10. What are the technical elements in the pigment dispersion process?
Pigment dispersion referred to in paint production generally refers to the stable and uniform dispersion of pigments in a specific medium in a solid state. It is mainly divided into four steps:
a. Wetting of the pigment surface;
b. Open aggregates of pigments;
c. Uniform distribution of pigment particles in the paint;
d. Long-term stability of the entire dispersed system.
Wetting: In fact, wetting is divided into two separate processes. At first, the dispersion medium (solvent or water) replaces the air and distributes on the surface of the pigment powder, and then softens the aggregate of the pigment with the help of a wetting agent.
To break aggregates of pigments and disperse them evenly:
Agglomerates of pigments are broken with the help of dispersing equipment. After this stage is completed, the pigment can be uniformly dispersed in the dispersion medium in the state of primary ions.
The success of the pigment depolymerization process mainly depends on whether the high-speed shearing, collision and friction of the dispersing equipment can achieve the best dispersion state and performance of the pigment. Shear or friction forces must be maximized.
It is very important to choose the correct dispersion equipment (determined by the chemical properties and viscosity of the dispersion medium) to achieve this ideal state.
11. What is the aggregation of pigments in the coating system?
The purpose of dispersion is to wrap sufficient vehicle or resin on the surface of the pigment, so as to avoid the mutual contact between the pigment particles. Sometimes, however, the dispersed material will re-agglomerate, or form flocculation.
Reaccumulation and flocculation have different meanings. Re-accumulation means that the pigments are sticking together again, forming new accumulations. There is no binder barrier at the place where the pigment particles are in contact.
Flocculation means that the individual pigment particles do not lose the surface binder, the pigment particles are only loosely aggregated, and can be opened as long as a low shear force is applied.
The flocculation of pigments will lead to changes in the color characteristics of pigments in actual use, such as the reduction of tinting strength, gloss, and transparency. In the entire paint system, preventing pigment flocculation is regarded as an important performance index of paints. Surface properties and selection of the correct paint binder to prevent pigment flocculation.
12. How to test the floating and blooming phenomenon of pigments?
We can use many methods to test the floating and blooming of pigments.
a. Compare the tinting strength of the sprayed paint film and the scraped paint film to judge the floating and blooming situation.
b. By coating the experimental paint film on the glass plate to observe the floating and blooming situation.
c. Finger rubbing test is to wipe the coating film in a semi-dry state (after flashing) with your fingers (the coating film can be sprayed or scraped), and it is determined by the color difference between the paint film in the rubbing area and the original paint film The degree of floating color. It is also an indicator of flocculation.
13. How to measure the hiding power?
Pigment hiding power is measured in relation to the paint base into which the pigment is incorporated and the thickness to which the paint is applied. Under the given pigment concentration and film thickness parameters, the coating is prepared on the black and white control test cardboard for hiding power, and the hiding power is calculated by the difference in black/white surface color.
Simply put, hiding power refers to the ability of the color paint to cover the color or color difference of the substrate. Generally, the hiding power is expressed by the hiding power value. It is expressed in g/m2 as the amount of paint required to cover the black background of the cardboard under a given pigment concentration.
In the process of hiding power testing, light is a very important factor. Only by testing and comparing under natural light source environment conditions can objective and correct results be obtained.
14. Which pigments can be used to make camouflage coatings?
The camouflage coating needs the color to be integrated into the environmental background (vegetation, soil, desert or ocean, etc.) as much as possible. For example, the dark gray of the ship makes it invisible in the ocean.
With the development of modern military technology, humans have put forward higher requirements for camouflage coatings. Camouflage coatings must be able to make the painted objects invisible under the irradiation of infrared rays.
In other words, within the near-infrared spectrum with wavelengths from 400 to 1200 nanometers, the color of the camouflage paint requires the same color as the color corresponding to the dominant background.
In particular, camouflage paint can effectively simulate the spectral reflection curve of objects in the natural background, so that the target can be effectively integrated into the background. Many traditional pigments used for color matching in the visible range cannot be used in infrared camouflage paints.
The pigments suitable for this field are: pigment yellow 119, green 17, green 26, black 30, chromium oxide green, carbazole violet, iron oxide pigments.