Note: Descriptions are shown in the official language in which they were submitted.
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RELATED APPLICATIONS
This application is one of a group of applications which
are being filed on the same date. It should be noted that this
group of applications includes U.S. patent application serial
number 07/769 050 entitled "Hydrosonically Microapertured Thin
Thermoset Sheet Materials" in the names o~ Lee K. Jameson and
Bernard Cohen; U.S. patent application serial number
07/769,047 entitled "Hydrosonically Microapertured Thin
Thermoplastic Sheet Materials" in the names of Bernard Cohen
and Lee K. Jameson; U.S. patent application serial number
07/768 1 2 entitled l'Pressure Sensitive Valve System and
Process For Forming Said Systeml' in the names of Lee K.
Jameson and Bernard Cohen; U.S. patent application serial
number 071768 494 entitled " Hydrosonically Embadded Soft Thin
Film Materials and Process For Forming Said Materials" in the
names of Bernard Cohen and Lee K. Jameson; UOS~ patent
application number 071768.788 entitled "Hydrosonically
Microapertured Thin Naturally Occurring Polymeric Sheet
Materials and Method of Making the Same" in the names o~ Lee
K. Jameson and Bernard Cohen; U.S. patent application serial
number 071769 048 entitled "Hydrosonically Microapertured Thin
Metallic Sheet Mateials" in the names of Bernard Cohen and Lee
K. Jameson; U.S. patent application serial number 07/769,045
entitled "Process For Hydrosonically Microaperturing Thin
Sheet ~aterials" in the names of Lee K. Jameson and Bernard
Cohen; and U.S. patent application serial number 07/767 727
entitled "Process For Hydrosonically Area Thinning Thin Sheet
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Materials" in the names of Bernard Cohen and Lee K. Jameson.
All of these applications are hereby incorporated by
reference~
FIELD OF THE INVENTION
The field of the present invention encompasses thin sheets
formed from naturally occurring polymeric materials which have
been microapertured in a generally uniform pattern.
BACKGROUND OF THE INVENTION
Ultrasonics is basically the science of the effects of
sound vibrations beyond the limit of audible frequencies.
Ultrasonics has be n used in a wide variety of applications.
For example, ultrasonics has been used for (1) dust, smoke and
mist precipitation; (2) preparation of colloidal dispersions;
(3) cleaning of metal parts and fabrics; (4) friction welding;
(5) the formation of catalysts; ~6) the degassing and
solidification of molten metals; (7) the extraction of flavor
oils in brewing; (8) electroplatingi (9) drilling hard
materials; (10) fluxless soldering and (lo) nondestructive
testing such as in diagnostic medicine.
The object of high power ultrasonic applications is to
bring about some permanent physical change in the material
treated. This process requires the flow of vibratory power per
unit of area or volume. Depending on the application, the
power density may range from less than a watt to thousands
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of watts per square c~ntimeter. Although the original
ultrasonic power devices operatPd at radio frequencies, today
most operate at 20-69 kHz~
The piezoelectric sandwich-type tra~sducer driven by an
electronic power supply has emerged as the most common source
o~ ultrasonic power; the overall e~ficiency of such equip~ent
(net acoustic power per electric-line power) is typically
greater than 70%. The maximum power from a conv~ntional
transd~cer is inversely proportional to the sguare of the
frequency~ Some applications, such as cleaning, may have many
transducers working into a common load.
Other, more particular areas where ultrasonic vibratory
force has been utilized are in the areas of thin nonwoven webs
and thin films. For example, ultrasonic force has been use to
bond or weld nonwoven webs. See, for Pxample, U.S. patent
nu~hers 3~575,752 to Carpenter, 3,660,186 to Saqer et al.,
3,9~6,519 to Mitchell et al. and 4,6g5,454 to Sayo~itz_et al.
which disclose the usa of ultrasonics to bond or weld nonwoven
webs. U.S. patent nu~bers 3,488,240 to Roberts, describes the
use of ultrasonics to bond or weld thin films such as oriented
polyesters.
Ultrasonic force has also been utilized to aperture
nonwoven webs. See, for example, U.S. patent nu~bers 3,949,127
to Oste~eier ~_~1~ and, 3,966,519 to Mitchell et al..
Lastly, ultrasonic force has been used to aperture thin
~ilm material. See, for example, U. S. patent number 3,756,880
to Graczyk.
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Other methods for the aperturin~ of thin film have been
developed. For examplP, U.S. patent number 4,815,714 to
Douqlas discusses the aperturing of a thin film by first
abrading ~he film, which is in filled and unoriented form, and
then subjecting the film to corona discharge treatment.
one of the di~ficulties and obstacles in the use of
ultrasonic force in the formation of apertures in materials
is the fact that control of the amount of force which is
applied was difficult. This lack of control resulted in the
limitation of ultrasonic force to form large apertures as
opposed to small microapertures. Such an application is
discussed in U.K. patent application number 2,124,134 to
Blair. one of the possible reasons that ultrasonics has not
found satisfactory acceptance in the area of microap rture
formation is that the amount of vibrational energy required
to form a microaperture often resulted in a melt-through of
the film.
As has previously been stated, those in the art had
recognized that ultrasonics could be utilized to form
apertures in nonwoven webs. See, U.S. patent to Mitchell,_et
al.. ~dditionally, the Mitchell et al. patent discloses that
the amount of ultrasonic energy being subjected to a nonwoven
web could be controlled by applying enough of a fluid to the
area at which the ultrasonic energy was being applied to the
nonwoven web so that the fluid was present in uncombined form~
Importantly, the Mitchell et al. patent states that the fluid
is moved by the action of the ultrasonic force within the
nonwoven web to cause aperture formation in the web by fiber
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rearrangement and entanglement. The Mitchell et al. patent
also states that, in its broadest aspects, since these effects
are obtained primarily through physical movement of fibers,
the method of their invention may be utilized to bond or
increase the streng~h of a wide varisty of fibrous webs.
While the discovery disclosed in the itchell et al.
patent, no doubt, was an important contribution to the art,
it clearly did not address the possibility of aperturing
nonfibrous sheets or sheets having fixed fibers formed from
naturally occurring polym~ric materials. This fact is clear
b~cause the Mitchell et al. patent clearly states the belief
that the mechanism of aperture formation depended upon fiber
rearrangement. of cour~e, such sheet materials either do not
have fibers or have fibers which are in such a condition that
they cannot be rearranged. Accordingly, it can be stated with
conviction that the applicability of a method for aperturing
naturally occurring polymeric sheet materials by the
application of ultrasonic energy in c:onjunction with a fluid
at the point of application of the ultrasonic energy to the
naturally occurring polymeric sheet material was not
contemplated by the Mitchell et al. patent. Moreover, the
Mitchell et a~l~patent teaches away from such an application
because the patent states the belief that aperture formation
requires the presence of movable fibers to be rearranged.
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As used herein the terms l'polymer" or "polymeric" refer
to a macromolecule formed by the chemical union of five (5)
or more identical combining units called monomers.
As used herein the term "naturally occurring polymeric
material" refers to a polymeric material which occurs
naturally. The term is also meant to include materials, such
as cellophane, which can be regenerated from naturally
occurring materials, such as, in the case of cellophane,
cellulose. Examples of such naturally occurring polymeric
materials include, without limitation, (1) polysaccharides
such as starch, cellulose, pectin, seaweed gums (such as agar,
etc.), vegetable gums (such as arabic, etc.); (2)
polypeptides; (3) hydrocarbons such as rubber and gutta percha
(polyisoprene) and (4~ regenerated materials such as
cellophane or chitosan. Of course, the term "naturally
occurring polymeric material" is also meant to inclu~e
mixtures and combinations of two or more naturally occurring
polymeric materials as well as mixtures and combinations which
include at least fifty (50) percent, by weight, naturally
occurring polymeric materials.
As used herein the term "n~turally occurring polymeric
sheet material" refers to a gen~rally nonporous item formed
from a naturally occurring polymeric material that can be
arranged in generally planar configuration. If the material
is not a water soluble material, the material, in an
unapertured state prior to being modified in accordance with
the present invention, ha~ a hydrostatic pressure (hydrohead)
of at least about 100 centimeters of water when measured in
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accordance wiih Federal Test Method NO. 5514, standard no.
l91A. Unless otherwise stated herein all hydrohead values are
obtained in accordance with Federal Test Method NO. 5514,
standard no 191~. This term i8 also intended to include
multilayer materials which include at least one such sheet of
a naturally occurring polymeric material as a layer thereof.
It should be noted that the material does not have to occur
naturally in sheet form, rather it is the components of the
sheet that are l'naturally occurring". Gf course, if the
naturally occurring polymeric material is water soluble,
hydrohead measurements have little, if any meaning.
As used herein the term "thin naturally occurring
polymeric sheet material" refers to a naturally occurring
polymeric sheet material having an average thickness generally
of less than about ten (10) mils. Averags thickness is
determined by randomly selecting five ~5) locations on a given
sheet material, mPasuring the thickness of the sheet material
at each location to the nearest 0.1 mil, and averaging ths
five values (sum of the fi~e values clivided by five).
As used herein the term water vapor transmission rate
ref~rs to the rate water vapor will pass through a water
insoluble sheet material under a given set of conditions in
a particular time period. Unless otherwise specified, water
vapor transmission rate is measured in accordance with ASTM
E 96-80 using the water method referenced at paragraph 3.2
thereof. The test is run at 90 degrees fahrenheit and 50
percent relative humidity for twenty-four (24) hours.
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As used herein the t rm "mesh count" refers to the number
which is the product of the number of wires ln a wire mesh
screen in both the machine (MD) and cross-machine (CD)
directions in a given unit area. For example, a wire mesh
screen having 100 wires per inch in the machine direction and
100 wires per inch in the cross machine direction would have
a mesh count o~ 10,000 per square inch. As a result of the
interweaving of these wires, raised areas are present on both
sides of the mesh screen. The number of raised areas on one
side of such a wire mesh scre~n is genexally one-half of the
mesh count.
As used herein the term "aperture" refers to a generally
linear hole or passageway. Aperture is to be distinguished
from and does not include holes or passageways having the
greatly tortuous path or passageways found in membranes.
As used herein the term "microaperture" r~fers to an
aperture which has an area of less than about 100,000 square
micrometers. The area of the microape:rature is to be measured
at the narrowest point in the linear passageway or hole.
As used h~rein the term "ultrasonic vibrations" refers
to vibrations having a frequency of at least about 20,000
cycles per second. The frequency of the ultrasonic vibrations
may range from about 20,000 to about 400,000 cycles per second
or more.
As used herein the term "hydrosonics" refers to the
application of ultrasonic vibrations to a material where the
area of such application is has had a liquid applied thereto
to the extent that the liquid is present in sufficient
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quantity to generally fill the ~ap between the tip of th
ultrasonic horn and the surface of the material.
The approximate edge length of the thin microapertured
thermoplastic sheet material of the present invention is
calculated from the size of the microaperture using the
appropriate geometrical formula, depending upon th~
microaperture's general shap2.
OBJECTS OF TH~__NVENTION
Accordingly, it is a general object of the present
invention to provide thin naturally occurring polymeric sheet
materials which have been microapertured in a generally
uniform pattern
Still further objects and the broad scope of applicability
of the present invention will beco~e apparent to those of
skill in the art from the details given hereinafter. However,
it should be understood that the detailed description of the
presently preferred embodiments of the present invention is
given only by way of illustration because various changes and
modifications well within the spirit and scope of the
invention will become apparent to those of skill in the art
in view of this detailed description.
SUMMARY OF THE INVENTION
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In response to the foregoing problems and difficulties
encountered by those in the art, we have developed a method
for foxming microapertures in a thin naturally occurring
polymeric sheet material having a thickness o~ about 10 mils
or less where the area of each of the formed microapertures
is generally greater than about 10 square micrometers. The
method include.s the steps of: (1) placing the thin naturally
occurring polymeric sheet material on a pattern anvil having
a pattern of raised areas where the height of the raised areas
is greater than the thickness of the thin naturally occurring
polymeric sheet material; (2) conveying the thin naturally
occurring polymeric sheet material, while placed on the
pattern anvil, through an area where a fluid is applied to the
thin naturally occurring polymeric sheet material; and (3)
subjecting the thin naturally occurring polymeric sheet
material to ultrasonic ~ibrations in the area where the fluid
is applied to the thin naturally occurring polymeric sheet
material. As a resul~ of this method the thin naturally
occurring polymeric sheet material is microapertured in a
pattern generally the same as the pattern of raised areas on
the pattern anvil.
The thin naturally occurring polymeric sheet material may
be formed rom, for example, cellophane, cellulose acetate,
collagen or carrageenan.
The fluid may be selected from the group including one or
more of water, mineral oil, a chlorinated hydrocarbon,
ethylene glycol or a solution of 50 volume percent water and
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50 volume percent 2 propanol. The chlorinated hydrocarbon may
be 1,1,1 trichloroethane or carbon tetrachloride.
In some embodiments, the area of each of the formed
microapertures may generally range from at least ahout 10
square micrometers to a~out 100,000 square micrometers. For
example, the area of each of the formed microapertures may
generally range from at least about 10 square micrometers to
about 5,000 square micrometers. Mor~ particularly, the area
of each of the formed microapertuxes may generally range from
at least about 10 square micrometers to about 1,000 square
micrometers. Even more particularly, the area of each of the
for~ed microapertures may generally range from about at least
10 square micrometers to about 100 square micrometers.
The thin naturally occurring polymeric sheet material may
be microapertured with a microaperture density of at least
about 1,000 microapertures per square inch. For example, the
thin naturally occurring polymeric sheet material may be
microapertured with a microaperture d~ensity of at least about
5,000 microapertures per square inch. More particularly, the
thin naturally occurring polymeric sheet material may be
microapertured with a microaperture density o~ at least about
20,000 microapertures per square inch. Even more particularly,
the thin naturally occurring polymeric sheet material may be
microapertured with a microaperture density of at least about
90,000 microapertures per square inch. Yet even more
particularly, the thin naturally occurring polymeric sheet
material may be microapertured with a microaperture density
of at least about 160,000 microapertures per square inch.
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The pattern anvil may, for example, be a mesh screen with
knuckles serving as raised areas, a flat plate with raised
areas or a cylindrical roller with raised areas. If the
pattern anvil is a cylindrical roller with raised areas, it
is desirable for the pattern anvil to be wrapped or coated
with or made from a resilient material. Where the pattern
anvil is a mesh screen the resiliency is provided by the fact
that the screen is unsupported directly below the point of
application of ultrasonic vibrations tn the mesh screen.
In some embodiments it may be desirable to subject the
thin naturally occurring polymeric sheet material to multiple
passes through the microaperturing area so that at least steps
(b~ and (c~ are performed more than once on the thin naturally
occurring polymeric sheet material. To attain an microaperture
density which is greater that the number of raised areas on
the pattern anvil, the thin naturally occurring polymeric
sheet material may be moved slightly between passes.
In some embodiments it may be desirable for the
microaperturing of the thin naturally occurring polymeric
sheet material to be confined to a predesignated area or areas
of the thin naturally occurring polymeric sheet material. This
result may be obtained where only a portion of the thin
naturally occurring polymeric sheet is subjected to ultrasonic
vibrations. Alternatively, this result may be obtained where
only a portion of the pattern anvil is provided with raised
areas.
The thickness of the thin naturally occurring polymeric
sheet material is at least about 0.25 mil. For example, the
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thicXness of the thin naturally occurring polymeric shee~
material may range from about 0.25 mil to about 5 mils. More
particularly, the thickness of the thin naturally occurring
polymeric sheet material may range from about 0.25 mil to
about 2 mils. Even more particularly, the thickne9s of the
thin naturally occurring polymeric sheet material may range
from about 0.5 mil to about 1 mil.
If it is not a water soluble material, the hydrohead of
the thin naturally occurring polymeric sheet material may be
measured and may range from at least about 15 centimeters of
water. For example, the hydrohead of the thin naturally
occurring pol~meric shePt material may ran~e from at least
about 35 centimeters of water. More particularly, the
hydrohead ~f the thin naturally occurring polymeric sheet
material may range from at least about 45 centimeters of
water. Even more particularly, the hydrohead of the thin
naturally occurring polymeric sheet material may range from
at lea~t about 55 centimeters of water. Yet even more
particularly, the hydrohead of the thin naturally occl~rring
polymeric sheet material may range from at least about 7
centimeters of water.
If it is not a water soluble material, the water vapor
transmission rate of the thin naturally occurring polymeric
sheet material may range from at least about 200 grams per
square meter per day. For example, the water vapor
transmission rate of the thin naturally occurring polymeric
sheet material may range from at lea~t about 500 grams per
square meter per day. Even more particularly, the water vapor
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trans~ission rate of the thin naturally occurring polymeric
sheet material may range from at least about 1,000 grams per
square meter per day. Yet even more particularly, tha water
vapor transmission rate of the thin naturally occurring
polymeric sheet material may range from at least about 1,500
grams per square meter per day.
As a result of the microaperturing process the edge length
of the thin naturally occurring polymeric sheet material may
be increased by at least about 100 percent as compared to the
sheet's edge length prior to microaperturing. For example, the
edge length of the thin naturally occurring polymeric sheet
material may be increased by at least about 500 percent as
compared to the sheet's edge length prior to microaperturing.
More particularly, the edge length of the thin naturally
occurring polymeric sheet material may be increased by at
least about 1,500 percent as compared to the sheet's edgc
length prior to microaperturing. Even more particularly, the
edge length o~ the thin naturally occurring polymeric sheet
material may be increased by at least about 3,000 percent as
compared to the sheet's edge length prior to microaperturing.
THE FIGURES
Figure I is a schematic representation of apparatus which
utilizes ultrasonic vibrations to microaperture thin naturally
occurring polymeric sheet materials.
Figure II is a cross sectional view of the transport
mechanism for transporting the thin naturally occurring
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poly~eric sheet material to the area where it is subjected to
ultras~nic vibrations.
Fi~ure III is a detailed view of the area where the thin
naturally occurring polymeric sheet material is subjected to
ultrasonic vibrations. The area is designated by the dotted
circle in figure Io
Figure IV is a photomicrograph of a 0.8 mil thick sheet
of cellophane obtained under the trade name "Flexel V-58,
which has been microapertured in accordance with the present
invention. The photomicrograph is accompanied by a scale where
each unit on the scale represents ten microns (micrometers).
DE'rAILED DESCRIPTION OF THE INVENTION
Turning now to the figures where like reference numerals
represent like structure and, in particular to Figure I which
is a schematic representation of an apparatus which can carry
out the method of the present inventi.on, it can be seen that
the apparatus is generally represented by the reference
numeral 10. In operation, a upply roll 12 o~ a thin naturally
occurring polym~ric sheet material 14 to be microapertured is
provided. As has been previously stated, the term thin
naturally occurring polymeric sheet material refers to shee
materials which have an average thickn~ss of about ten (10)
mils or less. Additionally, generally speaking, the average
thickness of the thin naturally occurring polymeric sheet
material 14 will be at least about 0.25 mil. For example, the
average thickness of the thin naturally occurring polymeric
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sheet 14 material may range from about 0.25 mil to about 5
mils. ~ore particularly, the average thickness of the thin
naturally occurring polymeric sheet material 14 may range from
about 0.25 mil ~o about 2 mils. Even more specifically, the
average thickness of the thin naturally occurring polymeric
sheet material 14 may range from about 0.5 mil to about 1 mil.
The thin naturally occurring polymeric sheet material 14
may be formed from, for example, a material selected from one
or more of cellophane, cellulose acetate, collagen or
carrageenan. The thin naturally occurring polymeric sheet
material 14 may be formed from one or more naturally occurring
polymeric materials which may be combined to form the sheet
material 14.
The thin naturally occurring polymeric sheet material 14
is transported to a first nip 16 formed by a first transport
roll 18 and a first nip roller 20 by the action of an endless
transport mechanism 22 which moves in the direction indicated
by the arrow 24. The transport mechanism 22 is driven by the
rotation of the first transport roller 18 in conjunctlon with
a second transport roller 26 which, in turn are driven by a
conventional power source, not shown~
Figure II is a cross sectional view of the transport
mechanism 22 taken along lines A-A in Figure I. Figure II
discloses that the transport mechanism 22 includes a heavy
duty tran~port wire mesh screen 28 usually having a mesh count
of less than about 400 (i.e. less than about 20 wires per inch
MD by 20 wire wires per inch CD mesh screen if machine
direction (MD) and cross machine direction (CD) wire count is
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the same). Heavy duty mesh wire screens o~ this type may be
made from a variety of materials such as, for example, metals,
plastics, nylons or polyesters, and are readily available to
those in the artO Located above and attached to the transport
screen 28 is an endless flat shim plate 30. The shim plate 30
desirably is formed from stainless steel. However, those of
skill in the art will readily recognize that other materials
may be u~ilized. Located above and attached to the shim plate
30 is a ~ine mesh wire pattern screen 32 usually having a m~sh
count of at least about 2,000 (i.e. at least a 45 wires per
inch MD by 45 wires per inch CD mesh screen if MD and CD wire
count is the same). Fine mesh wire screens of this type are
readily available to those in the art. The fine mesh wire
screen 32 has raised areas or knuckles 34 which preform the
function of a pattern anvil as will be discussed later.
From the first nip 16 the thin naturally occurring
polymeric sheet material 14 is transported by the transport
mechanism 22 over a tension roll 36 to an area 38 (defined in
Figure I by the dotted lined circle) where th~ thin naturally
occurring polymeric sheet material 14 is subjected to
ultrasonic vibrations.
The assembly for subje~ting the thin naturally occurring
polymeric sheet material 14 to the ultrasonic vibrations is
conventional and is generally designated at 40. The assembly
40 includes a power supply 42 which, through a power control
44, supplies power to a piezoelectric transducer 46. As is
well known in the art, the piezoelectric transducer 46
transforms electrical energy into mechanical movement as a
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result of the transducer's vibrating in respon5e to an input
of electrical energy. The vibrations created by the
piezoelectric transducer 46 are transferred, in conventional
manner, to a mechanical movement booster or amplifier 48. As
is well known in the art, the mechanical movement booster 48
may be designed to increase the amplitude of the vibratione
(mechanical movement) by a known factor depending upon the
configuration of the booster 48. In fllrther conventional
manner, the mechanical movement (vibrational energy) is
transferred from the mechanical movement boo5ter 48 to a
conventional knife edge ultrasonic horn 50. It should be
realized that other types of ultrasonic horns 50 could be
utilized. For example, a rotary type ultrasonic horn could be
used. The ultrasonic horn 50 may be designed to effect yet
another boost or increase in the amplitude of the mechanical
movement (vibrations) which is to be applied to the thin
naturally o¢curring polymeric sheet material 14. Lastly, the
assembly includes an actuator 52 which includes a pneumatic
cylinder, not shown. The actuator 52 provides a mechanism for
raising and lowering the assembly 40 so that the tip 54 of the
ultrasonic horn 50 can apply tension to the transport
mechanism 22 upon the assembly 40 being lowered. It has been
found that it is necessary to have some degree of tension
applied to the transport mechanism 22 upon the lowering of the
assembly for proper application of vibrational energy to the
thin sheet material 14 to form microapertures in the thin
naturally occurring polymeric sheet material 14. One desirable
aspect of this tensioned arrangement is that the need to
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design a finely toleranced gap between the tip 54 of the horn
50 and the raised areas or knuckles 34 of the fine mesh wire
screen 32 i~ not nece~sary.
Fir~ure III is a schematic reprQsentation of the area 38
where the ultrasonic vibrations arP applied to the thin
naturally occurring polymeric sheet material 14. As can be
seen in Figure III, the transport mechanism 22 forms an angle
56 with the tip 54 of the ultrasonic horn 50. While some
microaperturing will occur if the angle 56 is as great as 45
degrees, it has been found th~t it i5 desirable for the angle
56 to range from about 5 degrees to about 15 degrees. For
example, the angle 56 may range from about 7 to about 13
degrees. More particularly, the angle 56 may range from about
9 to about 11 degrees.
Figure I~I al~o illustrates that the transport mechanism
22 is supported from below by the first tension roll 36 and
a second tension roll 58. Positioned somewhat prior to the tip
54 o~ the ultrasonic horn 50 is a spray nozzle 60 which is
confi~ured to apply a fluid 62 to the surface of the thin
naturally occurring polymeric sheet material 1~ just prior to
the sheet material's 14 being subjected to ultrasoni~
vibrations by the tip 54 of the ultrasonic horn 50. The fluid
62 desirably may be selected from the group including one or
more of water, mineral oil, a chlorinated hydrocarbon,
ethylene glycol or a solution of 50 volume percent water and
50 volume percent 2 propanol. For example, in some embodiments
the chlorinated hydrocarbon may be selected ~rom the group
including 1,1,1 trichloroethane or carbon tetrachloride. It
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should be noted that the wedge shaped area 64 formed by the
tip 54 of the ultrasonic horn 50 and the transport mechanism
22 should be subjected to a sufficient amount of the fluid 62
for the fluid 62 to act as both a heat sink and a coupling
agent for the most desirable results. Posit.ioned below the
transport mechanism 22 in the area where the tip 54 o~ the
ultrasonic horn 50 is located is a fluid collection tank 66.
(5ee figure I.) The fluid collection tank 66 serves to collect
fluid 62 which has been applied to the surface of the thin
naturally occurring polymeric shee~ material 14 and which has
either been driven through the sheet material 14 and/or the
transport mechanism 22 or over the edges of the transport
mechanism 22 by the action of the vibrations of the tip 54 of
the ultrasonic horn 50. Fluid 62 which is collected in the
collection tank 66 is transported by tubing 68 to a fluid
holding tank 70.
Figure I illustrates that the fluid holding tank 70 ~ :
contains a pump 72 which, by way of additional tubing 74,
supplies the fluid 62 to the fluid spray nozzle 60. According-
ly, th~ fluid 62 may be re-cycled for a considerable period
of time.
While the mechanism of action may not be fully understood
and the present application should not be bound to any
particular theory or mechanism of action, it is helieved that
the presence of the fluid 62 in the wedge-shaped area 64
during operation of the ultrasonic horn 50 accomplishes two
separate and distinct functions. First, the presence of the
fluid 62 allows the ~luid 62 ~o act as a heat sink which
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allows the ultrasonic vibrations to be applied to the thin
naturally occurring polymeric sheet material 14 without the
thin naturally occurring polymeric sheet material 14 being
altered or destroyed as by decomposition or possible melting.
Secondly, the presence of the fluid 62 in the wedge-shaped
area 64 allows the fluid 62 to act as a coupling agent in the
application of the vibrations from the ultrasonic horn 50 to
the thin naturally occurring polymeric sheet material 14.
It has been discovered that the action of the ultrasonic
horn 50 on the thin naturally occurring polymeric sheet
material 14 microapertures the thin naturally occurring
polymeric sheet material 14 in spite of the fact that there
are no fibers to re arrange to form microapertures as was the
case in Mitchell et al.. The microapertures are punched
through the thin naturally occurring polymeric sheat material
14 in the pattern of the raised area or knuckles 34 of the
fine mesh wire pattern screen 32. Generally, the number of
microapartures produced will be equa:L to the number of raised
areas or knuckles 3~ on the upper surface of the fine mesh
wire screen 32. Tha~ i5 ~ the number of microapertures will
generally be one-half the mesh count of a given ar0a o~
pattern screen 32. For example, if the pattern screen 32 is
100 wires per inch MD by 100 wires per inch CD mesh, the total
number of kn-lckles or raised areas 34 on one side of the
pattern wire 32, per square inch, will be 100 times 100
divided by 2. This equals 5,000 microapertures per square
inch. For a 200 wires per inch MD by 200 wires per inch CD
mesh pattern screen 32 the calculation yields 20,000
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microapertures per square inch. Depending somewhat on the
thickness of the thin naturally occurring polymeric sheet
material 14, at a mesh count of about 90,000 (300 wires per
inch MD by 300 wires per inch CD) the wires are s~ thin as to
allow the knuckles 34 on both sides to microaperture the thin
naturally occurring polymeric sheet material 14 if sufficient
force is applied. Thus, a 300 wires per inch MD by 300 wires
per inch CD mesh screen yields 90,000 microapertures per
square inch; for a ~00 wires per inch MD by 400 wires per inch
CD mesh--160,000 microapertures per square inch. Of course the
MD and CD wire count of the wire mesh screen does not have to
b~ the same. -~
It should also be noted that the number of microapertures
formed may also vary with the number of ultrasonic vibrations
to which the thin naturally occurring polymeric sheet material
14 is subjected per unit area for a given period of time. This
factor may be varied in a number of ways. For example, the
number and size of the microapertures will vary somewhat with
the line speed of the thin naturally occurring polymeric sheet
material 14 as it passes underneath the tip 54 of the
ultrasonic horn 50. Generally speaking, as line speed
increases, first the size of the microapertures decreases and
then the number of microapertures decreases. As the numbe. of
microapertures decreases the less the pattern of
microapertures resembles the pattern of raised areas 34 on the
pattern screen 32. The range of line speeds that usually
yields microapertures varies with the naturally occurring
polymeric material utilized to form the thin naturally
, ~
:, ' . ': :
:
occurring polymeric sheet material 14 and the materia~ d~ -3
as the fluid 62. For cellophane having a thickness of about
0.8 mil, typical line speeds which usually yield
microapertures for a wide variety of fluids range from about
4.5 to about 23.3 feet per minute. For example, if water is
used as the fluid with cellophane typical line speeds which
usually yield microapertures range from about 4 to about 5
feet per minute. It is believed that, to some extent, the
variations in the number of microapertures formed and the
size of the microapertures occurs due to the minute variations
in the height of the raised areas or knuckles 34 of the fine
mesh pattern screen 32. It should be noted that the fine mesh
pattern screens used to date have been obtained from
conventional everyday sources such as a hardware store. It is
also believed that if a pattern screen 32 could be created
where all of the raised areas 34 of the screen 32 were of
exactly the same height these variations would only occur in
uniform fashion with YariatiOnS of line speed.
As was stated above, the area or size of each of the
microapertures formed will also vary with the parameters
discussed above. The area of tha microapertures will also vary
with the area of the raised areas of the pattern anvil such
as the knuckles 34 on the fine mesh wire screen 32. It is
believed that the type of naturally occurring polymeric
material used in forming the thin naturally occurring
polymeric sheet material 14 will also vary the area of the
microapertures formed if all other parameters are maintained
the same. For example, the so~ter the thin naturally occurring
~7~
polymeric sheet material 14~ the easier it is to push the thin
naturally occurring polymeric sheet material 14 thxough the
raised areas o~ the fine mesh pattarn screen 32. Because the
raised areas (~nuckles) on the fine mesh screen are ge~erally
pyramidal in shape, the deeper the raised area penetrates tne
thin naturally occurring polymeric sheet material 14, the
larger the microaperture. In such situations the shape of the
microaperture will conform generally to the pyramidal shape
of the raised area of the fine mesh screen and the
microaperture will be generally pyramldally shaped, in the z
direction, and will have an area which is greater at one end
than at the other. As has been previously stated, the area of
the microaperture should be measured at the narrowest point
of the aperture. of course, the height of the raised areas
must be greater than the thickness of the thin sheet material
14 for microapertures to be formed and the degree of excess,
if any, necessary may vary with the type of naturally
occurring polymeric sheet to be microapertured. In any eYent
the height of the raised area~ must be sufficient to punch
through the naturally occurring polyn~eric material including
any elasticity which might be encountered in the punching
operation. That is, the more elastic the naturally occurring
polymeric material, the greater the height o~ the raised areas
has to exceed the thickness of the thin naturally occurring
polymeric sheet material~
In some embodiments it may be necessary to su~ject the
thin naturally occurring polymeric sheet material 14 to
multiple passes through the apparatus 10 in order to
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7 ~
microaper~ure the thin sheet material 14. In such situations
the thin sheet material 14 will initially only be thinned in
the pattern of the pattern anvil's raised areas. However,
after two or more passes through the apparatus 10, with the
thin naturally occurring polymeric sheet material 14 being
aligned in the same configuration with respect to the pattern
anvil, microapertures may be formed. Essentially what is
happening in these situations i5 that the thin naturally
occurring polymeric sheet material 14 is repeatedly thinned
by repeated application o~ ultrasonic vibrational force until
such time as microapertures are formed. Alternatively, the
~ine mesh wire diameter size may be increased with the
consequent decrease in mesh count. Increasing the wire
diameter size of the fine mesh screen 32 increases the
liklihood that microapertures will be. formed.
Another feature of the present invention is the fact that
the microapertures can be formed in a predesignated area or
areas of the thin naturally occurring polymeric sheet material
14. This can be accomplished in a number of ways. For example,
the thin naturally occurring polymeric sheet material 14 may
be 5ub; ected to ultrasonic vi~rations only at certain areas
of the sheet m~terial, thus, microaperturing would occur only
in those areas. Alternatively, the entire thin naturally
occurr.ing polymeric sheet material could be subjected to
ultrasonic vibrations with the pattern anvil having raised
areas only at certain locations and otherwise being flat.
Accordingly, the thin naturally occurring polymeric sheet
material would be microapertured only in those areas which
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~37fi~
corresponded to areas on the pattern anvil having raised
areas.
It should also be noted that some limitation exists in the
number of microapertures which can be formed in a yiven thin
naturally occurring polymeric sheet material 14 on a single
application of vibrational energy, i.P. a single pass through
the apparatus if a wire mesh screen is used as the patkern
anvil. This follows from the fact that, as was stated above,
the height of the raised areas must exceed the thickness of
the thin naturally occurring polymeric sheet material 14 in
conjunction with the fact that, generally, as the mesh count
incrsases the height of the raised areas or knuckles
decreases. In such situations, if the number of microapertures
desired per unit area is greater than the number which can be
formed in one pass through the apparatus, multiple passes are
necessary with the alignment of the thin naturally occurring
polymeric sheet material 14 with respect to the raised ares
being altered or shifted slightly on each pass.
Generally speaking the area of each of the microapertures
is greater than about ten square micrometers. That is the area
of each of the microapertures may range from at least about
10 square micrometers to about 100,000 square micrometers. For
example,the area of each of the formed microapextures may
generally range from at least about 10 square micrometers to
about 10,000 square micrometers. More particularly, the area
of each o~ the formed micxoapertures may generally range from
at least about 10 square micrometers to about 1,000 square
micrometers. Even more parkicularly, khe area of each of the
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2~57~
formed microapertures may generally ran~e from at least about
10 square micrometer to about 100 square micrometers.
A number of important observations about the process may
now be made. For example, it should be understood that the
presence of the fluid 62 is highly important to the present
inventive process which uses the fluid 62 as a coupling agent.
BecausP a couplinq agent is present, the microapertures are
punched through the thin sheet material 14 as opposed to being
fo~med by melting. Additionally, the presence of the shim
plate 30 or its equivalent is necessary in order to provide
an anvil mechanism against which the thin naturally occurring
polymeric sheet material 14 may be worked, that is apertured,
by the action of the tip 5~ of the ultrasonic horn 50. Because
the vibrating tip 54 of the ultrasonic horn 50 is acting in
a hammer and anvil manner when operated in conjunction with
the hevay duty wire mesh screen Z8/shim plate 30/fine wire
mesh 32 combination, it should he readily recognized that a
certain degree of tension must be placed upon the transport
mechanism 22 by the downward displacement of the ultrasonic
horn 50. If there is little or no tension placed upon the
transport mechanism 22, the shim plate 30 cannot perform its
function as an anvil and microaperturing generally does not
occur. Because both the shim plate 30 and the fine mesh
pattern wire 32 form the resistance that the ultrasonic horn
50 works against, they are collectively referred herein as a
pattern anvil combination. It should be easily recognized by
those in the art that the function of the pattern anvil can
be accomplished by other arrangements than the heavy duty wire
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mesh screen 28/shim plate 30/fine mesh screen 32 combination.
For example, the pattern anvil could be a flat plate with
raised portions acting to direct the microaperturing force of
the ultrasonic horn 50. Alternatively, the pattern anvil could
be a cylindrical roller having raised areas. If the pattern
anvil is a flat plate with raised areas or cylindrical roller
with raised areas, it is desirable for the pattern anvil to
be wrapped or coated with a resilient material. Where the
pattern anvil is a mesh screen the resiliency is provided by
the fact that the screen is unsupported directly below the
point of application of ultrasonic vibrations to the mesh
screen.
As a result of the microaperturing process the edge lenqth
of the thin naturally occurring polymeric sheet material may
be increased by at least about 100 percent as compared to the
sheet's edge length prior to microaperturing. For example, the
edge length of the thin naturally occurring polymeric sheet
material may be increased by at least about 500 percent as
compared to the sheet's edge length prior to microaperturing.
More particularly, the edge length of the thin naturally
occurring polymeric sheet material may be increased by at
least about 1,500 percent as compared to the sheet's edge
length prior to microaperturing. Even more particularly, the
edge lenqth of the thin naturally occurring polymeric sheet
material may be increased by at least about 3,000 percent as
compared to the sheet's edge length prior to microaperturing.
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The invention will now be discussed with regard to
specific examples which will aid those of skill in the art in
a full and complete understanding thereof.
Prior to utilizing the present process to microaperture
exemplary thin naturally occurring polymeric sheet materials
the hydrohead and water vapor transmission rate (wvtr) of the
selected materials were measured. Three different cellulosic
sheet materials were chosen for the present examples. These
were obtained from Flexel, Inc. Company of Atlanta, Georgia
under the trade designations (1) 0.8 mil thick Flexel V-58;
(2) 0.9 mil thick Flexel MST and (3) 1.0 mil thick Flexel
LST. Flexel, Inc. literature state that the Flexel V-58 is a
transparent cellulosic film coated on both sides with a
moistureproof, heat-sealable, high-barrier polymer (PVDC)
coating. Flexel, Inc. literature states that the Flexel MST
is a mois~ureproof, heat-sealable, transparent, two-sided
nitrocellulose coated cellulosic filmO Flexsl, Inc. literature
states that the Flexel LST is a two side nitrocellulose coated
cellulosic film with intermediate/decreased moistrueproofness
to permit breathing, while maintaining yood heat sealability,
water resistance ~or moist products, excellent coating
anchorage to base film, standard gas barrier properties, and
efficient machinability. The hydrohead of each of these
materials was in excess of 137 centimeters of water. (This is
the maximum hydrohead measurable by our equipment.) The wvtr
of the Flexel V-58 was measured as 0.0 grams per square meter
per day. The wvtr of the Flexel MST was measured as 0.8 grams
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~7~
per square meter per day. The wvtr of the Flaxel LST was
measured as 62.5 grams per square meter per day.
EXAMPLE I
A sheet of 0.8 mil thick cellulosic sheet having the trade
designation Flexel V-58 was cut into a length of about 11
inches and a width of about 8.5 inches. As wa~ stated above,
the hydrohead of the cellulosic sheet prior to hydrosonic
treatment was measured as being greater than 137 centimeters
of water. The sample was subjected to hydrosonic treatment in
accordance with the present invention.
A model 1120 power supply obtained from the Branson
Company of Danbury, Connecticut, was utilized. This power
supply, which has the capacity to deliver 1,300 watts of
electrical energy, was used to con~ert 115 volt, 60 cycle
electrical energy to 20 kilohertz alternating current. A
Branson type J4 power level control, which has the ability to
regulate the ultimate output of the nodel 1120 power supply
from o to lO0~, was connected to the model 1120 power supply.
In this exampl~, the power level control was set at 100%. The
actual amount of power consumed was indicated by a Branson
model A410A wattmeter. This amount was about 775 watts.
The output of the power supply was fed to a model 402
piezoelectric ultrasonic transducer obtained from the Branson
Company. The transducer converks the electrical energy to
mechanical movement. At 100% power the amount of mechanical
movement of the transducer is about 0.8 micrometers.
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The piezoelectric transducer was connected to a mechanical
movement booster section obtained from the Branson company.
The boos~er is a solid titanium metal shaft with a length
equal to one-half wava len~th of the 20 kilohertz resonant
frequency. Boosters can be machined so that the amount of
mechanical movement at their output end is increased or
decreased as compared to the amount of movement of the
transducer. ~n this example the booster increased the amount
of movement and has a gain ratio of about 1:2.5. That is, the
amount of mechanical movement at the output end of the booster
is about 2.5 times the amount of movement of the transducer.
The output end of the booster was connected to an
ultrasonic horn obtained from the Branson Company. The horn
in this example is made of titanium with a working face of
about 9 inches by about 1/2 inch. The leading and trailing
edges of the working face of the horn are each curved on a
radius of about 1/8 inch. The horn ~,tep area is exponential
in shape and yields about a two-fold increase in the
mechanical movement of the booster. That is, the horn step
area has about a 1:2 gain ratio. The combined increase, by the
booster and the horn step area, in the original mechanical
movement created by the transducer yields a mechanical
movement of about 4 .0 micrometers.
The forming table arrangement included a small forming
table which was utilized to transport and support the
cellulosic sheet to be microapertured. Tha forming table
included two 2-inch diameter idler rollers which were spaced
about 12 inches apart on the surface of the forming table. A
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transport mesh belt encircles the two idler rollers so that
a contim1ous conveying or transport surface is created. The
transport mesh belt i5 a square weave 20 x 20 mesh web of
0~020 inch diameter plastic filaments. The belt is about 10
inches wide and is raised above the surface of the forming
table.
The transducer/booster/horn assembly, hereinafter th~
as~embly, is secured in a Branson series 400 actuator. When
power is switched on to the transducer, the actuator, by means
of a pneumatic cylinder with a piston area of about 4.4 square
inches, lowers the assembly so that the output end of the horn
contacts the cellulosic sheet which is to be microapertured.
The actuator also raises the assembly 50 that the output end
of the horn is removed from contact with the cellulosic sheet
when power is switched off.
The assembly is positioned so that the output end of the
horn is adapted so that it may be lowered to contact the
transport mesh belt between the two idler rollers. An 8-inch
wide 0.005-inch thick stainless steel shim stock having a
length of about 60 inches was placed on the plastic mesh
transport belt to provide a firm support for a pattern screen
which is placed on top of the stainless steel shim. In this
example the pattern screen is a 120 by 120 mesh wire size
weave stainless steel screen. The cellulosic sheet which was
to be microapertured was then fastened onto the pattern wire
using masking tape.
The forming table arrangement also included a fluid
circulating system. The circulating system includes a fluid
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2~3 7~
reservoir tank, a fluid circulating pump which may convenient-
ly be located within the tank, associated tubing for transpor-
ting the fluid frnm ~he tank to a slotted boom which is
designed to direct a curtain of fluid into the juncture of the
output en~ of the horn and cellulosic sheet which is to be
microapertured.
In operation, the assembly was positioned so that the
output en~ of the horn was at an angle of ~rom about 10 to 15
degrees to the cellulosic sheet to be microapertured.
Accordingly, a wedge shaped chamber was formed between the
output end of the horn and the celluloslc sheet to be
microapexturecl. It is into this wedge shaped chamber that the
fluid, in this example a 50 percent 2 propanol/50 percent
water, by volume, mixture, at room tempexature, was directed
by the slotted boom.
It should be noted that the actuator was positioned at a
height to insure that, when the assembly is lowered, the
downward movement of the output end of the horn is stopped by
the tension of the transport mesh be~ore the actuator reaches
the limit of its stroke. In this example, actuating pressure
was adjusted ~o 7 pounds per square inch as read on a pressure
gauge which is attached to the pneumatic cylinder of the
actuator. This adjus~ment results in a total downward force
of 30.8 poundsO (7 psi times 4.4 square inches of piston area
equals 30.8 pounds of force.)
The sequence of operation was (1) the ~luid pUMp was
switched on and the area where the output end of the horn was
to contact the cellulosic sheet was flooded with the 50
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2~7~
percent 2 propanol/50 percent water, by volume, mixture; (2)
the transport mesh conveyor system was switched on and the
cellulosic sheet started moving at 23.3 feet per minute; and
~3) power to the assembly was supplied and the assembly was
lowered so that the output end of the horn contacted the
cellulosic shee~ while the sheet continued to pass under the
output end of the horn until the end of the sample was
reached. The reading on the A410A wattmeter during the process
is an i~dication of the ener~y required to maintain maximum
mechanical movement at the output end of the horn while
working against the combined mass of the 50 percent 2
propanol/ 50 percent water, by volume, mixture, the cellulosic
sheet, the pattern wire, the shim stock, and the transport
wire.
This example yielded a microapertured cellulosic sheet
having a maximum microaperture density o~ about 7,000
microapertures per square inch with the microapertures having
an area of about 40 square micrometers. The hydrohead of the
microapertured cellulosic sheet was measured as being about
54 centimeters of water and the wvtr o~ the microapertured
cellulosic sheet was measured as being about 219 grams per
square meter per day.
The edge length increase of this material was calculated
to be about 155 percent.
EXAMPLE II
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The process of example I was repeated with the exception
that the line speed of the cellose sheet was 20.9 feet per
minute as compaxed to the 23.3 feet per minute utilized in
example I. The actual amount of power consumed was indicated
by the Branson model A410A wattmeter as about 750 watts. The
actuating pressure was about 6 pounds per square inch, gauge.
This example yielded a microapertured cellulosic sheet having
a maximum density of about 7,000 microapertures per s~uare
inch with the microapertures having an area of about 1,070
square microme~ers. The hydrohead of this sample was measured
as being about 22 centimeters of water and the wvtr was
measured as being about 1,200 grams per square meter per day.
The edg~ length increase of the material was calculated as
being 766%.
Figure IV is a photomicrograph o~ the thin cellulosic
sheet material microapertured in accordance with example II.
EXAMPLE_III
The process of example I was repeated with the exception
that E'lexel MST was used as the cellulosic sheet material.
Additionally, the line speed o the cellose sheet was 4.S
feet per minute as compared to the 23.3 feet per minute
utilized in example I. The actual amount of power consumed was
indicated by the Branson model A410A wattmeter as about 850-
1,000 watts. The actuating pressure was 8 pounds per square
inch, gauge. A 250 by 250 wire count per inch MD and CD mesh
screen was used instead o~ the 120 by 120 wire count per inch.
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2~37~
water at room temperature was u~ed as the fluid instead of
50 parcen~ 2 propanol/50 percent water, by volume, mixture.
This example yielded a microapertured cellulosic sheet having
a maximum density of about 30,000 microapertures per square
inch with the microapertures having an area of about 225
square micrometers. The average of two hydrohead readings for
this sample was measured as being about 82 centimPters of
water and the average of three wvtr readings was about 240
grams per square meter per day. The edge length increase of
the material was calculated as being 1,635%.
'
EXAMPLE IV
The process of example I was repeated with the exception
that Flexel LST was u~ed as the cellulosic sheet material.
Additionally, the line speed of the cellose sheet was 4.5
feet per minute as compared to the 23.3 feet per minute
utilized in example I. The actual amount of power consumed was
indicated by the Branson model A410A wattmeter as about 900-
1,100 watts. The actuating pressure was 8 pounds per square
inch, gauge. A 250 by 250 wire count per inch MD and CD mesh
screen was used instead of the 120 by 120 wire count per inch.
Water at room temperature was used as the fluid instead of the
50 percent 2 propanol/50 percent water, by volume, mixture.
This example yielded a microapertured cellulosic sheet having
a maximum density of about 30,000 microapertures per square
inch with the microapertures having an area of about 600
square micrometers. The average of two hydrohead readings for
2~7~
this sample was about 76 cPntimeters of water and the average
of three wvtr rPadings was about 440 grams per square meter
per day. The edge length increase of the material was
calculated as being 2,670%.
EXAMP$E V
Example IV was repeated. This example yielded a
microapextured cellulosic sheet having a maximum density of
about 30,000 microapertures per square inch with the
microaperture~ having an area of about 600 square micrometers.
The average of tWQ hydrohead readings for this sample was
about 76 centimeters of water and the average of three wvtr
readings was about 950 grams per square meter per day.
Comparing the hydrohead and wvtr data for the cellulosic
sheets microapertured in examples I-V to the values obtained
for the untreated sheets, it is readily apparent that the
sheets have been rendered breathable to water vapor while
still maintaining a good hydrohead value. It is to ~e
emphasized that some variation is present from example to
example. (Note the differing wvtr results in examples IV and
V.) It is anticipated that with the use of better equipment
and the acquisition of additional knowledge in this area such
variations will be reduced accordingly.
The uses to which the microapertured naturally occurring
polymeric sheet material o~ the present invention may be put
are numerous. Of course, any application which is improved or
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otherwise enhanced if the edge length of the naturally
occurring polymeric sheet is increased is to be considered.
~dditionally, ~or nonwater soluble materials, applications
where materials having good wvtr values coupled with elevated
hydrohead values will present themselves. One such area of use
is in the filtration area. In particular, it should be noted
that the materials of the present invention are naturally
occurring, as defined herein, and they could well find use in
the packaginy of food where watar vapor breathability coupled
with product protection is desired. An example of an area
where increased edge length is benificial is the area of
biodegradability. When thin naturally occurring polymeric
sheet materials have been microapertured in accordance with
the present invention, the edge length of the sheet materials
is significantly increased. This increase in edge length
decreases the time it takes for the material to be decomposed.
It is to be understood that variations and modifications
of the present invention may be made without departing from
the scope of the invention. For exampl~, in some embodiments
the use of multiple ultrasonic horns aligned abreast or
sequentially may be desirable. It is also to be understood
that the scope of the present invention is not to be
interpreted as limited to the specific embodiments disclosed
herein, but only in accordance with the appended claims when
read in light of the foregoing disclosure.
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