Thixotroping agent

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...

Reexamination Certificate

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Details

C525S131000, C524S196000, C524S507000, C528S045000, C528S064000, C528S068000

Reexamination Certificate

active

06649706

ABSTRACT:

This application is a National Phase Application of Patent Application PCT/EP00/04082 filed on May 6, 2000.
The invention relates to a thixotropic agent obtainable from the reaction of an isocyanato-containing component with a primary or secondary amine or a mixture of such amines and/or water, to the use of such a thixotropic agent, and to a process for preparing such a thixotropic agent.
Coating materials with thixotropic agents are known. The literature references EP-A-192 304, DE-A-23 59 923, DE-A-18 05 693, WO 94/22968, and DE-C-27 51 761 describe coating materials comprising urea derivatives as thixotropic agents. Moreover, for example, the literature references WO 97/12945 and “farbe+lack”, 11/1992, pages 829 ff. describe coating materials which comprise modified, hydrophilic or hydrophobic silicas as thixotropic agents. In this literature reference, urea derivatives are also mentioned in passing as an alternative. Finally, the literature reference DE-A-37 26 959 discloses coating materials comprising urea in dissolved form. Since the urea is dissolved, it cannot play the part of a thixotropic agent.
The use of thixotropic agents in coating materials is intended, among other things, to allow the application of comparatively thick paint films without disruptive running. Especially in the case of nonaqueous paints which comprise a thixotropic agent based on urea derivatives, at high solids contents in any case, coating materials and paint surfaces are obtained which do not meet all of the requirements.
A key feature of thixotropic agents is that the viscosity of a paint prepared using them depends on the prior flow history and/or that the thixotropic agents are pseudoplastic, i.e., the viscosity of the paint decreases as the applied shear stress goes up. Starting from a base line viscosity, the viscosity decreases under shear stress and returns only gradually to the initial level after the shear stress has ended. A thixotropic gel, for example, liquefies as a result of input of mechanical energy (stirring or the like) and solidifies only gradually after the end of the input of energy. Pseudoplastic or thixotropic properties are advantageous for paint processing. In particular, the tendency of a paint to run on application at high wet-film thickness may be controlled and reduced. On the other hand, thixotropic agents must not adversely affect the optical and chemical properties of a finished coating produced using them. As a general rule, thixotropic agents are particulate and are present in dispersion in a coating material, whether aqueous or nonaqueous. In the case of the urea derivatives, these thixotropic agents are acicular crystals, in part with a helical twist, for which, preferably, a particle size distribution between 0.1 &mgr;m and 6 &mgr;m (95-99% of the particles, based on the volume) is set and 80% of the crystals (based on the number) are smaller than 2 &mgr;m.
The invention is therefore based on the technical problem of indicating a thixotropic agent which is obtainable by reaction of an isocyanate, especially a diisocyanate, with primary or secondary amines or a mixture of such amines and/or water and with which in coating materials a markedly reduced tendency toward running is achieved, and a coating obtained with such a coating material meets all of the requirements.
In order to solve this technical problem the invention teaches the use
Ia) of at least one isocyanate containing at least one diisocyanate structural unit which
i) has an unsaturated or aromatic or nonaromatic ring structure containing 5-10 ring atoms and
ii) has two isocyanate groups attached to the ring structure, where
iii) in the case of a nonaromatic ring structure
a) both isocyanate groups are attached to the ring structure via linear C
1
-C
9
alkyl and/or linear C
2
-C
10
ether alkyl, or
b) one isocyanate group is attached directly to the ring structure and the other is attached via linear C
2
-C
9
alkyl and/or linear C
2
-C
10
ether alkyl, and
iv) in the case of an unsaturated aromatic ring structure at least one of the two isocyanate groups is attached to the ring structure via linear C
2
-C
9
alkyl and/or linear C
2
-C
10
ether alkyl, both of which radicals contain no benzylic hydrogen atoms;
and/or
Ib) of at least one oligomer of this isocyanate Ia) containing from 2 to 10 isocyanate units, especially a trimer;
and/or
Ic) of at least one partially blocked isocyanate Ia) and/or of at least one partially blocked oligomer Ib)
for preparing the thixotropic agents.
Surprisingly, the use of the isocyanate component used in accordance with the invention leads to a thixotropic agent which has optimum properties in terms of thixotropy and gives rise to coatings, especially clearcoats, which satisfy all of the requirements, especially leveling and gloss. On vertical substrate surfaces, dry film thicknesses of up to 50 &mgr;m or more may be produced without running. The isocyanato-containing components of the invention may further comprise, in principle, isocyanates of customary structure that are described below.
One preferred embodiment of the invention is characterized in that the thixotropic agent is obtainable by reacting the isocyanato-containing component with an aliphatic, primary monoamine.
Although further isocyanates may be present, it is preferred for the isocyanato-containing component to be formed by the compounds Ia and/or Ib and/or Ic).
The invention further teaches the use of a thixotropic agent of the invention for preparing a coating material, preferably a nonaqueous coating material, very preferably a nonaqueous gloss clearcoat material. The coating material may be a one-component or a two-component or multicomponent system.
In the context of the present invention, a one-component (1K) system is a thermally curing coating material wherein the binder and the crosslinking agent are present alongside one another, i.e., in one component. A prerequisite for this is that the two constituents crosslink with one another only at relatively high temperatures and/or on exposure to actinic radiation.
In the context of the present invention, a two-component (2K) or multicomponent (3K, 4K) system is a coating material wherein in particular the binder and the crosslinking agent are present separately from one another in at least two components which are not combined until shortly before application. This form is chosen when binder and crosslinking agent already react with one another even at room temperature. Coating materials of this kind are employed above all to coat thermally sensitive substrates, especially in automotive refinish.
In the context of the use it is preferred if the coating material comprises at least one binder, preferably a polyacrylate resin, at least one crosslinking agent, preferably selected from the group consisting of polyisocyanates, polyepoxides, blocked polyisocyanates, tris(alkoxycarbonylamino)triazines, amino resins, beta-hydroxyalkylamides, siloxanes and polyanhydrides, and mixtures of these compounds the one according to the invention, and, optionally, coatings additives.
The invention relates finally to a process for preparing a thixotropic agent of the invention, where
a) the primary or secondary amine or a mixture of such amines and/or water is added to a binder solution, preferably a nonaqueous polyacrylate solution, and
b) the isocyanato-containing component or a solution of this component is added to the solution obtained in step a).
In detail, steps a) and/or b) may be conducted in a dissolver.
The thixotropic agent may be used in the coating material in an amount of from 0.1 to 5.0% by weight, preferably from 0.2 to 2.5% by weight, most preferably from 0.6 to 1.8% by weight, based on the overall solids content of the coating material.
The amines and the polyisocyanato-containing component may be reacted with one another in amounts such that the equivalents ratio between amino groups and isocyanate groups is between 1.2 and 0.4, preferably between 1.0 and 0.8.
Monoamines used are preferably monoamines, with particular preference araliph

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