Table tennis bat covering

Abstract

The invention relates to a table tennis bat covering (B) having a one-piece elastomer body (E) made of a fully cross-linked elastomer matrix material. The elastomer body (E) has a foamed inner region (C) and a smooth outer surface (A) on an outer side. The covering (B) is produced according to a method according to the invention by a two-step vulcanisation process, in which a partially vulcanised blank (H) mixed with a foaming agent is expanded between a first incomplete vulcanisation step (8) and a second vulcanisation step (12). In a variation of the method, the elastomer body (E) is formed by a combination and co-vulcanisation of two blank layers (S1, S2), at least one of which is mixed with the foaming agent to form the foamed inner region (C).

Description

[0001] Description

[0002] Table tennis racket covering

[0003] The invention relates to a table tennis racket covering and to a method for its production.

[0004] Conventional (table tennis) bat rubbers typically consist of two layers: a non-foamed, pimpled top layer, which, when assembled, forms the outer layer of the rubber (facing away from the blade of the bat), and a foamed bottom layer, which, when assembled, is positioned between the top layer and the blade of the (table tennis) bat. Both layers are usually made of a fully cross-linked elastomer (rubber). The top layer is therefore also referred to as the "top layer" or "pimpled rubber." The bottom layer is also referred to as the "sponge."

[0005] The main purpose of the topsheet is usually to ensure the best possible adhesion between the ball and the racket upon impact, and thus in particular to enable a reversal or increase of the ball rotation (spin) during impact. However, there are also "anti-rubbers" which are designed to achieve a deliberately low level of adhesion. The main purpose of the sponge is usually to efficiently transfer the kinetic energy during impact to the ball, and thus accelerate the ball as much as possible. The strength of the adhesion between the ball and the racket provided by the rubber is referred to as the "grip" of the rubber. The ability of the rubber to transfer the kinetic impact energy to the ball, and thus to accelerate the ball, is referred to as the "speed" of the rubber. The two layers of the rubber are usually manufactured separately.The sponge is split off as a thin layer from a block of cellular rubber and bonded to the topsheet using an elastic adhesive. During assembly, the resulting covering is bonded to the wood of the racket using another layer of adhesive, so that the sponge is positioned between the wood of the racket and the topsheet.

[0006] The topsheet is usually applied to the racket with the pimples facing inwards, meaning the smooth side of the topsheet faces outwards. However, there are also rackets where the pimpled side of the topsheet faces outwards when mounted. Rackets with outward-facing pimples sometimes lack the sponge. The topsheet is applied directly to the wood. Such rubbers, which consist only of the topsheet, are particularly easy and inexpensive to produce, as the steps for producing the sponge and gluing the two layers are eliminated. However, they are often of poor quality and, in particular, regularly have very poor grip and speed.

[0007] The invention is based on the object of simplifying the production of a high-quality table tennis racket surface.

[0008] With regard to a (table tennis racket) covering, this object is achieved according to the invention by the features of claim 1. With regard to a method for producing the covering, the above object is achieved according to the invention by the features of claim 9. Advantageous and partly inventive embodiments of the invention are set out in the subclaims and the following description.

[0009] In contrast to conventional high-quality rubbers, which consist of two rubber layers bonded together, the rubber according to the invention is formed from a single, one-piece rubber layer (i.e., a single, one-piece elastomer body made of a fully cross-linked, elastomeric matrix material). Unlike rubbers consisting only of the top rubber (and thus also only of a single, one-piece rubber layer) (as used in inexpensive rackets or rackets without reversal of the ball rotation), the one-piece elastomer body of the rubber according to the invention takes on the function of both the top rubber and the sponge. For this purpose, the elastomer body has a foamed inner region and a smooth (also: pore-free) outer surface on one side."Foamed" here means that the elastomer body has a foam- or sponge-like structure in the interior region, in which the matrix material encloses a plurality of gas-filled cavities ("pores"). "Smooth" or "pore-free" means that the pores of the foamed interior region - in contrast to the sponge of a conventional table tennis racket covering - are closed to the outer surface. Preferably, the covering has an edge region adjacent to its outer surface in which the elastomer body is unfoamed, i.e., has no foam- or sponge-like structure and thus - apart from possible isolated manufacturing defects or holes introduced after the vulcanization process - has no gas-filled cavities.

[0010] Due to the interaction of the smooth outer surface with the foamed inner area, the inventive covering exhibits similar speed and grip to a conventional covering made of comparable material and thickness, with a top layer of rubber and a separately manufactured sponge. However, due to the one-piece structure of the elastomer body, the inventive covering is characterized by significantly simplified manufacturing compared to such conventional coverings.

[0011] In a simpler and therefore particularly efficient variant of the covering according to the invention, the matrix material of the elastomer body has a homogeneous elastomer composition. In other words, the elastomer body is formed by a single rubber layer made of a single rubber material, in which the foamed inner region and the edge region forming the smooth outer surface merge into one another without a material boundary of the matrix material.

[0012] In this single-layer variant of the covering, the elastomer body preferably has a thickness of 1.5 to 6 mm [millimeters]. The foamed inner region of the single-layer elastomer body has, in an advantageous dimension, a density of 0.3 to 0.9 g / cm 3 [grams per cubic centimeter], while the matrix material of the elastomer body itself (without taking into account the gas-filled pores enclosed in the interior) has a density of 0.8 to 1.5 g / cm 3has.

[0013] In a more complex manufacturing process, but more flexible and capable of delivering higher quality, the elastomer body comprises a top layer and a bottom layer that are directly bonded together. The bottom layer forms the foamed inner area, while the smooth outer surface is formed on the top layer. Unlike conventional floorings, the top layer and bottom layer are manufactured in a single manufacturing process. Specifically, the top layer and bottom layer are co-vulcanized and bonded together simultaneously.

[0014] "Material bond" or "material bond" is understood here and below to mean that the interconnected parts are held together at their contact surfaces by material bonding or cross-linking (e.g., due to atomic or molecular bonding forces, namely covalent bonds). The material bond between the two layers of the covering is "direct" in the sense that no adhesion promoter, in particular no adhesive, is interposed between the two layers. The adhesive layer, which connects the two separately manufactured layers in conventional coverings, is therefore missing in the covering according to the invention.

[0015] Preferably, the top layer is unfoamed across its entire thickness. In this embodiment, the entire top layer thus forms an unfoamed edge region, which also forms the smooth outer surface. In an alternative embodiment, the top layer also has foaming in an area adjacent to the bottom layer.

[0016] Preferably, the upper layer has a thickness of 0.1 to 2 mm (especially between 0.5 mm and 2 mm), and the lower layer has a thickness of 1.5 to 6 mm (especially between 2 mm and 5 mm). The density of the lower layer forming the foamed inner region of the covering is advantageously 0.3 to 0.9 g / cm 3 The top layer preferably has a density between 0.5 g / cm 3 and 1.5 g / cm 3, which also depends on whether and, if so, how pronounced any foaming of the top layer is. The matrix material itself preferably has a density of 0.8 to 1.5 g / cm in both layers of the multi-layer covering. 3 .

[0017] According to the method according to the invention, the covering is produced by a two-stage vulcanization process in which a partially vulcanized blank mixed with a blowing agent is expanded between a first incomplete vulcanization step and a second vulcanization step. "Vulcanization" refers here and below to the process leading to the production of a vulcanized end product, i.e., a fully crosslinked elastomer. The term "vulcanization" (e.g., vulcanization step, vulcanization time, vulcanization temperature, etc.) refers to individual steps or variables in the vulcanization process, even if they do not lead to the vulcanized end product.

[0018] To produce the single-layer variant of the covering according to the invention, in a first variant of the process according to the invention, unreactive starting materials of an elastomer composition are first mixed to form a premix in a first mixing step, preferably using an internal mixer. The unreactive starting materials of the 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. In various embodiments of the invention, either natural rubber or a synthetic rubber, in particular EPDM, is used as the polymer.

[0019] In a second mixing step, reactive starting materials of the elastomer composition are added to the premix – preferably using a rolling mill or an internal mixer. The reactive starting materials comprise 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, referred to as the elastomer body blank.

[0020] From this blank, the (fully cross-linked) elastomer body and thus the finished covering are then produced in a two-stage vulcanization process. In a first vulcanization step, the blank is partially vulcanized for a first vulcanization time at a first vulcanization temperature. "Partially vulcanized" (also "pre-vulcanized") means that the first vulcanization step is ended before the vulcanization process—i.e., the complete cross-linking of the polymer to form the elastomer material—is complete. 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 it contains is only partially cross-linked.

[0021] During and / or after the first vulcanization step, the partially vulcanized semi-finished product is expanded (also called "blowing") under the influence of the blowing agent, which is decomposed by the heat, so that the partially vulcanized semi-finished product expands, forming pores (also called "cell formation"). This expansion process forms the foamed interior of the elastomer body.

[0022] In a second vulcanization step, the (partially vulcanized and) expanded semi-finished product (also referred to as an "expanded blank") is fully vulcanized for a second vulcanization time at a second vulcanization temperature. 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 crosslinked elastomer body is formed. For example, the first vulcanization step and the second vulcanization step are dimensioned such that the first vulcanization time is between 5% and 25%, in particular approximately 10%, of the second vulcanization time; correspondingly, the first vulcanization time is between approximately 4.5% and 20%, in particular approximately 9%, of the total vulcanization time resulting from the sum of the first and second vulcanization times.

[0023] A second variant of the process according to the invention serves to produce the multi-layer (in particular two-layer) variant of the covering according to the invention. This process variant is similar to the process described above, with the exception of the deviations described in more detail below. In the first mixing step, however, to form the two blank layers, unreactive starting materials of a first elastomer composition and unreactive starting materials of a second elastomer composition are mixed to form a first premix and a second premix, respectively. The unreactive starting materials of the first and second elastomer compositions each comprise at least one polymer (i.e. a pure polymer or a polymer mixture) and zinc oxide and - optionally - at least one plasticizer and / or at least one filler.

[0024] In the second mixing step, the two premixes are further processed by adding reactive starting materials of the first and second elastomer compositions to form the first and second blank layers, respectively. The reactive starting materials of the first and second elastomer compositions each comprise at least one accelerator and sulfur. The reactive starting materials of the second elastomer composition additionally comprise a blowing agent.

[0025] In a subsequent combination step, the two blank layers are placed flat against each other and bonded to form the blank by applying pressure, particularly using a pressure roller. The blank composed of the two blank layers is then – analogous to the production of the single-layer covering described above –

[0026] - partially vulcanised in a first vulcanisation step for the duration of the first vulcanisation time at the first vulcanisation temperature,

[0027] - expanded during the first vulcanisation step and / or subsequently to form the foamed inner region of the elastomer body as a result of the pressure build-up caused by the decomposition of the blowing agent, and

[0028] - vulcanized in (partially vulcanized and) expanded state for the duration of the second vulcanization time at the second vulcanization temperature to form the fully crosslinked elastomer body.

[0029] In both variants of the process, the first vulcanization step and the second vulcanization step are carried out in different molds (i.e., a first mold and a second mold), with these two molds differing in the thickness of the cavities enclosed in their closed state; the second mold leaves more space for the (then expanded) semi-finished product than the first mold. In particular, the first mold is preferably gas-tight when closed to prevent the gaseous blowing agent from escaping during the first vulcanization step. Optionally, the second mold is also gas-tight when closed.

[0030] The process according to the invention (in the two process variants described above) corresponds in its basic features to the expansion process used for the production of cellular rubber, as described, for example, in DE 821 423 B. For details of the process according to the invention, reference is made to this document.

[0031] The starting materials of the elastomer composition of the single-layer covering or the two elastomer compositions of the two-layer covering preferably contain - in addition to 100 phr of the respective polymer or polymer mixture - each:

[0032] - 2 - 10 phr zinc oxide,

[0033] - 0 - 2 phr stearic acid,

[0034] - 0 - 40 phr of a filler, in particular magnesium carbonate or chalk,

[0035] - 0 - 30 phr (in particular 10 - 30 phr) of a plasticizer, in particular a naphthenic oil or phthalate,

[0036] - 1 - 3 phr of a sulfenamide-based primary accelerator, in particular TBBS or CBS,

[0037] - 0 - 2.5 phr of a secondary accelerator based on thiuram, dithiocarbamate and / or dithiophosphate, in particular TMTD, TMTM, ZBEC, ZDMC or TP,

[0038] - 0 - 2 phr of a vulcanization retarder, in particular N-phenyl-N-[(trichloromethyl)thio]benzenesulphonamide)), and

[0039] - 0.5 - 4 phr sulfur.

[0040] Starting materials for which a lower limit of 0 phr is specified are optional components.

[0041] In the process variant for producing the single-layer covering, the starting materials of the (single) elastomer composition additionally contain 1–5 phr of a blowing agent, in particular OBSH. In the process variant for producing the two-layer covering, the starting materials of the second elastomer composition (preferably only) additionally contain 1–5 phr of a blowing agent, in particular OBSH.

[0042] The polymers or polymer mixtures used in the invention comprise natural rubbers or synthetic rubbers, in particular an ethylene-propylene-diene rubber (EPDM).

[0043] The term "phr" (parts per hundred rubber) refers to a unit of measurement commonly used in rubber production, which sums up the total amount of rubber in the raw materials of an elastomer composition to 100%. All other components of the raw materials, especially fillers, plasticizers, accelerators, vulcanization retarders, etc., are added, so that the total amount of raw materials specified in phr is usually more than 100%.

[0044] In the process variant for producing the two-layer covering, the starting materials of the two elastomer compositions are preferably different, regardless of the blowing agent content. In some embodiments of the invention, however, the two elastomer compositions partially coincide, in particular in the polymer used and optionally 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, one or more steps for producing the first blank layer and the second blank layer are preferably carried out together, where possible. For example, in certain embodiments of the invention, the first elastomer composition and the second elastomer composition can be based on unreactive starting materials with identical compositions.In this case, the first mixing step and, optionally, parts of the second mixing step are preferably carried out jointly for both elastomer compositions. In particular, the two premixes are separated only before the selective addition of the blowing agent.

[0045] In summary, the invention relates to a table tennis racket covering with a one-piece elastomer body made of a fully cross-linked, elastomeric matrix material. The elastomer body has a foamed inner region and a smooth outer surface on one side. The covering is produced according to the method according to the invention through a two-stage vulcanization process in which a partially vulcanized blank, mixed with a blowing agent, is expanded between a first incomplete vulcanization step and a second vulcanization step. In one process variant, the elastomer body is formed by combining and co-vulcanizing two blank layers, at least one of which is mixed with the blowing agent to form the foamed inner region.Compared to conventional floorings, which consist of two bonded layers—namely, a dimple layer and a sponge layer—the production of the flooring according to the invention eliminates one of two vulcanization processes and the bonding process. The flooring according to the invention can therefore be manufactured much more easily and cost-effectively while maintaining comparable quality.

[0046] Also unlike conventional coverings, which are formed from a nub layer and a sponge layer glued to it, in multi-layer variants of the covering according to the invention the upper layer has no nubs, especially not on the side facing the lower layer.

[0047] The process according to the invention is specifically designed for the production of a table tennis racket covering from a single- or multi-layered, but always integrally manufactured elastomer body. A particular embodiment of the process therefore consists in the use of the elastomer body resulting from the process according to the invention as a table tennis racket covering.

[0048] In the following, exemplary embodiments of the invention are explained in more detail with reference to a drawing. In the drawings:

[0049] Fig. 1 shows a schematic flow diagram of a process for producing a (table tennis racket) covering formed from a one-piece elastomer body made of a fully cross-linked, elastomeric matrix material, wherein the elastomer body is formed from a foamed lower layer and an unfoamed upper layer with a smooth outer surface, and wherein the lower layer and the upper layer are produced together by co-vulcanization and directly bonded to one another,

[0050] Fig. 2 shows a sectional view of an example of the covering produced by the method according to Fig. 1, Fig. 3 shows an alternative method for producing a (table tennis racket) covering in accordance with Fig. 1, the one-piece elastomer body of which is formed from a fully cross-linked, elastomeric matrix material with a homogeneous elastomer composition, wherein the elastomer body in turn has a foamed inner region and a smooth outer surface on an outer side, and

[0051] Fig. 4 in representation according to Fig. 2 an example of the covering produced by the method according to Fig. 3.

[0052] Corresponding parts and structures are always provided with the same reference symbols in all figures.

[0053] 1. Process variant for producing a covering B from a two-layer elastomer body E:

[0054] Fig. 1 illustrates a method for producing a (table tennis racket) covering B - shown by way of example in Fig. 2 - which is formed from two layers of fully cross-linked, elastomeric matrix material (i.e. a rubber). The two layers, namely a top layer 0 and a bottom layer U, are produced together by co-vulcanization and are thereby directly bonded together. There is no adhesive layer between the top layer 0 and the bottom layer U. They thus form the integrally produced elastomer body E. When the covering B is mounted on the wood of a (table tennis) racket, the top layer 0 points outwards. In the example shown, this top layer 0 is unfoamed and has a smooth, i.e. pore-free outer surface A. When the covering B is mounted, the bottom layer U is arranged between the top layer 0 and the wood of the racket.It has a foam- or sponge-like structure, in other words, it has a multitude of gas-filled cavities (also referred to as pores P) and thus forms a foamed inner region C of the covering B. The process begins with a first mixing step 2, in which, in an internal mixer, unreactive starting materials of a first elastomer composition are mixed separately to form a first premix V1 (sub-step 2a) and unreactive starting materials of a second elastomer composition are mixed to form a second premix V2 (sub-step 2b). 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.

[0055] 100 phr polymer, in particular natural rubber or synthetic rubber (in particular EPDM),

[0056] - 2 - 10 phr zinc oxide,

[0057] - 0 - 2 phr stearic acid,

[0058] - 0 - 40 phr filler, e.g. magnesium carbonate or chalk, and

[0059] - 0 - 30 phr plasticizer, e.g. naphthenic oil or phthalate.

[0060] Subsequently, in a second mixing step 4, reactive starting materials of the first elastomer composition are added to the first premix V1 by means of a rolling mill (sub-step 4a). Separately, reactive starting materials of the second elastomer composition are also added to the second premix V2 by means of the rolling mill (sub-step 4b). In the case of both elastomer compositions, the reactive starting materials comprise sulfur, a primary accelerator, and a secondary accelerator, for example

[0061] - 1 - 3 phr Primary accelerator based on sulfenamide, e.g. TBBS or

[0062] CBS,

[0063] - 0 - 2.5 phr Secondary accelerator based on thiuram, dithiocarbamate and / or dithiophosphate, e.g. Thiuram: TMTD, TMTM;

[0064] Dithiocarbamate: ZBEC, ZDMC; Dithiophosphate: TP,

[0065] - 0 - 2 phr vulcanization retarder, e.g. Vulkalent E (chemical name: N-phenyl-N-[(trichloromethyl)thio]benzenesulphonamide), and 0.5 - 4 phr sulfur.

[0066] A blowing agent (e.g. OBSH) is added to the second premix V2 as an additional starting material for the second elastomer composition, for example in a proportion of 1 - 5 phr.

[0067] By admixing the respective reactive starting materials, the first premixture V1 is further processed into a first blank layer S1, and the second premixture V2 is further processed into a second blank layer S2. The first blank layer S1 has, for example, a thickness of 0.1 to 2.0 mm (in particular, 0.5 to 2.0 mm). The second blank layer S2 has, for example, a thickness of 1.0 to 2.5 mm.

[0068] In a subsequent combination step 6, the two blank layers S1 and S2 are placed flat on top of each other. The superimposed blank layers S1 and S2 are pressed together using a pressure roller or cylinder, thereby directly bonding them together to form a blank R. After the combination step 6, the blank R has a thickness of, for example, 1.1 to 3.5 mm.

[0069] The elastomer body E is then produced from the blank R in a two-stage vulcanization process.

[0070] For this purpose, the blank R is placed in the cavity of a first heatable metal mold in a first vulcanization step 8 and is exposed to a first vulcanization temperature for a first vulcanization time. The cavity of the first mold has, for example, a flat, rectangular contour with a thickness of, for example, 1.0 to 3.4 mm. The blank R is cut to size so that it completely fills the cavity of the first mold. The first vulcanization time and the first vulcanization temperature are selected 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 between approximately 5% and 20% of the total vulcanization time that would be required to complete the vulcanization reaction, i.e. to fully crosslink the elastomer material.The heat applied in the first vulcanization step 8 also decomposes the blowing agent, releasing gas. The first mold is designed to form a gas-tight seal around the cavity it encloses, preventing the gas released from the blowing agent from escaping.

[0071] After the first vulcanization time has elapsed, the first mold is opened in an expansion step 10. The partially vulcanized semi-finished product H formed from the blank R by the first vulcanization step 8 is expanded (blown) by the action of the gas released from the blowing agent, forming the foamed inner region C of the covering B. The first vulcanization time controls the strength of the crosslinking after the first vulcanization step 8, and thus the expansion strength.

[0072] To carry out a second vulcanization step 12, the now partially vulcanized and expanded semi-finished product H' is placed in a second heatable metal mold which has a thicker cavity than the first mold, e.g., a thickness of between 2 and 6 mm. In the second mold, the expanded semi-finished product H' is exposed to a second vulcanization temperature for a second vulcanization time. The second vulcanization time and the second vulcanization temperature are selected such that the expanded semi-finished product H' is fully vulcanized in the second vulcanization step 12, i.e., the vulcanization reaction is fully completed. The result of the second vulcanization step 12 is the fully crosslinked elastomer body E. After the second mold has been opened, the elastomer body E has, for example, a thickness of 2 to 6 mm, with the unfoamed top layer 0 having a thickness of 0.1 to 2.0 mm, in particular approximately 0.5 mm.

[0073] In a final assembly step 14, the finished covering B is cut or punched to a final size of, for example, 17 x 17 cm. Furthermore, the elastomer body E is optionally cut or milled on an inner surface I (Fig. 2) opposite the outer surface A, so that—as with the sponge of a conventional table tennis racket covering—the porous structure of the base layer U is exposed on the inner surface I.

[0074] In the finished covering B, the matrix material of the elastomer body E, both in the upper layer 0 and in the lower layer U (without taking into account the gas-filled pores), has a density between 0.8 g / cm 3 and 1.5 g / cm 3 Taking the pores into account, the density of the sublayer U is between 0.3 g / cm 3 and 0.9 g / cm 3 . The finished covering B has a thickness of between 2 mm and 6 mm.

[0075] 1.1 Example 1 (Two-layer covering B based on natural rubber):

[0076] In a first example of the two-layer covering B that can be produced according to the process shown in Fig. 1, the starting materials used for the elastomer compositions of the upper layer O and the lower layer were:

[0077] - To prepare the first premix V1 (for the formation of the upper layer 0) in sub-step 2a of the first mixing step 2:

[0078] - 100 phr natural rubber,

[0079] - 5 phr zinc oxide,

[0080] - 2 phr color pigment black,

[0081] - 20 phr magnesium carbonate,

[0082] - 1 phr stearic acid, and

[0083] - 20 phr naphthenic plasticizer,

[0084] - To prepare the second premix V2 (for the formation of the base layer

[0085] U) in sub-step 2b of the first mixing step 2:

[0086] - 100 phr natural rubber,

[0087] - 5 phr zinc oxide,

[0088] - 2.4 phr titanium dioxide,

[0089] - 20 phr magnesium carbonate,

[0090] - 1 phr stearic acid, and

[0091] - 20 phr naphthenic plasticizer. The first mixing step 2 was carried out using an internal mixer for both the first premix V1 and the second premix V2.

[0092] To produce the first blank layer S1, the following reactive starting materials were added to the first premix V1 in sub-step 4a of the second mixing step 4:

[0093] - 3 phr CBS,

[0094] - 2.6 phr sulfur,

[0095] - 1 phr TMTD, and

[0096] - 1.2 phr ZBEC.

[0097] To produce the second blank layer S2, the following reactive starting materials were added to the second premix V2 in sub-step 4b of the second mixing step 4:

[0098] - 1.2 phr TBBS,

[0099] - 3 phr sulfur,

[0100] - 0.15 phr TMTD, and

[0101] - 4.8 phr OBSH.

[0102] The second mixing step 4 was carried out for both the first blank layer S1 and the second blank layer S2 using a rolling mill.

[0103] In combination step 6, the second blank layer S2 was rolled out to a layer thickness of 1.9 mm. The first blank layer S1 was rolled out to a layer thickness of 0.3 mm and applied flatly to the second blank layer S2 using a pressure roller to form the blank R.

[0104] The first vulcanization step 8 was carried out in the first mold at a first vulcanization temperature of 140 °C for a first vulcanization time of 150 s. The second vulcanization step 12 was carried out in the second mold at a second vulcanization temperature of 140 °C for a second vulcanization time of 1500 s.

[0105] A sectional view of the elastomer body E of the covering B resulting from Example 1 is shown in Fig. 2. In this sectional view, the unfoamed upper layer 0 provided with a smooth outer surface A and the foamed (ie provided with a plurality of pores P) lower layer U can be seen.

[0106] 1.2 Example 2 (Two-layer covering B based on EPDM for the top layer 0 and natural rubber for the bottom layer U):

[0107] In a second example of the two-layer covering B produced by the process according to Fig. 1, the starting materials for the elastomer compositions of the upper layer 0 and the lower layer U were used:

[0108] - To prepare the first premix V1 (for the formation of the upper layer 0) in sub-step 2a of the first mixing step 2:

[0109] - 100 phr EPDM rubber (medium ethylene and ENB content; used

[0110] Type: Keltan ECO 8550),

[0111] - 5 phr zinc oxide,

[0112] - 2 phr color pigment black,

[0113] - 20 phr magnesium carbonate,

[0114] - 1 phr stearic acid, and

[0115] - 20 phr naphthenic plasticizer.

[0116] - To prepare the second premix V2 (for the formation of the base layer

[0117] U) in sub-step 2b of the first mixing step 2:

[0118] - 100 phr EPDM rubber (medium ethylene and ENB content, used

[0119] Type Keltan ECO 8550),

[0120] - 5 phr zinc oxide,

[0121] - 2.4 phr titanium dioxide,

[0122] - 20 phr magnesium carbonate, - 1 phr stearic acid, and

[0123] - 20 phr naphthenic plasticizer.

[0124] To produce the first blank layer S1, the following reactive starting materials were added to the first premix V1 in sub-step 4a of the second mixing step 4:

[0125] - 2 phr CBS,

[0126] - 1.8 phr sulfur,

[0127] - 1 phr TMTD, and

[0128] - 1.5 phr ZBEC.

[0129] To produce the second blank layer S2, the following reactive starting materials were added to the first premix V2 in sub-step 4b of the second mixing step 4:

[0130] - 1.2 phr TBBS,

[0131] - 0.9 phr sulfur,

[0132] - 0.4 phr TMTD,

[0133] - 1 phr Vulkalent E, and

[0134] - 4.8 phr OBSH.

[0135] The combination step 6, the first vulcanization step 8, the expansion step 10, and the second vulcanization step 12 were carried out according to Example 1. However, in contrast to Example 1, the first vulcanization step 8 and the second vulcanization step 12 were carried out at a (first and second, respectively) vulcanization temperature of 170 °C. The first vulcanization time was 180 s. The second vulcanization time was - as in Example 1 - 1500 s.

[0136] 2. Process variant for producing a covering B from a single-layer elastomer body E: A simplified variant of the process, in which the elastomer body E of the covering B is produced in a single layer with a homogeneous elastomer composition, is shown in Fig. 3.

[0137] The process according to Fig. 3 is similar in its basic sequence to the process in Fig. 1, so reference is made to the above explanations. However, in the first mixing step 2 (instead of the two premixes V1 and V2), only a single premix V is produced from unreactive starting materials of the elastomer composition.

[0138] In the second mixing step 4, the reactive starting materials of the elastomer composition, including a blowing agent, are added to this premix V. In the process variant according to Fig. 3, the blank R results directly from the second mixing step 4. The combination step 6 of the process according to Fig. 1 is omitted here.

[0139] With regard to the first vulcanization step 8, the expansion step 10, the second vulcanization step 12 and the optional final assembly step 14, the process according to Fig. 3 is similar to the process according to Fig. 1.

[0140] In the finished coating B, the matrix material of the elastomer body E (without taking into account the gas-filled pores) has a density between 0.8 g / cm 3 and 1.5 g / cm 3 Taking the pores into account, the density of the elastomer body E is between 0.3 g / cm 3 and 0.9 g / cm 3 The finished covering has a thickness of between 2 mm and 6 mm.

[0141] 2.1 Example 3 (Single-layer covering B based on natural rubber):

[0142] In a first example of the single-layer coating B that can be produced according to the process shown in Fig. 3, the following starting materials were used for the production of the premix V in the first mixing step 2:

[0143] 100 phr natural rubber, - 5 phr zinc oxide,

[0144] - 2.4 phr titanium dioxide,

[0145] - 20 phr magnesium carbonate,

[0146] - 1 phr stearic acid, and

[0147] - 20 phr naphthenic plasticizer.

[0148] Premix V is again produced in an internal mixer.

[0149] To produce the blank R, the following reactive starting materials were added to the premix V in the second mixing step 4:

[0150] - TBBS: 1.2 phr

[0151] - Sulfur: 3 phr

[0152] - TMTD: 0.15 phr

[0153] - OBSH: 4.8 phr

[0154] The first vulcanization step 8 was carried out in the first mold at a first vulcanization temperature of 140 °C for a first vulcanization time of 150 s.

[0155] The second vulcanization step 12 was carried out in the second mold at a second vulcanization temperature of 140 °C for a second vulcanization time of 1500 s.

[0156] A cross-sectional view of the elastomer body E of the covering B resulting from Example 3 is shown in Fig. 4. This cross-sectional view shows the foamed inner region C and the smooth (i.e., pore-free) outer surface A of the elastomer body E. Compared to the two-layer covering from Fig. 2, the absence of a layer boundary within the elastomer body E is also clearly visible in Fig. 4.

[0157] 2.2 Example 4 (Single-layer covering B based on EPDM): In a second example of the single-layer covering B produced according to the process shown in Fig. 3, the following starting materials were used for the production of the premix V in the first mixing step 2:

[0158] - 100 phr EPDM rubber (medium ethylene and ENB content, used

[0159] Type Keltan ECO 8550),

[0160] - 5 phr zinc oxide,

[0161] - 2.4 phr titanium dioxide,

[0162] - 20 phr magnesium carbonate,

[0163] - 1 phr stearic acid, and

[0164] - 20 phr naphthenic plasticizer.

[0165] To produce the blank R, the following reactive starting materials were added to the premix V in the second mixing step 4:

[0166] - 1.2 phr TBBS,

[0167] - 0.9 phr sulfur,

[0168] - 0.4 phr TMTD,

[0169] - 1 phr Vulkalent E, and

[0170] - 4.8 phr OBSH.

[0171] The preparation of premixture V and blank R was carried out according to Example 3.

[0172] The first vulcanization step 8, the expansion step 10, and the second vulcanization step 12 were carried out as in Example 3. However, in contrast to Example 3, the first vulcanization step 8 and the second vulcanization step 12 were carried out at a (first and second, respectively) vulcanization temperature of 170 °C. The first vulcanization time was 180 s. The second vulcanization time was—as in Example 3—1500 s.

[0173] The invention is particularly clear from the exemplary embodiments described above, but is by no means limited to these examples. Rather, further embodiments of the invention can be derived by those skilled in the art from the claims and the above description.

[0174] In the above description and claims, the following abbreviations and trade names are used as synonyms (and without limitation to specific commercial products) for the following chemical substances:

[0175] - CBS: N-Cyclohexyl-2-benzothiazyl-sulfenamide

[0176] - ENB: Ethylidene norbornene

[0177] - EPDM: ethylene propylene diene rubber

[0178] - OBSH: p,p'-oxybisbenzenesulfonylhydrazide

[0179] - TBBS: N-tert-butyl-2-benzothiazyl-sulfenamide

[0180] - TMTD: Tetramethylthiuram disulfide

[0181] - TMTM: Tetramethylthiuram monosulfide

[0182] - TP: Dithiophosphat

[0183] - ZBEC: zinc dibenzyl dithiocarbamate

[0184] - ZDMC: zinc dimethyl dithiocarbamate and

[0185] - Vulkalent E: N-phenyl-N-[(trichloromethyl)thio]benzenesulphonamide

[0186] List of reference symbols

[0187] 2 (first) mixing step

[0188] 2a, 2b sub-steps

[0189] 4 (second) mixing step

[0190] 4a, 4b sub-steps

[0191] 6 Combination step

[0192] 8 (first) vulcanization step

[0193] 10 expansion steps

[0194] 12 (second) vulcanization step

[0195] 14 Assembly step

[0196] A outer surface

[0197] B (table tennis racket) surface

[0198] C (foamed) interior

[0199] E Elastomer body

[0200] H (partially vulcanized) semi-finished product

[0201] H' (expanded) semi-finished product

[0202] I Inner surface

[0203] 0 upper class

[0204] P pores

[0205] R blank

[0206] 51 (first) blank layer

[0207] 52 (second) blank layer

[0208] U Lower class

[0209] V Premix

[0210] VI (first) premix

[0211] V2 (second) premix

Claims

Claims 1. Table tennis racket covering (B) with a one-piece elastomer body (E) made of a fully cross-linked, elastomeric matrix material, wherein the elastomer body (E) has a foamed inner region (C) and a smooth outer surface (A) on an outer side.

2. Table tennis racket covering (B) according to claim 1, wherein the matrix material has a homogeneous elastomer composition.

3. Table tennis racket covering (B) according to claim 2, wherein the foamed inner region (C) of the elastomer body (E) has a thickness of 1.5 to 6 mm.

4. Table tennis racket covering (B) according to claim 2 or 3, wherein the foamed inner region (C) of the elastomer body (E) has a density between 0.3 g / cm 3 and 0.9 g / cm 3 and wherein the matrix material of the elastomer body (E) has a density between 0.8 g / cm 3 and 1.5 g / cm 3 has.

5. Table tennis racket covering (B) according to claim 1, wherein the elastomer body (E) comprises an upper layer (O) and a lower layer (U) which are directly bonded to one another, in particular by co-vulcanization, wherein the lower layer (U) forms the foamed inner region (C), and wherein the smooth outer surface (A) is formed on the upper layer (O).

6. Table tennis racket covering (B) according to claim 5, wherein the top layer (0) is unfoamed over its entire thickness.

7. Table tennis racket covering (B) according to claim 5 or 6, wherein the upper layer (0) has a thickness between 0.1 mm and 2 mm, and wherein the lower layer (U) has a thickness between 1.5 and 6 mm.

8. Table tennis racket covering (B) according to one of claims 5 to 7, wherein the top layer (0) has a density between 0.5 g / cm 3 and 1.5 g / cm 3 wherein the underlayer (U) has a density between 0.3 g / cm 3 and 0.9 g / cm3 and wherein the matrix material of the upper layer (0) and the lower layer (U) each has a density between 0.9 g / cm 3 and 1.5 g / cm 3 has.

9. A method for producing a table tennis racket covering (B) according to one of claims 1 to 8, wherein the elastomer body (E) is produced by a two-stage vulcanization process in which a partially vulcanized blank (R) mixed with a blowing agent is expanded between a first incomplete vulcanization step (8) and a second vulcanization step (12).

10. A method according to claim 9 for producing the table tennis racket covering (B) according to one of claims 1 to 4, - in which unreactive starting materials of an elastomer composition are mixed to form a premix (V), wherein the unreactive starting materials of the elastomer composition comprise at least one polymer or a polymer mixture and zinc oxide, - in which reactive starting materials of the elastomer composition are added to the premix (V) to form the blank (R) of the elastomer body (E), the reactive starting materials of the elastomer composition comprising at least one accelerator, sulphur and a blowing agent, - wherein the blank (R) is partially vulcanized in the first vulcanization step (8) for a first vulcanization time at a first vulcanization temperature, - wherein the partially vulcanized blank (H) is expanded to form the foamed inner region (C) of the elastomer body (E) with expansion of the blowing agent, and - wherein the expanded blank (H') is fully vulcanized in the second vulcanization step (12) for a duration of a second vulcanization time at a second vulcanization temperature to form the fully crosslinked elastomer body (E).

11. Method according to claim 9 for producing the table tennis racket covering (B) according to one of claims 5 to 8, - in which unreactive starting materials of a first elastomer composition are mixed to form a first premix (V1) and unreactive starting materials of a second elastomer composition are mixed to form a second premix (V2), wherein the unreactive starting materials of the first and second elastomer compositions each comprise at least one polymer or a polymer mixture and zinc oxide, - at which - the first premix (V1) for forming a first blank layer (S1) reactive starting materials of the first elastomer composition and - reactive starting materials of the second elastomer composition are admixed to the second premix (V2) to form a second blank layer (S2), wherein the reactive starting materials of the first elastomer composition and the second elastomer composition each comprise at least one accelerator and sulfur, and wherein the reactive starting materials of the second elastomer composition additionally comprise a blowing agent, - wherein the two blank layers (S1, S2) are placed flat on top of each other and joined to form the blank (R) by applying a contact pressure, - wherein the blank (R) is partially vulcanized in the first vulcanization step (8) for a first vulcanization time at a first vulcanization temperature, - wherein the partially vulcanized blank (H) is expanded to form the foamed inner region (C) of the elastomer body (E) as a result of the pressure build-up caused by the decomposition of the blowing agent, and - wherein the expanded blank (H') is fully vulcanized in the second vulcanization step (12) for a second vulcanization time at a second vulcanization temperature to form the fully crosslinked elastomer body.

12. A process according to claim 10 or 11, wherein the starting materials of the or each elastomer composition, in addition to 100 phr of the polymer or polymer mixture, in particular a natural rubber or synthetic rubber, each contain: - 2 - 10 phr zinc oxide - 0 - 2 phr stearic acid - 0 - 40 phr of a filler, in particular magnesium carbonate or chalk - 0 - 30 phr of a plasticizer, in particular a naphthenic oil or phthalate - 1 - 3 phr of a sulfenamide-based primary accelerator, in particular TBBS or CBS, - 0 - 2.5 phr of a secondary accelerator based on thiuram, dithiocarbamate and / or dithiophosphate, in particular TMTD, TMTM, ZBEC, ZDMC or TP, - 0 - 2 phr of a vulcanization retarder, in particular N-phenyl-N-[(trichloromethyl)thio]benzenesulphonamide)), and - 0.5 - 4 phr sulfur 13. Process according to claims 10 and 12, wherein the starting materials of the elastomer composition additionally contain 1 - 5 phr of a blowing agent, in particular OBSH.

14. The process according to claims 11 and 12, wherein the starting materials of the second elastomer composition additionally contain 1-5 phr of a blowing agent, in particular OBSH.

15. The process according to any one of claims 10 to 14, wherein the first vulcanization time is between 5% and 25%, in particular approximately 10%, of the second vulcanization time.

16. Use of the elastomer body (E) produced by the process according to any one of claims 9 to 15 as a table tennis racket covering (B).

Images