Pigments are the fine solid powder which are not soluble in the medium or career in which they are incorporated and provide colours (black, white, red, yellow, blue, green etc). There are two types of pigments-organic and inorganic. Both the pigments are used to impart colour in paints, printing inks, rubbers, plastics, papers etc. In addition to colour they also provide other optical properties e.g gloss, opacity etc and functional properties (mechanical and chemical)e.g. abrasion resistance, hardness, UV resistance, acid and alkali resistance, heat resistance etc.
A pigment – physically or chemically is not an inert component in a paint they interact both chemically (including photochemically) and physically with other paint components. Such factors as texture, particle size/shape, tinting strength, reducing power, volatile matter, matter soluble in water, bulking value, form and crystal habit, particle size distribution, oil absorption, surface character, solubility and density significantly affect tinctorial effects, working properties, durability, and stability to moisture, chemicals and light. transparency, hiding power, strength, gloss and gloss retention, dispersibility, chalk resistance, masstone color and depth.
Compatibility with vehicles, effect on viscosity, flow and levelling are some of the properties dependent not only on the vehicle system but on the physical and chemical properties of pigments in the finish
In this video we will discuss tinting strength, reducing power, volatile matter and bulking value or bulk density,.
TINTING STRENGTH
It is the power of a pigment to impart its colour to the paint specifically tested with white pigment. We avoid the use of pigment in paint due to loss of gloss, therefore only optimum quantity of pigments are used to have desired colour and gloss. A colour pigment imparting more colour value over the other colour pigment of same class are preferred. The explanation and test method have been discussed in this video.
REDUCING POWER
This is the power or strength of white pigments to reduce the colour of colour pigment. A white pigment if lighten the colour of colour pigment with lesser quantity, is preferred. The explanation and test method have been discussed in this video.
VOLATILE MATTER
It is defined as the percent of water present in pigments. As normally water is present as volatile matter hence we test the percent of water. The source of water can be the humidity in the atmosphere and/or the improper drying of pigment during their processing. The presence of moisture can cause several defects in paint film and can result failure of coating. For example if the moisture is trapped in the coating the film can have pin holes or the bubbles or it can develop corrosion on ferrous surfaces. The maximum allowable moisture is 0.75 to 1.00 percent. The test method along with discussion is given in this video.
BULKING VALUE
The bulking value is defined as the ratio of volume of the pigment to weight of the pigment. Raw materials of paints including pigments are purchased on weight basis while paints are sold on volume basis. Therefore the pigments which have high bulking value would reduce the cost of paint. The test method and description is given in this video.
