The formulation of a new paint (or coating) comes with many challenges where the final requirements define the starting point of the formulation.
The main ingredients are divided into 3 groups, as can be seen in the scheme below:
Important is to start with a suitable guideline formulation designed for the final application (for example indoor decorative or outdoor industrial). In this guideline formulation the suitable binder, pigments, fillers and additives are selected to start the design of the final paint. Depending on the final application the correct pigment binder ratio and PVC (pigment volume concentration) will be chosen.
Examples of guideline formulations, for various applications, can be found on UL Prospector> Formulations.
Pigment binder ratio and PVC
The Pigment to Binder Ratio (P:B) is used to determine hiding and opacity. P:B is calculated with primary pigments only, and is used in industrial coatings, but is relevant to all coatings. It is used to determine the amount of primary pigment needed for hiding on a weight basis.
On the other hand, the pigment volume concentration (PVC) is the ratio of pigment volume to the total volume of the solid coating (vol. %). The pigment volume is the sum of the pigment and filler volumes.
Vp = Volume of the pigments
Vf = Volume of the fillers
Vbm = Volume of the solid film of all binders
The PVC will be used as a guideline for the determination of the final gloss level of the paint. In general high gloss paints will have a PVC from 10 to 20%, matt paints will have a PVC of 40 to 85% and transparent varnishes may have a PVC of below 10%.
The critical PVC (CPVC), is the PVC at which the binder concentration is just barely sufficient to completely wet alle the pigments and fillers. When going above the CPVC, the paint film will become more porous and will therefore not be suitable for all final applications.
Binders
The binder, being the main ingredient in the formulation, will mostly determine the final properties of the paint layer. It will bring properties such as:
- Adhesion to the substrate
- (outdoor) durability
- Pigment wetting
- Chemical resistance
- Water barrier
- Gloss
- Biodegradability
- Flexibility
An important selection criteria for the choice of the suitable binder is in many cases costs versus performance. As the final application will have a price range for it to be viable in the market, cost of the binder can play a major role in the decision making process.
Binder Chemistry | Main properties | Applications |
Polyurethane | – excellent chemical resistance,
– durability – flexibility – good adhesion to various substrates |
Automotive coatings, industrial coatings, and high-performance architectural coatings. |
Epoxy | – exceptional adhesion
– chemical resistance – excellent corrosion protection – can be modified to improve flexibility and impact resistance. |
Heavy-duty coatings, such as marine coatings, tank linings, and industrial flooring. |
Acrylic | – good adhesion
– UV resistance – Weatherability – can be formulated to provide various levels of gloss, hardness, and flexibility. |
Exterior architectural coatings, automotive coatings, and wood coatings. |
Silicone | – excellent heat resistance
– weatherability – hydrophobicity |
High-temperature coatings, protective coatings for infrastructure, and industrial applications where extreme temperature variations are expected. |
Alkyd | – excellent durability
– gloss retention – good adhesion – resistance to yellowing – excellent flow and leveling properties. |
Architectural coatings, metal coatings, and wood finishes. |
Polyester | – excellent durability
– chemical resistance – weatherability – can be formulated to provide different levels of hardness and flexibility. |
High-performance coatings, including automotive coatings, coil coatings, and protective coatings. |
Bio-based binders
Bio-based binders are a main topic for formulators in order to provide a sustainable alternative to traditional petroleum-based binders commonly used in paint formulations. These binders are derived from renewable resources such as plants, trees, or agricultural waste, reducing the environmental impact associated with conventional paints. The benefits they offer, include a lower carbon footprint and reduced VOC emissions. A few examples of bio-based binders:
- Natural oil based: soybean oil, linseed oil or castor oil
- Cellulose based: derived from plants or wood pulp
- Starch based: derived from corn, wheat, or potatoes, can be modified to create bio-based binders
When looking to replace the binder in an existing formulation with a bio-based binder, it is important to find a comparable set of properties such as (for WB binders) solids content, pH, flexibility, and adhesion. As in most cases, the binder chemistry will be different this seems to pose the most challenging part in order to maintain the important characteristics of the final paint.
Examples of bio-based binders used in water-based paint are for instance:
- ALBERDINGK® Ren AC 8003 VP (Alberdingk Boley): acrylic copolymer with 45% renewable content (based on solids); Aqueous, fine disperse, APEO-free copolymer dispersion based on renewable resources without plasticizers and protective colloids.
Recommended for interior paints & exterior masonry paints as well as plasters
- Decovery® SP-2022 (Covestro): multi-purpose, breathable acrylic dispersion with 37% biobased content. It exhibits excellent multi-substrate adhesion, UV- and water resistance with low dirt pick-up. It provides good water vapor permeability, minimal water absorption with fast water release, excellent moisture regulation and high elongation.
- Secoia 4400 (Ecoat): Surfactant-free short-oil-length Alkyd Emulsion 99% Bio-based. Application for interior wall paints (matt to glossy), primers, undercoats and lacquers. It exhibits fast drying and hardness development with excellent water and stain resistance due to the lack of surfactants. A Low initial Color and limited Yellowing in time.
- SYNAQUA® 4804 (Arkema): short oil alkyd emulsion with 43% biobased content. Offers high gloss potential, excellent gloss retention and low yellowing. Provides block & scrub resistance, adhesion and washability. Very good hardness development and good stability with anti-corrosive pigments. It finds application in transparent and semi-transparent stains, trim paints, wall and ceiling paints, interior/exterior primers for wood and metal and direct-to-metal coatings with anticorrosive properties.
- Lacper® 4601 (Wanhua Chemical): 40% bio-based acrylic emulsion for waterborne wood coating solutions. More transparent due to smaller particle size, good sandability and block resistance.
Bio-based additives
As mentioned before, next to selecting the bio-based binders, additives can also be chosen from a bio or natural origin to increase the overall bio-based content of the paint formulation. Several examples of bio-based additives are the following:
- ECO Brij™ C10 (Croda): 100% bio-based, non-ionic, surfactant. It is produced from naturally occurring straight chain cetyl alcohol. It is also used as a versatile co-emulsifier for O/W emulsions, wetting agent, dispersing agent and solubilizer.
- Tego® Foamex 18 (Evonik): 98% based on vegetable oil defoamer concentrate. It is specially developed for architectural paints. It is based on 98% vegetable oil, a renewable raw material and is free of silicone, solvent & mineral oil. Suitable for the grinding or letdown stage of pigmented formulations.
- Innospers RBE (Allinova): 100% bio-based wax emulsion from ricebran. Improves surface slip and increases the scratch resistance.
- DAPRO® DF 9010 (Elementis): is an ultra-fine dispersion of wax in vegetable oil. Acts as a defoamer. It is economical in use, for universal waterborne applications. The product shows very good long-term efficiency. Suitable for waterborne applications.
- EDAPLAN 397 R (Münzig): 100% bio-based non-ionic, liquid dispersing agent for pigments. Particularly suitable for dispersing organic pigments and can be used in binder-free as well as binder-containing grinds and pigment concentrates. It reduces the viscosity of the grind, improves gloss and color strength and prevents flocculation.
- Exilva® F (Borregaard): 100% bio-based micro fibrillated cellulose produced from Norway Spruce.
It gives high viscosity at low shear securing good stability, and shows strong shear thinning enabling spraying. The relatively quick viscosity recovery prevents sagging, without sacrificing levelling of your coating.
The bio-based raw materials listed above are just a small example of the products available to formulate a paint. The most important is to design the formulation with the conditions and requirements for the final application. Discussion with the supplier of the raw materials can always benefit in selecting the right additive for the desired purpose.
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