PVC-free multilayered tube for medical uses, method for its manufacture and use

The invention relates to a PVC-free multilayer hose for medical purposes according to the preamble of claim 1, a method for producing such PVC-free multilayer hoses according to the preamble of claim 18 and the use of the PVC-free multilayer hoses according to the invention.

The state of the art<ul id="ul0001" list-style="none" compact="compact"><li>WO-A-92/11820 (= D1),</li><li>DE-A-28 31 034 (= D2),</li><li>US-A-4,948,643 (= D3),</li><li>EP-A-0 136 848 (= D4),</li><li>DE-PS-44 04 041 (= D5),</li><li>DE-OS-42 19 071 (= D6),</li><li>DE-OS-39 14 998 (= D7) and</li><li>WO-A-93/23093 (= D8)</li></ul> called.

PVC-free materials = non-PVC materials and single-layer hoses made from them with only one layer are known, for example, from D1. Herein a tube material for medical purposes is presented, which has a blend of polyurethane and polyester and which can be subjected to a sterilization treatment in an autoclave, heat sealable as well as sealable and fusible with high frequency energy. The hose material described is free of the PVC plasticizer DEHP, a phthalate that has been suspected to have carcinogenic properties. However, it may contain certain additional fractions of a citric acid ester (butyryl trihexyl citrate) as a softening substance and other processing aids such as internal or external lubricants. The thermoplastic material disclosed in D1 can be processed by known molding processes such as extrusion, injection molding or blow molding, but is essentially intended for use with medical bags or connectors made of PVC. Only in connection with these "classic" PVC materials does it show satisfactory compatibility, especially when forming connections using heat or high-frequency sealing.

PVC-free plastic materials are also known from the D2, which are suitable for the production of tubes for receiving or conducting blood or medical solutions. The D2 relates in particular to plastic compositions which consist of 10 to 40% by weight of a polyolefin essentially formed from propylene units, 40 to 85% by weight of a block copolymer made of a central polyethylene or polybutylene block with terminal polystyrene blocks, 10 to 40% by weight a polymeric plasticizer based on polyethylene and optionally an antioxidant. The disclosed materials are flexible, quite heat-resistant, have the softness of the material required for medical applications and can also largely solve the aging problem essentially caused by low-molecular plasticizers, but the stability and rigidity of the material leave something to be desired. In particular, the single-layer material shown would increase the rigidity by increasing the polypropylene content at the expense of the softness and flexibility of a finished tube or bag.

Multi-layer hoses for medical connection lines are the subject of the D3. Three-layer hoses are shown, the outer layer of which is based on ethylene vinyl acetate (EVA) and the inner layer of which is based on polyvinyl chloride (PVC). Since the adhesion between the inner and outer layers is poor, an adhesion-promoting layer made of an ethylene-based polymer, which contains vinyl acetates and acrylates, is co-extruded as a middle layer together with the other two materials. Plastic materials with the sequence of layers shown are particularly suitable for use as a connecting or connecting piece or hose with medical bags made of EVA (compatibility of the outer layer with the bag) and allow the introduction and secure connection, for example by solvent fusion, of a PVC membrane Hose inside the connector or pipe. From a medical point of view, the multilayer hoses shown in D3 are consistently questionable materials, since the PVC layer contains considerable amounts of trimellitic acid esters as plasticizers, but these compounds can be carcinogenic.

Finally, D4 is known for multilayer hoses, which are regarded as a potential replacement for PVC hoses in the medical sector. However, the use of PVC according to D4 is not completely ruled out, rather it is tolerated as a material or admixture for an intermediate layer or the inner layer.

In particular, the D4 relates to a three-layer hose for medical purposes, the inner layer of which consists of ethylene-propylene copolymer, a polypropylene, a copolyester made of a polyether and a polyethylene terephthalate, polyurethane, polyvinyl chloride or a blend of copolyester and ethylene-vinyl acetate copolymer.

The intermediate layer can consist of an LLDPE (linear low density polyethylene), ethylene-vinyl acetate copolymer (EVAC), modified EVAC, ethylene-methyl acrylate copolymer (EMAC), modified EMAC, PVC or a blend of the aforementioned compounds.

The outer layer according to D4 is formed from polypropylene, ethylene-propylene copolymer or modified ethylene-propylene copolymer.

The choice of materials for the intermediate layer depends essentially on the ability of these materials to give the entire structure of the multilayer hose the necessary flexibility. The criterion for the selection of the inner layer material is sufficient heat resistance to make the resulting tube autoclavable, while the choice of an outer layer material is essentially based on the desire to enable a relatively stable ultrasonic, hot or high-frequency energy sealing with a polycarbonate connector.

Apart from the fact that the hoses according to D4 do not completely exclude the use of PVC, the hoses are compatible with polycarbonate, but are less suitable for forming connections with other newer and more advantageous polypropylene-based bag or connector materials.

In addition, the flexible middle layer according to D4 is usually the strongest layer, which easily leads to insufficient rigidity of the entire hose. It is therefore generally and not only optionally necessary to irradiate the extruded tubes in order to achieve heat sterilization by radiation-induced crosslinking. This process is complex.

The D5 concerns polymer material from medical instruments. Disclosed are silane-grafted VLDPE's or ULPDE's which have been crosslinked with moisture in order to then obtain, for example, transparent, kink-resistant and sterilizable hoses, in particular by extrusion. A high degree of crosslinking is a prerequisite for the steam sterilizability of the end product. Although the material appears to be suitable for replacing PVC, the single-layer tubing available from it lacks the ability to make a good and direct connection with a built-in part during a simple heat sterilization treatment without having to give up the dimensional stability.

The D6 discloses radiation-sterilizable, recyclable infusion and transfusion devices in which all components made of thermoplastic or elastomeric homopolymers, copolymers, block copolymers based on polyolefins are shown. In particular, the D6 also makes connecting tubes made of PE-LLD or linear PE-LVLD accessible to the public, but does not rule out the use of EVA or special ionomers.

To connect these hoses are joined using organic solvents such as cyclohexane. Alternatively, the hoses can be ultrasonically welded or connected using light or UV-curable adhesives.

D7 is concerned with transmission systems for infusion or transfusion purposes, in which all components consist of a polymer, copolymer or block copolymer without the use of PVC for environmentally friendly recycling. The polymeric materials that are used are based on styrene polymers.

D8 relates to PVC-free co-extruded multi-layer tubing for medical purposes that has a core layer made from a blend of polyamide and EVA. An outer layer is applied to this inner core layer by means of an adhesive layer. The adhesive layer essentially contains copolyester and SEBS copolymer, optionally PP and EVA. The choice of material proves that the hose disclosed must have the disadvantages which result from the use of EVA, copolyester or polyamide.

In view of the disadvantages with which the embodiments described in the state of the art are afflicted, it is the object of the present invention to provide a hose for medical purposes which can be individually adapted to many different connectors, in particular those based on polypropylene or polycarbonate. or bag materials allowed. Furthermore, it is desirable that the new hose material enables a firm bond without additional adhesion promoter or the like. In addition, the new multi-layer hose should be sufficiently flexible, elastic and soft and still be as prone to kinking as possible, relatively rigid and thermally stable. After all, the hose should not release any dangerous substances into these fluids when it comes into contact with the fluids common in medicine, and should be inert to medical solutions at all. The aim of the invention is also to provide a method for producing such a multi-layer hose. Furthermore, the specification of possible uses of the hose material according to the invention is the object of the invention.

These and other tasks not mentioned in more detail are achieved by a PVC-free multi-layer hose for medical purposes of the type mentioned at the outset with the features of the characterizing part of claim 1. Special developments are protected in the claims dependent on claim 1. In procedural terms, the object of the invention is achieved by a method according to claim 18, while claims 26 and 28 protect the use of the PVC-free multilayer hose according to the invention.

Characterized in that in a PVC-free multi-layer hose for medical purposes with at least two layers, of which a base layer A) made of a first plastic material is connected to at least one connection layer B) made of a second plastic material, the first plastic material has at least one polymer that has a Withstands heat sterilization at ≥ 121 ° C without damage to the shape, has a Shore D ≤ 32, which has a residual stress at ≥ 121 ° C that is sufficient to form a press fit at a connection point, and from which a curl or loop with a diameter of up to 60 mm can be formed without kink damage, while the second plastic material comprises at least one polymer which during a heat sterilization at 121 ° C below the the resulting connection pressure tends to flow when a press fit is formed and has a Shore A ≤ 65 hardness, So that the dimensional stability of the first plastic material at temperatures ≥ 121 ° C and that of the second plastic material no longer exists, a flexible hose that is transparent after heat sterilization, has sufficient kink stability and can be sealed with hose clamps or the like, for To make available. In addition, the PVC-free multilayer hose according to the invention additionally has the ability to establish a firm and tight connection with an installation part, a medical bag or a connector, and in an extremely simple manner during a possible heat sterilization treatment.

The present invention is therefore based, inter alia, on the idea of ​​coordinating different plastic layers in a multi-layer hose material so that at least one layer acting as a base layer gives the hose material sufficient thermal stability during sterilization, while at least one other layer acts as a connection or connection layer forming a tight and tight connection with a bag, Connection piece, connector or any other hose allows, without the need to use additional adhesive, sealing or sealing compounds or auxiliary materials or other sealing methods (high-frequency energy or the like).

In the context of the invention, "sterilization" is generally understood to mean a process for killing or inactivating (viruses) all microorganisms, including the highly resistant permanent forms, the tubes according to the invention in particular steam sterilization in an autoclave with tensioned water vapor of at least 121 ° C., corresponding to an atmosphere of excess pressure, the so-called autoclaving or autoclaving treatment without being damaged.

Furthermore, for the invention, “plastic material” is understood to mean those materials whose essential constituents consist of macromolecular organic compounds, the plastic materials also being referred to as polymers, for which purpose in particular homopolymers and copolymers (statistical, block and / or graft polymers) and mixtures ( = Blends) from the aforementioned substances.

An important criterion for the selection and assignment of a polymer according to the invention to a plastic material and thus to a specific functional layer of the multilayer PVC-free hose for medical purposes is the dimensional stability during heat sterilization.

In this sense, a plastic material is considered to be dimensionally stable if a hose sample with a length of at least 10 mm, an inner diameter of 5 mm and an outer diameter of 7 mm undergoes steam sterilization at 121 ° C for at least 15 minutes. Warm-up time, at least 15 minutes. Holding time and at least 10 min. Cooling time with no visible change in shape such as "collapse" or "ovality", etc., survives.

The temperature which is of interest for the softening of the polymers or plastic materials according to the invention is the temperature of the steam sterilization, namely 121 ° C. The fact that the base layer has a polymer, the dimensional stability of which means temperature resistance with respect to deformation even at more than 121 ° C., largely precludes the possibility of flowable softening or reaching the liquid state of the base layer during steam sterilization, while a polymer of the plastic material of the connection layer achieves its flowable softening under pressure at 121 ° C., the softening of the connection layer is permitted under the standard conditions of steam sterilization. This enables a connection to be made at a contact point with a connection partner without the shape of the hose changing in an uncontrolled manner.

The temperatures given relate to the pressure during steam sterilization, i.e. approximately one atmosphere of positive pressure. However, it goes without saying that the pressure dependence of the softening temperature in the region under consideration between normal pressure and the excess pressure required for steam sterilization is generally negligible.

Depending on the desired function of the PVC-free hose according to the invention, it may be advantageous to arrange the layer B) which is capable of forming a connection on the outside, inside or both outside and inside. Accordingly, the PVC-free multilayer hose of the invention is preferably characterized by the sequence of layers B) A), A) B) or B) A) B), in each case from the inside to the outside.

In the first case, the hose according to the invention can, for. B. "plugged" onto a connector made of suitable material so that the inner layer of the hose is in contact with the outer surface of the connector. In the second case, the hose according to the invention is intended for insertion into a hollow part, the inner surface of which consists of a suitable material for forming a connection, while if two connection layers (outside and inside) are arranged in the PVC-free multilayer hose according to the invention, the two connection options mentioned can be implemented either selectively or simultaneously . In the case of a connection with a connector, the identification layer is preferred on the inside, while in the case of a connection, for example with a bag, the connection layer is on the outside.

In addition to the base and connection layers described so far, the PVC-free multi-layer hose of the invention in a preferred development has a further functional layer, namely additionally at least one transparent cover layer C) as an outer layer made of a third plastic material, one layer C) as the innermost or outermost Layer can be arranged.

The cover layer gives the multilayer hose an improved surface quality with regard to stickiness, bluntness and reduced friction, transparency and special sealing properties.

In principle, the layer C) can be provided as an end layer either inside or outside. However, it is preferred for the invention that, in the event that the outermost or innermost outer layer is a connection layer B), the correspondingly arranged outer layer corresponding thereto is a layer C).

A configuration as a lip tube is particularly advantageous, at least on the cover layer (FIG. 2). Accordingly, particularly preferred embodiments according to the invention are PVC-free multilayer hoses which, owing to the sequence of layers B) A) C) / C) A) B) / C) B) A) B) or B) A) B) C), are marked inside out. Depending on the use of the hose, the inner layer must be compatible with the solution flowing through the hose.

In order to ensure the aforementioned properties of layer C), in a further advantageous embodiment the cover layer C) consists of a third plastic material which has at least one polymer whose temperature resistance to deformation is still above&gt; 121 ° C.

In the case of PVC-free multilayer hoses preferred according to the invention, the first plastic material for the base layer is predominantly a synthetic rubber based on isoprene or polypropylene with a density ρ 0,9 0.9 g / cm³ and the second plastic material for the connection layer predominantly a polyethylene copolymer or a synthetic rubber with Mw &lt;100,000 g / mol. This combination for each base layer A) and the connection layer or layers B) can already offer a large number of required properties. A polymer use according to the following list is particularly advantageous for the invention. Percentages mean weight percent.<dl id="dl0001"><dt><u>Top layer</u>:</dt><dd>Thickness = 10 - 50µm</dd><dt>40% - 60% PP-R</dt><dd>(PP23M 10 cs 264, REXENE) and</dd><dt>60% - 40% SIS</dt><dd>(HVS 3, Kuraray); or Tuftec H 1052 (Asahi)</dd><dt><u>Base layer</u>:</dt><dd>Thickness: 900 - 980 µm at approx. 1 mm wall thickness of the hose</dd><dt>50 - 100% SIS</dt><dd>(HVS / 3, Kuraray) and</dd><dt>50 - 0% PP-R</dt><dd>(PP 23M10cs264, REXENE); - PP with Shore D ≤ 32, <img file="EP0765740A2_D0001.tif" /> = 0.9 g / cm³; (e.g. Adflex 100 G, Himont, with up to 50% rubber, e.g. PIB, styrene-ethylene-butylene rubber, styrene-ethylene-propylene rubber, SIS)</dd><dt><u>Connection layer</u>:</dt><dd>Thickness 10 - 50 µm</dd><dt>100% SEBS compound</dt><dd>(PR 3415, Wittenburg)</dd><dt>100 % SEPS / SEP</dt><dd>(Septon 2277, Kuraray) or</dd><dt>50 - 100% PE copolymer</dt><dd>(Engage XU58.000 52, DOW) and</dd><dt>0 - 50% SEBS / SEB</dt><dd>(Kraton G 1726, Shell);</dd></dl>

The abbreviations mean:<ul id="ul0002" list-style="none" compact="compact"><li>PP-R = polypropylene random copolymer</li><li>SIS = styrene-isoprene-styrene</li><li>SEBS = styrene-ethylene-butylene-styrene rubber</li><li>SEB = styrene-ethylene-butylene rubber</li><li>SEPS = styrene-ethylene-propylene-styrene rubber</li><li>SEP = styrene-ethylene-propylene rubber</li><li>PE copolymer = polyethylene copolymer</li></ul>

SEBS and SEB belong to the group of styrene-ethylene-butylene block copolymers which can advantageously be used in the context of the invention as connection layer materials or in the connection layer in a mixture with other materials in different block proportions.

SEBS compound is a mixture of different styrene-ethylene-butylene block copolymers.

The same applies to SEPS and SEP, which belong to the group of styrene-ethylene-propylene block copolymers. A SEPS compound is also a mixture of different styrene-ethylene-propylene block copolymers.

Again, with regard to the adhesion between layers made of materials A), B) and C), it can be said that this is basically sufficient. However, it can be increased in an advantageous manner in that the layers A), B) and / or C) in each case additionally up to 40% by weight, based on 100% by weight of their composition as described and defined above, of that plastic material have, which serves to form one or both adjacent layers of the PVC-free multilayer hose. A further intermediate layer made of the polymer materials of the respectively adjacent layers is also advantageous.

This "material mediation" or the substitution of material significantly increases the compatibility of the layers formed into a tube without questioning the other properties.

Another essential and particularly preferred feature of the invention can be seen in the fact that in a further development of the PVC-free multilayer hose according to the invention, the plastic materials for all layers of the hose are selected so that they essentially consist of polyolefin homopolymers or polyolefin copolymers or modifications thereof (e.g. SEBS) . It was particularly astonishing that the invention succeeded for the first time in creating a PVC-free multi-layer hose which consists exclusively of environmentally compatible materials, which allows problem-free connection formation with connectors during steam sterilization and at the same time meets all other requirements for a hose which can be used medically.

With regard to the geometry, the hoses themselves can be designed in all required and customary thicknesses and sizes. The PVC-free multilayer hose according to the invention preferably consists of more than 96-98% by volume, based on the total volume of the hose material, of the base layer A). The individual layers themselves preferably have the following thicknesses: the base layer A) a thickness&gt; 900 μm, the connection layer B) a thickness between 10 μm and 50 μm and the sealing layer C) a thickness between 10 μm and 50 μm.

The invention also relates to a method for producing a PVC-free multilayer tube for medical purposes, in which a first plastic material for forming a base layer A) and a second plastic material for forming at least one connected connection layer B are used to produce an at least two-layer multilayer film made of plastic ) coextruded with each other and forming an essentially coaxial and cylindrical multilayer tube, the method being characterized in that a first plastic material is used which has at least one polymer which can withstand heat sterilization at ≥ 121 ° C without damage to the shape, has a Shore D ≤ 32 hardness and has a residual stress at ≥ 121 ° C, sufficient to form a press fit at a connection point and from which a curl or loop with a diameter of up to 60 mm can be formed without kink damage, while using a second plastic material which has at least one polymer which tends to flow during heat sterilization at 121 ° C under the connection pressure resulting from the formation of a press fit and has a Shore A ≤ 65 hardness, so that the dimensional stability of the first plastic material at temperatures ≥ 121 ° C and the second plastic material no longer.

The shaping is carried out according to methods familiar to the person skilled in the art, such as vacuum calibration. It is particularly important for the invention that the coextrusion of several layers with one another enables several desired properties of individual components to be combined in one tube in order to increase the quality of the tube.

For this purpose, the coextrusion process offers the possibility, with a suitable selection of the extrusion partners, to provide tailor-made PVC-free multi-layer hoses, which make it possible in a unique way to dispense with any addition of adhesion promoters and still the required properties and, in addition, other important properties such as gas - and water vapor permeability, strength of the material, weldability, To influence the transparency and temperature resistance of the hose.

The selection of the layer materials to be extruded with one another is of great importance for the invention, plastic materials or layers being particularly preferably selected such that all layers of the PVC-free multilayer hose essentially consist of polyolefin homopolymers and / or polyolefin copolymers, or of polymers based thereon, for example Modifications of polyolefins (eg SEBS).

The coextrusion of such materials is known in principle, but based on existing experience, the successful implementation of such a complex multilayer hose as the one according to the invention was not readily predictable. In this respect, the success according to the invention was surprising, since in practice it has repeatedly been shown that even with the help of tabulated properties of polymers, such as data on bond adhesion, the use of such materials does not necessarily lead to success. This means that the solution to a given task by simply selecting from known materials is fundamentally not readily possible with a multilayer coextrusion tube. Coordinating the viscosity of the melt is particularly difficult when coextruding rubbers such as PIB with PP.

Furthermore, it is preferred in the process according to the invention that the plastic materials are selected for forming a PVC-free multilayer hose so that all layers of the hose can additionally contain up to 40% by weight of the material of the adjacent layer or layers. In this way, a slight adhesion between two adjacent layers can be compensated to a certain extent. After the actual shaping, the tube obtained can be processed further in the usual ways. It is preferably shock-cooled with water after molding. In this way, because of the "freezing" of the amorphous state, an optimal bond with high flexibility and sufficient rigidity is achieved, but above all, the shock-like cooling of the melt improves the transparency of the tube because no crystalline areas can form. This leads to a low degree of crystallinity and thus to high transparency and toughness.

The PVC-free multilayer hose according to the invention is excellently suitable for use in the medical field. The materials of the multi-layer hose are all selected so that the hose is transparent, kink-resistant and flexible, but in particular hot-sterilizable and can be connected firmly and bacteria-proof to the corresponding connector by the pressing force exerted by the hose. In addition, the non-PVC multilayer hose of the invention is also biocompatible. The use of PVC, which always contains plasticizers, is avoided, and no adhesion promoters are required that could possibly diffuse through the plastic material layers.

Because of its excellent material and usage properties, the PVC-free multilayer hose according to the invention is used with great advantage as a fluid-carrying line in dialysis, infusion or artificial nutrition. For this purpose, it is advantageously provided that at least the connection area for connection to the predicate bag is provided with a welding lip.

In this case, the compatibility of the connection layer material of the multilayer hose according to the invention with the connectors of medical bags (especially made of polypropylene) and / or especially in medical technology, for example in the form of connectors made of polypropylene, is used. Connectors or bags can be provided with a rough surface onto which a PVC-free multilayer hose according to the invention is plugged, so that the inner surface of the PVC-free multilayer hose with the connection layer B) of the hose is an interference fit with the rough outer surface of the connector or bag ( if necessary, connecting piece of the bag).

Due to the surface of the polypropylene parts and the flow properties of the connection layer B) of the hose when exposed to heat, for example during steam sterilization, an already good and firm connection is given by the material of the connection layer flowing into the unevenness of the surface of the connector or bag socket. The connection becomes even better if the plastic materials used to produce the connection layer B) of the hose have a proportion of between 1 and 40% by weight, based on 100% by weight of the material of the connection layer, with a plastic material from which the connector or the connection piece of the bag is made to be blinded. The connection can be improved by roughening the surface.

Further advantages and details of the invention result from the following examples, which are explained with reference to the attached figures.

Show in the figures<ul id="ul0003" list-style="none"><li>FIG. 1 shows a cross section of an embodiment of the PVC-free multilayer hose according to the invention,</li><li>Figure 2 shows another embodiment with lip formation.</li></ul>

A three-layer hose 1 according to the present invention can be seen in the figures. In the embodiment shown in FIG. 1, the outer layer 2 of the hose 1 is a cover layer C) made of a blend of SEBS compound, SEPS compound, a PP / SIS blend or PP / styrene-ethylene-butylene (-propylene) rubber -Blend, SEBS and / or SEPS.

The intermediate layer 3 represents the largest volume of the tubular casing as the base layer A). Suitable materials include styrene-ethylene-butylene rubber with PP PIP with PP SEPS with PP, PP and SIS with PP.

The connection layer 4 consists of SEBS compound with SEBS / SEB (Kraton G 1726 and Kraton G 1652, Shell), a PE copolymer (Engage XU58000, 52, DOW) optionally with SEBS / SEB (Kraton G 1726, Shell) or SEPS / SEP (Septon 2277, Kuraray). Kraton G 1726 is a low molecular weight SEBS with at least 20% diblock content, while Kraton G 1652 is a high molecular weight SEBS with no significant diblock content.

Layers A), B) and C) have the following dimensional stability, elastic modulus and hardness: <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" align="left">E-module</entry><entry namest="col3" nameend="col3" align="left">hardness</entry><entry namest="col4" nameend="col4" align="center">Dimensional stability during heat sterilization</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Main layer base A)</entry><entry namest="col2" nameend="col2" align="left">≤ 80N / mm²</entry><entry namest="col3" nameend="col3" align="left">Shore D≤32</entry><entry namest="col4" nameend="col4" align="right">&gt; 123 ° C</entry></row><row><entry namest="col1" nameend="col1" align="left">Connection layer B)</entry><entry namest="col2" nameend="col2" align="left">≤ 80N / mm²</entry><entry namest="col3" nameend="col3" align="left">Shore A≤65</entry><entry namest="col4" nameend="col4" align="right">&lt;121 ° C</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Top layer C)</entry><entry namest="col2" nameend="col2" align="left">&lt;1000N / mm²</entry><entry namest="col3" nameend="col3" align="left">&lt;R90 *)</entry><entry namest="col4" nameend="col4" align="right">&gt; 123 ° C</entry></row></tbody></tgroup><tgroup cols="4" colsep="0" rowsep="0"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><tbody valign="top"><row><entry namest="col1" nameend="col4" align="justify">*) R90 means Rockwell 90 hardness; see. DIN 10109-1</entry></row></tbody></tgroup></table></tables>

Further advantages and embodiments result from the following patent claims.