Solvent in Paints and Coatings: Types, Uses and Properties

Why solvents are required in paints and coatings?

Solvents in paints refer to liquids that are used to dissolve or disperse the components of paint. This allows the components to come together and form a liquid solution or suspension that can be easily applied as a uniform film. Solvents in paints and coatings formulations dissolve compounds like:

Pigments
Additives, and
Binders

After the paint is applied to the surface, the solvent evaporates. This allows the resin and pigment to produce a film of paint and to dry quickly. Adding solvents in a paint formulation helps to optimize the whole performance of the system.

Even if almost no solvents are present in the final dried coating due to evaporation, their role is essential in the coating formulation.

Solvents control the viscosity of the application
They have an important effect on film quality, which is strongly dependent on the solvent's evaporation rate during drying

As a result of this, they can affect properties such as film appearance, adhesion, or even corrosion.

Let’s understand more about solvating power. This is probably the most important parameter to select a solvent apart from its volatility and evaporate rate.

Estimating the solvating power of solvents

Solvating power describes the ability of a solvent to interact with other molecules. It thus leads to the dissolution of resins and formulation viscosity. Hansen Solubility Parameters (HSP) offer a good way to estimate the solvating power of solvents.

Basic principles of HSP

➤ HSP are a set of 3 numbers that describe the way solvents (but also polymers) will behave with other molecules. It describes if they want to be near each other or not.

➤ Each one of the 3 parameters, δD, δP, and δH, represents a type of interaction. They are London dispersion forces, polar forces, and hydrogen bonding forces respectively.

➤ As dispersion forces are similar for most of the common solvents/organic molecules, δD does not vary much.

➤ δP and δH are more important here and can differ a lot from solvent to solvent. These numbers are good indicators of the polar properties and ability of a solvent to form hydrogen bonds respectively.

➤ The smaller the δP the better the ability to dissolve the non-polar resin. The higher the δH the better the ability to form hydrogen bonds.

Although it remains important when formulating a solvent blend to consider all parameters of the blend, here we will take into account only δP and δH. Find more information on Hansen Solubility Parameters. Here we will take into account only δP and δH.

Below is a 2D map of the common solvents/families that can complement the matrix and help visualize solvent solvating properties.

Classes of Solvents: Decoding Properties and Uses

Selecting hydrocarbon solvents for optimal performance

Hydrocarbons are molecules that are composed only of carbon and hydrogen atoms. They can be divided into aliphatics, aromatics, and blends.

Aliphatic solvents are linear, branched, or cyclic hydrocarbon chains. For example, pure solvents like hexane.
Aromatic solvents feature a benzene group (cyclic structure of 6 carbons). For example, toluene and xylene.

Aliphatic and cyclic hydrocarbon blends are usually well-known as mineral or white spirits and special boiling point spirits. Blends of aromatic solvents are also available.

Hydrocarbon Solvents for Coatings

Special boiling point spirits
They have a flash point < 21 °C. They include different grades with different flash points and fixed boiling ranges. They are very fast-evaporating solvents and thus are used for fast drying coatings.

Mineral or white spirit
They have a flash point > 21 °C. They are also available in different grades with different flash points and fixed boiling ranges. Their names can usually refer to their flash points (30 °C, 40 °C, 60 °C, etc.). They are commonly used for oil-based and alkyd resins.

Aromatic hydrocarbon blends
They are sometimes called naphtha solvents. They are usually aromatic petroleum fractions (C9 to C13) with different grades having fixed boiling ranges. They are commonly used in many industrial coatings as part of the solvent systems even if they try to be avoided when possible. In general, aromatic solvents have higher dissolving power than aliphatics.

Toluene and xylene
They are commonly used with phenolic and amino formaldehyde in heat-curing systems as well as with alkyd resins.

Spirits of turpentine
They are specific solvents made from the distillation of tree resins and composed of different terpenes. They are commonly used for oil-based systems.

The below table shows an exclusive matrix focusing on the solvating power, evaporation rate/volatility, solubility in water, flammability, and toxicological/eco-tox profile of different types of hydrocarbon solvents. This helps to select hydrocarbon solvents keeping in view the properties they impart to the formulation.

Subtype	Solvating Power	Polarity	Volatility	Water Solubility (20 °C)	Flammability	Eco-tox Profile
Aliphatic hexane	-0	-0	⭐⭐⭐⭐	⭐	Yes	-
Blend Aliphatic Cycloaliphatic Special Boiling Point Spirits (flash point < 21 °C)	⭐	⭐	⭐⭐⭐⭐	⭐	Yes	Usually ⭐⭐
Blend Aliphatic Cycloaliphatic White Spirits Mineral Spirits (60°C > flash point > 21 °C)	⭐	⭐	⭐⭐	⭐	Usually yes	Usually ⭐
Blend Aliphatic Cycloaliphatic White Spirits Mineral Spirits (flash point > 60 °C)	⭐	⭐	⭐	⭐	No	-
Spirit of Turpentine (terpenoids)	⭐	⭐	⭐⭐	⭐	Usually yes	Usually ⭐
Aromatic Fractions (flash point < 60 °C)	⭐	⭐	⭐	⭐	Yes	Usually ⭐
Aromatic Fractions (flash point > 60 °C)	⭐	⭐	⭐	⭐	No	Usually ⭐
Toluene	⭐	⭐	⭐⭐⭐⭐	⭐	Yes	⭐
Xylene	⭐	⭐	⭐⭐⭐⭐	⭐	Yes	⭐⭐

Ketone solvents: Understanding their chemistry for efficient selection

Ketone solvents are considered to have good solvating power due to their carbonyl group, a hydrogen acceptor. Small ketones are good for polar resins. As the hydrocarbon chain gets more important for higher ketones, they become good for non-polar resins. Only small ketones are miscible with water.

Ketone solvents can also decrease the viscosity of resin systems by avoiding complex formation between polar resins. This happens when hydrogen bonds are formed between resin molecules.

Acetone — A fast evaporation solvent used in cellulosic coatings.
Methyl isobutyl ketone — A medium evaporation all-around solvent used in many systems.
Methyl amyl ketones — A low evaporation solvent with good solving power properties.
Isophorone — A very low evaporation solvent used in heat-curing systems. It is known to improve the wetting of surfaces and pigments.

Subtype	Solvating Power	Polarity	Volatility	Water Solubility (20 °C)	Flammability	Eco-tox Profile
Acetone	⭐⭐⭐	⭐⭐⭐⭐⭐	⭐⭐⭐⭐	⭐⭐⭐⭐⭐	Yes	⭐⭐
Methyl Ethyl Ketone (MEK)	⭐⭐⭐	⭐⭐⭐⭐⭐	⭐⭐⭐⭐	⭐⭐⭐⭐⭐	Yes	⭐⭐
Methyl IsoButyl Ketone (MIBK)	⭐⭐	⭐⭐⭐	⭐⭐⭐⭐	⭐	Yes	⭐⭐
Methyl Amyl Ketone (MAK)	⭐⭐	⭐⭐⭐	⭐	⭐	Yes	⭐⭐
Isophorone	⭐⭐⭐	⭐⭐⭐⭐	⭐	⭐	No	⭐
Diacetone Alcohol	⭐⭐⭐⭐	⭐⭐⭐⭐⭐	⭐	⭐⭐⭐⭐⭐	Yes	⭐⭐
Diisobutyl Ketone	⭐⭐	⭐⭐	⭐⭐	⭐	Yes	⭐⭐

Esters: The pleasant and versatile solvents for coatings

Like ketones, esters are also hydrogen acceptors and thus have similar solvating power. If small, esters are good solvents for polar resins. Their dissolving power for non-polar material increases with the size of their hydrocarbon chain. This is similar to ketones.

They usually have very limited miscibility with water as compared to ketones. Their usually more "fruity" odor makes them more pleasant. They can also be used to decrease viscosity when polar resin molecules form complexes due to hydrogen bonds.

Ethyl acetate — A fast evaporation solvent widely used in many fast drying systems.

Butyl acetate — It is a widely used ester-based solvent. Its moderate evaporation rate makes it perfect during drying, to avoid surface defects of the film (blushing, cratering, etc.).

Propylene glycol mono methyl ether acetate — A moderate evaporation solvent is also used in a lot of systems. It has a greater (but limited) miscibility with water compared to other esters.

Butyl glycol acetate — It is a slow evaporation solvent with very good solvating power making it suitable to improve the flow and gloss of coatings cured at high temperature.

Subtype	Solvating Power	Polarity	Volatility	Water Solubility (20 °C)	Flammability	Eco-tox Profile
General Esters	⭐⭐⭐	-	⭐⭐⭐	⭐ (No/Slightly miscible)	-	-
Ethyl Acetate	⭐⭐	⭐⭐⭐	⭐⭐⭐⭐	⭐	Yes	⭐⭐
Butyl Acetate	⭐⭐	⭐⭐	⭐⭐⭐	⭐	Yes	⭐⭐
Isopropyl Acetate	⭐⭐⭐	⭐⭐⭐	⭐⭐⭐⭐	⭐	Yes	⭐⭐
Isobutyl Acetate	⭐⭐⭐	⭐⭐	⭐⭐⭐⭐	⭐	Yes	⭐⭐⭐
Glycol Ether Esters	⭐⭐⭐	-	-	⭐	-	-
Propylene Glycol Mono Methyl Ether Acetate (PGMEA)	⭐⭐⭐	⭐⭐⭐	⭐⭐⭐	⭐	Yes	⭐⭐⭐
Ethylene Glycol Mono Butyl Ether Acetate (EGBEA)	⭐⭐⭐	⭐⭐⭐⭐	⭐	⭐	No	⭐⭐
Diethylene Glycol n-Butyl Ether Acetate (DEGBEA)	⭐⭐⭐	⭐⭐⭐	⭐	⭐	No	⭐⭐⭐

Choosing alcohol solvents based on polarity needs

Alcohols are hydrogen donors as well as acceptors. This gives them a very good solvating power for polar resins. As the hydrocarbon chain length increases, their solvating power for polar resins decreases. The position of the OH group also has an influence.

Small alcohols are soluble in water but miscibility falls off as the hydrocarbon chain length becomes longer. Alcohols can react with isocyanates and thus, can interfere with the drying process of such coatings. This effect can be reduced by using secondary or tertiary alcohols.

Ethanol — A high evaporation solvent, able to dissolve very polar resins. However, it is unable to dissolve very non-polar film formers like paraffin wax.

Butanol — A moderate evaporation solvent widely used in many systems. This solvent is known to be able to decrease the viscosity (even in small quantities) in non-polar resin systems. For example in alkyd paints and some waterborne coatings.

Subtype	Solvating Power	Polarity	Volatility	Water Solubility (20 °C)	Flammability	Eco-tox Profile
General Alcohols	⭐⭐⭐⭐⭐	-	-	-	-	-
Ethanol	⭐⭐⭐⭐⭐	⭐⭐⭐⭐	⭐⭐⭐⭐	⭐⭐⭐⭐	Yes	⭐⭐⭐
Butanol	⭐⭐⭐⭐⭐	⭐⭐⭐	⭐⭐⭐	⭐	Yes	⭐⭐

Glycol ether solvents: Enhancing flow and surface quality in paint films

Glycol ethers are usually divided into two categories:

Based on ethylene, E-series
Based on propylene, P-series

P-series are considered less toxic than E-series. Glycol ether solvents have usually a slow evaporation rate, which can limit their use to some specific applications. They have good solvating properties which enable them to improve the flow and surface quality of the paint film.

Ethylene glycol monobutyl ether — It is usually known as butyl glycol. It is a very versatile solvent. It has a higher (even if very slow) evaporation rate than most of the other glycol ethers. It is widely used in both solvent-borne and waterborne coatings.

Propylene glycol methyl ether — It has a moderate evaporation rate and full miscibility with water. This makes it a strong candidate for lots of coating systems.

Dipropylene glycol n-butyl ether — It is a very slow evaporating solvent making it a very good coalescing agent.

Glycol Ether Solvents Subtype	Solvating Power	Polarity	Volatility	Water Solubility (20 °C)	Flammability	Eco-tox Profile
Ethylene Glycol MonoButyl Ether (EGBE)	⭐⭐⭐⭐	⭐⭐⭐	⭐	⭐⭐⭐⭐⭐	No	⭐⭐
Ethylene Glycol Mono-n-propyl Ether (EGPE)	⭐⭐⭐⭐	⭐⭐⭐⭐⭐	⭐	⭐⭐⭐⭐⭐	No	⭐⭐
Diethylene Glycol Monobutyl Ether (DEGBE)	⭐⭐⭐⭐	⭐⭐⭐⭐	⭐	⭐⭐⭐⭐⭐	No	⭐⭐
Explore all the ethylene glycol solvents here »
Dipropylene Glycol Mono Methyl Ether (DPGME)	⭐⭐⭐⭐	⭐⭐⭐	⭐	⭐⭐⭐⭐⭐	No	⭐⭐⭐
Propylene Glycol Mono Methyl Ether (PGME)	⭐⭐⭐⭐	⭐⭐⭐⭐	⭐⭐⭐	⭐⭐⭐⭐⭐	Yes	⭐⭐
Propylene Glycol n-Butyl Ether (PGBE)	⭐⭐⭐⭐	⭐⭐⭐	⭐	⭐	No	⭐⭐
Dipropylen Glycol n-Butyl Ether (DPGBE)	⭐⭐⭐	⭐⭐⭐	⭐	⭐	No	⭐⭐⭐
Check out all the propylene glycol solvents here »

Compatibility Between Resins and Solvents

The compatibility depends on matching polarity between the resin and solvent. Polar resins dissolve in polar solvents while nonpolar resins need nonpolar solvents. Selecting the right match is key. Following is the list of resins that are compatible with various solvents:

➤ Alkyd resins — Compatible with aliphatic hydrocarbons, glycol ethers, aromatic hydrocarbons, and alcohols

➤ Epoxy resins — Compatible with esters, ketones, glycol ethers, aromatic hydrocarbons, alcohols

➤ Polyester resins — Compatible with esters, ketones, glycol ethers, aromatics

➤ Acrylic resins — Compatible with ketones, esters, glycol ethers, alcohols

➤ Vinyl resins — Compatible with aromatics, ketones, glycol ethers, alcohols

➤ Cellulosic resins — Compatible with alcohols, glycol ethers, ketones

➤ Amino resins — Compatible with aromatic hydrocarbons

➤ Phenolic resins — Compatible with aromatic hydrocarbons

➤ Chlorinated rubber — Compatible with aromatic hydrocarbons

➤ Silicone resins — Compatible with aromatic hydrocarbons

Select the specific solvent grade for your required resin efficiently using our universal selector:

Key Compliance Requirements for Solvents in Paints and Coatings

There are many key regulations and labeling requirements that solvents used in paints and coatings need to comply with:

Volatile Organic Compounds (VOCs) Regulations
Many countries have regulations limiting the amount of VOCs in paints and coatings. VOCs can contribute to air pollution and have adverse effects on human health. Compliance with VOC regulations may involve specifying maximum VOC content in products.

U.S. Environmental Protection Agency (EPA) Regulations
The U.S. EPA has regulations and guidelines for air quality, emissions, and hazardous air pollutants. Paints and coatings may need to comply with specific standards outlined by the EPA.

EU Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) Regulations
The EU REACH regulation allows to ensure the safety of chemicals, including those used in paints and coatings. This places the responsibilities on manufacturers and importers.

FDA Compliance
Paints and coatings require conformance with FDA testing guidelines for heavy metals and other toxins. These paints are used on children's goods, toys, furniture.

DOT Requirements
Solvent and paint containers used in transportation need DOT shipping names, UN numbers, hazard class information. Specific grade markings for aviation or marine paint solvents may be needed.

Find Suitable Solvents for Coatings

View a wide range of solvent grades available in the market today, analyze technical data of each product, get technical assistance or request samples.

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