PANG Wen-wu1 , CHEN Bing-yao2 , YAO Rong-mao2 , LUO Guo-tao1 , HE Dong-mei2 (1.Guangdong Shunde Sanvo Chemical Co., Ltd., Foshan 528325, Guangdong, China; 2.Guangdong Sanvo Chemical Industry Technology Co., Ltd., Zhongshan 528429, Guangdong, China)
Abstract: The phenomenon of floating color and fading of latex paint are analyzed and studied, and some main reasons for the floating color of latex paint are summarized, as well as several ways and solutions to solve the problem.
If latex paint is not stored properly after production, it will often appear floating and flooding, which will not only affect the paint’s own properties (such as color, gloss and adhesion), but also its use effect (such as Water resistance, water resistance, salt resistance, etc.). After the latex paint appears floating color and flooding, it will affect the coating opening effect, and it is difficult to apply uniform and uniform color difference when using. After the color latex paint has the problem of floating color and flooding, it will cause pigment delamination, which will seriously affect the color matching work efficiency, and even cause the color difference problem due to the deviation of the paint film color. Such latex paint can not meet the color requirements for color matching. of. In addition, if the general problem of floating color and flooding cannot be solved, the development of the domestic coatings market will also be a major hit, and the Chinese will tend to choose foreign products, which will be a huge development for the domestic coatings market. Challenge.
1 Factors Inducing Latex Paint Floating Color and Floating
During latex paint production, storage, transportation, and construction processes, floating color flooding often occurs, but the culprit is far more than one. The quality of coating raw materials, such as the emulsion and color slurry Compatibility, wetting and dispersing agent, difference in particle size of pigments and fillers, combination of thickeners, surface tension difference of each substance in the system, and hydrophilic affinity value (H LB) of each pigment, as well as production formula and production process, etc. Other factors will affect it. The following will analyze how these factors affect the floating and flooding of latex paint.
1.1 Effect of compatibility of emulsion and colorant on floating color
In the production process of latex paints, manufacturers often add anionic and non-ionic surfactants as wetting and dispersing agents to maintain the storage stability and water resistance of the latex paints. Pigments have good polar and ionic surfaces in water-based coatings. These surfaces interact with ionic surfactants to form a new adsorption layer, which in turn can form a protective layer. The new protective layer It has both intermolecular and electrostatic forces. The strength of the two forces varies. Therefore, when color slurrys with different forces are mixed with various colors of latex paint, the dispersion effect or stability performance will not be the same. Only when the pigment particle surfactant and the emulsion particle surfactant in the coating have greater affinity than water, the coating can have better storage stability; on the other hand, the quality of pigment flocculation in latex paint will appear, and the latex paint floats. Hidden quality of flowers. Generally speaking, the color development performance of latex paints depends on the wetting effect of the emulsion on the color slurry.
1.2 The effect of the difference in the particle size of pigments and fillers on the floating color and flooding.
After the latex paint is applied, the paint film dries with the evaporation of the solvent, and some pigments and fillers will float to the surface of the paint film during the evaporation of the solvent. Among them, some fine particles with a larger surface area are easier to be transported, while those coarse particles with a smaller surface area are retained in the surface layer, preventing volatilization. In addition, the desiccant contains ethylene glycol, which provides a continuously expanding hydrophilic network structure for the volatilization movement. The evaporated substance diffuses to the surface of the paint film through this structure, and the hydrophilic value of the substance The higher, the easier it is to evaporate, because they will preferentially enter the hydrophilic reticular tissue and thus diffuse faster. However, in the production, because the pigment particles of the white pigment are more hydrophilic than the pigment particles of the colored pigment, the pigment particles are more easily brought to the surface of the paint film during the volatilization process. The particle size difference between the fillers is too large, resulting in a low degree of mixing between them, especially when the coating contains more ultrafine particles.
1.3 The effect of the combination of thickeners on floating color and flowering
Thickeners are generally used in the industry to increase the viscosity of the system. It can reduce the Bernard vortex flow, control the flocculation of pigments, and reduce the floating color of the latex paint; however, excessive use or improper use will exacerbate the floating color. phenomenon. Some associative thickeners commonly used in latex paint production have a strong pseudoplasticity, and exhibit a great affinity with hydrophilic co-solvents such as surfactants. When the affinity value continues When it is increased, the tinting power of the latex paint will continue to decline. With the formation of pigment flocculation or aggregation on the pigment surface, the floating color and flooding of the latex paint will naturally appear.
1.4 Influence of Hydrophilic-Lipophilic Balance (HLB) on Floating Hairs Hydrophilic-Lipophilic Balance (HLB) exists in any one of the raw materials used in the production of latex paint, and each kind of material has different HLB value. If the HLB values of various materials match each other, they will complement each other, and the problem of floating color and flooding of latex paint can be solved, but the raw materials are fixed, and the matching degree of HLB values between them cannot be changed. Test data show that the surface tension of materials is closely related to their lipophilic value. The lipophilic materials are easy to float on the surface in water-based products. The root cause is that the surface tension of these lipophilic materials is too small. Therefore, in the selection of raw materials for the production of latex paints, pigments with a higher lipophilic value are more likely to float on the surface of the paint, which causes the floating color of the latex paints to become flooding. During the drying of the latex paint, the water in the paint gradually evaporates, and the ammonia in the ammonium salt in the dispersant will then become more hydrophobic after volatilization, which will cause the paint film to appear floating during the drying process, and this is a slow The process of slow accumulation will become more and more obvious in the end, and even appear in a large area.
1.5 Influence of Surface Tension Difference on Floating Hair
The storage stability of latex paint is closely related to the surface tension of the paint. As we all know, the surface tension of the coating is proportional to the surface energy. The higher the surface tension, the greater the surface energy, and the lower the surface tension, the lower the surface energy. In the selection of latex paint materials, materials with low surface tension must be selected to ensure the stability of the coating. This is because low surface tension can reduce the tendency of droplet aggregation, reduce the liquid shrinkage surface, reduce the additional pressure difference of the curved liquid surface, and promote the stability of the liquid surface and the dispersion system. In general, the surface tension of red, green, and black pigments is not the same as that of pure white pigments. This is the effect of the difference in particle surface properties between different pigments. Even under the same conditions using non-ionic surfactants, their surface tensions are different because of their different molecular structures at the hydrophobic end. In summary, the raw materials for the production of latex paint must choose a combination with a small difference in pigment surface tension, and only in this way can it reduce the quality problems such as floating and flooding in the storage and transportation of paint.
1.6 The influence of other factors
Finally, there is the influence of production formulas and production processes. These factors are highly subjective, and the causes of specific problems are also different, which cannot be analyzed more accurately. This is where the producers themselves need to improve in order to maintain the characteristics of the product and occupy the market.
2 Ways and methods to solve the problem of floating and flooding of latex paint
2.1 When choosing a polymer, pay attention to the matching degree or compatibility with the raw materials
during the formulation, the best way is to select the most suitable wetting and dispersing agents, To adjust the surface properties of pigment particles and balance the HLB value between pigment particles. The main choices are wetting and dispersing agents with the following functions: to improve the color development of coatings, to improve the surface properties of pigment particles, and to control or reduce the phenomenon of paint floating. It can be divided into anionic, cationic, non-ionic and multi-functional. The best choice is anionic and non-ionic. The main function of the wetting and dispersing agent is to rely on the affinity between the pigment particles and adsorb on the pigment surface, thereby adsorbing other impurities, decomposing and changing the structure of the pigment surface, and then changing the polarity of the pigment surface.
The surface properties of raw materials such as pigments and fillers in the production of latex paint are not static. If wetting and dispersing agents containing anions are added during the production process, the surface polar groups will be adsorbed after the pigments and filler particles are fully adsorbed by the wetting agent. In response to anionic wetting and dispersing agents, the surface properties gradually change. The wetting and dispersing agent contains non-polar or weakly polar particles. These particles have basically the same polarity as the white particles in the pigment. At the same time, the efficiency of adsorption and flocculation is no less than that of the polymer. Therefore, the movement ability is strong during the drying process. Can improve or control floating color. In order to reduce the surface tension of pigments, active agents that reduce the surface tension are often used, and silicone surfactants have become the primary choice. It has high surface activity and physiological inertness, and has been widely used in the coating industry.
2.2 Adding additives such as kaolin, silica, etc. During the
production process of latex paint, adding additives such as kaolin or silica appropriately, can produce a network-like paint film. On the one hand, the network structure can effectively prevent pigment separation in the feed liquid, thereby preventing the phenomenon of floating and flooding in the coating; on the other hand, the surface adsorption capacity of the latex paint with the network structure is significantly improved, and the latex is increased by increasing the density of the coating. The anti-flocculation and anti-floating ability of the lacquer finally achieves the effect of reducing the probability of pigment floating and flooding.
2.3 Adjusting the hydrophilic-lipophilic balance value to an appropriate range
If you want to control the hydrophilic-lipophilic balance value (HLB) within a proper range, you must use a reasonable combination of wetting and dispersing agents. We know that the ammonium salt component in the anionic wetting and dispersing agent is more lipophilic than the ammonium salt component in the sodium salt dispersing agent, so its HLB value will be smaller in comparison, and it will have a phenomenon of floating paint on the latex paint. Great improvement. This is because when the pigment particles are wrapped with an anionic wetting and dispersing agent, a force field is formed around it, including electrostatic resistance and space resistance. During the drying process, the ammonia in these dispersants will evaporate with the moisture, making the anionic wetting dispersant more hydrophobic, so the compatibility between the pigment particles and the paint film is greatly improved, plus space resistance The coating structure becomes more inflated, thereby suppressing the paint floating phenomenon in the dynamic process.
In summary, the compatibility of emulsions and colorants, the difference between the density and particle size of pigments, the surface tension of each component, and the hydrophilic-lipophilic balance value are all factors that cause the floating color of latex paints and paint films. . In the formulation of latex paint materials, it is necessary to take into account the compatibility of emulsions and colorants. Avoid using too many ultra-fine powders and powders with excessive density differences as pigments and fillers, and appropriately mix a certain amount of kaolin or silica in the filler. In the latex paint film, a network structure that prevents pigment separation is formed, thereby effectively preventing the appearance of floating and flooding.