Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1996-02-01
1997-10-14
Chin, Peter
Paper making and fiber liberation
Processes and products
Non-fiber additive
1621641, 1621643, 1621646, 1621682, 1621683, 1621811, 1621812, 1621813, 1621816, 1621818, 162183, D21H 2110
Patent
active
056767960
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the production of paper which may be filled or unfilled and may be lightweight or heavyweight. The paper may be, for instance, paper board.
It is standard practice to make paper by forming a thick stock cellulosic suspension from at least one thick stock-component cellulosic suspension, diluting this to form a thin stock, passing the thin stock towards a drainage screen through various items of apparatus such as a fan pump and/or a centriscreen, and draining the thin stock through the screen so as to form a sheet, which is then dried. The thick stock is usually made by blending several different thick stock-component suspensions. The thin stock and the resultant paper may be unfilled, but generally filler is included.
It is standard practice to include various polymeric materials and other additives during the process. For instance it is known to add to the thick stock polymeric materials variously described as pitch dispersants, pitch fixatives or runability aids. The term "pitch" is used as a generic term to refer to a variety of sticky materials that may be naturally occuring with the paper making fibres or that may be added as a result of, for instance, recycling waste paper that includes polymeric binder.
Pitch dispersants are low molecular anionic compounds that keep the pitch in dispersion. In view of the increasing tendency to recycle the drainage white water, this can lead to an unacceptable build up of dispersed pitch in the white water. It is therefore more common to include pitch fixatives or runnability aids. Pitch fixatives are intended to cause the pitch, while still in very fine dispersed state, to be deposited onto the paper fibres so as to prevent its accumulation in the suspension and its non-uniform and undesirable deposition as relatively large lumps on the paper or on the paper making machinery. Since the components of the pitch are generally regarded as anionic and since the paper making fibres are generally anionic, conventional practice has been to use, as pitch fixative, polymeric material having the highest possible cationic charge.
In practice, suitable polymers having maximum cationic charge (for instance being homopolymers of cationic monomer) all usually have a relatively low molecular weight, typically having molecular weight such that intrinsic viscosity is below 2, and often below 1, dl/g. Accordingly, the pitch fixatures that are conventionally used are low molecular weight, high cationic charge, polymers. Examples are polyethylene imine and polyDADMAC (diallyl dimethyl ammonium chloride homopolymer). The use of these low molecular weight polymers is reasonably convenient since they can be supplied as solutions that are easy to store and use. Accordingly the use of such polymers does not necessitate the provision of bulky dissolution apparatus such as is required when high molecular weight flocculant polymers are used as retention aids later in the system.
It is also known to add various other materials to promote pitch fixing. For instance bentonite is sometimes added to the thick stock for this purpose. The use of a low molecular weight polymer in combination with bentonite is described in W093/13265 and, for low molecular weight polymers of a particular molecular weight, in EP 586755.
There have been several recent proposals to improve pitch fixing or other properties by adding cationic polymers of DADMAC at various positions. Some such disclosures mention adding polymers to the thick stock wherein the polymers can fall within a wide range of molecular weights and cationic charge densities and so embrace high molecular weight polymers. In practice, however, the disclosures which relate to pitch fixing tend to be exemplified solely by the use of polymers which have high charge density, for instance above 3 meq/g and low molecular weight, for instance intrinsic viscosity below 4 dl/g.
Examples of relevant references includes CA 2,102,742 and U.S. Pat. Nos. 5,098,520, 5,185,062, 5,256,252, 5,266,164 and 5,292,404.
Although high cationic, low mole
REFERENCES:
patent: 5098520 (1992-03-01), Begala
patent: 5126014 (1992-06-01), Chung
patent: 5185062 (1993-02-01), Begala
patent: 5240561 (1993-08-01), Kaliski
patent: 5256252 (1993-10-01), Sarkar et al.
patent: 5266164 (1993-11-01), Novak et al.
patent: 5292404 (1994-03-01), Hartan et al.
patent: 5368692 (1994-11-01), Derrick
Allied Colloids Limited
Chin Peter
LandOfFree
Manufacture of paper does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Manufacture of paper, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Manufacture of paper will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1552360