Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF APPLYING PHOTOCATALYST NANOPARTICLES
ON BOARDS AND PANELS
TECHNICAL FIELD
The disclosure generally relates to methods of applying nanoparticles on a
surface to create a layer with embedded photo catalyst nanoparticles.
Furthermore, the invention relates to a method to achieve a homogenous
distribution of nanoparticles in the upper layer of boards and panels.
BACKGROUND
It is well known to produce laminated building panels with a surface
comprising
laminated paper sheets. Also known is a new type of panel called Wood Fibre
Floor (WFF) that is disclosed in W02009/065769, which shows both products
and methods to produce such a product also using nanopartides. Furthermore it
is shown in W02009/062516 to apply nanoparticles on a laminate surface or on
an overlay paper
The documents below describe several ways to treat papers or impregnated
papers prior to the final oven and before the paper can be used in laminate
panels.
US2009/0208646A1 describes a wet-in-wet application of a coating to an
impregnated overlay by means of a coating inlet. The control of the thickness
of
the layer Is obtained by wipers that wipe of the excess coating. The document
shows a method of producing an overlay, in particular for laminates, involving
impregnation of a paper with the following method steps:
1) Unrolling of an overlay base paper from a roll for the purpose of obtaining
a paper web (10);
2) Moistening of the paper web (1O)on one side with an impregnating
medium (14);
3) Impregnating the paper web (10) with an impregnating medium (18)
4) Wet-in wet application of a coarse corundum and resin dispersion (27) on
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one side onto the paper web (10)
5) Opposite wet-in-wet application of a coating substance (29), in the form of
resin and fine corundum, onto the paper web (10);
6) A dosage of the applied coating substance (29) by a wiper (32), to the
desired application weight;
7) Drying the paper web (10) using a drying duct.
US3798111 describes the incorporation of particles in the paper machine where
the particles can be found throughout the paper, entangled by the fibres.
W02007144718 discloses a hard nanoparticle suspension applied to the resin
pre-treated carrier sheet. The method states that the suspension comprises
resin. The method comprises adding the suspension by means of a wire doctor
roll and/or a raster roll or other methods comprising rolls and/or knifes.
Also air-
knives.
SUMMARY OF THE INVENTION
Embodiments of the invention relates to a method of applying nanoparticles on
a
surface to create a sheet or a surface layer with photocatalytic
nanoparticles.
The aim is to improve the effect of the photocatalytic nanoparticles when the
particles are embedded in the sheet or the surface layer, i.e. keeping the
activity
level at a high level and maintaining the desired properties of the sheet or
the
layer with the embedded particles.
It is shown in W02009/062516A2 to use photocatalytic nanoparticles in a
surface layer for improvement of e.g. the cleanability. Furthermore a method
to
apply the nanoparticles is disclosed. The method according to embodiments of
the invention provides an improved transparency, increased lifetime and
improved distribution of the nanoparticles.
A first aspect of the invention is a method of manufacturing a sheet
comprising
photocatalytic nanoparticles, the method comprising the steps of:
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= impregnating the sheet with a polymer resin, preferably comprising wear
resistant particles, in an uncured and wet state;
= spraying the sheet, freshly impregnated with the polymer resin in an
uncured and wet state, with an impregnation fluid composition comprising
dispersed photocatalytic nanoparticles;
= drying and/or at least partly curing said impregnated sheet comprising
the
polymer resin and the impregnation fluid composition.
The sheet may comprise cellulose fibres.
Preferably, the impregnation fluid composition comprises a solvent comprising
water.
The method may comprise a step between impregnating and spraying step in
which step the polymer resin is partly dried.
By applying the photocatalytic nanoparticles In a wet surface particularly the
distribution of the particles is improved.
.. The impregnation fluid composition may comprise photocatalytic
nanoparticles
and a solvent, said solvent being selected from water, ethylene glycol, butyl
ether, aliphatic linear, branched or cyclic or mixed aromatic-aliphatic
alcohols,
such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, benzyl
alcohol or methoxypropanot or combinations thereof.
A second aspect of the invention is a method to produce a laminate board or
panel by manufacturing a sheet according to a method as described herein,
arranging the sheet on a core, preferably an HDF panel and applying heat and
pressure.
A third aspect of the invention is a method of manufacturing a sheet
comprising
photocatalytic nanoparticles, the method comprising the steps of:
= mixing the photocatalytic nanoparticles in a polymer resin, to obtain an
impregnation mix;
= applying the impregnation mix to a sheet, preferably by spraying.
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A fourth aspect of the invention is a method to produce a paper sheet
comprising
photocatalytic nanoparticles in the paper plant, preferably prior to rolling
of the
paper.
A fifth aspect of the invention is a method to produce a WFF panel comprising
photocatalytic nanoparticles, the method comprises the step of:
1) Scattering of a dry mix comprising wood fibres, a thermosetting resin,
preferably melamine resin, and wear resistant particles on a core;
2) Applying an organic solvent on the mix on the core;
3) Spraying an impregnation fluid composition comprising dispersed
photocatalytic nanoparticles, preferably dispersed in water;
4) Applying heat and pressure.
Step 2 and 3 of the method may be applied in any of the methods disclosed in
W02009/065769 and W02009/124704 for production of WFF panels.
The method is preferably performed in the numbered order 1-4.
The organic solvent preferably comprises ketone, such as acetone and methyl
ethyl ketone, and/or alcohol, such as ethanol, propanol and methanol, and/or
acetate, such as butyl acetate, ethyl acetate. The organic solvent is in a
preferred embodiment ethanol.
In another embodiment the method comprised the step of applying, preferably
before step 2, a fluid with a wetting agent on the mix, preferably in the form
of
water containing 1% weight content of BYK-348 from BYK Chemie. The fluid
with the wetting agent and the organic solvent may also be applied together.
It is well known that a nanomaterial is not just a nanomaterial, and the
characteristics of the embedded nanoparticles are important for their
performance and e.g. the properties of said board or panel. In a particularly
preferred embodiment in any of the aspects the embedded nanoparticles have a
primary particle size or crystal size of < 50 nm, such as < 30 nm, preferably
a
primary particle or crystal size of < 20 nm. Hereby, the efficacy of the
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nanoparticles is improved and/or less nanoparticles are needed to obtain a
specific effect.
Primary particles are rarely present as individual primary particles, but in a
more
or less aggregated form. An efficient control of the agglomerate and/or
cluster
size is greatly preferred. Hence, in preferred embodiments the embedded
nanoparticles have a cluster or aggregate size of < 100 nm, such as < 80 nm,
preferably a cluster or aggregate size of < 60 nm, such as < 40 nm, and even
more preferably a cluster or aggregate size of < 30 nm, such as < 20 nm.
Thereby, said nanoparticles may be easier to disperse homogeneously in said
overlaying layer, and said layer become more optically transparent.
In any embodiment of the present invention, the concentration of said
nanoparticles in said impregnation fluid may be > 1 wt%, such as > 5 wt%,
preferably a concentration of said nanoparticles > 10 wt%, such as > 15 wt%,
and even more preferably a concentration of said nanoparticles > 20 wt%, such
as > 25 wr/o.
Further, in any embodiments the nanoparticles in said impregnation fluid
composition may have a cluster or aggregate size of < 100 nm, such as < 80 nm,
preferably a cluster or aggregate size of < 60 nm, such as < 40 nm, and even
more preferably a cluster or aggregate size of < 30 nm, such as < 20 nm.
In all of the aspects of the invention the amount of impregnation fluid
composition per square meter of overlaying sheet(s) may be in the range 1-200
ml/m2, such as in the range 5-100 ml/m2, and preferably in the range 10-50
ml/m2, such as 20-40 ml/m2, of said impregnation fluid composition per square
meter of overlaying sheet(s) to be impregnated.
The polymer resin used for said polymer resin composition comprising
nanoparticles, may be selected from the group comprising melamine
formaldehyde resin, phenol formaldehyde resin, urea formaldehyde resin,
melamine urea formaldehyde resin, acrylannide resins, urethane resins, epoxy
resins, silicon resins, acrylic resins, vinylic resins or mixtures thereof.
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In embodiments of the invention the photocatalytic nanoparticles in said
nanoparticle polymer resin composition may be introduced as a dry powder, as a
paste or as a suspension and then dispersed in the polymer resin.
In embodiments of the invention a solvent of said suspension of photocatalytic
nanoparticles to be dispersed in the polymer resin composition is selected
from
water, ethylene glycol, butyl ether, aliphatic linear, branched or cyclic or
mixed
aromatic-aliphatic alcohols, such as methanol, ethanol, propanol, isopropanol,
butanol, isobutanol, benzyl alcohol or methoxypropanol or combinations
thereof.
Embodiments of the invention may in a sixth aspect be obtained by a method of
manufacturing a board or a panel, the method comprising
¨ providing the upper surface of a base or an assembled laminate board or
panel with a coating applying a coating fluid composition comprising
photocatalytic nanoparticles; and
¨ drying and/or curing said base or laminate board or panel, subsequent to
said coating step.
The coating fluid may in any of the above aspects be applied to said material
surface by spraying, dipping, rolling, brushing or by other conventional
application methods. The amount of coating fluid composition per square meter
of said material surface may be in the range 1-200 ml/m2, such as in the range
5-100 ml/m2, and preferably in the range 10-50 ml/m2, such as 15-25 ml, of
said
coating fluid composition per square meter of said material surface.
In another aspect, the invention provides a panel produced with a method as
described herein, wherein the photocatalytic nanoparticles are homogenously
embedded in an uppermost layer of the panel.
Several combinations of the ingredients can be made into fully functional
products. Three examples are given below as to show three functional
embodiments of the innovation.
BRIEF DESCRIPTION OF THE DRAWINGS
The disclosure will in the following be described in connection to preferred
embodiments and in greater detail with reference to the appended exemplary
drawing, wherein
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Fig 1 Illustrates a production line for producing an overlay
paper.
Fig 2 Illustrates a production line for producing an overlay paper
comprising spraying unit.
DETAILED DESCRIPTION OF EMBODIMENTS
The present invention is concerned with manufacturing of an overlay or boards
or panels, such as laminate boards or panels, comprising different types of
photocatalytic nanoparticl es, which makes the manufactured products
photocatalytic active. Each layer and process step can be preferred from the
others e.g. depending upon the price of the laminate boards and panels (low
cost/high cost product) and the facilities available by the laminate
manufacturers.
Laminate boards and panels are typically made of a base of fibre board (mainly
high density fibre board HDF) and 3 or more sheets: a decor sheet, an overlay
sheet of cellulose on top and one or more backing sheets sitting on the
opposite
side of the fibre board base to balance the board and prevent it from curving.
Other sheets are often placed between the fibre board and the decor sheet. The
decor sheet could be monochromatic or patterned to look like e.g. wood, cork,
stone, tiles or a more abstract pattern. The overlay sheet typically contains
wear
resistant particles, normally a certain amount of alumina oxide (A1203), to
give
the laminate better abrasive resistance. Furthermore, the overlay sheet is
impregnated with a polymer resin, typically melamine formaldehyde resin. The
other sheets, most often paper sheets, are also impregnated with resin. The
decor sheet is typically impregnated with melamine formaldehyde resin whereas
phenol formaldehyde resin often is used in the core of the laminate. The
laminate board or panel is assembled applying heat and pressure, making the
resin polymerise in a thermosetting reaction. After lamination the polymerised
overlay sheet and decor paper constitute the top layer of the laminate board
or
panel and thus needs to be optically transparent right from the upper surface
of
the laminate through to the decorative print of the decor paper.
In one embodiment of the invention (fig 2) the photocatalytic nanoparticles
are
applied as a wet-in-wet spray coating (43, 40) to the upper and/or lower
surface
of the paper (10), after a first (42) and/or a second (41) impregnation of the
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paper (10) with a resin and wear resistant particles, preferably aluminium
oxide.
The paper may be dried (44,45) after each impregnation. Preferably the
photocatalytic nanoparticles are applied after the impregnation step but
before
the drying step. In one embodiment the paper (10) is in a first step (46)
moistened with a resin and/or impregnated in a resin through. This method of
spraying the photocatalytic nanoparticles may-be incorporated in any
production
line for producing overlay or decor paper, also in the line shown in fig 1 and
described above under US2009/0208646. The spraying of the photocatalytic
nanoparticles may in the fig 1 line be performed at any stage after the
moistening (14) of the paper web (10).
A suitable type of spray nozzle for the spray coating of photocatalytic
nanoparticles is an electronically controlled AutojertmPulsajet B10000jjau.
Preferred spray velocity of overlay or decor paper may be > 1 m/s, such as > 2
m/s, preferably a velocity of > 5 m/s, such as > 8 m/s, and even more
preferably
a velocity of > 10 m/s.
In another embodiment the photocatalytic nanoparticles are applied as a wet-on-
dry spray coating to the upper and/or lower surface of the overlay and/or
decor
paper, after a first or a second impregnation of the paper with resin and wear
resistant particles, preferably aluminium oxide. The paper is normally dried
after
each impregnation.
In a preferred embodiment of the invention the photocatalytic nanoparticles
may
be mixed with a wetting agent and/or an alcohol prior to the spray coating
step to
improve the wettability of the impregnation -fluid on the overlay and/or decor
sheet.
In another embodiment of the invention the photocatalytic nanoparticles may be
applied as a combination between wet-in-wet and wet-In-dry spray coating.
In another embodiment of the invention photocatalytic nanoparticles are
applied
as a polymer mixture in the resin impregnation step.
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In another embodiment of the invention photocatalytic nanoparticles are
incorporated into an overlay sheet, e.g., in the decor paper itself prior to
polymer
resin impregnation. Thus using said photocatalytic overlay sheet or decor
paper
a photocatalytic layer can be readily introduced applying the existing methods
used for manufacturing laminate boards or panels i.e. polymer resin
impregnation of the photocatalytic overlay sheet or decor paper followed by
laminate board fabrication in a heat pressing laminating step.
Said photocatalytic nanoparticle impregnation and drying/curing steps may be
incorporated into an existing production line immediately prior to the polymer
resin impregnation of said overlay sheet or decor paper or said photocatalytic
impregnated and cured overlay sheet or decor paper can be stored until needed.
A suitable type of nanoparticle for use in the coating fluid composition is
Titania.
The nanoparticles of Titania may according to some aspects of the present
invention further comprise other elements. In some embodiments such elements
may be introduced into said nanoparticles with the aim to improve the
photocatalytic activity of said nanoparticles by altering the absorption range
of
said titania photocatalytic nanoparticles.
The solvent of said coating fluid composition may comprise water, methanol,
ethanol or isopropanol or combinations thereof, or may just be water.
The particle concentration of said photocatalytic nanoparticles in the
manufactured board or panel may be increased by repeating said coating step
several times.
A preferred embodiment of the produced impregnated paper comprises discrete
photocatalytic nanoparticles on and in said overlay sheet or decor paper. Said
nanoparticles or clusters of nanoparticles may in many applications according
to
the present invention be of substantially the same size as the effective
particle
size in said impregnation fluid composition.
The produced impregnated paper, comprising the photocatalytic nanoparticles,
may be used in all known process, to produce laminated building panel,
preferably floorboards, wall panels and kitchen tabletops
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The photocatalytic composition to be dispersed in the polymer resin may
preferably comprise photocatalytically active nanoparticles of Titania (T102).
in a
preferred embodiment said nanoparticles comprise the anatase and/or the rutile
and/or the brookite crystal form of Titania or a combination thereof. Further,
said
photocatalytically active nanoparticles are according to the present invention
predominantly present in their final crystal form in said composition i.e. no
heat
treatment is required for transformation of said nanoparticles into their
active
form. The average primary particle size or crystallite Size of the
nanoparticles,
e.g. Titania expressed as an equivalent spherical diameter may preferably be
below 30 nm, such as below 20 nm, and preferably below 15 nm, such as below
10 nm. The average primary particle size or crystallite size may be measured
by
X-ray Diffraction (XRD) using Scherer's formula. It is further preferred that
the
particle size distribution of said nanoparticles is relatively narrow.
The photocatalytic composition to be dispersed in the polymer resin, whether
it is
introduced as a powder, a paste or a suspension, may be added to the polymer
resin at any given time. In one embodiment of the invention the photocatalytic
composition is dispersed into the polymer resin immediately prior to the
impregnation of overlay sheets or decor papers with polymer resin. Said
dispersion process may be aided by a specially designed machine or apparatus.
EXAMPLES
Having described the basics aspects of the invention, the following examples
are
given to illustrate specific embodiments thereof.
Example 1 Wet in Wet
This example illustrates the production of a polymeric surface containing
embedded nanoparticles. The particles were applied as dispersion via a spray
system onto the freshly impregnated polymeric surface while still wet.
The following dispersion was used as a feedstock. 30% TiO2 dispersion in water
containing particle agglomerates of no bigger size than 80 nm as determined
using the Particle MatriTMz Nanotrack NPA 252. The stock solution was then
sprayed onto freshly impregnated melamine paper right after the paper had left
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the impregnation roller. The dispersion was applied onto the paper using an
autojet spray system, pumping the fluid to the nozzles via a low pressure tank
whit a pressure of 1.8 bar. The nozzles were pulsejet nozzles with air
atomizing
tips (air pressure 1.5 bar) placed 35 cm above the freshly impregnated paper
right in front of the entrance to the first drying oven.
The autojet system was set to deliver 30m1fluid/m2 of paper; the paper was
then
dried in two consecutive heating ovens. This yielded a melamine paper with
embedded TiO2 agglomerates of a very small size, penetrating approximately
the first couple of hundred micrometers of the melamine paper.
.. Example 2 Wet on Dry
This example illustrates the production of a polymeric surface containing
embedded nanoparticles. The particles were applied as dispersion via a spray
system onto the polymeric surface after this was dried in the heating oven.
The same liquid and spray system as used in Example 1 was used in this
experiment.
Example 3 Wet on Raw Paper
This example illustrates the production of a polymeric surface containing
embedded nanoparticles.
The particles were applied as dispersion via a spray system onto the raw paper
before the paper was impregnated with melamine.
Test Results
The table below shows the result of different methods to apply the
photocatalytic
particles:
= Test 1: Applying a photocatalytic top layer by impregnation of overlay
paper wet-in-wet by spraying.
= Test II: Applying a photocatalytic top layer by impregnation of overlay
paper wet-on-dry by spraying.
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= Test III: Applying a photocatalytic top layer by impregnation of overlay
paper wet-on-dry by spraying on raw overlay paper before melamine
impregnation.
The appearance, the stability and the distribution are evaluated.
Treatment Appearance (a) Stability (b) Distribution (c)
Blank-Reference 1 1 -
Test I: Wet-in-wet 1 1 1
Test II: Wet-on-dry 2 1 3
Test Ill: Wet- in-dry 4 4 2
a) The appearance on a scale from 1-5, as judged by transparency and
haziness, where 1 is no visible difference from non-embedded laminate and 5 is
very hazy.
b) The process stability was evaluated on a scale from 1-5, as judged by
material lifetime and flexibility, where 1 is no difference from non-embedded
laminate and 5 is very sensitive to process changes.
C) The distribution of embedded particles was evaluated on a scale from 1-5,
where 1 is complete homogenous distribution of photocatalytic nanoparticles.
