The evaluation of Laropal A81: Paraloid B‐72 polymer blend varnishes for painted and decorative surfaces – appearance and practical considerations

Abstract

Abstract The search for stable varnishes which will saturate and provide a desired finish for a variety of painted and decorative surfaces is ongoing. Varnish blends were investigated, composed of ratios from 2% to 98%, of Laropal A81 (a highly stable and commercially available low molecular weight urea‐aldehyde resin) in Paraloid B‐72, in order to capitalise on the positive properties of the individual resins and allow tailoring for specific surface problems in a single application. Aspects relevant to appearance and practice are reported in this paper. The structure of dried films was microscopically examined and their refractive index (RI) measured. Their effect on painted surfaces was evaluated through both instrumental measurement of specular gloss and saturation, and through subjective evaluation, which was influenced by diffuse as well as specular reflectance. Dried films of the entire range of blends were found to exhibit useful optical and aesthetic properties on a variety of paint surfaces, although it was felt that blends at either end of the range produced the most promising varnishes. Although the blends produced films that were phase separated, this did not cause any detrimental optical effects and may even contribute to the range of achievable surface effects. Subjective evaluation of appearance and working properties is shown to be important in any such investigation.