Solvents used in resins and coatings

Generic solvents

Most of the resins, in their raw state (i.e. as ±100% polymer) are either solids or viscous liquids. In order to facilitate their packaging and further use by the coatings industry, it is customary to add a solvent, or solvents, to the resin prior to discharge. There are numerous solvents that are used depending on the end application of the coating and the solvent cost. As many of the solvents are common to many different types of coating systems, instead of individually listing those that are used for a specific resin against each resin type, for brevity, they have been split into 3 major categories in the following table:

Solvent Category	Description	Examples
Weak	Solvents that have fairly low solvency power	Water, Turpentine, Mineral/White Spirits, Alcohols, Low boiling point Aliphatics
Medium	Solvents that have medium solvency power	Xylene, Toluene and other aromatic solvents
Strong	Solvents that have very good solvency power	Butyl Acetate and a whole host of other aliphatic or aromatic Esters, Ethers, Ketones, Amines

"Solvency" refers to how well the solvent will dissolve the resin, generally indicated by how much a given quantity of solvent will reduce the viscosity of given quantity of a specific resin. Some solvents will rapidly reduce the viscosity of a resin ('Strong solvent') whilst in some instances, quite a lot of solvent is required to reduce the resin viscosity ('Weak solvent'). In some cases the resin shows no solubility in a specific solvent at all.
Aliphatic Solvents are those solvents based on straight, or branched, carbon chains containing associated hydrogen atoms.
Aromatic Solvents are those solvents based on carbon rings (benzene structure) and hydrogen atoms. These molecules may, or may not, have aliphatic molecules attached to the carbon ring as described above.
Oxygenated Solvents are those solvents that contain oxygen atoms as part of their molecular structure. They may be based on either aliphatic or aromatic carbon molecules. These solvents vary in evaporation rate from very fast evaporating (e.g. butyl acetate relative evaporation rate 1.0) to those which evaporate relatively slowly (e.g. butyl oxitol relative evaporation rate 0.07) from the coating surface.

Solvent classification

Solvents used in the manufacture of resins and coatings are classified by their effect on the resin, or coating viscosity. When considering solvents for a particular application it's always worth remembering the old adage "Like dissolves like". If the resin component is predominantly aliphatic, then an aliphatic solvent is indicated, if the resin contains little aliphatic raw materials, and has a high degree of, ester or ether groups, then an oxygenated solvent is indicated.

True solvents are those that provide almost complete solvency to the resin or coating. However, there is generally a limitation to how low in resin solids one can go before the resin 'kicks out' (precipitates or forms a gelatinous mass) below a certain resin solids content.
Diluents are those liquids that have a limited solvency for the resin or coating but remain compatible via a synergistic effect with the true solvent.The addition of diluents to a resin/coating system is to either lower the resin solids content whilst maintaining a high viscosity, or to reduce the cost of the resin/coating. As with the true solvents there is generally a limitation to how low in resin solids one can go before the resin 'kicks out' (precipitates or forms a gelatinous mass) as the diluent to true solvent ratio is increased.
Non solvents, as the name indicates, are those that provide almost no solvency to the resin or coating.

General chemistry

The following is a table of the more commonly used industrial grade solvents in resins and coatings, together with their approximate physical characteristics. The Industrial solvents are seldom rarely pure and subsequently the actual composition of many of these solvents changes from supplier to supplier. As a result of these variances, in practice the values provided by the solvent supplier should be used during the formulating of products:

Solvent	Alternative name	Carbon Atoms	Specific Gravity (20°C)	Flash point (°C)	Boiling Point (°C)	Relative evaporation rate (25°C)
ALIPHATIC
Hexane		C8	0.65	-23	69	8.3
White spirits	Mineral Spirits	C6 - C12	0.75	38 - 44	140 - 210	±0.15
Kerosene	Illuminating Paraffin	C8 - C12	0.81	38 - 65	150 - 300	±0.10
AROMATIC
Xylene	Xylenol	C8	0.87	25	136 - 144	0.60
Toluene	Toluol	C7	0.87	4	111	2.0
Solvent Naphtha 100	Light Aromatic	C8 - C10	0.85	40	150 - 190	0.27
Solvent Naphtha 150	Heavy Aromatic	C10 - C12	0.91	63	185 - 200	0.10
ESTERS
Ethyl Acetate	EA	C4	0.90	-4	77	5.5
Butyl Acetate	BA	C6	0.88	22	126	1.0
2-Ethoxyethyl Acetate	Cellosolve Acetate	C6	0.97	51	156	0.30
2-Butoxyethanol Acetate	Butyl Cellosolve Acetate	C8	0.94	78	192	0.04
Propylene glycol methyl ether acetate	PMA/MPA	C8	0.97	42	192	0.33
GLYCOL ETHERS
Ethylene glycol monomethyl ether	2-Methoxyethanol (Methyl Celloslve)	C3	0.97	39	124 - 125	0.50
Ethylene glycol monoethyl ether	2-Ethoxyethanol (Ethyl Cellosolve)	C4	0.93	44	135	0.32
Ethylene glycol monopropyl ether	2-Propoxyethanol (Propyl Cellosolve)	C5	0.91	49	150	0.20
Ethylene glycol monobutyl ether	2-Butoxyethanol (Butyl Cellosolve)	C6	0.90	67	171	0.08
KETONES
Dimethyl Ketone	Acetone	C4	0.78	-18	56	7.7
Methyl Ethyl Ketone	MEK	C4	0.80	-9	80	5.8
Methyl Isobutyl Ketone	MIBK	C6	0.80	14	116	1.6
OTHERS
Water	Aqua	0	1.00	0	100	0.30
n-Butanol	Butanol	4	0.81	35	116 - 119	0.42

Notes:

There are a number of alternate names for these chemicals, many of which are company trade names. Only the most generic names are provided.
The number of carbon atoms in the molecule has been added as an indication of how some of the other physical properties change with molecular mass. E.g. FP, BP and relative evaporation rate.
The relative evaporation rate is the ratio of the time required to evaporate a test solvent to the time required to evaporate the reference solvent under identical conditions of temperature and air movement. In the above table, the reference solvent used is n-butyl alcohol.