METHOD FOR COATING UNEVEN SUBSTRATES WITH THIN COATING MATERIALS AND A LAYER SUPPORT PRODUCED ACCORDING THERETO

PROCEDE POUR RECOUVRIR DES SUPPORTS NON PLANS AVEC DES MATERIAUX DE REVETEMENT DE FAIBLE EPAISSEUR ET SUPPORT AINSI REVETU

English Abstract

The invention relates to a method for coating uneven substrates, particularly
timber product surfaces, with thin coating materials to form an even and
uniformly smooth surface, whereby the support and the coating constituents are
pressed against a smooth metal sheet, laminating rolls, structured strips or
the like, and relates to layer supports comprised of a supporting material and
of a coating material. The aim of the invention is to also be able to reliably
and economically smooth materials that have uneven surfaces. To this end, a
top layer film and an adhesive system serve as the coating material, whereby
the adhesive system, during coating, gives the top layer film properties that
fill and span flaws in the material to be coated by means of chemical/physical
reactions. In a corresponding layer support, the coating materials comprise an
adhesive system and a top layer film, whereby the adhesive system contains
fillers that, during coating, fill and span flaws of the material to be coated
by means of chemical/physical reactions.

French Abstract

L'invention concerne un procédé pour recouvrir des supports non plans, notamment des surfaces constituées de matériaux dérivés du bois, avec des matériaux de revêtement de faible épaisseur afin de former une surface plane et lisse. Selon l'invention, le support et les composants de revêtement sont plaqués contre une tôle lisse, des rouleaux de contrecollage, des bandes structurées ou similaires. L'invention concerne également des supports ainsi revêtus, constitués d'un matériau support et d'un matériau de revêtement. L'objectif de l'invention est de permettre de lisser, de manière fiable et économique, même des matériaux présentant des surfaces irrégulières. A cet effet, on utilise comme matériau de revêtement un film servant de couche de recouvrement et un système de colle qui, lors de l'application, confère à ce dernier des propriétés de colmatage et de recouvrement des défauts du matériau à recouvrir, sous l'effet de réactions chimico-physiques. Dans un support ainsi revêtu, les matériaux de revêtement présentent un système de colle et un film servant de couche de recouvrement. Ledit système de colle contient des charges qui, lors de l'application, colmatent et recouvrent les défauts du matériau à recouvrir, sous l'effet de réactions chimico-physiques.

Claims

CLAIMS
1. A method for coating uneven bases, especially
surfaces of wooden materials, with thin coating
materials to form a flat and uniformly smooth
surface, wherein the support and the coating
components are pressed against a smooth metal sheet,
laminating rollers, structural strips or the like,
characterised in that used as coating material is a
covering layer film and an adhesive system which
imparts to the covering layer film during coating
properties of filling and spanning defects of the
material to be coated by chemical/physical
reactions.
2. The method according to claim 1, characterised in
that the coating takes place at elevated pressure.
3. The method according to claim 2, characterised in
that the coating takes place at a pressure of 1 .cndot. 10 5
Pa to 6 .cndot. 10 6 Pa.
4. The method according to any one of claims 1 to 3,
characterised in that the coating takes place at
elevated temperature.

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5. The method according to claim 4, characterised in
that the coating takes place at a temperature of 150
to 170° C.
6. The method according to any one of claims 1 to 5,
characterised in that the duration of the adhesion
at elevated pressure and/or elevated temperature is
5 to 300 sec.
7. The method according to any one of claims 1 to 6,
characterised in that the curing takes place after
the coating at room temperature or at elevated
temperature.
8. The method according to claim 7, characterised in
that the curing takes place at a temperature of 20
to 200° C.
9. The method according to any one of claims 1 to 8,
characterised in that the coating takes place
continuously.
10. The method according to any one of claims 1 to 8,
characterised in that the coating takes place
discontinuously.
11. A layer support consisting of a support material and
a coating material manufactured according to any one
of claims 1 to 10, characterised in that the coating
materials have an adhesive system and a covering
layer film and that the adhesive system contains

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fillers which fill and span defects of the material
to be coated by chemical/physical reactions.
12. The layer support according to claim 11,
characterised in that the adhesive system is a
foaming adhesive.
13. The layer support according to claim 11 or 12,
characterised in that the adhesive system is a
spanning dry gum film.
14. The layer support according to claim 11,
characterised in that the adhesive system is a
duroplastic dry gum adhesive or a corresponding dry
gum film.
15. The layer support according to claim 11,
characterised in that the adhesive system is a
thermoplastic dry gum adhesive or a corresponding
dry gum film.
16. The layer support according to any one of claims 11
to 13, characterised in that the adhesive system has
chemically/physically expandable contents.
17. The layer support according to any one of claims 11
to 14, characterised in that the covering layer film
is paper-based.

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18. The layer support according to any one of claims 11
to 14, characterised in that the covering layer film
is a thermoplastic film.
19. The layer support according to any one of claims 11
to 18, characterised in that the covering layer film
has a weight per unit area between 30 and 500 g/m2.
20. The layer support according to any one of claims 11
to 19, characterised in that the fillers consist of
substances which release CO2 or other gases.
21. The layer support according to any one of claims 11
to 20, characterised in that the adhesive coat, wet
or dry, has a weight per unit area between 20 and
300 g/m2.
22. The layer support according to any one of claims 11
to 21, characterised in that the filler content is
between 5 and 70 wt.%.

Description

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15. October 2004
Method for coating uneven bases with thin coating
materials and a layer support manufactured thereby
The invention relates to a method for coating uneven
bases, especially surfaces of wooden materials, with thin
coating materials to form a flat and uniformly smooth
surface, wherein the support and the coating components
are pressed against a smooth metal sheet, laminating
rollers, structural strips or the like, and a layer
support, consisting of a support material and a coating
material manufactured using such a method.
Various methods have been known for a long time for
treating workpieces with uneven bases, especially made of
wooden materials such that their exterior acquires a
surface which is as smooth as possible.
Here mention should first be made of the so-called polish
and varnish treatment in which the more or less rough
workpiece surfaces are to be treated by expensive and
costly treatment measures such as for example polishing,
smoothing and coating with multilayer (and therefore very
expensive) surface materials. These surface materials
can, for example, comprise varnishes which are applied in
large quantities to fill defects and achieve
corresponding surface smoothing. It is also known, as is
described for example in EP 1 010 730 A1 to use a filler
made of wood flour, resin, inert materials and a
cellulose solution for filling in order to reduce the
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price for the surface materials acting as fillers.
Finally methods are also known whereby workpieces are
coated with thin films, especially decorative films, to
improve the aesthetic effect of such workpieces.
It is clear that the expenditure on surface treatment
always depends on the surface quality of the material to
be smoothed or to be coated. In the case of wooden
materials, a distinction can be made according to the
following starting materials:
a) Chipboards for general purposes such as furniture or
interior work, gross density: between 600 and 680
kg/m3 ,
b) Chipboards for FPY coating boards with particular
dense coating layers, gross density: between 700
and 7 5 0 kg /m3 .
c) Chipboards for FPO structural boards for floors,
walls and roofs, gross density: about 750 kg/m3.
d) So-called 'OSB' (Oriented Structural Board), a
product of long chips which are either only
longitudinally oriented single--layer or strewn
crosswise with a transversely lying middle layer.
They are statically calculable products for the
building industry in the form of stiffening boards,
gross density: between 400 and 650 kg/m3.
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e) Wood fibre hard boards for back walls, drawer
bottoms or mouldings, gross density: about 1000
kg/m3 .
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f) MDF boards (MDF - medium density fibreboard), as
medium-density products, gross density: around 850
kg/m3. The density spread lies between 600 and 900
kg/m3, with the designation 'LDF' for 'low density
fibreboard' and 'HDF' for 'high density fibreboard'.
g) Plywood with fibre profile crossed by 90° per layer,
gross density about 400 kg/m3.
h) Solid wooden blockboards veneered with plywood or
strip plywood. These high-quality boards are only
used for high-quality furniture construction because
of their good bracing-free standing capacity.
Whereas r~F boards and chipboards have a sufficient to
good surface smoothness so that they can be constructed
in subsequent process steps also using thin coating
materials to give an acceptable, smooth and uniform
surface, the other said wooden materials have a more or
less rough surface according to their structure which can
only be smoothed by the expensive processing measures
specified further above.
Taking this as the starting point, it is the object of
the present invention to develop and further develop the
method of surface smoothing specified initially and
described in detail previously and the layer support
manufactured thereby such that even materials with rough
surfaces can be reliably and inexpensively smoothed.
Furthermore, it is desirable that even materials having a
lower gross density which hitherto could not be used for
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furniture construction or interior work, can enter this
market segment under economic conditions.
This object is solved with regard to the method by using
as coating material a covering layer film and an adhesive
system which imparts to the covering layer film during
coating properties of filling and spanning defects of the
material to be coated by chemical/physical reactions.
With regard to a corresponding layer support, the
solution of the problem consists in the fact that the
coating materials have an adhesive system and a covering
layer film and that the adhesive system contains fillers
which fill and span defects of the material to be coated
by chemical/physical reactions.
According to the invention, an expensive and laborious
processing before and during the coating with varnishes
or other surface materials can be dispensed with.
According to a further teaching of the invention, the
coating can take place under high pressure, preferably at
a pressure of 1 ~ 105 Pa to 6 ~ 206 Pa (1 to 60 bar). For
better reaction of the adhesive system located under the
covering layer film the coating can take place at
elevated temperature, preferably at a temperature of 150
to 170° C .
According to a further embodiment of the invention it is
provided that the duration of the adhesion at elevated
pressure and/or at elevated temperature is 5 to 300 sec.
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For better curing of the coating another teaching of the
invention provides that the curing also takes place after
the coating at room temperature or at an elevated
temperature. A temperature range of 20 to 200°C has
proved suitable here.
In this situation the surface according to the invention
can be manufactured continuously or discontinuously.
For the layer support according to the invention,
according to a further teaching of the invention a
foaming adhesive can be used as the adhesive system. Wet
adhesives having the following base polymers can be
considered for this purpose:
PVAc, EVAc, PUR, acrylates, styrene acrylates, styrenes,
styrene butadiene, UF, MF, resorcin, phenol, PVa or
mixtures thereof as well as natural and synthetic rubber,
epoxy resins, wherein the base polymers can acquire a
higher cohesivity via a chemical cross-linking such as
for example with isocyanates (single-component, two-
component) or reactively single-component.
In a further preferred embodiment of the invention, the
adhesive system located between the covering layer film
and the support material (workpiece) consists of a
duroplastic dry gum adhesive or a corresponding dry gum
film. In this situation, this can for example be a
melamine-impregnated overlay paper which, for coating, is
applied to the surface of the workpiece to be smoothed
and is pressed against a corresponding pressing sheet for
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a predetermined time under pressure and temperature. In
this case, good spanning is achieved.
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Alternatively, it is also feasible to use a thermoplastic
dry gum adhesive or a corresponding dry gum film as the
adhesive system located between the covering layer film
and the workpiece. This can, for example, be EVA hot
melt systems (EVA = ethylene vinyl acetate), systems
based on polyurethane or polyolefin. Dispersion-
impregnated or duroplastic impregnated papers or
thermoplastic films made of polyethylene (PE) or
polypropylene (PP) can also be used for this purpose.
According to a further teaching of the invention, the
adhesive system can have chemically expandable contents
wherein during the coating process a degassing or foaming
occurs as a result of chemical/physical reactions which
has the result that released gas (for example, Co2) acts
as propellant gas which carries solid particles (fillers
or polymer particles) from the starting polymer into the
defects present on the workpiece surface (indentations
and unevenness) which are thereby filled.
In this case it is possible that the application of the
adhesive system takes place either a) onto the base to be
coated, b) by spraying/application to the back of the
film or c) by transfer of a dry gum layer.
The covering layer films preferably consist of paper with
different impregnation such as for example starch gums,
resin gums, urea acrylate systems, melamine systems,
dextrines, polyvinyl alcohols or the like.
The covering layer film to be used preferably has a
weight per unit area of 30 to 500 g/m2 and the adhesive
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coat has a weight per unit area of 20 to 300 g/m2. The
filler content is between 5 and 70~.
The chemical/physical reaction for releasing the
propellant gas can also take place under the action of
acid donors, wherein preferably the acid donor is
supplied liquid or dry, either by spraying on, rolling or
by superposition from the back of the film or the top of
the base.
It is also possible to use a masked (encapsulated) acid
which is incorporated in the adhesive and under pressure
and/or temperature loses its protection but also its pH
drop in the adhesive system releases either COz or other
gassing materials. Both inorganic and organic acids can
be used as acids.
Finally it is also possible to stir an acid into the then
gassing adhesive directly before application of the
adhesive and apply this expanded-material-containing
adhesive like a foam onto the base to be filled and then
carry out the film coating.
Furthermore it is also possible to achieve the
expanding/foaming and thereby filling effect of a gum
join by additives known in the literature such as, for
example
- azo/diazo compounds
- polyurethane
- carbonates and many more.
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When used in a small quantity, the adhesive systems used
already show the decisive advantage that they can fill or
span the hollows or defects of the wooden boards and in
conjunction with the thinnest possible films especially
matched to these requirements, produce good spanning and
smooth surfaces.
Using the method according to the invention, for example,
OSB materials can be treated such that they are superior
in quality to other materials on the market such as
chipboards or r~F boards. As a result of a significantly
lower weight of 400 to 600 kg/m3 and other physical
properties such as a very high bending strength, high
drilling strength/drill extraction strength and their
significantly Iower swelling behaviour, they can easily
be used for furniture or interior work.
An example of a formulation of an adhesive system of a
layer support according to the invention is as follows:
OF resin . 10 - 70 wt.$
PVAc dispersion . 10 - 70 wt.~
EVAc dispersion . 10 - 70 wt.~
Cross-linking agent : 0.1 - 5.0 wt.~
Chalk (CaC03) . 5 - 60 wt.~
Acid donor (citric acid 3-50~ or malefic acid anhydride 5
- 30~) .
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