Coated mechanical papers are made from base sheets, which consist mainly of mechanical pulps. These sheets are then coated with various minerals and chemicals to form a smooth, bright surface that enhances ink holdout. These usually light weight coated (LWC) papers are used in magazines, catalogs and inserts and can be printed via offset or rotogravure printing processes. In North America, LWC papers are also classified as coated #4 or #5 papers.
The performance of a pigment on the surface of a paper is related to five major particle parameters: shape, size, size distribution, surface chemistry and surface area. Specialty Minerals Inc. (SMI) crystal-engineered precipitated calcium carbonate (PCC) pigments can deliver these properties, which combine to control the surface and brightness of the coating layer including optical properties, smoothness, bulk, stiffness and printability. Working together with the papermaker, our scientists create not only coating formulations but, more importantly, also provide the ability to meet the cost-efficient demands of tomorrow's paper markets for high quality, brighter papers. Specialty Minerals PCC helps LWC papermakers reduce premium pigment (TiO2) usage. Many mills can reduce bleaching costs as well.
Today, LWC papers are coated with Opacarb® coating grade PCC from SMI to enhance both optics and printability. With a range of aragonite particle sizes and narrow particle size distributions, Opacarb® PCCs are tailor made to maximize light scatter and fiber coverage, which provides an optimal coating structure for porosity control and ink receptivity. Color print images are sharp and vibrant.
Because the optical properties of coated mechanical papers are strongly influenced by the base sheet, the composition of filler pigments is critical. Whether incorporated into the base sheet as virgin filler or through coated broke, PCC provides significant quality improvements to coated mechanical papers. Refer to discussions on the advantage of PCC for uncoated mechanical papers.
Learn more about precipitated calcium carbonate's role in coated groundwood papers:
Specialty Minerals Offers a Broad Range of Precipitated Calcium Carbonate (PCC) Products
Opacarb® PCC family sets the standard for aragonite shaped coating grade PCC in the world today. With a narrow particle size distribution and a choice of specific aragonite particle sizes from 0.4 microns to 0.6 microns, it provides exceptional coated paper performance. Opacarb® PCC delivers outstanding performance at high levels (80 parts) in the coating formulation, developing high gloss and smoothness while enhancing brightness and whiteness. Opacarb® PCC is suitable for both offset and rotogravure formulations at all coater speeds.
Learn more:
