Polymer

Details Polymer Polymer

2002-04-16

2004-08-03

Niland, Patrick D. (Department: 1714)

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...

C524S507000, C524S589000, C524S590000, C524S591000, C524S839000, C524S840000, C525S123000, C525S128000, C525S440030, C525S455000, C525S902000

Reexamination Certificate

active

06770702

ABSTRACT:

The present invention relates to polymers and to their use, particularly in the field of automotive OEM finishing.
A conventional auto finish by the “basecoat/clearcoat” process, affording sufficient stone-chip resistance and effective UV protection, is generally composed of a total of four different coats (four-coat system). These four coats are applied successively in separate coating units.
The first coat, located directly on the sheet metal of the auto, is an electrophoretically applied coat (electrocoat) which to protect against corrosion is applied by electrodeposition coating—primarily cathodic deposition—and then baked.
The second coat, located atop the electrocoat and with a thickness of from about 30 to 40 &mgr;m, is a so-called primer-surfacer coat, affording on the one hand protection against mechanical attack (stone-chip protection function) while on the other hand smoothing the rough surface of the raw body for the subsequent topcoat, filling minor unevennesses, and protecting the electrophoretically deposited coat (electrocoat) against natural UV radiation. This coat is largely produced by applying a baking varnish, using electro-static high-speed rotating bells, followed by a baking operation at temperatures above 130° C.
The third coat, located atop the primer-surfacer coat, is the basecoat, which by means of appropriate pigments gives the body the desired color. The basecoat material is applied by the conventional spraying process. The thickness of this conventional basecoat, depending on shade, is between about 12 to 25 &mgr;m. In the case of metallic effect coating materials in particular, this coat is normally applied in two process steps. In a first step, application takes place by means of electrostatic high-speed rotating bells, followed by a second application using pneumatic atomization. This coat (when using aqueous basecoat material) is subjected to interim drying using infrared lamps and/or by means of hot-air convection.
The fourth and topmost coat, located on the basecoat, is the clearcoat, generally applied in one application by means of electrostatic high-speed rotating bells. It gives the body the desired gloss and protects the basecoat against environmental effects (UV radiation, salt water, etc).
The basecoat and the clearcoat are then baked together.
With a view to protecting the environment, more and more water-based automotive OEM paints are being used. Aqueous automotive OEM paints are very well established and it is now hard to conceive of industrial application without them, not only for reasons of protecting the environment. Aqueous paint systems are now no longer just a necessary evil, but instead constitute a serous alternative from the standpoints of technology and of the potential possibilities. Nevertheless, in recent years the requirements have risen considerably. The need to increase productivity while at the same time achieving further reductions in emission levels is imposing new requirements on aqueous basecoat systems. Those to be mentioned in particular include compatibility with low-emission clearcoats (powder, aqueous clearcoat, powder slurry) and the need, owing to shorter processing cycles, to increase application reliability. For example, it is very difficult to achieve the required adhesion properties using a prior art aqueous basecoat together with a powder clearcoat.
Compatibility with clearcoat materials based on powder slurry, in particular, is imposing particularly stringent requirements on aqueous basecoat materials.
The term powder slurry refers to a suspension of paint particles and water, normally consisting of from 60 to 70% by weight water and from 30 to 40% by weight solids. Such compositions are known, for example, from DE 196 13 547 C2 and DE 196 18 657 A1. The use of a powder slurry of this kind is notable for particularly simple application of the corresponding coating materials. Thus a coating material of this kind can be applied using a conventional coating unit for wet coating materials; in other words, there is no need to use specially separated coating equipment such as is needed for coating with powder materials. An unwanted effect observed when using conventional, water-based basecoat materials under a powder slurry clearcoat is that known as “mudcracking”. This term describes a surface condition of the cured paint surface which is attributable to cracking of the coats of paint and is comparable with the appearance of dried-out desert soil.
In the case of an aqueous metallic basecoat material, moreover, the “gassing stability” is particularly important. The expression “gassing stability” refers to the property of a metallic effect paint containing unprotected aluminum particles which do not react with the water solvent to form hydrogen. One way of influencing this property is to use specific, specially treated aluminum bronzes (EP-0 321 470). Aluminum bronzes of this kind are relatively expensive, not very bright, and may introduce unwanted properties into the system, such as an increased tendency toward agglomeration, for example.
Another way of preventing gassing is to add appropriate additives (EP-0 206 615 B1 and EP-0 238 222 B1). In many cases, the additives in question, in addition to their desired activities, may also introduce negative properties into the system.
Owing to the heightened profile of requirements imposed on an aqueous basecoat material that can be used in the automobile industry, the Theological properties of such a material are accorded an increased significance. What is understood by the term “rheological properties” is that the paint on the one hand has such a low viscosity during the spraying operation, i.e., at high shear rates, that it may easily be atomized, and on the other hand, when it impinges on the substrate, i.e., at low shear rates, has such a high viscosity that it is sufficiently firm and does not exhibit any running. The development of a pronounced metallic effect is also associated with these properties.
For improving the rheological properties and for improved development of the metallic effect, particular additives are described (EP-0 281 936). The additives in question are special phyllosilicates, which contain considerable amounts of alkali metal or alkaline earth metal ions. Because of their water-attracting effect, these ions often lead to poor condensation resistance in the overall system of an automobile coating.
Consequently, efforts are made by the paint manufacturers to avoid such additives where possible and to use as binders those polymers which provide the desired properties themselves: so-called “custom-tailored” polymers.
One of the most important representatives of these species are aqueous dispersions of crosslinked polymer microparticles.
For instance, EP-0 502 934 describes a microgel dispersion. This dispersion is used both to improve the Theological properties and to increase the gassing stability of aqueous metallic basecoat materials. These microgel dispersions are prepared by a single-stage polycondensation of a polyesterpolyol with an amino resin (melamine resin) in aqueous phase. The use of this microgel in basecoat materials for the coating of automobile bodies has the disadvantage, however, that the adhesion between the basecoat and a clearcoat applied atop it from a powder clearcoat material or a powder clearcoat slurry does not meet the requirements laid down by the automobile industry.
Furthermore, DE 195 04 015 A1 discloses microgels which are prepared by polymerizing an ethylenically monofunctional compound (polyacrylate) with at least one ethylenically difunctional or polyfunctional compound in the presence of a polyester. The polyester in this case acts as an emulsifier and stabilizer. These microgels have the disadvantage that the rheological properties of these paints no longer meet the heightened requirements of the automobile industry. This is evident with particular clarity with regard to the requirements in terms of viscosity, on the one hand, and in terms of firmness, on the other. For instance, it is not possi

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