Coating processes – Applying superposed diverse coating or coating a coated base – Synthetic resin coating
Reexamination Certificate
2001-08-02
2003-11-25
Gorr, Rachel (Department: 1711)
Coating processes
Applying superposed diverse coating or coating a coated base
Synthetic resin coating
C427S409000, C427S379000, C428S423100
Reexamination Certificate
active
06652919
ABSTRACT:
The present invention relates to a novel, highly scratch-resistant multicoat paint system comprising a multicoat clearcoat. The present invention further relates to a novel process for producing highly scratch-resistant multicoat paint systems which is based on the wet-on-wet technique. The present invention relates not least to the use of the novel, highly scratch-resistant multicoat paint systems particularly in automotive OEM finishing and in industrial coating.
The requirements imposed on the resistance of topcoats which are exposed to weathering, especially insolation and acid rain, and also, even more frequently, to mechanical stress, especially that produced by wash-brush cleaning installations, are becoming increasingly more stringent. This is so most particularly for vehicle finishes, which have to meet these requirements while also satisfying very high optical demands regarding gloss, surface smoothness, and color.
To date this problem has been solved by applying to the substrates a multicoat paint system which, in accordance with the heightened environmental compatibility requirements, is constructed substantially from aqueous coating materials. In the case of metal substrates, this multicoat paint system is conventionally produced from an aqueous electrocoat material, a water-based primer-surfacer, an aqueous basecoat material, and a solventborne clearcoat material. The electrocoat material and the water-based primer-surfacer are each baked following their application, and then constitute the primer. The aqueous basecoat material is applied atop said primer and the system is subjected to interim drying. Over this coat, which is not yet fully cured, the clearcoat material is applied, after which the two coats are cured together (wet-on-wet technique). Where the substrates used comprise plastics, water-based primers are conventionally employed in place of the electrocoat materials.
The wet-on-wet technique for producing multicoat topcoat systems is described, for example, in the patents U.S. Pat. No. 3,639,147, DE-A-33 33 072, DE-A-38 14 853, GB-A-2 012 191, U.S. Pat. No. 3,953,644, EP-A-0 260 447, DE-A-39 03 804, EP-A-0 320 552, DE-A-36 28 124, U.S. Pat. No. 4,719,132, EP-A-0 297 576, EP-A-0 069 936, EP-A-0 089 497, EP-A-0 195 931, EP-A-0 228 003, EP-A-0 038 127, and DE-A-28 18 100.
The optical or visual appearance and the weather stability are primarily the responsibility of the two topmost coats of the multicoat paint systems. Thus, the aqueous basecoat gives the multicoat paint system its color and/or optical effects such as metallic effects or interference effects, while the clearcoat provides not only scratch and etch resistance, i.e., resistance to damaging environmental substances, but also the appearance qualities, i.e., the gloss, brilliance, and evenness. In this system, aqueous basecoat material and clearcoat material must be very precisely matched to one another in order to produce a system having the desired advantageous profile of properties.
Aqueous basecoat materials and the corresponding paint systems which substantially meet these requirements are known from the patents EP-A-0 089 497, EP-A-0 256 540, EP-A-0 260 447, EP-A-0 297 576, WO 96/12747, EP-A-0 523 610, EP-A-0 228 003, EP-A-0 397 806, EP-A-0 574 417, EP-A-0 531 510, EP-A-0 581 211, EP-A-0 708 788, EP-A-0 593 454, DE-A-43 28 092, EP-A-0 299 148, EP-A-0 394 737, EP-A-0 590 484, EP-A-0 234 362, EP-A-0 234 361, EP-A-0 543 817, WO 95/14721, EP-A-0 521 928, EP-A-0 522 420, EP-A-0 522 419, EP-A-0 649 865, EP-A-0 536 712, EP-A-0 596 460, EP-A-0 596 461, EP-A-0 584 818, EP-A-0 669 356, EP-A-0 634 431, EP-A-0 678 536, EP-A-0 354 261, EP-A-0 424 705, WO 97/49745, WO 97/49747, and EP-A-0 401 565.
These aqueous basecoat materials principally comprise anionically stabilized polyurethanes, with polyfunctional amines and/or amino alcohols, such as triethylamine, methylethanolamine and/or dimethylethanolamine, being used as neutralizing agents.
The solventborne clearcoat materials are commonly one-component (1K), two-component (2K) or multi-component (3K, 4K) clearcoat materials such as are described, for example, in the patents EP-A-0 604 992, WO 94/22969, EP-A-0 596 460, and WO 92/22615.
Although this route leads to multicoat paint systems that satisfy the optical requirements, the one-component (1K) clearcoat often lack sufficient weathering stability, while the two-component (2K) or multi-component (3K, 4K) clearcoats are often not sufficiently abrasion-resistant.
Moreover, there has been no lack of attempts to master these problems through the use of powder clearcoat materials, such as are known, for example, from the German patent DE-A-42 22 194, powder slurry clearcoat materials, such as are known, for example, from the German patent DE-A-196 13 547, or UV-curable clearcoat materials, such as are described, for example, in the patents EP-A-0 540 884, EP-A-0 568 967, and U.S. Pat. No. 4,675,234. In certain circumstances, however, other disadvantages are then introduced, such as a not entirely satisfactory intercoat adhesion, without the problems of scratch resistance or of etch resistance being fully solved.
The patents U.S. Pat. No. 5,474,811, U.S. Pat. No. 5,356,669, U.S. Pat. No. 5,605,965, WO 94/10211, WO 94/10212, WO 94/10213, EP-A-0 594 068, EP-A-0 594 071, and EP-A-0 594 142 disclose coating materials which comprise at least one oligomer and/or polymer containing at least one pendant carbamate group of the formula
—O—(CO)—NH
2
and at least one crosslinking agent containing at least two functional groups which undergo crosslinking reactions with the carbamate group. These known coating materials produce clearcoats which possess extremely high scratch resistance and etch resistance. Cross-linking agents principally employed are highly etherified melamine-formaldehyde resins. The cross-linking itself is catalyzed by acid, catalysts used preferably comprising strong protic acids, especially sulfonic acids, which as a general rule are blocked with amines.
However, these advantageous coating materials cannot be used together with the abovementioned aqueous basecoat materials to construct multicoat paint systems, since if this is done there are frequently surface defects in the clearcoat owing to the shrinkage effect known as wrinkling.
It is an object of the present invention to provide a novel multicoat paint system which no longer has the disadvantages of the prior art but which instead possesses not only an outstanding profile of optical properties and an outstanding appearance but also high scratch resistance and etch resistance, and in which surface defects no longer occur. A further object of the present invention was to provide a novel process for producing multicoat paint systems which, simply, safely, and reliably, produces the novel multicoat paint systems.
The invention accordingly provides the novel, highly scratch-resistant multicoat paint system on a primed or unprimed substrate, comprising
(A) a basecoat,
(B) a first clearcoat as intermediate coat, and
(C) a second clearcoat as the topmost coat
lying above one another in that order, wherein the second clearcoat (C) is producible from a coating material (C) comprising
(C1) at least one oligomer and/or polymer containing at least one pendant carbamate group and/or allophanate group (c11), especially carbamate group (c11), of the formula:
—O—(CO)—NH
2
—O—(CO)—NH—(CO)—NH
2
and
(C2) at least one crosslinking agent containing at least two functional groups (c21) which undergo crosslinking reactions with the carbamate group and/or allophanate group (c11).
In the text below, the novel, highly scratch-resistant multicoat paint system is referred to as the “multicoat system of the invention”.
The invention also provides the novel process for producing a highly scratch-resistant multicoat paint system, comprising at least the following steps:
(I) applying a basecoat material (A) to a primed or unprimed substrate,
(II) carrying out interim drying of the applied base-coat material (A),
(III) applying a first clearcoat material (B), and
(IV)
Baumgart Hubert
Campbell Donald H.
Farwick Thomas
Röckrath Ulrike
BASF Coatings AG
Gorr Rachel
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