engleski

Investigationsof the physucochemical properties of the fountain solutions

Physicochemical properties of the fountain solutions, such as electrical conductivity, pH value, surface tension and contact angle in dependence of solutions concentration on non-image areas of the typographical form for offset printing method were estimated. Two samples of typographical form with classical diazo coating and thermal plate coating were used. The obtained results show that the surface tension of fountain solution decreases by the concentration increase of the fountain solution, while electrical conductivity for fountain solution samples constantly increases. The dampening process occurs in mild acid medium (pH value is between 5.0 and 5.1), which points out that salts acting as buffers are added to the solution. Contact angle, as a proper moistening measure is being decreased by increasing concentration of fountain solution, enabling good moistening of non-image areas on the printing plate. Fountain solution successfully moistens the non-image surfaces at the concentration of 30 – 40 vol %. Sample 1 showed best characteristics, because the contact angle is small enough, which indicates a good spreading of the fountain solution across the surface of the printing form, as well as a good wetting as one of the most important factors in plane printing. Presents of surface active substances decreases surface energy of solvents, which decreases contact angle measured on non-image areas. Contact angle has linear dependence on surface tension for all three examined samples. Sample 1 shows slightly higher values than samples 2 and 3. Linear dependence of contact angle on surface tension shows that there is a good combination of all additives in fountain solution, most of all surface active substances.

contact angle; fountain solutions; electrical conductivity; pH value; surface tension

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