Thermosetting two-component coating compositions

Details Thermosetting two-component coating compositions Thermosetting two-component coating compositions

2002-06-26

2003-11-04

Sergent, Rabon (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C428S423400, C428S423100, C428S425100, C528S059000, C528S065000, C528S085000

Reexamination Certificate

active

06642342

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to reactive mixtures which are based on NCO prepolymers and polyol chain extenders and are distinguished by a long pot life at room temperature and by a high reactivity at elevated temperatures, a process for their preparation and their use for coating substrates.
BACKGROUND OF THE INVENTION
Solvent-free or low-solvent two-component coating compositions based on NCO prepolymers are known. They include reactive mixtures containing functionalized prepolymers and crosslinking agents with low contents of organic solvents. These “high solids systems” then polymerize under the processing conditions and form a urethane film. Isocyanate components in which the terminal isocyanate groups are reversibly blocked by blocking agents, such as 2-butanone oxime, are employed in these systems. Curing subsequently takes place by a heat treatment, the ketoxime being split off and, where appropriate, the solvent evaporating. Reactive compositions of this type for coating flexible substrates are described in DE-A 29 02 090 (=EP-A 0 013 890, U.S. Pat. No. 4,248,756).
A disadvantage of these systems is that residues of the blocking agent always remain in the resulting coating and cause an unpleasant smell to the product. Furthermore, 2-butanone oxime is also a health risk because of its toxicological properties. Waste air treatment is therefore necessary even if the systems contain no solvent. Another disadvantage of blocking the free NCO groups is that this leads to additional urethane groups and therefore to an increase in the viscosity of the compositions, which in most cases must be compensated for by the addition of solvent.
Systems of the prior art in which splitting off of blocking agents can be omitted are also known (e.g. DE-A 196 32 925). The reactive compositions described therein contain catalysts which have a particularly high latency at room temperature, but are very reactive at elevated temperature. DE-A 196 32 925 discloses a system containing an aliphatic NCO prepolymer and a dispersed solid diol, which is reacted using a tin catalyst poisoned with sulfur. Such a system is complicated to prepare, and the choice of polyols is limited because certain particle size profiles should be maintained during grinding and the dispersion must be stabilized by various additives. However, because of the need to disperse the polyol, organic solvents must be used.
DE-A 199 31 323 describes composite structures with one or more polyurethane layers. The reactive coating compositions used contain polyols and NCO crosslinking agents. The reaction is catalyzed by nickel acetylacetonate. However, the use of these coating compositions is severely limited by the presence of relatively large amounts of a toxicologically unacceptable catalyst.
The suitability of nickel acetylacetonate as a latent catalyst system is known (e.g. U.S. Pat. No. 4,151,345) and attempts have previously been made to replace nickel by more advantageous metals. For example, the use of iron acetylacetonate and copper acetylacetonate is disclosed in DE-A 196 26 007. Both acetylacetonates are actually too reactive at room temperature to be used as latent catalysts. However, it has been found that the co-addition of additional acetylacetone is capable of eliminating this disadvantage. Nevertheless, free acetylacetone is also not toxicologically acceptable and the metal ions in question are colored.
It is an object of the present invention to provide thermosetting two-component coating compositions which do not have the disadvantages described above for the prior art. It is an additional object of the present invention to provide a new catalyst system which has a sufficiently high latency at room temperature, is sufficiently reactive at elevated temperature, is largely toxicologically and ecologically acceptable and colorless and is soluble in small amounts of organic solvent. The preparation of the coating compositions should be as simple as possible.
These objects may be achieved with the two-component coating compositions according to the present invention, which are based on NCO prepolymers and polyol chain extenders, are preferably liquid, and contain acetylacetonate complexes of sub-group three or acetylacetonate complexes of oxo compounds of sub-group six.
SUMMARY OF THE INVENTION
The present invention relates to thermosetting two-component coating compositions containing
A) at least one NCO prepolymer,
B) at least one amine-free chain extender,
C) at least one catalyst selected from metal 1,3-dicarbonylates and metal-oxo 1,3-dicarbonylates, wherein
i) the metal 1,3-dicarbonylate contains as a neutral complex a metal cation with the electron configuration d
0
of sub-group 3 or a lanthanide and
ii) the metal-oxo 1,3-dicarbonylate contains a metal-oxo cation of sub-group 6 with the electron configuration d
0
.
The present invention also relates to a process for preparing these coating compositions and to coated substrates prepared therefrom.
DETAILED DESCRIPTION OF THE INVENTION
The coating compositions according to the invention preferably contain
A) 50 to 99 parts by wt. of an NCO prepolymer,
B) 1 to 50 parts by wt. of an amine-free chain extender and
C) 0.01 to 10 parts by wt. of at least one catalyst selected from metal 1,3-dicarbonylates and metal-oxo 1,3-dicarbonylates, wherein
i) the metal 1,3-dicarbonylate contains as a neutral complex a metal cation with the electron configuration d
0
of sub-group 3 and a lanthanide and
ii) the metal-oxo 1,3-dicarbonylate contains a metal-oxo cation of sub-group 6 with the electron configuration d
0
,
wherein the sum of the components is 100, based on the weight of A), B) and C).
Particularly preferred are coating compositions containing 80 to 99 parts by wt. of A), 1 to 5 parts by wt. of B) and 0.05 to 1.0 parts by wt. of C), wherein the sum of the components is 100, based on the weight of A), B) and C). The equivalent ratio of free NCO groups from A) to NCO-reactive groups from B) is 0.90 to 1.35, preferably 1 to 1.25.
In the following, “average molecular weights” are in each case understood as molecular weights determined as the number-average.
NCO prepolymers A) contained in the coating compositions according to the invention have number average molecular weights of 500 to 10,000, preferably 700 to 8,000, and an NCO content of 1 to 8 wt. %, preferably 2 to 4 wt. %. The preparation of suitable NCO prepolymers A) is carried out by reaction of monomeric organic polyisocyanates a) with NCO-reactive compounds b).
Suitable organic polyisocyanates a) include aromatic, aliphatic and cycloaliphatic polyisocyanates having an average molecular weight below 800 and corresponding to the formula Q(NCO)
n
, wherein n is a number from 2 to 4 and Q represents an aromatic C
6
-C
15
-hydrocarbon radical, an aliphatic C
4
-C
12
-hydrocarbon radical or a cycloaliphatic C
6
-C
15
-hydrocarbon radical. Examples include 2,4- and/or 2,6-toluene-diisocyanate (TDI), diphenylmethane diisocyanate (MDI), triisocyanatononane (TIN), naphthylene diisocyanate (NDI), 4,4′-diisocyanatodicyclohexylmethane, 3-isocyanatomethyl-3,3,5-trimethylcyclohexyl-isocyanate (isophorone diisocyanate or IPDI), tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), 2-methyl-pentamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate (THDI), dodecamethylene diisocyanate, 1,4-diisocyanato-cyclohexane, 4,4′-diisocyanato-3,3′-dimethyl-dicyclohexyl methane, 4,4′-diisocyanato-2,2-dicyclohexylpropane, 3-isocyanatomethyl-1-methyl-1-isocyanatocyclohexane (MCI), 1,3-diisooctylcyanato-4-methyl-cyclohexane, 1,3-diisocyanato-2-methyl-cyclohexane, &agr;,&agr;,&agr;′,&agr;′-tetramethyl-m- or -p-xylylene diisocyanate (TMXDI) and mixtures of these compounds.
Aliphatic and/or cycloaliphatic diisocyanates are preferred, and 4,4′-diisocyanatodicyclohexylmethane is particularly preferred. 4,4′-diisocyanatodicyclohexylmethane is used in the form of the technical-grade product with 10 to 50, preferably 15 to 25 wt. %, of trans/trans-4

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