JP2007516879A - Droplet ejection assembly - Google Patents

Abstract

A fluid drop delivery device is disclosed. The device includes a plurality of nozzle openings from which fluid is ejected and a waste control aperture.

Description

  The present invention relates to droplet ejection.

  An ink jet printer is a type of apparatus for depositing droplets on a substrate. Ink jet printers generally include an ink path from an ink supply to a nozzle path. The nozzle path terminates at a nozzle opening through which ink droplets are ejected. Ink droplet ejection is typically controlled by applying pressure to the ink in the ink path with an actuator, which can be, for example, a piezoelectric deflector, a thermal bubble jet generator, or an electrostatic deflection element. A typical print assembly has an array of ink paths with corresponding nozzle openings and associated actuators. Droplet ejection from each nozzle opening can be controlled independently. In an on-demand drop firing print assembly, each actuator is activated to selectively eject drops to specific pixel locations in the image as the print assembly and the substrate to be printed move relative to each other. In high performance print assemblies, the nozzle openings are generally 50 μm or smaller, for example about 25 μm in diameter, separated by a pitch of 100-300 nozzles / inch (3.9-11.8 nozzles / mm); It has a resolution of 100 to 3000 dpi (3.9 to 118.1 dots / mm) or higher and provides droplets with a volume of about 1 to 120 picoliters (pL) or less. The droplet ejection frequency is generally 10 kHz or higher.

U.S. Pat. No. 6,057,037 to Hoisington et al. Describes a printed assembly having a semiconductor structure and a piezoelectric actuator. The structure is made of silicon with an ink chamber defined by etching. The nozzle openings are defined by individual nozzle plates attached to the silicon structure. Piezoelectric actuators have a layer of piezoelectric material that changes shape, ie, bends, in response to an applied voltage. The bending of the piezoelectric layer exerts pressure on the ink in the pump chamber located along the ink path. Piezoelectric inkjet print assemblies are also described in US Pat. Nos. 6,099,028 and 2,5, Hine, US Pat. No. 4, Moynihan, and US Pat. Is hereby incorporated by reference in its entirety.
US Pat. No. 5,265,315 US Pat. No. 4,825,227 US Pat. No. 4,937,598 US Pat. No. 5,659,346 US Pat. No. 5,757,391

  SUMMARY OF THE INVENTION An object of the present invention is to provide a means for enhancing droplet ejection performance in a print head of an ink jet printer.

  In one aspect, the invention features a flow path in which pressure is applied to a liquid therein to eject droplets from the nozzle opening, a piezoelectric actuator for applying pressure to the liquid, and / or one near the nozzle opening. A droplet ejection device with more waste liquid control apertures. The aperture is in communication with a vacuum source.

  In another aspect, the invention features a nozzle opening and at least one waste control aperture, wherein the waste control aperture is in communication with a vacuum, and the droplet ejection frequency is about 10 kHz or higher, about 5 inwg (1 inwg). = 249 Pa) or less, about 5% or less of the liquid ejected in an operating vacuum, is a droplet ejection by a droplet ejection device, which is drawn through the aperture. In this specification, the unit of vacuum pressure is inch water column (inwg).

  In one aspect, the invention features a droplet ejection device that has a nozzle opening and at least one waste control aperture and directs a liquid mass through the nozzle opening in a manner that communicates with the aperture without ejecting the droplet. Liquid injection.

  In one aspect, the invention features a droplet ejection comprising a flow path in which pressure is applied to a liquid therein to eject a droplet from a nozzle opening, a piezoelectric actuator, and one or more liquid control apertures. Device. The liquid control aperture is separated from the nozzle opening by a distance of about 200% or less of the nozzle opening width, and each aperture has an aperture width of about 30% or less than the nozzle opening width.

  Other aspects or embodiments may have the features of the aspects described above and combinations of one or more of the following features. The liquid control aperture is separated from the nozzle opening by a distance of about 200% or less of the nozzle opening width. The liquid control aperture is separated from the nozzle opening by a distance of about 200% to about 1000% or less of the nozzle opening width. The control aperture communicates with a flow path in which pressure is applied to the liquid. Each control aperture has a fluid resistance of about 25 times or more than the fluid resistance of the nozzle opening. The average total flow through the aperture is about 10% or less than the average flow through the nozzle opening. Each aperture has a width of about 30% or less than the nozzle opening width. The nozzle opening width is about 200 μm or less. Each control aperture has a diameter of about 10 μm or less. A non-wetting coating is applied in the vicinity of the nozzle opening. The flow path, nozzle opening and control aperture are defined in a common structure, the structure being a silicon material. The control aperture is isolated from the flow path. The control aperture has a wicking material. The control aperture communicates with the waste container. The droplet ejector has at least three apertures. The method includes drawing about 2% of the ejected liquid at a vacuum of about 2 inwg or lower. The control aperture and the nozzle opening communicate with a common liquid source, and the liquid source and the vacuum are connected by the liquid source. The diameter of the control aperture is about 30% or less of the nozzle opening. The method includes periodically inducing a liquid mass to maintain liquid in the aperture.

  Embodiments can have one or more of the following advantages. Print errors can be reduced by controlling the waste ink liquid that connects the adjacent ejection nozzles, where the waste ink liquid can interfere with ink ejection or fall on the substrate and blur the image. possible. The waste ink liquid can be controlled by directing the waste liquid into a controlled location and using it by using the effects of vacuum, capillary force, gravity and / or surface tension. The waste ink liquid can be returned to the ink supply source and reused, or can be led from the nozzle plate surface to the waste ink liquid container. A feature of the waste liquid control aperture is that it can be accurately formed on the nozzle plate by etching a semiconductor material such as a silicon material.

  The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. All publications and patent documents referred to herein are hereby incorporated by reference in their entirety.

  Further aspects, features and advantages are set forth below. For example, certain aspects have aperture dimensions, characteristics and operating conditions as discussed below.

  Referring to FIG. 1, the ink jet device 10 includes a liquid reservoir 11 containing supply ink 12 and a liquid passage 13 that leads from the liquid reservoir 11 to the pressure chamber 14. An actuator 15, for example a piezoelectric transducer, overlaps the pressure chamber 14. The actuator can be used to apply ink force to eject ink droplets 19 from the nozzle 17 toward the substrate 20 through the liquid passage 16 leading from the pressure chamber 14 to the nozzle openings 17 of the nozzle plate 18. In operation, the inkjet device 10 and the substrate 20 can be moved relative to each other. For example, the substrate can be a continuous web that is moved between rolls 22 and 23. The desired image is produced on the substrate 20 by selective ejection of droplets from the array of nozzles 17 on the nozzle plate 18.

  The ink jet device also controls the operating pressure at the ink meniscus near the nozzle opening when the system is not ejecting droplets. In the illustrated embodiment, pressure control is provided by a vacuum source 30 such as a mechanical pump that provides a vacuum to the headspace 9 above the ink 12 in the reservoir 11. The vacuum is transmitted to the nozzle opening 17 through the ink to prevent ink from dripping through the nozzle opening 17 due to gravity. A controller 31, for example a computer controller, monitors the vacuum above the ink in the reservoir 11 and controls the vacuum source 30 to maintain the reservoir at the desired vacuum. In another embodiment, the vacuum source is provided by placing an ink reservoir below the nozzle opening to create a vacuum near the nozzle opening. An ink level monitor (not shown) detects ink levels that drop as the ink is consumed during the printing operation, thus increasing the vacuum at the nozzles. The controller monitors the ink level and refills the reservoir from the bulk container to maintain the vacuum within the desired operating range when the ink drops below the desired level. In another embodiment, where the meniscus vacuum is sufficiently spaced to overcome the capillary action of the nozzle and a reservoir is located below the nozzle, pressure is applied to the ink to maintain the meniscus near the nozzle opening. Can do. Variations in the meniscus can cause variations in droplet velocity and can cause air ejection or dripping. In embodiments, the operating vacuum maintained at the meniscus is about 0.5 to about 10 inwg, such as about 2 to about 6 inwg.

Referring to FIGS. 2 and 3, a nozzle 17 having a nozzle width W _N is surrounded by waste ink control apertures 32 having an aperture width W _A. The aperture generally surrounds the nozzle and is spaced a distance S from the periphery of the nozzle. With particular reference to FIG. 3, the aperture communicates with the ink fluid path through the lumen 34 and opening 36 upstream of the nozzle opening. During ink ejection, ink can accumulate on the nozzle plate. Over time, the ink can form liquid masses that cause print errors. For example, liquid mass near the periphery of the nozzle opening can affect the trajectory, velocity or volume of the ejected droplet. Also, the liquid mass could be large enough to drop on the printed substrate to produce a meaningless mark. The liquid mass may protrude far enough from the nozzle plate surface to contact the printed substrate and cause the printed substrate to become soiled. The aperture 32 provides an area where waste ink liquid can be collected to avoid the formation of excessive liquid mass. The ink can be drawn into the aperture 32 by a capillary force and / or a vacuum created by the piezoelectric actuator 15 and / or the vacuum source 30.

  Referring to FIGS. 3C, the operation of the ink control aperture during droplet ejection is shown. With particular reference to FIG. 3, there is shown a non-ejection nozzle 17 in which an ink meniscus 24 is formed on the nozzle 17. With particular reference to FIGS. 3A and 3B, in operation, ink is directed out of the nozzle openings 17 and droplets 19 are formed and ejected. With particular reference to FIG. 3A, the ink can also extend from the aperture 32 but is not ejected from the aperture. With particular reference to 3B, waste ink liquid 38 may accumulate on the nozzle plate 18 during the ejection process. For example, the waste ink liquid can be deposited on the nozzle plate as droplets separated from the ink or splash back in flight, or satellite droplets can return to the nozzle plate. Referring to FIG. 3C, the meniscus 24 is pulled back by vacuum after droplet ejection, ie in preparation for the next droplet ejection. The vacuum is from a pressurized state where the actuator applies pressure to the vacuum source 30 and / or the ink 12 in the chamber 14 to eject a droplet, or a neutral or negative pressure state in preparation for the next droplet ejection. Can be generated by the piezoelectric actuator when it is shifted to. The vacuum applied to the nozzle 17 is also transmitted to the ink control opening 32, so that the waste ink liquid is drawn from the opening 32 through the lumen 34 in the direction indicated by the arrow 35. As a result, the waste ink liquid does not accumulate excessively on the nozzle plate. In an embodiment, the region 33 between the nozzle plate, particularly the nozzle opening and the aperture, prevents the ink liquid mass from being stably formed in this region, and promotes the inflow of waste ink liquid into the aperture. A non-wetting coating, for example a polymer such as a fluoropolymer (eg Teflon). The vacuum can also be generated by controlling the vacuum applied to the ink reservoir 11. A relatively wettable nozzle plate surface can be provided between the nozzle and the aperture, and the non-wetting coating can be terminated outside the circle created by the aperture to suppress ink flow beyond the aperture.

  The size, number, spacing, and pattern of the apertures are selected to prevent excessive waste ink pooling. For example, the size and number of apertures may be selected to prevent ink ejection from the apertures, but draw in the desired amount of waste ink liquid without the need for extra jetting force for droplet ejection. it can. In an embodiment, the aperture has a fluid resistance that is sufficiently greater than the nozzle opening to prevent ink ejection from the aperture during droplet ejection. In embodiments, the resistance of each aperture is about 25 times or more than the resistance of the nozzle, for example 100 times or 200 times or more. The total resistance of all apertures is chosen to draw back the desired amount of waste ink without having to significantly increase actuator displacement. The increase in actuator deflection can be estimated by comparing the average flow rate through the aperture to the nozzle flow rate. In embodiments, the average flow through the aperture is about 10% or less of the flow through the nozzle, such as 5% or 2% or less. In an embodiment, the aperture is arranged to draw 5%, 1%, 0.5%, 0.1% or less of the ejected ink.

For example, the fluid resistance of a circular cross-section channel is

Given in.

Here, l _C is the channel length, r _C is the radius, μ is the fluid viscosity, and R _C is the resistance. The average flow rate through the channel is obtained by dividing the average pressure by this resistance. A twelve system, each having a 3 μm aperture, corresponding to 20% of the nozzle width, would have the following characteristics: Since the fluid resistance varies inversely with the fourth power of the diameter, an aperture whose diameter is 20% of the nozzle diameter has a resistance of 625 times the nozzle resistance. The 12 apertures surrounding the nozzle have a total resistance of 52 times the nozzle resistance. The average flow through the aperture will be about 1/52 or 2% of the flow through the nozzle. For piezoelectric actuators, the actuator voltage causing actuator displacement is increased by about 2%. Twelve apertures with a radius of 3 μm with a 30 μm long lumen can draw 10 centipoise (1 centipoise = 10 ⁻¹¹ N · sec / m ² ) of ink 636 pL by a ² inwg vacuum created in the ink reservoir. it can. This corresponds to a jet of 10 pL droplets at 63.6 kHz, where 0.1% of the ink is captured. The vacuum at the aperture can be substantially increased by actuator displacement during the filling phase of the jet, which is created not only by the reservoir vacuum but also by the actuator.

  In the embodiment, the aperture is provided in a pattern surrounding the nozzle opening. The apertures are separated by a distance S such that no liquid accumulates in the area in contact with the nozzle opening where it will affect droplet ejection. In the embodiment, the distance between the aperture and the nozzle periphery is very small. For example, in embodiments, the spacing is about 200% or less of the nozzle width, such as 50% or less, such as 20% or less. In an embodiment, the apertures are spaced apart from the nozzle periphery, eg, 200% to 1000% or even larger of the nozzle diameter. In embodiments, the apertures can be provided at various intervals, including closely spaced apertures and large spaced apertures. In an embodiment, each nozzle is associated with three or more apertures.

  In certain embodiments, the aperture has a width that is about 30% to less than the nozzle width, such as 20% to less or 5% to less. The vacuum applied to the aperture during liquid withdrawal is about 0.5 to 10 inwg or less. The nozzle width is about 200 μm or less, for example, 10 to 50 μm. The ink or other jet liquid has a viscosity of about 1-40 centipoise. A plurality of nozzles are provided in the nozzle plate at a pitch of less than about 25 nozzles / inch (about 0.98 nozzles / mm), for example, 100 to 300 nozzles / inch (about 3.9 to 11.8 / mm). The droplet volume is about 1-70 pL.

  With reference to FIGS. 4-4A, to avoid ink stagnation or ink drying in the control aperture 32, the system may be operated to continuously introduce ink into the control aperture 32 when droplets are not being ejected. it can. Referring to FIG. 4, the actuator 15 is controlled so as to extend the ink liquid mass 27 from the nozzle 17 but not to give sufficient energy for droplet ejection. Referring to FIG. 4A, at the extension point, the liquid mass 27 is drawn back into the nozzle and some of the ink spreads on the surface of the nozzle plate 18. Next, the actuator 15 is operated so as to create a vacuum on the nozzle 17 and the control aperture 32. Ink on the nozzle plate is drawn into the control aperture 32. Circulating the ink periodically or continuously induces a flow for refreshing the ink in the aperture 32.

  Referring to FIGS. 5-5A, the control aperture 40 leads to a vacuum source that is independent of the ink supply. Referring to FIG. 5, the aperture 40 is connected to a channel 42 that leads to a vacuum source, such as a mechanical vacuum device (not shown) that creates a vacuum intermittently or continuously. Referring to FIG. 5A, the vacuum draws waste ink liquid from the nozzle plate (arrow 46). The ink drawn from the nozzle plate can be returned to the ink supply for reuse or directed to a waste container. The aperture can have a non-circular cross section. For example, the aperture can be elliptical with the major axis of the ellipse aligned with the radius of the nozzle opening.

  Referring to FIG. 6, the control aperture 50 has an absorbent material 52 for promoting the flow of the waste ink liquid 38 by wicking or capillary action. The absorbent material 52 can be placed in a channel 54 that leads to a large volume container (not shown) of ink. The material 52 can protrude slightly from the surface of the nozzle plate 18. Suitable wicking materials include polymer foam, such as urethane foam, or other porous materials. The polyurethane precursor material can be pumped into the aperture as a low viscosity liquid that is polymerized in situ within the aperture to form a wicking material.

  The apertures and / or nozzle openings of any of the embodiments described above can be formed by machining, laser ablation or chemical or plasma etching. The aperture can also be formed by molding, for example injection molding. The aperture and nozzle opening can be formed in a common structure or can be formed and combined in separate structures. For example, the nozzle opening can be formed in another component of the ink flow path, such as a structure that defines a pump chamber, and the aperture can be formed in another structure that is combined with the structure that defines the nozzle opening. In another embodiment, the aperture, nozzle opening and pressure chamber are formed in a common structure. The structure may be a metal, carbon, or silicon material, such as an etchable material such as silicon, silicon dioxide, silicon nitride, or other etchable material. The formation of printhead components using an etching method is described in US patent application Ser. No. 10/189947, filed Jul. 3, 2002, and US Patent Application No. 60/90, filed Oct. 10, 2003. This is described in detail in US Pat. No. 5,104,459, the entire contents of which are hereby incorporated by reference.

  The aperture is a protrusion described in US patent application Ser. No. 10 / 479,816, filed Dec. 30, 2003, and US patent application Ser. No. 10 / 7,622, filed Dec. 30, 2003. Can be used in combination with other waste control aspects such as wells described in the literature and / or channels described in US patent application Ser. No. 10 / 789,833, filed Dec. 30, 2003. it can. The entire contents of each of the above specifications are included herein by reference. For example, a series of channels can be provided on the nozzle face near the aperture. The aperture can be provided in the well or channel or in the vicinity of the protrusion. The cleaning structure can be combined with a manual or automatic cleaning and wiping system in which cleaning liquid is applied to the nozzle plate and wiped off. The cleaning structure can collect cleaning liquid and waste, not waste ink liquid after jetting.

  In embodiments, the droplet ejection system can be utilized to eject liquids other than ink. For example, the deposited droplets can be UV curable or other radiation curable materials, or other materials that can be delivered as droplets, such as chemical or biological fluids. For example, the described device could be part of a precision dispensing system. The actuator can be an electromechanical actuator or a thermal actuator. For example, the actuator can be electrostatic.

  Other embodiments are within the scope of the appended claims.

1 is a schematic representation of a droplet ejection assembly. It is a top view of a part of the nozzle plate. FIG. 3 is a sectional view of a nozzle showing droplet ejection. FIG. 3A is a cross-sectional view of a nozzle showing droplet ejection FIG. 3B is a cross-sectional view of a nozzle showing droplet ejection FIG. 3C is a sectional view of the nozzle showing droplet ejection. FIG. 4 is a sectional view of the nozzle. FIG. 4A is a sectional view of the nozzle. FIG. 5 is a sectional view of the nozzle. FIG. 5A is a sectional view of the nozzle. It is sectional drawing of a nozzle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 9 Head space 10 Inkjet apparatus 11 Liquid reservoir 12 Ink 13, 16 Liquid path 14 Pressure chamber 15 Actuator 17 Nozzle 18 Nozzle plate 19 Ink droplet 20 Substrate 22, 23 Roll 30 Vacuum source 31 Controller 32 Waste ink liquid control aperture

Claims (33)

In the droplet ejection device,
A flow path in which pressure is applied to the liquid in order to eject droplets from the nozzle opening,
A piezoelectric actuator for applying pressure to the liquid, and one or more waste control apertures near the nozzle opening;
Have
The aperture is connected to a vacuum source;
A device characterized by that.   The apparatus of claim 1, further comprising a liquid control aperture separated from the nozzle opening by a distance of about 200% or less of the width of the nozzle opening.   The apparatus of claim 1, further comprising a liquid control aperture spaced from the nozzle opening by a distance of about 200% to about 1000% or less of the width of the nozzle opening.   The apparatus of claim 1, wherein the control aperture is in communication with the flow path in which pressure is applied to the liquid.   The apparatus of claim 1, wherein each of said control apertures has a fluid resistance of about 25 times or greater than the fluid resistance of said nozzle opening.   The apparatus of claim 1, wherein the average total flow through the aperture is about 10% or less than the average flow through the nozzle opening.   The apparatus of claim 1, wherein each of the control apertures has a width of about 30% or less than the width of the nozzle opening.   The apparatus of claim 1, wherein the width of the nozzle opening is about 200 µm or less.   The apparatus of claim 1, wherein each of said control apertures has a diameter of about 10 µm or less.   The apparatus of claim 1 having a non-wetting coating in the vicinity of the nozzle opening.   The apparatus of claim 1, wherein the flow path, the nozzle opening, and the control aperture are defined in a common structure.   12. The apparatus of claim 11, wherein the structure is a silicon material.   The apparatus of claim 1, wherein the control aperture is isolated from the flow path.   The apparatus of claim 1, wherein the control aperture comprises a wicking material.   The apparatus of claim 1, wherein the control aperture is in communication with a waste container. In the droplet ejection device,
A flow path in which pressure is applied to the liquid in order to eject droplets from the nozzle opening,
A piezoelectric actuator, and a liquid control aperture separated from the nozzle opening by a distance of about 200% or less of the width of the nozzle opening;
Have
Each of the apertures has an aperture width of about 30% or less than the nozzle opening width;
A device characterized by that.   The apparatus of claim 16, comprising at least three liquid control apertures.   The apparatus of claim 16 having a non-wetting coating in the vicinity of the nozzle opening.   The apparatus of claim 16, wherein the control aperture is isolated from the flow path.   The apparatus of claim 16, wherein the flow path, the nozzle opening and the control aperture are defined in a common structure. In the droplet ejection device,
A flow path in which pressure is applied to the liquid in order to eject droplets from the nozzle opening,
And having one or more liquid control apertures,
The fluid control aperture has a wicking material;
A device characterized by that.   The apparatus of claim 21, wherein the wicking material protrudes from the control aperture. In a method of ejecting liquid,
Providing a droplet ejection device having a nozzle opening and at least one waste liquid control aperture, wherein the waste liquid control aperture is connected to a vacuum;
Injecting liquid at a frequency of about 10 kHz or higher, and about 5 inch water column (1 inch water column = 249 Pa) or lower operating vacuum, about 5% or less of the injected liquid Drawing through the control aperture;
A method comprising the steps of:   24. The method of claim 23, comprising at least three waste control apertures.   24. The method of claim 23, comprising drawing about 2% of the ejected liquid at an operating vacuum of about 2 inches of water or lower.   24. The method of claim 23, wherein the control aperture and the nozzle opening communicate with a common liquid supply, and the liquid supply and the vacuum are connected by the liquid supply.   24. The method of claim 23, wherein the diameter of the control aperture is about 30% or less of the diameter of the nozzle opening.   24. The method of claim 23, wherein the diameter of the nozzle opening is about 200 [mu] m or less. In a method of ejecting liquid,
Providing a droplet ejection device having a nozzle opening and at least one waste liquid control aperture; and guiding the liquid mass through the nozzle aperture in a manner that communicates with the aperture without ejecting a droplet. ,
A method comprising the steps of:   30. The method of claim 29, comprising periodically inducing a liquid mass to maintain liquid in the aperture. Temporarily stopping the induction of the liquid into the liquid mass; and ejecting droplets from the nozzle openings;
30. The method of claim 29, comprising:   30. The method of claim 29, wherein the liquid control aperture is connected to a vacuum.   30. The method of claim 29, wherein the control aperture and the nozzle opening lead to a common liquid supply, and the liquid supply and the vacuum are connected by the liquid supply.

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