Coating device and method

Abstract

The invention relates to a coating device and a method for coating a fibrous web, in particular a paper, packaging or cardboard web, the coating device comprising a coating nozzle for coating a coating medium, in particular a starch solution, on a running surface, and the coating nozzle having an outlet gap, in which the coating medium is arranged, the outlet gap is designed to generate a film formed by the coating medium or a curtain formed by the coating medium, and means for changing the coating amount are provided and are changed on the basis of a strength parameter.

Description

[0001] The present invention relates to a coating apparatus for coating fiber webs, particularly paper webs, packaging webs or paperboard webs, as described in the preamble of claim 1, and a method for coating when using the coating apparatus.

[0002] When manufacturing or processing fiber webs, especially paper webs, packaging webs, or paperboard webs, one or more coatings are typically applied to these webs.

[0003] These coatings can be pigmented coatings or barrier materials, such as those based on polyvinyl alcohol or micro / nanofibers of cellulose.

[0004] Another common application is coating the fiber web with a starch solution. This affects the surface of the web and also improves the strength properties of the fiber web by coating it with starch.

[0005] Various coating devices are known from the prior art.

[0006] For example, starch solutions can be coated using a film press. Here, excess coating medium is applied to a transfer roller, and the required amount is then measured by a suitable doctor blade metering system. Variations in the coating amount can be achieved by scraping off more or less excess coating medium. Typically, changing the coating amount requires replacing the doctor blade, which necessitates a machine shutdown.

[0007] Such a doctor blade metering system is described, for example, in document DE 102004029565 A1. In recent years, very hard-surfaced transfer rollers have been increasingly used to allow starch to better penetrate the fiber web. However, these metering systems have a drawback: the hard roller surface causes rapid wear of the doctor blade bar.

[0008] Alternatively, a coating apparatus is known, for example, from document EP 3332955 B1, in which the coating medium is sprayed onto a coating roller through a series of nozzles. Unlike a doctor blade metering system, this system does not require contact with the metering system. Since the amount of coating is measured by adjusting the coating amount at the nozzles, it can be done without stopping the machine.

[0009] However, both the doctor blade metering system and the nozzle have the drawback that the coating amount can only vary within a relatively small range.

[0010] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art.

[0011] In particular, the technical problem to be solved by the present invention is to provide a coating apparatus in which the coating amount can be adjusted within a wide range without stopping the machine.

[0012] Furthermore, the technical problem to be solved by the present invention is to propose a coating device that is both wear-resistant and easy to maintain.

[0013] The technical problem described herein is solved by the coating apparatus according to claim 1 and the method according to claim 11. Other advantageous embodiments of the invention are obtained in the dependent claims.

[0014] A coating apparatus is proposed for coating fiber webs, particularly paper webs, packaging webs, or cardboard webs, wherein the coating apparatus includes a coating nozzle for applying a coating medium to a running surface, and wherein the coating nozzle has an exit slit extending along the width direction of the coating nozzle and designed to produce a film or curtain formed by the coating medium. The coating apparatus also includes a device for changing the coating amount. Finally, the coating apparatus is specified to have a control unit configured to determine the change in coating amount based on at least one parameter provided regarding the strength of the fiber web.

[0015] This device is particularly suitable for coating with starch. Starch coating is one of the means to influence the strength of fiber webs. For webs with excessively low strength values, higher strength can be obtained by coating with starch or a similar suitable coating medium. To reduce the cost of the coating medium, it is advantageous not to apply more coating medium than necessary. The coating device includes means for changing the coating amount and a control unit for determining the optimized coating amount based on one or more strength parameters, thus greatly facilitating low-cost operation of the equipment.

[0016] With appropriate actuators, the coating device can also be easily integrated into a closed-loop control system.

[0017] It is known that the strength of fiber web can be described in a variety of ways. Examples include tensile strength and tear strength, burst strength, or crack strength along the machine direction and transverse direction, to name just a few. Typically, not all of these strength values ​​are relevant to a specific product; only one or a few strength values ​​are relevant to the product. One or more parameters related to the strength values ​​of the produced fiber web can be provided in the control unit.

[0018] The one or more parameters can be determined directly by measurement or indirectly.

[0019] Because many strength measurements today are still destructive and can only be performed in a laboratory rather than on a running machine, strength parameters are often determined indirectly.

[0020] For example, this can be achieved by measuring a parameter known to be related to the desired strength parameter, which can be obtained, for example, through experimental methods.

[0021] Alternatively, more complex correlations can be used. This allows for modeling of intensity parameters based on multiple measurements. For example, physical models or purely statistical models can be used. This model-based parameter determination is sometimes referred to as "virtual sensor".

[0022] Coating nozzles with outlet slits are known in themselves. Document DE 202020107431 U1 describes a curtain nozzle with a uniform nozzle gap. A coating nozzle is known from the applicant's patent application DE 102022105518.3, which sprays a curtain or film from a wide-slit nozzle and then atomizes it through an air jet head.

[0023] Compared to scraper metering systems, this nozzle offers advantages because metering does not require contact with the scraper element, thus eliminating the need for easily worn parts. Furthermore, it avoids overcoating, thereby eliminating the need for cumbersome recovery and treatment of excess coating media.

[0024] Compared to traditional nozzles, this coating nozzle with an outlet slit is not only cheaper than mass-produced nozzles, but it also produces significantly less contamination.

[0025] The device for changing the coating amount may, for example, include a delivery device (e.g., a pump) whose delivery rate can be varied. This can be achieved, for example, by a pump with adjustable rotation speed. This implementation is advantageous because it typically allows for very quick and easy retrofitting of existing coating nozzles.

[0026] However, these coating nozzles still have drawbacks, namely that the coating amount can usually only vary within a relatively small range, which is perfectly adequate for some applications where the range of intensity value variation is relatively small, while in other applications a larger coating amount variation may be required.

[0027] The inventors realized that this drawback could be overcome through alternative implementations by abandoning the fundamental principles of the nozzle structure as it has been so far. To date, for example, the goal in manufacturing curtain nozzles has been to maintain a constant exit gap as much as possible. For instance, document DE 202020107431 U1 devotes considerable effort to maintaining a constant gap. This is because curtain coating machines have so far been almost exclusively used for coating pigment-containing paints. Here, such precision is crucial for uniformly covering the paint web and obtaining uniform surface properties.

[0028] However, such nozzles will increasingly be used for coating starch in the future. Here, high precision of the slit is not important; what is important is the ability to vary the amount of starch coated over a wide range. Therefore, this invention proposes that the slit width of the outlet slit be designed to be variable.

[0029] By varying the slit width, a very wide range of coating amounts can be appropriately covered. For example, increasing the slit width from 0.5 mm to 1 mm can double the coating amount. Expanding it to 2 mm can even quadruple the coating amount. Such a large variation is advantageous for equipment operators because it allows for the production of various types of paper with different requirements on the same machine. Furthermore, in the corresponding implementation of the coating apparatus, the equipment does not need to be shut down.

[0030] Alternatively or additionally, the internal pressure of the coating nozzle can be adapted by changing the slit width.

[0031] For curtain nozzles or nozzles with jet heads, the internal pressure of the nozzle is an important parameter. Normally, the coating medium should not be forced out of the outlet slit, but should leave the slit freely under gravity. Therefore, the internal pressure of the nozzle should not be too high. However, depending on the rheological properties of the coating medium, the internal pressure of the nozzle may vary even with the same delivery rate and slit width. According to one aspect of the invention, the slit width can be adjusted by the coating nozzle to maintain the internal pressure of the nozzle within the desired range.

[0032] Advantageously, a suitable sensor is provided to determine the pressure inside the nozzle. This measurement can be performed directly inside the coating nozzle. However, since internal sensors are more susceptible to contamination, pressure measurement at the inlet of the coating medium is generally more suitable.

[0033] Variations in the gap width can be achieved through various methods or by using different adjustment devices.

[0034] Thus, for example, a fixed gap with a large gap width can be provided, which is more or less covered by a movable baffle.

[0035] Alternatively, at least one wall of the outlet gap may be specified as being formed by a movable wall member. The outlet gap can be narrowed or widened by said wall member.

[0036] Movement of the baffle or wall component can be achieved, for example, by one or more adjusting bolts, threaded rods, or similar actuators. Since the width of the coating nozzle can range from 1 meter to 10 meters or more, it is generally suitable to have multiple actuators distributed across the width of the coating nozzle to vary the slit width. These actuators can be moved manually or electrically.

[0037] To achieve a uniform slit width across the width of the coating nozzle, it is generally advantageous to distribute the actuators evenly across the width of the coating nozzle, such that the distance between adjacent actuators is equal across the width of the coating nozzle, or differs by less than 10%.

[0038] Other adjustment devices for changing the gap width are also feasible.

[0039] Advantageously, the coating apparatus is designed such that, by means of a device for changing the coating amount, for example by changing the slit width, the coating amount can be varied between a minimum amount and a maximum amount, wherein the maximum amount exceeds the minimum amount by at least 30%, especially at least 50%, and preferably at least 100%.

[0040] In order to change the width of the outlet gap without stopping the equipment, it is particularly advantageous that the change of the gap width can be achieved electrically and / or hydraulically and / or pneumatically.

[0041] The coating nozzles typically extend across the entire width of the fiber web to be coated or across the entire width of the running surface.

[0042] In modern equipment, the width of the fiber web and the width of the coating nozzle can reach 10 meters or more. Therefore, it is generally suitable to have multiple actuators distributed across the width of the coating nozzle to vary the slit width.

[0043] Furthermore, the coating apparatus may also include a control unit configured to automatically change the coating amount. This control unit can, for example, be integrated into a central machine and equipment control system, and is also, in particular, the same control unit used to determine changes in the coating amount. Therefore, a high degree of automation can be achieved, and the slit width can be adjusted, for example, based on values ​​measured or preset by the machine control system.

[0044] One embodiment may specify that the coating nozzle is designed as a curtain nozzle, wherein the coating medium falls onto the operating surface in the form of a free-falling curtain from the outlet gap under the influence of gravity. This is more advantageous than the curtain nozzle described in document DE 202020107431 U1.

[0045] In a particularly preferred embodiment, the coating nozzle may further include an air jet head designed to generate a linear jet of gaseous medium, wherein an impact line is provided at which the linear jet of gaseous medium impacts a film or curtain formed by the coating medium to form a spray curtain, and wherein the air jet head is arranged such that the spray curtain points toward the operating surface. The gaseous medium may in particular be air.

[0046] This is more advantageous than the coating apparatus described in document DE 102022105518.3.

[0047] The linear beams of the outlet gap and gaseous medium typically extend across the entire width of the running surface or fiber web.

[0048] According to various aspects of the present invention, the coating apparatus can be used for single-sided or double-sided coating of fiber webs.

[0049] For example, to perform double-sided coating, the coating apparatus may be specified to have a first coating nozzle for coating on a first running surface and a second coating nozzle for coating on a second running surface, wherein the first and second running surfaces are respectively designed as the surfaces of transfer rollers, and the two transfer rollers form a transfer roller gap in which the coating medium can be transferred to the fiber web.

[0050] Here, the same coating medium can be applied to both sides, or different coating media can be applied.

[0051] One or both transfer rollers can be designed as hard rollers. This means that the surface of the first transfer roller and / or the surface of the second transfer roller has a hardness of 55 Shore D or higher, especially 90 Shore D or higher.

[0052] A coating apparatus for coating starch includes two rigid rollers and is referred to as a "rigid roller coater". This allows for particularly good penetration of starch into the fiber web.

[0053] Furthermore, the present invention also includes a method for coating fiber webs, particularly paper webs, packaging webs, or cardboard webs, wherein a coating medium is applied to a running surface by a coating apparatus, wherein the coating apparatus is designed according to one aspect of the present invention.

[0054] In a preferred embodiment, the coating medium may be a starch solution.

[0055] Alternatively, various barrier media can also be used as coating media. In particular, fibrous media, such as MFC (microfibrillated cellulose) or NFC (nanofibrillated cellulose), can also be used.

[0056] Advantageously, the coating can be performed indirectly, wherein the coating medium is first applied to a running surface in the form of a transfer roller, and from there transferred to the fiber web through the gap between the transfer rollers. This indirect coating can be achieved, for example, by a "hard-pressed zone screener".

[0057] In a preferred embodiment, a parameter relating to the strength of the fiber width can be defined, and the coating amount can be varied according to said parameter. The variation in coating amount can be performed by an operator after evaluating the parameter. However, it is particularly advantageous that this variation is performed automatically by a control unit. For this purpose, preset values ​​or preset curves can be stored in the control unit, which can determine the optimal conveying power or optimal gap width based on the parameter and the preset values. The gap width can then be automatically adjusted by an electric, hydraulic, and / or pneumatic actuator. Therefore, no operator intervention is required.

[0058] Changes in delivery power, such as those via pump speed, can also be made automatically without operator intervention.

[0059] The parameters can be determined directly through measurement or indirectly.

[0060] Because many strength measurements today are still destructive and can only be performed in a laboratory, not on operating machinery, strength parameters are often determined indirectly. For example, this can be achieved by measuring known parameters associated with the desired strength, which can be obtained experimentally.

[0061] Alternatively, more complex correlations can be used. This allows for modeling of intensity parameters from multiple measurements. These could be, for example, physical models or purely statistical models. This model-based parameter determination is sometimes referred to as a "virtual sensor."

[0062] A highly advantageous application of this invention is improving type changeovers in papermaking machines. For example, it can be specified that when changing from a first type of fiber web to a second type of fiber web, the coating amount is automatically changed from a first preset value to a second preset value by altering the slit width. This simplifies type changeovers for the operator. Furthermore, it provides greater flexibility for production planning, as it allows for direct switching from a type with higher starch requirements to one with lower starch requirements without downtime. This is particularly advantageous because strength parameters are typically unavailable or only very inaccurate when changing types.

[0063] The present invention is described below with reference to the accompanying drawings. The present invention is not limited to these embodiments.

[0064] In the attached diagram:

[0065] Figure 1a and 1b A coating nozzle according to one aspect of the invention is shown.

[0066] Figure 2 A coating apparatus according to another aspect of the invention is shown.

[0067] Figure 1a and 1b A coating nozzle 1 is shown, which is designed as a curtain nozzle 1. The coating medium, such as a starch solution, is conveyed through a distribution channel 10 and distributed across the width of the coating nozzle 1. The width of the coating nozzle 1 typically extends across the entire width of the running surface 4 or the fiber web to be coated. The coating medium flows out of the coating nozzle 1 through an outlet slit 2 and then falls downwards onto the running surface in a curtain-like manner under gravity.

[0068] In order to change the gap width W, Figure 1a and 1b The adjusting device 3 of the coating nozzle 1 includes a wall of the outlet slit 2 formed by a movable wall member 7. The outlet slit 2 can be narrowed or widened by the wall member 7. Figure 1a The image shows locations with larger gap widths (W). To change the coating amount, one can... Figure 1b The slit width W is reduced as shown. For this purpose, the adjusting device 3 of the coating nozzle 1 has a suitable actuator 9. An adjusting bolt 9 is shown as an example. Since the width of the coating nozzle 1 can be 10 meters or more, it is generally suitable to arrange multiple adjusting bolts 9 or other actuators distributed along the width of the coating nozzle 1 to change the slit width W. The adjusting bolts 9 can be moved manually or electrically.

[0069] To achieve automatic adjustment, it is advantageous to use electric, hydraulic, and / or pneumatic actuators to drive the actuators. These actuators can be connected to a control unit that can automatically change the gap width W according to a preset value without stopping the equipment.

[0070] exist Figure 2 The coating apparatus shows a coating nozzle 1 that applies a coating medium onto a running surface 4 in the form of a transfer roller 4. The coating medium can then be transferred onto the fiber web through the transfer gap of the transfer roller 4.

[0071] The coating nozzle 1 includes, for example, Figure 1a and 1b The nozzle shown is different in that the coating medium does not fall as a curtain, but rather as a thin film onto the support surface 8 and is guided by it. Furthermore, the coating nozzle 1 includes an air jet 5 designed to generate a linear jet formed by a gaseous medium. The gaseous medium can be air. The linear jet formed by the gaseous medium impacts the coating medium film at the impact line to form a jet curtain 6. The air jet 5 is arranged here to direct the jet curtain 6 toward the operating surface 4.

[0072] The coating amount can also be changed by altering the width W of the outlet slit 2. For example... Figure 1a and 1b As shown, this is achieved by appropriately adjusting device 3. The jet head 5 or the linear jet formed by the gas medium does not affect the change in coating amount. This also allows for adjustment of the atomization degree or the impact angle of the spray 6.

[0073] List of reference numerals

[0074] 1 Coating nozzle

[0075] 2. Exit gap

[0076] 3 Adjustment Components

[0077] 4 Operating Surface

[0078] 5 jet heads

[0079] 6-jet curtain

[0080] 7 wall fittings

[0081] 8 support surfaces

[0082] 9. Actuator, Adjusting Bolt

[0083] 10 vertical passages

[0084] W gap width

Claims

1. A coating apparatus for coating fiber webs, particularly paper webs, packaging webs, or paperboard webs, wherein, The coating apparatus includes a coating nozzle (1) for coating a coating medium, particularly a starch solution, onto a running surface (4), and wherein the coating nozzle (1) has an outlet slit (2) extending along the width direction of the coating nozzle and designed to produce a film or curtain formed by the coating medium, and wherein the coating apparatus has a device for changing the coating amount, characterized in that the coating apparatus has a control unit configured to determine the change in coating amount based on at least one parameter provided with respect to the strength of the fiber width.

2. The coating apparatus according to claim 1, characterized in that, The device for changing the coating amount includes a conveying device, the conveying amount of which can be changed.

3. The coating apparatus according to any one of the preceding claims, characterized in that, The width (W) of the outlet slit (2) is designed to be variable to change the amount of coating.

4. The coating apparatus according to claim 3, characterized in that, Multiple adjustment elements (3) are provided for changing the gap width, including baffles and / or movable wall members (7).

5. The coating apparatus according to claim 3 or 4, characterized in that, Multiple adjustment elements (3) are provided for changing the slit width. These adjustment elements have one or more actuators (9) which are arranged in a particularly uniform manner across the width of the coating nozzle (1).

6. The coating apparatus according to claim 5, characterized in that, The change in the gap width can be achieved electrically and / or hydraulically and / or pneumatically.

7. The coating apparatus according to any one of the preceding claims, characterized in that, The control unit is configured to automatically change the coating amount.

8. The coating apparatus according to any one of the preceding claims, characterized in that, The coating amount can vary between a minimum amount and a maximum amount, wherein the maximum amount exceeds the minimum amount by at least 30%, particularly at least 50%, and preferably at least 100%.

9. The coating apparatus according to any one of the preceding claims, characterized in that, The coating apparatus has a first coating nozzle for coating on a first running surface and a second coating nozzle for coating on a second running surface, wherein the first and second running surfaces are respectively designed as the surfaces of transfer rollers, and the two transfer rollers form a transfer roller gap in which the coating medium can be transferred to the fiber web.

10. The coating apparatus according to claim 9, characterized in that, The surface of the first transfer roller and / or the surface of the second transfer roller have a hardness of 55 Shore D or higher, especially 90 Shore D or higher.

11. A method for coating fiber webs, particularly paper webs, packaging webs, or paperboard webs, wherein, The coating medium is applied to the operating surface (4) by a coating device, characterized in that the coating device is designed according to one of the preceding claims, wherein a parameter relating to the strength of the fiber width is determined and the coating amount is changed according to the parameter.

12. The method according to claim 9, characterized in that, The coating medium is a starch solution or a barrier medium.

13. The method according to claim 9 or 10, characterized in that, The coating is applied indirectly, wherein the coating medium is first applied to a running surface in the form of a transfer roller, and from there transferred to the fiber web in the gap between the transfer rollers.

14. The method according to any one of claims 11 to 13, characterized in that, The parameters are determined directly by measurement or indirectly.

15. The method according to any one of claims 11 to 14, characterized in that, When switching from the first type of fiber fabric to the second type of fiber fabric, the coating amount is automatically changed from the first preset value to the second preset value by adapting the device used to change the coating amount.

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