CA1155274A - Resilient plastic web exhibiting fiber-like properties and method and apparatus for its manufacture - Google Patents

Abstract

ABSTRACT
A resilient plastic web exhibiting a fiber-like appearance and tactile impression and method and apparatus for its manufacture. In a preferred embodiment, the web exhibits a three-dimensional microstructure comprising a regulated continuum of debossed areas of non-uniform cross-section along their length. In a particularly preferred embodiment, the debossed areas comprise capillary networks interconnecting the first and second surfaces of the web, said networks being of decreasing size in the direction of said second surface to promote fluid transport from the first surface of the web to the second surface and inhibit the flow of fluid in the reverse direction. Forming surfaces utilized to produce said webs are constructed by laminating a multiplicity of thin plates having dissimilar patterns of apertures therein to form an integral structure exhibiting properties and characteristics unachievable by prior art machining and weaving techniques. In a particularly preferred embodiment, the individual laminae from which the laminate forming structure is comprised are produced utilizing photoetching techniques, thus making it feasible to produce nearly any desired level of intricacy in the resultant laminate structure. Preferred means for interconnecting said laminate structures with one another without disrupting the three-dimensional pattern in the area of joinder are also disclosed.

Description

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2 G~t RESILIENT PLASTIG WEB EXHIBITING `.
FIBER--:LIKE PROPERTIES AND METHOD AND
APPARATUS FOR~ ITS MANUFACTURE
CLIFFORD RADEL
HUGH A . THOMP SON
TECHNICAL FIELD
-The present invention has relation to resilient plastic webs exhibiting many of the three-dimensional, fiber-like properties and characteristics previously obtainable only in fibrous webs.
The present invention has further relation ~.
to resilient fluid-pervious plastic webs which exhibit a combination of desirable, but previously incompatible attributes of prior art fibrous webs and prior axt plastic webs in a single structure wi~hout deleterious side effects.
1'hé present in~ention has ~urther relation to the provision Of a m~d and apparatus for ~n~ng plastic wehs exhibiting the aforementioned attributes.

BACKGROUND AP~T
It has long been known in the disposable ~:
absorbent bandage art that it is extremely desirable to construct absorptive devices, such as dispcsa~le diapers, sanltary napkins, and the like r presenting a dry surface feel to the user to improve wearing comfort and:to minimize the development of undesirable skin condition~ due to prolonged exposure to moisture absorbed within the bandage. One viable prior art : 25 ~olution o the aforementioned problem is disclosed in U.S. Patent 4,041,951 issued to Sanford on August 16, 1977, The Sanfoxd patent discloses a preferred disposable ~ diaper structure comprising a substantially planar, moisture absorbent ~ayer disposed between a soft 115-527~

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topsheet and a moisture-resistant backing sheet.
The nonwoven fibrous topsheet p~eferably comprises an integral structure containing a multiplicity of depressed areas which intimately contact the upper-most surface of a substantially planar, moistureabsorbent layer. The nondepressed areas of the topsheet contact the wearer's skin in-use. In a particularly preferred embodiment, the nonwoven fibrous topsheet is comprised of a substantially hydrophobic material exhibiting wet resilience such that the topsheet tends to resume its substantially three-dimensional character upon removal of pressure applied against the topsheet by the body movements of the wearer. The nondepressed areas of the top-sheet, which are of subst.antially the same densityas the depressed areas, tend to isolate the w~arer's skin from moisture contained within the moistuxe absorbent layer, thereby providing surface dryness and resistance to rewetting when the sbructure is temporarily subjected to pressure resulting from the wearer's body movements.
U.~S~ Patent 3,814,101 issued to Xozak on June 4, 1974, attacks the problem of a wet ~ topsheet in a mann~r slightly different rom the use of hydrophobic nonwoven materials. Xozak suggests a topsheet of a nonfibrous, hydrophohic film which is provided with a plurality of valvular slits which restrlct the reverse flow of liquid from the absorbent element of the device.
U.S. Patent 3,929,135 of ~ugh A. ~o~pson, which issued December 30, 1975, to The Procter and Gamble C~ y, ~aid patent being entitled "Adsorptive Str~x~s Having Tapered Capillaries"~ suggests a bopsheet co~prised of liquid~m~ble nHterial, but provided with , . .

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tapered capillaries, said capillaries having a base opening in the plane of the topsheet and an apex opening remote from the plane of the topsheet, said apex opening being in intimate contact with the absorbent pad utilized in the disposabIe absorbent bandage. The topsheet disclosed in the Thompson patent allows the free transfer of fluids from the body into the absorbent element~of the; device while inhibiting the~reverse flow of these~ fluids, thereby providing a relatively much drier~surface in contact with the user than;had been previously obtainable~
` However, contrary to~expectations, it has been leaxned that despite~ the;highly effecti~e fluid transfer and ~ 1uid isolation characteristics exhibited by plastic ~ ~ 15 topsheets of the type generally disclosed in ~he Thompson patent and their proven c~mpatibility with the wearer's skin, many users find it psychologically undesirable to employ a material which is perceivably plastic in contact with their skin. It is believed ~` 20 that this user~reaction is due~partly~to the highly regulated tapered~jcapillary~pattern on the wearer-contacting surface of;~the~topsheet and~partly~to the glossy appe;arance~of thé ~ilm. Users~are prone~to view both of these~characteristics~negatively when dealing wi~h plastic films which will contact the user's skin.
Prior~ art method~and apparatus for embossing, vacuum forming and/or~jperforatIng plastic film~have substantially preçluded the elimination~of~jsuch~plastlc characteristics exhibite~
by ormed ~i~lms. U.S. Patent ~809,392 ~issued to Armstrong on Octo~er 15, I957 discloses a prior art vacuum forming drum utilized to emboss a heat softened thermoplastic ~ilm drawn~across its suriace. ~rhe :

1~55274 vacuum drum comprises a rolled hollow shell provided with a plurality of circumferential grooves which are positioned progressively closer together toward the ends of the drum~ Holes about 1/16 inch in diameter 5 are drilled through the shell at circumferentially spaced points in the grooves. The heat softened film is embossed by the application of vacuum to the interior:surfaces of the drum while the film is in contact with the peri~hery thereof. As should be clear from the foregoing, the pattern of enbos~E~t is inherently governed by machining limitations ; utilized in constructing the drum.
U.S. Patent Re. 23,910 issued to Smith et : al. on Decem~er 14, 1954 discloses yet anothax prior art method and apparatus for producing textured plastic ilms. The Smith Pt al. patent suggests the use of a suction box located beneath the surface o~ a woven wire mesh to draw a heat softened plastic film into conformity with the woven wire mesh. The patent further suggests that a specially patterned belt or fabric could be employed to deform the film :~ in its own ~likeness by supporting the belt or fa~ric ~ :
on: the woven wire mesh. In yet another embodiment, ~:
the process is carried out utilizing the cylindrical :-25 sur~ace of a drum. Nonetheless, the patterns which ~ :~
can be impa~ted to the film are governed by weaving ~: : limitations in the case of the woven wire and fabric and machining/punching limitations in the case of the patterned bel~ or drum. ~urthermore, it is preferred,~according to the teachings of Smith et al., that the forming belt and the forming drum be utilized to produce discrete lengths of ~ilm rather than continuous webs in order to avoid creating joint marks where the ends of the belt or the ends I

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of the drum are joined together.
U.S. Patent 3,054,148 issued to Zimmerli on September 18, 1962 discloses a process for producing a perforated plastic sheet. The process comprises subjecting a plasticized plastic sheet or film to the action of pressure over a perforated support or molding element. The softened plastic material is caused to flow into the perforations of the molding element to a depth which can be regulated by control of such~fac~ors as the degree of softness of the material, the direction of pressure flow and the relative thickness~of the plastic sheet.
The molding~element preferably comprises a drum which may be made~from~a metal sheet having the perforated design stamped or otherwise~ cut from the sheet.
However, in the production of simulated fabrics or woven materials, the molding element pre~erably comprises a woven wire mesh.
A particularly preferred method for continuously debossing an~, if desired~, perforatin~ a plaatlc film is disclosed;~in the U.S.; patent o~ Ualcolm B. Lucas~
~and Robert H. Van Coney~entitled~"METHOD OF AND ~PPARATUS FOR
DEBQSSING AND PERFORATING A RUNNING RIBBON OF THERMOPLASTIC FILM", No. 4,151,240, granted Apri1 24, 1979 to The Proctex & Gam~le Company. The Lucas et a} patent whicht in a preferred embodiment, disclose~s means for~forming a plastic~;film exhibiting a regulated pattern of tapered~;~capillaries as ~enerally~disclosed in th~
aforementivned U.S.~Patent~3,92g,135 of Thompson, causes a ribbon of planar thermo-plastic film to~be forwarded~from a supply 30 ~ roll 9 thence !

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about a circumferentially extending portion of a rotating debossing~perforating cvlinder and then downstream where the debossed and perforated film may be further processed or wound on a spool to form a ro~l. The debossing/perforating cylinder preferably comprises a perforated tubular member through which a plurality of independently adjustable levels of vacuum can be applied from within the cylinder to circumferentially spaced sections of the film in contact with the exterior surface of the perforated tubular member. The apparatus further causes a virtual curtain of hot air to be directed radially inwardly towards a predetermined zone of the perforated tubular member. Thus, vacuum applied from within the cylindex acts in concert with khe cuxtain of hot air which ~lash heats the film sufficiently to effect debossing and perforating of ~he film running circumferentially about the rotating cylinder. The apparatus may further control tension in the film both upstream~and downstream o the debossing cylinder at predetermined constant levels. The disclosed method for making the perforated tubular forming member preferably entails forming the member inside out by electrodepositing nickel about the exterior surfaces of a pattern cylinder having outwardly extending conical projections located about its periphery, and then turning it right side out by slitting it longitudinally, reverse rolling it into the desired tubular shape, and seaming it along the edges thus formed. From the foregoing it is clear that, even in this preferred ~ilm forming process, the par~icular shape or pat rn imparted to the thermopla~tic film on the surface of the :~ 1 5527~

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forming cylinder is indirectly governed by limitations inherent in the machining or metal displacing processes _ utilized to form ~he pattern cylinder.
Accordingly, it i5 an object of the present invention to provide a plastic web exhibiting a three-dimensional pattern of embossments and/or perforations or any desired combination thereof which is independent of the machining and weaving limitations inherent in prior art forming surfaces.
It is another object of the present invention to provide a forming surface ~xhiblting nearly any desired three-dlmensional structure at a scaIe so fine that the resultant plastic sheets ~ormed thereon exhibit iber-like properties and ch~rac1eristics.
It is another object 4f the present invention to provide a continuous, three-dimensionally patterned forming surface, the ends of which may, if desired, be secured to one another substantially without disruption to the three-dimensional pattern contained therein.
It is yet another object of th2 present invention to provide a ~orming surface exhi~iting a I degree of surface roughness or texture to fur~her aid in reducing the ~lossy appearance typically exhi~ited by plastic films.
It is~ still another object of the present invention to provide;a fluid-pervious plastic~web exhibiting a fiber-like appearance and tactile impression, i.e., an overall impression of softness, said web further exhibiting a fine scale three-dimensional microstructure comprising a regulated continuum of capillary networks, preferably o~ steadily decreasing size, originatin~ in and extending from one surface of said film and terminating in the form of apertures in the opposite surface thereof to promote ~ ~552~4 - ~ ~

rapid liyuid transport in ~he direction of decreasing capillary si~e. A~ utilized herein, the term "microstructure" refers to a structure of such fine scale that its precise detail is readily perceived by the human eye Dnly upon magnification by microscopic or other means well known in the art~ The term nf~ber-like", as utilized herein to describe the appearance of plastic webs of the present invention, refers generally to any fine scale pattern of deboss-ments or apertures, random or non-random, reticulated or non-reticulated, which connotes an overall appearance and impression of a ~oven or non-woven fibrous web when viewed by the human eye.
In one aspect, the present inv~ntion resides in a resilient web havins first and ~econd sur~aces and compris~d or -luid-impervious plastic material, said first sur-ace of said web exhibiting a fiber-like appearance and tactile impression~ said web further exhi~iting a three-dimensional microstructure comprising a regulated continuum of debossed areas of non-uniform cross-section along their length, said debossed areas originating in and extendin~ continuously from the plane of ~id first surface in the direction of &aid second surface. This aspect o~ the invention is claimed in Canadian ~pplication No. 346,867, filed March 3, 1980, of which ~e present a~plication is a divisional.
In another a~x~t, the invention resides in a method for constructing a ~firee-d~mensional tubular member for co~tinuously imparting a three-dimensional fiber-like appearance and tactile impression to a plastic web brought in oontact with its peripheral surface, said method comprising:
ta) forming patterns of apertures in a multiplicity of planar sheets, ~t least a portion of said sheets having aperture pattexns which are dissimilar to ~e another;
~b) ~uperposing.said sheets having dissimilar aperture patterns on one ano~her so as to form a stack exhibiting a three-dimensional ~o continuum of capillary net~orks of ~teadily decreasing ~ize from the uppermost surface to the lowermost surface ~hereof;

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- 8a -(c~ bonding said su~rposed stack of sheets t~ one another at contact points to form an integral laminate structure without destroying said continuum of capillary networks;
(d) causing the uppermost surace of said laminate structure to assume a radius of curvature greater than that of said lowermost surface of said laminate structure without causing delamination thereof~ thereby causing said laminate structure to assume a substan-tially tubuiar shape; an~
(e) securing the opposing fxee edges of said tubular shaped laminate structure to one another while maintaining substantial continuity of said three-dimensional continuum of capillary networks about the entire periphery of the tubular me~ber thus formed.
In still another aspect, the invention resides in a method of continuously debossing a :running xibbon o~ s:ubstantially planar thermopl~stic film to impart a three-dimensional fiber-like appearance and tactile impression thereto, said method compxising ~he steps o~:
continuously bringing said film in ~ con~acting relation with a tubular-:! shaped perforate laminate forming surface .- exhibiting a thr~e-dimensional ... microstructure comprising a regulated : continuum of capillary networ~s of.:
; non-uniform cross-section along their length originating in and extending - continuously from the film contacting surface to the non-film contacting surface thereof;
heating a portion of said film in contact . with said ~orming surface above its thermoplastic temperature;
applying a sufficiently great pneumatic differential pressure to said heated thermoplastic film to c~use s~id film to be debossed in the~i~maq.e of ~aid ~ 1552~

- 8 b -perforate laminate forming surfaoe; and cooling the debossed film below its thermoplastic temperature before ~emoving ~aid ilm from ~aid forming ~urface. This aspect of th~
invention is claimed in Canadian Patent Application - No. 346,867, filed March 3, 1980, of which the present application is a divisional.
DISCLOSURE OF INVENTION
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The present invention pertains, in a preferred embodiment, to the provision of resilient plastic webs exhibiting a combination of fiber-like and plastic prop-erties previously unachievable utilizi~g known prior art methods and apparatus for their manufacture. In a par-ticularly preferred embodiment, it provides a fluid-per-vious plastic web having first and second surfaces, at least one ana preferably both of said surfaces exhibiting a fiber-like appearance and tactile impression. Said web preferably exhibits a ~ine scale three-dimensional micro-structure comprising a regulated continuum of capillary netwoxks o~ steadily decreasing size originating in and ext~nding from a ~irst surface of the web and terminating in the ~orm o~ apertures in a 5econd surface thereof to promote rapid fluid transport from said first surface to said second surface. Resilient plastic webs of the present in~ention have widespread application, particular~
ly in absorbent structures such as banda~es, diapers, and .

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~` , g . , catamenial appliances such as sanitary napkins~
tampons, and the like. Said webs, when made fluid-pervious, are particularly well suit~d for use as a wearer-contacting topsheet in such absorbent structures.
However, the present invention is in no way limited to use as a topsheet in such absorbent structures.
Its use may readi;ly~be extended to great advantage in ~ many applications as an improved replacement for prior ; art fibrous webs and/or prior art plastic webs where a ~ lO particular combination of previously unachievable i properties or characteristics is desired in a single structure. ~urthermore, plastic webs of the present invention may be used in lieu of prior art plastic webs to produce a superior end product. For example, a fiber-like plast1c web of the present inveDtion could ~ serve as a breathable backsheet resista~t to aqueous - liquid passage as generally taught by U.S. Patent

3,989,867 issued to Sisson on November 2, 1976, ~-l This would xequire orienting the web ~o as to place the surface exhibiting the finer scale capillary openings in contact with the absorbent pad and *he surface ~`~; exhibitin~ the larg~r scale capiIlary openings opposite the wearer-~contacting surface of the absorbent structure.
Forming sur~aces of the present invention . ~
are preferably constructed by stacking a multiplicity of thin metal sheets or laminae, at least a portion of ~ which exhibit dissimilar patterns of apertures therein, ; upon one another to form a three~dimensional continuum exhibiting the particular structural features desired for the application of interest and bonding said stack - of dissimilar sheets to one another at contact points .
to form an integral laminate structure without destroying said continuum. While saiA laminate structure may, of course, be utilized as a forming , .

~ 1~55274, surface while in a planar condition, it i5 preferably further processed by causing the uppermost surface of said laminate structure to assume a radius of curvature greater than that of the lowermost surface of said S laminate structure without causing delamination, thereby causing said laminate structure to assume a~substantially tubular shape, and securing the opposing free edges of said laminate structure to one another without creating a discontinuity in eit:ner the exterior surface or the three-dimensional continuum existing throughout the tubular member~ thus formed. In~a particularly . ~
;preferred embodiment of the present invention, the free edges of the tubular laminate structure are secured to one another by lap seaming to subs~antially avoid any discontinuity in the three-dimensional pattern exhibited at~ any point along its surface.
The lamlnate tubular member, which permits continuous web processing, is preferably utili~ed in a vacuum forming operation which is conducted in concert with a curtain of hot air which flash heats the plastic ~ilm sufficiently to e~ect substantial conformance to the three-dimensional~pattern embodied in the tubular ; member. In other embodiments, the ~ilm may be preheated prior to contac~wi~h the forming surface, or~the 2~ plastic material may be~direct cast from an extrud~r , , die onto the forming surface. In any event, the film is pxeferably cooled while~ in contact with the tubular orming member and thereater removed.
As will be apparent from the description ~130 contained herein, the present inven~ion may be practiced to great advantage to produce films exhibiting continuous regulated patterns, continuous random patterns, or interrupted patterns merely by constructing the tubular orminy member with the desired pattern on its periphery.
Furthermore, the film processed thereon may be debossed , ~

~155~7~ ' and perforated, debossed only, perforated only, or any desired combination thereof.

BRIEF DESCRIPTION OF THE DRA~qING_ While the specification concludes with claims particularly pointing out and distinctly claiming the present invention, it is believed the present invention will be better.understood from the following description in conjunction with the accompanying drawings in which:
: 10 Figure 1 is a simplified perspec-tive representation of an unfolded disposable diaper with porti~ns of its components cut away;
~igure 2 is a plan view photograph enlarged : approximately 27 times of a prior art nonwoven : 15 fibrous topsheet of the type genera~ly disclosed i.n U.S. Patent 4,041,951, as viewed from the wearer-contacting surfaoe thereo;
Figure 3 is a plan view photograph enlarged approximately 27 times of the nonwoven : 20 fibrous topsheet shown in Figure 2, but taken from the absorbent pad contacting surface of the topsheet;
: Figure 4 is a plaIl view photograp~ enlarged approximately 27 times of a prior art vacuum formed plastic web of the type generally disclosed in U.S.
~` 25 Patent 3,929,135, said photograph being taken rom the wearer-contacting surface of the web;
: Figure 5 is a plan view photograph enlarged approximately 27 times of the vacuum formed plastic web illustrated in Figure 4, but taken from the absorbent pad contacting surface of the web;
:~ Figure 6 is a plan view photograph enlarged approximately 27 times of a ~iber-like plastic web of the present invention, said fiber-like web having a ~ ~5~74 ~

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three-dimensional microstructure comprising a regulated continuum of capillary networks of steadily decreasing size extending from its uppermost to its lowermost surface;
Figure 7 is a plan view photograph enlarged approximately 27 times of the lowermost :~ surface of the web illustrated in Figure 6;
::. ~ Figure 8 is a plan view photograph enlarged ~ approximately 27 times of-a planar segment of a :~` 10 photoetched laminate structure of the type utilized to form plastic webs of the type generally illustrated `~ in Figures 6 and 7;
~ igure 9 is a plan view photograph enlarged approximately 27 times of an individual lamina of the type utilized in the uppermos~ por~ion o~ the ~: photoetched laminate stxucture illustrated in Figure 8;
Figure 10 is a plan view photograph enlarged approximately 27 times of yet another individual 20 lamina of the~type utilized in the intermediate ~;
portion of the photoetched laminate struct~re . I' ~; illustrated in Fi~gure 8, the peripheral outline of ~` each group of openings in said lamina being similar ~:: to the outline of the corresponding openings in the lamina illustrated in Figure 9, but further subdividedj ~- Figure 11 is an enlarged, partially exploded, ~`: perspective view of:a photoetched laminate structure of ~:~ the type generally illustrated in Figure B, the laminae ;~ ln the uppermost~portions of said structure being exploded 1 30 for clarity~to illustrate the manner in which the .. ~ opening patterns in each lamina are supexposed upon one another:to produce a unique three-dimensional continuum of capillary networks of steadily decreasing ,': , , :' I

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size extending from th'e,~~ppermost to the lowermost surface of the laminate;~-Figure 12 is-a- perspective view similar to Figure 11 of an alternat~ pattern comprised of ; 5 uniformly spaced holes -~ steadily decreasing diameter, said pattern ~ ng particularIy suited to formation of a prior a~Lplastic web having a ; pattern of the type~ge~rally illustrated in Figures 4 and 5;
Figure 13:is ~ perspective view of a tubular member formed'~olling a planar laminate structure o the type g~ rally illustrated in ~:' Figure 8 to the desire~ ~adius of curvature and joining the free ends ~reof to one another;
. Figure 14 is~n enlarged, simplified cross-~- sectional ~iew taken a~g sect.ion line 14-1~ of ~' Figure 13 illustrating ~F~referred lap seaming ': technique for joining-~Q.free ends of the photoetched laminate structure to'~ne~ another without substantially ;, ~ 20 disrupting ~he three-d~mensional pattern o the '~ ~laminate structure in-.~h~ area of joinder; ' I
Figure 15 -isl~ view similar to that of ~ .
Figure 14 illustrating'~t another lap seaming . ~echnique which can be ~'sed to join th free ends 25 of the photoetched lam~nate structure to one another ' without substantially ~srupting the three- .
; ~ dimensional pattern in,~.~he area of joinder; and ` Figure 16 is ~ simplified schem~tic ,~ .
' illustration of method-~nd apparatus for deb~ssing - 30 and/or perforating a F~astic film generally in accordance with the pr~sent invention.

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: ' ~" DETAILED DESCRIPTION OF THE PRESENT INVENTION
While the present invention will be described in the context of providing a fiber-like, resilient plastic web suitable fox use as a topsheet on an absorbent bandage such as a disposable diaper, the present invention is in no way limited to such application. To the contrary, the present invention may be~practiced to great advantage in many situations where it is desired to produce a plastic film or web exhibiting either a perfora~e or an imperforate three-dimensional structure having properties, characteristics, aesthetics,~ ~ineness of detail, etc~, not previously obtainable due to machinin~ and/or weaving limita-tions inherent in prior art processes for producing suitable film forming sur~aces. The patterns created may be o~ any desired shape, they may be regulated or random, reticulated or non-reticulated, continuous or interrupted, perforated or unperforated or any desired combination thexeof. The detailed description of a 1~ 20 pxeferred structure~and its use as a topsheet in a disposable d1aper wlll al~low one skllled in the art to readily adapt the invention to othe~ devices.
~ ~ Fi~ure 1 iS a perspective view o a -~ disposable~diaper in an unfolded conditionO Various ~,~ 25 layers have been cut away to~ more clearly show the structural detalls of this embodiment. The disposa~le diaper is referred to generally by the reference numeral 1. The fluid-pervious topsheet is shown at 2. The other two major components of the disposable `~ 30 diapex 1 axe the absorbent element or pad 3 and the 1uid-impervious backsheet 4. In general, the side f 1APS ~ Of the backsheet 4 are folded so as ~o cover the edges of the absorbent pad 3 and topsheet 2.
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Topshe~t 2 is generally folded to completely enclose the ends of the absorbent pad 3. The drawing of diaper 1 in Figure 1 is a simplified representation ~- of a disposable diaper. A more detailed description of a preferred embodiment of a disposable diaper is contalned in commonly assigned U.S. Patent 3,952,745 issued to Duncan on April 27, 1976, to which the reader is re f erred .
~::; Figure 2 is a plan view photograph enlarged approximately 27 t.imes of the wearer-. ~ contacting surface 14 of a prior art nonwoven, .~ generally hydrophobic fibrous web 10 which has been found suitable for use as a topsheet 2 in disposable diaper 1. The web 10 preferably ~
comprises an integral three-dimensional structure containing a mul~iplicity of depressed axeas 11 which intimately contact the uppermost surface of the moisture a~sorbent pad 3, while the nondepressed areas 12 contact.the wearer's skin in-use. Due to .~ 20 the wet resilience and increased overall caliper of the nonwoven fibrous web 10l the nond~epres5ed areas -~
12, which are of substantially the same densit~ as . :
the depressed~areas 11, tend to isolate the wearer's sXin from moisture contained within the moisture 2S absorbent pad 3, thereby providing improved surface dryness and improvad resistance to rewetting when the structure~is.temporarily subjected to pressure resulting ~rom the wearer's body movements.
~ : The prior art nonwoven fibrous web 10 : 30 shown in Figure 2 is generally in accordance with the ; teachings of U.S. Patent 4,041,951 i5sued to Sanford ~ on August 16, 197.70 ~L 15.5~7~
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: -16-An object achieved by the Sanford invention is the provision of a three-di~.ensional topsheet which permits the free transfer of fluids discharged from the wearer's body into the absorbent element of the absorptive device and thereafter tends to isolate the wearer's skin from the fluids absorbed within the absorbent element. A further object . achieved by the Sanford invention is the provision of a nonwoven fibrous topsheet which presents the user with a soft and dry nonirritating surface in contact with the skin.
Figure 3 is a plan view photograph enlarged approximately 27 times of the nonwoven fibrous web lO illustrated in Figure 2, but taken f~om the lowermost or absorbent element-contacting surface 15 of the material.
Figure q is a plan view photograph enlarged approximately 27 times of the wearer-contacting surface 24 of a prior art three-dimensional, fluid-pervious plastic web or film which has also ~een found particularly suitable as a topsheet 2 or disposable diaper 1. The fluid pervious plastic web 20 illustrated in Figure 4 exhibits a~multiplicity of tapered capillaries 21 of critical diameters and tapers, each capillary having a -base opening 22 in the wearer-contacting plane 28 of the web and an apex opening 23 remote from the wearer-contacting plane of the web. The 1uid-pervious plastic web 20, which was vacuum formed from 2.5 mil thick unembossed polyethylene, is generally in ~' 30 accordance with the teachings of U.S. Patent 3,929,135 .
of Thompson, issued December 30, 1975 to The Procter & Gamble - Company. The tapered capillaries 21 conkained in thermoplastic web 20 of Figure 4 1 15527~

have a base opening ~2 measuring approximately 0.040 inches, an apex opening 23 measuring approximately 0.016 inches, an overall height of approximately 0.12 inches and a density of approximately 62~ evenly spaced apertures per square ~: inch. The tapered capillaries 21 allow the free transfer o~ fIuids from the wearer's body into the absorbent element 3 of the diaper 1 illustrated in Figure 1 while inhibiting reverse flow o the absorbed fluids, thereby providing a relatively ary surface ;~ in contact with the wearer.
Despite the effective functioning of the prior art fluid-pervious plastic web 20 in topsheet :
~ applications ~or disposable abs~rbent banda~qesj it has : : 15 ~een observed that users ofken psychologically res.ist placing a plastic material in contact with the skin.
It is believed that this is due in large part to the extremely regulated nature o~ th~ ~attern of capillari.es 21 in the prior art plastic web 20, and also to the ~ 20 slickness or gloss which the user perceives in merely :~
;~ looking at any prior art plastic web or film. This slickness phenomenon is further illustxated in Figure - 5 which is~a~photographic reproduction~enlarged approxi-mately 27 times:of~ the lowermost or absorbent element-contacting surface 25 of the plastic web 20 shown in Figure 4.
In Figure 6 is shown a plan view photo~raph enlarged approximately 27 times actual size of a preferred embodiment of a three-dimensional, fiber-like fluid-pervious plastic web 30 of the present invention.
The fiber-like plastic web 30 is particularly well suited ; for use as a dia~er top5heet ~ in a disposable diaper 1 - o the type generally illustrated in Fiqure 1. Figure ~ 6 is an illustration of the wearer-contacting or : !

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' ~: uppermost surface 34 of the web 30. The web 3a ) ` which exhibits a fib~er-like appearance, embodies a three-dimensional microstructure comprising a :~
regulated continuum of capillary networks of steadily decreasing size extending from the uppermost or wearer-contacting surface 34 to the lowermost or .:, : absorbent pad-contacting surface 35 thereo~ to promote rapid liquid transport from the~uppermost to the~
~:~` lowermost surface of the web. ~:typical capillary ., network comprises an: uppermost capillary opening 31 `` located in uppermost plane 34a of the web 30, said ~,~ opening being further:subdlvided into smaller capillary :: openings 32 and 33:at an:intermediate plane 34b. Capillary openings 32 and 33 are further subdivided into even smaller capillary openings 36, 37 and 38, 39 r respectively, at lowermost plane 34c of thermoplastic ~ web 30, ., Figure 7 is a plan view photograph enlar~ed . approximately 27 times o~ the fiber-like web 30 shown in Figure~6, taken from the lowermost surface : 35 of the web.
From~:~igure 6 it should be noted that djacent capillary~networks,: while exhibiting a : : : :generally s:imilar~:regulated cont:inuum of capiIlary :~ 25 openings of.successlvely smaller~size in the direction of the lowermost surface 35 of said web, are~dissimilar in overall shape and~exact manner of subdivislon~. Accordingly,~the resultant plastic ~`~ : web 30 exhibits much more of a random three-dimensional ~ 30~ fiber-like appearance and tactile~impression to the.
-` user than has~been obtainable by pri~r art methods and ~ ~: apparatus. The increased fluid permeability and ~iner ~, "' '' . .

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~19-detail of the fiber-like plastic web 30 of Figure 6 are clearly apparent when contrasted to a prior art plastic web 20 of the type illustrated in Figure 4.
A comparison of the wearer-contacting surface 34 of a preferred plastic web 30 of the present invention, the wearer-contacting surface 24 of the prior art pIastic web 20 illustrated in Figure

4 and the wearer-contacting surface 14 of the prior art `~
nonwoven fibrous web lO illustrated in Figure 2 reveals }0 a much greater similarity between the fluid-pervi~us plastic web 30 of the present invention and the prior art nonwoven fibrous web lO illustrated iIl Figure 2 ; than between the prior art plastic web 20 and the nonwoven fibrous web lO. This is likewise true with respect to a comparison of the lowermost surface 3S
of a plastic web 30 of the present invention, the lowermost surface 25 of the prior art plastic web 20 illustrated in Figure 5 and the lowermost sur~ace 15 of the prior art nonwoven fibrous web lO illustrated 20 in Figure 3.
As should be readily apparent from the foregoing, the present invention, in a particularly :: pr.eferred embodiment, combines the desirable flu~d . transport and anti-rewet properties provided by the `~ 25 tapered capillaries 21 of prior art plastic ~eb 20 . with the air:permeability, wet and dry resilience, ~-` three-dimensionality, and, at least to a degree, the fiber-lik~feel and appearance o~ prior art nonwoven fibrous web lO in a single, three-dimensi~nal, : 30 resilient fluid-pervious plast:ic web 30.
: T~ further demonstrate the improved functional characteristics exhibited by plastic webs of the present inv~ntion~ samples of a prior art non-woven web as gen~rall~ shown in Figures 2 and 3 ; 1 15527~
.
.~ , (Example I), a prior art plastic web having tapered capillaries as ~enerally shown in Figures 4 and 5 ; (Example II) and a fiber-like plastic web of the ` present invention as genexally sho~n in Figures 6 and 7 (Example III) were subjected to strikethrouyh, surface wetness, permeability and tensile strength testing.
; The prior art non-woven web ~Example I) was comprised of non-woven polyester ~abric such as is available from The Kendall Company of Walpole, Massachuse~ts. The non-woven web, which had a maximum basis weight of approximately 18 grams per square yard, , exhibited a multiplicity of depressed areas as generally described in U.S. Patent 4,041,951 issued to Sanord on August 16, 1977, The prior art plastic web having tapered capillaries ~Example II) was comprised of 2.5 mil thick, ; low slip, unembossed polyethylene available from Visqueen Division of Ethyl Corporation o~ Baton Rouge, ~0 Louisiana under the specification Visqueen White ~1850 The tapered capillaries exhibited a base opening diameter o~ about 0.040 inches, a height of about ~;~ 0.120 inches, and an apex opening diameter of ; approximately 0.016 i~ches. The prior art tapered 25 - capillary film exhibited approximately 625 evenly spaced tapered capillaries per square inch.
~- The fiber-like plastic weh of the present , .......... .
invention (Example III) was comprised of 2.5 ~il ~; thick polyethylene film o~ the type utilized to form the web of Example II. The pattern exhibited by the ~; Example III web was identical to ~hat illustrated in ~ ~ .
~' ' ' ' ' :;

- - 115527~
. .

Figures 6 and 7, which are enlarged approximately ~7 times actual size.
The webs of Examples II and III were formed under similar conditions. Planar metal segments of the respective forming surfaces were preheated in a 225F
oven, and the films were heated to a temperature near their melting point prior to bringing them in contact with the ~orming surfaces. The lowermost sides of the respective forming surfaces were thereaftex exposed to a level of vacuum sufficient to draw the films resting on their uppermost surfaces into conforming contact therewith. Perforation of the films was carried out by directing air heated to a temperature of approximately 800F against the uppermost surfaces of the films while the lowermost surfaces of the films were exposed to vacuum on their respective foxming surfaces. The films were thereafter allowed to cool on the orming sur~aces and manually removed therefrom.
Several samples of each of the materials described in Examples I, II and III were thereafter subjected to comparative testing for strikethr~ugh, surface wetnessj air permeabilit~ and tensi1e strength.
The tests conducted on the webs described in Examples I, II and III are hereinafter described in greater detail.

. ~TRIKETHROUGH
Strikethrough, as utilized hexein, is a measure of the time required for a ~iven volume o~
surface-applied liquid to enter, or "strilcethrough", a topsheet material into an underlying absorbent structure. In the present series of tests it is a measure of the time in seconds to completely drain 5 milliliters of simulated urine solution having a ~ 1155274 ~ ;:
.
surface tension of 45 dynes/centimeter from a one inch diameter ~y:5/8 inch deep cavity having a multiplicity of holes in~its lowermost surface. The cavity is integrally formed in a 4 inch x 4 inch strikethrough plate which~is~placed on a 4 inch by 4 :inch composite - :~
structure comprising the:tapsheet:~eing tested and an ~` absorbent element consisting of a layer of airlaid comminuted wood pulp fibers envelaped hetween a pair : of wet strength tissue plies. The:~wearer-contacting :10~ surface o~ the~topsheet~sample is orlented;face-up.
An ~electric~timer~ls started~;by the simulated urine ~ :
solution:~contacting a~pair;o~ spaced~electrodes in.the ~ aforedescribed cavity. The timer automatically shuts ~ : off~when all;~of the::simulated urine solution has 15~:~d:r:ained from th~ caVity and into the absorbent element.
~ Times are reported in seconds.

.~ SURFACE WETMESS
In order to campare the surface wetnesq ~:: characterist1cs of Examples I, II and III, a test 20~ designed to;measure:the amount of~liqul~d which~ merges rom an absor~ent~::structure, such~as~the disposable ~ :
diaper 1 shown:~in~.~Figure~l, ;through a~ topshéet to cause wetness on the~sùrface:~of~the topsheet~was:conductedO
The;amount of moisture drawn through the~:topsheet is : 25 I termed "~urface~wetness"~and;serves as an estlmate~:of how:dry the~wearer' 5~ ~ski~n wauld~remain if placéd:in :: contact with the~absorbent:~s:tructure.
: Briefly~,;the test~comprises wetting a 4 inch . ~ ~ by 4 inch sample~o~ each topsheet~material while superposed, wearer-contac~ing side up, on a standardized ~: absorbent element.preferably comprising a layer of ;
: ~ airlaid co~minuted wood pulp fibers enveloped between a :

:
, . : ~ :, : , ~ -115527~

; :

.

pair of wet strength tissue plies with a simulated urine solution having a surface tension of approximately 45 dynes/centimeter until the absorbent portions of the structure, i.e., the absorbent element, including the S wet strength envelope tissue has become saturated. In the present series of tests saturation did not occur until a loading factor of 4.8 had been reached, i.e., until the absorbent sample contained 4.8 grams of simu~ated urine solution per gram of absorbent sample.
A uniform pressure loading of 0.5 p.s.i. i5 applied to each sample for a period of 3 minutes so tha* the fluid is uniformly distributed throughout the sample~ The pressure is momentarily removed, a preweighed sample of filter paper approximately 15 centimeters in diamet~r ~15 is insPrted over the uppermost surface of the topsheet of the absorbent sample, and the predetermined pressure loading is reapplied to the sample for a period of 2 minutes. Irhe filter paper is then removed and reweighed, and the amount of fluid absorbed b~ the filter paper is termed the 'isurface wetness" of the sample. Results are expressed in grams of fluid absorbed by the filter paper.
As should thus be apparent, a lower l'surface wetness"
number is indicative of~a dryer surface feel.
. ~ `
AIR PERMEABILITY
Air permeability of the sample webs, which is an indirect measure of breathability and comfort, was determined by placing a one inch ~iameter sample of each web material~on a Fra~ier High Pressure Differential Air Permeability Tester, such a5 is available from Frazier Pr~cision Instrument Company of Gaitbersburg, Maryland. A Frazier Nc. 8 orifice plate was utilized on Examples I ~nd III, while a No. 4 oritice plate was ~; . :

~ -24-, used on Example II to avoid blowing the fluid from .:he - attached manometer. Results were obtained directly from the manometer and converted by means of a standardized chart to provide air flow readings in cubic feet of air per square foot of web material peI minute at 30 inches Hg, 70F, 65% Relative Humidit-y, the conditions underwhich the tests were performed.
.~ :
; TENSILE STRENGTH
All tensile tests were made on an In~tron Model ~ 10 1122 Tensile Tester, such as is available from the ;~ Instron Corporation ~f Canton,~Massachusetts. Tests were conducted by clamping a one inoh wide by two inch long sample in the tester at an initial jaw spacing of -~ one inch. A crosshead speed of one inch per minute was applied until the sample ruptured. Readings at the point of ruptur~ were taken ~xom the Instron's chart recorder, and are expres~ed in terms of gra~ns per inch af sample width.
Results of the aforedescribed tests reported in Table I represent the averase value of all tests actually conducted for each Example. Between 2 and 5 ~ tests were conducted for each Example.

i .
:

11SS27~

TABLE I
;' ~ : _ _ ~ Test Example I Example II F.xample III
:~ (Prior art (Prio~ art (Fiber-like : non-woven fabric pIastic web plastic web ~: 5 web as shown in having of the ~ Figures 2 and 3) tapered present : . : capillaries invention as :- as shown in shown in . Figures 4 Figures ~ andand 5) 7) ~: Strike- 1.57 2.6~ 3.45 through : .
, (~ime in : :
: seconds) .
., : _ _ Surface 1.66 0.03 0.~3 wetness .
(grams of :~: simulated urine . .
::~: 20 absorbed : hy filter l paper) .
~: _ _ _ _ _ _ Air 841 185 677 : permea-25 bility .
~: ~cubic ft.
of air per sq. ft. of material :
30 ~ per minute :
. at 30 inches Hy, 70F, -~ 6S% Relative .
~:. Humidity :
:' ::: ~, , . . ~ . _ 35 Tensile 2,970 1,532 719 strength/
machine :
:: direction (grams per 40 inch) .
. _~ _ _ _ Tensile 291 1,~29 577 strength/ .
~ cross-machine :: direction 4S (grams per .
inch _,___ ___ ___ - ) 11~5274 .

~` , From the data in Table I it is clear tha~ the ': directional fluid handling characteristics of the fiber-like plastic web of Example III closely approxi-mate those exhibited by the prior art'plastic web of :5 Example II. While the performance of neithex af the plastic webs is quite~equal to that of the non-woven : ' fabric web of~Example I in terms of:strikethrough, : experience has demonstrated:that the stxikethrough , charac~er:istics exhib~ited by any of the webs considered in Examples~I, II and III are~quite satisfactory for : use as a disposable diaper topsheet. Furthermore, it is critical to note~that both plastic webs exhibit : tremendous improvement over the non-woven web in terms of surface wetness performance, a characteristic which : 15 :impacts signiicantly on wearPr comfort. Hence their use as a~topsh~et is highly preferred in structures : such as disposable diapers, sanitary napkins and the , like, wherein it is desired to isolate the wearer's skin from fluids absorbed into the absorbent element of the structuxe.
.
The desirable surface wetness characteristics exhibited b~:the web of Example III are even more astounding~when the results of the air permeability tests are compared.~ The air permeability of the fiber-like web of Example III~ is~ approximately 3-4 times that ~: : : of the prio~ art tapered capillary web of Example II, ~ and closely approaches tha~of the non-woven abric web ':~ of Example I.
While~the machine-direction tensile strength of the plastic~web of Example III is only about one half that~of the~ prior art plastic web o Example II and only about one fo,urth that of the non-woven fabric ~: web of Example I, it is notewoxthy that its cross-machine directi~n tensile stren~th is approximately 3S double that of the non-woven fabric web o~ Example I.

' Although the web of Example III exhibits adequate tensile strength for use as a topsheet in most disposable absorbent bandage applications, the reduction in machine-direction tensile strength can, if desired, be compensated for by any of vaxious reinforcin~ means well known in the art. In the case of a disposable diaper wherein the waistbands are subject to greatest tensile loading as the structure is being applied, this could be accomplished by any of various means well known in the art, i.e., reinforcing the waistband areas with beads of adhesive, leaving the .
waistband areas of the topsheet imperforate (this would not adversely affect the diapex's performance since body fluids are not normally discharged in this area), adding an independent reinforcing material in the waistband area, etc.
From the ~oregoing it is clear that plastic webs of the present invention can be made to exhibit desirable properties and characteristics which have been unachievable in a single prior art structure, i.e., the strikethrough~and surface wetness characteristics of prior art plastic webs employing tapered capillary openings ;; in conjunction with an aix permeability, so~tness, tactile impressionj~and handle approaching those of prior art non-woven fabrios.
Furthermore, plastic webs of the present invention may be parti~larly advantageous in situations - where the point of fluid entry is reasonably well defined, ~ such as in sanitary napkins. Fiber-like webs of the ; 30 present invention~may, if desired, be made to exhibit the overall three-dimensional pattern of the fiber-like forming ~ur~ace, but perforated only in the area where body fluids ~re likely to be discharged. The discharged fluids are allowed to enter the absorbent element of the structure through the perforated areas of the web, while j, 1~5~

the imperforate areas of the web erve not only to effectively contain, but also to mask or hide the fluids . absorbed by the structure. Because the unsightly appearance of the absorbed body fluids is masked, S the user feels more comfortable in wearing the structure until its full absorptive capacity has been utilized.
Figure 8 is a plan view photograph enlarged approximately 27 times of the film contacting surface ~: 10 84 of a photoetched laminate structure 80 utilized to vacuum form an initially impervious, substantially planar, heated plastic film to produce a fluid-pervious fiber-like web 30 of the type generally illustrated : in Pigures 6 and 7. A comparison of Figure 8 with the fiber-like plastic web 30 shown in Figure 6 reveals the corr~spondence of capillaxy opening 31 in the uppermost plane 3~a of plastic web 30 to opening 81 in ~h~ upper~
mos~ plane 84a o~ the photoekched laminate stxuc~ure 80.
: Likewise, capillary openings 32 and 33 in intermediate plane 34b o pla~tic web 30 correspond to intermediate : openings 82 and 83, respectively, in intermediate plane 84b of photoetched laminate structure 80.
~: Finally, capillary openings 36, 37 and 38, 39 in lowermost plane 34c of plastic web 30 correspond to ; 25 openings 86, B7 and 88, 89, respectivelyl in lowermost plane B4c of photoetched laminate structure 80.
In the particularly preferred embodiment of the present invention shown in Figure 8, the uppermost surface of:photoetched laminate structure 80 located in uppermost plane 84a is provlded with a fine ~cale micro-texture comprising a multiplicity of generally parallel .~ V-shaped grooves 90 which help to create a random, .

1 155i~

non-planar surface appearance in the processed plastic web. The ridges and valleys formed by the V-shaped groovès 90 tend to minimize the web's gloss.
This is preferably accomplished by utilizing a striated ~; S pattern exhibiting whatever shape or effec~ is desired in the res}st coating applied to the uppermos~ or film-contacting surface of the lamina during the photoetching process. When the lamina is photoetched, the uncoated striations permit partial etching of the uppermost surface to form the V-shaped grooves 90 across the entire uppermost surface of the resultant photoetched lamina. As will be appreciated by those skilled in the art, any of various techniques known in the art ~or providing the desired degree of surface roughness may be utilized in conjunction with l~nae of the present invention. While the surface rouyhening treatment ~` described herein has been limited to the uppermost lamina of the structure shown in Figure 8, ik may, if desired, also be applied to other lan~nae within the stack.
~igure 9 is a plan view photograph enlarged approximately 27 times of an individual lamina 100 of the type employed in~the uppermost por~ion, i.e., that portion intermediate planes 84 and 84b, of the photoetched laminate structure 80 ~5 illustrated in Figur~e 8. As is apparent from an inspection of th-e photograph, opening 101 corresponds to opening~81 in làminate structure 80. Note, however, that the V-shaped grooves 90 which provide a ~icrot xture effect in the~uppermost plane 84a of the laminate stxucture 30 80 axe not present since the lamina 100 is not the uppermost lamina in: the structure.
Figure 10 is a plan view photograph enlarged approximately 27 times of an individual lamina 1~0 of the type generally found intermediate planes 84b and 84c of the photoetcbed laminate structure 80 1.

. . .
.

1 ~5~7~ .

illustrated in Figure 8. Note the presence of openings 112 and 113 corresponding to openings 82 and 83 in the photoetched laminate structure 80.
Figure 11 is a simplified, partially exploded, perspective illustration of a laminate structure 120 generally similar to that of Pisure 8~ ~he laminate struc~ure 120 is comprised of a stack of individual lamunae 130, 131, 132, 133 and 134. ~ach lamina has a pattern of openings therein. L~e 132, 133 and 134 are identical to one another. In practice it is typical to employ several identical lamlnae superposed upon one another to provide sufficient depth of pattern in each dissimilar portion of the laminate structure. However, for simplicity o illustration 1~ a single uppermost lamina 130 and a single intermediate lamina 131 are shown. Lamina 130 exhibits a patterned arrangement o openings 121 which when supexposed on lamina 131 align generally with the periphexal border formed by each pair of openings 122, 123. Similarly, the peripheral b~rders foxmed by each group of openings 126, 127, 128 and 129 in lamina 132 are generally aligned with the peripheral borders formed by openings 122 and 123, respectively, in lamina 131 and opening 121 in lamina 130. From the foregoing, it is readily apparent how intricate three~dimensional geometric structures can be created in nearly any pattern which is desired. It should further be apparent that the resultant three-dimen5ional structure, in most instances, is not susceptible of machining or weaving due to inherent limitations in the machining and weaving processes. For example, non-uniform cross-sections in which ~he open area is greatest near the center of the laminate structure's thickness axe feasible. This can be done by employing centrally located l~nae having open areas greater th~n those of the la~nae employed for - ~ 15527~ :

:~ . . -31-the outer~ost layers Figure 12 illustrates yet another simplified ~ embodiment of a laminate structure 140 which could, if -: desired, be utiliæed to provide a surace suitable for debossing and perforating an initially imperforate, substantially planar plastic film to produce a fluid-pervious web exhibiting a pattern of the type generally ~- illustrated in Figures 4 and 5. The laminate structure 140 is compxised of a stack ~of indivîdual lanunae 150, : 10 151, I52, 153 and 154.~:Each lamina has a pattern -:~ of regularly spaced openings therein. The pattern :` of openings 141 in lamina 150 is concentrically aligned with the pattern of openings 142 in lamina : 151, the pattern of openings 143 in lamina 152, the pattern of openin~s 144 in lamina 153 and the pattern of openings 145 in lamina 154. The diameter of openings ; 141 is greater than the diameter of openings 142 which, in turn, is greater than~the diameter of openings 143, etc., all the way through laminae 15~ and 154. Thus the ~0 resultant laminate structure 140 pro~ides a r.egulated pattern o~ conicaL openings extendlng from the uppermost lamina 15Q~through the lowermost lamina 154. If.desired, the uppermost surface of lamina 150: could also be provided with a microtexture~effect~: i.eO / V-shaped grooves as : :
generally indicated at 90 in the~embodimen~ of Figure 8, : to provide the resultant plastic:web with a microtextured : effect. ~hus,~in addit~ion ~o~providing a vehicle ~or constructing forming surfaces which cannot be formed ~y prlor art means, the lamination techni~ue generally disclosed herein may be utili~ed as an improved vehicle for constructing forming surfaces which are capable of : construction by slower, more expensive and l~ss precise prior art means.

- 1~5.~274 .

While photoetched and other types of laminate structures per se have -or some time been generally known in the art for direct use in components such as turbines and the li~e, ap?lication of the lamination technique,~particularly the photoetched lamination technique, in accord~n^e with the present invention to create novel, continuous for~ing surfaces having unique properties and ch acteristics unachievable by prior art machinins and/or weaving techniques is of tremendous co~.ercial significance in that it virtual~ly frees the plastic web forming industry from the prior art macnining and/or weaving limitations inherent in prior art film forming surfaces.
~ 15 One relevant prior ar. process or c~nstruct-; ing a photoetched laminate structure is disclosed in U.S.
~ Reissue Patent 29,52~ reissued to Spencer on - January 24, l978, , The Spencer pa~ent disclose.s a method for constructing a multilayer porous material particularly suited for use in filtering and turbine ~` cooling applications~ In the disclosed embodiment, a -~ plurality of l~m~e, each having a parallel slot series formed therein, is stacked with the respective adjacent ; 25 slot series overlapping and extending transversely to each oth r. The stack is then bonded together to form a porous laminate. In a disclosed variation, the slots in one or more of the l~m~e are tapered to create a variable porosity in the resultant laminate structure.
Basically, the disclosed process includes the steps of photoetching metal sheets to create the 510t pattern r stacking a plurality of the sheets together with the slots in adjacent sheets extendins transversely to each .

. ~
1 15527~ : :

~ -33- . :
'~ .
other, diffusion bonding the stacked sheets to form a porous laminate, and calendering the finished laminate structure to modify or adjust.its permeability~
In a particularly preferred embodiment of ;

- 5 the present invention, photoetched laminate structures : such as the one illustrated in:Figure 8 are comprised ; of a multiplicity of photoetched laminar stainless steel plates, each plate o~ each series of plates ~ exhibiting a pattern of openings disslmilar to the ; s : 10 adjacent plate or series of plates. ,The laminar ~: : plates are bonded to one another at points of contact to form an integral three-dimensional structure at ~, whatever scale is desired ~or the particular application.
~` The fineness:of the patkern is of course subject to ~' 15 strength limitations inherent in the laminar plates.
These inherent strength limitations control the minimum cross~sectional size of any structural member remaininy ,'~
- within a given plate after the photoetching process ~' has been carried:out. ' '~
The preferred method of ma~ufactuxing laminate . ~ :
`~ ~ structures of the present invention includes~the step of : ~: photoetching the desired patterns into the individual ~ : lam~e. This process lnvolves the coating of one or both .-~
-~. sides of the lamnae~With a resist material i~ the areas to :~
:~ 25 remain solid.: This~:coating can be done in several ~ ~ ways well Xnown in the art~ including silk screen, painting,`, or by photographic means.~ If'a:surface microtexture is ~ desired in the resultant la~e0, the resist coating ', applied to the surface may include a fine pattern of ~,, 30 ~triati,ons or the like. This is followed by a ' chemical etching proces~ which dissolves or at '( least partially *issolves the uncoate~ material to thus crea~e the individual lamLnae. .Inasmuch as this process,is known to those skilled in the art, ..

~ 1 5~274 it is not felt necessary to se~ forth herein a complete detailed description thereof. While ~; photoetching, as outlined above, is generally preferred, it is of course recognized that other forming methods, such as precision stamping, could be used in some cases where the scale of reproduction and the fineness of the pattern will permit.
The photographic coating technique, which is particularly preferred in the practice of the present invention, permits creation o~ patterns specifically designed to provide the precise features desired in the resultant laminate, and consequently in the plastic web formed thereon, at a scale suf~iciently large to be accurately drawn. The finished larger scale drawings may then be photographically reduc~d in si3e to produce the identical pattern at whatever scale or degree of ~ineness is desired. This photo-graphic technique is particulaxly desirable in a fiber-like laminate structure of the type sho~m in Figure 8, wherein the continuum of capillary net~orks of steadily decreasing size is created by sequential subdivision of the~openin~s 81 originating in the uppermost plane 84a of the lami~ate structure 80.
The stainless steel from which the individual l~nae axe preferably comprised supply much of the strength ~ecessary in the extremely fine sections of a design such as the one shown in~Figure 8. The individual 1~
which are typically comprised of 410 stainless steel, may vary in thickness from about 1 mil to about 5 mils in any given laminate structure.
Furthermore, identical lam~e may be superposed upon one another to provide whatever depth or 1 ~552~-~

thickness is desired for any given pattern of openings within the laminate structure. To facilitate bonding, the individual lamunae are preferably electroplated with a coating of pure copper which may vary in thickness from between about 0.01 mils to about 0.1 mils, depending upon the fineness of the pattern in the laminae and the desired degree of bonding in the resultant laminate .
structure. In a par~icularly preferred embodiment, individual l~e of the present invention are first cleaned and struck with a coating of nickel having a thickness on the order of O.Ol mils to ensure more :
e~fective adherence of the copper plate to the ; stainless steel. While i21 most instances e~ery lamina l; in the stac~. is electroplated with copper, it has bee~
ound preferable where extremely fine or delicake patterns are involved to electroplate only every other lamina in the stack to avoid an excessi~e buildup of copper in the resultant laminate structure.
After electroplating with copper, the individual L~nae are stacked in the sequence and orientation des~ired to produce the resultant three-dimensional microstructure, and the stack is preferably~pinned through reg~stration holes which are ~25 photoetched in the~laminar plates at the same time the pattern is etched. ~To avoid disruption of t~e three-dimensional pattern exh~bited by the laminate structure, ~ registration~holes may be provided either in thP borders `~ of the desired pattern or on separate break-away borders of the laminate structure. The pins utili2ed to stack the laminaies are al50 preferably comprised of stainless steel to minimize thermal distortion, and are the exact diametex of the registration holes. A ceramic collar is preferably slipped over each pin on top and bottom of the stack of individual l~e and a stainless steel . ' .

~ 1 55;2~

.

;~ sleeve is then crimped onto the exposed portion of the - pins to hold the stack tightly together in proper registration. Since the brazing operatlon bonds the stainless steel pins to the resultant structure, their use is generally limited to situations where they may be left in place and their ends gxound off, or to situations employing break-away borders. In the event the pins must be removed after brazing, ceramic pins and ceramic collars must be employed.
After pinning, the laminate stack is subjected - to a ~urnace brazing operation to bond the stack of individual laminae into an integral structure. A
honeycomb pattern, silicon nitride ceramic plate is preferably placed adjacent the uppermost and lower~ost surfaces of the laminate stack, and a loading sufficient to provide good bonding but not so great as to cause distortion or deEormation of the laminate stack is applied to the ceramic plates durin~
the furnace brazin~ operation. To ensure the flattest possible surfaces being applied against the laminate stack, the laminate csntacting surfaces of the honeycomb plates are preferably surface ground. The honeycomb ceramic material allows uniorm heating of the surfaces ; of the laminate structure, thereby ensuring uniform bonding th~oughout the contacting portions of the stack of laminax plates. One material found particularly ~` suitable for this purpose is the silicon nitride honey-comb ceramic available from The Norton C~mpany of Worchester, Massachusetts~ While the material is a~ailable in various honeycomb ~izes, one half inch thick sheets having honeycomb openings measuring approximately 1/16 inch across the flats were empl4yed on the laminate structure shown in Figure 8. An alternative material also found suitable ~or this purpose is a - 11~527~

cordierite ceramic honeycomb material available from the General Refractories Company of Philadelphia, Pennsylvania.
- Furnace brazing of the laminate stack to bond the individual lamina to one another is preferably carried out in a brazing furnace utilizing a pure hydrogen atmosphere to prevent oxidation of the copper. In a particuIarly ~;10 preferred embodiment, the laminate stack assembly is placed in the furnace and heated to approximately 1800F until stabilized, i.e., until flashing of the copper plating is initiated. The furnace temperature i5 then elevated to approximately 2,025 F and held ;~15 for approximately three minutes to achieve a more normalized condition o the copper. This improves the ductility of the resultant laminate structure.
Normalizing is preferably followed by rapid cooling, ~ i.e., about 15 minutes, to approximately 200 F. The ; 20 stacked laminate assembly is thereafter removed from ` the brazing furnace and allowed to air cool to room - temperature.
It should be noted thak in furnace brazing operations, it is preferable that all the laminae in a given skack be of the same grade of stainless skeel and that the grain of each lamina be aligned throughout the stack to minimize the chance of distortion in the resultant laminate structure.
In photoetched laminate structures where extremely fine detail is present, a portion of the ~; copper may tend to filIet some of the sharp corners of the three-dimensional microstructure during the furnace brazing operation. This illeting copper may be subsequently stripped out by putting the laminate asserhly into a chromic acid bath for a period .~

- - - -, - , . .

~ 1 ~S27~
.. .. . .. . . .. .
. . . . .
.. .... , .. ...... . . . ~

of time sufficient to remove the excess copper, said period of time being determined by visual observation.
The stacked laminate is thereafter reinserted into the brazing furnace until it reaches a temperature of approxi-mately 1800F and is held at that temperature for aperiod of a~out 2 minutes to even out the remaining copper plating.
In a particularly preferred embodiment of the present invention, the resultant photoetched laminate structures are rolled by conventional techniques into a tubular forming member 160, as illustrated generally in Figure 13. Contrary to expectations, it has been determined that rolling the planar laminate structure into a tubular shape ~ 15 does not tend to cause delamination of the structure, - provided the furnace brazing operation has been properly carried out. Where extremely intricate patterns are present in the laminate structure, lt has been learned that placing a thin sheet of urethane on opposite sides of the laminate structure as it is passed through the metal rolls will minimize the chance of injury to the fine pattern while rolling the member into the desired tubular shape.
The outermost surace 164 of the tubular forming member 160 is~utiIized to form the plastic web brought in contact therewith while the innermost sur~ace 165 af the tubular member generally does not contact the plastic web during the forming operation. The tubulax member 160 may, in a pxeferred embodiment of the present 3~ i~ention,~be employed~as the forming surface on dehossing/
- perforating cylinder 555 in a process of the type generally illustrated in Fi~ure ~6 and described in detail in the aforementioned U .S. patent o~ Malcolm B. ~ucas and Robert ~l. Van Coney entitled "METHOD OF AND APPARATUS

1.

1 ~l5527~
.

FOR DEBOSSING PliND PERE'ORATING A RUNNING RIBBON OF
THERMiOPLASTIC FILM", No. 4,151,240, granted April 24, 1979, A significant advantage off~red by photo-etched laminate forming surfaces of the present invention when contrasted to prior art machined or woven forming surfaces is the ability to join the free ends of a single photoetched laminate section to one another or the ability to join one photoetched laminate section to another photoetched laminate section of similar pattern with substantial continuity in the three-dimensional pattern existing throughout the structure in the area of joinder. This technique may also be employed to join a multiplicity of small sections of similar photoetched laminate structures to one another where, for one reason or another, it is impractical to integrally form the individual laminae in large enough size.
Figure 14 which is a simplified cross-sectional view taken along section line 14-14 of Figure 13 illustrates one preferred manner of joining the free ends of tubular member 160 to one another to provide an integral tubular structure exhibitlng substantially no discontinuity in the three-dimensional pattern in the area of joinder. In the particularly preferred embodiment shown in Figure 14, a lap seam is created by allowing each ; free end of the planar photoetched laminate structure ~rom which tubular member 160 is formed to project in a manner resembling a series of parallel stairsteps. Since the pattern exhibited by each photoetched lamina is precisely regulated and highly repeatable, rolling the planar laminate structure , , i 1 1~527 .
~ , --~o--:~ into a tubular shape causes the mating free ends to align with one another in stairstep fashion as :~ illustrated in ~igure 14. Thus, if the slight differences in radius of curvature for each successive lamina in the stack are ignored, corresponding parts of the pattern employed in laminae170 mate with one another at 17I; ~orresponding parts of the pattern employed in laminael72 mate with one another at 173;
corresponding parts of the pattern employed in laminae .~ : 174 mate with one another at 175, corresponding parts .:l 10 o~ the pattern employed in laminae 176 mate with one ;~ another at 177; corresponding parts of the pattern . ~ ~ employed in laminae178 mate with one anothex at 179;
and corresponding parts of the pattern employed in laminae180 mate with one another at 181. As is :~; 15 apparent ~rom Figure 14, no individual lamina seam is radially al.igned with another, yet the three-dimensional pattern of the tubular member 160 existing between the ou*ermost surface 16~ and the innermost ~ surface 165~is substantially identical at any point .. ~ 20 along the~periphery of the tubular member, including .~: the area of jolnder. Furthermore,~ the resultant seam ; has much sreater strength than a radially aligned butt joint due to the reinforcing effect of one lamina on its~adjacent lamina. Joinder of the lap seam sho~7n in Figure 14 is preferably carried.out ;~ by appIyin~ a~low melting point/ i.e., under lOOO~F, metal bonding alloy to the area of joinder utilizing either a torch or a brazing furnace similar to that generally described in connection with laminat.ion of the planar laminar stack. The low rnelting point metal bonding alloy bonds itself to the laminate structure without creating any substantial discontinuity in the '::

~ 115527~ :

area of joinder while at a temperature which is su~ficiently low that it does not adversely affect ~ the copper bonding within the laminate structure -: per se. Alternatively, the joint could be furnace brazed in the same manner the laminate structure is bonded together, provided the areas outside the joint ~: are protected against excessive heat.
; Figure 15:is a view similar to that of ~ Figure 14, but illustrating yet another lap seamin~
:~ 10 technique which may, if desired, be employed to : join the free ends of:laminar structures of the present invention to one another. Care must, .~ however, be exercised with the construction : : generally illustrated in Figure 15 to prevent non-adjacent laminae from bonding to one another :~ at their free edges during the furnace brazing .. ~1 operation while:the laminate structure is in planar .~: condition. One method of avoiding such problems is ; to temporarily insert thin ceramia paper intermediate the non-adjacent~laminae at the exposed edges during :~ the planar phase of:the furnace brazing operation.
In the tubular embodiment o~ Figure 15; the free ends of tubular element 160l are interleaved with one another such that, if the slight diferences :~ 25 in radius of curvature for each: successive lamina in the stack.are ignored, correspondlng portions of the pattern contained in~laminae~170' are mated to one .~:: : another at 171'; corresponding portions of the pattern : contained in laminae 172' are mated to one~another :

. :

:

~: :

:~ :

.. .. . . ... .. .... ....

1~S27~

, at 173'; corresponding portions of the pattern contained in laminael74' are mated to one another at 175';
corresponding portîons of the pattern contained in ~` laminae 176' are mated to one another at 177' corresponding portions of the pattern contained in laminae 178' are mated to one another at 179'; ~
and corresponding portions of the pattern contained in laminael80' are mated to one another at 181'.~ Thus, -no lamina seam is in radial alignment with an adjacent lamina seam, yet the three-dimensional pattern existing between the outermost surface 164'~and the innermost ~' surface 165' of the tubular member 160' is substantially continuous at any point along the periphery of the drum, including the area of joinder o the free ends.
Thus the present inventiun, in addition to providing planar forming surfaces exhibiting a thr~e-dimensional pattern unobtainable by prior art ~; machining or weaving methods, may, if desired, be utilized to provide a cylindrical forming surface exhibiting substantial continuity~o~ pattern along its entixe~per~lphery. This permits continuous formation '~ of a plastic web~exhibiting the desired three-dimensional pattern without a~seam~dlscontinuity of the~type typically present in~prior art forming surfaces. As~ will be readily apparent to those skilled in the art, the ~resent invention may be applied~to great advantage to pxoduce either perforate or imper~orate plastic webs exhibiting nearly' any three-di~ensional pattern, characteristic, ~'' ~;~ property or~appearance desired. The webs may be made fluid-pervious in certain areas and fluid impervious in others by controlling the level of differential pressure applied to the film during the debossing operation.

1 155~7 ., The inherent flexibi]ity of photographic techniques makes it feasible to create nearly any structure desired by designing the particular characteristics sought into each layer and thereafter . 5 photographically reducing or enlarging the size of the .~ pattern to whatever scale is desired in the photoetched laminae. In other embodiments of the present invention photographs of existing structures exhibiting ~ desirable characteristics could be utilized to form :: 10 one or more of the photoetched laminae. A composite : stack comprised of individual laminae of varying ` patterns may thereafter be assembled to produce a : laminate forming surface exhibiting characteristics . and properties not achievable by prior art means.
A particularly preferred continuous film forming process which may employ a tubular laminate forming surface sf the type generally~shown in Figures 14 and 15 is schematically illustrated in Fiyure I6.
This process is generally described in the aforementioned i 20 U.S. patent of Malcolm B. Lucas and Robert H.
~i . Van Coney entitled "METHOD OF AND APPARATUS FOR
DEBOSSING AND PERFORATING A RUNNING RIBBON OF
: THERMOPLASTIC FILM", No. 4,151,240, granted ~ April 24, 1979.
; 25 . A particularly preferred apparatus 540 of the ; type disclosed in said patent is schematically : shown in Figure:16. It includes constant tension film :~ supply means 541, debossing and per~orating means 543, and constant tension film forwarding and windin~ means ; 30 545.~ The frame, bearlngs, supports and the like:which ~; must necessarily be provided with respect to the ~`' ~ ' ' .
;

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~ ~5527~

functional members of apparatus 540 are not shown or ~ described in detail in order to simplify and more : clearly depict and disclose the present invention, it being underst~od that such details would be obvious to persons of ordinary skill in the art of designing plastic film converting machinery.
Briefly, apparatus 540, Figure 16, comprises means for continuousIy converting a ribbon of thermo-plastic film 550 into a debossed and perforated film 551 by directing hot air jets agalnst one surface o~ the film while appIying vacuum adjacent the opposite surface of the ~ilmi and while maintaining sufficient control of the film 550 t:o substantially obviate wrinkling and/or ~ macroscopically distending the film. Th~s~ as wilI be :~ 15 more fully described hereinafter, appara~us 540 compris~s means for maintaining constant machine direction tension in the ~ both upstream and downstxeam o~ a zone where the temperature is greater than the thermoplastic temperature of the film, but in which zone there is 20 substantially zero machine direction and cross-machine direction tension tending to macroscopically distend the ~ilm. The tension is required to control and smooth~a running ribbon of thermoplastic film; the : zero tension zone results from the:film in the zone being at a sufficiently high temperature~to enable debossing and, if desired, perforating it through the use of heat and vacuum. Figure 16 a}so shows greatly enlarged scale perforations in:film 551 to enable visually perceiving the nature of the difference between the imperforate film 550 and the debossed and perforated fi].m 551 as more fully described hereinafter.
, , ~ ~5~4 As can be seen in Figure 16, the debossing and perforating means 543 includes a rotatably mounted debossing-perforating cylinder 555 having closed ends 580, a nonrotating triplex vacuum manifold assembly 556 and hot air jet means 559. The triplex vacuum manifold assembly 556 comprises three manifolds designated 561, 562, and 563. Also shown in Figure 16 is a freely rotatable lead-on idler roll 565, a power rotated lead-off/chill roll 566, and a soft-face (e.g., low density neoprene) roll 567 which is driven with the chill roll. Briefly, by prcviding means (not shown~ for independently controlling the degree of vacuum in the three vacuum manifolds, a thermoplastic ribbon of film running circumferentially about a portion of the debossing-perforating cylinder 555 is sequentially subjected to a first level of vacuum by manifold 561, a second level of vacuum by manifold 562, and a third level of vacuum by manifold 563. As will be described more fully hereinafter, the vacuum applied to the film by maniold 561 enables maintaining upstream tension in the film, vacuum applied by manifold 562 enables perforating the film when hot air is directed radially inwardly against the film, and vacuum applied by manifold 563 enables cooling the film to below its thermoplastic temperature and enables establishing downstream tension therein. If desired, the film-contacting surface of the debossing-perforating cylinder 555 may be praheated prior -~ to reaching vacuum manifold 562 by means well known in the ar~ (and therefore not shown) to facilitate better con-formance of plastic films comprised of flow-resistant pol~mers during the debossing operation. The nip 570 intermediate chill roll 566 and the soft-face roll 567 is only nominally loaded because high pressure would 27~

: iron-out the three-dimensional debossments which are formed in the ilm in the aforementioned manner.
However, even nominal pressure in nip 570 helps the vacuum applied b~y manifold 563 to isoIate downstream tension (i.e., roll winding tension) from the debossing-perforating portion of the debossing-perforating cylinder 555, and enables the nip 570 to peel the debossed and ~ perforated film~from the debossing-perforatin~ cylinder : 555. Moreover, while vacuum drawn ambient air passing -~ 10 through the film lnto manifcld 563 will normally cool : the film to below its~thermoplastic temperature, the : passage of coolant through the chill roll as indicated by arrows 573~ 574 in Figure 16 will enable the apparatus : to handle thicker films or be operated at higher speeds.
; 15 To summarize, the first vacuum mani~oId 561, ,.~
and the third vacuum manifold 563 loca~ed within the debossing-perforating cylinder 555 ~nable rnaintaining substantiaIly constant upstream and downstream tension respectively in a running ribbon of film while the intermediate portion of the ~ilm adjacent the second vacuum manifold 562 within the debossing-perforating cylinder 555 is subjected to tension vitiating heat and vacuum to effect debossing and per:forating of the ..:
film. ~ ~ :
:- ~ : 25 Referring again to Figure 16, the constant tens:ion film supply means 541 and the constant tension film forwarding and winding means 545 ma~, if desired, be substantially identical to and function substantially ~: ~ identically to:the corresponding portions of the apparatus showr and described in U S Patent Uc. 3,674,221 ~: ~

1 ~5527,~

issued to Riemersma on July 4, 1972. The debossing and perforating means 543 comprises the rotatably mounted debossing-perforating cylinder 555, means (not shown) for rotating the cylinder 555 at a controlled peripheral velocity, the non-rotating triplex vacuum manifold assembly ; 556 inside the debossing-perforating cylinder 55, means (not shown) for applying controlled levels of vacuum inside the three vacuum manifolds 561, 562 and 563 comprising the triplex manifold assembly 556, and hot air jet means 559.
~ The debossing perforating cylinder 555 may be -~ constructed by generally following the teachings of the aforementioned commonly assigned, U.S. Patent 4,151,240 of Malcolm B. Lucas and Rober H. Van Coney, but substituting a tubular laminate forming surface of the present invention for the perforated tubular ~on~ng surface disclosed therein.
; While a preferred application of the disclosed photoetched laminate structure is in a vacuum film forming ~- operation as generally outlined in the aforementioned U.S. patent of Malcolm B. Lucas et al, it is anticipated that photoetched laminate forming structures of the ; present invention could be employed with equal facility to directly ~orm a three-dimensional plastic structure of the present invention. Such a procedure would involve applying a fluid plastic material directly to the forming surface, allowing the fluid material to solidify, and thereafter removing the three-dimensional plastic structure from the forming surface. It is further anticipated that the present technology could, if desired, be incorporated in suitably reinforced film embossing rolls and the like, provided only that the embo~slng pressure~ to which the rolls :

~ ~J

-4~-will ultimately be subject are not so great as to destroy the~particular three-dimensional pattern exhibited by the laminate embossing surface. A resilient back-up roll could, if desired, be utilized in such an embossing operation to avoid damaging the laminate embossing surface. It is even further anticipated that laminate .
forming surfaces of. the present invention may find utility in applications other than plastic film forming.
While particular embodiments of the present invention have been illustrated and described, it will be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention, and it is intended to cover in the appended claims 15 all such modifications that are within the scope of this invention.

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Claims (6)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for constructing a three-dimensional tubular member for continuously imparting a three-dimensional fiber-like appearance and tactile impression to a plastic web brought in contact with its peripheral surface, said method comprising:
(a) forming patterns of apertures in a multiplicity of planar sheets, at least a portion of said sheets having aperture patterns which are dissimilar to one another;
(b) superposing said sheets having dissimilar aperture patterns on one another so as to form a stack exhibiting a three-dimensional continuum of capillary networks of steadily decreasing size from the uppermost surface to the lowermost surface thereof;
(c) bonding said superposed stack of sheets to one another at contact points to form an integral laminate structure without destroying said continuum of capillary networks;
(d) causing the uppermost surface of said laminate structure to assume a radius of curvature greater than that of said lowermost surface of said laminate structure without causing delamination thereof, thereby causing said laminate structure to assume a substan-tially tubular shape; and (e) securing the opposing free edges of said tubular shaped laminate structure to one another while maintaining substantial continuity of said three-dimensional continuum of capillary networks about the entire periphery of the tubular member thus formed.

2. The method of Claim 1, wherein said planar sheets are comprised of metal and said patterns of apertures are formed therein by photoetching.

3. The method of Claim 2, wherein at least the uppermost planar sheet in said stack of sheets is microtextured by photoetching a fine scale pattern of grooves in its uppermost surface prior to superposing said planar sheets on one another.

4. The method of Claim 1, wherein said planar sheets are superposed on one another prior to bonding with their opposing free edges vertically misaligned with one another so that said opposing free edges of said laminate structure mate with one another when said laminate structure is caused to assume a substantially tubular shape to provide substantial continuity of said three-dimensional continuum of capillary networks about the entire periphery of the tubular member thus formed.

5. The method of Claim 4, wherein said planar sheets are so vertically misaligned when superposed on one another that the opposing free edges thereof mate with one another in stairstep fashion when said laminate structure is caused to assume a substantially tubular shape.

6. The method of Claim 4, wherein said sheets are so vertically misaligned when superposed on one another that the opposing free edges thereof mate with one another in interleaved fashion when said laminate structure is caused to assume a substantially tubular shape.