Female Fastener and Resin Ring Spring for Female Fastener

The present disclosure may relate to a resin ring spring and the like for a female fastener. In particular, the disclosure may relate to a resin spring that is a component for a fastener (closure) having a male-female joint structure (which may be hereinafter called “snap fastener”), that is provided in the vicinity of a hole in a female fastener into which a stud of a male fastener is inserted, and that serves to hold the stud in the hole, and may relate to a resin spring and the like that can be suitably incorporated in the female fastener applicable to clothes and the like.

Fasteners having a male-female joint structure are widely used at an opening-closing part in daily commodities such as clothes, bags, and shoes. In this type of fasteners, a stud in a male fastener is inserted into a hole in a female fastener to establish the male-female joint. A spring is provided in the hole in the female fastener in order to hold the stud inserted in the hole. Commonly known springs for the female fastener include, for example, a ring spring type in which a metal ring is arranged on an inner circumferential surface around the hole, and a double spring type in which spring wires, made of a metal wire material and processed by bending, are arranged in parallel inside the hole in the female fastener.

The stud in the male fastener is composed of a fitting portion around its extreme end and a constricted portion having a smaller diameter than the fitting portion. Generally, the male and female fasteners are joined with each other in the following manner. To start with, the stud is inserted into the hole, with the fitting portion around the extreme end stretching the two metal spring wires or the metal ring wide open. After the stud is inserted, the two metal spring wires or the metal ring returns to the original shape. In this state, the constricted portion of the inserted stud stays between the two metal spring wires or on the inner circumferential surface of the metal ring, and the fitting portion is restricted in the hole and held therein.

For example, Patent Document 1 (see below) relates to an invention intended to provide a resin spring and a method for producing the same, wherein the resin spring does not make a metallic sound caused by shaking movement of a fastener and wherein the resin spring has a suitable elastic force for holding the stud. In a fastener having a male-female joint structure, an annular resin springis provided in a hole in a female fastener into which a stud of a male fastener is inserted, and serves to hold the stud in the hole. The annular resin springincludes projecting portionsthat are provided on an inner circumferential surfaceat equal intervals and that project inwardly (centripetally toward the center O of a circle defined by the inner circumferential surface). Portions between the projecting portionsare curved to expand outwardly (radially from the center O of the circle defined by the inner circumferential surface). Thick portionsare formed on the back of the respective projecting portions.

A basic structure of a snap fastener is illustrated into describe a structure and a functional expression mode of the snap fastener. In, any component for fixedly engaging the snap fastener with a piece of cloth (an object to be engaged by the snap fastener) is omitted. As shown in, a snap fastener is composed of a set of a male fastenerand a female fastener, with a circular ring springprovided in the female fastener.

A diameter of an extreme end of the male fasteneris greater than an inner diameter of the ring spring. When the male fasteneris fitted in, the ring springexpands for a moment and shrinks later to hold the male fastenerin the female fastener. Note that the ring spring, when made of metal, has following concerns. For one, frictional contact between a metal male fastenerand the metal ring spring causes their plating to peel off. For another, the snap fastener equipped with the metal ring spring requires a strong power for its fastening action, and thus is not friendly for socially vulnerable people.shows various modes of snap fasteners.

This disclosure intends, first and foremost, to solve the above-mentioned concerns and to replace the metal ring with a thermoplastic resin molded product. As for the structure and function of the ring springfor a snap fastener, the metal ring spring has a partially open circular shape, as shown in, and exhibits its spring function by opening and closing the open portion. In contrast, a resin ring spring cannot have the same shape because its modulus of elasticity is smaller than that of the metal ring spring.

Basically, a resin ring spring requires a closed circular shape without a break. As shown in, the resin ring spring having this shape can stretch and recover to its original shape in a circumferential direction to exhibit spring characteristics. On the other hand, a partial rupture in its circumference would impair the essential spring function.

In consideration of the above concerns, an object of the present disclosure is to propose a resin ring spring attachable to a female fastener in place of a metal ring spring, wherein the resin ring spring is fail-safe and does not lose its lock function for a snap fastener even if ruptured in use. Preferably, the present disclosure proposes a female fastener and a shape for a resin ring spring, wherein the resin ring spring basically has a concave polygon shape or a convex-concave shape that is subject to bending stress rather than tensile stress and wherein the resin ring spring can keep exhibiting its spring function even if ruptured.

A resin ring spring according to the present disclosure locks a male fastener inserted therein while the resin ring spring is accommodated in an accommodation housing of a female fastener. The resin ring spring has a continuous star-shaped polygonal shape, as viewed in plan view. The resin ring spring includes one or more multibridge portions that protrude(s) in an up-down direction that is vertical to a flat ring surface.

A female fastener according to the present disclosure holds a resin ring spring accommodated in an accommodation housing of the female fastener and locks a male fastener inserted therein, wherein the resin ring spring has a continuous star-shaped polygonal shape, as viewed in plan view. When the resin ring spring is in a natural state, convex portions of the resin ring spring abut on an innercircumferential wall of the accommodation housing of the female fastener or are spaced therefrom with a gap of 0.1 mm or less.

A female fastener according to the present disclosure holds a resin ring spring accommodated in an accommodation housing of the female fastener and locks a male fastener inserted therein, wherein the resin ring spring has a continuous star-shaped polygonal shape, as viewed in plan view. All convex portions, which are the most outwardly projecting portions as viewed in plan view, abut on an inner circumferential wall of the accommodation housing, at least at any timing during an insertion process of the male fastener.

The present disclosure can propose a resin ring spring attachable to a female fastener in place of a metal ring spring, wherein the resin ring spring is fail-safe and does not lose its lock function for a snap fastener even if ruptured in use. More preferably, the present disclosure can propose a female fastener and a shape for a resin ring spring, wherein the resin ring spring basically has a concave polygon shape or a convex-concave shape that is subject to bending stress rather than tensile stress and wherein the resin ring spring can keep exhibiting its spring function even if ruptured.

A resin ring spring described in the present embodiment has, for example, following features:

1) A structure in which an intended function is imparted by rupture-resistant bending deformation (a concave polygonal structure). Typically, a structure in which inward corners of a concave polygon can expand is subject to bending stress rather than tensile stress and develops resistance to rupture.

2) A structure that does not lose a snap fastener function even in the case of a partial rupture (a multibridge structure). Typically, a plurality of protrusions (multibridge portions) is arranged on a circumference of the resin ring spring. When the ring spring is accommodated and crimped in a main body (an accommodation housing), displacement of the protruding portions is restricted or fixed. This resin ring spring, even if partially ruptured, keeps its snap fastener function (prevents disengagement of the snap fastener).

3) Adoption of a production method that ensures excellent quality stability and productivity (an ultrasmall injection molding machine). For example, the number of cavity in a single shot is reduced to overwhelmingly facilitate conditional probability.

4) Adoption of a production method that minimizes generation of waste resin (a runnerless method). For example, use of a runnerless mold (a hot runner method) reduces waste resin and eliminates a loss in a channel part that cannot be made into a product.

are illustrations for describing a typical example of a shape of a resin ring springto be provided in a female fastener, wherein the female fastener is a part of a male/female fastener for clothes as described in the present embodiment.is a plan view of the resin ring springhaving a concave polygon shape. While a male fastener is fitted in, the resin ring springis configured to increase its diameter under bending stress rather than under tensile stress, for example, as shown in a plan view of. The resin ring spring having such a shape is significantly different from conventional, widely known, annular metal ring springs, both in shape and in functional expression mode.

Specifically, regarding the shape example shown in, an inner diameter of the resin ring springincreases by outwardly expanding displacement of concave portions() that are displaced more greatly than convex portions() that project in plan view (a change from the state ofto the state of). After an extreme end of the stud passes the resin ring spring, the inner diameter of the resin ring springdecreases at a constricted portion of the stud by inwardly shrinking displacement of the concave portions() that are displaced more greatly than the convex portions() that project in plan view (a change from the state ofto the state of).

As shown in, the resin ring springhas eight convex portions(), and every other one of them (a total of four convex portions()) is provided with multibridge portions() to() that protrude vertically to surfaces of the resin ring springby a predetermined height. The position and number of the multibridge portionsare not limited to the example shown in, and any number of multibridge portionsmay be provided at any position around the convex portions().describes a natural state, anddescribes a state with an expanded inner diameter.

Note thatare plan views of the resin ring spring, whereasis a side view of the resin ring spring. For example, when the resin ring springinhas a thickness hof about 0.7 mm to 1.0 mm, the multibridge portionsmay have a thickness hof 1.3 mm to 1.6 mm. Depending on the shape and size of the accommodation housing of the female fastener for accommodating the resin ring spring, the thickness hof the multibridge portionsmay be 1.3 mm or less. Additionally, when the resin ring spring has a thickness of 0.7 mm or greater, the thickness hmay be 1.0 mm or less. The accommodation housing may be also called spring plate.

In the course of test production and improvement of the resin ring spring, the present inventors detected following issues.

1) Increase in the number of cavity in a single shot results in a runner weight of 90% or greater.

2) Multicavity molding of about 24 to 32 pieces is still far below a recommended shot weight for the injection molding machine. In this case, the resin material remains in a heating cylinder for a longer time. Eventual thermal degradation causes molecular cleavage and deteriorates the product quality.

3) Increase in the number of cavity in a single shot results in greater variation in timing when molten resin for circular products is merging (welding). As a result, products with a small weld strength and products with voids are more likely to occur.

Presumably, such issues are partly because the resin ring spring is as light as about 0.05 g or less per piece, and is much lighter than the metal ring spring. Being faced with these issues, the present inventors reached a possible solution by molding small products with use of an ultrasmall molding machine.

The present inventors further conceived an innovative shape as exemplified in the present embodiment. The structure and material as disclosed herein can realize a fail-safe ring spring that is resistant to rupture and that can minimize a loss of its spring function even if ruptured.

are conceptual illustrations for describing a mode of use when the resin ring springaccording to the present embodiment is accommodated in the accommodation housing of the female fastener. The resin ring springaccording to the present embodiment has a fail-safe shape and does not lose its function even if its annular circumference ruptures partially. In order to avoid a functional loss in the case of rupture and to ensure production workability, the resin ring spring according to the present disclosure is accommodated in the same manner as the metal ring spring, by being inserted in the spring plate and crimped so as not to come out. If the resin ring spring had the same shape and other properties as the conventional all-metal snap fastener and were accommodated in the housing of the female fastener, the resin ring spring would not be fixed at all.

According to the present disclosure, the resin ring spring is equipped with a plurality of protrusions (multibridge portions) provided along its circumference and extending vertically to ring surfaces. The multibridge portions are semi-fixed or fixed in an up-down direction on the plane ofthrough the crimping process, and thereby restrict movement of the resin ring spring. Eventually, even if a part of the resin ring spring ruptures, the resin ring spring that is semi-fixed or fixed by the protrusions (the multibridge portions) retains the snap fastener function.

More preferably, while the resin ring spring is accommodated in the accommodation housing of the female fastener, the projecting portions on the outermost circumference of the resin ring spring (corresponding to the eight convex portions() inand) abut on an inner circumferential wall of the accommodation housing, and thereby restrict any further outward movement of the resin ring spring. This configuration ensures a stabler fail-safe function and minimizes a loss of the spring function due to rupture.

A preferable material for molding of the resin ring spring is polyacetal (POM). POM is a crystalline engineering plastic that shows excellent thermal resistance and that also shows excellent abrasion resistance, fatigue failure resistance, and chemical resistance. Where necessary, the material may be a polyamide resin or a PPS resin.

Injection molding of the resin ring spring having the above-mentioned fail-safe function requires more precise control than in the case of a simple ring spring. For this reason, the resin ring spring is produced not by large-scale simultaneous molding with use of a middle- or small-size molding machine but by small-scale molding with use of an ultrasmall molding machine. Use of the ultrasmall molding machine provides following advantages:

Multicavity molding is a method for producing a large number of products in a single shot, and requires as many cavities as the number of products. It is desirable to fill the material into all cavities at the same timing, the same temperature and the same pressure. Multicavity molding further requires a runner, as a channel for feeding the material to a plurality of cavities.

For production of the resin ring spring according to the present disclosure (a fail-safe ring spring or the like having a concave polygonal structure and a multibridge structure), a hot-runner type (runnerless) prototype mold may be manufactured with introduction of an ultrasmall injection molding machine (mold clamping force: 3 tons), so as to set shaping conditions and to perform technical verification and mass-productivity evaluation such as quality stability and productivity.

In, an upper illustration is a plan view of the resin ring spring, and a lower illustration is a side view thereof.shows an exemplary mode of use, with the resin ring springbeing accommodated in the female fastener. In, the convex portions() of the resin ring springabut on an inner circumferential wall() of the accommodation housing of the female fasteneror are slightly spaced therefrom (with a gap of 0.1 mm or less).

Specifically, the convex portions() are configured such that, when the inner diameter of the resin ring spring(in use, the spring is accommodated in the accommodation housing of the female fastener) is stretched by insertion of a male fastener (a stud), outward displacement of the convex portions() is restricted by their abutment on the inner circumferential wall() of the accommodation housing at least during the inner diameter expansion process. This preferable configuration can minimize a functional loss due to partial rupture or other trouble in the resin ring spring.

In other words, typically, at least when the inner diameter of the resin ring springis expanding or has been maximally expanded by the insertion of the stud, all of the convex portions() abut on the inner circumferential wall() of the accommodation housing of the female fastener, and have their further outward displacement restricted. Additionally, in a natural state where the stud is not inserted, all of the convex portions() may abut on the inner circumferential wall() of the accommodation housing of the female fastener, and may have their further outward displacement restricted.

This configuration reduces a loss of the spring function due to rupture. In the accommodation housing of the female fastener, the resin ring springmay be arranged to be constantly rotatable or constantly slidably rotatable relative to the accommodation housing of the female fastener. Having said that, the slidable rotation may be limited when the convex portions() are squeezed most strongly or more strongly against the inner circumferential wall of the accommodation housing, by a squeezing frictional force or the like.

Referring to, upward displacement of the multibridge portionsof the resin ring springis restricted by a flanged portion(),() of the female fastener. Specifically, when the resin ring springis arranged in the accommodation housing of the female fastener, its in-plane displacement vertical to the plane ofis restricted by the inner circumferential wall() of the accommodation housing, and its up-down displacement on the plane ofis restricted by the flanged portion(),().

When the resin ring springis crimped by the flanged portion(),(), the multibridge portionsmay be fixed by the accommodation housing such that the multibridge portionsare sandwiched and clamped by the flanged portion(),() in an up-and-down direction of. This configuration can also restrict displacement of the multibridge portions, can prevent outwardly expanding displacement of the multibridge portions(namely, a given number of convex portions()) during the insertion (press fitting) and removal of the stud, and can eventually reduce a loss of the spring function due to rupture.

To give a preferable example, the resin ring springhas a star-shaped polygonal (polygram) shape that is continuous without a break. When the resin ring springis accommodated in the accommodation housing of the female fastener, the above-described configuration can reduce a mobile region in the natural state where the male fasteneris not inserted, namely, can reduce backlash in an area surrounded by the flanged portion(),(). Hence, the above-described configuration can also reduce a clattering contact sound or other noise due to vibrations, etc.

Regarding the resin ring spring and the female fastener according to the present disclosure, their material, shape, structure/method, etc. are not limited to those described above and shown in the drawings. Such material, shape, structure/method, etc. may be adopted, varied, arranged, combined or optionally modified, within a range of the scope of the present disclosure by any suitable method or the like publicly or widely known to those skilled in the art. More specifically, those skilled in the art can easily understand that, for example, First Embodiment according to the present disclosure and Second Embodiment to be described below may be applied together to implement and embody a snap fastener and a resin ring spring that include features of both embodiments, and that such implementation does not particularly cause any trouble.

are schematic lateral cross sectional views, with the resin ring spring according to the present embodiment (indicated as (2) in the drawing) being accommodated in the accommodation housing (which is frequently made of metal, and which may be also called spring plate) (indicated as (1) in the drawing) of the female fastener. A star mark inindicates a gap between the inner circumferential wall of the accommodation housing and an outer circumferential end of the resin ring spring. The present embodiment provides a fail-safe effect by setting the star-marked gap to 0.05 mm or less. The term “fail-safe” as used herein means that the resin ring spring continues to function as the spring in the female fastener, even if the ring spring is broken due to abrasion or for some reason. For example, when the size of the female fastener is determined in advance, the resin ring spring to be accommodated therein is configured to have the shape and size as defined in the present disclosure and to keep a gap of 0.05 mm or less between the outer circumferential end of the resin ring spring and the inner circumferential wall of the accommodation housing. For example, when the size of the resin ring spring is determined in advance, the female fastener is configured to keep a gap of 0.05 mm or less between the accommodation housing for accommodating the resin ring spring and the outer circumferential end of the resin ring spring.

From a different point of view, a preferable relationship between the outer diameter (the diameter) of the resin ring spring and the inner diameter (the diameter) of the accommodation housing of the female fastener is such that the inner diameter of the accommodation housing of the female fastener is greater than the outer diameter of the resin ring spring by 0.1 mm or less.

The resin ring spring used herein has at least two or more alternating concave portions and convex portions in a radial direction, and hence does not have a shape of a perfectly exact circle. The resin ring spring is circumferentially continuous, but a distance from the circumference to the center of the ring spring may increase and decrease alternately, as described later. In other words, the resin ring spring as used herein can have such a shape and structure that the resin ring spring hardly loses its spring characteristics (elastic deformation characteristics) even if broken at any one point.

As shown in, the press fitting process of the male fastener (which may be also called stud, not shown) into the female fastener causes the inner diameter of the resin ring spring to stretch and expand outwardly (a thick left arrow on the plane of). In this state, it is more preferable that at least the outer circumferential end of the maximally expanded resin ring spring abuts on the inner circumferential wall of the accommodation housing. The abutment area is not necessarily the entire outer circumference of the resin ring spring, but may be the outwardly projecting portions only (typically, extreme ends of the convex portions() shown in). The configuration in which the diameter-expanded resin ring spring abuts on the inner circumferential wall of the spring plate serves to restrict positional variation and displacement (for example, expansion of the ring spring diameter) in at least a part of the resin ring spring positioned in the flanged portion of the spring plate. Even if the ring spring is broken or fails otherwise, a snap fastener having this configuration can continue to serve without losing its snap fastener function.

illustrate a typical example of the metal accommodation housing (the metal spring plate) of the female fastener, whereinshows the metal accommodation housing with the resin ring spring accommodated, andshows a back side of the accommodation housing. The view inis taken while the female fastener provided with the ring spring is halfway through its production, undergoing an assembly processing. From the state shown in, the female fastener is further required to go through an additional assembly processing step of forming the flanged portion, wherein an edge of the circumferential wall of the female fastener is folded inwardly so as to enclose the resin ring spring in a square U-shaped manner. Note that an arrow inindicates the inner diameter of the spring plate, and an arrow inindicates the outer diameter of the spring plate.

A certain component balance is required between the resin ring spring and the spring plate in the present embodiment. In the pre-assembly processing state of, if a dimensional difference between the inner diameter of the spring plate and the outer diameter of the resin ring spring is greater than 0.1 mm, there will be an excessive backlash gap/space that allows the resin ring spring to move in the spring plate (for example, swinging movement in the arrow direction in). In this state, breakage of the resin ring spring will result in a loss of the elastic deformation function, expansion of the inner diameter of the resin ring spring, a loss of the interface between the stud and the ring spring as well as a loss of application of the elastic force that would otherwise be applied on insertion of the stud (the male fastener). Such a resin ring spring no longer has the snap fastener function.