Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-06-18
2003-03-18
Moore, Margaret G. (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C525S100000, C525S101000, C427S384000, C427S387000, C427S388200
Reexamination Certificate
active
06534185
ABSTRACT:
The present invention relates to a novel coating composition which comprises a hydroxyl-containing polyacrylate as binder and a tris(alkoxycarbonylamino) triazine as crosslinking agent. The present invention further relates to the use of the novel coating composition to produce novel scratch-resistant clearcoats, especially for motor vehicles. The present invention additionally relates to a novel process for producing multicoat topcoats.
Coating compositions which comprise a hydroxyl-containing polyacrylate as binder and a tris(alkoxycarbonylamino)triazine as crosslinking agent are known from the European patent EP-A-0 604 992. These known coating compositions mandatorily include an acidic crosslinking catalyst, which may cause problems when they are used to produce clearcoats. For instance, the crosslinking catalysts may be fused to the underlying pigmented basecoat and impair the intercoat adhesion and the optical properties of the basecoat/clearcoat system. Moreover, these known clearcoats do not possess the scratch resistance which is a future requirement of the market, especially of the automobile manufacturers and the auto buyers.
The patent WO 92/22615 discloses clearcoat materials whose binders contain up to 5% by weight of polysiloxane macromonomers in copolymerized form. Higher proportions are regarded as deleterious. These clearcoat materials are applied directly to metallic basecoat films and baked together with them (wet-on-wet technique). The crosslinking of these clearcoat materials is by way of epoxide and carboxyl groups. This results in free hydroxyl groups, which may impair the weathering stability. Moreover, the use of these clearcoat materials as sole clearcoat materials may lead to an undesirably high silicone loading in the circuits of the coating plants.
It is an object of the present invention to find a novel coating composition for the preparation of a novel clearcoat material which no longer has the disadvantages of the prior art but which instead gives highly scratch-resistant topcoats which exhibit a so-called “maintenance free”, effect. These advantages ought not to be acquired at the expense of an undesirably high silicone loading in the circuits. Moreover, the novel coating material or the novel clearcoat material should no longer be tied to crosslinking by way of the epoxide and carboxyl groups but instead should be based on a system which, on crosslinking, gives a weathering-stable polyurethane network. A further object of the present invention is to propose a novel multicoat clearcoat system which provides the aforementioned advantages without any problems of delamination.
The invention accordingly provides the novel coating composition which comprises
A) at least one hydroxyl-containing polyacrylate containing in copolymerized form at least one polysiloxane macromonomer as binder and
B) at least one tris(alkoxycarbonylamino)triazine as crosslinking agent.
In the text below, the novel coating composition or the novel clearcoat material is referred to as the “coating composition of the invention” or “clearcoat material of the invention”.
The invention additionally provides the novel process for producing multicoat clearcoats, in which
(1) at least one clearcoat film is applied to the substrate surface and baked, and then
(2) the coating composition of the invention is applied and likewise baked.
The invention further provides the novel process for producing a multicoat topcoat on a substrate, in which
(1) a pigmented basecoat material is applied to the substrate surface,
(2) the basecoat film applied in process step (1) is dried,
(3) a nonaqueous transparent clearcoat material is applied to the basecoat film dried in process step (2),
(4) and then the basecoat film and the clearcoat film are baked together,
which involves applying to the baked clearcoat
(5) a further clearcoat film of the coating composition of the invention, and then
(6) baking it.
In the text below, the two novel processes for producing a multicoat clearcoat and for producing a multicoat topcoat are referred to collectively as the “processes of the invention”.
The invention not least provides the novel multicoat clearcoat and the novel multicoat topcoat which both comprise
(I) at least one clearcoat and
(II) at least one clearcoat obtainable from the coating composition of the invention.
In the text below, the novel multicoat clearcoat is referred to as the “multicoat clearcoat of the invention” and the novel multicoat topcoat is referred to as the “topcoat of the invention”.
In the light of the prior art there was no reason to expect that the object on which the present invention is based could be achieved by means of the coating composition of the invention.
The first key constituent of the coating composition of the invention is the binder (A). In accordance with the invention this binder comprises a hydroxyl-containing polyacrylate containing in copolymerized form at least one polysiloxane macromonomer.
Suitable polyacrylate resins for use in the coating composition of the invention include in principle all polyacrylate resins (A) having an OH number of from 80 to 200 mg KOH/g and an acid number <20 mg KOH/g. The polyacrylate resins preferably have a number-average molecular weight Mn of from 1500 to 30,000, more preferably from 2000 to 15,000, and in particular from 2500 to 5000.
Particular preference is given to the use of the polyacrylate resins (A) obtainable by polymerizing the following monomers in an organic solvent or solvent mixture and in the presence of at least one polymerization initiator, and in the presence or absence of regulators:
a1) a (meth)acrylic ester which is different from but copolymerizable with (a2), (a3), (a4), (a5), (a6) and (a7) and is substantially free from acid groups, or a mixture of such monomers,
a2) an ethylenically unsaturated monomer which is copolymerizable with (a1), (a3), (a4), (a5), (a6), and (a7), is different from (a5), carries at least one hydroxyl group per molecule, and is substantially free from acid groups, or a mixture of such monomers,
a3) an ethylenically unsaturated monomer which carries per molecule at least one acid group which can be converted into the corresponding acid anion group, and which is copolymerizable with (a1), (a2), (a4), (a5), (a6), and (a7), or a mixture of such monomers,
a4) if desired, one or more vinylaromatic hydrocarbons,
a5) and, if desired, at least one reaction product of acrylic acid and/or methacrylic acid with the glycidyl ester of an alpha-branched monocarboxylic acid having from 5 to 18 carbon atoms per molecule (e.g., the glycidyl esters available commercially under the name Cardura®) or, instead of the reaction product, an equivalent amount of acrylic and/or methacrylic acid which is then reacted, during or after the polymerization reaction, with the glycidyl ester of an alpha-branched monocarboxylic acid (e.g., the glycidyl esters available commercially under the name Cardura®) having from 5 to 18 carbon atoms per molecule,
a6) at least one polysiloxane macromonomer described in detail below and intended for use in accordance with the invention, and
a7) if desired, an ethylenically unsaturated monomer which is copolymerizable but different from (a1), (a2), (a3), (a4), (a5) and (a6) and is substantially free from acid groups, or a mixture of such monomers,
the nature and amount of (a1), (a2), (a3), (a4), (a5), (a6) and (a7) being selected such that the polyacrylate resin (A) has the desired OH number, acid number, and molecular weight.
To prepare the polyacrylate resins (A) used in accordance with the invention, use may be made as component (a1) of any ester of (meth)acrylic acid which is copolymerizable with (a2), (a3), (a4), (a5), (a6) and (a7) and is substantially free from acid groups, or a mixture of such (meth)acrylic esters. Examples include alkyl acrylates and alkyl methacrylates having up to 20 carbon atoms in the alkyl radical, such as methyl, ethyl, propyl, n-butyl, sec-butyl, tert-butyl, hexyl, ethylhexyl, stearyl, and lauryl acrylate or methacrylate, for example, or cy
Baumgart Hubert
Farwick Thomas
Poth Ulrich
Röckrath Ulrike
Zumbrink Andrea
BASF Coatings AG
Keehan Christopher
Moore Margaret G.
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