DUAL STRUCTURED FASTENER ELEMENTS

Abstract: A fastener and a method of fastening articles employing the fastener are provided. The fastener includes a fastener (7) element adapted to be mated in an interlocking arrangement to a complementary fastener element (8). The fastener element has a plurality of mating cavities (6). The mating cavities (6) include a mating surface (5) which is adapted to interlockingly engage a mating element (4a, 4b) projecting from the complementary fastener element.

Description: DUAL STRUCTURED FASTENER ELEMENTS Background ofthe Invention A variety of ways have been devised to fasten articles together. For example, it has been proposed to taper the sides of a shaft so that a head portion consisting of, for example, a toothbrush or tool, may be attached, while permitting removal and interchange ofthe head portion, as disclosed in U.S. Patent Nos. 1,887,913 (Bell), 3,039,340 (Livermont), 3,182,345 (Smith) and 3,369,265 (Halberstadt et al ). Also, intermeshing joints have been utilized for connecting in woodworking, as disclosed in U.S. Patent Nos. 1,212,262 (Rockwell), 1,214,261 (Balbach), 1,342,979 (Beitner) and 1,954,242 (Heppenstall), and in metal working, as disclosed in U.S. Patent Nos. 2,895,753 (Fentiman) and 3,000,658 (Sprouse). Further, inclined or tapered shafts have been utilized for interconnecting the ends of leather washers, as illustrated in U.S. Patent No. 281,760 (Gingras). However, all ofthe above have utilized a single shaft and, in some instances, either provided protruding elements along the sides or a T-shaped like-end to provide additional mechanical interference to enhance fastening. Containers ofthe type commonly known as "Tupperware" containers (Tupperware is a registered trademark of Kraft, Inc.) and similar containers are disclosed, for example, in U.S. Patent Nos. 2,487,400 (Tupper), 3,335,774 (Reed), 3,618,802 (Yates, Jr.), 3,730,382 (Heisler), and 3,817,420 (Heisler). The covers of such containers are precisely sized and when mounted, the covers are stretched to cause a tension to be developed in the cover rims between inner and outer retaining lip portions to provide mechanical interlocking for closure. A related patent, U.S. Patent No. 4,819,309 (Bayemer) discloses that the two parts of a fastener may be identical thereby creating what is referred to as a self-mating fastener. A number of fasteners utilizing a plurality of longitudinally extending rib and groove elements which deform, mechanically interfere and resiliently interlock with each other have also been disclosed. Examples of such fasteners are described in U.S. Patent Nos. 2,144,755 (Freedman), 2,558,367 (Madsen), 2,780,261 (Svecedahl), 3,054,434 (Ausnit et al ), 3,173,184 (Ausnit), 3,198,228 (Nato), and 3,633,642 (Segal). microprotrusions may include continuous microprotrusions, e.g., a ridge extending from the sides of a post in a screw thread configuration. Typically, the first mating cavities are defined by adjacent first mating elements projecting from the polymeric substrate. The complementary fastener element includes a polymeric substrate having a plurality of second mating elements projecting therefrom. The second mating elements include a mating surface such that a cross-section peφendicular to the second mating surface includes a plurality of second microprotrusions extending from the second mating surface. When the first and second fastener elements are engaged, at least one mating element projecting from the second fastener element is interlockingly retained in a mating cavity defined by adjacent mating elements on the first fastener element. The fastener elements typically may be releasably engaged with each other. This permits the fastener to be used in applications requiring a fastener which can be repeatedly joined and separated. The fasteners ofthe present invention have a wide assortment of potential applications, such as a fastener on a reclosable container, in place of a button or zipper on clothing or to attach an object to a dissimilar article. The fasteners allow articles to be fastened in a variety of positions and may not require any particular alignment prior to connection. The present invention also permits the construction of fasteners having a direct, continuous relationship between engagement and disengagement forces. Brief Description ofthe Drawings Figure 1 shows cross-sectional view of a fastener element ofthe present invention. Figure 2 A shows a cross-sectional view of first and second fastener elements ofthe type depicted in Figure 1 just after being brought into contact. Figure 2B shows a cross-sectional view of first and second fastener elements ofthe type depicted in Figure 1 interlockingly engaged. -4- generated between contacting surfaces ofthe intermeshing protrusions on each of the functional surfaces. The sides ofthe intermeshing protrusions consist of optically smooth flats. Examples of other fasteners of this type may be found in U.S. Patents 5,071,363 (Reylek et al ), 5,088,164 (Wilson et al.), 5,1 13,555 (Wilson et al.), and 5,201,101 (Rouser et al.). Yet another self-mating fastener which functions by engaging projections on one functional surface into receptacles on a complementary functional surface to form a releasable friction fit is disclosed in U.S. Patent 4,581,892 (Spier). The projections on one surface perforate a web on the second surface and alternate in rows from one side ofthe web to the other. Because ofthe wide variety of potential applications for fasteners there is a continued demand for new fasteners having enhanced performance with regard to a wide variety of factors, e.g., the number of closures, engagement and disengagement forces, noise, relative movement between fastener surfaces, washability, resistance to soiling or contamination, and the level of load or shear stress the fastener will support. There is a continued need for the development of fasteners having enhanced properties with regard to one or more of these factors that will also satisfy requirements concerning ease of manufacture and constraints on cost. Summary ofthe Invention The present invention provides a fastener and a method of fastening articles employing the fastener. The fastener includes a fastener element and a complementary fastener element. The fastener element and complementary fastener element may either be portions of a single structure or may consist of two separate components. The fastener element includes a polymeric substrate having a plurality of mating cavities which include a first mating surface. A cross-section peφendicular to the first mating surface includes a plurality of first microprotrusions extending from the first mating surface. The microprotrusions may include discontinuous microprotrusions, e.g., discrete microprotrusions of regular or amoφhous shape. In other embodiments ofthe invention, the Figure 13 is an electron micrograph (18 X magnification) of a portion of a fastener element of an alternate embodiment ofthe invention which includes a hexagonal array of screw threaded posts. Figure 14 depicts a cross sectional view of a portion of a master used to prepare a microstructured polymeric substrate ofthe present invention. Figure 15 is an electron micrograph of a cross-sectional view of portions of two fastener elements ofthe present invention prior to their being brought into engagement. Figure 16 is an electron micrograph of a cross-sectional view of portions of the two fastener elements of Figure 15 in interlocking engagement. Figure 17 is an electron micrograph (22 X magnification) of a portion of a fastener element of an alternate embodiment ofthe present invention which includes a square array of screw-threaded posts. Figure 18 is an electron micrograph (22 X magnification) of a portion of a fastener element of an alternate embodiment ofthe present invention which includes a square array of screw-threaded posts having four flat faces uniformly uniformly disposed around the circumference of each post. Detailed Description ofthe Invention Figure 1 depicts a cross-sectional view of a portion of a dual structured fastener element ofthe present invention. The fastener element consists of a unitary polymeric substrate 1 which includes a base 2 and solid mating elements 3 projecting from the base. The cross-sectional view shows microprotrusions 4 extending from the sides ("mating surfaces") 5 of mating elements 3. Adjacent mating elements 3a, 3b define a mating cavity 6 which is capable of receiving and interlockingly engaging a suitably sized mating element projecting from a second ("complementary") fastener element. Figures 2A and 2B schematically depict the interaction between two like fastener elements as they are brought into contact with each other. In Figure 2A, the two fastener elements 7, 8 have been pressed together such that only a fraction ofthe microprotrusions 4a, 4b on each ofthe mating surfaces are interlockingly Figure 3 shows a cross-sectional view of a portion of an alternate embodiment of a fastener element ofthe present invention. Figure 4 shows a cross-sectional view of a portion of an alternate embodiment of a fastener element ofthe present invention. Figure 5 shows a cross-sectional view of a portion of a fastener ofthe present invention. The cross-sectional view shows interlocking engaged mating elements from first and second fastener elements. Figure 6 shows a cross-sectional view of a portion of an alternate embodiment of a fastener element ofthe present invention which includes hollow posts. Figure 7 shows a cross-sectional view of a portion of an alternate embodiment of a fastener element ofthe present invention which includes hollow posts having the recesses filled with a polymeric material. Figure 8 shows a cross-sectional view of a portion of an alternate embodiment of a fastener element ofthe present invention which includes a plurality of dual structured mating elements on one face and a "slotted cup" fastener component on the opposite face. Figure 9 shows a cross-sectional view of a portion of an alternate embodiment of a fastener element ofthe present invention which includes a plurality of dual structured mating elements on one face and an adhesive layer covered by a release liner on the opposite face. Figure 10 shows a perspective view of a mating element of an alternate embodiment ofthe present invention. Figure 11 shows a top view of a portion of an alternate embodiment of a fastener element ofthe present invention which includes mating elements ofthe type depicted in Figure 10. Figure 12 is an electron micrograph (18 X magnification) of a portion of a fastener element of an alternate embodiment ofthe invention which includes a square array of cylindrical posts. "complementary fastener element") is capable of being brought into interlocking engagement. The mating elements are typically oriented such that adjacent mating elements on the fastener element define a mating cavity which is capable of interlockingly engaging a mating element projecting from a second fastener element. This may be achieved by a fastener element which has a randomly arrayed set of projecting mating elements. More typically, however, the present fastener elements include some form of regularly arrayed mating elements. For example, the mating elements may include a regular array of parallel ridges 20 ofthe type shown in Figure 3. Alternatively, the present mating elements may include a regular array of discontinuous mating elements, e.g., a square array of tapered posts 25 (as shown in Figure 4) or a hexagonal array of rod-like posts 50 (as shown in Figure 5). The fastener elements may be self-mating, i.e., a fastener element may be capable of interlockingly engaging a second fastener element having an identical or substantially similar structure. It is not necessary, however, that the fasteners ofthe present invention consist of two substantially similar fastener elements. Rather, the present fasteners are only required to include a first fastener element having a mating cavity which is capable of interlockingly retaining a mating element projecting from a second fastener element. For example, the present invention includes fasteners in which the first fastener element has a parallel array of ridge-like elements having a plurality of microscopic ridges projecting from their sides and the second fastener element has an appropriately spaced square array of truncated polygon-shaped elements (e.g., truncated square pyramids). As noted above, the mating cavities on the first fastener element are typically defined by adjacent mating elements projecting from the first fastener element. The portions ofthe outer surfaces ofthe projecting elements defining a mating cavity which come into contact with a second fastener element are referred to as "mating surfaces." Correspondingly, the surfaces ofthe mating elements projecting from the second fastener element which come into contact with the first fastener element also serve as "mating surfaces." The shape and orientation ofthe mating elements on the first fastener element are not necessarily the same as the shape and orientation ofthe mating engaged. As additional force is exerted on fastener elements 7, 8, mating element 9 projecting from second fastener element 7 is driven deeper into mating cavity 6, which is defined by adjacent mating elements 3a, 3b projecting from first fastener element 8. The force required to disengage fasteners ofthe type shown in Figures 2A and 2B is typically proportional to the engagement force applied to the fastener. Application of a relatively moderate engagement force results in projecting element 9 only being partially pressed into mating cavity 6 (see e.g., Figure 2A). As additional force is applied to the fastener elements, mating element 9 is forced deeper into mating cavity 6 and the number of microprotrusions 4a on mating surfaces 10 which become interlockingly engaged with microprotrusions 4b on mating surfaces 1 1 increases. The force required to disengage fastener elements 7 and 8 from each other thus correspondingly increases The mating elements projecting from the present fastener elements may have a wide variety of shapes and orientations. The mating elements may include any one of a number of regular geometric shapes, such as triangular pyramids, posts having a regular polygonal cross-section or fructoconical posts. Alternatively, the mating elements may include randomly oriented projections having an amoφhous shape. Other suitable examples of mating elements which may be present on the fastener elements ofthe invention include spherical or spheroidal shapes. The size and shape ofthe microprotrusions will vary somewhat as a function ofthe draft angle ofthe mating elements. In general, in order to be capable of interlocking engagement, mating elements whose sides have a larger draft angle require somewhat larger microprotrusions. The present mating elements typically include at least one side having a relatively steep draft For example, mating elements having a draft of less than about 30° (with respect to a vector peφendicular to the major surface ofthe polymeric substrate) may be employed. Fastener elements including mating elements having a sidewall which is quite close to being vertical, i.e., having a draft of less than about 10°, are included within the present invention. The size and positioning ofthe mating elements projecting from a polymeric film may be chosen such that a second polymeric film having similar features (the degradation will depend on the intended use for the fastener. For some applications, it is sufficient if the mating elements can survive being brought into interlocking engagement a single time. If the fastener elements are intended to be employed as a closure element on an article of clothing, the fastener elements are preferably sufficiently durable to be able to withstand hundreds or even thousands of engagement-disengagement cycles. Other applications may require fastener elements which are capable of being subjected to 5, 10 or 25 engagement- disengagement cycles. The microprotrusions on the mating surfaces ofthe present fastener elements may have a wide variety of shapes and may be arranged in a random and/or ordered array. The microprotrusions may be discontinuous, i.e., may consist of a plurality of discrete microscopic projections extending from the mating surfaces. For example, the microprotrusions may include a plurality of discrete mounds, posts, cones, pyramids, cylinders, partial spheres or spheroids, truncated cones ("fructoconical"), truncated pyramids, and/or other fructopolygonal shapes. In one embodiment ofthe invention, the microprotrusions include a plurality of small, random microprotrusions which are inverted replicas ofthe cells in the surface of a closed cell polymeric foam. Alternatively, the microprotrusions may be continuous in nature, e.g., a plurality of ridges or a single continuous ridge extending from the sides of a mating element in a screw thread configuration. The dimensions ofthe microprotrusions are typically small enough to leave the overall form ofthe mating elements substantially unaltered. For example, continuous microprotrusions typically have a maximum height or width of no more than about 400 μm. Similarly, discontinuous microprotrusions typically have a maximum height of no more than about 400μm and a maximum width of no more than about 400 μm. Preferably, discontinuous microprotrusions have a maximum height of no more than about 250μm and a maximum width of no more than about 250μm. Continuous microprotrusions preferably have a maximum dimension of no more than about 250μm. The discontinuous microprotrusions typically have a minimum height and width of at least about lOμm and preferably at least about 25μm. Similarly, where the microprotrusions are continuous in nature, the height -10- elements on the second fastener element. For example, the first fastener element may include ridge-like mating elements 20 having a plurality of microscopic ridges 21 projecting from their sides (see e.g., Figure 3). The mating elements 20 of such a fastener element define a plurality of grooved mating cavities 22. In one embodiment ofthe present invention, a fastener may include two such grooved fastener elements. Alternatively, the present fastener may include one such grooved fastener element and a second ("complementary") fastener element which has a different configuration. For example, the second fastener element may include a plurality of discontinuous tapered posts 25 ("mating elements") which have a plurality of ridge-like microprotrusions 26 projecting from at least one sidewall (see e.g., Figure 4). The spacing and orientation ofthe tapered posts on the second fastener element need not be such that the posts are capable of interlockingly engaging every ridged groove ("mating cavity") on the first fastener element. Rather, the size and orientation ofthe tapered posts on the second fastener element need only be such that a sufficient number of posts interact with the corresponding ridged grooves on the first fastener element to achieve interlocking engagement of the two fastener elements. For example, a fastener element ofthe type shown in Figure 4 may have tapered posts 25 oriented such that the posts are only capable of being interlockingly engaged in every second, third or fourth groove-like mating cavity 22 of a fastener element ofthe type shown in Figure 3. Similarly, the height ofthe mating elements on the first and second fastener elements ofthe present fasteners need not be identical so long as a sufficient number of mating elements on the two fastener elements are capable of being interlockingly engaged in order to hold the two fastener elements together. The present fastener elements typically may be brought into interlocking engagement at least once without the microprotrusions on either the fastener element or the complementary fastener being destroyed or having their shape substantially altered. Preferably, the microprotrusions are capable of being subjected to a number of engagement-disengagement cycles without being destroyed or substantially degraded. The number of cycles that a particular fastener will be capable of withstanding without the microprotrusions suffering substantial The resulting polymeric film 33 has a plurality of projecting hollow mating elements 30 having a hollow core 32 (see e.g., Figure 6). The outer surface ofthe mating elements 30 includes a plurality ofthe microprotrusions 31. Where a foam material is employed as the chill roll cover, a substantial number ofthe microprotrusions generated may be undercut-shaped. As used herein, the term "undercut-shaped" is defined as a shape having a cross-sectional surface area which increases and then typically decreases along a peφendicular vector away from the polymer surface. The cross-sectional surface area is measured in a plane peφendicular to the surface with respect to which the undercut-shaped microprotrusions in question are positioned. Because ofthe manner in which such undercut-shaped microprotrusions are formed, the microprotrusions are substantially inverted replicas of the cells in the foam surface ofthe chill roll cover. In another embodiment ofthe invention, a unitary polymeric fastener element which includes solid, mating elements projecting from a sheet of polymeric material (see e.g., Figure 1) may be formed by pressing a flowable polymeric material into a resilient mold (e.g., a silicone rubber mold). The resilient mold typically has a plurality of macroscopic depressions which include microdepressions extending from their sides into the mold. While the polymeric material is in intimate contact with the mold, it is solidified to a sufficient degree to allow the polymeric material to retain its shape as the polymer is pulled out of the mold. The resulting fastener element has a plurality of solid mating elements projecting from the element. At least one outer surface ofthe mating elements includes a plurality of microprotrusions which are inverted replicas ofthe microdepressions in the mold. In a preferred embodiment ofthe invention, a resilient mold ofthe type described above may be mounted as the cover on the chill roll of a nip. Extrusion of a flowable polymeric material, such as a softened thermoplastic polymer, into the nip results in the formation of a polymeric film having solid microstructured projecting mating elements which are inverted replicas ofthe depressions in the resilient mold. -12- and width ofthe microprotrusions are typically at least about lOμm and preferably at least about 25 μm. The present fastener elements may be produced by a variety of methods. For example, a fastener element ofthe type shown in Figure 6 may be formed by embossing a softened thermoplastic polymeric film in a manner that results in an array of hollow mating elements 30 projecting from one surface ofthe film 33 and simultaneously generating a plurality of microprotrusions 31 extending from the outer surface ofthe mating elements. This may be accomplished by passing the thermoplastic film through a nip which includes an embossing roll and a chill roll covered by a layer of resilient material. The resilient material is typically a foam material, e.g., a closed cell polymeric foam (such as LSI 525 polyurethane foam; available from EAR ™ Specialty Composites Coφoration, Indianapolis, IN). The exposed cells at the surface ofthe closed cell foam act as microscopic molds for the formation of microprotrusions on the thermoplastic film. When the softened thermoplastic polymeric film passes through the nip and contacts the embossing and chill rolls, hollow mating elements 30 projecting from the polymeric film are formed. As this occurs, the softened thermoplastic polymeric film is also thrust into intimate contact with the foam surface of resilient roll by the pressure in the nip. This forces the softened polymeric material to conform to the contours ofthe foam. The softened polymer is driven into any recesses, pores or crevices defined by the microscopic cells present on the foam surface, thereby generating microscopic protrusions 31 ("microprotrusions") on the polymeric surface in contact with the resilient surface. The microprotrusions formed on the polymeric surface are typically inverted replicas of corresponding microscopic cells. Contact between the foam surface and the polymeric material is maintained for sufficient time to allow the polymer to solidify to a sufficient degree such that the microprotrusions retain their shape as the microstructured polymeric film is pulled away from the resilient surface. This may be accomplished, for example, by maintaining the temperature ofthe chill roll below the softening point ofthe thermoplastic polymeric material. The overall result is the formation of microprotrusions on the portions ofthe polymeric material in contact with the foam. ■ l l- Examples of suitable thermoplastic polymeric materials which may be employed to produce the present fastener elements include polyolefins such as polypropylene, polyethylene, and polypropylene/polyethylene copolymers. Blends of polypropylene and or polyethylene, such as a high/low molecular weight polyethylene blend (e.g., Hostalloy™ 731; Hoechst Celanese, Somerville, N J ), are also suitable for use in the present invention. Other suitable thermoplastic polymers include polyvinyl chloride (PNC), polyamides such as a nylon (e.g., nylon 6, nylon 6,6, or nylon 6,9), polystyrene, and polyesters. Olefin copolymers such as ethylene/vinyl acetate copolymers or copolymers of an olefin and an a,b-unsaturated acid (e.g., an ethylene/methacrylic acid copolymer reacted with metal salts to confer ionic character; available from E.I. du Pont de Nemours & Co., Inc. as Surlyn™ 8527) may also be employed in the present invention. Resilient polymeric materials such as a silicone rubber, thermoplastic elastomers (e.g., Kraton™), resilient polyurethanes, and plasticized PVC may also be used to form the fastener elements ofthe invention. In a preferred embodiment, the polymeric material includes a polyolefin. The present fastener elements may also be formed from a thermoplastic polymer in the form of a plastisol. The plastisol includes a dispersion of thermoplastic resin particles (e.g., polyvinyl chloride resin particles) in a plasticizer and may also include a volatile organic solvent. Examples of suitable plastisols which may be used to produce the present fastener elements include vinyl plastisols such as #D 1902-50 Black and #D 1902-78 White available from Plast-O-Meric, Inc. (Waukesha, WI). Depending on the structural features and the type of polymeric material employed, the deformation during engagement/disengagement may occur in one of a number of modes. At one extreme, all ofthe deformation that occurs as fastener elements are brought into engagement is localized entirely within the microprotrusions while the body ofthe mating elements remains largely undistorted. This may occur where the microprotrusions are formed from a sufficiently resilient material. The deformation may also be almost totally confined to the microprotrusions where solid mating elements are formed from a rigid polymeric -14- A wide variety of polymers may be used to produce the fastener elements of the present invention. Typically the polymeric material is thermoplastic although other polymeric materials capable of being processed in a flowable state, such as a plastisol or a B-staged thermoset polymer, may also be readily employed. The material the mating elements are formed from as well as the shape ofthe microprotrusions and mating element sidewalls, influences the agressiveness with which a fastener engages. Depending on the fastener design and the nature ofthe disengagement forces it is subjected to, the fastener may optimally be formed from either a high durometer or low durometer (e.g., circa 50 durometer) polymeric material. For example, a fastener including fastener elements having longitudinal grooved ribs which is subjected to a lateral shear force is preferably formed from a relatively high durometer polymeric material (e.g., about 90-100 durometer). Suitable polymeric materials used to form the present fastener elements can be formed into mating elements having microprotrusions which are capable of substantially maintaining their structural integrity when subjected to the shearing forces generated when two ofthe present fastener elements are interlockingly engaged. The polymeric materials must be sufficiently durable to maintain the structural integrity ofthe microprotrusions through the number of engagement- disengagement cycles required by the intended use ofthe fastener. Some applications merely require a fastener having mating elements and microprotrusions capable of substantially sustaining their structure through a single engagement of the fastener elements. Other uses require fastener elements durable enough to withstand a large number of engagement-disengagement cycles without structural failure. In addition to being sufficiently durable, the microprotrusions and/or mating elements on at least one ofthe fastener elements must be capable of sufficiently deforming to allow the microprotrusions to be brought into interlocking engagement. The deformation that occurs during the engagement process is elastic or anelastic but not plastic. In other words, the microprotrusions and/or mating elements deform in a manner such that the structure is substantially maintained following the completion ofthe engagement and/or disengagement process. the mating elements 41 and alter their flexibility and resiliency. The overall resiliency ofthe mating elements on at least one fastener element of a fastener must allow the outer contour defined by microprotrusions 43 to deform sufficiently without be destroyed to enable a complementary mating element to be pressed into mating cavity 44 such that microprotrusions on the mating surfaces in contact are interlockingly engaged. Typically, mating elements on both fastener elements of a fastener are resilient and deform elastically or anelastically during engagement. In order to be achieve interlocking engagement, however, only the outer contour defined by the microprotrusions of one fastener element a pair need be capable of elastic or anelastic deformation. For example, the present invention includes fasteners where one fastener element includes mating elements with microprotrusions formed from a resilient polymeric material while the microprotrusions on the mating elements ofthe complementary fastener element are formed from a rigid polymeric material. The properties ofthe present fastener elements can be tailored by appropriate selection ofthe polymer used to form the hollow mating elements and the polymer used to fill the hollow elements. For example, the hollow mating element 41 and the microprotrusions thereon 43 may be formed from a relatively rigid polymeric material such as a polyolefin, an olefin copolymer, a polyamide, a polyester, PVC, a polystyrene, or a polycarbonate. Thermoset polymeric materials such as an epoxy may also be employed as the relatively rigid material. Fastener elements of this type typically include a relatively resilient polymer, such as a silicone rubber or a thermoplastic elastomer, at least partially filling the cores ofthe mating elements. The presence ofthe resilient material 42 in the core allows such mating elements to deform sufficiently to be placed in interlocking engagement with a second fastener element, while the rigid polymer which makes up the hollow outer shell confers structural integrity and durability on the mating elements. In another embodiment ofthe invention, the fastener elements may include hollow mating elements formed from a relatively resilient polymeric material, such as a silicone rubber, a resilient polyurethane, a plasticized PVC or a thermoplastic elastomer. Fastener elements of this type may have a hollow core which is filled -16- material. In this case, the dimensions ofthe microprotrusions permit them to be flexed in a manner akin to that of a leaf spring. Alternatively, the microprotrusions may be of a material and dimensions such that the microprotrusions are essentially undeformed during engagement and the necessary flexibility is derived entirely from the ability ofthe mating element bodies to deform. This can occur where the mating elements consist of hollow projections formed by embossing a thin film of rigid polymeric material. The hollow inner portion ofthe embossed fastener element may be at least partially filled with a resilient material. This allows the body ofthe mating element to flex even if the microprotrusions remain substantially undeformed during engagement ofthe fastener element. In many instances, however, both the microprotrusions and the body ofthe mating element are deformed to some degree as the fastener element is engaged. Fastener elements which permit a requisite degree of deformation may have one of a number of related structures. For example, the mating elements may include hollow structures projecting from the surface ofthe fastener element. Where the fastener elements are formed as a unitary polymeric structure and include solid mating elements, rigid polymeric materials such as polyethylene, polypropylene or copolymers which include ethylene or propylene may be employed. Other suitable polymeric materials which may be employed to make unitary fastener elements having solid mating elements include polyamides, polyesters, PVC, polystyrenes, and polycarbonates. The polymeric materials used to form solid mating elements are sufficiently rigid to provide structural integrity to the mating elements. The polymeric material must, however, not be so brittle that the microprotrusions are sheared off when two fastener elements are brought into interlocking engagement. The present fastener elements need not have a unitary polymeric structure. Rather, the fastener elements ofthe present invention may be formed from a male- female embossed polymer film having microprotrusions on the male surface ofthe embossed film. The film 40 may be embossed to create a plurality of hollow projecting mating elements 41 (see e.g., Figure 7). The hollow cores ofthe mating elements 41 may be filled with a polymeric material 42 to strengthen and support may be formed from a polymeric substrate having a plurality of such mating elements 70 oriented in a square array (see e.g., Figure 1 1). The mating elements 70 need only have microprotrusions on one or more ofthe surfaces 72 which face the mating cavity defined by four adjacent mating elements 70. When a mating element 71 from a second fastener element is pressed into the mating cavity, the interaction between the microprotrusions on the two sets of mating surfaces is sufficient to interlockingly engage the two fastener elements. The invention is further characterized by the following examples. These examples are not meant to limit the scope ofthe invention as set forth in the foregoing description. Variations within the concepts ofthe invention will be apparent to those skilled in the art. -18- with a relatively rigid polymeric material. To produce fastener elements of this type the hollow mating elements and the microprotrusions thereon are formed from a resilient polymer having sufficient structural integrity to allow the mating elements to withstand the desired number of engagement-disengagement cycles. Polyolefins and epoxies are examples of polymeric materials having the requisite rigidity to be employed as filler in the hollow core ofthe fastener elements. The present fastener elements may optionally include an additional attachment component on a face other than the surface which includes the dual structured mating elements. The attachment component permits the fastener element to be affixed to an article such as a wall, a diaper, a piece of sheet metal, a bulletin board, a container or an article of clothing. The attachment component may include a mechanical fastener element, e.g., a "slotted cup" attachment component 82 ofthe type shown in Figure 8. The fastener element illustrated in Figure 8 includes a plurality of threaded posts 81 on one side and two "slotted cup" projections 82 on the opposite side. Alternatively, a fastener element may have an attachment component which includes a layer of adhesive. For example, the fastener element may have a plurality of threaded posts on one face and a layer of adhesive on the opposite face (see e.g., Figures 7 and 9). The adhesive backing layer 45, 92 on the fastener elements depicted in Figures 7 and 9 allows the fastener element to be affixed to another object. For storage puφoses, adhesive backed fastener elements are typically produced with a removable liner 93 covering the adhesive layer (see, Figure 9). Fastener elements of this type may be employed as a tape substitute, a diaper closure or the like. While the outer surface ofthe present mating elements may be entirely covered with microprotrusions, this is not a requirement. The microprotrusions need only be present on at least one surface of a mating element which comes into contact with a mating surface bearing microprotrusions on a second mating element when two fastener elements are engaged. For example, the mating element 60 illustrated in Figure 10 only has microprotrusions 62 on the four mating surfaces 61 at its corners. The remaining surfaces 63 on the sides of mating element 60 need not have any microstructure and may even be optically smooth. A fastener element extended about 0.2 mm out from the sides ofthe posts. If the faces containing the threaded posts of two such polyethylene fastener elements were pressed together, the fastener elements formed a self-mating fastener. Example 2 A fastener element having a dual structured portion (hexagonal array of threaded posts) on one major face was made in a manner substantially identical to that described in Example 1, except that after the polyethylene was pressed into the depressions in the resilient mold, the Kapton™ layer was removed and the polyethylene was left on the hot plate in a molten state to form "Segment A" of a fastener. A fastener component having a "slotted cup" configuration was formed on the opposite face ofthe fastener element according to the following procedure. This mechanical fastener consisted of two "slotted cup" projections designed to lock into two 8 mm diameter holes. A silicone rubber master mold was formed from two "slotted cup" projections (#SJ3747, 3M, St Paul, MN) according to the procedure described in Example 1 except that an approximately 7.5 mm thick coating of uncured silicone rubber was applied to the two "slotted cup" projections. The "slotted cup" master mold was placed on a hot plate at 216°C, several layers of 152 μm thick polyethylene film (as per Example 1) were placed on top of the mold and a layer of 38 μm thick Kapton™ film was placed on top ofthe polyethylene. The polyethylene was allowed to melt (5 to 10 minutes) and then pressed into the holes in the mold and the Kapton™ film was removed from the top ofthe polyethylene to form "Segment B" of a fastener Segments A and B were then joined such that the unmolded faces ofthe two polyethylene layers were allowed to bond in a molten state. The two segments were maintained in contact while in a molten state for 5 to 10 minutes and then the entire polymeric assembly was moved off the hot plate and allowed to cool. The polyethylene fastener element was removed from the silicone rubber molds as a unitary polymeric assembly having a plurality of threaded mating elements projecting from one side and a "slotted cup" fastener projecting from the opposite -20- Example 1 The dual structured fastener element of this example was prepared starting from a master (which had the configuration ofthe fastener element). A resilient mold was then made ofthe master and the fastener element was formed from the resilient mold. The master was produced from a flat plate tapped with holes for an 0-80 UNF series designation screw (outside thread diameter of 1.5 mm and inside diameter of 1.3 mm). The holes were placed in a hexagonal array with hole to hole spacing of 2.4 mm and row to row spacing of 2.1 mm. The 0-80 screws were threaded into the plate so that approximately 6 threads showed on the non-head side (i.e., threaded posts about 2.1 mm in height projected from the flat plate). A patterned silicone rubber mold was then prepared ofthe above master by applying an approximately 5 mm thick coating of uncured silicone rubber (Silastic™ brand J-RTV silicone rubber; available from Dow Corning Coφoration, Midland, MI) over the surface containing the threaded posts. The rubber was cured at 67°C for one hour and then removed from the master to provide a resilient mold. The mold had a hexagonal pattern of threaded depressions which were inverted replicas ofthe threaded posts projecting from the surface ofthe master. The depressions were about 2.1 mm deep with threaded grooves (circa 0.2 mm deep) on the sides of the depressions. The rubber mold was placed on a hot plate at 216°C and several layers of 152 μm thick polyethylene film (formed from DOWEX™ 2047A; available from Dow Chemical Company, Midland, MI) were placed on top ofthe mold. A layer of 38 μm thick Kapton™ film (polyimide film available from E.I. duPont de Nemours and Company Incoφorated, Wilmington, DE) was placed on top ofthe polyethylene. The polyethylene was allow to melt (5 to 10 minutes) and then pressed into the depressions in the mold. After the polyethylene had cooled to a sufficient degree to allow the threaded posts to retain their shape, the polyethylene fastener element was removed from the mold and the Kapton™ film was removed. The resulting fastener element was a polyethylene film having 2.1 mm high threaded posts projecting from one major face ofthe film (see Figure 1). The threads diisocyanate (Rubinate 1920 available from ICΪ, Rubicon Chemicals, Geismer, LA); Part C - 4.77 php of a 70.9% (w/w) solution of a silicone surfactant (L- 5614, available from OSI Specialities) in a polyether glycol (Niax E-351, available from Arco Chemical Co.); and Part D - 6.71 php of an approximately 8% solids (w/w) dispersion of carbon black (Product No. 1607029, available from Spectrum Colors, Minneapolis, MN) in polyether glycol (Niax E-351). Separate feed streams ofthe four components were pumped into a 90 mm dual head Oakes Frother (available from ET Oakes Coφ., Hauppauge, NY) through an entrance manifold attached to the frother. The mixture was frothed by injecting high purity nitrogen through a capillary tube located at the entrance to the frother. The frothed mixture was processed through the frother at a mixing speed of 800 φm and a discharge pressure of about 0.55 MPa and dispensed from an approximately 2.6 m x 1.3 cm hose onto a polyester film and spread over the film using a knife coater (2.4 mm gap). The foam was cured by passage through a 3 chambered 13.7 m forced air oven at a line speed of 1.5-1.8 m/minute. The first chamber was maintained at 135°C. The second and third chambers were maintained at 154°C. When the embossed polypropylene film was folded back onto itself such that two portions ofthe male mating surface were brought into contact, the projecting elements interlockingly engaged. After a number of engagement-disengagement cycles, the fastener element would no longer lockingly engage with itself. Examination ofthe male surface ofthe film under an optical microscope revealed that the small protrusions on the sides ofthe posts had been flattened. This suggests that the interactions ofthe secondary structure (small, random protrusions) are necessary in order for the interlocking engagement ofthe posts. Example 4 The embossed polypropylene film of Example 3 was coated on the female side with a silicone rubber (Silastic™ brand E-RTV silicone rubber; available from -22- side (see Figure 8). The polymeric assembly was capable of being mechanically fastened on either or both sides. Example 3 A self mating fastener element was made by passing molten polypropylene (formed from DS7C50; available from Shell Chemical Co., Houston, TX) through a nip where the polypropylene was pressed between a metal tool and a chill roll covered with two 3.2 mm thick sheets of a closed-cell polyurethane foam (see description below). The metal tool had a hexagonal close packed array of projecting circular posts (1.0 mm in diameter, 1.0 mm in height) which were spaced 1.8 mm on center. This produced a male-female embossed polypropylene film having large hollow posts (1 mm in height, 1 mm in average diameter) projecting from one face ofthe film ("male mating surface") in a hexagonal array (1.8 mm on centers). The male surface ofthe embossed polypropylene film had a secondary structure consisting of small, random microprotrusions, which were inverted replicas ofthe cells in the surface of the foam sheet. The polyurethane foam used as the chill roll cover was prepared as generally described in U.S. Pat. Nos. 3,772,224 (Marlin et. al.) and 3,849, 156 (Marlin et. al). The foam was prepared from a four component mixture (A-D), the composition of which were as follows: Part A - 100 parts of a polyol mixture consisting of Niax 24-32 (97.77 parts) and Niax E-434 (2.23 parts), polyether polyols (available from Arco Chemical Co., Newton Square, PA) dipropylene glycol (9.18 parts per hundred parts (php) polyol; fragrance grade), Niax LC-5615 (3.74 php, a nickel catalyst composition available from OSI Specialities, Lisle IL), aluminum trihydrate filler (54.59 php, Aloca C-331, available from Aluminum Company of America, Bauxite, AR), and Hostaflam AP 442 flame retardant (16.38 php, available from Hoechst Celanese Corp., Charlotte, NC); Part B - 37.39 php of an isocyanate mixture consisting of 4,4'- diphenylmethane diisocyanate and a modified 4,4'-diphenylmethane approximately 6 threads showed on the non-head side (i.e., threaded posts about 2.2 mm in height projected from the flat plate). A silicone rubber mold was prepared from this master and a polyethylene fastener element was produced from the mold according to the procedure described in Example 1. The resulting fastener element was a polyethylene film having a square array of 2.2 mm high threaded posts projecting from one major face ofthe film (see Figure 17). The threads extended about 0 2 mm out from the sides ofthe posts. When the faces containing the threaded posts of two such polyethylene fastener element were pressed together, the fastener elements formed a self-mating fastener. Example 7 A fastener element having a square array of microstructured posts on one major face was made in a manner substantially identical to that described in Example 1, except that a different master was used to form the rubber mold. The master was made by machining the master used in Example 6 such that each screw 60 had four flat faces 63 uniformly disposed around the circumference ofthe screw (see Figure 10). The flat faces were separated by portions ofthe screw sidewalls 61 which still retained the threads 62. A silicone rubber mold was prepared from this master and a polyethylene fastener element produced from the mold according to the procedure described in Example 1. The resulting fastener element was a polyethylene film having a square array of 2.2 mm high threaded posts projecting from one major face ofthe film (see Figures 11 and 18). The posts had six ridges protruding about 0.2 mm on the post sidewalls 72 directed at the center ofthe mating cavity (see Figure 1 1). The mating cavity is defined by four adjacent posts 70 in the square array. When two such polyethylene fastener elements were pressed together, the fastener elements formed a self-mating fastener. The projecting posts on the two fastener elements were disposed so that the threads projecting from sidewalls ofthe corner ofthe posts were interlockingly engaged (see Fig. 1 1). -24- Dow Corning Coφoration, Midland, MI) such that only the recesses in the female side ofthe posts were filled with silicone rubber. The initial engagement- disengagement forces required with the silicone rubber-filled fastener element appeared to be higher than those for the fastener element of Example 3. However, after a number of cycles the small protrusions on the sides ofthe posts flattened, as with the fastener element described in Example 3, and the fastener element ceased to interlockingly engage with itself. Example 5 A self-mating fastener element was made by coating the patterned silicone rubber mold of Example 1 with a mixture of Kraton™ G1652 (available from Shell Chemical Co., Houston, TX) and toluene at 33% solids. As the toluene evaporated, a continuous Kraton™ film covering the threads and the land area between the threaded depressions was formed. The resulting resilient Kraton™ film was a replica ofthe mold and had a hexagonal pattern of 2.1 mm high hollow, threaded posts. The hollow posts were filled with an epoxy resin (a 5: 1 mixture of Epo-Kwik™ Resin No. 20-8136-128 and Epo-Kwik™ Hardener No. 20-8138-032; available from Buehler, Lake Bluff, EL) which was allowed to harden. When the faces containing the threaded posts of two such fastener elements were pressed together, the fastener elements interlockingly engaged. The engaged fastener elements were disengaged and reengaged a number of times demonstrating the fastener elements having resilient hollow posts filled with a rigid material can form a releasably engageable self-mating fastener. Example 6 A fastener element having a square array of microstructured posts on one major face was made in a manner substantially identical to that described in Example 1, except that a different master was used to form the rubber mold. As in Example 1, the master was produced from a flat plate tapped with holes for 0-80 UNF series designation screws placed in a square lattice array with hole to hole spacing of 2.0 mm. The 0-80 screws were threaded into the plate so that The grooved faces 105, 106 of two master elements (A, B) were nested together so that the acute tear angle edge 100 of one element (B in Fig. 14) extended beyond the obtuse tear angle edge 101 ofthe second element (A in Fig. 14) by four ridges. The smooth face 102 of a third master element (C in Fig. 14) was then placed against the smooth face 103 ofthe second master element (B) with the acute tear angle edges 100, 104 aligned. The grooved face 108 of a fourth master element (D in Fig. 14) was then nested with the grooved face 107 ofthe third master element (C) with the obtuse angle tear edge 109 being indexed four groves below the acute tear angle edge 104 ofthe third element (C) and aligned with the obtuse tear angle edge 101 of the first master element (A). The stacking pattern (ABCDABCD ) was repeated until a fastener master 112, approximately 1.2 cm X 6.5 cm was assembled. The total assembly was clamped together using a number of binder clips (5/8 inch capacity binder clip No. 100500 distributed by IDL Coφ., Carlstadt, NJ). A master mold ofthe fastener master was prepared according to the following steps: a) Forcing a vinyl siloxane dental impression material (3M ExpressO, available from 3M, St. Paul, MN) into the contoured edge ofthe fastener master with the manufacture's supplied application device, being careful to avoid entraining air bubbles between the impression material and the fastener master; b) Containing a pool ofthe dental impression material on a glass plate between two aluminum spacer bars (approximately 0.32 cm X 1.25 cm X 2 cm) positioned approximately 2.5 cm apart; c) Centering the fastener master over the spacer bars such that each end ofthe fastener master overlapped each spacer bar approximately 0.5 cm and forcing the impression filled face ofthe fastener master into the pool of impression material until the impression filled edge ofthe fastener master contacted the spacer bars; -26- Example 8 A fastener element prepared according to the procedure described in Example 6 was treated with a primer and coated with an adhesive on the flat side of the polyethylene film (the side opposite the mating elements). The flat side ofthe fastener element was primed with a acrylic based polyolefin primer (available as product number 4298 from 3M, St. Paul, MN) using a small brush. After the primer was allowed to air dry for 20 minutes, a 0.25 mm acrylic pressure sensitive transfer adhesive carried on a removable liner (F9473PC, available from 3M, St. Paul, MN) was laminated onto the primed side ofthe fastener element with a 2.4 kg hard, rubber roll. After removal of the liner, the fastener element was adhesively laminated to an aluminum plate. The adhesive backing thus allowed attachment of the self-mating fastener element to a substrate. Example 9 Another fastener element ofthe present invention was prepared by the following procedure. One end of a piece of 3MO Optical Lighting Film #2300 Acrylic (available from 3M, St. Paul, MN), approximately 90 cm X 10 cm, was secured, grooved face down, to a bench top with masking tape. The 3MO Optical Lighting Film includes a plurality of substantially 90° included angle ridges. The depressions in the surface ofthe film are about 0.18 mm in depth. The unsecured end ofthe film was grasped in a manner such that a tear could be initiated in a grove approximately 2 cm from the edge ofthe film and the film torn along its length. The film was torn at an angle of between approximately 15-30° from the horizontal to produce a clean, straight edge having a substantially constant acute angle along one piece ofthe film and a complementary obtuse angle on the edge ofthe corresponding piece of film. The strips produced in this manner were cut into approximately 6.5 cm lengths (herein after referred to as "master elements") and used to assemble a fastener master 112, a portion ofthe cross-section of which is illustrated in Fig. 14, in the following manner: All publications and patent applications in this specification are indicative of the level of ordinary skill in the art to which this invention pertains. The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope ofthe invention. -28- d) Positioning two additional aluminum bars (approximately 0.6 cm X 0.6 cm X 10 cm) in the impression material pool such that they contacted the ends ofthe spacer bars, thereby forming a containment well for the impression material; e) Allowing the impression material to cure; f) Removing the fastener master from the cured impression material and trimming the ends ofthe cured mold to provide an approximately 2.5 cm long mold ofthe master; and g) Securing end dams to the thus trimmed mold to provide a well for subsequent fastener element molding. Fastener elements were prepared by filing the master mold with a vinyl plastisol (#D 1902-50 Black, available from Plast-O-Meric, Inc. Waukesha, WI) and curing the plastisol in a circulating air oven at 204°C (400°F) for 15 minutes. The cured plastisol was demolded to produce a flexible, compliant fastener element (50 durometer) having a plurality of grooved ridges which were replicas ofthe grooved ridges 110 of master 112 (and inverted replicas ofthe depressions in the master mold). Two such fastener elements were engaged with light finger pressure and could be readily disengaged by pealing one fastener element from the other. Figures 15 and 16 show a cross-section ofthe fastener elements just prior to engagement and in interlocking engagement, respectively. The fastener had a good holding force without being fully engaged. Much like a zipper, only a small force was needed to close the fastener if the closure process was begun at one end ofthe fastener and progressed to the other end. A large force was required to open the fastener if applied along its entire length. Example 10 A related set of fastener elements were prepared using the master mold of Example 9, substantially following the procedure of Example 9, except that a firmer vinyl plastisol (#D 1902-78 White, available from Plast-O-Meric, Inc.) was used to form the fastener elements (78 durometer). The fastener elements were readily engaged and disengaged, with those described in Example 9. 8) An article comprising the fastener element of claim 1. 9) A first fastener element adapted to be mated in an interlocking arrangement to a second fastener element, the first fastener element comprising: a polymeric substrate comprising a plurality of mating cavities, the mating cavities comprising a first mating surface which is adapted to engage a second mating surface on a second mating element projecting from the second fastener element, wherein a cross-section peφendicular to the first mating surface comprises a plurality of microprotrusions extending therefrom. 10) The fastener element of claim 9 wherein the polymeric substrate comprises a plurality of first mating elements projecting therefrom, the mating cavities being defined by adjacent first mating elements. 11) A fastener comprising: first and second fastener elements; the first fastener element comprising a first polymeric substrate having a plurality of first mating elements projecting therefrom, the first mating elements comprising a first mating surface, wherein a cross-section ofthe first mating elements through the first mating surface comprises a plurality of first microprotrusions extending therefrom; the second fastener element comprising a second substrate having a plurality of second mating elements projecting therefrom, the second mating elements comprising a second mating surface, wherein a cross-section ofthe second mating elements through the second mating surface comprises a plurality of second microprotrusions extending therefrom; wherein the first and second fastener elements are adapted to be engaged such that at least one ofthe second mating elements is retained in a mating cavity -30-

Claims: WHAT IS CLAIMED IS: 1) A first fastener element adapted to be mated in an interlocking arrangement with a second fastener element, the first fastener element comprising: a polymeric substrate comprising a plurality of first mating elements projecting therefrom, the first mating elements comprising a first mating surface which is adapted to engage a second mating surface on a second mating element projecting from the second fastener element, wherein a cross-section ofthe first mating elements through the first mating surface comprises a plurality of microprotrusions extending therefrom. 2) The fastener element of claim 1 wherein the polymeric substrate and the first mating elements form a unitary polymeric structure. 3) The fastener element of claim 1 wherein the first mating elements comprise solid mating elements. 4) The fastener element of claim 1 comprising first mating elements having an outer surface and a hollow core, wherein a portion ofthe outer surface comprises the microprotrusions. 5) The fastener element of claim 1 wherein the first mating elements comprise a plurality of discontinuous mating elements. 6) The fastener element of claim 1 comprising the first mating elements on a first major face and further comprising an attachment component on a second major face. 7) The fastener element of claim 1 wherein the first mating elements comprise ridge-like mating elements and the microprotrusions comprise microscopic ridges projecting from the ridge-like mating elements. defined by adjacent first mating elements through an interlocking interaction ofthe first and second mating surfaces. 12) A method of fastening articles comprising: (a) providing a first fastener element and a second fastener element; the first fastener element comprising a polymeric substrate comprising a plurality of first mating elements projecting therefrom, the mating elements having a first mating surface, wherein a cross-section peφendicular to the first mating surface comprises a plurality of first microprotrusions extending from the first mating surface; the second fastener element comprising a plurality of second mating elements projecting therefrom, the second mating elements having a second mating surface, wherein a cross-section perpendicular to the second mating surface comprises a plurality of second microprotrusions extending therefrom; and (b) engaging the first and second fastener elements, wherein at least one first mating element is retained by an interlocking interaction ofthe first and second mating surfaces in a mating cavity defined by adjacent second mating elements.

Inventors: AAMODT JENNIFER M, BERG JAMES G, CALHOUN CLYDE D, KRINKE HARLAN L, AAMODT, JENNIFER, M., BERG, JAMES, G., CALHOUN, CLYDE, D., KRINKE, HARLAN, L.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1996
Main classification: F16B5
IPC codes: A44B18, F16B5