How to choose a diluent
Given the importance of the quality of the diluents, we summarize the main characteristics of a good polyurethane diluent, which should be guaranteed “black on white” by the suppliers:
· Must not contain more than 0.05% of water
· Must not contain hydroxyl compounds (primary alcohols, glycols or glycol ethers) over 1%
· Must respond to specific technical requirements concerning its specific use
· Must comply with the rules on harmfulness (and labeling)
it must be the least polluting possible in relation to emissions into the atmosphere (highest possible class according to the Ministerial Decree 12/7/90).
With regard to the limit of 1% of primary alcohols, this is a precaution that avoids crosslinking problems of the paints. Here too it is a problem of quantity and certainly the paint manufacturer does not use such solvents in the formulation of the products unless it is absolutely forced. However, polyurethane diluents containing methyl or ethyl alcohol should be wary of the presence of poor quality solvents.
A good spray diluent will consist of a mixture of solvents particularly suitable for increasing distension, smoothing out any matting, avoiding dripping and pitting: a mixture of esters or light ketones must be expected (30/40% ethyl acetate, MEK), esters, ketones and aromatics medium (30/40% butyl acetate, MIBK, toluene, xylenes), and a good presence of slow esters (20/30% methoxypropylacetate, ethoxypropylacetate). The latter, in summer weather, may also be present in larger quantities.
A good thinning diluent will have to provide the greatest possible pot-life and will not have particular requirements for the distension, although it must ensure excellent surface uniformity. Therefore, light and medium ketones are generally preferable (MEK and MIBK increase the useful life), while the presence of slow solvents is not essential. In both cases the presence of aromatics (toluene, xylol) is not technically negative. Acetone, in itself very rapid and generally easily hydrated, is not normally used in a good polyurethane diluent, especially in summer.
A diluent should contain harmful products in the smallest possible amount, and in this sense contain less than 12% of aromatics, be free from ether-ethylglycol, acetates, ethylglycolacetate, methylglycolacetate (also called ethoxyethylacetate and methoxyethylacetate), ultimately replaced by propyl derivatives: methoxypropylacetate (MPA) and ethoxypropylacetate (EPA). A good diluent, correctly formulated, must also respond as best as possible to the regulations regarding emission limits in the atmosphere. In this sense it should not contain class II solvents (for example the glycols-ethers-acetates already mentioned), but be almost totally made up of class IV and V solvents, and of class III only when it is indispensable (compare the safety of your suppliers to get the best price / safety ratio).
As regards the main characteristics of a good “nitro” diluent, light alcohols (ethyl, methyl) are to be excluded, while propyl alcohol and butyl alcohol are acceptable.
Glycols and glycol ethers must be present in percentages lower than 10%. Furthermore, it is better to have little acetone, while it is good practice to insert methylethylketone (MEK), isobutyl acetate, butylglycol.
In the use of color diluents the casuistry is very varied and can not be generalized.
Finally, for washing operations, any product is suitable, consistent with the criteria of correct hygiene of the work, provided they are not used to dilute the paints!
To conclude, it is evident that diluents containing solvents recovered from other sectors (for example the pharmaceutical or mechanical), can hardly meet all the characteristics listed above and in addition may contain foreign substances normally not used by the paint manufacturer (for example chlorinated , which can damage pumps, gaskets and metal parts of spraying equipment).
The use of low-cost recovery thinners is therefore acceptable only after a careful evaluation of the technical data sheet and the product safety data sheet.
The phenomenon is now widespread throughout Italy. With the excuse of “supersconto”, unscrupulous sellers realize the good earnings on the skin of “chickens” who buy diluents labeled “nitro antinebbia” or “poliuretanici”, but that actually contain a wide range of solvents more or less dangerous and almost always of poor quality.
The most wary painters know how to distinguish the “bin” already from the smell, but even without arriving at the gas chromatographic analysis, one can begin to become suspicious when products are offered at prices 20-30% lower than those on the market. A product with a low technical content such as the thinner, whose price is already pulled to the bone, if it is sold at prices well below the average, hides its true identity: in fact it is recycled diluents coming from various industrial processes (mechanical, pharmaceutical and other industries), which contain mixtures of various kinds.
The substances contained in these diluents (formulated not to meet specific requirements, but to dispose of more or less toxic waste in a speculative way), can cause technical problems to painting and application equipment, while in serious cases they cause serious problems to the health of the operators.
Obviously the bins of these diluents, or rather these “diluents-bins”, often are not labeled according to the rules and are not accompanied by the regulatory safety data sheet, which would identify them with precision and use them only for washing and maintenance operations ( in cases where the rules allow it).
Recovery diluents are an important resource, if they are called by their name and declare their content, but the results that emerge from the analysis of samples taken in various areas of Italy are worrisome and should seriously alarm the most unwary users. , because the damage to health can be very serious, even if not immediate, making it even more subtle a criminal action that escapes the control of the bodies responsible, perhaps because of the scarcity of human and financial resources available to them or perhaps for a underestimation of the phenomenon.