High-performance additives for improved water resistance in decorative coatings

Do you want to increase the water resistance of your wood, masonry and other porous decorative coating formulations, but haven’t yet because of the high addition levels required for currently available silicone products? DOWSIL™ 87 Additive can help.

DOWSIL™ 87 Additive is a milky white silicone resin emulsion designed for use in waterborne paints. This additive improves water resistance by creating a hydrophobic silicone network in the paint that repels water but is permeable to water vapor coming from the substrate. As a result, water penetration is reduced while cracking and blistering are minimized.

Performance at additive levels: reduced water absorption

Water absorption (W24) through a paint film is measured as a function of time. The lower the water absorption of a coating, the more water resistance the film offers and the greater protection it provides. Even at only 2% addition by weight, DOWSIL™ 87 Additive provides reduced water absorption.

Figure 1: W₂₄ of an acrylic-based emulsion paint with and without DOWSIL™ 87 (A) and 88 (B) Additives and vs. a competitor silicone resin emulsion. 

The best of both worlds: excellent water vapor permeability

While DOWSIL™ 87 Additive reduces water absorption, it still allows water vapor coming from the substrate to pass through the silicone network, preventing the cracking and blistering that can be a problem with some decorative coatings. Water vapor permeability is reported as the Sd value and is a function of the water vapor transmission rate.

Even in a high-PVC paint formulation that has excellent water vapor permeability, DOWSIL™ 87 Additive has a minimal impact on the Sd value when used at a high addition level (Figure 2).

Figure 2: Sd of water of a high-PVC paint formulation with and without DOWSIL™ 87 (A) and 88 (B) Additives.

Seeing is believing: visual results underscore real performance

Consumers often feel more comfortable with a product when they have visual confirmation of its performance. When it comes to water resistance, they want to see water beading on the coated surface. Better water beading is reflected in a higher contact angle of water on a paint film. DOWSIL™ 87 Additive shows a marked increase in contact angles in acrylic resin formulations, even at a low addition level of 2%, and clearly outperforms a competitor emulsion resin.

Figure 3: W24 of an acrylic-based emulsion paint with and without DOWSIL™ 87 (A) and 88 (B) Additives and vs. a competitor silicone resin emulsion.

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