| 摘要 |
PROBLEM TO BE SOLVED: To obtain a densely spiral binding state by providing an air gap in a core material of a binding string obtained by co-extruding the core material of multifilaments obtained by bundling glass fibers with specific mixed resin, thereby improving its strength. SOLUTION: An air gap 3 is provided in a core material 1 obtained by covering an outer periphery of a core material 1 with a coating material 4. The material 1 is formed of multifilaments containing non-alkaline glass as a component and bundled by twisting monofilaments 2. Number of bundles is 50 to 1,000. And, the material 4 is formed of mixed resin of polyethylene terephthalate resin and polybutylene terephthalate resin so that its mixing ratio is 70 to 95 wt.% of the polyethylene terephthalate resin and 5 to 30 wt.% of polybutylene terephthalate resin. The gap 3 is preferably provided at about 0.01 to 10% of a sectional area of the core material. The gap 3 is provided to increase a density of a twisted part of the binding string to enhance a strength of the core material and to obtain a densely spiral binding. |
