An acrylic emulsion is a stable dispersion of solid acrylic polymer particles in water, typically at 40-55% solids. It is not a solution — the polymer is not dissolved, it is suspended as discrete particles stabilised by surfactants.
Film formation works differently from a solvent system. As water evaporates, the particles pack together, then deform and fuse into a continuous film. That fusion is called coalescence, and it only happens above a specific temperature — the minimum film-forming temperature (MFFT). Below it, the coating dries to a powder and performance collapses entirely.
This is why water-based systems are more sensitive to line conditions than solvent systems. Temperature and humidity on your line are not incidental; they determine whether you get a film at all.