Racket strings and method for manufacturing the same

Abstract

To provide a polyester-made filament that has a small friction coefficient and excellent abrasion resistance, and a polyester-made string that can obtain excellent durability and vibration damping performance and soft ball hitting feeling.SOLUTION: A surface of a polyester filament is treated by plasma, and then silicone oil is applied to the surface, by which a yarn including a polyester filament whose surface is covered with the silicone oil is obtained. At this point, it is preferable that the plasma treatment be an atmospheric pressure low-temperature plasma treatment. Further, it is also preferable that the silicone oil have a polar functional group which is at least one kind selected from the group consisting of amino group, epoxy group, mercapto group, carboxyl group, carboxylic acid anhydride group, hydroxyl group and (meth)acrylic group. An obtained yarn is suitable for a string of a racket for tennis or the like, and in the case where the racket is strung, it gives excellent durability, excellent vibration damping performance, and soft ball hitting feeling.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a yarn containing polyester filaments, particularly a yarn for strings of rackets such as tennis. The present invention also relates to a method for producing such a yarn.

Background Art

[0002] As a material for strings (guts) used in rackets such as tennis, badminton, and squash, natural strings made of animal fibers have been used for a long time. However, natural strings have problems with durability and price, and in recent years, they have been increasingly replaced by synthetic fiber strings.

[0003] The structures of synthetic fiber strings are diverse according to their uses and required performances, and strings made of multifilament yarns, monofilament yarns, twisted yarns, etc. are used, and synthetic resin materials such as nylon and polyester are adopted. In addition, techniques for compositeizing, adhering to each other, or coating with resin these yarns are also known. When such a string is stretched on a racket, silicone oil may be applied to facilitate the work (for example, Patent Document 1).

[0004] Typical synthetic fiber materials constituting strings for tennis rackets include nylon and polyester. Nylon strings are widely used including by elderly people, children, and women because a soft hitting feeling can be obtained. On the other hand, polyester strings are harder than nylon strings and natural strings, have a hard hitting feeling, and are excellent in durability. Therefore, recently, polyester strings have become mainstream among professional players and competitive players.

[0005] However, because polyester is a hard material, it has the problem of producing a hard feel when hitting the ball, and the impact and vibration transmitted to the hand are too great, which can easily cause injuries such as tennis elbow. Therefore, there is a need for a string that has the durability of polyester strings while providing the soft feel of nylon strings.

[0006] Patent Document 2 describes a racket string using a monofilament made of a polyester resin composition containing 0.5 to 10% by weight of silicone oil. It states that this racket string is less susceptible to changes in properties due to environmental changes, has ball control comparable to natural strings, and maintains its properties without impairing the characteristics of a racket string made of a polyester resin composition. It also states that even after repeated use, the initial characteristics of the racket string change very little, and that a racket string is provided that balances ease of applying spin to the ball with durability. It states that while the silicone oil tends to fall off if only applied to the surface of the polyester monofilament, by causing the silicone oil to bleed out from inside the monofilament, low frictional resistance can be maintained over a long period of time.

[0007] However, when silicone oil is incorporated into polyester monofilament, a decrease in the monofilament's tensile strength is unavoidable. On the other hand, simply applying silicone oil to the surface of the monofilament does not maintain low frictional resistance over a long period.

[0008] On the other hand, in Patent Document 3, the present inventors have proposed a plasma treatment method in which plasma treatment is performed by bringing plasma into contact with a long workpiece. In the embodiment described, in order to improve the water repellency of fishing line, atmospheric pressure low-temperature plasma treatment is performed on the surface of a polyamide monofilament and then silicone oil is applied. This is an attempt to obtain water repellency by covering the surface of the polyamide fishing line with a hydrophobic compound, and therefore it is a treatment method that does not make sense to apply to polyester monofilaments, which originally have a hydrophobic surface. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] WO2020 / 031529A1 [Patent Document 2] Japanese Patent Publication No. 2009-219518 [Patent Document 3] WO2014 / 167626A1 [Overview of the project] [Problems that the invention aims to solve]

[0010] This invention was made to solve the above problems and aims to provide a polyester filament with a low coefficient of friction and excellent wear resistance, as well as a suitable method for manufacturing the same. In particular, it aims to provide a polyester string that, when strung on a tennis racket, has excellent durability and vibration damping properties, resulting in a soft feel when hitting the ball. [Means for solving the problem]

[0011] The above problems are solved by providing a yarn containing a polyester filament having a plasma-treated surface, the surface of which is covered with silicone oil. In this case, it is preferable that the silicone oil has polar functional groups, and it is more preferable that the polar functional group is at least one selected from the group consisting of amino groups, epoxy groups, mercapto groups, carboxyl groups, carboxylic acid anhydride groups, hydroxyl groups, and (meth)acrylic groups. It is preferable that the polyester filament is a monofilament. It is also preferable that the plasma treatment is atmospheric pressure low-temperature plasma treatment.

[0012] A preferred embodiment of the yarn is a racket string made of the yarn. A preferred method for manufacturing the yarn is to plasma-treat the surface of a polyester filament and then apply silicone oil to the surface. In this case, it is preferable to apply the silicone oil by applying a silicone emulsion and then drying it. [Effects of the Invention]

[0013] The yarn containing polyester filaments according to the present invention has a low coefficient of friction and excellent abrasion resistance. In particular, when strung on a tennis racket, it has excellent durability and vibration damping properties, resulting in a soft feel when hitting the ball. Furthermore, such yarn can be easily manufactured according to the manufacturing method of the present invention. [Brief explanation of the drawing]

[0014] [Figure 1] This is a perspective view showing the plasma processing apparatus used in the example. [Figure 2] Figure 1 shows a cross-sectional view of the plasma processing apparatus of the present invention, where (a) is a cross-sectional view in the direction of filament propagation and (b) is a cross-sectional view of BB. [Modes for carrying out the invention]

[0015] The present invention relates to a yarn comprising a polyester filament having a plasma-treated surface, the surface of which is covered with silicone oil.

[0016] The polyester constituting the polyester filament contained in the yarn of the present invention is a polyester obtained by condensation polymerization of a dicarboxylic acid or its ester and a diol, and contains dicarboxylic acid units and diol units. Examples of dicarboxylic acids include terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, 1,4-cyclohexanedicarboxylic acid, adipic acid, sebacic acid, and dimer acid. Examples of diols include ethylene glycol, propylene glycol, tetramethylene glycol, 1,4-cyclohexanedimethanol, and diethylene glycol. These dicarboxylic acids and diols can be used in appropriate combinations. In this case, small amounts of polyvalent monomers such as pentaerythritol, trimethylolpropane, trimellitic acid, and trimesic acid can also be used in combination.

[0017] Among these, polyethylene terephthalate (hereinafter sometimes referred to as PET), in which 90 mol% or more of the dicarboxylic acid units are terephthalic acid units and 90 mol% or more of the diol units are ethylene glycol, is suitable for use as the polyester filament of the present invention because the resulting filament has a high elastic modulus and is less susceptible to changes in physical properties due to environmental changes such as temperature and humidity. Here, the content of terephthalic acid units is more preferably 95 mol% or more, and even more preferably 98 mol% or more. Furthermore, the content of ethylene glycol units is more preferably 95 mol% or more.

[0018] The polyester filament used in the present invention may be a monofilament or a multifilament, but from the viewpoint of obtaining a yarn with low frictional resistance, it is preferably a monofilament. Also, from the same viewpoint, rather than using a plurality of monofilaments, it is preferable to form a yarn with only one monofilament. Its cross-sectional shape is not particularly limited, but it is preferably circular. The diameter of the monofilament varies depending on the application, but is usually 0.05 to 5 mm. Preferably it is 0.1 mm or more, more preferably 0.5 mm or more. On the other hand, preferably it is 3 mm or less, more preferably 2 mm or less. When used as a string for a racket, the diameter of the monofilament is usually 0.5 to 2 mm. Preferably it is 0.8 mm or more, more preferably 1 mm or more. On the other hand, preferably it is 1.7 mm or less, more preferably 1.5 mm or less. In addition, even when using a multifilament or a monofilament sewing thread as the string, the preferred diameter is the same as that of the monofilament in the above case, and it is plasma-treated after forming it into the form of a string.

[0019] The surface of the polyester filament used in the present invention is plasma-treated. The plasma treatment apparatus used in the present invention is not particularly limited as long as it can generate plasma and can bring the polyester filament into contact with the plasma. In order to continuously bring plasma into contact with the polyester filament, it is preferably plasma under atmospheric pressure. Also, in order to prevent the polyester resin from melting, it is preferably low-temperature plasma, specifically, preferably plasma at a temperature lower than 250°C, which is the melting point of polyethylene terephthalate. Therefore, the plasma treatment preferably employed in the present invention is atmospheric pressure low-temperature plasma treatment.

[0020] An atmospheric pressure low-temperature plasma processing apparatus has a pair of opposing electrodes, and an AC power supply can be connected to each electrode to apply a voltage. By doing so, low-temperature plasma is generated under atmospheric pressure. At this time, dielectric barrier discharge can be caused by arranging a dielectric that does not conduct electricity between the electrodes, and atmospheric pressure low-temperature plasma can be easily generated. The type of gas for generating the plasma is not particularly limited, but nitrogen gas is preferably mentioned. It is preferable to have an opening so that the polyester monofilament can continuously pass through.

[0021] By subjecting the polyester filament to plasma treatment, radicals are generated in the polymer chains present on the surface of the filament, and then polar functional groups are presumably introduced onto the filament surface by reacting with oxygen or water, etc. Generally, in corona discharge treatment widely used as a surface treatment for plastics, the surface of the plastic is roughened by the discharge and fine irregularities are formed. Therefore, when the filament is subjected to corona treatment, there is a possibility that the tensile strength may decrease due to the formed irregularities. In that regard, in the case of plasma treatment, the chemical structure of the surface can be changed hardly forming irregularities, so that almost no decrease in tensile strength is observed.

[0022] Generally, polyester, especially PET, is known to have almost no reactive functional groups and low adhesiveness to other materials. Therefore, the significance of surface modification by plasma treatment to improve adhesiveness to other materials is great.

[0023] The yarn of the present invention has a surface thus plasma-treated, and the surface is covered with silicone oil. At this time, it is preferable to apply silicone oil to the surface of the polyester immediately after plasma treatment. There is a possibility that the radicals generated by plasma treatment may remain alive without disappearing, and it is possible to prevent the surface from being contaminated by moisture and organic substances in the air.

[0024] The silicone oil applied to the polyester filament has a polydimethylsiloxane structure consisting of numerous linked dimethylsiloxane [-Si(CH3)2-O-] units. Some of the methyl groups may be replaced with phenyl groups, hydrogen atoms, or other substituents. The silicone oil used in this invention is an "oil" and has fluidity. This allows for an effective reduction in the coefficient of friction. Silicone oils that are cured by crosslinking after application to form a solid film cannot sufficiently reduce the coefficient of friction.

[0025] In the present invention, the silicone oil is preferably such that the methyl groups in the side chains of the polydimethylsiloxane structure and the molecular ends are replaced with substituents containing functional groups, particularly polar functional groups. The presence of polar functional groups in the silicone oil allows it to react with radicals and other polar functional groups formed on the filament surface by plasma treatment, forming covalent bonds or hydrogen bonds. Specifically, it is preferable to have at least one polar functional group selected from the group consisting of amino groups, epoxy groups, mercapto groups, carboxyl groups, carboxylic acid anhydride groups, hydroxyl groups, and (meth)acrylic groups. The presence of polar functional groups allows for a lower coefficient of friction compared to cases without functional groups.

[0026] The method of applying the silicone oil is not particularly limited. An aqueous emulsion may be applied, or a solution dissolved in an organic solvent may be applied. In either case, it should be diluted as appropriate to ensure uniform application. From the viewpoint of avoiding adverse environmental impacts, it is preferable to apply an aqueous silicone emulsion. The application method is not particularly limited; it may be immersed in the coating liquid or applied with a roller or the like. After application, it should be dried by heating or other means.

[0027] The resulting polyester filament is coated with silicone oil on its surface. Therefore, it has a low coefficient of friction and excellent wear resistance. While its applications are not particularly limited, a suitable application is as a racket string.

[0028] Polyester strings have always been more durable than nylon strings. However, by applying silicone oil after plasma treatment, as in the present invention, it is possible to improve abrasion resistance by reducing friction while preventing a decrease in tensile strength. In other words, it is possible to further improve durability while maintaining the strength of polyester strings. On the other hand, the reduced friction allows the contacting strings to move more easily with each other, improving vibration absorption performance and resulting in a softer feel when hitting the ball. That is, it is possible to achieve a soft feel like nylon strings while having durability that is superior to polyester strings. This balance of feel and durability has not been achieved with conventional strings. [Examples]

[0029] The present invention will be described in more detail below with reference to examples. The analytical and evaluation methods in the examples were as follows.

[0030] (1) Measurement of friction coefficient A test thread was attached to a 10cm square acrylic plate using double-sided tape to create a sample. Next, using a "KES-SE friction tester" manufactured by Kato Tech Co., Ltd., a 10mm square piano wire sensor was used to scan the sample thread along its longitudinal direction with a load of 50g, a test length of 2cm, and a speed of 0.5mm / min. The mean and standard deviation of the friction coefficient (MIU) on the surface of the test thread were calculated (n=5).

[0031] (2) Measurement of tensile strength In accordance with the method described in Section 8.5 of JIS L1013 (2010), the test yarn was measured using ORIENTEC RTE-1210 manufactured by Orientec Co., Ltd., with a test length of 25 cm and a tensile speed of 30 cm / min (n=5), and the tensile strength (kgf) was determined from the average value.

[0032] (3) Abrasion resistance test In accordance with the method described in Section 9.2 of JIS L0849, a friction tester (Type II) manufactured by Yasuda Seiki Seisakusho Co., Ltd. was used to attach abrasive paper (1500 grit) to the surface of the friction element. A test thread cut to a length of 20 cm was subjected to 500 friction cycles with a load of 300 g. Next, the tensile strength (kgf) of the friction-treated test thread was measured according to the tensile test method, and the abrasion resistance (%) was determined by dividing it by the tensile strength (kgf) before friction was applied and multiplying by 100.

[0033] The coating agents used in the following examples are as follows: • Amino-modified silicone emulsion Matsumoto Silicone Softener N-800, manufactured by Matsumoto Oil & Fat Pharmaceutical Co., Ltd. This is an aqueous emulsion in which liquid particles of modified silicone containing amino groups are dispersed in water. • Unmodified silicone oil Dimethyl silicone oil "Element14 PDMS 10JC" manufactured by Momentive Performance Materials Japan LLC. Viscosity at 25℃ is 10mm 2 / s is a colorless, transparent silicone oil. Both ends of the polydimethylsiloxane are trimethylsilyl groups, and it does not contain polar functional groups. • Curing silicone emulsion Momentive Performance Materials Japan LLC's film-forming silicone hybrid emulsion "XS53-C2459" This is an aqueous silicone emulsion that forms a cured film upon drying after application.

[0034] Example 1 As the raw material, a monofilament made of polyethylene terephthalate with a circular cross-section and a diameter of 1.3 mm was used. The raw material was wound onto a bobbin, set on a creel stand, and the surface was modified by passing it through a plasma gas atmosphere of nitrogen gas at a flow rate of 3 L / min while being transported at a speed of 50 m / min using a plasma processing device 1.

[0035] The structure of the plasma processing apparatus 1 used here will be explained with reference to Figures 1 and 2. The plasma processing apparatus 1 comprises a flat upper electrode 10a and a lower electrode 10b arranged opposite each other and to which power is supplied from an AC power source, an insulating plate 11 positioned on the lower surface of the upper electrode 10a between the upper electrode 10a and the lower electrode 10b, a pair of spacers 12 arranged parallel to the transport direction of the polyester monofilament (thick line in the figure) and supporting the insulating plate 11 on the lower electrode 10b while forming a predetermined gap 12a between the insulating plate 11 and the lower electrode 10b, and a guide portion 15 that guides the polyester monofilament, which is the material to be processed, to move through a region with high plasma density in the gap 12a formed by the insulating plate 11 and the lower electrode 10b.

[0036] As shown in Figure 2, the upper electrode 10a has a plasma generation gas inlet 13 for introducing nitrogen gas, which is used to generate plasma, and the insulating plate 11 has multiple plasma generation gas outlets 14 that open to the inner surface of the gap 12a formed between the insulating plate 11 and the lower electrode 10b, for ejecting the plasma generation gas introduced from the plasma generation gas inlet 13 formed in the upper electrode 10a into the gap 12a formed between the insulating plate 11 and the lower electrode 10b. In the plasma processing apparatus 1, with the plasma generation gas introduced, power is applied from an AC power source to the upper electrode 10a and the lower electrode 10b to generate a dielectric barrier discharge and generate plasma in the gap 12a formed by the insulating plate 11 and the lower electrode 10b. In the plasma processing apparatus 1, a plasma is formed in which the density is high in the gap 12a located near the center of the overlapping area of ​​the upper electrode 10a and the lower electrode 10b, and the density gradually decreases from the center toward the outer periphery. The guide section 15 consists of a guide member 15 having a plurality of annular holding sections 15a that form a transport path for the polyester monofilament, and leg sections 15b that fix each holding section 15a to a predetermined position within the gap 12a. The guide section 15 is positioned approximately in the center of the overlapping area of ​​the upper electrode 10a and the lower electrode 10b so as to allow the polyester monofilament to pass through the region of high plasma density.

[0037] A coating solution was prepared by diluting 20 parts by mass of the amino-modified silicone emulsion "Matsumoto Silicone Softener N-800" with 80 parts by mass of water. The coating solution was applied to the monofilament immediately after plasma treatment as described above using an oiling roller. Subsequently, the monofilament was passed through a drying chamber at 120°C to remove moisture from the coating layer. The surface of the resulting monofilament had a thin, uniform layer of amino-modified silicone oil, and the oil was fluid. The resulting monofilament was subjected to friction coefficient measurement, tensile strength measurement, and abrasion resistance test according to the method described above. The results are summarized in Table 1.

[0038] Example 2 A coating solution was prepared by diluting 2 parts by mass of dimethyl silicone oil "Element14 PDMS 10JC" with 98 parts by mass of isopropyl alcohol. A monofilament with a thin, uniform coating of dimethyl silicone oil was obtained in the same manner as in Example 1, except that this coating solution was used. The oil was fluid. The monofilament thus obtained was subjected to friction coefficient measurement, tensile strength measurement, and abrasion resistance test in the same manner as in Example 1. The results are summarized in Table 1.

[0039] Comparative Example 1 A coating solution was prepared by diluting 20 parts by mass of the curable silicone emulsion "XS53-C2459" with 80 parts by mass of water. A monofilament with a thin, uniform coating of silicone resin was obtained in the same manner as in Example 1, except for the use of this coating solution. The silicone resin had cured and formed a film, and was not fluid. The obtained monofilament was subjected to friction coefficient measurement, tensile strength measurement, and abrasion resistance testing in the same manner as in Example 1. The results are summarized in Table 1.

[0040] Comparative Example 2 A monofilament with a thin, uniform coating of amino-modified silicone oil was obtained in the same manner as in Example 1, except that the raw yarn was not plasma-treated and the coating solution was applied directly. The oil was fluid. The monofilament thus obtained was subjected to friction coefficient measurement, tensile strength measurement, and abrasion resistance test in the same manner as in Example 1. The results are summarized in Table 1.

[0041] Comparative Example 3 A monofilament with a thin, uniform coating of dimethyl silicone oil was obtained in the same manner as in Example 2, except that the raw yarn was not plasma-treated and the coating solution was applied directly. The oil was fluid. The monofilament thus obtained was subjected to friction coefficient measurement, tensile strength measurement, and abrasion resistance test in the same manner as in Example 1. The results are summarized in Table 1.

[0042] Comparative Example 4 A monofilament with a thin, uniform coating of silicone resin was obtained in the same manner as in Comparative Example 1, except that the raw yarn was not plasma-treated and the coating solution was applied directly. The silicone resin had hardened and formed a film, and did not have fluidity. The monofilament thus obtained was subjected to friction coefficient measurement, tensile strength measurement, and abrasion resistance test in the same manner as in Example 1. The results are summarized in Table 1.

[0043] Comparative Example 5 The monofilament of the raw yarn was subjected to friction coefficient measurement and tensile strength measurement in the same manner as in Example 1. The results are summarized in Table 1.

[0044] [Table 1]

[0045] As shown in Table 1, Examples 1 and 2, in which plasma treatment was performed before applying silicone oil, exhibited a low coefficient of friction and excellent wear resistance. Example 1, which used amino-modified silicone oil, showed a particularly low coefficient of friction. On the other hand, Comparative Examples 2 and 3, which did not undergo plasma treatment, and Comparative Examples 1 and 4, in which cured silicone resin was applied, showed a high coefficient of friction.

[0046] Example 3 The monofilament obtained in Example 1 was strung onto a Mizuno tennis racket "F series 300" at a tension of 50 pounds. A PCB accelerometer "352A21" was attached and fixed 50 mm from the end of the handle of the resulting racket. Next, the racket was suspended in the air with the handle end and the racket tip suspended by a rubber band. In this state, the string surface 80 mm from the racket tip was manually vibrated using an impulse hammer, and the acceleration response was measured using the accelerometer to obtain the natural frequency and its damping ratio. As a result, a first-order bending vibration at a frequency of 150 Hz was observed, with a damping ratio of 0.369. A second-order bending vibration at a frequency of 439 Hz was also observed, with a damping ratio of 0.323. Furthermore, a first-order string vibration at a frequency of 514 Hz was observed, with a damping ratio of 0.083. These results are summarized in Table 2.

[0047] Comparative Example 6 A tennis racket was strung with strings in the same manner as in Example 3, except that the monofilament obtained in Comparative Example 2 was used. A vibration test was then performed using the resulting racket in the same manner as in Example 3. The results are summarized in Table 2.

[0048] [Table 2]

[0049] As shown in Table 2, the racket of Example 3, which had plasma treatment on the raw yarn, had a greater damping ratio than the racket of Comparative Example 6, which did not have plasma treatment on the raw yarn, for all of the primary bending vibration, secondary bending vibration, and primary string vibration. This indicates that the vibration damping immediately after hitting the ball in Example 3 was faster than in Comparative Example 6, and that it can reduce the burden on the elbow, etc. Furthermore, when testers performed test shots using the racket of Example 3 and the racket of Comparative Example 6, they evaluated the racket of Example 3 as having a softer feel when hitting the ball compared to the racket of Comparative Example 6. [Explanation of Symbols]

[0050] 1. Plasma processing equipment 10a upper electrode 10b Lower electrode 11 Insulating board 12 Spacers 12a gap 13. Gas inlet for plasma generation 14. Gas nozzle for plasma generation 15 Guide section 15a Holding part 15b Legs

Claims

1. A racket string made of polyester filament having a plasma-treated surface, the surface of which is covered with silicone oil.

2. The string according to claim 1, wherein the silicone oil has polar functional groups.

3. The string according to claim 2, wherein the polar functional group is at least one selected from the group consisting of an amino group, an epoxy group, a mercapto group, a carboxyl group, a carboxylic acid anhydride group, a hydroxyl group, and a (meth)acrylic group.

4. The string according to claim 1 or 2, wherein the polyester filament is a monofilament.

5. The string according to claim 1 or 2, wherein the plasma treatment is atmospheric pressure low-temperature plasma treatment.

6. A method for manufacturing a string according to claim 1 or 2, wherein the surface of a polyester filament is plasma-treated, and then silicone oil is applied to the surface.

7. A method for producing a string according to claim 6, wherein silicone oil is applied by applying a silicone emulsion and then drying it to remove moisture.

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