JPH0411389B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is applied to a liquid jet recording method in which recording is performed by forming flying droplets. The present invention relates to an invention specific to a recording head having a circuit on a substrate. [Prior Art] Non-impact recording methods have recently attracted attention because the noise generated during recording is so small that it can be ignored. Among them,
The so-called inkjet recording method (liquid jet recording method) is an extremely useful recording method that enables high-speed recording and does not require special processing such as fixing on so-called plain paper. Various methods have been devised, some have been improved and commercialized, and others are still being worked on to put them into practical use. In this liquid jet recording method, recording is performed by causing droplets of a recording liquid called ink to fly and adhere to a recording member, and the generation of droplets of the recording liquid is There are several types of methods depending on the method used to control the method and the flying direction of the generated droplets. Among them, for example, the liquid jet recording method described in publications such as U.S. Patent No. 3,683,212 and U.S. Pat. This is a so-called on-demand recording method in which recording is performed by attaching liquid to a surface, and only the droplets necessary for recording are ejected, so a special means is provided to collect or process the ejected liquid that is unnecessary for recording. It has become particularly popular these days because the device itself can be simplified and miniaturized without the need for it, there is no need to control the flight direction of droplets ejected from the ejection orifice, and multicolor recording can be easily performed. are collecting. Furthermore, there is a liquid jet recording method that uses a completely different droplet formation principle from the liquid jet recording method described above, which was published in Japanese Patent Application Laid-Open No.
It is disclosed in Japanese Patent No. 54-59936. This liquid jet recording method can not only be applied extremely effectively to the above-mentioned on-demand recording method, but also easily realize a full-line type recording head with high-density multi-orifice structure, resulting in high-resolution, high-quality images. It has the characteristic that it can be obtained at high speed. The structure of the recording head applied to these liquid jet recording methods is designed and the necessary means are provided so that the characteristics of each recording method can be maximized. They have a common structure. That is, the heads applied to these recording methods are:
an energy action area that is the area where the energy utilized to eject the liquid is imparted to the liquid;
A liquid introduction region between the energy action region and the liquid introduction port from the liquid chamber, a liquid discharge region between the energy action region and the discharge port that discharges the liquid, and a direct communication with the discharge port. and a liquid path having a shaped portion and a heating element that applies thermal energy to the straight portion. Energy action areas include, for example, U.S. patents
In the recording methods disclosed in US Pat. No. 3,683,212 and US Pat. No. 3,946,398, electromechanical transducers such as piezo elements are provided in a mechanically coupled relationship. Recording is performed by ejecting and flying droplets using pressure energy (pressure waves) generated by inputting a recording signal to the converter. Furthermore, in one of the recording methods disclosed in Japanese Patent Application Laid-Open No. 54-59936, an electric/thermal converter is provided in the energy action area. Thermal energy generated by inputting a recording signal to the converter causes droplets to be ejected and flown for recording. Alternatively, in another recording method disclosed in this Japanese Patent Application Laid-Open No. 54-59936, no special means is provided in the energy action area, and the action area is irradiated with electromagnetic waves such as a laser to record the information that exists there. It is absorbed into a liquid and generates heat, and the action of the generated heat causes droplets to be ejected and flown for recording. In the recording method disclosed in JP-A-54-59936, thermal energy is applied to the liquid as described above to obtain the driving force for ejecting droplets. The liquid subjected to the action undergoes a state change accompanied by a sharp increase in volume, and due to the acting force based on the state change, the liquid is ejected, flies, and adheres to the recording member to perform recording. [Problems to be Solved by the Invention] However, unlike the recording head that is equipped with a thermal energy generating element in the curved liquid path described in Japanese Unexamined Patent Publication No. 55-59976, the heating element for ejecting liquid cannot be connected directly to the recording head. In the recording head having a substantially straight liquid path on the substrate, a different tendency was observed in the liquid supply performance. By the way, JP-A-55-132273, JP-A-55
-132275, Japanese Patent Application Laid-open No. 56-46769,
Regarding the recording head using thermal energy mentioned above,
An example is described in which the distance of the liquid introduction region from the liquid chamber to the heat generating element of the liquid path in a liquid path with a constant cross-sectional area was studied. Among these publications, JP-A-56-
Publication No. 46769 has a relatively high recording frequency of 1K.
A recording head that can obtain frequency characteristics of Hz or higher and is suitable for continuous ejection is disclosed. This excellent recording head has a liquid introduction area distance of 95 μm or more and 2.76 mm.
As described below, there was no margin in the range of driving conditions to achieve stable ejection. Because this is a nearly straight liquid path, during high-speed recording during liquid refilling,
There were cases where it was not possible to follow up. Therefore,
There is a need for a head that can take advantage of the above-mentioned liquid path. [Summary of the Invention] The present invention was developed in view of the technical problems peculiar to a substantially straight liquid path, and is capable of stabilizing continuous droplet formation characteristics over a long period of time, and at the same time reducing the droplet formation frequency. An object of the present invention is to provide an improved liquid jet recording head. The present invention focuses on the cross-sectional area of the liquid path, which has not been paid attention to in the past, in the conventional droplet jet recording head described above, and creates a liquid introduction region having a typical length for droplet jetting, and a thermal energy source. This invention is based on the relationship between areas of action. The present invention achieves the above-mentioned object, and includes a liquid chamber and a liquid chamber on a plane surface of a substrate including a droplet ejection heating element that generates thermal energy for forming bubbles in the liquid in order to eject droplets. a liquid path having a straight part that communicates with the chamber and has a discharge port at the end and is provided with the heating element; and a thermal energy action within the straight part that corresponds to the heating element for ejecting droplets. and a liquid introduction region that is a section between the liquid chamber and the liquid chamber, the liquid path is perpendicular to the central axis of the width of the liquid path on the substrate plane and is perpendicular to the substrate plane. Regarding the vertical cross-sectional area of the liquid path, the average value S1 of the cross-sectional area of the liquid path in the thermal energy action area satisfies 3≧S2/S1>1 with respect to the average value S2 of the cross-sectional area of the liquid path in the liquid introduction area. The liquid droplet jet recording head is characterized in that the cross-sectional area of the liquid path in the liquid introduction region becomes smaller toward the thermal energy action region. The voltage margin used in the evaluation of the present invention is an allowable voltage value that can stably achieve desired droplet ejection, and the difference between the maximum and minimum values of this value is referred to as the voltage margin width. A large voltage margin width has the effect of achieving stable recording against instantaneous voltage fluctuations during driving of the multi-liquid path and variations during manufacturing. In the above configuration, the present invention provides 3≧S2/S1>1
By satisfying the following, we solve the problem of unstable discharge due to the influence of dissolved bubbles during the formation of discharge bubbles, resulting in poor discharge, and efficiently remove dissolved bubbles from the heat-acting part, which affects discharge in the long term. can be suppressed to the extent that it does not cause any damage. A preferred configuration of the present invention is 3≧S2/S1≧1.3. According to the present invention, when the recording head is designed and manufactured in this manner, the continuous droplet formation ability is stably maintained over a long period of time, and the droplet formation frequency is also significantly improved. In other words, according to the present invention, the quality of the recorded image is improved and the continuous and repeated ejection of droplets is performed by the recording head over a long period of time under conditions that enable high-speed recording. The improvement in frequency (number of droplets formed per unit time = droplet formation frequency per unit time) and stabilization of droplet formation characteristics were achieved. [Example of Embodiment] The present invention will be described below according to an example of embodiment using drawings. FIG. 2 shows one of the preferred embodiments of the present invention. As shown in FIG. 6, the recording head's thermal energy acting section installation substrate was prepared by forming a SiO ₂ layer 607 to a thickness of 3 μm on a rectangular 10 mm×20 mm alumina substrate 601 with a thickness of 1 mm by sputtering. ,
1000〓 of HfB ₂ as the heating element 603, as the electrode
After sputtering 5000 μm of Al, selectively etching the heating element 6 with a width of 50 μm and a length of 300 μm.
03 and electrodes 608 and 609 having a width of 50 μm were formed, and then a SiO ₂ layer with a thickness of 5000 μm was coated by sputtering. Next, a groove plate 202 with a constant depth of 75 μm is formed by photo-etching photosensitive glass with a thickness of 1 mm so that the dimensions of the discharge port 206 are 75 μm x 75 μm and the groove width becomes wider toward the inlet 205. A heating element 203 was adhered to a substrate 201 as shown in FIG. 6 so as to cover the groove, and the end surface was polished. Next, a glass plate was cut into a suitable size and was attached to the inlet 205 side with an adhesive to form a liquid chamber 204. In the figure, 211 is a liquid discharge area, 212 is an energy action area, and 213 is a liquid introduction area, and these three areas together constitute a substantially straight liquid path. Further, an ink supply pipe 210 is connected to the liquid chamber 204 as shown in the figure. Further, FIG. 3 shows another example of the preferred embodiment of the present invention, in which the substrate and the common liquid chamber are formed by the same method as shown in FIG. A groove with a depth of 1 mm and width of 75 μm was cut into glass with a diameter of 2 mm using a diamond cutting grindstone, and then the groove was polished at an angle so that the depth of the groove became shallower on the orifice side, making the groove depth at the orifice part 75 μm. The groove plate 302 is inserted into the substrate 3 so that the groove covers the heating element 303.
01, and the end face is polished. FIG. 1 shows a conventional example, which can be manufactured by a method similar to that described in the embodiments of FIGS. 2 and 3. With respect to the recording head described as the conventional example and the embodiment example, the present inventors have found that the center of the straight part of the liquid path of the thermal energy application area, which is the area where the thermal energy from the liquid jet heating element is applied to the liquid, is The ratio of the average value S ₁ of the cross-sectional area perpendicular to the axis to the average value S ₂ of the cross-sectional area perpendicular to the substrate of the liquid introduction region of the liquid introduction port where the liquid chamber and the liquid path communicate with each other, S ₂ /
We designed and manufactured many heads with various variations on the _S1 . Then, we measured the voltage margin that allows stable droplet formation for 10 ⁷ pulses or more for each head, and found that S ₂ is larger than S ₁ and the voltage margin is smaller for the liquid path where the cross-sectional area is smaller toward the ejection port. Although a wide margin was obtained, in the case where S ₁ =S ₂ (head in FIG. 1), ejection stopped after about 3×10 ⁵ pulses. Furthermore, the results showed that the droplet formation frequency limit becomes higher when S ₂ is larger than S ₁ and the cross-sectional area of the liquid path is smaller toward the ejection port. The table below shows, as an example, that S ₂ /S ₁ is 1
(head in Figure 1), 1.3, 1.5, 2, 3 (the above are heads in Figure 2), the voltage margin width at which droplet formation is stable up to ¹⁰⁶ pulses at 1KHz,
and droplet formation frequency limits are collectively shown.

[Table] As described above, according to the present invention, there are great advantages such as improved reliability of droplet ejection due to increased voltage margin width, easier design of the drive circuit of the energy application part, and smaller size. Furthermore, there is an advantage that the frequency limit is improved and high-speed recording becomes possible. In the above study, the ink used was obtained by mixing and dissolving the compositions shown below and filtering the mixture using a filter. Water 50 parts Diethylene glycol 48 parts Black dye 2 parts The resistance value of the heating element is 150Ω, and
A rectangular pulse of 5 μsec (45 V) was applied to eject a droplet. FIGS. 4 and 5 similarly show other examples of the embodiment of the present invention, and show an example in which the cross-sectional area of the liquid path becomes intermittently smaller toward the discharge port. In the figure, when the last two digits are the same as those in FIG. 2, they mean the same components. In these cases, almost the same effect as that of the embodiment shown in FIGS. 2 and 3, in which the cross-sectional area of the liquid path becomes smaller continuously toward the discharge port, was observed. Furthermore, when the recording head is constructed in the embodiment shown in FIGS.
It is possible to obtain high-resolution recording by achieving a high density of about 1000 nm/mm, and in combination with the effect of improving the droplet formation frequency according to the present invention, there is a very large advantage in miniaturizing the recording head. be. [Effects of the Invention] As detailed above, according to the liquid jet recording head of the present invention, it is possible to repeatedly eject liquid stably and continuously for a long period of time, and the droplet formation frequency can be improved. can.

[Brief explanation of drawings]

FIG. 1 is a perspective view schematically depicting the structure of a conventional recording head with its main parts cut away, and FIGS. 2 to 5 show preferred embodiments of the recording head of the present invention, respectively. FIG. 6 is a perspective view schematically depicting a main part cut away to explain an example, and FIG. 6 is a schematic perspective view showing the structure of a substrate having a heat generating element. In the figure, 101, 201, 301, 40
1,501,601 is a thermal energy action unit installation board, 102,202,302,402,502 is a groove plate, 103,203,303,403,50
3,603 is a heating element, 104,204,304,
404, 504 are liquid chambers, 105, 205, 30
5,405,505 is the introduction port, 106,206,
306, 406, 506 are discharge ports, 111, 21
1, 311, 411, 511 are liquid ejection areas, 1
12, 212, 312, 412, 512 are energy action areas, 113, 213, 313, 41
3,513 is a liquid introduction area.

Claims (1)

[Scope of Claims] 1. A liquid chamber and a liquid chamber communicating with the liquid chamber on the plane of the substrate, which is provided with a droplet ejection heating element that generates thermal energy for forming bubbles in the liquid in order to eject the liquid droplet. a liquid path having a straight portion having a discharge port at an end and provided with the heating element; a thermal energy acting area within the straight portion corresponding to the heating element for ejecting droplets; a liquid introduction region that is a section between the recording head and the chamber, a liquid path that is perpendicular to the central axis of the width of the liquid path on the plane of the substrate and perpendicular to the plane of the substrate; Regarding the cross-sectional area, the average value S1 of the cross-sectional area of the liquid path in the thermal energy action area is 3≧S2/S1>1 with respect to the average value S2 of the cross-sectional area of the liquid path in the liquid introduction area.
A droplet jet recording head which satisfies the following: and wherein the liquid path cross-sectional area of the liquid introduction region becomes smaller toward the thermal energy action region. 2. A droplet jet recording head according to claim 1, wherein the liquid path cross-sectional area of the liquid introduction region becomes continuously smaller toward the thermal energy action region. 3. A droplet jet recording head according to claim 1, wherein the liquid path cross-sectional area of the liquid introduction region gradually decreases toward the thermal energy action region.