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New aspects in corrosion protection with polymer dispersions

: Christ, Ulrich; Nothelfer-Richter, Rolf; Englert, Cornelia

Hilt, Michael (Chairman) ; Fédération d'Associations de Techniciens des Industries des Peintures, Vernis, Emaux et Encres d'Imprimerie de l'Europe Continentale -F.A.T.I.P.E.C.-; Gesellschaft Deutscher Chemiker -GDCh-, Frankfurt/Main; Gesellschaft Deutscher Chemiker -GDCh-, Fachgruppe Lackchemie; Verband der Ingenieure des Lack- und Farbenfaches; The Oil & Colour Chemists' Association -OCCA-:
New functions and sustainability - drivers for future coatings : European Technical Coatings Congress, 3-5 September 2014, Cologne, Germany
Frankfurt am Main, 2014
44 Folien
European Technical Coatings Congress (ETCC) <2, 2014, Cologne>
Bundesministerium für Wirtschaft und Technologie BMWi
IGF; 17239N
Conference Paper
Fraunhofer IPA ()
Dispersion; Dispersionsschicht; dispersion layer; Korrosionsschutz; Polymer

Organic coatings play a prominent economical role for protection of steel against corrosion. The driving forces for the development and application of water based coatings for corrosion protection are the challenges of increasing environmental requirements and the compliance with legislative regulations.
In terms of these requirements, anti-corrosive coatings, based on polymer dispersions, e.g. acrylates and acrylate co-polymers, may offer best preconditions since they have further advantages concerning toxicity and work hygiene.
Up to now polymer dispersions show intrinsic weaknesses in anti-corrosive behaviour. Especially in contrast to coatings, based on two-pack EP binders, coatings with polymer dispersions reveal low performance under salt spray conditions, according to corrosivity categories greater than or equal to C3.
One objective of this study is the search for the causes of these weaknesses, in order to find out principles or criteria for selecting polymer dispersions with a high anticorrosive potential for coatings.
The other approach is to study specific contributions and synergies of fillers and anticorrosive pigments. Functional additives and their structure/property-relationships with polymer dispersions for significantly improving the barrier properties of coatings are studied as well.
Derived from the frequently occurring failure modes, i.e. blistering and undercreepage due to cathodic delamination, another focus of this work is on the question, how to block the pathways for water, electrolytes and oxygen through the coating film and along the interface between coating film and steel surface, to improve the lateral barrier against cathodic delamination. This could be done via means of better modelling of the polymer to/on the steel surface topography. Also under consideration is the role of electrolytes, trapped as traces in polymer films, as an inherent weakness of polymer dispersions, originating from the polymerization process.
Within this work a screening with over ten different polymer dispersions, based on styrene acrylates, formulated in three variants, is performed. The formulated coatings are applied to blasted steel surfaces. After standardized drying, the coated samples are tested with standard short-time corrosion tests, under salt spray and condensation-water atmosphere. The undercreepage on defined scribes, respectively the extent of blistering on the coating surface, were evaluated as a function of polymer dispersion type, pigmentation, anticorrosion pigment, film thickness, and single or two layer systems.
Studies of water and electrolyte penetration through the polymer film to and along the interfaces between steel and organic coating with EIS, SKP and sorption kinetics measurements will give insights into the start, progress and extent of the corrosion process and are a measure for the estimation of the corrosion protection performance of the system.
These results can help to identify the main factors of polymer dispersions influencing the anti-corrosion properties of coatings, and, in addition, important indications for paint producers and suppliers of polymer dispersions can be derived.