| 摘要 |
According to the invention a dust-proof reinforcing sheet material is provided. The sheet material is applied over and around a handling opening of a box. The sheet material comprises a base sheet having through-holes punched out, an adhesive layer applied on one side of the base sheet and an elastic film applied on the other side of the base sheet. The elastic film is stretchable five times as the original size and is transparent or translucent to allow light rays to transmit therethrough. The light rays passed through the elastic film and the through-hole is sensed by photo-sensor to cut the sheet material at a pre-set position.
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