Enhancing Performance in Paints and Emulsion Polymers Through the Use of Special Monomers and Surfactants

Emulsion polymers are widely used in products with different structures for many applications. Important examples include synthetic rubbers, adhesives, binders, sealants, printing inks, etc. Due to increasing environmental regulations, the paints industry continues to shift toward more environmentally friendly and healthier paints and coatings, and at this point, the use of water-based systems has increased significantly in recent years. Emulsion polymers are used as binders in most of the aforementioned water-based coatings and play a very important role in determining the performance of the final paint, coating, ink and adhesive systems. However, there are performance challenges that must be overcome for water-borne systems to be successful. One of the most important characteristics is reducing water resistance, adhesion, corrosion resistance and surfactant leaching to improve the quality and appearance of the final coat. Phosphate ester products are increasingly used in emulsion polymerization and paints. In recent years, through the incorporation of phosphate groups into polymeric chains and/or formulations, it has been observed that gloss and color acceptance properties have been significantly improved, paint viscosity has been reduced with aging, rust corrosion has been prevented (instantaneous rusting and long-term corrosion resistance), adhesion to metal surfaces has been improved, and films have been obtained that exhibit lower water sensitivity compared to coatings with conventional surfactant additives. Typically, most phosphate esters found on the market contain significant amounts of residual phosphoric acid that can harm final use properties. This situation, when combined with the high dialkyl phosphate content of these monomers (low monoalkyl phosphate (MAP) with dialkyl phosphate (DAP)), makes it particularly difficult to use in solution polymerization processes, because dialkyl phosphate has two double bonds and is a crosslinker for polymerization. Solvay has developed a special technology that enables the production of phosphate monomers with a high MAP/DAP ratio, low acid content, and good compatibility with commonly used monomer compositions or solvents. Solvay's special phosphate ester monomers and surfactants have been developed to impart specific functionality to polymer dispersions. In this article, a summary of specific examples along with various benefits including improvements in water resistance, metal adhesion, and corrosion resistance has been evaluated.

Use of Phosphate Ester Monomers in Emulsion Polymerization

The ability of a coating to adhere to different surfaces under both dry and wet conditions is critical for many applications. One method of improving adhesion is to include functional groups that promote adhesion to resins. These functional groups enter into specific interactions with substrates and thus improve adhesion. In this article, applications of phosphate ester monomers in polymers synthesized by emulsion polymerization can be seen. These polymers are designed to improve the adhesion of coatings to metal surfaces. Phosphate ester monomers were seamlessly incorporated into polymer resins without major formulation or procedure changes. These monomers have been used in a wide range of applications to improve properties found on various surfaces. For formulated coatings, other relevant properties such as adhesion and corrosion resistance have been notably improved.

Sipomer PAM 600

Sipomer PAM 600 is a newly developed special monomer carrying functional groups that increase adhesion to metal, concrete and glass and increase corrosion resistance. In this study, pure acrylic resin was synthesized by emulsion polymerization and Sipomer PAM 600 was incorporated at 0-4 phm levels. Table 1 lists the properties of the resulting latex. It can be seen that the inclusion of Sipomer PAM 600 did not affect conversion and resulted in latex exhibiting good balance. For comparison, resins without Sipomer PAM 600 were synthesized.

Table 1. Polymerization experimental conditions and resin characterization.

The resins were formulated as light industrial paint and corrosion resistance was tested by salt spray test. The resin synthesized with Sipomer PAM 600 showed better corrosion resistance compared to the control (Figure 1).

Figure 1. Salt spray test for paints formulated with pure acrylic resins containing Sipomer PAM 600 and control.

Figure 2. Scrub test for paints formulated with resins containing Sipomer PAM 600.

During emulsion polymerization, Sipomer PAM 600 polymerizes easily with styrene. Styrene-acrylic resins were synthesized and the aforementioned resins were formulated into paints. Improvement in adhesion and corrosion can be seen in Figure 2.

Sipomer COPS-3

Sipomer COPS-3 is a special monomer containing functional groups that provide strong binding power to inorganic pigments and fillers, and also provide blocking and stain resistance and improved color acceptance in paint formulations. Sipomer COPS-3 (0.5% BOTM) was used in a styrene-acrylic polymerization and latex properties are listed in Table 2. It should be emphasized that the inclusion of Sipomer COPS-3 did not affect conversion and resulted in a resin exhibiting good mechanical stability and excellent freeze-thaw stability.

Table 2. Properties of styrene-acrylic resin synthesized with Sipomer COPS-3

A resin containing Sipomer COPS-3 was evaluated reciprocally with a resin available on the market. In high PVC paint (PVC = 84), both resins were formulated and their scrub resistances were compared. The system containing 1% Sipomer COPS-3 showed improvement as 17 against 36 (microns) according to ISO test and 4000 against 1050 (cycles) according to DIN test.

Phosphate Ester Surfactants in Emulsion Polymerization

In this section, we compared the effects of replacing a sulfated surfactant with an equivalent phosphate ester (Rhodafac RS 610 E). Both of these products are ammonium salts. These surfactants were used to prepare a typical polymer with an all-acrylic backbone (51 MMA / 47 BA / 2 MAA). Both systems produced latex with minimum coagulation and average particle sizes of 130 nm. However, the polymer prepared with Rhodafac RS 610 E showed slightly better mechanical stability. In addition, when these latexes were evaluated in terms of water sensitivity, the superior results obtained with Rhodafac RS 610 E latex can be seen in Figure 3.

Figure 3. Polymer film (150 microns) after immersion in water for 72 hours.

Resins synthesized with sulfated surfactant and Rhodafac RS 610 E were formulated into a gloss paint formulation and gloss was evaluated. Gloss results in the paint formulation containing polymer synthesized with Rhodafac RS 610 E showed significant improvement (62.5 against 67.8, Gloss 20° (after 24 hour cure). Fabio Trezzi / R&D Specialist / Solvay Inc. Centre for Research & Technology Berkay Yarız / Distribution Manager / Solvay Inc. Centre for Research & Technology Nemesio Martinez-Castro / R&D Lab. Manager / Solvay Inc. Centre for Research & Technology