Folding Carton Paperboard Choices

Folding Cartons Paperboard

Superior folding cartons begin with the proper choice of substrate, paperboard with the performance and graphics quality to successfully market the packaged product. The wide variety of substrates available to the folding carton producer, make it easy to make the wrong choice.

Converters must carefully assess printability, packaged product protection, package design requirements, processability, and package value to appreciate the tradeoffs.

Folding cartons represent a form of paperboard packaging that is constructed from 10 to 36-point (thick) board. These board types consist of a wide range of virgin and/or recycled grades (SBS, FBB, SUS, CUK, CRB, UKB, etc.). These grades possess varying characteristics that make each right for specific packaging requirements.

Printability requirements run the gamut from sheet & web offset, flexo, gravure, digital ink jet, laser, and rotary screen. Inks and coatings used may be aqueous, solvent, oil based, UV or EB.

The paperboard producing industry has undergone major changes recently with improvements being sought in productivity, and sustainability, leading to consolidation. This has resulted in an opportunity for foreign South American, Asian and European paper mills to export and seek U.S business.

Folding BoxboardThe significant European product is Folding Boxboard (FBB). FBB is always multi-ply, combining chemical and mechanical or thermal mechanical pulp. FBB, a lightweight, low-density, high stiffness board uses sustainable, renewable resources, consumes fewer trees, has yield advantages over both SBS & CRB, and reduces shipping costs.

FBB is most often 3 plies, with the middle layer using lighter-weight pulp and the outer plies using bleached chemical pulp. FBB is finished with optional backside single and frontside double clay coating for a final product with less variation than SBS and a very smooth print surface. Ink settings can be reduced up to 20% to equalize with SBS densities. Caliper consistency can shorten make-ready and set-up times.

Both print quality and cold and hot foil stamping are enhanced. High end applications are seen in packaging frozen, refrigerated and other foods, beauty and health products, candy, pharmaceuticals, cigarettes, and graphic production, competing with SBS.

In North America three major paperboard grades for folding carton dominate SBS, CUK, and CRB. They differ in big ways in terms of manufacturing process, functional properties, and price. The major paperboard product produced is Solid Bleached Sulfate (SBS), which can be single or multi-ply. It’s traditionally made of 100% chemical pulp, but some may now contain recycled fiber. Most SBS board is clay coated one side only (C1S), but a variation is coated both sides (C2S).

Board Coated Two Sides C2SThe result is a very smooth print surface that is conducive to quality printing, cold and hot foil stamping, film and metalized foil laminating. SBS has moderate tear strength, good stiffness, compression strength and is a top embossing, gluing, cutting and high-speed filling performer.

SBS is made from sustainable renewable resources. SBS is generally higher priced than alternatives. Its high quality graphic capabilities attract high end applications in candy, media, pharmaceutical, personal care, cosmetics, medical and tobacco packaging.

Coated Unbleached Kraft (CUK), also manufactured as (SUS) and (CNK), is a 2 or 3 ply board made from chemical pulp long soft wood fibers with a thin layer of hardwood fibers added to the top layer for better smoothness. Its brown Kraft color is top coated with an opaque titanium-based coating for printing. CUK offers superior tear, tensile and compression strength with very good cutting and gluing properties. CUK is made from sustainable renewable resources using a furnish of at least 80% virgin unbleached natural wood pulp with up to 17% recycled content.

CUK finds use in frozen and dry food, automotive, electronics, detergent, multi-packs, and sporting goods packaging. A wet strength grade finds a high percentage of use in the packaging of beer, and beverage packaging.

Coated Recycled Board (CRB) (aka clay coated news) finds heavy use as the substrate of choice for low cost folding cartons where recycled content is favored. It is made from a 100% mix of recycled newsprint, corrugated and other papers laid up in many plies (5-9) grey backside with the top ply being bleached and clay coated for acceptable printing.

CRB is made from sustainable renewable resources. Not as strong as other grades it is also apt to be higher in moisture content. More absorbent than SBS and CUK it needs more ink or stronger inks to build density. Its acceptable strength, including bulge, adequate cutting and gluing finds applications in packaging granular products, cereals, crackers, toothpaste, tissues, etc.

Uncoated Kraft Boxboard (UKB) similar to (CRB) is made from mainly virgin chemical pulp softwood fiber with a top layer of hardwood fiber for smoothness. Being uncoated, it is less smooth, prints just OK, embosses and accepts foil stamping. It is very cost effective and its brown color tends to attract environmentally friendly applications. It is made from sustainable renewable resources and weighs less than other grades of equal caliber. Safe for direct food contact, it finds applications in institutional food, lawn & garden, hardware, sporting goods, and other durable goods packaging.

SBS and FBB are recognized as being better in terms of appearance (smoothness and brightness) and printability than recycled grades. Important substrate printability criteria include: smoothness, ink receptivity and holdout, rub resistance, board coating strength, ink and varnish gloss and mottle resistance. Substrate strength (stiffness, tear, and compression), scoring and bending are important physical criteria. Stiffness is the most important strength factor followed by tear. CUK is recognized as being better in terms of strength than SBS with recycled grades being poorer.

Generally, printability and stiffness tend to tradeoff against each other. Recycled grades have lower panel and corner stacking strength than SBS or CUK grades. Typically, clay coated recycled grades crack easier in the grain direction than SBS or CUK grades. At the same basis weight SBS and FBB are stronger than recycled grades. Recycled grades are known to be dustier and absorb moisture sooner than SBS, FBB and CUK, both of which have a negative effect on printability.

The bottom line is, there are a multitude of substrate choices available to the folding carton converter. The converter, must be on top of his game to make the proper choices to best serve both his operation and his customers’ needs.

Our business at Cork is the development and formulation of Aqueous, energy curing Ultraviolet (UV), and Electron Beam (EB) specialty coatings and adhesives. Cork thrives on its ability to formulate novel, useful specialty products that offer the graphic arts industry printer/coater a competitive advantage.


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About the Author

Elmer W. Griese Jr, having accumulated 35+ years of knowledge working in the coatings and printing ink industries has now authored the Cork Tech Talk News, newsletter since 1992 producing 112 issues. He remains dedicated to educating and illuminating technological progress that offers the potential to advance coating technology and its applications.

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