JPS62240558A - Liquid jet recording head - Google Patents

Abstract

PURPOSE:To prevent the discharge failure of liquid drop after being-left for a long time and besides, to enable the high speed stable recording by high repetitive driving frequency, by a method wherein the first heating means is established to a nozzle in addition to a discharge energy generation means and the second heating means is provided for a liquid chamber. CONSTITUTION:A discharge energy generation means 2 and the first heating means 3 are successively arranged from an orifice 30 side in the nozzle 7 of a recording head and the second heating means 4 is established in the liquid chamber 8 at the back of the nozzle 7. When above-mentioned heating means 3 and a discharge energy generation means 2 are operated, vapour bubbles 9 and 10 are generated in the recording liquid of the parts respectively contacting thereto. Therefore, because vapour bubbles 9 are also generated and the discharge energy can be utilized to the high viscous recording liquid after standing for a long time, liquid drop 13 can be discharged. Further, when the vapour bubble 10 is contacted, the liquid drop 13 is formed and the recording liquid starts to be fed. At that time, when the second heating means 4 is made to be of an operation state, a vapour bubble 11 is formed in the recording liquid inside the liquid chamber 8 contacted with said means 4 and the recording liquid is forcedly pushed into the nozzle 30. By this operation, the recording by high repetitive driving frequency can be realized.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a liquid jet recording head that performs recording by ejecting and flying a recording liquid as droplets from a liquid discharge port and making the droplets land on a recording medium such as paper, and particularly relates to a print signal. The present invention relates to an on-demand liquid jet recording head that performs ejection when a liquid is applied, and particularly relates to a liquid jet recording head that has high-speed response and excellent ejection stability. [Prior Art] A liquid jet recording method (inkjet recording method) in which recording is performed by ejecting and flying a recording liquid has been known. This method has excellent features such as high-speed printing, low noise, high recording quality, easy color image recording, and the ability to record on plain paper. An inkjet recording device used in such an inkjet recording method generally includes a liquid ejection opening (orifice) for ejecting the recording liquid as flying droplets, a liquid flow path (nozzle) communicating with the orifice, and the nozzle. An inkjet recording head having an ejection energy generation means provided in a part of the nozzle and providing ejection energy for forming flying droplets in the recording liquid in the nozzle, and a liquid chamber for supplying the recording liquid to the nozzle. We are prepared. Recording is performed by driving the ejection energy generating means to supply ejection energy to the recording liquid in the nozzle, ejecting the recording liquid as flying droplets from the orifice, and causing the droplets to land on the recording medium. The recording liquid used when recording with such an inkjet recording device generally consists of a recording agent such as a pigment or dye, and mainly water, or water and a water-soluble organic solvent for dissolving or dispersing it. Alternatively, it is formed from a solvent component consisting of a non-aqueous solvent. In an inkjet recording device, an orifice provided at the tip of a nozzle through which recording liquid is ejected is often constantly open to the outside air of the device, regardless of whether or not the device is being driven. Therefore, if no recording is performed for a long time, part of the solvent evaporates from the orifice into the outside air, and recording agent components and solvent components that are difficult to volatilize remain in the recording liquid. The composition of the recording liquid stagnant in the nozzle portion changes and the viscosity increases, resulting in an increase in the viscous resistance of the nozzle portion. Therefore, immediately after restarting recording after the printing material has stopped, droplet ejection failure is likely to occur, in which droplets are not ejected even though the ejection signal is applied, and defects may occur in the initial printed area of the recorded image. There was a problem in that it caused Furthermore, in order to eject liquid droplets in an edgewise manner using an inkjet recording apparatus, the amount of liquid lost due to ejection must be replenished before the next ejection. A typical method for this purpose is to use the surface tension of the liquid to guide the liquid to an orifice by capillary action. In this case, the time L2 required to introduce the liquid to the orifice is
It is determined by t2 = d/u. However, d is the distance that the liquid remaining in the nozzle retreated from its original position after the droplet was cut, and U is the moving speed of the liquid due to capillary action. The above time t2 is usually much longer than the time t required for a droplet to form, and the repeatable drive frequency f determined by f = 1/(L, +L2) is, in fact,

[No matter how far a droplet forms, it is limited by the electric current.
There was a problem in that the repeat drive frequency could not be increased. One effective way to solve these problems is to shorten the length of the nozzle. Reducing the length of the nozzle is equivalent to reducing the resistance of the nozzle wall to the flow, which leads to a reduction in t2. However, shortening the nozzle causes a decrease in the speed of flying droplets and an increase in speed instability, causing the problem that stable recording cannot be performed. [Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned problems of the prior art. The purpose of the present invention is to provide a new inkjet recording head capable of recording. [Means for Solving the Problems] The above objects of the present invention are achieved by the present invention below. An inkjet recording head having a nozzle terminating in an orifice for discharging a recording liquid, a liquid chamber communicating with the nozzle, and an ejection energy generating means attached to the nozzle and supplying ejection energy to the recording liquid. , a first heating means is provided in the nozzle and a second heating means is provided in the liquid chamber separately from the ejection energy generating means, and the first heating means is connected to the ejection energy generating means and the ejection energy generating means. An inkjet recording head characterized in that it is provided between a second heating means. That is, the present invention provides, in addition to the ejection energy generating means, a first heating means mainly for the purpose of increasing and stabilizing the speed of the ejected droplet, and a second heating means mainly for the purpose of shortening the above-mentioned t2. By using these first and second heating means, it is possible to achieve high-speed responsiveness of droplet ejection during recording, and also eliminate the problem of recording liquid ejection failure when resuming recording after being left unused for a long time. This is what I did. [Example] Hereinafter, the present invention will be described in detail with reference to the drawings as necessary. FIG. 1 is a schematic illustration of a preferred embodiment of the present invention. The recording head of this example includes an ejection energy generating means 2,
On the substrate 1 on which the first heating means 3 and the second heating means 4 are provided, a partition wall 5-1 and an outer wall 5-2 are further provided, and a top plate 5 is stacked thereon to form a nozzle 7 and a liquid chamber 8. This is what I did. 30 is an orifice located at the end of the nozzle 7 for ejecting the recording liquid as flying droplets, and 6 is a liquid supply provided as necessary to supply recording liquid to the liquid chamber 8 from outside the recording head. It is the mouth. In the present invention, the discharge energy generating means 2 and the first heating means 3 are placed in the nozzle 7 in this order from the orifice 30 side, and the second heating means 4 is placed inside the nozzle 7 in this order. However, other than the provision of such a heating means, there are no particular limitations on the component structure or formation method of the recording head, and it is similar to that in conventional inkjet recording heads. The same may be desired. Of course, it goes without saying that the number of nozzles, the shape of the orifice, the shape of the liquid chamber, etc. may be set as desired. The ejection energy generating means 2 in the present invention may be of any type as long as it can eject droplets in the same manner as in conventional inkjet recording heads, and specifically, for example, it may use various heating resistors. Typical examples include thermal energy generating means and pressure energy generating means using various piezoelectric bodies. Incidentally, in FIG. 1, a heating resistor is illustrated as an example of the ejection energy generating means 2. The first and second heating means are provided separately from the ejection energy generating means 2, but are not particularly limited in their material, shape, etc., and may be heat generating resistors similar to the ejection energy generating means described above. are listed as typical examples that can be used. Incidentally, in order to make the present invention effective, it is necessary to replace the first heating means 3 with the discharge energy generating means 2.
It is better to have it close to. It is also preferable that the second heating means 4 be located in the liquid chamber 8 immediately after the nozzle 7 and as close to the nozzle 7 as possible to ensure the necessary recording liquid during supply. Hereinafter, the discharge energy generating means 2, the first heating means 3,
The present invention will be further explained by showing an example of the operation during recording when all of the second heating means 4 are heat generating resistors. FIGS. 2(a) to 2(f) show the discharge energy generating means 2.
FIG. 2 is a schematic partial view taken along the line AA in FIG. 1 over time to explain the operations of the first heating means 3 and the second heating means 4. FIG. FIG. 2(a) shows that the discharge energy generating means 2, the first heating means 3, and the second heating means 4 are in a non-operating state, and the liquid chamber 8 is in a non-operating state.
This is a view of the recording head in a printable state with recording liquid being supplied to the nozzles 7. From such a non-operating state (a), a recording signal is first sent to the first heating means 2 to bring it into an operating state. First heating means 3
Immediately after the start of the operation, the operation of the ejection energy generating means 2 is started. Thermal energy is supplied to the recording liquid by the operation of the heating means 3 and the ejection energy generating means 2, and this thermal energy causes a bubbling phenomenon in the recording liquid, and a second figure(
Steam bubbles 9 and 10 are generated as shown in b). FIG. 2(b) shows the state of the steam bubbles 9 generated by operating the first heating means 3 at the maximum volume. FIG. 2(C) shows the state of the vapor bubbles 10 when the volume is at its maximum due to the discharge energy generating means 2 (heating resistor). still,(
It is desirable that the state C) is between immediately before and immediately after the steam bubbles 9 start to self-contract by the first heating means 3. In these states (b) to (C), droplets are not discharged from the vapor bubbles 9 formed by the first heating means. This is because the orifice direction component of the acting force due to the growth of the vapor bubbles 9 has a large resistance loss against the flow caused in the recording liquid by the nozzle forming wall. Further, the purpose of forming the vapor bubbles 9 by the first heating means is not to discharge the vapor bubbles 9, but to eliminate energy loss during liquid droplet discharge and effectively utilize the discharge energy to the liquid, as described below. Since the purpose is to function as a diode, it does not matter at all that it contributes to discharge. The formation of droplets 3 is carried out in the process of foaming and growing of vapor bubbles 1O by the ejection energy generating means and self-shrinking (
(See Figure 2(d)). The acting force when the vapor bubble IO foams and grows includes a component toward the liquid chamber that results in energy loss during droplet ejection. At this time, if you increase the resistance to the flow in that direction and reduce the acting force in the liquid chamber direction that does not contribute to droplet ejection, you can increase the contribution rate of the total acting force to ejection. be. Possible ways to improve this contribution rate include, for example, lengthening the nozzle to increase the resistance caused by the nozzle wall, or providing a barrier, but both of these methods involve lengthening the recording liquid supply time t2 after ejection. Put it away. In contrast, in the present invention, the resistance can be increased only when discharging droplets, and can be decreased during supply. That is, when discharging, the vapor bubbles 9 generated by the first heating means 3 increase the resistance of the nozzle 7 in the direction of the liquid chamber, increasing the contribution rate of the acting force to the discharging, and increasing the flying speed of the droplets. And it should be stable. Furthermore, even for highly viscous recording liquid that may cause ejection failure after being left for a long period of time, the ejection energy can be used effectively by the action of the first heating means, so that droplets can be formed by overcoming viscous resistance. Therefore, the frequency of occurrence of ejection failure immediately after resuming recording is reduced. When the vapor bubble IO self-contracts, a droplet is formed, the meniscus 12 retreats from the orifice 30 into the nozzle, and recording liquid supply by capillary force begins. At this time, the second heating means 4
By activating the liquid chamber 8 in contact with the means 4,
Vapor bubbles 11 are formed in the recording liquid inside the nozzle, and this foaming forces the recording liquid into the nozzle. Figure 2(d)~
(e) shows this situation. This operation significantly shortens 1z, making it possible to record at a high repetitive drive frequency. The vapor bubble 11 then self-contracts and disappears, but at this time the meniscus I2 is hardly drawn into the nozzle. This situation is shown in FIG. 2(f). This seems to be due to the following reasons. That is,
Comparing the growth and contraction of vapor bubbles, we can see that during J-foaming, a nucleus of vapor with high pressure is generated, and the vapor bubble grows all at once until it reaches mechanical equilibrium with its surroundings, but in contraction, the vapor dissolves into the recording liquid. Since the growth is carried out simultaneously, it takes 3 to 5 times as long as the growth. The acting force during growth, which involves such a rapid volume change, is inevitably larger than that during contraction. This acting force during foaming is large enough to overcome the resistance of the nozzle wall, forcing the meniscus toward the orifice, but during contraction, the acting force is lost due to the resistance of the nozzle wall, preventing the meniscus from retreating. It is. The present invention will be further explained below by showing an example of a detailed configuration of a substrate on which ejection energy generating means and first and second heating means for performing such an operation are mounted, and an example of a method of manufacturing a recording head. . FIGS. 3(a) and 3(b) are a partial plan view and a sectional view taken along line AA of an example of a substrate used in the inkjet recording head of the present invention, respectively. This substrate 1 includes a heating resistor 2 as an ejection energy generating means, and a first resistor which increases the resistance to the flow toward the rear of the nozzle during droplet ejection and prevents the recording liquid from retreating.
a heating resistor 3 as a heating means, a heating resistor 4 as a second heating means that achieves a single-hour supply of recording liquid as described above after ejecting a droplet, and achieves high-speed responsiveness of droplet ejection; A common electrode 14 and individual electrodes 15 for applying desired electrical signals according to the ejection pattern to these bowl heating resistors.
．． 16.17 are installed. And Figure 3(b)
These include, for example, glass, ceramics,
A common electrode 14 is formed on a substrate 1 made of a desired material such as Si.
It has a laminated structure in which an insulating protective layer 18, each heating resistance layer 2.3.4, each individual electrode 15, 16, 17, and an insulating protective layer 19 are laminated in this order. Such a substrate is produced, for example, as follows. First, the common electrode 14 is formed on the substrate 1 using 8U, AI, or the like. In this example, 8U was ion beam deposited to a thickness of 0.5 μm on a Si substrate 1 having a thermal oxidation layer 2 to 5 scales thick on its surface. Next, the insulating protective layer 18 is created, and examples of materials constituting the protective layer 18 include titanium oxide, vanadium oxide, niobium oxide, molybdenum oxide, tantalum oxide, tungsten oxide, chromium oxide,
Transition metal compounds such as zirconium oxide, hafnium oxide, lanthanum oxide, yttrium oxide, manganese oxide, metal oxides such as aluminum oxide, calcium oxide, strontium oxide, barium oxide, silicon oxide, and their composites, silicon nitride, nitride High-resistance nitrides such as aluminum, boron nitride, tantalum nitride, and composites of these oxides and nitrides, as well as amorphous silicon,
Examples include thin film materials such as semiconductors such as amorphous selenium, which have low resistance in bulk but can become high in resistance during manufacturing processes such as sputtering, CVD, vapor deposition, gas phase reaction, and liquid coating. The thickness is generally 0.1u1 to 5u+, preferably 0.2p to 3p. In this example, a 5in2 layer with a thickness of 2μ was created by sputtering. Next, a heating resistor layer 2.3.4 is created. As the material constituting the heating resistor layer, almost any material can be used as long as it generates desired heat when energized. Specific examples of such materials include tantalum nitride, nichrome, silver-palladium alloy, silicon semiconductor,
Or hafnium, lanthanum, zirconium, titanium,
Preferred examples include borides of metals such as tantalum, tungsten, molybdenum, niobium, chromium, and vanadium. Among these materials constituting the heating resistor layer, metal borides are particularly excellent, and among these, hafnium boride has the best properties, followed by zirconium boride, The order is lanthanum boride, tantalum boride, vanadium boride, and niobium boride. The heating resistor layer can be formed using the above-mentioned materials using methods such as electron beam evaporation and sputtering. After that, unnecessary portions of these layers are removed using well-known buttering methods such as photolithography and etching, and then layers that will become the electrodes 14, 15, 16, and 17 are created, and the same patterning method as described above is used. Remove unnecessary portions to create an electrode layer with the desired pattern. Furthermore, an insulating protective layer 19 is formed if necessary. In this embodiment, the insulating protective layer 19 is formed by sputtering.
Two films of i02 were formed. Furthermore, in order to improve the durability performance against the mechanical impact force generated when vapor bubbles disappear, AJ, Ta, Ti,
Zr, +lf, V, Nb, Mg, Si,
Mo, W, Y. The protective layer may be formed using metals such as La, alloys thereof, or oxides, carbides, nitrides, borides, etc. of these metals and alloys. Although not particularly shown in the figure, each electrode is provided with an exposed portion for connection to the outside by a method such as bonding. Further, the heat generating resistors may be of any desired shape and size as long as they can achieve the purpose, and may have different shapes and sizes. However, in this embodiment, in order to avoid complicating the drive circuit, they are all the same size and shape, with a width of 30μ and a length of 150JLll. Nozzles, liquid chambers, liquid supply ports, etc. are provided on the inkjet recording head substrate prepared as described above to complete the inkjet recording head of the present invention as illustrated in FIG. 1, for example. FIG. 4 shows another example of such an ink jet recording head of the present invention, and FIG. 4 shows a partial perspective view of the head. The nozzle 7 may be formed using a photosensitive material such as a photosensitive resin film or photosensitive glass, or may be formed by forming a groove on a suitable flat plate such as glass by a mechanical method, etching, etc. It can also be manufactured by a method such as pasting it on the inkjet recording head substrate. Further, at this time, the liquid chamber, the liquid supply port, etc. may be manufactured in one piece. In this embodiment, a photosensitive resin film 31 is used to create a nozzle wall and a liquid chamber wall through a photolithography process and an etching process, and a glass plate with a liquid supply port (not shown) is bonded thereon to form an inkjet The recording head was configured. As mentioned above, the shorter the length of the nozzle 7, the shorter the above-mentioned t2, but this causes a reduction in the ejection speed and stability. In the present invention, this problem is solved by the first heating means 3, so the nozzle can be made as short as necessary, and the recording head can be made more compact. However, it is necessary that the first heating means 3 be installed within the nozzle 7. In this example, the nozzle length was set to 5QOp. The pulse signals shown in FIG. 5 (aL, (b), and (c)) are applied to the inkjet recording head illustrated in FIG. 4 created by the above method to sequentially operate each heating resistor 2.3. In this example, the three heating resistors have exactly the same shape and the same resistance value, so they can be driven with the same voltage waveform.The voltage waveform is a pulsed rectangular wave, and the pulse width is l.
OμSQC was used. The pulse width is the velocity of the flying droplet,
From the viewpoint of cyclic stability, the shorter the length, the better; however, if the length is short, it becomes necessary to apply a larger voltage to the heat generating resistor, which causes a shortening of the durability performance of the heat generating resistor. Furthermore, if the pulse width is made longer than necessary, unnecessary bubbles will be generated during ejection of the liquid layer, which is not preferable. Therefore, the selection of the pulse width is determined by a balanced design that takes into account the above points. The pulse width is preferably within 50 μsec, preferably within 20 μsec, and optimally within 10 μsec. The operation is performed as follows. First, the first heating resistor 3
is operated at the timing shown in FIG. 5(a) to generate steam bubbles. The 'fJ6 diagram is a growth curve of such a vapor bubble. As is clear from the figure, the vapor bubble caused by the first heating resistor 3 does not change sharply before and after its maximum volume, and functions sufficiently as a liquid diode in droplet ejection. When the vapor bubbles of the first heating resistor 3 are in this state, an electric signal is applied to the heating resistor 2 (the (See Figure 5(b)). In this embodiment, the ejection speed of droplets generated by operating the ejection energy generating means at the timing shown in FIG. 5(b) is increased by about 50% due to the presence of vapor bubbles caused by the first heating resistor 3. was completed. When the vapor bubbles caused by the first heating resistor 3 and the ejection energy generating means 2 disappear, the alternation of the meniscus is completed, and the supply of recording liquid is started, a pulse is applied to the second heating resistor 4. In this example, as shown in FIG. 5(C), the first heating resistor 3 was operated with a delay of 50 μsec from the start of its operation. This shortens the recording liquid supply time,
It was possible to obtain a repetition frequency of Hz at the highest IO. Furthermore, the vapor bubbles generated by the first heat generating resistor 3 increase the energy involved in ejection compared to the conventional method, making it possible to prevent ejection failure due to increased viscosity of the recording liquid after being left for a long time. It has also become possible to record stably. FIG. 7 shows an inkjet printer as an example of an inkjet recording apparatus using such an inkjet recording head of the present invention. The printer shown in FIG. 7 uses the recording head illustrated in FIG. 4. This printer discharges recording liquid while moving a recording head 20 mounted on a carriage 21 left and right on rails 22 and 23, and prints characters on a recording medium using a tod matrix of the recording liquid. 24 is a platen that supports the recording medium. [Function] In the present invention, the flying speed of droplets can be increased by providing the first heating means in the nozzle and the second heating means in the liquid chamber, separately from the ejection energy generating means. This stabilized the flight, reduced the error in the landing position on the recording medium, and improved the recording quality. Furthermore, since ejection energy can now be effectively applied to the recording liquid, stable ejection can be performed even after being left for a long time, and the reliability of the inkjet recording head can be improved. [Effects of the Invention] As described above, the present invention makes it possible to provide a novel inkjet recording head that is excellent in high-speed droplet ejection response and ejection stability.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of an example of an inkjet recording head of the present invention, and FIGS. 2(a) to (f) are for explaining operation examples of the ejection energy generating means and the first and second heating means. FIGS. 3(a) and 3(b) are a partial schematic view of an example of a substrate used in the inkjet recording head of the present invention and its A-A cross-sectional view, respectively. A sectional view, FIG. 4 is a schematic explanatory view of another example of the inkjet recording head of the present invention, and FIG.
a) to (C) are diagrams showing an example of a pulse signal pattern applied to the inkjet recording head of the present invention, FIG. 6 is a diagram showing an example of a growth curve of vapor bubbles by the first heating means,
FIG. 7 is a diagram illustrating an example of an inkjet printing head and an inkjet printer according to the present invention. 1; Substrate 2: Discharge energy generating means

Claims (1)

[Claims] (1) A liquid flow path that terminates in a liquid ejection port for ejecting recording liquid, a liquid chamber that communicates with the liquid flow path, and a liquid chamber that is provided alongside the liquid flow path and supplies ejection energy to the recording liquid. In the liquid jet recording head, the liquid jet recording head has a first heating means in the liquid flow path and a second heating means in the liquid chamber, separately from the ejection energy generating means, and a second heating means in the liquid chamber. A liquid jet recording head characterized in that a first heating means is provided between the ejection energy generating means and the second heating means.