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...
Reexamination Certificate
1999-07-27
2001-05-01
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...
C427S372200, C427S385500, C524S507000, C524S589000, C524S591000, C524S839000, C524S840000, C525S123000, C525S124000, C525S455000
Reexamination Certificate
active
06225400
ABSTRACT:
The present invention relates to a component system for a multicomponent coating composition comprising (1) a hydroxy-functional binder or a mixture of hydroxy-functional binders, (2) tris(alkoxycarbonylamino)triazine or a mixture of tris(alkoxycarbonylamino)triazines and (3) free (poly)isocyanates or a mixture of free (poly)isocyanates. The invention also relates to a process for preparing such a component system and to its use.
By component system is meant a package of different coatings components which are prepared and stored separately and yet are always dealt with in conjunction with one another and which are mixed to form a coating composition by a user wishing to produce a coating from the coating composition, before the coating is produced. Component systems of this kind are common, inter alia, in the preparation of topcoats. The term topcoats here refers to coating materials which are used to produce the topmost coat. This topmost coat can itself comprise one or more coats, especially two coats. Two-coat topcoat finishes consist of a pigmented basecoat film and, applied thereto, a clearcoat film which is pigmented only with transparent pigments if at all. Two-coat finishes are nowadays produced by the wet-on-wet method, in which a pigmented basecoat is applied first and the resulting basecoat film is coated over with a clearcoat, without a baking step, and then the basecoat film and clearcoat film are cured together. This method is very advantageous economically but places high demands on the basecoat and the clearcoat. The clearcoat applied to the as yet uncured basecoat must not cause bleeding of the basecoat film or any other disruption, since otherwise finishes of poor appearance are obtained. This applies in particular to finishes for which basecoats comprising special-effect pigments (e.g. metal pigments, especially aluminium flakes, or pearlescent pigments) are employed.
Component systems for clearcoats, which are used predominantly for the finishing of cars, consist usually of hydroxy-functional polyacrylates with free isocyanate trimers of hexamethylene diisocyanate. The resulting clearcoats in the application-ready state have a solids content of from 40 to 55% by weight. Their advantages lie in a low curing temperature of from 20 to 40 degrees C and high chemical resistance. These clearcoat systems, however, currently have a number of serious disadvantages compared with melamine resin-crosslinked one-component clearcoats:
1. Inadequate scratch resistance, especially to light superficial damage.
2. Poor stone-chip resistance (adhesion) after exposure to condensation, especially following a refinish.
3. Severe redissolution on conventional basecoats, which is manifested in reduced flop in the case of metallic basecoats or in changes in shade in the basecoat, especially if an attempt is made to raise the solids content by including acrylate resins of low molecular weight.
One-component clearcoats do not exhibit these problems, or at least not to the same extent, but because of their much poorer chemical resistance cannot be used in place of two-component clearcoats.
The object of the present invention, therefore, is to provide a coating composition which does not feature the abovementioned disadvantages of customary two-component clearcoat systems but which has a resistance to chemicals and to weathering which is comparable with that of customary two-component clearcoat systems.
This object is achieved in accordance with the invention by a component system which is characterized in that a first component (I) is formed from the hydroxy-functional binder or from the mixture of hydroxy-functional binders (1), in that a second component (II) is formed from the free (poly)isocyanates or from the mixture of free (poly)isocyanates (3), and in that a third component (III) is formed from the tris(alkoxycarbonylamino)triazine or from the mixture of tris(alkoxycarbonylamino)triazines (2).
Surprisingly, through the use of a crosslinker combination comprising tris(alkoxycarbonylamino)triazine and free isocyanates, the invention achieves considerable advantages over customary two-component clearcoats. These advantages include in particular:
reduced bleeding of conventional basecoats, evident in particular in an improved metal effect in the case of metallic basecoats;
improved adhesion in stone-chip tests;
improved scratch resistance coupled with high acid resistance.
Reference DE 195 29 124 C1 discloses in principle a coating composition which also uses tris(alkoxycarbonylamino)triazine as crosslinker. The coating compositions described in this reference, however, are without exception one-component coating compositions. While a general reference is made to the existence of multicomponent systems, no information whatsoever, or even mere indications, are given as to what might be the composition of various components.
For the hydroxy-functional binder or for the mixture of hydroxy-functional binders it is preferred to consider those from the group “binders based on hydroxy-functional polyacrylates, hydroxy-functional polyesters and/or hydroxy-functional polyurethanes” and/or mixtures of members of this group and/or mixtures of different binders of a member of this group.
In accordance with the invention it is preferred to employ polyacrylate resins which have hydroxyl numbers of from 40 to 240, preferably from 60 to 210 and, with very particular preference, from 100 to 200, acid numbers of from 0 to 35, preferably from 0 to 23 and, with very particular preference, from 3.9 to 15.5, glass transition temperatures of from −35 to +70° C., preferably from −20 to +40° C. and, with very particular preference, from −10 to +15° C., and number-average molecular weights of from 1500 to 30,000, preferably from 2000 to 15,000 and, with very particular preference, from 2500 to 5000.
The glass transition temperature of the polyacrylate resins is determined by the nature and amount of the monomers employed. The selection of the monomers can be made by the skilled worker with the aid of the following formula, by which the glass transition temperatures of polyacrylate resins can be calculated approximately:
1
Tg
=
W
1
Tg
1
+
W
2
Tg
2
…
W
i
Tg
i
;
n
=
i
Tg
=
glass
transition
temperature
of
the
polyacrylate
resin
W
n
=
proportion
by
weight
of
the
nth
monomer
Tg
n
=
glass
transition
temperature
of
the
homopolymer
of
nth
monomer
Measures to control the molecular weight (e.g. selection of appropriate polymerization initiators, use of chain transfer agents, etc.) are part of the expert knowledge of the skilled worker and need not be explained here.
As the hydroxy-functional binder component use is also made, for example, of polyester resins or alkyd resins which can be prepared by reacting (a1) a cycloaliphatic or aliphatic polycarboxylic acid or a mixture of such polycarboxylic acids, (b1) an aliphatic or cycloaliphatic polyol having more than two hydroxyl groups in the molecule or a mixture of such polyols, (c1) an aliphatic or cycloaliphatic diol or a mixture of such diols and (d1) an aliphatic linear or branched saturated monocarboxylic acid or a mixture of such monocarboxylic acids, in a molar ratio of (a1):(b1):(c1):(d1)=1.0:0.2-1.3:0.0-1.1:0.0-1.4, preferably 1.0:0.5-1.2:0.0-0.6:0.2-0.9, to form a polyester resin or alkyd resin. Examples of the constituent (a1) are hexahydrophthalic acid, 1,4-cyclohexanedicarboxylic acid, endomethylenetetrahydrophthalic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid. Examples of the constituent (b1) are: pentaerythritol, trimethylolpropane
Bartol Fritz
Baumgart Hubert
Rockrath Ulrike
BASF Coating AG
Niland Patrick D.
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