Pigments suitable for powder coatings can be roughly divided into four categories according to their performance and function: coloring pigments, metallic pigments, functional pigments, and body pigments. They are an important part of powder coatings, giving the coating a colorful color, improving the mechanical and chemical properties of the coating, or reducing the cost of the coating.
Coloring pigments are divided into two categories: organic and inorganic, which can cover almost all hue systems. Metal pigments mainly include floating and non-floating aluminum powder, various tones of copper and gold powder and pearlescent pigments, metal nickel powder and stainless steel powder. Functional pigments mainly include fluorescent pigments, luminous pigments, high temperature pigments, conductive pigments, etc. In a broad sense, the body pigment has titanium dioxide (anatase type and rutile type), calcium carbonate (light and heavy, etc.), barium sulfate (precipitation type and natural barite type), stone powder, bentonite, quartz powder, etc.
Some basic principles for the selection of pigments and fillers
The choice of pigments
• There are a wide variety of pigments with different properties, and not all pigments can be used in powder coatings. Powder coating due to its own process particularity, the choice of pigment should pay attention to the following points.
The pigment dispersion is better, the best dispersion particle size is 0.2~0.9?m, not easy to agglomerate.
• Pigment hiding power and tinting strength to be strong.
• Good thermal stability, at least need to withstand temperature above 160 ℃.
• Pigments should have a certain light and weather resistance, such as not easy to fade, powder resistance, physical properties to be durable.
• The pigment has moderate oil absorption and better color resistance.
Selection of filler
Adding a certain amount of filler to powder coatings can increase the mechanical properties such as hardness of the coating and reduce the cost, which is an effective way to adjust the cost of powder coatings.
The fillers used in powder coatings are mainly calcium carbonate and barium sulfate, while bentonite, talc, quartz powder, etc. can be regarded as functional fillers, and the overall dosage is very small.
According to the production process and raw materials and other factors, calcium carbonate can be divided into light calcium carbonate and heavy calcium carbonate two categories, these two types of calcium carbonate in the powder have applications.
Barium sulfate also has two types: precipitation type and barite type. The former is made by chemical reaction, and the latter is made by grinding natural barite.
The problems that should be paid attention to when selecting fillers are:
• filler whiteness to be high, can reduce the amount of titanium dioxide.
• Less impurities, taking into account the particularity of the powder coating process, more impurities in the filler will affect the surface decoration of the coating (coating surface particles, poor flow).
The particle size is too coarse filler do not choose, because it is not easy to disperse, the screw has wear.
• The filler should be loose, not agglomerated, and the water content should be low.
(1) the habit of color can be divided into red, orange, yellow, green, blue, purple, black, white and other categories. There is a certain relationship between the colors. We can use three parameters to characterize any color, namely hue, saturation and lightness.
Tone is to distinguish the basic characteristics of each color, determined by the spectral composition of the light source, and the surface of the reflected light wave on the human eye feeling, reflecting the color in the "quality" of the characteristics.
Saturation is the color purity shown on the basis of "quality", also known as "chroma".
Brightness is the human eye's perception of the brightness of the color of an object, and everyone has differences in judgment.
(2) Red, yellow and blue are the three primary colors and can no longer be decomposed. All other colors are made up of these three colors.
(3) Technicians should pay attention to what kind of color the required color belongs to, which color is the main color, and consider the color ratio (PVC value) and the hiding power of pigments and cost accounting.