Method and apparatus for preparing fold lines
The method and the apparatus are used for preparing fold lines on laminated materials on the basis of cardboard. At least one region intended for providing the fold line is subjected to heat such that an at least partial local reduction of shear fracture stresses of the material is produced in said region. The application of heat is done using a heating device, which is disposed adjacent to a guide device for the laminate. The local reduction of the shear fracture stresses supports local delamination, which supports the formation of a folding joint.
1. A method for preparing fold lines in laminated materials based on cardboard for producing containers for foodstuff, the laminated materials having an inner layer and an outer layer, wherein the inner layer is formed from at least two plies, the method comprising the step of thermally treating at least one area intended for preparation of a fold line for producing a corner region of the container so that shear fracture stresses of the material are at least partially decreased locally in this area, as a result of which local delamination in this area is supported, wherein, as a result of delamination in the corner region an inner ply of the inner layer of the laminate is partially separated from a neighboring ply of the inner layer in an outer direction of the laminate so that the inner ply of the inner layer extends away from the neighboring ply in the corner region so as to form a hollow space between the inner ply and the neighboring ply.
2. The method according to claim 1 , including supporting formation of a fold joint by a local decrease in the shear fracture stresses.
3. The method according to claim 1 , wherein the thermal treatment produces a local, reversible decrease in stiffness and strength.
4. The method according to claim 1 , further including carrying out a dynamic temperature treatment.
5. The method according to claim 4 , including heating the laminate in a heating area to a temperature of no more than 100° C.
6. The method according to claim 4 , including heating the laminate in a heating area to a temperature of 110-120° C.
7. The method according to claim 4 , including heating the laminate in a heating are to a temperature of more than 120° C.
8. The method according to claim 4 , wherein the temperature treatment results in evaporation of at least some residual moisture in the laminate.
9. The method according to claim 1 , wherein fiber bonds in the laminate are broken.
10. The method according to claim 1 , wherein, the thermal treatment is carried out using a hot-air nozzle.
11. The method according to claim 1 , further including, in addition to the thermal treatment, mechanically scoring in the area of the fold line.