Undercutting phenomenon
The essence of the phenomenon of undercutting is that the resin in the molten state during sealing is over-extruded under the action of pressure, which leads to the decrease of the thickness of the laminated film on the edge of the hot sealing tool and the decrease of its overall thermal sealing strength. It is the result of the comprehensive action of sealing temperature and sealing pressure. The on-board detection phenomenon is that the material at the seal is brittle, and most of the laminated film or the inner material is brittle at the seal.
In addition to the sealing temperature, pressure setting too large factors, in the following cases usually appear undercutting phenomenon.
(1) The edge of the hot sealing knife is sharp, which usually leads to too much pressure at the sealing line and excessive extrusion of resin.
(2) Uneven installation of hot sealing knife, tilt phenomenon, inevitably lead to one side of the sealing line pressure is too large.
(3) For the back sealing pouch, if the sealing knife is pressed against the position of the back sealing crease line, because the thickness of the crease line is thicker than other places, the pressure on the sealing line is too large, and the phenomenon of undercutting will also occur.
In addition, after pouch-making cutting out the side material, some resin on the edge is still melted and extruded, resulting in burr on the edge, which indicates that the temperature or pressure is set too high at this time.
(4) For the laminated film containing aluminum foil layer, because aluminum foil is easy to be broken, if the aluminum foil is basically broken in a straight line (the inner film may be stretched) when the machine tests the sealing strength, and the heat sealing strength is low at this time, the sealing pressure should be reduced or the edge state of the sealing knife should be checked or whether the installation is parallel.
