DE69509651T2 - METHOD AND DEVICE FOR COMBINED ROLL AND EXTRUSION COATING - Google Patents

Description

The present invention relates to coating processes. In particular, the present invention relates to coating processes using a nozzle as basically known from EP-A-0 466 420.

US-A-2 681 294 discloses a vacuum process for stabilizing the coating bead for direct extrusion and slip types of metered coating systems. Such stabilization improves the coating ability of these systems. However, these systems lack sufficient overall ability to provide the thin wet layers required for coated products, even at very low fluid viscosities.

US-A-4 445 458 discloses an extrusion bead coating die with a sloped take-off surface for applying a confining force to the downstream side of the coating bead and reducing the amount of vacuum required to maintain the bead. Reducing the vacuum reduces vibration defects and coating streaks. To improve coating quality, the obtuse angle of the sloped surface with respect to the slot axis and the position of the slope along the slot axis toward the moving web (overhang) and away from the moving web (underhang) must be optimized. The optimization results in the high quality required for coating with photosensitive emulsions. However, the thin film performance required for some coated products is lacking.

Fig. 1 shows a known coating nozzle 10 with a vacuum chamber 12 as part of a metered coating system. A coating liquid 14 is delivered by a pump 16 directly to the nozzle 10 for application to a gently moving web 18 supported by a back-up roll 20. The coating liquid is delivered through a channel 22 to a distributor 24 for distribution through a slot 26 in the nozzle and for application to the moving web 18. As shown in Fig. 2, the coating liquid passes through the slot 26 and forms a continuous coating bead 28 between the upstream nozzle lip 30 and the downstream nozzle lip 32 and the web 18.

The dimensions F1 and F2, the width of the lips 30, 32, are generally in the range of 0.25 to 0.76 mm. The vacuum chamber 12 applies a vacuum upstream of the bead in order to stabilize the bead.

From EP-A-0 466 420 a source coating device for applying a coating liquid to a web is known, in which the source is pivotable, the source angle being adjustable without changing the gap between the tip of the source and the surface to be coated. The source is delimited by two lips, the lip downstream in the direction of movement of the surface to be coated being longer than the other (upstream) lip. The tip of the downstream lip lies substantially on the pivot axis of the source. The slot formed between the two lips upstream of the mouth or the open end can be linear or, alternatively, curved, so that the angle between the emerging coating fluid stream and the surface to be coated is greater than the angle formed by the longitudinal direction of the source with the surface to be coated. the surface. In the known coating device, the distance between the front end of the upstream lip and the surface to be coated is greater than that between the front end of the downstream lip and the surface to be coated. The front end of the upstream lip is flat, while the part of the downstream lip between the tip thereof and the upstream lip may be curved.

Although the known designs work adequately in many situations, there is a need to provide a nozzle coating method and a nozzle coating device that improves the performance of known methods and devices.

According to the invention, this improvement is achieved by a nozzle coating device according to claim 1 and a nozzle coating method according to claim 6. The subclaims each relate to preferred embodiments.

The present invention relates to a nozzle coating device for applying a fluid coating to a surface. The device comprises a nozzle with an upstream element having an upstream lip and a downstream element having a downstream lip. The upstream lip is formed as a web and the downstream lip as a sharp edge with an edge radius of at most 10 micrometers. A passage extends between the upstream and downstream elements through the nozzle. The passage has a slot delimited by the upstream and downstream lips, and Coating fluid exits the nozzle from the slot to form a continuous coating bead between the upstream nozzle lip, the downstream nozzle lip and the surface to be coated. A metering roller removes excess coating fluid. The bead does not move significantly into the space between the web and the surface to be coated, even if the vacuum is increased.

Alternatively, the apparatus may comprise a roller to which the coating fluid is first applied and which contacts the web. An excess fluid removal device removes excess coating fluid from the roller. A nozzle applies the coating fluid to the roller. The removal device may be a doctor blade or a metering roller and the coating fluid on the roller may be applied to the web by spread coating.

The nozzle coating method of the invention comprises directing coating fluid through a slot; improving coating performance by changing at least one of the relative orientations of the land and the sharp edge having a radius of at most 10 micrometers; removing excess coating fluid from the surface to be coated using a metering roller; selecting the length of the land, the edge angle of the downstream element, the nozzle attack angle between the surface of the downstream element of the coating slot and a tangential plane through a line on the surface to be coated parallel to and directly opposite the sharp edge, and the coating gap length between the sharp edge and the area in combination with each other; and the selection of the slot height, the overhang, and the convergence in combination with each other.

In the following, preferred embodiments of the invention are described with reference to the drawings, which show:

Fig. 1 is a schematic cross-sectional view of a known coating nozzle.

Fig. 2 is a schematic cross-sectional view of the slot and lip of the nozzle of Fig. 1.

Figure 3 is a cross-sectional view of an extrusion die of the present invention.

Fig. 4 is an enlarged cross-sectional view of the slot and lip of the nozzle of Fig. 3.

Fig. 5 is a cross-sectional view of the slot and lip similar to Fig. 4.

Fig. 6 is a cross-sectional view of an alternative vacuum chamber arrangement.

Fig. 7 is a cross-sectional view of another alternative vacuum chamber arrangement.

Figure 8 is a cross-sectional view of an alternative extrusion die according to the present invention.

Fig. 9a and 9b are enlarged cross-sectional views of the slot, front face and vacuum chamber of Fig. 8.

Fig. 10a and 10b are schematic representations of the nozzle of Fig. 8.

Figure 11 shows coating test results comparing the performance of a prior art coating nozzle and the performance of a coating nozzle according to the invention for a coating liquid having a viscosity of 1.8 centipoise.

Fig. 12 shows comparative test results for a coating fluid with a viscosity of 2.7 centipoise.

Fig. 13 is a collection of data from coating tests.

Figure 14 is a graph of constant G/Tw lines for an extrusion coating die according to the invention for nine different coating liquids.

Fig. 15 is a schematic view of a three-roll reverse roll coating apparatus with the nozzle of the present invention.

Fig. 16 is a schematic representation of a two-roll reverse roll coating apparatus with the nozzle of the invention.

Fig. 17 is a schematic view of a gravure coating apparatus with the nozzle according to the invention.

Fig. 18 shows an extrusion coating device with the nozzle according to the invention.

Figures 19a, 19b and 19c are cross-sectional views of a deposition coating apparatus according to the present invention.

Figures 20a, 20b and 20c are cross-sectional views of a deposition coating apparatus using the nozzle of the present invention.

Figure 20d is a cross-sectional view of a deposition coating apparatus using the nozzle of Figure 19c.

The present invention relates to a nozzle coating method and a nozzle coating apparatus in which the nozzle has a sharp edge and a ridge arranged to improve and optimize performance. The ridge is designed to conform to the shape of the surface in the immediate area of application of the coating liquid. The ridge may be curved to conform to a web running around a back-up roll or the ridge may be flat to conform to a cantilevered portion of the web between rolls.

Fig. 3 shows the extrusion nozzle 40 according to the invention with a vacuum chamber 42. Coating liquid 14 is pumped by a pump 46 for application to a moving web 48 supported by a support roller 50. to the nozzle 40. The coating liquid is supplied via a channel 52 to a distributor 54 for distribution through a slot 56 and application to the moving web 48. As shown in Fig. 4, the coating liquid 14 passes through the slot 56 and forms a continuous coating bead 58 between the upstream nozzle lip 60, the downstream nozzle lip 62 and the web 48. The coating liquid may be one of numerous liquids or a different liquid. The upstream nozzle lip 60 is part of an upstream member 64 and the downstream nozzle lip 62 is part of a downstream member 66. The height of the slot 56 can be controlled by a U-shaped intermediate plate which can be made of brass or stainless steel and provided with a rim. The vacuum chamber 42 applies a negative pressure upstream of the bead to stabilize the coating bead.

As shown in Figure 5, the upstream lip 60 is formed as a curved ridge 68 and the downstream lip 62 is formed as a sharp edge 70. This configuration improves overall performance over known die coaters. Improved performance enables operation at higher web speeds and larger coating gaps, operation with higher coating fluid viscosities, and production of thinner wet coating layers.

The sharp edge 70 should be clean and free of nicks and burrs and should be straight within one micrometer over a 25 cm length. The edge radius should not be greater than 10 micrometers. The radius of the curved web 68 should be equal to the radius of the backup roll 50 plus a minimum and not critical clearance of 0.13 mm for coating gap and web thickness. Alternatively, the radius of the curved web 68 may exceed that of the backup roll 50 and intermediate plates may be used to align the web with respect to the web 48. A given convergence C achieved by a web with the same radius as the backup roll can be achieved by a web with a larger radius than the backup roll if the web is manipulated with the intermediate plates.

Figure 5 further shows dimensions of geometric operating parameters for extruding a single layer. The length L1 of the curved web 68 of the upstream member 64 can be between 1.6 and 25.4 mm. The preferred length L1 is 12.7 mm. The edge angle A1 of the downstream member 66 can be between 20° and 75° and is preferably 60°. The edge radius of the sharp edge 70 should be between about 2 microns and about 4 microns and preferably less than 10 microns. The nozzle attack angle A2 between the surface of the downstream member 66 of the coating slot 56 and the tangential plane P by a line on the surface of the web 48 parallel to and directly opposite the sharp edge 70 may be between 60º and 120º and is preferably 90º-95º, for example 93º. The coating gap G₁ is the perpendicular distance between the sharp edge 70 and the web 48. (The coating gap G₁ is measured at the sharp edge, but is shown away from the sharp edge in some figures for clarity of the drawings. Regardless of the position of G₁ in the drawings - and because of the curvature of the web, the gap increases as one moves away from the sharp edge - the gap is measured at the sharp edge.)

The height H of the slot can be between 0.076 mm and 3.175 mm. The overhang O refers to a positioning of the sharp edge 70 of the downstream member 66 with respect to the downstream edge 72 of the curved ridge 68 of the upstream member 64, toward the web 48. The overhang can also be viewed as a recess of the downstream edge 72 of the curved ridge 68 away from the web for any given coating gap G1 with respect to the sharp edge 70. The overhang can be from 0 to 0.51 mm and the settings at opposite ends of the die slot should be within a range of 2.5 microns from each other. A precision assembly system is required, for example, to achieve precise overhang uniformity. The convergence C is a counterclockwise angular position, as shown in Figure 5, of the curved land 68 away from a location parallel to (or concentric with) the web 48, with the downstream edge 72 being the center of rotation. The convergence can range from 0º to 2.29º, and the settings at the opposite ends of the die slot should be within a range of up to 0.023º. The slot height, overhang and convergence, as well as fluid properties such as viscosity, affect the performance of the die coating apparatus and process.

From the point of view of overall performance for fluids within the viscosity range of 1000 centipoise and below, it is preferred that the slot height be 0.18 mm, the projection 0.076 mm and the convergence 0.57º. Performance levels can be nearly equal using other slot heights. Performance advantages are also found for viscosities above 1000 Centipoise: If the convergence is kept at 0.57º, other optimal slot height and overhang combinations are as follows:

Slot height overhang

0.15mm 0.071mm

0.20mm 0.082mm

0.31mm 0.100mm

0.51mm 0.130mm

In the fluid viscosity range mentioned above and for any given convergence value, the optimal protrusion value appears to be directly proportional to the square root of the slot height value. Similarly, for any given slot height value, the optimal protrusion value appears to be inversely proportional to the square root of the convergence value.

As shown in Figure 6, the vacuum chamber 42 may be an integral part of the upstream member 64 or it may be clamped thereto to create a precise repeatable vacuum system gas flow. The vacuum chamber 42 is formed using a vacuum member 74 and may be connected to a vacuum source channel 80 via an optional vacuum restrictor 76 and a vacuum manifold 78. A curved vacuum web 82 may be an integral part of the upstream member 64 or part of the vacuum member 74 attached to the upstream member 64. The vacuum web 82 has the same radius of curvature as the curved web 68. The curved web 68 and the vacuum web 82 may be finish ground together so that they are "aligned" with each other. The vacuum web 82 and the curved web 68 then have the same convergence C with respect to the web 48.

The vacuum land gap G2 is the distance between the vacuum land 82 and the web 48 at the lower edge of the vacuum land and is the total of the coating gap G1, the overhang O and the displacement caused by the convergence C of the curved land 68. (Regardless of the position of G1 in the drawing, the gap is the vertical distance between the lower edge of the vacuum land and the web.) If the vacuum land gap G2 is large, excessive flow of ambient air into the vacuum chamber 42 occurs. Although the vacuum source may have sufficient capacity to compensate for this and maintain the specified vacuum level in the vacuum chamber 42, the inflow of air may degrade coating performance.

In Fig. 7, the vacuum land 82 is part of the vacuum land 74 which is attached to the upstream member 64. During manufacture, the curved land 68 is finished with "ground in" convergence C. The vacuum member 74 is then attached and the vacuum land 82 is finish ground using a different grinding center such that the vacuum land 82 is parallel to the web 48 and the vacuum land gap G2 is parallel to the coating gap G1 when the desired overhang value is set. The length L2 of the vacuum land can range from 6.35 mm to 25.4 mm. The preferred length is 12.7 mm. This embodiment has better overall coating performance under difficult coating situations than the embodiment of Fig. 6, but is always finish ground for a specific set of operating conditions. With the change of the coating gap G₁ or the projection O, the vacuum web gap G₂ may deviate from its optimum value.

In Figures 8 and 9, the upstream member 64 of the nozzle 40 is attached to an upstream arm positioner 86. The curved web 68 on the upstream member 64 and the vacuum web 82 on the vacuum element 74 are not directly connected to each other. The vacuum chamber 42 is connected to the vacuum source via the vacuum web 74 and the positioner 86. The attachment and positioning of the vacuum element 74 are separate from those of the upstream member 64. This improves the performance of the nozzle and enables accurate, repeatable vacuum system gas flow. The robust design of the vacuum element system further supports the improved performance compared to known systems. Furthermore, this configuration of the vacuum element 74 can improve the performance of known coating devices, such as slot, extrusion or slide coating devices. A flexible vacuum sealing strip 88 seals between the upstream member 64 and the vacuum member 74.

The gap G2 between the vacuum land 82 and the web 48 is not affected by changes in the coating gap G1, the overhang O or the convergence C and can be maintained at its optimum value throughout coating. The vacuum land gap G2 can be adjusted within a range of 0.076 mm to 0.508 mm. The preferred value for the gap G2 is 0.15 mm. The preferred angular position of the vacuum land 82 is parallel to the web 48.

During coating, the vacuum level is adjusted to produce the best quality coating. A typical vacuum level when coating with a 2 centipoise coating fluid at a wet film thickness of 6 microns and a web speed of 30.5 m/min is 51 mm H₂O. A reduction in wet film thickness, an increase in viscosity, or an increase in web speed may require higher vacuum levels in excess of 150 mm H₂O. Nozzles according to the invention have lower satisfactory minimum vacuum levels and higher satisfactory maximum vacuum levels than known systems and can operate in some cases at zero vacuum, which known systems cannot.

Figures 10a and 10b show some positioning adjustments and the closure of the vacuum chamber. The protrusion adjustment translates the downstream member 66 relative to the upstream member 64 such that the sharp edge 70 moves toward or away from the web 48 relative to the downstream edge 72 of the arcuate web 68. The convergence adjustment rotates the upstream member 64 and the downstream member 66 together about an axis passing through the downstream edge 72 such that the arcuate web 68 moves from the position of Figure 10 out of parallel alignment with the web 48 or back into parallel. Adjustment of the coating gap moves the upstream member 64 and the downstream member 66 together to change the distance between the sharp edge 70 and the web 48, the vacuum member remains stationary on the fixture 86, and the vacuum sealing strip 88 elastically deforms to prevent air leakage during adjustment operations. Air leakage at the ends of the nozzle into the vacuum pressure chamber are minimized by end plates 90 attached to the ends of the vacuum element 74 which overlap the ends of the upstream element 64. The vacuum element 74 is 0.10 mm to 0.15 mm larger than the upstream element 64 so that when centered the clearance between each end plate 90 and the upstream element 64 is between 0.050 mm and 0.075 mm.

An unexpected operating characteristic was observed during coating. The bead does not move significantly into the space between the curved web 68 and the moving web 48, even when the vacuum is increased. This allows higher vacuum levels to be used than in known extrusion coaters and provides a correspondingly higher level of performance. Even when little or no vacuum is required, the invention demonstrates improved performance over known systems. The fact that the bead does not move significantly into the space between the curved web 68 and the web 48 also means that the effect of "leakage" in the backup roll 50 on the downstream coating weight is no different from that in known extrusion coaters.

Fig. 11 shows graphically the results of coating tests comparing the performance of a known extrusion die with an extrusion die according to the invention. In the tests, the coating fluid containing an organic solvent was applied to a flat polyester film web at 1.8 centipoise. The performance criterion was a minimum wet film thickness at four different coating gap sizes for each of the two coating systems over the speed range of 15 to 60 m/min. Curves A, B, C and D use the known die and were formed with coating gaps of 0.254 mm, 0.203 mm, 0.152 mm and 0.127 mm. Curves E, F, G and H use a die according to the invention with the same coating gaps. The lower wet thickness values of the invention compared to the known die are readily apparent. Fig. 12 shows comparative test results for a similar coating fluid with a viscosity of 2.7 centipoise at the same coating gaps. The performance advantage of the invention is again clearly evident.

Fig. 13 is a collection of data from coating tests where fluids of seven different viscosities and with various organic solvents were applied to flat polyester film webs. The results compare performance of the known extrusion coater (KNOWN) and the present invention (NEW). The performance criteria are mixed. Performance advantages for this invention are found in web speed (Vw), wet film thickness (Tw), coating gap, vacuum level, or a combination of these.

One measure of the performance of a coating machine is the relationship between the coating gap and the wet film thickness (G/Tw) for a given coating liquid and web speed. Fig. 14 shows a series of constant G/Tw lines and viscosity values from an extrusion die according to the invention for nine different coating liquids. The liquids were applied to a flat polyester film base at a web speed of 30.5 m/min. Some viscosity values appear to be outside the norm due to the effects of other coatability factors. Four additional performance lines were calculated after calculating the G/Tw Values for 30.5 m/min web speed from Figures 11 and 12 added. From top to bottom, the solid performance lines are the G/Tw for liquids of 2.7 and 1.8 centipoise applied with a known extrusion die and the G/Tw for liquids of 2.7 and 1.8 centipoise applied with an extrusion die according to the invention. The lines for the die according to the invention show higher G/Tw values than the lines from the known coating die. In addition, the lines for the present invention are close to constant G/Tw lines, with an average of 18.8 and 16.8. The lines from the known coater show significantly greater G/Tw variations along the length. The present invention has significantly improved operating characteristics over known systems for maintaining a coating bead at low wet film thickness values.

Coating nozzles according to the invention can be used as high performance liquid delivery systems for roll and applicator coaters. Figure 15 shows a three-roll reverse roll coater that uses an extrusion nozzle 40 to deliver liquid 14 to a casting roll 330. Since the surface of the casting roll 330 passes the nozzle 40 in a downstream direction, the nozzle is inverted and the vacuum chamber 42 is above the slot and coating bead. This does not affect coating performance. A metering roll 332 removes excess coating liquid, leaving a precisely measured layer on the casting roll 330. A doctor blade 334 removes the excess coating liquid from the metering roll 332 and allows it to drip into a liquid return pan 336 for recirculation.

Meanwhile, a bead splitting operation transfers a portion of the coating liquid from the casting roll 330 to the web 48 moving around the backup roll 50. After splitting the bead, a second doctor blade 338 removes the remaining coating liquid from the casting roll 330 and directs it into the return pan 336. Alternatively, the backup roll 50 may be rubber coated so that the casting roll 330 can contact the web and transfer all of the coating liquid in that area to the web. The second doctor blade 338 would then remove any liquid from the casting roll 330 that is outside the web width.

Figure 16 shows a reverse roll coater using an extrusion die 40 to deliver coating liquid to the surface of the web 48 moving around the backup roll 14, which is a mantle cast roll. The metering roll 332 removes excess coating liquid from the surface of the web 48, leaving the desired precise wet coated layer. The doctor blade 334 removes the excess coating liquid from the metering roll 332 and returns it to the return pan 336. Using this system, in one example, increased the vacuum window from 5.08 mm to over 254 mm H₂O and increased the liquid delivery coating gap from 0.10 mm to 0.36 mm, thereby improving stability and virtually eliminating streaking.

Fig. 17 shows a gravure coating apparatus with an extrusion nozzle 40 for supplying coating liquid to the surface of a corrugated roller 340. The vacuum chamber 42 of the nozzle 40 is located above the coating slot. A doctor blade 342 removes excess coating coating fluid from the corrugated pattern so that the desired amount is transferred to the web 48 running around the rubber coated backup roll 314. The excess coating fluid recirculates through the pan 336. This method of supplying coating fluid to the surface of a corrugated roll can also be used for other forms of gravure coatings, such as reverse, offset and differential coatings.

Fig. 18 shows a two-roll extrusion coating apparatus using an extrusion die 40 to deliver coating fluid to the surface of the casting roll 330 with stability from the vacuum chamber 42. The layer of coating fluid is thin and precise so that a metering roll is not required. Bead pitch is directly onto the web 48 running around the backup roll 314. A doctor blade 338 removes the excess coating fluid from the casting roll 330 and recirculates it over the pan 336. Alternatively, the backup roll 50 can be coated with rubber so that the casting roll 330 can contact the web and all of the coating fluid in that area is transferred to the web. The second doctor blade 338 then removes fluid from the casting roll 330 outside the web width.

Fig. 19a shows a coating device in which an extrusion nozzle 40 applies coating liquid via a distributor 54 and a slot 56 to a transfer roller 344, for example a spindle with a diameter between 25.4 mm and 50.8 mm. The coating bead is stabilized by the vacuum chamber 42. The coating liquid on the transfer roller 344 is transferred by application to the coating layer on the web 48. The small diameter transfer roller 344 has a small application area and improves web stability over a larger transfer roller by reducing web flutter and cross-stress marks. The surface of the transfer roller 344 can be, for example, smooth, polished, medium ground, sandblasted, or corrugated.

Fig. 19b shows a coating device in which the extrusion nozzle 40 with a vacuum chamber 42 supplies coating liquid to the surface of an applicator roller 344. The roller 344 has a larger diameter than the spindle of Fig. 19a. The coating liquid is applied to form the layer on the web 48.

Fig. 19c shows a coating applicator in which a sliding coating nozzle 310 transfers coating liquid to the surface of an applicator roll 344. The coating liquid is applied to form the coating on the web 48.

Fig. 20a shows a deposition coating apparatus in which a dual layer extrusion die 100 supplies two coating liquids 116, 124 through channels 118, 126 to the surface of a spindle, for example a transfer roll 344 having a diameter between 25.4 mm and 50.8 mm. The two coating liquids on the transfer roll 344 are transferred to form two coatings on the web 48.

Fig. 20b shows a coating device in which a double-layer extrusion nozzle 100 supplies coating liquid to an applicator roller.

The roller 344 has a larger diameter than the roller of Fig. 20a. Two coating liquids 116, 124 are passed through two separate manifolds and two separate slots so that they meet at the coating bead. The two coating liquids are applied to the web to form wet applied layers.

Fig. 20c shows a transfer coating apparatus in which a dual layer extrusion die 100 supplies coating liquid to a transfer roll 344. The two coating liquids 116, 124 are supplied through two manifolds but only one slot and meet in the die. The two coating liquids on the surface of the transfer roll 344 are applied to form the two coatings on the web 48.

Fig. 20d shows a deposition coating apparatus in which a multi-layer coating version of the nozzle 220 of Fig. 19c directs four coating liquids onto the surface of the transfer roll 344. Four liquids 116, 124, 346, 348 are directed through the nozzle 100, down slide surfaces 236 to form four layers on the surface of the transfer roll 344. These layers are applied to the web 48 to form four coatings.

Claims (7)

1. A nozzle coating device for applying fluid coatings to a web moving around a support roller, comprising: - a nozzle (40) with an upstream element (64) with an upstream lip (60) and a downstream element (66) with a downstream lip (62), the upstream lip (60) being designed as a web (68) with a shape corresponding to the support roller (50), and the downstream lip (62) being designed as a sharp edge (70), - a passage (52) extending between the upstream and downstream elements (64, 66) and having a slot (56) formed by the upstream and downstream lips (60, 62), wherein coating fluid exits the nozzle (40) through the slot (56) to form a continuous coating bead (58) between the upstream nozzle lip (60), the downstream nozzle lip (62) and a surface to be coated, and - a doctor blade device that removes excess coating fluid from the surface to be coated, characterized in that - the doctor device is a doctor roller (332), and - the downstream lip (62) has an edge radius of not more than 10 micrometers. 2. A nozzle coating apparatus according to claim 1, further comprising: - a roller (344) on which the coating fluid is first applied and which subsequently transfers the coating fluid to the web (48), and - a device (338) for removing excess coating fluid from the roller 344, wherein the removal device (338) contacts the roller (344) for removing excess coating fluid, - wherein the upstream lip (60) is designed as a web (68) with a curved shape adapted to the roller (344). 3. Apparatus according to claim 2, wherein the removal device comprises a scraper blade (338). 4. The apparatus of claim 2, wherein the removal means comprises the squeegee roller (332). 5. Apparatus according to claim 3, wherein the coating fluid on the roll is applied to the web (40) in a spread coating process. 6. A method for jet coating a surface, comprising the following steps: - guiding coating fluid through a slot (56) formed by an upstream element (64) with an upstream lip (60) and a downstream element (66) with a downstream lip (62), the upstream lip (60) being designed as a web (68) with a shape corresponding to the support roller (50) and the downstream lip (62) being designed as a sharp edge (70), - Improving coating performance by changing the orientation of either the web (68) or the sharp edge (70), - removing excess coating fluid from the surface to be coated using a doctor device (332) which contacts the surface to be coated, - selecting a length (L) of the web (68), an edge angle (A₁) of the downstream element (66), a nozzle attack angle (A₂) between the downstream element surface of the coating slot (56) and a tangent plane through a line parallel to and directly opposite the sharp edge (70) on the surface to be coated, and a coating gap width (G) between the sharp edge (70) and the surface to be coated, in combination with one another, and - Select a slot height (H), a projection (O) and a convergence (C), in combination with each other, characterized in that - a roller (332) is used as doctor device, and - a downstream lip (62) with an edge radius of not more than 10 micrometers is used. 7. The method of claim 6, further comprising the step of applying vacuum upstream of a formed coating bead (58) to stabilize the bead (58), wherein the bead (58) does not move substantially into the space between the web (68) and the surface to be coated, even when the vacuum is increased.