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Solvents Selection for Industrial Coatings

In paints and coatings, solvents are majorly used to dissolve or disperse various components used in the formulation. Industrial Coatings made with solvents dry up to 10 times faster than low-solvent alternatives at room temperature, making painting fast and easy along with other benefits such as long-lasting protection, brilliant performance in extreme weather conditions and many more.

Explore main factors to be considered while selecting the right solvent for your industrial coating formulations from a range provided by the coatings market. Also, find out a primary evaluation of the different solvent families (hydrocarbons, ketones, esters, alcohols, glycol ethers….) and some specific solvents within them.

Role of Solvents in Paints and Coatings


Solvents for Industrial CoatingsSolvents are added to paint and coatings formulations to dissolve other compounds like:

  • Pigments
  • Additives, and
  • Binders

After the paint is applied on the surface, the solvent evaporates, allowing 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 coating formulation.

  • Solvents control the viscosity for the application
  • Solvents 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.

Solvents


» Select Right Solvent for Your Paints and Coatings Formulation 

This coatings database is available to all, free of charge. You can filter down your options by suitable resin, system or application (coatings, inks...), supplier and regional availability.

Before learning about what are the main families of solvents used in paints and coatings formulations, let’s understand more about solvating power which is probably the most important parameter to select a solvent apart from its volatility and evaporate rate…


Hansen Solubility Parameters 2D map (δP and δH)


Solvating Power describes the ability of a solvent to interact with other molecules and thus the dissolution of resins and formulation viscosity.

Hansen Solubility Parameters offer a good way to estimate the solvating power of solvents


Basic Principles of Hansen Solubility Parameters


  • Hansen Solubility Parameters are a set of 3 numbers that describe the way solvents (but also polymers) will behave with other molecules (Do they want to be near each other or not).

  • Each one of the 3 parameters, δD, δP and δH , represents a type of interactions: 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 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 Hansen Parameters of the blend (the reader is encouraged to look for more information on Hansen Solubility Parameters) here we will take into account only δP and δH. Below we have created a 2D map of the common solvents/families that can complement the matrix and help visualize solvent solvating properties.

Hansen Solubility Parameters Map


Main Types of Solvents Used in Paints and Coatings


The main types of solvents used in paints and coatings formulations are:


Hydrocarbon Solvents for Coatings


Hydrocarbons (molecules composed only of carbon and hydrogen atoms) can be divided in aliphatics, aromatics and blends

  • Aliphatic solvents are linear, branched or cyclic hydrocarbon chains such as pure solvent like hexane
  • Aromatic solvents feature a benzene group (cyclic structure of 6 carbons) like Toluene and Xylene
  • Aliphatic and cyclic hydrocarbons blends are usually well known as Mineral or White Spirit and Special Boiling Point Spirit. Blends of aromatic solvents are also available

Hydrocarbon Solvents for Coatings

  1. Special Boiling Point Spirit (Flash Point < 21°C) 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

  2. Mineral or White Spirit (Commonly with flash point > 21°C) are also available in different grades with different flash points and fixed boiling range. Their names can usually refer to the flash point (30°C, 40°C, 60°C …). They are commonly used for oil based and alkyd resins

  3. Aromatic hydrocarbons blends (sometimes called Naphtha solvents) 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

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

  5. Spirits of Turpentine are specific solvents made from distillation of tree resins and composed of different terpenes. There are commonly used for oil-based systems.

To help you select hydrocarbon solvents keeping in view the properties they impart to the formulation, below find 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.

Subtype  Solvating Power / Ability to form hydrogen bonds Solvating Power / Polarity Evaporation Rate/ Volatility Solubility in Water (20°C) Flammability Tox/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

Ketones as Solvents for Coatings


Ketones solvents are considered to have good solvating power thanks to their carbonyl group, a hydrogen acceptor. Small ketones are good for polar resins and as the hydrocarbon chain get more important for higher ketones; they become good for non-polar resins. Only small ketones are miscible with water.

Ketones solvents can also decrease viscosity of resin systems by avoiding complex formation between polar resins (when hydrogen bonds are formed between resin molecules).

» View all Ketone Solvents Suitable for Paints & Coatings 


  • 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 / Ability to form hydrogen bonds  Solvating Power / Polarity  Evaporation Rate/ Volatility   Solubility in Water (20°C) Flammability Tox/eco-tox Profile
Yes
 Methyl  Isobutyl  Ketone   (MIBK)
Yes
 Methyl  Amyl  Ketone  (MAK)     Yes
 Isophorone   No
 Diacetone  Alcohol Yes
 Diisobutyl  Ketone     Yes

Esters as 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, like ketones, with the size of their hydrocarbon chain.

They usually have a very limited miscibility with water but compared to ketones, their usually more "fruity" odor makes them often more pleasant. They can also be used to decrease viscosity when polar resins molecules form complexes due to hydrogen bonds.

  • Ethyl Acetate, a fast evaporation solvent widely used in many fast drying systems
  • Butyl Acetate is also widely used, its moderate evaporation rate makes it perfect, during drying, to avoid surface defects of the film (blushing, cratering...)
  • Propylene Glycol Mono Methyl Ether Acetate, a moderate evaporation, solvent is also used in lots of systems. It has a greater (but limited) miscibility with water compared to other esters
  • Butyl Glycol Acetate 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 / Ability to form hydrogen bonds Solvating Power / Polarity Evaporation Rate/ Volatility Solubility in Water (20°C) Flammability Tox/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

Alcohols as Solvents for Coatings

Alcohols are both hydrogen donors and acceptors giving them a very good solvating power for polar resins. As the length of the hydrocarbon chain increases their solvating power for polar resins decreases. Of course the position of the OH group has also an influence.

Small alcohols are soluble in water but miscibility falls off as the hydrocarbon chain length becomes longer. It is important to keep in mind that 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.

» See All Suitable Alcohol Solvents for Paints and Coatings  

  • Ethanol, a high evaporation solvent, able to dissolve very polar resins but unable to dissolve very non-polar film formers like
  • Butanol, a moderate evaporation solvent widely used in many systems. Among other properties, this solvent is known to be able to decrease viscosity (even in small quantities) in non-polar resin systems like alkyds paints and in some waterborne coatings

Subtype  Solvating Power/
Ability to form hydrogen bonds
Solvating Power/
Polarity
Evaporation Rate/ Volatility Solubility in Water (20°C) Flammability Tox/eco-tox Profile
General Alcohols          
Ethanol   Yes
Butanol Yes

Glycol Ether Solvents


Glycol ethers are usually divided in two categories: the ones based on ethylene, E-series and the ones 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. However, due to their good solvating properties, these solvents have the advantage of improving flow and surface quality of the paint film.

  • Ethylene Glycol MonoButyl Ether, usually known as Butyl Glycol, is a very versatile solvent. It has a higher (even if very slow) evaporation rate than most of other glycol ethers and is widely used in both solvent-borne and waterborne coatings.

  • Propylene Glycol Methyl Ether; its moderate evaporation rate and full miscibility with water make it a strong candidate for lots of coating systems.
  • Dipropylene Glycol n-Butyl Ether is a very slow evaporating solvent making it a very good coalescing agent.

Subtype  Solvating Power / Ability to form hydrogen bonds Solvating Power / Polarity Evaporation Rate/ Volatility Solubility in Water (20°C) Flammability Tox/eco-tox Profile
 Ethylene  Glycol MonoButyl  Ether (EGBE)  No 
 Ethylene Glycol Mono-  n-propyl  Ether (EGPE)  Yes
 Diethylene Glycol Monobutyl  Ether  (DEGBE)  No
 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

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