JPH0684075B2 - Liquid jet recording head - Google Patents

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.

Prior Art The non-impact recording method has recently attracted interest in that noise generation during recording is negligibly small. Among them, high-speed recording is possible,
The so-called inkjet recording method, which can record on plain paper without requiring a special fixing process, is an extremely powerful recording method. Various methods have been proposed and commercialized with improvements. Some have been made, while others are still trying to be put into practical use.

Such an inkjet recording method is one in which droplets of a recording liquid, so-called ink, are ejected and adhered to a recording member to perform recording. The method is roughly classified into several methods according to a control method for controlling the flight direction of the generated recording liquid droplets.

First, the first method is, for example, the one disclosed in USP3060429 (Tele type method), in which droplets of the recording liquid are generated by electrostatic attraction, and the generated recording liquid droplets are generated according to a recording signal. Recording is performed by controlling the electrolysis and selectively depositing a recording liquid droplet on the recording member.

This will be described in more detail. An electric field is applied between the nozzle and the acceleration electrode to eject uniformly charged droplets of the recording liquid from the nozzle, and the ejected droplets of the recording liquid are used as recording signals. Accordingly, recording is performed by flying between xy deflection electrodes configured to be electrically controllable, and selectively depositing small droplets on the recording member according to changes in the strength of the electric field.

The second method is a method (Sweet method) disclosed in, for example, USP3596275, USP3298030 and the like, which generates small droplets of a recording liquid whose charge amount is controlled by a continuous vibration generation method, and the generated charge is generated. By ejecting a droplet whose amount is controlled between deflection electrodes to which a uniform electric field is applied,
Recording is performed on the recording member.

Specifically, a nozzle orifice (ejection port) which is a part of a recording head provided with a piezoelectric vibration element.
The charging electrodes configured so that the recording signal is applied in front of are arranged a predetermined distance apart, and the piezoelectric vibrating element is mechanically vibrated by applying an electric signal of a constant frequency to the piezoelectric vibrating element, A small droplet of recording liquid is ejected from the ejection port. At this time, electric charges are electrostatically induced in the recording liquid droplets ejected by the charging electrodes, and the droplets are charged with an electric charge amount corresponding to the recording signal. The droplets of the recording medium whose charge amount is controlled are deflected according to the added charge amount when flying between the deflection electrodes to which a constant electric field is uniformly applied.
Only the droplets carrying the recording signal can be deposited on the recording member.

The third method is, for example, the method (Hertz method) disclosed in USP 3416153, in which an electric field is applied between a nozzle and a ring-shaped charging electrode to generate and atomize small droplets of a recording medium by a continuous vibration generation method. It is a method of recording. That is, in this method, the atomization state of the small droplet is controlled by modulating the electric field strength applied between the nozzle and the charging electrode according to the recording signal, and the gradation of the recorded image is produced and recording is performed.

The fourth method is, for example, the method (Stemme method) disclosed in USP374712, and this method is fundamentally different in principle from the three methods.

That is, in all of the three methods, the droplets of the recording liquid ejected from the nozzles are electrically controlled during the flight, and the droplets carrying the recording signal are selectively deposited on the recording member. On the other hand, the Stmme method is for performing recording by ejecting and ejecting a small droplet of the recording liquid from an ejection port according to a recording signal.

In other words, the Stemme method applies an electrical recording signal to a piezoelectric vibrating element attached to a recording head having a discharge port for ejecting a recording liquid, and converts this electrical recording signal into mechanical vibration of the piezoelectric vibrating element. Instead, recording is performed by ejecting and ejecting a small droplet of the recording liquid from the ejection port according to the mechanical vibration and adhering it to the recording member.

These four conventional methods have their respective characteristics, but there are some points that can be solved in the other.

That is, in the first to third methods, the direct energy for generating the droplet of the recording liquid is electric energy, and the deflection control of the droplet is electric field control. Therefore, the first method is simple in construction, but it requires high voltage to generate small droplets, and it is difficult to form the recording head with multiple nozzles. Therefore, the first method is not suitable 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 it is difficult and difficult to electrically control recording liquid droplets. However, there is a problem in that

The third method has a feature that an image with excellent gradation can be recorded by atomizing the recording liquid droplets, but on the other hand, it is difficult to control the atomized state, and a capri is generated in 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 as compared with the first to third methods. That is, the structure is simple, and the recording liquid is ejected from the ejection port of the nozzle on-demand to perform recording, so that the droplets ejected and ejected as in the first to third methods are ejected. Medium, there is no need to collect small droplets that were not needed for image recording, and there is no need to use a conductive recording liquid as in the first and second methods, and it is not necessary to use a recording liquid substance. It has great advantages such as a high degree of freedom. On the other hand, on the other hand, it is difficult to form a multi-nozzle recording head because of problems in processing the recording head, miniaturization of a piezoelectric vibrating element having a desired resonance number, and the like. However, since the recording liquid droplets are ejected and ejected by the mechanical energy of mechanical vibration of the piezoelectric vibrating element, it is not suitable for high-speed recording.

Furthermore, JP-A-48-9622 (corresponding to USP3747120) describes that, as a modified example, thermal energy is used instead of mechanical vibration energy by means such as the piezoelectric vibration element described above. Has been done.

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

However, in the above-mentioned publication, the liquid ink in a bag-shaped ink chamber (liquid chamber) having only one opening through which the liquid ink can flow in and out by energizing a heating coil as a pressure increasing means is directly vaporized. It is only described that, when performing continuous repeated liquid discharge, how to heat,
There is no suggestion. In addition, since the position where the heating coil is provided is provided at the deepest part of the bag-shaped liquid chamber far away from the liquid ink supply path, the head structure is complicated and continuous at high speed. For repeated use,
It is unsuitable.

Moreover, from the technical contents described in the above publication, it is not possible to promptly form the preparation state for the next liquid ejection after the liquid ejection is performed by 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, occurrence of satellite dots and occurrence of fog in recorded images. There was a constraint that it could only be applied.

Further, in JP-A-55-109670, a partition wall portion of a groove forming a part of a chamber (flow passage) for containing a recording liquid is formed on a substrate, and then the upper end of this partition wall portion is formed. A liquid jet recording head is disclosed in which the cover of the groove is joined to form a hole to be the chamber and an orifice.

FIG. 7 is an exploded view for explaining an example of the liquid jet recording head disclosed in JP-A-55-109670, in which 1 is a heating element installation substrate (for example, an alumina substrate), The heating element 2 is provided on the back surface, that is, the back surface in the figure. Further, as the material of the other substrate 3, glass ceramics, heat resistant plastic or the like is used, and one having good water resistance, solvent resistance, heat resistance and flatness is used. Next, as a material for the groove wall 4, an inorganic adhesive (for example, water glass) or a synthetic resin adhesive (for example, a thermosetting resin adhesive, and a thermosetting resin adhesive and a thermoplastic resin adhesive) Examples of such materials include thermal stability, impact resistance, water resistance,
Solvent resistance may be grooved. The material forming the groove wall 4 is laminated on the substrate 3 by printing. After screen-printing the groove wall 4 on the tatami mat 3, the two substrates 1 and 3 are faced to each other as shown in the figure, and the heat generating element 2 and the groove 5 are aligned so that they correspond to each other, and then adhered. Therefore, the heating element contact substrate 1 and the other substrate 3 are integrated.

FIG. 8 is a cross-sectional view when the head is cut along one of the grooves 5, and the recording liquid 6 is supplied into the head as indicated by an 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 has received heat energy in the liquid 6 in the heat acting portion 7 undergoes a state change such as volume expansion or generation of bubbles. And a pressure change is generated, and this pressure change is transmitted in the direction of the discharge orifice 8, and the liquid is discharged as a droplet 9 from the orifice 8.

FIG. 9 is an enlarged view showing a state of liquid ejection of the liquid jet recording head. When bubbles 10 are generated as described above, the bubbles are formed on the ceiling of the flow path 5 as shown in the figure. In that case, the flow path is immediately blocked by the bubbles, and the next recording liquid cannot be replenished sufficiently. Alternatively, the discharge direction may be disturbed.

The invention described in Japanese Patent Application Laid-Open No. 56-139970 solves the above-mentioned drawbacks, and the generation and disappearance of bubbles are performed so that the liquid flow in the pores is not blocked by the bubbles. It was designed to do.

FIG. 10 is a view for explaining an example of the liquid jet recording head disclosed in Japanese Patent Laid-Open No. 56-139970, 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. A boundary surface (liquid surface) between the ink 6 and the outside air is indicated by 11. 10 bubbles are generated on the heating element 2.
When, the state before discharge is shown in t _0, t ₀ and t ₁
A driving pulse is applied to the heating element 2 during the period. The temperature rise of the heating element 2 is started at the same time when the drive pulse is given. At t ₁ , the temperature of the heating element has reached the vaporization temperature of the ink or higher, and bubbles 10 have begun to form and the liquid level 11 swells in accordance with the pressure of the ink 6 by the bubbles 10 from the orifice surface. ing. At t ₂ , the liquid surface 11 further bulges with the bubbles 10 growing further. At t ₃ , the drive pulse falls,
When the temperature of the heating element 2 reaches almost the maximum, the liquid surface 11 further expands. t ₄ the heating element temperature is beginning to drop, but the bubble
The volume of 10 is at the highest level, and the liquid level 11 is swelling further. Even at this time, the flow of the ink 6 is not blocked in the ink chamber 5. At t ₅ , the volume of bubble 10 begins to contract. Therefore, the amount of ink 6 in the ink chamber 5 is reduced by the amount of the contraction of the bubble 10 with respect to the liquid surface 11 that bulges out of the orifice 8.
Will be pulled in reverse. As a result, the liquid surface 11 is constricted at the portion indicated by the arrow Q. At t ₆ , the contraction of the bubble 10 further progresses, causing separation between the droplet and the liquid surface 11 ′.

At this point, the backward movement of 11 is suppressed by the pressure of the ink 6 supplied from the arrow P. At t ₇ , the droplet 9 is ejected and flies, and the bubble 10 further contracts backward (arrow P). 11 'by the pressure of the ink 6 supplied from indicating that .t ₈ pushed back until near 8 side orifice was Dotsu to state similar t ₀ again supply portion of the ink 6 is completely performed.

As described above, at time t ₄ , the ink 6 is already refilled into the ink chamber 5 from the rear (arrow P), so that the liquid level 1
The degree of retreat of 1 ′ is reduced, and hence t ₅ ~ t
_The ink 6 is completely supplied into the ink chamber 5 by ₈ and the original state of t ₀ can be returned quickly.

However, the above-mentioned Japanese Patent Laid-Open No. 56-139970 only describes "Do not block by air bubbles", and does not clearly indicate what should be done. , Is very conceptual and difficult to realize.

Purpose The present invention has been made in view of the above-mentioned circumstances,
Especially in the bubble jet type liquid jet recording head,
The purpose is to stably discharge the recording liquid.

Structure In order to achieve the above object, the present invention is a thermal energy action for accommodating a recording liquid to be introduced and for generating bubbles in the recording liquid by heat and generating an acting force with the increase in volume of the bubbles. A channel provided with a section, an orifice for communicating with the channel to discharge the recording liquid as a droplet by the action force, and a channel for communicating the channel with the recording liquid. In a liquid jet recording head including a liquid chamber for introducing and a unit for introducing the recording liquid into the liquid chamber, the flow passage is blocked even if bubbles are generated in the ceiling of the flow passage near the thermal energy acting portion. It is characterized by the provision of a space that does not exist. Hereinafter, it demonstrates based on the Example of this invention.

FIG. 1 is an enlarged sectional view of an essential part for explaining an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are perspective views of an essential part for explaining an embodiment of the present invention, respectively. FIG. 3 is a diagram for explaining the operation of a valve jet head as an example of an inkjet head to which the present invention is applied, and FIG.
FIG. 5 is a perspective view showing an example of a valve jet head,
FIG. 5 (a) is a perspective view of the lid substrate (FIG. 5 (a)) and the heating element substrate (FIG. 5 (b)) constituting the head shown in FIG. 4 when disassembled. ) Is a perspective view of the lid substrate viewed from the back side, where 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,
26 is a region for forming a liquid chamber, 27 is an individual (independent) electrode, 28 is a common electrode, 30 is ink, 31 is a bubble, 32 is a flying ink drop, and the present invention is of such a bubble jet type. It is applied to a liquid jet recording head.

First, the ink jetting by the bubble jet will be described with reference to FIG. 3. (a) is a steady state, and 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 and heated until the surface temperature of the heater 29 rapidly rises and boiling development occurs in the adjacent ink layer, and the minute bubbles 31 are scattered.

In (c), the adjacent ink layer that is rapidly heated on the entire surface of the heater 29 is instantly vaporized to form a boiling film, and the bubble 31 is grown. At this time, the pressure in the nozzle rises by the amount of growth of the bubbles, the balance with the external pressure on the orifice surface is lost, and the ink column begins to grow from the orifice.

(D) is a state in which the bubbles have grown to the maximum, and the ink 30 corresponding to the volume of the bubbles is pushed out from the orifice surface. At this time, no current is flowing in 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 applying the electric pulse.

(E) shows a state in which the bubble 31 is cooled by ink or the like and starts to contract. At the tip of the ink column, the ink column moves forward while maintaining the pushed speed, and at the rear end, the ink flows backward from the orifice surface into the nozzle due to the decrease in the nozzle internal pressure due to the contraction of the bubbles, and the ink column becomes constricted. .

In (f), the bubble 31 is further contracted, the ink contacts the heater surface, and the heater surface is further rapidly cooled. On the orifice surface, the external pressure is higher than the internal pressure of the nozzle, so that a large meniscus enters the nozzle.
The tip of the ink column becomes a droplet and becomes 5-10 m / in the direction of the recording paper.
Flying at a speed of sec.

In (g), the ink is supplied (refilled) to the orifice again by the capillary phenomenon and returns to the state of (a), and the bubbles are completely extinguished.

Therefore, in the present invention, as shown by 21a in FIG. 1, the ceiling of the flow path in the vicinity of the thermal energy acting portion is raised, and therefore, even when the bubble 31 reaches its maximum, It never reaches the ceiling.

2 (a) and 2 (b) are main part configuration diagrams for explaining an embodiment of the present invention, respectively, and the embodiment of FIG. 2 (a) is an example of a case where a flow path side wall and a ceiling are integrally formed. In the embodiment of (b), the flow path side wall is made of a dry film, and a ceiling plate-like ceiling is joined to it. This corresponds to Example 4 described below.

Example 1 A lid plate member 21 constituting a side wall and a ceiling of a flow path is formed by plastic molding, and a recess 21a is formed in a portion facing a heat energy acting portion.

Example 2 The lid plate member 21 constituting the side wall and the ceiling of the flow path is made of glass, ceramic, or the like by mechanical processing (dicing, ultrasonic processing, or the like), and the recess 21a is formed in the portion facing the thermal energy acting portion. The recess 21a is formed by ultrasonic processing or photo etching.

Example 3 The lid plate member 21 that forms the side wall and ceiling of the flow path is formed by etching the photosensitive glass. The first etching forms the flow path portion, and the second etching forms the depression of the flow path portion (on the ceiling) facing the thermal energy acting portion.
21a is formed.

Example 4 A side wall of a flow path is formed by a photolithography technique using a dry film, and a flat plate is joined as a ceiling to be manufactured. When glass, ceramics or the like is used as the flat plate, ultrasonic processing or photoetching is used to form the recess 21a in the portion facing the thermal energy acting portion. Further, a highly accurate glass can be obtained by forming it by etching a photosensitive glass (for example, Photoserum (trade name) manufactured by Corning Inc.).

Effects As is clear from the above description, according to the present invention, since the flow path is not blocked by the air bubbles, the recording liquid replenished by the blocking is not sufficiently supplied, There is no ejection error, decrease in ejection speed, disturbance in ejection direction, etc., stable ejection is performed, and high printing quality is obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part for explaining an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are perspective views of the essential part, and FIG. FIG. 4 is a diagram for explaining the operation of a bubble jet head as an example of an inkjet head, FIG. 4 is a perspective view showing an example of a bubble jet head, FIG. 5 is an exploded perspective view, and FIG. 6 is a cover substrate. FIGS. 7 to 10 viewed from the back side are views for explaining an example of a conventional liquid jet recording head. 21 ... Lid substrate, 21a ... Dimple, 22 ... Heating element substrate, 29
…… Heating element, 30 …… Recording liquid, 31 …… Bubbles.

Claims (1)

[Claims] 1. A flow path provided with a thermal energy acting portion for accommodating a recording liquid to be introduced and generating a bubble in the recording liquid by heat and generating an acting force accompanied with an increase in the volume of the bubble, and the flow path. An orifice for communicating the recording liquid with the action force to discharge the recording liquid as a droplet, a liquid chamber for communicating with the flow channel to introduce the recording liquid into the flow channel, and the liquid chamber In the liquid jet recording head including a unit for introducing the recording liquid, a space is provided in the ceiling in the vicinity of the thermal energy acting portion of the flow passage so as not to block the flow passage even if bubbles are generated. Liquid jet recording head.