Hollow sphere plastic pigment improves high shear rheology of higher solids coating formulations, Solutions!, Online Exclusives, May 2004

Experience has shown the many advantages of running higher solids levels in coating formulations, including enhanced surface properties and more efficient drying; yet coating at higher solids levels usually results in higher blade pressure, which can lead to streaking, scratching and more frequent web breaks.

The answer to this dilemma may be new hollow pigments designed to provide lower blade tube loadings compared to coatings made with other hollow plastic pigments. For example, Figure 1 compares conventional hollow pigments with the HS 3028NA hollow pigment produced by Dow Chemical. The HS 3028NA plastic pigment reduces high shear rheology to meet the demands of blade metered high solids coating. As a result, mills can run higher solids and achieve higher operating rates while maintaining the gloss and opacity advantages they expect.

Figure 1.

Higher coating solids levels improve coating holdout, which can lead to increased sheet gloss. Improved holdout also enables papermakers to calender at lower pressure, which improves sheet opacity. Figures 2 and 3 show how a two percent increase in formulation solids can reduce calendering required to reach target gloss, and how this can translate into improved opacity.

Figure 2.

Figure 3.

Increased operating rates
With higher solids levels, drying is easier. Mills can operate coaters at higher speeds while maintaining target moisture because there is less moisture to remove from the formulation. This means additional tonnage can be produced without investing in additional mill equipment. Figure 4 shows the impact of increased formulation solids on sheet moisture and line speed. Use of hollow plastic pigments is also a proven way to increase sheet gloss.

Figure 4.

HS 3028NA is produced using Dow’s proprietary hollow sphere pigment technology and is offered at a 28 percent solids level, which is, on average, two percent higher than conventional materials. The actual solids increase delivered in a particular coating formulation depends on the level of plastic pigment used.

Dow continues to develop and commercialize new hollow plastic pigment products valued by paper and paperboard mills that seek to achieve specific surface property and/or operating goals. More information about higher solids coating formulations is available from Dow at the TAPPI Coating Conference, May 17-19, 2004 in Baltimore, Maryland, USA.

About the author: David Wolfe is application development leader, Emulsion Polymers business, The Dow Chemical Co., Midland, Michigan, USA. Contact him by email at dwolfe@dow.com or by phone at +1 989-636-9124.