Application method and device
[0001] The invention relates to a method for applying a liguid or pasty applica- tion medium to a moving material web, in particular a moving fibrous web, ac- cording to the preamble of Claim 1, as well as to a device for applying an applica- tion medium according to the preamble of Claim 9.
[0002] Coating material webs, such as in particular paper webs, with a liguid or pasty application medium is a technigue for which there are numerous solutions known from the prior art.
[0003] In particular it is known to spray the application medium, for example a coating colour, a starch solution or similar, onto the paper web by means of noz- zles.
[0004] The US 5 653 130 specification describes the application of liguids to flat surfaces.
[0005] The WO 2012/072873 describes a method in which a starch solution is sprayed directly onto the material web by means of nozzles. It is advantageous that the mechanical stress on the web by coating is low since no web-contacting components are used.
[0006] In the case of the nozzles used for this — mostly wide-slot or hole-type nozzles - the discharge velocity is dependent on the throughflow volume and on the dimensions of the slot or the borehole. It is in particular disadvantageous that when applying low application quantities high discharge velocities can then only be achieved if the nozzle opening is very small. Such nozzles are very expensive to manufacture, in particular to observe the high manufacturing precisions re- quired.
[0007] High discharge velocities and thus high impact speeds of the application medium are however advantageous in order to achieve the best possible rapid
< 9 - penetration into the material web even if the material web is moved at a high speed.
[0008] Furthermore in such a design there is the drawback that particularly when using solids-containing application media the small slots or bores guickly become blocked thus resulting in a high maintenance expense.
[0009] One possible alternative can be to spray the application medium onto the web not directly but indirectly via an auxiliary medium. Thus in DE 20 2017 100 655 as well as already slightly earlier in GB 108,340 a method is proposed in which the application medium is sprayed onto a roller, and then is transferred in a nip to the material web. The variation is moreover known from WO 2005 085 525 to apply the application medium to a belt and to transfer it from there to the material web by means of a nip or a comparable processing zone. By means of this method it is now possible to achieve a rapid penetration of the application medium into the material web via pressure penetration. The web must however be guided through a nip or the like which leads to mechanical stress on the web. Furthermore in many cases contacting the coated surface before sufficient drying of the application medium can lead to damage to the surface or to the cohesion of the coating.
[0010] It is therefore the object of the invention to provide a method and a device for carrying out the method which overcomes the problems known from the prior art.
[0011] It is moreover an object of the invention to provide an application method in which rapid penetration of the application medium can be achieved and moreo- ver the mechanical stress on the material web can be kept low.
[0012] A further object of the invention is to provide an application method which has a broad useful spectrum, and in particular is also suitable for the appli- cation of small amounts of application medium, as well as for application onto fast-moving material webs.
[0013] It is furthermore an object of the invention to provide an application de- vice which is easy and expedient. to maintain.
[0014] These objects are achieved completely by a method for the application of a liguid or pasty application medium onto a moving material web according to the characterizing part of Claim 1, as well as by a device for the application of an application medium according to the characterizing part of Claim 9.
[0015] With regard to the method, the object is achieved by a method for the ap- plication of a liguid or pasty application medium to a moving material web, in particular a moving fibrous web, wherein the application medium is applied to a first moving auxiliary belt by means of a pre-dosing device, and this first auxilia- ry belt changes its direction of movement at at least one first deflection. It is proposed here that the first auxiliary belt is moved at approximately the same or a higher speed than the moving material web, wherein the first auxiliary belt is not in contact with the material web, and that the application medium is transferred at least partially at the first deflection from the first auxiliary belt in the form of a jet to the moving fibrous web.
[0016] The term jet, which is used for transferring the application medium from the first auxiliary belt to the fibrous web, is to be interpreted vey widely within the scope of this application. It is to describe that the application medium is moved freely over a certain region, that is in particular without walls and unguid- ed by a belt in the direction the material web. The term is also to include in par- ticular that the application medium is moved as a closed film or in the form of individual drops in the direction of the fibrous web.
[0017] The moving web can preferably be a fibrous web, especially a paper, board, tissue or pulp web. The method is however not restricted to these. It can also advantageously be used for coating other webs, such as for example textile webs, non-woven webs or the like.
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[0018] In the present invention the application medium is pre-dosed onto a first auxiliary belt. With this pre-dosing it is not necessary to apply the application medium at a high speed to the auxiliary belt. Therefore a simple pre-dosing sys- tem can be selected for this where the risk of contaminating the nozzles known from the prior art does not occur or only occurs to a lesser extent.
[0019] Examples for suitable pre-dosing devices can be: overflow moulders, wide-slot nozzles, conventional injection nozzles or the like.
[0020] The application medium is accelerated by application onto the first auxil- iary belt to the speed thereof. It is proposed here that the auxiliary belt moves at approximately the same or higher speed than the moving material web. By ap- proximately the same speed is to mean in this connection that the speed of the first auxiliary belt can be egual to the speed of the material web, or where appli- cable can also be up to 25% or also 50% slower.
[0021] Through the first deflection which can be for example a deflection roller, but also another conventional deflection element, the direction of movement of the first auxiliary belt is changed guite abruptly, and the application medium is spun away from the first auxiliary belt and transferred in the form of a jet onto the moving fibrous web. According to the invention there is no contact between the material web and the first auxiliary belt. Therefore neither the surface guality of the coated material web is impaired, nor does any other mechanical stress on the material web take place.
[0022] It should be noted that the term “first deflection” is not to imply that it is the first deflection device of the auxiliary belt after the application of the applica- tion medium. Although this can certainly be advantageous, even further deflec- tions can however also be provided between the pre-dosing of the application me- dium and the first deflection, such as also after the first deflection. For the “sec- ond deflection” later described, the same applies. Through the application medi- um spinning away this medium receives an impulse in the direction of the materi- al web. The impact speed can be controlled without problem via the speed of the first auxiliary belt. If a higher impact speed is reguired for a rapid penetration, then it can be reached by increasing the speed of the first auxiliary belt.
[0023] Furthermore simple maintenance is also possible for example in the form of cleaning the auxiliary belt. This can happen also during the moving operation as opposed to the spray nozzles known from the prior art.
[0024] Further advantageous designs will be described in the dependent claims.
[0025] A second auxiliary belt is also provided which changes its direction at at least a second deflection and the application medium is transported at least in sections between the first auxiliary belt and the second auxiliary belt.
[0026] In particularly advantageous designs the first auxiliary belt and the second auxiliary belt are in the form of endless belt loops and is /are designed as a circu- lating auxiliary belt supported by further deflections.
[0027] It is advantageous here inter alia that a further increase in the jet speed can take place during the deflection. Thus the atomization and impact speed of the liquid which is to be applied can be controlled by the ratio of the belt speeds and the angle between the belts.
[0028] In a further advantageous design of the method it can be proposed that the first auxiliary belt and the second auxiliary belt together with the application me- dium pass a roller nip consisting of a first deflection roller and a second deflec- tion roller, wherein the first deflection roller represents the first deflection of the first auxiliary belt, and the second deflection roller represents a second deflection of the second auxiliary belt, and the application medium leaves the first auxiliary belt at least partially after the roller nip in the form of a jet.
[0029] This can be advantageous since here the roller nip forms a defined place at which the application medium leaves the auxiliary belt.
[0030] A particularly preferred design of the method exists where the application medium is applied by the jet to the entire width of the fibrous web or at least to 90% of the width of the fibrous web.
[0031] It is furthermore also advantageous if the application medium is applied by the pre-dosing device to the entire width of the first auxiliary web or at least to 90% of the width of the first auxiliary web.
[0032] The method is very advantageous for fast material webs when for example the moving material webs are moving at a speed of 200 m/min or more, in partic- ular at a speed between 400 m/min and 2000 m/min. Whereas in many cases the speed of the fibrous web is between 1000 m/min and 1400 m/min, extremely high speeds such as for example 3000 m/min are however also conceivable.
[0033] It can furthermore be proposed that between 5 ml/m? and 100 ml/m?, in particular between 10 ml/m? and 50 ml/m? of application medium are applied to the fibrous web.
[0034] The advantage of the method compared with the prior art is particularly great even when applying comparatively small amounts of application medium, in particular less than 50 ml/m 2, to fast moving material webs. However it can also be advantageously used for larger amounts up to for example 100 ml/m? or more.
[0035] One of the advantages of the present invention is indeed that by varying the speed of the first auxiliary belt the jet speed, and thus the impact speed of the application medium onto the material web, can be easily adapted.
[0036] It can then be particularly advantageous if the first auxiliary belt and/or the second auxiliary belt are moved at a speed of more than 600 m/min, in partic- ular between 2000 m/min and 10000 m/min, particularly preferably between 3000 m/min and 6000 m/min. In special cases even higher speeds can be advantageous in the range from 20.000 m/min or 40.000 m/min.
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[0037] In principle it is possible that the first auxiliary belt and the second auxil- iary belt move at the same speed or that their speeds differ. In the case of differ- ent speeds the second auxiliary belt can be operated both faster than and also slower than the first auxiliary belt.
[0038] As regards the running of the web it can be very advantageous if — in the area of the impact of the jet - the direction of movement of the moving material web runs vertically or has a component in the vertical direction, whilst the direc- tion of the jet runs horizontally or has a component in the horizontal direction.
[0039] In particular it can be advantageous if the first auxiliary belt runs horizon- tally in the region between the pre-dosing and the first deflection or has a compo- nent in the horizontal direction.
[0040] The ratio between the orientation of the material web and the jet can more advantageously be set so that the jet impacts perpendicularly onto the fibrous web, or at an angle which deviates from the perpendicular by a maximum of 452. This is therefore particularly advantageous since the penetration of the applica- tion medium into the material web is thus boosted particularly well.
[0041] In principle all standard coating media can be used as an application me- dium. In particular the application medium can be a starch solution or a pigment- containing coating colour. Alternatively it is however also possible to use a lig- uid, in particular water as the application medium.
[0042] An advantageous density range for the application medium is between p=0.7 / cm? and p = 1.5/cm?, in particular between p=0.8 /cm? and p = 1.1 /cm”.
[0043] The density of the application medium is meant here in relation to the en- vironmental conditions at which it is pre-dosed.
[0044] The application medium can as mentioned above contain solids, e.g. in the form of pigments such as for example CaCOa or TiO2. Solid contents above 50 wt% are however rare. Solid contents between 1 wt% and 30 wt% are preferably used.
[0045] In principle application media with a low viscosity are particularly well suited for the method. The viscosity of the application medium can more advan- tageously be in the range between 0.1 mPas to 200 mPas. The viscosity between mPas and 100 mPas is particularly preferred. Unless mentioned elsewhere, within the scope of this application the viscosity details are always the Brookfield viscosity, measured at 100 U/min and 55-C. 10
[0046] The thickness of the jet can more advantageously be between lum and 200um, preferably between 1um and 100 um, or 140um.
[0047] The dynamic pressure resulting from the jet impacting on the material web is generally below 300 bar. In advantageous designs this dynamic pressure can be between 8 bar and 150 bar.
[0048] Particularly at high dynamic pressures it can be advantageous if, as de- scribed below, a support element is provided in order to fix the position of the material web at the impact line of the jet.
[0049] With regard to the device, the object is achieved by a device for applying an application medium to a moving material web, in particular a moving fibrous web, wherein the device comprises a first moving auxiliary belt and a first deflec- tion at which the first auxiliary belt changes its direction, as well as a pre-dosing device for applying the application medium to the first auxiliary belt and wherein the first auxiliary belt is not in contact with the material web. The first auxiliary belt, the deflection, and the pre-dosing device are then arranged in such a way that the device is suitable for carrying out a method according to one of the pre- ceding claims.
[0050] Advantageous designs are described in the dependent claims.
[0051] The device comprises a second auxiliary belt and a second deflection which changes the direction of the second auxiliary belt wherein the first auxilia- ry belt and the second auxiliary belt are arranged so that the application medium can be transported at least in sections between the first auxiliary belt and the sec- ond auxiliary belt.
[0052] With such an arrangement the two auxiliary belts run parallel in at least some stretches.
[0053] In a further advantageous design, the width of the first auxiliary belt and/or of the second auxiliary belt can be between 80% and 120%, in particular between 95% and 105%, of the width of the material web. This is particularly advantageous when the material web is to be coated over its entire width, or at least over significant parts thereof, in one step.
[0054] It can be proposed further that the surface of the first auxiliary belt and/or of the second auxiliary belt comprises or consists of a metal or a polymer, in par- ticular a polyurethane. In particular one or both auxiliary belts can be a metal belt.
[0055] In further advantageous designs one or both auxiliary belts can comprise a basic structure, - for example a woven or non-crimp fabric -which is provided with a coating of a polymer such as for example a polyurethane.
[0056] In other advantageous designs one or both auxiliary belts can comprise a felt which comprises at least one layer of staple fibres.
[0057] Furthermore it can be proposed that the surface of the first auxiliary belt and/or of the second auxiliary belt is smooth or has a structure.
[0058] Furthermore it can be advantageous if the device comprises an orifice, in particular an adjustable orifice. This can be a slit orifice. This orifice can more advantageously be arranged between the first deflection and the material web in
= 10 - such a way that during operation of the device the jet of application medium can at least partially pass through the orifice. An orifice of this kind makes it easier to set a defined impact region of the jet onto the material web as well as a defined jet thickness when impacting on the material web.
[0059] It can furthermore be advantageous if the device comprises an enclosure which surrounds at least the pre-dosing device, the first deflection and at least parts of the first auxiliary belt. The enclosure then has at least one opening, in particular in the form of an orifice through which during operation of the device the jet of application medium can pass at least partially. This enclosure is inter alia advantageous because it thereby prevents contamination of the surroundings through possible sprays of application medium. Furthermore the elements inside the enclosure are also screened from the surroundings. Since it may happen that the first auxiliary belt and/or the second auxiliary belt rotate very fast in some corresponding uses, an enclosure of this type is also advantageous for safety rea- sons in order to prevent a risk of danger to the operating personnel. An enclosure of this kind can be made for example of metal or plastic. It can also be very ad- vantageous if the enclosure is designed transparent in at least some parts so that monitoring is possible from outside without having to open the enclosure.
[0060] It can furthermore be advantageous if means are provided for cleaning the first auxiliary belt and/or the second auxiliary belt during operation of the device. These can be scrapers for example which scrape any residues of application me- dium off from the respective belt. Alternatively or additionally, cleaning nozzles can also be provided in order to charge the respective belt with a cleaning liquid, in particular water.
[0061] Finally it can also be very advantageous if a support element is provided which is arranged on the non-coated side of the material web in the impact area of the jet. A support element of this kind can contact the material web, such as a support roller or a support plate. A support element of this kind can however also be designed so that the material web slides on an air cushion similar to an air ta-
ble.
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[0062] The invention will now be described in further detail with reference to the diagrammatic figures which are not shown to scale.
Fig. 1 shows a diagrammatic view of a device according to one aspect of the invention;
Fig. 2 shows a diagrammatic view of device according to a further aspect of the invention;
Fig. 3 shows diagrammatically the ratios during application of the applica- tion medium;
Fig. 4 shows estimations for connections between viscosity and pressure for a 100% penetration;
Fig. 5 shows estimations for connections between viscosity and jet speed for a 100% penetration.
[0063] Fig. 1 shows a device 1 for the application of an application medium 4 onto a moving material web 2, such as for example a paper web 2 or cardboard web 2. The fibrous web 2 runs here in this example vertically from top to bottom at a speed — which is normally between 400 m/min and 2000 m/min, for example 1000 m/min. The application device 1 comprises a revolving first auxiliary belt
10. This runs horizontally or at least approximately horizontally between a fur- ther deflection 12 and the first deflection 11. An application medium 4 for ex- ample in the form of a starch solution 4 is applied to the first auxiliary belt 10 in this horizontal region by means of a pre-dosing device 3. The pre-dosing device can be for example a slot nozzle 3 or an overflow moulder. The application medi- um 4 is transported by the first auxiliary belt 10 in the direction of the material web 2. The speed of the first auxiliary belt 10 is here greater than that of the ma- terial web 4, for example between 3000 m/min and 6000 m/min.
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[0064] The device 1 of Fig. 1 furthermore comprises a second revolving auxiliary belt 20. This also runs horizontally or at least approximately horizontally in this example between a further deflection 22 and the first deflection 21, and is ar- ranged so that in this region the application medium 4 is guided sandwiched be- tween the first auxiliary belt 10 and the second auxiliary belt 20. A design of this kind with two auxiliary belts 10, 20 is indeed advantageous but the invention is not however restricted to this. Thus in the design of Fig. 1 as also in the follow- ing device of Fig. 2, the second auxiliary belt 20, as well as the associated deflec- tions 21, 22 could be omitted.
[0065] A support element 5 is provided at the back of the material web 2 at the point where the jet impacts on the material web 2. The support element is ar- ranged in the region of the impact point of the jet and can extend a few centime- tres in front and after the impact point. The support element then more advanta- geously extends — viewed in the running direction of the material web — at least 5 cm, in particular at least 10 cm in front and/or behind the impact point of the jet.
[0066] Furthermore, in this design, means 6 are provided in order to clean the first auxiliary belt 10 during operation of the device 1. Alternatively or addition- ally, these means 6 can also be provided for the second auxiliary belt 20. A pos- sible embodiment can be a scraper 6 which can be placed against the auxiliary belt 10, 20 in particular in the region of a deflection 12. Alternatively or addi- tionally these means 6 can however also comprise cleaning nozzles for example which are not shown in the drawings.
[0067] The device illustrated in Fig. 1 comprises moreover an enclosure 8, 8a. This encloses the pre-dosing device 3 as well as the first and second auxiliary belts 10, 20 with the associated deflections 11, 12, 21, 22 as well as the scraper 6 for cleaning the auxiliary belt 10, 20.
[0068] The enclosure 8, 8a has here at least one opening 7, in particular in the form of an orifice 7, through which the jet of application medium 4 can at least partially pass during operation of the device 1. This enclosure 8, 8a is advanta-
= 13 - geous inter alia because it prevents contamination of the surroundings through possible sprays of application medium 4. Furthermore the elements inside the enclosure 8, 8a are also screened from the surroundings.
[0069] The enclosure in Fig. 1 is designed so that it has at least a transparent part
8a. Monitoring is thus possible from outside without having to open the enclo- sure 8, 8a.
[0070] Furthermore in Fig. 1 a collecting device 9 is provided in order to collect excess application medium 4 or application medium 4 remaining through sprays or settings of the orifice 7 in the enclosure 8, 8a and to make further processing accessible. For this, the enclosure can be configured in such a way, for example by a slight incline of the base or the like, so that the application medium 4 con- verges at one point and can be discharged there centrally into the collecting de- vice.
[0071] Fig. 2 shows by way of example an alternative configuration of the device
1. An enclosure 8, 8a would then be omitted for example. Only an orifice 7 is provided. This can however, as indicated in Fig. 2, be designed so large that it prevents undesired sprays of application medium 4 onto the material web 2. It can furthermore be advantageous if the collecting device 9 extends over the entire length of the device 1, or at least completely covers the area beneath the belt loop of the first auxiliary belt 10.
[0072] Fig. 2 furthermore shows that the first auxiliary belt 10 as well as the sec- ond auxiliary belt 20 need not automatically run horizontally. The incline of the belt in the area of the pre-dosing device 3 can move for example in the range up to 452.
[0073] With the design according to Fig. 2 the jet also does not impact perpendic- ularly onto the material web 2. It has however also proved advantageous if it de- viates by a maximum of 45° from the perpendicular.
[0074] Finally Fig.