Hot-melt adhesives comprising a bimodal polymer composition formed by polyolefins having low stereospecificity

A hot-melt adhesive formulation, characterised in that it comprises a polymer composition formed by two non-stereospecific polyolefins, said polymer composition having a melt flow rate (MFR) ranging between 10 dg/minute and 6,000 dg/minute, measured at 190° C. and under a weight of 2.16 kg, and comprising:

• A) a first non stereospecific polymer formed by a homopolymer of an olefin selected from ethylene, propylene, butene-1 or hexene, or by a copolymer among the same olefins, said polymer A) being characterised by a crystallisation enthalpy from the melt at time zero not greater than 15 J/g and by an average number molecular weight Mn(A) ranging from 3,000 g/mole to 30,000 g/mole;
• B) a second non stereospecific polymer formed by a homopolymer of an olefin selected from ethylene, propylene, butene-1 or hexene, or by a copolymer among the same olefins, said polymer B) being characterised by a crystallisation enthalpy from the melt at time zero not greater than 15 J/g and by an average number molecular weight Mn(B) ranging from 3,000 g/mole to 30,000 g/mole;
• and where said polymer composition has a ratio by weight between the first polymeric constituent A) and the second polymeric constituent B) ranging from 1:20 to 20:1, said polymeric constituents A) and B) being selected in such a way that the difference between the average number molecular weights of A) and B), Mn(A)−Mn(B), is not greater than 3,000 g/mole
• said hot-melt adhesive formulation being further characterised by the fact that:
• it shows a crystallisation enthalpy from the melt at time zero not greater than 12 J/g, measured by differential scanning calorimetry (DSC) at the cooling rate of 1° C./minute;
• it shows a solidification rate around its rheological setting point not greater than 3,000 Pa/° C.;
• it shows a decreasing rate of its rheological parameter tan delta around its own rheological setting point, that is not greater than 0.1 (° C.)−1, and
• when applied between two substrates, of which at least one is a fibrous substrate or a porous plastic film or a perforated plastic film, at a basis weight comprised between 0.5 g/m2 and 50 g/m2, it gives to the bonded structure an adhesive peel strength, measured after seven days of aging at 23° C. and 50% relative humidity, that is greater than 0.25 N per 50 mm of width.