Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Utility Patent
1999-05-13
2001-01-02
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S372000, C524S590000, C524S757000, C524S874000, C528S044000, C528S060000, C528S061000, C528S064000, C528S049000
Utility Patent
active
06169141
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high solids coating compositions containing polyaspartic acid esters, polyaldimines, polyisocyanates and special additives, and to their use for preparing anti-corrosive topcoats.
2. Description of the Prior Art
The annual damage caused by corrosion worldwide is estimated at more than $50 billion, so that the development of ever better anti-corrosive coatings is of great importance. As in almost all areas of coatings technology, more stringent requirements specifying a significant reduction in the solvent content of coating compositions must be taken into consideration in the development of these compositions. For example, the US authorities require a VOC content of max. 340 g/I for anti-corrosive topcoats. TL sheet 95 of the German Railways specifies a minimum solids content of 65 vol. % for low-solvent two-component (2K) topcoat compositions. If these specifications are complied with and a combination of hydroxy-functional polyacrylate resins with polyisocyanates is used as the 2K polyurethane (PU) system, it is only possible to prepare coatings having a maximum thickness of 50 &mgr;m. The application of thicker layers is associated here with a lack of non-sag properties.
Therefore, it is an object of the present invention to provide 2K PU top coat compositions which have a solids content of at least 80 vol. % and may be applied in thicknesses of up to 180 &mgr;m, which previously was not possible without blistering. It is an additional object of the present invention to provide compositions having a viscosity which is sufficiently low such that there are no substantial limitations on the method chosen for applying the coating. Finally, it is an object of the present invention of provide compositions having a sufficiently long pot life in combination with a short drying time so that optimum surface protection is obtained as rapidly as possible.
These objects can be achieved with the high solids, 2K PU coating compositions of the present invention which contain polyisocyanates and certain amino-functional reactive thinners as reaction components in combination with a special blend of additives.
The amino-functional reactive thinners are polyaspartic acid esters, polyketimines and polyaldimines, such as those described, e.g., in EP-A 0 689 881. In polyaspartic acid esters the otherwise very high reactivity of amino groups with isocyanate groups is reduced by steric and electronic effects (“hindered amines”). In polyketimines and polyaldimines the primary amino groups are blocked by reaction with aldehydes or ketones to form imino groups, and only regain their reactivity by hydrolysis or the action of heat (rearrangement reactions). Curing of these polyamines with polyisocyanates results in coatings with very good mechanical properties.
Compositions containing polyisocyanates, polyaspartic acid esters and polyaldimines or polyketimines and their use as a binder in 2K PU high-solids paints are known.
EP-A 0 531,249 describes the use of a binder mixture of polyisocyanates, polyaldimines or polyketimines and polyaspartic acid esters exclusively with hydroxy-functional compounds automotive refinish compositions. EP-A 0,699,696 describes a blend of polyisocyanates, polyaspartic acid esters, polyaldimines and mixed aspartic acid ester/aldimines corresponding to formula 1:
wherein
X is an alkylene radical and
a and b are integers between 1 and 5 and
a+b is an integer between 2 and 6.
Better compatibility between the polyisocyanate component and the aldimine component is mentioned as an advantage of this mixture.
Compositions containing only polyisocyanates, polyketimines or polyaldimines and polyaspartic acid esters—optionally together with the additives known from coatings technology—are described in EP-A 0,689,881. Coatings having a solids content of up to 95 wt. % can be achieved with these binder compositions. Such high solids, coating compositions not only are of great interest ecologically, but are also of economic importance because of the low solvent content. However, it is found that coatings produced therefrom no longer meet the special requirements of an anti-corrosive top coat with respect to adequate coating thickness and the absence of cracks.
When these coating compositions are applied in coating thicknesses of more than 80 mm, “sagging” as a result of insufficient non-sag properties, and 120 mm blisters in the coating are observed.
It has now been found that coating compositions containing polyisocyanates, polyaspartic acid esters and polyketimines or polyaldimine in combination with a special additive combination of bis-(2-phenoxyethyl) formal and castor oil, can satisfy the requirements of a high solids, anti-corrosive top coat composition:
i) a high solids content of>90 wt. %),
ii) good non-sag properties, i.e., no sagging on vertical surfaces,
iii) no blistering during drying of the coating,
iv) adequate pot lives,
v) dry times of less than 8 hours,
vi) diverse application possibilities,
vii) layer thicknesses of up to 180 nm,
viii) very good adhesion,
ix) no cracking in the coating on heating and
x) resistance of the coating to weathering.
SUMMARY OF THE INVENTION
The present invention relates to a coating composition containing
A) 25 to 50 wt. % of a polyisocyanate component,
B) 5 to 20% wt. % of one or more polyamines corresponding to formula II:
wherein
X represents an n-valent radical which is inert towards isocyanate groups and is obtained by removing the primary amino groups from an organic polyamine having a number average molecular weight of 88 to 400 and containing n primary (cyclo)aliphatically bound amino groups,
R
1
and R
2
are identical or different and represent organic radicals having 1 to 18 carbon atoms and
n represents an integer of at least 2,
C) 10 to 30 wt. % of one or more compounds having a number average molecular weight of 112 to 600 and corresponding to formula III:
wherein
R
3
and R
4
are identical or different and represent hydrogen or organic radicals having 1 to 18 carbon atoms and
Z represents an m-valent radical which is inert towards isocyanate groups and is obtained by removing the primary amino groups from an organic polyamine having a number average molecular weight of 88 to 400 and containing m primary (cyclo)aliphatically bound amino groups and
m represents an integer ≧2,
D) 0.1 to 5.0 wt. % of acetals corresponding to formula IV:
wherein
R
5
and R
6
are identical or different and represent hydrogen or organic radicals having 1 to 18 carbon atoms,
Y represents a divalent organic radical having 1 to 8 carbon atoms and
Ph represents an optionally substituted phenyl radical,
E) 0.1 to 5.0 wt. % of castor oil.
F) 0.1 to 10.0 wt. % of one or more organic solvents,
G) 15 to 35 wt. % of one or more pigments
H) 0 to 10 wt. % of one or more coating additives other than D, F or G,
wherein the sum of the percentages of components A to H is 100.
The present invention also relates to the use of this coating composition as an anti-corrosive topcoat.
DETAILED DESCRIPTION OF THE INVENTION
Suitable polyisocyanates A for the coating compositions according to the invention include the known lacquer polyisocyanates which have (cyclo)aliphatically bound isocyanate groups. Examples include derivatives of (cyclo)aliphatic diisocyanates having a molecular weight of 168 to 300, such as hexamethylene diisocyanate, 2,2,4- and/or 2,4,4-trimethyl hexamethylene diisocyanate, 2-methyl-1,5-diisocyanatopentane, 1,4-diisocyanatocyclohexane, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (IPDI) and/or 1-isocyanato-1-methyl-3(4)isocyanatomethyl-cyclohexane.
The “derivatives” of these starting diisocyanates include the known lacquer polyisocyanates which are prepared from these diisocyanates and contain biuret groups, isocyanurate groups, isocyanurate and uretdione groups, isocyanurate and allophanate groups, or urethane groups. The corresponding derivatives of aromatic diisocyanates, such as 2,4- and/or 2,6-diisocyanatotolue
Jahn Peter
Kurek Gerald
Schwindt J{umlaut over (u)}rgen
Bayer Aktiengsellschaft
Gil Joseph C.
Niland Patrick D.
Roy Thomas W.
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