JP2003136729A - Head and method for liquid jet recording - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable gradational recording (multi-valued recording) by changing a dot diameter on a body to be recorded which is known as the dot diameter modulation in a conventional recording head/recording method by a bubble ink jet system capable of only binary recording. SOLUTION: Bubbles are generated by heating a recording liquid introduced into liquid chambers by heat energy working parts 111 and 112 , and the recording liquid is discharged as liquid droplets from discharge openings into a nearly parallel direction to heat energy working parts faces by a working force in consequence of a volume increase of the bubbles. The heat energy working parts 111 and 112 comprise two heating units 111 and 112 which can drive independently and have different heating capacities. The heating capacity of one heating unit of the two heating units is set to be larger than one time and smaller than two times of that of the other one.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid jet recording head, and more particularly to a bubble ink jet type liquid jet recording head and a recording method for performing gradation recording using the recording head.

[0002]

2. Description of the Related Art The non-impact recording method has recently attracted interest in that noise generation during recording is negligibly small. Among them, the so-called inkjet recording method is capable of high-speed recording, and moreover, recording is possible on so-called plain paper without requiring a special fixing process.
There are extremely powerful recording methods, some of which have been proposed and improved so far, and some of which have been commercialized, while others are still being 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. Depending on the control method for controlling the flight direction of the recorded recording liquid droplets, it is roughly classified into several methods.

First, the first method is Tele type.
(For example, Patent Document 1), hereinafter, in this type, recording liquid droplets are generated by electrostatic attraction, and the generated recording liquid droplets are subjected to electric field control according to a recording signal to perform recording. Recording is performed by selectively depositing recording liquid droplets on the member. More specifically, the discharge port and the accelerating electrode are electrolyzed to cause uniformly charged droplets of the recording liquid to be discharged from the discharge port, and the discharged droplets of the recording liquid are used as recording signals. Accordingly, recording is performed by flying between xy deflection electrodes configured so as to be electrically controllable, and selectively depositing small droplets on the recording member according to changes in the electric field strength.

The second method is the Sweet method (for example,
Patent Documents 1 and 2), in which a droplet of a recording liquid having a controlled charge amount is generated by a continuous vibration generation method, and the generated droplet having a controlled charge amount is subjected to a uniform electric field. Recording is performed on the recording member by flying between the applied deflection electrodes. Specifically, a charging electrode configured so that a recording signal is applied is arranged at a predetermined distance in front of an ejection port, which is a part of a recording head provided with a piezoelectric vibration element, By applying an electric signal of a constant frequency to the piezoelectric vibrating element, the piezoelectric vibrating element is mechanically vibrated and a small droplet of the 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 liquid whose charge amount is controlled are deflected according to the added charge amount when flying between the deflecting electrodes to which a constant electric field is uniformly applied, and only the droplets that carry the recording signal are deflected. It is adapted to be attached onto the recording member.

The third method is based on the Hertz method (for example, Patent Document 4), in which an electric field is applied between the discharge port and the ring-shaped charging electrode to generate a small droplet of the recording liquid by the continuous vibration generating method. This is a method of recording after being converted. That is, in this method, the atomization state of the droplet is controlled by modulating the electric field strength applied between the discharge port and the charging electrode in accordance with the recording signal, and the gradation of the recorded image is produced and recording is performed.

The fourth method is based on the Stemme method (Patent Document 5) and has a fundamentally different principle from those of the three methods. That is, the above three methods are
In both cases, recording is performed by electrically controlling small droplets of the recording liquid ejected from the ejection port and selectively adhering the droplets carrying the recording signal onto the recording member. hand,
The Stemme method is for recording by ejecting small droplets of recording liquid from an ejection port in accordance with a recording signal.
That is, in the Stemme method, an electric recording signal is applied to a piezoelectric vibrating element attached to a recording head having an ejection port for ejecting a recording liquid, and this electrical recording signal is converted into mechanical vibration of the piezoelectric vibrating element. According to the mechanical vibration, the small droplet of the recording liquid is ejected and ejected from the ejection port and adhered to the recording member.

Each of these four conventional methods has its own characteristics, but, on the other hand, there are points that can be solved. That is, the first to third methods are
The direct energy of the generation of the recording liquid droplets is electric energy, and the deflection control of the droplets is also electric field control.

Therefore, the first method has a simple structure, but it requires a high voltage to generate small droplets, and it is difficult to form the recording head with multiple nozzles. Therefore, 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. However, it is complicated in structure, and the electrical control of recording liquid droplets is high and difficult. However, there is a problem that satellite dots are easily generated.

The third method has a feature that an image excellent in gradation can be recorded by atomizing recording liquid droplets, but on the other hand, it is difficult to control the atomized state, and the fog is recorded on the recorded image. However, there are various problems that it is not suitable for high speed recording because it is difficult to make the recording head multi-nozzle.

The fourth method has a relatively large number of advantages as compared with the first to third methods. That is, in order to perform the recording by ejecting the recording liquid from the ejection port on-demand, the first to third structures are simple in structure.
It is not necessary to collect the droplets that were not required to record an image among the droplets that are ejected and ejected as in the method of No. 1 and the conductive recording liquid is used as in the first and second methods. There is no need to do so, and there are great advantages such as a great degree of freedom in the material of the recording liquid. However, on the other hand, it is difficult to form a multi-nozzle print head because the print head has a problem in processing, and it is extremely difficult to downsize a piezoelectric vibrating element having a desired resonance number. Since the recording liquid droplets are ejected and ejected by mechanical energy called mechanical vibration of the vibrating element,
It has drawbacks such as not being suitable for high-speed recording.

Further, in Japanese Patent Application Laid-Open No. 48-9622 (Patent Document 6) corresponding to the above-mentioned Patent Document 5, as a modified example, heat is used instead of utilizing mechanical vibration energy by means such as the piezoelectric vibration element. It describes the use of energy. That is, the above-mentioned publication describes a so-called bubble ink jet liquid jet recording apparatus that uses a heating coil that directly heats a liquid in order to generate a 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 (Patent Document 6), a bag-shaped ink chamber (liquid chamber) having only one opening through which liquid ink can flow in and out by energizing a heating coil as pressure increasing means.
It only describes that the liquid ink in the inside is directly heated to be vaporized, and there is no suggestion as to how to heat the liquid ink when continuously and repeatedly ejecting the liquid. In addition, since the position where the heating coil is provided is provided at the deepest part of the bag-shaped liquid chamber far from the liquid ink supply path, in addition to being complicated in terms of the head structure, high speed It is not suitable for continuous repeated use. Moreover, from the technical content described in the above-mentioned publication (Patent Document 6), 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 merits and demerits in terms of configuration, high-speed recording, multi-nozzle recording head, generation of satellite dots, fog of recorded image, and the like. There was a constraint that it could only be applied.

However, this is also solved by the method (Patent Document 7) previously proposed by the present applicant. The one described in this publication (Patent Document 7) is so-called bubble inkjet type ink jet recording in which ink in a liquid chamber is heated to generate bubbles in the ink, and ink droplets are ejected from an ejection port by the action force of the bubbles. It is the basis of the device.

Thus, in such a bubble ink jet type ink jet recording apparatus, the mechanism of bubble generation utilizes the so-called film boiling phenomenon known in the field of heat transfer. Bubbles generated by this film boiling phenomenon have very good reproducibility of generation and disappearance, and are optimal as a driving force for ink jet of an inkjet. However, the behavior of the generation and disappearance of the bubbles is a binary behavior such as 1 or 0 (generation / elimination of bubbles), and it is difficult to change the size of the bubbles. Therefore, such a bubble inkjet type inkjet recording apparatus is a recording method suitable for binary recording.

However, in recent years, higher image quality has been demanded in the market, and so-called gradation recording has become necessary rather than simple binary recording image. Then, as one method for realizing such gradation recording, for example, there is a method disclosed in Japanese Patent Application Laid-Open No. 55-132259 (Patent Document 8). According to this, gradation recording is performed by appropriately shifting the input timing of the signal input to each of the at least two heating elements capable of inputting the signal independently. In other words, two heating elements generate two bubbles, and the generation timings of the bubbles are shifted to slightly change the amount of ink droplets ejected from the ejection port.

This idea applies to a bubble that originally has a binary behavior, though it is an interesting idea.
It is still impossible to give an analog effect, and changing the amount of ejected ink droplets has not always been realized with good reproducibility.

[0018]

[Patent Document 1] US Pat. No. 30,604,29

[Patent Document 2] US Pat. No. 3,596,275

[Patent Document 3] US Pat. No. 3,298,030

[Patent Document 4] US Pat. No. 3,416,153

[Patent Document 5] US Pat. No. 3,747,120

[Patent Document 6] JP-A-48-9622

[Patent Document 7] Japanese Patent Publication No. 56-9429

[Patent Document 8] JP-A-55-132259

[0019]

In the conventional recording head / recording method of the bubble ink jet system, which was capable of performing only binary recording, two heating elements having different heat generating capacities are provided corresponding to one ejection port, and an image is formed. Depending on the information, each heating element is driven independently or jointly to change the size of the bubble to be generated, the mass of the droplet discharged from the discharge port is changed, and gradation recording is performed. So,
It enables gradation recording (multi-value recording) by changing the dot diameter on the recording medium, that is, so-called dot diameter modulation. Furthermore, the difference in heat generation capacity between two heat generating elements is not multiplied by a natural number, Compared to the case where there are two heating elements with the same heating capacity that are usually considered to be larger and smaller than twice, or where the difference in heating capacity between two heating elements is a natural multiple. , When each of the heating elements is driven independently or in combination, the gradation level can be changed and the range of gradation range is widened to enable high quality recording. The purpose is to

In the recording method based on the bubble ink jet system as described above, the input energy to the two heating elements is changed and the electric energy is easily controlled by the electric control.
Liquid that is discharged from the discharge port when the heat generation amounts of the two heating elements can be changed so that the sizes of the bubbles formed by the heating elements are different and they are used alone or in combination. The mass of the droplet can be changed, and the dot diameter on the recording medium can be changed.
It is an object of the present invention to enable gradation recording (multi-value recording) by so-called dot diameter modulation only by simple electrical control, and to widen the range in which the gradation width can be obtained and to realize high-quality recording.

In the recording head of the bubble ink jet system, as compared with a recording head having heating elements of two sizes which are usually considered, each heating element is sequentially driven independently or a combination of the two is applied. It is an object of the present invention to widen the range in which the gradation width can be obtained when the gradation level is changed by driving the recording medium to drive high-quality recording.

[0022]

According to a first aspect of the present invention, there is provided a flow channel provided with a thermal energy acting portion, a liquid chamber for introducing the recording liquid into the flow channel, and a recording liquid introduced into the liquid chamber. Means for heating the introduced recording liquid by the thermal energy acting portion to generate bubbles, and the acting force associated with the increase in the volume of the bubbles causes the recording liquid to move in a direction substantially parallel to the surface of the thermal energy acting portion. In a liquid jet recording head that ejects liquid droplets from an ejection port, the thermal energy acting portion is composed of two heating elements that can be independently driven and have different heat generation capacities. The heating capacity is characterized by more than 1 and less than 2 times that of the other.

A second aspect of the present invention is a flow path provided with a heat energy acting portion at one of the two independent heat generating elements, the heat energy acting portion being larger than one time and less than two times larger than that of the other heat generating element on the upstream side and the downstream side. In the recording liquid introduced therein, bubbles are generated by the thermal energy acting portion, and the recording liquid is moved from the ejection port in a direction substantially parallel to the surface of the thermal energy acting portion by the action force accompanying the volume increase of the bubbles. In a liquid jet recording method in which droplets are ejected and recording is performed by attaching the droplets to a recording medium, the two heating elements are driven independently or jointly in accordance with image information, so that the ejection port It is characterized in that gradation recording is performed by changing the mass of droplets discharged from the.

A third invention is the same as the first invention,
The energy input to the two heating elements is not the same. In a fourth aspect based on the first aspect, the two heating elements have different heating areas. In the first or fourth aspect of the invention, the two heating elements have different resistance values. The first,
The invention of any one of claims 4 and 5 is characterized in that the two heat generating elements have different heat dissipation capacities. The first and fourth
The invention of any one of claims 5 and 6 is characterized in that the heat capacities of the electrodes connected to the two heating elements are different. In any one of the first, fourth, fifth, sixth and seventh inventions, a heat radiator is provided on either one of the two heating elements. In any one of the first, fourth, fifth, sixth, seventh and eighth inventions, the two heat generating elements are provided with heat radiating elements having different heat radiating capacities.

[0025]

1 is an exploded perspective view for explaining an example of a bubble ink jet recording head to which the present invention is applied. FIG. 1 (A) is a perspective view of the head, and FIG.
FIG. 1B is a perspective view of a lid substrate forming the head, and FIG.
1D is a perspective view of the heating element substrate, and FIG. 1D is a perspective view of the lid base seen from the back side. In the figure, 101 is a lid substrate, 102 is a heating element substrate, 103 is a recording liquid inlet, and 104 is a discharge port. exit,
Reference numeral 105 is a flow path, 106 is a region for forming a liquid chamber, 1
07 is an individual (independent) control electrode, 108 is a common electrode, 1
Reference numeral 09 is a heating element.

FIG. 2 is a diagram for explaining the principle of ink drop ejection of a so-called bubble ink jet type ink jet system utilizing heat to which the present invention is preferably applied.
FIG. 2A shows a steady state, in which the ink 110 is discharged on the ejection port surface.
Surface tension and external pressure are in equilibrium. In FIG. 2B, the heating element 109 is heated and heated until the surface temperature of the heating element 109 rises sharply and a boiling phenomenon occurs in the adjacent ink layer,
The micro bubbles 111 are scattered. Figure 2 (C)
Is a state in which the adjacent ink layer that has been rapidly heated on the entire surface of the heating element 109 is instantly vaporized to form a boiling film, and the bubble 111 has grown. At this time, the pressure in the ejection port rises by the amount of the bubble that has grown, the balance with the external pressure on the ejection port surface is lost, and the ink column begins to grow from the ejection port. Figure 2
In (D), the bubbles have grown to the maximum, and the ink 110 corresponding to the volume of the bubbles is pushed out from the ejection port surface. At this time, no current is flowing through the heating element 109, and the surface temperature of the heating element 109 is decreasing. The maximum value of the volume of the bubble 111 is slightly delayed from the timing of applying the electric pulse.

FIG. 2 (E) shows a state in which the bubble 111 is cooled by ink or the like and starts to contract. At the front end of the ink column, it moves forward while maintaining the pushed speed, and at the rear end, ink contracts back due to the contraction of air bubbles, causing the ink to flow backward from the ejection port surface into the ejection port, and the ink column becomes constricted. Has occurred. In FIG. 2F, the bubble 111 is further contracted,
The ink contacts the surface of the heating element and the surface of the heating element is further rapidly cooled. On the discharge port surface, the external pressure is higher than the internal pressure of the discharge port, so that a large meniscus has entered the discharge port. The front end of the ink column becomes a droplet 112, which flies toward the recording paper at a speed of 5 to 10 m / sec. In FIG. 2G, the bubbles are completely extinguished in the process in which the ink is supplied (refilled) to the ejection port again by the capillary phenomenon and returns to the state of FIG. 2A.

The above is a general structure of a bubble ink jet type recording head utilizing heat which has been conventionally known,
According to the principle, the present invention has two heating elements that are arranged at substantially the same distance from one ejection port, can be independently driven, and have different heat generation capacities. The present invention proposes an inkjet head that enables the above. Figure 3
An example of the heating element substrate of the present invention is shown in FIG. The present invention is shown in FIG.
It is understood that the heating element 109 of (C) is made into two heating elements 11 (11 ₁ , 11 ₂ ) which can be driven independently. 7 ₁ and 7 ₂ are control electrodes corresponding to each, and 8 is a common electrode.

FIG. 4 is a diagram for explaining the heating element substrate used in the present invention. FIG. 4 (A) is a front detailed partial view seen from the ejection port side of the ink jet head, and FIG. 4 (B).
FIG. 4 is a partial cross-sectional view of FIG. 4 (A) taken along the line BB. The recording head 10 shown in FIG. 4 has a substrate 12 having a heating element 11 (11 ₁ , 11 ₂ ) provided on the surface thereof.
An ejection port 1 for ejecting a liquid is formed by joining a flow path substrate 13 having a predetermined number of grooves of a predetermined width and depth with a predetermined linear density so as to cover the substrate 12.
4 (14 ₁ , 14 ₂ , 14 ₃ ) has a structure in which the liquid discharge portion 15 is formed. The liquid discharge part 15 has a discharge port 14
The heat acting portion 16 is where the heat energy generated from the heating element 11 acts on the liquid to generate bubbles, which causes a rapid state change due to expansion and contraction of the volume.

The heating elements 11 (11 ₁ , 11 ₂ ) are arranged at substantially the same distance from one discharge port 14 as described above, can be independently driven, and have a heat generating capability. Are two different heating elements, and either the heating element 11 ₁ or the heating element 11 ₂ is driven independently or the heating elements 11 ₁ and 11 ₂ are driven simultaneously according to the image information.

The heat acting portion 16 is the heat generating portion 1 of the heating element 11.
The heat-acting surface 18, which is located above the heat-generating portion 7 and is in contact with the liquid of the heat-generating portion 17, is its bottom surface. Heat generator 1
Reference numeral 7 denotes a lower layer 19 provided on the substrate 12, and the lower layer 1
Provided on the 9 heating resistor layer 20 (20-1 _1, 20-
1 _2, 20-2 _1, 20-2 _2, 20-3 _1, 20-
3 ₂ ), an upper layer 21 provided on the heating element resistance layer 20
Composed of and. Heat generating resistor layer 20 (20-1 _1, 20-
1 _2, 20-2 _1, 20-2 _2, 20-3 _1, 20-3 ₂₎
Is provided with electrodes 22 and 23 for energizing the layer 20 to generate heat, on its surface, and the heat generating layer 17 is formed by the heat generating resistance layer 20 between these electrodes.

In the heat generating portion 17, the upper layer 21 is
In order to chemically and physically protect the heating resistance layer 20 from the liquid used, the heating resistance layer 20 and the liquid filling the liquid flow path of the liquid discharge part 15 are separated from each other, and the electrodes 22, 23 are passed through the liquid. It has a role of preventing a short circuit between the electrodes and a function of preventing electrical leakage between adjacent electrodes. The upper layer 21 has the function as described above, but when the heating resistance layer 20 is liquid resistant and there is no need to electrically short the electrodes 22 and 23 through the liquid, The heating element is not necessarily provided, and may be designed as a heating element having a structure in which the liquid immediately contacts the surface of the heating resistance layer 20.

The lower layer 19 has a heat capacity control function.
That is, in the lower layer 19, when the droplets are discharged, the heat generated in the heating resistance layer 20 is conducted to the substrate 12 side rather than being conducted to the substrate 12 side.
The ratio of conduction to the heat acting portion 18 side is increased as much as possible,
After the liquid droplets are discharged, that is, after the power supply to the heating resistance layer 20 is turned off, the heat in the heat acting portion 18 and the heat generating portion 17 is quickly released to the substrate 12 side, and the liquid in the heat acting portion 16 is discharged. And it is provided for the generated bubbles to be rapidly cooled. In other words, it has a heat storage function when a bubble is generated and a heat dissipation function when the bubble is extinguished.

[0034] As a specific material, in the case where silicon is used as substrate for example, SiO ₂ and the like formed by SiO ₂ or sputtering, is grown on a silicon substrate by thermal oxidation. And
Their thickness is set to 1 μm to 10 μm. When glass or the like is used as the substrate in addition to the above, SiO ₂ formed by sputtering may be used. Since the glass itself has SiO _{2 as} its main component, the substrate can be formed without special SiO _2. It may also be used as the lower layer 19. In addition, when alumina is used as the substrate, a glassy so-called grace layer is used.

Materials useful as the material of the heating resistance layer 20 include tantalum-SiO ₂ mixture, tantalum nitride, nichrome, silver-palladium alloy, silicon semiconductor,
Alternatively, there may be mentioned borides of metals such as hafnium, lanthanum, zirconium, titanium, tantalum, tungsten, molybdenum, niobium, chromium and vanadium. Among these materials constituting the heating resistance layer 20, metal borides can be mentioned as excellent ones. Among them, hafnium boride has the most excellent characteristics, and then zirconium boride, Lanthanum boride, tantalum boride,
The order is vanadium boride and niobium boride.

The heating resistance layer 20 is made of the above material,
It can be formed using a technique such as electron beam evaporation or sputtering. The film thickness of the heating resistance layer 20 is determined according to the area, material and shape and size of the heat-acting portion, and the actual power consumption so that the amount of heat generated per unit time is as desired. But
In the usual case, 0.001 μm to 5 μm, preferably 0.0
It is set to 1 μm to 1 μm. In the present invention, as an example, H
fB ₂ was sputtered at 2000Å (0.2 μm).

As a material for forming the electrodes 22 and 23,
Many of the commonly used electrode materials are effectively used. Specifically, for example, Al, Ag, Au, Pt,
Cu or the like can be used, and these are used to provide a predetermined size, shape, and thickness at a predetermined position by a method such as vapor deposition. In the present invention, Al is formed to a thickness of 1.4 μm by sputtering.

The characteristics required of the protective layer (upper layer) 21 are such that the heat generation resistance layer 2 is more effective than the recording liquid without hindering the effective transfer of the heat generated in the heat generation resistance layer 20 to the recording liquid.
It means to protect 0. Examples of useful materials for forming the protective layer 21 include silicon oxide, silicon nitride, magnesium oxide, aluminum oxide, tantalum oxide, zirconium oxide and the like. These can be formed using a technique such as electron beam evaporation or sputtering. Ceramic materials such as silicon carbide and aluminum oxide (alumina) are also suitable materials. The film pressure of the protective film layer 21 is usually 0.
01 μm to 10 μm, preferably 0.1 μm to 5 μm,
Optimally, it is desirable that the thickness is 0.1 μm to 3 μm. In the present invention, SiO _{2 is formed} to a thickness of 1.2 μm by sputtering.
Formed.

The heating element substrate thus formed is completed as an ink jet head by laminating the flow path substrates as shown in FIG. As described above, a liquid jet recording method having a configuration similar to that of the present invention is disclosed in JP-A-55-132259 (Patent Document 8).
Two heating elements (heating elements) generate two bubbles, and the generation timings are shifted to slightly change the amount of ink droplets ejected from the ejection port. It is still impossible to give an analog effect to the air bubbles that take up, and it was not always possible to reproducibly change the amount of ejected ink droplets.

In view of this, in the present invention, two heating elements are provided for one discharge port, and these two heating elements have different heating capabilities. Then, these two heating elements are driven individually or simultaneously to generate bubbles of different sizes in the flow path in each case, thereby changing the amount of ink droplets ejected from the ejection port, It is to record the key.

The reason why the two heating elements have different heating capacities is to increase the gradation width. Now, assuming that the two heating elements have the same heating capacity, there are three possible gradation steps. That is, 1
If the heat generation capacity of one heating element is J, then 0, J, 2J
It is possible to take a fever state at a stage (3 values).

On the other hand, when the two heating elements are made to have different heating capacities as in the present invention, the heating state can be set in four stages. That is, assuming that the heat generating ability of the first heat generating element is J1 and the heat generating ability of the second heat generating element is J2, in the present invention, 0, J1, J2, J1 + J2 are obtained according to the image information.
A fever state can be taken at the stage of (4 values).

In the present invention, the difference in heat generation capability between the two heating elements is further set to be larger than one and smaller than twice. This is to prevent the gradation change width between binary and ternary values from becoming too large. A specific example will be described. Now, assuming that the heat generation capacity of J1 is 1 and the heat generation capacity of J2 is 2.5 (this is an example outside the scope of the present invention), the heat generation state is 0, 1, 2.5, 3.5. It becomes 4 values. However, the range of gradation change between binary and ternary values suddenly changes from 1 to 2.5, the rate of change is too large (2.5 times), and smooth gradation change cannot be obtained. When viewed, there is a problem that a pseudo contour occurs.

On the other hand, for example, if the heat generation capacity of J1 is 1, J2
If the heat generation capacity of the above is set to 1.5 (this is an example falling within the scope of the present invention), the heat generation state is 0, 1, 1.5, 2.5.
As described above, the gradation value is 4 values, and the gradation change width between 2 values and 3 values is 1 to 1.5. The change rate is not too large (1.5 times), and the gradation change is smooth. Is obtained, and when viewed as an image, pseudo contours are hardly seen. Of course, in this example, the heat generating ability of J2 is set to 1.5, but if the heat generating ability is close to 2, for example, 1.9, the range of gradation change between binary and ternary values is 1 to 1. The change rate is 1.9 times, and the change rate is 1.9 times, and the smoothness of gradation change gradually disappears. However, if the change rate is less than 2 times, it is experimentally found to be in a practical range. ing.

In the present invention, the two heating elements are arranged at substantially the same distance from the discharge port. Specifically, as shown in FIG. 3, the two heating elements 11 ₁ and 11 ₂ may be arranged in parallel, but on the other hand, two or more heating elements may be provided for one discharge port. As an example of providing, a method of arranging in series can be considered as shown in FIG.

In the method of FIG. 5, it is easier to provide two or more heating elements for one discharge port as compared with the present invention (the heating element arraying method of the present invention is
It is practically limited to two, and it is difficult to provide more heating elements than that, and it looks good at first glance, but in reality, in order to perform stable ink droplet ejection, the ejection port The distance between the heating elements is important, and the distance at which stable ink droplet ejection is obtained is not so large that the allowable value is 2
When two heating elements are provided, it is desirable that the distance between them and the discharge port be substantially equal.

That is, the method of arranging the heating elements as shown in FIG. 5 seems to have many heating elements (11 ₁ , 11 ₂ , 1) of two or more.
1 ₃₎ to be able to arranging, appears to better way than the present invention, in fact be only able to arrange two or more heating elements, stable can be ink droplet ejection between the outlets heating element It can be said that the configuration is unsuitable for performing good ink droplet ejection, since there is only one heating element with the optimum distance.

Next, a specific structure for differentiating the two heating element capacities will be described. The simplest method is to change the energy to the heating element. Also in this case, it is not necessary to simply change the input energy, and the difference in the input energy to the two heating elements is set to be larger than one of the one and smaller than twice. The reason for this is that, as in the case where the difference in the heat generation capacities of the two heating elements is larger than one and smaller than twice, the gradation change width between binary and ternary values does not become too large. To do so.

Still another reason is the durability of the heating element. As described above, such a heating element is formed on a substrate made of silicon, alumina, glass or the like by a process such as thin film formation and etching, but the two heating elements have substantially the same composition and film thickness. It Of course, as will be described later, the composition, the film thickness, etc. may be changed in order to change the heat generating ability, but basically, the process of forming the two heating elements is the same or similar, and is formed. The durability of the heating element is not so different. That is, when the input energy is changed for each of the two heating elements, it is actually impossible (damage) to make the energy input to one more times the energy input to the other. From the viewpoint of durability, it is necessary to place it up to twice as high as the other.

Specifically, for example, when changing the driving voltage, one of them should be set to 20V and the other should be set to less than 40V at the maximum. Alternatively, when changing the drive pulse width, if one is 5 μs, the other is 10 μs at maximum.
Should be less than. When changing them by combining them, if one is 30 μJ, the other is 6 at maximum.
Should be less than 0 μJ. In this way, by setting the difference in input energy to the two heating elements to less than double at the maximum, the gradation change rate between binary and ternary values does not become too large, and smooth gradation change is achieved. Moreover, the heating element is not damaged.

Next, another specific structure in which the two heating elements have different heat generating capacities will be described. As described above, the heating element of the present invention is formed on a substrate of silicon, alumina, glass or the like by a so-called semiconductor process such as thin film formation and etching. At that time, the pattern size of the photomask for etching is used. By changing, it is possible to easily form two heating elements having different sizes. In this case as well, the size of the two heating elements is determined so that the difference in heating capability between the two heating elements is larger than one and smaller than twice as in the case described above. Specifically, the area may be less than twice the area of the other.

Next, still another specific configuration in which the heat generating capacities of the two heating elements are made different will be described. Here, an example in which the resistance value of the heating element is made different will be described. For example, the heating element material, when using the mixture of tantalum -SiO _2, it is possible to change easily the resistance values of the two heating elements which are formed by varying the ratio of tantalum and SiO _2. The resistance value of the heating element is usually 50-
Although it is set to about 150Ω, for example, when the resistance value of one heating element is set to 100Ω, the other heating element is set to about 150Ω. In this case as well, the resistance value is less than twice the resistance value of one heating element even at the maximum.

To increase the resistance value, in this example, Si
It suffices to increase the ratio of O ₂ . Further, since the two heating elements have different resistance values, it is necessary to separately perform the steps of forming a thin film of the heating element portion to photolithography and the like for the two heating elements. Although an example of a mixture of tantalum-SiO ₂ is given here, the ratio may be changed similarly for other materials,
Alternatively, the resistance value can be changed by changing the amount of added impurities.

Next, still another specific structure in which the two heating elements have different heat generating capacities will be described. Here, an example in which the thickness of the heating element is different will be described.
As described above, the heating element of the present invention is formed on a substrate of silicon, alumina, glass or the like by a so-called semiconductor process such as thin film formation and etching. The film thickness may be changed by controlling the formation time. In this case as well, the difference in heat generation capability between the two heating elements is 1
The thickness of the two heating elements is determined so as to be more than twice and less than twice. Further, since the two heating elements have different thicknesses, it is necessary to separately perform the steps of thin film formation of the heating element portion to photolithography and the like for the two heating elements.

Next, still another specific structure in which the two heating elements have different heat generating capacities will be described. Here, an example in which the material of the heating element is different will be described. As described above, the material of the heating element used in the present invention is a mixture of tantalum-SiO ₂ , tantalum nitride, nichrome, silver-palladium alloy, silicon semiconductor, or hafnium, lanthanum, zirconium, titanium, tantalum, tungsten, Although there are borides of metals such as molybdenum, niobium, chromium, and vanadium, the thin films may be formed by using different materials for the two heating elements. In this case, the two heating elements formed have a resistance value less than twice that of one heating element even in this case at the maximum.

Next, still another specific structure in which the heat generating capacities of the two heating elements are made different will be described. Here, an example in which the heat dissipation characteristics of the heating element are made different will be described. In the present invention, the heating element is instantly heated in the ink, so-called film boiling bubbles are generated, and the ink droplets are ejected from the ejection port by the action force due to the growth of the bubbles. Needless to say, changes depending on the heat generating ability of the heating element, but also changes depending on the heat dissipation characteristics of the heating element. In other words, it depends on the heat dissipation characteristics of the heating element and its surrounding area, or the difference in heat capacity and heat conduction characteristics of the heating element and its surrounding area.

That is, even if the same input energy is applied to the two heat generating elements, if the heat radiating characteristics or the heat capacity of the heat generating elements are different, as a result, the heat generating ability for generating bubbles is different. In this case as well, the difference in the heat radiation characteristics or the heat capacities of the two heating elements is determined to be larger than one and smaller than twice as large as the one described above.

Next, description will be given of a specific configuration in which the heat dissipation characteristics or the heat capacities of the two heating elements are made different from each other. Figure 6 shows two heating elements (11 ₁ , 11 ₂ )
Is an example in which the widths of the electrodes (7 ₁ , 7 ₂ ) for independently driving are changed. Usually, a metal material such as Al is used for such an electrode, but since Al is a material having a very high thermal conductivity, heat generated in the heating element moves to Al at the same time as it is generated. In other words, such an A
This means that the electrode of 1 has good heat dissipation.

Therefore, as shown in FIG. 6, if the two heating elements have different electrode widths, even if the two heating elements have the same heat generating ability, the heat radiating ability is different, and as a result, bubbles are generated. The ability to do so will be different. That is, it can be said that the heat generating element having a smaller electrode width is more likely to release heat than the heat generating element having a larger electrode width, and thus has a larger bubble generating ability (larger bubble is generated). Although Al is taken as an example here, it goes without saying that other metal materials such as Au and Cu may be used.

Next, another specific structure for differentiating the heat radiation characteristics or the heat capacities of the two heating elements will be described. As described above, the lower layer 19 of the present invention
Has a heat capacity control function. That is, by changing the thickness of the lower layer 19 in the region where the two heating elements are formed, the heat radiation characteristics or the heat capacity of the two heating elements can be made different. Specifically, for example, silicon is used as a substrate, and SiO ₂ is grown on the silicon substrate by thermal oxidation, and then photolithography and etching are performed to form SiO 2 in one of the regions where two heating elements are formed.
Thin ₂ In this case as well, the thickness of the lower layer 19 is determined so that the difference in the heat generating ability of the heat acting region is larger than one time and smaller than twice the one.

Next, still another specific configuration for differentiating the heat radiation characteristics or the heat capacities of the two heating elements will be described. As described above, it has been described that the metal material such as Al has a high thermal conductivity, and the amount of heat generated by the heating element can be controlled. Therefore, here, as in the above-described example, an example of using not only a metal material such as Al as an electrode but also a heat radiator will be described.

That is, either one of the two heating elements is provided with a radiator, or both of them are provided with radiators having different heat dissipation capabilities. What is shown in FIG. 7 is an example thereof, and an example in which a metal material layer 24 of Al or the like is formed on (or below) one of the two heating elements shown in FIG. 3 to improve the heat dissipation characteristics in that region. Is. By thus increasing the heat dissipation characteristics of one heating element, the two heating elements have different heating capacities, and the size of the bubbles generated in each heating element can be changed.

In this case as well, the size of the heat radiating body forming region by the metal layer 24 is determined so that the difference in the heat generating ability of the heat acting region is larger than one and smaller than twice. Further, such a metal layer may be formed on the outermost surface (the surface in contact with the ink) of the heat generation region when it is a material having excellent ink corrosion resistance such as Au.
In the case of using a material having poor ink corrosion resistance as described above, it is formed somewhere below the protective layer so as not to come into direct contact with the ink. Needless to say, an insulation treatment is performed in order to avoid unnecessary conduction.

Next, still another specific structure for differentiating the heat radiation characteristics or the heat capacities of the two heat generating elements will be described. As described above, SiO ₂ is mentioned as a typical example of the protective layer (upper layer) 21 of the present invention, but this has a heat capacity control function as described in the example of the lower layer 19. Therefore, as in the case of the lower layer 19, by changing the thickness of the protective layer (upper layer) 21 in the region where the two heating elements are formed, the heat dissipation characteristics or the heat capacity of the two heating elements can be improved. Can be different. Specifically, after forming a protective layer of SiO ₂ by sputtering or the like, photolithography and etching may be performed to thin SiO ₂ in one of the regions where the two heating elements are formed. In this case as well, the thickness of the protective layer (upper layer portion) 21 is determined so that the difference in the heat generating ability of the heat acting region is larger than one and smaller than twice. In addition,
Although the example of SiO ₂ has been described as the material of the protective layer (upper layer) 21, it goes without saying that another material may be used.

[0065]

EFFECTS OF THE INVENTION Two heating elements having different heat generating capacities are provided corresponding to one ejection port, and each heating element is driven independently or jointly in accordance with image information to generate a bubble size. In this case, since the gradation recording is performed by changing the height and changing the mass of the liquid droplets ejected from the ejection port,
In the recording head / recording method of the bubble ink jet method, which can only perform binary recording, gradation recording (multi-value recording) by changing the dot diameter on the recording medium, that is, so-called dot diameter modulation, is possible. Furthermore, since the difference in the heat generation capacities of the two heating elements is not made to be a natural number multiple, but is made larger than one of the one and smaller than two times, there are usually two heat generating elements having the same heat generating ability. In comparison with the case where the difference in heat generation capability between the two heating elements is a natural number multiple, the respective heating elements are sequentially driven independently or in combination of the two, and When changing the gradation level, the range in which the gradation width can be taken becomes wide, and extremely high quality recording can be performed.

In the recording method using the bubble ink jet method as described above, since the input energy to the two heating elements is changed, it is possible to easily change the heating values of the two heating elements by electrical control. Became. As a result, the size of the bubbles formed by each heating element is different, and when these are used alone or in combination, the mass of the liquid droplets ejected from the ejection port can be changed. The gradation recording (multi-value recording) by changing the dot diameter in the so-called dot diameter modulation is possible only by simple electrical control,
Further, the range of the gradation range is wide, and recording with extremely high image quality can be performed.

In the bubble ink jet type recording head, as compared with a recording head having heating elements of two sizes which are usually considered, each heating element is driven independently in sequence, or a combination of the two is used. When the gradation level is changed by driving by driving, the range in which the gradation width can be taken is widened and extremely high image quality recording can be performed.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a liquid jet recording head to which the present invention is applied.

FIG. 2 is a diagram for explaining the principle of ink droplet ejection of a bubble inkjet system inkjet to which the present invention is applied.

FIG. 3 is a perspective view of a heating element substrate of the present invention.

4A and 4B are cross-sectional views for explaining a heating element substrate of the present invention, in which FIG. 4A is a detailed surface diagram and FIG.
It is a BB sectional view in (A).

FIG. 5 is a diagram for explaining an arrangement example of electrodes and heating elements.

FIG. 6 is a diagram for explaining another arrangement example of electrodes and heating elements.

FIG. 7 is a perspective view of a heating element substrate of the present invention including two heating elements having different heat dissipation characteristics or heat capacities.

[Explanation of symbols]

8, 108 ... Common electrode, 10 ... Nozzle, 11 ... Heating element,
12 ... Substrate, 13 ... Flow path substrate, 14 ... Discharge port, 15 ... Liquid discharge part, 16 ... Heat acting part, 17 ... Heat generating part, 18 ... Heat acting part, 19 ... Lower layer part, 20 ... Heating resistance layer, 21 ... Upper layer, 22, 23 ... Electrode, 24 ... Metal material layer, 101 ... Lid substrate, 102 ... Heating element substrate, 103 ... Recording liquid inlet,
104 ... Ejection port, 105 ... Flow path, 106 ... Region forming liquid chamber, 107 ... Individual control electrode, 109 ... Heating element, 11
0 ... Ink, 111 ... Bubbles, 112 ... Droplets.

Claims (9)

[Claims] 1. A flow path provided with a thermal energy acting portion, a liquid chamber for introducing the recording liquid into the flow path, and means for introducing the recording liquid into the liquid chamber, the introduced recording liquid Generate bubbles by heating with the thermal energy acting unit,
In the liquid jet recording head that ejects the recording liquid as droplets from the ejection port in the direction substantially parallel to the surface of the thermal energy acting portion by the acting force accompanying the increase in volume of the bubbles, the thermal energy acting portion is independently driven. A liquid jet recording head comprising two heat generating elements which are possible and have different heat generating ability, and one of the two heat generating elements has a heat generating ability of more than 1 time and less than 2 time of that of the other. . 2. Introducing into a flow path having upstream and downstream a thermal energy acting portion of one of the two independent heating elements, the heating capacity of which is greater than one time and less than twice that of the other heating element. Bubbles are generated in the recorded liquid by the thermal energy acting portion, and the recording liquid is ejected as droplets from the ejection port in a direction substantially parallel to the surface of the thermal energy acting portion by the action force accompanying the increase in volume of the bubble. In a liquid jet recording method for recording by depositing the droplets on a recording medium, a liquid ejected from the ejection port by driving the two heating elements independently or jointly according to image information. A liquid jet recording method, wherein gradation recording is performed by changing the mass of a droplet. 3. The liquid jet recording head according to claim 1, wherein the input energies to the two heating elements are not the same. 4. The liquid jet recording head according to claim 1, wherein the two heating elements have different heating areas. 5. The liquid jet recording head according to claim 1, wherein the two heating elements have different resistance values. 6. The liquid jet recording head according to claim 1, wherein the two heat generating elements have different heat radiating capacities. 7. The liquid jet recording head according to claim 1, wherein the electrodes connected to the two heating elements have different heat capacities. 8. A radiator is provided on either one of the two heating elements.
The liquid jet recording head according to any one of 1. 9. A heat-radiating body having different heat-radiating ability is provided to each of the two heat-generating bodies.
5. A liquid jet recording head according to any one of 5, 6, 7, and 8.