Coating machine with sensor and adjustment system

Abstract

The invention relates to a coating machine designed for applying a coating layer onto a substrate, particularly suitable for use in packaging applications. The machine comprises a reservoir for storing coating material and a coating module that includes a pan and at least two rollers, one of which interacts with the pan to transfer the coating material. A pressure roller cooperates with the coating module to ensure uniform application. A key feature of the invention is an adjustment system capable of independently modifying the gap or interference between the rollers at each axial end, enabling precise control over the coating profile across the substrate width. This is complemented by a sensor system configured to measure coating thickness at multiple lateral positions downstream of the coating module. A control unit processes sensor data to dynamically adjust roller positioning and rotational speed, optimizing coating uniformity and material usage. The system may include independent motors for each roller and supports skew angle adjustments to fine-tune the coating shape. The sensor system preferably includes an optical, reflective infrared sensor for accurate, non-contact measurement.

Description

[0001] Coating machine with sensor and adjustment system

[0002] The invention relates to a coating machine and to a method of operating a coating machine.

[0003] The coating machine serves for applying a coating onto a substrate. The substrate being coated can be paper, a film, an aluminum foil or similar materials which are usually provided as a long, “endless” web.

[0004] The coating which is being applied onto the substrate delivers to the substrate enhanced aesthetic and physical properties derived from the coating material. The coating material can be a varnish or lacquer, a water-based coating, a solvent-based or solventless coating, a UV-curable coating, a hot melt coating product, etc.

[0005] Generally speaking, the coating material is received by one of a plurality of rollers and is then transferred via other rollers onto the substrate.

[0006] There are many parameters which determine the amount of coating material applied onto the substrate and the thickness of the coating formed from the applied coating material. Wear of the rollers, misalignments, deviations in the viscosity of the coating material, etc. can result in the coating not having the desired thickness or having an uneven thickness across the width of the (path of the) substrate.

[0007] The object of the invention is to improve the coating quality and consistency achieved with coating machines, to reduce waste by preventing application of out-of-tolerance coating weight, and to save cost by preventing the application of excessive coating material on the substrate.

[0008] This object is achieved with a coating machine for coating a substrate with a coating layer, having a reservoir for coating material, and a coating module for transferring coating material onto the substrate, the coating module having a pan for receiving coating material from the reservoir, at least a first and a second roller of which at least one cooperates with the pan, and an adjustment system for adjusting the position of the first roller with respect to the second roller, the coating machine further having a sensor system adapted for obtaining information on the coating present on the substrate downstream of the coating module, and a control unit connected to the sensor system so as to receive a signal relating to the coating on the substrate, the control unit being adapted for controlling, based on a signal received from the sensor system, the adjustment system of the coating module so as to achieve a desired coating on the substrate. The information provided by the sensor system on the actually present coating allows the control unit to very precisely control, in a closed feedback loop, the adjustment system and therewith achieve the desired coating.

[0009] Preferably, the coating module has a drive system for the first and the second rollers, the control unit being adapted for adjusting the speed of rotation of the first and / or the second rollers. Adjusting the speed of rotation of the rollers can be done very conveniently under a closed loop control.

[0010] The drive system of the coating machine can have a first motor and a second motor, wherein the control unit being adapted for controlling the speed of rotation of the first roller and of the second roller and / or of the speed for rotation of the first and second rollers with respect to each other. This is another way to reliably control the amount of coating material applied onto the substrate.

[0011] The adjustment system is adapted for adjusting the gap / interference between the first and the second rollers, thereby controlling the amount of coating material applied onto the substrate. In the field of coating, the gap between two rollers is used to designate the distance between the two roller surfaces when the rollers don’t touch, while the interference is the sum of their radii minus their inter-axis distance when the rollers touch. But besides this difference in vocabulary, adjusting the gap or adjusting the interference refers to the same operation, which consists in adjusting the inter-axes distance between the rollers.

[0012] Also, the adjustment system is adapted for adjusting the gap / interference at a first axial end of the rollers independently from the other axial end. This allows adjusting the thickness of the applied coating at opposite lateral edges of the substrate.

[0013] The adjustment system can be adapted for adjusting the skew angle between the first and second rollers, for adjusting the shape of the thickness profile across the substrate’s width. In an embodiment, the sensor system is adapted for obtaining information on the thickness of the coating. The thickness of the coating is an important parameter for the quality of the applied coating, as the physical properties largely depend on the amount of coating material and thus on the thickness.

[0014] The thickness of the applied coating can be determined using a sensor system that comprises an optical sensor. The measurement can be based on reflective properties, which change with the thickness of the coating.

[0015] It is also possible to use a sensor system which comprises a chemical sensor. The chemical sensor can detect the presence of certain substances. The presence level of these substances provides information on the thickness of the coating.

[0016] The sensor system is adapted to obtain information on the thickness of the coating at different positions over the width of the substrate, thereby providing information on variations of the thickness across the width of the substrate. It is thus possible to detect local deviations from a desired thickness, or more generally, a deviation from a uniform, flat thickness.

[0017] In one embodiment, the sensor system comprises a plurality of sensors distributed over the width of the path of the substrate. The sensors can very conveniently be fixed at the desired locations, which are representative for the applied coating. For example, a sensor can be placed toward each edge of the substrate, and a third sensor can be placed in the middle of the path of the substrate.

[0018] In an alternative embodiment, the sensor system comprises a sensor that is displaceably mounted over the width of the path of the substrate. In addition to using fewer sensors, this embodiment is advantageous in that it allows obtaining information on the thickness of the coating at any point in the width direction.

[0019] In one embodiment of the invention, a scale is provided which is adapted for obtaining a weight signal indicative of the amount of coating material present in the reservoir, the control unit being adapted for controlling the coating module so as to deposit the desired amount of coating material per length unit onto the substrate. The scale allows the control unit to calculate the rate at which the coating material is taken from the supply system. In combination with the feeding speed of the substrate, the “volume” of the coating applied onto the substrate and thus the thickness can be calculated.

[0020] A database can be provided which contains a reference table correlating at least one of the change of the weight signal from the scale and a sensor signal with the absolute value of the mass of the applied coating per m2. The database can be established via a plurality of calibration steps in which changes of the weight signal from the scale are correlated with measured true thicknesses of the obtained coating.

[0021] A plurality of coating modules can be provided at the coating machine, with at least one dryer unit being arranged downstream of one coating module and upstream of a neighboring coating module. Using different coating modules allows applying a coating which consists of different coating materials.

[0022] The above object is also achieved with a method of operating a coating machine for coating a substrate with a coating layer, in particular for operating a coating machine as defined above, with the following steps: a control unit receives a signal from a sensor system configured for obtaining information on the coating present on the substrate downstream of the coating module in at least two positions across the substrate width, the control unit adjusts a gap / interference at a first axial end of a first roller and of a second roller independently from the other axial end for balancing the thickness of the applied coating layer.

[0023] In a further embodiment, the control unit receives said signal in at least three positions across the substrate width, and wherein the control unit adjusts a skew angle between the first and second rollers for adjusting the shape of the coating profile applied on the substrate and obtaining a shape that is neither convex nor concave.

[0024] In a further embodiment, the control unit receives a signal from a scale indicative of the amount of coating material present in a reservoir the control unit adjusts the gap / interference equally on both axial ends of the first and second rollers and / or adjusts the speed ratio between the first and the second roller, for controlling the amount of coating per unit area of applied on the substrate. In other words, the amount of coating is controlled by adjusting the value of the gap / interference, the left / right balance of the coating thickness is controlled by adjusting the parallelism of the gap / interference, and the concave / convex aspects of the coating profile shape are controlled by adjusting the skew. This setup allows the use of sensors that measure relative coating thickness on the substrate, thus not absolute values.

[0025] Regarding the advantages, reference is made to the above comments.

[0026] The invention will now be described with reference to the enclosed drawings. In the drawings,

[0027] Figure 1 schematically shows a coating machine which is part of a modular coating system comprising a coating machine,

[0028] Figure 2 schematically shows, in a perspective view, a coating module used in the machine of Figure 1,

[0029] Figure 3 schematically shows the coating module of Figure 2 in a broken side view,

[0030] Figure 4 schematically shows a first type of coating module used in the machine of Figure 1,

[0031] Figure 5 schematically shows the coating module of Figure 4 in an alternative mode of operation,

[0032] Figure 6 schematically shows an adjustment system used for the coating module,

[0033] Figure 7 is a graph showing a deviation from a reference position of the distance between the axis of rotation of two rollers of a coating module over the length of the rollers as a result of a skew adjustment, Figure 8 is a graph showing a deviation from a reference position of the distance between the axis of rotation of two rollers of a coating module over the length of the rollers due to deflection of the rollers,

[0034] Figure 9 is a graph showing a deviation from a reference position of the distance between the axis of rotation of two rollers of a coating module over the length of the rollers as a result of a deviation adjustment,

[0035] Figure 10 schematically shows a reservoir for the coating material of the machine of Figure 1,

[0036] Figure 11 schematically shows a sensor system as used in the machine of Figure 1 ,

[0037] Figure 12 schematically shows an alternative to the sensor system of Figure 11 ,

[0038] Figure 13 schematically shows a second type of coating module used in the machine of Figure 1 ,

[0039] Figure 14 schematically shows a third type of coating module used in the machine of Figure 1 ,

[0040] In Figure 1 , a coating machine 1 is schematically shown. It is adapted to provide a coating to a substrate 2 which is fed from a supply 3 through one or several coating stations 4 and dryer units 5 of the coating machine 1 to a receiving area 6.

[0041] The substrate 2 can be paper, a film, an aluminum foil or similar materials which are usually provided as a long, “endless” web.

[0042] The coating is applied to the substrate 2 for delivering to the substrate enhanced aesthetic and physical properties derived from the coating material. The coating material can be a varnish or lacquer, a water-based coating, a solvent-based or solventless coating, an UV-curable coating, a hot melt coating product, etc.

[0043] The supply 3 of substrate 2 can be a large roll from which the substrate 2 is unwound. The coating stations 4 serve for applying the desired coating to the substrate 2. In Figure 1, two coating stations 4 are shown as an example. The coating machine 1 can comprise any desired number of coating stations 4 from as low as a single coating station 4 to higher numbers than two. However, most machines have a single coating station sometimes followed by a laminating station.

[0044] The dryer units 5 are schematically shown here downstream of the respective coating station 4.

[0045] While a dryer is usually needed, the presence of a dryer is not essential in terms of the invention described here.

[0046] The receiving area 6 is the area in which the coated substrate is collected. It can be an area in which the substrate is wound into a large roll.

[0047] Each coating station comprises a pressure roller 7, which mainly serves for defining the path of the substrate 2 and for cooperating with a coating module 10, which applies the coating material onto the substrate.

[0048] Generally speaking, each coating module 10 serves for applying the coating material in the desired amount and distribution onto the substrate 2. To this end, it comprises in one embodiment (as shown in Figures 1 to 5) a pan 12, a dosing roller 14 and a metering roller 16.

[0049] The pan 12 serves for receiving a certain amount of coating material.

[0050] The dosing roller 14 is mounted relative to the pan 12 such that the lowest peripheral portion of the dosing roller 14 is below the upper edge of the pan 12. In other words, the pan 12 can accommodate enough coating material so that the dosing roller 14 is immersed, with a lower portion of its circumference, in the coating material present in the pan 12. The coating material present in the pan 12 is designated with reference numeral 18 in Figures 4 and 5.

[0051] The dosing roller 14 has an outer sleeve made from rubber or a similar, deformable material. For different amounts of coating material to be applied per surface unit (“grammage”), different sleeves can be used, which differ in hardness. Typically, a sleeve has a thickness of 2 cm and a hardness of 65 shores. The sleeve may be made of two sections with different hardness for better performance. For example, the sleeve can be made of an interior cylinder 141 with a hardness of 80 to 100 shores, for example, 90 shores, and an external cylinder 142 with a hardness of 50 to 60 shores, for example, 55 shores. Both sections have approximately the same thickness, for example, 1cm.

[0052] The metering roller 16 is typically metal chromium plated or made with an outer surface of tungsten carbonate.

[0053] In an embodiment, the dosing roller 14 and the metering roller 16 have identical dimensions. As an example, the diameter can be 250 mm.

[0054] The coating module 10 comprises a frame which has two vertical frame portions 20 and a horizontal frame portion 22 connecting the vertical frame portions 20 to each other. The vertical frame portions 20 serve for mounting the rollers 14, 16, and the horizontal frame portion can receive the pan 12.

[0055] The rollers 14, 16 are mounted in the frame 20, 22 so as to be rotatable and displaceable with respect to each other.

[0056] For driving the rollers 14, 16, a drive system is provided which consists of a first motor 24 associated with the dosing roller 14 and a second motor 26 associated with the metering roller 16. The motors 24, 26 are located in the coating unit. An axle with two gimbals 25 connects the motor 24 with the dosing roller, allowing the dosing roller 14 to move along the vertical direction without losing its connection to the motor 24.

[0057] In an alternative embodiment, a single motor can be provided for driving both rollers 14, 16, and the speed of rotation of the dosing roller 14 relative to the speed of rotation of the metering roller 16 and also the direction of rotation of one roller with respect to the other can be set by a gear connecting the “passive” roller to the actively driven roller.

[0058] The motors 24, 26 are controlled by a control unit 28 (please see Figure 1) which is part of the coating machine 1.

[0059] Looking at the coating module 10 shown in Figures 2, 3 and 4, the metering roller 16 and the dosing roller 14 are arranged below the pressure roller 7 so that their axes of rotation are arranged essentially in a single plane. The metering roller 16 is, in operation of the coating machine 1, in contact with the substrate 2 guided by pressing roller 7 and turns in a direction so that its circumference moves, at the point of engagement with the substrate 2, in the same direction as the substrate 2.

[0060] The dosing roller 14 rotates in a direction that is opposite the direction of rotation of the metering roller 16 so that the peripheral portions of the dosing roller 14 and the metering roller 16 move, at the point of the smallest distance between them, in the same direction. This mode of operation is called the forward mode.

[0061] The lower peripheral portion of the dosing roller 14 is immersed in the coating material 18 present in the pan 12. Because of the rotation of the dosing roller 14, it picks up some of the coating material 18 out of the pan 12 and transports it towards the dosing / metering area between the dosing roller 14 and the metering roller 16 where part of the coating material is picked up by the metering roller 16. The metering roller 16 transports this part of the coating material towards the substrate 2 where it is transferred, because of a contact pressure generated between the surface of the metering roller 16 and the substrate 2 abutting against the surface of the pressure roller 7, onto the substrate 2.

[0062] Because of the direction of rotation of the metering roller 16 relative to the pressing roller 7, the coating material is transferred by contact (“laminated”) onto the substrate 2. The rotational speed of coating roller 16 can be different, higher or lower, than the reference speed of substrate 2, thus creating a friction and a transfer effect of the coating media.

[0063] As shown in Figure 5, it is possible to drive the metering roller 16 and the dosing roller 14 in opposite directions as compared to the mode of operation shown in Figure 4. Then, the coating material is “scraped” off of the metering roller 16 by the substrate 2. This mode of operation is called the reverse mode. It allows transferring about 50% more coating material and results in a smoother result. In other words, when using the same substrate and coating material, the coated surface is smoother in the reverse mode compared to the forward mode. However, the setup of the coating module is more delicate and may break the substrate if the pressure and speed setting is off-limit (especially at the start of coating operations), which will result in a machine stop. In the reverse mode, the settings tolerances are much tighter and require an experienced operator. The amount of coating material transferred onto the substrate can be controlled in part by the speed of rotation of the dosing roller 14 and the metering roller 16, in particular by the following parameters:

[0064] A. Absolute speed of rotation of the dosing roller 14,

[0065] B. Absolute speed of rotation of the metering roller 16,

[0066] C. Speed of rotation of the metering roller 16 relative to the feeding speed of the substrate 2,

[0067] D. Speed of rotation of the metering roller 16 relative to the dosing roller 14.

[0068] Typically, it is however only the speed of rotation of the dosing roller which is changed in a closed feedback loop, to control the coating applied onto the substrate 2. An increase of the speed of rotation of the dosing roller 14 (parameter A) results in more coating material being transferred onto the substrate 2, thereby increasing the coating weight, and vice versa.

[0069] Another parameter involved in the transfer of the coating material from the metering roller 16 to the substrate 2 is the pressure in the area where the metering roller 16 cooperates with the pressure roller 7. The pressure is set by the distance between the axes of rotation of the pressure roller 7 and the metering roller 16 and their dimensions, as well as by the hardness of the rubber sleeve of the pressure roller 7. It is here assumed for the sake of simplicity that the distance between the pressure roller 7 and the metering roller 16 is set to be constant (and can be adjusted with mechanical stops that guarantee repeatable positioning).

[0070] Another parameter for controlling the amount of coating material transferred onto the substrate 2 is the area between the dosing roller 14 and the metering roller 16 where they contact each other. The distance between the axis of rotation of the dosing roller 14 and the axis of rotation of the metering roller 16 is usually less than the sum of the nominal diameters of the two rollers 14, 16 so that they contact each other, resulting in a deformation of the elastic sleeve of the dosing roller 14. For adjusting the interference and thus the pressure which is present in the area where the two rollers 14, 16 contact each other, in a desired manner, an adjusting mechanism 30 is provided at the coating module 10. The adjusting mechanism 30 serves for adjusting both the distance of the axes of rotation of the rollers 14, 16 in a vertical direction at both axial ends of the rollers 14, 16, thereby adjusting the distance and the parallelism of the axes of rotation of the rollers 14, 16

[0071] In a preferred embodiment, the adjustment mechanism 30 adjuststhe distance of the axes of rotation of the rollers 14,16 in a vertical direction, and a second adjustment mechanism, adjusts the skew angle between the axes of rotation of the rollers 14,16. Both adjustment mechanisms are located in the coating module. The skew angle is defined as the angle that causes the roller's 14,16 axis of rotation to become non-coplanar.

[0072] Looking at Figure 6, the distance between the axes of rotation of the rollers 14, 16 is adjusted by means of two actuators 32 arranged at opposite axial ends of the rollers 14, 16, effecting a displacement in a vertical direction V, thereby affecting the distance and the parallelism of the axes of rotation.

[0073] The skew angle between the axes of rotation of the rollers 14, 16 is adjusted by means of a skew mechanism 34 which displaces the axial ends of the dosing roller 14 in opposite directions S so that the dosing roller 14 is basically rotated around a central vertical axis. The skew mechanism 34 can comprise two motors for moving the opposite axial ends of the dosing roller 14 in opposite directions. Thus, a single control parameter for the skew mechanism 34 is sufficient.

[0074] The skew mechanism 34 can include a horizontal guide for the opposite axial ends of the dosing roller 14.

[0075] With the skew mechanism 34, sagging effects or unbalanced wear of the rubber sleeve of the dosing roller 14 can be corrected. In other words, the skew mechanism allows for adjustments when the applied coating has a concave or convex profile, thus obtaining. In practice, when using three measurement points, the skew mechanism is adjusted until the measurement point in the middle equals the average of the measurements on the points on the sides of the substrate 2. The average may be a weighted average if the middle point is not equidistant from the two measurement points on the side.

[0076] Figure 7 shows the size of a deviation (related to an interference) from a reference position of the distance between the axis of rotation of the rollers 14, 16 over the length of the rollers, with the deviation being the result of a skew adjustment. The deviation inversely corresponds to a change of the interference between the rollers 14, 16 from a reference position; a smaller deviation corresponds to a higher interference, and vice versa. By rotating the axis of rotation of the dosing roller 14 with respect to the axis of rotation of the metering roller 16 around a vertical axis away from a parallel position, the interference between the two rollers 14, 16 decreases at their axial ends. The distance between the rollers 14 ,16 at the location of the central vertical axis does not change.

[0077] Figure 8 shows the size of an interference between the two rollers 14, 16 which can be observed because of a deflection of the dosing roller 14 under the influence of the pressure exerted by the metering roller 16. The resulting interference is smallest in the center of the rollers 14, 16.

[0078] As the curves have an opposite curvature, a constant interference can be achieved by a skew adjustment.

[0079] Figure 9 shows the size of an interference between the two rollers 14, 16 which can be achieved with the operation of the actuators 32. These can adjust the distance of the axes of rotation at the axial ends of the rollers 14, 16 independently from each other.

[0080] By adjusting the distance of the axes of rotation at the axial ends of the rollers 14, 16 and the skew angle, the resulting interference between the rollers 14, 16 can be adjusted to the desired value and shape.

[0081] Assuming that the interference has been adjusted to a constant value along an axial direction of the rollers 14, 16, the area of contact (“footprint”) between the dosing roller 14 and the metering roller 16 can be adjusted by parallel operation of the actuators 34. Thus, the transfer coating weight is controlled.

[0082] The two main objects of the interference adjustment are to ensure that the coating material is applied evenly (meaning: with a constant thickness over the width of the substrate 2) to the substrate 2 and with the desired thickness. Generally speaking, a smaller interference results in more coating material being transferred towards the substrate 2. The coating material is supplied to the pans 12 of the coating modules 10 from reservoirs 40 which are associated with the pans 12. Each reservoir 40 has a larger capacity than the respective pan 12.

[0083] As shown in Figure 1, each coating module 10 has an assigned reservoir 40.

[0084] Integrated into each reservoir 40 (please see Figure 10) is a heating / cooling device 42 for maintaining the coating material within the reservoir 40 at a desired temperature (and to thus ensure a desired viscosity).

[0085] Reservoir 40 optionally comprises a level sensor 44 which monitors the level of coating material within the reservoir 40 and which allows notifying an operator if coating material is to be refilled.

[0086] The coating material is circulated between the reservoir and the respective pan 12 via a feed conduit 46 and returned conduit 48 by means of a circulation pump (not shown here). The pump is controlled to ensure a constant level of coating material within the respective pan 12. To this end, a level sensor can be associated with the pan 12.

[0087] It is also possible to equip each pan 12 with a temperature sensor.

[0088] Associated with the reservoir 40 is a scale 50 which is adapted for providing a signal indicative of the amount of coating material present in the reservoir.

[0089] The scale 50 is here formed from three load cells 52 which support the reservoir 40. Other implementations of the scale are possible. In particular, four load cells can be used, with one load cell each being arranged at a corner of the reservoir 40.

[0090] The coating machine 1 is provided with a sensor system 60 (please see Figures 1 and 11) for sensing relevant parameters of the coating applied onto the substrate 2. Preferably, there is a dedicated sensor system 60 downstream of each of the coating modules 10.

[0091] In the embodiment of Figure 1 , a sensor system 60 is arranged immediately downstream of the respective coating module 10. This allows obtaining information on a wet coating. In an alternative embodiment, the sensor system 60 can be arranged downstream of the dryer unit 5 assigned to the respective coating module 10. This allows obtaining information on a dry coating.

[0092] In a yet further alternative, two sensor systems 60 can be used, one upstream of the dryer unit 5 and one downstream of the dryer unit 5.

[0093] In a yet further alternative, an additional sensor system 59 may be used to read the substrate upstream from the coating station. This upstream sensor 59 allows for more precise calibration of the sensor systems 60 to read the absolute quantity of material coated on the substrate per unit surface.

[0094] In the embodiment of Figure 11, the sensor system 60 comprises a stationary holding bar 62 which extends over the widths of the substrate 2 from one side of the coating machine to the opposite side. A plurality of sensors 64 is attached to the holding bar 62 at the desired locations.

[0095] In an example, three sensors 64 can be used, which are assigned to the edges of the substrate 2 and to the center.

[0096] If desired, more sensors, preferably identical sensors, can be placed at the holding bar 62 or a scanning sensor can be installed. The scanning sensor is constantly moving right and left across the substrate 2 (in a transversal direction) thus providing detailed information about the coating weight in each position.

[0097] In the embodiment of Figure 12, the holding bar 62 is a rail that carries a slider 66 at which a single sensor 64 is arranged. The sensor 64 can be displaced laterally continuously or according to a predefined time pattern to collect the desired information.

[0098] In a preferred embodiment, the sensor 64 is an infrared optical sensor with an infrared light source, which may be part of the sensor 64 or separate. The sensor reads the intensity of infrared light reflected by the coated substrate in at least two positions across the substrate 2 width. Unless very precisely calibrated, this type of sensor 64 delivers a relative reading related to the thickness of the coating layer, which allows for comparing the two readings from the two positions, but which does not define the absolute thickness value of the coating layer. To regulate the absolute value of the coating thickness, it is preferred to measure the consumption of the coating material with a scale 50, which can measure how much coating is consumed per unit area of coated substrate, or with a flow sensor, as explained later in the document. The sensor 64 can be an optical sensor or a chemical sensor.

[0099] The sensor 64 can particularly be adapted for measuring the thickness of the applied coating. When the sensor 64 is an optical sensor, it can be a reflective optical sensor, for example using a laser source and measuring the intensity of the reflection. As an alternative, the sensor 64 is a transmission sensor. It is placed on one side of the substrate 2 and measures the intensity of light received from a light source which is arranged on the opposite side of the substrate 2.

[0100] When the coating is not water-based, the sensor 64 can be a chemical sensor which detects the presence of isocyanate. The particular advantage of detecting the presence of isocyanate is that the sensor reading is the same when the coating is wet or dried.

[0101] Apart from generally controlling the feed of the substrate through the coating machine 1 , the control unit 28 serves for controlling the coating that is applied onto the substrate 2 by the coating unit 10 or by the coating units 10. For better legibility, reference will in the following only be made to a single coating unit 10 and the associated reservoir 40 and the associated sensor system 60. All information retrieved by the control unit 28 from “the” coating unit 10 is retrieved from any other coating unit 10 as well if there is more than one coating unit 10, and all steps for adjusting “the” coating unit 10 are performed for any other coating unit 10 as well if present.

[0102] For controlling the coating applied to the substrate 2, the control unit 28 may receive signals from the scale 50 associated with the reservoir 40 and from the sensor system 60.

[0103] The signal from the scale 50 allows the control unit 28 to determine the amount of coating material deposited onto the substrate 2. More precisely, the reduction of the weight of the coating material in the reservoir 40 per time unit relative to the feeding speed of the substrate 2 allows determining the grammage of the coating material, assuming that the coating material is applied in a uniform manner onto the substrate 2 and also assuming that the amount of coating material present in the respective coating unit 10 (in particular within the pan 12) is constant.

[0104] The feed speed of the substrate 2 can, for example, be measured at the pressure roller 7.

[0105] In other words, the absolute coating weight is computed as the loss of weight of the reservoir 40 filled with coating material compared to the coated surface in real-time. This gives the wet coating grammage. The real coating weight can then be determined by multiplying the wet coating grammage with the solid ratio contained in the coating material. This value is known since the coating material consists of a diluent (a mix of water and / or a solvent) and solid material.

[0106] Should a solventless technology be used (Fig. 14), the coating grammage corresponds to the “loss” in weight of the coating material contained in the reservoir 40. However, a solventless system has more coating material between the reservoirs (as separate reservoirs are needed for each component of the solventless mixture) and the substrate compared to the other coating modules. Thus, in practice, it is preferred to use the sensor systems 60 in this situation, because of the lag between the scale reading and the applied coating layer.

[0107] It is to be noted here that when using a solventless system (as shown in Fig. 14), there is a positive gap / interference between the dosing roller and the metering roller, instead of an interference.

[0108] As an alternative to the scale (50) or in combination thereto, a flow sensor may be used to measure the flow of coating material that flows from the reservoir 14 to the pan 12. The flow can be used in a similar manner than the loss of weight from the scale 50 by the control unit 28 to control the thickness of the coating layer applied on the substrate. When a feed circuit is used between the reservoir and the pan 12, i.e., via a feed conduit 46 and returned conduit 48, two flow sensors can be used, one in each conduit 46,48. In this case, the difference between the flow sensors computed by the control unit 28 for controlling the thickness of the layer applied on the substrate.

[0109] As a further alternative or in addition to the determination of the grammage (e.g. in g / m2) based on a signal from the scale 50 and the feed speed of the substrate 2, the sensor system can be calibrated so as to use it for determining absolute values of the coating grammage instead of relative values.

[0110] Preferably, for calibrating the sensor system 60, some off-line measurements have to be performed for establishing a correlation table which indicates the grammage (for a specific combination of coating material and substrate) for a particular sensor signal and a particular combination of substrate and coating material.

[0111] It is also possible to perform an online calibration on the basis of the signals from the sensor system 60 and the scale 50. For doing so, a stationary condition is to be obtained in which the coating has a constant thickness over the width of the substrate 2, the feed rate of the substrate 2 is constant, and the “consumption rate” of the coating material is constant. Then, the sensor reading can be correlated with the average coating material consumption per surface area to obtain the coating weight directly from the sensor reading. However, in this situation, the loss of material that may occur between the reservoir and the substrate must be carefully controlled.

[0112] But even without a calibration (and thus in relative mode), the signal from the sensor system 60 allows the control unit 28 to determine the uniformity of the coating layer present on the substrate 2 downstream of the coating unit 10, as identical readings over the width of the substrate 2 indicate that the applied coating layer has a uniform thickness.

[0113] Taking into account the signals from the sensor system 60, the control unit 28 adjusts via the adjustment mechanism 30 the interference between the dosing roller 14 and the metering roller 16 (both with respect to the absolute value in order to influence the amount of coating material applied onto the substrate and with respect to a tapering interference in order to compensate for a variation in the thickness of the applied coating layer in a direction transverse to the feeding direction of the substrate 2).

[0114] During operation of the coating machine 1, the control unit 28 is part of a feedback and adjustment loop in terms of a closed control loop. Feedback comes in the form of signals or readings from the scale 50 and the sensor system 60 (please see the schematically indicated input lines I in Figure 1), and adjustment is done by suitably controlling the speed of rotation of the rollers 14, 16 and the interference between the rollers 14, 16 (by controlling the motors 24, 26 for setting the speed of rotation of the rollers 14, 16 and by adjusting the interference with the actuators 32 and the skew mechanism 34 via schematically indicated output lines O).

[0115] The amount / thickness of the coati ng / adhesive layer is regulated by controlling the speed of the dosing roller 14 and / or the metering roller 16, in accordance with the production speed (basically: the feed speed of the substrate 2).

[0116] In addition, the amount / thickness can be modified with the rubber footprint of the dosing roller 14. The coating thickness can also be regulated by changing the vertical position of dosing roller 14 with respect to the metering roller 16, using a skewing scheme. To regulate the convex / concave profile of the coating, the parallelism of the dosing roller 14 versus the metering roller 16 can be changed.

[0117] The coating module 10 of the type shown in Figures 2, 3 and 4 is part of a modular system which comprises this type of coating module 10, the coating machine 1 , and other types of coating modules 10. Because of the modularity, coating modules of different types can be mounted in the coating machine 1 for different coating jobs so as to cooperate with the pressure roller 7 which is part of the coating machine 1.

[0118] In order to allow for a quick change from a coating module of one type to another coating module of a different type, the coating machine 1 comprises a fixture 70 for receiving the different coating modules 10. Generally speaking, the fixture 70 allows for a quick exchange of the coating modules 10 and also for a mechanically stable positioning. The coating modules 10 of the different types have a complementary receiving portion 71 (please see Figure 3) which is adapted to the fixture 70.

[0119] Looking at Figure 2, the fixture 70 is here schematically indicated in the form of a support rail 75 and two supports 77 on which the frame of the coating module 10 is placed with a recess 71 in its frame, as well as an abutment 73 at one end of the rail 75.

[0120] In addition, all coating modules have a lower chassis with at least two wheels and a pneumatic system, which is made of an inflatable element 81, to elevate the frame of the module with respect to the chassis, and thus engage or dis-engage the frame with the fixture 70 and allowing moving the coating module 10 by hand.

[0121] Further, all coating modules 10 have quick connectors for connecting the pan 12 to the reservoir 40, and plug connectors for establishing the necessary electrical and electronic connections.

[0122] Also, all coating modules 10 have a connector for connecting pressurized air connected to the piston used to engage and disengage the module, by having the wheels 79 of the chassis protrude from the coating module. The module also has a valve to release the pressure in the piston for engaging the frame of the module with the fixture 70.

[0123] Thus, the coating modules 10 with their chassis constitute a coating trolley that can be moved by hand by a single operator on the shop floor.

[0124] A coating module 10 of a second type, called a flexo coating module, is shown in Figure 13. Unless specifically explained otherwise in the following, all statements made above for the coating module of the first type, called a semi-flexo coating module, are also applicable for the coating module 10 of the second type.

[0125] For the sake of clarity, the designations of the rollers known from the previous embodiments (based on their position in the coating module) will be used for the coating module 10 of the second type, even though often different designation are being used in a flexo coating module. Roller 14 is called the anilox roller, and roller 15 is called the inking roller.

[0126] The difference between the coating module of the first type and the coating module of the second type is that the coating module of the second type uses a second dosing roller 15 in addition to the dosing roller 14 known from the coating module of Figure 4.

[0127] The second dosing roller 15 has a rubber sleeve in a manner similar to the rubber sleeve of the metering roller 16.

[0128] A drive (not shown) is present for the second dosing roller 15 in order to rotate it.

[0129] The amount / thickness of the coati ng / adhesive layer is regulated by controlling the speed of the dosing rollers 14, 15 and / or of metering roller 16, in accordance with the production speed. If the speed of the first dosing roller 14 with respect to the second dosing roller 15 is constant, the second dosing roller 15 can be driven from the motor associated with the first dosing roller 14.

[0130] There are three possible regulations: either the speed of the dosing rollers 14, 15 can be changed, or the speed of the metering roller 16 can be changed, or both the speed of the dosing rollers 14, 15 and the speed of the metering roller 16 can be changed.

[0131] Skewing is regulated by influencing the distance between dosing rollers 14, 15, or by adjusting the distance between the assembly of the dosing rollers 14, 15 and the metering roller 16.

[0132] A coating module 10 of a third type is shown in Figure 14. Unless specifically explained otherwise in the following, all statements made above for the coating modules of the first and second types are also applicable for the coating module 10 of the third type.

[0133] The coating module 10 of the third type is used for solventless coating materials and is called a solventless module. For the sake of clarity, the designations of the rollers known from the previous embodiments (based on their position in the coating module) will be used for the coating module 10 of the third type, even though often different designation are being used in a coating module for solventless materials. Roller 14 is called the dispenser roller, roller 15 is called the doctoring roller, roller 17 is called the transfer roller and roller 16 is called the coating roller.

[0134] The difference between the coating module of the second type and the coating module of the third type is that the coating module of the third type uses a transfer roller 17 which is arranged between the first dosing roller 14 and the metering roller 16.

[0135] The third type of coating module 10, used for solventless coating materials, is the only setup where there is a precise distance between the first dosing roller 14 and the second dosing roller 15, instead of the interference which is present with the first and the second types of coating modules 10. All other rollers 14, 17, 16 are in contact. The amount / thickness of the coating / adhesive layer is here regulated by controlling the speed of the first dosing roller 14 and the speed of the transfer roller 17. The speed of rotation of the first dosing roller 14 versus the speed of rotation of the transfer roller 17 is constant. The distance is manually regulated between the first and the second dosing rollers 14, 15.

Claims

Claims1. A coating machine (1) for coating a substrate (2) with a coating layer, having a reservoir (40) for coating material, and a coating module (10) for transferring coating material onto the substrate (2), and a pressure roller (7) for cooperating with the coating module (10), the coating module (10) having a pan (21) for receiving coating material from the reservoir (40), at least a first and a second roller (14, 16) of which at least one cooperates with the pan (12), and an adjustment system (30) for adjusting the position of the first roller (14) with respect to the second roller (16), the coating machine (1) further having a sensor system (60) adapted for obtaining information on the coating present on the substrate (2) downstream of the coating module (10), and a control unit (28) connected to the sensor system (60) so as to receive a signal relating to the coating on the substrate (2), the control unit (28) being adapted for controlling, based on a signal received from the sensor system (60), the adjustment system (30) of the coating module (10) so as to achieve a desired coating on the substrate (2), wherein the adjustment system (30) is adapted for adjusting the gap / interference between the first and the second rollers (14, 16)Characterized in that the adjustment system (30) is adapted for adjusting the gap / interference at a first axial end of the rollers (14, 16) independently from the other axial end and wherein the sensor system (60) is configured for obtaining information on the thickness of the coating at multiple positions over the width of the substrate (2).

2. The coating machine (1) of claim 1 wherein the coating module (10) has a drive system (24, 26) for the first and the second rollers (14, 16), the control unit (28) being adapted for adjusting the speed of rotation of the first and / or the second rollers (14, 16).

3. The coating machine (1) of claim 2 wherein the drive system has a first motor (24) and a second motor (26) and wherein the control unit (28) is adapted for controlling the speed for rotation of the first and second rollers (14, 16) with respect to each other, for adjusting the rate at which coating material is consumed.

4. The coating machine (1) of any one of the preceding claims wherein the sensor system (60) is adapted for obtaining information on the thickness of the coating at three or more positions over the width of the substrate (2).

5. The coating machine (1) of the preceding claim wherein the adjustment system (30) is adapted for adjusting the skew angle between the first and second rollers (14, 16), for adjusting the shape of the coating profile applied on the substrate.

6. The coating machine (1) of any one of the preceding claims wherein the sensor system (60) comprises an optical sensor (64).

7. The coating machine (1) of the preceding claim, wherein the optical sensor (64) is a reflective infrared sensor.

8. The coating machine (1) of any one of claims 1 to 5 wherein the sensor system (60) comprises a chemical sensor (64).

9. The coating machine (1) of any preceding claims wherein the sensor system comprises a plurality of sensors (64) distributed over the width of the path of the substrate (2).

10. The coating machine (1) of any claims 1 to 8 wherein the sensor system (60) comprises a sensor (64) which is mounted so as to be displaceable over the width of the path of the substrate (2).

11. The coating machine (1) of any one of the preceding claims wherein a scale (50) is provided which is configured for obtaining a weight signal indicative of the amount of coating material present in the reservoir (40), the control unit (28) being adapted for controlling the coating module (10) so as to deposit the desired amount of coating material per length unit onto the substrate (2).

12. The coating machine (1) of claim 11 wherein a database is provided which contains a reference table correlating at least one of the change of the weight signal from the scale (50) and a sensor signal with an absolute value of the mass of the applied coating per m2.

13. The coating machine (1) of any one of the preceding claims wherein a plurality of coating modules (10) is provided, with at least one dryer unit (5) beingarranged downstream of one coating module (10) and upstream of a neighboring coating module (10).

14. A method of operating a coating machine (1) for coating a substrate (2) with a coating layer, in particular for operating a coating machine (1) as defined in any one of the preceding claims, with the following steps: a control unit (28) receives a signal from a sensor system (60) configured for obtaining information on the coating present on the substrate (2) downstream of the coating module (10) in at least two positions across the substrate (2) width, the control unit (28) adjusts a gap / interference at a first axial end of a first roller (14) and of a second roller (16) independently from the other axial end for balancing the thickness of the applied coating layer.

15. The method of claim 14, wherein the control unit (28) receives said signal in at least three positions across the substrate (2) width, and wherein the control unit (28) adjusts a skew angle between the first and second rollers (14, 16), for adjusting the shape of the coating profile applied on the substrate (2) for obtaining a shape that is neither convex nor concave.

16. The method of claim 14 or 15, wherein the control unit (28) receives a signal from a scale (50) indicative of the amount of coating material present in a reservoir (40) the control unit (28) adjusts the gap / interference equally on both axial ends of the first and second rollers (14, 16) and / or adjusts the speed ratio between the first and the second roller (14,16), for controlling the amount of coating per unit area of applied on the substrate (2).

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