Extrusion lamination with registered cold seal adhesive
The present invention is a method for forming a laminate for use as a flexible packaging wrapper for confections and other food bars. An outer clear film usually oriented polyolefin is printed, preferably reverse printed, with graphics. In a tandem extrusion lamination with registered cold seal process a molten, polyolefin extrudate is applied to bond the outer printed film to an inner film. The inner film is preferably oriented polyolefin and may have a metallized coating of aluminum buried against the extrudate. Finally, a pattern of cold seal adhesive is applied to the inner film surface. The flexible package made with the extrusion lamination process offers improved stiffness, puncture resistance, abrasion resistance and durability over a similar structure produced with adhesive lamination.
1. A tandem extrusion lamination with registered cold seal process comprising the steps of:
a) providing a web on a primary unwind;
b) transferring said web into a primer section wherein primer is applied to the web and then dried onto the web in a primer oven dryer;
c) transferring the primer-coated web to an extrusion laminator section wherein said primer-coated web is bonded to an inner film using an extrudate to form a laminate;
d) transferring said laminate to a web guide control where one edge of said laminate is aligned;
e) using an edge trim section which is linked to the web guide control to further align said laminate;
f) using an edge guide control sensor to detect the alignment of said laminate before said laminate enters a cold seal section;
g) using a photocell as said laminate enters said cold seal section to send a signal to a gravure cylinder drive to confirm registration and to send a signal to an encoder specifying the laminating web speed;
h) using a feedback system to send a signal to the encoder from the drive motor of the gravure cylinder indicating the revolutions per minute based on the number of cut-off repeats around the cylinder to the encoder;
i) using the encoder to match the photocell signal and the feedback system signal to control a drive motor of the gravure cylinder at a speed of from about 100 percent to about 105 percent;
j) applying cold seal adhesive to said laminate in a predetermined pattern by allowing said laminate to slide over a gravure cylinder and under a lay on roller;
k) drying said cold seal adhesive in a cold seal adhesive dryer to produce a flexible packaging material;
l) checking the quality of said flexible packaging material using a camera system to monitor the registration of the print image and the applied cold seal adhesive; and,
m) transferring said flexible packaging material into a turret rewind where it is fed and wound onto a core.
2. The process of claim 1 wherein said web is further printed with graphics on at least one face.
3. The process of claim 1 wherein said lay on roller comprises a soft crowned rubber or neoprene or polychloroprene roller with a durometer hardness of 45.
4. The process of claim 1 wherein said gravure cylinder has a diameter and a circumference matched to the desired graphic images.
5. The process of claim 4 wherein said gravure cylinder has a diameter and a circumference which is purposely oversized by about 2%.
6. The process of claim 1 wherein said gravure cylinder has a variable drive so that it is possible to speed up the cylinder or slow down the cylinder to maintain the registration with the laminate web.
7. The process of claim 1 wherein said gravure cylinder is engraved with 120 to 130 stylus, 110 to 125 line screen, surface roughness Rz of 10-20 in non-engraved areas and compressed cell 30 degrees to 40 degrees with sufficient cell depth to transfer the desired cold seal adhesive coating weight of from about 2.0 to about 4.0 pounds/ream.
8. The process of claim 1 wherein said photocell reads an eyespot mark of each printed image.
9. The process of claim 1 wherein said flexible packaging material registration is maintained at a predetermined value plus or minus 3 mm.
10. The process of claim 1 wherein said primer dryer temperature is set between about 125° F. and about 250° F.
11. The process of claim 1 wherein said cold seal adhesive dryer temperature is set between about 180° F. and about 250° F.
12. The process of claim 1 wherein said extrudate is an extruder resin selected from low density polyethylenes having a melt flow index of from about 7 to about 16.