Solvents

Organic solvents (hydrocarbons)

The most common and efficient way of cleaning films has been by using a solvent system. For the last 20 years or so 1,1,1 trichloroethane ('Genklene’) has been used, but because of concerns over depletion of the upper atmosphere ozone layer, it has been banned from manufacture. The most popular replacement solvent, perchloroethylene, is not as efficient a cleaner and has a greater need for vapour containment as it poses a health and safety risk.

Many other solvents that have been used for cleaning have significant drawbacks. Flammability is one such problem. Alcohols, such as ethanol, may be used for some cleaning applications but can be harmful to the film by dissolving plasticisers from the film base or adversely affecting the image forming dyes.

New solvents, such as 3M’s fluoroethers or HFE series, are very safe to use from a staff point of view, but tend to be less efficient cleaners and are currently very expensive.

Solvent Efficiency
Perchloroethylene (Perc, Tetrachloroethylene) Good
HFE 7100 (3M) Methyl Nonafluorobutyl ether/Methyl Nonafluoroisobutyl ether Adequate
HFE 7200 (3M) Ethyl Perfluoroisobutyl ether/ Ethyl Perfluorobutyl ether Adequate
HFC 43-10 mee (DUPONT) (1,1,1,2,3,4,4,5,5,5-decafluoro Pentane) Adequate
ASAHI KLIN AK-225 (ASAHI) (3,3-dichloro-1,1,1,2,2-pentafluoropropane) Good
ISOPROPANOL (2-propanol, secondary propyl alcohol, dimethyl carbinol, petrohol) Good
ISOBUTYLBENZENE (2-methylpropyl benzene, methyl-1-phenylpropane) Good
ACTREL 1064 L (EXXON) (Mixture of hydrocarbons) Good
Hydrotreated Naptha (Signal Inc.) Hydrocarbon Type Film Cleaner 40 Excellent
Isopar® G Naptha Exxon Chemical Excellent
Exxsol® D3135 Naptha Exxon Chemical Excellent
Soltrol® 100 Phillips Chemical Excellent

Table 12.1 Suitable solvents — from the Kodak Website (www.KODAK.com)

Aqueous (water)

Water combined with mild surfactants has some uses in film cleaning. There are some drawbacks with using aqueous systems with archival films. As cellulose ester film bases decompose the generated acid alters the solubility of the gelatin emulsion. Even the short exposure used in film cleaning applications can be sufficient to fully wet the emulsion. Gelatin can absorb water at a very fast rate and can be fully wetted in around three seconds. Once the pH of gelatin shifts beyond the iso-electric point the uptake of water is dramatically increased.