JPH02137932A - Liquid jet recorder - Google Patents

Abstract

PURPOSE:To obtain discharge of stable ink droplet and to improve repetition frequency characteristic by providing predetermined conditions of its axial length and length of passage direction in a thermal energy actuator of a liquid jet recorder. CONSTITUTION:In a liquid jet recorder having a liquid chamber for receiving recording liquid and means for introducing the liquid in the chamber, a thermal energy actuator has a shape for satisfying a relation formula 0.24<=a/b<=1.5, where a is the length of lateral direction with respect to a passage direction and b is the length of the passage direction. For example, a common electrode 7, selective electrodes 81-84, thermal actuating faces 91-94 are provided. In order to prevent it from corroding with ink in practice, protective films are provided on the electrodes 7, 8 and the faces 9.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid jet recording apparatus, and more particularly to the configuration of a recording head of a bubble jet printer.

(The non-impact recording method has recently attracted attention because the noise generated during recording is extremely small to the extent that it can be ignored. Among them, high-speed recording is possible.
However, the so-called inkjet recording method, which allows recording on plain paper without the need for special fixing treatment, is an extremely powerful recording method, and various methods have been proposed, improved, and commercialized. Some have been developed, while others are still being put into practical use even after the I51 era.

Such an inkjet recording method performs recording by causing droplets of a recording liquid called ink to fly and adhere to a recording member.

There are several types of methods depending on the method of generating recording liquid droplets and the control method for controlling the flying direction of the generated recording liquid droplets.

First, the first method is the one disclosed in, for example, US Pat. No. 3,060,429 (Tele type method), in which small droplets of recording liquid are generated electrostatically and Recording is performed by controlling the droplets with an electric field in accordance with a recording signal to selectively attach recording liquid droplets onto a recording member.

To explain this in more detail, an electric field is applied between the nozzle and the accelerating electrode to eject a negatively charged recording liquid droplet from the nozzle, and the ejected recording liquid droplet is converted into a recording signal. Accordingly, the droplet is caused to fly between x and y deflection electrodes configured to be electrically controllable, and the droplet is selectively deposited on the recording member by changing the intensity of the electric field to perform recording.

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

Specifically, the orifice (discharge port) of a nozzle, which is a part of the recording head to which the piezo vibrating element is attached.
A charged electrode configured to have a recording signal applied thereto is arranged at a predetermined distance in front of the piezo vibrating element, and an electric signal of a constant frequency is applied to the piezo vibrating element to mechanically vibrate the piezo vibrating element, A small droplet of recording liquid is ejected from the ejection port. At this time, the band i′! A charge is electrostatically induced in the recording liquid droplet ejected by the electrode, and the droplet is charged with an amount of charge corresponding to the recording signal. When a droplet of recording liquid with a controlled amount of charge flies between deflection electrodes to which a constant electric field is uniformly applied, it is deflected according to the amount of charge added, and the droplet carries the recording signal. only can be deposited on the recording member.

The third method is, for example, the method disclosed in U.S. Pat. No. 3,416,153 (Hertz method),
In this method, an electric field is applied between a nozzle and a ring-shaped charged electrode, and small droplets of recording liquid are generated and atomized using a continuous vibration generation method to perform recording. That is, in this method, the atomization state of droplets is controlled by modulating the electric field intensity applied between the nozzle and the charging electrode in accordance with the recording signal, and the gradation of the recorded image is produced.

The fourth method is, for example, the method disclosed in US Pat. No. 3,747,120 (Stemme method), and this method is fundamentally different in principle from the above three methods.

That is, in all three methods, the droplets of recording liquid ejected from the nozzle are electrically controlled while they are in flight, and the droplets carrying the recording signal are selectively attached to the recording member. In contrast, this Stamme method
Recording is performed by ejecting small droplets of recording liquid from an ejection port in response to a recording signal.

In other words, the Stemme method applies an electrical recording signal to a piezo vibrating element attached to a recording head that has an ejection port for discharging recording liquid, and converts this electrical recording signal into mechanical vibration of the piezo vibrating element. According to the mechanical vibration, a small amount of recording liquid is ejected from the ejection port and attached to the recording member, thereby performing recording.

These four conventional methods each have their own advantages, but there are also points that can be solved in the other method.

That is, in the first to third methods, the direct energy for generating droplets of the recording liquid is electrical energy, and the deflection control of the droplets is also electric field control.

Therefore, although the first method is simple in structure, it requires a high voltage to generate droplets, and it is difficult to use a multi-nozzle recording head, making it unsuitable for high-speed recording.

The second method allows the recording head to have multiple nozzles and is suitable for high-speed recording, but it has a complicated structure, and the electrical control of recording liquid droplets is sophisticated and difficult, and satellite dots are placed on the recording member. There are problems such as easy occurrence of.

The third method has the advantage of being able to record images with excellent gradation by atomizing recording liquid droplets, but on the other hand, it is difficult to control the atomization state and fog occurs in the recorded image. In addition, it is difficult to create a multi-nozzle recording head.
There are various problems such as being unsuitable for high-speed recording.

The fourth method has relatively many advantages compared to the first to third methods. In other words, the structure is simple, and since recording is performed by ejecting recording liquid from the ejection opening of the nozzle on-demand, it is possible to reduce the number of small droplets that fly as in the first to third methods. Second, it is not necessary to collect droplets that are not needed to record an image, and unlike the first and second methods, there is no need to use a conductive recording liquid, and the material of the recording liquid is It has great advantages such as a high degree of freedom. On the one hand, it is difficult to make a recording head with multiple nozzles due to problems in the processing of the recording head and the extremely difficult miniaturization of a piezoelectric vibrating element with a desired resonance number. This method has disadvantages such as that it is not suitable for high-speed recording because the recording liquid droplets are ejected into flight using the mechanical energy of the mechanical vibration of the piezoelectric vibrating element.

Furthermore, Japanese Patent Application Laid-Open No. 48-9622 (corresponding to the above-mentioned US Pat. No. 3,747,120) discloses, as a modification,
It is described that thermal energy is used instead of using mechanical vibration energy by means such as the piezo vibration element described above.

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

However, in the above publication, the liquid ink in the bag-shaped ink chamber (liquid chamber), which has only one opening through which liquid ink can go in and out, is directly heated and vaporized by energizing the heating coil as a pressure increasing means. However, when discharging liquid continuously and repeatedly, it is not clear how to heat it.
There is no suggestion whatsoever.In addition, the heating coil is located at the deepest part of the bag-shaped liquid chamber, far from the liquid ink supply path, so the head structure is complicated. In addition, for continuous repeated use at high speeds,
It is not suitable.

Moreover, with the technical content described in the above-mentioned publication, it is not possible to quickly prepare for the next liquid discharge after discharging the liquid using the generated heat, which is important in practice.

In this way, the conventional method has disadvantages in terms of structure and high-speed recording.

The use of multi-nozzle recording heads has advantages and disadvantages in terms of the generation of satellite dots and fogging of recorded images, and there is a restriction that it can only be applied to applications that take advantage of these advantages.

In JP-A-57-87958, the distance from the orifice to the thermal energy acting surface is changed to make the size of droplets ejected from each orifice uniform, but changing the distance Mtt does not necessarily stabilize the droplets. However, depending on the distance, the ejected droplets may become mist-like or the flying speed may be significantly reduced.

In Japanese Patent Application Laid-open No. 57-87960, the size of droplets discharged from each orifice is made uniform by changing the area of the thermal energy acting surface. Similarly, a stable droplet ejection state may not always be obtained in this case.

The present invention was made to solve the above-mentioned drawbacks, and proposes optimal conditions for stable ejection of ink droplets, and improves ink droplet ejection efficiency and ink droplet ejection. Stabilization and repetition frequency (continuous ejection of ink droplets) have been optimized to achieve high-speed recording.

The purpose of this invention is to provide a liquid jet recording device that can obtain high image quality.

SUMMARY OF THE INVENTION In order to achieve the above-mentioned objects, the present invention has at least a method for accommodating a recording liquid to be inserted, generating bubbles in the recording liquid by heat, and generating an acting force as the volume of the bubbles increases. a flow path provided with one or more thermal energy acting portions, and an orifice connected to the flow path for ejecting the recording liquid as droplets by the acting force;
In a liquid jet recording device comprising a liquid chamber connected to the flow path for introducing the recording liquid into the flow path, and a means for introducing a small droplet of the recording liquid into the liquid chamber, the thermal energy application section comprises: It is characterized by having a shape that satisfies the relational expression of 0.24≦a/b≦1.5, where the length in the width direction with respect to the flow path direction is a, and the length in the flow path direction is b. This is what I did.

First, the principle of ink jetting by a bubble jet will be explained based on FIG. 4. (a) is a steady state, in which the surface tension of the ink 30 and the external pressure are in equilibrium on the orifice surface.

In (b), the heater 29 is heated until the surface temperature of the heater 29 rises rapidly and boiling development occurs in the adjacent ink layer, and microbubbles 31 are scattered.

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

((1) is the state where the bubble has grown to its maximum, and ink 30 corresponding to the volume of the bubble is pushed out from the orifice surface. At this time, no current is flowing through the heater 29. The surface temperature of 29 is falling.

The maximum value of the volume of the bubble 31 is slightly delayed from the timing of electric pulse application.

(e) shows a state in which the bubbles 31 are cooled by ink or the like and begin to contract. At the tip of the ink column, it moves forward while maintaining the extruded speed, and at the rear end, the ink flows backward from the orifice surface into the nozzle due to the decrease in nozzle internal pressure as the bubbles contract, creating a constriction in the ink column. .

In (f), the air bubbles 31 are further contracted, the ink comes into contact with the heater surface, and the heater surface is cooled even more rapidly. At the orifice surface, the external pressure is higher than the nozzle internal pressure, so the meniscus is largely moving into the nozzle. The tip of the ink column becomes a droplet and drops 5 to 1 droplets toward the recording paper.
It is flying at a speed of 0m/see.

In (g), the air bubbles have completely disappeared in the process of refilling the orifice with ink by capillary action and returning to the state of (a). 32 is a flying ink droplet.

FIG. 5 is a perspective view of the bubble jet recording head, and FIG. 6 is an exploded view of the recording head, in which (a) shows the lid substrate, (b)
7 is a diagram showing the heating element substrate, and FIG. 7 is a back view of the lid substrate shown in FIG. 5 and FIG. 6(a). In the figure, 21 is a lid substrate, 22 is a heating element substrate, 23 is a recording liquid inlet, 24 is an orifice, 25 is a flow path, 26 is an area for forming a liquid chamber, 27
is an individual (independent) electrode, 28 is a common electrode, and 29 is a heating element (
heater).

FIG. 8 is a partial view of the bubble jet liquid jet recording head, (a) is a front partial view seen from the orifice side, (b)
) is a partial view taken along the - dotted chain line XX in (a).

The recording head 41 shown in FIG. 8 has a predetermined number of grooves of a predetermined width and depth at a predetermined linear density on a substrate 43 on which an electrothermal transducer 42 is provided on the back surface. By joining the grooved plate 44 so as to cover the substrate 43,
It has a structure in which a liquid discharge part 46 including an orifice 45 for causing liquid to fly is formed.

The liquid discharge part 46 has a heat acting part 47 where the thermal energy generated by the orifice 45 and the electrothermal converter 42 acts on the liquid to generate bubbles and cause a sudden change in state due to expansion and contraction of the volume. and has.

The heat acting part 47 is located above the heat generating part 48 of the electrothermal converter 42, and has a heat acting surface 49, which is a surface of the heat generating part 48 that comes into contact with the liquid, as its lower surface. The heat generating section 48 is
It is composed of a lower layer 50 provided on the base 43, a heating resistor JtW51 provided on the lower M2O, and an upper Jn52 provided on the heating resistor layer 51.

The heating resistance layer 51 is provided with electrodes 53 and 54 on its surface for supplying electricity to the core layer 51 in order to generate heat, and the heating resistance layer between these electrodes allows the heat generating portion 4
8 is formed.

The electrode 53 is an electrode common to the heat generating section of each liquid discharging section, and the electrode 54 is a selection electrode for selectively generating heat in the heat generating section of each liquid discharging section. It is provided along the flow path.

The layer 52 isolates the heat generating resistor layer 51 from the liquid in the liquid discharge part 46 in order to chemically and physically protect the heat generating resistor layer 51 from the liquid used, and also provides a connection between the electrodes 53 and 54 through the liquid. It has the protective function of the heating resistance layer 51 to prevent short circuits.

The upper layer 52 has the above-mentioned functions, but
Heat generating resistor) If the CIJ 51 is liquid resistant and there is no need for an electrical short circuit between the electrodes 53 and 54 through the liquid, it is not necessarily necessary to provide the heat generating resistor layer 51.
It may be designed as an electrothermal transducer with a structure in which the liquid comes into immediate contact with the surface of the electrothermal transducer.

The lower layer 50 has a heat flow control function, that is, when ejecting droplets, the heat generated in the heat generating resistor layer 51 is transferred to the substrate 43.
The proportion of conduction toward the heat-effecting portion 47 side is increased as much as possible than the conduction toward the side, and after the droplet is ejected, that is, after the electricity to the heat-generating resistor layer 51 is turned off, the heat-effecting portion 4
7 and the heat generating part 48 is quickly released to the substrate 43 side, and the liquid in the heat acting part 47 and the generated bubbles are rapidly cooled.

Hereinafter, the present invention will be explained based on examples.

FIG. 1 is a view of FIG. 8(b) viewed from the direction of the grooved plate 44 in order to explain the heat acting portion 49 of FIG. 8(b). 7 is a common electrode; 8. ~8. is a selective electrode; 9. ~9. indicates the heat acting surface. Further, a represents the length of the heat acting surface in the width direction with respect to the flow path direction, and b represents the length of the heat acting surface in the flow path direction. However, in practical use L, a protective layer is often provided on the common electrode 72, selection electrode 8, and heat acting part 9 to prevent corrosion by ink.

In the bubble jet technology, flying ink droplets are required to be ejected without satellite droplets and without flying in the form of a mist. Furthermore, it must not occur that the liquid drips from the discharge port (orifice) without being discharged. The inventors of the present invention have repeatedly conducted experiments and found that in order to solve the above-mentioned disadvantages, optimal discharge can be obtained when the following conditions are met.

0.24≦a/b≦1.5 Such conditions are based on the length a of the heat acting part 9 in FIG.
This was discovered by making prototype heads with various changes in and b, and observing the flying ink droplets by synchronizing them with a strobe and changing one phase. In the present invention, the relationship between the lengths a and b of the heat acting part 9, which is one of the factors that most influences the optimal ejection conditions, is determined, and the head is set to this condition. By driving the ink droplets, stable ink droplets can be ejected.

FIG. 2 is a diagram for explaining the structure of a bubble generating means using a heating resistor, in which 61 is a heating resistor, 62 is an electrode, 63 is a protective layer, 64 is a power supply device, and the heating resistor Useful materials for forming the body 61 include, for example, tantalum-3iO□ mixtures, tantalum nitride, nichrome, silver-palladium alloys, silicon semiconductors, or hafnium, lanthanum, zirconium, titanium, tantalum, tungsten, and molybdenum. , borides of metals such as niobium, chromium, and vanadium.

Among the materials constituting these heating resistors 61, metal borides are particularly excellent, and among them, hafnium boride has the most excellent properties.
This is followed by zirconium boride, lanthanum boride, tantalum boride, vanadium boride, and niobium boride.

The heating resistor 61 can be formed using the above-mentioned materials using techniques such as electron beam evaporation and sputtering. The film thickness of the heat generating resistor 61 is determined according to its area, material, shape and size of the heat acting part, and actual power consumption, etc. so that the heat generation per unit time is as desired. However, in the normal case, 0.001
~5 μm, preferably o, oi ~1 μm.

As the material constituting the electrode 62, many commonly used electrode materials can be effectively used, and specifically,
For example, AI2+ Ago An, Pt.

Examples include Cu, and these materials are used to provide a predetermined size, shape, and thickness at a predetermined location by a method such as vapor deposition.

The characteristics required of the protective layer 63 are to protect the heat generating resistor 61 from the recording liquid without preventing the heat generated by the heat generating resistor 61 from being effectively transferred to the recording liquid. Examples of useful materials for forming the protective layer 63 include silicon oxide, silicon nitride, magnesium oxide, aluminum oxide, tantalum oxide, and zirconium oxide. It can be formed by The thickness of the protective layer 63 is normally 0.01 to 10 μm, preferably 0.1 to 5 μm, and most preferably 0.1 to 3 μm.

FIG. 3 is a structural diagram of a heat acting section of a recording head according to the present invention.

101 is a Si substrate, 102 is a lower layer, 103 is a heating resistance layer, 104 is an electrode, 105 is a first protective layer, 106 is a second protective layer, and 107 is a resin layer.

108 is a heat acting surface.

Lower part 1f on Si substrate 101! SiO as j 102
After sputtering □ to a thickness of 5 μm, using photolithography, etching, sputtering, etc., Ta. The shape is as follows.

Next, as the first protective layer 105, 5000% of SiO2 was
sputtering to a thickness of about 100 yen, and then a second protective layer 1
As No. 06, Si and N were sputtered to a thickness of 5000 mm, and a resin layer was patterned only where AQ was laminated to form a heater board.

A photosensitive dry film is laminated on the heater board to form the walls of the desired ink chambers and channels. Next, it is bonded to the glass top plate via an adhesive layer.

A discharge port is formed by cutting this substrate with a slicer.

Using the ejection element manufactured in this way, the ejection state of flying ink droplets was measured. The results are shown in Table 1 below.

The unit in Table 1 is [μm] 0...good, You can see what you can get.

As is clear from the above description, according to the present invention, in a liquid jet recording device, stable ink droplet ejection can be obtained by selecting the heat acting surface of the liquid jet recording head to the above-mentioned optimum conditions. , improved repetition frequency characteristics, high-speed recording,
High image quality can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram for explaining one embodiment of the recording head of the present invention, and is a diagram showing the relationship between the length of thermal action, and FIG. Diagram,
FIG. 3 is a configuration diagram of the heat acting section of the recording head, and FIG.
A diagram of the principle of bubble jet ink ejection and bubble generation/disappearance in the print head. Fig. 5 is a perspective view of the print head. Fig. 6 is an exploded configuration diagram of the print head. (,) is the lid substrate, (b)
7 is a back view of the cover substrate of the recording head, FIG. 8 is a partial view of the recording head, and (a) is a partial front view of the head as seen from the orifice side. b) is (
, ) is a partial sectional view along line X-X. 7... common electrode, 8. ~...Selective electrode, 9. ~...
- Heat action surface, 24.45... orifice, 25 mountain flow path, 26... liquid chamber. Figure Figure Figure Figure Figure 3 Figure Figure Figure IQ) Figure (b

Claims (1)

[Scope of Claims] 1. At least one or more thermal energy acting portion that accommodates the introduced recording liquid, generates bubbles in the recording liquid by heat, and generates acting force as the volume of the bubbles increases. an orifice connected to the flow path for ejecting the recording liquid as droplets by the acting force; and an orifice connected to the flow path for introducing the recording liquid into the flow path. In the liquid jet recording device comprising a liquid chamber and a means for introducing recording liquid into the liquid chamber, the thermal energy applying section has a widthwise length a with respect to the flow path direction, and a length a in the width direction with respect to the flow path direction. A liquid jet recording device characterized by having a shape that satisfies the relational expression 0.24≦a/b≦1.5, where b is the length of .