Flocculation.Flocculation flocculation /floc·cu·la·tion/ (flok?u-la´shun) a colloid phenomenon in which the disperse phase separates in discrete, usually visible, particles rather than congealing into a continuous mass, as in coagulation. is not a surface defect in itself, but it causes a number of defects and contributes to many others. Flocculation is the clumping clumping /clump·ing/ (klump´ing) the aggregation of particles, such as bacteria, into irregular masses. clump·ing n. The massing together of bacteria or other cells suspended in a fluid. together of paint components, mainly pigment particles, to form a loose network as shown in Figure 1. We usually think of flocculation as a bad thing, but a certain degree of flocculation can be very useful. It prevents hard settle and helps to give resistance to sagging and cratering. However, too much flocculation definitely is bad. It prevents adequate flow-out and leveling (the surface may be quite rough), often produces streaks and blotches, prevents good color development, causes flooding, floating and Benard cells, and generally hurts appearance. How do we evaluate flocculation? The best way I know is to observe a drop of paint with an optical microscope optical microscope See under microscope. at 300-500x using transmitted light, but even that is qualitative. Also, some paints such as the one in Figure 2, may look bad, but still work well. It takes experience with comparing observations of performance in order to decide whether the degree of flocculation is acceptable or not. Figure 3 shows paint where the pigment is well dispersed. All three photographs were taken with bright field illumination (light from below the specimen). Unfortunately, microscopy does not work well for highly concentrated pigment pastes because the pigment is so jammed together that you cannot tell whether it is flocculated or not. Dilution allows observations to be made, but must be done very carefully (usually with the letdown letdown 1. the sudden flush of milk flow that occurs when the calf begins to suck or when milking commences in a properly prepared cow. Depends for its occurrence on the release of oxytocin from the pituitary gland in response to massage of the teats and udder. or resin solution) to reduce the chances of causing flocculation. A number of techniques can be used to measure properties of coatings or pastes where flocculation is suspected. For example, the tinting tint n. 1. A shade of a color, especially a pale or delicate variation. 2. A gradation of a color made by adding white to it to lessen its saturation. 3. A slight coloration; a tinge. 4. strength of a flocculated paste is low compared to a well dispersed one. Optical density (light transmittance) is lower for a flocculated paint. Flocculation raises low shear viscosity, often substantially, and addition of a wetting agent wet·ting agent n. A substance that reduces the surface tension of a liquid, causing the liquid to spread across or penetrate more easily the surface of a solid. Noun 1. or dispersant dis·per·sant n. Chemistry A liquid or gas added to a mixture to promote dispersion or to maintain dispersed particles in suspension. (along with shearing) lowers it. The sedimentation sedimentation In geology, the process of deposition of a solid material from a state of suspension or solution in a fluid (usually air or water). Broadly defined it also includes deposits from glacial ice and materials collected under the effect of gravity alone, as in talus volume of flocculated pigment is higher and paint poured into graduated cylinders can be used for making comparisons after a suitable rest time. A flocculated paint usually gives a lower Hegman number (fineness of grind), but the shearing action of the drawdown Drawdown The peak to trough decline during a specific record period of an investment or fund. It is usually quoted as the percentage between the peak to the trough. Notes: may break up the clumps. When such measurements are made or microscopy is carried out, a control should be evaluated at the same time. One-off measurements without a control can be misleading. Rub-up with a finger after the paint has been applied is useful. If the rubbed area is a different color from the rest, then the paint is flocculated. The appearance of dry films also can indicate flocculation. Low gloss, poor general appearance, and non-uniform or poorly developed color all suggest flocculation or, possibly, incomplete pigment dispersion. A quick look at the wet paint with a microscope will enable the observer to decide which problem is being faced. Prevention of flocculation depends on wetting and dispersing the pigments well and stabilizing that dispersion. Wetting agents and dispersing resins along with sufficient shear help to accomplish this. Unfortunately, in many paint manufacturing cases, especially with high solids coatings, the letdown process or the letdown solution itself causes the pigment to flocculate floc·cu·late v. floc·cu·lat·ed, floc·cu·lat·ing, floc·cu·lates v.tr. 1. To cause (soil) to form lumps or masses. 2. To cause (clouds) to form fluffy masses. v.intr. . Solvents in the letdown may be incompatible with the paste or may be such good solvents for the dispersing resin that they pull it off the pigment. Dropping a hot paste into a cold letdown or having a large viscosity difference between paste and letdown is likely to shock the pigment dispersion so that it flocculates. It does not do any good to have an excellent paste if the paint ends up being flocculated. 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