Fiber blend having high yield and enhanced pulp performance and method for making same

Abstract

The present disclosure relates to producing paper or paperboard having improved stiffness and strength, compared to the conventional paperboard at the same basis weight. It also discloses a method of wood pulping having a significantly increased yield and providing fiber pulps with enhanced properties such as strength and stiffness. Wood chips are chemically pulped to a high kappa number, providing a rejects component and an accepts component. The rejects component is subjected to a substantially mechanical pulping process, optionally in a presence of bleaching agent, prior to blending back into the accepts component. The resulting fiber blend is washed, optionally bleached, and subjected to a papermaking process to provide paper or paperboard with enhanced strength and stiffness at low basis weight.

Description

BACKGROUND OF THE INVENTION[0001]Two main processes have been used for wood pulping: mechanical pulping and chemical pulping. Mechanical pulping primarily uses mechanical energy to separate pulp fibers from wood without a substantial removal of lignin. As a result, the yield of mechanical pulping is high, typically in the range of 85-98%. The produced fiber pulps generally have high bulk and stiffness properties. However, mechanical pulping consumes a high level of operational energy, and the mechanical pulps often have poor strength.[0002]In order to reduce the required energy level and improve fiber strength, other process options have been used in a combination with mechanical energy. Thermomechanical pulping (TMP) grinds wood pulps under steam at high pressures and temperatures. Chemi-thermomechanical pulping (CTMP) uses chemicals to break up wood pulps prior to a mechanical pulping. The CTMP pulping has somewhat lower yield than mechanical pulping, but it provides pulp fibers w...

AI Technical Summary

Benefits of technology

[0016]The present disclosure relates to producing paper or paperboard having improved stiffness and strength, compared to the conventional paperboard at the same basis weight. It also discloses a method of wood pulping having a significantly increased yield and providing fiber pulps with enhanced properties such as strength and stiffness.

[0017]Wood chips are chemically pulped to a high kappa number, providing a rejects component and an accepts component. The rejects component is subjected to a substantially mechanical pulping process, optionally in a presence of bleaching agent, prior to blending back into the accepts component. The resulting fiber blend is washed, optionally in a presence of bleaching agent, and subjected to a papermaking process to provide paper or paperboard with enhanced strength and stiffness at low basis weight.

Problems solved by technology

However, mechanical pulping consumes a high level of operational energy, and the mechanical pulps often have poor strength.

However, using this prior technology, drawbacks exist from recooking the rejects which include an extremely low fiber yield, a potential increase in the level of pulp dirt, and a decrease in pulp brightness (poorer bleachability).

If a mill experiences cooking difficulties and accidentally undercooks the pulp, the amount of rejects increases exponentially.

Modern bleachable grade kraft pulp screen rooms are not physically designed to process pulps with greater than about 5% by weight of rejects.

However, all other known attempts to achieve a breakthrough of 5-10% yield increase have failed.

Additionally, the modified chemical pulping process often provides fiber pulps with lower tear strength.

However, a single-ply paperboard with an increased basis weight is economically undesirable because of a higher raw material cost and higher shipping cost for the packaging articles made of such board.

Good adhesion between each ply is critical to the performance of multi-ply board, leading to an additional factor that may deteriorate board properties.

However, a multiply-ply paperboard with an increased basis weight is economically undesirable because of a higher production cost and higher shipping cost for the packaging articles made of such board.

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