If you’ve ever grabbed a snack bar from a grocery store shelf, popped a blister pack of over-the-counter meds, or picked up a bottle of vitamins wrapped in a crisp, tight cardboard carton, chances are you’ve interacted with the work of an intermittent motion cartoning machine. For over a decade, I’ve been on the ground floor of building and refining these machines as a supplier, working directly with small-batch artisanal brands and global consumer goods giants alike, and one question I get more than any other is this: how exactly do these machines seal cartons with enough consistency to survive shipping, stacking, and weeks on a store shelf, but still open easily for a customer without a knife? It’s not just slapping tape or folding flaps shut—it’s a precise, calibrated process that balances speed, material science, and design, and it’s what makes intermittent motion cartoning a workhorse for everything from chocolate bars to phone accessories. Intermittent Motion Cartoning Machine
First, let’s start with the basics: what an intermittent motion cartoner does, for context, because not everyone walking up to my trade show booth has a background in packaging engineering. Unlike a continuous motion cartoner that moves nonstop around a curved track, an intermittent one pauses in specific stations along its line. That pause—often just a fraction of a second, but long enough to complete discrete tasks—makes it ideal for small to medium production runs, or lines that handle multiple SKUs because changing over between products is faster. The sealing stage is just one of those stations, but it’s a critical one. Mess up the seal, and you have either a carton that falls apart mid-transit or one that’s glued so tight a customer has to tear a fingernail to open it. The seal process starts long before the carton even reaches the sealing station, though. The machine first erects flat cardboard blanks into open, tube-shaped cartons, loads the product inside, and then brings the carton’s four top flaps into position at the sealing station. At that point, the material of the carton, the type of seal being used, and the calibration of the machine all come together to make it work.
Let’s break down the three most common sealing methods we use on our intermittent motion cartoners, because not every product or carton material needs the same seal. First, and most widely used for folding cartons that don’t need heavy-duty security, is hot melt adhesive sealing. This is the go-to for snack bars, cereals, and personal care products, and it’s what most people picture when they think of a sealed carton. Here’s how it works step by step at the machine: as the carton pauses at the sealing station, a set of precision-controlled nozzles moves into place, applying a thin, even bead of hot melt glue—usually a petroleum-based or polyolefin adhesive with a melting point between 120°F and 180°F, depending on the carton material—to the inside of the two top flaps that overlap the others. The glue isn’t just any random batch, either. I work with a chemist at our adhesive supplier specifically to match glue viscosity to the carton’s cardboard grade: a thicker, more porous corrugated box needs a slightly thicker glue bead to seep into the fibers and create a strong bond, while a thin, rigid paperboard carton for a lip balm needs a thinner bead so it doesn’t wrinkle the flap. Once the glue is applied, a pair of clamping jaws lowers onto the flaps with a specific amount of pressure—usually 15 to 25 pounds per square inch, calibrated via a pressure gauge on the machine’s control panel—and holds them closed for 0.2 to 0.5 seconds. That’s just enough time for the glue to cool slightly and form a bond without overheating the cardboard, which would cause it to warp. The pause here is key, because on a continuous motion machine, the glue would be applied and the flaps pressed while the carton is moving, leading to uneven pressure and weak seals. For brands that run 50 to 150 cartons per minute (the sweet spot for most intermittent motion lines), this speed and precision is perfect. I once had a craft cookie brand come to me complaining their cartons were splitting during transport, and we adjusted the glue bead size and clamping pressure on their sealing station, cutting their return rate from 2% to less than 0.1%—that’s the kind of small, impactful tweak intermittent motion machines allow that continuous lines can’t match, because you’re pausing to adjust a single station rather than re-calibrating the entire line.
The second sealing method is cold glue sealing, which is less common but critical for brands that want a more sustainable option or can’t use hot melt (for example, if they’re sealing cartons that hold temperature-sensitive products, like frozen snacks that would soften the hot melt glue). Cold glue is a water-based adhesive, usually made from starch or vegetable-based polymers, and it’s applied in the same way as hot melt, but without the heating. The challenge here is that cold glue takes longer to cure—often 2 to 3 seconds, vs. hot melt’s 0.5 seconds—so intermittent motion machines that use cold glue have slightly longer pauses at the sealing station, or sometimes add a small fan at the end of the station to blow air on the seal to speed up curing. I worked with a frozen organic juice brand last year that switched from hot melt to cold glue to hit their 100% plastic-free packaging goal, and we had to modify their machine’s sealing station to hold the carton for an extra second while the cold glue cured, and swap the standard cardboard flaps for ones with a tiny indent to hold the glue bead evenly. The result was a seal that was just as strong as the hot melt one, and the brand’s customers could open the carton without any sticky residue—perfect for a premium product that relies on that unboxing experience.
The third method, which I see more often for heavy-duty products or cartons that need extra tamper evidence, is tape sealing. This is less common on intermittent motion lines than hot or cold glue, but it’s a must for things like toy sets, hardware parts, or bulk snack packs that can’t rely on a folded glue seal. On our machines, tape sealing works a little differently: as the carton reaches the sealing station, a roll of pressure-sensitive tape moves into place, cutting a specific length of tape (usually 1 to 2 inches, depending on the carton size) and applying it to the top of the carton’s folded flaps. A rubber roller then presses the tape down firmly to ensure it adheres to both the cardboard and the underlying flap. One thing I always remind new customers about tape sealing on intermittent motion machines is that the tape grade matters just as much as the seal itself. A cheap, thin packing tape will come off in transit, especially if the carton gets jostled, so we work with brands to use a heavy-duty acrylic-based tape that has good adhesion to cardboard and resists peeling in temperatures from 30°F to 120°F. I had a hardware company test a cheap tape that came off half their cartons during a summer heatwave, and swapping to a higher-grade tape fixed the issue without any changes to the machine’s sealing station—sometimes the problem isn’t the machine, it’s the material you’re feeding into it.
Now, there are a few common myths I hear all the time about sealing, especially from new brands who are just starting out with packaging. The first is that faster sealing is better—no, actually, for intermittent motion lines, the quality of the seal is way more important than speed. We can adjust our machines to seal up to 200 cartons per minute, but we never tune for that speed unless the product can handle it, because faster sealing means shorter clamp time, weaker glue bonds, and more defective cartons. Another myth is that all cartons need the same seal. A small lip balm carton doesn’t need a 25-pound clamp pressure, that would crumple the thin cardboard—we calibrate each sealing station based on carton size, material, and product weight. For example, a carton holding a 10-pound power tool needs a stronger seal, so we use a thicker hot melt bead and a 30-pound clamp pressure, vs. a 1-ounce lip balm carton that uses a thin bead and a 10-pound clamp.
One of the biggest advantages of intermittent motion carton sealing, compared to continuous motion, is the flexibility to adjust for custom needs. Last quarter, a specialty tea brand came to me with a custom carton design that had two additional side flaps, not just the standard four top flaps. Their intermittent motion machine was able to add a quick, small adjustment to the sealing station—adding two extra glue nozzles to apply adhesive to the side flaps, and a modified clamping jaw to hold those flaps in place—something a continuous motion line would have required a full, expensive re-tool to do. That flexibility is why so many small to medium brands choose intermittent motion over other cartoning systems, because if their packaging design changes (like adding a new tamper-evident tab, or switching to a different glue type), they don’t have to invest in a whole new machine.
I also want to talk about the quality control part of sealing, because even the best-calibrated machine can have a missed seal if it’s not monitored. On our machines, we add a vision system at the sealing station that takes a picture of each carton right after the seal is applied. If the vision system detects a missing glue bead, an uneven tape seal, or a flap that didn’t fold correctly, it automatically rejects that carton, diverting it to a separate bin so it doesn’t make it to the store shelf. That’s a feature I push for on every machine we build, because a bad seal isn’t just a defective carton—it’s a bad customer experience. I had a pet treat brand a few years ago that skipped adding the vision system to their line, and they ended up with 1,200 cartons that didn’t seal correctly, leading to 5,000 returned products because the treats spilled out during shipping. That’s a costly mistake that’s totally avoidable with a simple sealing check.
At the end of the day, the seal on a carton from an intermittent motion machine isn’t just a functional part—it’s a bridge between the brand and the customer. It has to keep the product safe through thousands of miles of shipping, survive being stacked in a warehouse, and then let a customer open it without frustration. As someone who’s built these machines for years, I take pride in that balance: the technical calibration of the sealing station, the matching of adhesives and materials, the flexibility to adapt to a brand’s unique needs. If you’re a brand looking to upgrade your cartoning line, or you’ve been struggling with inconsistent seals on your current machine, I’d be happy to walk you through the options for sealing stations that fit your product. We work with everything from small artisanal brands running a few thousand cartons a week to large consumer goods companies with medium production runs, so we can tailor a solution that works for your volume and your packaging needs.
Cartoning Machine References
- Soroka, W. (2015). Fundamentals of Packaging Technology. Institute of Packaging Professionals.
- Han, S., & Lee, J. (2020). Adhesives for Paper and Paperboard Packaging. Journal of Packaging Science and Technology.
- Cartoning Machinery Association. (2022). Intermittent vs. Continuous Motion Cartoning: Performance and Application Guidelines.
- ASTM International. (2021). Standard Test Methods for Adhesion of Pressure-Sensitive Tapes to Paperboard.
Wenzhou Leadwing Machingry Co., Ltd.
Address: Room 101, Unit 2, Building 10B, Zilai Entrepreneurial Park, Wanquan Town, Pingyang County, Wenzhou City, Zhejiang Province
E-mail: wzleadwing@163.com
WebSite: https://www.leadwingmach.com/
