Process for making coated paper or paperboard

1. A method of producing a coated paper or paperboard, but excluding photographic papers, comprising the steps of:

(a) forming a free flowing curtain comprising at least one layer, whereby a composition forming at least one layer of the free flowing curtain has a Shear-Thickening Index, defined as the ratio of the viscosity at 30,000 s −1 to the viscosity at 3,000 s −1 at 25° C., of at least about 1.2, and wherein at least one layer of the free flowing curtain has a solids content of at least about 30 wt. %, and

(b) contacting the curtain with a continuous web substrate of basepaper and paperboard wherein the continuous web substrate has a velocity of at least about 400 m/min.

2. The method of claim 1 , wherein at least one layer of the free flowing curtain of step (a) has, at a temperature of 25° C. and at a shear rate of 500,000 s −1 , a high shear viscosity of at least about 75 mPa·s.

3. The method of claim 1 , wherein the free flowing curtain of step (a) is a multilayer free flowing curtain.

4. The method of claim 1 , wherein the free flowing curtain of step (a) comprises a top layer ensuring printability.

5. The method of claim 1 , wherein the free flowing curtain of step (a) comprises at least 3 layers.

6. The method of claim 1 , wherein at least one layer of the free flowing curtain of step (a) comprises at least one pigment.

7. The method of claim 6 , wherein the pigment is selected from the group consisting of clay, kaolin, calcined clay, co-structured pigments, talc, calcium carbonate, titanium dioxide, satin white, synthetic polymer pigment, zinc oxide, barium sulfate, gypsum, silica, alumina trihydrate, mica, and diatomaceous earth.

8. The method of claim 6 , wherein the pigment comprises synthetic magadiite.

9. The method of claim 1 , wherein at least one layer of the free flowing curtain of step (a) comprises at least one pigment having an aspect ratio of at least about 1.5:1.

10. The method of claim 1 , wherein at least one layer of the free flowing curtain of step (a) comprises a binder.

11. The method of claim 10 , wherein the binder is selected from the group consisting of styrene-butadiene latex, styrene-acrylate latex, styrene-butadiene-acrylonitrile latex, styrene-acrylate-acrylonitrile latex, styrene-butadiene-acrylate-acrylonitrile latex, styrene-maleic anhydride latex, styrene-acrylate-maleic anydride latex, polysaccharides, proteins, polyvinyl pyrrolidone, polyvinyl alcohol, polyvinyl acetate, cellulose derivatives and mixtures thereof.

12. The method of claim 1 , wherein the free flowing curtain of step (a) has a solids content of at least about 40 wt. %.

13. The method of claim 1 , wherein at least one layer of the free flowing curtain of step (a) comprises at least one optical brightening agent.

14. The method of claim 1 , wherein the free flowing curtain of step (a) comprises at least 4 layers.

15. The method of claim 1 , wherein at least one of the layers of the free flowing curtain of step (a) has a dry coatweight of less than about 10 g/m 2 .

16. The method of claim 1 , wherein the continuous web substrate of step (b) is neither precoated nor precalendered.

17. The method of claim 1 , wherein the continuous web substrate of step (b) has a web velocity of at least about 300 m/min.

18. The method of claim 1 , wherein the continuous web substrate of step (b) has a grammage of from about 20 to about 350 g/m 2 .

19. The method of claim 1 , wherein the free flowing curtain of step (a) comprises at least 5 layers.

20. The method of claim 1 , wherein the free flowing curtain of step (a) comprises at least 6 layers.

21. The method of claim 1 , wherein the continuous web substrate of step (b) has a web velocity of at least about 500 m/min.

22. The method of claim 1 , characterized in that at least one layer of the free flowing curtain of step (a) comprises at least one surfactant.

23. The method of claim 1 , wherein the continuous web substrate has a velocity of at least about 800 m/min.

24. The method of claim 1 , wherein the continuous web substrate has a velocity of at least about 1000 m/min.

25. The method of claim 1 , wherein the curtain is formed with a slot die.

26. The method of claim 1 , wherein the curtain is formed with a slide die.

27. The method of claim 1 , wherein at least one layer of the curtain comprises polyethylene oxide.

28. The method of claim 1 , wherein the curtain comprises polyethylene oxide in the interface layer.

29. The method of claim 1 wherein the contacting in step b) is done under conditions such that the average shear rate at a line where the curtain contacts the substrate is at least 3,000 s −1 .

30. The method of claim 29 wherein the contacting in step b) is done under conditions such that the average shear rate at a line where the curtain contacts the substrate is at least 10,000 s −1 .

31. The method of claim 1 wherein at least one layer of the free flowing curtain of step (a) has, at a temperature of 25° C. and at a shear rate of 500,000 s −1 , a high shear viscosity of at least about 50 mPa·s.

32. A method of producing a coated paper or paperboard, but excluding photographic papers, comprising the steps of:

(a) forming a free flowing curtain comprising at least one layer, whereby a composition forming at least one layer of the free flowing curtain has a Shear-Blocking Behavior, and wherein at least one layer of the free flowing curtain has a solids content of at least about 30 wt. %, and

(b) contacting the curtain with a continuous web substrate of basepaper and paperboard wherein the continuous web substrate has a velocity of at least about 400 m/min.

33. The method of claim 32 wherein the contacting in step b) is done under conditions such that the average shear rate at a line where the curtain contacts the substrate is at least 3,000 s −1 .

34. The method of claim 33 wherein the contacting in step b) is done under conditions such that the average shear rate a the line where the curtain contacts the substrate is at least 10,000 s −1 .