Film Formation Through Designed Diffusion Technology

Abstract

In latex polymer-based coatings, volatile organic compounds (VOC) are used as coalescent to soften the latex polymer to ensure film formation when the coating is applied and then the coatings become harder, tack-free, and durable after the VOC evaporates during the drying. There has been increasing pressure to reduce VOC and to maintain the minimum film formation temperature (MFFT) and hardness-related properties such as block, print, and dirt pick-up resistance at the same time. Traditional methods to lower VOC and maintain film hardness include lowering the dominant phase polymer glass transition temperature (T _g) and blending in small amounts of hard polymer to reinforce a soft film or manipulating latex morphology. In this chapter, a new strategy, namely, Film Formation through Designed Diffusion Technology is presented to advance the balance of VOC, MFFT, and hardness-related properties with mechanistic understanding and application results. The Designed Diffusion™ (DD) technology uses a two polymer system, in which small amounts of a specially designed, soft Polymer DD is added to a high T _g dominant phase Polymer A to accelerate early property development. The polymers (Polymer A and Polymer DD) have been chosen so that the coalescent partitions selectively into Polymer A in the wet state. Film formation triggers a change in the solubility of the coalescent in the two polymers. Transport of the coalescent into Polymer DD facilitates the removal of the coalescent from the dominant phase (Polymer A) and thus the coating develops properties at a faster rate.