WO2025248379A1

WO2025248379A1 - Spreading device for spreading an adhesive on a moving film

Info

Publication number: WO2025248379A1
Application number: PCT/IB2025/055187
Authority: WO
Inventors: Vincenzo CERCIELLO
Original assignee: Nordmeccanica SpA
Current assignee: Nordmeccanica SpA
Priority date: 2024-05-27
Filing date: 2025-05-19
Publication date: 2025-12-04
Anticipated expiration: 2026-11-27

Abstract

The present invention concerns a coating device, for coating a moving film with a layer of adhesive, comprising at least one first metering roller, at least one second metering roller, facing the first and which can rotate in contact with an adhesive, said rollers being heated, and an adjustment device to control the movement of the first metering roller with respect to the second metering roller; said coating device further comprises measuring means adapted to detect at least one parameter relative to the position of said first metering roller with respect to the shoulders of the machine and in which said adjustment device is controlled by a control unit, which is configured to command motor means of the adjustment device as a function of the temperature parameter of the metering rollers and the position parameter of the first metering roller.

Description

TITLE

SPREADING DEVICE FOR SPREADING AN ADHESIVE ON A MOVING FILM

DESCRIPTION

The present invention concerns a device for coating a moving film with an adhesive. In particular, the invention concerns a coating device to be used in an apparatus for the production of flexible multilayer films. The invention further concerns an apparatus for the production of multilayer film comprising such a coating device.

In various industrial sectors, particularly the packaging sector, flexible films are used consisting of several layers, also made of different materials, bonded to one another by gluing.

Of the various types of adhesive available, solventless adhesives are those most widely used in this sector, particularly for packaging intended for the food industry.

Methods and machines for bonding several layers of film with solventless adhesives are known, for example, from the patents EP0324892B2 and EP2085218B 1 of the same applicant.

According to these known methods, at least two flexible films, made of identical or different materials, are unwound from respective reels and are conveyed towards a bonding unit. To join the two films, a thin layer of solventless adhesive is deposited, by means of a coating assembly, on a face of one of the two films; the two films are then brought into contact in the bonding unit to create a laminated multilayer film.

In these processes, a bicomponent solventless adhesive is used, the two components of which, typically resin and hardener, are mixed prior to application on the film and, more precisely, prior to being conveyed to the bonding machine.

In other applications, as described in the patent EP EP 3454995 Bl, again of the applicant, the two components of the bicomponent adhesive are applied separately, by respective coating assemblies, on two films which are then brought into contact with the respective coated sides of the adhesive components, to form a multilayer laminated film.

The coating of the film with the adhesive is one of the most delicate steps in the process of production of a multilayer film since the quality of the finished product depends on it.

In the majority of applications for the production of multilayer flexible films, in particular for the packaging industry, among others, the thickness of the layer of adhesive between the two bonded films is extremely fine, typically between 0.5 micron and 5 micron, corresponding to approximately 0.5 - 5 g/m², with the solventless adhesives currently used.

In the following part of the description, reference will be made to the thickness of the layer of adhesive, referring clearly also to the mass of said adhesive deposited on the film, i.e. the gram weight, said values being correlated with each other.

To guarantee both the mechanical performance (resistance to peeling), and above all the aesthetic/optical characteristics of the multilayer film, it is fundamental for the thickness of the layer of coated adhesive to correspond to the scheduled nominal value (the variation in the thickness of the adhesive layer must not exceed 10% of the nominal value of the thickness, namely a few tenths of a micron) and to be maintained constant throughout the production process of a single batch of film, which can involve even thousands of metres of film per production batch.

With reference to the attached figure 1, a coating assembly of the known art is schematically illustrated, which generally comprises a first metering roller DI, a second metering roller D2, facing the first one, a conveyor roller TR which rotates in contact with the second metering roller D2 and a coating roller SP which rotates in contact with the conveyor roller TR and with a face of a layer of film F.

In the space between the two metering rollers DI, D2, a chamber is defined in the upper part where an adhesive is deposited which remains in contact with a part of the outer surface of both the metering rollers.

The surfaces of the metering rollers DI, D2 are spaced by a gap of a few hundredths of a millimetre so that, following the relative rotation of the surfaces of the two rollers, the adhesive is laminated through the gap and a thin uniform layer remains adhering to the surface of the second metering roller D2. From the latter, the adhesive is transferred to the conveyor roller TR and then to the coating roller SP, reducing the thickness of the adhesive each time until it is coated on the film.

Said known devices further comprise an adjustment device, not illustrated, which allows at least the first metering roller to be moved with respect to the second metering roller to vary the width of the gap and, therefore, the thickness of the adhesive layer taken from the second metering roller, and consequently the thickness coated on the film.

With the coating assemblies of the known art, however, it is difficult to always guarantee the required adjustment precision and, therefore, repeatability of the uniformity and thickness parameters of the adhesive.

This depends on various factors including, for example, the difficulty of obtaining extremely fine dimensional tolerances of the rollers and mechanical play of the adjustment device.

Another decisive factor in adjustment of the thickness of the coated adhesive, namely the gap between the metering rollers, is the thermal expansion of the latter. The coating assemblies that operate with bicomponent solventless adhesives are in fact equipped with heating means to bring the surface of the rollers to a temperature generally between 30°C and 90°C, thus maintaining the adhesive at a predefined operating temperature.

Said heating, however, causes a radial expansion of the rollers in the operating condition, with respect to the non-operating condition at ambient temperature, which significantly affects the width of the gap. A further aspect that makes the control of said coating assemblies complex is the fact that it is not possible to directly measure the width of the gap when the device is working, namely with the rollers in rotation covered with adhesive, with the known measuring instruments, whether optical, inductive or of other type.

For these reasons, the majority of coating assemblies on the market today are equipped with mechanical adjustment devices, operated by levers, handwheels and the like, manually controlled by the operator. The adjustment precision of the gap with the coating devices of the known art therefore depends almost exclusively on the ability and experience of the operator who carries out the initial setting of the device and the control thereof.

Said control, mainly visual, moreover, must last for the entire duration of the production process.

In general, during the initial setting phase and/or during the production process, a control of the gram weight can be scheduled; this is performed by taking samples of standardized dimensions of the multilayer film (bonded) from the wound reel, weighing said sample with a precision balance and, after delaminating the film and removing all the coated adhesive, re-weighing the cleaned layers of film so as to calculate the gram weight as the differential value between the two weights.

This operation takes time, particularly if it has to be performed several times to complete adjustment of the machine in several steps, slowing down production and generating potential waste.

In this context, the object of the present invention is to propose a device for coating a film with an adhesive that overcomes the above-mentioned drawbacks of the known art.

It is therefore the object of the present invention to propose a coating device that allows the thickness of the layer of an adhesive applied to a moving film to be controlled in a precise automatic manner. In particular, the object of the present invention is to provide a coating device in which said adjustment precision is independent of the ability and experience of the operator.

A further object of the present invention is to make available a coating device that guarantees the repeatability of said coating process parameters.

A further object of the present invention is to make available a coating device equipped with an adjustment device for adjusting the gap between the metering rollers which is simpler to control.

The object of the present invention is also to make available an apparatus for the production of a multilayer film equipped with the above-mentioned coating device.

These and other objects are achieved by a device for coating a moving film with an adhesive in accordance with the attached claim 1.

As mentioned, the device according to the invention is adapted to be used in an apparatus for the production of a flexible multilayer film, namely a bonding or laminating machine.

The coating device, like those of the known art, can be integrated in said apparatus as a fixed station or can be provided in the form of a movable carriage, so that it can be installed and removed from the apparatus rapidly according to requirements.

In detail, according to the present invention, the coating device comprises: at least one first metering roller; and at least one second metering roller, facing the first and which can rotate in contact with an adhesive; in which the surface of the first metering roller is spaced from the surface of the second metering roller by a gap such that, following the rotation of said second metering roller, a portion of its surface is coated with a uniform layer of adhesive. The angular position of the first metering roller is preferably fixed during operation.

As in the devices of the known art, the device of the present invention generally also comprises a conveyor roller, which rotates in contact with the second metering roller, and a coating roller that rotates in contact with the conveyor roller and, in general, with a face of a layer of film to be coated.

The first metering roller and the second metering roller are arranged with their respective axes parallel and are supported at their ends by respective shoulders of the coating device. The first metering roller is mounted on said shoulders via sliding means, adapted to allow the movement thereof in a direction orthogonal to its axis. Said movement direction of the first metering roller is preferably, but not necessarily, horizontal. Typically, said sliding means, for example slides, carriages or similar, are coupled to support shafts arranged at the ends of the roller.

According to one aspect of the invention, the coating device further comprises heating means for heating the surface of the first metering roller and second metering roller.

According to another aspect of the invention, the coating device further comprises measuring means for measuring a temperature parameter of the surface of the first metering roller and second metering roller.

According to another aspect of the invention, the coating device further comprises an adjustment device which controls the movement of the first metering roller, with respect to the second metering roller, to vary the width of the gap and, therefore, the thickness of the layer of adhesive transferred to the surface of the second metering roller. Said adjustment device, cooperating with the above-mentioned sliding means, comprises motor means and, possibly, a transmission.

Preferably, each of the sliding means at the ends of the first metering roller is associated with respective motor means, which can be operated in a synchronized manner or, if necessary, independently so as to micrometrically adjust also the angle between the axes of the first metering roller and second metering roller.

According to another aspect of the invention, the coating device further comprises measuring means, preferably associated with the sliding means, adapted to detect at least one parameter relative to the longitudinal position of said first metering roller, namely with respect to the direction of movement.

According to a preferred variation, each of the sliding means is associated with a measuring means to detect said position parameter for each lateral end of the first metering roller.

In accordance with a main aspect of the invention, said adjustment device is controlled by a control unit, which is configured to control the motor means as a function of the temperature parameter of the first metering roller, the second metering roller or both, and at least one position parameter of the first metering roller.

Thanks to the configuration of the coating device described above, the adjustment device can regulate in an automatic and extremely accurate manner the position of the first metering roller, therefore the width of the gap between the two metering rollers and, consequently, the thickness of the layer of adhesive coated on the film.

In particular, since the control unit can receive in real time the datum relative to the temperature parameter of the metering rollers, said unit is configured to control the motor means of the adjustment device in such a way as to compensate for the thermal expansions of said rollers.

Therefore, starting from a reference position of the first metering roller and with the metering rollers at a reference temperature, for example at ambient temperature, and providing the control unit with the desired value of the gap, the latter is able to calculate the value that must be reached by the measuring means of the position parameter of the first metering roller for the scheduled operating temperature of the metering rollers. In this way, after performing an initial calibration of the device as a function of the actual geometry of the metering rollers (the latter can have in general a cylindricity tolerance not exceeding 2/100 mm, preferably not exceeding 1/100 mm), the adjustment device can operate in a substantially automatic manner.

According to a preferred embodiment of the invention, the control unit comprises a memory unit in which a dataset is stored comprising a list of values of the temperature parameter of the metering rollers (preferably one single value considering the substantially identical temperatures of the metering rollers), where each temperature value is associated with a position parameter value of one or both the measuring means associated with the sliding means.

The minimum and maximum temperatures in said dataset correspond respectively to the ambient temperature and maximum operating temperature, generally approximately 80-90°C.

An accurate compensation of the thermal expansion due to heating of the rollers is absolutely necessary: in the majority of applications, a correct gap between the metering rollers is approximately 7-8 hundredths of a millimetre but the radial thermal expansion of each roller can reach 1/10 of a millimetre. This means that if the metering rollers are at the correct distance at ambient temperature, once brought to temperature, the respective surfaces would come into contact with each other with a certain pressure.

According to another aspect of the invention, the gap adjustment device comprises a motor, preferably a brushless gearmotor assembly, which drives a recirculating ball screw mechanism. Between the motor and the recirculating ball screw mechanism, a drive with belt and pulleys is interposed. The shaft of the recirculating ball screw mechanism is operated by a driven pulley, whereas the ball nut is rigidly connected to the sliding means of the first metering roller. The gearmotor assembly, furthermore, is preferably equipped with an integrated braking device.

The motor-transmission assembly thus configured is characterized by reduced play/tolerances and by a considerable resistance to the retrograde motion of the first metering roller, thus guaranteeing a high positioning precision.

According to another variation of the invention, the coating device can comprise a braking device, for example of pneumatic or electromagnetic type, configured to cooperate directly with the slides of the sliding means, to maintain the position of the first metering roller.

According to another aspect of the invention, the measuring means of the position parameter of the first metering roller comprise a linear measurement sensor. According to a preferred embodiment, said sensor comprises two mutually sliding parts, cooperating respectively, directly or indirectly, with the shoulders of the device and with the sliding means.

Said configuration allows the actual movement of the first metering roller to be detected. In fact, since said linear measurement sensor is positioned “at the tail end” of the kinematic chain of the drive, the effect of any mechanical play of the transmission components can be disregarded.

The measuring means thus configured therefore allow a much more accurate measurement of the position parameter than many known solutions where, for example, an encoder is used associated with the gearmotor.

According to a preferred variation, in order to limit effects of temperature disturbance on the value detected by the above-mentioned linear sensor, the parts of the sensor are fixed to the sliding means and to the shoulders of the device (which can reach temperatures of even 50-60°C) by means of supports made of a material with low thermal conductivity, preferably a thermoplastic polymer. According to another aspect of the present invention, the heating means of the metering rollers comprise a source of a heated fluid (typically water, possibly with the addition of glycol or similar) which is made to circulate inside chambers or passages obtained in the metering rollers.

In further detail, each metering roller comprises a fluid inlet and a fluid outlet at the ends of the roller, more precisely at the free ends of the support shafts. Said inlet and outlet can be arranged each at the respective ends or, according to a preferred variation, both at the same end.

According to the invention, the measuring means of the temperature parameter comprise a pair of temperature probes located at the heated fluid inlet and outlet of each roller.

With said configuration, it is possible to establish precisely when the surface of the roller has reached the scheduled operating temperature.

According to a possible embodiment, said control is carried out by the control unit which is configured to compare the inlet temperature value Ti and the outlet temperature value To and to establish that the operating temperature is reached when the difference AT = Ti-To is below a predefined threshold value (for example not exceeding 2°C).

Another embodiment considers the stabilized temperature, and therefore expansion, when the difference between the nominal operating temperature Tset and the temperature detected at the outlet To remains below a predefined threshold value (for example not exceeding 2-3 °C) for a predefined time.

In this way, the adjustment phase, more precisely the movement phase of the first metering roller in the predefined work position, is carried out only when the thermal expansion of the two metering rollers has been stabilized.

Unlike the solutions of the known art, where the temperature values are read with the temperature sensors integrated in the heating means, by using the values detected by the above-mentioned probes at the metering rollers, it is possible to obtain a more accurate datum that is not affected by the distance between the heating means and the coating device (based on the length of the tubes that circulate the heated fluid, there is a greater or lesser reduction of the temperature in the return fluid).

According to a further aspect of the present invention, the coating device can further comprise at least one further sensor of optical type adapted to measure the quantity of adhesive coated on the film. Said optical sensor is therefore downstream of the coating roller or, in any case, prior to the bonding unit of the multilayer film production apparatus, where the two films are bonded.

Said at least one measurement sensor of the adhesive thickness is connected to the control unit. The latter is configured to receive the value relative to the quantity of adhesive coated on the film and, according to said value, to control in feedback one or more parameters of the coating device to correct any deviations of the value detected with respect to a predefined nominal value.

In further detail, according to a variation of the invention, the control unit is configured to vary the rotation speed of the conveyor roller or, possibly, of the coating roller of both. Said variation determines a reduction or an increase in the adhesive transferred to the coating roller and, therefore, onto the film.

According to one aspect of the invention, said optical sensor is configured to detect the measurement of the quantity of adhesive in several points along a direction transverse to the film unwinding direction.

According to said variation, if said sensor detects a non-uniform quantity of adhesive in the above-mentioned transverse direction of the film, the control unit is further configured to command operation of the adjustment device motor means. In particular, by operating in a controlled manner the motor means of the respective sliding means of the first metering roller, the angle between the axes of the first and second metering roller can be varied in order to obtain the coating of a uniform layer throughout the width of the film.

According to another aspect of the invention, the first metering roller is mounted rotatable around its own axis so that it can be rotated during washing and/or maintenance operations. Said rotation is imparted by a motor, typically a motor gearbox unit, associated with an encoder which provides a datum relative to the angular position of said first metering roller.

As previously mentioned, said first metering roller is kept blocked in rotation during operation. However, it is important to know, according to its angular position, which area of its surface is working, namely is cooperating with the second metering roller to laminate the adhesive. This is because the calibration dataset (of positioning and temperature) stored in the control unit refers to a precise area (theoretically a geometric line) of the surface of the first metering roller.

Therefore, according to a preferred variation of the invention, in the storage unit of the control unit several datasets are stored comprising values of the temperature parameter of the metering rollers associated with corresponding position parameter values. Each dataset refers to a given angular work position of the first metering roller measured by said encoder.

In this way it is possible to make the first metering roller work in several angular positions (for example by periodically varying the position) thus avoiding excessive wear on one single area of the surface.

To maintain the first metering roller perfectly blocked in rotation during operation, the motor that rotates said roller is preferably equipped with a braking device.

Further characteristics and advantages of the present invention will appear clearer from the description of an embodiment example as illustrated in the attached figures in which: - figure 2 shows a schematized lateral view of the coating device according to the present invention;

- figure 3 shows a perspective view from a first side of the coating device according to the present invention;

- figure 4 shows another lateral perspective view, from an opposite side, of the coating device of figure 3;

- figure 5 shows a perspective view of the coating device of figure 3, in a partially assembled condition;

- figure 6 shows a perspective view of a detail of the coating device of figure 3, in a partially assembled condition;

- figure 7 shows a front view of a detail of the coating device of figure 3, in a partially assembled condition;

- figure 8 shows a flow chart illustrating a calibration procedure of the coating device according to a variation of the present invention;

- figure 9 shows a flow chart illustrating a calibration procedure of the coating device according to another variation of the present invention;

- figure 10 shows a flow chart illustrating a setting procedure of the coating device according to the present invention.

With reference to the attached figures, the number 1 indicates overall a device for coating a moving film with adhesive.

In the context of the present invention, by adhesive we mean an adhesive composition in fluid or paste form.

By film, we mean a flexible substrate with a thickness of less than 1 mm and preferably less than 0.5 mm. Suitable materials are, for example, paper, polymers and polymers with metallic coatings, metal sheets or non-woven fabric (NWF). The coating device comprises a first metering roller 10 and a second metering roller 11, arranged parallel and facing each other. The first metering roller 10 is preferably kept blocked in rotation during operation of the apparatus. The second metering roller 11 is rotated with respect to the first one in a rotation direction indicated by the arrow Rd (fig. 2). The outer surface of the metering rollers 10, 11 is preferably smooth and coated in, or made of, chrome-plated steel.

In the space between the two metering rollers 10, 11, in the upper part, a chamber 12 is defined in which an adhesive can be deposited in contact with a part of the outer surface of both the rollers. To maintain the fluidity of the adhesive at a desired value, the metering rollers 10, 11 are preferably provided with heating means to heat the outer surface.

The surfaces of the metering rollers 10, 11 are spaced by a gap of a few hundredths of a millimetre (generally 0.07-0.08 mm) so that, following the rotation of the second metering roller with respect to the first, the adhesive is laminated through the gap and a thin uniform layer remains adhered to the surface of the second metering roller 11. Said layer of adhesive, by means of one or more further rollers that rotate in contact with the second metering roller 11, is transferred to a moving film S.

In the variation illustrated, the coating device comprises a further conveyor roller 13 which rotates in contact with the second metering roller 11 in an opposite rotation direction Rt. The conveyor roller 13 is preferably coated with a layer of vulcanized rubber. The job of the conveyor roller 13 is to collect the layer of adhesive from the second metering roller 11 and transfer it to a coating roller 14 which rotates in contact with it in an opposite rotation direction Rs.

The coating roller 14, in turn, is placed in contact with the layer of moving film S, on which the adhesive is spread in a continuous uniform layer.

The rotation speed of the coating roller 14 is greater than that of the conveyor roller 13 which, in turn, is greater than that of the second metering roller 11. Said speed increase allows the thickness of the adhesive layer that is deposited on the surface of the rollers, and subsequently on the layer of film, to be gradually reduced.

In the example illustrated, the second metering roller 11 and the conveyor roller 13 are rotated by a single motor 50 which, by means of a belt transmission 51, drives two reducers 52, 53 connected to the second metering roller 11 and to the conveyor roller 13 respectively (fig. 3).

The coating roller 14, on the other hand, is rotated by a motor 60 via a belt transmission 61 (fig. 4).

The first metering roller 10 comprises a central working portion 10a comprised between two support shafts 10b (fig. 3, 5, 7) by means of which it is supported by respective shoulders 70 of the coating device 1.

Similarly, the second metering roller 11 comprises a central working portion I la and two support shafts 1 lb by means of which it is supported by the shoulders 70.

In further detail, the first metering roller 10 is supported by sliding means, configured to translate along a direction Dr substantially orthogonal to the axis of said first metering roller 10.

In the example illustrated, said sliding means comprise a pair of slides 30 each slidingly mounted on a respective shoulder 70 of the coating device. Each slide 30 is equipped with a support 31 (typically a bearing) which houses a support shaft 10b of the first metering roller 10.

The gap, namely the minimum distance between the surfaces of the metering rollers 10, 11, can be adjusted by means of an adjustment device, thus varying the thickness of the layer of adhesive taken from the second metering roller 11 and, consequently, the thickness of the adhesive layer applied to the film S.

Figure 6 illustrates a detail of the coating device showing the above-mentioned adjustment device, indicated overall by the number 20. In accordance with a preferred variation of the invention, said adjustment device acts on the first metering roller 10 moving it with respect to the second metering roller 11, the rotation axis of which is fixed.

In further detail, the adjustment device 20 is configured to move the slides 30 along the direction Dr by a few hundredths of a millimetre, to adjust said gap.

According to a preferred variation of the present invention, the adjustment device 20 comprises a brushless gearmotor assembly 21 rigidly fixed to the shoulders 70 of the coating device. The outlet shaft of said gearmotor assembly is connected to a motor pulley 22 which, by means of a belt 23, operates a driven pulley 24. Said driven pulley 24, in turn, is connected to a shaft 26 of a mechanism with recirculating ball screw 25. The ball nut 27 of the recirculating ball screw 25 is rigidly connected to the slide 30.

Said adjustment device 20 is provided at both ends of the first metering roller 10. Each adjustment device 20 can therefore control the movement of the respective slide 30.

To detect the movement of the first metering roller 10, and more specifically of each slide 30, the coating device 1 is equipped with a linear measurement sensor 28 which is fixed or resting on the shoulder 70 and on the slide 30. More precisely, said sensor 28 has a body 28a, which is fixed to the shoulder 70, and a feeler 28b which rests on the slide 30.

Said parts of the sensor 28 are fixed or rest on the slide 30 and shoulder 70 of the device by means of supports 29 made of polyether ether ketone (PEEK). Said material has both a reduced thermal conductivity, so as not to transmit the heat from the shoulders 70 and from the slides 30 to the sensors 28, and a high elastic modulus, which allows a high precision to be maintained in the reading of the movements of the slide 30.

As mentioned previously, according to a preferred embodiment of the invention, the first metering roller 10 is mounted rotatable around its axis in the slides 30. As already mentioned, said rotation is necessary for carrying out the washing operations.

For said purpose, the support shaft 10b of the first metering roller 10 is connected to an asynchronous gearmotor 40, which is coupled to an encoder 41, to allow precise identification of the angular position of said first metering roller 10 and therefore the area of its surface that faces the second metering roller 11. Said gearmotor 40 is equipped with a braking device integrated in the motor itself (not indicated in the figures) to keep the first metering roller 10 perfectly blocked in rotation during operation.

The gap adjustment device 20 is controlled by a control unit of the coating device, not illustrated in the figures. The control unit, generally integrated in the PLC module of the multilayer film production apparatus, has a calibration dataset which enables the unit to autonomously control the adjustment device 20 to arrange the metering rollers 10, 11 at the correct predefined working distance.

In further detail, the control unit comprises a memory unit in which datasets are stored relative to the parameters of temperature of the metering rollers 10, 11 and position of the first metering roller 10.

Each dataset is associated with an angular position of the first metering roller 10. According to the invention, the angular positions with which a dataset is associated are between 2 and 16, preferably between 4 and 8. Said positions are in general angularly equally spaced.

The above-mentioned parameters are obtained with an initial calibration phase of the device. Said calibration operation is performed only once and must be repeated only if one or both the metering rollers 10, 11 are replaced.

Figure 8 shows a flow chart that describes an example of a calibration procedure via which it is possible to identify and record the values of the temperature and position parameters for the above-mentioned datasets.

Said procedure comprises the following steps: a) the metering rollers 10, 11 are brought to a predefined distance (generally at least 1 mm, using a feeler gauge for the identification); b) the metering rollers 10, 11 are brought to an initial predefined temperature (a maximum operating temperature, for example 90°C, or a minimum operating temperature, for example 30°C); c) the metering rollers 10, 11 are moved closer or farther away until the distance detectable with the feeler gauge, inserting the latter between said metering rollers, is equal to a defined value, for example 0.08 mm; d) when the resistance of the feeler gauge located between the two metering rollers 10, 11 is correct, the value of the position parameter of the first metering roller 10 is recorded and said value is associated with the respective temperature; e) the temperature is reduced (if starting from the maximum temperature) or increased (if starting from the minimum temperature) by a predefined value with respect to the previous one (for example by 5°C or 10 °C); f) steps c), d) and e) are repeated a certain number of times until the entire temperature range between the minimum temperature and the maximum temperature is covered.

The movement of the rollers in step c) is carried out by a manual command that operates the motor means of the adjustment devices 20. The distance is measured with the feeler gauge in several points to ascertain that it is constant throughout the transverse extension of the rollers.

Said distance test via the use of the feeler gauge is performed when the reading of the temperature value with the respective measuring means corresponds to the predefined nominal value, namely when the temperature of the metering rollers is stabilized.

The recorded position parameter value generally corresponds to the reading value of the linear sensor 28. Said recording is preferably carried out for both the adjustment devices at the respective ends of the roller. The dataset relative to the temperature and position parameters can be recorded directly in the storage unit of the control unit or at a later time.

Once the calibration step has been completed as described above, the control unit is able to command the adjustment devices 20 to bring the first metering roller 10 to the correct position so that, for a given operating temperature, the value of the gap corresponds to the scheduled nominal value.

Figure 9 shows a flow chart that describes another example of a calibration procedure via which the values of the temperature and position parameters for the above- mentioned datasets are recorded.

With respect to the procedure described previously, according to this mode the position parameter of the first metering roller, for each temperature step, is detected for several points on the surface of said first metering roller 10.

In further detail, the position parameters are detected and recorded by arranging the first metering roller 10 in different angular positions.

Said procedure therefore entails the following steps: the metering rollers 10, 11 are brought to a predefined distance (generally at least 1 mm, using a feeler gauge for the detection) and the first metering roller 10 is set to a known angular position; the metering rollers 10, 11 are brought to an initial predefined temperature (a maximum operating temperature, for example 90°C, or a minimum operating temperature, for example 30°C); the metering rollers 10, 11 are moved closer or farther away until the distance detectable with the feeler gauge, inserting the latter between said metering rollers, is equal to a defined value, for example 0.08 mm; when the resistance of the feeler gauge positioned between the two metering rollers 10, 11 is correct, the value of the position parameter of the first metering roller 10 is recorded and said value is associated with the respective temperature; dl) the first metering roller is rotated by a known angle (for example 45°, 90°, etc.); d2) steps c), d) and dl) are repeated until an arc of 360° has been completed; the temperature is decreased (if starting from the maximum temperature) or increased (if starting from the minimum temperature) by a predefined value with respect to the preceding one (for example by 5°C or 10°C); steps c), d), dl), d2) and e) are repeated a certain number of times until the entire temperature range between the minimum temperature and the maximum temperature is covered.

According to this variation of the invention, it is possible to use several areas of the first metering roller 10 for spreading the adhesive, since the control unit has dedicated calibration parameters for each of said areas. In this way, it is possible to compensate for any geometrical tolerances of the roller surface which (although extremely small) could affect adjustment of the gap and therefore the thickness of the adhesive coating.

Figure 10 shows a flow chart that describes an operating mode for setting the coating device.

The setting entails the following steps: a) the operating temperature of the metering rollers 10, 11 is set in the heating means; b) when the temperature of both metering rollers 10, 11 detected with the measuring means is stable and equal to the set value, a command is given for positioning the first metering roller 10; c) the adhesive is fed into the coating device.

In step b), the control unit, according to the selected operating temperature and possibly the angular position of the first metering roller 10, calculates the correct value that must be read by the linear measurement sensors 28 so that the first metering roller 10 is spaced from the second metering roller 11 by the chosen gap. The control unit then gives the command to the adjustment devices 20 to move said first metering roller 10 to the calculated position. If necessary, the operator can carry out a further safety check with a feeler gauge before introducing the adhesive into the coating device.

If the operator detects a deviation from the nominal value, he/she can act on a manual control of the adjustment devices.

The present invention, as described and illustrated, is subject to numerous modifications and variations all comprised within the scope of the inventive concept; furthermore, all the details can be replaced by other technically equivalent elements.

Claims

1. A coating device (1), for coating a moving film with a layer of adhesive, comprising: at least one first metering roller (10), the angular position of which is preferably fixed during operation; and at least one second metering roller (11), facing the first metering roller (10) and which can rotate in contact with an adhesive; wherein the surface of the first metering roller (10) is spaced from the surface of the second metering roller (11) by a gap such that, following the rotation of said second metering roller (11), a portion of the surface thereof is coated with a uniform layer of adhesive, wherein the first metering roller (10) and the second metering roller (11) are arranged with the respective axes parallel and are supported at their ends by respective shoulders (70) of the coating device, said first metering roller (10) being mounted on said shoulders (70) via sliding means (30) adapted to allow the movement thereof in a direction orthogonal to its axis, wherein the coating device (1) further comprises heating means to heat the surface of the first metering roller (10) and second metering roller (11), wherein the coating device (1) further comprises measuring means for measuring a temperature parameter of the surface of the first metering roller (10) and second metering roller (11), wherein the coating device (1) further comprises an adjustment device (20) that controls the movement of the first metering roller (10), with respect to the second metering roller (11), to vary the width of the gap and, therefore, the thickness of the adhesive layer transferred to the surface of the second metering roller (11), said adjustment device (20) cooperating with the above-mentioned sliding means (30), comprising at least motor means (21), wherein the coating device (1) further comprises measuring means (28) adapted to detect at least one parameter relative to the position of said first metering roller (10) with respect to the shoulders (70), wherein said adjustment device (20) is controlled by a control unit, which is configured to control the motor means (21) of the adjustment device (20) according to the temperature parameter of the first metering roller (10), the second metering roller (11) or both, and at least one position parameter of the first metering roller (10).

2. The coating device (1) according to claim 1, wherein the control unit comprises a memory unit in which a dataset is stored for adjusting and controlling the adjustment device (20), said dataset comprising values of the temperature parameter of the metering rollers (10, 11) measured by the respective measuring means, where each temperature parameter value is associated with a corresponding position parameter value measured by the respective measuring means (28).

3. The coating device (1) according to claim 1 or 2, wherein the adjustment device (20) for adjusting the gap comprises a motor (21), a mechanism with recirculating- ball screw (25) and a drive with belt (23) and pulleys, with a drive pulley (22) and a driven pulley (24), wherein an outlet shaft of the motor (21) is connected to the drive pulley (22) and a shaft (26) of the mechanism with recirculating-ball screw (25) is connected to the driven pulley (24) and wherein the ball nut (27) of the mechanism with recirculating-ball screw (25) is rigidly connected to the sliding means (30) of the first metering roller (10).

4. The coating device (1) according to any one of the preceding claims, wherein said measuring means for measuring the position parameter of the first metering roller (10) comprise a linear measurement sensor (28), said sensor comprising two mutually sliding parts (28a, 28b), cooperating respectively with the shoulders (70) and with the sliding means (30) of the first metering roller (10).

5. The coating device (1) according to any one of the preceding claims, wherein said heating means comprise a source of a heated fluid which is made to circulate inside passages obtained in the metering rollers (10, 11), each metering roller comprising a fluid inlet and a fluid outlet, arranged at one or both ends of the roller, and wherein the measurement means for measuring the temperature parameter comprise a pair of temperature probes positioned at the inlet and outlet of the heated fluid of each metering roller (10, 11).

6. The coating device (1) according to the preceding claim, wherein the control unit is configured to calculate when the operating temperature of the metering rollers (10, 11) is stabilized, before controlling the adjustment device (20).

7. The coating device (1) according to claim 2, wherein the first metering roller (10) is mounted rotatable around its axis in the sliding means (30), to be rotated during washing or maintenance operations, said first metering roller (10) being connected to a motor (40) associated with an encoder (41) adapted to detect a datum relative to the angular position of said first metering roller (10), and wherein in the memory unit of the control unit several datasets are stored comprising temperature parameter values of the metering rollers (10, 11) associated with corresponding position parameter values of the first metering roller (10), where each dataset refers to an angular work position of the first metering roller (10) measured by said encoder (41).

8. The coating device (1) according to any one of the preceding claims, comprising a further optical sensor adapted to continuously measure the quantity of adhesive coated on the film, said optical sensor being connected to the control unit, and wherein said control unit is configured to receive the value relative to the quantity of adhesive coated on the film and, according to it, control in feedback one or more parameters of the coating device (1) to correct any deviations of the value detected with respect to a predefined nominal value.

9. The coating device (1) according to the preceding claim, further comprising a conveyor roller (13), which rotates in contact with the second metering roller (11), and a coating roller (14) which rotates in contact with the conveyor roller (13) and with a face of a layer of film, wherein the control unit is configured to vary the rotation speed of the conveyor roller (13) or of the coating roller (14) to vary the quantity of adhesive deposited on said coating roller (14) and, therefore, on the film.

10. The coating device (1) according to claim 8, wherein said optical sensor is configured to detect the quantity of adhesive in several points in a transverse direction of the film, and wherein, if said sensor detects a non-uniform quantity of adhesive in the above- mentioned transverse direction of the film, the control unit is configured to control operation of the motor means (21) of the adjustment device (20) to vary the angle between the axes of the first metering roller (10) and second metering roller (11), in order to obtain the coating of a uniform layer throughout the width of the film.

11. An apparatus for the production of a flexible multilayer film comprising at least a coating device (1) according to any one of the preceding claims.