WO2004052562A1

WO2004052562A1 - Shart dwell coater using sonic rods

Info

Publication number: WO2004052562A1
Application number: PCT/US2003/038696
Authority: WO
Inventors: Wayne A. Damrau
Original assignee: Stora Enso North America Corp.
Priority date: 2002-12-06
Filing date: 2003-12-05
Publication date: 2004-06-24
Also published as: AU2003298932A1

Abstract

A method and apparatus is disclosed wherein a short dwell time applicator (1,2) (SDTA) or film coater which is used to coat a moving surface (4), be it a roll surface or a moving board or web, is fitted with one or more sonic rods (7) at or near the coater’s overflow gap (11) to keep the gap (11) clear and improve coating application.

Description

Shart Dwell Coater Using sonic Rods

This United States PCT application is a continuation-in-part of United States provisional application Serial No. 60/431,259, filed December 6, 2002, of the same title and by the same inventor on which a claim of priority and benefit of filing date is made. This invention relates to method and apparatus for a short dwell time applicator, having an overflow gap and sonic rods, and more particularly, to utilizing a sonic rod in such type coater to keep the gap clean and/or clear.

Background of the Invention

Heretofore, it is known to construct and use short dwell time applicators ("SDTA") to coat a moving surface be it a paper or board web, say moving on a back roll, or a roll surface which subsequently transfers the coating to a paper or board web. See U.S. Patents 4,250,211 and 5,112,653, which are hereby incorporated by reference. The gap in these coaters over a period of time of operation tended to partially close or clot up causing irregularities in the coating supply and subsequent coating on the web or sheet. Also, the paper industry has long sought ways to make the integral wetting of the paper sheet or board more consistent.

It is also known to construct an improved type SDTA, having a curved surface and curved flow modifier therein, shown in co-pending application, Serial No.

09/859,061, filed on May 16, 2001, by the same inventor as the present application and assigned to the same assignee as the present application, which are hereby incorporated by reference.

It is also known to use a sonic rod in a coater to keep a surface clear or clean as shown in co-pending Provisional application, Serial No. 60/421,214, filed on October 25, 2002, by the same inventor as the present application and assigned to the same assignee as the present application. Neither of these copending applications are prior art to the present application. To the extent permissible, said Provisional application and/or any subsequently filed non-provisional applications/issued patents thereon are hereby incorporated by reference. Summary of the Invention

The present invention is a method and apparatus for a short dwell time applicator (SDTA) which has an overflow gap. In the present invention, one or more sonic rods are fitted to the SDTA coater at the overflow gap to cause sonic vibrations to keep that gap clear or clean. The sonic rod also helps more uniformly wet the moving surface, be it a roll surface or a moving board or paper web.

Additionally, the sonic rod's vibrations at the gap can free up, reduce and/or collapse air bubbles in the coating and/or on the moving surface, be it roll surface or paper or board web. The SDTA that can be adapted to utilize the present invention could be of the conventional type, such as shown in U.S. Patent 4,250,211 or of the type previous to the filing date of this application sold by Voith Sulzer, Valmet or Beloit and their predecessors or successors, or could be of the improved type shown in my U.S. Patent application, Serial No. 09/859,061. The invention could also be used in connection with film coaters which apply coating to a roll surface for subsequent transfer to a web.

As the sonic rod operates at certain frequencies and has nodes, continually varying the frequency to vary node position is advisable, especially when only one rod is used. Also, to minimize the effect of the nodes on the coating, two or more sonic rods may be used, operating at different frequencies. Thus, the nodes of each of the sonic rods is masked by the other (one or more) sonic rods. Further to assist in and speed up changes should a sonic rod need be replaced, they may be built, made or slid into a retainer or cartridge. Thus, the sonic rod can simply be changed out by changing the entire cartridge which could hold one or more sonic rods. Description of the Drawing

Figure 1 is a full size (as filed), schematic, cross-sectional elevational view of an SDTA similar to that shown in U.S. Patent No. 4,250,211 but fitted with a sonic rod to keep the coater's overflow gap clear.

Figure 2 is a full size (as filed), schematic, cross-sectional elevational view of an SDTA of the type shown in my said Provisional Application Serial No. 60/421,214 but fitted with a sonic rod to keep the coater's overflow gap clear.

Figure 3 is a view similar to Figure 1, but showing more than one sonic rod. Figure 4 is a partial sectional view similar to Figure 2 showing how one or more sonic rods can be fitted or slid into a retainer or cartridge to simplify servicing/replacement of sonic rods.

Figure 5 is a partial sectional view showing how one or more sonic rods can be fitted into the flow modifier of a coater similar to that shown in Figure 2. Description of the Preferred Embodiment

This invention relates to modifications to coaters of the SDTA type coating applicators. More specifically, to the addition of sonic or ultrasonic rods to the orifice plate tip of SDTA type coating applicators, to apply energy to the coating materials being applied to a moving surface, be it paper, board or roll surface, as where an SDTA applies coating to a roll surface (film coater), and it is subsequently transferred to a paper or board web.

The sonic or ultrasonic rods may be of the type known as Sonotrode, made by the Martin Walter Company of Europe. They are composed of an ultrasonic generator with automatic frequency control and amplitude adjustment. PZT high output converters are used in cooperation with the Sonotrode rod to provide the sonic or ultrasonic energy to the coating material. It is believed that incorporating these rods into the SDTA design, including of the film coater type, will allow a smaller gap between the orifice tip and the surface to which coating is being applied without the gap becoming plugged from dried coating materials. A smaller gap would allow lower recirculation rates of coating materials being supplied to the coating applicator, reducing the size of the coating supply system, i.e., pumps, tanks, coating filters, etc., and thus reducing entrained air in the coating supply reducing coating skip. A smaller gap would also produce a more even contact line of the coating application and therefore a more uniform dwell time laterally across the coated width of the machine. All of these points should produce a more uniformly coated surface, and reduced costs of installation and operation.

With reference to the attached drawings, the concept will be understandable to one skilled in the art of coating application. Figure 1 shows a sonic or Sonotrode rod incorporated into a conventional

SDTA that does not have a curved lip and/or a flow modifier. The main beam 1 of the SDTA supports the coating applicator laterally across the coating machine and forms one wall 1 A of the coating application. The assembly 2 generally forms the other wall 2A of the applicator. The coating supply enters the applicator upward between the two walls 1A and 2A. Coating material is applied to the traveling paper or board web. A web 4 is supported on the rotating backing roll 5 or in the case of a film coater, is applied directly to the outer roll surface itself. A doctor 6, be it blade (as in Figure 1) or doctor roll, smoothes and levels the desired coating weight onto the web or roll surface. The doctor also removes any excess coating from the web or roll surface and allows the excess coating to be recirculated with the fresh incoming coating material. The sonic or Sonotrode rod 7 forms the orifice tip on assembly 2. Elastomeric potting material 8 which holds the Sonotrode rod in place, but yet allows it to vibrate. See below for further details. A sonic rod mount 9 is bolted laterally with bolts 9A to movable support or orifice plate 3. Moving the plate 3 upward narrows the gap 11, while lowering it widens the gap 11.

Figure 2 is a cross-section of an SDTA with a curved wall and flow modifier in the coating path, as well as a sonic or Sonotrode rod at the orifice tip. The Sonotrode rod should perform as stated in the previous paragraph. Referring to Figure 2, generally the main beam 21 of an SDTA forms one wall 21 A and supports the coating applicator laterally across the coating machine. An element or front wall 22 provides an opposite sidewall 22A and is hinged at its low end (not shown) to the main beam for support. Coating material is pumped in the direction shown between the two walls 21A and 22A. A doctor 37, be it doctor roll, or blade, as shown, levels and smoothes the desired amount of material onto the roll surface or board or paper web 30 as shown, and removes any excess coating from the web. The excess material is then circulated (as shown by the arrow), merged and then reapplied with the fresh incoming coating supply. As mentioned, element 23 is part of the pivoted wall structure that is hinged to the main beam 21. The member, or orifice plate 24 is slidably attached to 23. A sonic rod mount 25 is attached to the plate 24 with, in this instance, bolts 26. A flow modifier 27 is mounted, here bolted, to the mount 25. A sonic rod or Sonotrode rod 28 is potted in a soft elastomeric material 29, such as silicone rubber, polyurethane or similar material, to allow the sonic rod or Sonotrode rod to vibrate at its designed amplitude and frequency. The amplitude of the Sonotrode rod should be operated in its range, which here is in the range of 10 microns amplitude with a frequency in the range of 20,000 Hz. As stated previously, coating material is pumped upward between the walls 21A and 22A as shown to apply it to the paper or board web or roll surface 30, which is traveling on or forms the outer surface of the rotating bacldng roll 31. It should be understood that the coating could be applied directly to a roll surface as in a film coater. Two gaps, 32 and 33, can be adjusted in relation to the paper surface supported on the rotating roll or roll surface itself. These gaps can be adjusted by moving plate 24 upward, to narrow the gaps or downward to widen the gaps. Gaps 32 and 34, can be adjusted by loosening the bolt 35, then adjusting setscrews 36, and then by retightening the bolt 35.

It is known that the Sonotrode rod develops nodes where there is no vibration. To prevent streaking at each node, the nodes can be varied along its length by changing frequency constantly. Also, the nodes can be masked or minimized by using two or more, like shown in Figure 3, parallel Sonotrodes with different complementing frequencies, i.e., by alternating the node positions. Figure 3 shows this multiple sonic rod or Sonotrode concept in the environment of a coater similar to that in Figure 1. Similar reference numerals are used in Figure 3 as in Figure 1, except as there are two Sonotrodes, there are two number "7's."

The Sonotrode rods may produce heat when operating. It is thought that the coating material flowing over them may provide sufficient cooling for them. Should this cooling be insufficient, additional cooling may be provided by providing cooling channels in their supports. These supports are shown at reference numeral 9 in Figures 1 and 3 and 25 in Figures 2 and 4. Optional cooling channels 12 are shown in dashed lines in Figure 3. Similar cooling channels could be provided in any of the other embodiments.

Referring to Figure 4, as it is similar to Figure 2, similar reference numerals are used. It should be understood that the Sonotrodes could be potted into a holder, retainer or cartridge 13 and then this assembly of the sonic rod, potting and retainer or cartridge be supported laterally across the coating applicator in a support such as shown at reference numerals 9 and 25 (Figure 2). The retainer 13 could be formed of plastic, such as polycarbonate, or metal, such as steel, stainless steel or aluminum. The retainer 13 could be held in place in a complementary groove 13 A by a plurality of, say set screws 15. This construction would make it easier to change the Sonotrode rod when worn out or damaged. The retainer, holder or cartridge could be used with more than one Sonotrode and/or any of the other embodiments shown and in the film coater version.

Referring to Figure 5, it is similar to Figure 2, the same reference numerals are used. It should be understood that a sonic rod or Sonotrode rod 28' could be incorporated into the flow modifier 27', shown in Figure 5. Locating the Sonotrode into this part laterally across the coating applicator and in a similar position relative to the web as it is when at the orifice tip may also improve the coating uniformity and evenness of the coating on the web or roll surface. Again, this type coater (Figures 2 or 5) could also have, instead of the sonic rod or Sonotrode rod 28', a similar or multiple sonic rods described in conjunction with Figure 3. Also the Sonotrode 28' could utilize the cartridge concept of Figure 4.

Again, it should be appreciated that one or more of the concepts described could be combined into a coater like that shown in any of these drawings and/or any other similar type coaters. For example, the cartridge concept, multiple sonic rods or Sonotrodes could be incorporated into a jet type coater such as that shown in U.S. Patent No. 5,968,270 and/or disclosed in my provisional application, Serial No. 60/421,214, field on October 25, 2002.

It should also be noted that any type doctor could be used, be it blade, bent or flexible, or doctor roll, plain or grooved. As is conventional, the doctor roll may be rotated to move in a direction opposite that of the moving surface, be it roll surface, paper or board. The doctor roll could also be of the type shown in my copending Provisional application, Serial No. 60/421,214, filed October 25, 2002 having a rear support to limit backward and/or upward movement of the doctor roll.

These discussed and other advantages should be apparent from the above disclosure and accompanying drawings.

While the Sonotrode rod has been mentioned, it should be understood that other sonic or ultra sonic type vibrating rods or devices may be used. While specific elements and steps have been described, it should be understood that equivalent elements and steps will fall within the scope of the following claims.

Claims

What Is Claimed Is:

1. An applicator having an overflow gap and is used to apply coating to a moving surface for coating one of paper or board, comprising a coater body forming an overflow gap with the moving surface, and a sonic rod located adjacent said overflow gap for causing vibrations from said sonic rod to keep the overflow gap clear, whereby coating can be transferred to the moving surface with the overflow gap free of obstructions.

2. An applicator as in Claim 1, wherein said sonic rod is continuously operated.

3. An applicator as in Claim 1, wherein said sonic rod is operated at varying frequencies.

4. An applicator as in Claim 1, wherein said sonic rod is operated intermittently.

5. An applicator as in Claim 1, wherein a plurality of sonic rods are used in the applicator.

6. An applicator as in Claim 1, wherein said sonic rod is contained in a retainer or cartridge, and said applicator has means for receiving said retainer or cartridge.

7. An applicator as in Claim 6, wherein said means for receiving is a cooperating groove in said applicator.

8. An applicator as in Claim 6, wherein said retainer or cartridge contains two or more sonic rods.

9. An applicator as in Claim 1, wherein said applicator is a short dwell time applicator and said sonic rod is located adjacent said overflow gap of said short dwell time applicator.

10. An applicator as in Claim 9, wherein said moving surface is a web and said sonic rod is adjacent said web.

11. An applicator as in Claim 10, wherein said web is a board web and said sonic rod is adjacent said board web.

12. An applicator as in Claim 10, wherein said web is a paper web, and said sonic rod is adjacent said paper web.

13. An applicator as in Claim 1, wherein said applicator is a film coater, and operates on a roll surface, said sonic rod being adjacent said roll surface.

14. An applicator as in Claim 13, wherein said roll surface carries coating for coating a board web, and said sonic rod keeps said gap of said applicator for coating said board web clean.

15. An applicator as in Claim 13, wherein said roll surface carries coating for coating a paper web, and said sonic rod keeps said gap of said applicator for coating said paper web clean.

16. An applicator as in Claim 11, wherein said sonic rod has an amplitude of about 10 microns.

17. An applicator as in Claim 16, wherein said sonic rod has a frequency of about 20,000 Hz.

18. An applicator as in Claim 17, wherein said sonic rod is a Sonotrode rod.

19. An applicator as in Claim 16, wherein said sonic rod is a Sonotrode rod.

20. An applicator as in Claim 6, wherein said retainer or cartridge contains one or more sonic rods, said moving surface being a web and said sonic rod is adjacent said web, said sonic rod having an amplitude of about 10 microns and a frequency of about 20,000 Hz.

21. An applicator as in Claim 6, wherein said retainer or cartridge contains one or more sonic rods, said applicator being a film coater and operates on a roll surface, said sonic rod being adjacent said roll surface, said sonic rod having an amplitude of about 10 microns and a frequency of about 20,000 Hz.

22. The method of operating a coater having an overflow gap for coating a moving surface, comprising the steps of: supplying coating under pressure to the overflow gap; overflowing coating out of the overflow gap; locating a sonic rod adjacent to overflow gap; and operating said sonic to keep the overflow gap clear, whereby the moving surface may be coated with the overflow gap free of obstructions.

23. The method of Claim 22, comprising: operating the sonic rod with amplitude of about 10 microns.

24. The method of Claim 22, comprising: operating the sonic rod at a frequency of about 20,000 Hz.

25. The method of Claim 22, comprising the steps of locating more than one sonic rod in the coater.

26. The method of Claim 25, comprising the step of operating each sonic rod at a different frequency.

27. The method of Claim 26, comprising the step of varying the frequencies.

28. The method of Claim 22, comprising the step of operating the sonic rod at varying frequency.

29. The method of Claim 22, comprising the step of locating the sonic rod in a retainer or cartridge and then installing the cartridge or retainer in the coater.

30. The method of Claim 22, comprising the step of removing the cartridge or retainer to change out the sonic rod and replace it.

31. The method of Claim 29, comprising the step of locating two or more sonic rods in said retainer.

32. The method of Claim 22, wherein said coater is a short dwell time applicator coating having an overflow gap for coating a moving web surface, comprising the steps of locating one or more sonic rods in the coater, locating the one or more sonic rods in a retainer or cartridge.

33. The method of Claim 22, wherein said coater is a film coater having an overflow gap for coating a moving roll surface and subsequently transferring the coating to a paper/board web, locating one or more sonic rods in the coater, locating the one or more sonic rods in a retainer or cartridge.