TopDown Silicones for Paints

Modern paints are expected to offer a range of effects from hammer-effects to special textures. Paints have to adhere well to different substrates. Printing inks and paints should not foam more than necessary during manufacture and application. And it is desirable for waterborne dyes to be used wherever possible.
Silicone additives can meet all these requirements. Automotive finishes illustrate this well. An automotive finish has to meet esthetic requirements in addition to protecting the bodywork. Colorfastness and lasting gloss are key quality determinants here. The difference between good gloss and poor gloss is shown in the following diagram:

Irregularities in the surface structure of paint during finishing have various causes. These include foaming as the paint is being sprayed and uneven evaporation of the solvent during the drying process.

TopDown Foaming

The finishes are sprayed in fine jets under high pressure by automatic painting equipment. Turbulence of the micro-droplets can cause air bubbles to be trapped, and this can lead to flaws in the finish. With increased use of solventless, waterborne surface-coating systems, foaming also occurs. It is caused by the surfactants contained in the waterborne solvents. The counter-measure is to admix silicone-based foam inhibitors. These lower the surface tension so much that the foam literally collapses. The following diagram time shows how a silicone foam-control agent works (see also the experiment “Silicones for antifoams”):

Bubbles are formed when surfactant molecules accumulate at the boundary surface to air, lowering the surface tension of the water and trapping air. Provided that the surfactant doesn't drain away, the bubbles will remain stable for quite a long time. Since the silicone antifoams have a lower surface tension than even the surfactants, they take their place. The foam lamella becomes thinner as a result, becomes unstable and then collapses.

Silicone antifoams are used wherever excessive foaming is unwanted. Even in modern detergents.

TopDown Solvent Additives

As already mentioned, uneven evaporation of the solvent causes irregularities in the finish. Differences in surface tension lead to cratering by dust particles, poor wetting of the substrate, poor mar resistance as well as flow problems. These effects are combated by admixing silicone additives to lower the surface tension of the paint and increase its spreading properties. The microscopic ripple structure of the paint becomes smoothed, incident light is reflected better and the desired gloss effect is obtained. This shown in the following diagram:

Without appropriate additives, the dried paint surface is irregular and rough (left diagram).

The appropriate additives ensure that the surface appears uniform and smooth. It is possible to create “long-wave” and “short-wave” ripple structures by varying the type and quantity of additive (right diagrams).

TopDown Heat-Resistant Paints

Silicone-based paints have enough durability and fastness to meet extreme demands. They are ideal for objects that have to withstand high temperatures. These include barbecues and all kinds of stoves as well as colored light bulbs and space rockets.
The paint must be non-flammable, non-oxidizable and offer adequate adhesion across all temperature ranges. Silicone resins meet all these requirements. A broad range of colors can be produced by adding heat-resistant inorganic pigments . See also the videos on this (wmv or mov).

Three Typical Applications of Heat-Resistant Paints Are Shown Below: