Racket strings and their manufacturing process

Abstract

A racket string has been disclosed that improves shock absorption and eliminates the reduction in bounce feel, and is preferred by both recreational and professional players. This racket string is made from a single-layer monofilament in which a propylene-ethylene copolymer resin and a polyethylene resin are contained within a polyethylene terephthalate resin, which is the main resin. Alternatively, the racket string is made from a conjugated sheath-core monofilament in which the sheath component comprises a polyethylene terephthalate resin, which is the main resin, containing a propylene-ethylene copolymer resin and a polyethylene resin, and the core component comprises a polyethylene terephthalate resin containing polyethylene.The contents of the propylene-ethylene copolymer resin and the polyethylene resin are 2 to 4 parts by mass for the propylene-ethylene copolymer resin and 2 to 4 parts by mass for the polyethylene resin, based on 100 parts by mass of the polyethylene terephthalate resin.

Description

Title of the invention: Racket string and method for manufacturing it. Technical field

[0001] The invention relates to a string for use with a tennis racket or similar and a method for producing the string, and particularly relates to a string having a good ball-striking feel and a method for producing the string. Previous art

[0002] Conventionally, as strings for tennis rackets or similar equipment, strings made from bovine, sheep, or similar animal intestines, or strings made from polyethylene terephthalate resin monofilaments, have been used. The latter are widely used because they are superior in durability and inexpensive compared to the former. However, strings made from polyethylene terephthalate resin have a problem with poor shock absorption, and a large load tends to be applied to a player when striking the ball.

[0003] Document JP 7499642 B2 describes how, in order to improve shock absorption when striking the ball, a thermoplastic elastomer such as a polyester elastomer and a polyolefin-based resin are contained within a polyethylene terephthalate resin, thereby enhancing shock absorption. Such a string is preferred by recreational tennis players, but has the drawback of reducing the bounce feel and is therefore not preferred by professional players. Description of the invention

[0004] In other words, one of the aims of the invention is to provide a racket string that improves shock absorption and eliminates the drop in bounce feel, and is preferred by both ordinary and professional players.

[0005] The present invention overcomes the above challenge by containing only a specific polyolefin-based resin without allowing the presence of a thermoplastic elastomer. That is to say, the present invention relates to a racket string made from a monofilament in which a propylene-ethylene copolymer resin and a polyethylene resin are contained, and a method for producing the racket string.

[0006] The racket string according to the present invention may be a single-layer monofilament or a multi-layer monofilament. Examples of multi-layer monofilaments include sheath-core monofilaments and an islet-in-the-sea type monofilament. In the present invention, the racket string is preferably in the form of a single-layer type monofilament or a sheath-core type monofilament.

[0007] A first object of the present invention relates to a racket string comprising a monofilament in which a propylene-ethylene copolymer resin is contained within a polyethylene terephthalate resin, which is the main resin. First, a racket string made from a single-layer monofilament will be described. The single-layer monofilament comprises a polyethylene terephthalate resin as the main resin. A publicly known polyethylene terephthalate resin is used, and a polyethylene terephthalate resin having a relative viscosity of approximately 1.4 to 1.8 is preferably employed. Those having this degree of relative viscosity are superior in dimensional stability when made into racket strings.The relative viscosity is measured under temperature conditions of 20°C via a procedure involving the preparation of a mixed solvent with equal volumes of phenol and tetrachloroethane as solvent and the dissolution of the polyethylene terephthalate resin in the solvent at a concentration of 0.5% by mass.

[0008] The polyethylene resin as the main resin contains a propylene-ethylene copolymer resin. The propylene-ethylene copolymer resin may be a random copolymer resin or a block copolymer resin. As a random propylene-ethylene copolymer resin, a conventionally known resin may be used, and as a commercially available product, WINTEC (registered trademark) WFX4M, WFW4M, WXK1233, or WFX4TA manufactured by Japan Polypropylene Corporation may be used. In addition, PC630A, PC630S, PF621S, PM731M, or PM731V manufactured by SunAllomer Ltd. may also be used. Also, as a block propylene-ethylene copolymer resin, a conventionally known resin may be used, and as a commercially available product, NOVATEC (registered trademark) PP BC03B, BC03GS, BC05B, BC06C, or BC08F manufactured by Japan Polypropylene Corporation may be used. In addition, PM970A, PM970W, PM972Z, PMA60Z, or CMA70C manufactured by SunAllomer Ltd.can also be used. The proportion of propylene-ethylene copolymer resin contained in polyethylene terephthalate resin is preferably about 1 to 7 parts by mass, and preferably 2 to 4 parts by mass on the basis of 100 parts by mass of polyethylene terephthalate resin.

[0009] According to one embodiment, the polyethylene terephthalate resin, which is the main resin, further contains a polyethylene resin. The polyethylene terephthalate resin as the main resin preferably also contains a resin polyethylene. As a polyethylene resin, a conventionally known polyethylene resin may be used, and a high-density polyethylene resin is particularly preferable. Commercially available products include NOVATEC (trademark) HD ​​HF111K, HF313, HF560, HF562, HE481, or HE490 manufactured by Japan Polyethylene Corporation. Additionally, HI-ZEX (trademark) 7700M, 7800M, 7000F, or 8000F manufactured by Prime Polymer Co., Ltd. may also be used. The proportion of polyethylene resin in the polyethylene terephthalate resin is preferably about 1 to 7 parts by mass, and preferably 2 to 4 parts by mass, based on 100 parts by mass of the polyethylene terephthalate resin.The proportion of the total quantity of propylene-ethylene copolymer resin and polyethylene resin contained in polyethylene terephthalate resin is preferably 1 to 7 parts by mass on the basis of 100 parts by mass of polyethylene terephthalate resin.

[0010] Next, a racket string made from a sheath-core type monofilament will be described. In the case of the sheath-core type monofilament, what is used is a monofilament in which the core component comprises a polyethylene terephthalate resin, and the sheath component comprises a polyethylene terephthalate resin, which is a main resin containing a propylene-ethylene copolymer resin. It is preferable to use the same type of polyethylene terephthalate resin for both the core component and the sheath component, and it is particularly preferable to use the same polyethylene terephthalate resin. This is because peeling is less likely to occur at the interface between the core component and the sheath component.The propylene-ethylene copolymer resin contained in the sheath component is preferably the same resin in the same quantity as in the case of the single-layer monofilament.

[0011] The sheath component preferably also contains a polyethylene resin, as is the case with the single-layer monofilament. The polyethylene resin contained in the sheath component is preferably the same resin in the same quantity as in the single-layer monofilament. The core component may be formed solely from polyethylene terephthalate resin, but it is preferable that a polyethylene resin of the same type as the polyethylene resin contained in the sheath component be present in an amount of approximately 1 to 7 parts by mass. Furthermore, it is also preferable that a polyester resin other than polyethylene terephthalate, such as polybutylene terephthalate, be present in an amount of approximately 10 to 40 parts by mass. In this way, shock absorption can be improved.

[0012] The diameter of the racket string according to the present invention is approximately 0.8 to 1.5 mm, and particularly preferably 1.0 to 1.3 mm. Furthermore, it is preferable that the monofilament of the racket string according to the present invention be colored by a mixture of a dye or pigment. With the exception of the dye or pigment, it is preferable to avoid the presence of compounds such as a filler composed of inorganic particles and a surfactant. When such compounds are present, the feel of the ball can be impaired.

[0013] A method for producing racket string according to the present invention is as follows. In the case of racket string made from a single-layer monofilament, a resin composition in which a propylene-ethylene copolymer resin is contained within a polyethylene terephthalate resin, which is a main resin, or a resin composition in which a propylene-ethylene copolymer resin and a polyethylene resin are contained within a polyethylene terephthalate resin, which is a main resin, is prepared as a raw material. The resin composition is fed into a melt-spinning apparatus and melt-spun, then cooled to obtain an unstretched filament. The unstretched filament is subjected to drawing in a single or multiple stages under heating to obtain racket string made from a single-layer monofilament.The drawing process is preferably a multi-stage drawing process, and the drawing ratio is preferably fixed at a total drawing ratio of 3 to 6.

[0014] In the case of a racket string made of a sheath-core type monofilament, a polyethylene terephthalate resin serving as the core component and a resin composition serving as the sheath component are prepared. A polyester resin other than polyethylene terephthalate, such as a polyethylene or polybutylene terephthalate resin, may be contained within the polyethylene terephthalate resin serving as the core component. The resin composition may be prepared for a monolayer type monofilament. Subsequently, a polyethylene terephthalate resin serving as the core component and a resin composition serving as the sheath component are introduced into a conjugate melt spinning apparatus and spun by conjugate melt spinning, then cooled to obtain an unstretched sheath-core type filament.Subsequently, the drawing process is carried out in the same way as in the case of single-layer monofilament to obtain a racket string made of a conjugated sheath-core type monofilament.

[0015] According to one embodiment, the monofilament is conjugated and of the sheath-core type, where:

[0016] - the core component comprises polyethylene terephthalate resin and, - the sheath component includes polyethylene terephthalate resin, which is the main resin containing propylene-ethylene copolymer resin.

[0017] According to another embodiment, the monofilament is conjugated and of the sheath-core type, where:

[0018] - the core component comprises a polyethylene terephthalate resin and, - the sheath component comprises a polyethylene terephthalate resin, which is the main resin, containing a propylene-ethylene copolymer resin and a polyethylene resin.

[0019] If desired, the resulting racket string can be made more maneuverable by applying an oily agent to its surface. Furthermore, the product can be customized to consumer preferences by printing characters or designs on its surface.

[0020] The racket string according to the present invention has the effect of having an appropriate impact absorption capacity and a sensation of repulsion. Consequently, the racket string is preferred by both ordinary and professional players.

[0021] According to one embodiment, the propylene-ethylene copolymer resin is contained in an amount of 2 to 4 parts by mass on the basis of 100 parts by mass of the polyethylene terephthalate resin.

[0022] According to a particular embodiment, the propylene-ethylene copolymer resin is contained in an amount of 2 to 4 parts by mass and the polyethylene resin is contained in an amount of 2 to 4 parts by mass, both on the basis of 100 parts by mass of the polyethylene terephthalate resin.

[0023] According to a particular embodiment, the polyethylene resin is contained in the polyethylene terephthalate resin, which is the core component.

[0024] According to a particular embodiment, the polyethylene resin is contained in an amount of 1 to 3 parts by mass on the basis of 100 parts by mass of polyethylene terephthalate resin.

[0025] The invention also relates to a method for producing a racket string, comprising:

[0026] - melt spinning using a resin composition in which a resin Propylene-ethylene copolymer is contained within a polyethylene terephthalate resin, which is a main resin, to obtain an unstretched filament.

[0027] - then stretch the unstretched filament under heating to obtain a monofilament.

[0028] According to a particular embodiment, the process comprises:

[0029] - melt spinning using a resin composition in which a resin Propylene-ethylene copolymer and polyethylene resin are contained within a polyethylene terephthalate resin, which is the main resin, to obtain an unstretched filament,

[0030] - then stretch the unstretched filament under heating to obtain a monofilament.

[0031] According to a particular embodiment, the process comprises:

[0032] - conjugate melt spinning using a polyethylene terephthalate resin serving as a core component and a resin composition serving as a sheath component, the resin composition comprising a polyethylene terephthalate resin, which is a main resin, the polyethylene terephthalate resin containing a propylene-ethylene copolymer resin, to obtain a conjugated unstretched filament of the sheath-core type,

[0033] - then stretch the unstretched filament under heating to obtain a monofilament sheath-core type conjugate.

[0034] According to a particular embodiment, the process comprises:

[0035] - conjugate melt spinning using a polyethylene terephthalate resin serving as a core component and a resin composition serving as a sheath component, the resin composition comprising a polyethylene terephthalate resin, which is a main resin, the polyethylene terephthalate resin containing a propylene-ethylene copolymer resin and a polyethylene resin, to obtain a conjugated unstretched filament of the sheath-core type,

[0036] - then stretch the unstretched filament under heating to obtain a monofilament sheath-core type conjugate. Examples of implementation of the invention

[0037] Example 1: A resin composition was prepared in which 3.4 parts by mass of high-density polyethylene ("NOVATEC (registered trademark) HD ​​HF313" manufactured by Japan Polyethylene Corporation) and 2.5 parts by mass of propylene-ethylene random copolymer ("WINTEC (registered trademark) WFX4M" manufactured by Japan Polypropylene Corporation) were mixed with 100 parts by mass polyethylene terephthalate chips (relative viscosity: 1.62). The resin composition was loaded into a standard extruder-type melt spinning apparatus, melt spun at a temperature of 300°C, and then cooled in a warm water bath at 75°C, obtaining an unstretched monofilament.Without winding the unstretched monofilament, it was first drawn with a draw ratio of 3.38 in a warm water bath at 98°C, then drawn a second time with a draw ratio of 1.32 while passing through a heating zone at 200°C, and then again through a heating zone at 240°C, resulting in a total draw ratio of 4.75. This produced a racket string made of a single-layer monofilament with a diameter of 1.25 mm. This racket string had a tensile strength of 511.2 N and an elongation of 34.4%.

[0038] Example 2: A monofilament racket string of the single-layer type having a diameter of 1.25 mm was obtained by the same method as in Example 1, except by using a random copolymer of propylene-ethylene ("WINTEC (registered trademark) WFW4M" manufactured by Japan Polypropylene Corporation) instead of the random propylene-ethylene copolymer ("WINTEC (trademark) WFX4M" manufactured by Japan Polypropylene Corporation). This racket string had tensile strength characteristics of 509.7 N and an elongation of 35.1%.

[0039] Example 3: A monofilament racket string of the single-layer type having a diameter of 1.25 mm was obtained in the same manner as in Example 2, except using high-density polyethylene (“HI-ZEX (registered trademark) 7700M” manufactured by Prime Polymer Co., Ltd.) instead of high-density polyethylene (“NOVATEC (registered trademark) HD ​​HF313” manufactured by Japan Polyethylene Corporation). This racket string had tensile strength characteristics of 510.3 N and an elongation of 34.8%.

[0040] Example 4: A resin composition was prepared, in which 3.0 parts by mass of a propylene-ethylene block copolymer ("NOVATEC (registered trademark) BC05B" manufactured by Japan Polypropylene Corporation) were mixed with 100 parts by mass of polyethylene terephthalate (relative viscosity: 1.62). The resin composition was loaded into a melt spinning apparatus of the ordinary extruder type, melt spun at a temperature of 300°C, and then cooled in a hot water bath at 75°C, obtaining an unstretched monofilament.Without winding the unstretched monofilament, it was first drawn with a draw ratio of 3.53 in a hot water bath at 98°C, then drawn a second time with a draw ratio of 1.39 while passing through a heating zone at 230°C, and finally through a heating zone at 250°C, resulting in a total draw ratio of 4.90. This produced a racket string made of a single-layer monofilament with a diameter of 1.25 mm. This racket string had a tensile strength of 536.3 N and an elongation of 25.9%.

[0041] Example 5: A racket string made of a single-layer monofilament with a diameter of 1.25 mm was obtained by the same method as in Example 4, except using a propylene-ethylene block copolymer ("PMA60Z" manufactured by SunAllomer Ltd.) instead of the propylene-ethylene block copolymer ("NOVATEC (registered trademark) BC05B" manufactured by Japan Polypropylene Corporation). This racket string had tensile strength characteristics of 540.5 N and an elongation of 24.6%.

[0042] Example 6: A resin composition intended to serve as a sheath component was prepared in which 3.4 parts by mass of high-density polyethylene ("NOVATEC (registered trademark) HD ​​HF313" manufactured by Japan Polyethylene Corporation) and 2.5 parts by mass of propylene-ethylene random copolymer ("WINTEC (registered trademark) WFX4M" manufactured by Japan Polypropylene Corporation) were mixed with 100 parts by mass of polyethylene terephthalate (relative viscosity: 1.62). A resin composition intended to serve as a core component was prepared in which 18.1 parts by mass of polybutylene terephthalate ("NOVADURAN 5020" manufactured by Mitsubishi Chemical Corporation) and 2.4 parts by mass of high-density polyethylene ("NOVATEC (registered trademark) HD ​​HF313" manufactured by Japan Polyethylene Corporation) were mixed with 100 parts by mass of polyethylene terephthalate (relative viscosity: 1.62). Next, the resin composition intended for use as the sheath component and the resin composition intended for use as the core component were introduced into a conjugate melt spinning apparatus of the extruder type. The melt spinning was carried out at a temperature of 295°C, and then the spun conjugate material was cooled in a hot water bath at 75°C, thus obtaining an unstretched sheath-core filament. The feed quantities of the resin composition intended for use as the sheath component and the resin composition intended for use as the core component were adjusted so that the volume ratio of the sheath component to the core component was 6:4 (sheath component:core component).Subsequently, the unstretched sheath-core filament was subjected to a first drawing with a drawing ratio of 3.29 in a hot water bath at 98°C, then to a second drawing to achieve a total drawing ratio of 4.60 while passing through a heating zone at 200°C, and then again through a heating zone at 240°C, thus obtaining a racket string made of a conjugated sheath-core monofilament with a diameter of 1 mm (the core-to-sheath volume ratio is core:sheath = 4:6). This racket string had tensile strength characteristics of 350.3 N and an elongation of 22.6%.

[0043] Example 7: A racket string made of a conjugated monofilament of the sheath-core type having a diameter of 1 mm (the core-to-sheath volume ratio is core:sheath = 4:6) was obtained in the same way as in Example 6, except that instead of using the resin composition serving as the core component of Example 6, a resin composition obtained by mixing 34.2 parts by mass of polybutylene terephthalate (“NOVADURAN 5020” manufactured by Mitsubishi Chemical Corporation) and 2.7 parts by mass of high-density polyethylene (“NOVATEC (registered trademark) HD ​​HF313” manufactured by Japan Polyethylene Corporation) with 100 parts by mass of polyethylene terephthalate (relative viscosity: 1.62) is used. This racket string had tensile strength characteristics of 341.4 N and an elongation of 21.8%.

[0044] The racket strings obtained by the methods of Examples 1 to 7 were each mounted on a tennis racket, and the ball-striking feel was confirmed when a tennis ball was actually struck. Consequently, the feel The ball striking was very good. Therefore, these were racket strings with a feel for use that was widely usable by both professional and amateur players.

Claims

Demands

1. Racket string comprising a monofilament in which a propylene-ethylene copolymer resin is contained in a polyethylene terephthalate resin, which is the main resin.

2. Racket string according to claim 1, characterized in that the polyethylene terephthalate resin, which is the main resin, further contains a polyethylene resin.

3. Racket string according to claim 1, characterized in that the monofilament is conjugated and of the sheath-core type, where: - the core component comprises polyethylene terephthalate resin and, - the sheath component comprises polyethylene terephthalate resin, which is the main resin containing propylene-ethylene copolymer resin.

4. Racket string according to claim 2, characterized in that the monofilament is conjugated and of sheath-core type, where: - the core component comprises a polyethylene terephthalate resin and, - the sheath component comprises a polyethylene terephthalate resin, which is the main resin, containing a propylene-ethylene copolymer resin and a polyethylene resin.

5. Racket string according to any one of claims 1 to 4, characterized in that the propylene-ethylene copolymer resin is contained in an amount of 2 to 4 parts by mass on the basis of 100 parts by mass of the polyethylene terephthalate resin.

6. Racket string according to any one of claims 2 and 4, characterized in that the propylene-ethylene copolymer resin is contained in an amount of 2 to 4 parts by mass and the polyethylene resin is contained in an amount of 2 to 4 parts by mass, both on the basis of 100 parts by mass of polyethylene terephthalate resin.

7. Racket string according to claim 4, characterized in that the polyethylene resin is contained in the polyethylene terephthalate resin, which is the core component.

8. Racket string according to claim 7, characterized in that the polyethylene resin is contained in an amount of 1 to 3 parts in niasse based on 100 parts by mass of polyethylene terephthalate resin.

9. A method for producing a racket string, comprising: - melt spinning using a resin composition in which a propylene-ethylene copolymer resin is contained in a polyethylene terephthalate resin, which is a main resin, to obtain an unstretched filament, - then drawing the unstretched filament under heating to obtain a monofilament.

10. A method for producing a racket string according to claim 9, the method comprising: - melt spinning using a resin composition in which a propylene-ethylene copolymer resin and a polyethylene resin are contained in a polyethylene terephthalate resin, which is a main resin, to obtain an unstretched filament, - then drawing the unstretched filament under heating to obtain a monofilament.

11. A method for producing a racket string according to claim 9, characterized in that the method comprises: - conjugate melt spinning using a polyethylene terephthalate resin as a core component and a resin composition as a sheath component, the resin composition comprising a polyethylene terephthalate resin, which is a main resin, the polyethylene terephthalate resin containing a propylene-ethylene copolymer resin, to obtain a conjugated unstretched filament of the sheath-core type, - then drawing the unstretched filament under heating to obtain a conjugated monofilament of the sheath-core type.

12. A method for producing a racket string according to claim 10, characterized in that the method comprises: - conjugate melt spinning using a polyethylene terephthalate resin as a core component and a resin composition as a sheath component, the resin composition comprising a polyethylene terephthalate resin, which is a main resin, the polyethylene terephthalate resin containing a propylene-ethylene copolymer resin and a resin of polyethylene, to obtain a conjugated unstretched filament of the sheath-core type, - then stretch the unstretched filament under heating to obtain a conjugated monofilament of the sheath-core type.