Unsaturated polyester resin (UPR), is an easily printable liquid polymer which, once cured, keeps the solid shape taken in the mold. The curing is done by cross-linking it with styrene, by the use of particular substances, organic peroxides, named hardeners.
The items so realized have exceptional strength and durability characteristics. Unsaturated polyester resins are mostly used in combination with reinforcing materials such as glass fibres that give life to the FRP products. In this case, the polyester resin has an array function, channelling the forces applied to the material to the fibres that are designed to withstand these forces, increasing the strength and avoiding breakages of the product.
Together with or separately from the glass fibres, the liquid unsaturated polyester resin may be loaded with powders or granules of various sizes, which give details of rigidity and resistance characteristics, or aesthetic qualities to the imitation of natural marble and stones, sometimes with better results.
The main features of the unsaturated polyester resins include:
Liquid, in their use:
• Poor linear shrinkage
• Excellent wettability of the fibres and charges
• Cold cross-linking by addition of hardener
• Minimisation of the effect of sagging in vertical stratification (thixotropic properties)
Solid, after cross-linkage:
• Exceptional lightness
• Good electrical insulation
• Dimensional stability against temperature changes
• A higher strength / weight ratio than steel
• Resistance to chemicals
• Excellent surface finish
• Water repellence
• Resistance to wear and high temperatures
• Good mechanical resistance