The paint manufacturing process is a complex and intricate one that involves a wide range of steps and materials to produce a high-quality product. From the selection of raw materials to the mixing and blending of various components, each step in the process plays a crucial role in determining the final characteristics of the paint. In this article, we will take a closer look at the various stages involved in the paint manufacturing process.
Paint making process
Before production starts each separate paint has a unique formula developed for it in the laboratory. During this development stage the paint’s quality aspects are comprehensively tested. The laboratory is also responsible for inspecting the raw materials before they go into the product and monitoring the quality during the production process. In addition to the above activities, particular attention is also given to research into new raw materials and paint systems.
Weighing the raw materials
At the start of the production process the dry raw materials are weighed here accurately to the gram and prepared for transport to the next department, the pre-mixing department. The pre-mixing department stores the liquid binders and additives. The correct amount is tapped off, after which the weighed dry raw materials are added. As small amounts of dry raw materials are left behind in the sacks during this process, the paint has to be checked at each subsequent production step against standards for the relevant product according to colour and viscosity, and is adjusted if necessary.
Pigments are insoluble in the binder. They therefore have to be regularly dispersed in the binder, that is to say finely distributed. This dispersal occurs in two steps: first through pre-mixing with a mixer and then the final fineness is determined with a triple roll mill.
The pigments are supplied in dry powder form, with the pigment components held together in clusters. During the pre-mixing these are turned to smaller clusters and homogenously distributed throughout the binder. The tinting strength of the paint is now relatively low, but this will increase as the pigment is ground finer in the next production phase.
Grinding the pigments
In the triple roll mill the pigment clusters are ground further to the desired fineness. During this process the pigment particles must not get damaged as this may result in a change of colour. The three rollers rotate in opposite directions with different speeds. The difference in speed helps to grind the pigment lumps and the paint goes from one roller to the other. The paint is finally removed using a scraper.
The distance between the rollers determines the fineness of the grind. This process is run through for a maximum of five times. The finer the grind, the greater the tinting strength of the paint. After the last grinding the paint finally has the required viscosity.
After the grinding the fineness is checked using the Hegman bar. The depth of the groove in the bar gradually increases, indicated in microns. The paint is thinned to a certain viscosity and then applied to the groove and levelled off. At the point where the pigment particles are larger than the thickness of the paint layer they stick up above the surface of the paint film. At this point, visible to the human eye under skimming light, the fineness is read off.
The new colour is now compared against the standard colour. Both are applied thick as well as thin so that both the mass tone and the undertone of the colour can be seen. There must not be a difference between the new colour and the standard colour.
In order to ensure that only quality products are sold, each batch is left to stand for a certain time in order to check the stability. After this period another laboratory check is carried out, and after approval the paint is filled into containers.
Tubes are filled from the underside, with the top already in place. Plastic tubes are closed by melting the material, while the aluminium tubes are folded step-by-step and squeezed shut. Bottles are filled, closed and then labelled. The final step is to check that the packaging contains the right amount of paint.
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Video source: Machine India