US 4,986,882 AGranted

Absorbent paper comprising polymer-modified fibrous pulps and wet-laying process for the production thereof

AssigneeThe Proctor & Gamble Company

InventorsLarry N. Mackey, Seyed E. Seyed-Rezai

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Abstract

Processes are described for making highly absorbent tissues and towels by wet-laying pulps comprising particular polycarboxylate polymer-modified fibrous pulps such as mildly hydrolyzed methyl acrylate-grafted softwood kraft pulps; these pulps have distinct protonated and alkali-metal-cation-exchanged states. The wet-laying processes are adapted to exploit the very different behavior of the polymer-modified fibrous pulps in function of the two states. The preferred wet-laying processes described herein are continuous processes embodying one or more on-line chemical treatment steps which chemically switch state of the polymer-modified fibrous pulp component in a wet web on the papermaking machine to improve the processing thereof by averting or minimizing tendencies to mechanically or thermally degrade.

Claims20

Dependent claims

In a continuous wet-laying papermaking process for the manufacture of absorbent paper sheets from two or more fibrous cellulosic pulps, wherein at least one of said fibrous cellulosic pulps, A, is a polymer-modified fibrous cellulosic pulp, capable of being protonated, which, in its alkali-metal-cation exchanged state, imbibes water by hydrocolloidal swelling, and wherein the balance of said fibrous cellulosic pulps, B, is non-polymer modified and comprises conventional cellulosic papermaking pulps, said process comprising the steps of web lay-down and dewatering starting from an aqueous suspension, slurry or stock containing a mixture of the pulps, the improvement which comprises conducting the wet-laying process by wet-laying an acidified mixture of the A and B pulps in the absence of interfering cationic materials, under conditions wherein pulp A is laid down in an embryonic web in the protonated state and wherein said embryonic web is at least partially dewatered while maintaining pulp A in said protonated state;

said process comprising the sequence of steps:
(a) treating stock of said fibrous cellulosic pulps with acid;
the amount of said acid being sufficient to ensure that in subsequent step (b), the type A component of said fibrous pulps is maintained in said protonated state;
(b) wet-laying the acidic stock formed in step (a) from a single-channel or multi-channel headbox onto a first foraminous member, thereby draining water to the extent of forming an embryonic web, said embryonic web having one or more layers;
(c) at least partially dewatering the embryonic web in one or more steps to provide a partially dewatered web;
(d) contacting the partially dewatered web of step (c) with an aqueous solution of alkali so as to at least partially bring the fibrous cellulosic pulp type A component of the web to the alkali-metal cation-exchanged state;
and
(e) drying the web.

5 more elements

An absorbent structure, in the form of wet-laid paper sheet, comprising:

from about 5% to about 15% of fibrous pulp type A, consisting essentially of a polymer-modified fibrous pulp having distinct protonated and alkali-metal-cation-exchanged states;
which pulp, as characterized in the protonated state, has relatively non-swollen fibrous morphology and which, as characterized in the alkali-metal-cation-exchanged state, has the form of a substantially fibrous polyanionic hydrocolloid further characterized by hydrocollodial swelling upon wetting, to the extent that said fibrous pulp type A has a water or aqueous fluid absorbency of from about 20g/g to about 60g/g, measured by the TBGV method, and a rate of water or aqueous fluid absorption such that said fibrous pulp type A reaches at least 90% of its maximum water-absorbing capacity within 10 seconds, measured by the VELM method;
said polymer-modified fibrous pulp type A in the alkali-metal-cation-exchanged state being relatively fragile and difficult to dewater when wet as compared with conventional papermaking fibers and being susceptible to deactivation as an absorbent upon exposure to either of both of the classes of cationic materials (i) multivalent metal ions such as are commonly present in papermaking process water and (ii) cationic polymers or cationic polyelectrolytes conventionally known for use in papermaking for improving paper wet-strength;
said polymer-modified fibrous pulp further being characterized by a significant relative decrease in fragility, increase in ease of dewatering and increase in resistance to multivalent metal ions in the protonated state as compared with said alkali-metal-cation-exchanged state;
the balance comprising conventional papermaking pulps and, non-interfering wet-strength additives, said additives being in the form of from 0.1% to 2% of a glyoxylated anionic polyacrylamide;
said paper sheet being characterized by a density in the range from about 0.05 g/cm.sup.3 to about 0.25 g/cm.sup.3 ;
a mean water or aqueous fluid absorbency of the sheet in the range from about 2 g/g to about 10 g/g as measured by the TBGV method;
and a total wet tensile, machine direction plus cross-machine directions, in the range from about 500 g/inch to about 1500 g/inch;
said paper sheet being the product of a process comprising both wet-laying said pulps and at least partially dewatering the resulting wet paper sheet whilst maintaining fibrous pulp type A in the protonated state;
said wet-laying and partial dewatering operations being conducted in the substantial absence of interfering cationic materials.

7 more elements

Dependencies are inferred from the claim text.