WO2011067664A2

WO2011067664A2 - Process for coating an article

Info

Publication number: WO2011067664A2
Application number: PCT/IB2010/003112
Authority: WO
Inventors: Max Canti
Original assignee: Biesse S.P.A.
Priority date: 2009-12-04
Filing date: 2010-12-06
Publication date: 2011-06-09
Also published as: ITPS20090023A1; WO2011067664A3; IT1397259B1; EP2506986A2

Abstract

A process for coating a surface (6) of an article (2); the process provides spreading on the surface (6) particles (5) having a size from 20 μm to 11 μm, providing heat up to at least 100°C and then compressing and, simultaneously, cooling below 50°C; a resistant layer (L) bound very strongly to the article is obtained in a simple and cost-effective manner.

Description

PROCESS FOR COATING AN ARTICLE

TECHNICAL FIELD

The present invention relates to a process and to a machine for coating an article and to an at least partially coated article. The present invention also relates to a method and to a device for producing particles .

BACKGROUND OF THE INVENTION

In the known art, the decoration of a ceramic biscuit takes place by the deposition of colouring oxides and of a layer of protection glaze after having cooled the ceramic biscuit coming out from the firing oven at temperatures below 100°C. Subsequently, the biscuit with the oxides and the glaze is fired again (usually at a temperature between 1200 °C and 1300°C) in an operation designated "third firing" .

This involves a considerable waste of energy as well as implying a reduced possibility of decoration due to the limited use of the colouring oxides (the latter cannot be organic pigments which would decompose) .

In the ennoblement of wooden conglomerates, it is known to press treat surfaces with decorative papers impregnated with melamine at temperatures of about 200°C with the simultaneous application of a pressure of at least 25 Kg/cm². This method requires the availability of a production chain (present only in some industrialised countries) that comprises specialised companies capable of producing enormous amounts of background printing of coloured paper, of gravure printing great amounts of paper with a single picture, of impregnating in a water suspension bath of modified melamine, of straining and drying in hot air at a temperature of 110-130°C with a subsequent energy waste. It is clear that this kind of methodology is complex, expensive and also requires a high energy consumption. In this connection, it should be noted that small production batches are currently extremely expensive (for this reason great amounts must be produced) .

Another drawback is the fact that this ennoblement cannot be performed on conglomerates having low density because under the required pressure, these would collapse. Accordingly, the conglomerate wood industry is often forced to use toxic recycled wood due to lack of raw material . The toxicity increases with each recycling .

Furthermore, surfaces other than wooden conglomerates, such as sheets of plastic composite materials, alveolar panels, asbestos cement, plasterboard etc., cannot be ennobled by this technique.

It has also been suggested to use powder coatings to cover wooden panels. Coating powders for wood are not applied by gravity but instead by electrostatic effect such as for metal with the difference that wood must first be made conductive by spraying a solution of conductive salts which must then be dried. This causes, due to the water in the solution, a swelling of the wooden fibres that deforms the surface of the panel. Furthermore, the employed salt, which is hygroscopic, retains the water that evaporates during a subsequent step of firing of the coating in a hot environment at 130-180°C causing the formation of vesicles on the surface. Therefore, the resulting finishing is an aesthetically unpleasant finishing which is generally poorly appreciated (for example in the industry of furniture) .

Conductive graphitized coatings have also been used on the raw panel to overcome the drawback of hygroscopic salt, but after some time (about one year) partial detachment of the paint occurred.

It is an object of the present invention to provide a process and a machine to coat at least one surface of an article, an at least partially coated article, and a method and a device for producing particles, which allow to overcome, at least partially, the drawbacks of the state of the art and are at the same time easy and cost- effective to implement.

SUMMARY

According to the present invention, there are provided a process and a machine to coat at least one surface of an article, an at least partially coated article, and a method and a device for producing particles according to the following independent claims and, preferably, according to any of the claims directly or indirectly dependent on the independent claims .

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described with reference to the accompanying drawings, which show non- limitative embodiments thereof, in which:

- figure 1 diagrammatically shows a machine, made according to the present invention, for coating an article;

- figure 2 diagrammatically shows a part of the machine of figure 1 which is not shown in the latter figure;

- figure 3 is an alternative embodiment of details of figure 1;

- figure 4 is a drawing on an enlarged scale of details of the machine of figure 1;

- figure 5 is a section of a detail in figures 2 and 3 ;

- figure 6 is a perspective view of an alternative embodiment of details of figure 1;

- figure 7 shows another embodiment of the machine of figure 1; and

figures 8 and 9 are respectively perspective views of an article before and after the deposition of a coating layer.

EMBODIMENTS OF THE INVENTION

In figure 1, numeral 1 indicates as a whole a machine for at least partially coating an article 2 (in particular a panel - see figures 8 and 9) comprising a conveying system 3 to feed article 2 along a determined path P; a deposition device 4 (which is arranged along path P) to spread particles 5 (in particular, having size from 20 μπι to 2 mm) comprising at least one organic binder on a surface 6 (figure 8) of article 2; a heating device 7 (which is arranged along path P, in particular downstream of deposition device 4) to heat particles 5 so as to obtain a layer L, which is at least partially liquid; a surface treatment device 8, which is arranged (along path P) downstream of heating device 7 and comprises a compression assembly 9 having a contact surface 10, which is adapted to come into contact with layer L and exert a pressure on layer L.

Heating device 7 is adapted to heat particles 5 to a temperature above 100°C, in particular so that particles 5 are at least partially bound to one another. Advantageously, device 7 comprises an infrared radiation source (which is arranged above a segment of path P) to emit infrared radiation towards particles 5 deposited on surface 6.

Compression assembly 9 is provided with a membrane 11, which membrane 11 has said contact surface 10. Assembly 9 also comprises a handling system 12 to feed membrane 11 synchronously to article 2 along a segment of path P. More specifically, in use, membrane 11 (more precisely a segment of membrane 11) and article 2 are fed in contact and at the same speed along the mentioned segment. In this case, handling system 12 comprises three pulleys, of which one is typically driven by a motor and the others idle .

Advantageously, membrane 11 is a membrane comprising (in particular made of) a silicon rubber. More specifically the membrane comprises (in particular is made of) the RTV2 16 Shore A silicon rubber. The silicon rubber promotes the detachment from layer L.

Surface treatment device 8 comprises a cooling unit (of the type known per se and not shown) , which has a fluidic circuit, along which a cooling liquid flows. In particular, the fluidic circuit is in contact with membrane 11.

According to alternative embodiments (not shown) , compression assembly 9 comprises a roller, which has said contact surface 10, and a handling system to rotate the roller on article 2 while article 2 is fed along path P at surface treatment device 8. In this case, the cooling circuit is arranged (at least partially) within the roller so as to cool contact surface 10. In particular, the roller has a substantially cylindrical shape (having a uniform circular cross section) . Contact surface 10 is defined by an outer chromium layer (of the chromed roller) having a continuous thickness of at least 1 mm. The chromium plating (i.e. the layer of chromium) aids the detachment of layer L.

According to other embodiments (not shown) , the compression assembly 9 comprises a membrane mould. Membrane moulds are moulds known per se and operate by creating a depression between article 2 to be treated and a membrane (of the mould) , which thereby presses article 2 thus adapting to (and deforming according to) the shape of article 2. Thereby, conveying system 3 feeds article 2 discontinuously (stepwise) so as to allow the membrane mould to close on article 2. The use of membrane moulds is especially useful when surface 6 is not completely flat; in particular, when surface 6 has depressions and/or reliefs (for example, when article 2 is a panel provided with one or more relief or depression decorations) . It should be noted that the membrane mould is also advantageously connected to the cooling unit.

Advantageously, machine 1 comprises a heating device 13, which is arranged upstream of deposition device 4 (along path P) and is adapted to heat article 2.

Heating device 13 is adapted to heat article 2, in particular to a temperature above 100 °C (advantageously above 130 °C, more precisely to 150°C) . According to some embodiments, device 13 comprises an infrared radiation source (which is arranged above a segment of path P) to emit infrared radiations towards particles 5 deposited on surface 6.

Advantageously, device 13 comprises a plate (of the type known per se and not shown) which is heated (for example by a heating element) adapted to come into contact with surface 6. This solution (with respect to infrared irradiation) allows to save energy.

The use of heating device 13 is especially useful when surface 6 is not completely flat; in particular, when surface 6 has depressions and/or reliefs (for example, when article 2 is a panel provided with one or more relief or depression decorations) . In these cases, the heating of article 2 before the deposition of particles 5 allows particles 5 to also remain on portions of surface 6 which are not horizontal.

According to some embodiments, machine 1 comprises device 13 but not device 7. In this case, device 13 also has the same function of device 7. The heat of article 2 is sufficient to obtain layer L as defined above.

According to some embodiments, machine 1 comprises a heating device 14 , which is arranged downstream of surface treatment device 8 (along path P) .

Heating device 14 is adapted to heat article 2 to a temperature above 100°C (in particular above 130°C, more precisely to 150°C) . Advantageously, device 14 comprises an infrared radiation source (which is arranged above a segment of path P) to emit infrared radiation towards layer L deposited on surface 6.

Machine 1 further comprises a cooling device 15, which is arranged downstream of device 8 (and of heating device 14 - along path P) and is adapted to cool the layer deposited on surface 6.

Device 15 comprises a fan to direct the air flow towards article 2. According to some embodiments, device 4 comprises a deposition unit 4' .

Advantageously, device 4 comprises a plurality of deposition units 4' arranged in series along path P. This allows to obtain a better distribution of the particles on surface 6.

Referring in particular to figure 4, deposition unit (or each unit) 4' comprises a perforated element 16, which is arranged above path P and above at least part of which particles 5 are arranged. Element 16 has a plurality of holes having diameter (slightly) larger than the size of particles 5; in particular, the diameter of the holes is larger than the average size of particles 5 and smaller than twice the average size of particles 5.

More precisely, the diameter of the holes is from 60 μπι to 1.1 mm (advantageously from 0.4 to 0.45 mm) . According to some embodiments the diameter of the holes is from 70 μπι to 400 μτη. According to alternative embodiments, the diameter of the holes is from 250 μιη to 1 mm. According to specific embodiments, the holes are distributed so as to be from about 49 to about 144 holes per cm².

Advantageously, element 16 is a belt, in particular made of laminated material (specifically polyethylene terephthalate) . Element 16 has a thickness from 0.25 to 0.5 mm .

Unit 4' also comprises a pulley 17, about which element 16 is partially wound; a handling unit (known per se and not shown) to rotate pulley 17; and at least one transmission member 18, about which element 16 is partially wound and which has at least one opening 19 (facing downwards) . Device 4 also comprises a feeding unit 20 to convey particles 5 between pulley 17 and transmission member 18 (above at least one segment of element 6) .

In use, particles 5 collect above member 18 and pass through opening 19 and the holes of element 16 in virtue of the motion of element 16 (in particular the sliding on member 18) driven by pulley 17. Particles 5 exiting the holes are deposited on surface 6.

It should be noted that the holes on element 16 may be distributed so as to form patterns on surface 6. This is especially promoted where device 4 comprises several deposition units 4' . In these cases, particles of a second type (coming from a second unit 4') are deposited (or deposited in a greater amount) where particles 5 of a first type (coming from a first unit 4') are not deposited (or deposited in a smaller amount) . The particles of the different types have, for example, different colours.

According to a variant (see figure 3), deposition unit (or each deposition unit) 4' comprises a conveyor 21 provided with a conveyor belt 22. As shown in greater detail in figure 5, which shows a section of belt 22, belt 22 has a plurality of cells 23, which are adapted to each house a relative particle 5. Deposition unit 4' also comprises a hopper 24, from which particles 5 are withdrawn. The withdrawal of particles 5 is allowed by the presence of cells 23. In use, withdrawn particles 5 are fed by conveyor 21 until they are dropped on surface 6.

According to another variant (see figure 6) , unit (or each unit) 4' comprises a hollow cylindrical element 25, the outer wall 25' of which is provided with holes and which is arranged above path P. A feeding unit 26 conveys particles 5 within cylinder 25 which by rotating allows particles 5 to pass through the holes of the outer wall 25' and be deposited on surface 6.

According to some embodiments, outer wall 25' is made of silk (a material which is naturally provided with small holes) . Also in this case, patterns may be obtained on surface 6 by distributing the holes in a specific manner. More precisely, when silk is used, part of the surface of the silk is coated (for example with a layer having a predetermined shape of photoresist material) .

Advantageously, conveying system 3 feeds articles 2 continuously along path P (in particular at a substantially constant speed) .

Referring in particular to figure 1, it may be noted that conveying system 3 comprises a plurality of rollers, which are spaced (slightly - i.e. at least so as to prevent articles from falling or make this unlikely), (at least) at deposition device 4. Thereby, particles 5 which should possibly not remain on surface 6 can freely fall and possibly be recovered and recycled. This is especially advantageous when conveying system 3 feeds articles 2 continuously and deposition device 4 is not stopped. Thereby, particles 5 which fall between two subsequent articles 2 may easily be recovered without creating substantial problems in the following processing steps. Particles 5 which are possibly deposited on a conveyor belt could for example bind to the belt in the following processing steps.

Machine 1 shown in figure 1 is especially suitable for coating articles 2 when particles 5 comprising (in particular consisting of) at least one thermosetting pre-polymer are used. In this case a further heating after compression is required to harden layer L deposited on surface 6.

Figure 7 shows a variant of machine 1 which is different from that shown in figure 1, in not having heating devices 13 and 14 and cooling device 15. This kind of machine is especially suitable for coating articles 2 when particles 5 comprising (in particular consisting of) a thermoplastic polymer are used.

According to a second aspect of the present invention there is provided a device 27 for producing combined particles 5 (i.e. made of composite material). Device 27 may be connected to or may be part of machine 1. Device 27 comprises two feeding units 28 and 28' which are structurally substantially identical to deposition unit 4' shown in figure 3. Feeding units 28 and 28' define a common falling channel 29, towards which are conveyed particles 30 comprising (in particular consisting of) a substantially inert material and particles 5 comprising at least one organic binder, respectively. Device 27 comprises a heating system adapted to heat particles 5 and/or 30 so as to allow the coupling of at least part of particles 5 with at least part of particles 30 and therefore obtain combined particles 5 (particles 5 each bound to - incorporating - a particle 30) .

Device 27 also comprises a cooling unit 31 to cool combined particles 5. In particular, cooling unit 31 comprises a vibrating plate 32, which is arranged below channel 29 and on which, in use, combined particles 5 fall.

Plate 32 is adapted to vibrate so as to move particles 5 outwards and therefore let them fall on collecting system 33.

According to a third aspect of the present invention there is provided a method for producing combined particles 5 (i.e. made of composite material). The method comprises a heating step, during which particles 30 comprising (in particular consisting of) a substantially inert material and/or particles 5 (comprising, in particular consisting of) at least one organic binder, are heated to a temperature above 50 °C (in particular above 80 °C) . According to some embodiments, particles 30 and/or 5 are heated to a temperature below 100 °C. Advantageously, it is particles 30 which are heated (while particles 5 remain at a room temperature) .

Particles 5 are defined according to the fourth aspect of the present invention.

The method also comprises a coupling step, during which particles 30 and 5 are directed one against another so as to create combined particles 5. Particles 30 and/or 5 have approximately the above indicated temperatures with respect to the heating step.

Advantageously, particles 30 have the above indicated temperatures with respect to the heating step (while particles 5 are at a room temperature) .

In particular, the coupling step at least partially (more specifically totally) follows the heating step.

Furthermore, the method comprises a cooling step, during which combined particles 5 are cooled (approximately at a room temperature) . During the step of cooling, combined particles 5 are mixed so as to disperse heat (and reduce the possibility of them binding to one another) .

According to some embodiments the method is implemented by a device 27 as disclosed above. In particular, the step of coupling is performed by feeding units 28 and 28' . The cooling step is performed by cooling unit 31.

It should be noted that the substantially inert material is selected so that particles 30 cannot bind to one another if placed in contact and subjected to a temperature up to 200°C, at a pressure up to 100 Kg/cm² and in the absence of other elements .

According to some embodiments, the substantially inert material comprises (more specifically consists of) (at least) one inorganic material.

In particular, according to some embodiments, particles 30 comprise (specifically consist of) materials selected from the group consisting of: compounds of silicon, aluminium oxide (in particular corundum - A1₂0₃) , aluminium hydroxide (and a combination thereof) .

In particular, the silicon compounds are silicates, more specifically (at least) one material selected from the group consisting of: glass, quartz, cristobalite (and a combination thereof) . Cristobalite may be natural or artificial obtained by the processing of quartz sands in an oven at about 1880°K. In particular, the silicates are selected from the group consisting of: glass, quartz (and a combination thereof) .

According to some variants, particles 30 comprise (specifically consist of) materials selected from the group consisting of: glass, quartz, aluminium hydroxide (and a combination thereof) .

Aluminium hydroxide may be particularly advantageous. In this connection it should be noted that aluminium hydroxide may be cut by the same processing tools as wood.

According to some embodiments, particles 30 comprise (in particular consist of) marble particles, which in turn contain carbonates (in particular calcium carbonates) and/or silicates.

In particular, particles 30 have a size (i.e. diameter) of at least 20 μτη (advantageously at least 50 μπι) . According to some embodiments, particles 30 have a size (i.e. diameter) up to 5 mm (more precisely, up to 1 mm). More specifically, particles 30 have a size (i.e. diameter) up to 500 μιη (in particular, 250 urn) .

The size (as regards all particles cited in the present text) is obtained by subsequent sievings with sieves having holes displaying decreasing size (diameters) . The diameters of the holes of the first sieve that does not allow the passage of the particles indicates the size (i.e. diameter) of the particles.

The measuring by following sievings is performed until the size (i.e. the diameters) of the particles and holes of the sieves allow to (in particular, up to a minimum of 0.05 mm) . Below this size (in particular 0.05 mm) , the size of the particles is measured as average diameter D(v,0.5) measured by means of a laser granulometer - in particular using a laser Mastersizer

®

Microplus granulometer Ver.2.19 (Malvern Instruments Ltd) . According to a fourth aspect of the present invention, there is provided a process to coat at least surface 6 of article 2, the process comprising: a deposition step, during which particles 5 having a size (i.e. diameter) of at least 20 μπι are spread on surface 6; a first heating step, during which particles 5 spread on surface 6 are heated so that the melting point of the organic binder is reached at least and a first layer L, which is partially liquid is obtained; a compression step, which at least partially follows the first heating step and during which first layer L is compressed against surface 6; a first cooling step, which is at least partially simultaneous to the compression step and during which the temperature of the first layer is reduced (in particular, below 80°C) . Advantageously, the first cooling step is substantially simultaneous to the compression step.

The method usually also comprises a second cooling step, which at least partially follows the first cooling step and during which the temperature of first layer L is cooled to a room temperature so as to obtain a coating layer L.

According to some embodiments, the second cooling step is not performed by any thermal conditioning, but instead, for example, by only leaving article 2 at a room temperature .

According to some embodiments, the first and the second cooling steps take place one after another substantially continuously.

In particular (referring to figures 8 and 9) , article 2 is a panel. It should be noted that surface 6 may not be (totally) flat. As a matter of fact, according to some embodiments, panel has depressions and/or reliefs (i.e., may be provided with one or more decorations in relief or recessed) .

Particles 5 comprise at least one organic binder. According to some embodiments, the binder can melt at least partially at a temperature (has a melting point) below or equal to 200°C and above 60°, in particular above 100°C. According to some embodiments, the binder can melt at least partially at a temperature (has a melting point) from 110°C to 130°C. The melting point (temperature) is indicated in the present text as measured at a standard pressure (1 atm) .

In particular, the binder is selected from the group consisting of: thermoplastic polymers, thermosetting prepolymers (and a combination thereof) . It should be noted that thermoplastic polymers deriving from the recycling of waste plastic materials containing hard to separate impurities of other thermoplastic materials, may be used.

The thermosetting prepolymers are materials which are still not totally polymerised and/or crosslinked, which first soften (melt) if heated and then harden in a substantially irreversible manner (i.e. if simply heated again, do not soften) . In particular, the hardening is due to crosslinking reactions.

According to some embodiments, the binder comprises (in particular, consists of) a resin selected from the group consisting of: polyurethanes , polyesters (for example polylactic acid) , acrylic resins, methacrylic resins (and a combination thereof) . According to specific embodiments, the binder comprises (in particular consists of) a polyester. In particular, the binder comprises (more in particular consists of) an epoxy-polyester (i.e. a combination of an epoxy resin and a polyester) .

According to some embodiments, particles 5 comprise (in particular consist of) particles of powder coating. In these cases, particles 5 comprise a thermosetting prepolymer. Different suppliers of powder coatings, which can be used without further modifications in the present process, are available on the market. One of these companies is Tiger (Austria) . An example of powder coating that may be used is the transparent epoxypolyester powder coating 530 by Tiger.

According to further embodiments, particles 5 comprise (in particular consist of) powder particles for dynamic rotomoulding . In these cases, particles 5 comprise a thermoplastic polymer. Different suppliers for dynamic rotomoulding are available on the market, such as for example SDT (Brescia, Italy) . An example of powder for dynamic rotomoulding is ICOPOLIMERS 3545 (powder polyethylene) by SDT. Usually, particles 5 have a size (i.e. diameter) smaller than 2 mm (in particular, up to 1 mm) . Advantageously, particles 5 have a size (i.e. diameter) larger than 50 urn. According to some embodiments, particles 5 have a size (i.e. diameter) up to 500 μττι (more precisely up to 200 μπι, in particular up to 180 μτη) . Usually, in these cases, particles 5 comprise (consist of) a thermosetting prepolymer.

According to some embodiments, particles 5 have a size (i.e. diameter) from 200 μιη (in particular up to 500 μπι) . Usually, in these cases, particles 5 comprise (consist of) a thermoplastic polymer.

It should be noted that, according to some variants, particles 5 comprise particles 30 as defined according to the third aspect of the present invention. As an alternative or in addition, particles 5 comprise (in particular consists of) composite particles 5 as defined according to a third aspect of the present invention. It should be noted that composite particles 5 usually have a size (i.e. diameter) from 100 μπι (in particular from 200 μπι) to about 1 mm (in particular, to 750 μπι) .

It is also important to point out that the use of particles 30 (separately or incorporated in composite particles 5) allows to obtain several advantages. Among these, we cite the followings: the possibility of producing thicker layers with lower costs; the possibility of obtaining special aesthetical effects (for example create materials that are aesthetically similar to marble) ; the possibility of increasing the resistance to scratches and/or the hardness of surface 6; the possibility of making the surface 6 draining and/or antislip.

Typically, particles 5 comprise from 5% to 80% (in particular, at least 20%) in weight, with respect to the overall weight of particles 5, of particles 30 (incorporated or separate). For some applications, it is advantageous to use particles 5 comprising at least 60% (in particular from 60% to 80%) in weight, with respect to the overall weight of particles 5, of particles 30 (separate or incorporated) .

Particles 5 comprise at least 15% (in particular from 15% to 95%; more in particular at least 20%) in weight, with respect to the overall weight of particles 5, of the organic binder. According to some embodiments, particles 5 comprise at least 50% (in particular from 50% to 95%; more in particular from 60% to 90%) in weight, with respect to the overall weight of particles 5, of the organic binder. According to alternative embodiments, particles 2 comprise from 20% to 40% in weight, with respect to the overall weight of particles 5, of organic binder.

During the first heating step, particles 5 are heated so as to bind at least partially to one another. In particular, particles 5 are heated at a temperature above 80°C (more precisely, above 100°C) . According to some embodiments, particles 5 are heated to a temperature above 130°C (in particular, above 150°C) . Advantageously, particles 5 are heated to a temperature below 250 °C (below this temperature some materials, for example wood, could catch fire) . More precisely, particles 5 are heated to a temperature below 200°C (in some cases, below 180°C) .

In this connection, it should be noted that in some cases (in particular, when a thermosetting pre-polymer is used) it is preferable to remain below 200°C (in particular below 180°C) . Advantageously, in these cases, particles 5 are heated to a temperature below 150 °C (in particular, below 130°C) .

It should be noted that, during the first heating step, the hardening of the thermosetting prepolymer should be avoided (at least minimised) .

According to some embodiments, a surface treatment device 8 comprises a compression assembly 9 having a contact surface 10, which comes into contact with first layer L and exerts a pressure on first layer L during the compression step and the first cooling step. The pressure is at least 1.1 atm (advantageously 1.5 atm).

Surface treatment device 8 comprises a cooling unit, which cools the contact surface. In particular, device 8 is as disclosed above according to the first aspect of the present invention.

During the first cooling step, layer L is advantageously taken to a temperature below 80 °C (in particular, below 50°C) . Specifically, the cooling should not proceed to below 15 °C. According to some embodiments, layer L is cooled to a temperature below 30°C (approximately room temperature) .

Advantageously, the process comprises a pre-heating step, during which article 2 is heated before the deposition step so as to reach a temperature above 100 °C (in particular above 120°C) . According to some embodiments, the preheating step precedes (or is part) of the first heating step. The pre-heating step is especially useful when surface 6 is not completely flat; in particular, when surface 6 has depressions and/or reliefs (for example, when article 2 is a panel provided with one or more relief or depression decorations) . According to some embodiments, during the pre-heating step, article 2 is heated to temperatures such as those defined relatively to the first heating step as regards particles 5.

According to some embodiments, particles 5 comprise at least one pigment. In particular, particles 5 comprise from about 5% to about 50% (in particular from 10% to 40%) in weight, with respect to the overall weight of particles 5, of the pigment.

According to some embodiments, the process comprises a hardening step, which at least partially follows (in particular, follows) the first cooling step and at least partially precedes (in particular precedes) the second cooling step and during which the thermosetting prepolymer is hardened (polymerised and/or crosslinked) .

More specifically, the hardening step comprises a second heating step, which at least partially follows (in particular, follows) the first cooling step and at least partially precedes (in particular, precedes) the second cooling step and during which the thermosetting prepolymer is heated to a temperature above or equal to its hardening temperature.

According to specific embodiments, the thermosetting prepolymer is heated to a temperature as indicated with respect to the first heating step and/or to the preheating step. In particular, the thermosetting prepolymer is heated to a temperature above 120 °C (and below 250°C) . More precisely, the thermosetting prepolymer is heated to a temperature of at least 130 °C (in particular of at least 150°C) .

Layer L which is deposited during the deposition step has a thickness of at least about 100 μιη. For some applications (and in particular when particles 30 are also used) a thickness of a few dozen millimetres (for example up to 20 mm) may be obtained. Typically (in particular when particles 30 are substantially absent) layer L has a thickness up to 500 μτη (advantageously, up to 200 μπι) .

According to some embodiments, article 2 comprises (more specifically consists of) a material selected from the group consisting of: composite plastic materials, alveolar materials, asbestos cement, plasterboard, glass, ceramics, wood (and a combination thereof).

More precisely, article 2 comprises (more specifically consists of) a material selected from the group consisting of: glass, ceramics, wood (and a combination thereof) . Advantageously, article 2 comprises (more specifically consists of) wood.

By wood there is intended also any material comprising a wooden chipboard conglomerate.

According to some embodiments, the disclosed process is implemented by machine 1 of the first aspect of the present invention. In particular, the deposition step is performed by deposition device 4. The first heating step is performed by heating device 7. The pre- heating step is performed by heating device 13. The second heating step is performed by heating device 14. The second heating step is performed by heating device 15.

After the first (and optionally the second) cooling step, patterns may be printed on layer L (for example by contact flexographic printing or by digital techniques of jet ink printing) . Coloured layer L may possibly serve as background or base colour.

The pattern obtained thereby may be protected by depositing another layer L thereover by performing the same process disclosed above.

The above disclosed process has several advantages with respect to the state of the art. By way of example, we cite:

saving in costs and energy,

possibility of decorating surface 6 with colours over the whole RAL range;

effective and long protection of surface 6 ;

possibility of obtaining stone- like aesthetical effects (for example, marble-like) ; and

the possibility of obtaining draining and/or antislip and/or anti-scratch surfaces.

According to a further aspect of the present invention, an at least partially coated article 2 obtained or obtainable by the process of the fourth aspect of the present invention is provided. In this connection, it should be noted that the known methodologies did not allow to obtain an article 2 which is qualitatively identical to that obtainable by the above disclosed process.

Further features of the present invention will result from the following disclosure of an example given by mere way of non-limitative illustration.

Example 1

A medium-density fibreboard (MDF) was introduced in a preheated oven at a temperature of 150°C for about 3 minutes . It was then extracted from the oven and quickly coated with a layer of about 500 μτη of transparent epoxypolyester powder coating 530 by Tiger. The powder was previously sieved so as to eliminate particles having a size smaller than 50 μιη and was deposited by shaking a belt (mayler) with about 135 holes per cm². The holes had a diameter of about 0.4 mm and were obtained by means of a laser.

The coated fibreboard was compressed by means of a chromed roller and subsequently introduced again in the oven at a temperature of 150 °C for 4 minutes (so as to obtain a complete hardening of the powder) . The resulting coating layer was tested and proved very strong. Detachment was obtained only with the simultaneous removal of wooden particles. This proves that the layer was bound with a greater force than the cohesion of the components of the board.

Claims

1. A process for coating at least one surface (6) of an article (2), the process comprises:

a deposition step, during which particles (5) made of at least one coating material are spread on the surface (6) ; the particles (5) comprising at least one organic binder and having a size from 20 μτη to 2 mm;

a first heating step, during which the particles (5) spread on the surface (6) are heated to a temperature above 100 °C and so that the melting point of the organic binder is at least reached, the particles (5) bind at least partially to one another and a at least partially liquid first layer (L) is obtained;

a compression step, which at least partially follows the first heating step and during which the first layer (L) is compressed against the surface (6) ; a first cooling step, which is performed at least partially simultaneously to the compression step and during which the temperature of the first layer (L) is reduced below 80°C;

a second cooling step, which at least partially follows the first cooling step and during which the temperature of the first layer (L) is cooled to a room temperature so as to obtain a coating layer (L) .

2. The process according to claim 1, wherein the particles (5) have a size from 50 μτη to 500 μιη; a surface treatment device (8) comprises a compression assembly (9) having a contact surface (10) , which comes into contact with the first layer (L) and exerts a pressure on the first layer (L) during the compression step and the first cooling step; the surface treatment device (8) comprises a cooling unit, which cools the contact surface, in particular below 30°C.

3. The process according to any of the preceding claims, wherein the article (2) is heated before the deposition step so as to reach a temperature above 100°C (in particular above 120°C) .

4. The process according to any of the preceding claims, wherein during the compression step the first layer (L) is subjected to a pressure of at least 1.1 atm; the first cooling step is substantially simultaneous to the compression step.

5. The process according to one of the preceding claims, wherein the particles (5) comprise at least one additional component selected from the group consisting of: at least one pigment, particles comprising a substantially inert material, a combination thereof.

6. The process according to claim 5, wherein the substantially inert material is an inorganic material selected from the group consisting of: glass, quartz, cristobalite, aluminium silicate, aluminium hydroxide, aluminium oxide and a combination thereof.

7. The process according to claim 5 or 6, wherein the particles (5) comprise from 50% to 95% in weight, with respect to the overall weight of the particles (5) , of the organic binder and from 5% to 50% in weight, with respect to the overall weight of the particles (5) , of the additional component .

8. The process according to one of the preceding claims, wherein the organic binder comprises at least one thermosetting prepolymer; the process comprising a hardening step, which at least partially follows the first cooling step and at least partially precedes the second cooling step and during which the thermosetting prepolymer is polymerised and/or crosslinked.

9. The process according to claim 8, wherein the hardening step comprises a second heating step, which at least partially follows the first cooling step and at least partially precedes the second cooling step and during which the thermosetting prepolymer is heated to a temperature above or equal to its hardening temperature, in particular to a temperature above 120 °C.

10. The process according to any of the preceding claims, wherein the second cooling step is substantially simultaneous to the compression step.

11. The process according to one of the preceding claims, wherein the article (2) is a panel and is made of a material selected from the group consisting of : glass, ceramics, wood and a combination thereof.

12. An at least partially coated article obtained according to one of the preceding claims.

13. A machine for coating at least one surface (6) of an article (2) , the machine (1) comprises at least one conveyor (3) to feed the article (2) along a determined path (P) ;

a deposition device (4) for distributing particles (5) having size from 20 μπι to 1 mm on the surface (6) ; a first heating device (7) for heating the particles (5) spread on the surface (6) at a temperature above 100 °C so that the particles (5) are bound at least partially to one another and a first layer (L) is obtained, which is at least partially liquid;

a surface treatment device (8) , which is arranged downstream of the first heating device (7) and comprises a compression assembly (9) having a contact surface

(10) , which is adapted to come into contact with the first layer (L) and exert a pressure on the first layer (L) ; the surface treatment device (8) comprises a cooling unit, which is adapted to cool the contact surface (10) .

14. The machine according to claim 13 , wherein the compression assembly (9) comprises a membrane (11) comprising silicone, which has said contact surface (10) , and a handling system (12) to feed the membrane

(11) in contact with and synchronously to the article (2) along a segment of the predetermined path (P) .

15. The machine according to claim 14, wherein the compression assembly (9) comprises a chromed roller, which has said contact surface (10) , and a handling system to rotate the roller on the article (2) while the article (2) is fed along the determined path (P) at the surface treatment device (8) .

16. A device for producing combined particles (2), the device (27) comprises two feeding units (28, 28'), which define a channel (29) and are adapted to convey particles {30) of at least one substantially inert material and particles (2) comprising at least one organic binder, respectively, towards the channel (29) ; a heating system to heat at least one of the particles of at least one substantially inert material and the particles comprising at least one organic binder; and a cooling unit to cool combined particles (2) obtained by the coupling of the particles of at least one substantially inert material and the particles comprising at least one organic binder.