Technical Field

The present invention relates to a padel racquet, the hitting area of which is modified by the use of a material that improves its surface properties.

Background Art

Padel is a racquet sport that combines elements of tennis, squash and racquetball, wherein during the game players can, within the framework of the rules, also use the walls that partially line the playing court to their advantage.

According to the international rules of this game, a padel racquet consists of two parts: a head and a handle. The handle can have a maximum length of 20 cm, a maximum width (of the throat, regardless of the free space in the middle) of 50 mm and a maximum thickness of 50 mm. The head length can be variable. The total length of the padel racquet, i.e. the head length plus the handle length, must not exceed 45.5 cm, a maximum width of 26 cm and a maximum thickness of 38 mm. A tolerance of 2.5 % in the thickness is allowed when conducting a check of the racquet measurements. The hitting area of the racquet is perforated with an unlimited number of cylindrical holes, each of which has dimensions from 9 to 13 mm in the central part. In the area of no more than 4 cm around the edge (measured from the edge of the racquet), the holes can have a larger diameter or a different shape with variable length and width. Both sides of the racquet must be flat, but may be smooth or rough.

The head of the racquet consists of a frame or a profile, wherein the frame refers to the part surrounding the hitting area and giving the racquet its hardness and strength; and of the hitting area, which is the most important part of the racquet being the spot with which the player hits the ball. The composition of the hitting area provides the player with a specific game feel and performance. The racquet handle is also known as a shaft, which is usually wrapped with a grip made of rubber or other material, or as a grip, i.e. where the racquet is held.

The popularity of padel in Europe has grown considerably in recent years. The sporting goods market has responded adequately to this increase in popularity and currently offers padel players a wide range of options when choosing a padel racquet, depending on the player's individual needs and preferences, while respecting the requirements set forth in the international rules (listed above). When choosing a padel racquet, the player's playing level (beginner, regular player, advanced or professional), as well as the speed and style of the game, can be taken into account.

Padel racquets currently available on the market tend to be classified a) According to the hardness of the material from which the hitting area is made; b) According to weight, where racquets are divided into lighter (up to 375 grams) or heavier (over 375 grams); and c) According to the balance - low, medium and high balance, which usually corresponds to the shape of the racquet head, which is round, diamond or teardrop-shaped respectively.

The hitting area of the padel racquet is solid and with holes that facilitate the flow of air through the racquet, thus reducing its resistance. This area can be hard or soft and significantly conditions the racquet's performance. The hitting area is most often made of EVA (ethylene- vinyl-acetate - hard) or FOAM (e.g., polyethylene, polyurethane - soft) materials and then covered with various materials depending on the manufacturer, especially fiberglass and carbon fiber.

A softer racquet will make the shots stronger because it has more flexibility and will give the ball extra energy. On the other hand, it provides lower ball control. This means that this type of racquet will help the player defend better (shots fly further from the racquet) and at the same time play stronger and faster volleys. Of course, soft racquets last less than hard ones, as softer materials are easier to wear out.

A hard racquet provides the player with control and strength in the game. However, its use places greater demands on the player's physical condition, as it makes it more difficult to hit the ball, which must be compensated by the strength produced by the player's hand. They therefore need to have a good technique and know how to time individual shots well.

When choosing the weight of the racquet, it is necessary to remember that the lower the weight of the racquet, the easier and faster it can be moved in the course of the game on the court, but at the same time as the weight of the racquet is lower, the power of the shots that can be made with such a racquet will also decrease, especially with growing fatigue in the match. As a general rule, the heavier the racquet, the stronger the shot that can be played. The key to managing the weight of the racquet can be the fact how its weight is distributed, i.e., what is its weight balance. It is essentially an indication of the spot at which the racquet's mass is concentrated on its vertical axis. Balance can therefore be high (weight is centered in the head at the top), medium (weight is situated closer to the handle) and low (weight is very close to the handle).

Padel racquets are known e.g., from the documents EP 3 305 378, EP 3 225 288 or EP 2 658 919. These documents describe various racquet designs, including a racquet core, a hitting area, a frame surrounding the hitting area and a racquet handle, which are intended to increase the durability of the racquet, improve the impact, or improve the grip of the racquet. None of these documents address the properties of the surface of the hitting area with the aim to improve ball control and spin in play.

Document EP 3 197 569 describes a racquet for a ball game, in particular padel or beach tennis, comprising a head and a handle, in which the head is formed by a deformable core material covered with a rigid covering layer of thermoplastic or thermoset foil covering part of the peripheral surface of the core and overlapping each other in different ways at the edge surface of the racquet. The rigid covering layer covering the racquet gives the racquet higher mechanical resistance and homogenous mechanical properties and better vibration absorption.

Patent application US 2015024879 Al describes a racquet for padel with improved hitting area for imparting more spin to the ball and without causing irritation or injury to the player. One of the options for improving the spin of the ball mentioned in the application is roughening the surface of the hitting area but there is no specific technical solution described here how to achieve such improvement. Another issue addressed by the application is players' hands rubbing against the roughened hitting area located near the racquet handle.

Document EP 3501613 describes a method for manufacturing a padel racquet where both the head and handle surfaces comprise a composite material, for example made of glass fibers and/or carbon fibers pre-impregnated with a thermoset resin such as an epoxy resin or a thermoplastic or thermoset material such as polycarbonate or polyethylene while a film based on silicon dioxide is applied to the surface of the head and possibly also the handle before hardening. This film serves directly to decorate the hitting surface or as a base for applying decorative elements of the racquet. The document thus deals with the method of modifying the surface of the head and possibly also the handle with the aim of decorating the racquet and does not deal with the modification of the hitting surface for achieving improved control of the spin of the ball during the game.

Document SE 2050824 Al describes a padel racquet which, in order to improve the player's comfort and game, has a film applied to the hitting area to absorb the vibrations caused by the racquet hitting the ball. This film is made of an elastic material such as synthetic or natural rubber and can be releasably or permanently attached to the hitting area with an adhesive. It may also contain areas with deposited hard corundum particles. The film is applied to the hitting area in order to reduce unwanted vibrations. The document does not address the modification of the hitting area for increasing the friction coefficient between the surface of the hitting area and the ball and achieving better control and spin of the ball during the game.

Some of the mentioned documents, as for instance patent application US 2015024879 Al, EP 3501613, SE 2050824 Al, underline only certain properties of a racquet for padel, which are not featured in the solution according to this invention, what means that they do not address the modification of the hitting area for increasing the friction coefficient between the surface of the hitting area and the ball and achieving better control and spin of the ball during the game.

There are perforated holes in the hitting area of the padel racquet, which are arranged differently depending on the model and manufacturer of the racquet. Their arrangement and number affects the weight and balance of the racquet and its playing characteristics. In addition to being perforated with holes, the hitting area may be smooth or rough, in compliance with the international rules. For most padel racquets, especially at the lower price level, their surface is usually smooth, but there are also racquets on the market the surface of the hitting area of which is modified by various protrusions, grooves, bumps, often forming a decorating or recurring pattern. Currently, especially with more expensive racquets, manufacturers try to influence the result of hitting the ball precisely by roughening the hitting area, which should provide a change in the level of friction between the surface of the hitting area and the ball. Increasing the coefficient of friction between the surface of the hitting area and the ball could give the player the ability to better spin and control the ball in play, which would increase the player's hitting accuracy. There is a need on the market for a padel racquet that has a surface that would demonstrably and significantly (to a significant degree) interact with the ball during play.

Summary of the Invention

The aim of the invention was to provide a padel racquet, the hitting area of which would be improved by roughening in such a way as to increase the coefficient of friction between the surface of the hitting area of the racquet and the ball significantly, which would accordingly affect the racquet’s performance during play in a positive manner. The term "significantly" means an increase in the coefficient of friction not only by a few percent, but at least by several tens of percent, preferably at least a 50 percent to multiple increase in the value of the coefficient of friction.

This task is solved by the subject of an independent patent claim. Preferable further embodiments are provided in the dependent patent claims.

The essence of the invention is thus a padel racquet, the hitting area of which is provided with an epoxy-based resin layer with a thickness of max. 0.5 mm and a surface weight of max. 450 g/m ² , preferably max. 350 g/m ² , and containing coarsening grains. It is preferable to use grains with a size of max. 0.1 mm and a surface weight of 15 to 20 g/m ² . The coarsening grains preferably occupy a maximum of 30 % of the surface created by the epoxy resin layer on the hitting area of the racquet head. These grains are placed in the resin in such a way that there is a layer of epoxy resin under the grains forming a base forthem and anchoring them from below, and at the same time, these grains are covered with a very thin layer of epoxy resin from above as well. This very thin layer of epoxy resin applied to the surface of the grains in a thickness of approximately up to a maximum of 0.04 mm helps anchor the grains in the resin more firmly and, at the same time, serves as an abrasion-resistant layer.

The same resin can be used to anchor the grains from below, as well as to cover them from above, from the point of view of its composition, but it is preferable to use a resin with a higher viscosity (that is, denser, e.g. in the case of using a water-soluble resin, a resin with a lower water content) than the resin used to anchor the grains from below. It would also be possible to use one resin to anchor the grains and a different one to cover them, provided they are compatible and will bond with each other.

The terms "epoxy resin" and "epoxy-based resin" as used herein are equivalent and interchangeable. Also, the terms "epoxy resin layer", "layer of epoxy resin" and "epoxy-based resin layer" as used herein are equivalent and interchangeable.

According to the invention, grains of corundum (aluminum oxide), quartz, silicon carbide, ceramic abrasive, hard plastic, glass and the like can be used as coarsening grains, individually or in combination with each other. The use of corundum grains is preferable.

Epoxy resins are known for their excellent adhesion, chemical and thermal resistance, excellent mechanical properties and are very good electrical insulators.

Because of these great properties of epoxy resin, it is possible to create a layer that is thick enough to anchor the coarsening grains firmly enough, yet thin enough to be applied to the surface of the hitting area of an existing padel racquet with certain claimed properties in terms of the racquet's hardness, weight, shape and balance without significantly changing these declared characteristics of the racquet as a result of using this layer. This means that if the racquet is classified before applying the resin layer as, for example, hard, it will remain so after it is applied, or if the racquet is classified, for example, as a lighter racquet before applying the resin layer, it will remain so after applying, etc. This claim is of course generalized, as the expert will understand that in the case of a racquet with a weight right in between two weight classes, adding even a low weight can move it across the respective limit. Furthermore, the addition of a resin layer containing coarsening grains to the surface of the hitting area of the racquet will provide the above-declared benefit of improved ability to spin and control the ball during the game, thus increasing the accuracy of the player's shot without negatively affecting the bounce of the ball from the racquet. The resulting layer is light, thin, and the increase in the coefficient of friction provides the player with an improved ability to spin and control the ball during play, increasing the accuracy of the shot, while not negatively affecting the bounce of the ball from the hitting area of the racquet.

The object of the invention was not to provide a racquet with an innovative hitting area in the sense of its completely new qualitative composition, but to improve the hitting area of any existing padel racquet by increasing the coefficient of friction without affecting other properties of a specific racquet.

The preferred epoxy resin for application onto the hitting area of a racquet according to the invention is a water-based epoxy resin.

The advantage of the epoxy resin layer with coarsening grains used for application to the hitting area of the racquet according to the invention is also the fact that its shape can be easily adapted to the shape of the sports equipment (different types of racquets - different shape of the hitting area, different sizes, different distribution of holes on the hitting area, possibly no holes at all). Due to the fact that the padel racquet head contains two equal, mutually opposite hitting areas, the epoxy resin layer with coarsening grains can be applied to the surface of only one hitting area of the racquet; alternatively, it can be applied to the surface of both hitting areas of the racquet at the same time. Preferably, an epoxy resin layer containing coarsening grains can be applied to a maximum of 80 % of the surface of the hitting area of the racquet, while also covering the so-called "sweet spot" zone of the hitting area. The "sweet spot" is a zone on the hitting area of the racquet that is most suitable for hitting the ball because it allows the ball to be hit in the most efficient way (gives the most force when hitting the ball with the least effort); it is usually located in the center of the hitting area of a round shaped racquet.

Epoxy resin can be applied onto the surface of the hitting area to create an epoxy resin layer by methods known in the field of technology, and they can generally be characterized as follows:

- either in liquid form, wherein the epoxy resin adheres to the surface, and subsequently, coarsening grains are applied to the thus formed, not yet hardened layer, which are then poured on from above, and the resin layer thus formed is subjected to curing; or

- with the help of a fibrous mesh on which epoxy resin is applied by soaking this mesh in liquid resin and subsequently (while the resin is in a liquid state) it is applied onto the surface of the hitting area of the racquet and with the help of resin, which thus also fulfils the function of glue for the fibrous mesh, it adheres to this surface. If necessary, the total thickness of the layer is adjusted by applying or removing a certain amount of liquid resin, then coarsening grains are applied to the resin, which are then poured on from above and the resin layer created in this way is subjected to curing; or

- the epoxy resin is formed, with the help of a fibrous mesh, into the required form (in terms of shape, size, segmentation, thickness, etc.) outside the hitting area of the racquet with the subsequent application of the coarsening grains described above, and it is cured, while it subsequently adheres to the surface of the hitting area of the racquet with the help of an adhesive or by using heat (i.e. by heating the material).

The use of a fibrous mesh is preferable, as it will additionally provide the resulting resin layer with coarsening grains with additional strength and durability, thereby extending its useful life. As can be seen from the abovementioned, the fibrous mesh is located in the resin layer in the space below the coarsening grains, closer to the surface of the hitting area of the racquet.

Materials commonly used for this purpose, such as synthetic polymer fibers, organic or inorganic fibers, can be used as the fibrous mesh. Suitable examples are cotton, viscose, glass fibers or polymer fibers such as polyester fibers, or combinations thereof. It is preferable to use polyester fibers, such as polyethylene terephthalate, polybutylene terephthalate or polytrimethylene terephthalate. The fibrous mesh that can be used according to the invention has a thickness of max. 0.2 mm, tensile strength min. 300 N and surface weight max. 120 g/m ² , preferably from 80 g/m ² to 120 g/m ² . Preferably, it is possible to treat the fibrous mesh before applying epoxy resin to this mesh in a way that includes impregnation, i.e. impregnation of the mesh with a solution containing various substances, such as styrene-butadiene-acrylonitrile copolymer, acrylate or melamine-formaldehyde resin, or their combination, and it is possible to further apply, for example, a fibrous mesh treatment layer containing acrylate, styrene-acrylate, polyurethane or melamine-formaldehyde resin, or their combination, to the mesh treated in this way. Preferably, the solution for impregnating the mesh contains approximately 47 % up to approximately 53 % water by weight, approximately 17 % up to approximately 23 % styrene-butadiene-acrylonitrile copolymer by weight, approximately 7 % up to approximately 13 % acrylate by weight and approximately 17 % up to approximately 23 % melamine-formaldehyde resin by weight, based on the weight of the solution. The mesh treatment layer preferably contains approximately 7 % up to approximately 13 % acrylate by weight, approximately 37 % up to approximately 43 % styrene-acrylate by weight, approximately 27 % up to approximately 33 % polyurethane by weight and approximately 17 % up to approximately 23 % melamine-formaldehyde resin by weight, based on the weight of the fibrous mesh treatment layer. The thickness of the fibrous mesh treatment layer applied to one side of the mesh is max. 0.04 mm. Preferably, the fibrous mesh treatment layer is applied to both sides of the fibrous mesh (on both the reverse side and the front side of the mesh).

Before impregnation and application of the fibrous mesh treatment layer described above, it is also possible to subject the mesh to further treatments, such as washing and subsequent shape and dimensional stabilization (so-called fixation), for example using high temperatures (150 - 200 °C), and/or dyeing using known procedures and suitable dyes.

In the event that the epoxy resin is applied to the hitting area of the racquet according to the invention only after it is formed outside the hitting area with the help of a fibrous mesh into the desired shape with the subsequent application of coarsening grains to form an epoxy resin layer with coarsening grains and hardened, a layer of adhesive is necessary for this purpose. An adhesive suitable for such a purpose is any suitable adhesive known from the state of the art, which is suitable for use in bonding together synthetic materials such as polymers, composite materials, etc., that is, the materials that form the surface of the padel racquet, with the material that forms the fibrous mesh, or optionally treated with impregnation and/or a fibrous mesh treatment layer containing acrylate, styrene-acrylate, polyurethane or melamine-formaldehyde resin, or a combination thereof, as mentioned above. The thickness of the adhesive used is no more than 0.25 mm. An example of a suitable adhesive is an acrylic adhesive, such as 3M™ High Performance Acrylic Adhesive 468 MP, which is also preferable because, thanks to its properties, it allows the applied layer to be easily removed if necessary (whether due to damage or wear of the epoxy resin layer) by peeling it off and replacing it with a new one.

Curing of the epoxy-based resin layer is carried out by any method for curing epoxy resins known from the state of the art, e.g. using UV light, heat, standing in the air and the simultaneous addition of curing agents to the epoxy resin, such as curing agents based on polyfunctional amines, aliphatic amines, cycloaliphatic amines, polyoxyetheramines, polyamine adducts, phenols, alcohols, thiols, etc.

The epoxy resin layer can also be used as an advertising carrier, wherein the advertisement can be placed either on top of it or, if a transparent epoxy resin is used, the advertisement can be placed under the resin layer.

For this purpose, i.e., to make all layers as transparent as possible, it is also advantageous to use a thin polyester layer in the form of a film, which completely replaces the fibrous mesh. An example of a suitable polyester film used is a product from Mirka Ltd. called Novastar 150. In the event that the epoxy resin is applied to the hitting area of the racquet according to the invention only after it is formed outside the hitting area with the help of a polyester film into the desired shape with the subsequent application of coarsening grains to form an epoxy resin layer with coarsening grains and hardened, a layer of adhesive is necessary for this purpose. An adhesive suitable for such a purpose is any suitable adhesive known from the state of the art, which is suitable for use in bonding together synthetic materials such as polymers, composite materials, etc., that is, the materials that form the surface of the padel racquet, with the material that forms the polyester film. The thickness of the adhesive used is no more than 0.25 mm. An example of a suitable adhesive is an acrylic adhesive, such as 3M™ High Performance Acrylic Adhesive 468 MP, which is also preferable because, thanks to its properties, it allows the applied layer to be easily removed if necessary (whether due to damage or wear of the epoxy resin layer) by peeling it off and replacing it with a new one.

Using a padel racquet with an improved hitting area according to the presented invention, there is some wear of the epoxy resin layer with the coarsening grains. The term "wear of the epoxy resin layer with coarsening grains" is to be understood as a process in which, as a result of the repeated forceful contact of the ball with the resin layer with the coarsening grains, the integrity of the thin resin layer located on the surface of the grains is broken, resulting in the destruction of the structure of the grains, which subsequently break, gradually reducing their size. There may also be some loosening of grains from the resin layer and their gradual falling out. As the wear of the resin layer with coarsening grains on the hitting area increases, the beneficial effect provided by these grains stored in the resin layer gradually decreases, i.e., the coefficient of friction decreases. In the event that, due to the aforementioned wear and tear, the hitting area no longer fulfils the declared purpose, it is necessary to replace the racquet or the resin layer with coarsening grains according to the invention. Here, an embodiment of the invention is shown to be preferred, in which, outside the hitting area of the racquet, the epoxy resin is shaped into the desired form (in terms of shape, size, fragmentation, thickness, etc.) with the help of a fibrous mesh, with the subsequent application of coarsening grains to the resin to form an epoxy resin layer with coarsening grains, which is then cured and provided with a layer of adhesive that allows the already worn resin layer with coarsening grains to be peeled off and simply replaced with a new one. In this preferred embodiment, a polyester fiber mesh is used as the fibrous mesh, which is stabilized in shape and size, impregnated with the above-mentioned impregnation solution, and the above-mentioned mesh treatment layer is applied to it.

Brief description of the drawings

Figure 1 presents a view of a racquet according to the invention with an epoxy resin layer with coarsening grains applied to the hitting area.

Figure 2 schematically presents a detailed cross-sectional view of the epoxy resin layer with coarsening grains applied to the hitting area of the racquet according to the invention of Figure 1, showing the mutual arrangement of the resin and the coarsening grains.

Figure 3 presents a view of the racquet according to the invention in a partially exploded view of the individual layers of the preferred embodiment, while the fibrous mesh treatment layer is applied on both sides of the fibrous mesh.

Figure 4 schematically presents a detailed cross-sectional view of the arrangement of the individual layers of the preferred embodiment of the racquet according to the invention.

Figure 4a schematically presents a detailed cross-sectional view of the alternative arrangement of the individual layers of the preferred embodiment of the racquet according to the invention. Figure 5 presents graphs showing coefficients of friction for various padel racquets with original surfaces of the hitting area and with an epoxy resin layer with coarsening grains applied onto the hitting area.

Figure 6 presents graphs showing coefficients of friction for various padel racquets with original surfaces of the hitting area and with an epoxy resin layer with coarsening grains applied onto the hitting area grouped according to individual racquets.

Figure 7 presents graphs showing aggregated data for all racquets used to measure the coefficient of friction, where graph a) presents the coefficient of friction for all racquets for different added weights, graph b) presents the friction force as a function of added weight, and graph c) presents a direct comparison of friction forces using the increment coefficient of the epoxy resin layer with coarsening grains. Error bars are calculated as the standard deviation of all data per point.

Figure 8 presents the coefficient of rebound for the hitting areas of different racquets with the original surface of the hitting area and with the surface of the hitting area with an applied epoxy resin layer with coarsening grains.

Examples

Individual examples and embodiments of the present invention should be understood as illustrating the present invention, but in no way limiting its scope. Experts in the relevant field of technology will find, or be able to determine using no more than routine experimentation, a number of equivalents to the present embodiments. Even such equivalents will fall within the scope of the attached patent claims.

The thickness measurements of the materials and layers mentioned in this document were carried out using methods and equipment known in the art, such as ultrasonic thickness gauges, calipers or micrometers. Coarsening grain size measurement and control was performed in accordance with FEPA standards.

Example 1

Onto the surface of the hitting area 3 of the racquet, which was degreased using ethyl alcohol, an epoxy resin with a surface weight of 350 g/m ² was applied in a liquid form in a layer of 0.4 mm, into which corundum coarsening grains 6 with a grain size of 0.08 mm and a surface weight of 18 g/m ² were manually applied. The thus applied layer 5a of epoxy resin with coarsening grains 6 was allowed to stand in the air at room temperature and partially cure, and then a layer 5b of epoxy resin was applied in liquid form to this layer, which enveloped the part of the grains protruding into the space. The thickness of this epoxy resin layer 5b was 0.02 mm. The thus applied epoxy resin layer with coarsening grains onto the surface of the hitting area of the racquet was allowed to further harden in the air.

The result of this procedure is a padel racquet with an improved hitting area, which is provided with an epoxy resin layer 5 with a surface weight of 350 g/m ² containing coarsening grains 6 of corundum with a size of 0.08 mm and a surface weight of 18 g/m ² , with a total thickness of the layer applied onto the hitting area of no more than 0.5 mm.

Example 2

Onto the surface of the hitting area 3 of the racquet, which was degreased using a detergent, epoxy resin with a surface weight of 250 g/m ² was applied in a liquid form in a layer of 0.3 mm, into which coarsening grains 6 of quartz with a grain size of 0.07 mm and a surface weight of 20 g/m ² were applied by machine, while the grains occupy a maximum of 30 % of the surface created by the resin layer on the hitting area. The thus applied layer 5 a of epoxy resin with coarsening grains 6 was allowed to stand in the air at room temperature and partially cure, and then a layer 5b of epoxy resin was applied in liquid form to this layer, which enveloped the part of the grains 6 protruding into the space. The thickness of this epoxy resin layer 5b was 0.02 mm. The thus applied epoxy resin layer with coarsening grains onto the surface of the hitting area of the racquet was allowed to further harden in the air.

The result of this procedure is a padel racquet with an improved hitting area, which is provided with an epoxy resin layer 5 with a surface weight of 250 g/m ² containing coarsening grains 6 of quartz with a size of 0.07 mm and a surface weight of 20 g/m ² , which occupy a maximum of 30 % of the surface formed by the resin layer on the hitting area of the racquet, with the total thickness of the layer applied onto the hitting area of no more than 0.39 mm.

Example 3

Onto the surface of the hitting area 3 of the racquet, which was cleaned of dust and dirt with water and degreased using ethyl alcohol, a fibrous mesh 7 of polyester fibers with the following parameters was applied: thickness 0.18 mm (measured according to EN ISO 5084), tensile strength 700 N (measured according to EN ISO 13934-1) and a surface weight of 120 g/m ² . The fibrous mesh 7 was soaked in liquid epoxy resin with a surface weight of 200 g/m ² before being applied onto the surface of the hitting area 3 of the racquet. Partial curing of the resin with the help of a UV lamp with a power of 6 W (UV light was applied to the resin surface for 20 seconds) was started only after it was applied together with the fibrous mesh 7 onto the surface of the hitting area 3 of the racquet in a total layer thickness of 0.3 mm (mesh thickness + resin thickness) and after applying silicon carbide coarsening grains 6 with a grain size of 0.07 mm and a surface weight of 20 g/m ² into the resin, while the grains occupy a maximum of 30 % of the surface created by the resin layer on the hitting area. On the thus partially cured layer 5a of epoxy resin with coarsening grains 6 and reinforcing fibrous mesh 7, a layer 5b of epoxy resin was subsequently applied in liquid form, which enveloped the part of the grains 6 protruding into the space. The thickness of this epoxy resin layer 5b was 0.02 mm. The thus applied epoxy resin layer with coarsening grains onto the surface of the hitting area of the racquet was placed under a UV lamp for 45 seconds and cured. The layer was applied onto the hitting area in such a way that it occupied 60 % of the racquet's surface of the hitting area and covered the "sweet spot" zone of the hitting area allowing it to hit the ball in the most efficient way.

The result of this procedure is a padel racquet with an improved hitting area, which is provided with an epoxy resin layer 5 with a surface weight of 200 g/m ² containing coarsening grains 6 of silicon carbide with a size of 0.07 mm and a surface weight of 20 g/m ² , which occupy a maximum of 30 % of the surface formed by a layer of resin on the hitting area, reinforced with a fibrous mesh 7 of polyester fibers with a surface weight of 120 g/m ² , while the fibrous mesh 7 is placed under the epoxy resin layer 5, with the total thickness of the layer applied onto the hitting area 3 of no more than 0.39 mm, while the layer applied onto the hitting area 3 occupies 60 % of the surface of the hitting area and covers the "sweet spot" zone of the hitting area of the racquet, which allows the ball to be hit in the most efficient way.

Example 4

Onto the surface of both hitting areas 3 of the racquet, which was cleaned of dust and dirt with water and degreased using ethyl alcohol, a fibrous mesh 7 of polyester fibers with the following parameters was applied: thickness 0.15 mm (measured according to EN ISO 5084), tensile strength 500 N (measured according to EN ISO 13934-1) and a surface weight of 80 g/m ² . Before applying the fibrous mesh 7 onto the surface of the hitting area 3 of the racquet, its shape and dimensions were first stabilized by washing and drying for 60 seconds at 180 °C, then it was soaked in liquid epoxy resin with a surface weight of 250 g/m ² . Partial curing of the resin with the help of a UV lamp with a power of 6 W (UV light was applied to the resin surface for 20 seconds) was started only after it was applied together with the fibrous mesh 7 onto the surface of the hitting area 3 of the racquet in a total layer thickness of 0.25 mm (mesh thickness + resin thickness) and after applying silicon carbide coarsening grains 6 with a grain size of 0.09 mm and a surface weight of 15 g/m ² into the resin. On the thus partially cured layer 5a of epoxy resin with coarsening grains 6 and reinforcing fibrous mesh 7, a layer 5b of epoxy resin was subsequently applied in liquid form, which enveloped the part of the grains 6 protruding into the space. The thickness of this epoxy resin layer 5b was 0.02 mm. The thus applied epoxy resin layer with coarsening grains onto the surface of the hitting area of the racquet was placed under a UV lamp for 45 seconds and cured.

The result of this procedure is a padel racquet with an improved hitting area, which is provided with an epoxy resin layer 5 with a surface weight of 250 g/m ² containing coarsening grains 6 of silicon carbide with a size of 0.09 mm and a surface weight of 15 g/m ² , reinforced with a fibrous mesh 7 of polyester fibers with a surface weight of 80 g/m ² , while the fibrous mesh 7 is placed under the epoxy resin layer 5, with the total thickness of the layer applied onto the hitting area of no more than 0.36 mm, with both hitting areas of the racquet being provided with this layer.

Example 5

Onto the surface of the hitting area 3 of the racquet, which was cleaned from dust and dirt with water and degreased using ethyl alcohol, a fibrous mesh 7 made of glass fibers with a thickness of 0.08 mm, a tensile strength of 500 N and a surface weight of 108 g/m ² was applied, which was soaked in liquid epoxy resin with a surface weight of 200 g/m ² before being applied onto the hitting area surface of the racquet. Partial curing of the resin with the help of a UV lamp with a power of 6 W (UV light was applied to the resin surface for 20 seconds) was started only after it was applied together with the fibrous mesh 7 onto the surface of the hitting area 3 of the racquet in a total layer thickness of 0.3 mm (mesh thickness + resin thickness) and after applying ceramic abrasive coarsening grains 6 with a grain size of 0.085 mm and a surface weight of 18 g/m ² into the resin. On the thus partially cured layer 5a of epoxy resin with coarsening grains 6 and reinforcing fibrous mesh 7, a layer 5b of epoxy resin was subsequently applied in liquid form, which enveloped the part of the grains 6 protruding into the space. The thickness of this 5b epoxy resin layer was 0.03 mm. The thus applied epoxy resin layer with coarsening grains onto the surface of the hitting area of the racquet was placed under a UV lamp for 45 seconds and cured. The result of this procedure is a padel racquet with an improved hitting area, which is provided with an epoxy resin layer 5 with a surface weight of 200 g/m ² containing coarsening grains 6 of ceramic abrasive with a size of 0.085 mm and a surface weight of 18 g/m ² , reinforced with a fibrous mesh 7 of glass fibers with a surface weight of 108 g/m ² , while the fibrous mesh 7 is placed under the epoxy resin layer 5, with the total thickness of the layer applied onto the hitting area of no more than 0.405 mm.

Example 6

First, an epoxy resin layer 5 with coarsening grains 6 was prepared outside the hitting area 3 of the racquet using a fibrous mesh 7, which was then applied onto the cleaned and degreased hitting area 3 of the racquet using an acrylic-based adhesive 9. Epoxy resin layer 5 with coarsening grains 6 was prepared outside the hitting area 3 with the help of fibrous mesh 7 in the following way: The fibrous mesh 7 of 100 % polyester with the parameters listed below was dyed, washed and then stabilized in shape and size by stretching it on a frame and drying it for 40 seconds at 195 °C. The parameters of the fibrous mesh used are as follows: surface weight 105 g/m ² , density per 1 cm in warp 28, density per 1 cm in weft 28, fineness of Tex yam 16.5, thickness of mesh 0.16 mm (measured according to EN ISO 5084), tensile strength in warp and weft 600 N (measured according to EN ISO 13934-1). Subsequently, the thus treated fibrous mesh was impregnated with a solution containing approximately 53 % water by weight, approximately 19 % styrene-butadiene-acrylonitrile copolymer by weight, approximately 9 % acrylate by weight and approximately 19 % melamine-formaldehyde resin, based on the weight of the solution. On the fibrous mesh impregnated in this way, a layer 8 for the treatment of the fibrous mesh containing approximately 9 % acrylate by weight, approximately 41 % styreneacrylate by weight, approximately 29 % polyurethane by weight and approximately 21 % of melamine-formaldehyde resin by weight was applied to both sides of the mesh (back and front), based on the weight of the fibrous mesh treatment layer. After applying layer 8 for the treatment of the fibrous mesh, the fibrous mesh 7 had a thickness of 0.17 mm and a surface weight of 135 g/m ² . Subsequently, a layer 5a of a waterborne epoxy resin containing epoxy resin, curing agent and water in a weight ratio of 9:4:3 was applied to one side of the fibrous mesh 7 prepared in this way. Coarsening grains 6 of corundum with a grain size of 0.082 mm (size P180 according to FEPA) and a surface weight of 18 g/m ² were then electrostatically applied to the layer 5a of epoxy resin. A layer 5b of waterborne epoxy resin containing epoxy resin, curing agent and water in a weight ratio of 9:4:2.5 was then applied in liquid form to layer 5a of epoxy resin with coarsening grains 6, which enveloped the protruding part of grains 6. The total thickness of the thus formed epoxy resin layer 5 with coarsening grains 6 reinforced with fibrous mesh 7 prepared in the manner mentioned above in this example was 0.25 mm and its surface weight was 170 g/m ² . The thus prepared epoxy resin layer 5 with coarsening grains 6 reinforced with fibrous mesh 7 was subsequently subjected to heat treatment for 40 min at 90 °C. After heat treatment, 3M™ High Performance Acrylic Adhesive 467 MP adhesive 9 was applied to the mesh-reinforced epoxy resin layer with coarsening grains, with adhesive 9 applied to the side of the mesh 7 with the mesh treatment layer 8 applied, to which the epoxy resin layer 5 with coarsening grains 6 was not applied. The thickness of the epoxy resin layer 5 with the coarsening grains 6 reinforced with the fibrous mesh 7 after the application of the adhesive 9 was 0.31 mm and its surface weight was 300 g/m ² .

The thus prepared epoxy resin layer with coarsening grains was finally cut into the desired shape of the hitting area of the racquet and applied with the help of the mentioned adhesive onto the hitting area of the racquet.

The result of this procedure is a padel racquet with an improved hitting area, which is equipped with an epoxy resin layer 5 containing coarsening grains 6 of corundum with a size of 0.082 mm and a surface weight of 18 g/m ² reinforced with a fibrous mesh 7 of polyester fibers with a surface weight of 105 g/m ² , while the fibrous mesh is impregnated with a solution containing approximately 53 % water by weight, approximately 19 % styrene-butadiene- acrylonitrile copolymer by weight, approximately 9 % acrylate by weight and approximately 19 % melamine-formaldehyde resin, based on the weight of the solution, and on both sides (back and front) the fibrous mesh 7 has an applied fibrous mesh treatment layer 8 containing approximately 9 % acrylate by weight, approximately 41 % styrene-acrylate, approximately 29 % polyurethane by weight and approximately 21 % melamine-formaldehyde resin by weight, based on the weight of the fibrous mesh treatment layer 8. An epoxy resin layer 5 containing coarsening grains 6 is applied to one side of the fibrous mesh 7 with an applied layer 8 for the treatment of the fibrous mesh, and an adhesive 9 is applied to the other side of the fibrous mesh 7 with an applied layer 8 for the treatment of the mesh. The total thickness of the layer applied onto the hitting area of the racquet is 0.31 mm and its surface weight is 300 g/m ² .

Example 7

As an alternative to embodiment in example 6, the fibrous mesh 7 made of 100% polyester, see above, can be replaced with a polyester film of the following parameters: surface weight of 120g/m2 and thickness of 0.15 mm and tensile strength 1000 N. This polyester film does not need to be further treated, so it does not change its parameters mentioned in the previous sentence. Subsequently, a layer 5a of a waterborne epoxy resin containing epoxy resin, curing agent and water in a weight ratio of 9:4:3 was applied to one side of the polyester film 7a prepared in this way. Coarsening grains 6 of corundum with a grain size of 0.082 mm (size Pl 80 according to FEPA) and a surface weight of 18 g/m ² were then electrostatically applied to the layer 5a of epoxy resin. A layer 5b of waterborne epoxy resin containing epoxy resin, curing agent and water in a weight ratio of 9:4:2.5 was then applied in liquid form to layer 5a of epoxy resin with coarsening grains 6, which enveloped the protruding part of grains 6. The total thickness of the thus formed epoxy resin layer 5 with coarsening grains 6 reinforced with polyester film 7a prepared in the manner mentioned above in this example was 0.25 mm and its surface weight was 250 g/m ² . The thus prepared epoxy resin layer 5 with coarsening grains 6 reinforced with polyester film 7a was subsequently subjected to heat treatment for 40 min at 90 °C. After heat treatment, 3M™ High Performance Acrylic Adhesive 467 MP adhesive 9 was applied to the polyester film-reinforced epoxy resin layer with coarsening grains, with adhesive 9 applied to the side of the polyester film 7a, to which the epoxy resin layer 5 with coarsening grains 6 was not applied. The thickness of the epoxy resin layer 5 with the coarsening grains 6 reinforced with the polyester film 7a after the application of the adhesive 9 was 0.31 mm and its surface weight was 400 g/m ² .

The thus prepared epoxy resin layer with coarsening grains was finally cut into the desired shape of the hitting area of the racquet and applied with the help of the mentioned adhesive onto the hitting area of the racquet.

The result of this procedure is a padel racquet with an improved hitting area, which is equipped with an epoxy resin layer 5 containing coarsening grains 6 of corundum with a size of 0.082 mm and a surface weight of 18 g/m ² reinforced with a polyester film 7a with a surface weight of 120 g/m ² . An epoxy resin layer 5 containing coarsening grains 6 is applied to one side of the polyester film 7a, and an adhesive 9 is applied to the other side of the polyester film 7a. The total thickness of the layer applied onto the hitting area of the racquet is 0.31 mm and its surface weight is 400 g/m ² .

Example 8 - Measurement of the coefficient of friction of the surface of the hitting area of padel racquets

The coefficient of friction expresses the maximum share of the normal force (force perpendicular to the surface of the hitting area of the racquet), which can be transferred to the longitudinal force. All friction coefficients were measured for different forces acting on the hitting area of the racquet.

Six different racquets made by Dunlop (racquet 1), Stiga (racquet 2), Adidas (racquet 3), Babolat (racquet 4), Starvie (racquet 5), Bullpadel (racquet 6) were used to measure the friction coefficient, while the weight of the racquets ranged from 0.360 kg to 0.375 kg. For each of them, one hitting area of the racquet was left in its original form, and an epoxy resin layer with coarsening grains reinforced with fibrous mesh prepared by the procedure described in Example 6 was applied to the other hitting area. The racquet was then placed horizontally on a six-ball holder fixed to the table. Weights ranging from 2 kg to 25 kg were placed on the racquet to simulate the different forces acting on the racquet during the ball strike. The horizontal force required to start the racquet movement (along with the weight) was then measured with a precision load cell. Five measurements were taken for each configuration. The friction coefficient was then calculated using the formula where FN is the normal force calculated as the product of the total racquet mass m _r and the added mass m _w and the gravitational acceleration g. FT is the maximum tangential force measured by the load cell. The accuracy of all measurements was 10 mN, i.e. better than 1% for all configurations.

Fig. 5 shows the coefficients of friction for the surfaces of the hitting areas of various racquets. It can be seen that for all the added weights, the coefficients of friction are almost independent of the type of surface of the hitting area of the racquet, but the coefficients of friction with the applied epoxy resin layer with coarsening grains are significantly higher. This is especially interesting with original surfaces - different brands of racquets declare different properties of their surfaces, and these can be partially observed directly. However, in reality, they hardly affect the coefficient of friction, which is the decisive factor in determining a player's ability to spin and control the ball.

Fig. 6 shows the same data grouped by individual racquets. For each of the racquets, it can be seen that the coefficients of friction for smooth surfaces increase slightly with added weight up to about 12 kg (120 N) and then stabilize or even decrease slightly with further increases in power. The situation is different for the sides of racquets with an epoxy resin coating with coarsening grains - coefficients of friction decrease with added weight. Possible causes are listed below.

As it turned out that in reality the properties of the individual racquets have only a very limited effect on the friction coefficients for the original surfaces as well as for the surfaces coated with an epoxy resin layer with coarsening grains, in Fig. 7 we present summary data for all racquets. The first graph 7a corresponds to Fig. 6, while the second graph 7b shows the frictional force per se. It naturally rises with the normal force (added weight) with a slope given by the coefficient of friction. In the last graph 7c, we show the gain of the epoxy layer with the coarsening grains in friction force in percentage (100 % gain means doubling the force). It can be seen that although this gain slowly decreases with increasing force, it can still be stated that the gain is at least 100 % for the entire spectrum of measured forces. This means that a racquet with an epoxy coated hitting area with coarsening grains basically allows you to achieve the same ball spin with significantly less impact (weaker shot).

The results clearly show that an epoxy resin layer with coarsening grains applied onto the hitting area of the racquet leads to a significantly higher coefficient of friction for all configurations. It can be seen that the coefficient of friction for smooth surfaces increased to some extent with added weight and then practically stabilized. We believe this was caused by the higher normal force causing a higher deformation of the balls, which increased the interaction with the holes in the racquet. More specifically, a more deformed ball fills the hole better, which increases the force required to move it. At a certain power, this effect becomes saturated (the holes under the balls are filled), which stabilizes the coefficient.

Although this effect also works for surfaces covered with an epoxy resin layer with coarsening grains, here we noticed a different scenario with a clear decrease in the coefficient of friction especially at lower forces. We believe that the combination of the coarse surface of the racquet with the hairy surface of the ball resulted in a "Velcro" effect. The hairs were bound to the surface, which caused a component of the frictional force independent of the normal

F =F + f F force, i.e. going beyond the standard formula mentioned above. If we assume ^{f 0} ' , we get where Fo is the constant force of the "Velcro", f _e ff is the measured coefficient and f is the coefficient for very large forces. This idea agrees with the obtained data and leads to a minimum coefficient of friction with epoxy resin layer with coarsening grains for high forces f=0.48, which is still almost twice the maximum coefficient obtained for smooth surfaces for a maximum load f=0.26, which also corresponds to the average value for all loads. So even with particularly powerful shots that exceed 250 N, the epoxy resin layer with the coarsening grains should provide a potential increase in maximum rotation of at least 100 %. However, this gain can only be materialized if the player is able to move the racquet quickly enough in the transverse direction when hitting the ball.

Based on the above, it can therefore be concluded that by applying an epoxy resin layer with coarsening grains onto the hitting area of the racquet, the friction coefficients in all cases increased more than twice and that a racquet with a hitting area improved by an epoxy resin layer with coarsening grains applied onto the hitting area will allow significantly more spin and control of the ball in play, especially for shots played with low and medium speed and power.

Example 9 - Measuring the coefficient of rebound of padel balls

The rebound coefficient represents the share of energy that the ball has after bouncing off a static racquet. A higher rebound coefficient means that the ball will fly faster after an equally strong shot.

Six racquets from different brands Dunlop, Stiga, Adidas, Babolat, Starvie and Bullpadel were used to measure the rebound coefficient. On each racquet, the original surface was left on one hitting area and an epoxy resin layer with coarsening grains reinforced with fibrous mesh prepared by the procedure described in Example 6 was applied onto the other hitting area. The racquet was placed horizontally and a padel ball (HEAD Padel Pro, the official ball of the World Padel Tour) was dropped from a height of one or two meters onto both surfaces. The ball was released through a tube formed by two padel ball containers with a cut bottom to ensure a vertical flight of the ball. Subsequently, the height to which the ball bounced off the surface of the racquet was measured. Only a fully vertical rebound was considered a successful rebound, when the bounced ball returned back towards the release tube. About 70 % of the experiments were successful, while the success rate of the experiment was independent of other parameters.

Five measurements were made for each parameter configuration. The rebound coefficient was calculated as where h _r is the release height of one or two meters and hf is the maximum height of the ball after the first bounce off the racquet. The maximum height measurement error was limited to 1 cm, or less than 2 % for all configurations.

The measurement results are shown in Fig. 8. It can be seen that for individual racquets the rebound coefficient for both heights and both surfaces is the same within experimental accuracy. It can therefore be concluded that the epoxy resin layer with coarsening grains applied onto the hitting area of the racquet does not affect the rebound properties of the racquet. This conclusion is expected since the material is thin enough not to change the rebound properties.

On the other hand, it can be stated that the rebound coefficient differs for different racquets. It is clear from the data that for both heights and both surfaces (the original racquet surface of the hitting area and the racquet hitting area surface with an applied epoxy resin layer with coarsening grains) the Stiga racquet has a statistically significantly higher rebound coefficient than the Adidas and Bullpadel racquets. The Babolat and Dunlop racquets have an average rebound, while the Starvie racquet shows very stable, higher values. Therefore, it can be concluded that regardless of the surface finish of the racquets, Stiga and Starvie will deliver the highest ball speed with the same racquet movement among the tested manufacturers.

Thus, it can be concluded that there are differences between the racquets themselves in relation to the coefficient of rebound, however, no change in the coefficient of rebound was observed after the application of an epoxy resin layer with coarsening grains onto any of the racquets used in the experiment.

It is clear from the given examples that the inventors tested padel racquets with various coarsened surfaces according to the present invention as well as commercially available padel racquets from various manufacturers and surprisingly found that if the surface of the racquet is provided with a layer of material according to the present invention, there is a several-fold increase in the coefficient of friction between the surface of the hitting area and the ball, which positively affects the performance of the racquet during the game and at the same time does not affect the rebound properties of the hitting area of the racquet. Such improvement of the hitting area of the racquet as proposed by the invention could also find application in other racquet sports games, such as pickleball or beach tennis.

Relational Signs List:

1 - Racquet head

2 - Racquet frame

3 - Hitting area of the racquet

4 - Racquet handle

5 - Layer of epoxy-based resin

5a - Layer of epoxy-based resin below the coarsening grains 5b - Layer of epoxy-based resin above the coarsening grains

6 - Coarsening grains

7 - Fibrous mesh

7a - Polyester film

8 - Fibrous mesh treatment layer

9 - Adhesive

10 - Holes