Three-dimensional net-like structure

Abstract

Provided is a three-dimensional net-like structure which is lighter than existing three-dimensional net-like structures even while having excellent cushioning performance. The three-dimensional net-like structure comprises a continuous wire composed of a thermoplastic resin composition and has a three-dimensional random loop joining structure, the three-dimensional net-like structure being characterized in that: both surfaces of the three-dimensional net-like structure in the thickness direction are skin layers; and a value obtained by dividing the apparent density of the skin layer by the apparent density of the three-dimensional net-like structure is 1.25 or less.

Description

Three-dimensional mesh structure

[0001] The present invention relates to a three-dimensional network structure.

[0002] BACKGROUND ART Three-dimensional netted structures have been widely used as cushioning materials for furniture, bedding such as beds, and seats for vehicles such as trains, automobiles, and motorcycles because of their excellent breathability and recyclability.

[0003] For example, Patent Document 1 discloses a network structure that is lightweight, has excellent hardness, and is highly durable, which is obtained by foaming a continuous filament that constitutes a three-dimensional random loop bonded structure, and then forming a composite structure by covering the outside of the foamed layer with a non-foamed layer.

[0004] International Publication No. 2014 / 192790

[0005] However, the manufacturing method of Patent Document 1 has problems in terms of production stability due to the difficulty in controlling the foaming property during the extrusion molding process. On the other hand, the three-dimensional netted structure obtained by the conventional manufacturing method described in the comparative example below has not been sufficiently lightweight.

[0006] The present invention has been made in view of the above circumstances, and its object is to obtain a three-dimensional netted structure that can be produced by a relatively simple method, has excellent cushioning performance, and is lighter than conventional structures.

[0007] The three-dimensional network structure according to the present invention is as follows. [1] A three-dimensional network structure comprising continuous filaments made of a thermoplastic resin composition and having a three-dimensional random loop bonded structure, wherein both surfaces in the thickness direction of the three-dimensional network structure are skin layers, and the apparent density of the skin layers divided by the apparent density of the three-dimensional network structure is 1.25 or less. [2] The three-dimensional network structure according to [1] above, wherein the three-dimensional network structure has an inner layer sandwiched between two of the skin layers, and the filaments constituting the skin layer and the inner layer each have an average fiber diameter of 0.1 mm to 3.0 mm. [3] The three-dimensional network structure has an apparent density of 0.01 g / cm ３ ~0.20 g / cm ３ and the skin layer has an apparent density of 0.01 g / cm３ ~0.20 g / cm ３ [4] The three-dimensional mesh structure according to any one of the above [1] to [3], which has a thickness of 10 to 300 mm.

[0008] The three-dimensional network structure of the present invention can be produced by a relatively simple method, and by reducing the apparent density of the skin layer, it is possible to obtain a three-dimensional network structure that is lighter than conventional structures while still having excellent cushioning performance. The use of the three-dimensional network structure of the present invention enables weight reduction in a variety of applications, which is expected to result in a reduction in environmental impact. In addition to the reduction in environmental impact due to the weight reduction, when used as bedding, the bedding can be made lighter, which reduces the burden of carrying it. When used as seats for vehicles such as trains, automobiles, and motorcycles, the vehicle mass can be reduced, which reduces the energy required for vehicle operation.

[0009] The three-dimensional network structure of the present invention is composed of continuous filaments made of a thermoplastic resin composition and has a three-dimensional random loop bonded structure. Specifically, the continuous filaments made of a thermoplastic resin composition are meandered to form random loops, and the individual loops are brought into contact with each other in a molten state to form the three-dimensional random loop bonded structure.

[0010] In the three-dimensional network structure of the present invention, both surfaces in the thickness direction are skin layers, and the layer sandwiched between the two skin layers provided on both surfaces of the three-dimensional network structure is called an inner layer. Hereinafter, the thermoplastic resin composition constituting the three-dimensional network structure of the present invention, the properties of the three-dimensional network structure of the present invention, and the method for producing the three-dimensional network structure of the present invention will be described in this order.

[0011] <Thermoplastic Resin Composition> The thermoplastic resin is not particularly limited, but is preferably a thermoplastic elastomer or a biodegradable thermoplastic resin. From the viewpoint of cushioning properties, the thermoplastic resin is preferably a thermoplastic elastomer. On the other hand, in applications where excellent environmental compatibility is important, the thermoplastic resin is preferably biodegradable. Examples of the thermoplastic elastomer include polyester-based thermoplastic elastomers, polyolefin-based thermoplastic elastomers, styrene-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, and thermoplastic ethylene-vinyl acetate copolymer elastomers.

[0012] Examples of polyester-based thermoplastic elastomers include polyether ester block copolymers having a thermoplastic polyester as a hard segment and a polyalkylene diol as a soft segment, and polyester ester block copolymers having an aliphatic polyester as a soft segment.

[0013] Examples of polyether ester block copolymers include block copolymers composed of a dicarboxylic acid, a diol component, and a polyalkylene diol. The dicarboxylic acid is not particularly limited, but is preferably at least one dicarboxylic acid selected from aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, naphthalene-2,7-dicarboxylic acid, and diphenyl-4,4'-dicarboxylic acid; alicyclic dicarboxylic acids such as 1,4-cyclohexanedicarboxylic acid; aliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacic acid, and dimer acid; or ester-forming derivatives thereof. The diol component is not particularly limited, but is preferably at least one diol component selected from aliphatic diols such as 1,4-butanediol, ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, and hexamethylene glycol; alicyclic diols such as 1,1-cyclohexanedimethanol and 1,4-cyclohexanedimethanol; or ester-forming derivatives thereof. The polyalkylene diol is not particularly limited, but is preferably at least one of polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and glycols consisting of ethylene oxide-propylene oxide copolymers. The polyalkylene diol preferably has a number average molecular weight of 300 to 5,000, more preferably 500 to 3,000.

[0014] Examples of polyester ester block copolymers include block copolymers composed of dicarboxylic acids, diol components, and polyester diols. Examples of dicarboxylic acids and diol components include the dicarboxylic acids and diol components used in constructing polyester ester block copolymers. Examples of polyester diols include polylactones having a number average molecular weight of approximately 300 to 5,000.

[0015] Considering thermal adhesiveness, hydrolysis resistance, stretchability, heat resistance, etc., it is particularly preferred that the dicarboxylic acid of each unit constituting the polyetherester block copolymer be terephthalic acid and / or naphthalene-2,6-dicarboxylic acid, the diol component be 1,4-butanediol, and the polyalkylene diol be polytetramethylene glycol. It is also particularly preferred that the dicarboxylic acid of each unit constituting the polyesterester copolymer be terephthalic acid and / or naphthalene-2,6-dicarboxylic acid, the diol component be 1,4-butanediol, and the polyester diol be polylactone. It is also possible to use a polyetherester block copolymer incorporating a polysiloxane-based soft segment.

[0016] The soft segment content of the polyester-based thermoplastic elastomer is preferably 15 to 80% by mass, more preferably 25 to 70% by mass, even more preferably 30 to 60% by mass, and particularly preferably 35 to 50% by mass. When the soft segment content is 15% by mass or more, compression durability can be easily improved. Furthermore, when the soft segment content is 80% by mass or less, hardness and heat resistance and settling resistance can be easily maintained.

[0017] The polyolefin-based thermoplastic elastomer is preferably an ethylene-α-olefin copolymer obtained by copolymerizing ethylene with an α-olefin having 3 or more carbon atoms, more preferably an ethylene-α-olefin copolymer obtained by copolymerizing ethylene with an α-olefin having 3 to 10 carbon atoms, and even more preferably an ethylene-α-olefin copolymer obtained by copolymerizing ethylene with an α-olefin having 3 to 8 carbon atoms.

[0018] Examples of α-olefins having 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-nonadecene. Examples of the α-olefins having 3 or more carbon atoms include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, and 1-eicosene. The α-olefins having 3 or more carbon atoms may be used alone or in combination of two or more thereof.

[0019] The ethylene-α-olefin copolymer may be a random copolymer or a multi-block copolymer. Random copolymers can be obtained by copolymerizing ethylene and an α-olefin using a metallocene compound as a catalyst, and multi-block copolymers can be obtained by copolymerizing ethylene and an α-olefin using a chain shuttling reaction catalyst. If necessary, two or more polymers polymerized by the above methods, or polymers such as hydrogenated polybutadiene and hydrogenated polyisoprene, can be blended.

[0020] The ratio of ethylene to α-olefin having 3 or more carbon atoms in the ethylene-α-olefin copolymer is preferably 70% by mass or more and 95% by mass or less of ethylene and 5% by mass or more and 30% by mass or less of α-olefin having 3 or more carbon atoms. It is generally known that polymer compounds acquire elastomeric properties due to the presence of hard and soft segments within the polymer chain. In the polyolefin-based thermoplastic elastomer used in the present invention, ethylene is thought to play the role of hard segments, and the α-olefin having 3 or more carbon atoms plays the role of soft segments. Therefore, if the ethylene ratio is less than 70% by mass, the hard segments are scarce, resulting in a decrease in the recovery performance of rubber elasticity. The ethylene ratio is more preferably 75% by mass or more, and even more preferably 80% by mass or more. On the other hand, if the ethylene ratio exceeds 95% by mass, the soft segments are scarce, resulting in a lack of elastomeric properties and a risk of poor cushioning performance. The ethylene ratio is more preferably 93% by mass or less, and even more preferably 90% by mass or less.

[0021] A typical example of a polyurethane-based thermoplastic elastomer is a polyurethane elastomer obtained by reacting a hydroxyl-terminated polyether and / or polyester having a number-average molecular weight of 1000 to 6000 with a polyisocyanate primarily composed of an organic diisocyanate in the presence or absence of a conventional solvent (e.g., dimethylformamide, dimethylacetamide), to form a prepolymer having isocyanate groups at both ends, and then chain-extending the resulting prepolymer with a polyamine primarily composed of a diamine. Preferred examples of the polyester and / or polyether include polybutylene adipate copolymer polyesters having a number-average molecular weight of approximately 1000 to 6000, preferably 1300 to 5000, polyalkylene diols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and glycols composed of ethylene oxide-propylene oxide copolymers. Conventional polyisocyanates can be used as the polyisocyanate, including isocyanates primarily composed of diphenylmethane 4,4'-diisocyanate, with the addition of trace amounts of conventional triisocyanates, if necessary. The polyamine is mainly a known diamine such as ethylenediamine or 1,2-propylenediamine, and may contain a small amount of triamine or tetraamine in combination as needed. The polyurethane-based thermoplastic elastomer may be used alone or in combination of two or more kinds.

[0022] The soft segment content of the polyurethane-based thermoplastic elastomer is preferably 15% by mass or more, more preferably 25% by mass or more, even more preferably 30% by mass or more, and most preferably 40% by mass or more from the viewpoint of excellent compression durability, and is preferably 80% by mass or less, more preferably 70% by mass or less from the viewpoint of ensuring hardness and excellent heat resistance and setting resistance.

[0023] Examples of polyamide-based elastomers include copolymers of a polyamide as a hard segment and a polyol as a soft segment. The polyamide as the hard segment may be at least one of polyamide oligomers obtained from the reaction products of a lactam compound and a dicarboxylic acid, or a diamine and a dicarboxylic acid. The polyol as the soft segment may be at least one of polyether polyols, polyester polyols, polycarbonate polyols, etc.

[0024] The lactam compound may be at least one of aliphatic lactams having 5 to 20 carbon atoms, such as γ-butyrolactam, ε-caprolactam, ω-heptalactam, ω-undecalactam, and ω-lauryllactam.

[0025] Examples of dicarboxylic acids include at least one of dicarboxylic acid compounds such as aliphatic dicarboxylic acids having 2 to 20 carbon atoms, such as oxalic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid; alicyclic dicarboxylic acids, such as cyclohexanedicarboxylic acid; and aromatic dicarboxylic acids, such as terephthalic acid, isophthalic acid, and orthophthalic acid.

[0026] Examples of diamines include at least one aliphatic diamines such as ethylenediamine, trimethylenediamine, tetramethylenediamine, hexamethylenediamine, heptamethylenediamine, octamethylenediamine, nonamethylenediamine, decamethylenediamine, undecamethylenediamine, dodecanemethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, and 3-methylpentamethylenediamine, and aromatic diamines such as metaxylenediamine. Examples of polyols include polyether polyols, such as at least one polyalkylene diol, including polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and glycols composed of ethylene oxide-propylene oxide copolymers, each having a number average molecular weight of about 300 to 5000. Examples of polycarbonate diols include those that are reaction products of low-molecular-weight diols and carbonate compounds and have a number average molecular weight of about 300 to 5000. Examples of low molecular weight diols include at least one aliphatic diols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol, and alicyclic diols such as cyclohexanedimethanol and cyclohexanediol. Examples of carbonate compounds include at least one dialkyl carbonate, alkylene carbonate, diaryl carbonate, and the like. Examples of polyester polyols include at least one polyester diol such as polylactone having a number average molecular weight of about 300 to 5,000.

[0027] The soft segment content of the polyamide-based thermoplastic elastomer is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and most preferably 20% by mass or more from the viewpoint of excellent compression durability, and is preferably 80% by mass or less, more preferably 70% by mass or less from the viewpoint of ensuring hardness and excellent heat resistance and setting resistance.

[0028] The thermoplastic ethylene-vinyl acetate copolymer elastomer preferably has a content of structural units derived from vinyl acetate monomer of 1 to 35% by mass, more preferably 2 to 30% by mass, and even more preferably 3 to 26% by mass. By having the content of structural units derived from vinyl acetate monomer within the above range, it is easy to achieve both rubber elasticity and heat resistance.

[0029] The thermoplastic ethylene vinyl acetate copolymer elastomer may also be copolymerized with an α-olefin having 3 or more carbon atoms. Examples of the α-olefin having 3 or more carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, Examples of the α-olefins having 3 or more carbon atoms include 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, and 1-eicosene. The α-olefins having 3 or more carbon atoms may be used alone or in combination of two or more thereof.

[0030] The biodegradable thermoplastic resin is not particularly limited, but examples thereof include polybutylene succinate, poly(butylene succinate / adipate), poly(butylene adipate / terephthalate), polylactic acid, (polylactic acid / polybutylene succinate-based) block copolymers, polycaprolactone, poly(caprolactone / butylene succinate), poly(butylene succinate / carbonate), poly(ethylene terephthalate / succinate), poly(tetramethylene adipate / terephthalate), polyethylene succinate, polyvinyl alcohol, polyglycolic acid, etc. Among these, poly(butylene adipate / terephthalate) is preferred from the viewpoint of cushioning properties.

[0031] The thermoplastic resin composition constituting the continuous filaments may be a mixture of two or more different thermoplastic resins depending on the purpose. When the thermoplastic resin composition constituting the continuous filaments is a mixture of two or more different thermoplastic resins, the total content of the polyester-based thermoplastic elastomer, polyolefin-based thermoplastic elastomer, styrene-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, and thermoplastic ethylene-vinyl acetate copolymer elastomer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. In particular, the total content of the polyester-based thermoplastic elastomer and polyolefin-based thermoplastic elastomer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0032] The thermoplastic resin composition constituting the continuous filaments may contain various additives depending on the purpose. Examples of additives include plasticizers such as phthalate esters, trimellitates, fatty acids, epoxy compounds, adipates, and polyesters; known antioxidants such as hindered phenols, sulfur compounds, phosphorus compounds, and amines; light stabilizers such as hindered amines, triazoles, benzophenones, benzoates, nickel compounds, and salicylic acid compounds; antistatic agents; molecular weight modifiers such as peroxides; compounds having reactive groups such as epoxy compounds, isocyanate compounds, and carbodiimide compounds; metal deactivators, neutralizing agents, antacids, antibacterial agents, fluorescent brighteners, fillers, flame retardants, flame retardant assistants, organic and inorganic nucleating agents, and organic and inorganic pigments. These additives may be used alone or in combination of two or more. The total amount of the various additives is preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less, based on 100% by mass of the thermoplastic resin composition.

[0033] <Characteristics of the three-dimensional network structure> The three-dimensional network structure of the present invention has an apparent density of 0.01 g / cm ３ ~0.20 g / cm ３ It is preferable that the density is 0.02 g / cm ３ ~0.10 g / cm ３ More preferably, it is 0.02 g / cm ３ ~0.07g / cm ３ The apparent density of the skin layer is more preferably 0.01 g / cm ３ ~0.20 g / cm ３ It is preferable that the density is 0.02 g / cm ３ ~0.10 g / cm ３ More preferably, the apparent density is 0.02 g / cm ３ ~0.07g / cm ３ It is more preferable that:

[0034] The value obtained by dividing the apparent density of the skin layer by the apparent density of the three-dimensional network structure (skin layer density ratio) is 1.25 or less, preferably 0.7 to 1.25, more preferably 0.8 to 1.2, and even more preferably 0.85 to 1.15. The inventors have found that the contribution of the skin layer to the compression hardness is small, and by setting the density ratio of the skin layer to 1.25 or less using the manufacturing method described below, a lightweight three-dimensional network structure can be obtained without reducing the compression hardness. Unless otherwise specified, the "apparent density of the skin layer" refers to the average value of the apparent densities of both surfaces.

[0035] From the viewpoint of achieving both weight reduction and excellent compression hardness, it is preferable to make the apparent density of the skin layer close to the apparent density of the entire three-dimensional network structure. ３ ) and the apparent density B of the skin layer (g / cm ３ ) preferably satisfies A+0.012≧B≧A−0.004, and more preferably satisfies A+0.010≧B≧A−0.002. In addition, it is preferable that the apparent densities of the skin layers on both surfaces are approximately the same, and the difference in apparent densities of the skin layers provided on both surfaces is 0.005 g / cm ３ It is preferable that the density is 0.003 g / cm or less. ３ More preferably, it is:

[0036] The average fiber diameter of the filaments (fibers) constituting the skin layer is preferably 0.1 mm to 3.0 mm, more preferably 0.2 mm to 3.0 mm, and even more preferably 0.3 mm to 1.0 mm. The average fiber diameter of the filaments (fibers) constituting the inner layer is preferably 0.1 mm to 3.0 mm, more preferably 0.2 mm to 3.0 mm, and even more preferably 0.3 mm to 1.0 mm.

[0037] From the viewpoint of achieving both lightweight and excellent compression hardness, the three-dimensional network structure of the present invention preferably has a thickness of 10 to 300 mm, more preferably 15 to 200 mm, even more preferably 20 to 100 mm, and particularly preferably 30 to 60 mm.

[0038] The continuous filament may be a composite filament of a sheath-core type, a side-by-side type, an eccentric sheath-core type, or the like. The composite filament may be a composite filament combining a thermoplastic elastomer with a thermoplastic resin other than a thermoplastic elastomer. The cross-sectional shape of the continuous filament may be either a hollow or solid cross-section, but a hollow cross-section is preferred from the viewpoint of weight reduction. The lower limit of the hollowness of the continuous filament is preferably 5% or more, more preferably 10% or more, and particularly preferably 15% or more. On the other hand, the upper limit of the hollowness of the continuous filament is not particularly limited and is, for example, 60% or less. The hollowness of the continuous filament can be measured by the method described in the Examples below.

[0039] The cross-sectional shape of the continuous filaments constituting the three-dimensional network structure of the present invention is not particularly limited, and may be a substantially circular cross-section or a non-circular irregular cross-section. The irregular cross-section may impart compression resistance and a touch.

[0040] The three-dimensional network structure of the present invention may have a multilayer structure as long as it does not impair the object of the present invention. Examples of multilayer structures include those in which the surface and back layers are made of continuous filaments of different finenesses, those in which the surface and back layers are made of different raw materials, those in which the surface and back layers are made of structures with different apparent densities, and those in which long-fiber nonwoven fabrics, short-fiber nonwoven fabrics, etc. are laminated. Examples of multilayering methods include stacking network structures on top of each other and fixing them with a side fabric, melting and solidifying them by heating, bonding them with an adhesive, and restraining them with sewing or a band, etc.

[0041] The shape of the three-dimensional network structure of the present invention is not particularly limited. Examples thereof include a plate, a polygon such as a triangular prism or a quadrangular prism, a cylinder, a sphere, and a combination thereof. The three-dimensional network structure may be formed by cutting, heat pressing, nonwoven fabric processing, etc.

[0042] The appropriate hardness of a three-dimensional network structure varies depending on the application, and therefore it is not possible to define a specific value for the appropriate hardness. However, if the hardness is too high, the cushioning properties are impaired, and if the hardness is too low, the structure will bottom out and will not function as a cushioning material, so it is necessary to adjust the hardness to an appropriate level depending on the application.

[0043] <Method for producing a three-dimensional network structure> Next, a method for producing a three-dimensional network structure of the present invention will be described below, but the following method is an example and is not intended to be limiting.

[0044] First, a thermoplastic resin composition is dispensed into the nozzle orifices through a multi-row nozzle having multiple orifices and extruded downward from the nozzle at a spinning temperature of at least 10°C above the melting point of the resin and at most 120°C above the melting point. Next, a continuous filament made of the thermoplastic resin composition molten at the spinning temperature is dropped onto a pair of adjustable-gap take-up conveyors installed above a cooling medium. The molten continuous filament is sandwiched between the take-up conveyors and allowed to meander, causing the continuous filaments to come into contact with each other and fuse together, forming a three-dimensional random loop bonded structure with random loops. The network structure having the three-dimensional random loop bonded structure is then drawn into a cooling medium and solidified, yielding the three-dimensional network structure of the present invention. The orifice pitch must be adjusted in advance to form the loops.

[0045] The thickness of the three-dimensional network structure is determined by the spacing between the pair of take-up conveyors. Conventionally, the resin discharge range has been set wider than the spacing between the take-up conveyors to ensure smooth transport by the take-up conveyors. The filaments discharged outside the take-up conveyors are concentrated on the surface of the three-dimensional network structure to form a skin layer. The apparent density of the skin layer is higher than the apparent density of the entire three-dimensional network structure. In the present invention, however, the density ratio of the skin layer is set to 1.25 or less, which is lower than conventional values, and the apparent density of the skin layer is brought closer to the apparent density of the entire three-dimensional network structure, thereby enabling the production of a three-dimensional network structure that efficiently exerts repulsive force. Methods for reducing the density ratio of the skin layer include, for example, controlling the amount of resin discharged from the nozzle by independently setting a gear pump for each discharge range in the thickness direction; changing the density of the nozzles (nozzles that discharge the resin used to form the skin layer) located in the range corresponding to the skin layer; adjusting the resin discharge range in the thickness direction (the range of resin discharged from the nozzle) relative to the spacing between the pair of take-up conveyors; and generating a water flow or air bubbles near the center of the pair of take-up conveyors in a direction opposite the transport direction. These methods can reduce the apparent density of the skin layer, which contributes little to compression hardness, and thereby produce a lightweight three-dimensional network structure without reducing compression hardness. Among these, it is preferable to control the resin discharge rate from the nozzles by, for example, independently setting a gear pump for each discharge range in the thickness direction, and to increase the ratio (hereinafter referred to as the "single-hole discharge rate ratio") obtained by dividing the resin discharge rate from each nozzle that discharges the resin used to form the inner layer (single-hole discharge rate) by the resin discharge rate from each nozzle that discharges the resin used to form the skin layer (single-hole discharge rate) (preferably 1.2 to 3.0, more preferably 1.3 to 2.5). However, even if the single-hole discharge rate ratio is about 1.0, the density ratio of the skin layer can be made 1.25 or less by changing manufacturing conditions other than the single-hole discharge rate ratio.On the other hand, if the single-hole output rate ratio is too large, the average fiber diameter of the skin layer may become extremely small. However, this can be avoided by, for example, lowering the spinning temperature only in the skin layer area, partially changing the distance to the water tank by providing a step on the nozzle surface, or varying the outer diameter of the nozzle. Note that the above-mentioned method for controlling the single-hole output rate ratio is one example and is not limited to the above-mentioned method. Furthermore, if the average fiber diameter of the skin layer is extremely small compared to the average fiber diameter of the inner layer, cushioning properties may decrease. Therefore, as described above, it is preferable that the difference in average fiber diameter between the skin layer and the inner layer is small.

[0046] A three-dimensional mesh structure having a low density ratio of the skin layer may be unstable during transport. However, if this occurs, stable transport can be achieved by increasing the gripping force of the take-up conveyor by applying a coating to the surface of the take-up conveyor to increase the friction between the take-up conveyor and the three-dimensional mesh structure, or by providing small protrusions near the surface of the take-up conveyor.

[0047] Cooling of the thermoplastic resin after melt molding is preferably performed using cooling water.

[0048] In order to further improve the heat resistance and resistance to setting of the three-dimensional network structure, it is preferable to perform an annealing treatment after the cooling. The annealing treatment may be performed using a commercially available hot air drying oven or in a warm water bath. It is believed that the annealing treatment rearranges the hard segments, forming pseudo-crystallization-like crosslinking points and improving the heat resistance and resistance to setting. The temperature at which the annealing treatment is performed is preferably 80°C or higher, and more preferably 100°C or higher.

[0049] This application claims the benefit of priority based on Japanese Patent Application No. 2024-052441, filed on March 27, 2024. The entire contents of the specification of Japanese Patent Application No. 2024-052441, filed on March 27, 2024, are incorporated herein by reference.

[0050] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples. Furthermore, modifications can be made within the scope of the above and below-described aims, and all such modifications are within the technical scope of the present invention.

[0051] The evaluation methods used in the examples and comparative examples are as follows.

[0052] (1) Thickness and apparent density The three-dimensional network structure was cut into a size of 30 cm x 30 cm in the length and width directions, and the obtained sample was left unloaded for 24 hours. Thereafter, the height was measured at one point in the center using a test piece thickness measuring instrument (FD-80N model manufactured by Kobunshi Keiki Co., Ltd.), and the average value was taken as the thickness of the three-dimensional network structure. Furthermore, the sample was placed on an electronic balance and the mass of the sample was measured. The height and the area (900 cm) of the sample were measured. ２ The apparent density was calculated by dividing the mass of the sample by the volume. The above operation was repeated four times to calculate the average values ​​of the thickness and apparent density of the three-dimensional network structure.

[0053] (2) Density ratio of the skin layer The three-dimensional network structure was cut into a size of 5 cm x 5 cm in the length and width directions, and the thickness and apparent density (overall apparent density) of the obtained sample were measured in the same manner as in (1) above. Next, the sample was cut at a position 0.5 cm away from both surfaces in the thickness direction, and the total mass (g) of the two cut samples was divided by the volume (5 cm x 5 cm x 0.5 cm x 2) to determine the apparent density (g / cm) of the skin layer. ３ Finally, the apparent density of the skin layer was divided by the total apparent density to obtain the density ratio of the skin layer. The above measurement was carried out three times to determine the density ratio of the skin layer (n=3).

[0054] (3) Average Fiber Diameter The three-dimensional network structure was cut into pieces measuring 10 cm x 10 cm in both the longitudinal and transverse directions. Next, 10 fibers located on the outermost surface of the three-dimensional network structure in the thickness direction, i.e., 10 fibers located at a location where no fibers existed outside of the surface in the thickness direction, were sampled as skin layer fibers. Finally, the diameters of the sampled continuous filaments were measured using an optical microscope, focusing on the location where the fiber diameters were to be measured. The average value (n = 10) of the fiber diameters at the 10 locations was calculated and used as the average fiber diameter of the fibers in the skin layer. The average fiber diameter of the fibers in the inner layer was calculated in the same manner as the average fiber diameter of the fibers in the skin layer, except that the fibers were sampled from within 30% of the thickness of the three-dimensional network structure from the center in the thickness direction (within a range of 35 to 65% in the thickness direction from one surface).

[0055] (4) Hollow Ratio The sample was cut into a size of 10 cm x 10 cm. Next, 10 fibers located at the outermost surface in the thickness direction of the three-dimensional network structure were sampled as fibers for the skin layer. That is, 10 fibers located at a location where no fibers existed outside of these fibers in the thickness direction were sampled. The sampled fibers were sliced ​​into rings and placed on a cover glass with the fiber axial direction aligned. The fiber cross sections in the cross section direction were observed under an optical microscope. The peripheral area (a) and hollow area (b) of the fibers were calculated, and the hollow ratio was calculated using the following formula. The average hollow ratio of the 10 fibers was taken as the hollow ratio of the fibers in the skin layer. Hollow ratio = 100 x (b) / (a) (unit: %). The hollow ratio of the fibers in the inner layer was calculated in the same manner as the hollow ratio of the fibers in the skin layer, except that the fibers were sampled from within 30% of the thickness of the three-dimensional network structure from the center in the thickness direction (within a range of 35 to 65% in the thickness direction from one surface).

[0056] (5) Compression Hardness The three-dimensional network structure was cut into a size of 30 cm x 30 cm, and the resulting sample was left in an environment of 20°C ± 2°C without load for 24 hours. Then, in an environment of 20°C ± 2°C, compression hardness was measured in accordance with JIS L 4500 using a Tensilon manufactured by Orientec Co., Ltd. Specifically, a pressure plate with a diameter (φ) of 200 mm and a thickness of 3 mm was placed at the center of the sample, and compression of the center of the sample was initiated at a rate of 10 mm / min. The thickness when the load reached 5 N was measured and defined as the initial thickness. The position of the pressure plate at this time was defined as the zero point, and pre-compression was performed once in the thickness direction to 75% (25% of the initial thickness) at a rate of 100 mm / min, and the pressure plate was returned to the zero point at the same speed. Thereafter, the specimen was immediately compressed 25% in the thickness direction at a speed of 100 mm / min (compressed to a thickness of 75% of the initial thickness), the load at this time was measured, and this weight was defined as the hardness at 25% compression (N / φ200 mm). The above operation was performed three times, and the average value (n=3) of the hardness at 25% compression was calculated. Subsequently, the specimen was compressed 50% in the thickness direction at a speed of 100 mm / min (compressed to a thickness of 50% of the initial thickness), the load at this time was measured, and this weight was defined as the hardness at 50% compression (N / φ200 mm). The above operation was performed three times, and the average value (n=3) of the hardness at 50% compression was calculated.

[0057] The thermoplastic resin compositions used in the Examples and Comparative Examples were prepared as follows: Resin A, a polyester-based thermoplastic elastomer; Resin B, a polyolefin-based thermoplastic elastomer; and Resin C, a biodegradable resin. <Resin A> Dimethyl terephthalate (DMT) and 1,4-butanediol (1,4-BD) were charged with a small amount of catalyst and transesterified using a conventional method. Polytetramethylene glycol (PTMG) with a number-average molecular weight of 1,000 was then added, and polycondensation was carried out while increasing the temperature and reducing the pressure to produce a polyetherester block copolymer elastomer. Next, 1% of an antioxidant was added, and the mixture was mixed and kneaded. The mixture was pelletized and vacuum-dried at 50°C for 48 hours to obtain a polyester-based thermoplastic elastomer (Resin A). Resin A had a soft segment content of 40% by mass and a melting point of 198°C. <Resin B> Hexane, 1-hexene, and ethylene were polymerized by a known method using a metallocene compound as a catalyst to obtain an ethylene-α-olefin copolymer, which was then mixed and kneaded with 1% of an antioxidant and pelletized to obtain a polyolefin-based thermoplastic elastomer (Resin B). Resin B was a random copolymer, with a content of 1-hexene-derived structural units of 6.2% by mass and a density of 0.912 g / cm. ３ The melting point was 110°C, and the intrinsic viscosity was 0.99 dL / g. <Resin C> 1.5 mol of 1,4-butanediol, 0.40 mol of adipic acid, and 0.60 mol of dimethyl terephthalate were mixed in a reaction vessel equipped with a stirrer, a thermometer, and a distillation condenser. Next, 300 ppm of tetrabutyl titanate (Aldrich) was added as a titanium catalyst to the resulting mixture. Thereafter, transesterification and esterification reactions were carried out at 220°C under atmospheric pressure for 2 hours to prepare a prepolymer. The resulting prepolymer was heated to 240°C and then polycondensed at 0.1 mmHg for 2 hours. The mixture was then cooled and cut with a pellet cutter to obtain pellets of poly(butylene adipate / terephthalate) resin (Resin C).

[0058] Example 1: Resin A was melted and discharged below a nozzle surface equipped with discharge nozzles. The nozzles were arranged in eight rows in the thickness direction on an effective nozzle surface measuring 97 cm in width and 59.7 mm in thickness. The nozzles were triple-bridge orifices with an outer diameter of 5.8 mm and an inner diameter of 5.3 mm, each with a hollow cross section. The second to seventh rows were arranged in a staggered pattern with a hole-to-hole pitch of 9.0 mm in the width direction and 7.8 mm in the thickness direction, while the first and eighth rows were arranged with a hole-to-hole pitch of 12 mm in the width direction and 11.5 mm in the thickness direction. The resin discharged from the nozzles in the first and eighth rows in the thickness direction formed a skin layer, and the resin discharged from the nozzles in the second to seventh rows in the thickness direction formed an inner layer.

[0059] The spinning temperature (melt temperature) was 240°C, the average single-hole output rate was 4.0 g / min, and the ratio (hereinafter referred to as the single-hole output rate ratio) of the single-hole output rate of the nozzles in the 2nd to 7th rows forming the inner layer divided by the single-hole output rate of the nozzles in the 1st and 8th rows forming the skin layer was 2.0. The molten resin A was extruded below the nozzle surface. Below the nozzle surface, a water tank was placed so that the cooling water surface was located 35 cm below the nozzle surface of the extrusion nozzle, and a pair of take-up conveyors were placed in the water tank so that a portion of them was above the water surface. The take-up conveyor had a stainless steel endless net with a width of 150 cm, and the conveyor net was arranged parallel to the width direction of the nozzle surface, and the opening width of the endless net was 43 mm.

[0060] The molten resin was extruded into a filament onto a take-up conveyor above the water surface, and the continuous filament was dropped to form a meandering loop, fusing the contact portions to form a three-dimensional network structure. Both sides of the molten three-dimensional network structure were sandwiched between take-up conveyors and pulled into cooling water at a take-up speed of 2.70 m / min to solidify. Solidification flattened both sides in the thickness direction. Next, the structure was cut to a predetermined size and heat-treated with hot air at 110°C for 15 minutes to obtain a three-dimensional network structure.

[0061] In the obtained three-dimensional network structure, the fibers in the skin layer had an average fiber diameter of 0.80 mm, and the fibers in the inner layer had an average fiber diameter of 0.85 mm. The fibers in the skin layer had a cylindrical cross-sectional shape with a hollow cross-section having a hollow ratio of 31%, and the fibers in the inner layer had a cylindrical cross-sectional shape with a hollow cross-section having a hollow ratio of 35%. The apparent density of the obtained three-dimensional network structure was 0.033 g / cm. ３ The skin layer density ratio was 1.00 and the thickness was 41 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 140.1 N and at 50% compression was 242.0 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 1.

[0062] Example 2 A three-dimensional network structure was obtained in the same manner as in Example 1, except that the single-hole discharge rate ratio was set to 1.4, the water tank was positioned so that the cooling water surface was located 34 cm below the nozzle surface, and the take-up speed was set to 2.55 m / min.

[0063] In the obtained three-dimensional network structure, the fibers in the skin layer had an average fiber diameter of 0.78 mm, and the fibers in the inner layer had an average fiber diameter of 0.85 mm. The fibers in the skin layer had a cylindrical cross-sectional shape with a hollow cross-section of 32%, and the fibers in the inner layer had a cylindrical cross-sectional shape with a hollow cross-section of 36%. The apparent density of the obtained three-dimensional network structure was 0.035 g / cm. ３ The skin layer density ratio was 1.22 and the thickness was 40 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 138.1 N and at 50% compression was 239.5 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 1.

[0064] Example 3 A three-dimensional network structure was obtained in the same manner as in Example 1, except that the single-hole discharge rate ratio was set to 2.3, the water tank was positioned so that the cooling water surface was located 32 cm below the nozzle surface, and the take-up speed was set to 2.62 m / min. In the obtained three-dimensional network structure, the fibers in the skin layer had an average fiber diameter of 0.75 mm, and the fibers in the inner layer had an average fiber diameter of 0.89 mm. Furthermore, the fibers in the skin layer had a cylindrical cross-sectional shape with a hollow cross-section having a hollow ratio of 29%, and the fibers in the inner layer had a cylindrical cross-sectional shape with a hollow cross-section having a hollow cross-section having a hollow ratio of 35%. The obtained three-dimensional network structure had an apparent density of 0.034 g / cm ３The skin layer density ratio was 1.10 and the thickness was 40 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 137.9 N and at 50% compression was 245.3 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 1.

[0065] Comparative Example 1 A three-dimensional network structure was obtained in the same manner as in Example 1, except that the nozzles were arranged in eight rows in the thickness direction on an effective nozzle surface having a width length of 97 cm and a thickness length of 54.6 mm, the nozzles were triple-bridge orifices with an outer diameter of 5.0 mm and an inner diameter of 4.4 mm and a hollow cross section, and the nozzles in the first to eighth rows were arranged in a staggered pattern with a width-to-width hole pitch of 9.0 mm and a thickness-to-thickness hole pitch of 7.8 mm, the single-hole discharge rate ratio was 1.0, the water tank was positioned so that the cooling water level was located 32 cm below the nozzle surface, and the take-up speed was 2.34 m / min. Note that in Comparative Example 1, the nozzles for forming the skin layer and the nozzles for forming the inner layer were not separated, but for convenience, the single-hole discharge rate ratio is described as 1.0.

[0066] In the obtained three-dimensional network structure, the fibers in the skin layer had an average fiber diameter of 0.86 mm, and the fibers in the inner layer had an average fiber diameter of 0.84 mm. The fibers in the skin layer had a cylindrical cross-sectional shape with a hollow cross-section of 34%, and the fibers in the inner layer had a cylindrical cross-sectional shape with a hollow cross-section of 33%. The apparent density of the obtained three-dimensional network structure was 0.038 g / cm. ３ The skin layer density ratio was 1.38 and the thickness was 42 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 140.2 N and at 50% compression was 241.0 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 1.

[0067] Example 4: Resin A was melted and discharged below a nozzle surface equipped with discharge nozzles. The nozzles were arranged in nine rows in the thickness direction on an effective nozzle surface measuring 97 cm in width and 67 mm in thickness. The nozzles were triple-bridge orifices with an outer diameter of 5.8 mm and an inner diameter of 5.3 mm, each with a hollow cross section. The second to eighth rows were arranged in a staggered pattern with a hole-to-hole pitch of 9.0 mm in the width direction and 7.8 mm in the thickness direction, while the first and ninth rows were arranged with a hole-to-hole pitch of 12 mm in the width direction and 11.5 mm in the thickness direction. The resin discharged from the first and ninth rows in the thickness direction formed a skin layer, and the resin discharged from the second to eighth rows in the thickness direction formed an inner layer.

[0068] The molten resin A was extruded below the nozzle surface so that the spinning temperature (melt temperature) was 240 ° C, the average single-hole discharge rate was 3.3 g / min, and the single-hole discharge rate ratio was 2.0. Below the nozzle surface, a water tank was placed so that the cooling water surface was located 30 cm below the nozzle surface of the extrusion nozzle, and a pair of take-up conveyors were placed in the water tank so that a portion of them was above the water surface. The take-up conveyor had a stainless steel endless net with a width of 150 cm, and the take-up conveyor was arranged parallel to the width direction of the nozzle surface, and the opening width of the endless net was 52 mm.

[0069] The molten resin was extruded into a filament onto a take-up conveyor above the water surface, and the continuous filament was dropped to form a meandering loop, fusing the contact portions to form a three-dimensional network structure. Both sides of the molten three-dimensional network structure were sandwiched between take-up conveyors and drawn into cooling water at a take-up speed of 2.24 m / min to solidify. Solidification flattened both sides in the thickness direction. Next, the structure was cut to a predetermined size and heat-treated with hot air at 110°C for 15 minutes to obtain a three-dimensional network structure.

[0070] In the obtained three-dimensional network structure, the fibers in the skin layer had an average fiber diameter of 0.81 mm, and the fibers in the inner layer had an average fiber diameter of 0.89 mm. The fibers in the skin layer had a cylindrical cross-sectional shape with a hollow cross-section of 42%, and the fibers in the inner layer had a cylindrical cross-sectional shape with a hollow cross-section of 40%. The apparent density of the obtained three-dimensional network structure was 0.031 g / cm. ３ The skin layer density ratio was 0.94 and the thickness was 49 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 119.4 N and at 50% compression was 205.6 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 1.

[0071] Comparative Example 2 A three-dimensional network structure was obtained in the same manner as in Example 4, except that the nozzles were arranged in nine rows in the thickness direction on an effective nozzle surface having a width length of 97 cm and a thickness length of 62.4 mm, the nozzles were triple-bridge orifices with an outer diameter of 5.0 mm and an inner diameter of 4.4 mm and a hollow-forming cross section, the first to ninth rows were arranged in a staggered pattern with a hole-to-hole pitch of 9.0 mm in the width direction and a hole-to-hole pitch of 7.8 mm in the thickness direction, the single-hole output rate ratio was 1.0, and the take-up speed was 1.98 m / min. Note that in Comparative Example 2, the nozzles were not separated into those for forming the skin layer and those for forming the inner layer, but for convenience, the single-hole output rate ratio is described as 1.0.

[0072] In the obtained three-dimensional network structure, the fibers in the skin layer had an average fiber diameter of 0.88 mm, and the fibers in the inner layer had an average fiber diameter of 0.84 mm. The fibers in the skin layer had a cylindrical cross-sectional shape with a hollow cross-section of 32%, and the fibers in the inner layer had a cylindrical cross-sectional shape with a hollow cross-section of 31%. The apparent density of the obtained three-dimensional network structure was 0.035 g / cm. ３ The skin layer density ratio was 1.26 and the thickness was 50 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 118.0 N and at 50% compression was 203.0 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 1.

[0073] Example 5 A three-dimensional network structure was obtained in the same manner as in Example 1, except that the nozzles were arranged in 10 rows in the thickness direction on an effective nozzle surface having a width length of 97 cm and a thickness length of 70.2 mm, the nozzles were triple-bridge orifices with an outer diameter of 5.0 mm and an inner diameter of 4.4 mm, each with a hollow cross section, and the nozzles were arranged in a staggered pattern with a width-to-thickness pitch of 9.0 mm and a thickness-to-thickness pitch of 7.8 mm, the average single-hole output rate was 4.6 g / min, the single-hole output rate ratio was 1.0, the water tank was positioned so that the cooling water surface was located 40 cm below the nozzle surface, the opening width of the endless net was 62 mm, and the take-up speed was 2.13 m / min. Note that in Example 5, the nozzles for forming the skin layer and the nozzles for forming the inner layer were not separated, but for convenience, the single-hole output rate ratio is described as 1.0.

[0074] In the obtained three-dimensional network structure, the fibers in the skin layer had an average fiber diameter of 0.65 mm, and the fibers in the inner layer had an average fiber diameter of 0.63 mm. The fibers in the skin layer had a cylindrical cross-sectional shape with a hollow cross-section of 36%, and the fibers in the inner layer had a cylindrical cross-sectional shape with a hollow cross-section of 34%. The apparent density of the obtained three-dimensional network structure was 0.035 g / cm. ３ The skin layer density ratio was 0.93 and the thickness was 59 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 148.2 N and at 50% compression was 261.0 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 1.

[0075] Comparative Example 3 A three-dimensional network structure was obtained in the same manner as in Example 5, except that the nozzles were arranged in 11 rows in the thickness direction on an effective nozzle surface having a width length of 97 cm and a thickness length of 77.9 mm, the nozzles were triple-bridge orifices with an outer diameter of 5.0 mm and an inner diameter of 4.4 mm and a hollow cross section, and the nozzles in the first to eleventh rows were arranged in a staggered pattern with a width-to-hole pitch of 9.0 mm and a thickness-to-hole pitch of 7.8 mm, the average single-hole output rate was 4.1 g / min, the water tank was positioned so that the cooling water level was located 37 cm below the nozzle surface, and the take-up speed was 1.91 m / min. Note that in Comparative Example 3, the nozzles for forming the skin layer and the nozzles for forming the inner layer were not separated, but for convenience, the single-hole output rate ratio is described as 1.0.

[0076] In the obtained three-dimensional network structure, the fibers in the skin layer had an average fiber diameter of 0.68 mm, and the fibers in the inner layer had an average fiber diameter of 0.66 mm. The fibers in the skin layer had a cylindrical cross-sectional shape with a hollow cross-section of 32%, and the fibers in the inner layer had a cylindrical cross-sectional shape with a hollow cross-section of 31%. The apparent density of the obtained three-dimensional network structure was 0.039 g / cm. ３ The skin layer density ratio was 1.31 and the thickness was 59 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 147.2 N and at 50% compression was 259.8 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 1.

[0077] Example 6: Resin C was melted and discharged below a nozzle surface equipped with discharge nozzles. The nozzles were arranged in 10 rows in the thickness direction on an effective nozzle surface measuring 97 cm in width and 70.2 mm in thickness. The nozzles were triple-bridge orifices with an outer diameter of 5.0 mm and an inner diameter of 4.4 mm, each with a hollow cross section. The first to tenth rows were arranged in a staggered pattern with a hole-to-hole pitch of 9.0 mm in the width direction and 7.8 mm in the thickness direction. The resin discharged from the nozzles in the first, second, ninth, and tenth rows in the thickness direction formed a skin layer, while the resin discharged from the nozzles in the third to eighth rows in the thickness direction formed an inner layer.

[0078] The melted resin C was discharged below the nozzle surface so that the spinning temperature (melt temperature) was 240 ° C, the average single-hole discharge rate was 3.9 g / min, and the single-hole discharge rate ratio was 2.1. Below the nozzle surface, a water tank was placed so that the cooling water surface was located 33 cm below the nozzle surface of the discharge nozzle, and a pair of take-up conveyors were placed in the water tank so that a portion of them was above the water surface. The take-up conveyor had a stainless steel endless net with a width of 150 cm, and the take-up conveyor was arranged parallel to the width direction of the nozzle surface, and the opening width of the endless net was 58 mm.

[0079] The molten resin was extruded into a filament onto a take-up conveyor above the water surface, and the continuous filament was dropped to form a meandering loop, fusing the contact portions to form a three-dimensional network structure. Both sides of the molten three-dimensional network structure were sandwiched between take-up conveyors and drawn into cooling water at a take-up speed of 2.51 m / min to solidify. Solidification flattened both sides in the thickness direction. Next, the structure was cut to a predetermined size and heat-treated with hot air at 90°C for 20 minutes to obtain a three-dimensional network structure.

[0080] In the obtained three-dimensional network structure, the fibers in the skin layer had an average fiber diameter of 0.70 mm, and the fibers in the inner layer had an average fiber diameter of 0.82 mm. The fibers in the skin layer had a cylindrical cross-sectional shape with a hollow cross-section of 16%, and the fibers in the inner layer had a cylindrical cross-sectional shape with a hollow cross-section of 23%. The apparent density of the obtained three-dimensional network structure was 0.034 g / cm. ３ The skin layer density ratio was 1.05 and the thickness was 51 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 112.8 N and at 50% compression was 231.5 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 1.

[0081] Comparative Example 4 A three-dimensional network structure was obtained in the same manner as in Example 6, except that the single-hole discharge rate ratio was set to 1.0 and the take-up speed was set to 2.36 m / min. In the obtained three-dimensional network structure, the fibers of the skin layer had an average fiber diameter of 0.84 mm, and the fibers of the inner layer had an average fiber diameter of 0.81 mm. Furthermore, the fibers of the skin layer had a cylindrical cross-sectional shape with a hollow cross-section having a hollow ratio of 20%, and the fibers of the inner layer had a cylindrical cross-sectional shape with a hollow cross-section having a hollow ratio of 20%. The obtained three-dimensional network structure had an apparent density of 0.037 g / cm. ３ The skin layer density ratio was 1.50 and the thickness was 51 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 113.0 N and at 50% compression was 230.0 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 1.

[0082]

[0083] Example 7: Resin A was melted and discharged below a nozzle surface equipped with discharge nozzles. The nozzles were arranged in 12 rows in the thickness direction on an effective nozzle surface measuring 97 cm in width and 57.2 mm in thickness. The nozzles had orifices with a hole diameter of 1.0 mm, and the first to twelfth rows were arranged in a staggered pattern with a hole-to-hole pitch of 6.0 mm in the width direction and 5.2 mm in the thickness direction. The resin discharged from the nozzles in the first, second, eleventh, and twelfth rows in the thickness direction formed a skin layer, and the resin discharged from the nozzles in the third to tenth rows in the thickness direction formed an inner layer.

[0084] The molten resin A was extruded below the nozzle surface so that the spinning temperature (melt temperature) was 240 ° C, the average single-hole discharge rate was 1.2 g / min, and the single-hole discharge rate ratio was 1.8. Below the nozzle surface, a water tank was placed so that the cooling water surface was located 22 cm below the nozzle surface of the extrusion nozzle, and a pair of take-up conveyors were placed in the water tank so that a portion of them was above the water surface. The take-up conveyor had a stainless steel endless net with a width of 150 cm, and the take-up conveyor was placed parallel to the width direction of the nozzle surface, and the opening width of the endless net was 40 mm.

[0085] The molten resin was extruded into a filament onto a take-up conveyor above the water surface, and the continuous filament was dropped to form a meandering loop, fusing the contact portions to form a three-dimensional network structure. Both sides of the molten three-dimensional network structure were sandwiched between take-up conveyors and drawn into cooling water at a take-up speed of 1.76 m / min to solidify. Solidification flattened both sides in the thickness direction. The structure was then cut to a predetermined size and heat-treated with 110°C hot air for 15 minutes to obtain a three-dimensional network structure.

[0086] In the obtained three-dimensional network structure, the fibers of the skin layer had a cylindrical solid cross section and an average fiber diameter of 0.42 mm, and the fibers of the inner layer had a cylindrical solid cross section and an average fiber diameter of 0.46 mm. The apparent density of the obtained three-dimensional network structure was 0.039 g / cm. ３ The skin layer density ratio was 1.10 and the thickness was 37 mm. The hardness of the resulting three-dimensional network structure when compressed by 25% was 70.8 N and when compressed by 50% was 142.3 N. The production conditions and the physical properties of the resulting three-dimensional network structure are summarized in Table 2.

[0087] Comparative Example 5 A three-dimensional network structure was obtained in the same manner as in Example 7, except that the single-hole discharge rate ratio was set to 1.0 and the take-up speed was set to 1.60 m / min. In the obtained three-dimensional network structure, the fibers of the skin layer had a cylindrical solid cross-sectional shape and an average fiber diameter of 0.47 mm, and the fibers of the inner layer had a cylindrical solid cross-sectional shape and an average fiber diameter of 0.44 mm. The apparent density of the obtained three-dimensional network structure was 0.043 g / cm. ３ The skin layer density ratio was 1.48, and the thickness was 38 mm. The hardness of the resulting three-dimensional network structure when compressed by 25% was 72.2 N, and the hardness of the resulting three-dimensional network structure when compressed by 50% was 141.0 N. The production conditions and the physical properties of the resulting three-dimensional network structure are summarized in Table 2.

[0088] Example 8: Resin B was melted, and the melted resin A was discharged below the nozzle surface on which the discharge nozzles were provided. The nozzles were arranged in eight rows in the thickness direction on an effective nozzle surface measuring 97 cm in width and 54.56 mm in thickness. The nozzles had orifices with a hole diameter of 1.0 mm, and the first to eighth rows were arranged in a staggered pattern with a hole-to-hole pitch of 9.0 mm in the width direction and 7.8 mm in the thickness direction. The skin layer was formed by the resin discharged from the nozzles in the first, second, seventh, and eighth rows in the thickness direction, and the inner layer was formed by the resin discharged from the nozzles in the third to sixth rows in the thickness direction.

[0089] The melted resin B was extruded below the nozzle surface so that the spinning temperature (melt temperature) was 200 ° C, the average single-hole discharge rate was 3.5 g / min, and the single-hole discharge rate ratio was 2.0. Below the nozzle surface, a water tank was placed so that the cooling water surface was located 25 cm below the nozzle surface of the extrusion nozzle, and a pair of take-up conveyors were placed in the water tank so that a portion of them was above the water surface. The take-up conveyor had a stainless steel endless net with a width of 150 cm, and the take-up conveyor was arranged parallel to the width direction of the nozzle surface, and the opening width of the endless net was 45 mm.

[0090] The molten resin was extruded into a filament onto a take-up conveyor above the water surface, and the continuous filament was dropped to form a meandering loop, fusing the contact portions to form a three-dimensional network structure. Both sides of the molten three-dimensional network structure were sandwiched between take-up conveyors and drawn into cooling water at a take-up speed of 1.50 m / min to solidify. Solidification flattened both sides in the thickness direction. The structure was then cut to a predetermined size and heat-treated with hot air at 90°C for 20 minutes to obtain a three-dimensional network structure.

[0091] In the obtained three-dimensional network structure, the fibers of the skin layer had a solid cylindrical cross section and an average fiber diameter of 0.76 mm, and the fibers of the inner layer had a solid cylindrical cross section and an average fiber diameter of 0.88 mm. The apparent density of the obtained three-dimensional network structure was 0.048 g / cm. ３The skin layer density ratio was 1.12 and the thickness was 43 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 189.5 N and at 50% compression was 305.1 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 2.

[0092] Comparative Example 6 A three-dimensional network structure was obtained in the same manner as in Example 8, except that the single-hole discharge rate ratio was set to 1.0 and the take-up speed was set to 1.38 m / min. In the obtained three-dimensional network structure, the fibers of the skin layer had a cylindrical solid cross-sectional shape and an average fiber diameter of 0.88 mm, and the fibers of the inner layer had a cylindrical solid cross-sectional shape and an average fiber diameter of 0.86 mm. The apparent density of the obtained three-dimensional network structure was 0.052 g / cm. ３ The skin layer density ratio was 1.35 and the thickness was 43 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 189.0 N and at 50% compression was 306.7 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 2.

[0093] Example 9 A three-dimensional network structure was obtained in the same manner as in Example 8, except that Resin A was used instead of Resin B, the spinning temperature (melting temperature) was set to 240°C, the average single-hole discharge rate was set to 2.5 g / min, the water tank was positioned so that the cooling water surface was located 32 cm below the nozzle surface, the take-up speed was set to 1.23 m / min, and heat treatment was performed with 110°C hot air for 15 minutes.

[0094] In the obtained three-dimensional network structure, the fibers of the skin layer had a solid cylindrical cross section and an average fiber diameter of 0.38 mm, and the fibers of the inner layer had a solid cylindrical cross section and an average fiber diameter of 0.41 mm. The apparent density of the obtained three-dimensional network structure was 0.042 g / cm. ３ The skin layer density ratio was 1.10 and the thickness was 43 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 132.2 N and at 50% compression was 250.9 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 2.

[0095] Comparative Example 7 A three-dimensional network structure was obtained in the same manner as in Example 9, except that the single-hole discharge rate ratio was set to 1.0 and the take-up speed was set to 1.10 m / min. In the obtained three-dimensional network structure, the fibers of the skin layer had a cylindrical solid cross-sectional shape and an average fiber diameter of 0.42 mm, and the fibers of the inner layer had a cylindrical solid cross-sectional shape and an average fiber diameter of 0.38 mm. The apparent density of the obtained three-dimensional network structure was 0.047 g / cm. ３ The skin layer density ratio was 1.35 and the thickness was 43 mm. The hardness of the resulting three-dimensional network structure at 25% compression was 135.0 N and at 50% compression was 257.3 N. The production conditions and physical properties of the resulting three-dimensional network structure are summarized in Table 2.

[0096]

[0097] The three-dimensional network structures of Examples 1 to 3 all have a thickness similar to that of the three-dimensional network structure of Comparative Example 1, and the hardness when compressed is also similar, but the apparent density of Comparative Example 1 is 0.038 g / cm ３ In contrast, in Examples 1 to 3, the density was 0.033 to 0.035 g / cm ３ From this, it can be seen that in Examples 1 to 3, although the apparent density was reduced by 8 to 13% compared to the three-dimensional network structure of Comparative Example 1 to achieve weight reduction, three-dimensional network structures having the same degree of hardness upon compression were obtained.

[0098] The same was true between Example 4 and Comparative Example 2, Example 5 and Comparative Example 3, Example 6 and Comparative Example 4, Example 7 and Comparative Example 5, Example 8 and Comparative Example 6, and Example 9 and Comparative Example 7. In these Examples, the apparent density was reduced by about 10% compared to the three-dimensional network structures of the corresponding Comparative Examples in order to reduce weight, but three-dimensional network structures with similar hardness upon compression were obtained.

[0099] The three-dimensional network structure of the present invention is suitable for use in cushions, which can be used for applications requiring elasticity to support objects or for applications requiring impact reduction, for example, office chairs, furniture, sofas, bedding such as beds, and vehicle seats for trains, automobiles, motorcycles, etc.

Claims

1. A three-dimensional network structure consisting of continuous filaments made of a thermoplastic resin composition and having a three-dimensional random loop bonded structure, wherein both surfaces in the thickness direction of the three-dimensional network structure are skin layers, and the apparent density of the skin layers divided by the apparent density of the three-dimensional network structure is 1.25 or less.

2. The three-dimensional mesh structure according to claim 1, wherein the three-dimensional mesh structure has an inner layer sandwiched between two of the skin layers, and the filaments constituting the skin layer and the inner layer each have an average fiber diameter of 0.1 mm to 3.0 mm.

3. The three-dimensional network structure has an apparent density of 0.01 g / cm ３ ~0.20 g / cm ３ and the skin layer has an apparent density of 0.01 g / cm ３ ~0.20 g / cm ３ The three-dimensional network structure according to claim 2, wherein 4. The three-dimensional network structure according to claim 3, which has a thickness of 10 to 300 mm.

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