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Handbook of Solvents - George Wypych - ChemTech - Ventech!

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1234 Tilman Hahn, Konrad Botzenhart, Fritz Schweinsberg, Gerhard Volland<br />

18.3 INDOOR AIR POLLUTION BY SOLVENTS CONTAINED IN PAINTS<br />

AND VARNISHES<br />

Tilman Hahn, Konrad Botzenhart, Fritz Schweinsberg<br />

Institut f�r Allgemeine Hygiene und Umwelthygiene<br />

Universit�t T�bingen, T�bingen, Germany<br />

Gerhard Volland<br />

Otto-Graf-Institut, Universit�t Stuttgart, Stuttgart, Germany<br />

18.3.1 COMPOSITION - SOLVENTS IN PAINTS AND VARNISHES.<br />

THEORETICAL ASPECTS<br />

<strong>Solvents</strong> are normally defined as fluids having a maximum b.p. <strong>of</strong> 250 o C, which are able to<br />

dissolve other components <strong>of</strong> paints, especially binders. They evaporate under drying conditions<br />

when paint films are formed. 1,2,3,4 <strong>Solvents</strong> must not react with the painted or varnished<br />

product.<br />

The composition <strong>of</strong> paints and varnishes is determined by application requirements,<br />

drying temperature, and drying time. 2,5 Depending on the properties <strong>of</strong> paints and varnishes,<br />

different mixtures <strong>of</strong> solvents are added.<br />

Functions and properties <strong>of</strong> solvents in paints and varnishes: 2,5<br />

• Dissolve several components, especially binders<br />

• Influence and control paint viscosity<br />

• Wet pigments (influence on solubility, hydrogen bonding by solvents, prevent the<br />

separation <strong>of</strong> pigment)<br />

• Influence and control flow properties (e.g., butyl acetate, butanol, glycol ethers)<br />

• Influence skin formation. 6 The aim is to produce a homogeneous cure when the<br />

paint or varnish film hardens without the formation <strong>of</strong> a stable surface film during<br />

the drying period. The correct composition <strong>of</strong> the solvent will avoid trapping<br />

solvents under the surface film.<br />

• Influence drying process. Acceleration by low boilers, production <strong>of</strong> a flawless<br />

surface by medium and high boilers (chemical and physical drying processes)<br />

• Influence surface tension (e.g., increase by rapid evaporation <strong>of</strong> solvents)<br />

• Influence mechanical properties <strong>of</strong> paints (e.g., adhesion properties)<br />

• Influence blushing or blooming <strong>of</strong> paints by preventing the absorption <strong>of</strong> condensed<br />

water by various solvents, e.g., ethanol and glycol ether<br />

• Influence gloss (e.g., improvement with high boilers)<br />

• Prevent defects particularly in varnish coating (e.g., background wetting)<br />

• Influence electrostatic properties (spray painting)<br />

• Influence defined surface properties (structural change)<br />

• Influence durability <strong>of</strong> paints and varnishes<br />

• Influence product suitability, e.g., spraying and dipping lacquers which need to dry<br />

at room temperature<br />

In addition to their effect on performance and properties solvents interact with other<br />

components in paints and varnishes in significant ways.<br />

Interactions between binders and solvents in paints and varnishes are very important.<br />

2,5 With the aid <strong>of</strong> solubility parameters solvents or mixtures <strong>of</strong> solvents which produce

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