Driven by low-VOC requirements, softer polymers with low minimum film formation temperature (MFFT) are being utilized in waterborne architectural coatings. An obvious drawback of such soft binders is poor film hardness, which impacts many important resistance properties, such as block, print, scratch, abrasion and dirt pickup. Poor antiblocking characteristics cause the two contacting surfaces (for example, newly painted doors and windows) to stick, resulting in tearing or peeling of the paints upon separation. Print resistance measures the resistance of coating films to deformation from objects (for example, picture frames) placed on top of the coating.
The coatings industry has made great strides in enhancing the performance of low-VOC waterborne coatings. Blending a soft, film-forming latex with a small-particle-size, high-Tg modifier has been a common practice to enhance block resistance and wet adhesion properties.1-8 However, inherent incompatibility between most polymer pairs in general hinders the development of cohesive strength as reflected in decrease of scrub resistance.9 A more elegant approach to fulfilling the contradictory requirements of film formation and hardness is to design structured emulsion polymers with internal hard and soft domains inside the latex particle.10-15 Yet, antiblocking and print resistance are still found to be deficient because most self-filming binders have limited potential to develop adequate bulk modulus and surface hardness. Additionally, such multiphase particles often compromise scrub durability, attributable to inherent incompatible compositions of different polymer phases.