Benefits of Hollow Sphere Pigments in Metered Size Press Coated Paper Grades, 2002 Metered Size Press Forum

Metered size press (MSP) coated grades finished with hot/soft calendering technology are becoming a growing segment of the coated paper industry. Increasing quality demands such as higher sheet gloss targets have led to the increased use of hollow sphere pigments (HSP) in these grades in order to extend the capabilities of this equipment. The data summarized in this paper was obtained from pilot trials in Germany conducted for a new machine installation that is being designed to produce a woodfree grade with a targeted sheet gloss of 60. Coat weights of 10 g/m2 per side were the maximum obtained without excessive misting at 1,000 m/min. Hot/soft calendering conditions including speed, roll surface temperature, and pressure were varied to determine the impact on sheet gloss, smoothness, caliper, and bulk for the standard formulation and the HSP-containing formulation. The results indicate that up to 11 points higher sheet gloss can be achieved at equal calendering conditions when using 7 parts of HSP, or that equal gloss can be obtained with significantly reduced calendering (100 N/mm lower pressure, 400 C lower temperature, or 300 m/min higher speed). The reduced calendering contributed to higher caliper and bulk at equal gloss when using HSP. The data also indicated that equal gloss could be obtained with 20% lower coat weights when using HSP. Overall, it illustrates how hollow sphere pigments are being used in production grades to enhance sheet gloss, reduce calendering conditions, or produce high gloss levels with limited coat weights.