JP6577932B2 - Printing system with self-purge, precipitation prevention, and gas removal structure - Google Patents

Description

  This embodiment relates generally to the field of printing, and more particularly to a printing system with an integrated, self-purge, anti-settling, and gas removal structure.

  Inkjet printheads are known in the printing art to require periodic purges to clean the print nozzles, remove air bubbles, and maintain print quality. Simply put, an ink jet printer has a corresponding small in a nozzle plate fixed in close proximity from multiple nozzles to paper or the front of a solar cell or other media to be printed or marked. It works by discharging a small amount of ink through the opening. These openings are located in the nozzle plate so that a selected number of nozzles eject ink droplets to a specific location on the media to produce the desired character or part of an image. Arranged. By controlling and repositioning the media and then ejecting the ink droplets separately, more portions of the desired character or image are generated.

  A solar cell is a solid-state semiconductor device that directly converts sunlight energy into electricity. Most large commercial solar cell factories produce printed polycrystalline silicon solar cells. Printed polycrystalline silicon solar cells have grid-like metal contacts consisting of fine fingers and larger bus bars printed on the front surface using silver paste inkjet printing. The metal contacts of the grid-like grid are made of 60-100 printed silver wires at 2 millimeter (mm) intervals and typically have a width of 100 micrometers ([mu] m).

  The frequency with which the print head is purged depends on the particular application for which the print head is being used. Purging involves squeezing the printing liquid out of the inkjet head through the nozzles under an overpressure of approximately 0.5 bar. The excess pressure force is associated with the normal vacuum used during printing at about -0.01 bar.

  One drawback of conventional purging techniques is that the purge head can be dripped from the print head and the print head is removed from the print area to a maintenance area where any liquid dripping from the head does not adversely affect the printing process. It is necessary to move. As is generally known in this work, the nozzle plate is placed on the print surface of the print head and provides access to the nozzles for printing while protecting the print head, among other features.

  After purging, the nozzle plate is preferably cleaned (also known as wiping) to remove the purged liquid so that the printing liquid can be ejected correctly from the nozzle. In order to maintain the smoothness and anti-wetting properties of the nozzle plate, it is desirable to wipe without contacting the nozzle plate.

  One conventional technique for wiping without touching the nozzle plate is vacuum wiping, where the vacuum head moves across the nozzle plate. The vacuum head does not contact the nozzle plate, but is close enough to allow the vacuum, also known as the suction tube, to remove liquid from the nozzle plate. Since the vacuum head does not contact the nozzle plate, there is suction (not only from the direction of the nozzle plate) from all sides of the vacuum head, and the cleaning efficiency of the nozzle plate is deteriorated.

  The disadvantages of conventional vacuum wiping include cost, printing speed, reliability, and wiping quality. Examples of drawbacks of conventional vacuum wiping include the following: (a) The purged liquid can drip from the print head, which necessitates moving the print head from the print area to the maintenance area. is there. (B) Since it takes time to move the print head from the printing area to the maintenance area, the printing speed decreases, and the cost increases accordingly. (C) The printing press has very high precision elements and structures so that the vacuum slit can traverse the nozzle plate without contact, for example by a small distance of about 0.15 mm. I need. High precision elements increase the cost of the printing press and the wiping reliability depends on maintaining high precision. (D) Effective wiping requires a vacuum slit to traverse the nozzle plate at a low speed of, for example, about 2 mm / s (millimeter per second). The time required for effective wiping slows the printing speed and consequently increases the printing cost.

  Thus, a printing system that may be used to print the grid-like metal contacts of a solar cell, for example, allowing a purge that does not drip the purged liquid from the nozzle plate (or generally from the print head) A printing system is needed. It is even more desirable to have high quality cleaning that is less costly and more reliable than current technology. Furthermore, it is necessary to remove some of the gas that accumulates on the nozzle surface in order to prevent the formation of precipitates on the nozzle plate and to prevent deflection of the printed ink jet.

  Embodiments of the present invention disclose a printhead assembly with an integrated purge mechanism. The printhead assembly includes: (a) a liquid dispensing head including one or more dispensing nozzles surrounded by a nozzle plate driven by at least first and second pressures; and (b) one Or having a shielding mask including an opening in front of more nozzles, and when the printing liquid is driven by the first pressure and dispensed from the head, the printing liquid is opened in the shielding mask. And (ii) when the purge printing liquid is dispensed from the head driven by a second pressure, the purge printing liquid is dispensed with a shielding mask and nozzles. The opening is configured to be drawn into an elongated gap formed between the plates, thereby removing purge printing liquid from nearby nozzles. It is.

  According to further features in embodiments of the present invention, the printhead assembly includes one or more printhead assemblies with an integral purge mechanism.

  According to further features in embodiments of the present invention, the printhead assembly includes a plurality of printheads and the shielding mask includes an opening in front of each of the printheads.

  According to a further feature of the embodiments of the present invention, the opening of the shielding mask includes a slit.

  According to a further feature of embodiments of the present invention, one or more nozzles are configured proximate to the slit edges in each of the print heads so that the purge printing liquid is routed through the slit edges. To be drawn into the elongated gap.

  According to a further feature of an embodiment of the present invention, the distance from the nozzle to one edge is 20 times the distance from the nozzle to the opposite edge of the slit because the slit is off-center with respect to the nozzle. %.

  According to a further feature of an embodiment of the present invention, the suction system is fluidly interconnected with the elongated void, and the suction system provides a pressure gradient to the elongated void, thereby purging the purge printing liquid from the elongated void. remove.

  According to a further feature of the embodiments of the present invention, the suction system fluidly interconnects with an elongated cavity removably mounted directly below the opening, the suction system providing a pressure gradient to the opening, which To remove the purge printing liquid from the elongated gap through the opening.

  According to further features in embodiments of the present invention, the shielding mask further includes a printhead housing.

  According to further features in embodiments of the present invention, the printhead assembly includes a cooling system that cools the printhead housing.

  According to further features in embodiments of the present invention, the printhead assembly further comprises a printing fluid storage and recirculation system that returns purge printing fluid captured in the elongated gap to the printing head assembly printing fluid reservoir.

  According to a further feature of embodiments of the present invention, the purge printing liquid may be dispensed while the print head is in the print area.

  According to a further feature of an embodiment of the present invention, the print head housing is heated when the print head exits the print area to maintain a predetermined level of moisture in the vicinity of the nozzle plate. It further comprises an auxiliary suction system arranged to evacuate at least part of the gas spouted from the printing liquid dispensed above or from a hot pool of volatile liquid directly under the print head.

  According to further features in embodiments of the present invention, a method of printing is disclosed. The method includes the following steps: (a) providing an integrated purge mechanism to the printhead assembly, each printhead assembly (i) including one or more nozzles. A printing head, and (ii) a shielding mask including openings aligned to fit a number of nozzles, wherein an elongated gap is formed between the printing head and the printing mask, (b) a printing fluid Printing by activating the print head with a first pressure so as to be dispensed in pulses from the print head through the opening, and (c) the dispensed liquid is drawn into the elongated gap And purging by passing the printing liquid through one or more nozzles with a second pressure.

  According to a further feature of an embodiment of the present invention, the method uses one or more printhead assemblies with an integral purge mechanism.

  According to further features in embodiments of the present invention, the shielding mask includes an opening in front of each of the print heads.

  According to a further feature of the embodiments of the present invention, the opening of the shielding mask includes a slit.

  According to a further feature of an embodiment of the present invention, the method comprises configuring one or more nozzles near the edge of each slit in the print head so that the purge printing liquid is slit. Drawing into the elongated gap through the edge of the.

  According to a further feature of the embodiments of the present invention, the method is such that the distance from the nozzle to one edge of the slit is less than 20% of the distance from the nozzle to the opposite edge of the slit. A step of forming a slit off the center.

  According to a further feature of an embodiment of the present invention, the method includes the step of recirculating the printing fluid drawn into the elongated gap to the printhead assembly printing fluid reservoir.

  According to a further feature of an embodiment of the present invention, the method uses a suction system fluidly connected to the elongated void to remove printing fluid from the elongated void, wherein the vacuum system is pressured against the elongated void. Providing a gradient, thereby removing the printing fluid from the elongated void.

  According to further features in embodiments of the present invention, the method removes printing fluid from an elongated void using a suction system that is fluidly interconnected with an elongated void that is removably mounted directly beneath the opening. A suction system applying a pressure gradient to the opening, thereby removing the purge printing liquid from the elongated void through the opening.

  According to further features in embodiments of the present invention, a method for printing with an inkjet head is disclosed. The method includes a jet nozzle surrounded by a nozzle plate, which is kept wet during printing to prevent accumulation of solid deposits on the nozzle plate.

  According to a further feature of an embodiment of the present invention, the step of keeping the nozzle plate moist is performed by gas ejected from the discharged printing liquid that accumulates on the heated substrate.

  According to a further feature of an embodiment of the present invention, the step of keeping the nozzle plate moist is a gas that emanates from a hot pool of volatile liquid directly under the print head while the print head leaves the print area. Is done by.

  According to a further feature of embodiments of the present invention, the step of removing a portion of the gas by the auxiliary suction system is performed to maintain a predetermined level of moisture in the vicinity of the nozzle plate.

  According to a further feature of embodiments of the present invention, the step of intermittently wiping the nozzle plate controls the size of the water droplets on the nozzle plate.

  According to a further feature of an embodiment of the present invention, the step of protecting a portion of the print inkjet head from the heat and gas of the printed circuit board using a shielding mask including an opening is preliminarily applied to moisture in the vicinity of the nozzle plate. Maintain a defined level.

  According to a further feature of the embodiments of the present invention, the amount of gas diffusing near the jet nozzle is controlled by placing the nozzle close to the edge of the opening by means of a shielding mask.

  According to a further feature of embodiments of the present invention, the print inkjet head purge sequence removes the spread of droplets on the nozzle plate.

  Additional features and advantages of the invention will be apparent from the following drawings and specification.

  For a better understanding of the present invention and to show how the same can be implemented, reference will now be made, by way of example only, to the accompanying drawings. In the drawings, like numerals designate corresponding elements or portions throughout.

  Referring now in detail to the drawings, the details shown are by way of example only, and are for illustrative purposes only of preferred embodiments of the invention and are illustrative of the principles and conceptual aspects of the invention. It is emphasized that is also provided for what is considered the most useful and easy description. In this regard, no attempt has been made to show structural details of the invention in more detail than is necessary for a basic understanding of the invention, and the specification incorporated with the drawings is It will be apparent to those skilled in the art how the embodiments of the present invention are actually embodied.

1 illustrates a printing system with an integrated self-purge arrangement, according to an embodiment of the present invention. FIG. 2 shows a second view of a printing system with an integrated self-purge structure according to an embodiment of the present invention. FIG. 6 shows a third view of a printing system with an integrated self-purge structure from the direction in which ink is printed, according to an embodiment of the invention. FIG. 2 shows a front view of a vacuum pipe system for cleaning purged liquid according to an embodiment of the present invention. FIG. 3 shows a side view of a vacuum pipe system for removing purged liquid according to an embodiment of the present invention. Fig. 5 illustrates a mechanism for removing purged liquid according to an embodiment of the present invention. FIG. 3 shows a detailed view of a mechanism for removing purged liquid according to an embodiment of the present invention. FIG. 6 illustrates an elongated void of a printing system and purge printing liquid discharge according to an embodiment of the present invention. Fig. 6 illustrates a mechanism for removing gas from a gap between a print head and a printed circuit board according to an embodiment of the present invention. FIG. 6 illustrates a mechanism for removing a portion of a gas from a gap between a print head and a printed circuit board according to an embodiment of the present invention. Fig. 4 illustrates a gas for wetting a nozzle plate of a print head according to an embodiment of the present invention. Fig. 4 shows a small water droplet formed on a nozzle plate of a print head according to an embodiment of the present invention. Fig. 4 illustrates a large drop of water that may interfere with ink ejection through a nozzle, according to an embodiment of the present invention. Fig. 5 shows an ink drop floating on a small water drop, according to an embodiment of the present invention. Fig. 2 shows an evaporation bath as a source of gas according to an embodiment of the present invention. Fig. 5 shows a nozzle arranged near the edge of a slit according to an embodiment of the present invention. FIG. 3 shows a bottom view of a slit in a nozzle plate according to an embodiment of the present invention. 2 illustrates a printhead assembly with an integrated self-purge and gas removal structure in accordance with an embodiment of the present invention.

  Embodiments of the present invention provide a printing system with an integrated self-purge, anti-sedimentation, and gas removal structure that does not drip purge liquid from the nozzle plate. An integrated self-purge structure is desirable for high quality cleaning that is less costly and reliable than current technology. Among other things, this embodiment facilitates printing while reducing the time it takes to move the print head to the maintenance area compared to the time required for the prior art. In addition, in a multi-head system (or a system having a large number of heads) in which one maintenance area (or maintenance area that is generally smaller than the head) is used for purging, this embodiment reduces the complexity of the system. make it easier. For example, each head (or group of heads) has an integrated self-purge structure that eliminates head competition and adjustment for the maintenance area. Although this embodiment is described with respect to an inkjet printhead, the described system and method are generally applicable to liquid discharge nozzles of liquid discharge mechanisms such as nozzle dispensers.

  In the context of this specification, the terms printing fluid and ink generally refer to materials used for printing, but are homogeneous and non-uniform, such as, for example, a carrier liquid that includes metal particles deposited by the printing process. It is not limited to homogeneous materials.

  According to a first aspect of the present invention, a printhead assembly with an integrated purge mechanism comprises (a) one or more surrounded by a nozzle plate driven by at least first and second pressures. A liquid dispensing head including a dispensing nozzle, and (b) a shielding mask including an opening in front of one or more nozzles, wherein the printing liquid is driven by the first pressure to dispense from the head As the printing liquid is dispensed in pulses through the openings in the shielding mask, and the purge printing liquid is dispensed from the head driven by the second pressure, the purge printing liquid is shielded The opening is configured to be drawn into an elongated gap formed between the mask and the nozzle plate, thereby removing purge printing liquid from nearby nozzles.

  According to an embodiment of the present invention, capillary action is used to capture the printing liquid and to prevent the printing liquid from dripping from the print head to the printed circuit board.

  Capillary action is the property of a liquid being drawn into a small opening. Capillary phenomenon, also known as capillary action, is the result of intermolecular attractive forces inside liquid and solid materials. A well-known example of capillarity is the nature of a dry paper towel that absorbs liquid by sucking it into narrow openings between fibers. Another example is the nature of the liquid rising in a narrow tube. The mutual attractive force that exists between similar molecules in a particular liquid is called aggregation. Aggregation produces a phenomenon known as surface tension. When an attractive force exists between two different materials, eg, a liquid and an edge of a solid container, the attractive force is known as adhesion. Capillary action is the result of the aggregation of liquid molecules and the adhesion of liquid molecules to a space (eg, a space formed by a narrow tube wall). For example, when the edges of a container are brought close together in a narrow tube, liquid is drawn into the space formed by the edges of the container (in the current example, into the narrow tube) due to the cohesive and adhesive interaction. In the context of this specification, the space is formed by an elongated gap between the nozzle and the shielding plate.

  A further aspect of the invention is to prevent deposit buildup on the printhead nozzle plate that uses gas to block or divert the ink jet and to remove some of the gas that has accumulated beneath the printhead on the nozzle plate. Of the method.

  According to a further aspect of the invention, certain embodiments provide a method of printing using an integrated self-purge, anti-sedimentation, and gas removal structure. The method includes: (a) providing a printing system including one or more printhead assemblies including a printhead assembly with an integrated purge mechanism, each printhead assembly including one Or a print head including a nozzle plate with an opening and a printing mask including a nozzle plate with an opening, the opening being aligned with one or more nozzles in the nozzle plate opening and printing an elongated gap (B) activating the print head with a first pressure so that the printing liquid passes through the nozzle plate opening and is discharged from the print head, formed between the head and the print mask. (C) purging by starting the print head with a second pressure, and therefore one step through the second pressure. Other printing liquid discharged through more nozzles are captured by the elongated cavity, comprising the steps.

  According to a further aspect of the invention, the print head is protected from the heat and gas of the substrate by a mask, the mask including a slit through which ink is dispensed onto the substrate. Furthermore, the print head nozzle is located near one edge of the slit, so that most of the gas entering the slit is condensed in the central area of the nozzle plate when viewed through the slit, with only a portion of the gas. Condenses near the edge of the slit.

  Various aspects of the present invention are illustrated herein primarily by reference to non-limiting examples of systems and methods for printing grid-like contacts of solar cells. Various aspects of the invention are equally applicable to a wide variety of other inkjet printing systems.

FIG. 1A shows a first view of a printing system with an integrated self-purge structure, according to an embodiment of the present invention. For convenience, FIGS. 1A and 1B are referred to as front and side views, as appropriate. Note that the figures are not drawn to scale. The inkjet print head (100) includes a nozzle plate (102). Ink is printed from a plurality of nozzles (not shown) in the direction of arrow (108) onto a printed circuit board (not shown) which is the front surface of the polysilicon solar cell. Note that normal use in this field involves many nozzles, but the system can be used with one or more nozzles. For convenience, the direction of ink from the print head to the printed circuit board indicated by arrow (108) is referred to as downward. FIG. 1A shows a plurality of arrows (108) indicating the printing direction of ink from an array of nozzles, while the side view of FIG. 1B shows that only one array is visible from the side view. Only the book arrow is shown. This implementation is characterized by positioning a print mask (104), also referred to herein as a mask, in alignment with the nozzle plate (102) to form an elongated gap (110) between the nozzle plate and the print mask. . During purging, the purged liquid adheres to the surface of the elongated void (110) and capillary action draws the purged liquid into the elongated void.
The nozzles of the print head are aligned with the slits (106) in the print mask (104) to facilitate printing.

  FIG. 1C shows a third view of a printing system with an integrated self-purge structure from the direction in which ink is printed. For convenience, FIG. 1C is also referred to as a bottom view. For reference, the slit (106) has a width (112) and a length (114). The height (116), also called depth, is generally about the same as the thickness of the print mask.

  The print mask (104) is aligned with the nozzle plate (102) and positioned to form an elongated gap (110) between the print mask and the nozzle plate. In the context of this specification, a mask refers to a plate that partially covers the nozzle plate (102) and has openings to facilitate printing from the nozzle to the print area. The nozzle plate (102) is generally used during the printing process to facilitate printing from the nozzles and can also protect the print head (100) and nozzles. During normal operation, the slits (106) in the print mask (104) are wide enough to facilitate printing and are aligned precisely enough to the print nozzles. In the case of an ink jet print head (100), printing is accomplished by nozzles with pulses (not shown) where jet pressure is formed inside the print head (100) by piezoelectric crystals (one piezoelectric crystal for each nozzle). From the ejection of ink droplets. In the ejection, an appropriate pressure is applied to the print head for an appropriate time, so that a droplet of printing liquid (ink) is applied to the print head from the nozzle through an opening (not shown) of the nozzle plate (102). And across the gap (110) and through a slit (106) in the print mask (104) to be released onto a printed circuit board (not shown). In one non-limiting example, a 20 μm wide nozzle is printed through a slit having a width (112) between 100 μm and 300 μm.

  During purging, an appropriate extra pressure is applied to the printing fluid from the outside and through the print head (100) for an appropriate amount of time to force the ink out of the print head through the nozzles. The ink ejected from the nozzles during the purge adheres to the nozzle plate (102) by adhesion (attraction between two different materials as defined below), which in this case wets the nozzle plate. Also known as the nature of ink. Wetting of the nozzle plate occurs even when the nozzle plate is covered with an anti-wetting coating. When arranging the mask (104) close enough to the nozzle plate (102), the mask is also moistened by the ink. By bonding, the ink does not pass through the slit (106). When the mask (104) is properly positioned with respect to the nozzle plate (102), the purged ink tends to be drawn into the elongated void (110) by capillary forces. The edge of the elongated gap (110) shares at least part of the edge of the slit (106). This technique is colloquially "hidden" because purging does not require any additional hardware under the mask (104) (to collect ink that may drip while purging and wiping the nozzle plate). This is called “purge”.

  The size of the elongated void necessary to provide the desired capillary action depends on the particular application, and more specifically on the surface itself and the properties of the liquid. In the context of this specification, reference to the size of the elongated gap refers to the distance between the nozzle plate (102) and the mask (104) unless otherwise specified. In view of the physical characteristics of the printing fluid, nozzle plate, and mask plate, one skilled in the art can calculate the required size of the elongated gap to provide the desired capillary action.

  In a non-limiting example where the nozzle is 20 μm wide, the elongated gap (110) may be as large as 50-500 μm. Within the scope of the above embodiments, the preferred size of the elongated gap (110) is as small as possible, thus allowing the nozzle to be as close as possible to the printed circuit board, facilitating high quality printing. Similarly, the elongated voids should be as small as possible to enhance capillary action. The size of the smallest elongated void depends at least in part on the physical properties of the printing fluid. The size of the elongated gap must be large enough to facilitate printing fluid flow and collection for a particular application. In order to promote capillary action, the purged printing liquid should preferably adhere to at least one of the slit edges (void edges), so that the nozzle is possible at the slit edges. As close as possible, the purged ink must be promoted to adhere to at least one slit edge (the edge of the elongated void). In the present embodiment, it is appropriate that the distance from the nozzle to the slit edge is 50 to 300 μm.

  The slit is preferably large enough to facilitate occasional wiping of the nozzle plate, for example by an elastic thin wiper. In this embodiment, a slit width of 0.7 to 1.5 mm is sufficient. In this case, the nozzle is positioned close to the edge of the slit (as opposed to being positioned in the middle of the slit) to facilitate the purged printing fluid adhering to the edge of the slit. Is preferred.

  Similarly, the mask (104) needs to be thick enough to provide the required mechanical strength and heat transfer (dimension 116) so that the nozzles are as close as possible to the printing surface. It is preferable to be as thin as possible. After purging, the delay provides sufficient time for almost all of the purged liquid to flow from the nozzle plate (102) to the elongated void (110). In a non-limiting example, after purging the inkjet head, a delay of 2-8 seconds is sufficient to remove the ink from the nozzle plate and provide high quality cleaning. After the delay, the print head is ready to be used for printing.

  It is desirable that both the nozzle plate and the inside of the printing mask (in this context, the side of the printing mask facing the nozzle plate) be covered with an anti-wetting coating. The anti-wetting coating reduces the tendency of the printing fluid to adhere to the surface of the nozzle plate and the inside of the print mask. The purged printing liquid needs to be removed from the elongated gap, in other words, needs to be cleared from the elongated gap. The frequency with which the elongated gap is cleaned depends on the application. In one case, the elongated gap is cleaned after every purge. The implementation of the cleaning system depends on the application.

  2A and 2B show a front view and a side view, respectively, of a vacuum pipe system for removing purged liquid, where the vacuum pipe system (200) includes a mask (104) covering a portion of the slit (106). Shown below. In this case, the vacuum pipe system (200) includes a vacuum head (202) that moves along the slit (106) from below. The vacuum head (202) connects to or is part of a tube (204) that is connected to a pump (not shown). A vacuum, for example a vacuum of -0.4 to -0.8 bar, is applied to the tube (204) by the pump, and the pressure gradient force is passed through the slit (106) from the elongated gap (110) to the arrow (206). Aspirate the purged liquid in the direction.

  Since the vacuum head (202) can be firmly attached to the floor of the mask (104) covering the slit (106), the suction of the vacuum head is mainly from the slit, while the vacuum head does not contact the nozzle plate. As can be seen from FIG. 2B, the vacuum head (202) contacts the mask (104) and covers the width of the slit (106). In contrast, in the conventional vacuum wiping technique described above, the vacuum head does not come into contact with the nozzle plate, which reduces the cleaning efficiency of the nozzle plate. In the present embodiment, the nozzle plate (102) is cleaned during or after the purge, and when the purged ink is drawn into the gap by capillary action with high cleaning efficiency, the vacuum pipe system (200). Drains the liquid purged from the elongated gap (110) by the slit (106). In another embodiment, cleaning of the nozzle plate (102) may be performed during or after the purge by a vacuum pipe system (200) that discharges the purged liquid from the nozzle plate by a slit. Furthermore, the cleaning time is shortened as compared with the conventional vacuum wiping. Vacuum pipe systems are known in the art, and based on this description, one skilled in the art will be able to implement a vacuum pipe system appropriate for the application.

  The above method is effective. However, in certain cases, it is preferable to clean an elongated gap without a system element under the print mask. This feature is desirable when the head is on the printing surface during cleaning and printing speed is increased by facilitating shortening the time required for maintenance.

  FIG. 3 shows a mechanism for removing purged liquid, wherein the print head further includes a print head housing (300), also known as a housing, which partially includes the print head (100). Enclose. Note that in the art, the printhead housing (300), often referred to as a "mask", should not be confused with the mask (104) used herein. The housing (300) includes a side portion (302) surrounding the side of the print head (100). The bottom portion (304) of the housing (300), also known as the floor, functions as a mask (104) and partially surrounds the nozzle plate (102). The housing (300) includes one or more suction ports (306) connected to a vacuum system (310). The suction port (306) facilitates the purged liquid being sucked out of the housing from the elongated gap (110). The vacuum system (310) can be implemented similarly to the vacuum pipe system (200) described above without having to move the vacuum head (202) of the vacuum pipe system. The vacuum system (310) can remain connected to the housing (300).

  In one non-limiting example, the system purges and then the vacuum system (310) is operated. In this case, the purged liquid is drawn into the elongated gap as described above. At the measurement time after the purge is complete, the vacuum system (310) is activated and drains the purged liquid from the housing as described above. In another non-limiting example, the vacuum system (310) operates during the purge. In this case, the purge will apply additional pressure to the capillary action, helping to prevent the purged liquid from dripping and promoting a quick purge, thereby reducing the cleaning time compared to the above techniques. It is more efficient in terms of shortening. In contrast, conventional purge techniques purge from all nozzles at the same time, so vacuum wiping cannot be performed during the purge, while the vacuum head moves across the nozzle plate. Then, vacuum wiping is performed by a vacuum head that covers only a part of the nozzles at a time. In an optional embodiment, the vacuum system (310) can operate independently of capillary action during or after the purge, and purged liquid is ejected from the nozzle plate by the air gap (110). Optionally, the purged liquid can be recycled from the vacuum system through an appropriate filtration system to the ink supply system. Vacuum systems are known in the art, and based on this description, one skilled in the art can implement a vacuum system (310) appropriate for the housing (300) and application.

  FIG. 4 shows a detailed mechanism for removing purged liquid, wherein the housing (300) further includes a cooling water channel (400) through which the cooling liquid passes. Depending on the application, the print head (100) and / or the housing (300) can become hot by printing, for example to cool the system from damage and / or to maintain print quality. It may be necessary to be done. Generally, the heat source is external to the housing (300), which protects the print head (100) from thermal damage. In a non-limiting example, the main heat source is a printed circuit board directly under the housing (300), such as a solar cell silicon wafer on which metal wires are printed. The solar cell silicon wafer may enter the printing area after being warmed to 250 degrees Celsius. This temperature may be required to evaporate a liquid carrier of metal particles including ink such as silver particles. In this case, the housing (300) functions as a thermal barrier that prevents heat from the solar cell wafer from reaching the nozzle plate (102) of the print head (100). In one optional embodiment, the cooling water channel (400) has a path for the coolant. The coolant circulates through the path appropriate for the application to cool the system. The housing (300) may be constructed from aluminum, copper, or other material suitable for the application, preferably a material that is a good thermal conductor.

  In a non-limiting example, the housing (300) is made from aluminum and the print head (100) is an inkjet head. Referring to FIGS. 1A, 1B, and 1C, the slit (106) has a width (112) of 0.3 millimeters (mm). The slit width may be small or large depending on the application. It is desirable that the slit width be larger than the diameter of the ejected droplets and be large enough to allow for nozzle straightness and placement inaccuracy. In a non-limiting example, if the droplet diameter is 20 μm, the slit width of 50 μm is preferably the minimum width. In cases where the slit is larger than the preferred minimum, the nozzle is brought close enough to the edge (side) of the slit to facilitate the purged liquid adhering to the edge of the elongated void (110). Is desirable. A non-limiting example in this case is when the slit width of 1-2 mm is used instead of the minimum slit width of 0.3 mm, and the nozzles are arranged to be 0.1 mm from the edge of the slit. As described above, once the purged liquid has adhered to the edge of the elongated void (110), capillary action draws the purged liquid into the elongated void behind the mask (104). Note that it is generally sufficient to draw the purged liquid into an elongated gap on one side of the slit, in this case the side closer to where the nozzles are arranged. In an example with a nozzle array that includes two rows of nozzles, the width and placement of the slits can be designed such that each row of nozzles is close to the respective edge of the slit. A slit height (116) of 0.3 mm corresponds to the thickness of the mask and is realized as the floor (304) of the housing (300). The height may be lower or higher depending on the application. The height can be low (for example, 0.2 mm), but is limited by considering the feasibility of implementation. Implementation feasibility considerations include, but are not limited to, a low height corresponding to a thin mask that generally has insufficient thermal conductivity and is susceptible to damage. Higher heights are possible (eg 1 mm), but higher heights include (but are not limited to) implementation feasibility considerations, including the need to significantly separate the printhead and printed circuit board. Which reduces the print quality as described above. The elongated gap (110) between the nozzle plate and the mask is preferably 0.3 mm, but depending on the application, the elongated gap can be from 0.05 mm to about 0.5 mm. The spacing (410) between the side portion (302) of the housing and the print head (100) is preferably 0.3 mm, but depending on the application, the elongated gap can be from 0.1 mm to 1 mm.

  Arrow (402) indicates the direction of flow of the purged liquid. In the plan view of FIG. 4, the arrows indicate the flow left and right away from the slit (106), but in an actual three-dimensional system, the flow was connected from the slit (106) to the vacuum system (310). Note the outward direction to the suction port (306). Cleaning can be initiated by activation of an optional valve Vf of the vacuum system (310) or other means suitable for the application. In an alternative embodiment, the printing liquid ejected from the nozzles adheres to the nozzle plate during purging. The vacuum system (310) applies negative pressure through the gap (110) and removes the purged printing liquid from the nozzle plate (102) by suction.

  FIG. 5 illustrates an elongated void of the printing system and purge liquid drain according to an embodiment of the present invention. A printhead (100) and a housing (300) with optional coolant (400) are shown. The purge liquid (510) passes through the array of nozzles (not shown) and the nozzle plate (102). Purge fluid (510) is drawn into the elongated gap (110) and is exhausted by the vacuum pipe system through the elongated gap (110) and out of the printhead housing (520). The purge liquid may be circulated again and stored in the inner portion of the print head configured to contain the printing liquid.

  The nozzle plate (102) of the inkjet head (100) is often covered with a non-invasive material that does not mix with the printing fluid and prevents the printing fluid from sticking to the plate. As a result, the liquid flowing over the nozzle plate (102) can be easily turned into large droplets (510) that tend to adhere to the nozzle plate and can be removed from the nozzle plate by the elongated gap (110) and the vacuum pipe system.

Ink may accumulate on the nozzle plate (102) in several ways: During purging, the ink flows continuously from the nozzles, and even with the best non-invasive coating, the ink spreads over the nozzle plate rather than dripping out into the air or dropping onto the substrate. 2. An ejected satellite (ie, a very small parasitic droplet with a much larger major droplet containing ejected ink) is vigorous (due to friction with the atmosphere) immediately after rising from the nozzle. , And easily flows backward in the atmosphere to land on the nozzle plate.
3. Part of the ejected ink that affects the substrate returns to the nozzle plate and sticks to it like a ricchet. 4). In particular, when printing on a heated substrate, the printing fluid solvent deposited on the substrate quickly evaporates, producing a solvent vapor gas that condenses on the cold nozzle plate (102).

  When printing with a printing fluid containing solid particles ("ink"), such as, but not limited to, a particularly preferred example of printing using conductive metal particles such as silver, the presence of ink on the nozzle plate can lead to enormous problems. Sometimes. Specifically, when the ink on the nozzle plate may be dried, a layer of particles is deposited on the surface. Over time, multiple such layers may accumulate. These layers reduce the non-invasive surface properties of the nozzle plate and, when constructed sufficiently close to the nozzle, directly reduce the print quality and, as a result, can cause the nozzle to become completely clogged. is there.

  According to a further aspect of the invention, such deposition of particles is eliminated by ensuring that the liquid vapor is in close proximity to the nozzle plate so that any ink present on the nozzle plate does not dry. Or reduced. The ink that is still wet is then periodically removed by mechanical wiping or suction to prevent material from accumulating on the nozzle plate. In particular, in the preferred case of printing on a hot substrate such as a heated semiconductor wafer, the solvent vapor is essentially generated from the ink deposited on the substrate. However, excess vapor causes large droplet accumulation on the nozzle plate, which itself interferes directly with the printing process. Therefore, this aspect of the present invention removes excess steam, leaving enough steam in the immediate vicinity of the nozzle plate without forming large droplets so that any ink on the surface does not dry out. Provide a management system (or “gas”).

  Assuming the printhead includes an array of nozzles, there are two ways to control the amount of gas: exhausting part of the gas through an auxiliary vacuum opening before the gas reaches the nozzle area; The second method refers to the case where the head is protected from the heat and gas of the substrate by a mask, which includes a slit through which ink is dispensed onto the substrate. In such a case, most of the gas entering the slit condenses in the central region of the nozzle plate as viewed from the slit, and only a small amount of gas condenses near the edge of the slit. To take advantage of this phenomenon in accordance with certain preferred implementations of the present invention, the mask slits are positioned so that the nozzles of the print head are near one edge of the slits. This positioning of the nozzle near one edge of the slit is also advantageous for the aforementioned capillarity uptake during the purge process, so that the droplets formed at the nozzle during the purge process In contact with the elongated gap to ensure that it is drawn into the gap.

  FIG. 6A illustrates a mechanism for removing excess gas from the gap between the print head and the printed circuit board according to an embodiment of the present invention. After the printing fluid is released from the print head (100) through the nozzles in the nozzle plate (102), the gas (610) formed by the hot substrate (620) assists through the print head housing (300). Removed by suction system.

  FIG. 6B illustrates a mechanism for removing a portion of the gas from the gap between the print head and the printed circuit board in accordance with an embodiment of the present invention. A portion of the gas (610), typically 90% of the gas, is exhausted by the auxiliary suction system (640) and the remainder of the gas (615) accumulates on the nozzle plate (102). At very low gas pressures, the nozzle plate is gradually covered by ink droplets and thus by solid precipitates contained in the ink, for example silver particles. Due to the high gas pressure, the droplets of the printing liquid may aggregate and deflect or block the nozzles of the nozzle plate (102).

  FIG. 7 illustrates gas that wets the nozzle surface of the print head, in accordance with an embodiment of the present invention. Part of the gas (615) accumulates in the nozzle plate (102).

  According to the embodiment of the present invention, since deposition of a solid precipitate is prevented by maintaining moisture of the nozzle plate, the accumulated ink is removed by a service action using an absorbent sponge or the like. Can be wiped off intermittently. Repeated friction will cause the non-invasive coating of the nozzle plate to be decomposed. In accordance with the present invention, since the ink on the nozzle plate is prevented from drying, the time between successive mechanical wiping of the nozzle plate can be reduced with conventional systems that rely solely on wiping without controlling the steam. In comparison, it may be greatly increased.

  FIG. 8 shows small droplets formed on the nozzle surface of the print head according to an embodiment of the present invention. The non-invasive coating applied to the nozzle plate (102) prevents large droplets from sticking to the nozzle plate surface. However, hot gas (615) generated from the printed image (660) of the hot substrate forms small droplets (670) on the nozzle plate surface (102).

  FIG. 9 shows a large droplet that obstructs the ejection of ink through a nozzle, in accordance with an embodiment of the present invention. The small droplets (670) shown in FIG. 8 collect and clump together on the nozzle plate surface (102) to form a few large droplets (680) that deflect the inkjet and nozzle nozzles on the nozzle plate with too high gas pressure. May even block.

  FIG. 10 shows ink droplets floating in small droplets according to an embodiment of the present invention. Experiments show that if the nozzle plate is wet with small droplets (670), the printing fluid that contacts the nozzle plate with large droplets (690) does not leave a trace of solid precipitate on the nozzles. I understood. This means that the intimate contact of the solid material in the ink to the surface of the nozzle plate is a transparent liquid that spreads across the nozzle plate, acting as a buffer between the solid particles (or dissolved material) and the nozzle plate This can be explained in terms of being prevented by the layer. Close contact may be prevented if the ink does not actually contact the nozzle plate, but rather depends on a small droplet of clear liquid. The last sentence may explain the fact that even ink drops that stick to the nozzle plate do not leave a solid precipitate once removed. According to an alternative hypothesis, the ink droplets (690) sticking onto the nozzle plate do not contaminate the nozzle plate because a clear liquid spray or gas or vapor after the ink droplets have accumulated on the nozzle plate. This is to prevent the solid matter from being continuously supplied on the nozzle. The ratio of the exhausted gas to the gas stored in the nozzle plate (102) can be controlled by those skilled in the art depending on the efficiency of the auxiliary suction system. According to embodiments of the present invention, a small amount of gas on the nozzle plate prevents the accumulation of both precipitation and printing liquid droplets, as previously described herein.

  FIG. 11 shows an evaporation tank as a gas supply according to an embodiment of the present invention. While the head exits the print area (700), the gas (615) may be generated, for example, by a warm pool of volatile liquid (665) just below the head. This option is particularly useful in situations where printing is performed on a cold (unheated) substrate, and thus the printing process does not produce essentially enough gas to maintain the desired amount of moisture on the nozzle plate. Is suitable.

  Wetting the nozzle plate may be required between each printing pass (eg, each printed page). However, it may be sufficient to wet the nozzle plate only once before and after purging, or before and after any other maintenance operation. In this case, moistening is not performed as often as necessary. Another embodiment is the liquid vapor on the nozzle plate or between the printing operations (e.g., different intermediate pages in 2D printing, or layers in 3D printing, or wafers in printed metal lines on solar cells). Spraying or directing steam.

  Assuming the printhead includes a nozzle array, there are two ways to control the amount of gas: exhausting a portion of the gas through an auxiliary vacuum opening before the gas reaches the nozzle area; The second method refers to the case where the head is protected from the heat and gas of the substrate by a mask, which includes a slit through which ink is dispensed onto the substrate. In such a case, most of the gas entering the slit condenses in the central region of the nozzle plate as viewed from the slit, and only a small amount of gas condenses near the edge of the slit. Thus, the head is positioned behind the mask so that the nozzle approaches one edge of the slit.

  FIG. 12 shows a nozzle placed close to the edge of the slit, in accordance with an embodiment of the present invention. An inkjet (715), typically having a diameter of 20 μm, is shown passing near the slit edge.

  FIG. 13 shows a bottom view of the slits of the nozzle plate according to an embodiment of the present invention. The mask (720) has an opening in the form of a slit (730), and a nozzle plate (102) is shown directly below the slit. Since the slit (730) is off-center with respect to the nozzle (750), the distance from the nozzle to one edge of the slit is less than 20% of the distance from the nozzle to the opposite edge of the slit. Such an arrangement of nozzles (750) is described. The condensed droplets (760) aggregate at approximately the center of the slit (730), and only a small portion of the droplets with a small diameter reach the slit edge where the array of nozzles (750) is located.

  FIG. 14 illustrates a printhead assembly with an integrated self-purge and gas removal structure in accordance with an embodiment of the present invention. An auxiliary suction system (640) is installed to maintain a predetermined level of moisture in the vicinity of the nozzle plate (102). The auxiliary suction system (640) removes most of the gas (695) while a small amount of gas (615) reaches the nozzle plate (102). The elongated void (110) draws large droplets of purge printing liquid (510) that is removed by a vacuum pipe system (not shown). The suction system applies a pressure gradient to the elongated void (110), thereby removing purge printing liquid (510) from the elongated void (110). The purge printing liquid (510) may be circulated again to the inner portion of the print head configured to contain the printing liquid.

  The frequency of purging depends on the particular application for which the print head is being used. In one embodiment, the purge is initiated periodically as a step in a continuous printing process. In another embodiment, the purge is initiated according to a predetermined schedule, and in another embodiment, the purge is initiated based on system requirements. One non-limiting example of system requirements uses an inspection camera to track print quality. If the print quality does not meet the given parameters, a purge is started.

  Embodiments of the present invention facilitate efficient printing sequences and maintenance cycles, utilize purging without dripping, and cleaning without the inclusion of system elements under the printing mask. In one embodiment of the purge maintenance cycle, during continuous printing, the print head stops printing and stays in place on the printing surface. A purge starting from 0.2 seconds to 0.5 seconds is started. After purging, the delay of about 5 seconds allows enough time for almost all of the purged liquid to flow from the portion of the nozzle plate aligned with the slit to the gap between the nozzle plate and the mask. provide. Operation of the vacuum system for 1-3 seconds provides pressure to aspirate the purged liquid from the gap. Printing can be resumed when suction is complete. Printing can be resumed during suction, as described above, in which case the suction pressure must be verified to be at an appropriate level to allow accurate printing and accurate jetting direction. I must. Printing resumes without a print head that takes time to move from the print area to the maintenance area.

  In an optional embodiment, if the purge is not sufficient to clean the print nozzles and maintain print quality, a vacuum can be applied in the vicinity of the nozzles from a source other than the print head. In contrast to applying positive pressure to the nozzles from inside the print head, applying a pressure gradient can be more effective at opening clogged nozzles. The system described with respect to FIG. 2 can provide the required vacuum of about −0.4 to −0.8 bar to facilitate this method of cleaning the print nozzles.

  According to embodiments of the present invention, the printing system may be used in mass continuous printing, such as when printing solar cell metal contact lines on a conveyor system in a solar cell production line. In normal operation, the conveyor system operates continuously, thus requiring a printing system that operates continuously or with minimal maintenance time. Normally, the conveyor system cannot be stopped to allow printing system maintenance time. Since the print head in the printing system needs to be purged, the conventional solution is to provide an extra second print head to replace the active first print head, and another purge mechanism And a mechanism for moving the print head to the purge area, printing can be continued without stopping the conveyor system.

  With embodiments of the present invention, depending on the details of the application, the active first print head does not have to move the print head to the maintenance area, i.e. without delaying continuous printing, between successive solar cells. In addition, purging can be performed between battery groups within a slight time delay inherent in the battery group. The extra second print head can be activated to ensure continuous printing and the previously active first print head can be quickly purged using embodiments of the present invention. Can help prepare the first print head for quick replacement with the second print head and maintain continuous printing with the required print quality.

  According to embodiments of the present invention, a printing system typically includes at least one processor and a control system configured with appropriate hardware and / or software to coordinate the operation of the printhead ( (Not shown), including various suction systems, steam control structures, and / or cooling systems for performing the various functions described herein.

  Advantageously, the printhead assembly of the present invention is for printing a solar cell grid-like contact on a hot solar cell polysilicon substrate, typically comprising a 50 μm wide line and a 20 μm high line. May be used.

  Another advantage of the printhead assembly described above is that high volume printing is performed continuously when the printhead assembly is purged during printing in the print area without having to move the printhead to the maintenance area. It is good.

  Another advantage of the printhead assembly described above is that the printing fluid evaporates quickly, so that the next printing head releases the printing fluid on the printed silver dry line, and thus If the print line accumulates vertically in the layer on the hot surface and spreads horizontally to a minimum, the metal contact line print formation may be done in one path of the printhead assembly on the substrate. is there.

  Furthermore, the head assembly of the present invention may be used in other ink jet printing applications, such as ink jet printing on paper. Any other application where the printhead requires an efficient purge is within the scope of the present invention.

  In summary, the printhead assembly of the present invention improves upon the prior art solar cell grid-like contact printing inkjet head by introducing self-purge, sediment prevention, and gas removal structures. The printhead assembly may allow for rapid and high quality mass ink jet printing.

  Of course, for clarity, the features of the invention described in the context of separate embodiments may be provided in combination in one embodiment. Conversely, for the sake of brevity, the various features of the invention described in the context of one embodiment may also be provided separately or in any suitable subcombination.

  Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described herein.

  All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the patent specification, including definitions, will prevail. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

  It will be appreciated by those skilled in the art that the present invention is not limited to what has been particularly shown and described herein for steam. Rather, the scope of the present invention is defined by the appended claims, and the various features described above in this specification, as well as combinations and subcombinations of variations and modifications thereof, should be read from the foregoing description. Will be apparent to those skilled in the art.

Claims (17)

A printing system for printing on an object using a mixture of materials comprising metal particles, the system comprising:
A housing for supporting a print head having a plurality of nozzles and disposed in the nozzle region;
A printed circuit board for supporting an object to be printed arranged in a printing region in a step of discharging a printing liquid containing a solvent and metal particles from a nozzle to the printed circuit board to form a plurality of layers;
A shielding mask disposed between the nozzle region and the printing region, the shielding mask including an opening through which a printing liquid discharged toward the printed material passes;
A heat source configured to heat the printed circuit board to generate gas from a solvent of the printing fluid deposited on the printed circuit board; and a gas configured to remove at least a portion of the generated gas from the printing area A gas management system comprising an auxiliary suction system configured to control a ratio of gas removed to gas accumulated in the nozzle area;
Only including,
A printing system further configured to direct steam to the nozzle area between printing layers on the object to maintain the vapor level in the nozzle area at a predetermined level .   The printing system of claim 1, wherein the gas management system is further configured to maintain a vapor level in the nozzle region at a predetermined level to prevent accumulation of metal particles in the nozzle region. The printing system of claim 1 , wherein the auxiliary suction system depressurizes a plurality of nozzles in the range of −0.4 to −0.8 bar.   The gas management system is further configured to remove excess vapor from the print area, leaving sufficient vapor near the nozzle area to prevent the printing liquid from drying in the nozzle area. The printing system described.   The printing system of claim 1, wherein the heat source is located directly under the housing.   The gas management system of claim 1, comprising an auxiliary suction system configured to remove at least a portion of the generated gas from the printing area and maintain the vapor level of the nozzle area at a predetermined level. Printing system. The printing system of claim 6 , wherein maintaining the nozzle area vapor level is performed during a process of forming multiple layers.   The printing system of claim 1, wherein the shielding mask is used to protect the print head from heat of the printed circuit board.   The printing system of claim 1, further comprising a vacuum pipe system for applying reduced pressure in the vicinity of the plurality of nozzles to open the clogged nozzles. A printing method for printing on an object using a mixture of materials comprising metal particles, the method comprising:
Supporting a print head having a plurality of nozzles and disposed in a nozzle region;
Supporting a target to be printed in a process of discharging a printing liquid containing a solvent and metal particles from a nozzle toward a printed circuit board disposed in a printing region to form a plurality of layers;
Discharging printing fluid from the print head through an opening in a shielding mask disposed between the plurality of nozzles and the printing area;
Heating the printed circuit board to generate gas from a solvent of the printing fluid deposited on the printed circuit board;
Using an auxiliary suction system to remove at least a portion of the generated gas from the printing area; and maintaining the vapor level in the nozzle area at a predetermined level;
Only including,
A method of printing, wherein the step of maintaining the vapor level of the nozzle region is performed during a process of forming multiple layers . Maintaining the nozzle area vapor level at a pre-determined level is to remove excess vapor, leaving sufficient vapor near the nozzle area to prevent the printing liquid from drying in the nozzle area. The printing method according to claim 10 , comprising: Removing the first portion of the generated gas from the print area and allowing the second portion of the generated gas to reach the nozzle area, the first portion being the second The printing method according to claim 10 , wherein there are more than the portions. The printing method according to claim 10 , further comprising a step of controlling a ratio of a product gas to be removed to a product gas accumulated in a nozzle region. The printing method according to claim 10 , wherein the shielding mask is used to protect the print head from heat of the printed circuit board. The method of claim 10 , wherein maintaining the vapor level in the nozzle area includes directing the vapor to the nozzle area between printing layers on the object. The printing method of claim 10 , wherein maintaining the vapor level in the nozzle area comprises applying a vacuum near the plurality of nozzles to open a clogged nozzle. 17. A printing method according to claim 16 , wherein the reduced pressure is in the range of -0.4 to -0.8 bar.