The Precipitated Calcium Carbonate (PCC) Advantage for Uncoated Paperboard: White Top Linerboard
The high light scattering and brightness properties of Specialty Minerals' precipitated calcium carbonate create a strong incentive for paper mills to economically increase the brightness of white top linerboard while reducing bleached fiber usage. The addition of a 1.2 mm - 1.4 mm average particle size filler PCC delivers maximum light scattering (hiding power). Brightness increases of 2 to 7 points can be achieved while reducing bleached ply coverage. This coupled with the added benefits of increased bulk allows the paper mill to optimize sheet appearance while adhering to quality and cost goals. Changing from filler systems containing combinations of calcined kaolin, ground calcium carbonate (GCC), and titanium dioxide (TiO2) to a precipitated calcium carbonate system can result in additional cost savings per ton of board as well. Precipitated calcium carbonate requires an alkaline or neutral wet-end pH for the top ply.
For white top linerboard coverage, a 42 lb (205 gsm) sheet can reduce the demand for bleached fiber by as much as 5 percent (e.g., from 36 percent to 31 percent top ply coverage). These results are achieved through the use of 8 percent - 15 percent PCC filler in the virgin bleached top ply, and 5 percent - 10 percent PCC in the recycled mixed office waste (MOW) bleached top ply. However, when bleached recycled fiber is used, a combination of filler carryover and lower fiber strength limits PCC addition.
Changing from kaolin or GCC filled to precipitated calcium carbonate filled white top linerboard, opens up the sheet's porosity. This allows for uniform controlled receptivity of flexographic inks and results in improved print quality.
The trend in white top linerboard toward higher graphic quality consisting of improved appearance and printability can be achieved with the application of PCC. The brightness, bulking, and light-scattering characteristics of PCC fillers can assist in balancing critical paperboard properties and provide cost savings to meet the needs of a dynamic and changing paperboard market.
The benefits of alkaline conversion with precipitated calcium carbonate include:
- Excellent opacity
- Maintenance of strength properties
- Economical brightness improvement
- Reduction of TiO2
- Filler-for-fiber substitution
- Reduced wet-end furnish costs
- Increased coefficient of friction
- Improved flexographic printability
Specialty Minerals delivers these benefits consistently with a successful history of acid-to-alkaline conversion experience and technical support.