METHOD FOR PRODUCING FRAUDPROOF WINDOW PAPER AND PRODUCTION APPARATUS

PROBLEM TO BE SOLVED: To surely form a thread-exposing window by surely removing the slurry existing on the upper face of the thread of a paper slurry layer containing inserted fraudproof thread. SOLUTION: A fraudproof thread 5 is inserted at the nearly middle part of the depth (or thickness) of the slurry 4a and 4b supplied on a Foudrinier wire of a Foudrinier machine, a liquid 2 such as water is ejected from a liquid ejection nozzle 1a placed above the surface of the slurry 4a at the position of the thread 5 inserted in the undried paper holding the inserted thread, the slurry 4a on the thread 5 is pushed out with the ejected water and the position is occupied by the water to form a part free from slurry on the thread 5. The slurry is dehydrated to form the window (opening) 3 holding the exposed thread.