Paper making and fiber liberation – Processes and products – Non-fiber additive
Patent
1992-01-06
1993-11-30
Chin, Peter
Paper making and fiber liberation
Processes and products
Non-fiber additive
1621811, 1621812, 1621813, 162183, D21H 1769
Patent
active
052661636
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the treatment of a pigment, suspended in water and intended for the papermaking industry, with an aqueous binder or the pigment treated thus. Furthermore, the invention relates to a process for the manufacture of pigment-containing paper with increased resistance to tearing or with increased pigment content.
PRIOR ART
For over one hundred years it has been common practice in the manufacture of printing papers to coat the surface in order to obtain a good printing view. The coated papers are also called art paper. Machine coated paper or chrome paper and in the highest quality as enamel paper. The purpose of the coating is to form a layer for the print, which consists exclusively of pigments and a binder. This layer is usually also compacted by means of calendaring and brought to a gloss. It enables the reproduction of the finest dots.
Coating in an expensive process that is usually performed in a separate coating installation after the papermaking machine. Since printing on pigments or pigment layers leads to significantly better printing results than printing on a pure fibre web. For decades there have been efforts to introduce more pigments into the paper directly on the papermaking machine without reducing its resistance to tearing. Thus the expensive coating process could be avoided.
Wood-containing, highly filled, super calendared gravure papers with a pigment content ranging from 17 to 30 wt. % are wide spread. They are called super calendared papers. When they are manufactured, the pigments, usually kaolin or talcum, are bonded adsorptively and filtratively in the fibre web.
To improve the bonding of the pigment, binders have also been already used, e.g. modified starch, carboxymethyl cellulose, alginates, mannogalactans (Meyproid), gelatin and hide glue. They are added into the furnish as colloid solutions and are bonded adsorptively to the pigment and the fiber by means of electrokinetic forces. This bonding is never complete. Therefore, a portion of the added binder, is found in the recycling water and in the waste water of the papermaking plants which portion is thus lost and necessitates a purification of the waste water.
EP-A 50 316 described a paper manufacturing process in which in a first process step an aqueous suspension of an inorganic pigment is treated with a classic organic paper binder such as dextrin, starch, carboxymethyl cellulose, polyvinyl alcohol or polymer dispersions; and the binder is precipitated by means of a cationic flocculent. Suitable flocculants are polycationic compounds such as polyethylene imine, cationically modified polyacrylamides, polyaluminum chloride and cationic starch. The added pigment suspension can optionally contain conventional dispersants such as polyphosphates or sodium polyacrylate; such dispersants do not act as binders.
In the second process step the pigment pretreated thus is added to an aqueous fibre stock and finally the sheet of paper is formed. When forming the sheet, excellent retention of the pigment is achieved, and paper with improved resistance to tearing is obtained.
In a process described in the DE-A 2 115 409 mineral fillers for the papermaking industry are used, primarily calcium carbonate. with a coating made of an organic polymer, wherein primarily the decomposition of the calcium carbonate in the acidic range is to be suppressed. The coating can be formed, e.g., from an aqueous solution of a neutralized acrylic acid polymerizate by means of precipitation with aluminum sulfate. The aluminum ions have the effect of imparting a positive charge to the filler or the pigment and thus intensifying their affinity for the cellulose fibers.
The inventors have found that binders precipitated by means of electrokinetic effects are not bonded so as to be shear stable so that during the subsequent formation of the sheet some binder always gets into the water circuit.
PROBLEM AND SOLUTION
The object of the invention is a process for the treatment of a pigment, suspended in water and intended for the p
REFERENCES:
patent: 4282059 (1981-08-01), Davidson
patent: 5030325 (1991-07-01), Saji et al.
Chin Peter
Rohm GmbH
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