Papermaking method and papermaking system

The present invention relates to a method and a system for performing papermaking using a paper machine provided with a head box including a manifold having a cell-structure.

Generally, a paper manufacturing process includes a pulp step for forming a material pulp slurry and a papermaking step for making paper from the pulp slurry. In the pulp step, a material pulp slurry is prepared by forming chips from wood and performing digestion, cleaning, picking, bleaching and so on. In the papermaking step, the material pulp slurry is supplied from a head box onto a wire element for dewatering, and then processes such as pressing and drying are performed to produce paper.

Various kinds of paper machines are known such as a cylinder machine, a Fourdrinier machine, a “tanmo” machine, a twin wire machine and a crescent former.

Generally, in the papermaking process using a cylinder machine, a large shearing force is not mechanically applied to the material pulp slurry in the head box, so that the pulp is not sufficiently dispersed. Thus, to produce paper having a relatively low basis weight such as tissue paper or toilet paper using a cylinder machine, a viscous agent for dispersing pulp is generally used. For instance, polyethylene oxide may be used as the viscous agent. Specifically, an aqueous solution of polyethylene oxide having the concentration of not more than about 0.01 wt % and appropriate viscosity may be added to the material pulp slurry. Owing to the pulp dispersion effect of the viscous agent added in the papermaking process, paper in which pulp fibers is uniformly dispersed and which has excellent formation is obtained.

Paper machines such as a Fourdrinier machine, a “tanmo” machine, a twin wire machine and a crescent former (hereinafter, these machines are referred to as “high-speed paper machines”), which have been developed to achieve a productivity higher than that of a cylinder machine and whose papermaking speed (wire traveling speed) is relatively high, include a manifold having a cell-structure and provided in a head box. In these machines, therefore, when the material pulp slurry passes through the manifold, a large shearing force is applied to the material pulp slurry, whereby the slurry is mechanically dispersed. Thus, by using a high-speed paper machine, low-basis-weight paper having excellent formation is obtained without using a viscous agent. However, as compared with the papermaking process using a cylinder machine, the time taken for dewatering on the wire element in the papermaking process using a high-speed paper machine is shorter, because of the higher papermaking speed. Further, since a viscous agent is not used, the. dispersion of pulp on the wire element in a high-speed paper machine is inferior to that in a cylinder machine. As a result, although the productivity of a high-speed paper machine is higher than that of a cylinder machine, the quality of the obtained paper in terms of the formation is lower.

In recent years, competition for high quality paper is heating up in the field of papermaking, and a system capable of stably and easily making paper having excellent formation is demanded. Although improvement of paper machines is being carried out, studies of the addition-of an agent for improving the pulp dispersion in a high-speed paper machine are not making much progress. A conceivable reason for this is that, even if such a viscous agent as a polyethylene oxide-based viscous agent, which is known to be relatively vulnerable to shearing, is used for a high-speed paper machine, the viscous agent is sheared due to a large shearing force applied within the head box. As a result, the viscosity is. reduced, and hence, the effect of the viscous agent is reduced, so that the improvement of the formation like that obtained in the case of a cylinder machine is not expected.

Although the Patent Document 1 described below discloses a viscous-agent to replace polyethylene oxide, only a cylinder machine is disclosed as the application.

Patent Document 1: JP-A 2000-290892

An object of the present invention, which is proposed in view of the above-described problems of the prior art, is to provide a papermaking method and a papermaking system capable of making paper having excellent formation even by the use of a high-speed paper machine by optimizing the concentration of a viscous agent solution to be added to the material pulp slurry.

To solve the above-described problems, the inventors of the present invention have studied changes in viscosity of aqueous solution of polyethylene oxide caused by shearing to find that the viscosity is hardly degraded by shearing when the aqueous solution has a concentration higher than a predetermined value. By applying this result of the studies to papermaking, the inventors have found that paper having excellent formation is obtained even by the use of a high-speed paper machine and achieved the present invention.

According to a first aspect of the present invention, there is provided a method of making paper using a paper machine provided with a head box including a manifold having a cell-structure. The method comprises the steps of adding an aqueous solution of a viscous agent having a concentration of 0.03 to 0.4 wt % to a material pulp slurry, and introducing a mixed pulp slurry containing the material pulp slurry and the aqueous solution of the viscous agent into the manifold.

With the above-described papermaking method, the pulp dispersion effect by a viscous agent is properly exhibited even in a paper machine which includes a cell-structure manifold in the head box. As a result, paper in which pulp fibers are uniformly dispersed and which has excellent formation is obtained. In this way, according to this papermaking method, a viscous agent is effectively used to improve the quality of paper.

Further, with the papermaking method according to the present invention, the use of a proper viscous agent reduces the defects such as the breakage of paper due to insufficient dispersion of pulp fibers, and hence, stable papermaking is possible. Thus, the yield of papermaking is enhanced, and the production efficiency is improved.

Preferably, the addition of the aqueous solution of the viscous agent is performed between the head box and a screen located closest to the head box. In this case, the pulp dispersion effect by the viscous agent is properly exhibited.

Preferably, the viscous agent is a polyethylene oxide-based viscous agent. Preferably, in this case, the viscous agent may comprise solely of polyethylene oxide.

According to a second aspect of the present invention, there is provided a papermaking system comprising a screen for removing impurities from a material pulp slurry, a paper machine provided with a head box including a manifold having a cell-structure arranged on a downstream side of the screen, and viscous agent adding means for supplying an aqueous solution of viscous agent having a concentration of 0.03 to 0.4 wt % into a pipe connecting the screen and the head box to each other.

Preferably, the viscous agent is a polyethylene oxide-based viscous agent.

Other features and advantages of the present invention will become more apparent from the detailed description given below with reference to the accompanying drawings.