Low compaction, pneumatic dewatering process for producing absorbent sheet
View Patent ↗A low-compaction method of making an absorbent cellulosic web includes: forming a nascent web from a papermaking furnish; dewatering the nascent web to a consistency of from about 10 to about 30 percent on a foraminous forming support traveling at a first speed; rush-transferring the web at a consistency of from 10 to about 30 percent to an open texture fabric traveling at a second speed slower than the first speed of the forming support; further dewatering the web on the impression fabric to a consistency of from about 30 to about 60 percent by way of (i) combining the open texture fabric bearing said web with a fluid distribution membrane and an anti-rewet felt as the three pass through a nip into a pressure chamber defined in part by a plurality of nip rolls, the fluid distribution membrane bearing against the side of the open texture fabric away from the web, with the anti-rewet felt bearing against the web, and (ii) applying a pneumatic pressure gradient from the distributor membrane through the web thereby dewatering the web; and drying the web. Preferably the process includes the steps of selecting the papermaking furnish and controlling the process such that the dried web has a void volume fraction of at least 0.7, a hydraulic diameter in the range of from about 3 to about 20 microns and a Wet Springback Ratio of at least about 0.65. Optionally provided is a high solids fabric crepe in a pressure nip.
1. A method of making an absorbent cellulosic sheet comprising:
a) forming a nascent web having an apparently random distribution of fiber orientation from a papermaking furnish;
b) rush transferring the web to an open texture fabric;
c) drying the web to a consistency of from about 30 to about 60 percent by way of (i) combining the open texture fabric bearing said web with a fluid distribution membrane and an anti-rewet felt as the three pass through a nip into a pressure chamber defined in part by a plurality of nip rolls, the fluid distribution membrane bearing against the side of the open texture fabric away from the web, with the anti-rewet felt bearing against the web, and (ii) applying a pneumatic pressure gradient from the fluid distribution membrane through the web thereby dewatering the web;
d) thereafter transferring the web to a translating transfer surface moving at a first speed;
e) fabric-creping the web from the transfer surface at a consistency of from about 30 to about 60 percent utilizing a creping fabric, the creping step occurring under pressure in a fabric creping nip defined between the transfer surface and the creping fabric wherein the fabric is traveling at a second speed slower than the speed of said transfer surface, the fabric pattern, nip parameters, velocity delta and web consistency being selected such that the web is creped from the surface and redistributed on the creping fabric to form a web with a reticulum having a plurality of interconnected regions of different fiber orientation including at least (i) a plurality of fiber enriched regions of having an orientation bias in a direction transverse to the machine-direction, interconnected by way of (ii) a plurality of colligating regions whose fiber orientation bias is offset from the fiber orientation of the fiber enriched regions; and
f) drying the web.
2. The method according to claim 1 , fabric-creped from the transfer surface at a Fabric Crepe of from about 10 to about 100 percent.
3. The method according to claim 1 , fabric-creped from the transfer surface at a Fabric Crepe of at least about 40 percent.
4. The method according to claim 1 , fabric-creped from the transfer surface at a Fabric Crepe of at least about 60 percent.
5. The method according to claim 1 , fabric-creped from the transfer surface at a Fabric Crepe of at least about 80 percent.
6. The method according to claim 1 , wherein the transfer surface is the surface of a rotating cylinder.