Patent Description:
Mainly flat panel means a panel wherein two out of three dimensions are much wider than the third dimensions. Typically, the measures of such panels range 100x300x18 mm to 1250x2400x30 mm.

As known, such panels are coated in order to provide them with an aesthetic effect. , in the case of fibreboard panels, i.e. a low-cost material, side coatings are applied so as to cover their uneven surface.

In a known way in the art, such coating is applied through a coating device making use of suction, of the kind comprising a coating head (vacuum coating head) provided with a chamber fed with a liquid painting product to be applied on the wooden panels.

The chamber of each vacuum coating head typically is provided with an opening shaped according to the shape of the transversal section of the panels to be coated. In particular, the opening is counter-shaped to the transversal profile of the panel edge. The opening is placed aligned along a conveying direction of the panel, corresponding to the longitudinal profile of the edge to be coated.

During the conveying of said panel, the panel edge is conveyed near said opening, which supplies the painting product through an output slot for the liquid painting product. Said slot defines a nozzle that at least partially follows the transversal perimeter of the panel edge, at a constant distance so as to lap the whole surface to be coated.

The dispensing slot is adjacent to at least one suction opening, provided for suctioning the liquid painting product, so as to prevent that said painting product can leak out from the coating head.

In this way, the excess liquid painting product, which is not applied on the edge of the conveying panel, is recovered by the suctioning opening and channelled to a reservoir of the liquid painting product.

By adjusting: a) the viscosity of the liquid painting product; b) the flow rate through the dispensing slot; c) the conveying speed of said panel; d) the degree of vacuum provided by the suction recovering excess painting product, the thickness of the painting product applied on said panel is determined.

In addition to the unevenness typical of wooden surfaces, it is known that the use of vacuum suction tends to raise wood fibres, which protrude outside the film of the applied painting product. In order to avoid this drawback, two strategies can be used: a) using a very thick layer of painting product, so as to cover the raised wood fibre; or alternatively b) sanding the coated edge. The first strategy leads to a high and costly consumption of painting product; the second strategy leads to a more complex coating machine, provided with a greater length due to the presence of many sanding groups.

The applicant has been producing machines provided with one or more vacuum coating heads for suction coating for a long time, one of which is e.g. described in <CIT>. Said application describes a vacuum coating head comprising a body, at least a top form and at least a lower form.

In the art, there are known also vacuum coating heads made of a plurality of adjacent plates, e.g. from <CIT>.

In the art, it is known that in edge coating the greatest difficulties are coating Jpull or undercut edges (see <FIG>). In particular, the more complex the surface, the higher the number of sanding groups.

In the art it is known that in order to obtain panels provided with edges having a suitable quality, coating cycles comprising many successive steps must be performed. The traditional coating cycle today performed by the applicant comprises the following steps:.

A second coating cycle for a finishing of superior quality comprises the following steps:.

The number of painting product applications can range one to six (consequently the apparatus comprises one to six vacuum coating heads), depending on the desired quality of the final product.

<CIT> describes a method for producing engineered-wood fence pickets. The edge-sanding process produces a smooth side surface on the edges, significantly reducing the number of loose fibres and/or strands, and fills in and/or reduces void spaces. The painting of the pickets is performed through spraying.

<CIT>describes an apparatus for finishing the edge of particleboard, plywood and the like. The finishing is performed by extruding a fast-drying material.

<CIT> describes a method for smoothing the edges of workpieces which have at least one porous layer. Said method comprises the following steps: conveying the workpieces on a conveyor in a direction parallel to the edge to be smoothed; allowing a continuous carrier strip to pass over deflection rollers at a speed which is synchronous to the conveying speed of the workpieces, such that a contact section of the carrier strip rests on a section of the edge of at least one workpiece to be smoothed over a certain length; applying, upstream of the contact section, a curable filler onto the carrier strip; transferring the filler on the contact section onto the edge such that it forms a continuous layer of predetermined thickness; and allowing the filler to cure, once the carrier strip has been removed, until the continuous layer forms a smooth, solid surface.

<CIT> of Joseph Schiele OHG describes a device for coating the lateral edge faces of elongate work pieces with a liquid coating medium. The inventive device comprises an adjustable coating head with a coating slot that extends in the direction of transport of the work piece. Said coating head applies the liquid coating medium through just one nozzle at a time.

ITFI20090093 of Makor SRL describes a coating vacuum head for panels comprising a screeding organ placed downstream the organ supplying a coating product, in order to uniformly distribute said coating product and to remove from said panel a portion of the coating medium in excess.

In the art, it is known using painting products comprising photopolymerizing agents activated by ultraviolet (UV) radiations. Such painting products comprise a plurality of monomers that, once activated by UV radiations emitted by lamps of suitable wavelength, are involved in a photopolymerizing process leading to the formation of a polymer network. The quantity of radiation administered to the film of painting product applied on the panel can lead to an incomplete polymerization (gelling) or to a complete polymerization, wherein all the monomers contained in the painting product are concatenated in a polymer network (drying).

The gelling/drying of the painting product can be described in terms of percentage of monomers that react after undergoing UV radiation: indicatively, if complete drying corresponds to about <NUM>% of polymerized monomers, gelling corresponds to about <NUM>% of polymerized monomers after the action of UV radiation. It is intuitive that sanding must occur on a painting product sufficiently polymerized so that it does not stick to sanding groups.

In terms of adjusting the apparatus for coating edges, the percentage of polymerization of the applied painting product depends also on the power of the lamp used for the gelling step. Again indicatively, the polymerizing lamps emitting UV radiations for gelling are set on about <NUM> W/cm, while for drying the polymerizing lamps are set on about <NUM> W/cm. It is also worth mentioning that gelling is preferably performed using gallium lamps, while drying is preferably performed using mercury lamps.

The known art coating method is performed through known art apparatuses, which substantially are apparatuses having a given length, in that each of the above-described ten or fifteen steps is performed by a group (sanding group, coating group, gelling group, drying group) placed in series with respect to the preceding and following group. The working of panel edges occurs in passing. Typically, a known art apparatus is <NUM> to <NUM> metres long. The length of the apparatus is directly proportional to the number of groups provided in the apparatus, which in turn is directly proportional to the desired quality of the finished panel.

Aim of the present invention is providing a method and an apparatus to perform such method for vacuum coating making use of one or more vacuum coating heads, which is cheaper to perform and that allows to obtain better results in terms of the quality of the coated panel.

This object is achieved by a method and an apparatus having the features of the independent claims. Advantageous embodiments and refinements are specified in claims dependent thereon.

The method according to the present invention provides the following successive steps:.

In an alternative embodiment, for a superior quality of the coated edge, the successive steps are:.

Substantially, the novelty of the present method with respect to the known art lies in the following two features:.

By performing a sanding step after the first application of coating followed by gelling the following results are obtained:.

The new coating cycle allows to obtain many advantages:.

Experimentally, it was shown that by using a vacuum coating head applying two layers of painting product each according to the new method, the same qualitative result as using two known art vacuum coating heads is obtained.

Experimentally, it was shown that by using three vacuum coating heads applying two layers of painting product each according to the new method, the same qualitative result as using six known art vacuum coating heads is obtained.

Overall, the number of coating heads is reduced, and therefore there is a saving in the number of elements used both for applying and drying the painting product, which allows to reduce the overall length of the apparatus. Experimentally, it was shown that the quality of the finished panel being the same, the new method for applying a painting product allows to produce apparatuses that are <NUM>-<NUM> metres shorter with respect to the currently used apparatuses performing the known art coating cycle, with a significant saving in the required industrial space.

It is worth noting that the number of sanding groups placed downstream the coating groups, affecting the overall length of the apparatus, depends on the geometrical shape of the edge to be sanded and on the quality of the desired finishing.

All this translates into an apparatus that provides a coating of outstanding quality but much cheaper to produce and of shorter length, without considering the savings in terms of energy consumption during the functioning of the apparatus.

Further advantages and properties of the present invention are disclosed in the following description, in which exemplary embodiments of the present invention are explained in detail based on the drawings:.

For the sake of clarity, in this Description a vacuum tower, indicated in this Description with the numeral <NUM>, means a unit providing both the painting product and the vacuum to the vacuum head.

<FIG> shows a first mainly flat panel <NUM> provided with an undercut edge <NUM>, a second mainly flat panel <NUM>' provided with a Jpull edge <NUM>, and a third mainly flat panel <NUM>" provided with a radius edge <NUM>. Said Jpull edges are e.g. used in kitchen cabinet doors, as they allow to open said doors while their external surface is free of handles or doorknobs. <FIG> is illustrative only, having the aim to show the plurality of different edges that can be coated by a vacuum coating head according to the present invention. There is provided a wide variety of edges that are not shown in <FIG>.

Any panel is provided with two main sides and four edges, each of which must be coated. Panel coating typically occurs in production lines comprising a plurality of apparatuses placed in series. According to the organization of the production line characteristic of each production plant, for coating each side and edge there can be provided a specific apparatus, and between said apparatuses there is provided a turning device allowing to provide the following apparatus with the side or edge to be coated by that specific apparatus. Alternatively, the same apparatus can paint the four edges: the panel is conveyed four times inside the same apparatus. Alternatively, an apparatus according to the present invention coats the geometrically more complex edge, while one or further apparatus/es is/are provided for the coating of the geometrically less complex edges.

In the art, there are known apparatuses provided with variable numbers of post-coating sanding groups. The more geometrically complex the edge <NUM>, <NUM>, <NUM>, the higher the number of sanding groups provided in the apparatus in order to have a perfectly coated panel, in that each of them is adjusted to sand just one portion of said edge. It is worth noting that, according to the kind of batch produced in a given moment, in an apparatus provided with a high number of sanding groups, some sanding groups might be inactive during the production of that specific batch.

In <FIG> a known art apparatus <NUM> with four coating heads according to the known art and an apparatus <NUM> applying four layers of painting product according to the present invention are compared. This is just one of many possible configurations, some of which are shown in <FIG>.

It is worth mentioning that in the following Description, the apparatuses indicated by the numeral <NUM> preceded by a digit indicate apparatuses according to the known art, while the apparatuses indicated by the numeral <NUM> preceded by a digit indicate apparatuses according to the present invention. The digit preceding <NUM> or <NUM> indicates the number of applications of painting product performed by the apparatus.

Both in the known art apparatuses *<NUM> and in the apparatuses *<NUM> according to the known art, a panel <NUM> is conveyed by a (not shown) conveying band (chain conveyor) that is narrower than the panel dimension perpendicular to the conveying direction. The panel is cantilevered with respect to the apparatus * <NUM>, *<NUM>. Just one edge at a time of the panel <NUM> is worked during each passage inside the apparatus *<NUM>, *<NUM>; obviously, the edge undergoing coating is the one adjacent to the apparatus. Panels <NUM> can be manually uploaded/downloaded in/from the apparatus *<NUM>, *<NUM> by a human operator, or loading/unloading can occur automatically using known conveyors. In a known way, apparatuses * <NUM>, *<NUM> are provided with an aligner pushing the panel <NUM> against a reference stop. Optionally the same apparatus *<NUM>, *<NUM> can be used to coat also the other edges of panels <NUM>, one at a time.

As explained above, the length of the apparatus varies proportionally to the numerousness of groups. In this first comparison (<FIG>) a known art apparatus provided with four coating head according to the known art and an apparatus applying four layers of painting product according to the present invention are compared. The number of sanding groups placed downstream the drying group is the same, so as to show a meaningful comparison in terms of apparatus length between the known art apparatus and an apparatus according to the present invention.

The bold arrows show the conveying direction of the panel <NUM>, whose edges must be coated.

<FIG> shows a known art apparatus <NUM> currently produced by the applicant, in a top view.

The known art apparatus <NUM> comprises:.

<FIG> shows an apparatus <NUM> according to the present invention, in top view.

The apparatus <NUM> according to the present invention comprises:.

At a glance, it can be observed that the apparatus <NUM> according to the present invention is shorter than the known art apparatus <NUM>.

<FIG> compares a known art apparatus <NUM> provided with two coating heads <NUM>, <NUM>' and an apparatus <NUM> applying four layers of painting product according to the present invention. In the Figure, just the portions concerning the coating are indicated. As explained above, the portions downstream the coating portion are variable according to the panels to be coated. The downstream portion comprising the sundry sanding groups is purposefully identical in the two apparatuses, so as to facilitate the comparison between the known art apparatus <NUM> and the apparatus <NUM> according to the present invention.

In the case of a panel requiring four applications of painting product, with the apparatus <NUM> according to the present invention, the panel is conveyed just once inside the apparatus. Instead, with the known art apparatus <NUM>, the same panel must be conveyed twice inside the apparatus <NUM>: the apparatus is shorter, but the coating cycle must be repeated in order to obtain a qualitative result comparable to that obtainable with just one cycle in the apparatus <NUM> according to the present invention.

<FIG> compares a known art apparatus <NUM> provided with three coating heads <NUM>, <NUM>', <NUM>" and an apparatus <NUM> applying four layers of painting product according to the present invention. In the Figure, just the portions concerning the coating are indicated. As explained above, the portions downstream the coating portion are variable according to the panels to be coated. The downstream portion comprising the sundry sanding groups is purposefully identical in the two apparatuses, so as to facilitate the comparison between the known art apparatus <NUM> and the apparatus <NUM> according to the present invention.

The result obtained with the apparatus <NUM> and the apparatus <NUM> is not equivalent: in fact, with the apparatus <NUM> three layers of painting product are applied, while with the apparatus <NUM> four layers of painting product are applied. With a comparable length of the two apparatuses, the qualitative result is better with the apparatus <NUM>. Moreover, with the apparatus <NUM> a vacuum tower is dispensed with.

<FIG> compares a known art apparatus <NUM> provided with five coating heads <NUM>, <NUM>', <NUM>", <NUM>"', <NUM>"" according to the known art and an apparatus <NUM> applying four layers of painting product according to the present invention. In the Figure, just the portions concerning the coating are indicated. As explained above, the portions downstream the coating portion are variable according to the panels to be coated. The downstream portion comprising the sundry sanding groups is purposefully identical in the two apparatuses, so as to facilitate the comparison between the known art apparatus <NUM> and the apparatus <NUM> according to the present invention.

<FIG> shows a particular embodiment, wherein each vacuum coating head <NUM>, <NUM>' of the apparatus <NUM> is supplied by a respective vacuum tower <NUM>, <NUM>'. As explained above, a vacuum tower <NUM> can supply two and even three vacuum coating heads <NUM>, <NUM>'. In this case, though, there are provided two distinct vacuum towers <NUM>, <NUM>': the first vacuum tower supplies a primer to the first vacuum coating head <NUM>, while the second vacuum tower <NUM>' supplies a painting product to the second vacuum coating head <NUM>'.

<FIG> compares a known art apparatus <NUM> provided with six coating heads <NUM>, <NUM>', <NUM>", <NUM>‴, 13ʺʺ, 13ʺ‴ according to the known art and an apparatus <NUM> applying six layers of painting product according to the present invention. In the Figure, just the portions concerning the coating are indicated. As explained above, the portions downstream the coating portion are variable according to the panels to be coated. The downstream portion comprising the sundry sanding groups is purposefully identical in the two apparatuses, so as to facilitate the comparison between the known art apparatus <NUM> and the apparatus <NUM> according to the present invention.

In the case of the apparatus <NUM> applying six layers of painting product, the second gelling step is performed by just one gelling group <NUM>" followed by a third application of painting product performed by a third vacuum coating head <NUM>". Finally, the last gelling/drying step is performed by a gelling/drying group <NUM>, <NUM>'. Of course, this apparatus is used for finishing of a particularly high quality.

<FIG>, <FIG> and <FIG> allow to visually appreciate the reduction in the length of the apparatuses according to the present invention with respect to the known art apparatuses, the number of applications of painting product being the same. Said reduction in length can indicatively range <NUM> to <NUM> metres.

The method according to the present invention comprises the following steps performed by an apparatus <NUM>:.

In an alternative embodiment, suitable for a superior quality of the coated edge, the method according to the present invention comprises the following steps performed by an apparatus <NUM>:.

It is worth mentioning that in the apparatuses *<NUM> according to the present invention, the gallium lamp in the gelling group <NUM>, <NUM>' are set on <NUM> W/cm, the gallium lamps in the gelling group <NUM> are set on <NUM>-<NUM> W/cm, while the mercury lamps in the drying group <NUM>' are set on <NUM>-<NUM> W/cm. These power levels, too, contribute to the reduced energy consumption with respect to the known art apparatuses.

Alternatively, in lieu of the gallium and mercury lamps, LED lamps ranging <NUM> W up to <NUM> W can be used. In this case, indicatively, for gelling steps <NUM> W LED lamps are set on <NUM>-<NUM> W/cm<NUM>, while for drying steps <NUM> W LED lamps are set on <NUM>-<NUM> W/cm<NUM>.

The sanding group <NUM> is preferably provided in the form of a sanding wheel with a cloth Trizact© <NUM>®, comprising a ceramic abrasive material supported by a polyester cloth.

The sanding performed by the sanding group <NUM>, placed between the application of the first two layers of painting product applied by the first vacuum coating head <NUM>, and the application of the second two layers of painting product applied by the second vacuum head <NUM>', allows to obtain a coated surface that is smoother and more even. Consequently, with the following applications of painting product an even better result is obtained. The final sanding performed with the sanding groups downstream the second vacuum coating head <NUM>' allows to obtain a perfectly smooth surface.

<FIG> show a vacuum head <NUM> that is advantageously comprised inside the apparatuses *<NUM> according to the present invention. Said vacuum head allows to maximize the advantages applying the method according to the present invention.

Said vacuum coating head <NUM> comprises:.

In the preferred embodiment, between the first suction nozzle <NUM> for suctioning a painting product and the second dispensing nozzle <NUM> for dispensing a painting product, there is provided a screed <NUM> protruding with respect to the profile of the vacuum coating head for a length ranging <NUM>,<NUM> to <NUM>,<NUM>. This minimal protrusion, difficult to be appreciated in the Figures, allows the screed <NUM> to perform two actions:.

Here is worth noting that up to the introduction of 3D printing the vacuum coating heads used to be produced in the form of coating heads made of a plurality of plates, as in this way obtaining cavities in solid pieces used to be easier. It is known obtaining said plates in metallic materials, in a plastic material, or even in a wooden material (phenolic wood).

Nowadays, with 3D printing, pieces provided with internal cavities can be produced through additive manufacturing; therefore, the vacuum head <NUM> according to the present invention can be produced in a single solid piece, produced in plastic material, e.g. in epoxy resin, or in a metallic material, e.g. aluminium or stainless steel, provided with suitable characteristics.

It is worth noting that the vacuum coating head <NUM>, provided with two dispensing nozzles <NUM>, <NUM> in fact applies two layers of painting product with respect to the vacuum known art coating head <NUM>, which is provided with just one dispensing nozzle. The application of painting product by the second dispensing nozzle <NUM> on the first layer of painting product dispensed by the first dispensing nozzle <NUM> is in fact a wet-on-wet application, as the gelling group <NUM> is placed downstream each vacuum coating head <NUM>.

Claim 1:
Method for applying a painting product, preferably an UV painting product, to an edge of wooden panels (<NUM>) through an apparatus comprising pre-coating sanding groups (<NUM>, <NUM>) and post-drying sanding groups (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>), at least a painting group provided in the form of a vacuum coating head (<NUM>) supplied with both said painting product and vacuum by a vacuum tower (<NUM>), at least a gelling group (<NUM>), at least a drying group (<NUM>) placed in series comprising the following successive steps:
<NUM>. sanding of the rough edge;
<NUM>. first application of painting product to the edge;
<NUM>. first gelling;
<NUM>. post-gelling sanding of the edge;
<NUM>. second application of said painting product to the edge;
<NUM>. drying;
<NUM>. final post-drying sanding;
characterized in that
- in each one of steps <NUM> and <NUM>, the application of said painting product to the panel edge occurs through two layers of painting product applied in a wet-on-wet close succession;
- in step <NUM>, the post-gelling sanding occurs on a layer of painting product that underwent gelation only.