Resins

Polyurethane Resin

Its various physical and chemical properties, as well as its electrical characteristics make polyurethane resin a material of choice in the electronics industry for potting fragile elements and in the electro-technical industry for potting medium and low voltage transformers, as well as capacitors.

Preparing of the resin

  • Polyurethane resins are supplied as two components reacting together at room temperature. They are easily mixed manually and in automatic flow machines.
  • The resin may be heated to 40℃ approximately to avoid the phenomenon of cold crystallisation.
    Attention: This operation can shorten the mixture’s life in the pot.
  • The pre-polymer contains non-abrasive fillers. Mix the fillers together by slow mechanical agitation at the bottom of the pot, to avoid including air (avoid decanting the fillers).
  • Add the hardener in the proportions indicated in the table and mix together with a slow mechanical action taking care to avoid the inclusion of air.

Using the resin

Depending on the type of resin and the particular application, it is recommended: 
  • To preheat parts (60°C maximum) to remove any moisture and promote penetration of the resin by reducing its viscosity.
  • Pour the resin at room temperature and atmospheric pressure.
  • In certain cases, to optimise the resin’s characteristics, it can be used in a vacuum (a few mbars).

Polymerization

  • At the recommended room temperature (23°C) 
  • It is possible to accelerate the polymerisation by placing the parts in an oven at a maximum temperature of 60°C. 
  • A post-hardener, in certain cases, after complete hardening, gives the resin optimum thermal and mechanical performance. (4 - 5 hours at 90°C.)

Precautions concerning the hardener 

  • By virtue of the chemical properties of the hardener, we recommend not leaving it too long in contact with the air because of its sensitivity to humidity, and closing the package after use.

Storage conditions

  • Three to six months, depending on the product being kept closed in its original packing, out of the sun and away from heat sources (store at less than 25°C).

Packaging

  • In tubs of 1, 5 and 30 litres and drums of 200 litres.
Impregnation / Potting / Encapsulation
Polyurethane resins are distinguished by the following properties:
  • Low exothermy. In equivalent proportions an epoxy resin can reach 90°C or more while polyurethane resin will not exceed 40-50°C.
  • Low shrinkage, as a general rule lower than 1% (epoxy <5% and polyester < 8%).
  • Penetration (wettability).
  • Adhesive property.
  • Self-extinguishing.
  • Thermal conductivity through the addition of appropriate fillers.

Health and safety
Polyurethane resins present no particular toxic character. However, we advise working in a ventilated area and to avoid all contact with the skin.

Refer to the CRAM brochure for the use of polyurethane resins (polyols and poly-isocyanates).