Solid unbleached sulfate (SUS) is a widely used product in the consumer packaging industry, particularly for beverage packages.

SUS is a multi-ply board with a basis weight of up to 500 g/m2 and is commonly sold in rolls.

The construction of solid unbleached board typically consists of two or three plies, all made from unbleached furnish. The top ply, which provides a smooth surface for coating, is usually made from hardwood furnish. The middle ply, or in the case of two plies, the back ply, is made from unbleached softwood kraft and broke. Additionally, recycled fiber, such as old corrugated containers, can be incorporated into the middle ply. The back ply is typically made from unbleached softwood kraft.

Stiffness is a crucial property for SUS, as it ensures the integrity and durability of the packaging. To achieve good stiffness, the back and top plies are refined to the appropriate degree, surface sizing is applied, and bulk is maximized. High tear strength is also essential to prevent any cracking of the beverage package. Furthermore, a certain level of z-directional strength is necessary for the packaging to withstand the stresses of transportation and handling.

Printing properties are of great importance for SUS, as it is often used for demanding printing jobs. The top surface must have excellent smoothness, which is typically measured using the Parker Print Surf (PPS) roughness measurement. A smooth surface ensures high-quality printing and enhances the visual appeal of the package.

In summary, solid unbleached sulfate (SUS) is a versatile and robust product used in the consumer packaging industry, particularly for beverage packages. Its multi-ply construction, with plies made from unbleached furnish, provides strength, stiffness, and tear resistance. The smooth top surface allows for excellent printing properties, ensuring high-quality graphics and visual appeal. SUS is a reliable choice for demanding packaging applications.