| Résumé : |
For certain applications requiring unusually high bond strength or fast setup time, or where a substrate is subjected to extreme temperature or humidity, polyurethane reactive (PUR) adhesives are finding many new uses. The versatile performance of PUR provides an effective solution for unusual assembly challenges. This material's strength maintains the structural integrity of bonded joints during years of harsh service.
As a 100% solids, moisture-curing material, PUR reacts when exposed to ambient humidity and crosslinks into a permanent structure. In addition to the chemistry, the open time of this adhesive is dependent, to a significant extent, on the thermal conductivity of the substrate being coated. The open time with metals may be short, whereas for wood, high pressure laminates, foamed plastics and other substrates possessing good insulating qualities, the open time may range up to five minutes. Once a substrate is PUR wetted, the parts should be joined rapidly to gain an optimum bond. A full cure typically occurs in one to three days, continually strengthening the bond to far surpass the strength and environmental durability of convertional hot melts.
When fully cured, PUR demonstrates an ability to withstand high temperatures and humidity. It Is resistant to many oils, solvents, acids and plasticizers. The material is solvent-free and non-flammable, although precautions must be taken to properly ventilate PUR application areas in order to control isocyanate vapor concentrations. A lower application temperature facilitates the bonding of temperature-sensitive substrates not ordinarily bondable with high temperature hot melts. |
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PUR adhesives offer solutions for assembly challenges in ADHESIVES AGE, Vol. 41, N° 5 (05/1998)
