Manufacturing
Ideally, Nitrocellulose lacquers are prepared with modern high speed stirrers which are first charged with non-active solvents (or diluents) and alcohols (or co-solvents).
Solvent Types and Relation to Systems Selection
The solvent system used for preparation of the solution has a very important role in the final property of the solution including its viscosity.
The choice of the solvent depends upon:
- Viscosity
- Solids content that gives a particular viscosity
- Speed of evaporation
- Cost
Therefore the properties of solvent of relevance to the nitrocellulose solution are:
- Solubility of nitrocellulose in the given solvent
- Boiling point and evaporation rate of the solvent
- The solvents are categorized into 2 broad categories viz., solubility and boiling point range:
Schematic Flowchart of Manufacturing Process
Solubility based categorization
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True Solvents that can dissolve nitrocellulose on their own e.g.:
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Co-Solvents or latent solvents that act as solvents but only in the presence of true solvents e.g.:
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Non-Solvents or diluents or extenders that are used primarily on account of low cost but in which the nitrocellulose is not soluble e.g.
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- Keytones - acetone, methyl ethyl ketone, methyl isobutyl Ketones
- Esters - ethyl acetate, propyl acetate, butyl acetate, amyl acetate
- Glycol ethers - methyl / ethyl / isopropylglycol others
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- Alcohol - methanol, ethanol, propanol, butanol etc.
- Ethers - diethyl ether
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- Aliphatic & aromatic hydrocarbons e.g. - benzene, xylenetoluene, white spirit etc.
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Boiling Point Range based categorization
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Low boilers with boiling point ranges below 100oC e.g. ethyl acetate, Methylethyl ketone, Acetone, Isopropyl alcohol, industrial methylated spirit and toluene
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Medium boilers with boiling point ranges between 100oC & 150oC e.g. butyl acetate, MIBK, ethylene glycol, N-Butanol, xylene etc.
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High boilers boiling point above 150oCwhich are slow evaporators.
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Low boilers yield solutions of low viscosity and quick evaporation. The medium boilers check the rate of evaporation, impart good flow properties and reduce the defects caused by too rapid an evaporation. High boilers also act similarly and impart high gloss and brushing properties. Evaporation rates of pure solvents and their mixtures give only an approximate guide to the rate of evaporation from lacquer film.
Taking the evaporation of butyl acetate equal to one as standard, the following are the relative rates of evaporation at 50% loss of some of the common solvents used in lacquers.
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Ethyl alcohol
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2.1
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MIBK
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1.8
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Isopropyl alcohol
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2.1
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Aliphatic diluent
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2.6
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Butyl alcohol
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0.4
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Toluene
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2.6
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Ethyl acetate
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8.9
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Xulene
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0.7
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Acetone
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20
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Butyl acetate
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1.0
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Diacetone
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0.09
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