Properties

Under construction notice: this section is under construction, text is in draft mode. Your comments will be highly welcomed.


Cationic paints are wellknown thanks to its outstanding capacity of blocking tannins and a number of different stains in a more efficient way than most common anionic waterborne paints. But they are also well known thanks to their outstanding capacity of adhering on most common substrates.
In this

Stain blocking

"Stainblocking" refers to the ability of a coating to prevent water soluble stains, present in or on a substrate or substrate coating, from migrating through a newly applied coating. These stains may result from the presence of certain chemicals in the substrate itself. For example, certain woods such as redwood, cedar, mahogany and the like contain tannin and lignin staining agents which are particularly concentrated in the knots and grains. If contacted by a conventional aqueous latex coating, these staining agents become extracted from the wood and migrate through the coating to the air interface. Repeated applications of the same or a similar type of aqueous latex coating will not successfully prevent these stains from reappearing on the new coating surface. Other water soluble stains which present the same type of problem include marks made by children's markers, felt or ballpoint pens and stains due to water damage on ceilings or walls. All these water soluble stains are effectively blocked by solvent based coatings in which the stain is not solubilized by the coating solvent.

While solvent based alkyd coatings have certain desirable film properties, aqueous based coatings are preferred in many ways over solvent based coatings like alkyds. One reason is due to the potential environmental, health and safety concerns caused by the organic solvents in the coating formulation. In addition, alkyd coatings are not generally as crack and flake resistant as latex based coatings, particularly in exterior applications. Furthermore, alkyds do not perform well over alkaline, cement based substrates, have poor adhesion to galvanized steel, and do not offer the easy water clean-up possible with aqueous latex coatings.

Therefore, it would be desirable if workers in the art could develop an aqueous latex coating which could be used as a substitute for solvent based alkyd coatings, such as for example as a primer coating, to provide the desirable adhesion and stain blocking properties of conventional alkyd coatings as well as the other desirable properties of conventional aqueous based latex coatings.

(text from Patent "Cationic latex coatings" US 5312863 A)

Tannins

Tannins are high molecular weight, water soluble, poly-phenolic molecules found in many types of wood around the world.

Image property of Halox, a company of ICLGroup
http://www.halox.com/products/files/tannin-stain-inhibitors.pdf?v=1.1.3

Chelation mechanism

Metallic tannin stain inhibitor works on chelation. The chelation process is the reaction of soluble metal cations from tannin stain inhibitive pigments with anionic groups on the phenolic rings present in tannins.

Image property of Halox, a company of ICLGroup
http://www.halox.com/products/files/tannin-stain-inhibitors.pdf?v=1.1.3

Major controlling factors in this reaction is the pH of the dry paint film. The pH should be distinctly basic in nature so that the phenol groups will react with the available metal cations. The pH does not seem to have a measurable effect of the solubility of the tannins, but does control their reactivity.

The two most important formulating variables in tannin blocking primers are considered to be inhibitor loading and pigment volume concentration.


Cationic mechanism

Adhesion