CA2057727A1

CA2057727A1 - Process for hydrosonically microaperturing thin sheet materials

Info

Publication number: CA2057727A1
Application number: CA002057727A
Authority: CA
Inventors: Lee Kirby Jameson; Bernard Cohen
Original assignee: Kimberly Clark Corp
Current assignee: Kimberly Clark Corp
Priority date: 1991-09-30
Filing date: 1991-12-16
Publication date: 1993-03-31
Also published as: US5269981A; TW237411B

Abstract

ABSTRACT OF THE DISCLOSURE
A method for forming microapertures in a thin sheet material where the area of each of the formed apertures generally ranges from about 10 square micrometers to 100,000 square micrometers is disclosed. The method includes the steps of (1) placing the sheet material on a pattern anvil having a pattern of raised areas wherein the height of the raised areas is greater than the thickness of the sheet material: (2) conveying the sheet material, while placed on the pattern anvil, through an area where a fluid is applied to the sheet material; and (3) subjecting the sheet material to a sufficient amount of ultrasonic vibrations in the area where the fluid is applied to the sheet material to microaperture the sheet material in a pattern generally the same as the pattern of raised areas on the pattern anvil.

Description

2~772~
RELATED APPLICATIONS

This application is one of a group of applications which are being ~iled on the same date. It should be noted that this group of applications includes U.S. patent application serial number 07/769,050 entitled "Hydrosonically Microapertured Thin Thermoset Sheet Materials" in the names of Lee K. Jameson and Bernard Cohen; U.S. patent application serial number 07/769.047 entitled "Hydrosonically Microapertured Thin Thermoplastic Sheet Materials" in the names of Bernard Cohen and Lee K. Jameson; U.S. patent application serial number 07/768 782 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" in the names of Bernard Cohen and Lee K. Jameson; U.S. patent application number 07/768~788 entitled "Hydrosonically Microapertured Thin Naturally Occurring Polymeric Sheet Materials and Method of Making the Same" in the names of Lee K. Jameson 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.S. patent application serial number 07/769.045 entitled "Process For Hydrosonically Microaperturing Thin Sheet Materials" in the names of Lee K.
Jameson and Bernard Cohen; and U.S. patent application serial number 07/767.727 entitled "Process For Hydrosonically Area 2~57727 Thinning Thin Sheet Materials" in the names of Bernard Cohen and Lee K. Jameson. All of these applications are hereby incorporated by reference.

FIELD OF THE_INVENTION

The field of the present invention encompasses processes for aperturing thin sheet materials 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) friction 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 2~7727 of wat~s per-- square centimeter~ Although_ the_ original_ ultrasonic power devices operated at radio frequencies, today most operate at 2~-69 kHz.
The piezoelectric sandwich-type transducer driven by anL
electronic power supply has emerged as the most com~on source of ultrasonic power: the overall efficiency of such equip~ent (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 Yibratoryr 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, U.S. patent-numbers 3,575,752 to Carpenter, 3,660,186 to Saqer 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 numbers 3,488,240 to Roberts, describes the use of ultrasonics to bond or weld thin films such as oriented polyesters.
Ultrasonic Corce has also been utilized to aperture nonwoven webs. See, for example, U.S. patent numbers 3,949,127 to Oster~çier et al. and 3,966,519 to Mitchell t al~.
Lastly, ultrasonic force has been used to aperture thin film material. See, for example, U. S. patent numker 3,756,880 to Gr~~Y~-2~77~7 Other-mekhods_fo~ the aperturing of thin film have been developed. For example, U.S. patent number 4,815,714 to Do~glas 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 difficulties and o~tacles in the use of-ultrasonic force in-the formation of apert~res in materials is the fact-that control of the a~ou~t 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. p~tent- 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 an aperture often resulted in a melt-through of the film.
As has previously been stated, those in the art had recognized that ultrasonics could be utilized to form 2~ 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 apertur~ formation in the web by fiber 2~7727 rearrangement and entanglement. The Mitchell et al. patent also states that, in its broadest aspects, since these effects are obtained primarily through physical movement of fibers, the method o~` their invention may be utilized to bond or increase the strength of a wide variety of fibrous webs.
While the discovery disclosed in the patent, no doubt, was an important contribution to the art, it clearly did not address the possibility of aperturing nonfibrous thin sheet materials or thin sheet materials having fibers in such a condition that they could not be moved or-rearranged. This fact is clear because the Mitchell et al.
patent clearly states the belief that the mechanism of aperture formation depended upon fiber rearrangement. of course, such thin sheet materials do not have fibers which can be rearranged. Accordingly, it can be stated with conviction that the applicability of a method for aperturing such thin sheet materials by the application of ultrasonic energy in conjunction with a fluid at the point of application of the ultrasonic energy to the sheet material was not contemplated by the Mi~chell et al. patent. Moreover, the Mitchell et al.
patent teaches away from sucn an application because the patent states the belief that aperture formation requires the presence of fibers to be rearranged.

DEFINI_IONS

As used herein the term "sheet material" refers to a generally nonporolas item that can be arranged in generally ~7727 planar configuration which, in an unapertured state, prior_to being modified in accordance with the present invention, has a hydrostatic pressure (hyd-ohead) of at least about lO0 inches of water when measured in accordance with Federal Test S Method N0. 5514, standard no. l91~. ~his term is aiso intended to include multilayer materials which include at least one such sheet as a layer thereof.
As used herein the term "thin sheet material" refers to a sheet material having an average thickness generally of less than about ten (10) mils. Average thickness is determined by randomly ~electing five (5) locations on a given sheet material, measuring the thickness of the sheet material at:
each location to the nearest 0.1 mil, and averaging the five values (sum of the five ~alues divided by five).
As used herein the term "mesh count" refers to the nl~mber 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 lOo wires per inch in the machine direction and 100 wires per inch in the cross machine direction would have a mesh count of lO,000 per square inch. As a result of the interweaving of these wires, raised areas are presant on both sides of the mesh screen. The number of raised areas on one side of such a wire mesh screen is generally one-half of the 2S mesh count.
As used herein the term "aperture" refers to a generally linear hole or passageway. Aperture is to be distinguished 2~7727 from and does not include_holes or passayeways having thQ_ greatly tortuous path or passageways found in membranes.
As used herein the term "microaperture" refers to an aperture which has an area o~ less than about lOO,OOo square micrometers. The area of the microaperture is to be measured at the narrowest point in the linear passageway or hole.
As used herein the term " ultrasonic vibrations" refers to vibrations having a freouency of at least about 20,000 cycles per secor.d. The frequency of the ultrasonic vibration~
10may ranqe from about 20,000 to about 400,000 cycles per second.
As used herein the terms "polymer" or "polymeric" refer~
to a macromolecule formed by the chemical union of five (S) or more identical combining units called monomers.
15As used herein the term "naturally occurring polymeric material" refers to a polymeric material which occurs naturally. The term is also meant to include materials, such as cellophane, which can be regenerated from naturally occurring materials, such as, in the case of cellophane, cellulose. Examples of such naturally occurring polymeric materials include, without limitation, (l) polysaccharides such as starch, cellulose, pectin, seaweed gums (such as agar, etc.), vegetable gums (such as arabic, etc.); (2) polypeptides; (3) hydrocar~ons such as rubber and gutta percha (polyisoprene) and (4) regenerated materials such as cellophane or chitosan.
As used herein the terms " me~al" or "metallic" refer to an element that forms positive ions when its compounds are in 2~57727 solution and whose oxides form hydroxldes rather than acids with water.
As used herein the term "thermoset material" refers to a high polymer that solidifies or "sets" irreversibly when heated. This property is almost invairably as ociated 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 tD a thermosetting material either by radiation or-by chemical reaction. A general discussion of cross-linking can be found at pages 331 to 414 of volume 4 of the Encyclopedia of Polymer Science and Technology, Plastics, Resins, Rubbers, Fibers published 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 "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. Another procedure for determining whether a material is cross-linked vel non is to reflux 0.4 2~577~7 ~ram 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 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 weight percent of the material remains upon conclusion of the second refluxing the material is considered to be cross-linked. 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 2300 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.
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.
As used herein the term "thermoplastic material" refers to a high polymer that softens when exposed to heat and returns to its original condition when cooled to roo~
temperature. Natural substances which exhibit this behavior are crude rubber and a number of waxes. Other exemplary thermoplasticmaterials include, withoutlimitation, polyvinyl 2~57727 chloride, polyesters, nylons, fluorocar~ons, linear polyethylene such as linear low density polyethylen~
polyurethaneprepolymer,polystyrene,polypropylene,polyvinyl alcohol, caprolactams, and cellulosic and acrylic recins.
As used herein the term "hydrosonics" refers to the application of ultrasonic vibrations to a material where the area of such application is has had a li~uid applied thereto to the extent that the liquid i~ present in sufficient-quantity to generally fill the gap between the tip of the ultrasonic horn and the surface of the material.

OBJECTS OP T~E INVENTION

Accordingly, it is a general object of the present invention to provide a process for microapert ring thin sheet materials in a qenerally 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. ~owever, it should be understood that the detailed description of the presently preferred embodiments of the present invention is given only by way of illustration because various changes and modifications well within the spirit and scope of the invention will become apparent to those of skill in the art-in view of this detailed description.

SuM~ARy OF THE INVE~TION

2~77~7 In response to the rorgoing problem~-a~ dif~icultie~_ encountered by those in the art-, we have developed a method-for forming microapertures in a thin sheet materlal having a thickne~s of about 10 mils or le88 where the area of each of the formed microapertures is generally greater than about 10 square micrometers. The method includes the steps of: (1) placing the thin sheet material on a pattern anvil having a pattern of raised areas where the height of the raised areas is greater than the thickness of the thin sheet material: (2) conveying the thin sheet material, while placed on the pattern anvil, through an area where a fluid is applied to the thin sheet material: and (3J subjecting the thin sheet material to-ultrasonic vibrations in the area where the fluid is applied to the thin sheet material. As a result of this method thQ
thin sheet material is microapertured in a pattern generally the same as the pattern of raised areas on the pattern anvil.
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 it may be desirable for the microaperturing of the thin sheet material to be confined to a predesignated area or areas of the thin sheet material.
This result may be obtained where only a portion of the thin sheet is subjected to ultrasonic vibrations. Alternatively, this result may be obtained where only a portion of the pattern anvil is provided with raised areas.

-~2-2~7727 THE FIGURES

Figure I is a schematic repxesentation of apparatus which may be utilizes ultrasonic vibrations to microaperture thin sheet materials.
Figure II is a cross sectional view of the transport mechanism for transporting the thin sheet material to the area where it is subjected to ultrasonic vibrations.
Figure III is a detailed view of the area where the thin 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 0.45 mil thick sheet of aluminum foil which has been microapertured in accordance with the pre~ent invention. The photomicrograph is accompanied by a scale where each unit repre~ents ten (10) microns (micrometers).
Figure V is a photomicrograph of a 0.8 mil thick cellulosic sheet which has been microapertured in accordance with the present invention. The photomicrograph is accompanied by a scale where each unit represents ten (10) microns (micrometers).
Figure VI is a photomicrograph of a 0.5 mil thick sheet-of polyethylene film which has been microapertured in accordance with the present invention. The photomicrograph is accompanied by a scale where each unit represents ten (10) microns (~icrometers).

2~77~7 Figure VII is a photomicrograph of a 0.5 mil th~ck PVDC
coated po~yes~er sheet which has been microapertured in accordance with the present invention. The photomicrograph is accompanied by a scale where each unit represents ten (10) microns (micrometers).

DE~AI~ED DESCRIP'rION 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 in~ention, it can be seen that the apparatus is generally represented by the reference numeral 10. In operation, a supply roll 12 of a thin sheet material 14 to be microapertured is provided. As has been previously stated, the term thin sheet material refers to sheet materials which have an average thickness of about ten (10) mils or less. Additionally, generally speaking, the average thickness of the thin sheet material 14 will be at least about 0.25 mil. For example, the average thickness of the thin sheet 14 material may range from about 0.25 mil to about 5 mils. More particularly, the average thickness of the thin sheet material 14 mày range from about 0.25 mil to about 2 mils. Even more specifically, the average thickness of the thin sheet material 14 may range from about 0.5 mil to about 1 mil.
The thin sheet material 14 may be formed from a thermoplastic film. The thermoplastic film may be formed from 2~772'7 a material selected from the group including one or more polyolefins, polyurethane , polyecters, A-B-A' bl~ck copolymers where A and A' are each a thermoplastic polymer endbloc~ which includes a styrenic moiety and where A may be--S the same thermoplastic polymer endblock as A', and where B isan elastomeric polymer midblock such a~s a conjugated diene or-a lower alkene or ethylene vinyl acetate copolymer. The polyolefin may be selected fxom the group including one or-more of linear low density polyethylene, polyethylene or polypropylene. The thermoplastic film may be a filled film with the filled film being selected form the group including a polyethylene film filed with starch, titanium dioxide, wax, carbon or calcium carbonate.
Alternatively, the sheet material may be a thermoset film.
The thermoset film may be formed from a material selected from the group including of one or more cross-linked polyesters, cross-linked natural rubber or cross-linked dimethyl siloxane.
In other embodiments the sheet material may be a metal.
For example, the metal may be selected from the group including aluminum, copper, gold, silver, zinc, lead, iron or-platinum.
In even further embodiments the sheet material may be a naturally occurring polymeric material. For example, the naturally occurring polymeric material may be is selected from the group including cellophane, cellulose acetate, collagen or carrageenan.

2~57727 Other-appropriate sheet--materials will-b~_apparent-t~_ those of skill in the art- af~er review of the present-disclosure.
The thin sheet material 14 is transported to a first nip 16 formed by a first transport roll 18 and a first nip roller 20 by the action of an endless transport mechanism 22 which mo~es in the direction indicated by the arrow 24. The_ transport mechanism 22 is driven by the rotation of the first-transport roller 18 in conjunction with a second transport-roller 26 which, in turn, are driven by a conventional powersource, 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 28 usually having a mesh count of less than about 400 (i.e. less than about 20 wires per inch by 20 wires per inch 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 of materials such as, for example, metals, plastics, nylons-or polyesters, and are readily available to those in the art.
Located above and attached to the transport-screen 28 is an endless flat shim plate 30. The shim plate 30 desirably is formed from stainles6 steel. However, 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 l~ast about 10,000 per square inch (i.e. at least a 100 l6-~7727 wire~-per M~ ch-.by-100 wires-per~CD inch me~h screen if MD
and CD-wir~-count is the same). Flne mesh wire screens of this type are readily available to those in the art. The fine mesh wire screen 32 ha~ raised areas or- ~nuckles 34 which preform the functlon of a pattern anvil as.will be discussed later.
Fr~m the- first nip 16 the thin sheet material 14 i8.
transported by the transport-mechanism 22 over a tension roll 36 to an-area 38 (defined in Figure I by the do~ted lined circle) where the thin sheet material 14 is subjected to ultrasonic vibrations.
The assembly for subjecting the thin sheet--material 14-to the.uLtr~sonic vibrations is conventional and is generally designated at 40. The assembly 40 includes a power supply 42 which, through a power control 44, supplies power to a piezoelectric transducer 46. As is well known in the art, the piezoelectric transducer 46 transforms electrical energy into mechanical movement as a result of the transducer's vibrating 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, the mechanicaL
movement booster 48 may be designed to increase the amplitude of the vibrations (mechanical movement) by a known factor:
depending 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 horr. 50. It should be realized that other types of ultrasonic horns 50 could be 2~7727 utilized. For example, a rotary type ultrasonic horn could be used. The ultrasonic horn 50 may be designed to effect yet-another boost or increase in the amplitude of the mechanical movement (vi~rations) which is to be applied to the thin sheet material 14. Lastly, the assembly includes an actuator 52 which includes a pneumatic cylinder, not shown. The actuator S2 provides a mechanism for raising and lowering the assembly 40 so that the tip 54 of the ultrasonic horn 50 can apply tension to the transport mechanism 22 upon the assembly 40 being lowered. It has been found that it is necessary to have some degree of tension applied to the transport mechanism 22 upon the lowering of the assembly for proper application of vibrational energy to the thin sheet material 14 to form microapertures in the thin 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 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 dagrees. More particularly, the angle 56 may range from about 9 to about 11 degrees.

2~772~
Figure III also illustrates that the transporcmechanism=
22 is supported from below oy the first tension roll 36-an~-a second tension roll 58. Positioned somewhat prior to the tip 54 of the ultrasonic horn S0 is a spray nozzle 60 which i5 configured to apply a fluid 62 to the surface of the thin shee~ 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 includin~ one or more of water, mineral oil, a chlorinated hydrocarbon, ethylene glycol or a solution of-50 volume percent water and 50 volume percent 2 propanol. For--example, in some em~odiments the chlorinated hydrocarhon may-be selected from the group including 1,1,1 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 subjected to a sufficient amount of the fluid 62 for the fluid 62 to act as both a heat sink and a coupling agent for the most desirable results.
Positioned below the transport mechanism 22 in the area where-the tip 54 of the ultrasonic horn S0 is located is a fluid_ collection tank 66. (See figure I.) The fluid collection tank 66 serves to collect fluid 62 which has been applied to the surface of the thin sheet material 14 and which has either been dri~en through the sheet material 14 and/or the transpo,t 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 _19_ 2~772~
collection tank--66 is transported-by-tuhing 68_to a fluid_ holding tank 70.
Figure I illustrates that the fluid holding tank 70 contains a pump 72 which, by way of additional tubing 74, supplies the fluid 62 to the fluid spray nozzle 60. According--ly, 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 be 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 tw~
separate and distinct functions. First, the presence of the fluid 62 allows the fluid 62 to act as a heat sink which lS allows the ultrasonic vibrations to be applied to the thin sheet material 14 without the thin 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 sheet-material 14.
It has been discovered that the action of the ultrasonic horn 50 on the thin sheet material 14 microapertures the thin sheet material 14 in spite of the fact that there are no fibers to re-arrange to form microapertures as was the case in Mitchell et al.. The microapertures are punched through the thin sheet material 14 in the pattern of the raised areas or-knuckles 34 of th~ fine mesh wire pattern screen 32.

2~7727 Gen~rally, th~-number-of microapertures-produced will be equal to the num~r of raised areas or knuckles 34 on the upper surface of the fine mesh wire screen 32. That is, the numbsr of microapertures will generally be one-half the mesh count of a given area of pattern screen 32. For example, if the pattern screen 32 is 100 wires per inch MD by 100 wires per inch CD, the total nu~ber of knuckles or raised areas 34 on one side of the pattern wire per squaxe inch 32 will be lO0 times 100 divided by 2. This equals 5,000 microapertures per square inch. For a 200 wires per inch MD by 200 wires per inch CD pattern screen 32 the calculation yields 20,000 m~croapertures per-square inch. Depending somewhat on the thickness of the thin 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 so thin as to allow the knuckle~ 34 on both sides to microaperture the thin sheet material 14 if sufficient force is applied. Thus, a 300 wires per inch MD by 300 wires psr 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 course the MD and CD wire count of the wire mesh screen does not have to be the same.
Also as a result of the microaperturing process the edge length of the thin sheet material may be increased by at leas~
about 100 percent as compared to the sheet's edge length prior to microaperturing. For example, the edge length of the thin sheet material may be increased by at least about 590 percent as compared to the sheet's edge length prior to 2~7727 microaper~uring. More particularly, the edge length of the thin sheet material may be increased by at least about 1,500 percent as compared to the sheet's edge len~th prior to microaperturing. Even more particularly, t~e edge length of the thin sheet material may be increased by at least about 3,000 percent as compared to the sheet's edge length prior to microaperturing.
It should al80 be noted that the number of microaperture~
formed may also vary with the number of ultrasonic vibrations to which the thin 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 sheet material 14 as it passes underneath the tip 54 of the ultrasonic horn 50. Generally speaking, as line speed increaseQ, 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. Th~ range of line speeds that usually yields microapertures varies with the material utilized to form the thln sheet material 14 and the material used as the fluid 62. For aluminum foil having a thickness of about o.45 mil, it- is believed that typical line speeds which should yield microapertures for a wide variety of fluids should range from about 5 to about 15 feet per minute. For example, if water is used as the fluid with aluminum foil typical line speeds which usually yield microapertures range from about 6 -2~-2~77~7 to about 9 ~eet per minute. If water is used as the fluid with 0.4 mil thick cross-linked natural rubber typical line speeds which usually yield microapertures range from about 3 to about 10 feet per mlnute. For cellophane having a thickness of about 0.8 mil, typical line speeds which usually yield microapertures for a wide variety of fluids range from about 4.5 to about 23.3 feet per minute. For example, if water is used as the fluid with cellophane typical line speeds which usually yield microapertures range from about 4 to about 5 feet per minute. For polyethylene having a thickness of about 0.5 mil, typical line speeds which usually yield microapertures for a wide variety of fluids range from about 5 to about 25 feet per minute. For example, if water is used as the fluid with polyethylene typical line speeds which usually yield microapertures range from about 5 to about 23 fëet per minute. It is believed that, to some extent, the variations in the number of microapertures formed and the size of the microapertures occurs due to the minute variations in the height of the raised areas or knuckles 34 of the fine mesh pattern screen 32. It should be noted that the fine mesh p~ttern screens used to date have been obtained from conventional everyday sources such as a hardware store. It is also believed that if a pattern screen 32 could be created where all of the raised areas 34 of the screen 32 were of exactly the same height these variations would only occur in uniform fashion with variations of line speed.
As was stated above, the area or size of each of the microapertures formed will also vary with the parameters 2~7727 discussed above. 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. It is believed that the t~pe of material used in forming the thin sheet material 14 will also vary the area of the microapertures formed if all other parameters are maintained the same. For example, the softer the thin sheet material 14, the easier it is to push the thin sheet material 14 through the raised areas of the fine mesh pattern 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 sheet material 14, the larger the microaperture. In such situations the shape of the microaperture will conform generally to the pyramidal shape of the raised area of the fine mesh screen and the microaperture will be generally pyramidally shaped, in the z direction, and will have an area which is greater at one end than at the other. As has been previously stated, the area of the microaperture should be measured at the narrowest point of the aperture. Of course, the height of the raised areas must be greater than the thickness of the thin sheet material 14 for microapertures to be formed and the degree of excess necessary may vary with the type of sheet material to be microapertured.
In some embodiments it may be necessary to subject the thin 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 ~77~7 initially only be thinned in the pattern--of the pattern-anvil's raised areas. However, after two or more passes=
through the apparatus 10, with the thin sheet material 14 being aligned in the same configuration with respect to the pattern an~il, yields microapertures. Essentially what is happening in these situations is that the thin sheet material 14 is repeatedly thinned by repeated application of ultrasonic vibrational force until such time as microapertures are formed. 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 increaseC the likelihood 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 sheet material 14. This can be accomplishedin a number of ways. For example, the thin sheet material 14-may be subjected to ultrasonic vibrations only at certain areas of the sheet material, thus, microaperturing would occur only in those areas. Alternatively, the entire thin sheet-material could be subjected to ultrasonic vibrations with thepattern anvil having raised areas only at certain locations and otherwise being flat. Accordingly, the thin sheet material 14 would be microapertured only in those areas which corresponded to areas on the pattern anvil having raised areas.
It should also be noted that some limitation exists in the number of microapertures which can be formed in a given thin sheet material 14 on a single application of vibrational 2~57~27 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 sheet material 14 in conjunctlon with the fact that, generally as the mesh count increases the height of the raised areas or knuckles decreases. In such situations, if the number of microapertures desired per unit area is greater than the number which can be formed in one pass through the apparatus, multiple passes are necessary with the alignmen~ of the thin 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 usually greater than about ten square micrometers. That is the area of each of the microapertures may range from at least about 10 square micrometers to about lOO,ooo square micrometers. For example, 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 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 at least about 10 square micrometers to about 100 square micrometers.
A number of important observations about the process may now be made. For example, it should be understood that the presence of the fluid 62 is highly important to the present 2~577~7 inventive-process which uses the fluid as a coupling agent.
Because a coupling agent is present, the microapertures are punched in the thin sheet material 14 as opposed to being formed by melting. The importance of the fluid 62 is further exemplified by the fact that the proce~s has been attempted without the use of ~he fluid 62 and was not generally successful. Additionally, the presence of the shim plate 30 or its equivalent is necessary in order to provide an anvil mechanism against which the thin sheet material 14 may be worked, that is apertured, by the action of the tip 54 of the ultrasonic horn 50. Because the vibrating tip 54 of the ultrasonic horn 50 is acting in a hammer and anvil manner when operated in conjunction with the 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 preform its function as an anvil and microaperturing generally does not occur. Because both the shim plate 30 and the fine mesh pattern wire 32 form the resistance that the ultrasonic horn 50 works against, they are collectively referred herein as a pattern anvil combination.
It should be easily recognized by those in the art that the function of the pattern anvil can be accomplished by other arrangements than the heavy duty wire mesh screen 28/shim plate 30/fine mesh screen 32 combination. For example, the pattern anvil could be a flat plate with raised portions 2~7727 acting to dixect the microaperturing force of th2 ultra~onic horn 50. Alternatively, the pattern anvil could be a-cylindrical roller having raised areas. If the patt~rn anvil is a cylindrical roller with raised areas, it is desirable for the pattern anvil to be wrapped or coated with or made from a re~ilient material. Where the pattern anvil is a mesh screen the resiliency is provided by the fact that the screen is unsupported directly below the point of application of ultrasonic vibrations to the mesh screen.
The invention will now be discussed with regard to specific examples which will aid those of skill in the art in a full and complete understanding thereof.

EXAMPLE I

A sheet of 0.45 mil thick aluminum foil having the trade desi~nation #01-213 was obtained from the Fischer Scientific Co. of Pittsburgh, Pennsylvania and was cut into a length of about ten (10) inches and a width of about three (3) inches.
The hydrohead of such aluminum foil prior to hydrosonic treatment has been measured as being greater than 137 centimeters of water. (This is the highest value obtainable with the equipment used.) The sample was subjected to hydrosonic treatment in accordance with the present invention.
A model 1120 power supply obtained from the Branson Company of Danbury, Connecticut, was utilized. This power supply, which has the capacity to deliver 1,300 watts of electrical energy, was used to convert 115 volt, 60 cycle 2~77~7 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 by a Branson model A410A wattme~er. This amount was about 900 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 mechanic~l 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 shaft with a length equal to one-half 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.
The output end of the booster was connected to an-ultrasonic horn obtained from the Branson Company. The hornin this example is made of titanium with a working face of about 9 inches by about 1/2 inch. The leading and trailing edges of the working face of the horn are each curved on a 2!3~7727 radius of a~out 1/8 inch. The horn step area_is exponential in shape and yield-~ about a two-fold increase in the-mechanical movement of the booster. That is, the horn step area has about a 1:2 gain ratio. The combined increase, by the booster and the horn step area, in the original mechanical movement created by the transducer yields a mechanical movement of about 4.0 micrometers.
The forming table arrangement included a small forming table which was utilized to transport and support the sheet of foil ~o be microapertured. The forming table included two 2-inch diameter idler rollers which were spaced about 12 inches apart on the surface of the forming table. A transport mefih 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 filaments. 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 of the horn contacts the sheet of aluminum foil which is to be microapertured. The actuator also raises the assembly so that the output end of the horn is removed from contact with the sheet of aluminum foil 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 2~7727 transport-mesh belt between the two idler rollers. An 8-inch wide 0.005-inch thick stainless steel shim stock having a length of about 60 inches was placed on the plastic mesh transport belt to provide a firm support for a pattern screen which is placed on top of the stainless steel shim. In this example the pattern screen is a 250 by 2S0 mesh wire size weave stainless steel screen. The sheet of aluminu~ foil 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 circulatinq system includes a fluid reservoir tank, a fluid circulating pump which may convenient-ly be locate~ within the tank, associated tubing for transpor-ting the fluid from the tank to a slotted boom which is designed to direct a curtain of fluid into the juncture of the output end of the horn and sheet of aluminum foil 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 10 to 15 degrees to the sheet of aluminum foil to be microapertured.
Accordingly, a wedge shaped chamber was formed between the output end of the horn and the sheet of aluminum foil to be microapertured. It is into this wedge shaped chamber that the fluid, in this example water at room temperature, is directed by the slotted boom.
It should be noted that the actuator was positioned at a height to insure that, when the assembly is lowered, the downward movement of the output end of the horn i5 stopped by 2~7727 the tension of the transport mesh ~efore the actuator reaches the limit of its stroke. In this example, actuating pressure was adjusted to 8 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 35.2 pounds. (8 psi times 4.4 square inches of piston area equals 35.2 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 sheet of aluminum foil was flooded with water;
(2) the transport mesh conveyor system was switched on and the aluminum foil started moving at 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 sheet lS of aluminum foil 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 fluid, the sheet of aluminum foil, the pattern wire, the shim stock, and the transport wire.
This example yielded a microapertured aluminum foil having a maximum microaperture density of about 30,000 microapertures per square inch with the microapertures having an area of about 1,800 square micrometers.
Figure IV is a photomicrograph of the thin aluminum foil sheet material apertured in accordance with example I.

2~7727 ExA~ U

The process of example I was repeated with the exception that a sheet of annealed copper having a thickness of about 0.1 mil was utilized as the thin sheet material. The line speed of the copper sheet was 4 feet per minute as compared to the 8 feet per minute utilized in example I. The actua~
amount of power consumed was indicated by the Branson model A410A wattmeter as about 1,000 watts. This example yielded a microapertured copper sheet having a maximum density of about-30,000 microapertures per square inch with the microapertures~
having an area which varied from about 20 to 1,000 square micrometers. Significant microaperture density variation was encountered in this example.

EXAMPLE III

The process of example I was repeated with the exception that tl) a 0.8 mil thick cellulosic sheet obtained under the, trade designation Flexel V-58 was used as the sheet; (2) the sheet was cut into a 8.5 by 11 inch sample: (3) about 775 watts were consumed; (4) a 120 by 120 stainless steel fine mesh screen was used: (5) a solution of 50 percent 2 propanol/50 percent water, by volume, was used as the fluid;

(6) the actuating pressure was about 7 pounds per square inch and (7) the line speed about 23.3 feet per minute.

20~7727 This example yielded a microapertured cellulosic sheet having a maximum microaperture density o~ about 7,000 microapertures per square inch with the microapertures having an area of about 40 square micxometers. The hydrohead of the microapertured cellulosic sheet was measured as being about 54 centimeters of water and the wvtr of the microapertured cellulosic sheet was measured as being about 219 grams per-square meter per day.
Figure V is a photomicrograph of the thin cellulosic sheet material microapertured in accordance with example III.

EXAMPLE IV

The process of example III was repeated with the exception that the line speed of the cellose sheet was 20.9 feet per minute as compared to the 23.3 feet per minute utilized in example III. The actual amount of power consumed was lndicated by the Branson model A410A wattmeter as about 750 watts. The actuating pressure was about 6 pounds per square inch, gauge.
This example yielded a microapertured cellulosic sheet having a maximum density of about 7,000 microapertures per square inch with the microapertures having an area of about 1,070 square micrometers. The hydrohead of this sample was measured as being about 22 centimeters of water and the wvtr was measured as being about 1,200 grams per square meter per day.
The edge length increase of the material was calculated as being 766%.

2~772~

EX~MP~ ~

The process of example I was repeated with the exception that (1) a 0.5 mil thick polyethylene film obtained from the Edison Company under the trade designation "S/E 702" was used as the sheet; (2) the sheet was cut into a 8.5 by 11 inch sample; (3) about 750 watts were consumed and (4) the line speed about 14.5 feet per minute.
This example yielded a microapertured polyethylene film having a maximum microaperture density of about 31,000 microapertures per square inch with the microapertures having an area of about 16 square micrometers. The average of three-hydrohead values of the microapertured polyethylene film was measured as being about 21 centimeters of water and the average of three wvtr values of the microapertured polyethylene film was measured as being about 1,385 grams per-square meter per day.
Figure VI is a photomicrograph of the thin polyethylene material microapertured in accordance with Example V.

EXAMPLE VI

The process of Example V was repeated with the exception that the line speed was 22 feet per minute and the watts consumed was about 800.
This example yielded a microapertured polyethylene film having a maximum microaperture density of about 31,000 microapertures per square inch with the microapertures having 2~37727 an area of about 15 square micrometers. The aVeragQ of three hydrohead values of the microapertured polyethylene film was about 28 centimeters of water and the averhge of three wvtr values of the microapertured polyethylene film was measured as being about 1,083 grams per square meter per day.

EX~LE VII

The process of example I was repeated with the exception that (1) a 0.5 mil thick polyester sheet coated on both sides with PVDC having the trade designation of Flexel Esterlock 50 was used as the sheet; (2) the sheet was cut into a 8.S by 11 inch sample; (3) about 1,100 watts were consumed; (4) a 200 by 200 stainless steel fine mesh screen was used; (5) the actuating pressure was about 10 pounds per square inch and (7) the line ~peed about 3.8 feet per minute.
This example yielded a microapertured PVDC coated sheet having a maximum microaperture density of about 20,000 microapertures per square inch with 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 wvtr measurement is an average of two measurements.) Figure VII is a photomicrograph of the thin PVDC coated polyester sheet material microapertured in accordance with Example VII.

2~7727 ILLUSTRATIVE EXAMPLE A

In order to illustrate the importance of the presence of the fluid as a coupling agent an illustrative example was run.
This example attempted to duplicate Example V with the exception that no fluid was provided to the area whers ultrasonic vibrations were being applied to the Edison polyethylene film. All process parameters of this illustrative example were the same as those of Example V with the exception that the line speed was seven (7) feet per minute and the actual amount of power consumed was indicated by the Branson model A410A wattmeter as about 800 watts.
Importantly, not only were no microapertures formed in the Edison polyethylene film and the film melted.

ILLUSTR~TIVE EXAMPLE B

In order to further illustrate the importance of the presence of the fluid as a coupling agent an illustrative example was run. This example attempted to duplicate example I with the exception that no fluid was provided to the area where ultrasonic vibrations were being applied to the aluminum foil. All process parameters of the illustrative example were the same as those of example I with the exception that the line speed was seven (7) feet per minute and the actual amount of power consumed was indicated by the Branson model A410A

2~7727 wattmeter as about 800 watts. Importantly, no microapertures were formed in the aluminum foil.

The uses to which the microapertured sheet material of the present invention may be put are numerous. An example of such is the area of f iltration. For example, the microapertured thin sheet material of the present invention can be utilized as a filtration media for collecting charged particulates or particles from fluids such as the air or water. The fluid would circulate through the microapertures of the thin sheet material which, if it was metallic, could be provided with a charge to assist in the collection of the charged particulate or particle. Conveniently, the filter could be cleaned by reversing the charge on the thin microapertured sheet material whereby the collected pàrticulates and/or particles would fall off of the thin sheet material. An example of where increase edge length would be important would be in the area of biodegradable sheet materials. If such sheet materials are microapertured in accordance with the present invention, the rate of biodegradation is increased as a result of the increased edge length~
It is to be understood that variations and modifications of the present invention may be made without departing from the scope of the invention. For 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 2~57727 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.

Claims

1. A method for forming microapertures in a thin sheet material having a thickness of about 10 mils or less wherein the area of each of the formed microapertures is generally greater than about 10 square micrometers, the method comprising the steps of:
(a) placing the thin sheet material on a pattern anvil having a pattern of raised areas wherein the height of the raised areas is greater than the thickness of the thin sheet material;
(b) conveying the thin sheet material, while placed on the pattern anvil, through an area where a fluid is applied to the thin sheet material; and (c) subjecting the thin sheet material to a sufficient amount of ultrasonic vibrations in the area where the fluid is applied to the thin sheet material to microaperture the thin sheet material; and whereby the thin sheet material is microapertured in a pattern generally the same as the pattern of raised areas on the pattern anvil.

2. The method of claim 1, wherein the fluid is selected from the group consisting of 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.

3. The method of claim 2, wherein the chlorinated hydrocarbon is selected form the group consisting of 1,1,1 trichloroethane or carbon tetrachloride.

4. The method 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.

5. The method 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.

6. The method of claim 1, wherein the area of each of the formed microapertures generally ranges from at least about 10 square micrometers to about 100 square micrometers.

7. The method of claim 1, wherein the thin sheet material is microapertured, with a microaperture density of at least about 5,000 microapertures per square inch.

8. The method of claim 1, wherein the thin sheet material is microapertured, with a microaperture density of at least about 20,000 microapertures per square inch.

9. The method of claim 1, wherein the thin sheet material is microapertured, with a microaperture density of at least-about 90,000 microapertures per square inch.

10. The method of claim 1, wherein the thin sheet material is microapertured, with a microaperture density of at least about 160,000 microapertures per square inch.

11. The method of claim 1, wherein the pattern anvil is a mesh screen.

12. The method of claim 1, wherein the pattern anvil is a flat-plate with raised areas.

13. The method of claim 1, wherein the pattern anvil is a cylindrical roller with raised areas.

14. The method of claim 1, wherein the thin sheet material is microapertured only in selected predesignated areas.

15. The method of claim 1, wherein the thin sheet material is subjected to at least to steps (b) and (c) more than one time.

16. A method for forming microapertures in a thin sheet material having a thickness of about 0.5 mil to about 5 mils wherein the area of each of the formed microapertures is generally greater than about 10 square micrometers, the method comprising the steps of:
placing the thin sheet material on a pattern anvil comprising:
a heavy duty wire mesh screen;
a shim plate; and a fine me h wire mesh screen a having a pattern of raised knuckles wherein the height of the raised knuckles is greater than the thickness of the thin sheet material;
conveying the thin sheet material, while placed on the fine mesh wire mesh screen, through an area where water is applied to the thin sheet material; and utilizing an ultrasonic horn to subject the thin sheet material to a sufficient amount of ultrasonic vibrations in the area where the water is applied to the thin sheet material to microaperture the thin sheet material ; and whereby the thin sheet material is microapertured with a microaperture density of at least about 100,000 microapertures per square inch in a pattern generally the same as the pattern of raised knuckles on the fine mesh wire mesh screen.

17. The method of claim 16, wherein the ultrasonic horn has a tip which is aligned, with respect to the thin sheet-material, at an angle of from about 5 degrees to about 15 degrees.

18. The method of claim 16, wherein the ultrasonic horn has a tip which is aligned, with respect to the thin sheet material, at an angle of from about 7 degrees to about 13 degrees.

19. The method of claim 16, wherein the ultrasonic horn has a tip which is aligned, with respect to the thin sheet material, at an angle of from about 9 degrees to about 11 degrees.

20. A method for forming microapertures in a thin sheet material having a thickness of about 0.25 mil to about 1 mil wherein the area of each of the formed microapertures is generally ranges from about 10 square micrometers to about 100 square micrometers, the method comprising the steps of:
placing the thin sheet material on a pattern anvil comprising:
a heavy duty wire mesh screen;
a shim plate; and a fine mesh wire mesh screen a having a pattern of raised knuckles wherein the height of the raised knuckles is greater than the thickness of the thin sheet material:
conveying the thin sheet material, while placed on the fine mesh wire mesh screen, through an area where water is applied to the thin sheet material; and utilizing an ultrasonic horn to subject the thin sheet material to a sufficient amount of ultrasonic vibrations in the area where the water is applied to the thin sheet material to microaperture the thin sheet material ; and whereby the thin sheet material is microapertured with a microaperture density of at least about 100,000 microapertures per square inch in a pattern generally the same as the pattern of raised knuckles on the fine mesh wire mesh screen.

21. The method of claim 20, wherein the ultrasonic horn has a tip which is aligned, with respect to the thin sheet material, at an angle of from about 5 degrees to about 15 degrees.