Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Treatment with particular chemical
Reexamination Certificate
1998-06-25
2002-10-22
Alvo, Steve (Department: 1731)
Paper making and fiber liberation
Processes of chemical liberation, recovery or purification...
Treatment with particular chemical
C162S149000, C435S277000, C435S278000
Reexamination Certificate
active
06468391
ABSTRACT:
TECHNICAL FIELD
This invention relates to a method for making sanitary paper.
BACKGROUND ART
Sanitary paper such as toilet paper, facial tissue paper, paper napkin, wiper, paper towel, sanitary napkin, diaper etc. is commonly made from papermaking pulp. It is generally desirable to make the sanitary paper softer without reducing the paper strength.
Japanese laid-open patent application Tokkai Hei (JP-A) 5-148794 discloses that a treatment of the pulp with a cellulase preparation is effective for this purpose. The cellulase preparations described therein are produced by cultivation of microorganisms and are known to contain mixtures of various cellulase components with and without cellulose binding domains.
It is the purpose of this invention to improve the known process to achieve a better effect.
STATEMENT OF THE INVENTION
We have, surprisingly, found a certain type of cellulase component to be very effective in reducing the paper stiffness without significant loss of paper strength (or, in some cases, even with an increase of paper strength). The cellulase component in question is characterized by not containing a cellulose-binding domain (CBD), and is more effective than a conventional cellulase preparation which contains a mixture of various cellulase components.
Accordingly, the invention provides a method wherein a papermaking pulp is treated with a cellulase in the absence of a cellulose-binding domain. The treated pulp is used for making sanitary paper.
DETAILED DESCRIPTION OF THE INVENTION
Sanitary Paper
The sanitary paper produced according to the invention may be toilet paper, facial tissue paper, wiper, paper napkin, paper towel, sanitary napkin, diaper etc.
Papermaking Pulp
Any papermaking pulp conventionally used for the production of sanitary paper can be treated according to the invention. This pulp can be supplied as a virgin pulp, or can be derived from a recycled source.
The papermaking pulp may be a wood pulp, a non-wood pulp or a pulp made from waste paper. A wood pulp may be made from softwood such as pine, redwood, fir, spruce, cedar and hemlock or from hardwood such as maple, alder, birch, hickory, beech, aspen, acacia and eucalyptus. A non-wood pulp may be made, e.g., from bagasse, bamboo, cotton or kenaf. A waste paper pulp may be made by re-pulping waste paper such as newspaper, mixed office waste, computer print-out, white ledger, magazines, milk cartons, paper cups etc.
Preferably, the papermaking pulp to be treated comprises both hardwood pulp and softwood pulp. Advantageously, we have found that a cellulase without a cellulose-binding domain (CBD) used according to the invention is particularly effective for softening such a mixed pulp. Thus, the papermaking pulp may comprise comprise 5-95% (particularly 25-75% ) of softwood pulp and 5-95% (particularly 25-75%) of hardwood pulp (% of pulp dry matter).
The wood pulp to be treated may be mechanical pulp (such as ground wood pulp, GP), chemical pulp (such as Kraft pulp or sulfite pulp), semichemical pulp (SCP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), or bleached chemithermomechanical pulp (BCTMP).
The Kraft pulp to be treated may be a bleached Kraft pulp, which may consist of softwood bleached Kraft (SWBK, also called NBKP), hardwood bleached Kraft (HWBK, also called LBKP) or a mixture of these. A good softening effect according to the invention is seen with a mixture of NBKP and LBKP, e.g. with a eight ratio (on dry basis) of NBKP:LBKP in the range from 3:1 to 1:3. One preferred mixture consists of SWBK having a coarseness above 18 and HWBK having a coarseness above 10. Another preferred mixture consists of SWBK having a coarseness below 18 and HWBK having a coarseness below 10. The coarseness of the pulp is determined according to TAPPI method T271 (pm-91) and is expressed in units of mg per 100 m.
When treating a waste paper pulp, the cellulase treatment can take place during or after pulping of the waste paper. The cellulase treatment can simultaneously serve to release ink particles from the cellulose fibers, whereafter the released ink particles can be removed to obtain a de-inked pulp, as described in JP-A 59-9299, JP-A 63-59494, JP-A 2-80683, and JP-A 3-882.
The sanitary paper can be made from dried pulp. In this case, the cellulase treatment can be applied in the production of the dried pulp, or it can be applied during or after re-pulping (disintegration) of the dried pulp.
Cellulase without CBD
The invention uses a cellulase in the absence of a cellulose-binding domain (CBD). The term “cellulose” denotes an enzyme that contributes to the hydrolysis of cellulose, such as a cellobiohydrolase (Enzyme Nomenclature E.C. 3.2.1.91), an endo-glucanase (hereinafter abbreviated as “EG”, E.C. 3.2.1.4), or a beta-glucosidase (E.C. 3.2.1.21).
Cellulose-binding domains have been described by P. Tomme et al. in J. N. Saddler & M. H. Penner (eds.), “Enzymatic Degradation of Insoluble Carbohydrates” (ACS Symposium Series, No. 618), 1996. A number of cellulases are known to contain a catalytic domain without a CBD; such a cellulase may be used as such in the invention. It is also known that other cellulases contain a catalytic domain and a CBD; such a cellulase may be truncated to obtain a catalytic core domain without the CBD, and this core may be used in the invention.
The cellulase used in this invention may be a single component, or a mixture of cellulases may be used, provided each cellulase has no CBD.
Cellulases may be classified into families on the basis of amino-acid sequence similarities according to the classification system described in Henrissat, B. et al.:
Biochem. J.,
(1991), 280, p. 309-16, and Henrissat, B. et al.:
Biochem. J.
, (1993), 293, p. 781-788. Some preferred cellulases are those belonging to Family 5, 7, 12 and 45.
Family 5 Cellulase
A preferred Family 5 cellulase without CBD is an alkaline cellulase derived from a strain of Bacillus. One such Family 5 cellulase is the endo-glucanase from Bacillus strain KSM-64 (FERM BP-2886). The cellulase and its amino acid sequence are described in JP-A 4-190793 (Kao) and Sumitomo et al.,
Biosci. Biotech. Biochem.,
56 (6), 872-877 (1992).
Another Family 5 cellulase from Bacillus is the endo-glucanase from strain KSM-635 (FERM BP-1485). The cellulase and its amino acid sequence are described in JP-A 1-281090 (Kao) , U.S. Pat. No. 4,945,053 and Y. Ozaki et al.,
Journal of General Microbiology,
1990, vol. 136, page 1973-1979.
A third Family 5 cellulase from Bacillus is the endo-glucanase from strain 1139. The cellulase and its amino acid sequence are described in Fukumori F. et al.,
J. Gen. Microbiol.,
132:2329-2335 (1986) and JP-A 62-232386 (Riken).
Yet another preferred Family 5 cellulase without CBD is an endo-beta-1,4-glucanase derived from a strain of Aspergillus, preferably
A. aculeatus
, most preferably the strain CBS 101.43, described in WO 93/20193 (Novo Nordisk).
Family 7 Cellulase
The Family 7 cellulase may be derived from a strain of Humicola, preferably
H. insolens.
An example is endo-glucanase EG I derived from
H. insolens
strain DSM 1800, described in WO 91/17244 (Novo Nordisk). The mature cellulase has a sequence of the 415 amino acids shown at positions 21-435 in FIG. 14 of said document and has a specific activity of 200 ECU/mg (based on pure enzyme protein). This cellulase may further be truncated at the C-terminal by up to 18 amino acids to contain at least 397 amino acids. As examples, the cellulase may be truncated to 402, 406, 408 or 412 amino acids. Another example is a variant thereof denoted endo-glucanase EG I* described in WO 95/24471 (Novo Nordisk) and having a sequence of 402 amino acids shown in FIG. 3 therein.
Alternatively, the Family 7 cellulase may be derived from a strain of Myceliophthora, preferably
M. thermophila,
most preferably the strain CBS 117.65. An example is an endo-glucanase described in WO 95/24471 (Novo Nordisk) comprising the amino acids 21-420 and optionally also the amino acids 1-20 and/or 421-456 of the sequence shown in FIG. 6 therein.
As another alte
Franks Neal
Kida Katsunori
Ohishi Masahiro
Sakaguchi Hiromichi
Schulein Martin
Alvo Steve
Garbell Jason
Lambiris Elias
Novozymes A/S
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