The present invention relates to a slide fastener and an article including a slide fastener.

Known slide fasteners (also referred to as zip fasteners) are generally constructed as follows.

A coupling portion, usually in the form of a plurality of coupling elements (also referred to as teeth) is attached to the edge of a tape to form a stringer. The tape is usually woven or knitted and may be formed from, for example, polyester. The coupling elements may be attached to the tape by, for example, crimping or moulding the coupling elements onto a reinforced edge of the tape, which may be referred to as a cord. Alternatively, the coupling elements may be formed as a continuous coil. In this case the coupling elements are most commonly woven or knitted into the tape or, alternatively, are stitched to a surface of the tape at the edge of the tape.

The invention discussed in more detail below is of most use in combination with a slide fastener of the type which includes a plurality of separate coupling elements (as opposed to coils).

Two stringers are brought together, such that the coupling elements of each stringer can attach to one another, for example, by interdigitating, to form chain. The chain is generally planar, and the chain (and the coupling portions which form part of the chain) extends along a longitudinal axis. A slider is mounted to the chain such that it can move along the chain between the two stringers.

The slider commonly includes a main body through which the coupling elements of each stringer pass and a pull tab attached to the main body which may be grasped by a user in order to effect movement of the slider along the chain.

Movement of the slider along the chain in a first sliding direction causes the coupling elements of the first stringer to attach to the coupling elements of the second stringer. When substantially all the coupling elements of the first stringer are attached to substantially all the coupling elements of the second stringer, the slide fastener may be said to be in a fully closed configuration. Whereas movement of the slider along the chain in a second sliding direction, opposite to the first sliding direction, causes the coupling elements of the first stringer to detach from the coupling elements of the second stringer. When substantially all the coupling elements of the first stringer are detached from the coupling elements of the second stringer, the slide fastener may be said to be in a fully open configuration.

The chain is cut to a desired length to form a desired length of slide fastener. Stops (often referred to as top stops and bottom stops) are attached to either end of the chain. The stops limit the extent of movement that the slider can undertake along the chain.

Some slide fasteners, may have a single bottom stop which is attached to both the first and second stringers. Other slide fasteners, which may be referred to as a separating slide fasteners, may have two separate bottom stops each attached to a corresponding one of the stringers. The two bottom stops may take the form of a retainer box and an insertion pin. The insertion pin can be inserted into the retainer box in order to attach the first and second stringers to one another. Conversely, the insertion pin can be removed from the retainer box when the slider is located adjacent the retainer box in order to detach the first and second stringers from one another.

Some slide fasteners may have two separate top stops attached to a corresponding one of the stringers. Other slide fasteners may have a single top stop attached to both of the stringers.

As previously discussed, the chain of a slide fastener is generally planar. However, in certain situations a slide fastener may be used in a manner in which it is required to bend out of the plane of the slide fastener. For example when a slide fastener is incorporated in part of a curved article, such as the corner of a suitcase, the slide fastener must bend to follow the shape of the curved article. Some known slide fasteners are capable of accommodating such a curve due to their flexibility. However, by bending the slide fastener out of plane this may apply stress to the slide fastener because it is deformed out of its natural state. A slide fastener stressed in this way may require additional force to be applied to the slider of the slide fastener in order to operate the slide fastener. Furthermore, the slider may be more likely to snag when the slide fastener is deformed out of its natural state.

In order to address these problems some known slide fasteners are configured such that in their natural state they curve out of plane so that they have a curvature which follows the shape of a curved article to which the slide fastener is to be applied.

It is an object of the present invention to provide a slide fastener or article including a slide fastener which obviates or ameliorates the problems discussed above. In particular, it is a further object of the invention to provide an alternative slide fastener which is configured such that in its natural state, when the coupling elements of the first and second stringers are interdigitated, it curves out of plane; this object being achieved in a straightforward manner without resulting to a complicated structure of slide fastener and/or a structure which utilises a relatively large amount of material to construct.

According to a first aspect of the invention there is provided a slide fastener chain comprising first and second stringers each comprising a tape having a row of coupling elements mounted on a longitudinal edge thereof, wherein, in use, the row of coupling elements of the first stringer may be interdigitated with the row of coupling elements of the second stringer in order to secure the first stringer and a second stringer together; wherein at least one of the coupling elements of the first stringer is received between first and second adjacent coupling elements of the second stringer when the row of coupling elements of the first stringer is interdigitated with the row of coupling elements of the second stringer; each of said at least one of the coupling elements of the first stringer and said first and second adjacent coupling elements of the second stringer being shaped such that they comprise a main body having a shoulder portion, and a head portion extending parallel to a lateral axis away from the shoulder portion via a neck portion, wherein the main body of said at least one of the coupling elements of the first stringer is mounted to the tape of the first stringer, and the main body of each of said first and second adjacent coupling elements of the second stringer is mounted to the tape of the second stringer; wherein the head and neck portions of said at least one of the coupling elements of the first stringer comprise an upper head portion and an upper neck portion respectively which are located above said plane of the tape of the first stringer; and wherein each of the first and second adjacent coupling elements of the second stringer comprise an upper head portion and an upper neck portion which are located above said plane of the tape of the second stringer; wherein, when said at least one of the coupling elements of the first stringer is received between said first and second adjacent coupling elements of the second stringer:

a) the upper head portion of the at least one of the coupling elements of the first stringer is received between the upper neck portion of the first adjacent coupling element of the second stringer and the upper neck portion of the second adjacent coupling element of the second stringer, such that the upper head portion of the at least one of the coupling elements of the first stringer contacts the upper neck portion of the first adjacent coupling element of the second stringer at a first contact point, and the upper head portion of the at least one of the coupling elements of the first stringer contacts the upper neck portion of the second adjacent coupling element of the second stringer at a second contact point; and b) the upper neck portion of the at least one of the coupling elements of the first stringer is received between the upper head portion of the first adjacent coupling element of the second stringer and the upper head portion the second adjacent coupling element of the second stringer, such that the upper neck portion of the at least one of the coupling elements of the first stringer contacts the upper head portion of the first adjacent coupling element of the second stringer at a third contact point, and the upper neck portion of the at least one of the coupling elements of the first stringer contacts the upper head portion of the second adjacent coupling element of the second stringer at a fourth contact point; such that the head and neck portions of the at least one of the coupling elements of the first stringer co-operate with the head and neck portions of the first and second adjacent coupling elements of the second stringer to prevent lateral separation in a direction generally parallel to the lateral axis of the at least one of the coupling elements of the first stringer and the first and second adjacent coupling elements of the second stringer; wherein a first plane is defined perpendicular to the longitudinal edge of the second stringer and which passes through the first adjacent coupling element of the second stringer at a location longitudinally outboard, with respect to said at least one of the coupling elements of the first stringer, of both the first and third contact points, and a second plane is defined perpendicular to the longitudinal edge of the second stringer and which passes through the second adjacent coupling element of the second stringer at a location longitudinally outboard, with respect to said at least one of the coupling elements of the first stringer, of both the second and fourth contact points; wherein the head and neck portions of said at least one of the coupling elements of the first stringer is shaped such that, when said at least one of the coupling elements of the first stringer is received between said first and second adjacent coupling elements of the second stringer, a first distance between the first plane and the second plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said at least one of the coupling elements of the first stringer is mounted, and which passes through at least one of the first and second contact points; and/or a second distance between the first plane and the second plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said at least one of the coupling elements of the first stringer is mounted, and which passes through at least one of the third and fourth contact points; is greater than a third distance between the first plane and the second plane along the longitudinal edge of the first stringer; such that, when said coupling elements of the first stringer are interdigitated with coupling elements of the second stringer, the longitudinal edge of the second stringer in the region of said at least one of the coupling elements of the first stringer, and of said first and second adjacent coupling elements, forms a curve having a centre of curvature which lies beneath the plane of the tape of the second stringer.

It follows that a slide fastener chain according to the present invention, when the coupling elements of the first and second stringer are coupled together, is caused to curve out-of-plane of the tape of the second stringer as compared to when the coupling elements of the first and second stringer are not coupled together. This curvature results from the shape of the head and/or neck portions of the at least one of the coupling elements of the first stringer. The greater distance between the first and second planes when passing through at least one of the contact points of the upper head portion or upper neck portion (first or second distances), as compared to the distance between the first plane and the second plane along the longitudinal edge of the first stringer (third distance) causes the adjacent coupling elements to pivot relative to the tape of the second string, thus producing curvature.

Because it is the shape of the head and/or neck portions of the at least one of the coupling elements of the first stringer which results in the curvature, and not that of any other portion of the at least one of the coupling elements of the first stringer, this means that such curvature can be obtained by only making a relatively minor adjustment to the shape of the head and/or neck portions of the at least one of the coupling elements of the first stringer, as opposed to adding additional, more complicated structure to the at least one of the coupling elements. In addition, this means that, because no additional structure is required to produce the curvature, the coupling elements are easier to produce and require less material than other known types of slide fastener chain which produce such out-of-plane bending. In some embodiments, a coupling element of a stringer which forms part of a slide fastener chain according to the present invention may, in fact, include slightly less material than an equivalent coupling element of a standard well-known slide fastener which does not exhibit out-of-plane curvature. According to the invention the head and neck portions of the at least one of the coupling elements of the first stringer co-operate with the head and neck portions of the first and second adjacent coupling elements of the second stringer to prevent lateral separation in a direction generally parallel to the lateral axis of the at least one of the coupling elements of the first stringer and the first and second adjacent coupling elements of the second stringer. This is the standard purpose of the head and neck portions of coupling elements of a slide fastener - the reduced maximum width (parallel to the longitudinal edge of the tape to which the coupling element is mounted) of the neck portions as compared to that of the head portions means that when the coupling elements of the stringers are interdigitated, it is not possible for the head of a coupling element on one stringer to be pulled, parallel to the lateral axis, out of the recess formed between the neck portions of adjacent coupling elements on the other stringer.

According to the present invention the head portion and neck portion refer only to the portions of the coupling elements which cooperate to prevent lateral separation of the stringers in the manner discussed. Put another way, any portion of a coupling element which does not co-operate with a portion of an adjacent coupling element on the other stringer (when the coupling elements are interdigitated) to prevent lateral separation of the stringers in the manner discussed is not considered to be a head portion or neck portion within the meaning of the present invention.

Some embodiments of the invention include no other features of the coupling elements or stringers (other than the shape of the head and/or neck portions) which urge the stringer to curve out of plane when the coupling elements are interdigitated. Such embodiments benefit, as previously discussed by being able to produce out-of-plane curvature of the string in a relatively straightforward and cost effective manner utilising less material to produce the coupling elements as compared to coupling elements of other know stringers which exhibit out-of-plane curvature.

In other embodiments according to the present invention the coupling elements or stringers may include other features which produce out-of-plane curvature of the stringer when the coupling elements of the stringer are interdigitated. In such embodiments, the other features which produce out-of-plane curvature of the stringer may co-operate with the head and/or neck portions according to the present invention so that the head and/or neck portions according to the present invention assist said other features in producing the out-of-plane curvature. This may have the benefit that it makes it easier for the slide fastener to assume its out-of-plane curvature when the coupling elements are interdigitated, as compared to if said other features alone were used to produce the out of plane curvature. The tape of each of the first and second stringers may be generally planar when the coupling elements of the first stringer are not interdigitated with the coupling elements of the second stringer. When it is said that the tape of the slide fastener is generally planar, what is meant is that, when the stringer is not coupled to another stringer as part of a chain, the tape is generally planar. Put another way the stringer, in isolation of anything else, has a tape which is generally planar.

The longitudinal edge of the second stringer in the region of said at least one of the coupling elements of the first stringer, and of said first and second adjacent coupling elements, forms a curve having a centre of curvature which lies beneath the plane of the tape of the second stringer. The centre of curvature may lie beneath the plane of the tape of the first stringer. The centre of curvature may lie beneath the plane of both the tape of the first stringer and the tape of the second stringer. The centre of curvature may be said to lie beneath the plane of the chain. Said at least one of the coupling elements may additionally comprise some form of taper so as to accommodate curvature of the stringer when said coupling elements of the stringer are interdigitated with coupling elements of the second stringer in order to secure the stringer and second stringer together. Such tapering may form part of the lower head portion and/or a lower portion of a main body of said at least one of the coupling elements .Such tapering may in addition or alternatively form part of the upper head portion and/or an upper portion of a main body of said at least one of the coupling elements.

Said first distance may be a distance between the first plane and the second plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said at least one of the coupling elements of the first stringer is mounted, and which passes through both the first and second contact points.

Said second distance may be a distance between the first plane and the second plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said at least one of the coupling elements of the first stringer is mounted, and which passes through both the third and fourth contact points.

The first distance and the second distance may be equal, and the first distance and second distance may be each greater than the third distance.

The head and neck portions of said at least one of the coupling elements of the first stringer may comprise a lower head portion and a lower neck portion respectively which are located below said plane of the tape of the first stringer; and wherein each of the first and second adjacent coupling elements of the second stringer comprise a lower head portion and a lower neck portion which are located below said plane of the tape of the second stringer; wherein, when said at least one of the coupling elements of the first stringer is received between said first and second adjacent coupling elements of the second stringer:

a) the lower head portion of the at least one of the coupling elements of the first stringer is received between the lower neck portion of the first adjacent coupling element of the second stringer and the lower neck portion of the second adjacent coupling element of the second stringer, such that the lower head portion of the at least one of the coupling elements of the first stringer contacts the lower neck portion of the first adjacent coupling element of the second stringer at a fifth contact point, and the lower head portion of the at least one of the coupling elements of the first stringer contacts the lower neck portion of the second adjacent coupling element of the second stringer at a sixth contact point; and b) the lower neck portion of the at least one of the coupling elements of the first stringer is received between the lower head portion of the first adjacent coupling element of the second stringer and the lower head portion the second adjacent coupling element of the second stringer, such that the lower neck portion of the at least one of the coupling elements of the first stringer contacts the lower head portion of the first adjacent coupling element of the second stringer at a seventh contact point, and the lower neck portion of the at least one of the coupling elements of the first stringer contacts the lower head portion of the second adjacent coupling element of the second stringer at an eighth contact point; wherein the first plane is located at a location longitudinally outboard, with respect to said at least one of the coupling elements of the first stringer, of both the fifth and seventh contact points, and the second plane is located at a location longitudinally outboard, with respect to said at least one of the coupling elements of the first stringer, of both the sixth and eighth contact points; wherein the head and neck portions of said at least one of the coupling elements of the first stringer is shaped such that, when said at least one of the coupling elements of the first stringer is received between said first and second adjacent coupling elements of the second stringer, a fourth distance between the first plane and the second plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said at least one of the coupling elements of the first stringer is mounted, and which passes through at least one of the fifth and sixth contact points; and/or a fifth distance between the first plane and the second plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said at least one of the coupling elements of the first stringer is mounted, and which passes through at least one of the seventh and eighth contact points; is less than said third distance. An embodiment having the optional features discussed in this paragraph includes said at least one of the coupling elements of the first stringer having lower head and lower neck portions. In other embodiments this need not be the case. For example, in some embodiments the head and neck portions of the said at least one of the coupling elements of the first stringer may not extend beneath the plane of the tape of the first stringer.

Said fourth distance may be a distance between the first plane and the second plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said at least one of the coupling elements of the first stringer is mounted, and which passes through both the fifth and sixth contact points.

Said fifth distance may be a distance between the first plane and the second plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said at least one of the coupling elements of the first stringer is mounted, and which passes through both the seventh and eighth contact points.

The fourth distance and the fifth distance may be equal, and the fourth distance and fifth distance may each be less than the third distance.

A maximum width, in a direction parallel to the longitudinal edge of the first stringer, of the upper head portion of the at least one of the coupling elements of the first stringer may be greater than a maximum width, in a direction parallel to the longitudinal edge of the first stringer, of the lower head portion of the at least one of the coupling elements of the first stringer.

Said maximum width of the lower head portion may extend between the fifth and sixth contact points.

Said maximum width of the upper head portion may extend between the first and second contact points.

A minimum width, in a direction parallel to the longitudinal edge of the first stringer, of the upper neck portion of the at least one of the coupling elements of the first stringer may be greater than a minimum width, in a direction parallel to the longitudinal edge of the first stringer, of the lower neck portion of the at least one of the coupling elements of the first stringer. Said minimum width of the lower neck portion extends between the seventh and eighth contact points. Said minimum width of the upper neck portion may extend between the third and fourth contact points.

The longitudinal edge of the tape of the first stringer at which the coupling elements are attached may include a cord.

The said at least one of the coupling elements of the first stringer may be formed of a plastics material. Said at least one of the coupling elements of the first stringer may be overmoulded onto the cord and the tape.

The tape of the first and/or second stringer may be of a construction selected from a group consisting of knitted, woven and non-woven.

At least one of the coupling elements of the first stringer may be of a second type, being received between third and fourth adjacent coupling elements of the second stringer when the row of coupling elements of the first stringer is interdigitated with the row of coupling elements of the second stringer; each of said coupling elements of the second type and said third and fourth adjacent coupling elements of the second stringer being shaped such that they comprise a main body having a shoulder portion, and a head portion extending parallel to the lateral axis away from the shoulder portion via a neck portion, wherein the main body of said at least one of the coupling elements of the second type is mounted to the tape of the first stringer, and the main body of each of said third and fourth adjacent coupling elements of the second stringer is mounted to the tape of the second stringer; wherein, when said at least one of the coupling elements of the second type is received between said third and fourth adjacent coupling elements of the second stringer the head and neck portions of the at least one of the coupling elements of the second type co-operate with the head and neck portions of the third and fourth adjacent coupling elements of the second stringer to prevent lateral separation in a direction generally parallel to the lateral axis of the at least one of the coupling elements of the second type and the third and fourth adjacent coupling elements of the second stringer; wherein the head and neck portions of said at least one of the coupling elements of the second type comprise an upper head portion and an upper neck portion respectively which are located above said plane of the tape of the first stringer; and wherein the head and neck portions of said at least one of the coupling elements of the second type comprise a lower head portion and an lower neck portion respectively which are located below said plane of the tape of the first stringer; and wherein the upper head portion of the coupling elements of the second type and the lower head portion of the coupling elements of the second type are substantially identical; and wherein the upper neck portion of the coupling elements of the second type and the lower neck portion of the coupling elements of the second type are substantially identical. The second type of coupling element has head and neck portions shaped such that the second type of coupling element does not cause any out-of-plane curvature of the stringers when the coupling element are interdigitated. The reason for this is that, because the upper head portion is substantially identical to the lower head portion, and the upper neck portion is substantially identical to the lower neck portion, the total width of the interdigitated coupling elements for a given length of chain is the same above and below the tapes. As such, the coupling elements of the second type do not cause the adjacent coupling elements on the second stringer to pivot relative to the tape of the second stringer. The presence of a second type of coupling element on the first stringer means that it is possible for a chain according to the present invention to include at least one portion which exhibits out-of-plane curvature when the coupling elements of the stringers are interdigitated and at least one portion which exhibits no out-of-plane curvature when the coupling elements of the stringers are interdigitated.

At least one of the coupling elements of the first stringer may be of a third type and is received between fifth and sixth adjacent coupling elements of the second stringer when the row of coupling elements of the first stringer is interdigitated with the row of coupling elements of the second stringer; each of said at least one of the coupling elements of the third type and said fifth and sixth adjacent coupling elements of the second stringer being shaped such that they comprise a main body having a shoulder portion, and a head portion extending parallel to the lateral axis away from the shoulder portion via a neck portion, wherein the main body of said at least one of the coupling elements of the third type is mounted to the tape of the first stringer, and the main body of each of said fifth and sixth adjacent coupling elements of the second stringer is mounted to the tape of the second stringer; wherein the head and neck portions of said at least one of the coupling elements of the third type comprise an lower head portion and an lower neck portion respectively which are located below said plane of the tape of the first stringer; and wherein each of the fifth and sixth adjacent coupling elements of the second stringer comprise an lower head portion and an lower neck portion respectively which are located below said plane of the tape of the second stringer; wherein, when said at least one of the coupling elements of the third type is received between said fifth and sixth adjacent coupling elements of the second stringer:

a) the lower head portion of the at least one of the coupling elements of the third type is received between the lower neck portion of the fifth adjacent coupling element of the second stringer and the lower neck portion of the sixth adjacent coupling element of the second stringer, such that the lower head portion of the at least one of the coupling elements third type contacts the lower neck portion of the fifth adjacent coupling element of the second stringer at a ninth contact point, and the lower head portion of the at least one of the coupling elements of the third type contacts the lower neck portion of the sixth adjacent coupling element of the second stringer at a tenth contact point; and b) the lower neck portion of the at least one of the coupling elements of the third type is received between the lower head portion of the fifth adjacent coupling element of the second stringer and the lower head portion the sixth adjacent coupling element of the second stringer, such that the lower neck portion of the at least one of the coupling elements of the first stringer contacts the lower head portion of the fifth adjacent coupling element of the second stringer at a eleventh contact point, and the lower neck portion of the at least one of the coupling elements of the third type contacts the lower head portion of the sixth adjacent coupling element of the second stringer at a twelfth contact point; such that the head and neck portions of the at least one of the coupling elements of the third type co-operate with the head and neck portions of the fifth and sixth adjacent coupling elements of the second stringer to prevent lateral separation in a direction generally parallel to the lateral axis of the at least one of the coupling elements of the third type and the fifth and sixth adjacent coupling elements of the second stringer; wherein a third plane is defined perpendicular to the longitudinal edge of the second stringer which passes through the fifth adjacent coupling element of the second stringer at a location longitudinally outboard, with respect to said at least one of the coupling elements of the third type, of both the ninth and eleventh contact points, and a fourth plane is defined perpendicular to the longitudinal edge of the second stringer which passes through the sixth adjacent coupling element of the second stringer at a location longitudinally outboard, with respect to said at least one of the coupling elements of the third type, of both the tenth and twelfth contact points; wherein said at least one of the coupling elements of the third type is shaped such that, when said at least one of the coupling elements of the third type is received between said fifth and sixth adjacent coupling elements of the second stringer, a sixth distance between the third plane and the fourth plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said at least one of the coupling elements of the third type is mounted, and which passes through at least one of the ninth and tenth contact points; and/or a seventh distance between the third plane and the fourth plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said at least one of the coupling elements of the third type is mounted, and which passes through at least one of the eleventh and twelfth contact points; is greater than an eighth distance between the third plane and the fourth plane along the longitudinal edge of the first stringer; such that, when said coupling elements of the first stringer are interdigitated with coupling elements of the second stringer, the longitudinal edge of the second stringer in the region of said at least one of the coupling elements of the third type, and of said fifth and sixth adjacent coupling elements forms a curve having a centre of curvature which lies above the plane of the tape of the second stringer.

The third type of coupling element has a head and neck portions shaped such that the third type of coupling element causes out-of-plane curvature of the stringers, when the coupling element are interdigitated, in the opposite direction to the out-of-plane curvature caused by said at least one of the coupling elements of the first stringer. The reason for this is that the total width of the interdigitated coupling elements for a given length of chain is greater below the tapes than it is above the tapes. As such, the coupling elements of the third type cause the adjacent coupling elements on the second stringer to pivot relative to the tape of the second stringer in the opposite direction as compared to that caused by a said at least one of the coupling elements of the first stringer. The presence of a third type of coupling element on the first stringer means that it is possible for a chain according to the present invention to include at least one portion which exhibits out-of-plane curvature in a first direction when the coupling elements of the stringers are interdigitated, and at least one portion which exhibits out-of-plane curvature in a second direction opposite the first when the coupling elements of the stringers are interdigitated. The first and second stringers are substantially identical. The stringers may be considered to be substantially identical if the only difference between the two is that they are generally reflections of one another in a plane parallel to one which includes the longitudinal edge of the first or second stringer.

According to a second aspect of the invention there is provided a slide fastener comprising a slide fastener chain according to the previous aspect. A slider may be movably mounted on the first and second stringers, such that the slider is movable relative to the first and second stringers along a sliding axis: in a first direction in order to interdigitate the row of coupling elements of the first stringer with the row of coupling elements of the second stringer in order to secure the first stringer and the second stringer together; and in a second direction in order to decouple the row of coupling elements of the first stringer from the row of coupling elements of the second stringer in order to decouple the first stringer and the second.

The slide fastener may comprise at least one top stop configured to provide a limit of movement of the slider along the sliding axis in the first direction.

The slide fastener may comprise a bottom stop configured to provide a limit of movement of the slider along the sliding axis in the second direction.

According to a third aspect of the invention, there is provided an article including a slide fastener according to the previous aspect.

Other aspects and preferred features of the present invention will be apparent from the following description and the accompanying claims.

The invention will now be further described by way of example and with reference to the accompanying drawings, in which:

Figure 1 shows a schematic view of a known type of slide fastener including a slider; Figure 2 shows a schematic view of a known type of slider for a slide fastener of the type shown in Figure 1 ;

Figure 3 shows a schematic cross-sectional view of a portion of the slider shown in Figure 2; Figure 4 shows a schematic view of the slider of the slide fastener similar to that shown in figure 1 with the slider being shown in cross-section;

Figure 5 shows a schematic plan view of a coupling element;

Figure 6 shows a schematic side view of a coupling element;

Figure 7 shows a schematic end view of a known coupling element; Figure 8 shows a schematic plan view from above of coupling elements of a portion of a chain of a slide fastener according to an embodiment of the present invention;

Figure 8a shows a schematic plan view from below of coupling elements of a portion of a chain of a slide fastener according to an embodiment of the present invention;

Figure 9 shows a schematic cross-sectional side view of coupling elements of the portion of a chain shown in Figures 8 and 8a;

Figures 10 and 1 1 show a schematic end view of a coupling element according to an embodiment of the present invention;

Figure 12 shows a schematic cross-sectional side view of coupling elements of the portion of a chain shown in Figures 8 and 8a; Figure 13 shows a schematic cross-sectional side view of coupling elements of a portion of a chain of a slide fastener according to the present invention;

Figures 13a and 13b show schematic cross-sectional plan views of coupling elements of the portion of a chain shown in Figure 13;

Figure 14 shows a schematic cross-sectional side view of coupling elements of a portion of a chain of a slide fastener according to an embodiment of the present invention;

Figure 15 shows a schematic perspective view of a slide fastener in accordance with an embodiment of the present invention; and Figure 16 shows a schematic perspective view of an article incorporating a slide fastener according to the present invention.

Figure 1 shows a known slide fastener 10. The slide fastener comprises a slider 1 1 and a pair of stringers 12a, 12b. Each stringer 12a, 12b comprises a coupling portion in the form of a plurality of coupling elements 14a, 14b (also referred to as teeth) which are attached to the edge of a tape 16a, 16b. The tape may be woven or knitted and may be formed from, for example, polyester. The coupling elements 14a, 14b may be attached to their respective tape 16a, 16b by, for example, crimping or moulding the coupling elements onto a reinforced edge of the tape 16a, 16b. The reinforced edges of the tapes may take the form of a cord having a thickness which is greater than that of the tape, as is very well known in the art. Alternatively, the coupling elements may be formed as a continuous coil. In this case the coupling elements are most commonly woven or knitted into the tape or alternatively are stitched to a surface of the tape at the edge of the tape. In the case of a watertight slide fastener the tape may be coated with a waterproof film or extrudate and the coupling elements may be mounted to the tapes in a waterproof manner.

The two stringers 12a, 12b when brought together (as shown in the bottom portion of Figure 1 ), are such that the coupling elements 14a, 14b of each stringer 12a, 12b can attach to one another, by interdigitating, to form chain 18. The chain 18 is generally planar, and the chain 18 (and the coupling portions which form part of the chain 18) extends along a longitudinal axis L of the chain 18.

As discussed in more detail below, each of the coupling elements 14a, 14b include head and neck portions. When the coupling elements 14a and 14b are brought together such that they interdigitate, the head and neck portions of the coupling elements 14a of the first stringer 12a co-operate with the head and neck portions of the coupling elements 14b of the second stringer 12b to prevent lateral separation in a direction generally parallel to a lateral axis T of the coupling elements 14a, 14b.

The slider 1 1 is mounted to the chain 18 such that it can move along the chain 18 between the two stringers 12a, 12b. Movement of the slider 1 1 along the chain 18 in a first sliding direction E causes the coupling elements 14a of the first stringer 12a to attach to the coupling elements 14b of the second stringer 12b. Whereas movement of the slider along the chain in a second sliding direction D, opposite to the first sliding direction E, causes the coupling elements 14a of the first stringer 12a to detach from the coupling elements 14b of the second stringer 12b.

The chain 18 is commonly cut to a desired length to form a desired length of slide fastener 10. Stops (often referred to as top stops and bottom stops) are attached to either end of the chain 18. The stops limit the extent of movement that the slider 1 1 can undertake along the chain 18.

In the slide fastener shown in Figure 1 , the stops 20a and 20b are top stops attached to a top end of the chain 18 on the first tape 16a and second tape 16b respectively. Other slide fasteners may have a single top stop attached to both stringer tapes. The slide fastener has a single bottom stop 22 which is attached to the tapes 16a, 16b of both the first and second stringers 12a, 12b and which secures the tapes 16a and 16b together.

As seen best in figures 2, 3, and 4, the slider 1 1 includes a main body 24, through which the coupling elements 14a, 14b of each stringer 12a, 12b pass, and a pull tab 26 attached to the main body 24 via a bridge portion 28. The pull tab 26 may be grasped by a user in order to effect movement of the slider 1 1 along the chain 18 (for example, in the first and second sliding directions E, D previously discussed).

In more detail, the main body 24 of the slider 1 1 comprises an upper portion 30 connected to a lower portion 32 by a connection post 34 extending in a third direction B from the upper portion 30 to the lower portion 32. The upper portion 30 may be referred to as an upper wing or an upper blade. Likewise, the lower portion may be referred to as a lower wing or lower blade. The connection post 34 may be referred to as the diamond.

The upper portion 30, lower portion 32 and connection post 34 co-operate to define a Y-shaped channel 36. The Y-shaped channel 36 is also defined by lateral flanges 42 and 44 on either side of the slider 1 1 which extend towards each other from the upper portion 30 and lower portion 32 respectively. The Y-shaped channel 36 has a first arm 36a separated from a second arm 36b by the connection post 34.

The slider 1 1 extends in a second direction C, generally perpendicular to the third direction B, from a head end 38 of the slider to a tail end 40 of the slider 1 1 . The Y- shaped channel 36 also includes a third arm 36c which adjoins the first and second arms 36a, 36b in the vicinity of a tail end of the connection post 34.

The first arm 36a and second arm 36b have respective first and second openings 46a, 46b at the head end 38 of the slider 1 1 . The third arm 36c has a third opening 46c at the tail end 40 of the slider 1 1 .

The slide fastener shown in Figure 4 is a coil zipper - i.e. a slide fastener in which the coupling elements of each stringer are formed as a continuous coil. The embodiments shown in other Figures within the application are injection moulded or possibly metal zippers in which the coupling elements of each stringer are formed as a plurality of separate teeth. For the sake of ease, the coupling elements shown within figure 4 may be considered to be equivalent to those shown in each of the remaining figures. Figures 5, 6 and 7 show schematic plan, side and end views respectively of a tooth 14c which may form one of the coupling elements 14a, 14b of a known slide fastener. In both figures 5 and 7 dashed line R shows the location of the longitudinal edge (e.g. cord) of a tape when the tooth 14c has been mounted on to a tape 16a, 16b of a stringer 12a, 12b. The tooth may be mounted on to the tape in any appropriate manner, for example, by over moulding the tooth on to the edge of the tape. The tooth 14c (or coupling element) is shaped such that it comprises a main body 50 including a shoulder portion 52 which, when the tooth 14c is mounted to a tape, is located adjacent the longitudinal edge of the tape. In addition, the tooth 14c includes a head portion 54 extending parallel to a lateral axis T away from the shoulder portion 52 via a neck portion 56.

Furthermore the tooth 14c includes an aperture 58 which passes through the main body 50 of the tooth in a direction which is generally perpendicular to the lateral axis T. The aperture 58 includes a first portion 58a which has a generally circular cross-section and which is sized and shaped to accommodate the longitudinal edge of a tape to which the coupling element is mounted; and a second portion 58b which is generally slot-shaped and which is sized and shaped so as to accommodate a portion of the tape to which the tooth is mounted which is adjacent to the longitudinal edge of the tape. Finally, the tooth 14c incorporates a recess 60 located at the tip of the head portion 54 which is located farthest from the shoulder portion 52. The recess 60 has a cross- section which is generally semi-circular. The recess 60 extends longitudinally in a direction which is generally perpendicular to the direction in which the head portion 54 extends away from the shoulder portion 52. This direction, when the tooth 14c is mounted to a tape, is generally parallel to the longitudinal axis L of the stringer/slide fastener of which the tooth 14c forms a part.

The purpose of the recess 60 is that, when the tooth 14c forms part of a first stringer and is coupled to teeth of a second stringer in order to secure the first and second stringers together (in a manner discussed in more detail below) the recess 60 can accommodate one or more securing lugs 62 of similar teeth located on the second stringer which interdigitate with the tooth 14c being described. The securing lugs 62 in the present embodiment are located at a location in line with the longitudinal edge of a tape to which the tooth 14c is mounted. The securing lugs 62 extend from either side of the neck portion 56 in a direction which is generally perpendicular to the direction in which the head portion 54 extends away from the neck portion 52. In use, when the tooth 14c is interdigitated with teeth from another stringer such that the lug 62 of each adjacent tooth is received by the recess 60, this acts so as to stabilise the tooth and prevent the slide fastener from being unintentionally separated by applying a force to the slide fastener which is generally perpendicular to the plane of the slide fastener.

As can be seen most clearly in figure 1 , known slide fasteners (and in particular the chain of known slide fasteners) are generally planar. That is to say, where a known slide fastener is in a closed configuration (whereby the teeth of both stringers of the slide fastener are interdigitated so as to secure the stringers together), the slide fastener generally lies in a plane.

However, in certain situations, a slide fastener may be used in the manner in which it is required for the slide fastener to bend out of the plane of the slide fastener. For example, when a slide fastener forms part of a curved article, such as the corner of a suitcase or the like, the slide fastener must bend to follow the shape of the curved article. Some known slide fasteners are capable of accommodating such a curve by virtue of their flexibility. However, by bending the slide fastener out of plane this may apply stress to the slide fastener because it is deformed out of its natural state. A slide fastener stressed in this way may require additional force to be applied to the slider of the slide fastener in order to operate the slide fastener (for example opening the slide fastener). Furthermore, the slider may be more likely to snag when the slide fastener is deformed out of its natural state.

Put another way, the force required to slide the slider 1 1 along the slide fastener 10 (i.e. relative to the stringers 12a, 12b) may be increased if the slide fastener 10 is bent out of plane. The increase in force required to slide the slider 1 1 may prevent a user from being able to operate the slide fastener 10. This will occur if the user is unable to apply sufficient force to the slider 1 1 to cause the slider to slide along the slide fastener 10. The force applied by a user may be relatively large in the case of an able-bodied user or relatively small in the case of a physically impaired user - for example, a physically disabled user or an elderly user.

The increase in force required to slide the slider 1 1 may additionally or alternatively place increased stress on the slide fastener 10 and/or an article that the slide fastener 10 is attached to. Increased stress on the slide fastener 10 may result in damage to the slide fastener 10. Increased stress on the article that the slide fastener is attached to may result in the slide fastener 10 becoming detached from the article and/or damage to the article.

The present invention seeks to overcome the above discussed problems with bending a known side fastener out of plane.

Before discussing the invention in detail some further discussion of the prior art may be useful. In particular, referring again to figure 7, this shows a schematic end-on view of a known tooth (or coupling element) 14c. The head portion 54 of the coupling element 14c has an upper head portion 54a which is located above the plane of the tape to which the tooth 14c is mounted and a lower head portion 54b which is located below the plane of the tape. Although the tape to which the tooth 14c is mounted is not shown in figure 7, the plane of the tape is represented by the position of the longitudinal edge of the tape which is illustrated by the dashed line R. In particular, if the tape was shown in figure 7 it would extend into the page of the figure in a direction perpendicular to the plane of the figure.

For the avoidance of doubt, within figure 7, the upper head portion 54a is shown as being the portion of the head which is located above the line R; and the lower head portion 54b is located below the line R.

It will be noted that within the prior art tooth 14c shown in figure 7, the upper head portion 54a and lower head portion 54b are substantially the same and are symmetrical with respect to one another about the line R. In this way the upper head portion 54a has a maximum width W _ma in a direction parallel to the longitudinal edge R which is equal to a maximum width W _mb of the lower head portion 54b in said direction parallel to the longitudinal edge R. As is the case with teeth of many known slide fasteners, the maximum width of the upper head portion and maximum width of the lower head portion is one and the same and occurs in the plane of the tape to which the tooth is mounted (i.e. at the location where the upper head portion boarders the lower head portion - at line R).

Figures 8 and 9 show schematic plan and side cross-sectional views through a portion of a slide fastener according to the present invention. As is the case with known slide fasteners, the slide fastener according to the present invention shown in Figures 8 and 9 comprises a chain 18' which includes first and second stringers. As previously discussed, the first and second stringers each comprise a tape (which is omitted within Figures 8 and 9 to enhance the clarity of the figures) and a row of coupling elements mounted on a longitudinal edge of the tape. The first stringer includes a first row of coupling elements 68 and the second stringer includes a second row 70 of coupling elements. As shown in Figures 8 and 9, the row of coupling elements 68 of the first stringer may be interdigitated with the row of coupling elements 70 of the second stringer in order to secure the first stringer and second stringer together. It goes without saying that when the row of coupling elements 68 of the first stringer and the row of coupling elements 70 of the second stringer are uncoupled, the first and second stringers are not coupled together by the coupling elements 68, 70.

Again, as previously discussed in relation to known slide fasteners, the tape of each of the first and second stringers on the slide fastener chain according to the present invention are generally planar when the coupling elements of the first stringer are not interdigitated with (or are uncoupled from) the coupling elements of the second stringer. Features of several of the coupling elements which make up the portion of the slide fastener chain 18' shown in Figures 8 and 9 are now discussed in more detail. A first coupling element 14d of the first stringer is received between the first and second adjacent coupling elements 14e, 14f of the second stringer. In the present embodiment, despite the fact that coupling elements 14d, 14e and 14f are given different reference numerals, they are in fact all generally identical. However, in other embodiments, this need not be the case.

As previously discussed, again in common with known slide fasteners, each of the coupling elements 14d, 14e and 14f are shaped such that they comprise a main body 50 including a shoulder portion 52 and a head portion 54 which extends parallel to a lateral axis T away from the shoulder portion 52 via a neck portion 56. The main body 50 of the coupling element 14d is mounted to the tape of the first stringer. The main body 50 of each of the first and second adjacent coupling elements 14e, 14f is mounted to the tape of the second stringer.

The head and neck portions 54, 56 of the coupling element 14d include an upper head portion 54a and an upper neck portion 56a which are located above the plane of the tape of the first stringer. Likewise, the head and neck portions 54, 56 of the coupling elements 14e, 14f each include an upper head portion 54a and an upper neck portion 56a which are located above the plane of the tape of the second stringer.

When the rows of coupling elements 68, 70 are interdigitated such that the coupling element 14d is received between the coupling elements 14e and 14f this results in the coupling elements engaging in the following manner.

The upper head portion 54a of the coupling element 14d is received between the upper neck portion 56a of the first adjacent coupling element 14e and the upper neck portion 56a of the second adjacent coupling element 14f. The upper head portion 54a of the coupling element 14d contacts the upper neck portion 56a of the coupling element 14e at a first contact point 200. The upper head portion 54a of the coupling element 14d contact the upper neck portion 56a of the coupling element 14f at a second contact point 202.

In addition, the upper neck portion 56a of the coupling element 14d is received between the upper head portion 54a of the coupling element 14e and the upper head portion 54a of the coupling element 14f. The upper neck portion 56a of the coupling element 14d contacts the upper head portion 54a of the coupling element 14e at a third contact point 204. The upper neck portion 56a of the coupling element 14d also contacts the upper head portion 54a of the coupling element 14f at a fourth contact point 206.

The head and neck portions 54, 56 of the coupling element 14d of the first stringer cooperates with the head and neck portions 54, 56 of the coupling elements 14e, 14f of the second stringer to prevent lateral separation in a direction generally parallel to the lateral axis T of the coupling elements 14d, 14e, 14f. This is the conventional purpose of the head and neck portions of coupling elements of a slide fastener - the reduced maximum width (parallel to the longitudinal edge of the tape to which the coupling element is mounted) of the neck portions as compared to that of the head portions means that when the coupling elements of the stringers are interdigitated, it is not possible for the head of a coupling element 14d on one stringer to be pulled, parallel to the lateral axis T, out of a recess formed between the neck portions of adjacent coupling elements 14e, 14f on the other stringer.

A first plane 208 is defined perpendicular to the longitudinal edge of the second stringer. The first plane 208 passes through the coupling element 14e at a location which is longitudinally outboard, with respect to coupling element 14d, of both the first and third contact points 200, 204.

A second plane 210 is defined perpendicular to the longitudinal edge of the second stringer. The second plane 210 passes through the coupling element 14f at a location longitudinally outboard, with respect to the coupling element 14d, of both the second and fourth contact points 202, 206.

Within Figures 8 and 9 only an edge of the first and second planes 208, 210 can be seen. This is because, in each figure, the plane is generally perpendicular to the plane of the figure. It is worth noting that if the curvature of the chain (discussed in more detail below) was greater, then it would be possible to see more than just the edge of the plane in Figure 8. In the description above the planes are described as being located at a location which is longitudinally outboard, with respect to the coupling element 14d, of various contact points. What is meant by this is that each of the planes 208, 210 is located at a position along the longitudinal axis defined by the longitudinal edge of the second stringer which is further away along the longitudinal axis from a centre portion of the coupling element 14d than the distance along the longitudinal axis between said centre portion and either of the relevant contact points.

Within Figures 8 and 9 and the position of the first and second planes 208, 210 has been chosen such that the first plane 208 bisects the coupling element 14e into equal parts and the second plane 210 bisects the coupling element 14f into equal parts. This need not be the case: the first and second planes 208, 210 may be located at any appropriate position which is longitudinally outboard of either of the respective contact points. For the avoidance of doubt, the first and second planes do not exist as physical entities, but are rather mental constructs to enable the invention to be understood.

The coupling element 14d is shaped such that when the coupling elements of the first and second stringer are interdigitated, such that the coupling element 14d is received between the coupling elements 14e and 14f, the following features of the slide fastener chain according to the present invention are present:

First, a first distance 212 between the first plane 208 and the second plane 210 along a line which is parallel to the position of the longitudinal edge of the first stringer upon which the coupling element 14d is mounted, and which passes through both the first and second contact points 200, 202 is greater than a third distance 216 between the first plane and the second plane along the portion of the longitudinal edge of the first stringer. Secondly, a second distance 214 between the first plane 208 and the second plane 210 along the line which is parallel to the portion of the longitudinal edge of the first stringer upon which the coupling element 14d is mounted and which passes through both of the third and fourth contact points 208, 21 0 is greater than the third distance 216.

In this manner, when the coupling elements of the first stringer are interdigitated with coupling elements of the second stringer, the longitudinal edge of the second stringer in the region of the coupling elements 14d, 14e and 14f forms a curve having a centre of curvature CC which lies beneath the plane of the tape of the second stringer.

In summary, the shape of the head and neck portions of the coupling element 14d results in out-of-plane curvature of the slide fastener chain. The reason for this is that for a given length of tape of the second stringer, which, when the coupling elements of the second stringer are interdigitated with coupling elements of the first stringer, includes the coupling element 14d, the width of the upper head and neck portions of the coupling elements is greater than the length of the edge of the second stringer. This results in the upper portion of the coupling elements pivoting about the longitudinal edge of the second stringer thereby producing curvature of the second stringer (and hence the attached first stringer) out of the plane of the tape of the second stringer, as compared to generally planar shape of the first and second stringers when the first and second stringers are uncoupled. This compares to known slide fasteners having coupling elements like that shown in figure 7 which, because the shape of the head and neck portions of the coupling elements is generally symmetrical about the plane of the tape to which the coupling element is attached, when the coupling elements are interdigitated, the width of the upper head and neck portions of the coupling elements is the same as the width of the lower head and neck portions. As such there is no pivoting of the coupling elements about the longitudinal edge of the second stringer and therefore no curvature of the second stringer (and hence the attached first stringer) out of the plane of the tape of the second stringer.

When the coupling elements of the first and second stringer are coupled together the slide fastener is caused to curve out-of-plane of the tape of the second stringer. This curvature specifically results from the shape of the head and/or neck portions of the at least one of the coupling elements of the first stringer. The greater distance between the first and second planes when passing through at least one of the contact points of the upper head portion or upper neck portion (first or second distances), as compared to the distance between the first plane and the second plane along the longitudinal edge of the first stringer (third distance) causes the adjacent coupling elements to pivot relative to the tape of the second string, thus producing curvature.

Because it is the shape of the head and/or neck portions of the at least one of the coupling elements of the first stringer which results in the curvature, and not that of any other portion of the at least one of the coupling elements of the first stringer, this means that such curvature can be obtained by only making a relatively minor adjustment to the shape of the head and/or neck portions of the at least one of the coupling elements of the first stringer, as opposed to adding additional, more complicated structure to the at least one of the coupling elements. In addition, this means that, because no additional structure is required to produce the curvature, the coupling elements are easier to produce and require less material than other known types of slide fastener chain which produce such out-of-plane bending/curvature. In some embodiments, a coupling element of a stringer which forms part of a slide fastener chain according to the present invention may, in fact, include slightly less material than an equivalent coupling element of a standard slide fastener which does not exhibit out-of-plane curvature.

According to the present invention the head portion 54 and neck portion 56 refer only to the portions of the coupling elements 14d, 14e, 14f which cooperate to prevent lateral separation of the stringers in the manner discussed. Put another way, any portion of a coupling elements 14d, 14e, 14f which does not co-operate with a portion of an adjacent coupling element on the other stringer (when the coupling elements are interdigitated) to prevent lateral separation of the stringers in the manner discussed is not considered to be a head portion or neck portion within the meaning of the present invention. Although in the above described embodiment the first and second distances pass through both the first and second contact points, and the third and fourth contact points respectively, in other embodiments of the invention this need not be so. For example, the first distance may pass through only one of the first and second contact points, and/or the second distance may pass through only one of the third and fourth contact points. In addition, in the preferred described embodiment, both the first distance and the second distance are greater than the third distance. In some embodiments this need not be the case. That is to say, in some embodiments only one of the first distance and the second distance may be greater than the third distance. It is thought that such an example the slide fastener will still exhibit out-of-plane curvature such that the centre of curvature lies beneath the plane of the tape of the second stringer. However, in addition, the slide fastener may exhibit curvature within the plane of the slide fastener - that is to say, the longitudinal axis of the slide fastener may not be a straight line within the plane of the slide fastener.

As in the embodiment shown within Figures 8 and 9, it is preferable that the first distance 212 and the second distance 214 are equal. It is thought that this will substantially prevent the head and neck portions of the coupling element 14d from causing any in-plane bending or curvature of the slide fastener chain when the coupling elements of the first and second stringers are interdigitated.

So far, only the configuration of the upper head and neck portions of the coupling elements 14d, 14e and 14f have been discussed. The configuration of the lower head and neck portions of the coupling elements is discussed further below. However, it should be noted that the present invention would still function if the coupling element 14d did not include a lower head and/or neck portion at all.

As can be seen clearly in Figure 8a, which shows a view from below of the portion of the chain shown in Figure 8, the head and neck portions 54, 56 of the coupling element 14d comprise a lower head portion 54b and a lower neck portion 56b respectively which are located below said plane of the tape of the first stringer. Likewise, each of the coupling elements 14e, 14f also comprise lower head and neck portions which are located below the plane of the tape of the second stringer.

In a similar manner to that discussed above in relation to the upper head and neck portions of the various coupling elements, various aspects of the lower head and neck portions of the coupling elements when the coupling element 14d is received between the coupling elements 14e and 14f is discussed below. The lower head portion 54b of the coupling element 14d is received between the lower neck portion of the coupling element 14e and the lower neck portion of the coupling element 14f. The lower head portion 54b of the coupling element 14d contacts the lower neck portion of the coupling element 14e at a fifth contact point 218. Likewise, the lower head portion 54b of the coupling element 14d contact the lower neck portion of the coupling element 14f at a sixth contact point 220. As best shown in Figure 8a, the lower neck portion 56b of the coupling element 14d is received between the lower head portion of the coupling element 14e and the lower head portion of the coupling element 14f. The lower neck portion of the coupling element 14d contacts the lower head portion of the coupling element 14e at a seventh contact point 219. In addition the lower neck portion of the coupling element 14d contacts the lower head portion of the coupling element 14f at an eighth contact point 221.

The first plane 208 is located at a location longitudinally outboard, with respect to the coupling element 14d, of both the fifth contact point 218 and the seventh contact point 219. The second plane 210 is located at a location longitudinally outboard, with respect to the coupling element 14d, of both the sixth contact point 220 and the eighth contact point 221 . The head and neck portions of the coupling element 14d are shaped such that when the coupling element 14d is received between the coupling elements 14e and 14f the slide fastener chain has the following features.

First, a fourth distance 222 between the first plane 208 and the second plane 210 along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which the coupling element 14d is mounted, and which passes through at least one of the fifth and sixth contact points 218, 220 (in this case both) is less than the third distance 216. Secondly, in addition to the first point above, or as an alternative, a fifth distance 223 between the first plane 208 and the second plane 210 along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which the coupling element 14d is mounted, which passes through at least one of the seventh and eighth contact points 219, 221 (and in this case both) is less than the third distance 216. In some embodiments of the present invention only one of the first and second features discussed above may be present. However, in the presently described embodiment both are present. In some embodiments, like the presently described embodiment, the fourth distance 222 and the fifth distance 223 are equal. However, in some embodiments this need not be the case.

In the presently described embodiment, a maximum width W _ma ', in a direction parallel to the longitudinal edge of the first stringer, of the upper head portion 54a is greater than a maximum width W _mb ', in a direction parallel to the longitudinal edge of the first stringer, of the lower head portion 54b.

In the presently described embodiment the maximum width W _mb ' of the lower head portion 54b of the coupling element 14d extends between the fifth and sixth contact points 220, 222, and the maximum width W _ma ' of the upper head portion 54a of the coupling element 14d extends between the first and second contact points 208, 210. In other embodiments this need not be the case. A minimum width of the lower neck portion 56b of the coupling element 14d is defined as the minimum width of the portion of the lower neck portion 56b of the coupling element 14d which contacts the lower head portions of coupling elements 14e and 14f. A minimum width of the upper neck portion 56a of the coupling element 14d is defined as the minimum width of the portion of the upper neck portion of the coupling element 14d which contacts the upper head portions of the coupling elements 14e and 14f. The minimum widths discussed above are measured in a direction parallel to the longitudinal edge of the first stringer.

The minimum width of the upper neck portion of the coupling element 14d is greater than a minimum width of the lower neck portion of the coupling element 14d. In some embodiments, the difference between the earlier mentioned maximum width of the upper head portion of the coupling element and the maximum width of the lower head portion of the coupling element 14d may be equal to the difference between the minimum width of the upper neck portion of the coupling element 14d and the minimum width of the lower neck portion of the coupling element 14d. In the presently described embodiment the minimum width of the lower neck portion of the coupling element 14d extends between the seventh and eighth contact points and the minimum width of the upper neck portion 56a of the coupling element 14d extends between the third and fourth contact points 204, 206.

Figures 10 and 1 1 both show schematic end-on views of a coupling element 14d which may form part of a stringer or slide fastener according to the present invention. The plan and side views of the coupling element 14d is substantially the same as those shown in Figures 5 and 6.

As previously discussed, the coupling element 14d differs from the known coupling element discussed above in that a maximum width W _ma ' of the upper head portion 54b in a direction parallel to the longitudinal edge R of the tape (not shown) is greater than a maximum width W _mb ' of the lower head portion 54a in a direction parallel to the longitudinal edge R of the tape. Put another way, the maximum width W _ma ' of the upper head portion 54a in a direction parallel to the longitudinal edge R of the tape is the maximum width of the head portion 54 in said direction parallel to the longitudinal edge R of the tape.

In addition, the outer edges 64 of the lower head portion 54b taper inwards, such that the width of the lower head portion 54b in a direction parallel to the longitudinal edge R of the tape decreases the greater the distance from the plane of the tape. Likewise, a lower portion of the main body 50 of the coupling element 14d (i.e. the portion of the main body located below the plane of the tape to which the coupling element is mounted) includes outer edges 66. The outer edges 66 taper inwards, such that the width of the lower portion of the main body 50 in a direction parallel to the longitudinal edge R of the tape decreases the greater the distance from the plane of the tape. Figure 12 shows another schematic cross-sectional view of the portion of the chain 18' shown in Figure 10 taken along the line F shown in Figure 10. The figure shows that when coupling elements 14d of the first stringer are interdigitated with coupling elements of the second stringer in order to secure the first stringer and second stringer together, the longitudinal edge R in the region of said at least one coupling element (in the illustrated embodiment all of the coupling elements) forms a curve having a centre of curvature CC such that the upper head portion 54a, lower head portion 54b and centre of curvature CC all lie on a line LL, the lower head portion 54b being intermediate the upper head portion 54a and centre of curvature CC. In this way, by utilising coupling elements of the type discussed above, the invention provides a stringer and slide fastener which is such that when the coupling elements of two stringers are interdigitated in order to secure the stringers together, each stringer, and hence the slide fastener, has a natural state in which the stringers, and hence slide fastener bend out of plane. That is to say, the stringers, and hence slide fastener, have a natural state in which the stringers, and hence slide fastener, form a curve about a centre of curvature which is located out of the plane of the slide fastener.

Without wishing to be bound by theory, it is thought that the shape of the head portion of the coupling elements according to the present invention results in the aforementioned curvature of the stringer/slide fastener of which the coupling elements form part as follows. When the slider couples the coupling elements of two stringers together this causes each head portion of a coupling element to be received by the neck portions of adjacent coupling elements when the coupling elements are interdigitated. This engagement of the coupling elements draws the coupling elements together, not only in a direction perpendicular to the longitudinal edges of the tapes of the stringers, but also in a direction parallel to the longitudinal edges of the tapes of the stringers. The maximum width of the upper head portion, which is received by neck portions of the adjacent interdigitated coupling elements, is greater than that of the lower head portion. This results in the total length of the interdigitated portion of the interdigitated coupling elements above the longitudinal edge of the tape being greater than the total length of the interdigitated portion of the interdigitated coupling elements below the longitudinal edge of the tape. The difference between the total length of the interdigitated coupling elements above the longitudinal edge of the tape as compared to that of the coupling elements below the longitudinal edge of the tape results in the tendency of the longitudinal edge of the tape (and hence the rest of the tape) to which the coupling elements are mounted to bend (or curve) out of the plane of the tape in the manner previously discussed.

By creating a slide fastener which has a natural state which exhibits a degree of out of plane curvature, such a slide fastener can be integrated into a product having a curved shape such that the curvature of the slide fastener when the slide fastener is in a closed configuration substantially matches or approaches the curvature of the item to which the slide fastener is secured. Because the curvature of the slide fastener in the closed state matches or approaches the curvature of the article to which incorporates the slide fastener, this helps to minimise or prevent the problems discussed above which exist when a slide fastener having a natural state which is planar is integrated into a curved item. For example, the out of plane curvature of a stringer/slide fastener according to the present invention may reduce the force that needs to be applied to a slider of the slide fastener in order to open or close the slide fastener. Additionally, use of such a curved slide fastener incorporated into a curved article may reduce the probability that the slider of the slide fastener will snag on either the teeth or the tapes of the stringers of the slide fastener.

It follows that the invention provides an alternative slide fastener which is configured such that in its natural state (when the coupling elements are interdigitated) it curves out of plane. This object is achieved by a slight change in the shape of a relatively small part of the stringer (i.e. the head portion of each coupling element). This is a relatively straightforward way of achieving the effect of the invention - the general shape of the stringer / slide fastener (and, in particular, the coupling elements) is relatively unchanged. As such there is no complicated additional structure required to achieve the effect of the invention. By avoiding complicated additional structure the risk of damage to the coupling element during use is reduced. In addition, because the invention is achieved by a slight change in the shape of a relatively small part of the stringer only a relatively small amount of additional material (or perhaps even a slight reduction in material) is required to construct a stringer according to the present invention, as compared to a known stringer which forms a generally planar chain.

It will be appreciated that it is possible to "tune" the extent of curvature of a stringer/slide fastener according to the present invention. For example, it may be desirable to tune the curvature of a stringer/slide fastener so that it matches the curvature of an article in which the slide fastener is to be incorporated. Such tuning of the out of plane curvature of the stringer/slide fastener (for example determining the radius of curvature of a stringer/slide fastener) according to the present invention may be achieved by altering various characteristics of the stringer/slide fastener. Such examples include varying the dimensions of the head portion of the teeth according to the present invention which form part of the stringer/side fastener. For example, the maximum width of the upper and lower head portions (in a direction parallel to the longitudinal edge) may be varied, thereby varying the difference between these measurements. Another example of a characteristic of which can be varied is the distance between the location of the maximum width of the upper head portion and the longitudinal edge of the tape to which the coupling element is mounted. Other examples include varying the dimensions of the neck portion of the teeth according to the present invention which form part of the stringer/side fastener. For example, the minimum width (in a given plane) of the upper and lower neck portions (in a direction parallel to the longitudinal edge) may be varied, thereby varying the difference between these measurements. Another example of a characteristic of which can be varied is the distance between the location of the minimum width of the upper neck portion and the longitudinal edge of the tape to which the coupling element is mounted. Further possible variations also include changing the degree of tapering of the type previously discussed of the lower head portion and/or the lower portion of the main body. In addition, it may be possible to alter the degree of curvature by using different materials for various parts of a stringer according to the present invention. For example, varying the material that the head portion and/or main body of the coupling elements are made from (for example using materials which have different compressibility). Furthermore, different materials may be used for the tape of a stringer according to the present invention (for example materials which have different flexibility).

The person skilled in the art would readily be able to alter characteristics a slide fastener according to the present invention (such as those discussed above) in a trial— and-error manner so as to produce a stringer which has the desired degree of out of plane curvature. Consequently, further description of this point is omitted for the sake of brevity.

Figures 13, 13a and 13b are further related figures which show the coupling elements of a chain 18' according to the present invention. In particular, figure 13 shows a side view of the chain 18' and figures 13a and 13b show plan cross-sectional views through the coupling elements of the chain 18' at two separate locations. Figure 13a shows a cross-section at the location indicated by K within figure 13 and figure 13b shows a cross-section at the location J within figure 13. The portions of chain which form part of a side fastener according to the present invention discussed above include coupling elements such that all the coupling elements of both stringers are identical. This need not always be the case. Figure 14 shows a schematic cross-sectional view through a chain 18" which includes two different types of coupling element. A first portion 72 of the chain 18" (which is located above line 74 (which is included for illustrative purposes only and does not form part of the shown chain) includes coupling elements of a normal known type, whereas a second portion 76 of the chain 18" which is located below the line 74 comprises coupling elements which are of the type according to the present invention already discussed in relation to figures 8 to 13.

It will be appreciated that the known normal coupling elements 73 which form part of the first portion 72 of the chain 18" are of the type shown in figure 7. Coupling element 73 of the first stringer is received between third and fourth adjacent coupling elements 73a, 73b of the second stringer when the row of coupling elements of the first stringer is interdigitated with the row of coupling elements of the second stringer.

Each of the coupling elements 73, 73a, 73b are shaped such that they comprise a main body having a shoulder portion, and a head portion extending parallel to the lateral axis away from the shoulder portion via a neck portion, wherein the main body of the coupling element of the second type 73 is mounted to the tape of the first stringer, and the main body of each of said third and fourth adjacent coupling elements 73a, 73b of the second stringer is mounted to the tape of the second stringer. When the coupling element 73 is received between said third and fourth adjacent coupling elements 73a, 73b of the second stringer the head and neck portions of the coupling element of the second type 73 co-operate with the head and neck portions of the third and fourth adjacent coupling elements 73a of the second stringer to prevent lateral separation in a direction generally parallel to the lateral axis of the coupling element of the second type 73 and the third and fourth adjacent coupling elements 73a, 73b of the second stringer.

The head and neck portions of the coupling elements of the second type 73 comprise an upper head portion and an upper neck portion respectively which are located above said plane of the tape of the first stringer. The head and neck portions of said coupling elements of the second type 73 comprise a lower head portion and a lower neck portion respectively which are located below said plane of the tape of the first stringer.

The upper head portion of the coupling elements of the second type 73 and the lower head portion of the coupling elements of the second type 73 are substantially identical. In addition, the upper neck portion of the coupling elements of the second type 73 and the lower neck portion of the coupling elements of the second type 73 are substantially identical. When it is said that various portions are identical, it is the case, however, the identical portions are flipped horizontally relative to one another about the plane of the tape of the stringer to which the coupling elements are mounted.

Because the upper and lower head portions are substantially identical a maximum width of the lower head portion in a direction parallel to the longitudinal edge of the tape to which the coupling element is mounted is substantially the same as the maximum width of the upper head portion in a direction parallel to the longitudinal edge. Likewise, a minimum width of the lower neck portion in a direction parallel to the longitudinal edge of the tape to which the coupling element is mounted is substantially the same as the minimum width of the upper neck portion in a direction parallel to the longitudinal edge.

It can be seen that, as a result of the different types of coupling element used in each of the first portion 72 and second portion 76 of the chain 18", the first and second portions of the chain have a different shape. In particular, the natural state (when the coupling elements of the chain are interdigitated) of the first portion 72 of the chain 18" is general planar, whereas the second portion 76 of the chain 18" curves out of plane about a centre of curvature CC.

Figure 15 shows a schematic perspective view of a portion of a slide fastener according to an embodiment of the present invention. The slide fastener 10' includes a slider 1 1 ' and a pair of stringers 12a', 12b'. Each stringer includes a tape 16a' 16b'. Each tape may be knitted, woven or non-woven. Each tape has a longitudinal edge 15a', 15b'. Each longitudinal edge 15a', 15b' includes a cord of the type well known in the art. Each stringer 12a', 12b' includes a row of coupling elements 14a', 14b' which are mounted to the longitudinal edge 15a', 15b' of the respective stringer 12a', 12b'. In particular, the coupling elements of the rows of coupling elements 14a', 14b' are formed of a plastics material and are over-moulded on to the cord of the tape.

In the present embodiment it may be said that the stringers 12a', and 12b' are substantially identical (albeit generally reflected in the longitudinal axis of the slide fastener).

The slider 1 1 ' is mounted to the stringers 12a', 12b' such that the slider is movable relative to at least one stringer (and in this case both) along a sliding axis. In the present embodiment the sliding axis is the curved axis which follows both of the rows of the coupling elements 14a', 14b' along the slide fastener. The sliding axis may also be said to run parallel to the longitudinal edge 15a', 15b' of each of the stringers 12a', 12b'. The slide fastener 10' also includes a first top stop 20a' located on the first stringer 12a', and a second top stop 20b' located on the second stringer 14b'. The top stops are shown in white for clarity purposes. Each top stop is configured to provide a limit of movement of the slider 11 ' along the sliding axis in a first direction E. The slide fastener 10' also comprises a bottom stop 22' configured to provide a limit of movement of the slider 11 ' along the sliding axis in a second direction D.

It can be seen that the slide fastener 10' includes three sections S1 , S2 and S3. Each section is bounded by the relevant dashed lines shown on the figure.

Section S1 is a portion of the slide fastener which has a generally planar natural state when the coupling elements of the stringers 12a', 12b' are interdigitated such that the slide fastener is in a closed configuration. The coupling elements of the portion of each row of coupling elements 14a' and 14b' which are located in section S1 are coupling elements having the known normal shape as discussed in relation to figure 7 and in relation to section 72 shown in Figure 14.

The coupling elements of the portion of the rows of coupling elements 14a', 14b' which are located in section S2 of the slide fastener are of the type according to the present invention discussed in relation to figures 8 to 13. As such, when the coupling elements in section S2 are interdigitated whilst the slide fastener is in a closed configuration, the natural state of the second portion S2 of the slide fastener 10' is an out of plane curve which has a centre of curvature CC2. Finally, the coupling elements within the portion of each of the rows of coupling elements 14a', 14b' which are located in the section S3 of the slide fastener 10' have a similar shape to that already discussed in relation to figures 8 to 13 except that the shape of the head portion of each of these coupling elements is flipped about the plane of the relevant tape of the stringer to which the relevant coupling element is mounted, as compared to that discussed in relation to figures 8 and 9. In particular, the coupling elements which are located in the section S3 are of a third type. The coupling elements of the first stringer of a third type (e.g. the coupling element 75) are received between fifth and sixth adjacent coupling elements 75a, 75b of the second stringer when the row of coupling elements of the first stringer is interdigitated with the row of coupling elements of the second stringer.

Each of the coupling elements 75, 75a, 75b are shaped such that they comprise a main body having a shoulder portion, and a head portion extending parallel to the lateral axis away from the shoulder portion via a neck portion, wherein the main body of coupling element 75 is mounted to the tape of the first stringer, and the main body of each of coupling elements 75a, 75b of the second stringer is mounted to the tape of the second stringer.

The head and neck portions of the coupling element of the third type 75 comprise a lower head portion and a lower neck portion respectively which are located below said plane of the tape of the first stringer. Each of the fifth and sixth adjacent coupling elements 75a, 75b of the second stringer comprise a lower head portion and a lower neck portion respectively which are located below said plane of the tape of the second stringer.

When the coupling element of the third type 75 is received between said fifth and sixth adjacent coupling elements 75a, 75b of the second stringer, the following two statements are true. First, the lower head portion of the coupling element 75 is received between the lower neck portion of the fifth adjacent coupling element 75a of the second stringer and the lower neck portion of the sixth adjacent coupling element 75b of the second stringer, such that the lower head portion of the coupling element 75 contacts the lower neck portion of the fifth adjacent coupling element 75a of the second stringer at a ninth contact point, and the lower head portion of the coupling element 75 contacts the lower neck portion of the sixth adjacent coupling element 75b of the second stringer at a tenth contact point. Secondly, the lower neck portion of the coupling element 75 of the third type is received between the lower head portion of the fifth adjacent coupling element 75a of the second stringer and the lower head portion the sixth adjacent coupling element 75b of the second stringer, such that the lower neck portion of the coupling element 75 of the first stringer contacts the lower head portion of the fifth adjacent coupling element 75a of the second stringer at a eleventh contact point, and the lower neck portion of the coupling element 75 of the third type contacts the lower head portion of the sixth adjacent coupling element 75b of the second stringer at a twelfth contact point.

The head and neck portions of the coupling element 75 of the third type co-operate with the head and neck portions of the fifth and sixth adjacent coupling elements 75a, 75b of the second stringer to prevent lateral separation in a direction generally parallel to the lateral axis of the coupling element 75 of the third type and the fifth and sixth adjacent coupling elements 75a, 75b of the second stringer. A third plane (analogous to the first plane shown in figures 8 and 9) is defined perpendicular to the longitudinal edge of the second stringer which passes through the fifth adjacent coupling element 75a of the second stringer at a location longitudinally outboard, with respect to the coupling element 75 of the third type, of both the ninth and eleventh contact points. A fourth plane (analogous to the second plane shown in figures 8 and 9) is defined perpendicular to the longitudinal edge of the second stringer which passes through the sixth adjacent coupling element 75b of the second stringer at a location longitudinally outboard, with respect to the coupling element 75 of the third type, of both the tenth and twelfth contact points. The head and neck portions of the coupling element 75 of the third type are shaped such that, when the coupling element 75 of the third type is received between said fifth and sixth adjacent coupling elements 75a, 75b of the second stringer, a sixth distance between the third plane and the fourth plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said coupling element 75 of the third type is mounted, and which passes through at least one of the ninth and tenth contact points is greater than an eighth distance between the third plane and the fourth plane along the longitudinal edge of the first stringer. In addition or alternatively, a seventh distance between the third plane and the fourth plane along a line which is parallel to the portion of the longitudinal edge of the first stringer upon which said coupling element 75 of the third type is mounted, and which passes through at least one of the eleventh and twelfth contact points is greater than an eighth distance between the third plane and the fourth plane along the longitudinal edge of the first stringer.

In this way, when said coupling elements of the first stringer are interdigitated with coupling elements of the second stringer, the longitudinal edge of the second stringer in the region of said coupling element 75 of the third type, and of said fifth and sixth adjacent coupling elements 75a, 75b forms a curve having a centre of curvature which lies above the plane of the tape of the second stringer.

By way of further example, the shape of the head portion of each of the coupling elements of the third type differs as compared to that discussed in relation to the coupling elements shown in figures 8 to 13 in that a maximum width of the lower head portion in a direction parallel to the longitudinal edge (of the tape to which the coupling element is mounted) is greater than the maximum width of the upper head portion in a direction parallel to the longitudinal edge. This means that, in use, when said coupling elements of the first stringer 12a' in section S3 are interdigitated with coupling elements of the second stringer 12b' in section S3 in order to secure the first and second stringers together (as shown in figure 14), the longitudinal edge 15a', 15b' in the region of each coupling element forms a curve (which is out of plane) having a centre of curvature CC3 such that the upper head portion, lower head portion and centre of curvature will lie on a line in which the upper head portion is intermediate the lower head portion and the centre of curvature CC3. As can be seen clearly in figure 15, the use of coupling elements having a head shape which is flipped relative to the plane of the respective tape to which the coupling element is mounted, as compared to that of the coupling element in the section S2 of the slide fastener 10', results in the section S3 of the slide fastener exhibiting out of plane curvature in the opposite direction to that of the slide fastener in the second section S2.

It will be appreciated that by choosing the geometry of the coupling elements (first, second or third type) according to the present invention depending upon their position along the stringer / slide fastener it is possible to create any desired curved shape of slide fastener formed when the slide fastener is in the closed configuration.

In relation to the third type of coupling element 75 discussed above, as compared to the coupling elements discussed in relation to figures 8 to 13, it is worth noting that, although the specific configuration of the third type of coupling element 75 is different to the coupling element 14d discussed in relation to figures 8 to 13, portions of figures 8 to 13 are broadly equivalent to the features which are discussed in relation to the third type of coupling element. For example, coupling element 14d is equivalent to coupling element 75, adjacent coupling elements 14e, 14f are equivalent to coupling elements 75a, 75b, the fifth contact point 218 is equivalent to the ninth contact point, the sixth contact point 220 is equivalent to the tenth contact point, the seventh contact point 219 is equivalent to the eleventh contact point, the eighth contact point 221 is equivalent to the twelfth contact point, the first plane 208 is equivalent to the third plane, the second plane 210 is equivalent to the fourth plane, the fourth distance 222 is equivalent to the sixth distance, the fifth distance 223 is equivalent to the seventh distance, and the third distance 216 is equivalent to the eighth distance.

Figure 16 shows a schematic view of an article 100 including a slide fastener 10" according to the present invention. In particular, the slide fastener 10" is incorporated into the article 100 such that the slide fastener follows the curvature of a portion of the article. The slide fastener 10" may be configured in the manner discussed above such that the slide fastener in its closed configuration has a natural state which exhibits out of plane curvature which matches or approaches the curvature of the portion of the article 100 to which the slide fastener 10" is incorporated. It will be appreciated that in the embodiments of a slide fastener according to the present invention described above each stringer, and, in particular, the coupling elements of each stringer, are substantially identical to the corresponding stringer (albeit flipped relative to the longitudinal axis of the slide fastener). This need not be the case. For example, in some embodiments, the coupling elements (e.g. teeth) on one stringer may all be of the known normal type as shown in figure 7, whereas the coupling elements on the other stringer may have a shape according to the present invention (e.g. as shown in figure 1 1 ). When these two stringers are coupled together the presence of one stringer of coupling elements according to the present invention will still result in out of plane curvature of the stringers when coupled together.

In addition, although each of the coupling elements forming part of a stringer according to the present invention as discussed above are substantially the same as other coupling elements in the same section of stringer/slide fastener thus resulting in a constant radius of curvature for the relevant portion of stringer/slide fastener concerned, this need not be the case. For example, the shapes of adjacent coupling elements according to the present invention may be different such that the radius of curvature of the stringer/slide fastener in the region of each coupling element according to the present invention is different.

It will be appreciated that where examples of coupling element according to the present invention have been discussed above in which the maximum width of the upper head portion is different to the maximum width of the lower head portion, coupling elements according to the present invention may, in addition, or alternatively, have a minimum width of the upper neck portion which is different to the minimum width of the lower neck portion.

Reference is made throughout this document to various contact points (first to twelfth) between coupling elements when they are interdigitated. It will be appreciated that, in fact, the interdigitated coupling elements may contact over a greater area than the referred to contact points. For example, interdigitated coupling elements may contact along a surface of contact. In such a case the contact points referred to are points on (or within) the surface of contact. That is to say, if interdigitated coupling elements contact along one or more surfaces of contact, they still fall within the scope of the claims, the claims merely refer to a particular point of contact within the surface of contact. That is to say, in such an example, the interdigitated coupling elements contact one another not only at the relevant contact point (or point of contact), but also over the rest of the surface of contact other than the contact point. The referred to contact points may be at an edge of the surface of contact. The contact points may be located at any appropriate point of contact between adjacent interdigitated coupling elements. In some examples the contact points are at a point of the greatest protrusion (i.e. greatest width parallel to the longitudinal edge of the respective tape) of the relevant head portion or the point of the greatest hollowing (i.e. smallest width parallel to the longitudinal edge of the respective tape) of the relevant neck portion.