EP2083928B1

EP2083928B1 - Buffer layer for strings

Info

Publication number: EP2083928B1
Application number: EP07864530A
Authority: EP
Inventors: Zvi Yaniv; Yunjun Li; Dongsheng Mao
Original assignee: Applied Nanotech Holdings Inc
Current assignee: Applied Nanotech Holdings Inc
Priority date: 2006-11-16
Filing date: 2007-11-16
Publication date: 2011-10-26
Anticipated expiration: 2027-11-16
Also published as: US20080124546A1; JP2010510400A; ATE530230T1; WO2008061229A1; TW200840890A; CN101534909A; EP2083928A1; WO2008061229A9

Abstract

A thin buffer layer is used to coat on the multi-filament wrapped string to fill the gaps. The polymers of the buffer-layer coating have a high melt-flow (low viscosity) during coating process to fill all the gaps between the filaments, and the filaments are fixed by the coatings onto base core materials.

Description

BACKGROUND

The strings for sports equipment (e.g., tennis racquets) or musical instruments are usually coated with a thin layer at their outmost surface to improve their durability, spin, feeling, etc. Polyamide (nylon), polyester, and other polymers have been used to coat on strings. Nanocomposites, such as clay and carbon nanotube reinforced nylon 6 nanocomposites, having better physical properties than neat nylon 6, are of a potential to be highly durable string coating materials with other functionalities. The reinforcing polymeric composites using nano-sized clay particles with high aspect ratio have been investigated since the 1980's (see U.S. Patent No. 4,739,007 ). Strings are usually polymer materials with a multi-layer structure - core filament, wrapping filaments on the core filament, and coating. For the strings with multi-layer structures, coating materials are required to match the base materials and have good melt-flow properties (acceptable viscosity) at certain temperature to allow them to be penetrated into the gaps between the wrapping filaments. Viscosity of a nanocomposite is usually higher than neat nylon 6 at the same temperature. Thus, the nanocomposite may not easily penetrate into the gaps between the wrapping filaments. Figure 1 shows an SEM image of a cross-section view of a nylon 6/clay nanocomposite coated on a wrapping filament. It can be seen that the nanocomposite material did not successfully fill out the gaps. Many defects were left in the string which will result in unacceptable durability of the strings. The gaps will result in chipping-off or unacceptable durability of coatings during high impact hitting of balls. More over, due to creation of the gaps, coatings also fail to a fix the filaments on the core materials of the string. Figure 2 shows the chipped materials from filaments and coatings after high impact tests on the strings.
US 6,460,321 discloses a racquet string comprising a core surrounded by at least one sheath, having a plurality of sheath fibres wound around said core, and a coating resin uniting the core and sheath fibres into a unitary body. The sheath fibres are helically wound about the core at a high wind angle, i.e., at a wind angle between 25 and 40 degrees relative to the core axis. Preferably, the sheath comprises a plurality of main sheath fibres and a plurality of non-main sheath fibres, and the core, the main sheath fibres, and the coating resin are transparent. Preferably, the non-main sheath fibres have a relatively low transparency. In this manner, the non-main fibres produce a multi-helix appearance when the string is observed from the side.

SUMMARY OF THE INVENTION

The present invention provides a string for sports equipment (e.g. tennis rackets) or musical instruments, comprising a core filament wrapped with a plurality of wrapping filaments of a smaller diameter than the core filament, characterized by the following combination: a buffer layer coating filling in gaps between the wrapping filaments and between the wrapping filaments and the core filament, the buffer layer coating being a melt extruded nylon; and an outer composite coating covering over the buffer layer coating, wrapping filaments and core filament, wherein the outer composite coating comprises a composite of nylon and a material selected from clay, carbon nanotubes, ceramic particles such as SiO₂ and Al₂O₃, or glass particles

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows an SEM image of a cross-section view of a nylon 6/clay nanocomposite coated on a wrapping filament;
Figure 2 shows an SEM image of chipped materials from filaments and coatings after high impact tests on a string;
Figure 3A illustrates a cross-section of a core filament with wrapping filaments surrounding it;
Figure 3B illustrates a buffer layer applied onto the wrapping filament;
Figure 3C illustrates a coating applied onto the buffer layer; and
Figure 4 illustrates another embodiment of the present invention.

DETAILED DESCRIPTION

Although polymer nanocomposites have higher physical/mechanical properties than neat polymer materials, they normally have higher viscosity or melt-flow during an extrusion or coating process. To solve this problem, a thin buffer layer is used to coat on the multi-filament wrapped string to fill the gaps. The polymers of the buffer-layer coating have a high melt-flow (low viscosity) during coating process to fill all the gaps between the filaments, and the filaments are fixed by the coatings onto base core materials. More particularly, the invention provides a string for sports equipment (e.g. tennis rackets) or musical instruments as described above under the heading "Summary of the Invention".

Example 1: A coating system with a nylon 6 buffer layer

Figure 3A illustrates a cross-section of a string for coating comprised of one monofilament core 301 wrapped with smaller-diameter multi-filaments 302. Neat nylon 6 pellets as may be obtained from UBE Industries Inc. (product name: UBE SF 1018 A) are melted. The buffer layer coating 303 is applied by an extrusion process at temperatures ranging from 220°C to 270°C. The thickness of the buffer layer 303 may be from 10 to 100 micrometers. The gaps between the multi-filaments 302 are fully filled by the neat nylon 6 coating.
A wear-resistant coating 304 is then coated (Figure 3C) by an extrusion process at temperatures ranging from 240°C to 280°C. A nylon 6/clay or nylon 6/carbon nanotube nanocomposite may be employed as the wear-resistant coating material 304. The nylon 6 nanocomposite produced by in-situ polymerization may contain 4% nano-clay filler. Other nylon 6 nanocomposites produced by melt-compounded process may also be used for the wear-resistant coatings 304. Except for the clay, carbon nanotubes, ceramic particles such as SiO₂ and Al₂O₃, or glass particles may be used to make nylon6 nanocomposites. The Nylon 6 nanocomposites may also be modified by rubber modifiers to improve the ductility and toughness. The thickness of the wear-resistant coating may be from 1 to 100 micrometers.

Example 2: A coating system with a nylon 11 buffer layer

Again referring to Figure 3A, the string for coating is one monofilament core 301 wrapped with smaller-diameter multi-filaments 302. Neat nylon 11 may be obtained from ARKEMA Inc. Nylon 11 has a very good melt flow at temperatures over 220°C. Good impact strength and shear strength also make nylon 11 a good buffer layer material. In Figure 3B, the buffer layer coating 303 is applied by an extrusion process at temperatures ranging from 190°C to 270°C.
The thickness of the buffer layer 303 may be from 10 to 100 micrometers. The gaps between the multi-filaments 302 are fully filled by the neat nylon 11 coating.
Referring to Figure 3C, a wear-resistant coating 304 is then coated by an extrusion process at temperatures ranging from 240°C to 280°C. Nylon 6/clay or a nylon 6/carbon nanotube nanocomposite may be employed as the wear-resistant coating material 304. The nylon 6 nanocomposite produced by in-situ polymerization may contain 4% nano-clay filler. Other nylon 6 nanocomposites produced by melt-compounded process may also be used for the wear-resistant coating 304. The nylon 6 nanocomposites may also be modified by rubber modifiers to improve the ductility and toughness. The thickness of the wear-resistant coating 304 may be from 1 to 100 micrometers.
Except for the extrusion process to deposit a coating on the string, other methods such as spraying, dipping, spin coating, brushing, painting, and immersing processes can be used to deposit a coating on the surface of strings. Nylon 6 nanocomposites may be melted at higher than 190°C and extruded to deposit a coating on the strings. Nylon 6 nanocomposites may be dissolved in a solvent such as formic acid and sprayed, dipped, spin coated, brushed, painted, or immersed to deposit a coating on the string at room temperature or elevated temperatures. The solvent may be then removed by a follow-up process such as an evaporation method.
Figure 4 illustrates another embodiment of the present invention. Essentially, the coated string structure of Figure 3C is then coated again with smaller-diameter multi-filaments 401. A buffer layer coating 402, similar to layer 303, is applied by an extrusion process at temperatures ranging from 190°C to 270°C. The thickness of the buffer layer 402 may be from 10 to 100 micrometers. The gaps between the multi-filaments 401 are fully filled by the neat nylon 11 1 coating. A wear-resistant coating 403 is then coated by an extrusion process at temperatures ranging from 240°C to 280°C. Nylon 6/clay or a nylon 6/carbon nanotube nanocomposite may be employed as the wear-resistant coating material 403. The nylon 6 nanocomposite produced by in-situ polymerization may contain 4% nano-clay filler. Other nylon 6 nanocomposites produced by melt-compounded process may also be used for the wear-resistant coating 403. The nylon 6 nanocomposites may also be modified by rubber modifiers to improve the ductility and toughness. The thickness of the wear-resistant coating 403 may be from 1 to 100 micrometers.

Claims

A string for sports equipment (e.g. tennis rackets) or musical instruments, comprising a core filament (301) wrapped with a plurality of wrapping filaments (302) of a smaller diameter than the core filament, characterized by the following combination:
a buffer layer coating (303) filling in gaps between the wrapping filaments (302) and between the wrapping filaments (302) and the core filament (301), the buffer layer coating (303) being a melt extruded nylon; and

an outer composite coating (304) covering over the buffer layer coating (303), wrapping filaments (302) and core filament (301), wherein the outer composite coating (304) comprises a composite of nylon and a material selected from clay, carbon nanotubes, ceramic particles such as SiO₂ and Al₂O₃, or glass particles.
The string of claim 1, wherein the buffer layer coating (303) comprises nylon 6 or nylon 11.
The string of claim 1 or claim 2, wherein the outer coating (304) comprises a composite of nylon and clay nanoparticles or a composite of nylon and carbon nanotubes.
The string of claim 3, wherein the outer coating (303) further comprises a rubber modifier.
The string of claim 1, further comprising:
another plurality of wrapping filaments (401) wrapped around the outer coating;

another buffer layer coating (402) filling in gaps between the another plurality of wrapping filaments; and

another outer coating covering (403) over the another buffer layer coating.
The string of any preceding claim, wherein the nylon buffer layer is between 10 and 100 micrometers thick.
The string of any preceding claim, wherein the coating (304) is between 1 and 100 micrometers thick.
The string of claim 1, wherein the outer coating (304) comprises a composite of nylon and glass particles or a composite of nylon and ceramic particles.
A method for coating a string for sports equipment (e.g. tennis rackets) or musical instruments, comprising wrapping a core filament (301) having a first diameter with one or more wrapping filaments (302) having a second diameter that is less than the first diameter; characterized in that the method further comprises:
extruding a melted nylon (303) into gaps between the one or more wrapping filaments (302) and into gaps between the wrapping filaments (302) and the core filament (301); and

extruding a composite coating (304) on a circumference of the string so that it covers the one or more wrapping filaments (302) and the melted nylon (303) in the gaps, wherein the composite coating (304) comprises a composite of nylon and clay nanoparticles, or a composite of nylon and carbon nanotubes, or a composite of nylon and ceramic particles, or a composite of nylon and glass particles.
The method of claim 9, wherein the melted nylon (303) comprises nylon 6 or nylon 11.
The method of claim 9 or claim 10, wherein the outer coating (304) comprises a composite of nylon and clay nanoparticles or a composite of nylon and carbon nanotubes.
The method of claim 11, wherein the outer coating (303) further comprises a rubber modifier.
The method of any of claims 9 to 12, wherein the nylon buffer layer is between 10 and 100 micrometers thick.
The method of any of claims 9 to 13, wherein the coating (304) is between 1 and 100 micrometers thick.
The method of claim 9, wherein the outer coating (304) comprises a composite of nylon and glass particles or a composite of nylon and ceramic particles.