METHOD AND APPARATUS FOR APPLYING A TREATMENT SUBSTANCE ON A RUNNING PAPER WEB OR BOARD WEB

Abstract

Method and apparatus for applying a treatment substance to a running paper or board web comprising an applicator with at least one free-jet nozzle having an outlet gap for applying the treatment substance, being a machine-width, film-like jet, to a moving substrate, in particular at least one applicator roll which transfers the treatment substance to the paper or board web in a treatment nip defined by the at least one applicator roll with a counter element, wherein the free-jet nozzle is positioned at an angle to the moving substrate in such a way that an angle to the perpendicular of an impingement line of the coating on the moving substrate is between 5 and 85, and the intensity of the jet impulse at the impingement line is increased by a gravitational acceleration of the jet caused by an adjustable effective height H from the outlet gap of the free-jet nozzle, and a jet curvature along a path length is modulated via the angle .

Claims

1. Method for applying a treatment substance to a running paper or board web comprising an applicator with at least one free-jet nozzle having an outlet gap for applying the treatment substance, being a machine-width, film-like jet, to a moving substrate, in particular at least one applicator roll which transfers the treatment substance to the paper or board web in a treatment nip defined by the at least one applicator roll with a counter element, wherein the free-jet nozzle is positioned at an angle to the moving substrate in such a way that an angle to the perpendicular of an impingement line of the coating on the moving substrate is between 5 and 85, and the intensity of the jet impulse at the impingement line is increased by a gravitational acceleration of the jet caused by an adjustable effective height from the outlet gap of the free-jet nozzle, and a jet curvature along a path length is modulated via the angle .

2. Method according to claim 1, wherein a jet curvature is determined on a path length by a jet exit angle between an exiting jet at the outlet gap of the free jet nozzle and the tangent at the at least one applicator roll to the impingement line and a jet impingement angle between the tangent of a jet impinging on the applicator roll and the tangent at the applicator roll at the impingement line.

3. Method according to claim 2, wherein the ratio of the jet impingement angle to the jet exit angle from the nozzle is selected in the range between /=1 and 6, preferably between /=1 and 3, in order to adapt the intensity of the jet impulse at the impingement line to specific volume flows of the treatment medium.

4. Method according to claim 1, wherein the angle is adjustable as a function of the web speed, viscosity/solids content, volume flow of the treatment medium.

5. Method according to claim 2, wherein the jet impingement angle is selected in the range between 10 and 90, preferably between 20 and 60, most preferably between 10 and 40.

6. Method according to claim 1, wherein the jet exit angle from the nozzle is selected in the range between 10 and 45, preferably between 15 and 35.

7. Method according to claim 1, wherein the angle a is selected in the range between 0 and 90, in particular between 15 and 45.

8. Method according to claim 1, wherein the treatment medium is starch, a sizing agent or a coating color.

9. Method according to claim 1, wherein the effective height from the outlet gap of the nozzle to the applicator roll and the jet exit angle are selected in such a way that the effective height is between 10 mm and 300 mm, preferably between 10 mm and 100 mm.

10. Method according to claim 1, wherein an apparatus for boundary layer air removal is arranged upstream of the line of impingement of the jet on the applicator roll with a distance of 1 to 100 mm, preferably 10 to 30 mm.

11. Method according to claim 1, wherein the angle to the perpendicular of an impingement line of the coating on the moving substrate is between 30 and 70 and the ratio of the distances H and D at the outlet gap to the impingement line of the impingement position is H/D<3.

12. Method according to claim 1, wherein the application weight of the treatment medium is in the range between 0.2-15 g/m.sup.2 per side of the paper or board web.

13. Method according to claim 1, wherein the paper or board web is coated in an upward or downward direction.

14. Method according to claim 1, wherein the effective height is a vertical height difference between reference horizontal lines, one of which intersects the mouth of the outlet gap of the free jet nozzle and the other of which intersects the impingement line on the surface of the substrate.

15. Apparatus for applying at least one liquid or pasty treatment medium by means of a free-jet applicator to a moving substrate, the substrate being, in the case of direct application, the surface of a paper, board or other fibrous web and, in the case of indirect application, the surface of a transfer element, in particular an applicator roll, which transfers the treatment medium to the surface of the fibrous web, in particular in a treatment nip, and the free-jet applicator having at least one free-jet nozzle which has an outlet gap for discharging a medium jet, which has a free-jet nozzle that transfers the medium jet in a film-like manner onto the surface of the substrate and achieves a desired width of an application layer there in an impingement line, wherein an apparatus for adjusting the intensity of the jet impulse of the medium jet is arranged in the line of impingement, the apparatus being designed as a positioning system for positional and angular shiftings of the free-jet nozzle relative to the substrate, a reference direction for describing the instantaneous spatial and angular position of the free-jet nozzle relative to the line of impingement being given by the gravitational field.

16. Apparatus according to claim 15, wherein for setting a selectable jet curvature on a path length of the medium jet, the positioning system for locational and angular displacements or shiftings of the free-jet nozzle performs a vertical and/or longitudinal adjustment of the free-jet nozzle in the direction of machine travel relative to the substrate in a gravity-oriented reference system.

17. Apparatus according to claim 16, wherein the gravity-oriented reference system defines systems of spatial Cartesian coordinates, of which one origin for the angular displacement or shifting lies in a mouth of the outlet gap of the free-jet nozzle and another for the positional displacement or shifting in the impingement position on the surface of the substrate.

18. Apparatus according to claim 17, wherein the respective X-axis is directed in such a way that a right-hand system or left-hand system is defined and the perpendicular direction is determined by the gravity field-related local perpendicular direction.

19. Apparatus according to claim 15, wherein the free-jet nozzle is arranged at an angle with respect to the local perpendicular direction related to the gravity field, which is in a range from 5 to 85, preferably from 30 to 70.

20. Apparatus according to claim 15, wherein due to the positioning of the free jet nozzle, the impulse force of the jet in the impingement position is selected to be greater, depending on the coating parameters, than an impulse force on the rear side of the jet surface due to a dynamic pressure caused by a boundary layer air on the moving substrate.

Description

[0027] The invention is explained in more detail below using the exemplary embodiments shown in the appended figures.

[0028] FIG. 1 schematically shows a cross-section of a device according to the invention for applying treatment substance or medium using a free-jet nozzle according to a first exemplary embodiment,

[0029] FIG. 2 schematically shows a cross-section of a device according to the invention for applying treatment substance or medium using a free-jet nozzle according to a second exemplary embodiment,

[0030] FIG. 3 schematically shows a cross-section of a device according to the invention for applying treatment substance or medium using a free-jet nozzle according to a third exemplary embodiment,

[0031] FIG. 4 schematically shows a cross-section of a device according to the invention for applying treatment substance or medium by using a free-jet nozzle according to a fourth exemplary embodiment,

[0032] FIG. 5 schematically shows a section of FIG. 1 with a positioning system for locational and angular shifting of a free-jet nozzle relative to a substrate in a gravity-oriented reference system,

[0033] FIG. 6 schematically shows the physical processes in the impingement zone of the parabolic jet on the moving substrate with the impulse force of the boundary layer air (air-pressure S) and the impulse force of the jet perpendicular to the substrate (stabilizing impulse force Fy),

[0034] FIG. 7 shows jet contours for different operating points depending on the speed (m/min) of the substrate and the specific volume flow (l/minm) of a treatment medium,

[0035] FIG. 8 schematically shows a cross-section of a device according to the invention for applying treatment medium by means of a free-jet nozzle according to a fifth exemplary embodiment comprising an additional blow nozzle.

[0036] As FIG. 1 shows, the invention relates to a method for applying a treatment substance or medium to a running paper or board web 9 by means of an applicator with at least one free jet nozzle 1.1, 1.2 having an outlet gap B for applying the treatment medium in the form of a machine-width, film-like jet 2.1, 2.2 to a moving substrate. The moving substrate here is preferably at least one applicator roll 4, 5. The treatment medium is transferred to the paper or board web 9, in particular to the surface of the paper and board web 9, in a treatment nip N, which is formed by the at least one applicator roll 4, 5 with a counter element, which is preferably also an applicator roll 4, 5.

[0037] Here, for example, the treatment medium is first applied to both sides of the rotating applicator rolls 4, 5 using two nozzles 1.1, 1.2. Each of the nozzles 1.1, 1.2 is positioned relative to the respective applicator roller 4, 5 such that an angle a for the impingement position 12 of the coating on the applicator roller 4, 5 is between 0 and 90, preferably between 15 and 45 to the vertical. The angle a is specified relative to the center of rotation of the respective applicator roll 5.

[0038] Furthermore, an air barrier scraper 3.1, 3.2, i.e. a device for combating the boundary layer air carried along by the substrate, is preferably assigned to the coating unit. Without this control device, the stability of the jet 2.1, 2.2 and the coating quality would be impaired due to the influence of the boundary layer air, as already explained above. Such an air barrier scraper 3.1, 3.2 is preferably assigned to each of the nozzles 1.1, 1.2, in order to at least minimize the boundary layer air introduced with the fast-running respective applicator roll 4, 5. The air barrier scrapers 3.1, 3.2 can be in contact with the roll 4, 5 (and thus with the roll surface) under pressure in order to work particularly effectively. Non-contact operation of the scrapers 3.1, 3.2 to prevent wear reduces the effectiveness of the boundary layer air removers, but may be provided, in particular in conjunction with other devices for combating the boundary layer air entrained by the substrate. A boundary layer air extraction system can also be provided as a supplement or alternative, as described below.

[0039] To reduce the boundary layer air, that can reach the applicator unit and negatively affect the applying result, the respective air barrier scraper 3.1, 3.2 is preferably at a distance of 1 to 100 mm, particularly preferably 10 to 30 mm, from the free jet nozzle 1.1, 1.2, i.e. in the direction of rotation upstream of the substrate, in this case the applicator roller 4, 5. This distance is adjustable and is defined according to the invention as the distance L from the scraper 3.1, 3.2 to the impact position 12 of the jet 2.1, 2.2 on the application roller 4, 5 (see FIG. 5). In FIG. 5, the direction of the disturbing air flow is indicated by the arrow 15 and the machine direction of the moving substrate, in this case the applicator roll 5, is indicated by the arrow 14.

[0040] As FIG. 1 shows in combination with FIG. 5, the method according to the invention provides that the respective free-jet nozzle 1.2 is positioned at an angle to the moving substrate, in this case the applicator roll 5, such that an angle to the perpendicular of an impingement line A of the coating on the moving substrate is between 5 and 85, preferably 30 and 70, and the intensity of the jet impulse at the impingement line A is increased by a gravitational acceleration of the jet 2.2 is increased by an adjustable effective height or distance H from the outlet gap B of the free jet nozzle 1.2, whereby the utilization of a jet curvature of the respective jet 2.2 can be modulated over a path length via the angle .

[0041] The distance length is preferably the geometric distance between the measuring points outlet gap B and impingement line A of the impingement position 12. The effective height H is preferably a vertical height difference between reference horizontal lines, one of which intersects the outlet gap B or the mouth of the free jet nozzle 1.2 and the other the impingement line A on the surface of the substrate. The effective height H is then the distance H, as shown in FIG. 5

[0042] For setting a selectable jet curvature on a path length of the medium jet 2.2, a device can be provided as a positioning system for positional/locational displacements 11, 13 and angular adjustments 18 of the free-jet nozzle 1.2 for height adjustment by means of distance H and longitudinal adjustment by means of distance D of the free-jet nozzle 1.2 in the direction of travel 14, in particular the direction of rotation of the roll, relative to the substrate, in particular the applicator roll 5, which is designed in a gravity-oriented reference system, as described below.

[0043] The functional principle on which the method according to the invention is based is further explained with reference to FIG. 5 as follows. The nozzle 1.2 is preferably positioned in the upper position relative to the applicator roll 5. The jet 2.2 is directed from top to bottom. As a result, an additional component of the jet impulse is generated by the effect of gravity. The effect of gravity is indicated by the arrow labeled gravity. The angle to the vertical, which defines the impact position 12 of the coating on the application roller, is approx. 30 to 46 in this example (according to FIG. 5).

[0044] The height, specified as distance H, is a distance that can be adapted from the outlet gap B of the nozzle 1.2 to the applicator roll 5 to the specific volume flow of a treatment medium. A higher position of the nozzle 1.2 generates a larger jet impulse. This is used to remove the boundary layer air at the impingement line A even at higher speeds.

[0045] The ratio of a jet impingement angle to a jet exit angle can have an amount /=1 to 6, preferably 1 to 3. The jet impingement angle lies between the tangent 16 to the applicator roller 5 at the impingement line A and the tangent 19 of the jet 2.2 at the intersection of the impingement line A. The jet exit angle lies between the tangent 16 to the applicator roll 5 at the impingement line A and the center line 17 of the jet 2.2 in the outlet gap B of the nozzle 1.2.

[0046] In embodiment shown in FIG. 5, the jet exit angle is 35, for example, and the jet impingement angle is 58, for example, so that the ratio /=1.7. Due to the angular orientation of the jet 2.2, caused by the modulation of the angle , the resulting impulse force acts in the direction of travel of the roll on impact. In addition to increasing the impulse force, this can prevent the treatment medium, in particular the starch, from splashing back.

[0047] The jet outlet angle can be adjusted via the angular position of nozzle 1.2. The angle of nozzle 1.2 can be adjusted manually or by motor. The jet impingement angle can be determined using a camera and digital image processing, for example. This data can then be used to automatically adjust the jet exit angle .

[0048] The ratio of the height adjustment/length adjustment distances (H/D) characterizes the difference between a jet applicator with free jet nozzle and a curtain applicator. While the ratio is very large in the curtain applicator and normally approaches as the point at which the curtain hits the roll is vertically below the exit point from the nozzle, it is relatively small in the jet applicator and is preferably below 3.

[0049] Typical values for common operating points and commercially available starches are between 1 and 2.

[0050] Consequently, the method according to the invention can be designed in such a way that a jet curvature is determined over a path length by a jet exit angle between an exiting jet 2.1, 2.2 at the exit gap B of the free jet nozzle 1.1, 1.2 and the tangent 16 on the at least one application roller 4, 5 to the impingement line A and a jet impingement angle between the tangent 19 of a jet 2.1, 2.2 impinging on the applicator roll 4, 5 and the tangent 16 on the applicator roll 4, 5 at the impingement line A.

[0051] The ratio of the jet impingement angle to the jet exit angle from the nozzle 1.1, 1.2 can be selected in the range between /=1 and 6, preferably between /=1 and 3, in order to adapt the intensity of the jet impulse at the impingement line A to specific volume flows of the treatment medium. The jet impingement angle can be set as a function of the web speed, viscosity/solids content, volume flow of the treatment medium. The jet impingement angle can be selected in the range between 10 and 90, preferably between 10 and 60, and particularly preferably between 20 and 40. The jet exit angle from the nozzle 1.1, 1.2 can be selected in the range between 10 and 90, preferably between 10 and 45, and particularly preferably between 15 and 35. The angle a can be selected in the range between 0 and 90, preferably between 15 and 45.

[0052] The application medium can be starch, a sizing agent or a coating color.

[0053] The distance H from the outlet gap B of the nozzle 1.1, 1.2 to the substrate, in particular to the applicator roll 4, 5, and the jet outlet angle can be selected in such a way that the effective height H is between 10 mm and 300 mm, preferably between 10 mm and 150 mm, and particularly preferably between 25 mm and 100 mm.

[0054] A device 3.1, 3.2 for boundary layer air removal can be arranged upstream of the impingement line A of the jet 2.1, 2.2 on the substrate, in particular the applicator roll 4, 5, with a distance L of 1 to 100 mm, preferably 10 to 30 mm. The paper or board web speed can be between 250 m/min and 2000 m/min, preferably between 600 m/min and 1800 m/min. The outlet gap B of the nozzle 1.1, 1.2 can be 100-500 m. The weight of the treatment medium can be in the range between 0.2-15 g/m.sup.2 per side of the paper or cardboard web. Starch with a solids content of between 6% and 35%, preferably between 15% and 35%, and particularly preferably between 10% and 25%, and a viscosity of between 20 mPa*s and 200 mPa*s can be selected as the treatment medium.

[0055] The temperatures of the starch can be between 50 C. and 110 C., preferably between 60 C. and 100 C. The temperature of a treatment medium, in particular a coating color or pigment color, can be 25-45 C. The paper or board web can be coated in an upward or downward direction.

[0056] In the case of direct applying, the running substrate can be the surface of a paper, paperboard or other fibrous web and, in the case of indirect applying, the surface of a transfer element that transfers the treatment medium to the surface of the fibrous web in a treatment nip. The above remarks on indirect application by means of an applicator roll 4, 5 thus apply in the same way to direct application of treatment medium to the fibrous web. The applying of treatment medium can be carried out on one or both sides.

[0057] The device according to the invention for applying at least one liquid or pasty treatment medium by means of a free-jet applicator to a moving substrate is designed such that the substrate is the surface of a paper, paperboard or other fibrous web in the case of direct application and the surface of a transfer element, in particular an applicator roll 4, 5, in the case of indirect application, which transfers the application medium to the surface of the fibrous web, in particular in a treatment nip N. The free jet applicator has at least one free jet nozzle 1.1, 1.2 with an outlet gap B for emitting a medium jet 2.1, 2.2, which applies the medium jet 2.1, 2.2 to the surface of the substrate like a film and achieves a desired width (in the transverse direction of the machine) of an application layer at an impingement position 12. A device for adjusting the intensity of the jet impulse of the medium jet in the impingement position 12 is arranged, wherein the device is designed as a positioning system for locational and angular shifts 11, 13, 18 of the free jet nozzle 1.1, 1.2 relative to the substrate, wherein a reference direction for describing the instantaneous spatial and angular position of the free jet nozzle 1.1, 1.2 relative to the impingement position 12 is given by the gravitational field.

[0058] In order to set a selectable jet curvature on a section length of the medium jet 2.1, 2.2, the positioning system for positional and angular shifts or displacements of the free jet nozzle can be designed for a vertical and/or longitudinal adjustment of the free jet nozzle 1.1, 1.2 in direction 14 of the machine running direction relative to the substrate in a gravity-oriented reference system.

[0059] The gravity-oriented reference system can be designed with systems of spatial Cartesian coordinates X, Y, Z, of which one origin for the angular displacement can be located in a mouth of the outlet gap B of the free jet nozzle 1.1, 1.2 and another origin for the positional displacement in the impingement position 12 and the impingement line A on the surface of the substrate. The respective X-axis can be directed in such a way that a right-hand system or left-hand system is provided and the perpendicular line is determined by the gravity field-related local perpendicular direction. The free-jet nozzle 1.1, 1.2 can be positioned at an angle to the local perpendicular direction in relation to the gravity field, preferably in the range from 30 to 70. Due to the positioning of the free jet nozzle 1.1. 1.2, the impulse force of the jet 2.1, 2.2 in the impingement position 12 can be selected to be greater, depending on the coating parameters, than an impulse force on the rear side of the jet surface due to a dynamic pressure caused by a boundary layer air on the moving substrate.

[0060] FIG. 7 shows operating windows for different paper or board web speeds in conjunction with different volume flows for the positioning of the free jet nozzle 1.1, 1.2 according to FIG. 1 in conjunction with FIG. 5 with regard to the positioning of the outlet gap B in the system x, y in order to adjust the jet curvature of the jet 2.1, 2.2 in relation to the impingement line A.

[0061] FIG. 1 shows spray water or water vapor nozzles 8.1, 8.2 and scrapers 7.1, 7.2 with associated collecting tray 6.1, 6.2 preferably provided for cleaning the applicator rolls 4, 5.

[0062] FIG. 2 shows a second embodiment of the invention. In contrast to FIG. 1, the air barrier scraper 3.1, 3.2 is attached directly to the nozzle 1.1, 1.2. The embodiment shown here is, for example, with a DST scraper for lifting the scraper blade on and off. A uniform and sensitively adjustable contact pressure is advantageous here. However, other versions of the scraper are also conceivable.

[0063] FIG. 3 shows a third embodiment of the invention. In contrast to FIG. 1, a boundary layer air removal device 3.1, 3.2 is provided here instead of the air barrier scraper. This can be, for example, a boundary layer air suction device or a so-called air scraper.

[0064] FIG. 4 shows a further embodiment of the invention. In contrast to FIG. 1, the direction of paper travel is opposite here.

[0065] The physical processes in the impingement position 12 of the jet 2.1, 2.2 on the roll 4, 5 are explained in more detail with reference to FIG. 6 in combination with FIG. 5 and FIG. 1.

[0066] The movement of the substrate, in particular the roll 4, 5, creates a boundary layer air that runs into the jet 2.1, 2.2 from behind and causes a dynamic pressure there. The dynamic pressure can also be seen as the impulse force of the boundary layer air. This impulse force disrupts the coating process. The component S.sub. of this impulse force presses on the back of the jet surface. This can cause the jet to lift off the roll 4, 5 so that the starch film detaches from the roller 4, 5 again. The air then penetrates between the roll surface and the treatment film and hinders the wetting of the roll 4, 5.

[0067] A stabilizing force acts against this, being the impulse force of the jet 2.1, 2.2. The component F.sub.y of this force presses the jet 2.1, 2.2 onto the roll 4, 5 at the point of impact of the impingement line A and acts against the lifting of the starch film from the roll surface. The impulse force F.sub.y acts perpendicular to the roll surface.

[0068] The jet impulse F and the component F.sub.y can be calculated using the following equations, which are known from the publication Guyon, E., Hulin, J. P. and Petit, L.: Hydrodynamik, 1997, Braunschweig/Wiesbaden, p. 188:

[00001]$\begin{array}{cc}F={}_f{U_f}^{2}h& \left(1\right)\end{array}$$\begin{array}{cc}{F}_{y^{}}=F\sin & \left(2\right)\end{array}$

[0069] F.sub.x Component of the impulse force F of jet 2.2 in x direction (FIG. 6), N

[0070] F.sub.y Component of the impulse force F of the jet 2.2 perpendicular to the surface of the applicator roll 5 (FIG. 6), N

[0071] .sub.f Density of the treatment medium, kg/m.sup.3

[0072] U.sub.f Velocity of the jet 2.2 of the treatment medium in the impingement point of the impingement line A, m/s

[0073] h jet thickness at the point of impingement of the impingement line A on the applicator roll 5, m

[0074] The jet thickness h (FIG. 6) at the point of impact of the impingement line A can be calculated from the law of conservation of mass and is the same:

[00002]$\begin{array}{cc}h=\frac{U_{\mathrm{fo}}}{U_f}{h}_o& \left(3\right)\end{array}$

[0075] h.sub.o Jet thickness at the exit point from nozzle 1.2 (at the outlet gap), m

[0076] U.sub.fo Velocity of the jet at the exit point from the nozzle 1.2, m/s

[0077] The jet velocity U.sub.f at the point of impact:

[00003]$\begin{array}{cc}{U}_f=\sqrt{U_{\mathrm{fx}}^2+U_{\mathrm{fy}}^2}& \left(4\right)\end{array}$

[0078] U.sub.fx and U.sub.fy are the components of the jet velocity in the x and y directions at the point of impact.

[0079] The component U.sub.fx of the jet velocity in the x-direction:

[00004]$\begin{array}{cc}{U}_{\mathrm{fx}}=U_{\mathrm{fo}}\cos \left(90-\right)=U_{\mathrm{fo}}\sin & \left(5\right)\end{array}$

[0080] Angle for the position of nozzle 1.2 according to FIG. 5

[0081] The component U.sub.fy of the jet velocity in the y-direction at the point of impact:

[00005]$\begin{array}{cc}{U}_{\mathrm{fy}}=\sqrt{U_{\mathrm{fo}}^2{\sin }^2\left(90-\right)+2{\mathrm{gy}}_a}=\sqrt{U_{\mathrm{fo}}^2{\cos }^2+2{\mathrm{gy}}_a}& \left(6\right)\end{array}$

[0082] The coordinates x.sub.a and y.sub.a of the point of impact of the jet 2.2 on the applicator roller 5 as shown in FIG. 5 are determined by solving equations (7) and (8):

[0083] Equation for the contour of the roll surface:

[00006]$\begin{array}{cc}y=\sqrt{r^2-{\left(x-x_o\right)}^2}+y_o& \left(7\right)\end{array}$

[0084] Equation for the jet contour or for the trajectory parabola:

[00007]$\begin{array}{cc}y=x\tan \left(90-\right)-\frac{x^{2}g}{2U_{\mathrm{fo}}^2{\cos }^2\left(90-\right)}=x\cot -\frac{x^{2}g}{2U_{\mathrm{fo}}^2{\sin }^2}& \left(8\right)\end{array}$

[0085] In equations (7) and (8), the coordinates of the point of impact of the jet 2.2 on the applicator roll x=x.sub.a and y=y.sub.a must be entered.

[0086] The absolute values for x.sub.a and y.sub.a correspond to the effective height H and the horizontal distance D as shown in FIG. 5:

[00008]$.Math.x_a.Math.=D$$.Math.y_a.Math.=H$

[0087] x.sub.o and y.sub.o Coordinates of the roller center point according to FIG. 1

[0088] r Radius of the applicator roller 4, 5.

[0089] The jet impingement angle can be determined using the equations for the tangents 16, 19 for the contour of the roll surface and for the jet contour, which are derived from the differentiation of equations (7) and (8) according to x.

[0090] Equation for the tangent 19 of the jet contour:

[00009]$\begin{array}{cc}y=\left(\tan \left(90-\right)-\frac{x_{a}g}{U_{\mathrm{fo}}^2{\cos }^2\left(90-\right)}\right).Math.\left(x-x_a\right)+y_a=\left(\cot -\frac{x_{a}g}{U_{\mathrm{fo}}^2{\sin }^2}\right).Math.\left(x-x_a\right)+y_a& \left(9\right)\end{array}$

[0091] Equation for the tangent 16 to the roll surface:

[00010]$\begin{array}{cc}y=-\frac{x_a-x_o}{\sqrt{r^2-{\left(x_a-x_o\right)}^2}}.Math.\left(x-x_a\right)+y_a& \left(10\right)\end{array}$

[0092] Angle .sub.1 between the jet tangent 19 and the x-axis at the point of impact of the impingement line A:

[00011]$\begin{array}{cc}\tan {}_1=\tan \left(90-\right)-\frac{x_{a}g}{U_{\mathrm{fo}}^2{\cos }^2\left(90-\right)}=\cot -\frac{x_{a}g}{U_{\mathrm{fo}}^2{\sin }^2}& \left(11\right)\end{array}$

[0093] Angle .sub.2 between the tangent 16 to the roll surface and the x-axis at the point of impact:

[00012]$\begin{array}{cc}\tan {}_2=-\frac{x_a-x_o}{\sqrt{r^2-{\left(x_a-x_o\right)}^2}}& \left(12\right)\end{array}$

[0094] If the angles .sub.1 and .sub.2 are known, the jet impingement angle can be calculated:

[00013]$\begin{array}{cc}={}_1-{}_2& \left(13\right)\end{array}$

[0095] The following formula can be used to calculate the component of the impulse force of the disturbing (troublesome) air flow S.sub.:

[00014]$\begin{array}{cc}{S}_{}={}_{a}q{U}_a\frac{1+\cos }{\sin }& \left(14\right)\end{array}$

[0096] S.sub. Component of the momentum force of the disturbing air flow perpendicular to the jet 2.2, N

[0097] .sub.a Density of air, kg/m.sup.3

[0098] q specific volume flow of the disturbing air flow, m.sup.3/(m*s)

[0099] U.sub.a Average velocity of the disturbing air flow, m/s

[0100] This equation is known from the publication Eklund, D. E.: Influence of blade geometry and blade pressure on the appearance of coated surface. Tappi Journal, May (1984), pp. 66-70, equation (1).

[0101] The specific volume flow of the air in the boundary layer can be calculated according to Sakiadis, as described below.

[0102] Source: Sakiadis, B. .: Part II. The Boundary Layer on a Continuous Flat Surface. AlChE Journal, Vol. 7 (1961), no. 2, p. 221-225

[0103] Thickness of the boundary layer air (m):

[00015]$\begin{array}{cc}=\sqrt{\frac{4}{0.183}}\sqrt{\frac{v{x}^{}}{U_s}}& \left(15\right)\end{array}$

[0104] Us Speed of the applicator roll, m/s

[0105] v kinematic viscosity of air, m.sup.2/s

[0106] The specific volume flow of the disturbing air flow q results from the integration of the velocity distribution u (y) over the thickness of the air boundary layer y and can be calculated using equation (16):

[00016]$\begin{array}{cc}\frac{q}{U_s}=-{}^2+\frac{1}{2}{}^4-\frac{1}{5}{}^5& \left(16\right)\end{array}$

[0107] x and y are the coordinates shown in FIG. 6.

[0108] At the point of impact of jet 2.2 on roll 5, x=L.

[0109] The mean velocity of the disturbing air flow U.sub.a can be calculated by integrating equation (25) in the publication Sakiadis, B.C. (1961):

[00017]$\begin{array}{cc}\frac{U_a}{U_s}={}_0^1\mathrm{erfc}\left(\frac{}{2}\right)d& \left(17\right)\end{array}$

[0110] The greater the jet velocity, the greater the stabilizing component F.sub.y of the impulse force of the jet 2.2. As the velocity of the roll 5 increases, the velocity of the disturbing air flow increases and thus also the disturbing component S.sub..

[0111] To ensure that the interfering air is displaced from the coating zone, the force F.sub.y should be greater than S.sub.. On the other hand, the ratio F.sub.y/S.sub. must not be too high so that the jet does not bounce off the roll surface. For a good coating, the ratio F.sub.y/S.sub. must be within an optimum range. This range must be redetermined for each system configuration, as adhesion forces are also effective in addition to the jet impulse, which can assume different values depending on the roll coating or the type of thickness, for example. For this purpose, reference points must be determined for the lower and upper limits of the current configuration. If these are known, the valid ratio of F.sub.y/S.sub. can be derived. The formulas then make it possible to predict the areas in which the system must be operated.

[0112] The meaning of the ratio F.sub.y/S.sub. is explained in Table 1. The typical coating parameters for the production of CM are given here as an example. In setting no. 1, CM is produced with 160 g/m.sup.2 at a speed of 800 m/min. Starch of 3.5 g/m.sup.2 per side with a typical solids content of 12.5% is applied. The distance H is 33.8 mm, for example. The distance D is 30 mm, for example. With these settings, the ratio F.sub.y/S.sub. is greater than 1, i.e. the force F.sub.y is greater than S.sub.. The starch film remains stable in the point of impact of the impingement on the roll. The jet velocity at the outlet of the nozzle is 1.4 m/s and increases to 1.65 m/s at the point of impact.

[0113] When changing to CM with 130 g/m.sup.2, the weight of the treatment substance is reduced to 3 g/m.sup.2 and the speed is increased to 1100 m/min (settings no. 2, table 1). The distance H, for example, is 34.9 mm. The increase in speed leads to a deterioration of the ratio F.sub.y/S.sub. by approx. 36% to 0.7, i.e. the disturbing component S.sub. has become greater than F.sub.y. The impulse force F.sub.y is no longer sufficient to counteract the disruptive effect of the boundary air flow. The starch jet lifts off the roll. The wetting of the roll is disturbed. Coating of the paper is no longer possible.

[0114] To stabilize the coating process, the nozzle is positioned higher. The distance H to the roll increases accordingly (setting no. 3), for example 99 mm. With these settings, the ratio F.sub.y/S.sub. increases to 1.6 and is significantly greater than 1, i.e. the disruptive component S.sub. is significantly smaller than F.sub.y. With these settings, the impulse force F.sub.y is sufficient to compensate for the disruptive effect of the boundary air flow. The starch jet no longer lifts off the roll. Wetting of the roll is restored. Coating the paper is possible again with this setting.

[0115] At low roll speeds, the effect of the boundary layer air becomes weaker and the ratio F.sub.y/S.sub. becomes >1 (setting 4) even at low jet speeds at the nozzle outlet.

TABLE-US-00001 TABLE 1 Settings No. 1 2 3 4 Paper grade CM CM CM CM Basis weight g/m.sup.2 160 130 130 170 Roll speed m/min 800 1100 1100 600 Treatment substance g/m.sup.2 3.5 3.0 3.0 3 weight per side Solids content % 12.5 12.5 12.5 12.5 Specific volume flow I/(min 21.6 25.4 25.4 13.9 rate, q m) Jet velocity coming m/s 1.4 1.7 1.7 0.9 out of the nozzle Jet thickness in the m 218 225 193 192 impingement point, h Angle 15.7 15.5 17.7 16.1 Angle 22.3 20.7 29.2 28 Angle ratio / 1.4 1.3 1.65 1.73 Distance L mm 22 22 22 22 Distance D mm 30 31.7 78.6 24.1 Distance H mm 33.8 34.9 99 30.6 Ratio H/D 1.13 1.1 1.26 1.27 Angle position of the 45.2 45.2 45.2 45.2 nozzle, Jet velocity in the m/s 1.65 1.9 2.2 1.2 impingement point Force ratio F.sub.y/S.sub. 1.1 0.7 1.6 1.1

[0116] FIG. 7 shows different distances H of the outlet gap B of a free jet nozzle 1.2 (see FIG. 5 and FIG. 6). Preferably, two boundary conditions determine the gap width h.sub.o of the outlet gap B. A first boundary condition is determined by the impulse ratio at the point of impact of the impingement line A, which should preferably be greater than 1. The smaller the nozzle gap, the greater the jet impulse. It therefore makes sense to make the nozzle gap as small as possible. However, this increases the probability of the nozzle gap becoming blocked by particles in the application medium. The filtering of the treatment medium is subject to technological and economic restrictions. For this reason, gap widths h.sub.o of less than 100 m are difficult to achieve. In the example shown in FIG. 7, for example a gap width of 250 m was calculated. The positioning of the position/location of the nozzle 1.2 by means of position shifts, shown by double arrows 11 (distance H), 13 (distance D), and angle settings of the free jet nozzle 1.2 with the outlet gap B (cf. FIG. 5) results from the above formulae.

[0117] Numerical data of the graphical representation of FIG. 7 are summarized in Table 2 below.

TABLE-US-00002 TABLE 2 No. Settings 5 6 7 8 9 Paper grade CM CM CM CM CM Basis weight g/m.sup.2 175 170 130 120 115 Roll speed m/min 400 600 800 1000 1200 Treatment substance g/m.sup.2 2 2 2 2 2 weight per side Solids content % 12.5 12.5 12.5 12.5 12.5 Specific volume flow l/(min 6.2 9.3 12.3 15.4 18.5 rate, q m) Jet velocity coming m/s 0.4 0.6 0.8 1.0 1.2 out of the nozzle Jet thickness in the m 129 164 188 199 211 impingement point, h Angle 10.8 10.6 10.4 26.4 26.3 Angle 41 37.4 33.4 36.9 34.4 Angle ratio / 4.0 3.5 3.2 1.4 1.3 Distance L Mm 20 20 20 20 20 Distance D Mm 11.4 14.8 17.2 25.4 27.3 Distance H Mm 23.7 25.5 26.8 31.2 31.8 Ratio H/D 2.0 1.7 1.6 1.2 1.17 Angle position of the 38.9 38.9 38.9 45.2 45.2 nozzle, Jet velocity in the m/s 0.8 0.9 1.1 1.3 1.5 impingement point Force ratio F.sub.y/S.sub. 1.4 1.0 0.9 1.1 1.0

[0118] In order to stabilize the coating process, the jet stability in the impingement zone can be improved by additional measures. A method for stabilizing the coating process with air blow nozzles is known from patent specifications DE 10 2020 117 953 A1 and EP 1 266 093 A1. A blow nozzle 10.1, 10.2 (FIG. 8) or a series of blow nozzles can be arranged in the upper position between the nozzle and the treatment nip. The blowing air is directed at the point of impact/impingement of the jet perpendicular to the roll 4, 5 or at a slight angle to the roll tangent. A blow nozzle will increase the ratio of F.sub.y/S.sub. and thus improve the jet stability.

[0119] For this purpose, the coating medium is engaged with air between the treatment nip of the rolls 4, 5 and the transfer to the web. In order to minimize the volume flow of the interfering boundary layer air, the distance L from the air barrier scraper/blade 3.1, 3.2 to the impingement line A of the jet is set to 1 to 100 mm, preferably 10 to 30 mm.

[0120] The treatment/coating medium can be starch, coating colors, plastic compounds such as PVA or a mixture of these media. The coating medium is then transferred to the paper or board web in the nip between the applicator rolls. One applicator roll can be a hard (heated) roll, which can be equipped with a ceramic cover. The other applicator roll can be a profiling roll, which is equipped with a hard ceramic cover or a soft polymer cover with a hardness of 15-30 P &J, for example. The applicator rollers are usually tempered.

[0121] The new process can be used for starch application (sizing) and pigmentation (pigmenting).

[0122] The starch is applied with a solids content of between 6% and 35%, preferably between 15% and 35%, particularly preferably between 10% and 25%, and a viscosity of between 20 mPa*s and 200 mPa*s. The treatment substance weight is in the range between 0.2 g/m.sup.2 and 6 g/m.sup.2 per side. A film of thickness in the range of 10 ml/m.sup.2 to 40 ml/m.sup.2 is applied to the applicator roll.