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
2002-03-28
2004-08-10
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...
C427S372200, C427S385500, C428S423100, C524S839000, C524S840000
Reexamination Certificate
active
06774177
ABSTRACT:
The present invention relates to a novel electrically conductive hydroprimer (water based primer) for plastics. The present invention further relates to a novel process for painting plastics.
In industry nowadays the use is on the increase of plastic based moldings which are used together with metal parts and which require a paint finish. This is true particularly of automotive parts, which are increasingly being manufactured from plastics parts, such as, for example bumper fascias, spoilers, sills, wheel arch linings and side trims or protection strips.
In order to improve the impact strength, especially the low temperature impact strength, these plastics include hydrophobic oligomeric rubbers, which are fundamentally incompatible with aqueous paints. These rubbers contribute to the formation of a hydrophobic boundary layer between hydroprimer and plastics part and hence to the delamination of the multicoat paint system.
This problem can be countered by using organic solvent based primers which bring about a certain partial dissolution or partial swelling of the plastics surface and hence better anchoring of the primer coat. However, the high solvent content may lead to damage to the plastics part as a result, for example, of microcracks. Moreover, in production, application, and curing, considerable quantities of solvents are released, which is no longer acceptable on environmental grounds.
It would be possible to prevent the delamination of hydroprimer coatings by baking the hydroprimer film at temperatures >100° C. This cannot be done, however, because of the absence of dimensional stability in the majority of plastics at these temperatures. Delamination of the hydroprimer coating can also be suppressed by flaming the surface of the plastics parts. This pretreatment, however, represents an additional step in the process and hence an additional cost factor and an additional source of error.
It is an object of the present invention to find a novel hydroprimer plastics parts which no longer has the disadvantages of the prior art but instead makes it possible to produce hydroprimer coatings for multicoat paint systems which adhere firmly, without delamination, even to unflamed plastics surfaces, and do so after thermal cure at temperatures <100° C. and which permit or assist the subsequent electrostatic spray application of solid color topcoat materials, basecoat materials and/or clearcoat materials. Moreover, as part of a multicoat color and/or effect paint system, the primer coatings ought to have excellent intercoat adhesion. Accordingly, the novel hydroprimer for plastics has been found which comprises
I) at least one component comprising
A) at least one aqueous polyurethane dispersion
B) at least one electrically conductive pigment; and
II) at least one component comprising at least one polyisocyanate,
at least one of the components I and II comprising at least one aromatic solvent (D).
Below, the novel electrically conductive hydroprimer for plastics is referred to as “hydroprimer of the invention”.
Also found has been the novel process for producing multicoat color and/or effect paint systems on plastics parts by
1a) applying the hydroprimer of the invention and heat curing the resultant hydroprimer film to give the electrically conductive hydroprimer coating; or alternatively
1b) applying the hydroprimer of the invention, drying the resultant electrically conductive hydroprimer film, applying a light-colored hydroprimer film, and jointly heat curing the resultant electrically conductive hydroprimer film and the light-colored hydroprimer film, to give the electrically conductive hydroprimer coat and the light-colored hydroprimer coat; and
2a) applying a solid-color topcoat material and heat curing the resultant solid-color topcoat film to give a solid-color topcoat; or alternatively
2b) applying an aqueous basecoat material and partially drying the resultant aqueous basecoat film, and
3) applying a clearcoat material and subjecting the resultant clearcoat film and the aqueous basecoat film to a joint heat cure or a heat cure and a cure with actinic light, to give the basecoat and the clearcoat.
Below, the novel process for producing multicoat color and/or effect paint systems on plastics parts is referred to for the sake of brevity as “process of the invention”. In addition, the novel multicoat color and or effect paint system for plastics parts has been found, which comprises the following coats atop one another in the stated sequence:
1a) a hydroprimer coating of the invention or alternatively
1a) a hydroprimer coating of the invention and
1b) a light-colored hydroprimer coating, and
2a) a solid-color topcoat or alternatively
2b) a basecoat, and
3) a clearcoat.
Below, the novel multicoat color and or effect paint system for plastics parts is referred to as “multicoat paint system of the invention”.
Not least there have been found the novel plastics parts which are coated with at least one multicoat paint system of the invention and/or with at least one multicoat paint system produced by the process of the invention and which are referred to below as plastics parts of the invention. Further subject matter of the invention will emerge from the description which follows.
In the light of the prior art it was surprising and unforeseeable for the skilled worker that the object of the present invention can be achieved specifically by adding comparatively small amounts of an aromatic solvent to the hydroprimer of the invention. In particular it was surprising that this measure solved the problems of adhesion not only between the plastics parts and the hydroprimer coating but also between the hydroprimer coating and the other coatings present thereon, especially the light-colored hydroprimer coating, the solid-color topcoat or the basecoat/clearcoat, and did so when a curing temperature ≦100° C. was employed. In this context it proves to be a further surprising advantage of the hydroprimer of the invention that it does not cause any damage to the plastics parts as a result, for example, of microcracking and of the emission of organic compounds during handling and curing of the hydroprimer of the invention is not significantly increased as compared with conventional hydroprimers.
The hydroprimer of the invention is a two-component or multicomponent system, in particular a two-component system.
In the context of the present invention, this means a coating material in which in particular the binder, especially the aqueous binder dispersion, and the crosslinking agent are present separately from one another in at least two components which are not combine d until shortly before application. This form is chosen when binder, especially the aqueous binder dispersion, and crosslinking agent react with one another even at temperatures ≦100° C., in particular at room temperature. Coating materials of this kind are employed in particular for coating heat sensitive substrates such as plastic s parts.
The hydroprimer of the invention accordingly comprises at least one, especially one, component I and also at least one, especially one, component II, or consists of these components.
Component I includes as an essential constituent at least one, especially one polyurethane dispersion (A).
Suitable polyurethane dispersions (A) are customary and known and are available commercially. As is known, they comprise at least one water-soluble or -dispersible polyurethane (A), which comprises, in particular, polyester-polyurethanes (A).
Suitable polyester-polyurethanes (A) normally contain (potentially) cationic functional groups (a11) or (potentially) anionic functional groups (a12). Instead of these functional groups or in addition to them they may contain nonionic functional groups (a13) based on polyalkylene ethers.
Examples of suitable functional groups (a11) for inventive use which can be converted into cations by neutralizing agents and/or quaternizing agents are primary, secondary or tertiary amino groups, secondary sulfide groups or tertiary phosphine groups, especially tertiary a
BASF Coatings AG
Niland Patrick D.
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