Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2001-12-14
2003-09-16
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S423100, C524S591000, C524S539000, C524S839000, C524S840000, C427S409000, C427S410000, C427S386000
Reexamination Certificate
active
06620511
ABSTRACT:
DESCRIPTION
The invention relates to an aqueous coating material, especially an aqueous surfacer or antistonechip primer, comprising (A) a water-dispersible hydroxy-functional binder component containing urethane groups, (B) a water-dispersible binder component containing urethane groups and blocked isocyanate groups, (C) a water-dispersible amino resin, (D) optionally, a water-dispersible hydroxy-functional polyester, and (E) optionally, customary coatings additives. The invention further relates to a process for preparing such a coating material and to the uses thereof.
The provision of stonechip-resistant coatings on metallic substrates is of particular importance in the field of motor vehicle production. Stonechip-resistant coatings are applied in particular in the front area and in the underbody area of a motor vehicle body. For reasons both economic and environmental, a coating material suitable for this purpose ought to contain little or no organic solvents. Only (apart from powder coating materials) aqueous coating materials are suitable for this purpose.
A surfacer or antistonechip primer is subject to a number of requirements. It must be bakeable at a temperature of 120-160° C. and after baking at such temperatures must exhibit outstanding properties such as high stonechip resistance (particularly the combination of multiple and single chipping), effective adhesion to the primer coat, a cathodic electrode coat, for example, and to the base coat, good filling properties (masking of the structure of the substrate) at a coat thickness of 20-35 &mgr;m, and an excellent appearance in the final clearcoat. The combination of these properties is difficult to realize on account of the fact that they are in part divergent properties, where improving one property automatically results in a deterioration in another property. Such divergent or contradictory properties are, for example, very good resistance to multiple chipping and to single chipping, low coat thickness and very good filling power/topcoat appearance, low baking temperature and very good topcoat appearance, and low baking temperature and high adhesion.
A coating material of the composition specified at the outset is known from the reference EP 0 427 028 B1. In this material, component (B) is the reaction product of a diisocyanate and a low molecular mass polyol. With the known coating material, not all of the abovementioned divergent properties are obtained to a satisfactory extent. For a solventborne antistonechip primer, refer, for example, to the reference DE 31 08 861 C2. Solventborne coating materials are unsatisfactory on environmental grounds alone. The reference DE 41 42 816 C1 discloses a surfacer for which the abovementioned components (A) and (B) are first of all reacted with one another and then the reaction product is mixed with a polyisocyanate and a melamine resin to give the application-ready coating material. Technically speaking, this is a comparatively laborious preparation. Moreover, even with the known coating material, not all of the abovementioned divergent properties are realized to a sufficient extent. Further stonechip protection compositions are known, for example, from the references DE 38 05 629 C1 and DE 195 04 947 A1.
In opposition to the prior art specified at the outset, the technical problem on which the invention is based is to specify a coating material with which the desired divergent properties mentioned are obtained in a way which, overall, meets all of the requirements.
To solve this technical problem, the invention teaches that the binder component (B) specified at the outset is preparable by
(B1) preparing a polyurethane prepolymer containing isocyanate groups from a polyol or mixture of polyols and from a polyisocyanate or mixture of polyisocyanates,
(B2) reacting the polyurethane prepolymer (B1) containing isocyanate groups by means of a chain extender to give a hydroxyl-containing chain-extended polyurethane prepolymer,
(B3) reacting the hydroxyl-containing chain-extended polyurethane prepolymer (B2) with a polyisocyanate or mixture of polyisocyanates to give a further polyurethane prepolymer containing isocyanate groups, and
(B4) blocking some or all of the isocyanate groups of the chain-extended polyurethane prepolymer (B3) containing isocyanate groups with a blocking agent to give a polyurethane containing blocked isocyanate groups, and then, where appropriate,
(B5) reacting remaining free isocyanate groups in the polyurethane (B4) with a chain extender.
Surprisingly, using the above-defined component (B) for use in accordance with the invention in the coating material specified at the outset, comprising components (A) and (C) and also, where appropriate, (D) and (E), gives a coating material which satisfies all of the requirements.
The binder component (B) for use in accordance with the invention is obtainable by reacting, in a first process step, at least one polyol with at least one polyisocyanate to give the polyurethane prepolymer (B1) containing isocyanate groups.
Examples of suitable polyols are saturated or olefinically unsaturated polyesterpolyols having a number-average molecular weight of from 300 to 5000, preferably from 1000 to 2000, and in particular from 1200 to 1600, which are prepared by reacting
sulfonated or unsulfonated saturated and/or unsaturated polycarboxylic acids or their esterifiable derivatives, together if desired with monocarboxylic acids, and
saturated and/or unsaturated polyols, together if desired with monools.
Examples of suitable polycarboxylic acids are aromatic, aliphatic and cycloaliphatic polycarboxylic acids. Preference is given to using aromatic and/or aliphatic polycarboxylic acids.
Examples of suitable aromatic polycarboxylic acids are phthalic acid, isophthalic acid, terephthalic acid, phthalic, isophthalic or terephthalic monosulfonate, or halophthalic acids, such as tetrachloro- and/or tetrabromophthalic acid, of which isophthalic acid is advantageous and is therefore used with preference.
Examples of suitable acyclic aliphatic or unsaturated polycarboxylic acids are oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid or dimer fatty acids or maleic acid, fumaric acid or itaconic acid, of which adipic acid, glutaric acid, azelaic acid, sebacic acid, dimer fatty acids and maleic acid are advantageous and therefore used with preference.
Examples of suitable cycloaliphatic and cyclic unsaturated polycarboxylic acids are 1,2-cyclobutanedicarboxylic acid, 1,3-cyclobutanedicarboxylic acid, 1,2-cyclopentanedicarboxylic acid, 1,3-cyclopentanedicarboxylic acid, hexahydrophthalic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 4-methylhexahydrophthalic acid, tricyclodecanedicarboxylic acid, tetrahydrophthalic acid or 4-methyltetrahydrophthalic acid. These dicarboxylic acids may be used both in their cis and in their trans form and also as a mixture of both forms.
Also suitable are the esterifiable derivatives of the abovementioned polycarboxylic acids, such as, for example, their monoesters or polyesters with aliphatic alcohols having from 1 to 4 carbon atoms or hydroxy alcohols having from 1 to 4 carbon atoms. Moreover, it is also possible to use the anhydrides of the abovementioned polycarboxylic acids, where they exist.
If desired it is possible, together with the polycarboxylic acids, to use monocarboxylic acids too, such as benzoic acid, tert-butylbenzoic acid, lauric acid, isononanoic acid, fatty acids of naturally occurring oils, acrylic acid, methacrylic acid, ethacrylic acid or crotonic acid, for example. As monocarboxylic acid it is preferred to use isononanoic acid.
Examples of suitable polyols are diols and triols, especially diols. Normally, triols are used in minor amounts alongside the diols in order to introduce branches into the polyesterpolyols.
Suitable diols are ethylene glycol, 1,2- or 1,3-propanediol, 1,2-, 1,3- or 1,4-butanediol, 1,2-, 1,3-, 1,4- or 1,5-pentan
Röckrath Ulrike
Schilling Marita
Stein Ralf
Wiatr Bärbel
Wigger Georg
BASF Coatings AG
Dawson Robert
Keehan Christopher
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