Butvar brand resins generally are soluble in alcohols, glycol ethers, and certain mixtures of polar and nonpolar solvents. In general, Butvar B-98 (PVB Resin B-05SY) resin will show the same general compatibility characteristics as Butvar B-90 (PVB Resin B-02HX) and, therefore, should prove advantageous where physical and chemical properties of B-90 are desired but lower solution viscosities are necessary. The same is true for Butvar B-79 in relation to Butvar B-76.
The lower hydroxyl content of Butvar B-76 and Butvar B-79 permits solubility in a wider variety of organic solvents as compared to the other grades of Butvar. One notable exception, however, is the insolubility of Butvar B-76 and Butvar B-79 in methanol. All other types of Butvar contain sufficient hydroxyl groups to allow for solubility in alcohol and in hydroxyl-containing solvents. The presence of both butyral and hydroxyl groups permits solution in mixtures of alcohol and aromatics. Viscosities of Butvar resin solutions containing mixed solvents depend on the ratio of alcohol to aromatic. Viscosity curves for Butvar B-76, Butvar B-90, and Butvar B-98 in Graph 2 show minimum points in the general vicinity of 50% alcohol: 50% aromatic.
A common solvent for all of the Butvar resins is a combination of 60 parts toluene and 40 parts ethanol (95%) by weight. For compositions of Butvar, methyl alcohol will tend to give the lowest viscosity and, therefore, will permit the use of higher solids when used as a component of a solvent blend. When much more than 10% to 15% alcohol is used in a formulation for spray application, blushing may result. They are useful as starting points in the development of solvent blends for the other types.
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