METHODS AND SYSTEMS FOR COATING A FOIL

Abstract

In a coating system, two rollers are arranged adjacent to one another. A donor foil with rheological material dispensed thereon is advanced through a gap between the two rollers. Such gap spreads the dispensed material over the donor foil, coating the donor foil with a layer of the material with a uniform thickness associated with the gap width. Each roller is supported on a holder. Adjustment of the gap width may be effected by keeping the position of one of the holders fixed, while horizontally translating the position of the other holder. The position of the translatable holder may be adjusted by pistons and linear actuators. The pistons may bias the moveable holder towards the stationary holder. The linear actuators mounted on the moveable holder may extend respective arms against the stationary holder, thereby countering the biasing of the pistons and pushing the moveable holder away from the stationary holder.

Claims

1. A coating system, comprising: a dispensing unit arranged to apply a material on a first foil advanced through a first gap between a first roller supported by a first holder and a second roller supported by a second holder, the first gap being associated with a thickness of a layer of the material applied on the first foil; a first linear actuator mounted on the second holder for adjusting a position of a first arm; a second linear actuator mounted on the second holder for adjusting a position of a second arm; a first piezoelectric sensor mounted on the first holder for detecting contact of the first arm on the first piezoelectric sensor; a second piezoelectric sensor mounted on the first holder for detecting contact of the second arm on the second piezoelectric sensor; and a controller configured to control the first and second linear actuators so as to adjust a position of the second roller relative to a position of the first roller, thereby adjusting a width of the first gap between the first roller and the second roller.

2. The coating system of claim 1, further comprising: a first displacement sensor mounted on the second holder, the first displacement sensor configured to measure a first distance between the first displacement sensor and the first holder; and a second displacement sensor mounted on the second holder, the second displacement sensor configured to measure a second distance between the second displacement sensor and the first holder.

3. The coating system of claim 1, further comprising a second foil for protecting a surface of the second roller.

4. The coating system of claim 3, further comprising a third and fourth roller separated from one another by a second gap that is larger than the first gap, the first foil contacting the first and third rollers and the second foil contacting the second and fourth rollers.

5. The coating system of claim 1, wherein the first holder is stationary and the second holder is movable with respect to the first holder.

6. The coating system of claim 1, wherein the material comprises a liquid, a paste, an adhesive or a polymeric solution.

7. The coating system of claim 1, wherein the first and second rollers are made from metal, ceramic, plastic or rubber.

8. The coating system of claim 1, further comprising a first motor for rotating the first roller about an axis of the first roller and a second motor for rotating the second roller about an axis of the second roller.

9. The coating system of claim 1, further comprising a cleaning system disposed adjacent to each of the first and second rollers, wherein the cleaning system comprises a knife, a scraper, or a sponge with solvent.

10. The coating system of claim 1, further comprising an ultrasound transducer disposed adjacent to at least one of the first roller or second roller.

11. A method comprising: applying a material by a dispensing unit on a first foil; advancing the first foil through a first gap between a first roller supported by a first holder and a second roller supported by a second holder, the first gap being associated with a thickness of a layer of the material applied on the first foil; adjusting a position of a first arm by a first linear actuator mounted on the second holder; adjusting a position of a second arm by a second linear actuator mounted on the second holder; detecting, by a first piezoelectric sensor mounted on the first holder, contact of the first arm on the first piezoelectric sensor; detecting, by a second piezoelectric sensor mounted on the first holder, contact of the second arm on the second piezoelectric sensor; and controlling the first and second linear actuators so as to adjust a position of the second roller relative to a position of the first roller, thereby adjusting a width of the first gap between the first roller and the second roller.

12. The method of claim 11, further comprising advancing a second foil through the first gap with the second roller so as to remove residue on the second foil from a previous coating or to recover unused material on the second foil.

13. The method of claim 11, further comprising: maintaining the first holder in a stationary position; and moving the second holder with respect to the first holder.

14. The method of claim 11, further comprising: measuring, by a first displacement sensor mounted on the second holder, a first distance between the first displacement sensor and the first holder; and measuring, by a second displacement sensor mounted on the second holder, a second distance between the second displacement sensor and the first holder.

15. The method of claim 11, wherein the material is a liquid, a paste, an adhesive or a polymeric solution.

16. The method of claim 11, further comprising: a rotating the first roller by a first motor about an axis of the first roller; and a rotating the second roller by a second motor about an axis of the second roller.

17. The method of claim 11, further comprising removing residual material from the first and second rollers with cleaning systems, wherein each of the cleaning systems comprises a knife, a scraper, or a sponge with solvent.

18. The method of claim 11, further comprising vibrating the first roller or second roller with an ultrasound transducer.

19. The method of claim 11, further comprising: prior to advancing the first foil through the first gap, positioning the second roller to contact the first roller; and measuring, by a displacement sensor mounted on the second holder, a distance between the displacement sensor and the first holder.

20. The method of claim 11, further comprising: prior to advancing the first foil through the first gap, positioning the second roller to contact the first roller; extending the first arm until the contact of the first arm on the first piezoelectric sensor is detected; and at a moment the contact of the first arm on the first piezoelectric sensor is detected, recording a position of the first arm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention illustrated by way of example, and not limitation, in the figures of the accompanying drawings, in which:

[0021] FIG. 1 depicts a top view of a coating system, in accordance with one embodiment of the invention.

[0022] FIG. 2A depicts a simplified side view of the coating system showing a dispensing unit dispensing material onto a donor foil that is advanced through a gap between two rollers, in accordance with one embodiment of the invention.

[0023] FIG. 2B depicts a more complete side view of the coating system, in accordance with one embodiment of the invention.

[0024] FIG. 3 depicts a simplified side view of the coating system showing possible horizontal and vertical adjustment in the positions of the upper pair of rollers, in accordance with one embodiment of the invention.

[0025] FIG. 4 depicts a simplified side view of the coating system showing possible rotational movement of the lower pair of rollers, in accordance with one embodiment of the invention.

[0026] FIGS. 5A-5B depict the calibration of the coating system, in accordance with one embodiment of the invention.

[0027] FIGS. 6A-6C depict the operation of the coating system to transition between a coating step (with narrow gap width) and a foil retraction step prior to recoating (with wider gap width), in accordance with one embodiment of the invention.

[0028] FIG. 7 depicts one or more optional ultrasound transducers for improving the coating quality when highly viscous materials are used, in accordance with one embodiment of the invention.

[0029] FIG. 8 depicts an optional cleaning system for reducing the frequency of maintenance of the coating system, in accordance with one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0030] In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. Descriptions associated with any one of the figures may be applied to different figures containing like or similar components.

[0031] Before describing the invention in detail, it is helpful to present an overview. FIG. 1 depicts a top view of the coating system 100 that contains several components for accurately controlling the width of the gap 16 between a pair of rollers 14a, 14b. Such width is associated with a thickness of a coating that is formed on a donor foil 10 as that foil 10 is advanced through the gap 16.

[0032] Roller 14a may be held stationary in the horizontal direction by a holder 22a, and may be rotated about its axis by motor 28a. The other roller 14b may be supported by another holder 22b, and similarly may be rotated about its axis by motor 28b.

[0033] In contrast to roller 14a, roller 14b can be translated in the horizontal direction, and the translation in the horizontal direction may be controlled as follows. A force may be constantly exerted by pistons 32a, 32b on holder 22b in the direction towards holder 22a, which biases roller 14b towards roller 14a. A pair of linear actuators 24a, 24b may be mounted on the holder 22b for adjusting a respective position of the arms 25a, 25b. While the arms 25a, 25b are in contact with holder 22a (or a component rigidly mounted to holder 22a), retraction of the arms 25a, 25b allows the biasing of pistons 32a, 32b to take effect, narrowing the width of gap 16. While the arms 25a, 25b are in contact with holder 22a (or some component rigidly mounted to holder 22a), extension of the arms 25a, 25b counteracts the biasing by the pistons 32a, 32b, increasing the width of gap 16. As shown in FIG. 1, each of the arms 25a, 25b may be disposed beyond one end of the roller 14b, or stated another way, the roller 14b may be disposed between the two arms 25a, 25b.

[0034] Piezoelectric sensors 30a, 30b may be mounted on the holder 22a for detecting an initial contact of the respective arms 25a, 25b on the piezoelectric sensors 30a, 30b. Knowledge of such initial contact is important as the length of the arms that coincides with such initial contact will correspond with a zero distance in the width of gap 16. Thereafter, an increase in the length of the arms 25a, 25b by a certain distance will translate into an increase in the width of gap 16 by the same distance. As the change in the length of the arms 25a, 25b may be an output of the linear actuators 25a, 25b, the distance of the gap 16 may be inferred based on the knowledge of such initial contact and the subsequent change in the length of the arms 25a, 25b.

[0035] The distance of the gap 16 may further be inferred based on the measurements of one or more distance sensors 26a, 26b mounted on holder 22b. In one embodiment, each distance sensor 26a, 26b may transmit a laser beam 27a, 27b, and the distance between the distance sensor 26a, 26b and the holder 22a may be computed based on the round trip time of the laser beam 27a, 27b and the speed of light. The use of distance sensors 26a, 26b will be more fully explained in connection with FIGS. 5A-5B and 6A-6C.

[0036] An ultrasonic transducer 34 may be used to drive the dispensed material from the center of the donor foil 10 towards to the sides of the donor foil 10. The ultrasonic transducer 34 will be described in more detail below in FIG. 7.

[0037] A controller 50 is further depicted in FIG. 1. While not depicted in detail, it is understood that such controller 50 may be communicatively coupled to the components depicted in FIG. 1 (e.g., linear actuators 24a, 24b, distance sensors 26a, 26b, motors 28a, 28b, piezoelectric sensors 30a, 30b, and ultrasonic transducer 34). For example, the controller 50 may be configured to control the linear actuators 24a, 24b so as to adjust a position of roller 14b relative to a position of roller 14a, thereby adjusting the width of the gap 16 between these rollers 14a, 14b. Further, controller 50 may be configured to receive distance measurements from the distance sensors 26a, 26b. Further, controller 50 may be configured to receive the respective length of the arms 25a, 25b or the relative change in the respective length of the arms 25a, 25b from the linear actuators 24a, 24b. Further, controller 50 may be configured to receive measurements from the piezoelectric sensors 30a, 30b that indicate whether a contact has been formed between the arms 25a, 25b and the piezoelectric sensors 30a, 30b. Further, controller 50 may control the operation of motors 28a, 28b in order to rotate the rollers 14a, 14b during a cleaning operation. Further, controller 50 may turn the ultrasonic transducer 34 on or off.

[0038] FIG. 2A depicts a simplified side view of the coating system 100 showing a dispensing unit 38 dispensing material 40 onto a donor foil 10 that is advanced through the gap 16 between the above-described rollers 14a, 14b. A cleaning foil 12 may be present to protect the surface of roller 14b. In the event that material 40 adheres to the cleaning foil 12 in the proximity of gap 16 (e.g., residual material that is left over from a coating operation), roller 14b may be rotated to advance a clean section of the cleaning foil 12 next to the gap 16. Such ability of the cleaning foil 12 may be particularly useful if the coating system 100 is used to form coatings of different types of materials 40, so that the coating of one material does not contaminate the coating of another material in a subsequent coating step.

[0039] Rollers 18a, 18b may be disposed above the rollers 14a, 14b for creating a tapered constriction 23. That is, the width of the gap 21 between rollers 18a, 18b may be greater than the width of the gap 16 between rollers 14a, 14b, thereby creating a tapered constriction 23 between the two foils 10, 12, which allows a better coating to be formed on the donor foil 10.

[0040] In one embodiment, the rollers 14a, 14b are stationary during the coating phase, and are only rotated during a cleaning phase. Therefore, during the coating operation, rollers 18a, 19 and 20 may be rotated about their respective axes in order to advance the donor foil 10 through the gap 16 and towards a print area (not depicted). As in known in the art, in the print area, a laser may be used to jet material from the donor foil 10 towards a receiver substrate in a laser-enhanced jetting printing process. The number of the rollers may depend on other design parameters of the coating system 100. Some designs will need more rollers than others while some designs will not need rollers 18a, 18b, 19, and 20 at all.

[0041] FIG. 2B depicts a more complete side view of the coating system 100. As shown, a vertical offset may be present between the rollers 14a, 14b and the distance sensors 26a (26b not visible in FIG. 2B). A vertical offset may be present between the rollers 14a, 14b and the linear actuators 24a (24b not visible in FIG. 2B). Similarly, a vertical offset may be present between the rollers 14a, 14b and the piezoelectric sensors 30a (30b not visible in FIG. 2B). As shown in FIG. 2B, gap 16 may be the smallest distance separating roller 14a from roller 14b.

[0042] FIG. 3 depicts a simplified side view of the coating system 100 showing possible horizontal and vertical adjustment in the respective positions of the rollers 18a, 18b. By changing the position of the rollers 18a, 18b, the shape of the tapered constriction 23 formed by the foils 10, 12 may be adjusted. Adjusting the rollers 18a, 18b in the horizontal direction may create a wider or narrower mouth of the tapered constriction 23, while adjusting the rollers 18a, 18b in the vertical direction may adjust the volume of the material 40 in the tapered constriction 23. Both of those adjustments (i.e., horizontal and vertical) are important to the coating process and the desired adjustments will depend on the particular material 40 that is used, in which more viscous materials tend to work better in narrower constrictions 23.

[0043] FIG. 4 depicts the rotation of the rollers 14a, 14b about their respective axes during a cleaning operation. As previously described, each roller 14a, 14b may be stationary during the coating process to provide the best coating quality. However over time, some material 40 may flow out of the tapered constriction 23 and contaminate the rollers 14a, 14b. If the contamination is widespread, the operator will need to clean it, but if only a small amount of material 40 has contaminated the rollers 14a, 14b, the rollers 14a, 14b can be rotated so that uncontaminated regions of the rollers 14a, 14b are used to form the gap 16. The rollers 14a, 14b still may require periodic cleaning by a human operator to remove the contaminants from the rollers 14a, 14b, but the time between such periodic human cleaning may be increased.

[0044] Another approach to address this issue is presented in FIG. 8, in which a cleaning system 36a, 36b is disposed adjacent to each of the rollers 14a, 14b (i.e., on their respective sides facing away from the gap 16). In one embodiment, each of the cleaning systems 36a, 36b can be a scraper or knife that removes residual material from the rollers 14a, 14b. In another embodiment, each of the cleaning systems 36a, 36b can include a sponge and a reservoir of solvent to clean the rollers 14a, 14b from time to time. Such cleaning systems 36a, 36b may be particularly needed with low viscosity materials that will tend to more frequently flow out of the tapered constriction 23 or to remove reactive materials such as epoxies that can progressively and/or permanently damage the rollers 14a, 14b if not removed in a timely manner.

[0045] FIGS. 5A-5B depict the calibration process of the system. As shown in FIG. 5A, to find the starting position of the holder 22b, the respective arms 25a, 25b of the linear actuators 24a, 24b are retracted, and the pistons 32a, 32b are used to push the moveable holder 22b towards the stationary holder 22a. Once the rollers 14a, 14b are in contact with one another, the starting position of the holder 22b is reached, and the displacement sensors 26a, 26b may be used to measure respective starting distances d.sub.a, d.sub.b between the displacement sensors 26a, 26b and the holder 22a.

[0046] Next, as shown in FIG. 5B, the arms 25a, 25b of the actuator 24a, 24b are extended until they contact the piezoelectric sensors 30a, 30b. Once the piezoelectric sensors 30a, 30b detect the contact of the arms 25a, 25b, such lengths of the arms 25a, 25b may be recorded as the starting lengths l.sub.a, l.sub.b of the arms. In another embodiment, the moment the distance sensors 26a, 26b measure the respective distances deviating from the respective starting distances d.sub.a, d.sub.b, such lengths of the arms 25a, 25b may be recorded as the starting lengths l.sub.a, l.sub.b of the arms. In another embodiment, once the piezoelectric sensors 30a, 30b detect the contact of the arms 25a, 25b (or the distance sensors 26a, 26b measure the respective distances deviating from the respective starting distances d.sub.a, d.sub.b), the lengths of the arms 25a, 25b may be set to a relative zero value (similar to the process of taring a scale), in which case l.sub.a and l.sub.b are set to zero.

[0047] To adjust the width of the gap 16 to a desired width value, w.sub.1, the coating system 100 may rely upon one or more of the starting distances d.sub.a, d.sub.b measured by the distance sensors 26a, 26b and the starting lengths l.sub.a, l.sub.b of the arms 25a, 25b. In the former case, linear actuator 24a may adjust arm 25a until the distance measured by distance sensor 26a equals d.sub.a+w.sub.1, and linear actuator 24b may adjust arm 25b until the distance measured by distance sensor 26b equals d.sub.b+w.sub.1. In the latter case, linear actuator 24a may adjust arm 25a until the length of the arm 25a equals l.sub.a+w.sub.1, and linear actuator 24b may adjust arm 25b until the length of the arm 25b equals l.sub.b+w.sub.1. FIG. 6A depicts the gap 16 of the coating system 100 after it has been adjusted to the desired width, w.sub.1, and such width may be maintained during the coating of donor foil 10 with material 40.

[0048] During laser-enhanced printing in the print area, some portions of the material 40 on the donor foil 10 may be jetted from the donor foil 10 onto a receiver substrate, while other portions of the material 40 may remain on the donor foil 10. One approach would be to continue advancing the donor foil 10 past the print area and dispose the material 40 that is left on the donor foil 10. However, this is a wasteful approach and should only be used if speed is the most important parameter of the coating system 100 and the material cost is very low. A better approach to reduce the amount of wasted material would be to attempt to reuse the material 40 that remains on the donor foil 10 after the printing. To that end, the donor foil 10 with the unused material 40 thereon may be returned back into the constriction 23 and together with a small amount of additionally dispensed material 40 from dispensing unit 38, the coating system 100 may form a new coating of material 40 on the donor foil 10 during a recoat process.

[0049] FIG. 6B depicts the configuration of the coating system 100 in preparation for the recoat process in which the pistons 32a, 32b have been retracted while keeping the lengths of the arms 25a, 25b of the linear actuators 24a, 24b unchanged. As shown in FIG. 6B, such retraction of the pistons 32a, 32b increases the gap width to a value w.sub.2 greater than w.sub.1, which allows the donor foil 10 to be more easily retracted back through the gap 16, reducing the possibility for the remaining material 40 on the donor foil 10 to get dislodged onto the rollers 14a, 14b. While the holder 22b is being retracted, the displacement sensors 26a, 26b may be used to verify whether the holder 22b has been fully retracted.

[0050] Once the displacement sensors 26a, 26b have determined that the holder 22b has been fully retracted, the foil 10 may be translated back through the gap 16 to position used areas of the donor foil 10 under the dispensing unit 38, and additional material 40 may be dispensed onto the donor foil 10 by the dispensing unit 38. The pistons 32a, 32b may be re-engaged (i.e., turned on), returning the gap 16 back to the narrow gap width w.sub.1. Advantageously, the respective lengths of the arms 25a, 25b remains unchanged during the re-engaging of the pistons 32a, 32b, allowing the re-positioning of the roller 14b back into the coating position with high precision. The arms 25a, 25b may function similarly to the door stopper on a door. Just as the length of a door stopper fixes a distance between the opened door and a wall, the arms 25a, 25b fixes the width, w.sub.1, of the gap 16 between the horizontally moveable roller 14b and the horizontally fixed roller 14a. Once the gap 16 has returned to the narrow width, w.sub.1, the donor foil 10 may be translated (in the forward direction) through the gap 16 so as to recoat the donor foil 10. The newly dispensed material 40 may be spread over areas of the donor foil 10 where voids of the material 40 had formed due to the printing step, thereby creating another uniform layer of the material 40 over the donor foil 10.

[0051] The recoat process can be efficiently performed only if the gap 16 can be adjusted in a very fast and accurate manner between the width, w.sub.1, during the coating and recoating operations and the wider width, w.sub.2, during the foil retraction operation. To achieve such goal, the holder 22b may be horizontally translated back and forth by pistons 32a, 32b, allowing the holder 22b to be re-positioned in a fast manner between the coating/recoating position and the foil retraction position, as shown in FIG. 6C.

[0052] FIG. 7 depicts an optional ultrasound transducer 34 that can be added to the coating system 100. The ultrasound transducer 34 can be used to create a better coating on the donor foil 10 and is relevant mostly for highly viscous materials. One or more ultrasound transducers 34 may be placed in contact with the gap rollers 14a, 14b. The gap rollers 14a, 14b may transfer such vibration to the donor foil 10 and material 40, enabling a better coating for viscous materials 40 by driving the material 40 from the center of the donor foil 10 (where the material 40 is dispensed onto the donor foil 10) toward its respective sides.

[0053] Thus, methods and systems for coating a foil have been described. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.

LIST OF REFERENCE NUMERALS

[0054] 10 Donor Foil [0055] 12 Cleaning Foil [0056] 14a Roller [0057] 14b Roller [0058] 16 Gap [0059] 18a Roller [0060] 18b Roller [0061] 19 Roller [0062] 20 Roller [0063] 21 Gap [0064] 22a Holder [0065] 22b Holder [0066] 23 Constriction [0067] 24a Linear Actuator [0068] 24b Linear Actuator [0069] 25a Arm [0070] 25b Arm [0071] 26a Displacement Sensor [0072] 26b Displacement Sensor [0073] 27a Laser beam [0074] 27b Laser beam [0075] 28a Motor [0076] 28b Motor [0077] 30a Piezoelectric Sensor [0078] 30b Piezoelectric Sensor [0079] 32a Piston [0080] 32b Piston [0081] 34 Ultrasonic Transducer [0082] 36a Cleaning System [0083] 36b Cleaning System [0084] 38 Dispensing Unit [0085] 40 Material [0086] 50 Controller [0087] 100 Coating System [0088] w.sub.1 Gap width [0089] w.sub.2 Gap width