Functional Silicones for Easy-to-Clean Coatings

Functional Silicones for Easy-to-Clean Coatings

Introduction

Coatings are widely used and play a vital role in protecting and decorating underlying surfaces. Good adhesion to the substrate, durability, and resistance to damage from environmental effects are fundamental requirements for most coating systems. These coatings, commonly referred to as "functional" or "smart" coatings, can help deliver added value to end users. One such sought-after function is "easy-to-clean" properties, which is critical for the construction/architectural, automotive, and personal electronics industries. It is well known that silicone and fluoro materials reduce the effects of coating surface energy. Often, both are used to provide easy-to-clean properties. As concerns about potential environmental and health damage from fluorinated chemicals increase, people are now turning to fluorine-free solutions. Functional silicones, owing to their low surface energy and versatility, are excellent candidates to replace fluorinated chemicals in easy-to-clean coating applications. Unlike conventional silane/silicone oligomers or polymers, functional silicones possess one or more organic functionalities that, in addition to providing various performance advantages, help improve compatibility in different coating systems (Figure 1). In this article, we will introduce CoatOSil™ CLEAN, a functional silicone that can provide easy-to-clean properties in acrylic paints.  

Easy-to-Clean Solution for Water-Based Acrylic Latex Paint

This study was conducted to investigate the effects of additives on the stain-resistant or easy-to-clean performance of interior paints against common stain sources such as friction marks resulting from objects physically rubbing against walls, surfactant leaching, and other household stains.

Model Formulation and Test Methods

A semi-gloss formulation shown in Table 4 was used to evaluate different additives from Momentive. A commercial pure acrylic latex was used as the binder for the base paint. Each silicone additive was post-added to the base paint at a loading level of 3% by weight based on the total formulation. The standard ASTM methods used in this study are listed in the results section. An in-house test method was used for abrasion resistance. Different materials such as rubber stoppers, pen caps, and metal spatulas were rubbed by hand onto a fully cured paint surface with moderate pressure applied. Equal pressure and rubbing time were applied to all paint samples, and the resulting marks and stains on the surface were rated. Water dynamic contact angle and oil dynamic contact angle were measured using a Thermo Cahn DCA 322 microbalance. Paint was applied with a sponge applicator to both sides of a Leneta black rub test panel (1" X 1.5" rectangle). The dry paint film thickness was approximately 50 microns. Sample immersion speed and total depth were measured at 80 microns/s and 8 mm, respectively. The initial surface tension of water was measured with a platinum Wilhelmy plate at 72 mN/m. The oil used for contact angle measurement was Agri-Pure 25 soybean oil from Cargill. The surface tension of soybean oil was measured at 33 mN/m. The dynamic friction coefficient was measured using a CSM tribometer with 0.5 mm amplitude linear reciprocal stroke, stainless steel ball (5 mm diameter), 2 N load, and 1 cm/s sliding speed.

Results and Discussion

The results of easy-to-clean properties and other paint performance characteristics are shown in Table 3. As shown in Figure 3, the paint containing CoatOSil CLEAN silicone performed significantly better compared to both the control paint and the comparative silicone emulsion-containing paint. The same trend was observed in the surfactant leaching test where paint samples containing CoatOSil CLEAN silicone showed the least water spotting (Figure 4). Figure 2 shows the results of the abrasion resistance test. Both the competitive silicone emulsion and CoatOSil CLEAN left significantly fewer abrasion marks from rubber stoppers, metal spatulas, and pen caps compared to the control paint. Figure 2: Abrasion resistance results in acrylic latex paint with and without different silicone additives (top: pen cap, middle: metal spatula, bottom: rubber stopper) Figure 3: Lipstick stain removal results in acrylic latex paint with and without different silicone additives.   Figure 4: Surfactant leaching stain resistance results in acrylic latex paint with and without different silicone additives Figure 5: Block resistance results in acrylic latex paint with and without different silicone additives. Overall, CoatOSil CLEAN silicone demonstrated the best performance against stains resulting from abrasion, lipstick, and surfactant leaching. Additionally, it increased gloss without negatively affecting abrasion resistance and improved anti-blocking (shown in Figure 5). These improvements can be attributed to proprietary functionalities on the silicone backbone. Its unique structure provided a balanced combination of hydrophobicity and oleophobicity to the paint surface and reduced friction coefficient. Dynamic contact angle and advancing contact angle measurements were used to observe these effects. As shown in Figure 6, the water and oil contact angles of paint containing CoatOSil CLEAN silicone were significantly higher compared to the control/base paint. Additionally, the friction coefficient of the base paint and paint containing CoatOSil CLEAN silicone was measured at 0.3 and 0.16, respectively. This study demonstrated that CoatOSil CLEAN silicone can significantly help improve the easy-to-clean properties of a paint by increasing slip and reducing the surface energy of the paint surface. [caption id="attachment_149604" align="aligncenter"] Figure 6: Dynamic contact angle measurement of a commercial interior paint with and without CoatOSil CLEAN silicone added.[/caption]

Conclusion

In the water-based latex paint study, CoatOSil CLEAN silicone, a new additive from Momentive, provided the best overall performance in abrasion, stain, surfactant leaching resistance, and block resistance. This study demonstrated that CoatOSil CLEAN silicone can significantly help improve the easy-to-clean properties of a paint by increasing slip and reducing the surface energy of the paint surface.   Contributors Dmitry Chernyshov, Rosemeire Ciro, Anne Dussaud, Yogesh Tiwary Ning Lu, Christine Lacroix*, Michaud Hélène* *Momentive Performance Materials     Author: Hélène Michaud Application Development Engineer Momentive Performance Additives   Technical Communications: Hakan Askun CASE Laboratory Manager Azelis Turkey