Plastic thread bonding method and structure for folding edge of flexible intermediate bulk containers

A plastic thread bonding method for a folding edge of a FIBC, comprising the steps of:

• (Step 1) setting the folding edge of the FIBC flatly on a metal solid surface;
• and using a cooling device to maintain a condensation temperature at the solid surface;
• (Step 2) performing a needle insertion action at a site of the folding edge coupled to a plastic injection needle of an injection molding machine, and the needle insertion action piercing the plastic injection needle through the folding edge to form an eyelet, and the plastic injection needle injecting a melted plastic from a needle tip of the plastic injection needle, and the melted plastic being cooled instantly when touching the solid surface, and solidified and crystallized at the position of the eyelet corresponsive to the bottom surface of the folding edge to form a base point, wherein the base point has a range greater than that of the diameter of the eyelet;
• (Step 3) performing a needle withdrawal action of the plastic injection needle to separate the plastic injection needle from the eyelet, and the needle withdrawal action being performed in a direction opposite to that of the needle insertion action;
• continuing to inject the melted plastic from the needle tip while performing the needle withdrawal action, so that the eyelet is filled up with the melted plastic, while a pressurized cold air is being applied from an upper surface of the folding edge to the eyelet;
• cooling and condensing the melted plastic filled in the eyelet instantly to form a thread post by the cooling effect of the pressurized cold air, and the thread post, the folding edge, and the base point are condensed into one piece;
• (Step 4) performing a horizontal translation action of the plastic injection needle or the folding edge through a distance, continuing to inject the melted plastic onto the upper surface of the folding edge while the needle tip is moving and continuing to supply the pressurized cold air, so that the melted plastic is condensed instantly to form a thread bridge, and the thread bridge and the upper surface of the folding edge are condensed into one piece;
• and
• (Step 5) repeating the Steps 2 to 4, wherein the needle insertion action of the Step 2, the needle withdrawal action of Step 3, and the horizontal translation action of the Step 4 are performed at a next site of the folding edge to form a next base point, a next thread post, and a next thread bridge;
• and the plurality of base points, thread posts, and continuous thread bridges disposed along the folding edge form a plastic thread bonding structure with a high strength and low rate of elongation.