Binders and resins – the all-important coating vehicle
A paint or coating is the combination of a pigment, a binder, a solvent, and additives. The binder, or resin, is usually what gives the coating its name, such as polyurethane or acrylic. While the pigment provides a paint with color, the additives give it extra desirable characteristics, and the solvent gives it the necessary consistency for application, it is the binder that, as the name suggests, binds it all together. The binder is the film-forming component of paint, the vehicle that carries the pigment and then dries or cures, holding it in place. The binder is also responsible for adhesion, durability, flexibility, gloss, and other physical properties. Binders and resins are one of the most important elements of a coating.
In this article we look at the different binders and resins technologies and their applications across the coatings industry. We also look at some of the main binders and resins companies and manufacturers in the US.
The setting mechanisms of binders and resins – Thermoset vs thermoplastic
Though there are many types of resins, there are two setting methods for the synthetic resins used in paints: thermoset and thermoplastic.
- THERMOSETTING RESINS – These resins cure irreversibly when exposed to the right conditions. These can be extreme heat, chemical reaction or irradiation in the case of UV-cured thermoset resins. Uncured, thermoset resins are in a viscous, liquid state. During the curing process, the molecules that make up the resin form crosslinks, combining into long, tightly-bound polymers which set permanently. Because of these crosslinks, thermoset resins provide excellent adhesion as well as resistance to heat, chemicals, and water.
- THERMOPLASTIC RESINS – Resins which are thermoplastic remain plastic after setting. They do not cure irreversibly, but soften with heat. Film formation occurs through evaporation of the solvent or water. Thermoplastic resins provide excellent protection against corrosive materials and environments.
The main binders and resins in the coating industry
A resin is a solid or highly viscous substance of plant or synthetic origin. The term “resin” is applied to the component of a liquid that dries to a hard film or finish. In the coatings industry, natural resins (such as plant resins) have been almost entirely replaced by synthetic resins. Below are the top resins in the coatings industry, their applications, and the companies that provide them.
1. Acrylic resins
RESIN TYPE – Thermosetting and thermoplastic
Acrylic resins account for nearly 30% of the coating resin market. Acrylic resin is derived from the polymerization of acrylate and methacrylate monomers (such as methyl methacrylate or MMA) and can be thermoset or thermoplastic. Acrylic resins are included in both water-based and solvent-based coatings as lacquers (lower volume solids), enamels (higher volume solids), and powders (100% solids). They are also used to modify other coating types (such as polyurethane or epoxy) in order to enhance their appearance attributes.
ADVANTAGES – Acrylic resins are known for their good color and gloss retention, as well as their superior weathering and UV resistance.
USES – Solvent-based acrylic coatings (lacquers and enamels) are used for industrial flooring, coil coating, metal furniture coatings, appliance coatings and automotive coatings, although the tightening restrictions on VOC emissions mean that there is a move towards water-based coatings across the entire industry. Other uses of acrylic resins include architectural coatings (latex paint in the US, and emulsion paint in the UK) especially for exterior applications.
2. Polyurethane resins
RESIN TYPE – Thermosetting
Polyurethanes are reaction polymers created by reacting an isocyanate with a polyol. The types of isocyanate and polyol that form the polymer influence the resulting polyurethane. This is one of the strengths of polyurethanes – it has a great variety and versatility depending on its constituents. Polyurethanes are thermosetting polymers and the degree of crosslinking is one of the factors which determines the properties of the coating – for example, more crosslinking means a tougher coating where a polymer with fewer crosslinks or longer chains is more flexible. Polyurethane coatings come in one or two component varieties and can be either water or solvent based
ADVANTAGES – Polyurethanes have excellent chemical and solvent resistance, corrosion resistance, weather resistance, UV stability, abrasion resistance, gloss durability, hardness, and flexibility. They also come in a great variety and versatility depending on the constituents.
USES – In general, polyurethanes are high performance coatings for metal, concrete, wood, plastic, and more. Their versatility means they have application across a wide range of markets including architectural, automotive, industrial, and marine and protective coatings.
3. Epoxy resins
RESIN TYPE – Thermosetting
Epoxy resins, like polyurethanes, are thermosetting polymers that form a tough film through the process of crosslinking. There are a variety of formulations of epoxy resin including bisphenol A epoxy, bisphenol F epoxy (which has lower viscosity than bisphenol A epoxy), novolac epoxy, and aliphatic epoxy. Each of these resin formulations result in a slightly different epoxy resin coating, with different strengths. Curing of epoxy resins is an exothermic reaction, and can be achieved through mixing the resin with a curative or hardener before application, or through heat. Epoxy resins are generally two component, though single component formulations are available, and they are water or solvent based.
ADVANTAGES – Epoxy resins have a range of desirable qualities – water resistance, chemical and solvent resistance, temperature resistance, excellent adhesion, and durability, all add up to make epoxy an easy choice.
USES – Epoxy is the go-to industrial and protective coating for many markets. Common uses for epoxy resin coatings include flooring, can coating, waterproofing cement, steel, tanks, pipes and shipping elements, offshore and oil and gas applications, automotive coating, industrial coating, and more.
4. Polyester and vinylester resins
RESIN TYPE – Thermosetting
A polyester resin is formed by the polymerization of an alcohol and an acid. A vinylester resin is a subclass of polyester resins where the polyester base is modified by an epoxy, typically a bisphenol A epoxy or a novolac epoxy. Polyester and vinylester resins are both thermosetting resins, and the resin is usually dissolved in a monomer such as styrene in order to reduce their viscosity and make them workable. The curing process for these resins involves a reaction with a catalyst (often methyl ethyl ketone peroxide or MEKP). Both resins are highly reactive, so only have a short shelf life.
ADVANTAGES – Polyester and vinylester provide superior chemical and temperature resistance to most coatings. They are also abrasion resistant, quick curing, and provide long term corrosion protection, hence their use in marine coating. Polyester coatings also have the benefit of being cheaper than other coatings on the market. Vinylesters have better water and chemical resistance, and more resilience than polyester resins.
USES – Polyester and vinylester coatings are both used in severe chemical environments. They are extensively used in coil coating among other applications.
5. Alkyd resins
RESIN TYPE – Thermoplastic, also used in thermosetting plastics
An alkyd is the result of the polymerization reaction between an alcohol (like glycerol) and an acid, modified by the addition of oils. They are also known as oil-modified polyesters. The oil content of the formulation varies; a short oil alkyd has the lowest percentage of fatty acid by weight (less than 40%), then medium oil (40-60%), then finally long oil (60-70%). Long oil alkyds are the slowest drying and most flexible, where short oil alkyds are fast drying and form the hardest films. The recent trend towards water based coatings has seen alkyd popularity drop off in favor of acrylics, epoxies, and polyurethanes.
ADVANTAGES –The desirable properties of alkyds include good adhesion, hardness, flexibility, corrosion resistance, and gloss retention.
USES – Alkyd resins are used across a range of substrates, from metal and wood to plastics and more, and in industries such as architectural coatings (particularly decorative gloss paints), furniture coatings, automotive coatings (including underhood and underbody coatings), insulating enamels, coil coatings, and more. Long alkyds are commonly used in architectural coatings, where short alkyds are more commonly found in industrial baking enamels.
A small selection of binders and resins from top manufacturers
Below is a table outlining just a very small few of the coating binders and resins available from some of the top coating resins companies.
|Coating Resins Manufacturer/Product||Binder/resin type||Description|
|Allnex Crylcoat 2415-2||Polyester resin||Architectural resin for matte dry blend, for smooth powder coatings with excellent outdoor weathering resistance.|
|Allnex BeckoPox EP147w||Bisphenol A/bisphenol F epoxy resin||Water-based, liquid epoxy resin for metallic and mineral substrates to provide chemical, abrasion, and corrosion protection.|
|Arkema ENCOR Flex 187||100% acrylic resin||An acrylic binder designed for elastomeric roof and wall coatings. Resistant to dirt pick up, high solids, and low VOC.|
|Arkema CHEMPOL 801-6050||Long oil alkyd resin||A flexible air dry alkyd with a mineral spirits solvent. Excellent for exterior applications.|
|Dow Chemical Company ROVACE 9900||Vinyl-acrylic resin||A solvent-free PVA for architectural coatings. Low-odor, excellent gloss capability, and scrub resistance.|
|DSM Uralac Ultra||Polyester resin||A specially designed powder coating resin for MDF substrates and other heat-sensitive wood products.|
|Helios DOMALKYD 4161||Polyurethane alkyd resin||A resin for use with wood (parquet floor lacquers) and metal.|
|Helios DOMALKYD 1492||Medium oil alkyd resin||Quick drying medium oil alkyd resin for paints for metalwork (industrial machine, and radiator paints).|
The future of binders and resins
The binders and resins market has grown over recent years, and it is expected to continue with its upward trajectory. The main companies in the coating resins market are Allnex, Arkema, BASF, Dow Chemical Company, DSM, Evonik, Helios, Momentive, and Valspar Corporation. The market has in recent years has shown a distinct trend towards environmentally friendly and sustainable coatings, as shown through the decline in popularity of the previously dominant alkyd market. Resins that produce solvent-free, low or zero VOC emission coatings are preferred. Regulations on these pollutants are also becoming more restrictive, forcing manufacturers to preemptively focus on products in this trend.
Newer coating technologies are also making their mark. Fluoropolymers, UV curable coatings, silicone-modified coatings, super polyesters for coil coatings, polyurea coatings, and many more are making waves in the coating world. Whether your project requires traditional binders or you are interested in the newer resins, we’ll find you the right supplier. For more information or requesting a quote, contact us via email or by clicking on the button below.