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Question and Answer

Folding/Gluing Folding Cartons - Those Unforeseen Challenges

by staff

August-September, 2000
A graphic finisher can preach and preach about being involved with the design of a carton before it is printed. If communication between the printing process and folding/gluing process were always perfect, there would not be a need for this article. Unfortunately, this is not always the case. Many of the calls folding/gluing machine manufacturers receive deal with how to run a particular carton design because it was printed wrong or coated incorrectly. InsideFinishing has gathered a few experts on the subject to help determine the answers to common challenges finishers face when folding/gluing carton jobs.

1. What can I do if the sheets come in with a coating over the glue flaps that will not accept glue?

This is probably the most common challenge a finisher runs into. The best answer, of course, is to keep the glue flap or the areas that will receive adhesive during the folding/gluing of the carton blank free of printing or coatings. However, in the real world this is not always a feasible option for the printer, and, in many cases, simply doesn’t happen.

From a glue standpoint, there are glue systems that can extrude special glues made with solvents to cut through certain coatings. These glues can easily extrude liquid adhesive with viscosities up to 5,000 cps. In addition, the use of hot melt glues, in which there are many different types, can sometimes work quite well on certain aqueous coatings and varnishes. An experienced glue supplier is aware of the problems finishers face with coatings and should be able to match the appropriate glue with the corresponding coating.

If the graphic finisher is diecutting as well as folding/gluing the cartons, glue assists can be used on the glue flaps. Glue assists are a special set of knives or steel rule that are installed on the cutting die that will penetrate (not perforate) the coating. When the surface of the coating has been broken with the glue assists, glue will be able to pass through the coating into the fibers of the board, allowing proper adhesion. If the diecut is too deep and penetrates through the carton, the glue could pass into the inside of the carton and create an undesirable look to the finished carton. This method can be very successful; however, caution must be taken to ensure the glue assists do not penetrate the carton, which can result in a high number of rejects.

If a special glue does not work or the sheets are already diecut, all hope is not lost. Many folding/gluing machines on the market today are equipped with a skiver or grinder that can literally remove the layer of coating on the flaps in-line before the folding/gluing process. A sciver is an apparatus with a blade that removes the coating on the glue flap as the carton travels over it. Typically, the sciver is an electric or pneumatic cutter that is installed on the folder/gluer during set-up. The operator adjusts the sciver to remove the coating only in the areas needed and only as deep as necessary to achieve proper glue adhesion. Although this method can achieve desired results, it can be an expensive and time consuming method in terms of set-up and makeready.

A more simple method of removing the coating is to utilize a grinding wheel. An electric or air driven grinding wheel can be mounted immediately after the glue flap prebreaker in the pre-fold section of most folder/gluers. The top surface of the wheel should be positioned so that it will contact the glue flap immediately after it has been pre-broken and re-opened. Grinding systems have become very sophisticated because of the ever-increasing need to grind down the gluable areas on the carton.

The key to a productive sciver or grinding wheel is to have a vacuum dust pick-up system to remove the grinded down excess from the folding/gluing area. The dust can cause problems with glue adhesion, as well as create potential machinery problems down the road. A well-designed vacuum system will remove the excess coating created by the sciver or grinding wheel, and virtually eliminate dust problems usually associated with this process.

2. What solutions are there for carton stock that come in curled or with varying board caliper?

Although carton stock is usually fairly thick, paperboard will still absorb moisture in high humidity and curl in dry periods or conditions. Of course, the best solution to this challenge is to try to keep the stock in a climate controlled environment. Again, every finisher knows that it just doesn’t happen this way every time.

Curled carton blanks can still be successfully fed into a folder/gluer by simply working with the curl as opposed to fighting it. This can be achieved by raising the trailing edge of the carton blank stack in the feed hopper of the folder/gluer a little higher than you normally would. Utilize the rear pile supports which are provided with the folder/gluer and are positioned on the mounting bar that spans the width of the feed at the front of the folder/gluer. Raising the rear of the feed pile will force the lead edge of the carton blank down and under the feed gate. Folding/Gluing machines with a rear pile support mounting bar that mechanically vibrates will jog the blank pile in the feed and aid with separating the blanks, ensuring that only one blank at a time is fed. This will help eliminate skips and doubles, which, when they occur, can decrease production speeds tremendously due to jams downstream in the process.

Bearing trucks located immediately behind the feed gate and the upper carriers throughout the fold sections hold the carton blanks as they are transported through the folder/gluer. It is recommended to pay particular attention to the carrier nose roll adjustments to assure proper transition from section to section is accomplished successfully.

If the carton blanks begin to curl from side to side, due to the grain direction of the carton material, removing some of the feed belts in the center will lower the carton blanks down so that they can easily be fed under the feed gate.

Varying board caliper is another challenge finishers often face when folding/gluing folding cartons. To help overcome this potential problem, the feed gate gap should be adjusted to allow the largest caliper to be fed under the gate, yet not so wide as to allow doubles to be fed. Again, raising the rear of the feed pile with the aid of rear pile supports and then jogging the feed pile to help separate the blanks will help feed blanks with varying caliper.

InsideFinishing would like to thank Bonnie Barraclough of Can-Am Packaging Equipment (603-635-1316), Frank LaCroix of Matik North America (860-232-2323), and Jeff Wilcox of American International Machinery (414-764-3223) for their contribution to this article.