In industrial coatings, these characteristics can be divided according to the state of the paint: liquid paint or dry paint.
Features of liquid paint
Among the main measurable characteristics of liquid paint are
- Stability: the paint must have a uniform, lump-free appearance in its packaging.
- Viscosity: is one of the most visible characteristics in paint and affects its stability and application. It indicates the consistency of the product. Ambient temperature influences the paint’s viscosity.
- Specific gravity or density: indicates the unit weight in volume. This is an important piece of information to take into account as it serves to calculate the returns. A high specific weight will result in low returns.
- Fineness of grinding:a good dispersion of the pigment and binder ensures the quality of the paint and allows to take full advantage of the colouring power of the pigments, improving the application and levelling of the paint. In gun-spray applications it is a factor to be taken into account as the paint’s fineness is conditioned by the diameter of the nozzle.
- Solids content by weight or volume: percentage of total paint pigment and binder. This aspect influences the cost and quality of the paint.
- Product life: in 2-component paints, it is important to know the time the mixture can be used after preparation. It will depend on environmental conditions, among other factors.
- Application: the paint must be in good condition to be applied after being shaken. If you add solvent, the amount must be right to achieve a good viscosity, without reducing excessively the solids content.
- Drying: during drying, different phases take place due to the evaporation of the solvents and the polymerisation reactions (touch drying, powder drying, total drying, hard drying).
Features of the dry paint film
Once the paint coat is dry, a number of characteristics of the film that has been formed can be determined and assessed.
The thickness deposited will depend on the composition of the paint (solid content) and the way it is applied. Each paint must be applied with the thickness recommended by the manufacturer in the technical data sheet.
- Appearance: once the paint is dry, the film must be smooth, uniform colour and gloss, no defects in the surface paint, and good adherence between coats or to the support.
- Scratchability:the greater or lesser resistance to scratching is related to the hardness of the paint. The use of small percentages of special additives can significantly increase this feature.
- Salt fog resistance (marine environments):this is an accelerated test (measured by hours) to try to predict the possible behaviour of the paint in what regards corrosion in maximum humidity conditions.
- Gloss:the surface can be glossy, semi-glossy, satin or matte. In paint the level of gloss is determined by the pigment/binder ratio, the dispersion levels, the thickness of the coat or the method used for its application and drying.
- Adherence: this is one of the main requirements of the paint, since the protection that is expected to be achieved depends on this. The capacity of a paint to resist detachment from the support where it has been applied is verified by performing different tests.
- Weather resistance: it is an essential characteristic of the paint. This check is usually carried out in artificial climate, where you can programme different cycles of temperature, humidity, condensation, ultraviolet radiation, etc.
- Covering power: this measures the paint’s capacity to cover by opacity the surface on which it has been applied. It is determined directly by the thickness of the coat deposited.
- Flexibility: the following methods are available to test the flexibility of a dry paint film. Among the best known are mandrel stamping and bending.
- Yellowing: this phenomenon usually occurs in white or light-coloured paints formulated with resins containing unsaturated oils such as alkyd. It is produced mainly by rusting reactions during drying or by degradation that produces a continuous exposure of the surface to ultraviolet radiation.
- Colour: the colour of an object depends on the type of light under which it is observed. In order to have accurate colour information, you can use different tools, such as a spectrophotometer.
- Resistance to impacts, scratches and abrasions: a series of tests are carried out to check the resistance and hardness of a paint against different mechanical impacts.
- Hardness: there are devices and tests to check the hardness of the paint, in order to measure the paint coat’s resistance to penetration.
- Resistance to extreme temperatures: surfaces exposed to extreme temperatures require a careful choice of the paint to be used, as unsuitable pigments and binders can lead to loss of adherence, cracking, colour changes or destruction of the film.
Types of industrial paint
It is difficult to classify the different types of industrial paints and coatings in a defining way, since there can be different interpretations based on factors such as their composition, their position in the finish system or even according to the way the paint dries and hardens after application.
Depending on the position in the finishing system
For an industrial paint to fulfil its protective and decorative functions, it is essential to know the particularities of each painting system and process. We can classify the industrial paint according to its position in the application coat:
► Primer
These are the first coats of paint in direct contact with the substrate, highly pigmented and with a low binder content.
Its mission is to serve as an anchor for the following coats of paint and to prevent rusting on metal surfaces by means of the anti-corrosion pigments it contains. Types of primers for industrial paint.
► Intermediate coats of paint
These coats are applied over the primer, generally with the mission of increasing the thickness of the paint system, in order to avoid giving several coats of finish, reducing costs in the application.
The pigment/binder ratio is lower than that of primers but higher than that of finishing paints.
Nowadays, high thickness intercoats are widely used to achieve films of 100 or 200 microns per coat.
► Finishing paints
As the name suggests, they are those that are applied as last coat of the painting system, either to the primer or to the intermediate coat.
They are formulated with a low pigment/binder ratio to achieve the best permeability and strength features. They are usually gloss paints, although there is an increasingly growing demand for satin and matt finishes in the market.
