Coating additives for special properties and reduced problems
At its most simplified, a paint or coating is the combination of a pigment, a binder (or resin), and optionally, a solvent and additives. The pigment is the substance which provides the coating with its colour, the binder provides both adhesion and cohesion, holding the paint together as well as binding it to the substrate, finally, the solvent gives the coating the necessary viscosity and flow in order for it to be most effectively applied to a substrate. A paint takes its name from the binder used, such as polyurethane or epoxy. Coating additives are the component that imparts special or desired qualities and characteristics to the coating, or reduces problems that may hinder the production process.
The properties altered or enhanced by coating additives include viscosity, foaming, rheology, and odour. In this article we take a look at the additives commonly used in coatings and their effects.
Coating additives influence coating quality in 4 ways
The reason for including additives in a coating is to heighten its performance or add extra properties not otherwise provided by the coating alone – such as with antimicrobial or biocidal additives. Additives can be used for coatings from all sectors, for architectural coatings, industrial coatings, powder coatings, protective and marine coatings, automotive coatings, and more. The full range of additive qualities is too extensive to cover here, but includes surface altering additives, adhesion promoters, anti-caking agents, nanotechnology-based additives, UV-absorbers, flame-retardant additives, corrosion inhibitors, etc. Below are four of the main qualities modified by additives and why they matter to a coating.
1. Improve flow and levelling: Rheology modifiers
Rheology is the branch of physics that deals with the study of ‘flow’. Rheological characteristics or flow behaviours in coating include viscosity, sedimentation, and sagging. Rheology modifiers work to alter the flow and levelling of a coating, and so are also called flow and levelling agents. These are one of the more important classes of additives simply because there are so many problems and defects that can occur in the film forming stage of coating when the rheology of the paint is not optimal. A rheology modifier improves a paint’s viscosity while also improving its application and flow characteristics. They also prevent pigments from sedimenting within a container during storage.
These rheology additives work by affecting viscosity and flow behaviour, including the shear rate, to reduce issues like sagging and sedimentation. Shear rate is the rate at which fluid layers move past each other. In Newtonian fluids this is a constant, so viscosity does not change, but most fluids are non-Newtonian and their viscosities are dependent on the differing shear rates. With paint this matters because a coating endures many different shear rates from production (dispersing, blending) to application (rolling, brushing, or spraying) and storage. Rheology modifiers adapt the flow behaviour of a coating to ensure the viscosity is ideal for application.
|Additive Company||Coating Additive Product||Description|
|Allnex||Additol XL 270||Multi purpose additive to improve rheology and prevent settling. A special fatty acid modified silicone.|
|BASF||Efka RM 1920||A hydrogenated castor oil additive for excellent sag resistance with non-aqueous formulations.|
|BYK/Altana||Aquatix 8421||A wax emulsion to improve the effect pigment orientation in aqueous formulations for automotive OEM coatings.|
|Dow Coating Materials||ACRYSOL HASE Rheology Modifiers||A range of coating additives which contain methacrylic acid and acrylate ester. They provide a thickening of the coating with higher film build and sag resistance.|
2. Prevent pinholes and gas pockets: Foam control agents
Foam is the distribution of a gas through a liquid which can cause defects in coating application such as pinholes and gas pockets. In this way, foam negatively affects both the aesthetic and protective functions of a coating. A surfactant (from surface-active agent) is a substance that helps determine the surface tension behaviour of liquids at the liquid/liquid, liquid/gas, or liquid/solid interface. They are amphiphilic molecules, meaning they have both hydrophobic and hydrophilic groups (their tails and heads respectively). Foam forms due to the interaction of these groups between the ‘surfaces’ of the individual foam bubbles. To counteract the effects of these surfactants defoamers are used.
Defoamers either prevent the formation of foam or they quickly destroy the foam produced. They do this by displacing the foam-stabilising surfactants which maintain the foam and replacing them with a film which is not capable of generating the forces required to maintain bubbles. Essentially the foam is deprived of its structural integrity. The more defoamer is used the better the defoaming effect, but this comes at the price of an increase in defects. The dosage needs to be determined carefully to balance the two.
Foam control additive products and companies
The importance of foam control in coatings means that it is a widely supplied product in Australia. Companies include Air Products and Chemicals Inc (Airase defoamers and deaerators), Borchers OM Group (Borchers AF 0550 and Borchi line), and BYK/Altana(BYK-012, BYK-016, BYK-052 N and more)
3. Work against microorganisms: Antimicrobial/biocidal additives
A biocide is a substance that kills or inhibits the growth of organisms through chemical or biological means. Biocides are used to prevent the buildup of biofouling on ship bottoms with antifouling paint, to prevent the growth and spread of harmful microorganisms across hospital and food preparation surfaces in antimicrobial coating, or to prevent the growth of mould and mildew in exterior paints. The biocides used in these paints include silver, copper, zinc oxide, as well as a variety of organic additives.
As well as using biocides as part of the purpose and end use of a coating, biocides can be used to extend the life of a coating and prevent it deteriorating. Coatings are vulnerable to microbial contamination at all stages from production to application because a majority of them include water which makes them susceptible to the growth of bacteria, algae, and fungi. By adding a biocide the paint is guarded against the possibility of microbial attack and product spoilage.
4. Support deflocculation and stabilisation: Wetting and dispersion additives
Wetting and dispersion is an important step in the homogeneous distribution of solid pigments within the liquid binder. Pigments are added to a paint in the form of a powder, and the combination of dry powder and liquid binder leads to ‘clumping’ or agglomerates. These agglomerates are broken down through mechanical forces (think whisking flour into a pancake batter) and smaller particles are formed which have a far greater surface area in contact with the binder. When clumping forms again the interstitial spaces are filled with binder not air and these groups are called flocculates. This process is known as ‘wetting’ because the pigments are being wetted by the binder solution. The work of wetting additives is to accelerate the wetting of the pigment agglomerates.
Once the pigments are wetted, their optimum dispersion needs to be ensured. Flocculation causes poorer colour strength, decreased gloss, and it also changes the rheology of the coating. Ideally pigments are stabilised at the point where they have formed wetted particles, before intermolecular forces draw them back together to form flocculates. This is the job of the dispersion additive: they act to improve the stabilisation of the dispersion of the pigment. A dispersion additive adsorbs on the surface of the pigment and works against the attractive intermolecular forces that cause flocculation, keeping the particles apart. With deflocculation comes improved pigment utilisation, colour expression, levelling, and reduced viscosity.
|Additive Company||Coating Additive Product||Description|
|BYK/Altana||Anti-Terra U||Wetting and dispersing additive for solvent-borne industrial and architectural coatings to stabilize inorganic pigments|
|Dow Coating Materials||Tamol 2011||A hydrophobic polyacid copolymer with efficient pigment stabilization through charge-charge repulsion.|
|Ethox Chemicals LLC||E-Sperse 4754||A dispersant for inorganic pigments in solvent and resin based formulations, particularly mixed metal oxides and TiO2, in the aerospace industry.|
|Evonik||Carbowet 300||A solvent and APE-free surfactant for resinated pigment dispersions.|
Coating Additives Australia: manufacturers, products and suppliers
The above list is just a few of the different additive types available for coating. The top five global coating additives companies are AkzoNobel, Altana/BYK, BASF, Evonik Industries, and the Dow Chemical Company. As well as these big global players, smaller companies make up a significant share of the market. Other companies include Allnex, Arkema, Crayvallac, Clariant, Coatex, Pilot, Siltech, Unimin and more.
Due to the sensitive nature of coatings, additives are not one size fits all. As a result, coating additives companies produce a broad range of additive solutions to suit your needs. For example, the BASF catalogue has 56 different products for dispersing agents for general industrial coatings. BYK/Altana has a portfolio of hundreds of coating additives suitable for many application areas, including industrial coatings, can coatings, coil coatings, wood and furniture coatings, powder coatings, and protective and marine coatings.
Whether wetting and dispersing, rheology modifying, surface additives, corrosion and fire resistant, or antimicrobial, there is an additive for your project. If you need any assistance in finding the most suitable additives or a reliable supplier, contact us by email or through the ‘request a quote’ button below. Our experts are here to help!