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...
Reexamination Certificate
2001-01-30
2003-03-25
Gorr, Rachel (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...
C528S059000, C252S182210, C252S182220, C427S385500, C428S423100
Reexamination Certificate
active
06538096
ABSTRACT:
The present invention relates to mixtures comprising
a) polyisocyanates (polyisocyanates A), comprising structural units selected from the isocyanurate and biuret group, derived from aliphatic or cycloaliphatic diisocyanates (diisocyanates C),
b) non-A polyisocyanates (polyisocyanates B), comprising structural units selected from the allophanate and urethane group, derived from
b1) aliphatic or cycloaliphatic diisocyanates (polyisocyanates C) and
b2) polyhydric aliphatic or cycloaliphatic alcohols (alcohols A),
the molar ratio of the polyisocyanates A to the polyisocyanates B being from 200:1 to 5:1.
Crosslinking polyisocyanates and binder components containing isocyanate-reactive groups are known in general in the form, for example, of 2-component (2K) coating materials (cf. Kunststoff Handbuch, Volume 7, Polyurethanes, 2nd edition, 1993, Carl Hanser Verlag Munich, Vienna, pp. 599 to 642; M. Bock, Polyurethane fur Lacke und Beschichtungen, Vincentz-Verlag, Hanover, 1999, and Journal fur praktische Chemie, 336 (1994) 185-200). These 2-component coating compositions comprise as their binder, for example, a polymeric polyol and as their crosslinker component (curing agent) a compound containing two or more free isocyanate groups.
The service properties of coatings whose polymeric binders have been crosslinked with the isocyanates are greatly improved over those of systems comprising binders of low molecular mass. This relates in particular to service properties such as
insensitivity to mechanical stress such as tension, elongation, impact or abrasion,
resistance to moisture (in the form of water vapor, for example) and dilute chemicals,
resistance to environmental effects such as temperature fluctuations and UV radiation,
high gloss of the coated surfaces, and
high transparency.
It is expected that the curing agents not only give the fully cured coatings the aforementioned service properties but also improve, or at least detract very little from, the processing properties of the coating materials prior to their application.
In order that the coating materials can be applied without problems to the target surface by conventional techniques, e.g., by spraying, the coating materials ought to have a limited viscosity. Coating materials based on 2-component coating compositions therefore normally include solvents. The high solvent content of these coating materials, however, causes problems, since the processors of the coating materials have to take technically complex measures in order to prevent the solvents released on application and drying of the coating materials from entering the atmosphere. Consequently, the search has been on for curing agents which cause very little increase, or, even better, which lower, the viscosity of the binder-containing component. of course, these curing agents must themselves not exhibit any notable volatility even at room temperature, as is the case with commercially customary monomeric isocyanates such as hexamethylene diisocyanate or isophorone diisocyanate. Moreover, even on prolonged storage, the curing agents must not increase their viscosities, since for the user this would necessitate a further addition of solvent during the preparation of the coating formulation.
Additionally, the 2-component coating compositions should cure fully as soon as possible after application, so that the coated articles following application may rapidly be processed further or utilized.
Products which possess this profile of properties, at least to a satisfactory extent, include polyisocyanates which carry allophanate units, for example, and which are known from EP-A- 303150. Polyisocyanates containing isocyanurate units are known, for example, from EP-A-0017998 and US 4015155.
However, these polyisocyanates are still in need of improvement as far as the stability on storage is concerned, especially under hot conditions. On prolonged storage, the products become more viscous, turn cloudy, form flocs, or gel.
It is an object of the present invention to provide a polyisocyanate having the aforementioned profile of properties which can be stored for prolonged periods without undergoing substantial changes in its properties.
We have found that this object is achieved by the mixtures defined at the outset and processes for preparing them, by 2-component coating compositions which comprise these mixtures, and by articles coated with said 2-component coating compositions.
The polyisocyanates A are known per se. They comprise preferably 1, 2 or 3 structural units selected from the isocyanurate and biuret group. Polyisocyanates C from which the polyisocyanates A are derived include in particular those of the formula (I) OCN-R
1
-NCO, where R
1
is an alkylene or cycloalkylene unit having 4 to 20 carbon atoms, preferably derived from hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI) by abstraction of the NCO groups.
Particular preference is given to the following polyisocyanates A:
I. polyisocyantes of aliphatic or cycloaliphatic diisocyanates, containing isocyanurate groups. Particular preference is given in this context to the corresponding isocyanato-isocyanurates based on hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI). The isocyanurates in question comprise, in particular, simple trisisocyanatoalkyl or trisisocyanatocycloalkyl isocyanurates, which constitute cyclic trimers of the diisocyanates, or comprise mixtures with their higher homologs containing more than one isocyanurate ring (e.g., 2 or 3 such rings). The isocyanato-isocyanurates generally have an NCO content of from 10 to 30% by weight, in particular from 15 to 25% by weight, and an average NCO functionality of from 2.6 to 4.5.
Particularly appropriate compounds are isocyanurates of the formula (IVa)
or the oligomeric forms deriving therefrom, in which R
4
has the same definition as R
1
in polyisocyanate A.
II. Polyisocyanates containing biuret groups and containing isocyanate groups attached to aliphatic or cycloaliphatic moieties, the preparation of such polyisocyanates being described, for example, in H. J. Laas et al., J. prakt. Chem. 336 (1994) 185-200, or EP-A-809663 (polyisocyanates AII). These polyisocyanates include in particular those derived from IPDI and also bis(4-isocyanatocyclohexyl)methane (HMDI). Particular preference is given to tris(6-isocyanatohexyl)biuret or its mixtures with its higher homologs. These polyisocyanates containing biuret groups generally have an NCO content of from 10 to 30% by weight, in particular from 18 to 25% by weight, and an average NCO functionality of from 2.8 to 4.5.
The biuretizing agents from which the polyisocyanates A containing biuret groups are derived comprise water, amine, and a substance which generates water. Suitable water-generating substances are, for example, monohydric tertiary alcohols such as tert-butanol or isobutanol, or ion exchangers.
The polyisocyanates B, too, are compounds already known per se.
They are preferably derived from the same polyisocyanates C which were described above, with particular preference from HMDI, HDI, and IPDI.
Regarding the alcohols A, it is possible to use any aliphatic or cycloaliphatic polyhydric alcohol. The alcohols in question are preferably those of the formula (II) HO—R
2
—OH, where R
2
is an alkylene or cycloalkylene unit having 2 to 20 carbon atoms, which is uninterrupted or interrupted by oxygen atoms and in which, if desired, 1 to 4 hydrogen atoms are substituted by C
1
to C
12
alkyl radicals. Branched diols are particularly preferred, such as propylene glycol, 1,2- and 1,3-butanediol, 2,2,4,4-tetramethyl-1,3-cyclobutanediol, 2-methyl-1,4-butanediol, 3-methyl-1,3-butanediol, 1,2- and 1,3-pentanediol, 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 2,4-dimethyl-2,4-pentanediol, 2,4-dimethyl-1,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,2-, 1,3- and 1,4-hexanediol, 2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol, dipropylene glycol, tripropylene glycol, neopentyl glycol, and neopentyl glycol hydroxypivalate; particular preference is given to the use of
Bruchmann Bernd
Jähme Joachim
Mohrhardt Günter
Renz Hans
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