JPH01214446A - Ink jet head - Google Patents

Abstract

PURPOSE:To reduce the flow passage resistance loss of the ink to an ink chamber, by providing a supply passage successively expanding toward the ink chamber between a pressure chamber and the ink chamber and specifying the angle thetaof expanse thereof. CONSTITUTION:Between a pressure chamber 22 generating pressure in ink and an ink chamber 24 for temporarily storing the ink in a head from the outside, a supply passage 23 having a conical expanse toward the pressure chamber 22 at an angle of expanse of 5-30 deg. is provided. The loss factor xsiin the flow passage resistance when the ink flows from the ink chamber and the supply passage to the pressure chamber at the times of the introduction and injection of the ink is min. at an angle theta of expanse of 5-6 deg. and the ink can be smoothly injected in the pressure chamber at an angle theta of expanse up to 30 deg. without leaving air bubbles and an ink filling time is shortened and a repeated frequency characteristic is also enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inkjet head used in a drop-on-demand type inkjet printer.

[Conventional technology]

FIG. 3(a) is a plan view showing the basic configuration of a spatula 1 used in a drop-on-demand type inkjet printer, and FIG. 3(b) is a sectional view of FIG. 3(a). As shown in FIGS. 3(a) and 3(b), the head used in this drop-on-demand type inkjet printer includes a nozzle 21 for ejecting ink particles 27 and an ink chamber 2.
A flexible thin flat elastic plate 25 made of a material such as glass ceramic or stainless steel is bonded to the substrate 20 on which an injection channel system having a pressure chamber 22 and a supply path 23 is formed between the substrate 4 and the substrate 20 by diffusion welding or the like. An electromechanical transducer, that is, a piezoelectric element 26 made of a material such as zircon titanate or barium titanate is bonded to an elastic plate 25 at a position corresponding to the pressure chamber 22.

Now, in the above configuration, when an electric signal is applied to the piezoelectric element 26 in accordance with a recording signal, the portion of the elastic plate 25 at a position corresponding to the pressure chamber 22 is instantly bent and deformed, and the pressure chamber 22
The volume of the ink decreases instantaneously, and a pressure wave is generated in the ink within the pressure chamber 22. This method is based on the principle that the ink inside the nozzle 21 becomes ink particles 27 and flies due to the propagation of the pressure waves.

[Problem to be solved by the invention]

When the conventional inkjet head described above is installed in a printer and prints by jetting ink particles, the pressure waves of the ink in the pressure chamber 22 that are generated to jet the ink particles are propagated to the nozzle 21 and at the same time. , this pressure wave is also propagated to a supply path 23 having approximately the same cross-sectional area as the nozzle 21. This pressure wave is then reflected by the supply path 23 and reaches the nozzle 21. Optimize the balance between the time difference between the first pressure wave heading from the pressure chamber 22 to the nozzle 21 and the second pressure wave reflecting off the supply path 23 and heading towards the nozzle 21, and the cycle time of the first pressure wave. A more efficient head can be obtained if the head is designed to satisfy the following conditions (Patent Application No. 60-218377)
>. Further, the ink lost by the amount of ink ejected is filled into the pressure chamber 22 via the supply path 23. During the ejection stroke, if air bubbles exist in the pressure chamber 22, the air bubbles will absorb the compressive deformation of the ink, which will prevent the ink pressure from increasing which is necessary to eject the ink droplets 27 from the nozzle 21, and the ink droplets will not be ejected. It becomes impossible.

Therefore, the ink within the pressure chamber 22 must be free of air bubbles. Therefore, when ink is injected into the manufactured head for the first time, it is necessary to inject the ink without leaving any air bubbles from the ink chamber 24 to the nozzle 21. The problem here is the change in the cross-sectional area of the flow path from the supply path 23 to the pressure chamber 22. FIG. 4 is an enlarged sectional view showing an example of the supply path 23. If the change in the cross-sectional area between the supply F1% 23 and the pressure chamber 22 suddenly increases as shown in the figure, the flow of ink may peel off from the wall. As shown in the flow velocity distribution 31 in the figure, the fluid (ink) collides with the downstream flow to create a vortex 30.
The internal friction within the tube increases, creating a large flow path resistance. In order to solve this problem, the supply path 23 was abolished and the pressure chamber 22 and the ink chamber 24 were directly connected.

As a result, ink could be injected into the head without leaving any bubbles. However, as mentioned above, by making the supply path 23 smaller than the cross-sectional area of the pressure chamber 22, the effect of increasing ink ejection efficiency is lost, so the impact given to the ink in the pressure chamber must be increased, and the ink Since the amount of ink flowing out into the ink chamber 24 also increases, the filling time in the ink ejection process becomes longer, causing another problem in that the ink repetition frequency characteristics deteriorate. A second problem is that when the head is a multi-nozzle head having a plurality of ejection channel systems, the pressure waves are propagated to other ejection channel systems via the ink chamber 24. Therefore, nozzle 2 of other injection channel system
The meniscus (unevenness on the liquid surface) 33 of No. 1 vibrates violently.

As a result, mutual interference between each ejection channel system occurs, resulting in unstable ink drop ejection. In other words, a certain 1
A phenomenon occurs in which the ink droplet ejection speed decreases or increases when two or more ejection channel systems are driven compared to the ink droplet ejection speed when only the book's ejection channel system is driven. Therefore, a problem arose in that printing quality was adversely affected. Furthermore, if the generated pressure waves are strong, the pressure fluctuations overcome the surface tension of the meniscus 33, causing ink to drip from the nozzle 21. A nozzle 21 with dripping ink cannot properly eject ink particles, which is a fatal problem for the inkjet head.

The purpose of the present invention is to solve the above problems, provide good printing quality,
An object of the present invention is to provide a highly reliable inkjet print head capable of high-speed recording.

[Means to solve the problem]

The inkjet head of the present invention includes a nozzle that ejects ink particles, a pressure chamber that generates pressure on the ink, an ink chamber that temporarily stores ink in the head from the outside, and supplies ink from the ink chamber to the pressure chamber. In an inkjet head consisting of an ejection channel system consisting of a supply path, a cone-shaped spread with a radius 6 and an angle of 5° to 30° toward the pressure chamber is provided between the pressure chamber and the ink chamber. It is constructed by providing a supply path.

[Effect]

During ink filling during ink injection and ink jetting, when ink flows from the ink chamber and supply path to the pressure chamber, no vortex is generated at the part where the cross-sectional area changes, so there are no air bubbles or residual <<
Since the flow path resistance is also small, the ink filling time is shortened and the repetition frequency characteristics are also improved.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partially enlarged view of the ink supply path and its surroundings in one embodiment of the present invention. As shown in the figure, a bell-shaped channel is provided between the ink supply channel 23 and the pressure chamber 22 at an angle θ. If the spread angle θ is an appropriate value, the flow will not separate from the wall, as shown in the flow velocity distribution 32 in the figure, that is, the flow will be free of eddies. The spread angle θ will be explained.

FIG. 2 is a diagram of the relationship between the divergence angle θ of a flared tube with a circular cross section and its flow path resistance, which is known from fluid mechanics, where θ is the flare angle of the flared tube and ξ is the loss coefficient due to fluid resistance. As can be seen from the figure, the loss coefficient ξ is the smallest when the spread angle θ is 5° to 6°, the loss coefficient ξ is maximum at θ -60° to 70°, and when θ = 180° (in the case of rapid expansion), the loss coefficient ξ is the smallest. I settled down at Cape 1. Also, in a rectangular cross section,
There is an experimental result in which ξ is minimum when θ-10° to 12°. Based on these hydrodynamic facts, we redesigned the inkjet head, produced a prototype, and conducted experiments. As a result, ink can be injected without any problem and leaving no bubbles inside the pressure chamber up to the spread angle θ of 30°, and the ink ejection repetition frequency characteristics are similar to those when the spread angle θ is 180° (Figure 4). Characteristic results were obtained. Furthermore, even in the case of a multi-nozzle head, there was little mutual interference between the nozzles.

〔Effect of the invention〕

As explained above, a supply path that gradually widens toward the ink chamber is provided between the pressure chamber and the ink chamber, and the spread angle θ is set to 5.
By setting the angle to ~30°, it is possible to reduce the resistance loss of the ink flow path into the ink chamber, resulting in an inkjet head with better printing quality and higher reliability than conventional heads. This has the effect of solving the problems of the head.

[Brief explanation of the drawing]

Fig. 1 is a partially enlarged view of the ink supply path and its surroundings in an embodiment of the present invention, Fig. 2 is a diagram of the relationship between the opening angle θ of the expanding tube and its fluid resistance loss coefficient ξ, and Fig. 3 is the principle of the inkjet head. 4 are partially enlarged views of the supply path of a conventional inkjet head. 21... Nozzle, 22... Pressure chamber, 23... Supply path, 24... Ink chamber, θ... Spread angle.

Claims (1)

[Claims] It consists of a nozzle that ejects ink particles, a pressure chamber that generates pressure on the ink, an ink chamber that temporarily stores ink from the outside in the head, and a supply path that supplies ink from the ink chamber to the pressure chamber. An inkjet head consisting of an ejection channel system, characterized in that a supply path having a cone-shaped spread with a spread angle of 5° to 30° is provided between the pressure chamber and the ink chamber toward the pressure chamber. head.