Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Patent
1995-11-17
1998-02-10
Dudash, Diana
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
427379, 524548, 524590, 524561, 525124, 525127, 525458, 525440, 528 45, 528 66, B05D 138, B05D 302, C08L 3306, C08G 1863
Patent
active
057166781
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for the production of a two-coat finish on a substrate surface, in which and subsequently
The invention also relates to nonaqueous coating materials suitable, in particular, for the process described above.
BACKGROUND AND SUMMARY OF THE INVENTION
The above-described process for the production of a two-coat finish of the basecoat/clearcoat type is known and is employed in particular for the production of two-coat finishes, especially two-coat metallic finishes, on car bodies (cf. e.g. U.S. Pat. No. 3,639,147 and EP-A-38 127).
The finishes which can be produced with the basecoat/clearcoat process, in comparison to one-coat finishes, are distinguished by an improved rendering of the effect and by the possibility producing finishes having brighter and purer colors.
The basecoat applied first in step (1) determines, depending on the nature, quantity and spatial orientation of the pigments employed, the color and--if relevant--the effect (e.g. metallic effect or pearlescent effect) of the finish.
In step (2) of the process, in a flash-off phase, at least part of the organic solvents or at least part of the water is removed from the basecoat film applied in step (1). Step (3) comprises the application, to this initially dried but not baked basecoat, of a nonaqueous, transparent topcoat (wet-on-wet method), and in step (4) basecoat and topcoat are then baked together.
The transparent topcoat applied in step (3) gives the two-coat finish gloss and fullness and protects the pigmented coat applied in step (1) against chemical and physical attack.
The process under discussion can only furnish high-quality two-coat finishes if the transparent topcoat applied in step (3) does not interfere with the basecoat applied in steps (1) and (2) in such a way that the optical effect is impaired (e.g. clouding). On the other hand, the transparent topcoat must have a composition such that, after the baking procedure carried out in step (4), it adheres well to the basecoat. Other important properties which the transparent topcoat obtained after the baking procedure must have are high transparency, good gloss and good mechanical properties, such as hardness, scratch resistance and elasticity. The transparent topcoat obtained after the baking procedure must not at least have a high resistance to climatic effects (e.g. temperature fluctuations, moisture in the form of water vapor, rain or dew, radiation stress etc.) and against attack by acids or other chemicals, for example organic solvents.
JP-A-1-158079 describes nonaqueous, transparent topcoats, for two-coat finishes of the basecoat/clearcoat type, which contain a polyacrylate resin which contains hydroxyl groups and is obtainable by polymerizing from 10 to 50% by weight of an adduct of a cyclic ester, for example caprolactone, with hydroxyethyl acrylate or methacrylate, from 0 to 40% by weight of a hydroxyalkyl acrylate or methacrylate and from 30 to 80% by weight of a copolymerizable vinyl monomer, to give a polyacrylate resin having a hydroxyl number of from 60 to 160, an acid number of from 0 to 40 and a glass transition temperature of from -50.degree. to +40.degree. C. The transparent topcoats described in JP-A-1-158079 give finishes which, in particular with regard to their acid resistance, are in need of improvement.
The present invention relates to a process for the production of a two-coat finish, as described above, in which in step (3) a nonaqueous, transparent topcoat is applied which contains a hydroxyl group-containing polyacrylate resin which is obtainable by polymerizing 4-hydroxy-n-butyl methacrylate or a mixture of 4-hydroxy-n-butyl acrylate and 4-hydroxy-n-butyl methacrylate, acid or of a hydroxyl group-containing ester of methacrylic acid, which is different from (a), or of a mixture of such monomers, methacrylic acid which is different from (a) and (b) and has at least 4 carbon atoms in the alcohol radical, or of a mixture of such monomers, or of a mixture of ethylenically unsaturated carboxylic acid
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Bartelt Angelika
Bartol Fritz
Betz Peter
Rockrath Ulrike
Stubbe Wilfried
BASF Lacke & Farben AG
Dudash Diana
Sabourin Anne Gerry
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