Contact versus Non-Contact Gluing a Corrugated Box Manufacturer's Joint

Pressure
In addition to using thinner adhesive, higher pressures are required to jet adhesives non-contact. With contact applications, the contact with the board helps draw the adhesive out of the valve and onto the board. Because the adhesive must be ejected as far as 10mm to the board, sufficient pressure is required to develop enough velocity for the stream to reliably apply the glue in the correct position. If the glue pressure is too low, the stream will not be straight and buildup will occur on the nozzle tip.

Trailing
Trailing is the presence of glue on the flap or fourth panel after the pattern is supposed to end and occurs after the valve has shut off. Trailing can occur in both contact and non-contact applications. In a contact scenario, trailing occurs because the applicator head is not at the right angle for angled heads and for straight heads, the cause is usually that the board is not making good contact with the head. However, trailing can occur in non-contact applications due to quality adhesive, a sluggish or plugged valve or the valve adjusted too high off the board.

Central Pumping Systems
Many plants operate with a glue tote located in a convenient place on the floor and are plumbed with PVC pipe to each Flexo-Folder-Gluer or Specialty Folder Gluer where the glue pressure is regulated down. In this case, switching one machine to non-contact adhesive will, in most cases, require a different adhesive product entirely, or at least a thinner formulation of the plant's existing manufacturer's joint adhesive. This means individual drums need to be brought to that machine and a pumping system needs to be installed.

Cost
In many cases, a higher quality adhesive is needed to accurately glue using non-contact. This will often lead to a higher price per pound for the new adhesive. The plant should weigh the process improvements expected from non-contact application with the additional glue cost.

Pattern Flexibility
Non-contact and contact methods of glue application both apply good quality beads to the manufacturer's joint. However, there are limitations to each method that need to be considered before dedicating a particular machine to one method.

Pattern Width Limitations
Non-contact glue stations are typically constructed using one large valve and a multi-orifice (2-4) nozzle or 2-4 individual single-orifice valves in a row. As a result, pattern widths are generally limited to 2-4 beads on ¼” centers or a total bead width of approximately 1 inch. While this is often satisfactory for smaller machines running boxes with smaller tabs, larger tab sizes will not have sufficient coverage. Contact systems offer the advantage of using interchangeable applicator heads that can cover tabs up to 4 inches wide on standard glue stations or 6 inches wide on jumbo glue stations.

Different bead lengths
By contrast, the non-contact glue station with multiple valves can actually apply beads of different lengths on one manufacturer's joint. This would be useful, for example, if a glue pattern was needed that was tapered at each end to match the tab angle.

Glue Station Considerations
As the mechanical application point of the glue, the glue station can mean the difference between large numbers of defects or consistent production on any machine. Both contact and non-contact stations have special requirements that need to be considered when selecting or upgrading equipment.

Tip Sealing
Because of its smaller orifice size and longer restriction length (the length of the small hole in the nozzle through which the adhesive is dispensed) non-contact orifices plug faster due to glue drying. This effect is made worse with fast-drying aggressive glues used for special board types. If the machine is not running boxes for even a few minutes, enough glue may dry in the tip to improperly glue the first box through the station. For this reason, tip sealers are often required that cover the nozzle tips while no board is being fed. As soon as board is fed, the tip-sealer uncovers the nozzle and the adhesive in the nozzle is fresh and the first box is perfectly glued. Without this additional feature, the “first boxes” should be sorted out of the stacks. Worse yet, partially clogged nozzle tips cause adhesive to drip onto other areas of the box, especially on fourth panel installations, causing potential “stickers,” or boxes that either stick closed to stick to each other.

Bottom-up
Typically, machines that require bottom-up application are not suitable for using non-contact gluing. Although it is sometimes done, the end result is usually glue residue that eventually builds up on the nozzle and valve which requires periodic purging and operator attention.

Board Guiding
Similarly, contact glue applications require that the board makes good contact with the glue head. When the board does not make good contact, the adhesive does not always adhere to the board but splashes out of the glue station in the direction of travel of the board resulting in contamination of the machine and the floor downstream from the glue station. It is especially important that springs or guides that constrain the box create a level, smooth flow through the glue station to apply a perfect glue joint. Any guiding issues are amplified by higher-speed machines that run in excess of 20,000 boxes per hour.

Setting Up a Non-Contact System
If the plant is 100 percent contact gluing, it may be worthwhile to run a non-contact trial on a particular machine to see if the customer reject rate is lower and if operators and maintenance staff can support the new method. When installing and setting up the system, care should be taken to keep the nozzle tips approximately ¼” away from the board. This keeps the tips close enough to get good pattern results, but far enough away that the board cannot accidently touch the tip and disturb the glue application.

Depending on adhesive viscosity and nozzle orifice size, glue pressures will have to be at least 80psi at full speed and often as high as 150psi. The plant's adhesive supplier should be consulted to supply a high-quality extrusion adhesive suitable for non-contact valves. Electric valves should be exclusively used because of their fast opening and closing times and their repeatability. These valves typically require special settings in the glue control.

Either Contact or Non-Contact gluing can produce a defect-free manufacturer's joint if consideration is given to the equipment and adhesive selection, as well as the product mix, to be run on the machine.