Inorganic pigments related presentations:
Inorganic pigments are natural mineral pigments or inorganic compounds formed.
English name: inorganic pigment
Inorganic pigments are non-ferrous metal oxide, or some insoluble metal salts, inorganic pigments and inorganic pigments are divided into natural and artificial inorganic pigments, inorganic pigments are natural mineral pigments. Natural mineral pigments are generally lower purity, color is dark, but the low price. The synthetic inorganic pigment variety chromatography complete, bright color, pure, strong hiding power.
Features Purpose:
Inorganic pigments Light, heat, weather, solvent resistance, hiding power. Inorganic pigment widely used in paints, plastics, synthetic fibers, rubber, building materials, stationery, paints, inks, paper, glass, enamel, ceramics and other industrial production sectors.
Mechanism of inorganic pigments:
The basic optical properties of inorganic pigments and pigment properties, primarily determined by the following three aspects:
① difference between the refractive index of the pigment and the dispersion medium;
② light is absorbed by the solid (including solid impurities);
③ particle size and particle size distribution. Wherein the particle size and particle size distribution can be improved by surface treatment.
In the paint production process, no matter how fine the pigment is milled powder, always contains some aggregation and flocculation of particles. Pigment in the transport, storage process, due to compression, moisture will further flocculation larger particles, and the finer the pigment, the greater the surface area, surface energy higher, more easily flocculation together. If through appropriate surfactant treatment, these large particles flocculation, when used can easily be spread out, the dispersion mechanism is mainly as follows:
1. wetting
An inorganic pigment powder dispersed in a liquid mainly through the following three stages: ① wet powder, the liquid not only to wet the surface of the powder, the powder but also to air and moisture between the particles displace; ② powders by wet and displace particles After air and moisture between the pigment powder floc and aggregates are destroyed; ③ is moist and destruction of floc and stable powder aggregates dispersed in the liquid state. That dispersion wetting - dispersing - keeping the dispersion stable process. Under normal circumstances, inorganic pigments before use is rarely drying process, the surface of the pigment in addition mixed with air, also adsorb a water film. Typically the amount of water adsorbed on the pigment surface, equivalent to the amount of water required for a monomolecular film formed on the solid surface.
E.g., TiO 2 surface area per gram of 10m 2, water molecules adsorbed layer thickness is 10 × 10 -10 m, the amount of water required for a monomolecular film was about 0.3% by weight of the pigment, so that the moisture content of the pigment in its dispersing properties also affect One of the main factors. Wet solids are good or bad, according to the contact angle to determine the contact angle of 0 ° indicates complete wetting, the liquid is completely spread on a solid surface; a contact angle of 180 ° indicates complete non-wetting liquid was like drops of water attached the surface of solids.
Can solid good wetting liquids, except that the contact angle to determine the size, can also be measured to determine the size of the heat of wetting, usually Hydrophilic powders (eg TiO 2) in a polar liquid in the humid heat a large, non- small polar liquid moist heat, moist heat and hydrophobic powder in polar and non-polar liquids is substantially constant.
Solid powder in liquid sedimentation velocity and sedimentation volume size can be judged good or bad wetness (see Table 1), such as TiO 2 polar solids settling in a small volume of polar solution, small polar solution is large; nonpolar solid powder generally have large sedimentation volume. Through the addition of a surface active agent, since the surfactant molecules are oriented strongly adsorbed on the solid surface, help to reduce the surface tension of the liquid, to improve the wetting and dispersion properties.
2. The electrical repulsion (ξ potential)
Inorganic pigment dispersion and dispersion stability in aqueous solution, primarily dependent on its water repulsion i.e. ξ electric potential to determine the size.
Electrical repulsion is the use of a charge repulsion to maintain dispersion stability.
Surfactants can ionize in aqueous solution with a large number of negatively charged (or positively charged) ions, firmly attached to the surface of the pigment particles, these particles with the same charge, the other with oppositely charged ions are diffused into the liquid media freedom around, forming a diffusion layer (electric double layer) of charged ions. Potential difference from a solid surface to the diffusion layer farthest (ie oppositely charged to 0 places) ions between two layers called the ξ potential. Electrostatic repulsion between particles is the resulting of these particles with the same charge repel each other upon contact you to maintain a stable dispersion system, known DLVO theory.
In the case of electrical repulsion, the surfactant must have a high ionization performance, generally used is an anionic surfactant and a number of inorganic dielectric, such as: tripotassium phosphate, potassium pyrophosphate, sodium polyphosphate, alkyl aryl sulfonate sodium, hypophosphorous methyl naphthalene sulfonate, sodium polycarboxylate.
3. steric effect (or entropy effect)
When the pigment is dispersed in a non-aqueous medium, then the ion reactions much ruled out the possibility of non-ionic surfactants are not ionized in water, in this case, the role of surfactant called steric effect or entropic effects. Because surfactants can be adsorbed on the surface orientation of the pigment particles to form a monomolecular adsorption layer, this orientation of the buffer layer can be prevented between the particles together, so as to maintain a stable dispersion system (also known as protective colloid or micelle).
Surfactant molecules cluster pigment surface, with the increase of surfactant concentration, the entropy decreases, the movement will be limited, the closer the pigment particles, the more compression, which will further reduce the entropy, thereby enabling a stable dispersion system.
