Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2000-07-14
2002-08-13
Beck, Shrive P. (Department: 1762)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
C427S409000, C427S410000, C523S404000, C523S415000
Reexamination Certificate
active
06432485
ABSTRACT:
The invention provides two-component coating agents based on aqueous epoxide/amine systems with modified epoxide components. The invention also provides use of the coating agents as fillers and/or primers for multilayered lacquering, in particular in the vehicle and vehicle parts lacquering sector.
Due to ever more stringent conditions being placed on the protection of the environment, aqueous systems for the surface coating of items are becoming more and more important. Their properties also have to match those of conventional, i.e. solvent-containing, systems. Water dilutable epoxide resin systems have gained significance among surface coating agents which can be hardened at room temperature. These two-component (2C) systems are characterised by a number of good properties such as a very low proportion of, or no, solvent, good drying properties and rapid curing, good inter-layer adhesion and good anticorrosive properties on metals.
Various aqueous epoxide/amine systems based on different binders have already been described. For example, non-ionic stabilised aqueous epoxide resin dispersions are described in DE-A-36 43 751. These are based on the condensation products of epoxide compounds, aromatic polyols and condensation products of epoxide compounds and aliphatic polyols. EP-A-0 387 418, DE-A-43 44 510 and DE-A-196 25 345 describe various amine hardeners for aqueous epoxide systems based on specific epoxide/amine adducts and based on aminourethanes which have been reacted with a variety of non-ionic emulsifiers. DE-A-41 23 860 mentions conventional aqueous epoxide/amine systems which also contain a non-ionic polyurethane resin.
Furthermore, U.S. Pat. No. 4,399,242 describes aqueous epoxide resin dispersions consisting of 50 to 70 wt. % of a self-emulsifying epoxide resin, 1 to 25 wt. % of an aliphatic monoepoxide which is not miscible with water, as a reactive diluent, and 5 to 20 wt. % of a glycol or glycol ether. The self-emulsifying epoxide resin is a reaction product of 40 to 90 wt. % of a diglycidyl ether of a dihydric phenol, 5 to 35 wt. % of a dihydric phenol and 2 to 15 wt. % of a diglycidyl ether of a polyoxyalkylene glycol with 2 to 6 wt. % of a diisocyanate. It may be cross-linked with a polyamine.
The disadvantage of known aqueous epoxide/amine systems is that the coating agents prepared therefrom have insufficient sandability, in particular insufficient dry sandability. On the one hand the coatings obtained are so hard that an adequately large amount of material can be sanded off only with the expenditure of a great deal of time, or else sometimes no sanding at all is possible and the surface is simply scratched. On the other hand, there are aqueous epoxide amine systems which rapidly soften during sanding, due to their pronounced thermoplasticity and this causes blocking to the sandpaper within a short time.
Furthermore, the disadvantage of most known aqueous epoxide/amine systems is that they cannot be applied in a bubble-free manner, especially in very thick layers of, for example, 140 &mgr;m and even after drying at elevated temperatures of, for example, 40 to 60° C., bubble-formation may take place in the surface coating. In particular in the case of the amine hardeners for aqueous epoxide resins described in DE-A-43 44 510 and DE-A-196 25 345, variations in the binder quality can occur, due to the method of production, which has a negative effect on the characteristics of the final lacquer or the resulting surface coating.
The object of the invention was, therefore, to provide aqueous two-component surface coating agents which have adequate processing times, can be applied bubble-free, even in thicker layers and produce coatings with defect-free surfaces. The coatings should be readily sandable in the wet and in particular in the dry state and should have no detachment or creep characteristics, especially when subjected to the humidity/heat test. Variations in the binder quality of the amine hardener resulting from the method of production should not have a negative effect on the characteristics of the lacquer or the surface coatings resulting therefrom. The surface coating agents should have a sufficiently long pot-life. The surface coating agents should be suitable for producing, for example, filler layers during a multi-layer lacquering process.
The object is achieved by two-component aqueous surface coating agents containing
A) as an amine component, one or more aminourethanes A1), which are obtainable by reacting
a) compounds with at least one cyclic carbonate group, in particular a 2-oxo-1,3-dioxalan group and/or a 2-oxo-1,3-dioxan group, with
b) one or more amines with at least one primary amine group, wherein the ratio of the number of cyclic carbonate groups to the number of primary amine groups is 1:10 to 1:1.1,
and which may optionally be reacted with
one or more hydrophilic water-dilutable epoxide compounds A2), wherein the ratio of the number of all the amine hydrogen atoms in A1) to the epoxide groups in A2) is preferably 2:1 to 20:1, and
B) as an epoxide component, one or more urethane group-containing epoxide compounds which are obtainable by reacting one or more epoxide compounds c) with one or more polyisocyanates d), wherein the polyisocyanates are used in an amount of 0.1 to 50 wt. %, preferably 0.5 to 25 wt. %, in particular 2 to 15 wt. %, with respect to the amount of epoxide compound (solids to solids).
A preferred variant of the invention consists of reacting the aminourethanes A1) with hydrophilic non-ionic epoxide compounds A2) in order thus to ensure improved water-dilutability and stable dispersion of the amine hardener.
Surprisingly, it was found that when using surface coating agents according to the invention, quality variations in the amine components, due to the method of production, can easily be compensated for so that negative effects on the characteristics can no longer be detected in the final lacquer or the resulting surface coatings.
The amine component A) and the epoxide component B) will be described more precisely in the following.
The amine component A) is an aminourethane A1), these being obtained by reacting compounds with at least one cyclic carbonate group (a) with one or more amines with at least one primary amine group (b).
The compounds which contain cyclic carbonate groups which can be used as component a) to prepare aminourethanes A1) are in particular those which contain one, preferably two or more, 2-oxo-1,3-dioxalan or 2-oxo-1,3-dioxan groups, wherein these are preferably in the terminal position. Component b) consists of amines which contain at least one primary, preferably several primary, and optionally also secondary and tertiary amine groups.
To prepare aminourethanes A1), conventional cyclic carbonates which can be prepared, for example, by reacting carbon dioxide with epoxide compounds in a known manner, are used as component a). These epoxide compounds are preferably polyglycidyl ethers based on polyhydric, preferably dihydric alcohols, phenols, hydrogenation products of these phenols and/or on Novolaks (reaction products of monohydric or polyhydric phenols with aldehydes, in particular formaldehyde, in the presence of acid catalysts). The epoxide equivalent weights of these epoxide compounds are preferably between 100 and 2000, in particular between 100 and 350. The epoxide compounds may be used individually or as a mixture.
Furthermore, conventional cyclic carbonates may be used as component a), such as, for example, those obtained by reacting carbonates such as e.g. dimethyl carbonate, diethyl carbonate, diphenyl carbonate, ethylene carbonate or propylene carbonate with polyols, wherein the polyols contain at least four hydroxyl groups, two each of which react with carbonates in a transesterification reaction to give cyclic five-membered or six-membered ring carbonates. Polyhydric polyols which may be mentioned are, for example: diglycerine, triglycerine, polyglycerine, sugar alcohols (e.g. xylitol, mannitol, erythritol), dimethylol- and trimethylolpropane, dimethylol- and trimethy
Beyers Heike
Maag Karin
Vogt-Birnbrich Bettina
Beck Shrive P.
Crockford Kirsten A.
E. I. duPont de Nemours & Company
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