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Fifty terms that come up when specifying, buying or running packaging and printing machinery — materials, processes, bag formats, systems, compliance and commercial terms. Each entry explains what it is and why it changes something on the shop floor.
Grams per square metre — the weight of one square metre of paper or board, and the first number that decides how a material behaves on a machine. It is not the same as thickness: two 120 gsm papers can differ in caliper by 30% depending on how heavily the sheet is calendered. For bags, 80–120 gsm is grocery grade, 120–200 gsm retail, above 200 gsm premium. Cup body stock runs 190–300 gsm with a coating on top. Heavier stock needs more crease pressure, more glue, slower running speeds and often a different die. Ask for GSM and caliper together, and check a delivered lot by weighing a 100 × 100 mm sample.
back to index ↑The dominant paper for bags and wrapping, made by the sulphate process from softwood pulp. Unbleached kraft is the familiar brown; bleached kraft is white and takes print better. Its long fibres give tear resistance that recycled grades struggle to match at the same weight, which is why grocery bags are usually virgin kraft even when the brand claims sustainability elsewhere. On a bag machine, kraft glues well with hot melt but absorbs adhesive quickly, so open time matters. Watch moisture content: a reel that has absorbed water in transit will curl, jam the forming section and produce bags with a memory for the fold.
back to index ↑Coated paper with a clay-based layer on one or both sides, calendered to a smooth finish. It is the standard stock for labels, cartons and any surface that has to carry detailed print, because the coating holds ink on the surface instead of letting it sink into the fibre. The trade-off is that coated surfaces are harder to glue and crease: the coating can crack along a fold line, which is why art paper cartons need scoring and sometimes a crease-line varnish. On a sheet-fed press it behaves predictably; on a web press, watch for coating pick-off at high speed.
back to index ↑Solid bleached sulphate board — white throughout, with a smooth coated surface on one or both sides. It is the default material for folding cartons in cosmetics, food and pharmaceuticals where the inside of the pack is visible or must look clean. SBS creases and die-cuts cleanly, which is why it dominates high-quality carton work. Above roughly 350 gsm the crease needs a wider matrix and more pressure, otherwise the board cracks along the fold. It is also the most expensive of the common carton boards, so quotes that mix SBS with FBB are not comparable unless the grade is written down.
back to index ↑Folding boxboard — a multilayer board with mechanical pulp in the middle and bleached chemical pulp on the outer layers. It is lighter and cheaper than SBS at the same stiffness, and is the workhorse grade for food packaging, cereals and general retail cartons. The greyish core is invisible in the finished pack but shows on an unprinted edge, so it is a poor choice where the cut edge is exposed. On the machine it behaves much like SBS: crease pressure, die-cutting make-ready and glue absorption all follow the coating rather than the core.
back to index ↑A polyethylene layer extruded onto paper or board to make it liquid-resistant — the reason a paper cup holds coffee. Typical coating weights are 15–25 gsm per side, and the coating is what the sealing jaws actually bond, not the paper. Coating quality decides seal strength, so a cup that leaks usually has a coating or seal problem rather than a paper problem. On the machine, coating thickness affects heat transfer: too thin and the seal burns through, too thick and the seam is weak at normal temperature. Ask for the coating weight and the seal-initiation temperature, not just "PE coated".
back to index ↑Biaxially oriented polypropylene — a film stretched in both directions to build stiffness and clarity. It is the standard transparent wrap for cartons, snacks and labels, and the base for most pressure-sensitive label stock. BOPP accepts print well after corona treatment but has low surface energy before treatment, so untreated film will not hold ink. On a bag machine it is stiff and noisy, runs fast, and seals only within a narrow temperature window; on a labelling line the web tension has to be stable or the label distorts. Heat resistance is limited, which matters if the packed product is filled hot.
back to index ↑Cast polypropylene — a softer, more heat-resistant film than BOPP, usually used as the inner sealing layer of a laminate rather than on its own. Because it is not stretched, it seals at lower temperatures and gives a wider operating window, which is why retort pouches and food laminates rely on CPP or a similar cast sealant layer. On its own it is less stiff and less optically clear than BOPP. When specifying a laminate, the sealant side is a separate decision from the print side, and the two are often different films.
back to index ↑Low-density polyethylene — the soft, branched polymer behind most blown film for bags, liners and shrink wrap. It is easy to process, seals at moderate temperatures and gives good elongation, which is why it dominates carrier bags and industrial liners. Its weakness is strength per unit weight: HDPE and LLDPE give more stiffness and puncture resistance at the same thickness. On a blown film line, LDPE runs at lower melt pressure and a wider bubble stability window than LLDPE, so the two are rarely interchangeable without changing screw speed, die gap and cooling.
back to index ↑High-density polyethylene — a linear polymer with higher crystallinity, giving more stiffness, better barrier and higher tensile strength than LDPE at the same thickness. It is the material behind T-shirt bags, bottle crates and thin-gauge films. On a blown film line it needs a narrower die gap, higher melt temperature and more cooling, and the bubble is less forgiving: a small change in air flow shows up as thickness variation. HDPE films also split along the machine direction more readily, which affects how a bag tears — often a feature, sometimes a complaint.
back to index ↑Polyvinyl chloride film — plasticised for softness, used for shrink sleeves, cling film and some industrial packaging. It seals readily and shrinks at low temperature, which makes it convenient on older shrink tunnels. The drawbacks are regulatory and environmental: PVC contains chlorine, complicates recycling, and is restricted in some food-contact and packaging markets. Where a customer specifies PVC for shrink performance, check whether a PETG or OPS alternative meets the same shrink curve before committing, because changing material later usually means retuning the tunnel.
back to index ↑Films designed to break down under defined conditions — PLA from plant starch, PBAT, or blends. The critical detail is that "biodegradable" without a standard and a timeframe means very little: industrial composting, home composting and soil burial are different environments with different results. For machine selection, biodegradable films behave differently from PE — lower melt strength, narrower sealing window, more sensitivity to moisture — so a line specified for PE may need slower speeds and different seal parameters. Ask for the certification (EN 13432 or equivalent) and the thickness the certificate covers.
back to index ↑The ratio between the diameter of the blown film bubble and the diameter of the die. A 200 mm die producing a 500 mm bubble gives a blow-up ratio of 2.5. It controls the balance between machine-direction and transverse-direction strength: too low and the film tears along the machine direction, too high and bubble stability suffers. Most PE bag films run between 2:1 and 3:1, with LDPE tolerating higher ratios than HDPE. Changing the ratio changes the layflat width, so it is one of the first settings to revisit when a new bag size is introduced.
back to index ↑The process of melting polymer pellets and forcing them through a die to form a continuous profile or film. On a blown film line, resin is fed into a screw, melted and homogenised, filtered, and pushed through an annular die where air inflates it into a bubble. Screw design, barrel temperature profile and output rate together decide melt quality; a starved screw or a cold zone shows up as gels and thickness variation rather than as an obvious fault. Extrusion is also the stage where regrind content matters — above roughly 20% regrind, film quality usually becomes visible to the customer.
back to index ↑The annular tool at the top of a blown film extruder that shapes the melt into a tube. Die diameter sets the base layflat width together with the blow-up ratio; die gap sets shear and therefore output and melt quality. Spiral mandrel designs are standard because they distribute melt evenly around the circumference. Die condition matters more than most operators expect: a scored lip produces a thin line in the film that becomes a seal failure months later. Cleaning intervals and lip inspection belong in the maintenance schedule, not in reactive repairs.
back to index ↑A surface treatment that raises the surface energy of a film so ink and adhesive will bond to it. A high-frequency discharge between an electrode and a grounded roll oxidises the surface; the effect is measured in dynes per centimetre, and most films need 38–42 dynes to print reliably. The treatment decays over time, especially on treated film stored in warm conditions, so a roll treated last month may not print like one treated yesterday. If print adhesion fails while everything else looks correct, check dyne level before changing ink.
back to index ↑Automatic lateral positioning of a moving web, using a sensor to detect an edge (edge position control) or a printed line (line position control) and an actuator to move a roller assembly. Without it, a roll wound slightly off-centre will drift across the machine within a few hundred metres, and print registration or bag width will follow. EPC suits plain film and paper where the physical edge is the reference; LPC is needed when the printed pattern, not the edge, has to stay in position. Sensor choice and mounting position usually decide whether the system works better than a manual guide.
back to index ↑Holding the web at a constant, appropriate tension between unwind, process stations and rewind. Too little tension and the web wanders, wrinkles and registers poorly; too much and it stretches, curls, or necks down after the die. Systems range from a simple dancer roller to load-cell feedback with dancer or dancerless control. Tension should be tapered as the roll diameter changes — a setting that works on a full roll will be too tight on a nearly empty one. Most registration and cut-length complaints trace back to tension rather than to the servo.
back to index ↑The alignment of one print impression relative to another, or of print relative to a cut, seal or fold. On a multi-colour press it is measured in fractions of a millimetre and held by print-mark sensors and register rollers; on a converting line it decides whether the printed design lands in the middle of the bag. Registration errors come from three places: tension variation, inadequate print-mark contrast, and mechanical backlash in the compensator. Before retuning the servo, check that the mark is actually readable at production speed — many faults are optical, not mechanical.
back to index ↑A relief printing process using a flexible photopolymer plate mounted on a cylinder, transferring ink from an anilox roll. It dominates packaging because it prints on film, paper and board at high speed with water-based or UV inks. Anilox line count and cell volume set ink laydown; plate hardness and mounting tape set dot gain. The common quality issues are not exotic: dirty anilox, worn plates, inconsistent impression pressure. Compared with gravure it has lower setup cost and slightly lower image quality, which is why short and medium runs usually go flexo.
back to index ↑An intaglio process where the image is engraved into a copper-plated cylinder and ink is drawn out of the cells by an electrostatic assist. It gives dense, consistent colour on long runs and handles thin films at high speed, which is why it dominates flexible packaging at volume. The cost sits in cylinder engraving, so gravure is uneconomical for short runs and slow to change over. Solvent recovery and emissions control are part of the machine scope, not an afterthought — a gravure line without them will not pass permitting in most markets.
back to index ↑A planographic process where ink transfers from plate to blanket to substrate, with water keeping the non-image areas clean. Sheet-fed offset is the standard for folding cartons, labels and litho-laminated corrugated because it delivers fine detail and consistent colour across long runs. Web offset is used for high-volume publication and some packaging. On carton work the press is only half the story: coating, drying and the ability to hold register through a heavy board matter as much as the printing units themselves.
back to index ↑Printing directly from a digital file without plates — inkjet or electrophotographic. Its value is short runs, versioning and variable data: a hundred cartons with different codes cost roughly the same per unit as a hundred identical ones. The trade-offs are cost per square metre at volume, a narrower substrate range, and colour consistency that depends on calibration rather than on ink keys. For packaging, digital works best alongside conventional printing rather than replacing it — short runs and prototypes digital, volume flexo or offset.
back to index ↑The oldest of the main printing methods: a raised image is inked and pressed into the substrate. In packaging it survives in specific niches — labels, tags, embossing and die-stamping — where the physical impression is part of the product. Modern letterpress for labels is web-fed with UV inks and runs at speeds that would surprise anyone who associates the term with a platen press. As with flexo, plate condition and impression pressure decide quality; too much pressure produces the halo that gives letterpress its characteristic look and its characteristic wear.
back to index ↑Cutting a shape out of paper, board or film with a shaped tool — a flatbed die for sheets, a rotary die for webs. On cartons it is paired with creasing in the same tool; on labels and bags it shapes the finished product. Quality depends on the tool, the make-ready and the material: a new die in a worn anvil cuts differently from the same die a month later. Cutting pressure rises with caliper, so a tool set for 250 gsm board will not cut 350 gsm cleanly without adjustment. Nicking, stripping and edge quality are the three things to inspect on a sample.
back to index ↑Pressing a line into board so it folds without cracking the surface. The crease is a controlled weakening: too shallow and the fold is ragged, too deep and the board delaminates along the line. Crease width should roughly follow board caliper, and the matrix has to match the crease rule. On coated boards, a crack along the fold usually means insufficient crease depth or a matrix that is too narrow, not a paper defect. For heavy boards, pre-creasing or a crease-line varnish is sometimes needed before folding.
back to index ↑Removing the waste between and around cut blanks after die cutting. On cartons the waste is pushed out by pins or male/female tooling; on labels it is pulled away as a matrix. Poor stripping leaves nick marks on the product edge and slows the line, because operators end up picking waste by hand. Tool design decides most of it: too few pins, the wrong rubber, or a die layout that leaves small islands of waste will cause problems regardless of press settings. It is the least glamorous station on a die-cutter and the one that most often limits running speed.
back to index ↑Cutting a wide web into narrower rolls. Two methods dominate: razor slitting for thin films, and shear slitting with circular knives for paper and heavier film. The cut quality depends on knife sharpness, overlap, and web tension — a dull shear cut produces dust and a ragged edge that later jams a bag machine. Slit width tolerance is usually tighter than it looks on paper, because a 0.5 mm error accumulates across a multi-up layout. When a customer reports inconsistent bag width, check the slit roll first.
back to index ↑Winding the slit web back into saleable rolls with controlled tension and acceptable hardness. A roll wound too soft collapses or telescopes in transit; one wound too hard blocks and produces creases when it is unwound weeks later. Winding tension should follow a taper curve, and the lay-on roller pressure matters as much as the tension setpoint. Rewinding is also where splices happen: a splice that is too thick will mark every layer beneath it, and one that is too weak will fail inside the customer's machine rather than in yours.
back to index ↑Bonding two or more webs together to combine properties neither has alone — printability from one layer, barrier or sealability from another. Adhesive lamination uses solvent-based, solventless or water-based adhesive; extrusion lamination uses a molten polymer as the bond. The critical variables are coating weight, nip pressure and curing: solventless adhesive needs time to cure before the laminate is slit, and skipping that time is a common cause of delamination complaints months later. Barrier performance is decided here, not at the printing press.
back to index ↑A thermoplastic adhesive applied molten that sets as it cools. It is the standard for bag bottoms, carton side seams and case sealing because it grabs quickly and needs no drying. Three parameters decide the bond: application temperature, open time and compression time. Too cool and the glue strings; too hot and it degrades in the tank, turns yellow and loses tack. On paper bags, the bottom fold is the highest-stress joint, so glue pattern and compression length matter more than total quantity. Ask for the adhesive grade, not just "hot melt".
back to index ↑Joining films by high-frequency mechanical vibration that melts the material at the interface, without adhesive. It is used where contamination, dust or product residue would defeat a heat seal, and on films that are difficult to seal thermally. The tooling — sonotrode and anvil — has to match the film structure, and the process window is narrower than heat sealing: amplitude, pressure, and dwell all interact. It works well on laminates with a suitable sealant layer and poorly on films that do not transmit vibration, which is why trials on the actual material are essential.
back to index ↑Bonding thermoplastic films by applying heat and pressure for a set dwell time. The three variables — temperature, pressure, dwell — are interdependent, which is why copying a setpoint from another machine rarely works. Seal quality is judged by strength and by appearance: a seal that is strong but has a visible wire or a burnt edge will fail a customer's visual check even though it holds. Seal-initiation temperature testing on the actual film is the fastest way to set a starting point, and a pull test at the start of each shift catches drift.
back to index ↑A bag formed from a tube of film with a seal across the bottom and a cut at the top — the simplest and most common bag format, used for produce, liners and general packaging. On the machine, the tube is formed over a triangle or gusset board, sealed and cut in one cycle; the bag length is set by the cut-off repeat. Because there are no side seals, the film's machine-direction strength carries the load, so film quality matters more than on a side-seal bag. Gussets are added by folding the tube before sealing.
back to index ↑A bag made from two webs (or a folded web) sealed along both side edges, leaving the top open. It is the format behind most flat pouches and many medical and food bags, and it allows printing on both faces. Machine complexity is higher than a bottom-seal bag: two webs have to be aligned, and both side seals must be consistent or the bag leans. Registration between front and back print is the usual quality complaint, and it is a web-guiding and tension problem rather than a sealing one.
back to index ↑A paper or film bag with a flat, rectangular base that lets it stand unaided — the format used for retail shopping bags and takeaway food. Making one requires folding, gluing and forming a base with four corners, which is why square-bottom machines have more stations than flat bag machines and why setup takes longer. Paper grade matters: too light and the base will not hold its shape, too heavy and the folds crack. The bottom glue pattern is the highest-stress joint on the bag and the first place to look when a bag fails in use.
back to index ↑A motor and controller that follow a commanded position or speed precisely, rather than running at a fixed speed from the mains. On packaging machines, servos make electronic registration, quick size changes and repeatable sealing possible: the seal bar can be moved to match the print mark instead of the print being adjusted to the machine. The trade-off is setup knowledge — parameters, tuning and backlash compensation all affect quality. A servo machine that runs worse than a mechanical one is almost always badly tuned or badly specified, not fundamentally inferior.
back to index ↑The stations that hold the incoming and outgoing rolls and control web tension. They set the ceiling on line speed more often than the process stations do: a machine that claims 200 bags per minute needs an unwind that can accelerate a full roll and hold tension as the diameter falls. Shafted versus shaftless mounting, splicers and roll-lifting equipment are all part of the decision. When a line runs well on a fresh roll and poorly near the core, the unwind is the place to look.
back to index ↑A vision system that checks the web or the finished product for defects in real time and signals the machine to mark, reject or stop. Typical checks are print defects, missing glue, seal width, contamination and dimensional error. Performance depends far more on lighting and camera resolution than on the software: a defect that is not visible under the installed lighting will not be detected, whatever the algorithm. Before buying, run the camera on your actual material at production speed — a system that works at 50 m/min may fail at 150.
back to index ↑Acceptable quality limit — a sampling scheme (ISO 2859-1) that defines how many pieces to inspect from a lot and how many defects are allowed before the lot is rejected. AQL is built for lot-by-lot inspection of goods, not for machine acceptance, but the discipline transfers: define the lot, the sample size, the defect classes and the accept/reject numbers in advance. For machinery acceptance, simpler numbers usually work better — inspect a fixed number per hour, with zero critical and a stated limit on major defects — as long as they are written into the purchase order.
back to index ↑The manufacturer's declaration that a machine meets the applicable European directives, most commonly the Machinery Directive 2006/42/EC, the EMC Directive 2014/30/EU and the Low Voltage Directive 2014/35/EU. The sticker is trivial; the file behind it is not. Expect a signed Declaration of Conformity naming the machine and the harmonised standards, a technical file available on request, a manual in the language of the destination country, and a nameplate showing voltage, frequency and serial number. Where the machine is integrated into a line, the integrator usually carries responsibility for the final assembly.
back to index ↑The international standard for a quality management system — how a company controls design, purchasing, production and corrective action. For a buyer it is a proxy, not a guarantee: it says the supplier has documented processes and audits them, not that the machine will be good. In practice it correlates with fewer surprises in documentation, traceability of components and consistent handling of complaints. Ask for the certificate scope and the certification body; a certificate covering "trading" rather than "manufacturing" tells you something about who actually builds the machine.
back to index ↑The two electrical parameters that must be agreed before a machine is built. Voltage differences (380–415 V in much of the world, 440–480 V in North America and parts of the Middle East) can be handled with transformers or matched components. Frequency cannot: a 50 Hz motor running on 60 Hz turns about 20% faster, which changes output rate and can overload gearing. Inverter-driven axes are largely immune, fixed-speed motors and heaters are not. Write voltage, phases, frequency and control-circuit voltage into the purchase order, and measure at the machine before first start-up.
back to index ↑Standard trade terms (FOB, CIF, EXW, DAP and others) that define who arranges transport, who pays for it and where risk passes from seller to buyer. They matter in machinery purchases because the machine is only part of the cost: freight, insurance, unloading and inland transport can move the landed price materially. FOB means the seller clears export and loads at the port; CIF adds freight and insurance to the destination port but not unloading. The term must be stated with a named place — "FOB" alone is ambiguous and is where disputes start.
back to index ↑The two container types most packaging machines ship in. A 20GP is about 5.9 m long internally, a 40HQ about 12.0 m with a higher roof (2.69 m versus 2.39 m). Height is often the deciding factor: a machine that needs partial dismantling for a standard container may fit a high cube intact. Payload is rarely the limit for machinery — volume and lifting are. Ask for packed dimensions, gross weight, lifting points and centre of gravity before booking, and allow 100–150 mm per side for crating.
back to index ↑Minimum order quantity — the smallest number of units a supplier will produce or sell in one order. For machines, MOQ is usually one unit, but the term reappears for tooling, spare parts and consumables: a die set or a printed film may have a minimum run that is far above what a trial needs. MOQ is negotiable in ways that price is not, especially when an order combines several items. Ask what drives the number — a setup, a material minimum, or a purchasing lot — because the answer tells you where the flexibility is.
back to index ↑The interval between order confirmation and the machine being ready to ship, excluding transport. For packaging machinery it is usually quoted in weeks and depends on standard versus custom configuration, component availability and the factory's backlog at the time of order. Two details matter more than the headline number: what event starts the clock (purchase order, deposit, drawing approval) and what is included at the end (factory test, packing, documentation). A lead time that excludes the FAT often slips by two weeks at exactly the wrong moment.
back to index ↑Factory acceptance test and site acceptance test — the two checkpoints where a machine is proven before money changes hands and again before it is accepted on site. The FAT runs the machine on material close to production, at rated speed, with output counted, samples taken and safety functions checked. The SAT repeats the essentials with the buyer's material and utilities, then runs long enough for thermal drift to appear. Both should produce a signed checklist, retained samples and a list of open items with owners and dates.
back to index ↑The period between the machine arriving and it running at rated output with acceptable quality. It covers installation, utility connection, first runs, parameter setting for each product, operator training and handover. Most commissioning problems are not mechanical: missing air capacity, the wrong voltage, material that differs from the sample, or an operator who has not been shown the settings. A written commissioning plan with daily targets and a named counterpart on each side turns it from an open-ended visit into a finite task.
back to index ↑Overall equipment effectiveness — availability multiplied by performance multiplied by quality, expressed as a percentage. It is the standard way to describe how much of a machine's theoretical capacity actually produces good product: a line that runs 90% of the time, at 80% of rated speed, with 2% rejects has an OEE of about 70%. The value is in the split, not the total: a low availability number points to changeovers and breakdowns, a low performance number to speed losses, a low quality number to the sealing or cutting station.
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