The Precipitated Calcium Carbonate (PCC) Advantage for Uncoated Paperboard: Bleached Paperboard Filling

Specialty Minerals’ structured scalenohedral, clustered prismatic and aragonitic precipitated calcium carbonates (PCCs) are unique minerals. They contribute a higher degree of bulk to the paper sheet than other mineral fillers. In bleached paperboard grades, the addition of 3 percent to 9 percent of a 2.1 mm to 3.2 mm average particle size filler PCC maintains or increases board bulk while balancing other critical properties such as stiffness. Board brightness improves by 1 point or more at these filler levels. The replacement of bleached fiber with precipitated calcium carbonate filler also results in significant manufacturing cost savings.

For coated paperboards, a brighter baseboard makes it easier for mills to meet more stringent coated board brightness targets. 

Paper mills utilizing increasing levels of carbonates in their board coating formulation sometimes encounter foam (entrained air) with deposits caused by coated broke returning and dissolving in the acid wet-end. The digestion of carbonates hinders machine runnability and can be virtually eliminated with alkaline conversion and PCC addition. Precipitated calcium carbonate acts as a pH buffer in the bleached board wet-end and provides alkalinity thus eliminating the need for sodium bicarbonate. The wet-end is much more stable with the alkaline chemistry in place. 

The economics of PCC-filled alkaline bleached board can be maximized with the efficient use of microparticle retention aid systems. Drainage improves which results in higher press solids. This reduces main section steam usage. Mills typically take advantage of the reduced steam demand by increasing productivity 1-2 percent. 

The star chart shows the typical properties achieved by alkaline bleached board mills with Specialty Minerals PCC products. Almost all of the major board properties improve or remain unaffected when switching from an acid to an alkaline wet-end system along with addition of 5 percent PCC filler.

PCC Benefits
Precipitated calcium carbonate fillers are used effectively in solid bleached paperboards. The brightness and bulking characteristics of PCC fillers can assist in balancing critical board properties and provide cost savings to meet dynamic and changing market needs. 

The benefits of alkaline conversion with PCC include:

• Excellent paperboard bulk
• Maintenance of strength properties
• Economical brightness improvement
• Filler-for-fiber substitution 
• Reduced wet-end furnish costs
• Elimination of corrosion and foam
• Improved carbonate yield
• Improved productivity

Specialty Minerals delivers these benefits consistently with a successful history of acid-to-alkaline conversion experience and technical support.