Active fasteners

Abstract

Fastener products, for example for use in hook and loop fasteners are provided. The fastener products include a sheet form backing, and, extending from the backing, a plurality of fastener elements that include a shape memory polymer. Method of making and using such fastener products are also provided.

Description

TECHNICAL FIELD

[0001] This invention relates to hook and loop fastening, and more particularly to male fastener elements adapted to engage female fastener elements to form a releasable closure.

BACKGROUND

[0002] Arrays of molded male fastener elements, e.g., hooks, are often formed integrally with a sheet-form base, to provide a sheet-form male fastener component. This component can then be engaged with a similar component of female fastener elements to form a “hook and loop” fastener. It is desirable that the fastener elements have good strength and toughness, so as to provide strong engagement during repeated use of the fastener.

[0003] Such male fastener components can be produced in a continuous molding process described by Fischer in U.S. Pat. No. 4,794,028, hereby incorporated by reference. Male fastener components generally have small hook members integrally molded to extend from a broad side of the sheet form base, and each hook member generally has a head portion overhanging the base to form an engageable crook in at least one direction along the longitudinal molding direction of the hook tape. Mushroom-type hook fasteners may be formed by molding stems in a Fischer-type continuous molding process, and then flattening the ends of the molded stems to form heads overhanging the base in generally all directions.

SUMMARY

[0004] The inventors have recognized that in some cases it may be advantageous to have a male fastener element change its shape in response to an environmental change such as a change in temperature.

[0005] For instance, it may be desirable for safety reasons to have an engaged hook and loop fastener disengage when a certain temperature is reached, e.g., during a fire. In this case, the change in shape would be from a normal hook shape to a relatively straighter shape in which the crooks of the hooks would no longer engage the female fastener elements.

[0006] Alternatively, it may be desirable to have a hook and loop fastener engage when a certain temperature is reached. In this case, the change in shape would be from a non-engaging shape, e.g., a relatively straight shape or a flattened shape, to a hook shape that would engage female fastener elements.

[0007] To achieve this temperature-responsiveness, we have incorporated shape memory polymers into male fastener elements of a hook and loop fastener. As will be discussed below, the shape memory polymer renders the male fastener elements capable of changing shape in a predetermined way in response to temperature changes.

[0008] In the safety applications described above, for example, the male fastener element can be initially molded as a straight stem, then deformed at an elevated temperature to a metastable loop-engaging shape and then cooled to “set” the element in this metastable shape. When re-exposed to elevated temperature, the fastener element returns to an approximation of its initial shape, losing its loop-engaging ability.

[0009] If it is desirable that the hook and loop fastener have a weaker strength at elevated temperature, rather than completely disengaging, the fastener may include some hooks formed of shape memory polymer and other hooks formed of a conventional polymer. In this way, it is possible to adjust the strength characteristics (e.g., shear and peel) of the fastener as a function of temperature. The change in properties in response to a temperature change may be an “on-off” change, from full engagement to full disengagement, or a gradual change, e.g., if several different shape memory polymers having different transition temperatures are included in the fastener.

[0010] Shape-changing fastener elements are useful in other applications. For instance, male fastener elements may be initially molded in a loop-engaging shape, e.g., a hook shape, and then heated to an elevated temperature and deformed to a relatively straighter metastable shape and cooled. In this case, when the element is reheated to the elevated temperature, it will return to the loop-engaging shape. Thus, for example, the fastener element may be used as a projection for securing a product to a panel with a blind hole, e.g., in the assembly of automotive trim. The straight, metastable projection is inserted through the hole, and is then heated so that it returns to its original shape and its loop-engaging portion crimps the panel to the product. Other uses for this type of fastener include “single use” fasteners that engage a loop material firmly and without free motion until disengaged. In this case, for example, the straight, metastable projections can be used to penetrate a dense mat of loops or fibers, and then reheated to capture the loops or fibers and pull the loop product firmly into engagement with the male fastener.

[0011] Similarly, instead of straightening the hooks at the elevated temperature, the hooks can be flattened against the base sheet, e.g., by pulling the sheet of fastener elements through a calendar. In this implementation, the hooks will be “latent” (will remain in the flattened position) until the fastener is exposed to an elevated temperature, when the hooks will be activated (will return to their original, loop-engaging position).

[0012] In one aspect, the invention features a fastener product including a sheet form backing; and, extending from the backing, a plurality of fastener elements including a shape memory polymer.

[0013] Some implementations include one or more of the following features. The fastener elements include male fastener elements, e.g., hooks. The hooks include crooks and stems, and the crooks are formed of a shape memory polymer. A loop-engaging portion of the fastener element is formed of a shape memory polymer, and a stem portion of the fastener is formed of a non-shape memory polymer. The stems include a non-shape memory polymer. The sheet form backing is formed of a non-shape memory polymer. The fastener elements include more than one shape memory polymer, and the shape memory polymers have different glass transition temperatures. The glass transition temperature of the shape memory polymer is from about −40 to 150° C. The glass transition temperature of the shape memory polymer is from about 60 to 100° C. The shape memory polymer includes a polyurethane. The fastener element is configured to change from a metastable hook or mushroom shape to a stable substantially non-engaging shape in response to a temperature change. The substantially non-engaging shape is a substantially straight stem. The substantially non-engaging shape is a bent-over hook or mushroom shape. The fastener element is configured to change from a metastable substantially non-engaging shape to a stable hook or mushroom shape in response to a temperature change. The substantially non-engaging shape is a substantially straight stem. The substantially non-engaging shape is a bent-over hook or mushroom shape.

[0014] In another aspect, the invention features a fastener product including a sheet form backing; and, extending from the backing, a plurality of fastener elements comprising two or more shape memory polymers.

[0015] Some implementations include one or more of the following features. Each fastener element includes at least two shape memory polymers. A first set of the fastener elements includes a first shape memory polymer, and a second set of the fastener elements includes a second, different shape memory polymer. The shape memory polymers are selected to modulate a change in the physical properties of the fastener product as a function of temperature.

[0016] In another aspect, the invention features a method of forming a fastener product including forming a plurality of fastener elements extending from a sheet form base, at least some of the fastener elements comprising a shape memory polymer.

[0017] Some implementations may include one or more of the following features. The molding step includes forming male fastener elements, e.g., hooks. The hooks include crooks and stems, and the crooks are formed of a shape memory polymer. The stems include a non-shape memory polymer. The method further includes co-extruding the shape memory polymer and the non-shape memory polymer to form the sheet-form base, wherein the forming step includes forming the fastener elements from a portion of the sheet-form base. The fastener elements include more than one shape memory polymer, and the shape memory polymers have different glass transition temperatures. The method further includes co-extruding the shape memory polymers to form the sheet-form base, wherein the forming step includes forming the fastener elements from a portion of the sheet-form base. The glass transition temperature of the shape memory polymer is from about −40 to 150° C. The glass transition temperature of the shape memory polymer is from about 60 to 100° C. The forming step includes forming fastener elements having a substantially non-engaging shape. The method further includes heating the fastener elements to a formation temperature and deforming the fastener elements to a metastable hook or mushroom shape. The substantially non-engaging shape is a substantially straight stem. The substantially non-engaging shape is a bent-over hook or mushroom shape. The forming step includes forming fastener elements having a hook or mushroom shape. The method further includes heating the fastener elements to a formation temperature and deforming the fastener elements to a metastable substantially non-engaging shape. The substantially non-engaging shape is a substantially straight stem. The substantially non-engaging shape is a bent-over hook or mushroom shape.

[0018] In a further aspect, the invention features a method of attaching a fastener product to a substrate including: inserting a substantially straight stem of the fastener product through a blind opening in the substrate so that a terminal portion of the stem extends beyond the opening, the stem including a shape memory polymer in a metastable state; and heating the terminal portion of the stem to a temperature at which the shape memory polymer returns to a stable state in which the configuration of the terminal portion provides an interference fit that prevents the stem from being removed from the opening.

[0019] The invention also features absorbent articles including the fastener products described above. In one aspect, the invention features an absorbent article including: (a) a disposable garment including an absorbent material; and (b) a fastener for securing the garment on a wearer, the fastener comprising a female fastener component on a first portion of the garment, and a male fastener component on a second portion of the garment, arranged for cooperative engagement with the female fastener component; the male fastener component including a plurality of male fastener elements comprising a shape memory polymer.

[0020] Some implementations may include one or more of the following features. The article is selected from the group consisting of diapers and incontinence products. The male fastener elements include hooks. The shape memory polymer is selected to modulate a change in the physical properties of the fastener as a function of temperature. The shape memory polymer is selected to modulate the change in the physical properties of the fastener when it is heated from ambient temperature to the surface temperature of a wearer of the article.

[0021] In another aspect, the invention features a fastener product including a sheet form backing comprising a shape memory polymer, and, extending from the backing, a plurality of fastener elements. The invention also features absorbent articles including such fastener products.

[0022] In some implementations the shape memory polymer is selected to modulate the change in the physical properties of the fastener when it is heated from ambient temperature to the surface temperature of a human.

[0023] The term “shape memory polymer,” as used herein, refers to a polymer that exhibits shape memory properties, i.e., that can be shaped to a first “stable” shape, deformed to a second “metastable” shape when heated to a predetermined temperature that is characteristic of the polymer, and cooled to retain this second shape, and that, when reheated to a temperature greater than or equal to the predetermined temperature, will return substantially to its first stable shape.

[0024] The term “non-shape memory polymer,” as used herein, refers to a polymer that does not exhibit shape memory properties.

[0025] Other features and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is a side cross-sectional view of a male fastener according to one embodiment of the invention, with the two positions of the hook shown in solid and dotted lines.

[0027] FIG. 2 is a side cross-sectional view of a male fastener according to an alternate embodiment of the invention.

[0028] FIG. 3 is a side cross-sectional view of a male fastener according to another alternate embodiment of the invention.

[0029] FIG. 4 is a diagrammatic view of a process for making the fastener of FIG. 1.

[0030] FIG. 5 is a diagrammatic view of a process for making the fastener of FIG. 2 or 3.

[0031] FIGS. 6 and 7 are diagrammatic views of alternate processes for making the fastener of FIG. 2 or 3.

[0032] FIG. 8 is a diagrammatic view of an alternate process for making a fastener product.

[0033] FIGS. 8A-8C are enlarged views of detail A in FIG. 8, according to different embodiments of the invention.

[0034] FIG. 9 is a top view of a fastener product produced using the process shown in FIGS. 8 and 8C.

[0035] FIGS. 10-10C are side cross-sectional views of male fasteners according to various alternate embodiments of the invention.

[0036] FIGS. 11-11B are side cross-sectional views showing a fastener being attached to a panel.

[0037] FIG. 12 is a schematic perspective view of a personal care product including a fastener product according to one aspect of the invention.

[0038] FIGS. 13 and 13A are diagrammatic side views of a fastener element in two states of engagement.

DETAILED DESCRIPTION

[0039] Referring to FIG. 1, fastener 10 includes a plurality of hook-shaped fastener elements 12 that are integral with, and extend from, a sheet-form base 14. The fastener 10 is formed of a shape memory polymer. During normal use, the hooks 12 remain in the position shown in solid lines. However, when the hooks are exposed to a predetermined elevated temperature (or a temperature higher than the predetermined temperature) the hooks straighten out, forming relatively straight projections 13, as indicated in dotted lines in FIG. 1. This change in shape is the result of the shape memory polymer changing from its metastable position (the more bent shape) to its stable position (the straighter projection shape).

[0040] FIG. 4 illustrates a suitable process for forming fastener 10. A shape memory polymer 16 is extruded by extruder 18 onto a roll 19 having forming cavities 20 that have the shape of straight projections 13 in FIG. 1. A roll suitable for use as roll 19 is described, e.g., in U.S. Pat. No. 4,872,243, the disclosure of which is incorporated herein. This results in straight projections 21 extending from a base 22. The shape memory polymer is generally extruded at a temperature that is in the “fluid temperature region” of the polymer, i.e., at a temperature at which the polymer will flow readily. This temperature range is generally significantly higher than the glass transition temperature of the polymer, e.g., at least 100° C. above the glass transition temperature. The resulting projections are the stable shape of the shape memory polymer.

[0041] It is noted that this molding procedure can be replaced by any desired method of molding male fastener elements on a base, e.g., the processes described in U.S. Pat. Nos. 4,894,060, 4,794,028 and 5,441,687, the disclosures of which are incorporated by reference herein.

[0042] The resulting projection-carrying base 22 then passes to a station 200, where the projections are heated to a temperature that is generally not more than about 5 to 30° C. above the glass transition temperature of the shape memory polymer. If the projections are heated to too high a temperature, the deformation that takes place in the next step of the process may be partially or completely irreversible.

[0043] Next, the base 22 passes through a nip 202, between rolls 204 and 206, causing the heated projections 21 to be flat-topped, changing the initial, as-molded straight shape to metastable hook or mushroom shaped male fastener elements 23. The male fastener elements are then cooled (not shown), e.g., with cool air or water, to set them in the metastable position. Cooling the fastener elements results in the recovery of the elastic modulus of the polymer. Cooling is generally performed as quickly as possible after deformation is complete. If desired, cooling may begin during the deformation process, as long as the desired degree of deformation can still be achieved.

[0044] The temperature to which the projections were heated in station 200 is substantially equal to the temperature at which the finished fastener product will change from its metastable shape to its stable shape, i.e., from hooks to straight projections in the embodiment shown in FIG. 1.

[0045] FIG. 2 shows a fastener 62 in which the hooks 64 are formed of a shape memory polymer and the base 66 is formed of a second polymer, e.g., a non-shape memory polymer. FIG. 3 shows a fastener 70 in which only the hook tips 72 are made of the shape memory polymer, and the base and a lower portion 73 of the hooks 75 is formed of a second polymer. These configurations may be advantageous from a cost standpoint, as shape memory polymers tend to be relatively expensive and in many applications only the crooks of the hooks need to be movable between the metastable and stable positions. In these embodiments, as in the embodiment shown in FIG. 1, the hooks are the metastable position of the shape memory polymer, and when exposed to heat the hooks will straighten out to the as-molded, straight position (not shown in FIGS. 2-3).

[0046] A suitable process for forming a two-polymer fastener, e.g., as shown in FIG. 2 or FIG. 3, is shown in FIG. 5. A first extruder 35 extrudes a shape memory polymer 38 onto mold roll 40, forcing some of the polymer into projection-forming cavities 42 and leaving a layer of polymer on the surface of the mold roll. As mold roll 40 rotates in the direction of arrow A, doctoring blade 44 removes the polymer on the surface of the mold roll without disturbing the polymer in cavities 42. The removed polymer, which has been exposed to air while on the mold roll and may have begun to solidify, may be either discarded or recycled. The thickness of polymer left on the surface of the roll by the doctoring blade will depend, in part, on how close the blade is positioned to the surface of the mold roll (the position is adjustable in the direction indicated by arrow B). In some cases, the sharp, distal end of blade 44 rides against the mold roll, thereby literally scraping off essentially all of the polymer on the surface of the roll. In such cases it is recommended that the end of the blade be coated with a lubricious material to avoid damaging the surface of the mold roll. In other cases, the position of the blade is adjusted to leave a predetermined thickness of polymer on the roll, to become a part of the base of the product. In such cases, the doctoring blade effectively trims the polymer thickness rather than actually “scraping” against the surface of the roll.

[0047] Next, a second extruder 47 extrudes a second, base-forming polymer 50 (generally a non-shape memory polymer) onto the surface of the mold roll (or onto any of polymer 38 left on the surface of the roll by blade 44). A gear pump 36, 48, is positioned at the outlet of each extruder, to accurately control the rate of polymer delivered to the mold roll. The final thickness of the base of the product is then adjusted by roll 52, rotating in the direction of arrow C, and the fastener product 60, carrying projections 61, is stripped from the mold roll 40 by passing it around exit roll 54.

[0048] The projections 61 are then heated, and then subjected to the flat-topping process shown in FIG. 4, or any other desired deformation process, to deform the projections 61 into a metastable male fastener shape.

[0049] FIGS. 6 and 7 show alternative processes for forming a two-polymer fastener. In the process shown in FIG. 6, the first and second polymers are applied to the mold roll by a coextruder 110. In the process shown in FIG. 7, the shape memory polymer is applied to the mold roll by an extruder 112, and most of the polymer is scraped from the surface of the mold roll by a doctoring blade 114, leaving a thin film of polymer, as described above with reference to FIG. 5. The base-forming polymer 116 is then laminated to the thin film of hook-forming polymer while the latter is still on the mold roll, such as in the nip between the mold roll and roll 118, as shown. In each of these processes, the resulting product is then heated and flat-topped or otherwise deformed, and cooled to set the fasteners in the metastable position, as described above.

[0050] FIG. 8 shows a process similar to that shown in FIG. 4 and described above, except that mold cavities 20′ are hook-forming cavities, resulting in hooks 21′ carried on base 22. Thus, in this case the stable form of the fastener elements is a hook shape. The base 22 is then passed through a processing station 24, in which the hooks 21 are deformed to a different, metastable position. Suitable processing stations are shown, for example, in FIGS. 8A-8C.

[0051] In FIG. 8A, the hooks 21′ are heated (arrows H), and then deformed (arrow D) to form straight projections 208. The hooks may be straightened, e.g., by engaging the hooks with a screen, heating the screen and at least the crooks of the hooks, and pulling the screen away from base 22. When straightening the hooks, it may be desirable to have the hooks facing downwards, so that gravity assists with the straightening process. If desired, a cooling fluid 26 can be applied to the base 22 during heating, to protect the base.

[0052] In the embodiment shown in FIG. 8A, when the metastable straight projections are reheated to the temperature to which they were exposed in processing station 24 (or a higher temperature), the projections will return to the initial hook shape. As discussed above, this fastener product is useful, e.g., for securing a product to a panel with a blind hole by inserting the straight projection 208 through the hole, and then heating the projection so that it returns to its hook shape and crimps the panel to the product (see, e.g., FIGS. 11-11B, in which projections 208 are inserted through holes 209 to secure a panel 211 to the fastener). This fastener product is also useful in single use fasteners, as discussed above.

[0053] In FIG. 8B, the hooks 21′ are heated (arrows H) and then deformed, e.g., by a roll 210 or other application of downward pressure, to form flatter hooks 212. Thus, for example, a “J” shaped hook can be crooked further down from the original shape. In this case, the shape memory polymer can be used to form a shape that would be difficult to mold using conventional methods. If it is desired that the hook shape 212 be the permanent shape of the fastener element, a shape memory polymer is selected that has a forming temperature that is higher than the expected use temperature of the product, so that the shape memory polymer will not return to its original position during use.

[0054] In FIG. 8C, the hooks 21′ are heated and then deflected by a force D, directed into the plane of the paper. This force causes the crooks of the hooks to be deflected out of the plane of the fastener element to form deflected hooks 214, shown in FIG. 9 (a top view of the fastener product). Again, the shape memory polymer is used to form a shape that would be difficult to mold using conventional methods. If it is desired that the hook shape 214 be the permanent shape of the fastener element, a shape memory polymer is selected that has a forming temperature that is higher than the expected use temperature of the product.

[0055] Advantageously, due to the relatively low glass transition temperatures of shape memory polymers, post-molding deformation, e.g., as shown in FIGS. 8B and 8C, can be performed at relatively low temperatures, allowing lower temperature processing equipment to be used relative to the equipment that is generally required to perform similar processing steps on a conventional non-shape memory polymer. Thus, it may be advantageous to use a shape memory polymer to obtain a desired fastener element shape, even if shape memory properties will not needed when the fastener product is in use.

[0056] Suitable shape memory polymers are described, e.g., in U.S. Pat. Nos. 5,145,935, 5,189,110 and 4,051,217, the disclosures of which are incorporated herein by reference. Shape memory polymers are also described in WO 86/03980. Suitable shape memory polymers are commercially available from the Diaplex division of Mitsubishi Heavy Industries.

[0057] Preferably, the shape memory polymer is thermoplastic, so that it can be processed using conventional molding techniques. A thermoplastic shape memory polymer is described in U.S. Pat. No. 5,145,935. This polymer is a polyurethane elastomer, which has a degree of crystallinity of 3 to 50 weight percent, contains approximately equal amounts of [NCO] groups and [OH] groups at the terminals of the polymer, and is polymerized by the prepolymer method from a difunctional diisocyanate, a difunctional polyol, and a difunctional chain extender containing active hydrogen groups. These compounds are formulated in a molar ratio of diisocyanate to polyol to chain extender of 2.0-1.1:1.0:1.0-0.1, e.g., 1.8-1.2:1.0:0.8-0.2. The polymer may exhibit a ratio of the tensile modulus at a temperature 10° C. higher than the glass transition temperature to the tensile modulus at a temperature 10° C. lower than the glass transition temperature of from 50 to 250 (the tensile modulus being measured according to Japanese Industrial Standards (JIS) K7113). Generally, the glass transition temperature of these polymers is in the range of −50° C. to 60° C.

[0058] An important consideration when selecting the glass transition temperature is the operating temperature that the fastener will see in a given application. It is desirable, for reasons of cost and ease of processing, that the “formation” temperature at which the polymer is deformed to its metastable shape (which is equal to or slightly above the glass transition temperature) be relatively low. However, the formation temperature generally must be higher than the highest expected normal operating temperature, so that, in use, the fastener does not take on its metastable shape under normal temperature conditions. If the highest operating temperature will be around room temperature, it is generally preferred that the glass transition temperature be from about 60 to 100° C. If the fastener will see higher temperatures under normal conditions, e.g., if the fastener will be used in the trunk of a car, the glass transition temperature is adjusted upwards accordingly. Preferably, the glass transition temperature is about 30 to 80° C. higher than the highest expected normal use temperature.

[0059] These polymers may be obtained by reacting the isocyanate component and polyol component without catalyst to obtain a prepolymer. After the completion of the reaction, the chain extender is added, the mixture is defoamed and poured into a mold, and a cross-linking reaction is performed, e.g., at a temperature of 80° C. for one to two days in a constant temperature dryer, resulting in the polyurethane elastomer. The synthesis may be performed with either a solvent or non-solvent system. The polyurethane elastomer can be represented by the following general formula:

HOR″OCONH(RNHCOOR′OCONH′)nRNHCOOR″OCONH(RNHCOOR′)—OCONH)mRNHCOOR″OH

[0060] where n=0-16 and m=1-16.

[0061] Preferably, the non-shape memory polymer, if one is included (e.g., in the embodiments shown in FIGS. 2 and 3), is chemically compatible with the shape memory polymer so that it will adhere to the shape memory polymer during coextrusion. If the shape memory polymer is a polyurethane, as discussed above, suitable non-shape memory polymers include other polyurethanes, polyesters that are compatible with polyurethanes, and ABS polymers.

[0062] Other embodiments are within the scope of the following claims.

[0063] For example, fasteners containing shape memory polymer may be used in many other applications. For instance, in electrical applications the fastener elements may be coated with a coating that is broken by movement of the fastener element from its metastable to its stable position, breaking a circuit. As another example, the release of the hook and loop fastener can be used to perform a function, e.g., to open a valve that is secured by the fastener when the valve is exposed to a predetermined temperature.

[0064] The fasteners can also be used in personal care articles, e.g., absorbent articles such as diapers and incontinence products. Referring to FIG. 12, for example, an absorbent article 300 may include a pair of tabs 302 that each carry a male fastener strip 304. The absorbent article also includes a corresponding female fastener strip 306 of loop material, arranged for cooperative engagement with fastener strips 304. Fastener strip 304 includes a plurality of hooks of a shape memory polymer that is selected to be responsive to changes in temperature from ambient to the surface temperature of a wearer of the absorbent article. As shown in FIG. 13, in their initial state these hooks 305 are only slightly curled. This hook shape allows for easy engagement, while providing adequate initial strength to hold the absorbent article in place on a wearer. As the user wears the article, the user's body temperature causes the hooks to revert to a normal, more curled hook shape, as shown in FIG. 13A. The more curled hook shape tends to trap fibers 310 of the loop material, increasing the peel and shear strength of the engaged fasteners. As bodily fluid is introduced to the absorbent article, the article will get heavier, putting more stress on the fasteners. The increase in peel and shear strength will compensate for this increased stress, providing a more secure fit and minimizing the possibility of fastener failure during use. The change in hook shape will also tend to maintain the fit of the absorbent article, by preventing the fasteners from “drifting” (i.e., the male fastener strips moving laterally with respect to the female fastener strip in response to shear stress).

[0065] It may also be desirable, in personal care articles, for the base of one or both of the fastener strips to be formed of a shape memory polymer, in addition to or instead of forming the fastener elements from a shape memory polymer. Again, the shape memory polymer is selected to be responsive to changes in temperature between ambient and the surface temperature of the wearer of the article. The base is processed so that at ambient temperature it will have an initial generally flat shape, but when heated to the surface temperature of a wearer it will revert to a normal shape that is better suited for use in the garment. For example, the normal shape may be a curved shape, to conform the fastener shape to the body shape of the wearer. Alternatively, the base may contract when it returns to its normal shape, causing the fastener strips to decrease in length and thus hold the garment more snugly in place on the wearer.

[0066] Moreover, the shape memory polymer can be used to obtain many other fastener shapes, in addition to those that are shown in FIGS. 8B and 8C by way of example.

[0067] Also, other combinations of shape memory and non-shape memory polymers can be used, in addition to those shown in FIGS. 2 and 3. Examples of other arrangements of multiple polymers are shown in FIGS. 10-10C.

[0068] FIG. 10 shows a fastener 68 in which the hooks 170 and the upper portion 172 of the base 174 are formed of a shape memory polymer, and the lower portion 176 of base 174 is formed of a second polymer. Using the process shown in FIG. 5, such a fastener can be formed by adjusting doctoring blade 46 away from the mold roll surface so that a thin layer of the first polymer remains on the mold roll surface when the second polymer is applied.

[0069] FIG. 10A shows a fastener 78, in which the hooks 80 are formed of a shape memory polymer 82 and a second polymer 84, and the base 86 is formed of a third polymer 88. To form this fastener, the process shown in FIG. 5 is modified so that the first extruder 35 applies an amount of the shape memory polymer that only partially fills the mold cavities, and then another extruder (not shown in FIG. 5) applies the second hook-forming polymer to completely fill the cavities. The process then continues as shown in FIG. 5, with scraping and application of the base-forming polymer by extruder 47. This arrangement may be useful, for example, if the polymers 82, 86 are not compatible, or do not adhere well to each other, in which case the second polymer 84 can be selected to adhere well to both polymers and used as a tie layer to adhere polymers 82 and 86.

[0070] FIG. 10B shows a fastener 90 in which the hooks 92 are formed of three different polymers 94, 96, 98. This fastener would be formed in a manner similar to that described with reference to FIG. 10B, adding a further extruder to apply the third hook-forming polymer. This embodiment can provide combinations of properties difficult to obtain with only two polymers. Alternatively, the middle polymer 96 may be used as a “tie layer” to bond polymers 94 and 98 if, for example, these polymers are incompatible or do not adhere well to each other.

[0071] In either of the embodiments shown in FIG. 10A and 10B, more than one of the polymers may be a shape memory polymer. For example, two shape memory polymers that have different glass transition temperatures can be used, to give different degrees of shape change at different use temperatures.

[0072] FIG. 10C shows a fastener 100, similar to fastener 70 in FIG. 3, in which the base 102 and a lower portion 104 of hooks 106 are formed of a first polymer, and the upper portion 108 of the hooks is formed of a second polymer (upper portion 108 is somewhat larger in this case than tip portion 72 in FIG. 3). This fastener can be formed by the process of FIG. 5, by only partially filling the molding cavities using extruder 35, and then completing the filling of the cavities with extruder 47.

[0073] By utilizing combinations of two or more shape memory polymers on a single fastener tape, the fastener tape can be designed to exhibit peel or shear behavior that is a function of temperature. For example, if one third of the hooks return to a stable non-engaging position at 60° C., one third at 80° C., and one third at 100° C., the peel and shear of the tape will vary accordingly in that temperature range, from 100% at 60° C. to 0% at 100° C. Such a fastener can be formed, for example, by coextruding, side-by-side, streams of the three materials to form a unitary web, and then processing the web to form a fastener, e.g., as shown in FIG. 4. This creates an “intelligent” fastener tape that “senses” the temperature and changes its properties accordingly.

Claims

1. A fastener product comprising a sheet form backing; and extending from the backing, a plurality of fastener elements comprising a shape memory polymer.

2. The fastener product of claim 1 wherein the fastener elements comprise male fastener elements.

3. The fastener product of claim 2 wherein the fastener elements comprise hooks.

4. The fastener product of claim 3 wherein the hooks comprise crooks and stems, and the crooks are formed of a shape memory polymer.

5. The fastener product of claim 2 wherein a loop-engaging portion of the fastener element is formed of a shape memory polymer, and a stem portion of the fastener is formed of a non-shape memory polymer.

6. The fastener product of claim 4 wherein the stems comprise a non-shape memory polymer.

7. The fastener product of claim 1 wherein the sheet form backing is formed of a non-shape memory polymer.

8. The fastener product of claim 1 wherein the fastener elements comprise more than one shape memory polymer, and the shape memory polymers have different glass transition temperatures.

9. The fastener product of claim 1 wherein the glass transition temperature of the shape memory polymer is from about −40 to 150° C.

10. The fastener product of claim 1 wherein the glass transition temperature of the shape memory polymer is from about 60 to 100° C.

11. The fastener product of claim 1 wherein the shape memory polymer comprises a polyurethane.

12. The fastener product of claim 1 wherein the fastener element is configured to change from a metastable hook or mushroom shape to a stable substantially non-engaging shape in response to a temperature change.

13. The fastener product of claim 12 wherein the substantially non-engaging shape is a substantially straight stem.

14. The fastener product of claim 12 wherein the substantially non-engaging shape is a bent-over hook or mushroom shape.

15. The fastener product of claim 1 wherein the fastener element is configured to change from a metastable substantially non-engaging shape to a stable hook or mushroom shape in response to a temperature change.

16. The fastener product of claim 15 wherein the substantially non-engaging shape is a substantially straight stem.

17. The fastener product of claim 15 wherein the substantially non-engaging shape is a bent-over hook or mushroom shape.

18. A fastener product comprising a sheet form backing; and extending from the backing, a plurality of fastener elements comprising two or more shape memory polymers.

19. The fastener product of claim 18 wherein each fastener element comprises at least two shape memory polymers.

20. The fastener product of claim 18 wherein a first set of the fastener elements comprises a first shape memory polymer, and a second set of the fastener elements comprises a second, different shape memory polymer.

21. The fastener product of claim 18 wherein said shape memory polymers are selected to modulate a change in the physical properties of the fastener product as a function of temperature.

22. A method of forming a fastener product comprising forming a plurality of fastener elements extending from a sheet form base, at least some of the fastener elements comprising a shape memory polymer.

23. The method of claim 22 wherein the forming step comprises forming male fastener elements.

24. The method of claim 23 wherein the male fastener elements comprise hooks.

25. The method of claim 24 wherein the hooks comprise crooks and stems, and the crooks are formed of a shape memory polymer.

26. The method of claim 25 wherein the stems comprise a non-shape memory polymer.

27. The method of claim 26 further comprising co-extruding the shape memory polymer and the non-shape memory polymer to form the sheet-form base, wherein the forming step includes forming the fastener elements from a portion of the sheet-form base.

28. The method of claim 22 wherein the fastener elements comprise more than one shape memory polymer, and the shape memory polymers have different glass transition temperatures.

29. The method of claim 28 further comprising co-extruding the shape memory polymers to form the sheet-form base, wherein the forming step includes forming the fastener elements from a portion of the sheet-form base.

30. The method of claim 22 wherein the glass transition temperature of the shape memory polymer is from about −40 to 150° C.

31. The method of claim 22 wherein the glass transition temperature of the shape memory polymer is from about 60 to 100° C.

32. The method of claim 22 wherein the forming step comprises forming fastener elements having a substantially non-engaging shape.

33. The method of claim 32 further comprising heating the fastener elements to a formation temperature and deforming the fastener elements to a metastable hook or mushroom shape.

34. The method of claim 32 wherein the substantially non-engaging shape is a substantially straight stem.

35. The method of claim 32 wherein the substantially non-engaging shape is a bent-over hook or mushroom shape.

36. The method of claim 22 wherein the forming step comprises forming fastener elements having a hook or mushroom shape.

37. The method of claim 36 further comprising heating the fastener elements to a formation temperature and deforming the fastener elements to a metastable substantially non-engaging shape.

38. The method of claim 37 wherein the substantially non-engaging shape is a substantially straight stem.

39. The method of claim 37 wherein the substantially non-engaging shape is a bent-over hook or mushroom shape.

40. A method of attaching a fastener product to a substrate comprising inserting a substantially straight stem of the fastener product through a blind opening in the substrate so that a terminal portion of the stem extends beyond the opening, the stem including a shape memory polymer in a metastable state; and heating the terminal portion of the stem to a temperature at which the shape memory polymer returns to a stable state in which the configuration of the terminal portion provides an interference fit that prevents the stem from being removed from the opening.

41. An absorbent article comprising: a disposable garment including an absorbent material; and a fastener for securing the garment on a wearer, the fastener comprising a female fastener component on a first portion of the garment, and a male fastener component on a second portion of the garment, arranged for cooperative engagement with the female fastener component; the male fastener component including a plurality of male fastener elements comprising a shape memory polymer.

42. The absorbent article of claim 41 wherein the article is selected from the group consisting of diapers and incontinence products.

43. The absorbent article of claim 41 wherein the male fastener elements comprise hooks.

44. The absorbent article of claim 41 wherein said shape memory polymer is selected to modulate a change in the physical properties of the fastener as a function of temperature.

45. The absorbent article of claim 44 wherein said shape memory polymer is selected to modulate the change in the physical properties of the fastener when it is heated from ambient temperature to the surface temperature of a wearer of the article.

46. A fastener product comprising a sheet form backing comprising a shape memory polymer; and extending from the backing, a plurality of fastener elements.

47. The fastener product of claim 46 wherein the shape memory polymer is selected to modulate the change in the physical properties of the fastener when it is heated from ambient temperature to the surface temperature of a human.

48. An absorbent article comprising a disposable garment including an absorbent material; and a fastener for securing the garment on a wearer, the fastener comprising a female fastener component on a first portion of the garment, and a male fastener component on a second portion of the garment, arranged for cooperative engagement with the female fastener component; the fastener components each including a base comprising a shape memory polymer.

49. The absorbent article of claim 48 wherein the shape memory polymer is selected to modulate the change in the physical properties of the fastener when it is heated from ambient temperature to the surface temperature of a wearer of the article.

50. A method comprising providing a fastener product having a fastener element including a stem and a terminal portion that is crooked at ambient temperature, the stem including a shape memory polymer in a metastable state; and heating the terminal portion of the fastener element to a temperature at which the shape memory polymer returns to a stable state in which the terminal portion has a different shape.

51. The method of claim 50 wherein in the stable state the terminal portion is substantially straight.