Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Chemical treatment after start or completion of mechanical...
Patent
1996-12-13
1999-03-09
Silverman, Stanley S.
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Chemical treatment after start or completion of mechanical...
162 26, 162 28, 162 19, 162 24, 162 78, 162 76, 162 55, D21B 102
Patent
active
058795103
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a long-fiber, readily dewatered, bulky, high yield chemimechanical pulp produced from lignocellulosic fiber material at a high yield (>88%) and having a low shive content, low fine-material content and an extract content of less than 0.15%. The invention also relates to a method of producing the pulp.
BACKGROUND OF THE INVENTION
In certain paper products it is advantageous to be able to achieve the highest possible bulk (low bulk density) at a given strength while satisfying high requirements placed on the surface properties of the products. Examples of such products are tissue products, with which high liquid absorption is a preferential property, and paperboard material or so-called liners for corrugated fiberboard boxes, with which a high degree of flexural rigidity is desired.
High bulk is, of course a necessary factor in achieving high liquid absorption. High bulk also contributes positively to the rigidity or stiffness of the board and the liner products. Since high requirements are also placed on the surface properties of this type of product, i.e. properties which will impart smoothness and softness to tissue products and enable print to be applied easily to the surfaces of paperboard and liners the shive content of the pulps used must be extremely low. The requirement of a low shive content and a given lowest mechanical strength has hitherto limited the possibility of using the most extremely long-fiber chemimechanical pulps of low fine-material contents, which provide the bulkiest products. The methods hitherto known for the production of extremely long-fiber chemimechanical pulps have resulted in pulps which are too weak or in which the coarse shive content is much too high.
High yield mechanical and chemimechanical pulps (>88%) are characterized in that the long whole fibers in the pulp (measured for instance as the fraction captured on a 30 mesh (Tyler standard) wire when fractionating in a Bauer McNett-apparatus) have a high flexural rigidity, which is also a prerequisite for manufacturing products which have a very high bulk. In order to produce pulp whose strength properties are sufficiently good for the pulp to be used in the manufacture of tissue, paperboard or liner products for instance, it has also been necessary hitherto for mechanical and chemimechanical pulp to contain a very high proportion of fiber fragments and fine-material, since these materials function as a binder between the long, stiff fibers. When fractionating in a Bauer McNett-apparatus, it has hitherto been considered necessary for the fine-material content, which is normally characterized as the fraction that can pass through a 200 mesh wire (Tyler standard), to be greater than 10%, preferably greater than 12%, in order to be able to obtain strength properties that are sufficiently good for use in tissue, fiberboard or liner products. Another reason why it has hitherto been considered necessary for mechanical or chemimechanical pulps to contain more than 12% fine-material is because at least this amount is formed nevertheless when working the pulp to reduce its shive content (measured according to Somerville with a 0.15 mm mesh width) to levels that are sufficiently low (less than 0.50%, preferably less than 0.25%) to obtain the desired surface properties.
SE-B-397 851 teaches a method of producing a chemimechanical pulp in which the chips are first impregnated with an alkaline sodium sulphite solution and then preheated with steam at 135.degree.-170.degree. C. for about 10 minutes. The following refinement is effected in an open refiner at a temperature slightly above 100.degree.C. The pulp is refined to 400 ml CSF and a very low shive content is obtained. Thus, when practicing this known method it is elected to refine at a relatively low temperature, i.e. a temperature which is much lower than the so-called lignin softening temperature. A relatively high energy input is then required in the refining process in order to obtain a low shive content, which
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patent: 4562969 (1986-01-01), Lindahl
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Hans Hoglund et al., "Modified thermo-mechanical pulp", Svensk Papperstidning, vol. 79, No. 11, 1976, pp. 343-347 and 353.
Back Roland
Ekebro Ingela
Hagglund Tjell-Ake
Hoglund Hans
Fortune Jose S.
SCA Hygiene Products AB
Silverman Stanley S.
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