Method of opening a packing box

Abstract

A packing box enables easy release a slit lock in which slits in an insertion piece of an openable lid engage side flaps connected to openable lid side edge portions of lid side members, even if the interior of a box body of the packing box is tightly filled with a product. The top face lid of the packing box includes a part that can be torn along a tear inducing line extending from the flap opposing edge of the top face lid to the front end edge of the top face lid. This part is held and torn along the tear inducing line by a human hand, and is raised up with respect to the top face lid to form the slit lock release gripping piece that can be used for releasing engagement created by the slit lock engaging structure, so that the engagement by the slit lock engaging structure, which is the engagement between the insertion piece and the side flap in the slit on the side in the lateral direction of the insertion piece where the slit lock release gripping piece is formed, can be easily released even if the interior of the box body of the packing box is tightly filled.

What is claimed is: 
     
         1 . A method for opening a packing box, wherein the packing box comprises:
 a box body for housing a product, the box body having a front wall plate member, a rear wall plate member, and a plurality of side wall plate members;   a side flap that is connected via a first folding line to an upper end portion of the side wall plate members for preventing protrusion of the product;   a top face lid that is connected via a folding line to an upper end portion of the rear wall plate member for openably sealing an upper end portion of the box body; and   an insertion piece that is connected to a front end edge of the top face lid via a third folding line and is inserted into the box body for holding the top face lid, the packing box having a slit lock engaging structure that maintains a state in which the top face lid is closed by engaging a part of the side flap into a slit created by cutting a part of a connection base end of the insertion piece along the direction of said third folding line; and   wherein the slit is formed by an L-shaped cut having a first leg extending perpendicularly from said folding line, the length of said first leg being at least as great as the thickness of the side flap, and a second leg extending in the direction of said third folding line to a side end of the insertion piece, the insertion piece being folded along said third folding line with respect to the top face lid for forming the slit; and   
       wherein the packing box is opened by:
 manually gripping a part of the top face lid and tearing said part of the top face lid along a tear inducing line extending from a side flap opposing edge of the top face lid to a front end edge of the top face lid; 
 manually raising said part of the top face lid up with respect to the top face lid, thereby forming a slit lock release gripping piece; and 
 manually pulling forward and upward on said slit lock release gripping piece to release engagement created by the slit lock engaging structure. 
 
     
     
         2 . The method according to  claim 1 , wherein said first leg of the L-shaped slit extends rearward from said second leg toward said rear wall plate member, and wherein a part of the top face lid projecting forward from the folding line when the insertion piece is folded with respect to the top face lid forms an unlock projection piece, and wherein, when said slit lock release gripping piece is pulled forward and upward, said unlock projection piece abuts a said part of the side flap, and thereby releases the engagement created by the slit lock engaging structure.