Mating fasteners that include two opposed fastener members are popular in a variety of applications. The particular type of mating fastener with which the present invention is concerned includes two opposed fastener members, each including a surface having a plurality of arranged headed stems projecting therefrom. Such fasteners are particularly useful in an environment where it is desirable to interengage the fastener using a relatively small amount of force, while requiring a larger force to separate the fastener members.
A conventional molded polymeric fastener is shown in FIG. 1. Included are opposed fastener members 10 and 12, including bases 14 and 16, respectively. Each base includes a plurality of arranged stems 18 orthogonally projecting therefrom, and each terminating in a head 20 at the respective distal ends of stems 18. The heads have generally arcuate surfaces 22 opposite the respective bases 14 and 16, which surfaces are adapted for sliding contact with the encountered arcuate surfaces 22 of heads 20 when the fastener members are first brought together. Heads 20 also each include a generally planar latching surface 24 extending radially outwardly of the stem, which is adapted to engage a latching surface of an opposed head, as shown in FIG. 2.
FIG. 1 shows fastener members 10 and 12 prepared for engagement, with the heads of one fastener member positioned generally between the heads of the other fastener member. To engage the fastener, fastener members 10 and 12 are urged toward each other with the respective bases generally parallel, causing heads 20 to contact and to deflect the attached stems laterally. The lateral deflection of the stems allows the heads of one fastener member to pass the heads of the opposed fastener member to engage the fastener members in the manner illustrated in FIG. 2.
In the past, fasteners of the type discussed above were generally formed by passing a backing layer having a multiplicity of projecting stems beneath a heat source, which heat source tends to melt the stems to form heads atop each of the stems. Such a process is known in the art, as illustrated by U.S. Pat. No. 4,290,832 (Kalleberg), entitled "Method for Making Fasteners." The '832 patent discloses a multi-step process for producing a fastener member having a backing layer, a plurality of monofilament stems projecting normally from the backing layer, and a head atop each stem.
The process, illustrated schematically in FIG. 3, includes moving two backing layers 50 and 52 in parallel paths while feeding monofilament 54 between the layers, and pressing the monofilaments using applicators 56 and 58, so that the monofilaments extend normally between the layers. The monofilaments are severed halfway between the backing layers by blade 60, which produces dual, opposed backing layers each having a plurality of monofilaments extending from each backing. The newly severed terminal ends of the monofilaments are then heated by heat sources 62 and 64 to a temperature sufficient to form a head atop each of the stems. After the heads have solidified, the two fastener members 66 and 68 are wound onto separate rollers 70 and 72, respectively, for dispensation and use.
While having their own utility, the fasteners formed by the process described above tend to exhibit inconsistently shaped heads, which can potentially affect release performance. For example, a generally spherical head having an arcuate latching surface may be unintentionally formed by such a process. An arcuate latching surface tends to disengage more easily than a planar latching surface extending radially from the stem, and could lower the force required to disengage the fastener. Alternatively, the heads could be irregularly formed due to the inconsistent application of heat, differences in production speed, and the like. Such irregularities could prompt inconsistent release characteristics, which may be undesirable under some circumstances.
Furthermore, for certain applications it may be preferable to provide heads that are generally conical, spherical, or some other such desired shape in order to obtain certain engagement and release characteristics. For example, U.S. Pat. No. 4,454,183 (Wollman) discloses a three lobed head structure formed by the application of heat to a triangular monofilament stem. However, as discussed above, heads formed by the application of heat to a monofilament stem tend not to be consistently formed. Furthermore, the number of different head structures is generally limited by the size and shape of the stems from which they are formed.
Another approach to forming heads atop stems in a desired shape is disclosed in Japanese patent publication no. 1-238805 (Anzai). The method disclosed in the '805 publication involves forming individual rows of stems by injection molding. Each individual row of stems, which stems may include spherical, conical, or other shaped heads, is typically formed in a mold that is split along the longitudinal axis of the stem. After the molten material has been injected and solidified, the halves of the mold may be separated, and the individual row of stems removed.
In order to form a fastener from the individual rows of stems, several such rows must be aligned and connected together. The individual rows may be connected by means of adhesive, thermal bonding, high frequency bonding, and the like. Although this method of forming a fastener may represent an improvement over the prior art in terms of head formation, it involves a greater investment of time and equipment to connect the individual rows together to form the fastener, and is therefore more expensive and undesirable.
Finally, it is often desirable to form a secondary fastening portion on one surface of the fastener, typically the back surface, in order to enable the fastener to be easily attached to a surface, body, or the like. At present, the secondary fastening portion is typically attached to the back of the fastener member by welding (either solvent, heat, or ultrasonic welding), which requires a manufacturing step separate from the formation of the fastener portion. The second manufacturing step increases the cost of the article, and is therefore undesirable.
It is therefore desirable to provide a method of making a unitary fastener member having rows and columns of stems having consistently identical head structures of a desired shape, to provide a method of making a unitary fastener having head structures of different desired shapes, and to provide a fastener member having an integral secondary fastening portion that is formed concurrently with the fastener member.