EP2309060A2 - Curtain application device - Google Patents

Abstract

Curtain-application unit for delivering an application medium in the form of a curtain moving due to gravity on a moving paper- or a cardboard web, comprises: a nozzle body; and a distribution chamber (7) extending along a feeding width, where the application medium is fed via at least two supplying lines, each exhibiting a device for adjusting a volumetric flow of the medium to be supplied, and a flowing channel (6) to deliver the application medium as the curtain via an outlet gap (3). The flowing channel is divided into many individual widening guiding channels of a diffuser block. Curtain-application unit for delivering an application medium in the form of a curtain moving due to gravity on a moving paper- or a cardboard web, comprises: a nozzle body; and a distribution chamber (7) extending along a feeding width, where the application medium is fed via at least two supplying lines, each exhibiting a device for adjusting a volumetric flow of the application medium to be supplied, and a flowing channel (6) to deliver the application medium as the curtain via an outlet gap (3). The flowing channel is divided into many individual widening guiding channels of a diffuser block, where an inlet side connected to the distribution chamber along the feeding width is at least partially divided into sections, and each of these sections are connected to the supplying line, and exhibit a partitioning-width, which over-spanned the many guiding channels of the diffuser block.

Description

The invention relates to a curtain applicator for dispensing liquid or pasty application medium in the form of a substantially gravity-related moving curtain or veil on a moving surface, in particular of paper or cardboard.

Out DE 100 57 733 A1 It is known that such a curtain coating unit comprises a nozzle chamber, which is supplied to the application medium via a supply line, and which emits the application medium through an outlet opening as a curtain or veil. The curtain applicator is located at a distance from the substrate, resulting in the advantage of contactless application.

To form a curtain, the Curtain Coater can be used with a slot die or a cascade die. In a slot die (slot-fed die) of a single-layer curtain applicator, the curtain forms directly at the exit from the die gap. The curtain commissioned works with a Slot nozzle are for example off DE 197 16 647 A1 and DE 10 2005 017 547 A1 known. The cascade nozzles (Slide-Fed Die) are used in the multilayer web coating. In a cascade nozzle, the coating material first flows from a distribution chamber up to the outlet gap. From the exit slit, the coating material flows on an inclined plane, where it is superimposed with the coating slips of the upper layers and then passed to the nozzle lip. Only at the trailing edge of the nozzle lip forms a curtain. The cascade nozzles are described for example in WO 01/54828 A1 and WO 2005/024133 A1 ,

The distribution system of the nozzle is located above the moving paper web and is located between the die lip and the paper web. The problem with the cascade nozzles is that the space for the distribution system and for the nozzle is very limited by the curtain height, which is usually 100 to 250 mm.

When coating the paper or board web with a curtain coater, the coating should be applied as evenly as possible over the entire web width. The application thickness must be as constant as possible over the entire web surface. However, it is difficult to achieve a uniformly thick application medium curtain over the entire working width, the larger the working width. High web speeds place another high burden on the stability of the application medium curtain as it is stretched on contact with the ground due to the difference between the speed just before landing on the ground and the running speed of the moving ground. To achieve a high-quality order result, therefore, the uniformity of the application medium curtain, with which it leaves the outlet opening of the dispensing nozzle, is of great importance. This is especially true if the application medium is to be brought to the substrate essentially completely metered, ie a "1: 1" order, and if, moreover, only very small quantities of application medium are to be applied to the substrate, ie low coating weight.

The application thickness must therefore be as constant as possible over the entire web surface. The basic prerequisite for this is a uniform distribution of the coating over the outlet width with regard to the volume flow and the speed. This requirement is particularly difficult to meet for large working widths of for example 8 to 10 m and low application weights of, for example, 2 to 10 g / m ² . Varying operating conditions, such as large ranges of variation in coating viscosity and application quantities, present an additional challenge in achieving an even distribution of the job.

In order to achieve the most homogeneous possible distribution with a large variation of the volume flows and the material parameters, a distributor system with two chambers, the so-called side-fed dual cavity die, is also known, cf. Stephan F. Kistler, Peter M. Schweizer, Liquid Film Coating, Scientific principles and their technological implications, Chapman & Hall, New York 1997, pp. 752-767 , After distribution in a first distribution chamber, the coating composition is passed through a first distribution chamber gap into a second distribution chamber. The distributor chamber gap must produce a high flow resistance. The resulting pressure in the first distribution chamber is significantly greater than the transverse pressure loss in the flow direction. The pressure differences in the flow direction of the first distribution chamber are very small compared to the total pressure in the first distribution chamber. The pressure distribution and thus the distribution of the volumetric flow density over the distributor chamber gap are thereby approximately uniform with large variations of the volumetric flows and the material parameters. The remaining deviations are compensated in the second distribution chamber. In order to produce a high flow resistance, the distribution chamber gap must be made in small dimensions, which are in the range of 200 to 500 microns. The volume flow deviations over the outlet width must not exceed a range of 1 to 2%. For this purpose, the flat parts forming the distribution chamber gap must be made with a deviation from the parallelism in a range of ± 1 to 3 microns. The length of the distributor chamber gap is usually 20 to 40 mm. The production cost of flat parts in such dimensions with the required precision, especially for large outlet widths of 10 to 12 m, is very large and associated with considerable costs.

Out DE 197 55 625 A1 a curtain applicator is known in which the nozzle body consists of two wall-shaped parts which have a desired working width corresponding length. In a longitudinal side of one of the parts, a longitudinal groove is incorporated, which forms a distribution chamber after the joining of the two parts. To the distribution chamber an over the working width extending discharge channel is connected, from which the coating color emerges. In order to be able to apply uniformly over the working width on paper or board webs with a large width even small amounts of coating under fluctuating conditions, eg fluctuating viscosity or changing application quantities, the flow conditions in the distribution chamber are influenced by the supplied volume flows. For this purpose, at least two supply channels are connected to the distribution chamber, each having a device for adjusting the supplied volume flow of coating color. Preferably Schlauchklemm- or diaphragm valves are used for the flow adjustment. The volume flows of each feed channel are therefore set separately. For a further homogenization, a second distributor chamber is arranged between the distributor chamber and the outlet channel. Between the then first distribution chamber and the second distribution chamber is an additional flow channel. The hose clamp valves and diaphragm valves are preferred for volumetric flow adjustment to avoid coating of coating pigments. The guide channels are inclined towards the lateral edge against the vertical inclined to the distribution chamber connected to minimize the space requirement for the feed channels. The boundary wall of the feed channels is designed with large radii of the deflection in order to avoid detachment of the flow on the walls and thus the segregation of the coating color.

The extension of the feed channel should be designed so that the velocity distribution of the channel flow has a high symmetry and the backflow is avoided. The extension angle must therefore be below a critical value. With a low viscosity of the coating color, the expansion angle is relatively small, for example 8 to 12 °. At high viscosity, the feed channels can be made with a large extension angle, for example 20 to 25 °. The disadvantage of this solution is that the distance between the feed channels and the dimensions of the feed channels must be large. The connection distance of the feed channels is in the range of 100 to 1500 mm, preferably between 500 and 800 mm. At shorter intervals, additional controls are required, which significantly increase the costs for the curtain coater. Another disadvantage is that the supply channels take up a very large amount of space, especially at small expansion angles, making the technical implementation is impossible especially at the cascade nozzles, since the space that is available for it, is very limited by the curtain height.

Out WO 2005/024132 a nozzle unit is known which has feed bores whose cross sections and their flow resistances can be changed. This allows the volume flow in each hole to be regulated. The supply bores are arranged between a machine-width supply chamber and a compensation chamber and positioned at a distance from each other in the direction of the discharge width. Although this embodiment has a small footprint, but the disadvantage that the supply holes must be positioned at very small distances from each other in order to achieve optimum flow conditions in the machine-width compensation chamber, where the individual partial streams are brought together again from the supply holes. The supply holes must therefore be very small dimensions. The danger of blockages is then particularly large and absolutely undesirable because production disturbances can be caused.

The object of the invention is therefore to provide a curtain coater, which ensures a high uniformity of the distribution of a coating medium over a discharge width under varying operating conditions with respect to the volume flows and the viscosity of the application medium and is inexpensive to produce.

This object is solved by the features of claim 1.

According to the invention, the volumetric flow influencing and the generation of a uniform velocity profile in a machine-wide outlet gap take place separately in two different functional elements. The space required is small, so that the solution according to the invention can also be used on cascade nozzles.

The adjustable volume flow control is a zone-wise adjustable volume control, for which a separate device is provided which connects at least two feed channels to at least partially subdivided into sections along a feed width distribution chamber, which forms an intermediate chamber. For generating a uniform velocity profile in the outlet gap (flow gap), a diffuser block is provided, which consists of a plurality of guide channels. The number of divisions of the compartmentalized intermediate chamber for zonal flow control is smaller than the pitch of the guide channels of the diffuser block.

This results in different pitch widths for influencing the volume flow on the one hand and the speed profile influencing on the other hand, wherein preferably the respective pitch width of the intermediate chamber is an integer multiple of a pitch width of the diffuser block. According to the invention, the flow gap is replaced by a plurality of guide channels, thereby achieving a homogenization of the velocity profile. Each guide channel may comprise a pipe section, which is preferably a part with a is circular cross-section, and a subsequent flow in the extension of the channel flow, the so-called diffuser of the guide channel. The guide channels produce an approximately equal flow resistance.

Further embodiments of the invention are described in the following description and the dependent claims.

• Fig. 1 zeigt schematisch eine Querschnittsansicht eines Düsenkörpers eines Vorhang-Auftragswerks für eine Kaskadendüse gemäß einem ersten Ausführungsbeispiel,
• Fig. 2 zeigt schematisch einen Schnitt eines Düsenkörpers in Querrichtung des Auftragswerks nach A-A gemäß Fig. 1,
• Fig. 3 zeigt schematisch einen Schnitt eines Düsenkörpers in Querrichtung des Auftragswerks gemäß einem zweiten Ausführungsbeispiel,
• Fig. 4 zeigt schematisch eine Querschnittsansicht eines Düsenkörpers eines Vorhang-Auftragswerks für eine Kaskadendüse gemäß einem dritten Ausführungsbeispiel,
• Fig. 5 zeigt schematisch eine Querschnittsansicht eines Düsenkörpers eines Vorhang-Auftragswerks für eine Schlitzdüse gemäß einem vierten Ausführungsbeispiel.

The invention will be explained in more detail with reference to the embodiments illustrated in the accompanying drawings.

• Fig. 1 1 schematically shows a cross-sectional view of a nozzle body of a curtain applicator for a cascade nozzle according to a first embodiment,
• Fig. 2 schematically shows a section of a nozzle body in the transverse direction of the commissioned work according to AA Fig. 1 .
• Fig. 3 schematically shows a section of a nozzle body in the transverse direction of the commissioned work according to a second embodiment,
• Fig. 4 1 schematically shows a cross-sectional view of a nozzle body of a curtain applicator for a cascade nozzle according to a third embodiment,
• Fig. 5 schematically shows a cross-sectional view of a nozzle body of a curtain applicator for a slot nozzle according to a fourth embodiment.

The invention relates to a curtain applicator for dispensing application medium in the form of a substantially gravitationally moving curtain to a moving paper or board web.

As Fig. 1 and Fig. 2 show the curtain applicator comprises a nozzle body 1, the upper surface forms a supply lip 2 in a cascade nozzle. Via the supply lip 2, the discharge from a discharge gap 3 exiting medium flows to to get to the surface of the paper or board web to be spread, which moves under the coater. The outlet gap 3 forms the end portion of a flow channel 6, which emits the application medium via the outlet gap 3 as a flowing or falling curtain.

The nozzle body 1 comprises a machine-wide supply chamber 14, which extends along a feed width. This supply chamber 14 supplies at least two supply lines 12 which supply the application medium to a distribution chamber 7 extending along a feed width. The supply lines 12 each have a device for adjusting the supplied volume flow of application medium. This device is preferably in each case a valve 10, an actuating cylinder 11 and a servomotor 13.

The distribution chamber 7 belongs to a device 8 for influencing the volume flow and is subdivided into sections 7.1, 7.2, 7.3 at least regionally along the feed width. Each of these sections 7.1, 7.2, 7.3 is connected to a supply line 12. The number of sections is selectable as 7.1 to 7.n.

The flow channel 6 is broken down into a plurality of individual expanding guide channels 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 of a diffuser block, which connect to the distribution chamber 7 on the inlet side. The distribution chamber 7 with its sections 7.1, 7.2, 7.3 forms an intermediate chamber which feeds the partial flows supplied by the device 8 for zonal volume flow control to the individual guide channels 6.1, 6.2, 6.3, 6.4, 6.5, 6.7, 6.8, 6.9. There is a grading, wherein the division number for the distribution chamber 7 is different than that for the flow channel 6. The division number for the distribution chamber 7 is smaller than that for the flow channel 6. It follows that the sections 7.1, 7.2, 7.3 of Distribution chamber 7 each have a pitch width spanning a plurality of guide channels 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9 of the diffuser block. According to Fig. 2 The sections 7.1, 7.2, 7.3 each span three guide channels 6.1, 6.2, 6.3 or 6.4, 6.5, 6.6 or 6.7, 6.8, 6.9. According to Fig. 3 Section 7.1 spans ten guide channels 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, 6.10.

For the zone-adjustable volume flow control so a separate device 8 is provided, which is divided into several sections 7.1 to 7.n in the transverse direction. For the generation of a uniform velocity profile in the outlet gap 3, the flow channel 6 is formed as a diffuser block, which consists of a plurality of guide channels 6.1 to 6.n.

The pitch width of the sections 7.1 to 7.n is preferably significantly greater than the pitch width of the guide channels 6.1 to 6.n and particularly preferably corresponds to an integer multiple of the pitch width of the guide channels 6.1 to 6.n. It is thereby achieved that the distance between the guide channels 6.1 to 6.n (zone width) can be selected to be large in order to reduce the number of control elements compared to the prior art and accordingly to keep the investment costs low. The connection distance between in each case two of the guide channels 6.1 to 6.n can be selected in the range between 15 and 300 mm, preferably 20 and 50 mm.

The pitch widths of the sections 7.1 to 7.n and guide channels 6.1 to 6.n can be selected in a ratio of 2 to 10 to 3 to 5. The sectioned design of the distribution chamber 7 is preferably provided machine width.

Each of the sections 7.1 to 7.n is preferably connected via a valve 10 to a supply line 12 and thereby connected to the supply chamber 14. In order to minimize the space required, the valve 10 preferably has a rotary cylinder about its own axis actuating cylinder 11 with an L-shaped flow channel, which deflects the flow by 90 °. The adjusting cylinder 11 is adjusted by the servomotor 13.

The feed chamber 14 is supplied via at least one line (not shown), the application medium. The flow direction of the application medium to be supplied proceeds from the supply chamber 14, as shown in FIG Fig. 1 is shown. The nozzle body preferably further comprises a further compensation chamber 4, which emits the application medium via the outlet gap 3 as a curtain.

As Fig. 2 and Fig. 3 show, the guide channels 6.1 to 6.n are formed so that they join the intake side and along the feed width with spaced pipe sections to the sections 7.1 to 7.n the distribution chamber 7. The lengths and opening widths of the pipe sections can be selected to equalize the flow resistance along the feed width. In the direction of flow S, the pipe sections each pass into a diffuser for merging the partial flows of the guide channels 6.1 to 6.n on the outlet side. Between the outlet ends of the diffusers of the guide channels 6.1 to 6.n and the compensation chamber 4 may still be a residual partial height of the flow channel in the form of a machine-width flow gap 5 to merge the individual streams from the individual guide channels 6.1 to 6.n again before the entry into the compensation chamber 4 takes place. The spaced and widening guide channels 6.1 to 6.n are preferably arranged in a main body of the nozzle body 1.

The guide channels 6.1 to 6.n extend from the sectioned distribution chamber 7 perpendicular to the transverse direction of the commissioned work, ie preferably perpendicular to the cross-machine direction (CD) of the moving paper or board web. The guide channels 6.1 to 6.n are preferably arranged in a row. This preferably applies in the same way to section channels 9 of the device 8 for influencing the volume flow, via which the sectioned distribution chamber 7 is connected to the supply lines 12. Each section 7.1 to 7.n is preferably connected to a section channel 9, which is fed via a supply line 12 with application medium, wherein the supplied volume flow through the respective valve 10 is adjustable. According to the number of sections 7.1 to 7.n are Consequently, a corresponding number of section channels 9 and supply lines 12 are provided.

The flow resistances of the guide channels 6.1 to 6.n along the discharge width are substantially equal and amount to at least 1 mWS (9.81 kPa). The pipe sections of the guide channels 6.1 to 6.n preferably have a circular cross-section. The number of guide channels 6.1 to 6.n per meter of output width or discharge width can be selected. Preferably, the number of guide channels in the range between 3 and 66. To counteract edge currents, it is advantageous to make the distance between the guide channels over the outlet width variable. Under fluidic aspects, it is advantageous to make the guide channels 6.1 to 6.n so that they have in their end, seen in the flow direction S, a blunt end with a web width less than 0.3 mm or a rounded end to the formation of to avoid unwanted vortex shedding at the end edges.

The extension of the guide channels 6.1 to 6.n is preferably designed so that the velocity distribution of the diffuser flow has a high symmetry and a backflow is avoided. Due to the high viscosity of the coating and its relatively low velocity, this is a divergent Jeffery-Hamel flow. The expansion angle is preferably less than 25 °, between the axis of the diffuser and the wall (half angle).

The flow-contacting parts of the curtain applicator are mechanically and chemically stressed. It is therefore advantageous to form the guide channels 6.1 to 6.n in individual modules which comprise, for example, 2 to 10, in particular 3 to 5, guide channels 6.1 to 6.n. This allows the modules to be replaced more easily to adapt to, for example, a changed operating window.

In the device 8 for the zone-wise volume control and in the guide channels 6.1 to 6.n pressure losses are generated. Preferably, the pressure loss through the valve 10 of the device 8 is greater than the flow resistance through one of the guide channels 6.1 to 6.n, the input-side pipe sections also form chokes. A division of the pressure losses is preferred, wherein at least 50%, preferably up to 75%, of the sum of the two flow resistances are assigned to the throttle points of the device 8. The pressure losses in the zone-wise volume influencing of the flow are thus preferably greater than the pressure losses in the region of equalization of the velocity profiles of the flow. The valves 10 each generate a pressure loss in a partial flow, which expands into a chamber width corresponding to the pitch width.

As Fig. 1 shows, the supply chamber 14 may be designed as a cross-flow distributor. As Fig. 4 shows, alternatively, a standing rotary distributor 15 with a central feed 16 and radially arranged outlet supports 20 may be provided. The rotary distributor 15 may comprise in a known manner a pulsation damper with air cushion 17 and a membrane 18 with perforated plate 19. The rotary distributor 15 is connected to the section channels 9 via flexible feed lines 12 to the outlet supports 20.

Fig. 5 shows a nozzle body 1, which is designed as a slot nozzle (slot die). The above statements apply here accordingly, since the nozzle body 1 described according to the invention can be used for a curtain coating by the slide-type method or a slot-type method.

Claims (14)

Curtain coater for dispensing application medium in the form of a substantially gravitationally moving curtain to a moving paper or board web, comprising a nozzle body (1) having a dispensing chamber (7) extending along a feed width, said dispensing medium passing through at least two feed lines (12) is supplied, each having a means for adjusting the volume flow supplied to application medium, and a flow channel (6) which emits the application medium via a discharge gap as a curtain, characterized in that the flow channel (6) is disassembled in a multiplicity of individual, expanding guide channels (6.1 to 6.n) of a diffuser block, which adjoin the inlet side to a distribution chamber (7) which is subdivided at least partially into sections (7.1 to 7.n) along the feed width, each of these sections (7.1 to 7. n) is connected to a feed line (12) and has a pitch width points, which spans several guide channels (6.1 to 6.n) of the diffuser block. Curtain coater according to claim 1, characterized in that the guide channels (6.1 to 6.n) of the diffuser block are arranged perpendicular to the sectioned distribution chamber (7). Curtain coater according to claim 1 or 2, characterized in that the ratio of the pitch width of the sections (7.1 to 7.n) of the distribution chamber to the pitch widths of the guide channels (6.1 to 6.n) in the range 2 to 10 to 3 to 5 , Curtain coater according to one of claims 1 to 3, characterized in that the sections (7.1 to 7.n) of the distribution chamber (7) each inlet side has a section channel (9) for forming a pressure loss generating partial flow, which is in one of the pitch width extended corresponding chamber width. Curtain coater according to claim 4, characterized in that the pressure losses in the valves (10) are greater than in the guide channels (6.1 to 6.n). Curtain coater according to one of claims 1 to 3, characterized in that the guide channels (6.1 to 6.n) have individual, inlet side spaced pipe sections, each in an extension section for a discharge side merging of the partial flows of the guide channels (6.1 to 6. n) pass over. Curtain coater according to claim 6, characterized in that the lengths and opening widths of the pipe sections of the guide channels (6.1 to 6.n) for equalizing the flow resistance along the feed width can be selected. Curtain coater according to one of claims 1 to 7, characterized in that a compensation chamber (4), which discharges the application medium via the outlet gap (3) as a curtain, is provided, and the flow channel (6) between the distribution chamber (7) and the compensation chamber (4) is arranged. Curtain coater according to one of claims 1 to 8, characterized in that the flow resistance of the guide channels (6.1 to 6.n) along the feed width are substantially equal and amount to at least 1 mWS. Curtain coater according to one of claims 1 to 9, characterized in that the guide channels (6.1 to 6.n) are arranged in a row. Curtain coater according to one of claims 1 to 10, characterized in that the expansion angle of the flow-limiting walls of the respective guide channel (6.1 to 6.n) is selected as a function of Volume flow, density and dynamic viscosity of the respective application medium. Curtain coater according to one of claims 1 to 11, characterized in that the guide channels (6.1 to 6.n) are designed as replaceable modules having a plurality of guide channels. Curtain coater according to one of claims 1 to 12, characterized in that a machine-wide supply chamber (14) is designed as a cross-flow distributor. Curtain coater according to one of claims 1 to 12, characterized in that a rotary distributor (15) with radially arranged outlet supports (20) is connected to the feed lines (12).

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