Monofilament string of racket and method for manufacturing the same
阅读说明：本技术 球拍的单丝弦线和制造该单丝弦线的方法 (Monofilament string of racket and method for manufacturing the same ) 是由 S·杜瓦尔 于 2018-06-20 设计创作，主要内容包括：本发明涉及球拍的单丝弦线,所述单丝弦线包括内芯和护套,所述内芯由单一长丝组成,所述护套围绕内芯延伸并与所述内芯接触,所述单丝弦线的特征在于：内芯(2)由第一材料制成,所述第一材料包括聚酰胺6以及聚酰胺6和聚酰胺6.6的第一共聚物,护套(3)由第二材料制成,所述第二材料包括聚酰胺6和聚酰胺6.6的第二共聚物,第一材料具有比第二材料更大的拉伸模量。本发明还涉及通过内芯和护套的共挤出以及共挤出弦线的拉伸制造该单丝弦线的方法。(The present invention relates to a monofilament string of a racquet, said monofilament string comprising an inner core comprised of a single filament and a sheath extending around and in contact with the inner core, said monofilament string being characterized in that: the inner core (2) is made of a first material comprising polyamide 6 and a first copolymer of polyamide 6 and polyamide 6.6, and the sheath (3) is made of a second material comprising a second copolymer of polyamide 6 and polyamide 6.6, the first material having a greater tensile modulus than the second material. The invention also relates to a method for manufacturing the monofilament string by co-extrusion of the inner core and the sheath and stretching of the co-extruded string.)
1. A monofilament string (1) of a racket (5), said monofilament string (1) comprising an inner core (2) and a sheath (3), said inner core (2) consisting of a single filament, said sheath (3) extending around the inner core (2) and being in contact with said inner core (2), said monofilament string (1) characterized in that:
-the inner core (2) is made of a first material comprising polyamide 6 and a first copolymer of polyamide 6 and polyamide 6.6,
-the sheath (3) is made of a second material comprising polyamide 6 and a second copolymer of polyamide 6.6,
the first material has a greater tensile modulus than the second material.
2. The monofilament string of claim 1, wherein the first material comprises:
70 to 90% by weight, preferably 75 to 85% by weight, of polyamide 6 relative to the total weight of the first material,
-10 to 30% by weight, preferably 15 to 25% by weight, relative to the total weight of the first material, of a first copolymer of polyamide 6 and polyamide 6.6.
3. The monofilament string of claim 1 or 2 wherein the second material is comprised of a second copolymer of polyamide 6 and polyamide 6.6.
4. A monofilament string according to any of the preceding claims, wherein the sheath (3) represents from 5 to 20% by weight, preferably from 8 to 16% by weight, of the total weight of the string (1).
5. A monofilament string according to any preceding claim, wherein the inner core (2) represents from 80 to 95 wt.%, more preferably from 84 to 92 wt.%, of the total weight of the string (1).
6. A monofilament string according to any of the preceding claims, wherein the thickness of the sheath (3) represents 2 to 7%, preferably 3 to 6% of the total thickness of the string (1).
7. A monofilament string according to any one of the preceding claims, wherein the thickness of the inner core (2) represents 93% to 98%, preferably 94% to 97% of the total thickness of the string (1).
8. The monofilament string of any preceding claim, wherein the inner core has a thickness of between 1200 and 1500 microns and the jacket has a thickness of between 20 and 50 microns.
9. The monofilament string of any preceding claim, wherein the second material further comprises at least one additive selected from a slip agent and a hydrophobic agent.
10. A monofilament string as claimed in any of the preceding claims, wherein the monofilament string (1) is obtained by co-extrusion of an inner core (2) and a sheath (3).
11. Method of manufacturing a monofilament string of a racket (5) according to any of the claims 1 to 9, characterized in that it comprises a co-extrusion of an inner core (2) and a sheath (3) to make a string, and at least one stretching step of the string.
12. The method of claim 11, further comprising the step of:
-a first stretching of the co-extruded string by applying a first predetermined traction force, wherein the ratio of the length of the co-extruded string in stretched state to the length of the co-extruded string in relaxed state is between 1 and 10, preferably between 3.5 and 4.5,
-a second stretching of the string by applying a second predetermined traction force, wherein the ratio between the length of the co-extruded string in stretched state and the length of the co-extruded string in relaxed state is between 1 and 2, preferably between 1.05 and 1.55.
13. The method of claim 12, wherein the first stretching step and the second stretching step are continuous.
14. The method of claim 12, wherein the first stretching step and the second stretching step are sequential.
15. The method according to any one of claims 11 to 14, wherein at least one additive is added to the second material in the co-extrusion step, the additive being selected from a slip agent and a hydrophobic agent.
16. A racket (5) comprising a set (6) of monofilament strings (1) according to any of claims 1 to 10.
Technical Field
The present invention relates to monofilament strings and a set of such monofilament strings for use in a racquet (e.g., tennis racquet, squash racquet, badminton racquet, etc.). The invention also relates to a method for preparing the monofilament string.
Background
In the field of racquet sports, a racquet consists of a handle and a frame through which a set of strings extend in two orthogonal directions and are intended to withstand the impact of a ball, shuttlecock, or the like.
In this field, technological developments have led to increasingly competitive racquets, which involve great improvements in the structure of the strings and in the manufacturing process (particularly in the material composition of the strings).
From a general point of view, a racquet is sought in which the strings exhibit good (or at least average) strength, control, comfort and durability. Momentum refers to the ability of a string to increase the speed of a ball as it leaves the string when the player hits the ball. Controllability refers to the ability of the string to influence the behavior of the ball so that a player can accurately hit the ball to a predetermined position, slow the ball down, and influence the spin of the ball. Comfort refers to the ability of the strings to reduce the shock of the racquet caused by the strings bearing the impact of a ball when struck by a player. Finally, durability means that the string has reduced structural degradation over time and use, which in particular results in reduced tension loss, thereby allowing the string to maintain its strength, control and/or comfort.
Among the different types of strings, strings made of natural catgut have a lower stiffness, so that the athlete does not need to have a higher strength to accelerate the ball. However, it has poor control over the ball. The same is true of multifilament strings, which are typically made of polyamide.
Monofilament strings are typically made of polyethylene, polyester or polyamide. Monofilaments made of polyethylene and polyester have a high stiffness, which allows the player to maintain accuracy and better control of the ball. However, the player needs a large amount of power to accelerate the ball. Monofilaments made of polyamide exhibit these characteristics while also providing excellent ability to dissipate racket vibrations, but are susceptible to degradation and rapid loss of tension.
Thus, there is a need for a monofilament string that exhibits a good balance between output and control, while also having good comfort and durability.
In particular, there is a need for monofilament strings that exhibit a high power capability, thereby allowing players to easily increase the speed of the ball without requiring a great deal of power, while allowing players to better control the ball and maintain a substantially constant tension over time within a reasonable time (preferably a playing time, for a few hours, especially 2 to 4 hours for experienced players).
Document FR 2934958 aims at improving the durability of racket strings and discloses a monofilament string comprising a central inner core, a peripheral protective layer and an intermediate reinforcing layer made of composite material and located between the central inner core and the peripheral protective layer.
The intermediate reinforcement layer improves the durability of the string by sacrificing string elasticity and increasing string stiffness, but this results in a decrease in the strength of the string due to the reduced ability of the string to bend under ball impact.
Disclosure of Invention
It is an object of the present invention to provide a monofilament string of a racquet comprising an inner core comprised of a single filament and a sheath extending around and in contact with the inner core, wherein:
the inner core is made of a first
the sheath is made of a second material comprising a second copolymer of
the first material has a greater tensile modulus than the second material.
According to other optional features of the monofilament string:
-the first material comprises:
70 to 90% by weight, preferably 75 to 85% by weight, of
-10 to 30% by weight, preferably 15 to 25% by weight, relative to the total weight of the first material, of a first copolymer of
according to one embodiment, the second material is made of (or substantially made of) a second copolymer of
the sheath represents from 5% to 20% by weight, preferably from 8% to 16% by weight, of the total weight of the string;
-the inner core comprises from 80 to 95 wt%, more preferably from 84 to 92 wt%, of the total weight of the string;
the thickness of the sheath represents from 2% to 7%, preferably from 3% to 6%, of the total thickness of the string;
the thickness of the inner core represents 93% to 98%, preferably 94% to 97%, of the total thickness of the string;
-the thickness of the inner core is between 1200 and 1500 microns and the thickness of the sheath is between 20 and 50 microns;
-the second material further comprises at least one additive selected from a slip agent and a hydrophobic agent;
-obtaining a monofilament string by co-extrusion of the inner core and the sheath.
Another object of the present invention is a method of making a monofilament string of a racquet as described above, said method comprising co-extruding a core and a sheath to produce a string, and at least one stretching step of the string.
According to other optional features of the method:
-the method further comprises the steps of:
-a first stretching of the co-extruded string by applying a first predetermined traction force, wherein the ratio of the length of the co-extruded string in stretched state to the length of the co-extruded string in relaxed state is between 1 and 10, preferably between 3.5 and 4.5,
-a second stretching of the string by applying a second predetermined traction force, wherein the ratio between the length of the co-extruded string in stretched state and the length of the co-extruded string in relaxed state is between 1 and 2, preferably between 1.05 and 1.55;
-the first stretching step and the second stretching step are consecutive. In other words, a second stretch is applied immediately after the string returns to a relaxed position in the first stretch;
the first stretching step and the second stretching step are preferably sequential. In other words, after the first stretching, the string is left standing for a predetermined time and then the second stretching is performed;
-adding at least one additive selected from a slip agent and a hydrophobic agent to the second material in the co-extrusion step. Preferably, the at least one additive is added continuously during at least a portion of the co-extrusion step. Furthermore, at least one additive is preferably added to the second material at the outer surface of the sheath.
Another object of the present invention is a racket comprising a set of monofilament strings as described above.
Drawings
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:
FIG. 1 is a cross-sectional view of a monofilament string of the present invention;
FIG. 2 is a schematic view of a racquet including a set of monofilament strings according to the present invention;
figure 3 is a graph showing the elastic deformation of a monofilament string according to the invention compared to existing monofilament strings and multifilament strings,
fig. 4 is a graph showing the tension retention of a monofilament string according to the invention compared to existing monofilament and multifilament strings.
Detailed Description
The invention provides a monofilament string of a racket.
According to fig. 1, a
The following gives definitions of several terms used further in this specification.
The term "stiffness" as used herein refers to the tensile modulus (also referred to as "young's modulus" or "elastic modulus") of a material. Materials with high stiffness exhibit a higher tensile modulus and lower elasticity.
The term "geometric stiffness" as used herein is similar to the term "rigidity", but relates to structure. The geometric stiffness of the structure depends on the rigidity of the materials used and their dimensional characteristics.
Referring to fig. 1, the core 2 is made of a first material comprising a first copolymer of
By way of example, the tensile modulus of
The mechanical properties of the copolymer PA6/6.6 are generally between those of
Likewise, the tensile strength of the copolymer PA6/6.6 is between that of
The first material is selected to have a tensile modulus greater than the tensile modulus of the second material.
For this purpose, the first material comprises, in addition to the first copolymer PA6/6.6,
Thus, the inner core 2 provides the
One result is that the racket 5 enables the player to slow down the ball after catching and hitting it, thereby giving better control over the ball. Another result is that the player is subjected to less shock and impact when hitting the ball to obtain better comfort and thus to prevent injuries (e.g. tennis elbow in the case of a tennis racket).
Preferably, the sheath does not comprise
Similarly, the amount of
Thus, the tensile modulus of the second material (sheath) is lower than the tensile modulus of the first material (core). Thus, the second material is more elastic than the first material, absorbing less energy and releasing more energy when elastically deformed.
Thus, the sheath 3 provides the
One result is that the racquet allows the player to accelerate the ball strongly when hitting the ball.
The
Co-extruding the core 2 and the sheath 3 forms an interface 4 at the contact area between the core and the sheath (where the core and the sheath are in close connection).
As previously mentioned, the inner core 2 and the sheath 3 of the
The strong mechanical and chemical cohesion of the inner core 2 and sheath 3 at the interface 4 shown in fig. 1 allows the core and sheath to act in concert when mechanical requirements are placed on the string, further improving the overall mechanical properties of the string, particularly durability and the ability to influence the rotation of the ball.
In the string, the weight proportion of the sheath 3 is small compared to the weight proportion of the inner core 2. In particular, the jacket preferably comprises from 5 to 20 weight percent, more preferably from 8 to 16 weight percent of the total weight of the
In terms of thickness, the sheath 3 has a thickness of 2% to 7%, preferably 3% to 6%, of the total thickness of the
In more detail, the thickness of the sheath preferably ranges from 20 to 50 microns, while the thickness of the core (corresponding to the diameter) ranges from 1200 to 1500 microns.
Such a high weight ratio of the inner core relative to the sheath, along with the composition of the first and second materials of the inner core and sheath, provides the string with a high degree of control.
Surprisingly, the sheath, despite its lower weight proportion, is sufficient to provide the string with a higher amount of force (particularly by imparting explosiveness to the string). In this context, "burst" means that the racquet returns at an extremely rapid rate.
Thus, the combination of the core and sheath provides a good balance between control and strength.
Of course, depending on the intended mode of movement of the user, the composition and proportions of the core and sheath may be adjusted to provide the best compromise between control and strength.
Another aspect that affects the force properties of the racquet strings is the sliding of the strings relative to each other and the frictional forces created by the contact of the strings as they slide. In more detail, when a player hits a ball, the ball hits the strings causing them to bend and thus causing them to slide relative to each other in a first direction when pressed against each other. After striking the ball, the ball moves away from the string, returning the string to its original rest position, and slides relative to each other in a second direction opposite the first direction.
To reduce the frictional forces between the strings during sliding, the jacket advantageously includes one or more additives that promote sliding of the strings relative to each other, thereby providing the strings with enhanced dynamic and elastic capabilities (typically enhanced force capability).
The additive is preferably selected from the group consisting of slip agents and hydrophobing agents.
In the case of the slip agent, preferred additives are selected from: erucamide (e.g. stearyl erucamide), ethylene bis stearamide, polyamido polydimethylsiloxane, polyamido siloxane with ultra high molecular mass, fluorine based polymer, polymer with molybdenum disulfide.
Among the hydrophobing agents, preferred additives are selected from: siloxane-based polymers, polydimethylsiloxane-based polymers, silica-based compounds, ceramic nanoparticle-based compounds having ultra-high molecular mass.
For the purpose of reducing the friction between the strings during sliding, particularly during the manufacturing of the strings, a coating of such additives or other substances may also be applied to the outer peripheral surface of the sheath.
According to one embodiment, a coating may be applied on the outer surface of the sheath in addition to (or instead of) the slip agent or hydrophobic agent present in the sheath. The coating may have anti-slip properties and/or water-repellent properties.
The
the ability to absorb shocks provided by the lower elasticity of the core 2;
the dynamic and elastic capacity provided by the high elasticity and low friction of the sheath 3;
higher durability and reduced structural and tensile deterioration over time and use due to the relatively higher tensile modulus of
the aforementioned properties of the string, as well as the overall mechanical properties, are further improved by the co-extrusion of the core and sheath, and the formation of the interface 4 between the two.
Thus, the monofilament string exhibits a good balance between output and control properties, while also having good comfort and durability.
Another aspect of the invention relates to a method of making the monofilament string disclosed above.
The first step of the method is co-extrusion of the inner core and sheath to produce a string. According to the general principle of co-extrusion, an extrusion die is provided in which an extruded strand of a first material is intended to form the inner core of the string and an extruded strand of a second material is intended to form the sheath of the string.
As described above, the co-extrusion of the inner core and sheath results in the formation of an interface at the contact area of the inner core and sheath, thereby improving the mechanical properties of the string.
At least one of the aforementioned additives may be added (preferably continuously) during at least a portion of the coextrusion step. Furthermore, the additive is preferably added to the second material at the outer surface of the sheath.
The method further includes stretching the monofilament string under determined temperature and humidity conditions.
The method further includes first stretching the string by applying a first predetermined pulling force to the string. The value of the tractive effort is selected according to the following conditions:
tensile strength and elongation at break of the string (both measurable by suitable tensile tests),
the desired mechanical properties of the manufactured string.
This first drawing can be carried out directly after the removal of the monofilament from the extrusion die.
Advantageously, the string is stretched a second time by applying a second predetermined pulling force to the string. The value of the second traction force is preferably smaller than the value of the first traction force.
The stretch ratio (the ratio of the length of the coextruded string in the stretched state to the length of the coextruded string in the relaxed state) is preferably between 1 and 10 for the first stretch, more preferably between 3.5 and 4.5, and between 1 and 2 for the second stretch, more preferably between 1.05 and 1.55.
Since the core and sheath are intimately connected by a co-extrusion process, stretching has an effect on the mechanical properties of both the core and sheath.
According to a first embodiment, the first stretching step and the second stretching step are consecutive. A second stretch is applied immediately after the string returns to a relaxed position in the first stretch.
According to a second embodiment, the first stretching step and the second stretching step are sequential. After the first stretching, the string is left to stand for a predetermined time and then stretched for a second time.
Each drawing step increases the tensile modulus of the inner core and the sheath, wherein the sheath is more affected than the inner core. This increases the geometric stiffness of the string and provides high mechanical stability to the string, in particular increased tension retention.
The elastic deformation of the string after the stretching step is indeed reduced compared to the string before the stretching step and remains substantially stable over a long period of time when in use.
Of course, more than two sequential or sequential stretching steps may be performed without departing from the scope of the invention.
Monofilament strings as described above may be used in tennis rackets, squash rackets, badminton rackets, etc., a group of such monofilament strings being stretched in two orthogonal directions through the frame of the racket.
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