Binding agents for polyurethane-based paints

Details Binding agents for polyurethane-based paints Binding agents for polyurethane-based paints

1998-08-20

2000-10-10

Gorr, Rachel

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

525123, 524500, 524539, 524562, 524591, 4284231, 4284258, 4273884, C08G 1862

Patent

active

061303089

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention relates to a coating composition for the production of coatings which are resistant to condensed water, comprising binders based on polyurethane which contain alpha,omega-polymethacrylatediols as structural units. The novel coating compositions are preferably employed as fillers, basecoats, clearcoats and/or topcoats.


PRIOR ART

Conventional coating compositions, i.e. those dissolved in organic solvents, based on hydroxyl-containing binders and on crosslinking agents containing isocyanate groups are usually multicomponent systems. One component contains the binder, any pigments and fillers, and customary auxiliaries and additives, the other component contains the crosslinking agent. In addition, a standardizing additive consisting essentially of a mixture of different solvents is also prepared in order to establish the desired viscosity of the coating composition. For ecological and economic reasons, the coatings industry is continuing to make efforts to replace as large as possible a proportion of the organic solvents employed in coating materials by water. In automotive finishing, in particular, there is a great demand for aqueous coating materials. This applies both to the sector of automotive production-line finishing and to the sector of automotive refinishing.
In this context, aqueous coating compositions are employed in particular in the topcoats sector. Topcoats in this context refers to coating materials which are used to produce the topmost coat. This topmost coat can be single-layer or multilayer, especially two-layer. Two-layer topcoats consist of a pigmented basecoat and, applied thereto, a clearcoat which is not pigmented or is pigmented only with transparent pigments.
Two-coat finishes are nowadays produced by the wet-on-wet method, in which a pigmented basecoat is first applied, and the basecoat thus obtained is overcoated with a clearcoat, without a baking step, and then basecoat and clearcoat are cured together. This method is highly advantageous economically but places high requirements on the basecoat and the clearcoat. The clearcoat applied to the as yet uncured basecoat must not disrupt the basecoat, since otherwise finishes of poor appearance are obtained. This applies in particular to finishes for which basecoats containing special-effect pigments (for example metal pigments, especially aluminum flakes or pearlescent pigments) are employed. Furthermore, the topcoat compositions have to be able to be applied by spraying. For this purpose, they must have a solids content at spray viscosity which is high enough for paint films of adequate thickness to be obtained by one to three spray passes (cross-passes), and they must give baked films of good appearance (good evenness, high gloss, low tendency toward boil marks, good topcoat holdout and a high degree of hardness) and good weather resistance.
EP-B-0 358 979 discloses aqueous two-component polyurethane coating compositions comprising a hydroxyl-containing polyacrylate resin dispersed in water, and a polyisocyanate component. However, these coating materials described in EP-B-0 358 979 exhibit great disadvantages in terms of gloss, stretching (low grain in the coating), tendency toward boil marks and, as a consequence thereof, spray safety, and in terms of weathering resistance, especially in terms of the resistance in constant condensed-water conditions (40 degrees C, 240 hours), processibility (drop in viscosity and insufficient pot life) and hardness.
DE-A-44 21 823 describes three-component coating compositions which are characterized in that which is dissolved or dispersed in one or more organic, water-dilutable solvents and has a number-average molecular weight of between 1000 and 30,000, an OH number of from 40 to 200 mg of KOH/g and an acid number of from 5 to 150 mg of KOH/g, and/or which is dissolved or dispersed in one or more organic, water-dilutable solvents and has a number-average molecular weight of between 1000 and 30,000, an OH number of from 30 to 250 mg of KOH/g and an acid nu

REFERENCES:
patent: 4719132 (1988-01-01), Porter

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