In water based paint formulations, the base material is the key component that forms the paint film and determines its performance. When designing the formulation, the amount of waterborne resin should be maximized, accounting for 60-70% by volume, to ensure the highest possible content of effective film-forming agents in the paint. This guarantees a thicker, fuller paint film in a single coat.

Waterborne Acrylic Resins

Acrylic emulsions, due to their versatility, weather resistance, and diversity, have been widely used in various fields of the coatings industry.

Waterborne acrylic emulsions are produced by emulsion polymerization of vinyl monomers, primarily acrylate monomers. Various additives, such as emulsifiers, stabilizers, and pH adjusters, are added during the polymerization process, making the system quite complex.

Paint films made from waterborne acrylic emulsions have good weather resistance, are less prone to yellowing, have high hardness, and good gloss.

In recent years, with the continuous development of waterborne acrylic emulsion polymerization technology, multiphase polymerization, core-shell technology, self-crosslinking technology, and the application of polymeric surfactants, the properties of waterborne acrylic emulsions have been further improved and enhanced. This has expanded the application range of waterborne acrylic emulsions to meet the needs of different construction and usage conditions. Currently, the application of waterborne acrylic emulsions has expanded to industrial applications with higher performance requirements.

Polyurethane Dispersions

Polyurethane materials are a general term for a class of macromolecular compounds with urethane structures in their molecular structure, usually produced by polyaddition reactions of diisocyanates and polyols.

Polyurethane polymers possess both polar functional groups that enable physical crosslinking and non-polar and flexible segments. When used properly, their polar functional groups can undergo further chemical crosslinking. These molecular characteristics give polyurethane materials high strength, toughness, and solvent resistance.

As a high-strength, weather-resistant, and strong-adhesion material, polyurethane has been widely used in the coatings industry.

Based on the type of isocyanate used in the preparation of polyurethane, polyurethane emulsions and corresponding paints can be divided into two main categories: aliphatic and aromatic. Aliphatic paint films exhibit excellent weather resistance and anti-yellowing properties; aromatic waterborne polyurethanes are mostly used for interior decorative paints.

According to the particle size obtained from polymerization, polyurethane emulsions and polyurethane dispersions are also classified. Waterborne polyurethane dispersions utilize a unique process to disperse polyurethane particles in water, thereby achieving film formation with water as the carrier. Similar to the film-forming mechanism of other emulsions, the film-forming effect depends on the interpenetration ability of the polymers between particles.

To increase penetration, on the one hand, the polyurethane molecular chains must be sufficiently flexible and have good flowability; on the other hand, the emulsion particles must be as small as possible, which increases the contact area between particles and reduces the migration distance of the polymers. Waterborne polyurethane dispersions typically have nanoscale particle sizes, are semi-transparent or even completely transparent in appearance, and are one of the best waterborne paint base materials. Waterborne polyurethane dispersions are sometimes referred to as nanoemulsions to distinguish them from ordinary emulsions, which have a white appearance.

Styrene

The main reason for introducing this monomer into polyacrylate emulsions is its ability to provide a high glass transition temperature (Tg), thereby improving the hardness of the film; another reason is cost. Styrene is used extensively in the packaging industry and is one of the most important and mature downstream products of the petroleum industry. Its price is low but highly susceptible to macroeconomic fluctuations.

However, the introduction of styrene, especially when its content exceeds 15% of the total monomers, can also have many negative impacts on the film-forming properties of waterborne paints.

Firstly, styrene-containing polymer chains lack flexibility, macroscopically manifesting as a hard but not tough film in waterborne paints. Secondly, the benzene rings in styrene are absorbers of ultraviolet light. When the monomer content is high, ultraviolet light passing through adjacent benzene rings will cause a shearing reaction in the polymer chain, making the waterborne paint film brittle, reducing gloss, and shortening its lifespan. The structure of styrene also determines its affinity for many organic solvents, and the solvent resistance of waterborne paint films is significantly different from other resins.

Acrylic Monomers

There are many types of acrylate monomers, with vastly different properties and prices. The most commonly used monomer in China is butyl acrylate, which has the lowest cost and is used by most emulsion manufacturers in conjunction with styrene to produce inexpensive wall paint emulsions. Its function is to provide flexibility to the water-based paint film.

Because the main chain of acrylate polymers does not contain groups other than ester groups, both the main chain and the ester side chains have good flexibility, resulting in a lack of hardness in the water-based paint film. Although this type of polyacrylate emulsion is a choice for interior and exterior wall coatings, its performance is insufficient for wood coatings, which require high hardness and toughness.

Methacrylate monomers

Methacrylate monomers represent a further improvement in performance compared to acrylate monomers. Because methacrylate polymers have methyl groups on their main chain, the mobility of the main chain is restricted, increasing its rigidity. Simultaneously, the ester side chains provide flexibility, resulting in an optimal balance between hardness and toughness in methacrylate monomers. For example, polymethyl methacrylate (PMMA) is commonly known as acrylic glass. Due to the absence of benzene rings, methacrylate monomers have significant advantages over styrene monomers in terms of UV resistance, durability, and solvent resistance.

In summary, waterborne acrylic resin manufacturers have a wide range of monomer choices, allowing them to vary not only the types but also the relative proportions and compositions. When selecting waterborne acrylic emulsions, waterborne coating manufacturers should not only consider vague terms like "pure acrylic" or "styrene-acrylic," but should use the actual performance of the waterborne acrylic resin and its formulation as the benchmark.

In waterborne paint formulations, the binder is a key component that forms the paint film and determines its performance. When designing the formulation, the amount of water-based resin should be increased as much as possible, accounting for 60-70% by volume, so that the content of effective film-forming substances in the paint is as high as possible. This will ensure that the resulting paint film is thicker and has higher fullness in one coat.