With the development of the economy, the people's living standards have improved. People's demand for a house is not only a place to shelter from wind and rain, but also a comfortable, beautiful, multi-faceted, performance-compatible residence. Indoor paint is an indispensable part of the overall house, and the color and performance of the paint are gradually improved. 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 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 to observe and judge the floating color fading phenomenon in the laboratory? It can be started from two aspects: static floating color in the tank: one or more kinds of tanks appear after being allowed to stand in the tank for a period of time after the paint is evenly dispersed. The phenomenon that the pigment separates 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 pigment separation of the dynamic floating color is divided into two cases: one is that the color of the surface of the coating film is uneven, and the other is The surface color of the coating film is uniform, but the surface layer and the bottom layer color are different. Use your fingers to identify the floating color. First, pour or coat the paint on a glass plate or black and white cardboard. When leveling, rub the fingers 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 éš 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 the paint, the difference of the particle size of the pigment and filler, the surface tension of each substance in the system, the hydrophilic-lipophilic balance value (HLB) of each substance, the compatibility of the emulsion and the color paste, etc. Floating color fading has a large impact, as discussed below.
1. The effect of particle size of pigment particles on the floating color of paint
During the drying process, as the volatiles in the coating evaporate, these volatiles will also entrain a part of the pigment and filler to bring them to the coating film. These pigment and filler particles have a higher surface area when transported to the surface. The finer particles are easier to transport, while the coarse particles with a relatively low specific surface area hinder the movement. When the latex paint film is dry, the more hydrophilic material tends to evaporate quickly, if the white pulp is hydrophilic relative to the color paste. It is stronger, that is, the hydrophilicity of the white pigment particles is more hydrophilic than the pigment particles in the color paste, and they are more easily brought to the surface by the highly polar volatile substances. 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 the construction process. 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 on the floating color of the paint
In the usual coloring, it is often found that some color pastes are difficult to disperse evenly in the white base paint. After the dispersion of the color paint, the color separation or floating phenomenon occurs soon after a period of time, or the can opening effect of the paint. 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 The anionic dispersant is used in combination, so that 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 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 float.
3. Compatibility between systems
When the emulsion and the color paste are compatible, the floating color of the paint and the coating film will be much better. When the emulsion is wetted by the color paste, the color development of the color 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. Acting to form a two-layer adsorption layer. In the aqueous pigment slurry, the surface of the pigment particles adsorbs the surfactant to form a protective layer, but the force between the protective layers is divided into intermolecular force and electrostatic force, so the force between them is different, when the above color paste When mixed with various 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 granules is compatible with the surfactants other than the pigments and filler particles in the color paste, the emulsion will wet the pigments and the filler particles, and the color development of the entire lacquer is good. Colorful and not floating.
4. Effect of hydrophilic-lipophilic balance on floating color
Hydrophilic lipophilic balance (HLB) is a very sensitive problem. A variety of materials are often used in the production of coatings: 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 used in our selection, the hydrophilic-lipophilic balance value, ie, the HLB value, cannot be changed, but the HLB of the whole system can be adjusted by carefully selecting additives, namely wetting and dispersing agents, thickeners, 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 oleophilic end, and the paint is stored in a container storage tank. These oleophilic 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 film state is not good. If the paint floats white, it indicates that the HLB value of the white pulp is relatively small, and the white pulp is relatively oleophilic. Therefore, when producing white pulp, the white pulp should be made a little hydrophilic; if the paint floats the color of the color paste, it indicates that the white pulp HLB The value is relatively large and relatively hydrophilic. In the production of 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 the dispersant more hydrophobic, so that the pigment filler particles encapsulating such dispersant are more compatible with the film-forming material, and the steric hindrance makes the structure become bulky, so that the coating film is in the drying process. The middle coating film floats, that is, the floating color is also suppressed during the dynamic process.
5, the effect of thickener on the floating color of latex paint
Some pseudoplastic strong associative thickeners have a great affinity with surfactants with larger HLB values, causing them to desorb on the surface of the pigment, causing aggregation and flocculation of the pigment, which in turn reduces the coloring power of the system. Generate floating color hair. 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. Some groups such as thickeners or dispersants, such as hydrophobic end groups, pigment particles have a strong affinity, adsorption of pigment particles to form bridge flocculation leads to coating color, strong hydrophobic association thickener, such as due to hydrophobic groups The adsorption of color paste particles causes the flocculation coloration of the bridge to be poor. The alkali-swelling thickener has different charge charges, and the salt is thickened and the film is charged in the drying process. The affinity of the pigment particles is different, the severity of the floating color, and the differences in the color development of different systems.
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