JPH0363138A - Ink-jet recording device - Google Patents

Abstract

PURPOSE:To stabilize ink discharge by installing a constitutional blank, characteristic acoustic impedance of which is approximately 1.1-3.0 times as high as ink and which has length substantially the same as or shorter than the effective length of an electromechanical transducer and is used for absorbing and diffusing sound waves. CONSTITUTION:A material having a value between the acoustic impedance of ink and the acoustic impedance of an ink-liquid injection nozzle 22 is selected as the Material of a constitutional blank 3. It is effective that the characteristic acoustic impedance of the constitutional blank 3 is set substantially within a range of approximately 0.1 times or 3 times of that of ink. The constitutional blank 3 is expanded and contracted properly with the pressure fluctuation of the inside, and dissipates sound waves. Accordingly, the flow rate of ink is maintained sufficiently, flow resistance is not increased, unnecessary pressure waves can be absorbed and diffused, and structure can be made simpler than a filter is mounted on the ink supply-port side of the ink-liquid injection nozzle.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention converts an electrical signal into a pressure wave through an electromechanical conversion element, and thereby performs recording such as ejecting ink droplets and printing dots. This invention relates to an inkjet recording apparatus.

(Prior Art) This type of inkjet recording apparatus is known as an on-demand type, and has a configuration as shown in FIG. 2, for example. Here, an ink flow 'l & 13 is formed in the ink liquid ejection nozzle 22 made of glass, and in order to eject 14 ft of ink liquid fi from the meniscus-shaped orifice 20, an electric/mechanical device is installed in the body of the ink liquid ejection nozzle 22. A conversion element 11 is provided. When a voltage is applied from the drive circuit 12 to this electro-mechanical transducer 11, the electro-mechanical transducer 11 contracts and expands, thereby creating a pressure wave (longitudinal wave) in the vertical flow path 13. This generates ejection energy and gives ejection energy to the ink in the ink flow path. It is located at the rear end of the ink liquid jet nozzle 22 and has a flow resistance of 1! The ink flow path 13 is communicated with an ink tank 17 via the filter 21, and is supplied with ink 16. Furthermore, since this filter is porous, it also has the role of absorbing undesired pressure waves generated within the ink flow path.

(Problems to be Solved by the Invention) However, in the conventional inkjet recording apparatus described above, since the filter 21i is provided in the ink flow path 13 to provide flow resistance, the limit of the amount of ink discharged becomes low.

If you look closely at the surface of the filter's constituent material, which absorbs the eternal pressure waves inside the filter, there are large gaps. In other words, the material for the filter 21 is a sintered body or the like, which is similar to that of ink.

Since materials with different characteristic acoustic impedances are used, when the pressure waves generated by the electromechanical elements reach the surface of the constituent materials of the filter 21, large pressure fluctuations occur. As a result, bubbles form inside the filter, causing the filter to lose its function as a filter. This situation is schematically shown in FIG. This figure is an enlarged view of a filter with irregularities, and the irregularities appear flat. Here, the horizontal axis shows the position in the direction perpendicular to the surface of the filter constituent material (unrelated to the direction of the ink flow path), and the vertical axis The pressure is shown. And the left side of the vertical axis is the ink area,
On the right is the internal region of the filter component. Now, assume that the characteristic acoustic impedance of the material of the filter 21 is sufficiently larger than that of the ink. (In al, pressure pulse 1 from the ink region is about to enter the boundary surface at It is convenient for explanation to assume a pressure pulse 2 (reflected pressure/zerus) of the same height as pressure/zerus 1 as shown by the dotted line inside the region of the constituent materials. After some time has elapsed, the pressure pulse l has just reached the surface of the filter constituent material.

At this time, the ink pressure near the boundary surface is expressed as the sum of pressure pulse 2 and pressure pulse 2. (e) shows this situation, where the pressure near the interface is twice that of the incident pulse. As a result of the reflection at the interface, a pressure pulse 2 remains in the ink as shown in (d). In addition, in the figure, compressive pressure/9 Lus was considered, but the same thing occurs with expansive pressure waves.

Usually 0.1-0.3 μg ink droplet t 50 μ
Accelerate within a time of about 100μ11 from the discharge port of m to 1
In order to give a speed of about 0.1v/s, 0.1 to 1
．． A pressure change of approximately 0 atmospheres is required. Normally, the pressure of ink is 1 atm, so a maximum pressure increase of 2 atm will occur at the ink interface.For example, if the ink's characteristic impedance zi is 1.6X10 g/ctyr・-
.

Characteristics of constituent materials of sintered body as filter 21 Acoustic impeder 7 Z42>(10z 20 x 105g
/cm' m is about 0.7 to 0.8, and the maximum pressure is about 1.7 to 1.8 atmospheres. Conversely, the pressure may be reduced to θ atmospheric pressure O, and at this time the water contained in the ink at the boundary surface boils, causing so-called cavitation. Then, bubbles are generated. These bubbles are generated within 1% of the filter area on the filter surface and inside the filter near the surface.The microbubbles generated by the remaining cavitation bubbles partially grow into large bubbles and absorb the pressure waves necessary for ink ejection. Otherwise, it may cause irregular reflections, making ink ejection extremely unstable. This will lead to a decline in printed goods trade. In some cases, as a result of the ink ejection being disturbed, air may be taken in from the ink ejection port, and a large air column may block the ink flow path, making it impossible to eject ink. The casing and the above-mentioned filters are expensive and have a small structure, so it takes time to install them in the ink flow path, which causes high costs. However, the filter has the role of absorbing unstable pressure waves generated in the ink flow path, and even if the filter is removed, the pressure waves cannot be removed.

(Object of the Invention) The present invention has been made based on the above circumstances, and is an inkjet recording system that enables a sufficient supply of ink to be applied to an ink flow path, absorbs pressure waves, and enables stable ink ejection. The aim is to provide equipment.

(Means for Solving the Problems) Therefore, in the present invention, an electrical/mechanical transducer is disposed along the ink flow path of an ink liquid ejection nozzle, and the electric/mechanical transducer generates a In an on-demand type inkjet recording device that uses pressure waves in the ink flow path to eject ink droplets from the tip opening of the ink jet nozzle, an ink droplet is located at the rear end of the ink jet nozzle and is connected to the ink flow path. On the ink supply side, its bony acoustic impedance is approximately 1.1 to 3.1 times that of the ink.
A component material for absorbing and diffusing sound waves is provided, which is made of a material with a range of 0x and has a length substantially equal to or shorter than the effective length of the electromechanical transducer.

(Function) For this reason, unlike the case where a filter is provided on the ink supply side, there is no restriction on the ink supply amount, and the above-mentioned constituent material can sufficiently absorb and dissipate pressure waves, so ink ejection is improved. This makes it possible to achieve stable, clear, uniform density printing.

(Example) Hereinafter, an example of the present invention will be specifically described with reference to the drawings. Among them, the same constituent parts as those shown in the explanation of the conventional example are given the same reference numerals, and the explanation thereof will be omitted. In the embodiment shown in FIG. 1, a cylinder for absorbing and diffusing sound waves is located at the rear end of the ink liquid jet nozzle 22, that is, on the ink supply side of the ink flow path 13 communicating with an ink tank (not shown). A structural material 3 having a shape is provided. The effective length t2 of the constituent material 3 is the effective length of the electromechanical conversion element 11.

t, to t2. Under such setting conditions, the constituent material 3 can most efficiently prevent unnecessary sound waves generated within the ink flow path 13 from being reflected back to the ink flow path. This point will become clear from consideration of the wavelength of the sound wave generated by the electromechanical transducer 11 within the ink flow path 13 (described below).

FIG. 4 shows an example of an applied voltage waveform when the electro-mechanical transducer 11 is composed of a piezoelectric element.

When printing one dot, a voltage with this waveform is applied to the electromechanical conversion element 11. This maximum repetition rate is approximately 3 kHz.

Generally, the wavelength of the sound waves generated in the ink flow 'Nr13 is often considered to be associated with this frequency, or it is often associated with the length between the ink ejection port (orifice) 20 and the ink supply port. However, the wavelength that must be taken into consideration when actually providing the above-mentioned component 3 must be considered in a different way. This point will be specifically explained with reference to FIG. As mentioned above, when voltage is applied to the electro-mechanical transducer 11, the electro-mechanical transducer 11 suddenly contracts at voltage step 7'IO in FIG. 5, and as shown in FIG. 5(a) The ink within the area of the effective length (dotted lines 4 and 5) in the ink flow path 13 shown in is pressurized by a pressure JP compared to the surrounding ink pressure. The effective length indicated by the dotted lines 4 and 5 depends on the mechanical properties of the electromechanical transducer 11, such as the mass, elastic modulus, sharpness of the rise of the voltage step, and propagation velocity in the ink. Determined. To illustrate this, the electromechanical conversion element 11 is made of commercially available PZT (length: 10-1, outer diameter: about 1 m).
If the sound velocity in the ink is about 1500 m7m and the voltage step is about i o o Vμ-, dotted line 4
The distance (length) between the lines 5 and 5 is about 2°0- over 10m. This pressurized area (area of pressure JP) is then divided into two high pressure areas (dotted lines 6 and 7) as shown in FIG.
% and the area surrounded by points [8> and 9), one side is to the left, the other to the right, and is propagated through the ink as a sound wave. At this time, the size surrounded by each high pressure area is point #! 4 and 5, but each pressure is υ higher than the ambient pressure by 1/2 J P.

This is half that of 5th fk(a). Figure 5 (b
), assuming that the ink ejection port (orifice) 20 exists in the left direction, the area (the area surrounded by dotted lines 6 and 7) is consumed as energy to accelerate the ink when it reaches the ink ejection port, You lose your vibrational energy. On the other hand, the area (the area curved by dotted lines 8 and 9) goes toward the ink supply port. The problem of the present invention is how to eliminate this sound wave. Here, it can be seen that the meaningful length associated with the wavelength of the sound wave is the interval between dotted lines 8 and 9,
This length is ultimately the interval between dotted lines 4 and 5, that is,
This is approximately equal to the effective length of the electromechanical transducer 11. When the high-pressure region matches the component 3, the phase of dynamic elastic deformation is the same everywhere in the component 3, and the ink in the ink tank 16 flows through the wall surface of the component 3. and dissipate sound waves.

Incidentally, if the length t2 of the component material differs greatly from the length t of the electromechanical transducer, the phase of the dynamic elastic deformation of the component material will differ depending on the location, and as a result, the sound wave will Not sufficiently dissipated into the ink.

Sound waves are reflected to the ink flow path 13, reducing the stability of ink ejection.

Next, the characteristic acoustic impedance of the constituent material 3 will be considered. Suppose that the constituent material 3 had exactly the same impedance as the ink.

The acoustic effect is the same as when this component material 3 does not exist, and the sound waves propagating from the left direction (ink ejection port @) are reflected at the ink supply port end of the ink liquid jet nozzle 22, causing In addition, the phase is reversed and the signal is propagated to the left without losing any energy. Also,
Assuming that the constituent material 3 has the same acoustic impedance as the ink jet nozzle 22, the length of the ink flow path 13 is simply extended.

In this case as well, reflection of sound waves occurs. In consideration of this point, it is appropriate to select a material for the constituent material 3 having a value intermediate between the acoustic impedance of the ink and the acoustic impedance of the ink jet nozzle 22. As mentioned above, when the amplitude reflectance B of the sound wave is 0.7 to 0.8, the component material 3 becomes acoustically indistinguishable from the ink jet nozzle 22 when viewed from the ink, so R is set to 0.5 or less. This is desirable. Considering this point, the impedance ratio (
z2/z, ) is set to 3 or less. Then, if the impedance ratio (Z2/2.) is lowered to 1/:1.0, it becomes R-0, and there is no point in installing component material 3 again. The impedance is essentially about 1.1 of that of the ink.
It is effective to set it within a range of 3.0 times to 3.0 times. At this time, the constituent material 3 expands and contracts appropriately as the internal pressure fluctuates, and dissipates sound waves. Incidentally, the amplitude reflectance of longitudinal waves applied to the interface between the ink and the constituent material 3 is about 0.05 to 0.5. Now, the characteristic acoustic impedance of the ink is the normal value, 1.6 x 105g1
If it is about ad'・S, the corresponding constituent material is nylon (2,86X10'(/a7・s),
yf! rie f v y (1,75x105g/m”
s), $9 sfy (2,48X 10'g/J・
s), Ho I) 7' Lobivy (2,42X 10
5 (/m's) or the like is suitable.

FIG. 6 shows another embodiment of the invention. Here, a large number of holes 3A are formed on the surface of the component material 3, and open into the ink tank 17. Moreover, FIG. 7 shows still another embodiment of the present invention. Here, the terminal of the component 3 is closed. In this case, it is necessary to prevent the ink flow resistance from increasing by considering the number and size of the openings 3A, but if this point is taken into consideration, the same effect as in the previous example can be achieved. is obtained. It was a cabinet. FIG. 8 shows another embodiment of the present invention. Here, on the ink supply port side, the end of the component material 3 is cut diagonally so that the cross-sectional area of the cut is large by >6°, and the efficiency of sound wave dissipation is high. In other words, the length of the constituent material 3 is determined by the average length.

(Effects of the Invention) As described in detail above, the present invention is such that the constituent material for absorbing and diffusing sound waves is a material having an acoustic impedance of about 1.1 to 3 times the acoustic impedance of the ink. The effective length of the casing is equivalent to that of an electromechanical transducer, so it is possible to maintain a sufficient ink flow rate and absorb and diffuse unnecessary pressure waves without increasing flow resistance. It is structurally simpler than the case where a filter is provided on the ink supply port side of the ink liquid ejecting nozzle as in the case of the above method, and it is possible to significantly reduce manufacturing costs.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional side view showing one embodiment of the present invention. FIG. 2 is a longitudinal sectional view showing a conventional example, and FIGS. 3(a) to 3(i) are explanatory diagrams for explaining the reflection situation of pressure waves. Fig. 4 is a graph showing the relationship between applied voltage and time when pressure waves are generated, Figs. 8 are longitudinal sectional views showing other embodiments of the present invention. 3... Constituent material for sound wave absorption/diffusion, 11... Electrical/mechanical conversion element, 20... Orifice, 13... Ink flow path %22... Ink liquid jet nozzle.

Claims (1)

[Claims] 1) An electrical/mechanical transducer is disposed along the ink flow path of the ink liquid ejection nozzle, and pressure waves in the ink flow path generated by contraction/expansion of the electrical/mechanical transducer In an on-demand inkjet recording device that ejects ink droplets from the tip opening of the ink liquid ejecting nozzle, a characteristic acoustic impedance is located at the rear end of the ink liquid ejecting nozzle on the ink supply side to the ink flow path. is composed of a material that is approximately 1.1 to 3.0 times that of the ink, and has a length that is substantially the same as or shorter than the effective length of the electromechanical transducer. An inkjet recording device characterized by being provided with constituent materials for absorption and diffusion. 2) The inkjet according to claim 1, wherein the constituent material is a cylindrical body having a flow path having approximately the same diameter as the ink flow path, and has a shape in which several openings are bored in the peripheral wall. Recording device. 3) The inkjet recording apparatus according to claim 1, wherein the constituent material is a cylindrical body having a flow path having approximately the same diameter as the ink flow path, and the ink supply terminal is an opening cut diagonally.