U.S. patent application number 12/344854 was filed with the patent office on 2010-07-01 for tissue with improved dispersibility.
Invention is credited to Michael Alan Hermans, Kristina Fries Smits.
Application Number | 20100163197 12/344854 |
Document ID | / |
Family ID | 42283465 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100163197 |
Kind Code |
A1 |
Smits; Kristina Fries ; et
al. |
July 1, 2010 |
Tissue With Improved Dispersibility
Abstract
Soft tissue sheets, such as bath tissues, are provided with
increased dispersibility and fiber opacity efficiency, while
maintaining suitable strength, by the addition of acid-treated seed
fibers to the fiber furnish.
Inventors: |
Smits; Kristina Fries;
(Menasha, WI) ; Hermans; Michael Alan; (Neenah,
WI) |
Correspondence
Address: |
KIMBERLY-CLARK WORLDWIDE, INC.;Tara Pohlkotte
2300 Winchester Rd.
NEENAH
WI
54956
US
|
Family ID: |
42283465 |
Appl. No.: |
12/344854 |
Filed: |
December 29, 2008 |
Current U.S.
Class: |
162/141 |
Current CPC
Class: |
D21H 11/00 20130101;
D21H 27/002 20130101 |
Class at
Publication: |
162/141 |
International
Class: |
D21H 11/00 20060101
D21H011/00 |
Claims
1. A soft tissue having a bone dry basis weight from about 15 to
about 35 grams per square meter, from about 5 to about 40 dry
weight percent softwood fibers and from about 60 to about 95 dry
weight percent hardwood fibers, a geometric mean tensile strength
from about 500 to about 1000 grams per 3 inches of width and a
Dispersibility of about 1.5 cycles or less.
2. The tissue of claim 1 having a Dispersibility from about 0.5 to
about 1.5 cycles.
3. The tissue of claim 1 having a Dispersibility from about 0.5 to
1.0 cycles.
4. The tissue of claim 1 having a Dispersibility of about 1
cycle.
5. The tissue of claim 1 having a ratio of opacity divided by bone
dry basis weight of about 2.5 percent/gsm or greater.
6. The tissue of claim 1 having a ratio of opacity divided by bone
dry basis weight from about 2.5 to about 3.0 percent/gsm.
7. The tissue of claim 1 having a ratio of opacity divided by bone
dry basis weight from 2.56 to 2.70 percent/gsm.
8. The tissue of claim 1 consisting of a single ply.
9. The tissue of claim 1 having from about 10 to about 20 dry
weight percent softwood fibers and from about 80 to about 90 dry
weight percent hardwood fibers.
10. A soft tissue having a bone dry basis weight from about 15 to
about 35 grams per square meter, from about 5 to about 40 dry
weight percent softwood fibers and from about 60 to about 95 dry
weight percent hardwood fibers, and from about 0.5 to about 5 dry
weight percent of an Enhanced Fiber Additive, said tissue having a
geometric mean tensile strength from about 500 to about 1000 grams
per 3 inches of width and a Dispersibility of about 1.5 cycles or
less.
11. The tissue of claim 10 having from about 0.5 to about 4 dry
weight percent of an Enhanced Fiber Additive.
12. The tissue of claim 10 having from about 1 to about 3 dry
weight percent of an Enhanced Fiber Additive.
13. The tissue of claim 10 having a Dispersibility from about 0.5
to 1.5 cycles.
14. The tissue of claim 10 having a Dispersibility of about 1
cycle.
15. The tissue of claim 10 having a ratio of opacity divided by
bone dry basis weight of about 2.5 percent/gsm or greater.
16. The tissue of claim 10 having a ratio of opacity divided by
bone dry basis weight from about 2.5 to about 3.0 percent/gsm.
17. The tissue of claim 10 having a ratio of opacity divided by
bone dry basis weight from 2.56 to 2.70 percent/gsm.
18. The tissue of claim 10 consisting of a single ply.
19. The tissue of claim 10 having from about 10 to about 20 dry
weight percent softwood fibers and from about 80 to about 90 dry
weight percent hardwood fibers.
Description
BACKGROUND OF THE INVENTION
[0001] Most consumers want bath tissue that is not only
sufficiently strong for cleaning purposes, but they also want the
comfort of mind that the tissues will disperse when flushed down
the toilet so that they do not clog sewer or septic lines. While
commercially-available bath tissues do disperse, there is room for
improvement. Unfortunately, increased dispersibility usually comes
with a decrease in strength, which is undesirable. Therefore there
is a need for bath tissues having adequate strength with increased
dispersibility, while at the same time exhibiting good opacity for
perceived hand protection in use.
SUMMARY OF THE INVENTION
[0002] It has now been discovered that soft tissues, such as bath
tissue, can be made with improved dispersibility and strength as
compared to currently available commercial bath tissue products. In
addition, the fiber opacity efficiency (hereinafter defined) can
also be improved.
[0003] Hence in one aspect, the invention resides in a soft tissue
having a bone dry basis weight from about 15 to about 35 grams per
square meter, a geometric mean tensile strength from about 500 to
about 1000 grams per 3 inches of width and a Dispersibility
(hereinafter defined) of about 1.5 cycles or less.
[0004] In another aspect, the invention resides in a soft tissue
having a bone dry basis weight from about 15 to about 35 grams per
square meter and from about 0.5 to about 5 dry weight percent of an
Enhanced Fiber Additive (hereinafter defined), said tissue having a
geometric mean tensile strength from about 500 to about 1000 grams
per 3 inches of width and a Dispersibility of about 1.5 cycles or
less.
[0005] For purposes herein, a "soft tissue" is sheet of cellulosic
papermaking fibers suitable for use as a bath tissue. Such soft
tissue sheets are characterized by a relatively high bulk and low
stiffness (as measured by the geometric mean slope). More
specifically, the soft tissue sheet bulk can be about 3 cubic
centimeters or greater per gram of fiber, more specifically from
about 4 to about 20 cubic centimeters per gram of fiber (cc/g), and
still more specifically from about 5 to about 10 cc/g. The
geometric mean slope of the soft tissue sheet can be from about 1
to about 10 kilograms, more specifically from about 1.5 to about 8
kilograms, and still more specifically from about 2 to about 6
kilograms.
[0006] For purposes herein, an "Enhanced Fiber Additive" is a known
seed-based fiber additive, such as fibers derived from corn or
soybeans, which have been modified by acid treatment. The acid
treatment may optionally be followed by a mild acid chlorite
solution, a peroxide solution, or a combination of both. The
resulting Enhanced Fiber Additive is high in hemicellulose, which
increases fiber-to-fiber bonding, and is normally used as a
strength agent in high density papers. The production and uses of
Enhanced Fiber Additives is disclosed in U.S. Pat. No. 6,902,649 B1
entitled "Enhanced Fiber Additive; and Use", issued Jun. 7, 2005 to
Satyavolu et al., which is hereby incorporated by reference in its
entirety. A commercially available line of Enhanced Fiber Additive
is available from Cargill, Incorporated, Minneapolis, Minn., under
the trade name HemiForce.TM.. For purposes of this invention, the
amount of Enhanced Fiber Additive in the soft tissue can be from
about 0.5 to about 5 dry weight percent, more specifically from
about 0.5 to about 4 dry weight percent, and still more
specifically from about 1 to about 3 dry weight percent.
[0007] The bone dry basis weight of the soft tissues of this
invention can be from about 15 to about 15 to about 35 grams per
square meter (gsm), more specifically from about 15 to about 30
gsm, and more specifically from about 15 to about 25 gsm.
[0008] The geometric mean tensile strength (GMT) of the soft
tissues of this invention can be from about 500 to about 1000 grams
per 3 inches of width, more specifically from about 500 to about
900 grams per 3 inches of width, and still more specifically from
about 550 to about 650 grams per 3 inches of width. For purposes of
simplicity, the GMT is sometimes reported as "grams".
[0009] The Dispersibility of the soft tissues of this invention can
be about 1.5 cycles or less, more specifically from about 0.5 to
about 1.5 cycles, more specifically from about 0.5 to about 1.0
cycle, and still more specifically about 1.0 cycle.
[0010] The opacity of the soft tissues of this invention can be
from about 42.0 to about 47.0 percent, more specifically from about
42.0 to about 46.5 percent, and still more specifically from about
42.5 to about 46.5 percent.
[0011] The fiber opacity efficiency for the tissues of this
invention, which is the ratio of the opacity divided by the bone
dry basis weight and is a measure of the efficiency of the fibers
in providing opacity to the tissue sheet, can be about 2.5
percent/gsm or greater, more specifically from about 2.5 to about
3.0 percent/gsm , and still more specifically from 2.56 to 2.70
percent/gsm.
[0012] Suitable papermaking fibers particularly include, without
limitation, softwood and hardwood fibers. As used herein, the term
"furnish" means the papermaking fibers, such as the softwood and
hardwood fibers, used to make the tissue, excluding other furnish
components or additives, such as EFA. The amount of softwood fibers
in the furnish can be from about 5 to about 40 dry weight percent,
more specifically from about 10 to about 40 percent, more
specifically from about 10 to about 30 percent, and still more
specifically from about 10 to about 20 percent. Similarly, the
amount of hardwood fibers in the furnish can be from about 60 to
about 95 dry weight percent, more specifically from about 60 to
about 90 dry weight percent, more specifically from about 70 to
about 90 percent, and still more specifically from about 80 to
about 90 dry weight percent. Relatively speaking, higher amounts of
softwood fibers will increase tensile strength, while higher levels
of hardwood fibers will increase surface softness and opacity.
[0013] In the interests of brevity and conciseness, any ranges of
values set forth in this specification contemplate all values
within the range and are to be construed as written description
support for claims reciting any sub-ranges having endpoints which
are whole number or otherwise of like numerical values within the
specified range in question. By way of a hypothetical illustrative
example, a disclosure in this specification of a range of from 1 to
5 shall be considered to support claims to any of the following
ranges: 1-5; 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5.
Similarly, a disclosure in this specification of a range from 0.1
to 0.5 shall be considered to support claims to any of the
following ranges: 0.1-0.5; 0.1-0.4; 0.1-0.3; 0.1-0.2; 0.2-0.5;
0.2-0.4; 0.2-0.3; 0.3-0.5; 0.3-0.4; and 0.4-0.5. In addition, any
values prefaced by the word "about" are to be construed as written
description support for the value itself. By way of example, a
range of "from about 1 to about 5" is to be interpreted as also
disclosing and providing support for a range of "from 1 to 5",
"from 1 to about 5" and "from about 1 to 5".
Test Methods
[0014] As used herein, sheet "bulk" is calculated as the quotient
of the sheet "caliper" (hereinafter defined), expressed in microns,
divided by the basis weight, expressed in grams per square meter.
The resulting sheet bulk is expressed in cubic centimeters per
gram. More specifically, the sheet caliper is the representative
thickness of a single sheet measured in accordance with TAPPI test
methods T402 "Standard Conditioning and Testing Atmosphere For
Paper, Board, Pulp Handsheets and Related Products" and T411 om-89
"Thickness (caliper) of Paper, Paperboard, and Combined Board" with
Note 3 for stacked sheets. The micrometer used for carrying out
T411 om-89 is an Emveco 200-A Tissue Caliper Tester available from
Emveco, Inc., Newberg, Oreg. The micrometer has a load of 2
kilo-Pascals, a pressure foot area of 2500 square millimeters, a
pressure foot diameter of 56.42 millimeters, a dwell time of 3
seconds and a lowering rate of 0.8 millimeters per second.
[0015] As used herein, the "geometric mean tensile strength" is the
square root of the product of the machine direction tensile
strength multiplied by the cross-machine direction tensile
strength. The "machine direction (MD) tensile strength" is the peak
load (grams-force) per 3 inches (76.2 mm) of sample width when a
sample is pulled to rupture in the machine direction. Similarly,
the "cross-machine direction (CD) tensile strength" is the peak
load per 3 inches (76.2 mm) of sample width when a sample is pulled
to rupture in the cross-machine direction. The "stretch" is the
percent elongation of the sample at the point of rupture during
tensile testing. The procedure for measuring tensile strength is as
follows.
[0016] Samples for tensile strength testing are prepared by cutting
a 3 inches (76.2 mm) wide by 5 inches (127 mm) long strip in either
the machine direction (MD) or cross-machine direction (CD)
orientation using a JDC Precision Sample Cutter (Thwing-Albert
Instrument Company, Philadelphia, Pa., Model No. JDC 3-10, Serial
No. 37333). The instrument used for measuring tensile strengths is
an MTS Systems Sintech 11S, Serial No. 6233. The data acquisition
software is MTS TestWorks.RTM. for Windows Ver. 3.10 (MTS Systems
Corp., Research Triangle Park, N.C.). The load cell is selected
from either a 50 Newton or 100 Newton maximum, depending on the
strength of the sample being tested, such that the majority of peak
load values fall between 10-90% of the load cell's full scale
value. The gauge length between jaws is 4.+-.0.04 inches
(101.6.+-.1 mm). The jaws are operated using pneumatic-action and
are rubber coated. The minimum grip face width is 3 inches (76.2
mm), and the approximate height of a jaw is 0.5 inches (12.7 mm).
The crosshead speed is 10.+-.0.4 inches/min (254.+-.1 mm/min), and
the break sensitivity is set at 65%. The sample is placed in the
jaws of the instrument, centered both vertically and horizontally.
The test is then started and ends when the specimen breaks. The
peak load is recorded as either the "MD tensile strength" or the
"CD tensile strength" of the specimen depending on direction of the
sample being tested. At least six (6) representative specimens are
tested for each product or sheet, taken "as is", and the arithmetic
average of all individual specimen tests is either the MD or CD
tensile strength for the product or sheet.
[0017] The "geometric mean slope" (GM Slope) is the square root of
the product of the machine direction tensile slope and the
cross-machine direction tensile slope. The tensile slope is the
least squares regression slope of the load/elongation curve
described above measured over the range of 70-157 grams (force).
The slope is in kilograms per unit elongation (i.e. 100% strain)
for a 76.2 mm (3 inches) wide sample, but for purposes of
simplicity sometimes reported herein as "kilograms".
[0018] As used herein, "Dispersibility" is a measure of the
propensity of a tissue product to break apart when placed in water
under mild agitation. It is determined by placing a sample of the
product into a slosh box and observing the dynamic break-up of the
sample as the slosh box tips (cycles) back and forth. For rolls of
bath tissue, the sample to be tested is a single "sheet" which, for
purposes herein and well understood within the tissue industry, is
the segment of the bath tissue sheet located between consecutive
lines of perforation. It can consist of one or more plies. Such
sheets are typically about 4 inches square. The actual size,
however, is not particularly important since the size of the slosh
box is sufficiently large to accommodate any known tissue sheets.
For purposes of testing tissue sample basesheets, which have not
been converted into actual final product, a 4 inches-by-4 inches
sample is sufficient.
[0019] The slosh box used for the dynamic break-up of the sample
consists of a plastic box having inside dimensions measuring 18
inches wide (as viewed from the front), 12 inches deep (front to
back) and 6.5 inches high. It is constructed from 0.5 inch thick
Plexiglas.RTM. and is provided with a tightly fitting lid. The
slosh box rests securely on a rocking platform and rocks back and
forth from short side (12 inch end) to short side (opposite 12 inch
end). The underside of the platform is attached to a reciprocating
cam. In operation, the rotational movement of the cam cyclically
raises one side of the platform and thereby also lowers the
corresponding side of the slosh box, pivoting at the center of the
box. The amplitude of the rocking motion of the one side of the
slosh box is .+-.2 inches (a range of 4 inches from the top to the
bottom of the rocking cycle). The rotational speed of the cam is
set to a constant speed of 26 revolutions per minute (.+-.2
revolutions per minute), which results in 43 slosh cycles per
minute. For purposes herein, a "cycle" consists of one "up and
down" motion of the slosh box.
[0020] Prior to testing, the slosh box is filled with 2000 ml.+-.20
ml of a soak solution. The soak solution consists of distilled
water mixed with 0.25 teaspoon of sodium bicarbonate in order to
keep the pH of the soak solution higher than 7. The temperature of
the soak solution is maintained at 23.degree. C..+-.3.degree. C.
Solution is drained and the box chamber is rinsed and refilled
between each specimen characterization. To carry out the test, the
tissue sample is placed flat on the surface of the water in the
slosh box and the slosh box is started immediately. The break-up of
the sample in the slosh box is visually observed and the number of
complete cycles required to separate the sample into two distinct
pieces is recorded. (For multi-ply products, ply separation does
not constitute separation of the sample into two distinct pieces
for purposes of this test. Instead, at least one of the plies must
separate into two distinct pieces.) Five replicates of the tissue
sample are tested. The observed number of cycles needed to break up
the test samples is averaged to achieve a Dispersibility value (in
"cycles") for the product sample.
[0021] As used herein, "opacity" is measured using a Technibrite
Micro TB-1C tester, which is well known in the paper industry,
available from Technidyne Corporation, 100 Quality Avenue, New
Albany, Ind., USA. The Technibrite Micro TB-1C tester, which is a
dual beam optical system, is a fully automatic
microprocessor-controlled instrument that provides brightness,
color, opacity and fluorescence in conformance with ISO and other
international standards. Tests are conducted in a standard
laboratory atmosphere (23.degree. C..+-.1.degree. C. and 50%.+-.2%
humidity) following the instructions for the instrument. For
measuring tissue opacity, the QC routine is used with the black
body cup and with the Y (green) filter in the active position. When
taking measurements, the operator should avoid taking readings in
areas of the sample which contain printing or perforations.
Measurements should be taken on the outside of the sheet (the side
of the sheet that consumers would see). Fifteen representative
samples should be tested and the results averaged to obtain a value
for the particular product. The measurement values represent
reflectance and are expressed as a percent.
EXAMPLES
[0022] In order to further illustrate this invention, a number of
tissues were produced using conventional creped, wet-pressed
technology, such as the method disclosed in U.S. Pat. No. 6,368,454
entitled "Method of Making Soft Bulky Single Ply Tissue" issued
Apr. 9, 2002, to Dwiggins et al. (without embossing), which is
hereby incorporated by reference. Unless stated otherwise, the
particular tissue making method used is not critical.
Example 1 (Invention)
[0023] Single-ply bath tissue basesheet was produced in a
conventional manner on a pilot scale tissue machine. More
particularly, a tissue web was formed on a forming fabric,
transferred to a felt, and thereafter transferred to a Yankee dryer
in a conventional manner. The tissue web was dried to approximately
95 percent consistency on the Yankee dryer and creped using
standard creping technology. The resulting creped tissue sheet was
wound into a parent roll for testing.
[0024] The tissue furnish was a blended furnish comprising
eucalyptus hardwood (HW) fibers and refined northern softwood kraft
(SW) fibers. Prior to formation of the web, the northern softwood
fibers were pulped for 30 minutes at 2.5 percent consistency, while
the eucalyptus hardwood fibers were pulped at 2 percent
consistency. The northern softwood fibers were refined for 5
minutes. The pulp mix (expressed as bone dry weight percent) was
39.2 percent SW, 58.8 percent HW, and 2 percent Cargill
HemiForce.TM. Enhanced Fiber Additive (EFA). The EFA was diluted to
below 2 percent consistency and allowed to mix in the blended stock
chest for 20 minutes before starting formation of the tissue web.
The tissue machine speed (the speed of the Yankee dryer) was 50
feet per minute (fpm).
Example 2 (Invention)
[0025] A single-ply bath tissue was made as described in Example 1,
except the pulp mix was 19.8 percent SW, 79.2 percent HW and 1
percent EFA.
Example 3 (Invention)
[0026] A single-ply bath tissue was made as described in Example 1,
except the pulp mix was 9.7 percent SW, 87.3 percent HW and 3
percent EFA.
Example 4 (Control 1)
[0027] A single-ply bath tissue was made as described in Example 1,
except the softwood fibers were not refined and the pulp mix was 40
percent SW and 60 percent HW. No EFA was added to the pulp mix.
Example 5 (Control 2)
[0028] A single-ply bath tissue was made as described in Example 1,
except the softwood fibers were refined for 9 minutes and the pulp
mix was 40 percent SW and 60 percent HW. No EFA was added to the
pulp mix.
Example 6 (Control 3)
[0029] A single-ply bath tissue was made as described in Example 1,
except the pulp mix was 40 percent SW and 60 percent HW. No EFA was
added to the pulp mix.
Example 7 (Control 4)
[0030] A single-ply bath tissue was made as described in Example 1,
except the pulp mix was 39.6 percent SW, 59.4 percent HW and 1
percent EFA.
Examples 8-16 (Commercial)
[0031] A number of commercially-available bath tissue samples were
collected and tested for various properties. The furnish
compositions are not known.
[0032] All of the tissues were measured for bone dry basis weight,
geometric mean tensile strength, Dispersibility (slosh box cycles)
and opacity. The Invention 1 and 2 samples and the Control 3 and 4
samples were also ranked for panel softness. These samples were
chosen for softness testing since they all had approximately the.
same geometric mean tensile strength. The tissue samples were given
to a trained panel which ranked the tissue samples for surface
softness on a relative scale. A ranking of "A" is considered
relatively softer than a ranking of "B". The results are presented
below in Table 1.
TABLE-US-00001 TABLE 1 Basis EFA Surface Weight Furnish (weight GMT
Dispersibility Opacity Opacity/Basis Softness Example (gsm) (% SW/%
HW) percent) (grams) (Cycles) (Percent) Weight Ratio (Grouping)
1-Invention 1 15.69 39.2/58.8 2 651 1 42.332 2.70 B 2-Invention 2
18.06 19.8/79.2 1 554 1 46.276 2.56 A 3-Invention 3 17.00 9.7/87.3
3 637 1 46.008 2.71 4-Control 1 18.17 40/60 0 311 1 45.44 2.50
5-Control 2 18.54 40/60 0 894 6.4 46.108 2.52 6-Control 3 18.73
40/60 0 586 2.6 46.158 2.46 B 7-Control 4 17.10 39.6/59.4 1 597 1.8
43.478 2.54 B 8-Marcal 16.30 -- 942 5 46.76 2.87 9-Kroger 15.57 --
601 5 40.24 2.58 10-Scott 1000 17.22 -- 773 6 44.63 2.59
11-Albertson's 17.68 -- 684 2 44.29 2.51 12-Pert 16.39 -- 419 3
44.04 2.69 13-Walgreen's 19.16 -- 800 4 52.95 2.76 14-CVS 16.39 --
419 3 44.04 2.69 16-Homelife 17.43 -- 895 7 41.31 2.37
[0033] The results show, with regard to softness, that the
Invention 2 sample had the highest surface softness (95% confidence
level) among the tissues tested. The other inventive sample tested
(Invention 1) was judged to have surface softness similar to that
of the controls. This data indicates that the inventive tissues
were at least as soft as the control codes.
[0034] The results further show that the tissues of this invention
have an improved Dispersibility and better opacity (as measured by
the ratio of the opacity divided by the basis weight) at a fixed
geometric mean tensile strength. Obtaining the desired combination
of softness, tensile strength, Dispersibility and fiber opacity
efficiency required furnish and chemistry manipulation. As the data
of Table 1 indicates, the Control 1 sample had very good
Dispersibility (1 cycle) by not refining the softwood fibers in the
furnish. However, that sample also had a very low geometric mean
tensile strength of 311 grams. On the other hand, the Control 4
sample, which included 1 dry weight percent EFA in the fiber
furnish, had a good geometric mean tensile strength of 597 grams,
but a higher Dispersibility (1.8 cycles), which was only somewhat
better than the best of the commercially available bath tissues (2
cycles for the Albertson's product). Therefore, to further improve
the Dispersibility, the furnish was adjusted for the inventive
samples to include additional hardwood fiber and/or EFA. For the
Invention 1 sample, the EFA content of the furnish was increased to
2 dry weight percent. For the Invention 2 and 3 samples, the
hardwood portion of the furnish was increased to approximately 80
percent and 90 percent, respectively. In all cases, the
Dispersibility was 1 cycle and the geometric mean tensile strength
was above 550 grams.
[0035] Without being bound by theory, it is believed the increase
in the hardwood portion of the furnish increased the Dispersibility
of the product (i.e. reduced the number of cycles) and increased
the opacity of the product. This is thought to be due to the higher
fiber count and reduced fiber length associated with the
substitution of hardwood fiber for a portion of the softwood fiber.
The higher fiber count of the hardwood pulp is thought to have
increased the opacity and the lower fiber length is thought to have
increased the product Dispersibility. However, the increase in
hardwood fiber content also decreased the tensile strength of the
product, perhaps reducing it below the required strength level.
This was countered, where necessary, by further increasing the
level of EFA as the EFA provided improved strength and fiber
opacity efficiency as well as good Dispersibility.
[0036] It will be appreciated that the foregoing examples, given
for purposes of illustration, are not to be construed as limiting
the scope of this invention, which is defined by the following
claims and all equivalents thereto.
* * * * *