Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1995-10-04
1998-03-31
Chin, Peter
Paper making and fiber liberation
Processes and products
Non-fiber additive
1621641, 162165, 1621682, 1621683, 162183, D21H 2110
Patent
active
057334145
DESCRIPTION:
BRIEF SUMMARY
It is standard practice to make paper by a process comprising forming a cellulosic suspension, adding a retention system to the suspension, draining the suspension through a screen to form a sheet, and drying the sheet in conventional manner to make the desired paper, which can be a paper board.
The retention system is included in the suspension before drainage in order to improve retention of fibre and/or filler. The retention system can consist of a single addition of polymer in which event the polymer is usually a synthetic polymer of high molecular weight, or the retention system can comprise sequential addition of different retention aids. Before adding a high molecular weight polymer or other retention aid it is known to include low molecular weight cationic polymer, for instance as a wet strength resin or as a pitch control additive. The molecular weight of such polymers is generally too low to give useful retention.
A common retention system comprises the use of high molecular weight (for instance intrinsic viscosity above 4 dl/g) cationic polymer formed from ethylenically unsaturated monomers including, for instance, 10 to 30 mol % cationic monomer. Retention systems are also known in which high molecular weight non-ionic polymer or high molecular weight anionic polymer is used.
Some of the known retention systems using polymers formed from water soluble ethylenically unsaturated monomers can give good results on a range of pulps. For instance the Hydrocol (trade mark) process that uses a cationic polymer followed by a swelling clay (see EP-A-235893) gives good retention and drainage results on many stocks. However the need to handle and supply bentonite or other swelling clay is sometimes inconvenient and with some stocks a more cost effective treatment may be desirable, especially when good formation is required.
The use of phenol- or napthol- sulphur resins, or of phenol- or napthol- formaldehyde resins, followed by polyethylene oxide is described in U.S. Pat. No. 4,070,236. The phenol formaldehyde resins are exemplified by commercial products and it is stated that the preferred products are formed by condensation of formaldehyde with m-xylene sulphonic acid and dihydroxy diphenyl sulphone. The commercial products that are named are described as synthetic tanning agents. The molar proportions used for making the phenol formaldehyde resins are not described but we believe that the commercial tanning agents were probably made using an amount of the sulphone such as to provide about half the recurring groups in the polymer.
We are aware that there has been some commercial use of retention systems comprising water soluble phenol formaldehyde resin followed by polyethylene oxide on relatively dirty cellulosic suspensions (i.e., suspensions having a high cationic demand). Although in some instances such processes have given useful results, they have proved to be of very limited commercial applicability.
It would be desirable to provide an entirely new type of retention system since this would afford the opportunity to optimise it for a wide variety of stocks and would give the paper-maker a widened choice of retention systems. It would also be desirable to provide such a system that can give a good combination of retention, drainage and formation on a variety of stocks, including dirty stocks. It would be desirable to provide a system that utilises cost effective materials that are easy to handle, and that preferably does not require the use of bentonite or other swelling clay.
According to the invention, a process of making paper comprises forming a cellulosic suspension, adding to the suspension a water soluble cationic retention aid which is a polymer which is cationic in the suspension and which is formed from a water-soluble ethylenically unsaturated monomer blend containing 0.1 to 15 mol % cationic (including potentially cationic) monomer, and has intrinsic viscosity at least 4 dl/g, and then adding a substantially soluble condensate of formaldehyde with one or more aromatic hydroxyl compounds
REFERENCES:
patent: 4070236 (1978-01-01), Carrard et al.
patent: 4680212 (1987-07-01), Blyth et al.
patent: 5538596 (1996-07-01), Satterfield et al.
Allied Colloids Limited
Chin Peter
LandOfFree
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