Paper making and fiber liberation – Processes and products – Plural fiber containing
Patent
1998-05-21
2000-05-30
Silverman, Stanley S.
Paper making and fiber liberation
Processes and products
Plural fiber containing
162149, 162147, 162142, 162100, D21H 1110, D21H 1102
Patent
active
060687347
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a soft, bulky absorbent paper. Soft paper or tissue paper, which is used in household paper products, toilet paper, serviettes, paper handkerchiefs, face tissues, etc., can be produced from a number of different types of pulp fibres. When disregarding recycled fibres, which at present are used to a large extent primarily in the manufacture of toilet paper and household paper, and considering solely the use of primary fibres, chemical pulp is the most usual type of pulp used in the manufacture of soft paper. Chemical pulp is produced by impregnating wood chips with chemicals and thereafter cooking the chips so that the lignin, resins and hernicellulose present pass into the liquor used. Upon completion of the cooking process, the pulp is screened and washed prior to being bleached, Such pulp contains practically no lignin and the fibres, which consist substantially of pure cellulose, are relatively slender and flexible. Chemical pulp may be comprised of either long fibres or short fibres, depending on the nature of the wood used, and may be either a sulphate pulp or a sulphite pulp, depending on the composition of the cooking liquor. Chemical long-fibre pulps, particularly sulphate pulps, have a favourable influence on the strength properties of soft paper with regard to both dry strength and wet strength.
Chemical pulp is a low yield pulp, since it gives a yield of only about 50% calculated on the wood starting material used. Chemical pulp is therefore a relatively expensive pulp. Consequently, less expensive so-called high-yield pulps have been used in soft paper, for instance mechanical or thermomechanical pulps; see GB Patent Specification 1,533,045 in this regard. Mechanical pulps are produced by grinding or refining the wood starting material. The principle applied in the manufacture of mechanical pulp is to break down the wood mechanically. All of the wood material is used and the lignin thus remains in the fibres, which are relatively short and stiff. Thermomechanical pulp (TMP) is produced by refining the wood in disc refiners at an elevated steam pressure. The lignin also remains in the fibres of thermomechanically produced pulp.
Chemithermomechanical pulp (CTMP) is the designation given to a thermomechanical pulp that has been modified by adding small quantities of chemicals, usually sulphite, which are added prior to the refining process. The admixture of a given amount of chemithermomechanical pulp in soft paper has positive effects on such properties as bulk and absorbency.
All of the aforementioned pulp types are at present used in the manufacture of soft paper.
OBJECTS OF THE INVENTION AND THE MOST IMPORTANT CHARACTERISTICS THEREOF
The object of the present invention is to provide a soft paper whose properties have been further enhanced with regard to bulk and absorbency. This object has been achieved by including in the paper at least 20 percent by weight, calculated on the total fibre weight, of high-temperature chemithermomechanical pulp (HT-CTMP) which exhibits the following properties: retained on a wire having a mesh width of 30 mesh) when fractionating in accordance with Bauer McNett, a fine-material content of at most 14% (fibres that pass through a wire having a mesh width of 200 mesh) when fractionating in accordance with Bauer McNett, a freeness of at lowest 600 ml CSF, a shive content lower than 0.5%, preferably lower than 0.25%, and a tensile index of at least 10 kNm/kg, wherein the paper also includes at least 10 percent by weight of a pulp that has good strength propernes, such as chemical pulp and/or recycled fibre pulp.
It has surprisingly been found that an admixture of at least 20% HT-CTMP will give the paper a much greater bulk than will a corresponding amount of admixed conventional CTMP. The absorbency and liquid dispersion rate of the paper is also improved when admixing HT-CTMP with the paper pulp. The bulk, absorbency and liquid-dispersion properties of the paper are improved with increasing amounts of
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Nordqvist Bengt
Wallenius Hans
Fortun Jose A
SCA Hygiene Paper AB
Silverman Stanley S.
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