Device for applying an applied medium

Abstract

Device for applying a coating medium (2.1, 2.2), in particular starch, to at least one side of a running material web (13), in particular a paper or cardboard web, by means of at least one curtain coating unit (1.1, 1.2) with a dispensing nozzle (14.1, 14.2) and at least one press gap (N) following the curtain coating unit (1.1, 1.2) to generate hydraulic pressure as the material web (13) passes through a press gap (N) formed by two rotating press rollers, which allows the coating medium (2.1, 2.2) to penetrate the material web (13), wherein, to increase the penetration of the coating medium (2.1, 2.2) into the material web (13), the at least one press gap (N) is equipped with at least one heated coating roller (7, 8) as a press roller, and at least one of the two press rollers (8) is designed with a fixed or adjustable crown (16) for adjustment a line load in a range of 20 to 200 kN / m.

Description

[0001] The invention relates to a device for indirectly applying an application medium to at least one side of a moving material web according to the preamble of claim 1.

[0002] A combined coating and smoothing process is known from EP 2 090 694 A1.

[0003] The application of a coating medium, particularly starch, has long been a standard procedure for increasing the resistance of the paper web to moisture, as well as its surface strength and overall strength. The coating medium can be introduced directly into the fiber suspension or sprayed onto a wet web in the wire section of a paper machine. However, it is more efficient to apply the coating medium after the press section and a pre-drying section. Besides size presses or film presses, curtain applicators are also commonly used for applying the coating medium.

[0004] As a result of higher production speeds, there is a need in industry for the provision of more efficient machines for applying a coating medium to a moving web of material.

[0005] From DE 100 12 344 A1, a generic device for coating a material web on one or both sides is known, in which the coating medium is applied by one or two curtain-type coating units to the surface of mutually rotating rollers. These rollers form a press gap or press nip between them, through which the material web is guided. The rotation of the rollers conveys the coating medium applied to their surface towards the material web and brings it into close contact with the web in the press nip. For this purpose, the material web, with the still-moist coating medium applied to it, can be guided through the press gap. At least one of the pressing elements of the press gap can also serve as a transfer element, onto whose surface the coating medium is applied and transported to the material web. This is intended to ensure a good bond between the material web and the coating medium.

[0006] When coating webs of material using a curtain coating system with a dispensing nozzle, also known as a curtain coater, the coating medium is dispensed onto the substrate in the form of a curtain of coating medium, which moves from the coating system to the substrate primarily due to gravity. The shape of the curtain emerging from the dispensing nozzle is determined solely by the interplay between the surface tension of the coating medium and gravity. To control the thickness of the coating medium curtain, the gap width of the dispensing nozzle can be adjusted between 0.2 and approximately 1.5 mm.

[0007] To precisely control the layer thickness of the coating medium applied to the substrate in both longitudinal and transverse directions (longitudinal profiling, transverse profiling), the gap width of the dispensing nozzle is adjustable across the entire working width. Furthermore, it is known that the sensitive control or regulation of the application quantity is important with regard to the final metering of the coating medium by the curtain applicator, i.e., 1:1 application.

[0008] It is also known that the material web, in the area where the application medium of the application medium curtain impacts the substrate, can be supported by a counter element, for example, a counter roller or an endlessly circulating support belt. However, it is equally possible that the application medium is applied to the material web in a free web section, i.e., in a section of the material web's travel path where it is not supported by a counter element.

[0009] A disadvantage is that, with paper and cardboard machine widths of up to, for example, 8 m, the manufacturing effort for nozzle parts of the discharge nozzle in such dimensions with the required precision is very high, especially with large discharge widths, and involves considerable costs.

[0010] Well-known coating machines, such as film presses, are used to precisely meter and transfer film onto paper. The application of the coating material is achieved, as in coating, via nozzle or roller systems. The term "film press" is commonly used generically, although other well-known solutions include the Speedsizer and the Metering Blade Size Press.

[0011] Film presses are known, for example, from DE 34 17 487 A1 and DE 41 31 131 C2, in which the starch, glue suspension, or coating ink is applied to an application roller by means of a metering applicator and metered by means of a metering squeegee. The coating of the paper or cardboard web takes place on both sides in a press gap between the application rollers.

[0012] During starch application, the starch temperature is typically between 50°C and 80°C. The typical solids content of the starch is between 8% and 15%, with an application weight of 0.5 to 6 g / m² per side. In some cases, it is also possible to apply starch with a solids content of up to 15% to the paper or board web using a film press of this type. During pigmentation, the solids content consists of the starch and pigment components and is typically between 15% and 40%. The line forces between the application rollers are typically between 40 and 70 kN / m.

[0013] When coating a paper web, the starch should be applied as evenly as possible. The application rate must be as constant as possible across the entire working width. In film presses of this type, the volume flow in the application zone is divided into two partial flows. One portion of the starch flows with the application roller to the metering blade and is used for coating the paper. The other portion flows back through the overflow gap, against the direction of travel of the application roller, into a collection tray for reprocessing. The overflow gap between the rim of the application chamber and the application roller significantly influences the uniformity of the starch distribution across the working width.

[0014] One disadvantage of this design is that the overflow gap widens, particularly in the center of the paper web. This leads to higher volume flows in the middle and thus to an uneven distribution of starch across the working width. To compensate for this, the starch overflow rate must be kept very high. Depending on the paper web speed, the starch overflow rate is 10 to 30 times the amount required to coat the web. Due to the high pump output, these film presses have high energy consumption and consequently poor economic efficiency.

[0015] To improve the efficiency of film presses of this type, presses with a perforated sealing blade were developed. The perforated blade is arranged as a piercing or embossing blade on the coating roller. These film presses are known, for example, from EP 2 646 169 B1 and EP 3 023 163 A1. The excess starch flows evenly across the working width through holes or slots in the blade into a collection tray. While this solution can reduce the amount of starch overflow by 10% to 20%, a continuous flow of starch from the coating zone is still necessary to prevent disruptive air inclusions in the coating zone. Therefore, efficiency is not particularly good with this design either.

[0016] To reduce the amount of starch circulated, the application chamber in the film presses was replaced by spray nozzles. The starch is pre-metered via free-jet nozzles. The starch is sprayed as a thin film onto the application roller. Subsequent leveling can be carried out using a conventional metering blade, as described, for example, in EP 0 881 330 B1. Film presses with free-jet nozzles without a metering blade are also known and described, for example, in EP 0 670 004 B1 and DE 20 2017 100 655 U1.

[0017] The free-jet nozzles allow for a very thin film application onto the coating roller. This reduces the amount of starch circulating to a minimum. Film presses with spray nozzles have the significant disadvantage that the maximum solids content of the starch is limited to approximately 14%. Particularly with high solids content, starch particles adhere to the free-jet nozzles. This leads to streaking and a resulting uneven distribution of the starch across the web width. In the worst case, this can cause blockages in the nozzles and interruptions in production. Another disadvantage is the formation of a mist of starch particles in the coating zone. This causes the small starch particles to adhere to the entire surface of the film press. This increases cleaning requirements and the risk of deposits that can affect the paper web.Additional technical effort is required to extract the mist from the application zone, which in turn causes further problems with a fluttering paper web. To stabilize the web, an airflow can be introduced into the application zone, as described, for example, in EP 2 811 069 B1.

[0018] Another disadvantage of spray nozzles is the cooling of the atomized starch particles in the airflow within the application zone. This temperature reduction impairs the starch's penetration into the paper due to increased viscosity. To counteract this cooling, steam is introduced to heat the starch particles in the application zone. This solution is technically very complex.

[0019] A multi-layer coating system is also known, as described, for example, in DE 10 2006 057 870 A1. The thickness is applied in several layers to the coating rollers using curtain coating systems and then transferred together in a single nip to the material web.

[0020] From DE 10 2018 100 924 A1, it is known that for applying starch to a moving fiber web, the web with the still-moist starch coating is guided through a treatment press gap formed by a first and a second roller. At least one of the two rollers, preferably both rollers, has a hardness of 15 P&J (Pusey & Jones) or less. Even harder rollers of 5 P&J or less, and at most 1 P&J or less, can be used. The pressing force of the treatment press gap is set between 30 kN / m and 140 kN / m. The use of one or even two rollers with relatively high hardness in a treatment gap enables the starch to be transferred to the fiber web much more efficiently.

[0021] The term "hardness" of a roller refers to the hardness of the outer layer or surface of the roller. The P&J hardness test is a common measure for rollers. It can be determined using commercially available devices, such as the P&J Zwick 3108 hardness tester, which meets the requirements of ASTM D531-89.

[0022] However, a disadvantage here as well is that the solids content for starch penetration is only up to 25%, which significantly reduces the efficiency of the system.

[0023] The object of the invention is therefore to create a device that allows for a more economically efficient application of an application medium, in particular starch, to a moving web of material when the web of material is guided through a treatment press gap after the application of the starch, as described in the preamble of claim 1.

[0024] This problem is solved by the features of claim 1.

[0025] This creates a device that operates more efficiently, both technologically and economically, by increasing the penetration of the coating medium, particularly the starch. As a result, the strength properties of the paper or cardboard can be improved.

[0026] According to the invention, a curtain applicator is used as the applicator, with which very high solids contents of the applicator medium, in particular starch, of up to 40%, preferably 15% to 35%, can be applied in one or more layers. The applicator medium is transferred indirectly to the material web via a heated transfer element.

[0027] To ensure high penetration of the coating medium into the material web despite the high solids content, precise control of the line load distribution across the roller width is provided. For this purpose, the press gap includes at least one roller with adjustable crowning, in particular a bending adjustment roller. Line forces in the press gap between 20 kN / m and 200 kN / m, preferably 80 kN / m and 120 kN / m, can then be varied across the entire press force range, since precise thickness cross-profile control is possible regardless of the line load level. The same applies to the temperature of a heated roller, so the invention further provides for at least one coating roller to be designed as a heated roller. The temperature of the heated roller is preferably in the range of 50°C to 150°C, more preferably in the range of 90°C to 120°C.

[0028] If application of a coating medium to both sides is intended, the press gap can be formed by two coating rollers, both of which can be heated. The coating rollers are preferably hard rollers with a hardness of less than 30 P&J (Pusey & Jones).

[0029] Increased efficiency of the device results in particular from a significantly reduced energy consumption for the evaporation of excess water at high application medium concentrations.

[0030] Furthermore, the inventors deserve credit for recognizing that lower accuracy in the nozzle gap width of a curtain coating unit, particularly a curtain coater, can be compensated for across the working width by a sump that forms at or immediately in front of the press gap due to the process, especially when a sensitive adjustment of the linear force profile perpendicular to the web or along the press gap is possible. If parallelism of the roller contact surfaces is ensured perpendicular to the web, for example by means of a bending adjustment roller as the coating roller, a compensating sump forms in the infeed area of ​​the press gap.

[0031] The high manufacturing tolerance typically required in curtain coating systems, particularly curtain coaters, is therefore unnecessary according to the invention and can be increased. This reduces the manufacturing effort of the dispensing nozzles and the investment costs. The accuracy of the discharge gap of the dispensing nozzle for the curtain coating system is preferably in the range of ± 2.5 µm to ± 10 µm, and particularly preferably in the range of ± 4 µm to ± 8 µm. This applies especially to typical gap widths in the range of 0.2 to 1.5 mm.

[0032] Further advantages and embodiments of the invention can be found in the following description and the dependent claims.

[0033] The invention is explained in more detail below with reference to the exemplary embodiments shown in the accompanying figures. Fig. 1 schematically shows a device with curtain applicators and dispensing nozzles according to a first embodiment, Fig. 2 schematically shows a device with curtain applicators and dispensing nozzles according to a second embodiment.

[0034] How Fig. 1 As shown in the figure, the invention relates to a device for the indirect application of an application medium 2.1, 2.2, in particular starch, to at least one side of a moving web of material 13, in particular a paper or cardboard web, by means of at least one curtain application unit 1.1, 1.2 with a dispensing nozzle 14.1, 14.2. The at least one curtain application unit 1.1, 1.2 is followed by a press gap N for generating hydraulic pressure as the web of material 13 passes through the press gap N, which allows the moist application medium 2.1, 2.2 to penetrate the web of material 13. The press gap N is preferably a hard nip formed by two hard rollers, the application rollers 7, 8.

[0035] The at least one curtain applicator 1.1, 1.2 is designed to dispense an applicator medium 2.1, 2.2 with a solids content in at least one layer of between 10% and 40%. To increase the penetration of the applicator medium 2.1, 2.2 into the material web 13, the at least one press gap N is equipped with at least one heated applicator roller 7, and the heated applicator roller 7 and / or a counter element is designed as an applicator roller 8 with adjustable crown 16.

[0036] The curtain applicator 1.1, 1.2 has a dispensing nozzle 14.1, 14.2 with a discharge gap 15 which has an accuracy in the range of ± 2.5 µm to ± 10 µm in gap length at a gap width of preferably 0.2 to 1.5 mm.

[0037] As the arrows X show, the spatial position of each curtain application unit 1.1, 1.2 relative to the press gap N is adjustable for an arrangement for the indirect application of the application medium 2.1, 2.2 with selectable residence time of a heat transfer from the at least one heated application roller 7 to the application medium 2.1, 2.2 and / or the material web 13, as will be explained below.

[0038] The coating roller 8 with adjustable crown 16 is preferably a bending compensation roller. Preferably, both coating rollers 7, 8 of the press gap N are designed as heated rollers. The coating rollers 7, 8 of the press gap N preferably have coatings with less than 30 P&J. Furthermore, the coating rollers 7, 8 of the press gap N are designed for a roller surface temperature of 50°C to 150°C, particularly preferably 100°C to 120°C. The line load can be selected in the range of 20 kN / m to 200 kN / m.

[0039] An angle α for the point of impact of the curtain of the coating medium 2.1, 2.2 on a coating roller 7, 8 of the press gap N is preferably between -90° and +45°. Furthermore, the respective curtain coating unit 1.1, 1.2 is designed to control the solids content of the coating medium 2.1, 2.2 in at least one layer from 25% to 55%.

[0040] The application weight of the coating medium per side can be 0.5 to 6 g / m², and the temperature of the coating medium, particularly the starch, can be in the range of 55° to 99°C before application to a coating roller 7, 8. Furthermore, the viscosity of the coating medium can be significantly higher than in film presses, namely 20 to 500 mPa s (Brookfield 100 rpm). The specific volumetric flow rate from the nozzle of the curtain coating unit 1.1, 1.2 is in the range of 4 l / (min xm) to 30 l / (min xm). A film of the coating medium 2.1, 2.2, particularly starch, is preferably applied to the respective coating roller 7, 8 in the range of 5 ml / m² to 100 ml / m².

[0041] Finally, guide rollers 12 can also be provided, which determine a treatment path of the running material web 13 between curtain application unit 1.1, 1.2 and press gap N.

[0042] According to Fig. 1 For a single-sided, single-layer application, the application medium 2.1, in particular starch, is first applied to a rotating application roller 7 by a curtain application unit 1.1. For a double-sided application, a further application medium (film) 2.2, for example a single layer, is applied to a second rotating application roller 8 by a second curtain application unit 1.2. The dwell time of the application medium 2.1, 2.2 on the respective application roller 7, 8 until it enters the press gap N can be selected individually for each side and can therefore be different. The position of the respective curtain application unit 1.1, 1.2 relative to the associated application roller 7, 8 can be changed in the direction of arrow X, for example by horizontal and, if necessary, additionally vertical movement.

[0043] A specific outer circumference of the roller, corresponding to the residence time, can be set between the impact of the curtain and its entry into the press gap N, thereby increasing or decreasing the residence time as indicated by the angle α. If the coating roller 7, 8 is heated, the residence time can be used to influence the temperature increase of the coating medium 2.1, 2.2 before it enters the press gap N. The coating medium 2.1, 2.2 can then be thermally pretreated in this way before being pressed into the material web 1 on both sides in the press gap N between the coating rollers 7, 8.

[0044] In a known manner, each curtain application unit 1.1, 1.2 can be assigned a starter tray 4.1, 4.2 with a quick-start device 5.1, 5.2. The same applies to the provision of drip trays 9.1, 9.2, scrapers 10.1, 10.2, and spray nozzles or steam nozzles 11.1, 11.2 for cleaning the application rollers 7, 8. The diameter of the application rollers 7, 8 can, for example, be 400 to 1800 mm. Heated transfer belts can also be used instead of heated application rollers 7, 8.

[0045] According to Fig. 2 A multi-layered curtain coating system 1.1, 1.2 is provided in each case, which here, for example, is designed as a two-layer system. The two curtain coating systems 1.1, 1.2 can also each have different multi-layer configurations. In a two-layer configuration, for example, an inner layer can be used to introduce starch for penetration into the material web. The outer (second) layer can, for example, be a pigment coating. The solids content of the starch in the first layer can be, for example, 6% to 50%, preferably 15% to 35%. The solids content of the coating in the second layer can be in the range between 20% and 68%. Alternatively, the two-layer curtain coating system can consist of two starch layers. The first layer can have a lower starch concentration to achieve higher penetration for high splitting strength. A second layer can be...A layer with a higher starch concentration increases the modulus of elasticity of the outer, near-surface layers, thus achieving a higher bending stiffness.

[0046] This results in significant technological advantages, and the plant's high economic efficiency stems from a considerably reduced energy consumption for evaporating excess water at high starch concentrations. With the same strength, raw material savings are possible by reducing the amount of fiber in the paper or cardboard.

[0047] Furthermore, the above statements apply to Fig. 1 accordingly.

Claims

1. Device for applying indirectly a treatment substance (2.1, 2.2), in particular starch, on at least one side of a running product web (13), in particular a paper or board web, by means of a least one curtain coater (1.1, 1.2) having a discharge nozzle (14.1, 14.2) and at least one press nip (N) following the curtain coater (1.1, 1.2) for forming a hydraulic pressure when the product web (13) passes through a press nip (N) which is formed by one of two rotating press rolls and which causes the treatment substance (2.1, 2.2) to penetrate into the product web (13), characterized in that the curtain coater (1.1, 1.2) has a discharge nozzle (14.1, 14.2) having an outlet slot with a manufacturing tolerance in a range of ± 2,5 µm to ± 10 µm in slot length with a slot width of 0,2 to 2.0 mm, the at least one press nip (N) is equipped with at least one heated applicator roll (7, 8) as a press roll to increase the penetration of the treatment substance (2.1, 2.2) into the product web (13), and at least one of the two press rolls is designed with an adjustable crown (16) for the adjustment of a line load in a range of 20 to 200 kN / m, and a compensation sump is provided at the feed area of the press nip (N), which in case of a parallelism of roll contact surfaces, ensured across the web (13) using the press roll with an adjustable crown (16) as applicator roll (8) and line loads in the press nip (N), is formed.

2. Device according to claim 1, characterized in that the press nip (N) is designed as a hard nip.

3. Device according to claim 1 or 2, characterized in that the distance of the respective curtain coater (1.1, 1.2) with respect to the press nip (N) is adjustable for an arrangement for the indirect application of the treatment substance (2.1, 2.2) with a selectable dwell time for the transfer of heat from the least one heated applicator roll (7, 8) to the treatment substance (2.1, 2.2).

4. Device according to one of claims 1 to 3, characterized in that the curtain coater (1.1, 1.2) is designed to apply a multi-layer curtain.

5. Device according to one of claims 1 to 4, characterized in that guide rolls are provided which determine a treatment path of the running product web (13) between the curtain coater (1.1, 1.2) and the press nip (N).

6. Device according to one of claims 1 to 5, characterized in that the press roll with adjustable crown (16) is a controlled deflection roll.

7. Device according to one of claims 1 to 6, characterized in that both press rolls of the press nip (N) are designed as heated applicator rolls (7, 8).

8. Device according to one of claims 1 to 7, characterized in that the applicator rolls (7, 8) of the press nip (N) have coatings with less than a hardness of 30 P&J.

9. Device according to one of claims 1 to 8, characterized in that the press rolls of the press nip (N) are designed as applicator rolls (7, 8) for a roll surface temperature of 50°C to 150°C.

10. Device according to one of claims 1 to 9, characterized in that the press nip (N) is designed for line loads in the range of 20 kN / m to 200 kN / m.

11. Device according to one of claims 1 to 10, characterized in that an angle α for a contact point of the curtain of the treatment substance (2.1, 2.2) on an applicator roll (7, 8) of the press nip (N) is between -90° and +45°.

12. Device according to one of claims 1 to 11, characterized in that the curtain applicator (1.1, 1.2) is designed to control the solids content of the treatment substance (2.1, 2.2) in at least one layer of 25% to 55%.

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