Solvents are one of the three components of paints. They are petroleum-based chemicals which dissolve the pigment and binding agent for application. Most enamel-based paints use a mild petroleum-based solvent with an alkyd vehicle, and have a long drying and curing time. Conversely, lacquer-based paints require stronger solvents to speed the drying time. The most widely used aromatic hydrocarbons solvents in paint are benzene, toluene, mixed xylenes, ethylbenzene (BTEX), and high flash aromatic napthas; aliphatic hydrocarbons include hexanes, heptane, VM&P naphtha. Aromatic Hydrocarbon
Aliphatic Hydrocarbon
Oxygenated
Aromatic hydrocarbon solvents have a benzene ring structure. These solvents are produced in the petroleum refining industry from the distillation of petroleum stock and other chemical conversion processes, such as catalytic hydrogenation and alkylation. These solvents impart stronger odors and have higher solvency rates than aliphatic hydrocarbon solvents.Aromatic Hydrocarbon Solvents
Common aromatic hydrocarbon solvents used in paints and coatings are benzene, toluene, ethylbenzene, mixed xylenes (BTEX) and high flash aromatic naphthas. Additional information can be found under our Petrochemical Industry VOCs guide. Aromatic solvents are also widely used in printing inks, pesticides, insecticides, and agricultural chemicals.
Short-term exposure to these solvents from inhalation can result in irritation to the upper respiratory tract and eyes, also dizziness, fatigue and headaches. Long-term effects may cause disorders in blood (benzene); cardiovascular and kidney effects, unconsciousness, dysfunction of the CNS (xylene). Benzene is classified as a human carcinogen.
References
- ASTDR - Ethylbenzene (PDF)
- NIOSH Topic - Organic Solvents
- ASTM - Volume 06.04 March 2009: Paint, Solvents, Aromatic Hydrocarbons (list of standards) (PDF)
Aliphatic Hydrocarbon Solvents
Aliphatic hydrocarbon solvents do not contain a benzene ring. They are mixtures of either saturated, long straight chain (normal-paraffin) or branched chain (iso-paraffin) or cyclic paraffins. These solvents are produced by distillation of crude oil by the appropriate boiling point range fraction, then are treated to improve color and odor.
Short-term exposure to these solvents may cause dizziness, giddiness, nausea and headaches, irritation to skin and eyes, and euphoria sometimes resulting in unconsciousness. Long-term effects include muscular weakness, blurred vision, headache, fatigue, numbness, damage to lungs and skin, and neurological disorders.
In addition to their use as solvents or diluents in paints and thinners, they are widely used in oil extraction, degreasing, rubber manufacture, and as carriers for aerosols and disinfectants. Gasoline and kerosene are examples of aliphatic hydrocarbon solvents.
Common aliphatic hydrocarbon solvents used in paints and coatings are mineral spirits, hexanes, heptanes, and VM & P Naphthas.
Oxygenated solvents are synthetic compounds with oxygen functionality. These solvents are primarily used as active solvents for most synthetic resins due to their strong solvency. They dissolve resins and films; reduce viscosity of paints, varnishes and lacquers for application. The four most widely used in this category are: ketones, esters, glycol ethers, and alcohols. Ketones Other uses for Ketones: Acetone and MEK are components of solvent mixtures in neoprene, nitrile rubber, and urethane industrial adhesives. Acetone is widely used in the pharmaceutical industry to extract Vitamin B complexes, alkaloids, enzymes and antibiotics. MEK and MIBK are used to dewax oils and also to aid in the extraction and purification of antibiotics; production of smokeless powders, inks, degreasing applications, perfumes, cleaning fluids, antioxidants, and more.Oxygenated Solvents (Active Solvents)
Ketones are commonly synthesized from the oxidation of hydrocarbons. Ketones feature a carbonyl group bonded to two other carbon atoms or alkyl group. They have very strong solvency, a wide range of evaporation rates and also a very distinct, strong odor. The commonly used ketones in paints and coatings are: acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) and isophorone.
Esters Glycol Ethers Alcohols most commonly used in paints and coatings are butyl alcohol and ethyl alcohol. Alcohols have a low toxicity and can dissolve non-polar compounds and are used in paints and coatings to speed drying time or to thin paint viscosity.
Esters are typically derived from an inorganic acid or organic acid where there is at least one hydroxyl (-OH) group replaced by an alkyl (alkoxy) group and most commonly from carboxylic acids and alcohols. Esters as solvents are alkyl acetates and propionates and glycol ether acetates. Their volatility is equivalent to ketones. They have strong solvency but generally weaker than ketones of the same volatility.
Glycol Ethers commonly known as Cellusolve® are a group of solvents based on alkyl ethers of ethylene glycol and they typically have both ether and alcohol functionality. These compounds were used extensively in coatings until concerns arose about their safety risks. They are being replaced with propylene glycol ethers in many applications. These compounds have strong solvency combined with slow evaporation rate.References
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