EP2016868A1 - Pull-out core for mattresses and padded furniture - Google Patents

Abstract

The core has curved or bent cross-sectional shaped recesses (3, 4) penetrating into a thickness direction, and arranged so that the core is extended in a direction of tension (5) to form through holes. The recesses are formed such that the recesses are provided at a stretched out distance, in which the core is stable against contraction without application of tensile force. The recesses are arranged in pairs of rows (2a-2c) transverse to the direction of tension and a recess direction, and are interlocked with each other. The core is made of elastic polyurethane foam or natural latex.

Description

Technical area

The present invention relates to a core for a mattress or a furniture upholstery and a mattress made therewith or a furniture upholstery fabricated therewith.

State of the art

For mattresses and furniture upholstery cores are often used from a foam plastic material or on the basis of vulcanized latex. The core is usually provided with recesses or openings to ensure good air circulation. For this purpose, either elaborate shapes are necessary in the production, or the openings are subsequently cut or punched out, waste being obtained.

From the German utility model DE 20 2006 011 190 U1 a mattress is known whose core has rows of parallel, equally spaced and equally long incisions which pass through the core through its thickness. The incisions of adjacent rows are set against each other on the gap. As a result, the core can be pulled apart in a pulling direction running transversely to the direction of the incisions, wherein the incisions form diamond-shaped openings. In this way, a mattress is created, the core is provided with openings for air circulation, without causing waste.

A disadvantage of this known mattress core, however, is that the core must be kept permanently under a bias in the pulling direction, otherwise it would contract again by itself. In order to produce the necessary bias, the core is held by a carrier which surrounds the core either as a rigid ring or is designed as a cover plate increased compressive strength. However, such a hard edge or a corresponding hard cover plate are usually undesirable.

Presentation of the invention

It is therefore an object of the present invention to provide a mattress core or core for another type of furniture upholstery, which is indeed extendable, but in which a carrier in the form of a hard edge or a hard cover plate can be omitted.

This object is achieved by a core according to claim 1. Advantageous embodiments are specified in the dependent claims. The invention also provides a mattress made with such a core and a corresponding furniture cushion.

The core of the invention is made of an elastic material, preferably a foam material such as elastic polyurethane foam or a foam based on natural latex. He has a plurality of incisions, which enforce him in its thickness expansion. The core is at least partially expandable in a pulling direction, wherein the incisions expand in openings of the core. In this case, the elastic material of the core deforms in the vicinity of the incisions in a corresponding manner. The invention is based on the recognition that the incisions can be formed and arranged so that there is at least one exploded state in which the mattress core is stable even without the application of a tensile force in the pulling direction. The core is, so to speak, bistable, ie, there are at least two stable states in which the core has a different extent with respect to the pulling direction.

In a preferred embodiment, the incisions have a curved and / or bent plan view and are arranged in pairs of substantially transversely to the pulling direction and transverse to the thickness (cutting) extending, mutually parallel rows, the incisions of each of a pair of adjacent rows arranged interlocked are. The pairs of rows can be straight or (slightly) curved. In the present context, when the rows are straight, the term "toothed" in the mathematical sense means that there is at least one straight line along the rows intersecting all the cuts of both the first and second rows. If the rows are curved, there is a corresponding "smooth" line that runs parallel to the rows and cuts all the cuts. Preferably, the incisions of each of a pair of adjacent rows have the same plan shape and dimensions, but are oppositely oriented, ie, the incisions within one of these rows have a first orientation substantially, while the incisions of the other row second, opposite Have orientation.

The material between the incisions of a pair of adjacent rows is then subdivided into a chain of regions that are substantially equal in shape in a particular embodiment. These areas are essentially limited by the cuts and thus separated from the remaining material by these cuts. They are also referred to below as "intermediate areas". In the contracted state of the core, these regions assume a first stable orientation relative to each other. As the core is pulled apart they change their relative orientation. In this case, the intermediate regions are arranged so that they tilt relative to each other in a second stable orientation when the core is pulled apart beyond a certain point.

The intermediate areas are in the contracted state of the core preferably orientated so that they are elastically compressed (compressed) when pulling the core transverse to the pulling direction. This can be achieved by a zigzag arrangement of the intermediate regions, ie in that the regions each have an elongated shape and the longitudinal axes defined thereby enclose an angle of significantly less than 180 °, preferably less than 120 °. The regions are then arranged and bonded to each other and to the surrounding material so as to be able to avoid the forces resulting from the compression in the direction of the second stable orientation when the core is pulled apart beyond a certain point.

• nahe seinem ersten Ende über eine erste Materialbrücke mit dem nachfolgenden Bereich verbunden;
• nahe dem ersten Ende über eine zweite Materialbrücke mit dem Material zwischen zwei benachbarten Einschnitten der ersten der beiden benachbarten Reihen verbunden;
• nahe seinem zweiten Ende über eine dritte Materialbrücke mit dem vorhergehenden Bereich verbunden; und
• nahe dem zweiten Ende über eine vierte Materialbrücke mit dem Schaumstoffmaterial zwischen zwei benachbarten Einschnitten der zweiten der beiden benachbarten Reihen verbunden. Über die zweiten und vierten Materialbrücken werden folglich die Zugkräfte auf die Zwischenbereiche übertragen.

In particular, in a preferred embodiment, each area

• connected to the subsequent area near its first end via a first material bridge;
• connected to the material between two adjacent sipes of the first of the two adjacent rows near the first end via a second material bridge;
• connected to the preceding area near its second end via a third material bridge; and
• connected near the second end via a fourth material bridge with the foam material between two adjacent incisions of the second of the two adjacent rows. Consequently, the tensile forces are transmitted to the intermediate areas via the second and fourth material bridges.

Thus, while a change in orientation takes place between the rows within a pair, it is preferred that the distance from one pair of adjacent rows to the next pair of adjacent rows be sufficiently large that the material be in the range between the pairs of adjacent rows (preferably at least one continuous, parallel to extending the rows of material strip) substantially retains its shape and orientation when pulling the core apart. In this way, the pairs of rows are virtually "decoupled" from each other, ie, the length expansion when pulling apart takes place practically only within the row pairs, while the pairs do not influence each other when a row pair is pulled apart. The expression that the material "substantially retains" its shape and extent is understood to mean that the material area in question changes its dimensions in each spatial direction by less than 1% when the length of the core in the pulling direction is increased by 10% ,

In a preferred embodiment, the incisions have a curved plan without kinks, in particular a substantially part-circular, in particular semicircular plan.

• Der Abstand zwischen den Enden zweier benachbarter Einschnitte innerhalb derselben Reihe beträgt zwischen 2 und 10 mm, besonders bevorzugt 4 bis 6 mm.
• Die minimale Distanz zwischen zwei Einschnitten benachbarter Reihen in Zugrichtung beträgt zwischen 2 und 7 mm, besonders bevorzugt 4 bis 6 mm. Diese Zahlen sind insbesondere für halbkreisförmige Einschnitte mit einem Radius zwischen ca. 15 und ca. 30 mm, bevorzugt ca. 20 bis 25 mm, vorteilhaft.

The geometry of the incisions or the interstices between the incisions is preferably chosen as follows, in particular if a polyurethane cold foam material commonly used for mattress cores is used:

• The distance between the ends of two adjacent incisions within the same row is between 2 and 10 mm, more preferably 4 to 6 mm.
• The minimum distance between two incisions of adjacent rows in the pulling direction is between 2 and 7 mm, particularly preferably 4 to 6 mm. These numbers are particularly advantageous for semi-circular cuts with a radius between about 15 and about 30 mm, preferably about 20 to 25 mm.

The present invention also relates to a mattress or a furniture cushion having a core according to the invention, which is preferably in an at least partially exploded state, and a coating surrounding the core. The mattress preferably also comprises on one or both sides of the core a cover plate or cover layer, which rests flat on the core and at least partially connected thereto, in particular glued. Since the core itself is stable in the extended state, the cover plate does not need any, unlike the prior art To exempt longitudinal forces and can therefore be thin and / or flexible.

Brief description of the drawings

Fig. 1

eine perspektivische Ansicht eines Matratzenkerns;

Fig. 2

eine Draufsicht auf einen Ausschnitt des Matratzenkerns;

Fig. 3

eine perspektivische Ansicht des Matratzenkerns der Fig. 1 in ei- nem vollständig ausgezogenen Zustand;

Fig. 4

eine Draufsicht auf einen Ausschnitt des Matratzenkerns im aus- gezogenen Zustand;

Fig. 5

eine perspektivische Ansicht des Matratzenkerns der Fig. 1 in ei- nem teilweise ausgezogenen Zustand; sowie

Fig. 6

ein schematisches Diagramm der elastischen Energie in Abhän- gigkeit von der Längsausdehnung.

Preferred embodiments of the invention will now be described with reference to the drawings, in which:

Fig. 1

a perspective view of a mattress core;

Fig. 2

a plan view of a section of the mattress core;

Fig. 3

a perspective view of the mattress core of Fig. 1 in a fully extended condition;

Fig. 4

a plan view of a section of the mattress core in the extended state;

Fig. 5

a perspective view of the mattress core of Fig. 1 in a partially extended condition; such as

Fig. 6

a schematic diagram of the elastic energy as a function of the longitudinal extent.

Detailed description of preferred embodiments

The Fig. 1 shows a functional pattern of a mattress core according to the invention in a perspective view. The core is made of an elastic, not permanently deformable foam material, as it is commonly used for mattress cores, such as polyurethane cold foam. The core can also be made of a different foam plastic material or of a natural foam material based on latex.

That in the Fig. 1 shown functional pattern has only dimensions of length L ₁ = 60 cm, width B = 40 cm and thickness D = 4 cm, while a complete core will usually have much larger dimensions. However, this is of no significance for the function of the core explained below since it is largely independent of the overall dimensions of the core.

As in particular in the Fig. 2 Good, the core of a plurality of semicircular incisions 3, 4 through its entire thickness passes through. The incisions are produced, for example, by punching with a roller punch or a bridge punch in a simple manner, preferably after the preparation of the starting material.

The cuts are arranged in pairs 2a, 2b, 2c of parallel rows extending transversely to the longitudinal direction of the mattress in the transverse direction (hereinafter also referred to as lateral direction). In this case, all the incisions 3 of the first row of each pair are the same orientation, while the incisions 4 of the second row are oriented opposite thereto. The orientations of the cuts are chosen so that the openings of the semicircles point in the longitudinal direction of the mattress. In this case, the openings of the semicircles of the two rows of each pair to each other. The incisions of the second row are arranged symmetrically offset from the incisions of the first row such that the ends of each two adjacent semicircles of the second row extend into the opening of a semicircle of the first row. In other words, the incisions of the first and the second row, viewed in plan view, are interlocked with one another, thus protruding into one another into the material regions delimited by them.

The minimum distance S ₁ between the incisions of the two rows, here the distance of the end of each incision of the second row to center of the next portion of the first row, is relatively small in relation to the radius of the semicircles, here somewhat less than a quarter of the radius. Also, the lateral distance G of adjacent cuts of the same row relative to the radius of the semicircles is relatively small. In the present example, the distance G corresponds approximately to the distance S ₁ and is about 5 mm, while the radius is 22.5 mm.

• Eine erste Materialbrücke 11 verbindet den Bereich 8 mit dem nachfolgenden Bereich 9. Diese Brücke hat an ihrer schmalsten Stelle eine Breite, die dem Abstand S₁ entspricht.
• Eine zweite Materialbrücke 12 verbindet den Bereich 8 mit dem Material 6, das sich zum nächsten Paar von Reihen von Einschnitten hin befindet. Diese Brücke geht in die erste Materialbrücke 11 über, und die Trennlinie zwischen diesen beiden Materialbrücken ist nicht scharf zu ziehen. Die Breite dieser Brücke ist einerseits durch den Abstand S1, andererseits durch den Abstand G bestimmt.
• Entsprechende dritte und vierte Materialbrücken 13, 14 befinden sich am entgegengesetzten Ende des Bereichs 8.

Between the cuts of the two rows are thus limited in the transverse direction chains of material areas 7, 8, 9, for the purpose of better Recognizability in the Fig. 2 are shown hatched differently. These material areas are referred to below as "intermediate areas". The intermediate area 8 explains how these areas are connected to the surrounding material:

• A first material bridge 11 connects the region 8 with the subsequent region 9. This bridge has at its narrowest point a width which corresponds to the distance S ₁ .
• A second bridge of material 12 connects the area 8 to the material 6 which is toward the next pair of rows of sipes. This bridge merges into the first material bridge 11, and the dividing line between these two material bridges is not sharp. The width of this bridge is determined on the one hand by the distance S1, on the other hand by the distance G.
• Corresponding third and fourth material bridges 13, 14 are located at the opposite end of the area 8.

The intermediate regions 7, 8, 9 are thus connected to one another and to the surrounding material only by relatively narrow material bridges, while they are limited by incisions 3, 4 in a considerable area of their circumference.

The incisions make it possible to pull the mattress core apart in the longitudinal direction along a pulling direction 5. In the Fig. 3 the core is shown in its fully exploded position. It now has a length L ₂ , which corresponds to almost twice the original length L ₁ in the contracted state.

Unlike known mattress cores of the prior art, the core is in the state of Fig. 3 stable, ie it does not retract automatically back into its contracted state when no more pulling power.

It is also possible to pull the core apart only in partial areas. This is exemplary in the Fig. 5 shown. A first, contracted portion 51 is followed by a second, exploded portion 52, again followed by a third, contracted portion 53, by a fourth, again pulled-apart portion 54 and finally a fifth, contracted portion 55. In this way, a mattress can be made which has different hardness in different sections.

Each exploded section in the Fig. 5 is stable by itself. In fact, even in the Fig. 2 shown pair 2a, 2b, 2c, etc. of rows of successive interlocked incisions individually and independently bring in a stable exploded state.

Based on Fig. 4 Let us now explain what happens when pulling apart within a pair 2a ', 2b', 2c 'etc. of rows of incisions. First of all, it should be noted that the material regions 6 between the adjacent pairs of rows when being pulled apart essentially remain unchanged in their shape and orientation. The above-described intermediate regions 7, 8, 9, etc., which are located between the incisions of the two rows of the same pair of rows, on the other hand experienced via the second and fourth material bridges 12, 14, a tensile force in the longitudinal direction, which causes the orientation of these Areas opposite to the rest of the core as well as relative to each other changed. The intermediate areas "swing" from their original zigzag orientation, as they are in the Fig. 2 is shown, in the direction of a likewise zigzag-like orientation, as shown in the Fig. 4 is shown. They always form a coherent chain.

As a result of the movement of the intermediate regions 7, 8, 9, etc., the originally semicircular incisions 3, 4 enlarge to openings 3 ', 4'. These openings point towards the next pair of rows as before a semicircular boundary 21 on (since the material areas between the pairs of rows do not change their shape significantly). In contrast to the chain of regions 7, 8, 9, etc., the basic shape of the boundary 22, 23 of the apertures corresponds to two adjoining partial circles or arcs of the same length and different orientation.

If the mattress core from the starting position of Fig. 2 is pulled apart, first act in each row pair significant elastic restoring forces. In some sub-areas compression (compression) occurs, in other sub-areas an expansion. These forces are trying to pull the core together again. However, if the orientation of the intermediate regions 7, 8, 9, etc., once exceeds a certain angular position, the intermediate regions suddenly "snap" into the orientation of the Fig. 4 and remain stable in this orientation. To return the core back to the contracted position, a certain thrust or compressive force must be applied so that the material regions 7, 8, 9, etc. return to their original orientation Fig. 2 snap back.

The underlying physics of this behavior is in the energy diagram of Fig. 6 illustrated in a highly schematic way. This diagram qualitatively shows the course of the macroscopic "elastic energy" E (strictly speaking, the free enthalpy in the thermodynamic sense) in the region of a row pair, when this row pair is pulled apart by a length difference x. In the contracted state X ₁ = 0, the core is stable with regard to its length expansion: The elastic energy assumes its global minimum 61. When the core is compressed by a small amount (x <0) or pulled apart (x> 0, area 62), the elastic energy E increases respectively, and accordingly, a restoring force corresponding to the gradient of the energy acts. However, when the core is pulled apart beyond an amount x _m , the energy exceeds a local maximum 63 and then decreases again until it reaches a local minimum 64 at x = x ₂ . Thus, beyond the maximum 63, there is a force acting on the intermediate areas 7, 8, 9, etc. in the position of the local minimum 64 presses. In this position, the mattress core is stable again as long as it is not compressed again beyond X _m out.

In the following, it shall be pointed out which factors favor or impede this bistability in the orientation of the intermediate areas.

The phenomenon of "bistability" seems to be related to the present arrangement of the cuts in that the intermediate regions in the contracted position are angled relative to each other (angle α in FIG Fig. 2 ) and therefore form a chain with a zigzag shape. Now, if the core is pulled apart in the pulling direction 5, the angle α is greater until the intermediate areas form a straight chain (α = 180 °). However, since the total length of the chain just corresponds to the width B of the core and therefore remains unchanged, this means that the intermediate areas are highly compressed. This leads to a considerable increase in the elastic energy stored in the intermediate regions. If, however, the core continues to be pulled apart beyond the point at which the intermediate regions form a straight chain, the intermediate regions can expand again by moving into the orientation of the Fig. 4 fold. The angle α 'enclosed by the intermediate regions is again smaller than 180 °, but is enclosed on the other side of the intermediate regions seen in the pulling direction. This seems to be a basic principle that allows bistability in the present basic arrangement of the cuts. It is readily apparent that this principle can be practiced with other ground plan shapes of the cuts than the semi-circular shape shown here and with other dimensions, as long as the intermediate regions are compressed or compressed when the core is pulled apart transversely to the pulling direction, and in particular when the intermediate regions are initially form a zigzag chain.

An important, albeit secondary role for the bistability seems to be the Strength of the material bridges between the intermediate areas 7, 8, 9, etc. and the shape of the intermediate areas in the immediate vicinity of these bridges. If the material bridges are too wide and / or if the shape of adjacent intermediate areas obstructs a change in orientation, this counteracts the described folding over into the second stable position. The plan shape of the incisions and the relative arrangement of the incisions should therefore be chosen so that the forces that counteract a change in orientation of the intermediate regions in the direction of the folded position, are less than the forces that are beyond the point at which the chain in itself is aligned, act on the intermediate areas in the direction of the folded position.

The "optimal" strength of the material bridges can not be specified universally. It seems to depend above all on the shape of the incisions or the intermediate areas and the material of the mattress core. However, the expected magnitude can easily be illustrated by an example. Thus, a core was made of polyurethane cold foam, which had the following dimensions: radius of the incisions R = 22.5 mm; minimum spacing of incisions within a row G = 5 mm (ie, center distance between incisions of the same row 2R + G = 50 mm); Minimum longitudinal distance between cuts of the two rows of a row pair S ₁ = 5 mm in the contracted state; Center distance between row pairs A ₁ = 30 mm in the contracted state. This core could be pulled apart to almost twice the initial length (A ₂ ≈ 2 A ₁ ), and each pair of rows and thus also the core as a whole was stable in an exploded state. On the other hand, when S _{1 was} doubled to 10 mm, a stable extended state could no longer be achieved. In this example, therefore, the optimum value of S ₁ preferably appears to be in the range of the value of G and in particular in the range of about 2 to 7 mm: at a smaller value of S _{1 there} is a risk of tearing, while at a great value no more bistability is guaranteed. This range of values should also be more generally valid for other forms of intermediate areas, which spatially do not interfere with folding.

It should be emphasized that other dimensions are possible, especially for special forms of intermediate areas or other material choice. The invention is not limited to incisions with a semicircular plan. In particular, other curved shapes, in particular other types of bows, seem to be suitable. Instead, also bent forms are conceivable, e.g. the shape of the two catheters of an isosceles-right triangle. In all of these forms, the design principle seems to work with pairs of intermeshed series of cuts of the same size and shape, but with different orientations. In particular, it seems to be proven to select and arrange the cuts so that chains form of intermediate areas, which are connected by material bridges with material areas between the pairs of rows and can change their orientation.

Such a mattress core can be equipped directly with a mattress cover, so as to obtain a complete mattress. To improve comfort, a cover layer or cover plate of the same or of a different material can be applied to the core and e.g. glued to the core. The cover layer may e.g. be designed differently on the top or bottom. Since the cover layer does not need to absorb tensile forces, this layer can be correspondingly thin and / or flexible. You may also have openings or channels for the purpose of better ventilation.

With the inventive core, significant material savings can be achieved with simplified production. Thus, according to the above example, a core according to the invention can be extended by 100% or more without loss of comfort, so that for a given length of the mattress a material saving of more than 50% is possible. At the same time, a core with optimal ventilation is created. If appropriate breakthroughs on the other hand, traditional Ways are made by punching, on the other hand falls the punched material as waste. As a result of the core according to the invention, the waste volume is also reduced to virtually zero at the same time. Production and handling of the core are very simple. The storage and transport of the cores can take place in the collapsed state, whereby the space requirement is reduced. In this way, the essence of the present invention allows for further cost savings and reduced environmental impact during transport.

The invention has been described above with reference to a mattress core. Instead, the invention can also be used for upholstery in upholstered furniture, etc., where it offers similar advantages.

LIST OF REFERENCE NUMBERS

1

mattress core

2a, 2b, 2c

pair of rows

3, 4

incision

5

tensile direction

6

Material between two pairs of rows

7, 8, 9

between areas

11, 12, 13, 14

material bridges

21, 22, 23

limit

51, 52, 53, 54, 55

sections

61

global minimum

62

Area

63

local maximum

64

local minimum

L ₁ , L ₂

length

B

width

D

Thickness / height

A ₁ A ₂

center distance

S ₁

distance

R

radius

G

distance

x

length difference

X ₁ , X ₂ , X _m

length difference

e

"elastic energy"

Claims (13)

Core (1) made of an elastic material for a mattress or a furniture cushion, which has a plurality of incisions (3, 4) passing through the core in its thickness direction, arranged such that the core can be pulled apart in a pulling direction (5), such that the sipes form apertures (3 ', 4') of the core, characterized in that the sipes are formed and arranged such that there is at least one exploded state in which the core is stable without application of a tensile force against contraction. Core according to claim 1, characterized in that the notches (3, 4) have a curved and / or bent plan view and are arranged in pairs (2a, 2b, 2c) of transverse to the direction of pull and transverse to the Einschnittrichtung parallel rows, wherein the incisions of each of a pair (2a; 2b; 2c) of adjacent rows are interlocked with each other. A core according to claim 2, characterized in that the material between the incisions (3, 4) of each of a pair (2a; 2b; 2c) of adjacent rows forms a chain of intermediate regions (7, 8, 9) in the contracted state of the core assume a first stable orientation relative to one another and change their relative orientation when the core is pulled apart, wherein the intermediate regions (7, 8, 9) are arranged to tilt relative to each other into a second stable orientation when the core exceeds a certain point is pulled apart. Core according to claim 3, characterized in that the intermediate regions (7, 8, 9) are oriented in the contracted state of the core are that they are compressed transversely in the pulling apart of the core to the pulling direction and elastically to avoid the forces resulting therefrom in the direction of the second stable orientation when the core over a certain point is stretched. Core according to claim 4, characterized in that the intermediate regions (7, 8, 9) are arranged in a zigzag manner in the contracted state of the core. Core according to one of claims 3 to 5, characterized in that in each case an intermediate region (8). - Is connected near its first end via a first material bridge (11) with the subsequent intermediate region (9); - Is connected near the first end via a second material bridge (12) with the material between two adjacent incisions (3) of the first of the two adjacent rows; - Is connected near its second end via a third material bridge (13) with the preceding intermediate region (7); and - Is connected near the second end via a fourth material bridge (14) with the material between two adjacent incisions (4) of the second of the two adjacent rows. Core according to one of claims 2 to 6, characterized in that the distance of one pair (2b) of adjacent rows to the next pair (2a, 2c) of adjacent rows is chosen sufficiently large that the material (6) in the region between the pairs (2a, 2b, 2c) of adjacent rows when pulling the core substantially retains its shape and orientation. Core according to one of claims 2 to 7, characterized in that the incisions (3, 4) each have a pair (2a; 2b; 2c) of adjacent ones Rows have the same floor plan shape and the same dimensions, wherein the incisions (3) have substantially a first orientation within one of these rows, while the incisions (4) of the other row have a second, opposite orientation. Core according to claim 8, characterized in that - the distance between the ends of two adjacent cuts within the same row is between 2 and 10 mm; and that - The minimum distance between two cuts of adjacent rows in the pulling direction between 2 and 7 mm. Core according to one of claims 2 to 9, characterized in that the incisions (3, 4) have an arcuate outline shape without kinks and the same size, in particular a substantially semicircular planform. A mattress with a core according to any one of the preceding claims and a mattress cover surrounding the core. Mattress according to claim 11, which also comprises at least one cover plate which rests flat on the core and is at least partially connected thereto. Furniture cushion with a core according to one of the preceding claims and a coating which surrounds the core at least partially.

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