Composite sheet with sealing- and sheet layers also includes heat resisting, reinforcing and adhesive layers and is designed to seal packages reliably, whilst offering uniform, easy tear-off characteristics to consumer

摘要

The first sheet layer (16) is polyolefin (A) with distributed particulate filler comprising 25%-70% of its own weight. The sealing sheet (18) is unfilled polyolefin (B). Cohesive force K1 of material forming the first sheet is less than that (K2) of the second, and less than the bonding force (K3) between sheets. K2 and K3 are each greater than the tear initiation force K4 of the sealing sheet. Preferred features: A further sheet layer sandwiches the first with the sealing layer. Its cohesive force is K5, exceeding K1. Bonding strength K6 between first and second sheet layers exceeds K1 and K4. The second sheet layer has the same composition as the sealing layer. The composite has a reinforcing layer (24). This is the second layer (20). The polyolefin is polyethylene with filler comprising 25-60 wt%. The polyolefin (A) is a polypropylene with 30-70 wt% filler. Melting point of the first layer is no less than that of polyolefin (B). Crystallization temperature of the first sheet material is at least 5 deg C higher than that of polyolefin (B). Sealing sheet has thickness 5-15 mu m. The first sheet layer thickness is no less than that of the sealing sheet, and is some 10-250 mu m. The polyolefins (A) and (B) are derived from the same polymer family. The layer sequence is sealing layer, sheet layer, oxygen barrier layer, water vapor barrier layer. Between adjacent layers or between several adjacent layers, there is a bonding agent- or adhesive layer (22).