Curtain applicator for applying application media to at least one application roller

Abstract

Device for applying coating media, in particular starch or glue, to a moving paper and cardboard web (11), in particular testliner or corrugated board, by means of at least one curtain applicator (2.1, 2.2) with a curtain applicator nozzle for applying the coating medium to an applicator roller (6, 7), which forms a treatment nip (15) with a second roller (6, 7), in which the coating medium is transferred from the applicator roller (6, 7) to the respective side of the paper and cardboard web (11), and the curtain applicator nozzle has a gap adjustment (3.1, 3.2) for adjusting the exit gap (14.1, 14.2), wherein differently prepared coating media can be fed to the at least one curtain applicator nozzle, and a gap adjustment (3.1, 3.2) of the exit gap (14.1, 14.2) of the curtain applicator nozzle from 100 µm to 500 µm for a film operation and on 500 µm to 2.0 mm for a swamp operation that includes at least one curtain application unit (2.1, 2.2) capable of operating in these different modes of operation.

Description

[0001] The invention relates to a device for applying coating media, in particular starch or glue suspension, to a moving paper or cardboard web according to the preamble of claim 1.

[0002] The production of packaging papers and cardboard increasingly relies on recycled paper fibers. For example, testliner (TL) and corrugated board (CM) are predominantly produced from recycled paper fibers in the EU. Due to a high proportion of recycled fibers, the strength properties of packaging papers decrease. The use of starch in papermaking can compensate for this loss of strength. The starch is usually added either directly to the fiber suspension or sprayed onto the wet web in the forming section. Alternatively, the starch can be applied to the paper web immediately after the pre-drying section using contact or non-contact application methods.

[0003] For applying starch to packaging papers and cardboard, nip presses are used, as described, for example, in the Handbook of Paper Technology - 2nd edition, Chapter 10, Subchapter 10.7.2 "Paper Production". The majority of nip presses are equipped with two application rollers. According to current technology, the application rollers are arranged at an angle of 0° to 15° to each other. During operation, the application rollers close and, together with the passing paper web, form a nip. The starch or the sizing solution is fed to the nip via so-called sizing tubes. A slurry forms between each application roller and the paper web. The starch or sizing penetrates the paper while the paper web is guided through the slurry and the nip. The application weight of the starch or sizing solution is determined by the specific pressure applied to the paper.The application rate of the adhesive is primarily determined by the liquid level in the bath, the residence time, the concentration of the liquor, and the contact pressure in the roller nip. The temperature and viscosity of the liquor, as well as the porosity of the paper, also influence the penetration behavior and thus the application weight.

[0004] The starch temperature is typically between 50°C and 80°C. The typical solids content of the starch in a bottom press is between 5% and 12% with an application weight of 0.8 to 5.5 g / m² per side. The line forces between the application rollers vary between 40 and 100 kN / m. To achieve high penetration, bottom presses are operated in the upper line force range between 80 and 100 kN / m. The use of hard roller coverings between 1 and 15 (Pusey & Jones (P&J)) enables these high nip pressures. Hard roller coverings are therefore preferred for bottom presses. Compared to film presses, bottom presses have the advantage of high starch penetration into the paper.

[0005] Due to the low solids content of starch, however, sump presses have high energy consumption. This results in lower efficiency compared to, for example, film presses. Paper manufacturers are therefore always faced with the challenge of using the most economically viable process. On lines where testliner and fluting are produced together, combined film / sump presses are often used and operated accordingly, depending on the paper grade.

[0006] For the technological and economic improvement of film presses, new non-contact devices and methods for applying starch using a curtain sizer have been developed, as described, for example, in DE 20 2019 106 814 U1 and WO 2020 / 020626 A1. According to these methods, the application weight is metered via a volume flow control at the application nozzles themselves. The curtain sizer has the decisive advantage over film presses that the starch can be applied with a very high solids content of up to 25% and more. A method and device for applying an application medium using a curtain sizer are also known, for example, from EP 3 842 591 A1.

[0007] Besides its advantages, the curtain sizer also has technological limitations. It is limited with regard to low starch viscosities. At viscosities below 30 mPa·s (with solids contents below 10%), a thin liquid film of starch becomes unstable upon contact with the application roller, disrupting the uniform distribution of the starch application. Applying a uniform, thin film, as required in film press operation, is therefore no longer possible. However, low viscosities with low starch contents are necessary to achieve high starch penetration into the paper. As previously described, in these cases it is better to supply the starch via a sump than via a film.

[0008] Both coating methods, bottom coating and film coating, as different coating units, have their own operating windows with varying limitations. Bottom coating is advantageous at low viscosity (below 20-30 mPa·s) and low solids content (below 10%), while film coating is more suitable for higher viscosity (above 30 mPa·s) and higher solids content (above 10%). The state of the art is described below using the paper grades testliner (TL) and corrugated board (CM) as examples.

[0009] Testliner and corrugated board are papers with a basis weight ranging from 70 to 200 g / m², made from raw materials consisting of 100% recycled paper fibers. Corrugated board is used for the middle layer, forming the fluting, in the production of corrugated board, while testliner (TL) is used for the outer layer. Corrugated board (CM) uses higher-quality recycled paper fibers than testliner (TL).

[0010] Due to the different applications of test liner and corrugated material, different requirements are placed on the properties of these products. For test liner, surface smoothness and its hydrophobicity, as well as strength properties such as ring crush resistance (RCT), strip crush resistance (SCT), and burst strength are important. For corrugated material, surface smoothness and its hydrophobicity are less important, but strength properties such as burst strength, strip crush resistance (SCT), and especially flat crush resistance (CMT) are of great significance.

[0011] Due to the aforementioned quality requirements, the surface treatment of the two products with starch and glue has different objectives. While maximum penetration of the starch into the paper is required for the corrugated board, a surface treatment with starch and glue is the primary focus for the testliner.

[0012] While the corrugated board requires the highest possible starch penetration to meet quality requirements, the testliner aims to fix the starch to the surface (see Kießler, B.: Improvement of paper strength and process reliability in the surface treatment of corrugated base papers through specific starch digestion. PTS Research Report IW 050275, Heidenau, 2006). Accordingly, the starch solutions for these two applications are prepared differently to allow for targeted control of the penetration depth into the paper.

[0013] Since deep starch penetration is not required for testliner, the starch solutions used in testliner have a higher viscosity and, consequently, a higher concentration (13-15%) than the starch used for corrugated board (5-12%). This is economically advantageous because a higher solids content reduces the energy required for drying the paper. Paper manufacturers aim to further increase the starch concentration. The concentration limitation of approximately 15% in film presses was one of the main reasons for the development of a curtain sizer for coating cardboard. Paper manufacturers are therefore faced with the challenge of retrofitting their existing lines with additional coating units.

[0014] The swamp press and curtain sizer are two independent units that must be arranged sequentially in the plant, similar to blade coaters on a coating machine. Installing additional coating units typically requires extending the paper machine. This necessitates compromises in machine design and the production process, often at the expense of paper quality.

[0015] The object of the invention is therefore to create a device for applying coating media, in particular starch or glue, to packaging papers and cardboard, especially corrugated board (CM) and testliner (TL), which improves the achievable paper / cardboard quality, particularly in stable production.

[0016] This problem is solved by the features of claim 1.

[0017] This provides a device for applying coating media by means of at least one curtain applicator with a curtain applicator nozzle for applying the coating medium to an applicator roller, which combines the two operating modes of a film press and a sump press. The curtain applicator according to the invention can alternatively be operated as a film press or as a sump press and thus forms a combination unit.

[0018] By providing a curtain applicator, in particular a curtain sizer, with the gap adjustment of the discharge gap of the curtain applicator nozzle according to the invention, an applicator is created that differs from the design of known curtain applicators. The gap adjustment from 500 µm to 2.0 mm results in high curtain weights, the stabilization of which, due to the formation of a liquid sump above a roller nip, no longer directly determines the coating quality. Capillary forces during the residence time in the sump and the hydraulic pressure during passage through the nip allow the applicator to penetrate the web. The liquid level in the sump, which is influenced according to the invention via the gap adjustment, is a determining factor for the uptake of applicator and thus for the paper / board quality.

[0019] A simple retrofit of existing sump presses to a device according to the invention, with at least one coating unit according to the invention, is possible with minimal effort. Furthermore, the coating process can be changed from film coating to sump operation without shutting down the paper machine. This eliminates the disadvantage that existing paper and board machines often have limited flexibility for retrofitting with additional units, as this space was not originally provided.

[0020] Further embodiments of the invention can be found in the following description and the dependent claims.

[0021] The invention is explained in more detail below with reference to the exemplary embodiments shown in the accompanying figures. Fig. 1 schematically shows a cross-section of a device according to the invention for applying application media in a film factory, Fig. 2 schematically shows a cross-section of a device according to the invention for applying application media in a sump operation, Fig. 3 schematically shows a cross-section of a curtain application nozzle of a curtain application unit according to the invention with gap adjustment via an eccentric shaft, Fig. 4 schematically shows a cross-section of a curtain application nozzle of a curtain application unit according to the invention with gap adjustment via a linear actuator.

[0022] The invention relates to a device for applying coating media, in particular starch or glue, to a moving paper and cardboard web 11, in particular testliner or corrugated board. The device comprises at least one curtain applicator 2.1, 2.2 with a curtain applicator nozzle for applying the coating medium in the form of a curtain 4.1, 4.2 onto at least one applicator roller 6, 7. One applicator roller 6, together with the second roller 7, which in the case of double-sided application is also designed as an applicator roller, forms a treatment nip or roller nip 15 in which the coating medium is transferred from the applicator roller 6, 7 to the respective side of the paper and cardboard web 11. The curtain applicator nozzle of the respective curtain applicator 2.1, 2.2 further comprises a gap adjustment 3.1, 3.2 for adjusting the exit gap 14.1, 14.2 of the curtain applicator nozzle.

[0023] Differently prepared coating media can be fed to the at least one curtain coating nozzle. Furthermore, the at least one curtain coating unit 2.1, 2.2 is designed to be operable in different operating modes by adjusting the gap 3.1, 3.2 of the discharge gap 14.1, 14.2 to 100 µm to 500 µm for film operation and to 500 µm to 2.0 mm for sump operation.

[0024] For the technical implementation of the invention, the use of a curtain coating unit 2.1, 2.2 in conjunction with coating rollers 5, 6 is preferably provided, wherein at least one coating roller 7 can be designed as a bending-controlled roller. These rollers are known, for example, under the names S-roller, MHV roller or NIPCO roller.

[0025] The rollers 6, 7 for forming the roller nip 15 can be provided with hard coatings, for example ceramic or chrome, or can also be equipped with hard polymer coverings. The surface hardness is less than 30 Pusey & Jones, preferably less than 15 P&J. The application rollers 6, 7 can be temperature-controlled.

[0026] Fig. 1 Figure 1 shows an embodiment of the device according to the invention in film operation mode. Film operation is an application system that pre-meters a precise film, which is transferred to the web 11 in the roller gap 15 without any scum. The film operation of the curtain application unit 2.1, 2.2 allows for the application of a very high solids content of starch. Reference numeral 12 indicates a possible lateral guide for excess application medium.

[0027] The direction of travel of a web is from top to bottom and is indicated by an arrow. This is, for example, the coating of a test liner (TL). The solids content of the starch is relatively high at 15%. The volumetric flow rate for the coating is therefore relatively low. A cleaning scraper 9.1, 9.2 is positioned against the coating roller 6, 7 and is in the operating position. The coating roller 6, 7 is continuously cleaned by the cleaning scraper 9.1, 9.2 during production. Spray water or steam nozzles 10.1, 10.2 may be provided for cleaning the coating rollers 6, 7. Fibers and starch particles adhering to the roller surface are removed from the roller 6, 7 by the cleaning scraper. A drip tray 8.1, 8.2 prevents water from dripping onto the moving paper web 11.

[0028] The curtain applicator nozzle of the curtain applicator 2.1, 2.2 can be moved hydraulically or by motor. A pivoting movement of the entire unit can be provided for this purpose. In the event of a production interruption due to a malfunction or web break, the nozzle and the entire unit of the curtain applicator 2.1, 2.2 can be moved into a preparation position. In the preparation position, the starch preferably flows into a preparation trough 5.1, 5.2 and is from there returned to the workstation.

[0029] In operating mode, the curtain application nozzle of the curtain application unit 2.1, 2.2 is positioned such that, for example, the point of impact of the curtain 4.1, 4.2 is located on the axis of the application roller 6, 7. The angle α is between zero and 45°. This position of the curtain application nozzle is preferably selected such that the distance from the air boundary layer extraction point to the curtain is minimal. This prevents disruptive influences of the boundary layer airflow along the moving roller surface on the curtain. In this position, it is possible to generate a stable curtain without heel formation and without unwanted backflow on the moving roller 6, 7. Below a positioning angle α of approximately 45°, the thin curtain is disturbed by the boundary layer airflow, and uniform contact with the roller surface is no longer possible.

[0030] The application rollers 6, 7 are preferably arranged at an angle of 0° to 15° to each other. The application medium can be applied to both sides of the application rollers 6, 7 by means of a curtain 4.1, 4.2. A nozzle with a discharge gap 14.1, 14.2 of 100–500 µm is used to form a curtain 4.1, 4.2.

[0031] The application medium can be starch, glue, or a mixture of these media. The application medium is then transferred in nip 15 between the application rollers 6 and 7 onto the paper or cardboard web 11.

[0032] The respective curtain 4.1, 4.2 can have a curtain height in the range of 50 to 300 mm between the point of impact on the application roller 6, 7 and the nozzle exit.

[0033] How Fig. 2 As shown, in the operating mode of a sump press, the application medium, in particular the starch or the glue solution, can first be applied to the application roller via the nozzle or fed directly into a sump 13. The curtain application nozzle can be positioned, for example, by means of a linear guide 1.1, 1.2.

[0034] Since the starch concentration is significantly lower in sump operation, meaning the coating medium is prepared differently than in the film operation described above, the volumetric flow rates are correspondingly higher. Furthermore, sump operation requires an even higher volumetric flow rate to maintain a specific sump height. For example, the volumetric flow rate in sump operation can be two to three times higher than in the operating mode of a curtain sizer (film operation). With a high volumetric flow rate combined with a small nozzle exit gap, the starch exit velocities from the nozzle gap 14.1, 14.2 would be very high. These high exit velocities could cause splashing and turbulence when the starch impacts the coating roller 6, 7 or the sump 13. This could disrupt the coating process.

[0035] To reduce the exit velocities from the nozzle, the outlet gap 14.1, 14.2 is adapted to the volume flow rate according to the invention. The outlet gap 14.1, 14.2 of the nozzle for sump operation is selected to be larger than in curtain operation for film operation. An outlet gap 14.1, 14.2 of 0.5 to 2.0 mm has proven to be optimal for sump operation according to the invention. To correct or adjust the outlet gap 14.1, 14.2, a gap adjustment 3.1, 3.2 is provided on the nozzle lip.

[0036] The nozzle of the curtain applicator 2.1, 2.2 is positioned during sump operation such that the angle α for the point of impact of the curtain 4.1, 4.2 on the application roller 6, 7 or the sump 13 is in the range between 30° and 90°, preferably between 45° and 60°.

[0037] Cleaning of the application roller 6, 7 is preferably not necessary in sump operation mode, since the roller 6, 7 is cleaned by the flow of starch in the sump 13. The cleaning scraper 9.1, 9.2 is swung away.

[0038] Corrugated board (CM) and testliner (TL) are usually produced on the same paper machine. The changeover between grades often occurs without stopping the paper machine. During a smooth changeover from film operation to swamp operation, the curtain nozzle of the curtain applicator 2.1, 2.2, and the entire unit, can move towards nip 15.

[0039] Suppose that the production of testliner (TL) is switched to corrugated board (CM) on the paper machine during ongoing production. The process would then be as follows: When transitioning to the operation of a sump press, the starch continues to be applied to the coating roller 6, 7 via the curtain nozzle. The sump operation requires an additionally higher volume flow to achieve a specific sump height. According to the invention, the outlet gap 4.1, 4.2 of the nozzle is enlarged for sump operation to adapt the exit velocity to the higher volume flow. The outlet gap 4.1, 4.2 of the nozzle is therefore adjusted from, for example, 350 µm to approximately 1 mm to switch the coating unit to sump operation mode. The adjustment of the outlet gap 4.1, 4.2 can be implemented manually or automatically (motorized or hydraulically).

[0040] When using profiling rollers, it is also possible according to the invention to operate the system in pure calender mode. For this purpose, the hard coating roller 6 would have to be equipped so that higher surface temperatures can be set (thermal roller).

[0041] The Abb. 3 and Abb. 4 Figures 3.1 and 3.2, for example, show different embodiments of the gap adjustment at the outlet nozzle. Abb. 3 A gap adjustment 3.1, 3.2 is shown via an adjusting device that engages the nozzle lip. The adjusting device can be, for example, an eccentric shaft, a plunger, or a wedge. The adjusting device can be electrically and / or mechanically actuated.

[0042] The nozzle gap could also be adjusted, for example, with the aid of linear actuators 3.3. The position of the at least one curtain application nozzle relative to the application roller can be changed in such a way that the curtain height remains essentially the same in the different operating modes.

[0043] The line force in the roller nip 15 can be between 20 kN / m and 200 kN / m, preferably between 80 kN / m and 120 kN / m. 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 dry content of the paper or board web 11 can be greater than 90%, particularly between 92% and 98%. Starch as the coating medium can be provided with a specific volume flow rate between 15 l / (min*m) and 150 l / (min*m) for wetbed operation and between 5 l / (min*m) and 50 l / (min*m) for film operation. Starch as the coating medium can be provided with a solids content between 5% and 10% for wetbed operation and between 10% and 25% for film operation. The viscosity of the starch as the coating medium can be selected between 20 mPas and 200 mPas. The temperature of the starch as the coating medium can be selected between 50°C and 110°C, preferably between 70°C and 100°C.

Claims

1. A device for applying a treatment substance, in particular starch or size, to a running paper web or board web (11), in particular testliner or corrugating medium, by means of at least one curtain applicator (2.1, 2.2) comprising a curtain coating die for applying the treatment substance to an applicator roll (6, 7) which, together with a second roll (6, 7), creates a treatment nip (15) in which the treatment substance is transported from the applicator roll (6, 7) to the respective side of the paper web or board web (11), and the curtain coating die has a slot adjustment (3.1, 3.2) for adjusting an exit slot (14.1, 14.2), and differently prepared treatment substances can be supplied to the at least one curtain coating die, and characterized in that the curtain applicator (2.1, 2.2) is configured in such a way that it combines the two operating modes of a film operation mode and a sump operation mode by providing an electrically and / or mechanically operated adjustment device to the slot adjustment (3.1, 3.2) applied to the exit slot (14.1, 14.2) of the curtain coating die, which controls a die lip and sets the exit slot (14.1, 14.2) alternatively to 100 µm to 500 µm for a film operation mode or to 500 µm to 2.0 mm for a sump operation mode, so that the at least one curtain applicator (2.1, 2.2) is designed to be performed with two different operating modes.

2. Device according to claim 1, characterized in that the position of the at least one curtain coating die relative to the applicator roll (6, 7) is variable.

3. Device according to claim 2, characterized in that the position of the at least one curtain coating die relative to the applicator roll (6, 7) can be changed in such a way that a curtain height remains essentially the same in the different operating modes.

4. Device according to one of the preceding claims, characterized in that at least one of the two rolls (6, 7) creating the treatment nip (15) is designed as a deflection compensation roll (7).

5. Device according to one of the preceding claims, characterized in that the diameter of the at least one applicator roll (6, 7) is 1000 to 1800 mm, preferably 1200 to 1600 mm.

6. Device according to one of the preceding claims, characterized in that the hardness of a cover of a hard applicator roll (6, 7) is selected in the range of 0 to 5 P&J preferably 0 to 1 P&J.

7. Device according to one of the preceding claims, characterized in that one of the rolls (6, 7) is designed as a defection compensation roll (7) with 5 to 30 P&J, preferably 0 to 10 P&J.

8. Device according to one of the preceding claims, characterized in that an overflow funnel (12) is provided in an edge region of the at least one curtain coating die in each case per edge, which overflow funnel (12) is formed laterally of the nip (15).

9. Device according to one of the preceding claims, characterized in that the line force in the treatment nip (15) is between 20 kN / m and 200 kN / m, preferably between 80 kN / m and 120 kN / m10. Device according to one of the preceding claims, characterized in that the speed of the web (11) is between 250 m / min and 2000 m / min, preferably between 600 m / min and 1800 m / min.

11. Device according to one of the preceding claims, characterized in that the dry content of the paper or board web (11) is selected at more than 90%, in particular between 92% and 98%.

12. Device according to one of the preceding claims, characterized in that the starch is provided as an treatment substance with a specific volumetric flow of between 15 I / (min*m) and 150 I / (min*m) during the sump operation mode and between 5 I / (min*m) and 50 I / (min*m) during the film operation mode.

13. Device according to one of the preceding claims, characterized in that the starch is provided as treatment substance with a solids content of between 5% and 12% during the sump operation mode and between 10% and 25% during the film operation mode.

14. Device according to one of the preceding claims, wherein the viscosity of starch as the treatment substance is selected between 20 mPas and 200 mPas.

15. Device according to one of the preceding claims, characterized in that the temperatures of starch as application medium are selected between 50°C and 110°C, preferably between 70°C and 100°C.

16. Device according to one of the preceding claims, characterized in that in the film operation mode the angle α for the zone of impingement of the curtain on the at least one applicator roller (6, 7) is selected between 0° and 45°, preferably between 0° and 15°, and in sump operation mode between 30° and 90°, preferably between 45° and 60°, with respect to the vertical.

17. Device according to claim 16, characterized in that the position of the curtain coating die and its lip is determined via a control device for a change of the operating mode during a production run.

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