Patent Application
20050246873
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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).
In one aspect, the invention features a fastener product including a sheet form backing, and, extending from the backing, a plurality of male fastener elements each including a loop-engaging portion and a stem portion. One of the loop-engaging portion or stem portion includes a shape memory polymer, and the other of the loop-engaging portion or stem portion includes a non-shape memory polymer.
Some implementations include one or more of the following features. The fastener elements include hooks, mushroom shapes or palm tree shapes. 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, or to UV radiation.
In another aspect, the invention features a fastener product including a sheet form backing, and, extending from the backing, a plurality of male fastener elements comprising a shape memory polymer. The fastener elements can be configured in various ways. In some instances, the fastener elements are configured to change from a metastable engaging hook shape to a stable partially engaging shape, the partially engaging shape being configured such that a stem portion of the fastener elements defines a curve (e.g., an s-shape, double or triple s-shape, a zigzag, a coil, etc.). Alternatively, the fastener elements may be configured to change from a stable engaging hook shape to a metastable partially engaging shape, the partially engaging shape being configured such that a stem portion of the fastener elements defines a curve (e.g., an s-shape, double or triple s-shape, a zigzag, a coil, etc.). The hooks may also be configured to change from a metastable engaging position to a stable non-engaging position, the non-engaging position being configured so the stem portion of the hook is bent over into a substantially horizontal position relative to the sheet form backing. In yet another alternative implementation, the hooks are configured to change from a stable engaging position to a metastable non-engaging position, the non-engaging position being configured so the stem portion of the hook is bent over into a substantially horizontal position relative to the sheet form backing.
Some implementations include one or more of the following features. The male fastener elements include two or more shape memory polymers. The male fastener elements include a stem portion including a first shape memory polymer and an engaging portion including a second shape memory polymer, and the first shape memory polymer is different from the second shape memory polymer. The male fastener elements include a stem portion including a shape memory polymer and an engaging portion including a non-shape memory polymer.
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 a blend of two or more shape memory polymers.
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.
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.
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.
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.
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.
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.
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.
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.
In one aspect, the invention features a fastener product including a sheet form backing having an upper face and a lower face; a plurality of male fastening elements including a shape memory polymer extending from the upper face of the sheet form backing, and a plurality of female fastening elements extending from the lower face of the sheet form backing.
Some implementations include one or more of the following features. The male fastener elements include at least two shape memory polymers. The male fastener elements each include a stem and an engaging portion. The stem portion of the male fastener elements includes a first shape memory polymer and the engaging portion of the male fastener elements includes a second shape memory polymer, the first shape memory polymer being different from the second shape memory polymer. The stem portion of the male fastener element includes a shape memory polymer and the engaging portion of the male fastener element includes a non-shape memory polymer. The stem portion of the male fastener element includes a non-shape memory polymer and the engaging portion of the male fastener element includes a shape memory polymer.
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.
The term “non-shape memory polymer,” as used herein, refers to a polymer that does not exhibit shape memory properties.
The term “partially engaging,” is used when referring to fastener elements that have at least two positions, one of which is more engaging than the other. The term “partially engaging” refers to the position that is less engaging, such that a touch fastener, in which substantially all of the fastener elements are in their partially engaging position, has a reduced engagement strength with a loop material relative to the engagement strength with the same loop material when substantially all of the fastener elements are in their engaging position. One measure of engagement strength is closure peel.
A typical procedure to measure closure peel of a touch fastener is as follows: The engaging sides of the touch fastener and a loop material that engages the touch fastener are placed facing each other. The touch fastener is engaged with the loop material over the entire facing surface of the touch fastener. For example, a touch fastener can be engaged with a loop material by rolling a roll of standard characteristics over the back of the loop in a standard way. The degree of engagement of the touch fastener to the loop material is then measured by determining the peel force. Peel force can be measured by peeling apart a small section of the touch fastener at the end of the closure, e.g., by placing the end of the touch fastener in the jaws of a tensile testing machine, and disengaging the touch fastener and the loop in the machine under standard conditions. For example, a set of conditions includes placing the hook in the upper jaw and the loop in the lower jaw and separating the material at 12 in/min. Tensile testing machines are manufactured, for example, by Instron Corp.
Acceptable loop materials for use in testing engagement strength, e.g., closure peel, include the non-woven loop products disclosed in U.S. Ser. No. 08/922,292, filed Sep. 3, 1997, now U.S. Pat. No. 6,342,285, the contents of which are incorporated herein by reference.
Other features and advantages of the invention will be apparent from the description and drawings, and from the claims.
Referring to
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.
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.
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.
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
A suitable process for forming a two-polymer fastener, e.g., as shown in
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.
The projections 61 are then heated, and then subjected to the flat-topping process shown in
In
In the embodiment shown in
In
In
Advantageously, due to the relatively low glass transition temperatures of shape memory polymers, post-molding deformation, e.g., as shown in
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.
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 110° 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.
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.
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
where n=0-16 and m=1-16.
Preferably, the non-shape memory polymer, if one is included (e.g., in the embodiments shown in
Other embodiments are within the scope of the following claims.
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.
The fasteners can also be used in infant, child and adult personal care absorbent articles such as diapers, training pants, disposable swimwear, incontinence garments and pads, sanitary napkins, wipes and the like. Referring to
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.
Moreover, the shape memory polymer can be used to obtain many other fastener shapes, in addition to those that are shown in
In either of the embodiments shown in
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
In certain instances, hooks undergo damage during the manufacturing of the fastener product. Thus, it is desirable to provide a fastener product with male fastener elements that are better able to withstand manufacturing conditions. Often during manufacturing of the fastener product, hooks are bent over onto the sheet form base, for example, when the formed hooks are passed through a nip between two rolls. If the hook lacks the ability to spring back into its original shape, the hook may then become non-engageable. Thus, it is desirable to provide a fastener element that has the ability to return, after manufacturing is complete, to a stable shape in which the fastener element is loop-engaging.
Referring to
In some instances, it is desirable to provide fasteners having hooks that are less susceptible to damage while still providing some extent of engagement, for example, if the hook will not be returned to its stable shape until after use of the product has begun. Referring to
The S-shaped fastener element 502, depicted in
While an S-shaped fastener has been described as an example of a partially engaging fastener, other shapes in which the stem portion of the fastener elements defines a curve are also envisioned. For example, multiple-S-shaped hooks, spring shapes, zigzag shapes and coils can also help to disperse any forces to which the fastener elements are subjected during the processing of the touch fastener.
In some instances, touch fastener 600 can be a rug having female fastener elements 608 made of carpeting material. The rug can be used for example in automobile floor mats or other applications.
In some instances a laminate touch fastener 700 can be made having a central lane 760 substantially free of fastener elements, surrounded by two lanes of fastener elements 762 (e.g., hooks) all of which are positioned in the center of a spunbond web (see
While heat is described above as the energy that is provided to a shape memory polymer to enable transformation between a stable and a metastable shape, other energy sources are also appropriate, for example UV radiation, IR radiation, microwave, x-ray etc. These energy sources can be used both to initially form the polymer in its metastable shape (with application of a mechanical force) and also to return the polymer from its metastable to its stable shape.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US03/35698 | Nov 2003 | US |
| Child | 11123303 | May 2005 | US |
