JP2664220B2 - Liquid jet recording head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid ejecting recording head, and more particularly to applying a thermal energy to a recording liquid to boil the liquid, thereby ejecting (discharging) liquid droplets. The present invention relates to a liquid ejecting recording head of a type for performing recording.

[Prior art] The performance required of this type of liquid jet recording head or electrothermal transducer is that it has high responsiveness during high-speed driving,
In addition to being capable of heating sufficient to bring the liquid to a boil, it may have high durability. For this purpose, various improvements have been made in terms of materials and configurations.

For example, in Japanese Patent Application Laid-Open No. 58-33471 filed by the present applicant, the electrothermal transducer is configured to have a resistance distribution that reduces the current density at the connection portion with the electrode, thereby improving the electrical durability. A recording head is disclosed.

Japanese Patent Application Laid-Open No. 60-208246 discloses a recording head in which an electrothermal transducer is provided with a member for avoiding mechanical shock caused by liquid supply, thereby improving mechanical durability.

Japanese Patent Application Laid-Open No. 59-95155 discloses a configuration in which a conductive region is provided at the center of an electrothermal converter (resistor).

Furthermore, Japanese Patent Application Laid-Open No. 62-73588 filed by the present applicant discloses a configuration in which current concentration is eliminated by rounding the electrodes and the electrothermal converter (heating resistor).

[Problems to be Solved by the Invention] However, in a recording head having an electrothermal converter as a discharge energy generating means, in addition to the above conditions, high reproducibility of boiling is required.

According to the inventor of the present application, when a liquid is repeatedly boiled, when bubbles generated by a drive signal (heating pulse) given last time to the electrothermal converter disappear, microscopic residual gas is generated by the electrothermal converter. It has been confirmed that the reproducibility of boiling is not ensured because it randomly adheres to the surface and becomes foam nuclei when initial bubbles are generated in the next pulse heating.

If the boiling phenomenon is not stable as described above, the shape and size of the generated bubbles will not be constant, and therefore, there will be a problem in that the diameter of the droplets and the discharge speed vary, and the image quality is reduced.

An object of the present invention is to provide a recording head having high reproducibility of boiling.

It is another object of the present invention to provide a liquid jet recording head which has high image quality without variations in droplet diameter and ejection speed.

[Means for Solving the Problems] A liquid jet recording head according to the present invention includes a support, a heating resistor layer disposed on the support, and a pair of electrodes electrically connected to the heating resistor layer. A portion including a position where bubbles generated in the recording liquid on the recording liquid contact surface corresponding to the heat generating portion formed between the pair of electrodes disappear, and having an increased thickness. A heat converter,
A driving unit for heating and bubbling the recording liquid by the electrothermal transducer, and a member provided on the support for forming a liquid path of the recording liquid;
= T _H -T _O is characterized in that at 100 ° C. or less 20 ° C. or higher.

Here, T _O is a position where bubbles generated in the recording liquid on the recording liquid contact surface corresponding to the heat generating portion disappear.
Under the same driving conditions for heating and bubbling the recording liquid, the peak value of the temperature in the driving state of the electrothermal transducer when the recording liquid does not exist, and _TH is the heat generation portion. When the recording liquid does not exist under the same driving conditions for heating and bubbling the recording liquid at a position other than the position where the bubbles generated in the recording liquid on the corresponding recording liquid contact surface disappear. Is the peak value of the temperature when the electrothermal transducer is driven.

[Operation] According to the present invention, the layer thickness of the electrothermal transducer is increased at a portion of the passage of the current between the electrodes and at a portion including the position where the bubbles disappear, The heat flux transmitted from the electrothermal converter to the upper liquid is reduced at that portion.

Therefore, the temperature of this portion is lower than that of the other portions, and even if microscopic residual gas adheres to the portion after the bubbles have disappeared, it does not become a foam nucleus during the subsequent driving.

In addition, by appropriately selecting and configuring the temperature difference, high ejection performance is maintained, and together with the effect of this, the reproducibility of boiling is improved, and good recording quality is obtained.

Examples Hereinafter, the present invention will be described in detail with reference to the drawings.

FIGS. 1A and 1B show an example of a liquid jet recording head to which the present invention can be applied, in which a plurality of ejection sections including a plurality of liquid paths, electrothermal transducers, and ejection ports (orifices) are integrated. FIG. 1 is a perspective view showing a liquid jet recording head in a disposed form, and a cross-sectional view taken along line XX ′ of FIG.

In these figures, a heating resistor 107 (10
7-1 to 107-6), and a common electrode 106 and a selection electrode 105 are arranged as electrodes for energization. The bonding is performed by the adhesive layer 104 (104-1 to 104-7) so as to coincide with the groove 101 (101-1 to 101-6). A liquid (ink) is introduced into this, and the heating resistor 107
Is heated, bubbles are generated in the liquid on the heating resistor 107 due to a sharp change in state, and droplets corresponding to the increase in the volume are discharged from the orifice formed by the groove cover plate 102 and the substrate 103.

The heating resistor 107 according to the present example has a configuration in which the layer thickness is large at the bubble disappearance position, as described later.

Here, the bubble disappearance position (defoaming position) will be considered.

The defoaming position is determined by the shape of the liquid passage in which the heating resistor is disposed, the disposing position, temperature and other environmental conditions, and is affected by the inertia component Z of the hydrodynamic impedance in the flow area around the bubble. The inventor of the present application has confirmed that bubbles are eliminated near the position where the heating resistor is proportionally distributed at the inverse ratio of In other words, although the defoaming position slightly changes depending on the temperature, it almost depends on the shape of the flow path, and is substantially constant when the same head and the same ink are used.

As shown in FIG. ₂ , l ₁ and l ₂ extending from the open end of the flow path, that is, the supply port and the discharge port of the liquid path to the end of the low heat antibody 107
For a basin corresponding to the following (hereinafter referred to as a basin of interest), the position taken in the flow direction is x, the cross-sectional area at the position x of the basin is S _(x) , the length of the basin is l, and the fluid ( Assuming that the density of the recording liquid is ρ, the impedance inertia component Z of the basin is Required by

For example, as shown in FIG. 1, in the case where the liquid supply direction and the discharge direction coincide with each other with respect to the heating resistor 107, as shown in FIG. 2, the sectional area S _(x) Assuming that = S = constant, Z ₁ = ρl ₁ / S, Z ₂ = ρl ₂ / S (2) C ₁ : C ₂ Z ₂ : Z ₁ = l ₂ : l ₁ (3) In other words, the bubble disappears near the position determined by this relational expression.

Therefore, if the layer of the heating resistor 107 is made thicker at a portion including that position, the heat flux transmitted to the liquid at the top becomes smaller at that portion.

The above is the general relationship, but simply when the height of the nozzle ceiling at the position x is h (x), It was sufficient even if bubbles disappeared at the position of C ₁ : C ₂ = w ₂ : w ₁ .

Next, consideration will be given to how much the temperature difference between the region including the defoaming position and the other region can maintain the ejection performance satisfactorily.

Figure 3 is the peak value T _H of the surface temperature of the heating resistor, the difference ΔT (= T _H -T _O) of the peak value T _O of the surface temperature corresponding to a region where the layer thickness and large, the droplets The average value of the discharge speed and the standard deviation σv of the speed are plotted. Here, the temperature difference ΔT is a value in a state where ink does not exist in the flow path.

As is clear from the figure, it was confirmed that when the temperature difference ΔT was 20 ° C. or more, σv was substantially constant, and the dispersion of ejection was stabilized, but when the temperature difference ΔT exceeded 100 ° C., the average speed was reduced. Thus, in this case, the temperature difference ΔT is 20 ° C. or more.
It turns out that 100 degreeC or less is preferable.

More preferably, when the standard deviation of the liquid ejection speed can be neglected to some extent, that is, when mainly considering the liquid ejection speed, ΔT is 20 ° C. or more and 60 ° C. or less,
When the liquid discharge speed can be neglected to some extent, that is, when the above-mentioned standard deviation is mainly considered, ΔT is 25 ° C. or more.
It was below 100 ° C. Further, most preferably, ΔT is 2
It was 5 ° C or more and 60 ° C or less.

Further, in this embodiment, the dimensions of the region including the defoaming position where the thickness of the heat generating resistance layer is increased are appropriately determined.

FIG. 4 is a plot of the ratio S _O / S _H between the heat generating area S _{O of the} region and the total heat generating area S _{H of the} heat generating resistor, and σv. As is clear from the figure, S _O / S _H
Was set to 1/10 or more and 1/2 or less, and the σv value was stabilized, and it was confirmed that the ejection performance was good.

More preferably, when the standard deviation of the liquid discharge speed is negligible to some extent, that is, when mainly considering the liquid discharge speed, S _O / _SH is 1/10 or more and 1/4 or less, the liquid discharge speed. Can be neglected to some extent, that is, when mainly considering the above standard deviation, S _O / S _H is 1/8 or more 1 /
2 or less. Furthermore, most preferably, S _O / S _H 1/8
More than 1/4 or less.

Example 1 FIGS. 5A and 5B show a first example of a substrate according to the present invention.
FIG. 1 (A) is a plan view along a liquid path direction and FIG. 1 (A) is a sectional view taken along line AA ′.

Here, 1 is a substrate having a thickness of, for example, 525 μm, which can be formed of glass, Si, or the like. Reference numeral 2 denotes a 2.5 μm thick surface oxidized SiO ₂ layer, which is used as a heat storage layer. Reference numeral ₃ denotes a heating resistor layer made of, for example, HfB2 having a thickness of 0.1 μm, a heating portion width of 30 μm, and a heating portion length of 150 μm formed by a sputtering method.
The layer thickness is set to 0.2 μm in the portion 3-1 including the position where the bubble disappears (where l ₁ l ₂ in the formula (2) is near the middle of the path of the current between the electrodes 4). Reference numeral 4 denotes, for example, an electrode made of Al or the like having a thickness of 0.5 μm and formed by EB evaporation.

5 is, for example, a 1.5 μm thick film formed by a sputtering method.
SiO _2, a layer such as SiN of m, a layer such as of Ta ₂ O ₅ which has a thickness of 0.1μm is formed by sputtering, for example 6, 7 is a layer of Ta or the like having a thickness of 0.5μm was formed by a sputtering method, These serve as protection. Reference numeral 8 denotes a liquid (ink) to be boiled.

In the present embodiment, the relationship between the layer thickness d of the portion 3-1 of the heat generating resistance layer 3 and the temperature difference ΔT at the time of idling (when energizing without introducing ink) is as follows. Was.

Therefore, the thickness of the component 3-1 is 0.135 μm or more and 0.155 μm or more.
The following is appropriate, and in this example, d = 0.14 μm.

The length of the portion 3-1 is 25 μm, where S _O = 30.
× 25 (μm ² ), S _H = 30 × 150 (μm ² ), so that S _O /
Since S _H is a 1/6, also meet the conditions described for Figure 4.

The plane patterns of the heating resistor layer 3 and the electrode 4 were formed by etching. Further, as is apparent from the figure, the connection portion between the electrode 4 and the heating resistor layer 3 has a rounded corner so that durability is not reduced and local foaming due to current concentration is not caused.

In such a configuration, when a voltage is applied between the electrodes 4, a current flows through the heating resistor layer 3 to generate heat. The amount of heat generated in the heating resistor layer 3 per unit time / unit area is inversely proportional to the thickness of the heating resistor layer.
The amount of heat transferred to the liquid 8 through the upper layers 5, 6 and 7 is smaller than the amount of heat transferred to the liquid from other portions of the heating resistor 3 layer.

When bubbles were actually generated using the substrate according to the present example, as shown in FIG. 6, it was observed that bubbles 10 disappeared at the location 9 above the portion 3-1.
The heat transmitted to this part is small, and the temperature is lower than the rest, so even if residual gas adheres, random nucleate boiling does not occur and disturbs bubble generation, it is extremely reproduced from the rest Highly likely film boiling occurred. In this case, the shape and size of the bubbles were constant each time. Then, when recording was performed using this substrate as a recording head as shown in FIG. 1, the droplet diameter and discharge speed became uniform, and a good image was obtained.

The high reproducibility of boiling in the part other than the upper part of the part 3-1 is because the liquid 8 is heated rapidly because the residual gas is not attached and the liquid 8 reaches the vicinity of the overheating limit. This is because bubbles are formed by a spontaneous nucleation phenomenon based on internal molecular motion.

Comparative Example FIG. 7 (conventional example) shows a case in which bubbles are generated using an electrothermal converter having the same configuration as that of the present example except that the multilayered heating resistor layer 3 is made uniform. Unlike the present embodiment, random nucleate boiling occurs when the bubbles 10 disappear and the reproducibility of bubble generation is reduced.

That is, in the case of (a) in the figure, although there is only one place where nucleate boiling occurs, relatively good bubble generation is realized, but such bubble generation is not always realized. In some cases, nucleate boiling occurs from a plurality of locations as in b) or (c). In this case, heat energy escapes into the liquid due to nucleate boiling heat transfer, and the volume of bubbles decreases. In such an example, since the shape and size of the bubbles are not constant, when a recording head is configured and recording is performed, it is confirmed that the droplet diameter and the discharge speed vary, and the image quality is reduced. Was done.

Embodiment 2 FIG. 8 shows a second embodiment of the substrate according to the present invention.

In the first embodiment, the portion 3-1 is formed simultaneously with the heating resistor layer 3, whereas in the present embodiment, the heating resistor layer 3 'is formed.
Is formed in a multi-layered structure in which a portion 3'-1 forming an electrothermal converter is formed after the formation. This layer portion 3'-1 is
It may be formed of the same material as the heating resistor layer 3 '(lever HfB _2), or different material (e.g., Ta and TaAl) may be used. In this embodiment, the same effect as that of the first embodiment was obtained.

As long as the position at which the bubble disappears is completely included in this manner, any mode of forming the layer for increasing the thickness may be used.

(Embodiment 3) In the above embodiment, the case where the present invention is applied to the recording head in which the liquid path is linear has been described. However, a recording head in which the supply direction and the ejection direction are different, for example, as shown in FIG. As shown in the drawing, even in the case where the discharge is performed in the direction perpendicular to the substrate 1 ′, by increasing the thickness of the heating resistor layer 107 ′ in the portion including the defoaming position 9 shown in the drawing. The same effect as described above can be obtained.

(Still Another Embodiment) The present invention can of course be applied regardless of the shape of the heating resistor. That is, a thicker portion may be provided at the defoaming position also in the heating resistor employed in the above-described conventional example.

It is also effective for a recording head having an electrothermal transducer of a shape capable of gradation expression developed in recent years, for example, one disclosed in Japanese Patent Publication No. 59-31943 proposed by the present applicant. Applicable. That is, a structure that generates a temperature distribution that can control the electrothermal transducer according to the level of a signal input to the heat generating portion (heat generation amount adjusting structure)
The present invention can also be applied to a recording head having a configuration in which bubbles are adjusted in multiple stages according to a signal level.

For example, in the electrothermal converter as shown in FIGS. 10 (A) to 10 (C), if the defoaming position is at the position indicated by reference numeral 9 ″, the portion including that position (the portion indicated by the broken line) performs the electrothermal conversion. body
What is necessary is just to increase the thickness of 107 "or the heating resistor layer 3". In addition, if the defoaming position is different depending on the size of the generated bubble, a plurality of such wide portions may be provided (see the portion shown by the dashed line in FIG. 10 (A)).

In addition, a structure in which the thickness of the heating resistor layer is changed along the direction of the current in order to adjust the bubbles in multiple stages (Japanese Patent Laid-Open No.
No. 31943) and a structure in which the thickness of the heating resistor layer is gradually increased toward the center line (Japanese Patent Laid-Open No. 62-201255).
It can also be applied to

That is, for example, in the former case, as shown in FIG. 11, the heating resistor layer 30 may be partially thickened in the portion 30-1 including the defoaming position. Of course, if the defoaming position changes depending on the size of the bubble, a plurality of such bubbles can be provided.

In addition, the present invention is not limited to the integrated type as shown in FIG. 1 as long as the electrothermal converter is used as the discharge energy generating means.
Further, it is needless to say that the present invention can be applied to a print head of a serial scanning type or a full multi-type print head in which discharge ports are selected over the entire width of a print medium.

[Effects of the Invention] As described above, according to the present invention, the reproducibility of boiling is achieved by increasing the thickness of the electrothermal transducer (heating resistor layer) in a portion including the position where bubbles disappear. And the quality of the obtained image is improved.

[Brief description of the drawings]

1A and 1B are an exploded perspective view and a front view, respectively, of a liquid jet recording head according to an embodiment of the present invention, FIG. 2 is an explanatory view for explaining the bubble erasing position, FIG. 3 is an explanatory diagram for explaining a range of an optimum temperature difference for ejection, FIG. 4 is an explanatory diagram for explaining an area ratio in the same manner, and FIGS. FIG. 6 is a plan view showing a first embodiment of the substrate according to the present invention and a sectional view taken along line AA ′ of FIG. 6; FIG. 6 is an explanatory view showing the bubble behavior when the present invention is used; FIG. 8 is a cross-sectional view of a substrate according to a second embodiment of the present invention, FIG. 9 is an explanatory diagram showing a recording head according to a third embodiment of the present invention, and FIGS. (C) and FIG. 11 are plan views showing still another embodiment of the present invention. 1, 1 '... substrate, 2 ... heat storage layer, 3, 3', 3 "... heating resistor layer, 3-1, 3'-1, 30-1 ... thickness of heating resistor layer 3 moiety large, 4 ...... electrode, 5 ...... protective layer (SiO _2), 6 ...... protective layer _{(Ta 2 O 5), 7} ...... protective layer (Ta), 8 ...... liquid, 9,9 ' , 9 ″… Bubble disappearance position, 10… Bubble.

Claims (5)

(57) [Claims] 1. A heating device comprising: a support; a heating resistor layer disposed on the support; and a pair of electrodes electrically connected to the heating resistor layer. The heating resistor layer is formed between the pair of electrodes. An electrothermal transducer having a thickened shape at a portion including a position where bubbles generated in the recording liquid on the recording liquid contact surface corresponding to the heat generating portion disappear, and the electrothermal transducer performs the recording. and drive means for foaming by heating use liquid, comprising a member provided on said support to form a liquid passage of the recording liquid, ΔT = T _H -T _O is 20 ° C. or higher A liquid jet recording head having a temperature of 100 ° C. or lower. T _O : at a position where bubbles generated in the recording liquid on the recording liquid contact surface corresponding to the heat generating portion disappear,
Under the same driving conditions for heating and foaming the recording liquid, the peak value of the temperature in the driving state of the electrothermal transducer when the recording liquid is not present T _H : the heat generating unit In a position other than a position on the recording liquid contact surface corresponding to the position where bubbles generated in the recording liquid disappear, under the same conditions as the driving conditions for heating and bubbling the recording liquid, Peak value of the temperature in the driving state of the electrothermal transducer when no liquid is present 2. The ΔT is more preferably 20 ° C. or more and 60 ° C. when mainly considering the ejection speed of the recording liquid.
2. The liquid according to claim 1, wherein the temperature is 25 ° C or higher and 100 ° C or lower, most preferably 25 ° C or higher and 60 ° C or lower, in consideration of the standard deviation of the ejection speed of the recording liquid. Jet recording head. 3. The inverse ratio of the inertial component Z of the hydrodynamic impedance of the basin on both sides of the heat generating section along the liquid path with the length of the heat generating section along the liquid path of the recording liquid. 2. The liquid jet recording head according to claim 1, wherein the position proportionally distributed in (1) is a position where the bubble disappears. x: Position taken in the flow direction from the open end of the liquid channel to the heat generating section l: Length of the flow area from the open end of the liquid path to the heat generating section S _(x) : Disconnection of the flow path at position x Area ρ: density of recording liquid 4. When the height of the liquid path at a position x in the flow area in the flow direction of the recording liquid is defined as h _(x) , 4. The liquid jet recording head according to claim 3, wherein a position at which the length of the heat generating portion is proportionally distributed at a reciprocal ratio is a position at which the bubble disappears. 5. 5. An area on the heat generating portion corresponding to the portion.
S _O , the ratio S _O / S _H of the total area S _H on the heat generating portion, preferably 1/10 or more and 以下 or less, more preferably when mainly considering the liquid discharge speed 1/10 or more and 1/4 or less, 1/1 when mainly considering the standard deviation of the liquid ejection speed
2. The liquid jet recording head according to claim 1, wherein the thickness is set to 8 or more and 1/2 or less, most preferably 1/8 or more and 1/4 or less.