Household absorbent paper

Details Household absorbent paper Household absorbent paper

1999-02-04

2001-05-22

Loney, Donald J. (Department: 1772)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including variation in thickness

C428S154000, C428S187000, C162S109000

Reexamination Certificate

active

06235373

ABSTRACT:

FIELD OF THE INVENTION
The invention concerns household absorbent papers made of cellulose wadding.
BACKGROUND OF THE INVENTION
More specifically, the invention relates to a compound web of two plies of absorbent paper made of conventional creped cellulose wadding and having a specific surface weight of 10 to 40 g/c
2
. The plies are embossed by calendering into fine patterns of protrusions and are bonded to each other, especially by glueing, at the surfaces of the peaks of the coinciding protrusions of the two plies.
U.S. Pat. No. 3,414,459 describes a method for embossing and bonding to each other two cellulose wadding plies using the so-called tip-to-tip technique. In this technique, the two plies are embossed separately using identical metal cylinders fitted with embossing protrusions and, respectively, cooperating with rubber-clad rollers. Next, a suitable glue is deposited on the protusion peaks of one of the plies. Lastly, the two plies are bonded to each other at the peaks of the protrusions by being clamped between the two embossing cylinders which are rotatably ganged to each other in such a manner that the embossing protrusions meet tip-to-tip. This technique entails that the two cylinders include symmetrical patterns and that the embossing protrusions of the two cylinders perfectly coincide inside the clamping gap. Radial or circumferential slippage between the embossing protrusions of the two cylinders can lead to a lack of adhesion in some zones of the compound web so made.
To remedy these drawbacks, U.S. Pat. No. 5,173,351 proposes using patterns of different repeats, in at least one direction, on the two embossing cylinders to ensure that there is at least one bonding site on the elementary compound webs produced by cutting the compound web issuing from the equipment.
Lastly, WO 96/32248 patent application suggests bonding only some zones of the two embossed plies by applying glue only to the ends of the protrusions of one of the plies taking part in the actual bonding. In this design as well, the two cylinders must have symmetrical patterns and the embossing protrusions of the two cylinders must accurately coincide in the clamping gap.
In the designs of these three documents, the embossing protrusions are mounted on the cylinders along generatrices of regularly spaced helices and great circles. Consequently, the protrusions formed in the plies by the embossing protrusion imprints are aligned in preferential directions and at constant distances. The observer viewing the outsides of the compound web is then under the impression that these surfaces are fitted with geometric designs solely constituted of straight lines or straight line segments.
It is clear that a slight axial or circumferential shift between the two cylinders caused by a lack of synchronization or by wear of the drive means can lead to a lack of coincidence between the embossing protrusions within the clamping gap of the embossing cylinders and thus shall entail rejects.
Other techniques for assembling the plies allow nesting of the protrusions of one of the plies between the protrusions of the other ply so as to achieve a so-called nested structure which offers improved absorption. Using such a technique, the embossing cylinders are moved apart and the embossed ply is removed from one of the cylinders to nest the ply in the other ply by passing in a clamping gap between the other embossing cylinder and a smooth complementary cylinder. This technique also requires perfect synchronization of the two embossing cylinders.
OBJECTS AND BRIEF DESCRIPTION OF THE INVENTION
The object of the invention is to improve both absorption and pliancy of the above defined compound webs in such a manner that the final product retains the appearance of the products made by current techniques, and whereby it becomes possible to lift the constraints which were set on the choice of patterns and on accurately ganging the embossing cylinders.
The goal of the invention is obtained in that:
(a) the frequency of the protrusions of each ply is greater than 10 protrusions/cm
2
and the surface of the peaks of the protrusions of each ply is greater than 5% of the surface of the ply, and
(b) at least one of the plies is embossed in the form of an artistic pattern wherein the distances and the directions of an arbitrary protrusion relative to adjacent protrusions are varied, the pattern being selected in such a manner that at least 25% of the protrusions of the ply take part in effective bonding with the coinciding protrusions of the other ply and in that the total bonded surface of the protrusion peaks of the ply that take part in bonding is at least 15% of the total surface of the peaks of the protrusion of the ply regardless of the relative positions of the patterns of the two plies.
Advantageously 30%, and even more advantageously 40%, of the protrusions of one ply take part in effectively bonding with the coincident protrusions of the other ply. It has been found there is improvement up to 70%.
Preferably, the total bonded surfaces of the protrusion peaks of a ply are at least 20% of the protrusion surfaces of the ply.
Advantageously the surface of the protrusion peaks of each ply are less than 30% of the total ply surface. This surface preferably is larger than 7.5% of the total surface of the ply and, preferably, less than 15% of the ply surface. The protrusion density of each ply is less than 30 protrusions/cm
2
and, preferably, less than 20 protrusions/cm
2
.
Advantageously the two plies are embossed with artistic patterns which can be identical or not.
The two patterns can be mutually offset by translating or rotating the pattern imprint of an embossing cylinder relative to the pattern imprint of the other cylinder.
Other features and advantages of the invention are elucidated in the illustrative description below and in relation to the attached drawings.


REFERENCES:
patent: 3414459 (1968-12-01), Wells
patent: 4978565 (1990-12-01), Pigneul et al.
patent: 5173351 (1992-12-01), Ruppel et al.

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