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The Hydrex® Value
Product characteristics
Hydrex® is a synthetic magnesium aluminosilicate manufactured by precipitating sodium silicate solution with a mixture of magnesium and aluminum sulfate. It is used as a filler in wood-containing printing papers as well as wood-free fine paper and multilayer board to improve optical performance, printability and friction. The precipitating conditions for Hydrex are carefully engineered and controlled. Thus the size and form of the primary particle of the agglomerates are carefully designed and maintained. Hydrex is manufactured using raw materials thoroughly approved by Huber Engineered Materials in order to ensure a consistent high quality product free of contaminants. Hydrex maintains a Food and Drug industry level of purity. Due to the pigment precipitation technique, no dispersion aids are required. The synthetic origin of Hydrex allows long shelf life without the need for biocides.
Optical properties
Hydrex® sodium aluminosilicate significantly improves the opacity of paper. This is because the light scattering ability of Hydrex is very high, almost 500 m²/kg. Thus it is able to enhance the paper's light scattering almost tenfold compared to fiber. The chemical composition of Hydrex results in a high refractive index. Hydrex provides the paper with a significant number of light scattering interfaces between air, pigment and fiber. This gives Hydrex the power to increase opacity at low addition levels. Hydrex inherently is an ultra-bright pigment, and it significantly increases the brightness of paper. While maintaining paper brightness, bleaching can be reduced, resulting in substantial cost savings.
Printability
Hydrex® sodium aluminosilicate improves the paper's printability: The high absorption capacity of Hydrex increases the print image density thus reducing ink demand. Hydrex keeps the ink at the paper surface and prevents the ink from migrating into the sheet. Hydrex reduces strike-through and show-through by preventing ink and solvents from penetrating the paper. As a result, opacity is maintained. Hydrex can also help in reducing registration problems in multicolor printing presses by increasing paper friction.
Friction Control
Certain furnishes tend to produce paper which has a low coefficient of friction. This can cause winding problems like snaking of the paper web, wrinkles, loose winding and telescoping of the reels. Another problem is slippage during paper transport, which shows up as breaks at the printing house. Hydrex® sodium aluminosilicate can solve all of these problems. Typically 1% Hydrex in the web increases the kinetic coefficient of friction by 15 %. At the same time an increase in optical properties can be noted.
Low Abrasiveness
Most pigments for filler or coating use tend to cause wear of the paper machine's parts like wires, foils and suction boxes. Also, printing presses and slitter knifes are subject to abrasion. Synthetic silicates reduce the wear substantially due to their amorphous nature with rounded surfaces and pores. In addition Hydrex is free of abrasive contaminants. As a result, the abrasiveness of Hydrex is very low.
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