Paper making and fiber liberation – Processes and products – Pore forming in situ
Patent
1997-01-15
1998-02-24
Chin, Peter
Paper making and fiber liberation
Processes and products
Pore forming in situ
162190, 162264, 162289, D21D 300
Patent
active
057208514
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of producing a foam-formed fibre or paper web, whereby a foamed fibre dispersion is formed by dispersing natural and/or synthetic fibres in a foamable liquid comprising water and a tenside in a dispersion vessel and by conveying the foamed fibre dispersion to a wire on a paper machine.
BACKGROUND TO THE INVENTION
Paper webs and other wet-laid fibre webs are normally produced by starting from pulp or other fibres in bale form and forming a fibre furnish in a carrier medium, normally water, by mechanical processing in a breaker vessel. Water addition is effected in order to regulate the fibre concentration to the desired level. Sometimes chemicals are also added. The fibre furnish is transferred from the breaker to vats for additional dilution before being conveyed to the inlet box of the paper machine via possible purification and screening stages.
Foam-formed fibre webs, i.e. fibre webs formed from a dispersion of fibres in a foamed liquid, are produced in a similar way. A pulp or fibre furnish is thus first prepared in water in a breaker. A certain dewatering occurs thereafter, before the furnish is mixed with a foamable liquid containing tenside and water. The fibres are dispersed in the foam and the foamed fibre dispersion is deposited on a wire, and the main portion of the liquid which is essentially in the form of a foam, is removed by the wire. The technique is described i.a. in GB 1,329,409 and U.S. Pat. No. 4,443,297. The thus-produced fibre webs present a high degree of uniformity in the fibre formation. One problem in connection with foam forming is the recirculation of the foam in the system drained from the wire in a controlled manner with the maintenance of a good balance in the system with respect to the air content and tenside content of the foam.
OBJECT OF THE INVENTION AND THE MOST IMPORTANT FEATURES
The object of the present invention is to achieve a method of producing foam-formed paper webs and other fibre webs, where the aforementioned problems are solved in a simple manner by conveying the foamed liquid which is removed from the wire to a closed foam tank in which a draining of the liquid to the bottom of the tank occurs, whilst the lighter foam is collected in the top of the foam tank. Liquid from the bottom of the foam tank is led to the dispersion vessel via a first pipeline, and the foam passes to the dispersion vessel via a second pipeline (130) in the top of the foam tank where the fibres are added and dispersed in the foamable liquid.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail with reference to two embodiments shown in the accompanying drawings.
FIG. 1 shows a flow diagram of the method according to the invention.
FIG. 2 shows a modified embodiment of the dispersion vessel and the foam tank.
DESCRIPTION OF EMBODIMENTS
FIG. 1 shows a process solution for a foam forming process according to the invention. The foam is generated by means of a tenside being added to the water in a pulper 111 where an intensive agitation and air intake occurs. Additional foam generation occurs in the process due to the turbulence which is created in the pumps as well as at the wire 118. A condition for foam generation is however that there is access to air.
The tenside can be of any suitable type; anionic, cationic, non-ionic or amphoteric. GB patent 1,329,409 describes tensides suitable for foam forming of fibre webs. There are however many other available tensides suitable for the purpose. The choice of tenside can for example be affected by factors like the chemical composition of possible other additives to the fibre furnish, like wet-strengtheners, binders, creping chemicals, etc.
A suitable tenside metering in order to achieve a relatively stable foam which is able to maintain a substantially uniform dispersion of fibres in the foam is adjusted for each individual case and is dependent on such factors as the type of tenside, the degree of hardness of the water, the water tempe
REFERENCES:
patent: 4443297 (1984-04-01), Cheshire et al.
patent: 4498956 (1985-02-01), Cheshire et al.
patent: 4543156 (1985-09-01), Cheshire et al.
patent: 4686006 (1987-08-01), Cheshire et al.
patent: 4944843 (1990-07-01), Wallace et al.
Chin Peter
SCA Hygiene Paper AB
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