Process for the production of a two-coat finish, and nonaqueous

Details Process for the production of a two-coat finish, and nonaqueous Process for the production of a two-coat finish, and nonaqueous

1994-08-23

1996-05-14

Lusignan, Michael

Coating processes

Applying superposed diverse coating or coating a coated base

Synthetic resin coating

427409, 525454, 525456, B05D 136, B05D 700

Patent

active

055165591

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for the production of a two-coat finish, in which layer, and subsequently
The invention also relates to nonaqueous coatings suitable for this process.
The basecoat/clearcoat process described above is known and is employed in particular for producing finishes, in particular metallic finishes on car bodies (c.f. e.g. U.S. Pat. No. 3,639,147 and EP-A-38 127).
Finishes which can be prepared using the basecoat/clearcoat process, in comparison to single-coat finishes, give an improved effect and enable the production of finishes with bright, purer colors.
The basecoat initially applied in step (1) determines, depending on the type, amount and spatial orientation of the pigments employed, the color and, if appropriate, the effect (e.g. metallic effect or pearlescent effect) of the finish.
In step (2) of the process, at least part of the organic solvents and/or at least part of the water is removed in a flash-off phase from the basecoat film applied in step (1). In step (3) a nonaqueous transparent topcoat is applied to this predried but unbaked basecoat layer (wet-on-wet method) and then in step (4) the basecoat layer and topcoat layer are baked together.
The transparent topcoat applied in step (3) gives the two-coat finish gloss and fullness, and protects the pigmented paint layer applied in step (1) against chemical and physical attack.
High-quality two-coat finishes can only be obtained by the process under discussion if the transparent topcoat applied in step (3) does not interfere with the basecoat layer 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 process carried out in step (4) it adheres well to the basecoat layer. Further important characteristics which the transparent topcoat layer obtained after the baking process must have are high transparency, high gloss and good mechanical properties, such as hardness, scratch resistance and elasticity. The transparent topcoat layer obtained after the baking process must have not least a high degree of resistance to climatic effects (e.g. temperature fluctuations, moisture in the form of water vapor, rain, dew, radiation stress etc) and to attack by acids or other chemicals, such as organic solvents. In addition, the transparent topcoats applied in step (3) should have as low a content of organic solvents as possible and good stability on storage.
JP-A-2-242,867 describes a basecoat/clearcoat process in which, in step (3), nonaqueous transparent topcoats are applied, which comprise (A) a synthetic resin containing hydroxyl groups, (B) an amino resin and (C) a blocked polyisocyanate, where components (B) and (C) are to be chosen such that the temperature at which a chemical reaction occurs between (A) and (C) should be not more than 20.degree. C. below and not more than 50.degree. C. above the temperature at which a chemical reaction between (A) and (B) starts.
Blocking agents which are mentioned for the preparation of component (C) are: volatile, low molecular weight compounds containing active hydrogen atoms, such as methanol, ethanol, propanol, butanol, hexanol, cyclohexanol, benzyl alcohol, ethylene glycol monoethyl ether and other aliphatic or aromatic monoalcohols, dimethyl- or diethyl-aminoethanol and other tertiary amines containing hydroxyl groups, acetone oxime, methyl ethyl ketone oxime and other oximes, acetylacetone, acetoacetates, malonates and other compounds containing active methylene groups, .epsilon.-caprolactam and other lactams, and phenol. The blocking agents preferably employed are aliphatic monoalcohols, oximes and caprolactams.
The transparent topcoats described in JP-A-2-242,867 give finishes which require improvement, in particular with regard to their resistance to organic solvents and acids, their gloss, transparency and resistance to yellowing.
DE-B-2,639,491 describes nonaqueous coatings which comprise a polyester resin and/or alkyd resin containing hydroxyl

REFERENCES:
patent: 3639147 (1972-02-01), Benefiel et al.
patent: 5281443 (1994-01-01), Briggs et al.

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