Three-dimensional net-like structure

Abstract

Provided is a biodegradable three-dimensional net-like structure that has excellent compression recovery properties after compression at a use environment temperature and excellent compression durability on both sides, and in which the difference in compression durability between both sides is small. The present invention is a three-dimensional net-like structure that has a three-dimensional random loop bonded structure and is formed from continuous filaments made from a thermoplastic resin composition, said three-dimensional net-like structure being characterized in that the thermoplastic resin composition contains at least 70 mass% of a polybutylene adipate terephthalate resin, one surface of the three-dimensional net-like structure has an apparent density higher than that of the other surface, the residual strain R1 after repeated compression 13,000 times at a load of 750 N from the one surface side and the residual strain R2 after repeated compression 13,000 times at a load of 750 N from the other surface side are each 20% or less, the absolute value of the difference between the value of R1 and the value of R2 is 10% or less, and the compressive residual strain of the three-dimensional network structure at 40°C is 15% or less.

Description

Three-dimensional mesh structure

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

[0002] Up until now, three-dimensional network structures have been widely used as cushioning materials for furniture, bedding such as beds, and seats for vehicles such as trains, automobiles, motorcycles, etc., due to their excellent breathability and recyclability. Due to the recent acceleration of efforts to address environmental issues, research has been conducted into biodegradable polymers that decompose in a shorter time period than conventional polymers, even for these three-dimensional network structures, and various technologies for biodegradable three-dimensional network structures have been disclosed to date.

[0003] Patent Document 1 discloses a technique for improving the plant retention of a biodegradable network structure. Patent Document 2 discloses a technique for improving local bonding of fiber materials in a biodegradable network structure. Patent Document 3 discloses a technique for forming coil spring-like or loop-like parts in a biodegradable three-dimensional structure, which allows the parts to deform favorably in response to compressive stress and disperse the stress.

[0004] JP 2001-032236 A JP 2020-128608 A JP 2000-328422 A

[0005] As described above, various attempts have been made to improve the functionality of biodegradable network structures, but no biodegradable network structure has yet been known that exhibits both excellent cushioning properties and recovery properties when compressed at the ambient temperature of use when used as a cushioning material. In particular, no three-dimensional network structure having different cushioning properties on both sides has yet been known that exhibits excellent compression durability on both sides. The present invention has been made in view of the above circumstances, and its object is to provide a biodegradable three-dimensional network structure that exhibits excellent compression recovery properties after compression at the ambient temperature of use, as well as excellent compression durability on both sides, with a small difference in compression durability between the two sides.

[0006] That is, the present invention includes the following inventions: [1] A three-dimensional network structure composed of continuous filaments made of a thermoplastic resin composition and having a three-dimensional random loop bonded structure, wherein the thermoplastic resin composition contains 70% by mass or more of a polybutylene adipate terephthalate resin, one surface of the three-dimensional network structure has a higher apparent density than the other surface, and a residual strain R after repeatedly compressing from the one surface side with a load of 750 N 13,000 times is 0.015 to 0.015. １ and the residual strain R after repeatedly compressing the other surface side with a load of 750 N 13,000 times. ２ are each 20% or less, and １ and the value of R ２ [2] The three-dimensional network structure according to [1] above, wherein the polybutylene adipate terephthalate resin contains adipic acid units and terephthalic acid units, and the molar ratio of the terephthalic acid units to the adipic acid units is 1.0 or more and 3.0 or less. [3] The three-dimensional network structure according to [1] or [2] above, wherein the polybutylene adipate terephthalate resin has a melting point of 125°C or more and 180°C or less. [4] An apparent density of 0.005 g / cm ３ 0.20g / cm or more ３ [5] The three-dimensional network structure according to any one of the above [1] to [3], wherein the larger value of the hardness at 25% compression when pressure is applied from one surface side and the hardness at 25% compression when pressure is applied from the other surface side is H １ , the smaller value is H ２ Then, H １ / H ２ [6] The three-dimensional network structure according to any one of the above [1] to [4], wherein the hardness at 40% compression when pressure is applied from one surface side and the hardness at 40% compression when pressure is applied from the other surface side are determined as H ３ , the smaller value is H ４ Then, H ３ / H ４[7] The three-dimensional network structure according to any one of [1] to [5] above, wherein the absolute value of the difference between the compression deflection coefficient when pressure is applied from the one surface side and the compression deflection coefficient when pressure is applied from the other surface side is 5.0 or less. [8] The three-dimensional network structure according to any one of [1] to [7] above, wherein the differential scanning calorimeter curve of the continuous filament, measured using a differential scanning calorimeter, has an endothermic peak with a minimum enthalpy in the range of 30°C to 70°C of 2.5 J / g or less. [9] The absolute value of the difference between the apparent density of the one surface and the apparent density of the other surface is 0.015 g / cm ３

[10] A cushioning material that includes the three-dimensional mesh structure according to any one of [1] to [9] above and can be used reversibly.

[0007] By virtue of the above-described configuration, the three-dimensional network structure of the present invention has excellent compression recovery after compression at the ambient temperature in use, and has excellent compression durability on both sides, with the difference in compression durability between the two sides being small.

[0008] 1 is an example of a differential scanning calorimetric curve for measuring the enthalpy of an endothermic peak having a minimum value in the range of 30° C. to 70° C. for the continuous filaments that make up the three-dimensional network structure.

[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. The thermoplastic resin composition contains 70% by mass or more of a polybutylene adipate terephthalate resin. Furthermore, one surface of the three-dimensional network structure of the present invention has a higher apparent density than the other surface.

[0010] The above-described configuration allows for a three-dimensional network structure to be obtained that exhibits excellent compression recovery after compression at the ambient temperature, and exhibits excellent compression durability on both sides while minimizing the difference in compression durability between the two sides. The above-described ambient temperature refers to the temperature at which the three-dimensional network structure of the present invention is used as a product such as a cushion. In this specification, the ambient temperature is set to 40°C, and the compression residual strain at 40°C is used as an index of compression recovery after compression at the ambient temperature. Hereinafter, the compression recovery after compression at the ambient temperature may be simply referred to as "compression recovery." Furthermore, the residual strain after repeated compression is used as an index of compression durability, with smaller residual strain after repeated compression indicating better compression durability. These measurement methods will be described later. Each configuration will be described in detail below.

[0011] <Thermoplastic Resin Composition> The thermoplastic resin composition constituting the continuous filaments contains 70% by mass or more of polybutylene adipate terephthalate resin. By selecting polybutylene adipate terephthalate resin from biodegradable resins and using a thermoplastic resin composition containing 70% by mass or more of polybutylene adipate terephthalate resin, a biodegradable three-dimensional network structure with excellent cushioning properties can be obtained. The content of the polybutylene adipate terephthalate resin relative to the thermoplastic resin composition is preferably 75% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 99% by mass or more. Furthermore, the thermoplastic resin composition constituting the continuous filaments may be 100% by mass of polybutylene adipate terephthalate resin.

[0012] Polybutylene adipate terephthalate resin is a biodegradable thermoplastic resin, a copolymer of adipic acid, terephthalic acid, and butanediol. Because of its biodegradability, polybutylene adipate terephthalate resin is expected to be a solution to waste disposal and microplastic problems. Adipic acid, terephthalic acid, and butanediol do not need to be copolymerized simultaneously; they can be copolymerized in multiple stages.

[0013] In the polybutylene adipate terephthalate resin, the molar ratio of the terephthalic acid units to the adipic acid units is preferably 1.0 or more and 3.0 or less, more preferably 1.1 or more and 2.5 or less, even more preferably 1.2 or more and 2.0 or less, and even more preferably 1.3 or more and 1.8 or less. A molar ratio of 1.0 or more facilitates improving the compression durability of both surfaces of the three-dimensional network structure and the compression recovery after compression at the usage temperature. On the other hand, a molar ratio of 3.0 or less improves flexibility and reduces the difference in compression durability between both surfaces. Therefore, the three-dimensional network structure is suitable for cushioning materials, etc.

[0014] The melting point of the polybutylene adipate terephthalate resin is preferably 125°C or higher and 180°C or lower, more preferably 130°C or higher and 175°C or lower, even more preferably 135°C or higher and 170°C or lower, particularly preferably 140°C or higher and 165°C or lower, and most preferably 145°C or higher and 160°C or lower. A melting point of 125°C or higher can easily improve the compression recovery of the three-dimensional network structure after compression at the usage temperature. On the other hand, a melting point of 180°C or lower improves flexibility, making it suitable for use as a cushioning material, etc.

[0015] The melt flow rate (MFR) of the polybutylene adipate terephthalate resin is preferably 3 g / 10 min to 60 g / 10 min. An MFR of 3 g / 10 min or more tends to improve compression recovery and double-sided compression durability. On the other hand, an MFR of 60 g / 10 min or less can increase the melt viscosity and the fiber diameter of the continuous filaments. The MFR is more preferably 4 g / 10 min to 50 g / 10 min, even more preferably 5 g / 10 min to 40 g / 10 min, particularly preferably 6 g / 10 min to 18 g / 10 min, and most preferably 10 g / 10 min to 15 g / 10 min. The MFR of the thermoplastic resin composition constituting the continuous filaments is also preferably within the above range. The MFR of the resin can be measured by the method described in the Examples below.

[0016] When a commercially available resin is used as the polybutylene adipate terephthalate resin, if the resin has a low melt flow rate (MFR), the MFR of the resin can be increased by adding water to the resin to hydrolyze the resin during melt extrusion. On the other hand, if the resin has a high MFR, the MFR of the resin can be decreased by drying the resin before melt extrusion.

[0017] The thermoplastic resin composition constituting the continuous filaments may contain a biodegradable resin other than polybutylene adipate terephthalate resin. Preferred examples of such other biodegradable resins include polylactic acid, polylactic acid / polycaprolactone copolymer, polylactic acid / polyether copolymer, polyethylene terephthalate succinate, polybutylene succinate, polybutylene succinate adipate, polyglycolic acid, polycaprolactone, polyvinyl alcohol, and cellulose acetate. These may be used alone or in combination of two or more. For details, please refer to the positive list of GreenPla (biodegradable plastic) classification number A-1 of the Japan BioPlastics Association. The thermoplastic resin composition constituting the continuous filaments may contain a resin other than biodegradable resin. Examples of such resins include thermoplastic resins such as polyolefin, polyurethane, and polyester.

[0018] The thermoplastic resin composition constituting the continuous filaments may contain, in addition to the polybutylene adipate terephthalate resin, a resin containing a copolymerization component other than adipic acid, terephthalic acid, and butanediol as a unit. Examples of the copolymerization component include dicarboxylic acids other than terephthalic acid and adipic acid, diols other than butanediol, polyalkylene glycols, and modifiers for the purposes of chain extension, terminal blocking, etc. These may be used alone or in combination of two or more.

[0019] Other dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, etc. These may be used alone or in combination of two or more.

[0020] Examples of other diols include methanediol, ethanediol, propanediol, pentanediol, and hexanediol. Examples of polyalkylene glycols include polymethylene glycol, polyethylene glycol, polypropylene glycol, and polybutylene glycol (polytetramethylene glycol). These may be used alone or in combination of two or more.

[0021] Examples of the modifier include polyisocyanate compounds and glycol compounds. Examples of the polyisocyanate compound include diisocyanate compounds. Examples of the diisocyanate compound include hexamethylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate, p-phenylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, tetramethylxylene diisocyanate, carbodiimide-modified MDI, and polymethylene phenyl polyisocyanate. These may be used alone or in combination of two or more.

[0022] Petroleum-derived monomers may be used as monomers for synthesizing the thermoplastic resin composition constituting the continuous filaments. However, it is preferable to use biomass-derived monomers from the viewpoint of reducing the environmental load. As the biomass-derived monomers, for example, monomers listed in the positive list of classification number A (biomass plastics) of the Japan Bioplastics Association can be used.

[0023] The total content of adipic acid units and terephthalic acid units relative to 100 mol% of dicarboxylic acid units contained in the thermoplastic resin composition constituting the continuous filaments is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, still more preferably 95 mol% or more, and particularly preferably 99 mol% or more. Furthermore, the content of butanediol units relative to 100 mol% of diol units contained in the thermoplastic resin composition constituting the continuous filaments is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, still more preferably 95 mol% or more, and particularly preferably 99 mol% or more.

[0024] The thermoplastic resin composition constituting the continuous filaments may contain additives to impart predetermined functions. Examples of additives include deodorants, antibacterial agents, antifungal agents, antimite agents, deodorizers, antifungal agents, fragrances, flame retardants, moisture absorbing and releasing agents, antioxidants, lubricants, etc. These may be used alone or in combination of two or more.

[0025] Examples of the antioxidant include known phenol-based antioxidants, phosphite-based antioxidants, thioether-based antioxidants, benzotriazole-based ultraviolet absorbers, triazine-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, N—H type hindered amine-based light stabilizers, N—CH ３ hindered amine type light stabilizers and the like.

[0026] Examples of phenolic antioxidants include 1,3,5-tris[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 4,4'-butylidenebis(6-tert-butyl-m-cresol), 3-(3,5-di-tert-butyl-4-hydroxyphenyl)stearyl propionate, pentaerythritol, methyl ... thiaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,2'-dimethyl-2,2'-(2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diyl)dipropane-1,1'-diyl bis[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propanoate], 2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)mesitylene, and the like.

[0027] Examples of the phosphite antioxidant include 3,9-bis(octadecyloxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 2,4,8,10-tetrakis(1,1-dimethylethyl)-6-[(2-ethylhexyl)oxy]- ... [C12-15]-12H-dibenzo[d,g]"1,3,2"dioxaphosphocine, tris(2,4-di-tert-butylphenyl) phosphite, tris(4-nonylphenyl) phosphite, tetraalkyl(C12-15)-4,4'-isopropylidene diphenyl diphosphite, diphenyl(2-ethylhexyl) phosphite, diphenylisodecyl phosphite, triisodecyl phosphite, triphenyl phosphite, and the like.

[0028] Examples of the thioether antioxidant include 2,2-bis[3-(dodecylthio)propionic acid]3-(dodecylthio)-1-oxopropyloxymethyl]-1,3-propanediyl bis[3-(dodecylthio)propionic acid], ditridecyl 3,3'-thiobispropionate, and the like.

[0029] To prevent thermal degradation of thermoplastic resins, a mixture of a phenolic antioxidant and a phosphite antioxidant may be used.

[0030] Examples of the lubricant include hydrocarbon waxes, higher alcohol waxes, amide waxes, ester waxes, and metal soap waxes.

[0031] <Continuous Filaments> 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. The continuous filaments are linear filaments having a continuous portion of at least 5 mm or more. The three-dimensional network structure is easily formed by having portions where the intersections of the continuous filaments are bonded. Therefore, it is preferable that the three-dimensional network structure has bonded portions where the intersections of the continuous filaments are bonded to each other.

[0032] For the continuous filaments constituting the three-dimensional network structure of the present invention, if the fineness is the same, hollow fibers have a higher moment of inertia than solid fibers, and therefore the use of hollow fibers results in a higher compressive resistance. Therefore, in order to obtain different cushioning performance on both sides, it is preferable to use both hollow fibers and solid fibers. Note that hollow fibers refer to fibers with a hollow cross section, and solid fibers refer to fibers with a solid cross section.

[0033] The hollow ratio of hollow fibers is preferably 1 to 30%, more preferably 2 to 30%, and particularly preferably 5 to 25% or more. The hollow ratio can be measured by the method described in the Examples below. The hollow ratio of solid fibers is less than 1%.

[0034] Furthermore, in order to obtain different cushioning properties on both sides, it is preferable that the average fiber diameter of the hollow fibers be larger than that of the solid fibers. When the average fiber diameter of the hollow fibers is larger than that of the solid fibers, the difference between the average fiber diameter of the hollow fibers and the average fiber diameter of the solid fibers is preferably 0.12 to 2.5 mm, more preferably 0.14 to 1.0 mm, even more preferably 0.16 to 0.40 mm, and particularly preferably 0.20 to 0.35 mm. When the difference between the average fiber diameter of the hollow fibers and the average fiber diameter of the solid fibers is 0.12 mm or more, it is easy to obtain a three-dimensional network structure having different cushioning properties on both sides.

[0035] The average fiber diameter of hollow fibers is preferably 0.1 mm to 3.0 mm, more preferably 0.3 mm to 2.0 mm, even more preferably 0.5 mm to 1.5 mm, and even more preferably 0.6 mm to 1.0 mm.The average fiber diameter of solid fibers is preferably 0.1 mm to 3.0 mm, more preferably 0.2 mm to 2.0 mm, even more preferably 0.3 mm to 1.5 mm, and even more preferably 0.4 mm to less than 0.6 mm.

[0036] Both solid and hollow fibers are preferably approximately circular, but in some cases, a modified cross section can provide resistance to compression and a comfortable feel. Furthermore, the continuous filaments constituting the three-dimensional network structure of the present invention may be combined with continuous filaments made of other thermoplastic resins to form composite filaments, provided that the object of the present invention is not impaired. Examples of composite forms include sheath-core, side-by-side, and eccentric sheath-core types, when the filaments themselves are composited.

[0037] The continuous filaments preferably have a melting enthalpy of 16 to 30 J / g. A melting enthalpy of 16 J / g or more can improve the compression durability and compression recovery of the three-dimensional network structure. Furthermore, a melting enthalpy of 30 J / g or less can improve the flexibility of the three-dimensional network structure and reduce the generation of noise during compression and recovery. The melting enthalpy is more preferably 17 J / g or more, even more preferably 18 J / g or more, still more preferably 19 J / g or more, even more preferably 20 J / g or more, and particularly preferably 21 J / g or more. Furthermore, the melting enthalpy is more preferably 28 J / g or less.

[0038] The enthalpy (J / g) of the endothermic peak of the continuous wire can be determined from the integral of the endothermic peak (melting peak) from a DSC curve measured using a differential scanning calorimeter with a sample mass of 2.0 mg±0.1 mg under a nitrogen atmosphere at a heating rate of 20°C / min. The integral can be determined by drawing a line connecting the start point and end point of the curve relating to the endothermic peak (melting peak), setting the start point as the point where the curve begins to deviate from the baseline on the low temperature side and the end point as the point where the curve begins to contact the baseline on the high temperature side, and integrating the area enclosed by the line and the curve. An example of a DSC curve is shown in Figure 1. The dashed line in Figure 1 is the line connecting the start point and end point of the endothermic peak (melting peak), and the area enclosed by the dashed line and the curve is the integration region where integration is performed.

[0039] The DSC curve of the continuous filaments constituting the three-dimensional network structure, measured using a differential scanning calorimeter, preferably has an endothermic peak enthalpy of 2.5 J / g or less, which has a minimum value in the range of 30°C to 70°C. In the present invention, the "enthalpy of the endothermic peak having a minimum value in the range of 30°C to 70°C" is sometimes referred to as the low-temperature phase enthalpy. A low-temperature phase enthalpy of 2.5 J / g or less facilitates reducing the compression set at 40°C. As a result, the feeling of settling when used as a cushioning material is easily reduced. Therefore, the low-temperature phase enthalpy is more preferably 1.5 J / g or less. The lower limit of the low-temperature phase enthalpy is not particularly limited, but due to technical difficulties, it is, for example, 0.2 J / g or more.

[0040] <Configuration of Three-Dimensional Network Structure> Before describing the configuration of the three-dimensional network structure of the present invention, we will first describe a typical network structure containing hollow fibers and solid fibers. For example, by forming a laminated network structure by overlapping a network structure made of hollow fibers with a network structure made of solid fibers, it is possible to impart different cushioning performance to both sides. Although such a laminated network structure can impart different cushioning performance to both sides, when pressure is applied from the side of the network structure with a lower compression hardness, only the network structure with a lower compression hardness is compressed and bends independently from the network structure with a higher compression hardness. Only when the network structure with a lower compression hardness can withstand the compressive load alone does the compressive stress propagate to the network structure with a higher compression hardness, causing deformation and bending of the network structure with a higher compression hardness. Therefore, repeated compression accumulates fatigue in the network structure with a lower compression hardness, resulting in a decrease in the thickness of the network structure with a lower compression hardness and a decrease in compression hardness. In other words, although the above-mentioned laminated network structure can be given different cushioning performance on both sides, a network structure with low compression hardness will have large residual strain when repeatedly compressed, resulting in a laminated network structure with significantly different compression durability on both sides.

[0041] As a laminated network structure other than the above-mentioned laminated network structures, it is conceivable to obtain an integrated laminated network structure by bonding a network structure made of hollow fibers and a network structure made of solid fibers with an adhesive. Although it is possible to impart different cushioning performance to both sides of such a laminated network structure, when the number of times of compression is small, both network structures deform and bend as a unit under pressure and compression load. However, as compression is repeated, stress concentrates on the adhesive surface, causing a decrease in adhesive strength and peeling, and therefore, even in a laminated network structure in which structures are bonded together, the difference in compression durability between the two sides is large.

[0042] Furthermore, a laminated network structure having a three-dimensional network structure can be obtained by discharging solid fibers onto a network structure made of hollow fibers, laminating the network structure made of solid fibers, and fusing and integrating them. Although such a laminated network structure can impart different cushioning performance to both sides, the solid fibers are fused after the hollow fibers have solidified, so the fusion strength at the interface between the hollow fiber layer and the solid fiber layer is low, and repeated compressive loads cause stress concentration at the interface, leading to interfacial peeling and resulting in poor durability.

[0043] The inventors have discovered that by providing a mixed region (hereinafter simply referred to as a "mixed region") in which solid fibers and hollow fibers are mixed between a region predominantly composed of hollow fibers on one surface and a region predominantly composed of solid fibers on the other surface, the difference in residual strain after repeated compression on both surfaces can be reduced (the difference in compression durability on both surfaces can be reduced). All three of the above-mentioned layered network structures have no or almost no mixed region. However, when a three-dimensional network structure is formed in which a region predominantly composed of hollow fibers, a mixed region, and a region predominantly composed of solid fibers are layered in this order from one surface to the other, the presence of a mixed region in a region located near the middle of both surfaces results in the formation of an integrated three-dimensional network structure in which the region predominantly composed of hollow fibers, the mixed region, and the region predominantly composed of solid fibers are not separated. Therefore, even when compression is applied from the side with lower compression hardness, stress propagates through the mixed region to the side with higher compression hardness from the point where the number of compressions is small, and the stress is efficiently distributed in the thickness direction, causing the entire network structure to deform and bend under the compression load. This makes it possible to reduce the difference in compression durability when compression is applied from the side with lower compression hardness and the side with higher compression hardness. In a three-dimensional network structure in which a region primarily made of hollow fibers, a mixed region, and a region primarily made of solid fibers are layered in this order, it is preferable that one surface (the surface of the high-density side) have a region primarily made of hollow fibers and the other surface (the surface of the low-density side) have a region primarily made of solid fibers, from the viewpoint of making one surface have a higher apparent density than the other surface.

[0044] <Physical Properties of Three-Dimensional Network Structure> The three-dimensional network structure of the present invention is characterized in that the residual strain after repeated compression when pressure is applied from one surface (the surface of the high-density side) and the residual strain after repeated compression when pressure is applied from the other surface (the surface of the low-density side) are both small, and the durability of compression is excellent on both sides. Specifically, the residual strain R after repeated compression from one surface (the surface of the high-density side) with a load of 750 N is １ and the residual strain R after repeated compression from the other surface (the surface of the low density surface) with a load of 750 N 13,000 times. ２ are all 20% or less. １ and R ２ are both preferably 15% or less, more preferably 13% or less, even more preferably 10.5% or less, and particularly preferably 9.5% or less.

[0045] The three-dimensional network structure of the present invention is also characterized in that the difference in compression durability between both surfaces is small, that is, the difference in residual strain after repeated compression between when pressure is applied from one surface (the surface of the high density surface) and when pressure is applied from the other surface (the surface of the low density surface) is small. １ The value of and R ２ The absolute value of the difference from the value of R is 10% or less. １ The value of and R ２ If the absolute value of the difference between the values ​​of R and R exceeds 10%, the difference in residual strain after repeated compression between the two surfaces will be too large, and when the three-dimensional network structure of the present invention is used reversibly, the surface on the side on which the residual strain after repeated compression is large will be more sagging than the surface on the side on which the residual strain after repeated compression is small. １ The value of and R ２ The absolute value of the difference from the value of R is preferably 9% or less, more preferably 8% or less, even more preferably 6% or less, and particularly preferably 1.5% or less. １ The value of and R ２ The lower limit of the absolute value of the difference from the value of is not particularly limited, and is, for example, 0% or more, and preferably 0.1% or more.

[0046] The three-dimensional network structure has a 40°C compression set of 15% or less, preferably 14.5% or less. By making the 40°C compression set 15% or less, compression recovery can be improved. There is no lower limit for the 40°C compression set, and it is, for example, 1% or more, preferably 5% or more. The 40°C compression set can be measured by the method described in the examples below.

[0047] When the three-dimensional network structure is compressed from the high-density side, the hardness at compression when compressed 25% in the thickness direction (when compressed to 75% thickness) (hereinafter referred to as "hardness at 25% compression") is preferably 5.0 N / φ50 mm or more and 100 N / φ50 mm or less, more preferably 8.0 N / φ50 mm or more and 80.0 N / φ50 mm or less, even more preferably 10.0 N / φ50 mm or more and 50.0 N / φ50 mm or less, particularly preferably 12.0 N / φ50 mm or more and 30.0 N / φ50 mm or less, and most preferably 15.0 N / φ50 mm or more and 25.0 N / φ50 mm or less. By having a hardness at 25% compression of 5.0 N / φ50 mm or more, the feeling of hitting the bottom when the three-dimensional network structure is used as a cushioning material or the like can be reduced. On the other hand, if the hardness at 25% compression is 100 N / φ50 mm or less, cushioning properties can be improved. The hardness at 25% compression can be measured by the method described in the examples below.

[0048] When the three-dimensional network structure is pressed from the low-density side, the hardness at 25% compression is preferably 5.0 N / φ50 mm or more and 100 N / φ50 mm or less, more preferably 5.0 N / φ50 mm or more and 80.0 N / φ50 mm or less, even more preferably 8.0 N / φ50 mm or more and 50.0 N / φ50 mm or less, particularly preferably 10.0 N / φ50 mm or more and 25.0 N / φ50 mm or less, and most preferably 12.0 N / φ50 mm or more and 20.0 N / φ50 mm or less. By having a hardness at 25% compression of 5.0 N / φ50 mm or more, the feeling of bottoming out when the three-dimensional network structure is used as a cushioning material, etc. can be reduced. On the other hand, by having a hardness at 25% compression of 100 N / φ50 mm or less, cushioning properties can be improved.

[0049] The larger of the hardness at 25% compression when pressure is applied from the high density side and the hardness at 25% compression when pressure is applied from the low density side is defined as H １ , the smaller value is H ２ Then, H １ / H ２ is preferably 1.03 or more, more preferably 1.05 or more, even more preferably 1.07 or more, particularly preferably 1.10 or more, and most preferably 1.13 or more. If the ratio of hardness at 25% compression is less than 1.03, there is a risk that the difference in cushioning performance between the two surfaces will be small. １ / H ２ The upper limit of is not particularly limited, and is, for example, 1.50 or less, and preferably 1.40 or less.

[0050] When the three-dimensional network structure is compressed from the high-density side, the hardness at 40% compression in the thickness direction (when compressed to 60% thickness) (hereinafter referred to as "hardness at 40% compression") is preferably 10 N / φ50 mm or more and 500 N / φ50 mm or less, more preferably 15 N / φ50 mm or more and 300 N / φ50 mm or less, even more preferably 17 N / φ50 mm or more and 200 N / φ50 mm or less, particularly preferably 20 N / φ50 mm or more and 100 N / φ50 mm or less, and most preferably 22 N / φ50 mm or more and 50 N / φ50 mm or less. By having a hardness at 40% compression of 10 N / φ50 mm or more, the feeling of bottoming out when the three-dimensional network structure is used as a cushioning material, etc. can be reduced. On the other hand, by having a hardness at 40% compression of 500 N / φ50 mm or less, cushioning properties can be improved. The hardness at 40% compression can be measured by the method described in the examples below.

[0051] When the three-dimensional network structure is compressed from the low-density side, the hardness at 40% compression is preferably 10 N / φ50 mm or more and 500 N / φ50 mm or less, more preferably 12 N / φ50 mm or more and 300 N / φ50 mm or less, even more preferably 15 N / φ50 mm or more and 200 N / φ50 mm or less, particularly preferably 17 N / φ50 mm or more and 100 N / φ50 mm or less, and most preferably 20 N / φ50 mm or more and 40 N / φ50 mm or less. By having a hardness at 40% compression of 10 N / φ50 mm or more, the feeling of bottoming out when the three-dimensional network structure is used as a cushioning material, etc. can be reduced. On the other hand, by having a hardness at 40% compression of 500 N / φ50 mm or less, cushioning properties can be improved.

[0052] The larger of the hardness at 40% compression when pressure is applied from the high density side and the hardness at 40% compression when pressure is applied from the low density side is defined as H ３ , the smaller value is H ４ Then, H ３ / H ４ is preferably 1.05 or more, more preferably 1.07 or more, and even more preferably 1.09 or more. If the ratio of hardness at 40% compression is less than 1.05, there is a risk that the difference in cushioning performance between the two surfaces will be small. ３ / H ４ The upper limit of is not particularly limited, and is, for example, 1.50 or less, and preferably 1.40 or less.

[0053] The compression deflection coefficient when pressure is applied from the high-density side and the compression deflection coefficient when pressure is applied from the low-density side are both preferably 2.5 or more and 10.0 or less. If the compression deflection coefficient is less than 2.5, the difference in cushioning performance with respect to changes in compression rate is small, which may result in poor sleeping and sitting comfort. Conversely, if it exceeds 10.0, the difference in cushioning performance with changes in compression rate becomes too large, which may result in a feeling of bottoming out or discomfort. The compression deflection coefficient when pressure is applied from the high-density side is more preferably 2.6 or more and 8.0 or less, even more preferably 2.7 or more and 6.0 or less, and particularly preferably 2.7 or more and 5.0 or less. The compression deflection coefficient when pressure is applied from the low-density side is more preferably 2.8 or more and 8.0 or less, even more preferably 3.0 or more and 7.0 or less, and particularly preferably 3.5 or more and 6.0 or less.

[0054] The absolute value of the difference between the compression deflection coefficient when pressure is applied from the high-density side and the compression deflection coefficient when pressure is applied from the low-density side is preferably 5.0 or less, more preferably 3.0 or less, even more preferably 2.0 or less, particularly preferably 1.5 or less, and most preferably 1.2 or less. If the absolute value of the difference in compression deflection coefficient exceeds 5.0, a feeling of bottoming out or discomfort may occur when using the side with the higher compression deflection coefficient. The lower limit of the absolute value of the difference in compression deflection coefficient is not particularly limited, and is, for example, 0 or more, preferably 0.1 or more. Furthermore, it is preferable that the compression deflection coefficient when pressure is applied from the low-density side is greater than the compression deflection coefficient when pressure is applied from the high-density side.

[0055] The apparent density of the three-dimensional network structure is preferably 0.005 g / cm ３ ~0.20 g / cm ３ and more preferably 0.010 g / cm ３ ~0.17 g / cm ３ and more preferably 0.020 g / cm ３ ~0.15g / cm ３ and particularly preferably 0.030 g / cm ３ ~0.12 g / cm ３ and most preferably 0.045 g / cm ３ ~0.10 g / cm３ The apparent density is 0.005 g / cm ３ When the apparent density is 0.30 g / cm or more, the hardness of the three-dimensional network structure is improved. As a result, when the three-dimensional network structure is used as a cushioning material or the like, the feeling of hitting the bottom can be reduced. ３ If the density is not more than 100%, the flexibility is improved and the structure can be suitably used as a cushioning material, etc. The apparent density of the three-dimensional network structure can be measured by the method described in the examples below.

[0056] The three-dimensional network structure of the present invention has different cushioning properties on both sides, and therefore one surface has a higher apparent density than the other surface. The absolute value of the difference between the apparent density of one surface (the surface of the high-density surface) and the apparent density of the other surface (the surface of the low-density surface) is 0.015 g / cm ３ It is preferable that the density is 0.020 to 0.100 g / cm or more. ３ More preferably, it is 0.030 to 0.080 g / cm ３ The apparent density of one surface and the other surface of the three-dimensional network structure can be measured by the method described in the examples below.

[0057] The thickness of the three-dimensional network structure is preferably 10 mm to 120 mm. A thickness of 10 mm or more makes it easier to use the three-dimensional network structure as a cushioning material, etc. Therefore, the lower limit of the thickness is more preferably 15 mm or more, even more preferably 20 mm or more, and particularly preferably 22 mm or more. On the other hand, taking into account the size of the manufacturing apparatus, the upper limit of the thickness is more preferably 100 mm or less, even more preferably 80 mm or less, and particularly preferably 50 mm or less. The thickness of the three-dimensional network structure can be measured by the method described in the examples below.

[0058] It is preferable that the three-dimensional network structure does not contain a bonding promoter. This makes it easier to prevent excessive hardening due to excessive bonding within the three-dimensional network structure caused by the bonding promoter. It also makes it easier to prevent a decrease in the density of the three-dimensional network structure due to an excessive increase in the bonding area per contact point. Examples of the bonding promoter include polycaprolactone, polybutylene succinate, polybutylene sebacate terephthalate, and polybutylene azelate terephthalate.

[0059] The three-dimensional network structure may be colored. For coloring, a colorant such as a pigment or a dye can be used. The colorant may be incorporated into the resin before melt spinning, or after the three-dimensional network structure is formed, the colorant may be coated on the continuous filaments by immersion or application.

[0060] The shape of the three-dimensional network structure is not particularly limited. Examples include a plate, a polygon such as a triangular prism or a quadrangular prism, a cylinder, a sphere, a combination of these, etc. When molding the three-dimensional network structure, a regulating plate may be used during melt extrusion of the resin, or the structure may be molded by cutting, heat pressing, etc.

[0061] The present invention also encompasses a cushioning material that includes the above-described predetermined three-dimensional netted structure and that can be used reversibly. While the term "reversible use" means that both the high-density side and the low-density side can be used as a cushion, the cushioning material of the present invention also includes a case where only one side is used as a cushioning material.

[0062] Examples of cushions include cushions used in bedding such as office chairs, furniture, sofas, and beds; vehicle seats such as those for trains, automobiles, motorcycles, child seats, and strollers; and cushions used in impact absorbing mats such as floor mats and collision and pinch prevention members.

[0063] <Method of Manufacturing a Three-Dimensional Network Structure> The following describes a method of manufacturing a three-dimensional network structure in which a region predominantly composed of hollow fibers, a mixed region, and a region predominantly composed of solid fibers are layered from one surface side to the other surface side in this order. The method of manufacturing the three-dimensional network structure preferably includes an extrusion step of discharging a molten thermoplastic resin composition from a nozzle, a molding step of obtaining a molded body by molding the three-dimensional network structure using continuous filaments composed of the thermoplastic resin composition extruded from the nozzle, and a heat treatment step of heat-treating the molded body. The three-dimensional network structure prior to completion of the heat treatment step is referred to as a molded body to avoid confusion with the three-dimensional network structure that is the finished product (the three-dimensional network structure after completion of the heat treatment step). The extrusion and molding steps are not particularly limited as long as they are known manufacturing methods, but specific manufacturing methods include, for example, the following methods.

[0064] First, a thermoplastic resin composition containing polybutylene adipate terephthalate resin is dispensed into the nozzle orifices through a multi-row nozzle having multiple orifices with different orifice diameters, and extruded downward from the nozzle at a spinning temperature of at least (melting point + 20°C) but less than (melting point + 180°C) of the resin. Specific examples of the multi-row nozzle will be described later. Next, the continuous filaments are brought into contact with each other in a molten state and fused to form a three-dimensional network structure, while being sandwiched between a take-up conveyor net and cooled with cooling water in a water tank. The solidified molded body is then drawn out and drained or dried to obtain a molded body with smoothed surfaces on one or both sides. For details of these spinning and cooling processes, see, for example, Japanese Patent Laid-Open No. 7-68061. To smooth only one side, the continuous filaments are extruded onto an inclined take-up net, and the continuous filaments are brought into contact with each other in a molten state and fused to each other. In this case, the three-dimensional network structure is formed, and only the take-up net surface is cooled while relaxing its shape. The obtained molded body is subjected to a heat treatment. The drying treatment of the molded body may be the heat treatment.

[0065] As a means for adjusting flexibility, water may be added to the thermoplastic resin composition before it is discharged from the nozzle. The amount of water added is preferably 2.0% by mass or less based on the thermoplastic resin composition. The method for adding water to the thermoplastic resin composition is not particularly limited. For example, before the resin is discharged from the nozzle, the thermoplastic resin composition is vacuum dried at 100°C for 12 hours or more to be bone dry. Next, a predetermined amount of pure water may be added to 100% by mass of the bone dried thermoplastic resin composition.

[0066] It is preferable to use cooling water to cool polybutylene adipate terephthalate resin after melt molding. Polybutylene adipate terephthalate resin may undergo molding shrinkage before cooling and solidifying. Therefore, it is sufficient to form a three-dimensional network structure with a width and thickness that takes molding shrinkage into consideration. For example, molding shrinkage can be reduced by lowering the melt solidification temperature. Therefore, the temperature of the cooling water in the water tank is preferably 20°C or less, more preferably 15°C or less. Furthermore, the cooling time using cooling water is preferably 30 seconds or more. The cooling and solidifying is preferably carried out in a water tank.

[0067] The heat treatment may be carried out using a commercially available hot air drying oven or in a warm water bath. The heat treatment temperature is preferably 50°C or higher, which can increase the enthalpy of fusion. The heat treatment temperature is more preferably 60°C or higher, and even more preferably 70°C or higher. The heat treatment may be carried out in multiple steps at different temperatures.

[0068] When carrying out the heat treatment, the melting point of the thermoplastic resin composition constituting the continuous filaments is preferably 125°C or higher and 180°C or lower. The lower limit of the melting point is more preferably 130°C or higher, even more preferably 135°C or higher, still more preferably 140°C or higher, and particularly preferably 145°C or higher. On the other hand, the upper limit of the melting point is more preferably 170°C or lower, even more preferably 160°C or lower. A melting point of 125°C or higher allows the heat treatment to be carried out within a suitable temperature range. On the other hand, a melting point of 180°C or lower improves flexibility, making the material suitable for use as a cushioning material, etc.

[0069] The heat treatment time in each heat treatment step is preferably 1 minute or more. This allows for a large melting enthalpy. The heat treatment time is more preferably 5 minutes or more, even more preferably 10 minutes or more, and particularly preferably 15 minutes or more. On the other hand, the upper limit of the heat treatment time in each heat treatment step is preferably 60 minutes or less, more preferably 50 minutes or less. This allows for a reduction in yellowing, odor, molecular weight reduction, and the like of the polybutylene adipate terephthalate resin that accompanies polymer decomposition and degradation during heat treatment. Furthermore, productivity can also be improved.

[0070] The molded body cooled and solidified in the water bath is preferably held at a temperature of 20°C to 50°C for 1 minute or more (preferably 10 minutes or more, more preferably 30 minutes or more) before heat treatment. During heat treatment, the thickness of the molded body may change due to its own weight. However, by holding the molded body at a temperature of 20°C to 50°C after cooling and solidifying, it is possible to reduce the change in thickness of the molded body due to heat treatment. For example, after cooling and solidifying in the water bath, a continuous dryer may be used to hold the molded body at a low temperature in the first half of a hot air oven, and then the temperature of the hot air oven may be increased to perform heat treatment.

[0071] The three-dimensional network structure may contain the various additives described above to impart predetermined functions, and the additives may be added at any stage from the thermoplastic resin production process to the three-dimensional network structure molding process, or a polybutylene adipate terephthalate resin containing additives in advance may be used. It is preferable to adjust the content of additives by kneading various additives into the resin during melt extrusion depending on the color tone and quality of the resin after melting.

[0072] The method for producing the three-dimensional network structure of the present invention is not limited to the above-mentioned production method. For example, the three-dimensional network structure of the present invention can be produced by stacking a network structure made of hollow fibers, a network structure made of a mixture of solid fibers and hollow fibers, and a network structure made of solid fibers in this order and integrating them by bonding.

[0073] <Nozzle> A multi-row nozzle having a plurality of orifices with different orifice diameters will be specifically described below.

[0074] To obtain the three-dimensional network structure of the present invention, it is preferable to optimize the nozzle shape, nozzle cross section, nozzle hole arrangement, etc. Regarding the nozzle shape, the orifice diameter for forming thin fibers is preferably 1.5 mm or less, and the orifice diameter for forming thick fibers is preferably 2.0 mm or more. Furthermore, the nozzle orifice shape for forming thick fibers preferably has a hollow-forming property, and examples thereof include a C-shaped nozzle and a triple-bridge nozzle. From the viewpoint of pressure resistance, a triple-bridge nozzle is preferable. The hole pitch for both the orifice for forming thin fibers and the orifice for forming thick fibers is preferably 4 mm or more and 12 mm or less, and more preferably 5 mm or more and 11 mm or less. Examples of nozzle hole arrangements include a lattice arrangement, a circumferential arrangement, and a staggered arrangement. From the viewpoint of the quality of the network structure, a lattice arrangement or a staggered arrangement is preferable. Here, the hole pitch refers to the distance between the centers of the nozzle holes. There is a hole pitch in the width direction of the obtained three-dimensional network structure (hereinafter referred to as the "width direction hole pitch") and a hole pitch in the thickness direction of the obtained three-dimensional network structure (hereinafter referred to as the "thickness direction hole pitch"). It is preferable that both the widthwise hole pitch and the thicknesswise hole pitch are within the above ranges.

[0075] Nozzles for obtaining a three-dimensional network structure having a mixed region include nozzles consisting of the following three groups (group a, ab mixed group, and group b). The nozzles are preferably arranged in the order of group b, ab mixed group, and group a from top to bottom in the thickness direction (height direction) of the nozzle arrangement region. Group a: an orifice hole group consisting of orifice holes for solid fibers arranged in multiple rows in the thickness direction; ab mixed group: an orifice hole group consisting of a mixture of orifice holes for solid fibers and orifice holes for hollow fibers arranged in multiple rows in the thickness direction; Group b: an orifice hole group consisting of orifice holes for hollow fibers arranged in multiple rows in the thickness direction.

[0076] Another nozzle for obtaining a three-dimensional network structure having a mixed region includes a nozzle consisting of the following two groups (group α and group β): group α: a group of orifice holes configured by arranging multiple rows of orifice holes for solid fibers in the thickness direction; group β: a group of orifice holes configured by arranging multiple rows of orifice holes for hollow fibers in the thickness direction.

[0077] From the viewpoint of simplifying the nozzle structure, a nozzle consisting of the above-mentioned α group and β group is more preferred, and it is preferable that the upper half of the nozzle arrangement area in the thickness direction (height direction) is the β group and the lower half is the α group. Although the nozzle has two orifice hole groups, the fibers spun near the boundary between the α group and the β group form a mixed region in which solid fibers and hollow fibers are mixed, so that a network structure consisting of three regions in the thickness direction of the present invention can be obtained.

[0078] In order to obtain a three-dimensional network structure with a small difference in compression durability between the two surfaces, it is preferable to reduce the difference between the widthwise hole pitch of the solid fiber orifices and the widthwise hole pitch of the hollow fiber orifices. Specifically, it is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0 mm, i.e., the widthwise hole pitches are the same. The reason why a small difference in the widthwise hole pitch between the solid fiber orifices and the hollow fiber orifices reduces the difference in compression durability between the two surfaces is not entirely clear, but is presumed to be as follows. In the following, the difference between the widthwise hole pitch between the solid fiber orifices and the widthwise hole pitch between the hollow fiber orifices will be simply referred to as the "difference in widthwise hole pitch."

[0079] In a mixed region where solid fibers and hollow fibers are mixed, a small difference in widthwise hole pitch means that the number of solid fibers and hollow fibers in the mixed region are similar. When the number of solid fibers and hollow fibers is similar, each solid fiber has multiple contact points with the hollow fibers, and each hollow fiber has multiple contact points with the solid fibers. Therefore, stress is easily transmitted when pressure is applied from either side, which is thought to reduce the difference in compression durability between the two sides.

[0080] In contrast, when a network structure is formed using a nozzle with a large difference in widthwise hole pitch, in a mixed region where solid fibers and hollow fibers are mixed, for example, when the number of solid fibers is greater than the number of hollow fibers, some of the solid fibers in the mixed region will have almost no contact points with the hollow fibers. Therefore, when pressure is applied from the side where the solid fibers are predominant, it is thought that the solid fibers that have almost no contact points with the hollow fibers cannot sufficiently transmit stress to the hollow fibers. Furthermore, when pressure is applied from the side where the hollow fibers are predominant, it is thought that the hollow fibers cannot sufficiently transmit stress to the solid fibers that have almost no contact points with the hollow fibers.

[0081] That is, when a three-dimensional network structure is formed using a nozzle with a large difference in the width-direction hole pitch, in the mixed region where solid fibers and hollow fibers are mixed, the direction of stress propagation is dispersed in the thickness direction and in the direction perpendicular to the thickness direction, resulting in a decrease in stress propagation efficiency. As a result, it is thought that the difference in compression durability between when pressure is applied from the solid fiber side and when pressure is applied from the hollow fiber side becomes large.

[0082] This application claims the benefit of priority based on Japanese Patent Application No. 2023-168862, filed on September 28, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-168862, filed on September 28, 2023, are incorporated herein by reference.

[0083] 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.

[0084] The characteristic values ​​of the three-dimensional network structures of Examples 1 to 4 and Comparative Examples 1 and 2 were measured according to the following methods. The sample sizes were standardized as described below, but when there were insufficient samples, measurements were performed using samples of the largest possible size.

[0085] (1) Average fiber diameter The three-dimensional network structure was cut into pieces measuring 10 cm × 10 cm in the longitudinal and transverse directions, and continuous filaments with hollow cross sections were collected in lengths of approximately 5 mm from 10 locations on each cut. Next, an optical microscope was used to measure the diameter of the collected continuous filaments, focusing on the location where the fiber diameter was to be measured, and the average value (n = 10) of the fiber diameters of the 10 hollow cross sections was calculated. The average value of the fiber diameters of the solid cross sections was also calculated in the same manner as the average value of the fiber diameters of the hollow cross sections.

[0086] (2) Hollowness Ten continuous filaments were randomly taken out from the three-dimensional network structure. The continuous filaments were then cut into cross sections, placed on a slide glass in a state where they were standing in the fiber axial direction, and the fiber cross sections in the cross section direction were observed under an optical microscope. In this case, only continuous filaments with hollow fiber cross sections were selected, and the area (a) within the outer periphery of the fiber and the area (b) of the hollow portion were calculated, respectively. The hollowness was calculated based on the following formula, and the average hollowness (n = 10) of the selected continuous filaments with hollow cross sections was determined. Hollowness (%) = (b) / (a) × 100

[0087] (3) Thickness and apparent density The three-dimensional network structure was cut into a size of 10 cm x 10 cm in the length and width directions, and the obtained sample was left unloaded for 24 hours. Thereafter, the height of one point at the center was measured using a test piece thickness measuring instrument (FD-80N type, manufactured by Kobunshi Keiki Co., Ltd.), and this height of the sample was taken as the thickness of the three-dimensional network structure. Furthermore, the sample was placed on an electronic balance and the weight of the sample was measured. The height of the sample and the area (100 cm) were used to measure the thickness of the three-dimensional network structure. ２ The apparent density was calculated by dividing the weight of the sample by the volume. The above operation was repeated three times to calculate the average values ​​(n=3) of the thickness and apparent density of the three-dimensional network structure.

[0088] (4) Apparent Density of One and the Other Surfaces The three-dimensional network structure was cut lengthwise and widthwise into a size of 5 cm x 5 cm, and the thickness (t1) and weight (w1) of the obtained sample were measured in the same manner as in (3). Thereafter, the sample was cut so that the cut surface was perpendicular to the thickness direction and so that it was divided into two equal parts in the thickness direction. The thickness (t2) and weight (w2) of the sample mainly composed of hollow fibers were measured, and the weight (w2 (g)) was calculated by multiplying the volume (5 x 5 x t2 (cm ３ )) to obtain the apparent density (g / cm) of the sample mainly composed of hollow fibers. ３The weight (w2 (g)) was subtracted from the weight (w1 (g)) to obtain the volume (5 × 5 × (t1 - t2) (cm ３ )) to obtain the apparent density (g / cm) of the solid fiber-predominant sample. ３ The apparent density of the other surface was calculated. The apparent density was the average value of n=3.

[0089] (5) Molar ratio of the terephthalic acid unit to the adipic acid unit of the polybutylene adipate terephthalate resin The molar ratio of the terephthalic acid unit to the adipic acid unit of the polybutylene adipate terephthalate resin is １ Measurement was performed by H-NMR. The measurement device used was a BRUKER AVANCE-NEO600 NMR device, and the measurement was performed as follows. 10 to 15 mg of sample was dissolved in deuterated chloroform / trifluoroacetic acid = 85 / 15 (volume ratio), and the solution was then filled into an NMR tube and measurement was performed. Deuterated chloroform was used as the lock solvent, the waiting time was 1 second, the data acquisition time was 4 seconds, and the number of integrations was 64. When the chloroform peak is at 7.28 ppm, the adipic acid peak is detected at 2.45 ppm, and the terephthalic acid peak is detected at 8.15 ppm. When the peak integral value of adipic acid is A and the peak integral value of terephthalic acid is B, the molar ratio of the terephthalic acid units to the adipic acid units of the polybutylene adipate terephthalate resin can be expressed by the following formula: Molar ratio = ((B / 4) ÷ (A / 4))

[0090] (6) Melting point (Tm) A sample was taken from the three-dimensional network structure and weighed to a mass of 2.0 mg ± 0.1 mg. Next, a differential scanning calorimeter (TA Instruments, Discovery DSC25) was used to measure the DSC curve under a nitrogen atmosphere at a heating rate of 20 ° C. / min. The endothermic peak (melting peak) temperature was determined from the DSC curve. The above operation was performed three times, and the average melting point (n = 3) was calculated.

[0091] (7) Melting Enthalpy A sample was taken from the three-dimensional network structure and weighed to a mass of 2.0 mg ± 0.1 mg. Next, using a differential scanning calorimeter (TA Instruments, Discovery DSC25), a DSC curve was measured under a nitrogen atmosphere at a heating rate of 20 ° C. / min. The melting enthalpy (J / g) was calculated from the integrated value of the endothermic peak (melting peak). The integrated value of the endothermic peak (melting peak) was calculated by taking the point where the curve relating to the endothermic peak (melting peak) begins to deviate from the low-temperature baseline as the starting point and the point where it begins to contact the high-temperature baseline as the end point. A straight line was drawn connecting the starting point and the end point, and integrating the area enclosed by the straight line and the curve to calculate the melting enthalpy. This operation was performed three times to calculate the average melting enthalpy (n = 3). The starting point was taken as the melting onset temperature (° C.).

[0092] (8) Low-Temperature Phase Enthalpy In the DSC curve (7) above, the enthalpy of the endothermic peak having the minimum value in the range of 30°C to 70°C was determined and defined as the low-temperature phase enthalpy. The integrated value of the endothermic peak in the low-temperature phase region was determined by drawing a line connecting the start point and the end point, taking the point where the curve relating to the endothermic peak begins to deviate from the baseline on the low-temperature side as the starting point and the point where it begins to contact the baseline on the high-temperature side as the end point, and integrating the area enclosed by the line and the curve over the range of 30°C to 70°C to determine the low-temperature phase enthalpy. This operation was performed three times, and the average value (n = 3) of the low-temperature phase enthalpy was determined. The onset point was defined as the low-temperature phase onset temperature (°C). An example of experimental data is shown in Figure 1.

[0093] (9) Melt Flow Rate (MFR) After vacuum drying the polybutylene adipate terephthalate resin at 80°C for 2 hours or more, the melt flow rate (MFR) was quickly measured so as to minimize the incorporation of moisture from the air. The melt flow was measured using a Melt Indexer F-F01 manufactured by Toyo Seiki Seisakusho, in accordance with ISO 1133. The measurement temperature was 190°C and the load was 2.16 kg. The above operation was performed three times to determine the average melt flow rate (n = 3).

[0094] (10) 40°C Compression Set The three-dimensional network structure was cut into a size of 10 cm x 10 cm. Next, the thickness (c) of the obtained sample before treatment was measured using the method described in (3) above. The sample whose thickness had been measured was clamped between a jig capable of maintaining it in a 50% compressed state, placed in a dryer controlled at 40°C, and left for 22 hours. Thereafter, the sample was removed, cooled, and the compression set was removed. After leaving it for 30 minutes, the thickness (d) was measured using the method described in (3) above. These thicknesses were entered into the following formula to determine the 40°C compression set. The above operation was performed three times to determine the average value (n = 3) of the 40°C compression set. 40°C Compression Set (%) = ((c) - (d)) / (c) x 100

[0095] (11) Residual Strain After Repeated Compression The three-dimensional network structure was cut into a size of 10 cm x 10 cm. The thickness (e) of the obtained sample before compression was measured using the method described in (3) above. Immediately after that, the sample whose thickness had been measured was repeatedly compressed from one surface (high-density surface) using a constant-load repeated compression tester (STM-536, manufactured by Kobunshi Keiki Co., Ltd.) under the following conditions: A circular pressure tool with a diameter of 250 ± 1 mm, a thickness of 3 mm, a bottom edge with a radius of curvature of 25 ± 1 mm, and a flat bottom surface was used; the load was 750 N ± 20 N, the compression frequency was 70 ± 5 times per minute, and the number of repeated compressions was 13,000. After the repeated compressions, the sample was left unloaded for 10 ± 0.5 minutes, and then the thickness (f) after repeated compression was measured using the method described in (3) above. These thicknesses were input into the following formula to determine the residual strain after repeated compressions. The above operation was carried out three times, and the average value (n=3) of the residual strain after repeated compression from one surface side was determined. Residual strain after repeated compression (%) = ((e) - (f)) / (e) x 100. Separately, a sample was prepared, and the residual strain after repeated compression from the other surface side was determined in the same manner as above, except that repeated compression was carried out from the other surface side (low density surface) of the sample. Finally, the residual strain R after repeated compression from one surface side was determined. １ The residual strain R after repeated compression from the other surface side is ２ Let R １ The value of and R ２ The absolute value of the difference between the values ​​was calculated.

[0096] (12) Hardness at 25% Compression The three-dimensional network structure was cut into a size of 10 cm x 10 cm, and the resulting sample was left unloaded in an environment of 23 ° C ± 2 ° C for 24 hours. Then, in an environment of 23 ° C ± 2 ° C, it was measured in accordance with ISO 2439 (2008) E method using an autograph AG-X plus manufactured by Shimadzu Corporation. Specifically, a pressure plate with a diameter (φ) of 50 mm was placed at the center position on one surface (high-density surface) of the sample, and the thickness when the load reached 0.5 N was measured, which was taken as the initial thickness. The position of the pressure plate at this time was set as the zero point, and pre-compression was performed once to 75% of the initial thickness at a speed of 100 mm / min. The pressure plate was then returned to the zero point at the same speed, and the sample was left in that state for 4 minutes. Thereafter, the specimen was immediately compressed to 75% of its initial thickness at a speed of 100 mm / min, and the load at this time was measured. This load was defined as the hardness at 25% compression (N / φ50 mm) when pressed from one surface side. The above operation was repeated three times to determine the average value (n=3) of the hardness at 25% compression when pressed from one surface side. The hardness at 25% compression when pressed from the other surface side was also determined in the same manner as above, except that a pressure plate with a diameter (φ) of 50 mm was placed at the center position on the other surface (low-density surface) side of the specimen. Separate specimens were prepared for the measurements of the hardness at compression when pressed from one surface side and the other surface side, and the same applies to the following (13) and subsequent sections. Finally, the larger of the hardness at 25% compression when pressed from one surface side and the hardness at 25% compression when pressed from the other surface side was determined as H １ , the smaller value is H ２ Toshi, H １ / H ２ The value was calculated.

[0097] (13) Hardness at 40% Compression After leaving it for 4 minutes, it was immediately compressed to 60% of the initial thickness at a speed of 100 mm / min, and the load at that time was measured. The hardness at 40% compression when pressed from one surface side was determined by the method described in (12) above, except that the load was used as the hardness at 40% compression when pressed from one surface side (N / φ50 mm). In addition, the hardness at 40% compression when pressed from the other surface side was determined in the same manner as the hardness at 40% compression when pressed from one surface side, except that a pressure plate with a diameter (φ) of 50 mm was placed at the center position on the other surface (low-density surface) side of the sample. Finally, the larger value of the hardness at 40% compression when pressed from one surface side and the hardness at 40% compression when pressed from the other surface side was determined as H ３ , the smaller value is H ４ Toshi, H ３ / H ４ The value was calculated.

[0098] (14) Compression Deflection Coefficient After leaving the specimen for 4 minutes, it was immediately compressed to 35% of its initial thickness at a speed of 100 mm / min. The load at this time was measured, and the hardness at 65% compression when compressed from one surface was determined by the method described in (12) above, except that the load was used as the hardness at 65% compression when compressed from one surface (N / φ50 mm). The hardness at 65% compression when compressed from the other surface was determined in the same manner as for the hardness at 65% compression when compressed from one surface, except that a pressure plate with a diameter (φ) of 50 mm was placed at the center of the other surface (low-density surface) of the specimen. The hardness at 65% compression when compressed from one surface was divided by the hardness at 25% compression when compressed from one surface, and the value was used as the compression deflection coefficient when compressed from one surface. The above procedure was repeated three times to determine the average compression deflection coefficient when compressed from one surface (n = 3). The compression deflection coefficient when pressure was applied from the other surface side was also determined in the same manner as the compression deflection coefficient when pressure was applied from one surface side. Finally, the absolute value of the difference between the compression deflection coefficient when pressure was applied from one surface side and the compression deflection coefficient when pressure was applied from the other surface side was determined.

[0099] Polybutylene adipate terephthalate resin was synthesized by the following method. <Resin A> 1.5 mol of 1,4-butanediol, 0.4 mol of adipic acid, and 0.6 mol of dimethyl terephthalate were mixed in a reaction vessel equipped with a stirrer, thermometer, and distillation condenser. Next, 300 ppm of tetrabutyl titanate (manufactured by Aldrich) was added as a titanium catalyst to the mixture. Subsequently, transesterification and esterification reactions were carried out at 220°C under atmospheric pressure for 2 hours to prepare a prepolymer. The prepolymer was heated to 240°C and then subjected to a polycondensation reaction at 0.1 mmHg for 2 hours. The resulting Resin A was cooled and then cut with a pellet cutter to produce pellets.

[0100] <Resin B> Resin B was produced in the same manner as in the production of Resin A, except that the amounts of adipic acid and dimethyl terephthalate were changed to 0.53 mol and 0.47 mol, respectively. The obtained Resin B was cooled and then cut with a pellet cutter to produce pellets.

[0101] [Example 1] Resin A was used as a raw material, and the molten resin was extruded downward from the nozzle at a spinning temperature of 240 ° C., a single-hole discharge rate of 1.2 g / min for hollow holes, and a single-hole discharge rate of 0.84 g / min for solid holes. In addition, on the effective nozzle surface having a width length of 96 mm and a thickness length of 31 mm, an outer diameter of 3.0 mm, an inner diameter of 2.6 mm, and a triple-bridge hollow-forming cross-section orifice with a width-direction hole pitch of 6 mm and a thickness-direction hole pitch of 5.2 mm were arranged in a staggered arrangement in the upper half of the thickness direction (height direction), and an outer diameter of 1.0 mm and a solid cross-section orifice with a width-direction hole pitch of 6 mm and a thickness-direction hole pitch of 5.2 mm were arranged in a staggered arrangement in the lower half of the thickness direction.

[0102] A water tank was placed so that the cooling water surface was located 30 cm below the nozzle surface of the nozzle for discharging the molten resin, the water temperature was set to 12°C, 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 20 cm wide stainless steel endless net, and the conveyor was placed parallel to the width direction of the nozzle surface. The opening width of the endless net was set to 30 mm. In order to form the side portions, an aluminum plate was placed at an angle to the net direction, and water was flowed at a rate of 1.0 L / min to form the side portions.

[0103] The molten resin was extruded linearly onto the opening of the conveyor net, onto the conveyor net, and onto the aluminum plate on the side surface, and the continuous filaments were dropped to form meandering loops, fusing the contacting 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 speed of 0.86 m / min to solidify. This flattened both sides in the thickness direction and the lateral direction. The structure was then cut to a predetermined size and allowed to stand in a space at 25°C for 1 hour. It was then heat-treated with hot air at 90°C for 20 minutes to obtain a three-dimensional network structure with a width of 100 mm.

[0104] [Example 2] A three-dimensional network structure was obtained in the same manner as in Example 1, except that the single-hole output rate for hollow holes was 1.8 g / min, the single-hole output rate for solid holes was 1.20 g / min, and the take-up speed was 1.43 m / min.

[0105] Example 3 A three-dimensional network structure was obtained in the same manner as in Example 1, except that the single-hole discharge rate for hollow holes was 1.8 g / min, the single-hole discharge rate for solid holes was 1.20 g / min, the distance from the nozzle surface to the surface of the cooling water in the water tank was 40 cm, and the take-up speed was 1.43 m / min.

[0106] Example 4 A three-dimensional network structure was obtained in the same manner as in Example 1, except that Resin A was replaced with a raw material Resin A to which 0.1% by mass of water was added relative to 100% by mass of solids, the distance from the nozzle surface to the surface of the cooling water in the water tank was 18 cm, and the take-up speed was 0.95 m / min.

[0107] Comparative Example 1 A nozzle was used, which had an effective nozzle surface of 96 mm in width and 31 mm in thickness, and which included orifices with an outer diameter of 3.0 mm, an inner diameter of 2.6 mm, and a triple-bridge hollow cross section, arranged in a staggered pattern with a width-to-hole pitch of 10 mm and a thickness-to-hole pitch of 7.5 mm, and orifices with an outer diameter of 0.7 mm and a solid cross section, arranged in a staggered pattern with a width-to-hole pitch of 2.5 mm and a thickness-to-hole pitch of 3.7 mm. A three-dimensional network structure was obtained in the same manner as in Example 1, except that the single-hole output rate of the hollow holes was 2.0 g / min, the single-hole output rate of the solid holes was 0.50 g / min, the distance from the nozzle surface to the cooling water surface in the water tank was 18 cm, and the take-up speed was 1.14 m / min.

[0108] Comparative Example 2 A three-dimensional network structure was obtained in the same manner as in Example 1, except that Resin B was used as the raw material, the spinning temperature was 190°C, the distance from the nozzle surface to the surface of the cooling water in the water tank was 28 cm, and the take-up speed was 0.95 m / min.

[0109] The production conditions and the properties of the resulting three-dimensional network structures in Examples 1 to 4 and Comparative Examples 1 and 2 are shown in Table 1. In Table 1, the numerical values ​​of properties evaluated multiple times are average values.

[0110]

[0111] The three-dimensional network structures of Examples 1 to 4 are excellent in compression recovery after compression at the ambient temperature in use, and are excellent in compression durability on both sides with only a small difference in compression durability between the two sides.

Claims

1. A three-dimensional network structure composed of continuous filaments made of a thermoplastic resin composition and having a three-dimensional random loop joint structure, wherein the thermoplastic resin composition contains 70% by mass or more of polybutylene adipate terephthalate resin, one surface of the three-dimensional network structure has a higher apparent density than the other surface, and the residual strain R after repeatedly compressing the one surface side with a load of 750 N 13,000 times is １ and the residual strain R after compressing the other surface side repeatedly 13,000 times with a load of 750 N. ２ are each 20% or less, １ The value of R ２ the absolute value of the difference between the value of and the value of 10% or less; and the three-dimensional network structure has a compression residual strain of 15% or less at 40°C.

2. The three-dimensional network structure according to claim 1, wherein the polybutylene adipate terephthalate resin contains adipic acid units and terephthalic acid units, and the molar ratio of the terephthalic acid units to the adipic acid units is 1.0 or more and 3.0 or less.

3. The three-dimensional network structure according to claim 1, wherein the polybutylene adipate terephthalate resin has a melting point of 125°C or higher and 180°C or lower.

4. Apparent density is 0.005 g / cm ３ 0.20g / cm or more ３ The three-dimensional mesh structure according to claim 1, wherein:

5. The larger of the hardness at 25% compression when pressure is applied from one surface side and the hardness at 25% compression when pressure is applied from the other surface side is defined as H １ , the smaller value is H ２ Then, H １ / H ２ The three-dimensional mesh structure according to claim 1, wherein the linearity is 1.03 or more.

6. The larger of the hardness at 40% compression when pressure is applied from one surface side and the hardness at 40% compression when pressure is applied from the other surface side is defined as H ３ , the smaller value is H ４ Then, H ３ / H ４ The three-dimensional mesh structure according to claim 1, wherein the ratio of the saturation angle to the saturation angle is 1.05 or more.

7. The three-dimensional mesh structure according to claim 1, wherein the absolute value of the difference between the compression deflection coefficient when pressure is applied from said one surface side and the compression deflection coefficient when pressure is applied from said other surface side is 5.0 or less.

8. The three-dimensional network structure according to claim 1, wherein a differential scanning calorimeter measures the continuous filament, and the differential scanning calorimeter curve measures an endothermic peak having a minimum value in the range of 30°C to 70°C, and the enthalpy of the endothermic peak is 2.5 J / g or less.

9. The absolute value of the difference between the apparent density of one surface and the apparent density of the other surface is 0.015 g / cm ３ The three-dimensional mesh structure according to claim 1 .

10. A cushioning material which comprises the three-dimensional mesh structure according to any one of claims 1 to 9 and can be used reversibly.

Images