Aqueous Basecoat Ester Additive Pinhole Reduction
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Solution Overview
Problem
Multicoat color and/or effect paint systems using the basecoat/clearcoat method often suffer from visible pinholes due to the wet-on-wet process, which limits the dry basecoat film thickness before pinholes occur.
Innovation Solution
Incorporating a specific ester with the structure R1 being ethyl or isopropyl and R2 being a C2 to C8 radical in the pigmented aqueous basecoat, used in amounts of 0.1% to 5% by weight, to enhance the pinholing limit and reduce pinhole formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a pigmented aqueous basecoat is applied using the basecoat/clearcoat method, then a multicoat color and/or effect paint system is produced, but visible pinholes occur in the clearcoat and basecoat film
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition of the basecoat through the addition of specific esters (0.1% to 5% by weight). This chemical parameter change alters the film formation characteristics and volatility profile, enabling the basecoat to maintain film integrity at higher dry film thicknesses without forming pinholes during the wet-on-wet clearcoat application process
2Quantity of substance
If the dry basecoat film thickness is increased, then more pigment coverage is achieved, but pinholes occur above a certain thickness threshold
Solution Approach 1:
The invention changes the physical-chemical parameters of the basecoat system by incorporating specific esters that modify evaporation rates and film formation kinetics. This allows the pinholing limit to be significantly increased, enabling application of thicker dry basecoat films (higher pigment coverage) without crossing the threshold into pinhole formation
3Productivity
If a wet-on-wet process is used to apply clearcoat over basecoat, then production efficiency is maintained, but pinhole formation increases
Solution Approach 1:
The patent modifies the volatility and film formation parameters of the basecoat through ester addition, creating a composition that can tolerate the moisture and solvents present during wet-on-wet clearcoat application. This parameter adjustment allows continuous production efficiency while preventing the pinhole defects that normally result from applying clearcoat before the basecoat is fully dried
Data Source
AI summary
Disclosed is a method for producing a multicoat color and/or effect paint system, comprising (1) applying a pigmented aqueous basecoat to a substrate, (2) forming a polymer film from the basecoat applied in stage (1), (3) applying a clearcoat to the polymer film, and then (4) curing the polymer film together with the applied clearcoat to form a clearcoat film. The pigmented aqueous basecoat comprises at least one ester characterized by the following structure:where R1 is selected from the group of ethyl and isopropyl and R2 is a C2 to C8 radical. The at least one ester is used here in an amount of 0.1% to 5% by weight, based on the total weight of the aqueous basecoat applied in stage (1). The invention further provides the corresponding coating materials and the use of the esters in pigmented aqueous coating materials.