Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Simultaneous mechanical defibration and chemical treatment
Patent
1990-05-15
1992-09-08
Jones, W. Gary
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Simultaneous mechanical defibration and chemical treatment
162 28, 162 55, 162 78, 162 24, D21B 116
Patent
active
051450100
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the production of mechanical pulp from softwood. More particularly, the present invention relates to the production of mechanical pulp which is intended for producing coated paper having a low grammage, or so-called LWC-paper (light weight costed), as well as uncoated calendered magazine paper, or so-called FSC-paper (filled supercalendered), or paper of similar quality.
BACKGROUND OF THE INVENTION
The production of the coated papers having low grammage such as those mentioned above creates extremely high demands on the pulp properties, primarily because the pulp is required to have a high strength as well as a low roughness. In addition, these coated papers also require a low porosity, and it is also particularly important that they have a smooth surface structure.
These types of papers normally contain both chemical and mechanical pulps. The mechanical pulp component has traditionally comprised groundwood pulp. More recently, however, thermomechanical pulp (TMP) has been used as an alternative to groundwood. This has had limited success, however, because the concomitant energy consumption is relatively high compared with that in the manufacture of groundwood. Furthermore, in a number of instances the use of TMP has resulted in unevennesses in the surface structure of the paper, which in turn causes poor coating and printability characteristics. These problems could thus be avoided only by the paper manufacturer taking special measures to modify or eliminate the negative effects of the long fiber fraction present in the thermomechanical pulp. The presence of this long fiber fraction negatively affects the smoothness of the paper, because it causes poor formation of the paper and because it contains some long stiff fibers, as well as having poor binding strength. TMP for use in LWC-paper and the like is usually manufactured by refining in two or more steps, with subsequent screening and reject processing, bleaching and post-refining.
SUMMARY OF THE INVENTION
In accordance with the present invention, it is now possible to reduce the energy consumption in the manufacture of thermomechanical pulp while at the same time improving the pulp quality, thus rendering it possible to increase the amount of mechanical pulp in the stock while decreasing the amount of chemical pulp compared with that traditionally used for different paper qualities. This has been accomplished according to the present invention by providing a method for producing mechanical pulp from softwood which comprises impregnating softwood chips with water and a complexing agent, refining the impregnated softwood chips in a first refining step utilizing a pair of counter-rotating refining disks so as to produce a first refined softwood pulp fractionating the first refined softwood pulp so as to produce a first accept portion and a first reject portion, said first reject portion comprising between about 15 and 35% of the first refined pulp and including an increased concentration of long and stiff fibers in the pulp, refining the first reject portion in second and third refining steps so as to produce a second refined softwood pulp the first refining step utilizing a first concentration of softwood pulp and the third refining step using a second concentration of softwood pulp, the first concentration being greater than the second concentration, and fractionating the second refined softwood pulp so as to produce a second accept portion and second reject portion. In a preferred embodiment the impregnation of the softwood chips is carried out at a pH of from about 5 to 9.
In accordance with one embodiment of the method of the present invention, the first refining step is carried out so as to produce a first refined softwood pulp having a long fiber content measured according to Bauer McNett characterization to .ltoreq.8% on +16 mesh and .ltoreq.26% on 16-30 mesh.
In a preferred embodiment this method includes fractionating the first refined softwood pulp so as to produce a first reject por
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Danielsson K. Ove
Falk Bo G. S.
Jackson Michael
Burns Todd J.
Jones W. Gary
Sunds Defibrator Industries Aktiebolag
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