Paint production
To guarantee consistently high performance of the final paint it is vital to ensure that all raw materials used in the manufacturing process are of high quality.
The paints used are formulated to run efficiently on the coating line and to give the specified performance for the subsequent manufacture and end use of the coated product.
The ingredients
There are 4 main elements that make up the paint used for coating:
Base resins
Resins form the coating film itself, and give the film many of the properties it needs. They are generally referred to by their generic name (polyester, polyurethane, epoxy). The resins used for coating are usually synthetic oil-based products.
Solvents and thinners
These liquids, also produced from petroleum, solubilise and dilute the base resin before evaporating during the baking process. This evaporation process helps to control the appearance and flow characteristics of the dry film. The majority of coils coating lines are equipped with incinerators that totally burn off the solvents thus preventing harmful pollution from being transmitted into the atmosphere.
Pigments and extenders
These consist of either organic or mineral solids that determine the finished product’s colouring. One of their key features is their ability to preserve their colour after being baked at a temperature of around 240°C. The most commonly used pigments are titanium dioxide (white), iron oxide (red, orange, black), chrome oxide (green) and copper derivatives (blue and green). Flakes of aluminium are used for metallic colours.
Anti-corrosion pigments are key ingredients in primers.
Extenders, usually mineral in nature, are normally white powders and control certain formula parameters such as the gloss (silicas), and the rheology (chalk, barites...). Generally they have little or no effect on the paint’s colour.
Additives
These allow either the paint’s reactivity to be stabilised (catalysts) or specific properties to be improved (examples of additives include dispersing agents, lubrication waxes, UV absorbers, etc.).
Using a range of a dozen or so pigments, the possibilities of colouring are endless. Nevertheless, certain colours cannot be reproduced for coil coating as some of the pigments do not have all the qualities required for this application. Standardised colour charts are used as the foundation for colour measurement and control (AFNOR in France, RAL in Germany, BS in England, NCS in Sweden and Pantone, as used in the printing trade….). Often these correspond to the corporate colour of important multi-national companies, for example petroleum companies; colour standards can also be created by a designer or derive from unusual objects such as cigarette packs and automobiles. An important part of the manufacturer’s work when producing paint for coil coating consists of determining the mixture of pigments that will enable him to obtain the colour desired by the client. This process is known as "matching" and it is not unusual for a paint supplier to have 600 to 1,500 matching requests in a year.
Paint making
There are five main stages:
Premixing
This operation involves the mixing of all the solid ingredients (pigments and extenders) with some of the liquid ingredients (resin and solvents) using high-speed shearing techniques.
Dispersion
The premix base is then subjected to a milling process to produce a refined dispersion. This can be achieved by pumping through a horizontal bead mill which contains glass or zirconium oxide beads, until optimum dispersion is achieved.
Let down
The remaining items of the formulation are then added under controlled conditions to make up the overall batch volume.
Tinting and viscosity adjustment
At this stage the colour and viscosity (and also gloss if necessary) are finely tuned according to the customers requirements.
Filtration and Packaging
The completed product is then quality control tested and passed through a filtration unit into drums, containers or even tankers before despatch to the coil coaters.
All these different phases of production are thoroughly controlled and quality control testing completed before issuing a certificate of conformance to the client.