GB1577450A - Coating machine and a method of coating employing such a machine - Google Patents

Description

(54) A COATING MACHINE, AND A METHOD OF COATING EMPLOYING SUCH A MACHINE (71) We, MECALIX ENDUCTION, a French Body Corporate, of 175 Boulevard Stalingrad, 94400 VITRY/SUR/SEINE FRANCE, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement The invention relates to a coating machine intended to coat a carrier with a coating material, the carrier being in the form of strips of sheets which may be wound on reels and may be fed out continuously. It is also rates to a method of coating which employs such a machine and to the carrier so obtained.

One of the main applications of the invention relates to the covering of strips, that is to say the operation which consists in coating the surface of a strip with as regular as possible layer of a substance which is preferably used hot. Once applied, this layer forms a deposit which may serve various purposes. It may provide a particular surface appearance or give qualities of imperviousness or heat-sealability for example. The carrier so obtained is intended either to be used as it is, or to be applied and laminated to another strip of the same kind as the carrier or of a different kind.

Another application of the application relates to a technique of impregnating paper or cardboard which is intended to be corrugated and which is used in the manufacture of corrugated cardboard, which is covered on either side by a flat section termed the covering. For the assembly to have good mechanical strength and especially resistance to moisture it is necessary inter alia for the corrugations to be reinforced, which is achieved by applying to them coating materials such as mixtures of resin-doped or polymer-doped waxes and parafins for example. This technique is one which is difficult to put into practice. The methods used hitherto restrict the speed of operation of conventional coating installations and in addition give rise to bonding problems between the corrugated section and the coverings. It is in fact difficult on the one hand to meter the quantity of wax and, in view of the difficulty of making an adhesive adhere to the wax, it is necessary on the other hand to resort to costly expedients to enable effective bonds to be made.

The technique of coating and laminating is used in many industries. Unfortunately it is difficult to perform and often proves expensive. For example, in installations of a known kind, the strips to be treated, or carriers to be coated, after picking up the coating material, pass between two rollers whose preset spacing determines the final thickness of the layer applied to the surface of the carrier. In the case of a substance which melts under heat, the rollers have to operate at a relatively high temperature which may be in the region of 200"C.

In coating of this kind, a number of problems are encountered: - the large temperature gradients upset the precise mechanical settings, for example the gauging of a layer between two rollers who spacing has been set beforehand.

- the viscosity of the material, which may be as much as 50,000 to 150,000 centipoises, has a number of effects on the coating. On the one hand, the material tends to adhere in a thick layer to any moving part and if a small thickness is set this leads to local pressures which become higher the greater the viscosity. On the other hand, if air bubbles enter into the material at any stage along its path they are then impossible to remove because of the high viscosity of the material. Air bubble inclusions result in imperfections in the coated layer. Finally the standards of adhesion between the material of the film and the standard of the coating depend on the graduation of the temperatures of the carrier, the material, and the various mechanical components of the coating machine.

The invention has as an object substantially to reduce or overcome these drawbacks and relates to the coating of films, paper, plastics materials and fabrics with products which melt at a high temperature, for example in the range 80 to 2000C, and which are of high viscosity.

Accordingly, the invention provides a coating machine intended to coat a carrier with a coating material by means of a coating roll part of which dips into a bath of the coating material and which, when set in rotation, picks up a certain amount of this material a system for guiding the carrier which is capable of holding it in local contact with the coating roll, thus causing the material picked up by the roll to be transferred to the carrier; and a system for driving the carrier to be coated, said machine further comprising a trough containing the said bath, whose shape ensures that the coating material contained in the trough flows substantially without turbulence, a metering means which adjusts to a given thickness the pick-up by the coating roll of the coating material to be applied, a smoothing means which ensures both that the layer of coating material transferred to the carrier is properly smoothed and that its final thickness is accurately adjusted, and a system for driving the coating roll which is independent of the system for driving the carrier.

In accordance with a feature of the invention the deposit of coating material, instead of being uniformly applied from the beginning, is initially in the form of coated areas forming patches substantially regularly distributed over the surface of the carrier which are separated from one another by uncoated areas. The existence of these areas free of coating material facilitates the bonding operations, since at these points the adhesives adhere to the carrier normally. It is only during the final drying treatment that as well as the residual moisture evaporating, the patches spread and diffuse. The impregnation into the finished product is therefore uniform and takes the form of a uniformly distributed layer of material.

The invention will be better understood from the following explanation given by way of example and with reference to the accompanying drawings, in which: Figure 1 is a schematic view of one embodiment of a coating machine according to the invention, Figure 2 is a schematic view of one of the essential components of the machine shown in Figure 1, Figure 3 shows the flows of the coating material in the feed compartment, and Figure 4 is a schematic view of a modified embodiment of coating machine according to the invention.

In all the figures, the same items bear the same reference numerals.

Figure 1 is a schematic view of one embodiment of a coating machine according to the invention. It includes a number of components which are arranged so as to co-operate in depositing a virtually uniform layer of consistent thickness of a coating material onto the surface of a strip to be treated or a carrier to be coated and to do so under hot or cold conditions.

The machine consists chiefly of: - a trough 1 having a plurality of compartments of which a compartment 2 termed the feed compartment contains the coating material.

- bath stabilising system 3 which ensures uniformity of temperature and causes the coating material contained in the feed compartment 2 to flow substantially without turbulence, - a coating roll 4, part of which dips into the bath and which, when set in rotation, picks up a certain amount of the material, - a means 5 of metering the thickness of the layer of material picked up, - a system 6 for guiding the strip of substance to be coated, which system is capable either of holding this strip in contact locally with the coating roll 4 when the system is in what is termed the working position, which it is for the period during which the coating takes place, or of holding it away from the roll (this position is shown in broken lines in Figure 1) when the carrier is not to be coated, i.e. when the guiding system is in what is termed the rest position, - a so-called applicator system 8 intended to apply pressure to the strip 7, - a smoothing means formed by a smoothing roll 9 which is responsible both for smoothing the layer deposited on the carrier and for adjusting its thickness accurately, - a means 17 for removing excess material at the point where the said smoothing roll is situated.

Such a combination of means, when arranged in accordance with the invention, allows the principal parameters on which the standard of the finished product depends to be adjusted independently of one another. The parameters involved are essentially: - in the case of the coating roll - its temperature tc, its speed of rotation VC and the arc (ab) over which the guiding means 6 produce contact between the strip 7 and the coating roll 4; - in the case of the smoothing roll 9 - its temperature td, its speed of rotation Vd and the arc (cd) which defines the area of contact between the strip 7 and the sand, smoothing roll 9 - in the caste of the coating material which may be a heat-meltable material - its temperature tp and the thickness (e) of material picked up by the coating roll 4 after the metering means .5 has performed its function.

The design of the installation upstream and downstream of the machine according to the invention likewise allows the temperature tb of the strip 7, its speed of movement Vb, and the tension Tb exerted on it to be adjusted.

In such a machine all these parameters may, in practice, be adjusted independently of one another. It is for example, possible to have the temperatures tb, tc, td and tp graduated and adjustable as desired which results in good adhesion of the coating material to the strip or coating carrier, good carry-over of the material from the coating roll to the carrier, and good metering and smoothing of the coated layer.

To enable the temperatures to be accurately controlled, it is useful to employ separate systems which heat by means of a heat-conveying fluid. Thus, the weight of the coating. that is to say the amount of material deposited on the carrier per unit area depends mainly on the accurate setting of the first metering means 5 dative to the coating roll. In fact, this means acts merely as a preliminary metering device, and the thickness is regulated chiefly by the com- bined effect of the temperatures selected and the speed Vd of the smoothing roll 9.

This speed can be adjusted independently from that of the coating roll for example as will be explained below. Furthermore the stabilising system 3 co-operates with the temperature regulating and thickness adjusting means to ensure that the coating roll is even more effectively wctted. It also helps the material to flow in the trough without turbulence and to keep its temperature uniform, whilst enabling the volume of the material which the trough needs to contain to be reduced to a very high degree.

This is a highly advantageous result since it leads to savings and reduces the dangers ot degradation such as by oxiclaiion, for exam- ple. Embodiments of each of the principal components of the machine according to the invention will now be described.

The trough 1 is fabricated from sheet steel, for example. with single or double walls and is heat insulated if the coating material used is of the kind which me under heat. It is heated hv a flow of a heat-conveying fluid which may h. hot water or a suitable heating fluid. The trough 1 is divided into a number of compartments; a first, so-called "fccd compartment' 2 is intended to contain the coating matcrial. It may be cii sr-ai vohT,1le, as explained above anet a preferably in the shape of part of a cylinder which flares on the side oppe. fiom from thi infeed. The infeed is provided hy a pump which is not shown in the fi,, ud s and this pump takes the material from a prcpat-ir.g vat and injects it into a feed duct -. c. of whose inlets is referenced 11. The level in this compartment is held constant by means of a set of adjustable partitions 12 whose height can be adjusted.

The feed compartment contains a bath stabiliser 3 whose form and function will be described in more detail below.

The trough 1 also includes a so-called "recovery" compartment 13 which is connected by a diet 14 to the vat for preparing the material (not shown in Figure 1). This recovery compartment is intended to receive the excess material which results from ovcrflow from the feed compartment 2 and also the excess material picked up by the coating roll. which is scraped off by the metering means 5. It also collects the material which is removed at the smoothing roll 9.

The coating roll 4 is of relatively large diameter and is made of hard chrome steel for example. It is driven, non-kinematically, generally in the direction of movement of the carrier 7, as shown by arrow 10, by a first. independent variable-speed motor assembly (not shown in the figure). The roll could, if required, be driven in the opposite direction from the direction in which the carrier moves. In this case the metering means 5, instead of being situated on the left of the figure would be on the right. If the coating material is heat-meltable, the roll is heated by a flow of a heat-conveying fluid.

The depth to which it dips into the bath, which is regulated by the level of the bath itsclf, is determined by the height of the adjustable partitions 12. The area of contact between the carrier 7 to be coated and the roll is defined by an arc (ab) whose length can be adjusted and is a parameter which plays an important part in the standard of coating. In cases where the material is heat-meltable the thickness may also be usted by varying the temperature of the .'r'aothing roll, the thickness of this layer being preliminarily adjusted by means of a first metering means 5 situated at the outlet of the bath which shaves the layer of material picked up by the coating roll before the carrier to be coated comes into contact with it. This first metering means is formed by a blade positioned at a distance (e) from the coating roll upstream of the area of contact between the carrier to be coated and the roll. Thi, sal.le (e) corresponds to the thickness of the layer of material actually carried round by the coating roll, the excess spilling back into the recovery compartment of the trough to be lead-off to the preparing vat as already explained above. An arrangement 20 formed by lateral flaps, which are generally made of plastics material or some other heat-resistant material, performs a cleaning function by wiping the edges of the coating roll. It thus creates uncoated zones at the margins of the strips or carriers 7.

Further to improve the standard of coating, there is provided a bath stabilising system 3 formed by set of fixed vanes mounted parallel to the axis of the coating roll which are installed in the trough under the coating roll. The position of the stabilising system can be adjusted relative to the coating roll by means of screws for example, the spacing to the ends of the vanes being determined as a function of the thickness of layer to be obtained. The purpose of the system is to prevent the coating material from being carried along and setting up a circulation within the trough. It ensures that the coating roll is effectively wetted by virtue of the increases in pressure caused against the vanes parallel to the axis of the coating roll. The path followed by the coating material is shown by the arrows 30 in Figure 2 and more particularly in the frontal view in Figure 3, in which figures the same items bear the same references as in Figure 1.

When the carrier to be coated has passed across the surface of the coating roll and picked up the coating material carried by the said roll, it becomes subject to the action of an applicator system which is mounted on two pivoted arms and which rotates about the axis of the smoothing roll 9. In what is termed the "working" position, corresponding to the coating phase, the applicator cylinder 8 brings the coated carrier and the smoothing roll 9 into contact over an area defined by an arc (cd) of predetermined length so that the smoothing system may perform its dual function : firstly to smooth the material on its carrier and secondly to adjust the thickness of the deposited layer.

The smoothing roll 9 is located after the coating roll and before the system for driving the carrier, which is merely represented by an arrow 15 in Figure 1, or before the laminating press in cases where two strips are to be laminated to one another.

The smoothing roll is one whose diameter is smaller than that of the coating roll and it is made of hard chrome steel dressed true. It is driven non-kinematically in the opposite direction from that in which the carrier to be coated moves, as indicated by arrow 16, by an independent variable-speed motor assembly, thus allowing an equally independent adjustment of its speed Vd. If the coating material employed is one which melts under heat, the smoothing roll 9 is also heated by a flow of heat-conveying fluid. The surface of the roll must be absolutely clean where it makes contact with the coated carrier so as not to mark the coating layer. This is achieved by using an oscillating blade 17 which removes the excess material applied by the coating roll.

The material so removed spills back into the trough 1 to be lead-off to the vat for preparing the material, as described above.

The adjustment of the thickness of the coated layer and its smoothing are performed by altering the speed of rotation of the smoothing roll and possibly its temperature. The more its speed is increased, the more the thickness of the coated layer is reduced.

The various means which have just been described, and the manner in which they are combined, make it possible to achieve particularly useful results, the chief of which are listed below a) the bath stabiliser compels the flows in the trough to take place substantially without turbulence or mixing. Its purpose is also to pre-size the layer which arnves under the blade. Because of this, there are no air-bubble inclusions in the material and the effects of pressure on the blade are reduced.

b) the various parts of the coating machine are suited to a regulation and adjustable graduation of the temperature. It is possible to adjust the temperature of the carrier for the material, and also that of the mechanical components such as the trough, the coating roll and the smoothing roll.

c) the thickness of the coated layer is adjusted, on the basis of the excess of deposited material after adjustment to the thickness (e) by the blade 5, by adjusting the speed of the coating roll relative to that of the carrier and also by adjusting the speed of the smoothing roll. Other parameters, although less important, may nevertheless play a part. Such parameters are for example the angle of incidence of the carrier, the tension on the carrier, and the temperature of the smoothing roll 9.

A method of coating according to the invention, such for example as may be implemented by means of a machine as described above, comprises the following principal steps - a coating roll 4 passes across coating material which is contained in a compartment and which is subject to the action of a bath stabilising system 3, - the coating material picked up by the coating roll is metered for a first time to a predetermined thickness (e), - a guiding system which applies the carrier to be coated to the coating roll is brought into position, - the coating material carried by the roll is transferred to the surface of the carrier, which is brought into contact with the said roll, and the thickness of the material is preadjusted, - pressure is applied to the carrier, and the layer of coating material carried by the carrier is smoothed by means of a smoothing roll, - excess material is removed at the smoothing roll, - the coating material removed at the point where the first metering of the thickness of the coating material takes place and at the smoothing roll is recovered, - the temperatures of the trough, the coating roll and the smoothing roll are set, - the speed Ve of the coating roll and the speed Vd of the smoothing roll are set.

A coating machine according to the invention, and the method in which such a machine is employed, make it possible to obtain coatings of material of the optimum weight. This weight, i.e. the amount of material deposited per unit area, is a function of the speeds Vc and Vd and of the thickness (e) of the layer pre-metered by the first metering means. For example, an original weight of 150 grammes per square metre may be adjusted, as a function of the speed Vd of the smoothing roll, to between 10 and 80 grammes per square metrc. The layer of heat-meltable coating material may be adjusted from a control panel which enables the various parameters listed above, namely speed, temperature, and the tension of the carrier to be coated, to be adjusted without having to alter the mechanical settings in the course of the coating operation itself.

Ancillary apparatus may easily be adapted to the coating machine according to the invention. This could be the case with a laminating press for example, which could be placed very close to the coating assembly.

The size of the assembly varies according to the application. As an example its minimum width may be 400 millimeters nd its maximum width may exceed 3000 millimeters. The rates of production are capable of wide variation, the most usual being in the region of 50 to 300 metres per minute.

Another application of the present apparatus relates to a technique of impregnation of paper or cardboard which is intended to be corrugated and which is uscd in the manufacture of corrugated cardboard.

For this purpose additional means are provided for cooling the carrier, which co-operate with the remainder of the machine to cool the carrier when it has just been coated and before it is transferred to a conventional installation where the cormga- tion are then formed and the operations of bonding the coverings and drying the finished product take placc.

The method of coating which employs such a r.sac"ne according to the present invention which, because of the many ad justments possible in it, enables - the degree of impregnation to be accurately adjusted whatever the speed of the machine, for example from 5 to 40% of the weight of the corrugated section, - the distribution of the penetration of the wax into the corrugated section to be controlled, - bonds to be made to the corrugations before the wax is uniformly distributed over them, the distribution and penetration of the wax only taking place at the time of travel over drying tables, - the corrugated-cardboard manufacturing machines to be used at their maximum speed of operation.

As Figure 4 shows, the machine consists in essence of: - a trough 1 having a plurality of compartment of which a compartment 2 termed the feed compartment contains the coating material, such as doped wax for example, - possibly, a bath stabilising system 3 which ensures uniformity of temperature in the coating material contained in the feed compartment 2, and which causes it to flow substantially without turbulence, - a coating roll 4, part of which dips into the bath and which, when set in rotation, picks up a certain amount of material, - a means 5 of metering the thickness of the layer of material picked up, - a system 6 for guiding the strip of substance to be coated, which system is capable either of holding this strip in contact locally with the coating roll 4 when the system is in what is termed a working position, which it is during the period when the coating takes place, or of holding it away from the roll (this position is shown in broken lines in the figure) when the carrier is not to be coated, i.e. when the guiding system is in the so-called rest position, - a so-called applicator system 8 in- tended to apply pressure to the strip 7, - a means of smoothing formed by a smoothing roll 9 which is responsible both for smoothing the layer deposited on the carrier properly and for accurately adjusting its thickness, - a means 17 of removing the excess material at the said smoothing roll (the means of recovering this excess material are identical to those earlier described), - a cooling system 50 which is in the form of a cooling roll around part of which is looped the strip 7 being treated, before being transferred to the corrugating line which is not shown in the Figure 4 (the transfcr is represented by an arrow 51).

Such a combination of means enables the main parameters, on which the structure of the deposit of coating material depends, to be adjusted independeoty of one another.

The parameters i questions are chiefly the following - in the case of the coating roll - its temperature, its speed of rotation and the are over which the guiding means ensure contact between the carrier to be coated and the coating roll; - in the case of the smoothing roll; - its temperature, its speed of rotation and the arc which defines the area of contact between the carrier to be coated and the smoothing roll.

As has already been stated above the coating obtained with such a machine when specially adjusted for the application in question takes the form of a sort of mosaic made up of patches adjoining uncoated areas. These patches are fixed momentarily in a certain outline shape by the effect of the cooling roll 50 and it is only at a later stage when the various bonding operations have taken place. that the patches diffuse during the drying operations to fill practically the whole of the corrugations, thus endowing them with exceptional mechanical qualities.

Such a method of coating consists of the following main steps a) a coating roll 4 passes across the coating material which, in the case of strips of paper or cardboard intended for the p?o(iiction of corrugated cardboard, is preferably doped wax contained in compartment 2 of the trough 1. If this compartment is fitted with the stabilizing system 3, the bath is subject to its effect, but in the case of wax this effect is not essential since the wax is liquid and is not sufficiently viscous to create homogeneity problems at this point.

The stabilising system is thus optional in this case. On the other hand, it may be of importance if there is any considerable addition of resins and polymers.

b) the coating material picked up by the coating roll is metered for a first time to a predetermined thickness (e), c) the guiding system 6 is brought into position to apply the carrier to be coated to the coating roll. and the arc (ab) is accurately set, d) the coating material carried by the roll is transferred to the surface of the carrier 7 which has been brought into contact with the said roll, this transfer resulting in the formation of thick patches whose shape and thickness are determined by the joint effect of the following, para- meters - the spacing e of the blade 5.

- the speed of thc coating roll N - the temperaturc of this roll, - the size of the arc (ab) over which there is contact between the carrier and the coating roll.

e) pressure is applied to the carrier and the patche. of wax carried by the corner are smoothed by me ins of the smoothing roll 9 whose speed Vl and temperature determine the final thickness of the patches, f) the carrier passes over a cooling roller 50 whose function is to fix the patches of wax on the surface of the carrier, g) the carrier bearing its fixed patches of wax is transferred to a corrugating line.

Entirely by way of non-limiting example the best economic advantage by selecting the most favourable relationship between the improvement in mechanical qualities and the moisture resistance. There are in fact two factors which can be altered: - the level of impregnation (5 to 40% as stated above) - the percentage of resin in the doped wax. The more resin there is, the greater the improvement in the mechanical characteristics under dry conditions. The more wax there is, the greater the improvement in strength in moist atmospheres. The compression strength under dry conditions may for example be increased by 50% and strength in moist atmospheres by 70%. With no reduction in speed, it enables a product of higher performance to be manufactured, or a product of the same quality to be obtained using constituents of lower cost.

WHAT WE CLAIM IS: 1. A coating machine intended to coat a carrier with a coating material by means of a coating roll part of which dips into a bath of the coating material and which, when set in rotation, picks up a certain amount of this material a system for guiding the carrier which is capable of holding it in local contact with the coating roll, thus causing the material picked up by the roll to be transferred to the carrier; and a system for driving the carrier to be coated, said machine further comprising a trough containing the said bath, whose shape ensures that the coating material contained in the trough flows substantially without turbulence, a metering means which adjusts to a given thickness the pick-up by the coating roll of the coating material to be applied, a smoothing means which ensures both that the layer of coating material transferred to the carrier is properly smoothed and that its final thickness is accurately adjusted, and a system for driving the coating roll which is independent of the system for driving the carrier.

2. A coating machine according to claim 1, wherein said trough has at least one feed compartment which receives the material to be applied from a preparation station and into which the coating roll dips, and at least one recovery compartment which is intended to collect the excess material removed at the metering means and at the smoothing means and to lead it back to the said preparation station.

3. A coating machine according to claim 2, wherein the level of the material contained in the feed compartment is determined by a set of adjustable partitions whose height can be adjusted.

4. A coating machine according to claim 1, 2, or 3, wherein said trough is heat insulated and incorporates means of heating the bath contained in the said trough to temperatures which can be varied.

5. A coating machine according to claim 2 or 3, including a bath stabilising system formed by a set of vanes mounted in the feed compartment under the coating roll parallel to the axis of the coating roll, the position of said vanes being adjustable relative to this roll thus assisting in adjusting the thickness of the layer deposited on the coating roll.

6. A coating machine according to any preceding claim, wherein said metering means is formed by a blade positioned at a distance from the coating roll upstream of the area of contact between the carrier to be coated and the coating roll.

7. A coating machine according to claim 6, wherein said metering means also include a set of lateral flaps intended to clean the edges of the coating roll by wiping.

8. A coating machine according to any preceding claim, wherein said smoothing means is formed by a smoothing roll which is driven in rotation and to which the carrier bearing the layer of material transferred from the coating roll is applied locally by means of an applicator member.

9. A coating machine according to claim 8, wherein the drive to the smoothing roll is independent of the drive to the coating roll and of the drive to the said carrier.

10. A coating machine according to claim 8, wherein said smoothing roll is provided with an oscillating blade intended to remove excess material.

11. A coating machine according to claim 8, wherein said smoothing roll includes means for heating to variable temperatures.

12. A coating machine according to claim 1, wherein said coating roll includes means for heating to variable temperatures.

13. A coating machine according to claims 4, 11 and 12, wherein the temperatures reached by means of the said heating means are adjustable independently of one another.

14. A coating machine according to any preceding claim, further comprising a cooling member which receives the coated carrier as it leaves the smoothing means and which is capable, by cooling the coating material deposited on the surface of the carrier, of fixing it to the outline shape and thickness which it has when it leaves said smoothing means.

15. A method of coating employing a coating machine according to claim 14, wherein the coating material is deposited on the surface of the carrier in the form of coated areas forming substantially uniformly distributed patches which are separated from one another by uncoated areas.

16. A method of coating according to claim 15 comprising the following main

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

**WARNING** start of CLMS field may overlap end of DESC **. the best economic advantage by selecting the most favourable relationship between the improvement in mechanical qualities and the moisture resistance. There are in fact two factors which can be altered: - the level of impregnation (5 to 40% as stated above) - the percentage of resin in the doped wax. The more resin there is, the greater the improvement in the mechanical characteristics under dry conditions. The more wax there is, the greater the improvement in strength in moist atmospheres. The compression strength under dry conditions may for example be increased by 50% and strength in moist atmospheres by 70%. With no reduction in speed, it enables a product of higher performance to be manufactured, or a product of the same quality to be obtained using constituents of lower cost. WHAT WE CLAIM IS:

1. A coating machine intended to coat a carrier with a coating material by means of a coating roll part of which dips into a bath of the coating material and which, when set in rotation, picks up a certain amount of this material a system for guiding the carrier which is capable of holding it in local contact with the coating roll, thus causing the material picked up by the roll to be transferred to the carrier; and a system for driving the carrier to be coated, said machine further comprising a trough containing the said bath, whose shape ensures that the coating material contained in the trough flows substantially without turbulence, a metering means which adjusts to a given thickness the pick-up by the coating roll of the coating material to be applied, a smoothing means which ensures both that the layer of coating material transferred to the carrier is properly smoothed and that its final thickness is accurately adjusted, and a system for driving the coating roll which is independent of the system for driving the carrier.

2. A coating machine according to claim 1, wherein said trough has at least one feed compartment which receives the material to be applied from a preparation station and into which the coating roll dips, and at least one recovery compartment which is intended to collect the excess material removed at the metering means and at the smoothing means and to lead it back to the said preparation station.

3. A coating machine according to claim 2, wherein the level of the material contained in the feed compartment is determined by a set of adjustable partitions whose height can be adjusted.

4. A coating machine according to claim 1, 2, or 3, wherein said trough is heat insulated and incorporates means of heating the bath contained in the said trough to temperatures which can be varied.

5. A coating machine according to claim 2 or 3, including a bath stabilising system formed by a set of vanes mounted in the feed compartment under the coating roll parallel to the axis of the coating roll, the position of said vanes being adjustable relative to this roll thus assisting in adjusting the thickness of the layer deposited on the coating roll.

6. A coating machine according to any preceding claim, wherein said metering means is formed by a blade positioned at a distance from the coating roll upstream of the area of contact between the carrier to be coated and the coating roll.

7. A coating machine according to claim 6, wherein said metering means also include a set of lateral flaps intended to clean the edges of the coating roll by wiping.

8. A coating machine according to any preceding claim, wherein said smoothing means is formed by a smoothing roll which is driven in rotation and to which the carrier bearing the layer of material transferred from the coating roll is applied locally by means of an applicator member.

9. A coating machine according to claim 8, wherein the drive to the smoothing roll is independent of the drive to the coating roll and of the drive to the said carrier.

10. A coating machine according to claim 8, wherein said smoothing roll is provided with an oscillating blade intended to remove excess material.

11. A coating machine according to claim 8, wherein said smoothing roll includes means for heating to variable temperatures.

12. A coating machine according to claim 1, wherein said coating roll includes means for heating to variable temperatures.

13. A coating machine according to claims 4, 11 and 12, wherein the temperatures reached by means of the said heating means are adjustable independently of one another.

14. A coating machine according to any preceding claim, further comprising a cooling member which receives the coated carrier as it leaves the smoothing means and which is capable, by cooling the coating material deposited on the surface of the carrier, of fixing it to the outline shape and thickness which it has when it leaves said smoothing means.

15. A method of coating employing a coating machine according to claim 14, wherein the coating material is deposited on the surface of the carrier in the form of coated areas forming substantially uniformly distributed patches which are separated from one another by uncoated areas.

16. A method of coating according to claim 15 comprising the following main

steps: a) the coating rol passes across the coating material n the bath, b) the coating material picked up by the coating roll is metered for a first time to a predetermined thickness, c) the guiding system is brought into position to apply the carrier to be coated to the coating roll, and the arc over which said carrier contacts the surface of the coating roll is accurately set, d) the coating material carried by the roll is transferred to the surface of the carrier, which has been brought into contact with the said roll, the said transfer resulting in the formation of thick patches whose outline shape and thickness are determined by the combined effect of the following parameters: - the speed of the coating roll, - the temperature of this roll, - the size of the arc of contact between the carrier and the coating roll, e) pressure is applied to the carrier and the patches are smoothed by means of the smoothing roll whose speed determines the final thickness of the patches, f) the carrier passes over a cooling roller whose purpose is to fix the patches on the surface of the carrier.

17. A method of coating according to claim 16. whe:-in said carrier bearing the fixed patches is transferred to a corrugating line, to be corrugated and then to undergo operations of bonding and finally drying.

this latter operation, as well as causing the traces of residual moisture to evaporate, also causing the patches to diffuse and thus bringing about a uniform impregnation of the corrugated section.

18. A coating machine substantially as hereinbefore described with reference to the accompanying drawings.

19. A method of operating a coating machine substantially as hereinbefore described with reference to the accompanying drawings.

20. Coated products produced by the method of any of claims 15, 16, 17 or 19.