U.S. patent application number 17/252917 was filed with the patent office on 2021-08-26 for two-component solvent-based coating composition, method for coating a substrate, coated substrate, and use of such coating composition for improving erosion resistance.
The applicant listed for this patent is Akzo Nobel Coatings International B.V.. Invention is credited to Andreas MEYERJURGENS, Dirk SEEGER, Igor SHISHKOV, Miriam WICKBOLD.
Application Number | 20210261816 17/252917 |
Document ID | / |
Family ID | 1000005624672 |
Filed Date | 2021-08-26 |
United States Patent
Application |
20210261816 |
Kind Code |
A1 |
MEYERJURGENS; Andreas ; et
al. |
August 26, 2021 |
Two-component solvent-based coating composition, method for coating
a substrate, coated substrate, and use of such coating composition
for improving erosion resistance
Abstract
The present disclosure relates to a two-component, solvent-based
coating composition comprising i) a base component comprising one
or more polyesterdiols with a hydroxyl value in the range of from
150 to 500 mg KOH/g and one or more organosilane-modified inorganic
fillers, and ii) a polyisocyanate curing component. Said
composition can be formulated such that it has a viscosity suitable
for spray application (low viscosity under high shear rate) and
yield coatings with very good erosion resistance. The present
disclosure further relates to a method for coating a substrate
using said two-component coating composition, to a coated substrate
obtainable by such method, and to use of such coating composition
for improving erosion resistance of a substrate.
Inventors: |
MEYERJURGENS; Andreas;
(Oldenburg, DE) ; SEEGER; Dirk; (Oldenburg,
DE) ; SHISHKOV; Igor; (Munster, DE) ;
WICKBOLD; Miriam; (Wildeshausen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Akzo Nobel Coatings International B.V. |
Amhem |
|
NL |
|
|
Family ID: |
1000005624672 |
Appl. No.: |
17/252917 |
Filed: |
June 27, 2019 |
PCT Filed: |
June 27, 2019 |
PCT NO: |
PCT/EP2019/067114 |
371 Date: |
December 16, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09D 175/06
20130101 |
International
Class: |
C09D 175/06 20060101
C09D175/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 2, 2018 |
EP |
18181251.2 |
Claims
1. A two-component, solvent-based coating composition comprising:
i) a base component comprising (A) one or more polyester diols
having a hydroxyl value in the range of from 150 to 500 mg KOH/g
polyester diol; (B) optionally one or more hydroxyl-functional
acrylate resins having a hydroxyl value in the range of from 75 to
500 mg KOH/g resin; and (C) one or more organosilane-modified
inorganic fillers; and ii) a curing component comprising (D) one or
more polyisocyanates, in such amounts that the coating composition
comprises: 5 to 50 wt % of the one or more polyester diols (A); 0
to 25 wt % of the one or more hydroxyl-functional acrylate resins
(B); 10 to 70 wt % of the one or more organosilane-modified
inorganic fillers (C); 5 to 40 wt % of the one or more
polyisocyanates (D); wherein the coating composition comprises one
or more organic solvents in an amount in the range of from 5 to 35
wt %, and has a viscosity in the range of from 50 to 2,000
mPas.
2. A two-component coating composition according to claim 1,
wherein the one or more polyester diols (A) have a hydroxyl-value
in the range of from 200 to 400 mg KOH/g polyester diol.
3. A two-component coating composition according to claim 1,
wherein the one or more polyester diols (A) are linear, aliphatic
polyester diols.
4. A two-component coating composition according to claim 1,
wherein the coating composition comprises in the range of from 2 to
15 wt % of the one or more hydroxyl-functional acrylate resin
(B).
5. A two-component coating composition according to claim 1,
wherein the one or more hydroxyl-functional acrylate resins (B)
have a hydroxyl value in the range of from 175 to 400 mg KOH/g
resin.
6. A two-component coating composition according to claim 1,
wherein the one or more organosilane-modified inorganic fillers (C)
are organosilane-modified silicates.
7. A two-component coating composition according to claim 1,
wherein the one of more polyisocyanates are selected from the group
consisting of uretdiones, tri-isocyanurates, and biurets of
aliphatic di-isocyanates, and mixtures thereof.
8. A two-component coating composition according to claim 1
comprising the one or more organic solvents in an amount in the
range of from 7.5 to 25 wt %.
9. A two-component coating composition according to claim 1
comprising: 10 to 30 wt % of the one or more polyester diols (A); 0
to 25 wt % of the one or more hydroxyl-functional acrylate resins
(B); 20 to 50 wt % of the one or more organosilane-modified
inorganic fillers (C); 10 to 30 wt % of the one or more
polyisocyanates (D); and 7.5 to 25 wt % of the one or more organic
solvents.
10. A two-component coating composition according to claim 1,
wherein the coating composition has a viscosity in the range of
from 1,000 to 10,000 mPas at a shear rate of 1 s.sup.-1, and the
coating composition has a viscosity at a shear rate of 1,000
s.sup.-1 that is 2 to 20 times lower than its viscosity at a shear
rate of 1 s.sup.-1.
11. A method for coating a substrate comprising: applying the
two-component coating composition according to claim 1 to the
substrate; and allowing the applied coating composition to
cure.
12. A method according to claim 11 wherein the two-component
coating composition is applied to the substrate by spray
application.
13. A method according to claim 11, wherein the substrate is a
substrate comprising one or more coating layers and the
two-component coating composition is applied as a topcoat
layer.
14. A coated substrate obtainable by a method according to claim
11.
15. The method of claim 11, further comprising improving erosion
resistance of the substrate.
16. A two-component coating composition according to claim 1,
wherein the one or more polyester diols (A) have a hydroxyl-value
in the range of from 250 to 350 mg KOH/g polyester diol.
17. A two-component coating composition according to claim 1,
wherein the one or more hydroxyl-functional acrylate resins (B)
have a hydroxyl value in the range of from 250 to 350 mg KOH/g
resin.
18. A two-component coating composition according to claim 1,
wherein the one of more polyisocyanates are selected from the group
consisting of uretdiones, tri-isocyanurates, and biurets of
hexamethylene di-isocyanate and isophorone di-isocyanate, and
mixtures thereof.
19. A two-component coating composition according to claim 1
comprising the one or more organic solvents in an amount in the
range of from 10 to 20 wt %.
20. The method of claim 11, further comprising allowing the applied
coating composition to cure at a temperature of at most 80.degree.
C.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a two-component,
solvent-based coating composition, to a method for coating a
substrate using such two-component coating composition, to a coated
substrate obtainable by such method, and to use of such coating
composition for improving erosion resistance of a substrate.
BACKGROUND OF THE INVENTION
[0002] In various application areas there is a need for protective
coatings fulfilling high mechanical demands. Examples include
surfaces of objects that are exposed to erosive substances at high
speed, such as rotor blades of wind turbines or helicopters, ship
screws, and transport vehicles such as aircraft, trains,
automobiles, and ships. Erosion is typically caused by liquid or
solid substances that impinge on object surfaces, such as airborne
sand, rain or hail. Erosive influences are particularly strong in
the edge regions of such objects.
[0003] Surfaces of objects are typically protected against wear, in
particular against erosion, by applying to such surfaces a
protective coating or multiple-layer coating system. For effective
erosion resistance, it is important to balance coating flexibility
or elasticity and coating hardness. Excessive hardness and/or
inadequate elasticity may be detrimental to effective erosion
resistance.
[0004] There are various coating materials known for erosion
protection of rotor blades of wind turbines. Polyurethane-based
protective coatings are for example described in WO 2010/122157, WO
2012/032113, and WO 2016/000845.
[0005] Known coating compositions for erosion protection of rotor
blades of wind turbines are often formulated free of organic
solvents. Accordingly, such compositions have a high viscosity and
cannot be satisfactorily applied to a substrate by spray
application. Instead, brush or roller coating is to be used. There
is a desire to use spray application, since it allows simpler and
more controllable application of coating compositions.
[0006] Known erosion-resistant coating compositions that are
suitable for spray application generally comprise a relatively
large amount of organic solvents to control viscosity.
[0007] In WO2016/128166 is disclosed a solvent-based two-component
coating composition comprising a base paint component with a
polycarbonate diol, a hydroxyl-containing acrylate resin, polyester
resin and/or polyester/acrylate resin with a hydroxyl number of 75
to 500 mg KOH/g, and at least one organosilane modified filler, and
a polyisocyanate hardener component. The coating composition of
WO2016/128166 has 100 to 350 g/L organic solvent and has a
viscosity suitable for spray application.
[0008] The coating compositions of WO2016/128166 are, however,
relatively expensive.
[0009] There is a need in the art for less expensive coating
compositions that provide coatings with improved erosion resistance
that can be applied by spray application, do not need the use of UV
initiators and/or high temperature for curing and do not comprise
large amounts of organic solvents.
SUMMARY OF THE INVENTION
[0010] It has now been found that a two-component, solvent-based
coating composition comprising i) a base component comprising one
or more polyesterdiols with a hydroxyl value in the range of from
150 to 500 mg KOH/g and one or more organosilane-modified inorganic
fillers, and ii) a polyisocyanate curing component can be
formulated such that it has a viscosity suitable for spray
application (low viscosity under high shear rate) and yield
coatings with very good erosion resistance.
[0011] Accordingly, in a first aspect the invention provides a
two-component, solvent-based coating composition comprising:
[0012] i) a base component comprising [0013] (A) one or more
polyester diols having a hydroxyl value in the range of from 150 to
500 mg KOH/g polyester diol; [0014] (B) optionally one or more
hydroxyl-functional acrylate resins having a hydroxyl value in the
range of from 75 to 500 mg KOH/g resin; and [0015] (C) one or more
organosilane-modified inorganic fillers and
[0016] ii) a curing component comprising [0017] (D) one or more
polyisocyanates, in such amounts that the coating composition
comprises: [0018] 5 to 50 wt % of the one or more polyester diols
(A) [0019] 0 to 25 wt % of the one or more hydroxyl-functional
acrylate resins (B); [0020] 10 to 70 wt % of the one or more
organosilane-modified inorganic fillers (C); [0021] 5 to 40 wt % of
the one or more polyisocyanates (D)
[0022] wherein the coating composition comprises one or more
organic solvents in an amount in the range of from 5 to 35 wt %,
and has a viscosity in the range of from 50 to 2,000 mPas, as
measured by means of a rotary viscometer at a shear rate of 1,000
s.sup.-1, a temperature of 23.degree. C., 30 seconds after
combining and mixing the base component and the curing
component.
[0023] It is an advantage of the coating composition according to
the invention that it is easy to apply, even on large objects such
as rotor blades for wind turbines or aircrafts. The compositions
can be applied by spray application and can be cured without using
UV initiators or high temperature.
[0024] In a second aspect, the invention provides a method for
coating a substrate comprising applying a two-component coating
composition according to the first aspect of the invention to the
substrate and allowing the applied coating composition to cure,
preferably at a temperature of at most 80.degree. C., more
preferably at a temperature in the range of from 15.degree. C. to
60.degree. C.
[0025] In a third aspect, the invention provides a coated substrate
obtainable by a method according to the second aspect of the
invention.
[0026] The coating composition according to the invention, when
applied to a substrate, can be cured without using high temperature
whilst yielding coatings with excellent erosion resistance. The
coating composition according to the invention is therefore
particularly suitable for application to substrates that are
subject to severe erosive forces, such as rotor blades.
[0027] Therefore, in a final aspect, the invention provides use of
a coating composition according to the first aspect of the
invention for improving erosion resistance of a substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0028] The coating composition according to the invention is a
two-component coating composition. It comprises a base component i)
and a curing component ii).
[0029] Components i) and ii) are prepared and stored separately,
and are not combined until shortly before application of the
coating composition. The pot life (the time during which a coating
composition can be applied at a temperature in the range of from
15.degree. C. to 25.degree. C. without the viscosity increasing as
a result of crosslinking reactions to the extent that application
is no longer possible) depends on the constituents used, in
particular polyesterdiol(s) (A), optional hydroxyl-functional
acrylate resin(s) (B), and polyisocyanate(s) (D). Typically, the
pot life of the coating composition is in the range of from 0.1
minutes to 10 minutes, preferably of from 0.5 minutes to 5
minutes.
[0030] Curing of the two-component coating composition occurs
through chemical reaction of reactive functional groups of the
binder constituents in the coating composition, in particular
through reaction of the hydroxyl groups of the one or more
polyesterdiols and the optional one or more OH-functional acrylate
resins with the isocyanate groups of the one or more
polyisocyanates. Through these crosslinking reactions a coating
film, i.e. a cured coating layer, is formed. The term "binder" is
used herein in relation to those constituents in the coating
composition that are primarily responsible for film formation, in
particular the polyesterdiol(s), the further resin(s), and the
polyisocyanate(s). The polyisocyanate is also referred to as curing
agent or crosslinking agent.
[0031] The coating composition according to the invention comprises
in its base component one or more polyesterdiols having a hydroxyl
value in the range of from 150 to 500 mg KOH/g polyesterdiol.
[0032] A polyesterdiol is a polymer having a backbone comprising
several ester groups, i.e. --C(O)O-- groups with the carbon atom
directly linked to a carbon atom, and two pendant or terminal
hydroxyl groups.
[0033] The one or more polyesterdiols can suitably be prepared by
esterification of one or more carboxylic diacids with one or more
diols. Examples of suitable diols include ethylene glycol,
propylene glycol, butylene glycol, 1,4-butanediol, 1,6-hexanediol,
neopentyl glycol, and dimethylolcyclohexane. Examples of suitable
carboxylic diacids include phthalic acid, isophthalic acid,
terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid,
tetrachlorophthalic acid, cyclohexane dicarboxylic acid, succinic
acid, adipic acid, azelaic acid, sebacic acid, maleic acid, fumaric
acid, glutaric acid, and/or dimerized fatty acids.
[0034] The one or more polyesterdiols are preferably linear
polyesterdiols. The one or more polyesterdiols are preferably
hydroxyl-terminated polyesterdiols, more preferably
hydroxyl-terminated polyesterdiols with a terminal hydroxyl group
at both ends of a linear polyesterdiol.
[0035] The one or more polyesterdiols are preferably aliphatic
polyesterdiols, i.e. without aromatic groups, since such groups
exhibit significantly restricted UV resistance. Linear, aliphatic
polyesterdiols are particularly preferred.
[0036] The one or more polyesterdiols have an OH number in the
range of from 150 to 500 mg KOH/g, preferably of from 200 to 400 mg
KOH/g, more preferably of from 250 to 350 mg KOH/g (measured
according to DIN 53240).
[0037] In case of a hydroxyl-terminated polyesterdiol with a
terminal hydroxyl group at both ends of a linear polyesterdiol, the
OH number and the number-average molecular weight of the polyester
diol are dependent on one another. The OH number thus provides
information on the number-average molecular weight. A high
number-average molecular weight goes hand in hand with a low OH
number. The number-average molecular weight may vary widely, for
example in the range of from 220 g/mole to 2,250 g/mole (measured
by means of GPC analysis with THF (+0.1% acetic acid) as eluent (1
ml/min) on a styrene-divinylbenzene column combination, calibration
using polystyrene standards).
[0038] Suitable polyesterdiols are commercially available, for
example in the product line Synthoester.TM. (from Synthopol),
Desmophen.RTM. (from Covestro), or Rokrapol.RTM. (from
Kraemer).
[0039] The amount of the one or more polyesterdiols is in the range
of from 5 to 50 wt %, more preferably of from 7.5 to 40 wt %, even
more preferably of from 10 to 30 wt %, based on the total weight of
the coating composition.
[0040] Preferably, the coating composition comprises one
polyesterdiol (A).
[0041] The coating composition according to the invention may
comprise one or more hydroxyl-functional acrylate resins (B) in an
amount up to 25 wt % based on the total weight of the coating
composition. Preferably, the coating composition comprises one or
more hydroxyl-functional acrylate resins in an amount in the range
of from 1 to 20 wt %, more preferably of from 2 to 15 wt %. The one
or more hydroxyl-functional acrylate resins (B) have a hydroxyl
value in the range of from 75 to 500 mg KOH/g resin, preferably of
from 100 to 450 mg KOH/g, more preferably of from 175 to 400 mg
KOH/g, even more preferably of from 250 to 350 mg KOH/g.
[0042] Acrylate resins, also referred to as poly(meth)acrylate
resins, are well known polymeric organic compounds obtained by
reacting acrylate and/or methacrylate monomers.
[0043] Examples of acrylate and methacrylate monomers that can
suitably be used to obtain acrylate resin(s) (B) are alkyl
(meth)acrylates and cycloalkyl (meth)acrylates, such as ethyl
acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate,
isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl
methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl
acrylate, tert-butyl methacrylate, amyl acrylate, amyl
methacrylate, hexyl acrylate, hexyl methacrylate, ethylhexyl
acrylate, ethylhexyl methacrylate, 3,3,5-trimethylhexyl acrylate,
3,3,5-trimethylhexyl methacrylate, stearyl acrylate, stearyl
methacrylate, lauryl acrylate or lauryl methacrylate, cyclopentyl
acrylate, cyclopentyl methacrylate, isobornyl acrylate, isobornyl
methacrylate, cyclohexyl acrylate and cyclohexyl methacrylate.
[0044] The one or more acrylate resins (B) contain hydroxyl groups.
Such hydroxyl groups are typically introduced by incorporation into
the polymer structure of acrylate and methacrylate monomers with
hydroxyl groups. Suitable hydroxyl-containing monomers include
hydroxyalkyl (meth)acrylates, for example 2-hydroxyethyl acrylate,
2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate,
2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate,
3-hydroxypropyl methacrylate, 3-hydroxybutyl acrylate,
3-hydroxybutyl methacrylate, especially 4-hydroxybutyl acrylate
and/or 4-hydroxybutyl methacrylate.
[0045] Suitable hydroxyl-functional acrylate resins with a hydroxyl
value in the range of from 75 to 500 mg KOH/g resin are
commercially available, for example under the trade names
WorleeCryl (from Worlee) and Synthalat (from Synthpol).
[0046] Further ethylenically unsaturated monomers may be used to
prepare the acrylate resins, for example: vinylaromatic
hydrocarbons such as vinyltoluene, alpha-methylstyrene and styrene;
amides or nitriles of acrylic acid or methacrylic acid; vinyl
esters or vinyl ethers; and in particular acrylic acid and
methacrylic acid.
[0047] Preferably, the coating composition comprises at most one
hydroxyl-functional acrylate resin (B).
[0048] Preferably, the base component does not comprise any resins,
or binder constituents, other than the polyester diol(s) (A) and
any hydroxyl-functional acrylate resin(s) (B). Preferably, the
coating composition does not comprise any binder constituents,
other than the polyester diol(s) (A), any hydroxyl-functional
acrylate resin(s) (B), and the polyisocyanate(s) (D).
[0049] The coating composition according to the invention comprises
one or more organosilane-modified inorganic fillers (C). The
inorganic filler to be modified may be any inorganic filler known
to be suitable for coating compositions. Such fillers include
various substances, typically in granular or powder form, used to
achieve particular physical properties of coating compositions.
Suitable inorganic fillers include: carbonates such as calcium
carbonate, dolomite or barium carbonate; sulfates such as calcium
sulfate and barium sulfate; silicates and optionally
phyllosilicates such as talc, pyrophyllite, mica, kaolin, feldspar,
precipitated calcium, aluminum, calcium/aluminum, sodium/aluminum
silicates, mullite, wollastonite, nepheline such as nepheline
syenite, and silicon dioxide such as quartz and cristobalite. For
the purpose of the present invention, the group of silicates
includes silicon dioxide. Other suitable inorganic fillers are
precipitated silicas or fumed silicas, and metal oxides such as
aluminum hydroxide and magnesium hydroxide. Preferably, the
inorganic filler is a silicate.
[0050] The one or more inorganic fillers (C) are modified with
organosilane. The inorganic filler to be modified serves as
substrate to which an organosilane is applied under typical
conditions for physisorption and/or chemisorption. Through the
addition of an organosilane, the surface of the inorganic filler is
hydrophobized. Thus, the compatibility of the filler with the
hydrophobic polymer matrix of the coating composition is increased
by improving physical adsorption and optionally chemical reaction
to the other constituents of the coating composition. As a result,
the filler can more effectively improve mechanical resistance of
the coating deposited from the coating composition.
[0051] Modification of inorganic fillers with organosilane is known
in the art. Such modification process and organosilanes suitable
for such modification are for example described in detail in WO
2017/207521 (page 9, line 23 to page 12, line 12), incorporated
herein by reference. Preferably, the inorganic filler is modified
with an organosilane containing an epoxide or amino group, more
preferably an organosilane containing an organic radical containing
an epoxide group or an amino group bonded to the silicon atom via a
carbon atom. By incorporating such epoxide or amino groups in the
inorganic filler, the polarity of the filler is tuned and physical
adsorption to other components of the coating composition is more
effective. Moreover, upon curing of the coating composition, the
thus-modified inorganic filler can react with the functional groups
of the polyesterdiol(s), the optional OH-functional acrylic
resin(s) and/or of the polyisocyanate(s). Therewith, the filler can
be incorporated more effectively in the polymer network that is
formed.
[0052] Organosilane-modified inorganic fillers are commercially
available, for example under the trade names Tremin, Treminex,
Tremica or Silbond (from HPF The Mineral Engineers).
[0053] The particle size of the one or more organosilane-modified
inorganic fillers is not in itself a critical parameter and may be
in the range common for fillers, typically of from a few
micrometers to a few hundreds of micrometers. Preferably, the
average particle size (D50) is in the range of from 0.1 .mu.m to
100 .mu.m, more preferably of from 1 .mu.m to 50 .mu.m, as measured
by laser diffraction in accordance with ISO 13320:2009.
[0054] The amount of the one or more organosilane-modified
inorganic fillers (C) in the coating composition is in range of
from 10 to 70 wt %, preferably of from 15 to 60 wt %, more
preferably of from 20 to 50 wt %, based on the total weight of the
coating composition.
[0055] Preferably, the coating composition comprises less than 10
wt %, more preferably less than 3 wt %, even more preferably less
than 1 wt % of inorganic fillers other than organosilane-modified
inorganic fillers (C). Still more preferably, the coating
composition is free of inorganic fillers other than the one or more
organosilane-modified inorganic fillers (C). The term `inorganic
filler` herein does not include inorganic color pigments, inorganic
additives, or inorganic molecular sieves.
[0056] The two-component coating composition comprises one or more
polyisocyanates (D) in curing component ii).
[0057] Polyisocyanates are organic compounds having on average more
than one isocyanate groups per molecule and are known in the art.
The one or more polyisocyanates (D) may be aliphatic or
aromatic.
[0058] The one or more polyisocyanates may be modified
polyisocyanates, such as for example polyether-modified and/or
polyester-modified polyisocyanates. The isocyanate groups in these
components may be free or may be blocked with known blocking
agents. Preferably the isocyanate groups are non-blocked, i.e.
free, isocyanate groups.
[0059] Di-isocyanates, and dimers or trimers of di-isocyanates,
such as uretdiones, tri-isocyanurates, or biurets, are preferred
polyisocyanates. Suitable di-isocyanates include hexamethylene
di-isocyanate, octamethylene di-isocyanate, decamethylene
di-isocyanate, dodecamethylene di-isocyanate, tetradecamethylene
di-isocyanate, trimethylhexane di-isocyanate, tetramethylhexane
di-isocyanate, isophorone di-isocyanate (IPDI),
2-isocyanatopropylcyclohexyl isocyanate, dicyclohexylmethane
2,4'-di-isocyanate, dicyclohexylmethane 4,4'-di-isocyanate, 1,4- or
1,3-bis(isocyanatomethyl) cyclohexane, 1,4- or 1,3- or
1,2-di-isocyanatocyclohexane, 2,4- or
2,6-di-isocyanato-1-methylcyclohexane, any C2-C18 alkylated
derivative thereof, or a mixture of two or more thereof.
[0060] Preferred di-isocyanates are aliphatic di-isocyanates, more
preferably 1,6-hexamethylene di-isocyanate (HDI), 1,3-cyclohexyl
di-isocyanate, 1,4-cyclohexyl di-isocyanate (CHDI), 2,2,4- and/or
2,4,4-trimethyl-1,6-hexamethylene di-isocyanate, dodecamethylene
di-isocyanate, isophorone di-isocyanate (IPDI), and mixtures
thereof.
[0061] Uretdiones, tri-isocyanurates, or biurets of di-isocyanates,
preferably of aliphatic di-isocyanates, more preferably of
hexamethylene di-isocyanate (HDI), isophorone di-isocyanate (IPDI),
or mixtures thereof, are preferred. Particularly preferred is a
biuret or tri-isocyanurate of hexamethylene di-isocyanate.
[0062] The one or more polyisocyanatse preferably have an
isocyanate content in the range of from 10% to 25%, more preferably
of from 16%to 24%, even more preferably of from 20% to 23.5%. The
isocyanate content is determined in accordance with DIN EN ISO
11909 by reacting the one or more polyisocyanates with excess
dibutylamine and back-titrating with hydrochloric acid against
bromophenol blue.
[0063] The amount of the one or more polyisocyanates (D) is in the
range of from 5 to 40 wt %, preferably of from 10 to 30 wt %, more
preferably of from 12 to 25 wt %, based on the total weight of the
coating composition.
[0064] Preferably, the coating composition comprises one
polyisocyanate (D).
[0065] Preferably, the total amount of components (A), (B), (C),
and (D) in the coating composition is at least 40 wt %, more
preferably at least 50 wt %, based on the total weight of the
coating composition.
[0066] Preferably, the composition comprises one polyester diol
(A), at most one OH-functional acrylic resin (B), one or more
organosilane-modified inorganic fillers (C), one polyisocyanate
(D), and is free of any inorganic fillers other than the one or
more organosilane-modified inorganic fillers (C).
[0067] The ratio of the total molar amount of hydroxyl groups in
polyesterdiol(s) (A) and OH-functional acrylic resin(s) (B) to the
molar amount of isocyanate groups in polyisocyanate(s) (D) is
preferably in the range of from 1.0:0.9 to 1.0:1.5.
[0068] The coating composition is solvent-based and comprises one
or more organic solvents in an amount in the range of from 5 to 35
wt %, preferably of from 7.5 to 25 wt %, more preferably of from 10
to 20 wt %, based on the total weight of the coating
composition.
[0069] Reference herein to "organic solvent" is to organic solvent
as specified in Directive 1999/13/EC of the Council of Mar. 11,
1999 (published in the Official
[0070] Journal of the European Union on March 29, 1999). In the
Directive an organic solvent is specified as a "volatile organic
compound" which is used alone or in combination with other agents,
and without undergoing a chemical change, to dissolve raw
materials, products or waste materials, or is used as a cleaning
agent to dissolve contaminants, or as a dissolver, or as a
dispersion medium, or as a viscosity adjuster, or as a surface
tension adjuster, or a plasticizer, or as a preservative. The
aforementioned directive defines a "volatile organic compound" as
an organic compound having, at 293.15 K, a vapour pressure of 0.01
kPa or more, or having a corresponding volatility under the
particular conditions of use.
[0071] Examples of suitable organic solvents include: aliphatic
and/or aromatic hydrocarbons such as toluene, xylene, solvent
naphtha, Solvesso 100, or Hydrosol.RTM. (from ARAL); ketones, such
as acetone, methyl ethyl ketone or methyl amyl ketone; esters, such
as ethyl acetate, butyl acetate, butyl glycol acetate,
3-methoxy-n-butyl acetate, pentyl acetate, methoxypropyl acetate or
ethyl ethoxypropionate; ethers such as dipropylene glycol methyl
ether; alcohols; and hydrochlorocarbons.
[0072] The amount of organic solvent is chosen such that the
coating composition of the invention has a content of volatile
organic compounds (VOC) of at most 350 g/L, preferably of from 100
to 325 g/L, more preferably of from 150 to 300 g/L.
[0073] Particularly preferred organic solvents are aprotic
solvents, such as esters, ketones or hydrocarbons. Examples of
particularly suitable esters are esters of acetic acid such as
C1-4-alkyl esters of acetic acid and C1-4-alkoxyalkyl esters of
acetic acid, butyl acetate, 1- and 2-methoxypropyl acetate, butyl
glycol acetate and 3-methoxy-n-butyl acetate. Examples of
particularly suitable ketones are methyl isobutyl ketone, or
diketones such as acetylacetone. Examples of particularly suitable
hydrocarbon solvents are Shellsol A, or alkylbenzenes such as
xylene and toluene.
[0074] The coating composition preferably contains no or only minor
amounts of water. Preferably, the coating composition contains less
than 1.0 wt %, more preferably less than 0.2 wt %, even more
preferably less than 0.01 wt % of water, based on the total weight
of the coating composition. Water is preferably not explicitly
added, e.g. to adjust the viscosity of the coating composition, but
merely present, if at all, in small amounts as part of typical
coating additives.
[0075] In a preferred embodiment, the coating composition
comprises:
[0076] 10 to 30 wt % of the one or more polyester diols (A);
[0077] 0 to 25 wt % of the one or more hydroxyl-functional acrylate
resins (B);
[0078] 20 to 50 wt % of the one or more organosilane-modified
inorganic fillers (C);
[0079] 10 to 30 wt % of the one or more polyisocyanates (D);
and
[0080] 7.5 to 25 wt % of one or more organic solvents.
[0081] The coating composition may comprise, typically in its base
component i), further components generally known as constituents
for coating compositions, such as color pigments, catalysts or
additives.
[0082] The coating composition may comprise a molecular sieve or a
plurality of molecular sieves. Reference herein to molecular sieves
is to natural or synthetic zeolites with a relatively large
internal surface area (about 600 to 700 m.sup.2/g) and uniform pore
diameter. Suitable molecular sieves have a pore size in the range
of from 2 to 10 angstroms, preferably of from 3 to 4 angstroms. For
example, high-porosity aluminium silicates with a pore size of 3
angstroms may be used.
[0083] Preferably, the coating composition comprises a molecular
sieve in an amount up to 20 wt %, preferably in the range of from 1
to 15 wt %, more preferably in the range of from 2 to 10 wt %,
based on the total weight of the coating composition.
[0084] The coating composition may comprise dyes, color pigments,
or further catalysts. Color pigments, including white pigments, may
be present in customary amounts; typically in the range of from 8
wt % to 30 wt %, based on the total weight of the coating
composition.
[0085] The coating composition may comprise one or more catalysts
for the catalysis of the reaction of hydroxyl groups with
isocyanate groups. The coating composition preferably contains 0.01
to 2 wt %, based on the total weight of the coating composition, of
such catalyst. Suitable catalysts are the known in the art and
include metal catalysts such as tin, molybdenum, zirconium or zinc
catalysts and amine catalysts such as 2-(2-dimethylaminoethoxy)
ethanol. Particularly suitable catalysts are tin compounds such as
dialkyltin dicarboxylates, in particular dimethyltin dilaurate or
dibutyltin dilaurate.
[0086] The coating composition may comprise typical additives such
as antioxidants, de-aerating agents, wetting agents, dispersants,
adhesion promoters, rheology modifiers such as thickeners, waxes
and wax-like compounds, biocides, matting agents, radical
scavengers, light stabilizers or flame retardants. Additives may be
present in customary amounts, typically in the range of from 0.1 to
10 wt %, based on the total weight of the coating composition.
[0087] The density of the coating composition is preferably in the
range from 1,100 to 1,700 g/L, more preferably of from 1,200 to
1,650 g/L, even more preferably of from 1,300 to 1,600 g/L.
[0088] The solids content of the coating composition according to
the invention is preferably in the range of from 70% to 95 wt %,
more preferably of from 75% to 92.5%, even more preferably of from
80 to 90 wt %.
[0089] By solids content (non-volatile fraction) is meant the
weight fraction which remains as a residue on evaporation under
specified conditions. In the present application, the solids
content is determined according to DIN EN ISO 3251. This is done by
evaporating the composition at 130.degree. C. for 60 minutes.
[0090] The coating composition of the invention has a viscosity in
the range of from 50 to 2,000 mPas as measured by means of a rotary
viscometer at a shear rate of 1,000 s.sup.-1, a temperature of
23.degree. C., 30 seconds after combining and mixing the base
component and the curing component. Preferably the coating
composition has, at a shear rate 1,000 s.sup.-1, a viscosity in the
range of from 50 to 2,000 mPas, more preferably in the range of
from 200 to 1,000 mPas (measured as indicated hereinbefore). The
measurement by means of a rotary viscometer is carried out
according to DIN 53019.
[0091] Thus, the coating composition has a relatively low viscosity
at high shear rate and can suitably be applied to a substrate via
spray application. At spray application, a coating composition is
subjected to high shear rate when leaving the spray nozzle.
[0092] Preferably, the coating composition has a viscosity in the
range of from 1,000 to 10,000 mPas at a shear rate of 1 s.sup.-1,
and the coating composition has a viscosity at a shear rate of
1,000 s.sup.-1 that is 2 to 20 times lower than its viscosity at a
shear rate of 1 s.sup.-1, wherein the viscosity is measured by
means of a rotary viscometer, at a temperature of 23.degree. C., 30
seconds after combining and mixing the base component and the
curing component (determined according to DIN 53019). More
preferably, the viscosity at a shear rate of 1 s.sup.-1 is in the
range of from 1,500 to 7,500 mPas and a factor 5 to 15 lower at a
shear rate of 1,000 s.sup.-1. Even more preferably, the viscosity
at a shear rate of 1 s.sup.-1 is in the range of from 2,500 to
5,000 mPas and a factor 6 to 10 lower at a shear rate of 1,000
s.sup.-1.
[0093] The coating composition has a low viscosity during spray
application, when high shear conditions exist, so that it can
reasonably be atomized. Immediately after application, when hardly
any or low shear forces are exercised, the viscosity is
sufficiently high to provide sag-resistance and avoiding the
coating to drip off the substrate.
[0094] The invention further relates to method for coating a
substrate comprising applying the two-component coating composition
according to the first aspect of the invention to the substrate and
allowing the applied coating composition to cure.
[0095] The coating composition may be applied by any technique
known in the art such as spraying, roller coating, brushing,
pouring, or by cartridge application. Preferably, the coating
composition is applied by spray application. Spray application is
well known in the art and includes techniques such as compressed
air spraying, airless spraying, rotary bell spray application,
electrostatic spray application, optionally combined with hot spray
application, and air induction spraying. As already described, the
coating composition of the invention is particularly suitable for
spray application because of its specific rheological properties,
in particular its low viscosity under high shear stress.
[0096] Following application, the applied coating is allowed to
cure, preferably at a temperature of at most 80.degree. C., more
preferably at most 60.degree. C., even more preferably at a
temperature in the range of from 15 to 60.degree. C., still more
preferably of from 15 to 50.degree. C.
[0097] The time needed for complete curing varies with the curing
temperature. Typical curing times are in the range of from 30
minutes to 10 days. Curing may for example require 30 minutes at a
curing temperature in the range of from 40.degree. C. to 60.degree.
C., or 7 days at a curing temperature in the range of from 15 to
25.degree. C.
[0098] The cured coating suitably has a dry film thickness in the
range of from 100 to 500 pm, preferably of from 150 to 400
.mu.m.
[0099] The substrate may be any suitable substrate. The substrate
preferably is a metal substrate, such as steel or aluminium, or a
plastic substrate, more preferably a fiber-reinforced plastic
substrate. Epoxy resin-based plastic substrates, in particular
fiber-reinforced epoxy resin-based plastic substrates, are
particularly preferred. Suitable fibers for reinforcement are glass
fiber, aramid fiber and/or carbon fiber, or natural fibers, such as
hemp or sisal. Preferred substrates are glass fiber-reinforced
epoxy resin based plastic substrates. The substrate may have any
desired size or shape.
[0100] The coating composition according to the invention is
advantageously applied to very large substrates, such as rotor
blades, since it can suitably be applied by spray application
followed by curing at room temperature (e.g. 15 to 25.degree. C.),
i.e. without the need for heat supply. Due to the very good erosion
resistance of the resulting coatings, the coating composition is
preferably applied to a substrate that will be exposed to rain or
sand erosion, such as rotor blades of wind turbines or helicopters,
ship screws, air vehicles such as airplanes. Particularly suitable
substrates are rotor blades of wind turbines, and surfaces of
airplanes.
[0101] Due to its high erosion resistance, the coating composition
according to the invention is preferably applied as a topcoat. The
substrate to which it is applied may already comprise one or more
coating layers (e.g. primer coating or surfacer coating) before
applying the coating composition according to the first aspect of
the invention as a topcoat layer.
[0102] The invention further relates to a coated substrate
obtainable by a method according to the second aspect of the
invention, i.e. to which a coating composition according to the
first aspect of the invention has been applied followed by curing.
Preferably the coated substrate comprises multiple coating layers
and the coating composition according to the first aspect of the
invention provides a topcoat layer.
[0103] The invention will be further illustrated by means of the
following non-limiting examples.
EXAMPLES
[0104] 1. Test Methods
[0105] 1.1 General Remarks
[0106] For laboratory determination of erosion resistance, a
variety of equipment can be used that moves the coated substrate to
be tested through an erosion medium or wherein the substrate is
fixed and erosion medium flows around it. A stationary test
specimen can for example be tested using high-pressure water
jetting as typically used for water jet cutting. The erosion effect
is controlled by water pressure, distance to the test specimen, and
type and size of the nozzles.
[0107] The effect can be intensified by the use of sand, corundum
or silicon carbide. Alternatively, sand blasting or steam blasting
may be used, wherein pressure, nozzle size, and distance to the
test specimen may likewise be used to control the erosion effect
and adapt it to realistic conditions.
[0108] In rain erosion tests for moving test specimen, the coated
substrate is attached to a rotor or a disk and is radially moved
through a curtain of water droplets or of mixtures of water
droplets and salt or sand. The most common test scenario used in
the wind energy industry operates with velocities of 140 m/s and a
rain volume of 30 I/h. In the airplane industry, velocities of up
to 220 m/s are used, with a comparable rain volume. The test for
rain erosion resistance may be carried out in accordance with ASTM
G 73.
[0109] 1.2 Test Conditions
[0110] Rain erosion resistance was tested in accordance with ASTM G
73. Test specimens were spun with a velocity of 140 m/s through a
curtain of water droplets. The rain volume was kept constant at 30
I/h. The droplet size of the applied "rain" was on average 5-6 mm.
The test was carried out at a temperature of 20 to 25.degree. C.
The test specimens were visually evaluated at time intervals of 15
minutes. The erosion resistance corresponds to the time until the
substrate was visible through the coating.
[0111] 2. Preparation of Coating Compositions and Coated
Substrates
[0112] Base components and curing components for various coating
compositions (I=according to the invention; C=comparative) were
prepared by combining the respective constituents and homogeneously
mixing them in a dissolver (see Table 1 for the composition of the
coating compositions). For each coating composition, the base
component and the curing component were homogeneously mixed in the
proportions indicated in Table 1.
[0113] The viscosity of the coating compositions prepared was
determined 30 seconds after combining and mixing the base component
i) and curing component ii), by means of rotary viscometer (HAAKE
RheoStress 600) under a shearing rate of 1 s.sup.-1 and under a
shear rate of 1,000 s.sup.-1, at a temperature of 23.degree. C.
(DIN 53019).
[0114] Immediately after preparation, the coating compositions were
applied by airmix spray application to a glass fiber-reinforced
epoxy resin based test specimen already coated with a commercially
available polyurea-based pore filler. Curing took place by storage
at 20 to 25.degree. C. for 7 days. The dry film thickness of the
cured coating was 300 micrometers.
[0115] The rain erosion resistance of the multiple coat (pore
filler coat and topcoat) thus formed was investigated. The results
are shown in Table 2.
TABLE-US-00001 TABLE 1 Composition and characteristics of coating
compositions Wt % in component i) or ii) (g/g) Constituent I1 I2 I3
I4 I5 C1 C2 Base component Linear, aliphatic 22.75 22.75 22.75 16.0
17.0 polyesterdiol; terminal OH groups; OH value 270 Linear,
aliphatic 23.0 polyesterdiol; terminal OH groups; OH value 100
Linear, aliphatic 17.0 polycarbonatediol; terminal OH groups; OH
value 270 OH-functional polyacrylate*; -- -- -- -- 6.0 6.0 OH value
260 Thixotrope 0.7 2 0.7 2.4 0.7 0.7 0.7 Aminosilane-modified 31 33
26 44.9 26 26 31 wollastonite Molecular sieve 3.7 3.7 3.7 3.7 3.7
3.7 3.7 Additive in organic solvent 4.0 4.0 4.1 4.1 4.1 4.1 4.0
White pigment 15.4 -- 21.4 13.86 21.4 21.4 15.4 Red pigment -- 3 --
-- -- Yellow pigment 6.7 Red pigment (metal oxide) 0.003 0.003
0.003 Pigment paste (black) 0.6 0.002 0.5 0.002 0.002 0.6 Violet
pigment 0.1 Yellow pigment (metal oxide) 0.8 -- 0.045 0.7 0.045
0.045 0.8 Matting agent 2.8 0.35 2.8 -- 2.8 2.8 2.8 Organic solvent
** 18.18 24.33 18.18 13.77 18.18 18.18 18.0 Catalyst (tin- based)
0.07 0.07 0.07 0.07 0.07 0.07 0.07 Total 100 100 100 100 100 100
100 Curing component Tri-isocyanurate of HDI; 23.3 23.3 23.3 16.7
23.3 10.0 23.3 isocyanate content 23% Total 123.3 123.3 123.3 116.7
123.3 110 123.3 Density (g/mL) 1.4 1.4 1.4 1.6 1.4 1.4 1.4 VOC
(g/l) 240 294 240 227 240 230 240 Viscosity at 1,000 s.sup.-1 1,000
1,500 1,100 2,000 1,900 1,800 1,200 (mPa s) Viscosity at 1 s.sup.-1
(mPa s) 4,800 7,100 3,800 6,200 6,000 7,200 3,780 *Synthalat AT-H
2104 ** mixture of butylglycol acetate (9.5 wt %) and butyl acetate
(90.5 wt %)
TABLE-US-00002 TABLE 2 Rain erosion resistance of coated substrates
I1 I2 I3 I4 I5 C1 C2 Rain erosion resistance >300 >300
>300 >600 >300 50 240 (minutes)
* * * * *