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Types of Acrylic Solution Resins
Paraloid resins are acrylic solution resins that dissolve in solvents and are used as consolidants and coatings in the art conservation field. They consist of different acrylic polymers and copolymers with different molecular weights. These properties determine which solvent will dissolve each resin, the viscosity of solution, and which end use they are most suitable for. The types of Paraloid resins are as follows:
- Paraloid B72- By far the most widely used and available of all the Paraloid resins. Soluble in acetone, ethyl alcohol, toluene, and xylene, this ethyl-methyl methacrylate copolymer can be used as an effective adhesive or coating for nonporous surfaces where a water-based glue would be undesirable. Another plus is that this resin can easily formulated with an acetone and alcohol solvent mix to reduce toxicity and objectionable solvent odor.
- Paraloid B67- The second most common Paraloid resin. This isobuty methacrylate polymer is less polar than other paraloids. With small (10%) portions of aromatic solvents present, this resin can be dissolved in aliphatic solvents like naphtha and mineral spirits. This nonpolar resin also blends well with drying oils and alkyd resin coatings to create beautiful, high-gloss, faster-drying coatings.
- Paraloid B48- This resin is a methyl methacrylate/butyl methacrylate copolymer. It is a harder resin than the others and has an adhesion promoter. This adhesion promoter makes adhesion to bare metals possible.
Paraloid Resin as a Glue
Paraloid resins are not only hard but also flexible, making them tough. This property can make them preferable as adhesives, especially if one or both surfaces is nonporous, like wood and paper. The solvent evaporation rate determines how quickly the glue sets up and hardens. In typical room temperatures, this set up is a matter of hours.
Modifying Alkyd Oil-Based Paint
Some acrylic resins can be used with other coating resins. Paraloid B67, which is a isobutyl methacrylate resin, is the most nonpolar of the acrylic resins. This property, along with its solubility in hydrocarbon solvents, allows it to be blended with drying oils such as linseed oil and oil-based alkyd resins.
The coatings produced by adding a solution of Paraloid B67 in naphtha or mineral spirits to alkyd oil paints are harder and have a significant increase in gloss. Along with these properties, the coating produced dried faster as well. The best application method is to spray with an airbrush or sprayer to get an even coat. Properly thinned, the paint will level out almost like glasslike finish.
Fast-Drying Lacquer Paints
Paraloid resins—especially when dissolved in ketones, aromatics, and alcohols—can easily be tinted with pigment dispersions to make rapid-drying paints. The speed of drying allows many coats to be applied in reasonably rapid succession. These are also beneficial if a different color is being applied over on top of the original coat to create designs or patterns.
Fast-Drying Primers and Grounds
With specialized pigments and fillers, a fast drying primer can be produced. Paraloid B48 is the best option for this, given its greater durability. The pigments and fillers chosen can be added based on opacity, corrosion resistance, and added durability. Talc, wollastonite, and red iron oxide are good for primers on bare steel that are properly cleaned and prepared. Titanium dioxide, zinc oxide, and barium sulfate are white pigments that can add hiding power to coating. Other pigments and colorants can be added to make a specialty primer of any color.
Protective Clear Coat
Solvent solutions of Paraloid resins can be applied as clear lacquer coatings. Paraloid B67 is very water-resistant and is very good over painted metals or other painted finishes that need protection. Paraloid B72 is an ideal lacquer for wood. A few light coats give a decent gloss lacquer finish. Paraloid B48 is good for a clear coat for bare or primed metal. This resin can be applied over bare copper, zinc, and bronze.