CA2057366A1 - Hydrosonically micrapertured thin thermoset sheet materials - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A microapertured thin thermoset sheet material is disclosed.

Description

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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 : ' ' , ' :~a 7~ ~
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 2~7~

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 -S--~ , ~ : .

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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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2~73~6 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 ~, 2~73~
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 , ~73~
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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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, -lg-.
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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 : ' .. , ~

2 ~ ~ 7 3 ~ 6 , 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 .

' "' ''' ' ' ' " '.' ~ 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 2~7~
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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 ~7~66 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 .

, '' :, ';' ~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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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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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.

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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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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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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Claims (30)

1. THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
   PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
   
   l. A microapertured thin thermoset sheet material, said thin thermoset sheet material having at least about 1,000 microapertures per square inch.
2. 2. The microapertured thin thermoset sheet material according to claim 1, having at least about 5,000 microapertures per square inch.
3. 3. The microapertured thin thermoset sheet material according to claim l, having at least about 20,000 microapertures per square inch.
4. 4. The microapertured thin thermoset sheet material according to claim 1, having at least about 90,000 microapertures per square inch.
5. 5. The microapertured thin thermoset sheet material according to claim 1, having at least about 160,000 microapertures per square inch.
6. 6. The microapertured thin thermoset sheet material according to claim 1, wherein the edge length of the sheet material is at least 100 percent greater than the edge length of the thin thermoset sheet material prior to microaperturing.
7. 7. The microapertured thin thermoset sheet material according to claim 1, wherein the edge length of the sheet material is at least 500 percent greater than the edge length of the thin thermoset sheet material prior to microaperturing.
8. 8. The microapertured thin thermoset sheet material according to claim 1, wherein the edge length of the sheet material is at least 1,500 percent greater than the edge length of the thin thermoset sheet material prior to microaperturing.
9. 9. The microapertured thin thermoset sheet material according to claim 1, wherein the edge length of the sheet material is at least 3,000 percent greater than the edge length of the thin thermoset sheet material prior to microaperturing.
10. 10. The microapertured thin thermoset sheet material of claim 1, wherein the average thickness of the thermoset sheet material is at least about 0.25 mil.
11. 11. The microapertured thin thermoset sheet material of claim 1, wherein the average thickness of the thermoset sheet material is from about 0.25 mil to about 5 mils.
12. 12. The microapertured thin thermoset sheet material of claim 1, wherein the average thickness of the thermoset sheet material is from about 0.25 mil to about 2 mils.
13. 13. The microapertured thin thermoset sheet material of claim 1, wherein the average thickness of the thermoset sheet material is from about 0.5 mil to about 1 mil.
14. 14. The microapertured thin thermoset sheet material of claim 1, wherein the area of each of the formed microapertures generally ranges from at least about 10 square micrometers to about 100,000 square micrometers.
15. 15. The microapertured thin thermoset sheet material of claim 1, wherein the area of each of the formed microapertures generally ranges from at least about 10 square micrometers to about 10,000 square micrometers.
16. 16. The microapertured thin thermoset sheet material of claim 1, wherein the area of each of the formed microapertures generally ranges from at least about 10 square micrometers to about 5,000 square micrometers.
17. 17. The microapertured thin thermoset sheet material of claim 1, wherein the area of each of the formed microapertures generally ranges from at least about 10 square micrometers to about 1,000 square micrometers.
18. 18. The microapertured thin thermoset sheet material of claim 1, wherein the microaperturing is confined to a predesignated area or areas of the thin thermoset sheet material.
19. 19. The microapertured thin thermoset sheet material of claim 1, wherein the thermoset material is a water insoluble material and the hydrohead of the sheet material is at least about 35 centimeters of water.
20. 20. The microapertured thin thermoset sheet material of claim 1, wherein the thermoset material is a water insoluble material and the hydrohead of the sheet material is at least about 45 centimeters of water.
21. 21. The microapertured thin thermoset sheet material of claim 1, wherein the thermoset material is a water insoluble material and the hydrohead of the sheet material is at least about 55 centimeters of water.
22. 22. The microapertured thin thermoset sheet material of claim 1, wherein the thermoset material is a water insoluble material and the water vapor transmission rate of the sheet material is at least about 200 grams per square meter per day.
23. 23. The microapertured thin thermoset sheet material of claim 1, wherein the thermoset material is a water insoluble material and the water vapor transmission rate of the sheet material is at least about 500 grams per square meter per day.
24. 24. The microapertured thin thermoset sheet material of claim 1, wherein the thermoset material is a water insoluble material and the water vapor transmission rate of the sheet material is at least about 1,000 grams per square meter per day.
25. 25. The microapertured thin thermoset sheet material of claim 1, wherein the thermoset material is selected from one or more of the group consisting of cross-linked natural rubber, cross-linked polyesters or cross-linked organosilicon polymers.
26. 26. Them microapertured thin thermoset sheet material of claim 25, wherein the cross-linked organosilicon polymer is cross-linked dimethyl siloxane.
27. 27. The microapertured thin thermoset sheet material of claim 1, wherein the microapertures are microslits.
28. 28. The microapertured thin thermoset sheet material of claim 1, wherein the microapertures are microcracks.
29. 29. A microapertured, substantially water insoluble, thin, thermoset sheet material having a thickness of about 1 mil or less, said sheet material having:
    an edge length which is at least 500 percent greater than the edge length of the thin thermoset sheet material prior to microaperturing;
    a microaperture density of at least about 100,000 microapertures per square inch;
    a hydrohead of at least about 75 ;
    a water vapor transmission rate of at least about 200;
    and wherein the area of each of said microapertures ranges generally from greater than about 10 square micrometers to less than about 1,000 square micrometers.
30. 30. A microapertured, substantially water insoluble, thin, thermoset sheet material having a thickness of about 1 mil or less, said sheet material having:
    an edge length which is at least 500 percent greater than the edge length of the thin thermoset sheet material prior to microaperturing;
    a microaperture density of at least about 100,000 microapertures per square inch;
    a hydrohead of at least about 75;
    a water vapor transmission rate of at least about 200;
    and wherein the area of each of said microapertures ranges generally from greater than about 10 square micrometers to less than about 100 square micrometers.