JPH02223450A - Liquid injection recording head - Google Patents

Abstract

PURPOSE:To obtain a liquid jet recording head having excellent ink drop delivery stability, delivery efficiency and delivery frequency by specifying the ratio between the horizontal and vertical diameters of an orifice for delivering the recording liquid. CONSTITUTION:A groove 25 constituting an ink flow path and a section constituting a common liquid chamber are formed in a cover substrate 21, while heating bodies 29, selective (independent) electrodes 27 for driving the heating bodies 29 and a common electrode 28 are formed on a heating body substrate 22. When the cover substrate 21 is adhered to the heater body substrate 22, an orifice 24 is formed through the groove 25. When the horizontal and vertical diameters (a), (b) of the orifice 24 satisfy the relation, 0.5<=a/b<=1.5, ink drops are ejected stably through the orifice 24, resulting in a high density highly integrated ink jet recording head having excellent delivery stability.

Description

[Detailed description of the invention] iL regional boundary The present invention relates to a liquid jet recording head.

Aizumi skin technique.

Non-impact recording methods have recently attracted attention because the noise generated during recording is so small that it can be ignored. Among these, the twin jet recording method is an extremely powerful recording method because it is capable of W6 speed recording and can record on so-called plain paper without the need for special fixing treatment. Various methods have been proposed, some have been improved and commercialized, and others are still being worked on to put them into practical use.

This type of inkjet recording method involves making droplets of a recording liquid called ink fly.
Recording is performed by attaching the recording liquid to a recording member, and it is roughly divided into several methods depending on the method of generating recording liquid droplets and the control method for controlling the flight direction of the generated recording liquid droplets. Ru.

First, the first method is the one (Tele type method) disclosed in, for example, US Pat. The droplet is controlled by an electric field according to the recording signal, and the recording liquid droplet is selectively attached to the recording member.
This is the 12th recording.

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 that are configured to be electrically controllable, and the droplet is selectively attached to the recording member by changing the intensity of the electric field to perform recording.

The second method is a method (Sweet method) disclosed in, for example, U.S. Pat. No. 3,596,275 (2), U.S. Pat. Recording is performed on a recording member by generating small droplets of recording liquid with a controlled amount of charge, and flying the generated droplets between deflection electrodes to which a −-like electric field is applied. It is something to do.

Specifically, the orifice (discharge ["
) A charged electrode configured to apply a recording signal is placed a predetermined distance apart in front of the piezo vibrating element, and electricity of a constant frequency is applied to the piezo vibrating element to mechanically activate the piezo vibrating element. 1) 1f recording discharge, and 11mm recording liquid droplets are discharged from 1) 1f and 11f. At this time, a charge is 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 small droplet of recording liquid with a controlled amount of charge flies between deflection electrodes to which a constant electric field is uniformly applied, it is deflected according to the applied charge ゛-1, and recording is performed. (Only the droplets carrying the number M are allowed to adhere to the recording member-1-.

The third method is, for example, the method disclosed in U.S. Pat. No. 3,416,153 (Hertz method),
In this method, an electric field is applied between a nozzle and a ring-shaped charged electrode, and small droplets of recording liquid are generated and atomized using a continuous vibration generation method to perform recording. 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 the method (Stemme method) disclosed in, for example, US Pat.

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 transferred to the recording member. In contrast to recording by attaching 3t (e m
The M.A. method performs recording by ejecting small droplets of recording liquid from an ejection port in response to a recording signal.

In other words, the StOmme method applies an electrical recording signal to a piezo vibrating element attached to a recording head that has an ejection port for ejecting 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 systems, the direct energy for generating a recording liquid droplet is r+S gas energy, and the droplet deflection control is also electric field control.

Therefore, the first method, Configuration 1-, is simple, but it requires high voltage to generate droplets, and it is difficult to make the recording head multi-nozzle, so it 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 has a complicated structure, and the electrical control of the recording liquid droplets is sophisticated and difficult. There are problems such as that 1 to 1- are 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. That is, the configuration-1 is simple, and in order to perform recording by discharging the recording liquid from 5 nozzles on-demand,
It is unnecessary to collect droplets that are not needed for recording an image from among the ejected flying droplets as in the third to third methods, and as in the first to second methods, It has great advantages such as there is no need to use a conductive recording liquid and the whiteness of the recording liquid material is high. However, on the other hand, it is difficult to make the recording head multi-nozzle because there are problems with the processing of the recording head, and it is extremely difficult to miniaturize the piezoelectric vibrating element having the desired resonance number. Furthermore, since the recording liquid droplets are ejected and ejected in flight using the mechanical energy of the mechanical vibration of the piezo-oscillating J element, it has the disadvantage that it is not suitable for high-speed recording.

Furthermore, Japanese Patent Application Laid-Open No. 18-9622 (corresponding to the above-mentioned US Pat. No. 3,747,120) discloses, as a modified example, that instead of using mechanical vibration energy by means such as the piezo vibrating element, It is stated that energy is used.

That is, the above-mentioned publication describes a so-called bubble jet liquid jet recording device using a heating coil that directly heats a liquid as a pressure raising means instead of a piezo vibrating element in order to generate steam that causes a pressure increase. is listed.

However, 1-, the 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 increasing means. However, 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.

As described above, the conventional method has advantages and disadvantages in terms of components, high-speed recording (1), multi-nozzle recording head (1), generation of satellite dots, and fogging of recorded images. There was a restriction that it could only be applied to certain purposes.

In this way, many conventional recording devices have structures such as
High-speed recording above KHz - 16 lines/m during processing
There were many problems in increasing the density beyond that.

Further, in Japanese Patent Application Laid-open No. 57-87960, recording dots are made uniform by changing the area of the heating element, but ejection stability cannot necessarily be obtained by changing the area.

In addition, Japanese Patent Publication No. 61-59912 describes an example of collecting single nozzles to form a multi-nozzle, but this method is limited to a few nozzles/mm at most, and high-definition image quality cannot be obtained. . Furthermore, JP-A-55-2
No. 7281 discloses a method of forming grooves on a substrate by fine cutting to form a nozzle, but even with this method, as stated in the specification, the limit is 10 pieces per box. In order to aim for higher-definition images, it is necessary to arrange the heat generating parts, or in other words, the nozzles, at a high density of 16 nozzles/m or more, and the most effective nozzle formation method to achieve this is a special method. As shown in Japanese Publication No. 62-59672, this is a method in which a flow path wall is provided on a heating element substrate using a photosensitive resin, and the flow path and nozzle are further bonded to a lid substrate to form a flow path and a nozzle. However, there is no relationship between the shape of the nozzle made by the forming method described in Japanese Patent Publication No. 62-59672 and the ink droplet ejection characteristics. In some cases, the nozzle is extremely fine, and the shape of the nozzle has a very large influence on the ink droplet ejection characteristics, but this point is not mentioned at all.
Since there is no description that would even suggest it, I had no idea what kind of nozzle shape to use to obtain stable ejection characteristics when producing a high-density head of 16 nozzles/mm or more.

In addition, in the so-called bubble jet method, in which liquid is directly heated and discharged to generate vapor that increases pressure, advanced thin film techniques such as sputtering, vapor deposition, and etching are used to form heating elements and flow channels. is requested,
Processing accuracy has a large effect on ink ejection. In other words, it has the disadvantage that stable ejection cannot be achieved due to variations in nozzle shape. Also, the size of the nozzle is
This is a major factor in the size of the ink droplets, but depending on the shape of the nozzle, they can become mist-like, the flying speed can drop significantly, and the ejection direction can be significantly different from the intended direction. .

Furthermore, in the case of multi-nozzles arranged at a high density of 16 nozzles/1 m or more, since adjacent nozzles are very close to each other, ink droplets ejected from multiple adjacent nozzles,
Alternatively, columns of ink may often merge or coalesce if they are ejected at approximately the same time. This is because the size of the ink droplets ejected t11 is usually larger than the orifice diameter, and another reason is that the ink droplet ejection conditions are not necessarily favorable (unstable ejection conditions, For example, this occurs when there is a splash or an asymmetric ejection of ink droplets (pillars). These are largely due to the shape and symmetry of the nozzle. Therefore, the nozzle shape, which was not a problem in the multi inkjet which is not so high in density, is a very serious problem in the multi inkjet inkjet, which has a higher density than the copier 311, from the viewpoint of ink droplet ejection characteristics.

In addition, the high frequency response of the Bubble Diene 1 type depends on the ink droplet ejection characteristics mentioned above. For example, above 4KHz)
The relationship between nozzle shape and ejection stability in this case has not been described in the prior art, and it was unclear how the nozzle shape should be selected.

Purpose The present invention was made in order to solve the above-mentioned drawbacks, and it is an object of the present invention to provide a liquid jet recording head that is excellent in ejection stability, ejection efficiency, and ejection frequency of ink droplets. It is something.

Another object of the present invention is to improve the ink droplet ejection performance of a multi-nozzle head arranged at a higher density (for example, arranged at a higher density of 16 nozzles/+nm or more).

Yet another object of the present invention is to improve the ink droplet ejection performance of a multi-nozzle head driven at higher speeds (eg, above 4 kHz).

In order to achieve the object stated in -1-, the present invention has a thermal energy generating means for applying thermal energy to the recording liquid in the liquid chamber, and the heat in the recording liquid is generated by the thermal energy action. In a liquid jet recording head that performs recording by generating air bubbles in an energy acting part and ejecting the recording liquid as droplets from an ejection orifice using an acting force accompanying an increase in the volume of the air bubbles and adhering them to a recording surface, the orifice The ratio of horizontal diameter a to vertical diameter is 0.5≦a
/b≦1.5.

Incidentally, such a relational expression is preferably applied to copiers and the like that require high-density and high-definition quality of 1.6 lines/m or more. In addition, in order to form a high-definition image like a copier, the pixel diameter becomes smaller, so the number of screwdrivers that need to be struck onto the paper surface inevitably increases. takes a lot of time. Therefore, it is better to drive the head at a high driving frequency, and in this sense, the above-mentioned relational expression of the present invention is not suitable for driving at a high frequency (for example, 4
It should be applied to heads with frequencies higher than kHz.

First, the principle of ink ejection using a bubble jet will be explained based on FIG. In the figure, 21 is a lid substrate, 2
2 is a heating element substrate, 27 is a selection (German party) electrode, 28 is a common electrode, 29 is a heating element, 30 is ink, 31 is a bubble, 32
is a flying ink droplet.

(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 and the surface temperature of the heater 29 rises rapidly until 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 instantaneously vaporizes to form a boiling film, and the bubbles 3] 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.

(,) indicates a state in which the bubble 3] is cooled by ink or the like and begins 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 0m/see.

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

FIG. 1 is a perspective view for explaining one embodiment of the recording head according to the present invention, FIG. 2 is a view of the recording head in FIG. 1 viewed from the orifice side, and FIG. 3 is an exploded view of the recording head. In the configuration diagrams, (a) is a diagram showing a lid substrate, (b) is a diagram showing a heating element substrate, and FIG. 4 is a back view of the lid substrate in FIG. 3(a). In the figure, 23 is an ink supply port, 24 is an orifice, and 25
2 is a groove (flow path), and 26 is an area for forming a liquid chamber. The lid substrate 21 has a groove 25 forming an ink flow path and a portion 26 forming a common liquid chamber.

Further, a heating element (heater) 29, a selection (independent) electrode 27 for driving the heating element 29, and a common electrode 28 are formed on the heating element substrate 22. The lid substrate 21 and the heating element substrate 22 are bonded together to form a structure as shown in FIG. 1, and an orifice 24 is formed by the groove 25. The grooves 25 are formed by etching the base (for example, glass) of the lid substrate.

Therefore, the horizontal/vertical ratio of the orifice 24 can be freely set by adjusting the etching rate and/or etching time of the groove 25.

As a result of various experiments, the present inventors found that the horizontal diameter a and the vertical diameter of the orifice in FIG. 2 were 0.5≦a/
It has been found that when the relationship b≦1.5 is satisfied, ink droplets are more stably ejected from the orifice.

The present inventors used a recording head having the configuration shown in FIG.
Experiments were conducted at KHz with different orifice diameters, and the first
The results shown in the table were obtained.

Table 1 (Experimental Results of Discharge Cylinder Stability) However, ○: Very good, Δ: Good, X: Unstable Here, the orifice diameter refers to the maximum diameter in the horizontal and vertical directions.

Further, Table 2 below shows an example of the results of trial production and evaluation of various heads by the present inventors. The number of nozzles in all of the prototype head units was 256. Furthermore, the liquid used was not an ink, but a vehicle with almost the same physical properties as the ink.

This is because a transparent liquid is required to observe bubbles.

Table 2 Also, in the embodiments of the present invention, the orifice is rectangular, but it goes without saying that the present invention is also effective with shapes such as a circular shape, an ellipse shape, and a diamond shape.

Further, other embodiments will be described based on FIGS. 6(a) to 6(f).

In the figure, 8 is a flow path, 9 is a liquid chamber, 10 is a heating element substrate (silicon, alumina, glass, etc.), 11 is a heating element, 12 is a dry film, 13 is a photomask, 15 is an orifice,
16 is a lid substrate, 17 and 18 are lead electrodes, and 19 is a portion of the taper. (a) The heating element 11 is placed on the heating element substrate 10.
and lead electrodes 17 and 18 are formed by a technique such as a CVD method. (b) After that, dry film 12
(c) After aligning the photomask 13 for forming the flow path 8 and the liquid chamber 9 to the heat generating body substrate 10, (d) exposing and etching the heat generating body 11 and the liquid chamber 8. Obtain a substrate having. The tip of the channel 8 is
A pa part 19 is provided.

(e) Furthermore, the lid substrate 16 is adhered onto the heating element substrate 10 of (d) to form a recording head. (f) is z in (e)
In the -z' cross-sectional view, c-c' in (e) is cut by dicing or the like to form orifices 15, and the recording head is completed. As the dry film 12, ordinary commercially available products can be used. When forming the channel 8 with the dry film 12, the horizontal/vertical ratio of the orifice 15 can be easily set by adjusting the width of the channel 8 in the mask pattern and/or the thickness of the dry film 12. In other words, the horizontal length is 1 due to the mask pattern width.
The length in the vertical direction can be adjusted depending on the Kleifilm thickness, making it possible to easily realize the present invention. In the embodiments of the present invention, a solid dry film was used, but a liquid film can also be used.

Regarding the manufacturing process and materials of the recording head,
What is described in Japanese Patent Application Laid-Open No. 61-249766 may be adopted.

Effects As is clear from the above explanation, according to the present invention, due to the relationship between the horizontal diameter and the vertical diameter of the orifice,
It is possible to provide a high-density, high-integration ink recording head with excellent ejection I13 stability.

[Brief explanation of the drawing]

FIG. 1 is a perspective view for explaining one embodiment of a liquid jet recording head according to the present invention, FIG. 2 is a view of the recording head in FIG. 1 viewed from the orifice side, and FIG. 3 is a diagram of the recording head. , in which (a) is a diagram showing the lid substrate, (b) is a diagram showing the heating element substrate, FIG. 4 is a back view of the lid plate of the recording head, and FIG. 5 is a diagram showing the bubble jet ink of the recording head. FIG. 6 is a diagram for explaining the principle of ejection and bubble generation/disappearance, and is a diagram showing the manufacturing process of another embodiment of the present invention. 8...Flow path, 9...Liquid chamber, 10.22...Heating element, (plate, 11.29...Heating element (heater), 1-2...
... Dry film, 13... Photomask, 15.
24... Orifice, 16.21... Lid substrate, 17
．． 27...Independent electrode, 18.28...Common electrode, 19.
... Part of the taper, 23... Ink supply port.

Claims (1)

[Scope of Claims] 1. A means for generating thermal energy for applying thermal energy to the recording liquid in the liquid chamber, and generating bubbles in the thermal energy acting portion of the recording liquid by the action of the thermal energy; In a liquid jet recording head that performs recording by ejecting the recording liquid in the form of droplets from an ejection orifice and adhering it to the recording surface using the acting force caused by the increase in the volume of air bubbles, the horizontal diameter a of the orifice and the vertical diameter A liquid jet recording head characterized in that a ratio of a/b to a diameter b satisfies the following relationship: 0.5≦a/b≦1.5.