Method for improving paper and board's resistance to the penetration of liquids

Abstract

This invention brings a new aspect in papermaking by spraying hydrophobic chemical directly onto the paper surface in the dryer section of the paper machine, as a two-step process where high solids starch is sprayed on the paper to seal the sheet's surface and thereafter the hydrophobic chemical is sprayed on the paper surface. This invention is a completely new method of hydrophobic sizing, spraying a small amount of a suitable hydrophobic chemical on the moving web in the dryer section, instead of adding hydrophobic chemical in the wet-end of the paper machine, or mixing it in with starch at a size press. This invention reduces the amount of hydrophobic chemical used compared to any of the other processes, it simplifies wet-end chemistry, and it puts the hydrophobic sizing exactly where it is needed, on the paper's surface, which in many cases will be a single side of the paper.

1 . A method to improve the surface of paper or board to repel water and to resist water penetration into the sheet by applying a hydrophobic chemical directly on the paper surface by spraying the chemical on to the moving paper web in the drying section of the paper machine. 
     
     
         2 . A method according to  claim 1  where the hydrophobic chemicals used for sizing are ASA, AKD or any other similar chemical which increases paper surface water repellency and resistance to water penetration. 
     
     
         3 . A method according to  claim 2  where the spraying is done with an application air nozzle where the gas, or air, or steam or a mix are pressurized and are the force for breaking up the hydrophobic chemical into small droplets forming a spray and carrying the hydrophobic chemical onto the paper web surface. 
     
     
         4 . A method to improve the surface of paper or board to repel water and to resist water penetration into the sheet by applying a hydrophobic chemical on the paper surface by spraying the chemical on to the moving paper web in the drying section of the paper machine, which is installed after a spray sizing system for starch which has a set of two rolls forming a nip to control the penetration of starch into the web surface. 
     
     
         5 . A method to improve the surface of paper or board to repel water and to resist water penetration into the sheet by a two-step integrated process for both paper and board where internal strength and surface strength properties are improved by spraying high solids starch at a solids content greater than 15% onto the moving web in the drying section followed by a set of two rolls forming a nip to control the penetration of starch into the web surface, thence followed by the spraying of hydrophobic sizing chemicals onto the moving web in the drying section to improve the paper surface's ability to repel water and to resist water penetration into the sheet by using a spraying device containing of a set of pressurized air nozzles arranged over the cross section of the sheet and in the machine direction in one or more rows.