Paperboard is a thick, rigid paper-based material, typically over 0.30 mm thick or with a grammage above 250 g/m². Its ability to be easily cut, formed, and printed makes it widely used in packaging for industries like food, cosmetics, and pharmaceuticals. It also finds applications in graphic printing for book covers and postcards, and in fine arts.
The Core Ingredients
Paperboard production primarily relies on two main types of fibrous raw materials: virgin wood fibers and recycled fibers. Virgin wood fibers come directly from trees, often from sustainably managed forests. These fibers are sourced from both softwood and hardwood trees; softwood fibers, like those from pine or spruce, are longer and contribute to strength, while shorter hardwood fibers from trees like birch or eucalyptus provide a smoother surface suitable for printing.
Recycled fibers come from post-consumer waste, like used boxes and newspapers, and post-industrial waste. Their use contributes to a circular economy by reducing the demand for new raw materials and minimizing waste. However, each time paper is recycled, the fibers can become shorter and weaker, so virgin fibers are periodically introduced to maintain desired strength, quality, and brightness.
From Fiber to Board: The Manufacturing Journey
The transformation of raw fibers into paperboard begins with the pulping process, which separates cellulose fibers from wood or liberates fibers from recycled paper. Mechanical pulping methods use physical forces to break down wood chips, preserving most of the wood material. Chemical pulping, like the Kraft process, uses chemical solutions to dissolve lignin, resulting in stronger and purer cellulose fibers.
After pulping, fibers are often bleached to achieve desired brightness and color. The prepared pulp, a dilute mixture of fibers and water, is then distributed onto a moving wire mesh on a paper machine. Water drains through the mesh, forming a continuous wet sheet of intertwined fibers.
This wet sheet then passes through a series of press rolls that squeeze out additional water, compacting the fibers and increasing the sheet’s density. Finally, the sheet moves through a drying section, often involving steam-heated cylinders, to remove remaining moisture. The dried paperboard may then undergo calendering, where it is pressed between rollers to achieve a smooth surface and uniform thickness, before being wound into large rolls.
Varieties of Paperboard and Their Makeup
Different types of paperboard are manufactured to possess unique properties, making them suitable for specific applications. Folding Carton Board (FBB) is a multi-layered board, often combining bleached chemical pulp layers with a core of mechanical or thermomechanical pulp. This composition provides FBB with a high stiffness-to-weight ratio, making it a common choice for cosmetic, food, and pharmaceutical packaging due to its good printability and creasing performance.
Solid Bleached Sulfate (SBS) paperboard is made entirely from chemically pulped and bleached virgin wood fibers, resulting in a clean, white board with excellent printability on both sides. Its purity and smooth surface make it preferred for high-end packaging such as cosmetics, pharmaceuticals, and food products where appearance and hygiene are important.
Coated Unbleached Kraft (CUK) is produced primarily from unbleached chemical pulp, giving it a natural, often brownish appearance. This type is known for its strength and moisture resistance, commonly used for beverage carriers and heavier items.
Coated Recycled Board (CRB), also known as clay-coated news back (CCNB), is made from recycled fibers, often with a clay coating to improve its print surface. CRB is a cost-effective option for general packaging, including dry food and laundry detergent boxes.
Paperboard’s Environmental Footprint
Paperboard is an environmentally conscious material, largely due to its origin from renewable resources. Trees, the primary source of virgin fibers, can be regrown, and many paperboard manufacturers source their materials from sustainably managed forests. These forests are often certified by organizations like the Forest Stewardship Council (FSC) or the Sustainable Forestry Initiative (SFI), which ensure responsible forestry practices.
The recyclability of paperboard significantly reduces its environmental impact, as used paperboard can be collected and reprocessed into new products, lessening landfill waste and conserving resources. In the United States, approximately 68% of paper and paperboard is recycled annually, demonstrating a high recycling rate. Even if not recycled, paperboard is biodegradable and can naturally break down, returning nutrients to the soil, making it an environmentally sound choice.