Note: Descriptions are shown in the official language in which they were submitted.
WO 2012/055793 CA 02810453 2013-03-05PCT/EP2011/068490
Absorbent multilayer coating system
The invention relates to a peelable multilayer coating system having an
absorbent
top layer.
International patent application WO 2008/157670 describes sacrificial barrier
coatings which may be used to protect a wide variety of substrates from
contaminants, including graffiti, as well as radioactive contaminants, dirt or
soil,
toxins, and the like. The barrier coating may be removed after deposition of a
contaminant. The barrier coating and contaminant material may be removed by
contacting the barrier coating and contaminant with a treating solution. The
treating
solution may be dehydrated to form a treating film. The barrier coating,
contaminant material and treating film may be peeled from the substrate in a
single
step.
International patent application WO 2008/148763 relates to an aqueous coating
composition for forming a peelable temporary coating on a substrate, said
aqueous
coating composition comprising at least one water-based film-forming polymer,
characterized in that the composition additionally comprises solid particles
of an
amino resin based polymer.
International patent application WO 2005/103171 describes an aqueous
strippable
paint comprising one or more pigments, a polyether polyurethane binder having
anionic stabilizing groups, and a second polyether having at least 20 wt. % of
lipophilic parts. The first polyether has an acid number of at least 8,
preferably at
least 12, and the second polyether has 30-70 wt % of lipophilic parts. The
mixing
ratio of the first and second polyethers is at least 20:1
There is a need for absorbent coatings which have an improved ability to
absorb
contaminants and which are easy to remove from a coated substrate.
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The invention now provides a peelable multilayer coating system comprising
a) a peelable coating layer and
b) an absorbent top coating layer pigmented above the critical pigment
volume concentration, and wherein the pigment comprises mesoporous
inorganic particles.
The multilayer coating system of the invention has an improved ability to
absorb
contaminants. Furthermore, the multilayer coating system can easily be removed
from a substrate by manual peeling.
The multilayer coating system comprises a peelable coating layer a). Suitable
coating compositions for preparing peelable coating layers a) are known in the
art.
Such coating compositions are, for example, described in international patent
applications WO 2005/103171 and WO 2008/148763, and in United States patent
US 5965195. The peelable coating layer may be prepared from an aqueous
coating composition or from a non-aqueous coating composition. It is preferred
that
the peelable coating layer comprises solid particles of an amino resin based
polymer. In one embodiment, the amino resin based polymer is a methyl urea
based polymer. Coating compositions for forming a peelable and comprising such
particles are described in more detail in international patent application WO
2008/148763, which is incorporated by reference. Suitable coating compositions
for forming peelable coatings are also commercially available from AkzoNobel
under the trade designations Intergarde 10220 and Sikkens Protect . The
peelable coating composition can be applied to a substrate by any of the known
methods for applying coating compositions to a substrate. Examples of such
application methods are spreading (e.g., brushing, rolling, by paint pad or
doctor
blade), spraying (e.g., airfed spraying, airless spraying, hot spraying, and
electrostatic spraying), flow coating (e.g., dipping, curtain coating, roller
coating
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and reverse roller coating), and electro-deposition. The substrate suitably is
a non-
porous substrate. Examples of suitable non-porous substrates are metals which
may have been pre-treated or not, pre-treated wood, synthetic polymeric
materials,
and glass. Further suitable substrates are other coats of paint, such as are
present
on transportation vehicles and motor vehicles or parts thereof, e.g.,
passenger cars,
bicycles, trains, trucks, buses, and airplanes.
After application of the coating composition for forming the peelable coating
layer
a), this layer is suitable at least partly dried before application of
subsequent layers.
Layer a) can be dried between 0 and 160 C, or between 5 and 80 C, or between
10 and 60 C, for example at ambient temperature. Drying at elevated
temperature
can be carried out in an oven. Alternatively, drying can be supported by
infrared
and/or near infrared radiation. In an alternative embodiment, a subsequent
layer
can also be applied to the wet coating layer a) in a so-called wet-on-wet
application.
The subsequent coating layer can be the absorbent top coating layer b). In
that
case, the peelable coating layer a) and the absorbent coating layer b) have a
common layer boundary. However, it is also possible to apply one or more
intermediate layers between layer a) and layer b), provided that the
peelability of
the entire coating system is not impaired.
As mentioned above, the absorbent top coating layer b) is a pigmented coating
layer wherein the pigment is present in an amount above the critical pigment
volume concentration (CPVC).
The pigment volume concentration (PVC) is the volume percentage of pigment in
the dry paint film. The CPVC is understood as the pigment volume concentration
where there is just sufficient binder to provide a completely adsorbed layer
of
binder on the pigment surfaces and to fill all the interstices between the
particles in
a close-packed system. The CPVC can be determined by wetting out dry pigment
with just sufficient linseed oil to form a coherent mass. This method yields a
value
known as the "oil absorption" (OA). It indicates the amount of oil required to
wet out
100 grams of dry pigment. From the OA the CPVC can be calculated. The method
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for determining the OA is described in British Standard 3483 (B53483). The
CPVC
can be calculated from the OA by the following formula:
CPVC = 100% / (1 + (densitypigment / densityresin)) x (OA / 100). If a mixture
of
pigments or resins having different densities is used, the respective average
density of the pigment or resin mixture has to be used for the calculation.
For
determination of the CPVC of specific coating compositions, it is preferred to
carry
out the process described in B53483 with the resin or mixture of resins used
in the
coating composition, rather than with linseed oil.
The absorbent coating layer b) also comprises mesoporous inorganic particles.
In
the context of the present invention, the mesoporous inorganic particles are
considered as pigments and thus to contribute to the overall pigment volume
concentration of coating layer b), although the mesoporous particles will not
necessarily provide colour and/or hiding power to coating layer b). Mesoporous
particles are particles containing pores with diameters in the range of 2 nm
to 50
nm. Typical mesoporous materials include silica and alumina, mesoporous silica
being preferred. Mesoporous oxides of niobium, tantalum, titanium, zirconium,
cerium, and tin are suitable as well. Mesoporous inorganic particles can be
prepared according to know methods, such as described in United States patents
US 3556725, US 3493341, and US 3383172. They are also available commercially,
for example from PQ Silica Corporation under the trade designation 5D4570.
Also
chromatography grade silica is suitable. Such silicas are available
commercially
and often have a pore diameter of 6 nm.
As mentioned above, the PVC in layer b) is higher than the CPVC. The PVC may
be at least 2, 3, or even 4 times the CPVC.
The pigments in coating layer b) may be a mixture of standard pigments and
mesoporous inorganic particles. The standard pigments may provide color,
hiding
and visual effect properties to the coating as desired and known in the art.
In one
embodiment, the pigments may also provide infrared radiation absorbent or
reflective properties. The mesoporous inorganic particles suitably contribute
at
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least 10% by weight of the total weight of the pigments, and they may
contribute up
to 50 %, or 70, or even above 90% by weight of the total weight of the
pigments in
coating layer b). In one embodiment, the pigment in coating layer b) consists
of or
essentially consists of mesoporous inorganic particles.
As mentioned above, the multilayer coating system is very suitable to absorb
contaminants, in particular airborne contaminants, such as gases or liquid
droplets.
These contaminants are generally organic compounds which often have a
lipophilic
nature. It has been found that absorption of such contaminants is particularly
efficient, when the mesoporous inorganic particles used in coating layer b)
have a
high oil absorption value. Generally, the oil absorption value of the
mesoporous
inorganic particles is at least 100, preferably it is at least 200, or even at
least 400.
Examples of suitable values for the upper limit of the oil absorption value
are 800,
1000, or 1200. The oil absorption value is determined according to British
Standard
3483 (B53483) with linseed oil.
Coating layer b) suitably comprises a film forming polymeric binder resin, for
example a polyurethane, a polyacrylate, a polyester, or mixtures thereof. The
coating composition for preparing coating layer b) may be an aqueous coating
composition or a non-aqueous coating composition. Aqueous compositions are
preferred. In addition to the components mentioned above, the coating
composition
may also comprise other components and additives which are usually present in
coating compositions, such as organic co-solvents, coalescing agents, and
rheology additives. Application and curing of the coating layer b) is usually
carried
out as described above for coating layer a).
The absorbent top coating layer b) generally has a dry film layer thickness of
at
least 50 pm, or at least 100 pm, and preferably at least 120 pm. The dry film
layer
thickness normally does not exceed 400 pm. A dry film layer thickness in the
range
of 120 pm to 180 pm, such as 150 pm, has been found to give very favourable
results.
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The invention further relates to a process of temporary protection of a
substrate
from a contaminant, comprising the steps of
a) applying to the substrate a multilayer coating system comprising a
peelable coating layer and an absorbent top coating layer pigmented
above the critical pigment volume concentration, and wherein the
pigment comprises mesoporous inorganic particles, and
b) exposing the substrate to a contaminant wherein at least a part of the
contaminant is absorbed in the absorbent top coating layer.
After absorption of a contaminant in the top coating layer the multilayer
coating
system can be removed from the substrate by peeling. Alternatively, removal is
also possible by treatment with a water jet. The removed multilayer coating
contains the absorbed contaminant and can be disposed properly. As a result,
the
substrate is free of contaminant.
The invention further relates to kit of parts for preparation of the peelable
multi
layer coating system of the invention, comprising
a) an aqueous coating composition for forming a peelable temporary
coating on a substrate, said aqueous coating composition comprising
i) at least one water based film-forming polymer, and
ii) solid particles of an amino resin based polymer, and
b) a coating composition for forming an absorbent top coating layer
pigmented above the critical pigment volume concentration, and wherein
the pigment comprises mesoporous inorganic particles.
The multilayer coating system and the process of the invention are very useful
for
temporary protection of vehicles and buildings against various contaminants,
for
example toxic gases, vapors, and liquids. In this case, the absorbent top
coating
may also comprise a component which supports the decomposition of the
contaminant in order to transform it into a less dangerous or non dangerous
form.
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This may be implemented by doping of the mesoporous inorganic particles with
catalytically active metals. The preparation of vanadium-doped mesoporous
silica
for this purpose is described in an article by C. Ringenbach et al. in
Chemistry of
Materials, Vol. 17 (2005), pp. 5580-5586. Alternatively or additionally, the
absorbent top coating may also comprise an indicator component, which provides
a visual indication of the loading of the coating with specific contaminants.
The
visual indication can for example be provided in the form of a color change.
In a further embodiment, the invention can be used to protect vehicles and
buildings against vandalism by graffiti sprayers. After application of
graffiti, the
multilayer coating can be removed easily to restore the original appearance of
the
building or vehicle.
In a still further embodiment, the multilayer coating can be applied to
interior walls
of buildings to absorb air contaminants, such as unpleasant or offensive
odours, for
example in kitchens, hospitals or changing rooms. Once the absorbent top
coating
is saturated with contaminants, it can be removed by peeling and, if required,
it can
be replaced with a fresh multilayer coating.
In a further embodiment, it is also possible to prepare the peelable
multilayer
coating system on a temporary substrate and to transfer the multilayer coating
system to the substrate to be protected when such protection is required.
Examples
Peelable multilayer coating systems were prepared on metal panel surfaces,
which
were pre-coated with a polyurethane coating layer. Hence, the substrate
surfaces
used in the Examples represented a typical vehicle surface.
A peelable coating layer was prepared by applying Intergarde 10220. Intergarde
10220 is a one-component aqueous polyurethane based coating composition for
preparation of peelable coatings. It is available from Akzo Nobel Aerospace
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Coatings. The material was applied in the accordance with the instructions
provided in the technical data sheet of the supplier.
Absorbent coating composition 1 was prepared by mixing the following
components:
Component Parts by weight
Aqueous acrylic polymer dispersion (Revacryl 274) 13.6
Pigment preparation 10.0
Water 58.0
Mesoporous silica 6.7
Ethylene glycol monobutyl ether 3.9
Rheology additives (thickener) 7.8
Absorbent coating composition 2 was prepared by mixing the following
components:
Component Parts by weight
Aqueous aliphatic polyurethane dispersion (NeoRez 987) 11.1
Water 66.2
Mesoporous silica 14.3
Ethylene glycol monobutyl ether 2.7
Rheology additives (thickener) 5.7
lo
Multilayer coating systems according to the invention were prepared by
applying
the above absorbent coating compositions on top of the coasting layers
prepared
from Intergarde 10220. The absorbent coating compositions were applied by
spraying. The dry film thickness was at least 150 pm. The multilayer coating
system prepared from absorbent coating composition 1 exhibited a cracked
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surface structure after drying. The multilayer coating system prepared from
absorbent coating composition 2 exhibited a smooth surface. Both multilayer
coating systems were tested for absorption of thickened sulfur mustard (tHD)
according to standards set in DEFSTAN 80-220 (10 mg/cm2, 5 pl drop size, 1 h
dwell time). Absorptions of 90% or higher were observed. The multilayer
coating
system prepared from absorbent coating composition 1 exhibited a faster
absorption than the multilayer coating system prepared from absorbent coating
composition 2. This is believed to be caused by the channeling effect of the
cracked surface.
The multilayer coating systems could be removed from the substrate by manual
peeling.
