The color modulation of the paint is very complicated. In the process of paint production and construction, the problem of floating color is often encountered. When the paint has floating color, the color difference between the color and the standard plate makes the coloring difficult, which wastes the pigment and does not color. Precisely, at the same time, the canning effect of the coating is very poor, and the color of the coating film after the coating is dried is difficult to be uniformly applied. One of the phenomena of dynamic separation of the genus genus: the pigment is separated in the horizontal direction, so that the color of the coating film is uneven and the flowering occurs. The floating color is the color that changes vertically. One or more pigments separate during the film formation and drying process. One pigment floats to the surface and the other pigment moves to the bottom or sinks to the bottom.
How do you observe and judge the phenomenon of floating color in the laboratory?
You can start from two aspects:
Static floating color in the tank: After the paint is evenly dispersed and left in the tank for a period of time, one or A phenomenon in which a plurality of pigments are separated and floats on the surface. For example, after storage for a period of time, after opening the can, the surface of the can appears to appear black, indigo or white.
The dynamic floating color of the coating film: the phenomenon that the pigment particles are separated during the drying process of the coating film is called dynamic floating color, and the dynamic floating color pigment separation is divided into two cases: one is the coating film fading surface. The color is uneven, and the other is that the surface of the film is uniform, but the surface layer is different from the color of the bottom layer. Use finger to spread to identify the floating color. First, pour or coat the paint on a glass plate or black and white cardboard. When leveling, rub the finger until the film begins to become viscous, and the pigment particles no longer migrate and separate. If the paint has floating color, the unhoned surface and the honed surface are different in hue. During the honing process, the pigment is easily separated and filamentous streaks appear. After the coating film is dried, the honed surface will have an angular vortex pattern. The degree of discoloration of the finger 随 varies with the conditions of the finger test, and the length of the honing time or the weight of the honing action and the drying speed of the film have a great influence on the degree of color change.
There are many factors in the floating color of paints, the difference in particle size of pigments and fillers, the difference in surface tension of various substances in the system, and the hydrophilic-lipophilic balance (HLB), emulsion and color paste of each substance. The compatibility and the like have a great influence on the floating color of the latex paint, and are discussed in detail below.
1, the effect of the particle size of the pigment particles on the floating color of the paint
During the drying process, with the volatilization of the volatiles in the paint, these volatiles It also carries a part of the pigment and filler to bring them to the coating film. When these pigment and filler particles are transported to the surface, the finer particles with higher surface area are easy to transport, while the coarse particles with relatively low specific surface area are hindered. In sports, when the latex paint film is dried, the more hydrophilic substance tends to evaporate quickly. If the white pulp is more hydrophilic than the color paste, the white pigment particles are more hydrophilic than the color paste. Pigment particles are more hydrophilic and they are more susceptible to being brought to the surface by highly polar volatiles. In addition, the particle size difference between the pigment and filler particles is too large, so that the compatibility between the pigment and the filler becomes very poor. Due to the above reasons, the color paint prepared by using the pigment is not suitable for construction, and the paint floats during construction. Severe, and the film appears to float. It is difficult to adjust the dark paint on floating white, and it will cause waste of paint. The solution is to carefully select the pigment and filler to match the particle size of the selected pigments and fillers; thus avoiding floating and fading.
2, the effect of surface tension difference on the floating color of the paint
In the usual coloring, it is often found that some color paste is difficult to disperse evenly in the white base paint. After the dispersion of the colored paint for a period of time, there is a phenomenon of color separation or floating color, or the canning effect of the paint is not good. In the process of painting, the preparation of white pulp is different from the preparation process of color paste. Anionic dispersant or ionic polyelectrolyte dispersant is often used for making white pulp, while non-ionic dispersant is used for color paste, or part of it. The anionic dispersant is used in combination, and thus the white pigment and the color pigment particles have different surface properties due to adsorption of a different wetting and dispersing agent, and the hydrophilic and lipophilic values are different, and the surface tension is also different. Generally, the ionic surfactant has a larger surface tension than the nonionic surfactant. They are all nonionic surfactants. Because of their different molecular structure at the hydrophobic end, the surface tension is also different, and the outermost link in the hydrophobic end structure of the molecule contributes the most to the surface tension. A molecule with a low surface energy means that the force between the molecules is small and the surface tension is also low. From the viewpoint of thermodynamics, substances with low surface tension are easily adsorbed and transferred to the interface, which makes the system stable. The decrease in surface tension weakens the tendency of the liquid shrinkage surface and the droplets to coalesce, and reduces the additional pressure difference of the curved liquid surface. Conducive to the stability of the liquid surface and dispersion system. Therefore, if the surface tension between the white pulp or the color paste differs greatly from the surface tension difference of the system, the paint disposed with the slurry is more likely to have a floating color.
3, the compatibility between the system
The compatibility of the emulsion and the color paste is good, the floating color of the paint and the coating film will be much better, the emulsion on the color paste If it is wet, the color development of the paint is also good. Anionic and nonionic surfactants are often used as wetting and dispersing agents in aqueous coatings. Inorganic pigments with polar and ionic surfaces in water systems can react with polar groups or ions of added ionic surfactants. The effect is to form a two-layer adsorption layer. In the aqueous pigment slurry, the surfactant particles are adsorbed on the surface of the pigment particles to form a protective layer, but the interaction between the protective layers is intermolecular force and electrostatic force, so the force between them is different, when the above color paste When mixed with various types of emulsions or latex paints, the dispersion stability of the color paste is different. When the surfactant on the surface of the pigment particles has a high affinity with the surfactant adsorbed on the surface of the emulsion particles, that is, an emulsifier or water, The surfactant adsorbed by the pigment particles is peeled off, so that the protective layer on the surface of the pigment particles is thinned, causing flocculation of the pigment, thereby causing floating coloration of the coating film. Of course, when the emulsifier outside the emulsion particles is compatible with the surfactants other than the pigment and filler particles in the color paste.When the emulsion is wetted by these pigments and filled particles, the color development of the whole color paint is good, the color is bright, and the color is not floating.
4, the effect of hydrophilic-lipophilic balance on floating color fading
Hydrophilic lipophilic balance (HLB) is a very sensitive problem, often in the production of coatings Use a variety of materials: emulsions, pigments, fillers, solvents, cosolvents and various additives. These materials all have their own hydrophilic-lipophilic balance (HLB value). The hydrophilic-lipophilic balance of each material matches the performance of the coating system. The floating color, hair color, water distribution and other phenomena will be get over. Of course, after the emulsion and pigments we use, the hydrophilic-lipophilic balance value, that is, the HLB value, cannot be changed, but the HLB of the whole system can be adjusted by carefully selecting the auxiliary agent, that is, wetting and dispersing agent, thickener, and the like. The value balances the HLB value of the entire system. We know that the lipophilic substance has a small surface tension at the lipophilic end, and the paint is stored in a container storage tank. These lipophilic substances are easily floated onto the surface. From a thermodynamic point of view, the energy of the whole system is lowered and the system is stable. When the latex paint produced is in a static state, it floats in the container, not only the canning effect is not good, the construction performance is not good, and the coating state is not good. If the paint floats white, it means that the HLB value of the white pulp is relatively small, and the white pulp is relatively oleophilic. Therefore, the white pulp should be made hydrophilic when producing the white pulp; if the paint floats the color of the color paste, it indicates the white pulp HLB The value is relatively large and relatively hydrophilic. When producing white pulp, the white pulp should be made lipophilic to prevent the paint from floating.
The matching of the hydrophilic-lipophilic balance value (HLB value) can be accomplished by careful selection of the wetting and dispersing agent. The ammonium salt dispersing agent with a hydrophobic group in the anionic dispersing agent is more lipophilic than the sodium carboxylate dispersing agent, and the HLB value is small, and the ammonium salt dispersing agent with a hydrophobic group also greatly improves the floating color of the latex paint film. Because when the pigment particles are wrapped with this type of dispersant, there are not only electrostatic resistance around the pigment particles, but also steric hindrance, and during the drying process, as the water evaporates, the ammonia in the ammonium salt also volatilizes. To make such dispersants more hydrophobic, so that the pigment filler particles encapsulating such dispersants are more compatible with the film-forming materials, and the steric hindrance makes the structure become bulky, so that the coating film is in the drying process. The floating color of the middle coating film, that is, the floating color during the dynamic process is also suppressed.
5, the effect of thickener on the floating color of latex paint
some pseudoplastic strong associative thickeners and surfactants with larger HLB values The great affinity makes it desorb on the surface of the pigment, causing the pigment to aggregate and flocculate, which in turn causes the coloring power of the system to decrease and produce a floating color. In the system of mixing organic and inorganic pigments, especially when titanium white is used in combination with cyan, cyan and carbon black pastes, a weakly plastic associative thickener can be used to obtain a latex paint with satisfactory color and good leveling. Sex.
(provided by Shenyang Building Materials Network) <
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