Corrugated fiberboard is a paper-based construction material consisting of a fluted corrugated sheet and one or two flat linerboards. It is widely used in the manufacture of corrugated boxes and shipping containers.
The corrugated medium and linerboard are made of paperboard, a paper-like material usually over ten mils (0.010 inch, or 0.25 mm) thick. Paperboard and corrugated fiberboard are sometimes called cardboard by non-specialists, although cardboard might be any heavy paper-pulp based board.
Corrugated (also called pleated) paper was patented in England in 1856, and used as a liner for tall hats, but corrugated boxboard would not be patented and used as a shipping material until December 20, 1871. The patent was issued to Albert Jones of New York City for single-sided (single-face) corrugated board. Jones used the corrugated board for wrapping bottles and glass lantern chimneys. The first machine for producing large quantities of corrugated board was built in 1874 by G. Smyth, and in the same year Oliver Long improved upon Jones' design by inventing corrugated board with liner sheets on both sides. This was now corrugated board as we know it today.
The Scottish-born Robert Gair invented the corrugated box in 1890; that is, pre-cut flat pieces manufactured in bulk that folded into boxes. Gair's invention, as with so many other great innovations, came about as a result of an accident: he was a Brooklyn printer and paper-bag maker during the 1870s, and one day, while he was printing an order of seed bags, a metal ruler normally used to crease bags shifted in position and cut them. Gair discovered that by cutting and creasing bags in one operation he could make prefabricated paper boxes. Applying this idea to corrugated boxboard was a straightforward development when the material became available. By the start of the 20th century, corrugated boxes began replacing the custom-made wooden crates and boxes previously used for trade.
The corrugated box was initially used for packaging glass and pottery containers, which are easily broken in transit. Later, the case enabled fruit and produce to be brought from the farm to the retailer without bruising, improving the return to the producers and opening up hitherto unaffordable export markets. (There had previously been a great deal of waste when, for example, oranges were craned out of the hold of a ship, having been bulk loaded into it.)
Corrugated board is manufactured on large high-precision machinery lines called corrugators running at 500 lineal feet per minute or faster. These machines over time have become very complex with the objective to avoid some common problems in corrugated board production, such as warp and washboarding. In the classical corrugator the paper is humidified by means of high pressure steam. The humidity aims to soften the paper fibres so that the formation of the flute and the consequent glueing will go smoothly. The process adds a considerable amount of water to the papers. After the formation of the board this humidity has to be removed by drying in the so-called dry-end. Here the newly formed corrugated board is heated from the bottom by hot plates. On the top various pressures are applied by a load system on the belt.
The corrugated medium is usually a 26 lb/1000 sq ft (127 g/m2) paperboard; higher grades are also available. It arrives to the corrugator on large rolls. At the single-facer, it is heated, moistened, and formed into a fluted pattern on geared wheels. This is joined to a flat linerboard with a starch based adhesive to form single face board. At the double-backer, a second flat linerboard is adhered to the other side of the fluted medium to form single wall corrugated board. Linerboards are often kraft paperboard (of various grades) but may be bleached white, mottled white, colored, or preprinted.
Common flute sizes are "A", "B", "C", "E" and "F" or microflute. The letter designation relates to the order that the flutes were invented, not the relative sizes. Flute size refers to the number of flutes per lineal foot, although the actual flute dimensions for different corrugator manufacuturers may vary slightly. Measuring the number of flutes per lineal foot is a more reliable method of identifying flute size than measuring board thickness, which can vary due to manufacturing conditions. The most common flute size in corrugated boxes is "C" flute.
Standard US Corrugated Flutes
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Corrugated fiberboard can be specified by the construction (single face, singlewall, doublewall, etc), flute size, burst strength, edge crush strength, flat crush, basis weights of components (pounds per thousand square feet, grams per square meter, etc), surface treatments and coatings, etc. TAPPI and ASTM test methods for these are standardized.
The choice of corrugated medium, flute size, combining adhesive, and linerboards can be varied to engineer a corrugated board with specific properties to match a wide variety of potential uses. Double and triple-wall corrugated board is also produced for high stacking strength and puncture resistance.
The corrugated board is creased or scored to provide controlled bending of the board. Most often, slots are cut to provide flaps on the box. Scoring and slotting can also be accomplished by die-cutting.
The "Flexo Folder Gluer" is a machine that in one single pass prints, cuts, folds, and glues flat sheets of board to convert them to boxes for any application, from storing old family pictures to shipping the biggest of plasma TV sets to the global market. The most advanced of FFG's can run at speeds of up to 26,000 boxes per hour (about 433 per minute).
The most common box style is the Regular Slotted Container. All flaps are the same length and the major flaps meet in the center of the box.
The manufacturer's joint is most often joined with adhesive but may also be taped or stitched. The box is shipped flat (knocked down) to the packager who sets up the box, fills it, and closes it for shipment. Box closure may be by tape, adhesive, staples, strapping, etc.
Many other styles of corrugated boxes and structures are available:
The size of a box can be measured for either internal (for product fit) or external (for handling machinery or palletizng) dimensions. Boxes are usually specified and ordered by the internal dimensions.
Box styles in Europe are typically defined by a 4-digit code specified by FEFCO: for example a regular slotted container (RSC) is coded 0201. FEFCO styles are normally the basis for more complicated special designs that incorporate, for example, locking tabs or internal fittings.
A more recent development popular in usage is a hybrid product featuring the structural benefits of corrugated combined with the high-graphics print of lithography previously relegated to paperboard folding cartons. This application, generally referred to as 'Single-Face Laminate', begins its process as a traditional fluted medium adhered to a single linerboard (single-face), but in place of a second long-fibered liner, a pre-printed sheet of paperboard such as SBS (solid bleached sulfate) is laminated to the outer facing. The sheet can then be converted with the same processes used for other corrugated manufacturing into any desired form.
Specialized equipment is necessary for the material construction of SFL, so users may expect to pay a premium for these products. However, this cost is often offset by the savings over a separate paperboard sleeve and the labor necessary to assemble the completed package.
Mill and corrugator scrap, or broke, is the cleanest source for recycling. The high rates of post-consumer recycling reflect the efficiency of recycling mills to clean and process the incoming materials. Several technologies are available to sort, screen, filter, and chemically treat the recycled paper.
Many extraneous materials are readily removed. Twine, strapping, etc are removed from the hydropulper by a "ragger". Metal straps and staples can be screened out or removed by a magnet. Film-backed pressure sensitive tape stays intact: the PSA adhesive and the backing are both removed together.
Materials which are more difficult to remove include wax coatings on corrugated boxes and "stickies", soft rubbery particles which can clog the paper maker and contaminate the recycled paper. Stickies can originate from book bindings, hot melt adhesives, PSA adhesives from paper labels, laminating adhesives of reinforced gummed tapes, etc.
Recycling corrugated fiberboard helps conserve natural resources and energy. It also helps countries without sustainable wood resources build a paper and packaging industry locally and develop their exports to global markets. Over 70% of the corrugated manufactured is recovered, recycled and made into new corrugated products throughout the world.
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