reference to FIG. 3. (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 suddenly rises by -1- and boiling development occurs in the adjacent ink layer, and microbubbles 31 are scattered.

(c) shows a state in which the adjacent ink layer that is rapidly heated on the entire surface of the heater 29 is 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.

(d) shows a state in which the bubble has grown to its maximum, and ink 30 corresponding to the volume of the bubble is pushed out from the orifice surface. At this time, no current is flowing through 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.

(e) 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 m/see.

In (g), the air bubbles have completely disappeared during the process in which ink is refilled (refilled) into the orifice by capillary action and returns to the state shown in (,).

Therefore, in the present invention, as shown at 21a in FIG. 1, the ceiling of the flow path near the thermal energy acting part is high, so even when the bubbles 31 are at their maximum,
Air bubbles do not reach the ceiling.

Figures 2 (a) and (b) are main part configuration diagrams for explaining the present invention in detail, respectively, and the embodiment shown in (,) is an example in which the channel side wall and ceiling are made integrally. , corresponds to Examples 1, 2, and 3 described below. In the example shown in Figure (b), the flow channel side wall is made of dry film and a top plate-like ceiling is joined to this. This corresponds to Example 4 described in .

A cover plate member 21 constituting the side wall and ceiling of the turbulent flow path is made by molding plastic, and a recess 21a is formed in the portion facing the thermal energy acting portion.

Example 2 The cover plate member 21 constituting the side wall and ceiling of the channel is made of glass,
It is made by mechanical processing (dicing, ultrasonic processing, etc.) of ceramic, etc., and has a depression 21a formed in the part facing the thermal energy acting part.
is formed by ultrasonic processing or photoetching.

Example 3 A cover plate member 21 constituting the side walls and ceiling of the flow channel is formed by etching photosensitive glass. The first etching forms the flow passage, and the second etching forms the recess 21a in the part of the flow passage (on the ceiling) facing the thermal energy source.

The side walls of the flow channel are formed using photolithography technology using dry film, and a flat plate is joined to form the ceiling. When glass, ceramic, or the like is used as the flat plate, the recess 21a in the portion facing the thermal energy acting portion is formed by ultrasonic machining or photoetching. Alternatively, high precision can be obtained by etching photosensitive glass (for example, Photoceram (trade name) manufactured by Corning Inc.).

Effects As is clear from the above explanation, according to the present invention, the flow path is not blocked by air bubbles, so that problems such as insufficient recording liquid replenishment and droplet ejection errors caused by the blockage can be avoided. There is no decrease in the ejection speed, no disturbance in the ejection direction, etc., stable ejection is performed, and high print quality is obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part for explaining one embodiment of the present invention, FIGS. 2(a) and (b) are perspective views of main parts, and FIG. 3 is a diagram to which the present invention is applied. Figure 4 is a perspective view showing an example of the bubble jet head, Figure 5 is an exploded perspective view, and Figure 6 is a lid substrate. FIGS. 7 to 10, viewed from the back side, are diagrams for explaining examples of conventional liquid jet recording heads. 21...Lid substrate, 21a...Indentation, 22...Heating element substrate, 29...Heating element, 30...Recording liquid, 31...
...Bubbles. Figure 7 Figure 9 Figure 8 Figure 10

Claims (1)

[Claims] 1. A flow path that accommodates the recording liquid to be introduced and is also equipped 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; and the flow path. an orifice that communicates with the flow path and causes the recording liquid to be ejected as droplets by the acting force, a liquid chamber that communicates with the flow path and introduces the recording liquid into the flow path, and the liquid chamber. 1. A liquid jet recording head comprising means for introducing the recording liquid into a liquid jet recording head, characterized in that a ceiling in the vicinity of the thermal energy acting part of the flow path is higher than a ceiling in other parts.