Sol-gel coating

Details Sol-gel coating Sol-gel coating

2002-02-12

2004-12-07

Cheung, William K. (Department: 1713)

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

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C106S287140, C106S287320, C427S387000, C428S447000

Reexamination Certificate

active

06828381

ABSTRACT:

The present invention relates to a novel sol-gel coating material for producing sol-gel coatings atop single-coat or multicoat paint systems. The present invention relates in particular to a novel process for producing coated substrates, especially coated automobile bodies, by initially providing the substrates with a multicoat paint system and then applying a sol-gel coating material thereatop and curing it.
Automobile bodies are for the most part provided with a multicoat coating system. As the final coat, it is common to apply clearcoat materials. Useful clearcoat materials include the customary and known one component (1K), two component (2K), multicomponent (3K, 4K) powder or powder slurry clearcoat materials or UV curable clearcoat materials.
One component (1K), two component (2K) or multicomponent (3K, 4K) clearcoat materials are described for example in the patent documents U.S. Pat. Nos. 5,474,811, 5,356,669, 5,605,965, WO 94/10211, WO 94/10212, WO 94/10213, EP-A-0 594 068, EP-A-0 594 071, EP-A-0 594 142, EP-A-0 604 992, WO 94/222969, EP-A-0 596 460 or WO 92/22615.
Powder clearcoat materials are known for example from German patent document DE-A-42 22 194 or BASF Lacke+Farben AG's 1990 Pulverlacke product bulletin.
Powder slurries are powder coating materials in the form of aqueous dispersions. Slurries of this kind are described for example in the US patent U.S. Pat. No. 4,268,542 and the German patent applications DE-A-195 18 392.4 and DE-A-196 13 547 and the German patent application DE-A-198 14 471.7, which was unpublished at the priority date of the present invention.
UV curable clearcoat materials are disclosed for example in the patent documents EP-A-0 540 884, EP-A-0 568 967 or U.S. Pat. No. 4,675,234.
Each of these clearcoat materials has its specific strengths and weaknesses. They do provide multicoat paint systems meeting the optical requirements. However, the mar-resistant one component (1K) clearcoat materials are occasionally not sufficiently weathering resistant, whereas the weathering resistant two component (2K) or multicomponent (3K, 4K) clearcoat materials are frequently insufficiently mar resistant. Some one component (1K) clearcoat materials are mar resistant and stable to weathering, but combined with frequently employed waterborne basecoat materials give rise to surface defects such as wrinkling.
Powder clearcoat materials, powder slurry clearcoat materials and UV curable clearcoat materials, by contrast, possess an unsatisfactory intercoat adhesion without fully solving the mar resistance or etch resistance problems.
Recently, materials known as sol-gel clearcoats and based on siloxane-containing coating formulations have been developed which are obtained by hydrolysis and condensation of silane compounds. These coating materials, which are used as coating compositions on plastics, are described for example in the German DE-A patent documents 43 03 570, 34 07 087, 40 11 045, 40 25 215, 38 28 098, 40 20 316 or 41 22 743.
Sol-gel clearcoats impart very good mar resistance to substrates made of plastic, such as spectacle lenses or motorcycle helmet visors, for example. This mar resistance is not achieved by the known OEM (original equipment manufacturing) clearcoat materials normally used for the original finishing of vehicles. The automotive industry is now demanding that this improved mar resistance be transferred to the clearcoats used in the finishing of automobiles as well.
Replacing the OEM clearcoat materials or OEM powder slurry clearcoat materials commonly used in automotive finishing by sol-gel clearcoat materials is not a straightforward matter, however, since the sol-gel clearcoats are too brittle for this purpose, for example, or since the attempt to conform them to the OEM requirements frequently provides only poor optical properties (appearance). Above all, the sol-gel clearcoat materials are too expensive. The economically more favorable use of the sol-gel clearcoat materials as an additional coat over the clearcoats or powder slurry clearcoats used to date gives rise to adhesion problems between the clearcoat and the sol-gel coat, these problems arising in particular after stone chipping and on exposure to condensation.
These problems can be solved by only partially curing the clearcoat which is to be coated with the sol-gel clearcoat material, so that the sol-gel coat can be chemically anchored, as it were, on the clearcoat in the course of the conjoint curing. However, this approach entails the requirement that, on one and the same coating line, the clearcoats on automobile bodies which are to be overcoated have to be cured at a different temperature than the clearcoats of the other automobile bodies which are not to be overcoated. The use of different curing conditions on one coating line constitutes a substantial disadvantage. This disadvantage is additionally aggravated by the fact that the second layer of clearcoat material requires a long oven drying time to cure.
It is an object of the present invention to provide a novel sol-gel coating material whereby the advantageous properties of the sol-gel coatings are combinable with the advantageous properties of the known single-coat or multicoat paint systems, especially the multicoat paint systems for automotive OEM coating, without any need for departures from the customarily employed coating techniques, especially the wet on wet technique of automotive OEM coating. In other words, the novel sol-gel coating material shall in particular permit the subsequent application, within a short time, of a mar resistant coating atop ready produced, previously cured paint systems without any adhesion problems arising in the process.
This object is achieved by the novel sol-gel coating material comprising
(A) an acrylate copolymer solution comprising at least one acrylate copolymer (A1) preparable by copolymerizing at least the following monomers:
a1) at least one (meth)acrylic ester which is substantially free of acid groups,
a2) at least one ethylenically unsaturated monomer which bears at least one hydroxyl group per molecule and is substantially free of acid groups, and
a3) at least one ethylenically unsaturated monomer which bears per molecule at least one acid group which is convertible into the corresponding acid anion group;
(B) a stock coating material preparable by hydrolyzing and condensing at least one hydrolyzable silane (B1) of the general formula I
SiR
4
  (I)
 where the variable R has the following meaning:
R=hydrolyzable groups, hydroxyl groups and nonhydrolyzable groups with the proviso that there is at least one and there are preferably at least two hydrolyzable group(s); and
(C) a sol preparable by hydrolyzing, condensing and complexing
C1) at least one hydrolyzable metal compound of the general formula II
MR
n
  (II)
 where the variables and the index have the following meaning:
M=aluminum, titanium or zirconium,
R=hydrolyzable groups, hydroxyl groups and nonhydrolyzable groups with the proviso that there is at least one and there are preferably at least two hydrolyzable group(s), and
n=3 or 4;
C2) at least one organic thio compound of the general formula III
S(R
1
X)
2
  (III)
 in which the variables have the following meaning:
R
1
=divalent radical deriving from at least one of the following organic compounds:
substituted and unsubstituted linear or branched alkanes, alkenes, cycloalkanes, cycloalkenes, alkylcycloalkanes, alkylcycloalkenes, alkenylcycloalkanes or alkenylcycloalkenes containing no heteroatom or at least one heteroatom in the chain and/or in the ring;
substituted and unsubstituted aromatics or heteroaromatics; and
alkyl-, alkenyl-, cycloalkyl-, cycloalkenyl-, alkylcycloalkyl-, alkylcycloalkenyl-, alkenylcycloalkyl- or alkenylcycloalkenyl-substituted aromatics or heteroaromatics whose substituents are substituted or unsubstituted and contain no heteroatom or at least one heteroatom in their chain and/or their ring;
X=—OH, —SH, —NHR
2
, in which the radical

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