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

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

1995-01-26

1997-02-11

Short, Patricia A.

Coating processes

With post-treatment of coating or coating material

Heating or drying

4274071, 427410, 4274191, 525166, 525167, 525173, 525174, 525176, 525934, C08L 6702, C08L 7302

Patent

active

056018789

DESCRIPTION:

BRIEF SUMMARY
The invention relates to a process for the production of two-coat finishes on a substrate surface, in which polyacrylate resin as binder is applied to the resulting basecoat film, and subsequently
The invention also relates to powder coatings which contain an epoxide group-containing polyacrylate resin as binder.
The process described above for the production of two-coat finishes is known. Using this process, finishes (for cars in particular) can be produced which, particularly with regard to gloss, hiding ability, decorative effect, weathering resistance and refinishability, have distinct advantages over one-coat finishes. To achieve these advantages, however, the coatings employed must have quite specific properties tailored to the coating process described above.
The basecoat applied in step (1) provides color, hiding ability and effect (especially when using metallic pigments for a metallic effect).
The pigmented basecoat film obtained after applying the basecoat is preferably coated in the unbaked state with a clearcoat. Basecoat and clearcoat are then baked together. It is of decisive importance here that the spatial distribution and/or the spatial orientation of the pigments contained in the basecoat should be disturbed neither during the coating with a clearcoat nor during the combined baking. A disturbance of this nature leads to impairment of the visual appearance of the coating. The clearcoat applied to the basecoat is intended to provide the two-coat finish in particular with gloss, body, topcoat appearance and resistance to weathering, chemicals, water and physical stresses. The clearcoat is not permitted to disturb the basecoat either during the overcoating of the basecoat or during the baking operation, but must provide clearcoat films which, after baking, adhere well to the basecoat and exhibit the stated properties.
For economic and ecological reasons it is desirable for the clearcoats employed in the process under discussion for the production of two-coat finishes to be powder clearcoats. Attempts have therefore been made to use powder clearcoats which contain an epoxide group-containing polyacrylate resin as binder to produce two-coat finishes of the type described above (cf. EP-A-299,420). However, it was found that the resulting two-coat finishes are in need of improvement.
The object on which the present invention is based consists in the provision of a process for the production of two-coat finishes of the type described above, in which a powder clearcoat is employed in step (3) which contains an epoxide group-containing polyacrylate resin as binder and with which two-coat finishes can be produced which in comparison to two-coat finishes of the prior art have improved properties.
This object is surprisingly achieved by a process of the type described above in which a powder clearcoat is employed in step (3) which contains as crosslinking agent a mixture of by weight of a compound which contains on statistical average at least two carboxyl groups and at least one, preferably at least two acid anhydride groups per molecule, or a mixture of such compounds, and by weight of a carboxyl group-containing polyester resin which is obtainable by reacting groups selected from hydroxyl, primary amino, secondary amino, carboxyl and acid anhydride groups, one acid anhydride group being regarded as equivalent to two carboxyl groups, or a mixture of such compounds, and dicarboxylic acids and/or dicarboxylic acid anhydrides 0.0 to 2.0:1.0:2.0 to 8.0, particularly preferably 0.5 to 2.0:1.0:2.0 to 6.0 to give a polyester resin having an acid value of 40 to 300, preferably 80 to 250, the percentages by weight relating to (A)+(B)=100 percent by weight.
Two-coat finishes obtained using the process according to the invention in relation to two-coat finishes of the prior art have improved resistance to alkalis, wood resin, pancreatin, premium-grade petrol and methyl ethyl ketone, better scratch resistances and better metallic effects, and are harder than two-coat finishes of the prior art.
In step (1) of th

REFERENCES:
patent: 3781379 (1973-12-01), Farmington
patent: 4091048 (1978-05-01), Labana
patent: 5055524 (1991-10-01), Pettit

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