Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2001-11-14
2003-11-25
Short, Patricia A. (Department: 1712)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S386000, C427S387000, C427S407100, C524S211000, C524S215000, C524S216000, C525S007200, C525S007300, C525S007400, C525S103000, C525S111000, C525S123000, C525S124000, C525S131000, C525S438000, C525S440030, C525S456000, C525S458000, C525S474000, C525S476000, C525S510000, C525S528000
Reexamination Certificate
active
06652916
ABSTRACT:
This application is a National Phase Application of Patent Application PCT/EP00/04621 filed on May 22, 2000.
The invention relates to a coating material comprising a binder and a crosslinking agent and also a thixotropic agent, to a process for preparing such a coating material, to the use of such a coating material for producing for producing clearcoat, and to a process for producing clearcoats in the course of the production of multicoat color and/or effect coating systems.
Coating materials featuring thixotropic agents are known. 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. The literature references WO 97/12945 and farbe+lack November 1992, pages 829 ff., for example, describe coating materials comprising modified, hydrophilic or hydrophobic silicas as thixotropic agents. In passing, this literature reference also mentions urea derivatives as an alternative. Literature reference U.S. Pat. No. 4,169,930 discloses reaction products of silica and amines, urea for example, for use in coating materials. Finally, literature reference DE-A-37 26 959 discloses coating materials comprising urea in dissolved form. Because the urea is dissolved, it cannot fulfill the function of a thixotropic agent.
The use of thixotropic agents in coating materials is intended, among other things, to allow the application of comparatively thick coats of paint without the incidence of disruptive running. Particularly in the case of nonaqueous paints comprising a thixotropic agent based on urea derivatives, paint surfaces are obtained which—at high solids contents at any rate—are unsatisfactory with respect to their visual appearance (especially leveling and gloss). Thixotropic agents based on silicas give coating materials which are likewise unsatisfactory with regard to leveling but which also, moreover, lead to coatings which lack sufficient condensation resistance (blushing due to water inclusion). Particularly in the case of the urea-based thixotropic agents, moreover, the storage stability is unsatisfactory.
A key feature of thixotropic agents is that the viscosity of a paint prepared using them depends on the flow history and/or that the thixotropic agents are pseudoplastic, i.e., that the viscosity of the paint decreases as the shear stress goes up. Starting from a baseline viscosity, the viscosity decreases during shear stress and only after the end of the shear stress does it gradually return to the initial level. A thixotropic gel, for example, is liquefied by the input of mechanical energy (stirring or the like) and solidifies gradually again only when the energy input is at an end. Pseudoplastic or thixotropic properties are advantageous for paint processing. In particular, it is possible to check and reduce the tendency toward running when a paint is applied with a high wet film thickness. On the other hand, thixotropic agents must not adversely affect the visual and chemical properties of a finished coating produced using them. As a general rule, thixotropic agents are particulate and are dispersed in a coating material, whether aqueous or nonaqueous. The urea derivatives are acicular crystals, in some cases with a helical twist, with a particle size distribution of between 0.1 &mgr;m and 6 &mgr;m (95-99% of particles, based on the volume) and with 80% of the crystals (based on the number) being smaller than 2 &mgr;m. In the case of the silicas, the fineness of grind in the finished coating material is typically less than 10 &mgr;m in accordance with DIN ISO 1524. The primary particle size of pyrogenic silicas is usually situated within the range from 5 to 20 nm.
The particles of the thixotropic agents, especially of the thixotropic agents based on urea derivatives, tend to settle and/or form lumps, thereby causing the low-satisfaction storage stability.
The invention is therefore based on the technical problem of specifying a coating material which on the one hand exhibits a reduced tendency toward running while at the same time meeting all of the requirements, especially with regard to good storage stability.
To solve this technical problem the invention teaches that the coating material further comprises a wetting agent which improves the wettability of the thixotropic agent.
Surprisingly, the use of wetting agents known per se leads to a considerable improvement in the storage stability of the coating materials. It is important in this context that the wetting agent is suitable and adapted to wet the particles of the thixotropic agent. A further surprise was that the inventive combination of wetting agent and thixotropic agent leads not only to a coating material which exhibits a reduced tendency toward running but also to clearcoats which are entirely satisfactory with regard to leveling and condensation resistance: on vertical substrate areas it is possible to produce dry film thicknesses of up to 50 &mgr;m or more without running. This applies both to one-component systems and to multicomponent systems. In the context of the present invention, a one-component (1K) system is a thermosetting coating material in which 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 undergo crosslinking with one another only at relatively high temperatures and/or on exposure to actinic radiation.
The coating material may also be a two-component (2K) or multicomponent (3K, 4K) system.
In the context of the present invention, this is a coating material in which in particular the binder and the crosslinking agent are present separately from one another in at least two components, which are not combined with one another until shortly before application. This form is chosen when binder and crosslinking agent react with one another even at room temperature. Coating materials of this kind are employed in particular for coating heat-sensitive substrates, especially in automotive refinish.
Wetting agents which have proven highly suitable are those known from the patent EP 0 154 678 A1.
These wetting agents are obtainable by reacting polyisocyanates having an average functionality of from 2.5 to 6 in a first stage a) with monohydroxy compounds of the formula Y—OH. In this formula, Y denotes
i) an aliphatic and/or cycloaliphatic C
8
-C
30
hydrocarbon radical, with or without hydrogen atoms substituted by halogen atoms and/or aryl radicals, and/or
ii) an aliphatic and/or cycloaliphatic and/or aromatic radical which contains at least one —O— and/or —COO— group and has a molecular weight of from 350 to 8000, with or without hydrogen atoms substituted by halogen atoms and/or aryl radicals.
The polyisocyanates and the monohydroxy compounds are reacted in an amount such that from 15 to 50%, preferably from 20 to 40% or from 20 to 35%, of the NCO groups undergo reaction.
In a second stage b), the resultant reaction product is reacted with compounds of the formula G—(E)
n
. In this formula E is —OH, —NH
2
and/or —NHR where R=C
1
-C
4
alkyl; n is 2 or 3; G is an aliphatic and/or cycloaliphatic hydrocarbon radical having at least two carbon atoms and a molecular weight of not more than 3000, it being possible for G to be an —O—, COO—, CONH—, —S— and/or —SH
2
group.
The proportions here are chosen so that a further 15 to 45%, preferably from 20 to 40% or from 20 to 35%, of the NCO groups of the polyisocyanates used originally undergo reaction, and the sum of the NCO groups reacted in stages a) and b) is from 40 to 75%, preferably from 45 to 65% or from 45 to 55%, of the NCO groups of the polyisocyanates used originally.
In the third stage c), the reaction product obtained in stage b) is reacted with compounds of the formula Z—Q. In this formula Q is —OH, NH
2
, —NHR where R is C
1
-C
4
alkyl, or —SH; Z is C
2
-C
10
alkyl containing at least one tertiary amine group or is a heterocyclic group having at least one basic ring nitrogen atom which carries no hydrogen atom, it bei
Baumgart Hubert
Schulze-Finkenbrink Guido
BASF Coatings AG
Short Patricia A.
LandOfFree
Coating material comprising a mixture that consists of at... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Coating material comprising a mixture that consists of at..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Coating material comprising a mixture that consists of at... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3183524