Textile for tennis ball covering and method for manufacturing the same

Abstract: A fabric for use as a tennis ball covering and method to manufacture the same. The fabric has a felted outer surface composed of entangled fibres, said outer surface being provided with a three dimensional pattern thereon.

Description: FIELD OF THE INVENTION This invention relates to a textile for use in the manufacture of tennis balls and to a method of manufacturing the same. BACKGROUND OF THE INVENTION Conventionally, tennis balls are manufactured with the use of a textile having a felted surface. This means that the outer surface of the ball presents a layer of entangled fibres. The felt has a significant influence on the flight characteristics and feel of a tennis ball. Over the last 50 years a large number of attempts have been made to propose other types, (generally cheaper or having an increased resistance to wear) of non-felted tennis ball covering but they have been found unsuccessful to equal the feel and characteristic of the felted fabric and to replace the classic felted covering. FR1158200 describes a method of manufacturing tennis balls, in which a relief pattern is created by cutting lines in the fabric covering of the ball. US Patent No. 4,874,169 describes a game ball having various types of depressions on one of its hemisphere. One particular ball is a tennis ball (see Fig. 5) having one hemisphere covered with a standard tennis ball covering and another covered by a plastic-like smooth material having grooves radiating from its pole. It has been further proposed in US Patent no. 1,287,766 to replace the standard fabric covering of the tennis ball by a smooth and soft rubber-like material. Said rubber covering is provided with regular holes in order to mimic the skin friction of a standard tennis ball felt cover. US Patent No 4,616,828 describes a tennis ball having a deep groove extending in the rubber spherical core of the ball in order to control the air turbulence during the ball trajectory. In one embodiment it is proposed to cover the ball with a non-felted fabric made of woven synthetic filaments or fibres. These synthetic filaments are woven so as define a series of rectangular areas. In US Patent No. 1,376,778 it is proposed to protect the seam of the textile and to produce a better controlling effect by compressing the outer fabric once provided on a tennis ball at various points along the seam. However, applying pressure to the tennis ball is not recommended as the pressure may alter the internal shape of the core of the ball. Also, compressed area obtained by such compression method are not very wear-resistant and disappear rapidly when used on a tennis ball. A problem with the modern game of tennis is that as players become more and more powerful, less skill is needed to play the game. The game is fast and rarely are more than two or three shots played in a rally. This makes the games less enjoyable for spectators. It would be desirable to have a felted tennis ball covering which would allow for greater control over the flight of the tennis ball. More particularly it would be desirable to have a felted tennis covering which, when applied to a tennis ball, alters substantially the flight and/or rebound characteristics when spin is imparted by the player to the ball. This would allow tennis players by imparting spin to various degrees to cause the ball to vary its course to a differing extent as it flies through the air and also to achieve a greater deviation from the expected path of the ball's rebound from the court. SUMMARY OF THE INVENTION According to a first aspect, the present invention provides a tennis ball covering fabric said fabric having a felted outer surface composed of entangled fibres, said outer surface being provided with a three dimensional pattern thereon. The fabric comprises at least a support layer and an outer layer, said outer layer having a pattern cut through it and being affixed on the support layer to create said three dimensional pattern. Advantageously, the support layer includes a scrim and constitutes between 40 and 70% of the weight of the fabric. It is preferred that the fabric be provided with a pattern of regular indentations on the surface of the fabric. Advantageously the pattern can be a pattern of dimples, eventually circular in shape. The indentations may be to between 30% and 70% of the full thickness of the fabric and each indentation may have a diameter which is at its widest part between 5mm and 20mm. It is further preferred that the indentations be separated by a portion of full thickness textile. It is further preferred that the three dimensional pattern be formed on the fabric before the fabric is applied to a tennis ball. The invention also provides a method of manufacturing a fabric according to the first aspect of the invention, which comprises providing at least a support layer and an outer layer, said outer layer having a pattern cut through it and affixing said outer layer on the support layer to create said three dimensional pattern. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the present invention will now be described, by the way of example only, with reference to the accompanying drawings in which: Fig 1 is a schematic cross-sectional view of a piece of a standard woven felt; Fig 2 is a schematic diagram representing a tennis ball travelling from left to right and showing the resultant Magnus force on the ball; Fig 3 is a schematic plan view of an outer layer of fabric used to make a fabric for covering a tennis ball according to the invention. Fig 4 is a schematic representation of the two layers of fabric used to make a sheet of fabric for covering a tennis ball according to the invention being brought together to form said fabric for covering tennis ball. Fig 5 is a schematic cross-sectional view of a fabric according the invention showing the general profile of a dimple. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The material usually used to cover a tennis ball is a felted fabric which can be either non-woven or woven. However, woven felt like the one shown in Fig 1 is preferred in order to achieve covering of a better quality and in particular wear-resistance. The standard woven felt 10 shown in Fig. 1 consists of a cotton warp yarn 12 and a wool/nylon weft yarn 14 which are woven together. An outer surface of entangled fibres 16 gives the fabric 10 a felted appearance. The felted surface 16 is the outer or playing surface, once the woven felt 10 is used to cover a tennis ball. In the fabric 10 each weft yarn 14 interlaces every six warp yarn 12. This frequency may vary from five to ten warp yarns or threads 12 and is typically seven. Usually the overall thickness of a woven felt 10 as the one shown in Fig 1 is uniform and typically between 2.5 and 3.8mm. However the thickness depends on the end product style and the measurement method carried out. Tennis balls can be made to curve in flight by imparting spin due to the physical phenomenon known as the "Magnus Effect". Air is a fluid medium. When a ball flies through the air its passage displaces the air but it also carries some air with it close to the surface of the ball. This is known as the "boundary layer". If the ball is spinning it imparts a spinning motion to the air in the boundary layer. The motion imparted to the boundary layer affects the way the air flow separates from the surface at the rear of the ball. Boundary layer separation is delayed on the side of the ball which is moving in the same direction as the free air flow, and occurs prematurely on the side moving against the free air flow. The turbulent wake of the ball is thus moved towards the side of the ball moving against the free air flow resulting in the flow past the ball being deflected and the resulting change momentum flux causes a force in the opposite direction. Fig 2 is a schematic diagram representing a tennis ball 2 travelling from left to right and spinning in a clockwise direction and shows the resultant Magnus force on the ball 2. Thus, were this illustrating topspin, the ball 2 would be deflected downward by the Magnus Force. The strength of the Magnus effect is in direct proportion to the rate of spin, the speed of the ball 2, the density of the air and the thickness of the boundary layer. It is believed that a felted covering associated with the patterned surface of the tennis ball increases the thickness of the boundary layer around the ball and also helps to increase the friction between the racquet and the ball when the ball is struck. The combination of the thicker boundary layer together with the player's ability to impart increased spin due to better 'grip' on the ball increases the Magnus Force and thus the degree of 'curve' imparted to the ball. A method of producing a patterned tennis ball felt is described as follows. This method is appropriate for producing patterned felt using non-woven technology. With this method two separate layers of standard needle felt material are produced and subsequently needled together. Preferably, one, the bottom layer, contains the support scrim, while the second, top or outer layer, contains no scrim. Each layer can be structured for fibre content, weight and needling density to optimise the end product performance. Preferably the bottom layer, including the scrim, will constitute between 40% and 70% by weight of the material. Preferably the scrim will be warp knitted from polyamide or polyester filament yarn. After pre-needling the top layer is processed through a stamping or die-cutting machine which punches out sections of material in a pre-determined pattern forming a punched fibre matrix. The hole size, shape and pattern punched out can be altered according to the requirements for the finished material. Preferably the punched holes are circular in shape with a diameter of between 5mm and 20mm. Preferably the holes are punched in a regular pattern. Preferably the holes so punched are separated by material with a width of between 50% and 150% of the diameter of the holes. Fig 3 shows a view of a possible punched piece of pre-needled top layer of a felted fabric 41, advantageously a felt. In this case the felt 41 has a pattern of 10mm circular holes 43 punched from it at 15mm centres. The holes 43 are set in parallel rows each row offset by 7.5mm. Obviously, in other embodiments these dimensions will vary depending on the desired hole shape and pattern. The two layers of felt, the bottom layer containing the scrim and the top layer containing the punched holes, are then needled together to form a single composite material. Fig 4 shows a cross sectional representation of the two layers of pre-needled felt being brought together to form the composite fabric 40. The outer layer 41 is punched with holes 43. The bottom layer contains the scrim 47. The composite needled fabric 40 may, if required, be subjected to finishing processes to enhance the aesthetic and wear characteristics of the felt and ball. A further possibility would be to pass a piece of felt through a conventional Calendering Machine. This would involve passing the felt between heated rolls under pressure. The roll pressing on the top (i.e playing) surface of the felt would have a embossed pattern which would be a "negative" of that required for the felt. The pressure and heat applied would compress the felt and set it into the desired pattern. According to another possibility, the dimples may be provided using conventional textile patterning techniques. For example, the textile patterning process described in US-A-5404626 (known as the MILLITEX process) may be used. However these two last methods (ie the Millitex process and the compression process) are less preferred. Fig 5 represents a cross-sectional schematic view of a woven fabric 50 made according to the invention having the preferred circular dimples 58 in the felted layer 56. Fig 5 aims to represent the general profile of such dimples 58. The actual structure of the fabric 50, and especially the felted layer 56, may vary depending of the method used to manufacture it. Woven felt produced as described above thus can be used by the ball manufacturer without any significant modification to the covering process. The back side of the fabric is smooth enough to be coated with adhesive in the conventional manner and dumbbell shapes, when cut, can be fitted to the ball core using standard semi-automatic covering equipment. Tennis balls made using the textile of the present invention have significant advantages over known tennis balls, for example because of the improved flight characteristics. Tennis players can exercise a far greater degree of control over the ball, and hence their game. Modifications and improvements may be made to the foregoing without departing from the scope of the claims.

Claims: A tennis ball covering fabric (40), said fabric having a felted outer surface composed of entangled fibres, said outer surface being provided with a three dimensional pattern (43) thereon, said fabric comprising at least a support layer (46) and an outer layer (41), characterised by said outer layer (41) having a pattern (43) cut through it and being affixed on the support layer (46) to create said three dimensional pattern. The fabric of Claim 1, wherein the support layer (46) includes a scrim (47) and constitutes between 40 and 70% of the weight of the fabric. The fabric of Claim 1 or Claim 2, wherein the three dimensional pattern (43) is a pattern of regular indentations on the surface of the fabric. The fabric of any one of Claims 1 to 3, wherein the three-dimensional pattern (43) is a pattern of dimples. The fabric of any one of Claims 1 to 4, wherein the indentations are circular in shape. The fabric of any one of Claims 1 to 5, wherein the indentations are to between 30% and 70% of the full thickness of the fabric. The fabric of any one of Claims 1 to 6, wherein the each indentation has a diameter which is at its widest part between 5mm and 20mm. The fabric of any one of Claims 1 to 7, wherein the indentations are separated by a portion of full thickness textile. A method to manufacture the fabric of Claim 1, which comprises the steps of providing at least a support layer (46) and an outer layer (41), said outer layer having a pattern (43) cut through it, and affixing said outer layer (41) on the support layer (46) to create said three dimensional pattern.

Inventors: BRASIER ALAN JOHN, BRASIER, ALAN JOHN
Applicants: MILLIKEN IND LTD, MILLIKEN INDUSTRIALS LIMITED
Application year: 1999
Main classification: A63B39
IPC codes: D03D13, D04H1, D03D27, B32B5, A63B39