Process for regenerating wastepaper using a double layer hydroxi

Details Process for regenerating wastepaper using a double layer hydroxi Process for regenerating wastepaper using a double layer hydroxi

1991-09-23

1993-07-13

Hastings, Karen M.

Paper making and fiber liberation

Processes of chemical liberation, recovery or purification...

Waste paper or textile waste

D21C 502

Patent

active

052270203

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a process for regenerating wastepaper and to the use of cationic layer compounds precipitated in situ for regenerating wastepaper.
2. Discussion of Related Art
"Deinking" is the removal of printing inks from wastepaper fiber suspensions. Deinking processes essentially comprise two steps, namely:
1. refining the wastepaper, i.e. fiberizing in water in the presence of the chemicals required for detachment of the printing ink particles and
2. removal of the detached printing ink particles from the fiber suspension.
The second step can be carried out by washing or flotation (Ullmanns Encyclopadie der technischen Chemie, 4th Edition, Vol. 17, pages 570-571 (1979)). In flotation, which utilizes the difference in wettability between printing inks and paper fibers, air is forced or drawn through the fiber suspension. Small air bubbles attach themselves to the printing ink particles and form a froth at the surface of the water which is removed by savers.
The deinking of wastepaper is normally carried out at alkaline pH values in the presence of alkali metal hydroxides, alkali metal silicates, oxidative bleaches and surfactants at temperatures in the range from 30.degree. to 50.degree. C. Soaps and/or fatty alcohol polyglycol ethers are often used as surfactants which are responsible for the detachment and separation of the printing inks (Ullmanns Encyclopadie der technischen Chemie, 4th Edition, Vol. 17, pages 571-572 (1979)).
In recent years, conventional printing ink systems, for example based on nitrocellulose, maleate resins and/or shellac, which contain esters and/or ketones, for example ethyl acetate and/or methyl ethyl ketone, or alcohols as solvent, have been increasingly replaced by water-dilutable printing inks for reasons of pollution control. Another reason for the increasing use of water-dilutable printing inks lies in the non-inflammability of water which eliminates the need for the expensive safety systems which normally have to be installed in the printing works where solvent-containing printing inks are used. Most water-dilutable printing inks contain as binder component anionic polymers, for example polymers containing carboxyl groups, of which the neutralization with bases makes the printing inks dilutable with water. However, water-dilutable printing inks have the major disadvantage that they can only be removed completely inadequately, if at all, with the surfactants typically present in the deinking liquor (Das Papier 42, V 84-V 88 (1988)). The result of this is that, hitherto, the wastepaper printed with water-dilutable printing inks, which is accumulating in ever-increasing quantities, is not recycled and, hence, is also not available as a wastepaper raw material for newsprint and sanitary papers.
Through the increasing constriction of water circuits in the paper industry, there has been a considerable increase in the concentration of ionic and/or nonionic, inorganic and/or organic substances soluble and/or colloidally dissolved in water. These substances, which are known as "trash" in the paper industry, on the one hand pollute the wastewater and, on the other hand, adversely affect paper manufacture, paper quality and the effectiveness of cationic auxiliaries (Wochenblatt fur Papierfabrikation 1984, 37-48). Starch, casein, polyvinyl alcohol, polymer dispersions, carboxymethyl celluloses and/or printing ink binders are examples of such trash.
The problem addressed by the present invention was to provide a process for regenerating wastepaper with which it would be possible to remove printing inks and, more particularly, water-dilutable printing inks, fillers and/or trash from fiber suspensions.
Cationic layer compounds, which are also referred to in the literature as "double-layer hydroxides" (R. Allmann "Doppelschichtstrukturen mit brucitahnlichen Schichtionen . . . " in Chimia 24, 99-108 (1970)) may be characterized by the following general formula H.sub.2 O represents at least one trivalent metal cation and A

REFERENCES:
patent: 5037508 (1991-08-01), Hyder et al.
Abstract Bulletin of the Paper Chemistry, 6493u, vol. 49, No. 7, Jan. 1979.

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