Application device and method

Abstract

The invention relates to an application device and method for coating a fibrous material web, in particular a paper, packaging or cardboard web, wherein the application device comprises an application nozzle for applying a coating medium, in particular a starch solution, to a moving surface, and wherein the application nozzle has an outlet gap extending in the width direction of the application nozzle and designed to produce a film of coating medium or a curtain of coating medium. According to the invention, the application nozzle has profiling means in order to vary the gap width of the outlet gap over the width of the application nozzle.

Description

[0001] Application device and method

[0002] The invention relates to an application device for coating a fibrous web, in particular a paper, packaging or cardboard web according to the preamble of claim 1, and to a method for coating using such an application device.

[0003] During the production or processing of fibrous webs, particularly paper, packaging or cardboard webs, it is common practice to provide these webs with one or more coatings.

[0004] These coatings can, for example, be the application of pigment-containing coatings or barrier media, for example based on polyvinyl alcohol or micro-Znanofibrillated cellulose.

[0005] Another common application is the application of a starch solution to the fibrous web. This can influence the surface of the web, while also improving its strength properties.

[0006] Various application devices are known from the state of the art.

[0007] For example, the starch solution can be applied using a film press. An excess of the coating medium is applied to the transfer roller and then metered to the desired application quantity using a suitable doctor blade metering system. The application quantity is varied by doctoring off more or less of the excess coating medium. Changing the application quantity usually requires changing the doctor rod, which necessitates a machine shutdown. Such doctor blade metering systems are described, for example, in DE102004029565 A1. Alternatively, application units are known, for example from EP3332955 B1, in which the coating medium is sprayed onto the application rollers via a series of spray nozzles. In contrast to doctor blade metering systems, these systems do not require contact metering systems.

[0008] Alternatively, application nozzles with an outlet gap are known. For example, DE202020107431 U1 describes a curtain nozzle with a uniform nozzle gap. The applicant's patent application DE 102022105518.3 describes an application nozzle in which a curtain or film is dispensed from a wide-slot nozzle, which is then atomized by a blowing head.

[0009] What all the described application units have in common is that they are designed to deliver as equal and uniform a quantity of coating medium as possible across the width of the running surface.

[0010] However, the properties of a paper web can vary significantly across its width. For example, shrinkage during drying can cause the properties at the edges of the web to differ significantly from those in the center.

[0011] This means that the requirement for strength, for example, to achieve a certain strength is not the same across the entire web width.

[0012] If the starch dosage is so high to achieve sufficient strength in the area with the highest demand, it will be overdosed in other areas, which is neither economically nor ecologically sensible. If the dosage is too low, the edge areas of the sheet will generally be of inferior quality due to a lack of strength.

[0013] It is therefore an object of the invention to overcome the weaknesses of the prior art.

[0014] It is a further object of the invention to propose an application device that can be specifically adapted to the web to be coated. It is also an object of the invention to propose a device and a method for producing a fibrous web of sufficient quality while avoiding waste.

[0015] The objects are fully achieved by an application device according to claim 1 and a method according to claim 10. Further advantageous embodiments of the present invention can be found in the subclaims.

[0016] Proposed is an application device for coating a fibrous web, in particular a paper, packaging, or cardboard web. The application device comprises an application nozzle for applying a coating medium, in particular a starch solution, to a moving surface. The application nozzle has an outlet gap designed to produce a film of coating medium or a curtain of coating medium. According to the invention, the application nozzle has profiling means for varying the gap width of the outlet gap across the width of the application nozzle.

[0017] The application nozzle and the outlet gap typically extend across the entire width of the fiber web to be coated, or across the entire width of the moving surface. Since this fiber web is usually somewhat narrower than the transfer roller, it can be arranged that no coating medium is applied for a few centimeters at the edge of the transfer roller.

[0018] The width of the application nozzle can therefore be up to 10m or more in modern systems.

[0019] With an applicator according to one aspect of the invention, it is now possible to specifically adjust the amount of coating medium across the width of the fibrous web to the required amount. This can be achieved by specifically adjusting the gap width of the outlet gap.

[0020] By varying the gap width, a very wide range of application quantities can be covered in an elegant way. For example, if the gap width is increased from 0.5 mm to 1 mm, the application quantity can be doubled. If it is increased to 2 mm, it can even be quadrupled. Such large variations are advantageous for the system operator because, particularly in the edge area of ​​the web, the properties of the web differ greatly from those in the center due to shrinkage, meaning that significantly different amounts of starch may have to be applied in these areas. With application nozzles with an outlet gap, this strong profiling can be achieved very efficiently by locally adjusting the gap width.

[0021] In an advantageous embodiment, it can be provided that the application nozzle is designed as a curtain nozzle, in which the coating medium is deposited from the outlet gap in the form of a freely falling curtain onto the moving surface under the influence of gravity.

[0022] Alternatively, the application nozzle may further comprise a blowing head configured to generate a linear jet of gaseous medium, and wherein an impact line is further provided at which the linear jet of gaseous medium impacts the film or curtain of coating medium, forming a spray curtain. The blowing head is arranged such that the spray curtain is directed toward the moving surface. Air, in particular, can be used as the gaseous medium.

[0023] In an advantageous embodiment, it can also be provided that the application nozzle has a diaphragm which extends in particular over the entire width of the application nozzle, and that the profiling means comprises a number of actuators which are arranged distributed over the width of the application nozzle and which are designed to open the outlet gap locally more or less by moving or deforming the diaphragm.

[0024] The actuators can be designed, for example, as mechanical actuators and / or electromagnetic actuators. The mechanical actuators can be operated manually, by motor, and / or hydraulically. In particular, a design with adjusting screws or threaded spindles is possible.

[0025] The cover can be made of metal, plastic or other suitable materials.

[0026] When using electromagnetic actuators, the entire aperture can be made of a magnetic material. Alternatively, the aperture can be made of a non-magnetic material, such as a plastic, to which elements made of a magnetic material and / or suitable permanent magnets are attached to cooperate with the electromagnets.

[0027] Alternatively or additionally, it can be provided that the profiling means comprise electromagnetic actuators which are arranged distributed over the width of the application nozzle and which are designed to locally vary the width of the outlet gap by varying the magnetic force.

[0028] Both attractive forces (narrowing the outlet gap) and repulsive forces (expanding the gap) can be generated to create a profile. The advantage of this design is that no mechanical components are required, which reduces the susceptibility to wear.

[0029] Since the width of the application nozzle 1 can be up to 10m or more, it will often be useful to provide several actuators distributed across the width of the application nozzle to change the gap width.

[0030] In particularly preferred embodiments, the mechanical actuators and / or the electromagnetic actuators can be arranged unevenly distributed across the width of the application nozzle, with the distances between adjacent actuators at the edges of the application nozzle being smaller than in the center of the application nozzle. This is particularly advantageous for compensating the shrinkage profile. Since the paper web shrinks considerably at the edges but remains virtually unchanged in the center of the web, such profiles have strong gradients in the edge zones but remain largely constant in the center. It is therefore advantageous to provide more actuators in the edge regions. For economic reasons, fewer actuators can be provided in the center of the web.

[0031] It is very advantageous if the application device has a control unit configured to automatically adjust the gap width. This control unit can, for example, be integrated into the central machine and system control system. This allows for a high degree of automation, and the gap width can, for example, be adjusted based on measured or specified values ​​from the machine control system.

[0032] The application device can be designed as a direct application device in which the coating medium is applied directly to the fibrous web as the moving surface.

[0033] Alternatively, the application device can also be designed as an indirect application device, in which the coating medium is transferred from the moving surface to the fibrous web. The moving surface can be the surface of a transfer roller.

[0034] In particular, the application device can be provided with a first application nozzle for application to a first moving surface and a second application nozzle for application to a second moving surface, wherein the first moving surface and the second moving surface are each designed as the surface of a transfer roller, and the two transfer rollers form a transfer nip in which the coating medium can be transferred to the fibrous web. Such application devices can be used for the simultaneous application, in particular of starch, to both sides of the fibrous web.

[0035] Furthermore, it may be advantageous if the surface of the first transfer roller and / or the surface of the second transfer roller have a hardness of more than 55 ShoreD, in particular more than 90 ShoreD.

[0036] A starch application device comprising two hard rollers is called a "hard-nip sizer." This allows for particularly good penetration of the starch into the fiber web.

[0037] Furthermore, a method for coating a fibrous web, in particular a paper, packaging or cardboard web, is proposed, wherein the coating is carried out by means of an application device according to one aspect of the present invention.

[0038] It is particularly advantageous if the coating medium is a starch solution.

[0039] It is preferred that the coating of the fibrous web takes place indirectly, wherein the coating medium is first applied to a moving surface in the form of a transfer roller and from there transferred to the fibrous web in a transfer nip.

[0040] In a variant of the method, it can be provided that the method comprises the steps of: a. specifying a default profile for the amount of coating medium to be applied across the width of the application nozzle and b. varying the gap width of the outlet gap across the width of the application nozzle so that the default profile is achieved.

[0041] Such a process can be used as part of your control or regulation system. The target profile can be specified, for example, depending on the variety produced. This target profile can be developed from experience or previous tests for the respective variety. If a suitable control unit is available, the profile can be automatically adjusted when changing varieties, without requiring machine downtime.

[0042] It can also be additionally provided that an actual profile of a property, in particular a strength property of the fibrous web, is determined and from this the specification profile for the coating medium is determined.

[0043] This is a very advantageous design in conjunction with the application of starch, since various strength properties of the fibrous web can be influenced by the application of starch.

[0044] The parameter can be determined directly by direct measurement or indirectly.

[0045] Since many strength measurements today are still destructive measurements that can only be carried out in the laboratory and not in the running machine, the strength parameters are often determined indirectly.

[0046] This can be done, for example, by measuring a quantity which is known - e.g. from tests - to correlate with the desired strength parameter.

[0047] Alternatively, more complex dependencies can also be used. For example, the strength parameter can be modeled from a variety of measured variables. This can be, for example, a physical or purely statistical model. Such model-based determinations of parameters are sometimes referred to as "virtual sensors."

[0048] The invention is explained below with reference to figures. The invention is not limited to the embodiments shown in the figures. Figure 1 shows an application device according to one aspect of the invention.

[0049] Figure 2 shows an application device according to a further aspect of the invention.

[0050] Figure 1 shows an application device with an application nozzle 1 configured as a curtain nozzle. The coating medium is deposited onto a moving surface 4 in the form of a freely falling curtain (14). In Figure 1, the moving surface 4 is configured as the surface of a transfer roller. From this transfer roller, the coating medium can be transferred to the web in a transfer nip. Alternatively, the curtain of coating medium 14 can also be applied directly to a fibrous web.

[0051] The application nozzle 1 usually extends across the entire width of the moving surface 4, or at least across the entire width of the fibrous web to be coated. Since this fibrous web is usually somewhat narrower than the transfer roller, it can be provided that no coating medium is applied for a few centimeters at the edge of the transfer roller.

[0052] The coating medium leaves the curtain nozzle through an outlet gap 2 with the width W. The gap width W correlates with the amount of coating medium discharged.

[0053] In the embodiment shown in Figure 1, the profiling means for varying the gap width W comprise a diaphragm 101 that extends across the width of the application nozzle 1. This diaphragm 101 can be made of metal or plastic. This diaphragm 101 is arranged on the outlet gap 2 such that by locally moving or deforming the diaphragm 101, the outlet gap 2 can be more or less closed or opened, thus varying the local gap width W.

[0054] For moving or deforming the panel 101, the profiling means further comprise suitable actuators 102. These actuators 102 can be designed as mechanical actuators 103, for example, in the form of threaded spindles 103. These can be operated manually, by motor, or even hydraulically.

[0055] In the application nozzle 1 of Figure 1, the actuators 102, 103 are arranged unevenly distributed across the width of the application nozzle 1, with the distances between adjacent actuators 102 at the edges of the application nozzle 1 being smaller than in the center of the application nozzle 1. This is particularly advantageous for compensating the shrinkage profile. Since the paper web shrinks significantly at the edges but remains virtually unchanged in the center of the web, such profiles exhibit strong gradients in the edge zones but remain largely constant in the center. Therefore, for economic reasons, fewer actuators can be provided in the area of ​​the center of the web.

[0056] Figure 2 shows an application device according to a further aspect of the invention. The application nozzle 1 again has a nozzle head with an outlet gap 2 extending in the width direction of the application nozzle 1. However, the coating medium is dispensed in the form of a film 15, which is deposited on a support surface 7. This support surface 7 can be designed as a separate component. Alternatively, however, it can also be provided that a part of the wall of the application nozzle 1 is used as the support surface 7.

[0057] In addition, the application nozzle 1 has a blow head 5 designed to generate a linear jet of gaseous medium, and further comprising an impact line at which the linear jet of gaseous medium impacts the film 15 of coating medium and forms a spray curtain 6. The blow head 5 is arranged such that the spray curtain 6 is directed toward the moving surface 4.

[0058] Here, too, profiling is not achieved by varying the blow head 5 or the jet of gaseous medium, but by varying the width W of the outlet gap 2. Suitable profiling means are provided on the application nozzle for this purpose. Instead of the also possible aperture 101, adjusting means 102 in the form of electromagnetic actuators 105 are provided. These are arranged distributed across the width of the application nozzle 1 and are designed to locally vary the width of the outlet gap by varying the magnetic force.

[0059] Both attractive forces (narrowing of the outlet gap 2) and repulsive forces (expanding the outlet gap) can be generated to effect profiling. The advantage of this design is that no mechanical components are required, thus reducing susceptibility to wear. These actuators 102, 105 can be arranged evenly or irregularly distributed across the width of the application nozzle.

[0060] List of reference symbols

[0061] 1 application nozzle

[0062] 2 Outlet gap

[0063] 4 running surface

[0064] 5 Blow head

[0065] 6 spray curtain

[0066] 7 Support surface

[0067] 14 Curtain of coating medium

[0068] 15 Film of coating medium

[0069] 101 aperture

[0070] 102 actuators

[0071] 103 mechanical actuators

[0072] 105 electromagnetic actuators

[0073] W gap width

Claims

Patent claims 1) Application device for coating a fibrous web, in particular a paper, packaging or cardboard web, wherein the application device comprises an application nozzle (1) for applying a coating medium, in particular a starch solution, to a moving surface (4), and wherein the application nozzle (1) has an outlet gap (2) which extends in the width direction of the application nozzle (1) and which is designed to produce a film of coating medium (15) or a curtain of coating medium (14), wherein the application nozzle (1) has profiling means in order to vary the gap width (W) of the outlet gap (2) across the width of the application nozzle (1).characterized in that the application nozzle (1) further comprises a blow head (5) which is designed to generate a linear jet of gaseous medium, and wherein an impact line is further provided at which the linear jet of gaseous medium impacts the film (15) or curtain (14) of coating medium to form a spray curtain (6), and wherein the blow head (5) is arranged such that the spray curtain (6) is directed in the direction of the running surface (4). 2) Application device according to one of the preceding claims, characterized in that the application nozzle (1) is designed as a curtain nozzle (1), in which the coating medium is deposited from the outlet gap (2) in the form of a freely falling curtain (14) under the influence of gravity onto the moving surface (4). 3) Application device according to one of the preceding claims, characterized in that the profiling means comprise a diaphragm (101) which extends in particular over the entire width of the application nozzle (1), and that the profiling means further comprise a number of actuators (102) which are arranged distributed over the width of the application nozzle (1) and which are designed to open the outlet gap (2) locally more or less by moving or deforming the diaphragm (101). 4) Application device according to claim 3, characterized in that the actuators are designed as mechanical actuators (103) which can be actuated manually and / or by motor and / or hydraulically or are designed as electromagnetic actuators (105). 5) Application device according to one of the preceding claims, characterized in that the profiling means comprise a number of actuators (102) which are designed as electromagnetic actuators (105) and which are arranged distributed over the width of the application nozzle (1) and which are designed to locally vary the gap width (W) of the outlet gap (2) by varying the magnetic force. 6) Application device according to claim 5, characterized in that the electromagnetic force has an attractive effect, so that the gap width (W) of the outlet gap (2) can be varied by stronger or weaker attraction. 7) Application device according to claim 5 or 6, characterized in that the electromagnetic force has a repulsive effect, so that the gap width (W) of the outlet gap (2) can be varied by stronger or weaker repulsion. 8) Application device according to one of the preceding claims, characterized in that the actuators (102) are arranged distributed unevenly over the width of the application nozzle, wherein the distances between adjacent Actuators (102) at the edges of the application nozzle (1) are smaller than in the center of the application nozzle (1). 9) Application device according to one of the preceding claims, characterized in that the application device has a first application nozzle (1) for application to a first moving surface (4) and a second application nozzle (1) for application to a second moving surface, wherein the first moving surface (4) and the second moving surface are each designed as a surface of a transfer roller (4), and the two transfer rollers form a transfer nip in which the coating medium can be transferred to the fibrous web. 10) Method for coating a fibrous web, in particular a paper, packaging or cardboard web, in particular with a starch solution, wherein the coating is carried out by means of an application device according to one of the preceding claims. 11) Method according to claim 10, characterized in that the coating of the fibrous web is carried out indirectly, wherein the coating medium is first applied to a moving surface (4) in the form of a transfer roller (4) and from there is transferred to the fibrous web in a transfer nip. 12) Method according to one of claims 10 or 11, characterized in that the method comprises the steps of: a. specifying a default profile for the amount of coating medium to be applied across the width of the application nozzle (1) and b. varying the gap width (W) of the outlet gap (2) across the width of the application nozzle (1) so that the default profile is achieved. 13) Method according to one of claims 10 to 12, characterized in that an actual profile of a property, in particular a The strength properties of the fibrous web are determined and the specification profile for the coating medium is determined from this. 14) Method according to claim 13, characterized in that the determination of the actual profile of a property takes place directly by direct measurement or indirectly.

Images