JPH02251458A - Liquid jet recording head - Google Patents

Abstract

PURPOSE:To obtain a recording head of high efficiency in recording liquid discharging performance by generating bubbles efficively stably by a method wherein a resistance value of a first and a second electrodes satisfies a specific relation to a resistance value between both electrodes of a heating resistant layer. CONSTITUTION:A resistance value Re of a first electrode 7 and a second electrode 8 is a resistance value between A and B or between C and D. Further, since the electrode is generally formed of a low resistant material, a value of Re is small, and the resistance value between A and B may be taken as the resistance value between A and X. However, X is an optional point in an orifice line direction of the electrode 8. Though a resistance value Rh of a heating element 9 is a resistance value between B and C, that between B' and C', between B'' and C'',... are also the same value. In the case where a relation between Re and Rh is made to be 3R<=Rh and a pulsed signal voltage is applied, a heating resistant layer is effectively heated, and bubbles stabilized in recording liquid are made to be generated. Especially in a bubble jet ink jet recording head which is arranged at high density of 16 lines/mm or over, in order to driver stably at a higher speed than 4kHz in continuous driven response frequency, generation of bubbles by heating is effectively performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid jet recording head, and more particularly to a liquid jet recording head that uses bubbles to jet ink droplets.

Shimai Kanyoshi In ejecting droplets from the discharge orifice.

Thermal energy is applied to the liquid using a heating resistor, etc., the energy is applied to the liquid, causing a state change accompanied by a sudden volume increase, and the liquid is ejected and jetted by the acting force based on the volume increase, thereby recording. A so-called bubble liquid jet recording apparatus for this purpose is known, for example, in Japanese Patent Application Laid-Open No. 184665/1983. Therefore, the above-mentioned Japanese Patent Application Laid-Open No. 59-18
The invention described in Japanese Patent No. 4665 is based on the resistance value Re of the electrode.
The resistance value Rh of the heat generating resistor layer is defined by the relational expression 0.5≦Re/Rh≦2.0 (1) to reduce the variation in the amount of heat generated in the heat generating resistor layer. , it is said that a value of around 1.0 is most desirable as the value of Re/Rh. However, if R
If e=Rh (or Ra4Rh), the heating resistor would have no meaning, and the above relational expression would be
This includes the case where Rh<Ra, and the resistance value of the electrode is greater than the resistance value of the heating element, a condition that completely ignores reality, and as a result, it is said that a very contradictory conclusion was drawn. I have no choice but to.

In addition, the conditions as defined in Japanese Patent Application Laid-open No. 184665/1984 are as stated in the specification of 12
It seems to be applied to items where the arrangement density is not so high, such as a book/shoe, but it is applicable to a case where the arrangement density is not so high, such as 16 pieces/m
For array densities above, it is necessary to stably form smaller ink droplets.In other words, it is necessary to stably form smaller ink droplets, or in other words, to form smaller bubbles on a smaller and more highly controlled pattern of heating resistors. It is necessary to generate the ink droplet stably, and it cannot be applied under conditions that include the contradictions mentioned above.Furthermore, for example, when the continuous drive response frequency is driven at a higher speed than 4kHz, the ink droplet ejection from bubble generation Since extremely high and stable conditions are required for the series of cycles, it is difficult to apply the method under conditions that include the above-mentioned contradictions.

The present invention was made in view of the above-mentioned circumstances.
In particular, the purpose is to effectively generate bubbles by heat in order to stably drive continuous drive response frequency faster than 4kHz in bubble jet type inkjet recording heads that are arranged at a high density of 16 lines/I or more. This was done as a.

In order to achieve the above object, the present invention includes an orifice for discharging a liquid to form flying droplets, and an orifice communicating with the orifice to provide thermal energy for forming the droplets. It is electrically connected to a liquid flow path that includes a heat acting part, which is a part that acts on the liquid, and a heat generating resistor layer provided on the substrate. The electrothermal transducer includes at least a pair of opposing first and second electrodes, and a heat acting portion made of the heat generating resistive layer is formed between these electrodes.

The electrothermal converters are arranged at a high density of 16 pieces/m or more,
Further, in a liquid jet recording head that is driven at a continuous drive response frequency higher than 4 kHz.

When the resistance value of the first and second electrodes is Re, and the resistance value between both electrodes of the heating resistance layer is Rh, the following relationship is satisfied: 3Re≦Rh. The following will explain one embodiment of the present invention.

FIG. 2 is a perspective view showing an example of a liquid jet recording head to which the present invention is applied, and FIG. 3 is a perspective view showing an example of a liquid jet recording head to which the present invention is applied, and FIG. Fig. 4 is an exploded perspective view of b)), which is a perspective view of the lid substrate seen from the back side, and in the figure, 1 is the lid substrate (channel plate), 2 is the substrate, 3 is the liquid inlet,
4 is a liquid discharge port, 5 is a groove, 6 is a region for forming an ink chamber, 7 is an individual (independent) electrode, 8 is a common electrode, 9 is a heating element, and the heating element 9 is provided on the surface of the substrate 2. is formed together with the common electrode 8, and by joining the lid substrate 1 and the substrate 2, the groove 5 is formed as a liquid (ink) flow path and an ejection port 4.
, and the area 6 contains the recording liquid introduced from the inlet 3 (
1. As is well known, when the channel plate 1 is bonded to the substrate 2, an ink channel is formed between the groove 5 of the channel plate 1 and the upper surface of the substrate 2. A heating element 9 is disposed on a part of the lower surface of the ink flow path on the ink discharge side, and the heating element 9 heats the ink to generate bubbles in the ink. Ink droplets are ejected from the end of the ink flow path by changing the volume.

Figures 5 (,) to (g) are diagrams showing the ink droplet generation process in the inkjet drop generator using bubbles as described above, in which 10 is ink, 20 is bubble,
30 is the generated ink droplet.

Other style board 1. The substrate 2, independent electrode 7, common electrode 8, heating element 9, etc. are as shown in FIG. 3, and as is well known,
By temporarily heating the heating element 9, the ink droplets 30
inject. Bubble inkjet, as described above, heats the liquid (ink) in the flow path by energizing it with a thin film resistor to rapidly boil the ink, and then ejects ink droplets from the ejection port by the pressure effect of the generated bubbles. , the ejected droplets land on a recording material such as paper to form recording pixels.6 The present invention is designed to stably generate bubbles in the bubble jet type inkjet as described above. First, the general principle of bubble jet will be explained.

The process of generation and disappearance of bubbles changes depending on the configuration of the heater and flow path, the current heating conditions, etc., and in order to be practical as an inkjet recording device, it is necessary to satisfy the following conditions.

(1) Sufficient pressure for discharge can be obtained.

(2) Good reproducibility of the phenomenon (bubble stability).

(3) High response frequency 3 Such conditions seem difficult to achieve considering the boiling phenomenon that is seen on a daily basis.

(1) In order to eject a droplet, it is necessary to overcome the surface tension of the liquid surface at the ejection port to form a droplet7. However, in the normal boiling phenomenon, the boiling start temperature is around the boiling point of the liquid. It is less than a few degrees Celsius, and the corresponding vapor pressure is not that high compared to atmospheric pressure.

(2) Boiling is a complex heat transfer phenomenon that involves phase changes and flow, and is much more random than electrical or mechanical phenomena. In addition, in order to repeatedly drive at a high frequency, the response time from foaming to foaming must be short, but there is a limit to reducing the time constant of temperature rise and fall under normal boiling conditions.

In a bubble jet recording device, a thin layer with low thermal conductivity (thermal storage layer) and a thin electrical resistor layer (heater) are formed on a highly thermally conductive substrate, and extremely short heating pulses (~several μ5ec) are used to record images. The above conditions are met by providing a high heat flux to the ink. (1) The ink can be heated to very high temperatures (~300° C. for water-based inks) by providing a high heat flux to the smooth heat transfer surface formed by thin film technology. The vapor pressure at this time reaches several tens of times the atmospheric pressure and is sufficient to discharge droplets.

(2) Foaming in a bubble jet differs from the normal boiling phenomenon in which the gas trapped in the recesses of the heater surface becomes the nucleus of foaming, but the ink near the heat transfer surface vaporizes all at once as it reaches its superheating limit. Therefore, the reproducibility of the phenomenon is high.

(3) During heating, the ink is sufficiently heated due to the effect of the heat storage layer. Due to the short heating time, some ink (
In addition, heat transfer from the heater almost stops due to the adiabatic effect of the steam after the bubbles are formed. Therefore, as the bubbles grow, the temperature of the ink and the pressure inside the bubbles decrease rapidly, resulting in a state of cavitation bubbles. The speed at which bubbles disappear is extremely high, so much so that the destruction of the heater due to impact when bubbles occur becomes a problem. Excess heat escapes to the substrate through the heat storage layer.

FIG. 1 is a configuration diagram for explaining the operating principle of the present invention, and the same figure is an enlarged view of FIG. 3(b) to show the definition of resistance value measurement points. Now, the resistance value Ra of the electrode (both the first electrode (independent electrode 7) and the second electrode (common electrode 8) is R
Expressed as e. ) is the resistance value between A and B or between C and D. Note that since the electrode is generally formed of a low-resistance material, the value of Re is small. Therefore, the resistance value between A and B may be the resistance value between A and X. However, X is the second
This is an arbitrary point in the orifice row direction of the electrode 8. The resistance value Rh of the heating resistance layer 9 is the resistance value between B-0, but B'
-C', B'=C', etc. The same applies.

In the present invention, the relationship between Re and Rh is set as 3Re≦Rh-(2), and when a pulsed signal voltage is applied, the heat generating resistive layer effectively generates heat and stabilizes in the recording liquid. It is designed to generate bubbles.

The reason for using the condition as in equation (2) is that 16 electrothermal converters (heating elements 9) are arranged at a high density of 7 m or more, and
When driving at a higher speed than the continuous drive response frequency of 4kHz, in order to obtain stable driving,
This is because bubble generation, growth, and disappearance must be repeated at high speed, so instantaneous bubble generation is most important.

For example, in the case of the equiband condition on the left side of the conditional inequality (O, 5=Re
/Rh), it is possible to simply generate bubbles. However, it is not possible to generate bubbles repeatedly, stably, and at high speed under these conditions.
This is because under this condition, the resistance value Rh of the heating resistance layer is too small, making it difficult to efficiently generate Joule heat.

The above relational expression (2) can be achieved by appropriately selecting the material of the electrode and the material of the heating resistor layer, or by appropriately selecting the pattern dimensions and thickness of the electrode or the heating resistor layer.

Although not described in detail here, it goes without saying that a suitable protective film is formed at the portions where the electrodes, heating resistance layer, etc. come into contact with the recording liquid.

Example 1 Hafnium boride was formed to a thickness of 0.3 μm and a size of 25 μm×120 μm as a heating element on a silicon substrate with a thermal oxide film, and aluminum was formed to a thickness of 1 μm as an electrode. The arrangement density at this time was 16 lines/m, which was 128 lines/m.
It was made into an element.

The results showed that stable bubble generation was achieved at a continuous driving frequency of 4.2 kHz, and ink droplet ejection was good.Example 2 The heating element material of Example 1 was bound with Ta-8iO, and the thickness was 0.2μ.
The thickness was m. Everything else is the same as in Example 1.

As a result, stable bubble generation was performed at a continuous driving frequency of 4.4 kHz, and ink droplet ejection was also good.
Formed into a size of 20 μm x 80 μm with a thickness of 4 μm,
Gold was formed to a thickness of 1 μm as an electrode. The array density at this time was 24 lines/m, and 128 elements.

The results showed that stable bubble generation was achieved at a continuous driving frequency of 4.1 kHz, and ink droplet ejection was good.Example 4 Instead of platinum in Example 3, aluminum was applied to a thickness of 1 μm, and were all the same as in Example 3.

As a result, no bubbles were generated and therefore no ink droplets were ejected.

As is clear from the above explanation, according to the present invention, by satisfying the condition of the above relational expression (2).

Since the heating resistor layer generates heat effectively, and therefore bubbles are generated effectively and stably, it is possible to provide a recording head with high efficiency and stable recording liquid ejection performance.

[Brief explanation of drawings]

FIG. 1 is an enlarged view of a main part for explaining the definition of resistance value measurement points of a recording head according to the present invention, and FIG. 2 is a perspective view showing an example of a liquid jet recording head to which the present invention is applied. 3
The figure shows a lid substrate (Fig. 3(a)) that constitutes the recording head.
FIG. 4 is an exploded perspective view of the lid substrate (FIG. 3(b)), FIG. 4 is a perspective view of the lid substrate seen from the back side, and FIG. It is a diagram. DESCRIPTION OF SYMBOLS 1... Lid board (channel plate), 2... Substrate, 3... Liquid inlet, 4... Liquid discharge port, 5... Groove, 6...
Ink chamber, 7... Individual (independent) electrode, 8... Common electrode, 9... Heating element. Figure Figure (d) C = = = (e) (¥: Sanini (f) O - Mi = = (9) o = 22

Claims (1)

[Scope of Claims] 1. An orifice for discharging liquid to form flying droplets, and a thermal effect that communicates with the orifice and is a part where thermal energy acts on the liquid to form the droplets. at least one pair of opposing first and second electrodes electrically connected to a heating resistance layer provided on the substrate; It comprises an electrothermal converter in which a heat acting part made of the heating resistance layer is formed between the electrothermal converters, the electrothermal converters are arranged at a high density of 16 pieces/mm or more, and have a continuous drive response frequency of 4kHz. In a liquid jet recording head driven at a higher speed, when the resistance value of the first and second electrodes is Re, and the resistance value between both electrodes of the heating resistance layer is Rh, the relational expression 3Re≦Rh is satisfied. A liquid jet recording head characterized by satisfying the following.