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Polyurethane pressure-sensitive adhesives

  • US 5,591,820 A
  • Filed: 05/09/1995
  • Issued: 01/07/1997
  • Est. Priority Date: 11/09/1992
  • Status: Expired due to Fees
First Claim
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1. A pressure-sensitive adhesive comprising a polyurethane polymer formed by the reaction of an isocyanate component and a polyol component having a molecular weight between about 1,000 and 10,000, said components being reacted at a molar ratio of isocyanate moieties to hydroxyl moieties of less than one, said polymer being free from any added tackifying and plasticizing agents, said polymer having a glass transition temperature of less than about 0°

  • C., a moisture absorption at equilibrium of at least 20% of its weight, and a peel adhesion to human skin of between about 0.3 and 4 newtons/cm width of the polymer, wherein said isocyanate and said polyol components each have a functionality of at least two and wherein at least one of said components has a functionality that is greater than 2, and further wherein said polyurethane polymer is crosslinked to a crosslink density α

    of between about 10-4 and 10-3 wherein α

    is defined by the equation ##EQU5## where i=1 to n where n is the number of the reactant components;

    Xi =the mole fraction of the ith component;

    Fi =the functionality of the ith component;

    r=the NCO/OH ratio; and

    Mw=the molecular weight of the polyol.

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