Materials Science
A new coalescing agent for high performance waterborne paint
3rd February 2020
By Marina C. Passarelli, Juliane P. Santos, Natália F. Paula, Robson A. Pagani, Rafael A. Caldato, Raquel da Silva and Silmar B. Barrios
The experts at Oxiteno explain the science behind their new low VOC, high-performance coalescing agent for waterborne paint. &n
The experts at Oxiteno explain the science behind their new low VOC, high-performance coalescing agent for waterborne paint.
Waterborne paints technology and market demands
Waterborne paints have been used in the decorative business for many years. In this technology the polymer phase, known as latex, is composed of high molecular weight polymer particles dispersed in water and stabilized by surfactants obtained by emulsion polymerization of acrylic and vinyl monomers.
During drying of paint, these latex particles need to coalesce and form a uniform film, requiring the use of coalescing agents. There is currently a growing demand for coalescing agents that are considered low VOCs (Volatile Organic Compounds), and that can also offer high performance properties like dirt pick-up resistance, reduced blocking, and low leaching. To express this commitment, Oxiteno has created the coalescent ULTRAFILM 5000, which aims to meet these market demands, due to its high interaction with the latex polymer.
How the coalescent works
To understand how ULTRAFILM 5000 performs in the paint it is necessary to understand the basics of latex film formation. This mechanism occurs through water evaporation and coalescence of the polymer particles, which can be described in three stages (Figure 1).
- Stage 1: Evaporation of water and packaging of polymer particles.
- Stage 2: Evaporation of water and deformation of particles with formation of a transparent and brittle film.
- Stage 3: Coalescence or interdiffusion of polymer chains from one particle to another, promoting the formation of a continuous, homogeneous film with high mechanical strength. Coalescence will only occur if the Glass Transition Temperature (Tg) of the polymer is below room temperature.
Paints containing polymers with a Tg below room temperature may form films, but they may develop lower hardness than needed, making them sticky, favouring blocking and dirt pick-up. Therefore, to meet the hardness required for decorative paints, polymers that have Tg higher than room temperature are usually used, in which case the use of coalescing agents is required.
During film formation, the coalescent must promote Tg reduction of latex particles so that they coalesce. Afterwards, the coalescent must evaporate from the system, at least partially, promoting the increase of Tg and hardness, generating a dry, homogeneous film of high mechanical resistance. Coalescing agents need to have solubility parameters compatible with those of the polymer phase to be plasticized and cannot destabilize the polymer particles, pigments and fillers present in paint formulations.
Benefits of the new coalescing agent
Increasing the boiling point reduces coalescent volatility while meeting environmental requirements. On the other hand, by evaporating more slowly, it is known that these coalescing agents can keep paint or polymer films permanently plasticized and with low hardness. This permanent decrease in hardness of paint films or polymer films considerably increases their tackiness, favouring adhesion between painted surfaces and adhesion of dirt on painted surfaces, decreasing their resistance to blocking and dirt pick-up. These two unwanted events decrease the performance and durability of paints, evidencing a demand for low VOC coalescing agents capable of yielding paints with high blocking and dirt pick -up resistance, which can be obtained by Oxiteno’s new coalescent, ULTRAFILM 5000.
ULTRAFILM 5000 is designed to maximize coalescing-polymer interaction and reduce the coalescing concentration required to form latex film at different temperatures by up to 50% from market coalescing agents, as will be seen by the results of AFM microscopy and hardness to follow. The new coalescent is able to deliver superior performance and meet environmental requirements.
Results at a glance
The physicochemical properties of ULTRAFILM 5000 are presented in Table 1.
AFM (Atomic Force Microscopy) micrographs of styrene-acrylic latex films also demonstrate that ULTRAFILM 5000 is more efficient than Competitor 1 (2,2,4-trimethyl-1,3-pentanediol monoisobutyrate) in generating coalesced and leveled latex films (Figure 2).
The micrograph of pure styrene-acrylic latex (Figure 2a) shows that the particles are packed and deformed and that the maximum height difference in the film is 18 nm. In the styrene-acrylic latex containing 4% of Competitor 1 (Figure 2b), it is still possible to observe the particle boundaries suggesting that the particles are not completely coalesced. The maximum height difference in the film is 12 nm. In the latex containing ULTRAFILM 5000 (Figure 2c) the particles are completely coalesced, and the film is very smooth and level with a maximum height difference of 3 nm.
Hardness development data show that paint formulated with ULTRAFILM 5000 develops greater hardness than paint formulated with Competitor 2 (2,2,4-trimethyl-1,3-pentanediol diisobutyrate), although both coalescing agents have a boiling point around 280oC. After 7 days of drying, paint formulated with ULTRAFILM 5000 has a hardness similar to paint formulated with Competitor 1 boiling at 254oC (Figure 3).
The excellent hardness evolution of ULTRAFILM 5000 formulated inks is a differential of ULTRAFILM 5000 from market coalescing agents with a boiling point greater than 280oC, allowing it to be used to formulate low VOC interior and exterior paints.
Final considerations
ULTRAFILM 5000 combines technical and environmental performance, has high plasticizing efficiency and generates more coalesced and leveled latex films than the market, as shown by the AFM results. ULTRAFILM 5000 formulated paints show excellent leaching resistance and hardness evolution, making it suitable for the use in indoors and outdoors.
References
- Gilbert JA. The Waterborne Symposium 2016.
- Barrios SB. Manual Descomplicado de Tecnologia de Tintas, Blucher, São Paulo, 2017.
- GS-11-Green Sea™ Environmental Standard for Paints and Coatings, Edição 2.1, 12 Julho, 2013.
- Juhué D et al, J Polymer Sci Part B 1995;33:1123–33.
Authors:
Marina C. Passarelli, Juliane P. Santos, Natália F. Paula, Robson A. Pagani, Rafael A. Caldato, Raquel da Silva and Silmar B. Barrios of Oxiteno, 9801 Bay Area Blvd, Pasadena, TX 77507, USA
ULTRAFILM 5000 is a registered trademark of Oxiteno.
