Physical and chemical properties of inorder pigments associated with coating dispersions

machine pigments play a dual role, first as fillers, providing greater use than simple formulation coloring, and they can also affect the physical properties of coating during construction and throughout the product life cycle. Pigments in coatings protect resins or substations from electromagnetic waves and heat degradation because they reflect short wavelengths of infrared light, which also helps keep the material containing them cool.
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Why do we use pigments
Before we understand the best way to disperse pigment-containing materials, it is necessary to understand what pigments are and the chemical and physical reasons for our use of pigments. Inorganica pigments are transition metal complexes
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, mainly the oxides of repeated ceramic lattic structure units that crystallize or semi-crystallize.
d-orbit of metal ions determines the properties of inoromic pigments
, including color, reactive activity, strength (expressed in Mohs hardness) and weather resistance. Pigments are unique as fillers because they are made up of transition metals that are surrounded by ligations (official groups). The way in which the d-orbit of a metal ion interacts with its bonded lids also affects the performance of the pigment;
as an interesting aspect, the metal ions and ligations in the pigments used in the coating act (i.e. provide a visible output color) much like photoresuming complexes in photodeveication. You can see why from Stark-Einstein's law. The law states that the absorbed photons activate the main chemical or physical reactions in the system
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. For paint pigments, this means that the transition metal d track is stimulated; For example, transition metal palladium can form four different ion-state complexes (i.e., V2 plus, V3 plus, V4 plus, V5 plus), which can give pigments different hues, from purple (V2 plus) to yellow (V5 plus)
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in Dispersed Pigments and Fillers, Jochen Winkler points out that "pigment attachment is a combination of London-van der Worrest interactions. ...... At least ten times as much energy is needed to destroy this chemical bond instead of the physical bond. The
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means that in order to reduce the aggregation of the appendosome, one-tenth of the energy is required to turn the appendicate into a primary particle; Surfactants are physically combined with aggregates and primary particles to prevent pigment aggregation from regeneration by destroying London-van der Worrest. It must be pointed out that the geometry of particles plays an important role in the size of the forces between molecules within a specific distance. The effect of surface defects and aspect ratios exceeds the effect of surface area-volume ratio increases, as this requires greater Vanderbilt attraction than simple spheres, and the probability of mechanical binding due to geometry increases.
understanding that
is a physical process that often leads to an increase in system entropy. An unstable dispersion causes flocculation, which is a state that reduces the potential quantity of system construction (i.e., decreases entropy or randomness). This is mainly due to the random Brown motion of dispersed particles, which are attracted (i.e., tend to conjure up) by short-distance London-van der Vader forces.
in order to fully disperse, it is important that the surface pressure of the liquid is less than that of pigments (and other solids, such as fillers). If a particular solvent, resin or other liquid is used with a solid that is not affinity - i.e. it is difficult to mix and moisturize - a surfactant is used to ease the inability to moisturize and prevent flocculation from forming.
important requirement for dispersing pigments (or any solids for this purpose) is that the solid has a higher surface pressure than the added liquid. For solids with very low surface pressure, additives can be added to reduce the surface pressure of the liquid parts, which can improve their wetting properties. This phenomenon can be expressed in Yang's equation:
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s This is a hypothetical solid-base composition system; often there is another liquid or soluble solid in the system to help disperse and prevent flocculation. If this is the case, the controlled equation is less simple because the materials create additional interactions between the pigment-base interface (in other words, at the interface) (Figure 1). In order to determine the actual properties of the dispersion, two interfaces must now be considered: the interaction between solid adsorption (pigment interface) and interface-substate (sol-liquid).
These inter-molecular forces can be overcome by adding surfactants, which can prevent flocculation by overcoming static electricity through charge stability, or by bit resistance (entropy), which physically impedes pigment movement and prevents flocculation blocks.
Sufficient energy must be applied to the system to ensure that: (1) the pigment powder is completely moisturized by the solvent/resin, (2) the polymer is reduced to aggregation and become primary particles, (3) the surfactant is added to distribute evenly, so that the system achieves a stable energy balance, so that it is not easy to flocculate or subside
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dry pigment powders can be modified with surface coatings, which can provide specific benefits for the final product or increase the susceptibleness of paint production containing these pigments. As an example, titanium dioxide coated with polysilica (often referred to as silicone oil) improves the
strength and compressibleness of pigments.
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for pigment dispersion purposes, the selected surface treatment of the Hamek constant number should be optimized to perfect the formula. The surface treatment of the low Hamek constant will produce a dispersion with low fusion strength. However, when not stirred and left for a longer period of time, it tends to flocculate quickly (a simple stirring in turn causes the particles to resusccate). Surface treatment of higher Hamek constants will take advantage of "favorable collosic chemistry" but must be achieved with a higher amount of addition to ensure "good dispersion".
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Modern pigments used in coating production today provide specific particle sizes and sealing ranges, and particle size reduction (i.e. strong chemical bonds) is not the primary purpose of pigment dispersion, but rather the de-grouping of pigment particles that are reduced by the loose binding of residual moisture.
when making paints containing pigments, you can purchase paints that are pre-ground in the form of dry cakes. Pigment manufacturers reduce the particle size of pigment particles by grinding them for hours or days on a three-roll grinder or similar machine. The pigment is then dried to remove most of the moisture, and due to capillary force and wetting, some solvents remain between the appendoids, causing the pigments to reunite like "cakes". When pigments are added to a paint formulation or solvent pre-dispersion, the dry "cake" quickly breaks into coarse particles due to the high shearing force generated by the disperser. What is left is the aggregate , which can be further broken by input with reasonable energy , which will require at least ten times the energy input to further crush into the original particle size.
in order to reduce the energy, time and labor costs associated with pigment grinding, particles should be completely moisturized (Figure 2).
the right equipment
the right equipment can have a positive impact on the quality of the hybrid product, and the selection of blades is important for proper dispersion. For products with higher pigment content and low to medium viscosity, dispersed blades with large higher blade teeth provide a good balance between high shear and high fluidity (Figure 3). This creates a flow state in which the attachment is hit at high speed by the blades due to high speed and torque from the rotating shaft. These particles also collide with each other at a rate sufficient to break the attachment, dispersing the pigment into milled particle sizes or smaller particles.
cut pigment particles are also necessary to reduce aggregates, and high flow ensures rapid batch turnover for a narrow particle size distribution. If there is insufficient fluidity, the pigments near the blades are ground, while the pigments around the bottom corners and sidewalls of the tank are still not ground. The dual-axis dispersion with independent drive shafts provides excellent batch turnover and high shear force. When the two axes rotate in the same direction, the overlapping high shear blades run in the opposite direction (Figure 4). In other words, the dispersed blades cut the material in reverse parallel motion, effectively double the shear rate, which provides a higher tip speed, expressed in feet per minute (FPM). Figure 5 shows a two-axis dual motor dispersor with four overlapping high shear dispersing blades.
conclusion
determine the appropriate dispersed equipment required for a task, consider not only the formulation, but also the various interactions between components. Process-specific equipment can be customized depending on the chemical and physical properties of the composition and the potential reactivity of the by-products.
References
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organic-color-pigments-end-pigments-for-demandingapplications
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5, Winkler, J. Dispersing Pigments and Fillers. Hannover: Vincentz Network, 2012. Print.
6,T. S. Chow. Wetting of rough surfaces. Journal of Physics: Condensed Matter, (1998) 10 (27): L445.
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