Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF MAKING A THICK AND SMOOTH EMBOSSED TISSUE
Field of the invention
The present invention relates to paper tissue products, and in particular to
facial
tissue, and disposable handkerchiefs. More particularly, the invention relates
to
converting steps for such tissue paper products, namely embossing and
calendering.
Backciround of the invention
Paper webs or sheets, sometimes called tissue or paper tissue webs or sheets,
and products made therefrom, such as paper handkerchiefs, sometimes also
called facial tissues, find extensive use in modern society. Such items as
facial
and toilet tissues and kitchen towels are staple items of commerce, all of
which
are herein referred to as paper tissue products. It has long been recognised
that
important physical attributes of these products are their strength and
thickness/calliper, their softness and smoothness, their absorbency, and their
lint
resistance. Research and development efforts have been directed to the
improvement of each of these attributes without seriously affecting the others
as
well as to the improvement of two or three attributes simultaneously.
Softness and smoothness relate to the tactile sensation perceived by the
consumer when holding a particular product, rubbing it across the skin, or
crumpling it within the hands. The tactile sensation is a combination of
several
physical properties. The tactile sensation can be well captured by the
objective
parameter of the physiological surface smoothness (PSS) parameter as known
e.g. from US 5,855,738. As important for the tactile sensation of consumers is
the thickness/calliper of a tissue product.
Strength is the ability of the product to maintain physical integrity and to
resist
tearing, bursting, and shredding under use conditions.
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Absorbency is the measure of the ability of a product to absorb quantities of
liquid, particularly aqueous solutions or dispersions. Overall absorbency as
perceived by the consumer is generally considered to be a combination of the
total quantity of a liquid a given mass of paper tissue will absorb at
saturation as
well as the rate at which the mass absorbs the liquid.
Lint resistance is the ability of the fibrous product, and its constituent
webs, to
bind together under use conditions, including when wet. In other words, the
lo higher the lint resistance is, the lower the propensity of the web to lint
will be.
WO 98/58124, published on 23rd December 1998, discloses an embossing
method wherein embossing elements of a height of at least 1 mm are employed.
EP 0 408 248, published 16th January 1991, discloses a converting method
wherein an embossing step is combined with a simultaneous calendering step.
EP 0 668 152, published 23rd December 1998, discloses an embossing method
employed unmatched male and female embossing elements.
EP 0 696 334, published on 10th March 1999, discloses an embossing step with
avoids an increase in bulk.
US 5,855,738 discloses a process for making smooth paper tissue comprising a
calendering step.
Relatively thick and yet soft disposable paper products, namely in the form of
paper handkerchiefs and facial tissues, are known. For example, TempoTM, sold
by The Procter & Gamble Company, is a four ply facial tissue paper product
3o experienced as thick and soft and having a calliper of about 0.3 mm. A high
calliper conveys the idea of high dry and wet strength to the consumer. A high
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wet strength, also referred to as wet burst strength, in particular prevents
tearing
or bursting which for a paper handkerchief in turn results in contamination of
the
user's hand with mucus or other bodily fluids.
In attempting to provide a very smooth surface it is common in the art to
subject
paper tissue to calendering. However, calendering always means a trade-off of
calliper and softness for smoothness (as discussed e.g. in US 5,855,738).
Products with high wet burst strength and typically a relatively high calliper
are
1o those produced by through-air-drying. Though-air-drying facilities,
however, are
not available on conventional paper making machines and the provision of such
equipment means a considerable financial investment. In a further aspect
though-air-drying facilities have an increased energy consumption as compared
to more conventional drying facilities. Therefore it is still of interest to
provide
superior paper qualities employing conventional paper machines.
Hence, there is a persisting challenge to provide a paperhandkerchief
satisfying
or even excelling the standards of known products in meeting all relevant
physical parameters without increasing the use of material or energy. Ideally,
the
same consumer benefit is provided using less cellulose raw material.
In view of the prior art and the consideration set out above there remains a
need
for a tissue product, in particular a facial tissue, which:
- combines optimal strength, namely wet burst strength, absorbency and lint
resistance
- further gives an ideal tactile sensation of softness, smoothness and
thickness
- is cost effective to manufacture and preferably can be manufactured on
conventional paper machines
- optionally provides skin care benefits
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Summary of the Invention
The present invention relates to a paper tissue, and in particular to facial
tissue,
and disposable handkerchiefs. Claimed and described is a method for making a
tissue paper product from a tissue paper web, the method comprising the steps
of:
- passing the tissue paper web through an embossing nip formed between
a first and a second embossing roll, wherein at least one of the embossing
rolls comprises at least 30 embossing elements per squarecentimetre
- passing the tissue paper web through a calendering nip formed between
a first and a second calendering roll, wherein the first and the second
calendering roll are in contact with the tissue paper web over a contact
length measured parallel to the direction of the axis of the first
calendering roll exert a pressure onto the paper web of at least 50 N per
centimetre of the contact length.
Further claimed are paper tissue products made in accordance with the above
method.
Detailed Description of the Invention
Suitable papermaking steps
According to the present invention, a cellulosic fibrous structure is wet-laid
using
principles and machinery well-known in the art of paper-making. A suitable
pulp
furnish for the process of making the paper tissue substrate preferably
contains
papermaking fibres consisting essentially of cellulose fibres (commonly-known
as wood pulp fibres) or cellulose-derived fibres (including, for example,
rayon,
viscose). Fibres derived from soft woods (gymnosperms or coniferous trees) and
hard woods (angiosperms or deciduous trees) are contemplated for use in this
invention. The particular species of tree from which the fibres are derived is
immaterial. The wood pulp fibers can be produced from the native wood by any
convenient pulping process. Chemical processes such as sulfite, sulphate
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(including the Kraft) and soda processes are suitable. Mechanical processes
such as thermochemical (or Asplund) processes are also suitable. In addition,
the various semi-chemical and chemi-mechanical processes can be used.
Bleached as well as unbleached fibers are contemplated for use. Preferably no
non-cellulosic fibres, such as latex, fibres are used.
The paper tissue according to the present invention may contain, as a highly
preferred component a wet strength chemical agent. Preferably up to about
3.0%, preferably at least 0.5%, and more preferably at least 0.8% by weight,
on
1o a dry fiber weight basis, of wet strength chemical agent, such as water-
soluble
permanent and temporary wet strength resin, are contained.
Wet strength resins useful herein can be of several types. For example,
Westfelt
described a number of such materials and discussed their chemistry in
Cellulose
Chemistry and Technology, Volume 13, at pages 813-825 (1979).
Usually, the wet strength resins are water-soluble, cationic materials. That
is to
say, the resins are water-soluble at the time they are added to the
papermaking
furnish. It is quite possible, and even to be expected, that subsequent events
such as cross-linking will render the resins insoluble in water. Further some
resins are soluble only under specific conditions, such as over a limited pH
range. Wet strength resins are generally believed to undergo a cross-linking
or
other curing reactions after they have been deposited on, within, or among the
papermaking fibres. Cross-linking or curing does not normally occur so long as
substantial amounts of water are present.
Of particular utility are the various polyamide-epichlorohydrin resins. These
materials are low molecular weight polymers provided with reactive functional
groups such as amino, epoxy, and azetidinium groups. The patent literature is
3o replete with descriptions of processes for making such materials, including
US-
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A-3 700 623, issued to Keim on October 24th 1972, and US-A-3 772 076, issued
to Keim on November 13th 1973.
Polyamide-epihydrochlorin resins sold under the trademarks Kymene 557H and
Kymene LX by Hercules Inc. of Wilmington, Delaware, are particularly useful in
this invention. These resins are generally described in the aforementioned
patents to Keim.
Base-activated polyamide-epichlorohydrin resins useful in the present
invention
1 o are sold under the Santo Res trademark, such as Santo Re 31, by Monsanto
Company of St. Louis, Missouri. These types of materials are generally
described in US-A-3 855 158 issued to Petrovich on December 17th 1974; US-A-
3 899 388 issued to Petrovich on August 12'" 1975; US-A-4 129 528 issued to
Petrovich on December 12 1978; US-A-4 147 586 issued to Petrovich on April
3'd 1979; and US-A-4 222 921 issued to Van Eenam on September 16 th 1980.
Other water-soluble cationic resins useful hererin are the polyacrylamide
resins
such as those sold under the Parez trademark, such as Parez 631 NC, by
American Cyanamid Company of Sandford, Connecticut. These materials are
generally described in US-A-3 556 932 issued to Coscia et al on January 19t"
1971; and US-A3 556 933 issued to Williams et al on January 19th 1971.
Other types of water-soluble resins useful in the present invention include
acrylic
emulsions and anionic styrene-butadiene latexes. Numerous examples of these
types of resins are provided in US-A3 844 880. Meisel Jr et al, issued October
29 th 1974. Still other water-soluble cationic resins finding utility in this
invention
are the urea formaldehyde and melamine formaldehyde resins. These
polyfunctional, reactive polymers have molecular weights on the order of a few
thousand. The more common functional groups include nitrogen containing
groups such as amino groups and methylol groups attached to the nitrogen.
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Although less preferred, polyethylenimine type resins find utility in the
present
invention.
More complete descriptions of the aforementioned water-soluble resins,
including their manufacture, can be found in TAPPI Monograph Series No. 29,
"Wet Strength in paper and Paperboard, Technical Association of the Pulp and
Paper Industry (New York; 1965).
Temporary wet strength agents, such as modified starch may also, optionally,
be
1o used. Combinations of permanent and temporary wet strength agents may be
used.
The present invention may contain dry strength chemical agents, preferably at
levels up to 3% by weight, more preferably at least 0.1 % by weight, on a
dryfiber
weight basis. A highly preferred dry strength chemical agent is carboxymethyl
cellulose. Other suitable dry strength chemical agents include polyacrylamide
(such as combinations of CyproTM 514 and AccostrengthTM 711 produced by
American Cyanamid of Wayne, N.J.); starch (such as corn starch or potato
starch); polyvinyl alcohol (such as AirvolTM 540 produced by Air Products Inc.
of
2o Allentown, PA); guar or locust bean gums; and polyacrylate latexes.
Suitable
starch materials may also include modified cationic starches such as those
modified to have nitrogen containing groups such as amino groups and methylol
groups attached to nitrogen, available from National Starch and Chemical
Company (Bridgewater, NJ).
Chemical softening compositions, comprising chemical debonding agents are
optional components of the present invention. US-A-3 821 068, issued June
3o 28th, 1974 teaches that chemical debonding agents can be used to reduce the
stiffness, and thus enhance the softness, of a paper tissue web. US-A-3 554
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862, issued on January 12th 1971 discloses suitable chemical debonding agents.
These chemical debonding agents include quaternary ammonium salts.
Preferred chemical softening compositions comprise from about 0.01 % to about
3.0% of a quaternary ammonium compound, preferably a biodegradable
quaternary ammonium compound; and from about 0.01% to about 3.0% of a
polyhydroxy compound; preferably selected from the group consisting of
glycerol, sorbitols, polyglycerols having an average molecular weight of from
about 150 to about 800 and polyoxyethylene glycols and polyoxypropylene
lo glycols having a weight average molecular weight from about 200 to 4000.
Preferably the weight ratio of the quaternary ammonium compound to the
polyhydroxy compound ranges from about 1.0:0.1 to 0.1:1Ø It has been
discovered that the chemical softening composition is more effective when the
polyhydroxy compound and the quaternary ammonium compound are first
premixed together, preferably at a temperature of at least 40 C, before being
added to the papermaking furnish. Either additionally, or alternatively,
chemical
softening compositions may be applied to the substantially dry paper tissue
web,
for example by means of a printing process (N.B. all percentages herein are by
weight of dry fibres, unless otherwise specified).
Examples of quaternary ammonium compounds suitable for use in the present
invention include either unmodified, or mono- or di- ester variations of :
well-
known dialkyldimethylammonium salts and alkyltrimethyl ammonium salts.
Examples include the di-ester variations of di(hydrogenated tallow)dimethyl
ammonium methylsulphate and di-ester variations of di(hydrogenated
tallow)dimethyl ammonium chloride. Without wishing to be bound by theory, it
is
believed that the ester moity(ies) lends biodegradability to these compounds.
Commercially available materials are available from Witco Chemical Company
Inc. of Dublin, Ohio, under the tradename "Rewoquat V3512". Details of
3o analytical and testing procedures are given in WO95/11343, published on 27
th
April, 1995.
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Examples of polyhydroxy compounds useful in the present invention include
polyoxyethylene glycols having a weight average molecular weight of from about
200 to about 600, especially preferred is "PEG-400".
While the addition of particular chemical agents listed above as preferred
agents, can have very beneficial effects on the paper products obtained,
namely
their softness, paper tissue webs useful for the present invention may be made
by any common method well-known to the person skilled in the art.
Such papermaking processes comrprise the dewatering of suitable pulp using,
for example, one or more papermakers felts and/or belts. For the present
invention conventional papermaking processes are preferred. Any process
referred to herein as conventional is a paper-making process which does not
comprise a step of through-air-drying. Alternatively, papermaking processes
comprising a through-air-drying step can be utilised.
Stretch embossing step
The present invention is specifically concerned with steps known in the art as
converting steps.
One important converting step to be carried out in accordance with the present
invention is an embossing step in which a very fine pattern is embossed using
a
low pressure.
Embossing of a paper tissue web is generally achieved by passing the web
through the nip formed between two embossing rolls, at least one embossing
roll
comprising embossing elements. An embossing roll typically comprises a
curved, but otherwise flat surface. Embossing elements are protrusions raising
3o above this surface and having a certain height as measured in a direction
perpendicular to the axis of the embossing roll from the curved flat roll
surface to
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the utmost point of the protrusion. Embossing elements have a certain width,
to
be measured in the plane of the essentially flat roll surface. The term width
as
used herein refers to the diameter of a round embossing element measured the
plane specified above (ie. at the bottom of the embossing element) or to the
largest width measured in said plane, when the embossing element is not round.
According to the present invention the embossing elements can have any shape,
such as pyramidal or half spherical, and the cross section of the embossing
elements can be circular, oval or square. The embossing elements may form a
1 o continuous pattern, but preferably are distinct form each other.
According to the present invention the embossing elements are disposed over at
least one embossing roll in a very fine pattern, comprising at least 30
embossing
elements, preferably at least 50, more preferably at least 60, yet more
preferably
at least 70, most preferably at least 80 embossing elements per
squarecentimetre surface area of the embossing roll.
According to the present invention the embossing elements are not high,
preferably they have a height of less than 1 mm, more preferably less than 0.8
mm, yet more preferably less than 0.6 mm, yet even more preferably less than
0.5 mm or less than 0.4 mm, and most preferably less than 0.3 mm.
Preferably the stretch embossing provides a ratio of embossed areas to
unembossed areas from 5% - 95%, more preferably 20% to 80% and most
preferably 40% - 60%, i.e. for the most preferred case 40% - 60% of the total
surface area of the tissue paper web are embossed.
Any known type of embossing roll and mode of operation of such roll is within
the scope of the present invention. In one preferred embodiment of the present
invention two hard metal, eg. steel, embossing rolls are used, wherein a first
roll
comprises protruding embossing elements, referred to as the male roll, and a
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second roll comprises matching recesses, referred to a the female roll. The
recesses may be mirror images of the protruding embossing elements or may be
adapted to be slightly smaller than exact mirror images, eg. due to a slight
difference in size or shape (eg. slope) of those recesses in the female roll.
In another highly preferred embossing step according to the present invention
a
first embossing roll comprises a web contacting surface provided from a hard
metal comprising protruding embossing elements and a second roll comprises a
web contacting surface comprising a softer material, eg. rubber, preferably a
1 o material of Shore A hardness 40-70, in which recesses are formed upon
sufficiently close contact with the protruding embossing elements. Providing
an
embossing nip from a hard metal roll in combination with a rubber roll has
numerous advantages, such as cheaper and easier production and operation,
since the adjustment of the rolls in much less critical than for a male and a
female hard metal roll. Surprisingly, it has been found that the method
claimed
herein also provides excellent results when a hard metal / rubber roll
combination is used.
The size of the nip formed between the two embossing rolls is to be adapted
2o depending eg. on the tissue paper web to be processed and depending on the
embossing pattern used. Also depending on those considerations no pressure or
some pressure may be applied to urge the first embossing roll and the second
embossing roll together.
When two hard metal rolls are employed in the process, a male and a female
role, the rolls should be operated so as to leave a space corresponding to 60%
to 140%, preferably 80% - 120% of the calliper of the unembossed tissue paper
between the protruding embossing elements of the male role and the bottom of
the recesses of the female role.
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When a hard metal roll is used in combination with a rubber roll, the rolls
should
be pressed against each other with a pressure of 10 N/squarecentimetre to 1000
N/squarecentimetre, preferably 20 N/squarecentimetre to 200
N/squarecentimetre and most preferably 50 N/squarecentimetre to 100
N/squarecentimetre.
Known modes of operation are suitable for the present invention, preferably
the
embossing rolls are not heated and run at the same speed, but in alternative
modes of operation at least one roll may be heated and the rolls may run at
1 o unequalspeed.
The above described embossing with a fine pattern, in one important aspect
serves to increase the calliper, or in other words the bulk of the paper
tissue
web. Therefore, in a highly preferred mode of the present invention a single
web
or a single ply of paper tissue is passed through the embossing nip. In
alternative modes of operation a multitude of plies of paper may be passed
through the nib at the same time. However, and without wishing to the limited
by
theory, the applicant believes that the deformation embossing described herein
achieved a stretching of the tissue paper, leading to deformation, but not to
any
substantial densification of the tissue paper and hence the applicant does not
consider the above described embossing method highly suitable for the joining
of juxtaposed plies. It is rather contemplated to employ a separate and
distinct
joining step as to provide a multiply tissue paper product, the joining step
preferably comprising an embossing step, such as "attachment embossing"
described hereinafter.
Calendering step
Any known method of calendering can be employed in the converting process,
however, in accordance with the present invention unusually high calendering
pressures are used.
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A calendering step in accordance with the present invention comprises passing
one or several tissue paper webs through a calendering nip formed between a
first and a second calendering roll. Typically both calendering rolls contact
the
web over a certain length, herein referred to a contact length, measured
parallel
to the direction of the axis of said first calendering roll. The calendering
rolls
exert a pressure onto the web of at least 30 N per centimetre of said contact
length and in order to do so will be pressed against each other with such a
pressure. More preferably the pressure per centimetre of said contact length
is
from 50 N to 300 N, more preferably 60 N to 250 N, yet more preferably 70 N to
1o 200 N and most preferably 120 N to 150 N. According to the present
invention
preferably as many paper tissue webs are calendered as the paper tissue
product will comprise plies, for example two, three or four webs can be
juxtaposed and calendered in one step.
Known equipment and known modes of operation are suitable for the present
invention, preferably the calendering rolls are not heated and run at the same
speed, but in alternative modes of operation at least one roll may be heated
and
the rolls may run at unequal speed.
Calendering is well known in the art to reduce the calliper of a tissue paper
web,
and typically employed to ensure the calliper of the paper tissue product
meets
the required specifications.
Due to the pressure employed, leading to a densification of the paper web,
calendering is known to reduce the perceived softness of a paper tissue
product.
Calendering is therefore, at least in the area of hygiene papers, such a paper
handkerchiefs, carried out at not too high pressures, typically for an
embossed
paper web 10 N/cm to 20 N/cm are selected.
When conceiving the present invention it has been surprisingly found that the
specific embossing step claimed in combination with the specific calendering
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step claimed leads to a rather thick and bulky and yet still very soft paper
product.
More particularly, it has been found that the paper tissue web after
undergoing a
stretch embossing step and a calendering step is of increased calliper as
compared to the untreated web. (When eg. three webs are calendered in one
step the comparison is to be made between three layers of untreated web
versus three layers of embossed and calendered web.) This effect is
particularly
surprising, a calendering with a high pressure is known to reduce the calliper
of
1o a paper web considerably, as for example stated in German patent
application
DE 0 44 14 238.2.
The method claimed in the present invention has been found to increase the
calliper of a paper tissue web by 10%, sometimes even 30% and even up to
40%, 60%, 80% or 100% when comparing the calliper of the untreated web with
the calliper of the treated web. The stretch embossing step alone achieves
calliper increases of typically 50% to 200%.
A paper tissue according to the present invention has a first and a second
surface, the surfaces being mutually opposed to each other, and a thickness
orthogonal to the first and second surface. The thickness is also referred to
a
calliper of the tissue. The calliper of a 3-ply paper tissue product according
to the
present invention is preferably from 0.1 mm tol mm, more preferably from 0.2
mm to 0.5 mm.
Moreover, a paper tissue according to the present invention has preferably a
wet
burst strength greater than 50g, more preferably greater than 100 g,
preferably
from 150 g to 500 g, more preferably from 250 g to 400 g.
It has been found that the method claimed herein leads to a considerable
reduction of the dry tensile strength of the paper tissue without seriously
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affecting the wet tensile strength of the paper tissue. Paper tissues treated
with
the claimed method typically achieve a dry tensile strength from 1000g to
2500g
and a wet burst strength of 100 g to 300 g and preferably achieve a dry
tensile
strength to wet burst strength ratio of 0.1 to 0.3, preferably 0.125 to 0.25
and
most preferably 0.15 to 0.2.
In a further aspect, a paper tissue product according to the present invention
preferably has a physiological surface smoothness parameter of less than 1000
microns, preferably from 650 microns to 50 microns, more preferably from 650
1o microns to 300 microns.
In one preferred embodiment of the present invention a paper tissue product is
provided from two plies to four plies, three plies being most preferred.
Preferably
all plies comprise a stretch embossing pattern extending over at least 50%,
but
preferably 80% of the whole surface area of the paper tissue product and most
preferably the whole surface area of the paper tissue product.
Optional process steps
2o The method for making a tissue paper product according to the present
invention may comprise a number of further optional steps:
A lotion may be applied by any suitable means, such as printing or spraying.
The
lotion can either be applied to the paper web or a paper tissue product,
either to
the whole surface of the web or product or only to a portion thereof. For a
multiple ply paper tissue product the lotion may be applied to all plies or
only
selected plies and to only one or to both surfaces of the plies. In one
preferred
embodiment lotion is applied to both outer surfaces of the paper tissue
product.
3o A lotion has been found to contribute to the smoothness of the paper
tissue, and
hence decrease its PSS parameter. Moreover, the lotion has skin care benefits.
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The lotion may comprise softening/debonding agents, emollients, immobilizing
agents and mixtures thereof. Suitable softening/debonding agents include
quaternary ammonium compounds, polysiloxanes, and mixtures thereof.
Suitable emollients .include propylene glycol, glycerine, triethylene glycol,
spermaceti or other waxes, petrolatum, fatty acids, fatty alcohols and fatty
alcohol ethers having from 12 to 28 carbon atoms in their fatty acid chain,
mineral oil, namely silicone oil e.g. dimethicone and isopropyl palmitate, and
mixtures thereof. Suitable immobilizing agents include ceresin, stearyl
alcohol
1o and paraffins, polyhydroxy fatty acid esters, polyhydroxy fatty acid
amides, and
mixtures thereof.
Other optional components include perfumes, antibacterial actives, antiviral
actives, disinfectants, pharmaceutical actives, film formers, deodorants,
opacifiers, astringents, solvents and the like. Particular examples of lotion
components include camphor, thymol, menthol, camomile extract, aloe vera,
calendula officinalis.
Particularly preferred lotions according to the present invention are highly
transferable lotions comprising the components listed above, as
transferability
ensures superior skin care and pharmaceutical benefits.
Juxtaposed plies of the paper tissue web may be joined as to provide a multi
ply
paper tissue product, preferably by attachment embossing. "Attachment
embosssing", as used herein, refers to an embossing by which all plies of a
multi-ply tissue according to the present invention are embossed in one
process
step. Preferably the attachment embossing does not or at least not to a large
extent affect the smoothness of any calendered ply. Therefore, preferably the
tissue has an unembossed surface over a major part of the surface area of the
tissue, preferably on the first and the second surface. As used herein, this
means that the tissue has one or more regions not comprising an attachment
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embossing and, optionally, one or more regions comprising an attachment
embossing, and that the region not comprising an attachment embossing is at
least 50%, preferably at least 80% and in some preferred embodiments as much
as 99%, of the surface area of the tissue. Most commonly the regions
comprising an attachment embossing lie close to the edge of the tissue (for
example along two or four edges); and a regions comprising an attachment
embossing may also be used for decorative purposes (for example to create a
pattern or to spell out a logo or brand name). The region not comprising an
attachment embossing is the continuous region between and/or around the
1o region comprising an attachment embossing. Attachment embossing is
preferably done by steel-to-steel pin-to-pin embossing and with 10 to 40
embossing elements per squarecentrimetre having a height from 0.01 mm to 1
mm, preferably 0.05 mm to 0.2 mm. The percentage of attachment embossed
areas to unembossed or fine embossed areas of the total surface area of a
paper tissue product is preferably 0.01 % to 5%. Attachment embossing involves
as substantive densification of the paper tissue products as to achieve the
attachment. Therefore the space between and embossing element and its
counterpart, eg. two pins where pin-to-pin embossing is employed, is less that
the calliper of the paper tissue to be embossed, typically 5% to 50%,
preferably
10% to 20% of the calliper of the paper tissue to be embossed, which leads to
embossing pressures of 10 000 to 50 000 N/squarecentimetre.
The method of the present invention may further comprise a step of providing
sheets suitable for paper tissue products, such as paper handkerchiefs. Such
step typically comprises cutting of portions of the paper tissue web.
If desired, the paper tissue products according to the present invention may
be
provided with functional or aesthetic indicia. The indicia may be applied to
either
or both of the surfaces of the paper tissue products. The indicia may cover
all or
part of the paper tissue products and be applied in a continuous or
discontinuous
pattern.
17
CA 02436514 2006-11-22
The indicia may be applied to the paper tissue products by any means
well known in the art, such as spraying, extruding, and preferably printing.
Either
gravure or flexographic printing may be utilized. If printing is selected as
the
means for applying the indicia, the printing apparatus may be constructed
according to the teachings of commonly assigned U.S. patent 5,213,037 issued
May 25, 1993 to Leopardi, II. If desired, the apparatus may have reservoir
baffles, as disclosed in commonly assigned U.S. patent 5,255,603 issued
October 26, 1993 Sonneville et al. If desired, the indicia may be requested
with
1o perforations or drop off cuts as disclosed in commonly assigned U.S. patent
5,802,974 issued Sept. 8, 1998 to McNeil.
Test Methods
Calliper is measured according to the following procedure: The tissue paper is
preconditioned at 21 to 24 C and 48 to 52 percent relative humidity for two
2o hours prior to the calliper measurement. If the calliper of toilet tissue
is being
measured, 15 to 20 sheets are first removed and discarded. If the calliper of
facial tissue is being measured, the sample is taken from near the center of
the
package. The sample is selected and then conditioned for an additional 15
minutes.
Calliper of the multi-ply paper tissue, as used herein, is the thickness of
the
paper when subjected to a compressive load of 14.7 g/cm2. Preferably, calliper
is
measured using a low load Thwing-Albert micrometer, Model 89-11, available
from the Thwing-Albert Instrument Company of Philadelphia, Pa. The calliper
per ply is the total calliper of the multi-ply paper tissue divided by the
number of
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WO 02/066240 PCT/US02/04615
plies comprised. For a single ply tissue calliper per ply and calliper are
identical.
Decorated regions, perforations, edge effects, etc., of the tissue should be
avoided if possible.
The wet burst strenqth is measured using an electronic burst tester and the
following test conditions. The burst tester is a Thwing-Albert Burst Tester
Cat.
No. 177 equipped with a 2000 g load cell. The burst tester is supplied by
Thwing-Albert Instrument Company, Philadelphia, PA 19154, USA.
1 o Take eight paper tissues and stack them in pairs of two. Using scissors,
cut the
samples so that they are approximately 228 mm in the machine direction and
approximately 114 mm in the cross-machine direction, each two finished product
units thick.
First age the samples for one to two hours by attaching the sample stack
together, with a small paper clip and "fan" the other end of the sample stack
to
separate the sheets, this allows circulation of air between them. Suspend each
sample stack by a clamp in a 107 C ( 3 C) forced draft oven for 5 minutes (
10 seconds). After the heating period, remove the sample stack from the oven
2o and cool for a minimum of three minutes before testing.
Take one sample strip, holding the sample by the narrow cross direction edges,
dipping the centre of the sample into a pan filled with about 25mm of
distilled
water. Leave the sample in the water four (4.0 0.5) seconds. Remove and
drain for three (3.0 0.5) seconds holding the sample so the water runs off
in
the cross direction. Proceed with the test immediately after the drain step.
Place
the wet sample on the lower ring of the sample holding device with the outer
surface of the product facing up, so that the wet part of the sample
completely
covers the open surface of the sample holding ring. If wrinkles are present,
3o discard the sample and repeat with a new sample. After the sample is
properly in
place on the lower ring, turn the switch that lowers the upper ring. The
sample to
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WO 02/066240 PCT/US02/04615
be tested is now securely gripped in the sample holding unit. Start the burst
test
immediately at this point by pressing the start button. The plunger will begin
to
rise. At the point when the sample tears or ruptures, report the maximum
reading. The plunger will automatically reverse and return to its original
starting
position. Repeat this procedure on three more samples for a total of four
tests,
i.e., 4 replicates. Report the results, as an average of the four replicates,
to the
nearest gram.
The dry tensile strength is measured according to the following procedure: The
1o test is performed on one inch by five inch (about 2.5 cm X 12.7 cm) strips
of
paper (including handsheets as described below, as well as other paper sheets)
in a conditioned room where the temperature is 28 C + 2.2 C and the relative
humidity is 50% + 10%. An electronic tensile tester (Model 1122, Instron
Corp.,
Canton, Mass.) is used and operated at a crosshead speed of 2.0 inches per
minute (about 5.1 cm per min.) and a gauge length of 4.0 inches (about 10.2
cm). Reference to a machine direction means that the sample being tested is
prepared such that the 5" dimension corresponds to that direction. Thus, for a
machine direction (MD) dry tensile strength, the strips are cut such that the
5"
dimension is parallel to the machine direction of manufacture of the paper
product. For a cross machine direction (CD) dry tensile strength, the strips
are
cut such that the 5" dimension is parallel to the cross-machine direction of
manufacture of the paper product. Machine-direction and cross-machine
directions of manufacture are well known terms in the art of paper-making. The
MD and CD tensile strengths are determined using the above equipment and
calculations in the conventional manner taking the arithmetic average of at
least
six strips tested for each directional strength. The dry tensile strength, as
used
herein, is the arithmetic average of the average MD and the average CD tensile
strengths.
3o For the physiological surface smoothness measurement, which reports the PSS
parameter, a sample of the paper tissue is selected which avoids wrinkles,
tears,
CA 02436514 2003-07-28
WO 02/066240 PCT/US02/04615
perforations, or gross deviations from macroscopic monoplanarity. The sample
is
conditioned at 22 to 24 C and 48 to 52% relative humidity for at least two
hours
prior to testing. The sample is placed on a motorised table and magnetically
secured in place. Either face of the sample may be selected for the
measurement, provided all traces are taken from the same face.
Physiological surface smoothness is obtained by scanning the paper tissue
sample in any direction with a profilometer to obtain the Z-direction
displacement
as a function of distance. The Z-direction displacement is converted to an
1o amplitude versus frequency spectrum by a Fourier Transform. The spectrum is
then adjusted for human tactile response using a series of filters. The peak
heights of the filtered amplitude frequency curve are summed from 0 to 10
cycles per millimetre to give the result.
The paper tissue sample is approximately 100 millimetres x 100 millimetres in
size and mounted on a motorised table. While any suitable table will suffice,
a
table with surface tester model KES-FB-4NKES-SE, available from Kato Tech
Company Limited of Koyota, Japan, or a CP3-22-01 DCI Mini Precision table
using a NuStep 2C NuLogic Two Axis Stepper Motor Controller in the closed
loop control mode have been found suitable. The table has a constant drive
motor which travels at the rate of 1 millimetre per second. The sample is
scanned 30 millimetres in the forward direction transversely indexed one
millimetre, then reversed. Data are collected from the centre 26 millimetres
of
the scan in both the forward and reverse directions. The first and last 2
millimetres of each scan are ignored and not used in the calculations.
The profilometer has a probe with a tip radius of 2.54 microns and an applied
force of 0.20 grams. The gauge range is calibrated for a total Z-direction
displacement of 3.5 millimetres. Over the scan distance of the sample, the
profilometer senses the Z-direction displacement of the stylus in millimetres.
The
output voltage from the gauge controller is digitised at a rate of at least 20
points
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WO 02/066240 PCT/US02/04615
per second. Over the entire 26 millimetre scan range, 512 pairs of time
surface
height data points are obtained for both the forward and reverse directions of
a
scan. The profilometer is mounted above the sample table such that the surface
topography can be measured. A suitable profilometer is a EMD 4320 WI Vertical
Displacement Transducer, having an EPT 010409 stylus tip, and an EAS 2351
Analog Amplifier. This equipment is obtainable from Federal Products of
Providence, Rhode Island.
The digitised data pairs are imported into a standard statistical analysis
package
lo for further analysis. Suitable software analysis packages included SAS of
Cary,
North Carolina, and preferably LabVIEW Instrument Control Software 3.1
available from National Instruments of Austin, Texas. When using the LabVIEW
software, raw data pairs linking surface height and time from the individual
scans
are centered about the mean using the Mean.vi analysis tool in the LabVIEW
software. The 512 data points from each of the 16 traces are converted to 16
amplitude spectra using the Amplitude and Phase Spectrum.vi tool. Each
spectrum is then smoothed using the method described by the PROC Spectra
Method of the SAS software. LabVIEW smoothing filter values of 0.000246,
0.000485, 0.00756, 0.062997, 0.00756, 0.000485, 0.000246 are utilized. The
output from this tool is taken as the Amp Spectrum Mag (vrms).
The amplitude data are then adjusted for human tactile response using a series
of frequency filters designed from Verrillo's data on vibrotactile thresholds
as a
function of vibration frequency as set forth in the Journal of Acoustical
Society of
America, in the article entitled "Effect Of Contactor Area On The Vibrotactile
Threshold", Vol. 35, 1962 (1963). The aforementioned data are reported in a
time domain as cycles per second and converted to the spatial domain in cycles
per millimetre. The conversion factor and filter values are found in the
procedure
set forth in the 1991 International Paper Physics Conference, TAPPI Book 1,
more particularly the article entitled "Methods For The Measurement Of The
Mechanical Properties Of Paper tissue" by Ampulski, et al., and found at page
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WO 02/066240 PCT/US02/04615
19, utilizing the specific procedure set forth at page 22 entitled
"Physiological
Surface Smoothness". The response from the filters are set at 0 below the
minimum threshold and above the maximum response frequencies and varies
from 0 to 1 therebetween as described by the aforementioned Ampulski et al.
article.
The physiologically adjusted frequency amplitude data are obtained by
multiplying the amplitude spectra described above by the appropriate filter
value
at each frequency. A typical amplitude spectrum and filtered amplitude
spectrum
1o are illustrated in Fig. 5 of the aforementioned Ampulski et al. article.
The Verrillo-
adjusted frequency amplitude curve is summed point by point between 0 and 10
cycles per millimetre. This summation is considered to be the physiological
surface smoothness. The eight forward and eight reverse physiological surface
smoothness values thus obtained are then averaged and reported in microns.
Physiological surface smoothness measurements using the SAS software is
described in commonly assigned U.S. Pat Nos. 4,959,125, issued Sept. 25,
1990 to Spendel; 5,059,282, issued Oct. 22, 1991 to Ampulski et al.;
5,855,738,
issued Jan. 5, 1999 to Weisman et al., and 5,980,691, issued Nov. 9, 1999 to
Weisman et al.
Either face of the tissue may be selected for the smoothness measurement,
provided all traces are taken from the same face. If either face of the tissue
meets any of the smoothness criteria set forth herein, the entire sample of
the
tissue is deemed to fall within that criterion. Preferably both faces of the
tissue
meet the above criteria.
Example
An aqueous slurry comprising 3% by weight of Nothern Softwood Kraft (NSK)
fibres was prepared in a conventional re-pulper. The NSK slurry was refined
gently and a 2% solution of the permanent wet strength resin (KymeneTM 617)
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WO 02/066240 PCT/US02/04615
was added to the NSK stock pipe at a rate of 0.9% by weight of the total dry
fibres. The absorption of the permanent wet strength resin onto the NSK fibres
is
enhanced by an in-line mixer. A 1% solution of the dry strength resin
(carboxymethyl cellulose) is added to the NSK stock before the fan pump at a
rate of 0.14% by weight of the total dry fibres. The NSK slurry was diluted to
about 0.2% consistency at the fan pump.
A chemical softening composition was prepared comprising di-hard tallow
diethyl
ester dimethyl quaternary ammonium chloride and polyoxyethylene glycol,
lo having an average molecular weight of 400 (PEG-400). The PEG-400 was
heated to about 66 C, and the quat was dissolved into the molten PEG-400 so
that a homogeneous mixture was formed.
An aqueous slurry comprising 3% by weight of eucalyptus fibres was prepared in
a conventional re-pulper. A 1% solution of the chemical softening composition
was added to the Eucalyptus stock pipe at a rate of 0.09% by weight of the
total
dry fibres. The Eucalyptus slurry was diluted to about 0.2% consistency at the
fan pump. The 1% solution of the chemical softening composition was also
added to the NSK slurry after post CMC addition and prior to dilution of the
slurry
to about 0.2% at the stock pump.
The two slurries were combined so that the ratio of NSK to eucalyptus fibres
was
40:60 and the resulting slurry was deposited, by means of a single layer
headbox onto a Fourdrinier wire to form an embryonic web. Dewatering occured
through the Fourdrinier wire and was assisted by a deflector and vacuum boxes.
The embryonic web was transferred from the Fourdrinier wire, at a fibre
consistency of about 20% at the point of transfer, to a conventional drying
felt.
The web was then transfered to the surface of a Yankee dryer with a sprayed
creping adhesive comprising 0.25% aqueous solution of Polyvinyl Alcohol (PVA).
The fibre consistency was increased to an estimated 96% before dry creping the
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WO 02/066240 PCT/US02/04615
web with a doctor blade. The doctor blade had a bevel angle of about 25 and
is
positioned with respect to the Yankee dryer to provide an impact angle of
about
81 . The Yankee dryer was operated at about 4 m/s and the dried, uncalendared
paper was formed into 1 ply rolls at a reel.
Three of these 1-ply rolls were taken to an off-line rewinding operation to
form 3-
ply rolls that were subsequently converted into a 3-ply tissue paper product,
having overall dimension of about 210 mm square.
io The 3-ply rolls were produced by simultaneously unwinding 3 of the 1-ply
rolls.
While unwinding the paper tissue webs of the 1-ply rolls were each passed
through an embossing nip formed between a hard rubber (Shore A hardness 60)
and a steel roll, the steel roll comprising 80 oval embossing elements, 0.26
mm
high. Subsequently the paper tissue webs are juxtaposed by a set of rolls, so
that three juxtaposed webs were passed through a calendering nip formed
between two steel calendering rolls, which were pressed against each other
with
a pressure of 160 N per cm contact length corresponding to a total pressure of
13440 N.
2o The 3-ply roll was subsequently converted into a 3-ply tissue product. The
three
ply web was unwound and subjected to an embossing step before folding. The
margin of the tissue paper product, extending about 15mm in from the edge was
embossed following the process described in W095/27429, published on 19tn
October 1995. The major part of the surface area of the tissue paper product
(i.e. all of the surface area within the 15mm margin) was unembossed. The
tissue was further decorated by embossing the brand name over a small area of
the previously unembossed area and four decorative leaf patterns where
embossed in the previously unembossed area was also added.
3o Lotion was printed on each of the outer surfaces of the 3-ply web via a two
step
application process before folding. The lotion was an aqueous solution of di-
hard
CA 02436514 2006-11-22
tallow diethyl ester dimethyl quaternary ammonium chloride. The printing was
accomplished by running the 3-ply web through two consecutive printing
stations
each consisting of an engraved anilox roll and a rubber backing roll pair.
The anilox roll was engraved to a cell volume of about 3 ml per square meter,
and with supplied with lotion from a closed supply chamber designed to fill
the
engraved volume with lotion. A gap of 0.35mm was established between the
anilox roll and backing roll, and the 3-ply web was run through this gap,
transferring lotion to the surface touching the anilox roll. The web was then
run
lo through the second printing station with an identical anilox/rubber roll
pair at a
0.35mm gap. The pairs were arranged such that the second anilox roll contacted
the as yet unlotioned surface, transfering lotion to it. This arrangement
transferred 0.45% active quat per dry weight of the finished 3- ply tissue.
The paper tissue obtained by the above described process had a basis weight of
54 g/m2, a total calliper of 0.35 mm, a calliper per ply of 0.12 mm, a wet
burst
strength of 250 g and a PSS parameter of 620 micron.
26
