Unsaturated polyester resin
You can define the polyester resin as a polymer obtained by the polycondensation reaction between polyacids and polyalcohols. The development of water is the by-product of this polycondensation process. Specifically, the unsaturated polyester resin, also known by the English acronym UPR, is an easily printable liquid polymer which, once cured (cross-linked with styrene, by the use of particular substances, organic peroxides, named hardeners), keeps the solid shape taken in the mold. 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 (an acronym deriving from the English), a polyester reinforced with glass fibres, better known with the name of fiberglass. 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 unsaturated polyester resin is used with great success in many industrial sectors, such as in watersports for the creation of windsurfers and pleasure boats. This polymer has been at the centre of a real revolution in the boat industry, because it can provide great performances and a very high flexibility of use. The unsaturated polyester resins are also commonly used in the automotive sector (car industry), for their great design versatility, light weight, lower system costs and mechanical strength. This material is used also for buildings, especially in the manufacture of hobs for cookers, tiles for roofs, bathrooms accessories, but also pipes, ducts and tanks.

Unsaturated polyester resins: characteristics

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
  • Rigidity
  • Good electrical insulation
  • Dimensional stability against temperature changes
  • A higher strength / weight ratio than steel
  • Resistance to chemicals
  • Excellent surface finish
  • Water repellency
  • Resistance to wear and and high temperatures
  • Good mechanical resistance

Unsaturated polyester resin: applications

The applications of the unsaturated polyester resin are varied. The polyester resins in fact represent one of the absolute compounds used in a wide range of industries. The most important, as well as those illustrated above, are:
  • Composite materials
  • Wood paints
  • Flat laminated panels, corrugated panels, ribbed panels
  • Gel coat for boats, automotive and bathroom fixtures
  • Colouring pastes, fillers, stucco, putties and chemical anchorings
  • Self-extinguishing composite materials
  • Quartz, marble and artificial cement