During the drying process of the paint film, blooming and floating color are caused by uneven distribution of pigments. The color of the blooming paint film is mottled and uneven, while the color of the floating paint film is uniform, but darker or lighter than it should be. Flooding and floating are the result of convection driven by surface tension gradients, causing pigment separation.
During the drying process, the solvent volatilizes, the concentration increases, and the temperature decreases, all of which increase the surface tension of the wet paint film surface, thus forming a surface tension gradient, and then the underlying paint flows upward, forming convection. Convection causes obvious turbulence, and the turbulent patterns are approximately circular. When they expand, they are compressed when they encounter adjacent flow patterns, forming a nearly hexagonal Bernard vortex.
Bernard has pointed out the ubiquity of hexagonal images in nature. As the solvent continues to volatilize, the viscosity increases, and it becomes difficult to flow together large particles with high density stop flowing first, and the small particles with low density can keep flowing for a longer time, so that the pigments will separate and bloom.
Flocculation usually causes flowering. If one pigment is flocculated, and the other pigment is not flocculated and has fine particles, flowering is likely to occur. The flow of fine pigments remains for a long time, and when the convection returns to the bottom of the film, it is trapped in the boundary formed with the adjacent vortex, resulting in the enrichment of fine particle pigments on the boundary and the enrichment of coarser pigments in the center of the vortex. Properly stabilizing the pigment dispersion so that neither pigment flocculates reduces blooming.
When the light blue glossy enamel board blooms, a dark blue mottled stripe pattern will appear on a lighter blue background. The pattern is nearly hexagonal , but it is rare to see a complete one. This is usually caused by the white pigment in the thousand light blue paint film Caused by flocculation and blue non-flocculation. If the blue pigment flocculates and the white one does not flocculate, light blue stripes are formed on a dark blue background.
Sometimes there is no flocculation, which is caused by the fact that the pigments used are too different in particle size and density. Using high-pigment carbon black and Qinbai to make gray paint, the particle size of Ti02 is several times larger than carbon black, and the density is also 4 times larger, so it is easy to bloom; use lamp black with larger particle size can reduce blooming .
Floating color means that the surface color is consistent, but not as it should be. Floating color is caused by different construction conditions, the color of the paint film is different, and the color on the same workpiece is different. The density of the pigments is different, and the settling speed is also different, which causes the pigments to be separated into layers , and one or several pigments are enriched on the surface, resulting in floating color. Thick wet film, low base material viscosity and slow solvent volatilization rate will make the wet paint film stay longer at low viscosity, more pigment sedimentation, and aggravate floating color.
Adjusting the paint formula, not using low-density and very fine pigments, but using fast-volatile solvents and high-viscosity base materials can reduce floating color. Pigment dispersants are used to reduce pigment flocculation, and leveling agents are used to form a monomolecular layer with low surface tension on the surface of the paint film to prevent the flow of eddy currents, all of which can prevent blooming. Thixotropes also prevent floating and blooming by controlling viscosity.
With conscious use of hair flowering, you can create beautiful hammered paint patterns, like the pattern a ball-nosed hammer strikes on a metal plate. Hammer varnish has been used extensively in the past to mask rough surfaces on iron castings. Hammer paint uses large-particle non-leafing aluminum powder and fine-particle transparent pigments (such as cyan blue), fast-evaporating solvents and fast-drying resins (such as styrene-modified alkyd resins), without splashing solvents , which gives the hammer pattern image. Another method is obtained by construction operation: first spray blue aluminum powder paint, then spray a small amount of solvent, the surface tension of the solvent landing point is the lowest, causing blooming, forming bluer streaks, and the aluminum powder is rich in the center. set, with a lighter blue in the center. Smooth molded plastic parts now replace the rough metal castings of the past, and the use of hammered paint has been reduced.
