Note: Descriptions are shown in the official language in which they were submitted.
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CREPED ABSORBENT PAPER SHEET, ROLL FOR EMBOSSING SUCH A
SHEET AND EMBOSSING PROCESS
The invention relates to a sheet of paper, especially a
sheet of absorbent paper made of creped tissue, having
an embossed pattern.
The invention relates in particular to a sheet of paper
composed of at least a first and a second ply of creped
tissue, intended for the field of wiping in a
household, domestic or industrial application, that is
to say capable of being used as kitchen roll, towel,
etc.
In the field of paper for sanitary or domestic use such
as toilet paper or kitcher.i roll, it is known to produce
sheets of paper composed of several plies of absorbent
paper, for example made of`. creped tissue having a basis
weight between 12 and 30 g/m2, provided with
protrusions that are obtained by embossing.
This is because embossing gives bulk to the sheet and
it improves the absorption of liquids, the feel and the
softness. Attempts have been made to increase the
absorption capacity st:ill further by creating
multilayer sheets which are obtained by combining at
least two layers, also known as plies, each consisting
of at least one of said embossed sheets.
Thus, a multilayer (or multiply) sheet is obtained
which has given mechanical properties such as tensile
strength and also absorption capacity.
Two methods of embossing and assembling the plies are
commonly used depending on the desired properties of
the end product.
The first is known in the field by the name "nested".
It consists firstly in embossing each of the plies
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separately so as to form, at the surface, protrusions
which are generally substantially frustoconical or in
the form of pyramid frustums. Next, adhesive is applied
to the top of the protrusions of one of the plies, and
the plies are arranged so that the faces having the
protrusions face each other, the protrusions of one
being between the protrusions of the other. Finally,
the plies are assembled ;so that the protrusions that
have been coated with adhesive nest between the
protrusions of the other ply. Thus, the two plies are
joined together by spots of adhesive between the tops
of the protrusions of one ply and the unembossed
regions between the prot:rusions of the other ply. A
structure is produced in which the voids thus formed
are able to give the sheet better absorption.
Furthermore, the outer faces have a smooth and soft
feel due to the hollow regions formed by the back of
the protrusions. This technique is illustrated, for
example, by Patent US-A-3 867 225.
The second method of assembly is known in the field
under the name "point-to-point". It differs from the
preceding method by the relative arrangement of the two
plies. These, after they have been separately embossed,
are brought together in such a way as to make the tops
of the protrusions, or at least part of these tops,
coincide. The plies are joined together by the tops of
the protrusions, point-to-point. This technique is
illustrated by Patent US-F.-3 414 459.
When the practical realizations of these structures are
considered, whether they are of the nested or point-to-
point type, the protrusions obtained during embossing
are usually produced so as to be distributed in a
pattern in which the protrusions are generally aligned
in one or more directions, uniformly. Such a pattern
makes it possible to obtain a sheet that is homogeneous
as regards its mechanical properties.
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However, in order to improve user satisfaction, it is
important to increase the flexibility, also called "the
bulk" of the sheet.
The flexibility of the sheet can be defined as being
its ability to deform uniformly when it is placed in
the hand of a user, theiif fingers being stretched out
as an extension of their palm and when the user then
closes their fingers.
A sheet of paper which has- a high flexibility will then
deform and bend or curve so as to remain substantially
parallel to the shape determined by the inside of the
palm of the user's hand.
A sheet of paper that has poor flexibility will fold
along one or more lines, each portion of the sheet
which extends between two fold lines remaining
substantially flat.
A sheet of paper that has high flexibility is more
pleasant to use.
Also known is an embossed multiply sheet such as
described in Patent Application EP 1 236 830 Al in
which at least one first ply has a first embossed
pattern consisting of a first series of first
protrusions of frustoconical overall shape projecting
from the inner face of the first ply, which in
particular form first alignments and the tops of which
are joined to the inner face of the second ply opposite
each other; the two plies each have a second embossed
pattern made up of a. second series of second
protrusions of frustoconical overall shape projecting
from the inner face of t:he corresponding ply, and in
that the tops of the second protrusions of one ply
extend opposite and near the tops of the second
protrusions of the other ply.
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The object of the invention is to provide a novel
design for embossed paper sheet which especially makes
it possible to improve the absorption of the sheet
without however decreasirig its mechanical properties
and which remains visually attractive.
For this purpose, the invention provides an embossed
sheet composed of at least a first and a second ply of
creped tissue having a basis weight between 12 and
30 g/m2 according to which the first ply has a first
embossed pattern composed of a series of first aligned
protrusions of frustoconical overall shape, the tops of
which are oriented towards the inside of the sheet, the
second ply comprises a first and a second series of
protrusions, the tops of which are oriented towards the
inside of the sheet of the first series and have a
height greater than that of the second series of
protrusions.
In accordance with the invention, the protrusions of
the first ply and the highest protrusions of the second
ply are nested inside one another, and the lowest
protrusions of the second ply are arranged between the
protrusions of the first ply so as to create empty
spaces between the two plies and promote a rapid
absorption of liquid.
According to other features of the invention:
- the protrusions of the first ply form series of
circles;
- preferably said circles are concentric in a set of
at least 3, preferably 4, circles;
- according to one preferred embodiment of the
invention, the outermost circles of the sets have
tangents;
- advantageously, the first ply comprises, in
addition, embossed protrusions arranged between the
series of circles, preferably forming square
alignments;
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- according to the invention, the lowest protrusions
of the second ply have a density greater than
30 protrusions/cmz;
- in agreement with o:ne advantageous mode of the
invention, the highest pr.otrusions of the second ply
especially form series of preferably concentric circles
in a set of at least 3;
- thus, the series of circles are juxtaposed and
tangent, the lowest protrusions are juxtaposed in said
spaces between the series of circles;
- preferably, some of the highest protrusions of the
second ply are arranged among the lowest protrusions of
the second ply, nested with respect to the protrusions
of the first ply and arranged between the series of
concentric circles; and
- finally, the second ply comprises, in addition, a
third series of protrusions having the overall shape of
a low wall that projects from the inner face of the
sheet, and of which each joins together two higher
protrusions which form concentric circles.
The invention also provides a pair of engraved rolls
for embossing an embossed sheet of which the first roll
comprises a first series of large pins of frustoconical
overall shape that forni first juxtaposed sets of
concentric circular alignments and second large pins
arranged between said concentric sets, and of which the
second roll comprises a series of large pins of
frustoconical overall shape that form second juxtaposed
sets of concentric circular alignments, and a series of
small pins arranged between said second sets.
In accordance with the invention, the second roll
comprises, in addition, third pins arranged in the main
at the centre of the small pins, and in order to emboss
the plies, the second rolls are keyed so that the large
pins of each roll are nested and the third pins of the
second roll and the second large pins of the first roll
are also nested.
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The invention finally provides a process for
manufacturing an embossed sheet by means of a pair of
rolls such as defined previously.
Other features, details ar.Ld advantages of the invention
will appear on reading the detailed description which
follows, for an understanding of which reference will
be made to the appended drawings among which:
- Figure 1 is a schematic section through the
thickness of a tissue sheet according to the prior art;
- Figure 2 is a schematic section through the
thickness of a multiply sheet according to one
embodiment of the invention;
- Figure 3 is an illustrative planar view of the
engraving of an embossinq roll used according to the
invention;
- Figure 4 is a planar view of the engraving of the
other embossing roll used according to the invention;
and
- Figure 5 gives comparative curves relating to the
absorption of a sheet according to the prior art and of
a sheet according to the invention.
Figure 1 therefore shows, in cross section, a sheet
according to the prior art, such as described in
European Patent Application EP 1 236 830 Al.
The sheet 10 of embossed paper comprises a first upper
ply 12 and a second lower ply 14 made of creped tissue,
intended for any type of Y:Lygiene or household products.
The tissue, having a basis weight between 12 and
30 g/m2, is preferably of the type obtained by
conventional wet pressing, known as CWP.
More particularly, the sheet of paper 10 represented in
Figure 1 is, for example, intended to be incorporated
into a roll of kitchen towel.
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A first embossed pattern of each ply 12 and 14, of
known overall design, is composed of first series of
first protrusions 18 and. 20, of frustoconical overall
shape, projecting front the inner face of the
corresponding ply 12, 14 while thus extending towards
the inside of the sheet 10.
The first protrusions 18 and 20 in particular form
first alignments in shapes, particularly in closed
loops which in this instance are circles.
Here, according to Figure 1, associated series of first
protrusions 18, 20 of each of the plies 12, 14 are
nested, concentrically, between the associated series
of protrusions 20, 18 of the other 14, 12 of the two
plies.
The first series of first protrusions 18 and 20 may be
aligned in two main directions so as to define a grid.
The two main directions are in this instance
perpendicular to one another, and are inclined at 45
relative to the longitudinal L and transverse T
directions of the sheet 10 as will be explained in
greater detail below.
According to a known technique, the first protrusions
18, 20 forming the components of the first pattern are
obtained by embossing the first 12 and second 14 plies
of the sheet 10 respectively, by means of a pair of
rolls such as that which is commonly known.
Thus, pins corresponding t.o the protrusions that it is
desired to obtain on the first 12 and second 14 plies
of the sheet 10 are formed in relief on the outer
convex cylindrical face of the associated roll.
In order to produce the series of first protrusions 18
on the first ply 12 of the sheet 10, the embossing roll
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has, on its convex cyli.ndrical face, a first homologous
series of pins in relief and of frustoconical overall
shape in relief, which are distributed in concentric
circles in the first alignments of the first
protrusions 18, so as to produce the corresponding part
of the first pattern of the first ply 12.
Similarly, the series of protrusions 20 on the second
ply 14 of the sheet 10 iz; produced by another embossing
roll, of which the frustoconical pins in relief can be,
are distributed in concentric circles.
In accordance with the teaching of this prior art, the
first ply 12 has a second embossed pattern composed of
second series of second protrusions 38, of
frustoconical overall shape projecting from the inner
face of the first ply 12, while thus extending towards
the inside of the sheet 10.
The second protrusions 38 are produced in a similar way
to the first protrusions 18 and 20, especially by a
second series of second pins of frustoconical shape
which extend over the convex surface of the second
embossing roll.
When they are arranged opposite the protrusions 20 of
the second ply 14, the protrusions 38 have a tendency
to reduce the height of the protrusions 20: such
protrusions are referenced 20' in Figure 1.
The protrusions 18 of the first ply 12 and the
protrusions 20 of the second ply 14 are nested inside
one another.
The present invention, iricluding an embodiment of a
sheet cut along its thickness, is represented in
Figure 2 and has the following characteristics:
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The first ply 4 comprises a first series of protrusions
20 of frustoconical overall shape of which the tops are
oriented towards the inside of the ply 1 and which may
be arranged as illustrated in Figure 3, namely by
forming alignments.
By way of example, the protrusions 20 may have a height
of around 0.8 mm and a surface area at the top of
around 2 mmz with an average density of around 4/cm2. In
the particular case represented here, found between the
series of circles is around eight first protrusions 20
grouped over a surface area of around 1 cm2.
The second ply 2 comprises a first and a second series
of protrusions respectively marked 3 and 5, of which
the tops are all oriented towards the inside of the
sheet, the first series of protrusions 5 having a
height greater than that of the second series 3.
By way of illustration, the first protrusions 3 having
a rounded surface at the top have a height of around
0.4 mm and a density of around 30 cmz. The second
protrusions 5 have a geornetry and a density closer to
those of the protrusions 20 of the first ply 4.
In accordance with one advantageous aspect of the
invention, the first protrusions 5 (the highest) of the
second ply 2 are positioned nested with respect to the
protrusions 20 of the first ply 4. One particularly
favourable arrangement will be described in relation to
Figures 3 and 4.
Moreover, the second protrusions (the lowest) 3 of the ~
second ply 2 are placed between the protrusions 20 of
the first ply, so as to form voids or pockets 6 between
the plies which promote the rapidity of the absorption
of liquids as is proved especially by the curve from
Figure S.
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Such an arrangement of the protrusions improves the
hold of the "small" protrusions 3 of the second ply 2
which are here closely held between the largest
protrusions 5. The structure thus formed collapses less
quickly in the wet state, which accelerates the passage
of liquid to the inside of the structure, thus
accelerating the rate of absorption of the sheet.
Figures 3 and 4 illustrate one particularly favourable
arrangement of the pins of each of the rolls used to
form each of the outer plies of the embossed sheet
according to the invention.
According to Figure 3, which illustrates the embossed
pattern of the first ply 4 seen from above, the pins
200 are mostly aligned in circles and more precisely
concentric circles Cl, C2, C3 and C4, here sets of four
concentric circles.
The sets of circles being generally juxtaposed, the
outermost circles C4 of said sets are tangent in
certain places.
Furthermore, pins 201 of the same type as those (200)
forming the circles are provided between the sets of
circles, and preferably form squares.
Figure 4 shows the embossed pattern of the second ply
2, comprising, in particular, a set of large pins 50
which form the highest protrusions 5 on the second ply,
and a set of small pins 30 which create the "small"
protrusions 3 of the secor.id ply.
The large pins 50 form in this instance sets of three
juxtaposed concentric circles.
The small pins 30 are arranged in the areas between the
sets of concentric circles; they are engraved in sorts
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of squares, the centre of which comprises a large pin
50.
Figure 2 is a cross section of a sheet obtained by the
rolls of Figures 3 and 4, along the line AA.
In order to simplify things to a degree, it may be
considered that Figures 3 and 4 represent the embossed
patterns of the first and of the second ply
respectively.
Thus, the concentric circles Cl, C2, C3 and C4
correspond to the sets of circles C'l, C'2, C'3 and
C'4, formed by the protrusions 20 of the first ply 4.
Thus, in accordance with the invention, the patterns of
each of the plies 2, 4 are complementary, and fitted to
one another so as to promote rapid absorption of liquid
inside the plies, as is clearly shown by the curves
from Figure 5.
The two curves from Figure 5 are given as the
absorption A in g/g of a sheet as a function of time t
in s.
In accordance with the tests carried out with respect
to the absorption, the sample was laid flat on a
porous, sintered glass sheet of which the pore size was
determined to be 40 pm. A plate bearing weights was
laid on the sample in order to keep the sample flat.
The sample was thus slightly compressed. The porous
sheet rested on a plate which had, in its centre, an
orifice of diameter equal to 3 mm into which a flexible
tube opened from beneatY:L in order thus to place the
volume of the porous sheet in communication with a
reservoir of liquid, the height level of which could be
adjusted with respect to the level of the porous sheet.
The reservoir was itself placed on a balance. This
means made it possible to determine the amount of
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liquid which passed into the sample when the reservoir
was raised relative to the porous sheet.
The liquid was water containing 9 g/l of sodium
chloride.
The procedure consisted in impregnating the sample
through the porous sheet while lowering the level of
the sample relative to the reservoir. The amount of
liquid absorbed was measured every ten seconds simply
by measuring the loss of water from the reservoir. This
is carried out with various weights.
Measurements of the absorption capacity may also be
carried out without applying pressure.
In Figure 5, the curve I relates to the invention and
the curve A to the prior art, more precisely a sheet
such as represented in transverse cross section in
Figure 1.
It is seen that the curve I has a slope that is
initially larger than the curve A which means that the
sheet according to the invention has an absorption rate
that is higher than a sheet according to the prior art.
This feature is very important, or even determining,
for purchasers, and users of this type of product.
Furthermore, the protrusions 20 of the first ply 4 may
be joined together by components in relief such as
disclosed, for example, in Application EP 1 101 866 Al.
This feature makes it possible to obtain a more
pronounced embossed pattern.
