Aqueous coating agent

Details Aqueous coating agent Aqueous coating agent

1999-09-27

2000-11-14

Cameron, Erma

Coating processes

Applying superposed diverse coating or coating a coated base

Synthetic resin coating

5263171, B05D 136, B05D 302

Patent

active

061467073

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND

1. Field of the Invention
The present invention relates to an aqueous coating composition which comprises as one binder component an aqueous polymer dispersion suitable for application as a basecoat to a substrate surface, to a process for producing a multilayer coating, and to the resulting coating. The aqueous polymer dispersion comprises -C.sub.8 -alkyl (meth)acrylate monomers, from 30 to 60% by weight of vinylaromatic monomers and from 0.5 to 10% by weight of (meth)acrylic acid based on C.sub.1 -C.sub.6 -alkyl (meth)acrylate and (meth)acrylic acid, and tris(alkoxycarbonylamino)-triazines.
2. Discussion of Relevant Art
The prior art discloses processes for coating vehicle bodies, especially automobile bodies, in which the substrate surface is coated in general first with an electrodeposition coating material and/or antistonechip intermediate primer or a filler coat and then, using a coating material comprising at least one pigment, a pigmented basecoat film is applied and this basecoat film is overcoated, if desired, with a transparent coating material. The single-coat or multicoat finish obtained in this way is subsequently stoved or baked.
The basecoat materials used to produce the basecoat film are usually water-based or solvent-based systems. As principal binders they generally comprise polyurethane dispersions or acrylate dispersions, in combination with water-miscible, crosslinkable polyesters and water-miscible melamine resins, which give rise to a series of problems, examples being low storage stability, tendency to yellow, and unstable viscosity.
For ease of processing and a good and uniform appearance of the coated substrate, the pigmented basecoat materials require a pseudoplastic behavior in combination with a certain non-Newtonian behavior. Ease of processing includes, in particular, good sprayability, storage stability, stirring stability, and stability in a closed pipeline circuit. The appearance of the coated substrate is notable for good coverage of sanding spots, a high metallic effect, good adhesion to the substrate and any further coatings applied thereto, water spray resistance, and weathering stability.
Properties of this kind are particularly advantageous, in the case of metallic finishes, for the development of a high metallic effect.
The pseudoplastic behavior and non-Newtonian behavior should be developed fully by the coating materials in particular from a pH of 6 to about 8 in view of the pH values of the binder solutions employed. In order to obtain such properties, it is common to employ thickeners or Theological assistants such as ionic sheet silicates, xanthan gum, diurea compounds, polyurethane thickeners, bentonite, waxes, and wax copolymers.
However, the use of these thickeners does not lead in every case to the desired coating results, and there may also be problems in the course of processing, i.e., in the course of painting.


SUMMARY OF THE INVENTION

An object of the present invention is to provide a coating composition and a process for producing multilayer coatings on a substrate surface, in which crosslinkers and Theological assistants are employed which give the coating composition the desired pseudoplasticity and non-Newtonian behavior and lead to coatings having an outstanding appearance and, in the case of metallic finishes, with a high metallic effect. A further object is to provide coating compositions which can be overcoated with any customary clearcoats.
The present invention accordingly provides an aqueous coating composition which comprises as one binder component an aqueous polymer dispersion comprising -C.sub.8 -alkyl (meth)acrylate monomers, from 30 to 60% by weight of vinylaromatic monomers and from 0.5 to 10% by weight of (meth)acrylic acid and based on C.sub.1 -C.sub.6 -alkyl (meth)acrylate and (meth)acrylic acid, and tris(alkoxycarbonylamino)-triazines.
Surprisingly, and in accordance with the invention, it is possible by using a combination of a nonassociative rheology stabilizer, which is an acrylate polymer based on C.sub.1 -C.sub

REFERENCES:
patent: 4719132 (1988-01-01), Porter, Jr.
patent: 5084541 (1992-01-01), Jacobs, III et al.
patent: 5565243 (1996-10-01), Mauer et al.
patent: 5596047 (1997-01-01), Wu et al.
translation of WO 9636670, Nov. 1996.

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