Refining of Reinforcement Kraft Pulp for Mechanical Printing Papers, 1997 Papermakers Conference Proceedings

Mechanical printing papers have typically been produced from various softwood and mechanical pulp mixtures. Today recycled fibers are increasingly used to replace mechanical pulp fibers. Long and coarse softwood fibers have their special task in improving the strength and the tunability of the paper. These fibers act as a reinforcement material whereas short and fine mechanical and recycled fibers form a good printing base. The strength of the reinforcement net depends on several factors, namely the length, the strength, the number and the bonding ability of those reinforcement fibers inside the paper web. The number of reinforcement fibers depends upon the coarseness of those fibers and cannot be affected in refining. Also, the strength potential of individual reinforcement fibers is determined by the wood species and on the chemical pulping process itself. The reinforcement ability of the long fiber chemical kraft pulp is improved by refining the fibers. The refining affects the bonding ability, the length and the strength of individual fibers. When refining me reinforcement kraft fibers the target is to develop a good reinforcement ability for those fibers. In practice, it means that the tensile strength (= bonding ability ) is improved to the required level with minimum shortening or weakening of fibers. The best reinforcement ability is obtained by using a multistage Conflo@ refining system. More than 100 modern conical refiners in the refining of reinforcement kraft pulp have proven their superiority over double disc refiners as they have a lower energy consumption, ensure a better tear-tensile combination and provide less fiber shortening than the disc refiners. An optimized refining of reinforcement fibers reduces the need for chemical kraft pulp which has a great effect on the economy as chemical kraft pulp is far more expensive than mechanical pulps or recycled fibers. On the other hand, the reduced amount of low opacity chemical kraft pulp improves the printability of the paper as higher opacity mechanical pulp and/or high opacity recycled fibers can be used.