Influences of Latex
Design Parameters
by Wenjun Wu,
Michael Anderson, and
Jeff Schneider
Dow Coating Solutions*
One of the biggest challenges for low-VOC coatings is simultaneously attaining smooth
film formation and acceptable block resistance and film hardness. Block resistance is a function of bulk and surface properties. This article investigates the influences of some latex design
parameters on block resistance of acrylic paints. The effects of latex particle size, surfactant
choice, and polymer Tg are discussed.
INTRODUCTION
Dry paint often comes in contact with itself, such as during the closing of windows and doors. Block resistance combats the tendency of paint
films to stick together (or block). It is a key performance requirement for
gloss and semi-gloss paints. A coating with good block resistance will retain
its film integrity upon reopening of a window or door. Poor antiblocking
properties cause the two contacting films to stick, resulting in tearing or
peeling of the paints upon separation. The blocking behavior of a paint
film depends on its hardness, the pressure, temperature, humidity, and the
duration of surface contact.
With increasing regulatory pressure to reduce the amount of volatile organic compounds (VOC) in paints and coatings, softer polymers with low
minimum film formation temperature (MFFT) are more frequently being utilized in waterborne architectural coatings. One of the challenges for low-VOC
coatings is simultaneously attaining smooth film formation and acceptable
block resistance and film hardness. Synthesizing structured latex with core-shell morphology is a common approach to enhancing block resistance of an
emulsion binder. 1-3 The blending of two latexes, one with high MFFT and the
other with low MFFT, has also proven to be a useful strategy to fulfill these
contradictory requirements. 4-8 Improved block resistance is attributed to increased bulk modulus and surface hardness of the blend system. 4 For homogeneous particles, crosslinking can effectively increase film hardness and therefore block resistance. 9-11 Certain additives have also demonstrated antiblock
characteristics in waterborne coatings systems. 12, 13 Combinations of above
techniques can be employed to improve antiblocking property of paints. 14, 15
Presented at FutureCoat! 2008, sponsored by FSCT, October 15–16, 2008, in Chicago, IL.
