Table tennis racket, associated rubber and method for its manufacture

Abstract

A table tennis racket (4) and a corresponding table tennis racket rubber (6), as well as a method for their manufacture, are described. The table tennis racket (4) is formed from two separately manufactured and bonded layers, namely a pimpled rubber (8) provided with pimples (18) on its side (16) and a sponge (10). The sponge (10) is formed by a fully cross-linked elastomer body (E) consisting of a foamed first layer (12) and an unfoamed second layer (14), which are directly bonded together by co-vulcanization.

Description

[0001] The invention relates to a table tennis racket rubber and to a method for its manufacture. The invention further relates to a table tennis racket.

[0002] Table tennis rackets are known to consist of a racket body with a blade and a handle attached to it, as well as two elastic rubbers glued to the two sides of the blade. The racket body is usually made of wood and is therefore commonly referred to as the "blade".

[0003] A conventional table tennis racket rubber typically consists of two layers: an unfoamed outer layer with pimples, which, when mounted, forms the outer surface of the rubber (facing away from the racket face), and a foamed layer, which, when mounted, is positioned between the outer layer and the racket face. Both layers are usually made of a fully cross-linked elastomer (rubber). The outer layer is typically pimpled on one side and is therefore also called the "pimpled rubber" (alternatively: "topsheet"). The bottom layer is also called the "sponge."

[0004] The primary function of the pimpled rubber is usually to ensure the best possible grip between the ball and the racket upon impact, thereby enabling, in particular, a reversal or increase of the ball's spin during the stroke. However, there are also "anti-spin" rubbers, which are specifically designed to achieve low grip. The sponge's main function is generally to efficiently transfer the kinetic energy of the stroke to the ball, thus accelerating it as much as possible. The strength of the grip provided by the rubber between the ball and the racket is referred to as the rubber's "grip." The rubber's ability to transfer the kinetic energy of the stroke to the ball, and thus accelerate it, is referred to as the rubber's "speed."

[0005] The two layers of the rubber are usually manufactured separately. The sponge is split as a thin layer from a block of cellular rubber and bonded to the pimpled rubber using an elastic adhesive. During assembly, the resulting rubber is bonded to the blade of the racket using another layer of adhesive, so that the sponge is sandwiched between the blade and the pimpled rubber.

[0006] Most often, the rubber pimples are applied to the racket so that the pimples face inwards, meaning the smooth side of the rubber faces outwards. However, there are also rackets where the pimpled side of the rubber faces outwards when mounted. Rackets with outward-facing pimples sometimes lack a sponge layer. In these cases, the rubber pimples are applied directly to the wood. Such rubbers, consisting solely of the pimples, are particularly easy and inexpensive to manufacture, as the steps for producing the sponge and bonding the two layers are eliminated. However, they are often of low quality and typically exhibit very poor grip and speed.

[0007] From DE 10 2023 203 317 A1, a (table tennis racket) rubber is known which consists of a one-piece elastomer body made of a fully cross-linked, elastomeric matrix material. The elastomer body has a foamed inner area and a smooth outer surface. The rubber is manufactured by a two-stage vulcanization process in which a partially vulcanized blank containing a blowing agent is expanded between a first incomplete vulcanization step and a second vulcanization step. In one variant, the elastomer body is formed by combining and co-vulcanizing two blank layers, one of which contains the blowing agent to form the foamed inner area. In contrast to conventional high-quality rubbers, which consist of two bonded rubber layers, the rubber described in DE 10 2023 203 317 A1 is in the form of a single, one-piece rubber layer (i.e., a single, one-piece rubber layer).formed from a single, one-piece elastomer body made of a fully cross-linked elastomeric matrix material. Unlike rubbers consisting only of the pimpled rubber (and thus also only a single, one-piece rubber layer), such as those used in inexpensive recreational rackets or rackets without ball spin reversal, the one-piece elastomer body from DE 10 2023 203 317 A1 performs both the function of the pimpled rubber and the function of the sponge. The one-piece manufacturing process, described above in two stages of vulcanization, enables the simple and efficient production of high-quality table tennis racket rubbers.

[0008] The invention is based on the objective of providing a table tennis racket and an associated table tennis racket rubber with particularly high performance, in particular particularly high spin reversal efficiency or spin generation efficiency, as well as an associated manufacturing method.

[0009] With regard to a (table tennis racket) rubber, this problem is solved according to the invention by the features of claim 1. With regard to a method for manufacturing the rubber, the above problem is solved according to the invention by the features of claim 7. With regard to a table tennis racket, the problem is solved according to the invention by the features of claim 10. Advantageous and partly inventive embodiments of the invention are set out in the dependent claims and the following description.

[0010] The table tennis racket rubber according to the invention is – in itself like a conventional table tennis racket rubber – formed from two separately manufactured and subsequently bonded (rubber) layers, namely a pimpled rubber with pimples on its side and a sponge. The pimpled rubber is designed in a conventional manner. However, unlike conventional table tennis racket rubbers, in which the sponge has a homogeneously foamed (porous) structure throughout its entire thickness, the sponge of the table tennis racket rubber according to the invention is again formed from two differently designed layers. Only one of these two layers (hereinafter referred to as the "first layer" or – without being limited to a specific orientation of the sponge – as the "top layer") is foamed in the manner of the sponge of an ordinary table tennis racket rubber.The other layer (hereinafter referred to as the "second layer" or – again without being limited to a specific orientation of the sponge – as the "bottom layer") is, in contrast, similar to the textured rubber (preferably across its entire thickness) and is unfoamed. The two layers of the sponge are directly bonded together by co-vulcanization, so that the sponge as a whole is formed by a single, fully cross-linked elastomer body.

[0011] The sponge layer of the table tennis racket rubber according to the invention thus has a similar structure and is also manufactured in a similar process to the rubber known from DE 10 2023 203 317 A1, except that the latter is designed as a complete table tennis racket rubber and is therefore intended to be used without additional pimpled rubber. The invention is based on the surprising finding that by using a two-layer elastomer body according to the teaching of DE 10 2023 203 317 A1 as a sponge, i.e., in combination with a pimpled rubber, the performance of a table tennis racket rubber can be significantly increased both compared to the rubber known from DE 10 2023 203 317 A1 and compared to conventional rubbers (with separate pimpled rubber and homogeneously foamed sponge).This performance increase is particularly effective in preferred embodiments of the invention in which the studded rubber and the sponge are bonded together in such a way that the studded rubber rests against the foamed first layer of the sponge, while the unfoamed second layer of the sponge faces away from the studded rubber.

[0012] The exceptionally high performance of the rubber according to the invention is particularly evident in its higher spin reversal efficiency or spin generation efficiency compared to a comparable conventional racket with a homogeneously foamed sponge. Under otherwise identical striking conditions (especially for topspin shots), the table tennis ball leaves a racket covered with the rubber according to the invention with higher spin. Therefore, in a topspin shot, the struck table tennis ball flies – compared to a ball with lower spin – at the same speed along a more curved trajectory. With the rubber according to the invention, the ball can thus be struck with greater force under otherwise identical striking conditions without falling into the net or flying over the table tennis table.

[0013] On its side facing away from the pimples, the rubber preferably has a smooth, uninterrupted surface – as is common with table tennis racket rubbers. This smooth surface forms, in particular, the outer surface of the rubber that faces outwards when mounted and is intended for contact with the table tennis ball.

[0014] "Foamed" in this context means that the elastomer body of the sponge has a foam- or sponge-like structure in the corresponding first layer, in which the matrix material encloses numerous gas-filled cavities ("pores"). "Unfoamed" means, correspondingly, that the elastomer body of the sponge does not have a foam- or sponge-like structure in the corresponding second layer and therefore—apart from isolated manufacturing defects or holes introduced after the vulcanization process—has no gas-filled cavities. "Smooth" or "pore-free" means that the surface described in this way—apart from isolated manufacturing defects or holes introduced after the vulcanization process—has no pores, depressions, or holes.

[0015] The term "material bond" or "material-bonded connection" is understood here and in the following to mean that the connected parts are held together at their contact surfaces by material union or cross-linking (e.g., due to atomic or molecular bonding forces, namely covalent bonds). The material-bonded connection between the two layers of the sponge is "direct" in that no adhesion promoter, in particular no adhesive, is placed between the two layers.

[0016] Preferably, as with most conventional table tennis racket rubbers, the pimpled rubber and the sponge are bonded together in such a way that the pimpled side of the rubber rests against the sponge (and is thus located on the inside). However, the present invention can also be advantageously applied to rubbers with pimples arranged on the outside. In such embodiments of the invention, the pimpled rubber and the sponge are bonded together in such a way that the pimpled side of the rubber faces away from the sponge.

[0017] In an advantageous dimension, the unfoamed second layer has a thickness between 0.1 mm and 0.7 mm, preferably between 0.1 mm and 0.5 mm, and particularly 0.3 mm. Additionally or alternatively, the sponge preferably has a total thickness between 0.3 mm and 2.7 mm, more preferably between 0.5 mm and 2.6 mm, and particularly 2.5 mm.

[0018] The foamed first layer of the sponge, when suitably designed, has a density between 0.3 g / cm³. 3 and 0.9 g / cm³ 3 The unfoamed second layer of the sponge preferably has a density between 0.8 g / cm³. 3 and 1.5 g / cm² 3 .

[0019] According to the inventive process, the sponge is produced in a two-stage vulcanization process in which a partially vulcanized blank containing a blowing agent is expanded between a first incomplete vulcanization step and a second vulcanization step. Here and in the following, "vulcanization" refers to the process leading to the production of a vulcanized end product, i.e., a fully cross-linked elastomer. The term "vulcanization" (e.g., in vulcanization step, vulcanization time, vulcanization temperature, etc.) denotes individual steps or parameters in the vulcanization process, even if these do not ultimately lead to the vulcanized end product.

[0020] Specifically, according to the inventive method, the sponge is produced by laying a first blank layer containing a blowing agent and a second blank layer without a blowing agent on top of each other and bonding them together to form a sponge blank by applying pressure, in particular by means of a pressure roller or cylinder. In the first vulcanization step, the sponge blank is partially vulcanized for the duration of a first vulcanization time at a first vulcanization temperature. "Partially vulcanized" (also "pre-vulcanized") means that the first vulcanization step is completed before the vulcanization process, i.e., the complete cross-linking of the polymer to form the elastomer material, is finished. The end product of the first vulcanization step is thus a partially vulcanized semi-finished product (also referred to as a "partially vulcanized blank") in which the polymer material is only partially cross-linked.

[0021] During and / or after the first vulcanization step, the partially vulcanized sponge blank is expanded ("inflated") due to pressure build-up caused by the decomposition of the blowing agent, forming the foamed first layer of the sponge. This expansion process creates pores (also known as "cell formation"). In the second vulcanization step, the expanded sponge blank is vulcanized again at a second vulcanization temperature for a second vulcanization period to form the fully cross-linked elastomer body that constitutes the sponge. The completed sponge is then bonded to the pimpled rubber to complete the table tennis racket covering.The term "fully vulcanized" here means that the second vulcanization step is carried out until the vulcanization reaction is complete, i.e., until the fully cross-linked elastomer body is formed. For example, the first and second vulcanization steps are dimensioned such that the first vulcanization time is between 10% and 40%, particularly about 25%, of the second vulcanization time; correspondingly, the first vulcanization time is between about 9% and 28%, particularly about 20%, of the total vulcanization time resulting from the sum of the first and second vulcanization times.

[0022] To produce the sponge, in a suitable embodiment of the process, unreactive starting materials of a first elastomer composition (which will later form the first layer of the sponge) are mixed in a first mixing step to form a first premix, for example, using an internal mixer. The unreactive starting materials of the first elastomer composition comprise at least one polymer (i.e., a pure polymer or a polymer mixture) and zinc oxide, as well as—optionally—at least one plasticizer and / or at least one filler. A natural rubber is preferably used as the polymer. However, in principle, a synthetic rubber can also be used in further embodiments of the invention.

[0023] In a second mixing step, reactive starting materials of the first elastomer composition are added to the first premix – for example, using a rolling mill or another internal mixer. These reactive starting materials include at least one accelerator (preferably at least one primary accelerator and at least one secondary accelerator), sulfur, and a blowing agent. The second mixing step results in a plastically deformable mass that forms the first blank layer of the future elastomer body.

[0024] Similarly, in corresponding first and second mixing steps, a second premix of a second elastomer composition (which will later form the second layer of the sponge) and the second blank layer of the future elastomer body are produced, although in this case, no blowing agent is added. Therefore, unlike the first blank layer, the second blank layer does not contain any blowing agent.

[0025] In a suitably implemented version of the process, the first and second vulcanization steps are carried out in different molds (i.e., a first mold and a second mold), the two molds differing in the thickness of the cavities enclosed in their closed state. The second mold provides more space for the (then expanded) semi-finished product than the first mold. The first mold, in particular, is preferably gas-tight in its closed state to prevent the escape of the gasifying blowing agent during the first vulcanization step. Optionally, the second mold is also gas-tight in its closed state.

[0026] The inventive method for producing the sponge corresponds in its basic features to the expansion process used for the production of cellular rubber, as described, for example, in DE 821 423 C. Furthermore, the inventive method for producing the sponge corresponds to the method for producing the table tennis rubber described in DE 10 2023 203 317 A1. For further details of the inventive method, reference is made to these documents.

[0027] The starting materials of the first elastomer composition of the first blank layer and the second elastomer composition of the second blank layer preferably contain - in addition to 100 phr of the respective polymer or polymer mixture - each: - 2 - 10 phr Zinc oxide, - 0 - 2 phr Stearic acid - 0 - 40 phr a filler, in particular magnesium carbonate and / or chalk, - 0 - 30 phr (especially 10 - 30 phr) of a plasticizer, in particular a naphthenic oil or phthalate, - 0.5 - 3 phr a primary accelerator based on sulfenamide, in particular TBBS and / or CBS, - 0 - 2.5 phr a secondary accelerator based on thiuram, dithiocarbamate and / or dithiophosphate, in particular TMTD, TMTM, ZBEC, ZDMC and / or TP, - 0 - 2 phr a vulcanization retarder, in particular N-phenyl-N-[(trichloromethyl)thio]benzenesulfonamides)), and - 0.5 - 4 phr Sulfur.

[0028] The elastomer composition of the first blank layer additionally contains 1–5 phr of a blowing agent, in particular OBSH. The second blank layer contains no blowing agent. Furthermore, the first blank layer and / or the second blank layer optionally contain at least one additive for coloring the respective layer, e.g., titanium dioxide.

[0029] The term "phr" (parts per hundred rubber) refers to a unit of measurement commonly used in rubber manufacturing, where the total amount of rubber in the raw materials of an elastomer composition is summed up to 100%. All other components of the raw materials, in particular fillers, plasticizers, accelerators, vulcanization retarders, etc., are added, so that the total amount of raw materials specified in phr is generally more than 100%. Raw materials for which a lower quantity limit of 0 phr is specified are considered optional components in this and subsequent discussions.

[0030] In a particularly preferred embodiment, the first blank layer is formed from an elastomer composition containing the following starting materials: - 100 phr natural rubber - 5 phr zinc oxide - 2.4 phr Titanium dioxide (optional) - 20 phr Magnesium carbonate - 1 phr Stearic acid - 1.2 phr TBBS, - 3 phr Sulfur, - 0.15 phr TMTD, and - 4.8 phr OBSH.

[0031] In this embodiment, the second blank layer is formed from an elastomer composition containing the following starting materials: - 100 phr natural rubber - 5 phr zinc oxide - 2.4 phr Titanium dioxide (optional) - 1 phr Stearic acid - 0.5 phr CBS, - 0.5 phr Sulfur, - 0.2 phr TMTD, and - 0.5 phr ZBEC.

[0032] The starting materials of the two elastomer compositions are preferably different, independent of the blowing agent content. In some embodiments of the invention, however, the two elastomer compositions partially correspond, in particular with respect to the polymer used and optionally with respect to other components of the respective composition, such as the same proportions of zinc oxide, the same filler, the same proportions of zinc oxide, stearic acid or sulfur, and / or the same accelerator. In this case, preferably—where possible—one or more steps for producing the first blank layer and the second blank layer are carried out together. For example, in certain embodiments of the invention, the first elastomer composition and the second elastomer composition can be based on identically composed unreactive starting materials.In this case, preferably the first mixing step and – optionally – parts of the second mixing step are carried out jointly for both elastomer compositions. In particular, the two premixes are only separated before the selective addition of the blowing agent.

[0033] Another embodiment of the invention is the use of an elastomer body, as is known per se from DE 10 2023 203 317 A1 (namely a fully cross-linked elastomer body formed from a foamed first layer and an unfoamed second layer, in which the layers are directly bonded together by co-vulcanization), as a sponge of a table tennis racket rubber, by bonding this elastomer body - in particular according to one of the above-described variants of the invention - to a rubber surface provided with pimples on its side.

[0034] Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. The drawing shows: Fig. 1 in a schematic cross-section a section of a (table tennis) racket with a (table tennis racket) covering applied to a (racket) wood, comprising a pimpled rubber and a sponge bonded to it, wherein the sponge is formed from a foamed first layer (top layer) and an unfoamed second layer (bottom layer) which are jointly produced by co-vulcanization, and Fig. 2. A process for producing the coating is shown in a schematic flowchart.

[0035] Corresponding parts and structures are always provided with the same reference symbols in all figures.

[0036] Fig.Figure 1 schematically shows a cross-section of a (table tennis racket) rubber 6 mounted on the wood 2 of a table tennis racket 4. The rubber 6 consists of two layers: a pimpled rubber 8 and a sponge 10, which are manufactured separately and then bonded together using an elastic adhesive 11 (in particular, a latex adhesive). The sponge 10, in turn, comprises two layers of a fully cross-linked elastomeric matrix material (i.e., a rubber). The two layers, namely a top layer 12 and a bottom layer 14, are manufactured together by co-vulcanization and are thus directly bonded. No adhesive layer is interposed between the top layer 12 and the bottom layer 14. Instead, the top layer 12 and the bottom layer 14 together form a single-piece elastomeric body E ( Fig.2) The top layer 12 of the sponge 10 is foamed, meaning it has a foam- or sponge-like structure. In other words, it has a large number of gas-filled cavities (also called pores). In contrast, the bottom layer 14 of the sponge 10 is unfoamed. Therefore, except for individual manufacturing defects or subsequently introduced holes, it has no air-filled cavities.

[0037] The studded rubber 8 is provided with studs 18 on one (studded) side 16 in the usual manner. On an outer side 20 opposite the studs 18, the studded rubber 8 has a smooth surface. As shown from Fig.As can be seen in Figure 1, the pimpled rubber 8 and the sponge 10 are bonded together in such a way that the pimpled rubber 8, with its pimpled side 16, rests against the foamed top layer 12 of the sponge 10, and the unfoamed bottom layer 14 of the sponge 10 faces away from the pimpled rubber 8. The outer surface 20 of the pimpled rubber 8 thus forms the outer surface of the rubber 6 intended for contact with the table tennis ball. The unfoamed bottom layer 14 of the sponge 10, on the other hand, forms the inner surface of the rubber 6, with which the rubber 6 is bonded to the wood 2 of the table tennis racket 4 as intended – using an elastic adhesive 21 (in particular a latex adhesive).

[0038] In Fig. 2 is a process for manufacturing in Fig. The surface shown in section 1 is schematically sketched in a block diagram.

[0039] The process begins with a first mixing step 22, in which, separately in an internal mixer, unreactive starting materials of a first elastomer composition are mixed to form a first premix V1 (sub-step 22a), and unreactive starting materials of a second elastomer composition are mixed to form a second premix V2 (sub-step 22b). The unreactive starting materials of the first and second elastomer compositions each comprise a polymer and zinc oxide, as well as – optionally – a plasticizer and / or one or more fillers, in particular - 100 phr Polymer, in particular natural rubber or synthetic rubber (especially EPDM), - 2 - 10 phr Zinc oxide, - 0 - 2 phr Stearic acid - 0 - 40 phr Filler, e.g. magnesium carbonate or chalk, and - 0 - 30 phr Plasticizers, e.g. naphthenic oil or phthalates.

[0040] Subsequently, in a second mixing step 24, reactive starting materials of the first elastomer composition are added to the first premix V1 by means of a rolling mill (sub-step 24a). Separately, reactive starting materials of the second elastomer composition are also added to the second premix V2 by means of the same rolling mill (sub-step 24b). In the case of both elastomer compositions, the reactive starting materials include sulfur, a primary accelerator, and a secondary accelerator, for example. - 1 - 3 phr Primary accelerator based on sulfenamides, e.g. TBBS or CBS, - 0 - 2.5 phr Secondary accelerator based on thiuram, dithiocarbamate and / or dithiophosphate, e.g. thiuram: TMTD, TMTM; dithiocarbamate: ZBEC, ZDMC; dithiophosphate: TP, - 0 - 2 phr Vulcanization retarders, e.g. Vulkalent E (chemical name: N-phenyl-N-[(trichloromethyl)thio]benzenesulfonamides), and - 0.5 - 4 phr Sulfur.

[0041] A blowing agent (e.g. OBSH) is added to the first premix V1 as an additional starting material for the first elastomer composition, for example in a quantity of 1 - 5 phr.

[0042] By adding the respective reactive starting materials, the first premixture V1 is further processed into a first blank layer S1, and the second premixture V2 into a second blank layer S2. The first blank layer S1 has, for example, a thickness of 0.1 mm to 2.0 mm, preferably 0.5 to 2.0 mm, and particularly 1.8 mm. The second blank layer S2 has, for example, a thickness between 0.1 mm and 0.7 mm, preferably between 0.1 mm and 0.5 mm, and particularly 0.3 mm.

[0043] In a subsequent combination step 26, the two blank layers S1 and S2 are placed flat against each other. The stacked blank layers S1 and S2 are pressed together using a pressure roller or cylinder, thereby directly bonding them to form a blank R. After combination step 26, the blank R has, for example, a thickness between 0.2 mm and 2.5 mm.

[0044] The elastomer body E is then produced from the blank R in a two-stage vulcanization process.

[0045] For this purpose, the blank R is placed in the cavity of a first heatable metal mold in a first vulcanization step 28 and exposed to a first vulcanization temperature for the duration of a first vulcanization time. The cavity of the first mold has, for example, a flat, rectangular contour with a thickness of, for example, 0.2 mm to 2.5 mm. The blank R is cut so that it completely fills the cavity of the first mold. The first vulcanization time and the first vulcanization temperature are chosen such that the blank R is only partially vulcanized, meaning that the vulcanization process is not completed. For example, the first vulcanization time is only about 9% to 28% of the total vulcanization time that would be required to complete the vulcanization reaction, i.e., to fully crosslink the elastomer material.The heat input in the first vulcanization step 28 also decomposes the blowing agent, releasing gas. The first mold is designed to seal the enclosed cavity gas-tight, preventing the gas released from the blowing agent from escaping.

[0046] After the first vulcanization period, the first mold is opened in an expansion step 30. The partially vulcanized semi-finished product H, formed from the blank R by the first vulcanization step 28, is expanded (inflated) by the action of the gas released from the blowing agent – ​​for example, by an expansion factor between 10% and 100% – thereby forming the foamed top layer 12 of the sponge 10. The strength of the cross-linking after the first vulcanization step 28, and thus the degree of expansion, is controlled via the first vulcanization period.

[0047] To carry out a second vulcanization step 32, the now (partially vulcanized and) expanded semi-finished product H' is placed in a second heatable metal mold, which has a cavity thicker than the first mold, e.g., between 0.5 and 2.7 mm. In the second mold, the expanded semi-finished product H' is exposed to a second vulcanization temperature for the duration of a second vulcanization time. The second vulcanization time and temperature are determined such that the expanded semi-finished product H' is fully vulcanized in the second vulcanization step 32, i.e., the vulcanization reaction is completely finished. The result of the second vulcanization step 32 is the fully cross-linked elastomer body E.

[0048] After completion of the sponge 10, it is glued in an adhesive step 34 using the elastic adhesive 11 to the conventionally produced nubbed rubber 8, so that the nubbed rubber 8 with the nubbed side 16 lies against the foamed top layer 12 of the sponge 10.

[0049] In a final assembly step 36, the completed covering 6 is cut or punched to a final dimension of, for example, 17 x 17 cm.

[0050] In the finished coating 6, the matrix material of the elastomer body E has a density between 0.8 g / cm³ in both the lower layer 14 and the upper layer 12 (there without taking into account the gas-filled pores). 3 and 1.5 g / cm² 3 Taking the pores into account, the density of the upper layer 12 is between 0.3 g / cm³. 3 and 0.9 g / cm³ 3The finished coating 6 has a thickness of between 2 mm and 4 mm. The sponge 10 has a thickness of between 0.5 mm and 2.7 mm. The unfoamed underlayer 14 has a thickness of between 0.1 mm and 0.7 mm.

[0051] In a specific example for the production of sponge 10, the elastomer composition of the first blank layer R1 contains the following starting materials: - 100 phr natural rubber - 5 phr zinc oxide - 2.4 phr titanium dioxide - 20 phr Magnesium carbonate - 1 phr Stearic acid - 1.2 phr TBBS, - 3 phr Sulfur, - 0.15 phr TMTD, and - 4.8 phr OBSH.

[0052] The elastomer composition of the second blank layer R2 contains the following starting materials in this example: - 100 phr natural rubber - 5 phr zinc oxide - 2.4 phr titanium dioxide - 1 phr Stearic acid - 0.5 phr CBS, - 0.5 phr Sulfur, - 0.2 phr TMTD, and - 0.5 phr ZBEC.

[0053] The two blank layers R1 and R2 are produced from these starting materials in the manner described above, wherein the first blank layer R1 is rolled out to a thickness of 1.8 mm and the second blank layer R2 to a thickness of 0.3 mm. The two blank layers R1 and R2 are then applied to each other using a pressure roller to produce the sponge blank 10.

[0054] The blank R of the sponge 10 is partially vulcanized in the first vulcanization step 8 in the first form at a first vulcanization temperature of 140 °C for a first vulcanization time of 300 s.

[0055] The second vulcanization step 12 is carried out in the second form at a second vulcanization temperature of 140 °C for a second vulcanization time of 1200 s.

[0056] The sponge 10 produced in this way is then glued and assembled with a conventional pimpled rubber 9 in the manner described above to complete the covering 6.

[0057] The invention becomes particularly clear in the embodiments described above, but is by no means limited to these embodiments. Rather, further embodiments of the invention can be derived from the claims and the preceding description. Reference symbol list 2 wood 4 table tennis rackets 6 (Table tennis racket) covering 8 studded rubber 10 sponges 11 Adhesive 12 Upper class 14 lower class 16 (studded) page 18 studs 20 (Outside) side 21 Adhesive 22 (first) mixing step 22a Sub-step 22b Substep 24 (second) mixing step 24a Sub-step 24b Substep 26 Combination step 28th vulcanizing step 30 Expansion step 32nd vulcanizing step 34 Gluing step 36 Assembly step E Elastomeric body H (partially vulcanized) semi-finished product H' (expanded) semi-finished product R blank S1 (first) blank layer S2 (second) blank layer V1 (first) premix V2 (second) premix

Claims

[1] Table tennis racket rubber (6) comprising two separately manufactured and bonded layers, namely a pimpled rubber (8) provided with pimples (18) on its side (16) and a sponge (10), wherein the sponge (10) is formed by a fully cross-linked elastomer body (E) consisting of a foamed first layer (12) and an unfoamed second layer (14) which are directly bonded together by co-vulcanization. [2] Table tennis racket rubber (6) according to claim 1, wherein the pimpled rubber (8) and the sponge (10) are bonded together in such a way that the pimpled rubber (8) is in contact with the foamed first layer (12) of the sponge (10) and the unfoamed second layer (14) of the sponge (10) is turned away from the pimpled rubber (8). [3] Table tennis racket rubber (6) according to claim 1 or 2, wherein the pimpled rubber (8) and the sponge (10) are bonded together in such a way that the pimpled side (16) of the pimpled rubber (8) is in contact with the sponge (10). [4] Table tennis racket rubber (6) according to one of claims 1 to 3, wherein the non-foamed second layer (14) has a thickness between 0.1 mm and 0.7 mm, preferably between 0.1 mm and 0.5 mm and particularly 0.3 mm. [5] Table tennis racket rubber (6) according to one of claims 1 to 4, wherein the sponge (10) has a total thickness between 0.5 and 2.7 mm, preferably between 1.8 mm and 2.5 mm and particularly 2.2 mm. [6] Table tennis racket rubber (6) according to one of claims 1 to 5, wherein the foamed first layer (12) of the sponge (10) has a density between 0.3 g / cm³ 3 and 0.9 g / cm³ 3 exhibits, and wherein the unfoamed second layer (14) of the sponge (10) has a density between 0.8 g / cm³3 and 1.5 g / cm² 3 exhibits. [7] Method for manufacturing a table tennis racket covering (6) according to any one of claims 1 to 6, - in which the sponge (10) is produced by - a first blank layer (R1) containing a blowing agent is laid flat on top of a second blank layer (R2) not containing a blowing agent and joined to form a blank (R) of the sponge (10) by applying pressure, - wherein the sponge blank (R) (10) is partially vulcanized in a first vulcanization step (28) for the duration of a first vulcanization time at a first vulcanization temperature to become a partially vulcanized sponge blank (H) (10), - wherein the partially vulcanized blank (H) is expanded to form the foamed first layer (12) of the sponge (10) as a result of a pressure build-up through decomposition of the blowing agent to form an expanded blank (H`) of the sponge (10), - wherein the expanded blank (H') is vulcanized in the second vulcanization step (32) for the duration of a second vulcanization time at a second vulcanization temperature to form the fully cross-linked elastomer body (E) forming the sponge (10), and - in which the sponge (10) thus completed is glued to the rubber (8). [8] Method according to claim 7, - wherein the first blank layer (R1) and the second blank layer (R2) are each formed from an elastomer composition which, in addition to 100 phr of a polymer or a polymer mixture, in particular a natural rubber or synthetic rubber, contains the following starting materials: - 2 - 10 phr zinc oxide - 0 - 2 phr Stearic acid - 0 - 40 phr at least one filler, in particular magnesium carbonate and / or chalk - 0 - 30 phr of a plasticizer, in particular a naphthenic oil or phthalate - 1 - 3 phr of at least one primary accelerator based on sulfenamide, in particular TBBS and / or CBS, - 0 - 2.5 phr of at least one secondary accelerator based on thiuram, dithiocarbamate and / or dithiophosphate, in particular TMTD, TMTM, ZBEC, ZDMC and / or TP, - 0 - 2 phr of a vulcanization retarder, in particular N-phenyl-N-[(trichloromethyl)thio]benzenesulfonamides)), and - 0.5 - 4 phr sulfur, and - wherein the elastomer composition of the first blank layer () additionally contains 1 - 5 phr of a blowing agent, in particular OBSH. [9] Method according to claim 7, - wherein the first blank layer (R1) is formed from an elastomer composition which, in addition to 100 phr of natural rubber, contains the following starting materials: - 5 phr zinc oxide - 1 phr stearic acid - 20 phr Magnesium carbonate - 1.2 phr TBBS, - 0.15 phr TMTD, - 3 phr sulfur, - 4.8 phr OBSH, and - wherein the second blank layer (R2) is formed from an elastomer composition which, in addition to 100 phr of natural rubber, contains the following starting materials: - 5 phr zinc oxide - 1 phr stearic acid - 20 phr Magnesium carbonate - 0.5 phr CBS, - 0.2 phr TMTD, - 0.5 phr ZBEC, and - 3 phr sulfur. [10] Table tennis racket (4) with a racket body having a racket blade and a handle attached thereto, and with two table tennis racket coverings (6) glued to the two sides of the racket blade according to one of claims 1 to 6. [11] Table tennis racket (4) according to claim 10, wherein the two table tennis racket coverings (6) are each glued onto the racket blade in such a way that the unfoamed second layer (14) of the sponge (10) is in contact with the racket blade. [12] Use of a fully cross-linked elastomer body (E) formed from a foamed first layer (12) and an unfoamed second layer (14) which are directly bonded together by co-vulcanization as a sponge (10) of a table tennis racket rubber (6) by bonding this elastomer body (E) to a pimpled rubber (8) provided with pimples (18) on one side (16). [13] Use according to claim 12, wherein the nubbed rubber (8) and the sponge (10) are bonded together such that the nubbed rubber (8) is in contact with the foamed first layer (12) of the sponge (10) and the unfoamed second layer (14) of the sponge (10) is turned away from the nubbed rubber (8). [14] Use according to claim 12 or 13, wherein the studded rubber (8) and the sponge (10) are bonded together such that the studded side (16) of the studded rubber (8) rests against the foamed first layer (12) of the sponge (10).

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