CA2057695A1 - Hydrosonically microapertured thin naturally occurring polymeric sheet materials and method of making the same - Google Patents
Hydrosonically microapertured thin naturally occurring polymeric sheet materials and method of making the sameInfo
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- CA2057695A1 CA2057695A1 CA 2057695 CA2057695A CA2057695A1 CA 2057695 A1 CA2057695 A1 CA 2057695A1 CA 2057695 CA2057695 CA 2057695 CA 2057695 A CA2057695 A CA 2057695A CA 2057695 A1 CA2057695 A1 CA 2057695A1
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- naturally occurring
- sheet material
- occurring polymeric
- polymeric sheet
- thin
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Abstract
ABSTRACT OF THE DISCLOSURE
A microapertured thin naturally occurring polymeric sheet material is disclosed.
A microapertured thin naturally occurring polymeric 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 07/769 050 entitled "Hydrosonically Microapertured Thin Thermoset Sheet Materials" in the names o~ Lee K. Jameson and Bernard Cohen; U.S. patent application serial number 07/769,047 entitled "Hydrosonically Microapertured Thin Thermoplastic Sheet Materials" in the names of Bernard Cohen and Lee K. Jameson; U.S. patent application serial number 07/768 1 2 entitled l'Pressure Sensitive Valve System and Process For Forming Said Systeml' in the names of Lee K.
Jameson and Bernard Cohen; U.S. patent application serial number 071768 494 entitled " Hydrosonically Embadded Soft Thin Film Materials and Process For Forming Said Materials" in the names of Bernard Cohen and Lee K. Jameson; UOS~ patent application number 071768.788 entitled "Hydrosonically Microapertured Thin Naturally Occurring Polymeric Sheet Materials and Method of Making the Same" in the names o~ Lee K. Jameson and Bernard Cohen; U.S. patent application serial number 071769 048 entitled "Hydrosonically Microapertured Thin Metallic Sheet Mateials" in the names of Bernard Cohen and Lee K. Jameson; U.S. patent application serial number 07/769,045 entitled "Process For Hydrosonically Microaperturing Thin Sheet ~aterials" in the names of Lee K. Jameson and Bernard Cohen; and U.S. patent application serial number 07/767 727 entitled "Process For Hydrosonically Area Thinning Thin Sheet ~,: .,.,: . - , .. . .
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Materials" in the names of Bernard Cohen and Lee K. Jameson.
All of these applications are hereby incorporated by reference~
FIELD OF THE INVENTION
The field of the present invention encompasses thin sheets formed from naturally occurring polymeric materials which have been microapertured in a generally uniform pattern.
BACKGROUND OF THE INVENTION
Ultrasonics is basically the science of the effects of sound vibrations beyond the limit of audible frequencies.
Ultrasonics has be n used in a wide variety of applications.
For example, ultrasonics has been used for (1) dust, smoke and mist precipitation; (2) preparation of colloidal dispersions;
RELATED APPLICATIONS
This application is one of a group of applications which are being filed on the same date. It should be noted that this group of applications includes U.S. patent application serial number 07/769 050 entitled "Hydrosonically Microapertured Thin Thermoset Sheet Materials" in the names o~ Lee K. Jameson and Bernard Cohen; U.S. patent application serial number 07/769,047 entitled "Hydrosonically Microapertured Thin Thermoplastic Sheet Materials" in the names of Bernard Cohen and Lee K. Jameson; U.S. patent application serial number 07/768 1 2 entitled l'Pressure Sensitive Valve System and Process For Forming Said Systeml' in the names of Lee K.
Jameson and Bernard Cohen; U.S. patent application serial number 071768 494 entitled " Hydrosonically Embadded Soft Thin Film Materials and Process For Forming Said Materials" in the names of Bernard Cohen and Lee K. Jameson; UOS~ patent application number 071768.788 entitled "Hydrosonically Microapertured Thin Naturally Occurring Polymeric Sheet Materials and Method of Making the Same" in the names o~ Lee K. Jameson and Bernard Cohen; U.S. patent application serial number 071769 048 entitled "Hydrosonically Microapertured Thin Metallic Sheet Mateials" in the names of Bernard Cohen and Lee K. Jameson; U.S. patent application serial number 07/769,045 entitled "Process For Hydrosonically Microaperturing Thin Sheet ~aterials" in the names of Lee K. Jameson and Bernard Cohen; and U.S. patent application serial number 07/767 727 entitled "Process For Hydrosonically Area Thinning Thin Sheet ~,: .,.,: . - , .. . .
., .. . .
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Materials" in the names of Bernard Cohen and Lee K. Jameson.
All of these applications are hereby incorporated by reference~
FIELD OF THE INVENTION
The field of the present invention encompasses thin sheets formed from naturally occurring polymeric materials which have been microapertured in a generally uniform pattern.
BACKGROUND OF THE INVENTION
Ultrasonics is basically the science of the effects of sound vibrations beyond the limit of audible frequencies.
Ultrasonics has be n used in a wide variety of applications.
For example, ultrasonics has been used for (1) dust, smoke and mist precipitation; (2) preparation of colloidal dispersions;
(3) cleaning of metal parts and fabrics; (4) friction welding;
(5) the formation of catalysts; ~6) the degassing and solidification of molten metals; (7) the extraction of flavor oils in brewing; (8) electroplatingi (9) drilling hard materials; (10) fluxless soldering and (lo) nondestructive testing such as in diagnostic medicine.
The object of high power ultrasonic applications is to bring about some permanent physical change in the material treated. This process requires the flow of vibratory power per unit of area or volume. Depending on the application, the power density may range from less than a watt to thousands , ~ ', ,' : ~; ' , ' of watts per square c~ntimeter. Although the original ultrasonic power devices operatPd at radio frequencies, today most operate at 20-69 kHz~
The piezoelectric sandwich-type tra~sducer driven by an electronic power supply has emerged as the most common source o~ ultrasonic power; the overall e~ficiency of such equip~ent (net acoustic power per electric-line power) is typically greater than 70%. The maximum power from a conv~ntional transd~cer is inversely proportional to the sguare of the frequency~ Some applications, such as cleaning, may have many transducers working into a common load.
Other, more particular areas where ultrasonic vibratory force has been utilized are in the areas of thin nonwoven webs and thin films. For example, ultrasonic force has been use to bond or weld nonwoven webs. See, for Pxample, U.S. patent nu~hers 3~575,752 to Carpenter, 3,660,186 to Saqer et al., 3,9~6,519 to Mitchell et al. and 4,6g5,454 to Sayo~itz_et al.
which disclose the usa of ultrasonics to bond or weld nonwoven webs. U.S. patent nu~bers 3,488,240 to Roberts, describes the use of ultrasonics to bond or weld thin films such as oriented polyesters.
Ultrasonic force has also been utilized to aperture nonwoven webs. See, for example, U.S. patent nu~bers 3,949,127 to Oste~eier ~_~1~ and, 3,966,519 to Mitchell et al..
Lastly, ultrasonic force has been used to aperture thin ~ilm material. See, for example, U. S. patent number 3,756,880 to Graczyk.
~ ' ' ' ' ' Other methods for the aperturin~ of thin film have been developed. For examplP, U.S. patent number 4,815,714 to Douqlas discusses the aperturing of a thin film by first abrading ~he film, which is in filled and unoriented form, and then subjecting the film to corona discharge treatment.
one of the di~ficulties and obstacles in the use of ultrasonic force in the formation of apertures in materials is the fact that control of the amount of force which is applied was difficult. This lack of control resulted in the limitation of ultrasonic force to form large apertures as opposed to small microapertures. Such an application is discussed in U.K. patent application number 2,124,134 to Blair. one of the possible reasons that ultrasonics has not found satisfactory acceptance in the area of microap rture formation is that the amount of vibrational energy required to form a microaperture often resulted in a melt-through of the film.
As has previously been stated, those in the art had recognized that ultrasonics could be utilized to form apertures in nonwoven webs. See, U.S. patent to Mitchell,_et al.. ~dditionally, the Mitchell et al. patent discloses that the amount of ultrasonic energy being subjected to a nonwoven web could be controlled by applying enough of a fluid to the area at which the ultrasonic energy was being applied to the nonwoven web so that the fluid was present in uncombined form~
Importantly, the Mitchell et al. patent states that the fluid is moved by the action of the ultrasonic force within the nonwoven web to cause aperture formation in the web by fiber "
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~7~:3 rearrangement and entanglement. The Mitchell et al. patent also states that, in its broadest aspects, since these effects are obtained primarily through physical movement of fibers, the method of their invention may be utilized to bond or increase the streng~h of a wide varisty of fibrous webs.
While the discovery disclosed in the itchell et al.
patent, no doubt, was an important contribution to the art, it clearly did not address the possibility of aperturing nonfibrous sheets or sheets having fixed fibers formed from naturally occurring polym~ric materials. This fact is clear b~cause the Mitchell et al. patent clearly states the belief that the mechanism of aperture formation depended upon fiber rearrangement. of cour~e, such sheet materials either do not have fibers or have fibers which are in such a condition that they cannot be rearranged. Accordingly, it can be stated with conviction that the applicability of a method for aperturing naturally occurring polymeric sheet materials by the application of ultrasonic energy in c:onjunction with a fluid at the point of application of the ultrasonic energy to the naturally occurring polymeric sheet material was not contemplated by the Mitchell et al. patent. Moreover, the Mitchell et a~l~patent teaches away from such an application because the patent states the belief that aperture formation requires the presence of movable fibers to be rearranged.
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As used herein the terms l'polymer" or "polymeric" refer to a macromolecule formed by the chemical union of five (5) or more identical combining units called monomers.
As used herein the term "naturally occurring polymeric material" refers to a polymeric material which occurs naturally. The term is also meant to include materials, such as cellophane, which can be regenerated from naturally occurring materials, such as, in the case of cellophane, cellulose. Examples of such naturally occurring polymeric materials include, without limitation, (1) polysaccharides such as starch, cellulose, pectin, seaweed gums (such as agar, etc.), vegetable gums (such as arabic, etc.); (2) polypeptides; (3) hydrocarbons such as rubber and gutta percha (polyisoprene) and (4~ regenerated materials such as cellophane or chitosan. Of course, the term "naturally occurring polymeric material" is also meant to inclu~e mixtures and combinations of two or more naturally occurring polymeric materials as well as mixtures and combinations which include at least fifty (50) percent, by weight, naturally occurring polymeric materials.
As used herein the term "n~turally occurring polymeric sheet material" refers to a gen~rally nonporous item formed from a naturally occurring polymeric material that can be arranged in generally planar configuration. If the material is not a water soluble material, the material, in an unapertured state prior to being modified in accordance with the present invention, ha~ a hydrostatic pressure (hydrohead) of at least about 100 centimeters of water when measured in :. , .: , . . . .
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accordance wiih Federal Test Method NO. 5514, standard no.
l91A. Unless otherwise stated herein all hydrohead values are obtained in accordance with Federal Test Method NO. 5514, standard no 191~. This term i8 also intended to include multilayer materials which include at least one such sheet of a naturally occurring polymeric material as a layer thereof.
It should be noted that the material does not have to occur naturally in sheet form, rather it is the components of the sheet that are l'naturally occurring". Gf course, if the naturally occurring polymeric material is water soluble, hydrohead measurements have little, if any meaning.
As used herein the term "thin naturally occurring polymeric sheet material" refers to a naturally occurring polymeric sheet material having an average thickness generally of less than about ten (10) mils. Averags thickness is determined by randomly selecting five ~5) locations on a given sheet material, mPasuring the thickness of the sheet material at each location to the nearest 0.1 mil, and averaging ths five values (sum of the fi~e values clivided by five).
As used herein the term water vapor transmission rate ref~rs to the rate water vapor will pass through a water insoluble sheet material under a given set of conditions in a particular time period. Unless otherwise specified, water vapor transmission rate is measured in accordance with ASTM
E 96-80 using the water method referenced at paragraph 3.2 thereof. The test is run at 90 degrees fahrenheit and 50 percent relative humidity for twenty-four (24) hours.
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As used herein the t rm "mesh count" refers to the number which is the product of the number of wires ln a wire mesh screen in both the machine (MD) and cross-machine (CD) directions in a given unit area. For example, a wire mesh screen having 100 wires per inch in the machine direction and 100 wires per inch in the cross machine direction would have a mesh count o~ 10,000 per square inch. As a result of the interweaving of these wires, raised areas are present on both sides of the mesh screen. The number of raised areas on one side of such a wire mesh scre~n is genexally one-half of the mesh count.
As used herein the term "aperture" refers to a generally linear hole or passageway. Aperture is to be distinguished from and does not include holes or passageways having the greatly tortuous path or passageways found in membranes.
As used herein the term "microaperture" r~fers to an aperture which has an area of less than about 100,000 square micrometers. The area of the microape:rature is to be measured at the narrowest point in the linear passageway or hole.
As used h~rein the term "ultrasonic vibrations" refers to vibrations having a frequency of at least about 20,000 cycles per second. The frequency of the ultrasonic vibrations may range from about 20,000 to about 400,000 cycles per second or more.
As used herein the term "hydrosonics" refers to the application of ultrasonic vibrations to a material where the area of such application is has had a liquid applied thereto to the extent that the liquid is present in sufficient 2 ~
quantity to generally fill the ~ap between the tip of th ultrasonic horn and the surface of the material.
The approximate edge length of the thin microapertured thermoplastic sheet material of the present invention is calculated from the size of the microaperture using the appropriate geometrical formula, depending upon th~
microaperture's general shap2.
OBJECTS OF TH~__NVENTION
Accordingly, it is a general object of the present invention to provide thin naturally occurring polymeric sheet materials which have been microapertured in a generally uniform pattern Still further objects and the broad scope of applicability of the present invention will beco~e apparent to those of skill in the art from the details given hereinafter. However, it should be understood that the detailed description of the presently preferred embodiments of the present invention is given only by way of illustration because various changes and modifications well within the spirit and scope of the invention will become apparent to those of skill in the art in view of this detailed description.
SUMMARY OF THE INVENTION
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In response to the foregoing problems and difficulties encountered by those in the art, we have developed a method for foxming microapertures in a thin naturally occurring polymeric sheet material having a thickness o~ about 10 mils or less where the area of each of the formed microapertures is generally greater than about 10 square micrometers. The method include.s the steps of: (1) placing the thin naturally occurring polymeric sheet material on a pattern anvil having a pattern of raised areas where the height of the raised areas is greater than the thickness of the thin naturally occurring polymeric sheet material; (2) conveying the thin naturally occurring polymeric sheet material, while placed on the pattern anvil, through an area where a fluid is applied to the thin naturally occurring polymeric sheet material; and (3) subjecting the thin naturally occurring polymeric sheet material to ultrasonic ~ibrations in the area where the fluid is applied to the thin naturally occurring polymeric sheet material. As a resul~ of this method the thin naturally occurring polymeric sheet material is microapertured in a pattern generally the same as the pattern of raised areas on the pattern anvil.
The thin naturally occurring polymeric sheet material may be formed rom, for example, cellophane, cellulose acetate, collagen or carrageenan.
The fluid may be selected from the group including one or more of water, mineral oil, a chlorinated hydrocarbon, ethylene glycol or a solution of 50 volume percent water and .:
: ' 2 ~ ~ 7 ~ 9 r~3 50 volume percent 2 propanol. The chlorinated hydrocarbon may be 1,1,1 trichloroethane or carbon tetrachloride.
In some embodiments, the area of each of the formed microapertures may generally range from at least ahout 10 square micrometers to a~out 100,000 square micrometers. For example, the area of each of the formed microapertures may generally range from at least about 10 square micrometers to about 5,000 square micrometers. Mor~ particularly, the area of each of the formed microapertuxes may generally range from at least about 10 square micrometers to about 1,000 square micrometers. Even more particularly, the area of each of the for~ed microapertures may generally range from about at least 10 square micrometers to about 100 square micrometers.
The thin naturally occurring polymeric sheet material may be microapertured with a microaperture density of at least about 1,000 microapertures per square inch. For example, the thin naturally occurring polymeric sheet material may be microapertured with a microaperture d~ensity of at least about 5,000 microapertures per square inch. More particularly, the thin naturally occurring polymeric sheet material may be microapertured with a microaperture density o~ at least about 20,000 microapertures per square inch. Even more particularly, the thin naturally occurring polymeric sheet material may be microapertured with a microaperture density of at least about 90,000 microapertures per square inch. Yet even more particularly, the thin naturally occurring polymeric sheet material may be microapertured with a microaperture density of at least about 160,000 microapertures per square inch.
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The pattern anvil may, for example, be a mesh screen with knuckles serving as raised areas, a flat plate with raised areas or a cylindrical roller with raised areas. If the pattern anvil is a cylindrical roller with raised areas, it is desirable for the pattern anvil to be wrapped or coated with or made from a resilient material. Where the pattern anvil is a mesh screen the resiliency is provided by the fact that the screen is unsupported directly below the point of application of ultrasonic vibrations tn the mesh screen.
In some embodiments it may be desirable to subject the thin naturally occurring polymeric sheet material to multiple passes through the microaperturing area so that at least steps (b~ and (c~ are performed more than once on the thin naturally occurring polymeric sheet material. To attain an microaperture density which is greater that the number of raised areas on the pattern anvil, the thin naturally occurring polymeric sheet material may be moved slightly between passes.
In some embodiments it may be desirable for the microaperturing of the thin naturally occurring polymeric sheet material to be confined to a predesignated area or areas of the thin naturally occurring polymeric sheet material. This result may be obtained where only a portion of the thin naturally occurring polymeric sheet is subjected to ultrasonic vibrations. Alternatively, this result may be obtained where only a portion of the pattern anvil is provided with raised areas.
The thickness of the thin naturally occurring polymeric sheet material is at least about 0.25 mil. For example, the . - ,,, . ~ : :
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thicXness of the thin naturally occurring polymeric shee~
material may range from about 0.25 mil to about 5 mils. More particularly, the thickness of the thin naturally occurring polymeric sheet material may range from about 0.25 mil to about 2 mils. Even more particularly, the thickne9s of the thin naturally occurring polymeric sheet material may range from about 0.5 mil to about 1 mil.
If it is not a water soluble material, the hydrohead of the thin naturally occurring polymeric sheet material may be measured and may range from at least about 15 centimeters of water. For example, the hydrohead of the thin naturally occurring pol~meric shePt material may ran~e from at least about 35 centimeters of water. More particularly, the hydrohead ~f the thin naturally occurring polymeric sheet material may range from at least about 45 centimeters of water. Even more particularly, the hydrohead of the thin naturally occurring polymeric sheet material may range from at lea~t about 55 centimeters of water. Yet even more particularly, the hydrohead of the thin naturally occl~rring polymeric sheet material may range from at least about 7 centimeters of water.
If it is not a water soluble material, the water vapor transmission rate of the thin naturally occurring polymeric sheet material may range from at least about 200 grams per square meter per day. For example, the water vapor transmission rate of the thin naturally occurring polymeric sheet material may range from at lea~t about 500 grams per square meter per day. Even more particularly, the water vapor trans~ission rate of the thin naturally occurring polymeric sheet material may range from at least about 1,000 grams per square meter per day. Yet even more particularly, tha water vapor transmission rate of the thin naturally occurring polymeric sheet material may range from at least about 1,500 grams per square meter per day.
As a result of the microaperturing process the edge length of the thin naturally occurring polymeric sheet material may be increased by at least about 100 percent as compared to the sheet's edge length prior to microaperturing. For example, the edge length of the thin naturally occurring polymeric sheet material may be increased by at least about 500 percent as compared to the sheet's edge length prior to microaperturing.
More particularly, the edge length of the thin naturally occurring polymeric sheet material may be increased by at least about 1,500 percent as compared to the sheet's edgc length prior to microaperturing. Even more particularly, the edge length o~ the thin naturally occurring polymeric sheet material may be increased by at least about 3,000 percent as compared to the sheet's edge length prior to microaperturing.
THE FIGURES
Figure I is a schematic representation of apparatus which utilizes ultrasonic vibrations to microaperture thin naturally occurring polymeric sheet materials.
Figure II is a cross sectional view of the transport mechanism for transporting the thin naturally occurring . ., ; . . : , :
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poly~eric sheet material to the area where it is subjected to ultras~nic vibrations.
Fi~ure III is a detailed view of the area where the thin naturally occurring polymeric sheet material is subjected to ultrasonic vibrations. The area is designated by the dotted circle in figure Io Figure IV is a photomicrograph of a 0.8 mil thick sheet of cellophane obtained under the trade name "Flexel V-58, which has been microapertured in accordance with the present invention. The photomicrograph is accompanied by a scale where each unit on the scale represents ten microns (micrometers).
DE'rAILED DESCRIPTION OF THE INVENTION
Turning now to the figures where like reference numerals represent like structure and, in particular to Figure I which is a schematic representation of an apparatus which can carry out the method of the present inventi.on, it can be seen that the apparatus is generally represented by the reference numeral 10. In operation, a upply roll 12 o~ a thin naturally occurring polym~ric sheet material 14 to be microapertured is provided. As has been previously stated, the term thin naturally occurring polymeric sheet material refers to shee materials which have an average thickn~ss of about ten (10) mils or less. Additionally, generally speaking, the average thickness of the thin naturally occurring polymeric sheet material 14 will be at least about 0.25 mil. For example, the average thickness of the thin naturally occurring polymeric 2~7~
sheet 14 material may range from about 0.25 mil to about 5 mils. ~ore particularly, the average thickness of the thin naturally occurring polymeric sheet material 14 may range from about 0.25 mil ~o about 2 mils. Even more specifically, the average thickness of the thin naturally occurring polymeric sheet material 14 may range from about 0.5 mil to about 1 mil.
The thin naturally occurring polymeric sheet material 14 may be formed from, for example, a material selected from one or more of cellophane, cellulose acetate, collagen or carrageenan. The thin naturally occurring polymeric sheet material 14 may be formed from one or more naturally occurring polymeric materials which may be combined to form the sheet material 14.
The thin naturally occurring polymeric sheet material 14 is transported to a first nip 16 formed by a first transport roll 18 and a first nip roller 20 by the action of an endless transport mechanism 22 which moves in the direction indicated by the arrow 24. The transport mechanism 22 is driven by the rotation of the first transport roller 18 in conjunctlon with a second transport roller 26 which, in turn are driven by a conventional power source, not shown~
Figure II is a cross sectional view of the transport mechanism 22 taken along lines A-A in Figure I. Figure II
discloses that the transport mechanism 22 includes a heavy duty tran~port wire mesh screen 28 usually having a mesh count of less than about 400 (i.e. less than about 20 wires per inch MD by 20 wire wires per inch CD mesh screen if machine direction (MD) and cross machine direction (CD) wire count is :. ~
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the same). Heavy duty mesh wire screens o~ this type may be made from a variety of materials such as, for example, metals, plastics, nylons or polyesters, and are readily available to those in the artO Located above and attached to the transport screen 28 is an endless flat shim plate 30. The shim plate 30 desirably is formed from stainless steel. However, those of skill in the art will readily recognize that other materials may be u~ilized. Located above and attached to the shim plate 30 is a ~ine mesh wire pattern screen 32 usually having a m~sh count of at least about 2,000 (i.e. at least a 45 wires per inch MD by 45 wires per inch CD mesh screen if MD and CD wire count is the same). Fine mesh wire screens of this type are readily available to those in the art. The fine mesh wire screen 32 has raised areas or knuckles 34 which preform the function of a pattern anvil as will be discussed later.
From the first nip 16 the thin naturally occurring polymeric sheet material 14 is transported by the transport mechanism 22 over a tension roll 36 to an area 38 (defined in Figure I by the dotted lined circle) where th~ thin naturally occurring polymeric sheet material 14 is subjected to ultrasonic vibrations.
The assembly for subje~ting the thin naturally occurring polymeric sheet material 14 to the ultrasonic vibrations is conventional and is generally designated at 40. The assembly 40 includes a power supply 42 which, through a power control 44, supplies power to a piezoelectric transducer 46. As is well known in the art, the piezoelectric transducer 46 transforms electrical energy into mechanical movement as a ,'; ~ :
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result of the transducer's vibrating in respon5e to an input of electrical energy. The vibrations created by the piezoelectric transducer 46 are transferred, in conventional manner, to a mechanical movement booster or amplifier 48. As is well known in the art, the mechanical movement booster 48 may be designed to increase the amplitude of the vibratione (mechanical movement) by a known factor depending upon the configuration of the booster 48. In fllrther conventional manner, the mechanical movement (vibrational energy) is transferred from the mechanical movement boo5ter 48 to a conventional knife edge ultrasonic horn 50. It should be realized that other types of ultrasonic horns 50 could be utilized. For example, a rotary type ultrasonic horn could be used. The ultrasonic horn 50 may be designed to effect yet another boost or increase in the amplitude of the mechanical movement (vibrations) which is to be applied to the thin naturally o¢curring polymeric sheet material 14. Lastly, the assembly includes an actuator 52 which includes a pneumatic cylinder, not shown. The actuator 52 provides a mechanism for raising and lowering the assembly 40 so that the tip 54 of the ultrasonic horn 50 can apply tension to the transport mechanism 22 upon the assembly 40 being lowered. It has been found that it is necessary to have some degree of tension applied to the transport mechanism 22 upon the lowering of the assembly for proper application of vibrational energy to the thin sheet material 14 to form microapertures in the thin naturally occurring polymeric sheet material 14. One desirable aspect of this tensioned arrangement is that the need to ~ "'':' ', ...
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design a finely toleranced gap between the tip 54 of the horn 50 and the raised areas or knuckles 34 of the fine mesh wire screen 32 i~ not nece~sary.
Fir~ure III is a schematic reprQsentation of the area 38 where the ultrasonic vibrations arP applied to the thin naturally occurring polymeric sheet material 14. As can be seen in Figure III, the transport mechanism 22 forms an angle 56 with the tip 54 of the ultrasonic horn 50. While some microaperturing will occur if the angle 56 is as great as 45 degrees, it has been found th~t it i5 desirable for the angle 56 to range from about 5 degrees to about 15 degrees. For example, the angle 56 may range from about 7 to about 13 degrees. More particularly, the angle 56 may range from about 9 to about 11 degrees.
Figure I~I al~o illustrates that the transport mechanism 22 is supported from below by the first tension roll 36 and a second tension roll 58. Positioned somewhat prior to the tip 54 o~ the ultrasonic horn 50 is a spray nozzle 60 which is confi~ured to apply a fluid 62 to the surface of the thin naturally occurring polymeric sheet material 1~ just prior to the sheet material's 14 being subjected to ultrasoni~
vibrations by the tip 54 of the ultrasonic horn 50. The fluid 62 desirably may be selected from the group including one or more of water, mineral oil, a chlorinated hydrocarbon, ethylene glycol or a solution of 50 volume percent water and 50 volume percent 2 propanol. For example, in some embodiments the chlorinated hydrocarbon may be selected ~rom the group including 1,1,1 trichloroethane or carbon tetrachloride. It -20~
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should be noted that the wedge shaped area 64 formed by the tip 54 of the ultrasonic horn 50 and the transport mechanism 22 should be subjected to a sufficient amount of the fluid 62 for the fluid 62 to act as both a heat sink and a coupling agent for the most desirable results. Posit.ioned below the transport mechanism 22 in the area where the tip 54 o~ the ultrasonic horn 50 is located is a fluid collection tank 66.
(5ee figure I.) The fluid collection tank 66 serves to collect fluid 62 which has been applied to the surface of the thin naturally occurring polymeric shee~ material 14 and which has either been driven through the sheet material 14 and/or the transport mechanism 22 or over the edges of the transport mechanism 22 by the action of the vibrations of the tip 54 of the ultrasonic horn 50. Fluid 62 which is collected in the collection tank 66 is transported by tubing 68 to a fluid holding tank 70.
Figure I illustrates that the fluid holding tank 70 ~ :
contains a pump 72 which, by way of additional tubing 74, supplies the fluid 62 to the fluid spray nozzle 60. According-ly, th~ fluid 62 may be re-cycled for a considerable period of time.
While the mechanism of action may not be fully understood and the present application should not be bound to any particular theory or mechanism of action, it is helieved that the presence of the fluid 62 in the wedge-shaped area 64 during operation of the ultrasonic horn 50 accomplishes two separate and distinct functions. First, the presence of the fluid 62 allows the ~luid 62 ~o act as a heat sink which -2~-, .,. : :
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allows the ultrasonic vibrations to be applied to the thin naturally occurring polymeric sheet material 14 without the thin naturally occurring polymeric sheet material 14 being altered or destroyed as by decomposition or possible melting.
Secondly, the presence of the fluid 62 in the wedge-shaped area 64 allows the fluid 62 to act as a coupling agent in the application of the vibrations from the ultrasonic horn 50 to the thin naturally occurring polymeric sheet material 14.
It has been discovered that the action of the ultrasonic horn 50 on the thin naturally occurring polymeric sheet material 14 microapertures the thin naturally occurring polymeric sheet material 14 in spite of the fact that there are no fibers to re arrange to form microapertures as was the case in Mitchell et al.. The microapertures are punched through the thin naturally occurring polymeric sheat material 14 in the pattern of the raised area or knuckles 34 of the fine mesh wire pattern screen 32. Generally, the number of microapartures produced will be equa:L to the number of raised areas or knuckles 3~ on the upper surface of the fine mesh wire screen 32. Tha~ i5 ~ the number of microapertures will generally be one-half the mesh count of a given ar0a o~
pattern screen 32. For example, if the pattern screen 32 is 100 wires per inch MD by 100 wires per inch CD mesh, the total number of kn-lckles or raised areas 34 on one side of the pattern wire 32, per square inch, will be 100 times 100 divided by 2. This equals 5,000 microapertures per square inch. For a 200 wires per inch MD by 200 wires per inch CD
mesh pattern screen 32 the calculation yields 20,000 " ~'. ' ',. ' ~ ' '' : '. ' . ' ~7~
microapertures per square inch. Depending somewhat on the thickness of the thin naturally occurring polymeric sheet material 14, at a mesh count of about 90,000 (300 wires per inch MD by 300 wires per inch CD) the wires are s~ thin as to allow the knuckles 34 on both sides to microaperture the thin naturally occurring polymeric sheet material 14 if sufficient force is applied. Thus, a 300 wires per inch MD by 300 wires per inch CD mesh screen yields 90,000 microapertures per square inch; for a ~00 wires per inch MD by 400 wires per inch CD mesh--160,000 microapertures per square inch. Of course the MD and CD wire count of the wire mesh screen does not have to b~ the same. -~
It should also be noted that the number of microapertures formed may also vary with the number of ultrasonic vibrations to which the thin naturally occurring polymeric sheet material 14 is subjected per unit area for a given period of time. This factor may be varied in a number of ways. For example, the number and size of the microapertures will vary somewhat with the line speed of the thin naturally occurring polymeric sheet material 14 as it passes underneath the tip 54 of the ultrasonic horn 50. Generally speaking, as line speed increases, first the size of the microapertures decreases and then the number of microapertures decreases. As the numbe. of microapertures decreases the less the pattern of microapertures resembles the pattern of raised areas 34 on the pattern screen 32. The range of line speeds that usually yields microapertures varies with the naturally occurring polymeric material utilized to form the thin naturally , ~
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occurring polymeric sheet material 14 and the materia~ d~ -3 as the fluid 62. For cellophane having a thickness of about 0.8 mil, typical line speeds which usually yield microapertures for a wide variety of fluids range from about 4.5 to about 23.3 feet per minute. For example, if water is used as the fluid with cellophane typical line speeds which usually yield microapertures range from about 4 to about 5 feet per minute. It is believed that, to some extent, the variations in the number of microapertures formed and the size of the microapertures occurs due to the minute variations in the height of the raised areas or knuckles 34 of the fine mesh pattern screen 32. It should be noted that the fine mesh pattern screens used to date have been obtained from conventional everyday sources such as a hardware store. It is also believed that if a pattern screen 32 could be created where all of the raised areas 34 of the screen 32 were of exactly the same height these variations would only occur in uniform fashion with YariatiOnS of line speed.
As was stated above, the area or size of each of the microapertures formed will also vary with the parameters discussed above. The area of tha microapertures will also vary with the area of the raised areas of the pattern anvil such as the knuckles 34 on the fine mesh wire screen 32. It is believed that the type of naturally occurring polymeric material used in forming the thin naturally occurring polymeric sheet material 14 will also vary the area of the microapertures formed if all other parameters are maintained the same. For example, the so~ter the thin naturally occurring ~7~
polymeric sheet material 14~ the easier it is to push the thin naturally occurring polymeric sheet material 14 thxough the raised areas o~ the fine mesh pattarn screen 32. Because the raised areas (~nuckles) on the fine mesh screen are ge~erally pyramidal in shape, the deeper the raised area penetrates tne thin naturally occurring polymeric sheet material 14, the larger the microaperture. In such situations the shape of the microaperture will conform generally to the pyramidal shape of the raised area of the fine mesh screen and the microaperture will be generally pyramldally shaped, in the z direction, and will have an area which is greater at one end than at the other. As has been previously stated, the area of the microaperture should be measured at the narrowest point of the aperture. of course, the height of the raised areas must be greater than the thickness of the thin sheet material 14 for microapertures to be formed and the degree of excess, if any, necessary may vary with the type of naturally occurring polymeric sheet to be microapertured. In any eYent the height of the raised area~ must be sufficient to punch through the naturally occurring polyn~eric material including any elasticity which might be encountered in the punching operation. That is, the more elastic the naturally occurring polymeric material, the greater the height o~ the raised areas has to exceed the thickness of the thin naturally occurring polymeric sheet material~
In some embodiments it may be necessary to su~ject the thin naturally occurring polymeric sheet material 14 to multiple passes through the apparatus 10 in order to -~5-.. . . . .
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microaper~ure the thin sheet material 14. In such situations the thin sheet material 14 will initially only be thinned in the pattern of the pattern anvil's raised areas. However, after two or more passes through the apparatus 10, with the thin naturally occurring polymeric sheet material 14 being aligned in the same configuration with respect to the pattern anvil, microapertures may be formed. Essentially what is happening in these situations i5 that the thin naturally occurring polymeric sheet material 14 is repeatedly thinned by repeated application o~ ultrasonic vibrational force until such time as microapertures are formed. Alternatively, the ~ine mesh wire diameter size may be increased with the consequent decrease in mesh count. Increasing the wire diameter size of the fine mesh screen 32 increases the liklihood that microapertures will be. formed.
Another feature of the present invention is the fact that the microapertures can be formed in a predesignated area or areas of the thin naturally occurring polymeric sheet material 14. This can be accomplished in a number of ways. For example, the thin naturally occurring polymeric sheet material 14 may be 5ub; ected to ultrasonic vi~rations only at certain areas of the sheet m~terial, thus, microaperturing would occur only in those areas. Alternatively, the entire thin naturally occurr.ing polymeric sheet material could be subjected to ultrasonic vibrations with the pattern anvil having raised areas only at certain locations and otherwise being flat.
Accordingly, the thin naturally occurring polymeric sheet material would be microapertured only in those areas which : ` : -, "
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corresponded to areas on the pattern anvil having raised areas.
It should also be noted that some limitation exists in the number of microapertures which can be formed in a yiven thin naturally occurring polymeric sheet material 14 on a single application of vibrational energy, i.P. a single pass through the apparatus if a wire mesh screen is used as the patkern anvil. This follows from the fact that, as was stated above, the height of the raised areas must exceed the thickness of the thin naturally occurring polymeric sheet material 14 in conjunction with the fact that, generally, as the mesh count incrsases the height of the raised areas or knuckles decreases. In such situations, if the number of microapertures desired per unit area is greater than the number which can be formed in one pass through the apparatus, multiple passes are necessary with the alignment of the thin naturally occurring polymeric sheet material 14 with respect to the raised ares being altered or shifted slightly on each pass.
Generally speaking the area of each of the microapertures is greater than about ten square micrometers. That is the area of each of the microapertures may range from at least about 10 square micrometers to about 100,000 square micrometers. For example,the area of each of the formed microapextures may generally range from at least about 10 square micrometers to about 10,000 square micrometers. More particularly, the area of each o~ the formed micxoapertures may generally range from at least about 10 square micrometers to about 1,000 square micrometers. Even more parkicularly, khe area of each of the ~, . . . .
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formed microapertures may generally ran~e from at least about 10 square micrometer to about 100 square micrometers.
A number of important observations about the process may now be made. For example, it should be understood that the presence of the fluid 62 is highly important to the present inventive process which uses the fluid 62 as a coupling agent.
BecausP a couplinq agent is present, the microapertures are punched through the thin sheet material 14 as opposed to being fo~med by melting. Additionally, the presence of the shim plate 30 or its equivalent is necessary in order to provide an anvil mechanism against which the thin naturally occurring polymeric sheet material 14 may be worked, that is apertured, by the action of the tip 5~ of the ultrasonic horn 50. Because the vibrating tip 54 of the ultrasonic horn 50 is acting in a hammer and anvil manner when operated in conjunction with the hevay duty wire mesh screen Z8/shim plate 30/fine wire mesh 32 combination, it should he readily recognized that a certain degree of tension must be placed upon the transport mechanism 22 by the downward displacement of the ultrasonic horn 50. If there is little or no tension placed upon the transport mechanism 22, the shim plate 30 cannot perform its function as an anvil and microaperturing generally does not occur. Because both the shim plate 30 and the fine mesh pattern wire 32 form the resistance that the ultrasonic horn 50 works against, they are collectively referred herein as a pattern anvil combination. It should be easily recognized by those in the art that the function of the pattern anvil can be accomplished by other arrangements than the heavy duty wire ~7~
mesh screen 28/shim plate 30/fine mesh screen 32 combination.
For example, the pattern anvil could be a flat plate with raised portions acting to direct the microaperturing force of the ultrasonic horn 50. Alternatively, the pattern anvil could be a cylindrical roller having raised areas. If the pattern anvil is a flat plate with raised areas or cylindrical roller with raised areas, it is desirable for the pattern anvil to be wrapped or coated with a resilient material. Where the pattern anvil is a mesh screen the resiliency is provided by the fact that the screen is unsupported directly below the point of application of ultrasonic vibrations to the mesh screen.
As a result of the microaperturing process the edge lenqth of the thin naturally occurring polymeric sheet material may be increased by at least about 100 percent as compared to the sheet's edge length prior to microaperturing. For example, the edge length of the thin naturally occurring polymeric sheet material may be increased by at least about 500 percent as compared to the sheet's edge length prior to microaperturing.
More particularly, the edge length of the thin naturally occurring polymeric sheet material may be increased by at least about 1,500 percent as compared to the sheet's edge length prior to microaperturing. Even more particularly, the edge lenqth of the thin naturally occurring polymeric sheet material may be increased by at least about 3,000 percent as compared to the sheet's edge length prior to microaperturing.
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The invention will now be discussed with regard to specific examples which will aid those of skill in the art in a full and complete understanding thereof.
Prior to utilizing the present process to microaperture exemplary thin naturally occurring polymeric sheet materials the hydrohead and water vapor transmission rate (wvtr) of the selected materials were measured. Three different cellulosic sheet materials were chosen for the present examples. These were obtained from Flexel, Inc. Company of Atlanta, Georgia under the trade designations (1) 0.8 mil thick Flexel V-58;
(2) 0.9 mil thick Flexel MST and (3) 1.0 mil thick Flexel LST. Flexel, Inc. literature state that the Flexel V-58 is a transparent cellulosic film coated on both sides with a moistureproof, heat-sealable, high-barrier polymer (PVDC) coating. Flexel, Inc. literature states that the Flexel MST
is a mois~ureproof, heat-sealable, transparent, two-sided nitrocellulose coated cellulosic filmO Flexsl, Inc. literature states that the Flexel LST is a two side nitrocellulose coated cellulosic film with intermediate/decreased moistrueproofness to permit breathing, while maintaining yood heat sealability, water resistance ~or moist products, excellent coating anchorage to base film, standard gas barrier properties, and efficient machinability. The hydrohead of each of these materials was in excess of 137 centimeters of water. (This is the maximum hydrohead measurable by our equipment.) The wvtr of the Flexel V-58 was measured as 0.0 grams per square meter per day. The wvtr of the Flexel MST was measured as 0.8 grams ~7~
per square meter per day. The wvtr of the Flaxel LST was measured as 62.5 grams per square meter per day.
EXAMPLE I
A sheet of 0.8 mil thick cellulosic sheet having the trade designation Flexel V-58 was cut into a length of about 11 inches and a width of about 8.5 inches. As wa~ stated above, the hydrohead of the cellulosic sheet prior to hydrosonic treatment was measured as being greater than 137 centimeters of water. The sample was subjected to hydrosonic treatment in accordance with the present invention.
A model 1120 power supply obtained from the Branson Company of Danbury, Connecticut, was utilized. This power supply, which has the capacity to deliver 1,300 watts of electrical energy, was used to con~ert 115 volt, 60 cycle electrical energy to 20 kilohertz alternating current. A
Branson type J4 power level control, which has the ability to regulate the ultimate output of the nodel 1120 power supply from o to lO0~, was connected to the model 1120 power supply.
In this exampl~, the power level control was set at 100%. The actual amount of power consumed was indicated by a Branson model A410A wattmeter. This amount was about 775 watts.
The output of the power supply was fed to a model 402 piezoelectric ultrasonic transducer obtained from the Branson Company. The transducer converks the electrical energy to mechanical movement. At 100% power the amount of mechanical movement of the transducer is about 0.8 micrometers.
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The piezoelectric transducer was connected to a mechanical movement booster section obtained from the Branson company.
The boos~er is a solid titanium metal shaft with a length equal to one-half wava len~th of the 20 kilohertz resonant frequency. Boosters can be machined so that the amount of mechanical movement at their output end is increased or decreased as compared to the amount of movement of the transducer. ~n this example the booster increased the amount of movement and has a gain ratio of about 1:2.5. That is, the amount of mechanical movement at the output end of the booster is about 2.5 times the amount of movement of the transducer.
The output end of the booster was connected to an ultrasonic horn obtained from the Branson Company. The horn in this example is made of titanium with a working face of about 9 inches by about 1/2 inch. The leading and trailing edges of the working face of the horn are each curved on a radius of about 1/8 inch. The horn ~,tep area is exponential in shape and yields about a two-fold increase in the mechanical movement of the booster. That is, the horn step area has about a 1:2 gain ratio. The combined increase, by the booster and the horn step area, in the original mechanical movement created by the transducer yields a mechanical movement of about 4 .0 micrometers.
The forming table arrangement included a small forming table which was utilized to transport and support the cellulosic sheet to be microapertured. Tha forming table included two 2-inch diameter idler rollers which were spaced about 12 inches apart on the surface of the forming table. A
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' transport mesh belt encircles the two idler rollers so that a contim1ous conveying or transport surface is created. The transport mesh belt i5 a square weave 20 x 20 mesh web of 0~020 inch diameter plastic filaments. The belt is about 10 inches wide and is raised above the surface of the forming table.
The transducer/booster/horn assembly, hereinafter th~
as~embly, is secured in a Branson series 400 actuator. When power is switched on to the transducer, the actuator, by means of a pneumatic cylinder with a piston area of about 4.4 square inches, lowers the assembly so that the output end of the horn contacts the cellulosic sheet which is to be microapertured.
The actuator also raises the assembly 50 that the output end of the horn is removed from contact with the cellulosic sheet when power is switched off.
The assembly is positioned so that the output end of the horn is adapted so that it may be lowered to contact the transport mesh belt between the two idler rollers. An 8-inch wide 0.005-inch thick stainless steel shim stock having a length of about 60 inches was placed on the plastic mesh transport belt to provide a firm support for a pattern screen which is placed on top of the stainless steel shim. In this example the pattern screen is a 120 by 120 mesh wire size weave stainless steel screen. The cellulosic sheet which was to be microapertured was then fastened onto the pattern wire using masking tape.
The forming table arrangement also included a fluid circulating system. The circulating system includes a fluid .
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reservoir tank, a fluid circulating pump which may convenient-ly be located within the tank, associated tubing for transpor-ting the fluid frnm ~he tank to a slotted boom which is designed to direct a curtain of fluid into the juncture of the output en~ of the horn and cellulosic sheet which is to be microapertured.
In operation, the assembly was positioned so that the output en~ of the horn was at an angle of ~rom about 10 to 15 degrees to the cellulosic sheet to be microapertured.
Accordingly, a wedge shaped chamber was formed between the output end of the horn and the celluloslc sheet to be microapexturecl. It is into this wedge shaped chamber that the fluid, in this example a 50 percent 2 propanol/50 percent water, by volume, mixture, at room tempexature, was directed by the slotted boom.
It should be noted that the actuator was positioned at a height to insure that, when the assembly is lowered, the downward movement of the output end of the horn is stopped by the tension of the transport mesh be~ore the actuator reaches the limit of its stroke. In this example, actuating pressure was adjusted ~o 7 pounds per square inch as read on a pressure gauge which is attached to the pneumatic cylinder of the actuator. This adjus~ment results in a total downward force of 30.8 poundsO (7 psi times 4.4 square inches of piston area equals 30.8 pounds of force.) The sequence of operation was (1) the ~luid pUMp was switched on and the area where the output end of the horn was to contact the cellulosic sheet was flooded with the 50 2~7~
percent 2 propanol/50 percent water, by volume, mixture; (2) the transport mesh conveyor system was switched on and the cellulosic sheet started moving at 23.3 feet per minute; and ~3) power to the assembly was supplied and the assembly was lowered so that the output end of the horn contacted the cellulosic shee~ while the sheet continued to pass under the output end of the horn until the end of the sample was reached. The reading on the A410A wattmeter during the process is an i~dication of the ener~y required to maintain maximum mechanical movement at the output end of the horn while working against the combined mass of the 50 percent 2 propanol/ 50 percent water, by volume, mixture, the cellulosic sheet, the pattern wire, the shim stock, and the transport wire.
This example yielded a microapertured cellulosic sheet having a maximum microaperture density o~ about 7,000 microapertures per square inch with the microapertures having an area of about 40 square micrometers. The hydrohead of the microapertured cellulosic sheet was measured as being about 54 centimeters of water and the wvtr o~ the microapertured cellulosic sheet was measured as being about 219 grams per square meter per day.
The edge length increase of this material was calculated to be about 155 percent.
EXAMPLE II
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The process of example I was repeated with the exception that the line speed of the cellose sheet was 20.9 feet per minute as compaxed to the 23.3 feet per minute utilized in example I. The actual amount of power consumed was indicated by the Branson model A410A wattmeter as about 750 watts. The actuating pressure was about 6 pounds per square inch, gauge.
This example yielded a microapertured cellulosic sheet having a maximum density of about 7,000 microapertures per s~uare inch with the microapertures having an area of about 1,070 square microme~ers. The hydrohead of this sample was measured as being about 22 centimeters of water and the wvtr was measured as being about 1,200 grams per square meter per day.
The edg~ length increase of the material was calculated as being 766%.
Figure IV is a photomicrograph o~ the thin cellulosic sheet material microapertured in accordance with example II.
EXAMPLE_III
The process of example I was repeated with the exception that E'lexel MST was used as the cellulosic sheet material.
Additionally, the line speed o the cellose sheet was 4.S
feet per minute as compared to the 23.3 feet per minute utilized in example I. The actual amount of power consumed was indicated by the Branson model A410A wattmeter as about 850-1,000 watts. The actuating pressure was 8 pounds per square inch, gauge. A 250 by 250 wire count per inch MD and CD mesh screen was used instead o~ the 120 by 120 wire count per inch.
2~37~
water at room temperature was u~ed as the fluid instead of 50 parcen~ 2 propanol/50 percent water, by volume, mixture.
This example yielded a microapertured cellulosic sheet having a maximum density of about 30,000 microapertures per square inch with the microapertures having an area of about 225 square micrometers. The average of two hydrohead readings for this sample was measured as being about 82 centimPters of water and the average of three wvtr readings was about 240 grams per square meter per day. The edge length increase of the material was calculated as being 1,635%.
' EXAMPLE IV
The process of example I was repeated with the exception that Flexel LST was u~ed as the cellulosic sheet material.
Additionally, the line speed of the cellose sheet was 4.5 feet per minute as compared to the 23.3 feet per minute utilized in example I. The actual amount of power consumed was indicated by the Branson model A410A wattmeter as about 900-1,100 watts. The actuating pressure was 8 pounds per square inch, gauge. A 250 by 250 wire count per inch MD and CD mesh screen was used instead of the 120 by 120 wire count per inch.
Water at room temperature was used as the fluid instead of the 50 percent 2 propanol/50 percent water, by volume, mixture.
This example yielded a microapertured cellulosic sheet having a maximum density of about 30,000 microapertures per square inch with the microapertures having an area of about 600 square micrometers. The average of two hydrohead readings for 2~7~
this sample was about 76 cPntimeters of water and the average of three wvtr rPadings was about 440 grams per square meter per day. The edge length increase of the material was calculated as being 2,670%.
EXAMP$E V
Example IV was repeated. This example yielded a microapextured cellulosic sheet having a maximum density of about 30,000 microapertures per square inch with the microaperture~ having an area of about 600 square micrometers.
The average of tWQ hydrohead readings for this sample was about 76 centimeters of water and the average of three wvtr readings was about 950 grams per square meter per day.
Comparing the hydrohead and wvtr data for the cellulosic sheets microapertured in examples I-V to the values obtained for the untreated sheets, it is readily apparent that the sheets have been rendered breathable to water vapor while still maintaining a good hydrohead value. It is to ~e emphasized that some variation is present from example to example. (Note the differing wvtr results in examples IV and V.) It is anticipated that with the use of better equipment and the acquisition of additional knowledge in this area such variations will be reduced accordingly.
The uses to which the microapertured naturally occurring polymeric sheet material o~ the present invention may be put are numerous. Of course, any application which is improved or .
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otherwise enhanced if the edge length of the naturally occurring polymeric sheet is increased is to be considered.
~dditionally, ~or nonwater soluble materials, applications where materials having good wvtr values coupled with elevated hydrohead values will present themselves. One such area of use is in the filtration area. In particular, it should be noted that the materials of the present invention are naturally occurring, as defined herein, and they could well find use in the packaginy of food where watar vapor breathability coupled with product protection is desired. An example of an area where increased edge length is benificial is the area of biodegradability. When thin naturally occurring polymeric sheet materials have been microapertured in accordance with the present invention, the edge length of the sheet materials is significantly increased. This increase in edge length decreases the time it takes for the material to be decomposed.
It is to be understood that variations and modifications of the present invention may be made without departing from the scope of the invention. For exampl~, in some embodiments the use of multiple ultrasonic horns aligned abreast or sequentially may be desirable. It is also to be understood that the scope of the present invention is not to be interpreted as limited to the specific embodiments disclosed herein, but only in accordance with the appended claims when read in light of the foregoing disclosure.
(5) the formation of catalysts; ~6) the degassing and solidification of molten metals; (7) the extraction of flavor oils in brewing; (8) electroplatingi (9) drilling hard materials; (10) fluxless soldering and (lo) nondestructive testing such as in diagnostic medicine.
The object of high power ultrasonic applications is to bring about some permanent physical change in the material treated. This process requires the flow of vibratory power per unit of area or volume. Depending on the application, the power density may range from less than a watt to thousands , ~ ', ,' : ~; ' , ' of watts per square c~ntimeter. Although the original ultrasonic power devices operatPd at radio frequencies, today most operate at 20-69 kHz~
The piezoelectric sandwich-type tra~sducer driven by an electronic power supply has emerged as the most common source o~ ultrasonic power; the overall e~ficiency of such equip~ent (net acoustic power per electric-line power) is typically greater than 70%. The maximum power from a conv~ntional transd~cer is inversely proportional to the sguare of the frequency~ Some applications, such as cleaning, may have many transducers working into a common load.
Other, more particular areas where ultrasonic vibratory force has been utilized are in the areas of thin nonwoven webs and thin films. For example, ultrasonic force has been use to bond or weld nonwoven webs. See, for Pxample, U.S. patent nu~hers 3~575,752 to Carpenter, 3,660,186 to Saqer et al., 3,9~6,519 to Mitchell et al. and 4,6g5,454 to Sayo~itz_et al.
which disclose the usa of ultrasonics to bond or weld nonwoven webs. U.S. patent nu~bers 3,488,240 to Roberts, describes the use of ultrasonics to bond or weld thin films such as oriented polyesters.
Ultrasonic force has also been utilized to aperture nonwoven webs. See, for example, U.S. patent nu~bers 3,949,127 to Oste~eier ~_~1~ and, 3,966,519 to Mitchell et al..
Lastly, ultrasonic force has been used to aperture thin ~ilm material. See, for example, U. S. patent number 3,756,880 to Graczyk.
~ ' ' ' ' ' Other methods for the aperturin~ of thin film have been developed. For examplP, U.S. patent number 4,815,714 to Douqlas discusses the aperturing of a thin film by first abrading ~he film, which is in filled and unoriented form, and then subjecting the film to corona discharge treatment.
one of the di~ficulties and obstacles in the use of ultrasonic force in the formation of apertures in materials is the fact that control of the amount of force which is applied was difficult. This lack of control resulted in the limitation of ultrasonic force to form large apertures as opposed to small microapertures. Such an application is discussed in U.K. patent application number 2,124,134 to Blair. one of the possible reasons that ultrasonics has not found satisfactory acceptance in the area of microap rture formation is that the amount of vibrational energy required to form a microaperture often resulted in a melt-through of the film.
As has previously been stated, those in the art had recognized that ultrasonics could be utilized to form apertures in nonwoven webs. See, U.S. patent to Mitchell,_et al.. ~dditionally, the Mitchell et al. patent discloses that the amount of ultrasonic energy being subjected to a nonwoven web could be controlled by applying enough of a fluid to the area at which the ultrasonic energy was being applied to the nonwoven web so that the fluid was present in uncombined form~
Importantly, the Mitchell et al. patent states that the fluid is moved by the action of the ultrasonic force within the nonwoven web to cause aperture formation in the web by fiber "
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~7~:3 rearrangement and entanglement. The Mitchell et al. patent also states that, in its broadest aspects, since these effects are obtained primarily through physical movement of fibers, the method of their invention may be utilized to bond or increase the streng~h of a wide varisty of fibrous webs.
While the discovery disclosed in the itchell et al.
patent, no doubt, was an important contribution to the art, it clearly did not address the possibility of aperturing nonfibrous sheets or sheets having fixed fibers formed from naturally occurring polym~ric materials. This fact is clear b~cause the Mitchell et al. patent clearly states the belief that the mechanism of aperture formation depended upon fiber rearrangement. of cour~e, such sheet materials either do not have fibers or have fibers which are in such a condition that they cannot be rearranged. Accordingly, it can be stated with conviction that the applicability of a method for aperturing naturally occurring polymeric sheet materials by the application of ultrasonic energy in c:onjunction with a fluid at the point of application of the ultrasonic energy to the naturally occurring polymeric sheet material was not contemplated by the Mitchell et al. patent. Moreover, the Mitchell et a~l~patent teaches away from such an application because the patent states the belief that aperture formation requires the presence of movable fibers to be rearranged.
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As used herein the terms l'polymer" or "polymeric" refer to a macromolecule formed by the chemical union of five (5) or more identical combining units called monomers.
As used herein the term "naturally occurring polymeric material" refers to a polymeric material which occurs naturally. The term is also meant to include materials, such as cellophane, which can be regenerated from naturally occurring materials, such as, in the case of cellophane, cellulose. Examples of such naturally occurring polymeric materials include, without limitation, (1) polysaccharides such as starch, cellulose, pectin, seaweed gums (such as agar, etc.), vegetable gums (such as arabic, etc.); (2) polypeptides; (3) hydrocarbons such as rubber and gutta percha (polyisoprene) and (4~ regenerated materials such as cellophane or chitosan. Of course, the term "naturally occurring polymeric material" is also meant to inclu~e mixtures and combinations of two or more naturally occurring polymeric materials as well as mixtures and combinations which include at least fifty (50) percent, by weight, naturally occurring polymeric materials.
As used herein the term "n~turally occurring polymeric sheet material" refers to a gen~rally nonporous item formed from a naturally occurring polymeric material that can be arranged in generally planar configuration. If the material is not a water soluble material, the material, in an unapertured state prior to being modified in accordance with the present invention, ha~ a hydrostatic pressure (hydrohead) of at least about 100 centimeters of water when measured in :. , .: , . . . .
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accordance wiih Federal Test Method NO. 5514, standard no.
l91A. Unless otherwise stated herein all hydrohead values are obtained in accordance with Federal Test Method NO. 5514, standard no 191~. This term i8 also intended to include multilayer materials which include at least one such sheet of a naturally occurring polymeric material as a layer thereof.
It should be noted that the material does not have to occur naturally in sheet form, rather it is the components of the sheet that are l'naturally occurring". Gf course, if the naturally occurring polymeric material is water soluble, hydrohead measurements have little, if any meaning.
As used herein the term "thin naturally occurring polymeric sheet material" refers to a naturally occurring polymeric sheet material having an average thickness generally of less than about ten (10) mils. Averags thickness is determined by randomly selecting five ~5) locations on a given sheet material, mPasuring the thickness of the sheet material at each location to the nearest 0.1 mil, and averaging ths five values (sum of the fi~e values clivided by five).
As used herein the term water vapor transmission rate ref~rs to the rate water vapor will pass through a water insoluble sheet material under a given set of conditions in a particular time period. Unless otherwise specified, water vapor transmission rate is measured in accordance with ASTM
E 96-80 using the water method referenced at paragraph 3.2 thereof. The test is run at 90 degrees fahrenheit and 50 percent relative humidity for twenty-four (24) hours.
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As used herein the t rm "mesh count" refers to the number which is the product of the number of wires ln a wire mesh screen in both the machine (MD) and cross-machine (CD) directions in a given unit area. For example, a wire mesh screen having 100 wires per inch in the machine direction and 100 wires per inch in the cross machine direction would have a mesh count o~ 10,000 per square inch. As a result of the interweaving of these wires, raised areas are present on both sides of the mesh screen. The number of raised areas on one side of such a wire mesh scre~n is genexally one-half of the mesh count.
As used herein the term "aperture" refers to a generally linear hole or passageway. Aperture is to be distinguished from and does not include holes or passageways having the greatly tortuous path or passageways found in membranes.
As used herein the term "microaperture" r~fers to an aperture which has an area of less than about 100,000 square micrometers. The area of the microape:rature is to be measured at the narrowest point in the linear passageway or hole.
As used h~rein the term "ultrasonic vibrations" refers to vibrations having a frequency of at least about 20,000 cycles per second. The frequency of the ultrasonic vibrations may range from about 20,000 to about 400,000 cycles per second or more.
As used herein the term "hydrosonics" refers to the application of ultrasonic vibrations to a material where the area of such application is has had a liquid applied thereto to the extent that the liquid is present in sufficient 2 ~
quantity to generally fill the ~ap between the tip of th ultrasonic horn and the surface of the material.
The approximate edge length of the thin microapertured thermoplastic sheet material of the present invention is calculated from the size of the microaperture using the appropriate geometrical formula, depending upon th~
microaperture's general shap2.
OBJECTS OF TH~__NVENTION
Accordingly, it is a general object of the present invention to provide thin naturally occurring polymeric sheet materials which have been microapertured in a generally uniform pattern Still further objects and the broad scope of applicability of the present invention will beco~e apparent to those of skill in the art from the details given hereinafter. However, it should be understood that the detailed description of the presently preferred embodiments of the present invention is given only by way of illustration because various changes and modifications well within the spirit and scope of the invention will become apparent to those of skill in the art in view of this detailed description.
SUMMARY OF THE INVENTION
,, :
In response to the foregoing problems and difficulties encountered by those in the art, we have developed a method for foxming microapertures in a thin naturally occurring polymeric sheet material having a thickness o~ about 10 mils or less where the area of each of the formed microapertures is generally greater than about 10 square micrometers. The method include.s the steps of: (1) placing the thin naturally occurring polymeric sheet material on a pattern anvil having a pattern of raised areas where the height of the raised areas is greater than the thickness of the thin naturally occurring polymeric sheet material; (2) conveying the thin naturally occurring polymeric sheet material, while placed on the pattern anvil, through an area where a fluid is applied to the thin naturally occurring polymeric sheet material; and (3) subjecting the thin naturally occurring polymeric sheet material to ultrasonic ~ibrations in the area where the fluid is applied to the thin naturally occurring polymeric sheet material. As a resul~ of this method the thin naturally occurring polymeric sheet material is microapertured in a pattern generally the same as the pattern of raised areas on the pattern anvil.
The thin naturally occurring polymeric sheet material may be formed rom, for example, cellophane, cellulose acetate, collagen or carrageenan.
The fluid may be selected from the group including one or more of water, mineral oil, a chlorinated hydrocarbon, ethylene glycol or a solution of 50 volume percent water and .:
: ' 2 ~ ~ 7 ~ 9 r~3 50 volume percent 2 propanol. The chlorinated hydrocarbon may be 1,1,1 trichloroethane or carbon tetrachloride.
In some embodiments, the area of each of the formed microapertures may generally range from at least ahout 10 square micrometers to a~out 100,000 square micrometers. For example, the area of each of the formed microapertures may generally range from at least about 10 square micrometers to about 5,000 square micrometers. Mor~ particularly, the area of each of the formed microapertuxes may generally range from at least about 10 square micrometers to about 1,000 square micrometers. Even more particularly, the area of each of the for~ed microapertures may generally range from about at least 10 square micrometers to about 100 square micrometers.
The thin naturally occurring polymeric sheet material may be microapertured with a microaperture density of at least about 1,000 microapertures per square inch. For example, the thin naturally occurring polymeric sheet material may be microapertured with a microaperture d~ensity of at least about 5,000 microapertures per square inch. More particularly, the thin naturally occurring polymeric sheet material may be microapertured with a microaperture density o~ at least about 20,000 microapertures per square inch. Even more particularly, the thin naturally occurring polymeric sheet material may be microapertured with a microaperture density of at least about 90,000 microapertures per square inch. Yet even more particularly, the thin naturally occurring polymeric sheet material may be microapertured with a microaperture density of at least about 160,000 microapertures per square inch.
' ~37~
The pattern anvil may, for example, be a mesh screen with knuckles serving as raised areas, a flat plate with raised areas or a cylindrical roller with raised areas. If the pattern anvil is a cylindrical roller with raised areas, it is desirable for the pattern anvil to be wrapped or coated with or made from a resilient material. Where the pattern anvil is a mesh screen the resiliency is provided by the fact that the screen is unsupported directly below the point of application of ultrasonic vibrations tn the mesh screen.
In some embodiments it may be desirable to subject the thin naturally occurring polymeric sheet material to multiple passes through the microaperturing area so that at least steps (b~ and (c~ are performed more than once on the thin naturally occurring polymeric sheet material. To attain an microaperture density which is greater that the number of raised areas on the pattern anvil, the thin naturally occurring polymeric sheet material may be moved slightly between passes.
In some embodiments it may be desirable for the microaperturing of the thin naturally occurring polymeric sheet material to be confined to a predesignated area or areas of the thin naturally occurring polymeric sheet material. This result may be obtained where only a portion of the thin naturally occurring polymeric sheet is subjected to ultrasonic vibrations. Alternatively, this result may be obtained where only a portion of the pattern anvil is provided with raised areas.
The thickness of the thin naturally occurring polymeric sheet material is at least about 0.25 mil. For example, the . - ,,, . ~ : :
.
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thicXness of the thin naturally occurring polymeric shee~
material may range from about 0.25 mil to about 5 mils. More particularly, the thickness of the thin naturally occurring polymeric sheet material may range from about 0.25 mil to about 2 mils. Even more particularly, the thickne9s of the thin naturally occurring polymeric sheet material may range from about 0.5 mil to about 1 mil.
If it is not a water soluble material, the hydrohead of the thin naturally occurring polymeric sheet material may be measured and may range from at least about 15 centimeters of water. For example, the hydrohead of the thin naturally occurring pol~meric shePt material may ran~e from at least about 35 centimeters of water. More particularly, the hydrohead ~f the thin naturally occurring polymeric sheet material may range from at least about 45 centimeters of water. Even more particularly, the hydrohead of the thin naturally occurring polymeric sheet material may range from at lea~t about 55 centimeters of water. Yet even more particularly, the hydrohead of the thin naturally occl~rring polymeric sheet material may range from at least about 7 centimeters of water.
If it is not a water soluble material, the water vapor transmission rate of the thin naturally occurring polymeric sheet material may range from at least about 200 grams per square meter per day. For example, the water vapor transmission rate of the thin naturally occurring polymeric sheet material may range from at lea~t about 500 grams per square meter per day. Even more particularly, the water vapor trans~ission rate of the thin naturally occurring polymeric sheet material may range from at least about 1,000 grams per square meter per day. Yet even more particularly, tha water vapor transmission rate of the thin naturally occurring polymeric sheet material may range from at least about 1,500 grams per square meter per day.
As a result of the microaperturing process the edge length of the thin naturally occurring polymeric sheet material may be increased by at least about 100 percent as compared to the sheet's edge length prior to microaperturing. For example, the edge length of the thin naturally occurring polymeric sheet material may be increased by at least about 500 percent as compared to the sheet's edge length prior to microaperturing.
More particularly, the edge length of the thin naturally occurring polymeric sheet material may be increased by at least about 1,500 percent as compared to the sheet's edgc length prior to microaperturing. Even more particularly, the edge length o~ the thin naturally occurring polymeric sheet material may be increased by at least about 3,000 percent as compared to the sheet's edge length prior to microaperturing.
THE FIGURES
Figure I is a schematic representation of apparatus which utilizes ultrasonic vibrations to microaperture thin naturally occurring polymeric sheet materials.
Figure II is a cross sectional view of the transport mechanism for transporting the thin naturally occurring . ., ; . . : , :
.
.
2~37~
poly~eric sheet material to the area where it is subjected to ultras~nic vibrations.
Fi~ure III is a detailed view of the area where the thin naturally occurring polymeric sheet material is subjected to ultrasonic vibrations. The area is designated by the dotted circle in figure Io Figure IV is a photomicrograph of a 0.8 mil thick sheet of cellophane obtained under the trade name "Flexel V-58, which has been microapertured in accordance with the present invention. The photomicrograph is accompanied by a scale where each unit on the scale represents ten microns (micrometers).
DE'rAILED DESCRIPTION OF THE INVENTION
Turning now to the figures where like reference numerals represent like structure and, in particular to Figure I which is a schematic representation of an apparatus which can carry out the method of the present inventi.on, it can be seen that the apparatus is generally represented by the reference numeral 10. In operation, a upply roll 12 o~ a thin naturally occurring polym~ric sheet material 14 to be microapertured is provided. As has been previously stated, the term thin naturally occurring polymeric sheet material refers to shee materials which have an average thickn~ss of about ten (10) mils or less. Additionally, generally speaking, the average thickness of the thin naturally occurring polymeric sheet material 14 will be at least about 0.25 mil. For example, the average thickness of the thin naturally occurring polymeric 2~7~
sheet 14 material may range from about 0.25 mil to about 5 mils. ~ore particularly, the average thickness of the thin naturally occurring polymeric sheet material 14 may range from about 0.25 mil ~o about 2 mils. Even more specifically, the average thickness of the thin naturally occurring polymeric sheet material 14 may range from about 0.5 mil to about 1 mil.
The thin naturally occurring polymeric sheet material 14 may be formed from, for example, a material selected from one or more of cellophane, cellulose acetate, collagen or carrageenan. The thin naturally occurring polymeric sheet material 14 may be formed from one or more naturally occurring polymeric materials which may be combined to form the sheet material 14.
The thin naturally occurring polymeric sheet material 14 is transported to a first nip 16 formed by a first transport roll 18 and a first nip roller 20 by the action of an endless transport mechanism 22 which moves in the direction indicated by the arrow 24. The transport mechanism 22 is driven by the rotation of the first transport roller 18 in conjunctlon with a second transport roller 26 which, in turn are driven by a conventional power source, not shown~
Figure II is a cross sectional view of the transport mechanism 22 taken along lines A-A in Figure I. Figure II
discloses that the transport mechanism 22 includes a heavy duty tran~port wire mesh screen 28 usually having a mesh count of less than about 400 (i.e. less than about 20 wires per inch MD by 20 wire wires per inch CD mesh screen if machine direction (MD) and cross machine direction (CD) wire count is :. ~
20~7 B9~
the same). Heavy duty mesh wire screens o~ this type may be made from a variety of materials such as, for example, metals, plastics, nylons or polyesters, and are readily available to those in the artO Located above and attached to the transport screen 28 is an endless flat shim plate 30. The shim plate 30 desirably is formed from stainless steel. However, those of skill in the art will readily recognize that other materials may be u~ilized. Located above and attached to the shim plate 30 is a ~ine mesh wire pattern screen 32 usually having a m~sh count of at least about 2,000 (i.e. at least a 45 wires per inch MD by 45 wires per inch CD mesh screen if MD and CD wire count is the same). Fine mesh wire screens of this type are readily available to those in the art. The fine mesh wire screen 32 has raised areas or knuckles 34 which preform the function of a pattern anvil as will be discussed later.
From the first nip 16 the thin naturally occurring polymeric sheet material 14 is transported by the transport mechanism 22 over a tension roll 36 to an area 38 (defined in Figure I by the dotted lined circle) where th~ thin naturally occurring polymeric sheet material 14 is subjected to ultrasonic vibrations.
The assembly for subje~ting the thin naturally occurring polymeric sheet material 14 to the ultrasonic vibrations is conventional and is generally designated at 40. The assembly 40 includes a power supply 42 which, through a power control 44, supplies power to a piezoelectric transducer 46. As is well known in the art, the piezoelectric transducer 46 transforms electrical energy into mechanical movement as a ,'; ~ :
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result of the transducer's vibrating in respon5e to an input of electrical energy. The vibrations created by the piezoelectric transducer 46 are transferred, in conventional manner, to a mechanical movement booster or amplifier 48. As is well known in the art, the mechanical movement booster 48 may be designed to increase the amplitude of the vibratione (mechanical movement) by a known factor depending upon the configuration of the booster 48. In fllrther conventional manner, the mechanical movement (vibrational energy) is transferred from the mechanical movement boo5ter 48 to a conventional knife edge ultrasonic horn 50. It should be realized that other types of ultrasonic horns 50 could be utilized. For example, a rotary type ultrasonic horn could be used. The ultrasonic horn 50 may be designed to effect yet another boost or increase in the amplitude of the mechanical movement (vibrations) which is to be applied to the thin naturally o¢curring polymeric sheet material 14. Lastly, the assembly includes an actuator 52 which includes a pneumatic cylinder, not shown. The actuator 52 provides a mechanism for raising and lowering the assembly 40 so that the tip 54 of the ultrasonic horn 50 can apply tension to the transport mechanism 22 upon the assembly 40 being lowered. It has been found that it is necessary to have some degree of tension applied to the transport mechanism 22 upon the lowering of the assembly for proper application of vibrational energy to the thin sheet material 14 to form microapertures in the thin naturally occurring polymeric sheet material 14. One desirable aspect of this tensioned arrangement is that the need to ~ "'':' ', ...
~37~
design a finely toleranced gap between the tip 54 of the horn 50 and the raised areas or knuckles 34 of the fine mesh wire screen 32 i~ not nece~sary.
Fir~ure III is a schematic reprQsentation of the area 38 where the ultrasonic vibrations arP applied to the thin naturally occurring polymeric sheet material 14. As can be seen in Figure III, the transport mechanism 22 forms an angle 56 with the tip 54 of the ultrasonic horn 50. While some microaperturing will occur if the angle 56 is as great as 45 degrees, it has been found th~t it i5 desirable for the angle 56 to range from about 5 degrees to about 15 degrees. For example, the angle 56 may range from about 7 to about 13 degrees. More particularly, the angle 56 may range from about 9 to about 11 degrees.
Figure I~I al~o illustrates that the transport mechanism 22 is supported from below by the first tension roll 36 and a second tension roll 58. Positioned somewhat prior to the tip 54 o~ the ultrasonic horn 50 is a spray nozzle 60 which is confi~ured to apply a fluid 62 to the surface of the thin naturally occurring polymeric sheet material 1~ just prior to the sheet material's 14 being subjected to ultrasoni~
vibrations by the tip 54 of the ultrasonic horn 50. The fluid 62 desirably may be selected from the group including one or more of water, mineral oil, a chlorinated hydrocarbon, ethylene glycol or a solution of 50 volume percent water and 50 volume percent 2 propanol. For example, in some embodiments the chlorinated hydrocarbon may be selected ~rom the group including 1,1,1 trichloroethane or carbon tetrachloride. It -20~
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should be noted that the wedge shaped area 64 formed by the tip 54 of the ultrasonic horn 50 and the transport mechanism 22 should be subjected to a sufficient amount of the fluid 62 for the fluid 62 to act as both a heat sink and a coupling agent for the most desirable results. Posit.ioned below the transport mechanism 22 in the area where the tip 54 o~ the ultrasonic horn 50 is located is a fluid collection tank 66.
(5ee figure I.) The fluid collection tank 66 serves to collect fluid 62 which has been applied to the surface of the thin naturally occurring polymeric shee~ material 14 and which has either been driven through the sheet material 14 and/or the transport mechanism 22 or over the edges of the transport mechanism 22 by the action of the vibrations of the tip 54 of the ultrasonic horn 50. Fluid 62 which is collected in the collection tank 66 is transported by tubing 68 to a fluid holding tank 70.
Figure I illustrates that the fluid holding tank 70 ~ :
contains a pump 72 which, by way of additional tubing 74, supplies the fluid 62 to the fluid spray nozzle 60. According-ly, th~ fluid 62 may be re-cycled for a considerable period of time.
While the mechanism of action may not be fully understood and the present application should not be bound to any particular theory or mechanism of action, it is helieved that the presence of the fluid 62 in the wedge-shaped area 64 during operation of the ultrasonic horn 50 accomplishes two separate and distinct functions. First, the presence of the fluid 62 allows the ~luid 62 ~o act as a heat sink which -2~-, .,. : :
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allows the ultrasonic vibrations to be applied to the thin naturally occurring polymeric sheet material 14 without the thin naturally occurring polymeric sheet material 14 being altered or destroyed as by decomposition or possible melting.
Secondly, the presence of the fluid 62 in the wedge-shaped area 64 allows the fluid 62 to act as a coupling agent in the application of the vibrations from the ultrasonic horn 50 to the thin naturally occurring polymeric sheet material 14.
It has been discovered that the action of the ultrasonic horn 50 on the thin naturally occurring polymeric sheet material 14 microapertures the thin naturally occurring polymeric sheet material 14 in spite of the fact that there are no fibers to re arrange to form microapertures as was the case in Mitchell et al.. The microapertures are punched through the thin naturally occurring polymeric sheat material 14 in the pattern of the raised area or knuckles 34 of the fine mesh wire pattern screen 32. Generally, the number of microapartures produced will be equa:L to the number of raised areas or knuckles 3~ on the upper surface of the fine mesh wire screen 32. Tha~ i5 ~ the number of microapertures will generally be one-half the mesh count of a given ar0a o~
pattern screen 32. For example, if the pattern screen 32 is 100 wires per inch MD by 100 wires per inch CD mesh, the total number of kn-lckles or raised areas 34 on one side of the pattern wire 32, per square inch, will be 100 times 100 divided by 2. This equals 5,000 microapertures per square inch. For a 200 wires per inch MD by 200 wires per inch CD
mesh pattern screen 32 the calculation yields 20,000 " ~'. ' ',. ' ~ ' '' : '. ' . ' ~7~
microapertures per square inch. Depending somewhat on the thickness of the thin naturally occurring polymeric sheet material 14, at a mesh count of about 90,000 (300 wires per inch MD by 300 wires per inch CD) the wires are s~ thin as to allow the knuckles 34 on both sides to microaperture the thin naturally occurring polymeric sheet material 14 if sufficient force is applied. Thus, a 300 wires per inch MD by 300 wires per inch CD mesh screen yields 90,000 microapertures per square inch; for a ~00 wires per inch MD by 400 wires per inch CD mesh--160,000 microapertures per square inch. Of course the MD and CD wire count of the wire mesh screen does not have to b~ the same. -~
It should also be noted that the number of microapertures formed may also vary with the number of ultrasonic vibrations to which the thin naturally occurring polymeric sheet material 14 is subjected per unit area for a given period of time. This factor may be varied in a number of ways. For example, the number and size of the microapertures will vary somewhat with the line speed of the thin naturally occurring polymeric sheet material 14 as it passes underneath the tip 54 of the ultrasonic horn 50. Generally speaking, as line speed increases, first the size of the microapertures decreases and then the number of microapertures decreases. As the numbe. of microapertures decreases the less the pattern of microapertures resembles the pattern of raised areas 34 on the pattern screen 32. The range of line speeds that usually yields microapertures varies with the naturally occurring polymeric material utilized to form the thin naturally , ~
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occurring polymeric sheet material 14 and the materia~ d~ -3 as the fluid 62. For cellophane having a thickness of about 0.8 mil, typical line speeds which usually yield microapertures for a wide variety of fluids range from about 4.5 to about 23.3 feet per minute. For example, if water is used as the fluid with cellophane typical line speeds which usually yield microapertures range from about 4 to about 5 feet per minute. It is believed that, to some extent, the variations in the number of microapertures formed and the size of the microapertures occurs due to the minute variations in the height of the raised areas or knuckles 34 of the fine mesh pattern screen 32. It should be noted that the fine mesh pattern screens used to date have been obtained from conventional everyday sources such as a hardware store. It is also believed that if a pattern screen 32 could be created where all of the raised areas 34 of the screen 32 were of exactly the same height these variations would only occur in uniform fashion with YariatiOnS of line speed.
As was stated above, the area or size of each of the microapertures formed will also vary with the parameters discussed above. The area of tha microapertures will also vary with the area of the raised areas of the pattern anvil such as the knuckles 34 on the fine mesh wire screen 32. It is believed that the type of naturally occurring polymeric material used in forming the thin naturally occurring polymeric sheet material 14 will also vary the area of the microapertures formed if all other parameters are maintained the same. For example, the so~ter the thin naturally occurring ~7~
polymeric sheet material 14~ the easier it is to push the thin naturally occurring polymeric sheet material 14 thxough the raised areas o~ the fine mesh pattarn screen 32. Because the raised areas (~nuckles) on the fine mesh screen are ge~erally pyramidal in shape, the deeper the raised area penetrates tne thin naturally occurring polymeric sheet material 14, the larger the microaperture. In such situations the shape of the microaperture will conform generally to the pyramidal shape of the raised area of the fine mesh screen and the microaperture will be generally pyramldally shaped, in the z direction, and will have an area which is greater at one end than at the other. As has been previously stated, the area of the microaperture should be measured at the narrowest point of the aperture. of course, the height of the raised areas must be greater than the thickness of the thin sheet material 14 for microapertures to be formed and the degree of excess, if any, necessary may vary with the type of naturally occurring polymeric sheet to be microapertured. In any eYent the height of the raised area~ must be sufficient to punch through the naturally occurring polyn~eric material including any elasticity which might be encountered in the punching operation. That is, the more elastic the naturally occurring polymeric material, the greater the height o~ the raised areas has to exceed the thickness of the thin naturally occurring polymeric sheet material~
In some embodiments it may be necessary to su~ject the thin naturally occurring polymeric sheet material 14 to multiple passes through the apparatus 10 in order to -~5-.. . . . .
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microaper~ure the thin sheet material 14. In such situations the thin sheet material 14 will initially only be thinned in the pattern of the pattern anvil's raised areas. However, after two or more passes through the apparatus 10, with the thin naturally occurring polymeric sheet material 14 being aligned in the same configuration with respect to the pattern anvil, microapertures may be formed. Essentially what is happening in these situations i5 that the thin naturally occurring polymeric sheet material 14 is repeatedly thinned by repeated application o~ ultrasonic vibrational force until such time as microapertures are formed. Alternatively, the ~ine mesh wire diameter size may be increased with the consequent decrease in mesh count. Increasing the wire diameter size of the fine mesh screen 32 increases the liklihood that microapertures will be. formed.
Another feature of the present invention is the fact that the microapertures can be formed in a predesignated area or areas of the thin naturally occurring polymeric sheet material 14. This can be accomplished in a number of ways. For example, the thin naturally occurring polymeric sheet material 14 may be 5ub; ected to ultrasonic vi~rations only at certain areas of the sheet m~terial, thus, microaperturing would occur only in those areas. Alternatively, the entire thin naturally occurr.ing polymeric sheet material could be subjected to ultrasonic vibrations with the pattern anvil having raised areas only at certain locations and otherwise being flat.
Accordingly, the thin naturally occurring polymeric sheet material would be microapertured only in those areas which : ` : -, "
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corresponded to areas on the pattern anvil having raised areas.
It should also be noted that some limitation exists in the number of microapertures which can be formed in a yiven thin naturally occurring polymeric sheet material 14 on a single application of vibrational energy, i.P. a single pass through the apparatus if a wire mesh screen is used as the patkern anvil. This follows from the fact that, as was stated above, the height of the raised areas must exceed the thickness of the thin naturally occurring polymeric sheet material 14 in conjunction with the fact that, generally, as the mesh count incrsases the height of the raised areas or knuckles decreases. In such situations, if the number of microapertures desired per unit area is greater than the number which can be formed in one pass through the apparatus, multiple passes are necessary with the alignment of the thin naturally occurring polymeric sheet material 14 with respect to the raised ares being altered or shifted slightly on each pass.
Generally speaking the area of each of the microapertures is greater than about ten square micrometers. That is the area of each of the microapertures may range from at least about 10 square micrometers to about 100,000 square micrometers. For example,the area of each of the formed microapextures may generally range from at least about 10 square micrometers to about 10,000 square micrometers. More particularly, the area of each o~ the formed micxoapertures may generally range from at least about 10 square micrometers to about 1,000 square micrometers. Even more parkicularly, khe area of each of the ~, . . . .
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2~57~
formed microapertures may generally ran~e from at least about 10 square micrometer to about 100 square micrometers.
A number of important observations about the process may now be made. For example, it should be understood that the presence of the fluid 62 is highly important to the present inventive process which uses the fluid 62 as a coupling agent.
BecausP a couplinq agent is present, the microapertures are punched through the thin sheet material 14 as opposed to being fo~med by melting. Additionally, the presence of the shim plate 30 or its equivalent is necessary in order to provide an anvil mechanism against which the thin naturally occurring polymeric sheet material 14 may be worked, that is apertured, by the action of the tip 5~ of the ultrasonic horn 50. Because the vibrating tip 54 of the ultrasonic horn 50 is acting in a hammer and anvil manner when operated in conjunction with the hevay duty wire mesh screen Z8/shim plate 30/fine wire mesh 32 combination, it should he readily recognized that a certain degree of tension must be placed upon the transport mechanism 22 by the downward displacement of the ultrasonic horn 50. If there is little or no tension placed upon the transport mechanism 22, the shim plate 30 cannot perform its function as an anvil and microaperturing generally does not occur. Because both the shim plate 30 and the fine mesh pattern wire 32 form the resistance that the ultrasonic horn 50 works against, they are collectively referred herein as a pattern anvil combination. It should be easily recognized by those in the art that the function of the pattern anvil can be accomplished by other arrangements than the heavy duty wire ~7~
mesh screen 28/shim plate 30/fine mesh screen 32 combination.
For example, the pattern anvil could be a flat plate with raised portions acting to direct the microaperturing force of the ultrasonic horn 50. Alternatively, the pattern anvil could be a cylindrical roller having raised areas. If the pattern anvil is a flat plate with raised areas or cylindrical roller with raised areas, it is desirable for the pattern anvil to be wrapped or coated with a resilient material. Where the pattern anvil is a mesh screen the resiliency is provided by the fact that the screen is unsupported directly below the point of application of ultrasonic vibrations to the mesh screen.
As a result of the microaperturing process the edge lenqth of the thin naturally occurring polymeric sheet material may be increased by at least about 100 percent as compared to the sheet's edge length prior to microaperturing. For example, the edge length of the thin naturally occurring polymeric sheet material may be increased by at least about 500 percent as compared to the sheet's edge length prior to microaperturing.
More particularly, the edge length of the thin naturally occurring polymeric sheet material may be increased by at least about 1,500 percent as compared to the sheet's edge length prior to microaperturing. Even more particularly, the edge lenqth of the thin naturally occurring polymeric sheet material may be increased by at least about 3,000 percent as compared to the sheet's edge length prior to microaperturing.
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The invention will now be discussed with regard to specific examples which will aid those of skill in the art in a full and complete understanding thereof.
Prior to utilizing the present process to microaperture exemplary thin naturally occurring polymeric sheet materials the hydrohead and water vapor transmission rate (wvtr) of the selected materials were measured. Three different cellulosic sheet materials were chosen for the present examples. These were obtained from Flexel, Inc. Company of Atlanta, Georgia under the trade designations (1) 0.8 mil thick Flexel V-58;
(2) 0.9 mil thick Flexel MST and (3) 1.0 mil thick Flexel LST. Flexel, Inc. literature state that the Flexel V-58 is a transparent cellulosic film coated on both sides with a moistureproof, heat-sealable, high-barrier polymer (PVDC) coating. Flexel, Inc. literature states that the Flexel MST
is a mois~ureproof, heat-sealable, transparent, two-sided nitrocellulose coated cellulosic filmO Flexsl, Inc. literature states that the Flexel LST is a two side nitrocellulose coated cellulosic film with intermediate/decreased moistrueproofness to permit breathing, while maintaining yood heat sealability, water resistance ~or moist products, excellent coating anchorage to base film, standard gas barrier properties, and efficient machinability. The hydrohead of each of these materials was in excess of 137 centimeters of water. (This is the maximum hydrohead measurable by our equipment.) The wvtr of the Flexel V-58 was measured as 0.0 grams per square meter per day. The wvtr of the Flexel MST was measured as 0.8 grams ~7~
per square meter per day. The wvtr of the Flaxel LST was measured as 62.5 grams per square meter per day.
EXAMPLE I
A sheet of 0.8 mil thick cellulosic sheet having the trade designation Flexel V-58 was cut into a length of about 11 inches and a width of about 8.5 inches. As wa~ stated above, the hydrohead of the cellulosic sheet prior to hydrosonic treatment was measured as being greater than 137 centimeters of water. The sample was subjected to hydrosonic treatment in accordance with the present invention.
A model 1120 power supply obtained from the Branson Company of Danbury, Connecticut, was utilized. This power supply, which has the capacity to deliver 1,300 watts of electrical energy, was used to con~ert 115 volt, 60 cycle electrical energy to 20 kilohertz alternating current. A
Branson type J4 power level control, which has the ability to regulate the ultimate output of the nodel 1120 power supply from o to lO0~, was connected to the model 1120 power supply.
In this exampl~, the power level control was set at 100%. The actual amount of power consumed was indicated by a Branson model A410A wattmeter. This amount was about 775 watts.
The output of the power supply was fed to a model 402 piezoelectric ultrasonic transducer obtained from the Branson Company. The transducer converks the electrical energy to mechanical movement. At 100% power the amount of mechanical movement of the transducer is about 0.8 micrometers.
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The piezoelectric transducer was connected to a mechanical movement booster section obtained from the Branson company.
The boos~er is a solid titanium metal shaft with a length equal to one-half wava len~th of the 20 kilohertz resonant frequency. Boosters can be machined so that the amount of mechanical movement at their output end is increased or decreased as compared to the amount of movement of the transducer. ~n this example the booster increased the amount of movement and has a gain ratio of about 1:2.5. That is, the amount of mechanical movement at the output end of the booster is about 2.5 times the amount of movement of the transducer.
The output end of the booster was connected to an ultrasonic horn obtained from the Branson Company. The horn in this example is made of titanium with a working face of about 9 inches by about 1/2 inch. The leading and trailing edges of the working face of the horn are each curved on a radius of about 1/8 inch. The horn ~,tep area is exponential in shape and yields about a two-fold increase in the mechanical movement of the booster. That is, the horn step area has about a 1:2 gain ratio. The combined increase, by the booster and the horn step area, in the original mechanical movement created by the transducer yields a mechanical movement of about 4 .0 micrometers.
The forming table arrangement included a small forming table which was utilized to transport and support the cellulosic sheet to be microapertured. Tha forming table included two 2-inch diameter idler rollers which were spaced about 12 inches apart on the surface of the forming table. A
~. .. .
'' , ~
' transport mesh belt encircles the two idler rollers so that a contim1ous conveying or transport surface is created. The transport mesh belt i5 a square weave 20 x 20 mesh web of 0~020 inch diameter plastic filaments. The belt is about 10 inches wide and is raised above the surface of the forming table.
The transducer/booster/horn assembly, hereinafter th~
as~embly, is secured in a Branson series 400 actuator. When power is switched on to the transducer, the actuator, by means of a pneumatic cylinder with a piston area of about 4.4 square inches, lowers the assembly so that the output end of the horn contacts the cellulosic sheet which is to be microapertured.
The actuator also raises the assembly 50 that the output end of the horn is removed from contact with the cellulosic sheet when power is switched off.
The assembly is positioned so that the output end of the horn is adapted so that it may be lowered to contact the transport mesh belt between the two idler rollers. An 8-inch wide 0.005-inch thick stainless steel shim stock having a length of about 60 inches was placed on the plastic mesh transport belt to provide a firm support for a pattern screen which is placed on top of the stainless steel shim. In this example the pattern screen is a 120 by 120 mesh wire size weave stainless steel screen. The cellulosic sheet which was to be microapertured was then fastened onto the pattern wire using masking tape.
The forming table arrangement also included a fluid circulating system. The circulating system includes a fluid .
' 2~3 7~
reservoir tank, a fluid circulating pump which may convenient-ly be located within the tank, associated tubing for transpor-ting the fluid frnm ~he tank to a slotted boom which is designed to direct a curtain of fluid into the juncture of the output en~ of the horn and cellulosic sheet which is to be microapertured.
In operation, the assembly was positioned so that the output en~ of the horn was at an angle of ~rom about 10 to 15 degrees to the cellulosic sheet to be microapertured.
Accordingly, a wedge shaped chamber was formed between the output end of the horn and the celluloslc sheet to be microapexturecl. It is into this wedge shaped chamber that the fluid, in this example a 50 percent 2 propanol/50 percent water, by volume, mixture, at room tempexature, was directed by the slotted boom.
It should be noted that the actuator was positioned at a height to insure that, when the assembly is lowered, the downward movement of the output end of the horn is stopped by the tension of the transport mesh be~ore the actuator reaches the limit of its stroke. In this example, actuating pressure was adjusted ~o 7 pounds per square inch as read on a pressure gauge which is attached to the pneumatic cylinder of the actuator. This adjus~ment results in a total downward force of 30.8 poundsO (7 psi times 4.4 square inches of piston area equals 30.8 pounds of force.) The sequence of operation was (1) the ~luid pUMp was switched on and the area where the output end of the horn was to contact the cellulosic sheet was flooded with the 50 2~7~
percent 2 propanol/50 percent water, by volume, mixture; (2) the transport mesh conveyor system was switched on and the cellulosic sheet started moving at 23.3 feet per minute; and ~3) power to the assembly was supplied and the assembly was lowered so that the output end of the horn contacted the cellulosic shee~ while the sheet continued to pass under the output end of the horn until the end of the sample was reached. The reading on the A410A wattmeter during the process is an i~dication of the ener~y required to maintain maximum mechanical movement at the output end of the horn while working against the combined mass of the 50 percent 2 propanol/ 50 percent water, by volume, mixture, the cellulosic sheet, the pattern wire, the shim stock, and the transport wire.
This example yielded a microapertured cellulosic sheet having a maximum microaperture density o~ about 7,000 microapertures per square inch with the microapertures having an area of about 40 square micrometers. The hydrohead of the microapertured cellulosic sheet was measured as being about 54 centimeters of water and the wvtr o~ the microapertured cellulosic sheet was measured as being about 219 grams per square meter per day.
The edge length increase of this material was calculated to be about 155 percent.
EXAMPLE II
;, , . j , , :
' . .
.
~, ; , , 2 ~3~
The process of example I was repeated with the exception that the line speed of the cellose sheet was 20.9 feet per minute as compaxed to the 23.3 feet per minute utilized in example I. The actual amount of power consumed was indicated by the Branson model A410A wattmeter as about 750 watts. The actuating pressure was about 6 pounds per square inch, gauge.
This example yielded a microapertured cellulosic sheet having a maximum density of about 7,000 microapertures per s~uare inch with the microapertures having an area of about 1,070 square microme~ers. The hydrohead of this sample was measured as being about 22 centimeters of water and the wvtr was measured as being about 1,200 grams per square meter per day.
The edg~ length increase of the material was calculated as being 766%.
Figure IV is a photomicrograph o~ the thin cellulosic sheet material microapertured in accordance with example II.
EXAMPLE_III
The process of example I was repeated with the exception that E'lexel MST was used as the cellulosic sheet material.
Additionally, the line speed o the cellose sheet was 4.S
feet per minute as compared to the 23.3 feet per minute utilized in example I. The actual amount of power consumed was indicated by the Branson model A410A wattmeter as about 850-1,000 watts. The actuating pressure was 8 pounds per square inch, gauge. A 250 by 250 wire count per inch MD and CD mesh screen was used instead o~ the 120 by 120 wire count per inch.
2~37~
water at room temperature was u~ed as the fluid instead of 50 parcen~ 2 propanol/50 percent water, by volume, mixture.
This example yielded a microapertured cellulosic sheet having a maximum density of about 30,000 microapertures per square inch with the microapertures having an area of about 225 square micrometers. The average of two hydrohead readings for this sample was measured as being about 82 centimPters of water and the average of three wvtr readings was about 240 grams per square meter per day. The edge length increase of the material was calculated as being 1,635%.
' EXAMPLE IV
The process of example I was repeated with the exception that Flexel LST was u~ed as the cellulosic sheet material.
Additionally, the line speed of the cellose sheet was 4.5 feet per minute as compared to the 23.3 feet per minute utilized in example I. The actual amount of power consumed was indicated by the Branson model A410A wattmeter as about 900-1,100 watts. The actuating pressure was 8 pounds per square inch, gauge. A 250 by 250 wire count per inch MD and CD mesh screen was used instead of the 120 by 120 wire count per inch.
Water at room temperature was used as the fluid instead of the 50 percent 2 propanol/50 percent water, by volume, mixture.
This example yielded a microapertured cellulosic sheet having a maximum density of about 30,000 microapertures per square inch with the microapertures having an area of about 600 square micrometers. The average of two hydrohead readings for 2~7~
this sample was about 76 cPntimeters of water and the average of three wvtr rPadings was about 440 grams per square meter per day. The edge length increase of the material was calculated as being 2,670%.
EXAMP$E V
Example IV was repeated. This example yielded a microapextured cellulosic sheet having a maximum density of about 30,000 microapertures per square inch with the microaperture~ having an area of about 600 square micrometers.
The average of tWQ hydrohead readings for this sample was about 76 centimeters of water and the average of three wvtr readings was about 950 grams per square meter per day.
Comparing the hydrohead and wvtr data for the cellulosic sheets microapertured in examples I-V to the values obtained for the untreated sheets, it is readily apparent that the sheets have been rendered breathable to water vapor while still maintaining a good hydrohead value. It is to ~e emphasized that some variation is present from example to example. (Note the differing wvtr results in examples IV and V.) It is anticipated that with the use of better equipment and the acquisition of additional knowledge in this area such variations will be reduced accordingly.
The uses to which the microapertured naturally occurring polymeric sheet material o~ the present invention may be put are numerous. Of course, any application which is improved or .
. .
otherwise enhanced if the edge length of the naturally occurring polymeric sheet is increased is to be considered.
~dditionally, ~or nonwater soluble materials, applications where materials having good wvtr values coupled with elevated hydrohead values will present themselves. One such area of use is in the filtration area. In particular, it should be noted that the materials of the present invention are naturally occurring, as defined herein, and they could well find use in the packaginy of food where watar vapor breathability coupled with product protection is desired. An example of an area where increased edge length is benificial is the area of biodegradability. When thin naturally occurring polymeric sheet materials have been microapertured in accordance with the present invention, the edge length of the sheet materials is significantly increased. This increase in edge length decreases the time it takes for the material to be decomposed.
It is to be understood that variations and modifications of the present invention may be made without departing from the scope of the invention. For exampl~, in some embodiments the use of multiple ultrasonic horns aligned abreast or sequentially may be desirable. It is also to be understood that the scope of the present invention is not to be interpreted as limited to the specific embodiments disclosed herein, but only in accordance with the appended claims when read in light of the foregoing disclosure.
Claims (29)
1. A microapertured thin naturally occurring polymeric sheet material having about 1,000 microapertures per square inch.
2. The microapertured thin naturally occurring polymeric sheet material according to claim 1, having at least about 5,000 microapertures per square inch.
3. The microapertured thin naturally occurring polymeric sheet material according to claim 1, having at least about 20,000 microapertures per square inch.
4. The microapertured thin naturally occurring polymeric sheet material according to claim 1, having at least about 90,000 microapertures per square inch.
5. The microapertured thin naturally occurring polymeric sheet material according to claim 1, having at least about 160,000 microapertures per square inch.
6. The microapertured thin naturally occurring polymeric 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 naturally occurring polymeric sheet material prior to microaperturing.
7. The microapertured thin naturally occurring polymeric 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 naturally occurring polymeric sheet material prior to microaperturing.
8. The microapertured thin naturally occurring polymeric 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 naturally occurring polymeric sheet material prior to microaperturing.
9. The microapertured thin naturally occurring polymeric 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 naturally occurring polymeric sheet material prior to microaperturing.
10. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the average thickness of the naturally occurring polymeric sheet material is at least about 0.25 mil.
11. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the average thickness of the naturally occurring polymeric sheet material is from about 0.25 mil to about 5 mils.
12. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the average thickness of the naturally occurring polymeric sheet material is from about 0.25 mil to about 2 mils.
13. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the average thickness of the naturally occurring polymeric sheet material is from about 0.5 mil to about 1 mil.
14. The microapertured thin naturally occurring polymeric sheet material of claim l, 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. The microapertured thin naturally occurring polymeric 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. The microapertured thin naturally occurring polymeric 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. The microapertured thin naturally occurring polymeric 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. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the microaperturing is confined to a predesignated area or areas of the thin naturally occurring polymeric sheet material.
19. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the naturally occurring polymeric material is a water insoluble material and the hydrohead of the sheet material is at least about 15 centimeters of water.
20. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the naturally occurring material is a water insoluble material and the hydrohead of the sheet material is at least about 35 centimeters of water.
21. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the naturally occurring polymeric material is a water insoluble material and the hydrohead of the sheet material is at least about 45 centimeters of water.
22. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the naturally occurring polymeric material is a water insoluble material and the hydrohead of the sheet material is at least about 55 centimeters of water.
23. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the naturally occurring polymeric material is a water insoluble material and the hydrohead of the sheet material is at least about 75 centimeters of water.
24. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the naturally occurring polymeric 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.
25. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the naturally occurring polymeric 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.
26. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the naturally occurring polymeric 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.
27. The microapertured thin naturally occurring polymeric sheet material of claim 1, wherein the naturally occurring polymeric material is selected from one or more of the group consisting of cellophane, cellulose acetate, collagen or carrageenan
28. A microapertured, substantially water insoluble, thin, naturally occurring polymeric sheet material having a thickness of about 1 mil or less, said sheet material having:
an edge length which is at least 100 percent greater than the edge length of the thin naturally occurring polymeric 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.
an edge length which is at least 100 percent greater than the edge length of the thin naturally occurring polymeric 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.
29. A microapertured, substantially water insoluble, thin, naturally occurring polymeric sheet material having a thickness of about 1 mil or less, said sheet material having:
an edge length which is at least 100 percent greater than the edge length of the thin naturally occurring polymeric 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.
an edge length which is at least 100 percent greater than the edge length of the thin naturally occurring polymeric 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.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US76878891A | 1991-09-30 | 1991-09-30 | |
| US768,788 | 1991-09-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2057695A1 true CA2057695A1 (en) | 1993-03-31 |
Family
ID=25083487
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2057695 Abandoned CA2057695A1 (en) | 1991-09-30 | 1991-12-16 | Hydrosonically microapertured thin naturally occurring polymeric sheet materials and method of making the same |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA2057695A1 (en) |
| ZA (1) | ZA927001B (en) |
-
1991
- 1991-12-16 CA CA 2057695 patent/CA2057695A1/en not_active Abandoned
-
1992
- 1992-08-25 ZA ZA927001A patent/ZA927001B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| ZA927001B (en) | 1993-10-04 |
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