Know everything about Paper -4
The paper must have fairly a smooth and even surface to take on the print or writing on it. The smoothness is derived both by a process called sizing and super calendering. The term sizing though related with Paper making process can not be delinked with paper as the coating used in sizing influences the smoothness along with porosity of the paper . Good sized paper will have higher strength. Similarly in order to smoothen the surface of the paper the finished paper is fed in between two highly polished rollers. Therefore smoothness is an important factor in the paper.Smoothness of the paper will often determine whether or not it can be successfully printed. Smoothness also gives eye appeal as a rough paper is unattractive.
Stiffness is the measure of force required to bend a paper at a specified angle and is an important property for box boards and to some extent for printing papers also. A flimsy paper without certain amount of stiffness can cause feeding and delivery problems in larger sheet run presses. At the same time on printing machines too stiff a paper may not cause feeding problem, they can cause problems in copier machines where it must traverse over, under, and around feed rollers.
9. Dimensional Stability:
Most physical properties of paper undergo changes as a result of atmospheric variations due to the presence of moisture in the air. Water has the effect of plasticizing the cellulose fiber and weakening of the inter fiber bonding. The electrical resistance ie static electricity (artificial sticking of paper) vary with moisture content. The amount of water plays an important role in calendaring, printing and converting process. Moisture control is also significant to the economic aspect of paper making. Poor moisture control can adversely affect many paper properties. Ability of paper to retain their exact size, which is called dimensionally stable paper is an important factor while printing multi color jobs. The paper should retain the dimensions even when affected by changes in moisture content or humidity in the press room atmosphere, during the printing .
Cotton fibers which is the main constituent of the paper, swell or shrink in diameter during extreme weather conditions and variation in the moisture content in the air. Since most of the fiber in the sheet are aligned in the machine run direction, absorption and de –absorption of moisture by paper causes the change in cross direction as the paper fibers when absorb water expand primarily in width, but only slightly in length. Uneven dimensional changes cause undesirable cocking and curling.
10. Folding endurance:
Fold endurance i.e ability to withstand multiple folds without getting tear will show the durability of paper when repeatedly folded under constant load. Therefore the paper used for printing special documents such as bank notes and currencies need to have sufficient folding endurance. This character is important to those documents which are quite frequently handled such as Currencies and Bank notes, Maps, Archival documents, Wrapping papers etc so that they do not deteriorate faster due to repeated bending, folding, and creasing etc. In short we may say that the Folding endurance is important for carton, box boards, ammonia print paper, and cover paper etc. It is important factor for printing grades where the paper is subjected to multiple folds like in books, maps, or pamphlets. Folding endurance is a requirement in Bond, Ledger, Currency, Map, Blue Print and Record Papers.