JP4936900B2 - Droplet ejection assembly - Google Patents

Abstract

A drop delivery printhead includes a well about a nozzle opening (17) to enhance jetting performance.

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 source to a nozzle path. The nozzle path terminates at a nozzle opening through which ink drops are ejected. Ink drop ejection is generally 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 (3.94-11.81 nozzles / mm); It has a resolution of 100 to 3000 dpi (3.94 to 118.11 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. 6,057,086, such as Hoisington, describes a printed assembly having a semiconductor body and a piezoelectric actuator. The body is made of silicon with an ink chamber defined by etching. The nozzle openings are defined by individual nozzle plates attached to the silicon body. 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 applies pressure to the ink in the pump chamber located along the ink path. Piezoelectric ink-jet print assemblies are also described in US Pat. No. 6,057,028 to Fishbeck, et al., 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, a feature of the present invention is droplet ejection. A printhead is provided having a flow path in which pressure is applied to the liquid in order to eject droplets from the nozzle openings. The nozzle openings are arranged in the well plate. Liquid is supplied to the well from the nozzle opening to form a meniscus. The meniscus defines a liquid depth above the end of the nozzle opening equal to about 1-15% of the nozzle opening width at which the well is filled with liquid.

  In another aspect, the present invention provides a printhead comprising a flow path in which pressure is applied to liquid to eject droplets from nozzle openings. The nozzle opening is disposed in the well. The ratio of the cross-section of the well to the cross-section of the nozzle opening is about 1.4 to about 2.75. In an embodiment, the ratio of the well depth to the cross-section of the nozzle opening is about 0.15 to 0.5.

  In another aspect, the printhead comprises a liquid flow path in which pressure is applied to the liquid to eject droplets from the nozzle openings. The nozzle opening is disposed in the well. The well has a relatively long axis and a short axis.

  Other aspects or embodiments may have features of the above aspects and / or combinations of one or more of the following characteristics. A meniscus is formed by controlling the pressure at the meniscus. The meniscus is formed by lowering the pressure of the liquid. A vacuum is applied at a location upstream of the nozzle opening. The vacuum at the nozzle opening is about 0.5 to about 10 inwg (in this specification, the unit of vacuum pressure is inch water column (inwg) (1 inwg = 249 Pa)).

The ratio of the well width to the nozzle opening width is about 1.4 to about 2.8. The well has a depth of about 0.15 to 0.5 of the nozzle opening. The distance between the well periphery and the nozzle periphery is about 0.2 or more of the nozzle width. The liquid has a surface tension of about 20-45 dynes / cm (1 dynes / cm = 10 ⁻³ N / m). The nozzle opening and the well are defined by a common structure. The nozzle openings and / or wells are for example defined in the silicon material. The nozzle openings and / or wells can also be defined in metal, carbon or plastic.

  Pressure is applied to the liquid by a piezoelectric element. The nozzle opening has a width of about 70 μm or less. The method includes a plurality of nozzle openings, and the pitch of the nozzle openings can be about 25 nozzles / inch (about 0.98 nozzles / mm) or less. The method includes ejecting droplets having a volume of about 1 to about 70 pL.

  Embodiments can have one or more of the following advantages. The operation of the print head is robust and reliable because the residual ink around the nozzle plate surface is controlled to reduce interference with droplet formation and ejection. In high performance printheads where a large array of small nozzles must eject ink precisely to a precise location on the substrate, drop velocity and trajectory linearity are maintained. The well structure controls the residual ink, enabling a head with varying desired jetting characteristics and varying pressure characteristics at the nozzle openings, such as inks with varying viscosity and surface tension characteristics. The well structure itself is robust and does not require moving parts and can be etched into a semiconductor material such as a silicon material.

  Further aspects, features and advantages are set forth below. For example, certain embodiments have well dimensions and characteristics discussed below.

  Like reference symbols in the various drawings indicate like elements.

  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 fluid path 16 leading from the pressure chamber 14 to the nozzle openings 18 of the nozzle plate 18. In operation, the inkjet device 10 and the substrate 20 can move relative to each other. For example, the substrate can be a continuous web that is moved between rolls 22 and 23. By selective ejection of droplets from the array of nozzles 17 on the nozzle plate 18, the desired image is produced on the substrate.

  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. A vacuum is transmitted through the ink to the nozzle opening to prevent ink from dripping through the nozzle opening 17 due to gravity. A controller 32, such as 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 detects ink levels that drop as ink is consumed during a 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 in which the meniscus vacuum is sufficiently separated to overcome the capillary action of the nozzle and the reservoir is located below the nozzle, pressure can be applied to the ink to maintain the meniscus near the nozzle opening. it can. In embodiments, the operating vacuum is maintained at about 0.5 to about 10 inwg.

  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 edge of the nozzle opening can affect the trajectory, velocity or volume of the ejected droplet. The liquid mass could also be large enough to drop onto the printed circuit board 20 and produce a meaningless mark. The liquid mass would protrude far enough from the surface of the nozzle plate 18 to come into contact with the printed substrate 20 and cause contamination on the printed substrate 20.

  Referring also to FIG. 1A, the nozzle plate 18 has an array of closely spaced nozzle openings 17, each nozzle opening 17 being disposed in a well 40. Referring also to FIG. 1B, in the illustrated embodiment, the nozzle opening 17 is defined in the floor 42 of the well 40 and is located in the center of the floor 42. The well floor 42 extends to the well wall 44 which extends outwardly to the nozzle plate surface 46.

Well dimensions, including well width W _W , depth d _W, and spacing S between the well wall and the nozzle opening periphery, are selected to control the residual ink. When the ink 50 is disposed in the well, a meniscus 52 is formed. Meniscus under the condition of operating pressure (arrow 54), in the edge of the nozzle opening has a smaller depth d _m compared to the nozzle width W _N. A predictable meniscus shape provides reliable injection. A shallow meniscus depth results in a jet that does not substantially affect the direction or velocity of the droplet. Further, the spacing S is chosen so as to reduce the possibility that residual ink on the surface 46 of the nozzle plate 18 will affect the formation or ejection of the droplets.

Referring to FIG. 2～2C, well width W _W is increased, the effect of the meniscus when the operating pressure is varied is shown. M _H, respectively M _I and M _L is expressed, a high vacuum pressure, the meniscus in the medium vacuum pressure and low vacuum pressures are shown. The meniscus depth across the nozzle opening decreases as the well width increases. With particular reference to FIG. 2, the meniscus is applied to the entire nozzle opening at any pressure. At high vacuum pressures, the meniscus depth is relatively shallow and a shallow meniscus is generally desirable for jetting. At low vacuum pressures, the meniscus depth increases and a deep meniscus can cause suboptimal injection. In this case, the meniscus depth can be reduced by reducing the well depth. Referring to FIG. 2A, the meniscus is at a selected depth at high and medium vacuum pressures and at a depth that is not optimal at low vacuum pressures. Referring to FIG. 2B, the meniscus is at the desired operating depth at medium vacuum pressure, at a suboptimal depth at low vacuum pressure, and too shallow and less optimal at high vacuum pressure. At high vacuum pressure, no meniscus is formed over the entire nozzle opening. Most of the ink is drawn into the nozzle openings and some residual ink is retained in the wells. Referring to FIG. 2C, no meniscus is formed over the entire nozzle opening at any operating pressure. The liquid collects at the corner between the well floor and the wall and spreads along the periphery of the nozzle opening. This condition is not optimal because the liquid at the periphery of the nozzle opening affects ejection. 2-2C, the radius of curvature R of the meniscus is calculated by 2 * surface tension / pressure. The meniscus liquid has a surface tension of 30 dynes / cm and the operating pressure is 2, 4 and 6 inwg. The dimension is mm.

The spacing S between the well wall and the nozzle periphery gives a distance that reduces the possibility that residual ink on the nozzle plate surface will affect the ejection. In embodiments, the spacing S is about 20% to greater than that of the nozzle width _{W N,} for example 25 to 100%. The well size provides the desired meniscus depth across the nozzle opening. In an embodiment, the well is filled with a liquid having a given surface tension and about 1-15% of the nozzle width over the nozzle open end when the nozzle is within a given operating pressure range. Meniscus depth is provided across the edge of the nozzle opening (the well is filled with liquid when there is sufficient liquid to substantially cover the wall of the well). In an embodiment, the meniscus depth measured at the nozzle edge is about 1-25% of the nozzle opening. In an embodiment, the desired meniscus depth is maintained over a desired operating pressure range. In embodiments, the operating pressure is about −0.5 to −10 inwg, such as −2 to −4 or −6 inwg. In embodiments, the liquid has a surface tension of about 20-40 dynes / cm. The ratio of well width to nozzle width is about 1.4 to about 2.8, for example 1.5 to about 1.7. The well depth is about 0.15 to 0.5 of the nozzle opening width. The well dimensions can also be chosen to accommodate the volume required to hold a certain amount of residual ink. For non-circular nozzle openings and / or wells, eg, asymmetric or irregular geometries, the well and nozzle widths are measured at a minimum. For wells of varying depth, the well depth is measured between the nozzle opening and the nozzle plate. In an embodiment, the nozzle width is about 200 μm or less, such as about 10-30 μm, and the nozzle pitch is about 100 nozzles / inch (about 3.9 nozzles / mm) or less, such as 300 nozzles / inch ( About 11.8 nozzles / mm) and the drop volume is about 1-70 pL. In embodiments, the liquid has a viscosity of about 1 centipoise to about 40 centipoise (1 centipoise = 10 ⁻¹¹ N · sec / m ² ).

Referring to FIG. 3 in one embodiment, the nozzle plate 70 has a circular nozzle opening 72 and an elliptical well 74. Major axis A _L of the ellipse are disposed in a direction (arrow 76) which can be washed or wiped in cleaning operation by or machine by hand the nozzle surface. Oval wells collects debris away from the nozzle openings along the length of the major axis A _L, thereby, the possibility of clogging of the nozzle openings due to carry put is debris in the well is reduced during the cleaning. In one embodiment, the length of the well along the major axis is about 300-600 μm and the width of the well along the minor axis is about 50-70 μm. In another embodiment, the nozzle opening has a non-circular geometry that matches or does not match the geometry of the well. Furthermore, the nozzle opening can be displaced from the well center. In embodiments, the well depth can vary between where the nozzle opening and the well periphery meet the nozzle plate.

  Wells and / or nozzle openings can be formed by machining, laser ablation or chemical or plasma etching. The well can also be formed by molding, for example with a plastic element. The well and nozzle openings can be formed in a common structure or separate structures to be assembled. For example, the nozzle opening is formed in a structure that defines another component of the ink flow path, and the well is formed in another structure that is assembled with the structure that defines the nozzle opening. In another embodiment, the well, nozzle opening and pressure chamber are formed in a common structure. The structure can be an etchable material such as a metal, carbon, or silicon material, eg, silicon or silicon dioxide. 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. The details of each of these specifications are included herein by reference. In embodiments, the well can have a non-wetting coating.

  There are still other embodiments. For example, ink can be ejected in a printing operation, but the print head can be used 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. Well arrays are described in US patent application Ser. No. 10/749829 filed Dec. 30, 2003, US patent application Ser. No. 10 / 7,816 filed Dec. 30, 2003. Used in combination with other residual liquid control aspects such as protrusions described in the specification and / or channels described in US patent application Ser. No. 10 / 7,833, filed Dec. 30, 2003. be able to. For example, a series of protrusions or channels can be provided inside the well or on the nozzle surface near the well, eg, surrounding the well. Apertures can be provided in the well or on the nozzle face. The liquid control 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 debris rather than jetted residual ink.

  Further embodiments are within the scope of the appended claims.

FIG. 1 is a schematic diagram of a droplet ejection assembly. FIG. 1A is a perspective view of a nozzle plate. FIG. 1B is an enlarged section through the nozzle opening of the nozzle plate. FIG. 2 is a cross section through the nozzle openings in the nozzle plate showing the meniscus under various conditions. FIG. 2A is a cross section through the nozzle openings in the nozzle plate showing the meniscus under various conditions. FIG. 2B is a section through the nozzle openings in the nozzle plate showing the meniscus under various conditions. FIG. 2C is a section through the nozzle openings in the nozzle plate showing the meniscus under various conditions. FIG. 3 is a perspective view of the nozzle liquid reservoir.

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 32 Controller 40 Well

Claims (40)

In the method of droplet ejection,
Providing a print head having a liquid flow path for applying a pressure to the liquid to eject droplets from a nozzle opening disposed in the well; and a liquid from the nozzle opening to the well to form a meniscus Supplying the process,
Having
The well has a peripheral edge on the outer surface of the printhead;
When the well is filled with liquid, the meniscus defines a liquid depth above the periphery of the nozzle opening equal to about 1-15% of the width of the nozzle opening and the periphery of the well A method characterized by touching .   The method of claim 1, comprising forming the meniscus by controlling the pressure of the liquid.   The method of claim 1, comprising forming the meniscus by lowering the pressure of the liquid.   4. The method of claim 3, comprising applying a vacuum at a location upstream of the nozzle opening.   5. The method according to claim 4, wherein the vacuum at the nozzle opening is about 0.5 to 10 inwg (1 inwg = 249 Pa).   The method of claim 1, wherein the ratio of the well width to the nozzle opening width is about 1.4 to about 2.8.   The method of claim 1, wherein the well has a depth of about 0.15 to 0.5 of the nozzle opening.   The method of claim 1, wherein the spacing between the well periphery and the nozzle periphery is about 0.2 to greater than the nozzle width.   The method of claim 1, wherein the liquid has a surface tension of about 20-45 dynes / cm (1 dynes / cm = 10 −3 N / m).   The method of claim 1, wherein the nozzle opening and the well are defined by a common structure.   The method of claim 1, wherein the nozzle openings and / or the wells are defined in a silicon material.   The method of claim 1, wherein the nozzle openings and / or the wells are defined in metal.   The method of claim 1, wherein the nozzle openings and / or the wells are defined in carbon.   The method of claim 1, wherein the nozzle openings and / or the wells are defined in plastic.   The method of claim 1, wherein the pressure is applied to the liquid by a piezoelectric element.   The method of claim 1, wherein the nozzle opening width is about 70 μm or less.   The method of claim 1, comprising a plurality of nozzle openings, wherein the nozzle openings have a pitch of about 25 nozzles / inch (about 0.98 nozzles / mm) or less.   The method of claim 1, comprising ejecting droplets having a volume of about 1 to about 70 pL.   The method of claim 18, wherein pressure is applied to the liquid by a piezoelectric element.   The method of claim 18, wherein the nozzle opening has a diameter of about 70 μm or less.   21. The method of claim 20, wherein the well is elliptical.   19. The method of claim 18, comprising a plurality of nozzle openings, the nozzle openings having a pitch of about 100 nozzles / inch (about 3.9 nozzles / mm) or less.   The method of claim 1, wherein the meniscus is concave with respect to the nozzle opening.   24. The method of claim 23, comprising forming the meniscus by controlling the pressure of the liquid.   24. The method of claim 23, comprising forming the meniscus by reducing the pressure of the liquid.   26. The method of claim 25 including applying a vacuum at a location upstream of the nozzle opening.   26. The method of claim 25, wherein the vacuum at the nozzle opening is about 0.5 to 10 inwg (1 inwg = 249 Pa).   24. The method of claim 23, wherein the ratio of the well width to the nozzle opening width is about 1.4 to about 2.8.   24. The method of claim 23, wherein the well has a depth of about 0.15 to 0.5 of the nozzle opening.   24. The method of claim 23, wherein the distance between the well periphery and the nozzle periphery is about 0.2 to greater than the nozzle width.   24. The method of claim 23, wherein the liquid has a surface tension of about 20-45 dynes / cm (1 dynes / cm = 10 <-3> N / m).   24. The method of claim 23, wherein the nozzle opening and the well are defined by a common structure.   24. The method of claim 23, wherein the nozzle opening and / or the well is defined in a silicon material.   24. The method of claim 23, wherein the nozzle openings and / or the wells are defined in metal.   24. The method of claim 23, wherein the nozzle opening and / or the well is defined in carbon.   24. The method of claim 23, wherein the nozzle opening and / or the well is defined in plastic.   The method of claim 23, wherein the pressure is applied to the liquid by a piezoelectric element.   24. The method of claim 23, wherein the nozzle opening width is about 70 [mu] m or less.   24. The method of claim 23, comprising a plurality of nozzle openings, the nozzle openings having a pitch of about 25 nozzles / inch (about 0.98 nozzles / mm) or less.   24. The method of claim 23, comprising ejecting a droplet having a volume of about 1 to about 70 pL.

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