Bubble stop object for inkjet printhead

Abstract

The present technology relates to the field of inkjet printing. The present technology provides a printhead comprising: a filter (12) arranged between an ink reservoir (10) and a standpipe (11), the filter (12) configured to filter out unwanted matter before ink (25) from the ink reservoir (10) enters the standpipe (11); and the standpipe (11) configured to receive ink (25) from the ink reservoir (10) that passes through the filter (12), wherein the standpipe (11) comprises an object (28, 29) arranged therein, the object configured to hinder bubble growth by directing the flow of received ink (25) incident on the object (28, 29) through one or more channels in the object (28, 29).

Description

Technical Field

[0001] This invention relates to the field of inkjet printhead technology, and more specifically to thermal inkjet printheads. Background Technology

[0002] Inkjet printers use thermal inkjet printheads to print ink based on the electrical activation of the printhead. When the printhead is electrically activated, the ink layer is vaporized into high-pressure bubbles. These high-pressure bubbles continue to expand, and this continuous expansion causes rapid movement of the surrounding ink. This results in the subsequent ejection of ink droplets from the nozzles of the printhead.

[0003] A challenge associated with conventional inkjet printheads is that external atmospheric gases such as nitrogen and oxygen tend to enter certain permeable sections of the printhead body and dissolve into the ink. Once the ink is ejected, only a portion of the dissolved gases can be released, but some may not be completely expelled from the printhead. Therefore, the remaining dissolved gases in the printhead can form bubbles that can partially or completely block the ink flow. This also leads to printhead clogging, which can eventually stop printing even before the printhead reaches the end of its natural lifespan.

[0004] Therefore, it is necessary to overcome the above challenges and propose a solution to prevent printhead clogging. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention provides a printhead comprising an object for reducing or preventing printhead clogging. According to the embodiments presented herein, the object may be an insert for reducing or preventing clogging in the printhead by inhibiting bubble formation or growth, as will be described in more detail later.

[0006] Specifically, the present invention provides a printhead comprising: a filter disposed between an ink reservoir and a standpipe, the filter being configured to filter out unwanted material before ink from the ink reservoir enters the standpipe; and the standpipe being configured to receive ink from the ink reservoir passing through the filter. Furthermore, the standpipe includes an object disposed therein, the object being configured to impede bubble growth to facilitate the flow of received incident ink across one or more channels in the object. Herein, “unwanted material” may include debris and particles and / or bubbles generated during manufacturing. Herein, “bubble growth” may refer to the growth of bubbles themselves by means of rectified diffusion, combining with more extracted gas, and / or the merging of multiple bubbles within the standpipe 11 to form larger bubbles.

[0007] Preferably, the filter corresponds to a mesh filter.

[0008] Preferably, the object is deformable.

[0009] Preferably, the object comprises a mesh structure. In an embodiment, the mesh structure has a cylindrical or conical shape. The mesh structure is formed from rolled-up polygonal mesh sheets that are partially pinched at one end. Additionally, the mesh structure is made of stainless steel. In an embodiment, the mesh size of the mesh structure is larger than the mesh size of the filter. One or more channels comprise one or more meshes within the object. These one or more channels may additionally or alternatively comprise one or more spaces between adjacent loops within the object.

[0010] Preferably, the object comprises a porous structure having a parallelepiped shape. In an embodiment, the porous structure comprises a porous foam material.

[0011] Preferably, the vertical tube is attached to an aperture configured to receive ink that has flowed through the object, and further configured to facilitate the flow of the received ink toward a microfluidic device externally attached to the printhead.

[0012] Preferably, the microfluidic device includes one or more ejection nozzles to eject one or more ink droplets when the microfluidic device is electrically activated by one or more electrical contact pads.

[0013] According to an embodiment of the invention, ink incident on an object flows through one or more channels within the object, and any air bubbles present in the riser are captured by the object and retained in place, thereby hindering air bubble growth within the riser. Therefore, the embodiment presented herein reduces the likelihood of premature ink clogging in the riser during the natural lifespan of the printhead. Attached Figure Description

[0014] Non-limiting and non-exhaustive embodiments of the present invention are described below by way of example with reference to the accompanying drawings, wherein:

[0015] Figure 1 A three-dimensional schematic diagram of a printhead of an inkjet printer known in the art is shown.

[0016] Figure 2 A cross-sectional view of a microfluidic device attached to a printhead, known in the art, is shown.

[0017] Figure 3 a) shows an exploded view of the printhead according to an embodiment.

[0018] Figure 3 b) shows an exploded cross-sectional view of the printhead according to an embodiment.

[0019] Figure 4 A cross-sectional view of a silicon chip included in a printhead according to an embodiment is shown.

[0020] Figure 5 a) shows a schematic diagram of a vertical tube including a bubble according to an embodiment.

[0021] Figure 5 b) shows a schematic diagram of a vertical tube containing a large bubble.

[0022] Figure 6 a) shows a mesh sheet according to an embodiment.

[0023] Figure 6 b) shows an object made of mesh sheets according to an embodiment, which can be arranged in a printhead to prevent clogging in the printhead.

[0024] Figure 7 A printhead including an object is shown according to an embodiment.

[0025] Figure 8 An open-cell foam according to an embodiment is shown.

[0026] Figure 9 A porous object according to an embodiment is shown, which can be arranged in a printhead to prevent clogging in the printhead. Detailed Implementation

[0027] To make the above and other features and advantages of the present invention clearer, the present invention will be further described below with reference to the accompanying drawings. It should be understood that the specific embodiments of the present invention are illustrative and not intended to be limiting.

[0028] Figure 1 A perspective view of the printhead 1 of an inkjet printer (not shown) known in the art is shown. Figure 1 As shown, the printhead 1 may include a body 4 to isolate the internal components of the printhead 1 from external factors such as shock, vibration, and environmental contaminants. In one example, the body 4 may be made of plastic or any other suitable material that adequately protects the body 4 from external factors. Furthermore, the microfluidic device 2 is externally attached to the body 4 via a suitable adhesive (e.g., but not limited to, sealant or other adhesives known in the art). The sealant can provide mechanical strength and a seal to the joint between the microfluidic device 2 and the body 4 of the printhead 1. Here, the microfluidic device 2 may be connected to an ink reservoir included in the printhead 1. Figure 1 (Not shown in the image) Fluid connection. In one example, the microfluidic device 2 can therefore be connected to the ink reservoir via a riser and a mesh filter as described below.

[0029] In one embodiment, the microfluidic device 2 can be configured to be electrically activated via one or more electrical contact pads 3 attached to the body 4. Figure 2 This aspect is described in more detail in the context of the passage.

[0030] Figure 2 A cross-sectional view of the microfluidic device 2 attached to the printhead 1 is shown. (As shown) Figure 2 As shown, the microfluidic device 2 may include a plurality of resistors 5. Each of the plurality of resistors 5 corresponds to a plurality of ejection chambers 6 that may be included in the fluid circuit 7. Furthermore, a nozzle plate 8 may be mounted on top of the microfluidic device 2. The nozzle plate 8 may include one or more ejection nozzles 9 for each of the plurality of ejection chambers 6. The ejection nozzles 9 may facilitate the ejection of ink from the printhead 1, as described later.

[0031] In this embodiment, a burst current pulse can be applied on demand via resistor 5, which is contained within a generally thin film. This electrical activation can cause rapid vaporization of a thin layer of ink available below the ejection chamber 6. In this embodiment, the burst current pulse through resistor 5 can cause a rapid increase in temperature within resistor 5 due to the Joule effect, as is known in the art. Therefore, heat flow can occur from resistor 5 to ink, through the thin dielectric layer of the film between resistor 5 and ink. In this embodiment, resistor 5 must be electrically insulated from the ink. Therefore, resistor 5 is covered by a thin dielectric layer, thin enough to allow a perceptible heat flow toward the ink to achieve this embodiment. In the example, the ink flow suddenly overheats the ink layer closest to resistor 5 (i.e., the ink layer in contact with the thin dielectric film) and turns it into vapor at pressures on the order of tens of bar. The high vapor pressure can also cause the expansion of bubbles, which can pull ink upwards from the ejection nozzle 9, resulting in the ejection of ink droplets through the ejection nozzle 9. Once ink has been ejected, new ink is retrieved from the ink reservoir to refill the ejection nozzle 9.

[0032] Figure 3 a) shows an exploded view of printhead 1 according to an embodiment. Figure 3 As shown in a), the body 4 of the printhead 1 may include a capillary porous member 14. In one embodiment, the capillary porous member 14 may be a porous material to accommodate the ink reservoir of the printhead 1. Figure 3A negative pressure is created within the ink reservoir (b). Precise control of the ink flow through the jet nozzle 9 is essential, as it is one of the fundamental prerequisites for achieving high-quality printing with an inkjet printer. The capillary porous member 14 can aid in this control of the ink flow by acting as a back pressure system, which creates a slight negative pressure within the ink reservoir. This negative pressure extends through the ink to the jet chamber 6. The negative pressure can be generated by the capillary effect of the pore network of the capillary porous member 14. In one example, as is known in the art, the porous material can be an open-cell foam, a fibrous component, or a combination of two or more elements. The negative pressure in the ink reservoir prevents any unintentional leakage of ink. Otherwise, such leakage could occur during the processing of the printhead 1, when the printhead 1 is idle while using ink, or when the ink reservoir is subjected to a sudden acceleration.

[0033] Furthermore, the body 4 of the printhead 1 can be closed at the top by a body cover 15. Additionally, the body 4 may include ink flow orifices 13 at its bottom to facilitate ink flow toward the microfluidic device 2. The body 4 of the printhead 1 also includes a mesh filter 12, which... Figure 3 Described in the context of b).

[0034] Figure 3 b) shows an exploded cross-sectional view of the printhead 1 according to an embodiment. Figure 3 As shown in b), the body cover 15 may be provided with an ink filling hole 16 through which a needle can pass to the capillary porous member 14 to fill the ink reservoir 10 (received in the body 4) with ink. To provide suitable communication with external atmospheric pressure, the body cover 15 may include an additional vent 17, the diameter of which is smaller than the diameter of the ink filling hole 16. The vent 17 may be formed at one end of a shallow, meandering vent channel 18 molded in the surface of the body cover 15.

[0035] Furthermore, the riser 11 may have a mesh filter 12 at its top at the boundary with the ink reservoir 10, and may terminate at the opposite end of the mesh filter 12, which has an ink flow orifice 13. The ink flow orifice 13 allows ink to flow from the ink reservoir 10 toward the microfluidic device 2 externally attached to the riser 11, where ink is supplied to the ejection chamber 6. In one example, the riser may be a tubular structure positioned between the mesh filter 12 and the orifice 13. In this example, the orifice 13 may be located at the end of the riser 11 and may be molded to the riser 11.

[0036] Figure 4A cross-sectional view of a silicon chip 19 included in a microfluidic device 2 according to an embodiment is shown. A layer stack 20 may be disposed on the surface of the silicon chip 19. As known in the art, the layer stack 20 may include suitable conductors, resistors (e.g., resistor 5), and dielectric layers implemented using thin-film technology. A fluid loop 7 is implemented onto the layer stack 20 by a appropriately patterned polymer, which may also be referred to as a barrier layer 21. The barrier layer 21 may be closed on top by a nozzle plate 8, in which an ejection nozzle 9 is implemented. In an embodiment, a bubble 22 can be formed by applying a current pulse transmitted through resistor 5. The expansion of the bubble 22 can cause ink droplets 23 to be ejected from the ejection nozzle 9. Furthermore, a through-slot 24 allows the fluid loop 7 to communicate with the ink reservoir 10 via an ink flow orifice 13 in the body 4. Thus, ink 25 flows from the ink reservoir 10 through the mesh filter 12, the riser 11, the ink flow orifice 13, the through-slot 24, and subsequently to the ejection chamber 6.

[0037] Figure 5 a) shows a schematic diagram of a vertical tube 11 including a bubble 26 according to an embodiment.

[0038] During the vaporization of ink 25, atmospheric gases dissolved in ink 25 may be partially released due to increased temperature, which reduces the solubility of gases in ink 25. Not only gases dissolved in the vaporization layer, but also some gases included in the surrounding ink may be released due to heat transfer during the bubble formation stage. When ink 25 is severely saturated, a large amount of gas may be released during ink heating and vaporization.

[0039] In one example, some of the released gas may be ejected with the ink during printing, but some gas may remain in the printhead 1, the ejection chamber 6, or the riser 11. Since the reabsorption of the released gas from the ink 25 is slower than its desorption, the released gas can remain within the printhead 1 as bubbles 26 for a certain period. If the bubble 26 is substantially small in size, the surface tension can overcome the bubble 26. Therefore, the bubble 26 can contract until the gas is reabsorbed by the ink 25 and the bubble 26 itself disappears. Conversely, if the bubble 26 is large enough, it can maintain its presence within the ink 25 and move through the ink 25 in the riser 11 over time.

[0040] Until the size of bubble 26 allows it to move within the riser 11, there may always be a side channel available for ink to move toward the nozzle without compromising print quality, such as... Figure 5 As shown in a).

[0041] On the other hand, such as Figure 5As shown in b), if the bubble 26 is large enough to block the riser 11, ink 25 may fail to flow from the ink reservoir 10 to the jet nozzle 9. This can cause blockage of the printhead 1, especially in high-density printing where strong ink flow is required. In this case, only a strong pressure differential applied externally between the ink reservoir 10 and the jet chamber 6 can push the bubble away and restore the functionality of the printhead 1. This poses a serious challenge to the reliability of thermal printheads, causing printing to stop even when sufficient ink remains in the ink reservoir 10. This problem occurs even more frequently when the riser 11 is small, such as in color printheads where multiple reservoirs are embedded in the same ink cartridge.

[0042] In the above scenario, the first possible impact of bubble 26 is interference with the normal vaporization of ink 25 during ejection. When bubble 26 is near resistor 5 of printhead 1, it can locally nucleate vapor, preventing the transferred heat energy from spreading uniformly across the ink above. The formation of bubble 22 in ink 25 has proven imperfect, and the ejected ink droplets 23 may lack kinetic energy and directionality. Even if bubble 26 can be expelled during a subsequent printing shot, new gas can be released, leading to interference with printhead function.

[0043] The second effect of the presence of bubble 26 is the growth of bubble 26 itself, which can combine with more gas extracted by the ink through so-called rectified diffusion. Rectified diffusion is a bubble growth phenomenon that occurs in an acoustic field. When subjected to oscillating pressure waves, bubbles of a suitable size undergo expansion and compression. Such oscillating pressure waves are very common in thermal printheads because ink vaporization causes pressure strokes of tens of bar in the surrounding ink. Although the internal pressure of the bubble is lower than atmospheric pressure at its maximum expansion, during this oscillation, the pressure inside the bubble decreases as it expands and increases as it compresses. Therefore, gas diffuses in and out of the bubble due to the pressure difference between the inside and outside of the bubble. Several effects contribute to the uneven diffusion in and out of the bubble, thus increasing the bubble size. In addition, due to fluctuations in ambient pressure and temperature, as well as the slow vaporization of the ink solvent, the bubbles tend to grow spontaneously over long periods.

[0044] Furthermore, multiple bubbles can migrate into the riser 11 and merge together to form larger bubbles 26. This concentration of bubbles is particularly pronounced when the printhead is positioned upright in the printer with the nozzles facing downwards. These bubbles can naturally move upwards into the riser 11 until they strike the mesh filter 12 at the top of the riser 11. Due to the strong capillary pressure exerted by the fine mesh of the mesh filter 12, the mesh filter 12 is difficult for the bubbles 26 to overcome. Therefore, the resulting large bubbles 26 tend to remain in the riser 11 and grow over time.

[0045] Figure 6 A) illustrates a mesh sheet 27 according to an embodiment. In one example, the mesh sheet 27 may be made of stainless steel or any other suitable deformable material. In one example, the mesh sheet 27 may have a polygonal shape or any other suitable shape that can be rolled up to form a cylindrical or conical mesh structure. In an embodiment, the polygonal mesh sheet 27 may be rolled up to form a mesh structure and partially clamped at one end to form an object 28 as an insert arranged in the printhead 1 to reduce or prevent clogging in the printhead. Figure 6 This aspect is described in more detail in the context of b).

[0046] Figure 6 b) shows an object 28 that can be arranged in the print head 1 according to an embodiment. In one example, Figure 6 The mesh sheet 27 shown in a) can be rolled up to form a cylindrical or conical mesh structure. In one example, according to an embodiment, the mesh structure can be partially clamped or compressed at one end to form an object 28 with a permanent shape.

[0047] In one example, object 28 may be made of stainless steel and may have a certain degree of elasticity. However, if object 28 is rolled, it may retain its permanent deformation, which can be made more stable by clamping object 28 at one end. For example, if object 28 is clamped at one end, the shape of object 28 may become “conical” rather than cylindrical. As is known in the art, object 28 may be clamped and / or rolled by suitable industrial equipment.

[0048] Figure 7 An object 28 is shown that can be arranged in the riser 11 of the printhead 1 in such a way that the object 28 provides multiple channels (e.g., mesh apertures) through which ink 25 incident on the object 28 can flow, such that the presence of the object 28 hinders the growth of bubbles within the riser 11 or otherwise prevents any trapped bubbles from increasing in size or merging into larger bubbles. This may mean that ink 25 can pass through one or more channels in the object 28 due to the mesh structure of the object 28. In embodiments, the object 28 can provide multiple channels for the flow of ink through the object 28. For example, one example of such channels may include flow paths created by one or more meshes in the mesh structure of the object 28. Furthermore, one or more narrow spaces between adjacent loops of the object 28 can be used as second flow paths to provide additional channels for the flow of ink, as the mesh sheets are rolled up.

[0049] Furthermore, the object 28 can be sealed at the top by the mesh filter 12 attached to the body 4 of the printhead 1. Therefore, the embodiment presented herein reduces or prevents obstruction to the ink flow because the presence of the object 28 hinders bubble growth. In one example, the object 28 can be inserted into the riser 11 at an angle, as shown in the figure. In this example, the object 28 can be in physical contact with the mesh filter 12. However, in another example, the object 28 can be inserted into the riser 11 such that the object 28 is not in physical contact with the mesh filter 12.

[0050] In this embodiment, object 28 may have a larger mesh size compared to the mesh size of mesh filter 12. Therefore, even in the presence of large air bubbles in riser 11, ink can find suitable channels on object 28 or between object 28 and the inner wall of riser. This ensures normal flow of ink 25 even when riser 11 is occupied by air bubbles. According to the embodiment presented herein, the object has a mesh structure. The mesh structure of object 28 and its wrapped surfaces can create spaces with high energy thresholds for air bubbles to penetrate and pass through object 28. Therefore, the embodiment presented herein ensures that one or more channels are always present within or on one side of object 28 for ink flow, providing a continuous ink flow.

[0051] Figure 8 An open-cell foam 29 according to an embodiment is shown. In one example, the open-cell foam 29 may be a parallelepiped-shaped structure with a plurality of pores to allow liquid (e.g., ink) to flow through the permeability of the pores.

[0052] Figure 9 A porous material 29, according to an embodiment, can be arranged in the riser 11 of the printhead 1 to reduce or prevent clogging. In one example, the porous material 29 can be an open-cell foam 29 or a fiber-based material with a porous structure. Therefore, the porous material 29 can create multiple interconnected spaces with a generally high energy threshold for bubble penetration, thus hindering bubble growth and facilitating the establishment of ink channels from the ink reservoir 10 to the ejection nozzle 9. Figure 9 As shown, the deformable porous object 29 can be easily inserted into the riser 11 to maintain a continuous ink flow. In another example, instead of open-cell foam, object 29 may comprise stainless steel “steel wool” to achieve a similar function as described above.

[0053] According to the embodiments presented herein, objects 28 and 29 maintain a continuous flow of ink incident on them when inserted into the riser tube 11. Channels (mesh apertures or holes) provided in objects 28 and 29 ensure a continuous ink flow by hindering the growth of air bubbles within the riser tube 11, thus reducing or preventing ink clogging in the riser tube 11. Therefore, the embodiments presented herein enable the printhead 1 to operate throughout its natural lifespan by reducing the likelihood of or preventing early clogging. Furthermore, all embodiments can be implemented in production fine-tuning within the manufacturing process and present cost-effective improvements in printhead reliability.

[0054] The various technical features described above can be combined arbitrarily. Although not all possible combinations of the various technical features are described, all combinations of these technical features should be considered within the scope described in this specification, provided that they do not conflict.

[0055] Although the invention has been described in conjunction with embodiments, those skilled in the art should understand that the above description and drawings are illustrative rather than restrictive, and the invention is not limited to the disclosed embodiments. Various modifications and variations are possible without departing from the spirit of the invention.

[0056] Explanation of reference numerals in the attached figures

[0057] 1-Print head

[0058] 2-Microfluidic Devices

[0059] 3-Electrical contact pad

[0060] 4-Printhead body

[0061] 5-Resistors

[0062] 6-Injection Chamber

[0063] 7-Fluid Circuit

[0064] 8-Nozzle Plate

[0065] 9-Injection Nozzle

[0066] 10-Ink Storage

[0067] 11-Vertical pipe

[0068] 12-Grid Filter

[0069] 13-Ink flow hole slit

[0070] 14-Capillary porous components

[0071] 15-Print head body cover

[0072] 16-Ink Filling Hole

[0073] 17-Ventilation hole

[0074] 18- Winding ventilation channels

[0075] 19-Silicon Chip

[0076] 20-layer stack

[0077] 21-Blocking Layer

[0078] 22-bubbles

[0079] 23-Ink Drop

[0080] 24-through groove

[0081] 25-Mo

[0082] 26-Air bubbles in the vertical tube

[0083] 27-Grid Piece

[0084] 28 - An object formed by rolled-up mesh sheets (bubble stop plug-in)

[0085] 29 - Objects formed from porous foam materials (foam stop inserts)

Claims

1. A printhead (1), comprising: A filter (12), arranged between the ink reservoir (10) and the riser (11), is configured to filter out unwanted substances before ink (25) from the ink reservoir (10) enters the riser (11); and The vertical tube (11) is configured to receive ink (25) from the ink reservoir (10) passing through the filter (12). The characteristic feature is that the vertical tube (11) includes objects (28, 29) disposed therein, the objects (28, 29) being configured to impede bubble growth to facilitate the flow of ink (25) received incident on the objects (28, 29) through one or more channels in the objects (28, 29). The object (28) therein comprises a grid structure, and the grid structure has a cylindrical or conical shape.

2. The printhead (1) according to claim 1, wherein, The filter (12) corresponds to the grid filter.

3. The printhead (1) according to claim 1, wherein, The objects (28, 29) are deformable.

4. The printhead (1) according to claim 1, wherein, The grid structure is formed by a rolled-up polygonal grid sheet (27) that is partially clamped at one end.

5. The printhead (1) according to claim 1, wherein, The grid structure is made of stainless steel.

6. The printhead (1) according to claim 1, wherein, The mesh size of the mesh structure is larger than the mesh size of the filter (12).

7. The printhead (1) according to claim 1, wherein, The vertical tube (11) is attached to the aperture (13), the aperture being configured to receive ink (25) that has flowed through the object (28, 29), and further the aperture (13) being configured to facilitate the flow of the received ink (25) to the microfluidic device (2) externally attached to the printhead (1).

8. The printhead (1) according to claim 7, wherein, The microfluidic device (2) includes one or more jet nozzles (9) for jetting one or more ink droplets (23) when the microfluidic device (2) is electrically activated by one or more electrical contact pads (3).

9. The printhead (1) according to claim 1, wherein, The one or more channels include one or more grids in the object (28).

10. The printhead (1) according to claim 1, wherein, The one or more channels comprise one or more spaces between adjacent rings of the object (28).

11. A vertical tube (11) for a printhead (1), the vertical tube (11) being configured to receive ink (25) passing through a filter (12) arranged between an ink reservoir (10) and the vertical tube (11), and characterized in that Includes objects (28, 29) arranged therein, said objects being configured to impede bubble growth such that an inflow of ink (25) received incident on said objects (28, 29) flows through one or more channels in said objects (28, 29), said objects (28) including a mesh structure having a cylindrical or conical shape.

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