TWI436898B - Inkjet printer - Google Patents

Description

Inkjet printer

This invention relates to an inkjet nozzle assembly. It is primarily developed to improve the efficiency of hot bending actuated inkjet nozzles and to improve droplet ejection characteristics.

The Applicant has previously discussed an excess of MEMS inkjet nozzles using Thermal Bend Actuation. Thermal bending actuation generally refers to the situation in which a material undergoes a bending movement caused by thermal expansion relative to another material as it flows therethrough. The resulting bending movement results can be used to eject ink from the nozzle opening, which is selectively achieved by the movement of a paddle or blade that creates a pressure wave within the nozzle chamber.

Typical thermal bending inkjet nozzle patterns are found in the patents and patent applications listed in the aforementioned cross-referenced section, the disclosure of which is incorporated herein by reference.

An ink jet nozzle is described in the applicant's U.S. Patent No. 6,416,167, which has a paddle disposed in the nozzle chamber and a thermal bending actuator disposed outside the nozzle chamber. The actuator is of the type in which a lower active beam made of a conductive material (titanium nitride) is welded to a passive beam above a non-conductive material such as cerium oxide. The actuator is coupled to the paddle via an arm that is inserted into a slot in the wall of the nozzle chamber. After passing the current through the lower active beam, the actuator will bend upwards, so the paddle will move toward the nozzle opening formed on the roof of the nozzle chamber. This ejects a drop of ink. The advantage of this design is its simplicity. A disadvantage of this design is that both sides of the paddle require work on the relatively viscous ink in the nozzle chamber.

An inkjet nozzle is described in the applicant's U.S. Patent No. 6,260,953, in which the actuator is formed as the active top portion of the nozzle chamber. The type of actuator is a curved conductive core surrounded by a polymeric material. Upon actuation, the actuator bends toward the floor of the nozzle chamber, increasing the pressure within the chamber, forcing a drop of ink to eject from the nozzle opening formed on the top of the chamber. The nozzle opening is formed on an inactive portion of the top. The advantage of this design is that only one side of the top active portion needs to work on a relatively viscous ink in the nozzle chamber. A disadvantage of this design is that the actuator is covered by a curved conductive element in the polymer material, which is relatively uncomfortable in a microelectromechanical process.

An ink jet nozzle is described in the applicant's U.S. Patent No. 6,623,101, which comprises a nozzle chamber having a movable top portion in which a nozzle opening is formed. The top portion of the activity is connected via an arm to a thermal bending actuator disposed outside the nozzle chamber. The actuator is of the type that an upper active beam is separated from a lower passive beam. By separating the active and passive beams, the effect of thermal bending can be maximized because the passive beam will not become the heat sink of the active beam. After passing an electric current through the upper active beam, the movable top portion having the nozzle opening formed thereon is rotated toward the bottom of the nozzle chamber, whereby ejection can be performed from the nozzle chamber. Since the nozzle opening moves with the top portion, the flight direction of the liquid droplets can be controlled by appropriately changing the shape of the outer edge of the nozzle. This design The benefit is that only one side of the top surface of the activity needs to work on a relatively viscous ink in the nozzle chamber. Another benefit is that by separating the active and passive beam members, it achieves the lowest heat loss. A disadvantage of this design is that separating the active and passive beam members results in a reduction in structural rigidity.

Prior to this, it has been known that a type of ink jet nozzle actuated by a curved actuator must be capable of displacing a necessary volume of ink to eject a predetermined volume of ink droplets from the nozzle opening. Therefore, the design of the inkjet nozzle is primarily focused on providing the maximum amount of displacement of the thermal bending actuator at a given energy input.

It is desirable to improve the bending actuation efficiency of a thermal bending actuator in situations where a denser nozzle configuration is made within the inkjet printhead and the droplet ejection characteristics are optimized.

A first aspect of the present invention provides an inkjet nozzle assembly including: a nozzle chamber for accommodating ink, the chamber having a nozzle opening and an ink inlet; and a pair of electrical contacts disposed on the One end of the assembly and connected to the drive circuit; and a thermal bending actuator for ejecting ink from the nozzle opening, the actuator comprising: an active beam connected to the electrical connections Pointing and extending longitudinally from the contacts, the active beam forming a bent current flow path between the contacts; a passive beam welded to the active beam such that when current is passed through the active beam, the active beam is heated and expanded relative to the passive beam, causing the actuator to flex, wherein the actuator has a working surface A positive pressure pulse is generated within the ink when the actuator is bent, the working surface having an area of less than 800 square microns.

Optionally, the working surface has an area of less than 600 microns.

Optionally, the working surface is formed by a surface of the passive beam.

Alternatively, the structuring can provide a peak actuator speed of at least 2.5 meters per second.

Optionally, the drive circuit is configured to transmit an arterial wave to the active beam, and each uniform arterial wave delivers less than 200 nJ of energy to the active beam.

Optionally, the drive circuit is configured to transmit an arterial wave to the active beam, each uniform arterial wave having a pulse width of less than 0.2 microseconds.

Optionally, the active and passive beams each have a length of less than 50 microns.

Optionally, the active and passive beams each have a width of less than 15 microns.

Optionally, the active and passive beams have a combined thickness of at least 1.5 microns.

Optionally, the active beam includes a first arm extending longitudinally from the first contact, a second arm extending longitudinally from the second contact, and a first and second connection The connecting member of the arm.

Optionally, the first and second arms each comprise a respective resistive heating element having a width of less than 5 microns.

Optionally, the connecting member connects the distal ends of the first and second arms, the distal ends being remote from the electrical contacts.

Optionally, the active beam is comprised of a material selected from the group consisting of titanium nitride, titanium aluminum nitride, and vanadium aluminum alloy.

Optionally, the passive beam is comprised of a material selected from the group consisting of cerium oxide, cerium nitride, and cerium oxynitride.

Optionally, the nozzle chamber includes a base and a top portion provided with an active portion such that actuation of the actuator moves the active portion toward the bottom portion.

Optionally, the active part contains the actuator.

Optionally, the nozzle opening is formed on the active portion such that the nozzle opening is movable relative to the base.

Optionally, the inkjet nozzle assembly has a footprint area of less than 1500 square microns.

Another aspect of the present invention provides an ink jet printer head including a plurality of nozzle assemblies, each of the assemblies including: a nozzle chamber for accommodating ink, the chamber having a nozzle opening and An ink inlet; a pair of electrical contacts disposed at one end of the assembly and coupled to the drive circuit; and a thermal bending actuator for ejecting ink from the nozzle opening, the actuator Including: an active beam connected to the electrical contacts and from the contacts Extending longitudinally, the active beam forms a bent current flow path between the contacts; and a passive beam is welded to the active beam such that when current passes through the active beam, the active beam Heating and expanding relative to the passive beam causing the actuator to flex, wherein the actuator has a working surface for generating a positive pressure pulse within the ink when the actuator is flexed, the working surface It has an area of less than 800 square microns.

A second aspect of the present invention provides an ink jet printer comprising: a print head having a plurality of nozzle assemblies, each nozzle assembly including: a nozzle chamber for accommodating ink, The chamber has a nozzle opening and an ink inlet; and a bending actuator for generating a positive pressure pulse in the ink when the actuator is bent to eject ink droplets from the nozzle opening And an ink supply system for supplying ink to the print head; and a means for changing the hydrostatic pressure of the ink supplied to the print head, wherein increasing the hydrostatic pressure of the ink increases the ejection The volume of the ink droplets, while reducing the hydrostatic pressure of the ink reduces the volume of the ejected ink droplets.

Alternatively, the volume of the ejected ink droplets can be increased by at least 100% relative to the minimum droplet volume.

Alternatively, the surface of a print head is defined by a lyophobic layer.

Optionally, the lyophobic layer is a PDMS layer.

Optionally, the lyophobic layer is deposited on a more lyophilic nozzle plate.

Optionally, an ink meniscus is affixed across each nozzle opening at a lyophilic/lyophilic interface.

Optionally, each nozzle assembly includes a drive circuit for transmitting an arterial wave to the bending actuator.

Optionally, the drive circuit is constructed to deliver less than 200 nJ of energy per uniform arterial wave to the actuator.

Optionally, the bending actuator comprises: an active beam coupled to the pair of electrical contacts; and a passive beam mechanically mated to the active beam such that when current is passed through the active beam, the active beam It will heat up and expand relative to the passive beam, causing the actuator to bend.

Optionally, each nozzle assembly includes the pair of electrical contacts disposed at one end thereof, and wherein the active beam extends longitudinally from the contacts to form a line between the contacts Bent current flow path.

Optionally, the active beam is welded to the passive beam.

Optionally, the active beam includes a first arm extending longitudinally from the first contact, a second arm extending longitudinally from the second contact, and a first and second connection The connecting member of the arm.

Optionally, each of the first and second arms includes a respective resistive heating element.

Optionally, the connecting member connects the distal sides of the first and second arms At the ends, the distal ends are remote from the electrical contacts.

Optionally, the active beam is comprised of a material selected from the group consisting of titanium nitride, titanium aluminum nitride, and vanadium aluminum alloy.

Optionally, the passive beam is comprised of a material selected from the group consisting of cerium oxide, cerium nitride, and cerium oxynitride.

Optionally, each nozzle chamber includes a base and a top portion that is provided with an active portion such that actuation of the actuator moves the active portion toward the bottom portion.

Optionally, the active part contains the actuator.

Optionally, the nozzle opening is formed on the active portion such that the nozzle opening is movable relative to the base.

Another aspect of the present invention provides a method of constructing a printhead that can eject a predetermined volume of ink droplets, the method comprising the steps of: (i) providing a printhead having a plurality of nozzle assemblies Each nozzle assembly includes: a nozzle chamber for accommodating ink, the chamber having a nozzle opening of a predetermined size; and a bending actuator for when the actuator is bent a positive pressure pulse wave is generated in the ink to eject the ink droplets from the nozzle opening; (ii) changing the static pressure of the ink supplied to the printing head, thereby changing the volume of the ejected ink droplets; Iii) determining an optimum ink hydrostatic pressure corresponding to the predetermined volume; and (iii) constructing an ink supply system to place the ink in the optimal ink Supply to the print head under hydrostatic pressure.

A third aspect of the present invention provides an ink jet printer constructed to form ink droplets having a volume in the range of 1 to 2.5 pL, the printer comprising: a printer head having a plurality of nozzles The assembly, each nozzle assembly includes: a nozzle chamber for accommodating ink, the chamber having a nozzle opening and an ink inlet having a maximum dimension ranging from 4 to 12 microns; a bending actuator for generating a positive pressure pulse in the ink to eject ink droplets from the nozzle opening when the actuator is bent; and an ink supply system The ink is supplied to the print head under positive hydrostatic pressure in a water column of 1 to 300 mm.

Optionally, the maximum size of the nozzle opening is in the range of 6 to 10 microns.

Optionally, the ink supply system is configured to supply ink to the printhead under positive hydrostatic pressure in a range of 5 to 200 mm water.

Optionally, the hydrostatic pressure provides a convex meniscus within the nozzle opening when the print head is filled.

Alternatively, the surface of a print head is composed of a lyophobic layer.

Optionally, the lyophobic layer is a PDMS layer.

Optionally, the lyophobic layer is deposited on a more lyophilic nozzle plate.

Selectively, an ink meniscus is fixed at a lyophilic/lyophilic interface Across each nozzle opening.

Optionally, each nozzle assembly includes a drive circuit for transmitting an arterial wave to the bending actuator.

Optionally, the drive circuit is constructed to deliver less than 200 nJ of energy per uniform arterial wave to the actuator.

Optionally, the bending actuator comprises: an active beam coupled to the pair of electrical contacts; and a passive beam mechanically mated to the active beam such that when current is passed through the active beam, the active beam It will heat up and expand relative to the passive beam, causing the actuator to bend.

Optionally, each nozzle assembly includes the pair of electrical contacts disposed at one end thereof, and wherein the active beam extends longitudinally from the contacts to form a line between the contacts Bent current flow path.

Optionally, the active beam is welded to the passive beam.

Optionally, the active beam includes a first arm extending longitudinally from the first contact, a second arm extending longitudinally from the second contact, and a first and second connection The connecting member of the arm.

Optionally, each of the first and second arms includes a respective resistive heating element.

Optionally, the active beam is comprised of a material selected from the group consisting of titanium nitride, titanium aluminum nitride, and vanadium aluminum alloy.

Optionally, the passive beam is comprised of a material selected from the group consisting of cerium oxide, cerium nitride, and cerium oxynitride.

Optionally, each nozzle chamber includes a bottom and an activity is provided The top of the portion, so actuation of the actuator can move the active portion toward the bottom.

Optionally, the active part contains the actuator.

Optionally, the nozzle opening is formed on the active portion such that the nozzle opening is movable relative to the base.

Embodiments of the present invention will now be described by way of example in the accompanying drawings.

Construct a thermal bending actuator for maximizing droplet ejection speed

Figures 1 and 2 show two different stages of a nozzle assembly 100 during the manufacturing process. The nozzle assembly is similar in construction to the nozzle assembly described in the U.S. Patent Application Serial No. 11/763,440, the entire disclosure of which is hereby incorporated by Used as a reference in this article.

Figure 1 shows the partially formed nozzle assembly to show the structure of the active and passive beam layers. Thus, referring to Figure 1, it is shown that the nozzle assembly 100 is formed on a CMOS substrate 102. A top portion 104 spaced from the base body 102 and a side wall 106 extending from the top portion to the base body 102 define a nozzle chamber. The top portion 104 includes a movable portion 108 and a fixed portion 110 with a gap 109 formed therebetween. A nozzle opening 112 is formed in the movable portion 108 for ejecting ink.

The movable portion 108 includes a thermal bending actuator having a pair of cantilever beams in the form of an upper active beam 114 welded to a lower passive beam 116. The lower passive beam 116 defines the vane of the active portion 108 of the top Wai. The upper active beam 114 includes a pair of arms 114A and 114B that extend longitudinally from the electrode contacts 118A and 118B, respectively. The arms 114A and 114B are joined by a connecting member 115 at their distal ends. The connecting member 115 can include a titanium conductive pad 117 that can contribute to electrical conductivity in the vicinity of the joint region. Thus, the active beam 114 forms a curved or curved conductive path between the electrode contacts 118A and 118B.

The electrode contacts 118A and 118B are disposed adjacent to each other at one end of the nozzle assembly, and are connected to a metal CMOS layer 120 in the substrate 102 via a connection post 119, respectively. This CMOS layer 120 contains the drive circuitry necessary to actuate the bend actuator.

Passive beam 116 typically contains any electrical and thermal insulating material such as hafnium oxide, tantalum nitride, and the like. The thermoelastic active beam 114 can comprise any suitable thermoelastic material such as titanium nitride, titanium aluminum nitride, and aluminum alloy. Vanadium-aluminum alloy is a preferred material as described in the applicant's U.S. Patent Application Serial No. 11/607,976 (Attorney Docket No. IJ70US), which is hereby incorporated by reference. Because they have the characteristics of high thermal expansion, low density, and high Young's modulus.

Referring to Figure 2, there is shown a complete nozzle assembly 100 in the next stage of the manufacturing process. The nozzle assembly of Figure 2 has a nozzle chamber 122 and an ink inlet 124 for supplying ink to the nozzle chamber. In addition, the top portion 104 forms part of the hard nozzle plate of the printhead and is covered by a layer of polymeric material 126, such as polydimethylsiloxane (PDMS). This polymer layer 126 has a variety of functions including protective bends A curved actuator that hydrophobizes the top portion 104 (and the surface of the print head) and a mechanical seal that provides a gap 109. Polymer layer 126 has a low Young's modulus for actuation and ejection of ink from nozzle opening 112. A detailed description of the polymer layer 126, including its function and manufacture, can be found, for example, in U.S. Patent Application Serial No. 11/946,840, the entire disclosure of which is incorporated herein by reference.

When a drop of ink needs to be ejected from the nozzle chamber 122, current will flow through the active beam 114 between the electrode contacts 118. The active beam 114 is rapidly heated by the current to expand relative to the passive beam 116, thereby causing the active portion 108 to flex downwardly relative to the fixed portion 110 toward the base 102. This action then causes the ink droplets to be ejected from the nozzle opening 112 as the internal pressure of the nozzle chamber 122 rapidly increases. When the current ceases to flow, the active portion 108 will return to its temporary position as shown in Figures 1 and 2, which will draw ink from the inlet 124 into the nozzle chamber 122 for preparation for the next injection.

In the nozzle design shown in Figures 1 and 2, it is advantageous for the bending actuator to constitute at least a portion of the active portion 108 of each nozzle assembly 100. This not only simplifies the overall design and manufacture of the nozzle assembly 100, but also provides a higher jetting efficiency because only one side surface (i.e., the "working surface" below) of the active portion 108 must perform work on a relatively viscous ink. . In contrast, the total achievement of the nozzle provided with the actuator paddle inside the nozzle chamber 122 is inefficient because both sides of the actuator must perform work on the ink inside the chamber.

However, it is still necessary to further improve the overall efficiency of the bending actuator. According to the invention, the working surface of the thermal bending actuator has an area of less than 800 square microns. Optionally, the working surface has an area of less than 700 square microns or less than 600 square microns.

As shown in FIGS. 1 and 2, the working surface of the thermal bending actuator is generally constituted by the lower surface (inner surface) of the passive beam 116, which works with respect to the ink contained in the nozzle chamber 122. .

Reducing the working surface area of the thermal bending actuator is a significant difference from the previous design of the thermal bending actuator. Prior to this, it has been understood that the displacement of the necessary volume of ink is a major factor in controlling the ejection of droplets from the nozzle opening. Therefore, in order to obtain a typical 1-2 pL (e.g., 1.2-1.8 pL) ink droplet volume at an acceptable droplet ejection speed (e.g., 5-15 m/sec), it has previously been understood that it must be A working surface with an area of at least 1500 square microns moves. Efforts to improve droplet ejection characteristics have previously focused on maximizing actuator displacement, which is typically achieved by lengthening the actuator, thereby increasing the area of its working surface. However, Applicants' experiments have found that, contrary to expectations, the peak velocity during the bending actuation of the actuator in terms of acceptable droplet velocity and droplet volume provides optimum liquid ejection, It is a more important factor.

This will result in an excellent droplet ejection effect even with a relatively low surface area working surface where sufficient peak actuator speed is obtained. A high enough peak actuator speed is typically at least about 2.5 meters per second.

The peak actuator speed can be controlled by how fast the active beam can be heated during actuation. If the applicant applied for it on May 5, 2008 The rapid heating of the active beam can transmit a very short arterial wave width of less than 0.2 microseconds (e.g., about 0.1 microseconds) as described in U.S. Patent Application Serial No. 12/114,826, the disclosure of which is incorporated herein by reference. And/or the active beam is provided with a heating element having a smaller cross-sectional area (eg, less than 10 square microns or less than 5 square microns). In general, each heating element has a width of less than 5 microns.

However, the peak actuator speed is also a function of the area of the working surface because when the working surface has a small area, only less work is required on the ink. It has been found that the present invention provides optimum droplet ejection characteristics when the working surface has an area of from 200 to 800 square microns, or from 250 to 700 square microns, or from 300 to 650 square microns. When the working surfaces are moved at a peak speed of at least 2.5 meters per second, an acceptable droplet ejection speed of 6-12 meters per second or 8-10 meters per second is typically obtained.

As can be appreciated from the foregoing, the present invention provides a significant reduction in area of the working surface within the inkjet jet assembly having a thermal bending actuator. Thus, the footprint of each inkjet nozzle assembly can be reduced, which allows for a denser nozzle configuration on the inkjet printhead. In general, the footprint of each nozzle assembly in the printhead according to the present invention is less than 1200 square microns, or less than 1000 square microns, or less than 800 square microns.

In more detail, the area of the working surface can be reduced by a thermal bending actuator having a length of less than 60 microns or less than 50 microns. Reducing the length of the actuator increases the rigidity of the actuator in the direction of the bend, which can be further improved The overall efficiency of the actuator. The stiffness of the actuator in the direction of the bend is also controlled by the overall thickness of the actuator. Optionally, the thickness of the bending actuator is at least 1.3 microns or at least 1.5 microns.

Furthermore, the area of the working surface can be reduced by a thermal bending actuator having a width of less than 20 microns or less than 15 microns. Reducing the width of the actuator has the greatest effect in increasing the nozzle configuration density on the printhead because a greater number of nozzles can be assembled into a series of nozzles.

Finally, the present invention can achieve both high nozzle placement density with good droplet ejection efficiency, good droplet characteristics, and the like. For example, in the case of a pulse width of about 0.1 microseconds, an input energy of less than 200 nJ (or less than 150 nJ) is sufficient to produce a peak actuator speed of at least 2.5 meters per second. This can result in a droplet ejection speed of 8-10 meters per second.

Furthermore, the ejected ink droplets are extremely well generated and surprising, with little or no accompanying droplets. Companion droplets are known in ink jet printing and are caused by droplets that are ejected from the end of the ejected droplets into small droplets that are separated from the main ink droplets. Accompanying droplets can be confusing and can affect overall print quality. The inventors have appreciated that higher peak actuator speeds of at least 2.5 meters per second can reduce the number of accompanying droplets. In general, accompanying droplets are associated with high droplet ejection speeds, but surprisingly, the invention is equivalent to at least 7 meters per second, or at least 8 meters per second, or at least 9 meters per second. At high droplet ejection speeds, a small amount of accompanying droplets still appear.

In summary, in controlling the droplet ejection characteristics, the peak displacement of the actuator combined with the larger working surface area is far more than the peak actuator speed. An unimportant factor; while minimizing the area of the working surface, a larger peak actuator speed can be obtained for a given input energy.

Use ink pressure to control droplet size

Most inkjet printers operate with a negative ink hydrostatic pressure. This is primarily to avoid uncontrolled flow of ink across the surface of the printhead, especially when the print job is stopped. Furthermore, when the ink meniscus is pulled by the surface tension and spans the nozzle opening, it is preferable to have a concave meniscus instead of a convex meniscus (projecting toward the outside of the head) because of the convexity. The meniscus is more likely to crack due to particulate matter on the surface of the print head, causing a slight flow. Figure 4A shows a typical inkjet nozzle 200 having a concave meniscus 202 due to negative ink hydrostatic pressure, while Figure 4B shows the same inkjet nozzle, but with hydrostatic pressure The convex meniscus 204.

There are various ways to control the hydrostatic pressure of the ink in the ink jet print head. A suitably constructed ink supply system can deliver ink at the necessary ink pressure, and a wide variety of different types of ink supply systems are known. For example, the position of the ink reservoir relative to the printhead provides a very simple version of the pressure control - the ink reservoir 206 is disposed above the printhead 205 to provide positive ink hydrostatic pressure (see Figure 4B); The sump 206 is disposed below the printhead 205 to provide a negative ink hydrostatic pressure (see Figure 4A). Various other means for controlling the hydrostatic pressure of the ink in the printhead are in the field of those skilled in the art, and the details of the particular pressure control means are not relevant to the present invention.

As discussed earlier, the applicant has developed a lyophobic table. The face of the inkjet print head. This is typically the PDMS layer 126, which is disposed on the nozzle tip 104 at a later stage in the manufacture of the printhead (see, for example, U.S. Patent Application Serial No. 11/ filed on Nov. 29, 2007. 946, 840). Since the top portion 104 of the nozzle chamber is substantially lyophilic, made of cerium oxide or tantalum nitride, the meniscus of the ink will be lyophilic/sparse between the top layer 104 and the PDMS layer 126. The liquid interface is pulled across the nozzle opening 112. Figure 5 shows the concave meniscus 150 of the ink in the nozzle configuration 100 described above under negative ink hydrostatic pressure.

The lyophobic PDMS layer 126 can help minimize surface flooding of the printhead as illustrated in U.S. Patent Application Serial No. 11/946,840. Thus, the PDMS layer 126 can help to maintain the convex meniscus 151 without the risk of flooding the surface of the high print head. As shown in Fig. 6, the convex meniscus 151 does not protrude outward from the surface of the printing head (defined by the outer side surface 128 of the PDMS layer) because of the thickness of the PDMS layer 126, also because of the meniscus 151 is fixed at the lyophilic/lyophobic interface. The PDMS layer 126 effectively shields the meniscus 151 from any particles while at the same time acts as an energy barrier that minimizes the flow of the surface of the printhead - the ink moves to the lyophobic PDMS layer 126 due to capillary action. The trend is lowest and energy is conducive to immobilization at the lyophilic/lyophobic interface.

Therefore, the PDMS layer 126 does not limit the nozzle assembly 100 only to the negative pressure ink supply situation. Without being limited to negative ink hydrostatic pressure, Applicants' experiments have found that, surprisingly, positive ink hydrostatic pressure with convex meniscus 151 can be achieved in the aforementioned bending actuated nozzles. Provided in 100 Quite different droplet ejection characteristics.

A surprising observation is that for a nozzle opening 112 of a given size (e.g., diameter), positive ink hydrostatic pressure provides greater size and volume than the same nozzle opening is supplied with negative ink hydrostatic pressure. Spray ink droplets. Prior to this, it is understood that the primary factor controlling the volume of the ink droplets is the diameter of the nozzle opening 112. In general, it may be desirable for the ejected ink droplets to have the same diameter as the nozzle openings ejected therefrom. Thus, a nozzle opening having a 12 micron diameter can typically eject ink droplets of about 0.9 pL, which is too small for some applications. A 14 micron nozzle opening typically ejects ink droplets of about 1.4 pL, which is considered acceptable for most inkjet applications. In general, droplet volumes in the range of 1-2.5 pL or 1-2 pL are considered to be acceptable droplet volumes.

However, when ejected from the nozzle assembly having the positive ink hydrostatic pressure shown in Fig. 6, it can be observed that compared with the nozzle assembly having the negative ink hydrostatic pressure shown in Fig. 5, Spray ink droplets 1.5 times, 2 times, or even 3 times larger.

For this reason, the print head having the thermal bending actuated nozzle 100 can be designed differently or differently depending on the hydrostatic pressure provided by the ink supply system. For example, in terms of the volume of droplets necessary, if a positive ink hydrostatic pressure is used, the nozzle opening can be made smaller relative to the more common negative hydrostatic pressure. This allows a denser nozzle configuration based on smaller nozzle openings on the printhead. In general, the positive ink hydrostatic pressure is in the range of 1 to 300 mm water column, and the choice is The range of 5 to 200 mm water column, or the range of 10 to 100 mm water column. At this positive ink pressure, the maximum size of the nozzle opening is in the range of 4 to 12 microns, optionally between 5 and 11 microns, or alternatively at 6-10 microns, while still achieving acceptable liquids. Drop volume. In the case of a circular nozzle opening, the largest dimension is its diameter; for an elliptical nozzle opening, the largest dimension is the length of its long axis.

Furthermore, by varying the hydrostatic pressure provided by the ink supply system, the printhead can be operated in a different manner as it is. In some print head applications (such as general black text printing) it may be necessary to operate with positive hydrostatic pressure to provide a larger droplet volume. Larger droplet volumes put more ink on the page to maximize optical density, which is most desirable when printing black text on standard office paper. In addition, some printhead applications (e.g., printed photographs) may need to be operated with a lower (e.g., negative) ink hydrostatic pressure to provide a smaller droplet volume. A smaller droplet volume results in a higher print resolution, which is particularly desirable for photo printing applications.

The ability to vary the volume of the droplet without fundamentally changing the design of the nozzle has significant versatility for inkjet printing. The purpose of inkjet printing is to provide a SOHO printer that can print general black text and/or photos without sacrificing optical density or photo quality, respectively. Similarly, the ability to optimize droplet volume in the same situation for printing on different paper types represents a significant advance in inkjet printing technology.

For example, Figures 4A and 4B schematically show that there is any The print head 205 and the printer of the ink supply system can supply different ink hydrostatic pressures by changing the position of the ink reservoir 206 relative to the print head. Of course, a more sophisticated means of varying the hydrostatic pressure of the ink through the ink supply system can be readily understood as it is known to those skilled in the art. For example, as shown in FIG. 7, a reversible air pump 210 can be used that communicates with the headspace 211 in the ink sump 206, and an ink pressure sensor 212 can provide a feedback signal 214 to the air pump. .

It is to be understood that the invention has been described by way of example only, and the details thereof may be varied within the scope of the invention as defined by the appended claims.

100‧‧‧Nozzle assembly

102‧‧‧ base

104‧‧‧ top

106‧‧‧ side wall

108‧‧‧Active parts

109‧‧‧ gap

110‧‧‧Fixed parts

112‧‧‧ nozzle opening

114‧‧‧Active beam

114A‧‧‧arm

114B‧‧‧arm

115‧‧‧Connecting members

116‧‧‧ Passive beam

117‧‧‧Electrical mat

118‧‧‧Electrode contacts

118A‧‧‧Electrode contacts

118B‧‧‧Electrode contacts

119‧‧‧ Connecting column

120‧‧‧ CMOS layer

122‧‧‧Nozzle chamber

124‧‧‧Ink entrance

126‧‧‧ polymer layer

150‧‧‧ concave meniscus

151‧‧‧Outer convex meniscus

200‧‧‧Inkjet nozzle

202‧‧‧ concave meniscus

204‧‧‧Outer convex meniscus

205‧‧‧Print head

206‧‧‧Ink storage tank

210‧‧‧Air pump

211‧‧‧ head space

212‧‧‧Ink pressure sensor

Figure 1 is a cutaway perspective view of a partially fabricated inkjet nozzle assembly.

Fig. 2 is a cutaway perspective view of the ink jet nozzle assembly shown in Fig. 1 after the final stage of the process step.

Fig. 3A schematically shows a print head for supplying ink with a negative liquid static pressure.

Fig. 3B schematically shows a print head that supplies ink in a positive hydrostatic pressure.

Figure 4 shows an inkjet nozzle assembly filled with ink under negative hydrostatic pressure.

Figure 5 shows an inkjet nozzle assembly filled with ink in positive hydrostatic pressure.

Figure 6 shows schematically that the construction can be supplied by variable hydrostatic pressure. Inkjet printers for ink supply systems.

100‧‧‧Nozzle assembly

102‧‧‧ base

104‧‧‧ top

106‧‧‧ side wall

108‧‧‧Active parts

109‧‧‧ gap

110‧‧‧Fixed parts

112‧‧‧ nozzle opening

114‧‧‧Active beam

114A‧‧‧arm

114B‧‧‧arm

115‧‧‧Connecting members

116‧‧‧ Passive beam

117‧‧‧Electrical mat

118A‧‧‧Electrode contacts

118B‧‧‧Electrode contacts

120‧‧‧ CMOS layer

Claims (17)

An ink jet printer comprising: a print head having a plurality of nozzle assemblies, each nozzle assembly comprising: a nozzle chamber for containing ink, the chamber having a nozzle opening defined by a top of the chamber, and an ink inlet; and a bending actuator disposed in the movable portion of the top, the bending actuator being constructed to be bent from the bottom of the nozzle chamber to open from the nozzle Spraying ink droplets out and generating a positive pressure pulse in the ink; and an ink supply system for supplying ink to the print head; and a pressure changing device acting on the ink supply system to cause the ink The liquid hydrostatic pressure in the supply system is variable, wherein increasing the hydrostatic pressure of the ink increases the volume of the ejected ink droplets, and decreasing the hydrostatic pressure of the ink reduces the volume of the ejected ink droplets. . The printer of claim 1, wherein the volume of the ejected ink droplets is increased by at least 100% relative to the minimum droplet volume. The printer of claim 1, wherein the surface of the print head is defined by a liquid repellency layer. The printer of claim 3, wherein the lyophobic layer is a polydimethylsiloxane (PDMS) layer. The printer of claim 3, wherein the lyophobic layer is deposited on a more lyophilic nozzle plate. Such as the printer described in claim 5, one of the inks The meniscus is fixed across each nozzle opening at a lyophilic/lyophilic interface. The printer of claim 1, wherein each nozzle assembly includes a drive circuit for transmitting an arterial wave to the bending actuator. The printer of claim 1, wherein the drive circuit is configured to deliver less than 200 nJ of energy per uniform arterial wave to the actuator. The printer of claim 1, wherein the bending actuator comprises: an active beam coupled to a pair of electrical contacts; and a passive beam mechanically coupled to the active beam to Such that when current is passed through the active beam, the active beam will heat up and expand relative to the passive beam, causing the actuator to bend. The printer of claim 9, wherein each nozzle assembly includes the pair of electrical contacts disposed at one end thereof, and wherein the active beam extends longitudinally from the contacts, And forming a bent current flow path between the contacts. The inkjet nozzle assembly of claim 10, wherein the active beam comprises a first arm extending longitudinally from the first contact, and a first extending longitudinally from the second contact a two arm portion and a connecting member connecting the first and second arm portions. The printer of claim 11, wherein the first and second arms each comprise a respective resistive heating element. Such as the printer described in claim 11, wherein the company A connecting member connects the distal ends of the first and second arms, the distal ends being remote from the electrical contacts. The printer of claim 9, wherein the active beam is welded to the passive beam. The printer of claim 9, wherein the active beam is composed of a material selected from the group consisting of titanium nitride, titanium aluminum nitride, and vanadium aluminum alloy. The printer of claim 9, wherein the passive beam is composed of a material selected from the group consisting of cerium oxide, cerium nitride, and cerium oxynitride. The printer of claim 1, wherein the nozzle opening is formed on the movable portion such that the nozzle opening is movable relative to the bottom portion.