Serving for archery bowstring

Abstract

A braided cord consisting of braided filaments or a twisted cord of filaments in which at least a part of the filaments are high tenacity multifilaments, and the rest of the filaments are monofilaments, which is preferably used as a serving for an archery bowstring.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a serving for an archery bowstring. In particular, the present invention relates to a braided cord consisting of braided filaments or a twisted cord of filaments which is useful as a serving for an archery bowstring.

2. Description of the Background Art

To reinforce a bowstring of a recurve bow (FIG. 1) and a compound bow (FIG. 2) which are collectively called an archery, a reinforcing material which is called a serving (a coating material) is provided to the edges 1, 1′ of the bowstring and the center 2 of the bowstring at which an arrow is notched. This is because a strong force is applied to those parts since those parts are repeatedly in contact with a bow body or arrows, and therefore they are required to have a very high strength at break, and excellent abrasion resistance, dimensional stability and durability.

Hitherto, as a serving used for an archery bowstring, a braided cord or a twisted cord made of 100% polyester multifilaments, 100% high tenacity multifilaments, or the blend of high tenacity multifilaments and polyester multifilaments has been used.

In these years, with the improvement of the quality and performances of archeries, a load applied to the bowstring and serving increases. Therefore, the conventional serving comprising polyester multifilaments cannot satisfy the required levels of strength at break, abrasion resistance, dimensional stability and durability.

To satisfy those requirements, braided cords comprising high tenacity filaments attract attentions, and several attempts thereon have been made. However, the braided cords comprising high tenacity filaments have the following problems.

That is, the braided cords comprising high tenacity filaments of poly(p-phenylene terephthalamide) (PPTA), polybenzimidazole (PBI), polybenzoxazole (PBO), etc. do not have sufficient weather resistance and light resistance in view of the fact that the archery is used in severe environments where it is exposed to UV rays.

The high tenacity multifilaments consisting of stretched ultrahigh molecular weight polyolefin have good weather resistance. Therefore, a braided cord or a twisted cord comprising 100% high tenacity multifilaments or the blend of high tenacity multifilaments and polyester multifilaments is practically used as a serving.

The braided cords comprising the high tenacity multifilaments which consist of stretched ultrahigh molecular weight polyolefin have excellent abrasion resistance because the fibers themselves have high strength at break and good slip properties. However, a serving is wrapped around an archery bowstring to cover the surface of the bowstring, slipping of the wound serving occurs as the number of usages increases. This is because the high tenacity multifilaments consisting of the stretched ultrahigh molecular weight polyolefin have a small elongation and substantially no recovering properties.

To solve the above problems, the use of a braided cord or a twisted cord consisting of the blend of high tenacity multifilaments of stretched ultrahigh molecular weight polyolefin and polyester multifilaments having recovering properties is started. Such a braided cord or a twisted cord has improved initial figure stability. However, the polyester multifilaments have low abrasion resistance, so that they are heavily fluffed, and thus, a serving of such a braided cord or a twisted cord suffers from slipping originated from the fluffed points. Therefore, this kind of a braided cord or a twisted cord is not satisfactory as a serving material.

In spite of those drawbacks, most of the servings currently used consist of a braided cord comprising polyester multifilaments, or multifilaments of stretched ultrahigh molecular weight polyolefin, or their blend.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a braided cord or a twisted cord which can solve the problems and drawbacks of the conventional braided or twisted cord for a serving of an archery bowstring, and which can satisfy the very high requirements for a serving in relation to strength at break, abrasion resistance, dimensional stability and durability.

Accordingly, the present invention provides a braided cord consisting of braided filaments or a twisted cord of filaments used as a serving for an archery bowstring, wherein at least a part of the filaments are high tenacity multifilaments, and the rest of the filaments are monofilaments.

The braided cord or twisted cord of the present invention can improve the strength at break, abrasion resistance, durability and dimensional stability in good balance in comparison with conventional braided cords or twisted cords consisting of 100% polyester multifilaments, or 100% high tenacity multifilaments, or their blend. Furthermore, the serving comprising the braided cord or twisted cord of the present invention hardly suffers from slipping even at the edges and center of a bowstring to which a force is applied to crush the surface of the serving.

When the serving of the present invention is wrapped around a part of a bowstring at which an arrow is notched, the surface of the serving wrapped has a pear-skin finish. Thus, the wrapped serving has smaller contact areas with a fingertip-protecting tab which is made of leather and has a high friction resistance with the serving. Accordingly, the serving of the present invention decreases the friction resistance and therefore does not decrease the initial speed of an arrow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a recurve bow.

FIG. 2 shows a compound bow.

FIG. 3 shows a schematic cross section of one example of a braided cord according to the present invention.

FIG. 4 schematically shows a testing machine used to evaluate the abrasion resistance of a serving in Examples.

DETAILED DESCRIPTION OF THE INVENTION

Herein, the phrase “at least a part of the filaments are high tenacity multifilaments, and the rest of the filaments are monofilaments” is intended to mean that at least one of the filaments constituting the cord consists of a high tenacity multifilament while the rest of the filaments are monofilaments, that high tenacity multifilaments and other filaments are aligned or twined together to form filaments and then the aligned or twisted filaments are braided or twisted to form a braided cord or a twisted cord, or that a core of a filament is formed of arbitrary filaments (e.g. high tenacity multifilaments, or multifilaments or monofilaments of polyester, polyamide, polyethylene, polyolefin, fluoropolymer fibers, etc.) while a sheath of the filament is formed of high tenacity multifilaments and monofilaments.

According to the present invention, the high tenacity multifilaments preferably have a strength at break of at least 15 cN/dTex, more preferably at least 25 cN/dTex. The high tenacity multifilaments preferably has an elongation at break of 7% or less, more preferably 6% or less, particularly preferably 5% or less. The initial elastic modulus of the high tenacity multifilaments is preferably at least 500 cN/dTex, more preferably at least 600 cN/dTex.

Preferably, multifilaments of ultrahigh molecular weight polyolefin having a weight average molecular weight of at least 1,000,000 is used as the high tenacity multifilaments. In particular, preferably used are the multifilaments of ultrahigh molecular weight polyethylene produced by stretching the ultrahigh molecular weight polyethylene at a high draw ratio of at least 10 times, which have lightweight as well as good strength at break, abrasion resistance, dimensional stability and durability.

Such ultrahigh molecular weight polyethylene multifilaments can be produced by per se known methods, which are disclosed in JP-A-59-216912, U.S. Pat. No. 4,617,233 (corresponding to JP-A-59-216913 and JP-A-59-216914), JP-A-60-45630, JP-A-60-52647, JP-A-60-52613, U.S. Pat. No. 4,668,577 (corresponding to JP-A-60-59172), JP-A-60-151311, JP-B-3-57964, and so on.

A method for producing a braided cord from such ultrahigh molecular weight polyethylene multifilaments is also known from, for example, JP-A-10-317289.

Polyester monofilaments are preferably used as the monofilaments used in combination with the high tenacity multifilaments. Besides the polyester monofilaments, the monofilaments of Nylon 6, Nylon 6,6, Nylon 6,10 and copolymer Nylons thereof, and the monofilaments of polyvinylidene fluoride may be used.

The monofilaments used in the present invention preferably has an elongation at break of 25% or less, preferably 20% or less, more preferably 17% or less.

Hereinafter, the preferred embodiments of the braided cord or twisted cord for a serving according to the present invention are explained.

The braided cord or twisted cord of the present invention consists of a braided cord produced by braiding the filaments in the form of a three strand-braided cord, a four strand-braided cord, a six strand-braided cord, an eight strand-braided cord, a twelve strand-braided cord, a sixteen strand-braided cord, a twenty-four strand-braided cord, a thirty-two strand-braided cord, etc., or by twisting the filaments in the form of a two strand-twisted cord, a three strand-twisted cord, a four strand-twisted cord, a five strand-twisted cord, a six strand-twisted cord, a seven strand-twisted cord, an eight strand-twisted cord, etc. Each strand may contain an arbitrary number of yarns.

Among the filaments constituting the braided or twisted cord according to the present invention, at least one filament is a high tenacity multifilament, while the rest of the filaments are monofilaments, and they are aligned or twined for use. For example, as shown in FIG. 3, four high tenacity multifilaments (11) and four monofilaments (12) are used to form a filament.

In view of the requirements for the properties of the serving, in a preferable embodiment, filaments consisting of ultrahigh molecular weight polyethylene filaments and filaments consisting of polyester monofilaments are aligned or twined respectively, four former filaments and four latter filaments are braided in the form of a four strand-braided cord used as a serving.

In the serving of the above preferred embodiment, the stress is concentrated only on the ultrahigh molecular weight polyethylene filaments having low elongation when a load is applied to the serving. As a result, the elongation of the entire serving can be suppressed and the diameter of the serving does not decrease when it is used with a load being applied thereto. Since the high tenacity multifilaments are used in combination with the hard polyester monofilaments, a cross-sectional shape of the serving is maintained. Furthermore, two kinds of filaments having different thicknesses are used in combination, the peripheral surface of the serving becomes uneven (see FIG. 3) and thus it has a pear-skin finish, so that a friction resistance with a bowstring to which the serving is in contact can be decreased and the abrasion resistance is improved.

The thickness (diameter) of each filament is not critical. The fineness of a high tenacity multifilament is preferably 11 to 5280 dTex, more preferably 55 to 1760 dTex, most preferably 110 to 880 dTex, while the fineness of a monofilament is preferably 5 to 2200 dTex, more preferably 10 to 1100 dTex, most preferably 15 to 275 dTex.

In the present invention, the high tenacity multifilaments and the monofilaments, preferably the polyester monofilaments are used in combination in an arbitrary ratio. The braided or twisted cord usually comprises at least 60% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, of the high tenacity multifilaments, and usually 40% by weight or less, preferably 20% by weight or less, more preferably 10% by weight or less, of the monofilaments.

The serving of the present invention, which makes use of the moderate elasticity and less collapsible hardness of the monofilaments, can prevent slipping. In general, the serving is wound around the bowstring at about 90 degrees in relation to the lengthwise direction of the bowstring, and the monofilaments bite into the bowstring like wedges so that the serving is fixed to the bowstring. In the case of a conventional serving consisting of multifilaments, the serving hardly bites into the bowstring because of the softness of the fibers of the multifilaments. Accordingly, the conventional serving drifts as the bowstring is repeatedly used for a number of times.

The filaments constituting the braided or twisted cord for a serving according to the present invention may be integrated with a thermal adhesive resin such as a polyolefin resin, a polyester resin, a polyamide resin, etc.

The surface of the braided or twisted cord for a serving according to the present invention may be coated with a resin to improve the abrasion resistance. The resin to be used to improve the abrasion resistance is not limited. Examples of such a resin include ethylene-acrylic acid copolymers, low molecular weight polyethylene, low molecular weight ionomers, high molecular weight ionomers, polyurethane, etc. Such a resin may be used in the form of a solution in water or an organic solvent. Furthermore, a conventional dye or a conventional pigment such as carbon black may be added to the coating resin for coloring the cord.

EXAMPLES

The present invention will be illustrated by the following examples, which do not limit the scope of the present invention in any way.

Examples 1-2 and Comparative Examples 1-3

In each of Examples and Comparative Examples, a serving having the following construction was produced:

Example 1

Structure: Single braid structure

Eight strand-braided cord consisting of 4 strands of ultrahigh molecular weight polyethylene multifilaments (weight average molecular weight: 4,000,000; strength at break: 26 cN/dTex; elongation at break: 4%; initial elastic modulus: 880 cN/dTex) (Dyneema® SK60 of Toyobo Co., Ltd.; 275 dTex), and 4 strands of polyester monofilaments (manufactured by YGK Co., Ltd.; strength at break: 8 cN/dTex; elongation at break: 17%; 27 dTex).

Example 2

Structure: Double braid structure

Core: Polyester monofilaments (110 dTex)

Sheath: Eight strand-braided cord consisting of 4 strands of Dyneema® SK60, and 4 strands of polyester monofilaments (manufactured by YGK Co., Ltd.; strength at break: 8 cN/dTex; elongation at break: 17%; 27 dTex).

Comparative Example 1

Structure: Single braid structure

Eight strand-braided cord of polyester multifilaments (manufactured by Toyobo Co., Ltd.; strength at break: 6 cN/dTex; elongation at break: 20%; 165 dTex).

Comparative Example 2

Structure: Single braid structure

Eight strand-braided cord of Dyneem® SK60 (165 dTex)

Comparative Example 3

Structure: Single braid structure

Eight strand-braided cord consisting of 4 strands of Dyneema® SK60 (165 dTex) and 4 strands of polyester multifilaments (manufactured by Toyobo Co., Ltd.; strength at break: 6 cN/dTex; elongation at break: 20%; 165 dTex).

The properties of a serving were evaluated as follows:

—Fineness

Fineness was measured according to JIS L 1013.

—Strength at Break, Tenacity at Break and Elongation at Break

These properties were measured according to JIS L 1013.

—Abrasion Resistance

A hexagonal rod abrasion tester for seat belts according to JIS L 1095 was modified such that a ceramic guide was used in place of a hexagonal rod, and used as a tester to evaluate the abrasion resistance of a serving. The measuring conditions including a stroke length, an angle, etc. were the same as those defined in JIS D 4604 (1995).

That is, as shown in FIG. 4, a test sample of a serving was threaded through a ceramic guide, and one end of the serving was fixed to a drum, while a load was applied to the other end of the serving. The load was 3.3% of the maximum tenacity of the sample. The number of abrading strokes until the serving was broken was counted as the measure of abrasion resistance.

As another measure of the abrasion resistance of a serving, the drum was reciprocally moved 1,000 times to abrade the serving with the ceramic guide. Then, the generation of naps in the abraded part was visually observed.

The results are shown in Table 1.

	TABLE 1
	Results
Property	Ex. 1	Ex. 2	C. Ex. 1	C. Ex. 2	C. Ex. 3
Fineness (dTex)	1298.3	1177.7	1125	1395.3	1454.7
Content of high tenacity	88.9	74.7	0	100	48.3
filaments in sheath (wt. %)
Strength at break (cN/dTex)	13.2	11.66	4.9	15.62	7.94
Tenacity at break (N)	171.4	137.3	55.1	217.9	115.5
Elongation at break (%)	7.3	10.5	16.7	5.2	8.9
Abrasion resistance	69,034	50,400	8,066	≧100,000	47,400
(number of strokes)
Generation of naps	No	No	Yes	No	Yes

The above results show that the servings of Examples 1 and 2 had very good abrasion resistance.

Example 5

The serving produced in Example 1 was dipped in a 10 wt. % solution of an ethylene-acrylic acid copolymer in water at 25° C., removed from the solution and then dried in an oven at 120° C. to adhere the copolymer to the serving. The amount of the copolymer adhered was 10.0% by weight of the weight of the serving.

Example 6

The serving produced in Example 1 was coated with the ethylene-acrylic acid copolymer and carbon black in the same manner as in Example 5 except that 2% by weight of carbon black based on the weight of the solution was added to the solution of the ethylene-acrylic acid copolymer.

Examples 7-8 and Comparative Examples 4-5

To evaluate the effect to prevent slipping, the following braided cords were produced and wrapped around a bowstring at its ends and center part. Then, 1,000 arrows were shot, and the degree of slipping was visually evaluated.

Example 7

Structure: Single braid structure

Eight strand-braided cord of 4 strands of Dyneema® SK60 (275 dtex), and 4 strands of polyester monofilaments (manufactured by YGK Co., Ltd.; strength at break: 8 cN/dTex; elongation at break: 17%; 27 dTex).

Example 8

Structure: Double braid structure

Core: Polyester monofilaments (110 dTex)

Sheath: Eight strand-braided cord of 4 strands of Dyneema® SK60 (220 dTex), and 4 strands of polyester monofilaments (manufactured by YGK Co., Ltd.; strength at break: 8 cN/dTex; elongation at break: 17%; 27 dTex).

Comparative Example 4

Structure: Single braid structure

Eight strand-braided cord of Dyneema® SK60 (165 dTex).

Comparative Example 5

Structure: Single braid structure

Eight strand-braided cord of 4 strands of Dyneema® SK60 (165 dTex), and 4 strands of polyester multifilaments (165 dTex).

With the servings of Examples 7 and 8, no slipping occurred after shooting 1,000 arrows. With the servings of Comparative Examples 4 and 5, apparent slipping or slip of the wrapped cord occurred and many gaps appeared between the turns of the wrapped cord.

Claims

1. A braided cord consisting of braided filaments or a twisted cord of filaments used as a serving for an archery bowstring, wherein a part of the filaments of the braided or twisted cord are high tenacity multifilaments and the rest of the filaments of the braided or twisted cord are monofilaments.

2. The braided cord or twisted cord according to claim 1, wherein said high tenacity multi filaments have a strength at break of at least 15 cN/dTex, an elongation at break of 7% or less, and an initial elastic modulus of at least 500 cN/dTex.

3. The braided cord or twisted cord according to claim 1, wherein said high tenacity multifilaments consist of multifilaments of polyolefin having a weight average molecular weight of at least 1,000,000.

4. The braided cord or twisted cord according to claim 1, wherein said filaments of the braided or twisted cord are integrated together with a thermal adhesive resin.

5. A serving for an archery bowstring comprising a braided cord consisting of braided filaments or a twisted cord of filaments, wherein a part of the filaments of the braided or twisted cord are high tenacity multifilaments and the rest of the filaments of the braided or twisted cord are monofilaments.

6. The serving according to claim 5, wherein said high tenacity multifilaments have a strength at break of at least 15 cN/dTex, an elongation at break of 7% or less, and an initial elastic modulus of at least 500 cN/dTex.

7. The serving according to claim 5, wherein said high tenacity multifilaments consist of multifilaments of polyolefin having a weight average molecular weight of at least 1,000,000.

8. The serving according to claim 5, wherein said filaments of the braided or twisted cord are integrated together with a thermal adhesive resin.