TITLE: Table-tennis blade

TECHNICAL FIELD

The present invention relates to a table-tennis blade including plies of wood joined together.

BACKGROUND

Table-tennis bats have a blade covered with rubber on one or on both sides. At least 85% of the blade by thickness shall be of natural wood according to the rules of the International Table Tennis Federation (ITTF). This leaves only 15% of the blade by thickness to other materials which can provide properties such as strength and stiffness to the blade. A blade usually consists of 5 to 9 plies of wood where each layer is approximately 0.5 mm thick. The blade has to be of suitable weight, thickness and stiffness for tournament players for them to be able to play at their maximum capacity. The stiffness of the blade has to be quite high in order to make the ball go fast but at the same time not be so stiff that the player feels that the control over the ball is lost. For a tournament player it is very important to "feel" the ball. This "feeling" is the impulse the nerve in the hand sends to the brain.

To obtain the proper weight, stiffness and thickness of the blade, multiple layers of wood are adhered to each other with adhesives. The types of wood that are used are important for the properties of the blade, but the properties of the material between the plies are also of importance.

In recent years there has been advancement in the technology of table- tennis blades. Materials with different properties may be combined with the wood in the blade to enhance its playing performance. Many blades today feature one or more carbon layers. Materials incorporated into table-tennis blades today include kevlar, titanium, arylate, aramid, and aluminum. The problem is to find a material that makes the blade fast but not too stiff, and at the same time is not too heavy or too thick. The speed-glue which is currently the most popular method of applying the rubber onto the blade is from 2008 prohibited by the ITTF. This is anticipated to increase the demand on more ridgid blades, due to the loss of strenght which Speed- glue provided.

The tournament players individualize their blade e.g. by rubbing or polishing them, and it takes time for a player to get properly accustomed to a blade.

As the blades are used, they eventually get softer and therefore have to be replaced.

It is desired that the blade maintains its stiffness as long as possible, that is, that it has a long life time.

Another reason why it is important to adhere the wood layers strongly to each other is to avoid shearing. Shearing does not only decrease the quality of the blades but also severely affects the production. Wood is a material prone to shearing and has to be treated with extra care in order to avoid this.

DISCLOSURE OF THE INVENTION

An object of the invention is therefore to provide a table-tennis blade that has excellent qualities as to stiffness, weight and thickness to thereby increase user feeling and ball speed. During their efforts to construct a superior table-tennis blade the present inventors have found that by reinforcing with carbon nanotubes the adhesive that adheres the wood layers of the blade to each other, a stiff blade which still allows the player to feel the ball can be obtained.

According to one aspect of the invention there is provided a table-tennis blade including plies of wood joined together, wherein the blade comprises carbon nanotubes between the plies.

In an embodiment of the invention, the plies have been joined together by an adhesive containing the carbon nanotubes.

According to another aspect of the invention there is provided a method of joining together layers of wood for a table-tennis blade comprising: providing an adhesive containing carbon nanotubes: applying the adhesive between the layers; and joining the layers together by applying pressure.

In yet another aspect of the invention there is provided an organic sol- vent-based or a water-based adhesive containing carbon nanotubes.

In a further aspect of the invention there is provided the use of carbon nanotubes in the production of table-tennis blades.

The amount of carbon nanotubes in a blade is decided by the required properties of the blade, and is decided by the manufacturer. However, an amount of

0.25% by weight of carbon nanotubes in the adhesive results in more than adequate stiffness of the blade. Lesser amounts will be used to obtain somewhat softer blades.

Other aspects, advantages and features of the invention are apparent from the detailed description and drawing and the features defined in the appended claims.

Accordingly, the inventors of the present invention have unexpectedly found that in order to enhance the stiffness of a table-tennis blade while maintaining a low weight, carbon nanotubes can be applied between the wood plies of the blade.

Carbon nanotubes (CNTs) are an allotrope of carbon. They take the form of cylindrical carbon molecules and they have excellent strength. CNTs are the strongest and stiffest materials known, in terms of tensile strength and elastic modules, respectively. Despite this strength they have a very low density.

In the present invention, these unique properties of CNTs are used in constructing a fast table-tennis blade which allows the player to feel the ball. The CNTs do not only form a strong network in the adhesive making the wood layers adhere strongly to each other but they are also unexpectedly found to reinforce the porous wood, thus making it stiffer. In an embodiment of the invention, it is contemplated to inject the CNTs, possibly included in the adhesive, into the wood layers. As CNTs have a low density, they will not add any substantial weight to the blade.

A blade containing carbon nanotubes will have improved stiffness which makes the blade fast, but the blade will not be so stiff that the feeling of the ball is lost. The blade also has a longer life time since the CNTs interactions with the wood and the adhesive improve the stiffness of the blade so that it can be operational for an extended period of time.

Another effect of these strong interactions of the CNTs is that shearing is prevented.

The CNTs interactions with the wood layers of the blade thus advantageously contribute to all those properties which are desired in a table-tennis blade. The CNTs provide sustained strength, prolonged operational life, a high amount of stiffness to the blade while the player can still feel the ball, and also prevent shearing. And at the same time, the CNTs do not increase the weight or the thickness of the blade.

_. „ .

4

BRIEF DESCRIPTION OF THE DRAWING

The single drawing figure is a cutaway view illustrating the structure of a typical table-tennis blade capable of being incorporated with the principles of the invention.

DETAILED DESCRIPTION

As is apparent from the drawing, a state-of-the-art table-tennis blade, designated generally by numeral 10, has a ball-striking blade portion 12 and a handle portion 24. A fully operational table-tennis bat also has rubber pads (not shown) glued to the blade portion 12. The blade portion 12 is composed of a plurality (three or typically five to nine) of plies 14-22 of wood shaped to the full outline of the bat by also extending over the handle portion 24. The handle portion 24 has also a pair of opposite handle pieces 26, 26 typically of wood and joined to the blade portion 12.

The blade composed of the plies 14-22, which may be of the same or of different thicknesses, is formed by joining together sheets or veneers of wood by glueing the sheets together (usually in 0- and 90-degree mutually alternating fiber orientations) and hardening the resulting joints during compression to obtain a composite plywood structure. The resulting blade portion 12 is cut to shape from the plywood structure, and the blade 10 is completed by glueing the handle pieces 26, 26 to the blade portion 12.

According to the invention, carbon nanotubes (CNTs) are provided between plies of the blade 10.

In an embodiment of the invention, the CNTs are provided in a solution. While other CNT solutions may be used, a useful CNT solution is the epoxy matrix Hybtonite® offered for sale by Amroy Europe Ltd., Lahti, Finland. Bending tests disclosed by Amroy on non-wood sandwich panels comprising tri-axial (90, +45, -45) woven CFEP (Cellular Fluorinated Ethylene Propylene) reportedly showed that bending strength at failure increased up to 20 percent when using Hybtonite® as compared to SPU (Segmented PolyUrethane). The CNT solution is mixed with the adhesive in an amount of, but not limited to, 10% v/v. The adhesive can be any adhesive, for example an adhesive based on organic solvents or a water-based adhesive. A hardener is supplemented if necessary.

The adhesive is spread between the sheets of wood corresponding to the resulting plies 14-22. The adhesive containing CNTs needs not necessarily be applied between every adjoining pair of sheets/plies but one or more joints may be bonded by an adhesive not containing CNTs, in accordance, for example, with de- sired qualities and properties of the blade 10. Also, the handle pieces 26, 26 may be bonded to the outermost plies 14, 22 by an adhesive containing or not containing CNTs. The sheets are then compressed for a few minutes. A composite wooden material for blades is thus obtained which is dried for about 2 to 3 months before further manufacturing takes place, including shaping the blade portions 12, glueing the han- die pieces 26, 26 and other finishing operations.

The foregoing detailed description is given primarily for clearness of un- > derstanding and no unnecessary limitations are to be understood therefrom. Modifications will become obvious to those skilled in the art upon reading this disclosure and may be made without departing from the spirit of the invention or the scope of the appended claims.