The present invention relates to the application of thin fluid coatings to substrates, particularly substrates in the form of indefinite length webs.
Two basic categories of coating application systems are excess coat and wipe systems and pre-metered systems. These systems are different in their method of controlling the amount of coating solution applied to a substrate. In excess coating application systems, an amount of solution in excess of the desired coat weight is applied to the substrate. A metering device then removes the excess coating material from the substrate to achieve the desired coating weight. The excess coating material is returned to the reservoir and reapplied to the substrate as it circulates through the system. Due to reuse of the coating material, it can be easily contaminated and then must be thrown away. When contaminated, the entire system must be cleaned and replenished with new coating material resulting in waste and significant production delays.
In a pre-metered application system, the amount of coating material is accurately measured and applied to the substrate to achieve the desired coating weight. Pre-metered application systems do not require removal of excess coating material from the substrate preventing the contamination issues of excess coat and wipe systems. Pre-metered coating application systems can use various types of coating equipment and smoothing devices, such as knives, blades, rods, or rolls, for evenly distributing the pre-metered amount of coating material after it is applied to the substrate surface. In addition, these systems do not provide for recirculation of the coating solution since none of the solution applied to the substrate is removed from the substrate surface and reused.
Slot coater configurations for pre-metered systems are known. One particular system for applying coating material to substrates includes a slot orifice coater, which is a coater that extrudes a solution through a gap and applies that extruded solution directly from the gap onto a moving substrate. In order to achieve a uniform distribution of coating material across the width of the substrate, it is necessary for the pressure within the slot coater to be relatively constant along the length of the slot. Therefore, slot coaters of this type are typically used with coating materials having high viscosities and being coated at high coating weights. Under these conditions, it is relatively easy to maintain a uniform coating across the web. When these coaters are used with lower viscosity coating materials and/or lower coating weights, it becomes more difficult to maintain uniform velocity and uniform hydrostatic pressure along the length of the slot resulting in non-uniform coating of the substrate.
The inventors have determined that use of a distribution manifold having a plurality of needle tubes for dispensing the coating material significantly improves the coating uniformity across the width of the substrate. Moreover, when the needle tubes can be readily removed and changed, the length and/or diameter of the needle tubes can be sized to improve the cross web uniformity and/or to meter more or less coating material onto the substrate resulting in rapid reconfiguration of the distribution manifold for coating different materials having substantially different viscosities.
Furthermore, the inventors have determined that the needle tubes on the distribution manifold can be inserted into the rolling bank of extruded coating material resulting in better coating uniformity than produced by round multiple orifice (RMO) coating dies as disclosed in U.S. Pat. No. 5,871,585. When the needle tubes are inserted into the rolling bank of extruded coating material, the distribution manifold positioning system can be less precise and less expensive than that of a RMO die for a given coating process.
In one aspect, the present disclosure is directed to a method of applying a coating material onto a substrate comprising: conveying the substrate past a contacting element; providing a distribution manifold having a cavity and a plurality of needle tubes in fluid communication with the cavity, the plurality of needle tubes each having a needle tip for dispensing coating material towards a point of contact between the substrate and the contacting element; and dispensing coating material from the needle tubes at a predetermined rate, the rate being less than or equal to a maximum rate that the interaction between the substrate and the contacting element would permit to pass the point of contact.
In another aspect, the present disclosure is directed to a system for applying a coating material onto a substrate comprising: a contacting element; a web path moving the substrate past the contacting element; a distribution manifold having a cavity and a plurality of needle tubes in fluid communication with the cavity, the plurality of needle tubes each having a needle tip dispensing a coating material towards a point of contact between the substrate and the contacting element; a flow control apparatus metering a flow of the coating material from the needle tubes at a predetermined rate.
In another aspect, the present disclosure is directed to a distribution manifold comprising: a manifold having a coating material inlet feeding an internal cavity and a plurality of conduits extending from the internal cavity, each of the plurality of conduits having their distal end located on a manifold mating surface; a removable cartridge having a body with a cartridge mating surface, a plurality of orifices located in the cartridge mating surface, and a plurality of needle tubes extending from the body in fluid communication with the plurality of orifices; and a clamping mechanism for securing the removable cartridge mating surface to the manifold mating surface such that the plurality of needle tubes are in fluid communication with the plurality of conduits in the manifold.
It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present disclosure, which broader aspects are embodied in the exemplary construction.
Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure.
Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure.
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A sliding spacer bar can be optionally present to reinforce and assist with maintaining the needle tube alignment if desired. The spacer bar can be designed such that it can be clamped into position without crushing the needle tubes. The linear position of the sliding spacer bar along the length of the needle tubes can be adjusted by moving the bar up and down as appropriate and then clamping it into position. The sliding spacer bar can be constructed from multiple segments that attach to a support bar on the opposite side of the needle tubes to change the CD width of the spacer bar. As the substrate width changes, needle tubes may need to be added or removed from the removable cartridge (unused threaded orifices in the removable cartridge being plugged) and the segmented, sliding spacer bar's length can be adjusted accordingly.
The distribution manifold 20 does not have to be divided into the manifold 22 and the removable cartridge 24 and the needle tubes 26 can be directly attached to the manifold; however, a removable cartridge can reduce cleaning and maintenance time. For example, when changing coating materials or colors, the removable cartridge can be removed and capped without flushing the coating material from the needle tubes and internal passages. The manifold can be flushed and a previously capped removable cartridge with a different coating material can be re-installed to quickly change over to a new coating material. Multiple removable cartridges can be provided for coating many different types or colors of coating materials. The removable cartridges can be readily capped and stored filled with the coating material for re-installation and use at a later time.
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A spring plate 35 located between the removable cartridge 24 and the clamp plate 28, which can be attached to the clamp plate in one embodiment, can be used to evenly distribute the clamping force across the width of the removable cartridge 24 and to apply a known clamping force. The clamping force can be calculated based on the spring constant of the spring plate and the allowed deflection of the spring plate as controlled by the length of the spacers 33. In one embodiment, the spring plate 35 produced about 35 pounds of clamping force per linear inch to the removable cartridge 24.
In one embodiment, as best seen in
An embodiment of the distribution manifold 20 also includes an entry port 36 and an exit port 38 for circulating temperature regulating fluid through the manifold 22. This fluid can be used to heat the manifold above ambient temperature in many useful applications of the distribution manifold and the method. If desired, appropriate temperature regulating passages in the removable cartridge 24 can also be provided to circulate the temperature regulating fluid through the removable cartridge. The temperature regulating passages in the removable cartridge can mate with temperature regulating passages in the manifold to circulate the fluid, or additional entry and exit ports can be provided for on the removable cartridge.
Coating material inlet 40 is provided to deliver the coating material that is supplied to the manifold's internal cavity 60 (
In many convenient embodiments, mounts 42 attached directly or indirectly to the manifold 22 will be present to install the distribution manifold 20 into a production line. Positioning mechanisms 44 may be conveniently located between the mounts 42 and the manifold 22 to provide for adjustment of the needle tips 27 in the X, Y, Z, or combinations thereof, directions. In the embodiment illustrated, linear slides are provided between the mounts 42 and the manifold 22 to move the distribution manifold 20 in the machine direction and in the cross machine direction to position the needle tips 27. Hoist points 46 may be present on the removable cartridge 24 for easier installation and removal during coating material changes.
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Desirably, the needle tubes 26 are made from stainless steel hypodermic needle tubing that is manufactured to make medical syringes. Other tubing materials can be used and the cross section of the needle tubes can be circular, square, triangular or other geometric shape. In one embodiment, the cross section of the needle tubes is circular. The internal diameter of the needle tubes and the length of the needle tubes can be selected based on the flow rate of the coating material that is applied, the viscosity of the coating material, and the desired operating pressure when coating material is supplied to the manifold 22. Typically, the internal diameter of the needle tubes is between about 10 mils to about 100 mils (0.25 to 2.54 mm), such as between about 40 mils to about 70 mils (1.02 to 1.78 mm). Selection of the internal diameter of the needle tubes is more a factor of the amount of the coating material to be applied and its viscosity. Not all needle tubes connected to the manifold or removable cartridge need to have the same internal diameter and it is possible to supply more or less coating material at various cross machine direction locations if desired.
The length of the needle tubes 26 can be adjusted to vary the manifold pressure needed to supply the desired amount of the second coating. Typically, the length of the needle tubes is between about 2″ to about 8″ (5.1 to 20.3 cm), such as between about 3″ to about 7″ (7.6 to 17.8 cm). Sufficient length is desired to produce a laminar flow of the coating material in the needle tubes and to produce a minimally diverging stream of the coating material from the tips of the needle tubes as opposed to a spray or droplets such as would be produced by a spray nozzle. The stream can be continuous or intermittent (pulsed) as needed for the coating application.
Longer needle tubes can be required to direct the coating material into a specific location or, in some embodiments, to place the needle tips 27 into a rolling bank of coating material 85 (coating pond) being transferred to the substrate (
The spacing of the needle tubes 26 along the removable cartridge 24 or manifold 22 can be selected to control the uniformity of the coating on the substrate. Additionally, longer spaces or gaps between the needle tubes can be present to create stripes or strips of coating material on the substrate. In general, the spacing between adjacent needles tubes when seeking to produce a uniform coating on the substrate is between about 0.050 in. (0.13 mm) to about 2 in. (5 mm), or between about 0.4 in. (1.0 mm) to about 1.0 in. (2.5 mm). A spacing less than about 0.5 in. generally requires direct attachment of the needle tubes to the manifold or removable cartridge without the use of the coupler illustrated in
It has been determined that better cross machine uniformity of the coating material, as applied to the substrate, occurs in some embodiments when the needle tips 27 are submerged into the rolling bank of coating material as opposed allowing a free fall of the coating material though the air when the needle tips are located above the rolling bank of coating material. Submerging the needle tips in the rolling bank of coating material as described can be done with any of the embodiments illustrated in
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Other modifications and variations to the present disclosure may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present disclosure, which is more particularly set forth in the appended claims. It is understood that aspects of the various embodiments may be interchanged in whole or part or combined with other aspects of the various embodiments. All cited references, patents, or patent applications in the above application for letters patent are herein incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control. The preceding description, given in order to enable one of ordinary skill in the art to practice the claimed disclosure, is not to be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2010/038582 | 6/15/2010 | WO | 00 | 9/20/2012 |