[0001] The present invention relates to a method for coating rigid panels made of wood or
other materials, like e.g. MDF (Medium Density Fibreboard) wood, fibreboard or other
wooden materials, with liquid painting products. In particular, the present invention
relates to a method comprising a plurality of successive steps for applying a fluid
coating substance, like a painting product, on an external edge of a panel made of
a rigid material with different shapes.
[0002] 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.
[0003] As known, such panels are coated in order to provide them with an aesthetic effect.
E.g., in the case of fibreboard panels, i.e. a low-cost material, side coatings are
applied so as to cover their uneven surface.
[0004] 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.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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
EP3315210A1. Said application describes a vacuum coating head comprising a body, at least a top
form and at least a lower form.
[0012] In the art, there are known also vacuum coating heads made of a plurality of adjacent
plates, e.g. from
IT102009901728856 of Makor.
[0013] In the art, it is known that in edge coating the greatest difficulties are coating
Jpull or undercut edges (see Figure 1). In particular, the more complex the surface,
the higher the number of sanding groups.
[0014] 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:
- 1. sanding of the rough edge;
- 2. first coating of the edge;
- 3. first gelling;
- 4. second coating of the edge;
- 5. second gelling;
- 6. third coating of the edge;
- 7. third gelling;
- 8. fourth coating of the edge;
- 9. drying;
- 10. final sanding (using at least four band sanding groups + two sanding wheels).
[0015] A second coating cycle for a finishing of superior quality comprises the following
steps:
- 1. sanding of the rough edge;
- 2. first coating of the edge;
- 3. first gelling;
- 4. second coating of the edge;
- 5. drying;
- 6. sanding (using at least four band sanding groups + two sanding wheels)
- 7. third coating of the edge;
- 8. third gelling;
- 9. fourth coating of the edge;
- 10. fourth gelling;
- 11. fifth coating of the edge;
- 12. fifth gelling;
- 13. sixth coating of the edge;
- 14. drying;
- 15. final sanding (using at least four band sanding groups + two sanding wheels).
[0016] 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.
[0017] US20210121912A1 of Louisiana Pacific Corp 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.
[0018] US3967581A of Edward Irvin Zirbel describes an apparatus for finishing the edge of particleboard, plywood and the like.
The finishing is performed by extruding a fast-drying material.
[0019] DE102014107492 of MHF GMBH 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.
[0020] DE10100518 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.
[0021] 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.
[0022] 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).
[0023] 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 100% of polymerized monomers, gelling corresponds to about 50%
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.
[0024] 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 80 W/cm, while for drying the polymerizing lamps are set
on about 150 W/cm. It is also worth mentioning that gelling is preferably performed
using gallium lamps, while drying is preferably performed using mercury lamps.
[0025] 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
10 to 30 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.
[0026] 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.
[0027] 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.
[0028] The method according to the present invention provides the following successive steps:
- 1. sanding of the rough edge;
- 2. first application of painting product to the edge;
- 3. first gelling;
- 4. post-gelling sanding of the edge;
- 5. second application of painting product to the edge;
- 6. drying;
- 7. post-drying sanding.
[0029] In an alternative embodiment, for a superior quality of the coated edge, the successive
steps are:
- 1. sanding of the rough edge;
- 2. first application of painting product to the edge;
- 3. first gelling;
- 4. post-gelling sanding of the edge;
- 5. second application of painting product to the edge;
- 6. second gelling;
- 7. third application of painting product to the edge;
- 8. drying;
- 9. post-drying sanding.
[0030] Substantially, the novelty of the present method with respect to the known art lies
in the following two features:
- the application of the painting product occurs through the application of two layers
of painting product in a close succession, in a wet-on-wet mode;
- the first sanding after the first application of painting product is performed on
the painted product which underwent gelation only, wherein a significant percentage
of monomers is not polymerized; obviously, the degree of polymerization must be suitable
so that the coated layer can be sanded.
[0031] By performing a sanding step after the first application of coating followed by gelling
the following results are obtained:
- a smooth surface, because the fibre of the wooden material protruding from the film
of painting product is cut (sanded);
- the following applications of painting products are much smoother:
the orange peel effect is nearly completely removed, and therefore the final sanding
of the panel is easier and requires a lesser number of sanding groups.
[0032] The new coating cycle allows to obtain many advantages:
- If instead of gelling it, the applied coating were dried, as oftentimes one must do,
the edge should be sanded over its whole coated surface using many sanding groups;
while with gelation, only the portion of the edge wherein the wooden fibre is raised
is sanded. The sanding on the gelled portion is easier, in that a lesser number of
sanding groups are necessary in order to reach all the surfaces of a complex edge
like e.g. a Jpull edge: just a sanding wheel or a band are sufficient;
- The following applications of painting products are eased by the lack of protruding
wooden fibres; the coating is more efficient, and finally this allows a reduction
in the number of steps and of the final thickness of the layers of applied painting
product;
- The quantity of energy is markedly reduced (of about 20%, up to 35% according to apparatus
configuration).
[0033] 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.
[0034] 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.
[0035] 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 1-5 metres shorter with
respect to the currently used apparatuses performing the known art coating cycle,
with a significant saving in the required industrial space.
[0036] 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.
[0037] 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.
[0038] 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:
- Figure 1
- Examples of panels provided with different edges: undercut edge, Jpull edge, radius
edge, in transversal section;
- Figure 2
- Known art apparatus provided with four coating heads, top view;
- Figure 3
- Apparatus according to the present invention configured for providing four painting
product applications, top view;
- Figure 4
- Known art apparatus provided with two coating heads and apparatus according to the
present invention configured for providing four painting product applications, top
view;
- Figure 5
- Known art apparatus provided with three coating heads and apparatus according to the
present invention configured for providing four painting product applications, top
view;
- Figure 6
- Known art apparatus provided with five coating heads and apparatus according to the
present invention configured for providing four painting product applications, top
view;
- Figure 7
- Known art apparatus provided with six coating heads and apparatus according to the
present invention configured for providing six painting product applications, top
view;
- Figure 8A, 8B
- Vacuum coating head according to the present invention in front and axonometric view.
[0039] For the sake of clarity, in this Description a vacuum tower, indicated in this Description
with the numeral 14, means a unit providing both the painting product and the vacuum
to the vacuum head.
[0040] Figure 1 shows a first mainly flat panel 1 provided with an undercut edge 2, a second
mainly flat panel 1' provided with a Jpull edge 3, and a third mainly flat panel 1"
provided with a radius edge 4. 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. Figure 1 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 Figure
1.
[0041] 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.
[0042] In the art, there are known apparatuses provided with variable numbers of post-coating
sanding groups. The more geometrically complex the edge 2, 3, 4, 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.
[0043] In Figure 2 and 3 a known art apparatus 410 with four coating heads according to
the known art and an apparatus 430 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 Figures 4-7.
[0044] It is worth mentioning that in the following Description, the apparatuses indicated
by the numeral 10 preceded by a digit indicate apparatuses according to the known
art, while the apparatuses indicated by the numeral 30 preceded by a digit indicate
apparatuses according to the present invention. The digit preceding 10 or 30 indicates
the number of applications of painting product performed by the apparatus.
[0045] Both in the known art apparatuses *10 and in the apparatuses *30 according to the
known art, a panel 1 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 * 10, *30. Just one edge at
a time of the panel 1 is worked during each passage inside the apparatus *10, *30;
obviously, the edge undergoing coating is the one adjacent to the apparatus. Panels
1 can be manually uploaded/downloaded in/from the apparatus *10, *30 by a human operator,
or loading/unloading can occur automatically using known conveyors. In a known way,
apparatuses * 10, *30 are provided with an aligner pushing the panel 1 against a reference
stop. Optionally the same apparatus *10, *30 can be used to coat also the other edges
of panels 1, one at a time.
[0046] As explained above, the length of the apparatus varies proportionally to the numerousness
of groups. In this first comparison (Figure 2 and 3) 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.
[0047] The bold arrows show the conveying direction of the panel 1, whose edges must be
coated.
[0048] Figure 2 shows a known art apparatus 410 currently produced by the applicant, in
a top view.
[0049] The known art apparatus 410 comprises:
- a sanding group 11 for a coarse pre-coating sanding;
- a sanding group 12 (here in the shape of a sanding wheel) for a finer sanding;
- four vacuum coating heads 13, 13', 13", 13''';
- two vacuum towers 14, 14' each vacuum tower supplies a painting product to two coating
heads:
in particular, the vacuum tower 14 supplies said painting product to the vacuum heads
13, 13', while the vacuum tower 14' supplies said painting product to the vacuum heads
13", 13"';
- three gelling groups 15, 15', 15" said gelling groups comprise preferably one or more
gallium lamps which partially polymerize the monomers of the painting product;
- two drying groups 16, 16' said drying groups comprise one or more mercury and/or gallium
lamps which completely polymerize the monomers of the painting product;
- a belt sanding group 17;
- four sanding groups 18, 18', 18", 18'" for a coarse post-coating sanding;
- three sanding groups 19, 19', 19" for a finer post-coating sanding (sanding wheels);
- two corner sanding groups 20, 20', for sanding the head and the tail of panel 1, respectively;
- a sanding group 21 for the final sanding: this is a sanding group provided with a
belt with a particularly fine grain.
[0050] Figure 3 shows an apparatus 430 according to the present invention, in top view.
[0051] The apparatus 430 according to the present invention comprises:
- a sanding group 11 for a coarse pre-coating sanding;
- a sanding group 12 (here in the shape of a sanding wheel) for a finer sanding;
- two vacuum coating heads 23, 23';
- one vacuum tower 14;
- two gelling groups 15, 15';
- a sanding group 22 placed immediately downstream the first gelling group 15, 15';
- two drying groups 16, 16';
- a belt sanding group 17;
- four sanding groups 18, 18', 18", 18'" for a coarse post-coating sanding;
- three sanding groups 19, 19', 19" for a finer post-coating sanding (sanding wheels);
- two corner sanding groups 20, 20', for sanding the head and the tail of panel 1, respectively;
- a sanding group 21 for the final sanding: this is a sanding group provided with a
belt with a particularly fine grain.
[0052] At a glance, it can be observed that the apparatus 430 according to the present invention
is shorter than the known art apparatus 410.
[0053] Figure 4 compares a known art apparatus 210 provided with two coating heads 13, 13'
and an apparatus 430 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 210 and the apparatus 430 according to the present
invention.
[0054] In the case of a panel requiring four applications of painting product, with the
apparatus 430 according to the present invention, the panel is conveyed just once
inside the apparatus. Instead, with the known art apparatus 210, the same panel must
be conveyed twice inside the apparatus 210: 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 430 according to the present invention.
[0055] Figure 5 compares a known art apparatus 310 provided with three coating heads 13,
13', 13" and an apparatus 430 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 310 and the apparatus 430 according
to the present invention.
[0056] The result obtained with the apparatus 310 and the apparatus 430 is not equivalent:
in fact, with the apparatus 310 three layers of painting product are applied, while
with the apparatus 430 four layers of painting product are applied. With a comparable
length of the two apparatuses, the qualitative result is better with the apparatus
430. Moreover, with the apparatus 430 a vacuum tower is dispensed with.
[0057] Figure 6 compares a known art apparatus 510 provided with five coating heads 13,
13', 13", 13"', 13"" according to the known art and an apparatus 530 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
510 and the apparatus 530 according to the present invention.
[0058] Figure 6 shows a particular embodiment, wherein each vacuum coating head 23, 23'
of the apparatus 30 is supplied by a respective vacuum tower 14, 14'. As explained
above, a vacuum tower 14 can supply two and even three vacuum coating heads 23, 23'.
In this case, though, there are provided two distinct vacuum towers 14, 14': the first
vacuum tower supplies a primer to the first vacuum coating head 23, while the second
vacuum tower 14' supplies a painting product to the second vacuum coating head 23'.
[0059] Figure 7 compares a known art apparatus 610 provided with six coating heads 13, 13',
13", 13'", 13"", 13ʺʺ′ according to the known art and an apparatus 630 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
610 and the apparatus 630 according to the present invention.
[0060] In the case of the apparatus 630 applying six layers of painting product, the second
gelling step is performed by just one gelling group 15" followed by a third application
of painting product performed by a third vacuum coating head 23". Finally, the last
gelling/drying step is performed by a gelling/drying group 16, 16'. Of course, this
apparatus is used for finishing of a particularly high quality.
[0061] Figures 2, 3, 6 and 7 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 1 to 5 metres.
[0062] The method according to the present invention comprises the following steps performed
by an apparatus 430:
- 1. sanding of the rough edge performed by the sanding groups 11 and 12 placed upstream
the vacuum head 23;
- 2. first application of painting product to the edge performed by the first vacuum
coating head 23;
- 3. gelling
performed by two gelling groups 15, 15', preferably comprising one or more gallium
lamps;
- 4. post-gelling sanding of the edge performed with sanding wheels, bands or any other
sanding system by the sanding group 22;
- 5. second application of painting product to the edge performed by the second vacuum
coating head 23'; the first vacuum coating head 23 and the second coating head 23'
are preferably supplied by just one vacuum tower 14;
- 6. drying
performed by the drying group 16, 16', preferably comprising one or more mercury lamps;
- 7. post-drying final sanding performed by a number of sanding groups 17, 18, 19, 20,
21 proportional to the desired quality of the finished panel.
[0063] 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 630:
- 1. sanding of the rough edge performed by the sanding groups 11 and 12 placed upstream
the vacuum head 23;
- 2. first application of painting product to the edge performed by the first vacuum
coating head 23;
- 3. first gelling
performed by at least one, preferably two gelling groups 15, 15';
- 4. post-gelling sanding of the edge performed with sanding wheels, bands or any other
sanding system by the sanding group 22;
- 5. second application of painting product to the edge performed by the second vacuum
coating head 23';
- 6. second gelling
performed by at least one gelling groups 15";
- 7. third application of painting product to the edge performed by the third vacuum
coating head 23";
- 8. drying
performed by the drying group 16, 16';
- 9. post-drying final sanding performed by a number of sanding groups 17, 18, 19, 20,
21 proportional to the desired quality of the finished panel.
[0064] It is worth mentioning that in the apparatuses *30 according to the present invention,
the gallium lamp in the gelling group 15, 15' are set on 80 W/cm, the gallium lamps
in the gelling group 16 are set on 60-65 W/cm, while the mercury lamps in the drying
group 16' are set on 120-150 W/cm. These power levels, too, contribute to the reduced
energy consumption with respect to the known art apparatuses.
[0065] Alternatively, in lieu of the gallium and mercury lamps, LED lamps ranging 8 W up
to 20 W can be used. In this case, indicatively, for gelling steps 20 W LED lamps
are set on 10-12 W/cm
2, while for drying steps 20 W LED lamps are set on 18-20 W/cm
2.
[0066] The sanding group 22 is preferably provided in the form of a sanding wheel with a
cloth Trizact
© 3M
®, comprising a ceramic abrasive material supported by a polyester cloth.
[0067] The sanding performed by the sanding group 22, placed between the application of
the first two layers of painting product applied by the first vacuum coating head
23, and the application of the second two layers of painting product applied by the
second vacuum head 23', 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 23' allows to obtain a perfectly smooth surface.
[0068] Figures 8A, 8B show a vacuum head 23 that is advantageously comprised inside the
apparatuses *30 according to the present invention. Said vacuum head allows to maximize
the advantages applying the method according to the present invention.
[0069] Said vacuum coating head 23 comprises:
- a pair of bores 50 for fixing said head to a support allowing to connect said head
to the apparatus 430;
- a first dispensing nozzle 51 for dispensing a painting product;
- a first suction nozzle 52 for suctioning said painting product;
- an optional screed 53;
- a second dispensing nozzle 55 for dispensing said painting product;
- a second suction nozzle 56 for suctioning said painting product.
[0070] In the preferred embodiment, between the first suction nozzle 52 for suctioning a
painting product and the second dispensing nozzle 55 for dispensing a painting product,
there is provided a screed 53 protruding with respect to the profile of the vacuum
coating head for a length ranging 0,1 to 0,5 mm. This minimal protrusion, difficult
to be appreciated in the Figures, allows the screed 53 to perform two actions:
- pressing the applied painting product inside wood pores;
- pressing the wooden fibres raised by the suction generated by the first suction nozzle
52.
[0071] 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).
[0072] Nowadays, with 3D printing, pieces provided with internal cavities can be produced
through additive manufacturing; therefore, the vacuum head 23 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.
[0073] It is worth noting that the vacuum coating head 23, provided with two dispensing
nozzles 51, 55 in fact applies two layers of painting product with respect to the
vacuum known art coating head 13, which is provided with just one dispensing nozzle.
The application of painting product by the second dispensing nozzle 55 on the first
layer of painting product dispensed by the first dispensing nozzle 51 is in fact a
wet-on-wet application, as the gelling group 15 is placed downstream each vacuum coating
head 23.
[0074] The skilled man has the entrenched prejudice that by gelling the applied layer before
applying the second layer of painting product a better result will be obtained, due
to the better adhesion of the successive layer of painting product on a dried or at
least gelled layer. Surprisingly, it was observed that the presence of the screed
compensates for the lack of gelation, and it presses the wood fibres raised by the
first suction nozzle 52. This overall allows to provide a higher quantity of painting
product on the panel 1 with respect to the usual coating method (application of painting
product - gelation - successive application of painting product).
- 1
- panel
- 2
- undercut edge
- 3
- Jpull edge
- 4
- radius edge
- 11
- coarse sanding group
- 12
- sanding group
- 13
- vacuum coating head
- 14
- vacuum tower
- 15
- gelling group
- 16
- drying group
- 17
- band sanding group
- 18
- coarse sanding group
- 19
- fine sanding group
- 20
- corner sanding group
- 21
- final sanding group
- 22
- sanding group
- 23
- vacuum coating head
- 50
- bore
- 51
- first dispensing nozzle
- 52
- first suction nozzle
- 53
- screed
- 55
- second dispensing nozzle
- 56
- second suction nozzle
- 57
- bore
- 58
- bore
- 210
- known art apparatus with two coating heads
- 310
- known art apparatus with three coating heads
- 410
- known art apparatus with four coating heads
- 430
- apparatus according to the present invention with four applications of painting product
- 510
- known art apparatus with five coating heads
- 530
- apparatus according to the present invention with four applications of painting product
- 610
- known art apparatus with six coating heads
- 630
- apparatus according to the present invention with six applications of painting product
1. Method for applying a painting product, preferably an UV painting product, to an edge
of wooden panels (1) through an apparatus comprising pre-coating sanding groups (11,
12) and post-drying sanding groups (17, 18, 19, 20, 21), at least a painting group
provided in the form of a vacuum coating head (23) supplied with both said painting
product and vacuum by a vacuum tower (14), at least a gelling group (15), at least
a drying group (16) placed in series comprising the following successive steps:
1. sanding of the rough edge;
2. first application of painting product to the edge;
3. first gelling;
4. post-gelling sanding of the edge;
5. second application of said painting product to the edge;
6. drying;
7. final post-drying sanding;
characterized in that
- in each one of steps 2 and 5, 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 4, the post-gelling sanding occurs on a layer of painting product that underwent
gelation only.
2. Method for applying a painting product, preferably an UV painting product, to an edge
of wooden panels (1) through a vacuum coating head (23) according to claim 1, wherein
for a superior quality of the finished panel a further application of painting product
is provided, according to the following successive steps:
1. sanding of the rough edge;
2. first application of painting product to the edge;
3. first gelling;
4. post-gelling sanding of the edge;
5. second application of painting product to the edge;
6. second gelling;
7. third application of painting product to the edge;
8. drying;
9. post-drying sanding.
3. Method for applying a painting product, preferably an UV painting product, to an edge
of wooden panels (1) through a vacuum coating head (23) according to claim 1 or 2,
wherein said wet-on-wet applications of painting product occurs through a vacuum coating
head (23) provided at least with two nozzles (51, 55) for applying said painting product.
4. Apparatus (430, 530, 630) for performing the method according to claims 1-3 for applying
a painting product, preferably an UV painting product, to an edge of wooden panels
(1), said apparatus comprising in that order:
1. first sanding groups (11, 12) placed upstream the first vacuum head (23);
2. first coating head (23) for applying a painting product to the panel edge, applying
two wet on wet layers of the painting product in a close succession;
3. at least one, preferably two gelling groups (15, 15'), preferably comprising one
or more gallium lamps;
4. post-gelling sanding group (22) of the edge, preferably in the form of sanding
wheels, bands;
5. second vacuum coating head (23') for applying a painting product to the edge, applying
two wet on wet layers of the painting product in a close succession:
6. at least a drying group (16, 16');
7. post-drying final sanding groups (17, 18, 19, 20, 21) in a number proportional
to the desired quality of the finished panel.
5. Apparatus (630) for applying a painting product, preferably an UV painting product,
to an edge of wooden panels (1) according to claim 4 comprising in that order:
1. first sanding groups (11, 12) placed upstream the first vacuum head (23);
2. first vacuum coating head (23) for applying a painting product to the panel edge,
applying two wet on wet layers of the painting product in a close succession;
3. at least one first, preferably two gelling groups (15, 15');
4. post-gelling sanding group (22), preferably in the form of sanding wheels, bands;
5. second vacuum coating head (23') for applying a painting product to the panel edge,
applying two wet on wet layers of the painting product in a close succession;
6. at least one second gelling group (15");
7. third vacuum coating head (23") for applying a painting product to the panel edge,
applying two wet on wet layers of the painting product in a close succession;
8. at least a drying group (16, 16');
9. post-drying final sanding groups (17, 18, 19, 20, 21) in a number proportional
to the desired quality of the finished panel.
6. Apparatus (430, 530, 630) according to claim 4 or 5, wherein each vacuum tower (14)
supplies one, preferably two or three vacuum coating heads (23, 23', 23").
7. Apparatus (430, 530, 630) according to one or more of claims 4-6, wherein when the
painting products to be applied to an edge are more than one, there is provided a
number of vacuum towers (14) equal to the number of painting products used in the
coating process.
8. Apparatus (430, 530, 630) according to one or more of claims 4-7, wherein the lamps
in said gelling groups (15) are gallium lamps, preferably set at 60-80 W/cm, or LED
lamps preferably set at 10-12 W/cm2.
9. Apparatus (430, 530, 630) according to one or more of claims 4-7, wherein the lamps
in said drying groups (16, 16') are gallium lamps or mercury lamps preferably set
at 120-150 W/cm or alternatively LED lamps preferably set at 18-20 W/cm2.