| 摘要 |
Thermoplastic fibers and reinforcing fibers are mixed together in the dry state, to form a continuous web. The mixed fleece (a) so obtained, is needled, consolidating it. It is heated to a temperature above the softening temperature of the thermoplastic. The heated mixture is hot-pressed. In a novel departure, the mixed fleece is pressed together with a hydrophobic mixed fiber fleece (b) of polyethylene terephthalate fibers and polypropylene fibers, on both sides. Alternatively, a hydrophobic mixed fiber fleece (b) is applied to one side of the core layer and a thermoplastic film (c) is applied to the other side, and they are all hot-pressed together. At the pressing stage, individual webs have the following weights: mixed fleece (a) 300-2000, hydrophobic mixed fiber fleece (b) 30-300,and film (c) 50-250, all expressed in gm/m 2>. The pressing stage takes place in a double-belt press, calender or smoothing rollers. Pressing in the double-belt press occurs in a heating zone at above 80[deg] C, at a pressure below 1.0 bar. In the subsequent cooling zone, the temperature is less than 30[deg] C and the pressure is less than 1.0 bar. The sheet composite produced (a') has a core layer comprising 20-60 wt% thermoplastic matrix with 80-40 wt% reinforcing fibers. These are irregularly-distributed in the matrix and are needled together. Alternatively the sheet composite produced (b') has one or more hydrophobic covering layers comprising 30-70 wt% of a polypropylene matrix and 70-30 wt% of a fibrous fleece of polyethylene terephthalate fibers. The sheet composite produced (c') optionally also has a covering layer of thermoplastic. In the composite material, the core layer (a') contains 20-80 vol% air pores. An independent claim IS INCLUDED FOR the corresponding composite. |
