Piezoelectric inkjet head and its flow channel structure, inkjet unit

Abstract

This disclosure provides a piezoelectric inkjet head and its flow channel structure and inkjet unit. The flow channel structure includes an ink supply end, a choke structure, a vibrating cavity, an ink outlet end, and a nozzle structure arranged sequentially. The first flow resistance of the choke structure is in a first proportion to the total flow resistance of the flow channel structure; the second flow resistance of the nozzle structure is in a second proportion to the total flow resistance; wherein the first proportion is less than the second proportion. This disclosure ensures effective droplet formation while avoiding backflow of air that could cause printhead failure, and ensures the highest flight speed of ink droplets of the same volume, effectively improving the inkjet efficiency of piezoelectric inkjet printing and avoiding ink interruption due to insufficient ink supply efficiency during high-frequency inkjet printing.

Description

Technical Field

[0001] This disclosure relates to the field of piezoelectric inkjet technology, and in particular to a piezoelectric inkjet head and its flow channel structure and inkjet unit. Background Technology

[0002] In piezoelectric inkjet technology, positive and negative pressures are generated in the vibrating cavity as the piezoelectric vibrating diaphragm moves back and forth. When the vibrating cavity is under negative pressure, ink flows into the vibrating cavity from the ink supply side; conversely, ink flows out of the vibrating cavity from the ink outlet side (i.e., the nozzle side). The ratio of ink flowing in and out is determined by parameters such as the fluid resistance on both sides.

[0003] When the flow resistance ratio on the ink outlet side is too high, the ink will backflow into the ink supply pipe when there is positive pressure in the vibrating cavity, which will not be able to form ink droplets effectively or will limit the flight speed of the ink droplets. When the flow resistance ratio on the ink outlet side is too low, the ink will draw air back into the cavity when there is negative pressure in the vibrating cavity, causing the printhead to fail.

[0004] Existing piezoelectric inkjet heads do not comprehensively consider the fluid resistance relationship between the nozzle structure and the flow channel structure when designing the nozzle structure and flow channel structure. This limits the function of the actuator, resulting in limited ink droplet flight speed and potential ink interruption risks due to insufficient ink supply efficiency during high-frequency inkjet printing. Summary of the Invention

[0005] The technical problem to be solved by this disclosure is to overcome the defects of the prior art, such as the limited flight speed of ink droplets and the ink interruption caused by insufficient ink supply efficiency during high-frequency inkjet printing, and to provide a piezoelectric inkjet head and its flow channel structure and inkjet unit.

[0006] This disclosure solves the above-mentioned technical problems through the following technical solution:

[0007] A first aspect of this disclosure provides a flow channel structure in a printhead, the flow channel structure comprising an ink supply end, a choke structure, a vibration cavity, an ink outlet end, and a nozzle structure arranged sequentially.

[0008] The first flow resistance of the pass structure is in a first ratio to the total flow resistance of the flow channel structure;

[0009] The second flow resistance of the nozzle structure is in a second ratio to the total flow resistance;

[0010] Wherein, the first ratio is less than the second ratio.

[0011] Optionally, the first flow resistance and / or the second flow resistance are determined based on ink inertia, ink compressibility, and inkjet efficiency.

[0012] Optionally, the first flow resistance and / or the second flow resistance are determined based on the simulation results of the ink inertia and ink compressibility under different flow resistances using a preset simulation model.

[0013] Optionally, the first ratio can be in the range of 15% to 35%.

[0014] Optionally, the second ratio can be in the range of 50% to 70%.

[0015] Optionally, the cross-section of the pass structure is rectangular;

[0016] The lengths of the long and short sides of the rectangle are determined based on the first flow resistance;

[0017] And / or,

[0018] The cross-section of the nozzle structure is circular;

[0019] The diameter of the circle is determined based on the second flow resistance.

[0020] Optionally, the length of the shorter side of the rectangle ranges from 19 to 25 μm (micrometers).

[0021] And / or,

[0022] The diameter of the circle is in the range of 20~25μm.

[0023] Optionally, the shorter side of the rectangle has a length of 22 μm;

[0024] And / or,

[0025] The diameter of the circle is 24 μm.

[0026] A second aspect of this disclosure provides a microelectromechanical system (MEMS) device, the MEMS device including the flow channel structure described in the first aspect of this disclosure.

[0027] A third aspect of this disclosure provides an inkjet unit that includes the microelectromechanical system (MEMS) device described in the second aspect of this disclosure.

[0028] A fourth aspect of this disclosure provides a piezoelectric inkjet head, the piezoelectric inkjet head including the inkjet unit described in the third aspect of this disclosure.

[0029] Based on common knowledge in the field, the above optional conditions can be combined arbitrarily to obtain the optional examples of this disclosure.

[0030] The positive and progressive effects of this disclosure are as follows: by setting a gutter structure with a first flow resistance and a nozzle structure with a second flow resistance, the first flow resistance of the gutter structure accounts for a first proportion of the total flow resistance of the flow channel structure, which is less than the second proportion of the second flow resistance of the nozzle structure to the total flow resistance. This ensures effective droplet formation while avoiding backflow of air that could cause printhead failure, and also ensures the highest flight speed of the droplets in the same volume. This effectively improves the inkjet efficiency of piezoelectric inkjet printing and avoids ink interruption due to insufficient ink supply efficiency during high-frequency inkjet printing. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the flow channel structure in the nozzle of this disclosure;

[0032] Figure 2 This is a schematic diagram of the flow channel structure chip connection in the nozzle of this disclosure;

[0033] Figure 3 This is a graph showing the relationship between the gate structure dimensions, nozzle diameter, and inkjet efficiency of this disclosure.

[0034] Figure 4 This is a graph showing the relationship between the gate structure dimensions, nozzle diameter, and nominal inkjet velocity of this disclosure.

[0035] Figure 5 This is the equivalent circuit diagram of the current resistance of this disclosure;

[0036] Figure 6 This is a flowchart illustrating an example of the flow channel structure design in the nozzle of this disclosure. Detailed Implementation

[0037] The present disclosure is further illustrated below by way of embodiments, but the present disclosure is not limited to the scope of the embodiments described herein.

[0038] The prefixes such as "first" and "second" used in this disclosure are merely for distinguishing different descriptive objects and do not limit the position, order, priority, quantity, or content of the described objects. The use of ordinal numbers and other prefixes used to distinguish descriptive objects in this disclosure does not constitute a limitation on the described objects. The description of the described objects is given in the context of the embodiments, and the use of such prefixes should not constitute unnecessary restrictions. Furthermore, in the description of this embodiment, unless otherwise stated, "multiple" means two or more.

[0039] Example 1

[0040] In one specific embodiment, a flow channel structure in a nozzle is provided, such as Figure 1 As shown, the flow channel structure includes an ink supply end, a choke structure, a vibration cavity, an ink outlet end, and a nozzle structure arranged in sequence.

[0041] The first flow resistance of the narrow passage structure is in the first proportion to the total flow resistance of the flow channel structure;

[0042] The second flow resistance of the nozzle structure is proportional to the total flow resistance.

[0043] The first proportion is smaller than the second proportion.

[0044] Specifically, the flow channel structure consists of an ink supply end, a choke structure, a vibrating cavity, an ink outlet end, and a nozzle structure arranged sequentially, as well as necessary connecting structures (e.g., nozzle flow channels) connecting the above components. When the vibrating cavity is under negative pressure, the liquid (e.g., ink) in the ink supply end of the flow channel enters the vibrating cavity through the choke structure. When the vibrating cavity is under positive pressure, the liquid in the vibrating cavity is pushed out at high speed from the nozzle structure through the ink outlet end of the flow channel, forming tiny droplets to complete the jetting action.

[0045] like Figure 2 As shown, the flow channel structure consists of three interconnected chips. The slot at the bottom of the flow channel structure chip will be closed in the subsequent packaging step. The ink enters through the slot at the top of the flow channel structure chip, flows into the actuator flow channel through the slot at the bottom of the ink storage cavity, and flows through key components such as the obstruction structure and the vibration cavity in the actuator flow channel. The ink then enters the flow channel structure chip again and finally enters the nozzle structure in the nozzle flow channel chip. During subsequent piezoelectric actuation, the ink forms droplets and is ejected.

[0046] Inkjet efficiency is defined as the ratio of the droplet volume extending from the nozzle to the deformation volume of the vibrating cavity during piezoelectric actuation. Simulation calculations show that to effectively form ink droplets while avoiding backflow of air that could cause printhead failure, the inkjet efficiency η must satisfy: 20% ≤ η ≤ 40%. When the inkjet efficiency is below this range, the droplet volume is too small and the momentum is insufficient to form droplets effectively; when the inkjet efficiency is above this range, the speed at which the ink fills the vibrating cavity will be insufficient to meet the requirements of high-frequency inkjet printing.

[0047] Therefore, when designing the flow channel structure, the first flow resistance of the obstruction structure is set to the first proportion of the total flow resistance of the flow channel structure, and the second flow resistance of the nozzle structure is set to the second proportion of the total flow resistance. The first proportion should be less than the second proportion, so that the inkjet efficiency η is within the range of 20% to 40%. This ensures that while effectively forming ink droplets, backflow of air is avoided, which could lead to printhead failure. At the same time, it ensures the highest flight speed of ink droplets of the same volume, thereby improving the inkjet efficiency of piezoelectric inkjet and avoiding ink interruption due to insufficient ink supply efficiency during high-frequency inkjet printing.

[0048] For example, the first flow resistance of the nozzle structure accounts for 15% to 35% of the total flow resistance of the flow channel structure, while the second flow resistance of the nozzle structure accounts for 50% to 70% of the total flow resistance of the flow channel structure. Components such as the ink supply end, vibrating cavity, and ink outlet end can be designed and adjusted to have sufficiently low flow resistance, thus avoiding a significant impact on inkjet performance.

[0049] It should be noted that the dimensions of the components in the flow channel structure are primarily limited by the design resolution of the nozzle structure. For example, when the nozzle resolution is 300 dpi / column (dots per inch / column), the center-to-center distance of the nozzle structure is 84.7 μm. Under this design, the width (or diameter, etc.) of the flow channel structure, nozzle structure, and other related designs must all be less than 84.7 μm. When width design is limited (micrometer-level dimensional design), the first and second flow resistances can be adjusted by changing parameters such as the thickness and length of the obstruction structure and the nozzle structure.

[0050] This specific implementation effectively improves the droplet flight speed and optimizes the overall inkjet efficiency by designing parameters for the fluid impedance of each flow channel component (including the ink supply end, the choke structure, the vibration cavity, the ink outlet end, the nozzle structure, etc.).

[0051] In one specific implementation, the first flow resistance and / or the second flow resistance are determined based on ink inertia, ink compressibility, and inkjet efficiency. Specifically, the first flow resistance and / or the second flow resistance are determined based on simulation results of inkjet efficiency under different flow resistances using a preset simulation model.

[0052] Under normal circumstances, ink is incompressible. However, as the size of the flow channel structure decreases, the ink volume becomes small enough and the frequency becomes high enough, and the ink exhibits slight compressibility. Therefore, when designing flow resistance, it is necessary to consider the combined effects of the ink's compressibility, the ink's inertia, and the inkjet efficiency.

[0053] Based on fluid mechanics principles, the relationship between the aperture structure size, nozzle diameter, and inkjet efficiency can be obtained, such as... Figure 3 As shown, the smaller the size of the nozzle structure and the larger the nozzle diameter, the higher the inkjet efficiency. However, when the nozzle diameter is small, the total amount of liquid moving towards the nozzle is small due to the greater flow resistance. While when the nozzle diameter is large, although more liquid moves towards the nozzle, the excessively large diameter leads to a shorter vibration distance, resulting in a lower nominal velocity (in meters per second) of ink ejected through the nozzle. Figure 4 As shown, there exists a maximum velocity extremum at different speeds.

[0054] To ensure the highest possible droplet velocity within a given volume and to effectively improve the inkjet efficiency of piezoelectric inkjet printing, this specific embodiment constructs a flow resistance equivalent circuit diagram based on the compressibility, inertia, and flow resistance of the ink, as follows: Figure 5 As shown, L i R represents the ink inertia of the i-th flow channel component. i C represents the flow resistance of the i-th flow channel component. i The ink compressibility of the i-th flow channel component is represented by a preset simulation model combined with an equivalent circuit diagram to simulate inkjet efficiency and droplet flight speed. This yields a first proportional range of the first flow resistance to the total flow resistance and a second proportional range of the second flow resistance to the total flow resistance, thus balancing ink jetting efficiency and jetting speed. Preferably, the first proportional range is 15% to 35%, and the second proportional range is 50% to 70%.

[0055] In the equivalent circuit diagram, ink compressibility, ink inertia, flow resistance, and other elements can be added to or adjusted according to the specific characteristics of the printhead product.

[0056] In one specific implementation, the cross-section of the pass structure is rectangular;

[0057] The lengths of the long and short sides of the rectangle are determined based on the first flow resistance.

[0058] Specifically, when the cross-section of the pass structure is rectangular, its fluid resistance is proportional to... Where 'a' represents the length of the longer side of the rectangle, and 'b' represents the length of the shorter side. Since the narrow passage is a slit-like structure, 'a' is much larger than 'b'. Therefore, the resistance to fluid flow is primarily constrained by the shorter side length 'b'. The value of the shorter side length 'b' ranges from 19 μm to 25 μm.

[0059] In one specific embodiment, the cross-section of the nozzle structure is circular;

[0060] The diameter of the circle is determined based on the second flow resistance.

[0061] Specifically, when the cross-section of the nozzle structure is circular, its fluid resistance is proportional to... Where r represents the radius of the nozzle. The fluid flow resistance of the nozzle structure is affected by the nozzle radius. The larger the nozzle radius / diameter ratio, the larger the effective flow size of the nozzle structure and the smaller the resistance; conversely, the smaller the nozzle radius / diameter ratio, the smaller the effective flow size of the nozzle structure and the greater the resistance. The diameter of the circle ranges from 20μm to 25μm.

[0062] In a preferred embodiment, when the short side length of the rectangle is b=22μm and the diameter of the circle is d=2r=24μm, the width of the slit structure and the diameter of the nozzle structure reach the optimal matching ratio. When this ratio is met, the droplet can achieve the highest flight speed for the same droplet volume.

[0063] In a specific example, such as Figure 6 As shown, after confirming key parameters such as printing technology, resolution, droplet size, number and arrangement of nozzles, drive frequency, and compatible ink types, as well as the preliminary design of the actuator structure, the fluid system is designed by allocating the proportions of each fluid element. Under the constraints of the proportions of each fluid element, the nozzle fluid elements are confirmed for nozzle structure design, and the choke fluid elements are confirmed for choke structure design. Finally, other structures are filled to ensure that the flow resistance of other structures is much smaller than the first flow resistance of the choke structure and the second flow resistance of the nozzle structure, so as to avoid significant impact on inkjet performance.

[0064] After completing the design and adjustment of the fluid system, the actual inkjet performance can be calculated based on the designed performance of the inkjet actuator chip, using a preset simulation model combined with the fluid flow. It should be noted that the droplet velocity satisfies v t =V / (S*t)+v0, where v t Let v0 represent the final velocity of the fluid, v0 represent the initial velocity of the fluid, V represent the volume of the fluid, S represent the cross-sectional area of ​​the flow channel structure, and t represent time. Under the premise that the actuator performance remains unchanged, determine the maximum velocity extreme value of the droplet.

[0065] This embodiment sets up a gutter structure with a first flow resistance and a nozzle structure with a second flow resistance, such that the first flow resistance of the gutter structure accounts for a first proportion of the total flow resistance of the flow channel structure, which is less than the second proportion of the second flow resistance of the nozzle structure to the total flow resistance. This ensures effective droplet formation while avoiding backflow of air that could cause printhead failure, and also ensures the highest flight speed of the droplets in the same volume. This effectively improves the inkjet efficiency of piezoelectric inkjet printing and avoids ink interruption due to insufficient ink supply efficiency during high-frequency inkjet printing.

[0066] Example 2

[0067] In one specific embodiment, a microelectromechanical system (MEMS) device is provided, which includes the flow channel structure in Embodiment 1.

[0068] Specifically, MEMS devices achieve miniaturization and integration of flow channels through microfabrication processes, and endow the flow channels with core functions such as sensing, driving, and control. The flow channel structure serves as the physical channel for fluid transmission in the MEMS system, ensuring that the MEMS device can achieve complex functions such as sensing, driving, separation, and reaction.

[0069] This embodiment sets up a gutter structure with a first flow resistance and a nozzle structure with a second flow resistance, such that the first flow resistance of the gutter structure accounts for a first proportion of the total flow resistance of the flow channel structure, which is less than the second proportion of the second flow resistance of the nozzle structure to the total flow resistance. This ensures effective droplet formation while avoiding backflow of air that could cause printhead failure, and also ensures the highest flight speed of the droplets in the same volume. This effectively improves the inkjet efficiency of piezoelectric inkjet printing and avoids ink interruption due to insufficient ink supply efficiency during high-frequency inkjet printing.

[0070] Example 3

[0071] In one specific embodiment, an inkjet unit is provided, which includes the microelectromechanical system device of embodiment 2.

[0072] Specifically, by embedding MEMS devices into the inkjet unit, the inkjet unit can achieve intelligent control requirements such as precise sensing, rapid control, and miniaturized integration through micron-level functional structures.

[0073] This embodiment sets up a gutter structure with a first flow resistance and a nozzle structure with a second flow resistance, such that the first flow resistance of the gutter structure accounts for a first proportion of the total flow resistance of the flow channel structure, which is less than the second proportion of the second flow resistance of the nozzle structure to the total flow resistance. This ensures effective droplet formation while avoiding backflow of air that could cause printhead failure, and also ensures the highest flight speed of the droplets in the same volume. This effectively improves the inkjet efficiency of piezoelectric inkjet printing and avoids ink interruption due to insufficient ink supply efficiency during high-frequency inkjet printing.

[0074] Example 4

[0075] In one specific embodiment, a piezoelectric inkjet head is provided, which includes the inkjet unit in embodiment 3.

[0076] Specifically, the piezoelectric inkjet head integrates an inkjet unit, which can eject ink droplets at high speed from a single nozzle. The voltage can be adjusted to control the size of the ink droplets, ensuring high-quality printing from the piezoelectric inkjet head.

[0077] This embodiment sets up a gutter structure with a first flow resistance and a nozzle structure with a second flow resistance, such that the first flow resistance of the gutter structure accounts for a first proportion of the total flow resistance of the flow channel structure, which is less than the second proportion of the second flow resistance of the nozzle structure to the total flow resistance. This ensures effective droplet formation while avoiding backflow of air that could cause printhead failure, and also ensures the highest flight speed of the droplets in the same volume. This effectively improves the inkjet efficiency of piezoelectric inkjet printing and avoids ink interruption due to insufficient ink supply efficiency during high-frequency inkjet printing.

[0078] While specific embodiments of this disclosure have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of this disclosure is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of this disclosure, but all such changes and modifications fall within the scope of protection of this disclosure.

Claims

1. A flow channel structure in a nozzle, characterized in that, The flow channel structure includes an ink supply end, a choke structure, a vibration cavity, an ink outlet end, and a nozzle structure arranged in sequence. The first flow resistance of the pass structure is in a first ratio to the total flow resistance of the flow channel structure; The second flow resistance of the nozzle structure is in a second ratio to the total flow resistance; Wherein, the first ratio is less than the second ratio, so that the inkjet efficiency is in the range of 20% to 40%, and the inkjet efficiency is the ratio of the droplet volume extending out of the nozzle to the deformation volume of the vibration cavity when piezoelectrically driven. The first flow resistance and the second flow resistance are determined based on ink inertia, ink compressibility, and the inkjet efficiency; The first flow resistance and the second flow resistance are determined based on the simulation results of the ink inertia and ink compressibility under different flow resistances using a preset simulation model.

2. The flow channel structure according to claim 1, characterized in that, The first ratio ranges from 15% to 35%.

3. The flow channel structure according to claim 1, characterized in that, The second ratio ranges from 50% to 70%.

4. The flow channel structure according to claim 1, characterized in that, The cross-section of the pass structure is rectangular; The lengths of the long and short sides of the rectangle are determined based on the first flow resistance; And / or, The cross-section of the nozzle structure is circular; The diameter of the circle is determined based on the second flow resistance.

5. The flow channel structure according to claim 4, characterized in that, The length of the shorter side of the rectangle ranges from 19μm to 25μm; And / or, The diameter of the circle is in the range of 20μm to 25μm.

6. The flow channel structure according to claim 5, characterized in that, The shorter side of the rectangle is 22 μm. And / or, The diameter of the circle is 24 μm.

7. A microelectromechanical system (MEMS) device, characterized in that, The microelectromechanical system device includes the flow channel structure as described in any one of claims 1 to 6.

8. An inkjet unit, characterized in that, The inkjet unit includes the microelectromechanical system device as described in claim 7.

9. A piezoelectric inkjet head, characterized in that, The piezoelectric inkjet head includes the inkjet unit as described in claim 8.

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