Note: Descriptions are shown in the official language in which they were submitted.
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=
Panel made of a wooden material with a surface coating
Wood materials which are processed to panels are
generally surface-coated. It is only the surface
coating that gives rise to the actual utility of the
panels, since it imparts decorative properties, water
resistance, abrasion resistance, chemical resistance,
if appropriate resistance toward algae, fungi and/or
insects. The surface coating is typically effected by a
coating of the panel with a synthetic resin-impregnated
decorative paper.
Alternatives to coating with decorative paper have been
described, for example in AT 351 744, but these
coatings have not become established in practice.
AT 351 744 describes the varnishing of a chipboard, a
first varnish application being referred to as priming.
The primer is applied on both surfaces, top side and
bottom side of the chipboard. A second varnish
application follows. The second varnish layer is
applied on one side, only to the top side of the
chipboard. The varnish application is from at least 50
to 500 g/m2. The process proposed here dispenses with
decorative paper. The aim is the saving of expensive
plant parts such as presses. However, the synthetic
resin proposed here predominantly for the varnish
layers is melamine, one of the most expensive varnish
components. The product proposed in AT 351 744 has not
become established in industry, for reasons including
cost. The application of the varnish has also been
found to be problematic, since it was considered to be
necessary to apply thick varnish coats on the
assumption that an appropriate, maximum layer thickness
is required to achieve the desired durability. However,
the application and curing of thick varnish layers is
technically complicated and hence costly.
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The application of visually satisfactory varnish layers
has to date entailed the provision of abrasive layers
in the varnish structure, which, after the application
and curing of a first varnish layer, cover this first
varnish layer. The abrasive layers are in each case
sanded off again largely or completely in order to
obtain a smooth substrate for the next varnish layer.
This multilayer method with intermediate sanding is
required to obtain visually appealing varnish layers.
The application of UV-curable varnishes provides a
remedy here. One example of the use of UV-curable
varnishes is shown by US 4 439 480. However, up to now
an intermediate sanding-off is also preferred when UV-
curable varnishes are used, especially - as described
in US 6,475,623 - where multi-layered and relatively
thick surface coatings are employed.
The use of decorative paper is also costly and entails
disadvantages; especially the shrinkage of the
decorative paper in the course of curing is considered
to be disadvantageous, since the prevention of warpage
of the panels associated with the shrinkage is
complicated.
Disregarding the surface coating of a wood material
panel with which simple utility can be established,
there is increasing demand for surface finishes which
meet particular demands, such as abrasion resistance,
sound and footfall deadening, complicated coloring,
particular thermal conductivity or electrical conduc-
tivity or discharge capacity and the like. The
adaptation of the wood material panels to such demands
is of particular significance for the complete coverage
of the market.
There is therefore a need for a panel made from wood
material and having a surface coating, especially a
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surface coating which includes at least one functional layer,
the surface coating being applicable in an inexpensive and
simple manner. Also proposed is a process for coating wood
materials and an apparatus therefor.
In a simple embodiment of the invention, the panel made from
wood material is coated with a primer and, atop it, with
at least two varnish layers. However, it has been found to be
sufficient for the achievement of strength and wear properties
suitable for use only to apply very little varnish. The
application of varnish, the coating thickness, is in total less
than 120 pm, preferably less than 80 pm, more preferably less
than 60 pm, advantageously less than 45 pm, more advantageously
less than 30 pm.
In one product aspect, the invention relates to a panel made
from a wood material and having a surface coating, comprising:
a primer applied to the wood material; at least one varnish
layer comprising corundum, wherein said at least one varnish
layer is not an outer varnish layer and is cured by means of
UV light or electron beam curing (EBC); and at least one other
varnish layer, wherein the total layer thickness of the at
least two varnish layers is less than 120 pm, and wherein at
least one functional component is provided which is applied as
an outer functional layer, or as a functional layer arranged
between said at least two varnish layers, wherein: the at least
one functional component applied is at least one layer of matt
varnish which covers a section of the surface of the panel, and
the at least one other varnish layer is a gloss varnish,
respectively, or the at least one functional component has at
least one first layer which covers a section of the surface of
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the panel and which repels a color-imparting coating, and at
least one second layer which consists of a color-imparting
coating which covers a section of the surface of the panel.
In one process aspect, the invention relates to a process for
coating a wood material, in which at least two layers of
varnish which cure by means of UV light are applied, the
applied varnish being exposed to UV light after application of
the first varnish layer, so that the first varnish layer begins
to cure, and at least the second layer of varnish being applied
before the first varnish layer is cured completely, and the
complete curing of the at least two varnish layers applied
being effected by means of UV light only after application of a
last layer of varnish, the first varnish layer comprising
corundum, wherein: at least one functional component is
provided which is applied as an outer functional layer, or as a
functional layer arranged between said at least two varnish
layers, and wherein: the at least one functional component
applied is at least one layer of matt varnish which covers a
section of the surface of the wood material, and at least the
second varnish layer being a gloss varnish, respectively, or
the at least one functional component comprises at least one
first layer which covers a section of the surface of the wood
material and which repels a color-imparting coating, and at
least one second layer which consists of a color-imparting
coating which covers a section of the surface of the wood
material.
In a further process aspect, the invention relates to a process
for coating wood material in which at least two layers of
varnish which cure by means of UV light are applied, the
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applied varnish being exposed to UV light after application of
the first varnish layer, so that the varnish begins to cure,
and at least the second layer of varnish being applied before
the first varnish layer is cured completely, and the complete
curing of the at least two varnish layers applied being
effected by means of UV light only after application of the
last layer of varnish, the first varnish layer comprising
corundum, wherein the at least two layers of varnish comprise
at least one functional component which is selected from the
group consisting of: an elastomer; a UV light-absorbing
=
substance; a UV light-reflecting substance, a
UV light-absorbing body; a UV light-reflecting body; a
flame-retardant substance; a substance which increases the fire
resistance of the wood material; a substance for adjusting the
sliding resistance of the surface of the wood material; a
substance for adjusting the tactile properties of the surface
of the wood material; a mixture of substances for adjusting the
sliding resistance of the surface of the wood material; a
mixture of substances for adjusting the tactile properties of
the surface of the wood material; a substance for adjusting the
gloss of the surface of the wood material; carbon black;
surfactants; grids made from conductive substances; and at
least one color layer.
=
In a further product aspect, the invention relates to a panel
made from a wood material and having a surface coating,
comprising: a primer applied to the wood material; at least
one varnish layer comprising corundum, wherein said at least
one varnish layer is not an outer varnish layer and is cured by
means of UV light or electron beam curing (EBC); and at least
one other varnish layer, wherein the total layer thickness of
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the at least two varnish layers is less than 120 pm, and
wherein at least one functional component is provided which is
applied as an outer functional layer, or as a functional layer
arranged between said at least two varnish layers, wherein:
the at least one functional component applied is at least one
layer of matt varnish which covers a section of the surface of
the panel, and the at least one other varnish layer is a gloss
varnish, respectively, or the at least one functional component
has at least one first layer which covers a section of the
surface of the panel and which repels a color-imparting
coating, and at least one second layer which consists of a
color-imparting coating which covers a section of the surface
of the panel, or the at least one functional component applied
is at least one of the following substances: a substance for
adjusting the sliding resistance of the surface of the wood
material; a substance for adjusting the tactile properties of
the surface of the wood material; a mixture of substances for
adjusting the sliding resistance of the surface of the wood
material; and a mixture of substances for adjusting the tactile
properties of the surface of the wood material.
The introduction of corundum with the varnish, when using
panels according to the invention, also increases the abrasion
resistance, which is an essential parameter' for defining the
use classes according to DIN EN 13329. At the most a finer
grain size of the corundum has to be chosen for the adaption to
the thinner varnish layer. Corundum is introduced as an outer
varnish layer. The one further varnish layer, which is
appliedfunctional component into a varnish layer, which is not
the according to the invention, does not contain corundum.
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Furthermore the surface coating shows at least one further
functional component.
The varnish, which essentially determines the use properties of
the panel, is applied in two or more layers. The above-
specified layer thickness of up to 120 pm in total is not
exceeded. This measure significantly improves the surface
coating of the panel. In the case of application of a
plurality of thin layers, for example, unlike in the
prior art, no
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undesired structure is depicted in the surface, i.e. no
roller structure when the varnish is applied by means
of a roller. Moreover, undesired changes in the
appearance of the varnish layer are prevented, which
can barely be avoided in the case of application of
thick varnish layers. In addition, the application of a
plurality of thin varnish layers improves the
stressability and the durability of the varnish layer
overall; the coating becomes harder-wearing. In the
context of this invention, a thin varnish layer is
understood to mean a varnish layer of up to 20 pm,
preferably of up to 15 pm, advantageously of up to
10 pm.
In a particularly preferred embodiment of the
invention, the at least two thin varnish layers, in the
case of use of UV-curing varnishes, are applied in such
a way that, in each case, an already applied layer is
partially gelled, and then the next layer is applied.
Apart from the rapid application of the thin varnish
layers, it is possible to dispense with the application
of an abrasive layer and the subsequent abrasion of the
individual varnish layers before the application of the
next layer in each case, because the individual layers
are thin and - if appropriate as a result of partial
gelling - can be applied sufficiently smoothly. The
quality, especially the smoothness, of the thin varnish
layer also satisfies high visual and mechanical quality
demands.
The varnish layer applied in a thin layer in accordance
with the invention can - depending on the selection of
the varnish - be cured completely or reacted completely
with ultraviolet light (UV light) or by electron beam
curing EBC; the latter can also be employed without use
of photoinitiators.
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According to the invention, the surface coating has at
least one functional component which is integrated in
one of the at least two varnish layers, or which may be
applied as the outer layer or under the at least two
varnish layers or as a layer arranged between the at
least two varnish layers. What should be emphasized is
that at least one functional component bonds
efficiently to the material of the varnish layer. When
the at least one functional component is applied as a
layer, the at least one functional layer binds
efficiently with the varnish layer(s). UV-curing
varnishes are surprisingly extremely tolerant toward
functional components. The curing and buildup of a
homogeneous surface coating, in spite of different
combinations of functional components and layers of
varnish and other substances, is readily possible in
accordance with the invention. Thus, as one and the
same functional components or layers can be integrated
in one or more layers into the surface coating, the
surface coating may also have two or more different
functional components or layers. By way of example,
mention is made only of a layer for footfall deadening
and a layer for improving the fire resistance, or two
color-imparting layers and one layer of varnish to
which a functional component is added to adjust the
absorption of UV light.
The functional component is in many cases incorporated
into one of the at least two varnish layers, especially
when this layer forms the outer layer af the surface
coating. For example, the scratch resistance, the
abrasion, the gloss, but also properties such as
antibacterial action or associated properties, of the
panel are determined both by selection of the suitable
UV- or radiation-curing varnish and by selection of
suitable functional components, for example nanosilver
to obtain antibacterial action or the addition of
conductive substances to ensure a given discharge
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capacity, but also addition of corundum to adjust the
abrasion.
A main field of use for panels, in addition to the use
as a roof or wall covering or worktop, is also use as a
floor covering. The suitability as a floor covering
depends essentially upon whether the surface of the
panel is sufficiently resistant toward the abrasion
caused by walking on the floor and attrition by
wheelchairs and other objects. In order that the use
W parameters such as abrasion properties, wheelchair
resistance, stain insensitivity and the like of panels
become comparable, EN 13329 lays down use classes for
laminate, i.e. for wood material panels which are
provided with a surface coating of decorative paper.
The use classes differ between the use of the panels
for living purposes and for commercial purposes. The
suitability as a worktop, for example in laboratories
or workshops, requires exceptional wear resistance,
which is tested by special tests, especially by EN 310,
319, 323, 324-1, 438 with requirements for abrasion,
scratch resistance, susceptibility to cracking,
lightfastness, stain insensitivity and behavior toward
steam, pan bottoms and lit cigarettes, and also
prEN 717 and DIN 52612.
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In the case of the panels of the invention, especially the
floor panels, but also in the case of worktops, the decorative
paper is specifically dispensed with in connection with the
surface coating. This is replaced by the extremely low varnish
application. In spite of the low varnish application, the
panels of the invention, using EN 13329, are attributable to
use classes which in any case meet the stress demands of living
spaces. The product of the invention is tested and evaluated
with the same testing methods that DIN EN 13329 provides for
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laminate. For example, in the case of panels which have
been provided with the inventive thin varnish layer,
according to EN 13329, the rating "Use class 31"
(commercial sector) is achieved when corundum has been
embedded into one first thin varnish layer, which does
not lie outside. This is considered to be an
exceptional economic advantage, since high resistance
against abrasion is achieved with minimal use of
varnish. Equally, the inventive surface coating
achieves the high demands of the standards which are
prescribed, for example, for worktops.
In a particularly advantageous embodiment of the
invention, at least one functional layer, which need
not, however, be on the surface of the coated panel,
consists of an elastomer. Especially ethylene-vinyl
acetate (EVA) or other suitable polyolefins or polymer
mixtures which comprise EVA or at least one other
polyolefin, but also polyurethanes, especially
thermoplastic polyurethanes (TPUs), are suitable for
this purpose. The elastic properties of these materials
improve the room acoustics properties, but also the
sound-deadening properties of the panel, to a great
extent. Especially the improved footfall deadening by
the use of EVA should be emphasized. In the case of
floor panels, especially in the case of elastomers
which are applied with relatively high layer thickness
(e.g. 5 mm and more), a damping effect on the joints of
people who walk on these floor panels is also
detectable. Panels provided in this way with functional
components and layers are suitable in particular for
sports halls. The sound-deadening properties are
particularly effective, for example, in the case of
wall or roof panels which have an enlarged surface
area. The elastomer is applied in a layer thickness of
from 0.1 mm up to 10 mm. Even a single layer of an
elastomer makes =a substantial contribution to the
deadening of footfall. However, it is also possible to
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arrange a plurality of layers which are optionally
separated by varnish layers or other functional layers.
The binding between primer, elastomer and varnish layer
is good. It even withstands high stresses, for example
those in commercial use.
The application of various UV-curing varnishes can be
utilized particularly advantageously to apply different
varnishes, especially matt varnishes and gloss
varnishes, in layers, these layers each covering
sections of the surface of the panel. Matt varnish is
applied in sections as a functional layer. In addition,
a varnish layer of gloss varnish is applied. Even this
simple two-layer surface coating enables optical
effects. In a preferred development of the invention,
the layer sequence of layers of matt varnish and gloss
varnish is arranged so as to form visually perceptible
structures. These structures are notable in that
viewers perceive three-dimensional patterns. These
patterns of three-dimensional appearance consist of a
sequence of gloss varnish and matt varnish layers and
can be used to create imaginative decorations, but also
to simulate natural decorations. What should be thought
of here is in particular the simulation of pore
structures.
An alternative to the production of visually
perceptible structures can likewise, in accordance with
the invention, be implemented by the introduction of at
least two functional layers. A first functional layer,
which covers sections of the surface of the panel and
repels a color-imparting coating, and at least one
second layer which consists of a color-imparting
coating which covers sections of the surface of the
panel. For example, a first functional layer comprising
waxes or oils can be applied in sections and prevents
the attachment of dye or of a coloi-imparting coating
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onto the surface of the wood material. In this way,
visually perceptible structures are obtained.
The above-described embodiments of panels made from
wood material with visually perceptible structures by
application of one functional layer or of at least two
functional layers preferably have surface coatings in
which at least one functional layer is covered by at
least one varnish layer.
In a preferred embodiment of the inventive panel, the
functional component used is a UV light-absorbing
substance. A typical possibility is that of bodies or
substances having dimensions in the nano range, i.e.
with dimensions up to 950 nm. UV light-absorbing
substances or compounds are usually metal compounds,
especially metal oxides such as zinc oxide, which are
known to reflect or absorb UV light. This substance
preferably is or appears to be transparent. It is also
preferred when this functional component is used in the
final varnish layer, or arranged at or close to the
surface of the surface coating. It displays exceptional
protective action when it is applied above color-
imparting coatings or coatings which can be altered by
UV light.
A further advantageous embodiment of the inventive
panel envisages that the functional component used is a
flame-retardant substance or a substance which
increases the fire resistanCe of the wood Material.
Flame-retardant substances or substances which improve
the fire resistance are known per se. These include,
for example, waterglass or other inorganic substances
such as vermiculites. Preference is also given here to
using transparent substances.
The functional component used is preferably also a
substance or a mixture of substances with which the
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sliding resistance of the surface of the wood material
can be adjusted. Typical substances are wax or oils or
mixtures thereof, but also mineral substances,
especially fine sand. This functional layer is
preferably arranged as the outer layer of the surface.
It is also advantageous to introduce at least one
functional component with which the tactile properties
of the surface of the wood material or of the coated
panel can be adjusted into the surface coating of a
panel. Here too, waxes, oils or mixtures thereof and
mineral substances, for example fine sand, which are
used as so-called matting agents, are suitable for
imparting a velvety feel to the surface of the panel.
This functional component may be applied as the
external layer of the surface coating. It may also be
arranged within the layer structure, since the surface
coating overall is generally sufficiently thin that,
for example, even layers arranged between the varnish
layers are active in adjusting the tactile properties.
Especially in conjunction with color-imparting layers,
the functional component used is a topcoat varnish with
defined gloss, which influences the gloss of the
surface coating or of the surface of the panel.
The invention also encompasses a panel in which the
invention provides that the functional layer applied is
a substance with which the antistatic properties of the
surface of the wood material can be adjusted. The
antistatic properties of the surface of the wood
material can be adjusted by adding carbon black,
although the coloring is greatly restricted.
Alternatively, surfactants may be added as the
functional component in order to promote water
absorption into the varnish. Finally, it is possible to
use conductive fabrics, which in turn impairs the
appearance of the surface. It is particularly preferred
in the context of the invention to use transparent
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conductive particles as the functional component or
layer. It has been found that a single layer of
synthetic resin or varnish admixed with small amounts
of the particles mentioned is sufficient to ensure a
significant improvement in the discharge capacity in a
permanent manner independent of further parameters such
as ambient moisture, for example to provide a surface
for a floor capable of discharge according to DIN
IEC 61 340.
Transparent conductive particles are obtained, for
example, by applying metal oxides to support particles.
For example, a mica particle which has been doped with
tin oxide and antimony oxide is suitable. Transparent
particles may be of platelet or spherical shape. Good
conductivity and transparency and also optimal
discharge capacity is achieved with particles with a
diameter of up to 25 pm, preferably up to 15 pm,
preferentially up to 10 pm.
According to the invention, it is sufficient when the
electrically conductive, transparent particle is
present in only one layer of a multilayer synthetic
resin structure on an overlay or a wood material panel.
According to the invention, up to 15% by weight of
electrically conductive transparent particles based on
the solids content of the synthetic resin are
sufficient; preference is given to using up to 10% by
weight, particular preference to using up to 8% by
= 30 weight, of particles based on the solids content of the
synthetic resin.
A surface capable of discharge on an overlay or a wood
material panel is formed when at least one layer, i.e.
up to 40 g/m2 of a synthetic resin admixed with
transparent conductive particles in accordance with the
=
invention, is applied. In a preferred embodiment, up to
25 g/m2, more preferably up to 15 g/m2, advantageously
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up to 10 g/m2, is sufficient. The layer structure of
the particular surface may overall quite possibly be
over 100 g/m2 in a multilayer structure. In spite of
this, only one layer of the synthetic resin admixed
with particles in accordance with the invention is
sufficient to obtain a surface which has significantly
improved discharge capacity.
The surface coating of the panel may, in an advan-
tageous embodiment of the invention, after the
application and curing of the varnish, also be provided
with a plastic deformation. In this case, relief-like
embossments which are permanent are introduced into the
partially gelled or cured surface coating under
pressure and if appropriate at elevated temperatures.
Surprisingly, it has been found that the surface of a
surface-coated material is indeed still plastically
deformable without the surface coating being subject to
damage. The sealing does not flake off, does not break,
and takes on deformations of a depth suitable for the
simulation of natural materials. The embossment can
thus achieve the perception of the surface of a
surface-coated material as a close simulation of
natural substances, since touching the surface imparts
exactly the structure which is known from natural
substances. This perception is promoted in most cases
by a coordinated color design. For example, a wood
material panel can simulate particular wood types by
virtue of a single-layer or multilayer color
application. The plastically deformed surface of the
sealed panel then complements the pore structure
familiar from the preconception of real wood.
In a simple embodiment of the inventive panel, the at
least two varnish layers are applied directly to the
primer. In industry, such a surface coating is entirely
capable of functioning, but very rarely satisfies
esthetic demands. Therefore, in a preferred embodiment
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of the invention, at least one layer, typically at
least two layers, of dye are applied as a functional
layer between primer and varnish layer. If required, in
conjunction with the dye application, it is also
possible to apply adhesion promoters or filler coats to
the primer, in order to improve the substrate for the
dye application.
The dye generally adheres very well on the primer. The
adhesion of the varnish on the dye can be improved - if
necessary - in a particularly preferred embodiment of
the invention by adding at least 5% by weight of
varnish to the dye before it is applied. If
appropriate, the varnish can be added only to
individual dye layers or to all dye layers when more
than one dye layer is applied.
Especially when dye layers are applied, the combination
of two different functional layers in the buildup of
the surface coating is obvious. However, it is pointed
out explicitly once again that the above-described
functional components may either be provided repeatedly
in the buildup of the surface coating or that different
functional components (two or more) may be combined
within one surface coating.
It is considered to be an independent inventive step
that a panel made from wood material whose one side
intended for use, for example for walking or working
on, is provided with a surface coating, and the
opposite side, usually referred to as the underside, is,
coated with varnish at least in sections. This varnish
applied at least in sections replaces the papers or
veneers which have been customary to date for use as a
backing layer. A backing layer is required in order to
compensate for the forces occurring in conjunction with
the surface coating, -especially shrink stresses which
occur in the course of drying or curing of the surface
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coating. It has been found that, surprisingly, in the
case of the particularly thin surface coating which is
applied to panels of the invention in particular,
even a varnish layer applied at least to sections of
the underside of the panel is sufficient to compensate
for the stress generated by the surface coating, so
that the ready-coated panel, after the curing of all
coating operations on topside and underside, is not
warped.
The varnish can be applied on the underside of the
panel in very small amounts. Sufficient amounts are up
to 120 g/m2, preferably up to 80 g/m2, more preferably
up to 60 g/m2, advantageously up to 45 g/m2, preferably
up to 30 g/m2. Specifically in the case of small
applications, it may be that a continuous varnish layer
is not formed. In this case, a continuous varnish layer
is not important; instead, the important factor is the
shrinkage that the varnish applied to the underside
develops in the course of curing. Known and available
varnishes shrink to very different degrees within a
wide range in the course of application and curing on
wood materials. According to the invention, a varnish
whose shrinkage is suitable to compensate for the
deformation that the particular surface coating
generates is selected. The forces which arise can also
be calculated, but it has been found to be simpler to
determine the varnish suitable for the underside of the
panel by simple tests.
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The varnish applied to the underside may be selected as
desired. It may be a solvent- or water-based varnish which
dries or cures under the action of heat. However, it may also
be a varnish which cures by means of UV light or electron beam
curing.
It is also considered to be an independent inventive step to
propose an apparatus with which the inventive
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panel can be produced. This apparatus for the coating,
especially varnishing, of panels has means of conveying
panels to a processing unit and away from a processing
unit, and means for applying a coating, especially a
varnish coat, and means of partly or completely curing
a coating, especially a varnish coat, the means for
applying a coating and the means for partly or
completely curing a coating being combined to one
processing unit by virtue of them being arranged in
immediate succession. According to the invention, at
least two processing units are provided.
In comparison to the prior art, the processing units
arc very compact, since apparatus for the sanding of
varnish layers can be dispensed with. The immediately
successive arrangement sequence of the means for the
application of coatings, generally of rollers which
apply varnish to the surface of the panel, and of means
for partly or completely curing these layers enables
the application of the coating to be closely adjusted
to its fixing. Regularly, coatings of the surface of a
panel also require fixing, usually referred to as
curing or reaction. As described in connection with the
inventive panel, it may also be partial curing or
reaction. A typical use of the means for curing is
considered to be the partial gelling of UV-curing
varnishes which have been applied immediately
beforehand to the surface of a panel. Only after the
application of the final varnish layer are the means
for curing- used in such a way that the coating overall'
is cured. Means of curing are therefore preferably
designed as UV light-emitting apparatus or as apparatus
for electron beam curing, but they may also be known
apparatus in which the curing is effected by supplying
heat.
The partial gelling of the lower varnish layers to
which further varnish layers are applied is found to be
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required to enable the application of further coatings.
Without the partial gelling, downstream means of
applying further coatings would not be able to deposit
the material to be applied correctly onto the layers
already applied.
According to the invention, at least two of these
processing units are provided; preference is given to
the arrangement of at least three processing units, for
example for the application of a two-layer undercoat
system or of an undercoat and of a functional layer,
for example a layer of an elastic polymer material with
low Shore hardness, and a layer of a topcoat.
Owing to the compact design of the inventive apparatus
and the few means or units required for the coating, it
has been found that the achievable operating speeds are
exceptionally high. The inventive apparatus can be
designed for operating speeds of at least 35 m/min,
preferably at least 50 m/min, more preferably at least
70 m/min.
Details of the invention are explained in detail below
using the example of working examples:
Example 1
A commercial primer is rolled onto a hardboard panel.
The application rate is approx. 14 g/m2. This primer
levels out unevenness, smoothes fibers and improves the
water-repellent properties of the hardboard -panel. The =
primer is essentially an aliphatic polyurethane
dispersion (from 80 to 90% by weight) which is applied
to the hardboard panel in conjunction with an acrylate
copolymer emulsion (between 10 and 15% by weight) and
small proportions of water (below 2% by weight) and
customary additives for stabil4.zation and defoaming
(between 2 and 5% by weight).
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A first and a second varnish layer are then applied to
the dried primer. In each case 30 g/m2 of a varnish
which cures under UV light are initially applied, then
the curing is induced under the action of UV light but
not completed. The second varnish layer is then applied
to the partially cured first varnish layer. This
varnish layer too is exposed to UV light but not
completely cured. Corundum is added to each of the
first two varnish layers. The varnish has the following
composition: the content of corundum is from 20 to 25%
by weight. An aliphatic polyurethane acrylate makes up
from 15 to 25% by weight. From 45 to 55% by weight are
made up by a high-functionality aliphatic polyester
acrylate. From 2 to 10% by weight is contributed by
additives which serve, for example, tor defoaming, for
stabilization of the varnish, for more rapid curing or
for prevention of discoloration of the varnish.
Varnishes of this composition are commercially
available.
Finally, a UV-curing topcoat is applied at 12 g/m2 to
these first two varnish layers. The UV light which is
then used finally cures all three applied varnish
layers through, which is possible without any further
measures owing to the low application rates overall.
The topcoat has such a composition that aliphatic high-
functionality polyester acrylate makes up from approx.
to 50% by weight, aliphatic polyurethane acrylate
approx. 15-25% by weight, monomers are added at from 5
30 to 15% by weight, silicatic constituents make up from
approx. 5 to 20% by weight, and additives are added in
amounts of from 10 to 25% by weight. These varnishes
too are commercially available.
This way of applying the varnish ensures a particularly
durable surface coating. The panels obtained in the
hardboard panel thus coated are suitable for use as a
floor covering. With an abrasion of 2400, they are
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attributable to abrasion class AC 3 and hence to use
class 31 (commercial use) according to EN 13329.
The above-described coating of the panel is effected by
means of roller coating. Both the primer and the
varnish layers are applied with a roller. The rollers
which apply the varnish layers are each part of a
processing unit to which, in addition to the rollers, a
UV light unit for the partial gelling and curing of the
varnish is also assigned. The first two processing
units are designed in such a way that the means of
application, the UV light units, only partially gel the
varnish layer applied. It is only the UV light unit of
the third processing unit that brings about complete
curing of the applied varnish layers. The inventive
apparatus may, depending on the type of coating to be
applied, be adjusted to operating speeds of 45 m/min or
of 55 m/min.
Example 2
A primer (14 g/m2) is applied to a high-density fiber-
board (HDF) which is 7 mm thick. Thermoplastic
polyurethane (TPU) dyed in a light wood color is
applied to the primer in a layer thickness of 0.2 mm. A
color print is applied to the TPU, with which simulated
wood is obtained on the light wood-colored substrate
of the TPU. UV-curing varnish is applied thereon in a
layer thickness of 30 pm. Alternatively, three layers
of UV-curing varnish are applied in a layer thickness
of in each case 15 pm.
The HDF panel provided with three layers of UV varnish
fulfills the prerequisites for a commercially usable
floor according to EN 13329 for use class 32.
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