Note: Descriptions are shown in the official language in which they were submitted.
CA 02221676 1997-11-20
Mo4632
MD-95-66-CT
COATINGS BASED ON POLYISOCYANATES
AND ALIPHATIC ALDIMINES THAT HAVE
IMPROVED MAR AND SCRATCH RESISTANCE
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention is directed to coatings that possess
improved mar and scratch resistance and are prepared from coating
compositions based on aliphatic aldimines and polyisocyanates
containing allophanate and/or uretdione groups.
10 Back~round of the Invention
As automotive finishes have become glossier and more mirror-like,
flaws in the coatings have become more visible. Two of the properties
that must be possessed by these coatings to reduce the number of flaws
are scratch and mar resistance and acid etch resistance, i.e., resistance
15 to acid rain, bird droppings, tree sap, etc. While melamine/acrylic based
coating compositions possess good scratch and mar resistance, they do
not possess good acid etch resistance.
Polyurethane coatings have been developed that overcome the
problems of acid etch resistance associated with melamine/acrylic resins.
20 However, many in the industry believe that polyurethane coatings do not
possess the level of scratch and mar resistance possessed by
melamine/acrylic coatings. Accordingly, it is an object of the present
invention to provide isocyanate-based coatings that possess good
scratch and mar resistance.
This object can be achieved with the coatings according to the
present invention, which are based on polyisocyanates containing
allophanate and/or uretdione groups and aldimines prepared form
aliphatic polyamines.
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Mo4632 -2-
Coating compositions based on polyisocyanates and aldimines are
known and disclosed, e.g., in U.S. Patents 5,446,771, 5,516,873 and
5,523,376, and in copending application, U.S. Serial No. 08/171,550.
U.S. Patent 5,446,771 is directed to coating compositions based on
5 allophanate group-containing polyisocyanates and aldimines and U.S.
Patent 5,523,376 is directed to coating compositions containing uretdione
group-containing polyisocyanates and aldimines. It disclosed that these
polyisocyanates possess improved compatibility with aldimines when
compared to other commercially available polyisocyanates.
U.S. Patent 5,516,873 is directed to coating compositions
containing aspartates in addition to polyisocyanates and aldimines. The
aspartates improve the compatibility between polyisocyanates and
aldimines. Copending application, U.S. Serial No. 08/171,550, is directed
coating compositions based on polyisocyanates and cycloaliphatic
15 aldimines. These coating compositions have long pot lives and may be
rapidly cured under ambient conditions. Finally, U.S. Patents 3,420,800
and 3,567,692 disclose coating compositions containing polyisocyanates
and either aldimines or ketimines, and U.S. Patent 5,214,086 discloses
coating compositions containing polyisocyanates, aldimines, polyols and
20 optionally polyaspartates.
While all of the preceding patents disclose coating compositions
containing various types of polyisocyanates and aldimines, none of these
patents teach that coatings obtained from the particular polyisocyanates
and aldimines required by the present invention would possess improved
25 scratch and mar resistance.
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Mo4632 -3-
SUMMARY OF THE INVENTION
The present invention is directed to coatings that have good
scratch and mar resistance and are prepared from coating compositions
containing
5 a) a polyisocyanate component containing
i) 0 to 25% by weight of allophanate groups (calculated as
HC2N2O3, MW 101 ) and/or
ii) 0 to 25% by weight of uretdione groups (c~lcul~ted as
C2N2O2, MW 84),
10 provided that polyisocyanate component a) contains a total of at least 2%
by weight of allophanate groups and uretdione groups,
b) an aldimine corresponding to the formula
X1-[N=cHcH(R1)(R2)]n
1 5 and
c) optionally a compound containing aspartate groups and
corresponding to the formula
X2 1~111 C--COOR3 ~)
CH--COOR4
n
25 wherein
X, represents the residue which is inert towards isocyanate
groups at a temperature of 100~C or less and is obtained by
removing the amino groups from an aliphatic polyamine
having n amino groups and a molecular weight of less than
400 and
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Mo4632 -4-
X2 represents an organic group which has a valency of n and
is inert towards isocyanate groups at a temperature of
100~C or less,
R, and R2 may be identical or different and represent organic
groups which are inert towards isocyanate groups at a
temperature of 100~C or less, or R1 and R2 together with
the ,B-carbon atom form a cycloaliphatic or heterocyclic ring,
R3 and R4 may be identical or different and represent organic
groups which are inert towards isocyanate groups at a
temperature of 100~C or less,
R5 and Rô may be identical or different and represent hydrogen or
organic groups which are inert towards isocyanate groups at
a temperature of 100~C or less and
n represents an integer with a value of at least 2,
15 wherein components a), b) and c) are present in an amount sufficient to
provide an equivalent ratio of isocyanate groups to aldimine groups and
aspartate groups of 0.5:1 to 5:1.
DETAILED DESCRIPTION OF THE INVENTION
When referring to isocyanate groups or isocyanate-reactive
20 groups, such as amino or hydroxy groups, the term "(cyclo)aliphatically
bound" means that the groups are bound to aliphatic and/or cycloaliphatic
carbon atoms. The term "aliphatically bound" means that the groups are
bound to aliphatic carbon atoms.
In accordance with the present invention it has been discovered
25 that coatings, which are prepared from coating compositions based on
polyisocyanates containing allophanate and/or uretdione groups and
aldimines prepared from aliphatic polyamines, have excellent mar and
scratch resistance. In addition to using the polyisocyanates containing
allophanate and/or uretdione groups as the polyisocyanate component,
30 these polyisocyanates may also be blended with other monomeric
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Mo4632 -5-
polyisocyanates, polyisocyanate adducts or NCO prepolymers, provided
that the polyisocyanate component has the required amount of
allophanate and/or uretdione groups.
The polyisocyanates containing allophanate groups may be
5 prepared by reacting mono-, di- or polyurethanes, which optionally
contain isocyanate groups, with monomeric di- or polyisocyanates at
elevated temperatures to form allophanate groups. The urethanes may
be prepared in an initial step by either 1 ) reacting monomeric di- or
polyisocyanates with monoalcohols or a mixture of mono and polyhydric
10 alcohols to form urethanes or 2) by reacting di- or polyhydric alcohols
with monoisocyanates or a mixture of mono- and di- or polyisocyanates
to form urethanes. If an excess of isocyanate groups is used, especially
according to method 1), the resulting urethanes will contain terminal
isocyanate groups. According to either method the urethane groups are
15 subsequently reacted with additional monomeric di- or polyisocyanates to
form allophanate groups. Alternatively, the polyisocyanates containing
allophanate groups may be prepared in situ by adding the alcohols to a
sufficient excess of monomeric di- and polyisocyanates to form both the
urethane and allophanate groups. Suitable processes for preparing
20 these products are described in U.S. Patents 4,160,080 and 3,769,318,
the disclosures of which are herein incorporated by reference.
If the urethanes are l.re,uared by using the stoichiometric amount
of isocyanate and hydroxy groups in accordance with either method 1 or
2, the resulting products will be substantially free of isocyanate groups.
25 The resulting urethanes can then be reacted with additional amounts of
di- or polyisocyanates in accordance with the processes described in the
previously mentioned U.S. patents.
Preferably the allophanate group-containing polyisocyanates are
prepared from a mixture of diisocyanates and either monohydric alcohols
30 or a mixture of mono- and polyhydric alcohols.
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Suitable monomeric di- and polyisocyanates that may be used to
prepare the allophanate group-containing polyisocyanates include the
known polyisocyanates, preferably diisocyanates, containing aliphatically-,
cycloaliphatically-, araliphatically- and/or aromatically bound isocyanate
groups that are described in U.S. Patents 5,466,771 and 5,523,376, the
disclosures of which are herein incorporated by reference.
Examples include of suitable organic diisocyanates include
1,4-tetramethyiene diisocyanate, 1,6-hexamethylene diisocyanate,
cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-3-isocyanatomethyl-
10 3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or IPDI), bis-(4-iso-
cyanatocyclohexyl)-methane, 2,4'-dicyclohexyl-methane diisocyanate,
1,3- and 1,4-bis-(isocyanatomethyl)-cyclohexane, bis-(4-isocyanato-3-
methyl-cyclohexyl)-methane, a,a,a',a'-tetramethyl-1,3- and/or -1,4-
xylylene diisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl
15 cyclohexane, 2,4- and/or 2,6-hexahydrotoluylene diisocyanate, 1,3-
and/or 1,4-phenylene diisocyanate, 2,4- and/or 2,6-toluylene
diisocyanate, and 2,4- and/or 4,4'-diphenylmethane diisocyanate.
Polyisocyanates containing 3 or more isocyanate groups such as
4-isocyanatomethyl-1,8-octamethylene diisocyanate and aromatic
20 polyisocyanates such as 4,4',4"-triphenylmethane triisocyanate and
polyphenyl polymethylene polyisocyanates obtained by phosgenating
aniline/formaldehyde condensates may also be used.
P~eferled diisocyanates are 1,6-hexamethylene diisocyanate,
isophorone diisocyanate and bis-(4-isocyanato-cyclohexyl)-methane. 1,6-
25 hexamethylene diisocyanate (HDI) is especially preferred.
Suitable mono- and polyhydric alcohols that may be used to
prepare the polyisocyanates containing allophanate groups include
saturated or unsaturated, preferably saturated, alcohols containing
aliphatically-, cycloaliphatically-, araliphatically- and/or aromatically-bound
30 hydroxy groups, such as the monoalcohols disclosed in U.S. Patents
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Mo4632 -7-
5,466,771 and 5,523,376, the disclosures of which are herein
incorporated by reference. The alcohols may be linear, branched or
cyclic, contain at least one carbon atom and have a molecular weight of
up to 2500. The alcohols may optionally contain other hetero atoms in
5 the form of, e.g., ether groups, ester groups, etc. Preferred
monoalcohols are hydrocarbon monoalcohols and monoalcohols
containing ether groups, more preferably the hydrocarbon monoalcohols.
The hydrocarbon monoalcohols preferably contain 1 to 36, more
preferably 1 to 20 and most preferably 1 to 8 carbon atoms. Examples
10 of suitable monoalcohols include methanol, ethanol, n-propanol,
isopropanol, n-butanol, isobutanol and tert. butanol, neopentyl alcohol, n-
hexanol, n-octanol, 2-ethyl hexanol, cyclohexanol, benzyl alcohol, phenol,
decanol, dodecanol, tetradecanol, hexadecanol and octadecanol. It is
also possible in accordance with the present invention to use mixtures of
15 the previously described monoalcohols or other alcohols.
Preferred polyhydric alcohols for preparing the allophanate group-
containing polyisocyanates are those having a molecular weight of less
than 400, such as ethylene glycol, propylene glycol, butanediol-1,4,
hexanediol-1,6, neopentyl glycol, 2-methylpropanediol-1,3, 2,2,4-
20 trimethylpentanediol-1,3, dimeric fatty alcohols, trimeric fatty alcohols,
glycerol, trimethylolpropane, trimethylolethane, the isomeric hexanetriols,
pentaerythritol and sorbitol. Also suitable are unsaturated alcohols such
as allyl alcohol, trimethylolpropane diallyl ether, butenediol and
monofunctional alcohols that are derived from corresponding acids or
25 acidic mixtures of unsaturated synthetic and naturally-occurring fatty
acids. Also suitable are alkoxylation products containing ether groups of
these polyhydric alcohols.
The polyisocyanates containing uretdione groups may be prepared
from any of the previously disclosed monomeric diisocyanates by any of
30 the known prior art methods, e.g., by catalytic dimerization in the
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presence of phosphine catalysts. These polyisocyanates may also be
prepared in accordance with U.S. Patent 4,929,724 (the disclosure of
which is herein incorporated by reference) by dimerizing a portion of the
isocyanate groups of an organic diisocyanate in the presence of a
5 dimerization catalyst containing phosphorus-nitrogen bonds and a co-
catalyst containing an isocyanate-reactive group and having a pKa-value
of at least 6. Another method for preparing these polyisocyanates is
through the use of dimerization catalysts which are covalently bound to
an insoluble inorganic matrix substrate as disclosed in U.S. Patent
10 5,315,004 (the disclosure of which is herein incorporated by reference).
The polyisocyanates containing allophanate and/or uretdione
groups may be blended with the previously described monomeric
diisocyanates, with other polyisocyanate adducts or with NCO
prepolymers, provided that the polyisocyanate component contains the
15 required amounts of allophanate groups and/or uretdione groups. The
other polyisocyanate adducts include those containing isocyanurate,
biuret, urethane, allophanate, carbodiimide and/or oxadiazinetrione
groups. The polyisocyanates adducts have an average functionality of 2
to 6 and an NCO content of 5 to 30% by weight. These polyisocyanate
20 adducts and methods for their preparation are described in U.S. Patents
5,466,771 and 5,523,376, the disclosures of which are herein
incorporated by reference.
Preferred polyisocyanate adducts are the polyisocyanates
containing isocyanurate groups, biuret groups or urethane groups,
25 especially isocyanurate groups.
Instead of using mixtures of polyisocyanates containing
allophanate groups and polyisocyanate adducts which have been
separately prepared, in certain cases it is possible to prepare these
mixtures in one step. For example, mixtures of polyisocyanates
30 containing allophanate and isocyanurate groups may be prepared by
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Mo4632 -9-
trimerizing the isocyanate starting material in the presence of
trimerization catalysts and monoalcohols, or by allophanatizing urethane
group-containing starting materials in the presence of a trimerization
catalyst. Suitable catalysts and methods of the production of these
polyisocyanate mixtures are disclosed, e.g., in U.S. Patents 5,124,427,
5,208,334, 5,235,018 and 5,444,146, the disclosures of which are herein
incorporated by reference. Similarly, it is possible to prepare mixtures of
polyisocyanates containing uretdione groups and isocyanurate groups in
one step by trimerizing the isocyanate starting material in the presence of
10 dimerization/trimerization catalysts such as tertiary phosphines or
peralkylated phosphorus acid triamides. Suitable catalysts and methods
of the production of these polyisocyanate mixtures are disclosed, e.g., in
U.S. Patents 4,614,785 and 4,994,541, the disclosures of which are
herein incorporated by reference.
Preferred mixtures of polyisocyanates are those containing
allophanate and isocyanurate groups or uretdione and isocyanurate
groups. The polyisocyanates according to the invention generally contain
a total of less than 2, preferably less than 1% of free (unreacted)
monomeric diisocyanates.
In addition to monomeric polyisocyanates and polyisocyanates
adducts, the polyisocyanates containing allophanate and/or uretdione
groups may also be blended with NCO prepolymers to improve their
compatibility with aldimines. Suitable NCO prepolymers are disclosed in
U.S. Patents 5,466,771 and 5,523,376, the disclosures of which are
25 herein incorporated by reference.
In accordance with the present invention the polyisocyanate
component may have an allophanate group content (c~lc~ ted as
HC2N2O3, MW 101 ) of at least 2%, preferably at least 4% by weight
and/or a uretdione group content (calculated as C2N2Oz, MW 84) of at
30 least 2%, preferably at least 4% by weight, in which the preceding
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Mo4632 -1 0-
percentages are based on the weight of polyisocyanate solids.
Polyisocyanate component a) should have a minimum total content of
allophanate groups and uretdione groups of 2%, preferably 4% by
weight, and a maximum total content of allophanate groups and
uretdione groups of 25%, preferably 20%, more preferably 15% by
weight, in which the preceding percentages are based on the weight of
polyisocyanate solids.
Suitable aldimines for as component b) include those prepared
from an aldehyde and polyamines corresponding to the formula
X1 (NH2)n
wherein
X, represents the residue which is inert towards isocyanate groups at
a temperature of 100~C or less and is obtained by removing the
amino groups from an aliphatic polyamine having n amino groups
and a molecular weight of less than 400, preferably a divalent
hydrocarbon group, and
n represents an integer with a value of at least 2, preferably 2 to 6,
more prererably 2 to 4 and most preferably 2.
Suitable low molecular aliphatic polyamine starting compounds
include tetramethylene diamine, ethylene diamine, 1,2- and 1,3-propane
diamine, 2-methyl-1,2-propane diamine, 2,2-dimethyl-1,3-propane
diamine, 1,3- and 1,4-butane diamine, 1,3- and 1,5-pentane diamine, 2-
methyl-1,5-pentane diamine, 1,6-hexane diamine, 1,7-heptane diamine,
1,8-octane diamine, 1,9-nonane diamine, 1,10-decane diamine, 1,11-
undecane diamine, 1,12-dodecane diamine, 4-aminomethyl-1,8-
octamethylene diamine, hydrazine, N,N,N-tris-(2-aminoethyl)-amine,
N-(2-aminoethyl)-1,3-propane diamine, and mixtures thereof.
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Mo4632 -1 1-
Preferred polyamines are 1,6-diaminohexane, 2-methyl-1,5-
pentane diamine, 4-aminomethyl-1,8-octamethylene diamine and
ethylene diamine.
Suitable aldehydes are those corresponding to the formula
O=CHCH(R,)(R2)
wherein
R, and R2 may be identical or different and represent organic
groups which are inert towards isocyanate groups at a temperature
of 100~C or less, preferably containing 1 to 10, more preferably 1
to 6, carbon atoms, or R, and R2 together with the ~-carbon atom
form a cycloaliphatic or heterocyclic ring.
Examples of suitable aldehydes include isobutyraldehyde, 2-ethyl
hexanal, 2-methyl butyraldehyde, 2-ethyl butyraldehyde, 2-methyl
valeraldehyde, 2,3-dimethyl valeraldehyde, 2-methyl undecanal and
15 cyclohexane carboxaldehyde.
The aldimines may be prepared in known manner by reacting the
polyamines with the aldehydes either in stoichiometric amounts or with
an excess of aldehyde. The excess aldehyde and the water which is
produced can be removed by distillation. The reactions may also be
20 carried out in solvents, other than ketones. The solvents may also be
removed by distillation after completion of the reaction.
Component c) is selected from compounds having at least two
aspartate groups and corresponding to the formula:
Rs
Xz r~l I C--COOR3 (1)
CH--COOR4
n
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Mo4632 -1 2-
wherein
X2 represents an organic group which has a valency of n and is inert
towards isocyanate groups at a temperature of 100~C or less,
preferably a hydrocarbon group obtained by removing the amino
groups from an aliphatic, araliphatic, cycloaliphatic or aromatic
polyamine, more preferably a diamine,
R3 and R4 may be identical or different and represent organic groups
which are inert towards isocyanate groups at a temperature of
1 00~C or less, preferably methyl or ethyl groups,
10 R5 and R6 may be identical or different and represent hydrogen or
organic groups which are inert towards isocyanate groups at a
temperature of 100~C or less, preferably hydrogen and
n represents an integer with a value of at least 2, preferably 2 to 6,
more preferably 2 to 4 and most preferably 2.
These compounds are prepared in known manner by reacting the
corresponding primary polyamines corresponding to the formula
X2 (NH2)n
with optionally substituted maleic or fumaric acid esters corresponding to
the formula
R3OOC-CR5=CR6-COOR4 (Ill)
Suitable polyamines include high molecular weight amines having
molecular weights of 400 to about 10,000, preferably 800 to about 6,000,
30 and low molecular weight amines having molecular weights below 400.
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Mo4632 -1 3-
The molecuiar weights are number average molecular weights (Mn) and
are determined by end group analysis (NH number).
Suitable low molecular weight polyamines include those previously
set forth for preparing aldimines b) and also 1-amino-3-aminomethyl-
5 3,5,5-trimethyl cyclohexane (isophorone diamine or IPDA), 2,4- and/or
2,6-hexahydro-toluylene diamine, 2,4'- and/or 4,4'-diamino-dicyclohexyl-
methane, 3,3'-dialkyl-4,4'-diamino-dicyclohexyl methanes (such as 3,3'-
dimethyl-4,4'-diamino-dicyclohexyl methane and 3,3'-diethyl4,4'-diamino-
dicyclohexyl methane), 1,3- and/or 1,4-cyclohexane diamine, 1,3-
10 bis(methylamino)-cyclohexane, 1,8-p-menthane diamine, phenylene
diamine, 2,4- and 2,6-toluylene diamine, 2,3- and 3,4-toluylene diamine,
2,4'- and/or 4,4'-diaminodiphenyl methane, higher functional polypheny-
lene polymethylene polyamines obtained by the aniline/formaldehyde
condensation reaction, guanidine, melamine, 3,3'-diamino-benzidine, 2,4-
15 bis-(4'-aminobenzyl)-aniline, polyoxypropylene amines, polyoxyethylene
amines and mixtures thereof.
Preferred polyamines are 1,4-diaminobutane, 1,6-diaminohexane,
2,2,4- and 2,4,4-trimethyl-1,6-diamino-hexane, 1,3- and/or 1,4-cyclo-
hexane diamine, 1-amino-3,3,5-trimethyl-5-aminomethyl-cyclohexane,
20 2,4- and/or 2,6-hexahydrotoluylene diamine, 4,4'-diamino-dicyclohexyl
methane, 3,3-dimethyl-4,4'-diamino-dicyclohexyl methane and 3,3-diethyl-
4,4'-diamino-dicyclohexyl methane.
Suitable high molecular weight aliphatic polyamines correspond to
the polyhydroxyl compounds used to prepare the NC0 prepolymers with
25 the exception that the terminal hydroxy groups are converted to amino
groups, either by amination or by reacting the hydroxy groups with a
diisocyanate and subsequently hydrolyzing the terminal isocyanate group
to an amino group. Preferred high molecular weight polyamines are
amine-terminated polyethers such as the Jeffamine resins available from
30 Texaco.
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Mo4632 -1 4-
Examples of optionally substituted maleic or fumaric acid esters
suitable for use in the preparation of the compounds corresponding to
formula I include dimethyl, diethyl and di-n-butyl esters of maleic acid and
fumaric acid and the corresponding maleic or fumaric acid esters
5 substituted by methyl in the 2- and/or 3-position.
The preparation of the "polyaspartic acid derivatives"
corresponding to formula I from the above mentioned starting materials
may be carried out, for example, at a temperature of 0 to 100~C using
the starting materials in such proportions that at least 1, preferably 1,
10 olefinic double bond is present for each primary amino group. Excess
starting materials may be removed by distillation after the reaction. The
reaction may be carried out solvent-free or in the presence of suitable
solvents such as methanol, ethanol, propanol, dioxane and mixtures of
such solvents.
The binders present in the coating compositions according to the
invention contain polyisocyanate component a), aldimine component b)
and optionally aspartate component c). The coating compositions may
contain other isocyanate-reactive compounds, such as polyols; however,
this is not preferred since their presence may reduce the overall
properties of the coating compositions and the resulting coatings.
Components a), b) and c) are used in amounts sufficient to provide an
equivalent ratio of isocyanate groups to aldimine groups and aspartate
groups of 0.5:1 to 5:1, preferably 0.8:1 to 3:1 and more preferably 1:1 to
2:1 .
When component c) is present, it is present in an amount of at
least 5%, preferably at least 10% by weight, up to an amount of 75%,
preferably up to 60% by weight, wherein these percentages are based on
the weight of components b) and c), to improve the compatibility between
polyisocyanates and aldimines so that the clarity, gloss and DOI of the
CA 02221676 1997-11-20
Mo4632 -1 5-
resulting coatings is also improved, and to improve the weatherability or
durability of the resulting coatings.
The binders to be used according to the invention are prepared by
mixing all of the individual components together or by premixing two of
the components before adding the third component. For example,
aspartate c) may be initially blended with the component a) or component
b), preferably component b) before the addition of the other component.
Preparation of the binders is carried out solvent-free or in the
presence of the solvents conventionally used in polyurethane or polyurea
10 coatings. It is an advantage of the process according to the invention
that the quantity of solvent used may be greatly reduced when compared
with that required in conventional two-component systems based on
polyisocyanates and polyols.
Examples of suitable solvents include xylene, butyl acetate, methyl
15 isobutyl ketone, methoxypropyl acetate, N-methyl pyrrolidone, Solvesso
solvent, petroleum hydrocarbons and mixtures of such solvents.
In the coating compositions to be used for the process according
to the invention, the ratio by weight of the total quantity of binder
components a), b) and c) to the quantity of solvent is about 40:60 to
20 100:0, preferably about 60:40 to 100:0.
In addition to binder components a), b) and c), the coating
compositions may also contain the known additives from coatings
technology, such as fillers, pigments, softeners, high-boiling liquids,
catalysts, UV stabilizers, anti-oxidants, microbiocides, algicides,
25 dehydrators, thixotropic agents, wetting agents, flow enhancers, matting
agents, anti-slip agents, aerators and extenders. The additives are
chosen based on the requirements of the particular application and their
compatibility with components a) and b). The coating compositions may
be applied to the substrate to be coated by conventional methods such
30 as painting, rolling, pouring or spraying.
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Mo4632 -1 6-
The coatings according to the invention have high hardness,
elasticity, very good resistance to chemicals, high gloss, good weather
resistance, good environmental etch resistance and good pigmenting
qualities. Most importantly, the coatings possess good mar and scratch
resistance.
The invention is further illustrated, but is not intended to be limited
by the following examples in which all parts and percentages are by
weight unless otherwise specified.
EXAMPLES
10 Polyisocyanate 1
An polyisocyanate which contains allophanate groups and
isocyanurate groups, is prepared from 1,6-hexamethylene diisocyanate
and has an isocyanate content of 19%, a monoallophanate group content
of 11%, a content of monomeric diisocyanate of <0.2% and a viscosity at
15 25~C of about 270 mPa s (available from Bayer Corporation as
Desmodur XP-7040).
Polyisocyanate 2
An polyisocyanate which contains allophanate groups and
isocyanurate groups, is prepared from 1,6-hexamethylene diisocyanate
20 and has an isocyanate content of 20.3%, a monoallophanate group
content of 4.4%, a content of monomeric diisocyanate of <0.2% and a
viscosity at 25~C of about 1100 mPa s (available from Bayer Corporation
as DesmodurXP-7100).
PolyisocYanate 3
A mixture containing 70 parts by weight of a uretdione group-
containing polyisocyanate, i.e., dimerized 1,6-hexamethylene
diisocyanate and 30 parts by weight of N,N',N"-tris-(6-isocyanatohexyl)-
isocyanurate together with minor quantities of higher homologs of both
products. In its 100% solvent free form, the polyisocyanate had an
CA 02221676 1997-11-20
- Mo4632 -17-
average viscosity of 150 mPa s at 23~C and an average NCO content of
22.5% (available from Bayer Corporation as Desmodur N 3400).
Polyisocyanate 4
An isocyanurate group-containing polyisocyanate prepared from
5 1,6-hexamethylene diisocyanate and having an isocyanate content of
21.6%, a content of monomeric diisocyanate of <0.2% and a viscosity at
20~C of 3000 mPa s (available from Bayer Corporation as
Desmodur N 3300).
Preparation of Aldimines
The following aldimines were prepared by initially charging 21
equivalents of isobutraldehyde and then slowly charging 20 equivalents
of the polyamine over a period of thirty minutes to avoid an exotherm.
After the addition of the polyamine the reaction mixture was stirred for
one hour. At this time stirring was stopped and water was allowed to
15 settle to the bottom of the reactor. As much water as possible was
drained from the bottom of the reactor. The reaction mixture was then
heated to 100~C to remove excess isobutraldehyde. While maintaining a
temperature of 100~C, a vacuum of approximately 20 mm Hg was
applied to remove any final traces of aldehyde. Thereafter the vacuum
20 was increased to 1 mm Hg to remove water until the water content was
less than 0.05% (approximately 1 to 3 hours.)
Aldimine 1
The aldimine of 2-methyl pentamethylene diamine and
isobutyraldehyde was prepared using the procedure described for
25 aldimine 1. The resulting aldimine had an equivalent weight of 112 and a
viscosity of 10 mPa s at 25~C.
Aldimine 2
The aldimine of hexamethylene diamine and isobutyraldehyde.
The resulting aldimine had an equivalent weight of 112 and a viscosity of
30 10 mPa s at 25~C.
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Aldimine 3
The aldimine of 4-aminomethyl-1,8-octamethylene diamine and
isobutyraldehyde. The resulting aldimine had an equivalent weight of
112 and a viscosity of 12-15 mPa s at 25~C.
5 Aldim ine 4
The aldimine of bis-(4-aminocyclohexyl)-methane and
isobutraldehyde. The resulting aldimine had an equivalent weight of 159
and a viscosity of 70 mPa s at 25~C.
Aldimine 5
The aldimine of isophorone diamine and isobutraldehyde. The
resulting aldimine had an equivalent weight of 140 and a viscosity of 30
mPa s at 25~C.
Preparation of Aspartates
1 mole of the diamine was added dropwise with stirring to 2 moles
15 of maleic acid diethylester that were previously charged at ambient
temperature to a 1 L three necked flask equipped with a stirrer,
thermometer and an addition funnel. The amine was added at a rate
such that the exotherm did not increase the temperature of the reaction
mixture above 50~C. Upon complete addition the contents of the reaction
20 flask were maintained at 50~C for a period of 12 hours. The resulting
product was a clear, colorless liquid.
Polyaspartate 1
The aspartate of 4,4'-diamino-dicyclohexylmethane, which has a
viscosity of about 1400 mPa s (25~C) and an equivalent weight of about
25 276 g/eq.
Polyaspartic Acid Ester 2
The aspartate of bis-(4-amino-3-methyl-cyclohexyl)-methane, which
has a viscosity of about 1500 mPa s (25~C) and an equivalent weight of
about 291 g/eq.
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ExamPles 1-8 and Comparison Examples 1-8
A commercial black waterborne OEM basecoat was spray applied
to pretreated steel panels at a dry film thickness of 0.7 to 0.8 mils. The
basecoats were flashed for 5 min. at ambient temperature and then force
5 dried for 10-15 min. at 83~C. They were cooled to ambient temperature
before the clearcoat was spray applied at a dry film thickness of 1.5 to
1.8 mils. The basecoaVclearcoat panels were then baked for 30 min. at
120~C.
The compositions of the binders for the clearcoats are set forth in
10 the following table. In addition to these binder components, the coating
compositions also contained 0.65% of an acrylate copolymer (available
as Byk 358 from Byk Chemie), 0.85% of a hindered amine light stabilizer
(available as Tinuvin 292 from Ciba-Geigy), 1.7% of a benzotriazole light
stabilizer (available as Tinuvin 1130 from Ciba-Geigy), 0.25% of octanoic
15 acid and 11.7% of butyl acetate, in which all percentages are based on
the total weight of the coating compositions. The binder components
were formulated an NCO:NH equivalent ratio of 1.1 :1Ø
Test Method to Assess Mar and Scratch Resistance of Coatings
An Atlas MTCC Crockmeter, Model CM-5 (Atlas Electric Devices
20 Company, Chicago, IL) wàs used to measure mar resistance.
BasecoaVclearcoat panels measuring 3"x 6" were prepared. A foam pad
about 4.4 cm wide by 1.9 cm deep was applied to the acrylic finger on
the Crockmeter. For east test, a fresh piece of linen cloth the size of the
pad was applied to the bottom of the foam pad. Bon Ami Cleanser was
25 applied to the coated panel and the excess tapped off, leaving a thin film
of cleanser on the panel. The panel was situated on the Crockmeter,
and the meter was set for 10 back and forth rubs. After testing, the
panel was washed with water to remove the cleanser, and carefully dried.
Mar resistance was determined by 20~ gloss loss, i.e., the gloss reading
30 after abrading the panel was subtracted from the reading before the test.
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The reported gloss loss is the average of 3 readings from each of the
duplicate panels.
Table
Examples according 1 2 3 4 5 6 7 8 ~
to the invention
Aldimine/Amount 1/287.2 2122.2 3124.6 3124.2 3/15.4 1/15.3 2/15.4 3/14.5
Aspartate/Amount -- -- -- -- 1/15.4 1/15.3 2/15.4 2/14.5
Isocyanate/Amount 2/316.6 1/48.4 3145.9 2147.3 2142.3 2/42.1 2/41.7 1/43.8
Gloss Loss 0.5 0 0.1 0 0.9 1.6 0 1.6 D
Comparison 1 2 3 4 5 6 7 8
Examples
Aldimine/Amount 5/329.8 5/308.0 4/30.7 -- 4/17.6 5/16.7 5/16.9 4/16.7
Aspartate/Amount -- -- -- 1/42.4 1/17.6 1/16.7 2/16.9 2/16.7
Isocyanate/Amount 2/519.4 1/541.1 3/40.3 2133.5 2138.2 2139.6 2139.3 1/39.7
Gloss Loss 13.1 23.3 19.6 17.1 28.1 7.3 6.5 11.2
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In the preceding examples, the examples according to the
invention are identical to the corresponding comparison examples (i.e.,
Example 1 is identical to comparison example 1, etc.) except for the fact
that aliphatic aldimines are used in the examples according to the
invention and cycloaliphatic or mixed aliphatic/cycloaliphatic aldimines are
used in the comparison examples.
The preceding examples demonstrate that coatings prepared from
aliphatic aldimines have much better gloss retention than coatings
prepared from cycloaliphatic aldimines or mixed aliphatic/cycloaliphatic
aldimines. The improved gloss retention is indicative of improved mar
and scratch resistance.
Example 9 and ComParison Examples 9 and 10
A commercial solvent-borne black refinish basecoat was spray
applied to aluminum panels at a dry film thickness of 0.7 to 0.8 mils.
The basecoats were then flashed for 30 min. at ambient temperature.
The clearcoat was spray applied over the basecoat at a dry film
thickness of 1.5 to 1.8 mils and the basecoaVclearcoat panels were then
baked for 30 min. at 120~C. The binder components for the clearcoats
were formulated an NCO:NH equivalent ratio of 1.1:1.0 and had the
following compositions:
Example 9 - According to the invention
20.4 parts aldimine 2
0.3 parts acrylate copolymer (available as Byk 358 from Byk
Chemie)
19.8 parts butyl acetate
30 41.0 parts polyisocyanate 2
Comparison Example 9
A commercial OEM clearcoat based on acrylic/melamine
chemistry.
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Comparison Example 10
45.9 parts acrylic/polyester blend polyol (Desmophen A-565, available
from Bayer Corp, OH equivalent weight, 654)
0.4 parts acrylate copolymer (available as Byk 358 from Byk
Chemie)
19.8 parts solvent (a 3:2:1:1 blend of butyl acetate/methylisobutyl
acetate/Solvesso 100 solvenVmethylamyl ketone)
15.6 parts polyisocyanate 4
Results - 20~ Gloss Loss
Example # 20~ Gloss Loss
Example 9 0
Comparison Example 9 9
Comparison Example 10 4
These examples demonstrate that even when compared to standard
commercials coatings, such as acrylic melamines (Comparison
Example 9) or polyurethanes (Comparison Example 10), the coatings
according to the invention possess improved scratch and mar resistance
20 as evidenced by the increase in gloss retention.
Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood that such
detail is solely for that purpose and that variations can be made therein
by those skilled in the art without departing from the spirit and scope of
25 the invention except as it may be limited by the claims.
