Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-12-13
2004-04-27
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S577000, C524S457000, C524S458000, C524S475000, C524S413000, C524S451000, C525S105000, C525S193000, C525S333300
Reexamination Certificate
active
06727316
ABSTRACT:
The present invention relates to a novel coating material. The present invention further relates to a process for preparing the novel coating material. The present invention additionally relates to the use of the novel coating material to produce surfacer coats and antistonechip primer coats, especially for motor vehicles. Moreover, the present invention relates to novel surfacers and antistonechip primers and to the primed or unprimed substrates coated with them, especially motor vehicle bodies.
The provision of stonechip-resistant coatings on metallic substrates is of particular importance in the field of motor vehicle production. Stonechip-resistant coatings are applied in particular in the front area and in the underbody area of a motor vehicle body. A coating material suitable for this purpose should on both economic and environmental grounds contain little or no organic solvents. Apart from powder coating materials, only aqueous coating materials are suitable for this purpose.
Surfacer coats or antistonechip primer coats are subject to a number of requirements. They must be bakable at a temperature of 100-160° C. and after baking at such temperatures must exhibit outstanding properties such as high resistance to stonechipping (especially the combination of multiple and single chipping), good adhesion to the primer coat, a cathodic electrocoat, for example, and to the basecoat or solid-color topcoat, good filling properties (masking of the structure of the substrate) at a coat thickness of from 20 to 35 &mgr;m, and excellent appearance in the final clearcoat. The combination of these properties is difficult to realize on account of the fact that they are in part divergent properties, where improving one property automatically results in a deterioration in another property. Examples of such divergent or contradictory properties are very good resistance to multiple chipping and single chipping, low coat thickness and very good filling power/topcoat appearance, low baking temperature and very good topcoat appearance, and low baking temperature and high adhesion.
Aqueous coating materials which are used to produce surfacer coats or antistonechip primer coats comprise as their binders, for example, water-soluble or water-dispersible polyesters and/or polyurethanes. Aqueous coating materials of this kind are known from the patents DE-A-43 37 961, DE-A-44 38 504, DE-C-41 42 816 or EP-A-0 427 028. Although these aqueous coating materials and the surfacers or antistonechip primers produced with them already meet many requirements of the market, they cannot be used to achieve, simply, all of the abovementioned contradictory properties to a satisfactory extent, but instead require adjustment by means of additional measures which in some cases are comparatively complex.
Coating materials based on acrylic copolymers might offer an alternative here. Such coating materials are described, for example, in the patents EP-B-0 447 428, EP-B-0 593 454, EP-B-0 052 776 or DE-A-42 04 518.
Acrylic copolymers may be prepared by widely known polymerization techniques in bulk, solution or emulsion. Polymerization techniques for preparing acrylic copolymers, especially polyacrylate resins, are widely known and have been much described (cf., e.g., Houben-Weyl, Methoden der organischen Chemie, 4
th
edition, volume 14/1, pages 24 to 255 (1961)).
Further examples of suitable copolymerization techniques for the preparation of acrylic copolymers are described in the patents DE-A-197 09 465, DE-C-197 09 476, DE-A-28 48 906, DE-A-195 24 182, EP-A-0 554 783, EP-B-0 650 979, WO 95/27742, DE-A-38 41 540 or WO 82/02387.
Suitable reactors for the copolymerization techniques are the customary and known stirred vessels, cascades of stirred vessels, tube reactors, loop reactors or Taylor reactors, as described, for example, in the patents DE-B-1 071 241 or EP-A-0 498 583 or in the article by K. Kataoka in Chemical Engineering Science, Volume 50, number 9, 1995, pages 1409 to 1416.
The free-radical polymerization employed for the preparation of the acrylic copolymers, however, is frequently highly exothermic and difficult to control. The implication of this for the reaction regime is the necessity to avoid high monomer concentrations and/or the batch mode, as it is known, where the entirety of the monomers is introduced into an aqueous medium, emulsified and then polymerized to completion. The targeted adjustment of defined molecular weights, molecular weight distributions, and other properties also causes difficulties on numerous occasions. The targeted adjustment of a defined profile of properties of the acrylic copolymers, however, is of great importance for their use as binders in coating materials used to produce surfacer coats and antistonechip primer coats, since by this means it is possible to exert a direct influence over the profile of performance properties of the coating materials and of the coatings.
There has therefore been no lack of attempts to exert targeted control over the free-radical copolymerization of olefinically unsaturated monomers.
For instance, the international patent application WO 98/01478 describes a process wherein the copolymerization is implemented in the presence of a free-radical initiator and a thiocarbonylthio compound as chain transfer agent.
The international patent application WO 92/13903 describes a process for preparing copolymers having a low molecular weight by free-radical chain polymerization in the presence of a group transfer agent having a carbon-sulfur double bond. These compounds act not only as chain transfer agents but also as growth regulators, so giving only copolymers of low molecular weight.
The international patent application WO 96/15157 discloses a process for preparing copolymers of comparatively narrow molecular weight distribution by reacting a monomer with a vinyl-terminated macromonomer in the presence of a free-radical initiator.
Moreover, the international patent application WO 98/37104 discloses the preparation of acrylic copolymers with defined molecular weights by free-radical polymerization in the presence of a chain transfer agent having a C—C double bond and having radicals which activate this double bond in respect of the free-radical addition of monomers.
Despite significant progress in this field, the art is still wanting of a universally applicable process for controlled free-radical polymerization which in a simple manner provides chemically structured polymers, especially acrylic copolymers, and by means of which it is possible to tailor the profile of properties of the polymers in respect of their use in coating materials used to produce surfacers and antistonechip primers.
Accordingly, even with the coating materials based on acrylic copolymers, it is still necessary to seamlessly adjust the properties—divergent in the sense outlined above—to the level required by the market by means of other measures, which in some cases are relatively complex.
It is an object of the present invention to provide a new coating material which is particularly suitable for the production of surfacer coats and antistonechip primer coats, which offers an alternative to the systems known to date and in which in terms of its profile of properties may be varied widely, so that even properties divergent in the sense outlined above can be brought seamlessly to the level required by the market.
The aim is to realize these objects in a simple manner by tailoring the profile of properties of the coating materials, in particular through the use of chemically structured copolymers obtainable by free-radical polymerization. These chemically structured copolymers should also be suitable for use as grinding resins, advantageously permitting the provision of pigment pastes which are particularly easy to incorporate by mixing for the clearcoat materials, basecoat materials and surfacers which are used to produce new multicoat color and/or effect coating systems.
Accordingly, we have found the novel use of a copolymer (A) in a coating material which is used to produce su
BASF Coatings AG
Sastri Satya B
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