Note: Descriptions are shown in the official language in which they were submitted.
~138078
Docket No. 49820CANlA
REINFORCED PARTICLE-LOADED FIBRILLATED PTFE WEB
5 BACKGROUND OF THE INVENTION
A. Field of the Invention
This invention describes a particle-loaded fibrillated
polytenfluoroethylene web with a reinforcing screen or scrim at least partially
embedded therein. Compared to an unreinforced web, this reinforced web can
0 resist a much greater pressure drop across it without deforming and displays
greater strength against various mechanical stresses.
B. Description of Related Art
Particle-loaded, non-woven, fibrous articles wherein the non-woven
fibrous web can be compressed, fused, melt-extruded, air-laid, spunbonded,
15 mechanically pressed, or derived from phase separation processes have been
disclosed as useful in separation science. Web products of non-woven webs
having dispersed therein sorbent particulate have been disclosed to be useful as,
for example, respirators, protective garments, fluid-ret~inin~ articles, wipes for
oil and/or water, and chromatographic and separation articles. Coated,
2 o inorganic oxide particles have also been enmeshed in such webs. Such webs
with enmeshed particles which are covalently reactive with ligands (including
biologically-active m~teri~l~) have also been recently developed.
Numerous examples of PTFE filled with or entrapping particulate
material are known in many fields. Mauly applications for PTFE filled with
25 electroconductive materials are known. These include circuit boards, oil leaksensors, electrical insulators, semipermeable webs, and various types of
electrodes. Other such combinations have been used as gasket or sealing
materials and wet friction materials. Still others have been used to produce
high-strength PTFE films and webs with applications as structural elements and
30 electronic components. Where the particulate has catalytic properties, this
type of combination provides a form which can be conveniently handled.
~138078
U.S. Patent No. 4,153,661 discloses various particulate distributed in a matrix
of entangled PTFE fibrils as being useful in, among other things, electronic
in~ul~tors and semipermeable webs.
Numerous combinations of PTFE and metals in which the metal is not
5 entrapped within a PTFE matrix are also known. These include PTFE webs
completely or partially coated with metal and metal matrices with a network of
fibrillated PTFE in the pores thereof. PTFE powder with metal filler has been
used (in paste form) as a battery electrode and as a self-lubricating layer coated
on bronze be~rin~. PTFE films coated onto metal films and plates are also
1 o known.
Methods of preparing fibrillated PTFE webs have been described in, for
example, U.S. Patent Nos. 4,153,661, 4,460,642, and 5,071,610.
The physical pro~.Lies of such particle-loaded fibrillated PTFE webs
are somewhat limited, however. They do not resist high pressure drops without
15 deforming and have limited strength against mechanical stresses created by, for
example, fluid flow, tensile force, mechanical impact, and abrasion.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a composite article
2 o comprising a fibrillated polytetrafluoroethylene (PTFE) web having particulate
entrapped therein and, at least parfially embedded in the web, means for
reinforcing the web. Preferably, this reinforcing means is a screen or scrim.
In another aspect, the present invention provides a method for malting
this article comprising the steps of providing a fibrillated PTFE web with
2 5 particulate entapped therein and pressure bonding to the web a means for
reinforcing the web so that the reinforcing means is at least partially embeddedin the web.
Unless otherwise indicated, the'following definitions apply in this
application:
"screen" means a reinforcing material with a regular geometric pattem
of threads which can be polymeric, glass, metallic, etc.;
~138078
"scrim" means a non-woven web the fibers of which are not in a regular
geometric pattem and which can be polymeric, glass, metallic, etc.; and
"partially embedded" (when used in connection with a reinforcing
means) means the reinforcing means is (a) at least partially depressed in the
5 web to which it has been pressure bonded so that the reinforced web, when
viewed from an edge, shows only up to 95%, preferably up to 90%, more
preferably up to 75 %, and most preferably up to 50 %, of the reinforcing
means and (b) at least partially mechanically entangled with the web.
Embedding a reinforcing means in a fibrillated PTFE web provides the
10 web with mechanical strength and resistance to deformation when a pressure
drop is applied across it. Use of such a reinforcing means also allows the web
to be formed into configurations that were previously difficult, if not impossible
to achieve.
The reinforcing means used in the composite article of the present
15 invention is at least somewhat porous, preferably very porous (i.e., at least50% voids), so as not to greatly interfere with the porosity of the fibrillated
PTFE web. This reinforcing means is at least partially embedded in the
fibrillated PTFE web. The PTFE fibrils appear to actually attach to or become
mechanically entangled with the reinforcing means. This is further illustrated
20 by reference to the drawings described below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. l is a scanning electron micrograph (SEM) of a fibrillated PTFE
web reinforced with a polymeric screen.
FIG. 2 is an SEM of the reinforced web from FIG. l with the screen
partially pulled away from the web.
FIG. 3 is an SEM providing a inore m~gnified view of the reinforced
web from FIG. 2.
FIG. 4 is an SEM of one screen thread of the reinforced web from
30 FIG. 3.
~138078
FIG. 5 is an SEM of a fibrillated PTFE web reinforced with a polymeric
scrim.
FIG. 6 is an SEM of the reinforced web from FIG. 5 with the scrim
partially pulled away from the web.
s FIG. 7 is an SEM providing a more m~gnified view of the reinforced
web from FIG. 6.
FIG. 8 is an SEM of one scrim fiber of the reinforced web from FIG. 7.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
FIG. 1 shows an SEM (60x m~gnification) of reinforced web 10
comprising particle-loaded fibrillated PTFE web 12 with screen 14 partially
embedded therein. In this particular embodiment, fibrillated PTFE web 12
entraps activated carbon particulate. Any particulate, regardless of shape, thatcan be entrapped in a nonwoven polymeric web can be used in the reinforced
15 fibrillated PTFE web of the present invention. Representative examples of
useful particulate include those listed in U.S. Patent Nos. 4,153,661,
4,460,642, 5,071,610, and 5,209,967 as well as U.S. Ser. No. 08/004,967,
which lists are herein incorporated by reference. Particularly useful particulate
m~eri~l~ include activated carbon, silica, derivatized silica, glass beads and
20 bubbles, chitin, and the like. In this particular embodiment, screen 14 is Nitex-
37 nylon (TETKO, Inc.; Rolling Meadows, IL). Any porous screen can be
used as a reinforcement means, although those with a very fine mesh can
interfere with the porosity of the web and cause undesirable resistance to flow
and channeling. Screen 14 can be pressed into web 12 by standard pleSSUle
25 bonding techniques as are well known in the art, optionally under elevated
temperature.
FIG. 2 shows an SEM (15 x m~gnification) of fibrillated PTFE web 12
with screen 14 partially pulled away theleîlo--l. The screen pattem can be seen
clearly in web 12.
21~8078
FIG. 3 shows a more m~gnified close-up SEM (35 x m~gnification) of
that seen in FIG. 2. Again, the pattem of screen 14 can be seen clearly in web
12.
FIG. 4 shows an SEM (500X m~gnific~tion) of PTFE fibrils 16 from
5 web 12 (of FIGS. 1-3) still attached to screen 14 after screen 14 has been
partially pulled away from web 12. That fibrils 16 become mechanically
entangled with or attached to screen 14 threads while screen 14 is embedded in
web 12 is readily apparent.
FIG. S shows an SEM (250X m~pnifit~tion) of reinforced web 20
10 comprising particle-loaded fibrillated PTFE web 22 with scrim 24 partially
embedded therein. In this embodiment, fibrillated PTFE web 22 entraps silica,
although, as mentioned above, many other types of particulate can be used. In
this embodiment, scrim 24 is a nonwoven polypropylene web available from,
for example, AMOCO Fabrics & Fibers Co. (Atlanta, GA). Any porous scrim
15 can be used as a reinforcement means, however.
FIG. 6 shows an SEM (35 x m~gnification) of fibrillated PTFE web 22
with scrim 24 partially pulled away therefrom. The scrim pattem can be seen
clearly in web 22.
FIG. 7 shows a more m~gnified close-up SEM (lSOX m~pnific~tion) of
20 that seen in FIG. 6. PTFE fibrils 26 can be seen being pulled away from web
22 as scrim 24 is removed thererrol-l.
FIG. 8 shows a more m~gnified close-up SEM (330X m~gnific~tion) of
that seen in FIG. 7. Silica particles 28 entrapped within fibrils 26 are apparent.
Once again, that fibrils 26 become mechanically entangled with or attached to
25 scrim 24 fibers while scrim 24 is embedded in web 22 is readily apparent.
To make the web in which are entrapped the active particulate, one
begins with an aqueous PIFE dispersion. This milky-white dispersion contains
about 20% to 705~ (by weight) of minute PTFE particles suspended in water.
A major portion of these PTFE particles range in size from 0.05 to about 0.5
3 o ~m. Commercially available aqueous PTFE dispersions may contain other
ingredients such as surfactants and stabilizers that promote continued
~138078
sl~spel~ion. Examples of such commercially available dispersions include
TeflonTU 30, Teflon~ 30B, and Teflonn' 42 (DuPont de Nemours Chemical
Corp.; Wilmington, DE). Teflonn' 30 and Teflon~ 30B contain about 59 % to
61 % (by weight) PTFE solids and about 5.5 % to 6.5 % (by weight, based on
5 the weight of PTFE resin) of a non-ionic wetting agent, typically octylphenyl
polyoxyethylene or nonylphenyl polyoxyethylene. Teflon~ 42 contains about
32 % to 35 % (by weight) PTFE solids and no wetting agent (but does contain
a surface layer of organic solvent to prevent evaporation).
The particle-loaded fibrillated PTFE web preferably is prepalc~d as
lo described in any of U.S. Patent Nos. 4,153,661, 4,460,642, and 5,071,610, theprocesses of which are incorporated herein by reference, by blending the
desired reactive particulate into the aqueous PTFE emulsion in the presence of
sufficient lubricant to approach or, preferably, exceed the sorptive capacity ofthe solids yet maintain a putty-like consistency. This putty-like mass is then
15 subjected to intensive mixing at a temperature preferably between 40" and
lOOOC to cause initial fibrillation of the PTFE particles. The resulting puttylike
mass is then repeatedly and biaxially calendered, with a progressive narrowing
of the gap between the rollers (while at least maintaining the water content),
until the shear causes the PTFE to fibrillate and enmesh the particulate and a
20 layer of desired thickness is obtained. Removal of any residual surfactant orwetting agent by organic solvent extraction or by washing with water after
formation of the web article is generally desirable. The resultant web is then
dried. Such webs preferably have thicknesses in the range of 0.1 to 0.5 mm.
Web articles with a thickness in the general range of 0.05 to 10 mm can be
2 5 useful.
If a web article with mulfiple particulate layers is desired, the
component layers themselves are stacked on each other and calendered until
they form a composite where the PTFE fibrils of the separate layers are
entwined at the interface of adjacent webs. Such multilayer webs demonstrate
30 little boundary mixing between adjacent layers of particles. Multilayer articles
preferably have thicknesses in the range of 0.1 to 10 mm.
~138~78
The void size and volume within such a web article can be controlled by
regulating the lubricant level during fabrication as described in U.S. Patent No.
5,071,610. Recause both the size and the volume of the voids can vary directly
with the amount of lubricant present during the fibrillation process, webs
s capable of entrapping particles of various sizes are possible. For instance,
increasing the amount of lubricant to the point where it exceeds the lubricant
sorptive capacity of the particulate by at least 3 % (by weight) and up to 200 %(by weight) can provide mean void sizes in the range of 0.3 ~m to 5.0 ~m with
at least 90% of the voids having a size of less than 3.6 ~m. This process can
lo be used to create a web article with one or more kinds of reactive particulate
enmeshed therein. The PTFE which forms the web within which particulate is
to be trapped can be obtained in resin emulsion form wherein the PTFE and
lubricant are already premixed (e.g., TeflonTY 30 or 30B, DuPont de Nemours;
Wilmington, DE). To this emulsion can be added additional lubricant in the
15 form of water, water-based solvents such as a water-alcohol solution, or easily-
removable organic solvents such as ketones, esters, and ethers, to obtain the
aforementioned desired proportion of lubricant and particulate.
Active particulate (i.e., those which perform a funtion such as chemical
reaction with or sorption of a solute or conduction) useful in the present
20 invention includes any such pafticulate that can be immobilized in a non-woven,
fibrous matrix. Representative sorptive particles include, but are not limited to,
activated carbon, silica, derivatized silica, ion exchange resins, intercalated
styrene divinylbenzene, and chitin. Conductive particles such as silver-coated
glass spheres can also be used. Particulate material can be of regular (flat,
2s spherical, cubic, rod- or fiber-like, etc.) or irregular shape. Average diameters
of useful particles are within the range of 0.1 to 100 ,um, more preferably
within the range of 0.1 to 50 ,~4m, and most preferably within the range of 1 to10 ,um. Such particulate can be incorporated directly into the web article.
Particulate is generally distributed uniformly in the web article, but
3 o matrices which include combinations of particulate can be prepared.
Altematively, layers containing different particulate can be calendered into a
213~078
single matrix with distinct strata of particulate. Such multilayer composite
articles show minim~l boundary mixing (between the various particulate) and
retain good uniformity throughout each layer. Whether in a helelogeneous or
homogenous form, this type of article can selectively sorb or react with one or
5 more chemical species to be removed from a fluid where these webs are to be
used in chromatographic or separations applications.
Total particulate content of the web article can range up to about 97%
(by weight), (although particulate amounts in the range of 80 to 95% (by
weight) tend to produce more stable web articles). The enm.oshing fibrils retain10 the enmeshed particulate, by entrapment or adhesion, within the matrix, and the
enmeshed particles resist sloughing.
The web article of the present invention preferably comprises active
particulate in an amount of at least 10% (by weight), more preferably
comprises active particulate in an amount of at least 50% (by weight), and most
15 preferably comprises active particulate in an amount of at least 80% (by
weight). High active particulate loading is desirable to maximize the sorptive
capacity or chemical activity of the substrate.
Non-active adjuvant particles with average diameters in the same ranges
as listed previously with respect to active particulate can be included.
20 Representative examples pf useful adjuvants that can be incorporated in the web
article include property modifiers such as glass beads and/br bubbles, glass
particles other than beads or bubbles, energy-expandable hollow polymeric
particles such as Expancel~ microspheres (Nobel Industries; Sundsvall,
Sweden) and mica. When present, such non-active particulate can comprise
25 from more than 0 to 95 % (by weight), preferably from more than 0 to 50%
(by weight), and most preferably from more than 0 to 10% (by weight) of the
web article.
Particle-loaded fibrillated PTFE webs that have been reinforced in the
above manner display improved resistance to ballooning and/or tearing and to
3 o shrinkage. This is very desirable in applications where the web must withstand
a pressure drop caused by fluid flowing through it or must display dimensional
2138078
stability. (Unreinforced fibrillated PTFE webs tend to shrink in the direction in
which they were last machined.) Also, reinforced webs are easier to handle and
less likely to be damaged during normal use.
If desired, a fibrillated PTFE web with particulate entlapped therein can
5 also be reinforced on both sides. In other words, reinforcement means can be
partially embedded in both sides of the web. This can increase the composite
article's resistance to the aforementioned undesirable properties. Additionally,multilayer web - reinforcing means composite articles also can be made. This
might be desirable where each web layer contains a different type of
1 o particulate.
The reinforced particle-loaded fibrillated PTFE webs of the present
invention can be used wherever unreinforced particle-loaded fibrillated PTFE
webs are useful, particularly in separation science (e.g., chromatographic and
other separations as well as extractions).
Objects and advantages of this invention are further illustrated by the
following examples. The particular materials and amounts thereof, as well as
other conditions and details, recited in these examples should not be used to
unduly limit this invention.
2 o EXAMPLES
Example I
The parficle-loaded fibrillated PTFE web described herein was made
essenti~lly according to the procedure described in columns 3 to 6 of U.S.
Patent No. 4,153,661.
The following materials were added together and the mixture was mixed
in a Ross~ mixer (Charles Ross & Son Co.; Hauppage, NY) at 30 rpm for 45
sec at 38C:
400 g dry super-activated carbon with a surface area of 2000 to 3000
m2/g and an average particle size of 30 ~m with a range of 3.9 to
200 ~m (Kansai Coke and Chemicals Co. Ltd.; Am~g~ki City,
Japan)
2138~7~
312 g FLUONr~ PTFE emulsion, 22.6% PTFE in water (ICI
Americas, Inc.; Wilmington, DE)
894 g deionized water
This mixing provided a doughy mass.
This dough-like mass was passed through a two-roll mill with an initial
gap setting of 3.81 mm. The first few passes resulted in a web without enough
strength to support its own weight; however, after a few more passes, the web
was strong enough to maintain its integrity so that it could be folded into three
layers and rotated 90 for its next pass through the mill. This biaxial
lo calendering was followed for a total of ten passes. Thereafter, the gap was
adjusted from 2.54 mm to 1.27 mm to 0.64 mm (with web passes through each
gap) to produce a long web.
After the above three passes, the web was folded into eight layers and
rotated 90. The gap was adjusted from 2.54 mm to 1.90 mm to 1.27 mm to
15 0.76 mm (with web passes through each gap). This process yielded a
fibrillated PTFE web that was 1.14 mm thick which was dried by passing
through a belt oven.
This web was reinforced by placing it between two layers of Naltex~
LWS filtration netting (Nalle Plastics, Inc.; Austin, TX) and passing this
20 composite article through a two-roll mill (gap = 0.89 mm, roll speed = 7.6
cm/sec). The tensile strength of the web-netting bond, measured by pulling the
netting away from the web in a tensile tester (Thwing-Albert Instrument Co.;
Philadelphia, PA), was 0.18 N/cm.
Example 2
A particle-loaded PTFE web was prepared as in Example 1 with the
exception that final web thickness was 0.76 mm. This web was reinforced as
in Example 1 with the exception that gap width during reinforcement was 0.51
mm. The tensile strength of this web-netting bond was 0.33 N/cm.
--10--
2~38o78
Example 3
A particle-loaded PTFE web was prepared as in Example 1 with the
excepfion that final web thickness was 1.52 mm. This web was reinforced as
in Example 1 with the exception that gap width during reinforcement was 1.14
5 mm. The tensile strength of this web-netting bond was 0.21 N/cm.
Example 4
A particle-loaded PTFE web was prepared as in Example 1 except that
extra calendering produced a final web thickness of 0.38 mm. This web was
10 sandwiched between two layers of 25 g/m2 basis weight polyethylene non-
woven web, and this composite article was passed through a two-roll mill with
a gap of 0.25 mm. The tensile strength of this web - non-woven web bond was
0.035 N/cm.
Example 5
A particle-loaded reinforced PTFE web was prepared as in Example 4
except that a polyester non-woven web with a basis weight of 45 gtm2 was
used. The tensile strength of this web - non-woven web bond was 0.14 N/cm.
2 o Example 6
A particle-loaded reinforced PTFE web was prepared as in Example S
except that only one layer of reinforcement was used and the gap thickness
during calendering was 0.64 mm.
This reinforced web and a similar unreinforced web were evaluated
25 three ways: 1) use as an absorbing means on a generic base, 2) tensile
strength, and 3) ~hrink~ge.
Use with a ~eneric base: Generic bases for in-line filter holders are those
designed for
paper or paper-like webs. They are available from a wide variety of
commercial sources such as Gelman Co. (Ann Arbor, MI) and Nalgene
Co. (Rochester, NY). Unreinforced webs were soft and conformed to
2i38078
the contours of the generic bases. Thus, when a blue food coloring
solution was passed through an unreinforced web, flow was restricted to
those areas where the web was not in direct contact with the base, and
the dye was absorbed only in those areas (i.e., channeling occurred).
When a similar dye solution was passed through a reinforced web
supported on a generic base, no such conformation was observed, and
the dye solution was evenly distributed throughout the web (i.e.,
ch~nneling, leaks, and/or breakthrough were not observed).
Tensile strength: The tensile strength of the reinforced webs were at least
10 an order of
magnitude greater. The tensile strength of various reinforced webs is
shown in Table I below.
Shrinkage: Shrinkage induced by mechanical stimulation and by long-term
exposure to
heat were both tested.
Disks (with diameters of 47 mm) of reinforced and unreinforced
webs were biaxially shaken on a sieve shaker (C.E. Tyler Co.; Mentor,
OH) for approximately 60 minutes. The unreinforced disks shrunk into
an elliptical shape with a minor axis of about 42 mm (i.e., 30 about
10% shrink~ge). Essentially no shrinkage of the reinforced disks was
observed.
Two disks (47 mm diameters) of reinforced web were placed in
an oven at 71C for 51 days. No shr1nk~ge was observed. Under
similar conditions, unreinforced webs would have shrunk by at least
10%.
Example 7
A particle-loaded fibrillated PTFE web was prepared using the same
procedure as that described in Example 1. Instead of activated carbon,
30 however, the particulate was a C,8-derivatized silica a.T. Baker Co.;
--12--
2138078
Phillipsburg, NJ). The final thickness of the web was 0.51 mm. The web was
90% (by weight) particulate.
A layer of Naltex~ LWS filtration netting was placed between two of
these webs. The layered composite was passed through a two-roll mill (gap =
5 1.27 mm).
A 50 mm x 50 mm square sample of this reinforced web was placed in a
47 mm manifold vacuum system (Millipore Corp.; Bedford, MA) with the
supporting screen removed thererrolll. A liter of water with one drop of blue
food coloring was pulled through the reinforced web. While removing dye
10 from the solution, the reinforced web did not balloon or tear and was not pulled
into the vacuum flask.
Example 8
A large web with Cl8 as the entrapped particulate was p-epared using the
15 same procedure as in Example 1. Portions of this web were reinforced with
various reinforcing materials, and these reinforced webs were tested against a
comparative unreinforced web. The results are summarized in Table I below.
NITEXn' nylon screens are made by TETKO, Inc. (Rolling Meadows,
IL). Monodur~ Nylon 475 and 850 screens a-re made by Industrial Fabrics
20 Corp. (Minneapolis, MN). Naltex~ filtration netting is made by Nalle Plastics,
Inc. (Austin, TX). Celestra~ and PBN Ir non-woven webs are made by
Fiberweb Inc. (Pensacola, FL). Brookings~ non-woven webs are made by
Minnesota Mining and Manufacturing Co. (St. Paul, MN). Typar~ and 4dpf~
Straight non-woven webs are made by Reemay, Inc. (Old Hickory, TN).
25 CoverstockTM non-woven webs are made by Bonar Fabrics (Greenville, SC).
RFX~ non-woven webs are made by AMOCO Fibers and Fabrics, Inc.
(Atlanta, GA).
TABLE I
Type of Sample Tradename of p~ r ~ g Means Average Threads Thread Average Failure Stress (Ibs. Average Failure Strain (% linear
12~ r ,- ~ No. basis wt. per inch diameter per linear inch width of increase in length at peak stress)
means (g/m~) (mils) material)
Crossweb Downweb Crossweb Downweb
NONE I N/A 323.7 N/A N/A 0.034 0.22 378.9 34.3
SCREEN 2 NITEX~ nylon 143.5 21 10 787 847 30 32
3 Monodur"' Nylon 475 116.3 37 7 973 786 28 46
4 Monodur Nylon 850 153.6 22 12 866 783 28 29
S Naltex~ filtration nening 53.6 15 N/A 3.11 1.64 193.9 24.0
6 Naltexn' filtration nening 166.3 44 N/A 11.63 13.97 168.0 44.0
SCRIM 7 Celestra~ .. .J . . web 19.2 N/A N/A 1.49 4.92 27.4 36.0
8 Brookings non-woven web 26.3 N/A N/A 1.25 5.92 34.9 24.6
9 Typar"' .... J._ web 44.9 N/A N/A 9.01 13.18 23.8 28.0
Fiberweb PBN II~ non-woven web 10.2 N/A N/A 1.94 4.34 46.9 50.3
I l Bonar G,. . ' ~ ..... ~, . . web 17.9 N/A N/A 11.83 2.46 23.4 43.4 0
12 Cerexn' ~ .. ~. web 50.9 N/A N/A 2.61 3.95 59.4 40.6
13 AMOCO RFX~ ....... J.. .web with AS 16.0 N/A N/A 0.66 1.35 259.4 27.4
14 Reemay 4dpf~ Straight .. ~.. web 23.7 N/A N/A 3.78 5.68 29.1 38.3
AMOCO RF~ .. web 17.0 N/A N/A 1.54 3.53 153.7 61.1
16 AMOCO RFX'Y non-woven web 33.9 N/A N/A 2.83 7.82 182.3 79.4
2l38o78
All samples other than No. 1 were reinforced. Stress and strain values
for reinforcement means only are not shown but are of the same order of
m~gnitl1de as for the corresponding reinforced webs.
Rec~llse samples 2-4 were illlplopelly cut, their stress and strain values
5 could be off by up to 30%; however, these numbers help to prove the overall
conclusion that can be drawn from Table I, i.e., that reinforced webs,
regardless of the type of reinforcement, are at least an order of m~gnitude
stronger in both the crossweb and downweb directions than an otherwise
identical unreinforced web.
Various modifications and alterations which do not depart from the
scope and spirit of this invention will become a~alellt to those skilled in the
art. This invention is not to be unduly limited to the illustrative embotlim~nt~set forth herein.
-15-
