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!76g 050 entitled "Hydrosonically Microapertured Thin
Thermoset Sheet Materials" in the names of Lee K. Jameson and
Bernard Cohen; U.S. patent application serial number
07~769.047 entitled "Hydrosonically Microap~rtured Thin
Thermoplastic Sheet Materials" in the names of Bernard Cohen
and Lee K. Jameson; U.S. patent application serial number
07/768 782 entitled "Pressure Sensitive Valve System and
Process For Forming Said System" in the names of Lee K.
Jameson and Bernard Cohen; U.S. patent application serial
number 07/768.494 entitled " Hydrosonically Embedded Soft Thin
Film Materials and Process For Forming Said Materials'l in the
names of Bernard Cohen and Lee K. Jameson; U.S. patent
application number 071768.788 entitled "Hydrosonically
Microapertured Thin Naturally Occurring Polymeric Sheet
Materials and Method of Making the Same" in the names of Lee
K. ~ameson and Bernard Cohen; U.S. patent application serial
number 07/769,048 entitled "Hydrosonically Microapertured Thin
Metallic Sheet Materials" in the names of Bernard Cohen and
Lee K. Jameson; U.SO patent application serial number
07/769 045 entitled "Process For Hydrosonically
Microaperturing Thin Sheet Materials" in the names of Lee X.
Jameson and Bernard Cohen; and U.S. patent application serial
number 07/767,727 entitled "Procéss For Hydrosonically Area
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Thinning Thin Sheet Materials" in the names of Bernard Cohen
and Lee K. Jameson. All of these applications are hereby
incorporated by re~erence.
FIELD OF THE INVENTION
The fiald of the present invention encompasses thin sheets
formed from thermoset materials which have been microapertursd
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 been 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) fricti~n welding;
(5) the formation of catalysts; (6) the degassing and
solidification of molten metals; (7) the extraction of flavor
oils in brewing; (8) electroplating; (9) drilling hard
materials; (10) fluxless soldering and (10) 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 centimeter. Although the original
ultrasonic power devic2s operated at radio rrequencies, today
most operate at 20-69 kHz.
The piezoelectric sandwich-type transducer driven by an
electronic power supply has emerged as the most common source
of ultrasonic power; the overall efficiency of such equipment
(net acoustic power per electric-line power) is typically
greater than 70~. The maximum power from a conventional
transducer is inversely proportional to the square of the
frequency~ Some applications, such as cleaning, may have many
transducers working into a common load.
Other, more particular areas where ultrasonic vibrato~y
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 example, UOS~ patent
numbers 3,575,752 to Carpenter, 3,660,186 to Saaer et al.,
3,966,519 to Mitchell et al. and 4,695,454 to Sayovitz et al.
which disclose the use of ultrasonics to bond or weld nonwoven
webs. U.S. patent numb~rs 3,488,240 to Roberts, describes the
use of ultrasonics to bond or weld thin films such as oriented
polyesters.
Ultrasonic ~orce has also been utilized to aperture
nonwoven webs. See, for example, U.S. patent num~ers 3,949,127
to Ostermeler et al. and 3,966,519 to Mitchell et al .
Lastly, ultrasonic force has ~een used to aperture thin
film material. See, for example, U. S. patent number 3,756,880
to Gracz~k.
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Other methods for the aperturing of thin film have been
developed. For example, U.S. patent number 4,815,714 to
Doualas discusses the aperturing of a thin film by first
abrading the film, which is in filled and unoriented form, and
then subjecting the film to corona discharge treatment.
One of the dificulties 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 microaperture
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 ultrasoni s could be utilized to form
apertures in nonwoven webs. See, U.S. patent to Mitchell, et
al.. Additionally, 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 throuyh physical movement of fibers,
the method of their invention may be utilized to bond or
increase the strength of a wide variety of fibrous webs.
While the discovery disclosed in the M.itchell et al.
patent, no doubt, was an important contribution to the art,
it clearly did not addre3s the possibility of aperturing
nonfibrous sheets or sheets having fixed fibers formed from
thermoset materials. This fact is clear because the Mitchell
et al. patent clearly states the belief that the mechanism of
aperture ~ormation depended upon ~iber rearrangement. Of
course, 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 b~ stated with conviction that
the applicability of a method for aperturing thermoset sheet
materials by the application of ultrasonic energy in
conjunction with a fluid at the point of application of the
ultrasonic energy to the thermoset sheet material was not
contemplated by the Mitchell et alO patent. Moreover, the
Mitchell et al. 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.
DEFINITIONS
As used herein the term "thermoset material" refers to
a high polymer that solidifies or "sets" irreversibly when
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heated. This property is almost invariably associated with a
cross-linking reaction of the molecular constituents induced
by heat or irradiation. In many cases, it is necessary to add
"curing" agents such as organic peroxides or (in the case of
natural rubber) sulfur to achieve cross-linking. For example
thermoplastic linear polyethylene can be cross-linked to a
thermosetting material either by radiation or by chemical
reaction. A general discussion of cross-linking can be found
at pagee 331 to 414 of volu~e 4 of the Encyclopedia of Polymer
Science and Te~hnology, Pla~tics, Resins, Rubbers, Fibers
p~blished by John Wiley & Sons, Inc. and copyrighted in 1966.
This document has a Library of Congress Catalog Card No. of
64-22188. Phenolics, alkylds, amino resins, polyesters,
epoxides, and silicones are usually considered to be
thermosets. The term is also meant to encompass materials
where additive-induced cross-linking is possible, e.g. cross-
linked natural rubber.
One method for determining whether a material is
i'cross-linked" and therefore a thermoset material, is to
reflux the material in boiling toluene, xylene or another
solvent, as appropriate, for forty (40) hours. If a weight
percent residue of at least 5 percent remains, the material
is deemed to be cross-linked and thus a thermoset material.
Another procedure for determining whether a material is
cross-linked vel non and there~ore a thermoset material is to
reflux 0.4 gram of the material in boiling toluene or another
appropriate solvent, for example xylene, for twenty (20)
hours. If no insoluble residue (gel) remains the material may
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not be cross-linked. However, this should be confirmed by the
"melt flow" procedure below. If, after twenty (20) hours of
refluxing insoluble residue (gel) remains the material is
refluxed under the same conditions for another twenty (20)
hours. If more than 5 wei~ht percent of the material remains
upon conclusion of the second re~luxing the material is
considered to be cross-linked and thus a thermoset material.
Desirably, a least two replicates are utilized.
Another method whereby cross~linking vel non and the
degree of cross-linking can be determined is by ASTM-D 2765-68
(Reapproved 1978).
Yet another method for determining whether a material is
cross-linked vel non is to determine the melt flow of the
material in accordance with ASTM D 1238-79 at 230 degrees
Centigrade while utilizing a 21,600 gram load. Materials
having a melt flow of greater than 75 grams per ten minutes
shall be deemed to be non-cross-linked and thus would not be
considered to be thermoset materials. This method should be
utilized to confirm the "gel" method, described above,
whenever the remaining insoluble gel content is less than 5%
since some cross-linked materials will evidence a residual gel
content of less than 5 weight percent. Of course, the term
"thermoset material" is al50 meant to include mixtures and
combinations of two or more thermoset materials as well as
mixtures and combinations which include at least fifty (50)
percent, by weight, thermoset materials.
As used herein the term "thermoset sheet materialll refers
to a generally nonporous item formed from a thermoset material
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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, has a hydrostatic pressure (hydrohead3
of at least about 100 centimeters of water when measured in
accordance with Federal Test Method N0. 5514, standard no.
191A. Unless otherwise stated herein all hydrohead values are
obtained in accordance with Federal Test Method N0. 5514,
standard No. l91A. This term is also intended to include
multilayer ma~erials which include at least one such sheet of
a thermose~ material as a layer thereof.
As used herein the term "thin thermoset sheet material"
refers to a thermoset sheet material having an average
thickness generally of less than about ten (10) mils. Average
thickness is determined by randomly selecting five (5)
locations on a given sheet material, measuring the thickness
of the sheet material at each losation to the nearest 0.1 mil,
and averaging the five values (sum of the five values divided
by five).
As used herein the term water vapor transmission rate
refers 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. ~he test is run at 90 degrees fahrenheit and 50
percent relative humidity for twenty-four (24) hours.
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~ s used herein the term "mesh count" refers to the number
which is the product of the number of wires in 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 of 10,000 per square inch. As a result of the
interw~aving of these wires, raised areas are present on both
sides of the m~sh screen. The number of raised areas on one
side o~ such a wire mesh screen is generally 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~' refers to an
aperture which has an area of less than about 100,000 square
microme~ers. The area of the microaperture is to be measured
at the narrowest point in the linear passageway or hole.
As used herein the term "microcrack" refers to a
microaperture having a maximum length measurement which is at
least about ten (10~ times longer than the widest width
measurement. In many cases, due to the extremely small width,
which may not be readily susceptible to measurement, the
length/width ratio may approach infinity. When tension is
applied to a microcracked sheet mat rial, the microcracks
evidence little, if any, distortion until permanent
deformation of the sheet material begins to occur.
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As us~d herein the term "microslit" refers to a
microapertur~ having a maximum lenyth measurement which is at
least about ten (10) times longer than the widest width
measurement. In many cases, due to the ~xtremely small width,
which may not be readily susceptible to measurement, the
length/width ratio may approach infinity. When tension is
applied to a microslit sheet material, the microslits readily
distort and, in many instances, close back up upon release of
the tensioning force.
As used herein the term "ultrasonic vibrations" refers
to vibrations having a frequency of at least about 20,000
cycles p r secondO The frequency of the ultrasonic vibrations
may range from about 20,000 to about 400,000 cycles per second
or more.
As usd 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
quantity to generally fill the gap between the tip of the
ultrasonic horn and the surface of the material.
The approximate edge len~th of the thin microapertured
thermoset sheet material of the present invention is
calculated ~rom the size of the microaperture ~sing the
appropriate geometrical formula, depending upon the
microaperture's general shape.
OBJE~TS OE' THE INVENTION
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Accordingly, it is a general obje~t of the present
invention to provide thin thermoset sheet materials which have
been microapPr~ured in a generally uniform pattern.
Still further objects and the broad scope of applicability
of the present invention will become 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 pref~rred embodiments of the present invention i5
given only by way of illustration because various changes and
modifications well within the spirit and SCOp8 of the
invention will become apparent to those of sXill in the art
in view of this detailed description.
SUMMARY OF THE INVENTION
In response to the foregoing problems and dif~iculties
encountered by those in the art, we have developed a method
for fonming microapertures in a thin t:hermoset sheet material
having a thickness of about 10 mils or less where the area of
each of the formed microapertures is generally greater than
about lo s~uare micrometers. The method includes the steps of:
(1) placing the thin thermoset sheet material on a pattern
anvil haviny a pattern of raised areas where the height of the
raised areas is greater than the thickness of the thin
thermoset sheet material; (2) conveying the thin thermoset
sheet material, while placed on the pattern anvil, through an
area where a fluid is applied to the thin thermoset sheet
material; and (3~ subjecting the thin thermoset sheet material
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to ultrasonic vibrations in the area where the fluid is
applied to the thin thermoset sheet material. As a result of
this method, the thin thermoset sheet material i5
microap~rtured in a pattern generally the same as the pattern
of raised areas on the pattern anvil.
The thin thermoset sheet material may be formed from, for
example, a material selected from the group including of one
or more of cross-linked natural rubber, cross-linked
polyesters or cross-linked organosilicon polymers such as
cross-linked dimethyl siloxane.
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
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 about 10
square micxometers to about 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. More particularly, the area
of each of the formed microapertures 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
formed microapertures may generally range from about at least
10 square micrometers to about 100 square micrometers.
The thin thermoset sheet material may be microapertured
with a microaperture density of at least about 1,000
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microapertures per square inch. For example, the thin
thermoset sheet material may be microapertur~d with a
microaperture density of at least about 5,000 microapertures
per square inch. More particularly, the thin thermoset sheet
material may ~e microapertured with a microaperture density
of at least about 20,oO0 microapertures per square inch. Even
more particularly, the thin thermoset sheet material may be
microaper~ured with a microaperture density of at least about
90,000 microapertur s per square inch. Yet even more
particularly, the thin thermoset sheet material may be
microapertured with a microaperture density of at least about
160,000 mlcroapertures per square inch.
In so~e embodiments it may be desirable for the
microaperturing of the thin thermoset sheet material to be
confined to a predesignated area or areas o~ the thin
thermoset sheet material. This result may be obtained where
only a portion o the thin thermose1: sheet is subjected to
ultrasonic vibrations. Alternatively, this result may be
obtained wAere only a portion of the pattern anvil is provided
with raised areas.
The thickness of the thin thermoset sheet material is at
least about 0.25 mil~ For example, the thickness of the thin
thermoset sheet material may range from about 0.25 mil to
about 5 mils. More particularly, the thickness of the thin
thermoset sheet material may range from about 0.25 mil to
about 2 mils. Even more particularly, the thickness of the
thin thermoset sheet material may range from about 0.5 mil to
about l mil.
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The hydrohead of the thin thermoset sheet material may
range from at least about 15 centimeters o~ water. For
example, the hydrohead of the thin thermoset sheet material
may range from at least about 35 centimeters of water. More
particularly, the hydrohead of the thin thermoset sheet
material may range from at least about 45 centimeters of
water. Even more particularly, the hydrohead of ths thin
thermoset sheet material may range from at least about 55
centimeters of water. Yet even more particularly, the
hydrohead of the thin thermoset sheet material may range from
at least about 75 centimeters of water.
The water vapor transmission rate of the thin thermoset
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 thermoset sheet material may
range from at least about 500 grams per s~uare meter per dayO
Even more particularly, the water vapor transmission rate of
the thin thermoset shPet material may range from at least
about 1,000 grams per square meter per day.
As a result of the microaperturing process the edge length
of the thin thermoset 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 l~ngth of the
thin thermoset 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 thermoset sheet material may be increased by at least
about 1,500 percent as compared to the sheet's edge length
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prior to microaperturing. Even more particularly, the edge
length of the thin thermoset sheet material may be increased
by at least a~out 3,000 percent as compared to the sheet's
edge leng~h prior to microaperturing.
In some embodiments, depending upon the t~pe of material
used to form the thin thermoset sheet material, the
microapertures may take th~ form of microcracks or micrnslits.
T~ FIGURES
Figure I is a schematic representation of apparatus which
utilizes ultrasonic vibrations to microaperture thin thermoset
sheet materials.
Figure II is a cross sectional view of the transport
mechanism for transporting the thin thermoset sheet material
to the area where i~ is subjected to ultrasonic vibrations.
Figure III is a detailed view of the area where the thin
thermoset sheet material is subjected to ultrasonic
vibrations. The area is designated by the dotted circle in
figure I.
Figure IV is a photomicrograph of a 0.5 mil thick sheet
of polyvinylidene coated polyester obtained under the trade
name "Flexel Esterlock", which has be~n microapertured in
accordance with the present invsntion. The photomicrograph
is accompanied by a scale where each unit on the scale
represents ten microns (micrometers).
Figure V is a photomicrograph of the material formed by
the process of Example V, with the material being maintained
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at about 100 percent stretch so that the presence of the
microsli~s can be demonstrated. The photomicrograph is
accompanied by a scale where each unit represerlts ten (10)
microns (micrometers).
Figure VI is a photomicrograph of the material of Example
VI both prior to processing and after processing. ::
Figure VII is a photomicrograph of the material of Example
VI after processing and while maintained at about 100 percent
elongation.
DETAILE~ pESCRIPTION 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 invention, it can be seen that
the apparatus is generally represe:nted by the reference
numeral 10. In operation, a supply roll 12 of a thin thermoset
sheet material 14 to be microapertured is provided. As has
be~n previously stated, the term thin thermoset 5heet material
re~ers to sheet materials which have an average thickness of
about ten (10) mils or less. Additionally, generally speaking,
the average thickness of the thin thermoset sheet material 14
will be at least about 0.25 mil. For example, the average
thickness of the thin thermoset sheet 14 material may range
from about 0.25 mil to about 5 mils. More particularly, the
average thickness of the thin thermoset sheet material 14 may
range from about 0.25 mil to about 2 mils. Even more
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specifically, the average thickness of the thin thermoset
sheet material 14 may range from about 0.5 mil to about 1 mil.
The thin thermoset sheet material 14 may be ~ormed from
a cross-linked material. For example, the thin thermoset sheet
material 14 may be fsrmed from a material selected from one
or more of cross-linked natural rubber, cross-linked
polyesters or cross-linked organosilicon polymers such as
cross-linked dimethyl siloxane. The thin thermoset sheet
material 14 may be formed from one or more thermoset materials
which may be comhined to form the sheet material 14.
The thin thermoset sheet material 14 is transported to a
~irst 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 th~ rotation of the first
transport roller 18 in con~unction with a second transport
roller 26 which, in turn are driven by a c4nventional 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 transport wire mesh screen 2~ usually having a mesh count
of less than about 400 (i.e. less than a 20 wires per inch MD
by 20 wire~ per inch CD mesh screen if machine direction (MD)
and cross machine direction (CD) wire count is the same).
Heavy duty mesh wire screens of this type may be made from a
variety o~ materials such as, ~or example, plastics, nylons
or polyesters, and are readily available to those in the art.
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Located above and attached to the transport screen 28 is an
endless ~lat shim plate 30. The shim plate 30 desirably is
formed from stainless steel. ~owever, those of skill in the
art will readily recognize that other materials may be
utilized. Located above and attached to the shim plate 30 is
a fine mesh wire pattern screen 32 usually having a mesh 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 ~he 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 p~rform the
function of a pattern anvil as will be discussed later.
From the first nip 16 the thin thermoset she2t material
14 is transport~d by the transport mechanism 22 over a tension
roll 36 to an area 38 ~defined in Figure I by the dotted lined
circle3 where the thin thermoset sheet material 14 is
subjected ~o ultrasonic vibrations.
The assembly for subjecting thQ thin thermoset 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 transducar 46 transforms electrical
energy into mechanical movement as a result of the
transducer's vibratîng in response 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,
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the mechanical movement booster 48 may be designed to increase
the ampli~ude of the vibrations (mechanical movement) by a
known factor d2pending upon the configuration of the booster
48. In further conventional manner, the mechanical movement
(vibrational energy) is transferred from the mechanical
movement booster 48 to a conventional knife edge ultrasonic
horn 50. It should be realized that other types of ultrasonic
horns 50 could be utilized. Por 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 thermoset 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 thP assembly 40 being lowered. It
has been found ~hat it is necessary to have some degree of
tension applied to the transport mechanism 22 upon the
lowering of the aasembly for proper application of vibrational
energy to the thin sheet material 14 to form microapertures
in the thin thermosek sheet material 14. One desirable aspect
of this tensioned arrangement is that the need to 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 is not necessary.
Figure III is a schematic representation of the area 38
where the ultrasonic vibrations are applied to the thin
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thermoset 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
that it is 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 degreesO More particularly, the
angle 56 may range from about 9 to about 11 degrees.
Figure III also 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 of the ultrasonic horn 50 is a spray nozzle 60 which is
configured to apply a fluid 62 to the surface of the thin
thermoset sheet material 14 just prior to the sheet material's
14 being subjected to ultrasonic vibrations by the tip 54 of
the ultrasonic horn 50. The fluid 62 desirably may be selected
from the group including one or more o~ water, mineral oil,
a chlorinated hydrocarbon, ethylene glycol or a solutlon of
50 volume percent water and 50 volume percent 2 propanol. For
example, in some embodiments the chlorinated hydrocarbsn may
be selected from the group including 1, 7, 1 trichloroethane
or carbon tetrachloride. It 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 subje~ted 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. Positioned below the transport mechanism 22 in the
area where the tip 54 o~ the ultrasonic horn 50 is located is
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a fluid collection tank 66. (See figure I.) The fluid
collection ~ank 66 serves to collect fluid 62 which has been
applied to the suxface of the thin thermoset sheet material
14 an~ which has either been driven through the sheet material
14 and/or ~he 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 coll0ction tank 66 is transported by tubing 68 to a
fluid holdin~ tank 70.
Figure I illustrates that the fluid holdin~ tank 70
con~ains a pump 72 which, by way of additional tubing 74,
supplies the fluid 62 to the fluid spray nozzle 60. According-
ly, the 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 ~e bound to any
particular theory or mechanism of action, it is believed 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 fluid 62 to act as a heat sinX which
allow~ the ultrasonic vibrations to be appli~d to the thin
thermoset sheet material 14 without the thin thermoset sheet
material 14 being altered or destroyed as by 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 thermoset sheet material 14.
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It has been discovered that the action of the ultrasonic
horn 50 on ~he ~hin the~moset sheet material 14 microapertures
the thin thermoset sheet material 14 in spite of the fact that
there are no fibers to re-arrange to form microapertuxes as
was the case in Mitchell et al.. The microapertures are
punched throu~h the thin thermoset sheet material 14 in the
pattern of the raised areas or knuckles 34 of the ~ine mesh
wire pat~ern screen 32. Generally, the number of
microapertures produced will be equal to the number of raised
areas or knuckle~ 34 on the upper sur*ace of the fine mesh
wlre screen 32. That is, the nu~ber of microapertures will
generally be one-half the mesh count of a given area of
pattern screen 32. For examplet if the pattern screen 32 is
100 wires per inch MD by 100 wires per inch CD, the total
number of knuckles or raised areas 34 on one side o~ the
pattern wire 32, per square inch, will be 100 times 100
di~ided ~y 2. This equals 5,000 microapertures per square
inch. For a 200 wires per inch MD by 200 wires per inch CD
pattern screen 32 the calculation yielcls 20,000 microapertures
per square inch. Depending somewhat on the thickness of the
thin thermoset 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 sv thin as to allow the knuckles 34 on both sides
to microaperture the thin thermoset 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 400 wires per inch MD by 400 wires per
inch CD mesh--160,000 microapertures per square inch. Of
2~3~
course the MD and CD wire count of the wire mesh screen does
not have to be the same.
It should al50 be noted that the number of microapertures
formed may also vary with the number of ultrasonic vibrations
to which the thin thermoset 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 thermoset 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 number 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 yield~ microapertures varies with the thermoset
material utilized to form the thin thermoset sheet material
14 and, it is believed from experiments with other types of
sheet materials, the material used as the fluid 62. If water
is used as the fluid with cross-linked natural rubber typical
line speeds which usually yield microapertures range ~rom
about 3 to about 11 feet per minute~ It is believed that,
to some extent, the vaxiations in the num~er 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 scraen 32. It should be
noted that the fine mesh pattern screens used to date have
been obtained from conventional everyday sources such as a
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~ 7 ~5
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 variations of line
speed.
As was stated above, the area or size o~ each of the
microapertures formed will also vary with the parameters
discussed above. The degree of cross-linking present also
plays a role not only in the area of the microapertures formed
but whether the microapertures are microslits or micxocracks.
If the degree of cross-linking is such that microapertures are
formed, the area of the 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. Because the
raised areas (knuckles) on the fine mesh screen are generally
pyramidal in shape, the deeper the raised area penetrates the
thin thermoset sheet material 14, the larger the
microaperture. In such situations, if the sheet material 14
is sufficiently cross-linked and thus generally in~lastic, the
shape of the microaperture will con~oxm generally to the
pyramidal shape of the raised area o~ the fine mesh screen and
the microaperture will be generally pyramidally shaped, in the
z direction, and will have an area which is greater at one end
than at the other. If the sheet material 14 is only lightly
cross-linked and thus elastomeric, the microapertures will
resume their orininal planar configuration. As has been
previously stated, the area of the microaperture should be
measured at the narrowest point of the apexture. 0~ course,
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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 thermoset sheet to be microapertured. In any
event, the height o~ the raised areas must be sufficient to
punch through the thermoset material including any elasticity
which might be encountered in the punching operation. That is, ~;
the more elastic the thermoset material, the greater the
height of the raised areas has to exceed the thickness o~ the
thin the~moset sheet material.
If the thermoset material is cross-linked to a relitively
low degree, the material may well possess elastomeric
properties. In such a situation, the microapertures will be
tran iently formed by the fine mesh wire screen 32 but will
close up to a certain degree, if not completely, after the
knuckles of the fine mesh screen 32 are withdrawn from the
elastomeric thermoset material. If this is the case, the
microapertures take on the form of microslits.
If the thermoset material is cross-linked to a significant
degree, the material may well be so inelastic that the effect
of the knuckles of the fine mesh screen on the sheet is
similar to a hammer hitting ice. In such a situation the
microapertures take on the form o~ microcracks.
In some embodiments it may be necessary to subject the
thin thermoset sheet material 14 to multiple passes through
the apparatus 10 in order to microaperture the thin sheet
material 14. In such situations the thin sheet material 14
will initially only be thinned in the pattern of the pattern
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.
anvil's raise~ areas. HowevPr, after two or more passe
through the apparatus 10, with the thin thermoset sheet
material 14 being aligned in the same con~iguration with
respect to the pattern anvil, microapertures may be formed.
Essentially what is happening in these situations is that the
thin thermoset sheet material 14 is repeatedly thinned by
repeated application of ultrasonic vibrational force until
such time as microapertures are ~ormed. Alternatively, the
fine 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 thermoset sheet material 14. This can be
accomplished in a number of ways. For example, the thin
thermose~ sheet material 14 may be subjected to ultrasonic ::
vibrations only at certain areas of the sheet material, thus,
microapsrturing would occur only in those areas.
Alternatively, the entire thin thermo~et 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 thermoset sheet material
would be microapertured only in those areas which corresponded
to areas on the pattern anvil having raised areas.
It should also be noted that sume limitation exists in the
number of microapertures which can be formed in a given thin
thermoset sheet material 14 on a single application of
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vibrational energy, i.e~ a single pass through the apparatus
if a wire mesh screen is used as the pattern anvil. This
follows from the fact that, as was stated above, the height
of the raised areas must exceed the thickness of the thin
thermoset sheet material 14 in conjunction with the fact that,
generally, as the mesh count increases the height of the
raised area~ or knucXle~ decreases. In such situations, if the
number of microapertures desired per unit area is greater than
the nu~ber which can be formed in one pass through the
apparatus, multiple passes are necessary with the alignment
of the thin thermoset 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 o~ the microapertures may range from at least a~out
10 square micrometers to about 100,000 square micrometers. For
exampl~,the area of each of the formed microapertures may
generally range from at least about 10 square micrometers to
about 10,000 square micrometers. More particularly, the area
of each o~ the fo~med microapertures may general~y range from
at least about 10 square micrometers to ahout 1,000 square
micrometers. Even more particularly, the area of each of the
formed microapertures may generally range from at least about
10 square micrometers to about 100 square micrumeters.
A nu~ber o~ 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 whlch use~ the fluid 62 as a coupling agent.
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Because a coupling agent is pr~-sent, the microapertures are
punched through the thin sheet material 14 as opposed to being
formed by melting O Additionally, the presence of the shim
plate 30 or its equivalent is necessary in order to provide
an anvil mechanism against which the thin thermoset sheet
material 14 may be work~d, that is apertured, by the action
of the tip 54 o~ the ultrasonic horn 50. Because the vibrating
tip 54 of the ultrasonic horn 50 is acting in a ha~mer and
a~il manner when operated in conjunction with the heavy duty
wire mesh screen 28/shim plate 30/fine wire mesh 32
combination, it should be 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 ~asily recognized by those in
the art ~hat the function of the pattern anvil can be
accomplished by other arrangements than the heavy duty wire
m~sh screen 28 shim plate 30/~ine mesh screen 32 combination.
For example, the pattern anvil could be a flat plate with
raised poxtions 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 cylindrical roller with raised areas, it is
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~7~66
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 ~he resiliençy is provided by the fact that the
screen is unsupported directly below ~he point of application
of ultrasonic vibrations to the mesh screen.
Also as a result of the microaperturing process the edge
length of the thin thermoset sheet material may be increased
by at least about 100 percent as compared to ths sheet's edge
length prior to microaperturing. For example, the edge length
of the thin thermoset sheet material may be increased by at
leas~ ab~ut 500 percent as compared to the sheet's edge length
prior to microaperturing. More particularly, the edge length
of the thin thermoset shePt material may be increasPd by at
least about 1,500 percent as compared to the sheet's edge
length prior to microaperturing. Even more particularly, the
edge length of the thin thermoset sheet material may be
increased by at least about 3,000 percent as compared to ~he
sheet's edge length prior to microaperturing.
The invention will now be discussed with regard to
specific exa~ples 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 thermoset sheet materials the hydrohead and
water vapor transmission rate (wvtr) of the selected materials
were measured. Three different thermoset sheet materials were
chosen for the present examples. The first was a 0.5 mil thick
cross-linked polyester film coatad on both sides by PVDC
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(polyvinylidene chloride) obtained from Flexel, In~. of
Atlanta, Georgia under the trade designation "Esterlock 50".
The second was a 4.0 mil thick cross-linked natural rubber
obtained ~rom the ~.P Stevens Elastomers Corp. of Northampton,
Ma. under the tra~e designation "Softlastic". The third was
a 5 mil thick cross-linked dimethyl siloxane obtained from the
Dow Corning Corp, of Midland, Michigan under the trade
designa~ion "SilastiC". The hydrohaad o~ each of these
materials was in excess of 137 centimeters of water. (Two
measurements were made for each makerial. This is the maximum
hydrohead measurable by our equipment.) The average of three
wvtr measurements of the Flexel Esterlock was O.00 qrams per
square meter per day. The average of three wvtr measurements
of the Stevens Softlastic material W25 41.7 grams per square
meter per day. The average of three wvtr measurements of the
Dow Silastic material was 218.7 grams per square meter per
day.
EXAMPLE I
A sheet of 0.5 mil thick polyester sheet coated on both
sides with PVDC having th~ trade designation Flexel Esterlock
50 was cut into a length of about 11 in hes and a width of
about 8.5 inches. As was stated above, the hydrohead of the
PVDC coated polyester sheet prior to hydrosonic treatment was
measured as being greater than 137 centimeters of water~ The
sample was subjected to hydrosonic treatment in accordanca
with the present invention.
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2~3 7~
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 convert 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 model 1120 power supply
from 0 to 100%, was connected to the model 1120 power supply.
In this example, the power level control was set at 100%. The
actual amount of power consumed was indicated hy a Branson
model A410~ wattmeter. This amount was about 1,100 watts.
The output of the power supply was fed to a model 402
piezoelectric ultrasonic transducer obtained from the Branson
Company. The transducer converts the electrical energy to
mechanical movement. At 100% power the amount of mechanical
movement of the transducer is about 0.8 micrometers.
The piezoelectric transducer was connected to a mechanical
movement booster section obtained from the Branson Company.
The booster is a solid titanium metal ~haft with a length
equal to one-half of the wave length 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. In 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.
: .
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~73~i~
The output end of the booster was connected to an
ultrasonic horn obtained from the Branson Company. The horn
in this example is made o~ 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 step area is exponential
in shape and yields about a two-fold increase in the
mechanical movement of the booster. Tha~ 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 PVDC
coated polyester sheet to be microapertured. The forming table
included two 2-inch diameter idIer rollers which were spaced
about 12 inches apart on the surface of the forming table. A
transport mesh belt encircles the two idler rollers so that
a continuous conveying or transport surface is created. The
transport mesh belt is a square weave 20 x 20 mesh web of
0.020 inch diameter plastic fila~ents. The belt is about 10
inches wide and is raised above the surface of the forming
table.
The transducer/booster~horn assembly, hereinafter the
assembly, 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 o~ the horn
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contacts the PVDC coated polyester sheet which is to be
microapertured. The actuator also raises the assembly so that
the output and o~ the horn is removed from contact with the
PVDC coated polyester 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 bel~ *o 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 200 by 200 mesh wire size
weave stainless steel screen. The PVDC coated po1yester 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
reservoir tank, a fluid circulating pump which may convenient-
ly be located within the tank, associated tubing for transpor-
ting the fluid from the tank to a slotted boom which is
design~d to direct a curtain of fluid into the juncture of the
output end of the horn and the PVDC coated polyester sheet
which is to be microapertured.
In operation, the assembly was positioned so that the
output end of the horn was at an angle of from about lO to 15
deyrees to the PVDC coated polyester sheet to be
microapertured. Accordingly, a wedge shaped chamber was formed
between the output end of the horn and the PVDC coated
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2~73~
polyester shee~ to be microapertured. It is into thi~ wedge
shaped chamber that the fluid, in this example water, at room
temperature, was directed by the slotted boo~O
It should be noted that the ackuat~r 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 ~he ~ransport mesh before the actuator reaches
the limit of its stxoke. In this example, actuating pressure
was adjusted to 10 pounds per square inch as read on a
pressure gauge which is attached to the pneumatic cylinder of
the actuator. This adjustment results in a total downward
force of 44 pounds. (10 psi times 4.4 square inches of piston
area equals 44 pounds of force.)
The sequence of operation was (1) the fluid pump was
switched on and the area where the output end of the horn was
to contact the PVDC coated polyester sheet was flooded with
w2ter; (2) the transport mesh conveyor system was switched on
and the PVDC coated polyester sheet started moving at 3.8 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 PVDC coated polyester sheet 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 indication of the energy
required to maintain maximum mechanical movement at the output
end of the horn while working against the combined mass of the
water, the PVDC coated sheet, the pattern wire, the shim
stock, and the transport wire.
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2~7~6
This example yielded a microapertured (microcracked) PVDC
coated sheet ha~ing a maximum microaperture density of about
20,000 microaper~ures per s~uare inch with each of the
microapertures having an area of about 30 square micrometers.
The hydrohead of the microapertured PVDC coated polyester
sheet was measured as being about 39 centimeters of water and
the wvtr of the microapertured PVDC coated polyester sheet was
measured as being about 141 grams per square meter per day.
~The wv~r measurement is an average of two measurements.) The
edge lsngth was calculated to increase a~out 380 percent.
EXAMPLF. II
The process of example I was repeated with the exception
that the actual amount of power consumed was indicated by the
Branson model A410A wattmeter was about 1,000 - 1,200 watts,
and a 120 by 12G mesh stainless steel fine mesh screen was
utilized. This example yielded a mlcrocracked PVDC coated
polyester sheet having a maximum den~ity of about 7,000
microcracks pex square inch. The hydrohead of this sample was
measured as being about 45 centimeters of water and the wvtr
was measured as being about 156 grams per square meter per
day. (The wvtr measurement i~ an average of two msasurements.)
The edge length of this sample was calculated to have
increased ab~ut 1,725 percent.
Figure IV is a photomicrograph of the thin PVDC coated
polyester sheek material microapertured in accordance with
Example II~
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EXAMPLE III
The process o~ Example I was repeated with the exception
that 4.0 mil thick J.PO Stevens Softlastic cros~-linked
natural rubber was used as the thermoset material. The cross-
linked natural rubber was elongated about 100 percent at the
time of hydrosonic treatment. Additionally, the line speed of
the cross-linked natural rubber sheet was 4.5 feet per minute
as compared to the 3.8 feet per minute utilized in Example I.
The actual amount of power consumed was indicated by the
Branson model A410A wattmeter as about 900 watts and a 120 by
120 mesh stainless steel fine mesh screen was utilizedO The
actua~ing pressure was about 6 pounds per s~uare inch, gauge.
This example yielded a microslit cross-linked natural rubber
sheet having a maximum density of about 7, ono microslits per
s~uare inch at 100 percent stretch. After remaoval of the
stretching force, the sample had about 14,000 microslits per
square inch. The hydrohead of this sample was measured as
being greater than 100 centimeters of water and the wvtr was
measured as being about 515 grams per square meter per day.
(The wvtr measurement is an average of two measurements.) The
edge length of this sample was calculated to have increased
about 4~0 percent.
EXAMPLE IV
The process of Example I was repeated with the exception
that 4.0 mil thick Stevens Softlastic cross-linked natural
:::. . ~ : .
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~373$~
rubber was used as the thermoset material. The cxoss-linked
natural rubber was elongated about 100 percent at the time of
hydrosonic treatment. Additionally, the line speed of the
cross-linked natural rubber sheet was about 4.9 feet per
minute as compared to the 3.8 feet per minute utilized in
Example I. The actual amount of power consumed was indicated
by the Branson model A410A wattmeter as about 1,100 watts and
a 120 by 120 mesh stainles~ steel fine mesh screen was
utilized. The actuating pressure was about 8 pounds per square
inch, gauge. This example yielded a microslit cross-linked
natural rubber sheet having a maximum density of about 7,000
microslits per quare inch. No hydrohead or water vapor
transmission testing of this sample was conducted.
EXAMPLE V ~ ;
The process of Example I was repeated with the exception
that 4.0 mil thick ~.P. Stevens Softlastic cross~linked
natural rubber was used as the thermoset material. The cross-
linked natural rubber was not elongated at the time of
hydrosonic treatment. Additionally, the line speed of the
cross-linked natural rubber sheet was about 8.2 feet per
minute as compared to the 3.8 feet per minute utilized in
Example I. The actual amount of power consumed was indicated
by the Bransun model A410A wattmeter as about 850 watts and
a 18 by 23 mesh phosphor/bronze screen was utilized. Each wire
of the screen in the MD was a twisted or braided arrangemPnt
of several smaller wires. The wires in the CD were singular.
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The actuating pressure was about 8 pounds per squaxe inch,
~auge.
This example yielded a microapertured cross-linked natural
rubber sheet having a maximum density of about 245
microapertures per square inch with each of the the
microapertures having an area of about 9,000 square
micrometers. The hydrohead of this sample was measured as 45
centimeters of water and the wvtr was measured as being about
188 grams per square meter per day. (The wvtr measurement is
an average of three measurements.) The edge length increase
was calculated to be about 1~0 percent.
Fiqure V is a photomicrograph of the material ~ormed by
the process of Example V, with the material being maintained
at about 100 percent stretch so that the presence of the
microslits can be demonstrated. The phntomicrograph is
accompanied by a scale where each unit represents ten (103
microns (micrometers).
EXAMPLE VI
The process of example I was repeated with the excaption
that 4 mil thick J.P. Stevens Softlastic material was used as
the sample, the sampla was stretched to about 100 percent
elongation during processing, the line speed was about 4 feet
per minute, the pattarn wire used was a 120 by 120 wires per
inch MD and CD fine mesh wire, the actuating pressure was
about 7 pounds per square inch and the watts consumed were
about 900.
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2~73~
This example yielded a microapertured sheet having a
maximum microaperture density of about 7,200 microapertures
per square inch with eac~ of the the microapertures having an
area of about 270 square micrometers at 100 percent stretch.
The hydrohead of this sample was measured as 98 centimeters
of water and the wvtr was measured as being about 562 grams
per square meter per day. The edge length increase was
calculated to be about 412 percent at 100 percent stretch.
Figure VI is a photomicrograph of the material of Example
VI both prior to processing and after processing.
Figura VII is a photomicrograph of the material of Example
VI after processing and while maintained at about 100 percent
elongation.
EX~LE_VII
The process of Example I was repeated with the exception
that 5 mil thick Dow Silastic cross-linked dimethyl siloxane
was used as the thermoset material. The cross-linked dimethyl
siloxane sheet was subjected to hydrosonic treatment eight
times at the conditions stated for Example I with the
exception that the line speed of the cross-lin~ed dimethyl
siloxane sheet was about 4.0 feet per minute as compared to
the 3.8 feet per minute utili~ed in Example I. The actuating
pressure was about 8 pounds per square inch, gauge.The actual
amount of power consumed was indicated by the Branson model
A410A wattmeter as about 800-1,000 watts and a 18 by 23 mesh
phosphor/bronze screen was utilized. Each wire of tha screen
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in the MD was a twisted or braided arrangemPnt of several
smaller wires. The wires in the CD were singular. Eight
processing passes were conducted.
This example yielded a microslit cross-linked dimethyl
siloxane sheet having a maximum density of about l,677
microapertures per square inch. The hydrohead of this sample
was measured as about 20 centimeters of water and the wvtr was
measured as being about 396 grams per square meter per day.
(The wvtr measurement is an average of three measurements.)
The edge length was calcualted to have increased about 275
percent.
The uses to which the microapertured, microslit or
microcracked thermoset sheet material of the present invention
may be put are numerous. Of course, any application which is
improved or otherwise enhanced if the edge length of the
thermoset sheet is increased is to be considered.
Additionally, for nonwater soluble materials, applications
where materials havin~ good wvtr values coupled with elevated
hydrohead values will present themselves. One such area of use
is in the filtration area. In particular, it ~hould be noted
that the materials of the present invention could well find
use in the packaging of food where water vapor breathability
coupled with product protection is desired. An example of an
area where increased edge length are beneficial is the areas
of biodegradability. When thin thermoset sheet materials have
been microapertured, microslit or microcracked in accordanc~
with the present invention, the edge length of the sheet
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materials is significantly increased. This incrase in edge
length is believed ~o dacrease the time it takes for the
material to be decomposed.
It i~ to be understood that variations and modifications
of the present invention may be made without departing from
the scope of the invention. For example, 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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