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The New Generation of Gluing Standards

by Christopher M. Leary, W.H. Leary Co., Inc.

August-September, 2011
“Our customers don’t pay for quality defects; we do!” This phrase was posted in the finishing department of a plant I recently visited. In addition to the price constraints that exist today, automation, machine efficiency and adding value to packaging are all realities that are completely different now when compared to five or ten years ago. The folding carton industry is diverse and ever changing, while customer quality expectations and demands are greater than ever. These expectations can lead to additional costs for the carton suppliers. One of our customers said, “Carton forming and glue seam bonding are the first things my customers look at. If they see a problem there, the flood gates are opened for printing and other defects.”

If you are a folding carton producer servicing the packaging industry, then you’re familiar with the quality requirements of customers that automate carton filling. Delivering glued cartons is the minimum standard, and if a few defective cartons are found, that truckload is likely to come back to your dock. In the most extreme cases, packaging converters are ‘back-billed’ for machine downtime related to quality defects.

If you are a trade finisher or have a bindery department, you may have heard of in-line quality inspection systems but haven’t yet had that customer demand. Maintaining high quality standards gives your customers confidence and will help differentiate your company. “Our customers love seeing their work running at our plant with the quality control systems functioning,” said Bob Codo, owner of Accord Carton in Alsip, IL.

How Glue Defects Occur
Simply put, glue defects can be boiled down to two basic elements: quality of adhesive and type of application system.

Consistency and quality of the adhesive are critical to accurate gluing and a good substrate bond. Different formulas are manufactured for bonding paperboard with different coatings and different substrates (i.e., paper to plastic). If you are using a non-contact extrusion gluing system, it’s important that your adhesive supplier provides an ‘extrusion grade’ or ‘jetting grade’ adhesive. This type of adhesive is filtered more at the factory, allowing it to machine better through a non-contact nozzle.

Two common types of application systems are used on folder-gluers: wheel systems and extrusion systems. Mechanical glue wheels are usually supplied by the machine manufacturer and are limited to gluing the side seam glue flap only. This device is used primarily when customers require ‘end-to-end gluing’ for sift-proof packaging containing products such as salt, flour, sugar, etc. Typically, the viscosity of glue pot adhesive ranges from 2000 – 2500 centipoise.

Extrusion systems come in two basic forms: standard pressure and high pressure. Contrary to what some equipment suppliers claim, both work well if you have the right adhesive. It may go without saying, but the main difference is that a high-pressure system has the capability of running a thicker adhesive due to the high fluid pressure range. Typically the viscosity range for a high-pressure system is 600 – 1000 centipoise.

A standard pressure system has been more common in years past, working well with a viscosity range of 300 – 600 centipoise. The right adhesive for the glue delivery system will ensure the system can run at the fastest folder-gluer speeds.

System Maintenance
If you are required to use a glue wheel system, ensure that the scraper is adjusted and cleaned regularly to prevent glue build up, which could then transfer to a carton and cause the cartons to be stuck together. Regardless of the type of adhesive, glue pots should be cleaned daily. Also consider adding glue level monitoring to the glue pot to let an operator know if the amount of glue in the pot gets too low.

For extrusion-type systems, it’s important that the systems are cleaned and flushed regularly. Simple flushing systems can be incorporated into your existing glue system to help keep the hoses and guns free of glue build-up. It is recommended that a complete system flush be performed every three months or when the type of adhesive changes. When glue is re-introduced into the system, make sure the air is bled out of the pump, regulator and hoses. Look for a consistent flow of glue. The glue filter must be cleaned on a regular basis, with frequency dependent upon the type of adhesive.

Keeping the glue valves (guns) clean also is important. Components inside the gun will wear over time and should be rotated occasionally, depending on the manufacturer of the system. By implementing basic maintenance on glue systems, fewer quality defects will be produced and the lifespan of the system will be extended.

Different Methods of Glue Detection
There are a variety of different glue detection tools, without one covering all the varieties of substrates. Gluing inconsistencies such as short glue lines, long glue tails, skips in a glue line and glue volume are all characteristics that can be monitored. Let’s look at the technology available today.

UV detection sensor – monitors for a UV fluorescent adhesive additive. It provides simple, operator-friendly set-up and works well if gluing over foil on the board. While it can tolerate some UV found in the carton board, it does have a limitation if there is too much UV in the board.

Moisture detection sensor – looks for optical wavelengths that are sensitive to moisture. This refined technology is very versatile and easy to use.

Microwave detection sensor – looks for the moisture in the board and glue using microwave wavelength technology. This sensing technology works ideally for glue wheel-applied adhesive, with its only limitation being foil board.

Capacitance detection sensor – looks for the density of the water content found in the adhesive v. the board.

Color contrast inspection sensor – looks for shade variation and contrast. This sensor works well if there is consistent color in the gluing area of the carton and good contrast v. the adhesive.

Laser inspection sensor – looks at the profile height of a glue bead. It can be used when there is a variety of color on the background carton board.

Vision inspection camera – captures images of glue lines and can be used to monitor where glue is not supposed to be. This technology provides complete carton inspection, with cameras that can be programmed to look for ‘glue sling’, which is common if running a glue wheel at high speeds.

Infrared inspection sensor – typically used for hot melt glue monitoring by measuring the temperature of the hot melt adhesive v. the substrate.

100-Percent Fit-for-Use Cartons

Some converters have successfully shipped millions of cartons without a single gluing defect. Perfection is achievable. The goal of zero gluing defects is a reality. Automation drives the need for cartons that form flawlessly on filling machines. As we know, downtime equals waste and loss of revenue.

Plants that successfully implement quality control systems have found these three key elements play an important role: Champion, Train and Challenge.

Champion – It’s important to have a ‘go to’ person for situational questions and troubleshooting to assist operators with issues. Ideally, this is determined before the quality control equipment is even installed, to ensure this person knows that he ‘owns’ the system at a technical level.

Train – Ongoing training should be mandatory in order to get the desired result of 100 percent quality systems. Simply training operators after the system is installed is not sufficient. Periodic training helps operators understand systems better and can be more specific to real-life challenges faced with different carton styles and variables. Many states offer grants to help subsidize training expenses.

Challenge – Once a quality control system is installed, it’s important to challenge the system to make sure the inspection stations are functioning properly. A challenging procedure is a controlled method of creating a quality defect to ensure the system is able to catch those defects. Throughout normal machine running, different variables can impact the system’s ability to monitor quality defects. These include board shade change, carton flutter, cables going bad, dirty sensors, etc. If a challenging procedure is in place, operators will know the system is performing to meet the desired quality standards. This procedure is mandatory for all pharmaceutical and food customers.

To deliver cartons at a new quality standard, a cultural awareness is required. Operators need to have a clear understanding of the impact they have on customer satisfaction and how it relates to them.

In summary, the cost of quality can be astronomical when you consider a truck load returned, the labor to unload and sort through each pallet for gluing defects, time to process paperwork and floor space needed to store returned product. Glue inspection and quality control systems allow folder-gluers to run at maximum rated speed without jeopardizing quality. This means both machine yield and profits can be maximized.

Providing great quality will distinguish you as a reputable company and help you earn more business.

Christopher M. Leary is director of sales for W. H. Leary. Founded in 1928 and servicing the packaging industry for over 35 years, W.H. Leary Company provides glue application and quality assurance systems for the paper converting industry. Systems range from single-function gluing systems to gluing and inspections solutions designed for the most demanding applications. QA options include glue detection, bar-code reading, 2D-code reading, insert verification and vision integration, along with other options. For more information, email chrisl@whleary.com, visit www.whleary.com or call 708.444.4900.