Hot-melt adhesives comprising butene-1 polymers and showing peculiar thermal characteristics

Hot melt adhesive, characterised in that it comprises a polymer blend consisting of at least two butene-1 polymers, A) and B), such blend comprising:

• A) from 5% to 95% by weight, referred to the overall weight of the blend, of at least one non-isotactic butene-1 copolymer, having a polydispersity index Mw/Mn not lower than 3.5 and a monomodal composition, such copolymer consisting of butene-1 with one or more alpha-olefins selected from ethene, propene and alpha-olefins from C5 to C12, said copolymer furthermore having a content of copolymerised comonomer(s) not lower than 20% by mole, a viscosity at 190° C. comprised between 1,000 mPa·s and 200,000 mPa·s and being further characterised by the following thermal properties, measured by DSC after five days of aging at 23° C. and 50% relative humidity:
• an enthalpy of Fusion not greater than 40 J/g,
• a peak melting temperature not higher than 80° C.;
• a glass transition temperature Tg not higher than −10° C.;
• B) between 95% and 5% by weight, referred to the overall weight of the blend, of at least one polymeric composition of isotactic butene-1, having a global polydispersity index Mw/Mn lower than 3.5 and a bimodal composition, such bimodal polymer composition comprising:
• B1) between 10% and 90% by weight of a butene-1 copolymer with one or more comonomers selected from ethene, propene and alpha-olefins with a number of Carbon atoms equal to or greater than five, said copolymer B1) having a content of copolymerised comonomer(s) lower than 20% by mole and a polydispersity index Mw/Mn lower than 3.5;
• B2) between 90% and 10% by weight of a butene-1 homopolymer or a butene-1 copolymer with one or more comonomers selected from ethene, propene and alpha-olefins having a number of Carbon atoms equal to or greater than five, said homopolymer or copolymer B2) having a content of copolymerised comonomer(s) not greater than 5% by mole and a polydispersity index Mw/Mn lower than 3.5;
• such polymeric composition of isotactic butene-1, having a bimodal composition, a viscosity at 190° C. ranging comprised between 1,000 mPa·s and 300,000 mPa·s and being further characterised by the following thermal properties, measured by DSC after five days of aging at 23° C. and 50% relative humidity:
• an Enthalpy of Fusion greater than 20 J/g,
• a melting peak temperature higher than 90° C.,
• a glass transition temperature Tg not higher than −20° C.