cushion

Abstract

The application pertains to a three-dimensional network structure comprising randomly bonded meshes of at least two continuous linear structures which structures comprising a thermoplastic elastomer and which structures are welded where they cross characterized in that the two different linear structures have different thickness and that the thinner of the linear structures forms an outer layer of the three-dimensional network structure and that the linear structures of different thicknesses are intermingled with each other.

Description

[0001] Cushion

[0002] Description:

[0003] The application pertains to a three-dimensional network structure for seating applications.

[0004] Seats are an important element of furniture in many parts of private and business life. Cushioned chairs, sofas and armchairs are part of private homes as well as of offices or public areas such as waiting rooms and lounges at airports or railway stations. An important field for the development of seats is equipment for all kinds of vehicles such as private cars, buses, railroad vehicles or airplanes. In all these vehicles, seats are essential for providing passengers with the comfort and security that is necessary during travel. Besides comfort and passenger security, an important requirement for vehicle seats is a low weight as higher weight adversely affects energy consumption of vehicles.

[0005] Throughout this application, the term “vehicle” should be interpreted as broad as possible. Thus, any device that can move people or goods should be a vehicle according to the present application no matter whether it travels on or under the ground, in the water or in the air, whether it comprises a motor or not and not depending on the question how many passengers it may carry. Thus, also a device that can carry just a driver should be a vehicle according to the present application.

[0006] Increasing efforts for environmental protection have also affected seat development. First, the requirements concerning weight have increased to save energy such as fuel and second, seats are more and more required to be recyclable. Seats of the prior art are typically based on foam-based cushions and paddings which are cheap and well-established. This is especially the case for polyurethane foams which are known for providing a lot of comfort to the person sitting on the seat also in cases where the person is seated on the seat for several hours. However, polyurethane foams suffer from two major disadvantages.

[0007] First, polyurethane foams have poor recyclability. For this reason, seats are typically burned when they are taken out of use.

[0008] Second, the production process of polyurethane cushion materials is timeconsuming and dangerous. As the raw materials for polyurethane foams are poisonous, special requirements are held for their handling and long reaction times must be kept to make sure that the poisonous components have completely reacted to the non-hazardous polymer. During reaction time, the material must remain in the mold which means that many molds are necessary as reaction times can last until 24 hours. This necessitates many molds if a high throughput rate of polyurethane cushions is sought. Thus, fibrous networks of different kinds have been proposed as possible alternatives, however it has been found that such fibrous networks do not offer the same seat comfort as the foam-based materials of the prior art. One reason for this is that fibrous materials are more heterogeneous than a typical foam which has small pores surrounded by an elastic material. The amount of open space in a fibrous network is typically larger and so are the pores which are not surrounded by material. The more heterogeneous character of the material has a special impact on the surface structure. The surface structure of a typical foam pad used as a seat cushion has an uncomfortable hand due to its grip caused by the large amount of small open pores. This problem is typically solved by providing the foam pad with a trim of textile, polymeric or leather material which does not only provide a more comfortable hand, but which also covers the often yellowish or brownish color of the foam pad.

[0009] While in foam pads the color creates an unwanted optical appearance, fiber-based cushions have a skeleton-like look which is also unwanted and which in principle can also be covered by a trim as provided in the prior art. However, with the trims of the prior art, the coarser surface of the fibrous material cannot be compensated and thus, fibrous-based seat cushions have a less comfortable hand also when they are provided with a trim which adversely affects the seat comfort.

[0010] It is thus the objective of the present invention to provide a cushion for a seat that is easier to produce, less hazardous, better to recycle and provide the same amount of comfort to the passenger as a polyurethane foam cushion.

[0011] The object is solved by a three-dimensional network structure comprising randomly bonded meshes of at least two continuous linear structures which structures comprising a thermoplastic elastomer and which structures are welded where they cross characterized in that the two different linear structures have different thickness and that the thinner of the linear structures forms an outer layer of the three-dimensional network structure and that the linear structures of different thicknesses are intermingled with each other.

[0012] According to the present application, the term “three-dimensional” should not be interpreted in a strictly mathematical manner. This means that in order to be called “three-dimensional” according to the present application, an object should have three dimensions which are all at least 5 millimeters. Thus, an object with a thickness of less than 5 millimeters is not to be considered three-dimensional according to the present application. The direction along the smallest dimension is called “thickness direction”.

[0013] Analog to the definition of the term “three-dimensional”, the term “linear” should also not be interpreted in a strictly mathematical manner. This means that in order order to be called “linear”, an object should have one dimension which should be at least a hundred times larger than both other dimensions. In practice, typical linear structures according to the present application are fibers, wires, filaments, cords or yams. While fibers, filaments and wires are to be interpreted as singular objects, cords or yams are objects which are made from fibers, filaments and / or fibers which are connected mechanically, e.g. by twisting or chemically, e.g. by adhesives or welding.

[0014] The linear structures according to the present application are continuous which means that their length is essentially infinite compared to their thickness. A typical continuous linear structure has a length of at least one meter, however, lengths of several hundreds of meters or even of several kilometers are possible.

[0015] The thickness of a linear structure according to the present application is the largest dimension that can be measured perpendicular to the length direction of the linear structure.

[0016] A network structure according to the present application is a structure which encloses air or gas in between interconnected solid carrying elements with the volume of enclosed air or gas being at least double as the volume of the interconnected solid carrying elements. The solid interconnected carrying elements are able to carry the network structure under its own weight in such a manner that it retains its form at least until external load is put onto the three- dimensional network structure.

[0017] The solid carrying elements of the three-dimensional network structure according to the present application are linear structures.

[0018] The three-dimensional network structure according to the present application comprises at least two different linear structures. The amount of linear structures in total is not particularly limited as long as the three-dimensional network structure comprises at least one linear structure which differs from the other linear structures comprised in the three-dimensional network structure by its thickness. In an embodiment, the three-dimensional network structures comprises two different groups of linear structures whereby the groups differ by their thicknesses. In an embodiment, the linear structures of different thicknesses may form several layers of the three-dimensional network structure.

[0019] In an embodiment, the three-dimensional network structure comprises three different layers wherein the first layer comprises thinner linear structures, the third layer comprises thicker linear structures and the second layer, which is located between the first layer and the third layer, is a transfer layer wherein the two different linear structures are mixed. Within the second layer, the contribution made by the different linear structures varies locally. In areas of the second layer which are closer to the first layer, the content of the linear structure forming the first layer (e.g. the thinner linear structure) may be larger while in areas closer to the third layer, the content of the linear structure concerning the third layer (e.g. the thicker linear structure) may be larger. The transfer layer may be thus interpreted as a transition layer.

[0020] Due to the character as a transition layer, a thickness of the second layer can only be defined as the distance in thickness direction of the three-dimensional network structure between the first occurrence of the thicker linear structure and the last occurrence of the thinner linear structure.

[0021] In an embodiment, the second layer is thinner than both the first layer and the third layer wherein the third layer is the layer comprising only the thicker linear structure and the first layer is the layer comprising only the thinner linear structure.

[0022] The thickness of the second layer depends on the production technique.

[0023] In an embodiment, the first layer comprises thinner linear structures than the third layer. In an embodiment, the contribution of the thinner linear structure to the three-dimensional structure is at least 30 weight-% (wt-%.), at least 40 wt.-%, at least 50 wt.-%, at least 60 wt.-% or at least 70 wt.-%. The thinner linear structure may be solid or hollow.

[0024] In an embodiment, the third layer comprises thicker linear structures than the first layer. In an embodiment, the contribution of the thicker linear structure to the three-dimensional structure is at least 30 weight-% (wt-%.), at least 40 wt.-%, at least 50 wt.-%, at least 60 wt.-% or at least 70 wt.-%. The thicker linear structure may be solid or hollow.

[0025] It is known to the person skilled in the art that solid and hollow linear structures, be it thicker linear structures or thinner linear structures may be combined with each other in any manner.

[0026] It is furthermore understood that the terms “thicker linear structure” and “thinner linear structure” are to be interpreted always in relation to each other and that they do not comprise any information on the absolute thickness of the linear structure.

[0027] It is important to mention that thickness does not have to be the only feature by which the two different linear structures in the three-dimensional network structure may differ. Furthermore, the linear structures may differ by cross section shape, material, color, hardness, by the question whether they are massive or hollow or any combination of the named features.

[0028] Randomly bonded according to the present application means that the amount and the distance of the points at which two objects do not follow any scheme and can thus only be characterized by average values. It is important to note that the term “randomly bonded” does not necessarily require that the objects which are bonded are different objects. An object can also be randomly bonded with itself e.g. when the object forms loops, meshes, circles, spirals or the like. Furthermore, the object may also be randomly bonded with itself and other objects at the same time. An illustrative example of randomly bonded linear structures is a plate of cooked spaghetti.

[0029] A mesh according to the present application is a structure formed by a linear structure which linear structure is arranged in a bent form in such a manner that it touches itself. In the present application, the term mesh is used synonymously with the terms loop, noose and stitch.

[0030] The linear structures of the present application are welded where they cross which means that at crossing points, there is an irreversible connection between two or more linear structures or by two or more different parts of the same linear structure which is formed by the same material which also forms the linear structures itself, i.e. not by any kind of glue or other adhesive material.

[0031] Welding can advantageously be carried out during the production process when the linear structure is obtained by melt-spinning and brought in contact either with itself or with other linear structures in an at least partially molten state.

[0032] Furthermore, the absence of additional binding materials such as glues or adhesives allows for easier recycling.

[0033] A thermoplastic elastomer according to the present application is a polymer which shows elastic properties at a temperature of 298 K and which, at the same time, can plastically be formed at higher temperatures.

[0034] In an embodiment, the thermoplastic elastomer according to the present application can only plastically be deformed at temperatures higher than 363 K. An important application of the three-dimensional network structure according to the present application is the formation of cushions for car seats and this ensures that even at highest temperatures in summer, the cushions are not plastically deformed.

[0035] In an embodiment, the thermoplastic elastomer retains its elastic properties at a temperature of 223 K which ensures that even in coldest environments the seat can provide a maximum amount of comfort to the person sitting thereon and does not get brittle and breaks if external load is put thereon.

[0036] In contrast to classical elastomers such as rubber, which are formed from weakly crosslinked macromolecules, thermoplastic elastomers comprise chain-like macromolecules which are not crosslinked. By heating, thermoplastic elastomers can be molten without chemical decomposition which is not possible with classical elastomers such as rubber. This allows for the recycling of thermoplastic elastomers which is not possible in the case of classical elastomers.

[0037] Typical thermoplastic elastomers belong to the known families of thermoplastic polymers such as polyamides or polyesters.

[0038] Polyamides are polymers which are formed by the formation of amdio groups between amino groups and carboxylic acid groups of their monomers. The simplest polyamides are e.g. formed either by polymerization of a diamine with a carboxylic diacid such as hexamethylene diamine and adipic acid which together form polyamide-6,6. Another possibility to form simple polyamides is polymerization of an amino acid or a lactam such as s-caprolactam which can be polymerized to polyamide-6. Polyamides, which consist of only one diamine and one carboxylic diacid, of one lactam or one amino acid do not have elastomeric properties. To achieve elastomeric properties, further monomers are necessary, such as e.g. one diamin and two different carboxylic diacids or two diamins and one carboxylic diacid. The number of additional monomers is not particularly limited. Additional monomers as parts of the polymeric chain prevent formation of large areas with a high order of the polymeric chain which would lead to the formation of crystalline regions of aggregated polymer chains which are detrimental for elastomeric properties. Thermoplastic elastomers have small crystalline regions wherein adjacent marcomolecules are crosslinked by non-bonding interactions in such a way that the crosslinking can be dissolved by the influence of heat and is restored under cooling.

[0039] Formation of such weak non-bonding interactions is possible for copolymers with chains that comprise more different monomers than are necessary for chain formation.

[0040] The simplest polyesters are formed by polymerization of a carboxylic diacid with a diole. With terephthalic acid as diacid and ethylene glycol as diole, polyethylene terephthalate is formed. Also, polymerization of a hydroxycarboxylic acid or of a lactone is possible with the results being e.g. polylactic acid in the case of lactic acid as hydroxycarboxylic acid or polycaprolactone in the case of caprolactone as lactam.

[0041] Polyesters which comprise only one diole and one carboxylic diacid or one lactam or one hydroxycarboxylic acid do not have elastomeric properties. In order to achieve elastomeric properties, the number of monomers must be increased such that e.g. at least two different dioles and / or at least two different carboxylic diacids, at least two different lactams or at least two different hydroxycarboxylic acids are used.

[0042] Polyester-based thermoplastic elastomers may be polyester-ester block copolymers or polyester-ether block copolymers. In both these groups the polymeric chains comprise “hard” and “soft” chain segments.

[0043] In thermoplastic elastomers from the group of polyester-esters both the hard and soft segments are formed from polyester units. As carboxylic diacids for both the hard and the soft segments aromatic carboxylic diacids such as terephthalic acid, isophthalic acids, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid and diphenyl-4,4’-dicarboxylic acid may be used as well as alicyclic carboxylic diacids such as 1 ,4-cyclohexane dicarboxylic acid or aliphatic dicarboxylic acides such as succinic acid, adipic acid, sebacic acid or dimer acids may be used. Instead of carboxylic diacids also derivatives thereof such as carboxylic anhydrides may be used. As diol component for the “hard” chain segments, aliphatic diols such as 1 ,4- butane diol, ethylene glycol, trimethylene glycol, pentamethylene glycol, hexamethylene glycol or alicyclic diols such as 1 ,1-cylohexane dimethanol or 1 ,4- cyclohexane dimethanol may be used. Also, ester forming derivatives of diols may be used such as chloroalkanes, bromoalkanes or iodoalkanes. Furthermore, also so-called polyester diols may be used. Polyester diols are oligomers from diols and carboxylic diacids, hydroxycarboxylic acids or lactones which comprise hydroxy groups on both termini of their chain. Possible polyester diols are e.g. polylactones such as polycaprolactone which are modified in such a manner that both chain ends comprise hydroxy groups. Modification may e.g. be carried out using a halogen alkane.

[0044] Polyester diols typically have a molar mass between 300 and 5000 g / mol. Typically, polyester-diols are based on aliphatic polyesters.

[0045] Embodiments of polyester-ester copolymers are block copolymers comprising terephthalic acid and / or naphthalene-2,6-dicarboxylic acid as carboxylic diacid, 1 ,4-butane diol as diol component and polycaprolactone as diol component. Polyester-ether copolymers may be based on the same dicarboxylic acids and diols as polyester-ester copolymers. Furthermore, they may also be based on a polymerized hydroxy carboxylic acid or a polymerized lactone. In contrast to polyester-ester copolymers, polyester-ether copolymers comprise a polyether diol component as “soft” chain segment. The polyether diol component can e.g. be a polyalkylenediol such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol or an ethylene oxide-propylene oxide-copolymer. The average molecular weight of a polyether diol component can be between 300 g / mol and 5000 g / mol.

[0046] In an embodiment, the three-dimensional network structure according to the present application consists of a thermoplastic elastomer.

[0047] The thickness of the two different linear structures comprised in the three- dimensional mat according to the present application differs by at least 10%. The thinner of the linear structures forms an outer layer of the three-dimensional network structure. Thinner linear structures can fill larger gaps between the thicker fibers of the three-dimensional network structure thus providing the three- dimensional network structure with a smoother surface which thus provides more comfort to a person seated on a seat which comprises the three-dimensional network structure according to the present application as cushioning material.

[0048] Thus, the layer of thinner fibers provides the fibrous network with a closer and thus smoother surface.

[0049] In an embodiment, the surface covering of the first layer of the fibrous network is at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85% or at least 90%.

[0050] In an embodiment, the surface covering of the first layer of the fibrous network is at most 70%, at most 75%, at most 80%, at most 85 %, at most 90% or at most 95%.

[0051] In an embodiment, the third layer of the fibrous network structure has a surface covering of at most 60%, of at most 55%, of at most 50%, of at most 45%, of at most 40% or of at most 35%. In an embodiment, the third layer of the fibrous network structure has a surface covering of at least 25%, at least 30%, at least 35%, at least 40%, at least 45% or at least 50%.

[0052] Thus, the surface covering of the third layer is significantly smaller than the surface covering of the outer layer.

[0053] In seating applications, the first layer will be typically oriented towards the trim of the seat while the third layer will be oriented towards the mount of the seat.

[0054] In general, it is noted that the surface covering of every part of the fibrous network according to the present application may also be measured after a cut through the fibrous network structure has been carried out and thus an outer surface has been “produced” by said cut. However, the surface coverings mentioned in this application are surface coverings of surfaces which are not produced by a cut unless stated otherwise.

[0055] In general, the term “surface covering” means the amount of material that is present at the outer surface of the three-dimensional network structure, thus the surface covering is part of the surface area that is in contact with a contacting surface in case the surfaces fit with each other. Thus in case the outer layer of the three-dimensional network structure is planar, then the surface covering is the amount of the surface area of the outer layer of the three-dimensional network structure where the material of the three-dimensional network structure is in contact with the contacting area.

[0056] The surface coverings according to the present application are measured using a 3D-Profilometer of the type VR-6200 available from KEYENCE® of Osaka, Japan, used with an optical magnification of 12 times. Measurements are carried our on a 100x100 mm sample of the three-dimensional network structure. An area of 69x69 mm of the sample was scanned by taking pictures of pictures of 24x18 mm. Thus 12 pictures of the sample were taken from which the surface area was calculated. According to the present application, the first layer of the three-dimensional network structure has the function of providing comfort of the seat while the mechanical stability and the actual cushioning property of the three-dimensional network structure is provided by the third layer of the network structure which comprises thicker and thus mechanically more stable fibers.

[0057] The first layer and the third layer of the three-dimensional network structure are not strictly separated. The linear structures forming the third layer and the first layer layer are intermingled with each other in such a manner that a transition layer is formed in which the linear structures of the first layer and the linear structures of the third layer are not only connected to each other but also in part penetrate through each other.

[0058] In the transition layer, forces are transferred from the first layer to the third layer of the three-dimensional network structure.

[0059] In an embodiment, the thickness of the first layer is less than half, less than one third, less than 20% or less than 10% of the thickness of the whole three- dimensional network structure. The choice of thickness of the first layer is a matter of balance between the seating comfort of a cushion comprising the three- dimensional network structure as a cushion and the mechanical stability and wear resistance of the three-dimensional network structure and may be different for different purposes of the three-dimensional network structure. In cases where higher wear resistance is sought, the first layer may be thinner at the compromise of lower seating comfort. On the contrary, the first layer may be chosen thicker when a high seating comfort is sought. In general, by the thickness of the first layer, the hardness of the three-dimensional network structure can be adjusted.

[0060] In an embodiment, the first and the second linear structure are made from different polymers which allows to use e.g. a polymer which provides more seating comfort and / or which easier to process to thinner linear structures for the outer layer. On the contrary, for the third layer of the three-dimensional network structure, a polymer may be chosen which is more wear-resistant, harder and / or stiffer.

[0061] In an embodiment, the first linear structure may be thicker than the second linear structure. In an embodiment, the first linear structure may be thinner than the second linear structure.

[0062] In an embodiment, the first and the linear structure may have any cross section known to the person skilled in the art such as circular, oval, oblong, rectangular, quadratic, triangular or hexagonal. It is understood that every cross section of a first linear structure may be combined with every cross section of a second linear structure.

[0063] It is understood that throughout the whole application thickness is understood to correspond to the outer diameter of the linear structure with the question whether the linear structure is solid or hollow being irrelevant.

[0064] In an embodiment, the two polymers in the first and the second linear structure may be part of the same polymer family. A polymer family according to the present application is a group of polymers which are from different but chemically related monomers and wherein the monomers are connected by the same type of chemical bonds. In the polymer family of polyamides, the monomers are e.g. connected by amido groups while in the polymer family of polyesters, the monomers are connected by ester groups.

[0065] Polymers from the same polymer family may differ in mechanical or other properties, however they are still easier to recycle than polymers from different polymer families. First, polymers from the same polymer family are typically miscible to that they may be processed to a polymer blend during recycling. Also, for recycling techniques which include chemical decomposition, polymers from the same polymer family are beneficial as they can easily be separated into their monomers which monomers may then be separated e.g. by distillation or crystallization.

[0066] In an embodiment, the density of the first layer of the three-dimensional structure according to the present application is larger than the density of the whole three- dimensional structure. The density according to the present application is the weight per volume of the material.

[0067] A higher density of the first layer combined to the third layer of the three- dimensional network structure provides the possibility to effectively fill up possible gaps between linear structures to increase the seating comfort.

[0068] In an embodiment, the number of welding points per volume is larger in the first layer compared to the third layer of the three-dimensional network structure.

[0069] A larger number of welding points per volume leads to a stronger connected more dense material which is able to provide a smoother surface and thus a higher seating comfort.

[0070] In an embodiment, the three-dimensional network structure according to the present application may have a compression hardness of 4-7 kPa according to DIN EN ISO 3386-1.

[0071] In an embodiment, the indentation hardness number of the three-dimensional network structure according to EIN 53579 is 125-250 N.

[0072] The present application further pertains to a seat for home furniture, a road or railroad vehicle or an airplane comprising a three-dimensional network structure according to anyone or more of the previous claims as cushion element. The seat according to the present application may also be a seat for home or business room furniture and thus be a sofa or an armchair.

[0073] The seat according to the present application may comprise one or more three- dimensional network structures according to the present application which network structures may serve as cushion materials in the backrest, the armrest and / or in the seat cushion of the seat.

[0074] Throughout this application, the term cushion means a material that has the main purpose to enhance the seating comfort provided to the person sitting on the seat by distributing forces in such a manner that the hardness of surfaces, edges, comers and surface irregularities is padded in such a manner that the amount at which they adversely effect the seating comfort is at least reduced. The term “cushion” in the present application is to be read in such a manner that it may also mean the related terms “upholstery” or “padding” if it is not explicitly stated otherwise.

[0075] In an embodiment, the seat according to the present application may comprise a cover material or trim which may be a textile material such as a woven or knitted fabric or a velour-based material. Furthermore, also leather or artificial leather are possible cover materials. Artificial leather typically comprises a textile carrier which is coated with a polymeric material.

[0076] In an embodiment, the cover material is made from a polymer from the same polymer family as the three-dimensional network structure. The effect of this constellation of materials is that the cushion and the cover material of the seat can be recycled together and do not have to be separated prior to recycling.

[0077] The present application furthermore pertains to a process for manufacturing a three-dimensional network structure, which may be a three-dimensional network structure according to the present application, the process comprising the steps providing a thermoplastic elastomer, melting the thermoplastic elastomer to obtain a melt, extruding the melt through a group of spinning nozzles to obtain melt jets which group is arranged in such a way that at least two rows of nozzles are formed, deforming and cooling the melt jets in such a manner that intermingled linear structures are formed, characterized in that the group of spinning nozzles comprises at least a first subgroup of nozzles and a second subgroup of nozzles with the subgroups of nozzles having different diameters.

[0078] Throughout this application, a row of nozzles according to the present application are at least three nozzles which are arranged in such a manner that they can be connected by a straight line. It is important to notice that to be part of a row nozzles do not have to be adjacent to each other. It is possible to provide groups of spinning nozzles according to the present application wherein the nozzles of a row are not nearest neighbors to each other in the group. The melt jets extruded from the nozzles may be cooled in any manner known to the person skilled in the art. Typically, a cooling fluid may be used such as a flow of air or any other gas or a cooling liquid such as water. The main advantage of air and water as cooling fluids is that they are cheap, and they do not form leftovers that have to be removed by cleaning steps. Water furthermore has the advantage that it has a high heat capacity and can thus have a strong and fast cooling effect. In an embodiment, the cooling will be carried out in a water tank.

[0079] In an embodiment, a combination of different cooling fluids may be used. Thus, the melt jets may e.g. first be injected into air and, afterwards, may fall into water. This way of cooling is known to the skilled person as “spinning a curtain of melt jets into a water tank”.

[0080] The cooling fluid may have any temperature that may be useful for the cooling process. In an embodiment, the temperature of the cooling fluid is 80°C, 90°C or even 100°C which allows for the cooling process to be carried in a controlled manner and to allow the melt jets to adhere to each other during the cooling process by keeping them in a sticky state for enough time form welding points before the polymer is completely solidified.

[0081] The nozzles in the group of spinning nozzles form at least two subgroups. A subgroup according to the present application is an array of spinning nozzles which comprises at least one row of spinning nozzles. The nozzles of different subgroups according to the present application have different diameters.

[0082] In an embodiment, the nozzles of different subgroups may also have different cross section shapes. Furthermore, the nozzles of different subgroups may produce melt jets with different characteristics. One subgroup may e.g. produce hollow melt jets while the other one may produce massive melt jets.

[0083] The different diameter, cross section and / or characteristic of the melt jets and the resulting different diameter, cross section and characteristic of the linear structures formed therefrom allow to produce a three-dimensional network structure with specific properties e.g. concerning compressibility, hardness and smoothness of the surface. In an embodiment of the process according to the present invention, the subgroups of nozzles comprise different amounts of nozzles. In one embodiment, the number of nozzles producing thinner melt jets and thus thinner linear structures is smaller than the number of nozzles producing melt jets and thus thicker linear structures. The thinner linear structures may form an first layer of the three-dimensional structure obtained in the process according to the present application. The outer layer of the three-dimensional structure may differ from the third layer of the three-dimensional structure by properties such as a higher density, a larger amount of welding points and a smoother outer surface. The application further pertains to an extrusion device comprising a group of extrusion pumps for transporting a polymer melt, every extrusion pump comprising an independent electronic control unit for controlling delivery volume and pressure, a distribution chamber comprising at least one inlet which every inlet being connected to an extrusion pump, a group of spinning nozzles as outlets of the distribution chamber, with the group of spinning nozzles comprising at least two rows of nozzles, characterized in that the nozzles of at least one outer row have a diameter that is smaller than the diameter of the other rows and that the distribution chamber is divided into two subchambers wherein the nozzles of the at least one outer row are the outlet of the first subchamber and the nozzles of the other rows are the outlets of the second subchamber.

[0084] In an embodiment, every group of spinning nozzles has at least one own extrusion pump.

[0085] The extrusion device according to the present application may be used to carry out a process according to the present application and / or to obtain a three- dimensional network structure according to the present application.

[0086] The extrusion pumps comprised in the device according to the present application are extrusion pumps known to the person skilled in the art.

[0087] Electronic control of the extrusion pumps may be carried out using a central electronic control device which can control every pump in the group independent of each other or every pump may have its own control device. In any case, the control device can control the delivery volume and the pressure of every extrusion pump separately.

[0088] The possibility to control the pressure and delivery volume separately allows for very precise control of the production process carried out with the device according to the present application. This is especially the case when the extrusion pumps deliver molten polymer to a group of spinning nozzles which comprises subgroups of spinning nozzles wherein the nozzles of the subgroups are distinguished by their diameter.

[0089] In an embodiment, the nozzles in the group of spinning nozzles form at least two subgroups. A subgroup according to the present application is an array of spinning nozzles which comprises at least one row of spinning nozzles. The nozzles of different subgroups according to the present application have different diameters. In an embodiment, the nozzles of different subgroups may also have different cross section shapes. Furthermore, the nozzles of different subgroups may produce melt jets with different characteristics. One subgroup may e.g. produce hollow melt jets while the other one may produce massive melt jets.

[0090] The different diameter, cross section and / or characteristic of the melt jets and the resulting different diameter, cross section and characteristic of the linear structures formed therefrom allow to produce a three-dimensional network structure which specific properties e.g. concerning compressibility, hardness and smoothness of the surface.

[0091] In an embodiment of the device according to the present invention, the subgroups of nozzles comprise different amounts of nozzles. In one embodiment, the number of nozzles producing thinner melt jets and thus thinner linear structures is smaller than the number of nozzles producing melt jets and thus thicker linear structures. Different diameters of the spinning nozzles lead to different pressure in different regions of the distribution chamber wherein the molten but viscous polymer melt is distributed to the spinning nozzles.

[0092] The distribution chamber is a volume into which the molten polymer is injected by the extrusion pumps. The molten polymer enters the distribution chamber through a group of inlets with every inlet being connected to one extrusion pump. The outlets of the distribution chamber are the spinning nozzles through which the molten polymer leaves the distribution chamber and enters a cooling fluid. Between the inlets and the spinning nozzles, there is a flow of molten polymer. The main purpose of the distribution chamber is to distribute the flow of molten polymer from the extrusion pumps to the spinning nozzles by offering the possibility to use a reasonably small amount of extrusion pumps to serve a larger number of spinning nozzles. In an embodiment, the number of extrusion pumps in the device is smaller than the number of spinning nozzles.

[0093] In an embodiment, the distribution chamber may be separated into several compartments by walls which separate the volume either in part or in total. Separation in part means that the flow of the polymer melt between the compartments is possible but limited while separation in total means that once the molten polymer has been injected into a compartment it will stay within this compartment during its whole passage through the distribution chamber. Total separation may e.g. be achieved by walls which reach through the whole distribution chamber in such a way that the flow of polymer melt is totally separated into several flows.

[0094] In case of separation of the distribution chamber - be it separation in part or separation in total - every compartment of the distribution chamber may comprise one or more inlets and may thus be served by one or more extrusion pumps. Different compartments of the distribution chamber allow for different flow rates of molten polymers through the distribution chamber. In case of total separation, these differences may be stronger than in case of separation in part. In case of total separation, the differences in flow rate may also be better controlled compared to separation in part.

[0095] In an embodiment, different compartments of the distribution chambers have different groups of spinning nozzles as outlets. In this case, separation allows for a precise regulation of the flow of molten polymers to the different groups of spinning nozzles which may require different pressures and / or supply rates. In case of total separation, the control can be very precise, and the flows may comprise different kinds of molten polymers which will not be mixed during passage through the distribution chamber. Figures

[0096] Fig. 1 shows a cross-sectional view of an embodiment of the three-dimensional network structure according to the present application. In this embodiment, the first linear structure is a solid linear structure while the second linear structure is a hollow linear structure. Fig. 2 shows an embodiment of the extrusion device according to the present application.

Claims

CushionClaims:1 . Three-dimensional network structure comprising randomly bonded meshes of at least two continuous linear structures which structures comprising a thermoplastic elastomer and which structures are welded where they cross characterized in that the two different linear structures have different thickness and that the thinner of the linear structures forms an outer layer of the three-dimensional network structure and that the linear structures of different thicknesses are intermingled with each other.

2. Three-dimensional network structure according to claim 1 wherein the thickness of the outer layer is less than half of the thickness of the three- dimensional network structure, preferably less than one third, more preferably less than 20% and even more preferably less than 10% of the thickness of the three-dimensional network structure.

3. Three-dimensional network structure according to claim 1 or 2 wherein the first linear structure and the second linear structure are from different polymers.

4. Three-dimensional network structure according to claim 3 wherein the different polymers are from the same polymer family.

5. Three-dimensional network structure according to claim 3 or 4 wherein the polymer of the linear structure forming the outer layer is softer than the other polymer.

6. Three-dimensional network structure according to anyone or more of the previous claims wherein the density of the outer layer is higher than the density of the complete three-dimensional network structure.

7. Three-dimensional network structure according to anyone or more of the previous claims wherein the amount of welding points per volume in the outer layer is larger than the amount of welding points per volume in the complete three-dimensional network structure.

8. A seat for home furniture, a road or railroad vehicle or an airplane comprising a three-dimensional network structure according to anyone or more of the previous claims as cushion element.

9. The seat according to claim 8 wherein the seat further comprises a cover material which is made from a polymer made from the same polymer family as the first and the second linear structure of the three-dimensional network structure.

10. Process for manufacturing a three-dimensional network structure comprising the steps• providing a thermoplastic elastomer,• melting the thermoplastic elastomer to obtain a melt,• extruding the melt through a group of spinning nozzles to obtain melt jets which group is arranged in such a way that at least two rows of nozzles are formed,• deforming and cooling the melt jets in such a manner that intermingled linear structures are formed, characterized in that the group of spinning nozzles comprises at least a first subgroup of nozzles and a second subgroup of nozzles with the subgroups of nozzles having different diameters.11 . Extrusion device comprising• A group of extrusion pumps for transporting a polymer melt, every extrusion pump comprising an independent electronic control unit for controlling delivery volume and pressure,• A distribution chamber comprising at least which every inlet being connected to an extrusion pump,• A group of spinning nozzles as outlets of the distribution chamber, with the group of spinning nozzles comprising at least two rows of nozzles, characterized in that the nozzles of at least one outer row have a diameter that is smaller than the diameter of the other rows and that the distribution chamber is divided into two subchambers wherein the nozzles of the at least one outer row are the outlet of the first subchamber and the nozzles of the other rows are the outlets of the second subchamber.

12. The Extrusion device of claim 11 wherein every subchamber is connected to at least one extrusion pump.

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