Note: Descriptions are shown in the official language in which they were submitted.
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WO 97/20107 PC'r/IB96/01325
1
ABSORBENT PAPER SHEET MARKED WITH PATTERN SIMULATING
WATERMARK, METHOD AND DEVICE FOR THE MARKING THEREOF
The present invention relates to a sheet of absorbent paper made of tissue
paper, comprising one or more plies, each having a basis weight of
approximately 12
to approximately 70 g/m2, and a part of the surface of which is marked. It
also relates
to a marking process in order to obtain this sheet and to a device for
implementing the
process.
The invention finds application in sanitary and domestic papers, such as
toilet
paper, papers for wiping, such as kitchen paper towel, disposable
handkerchiefs, facial
tissues or else products of the table range, such as disposable napkins and
tablecloths.
The invention allows finishing the tissue paper products.
The term « marking », as it is used in the following description, consists in
compressing certain parts of one side of the sheet, thus forming compacted
areas and
significantly reducing the thickness of the sheet in these areas without
forming a
corresponding relief on the opposite side.
In order to create a pattern on a sheet of absorbent paper made of tissue
paper,
of the type comprising several plies, and to bond the latter together, it is
common to
use the embossing technique which makes it possible to create, on part of the
surface
of each of the plies forming the sheet, reliefs with corresponding depressions
on the
opposite side of the plies. As a result, the sheet which has been embossed has
increased in thickness. In order to bond the plies together, an adhesive is
often used. A
pre-embossed first ply receives, via a sizing device, an adhesive on the end
of the
protuberances produced during the embossing operation. This ply is then
brought into
contact with another ply, also pre-embossed, in order for the two plies to be
adhesiveiy bonded together, connecting them at the contact points or surfaces
generated by the embossing. The use of an adhesive makes the process
particularly
tricky and, in fact, it is necessary to take care that the phenomenon of
filling does not
occur in the conversion installation. Moreover, the adhesive stiffens the
sheet in the
bonding areas. The fact of embossing and of creating reliefs increases the
roughness of
paper surface. Conventional embossing also adversely affects the mechanical
properties of strength and elongation and increases the thickness of the
structure.
Finally, the embossing technique limits the choice of patterns which can be
applied on the sheet of absorbent paper. The reason for this is that only
patterns which
are rounded and devoid of sharp angles may be used to engrave the embossing
surfaces so as in particular to avoid too great a loss of mechanical strength.
There is another way of bonding the plies without using adhesive, by
embossing the plies between a first engraved roll and a paper receiving roll
or a steel
receiving roll having female patterns or impressions of the patterns engraved
on the
CONFIRMATION COPY
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2
first roll. This technique is applied, for example, in order to bond the edges
of folded
handkerchieves and of table napkins.
The publication of international patent application WO 95/27429 discloses a
cellulose cloth for hygiene comprising at least two layers of tissue with an
embossed -
pattern consisting of a plurality of individual spot-shaped impressions which
deform
and mutually transversely connect the layers of tissue. The impressions are
formed by
embossed spots which originate from the two outer layers of tissue and are
curved
concaveIy inwardly in each case and which are mutually transversely aligned
and in
whose head-to-head base regions the tissue layers are connected to one another
by the
embossing action. The impressions are applied on both sides. The embossing
process
requires an appropriately precise arrangement and control of the rigid
embossing
rollers in such a way that the embossed mounds with which the external surface
of the
embossing rollers are provided, are arranged exactly head-to-head in each case
but do
not touch one another. This process might require a high level of precision
and
control.
Marking, simply by deforming under stress, without using adhesive, also exists
and is termed « press marking ». This technique consists in deforming, under a
stress
and when cold, a sheet of absorbent paper between an engraved roll made of
steel and
a smooth receiving roll also made of steel. The marking is performed in the
form of
bands by means of « roller-wheels » which form very small compressed surfaces
in the
contact areas during the deformation. However, a drawback is observed with
respect
to the pattern geometry, which is imperfect. This drawback results from the
localization of the pattern, limited to a band parallel to the edge of the
product,
combined with difficulty in guiding the sheet during press marking. In
addition, this
technique enables only the edges of a sheet to be bonded together and not the
surface
of the sheet over its entire width.
The choice of patterns is limited to the use of very small surfaces in the
form of
discs or diamonds, akin to points. A major drawback encountered in this type
of
marking is the lack of uniformity in the marking itself. The pattern is not
permanent
and is irregular, especially because of the wear of the roller-wheels, in
particular in the
case of the press marking of toilet paper. In addition, it is not easy to see
the pattern
by holding it up to the Light, unlike the watermarked designs which are
mentioned in
the following description.
Endeavours have been made to develop marking processes enabling the shape
of the patterns to be varied freely. In particular French Patent No. 2 672 843
describes
a process which consists in simultaneously marking patterns of any shape, in
particular
patterns having sharp angles, and adhesively bonding the plies. However, this
process,
even by reducing the amounts of adhesive applied, does not dispense with using
it
altogether. Moreover, the pressure exerted between the two engraved and
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3
undeformable steel rolls is relatively low and does not run the risk of
tearing the sheet.
The two rolls must be separated from each other by a distance barely less than
the
thickness of the two plies. There is also a limitation in the patterns as
regard to their
height and to the spacing of the protuberances on the roll, in order to enable
correct
application of the adhesive to the plies in the region of the protuberance
without
applying adhesive to those parts of the plies which lie between the
protuberances. This
process therefore results in certain constraints.
Watermarks have been used to mark papers, generally in fields quite far
removed from those of sanitary and domestic papers. A watermark is the
impression of
a design in the thickness or body of the paper, which is produced
intentionnaly in the
paper, and is visible when viewed against a contrasting background.
Watermarking is a
very ancient technique and has served since the XiIth and XIIIth centuries to
mark
sheets, to trace their movement in the market place and to vouch for their
provenance.
Currently, watermarks are more conventionally used for papers of low grammage
and
thickness. They are encountered on paper of the uncoated type, for example
letter
paper. It is usually applied on thin papers, such as cigarette paper having a
basis
weight of the order of 10 to 23 g/ma and which partly contains textile fibres
(hemp and
flax fibres), « bible » papers having a basis weight of approximately 25 to 36
g/ma and
on special papers such as bank notes or filter paper. Those papers are
different from
tissue paper and are illustrated by prior patent literature.
The watermark is termed a « wet » or « true » watermark, when it is produced
during the manufacture of the paper in the wet phase of the process, either by
means
of an impression in the form of reliefs or in the form of depressions in the
wire, for
example, of the wire mould or of the cylinder mould machine, or by means of an
impression in the form of reliefs or depressions at the surface of an open-
ended
cylinder rotating in contact with the wet pulp on the forming wire of a
Fourdrinier
former. This technique is used for the manufacture of bank notes. The design
is then
obtained by localized displacement of the fibers.
United-States Patent No. 5,328,565, without mentioning watermarks,
describes an absorbent paper made of tissue paper comprising a single ply and
including surfaces with a non-embossed pattern. This pattern produces regions
in the
paper having different opacity, height and creping frequency (the number of
times a
peak appears on the surface for a given distance). The various visually
discernible
regions forming a particular pattern have different basis weights.
The pattern is formed directly by the wire during the drying by means of the
blowing of air through the sheet in the wet state. After drying, a pattern is
certainly
formed on the sheet but it does not stand out in contrast with the other areas
since the
areas with patterns are not actually and clearly visible when viewed against a
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4
contrasting background, as conventionally the watermarked patterns are, and
these
areas do not have a smooth and glossy appearance.
The watermark is called a rubber mark (one still speaks of press marking) when
the impression is produced on the paper during its manufacture on the machine
by
passing the wet web through a roller-whell press.
An imitation or simulated watermark is an impression similar in appearance to
a true watermark, produced in the finished paper by mechanical means (for
example
the impression produced an cigarette paper). In this case, the fibres are
crushed and
compacted. The simulated watermark may also be produced by removing material
or
else by applying certain products, such as resin-based substances. Many
techniques far
producing a simulated watermark on small quantities of finished paper have
been
developed for replacing the wet watermarking which requires much heavier and
more
expensive installations.
European Patent Application No. 0,195,887 describes a process for producing
a watermarking resembling a wet watermark, which means that the paper
documents
obtained in this way cannot be falsified. This process consists in passing a
sheet of
paper between two rolls rotating in opposite directions, one of the rolls
including a
pattern and being made of steel. The pattern thus marked is visible when the
sheet is
held up to the light or by difference in reflection of light on the paper.
Canadian Patent No. 1,116,851 relates to the surface treatment of a sheet of
paper in order to create a pattern by removal of material. The process here
consists in
passing the sheet of paper between a roll which includes marking patterns and
an
abrasive roll ar else a roll provided with cutters, the two rolls rotating at
different
speeds. The abrasive material or the cutters remove from the sheet of paper a
constant
thickness of approximately 1/3 to 2/3 of the total thickness of the sheet.
Thus, a
simulated watermark is obtained which has a light transmission which is
different from
that of those parts of the sheet which have not undergone removal of material.
Papers
which have undergone this treatment are also unsfalsifiable.
The simulated watermark may also be produced by impregnating a resin-based
composition into a sheet of paper, which makes the sheet translucent in the
impregnation areas. This technique and compositions which can be used are
widely
described in the patent literature, for example British Patent No. 1,489,084
and United
States Patents No. 3,985,927, No. 4,824,486 and No. 4,919,044.
Another example of simulated watermark is described in European Patent No.
0,203,499. This entails a process which consists in preparing a sheet of paper
containing a suitable amount of a heat-sensitive material, a polymer of the
polyethylene
type, and in applying heat to part of the surface of the sheet so as to make
that part of
the surface of the sheet translucent.
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WO 97!20107 PC"T/IB96/01326
The subject of international Application WO 94/07694 is a device for making a
simulated watermark on paper (letterhead paper, certified documents, etc.) by
chemical means. The simulated watermark is made and the paper is printed
preferably
in one and the same step. More precisely, this device comprises the
combination of
coating rolls applying the chemical composition serving for making the
simulated
watermark with a roll provided with a matrix and an impression cylinder.
For another, different, type of paper, such as filter paper which contains
cellulosic fibres and synthetics fibres, it is known to create a repeating
pattern such as
a semi-perforation at regular intervals. The process coonsists in applying a
series of
fluid jets and then in heating in order to set the synthetic fibres. European
Patent
Application No. 0,446,138 relates more precisely to a process for
manufacturing filter
bags which consists, after producing, using a known technique, a non-woven
paper
composed of a layer based on synthetic fibres and of a layer of cellulosic
fibres which
are superimposed, in subjecting the non-woven paper to a calendering operation
between a support stnzcture, a smooth roll or a roll having an elastic pliant
external
surface, and a heated roll having reliefs.
in a similar application teabags made of paper (in this case a paper
consisting
of long fibres or else of non-woven material), the subjects of international
Patent
Application WO 94/06623 is a process for producing a pattern which is in the
form of
substantially transparent areas. The prior art in this field also uses the
technique of
creating perforations using jets. The novel process according to this
international
application consists in passing a sheet of paper through a heated calender
while
applying a liquid, a synthetic material such as polypropylene, which allows
the
enhancement of the embossing effect and limits the loss of strength in the
marked
areas.
The present invention relates to the application of a pattern or impression
resembling a watermarked pattern, to a sheet of absorbent paper made of tissue
paper,
when that sheet has already been manufactured and dried ; which process has
hitherto
never been employed. The watermark applied to the sheet of absorbent paper
according to the invention belongs to the category of imitation or simulated
watermarks produced on finished paper using mechanical means ; and the term
« watermark » used hereafter in the following description of the invention has
the
above-mentioned meaning.
The object of the invention is to provide a sheet of absorbent paper, made of
tissue paper, which mitigates all the drawbacks mentioned above for sheets of
paper of
this same kind which have been marked or embossed by processes in the prior
art.
A further object of the invention is to provide a sheet of absorbent paper
which
includes an aesthetic pattern without modifying the thickness of the sheet by
removal
of material ; or without modifying its mechanical and physical properties ;
and in
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particular without adversely affecting the softness
properties of the sheet. The invention allows an infinitude
of designs to be chosen for the patterns. It provides a
matt/gloss contrast effect on the sheet . the marked parts
s are smooth and glossy and the non-marked parts remain matt
and «fluffy». The contrast effect can be correlated with
the reflection of light. The invention also provides a
translucent effect ; the marked parts being visible when
viewed against a contrasting background.
io In the case of a sheet comprising at least two
plies, the object of the invention is also to connect the
two plies together easily.
Another object of the invention is to provide a
process for marking a sheet of absorbent paper made of
i5 tissue paper, based on short papermarking fibres, which has
neither the problems of the conventional marking processes
nor those)f the known processes, mentioned above, for
watermarking other types of paper; the watermarking process
according to the invention does not use, for example
2o synthetic components. The process according to the
invention makes it possible to mark the sheet over its
entire width unlike the known processes of press marking and
of embossing of edges without adhesive bonding by means of
steel/steel or steel/paper rolls.
2s The subject of the invention is a sheet of
absorbent paper made or tissue paper comprising one or more
plies, each having a basis weight of approximately 12 to
approximately 70 g/m2 and part of the surface of which is
marked.
3o According to an essential characteristic of the
invention, that pat of the said surface which is marked is
distinguished by an impressed pattern simulating a
watermark,
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- said impression being applied to one side of the
sheet, the opposite side corresponding to said impression
being plane,
- the marked surface being smooth, glossy and
translucent, and
- the marked surface comprising at least one marked
unit region wherein the ratio of the thickness to the area
of this marked unit region is less than 0.027 mm/mm2.
According to an advantageous characteristic of the
io invention, with regard to the light transmission through the
sheet, the difference between the average grey level of the
marked surface and the average grey level of the unmarked
surface is at least 20 by image analysis.
According to an other advantageous characteristic,
the sheet comprises at least two plies joined together at
the impression resembling the watermarked pattern.
The subject of the invention is also a process for
marking a pattern resembling a watermark on a sheet of paper
made of tissue paper comprising one or more plies, each
2o having a basis weight of approximately 12 to approximately
70g/mz, consisting in impressing one side of said sheet
without forming a corresponding relief on the other opposite
side, by deforming, the said sheet under stress, by at least
one pass between a hard engraved roll and a receiving roll
having a surface hardness of more than Shore-D 40, the
specific pressure exerted on the marked surface being at
least 14,7 MPa (150 kg/cm2) and the linear marking speed
being at least 50 m/min.
According to an advantageous characteristic of the
3o invention, the hardness of the receiving roll is at least
Shore-D 80 and preferably greater than Shore-D 90.
According to an advantageous characteristic of the
invention, the said engraved roll, preferably made of steel,
is heated to a temperature ranging from approximately 50°C
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to approximately 100°C and preferably from approximately
75°C to approximately 85°C.
According to another characteristic of the
invention, the process comprises a preliminary step of
treating the sheet before deformation, consisting in
bringing the surface of the sheet into contact with small
amounts of water in the form of liquid or steam.
The subj ect of the invention is also a device for
implementing the process, comprising at least one engraved
1o roll, optionally heated, and at least one receiving roll.
According to an advantageous characteristic, the
device comprises one engraved roll optionally heated,
arranged between two receiving rolls.
According to a further broad aspect of the present
i5 invention there is provided an absorbent tissue paper sheet
comprising one or more plies, each having a basis weight of
approximately 12 to approximately 70 g/m2 and a part of the
surface of which is marked, characterized in that:
- the said surface part is marked by an impressed
2o pattern simulating a watermark, said impression being
applied to one side of the sheet, the opposite side
corresponding to said impression being plane,
- said marked surface being smooth, glossy and
translucent, and
25 - said marked surface comprising at least one marked
unit region wherein the ratio of the thickness of said
marked unit region to the area of said marked unit region is
less than 0.027 mm/mm2.
According to a still further broad aspect of the
3o present invention there is provided a process for marking
with an impressed pattern resembling a watermark on a part
of a surface of an absorbent tissue paper sheet comprising
one or more plies, each having a basis weight of
approximately 12 to 70 g/mz, the marked surface part
35 comprising at least one marked unit region wherein the ratio
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of the thickness of said marked unit region to the area of
said marked unit region is less than 0.027 mm/mm2, said
process consisting in deforming, under stress, the said
sheet by at least one pass between a hard engraved roll and
a receiving roll having a surface hardness of more than
Shore-D 40, the specific pressure exerted on the marked
surface being at least 14, 7 MPa (150 kgJcmz? and the linear
marking speed being at least 50 m/min.
Other characteristics and advantages of the
io invention will appear more clearly on reading the following
description with reference to the drawings in which:
Figure 1 represents the surface of a sheet
comprising simulated watermarks according to the invention;
Figure 2 represents a cross-section of the sheet
i5 shown in Figure 1 along the line II-II
Figures 3A, 3B and 3C represent marked and
embossed patterns of the art and impressed patterns
according to the invention;
Figure 4 is a schematic diagram of an embodiment
20 of the process according to the invention,
Figure 5 represents a device according to one
embodiment of the invention,
Figure 6 represents a device according to another
embodiment of the invention; and -
25 Figure 7 represents a device according to another
embodiment of the invention.
According to the invention, a part of the surface
of the sheet is marked by an impressed pattern simulating a
watermark.
3o The impression is applied to one side or the two
sides of the sheet. The opposite side corresponding to the
applied impression is plane. The impression does not form a
relief on the corresponding opposite side of the sheet.
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If an impression is applied to the two sides of
the sheet, no impression is applied to the opposite side
corresponding to the side on which an impression is applied.
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Refernng to Figure 1, a sheet 1 of absorbent paper made of tissue paper
includes decorative patterns 2 and 3. These patterns produced in the sheet are
simulated watermarks. They are marked in the thickness of the sheet and the
lines 5
and 5', or the marking points defining them, are smooth, glossy and
translucent to that
the patterns are clearly visible when the sheet is viewed against a
contrasting
background. These lines 5 and 5' form an integral part of the decorative
pattern. The '
papermarking fibres are crushed in the region of the marked surfaces. The
pattern is
also visible by the impression of relief which it gives the parts of the sheet
surrounding
the pattern, because of the crushing. The sheet is also given a matt/gloss
effect. The
surface parts marked are smooth and glossy and the unmarked remaining parts
keep
the matt and more fluffy appearance of a conventional non-converted sheet of
tissue
paper. The marked surface is smooth due to the creped tissue paper sheet
elevations
which have been reduced or even removed by marking. This smooth and glossy
aspect
advantageously brings out the design of the pattern, enhancing the aesthetic
appearance of the sheet. Any design, whether of simple or complex shape, may
be
envisaged, such as flowers, for example a lotus flower, or calIigraphed words
or
combinations of Lines, strokes and curves defining a pattern. This pattern may
occur
just once, or more usually, it is repeated.
The sheet may comprise one or more plies. Each ply has a basis weight lying
within the range of approximately 12 to approximately 70 g/m2. The basis
weight
preferably lies within the range of approximately 12 to approximately 50 g/ma.
The density of the pattern, or alternatively the ratio of the marked surface
area
to the total surface of the sheet, is generally less than 30 per cent.
Figure 2 shows a cross-section of the sheet 1 comprising two plies 6 and 7.
The thickness of the sheet is reduced at the place where the marked surface
corresponding to the line 5' of the pattern of figure 1 is.
The marked surface area comprises at Least one marked unit region
fi,~IIfiIling
the following requirement. The ratio of the thickness of the marked unit
region to the
area of the marked unit region is less than 0.027. In other words, the marked
surface
of the sheet comprises at least one closed impression pattern having a reduced
thickness and a minimal surface area. This minimal surface area corresponds to
a
marked unit region.
According to figure 3, the patterns 3A Limited to a band of diamonds or
dashes, ,
parallel to the edge of the sheet, are obtained by « press marking » of a cold
and dry
sheet of tissue paper. The patterns 3B1 and 3B2 illustrate embossed flowers
for toilet
tissue. The patterns 3C1 and 3C2 represent a tulip and a stylized flower,
respectively,
and illustrate a simulated watermark pattern according to the invention.
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_ g _
Samples of tissue paper sheet have been made with
the corresponding patterns 3A, 3B, and 3C according to the
marking or embossing process corresponding thereof.
All the sample sheets of the art comprise two
plies. The sample sheets of the invention comprise one, two
or three plies.
Patterns 3B and 3C have been splitted up into unit
patterns (petals, stems, and leaves) to measure their
corresponding unit marked (or embossed) surface areas and
1o adding them to obtain the total pattern marked surface area.
The following table illustrates the thickness and
surface area of an impressed pattern (3C) according to the
invention compared with conventional marked and embossed
patterns (3A and 3B).
Patterns 3A 3B - 3C
Thickness of unmarked0.33 0.22 - 0.28 0.16 - 0.23
surface (mm)
Thickness of marked0.04 - 0.05 0.055 - 0.11 0.027 - 0.055
surface (mm
Thickness reduction85 - 88 % 50 - 80 % 65 - 88
Pattern marked 66 - 70 59 - 79
area (mm')
Average unit marked1 - 1.15 10 - 16.5 7 - 16
surface (mm=)
Marked surface < 5 % > 5 % < 5
/ total
surface
Thickness of unit
R _ marked surface35 x 10'3 - 33 x 10'~ - 17 x 10'~
(mm) 50 x 10'3 110 x 10-' - 79 x 10~'
average unit marked
surface area (mm2)
In view of the above table, the thickness
reduction is similar between the embossed patterns (3B) and
the simulated watermark patterns (3C). However, the average
35 unit marked surface area of the «press marking» samples 3A
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is clearly smaller than the average unit marked surface area
of the simulated watermark patterns (3C).
According to the invention, the simulated
watermark pattern distinguishes over the «press marking»
pattern by comprising at least one marked unit surface
having a ratio of the thickness thereof to the area thereof
of less than 0.027 mm/mm2. In other words, the simulated
watermark pattern can comprise marked unit surfaces with a
ratio less than 0.027 and other marked unit surfaces with a
io ratio greater than 0.027 mm/mm2 such as small patterns like
diamonds, circles, dashes, etc.
The simulated watermark patterns have marked unit
surfaces with a ratio which is close to the embossed pattern
one, but the obtained sheet is fundamentally different since
i5 the embossing technique creates, on part of the surface of
each of the plies forming the sheet, reliefs with
corresponding depressions on the opposite sides of the plies
whereas the simulated watermark pattern corresponds to an
impression applied to one side of the sheet, the opposite
2o side of the sheet being plane without corresponding
depressions.
The advantage of the simulated watermark pattern
is to provide a decorative pattern similar to an embossed
pattern with regard to the design, the site thereof and so
2s on, with in addition the simulated watermarked effect.
A further advantage of the simulated watermark
pattern is an unlimited choice of decorative patterns
without technical restraints, compared with the known «press
marked» or embossed patterns.
3o The marked surface of the sheet is visible when
viewed against a contrasting background. The marked surface
is translucent.
Paper tissue sheets according to the invention,
comprising impressed patterns simulating.a watermark, have
35 been analyzed with regard to light transmission. The method
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consists of providing a lighting through a sheet sample by
the means of optical fibers and a light diffuser, measuring
the grey level of an image by the means of a camera 3 CCD
and of a QUANTIMET* 600 S LEICA as an image analyzer
apparatus.
The following lighting parameters: luminosity,
contrast, etc... are adjusted.
To have an image, a surface is delimited. The
image is divided into pixels which correspond to the image
to units. Each pixel of that surface has a grey level. The
average value of all the pixels of the image gives the
average grey level of a surface.
According to the grey scale, black has a grey
level of zero and white has a grey level of 256.
The average grey level of a marked surface is
measured by delimiting a small closed marked surface area.
The average grey level of an unmarked surface is measured by
delimiting a corresponding unmarked surface area closed to
the selected marked one. And the difference between the two
2o average grey levels is made.
This method is reproducible.
Controls:
First tissue paper sheet samples (I) have patterns
resulting from the wire during the drying of the sheet in
the wet state. The papermarking fibers are probably
displaced and the pattern regions have different opacity.
The sheet samples (I) comprise two plies and have a total
basis weight of approximately 40g/m~.
Second tissue paper sheet samples (II) have
3o embossed pattern corresponding to the pattern 3B2 of figure
3. The sheet samples(II) also comprise two plies and have a
total basis weight of approximately 32 g/m2.
* Registered Trade Mark
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11
Third tissue paper sheet samples (III) have an embossed pattern corresponding
to the stylized flower pattern 3C2 of figure 3. These samples comprise three
plies and
have a total basis weight of approximately 52 g/m2.
Examples according to the invention
Example 1
A tissue paper sheet according to the Figure 1 of the invention, is made. This
tissue paper sheet comprises two plies and has a basis weight of approximately
30
g/m2. Samples corresponding to the calligraphic LOTUS pattern (la), the lotus
flower
pattern (1b) and the stroke pattern (lc), have been analysed by image
analysis,
respectively.
Example 2
A tissue paper sheet according to the invention with the stylized flower
pattern
ofFigure 3C2 is made. This tissue paper comprise two plies and has a basis
weight of
approximately 30 g/ma.
Example 3
A tissue paper sheet with the same pattern as the one of example 1 is made
except that it comprises three plies and has a basis weight of approximately
52 g/m2.
The samples corresponding to the calligraphic LOTUS pattern, the Lotus flower
pattern and the stroke pattern are numbered 3a, 3b and 3c, respectively.
Example 4
A tissue paper sheet with the same pattern as the one of example 2 is made
except that is comprises three plies and has a basis weight of approximately
52 g/ma.
Exam 1
A tissue paper sheet according to invention with a tulip pattern of figure 3C1
is
made. It comprises three plies and has a basis weight of approximately 52
g/m2.
The average grey level is determined for each marked and unmarked surface of
every control and example sample.
The differences between the two grey levels of each control (I, II or III) and
each example are listed in the following table.
CONTROLS I II III
Average grey level difference 10 5 l 0
Exam les Ex 1 a Ex Ib Ex 1 c Ex 2
Avera a a level difference 61 54 67 20
Exam les Control III Ex 3a Ex 3b Ex 3c 4 5
Avera a re level difference 0 72 52 83 30 41
CA 02238756 2004-10-14
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In view of the above table, same pattern obtained
by embossing (control III) and by simulating watermark
(example 4) does give none or an average grey level
difference, respectively. The light cannot go through the
control III with an embossed pattern.
The embossed tissue paper does not allow the light
to make the pattern stand out as a simulated watermark does.
A low average grey level difference is observed
for control I the pattern of which resulting from a wet end
io papermaking process.
Higher average grey level differences are obtained
with simulated watermarks: examples la, 1b, lc, 2, 3a, 3b,
3c, 4 and 5.
A lower limit of average grey level difference has
i5 been defined . 20. The average grey level difference of the
tissue paper sheet according to the invention is more than
20. It is believed that this characteristic is correlated
with the smooth and translucent aspect of the simulated
watermark disclosed therein.
2o With regard to the glossy appearance, or
brightness of the simulated watermark pattern, it is linked
to the reflection of light. The incident light rays are
reflected on the marked pattern surface into one single
direction whereas the same are reflected on the unmarked
25 surface into a plurality of directions by the patches of the
tissue paper sheet surface. The grey level values by image
analysis with a lighting directed onto the sheet surface,
show the differences between the marked regions which are
black and the unmarked regions which are lighter and have a
3o grey level more heterogenous resulting from the surface
patches and the fluffy appearance.
The brightness of the tissue paper has been
measured by the means of a mini GLOSSMATER ERICHSEN* (Model
507) apparatus. The measuring window is~a rectangle the
* Registered Trade Mark
CA 02238756 2004-10-14
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area of which is 13 cm2. The incident lighting has an angle
of 60° out of the verticale. The weight per cent of
reflected light is measured with regard to the surface state
of the sample.
s The values have been measured on black and white
backgrounds. The brightness values of the tissue paper with
a simulated watermark pattern according to the invention are
generally higher than the ones of the tissue paper wit a
«pressmarking» pattern illustrated by Figure 2, A.
1o Referring to figure 2, the two plies 6 and 7 are
advantageously bonded or connected together by the
watermarked pattern 5'. The sheet generally comprises
between one and three plies. When the sheet comprises
several plies, the object of the invention is especially to
i5 bond the plies together. The quality and appearance of the
watermark are directly related to the mutual bonding of the
plies.
A test is performed to analyze the behavior of a
tissue paper sheet with a simulated watermark pattern
2o according to the figure 3C2 (samples 1 and 2), comprising
three plies, compared with a tissue paper sheet having a
similar embossed pattern (T), comprising three plies. The
embossing of the control sheet is an ordinary embossing
without adhesive. Samples 1 and 2 and T having a width of 50
2s mm, have been cut.
The delaminating test consists of measuring the
average force of delaminating a sample at an angle of1800
and a constant speed of 100 mm/min. There is no value for
the samples corresponding to the embossed pattern since the
3o plies divide each other before measuring, in particular
between the first two plies. With regard to the samples
according to the invention, the average of the plotted
values during the continue testing of delaminating is not
representative. Only the pic values corresponding to the
* Registered Trade Mark
CA 02238756 2004-10-14
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pattern regions when the plies are bonded, can be
interpreted.
The maximum value of forces to delaminate the
plies are reported in the following table.
Force (Newton)
Facin the Cross wise
en ine
Between the Between the Between the Between the
1 st 2nd 1 st 2nd
and 2nd lies and 3rd liesand 2nd liesand 3rd lies
T - 0.008 - 0.07
Sam 1e 0.08 0.04 0.11 ' 0.07
1
Sam 1e 0.05 0.02 0.15 0.11
2
Even though these values are low, they show that
i5 the delamination of the samples according to the invention
are higher than those of the embossed control sheet.
For a similar pattern, the simulated watermark
tissue paper sheet according to the invention allows the
plies to bond together contrarily to the embossed tissue
2o paper sheet.
The average thickness of the watermarked sheet has
not changed. The sheet has kept all its physical and
mechanical properties, the strength properties have not
decreased and the elongation of the sheet has not been
2s changed. In particular, the softness properties have not
been adversely affected.
The main step in the process for marking with an
impressed pattern resembling a watermark, a sheet of
absorbent paper made of tissue paper, comprising one or more
3o plies, is the deformation under stress of the sheet by at
least one pass between a hard engraved roll and a receiving
roll having a hardness of more than Shore-D 40, the specific
pressure exerted on the marked or watermarked simulating
surface being at least 14, 7 MPa (150 kg/cm2) and the linear
35 marking speed being at least 50 m/min.
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Preferably, the sheet makes at least two passes
between an engraved roll and a receiving roll.
CA 02238756 1998-OS-27
WO 97/20107 PCT/IB96/01326
14
The resulting watermark may be distinctly improved by playing with the
following parameters.
The nature and hardness of the receiving roil are essential for marking
quality.
Preferably, receiving rolls having a hardness greater than Shore-D 80 are
used.
Heating the engraved roll also considerably improves the marking. The heating
temperature lies within the interval ranging from approximately 50°C to
approximately .
100°C and preferably from approximately 75°C to approximately
85°C.
Supplying the sheet, before marking, with water in liquid or steam form has a
surprising erect on the quality of the simulated watermark.
These parameters are described in more detail in the description which follows
with reference to Figure 4, which illustrates an embodiment of the process
according
to the invention.
Before the sheet undergoes the process, it initially comprises one ore more
superimposed and non-connected plies, each stemming from a conventional
process
for manufacturing absorbent tissue paper and being dried. The sheet may or may
not
be initially creped and/or calendered. The sheet may also be impregnated with
a
softening lotion partly or essentially comprising fatty components.
The process for marking according to the invention can be done on the
papermachine calender when the drying of the sheet is completed.
The process according to the invention is preferably entirety separate from
the
process for manufacturing the sheet. This is a conversion process closely
related to
simulated watermarking processes, which may be placed in a unit other than
that for
manufacturing the sheet.
According to Figure 4, the sheet coming from the unwind roll 8 is brought into
contact with water. Preferably, water is applied to the sheet in the form of
steam by
passing the sheet over a tank 9 containing water heated to a temperature
greater than
or equal to the boiling point of water. Steam 10 released from the tank comes
into
contact with the sheet surface which will subsequently undergo the
deformation.
Steam can also be applied with a steam pipe and a nozzle.The amount of steam
applied
is less than approximately 3 per cent by weight of the weight of the sheet and
is
preferably less than 2 per cent by weight. This supply of a small amount of
water in the
form of steam is a preparatory step for the next step in the formation of the
watermark, considerably improving the quality of the watermark. The steam has
an
effect on the definition and uniformity of the mark or simulated watermark. It
is
conceivable that the steam partially penetrates the sheet and acts on the
papermarking
fibers. Water may also be supplied in liquid form, for example by spraying
fine
droplets. The amount supplied is also less than 3, and preferably less than 2,
per cent
by weight of the weight of the sheet. Likewise, the definition of the
simulated
watermark is improved by supplying water in liquid form.
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15 -
The next step is the formation proper of the
simulated watermark. The sheet 1 then makes a first pass
between a steel engraved roll 11 which is hard and a first
receiving roll 12, and then a second pass between this same
engraved roll 11 and a second receiving roll 13.
The engraved roll 11 is heated to a temperature
which may lie within the range of approximately 50°"C to
100°C. Preferably, the heating temperature of this roll is
'75°C. It has been observed that increasing the temperature
io up to 75°C has an influence on the transparency of the
marked surfaces in the region of the patterns.
The combination of the application of water in the
form of steam and of the heating of the engraved roll gives
the best watermarking results.
i5 The receiving rolls 12 and 13 have a high
hardness, greater than Shore-D 80 and preferably greater
than Shore-D 90. They may be made of paper, of composite
material, or of any other material having this hardness.
When the receiving roll surface hardness is within
2o the range of approximately 80 to approximately 90 Shore-D,
the receiving roll is preferably substantially elastic and
deformable under the pressure exerted by the engraved roll.
This means that the receiving roll surface tends to take or
takes again its original form further to the pressure
25 exerted by the engraved roll.
The cylinder elasticity is defined herein by the
ratio of the energy restored by the cylinder following
deformation to the energy that was imparted to it for
deformation. This ratio can be determined from hysteresis
3o cycles entailed by consecutive tension and relaxation using
a dynamometer or by applying fly-based impact to a test bar.
Receiving rolls the surface of which have a
hardness more than 30 HRC (Rockwell hardness), can be
generally used. As for an example, the ceramic material
35 fulfills this hardness characteristic. The receiving rolls
CA 02238756 2004-10-14
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may also be made of steel for very high hardness. As a
matter of fact, these receiving rolls are first elastic and
then have a plastic behaviour when a pressure is applied on
the surface thereof.
In the case where the receiving roll surfaces have
a hardness more than 30 HRC, the hard engraved roll, in
particular a steel roll, can have a surface hardness which
is higher or lower than the receiving roll surface hardness.
The receiving cylinders may be of the same or
io different kind. Composite materials offer the best results
in terms of resistance to mechanical and thermal stresses.
The specific pressure applied to the patterns or
the local specific pressure is at least 14,7 MPa (150
kg/cm2). The force applied has been measured during the
i5 sheet s pass, under particular test conditions:
- a pattern density or pattern distribution of 9%;
- a roll configuration in which the steel engraved
roll is arranged between a paper receiving roll, having a
hardness of Shore-D 80 and a fixed central rotation axis,
2o and a receiving roll having a hardness of Shore-D 92, on
which the force is applied and
- an impression varying in this case from 4 mm to 8
mm (the impression arises from the deformation of the
receiving roll by the engraved roll and corresponds to the
z5 width of the area of contact between them).
From the measured value of the force applied, the
average specific: pressure is calculated and then, from the
latter and the surface area occupied by the engraved
patterns, the local specific pressure on each pattern is
3o calculated, this being at least 29,4 MPa (300 kg/cmz).
Above a local specific pressure of approximately 29,4 MPa
(300 kg/cm2) it has been found that the bonding of the plies
and the definition of the watermark were improved.
The impression according to the pattern may be
35 larger or smaller and tests have been carried out for
CA 02238756 2004-10-14
- 16a -
impressions ranging from 4 to 12 millimetres, these values
not being limiting.
The linear marking speed is at least 50 m/min.
Maximum speeds of 300 m/min have been experimentally tested.
However, under suitable conditions, higher theoretical
speeds would be conceivable, in particular for new types of
cover for the receiving roll, making them more resistant to
the stresses exerted. The transparency effect may be
improved for a given speed by supplying steam or by heating
io the engraved roll. For example, the effect may be
insufficient at a speed of 300 m/min with neither steam
supply nor heating, whereas the effect is entirely
satisfactory at this same speed with an engraved roll heated
to75°C. It has been found that the speed, heat and steam
i5 parameters act independently and may be cumulative.
The sheet may be calendered during the marking
process or thereafter.
The process allows the engraving pattern to be
easily changed by placing the engraved roll in the sheet-
2o conversion installation according to the customer's choice.
A simulated watermark has been produced on a sheet
of absorbent paper which had been impregnated beforehand
with a softening lotion. It has been found that the fact of
treating the surface of the sheet intending to be marked in
2s no case changed the parameters of the marking process, or
the actual simulated watermark on the finished product,
whereas in certain processes in the prior art (for examplel
he process described in United States Patent No. 4,481,243),
the regions intended to be marked.or embossed had not to be
3o impregnated with a lotion. The properties of the lotion-
impregnated sheet, which has been submitted to a simulated
watermarking, were unchanged.
The subject of the invention is also a device for
implementing the process described above.
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WO 97/2fl107 PCT/IB96/01326
I7
Such a device comprises at least one engraved roll, optionally heated, and at
least one receiving roll.
One of these devices is illustrated by Figure 5.
This device comprises a steel roll 110 which is engraved and optionally
heated.
This roll 110 is arranged between two receiving rolls 120 and I30 which are
substantially elastic further to the pressure exerted by the engraved roll I
I0. One of
the rolls has a fixed central rotation axis and the other two rolls can move
about an
axis which is other than their central rotation axis. In figure 4, the
receiving roll 130 is
fixed (its central rotation spindle i35 is fixed) and the roll 110 and 120 can
move
laterally. The roll 130 is fixedly mounted in the stack frame. The two rolls 1
IO and 120
are mounted in cases which are themselves positioned in vertical slideways.
Stops are
provided for the rolls. The upper mechanical stops can prove to be useful in
the case
of large vibrations. The lower stops serve to support the various rolls when
the device
is not running. The compressive force is exerted by the hydraulic rams 140 or
by any
equivalent means. The receiving roll I20 and the engraved roil 110 are
applied, by
means of pressure, against the receiving roll I30.
Devices according to other embodiments of the invention are illustrated by
figures 6 and 7.
According to figures 6 and 7, the central cylinder 200 or 300 is the engraved
roll and is fixed. The other two rolls 201 and 202 or 301 and 302, are
movable.
Compared with the rolls 110 and 120 of the device of figure 5, the rolls 201
and 202 of the device of figure 6 can come into contact with the fixed roll
200 by
rotation.
In figure 7, the receiving rolls 301 and 302 come into contact with the fixed
engraved roll 300 by a translatory movement.
The devices wherein the rolls, engraved and receiving rolls, having other
configurations, for example being not aligned, are also included by the
disclosure of
the invention.
Two engraved rolls can be contemplated. These engraved rolls can have same
or different patterns engraved in their surface. The two impressed patterns
can be
applied on the same side of the sheet or each pattern is applied on each side,
respectively.
When the impression corresponding to each pattern is applied on the same side
of the sheet and if the pattern of one engraved roll is different from the
pattern of the
other engraved roll, those patterns can preferably be complementary to obtain
a
complex pattern on the tissue paper sheet.
The present invention also encompasses tissue paper sheet comprising one or
more plies and having on the one hand, patterns obtained by embossing or «
press-
marking », and, on the other hand, simulated watermark patterns obtained
according
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WO 97/20107 PCT/IB96/OI326
18
to the process disclosed in the preceeding description. The embossing allows
the sheet
to increase its thickness, and the simulated watermarking allows the sheet to
obtain an
attractive aesthetic effect.
The simulated watermarking can be applied before or after the embossing or
press-marking step.
