Claims
- 1. A method of coating a web of paper with a liquid coating composition while the web is traveling over a web supporting surface, the method comprising the steps of:
- distributing coating liquid onto the web through an application zone of a short dwell time applicator, having a doctor blade at its rear edge and an overflow plate at its front edge and laterally spaced side edges;
- applying said doctor blade against the coating liquid on the supported web for doctoring the coating liquid on the supported web at the rear edge of the application zone to form on the traveling web a layer of coating liquid, wherein machine direction streaks are formed in the layer of coating liquid; and
- at a location spaced downstream and outside of the application zone, doctoring the layer of coating liquid having the machine direction streaks formed therein to remove excess coating liquid from the web and with it the machine direction streaks to level and smooth the coating liquid retained on the web to a final wet film thickness and smoothness.
- 2. The method of claim 1, wherein the step of distributing coating liquid onto the web comprises the step of forming and maintaining a reservoir of coating liquid on the web in the application zone between the rear and side edges thereof, the web moving through the application zone at a speed that is sufficiently high to create a turbulence in the coating liquid being applied to the web, the turbulence in the coating liquid causing the machine direction streaks formed in the layer of coating liquid.
- 3. The method of claim 2, wherein the step of doctoring the layer of coating liquid having the machine direction streaks formed therein is performed at a location that is physically and hydrodynamically isolated from the application zone and the turbulent coating liquid contained within the application zone.
- 4. The method of claim 1, further comprising the step of moving the web at a speed greater than about 3,000 feet per minute.
- 5. The method of claim 1, wherein a distance between a point where the coating liquid is doctored to produce the layer of coating liquid having machine direction streaks to a point where the layer of coating liquid having machine direction streaks is doctored, is within a range of about 4 to 24 inches.
- 6. The method of claim 1, wherein a time period from when the coating liquid is doctored to produce the layer of coating liquid having machine direction streaks until the layer of coating liquid having machine direction streaks is doctored, is equal to about 0.003 to 0.040 seconds.
- 7. The method of claim 1, wherein a thickness of the coating liquid applied to the web in the step of doctoring the coating liquid to produce the coating layer having machine direction streaks is between about 0.0010 and 0.0040 of an inch greater than the final wet-film thickness.
- 8. A method of applying coating liquid to a supported, moving web of paper comprising the steps of:
- applying an initial amount of coating liquid to the supported web in an application zone of a short dwell time applicator, the application zone having spaced front and rear edges defined by a doctor and a plate, respectively, and laterally spaced side edges, the initial amount of coating liquid applied to the supported web including an excess amount of coating liquid to be removed and a final amount of coating liquid to remain on the web for producing a desired final coating layer thickness and surface smoothness on the paper web;
- doctoring the coating liquid on the web at the rear edge of the application zone to remove a majority of the excess amount of coating liquid; and
- subsequently, at a location spaced downstream of the application zone, removing a remaining amount of the excess amount of coating such that a coating layer of the desired final thickness and surface smoothness remains on the web.
- 9. The method of claim 8, wherein the step of applying the initial amount of coating liquid comprises the step of forming and maintaining a reservoir of coating liquid on the web in the application zone between the rear and side edges thereof, the web moving through the application zone at a speed that is sufficiently high to create a turbulence in the coating liquid being applied to the web, the turbulence in the coating liquid causing machine direction streaks in the coating liquid remaining on the web as the web leaves the application zone.
- 10. The method of claim 9, wherein the step of doctoring the layer of coating liquid to remove the majority of the excess amount of coating liquid is performed at a location that is physically and hydrodynamically isolated from the application zone and the turbulent coating liquid contained within the application zone.
- 11. The method of claim 8, further comprising the step of moving the web at a speed greater than about 3,000 feet per minute.
- 12. The method of claim 8, wherein the step of doctoring the coating liquid on the web to remove the majority of the excess amount of coating liquid produces a generally uniform and relatively quiescent layer of coating liquid having a wet film thickness that exceeds the final amount of coating liquid required for achieving the final wet film thickness by an amount equal to about 0.25 to about 0.75 gallons per minute per inch of blade width.
- 13. The method of claim 8, wherein an amount of coating liquid removed in the step of subsequently doctoring the coating liquid remaining on the supported web is between about 0.267 and 0.318 gallons per minute per inch of web width.
- 14. The method of claim 8, wherein an amount of coating liquid applied to the web in the step of doctoring the coating liquid on the web to remove the majority of the excess amount of coating liquid is about two to ten times a final coat weight of the coating liquid applied to the web in the step of subsequently doctoring the coating liquid remaining on the supported web.
- 15. The method of claim 8, wherein the majority of the excess amount of coating liquid removed in the step of doctoring the coating liquid to remove the majority of coating liquid is equal to about 65 to 75 percent of volume of the initial amount of coating liquid applied to the web.
- 16. The method of claim 8, wherein the final amount of coating liquid applied to the web is equal to about 4 to 10 percent of volume of the initial amount of coating liquid applied to the web.
- 17. The method of claim 8, wherein the initial amount of coating liquid applied to the web is equal to about 25 to 85 bone dry pounds per 3300 square foot ream.
- 18. The method of claim 8, wherein the final amount of coating liquid applied to the web is equal to about 5 to 15 bone dry pounds per 3300 square foot ream.
- 19. A method as set forth in claim 8, wherein said subsequent removing step is carried out utilizing a doctor blade.
- 20. A method of producing coated paper, wherein the method includes the steps of:
- applying coating liquid to a supported, moving paper web in a short dwell coating liquid application zone having a front edge defined by an overflow plate, and a rear edge and side edges, the web moving through the application zone at a speed that is sufficiently high to create a turbulence in the coating liquid being applied to the web;
- applying a doctor blade against the coating liquid on the supported web for doctoring the turbulent coating liquid on the supported web at the rear edge of the application zone so as to form a layer of coating liquid on the web as the web leaves the application zone, the turbulence in the coating liquid causing machine direction streaks in the layer of coating liquid as the web leaves the application zone; and
- at a location spaced downstream from the rear edge of the application zone and outside of the application zone away from the turbulent coating liquid in the application zone, doctoring the layer of coating liquid to remove excess coating liquid from the web to level and smooth the coating liquid retained on the web to a final web film thickness and smoothness.
- 21. A method as set forth in claim 20, comprising the additional step of supercalendering after the leveling and smoothing of the coating liquid.
- 22. A method as set forth in claim 21, wherein the step of doctoring the coating liquid on the web at the rear edge of the application zone comprises the step of doctoring the coating liquid so that about 0.25 to about 0.75 gallons per minute per inch of web width remains on the web.
- 23. The method of claim 21, wherein both of the doctoring steps and the supercalendering step results in the paper having a smoothness of about 1.32 Parker Printsurf smoothness and a gloss in excess of 70 TAPPI 75.degree. gloss regardless of web speed.
- 24. The method of claim 20, further comprising the step of moving the web at a speed greater than about 3,000 feet per minute.
- 25. The method of claim 20, further comprising the step of forming and maintaining a reservoir of coating liquid on the supported web within the application zone by substantially sealing the side edges of the application zone to the web and by forming a liquid seal between the liquid in the application zone and the surface of the web in the vicinity of the gap between the web and the front edge of the zone.
- 26. The method of claim 25, further comprising the step of continuously flowing an excess of coating liquid through the application zone for purging the zone, for forming and maintaining the liquid seal, and for excluding air and foreign matter from the coating liquid adjacent the rear edge of the zone.
- 27. The method of claim 20, wherein the step of doctoring at the rear edge of the application zone occurs within about 0.004 to about 0.0100 of a second after the coating liquid is applied to the web within the application zone.
- 28. The method of claim 20, wherein the step of doctoring the coating liquid to the final web film thickness and smoothness occurs within about 0.003 to about 0.040 of a second after the step of doctoring at the rear edge of the application zone.
Parent Case Info
This application is a continuation of U.S. Ser. No. 07/881,677, filed May 12, 1992, now abandoned, which is a continuation-in-part of application Ser. No. 07/648,655, filed Jan. 31, 1991 now U.S. Pat. No. 5,112,653, which, in turn, is a continuation-in-part of application Ser. No. 07/375,241, filed Jul. 3, 1989, now abandoned, of the same title and by the same inventors, for which as to common disclosures, the benefit of the earliest filing dates is claimed.
US Referenced Citations (9)
Foreign Referenced Citations (2)
Number |
Date |
Country |
0403845 |
Dec 1990 |
EPX |
0436172 |
Jul 1991 |
EPX |
Non-Patent Literature Citations (1)
Entry |
Eklund, et al "The Characteristics of Flow in a Short-Dwell coater" Tappi Journal May 1986, pp. 56-58. |
Continuations (1)
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Number |
Date |
Country |
Parent |
881677 |
May 1992 |
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Continuation in Parts (2)
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Number |
Date |
Country |
Parent |
648655 |
Jan 1991 |
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Parent |
375241 |
Jul 1989 |
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