Field of the invention
-
The present invention relates to paper tissue, and in particular to facial tissue,
and disposable handkerchiefs. In one preferred embodiment a three-ply tissue
with embossed middle ply is provided.
Background of the invention
-
Paper webs or sheets, sometimes called tissue or paper tissue webs or sheets,
or herein called paper tissue, find extensive use in modern society. Such items
as facial and toilet tissues are staple items of commerce, all of which are herein
referred to as paper tissue. It has long been recognised that important physical
attributes of these products are their strength and thickness/caliper, 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. This tactile sensation is a combination of several
physical properties. One of the more important physical properties related to the
softness and smoothness is generally considered by those skilled in the art to be
the surface structure of the paper tissue from which the tissue product is made
and which is best captured by 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/caliper 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.
-
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
higher the lint resistance is, the lower the propensity of the web to lint will be.
-
W097/44528 discloses a multi-ply tissue product with high absorbency. Example
4 discloses a product where a patterned, relatively textured ply is disposed
between two substantially unpatterned, relatively untextured plies.
-
EP 0 264 676 discloses a process for the manufacture of multi-ply paper sheets.
Example 3 discloses a three-ply product made from wet-formed paper, where
the inner web is provided from embossed paper with a weight of 18g/m2 and the
outer webs are provided from calendered paper with a weight of 14g/m2. The
plies are assembled by a cellulose ether adhesive applied by nozzles.
-
US 5,855,738 discloses a process for making smooth paper tissue comprising a
calendering step.
-
Relatively thick disposable paper products, namely in the form of paper
handkerchiefs and facial tissues, are known. For example, TempoTM, sold by
The Procter & Gamble Company, has a caliper of about 0.3 mm. A high caliper
conveys the idea of high dry and wet strength to the consumer. A high wet
strength, also referred to as wet burst strength, in particular prevents tearing or
bursting which in turn results in contamination of the user's hand with mucus or
other bodily fluids.
-
Even thicker disposable paper products are known and typically used as kitchen
towels, such as BountyTM, sold by The Procter & Gamble Company, which has a
caliper of about 0.7 mm and a wet burst strength which is greater than 200 g.
However such kitchen towels to a considerable extent owe their caliper to
embossing over the whole surface which results in a surface texture which is
rough and does not provide a suitably smooth wiping surface for blowing the
nose.
-
Other products with high wet burst strength and typically a relatively high caliper
are 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 theory, the wet strength and caliper of a product can be increased by
increasing the number of plies to 5, 6 or even more (instead of embossing or the
like) and thereby maintaining a smooth outer surface. However, this approach
would be very costly and also lead to a stiff product, hence compromising tactile
perception.
-
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
caliper and softness for smoothness (as discussed e.g. in US 5,855,738).
-
In view of the prior art 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
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 paper tissue
comprising at least two plies, characterised in that the paper tissue has a
physiological surface smoothness parameter of less than 700 microns,
preferably from 650 microns to 50 microns, more preferably from 650 microns to
300 microns and in combination has a caliper per ply of more than 0.09 mm,
preferably from 0.09 mm to 0.5 mm, more preferably from 0.1 mm to 0.2 mm. In
one preferred embodiment a three-ply tissue with embossed middle ply is
provided. Further is a related process claimed and described.
Detailed Description of the Invention
-
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
(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
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
replete with descriptions of processes for making such materials, including US-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
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 12th 1975; US-A-4 129 528 issued to
Petrovich on December 12 1978; US-A-4 147 586 issued to Petrovich on April
3rd 1979; and US-A-4 222 921 issued to Van Eenam on September 16th 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 19th
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
29th 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.
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
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 dry fiber
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
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
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
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
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 0.1:1.0. 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
analytical and testing procedures are given in W095/11343, published on 27th
April, 1995.
-
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".
-
The paper tissue of the present invention may be made by common methods
well-known to the person skilled in the art, such as by dewatering 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. Such processes are
described in the patent literature referred to hereinafter with regard to through-air-dried
tissue.
-
According to the present invention a paper tissue is provided from at least 2 plies
which is thick but smooth and hence has a physiological surface smoothness
parameter of less than 700 microns, preferably from 650 microns to 50 microns,
more preferably from 650 microns to 300 microns and in combination has a
caliper per ply of more than 0.09 mm, preferably from 0.09 mm to 0.5 mm, more
preferably from 0.1 mm to 0.2 mm. According to the present invention it has
been found that the caliper per ply is a relevant parameter in expressing how
much caliper is provided in a cost effective way, i.e. per one ply. Any
combination of ranges given above for the PSS parameter and the caliper per
ply is within the scope of the present invention.
-
Preferably the paper tissue has a low ratio of caliper per ply over the PSS
parameter, the ratio being lower than 6500 microns/mm, more preferably lower
than 5000 microns/mm, yet more preferably lower than 3000 microns/mm.
-
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
caliper of the tissue.
-
The caliper of a tissue according to the present invention is preferably from 0.1
mm to1 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 100 g, preferably from 150 g to 500 g, more
preferably from 250 g to 400 g.
-
In one preferred embodiment of the present invention a paper tissue is provided
from two plies. In one preferred two-ply embodiment of the present invention one
ply is provided from a calendered paper tissue while the other ply is provided
from a textured, preferably embossed paper tissue. Without wishing to be bound
by theory, the following is believed: The embossing increases the overall caliper
of the product and thereby also the caliper per ply. The calendering typically
increases the smoothness of the respective ply and thereby a surface is
provided with a low PSS parameter.
-
"Calendered", as used herein, comprises high pressure calendering, high
pressure calendering denoting a calendering using a pressure per contact length
of at least 3 kN/m, more preferably 5 kN/m to 50 kN/m, yet more preferably 10
kN/m to 25 kN/m. Calendering with higher pressure increases the smoothness of
paper tissue and hence decrease the PSS parameter.
-
In accordance with the present invention preferably single plies are subjected to
calendering, but alternatively several plies at a time or a whole multi-ply paper
tissue may be calendered.
-
Alternatively other techniques known is the art to increase the smoothness of
paper tissue can be used, such as the selection of appropriate Fourdrinier wires,
felts, and belt in the dewatering stages, further creping under the appropriate
conditions (glue content, glue composition, blade impact angle, creping aides).
Further surface treatments, for example with a lotion, as disclosed hereinafter,
are within the scope of the present invention.
-
"Textured", as used herein, for a paper tissue refers to a paper tissue which is
either through-air-dried, or bulk embossed, or comprises regions of different
basis weights or is dried with a texture or creped under the appropriate
conditions (glue content, glue composition, blade impact angle, creping aides),
as explained hereinafter.
-
"Bulk embossed", as used herein, refers to an embossing which increases the
caliper of the paper tissue by at least 5%, preferably 15%, more preferably 25%
as compared to the caliper of the paper tissue before the bulk embossing.
Preferably bulk embossing provides a pattern of embossed and unembossed
areas, which is imparted to only a limited number of plies of the multi-ply paper
tissues of the present invention in one process step, preferably only to one ply in
one process steps. The outermost embossed areas of the pattern preferably
extends over at least 75%, preferably 85%, more preferably 95% of the total
surface area of the embossed paper plies. Knob to knob embossing is well
known in the art as illustrated by commonly assigned U.S. Patent No. 3,414,459,
issued Dec. 3, 1968 to Wells. The texture may also be imparted to the paper
tissue by nested embossing as illustrated by U.S. Patent No. 4,320,162, issued
Mar. 16, 1982 to Schulz et al. Alternatively, the texture may be imparted to the
paper tissue by dual ply lamination embossing as illustrated by commonly
assigned U.S. Patent No. 5,468,323, issued Nov. 21, 1995 to McNeil. Preferably
such bulk embossing pattern is provided by steel-to-steel knob-to-knob
embossing, the knobs preferably having an elliptical cross section and a height
in the range of 0.5 mm to 3 mm, more preferably in the range of 1 mm to 2 mm.
Preferably the bulk embossing provides a ratio of embossed areas to
unembossed areas of from 1:1 to 1:20, more preferably 1:2 to 1:15, yet more
preferably a ratio of from 1:5 to 1:10.
-
To obtain the texture on either, or both, of the first and second opposed surfaces,
the tissue may be alternatively through-air-dried. Through-air-dried tissue is
disclosed in commonly assigned U.S. Patent Nos. 4,529,480, issued July 16,
1985 to Trokhan; 4,637,859, issued Jan. 20, 1987 to Trokhan; 5,364,504, issued
Nov. 15, 1994 to Smurkoski et al.; 5,529,664, issued June 25, 1996 to Trokhan
et al.; 5,679,222 issued Oct. 21, 1997 to Rasch et al.; 5,714,041 issued Feb. 3,
1998 to Ayers et al.; 5,906,710, issued May 25, 1999 to Trokhan. Alternatively,
the paper tissue may be through-air-dried and made as disclosed in U.S. Patent
Nos. 5,429,686 issued July 4, 1995 to Chiu et al. and 5,672,248 issued Sept. 30,
1997 to Wendt et al.
-
Alternatively, the paper tissue may be textured by providing various regions of
differing basis weights, so that a multi-basis weight paper tissue is presented.
Multi-basis weight paper tissue is disclosed in commonly assigned U.S. Patents
Nos. 5,245,025, issued Sept. 14, 1993 to Trokhan et al.; 5,527,428 issued
June 18, 1996 to Trokhan et al.; 5,534,326 issued July 9, 1996 to Trokhan et al.;
5,654,076, issued Aug. 5, 1997 to Trokhan et al.; 5,820,730, issued Oct. 13,
1998 to Phan et al.; 5,277,761, issued Jan. 11, 1994 to Phan et al.; 5,443,691,
issued Aug. 22, 1995 to Phan et al.; 5,804,036 issued Sept. 8, 1998 to Phan et
al.; 5,503,715, issued Apr. 2, 1996 to Trokhan et al.; 5,614,061, issued March 25,
1997 to Phan et al.; 5,804,281 issued Sept. 8, 1998 to Phan et al.; and
5,900,122 issued May 4, 1999 to Huston.
-
Alternatively, the paper may be conventionally dried with a texture, for example,
according to commonly assigned U.S. Patent Nos. 5,549,790, issued Aug. 27,
1996 to Phan; 5,556,509, issued Sept. 17, 1996 to Trokhan et al.; 5,580,423,
issued Dec. 3, 1996 to Ampulski et al.; 5,609,725, issued Mar. 11, 1997 to Phan;
5,629,052 issued May 13, 1997 to Trokhan et al.; 5,637,194, issued June 10,
1997 to Ampulski et al.; 5,674,663, issued Oct. 7, 1997 to McFarland et al.;
5,693,187 issued Dec. 2, 1997 to Ampulski et al.; 5,709,775 issued Jan. 20,
1998 to Trokhan et al.; 5,776,307 issued Jul. 7, 1998 to Ampulski et al.;
5,795,440 issued Aug. 18, 1998 to Ampulski et al.; 5,814,190 issued Sept. 29,
1998 to Phan; 5,817,377 issued October 6, 1998 to Trokhan et al.; 5,846,379
issued Dec. 8, 1998 to Ampulski et al.; 5,855,739 issued Jan. 5, 1999 to
Ampulski et al.; 5,861,082 issued Jan. 19, 1999 to Ampulski et al., 5,871,887
issued Feb. 16, 1999 to Trokhan et al.; 5,897,745 issued April 27, 1999 to
Ampulski, et al.; and 5,904,811 issued May 18, 1999 to Ampulski et al.
-
In a highly preferred embodiment of the present invention a paper tissue is
provided from three plies. Preferably at least one ply is calendered and at least
one ply is textured, preferably embossed. More preferably two plies are
calendered and an embossed preferably is disposed there-between. This
particular embodiment has the advantage of providing a smooth surface to the
user on either side. Alternative embodiments of the present invention are for
example those with any number of textured, preferably embossed plies disposed
between two outer calendered plies, one of these being a four ply paper tissue
with two embossed plies disposed between two calendered plies.
-
When two or more plies of paper tissue are combined to form the paper tissue,
the plies may, optionally, be attached together by means, for example, of gluing
or embossing, herein referred to as "attachment embossing". Gluing is less
preferred because it tends to result in a stiffer, less soft product.
-
"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 embossing and, optionally, one or more regions comprising an
attachment embossing, and that the region not comprising an attachment
embossing is at least 50%, and 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 region comprising an attachment embossing.
Attachment embossing is preferably done by steel-to-steel pin-to-pin embossing.
-
If glue is to be used to attach the plies of a multi-ply paper tissue, according to
the present invention the glue is preferably applied unevenly over the surfaces of
the plies to be attached. Therefore the glue is preferably not applied by means
such a spraying nozzle, since such nozzles apply the glue evenly with no
preference for particular areas of the tissue, even when the glue is applied as to
form a discontinuous net.
-
A textured, preferably embossed, paper tissue comprises raised portions. In one
preferred embodiment of the present invention the glue to applied only to these
raised portions of the paper tissue. Since primarily these raised portions are in
context with adjacent plies, in particular with adjacent calendered plies,
application of glue to these raised portions is sufficient as to ensure good
attachment, but avoids the application of an amount of glue, which easily impart
stiffness to the paper tissue.
-
One preferred method of applying glue to a tissue ply is to apply the glue by print
rolling. Alternatively glue may be applied by melt blowing, so as to form areas of
preferential glue applications, e.g. strips of glue.
-
The paper tissue and preferably one or both surfaces, most preferably both
surfaces of the tissue may, optionally, be further treated with a lotion. A lotion
can contribute to the smoothness of the paper tissue, and hence decrease its
PSS parameter.
-
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, and
mixtures thereof. Suitable immobilizing agents include 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 and menthol.
-
A process according to the present invention may utilise any paper tissue made
by any method known in the art, preferred methods are disclosed herein.
-
The process comprises a step of supplying the paper tissue by unwinding at
least two plies, preferably three plies, from a corresponding number of patent
rolls. The process comprises a further step of applying a texture pattern to at
least one ply, preferably by bulk embossing as disclosed herein. The process
also comprises a step of high pressure calendering at least one ply using
calendering pressures as disclosed herein. Further the process comprises a step
of juxtaposing said plies to form a multi-ply tissue.
-
A more preferred process further comprises a step of applying lotion to the plies,
which will form the outer plies of the mulit-ply paper tissue, most preferably the
lotion is applied only to the surfaces which will form the outer surfaces of the
multi-ply tissue. Moreover a preferred process comprises a step of attaching the
juxtaposed plies by embossing, referred to and described above as attachment
embossing. Optionally the present process may also comprise the application of
glue, preferably only to the raised portions of the textured plies.
Test Methods
-
Caliper 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
hours prior to the caliper measurement. If the caliper of toilet tissue is being
measured, 15 to 20 sheets are first removed and discarded. If the caliper 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.
-
Caliper 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, caliper is
measured using a low load Thwing-Albert micrometer, Model 89-11, available
from the Thwing-Albert Instrument Company of Philadelphia, Pa. The caliper per
ply is the total caliper of the multi-ply paper tissue divided by the number of plies
comprised. For a single ply tissue caliper per ply and caliper are identical.
Decorated regions, perforations, edge effects, etc., of the tissue should be
avoided if possible.
-
The wet burst strength 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.
-
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
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,
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
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.
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For the physiological surface smoothness measurement, which reports the PSS
parameter, a sample of the paper tissue is selected which avoids wrinkles, tears,
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.
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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
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.
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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.
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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
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.
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The digitised data pairs are imported into a standard statistical analysis package
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).
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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
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.
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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
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.
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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.
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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
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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)
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,
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.
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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
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.
-
The 3-ply rolls were produced by simultaneously unwinding 3 of the 1-ply rolls,
running the centre ply through a rubber to steel bulk embossing operation and
rewinding the two unembossed outer plies with the embossed centre ply to form
a 3-ply roll. For the centre ply embossing a smooth rubber roll was loaded
against a patterned steel roll. The patterned steel roll has raised elliptical
emboss knobs about 1.7mm deep having a major axis at the surface of about
2mm and a minor axis of about 1mm. The embossments are arranged in
repeating pattern of concentric diamonds consisting of about 72 knobs in 900
square mm area.
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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 19th
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.
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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
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
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 caliper of 0.35 mm, a caliper per ply of 0.12 mm, a wet burst
strength of 375 g and a PSS parameter of 620 micron.
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A second example consists of substrate produced described above, in which the
outer plies are run through a smoothing calendering roll. Calendering at 12 kN/m
to 15 kN/m was found to further reduce the PSS parameter to about 500 to 450
microns.