Three-dimensional mesh-like structure

Abstract

Provided is a biodegradable three-dimensional mesh-like structure having excellent compression recovery properties and repeated compression properties after thermal compression at a use environment temperature. The three-dimensional mesh-like structure is composed of a continuous filament composed of a thermoplastic resin composition, and has a three-dimensional random loop joint structure, the three-dimensional mesh-like structure characterized in that: the thermoplastic resin composition contains 70 mass% or more of a polybutylene adipate terephthalate resin; the differential scanning calorimetry curve of the continuous filament, measured using a differential scanning calorimeter, has an enthalpy of 2.5 J / g or less at an endothermic peak having a minimum value in a range from 30°C to 70°C; the average fiber diameter of the continuous filament is between 0.1 mm and 3.0 mm both inclusive; and the three-dimensional mesh-like structure has an average fiber diameter in a surface layer portion which is 1.05 times or more the average fiber diameter in an inner layer portion, an apparent density between 0.01 g / cm3 and 0.20 g / cm3 both inclusive, a residual strain of 15% or less after repeated compression under a 750 N constant load, and a hardness retention ratio of 45% or more at 40% compression after the repeated compression with the 750 N constant load.

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 functions of biodegradable network structures, but no biodegradable three-dimensional network structure has yet been known that exhibits excellent recovery and repeated compression properties after heat compression at the ambient temperature of use when used as a cushioning material, and also exhibits excellent cushioning properties. 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 and repeated compression properties after heat compression at the ambient temperature of use. Note that "excellent repeated compression properties" means that the properties of the three-dimensional network structure are not significantly inferior even after repeated compression compared to before repeated compression.

[0006] The three-dimensional network structure according to the present invention is as follows: [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, the differential scanning calorimeter curve of the continuous filaments measured using a differential scanning calorimeter has an endothermic peak with a minimum enthalpy of 2.5 J / g or less in the range of 30°C to 70°C, the continuous filaments have an average fiber diameter of 0.1 mm or more and 3.0 mm or less, the three-dimensional network structure has an average fiber diameter of a surface layer portion that is 1.05 times or more the average fiber diameter of an inner layer portion, and an apparent density of 0.01 g / cm ３ 0.20g / cm or more ３ [2] The three-dimensional network structure according to [1], wherein the polybutylene adipate terephthalate resin contains adipic acid residues and terephthalic acid residues, and the molar ratio of the terephthalic acid residues to the adipic acid residues is 1.0 or more and 3.0 or less. [3] The three-dimensional network structure according to [1] or [2], wherein the polybutylene adipate terephthalate resin has a melting point of 125°C or more and 180°C or less. [4] The three-dimensional network structure according to any one of [1] to [3], wherein the hardness retention at 65% compression after repeated compression under a constant load of 750N is 60% or more. [5] The three-dimensional network structure according to any one of [1] to [4], wherein the three-dimensional network structure has a compression deflection coefficient of 2.5 or more. [6] The three-dimensional network structure according to any one of [1] to [5], having a thickness of 10 mm or more and 300 mm or less. [7] The three-dimensional network structure according to any one of [1] to [6], having a 40°C compression set of 25% or less.

[0007] According to the present invention, with the above-mentioned configuration, it is possible to provide a biodegradable three-dimensional network structure that is excellent in compression recovery property after thermal compression at the temperature of the environment in use and in repeated compression properties.

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

[0009] The three-dimensional network structure of the present invention is 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, and a differential scanning calorimetry curve (DSC curve) of the continuous filaments measured using a differential scanning calorimeter has an endothermic peak with a minimum enthalpy of 2.5 J / g or less in the range of 30°C to 70°C, and the continuous filaments have an average fiber diameter of 0.1 mm or more and 3.0 mm or less, and the three-dimensional network structure has an average fiber diameter of a surface layer portion that is 1.05 times or more the average fiber diameter of an inner layer portion, and an apparent density of 0.01 g / cm ３ 0.20g / cm or more ３ The following is a three-dimensional network structure characterized by a residual strain of 15% or less after repeated compression under a constant load of 750 N and a hardness retention rate at 40% compression of 45% or more after repeated compression under a constant load of 750 N. The above configuration can improve the compression recovery and repeated compression characteristics after thermal compression at the usage temperature. The usage 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, and in this invention, the usage temperature is 40°C. In other words, the compression residual strain at 40°C was used as an index of compression recovery after thermal compression at the usage temperature. Each configuration will be described in detail below.

[0010] <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 98% by mass or more. Furthermore, the thermoplastic resin composition constituting the continuous filaments may be 100% by mass of polybutylene adipate terephthalate resin.

[0011] Polybutylene adipate terephthalate resin is a biodegradable resin and 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 may be copolymerized in multiple stages. Furthermore, polybutylene adipate terephthalate resin is preferably a thermoplastic resin.

[0012] The polybutylene adipate terephthalate resin contains adipic acid residues (adipic acid units) and terephthalic acid residues (terephthalic acid units), and the molar ratio of the terephthalic acid residues to the adipic acid residues is preferably 1.0 or more and 3.0 or less. The lower limit of the molar ratio is more preferably 1.1 or more, and even more preferably 1.2 or more. On the other hand, the upper limit of the molar ratio is more preferably 2.5 or less, and even more preferably 2.0 or less. When the molar ratio is 1.0 or more, the compression recovery property and repeated compression durability after heat compression at the usage temperature of the three-dimensional network structure are easily improved. On the other hand, when the molar ratio is 3.0 or less, the flexibility is easily improved. Therefore, it is suitable for cushioning materials, etc.

[0013] The melting point of the polybutylene adipate terephthalate resin 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 140°C or higher, and even more preferably 145°C or higher. On the other hand, the upper limit of the melting point is more preferably 170°C or lower, and even more preferably 160°C or lower. A melting point of 125°C or higher facilitates improvements in compression recovery after heat compression at the ambient temperature of use of the three-dimensional network structure, as well as durability against repeated compression. On the other hand, a melting point of 180°C or lower facilitates improvements in flexibility, making the structure suitable for cushioning materials and the like.

[0014] 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 higher facilitates improvements in compression recovery after heat compression and durability against repeated compression. The lower limit of the MFR is more preferably 4 g / 10 min or higher, even more preferably 5 g / 10 min or higher, and even more preferably 6 g / 10 min or higher. On the other hand, an MFR of 60 g / 10 min or lower can increase the melt viscosity and increase the fiber diameter of the continuous filaments. The upper limit of the MFR is more preferably 50 g / 10 min or lower, even more preferably 40 g / 10 min or lower, and particularly preferably 30 g / 10 min or lower. 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.

[0015] When a commercially available resin is used as the polybutylene adipate terephthalate resin, if the resin has a low 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] The thermoplastic resin composition constituting the continuous filaments may contain, in addition to the thermoplastic resin, various additives such as deodorizers, antibacterial agents, antifungal agents, antimite agents, deodorizers, fragrances, flame retardants, moisture absorbing and releasing agents, antioxidants, and lubricants. These may be used alone or in combination of two or more. The total content 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.

[0024] <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 (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.

[0025] The continuous filaments constituting the three-dimensional network structure of the present invention may be combined with other thermoplastic resins to form composite filaments, provided that the object of the present invention is not impaired. Examples of composite forms include composite filaments of a sheath-core type, a side-by-side type, and an eccentric sheath-core type, when the filaments themselves are composited.

[0026] One of the characteristics of the three-dimensional network structure of the present invention is that the average fiber diameter of the surface layer portion is larger than the average fiber diameter of the inner layer portion in order to increase the surface rigidity of the three-dimensional network structure. Specifically, the average fiber diameter of the surface layer portion of the three-dimensional network structure of the present invention is at least 1.05 times, preferably at least 1.08 times, and more preferably at least 1.10 times, the average fiber diameter of the inner layer portion. If the average fiber diameter of the surface layer portion is less than 1.05 times the average fiber diameter of the inner layer portion, the required surface rigidity and contact strength between the continuous filaments in the surface layer portion may not be ensured, and the hardness retention required for cushioning properties may not be stably achieved. The upper limit of the ratio of the average fiber diameter of the surface layer portion to the average fiber diameter of the inner layer portion is not particularly limited, but is, for example, 1.25 times or less. The average fiber diameter of the surface layer portion is 0.1 mm or more and 3.0 mm or less, preferably 0.2 mm or more and 2.5 mm or less, more preferably 0.3 mm or more and 2.0 mm or less, and even more preferably 0.5 mm or more and 1.0 mm or less. The average fiber diameter of the inner layer portion is from 0.1 mm to 3.0 mm, preferably from 0.2 mm to 2.5 mm, more preferably from 0.3 mm to 2.0 mm, and even more preferably from 0.5 mm to 1.0 mm. The average fiber diameter of the surface layer portion and the average fiber diameter of the inner layer portion can be measured by the method described in the examples below.

[0027] Because the three-dimensional network structure of the present invention has different average fiber diameters in the surface layer and the inner layer, it is difficult to precisely calculate the average fiber diameter of the entire three-dimensional network structure (the average fiber diameter of the continuous filaments constituting the three-dimensional network structure). Therefore, in this specification, the average of the two values, the average fiber diameter of the surface layer and the average fiber diameter of the inner layer, is defined as the average fiber diameter of the continuous filaments constituting the three-dimensional network structure. The average fiber diameter of the continuous filaments constituting the three-dimensional network structure of the present invention is 0.1 mm or more and 3.0 mm or less, preferably 0.2 mm or more and 2.5 mm or less, and more preferably 0.3 mm or more and 2.0 mm or less. If the average fiber diameter of the continuous filaments is less than 0.1 mm, the continuous filaments are too thin, resulting in good density and a soft feel, but making it difficult to ensure the required hardness of the three-dimensional network structure. If the average fiber diameter of the continuous filaments is more than 3.0 mm, the three-dimensional network structure can achieve sufficient hardness, but the network structure becomes coarse, which may result in poor cushioning properties. From this perspective, the average fiber diameter of the continuous filaments needs to be set within an appropriate range.

[0028] The continuous filaments constituting the three-dimensional network structure of the present invention preferably have a melting enthalpy of 16 J / g or more. Having a melting enthalpy of 16 J / g or more can improve the compression durability of the three-dimensional network structure and its compression recovery after heat compression. 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. On the other hand, the melting enthalpy is preferably 30 J / g or less. This improves the flexibility of the three-dimensional network structure and reduces the generation of noise during compression and recovery. The melting enthalpy is more preferably 29 J / g or less, even more preferably 28 J / g or less.

[0029] The enthalpy (J / g) of the endothermic peak of the continuous filaments constituting the three-dimensional network structure of the present invention 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 low-temperature baseline and the end point as the point where the curve begins to contact the high-temperature baseline, 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.

[0030] The DSC curve of the continuous filaments constituting the three-dimensional network structure, measured using a differential scanning calorimeter, has an endothermic peak with a minimum value in the range of 30°C to 70°C, and the enthalpy is 2.5 J / g or less. In the present invention, the "enthalpy of the endothermic peak with 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 reduces the compression set at 40°C. As a result, the feeling of settling when used as a cushioning material can be reduced. Therefore, the low-temperature phase enthalpy is preferably 1.5 J / g or less, more preferably 1.0 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.

[0031] <Three-dimensional network structure> The three-dimensional network structure of the present invention may have a single-layer structure, but may have a multi-layer structure as long as the object of the present invention is not impaired. Methods for forming a multi-layer structure include a method of stacking three-dimensional network structures on top of each other and fixing them with a side fabric or the like, a method of melt-fixing them by heating, a method of bonding them with an adhesive, and a method of restraining them with sewing or a band or the like.

[0032] The cross-sectional shape of the continuous filaments that make up the three-dimensional network structure of the present invention is not particularly limited, but by making the cross-section hollow or irregular, it is possible to impart preferable compression resistance and feel.

[0033] The shape of the three-dimensional network structure of the present invention is not particularly limited. Examples include a plate, a polygon such as a triangular prism or a quadrangular prism, a cylinder, a sphere, and a combination thereof. When forming the three-dimensional network structure, a regulating plate may be used during melt extrusion of the resin, or the structure may be formed by cutting, hot pressing, or the like.

[0034] The apparent density of the three-dimensional network structure of the present invention is preferably 0.01 g / cm ３ ~0.20 g / cm ３ The apparent density is 0.01 g / cm ３ By setting the apparent density to 0.02 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 in a cushion or the like, the feeling of hitting the bottom can be reduced. Therefore, the lower limit of the apparent density is more preferably 0.02 g / cm.３ More preferably, 0.025 g / cm ３ More preferably, 0.03 g / cm ３ On the other hand, the apparent density is 0.20 g / cm or more. ３ When the apparent density is 0.15 g / cm or less, the flexibility is improved and the material can be suitably used as a cushioning material, etc. Therefore, the upper limit of the apparent density is more preferably 0.15 g / cm ３ More preferably, 0.10 g / cm or less ３ The apparent density of the three-dimensional network structure can be measured by the method described in the examples below.

[0035] The thickness of the three-dimensional network structure of the present invention is preferably 10 mm to 300 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 25 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 200 mm or less, even more preferably 150 mm or less, and particularly preferably 100 mm or less. The thickness of the three-dimensional network structure can be measured by the method described in the examples below.

[0036] The three-dimensional network structure of the present invention preferably has a 40°C compression set of 25% or less. This allows for improved compression recovery after heat compression. The upper limit of the 40°C compression set is more preferably 20% or less, and even more preferably 15% or less. The 40°C compression set is not particularly limited and may be, for example, 1% or more, or 5% or more. The 40°C compression set can be measured by the method described in the Examples below.

[0037] The hardness of the three-dimensional network structure of the present invention at 25% compression is preferably 10 N / φ200 to 600 N / φ200, more preferably 30 N / φ200 to 400 N / φ200, and even more preferably 50 N / φ200 to 200 N / φ200. If the hardness at 25% compression is less than 10 N / φ200, a feeling of hitting the bottom may be felt, and if it exceeds 600 N / φ200, it may be too hard and the cushioning properties may be impaired.

[0038] The hardness of the three-dimensional network structure of the present invention at 40% compression is preferably 40 N / φ200 to 1000 N / φ200, more preferably 60 N / φ200 to 700 N / φ200, and even more preferably 80 N / φ200 to 400 N / φ200. If the hardness at 40% compression is less than 40 N / φ200, a feeling of hitting the bottom may be felt, and if it exceeds 1000 N / φ200, the structure may be too hard and the cushioning properties may be impaired.

[0039] The hardness of the three-dimensional network structure of the present invention at 65% compression is preferably 80 N / φ200 to 2000 N / φ200, more preferably 100 N / φ200 to 1000 N / φ200, and even more preferably 150 N / φ200 to 600 N / φ200. If the hardness at 65% compression is less than 80 N / φ200, a feeling of hitting the bottom may be felt, and if it exceeds 2000 N / φ200, it may be too hard and the cushioning properties may be impaired.

[0040] The residual strain of the three-dimensional network structure of the present invention after repeated compression under a constant load of 750N is 15% or less, preferably 10% or less. If the residual strain after repeated compression under a constant load of 750N exceeds 15%, the thickness of the three-dimensional network structure will decrease over long-term use, making it unsuitable as a cushioning material. In this specification, "750N constant load repeated compression" means repeatedly compressing the three-dimensional network structure at a constant load of 750N, and "residual strain after 750N constant load repeated compression" means the thickness of the three-dimensional network structure reduced by the repeated compression. Note that the lower limit of the residual strain after repeated compression under a constant load of 750N is not particularly limited, but in the three-dimensional network structure obtained by the present invention, it is 0.1% or more.

[0041] The hardness retention rate at 40% compression of the three-dimensional network structure of the present invention after repeated compression under a constant load of 750 N is 45% or more, preferably 48% or more, and more preferably 50% or more. If the hardness retention rate at 40% compression after repeated compression under a constant load of 750 N is less than 45%, the hardness of the cushioning material will decrease over long-term use, and the user may feel that the hardness has changed significantly. Although there are no particular limitations on the upper limit of the hardness retention rate at 40% compression after repeated compression under a constant load of 750 N, it is 95% or less in the three-dimensional network structure obtained by the present invention.

[0042] The three-dimensional network structure of the present invention has a hardness retention rate at 65% compression after repeated compression under a constant load of 750 N of 60% or more, preferably 63% or more, and more preferably 65% ​​or more. If the 65% hardness retention rate after repeated compression under a constant load of 750 N is less than 60%, the hardness of the cushioning material will decrease over long-term use, and the user may feel a sense of bottoming out. The upper limit of the hardness retention rate at 65% compression after repeated compression under a constant load of 750 N is not particularly limited, but in the three-dimensional network structure obtained by the present invention, it is 99% or less.

[0043] The three-dimensional network structure of the present invention preferably has the properties of having a hardness retention rate of 45% or more at 40% compression after repeated compression under a constant load of 750 N, and a hardness retention rate of 60% or more at 65% compression after repeated compression under a constant load of 750 N. By setting the hardness retention rate within the above range, it is possible to obtain a three-dimensional network structure that exhibits little change in hardness after long-term use, little change in sitting or sleeping comfort, and can be used comfortably for long periods of time. This durability test using a 750 N constant load repeated compression is a test that evaluates durability at an even higher level than the 50% constant displacement repeated compression test that has been focused on in prior literature. In a 50% constant displacement cyclic compression test, the amount of compression is fixed at 50% of the thickness from the start of processing to the end of processing, but in the case of a durability test using a 750N constant load cyclic compression, even if a load of 750N corresponds to a displacement of 50% of the thickness at the start of processing, the hardness decreases during the cyclic compression process, so that the amount of compression exceeds 50% of the thickness by the end of processing, and the amount of deformation that the sample undergoes during the test is greater than in a 50% constant displacement cyclic compression test.

[0044] The compression deflection coefficient of the three-dimensional network structure of the present invention is preferably 2.5 or more, more preferably 2.8 or more, and even more preferably 3.0 or more. A compression deflection coefficient of less than 2.5 may impair the sitting and sleeping comfort of the cushioning material. By setting the compression deflection coefficient within the above range, a three-dimensional network structure with excellent sitting and sleeping comfort can be obtained. It has been found that, particularly when the hardness is relatively high, setting the compression deflection coefficient within the above range improves sitting and sleeping comfort. The compression deflection coefficient is calculated by dividing the hardness at 65% compression by the hardness at 25% compression. The compression deflection coefficient can be increased by either decreasing the hardness at 25% compression or increasing the hardness at 65% compression. While the mechanism by which the compression deflection coefficient is improved in the present invention has not been fully elucidated, it is presumed that this is due to the large fiber diameter and high surface rigidity of the surface layer of the three-dimensional network structure of the present invention, resulting in a high hardness at 65% compression. It is believed that this effect enables a stable increase in the compression deflection coefficient. There is no particular upper limit to the compression deflection coefficient, but in the three-dimensional network structure obtained in the present invention, it is 8.0 or less.

[0045] The present inventors have found that in order to obtain a three-dimensional network structure that maintains its hardness in a 750 N constant-load cyclic compression durability test, it is necessary to receive the external load (750 N) at the surface layer of the three-dimensional network structure, distribute the load at the surface layer surface, reduce the burden on the inner layer, and maintain this load distribution effect at the surface layer surface throughout the constant-load cyclic compression test. The former can be achieved by providing a structural difference between the surface layer and the inner layer, and the latter can be achieved by increasing the contact strength between the continuous filaments present in the surface layer. Specifically, the difference between the three-dimensional network structure of the present invention and previously known three-dimensional network structures with small 50% constant displacement repeated compression strain is that in the three-dimensional network structure of the present invention, the fusion of the continuous filaments that make up the three-dimensional network structure is further strengthened, thereby increasing the contact strength between the continuous filaments, and at the same time, the average fiber diameter of the surface layer portion of the three-dimensional network structure is made larger than the average fiber diameter of the inner layer portion, thereby creating a structural difference between the surface layer portion and the inner layer portion and increasing the contact area of ​​the continuous filaments, thereby increasing the contact strength of the surface layer portion of the three-dimensional network structure compared to the inner layer portion, thereby further suppressing damage to the contact points that occurs during repeated compression treatment and maintaining the effect of surface-dispersing the load (750 N) received during repeated compression over the surface layer portion. It is difficult to stably achieve a 40% hardness retention rate of 45% or more after repeated compression at a constant load of 750 N simply by increasing the contact strength between the continuous filaments that make up the three-dimensional mesh structure. Therefore, by selectively thickening the fibers in the surface layer to increase surface rigidity, designing the contact strength between the surface filaments to be high, and creating a structural difference between the inner layer and the surface layer, it was possible to stably achieve this.

[0046] To obtain the three-dimensional network structure of the present invention, as described above, it is necessary to impart a structural difference between the surface layer portion and the inner layer portion and to increase the contact strength between the continuous filaments in the surface layer portion. This can be achieved by making the average fiber diameter of the surface layer portion at least 1.05 times the average fiber diameter of the inner layer portion. If the average fiber diameter of the surface layer portion is less than 1.05 times the average fiber diameter of the inner layer portion, the structural difference between the surface layer portion and the inner layer portion is small, and the required surface rigidity cannot be obtained. As a result, the effect of surface distribution of the load received during repeated compression in the surface layer portion is reduced, and sufficient hardness retention cannot be obtained. Prior literature on network structures is known that improves cushioning and durability by providing a soft layer with a small fiber diameter on the surface and an inner layer with a large fiber diameter that provides durability to the basic layer. However, in the present invention, the fiber diameter of the surface layer is increased to increase surface rigidity and improve hardness retention, which is a fundamentally different design concept. Furthermore, although this manufacturing method was excellent in terms of the conventional repeated compression properties at a constant displacement of 50%, it was not necessarily excellent in terms of durability after repeated compression at a constant load of 750 N, which is the target of the present invention, and it was difficult to achieve the repeated compression properties required by the present invention.

[0047] 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.

[0048] 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.

[0049] The three-dimensional network structure of the present invention is suitable for use in cushions. The cushion may be any cushion that has elasticity to support an object or that reduces impact. Examples of cushions include cushions used in office chairs, furniture, sofas, beds, and other bedding; 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.

[0050] <Method for Manufacturing a Three-Dimensional Network Structure> The method for manufacturing a three-dimensional network structure of the present invention preferably includes an extrusion step of extruding a molten thermoplastic resin composition through a nozzle, a molding step of obtaining a molded body by molding the thermoplastic resin composition extruded through the nozzle into a three-dimensional network structure using continuous filaments, and a heat treatment step of heat-treating the molded body. The three-dimensional network structure prior to the heat treatment step is referred to as a molded body to avoid confusion with the finished three-dimensional network structure (the three-dimensional network structure after the heat treatment step). An example of the extrusion and molding steps is described below, but is not limited to the following method. First, a thermoplastic resin composition containing a polybutylene adipate terephthalate resin having a melting point Tm (°C) is dispensed into the nozzle orifices through a multi-row nozzle having a plurality of orifices with different orifice diameters, as described below, and extruded downward from the nozzle at a spinning temperature of Tm + 20°C or higher but lower than Tm + 180°C (preferably Tm + 75°C or higher but lower than Tm + 120°C). 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, drained, or dried to obtain a molded body with smoothed surfaces on both or one side. For details of these spinning and cooling processes, see, for example, JP-A-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. During this process, only the surface of the take-up net is cooled while relaxing its shape while forming a three-dimensional network structure. The resulting molded body is then heat-treated. The drying process of the molded body may also be used as heat treatment.

[0051] Water may be added to the thermoplastic resin composition before it is discharged from the nozzle. Adding water to the thermoplastic resin composition promotes hydrolysis of the thermoplastic resin during the production process of the three-dimensional network structure, improves the flexibility of the resin, and reduces the difference in compression durability when pressure is applied from either side. The amount of water added is preferably 2.0% by mass or less based on the thermoplastic resin composition. This prevents excessive decomposition of the thermoplastic resin during the production process of the three-dimensional network structure. As a result, the compression recovery after heat compression and the compression durability from both sides are easily improved. 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 completely dry it. Next, a predetermined amount of pure water may be added to 100% by mass of the completely dried thermoplastic resin composition.

[0052] The melt flow rate (MFR) of the polybutylene adipate terephthalate resin before melt extrusion is preferably at least 0.5 g / 10 min and less than 20.0 g / 10 min lower than the MFR of the continuous filaments that constitute the desired three-dimensional network structure. Because thermal degradation and shear degradation of the resin are induced during melt extrusion, controlling the MFR before melt extrusion as described above makes it easier to obtain continuous filaments with the desired MFR.

[0053] In order to obtain the three-dimensional network structure of the present invention, it is necessary to strengthen the fusion between the continuous filaments of the resulting three-dimensional network structure and increase the contact strength between the continuous filaments. Increasing the contact strength between the continuous filaments that make up the three-dimensional network structure results in improved durability against repeated compression of the three-dimensional network structure.

[0054] One method for obtaining a three-dimensional network structure with increased contact strength is, for example, to increase the spinning temperature of the thermoplastic resin. The spinning temperature varies depending on the properties of the resin, but is preferably from Tm+30°C to Tm+150°C, more preferably from Tm+40°C to Tm+140°C, even more preferably from Tm+50°C to Tm+130°C, and particularly preferably from Tm+75°C to less than Tm+120°C.

[0055] In the three-dimensional network structure of the present invention, one suitable method for imparting a difference in fiber diameter between the surface layer portion and the inner layer portion is to accelerate cooling of only the fibers near the surface of the three-dimensional network structure, thereby increasing the fiber diameter only in the surface layer portion. Methods of imparting a difference in fiber diameter by using a nozzle configuration, such as those known in prior art, in which the nozzle hole diameter is changed between the surface layer portion and the inner layer portion to increase the fiber diameter only in the surface layer portion, have problems in terms of quality, such as distortion of the loop shape in the surface layer portion and a clear difference in density between the surface layer portion and the inner layer portion, and problems in production, such as the tendency for the discharge balance between the surface layer portion and the inner layer portion to be disrupted, making it difficult to produce stable production and uniform products. Furthermore, it has been difficult to obtain a three-dimensional network structure with excellent durability after repeated compression under a constant load of 750 N, which is the aim of the present invention.

[0056] Methods for cooling only the fibers near the surface of the three-dimensional network structure include setting the ambient temperature low and selectively blowing cooling air onto the surface. In this specification, "ambient temperature" refers to the temperature measured with a thermometer located in the same space as the spinning machine, at a distance of 1 m to less than 1.5 m from the spinning machine, and at a height from the discharge surface to the water surface. When cooling the surface fibers at this ambient temperature, the ambient temperature is preferably 50°C or lower, more preferably 40°C or lower, and even more preferably 35°C or lower. From the viewpoint of preventing a significant decrease in contact strength, the ambient temperature is preferably -10°C or higher. When selectively blowing cooling air onto the surface, the temperature of the cooling air is preferably below the melting point of the resin, and preferably above the ambient temperature. Furthermore, it is preferable to design the cooling air so that it flows downward due to entrained flow on the surface, or that the air, heated by heat exchange with the surface fibers, penetrates the inner layer so as not to reduce the contact strength of the inner layer, even if it penetrates the inner layer. From this viewpoint, it is preferable not to actively perform cooling in the fiber direction. The cooling air velocity is preferably 0.3 m / sec or less, more preferably 0.2 m / sec or less. By using one or a combination of two or more of the above methods, the fiber diameter in the surface layer portion can be made larger than the fiber diameter in the inner layer portion.

[0057] The cooling air blowing device preferably has a structure that covers the entire width of the three-dimensional network structure in the thickness direction and blows from one or both sides. The cooling air blowing device can be appropriately selected depending on the three-dimensional network structure to be obtained. The height of the cooling air blowing device may be anywhere between the nozzle surface and the cooling water, and the height may be changed as necessary. The height does not need to be the same across the width and may be changed depending on the area. The cooling air may be blown only to areas where the surface formation needs to be more solid. Depending on the application, the cooling air may be blown only to one side, or from the entire surface in the thickness direction of the three-dimensional network structure. It is preferable that the cooling air has at least one straightening section such as a wire mesh to ensure as uniform a wind speed as possible. To increase the temperature of the cooling air, a hot air generator is preferably used, and exhaust heat from around the nozzle can also be used.

[0058] To obtain the three-dimensional network structure of the present invention, it is preferable to optimize the nozzle shape, dimensions, and nozzle hole arrangement. 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 mm or more. Furthermore, the nozzle orifice shape for forming thick fibers preferably has a hollow-forming property, and examples thereof include a C-type nozzle and a three-point bridge nozzle. From the viewpoint of pressure resistance, a three-point 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 three-dimensional 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.

[0059] 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, and particularly preferably 10°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.

[0060] 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.

[0061] The heat treatment time in the heat treatment step is preferably 1 minute or more. This can increase the 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 can reduce yellowing, odor, molecular weight reduction, etc. of the polybutylene adipate terephthalate resin associated with polymer decomposition and deterioration during heat treatment. Furthermore, productivity can also be improved. When the heat treatment is performed in multiple steps, it is preferable that the total heat treatment time be within the above range.

[0062] The molded body cooled and solidified in the water bath may be held at a temperature of 20°C to 50°C for 1 minute 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 perform heat treatment by holding the temperature at a low level in the first half of a hot air oven and then raising the temperature in the second half of the hot air oven.

[0063] At any stage from the manufacturing process of the thermoplastic resin used as the raw material for the three-dimensional network structure to the molding process, additives capable of imparting functions such as deodorizing, antibacterial, antifungal, antimite, deodorizing, aromatic, flame retardant, and moisture absorbing / releasing properties may be added to the thermoplastic resin. Furthermore, when manufacturing the three-dimensional network structure, the raw material polybutylene adipate terephthalate resin may contain function-imparting agents such as antioxidants and lubricants. These may be used alone or in combination of two or more. It is preferable to adjust the content of various function-imparting agents by kneading them into the resin during melt extrusion depending on the color tone and quality of the resin after melting.

[0064] 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.

[0065] 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 tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], Sumilizer AG 80, and 2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)mesitylene.

[0066] Examples of phosphite antioxidants 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]-12H-dibenzo[d,g]"1,3,2"dioxaphosphocin, tris(2,4-di-tert-butylphenyl) phosphite, tris(4-nonylphenyl) phosphite, and 4,4'-isopropylidenediphenol C12-15 alcohol. phosphite, diphenyl (2-ethylhexyl) phosphite, diphenyl isodecyl phosphite, triisodecyl phosphite, triphenyl phosphite, etc.

[0067] 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.

[0068] In order to prevent thermal degradation of the thermoplastic resin, a mixture of a phenolic antioxidant and a phosphite antioxidant may be used. When these two types of antioxidants are used, the total content of the two types of antioxidants is preferably 0.05% by mass or more and 1.0% by mass or less, based on 100% by mass of the thermoplastic resin composition.

[0069] Examples of the lubricant include hydrocarbon waxes, higher alcohol waxes, amide waxes, ester waxes, metal soap waxes, etc. If necessary, the lubricant is contained in an amount of preferably 0.5% by mass or less based on 100% by mass of the thermoplastic resin composition.

[0070] This application claims the benefit of priority based on Japanese Patent Application No. 2023-165925, filed on September 27, 2023. The entire contents of the specification of Japanese Patent Application No. 2023-165925, filed on September 27, 2023, are incorporated herein by reference.

[0071] 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.

[0072] The characteristic values ​​of the three-dimensional network structures of Examples 1 to 5 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.

[0073] (1) Average Fiber Diameter A sample was cut into a size of 10 cm x 10 cm, and filaments (fibers) approximately 5 mm long were collected from 10 locations each in the surface layer and inner layer of the three-dimensional network structure. The surface layer fibers were collected from the outermost layer in the thickness direction of the three-dimensional network structure, i.e., from a location where no fibers exist outside of the surface layer fibers. The inner layer fibers were collected from within 30% of the thickness of the three-dimensional network structure based on the center in the thickness direction (within a range of 35 to 65% in the thickness direction from one surface). The fiber diameters of the filaments collected from each of the 10 locations were measured using an optical microscope at an appropriate magnification, focusing on the fiber diameter measurement location. The average value of the fiber diameters obtained from the surface layer fibers was taken as the average fiber diameter of the surface layer, and the average value of the fiber diameters obtained from the inner layer fibers was taken as the average fiber diameter of the inner layer. The average of the average fiber diameter of the surface layer and the average fiber diameter of the inner layer was taken as the average fiber diameter of the entire sample.

[0074] (2) 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.

[0075] (3) Molar ratio of terephthalic acid residues to adipic acid residues in polybutylene adipate terephthalate resin The molar ratio of terephthalic acid residues to adipic acid residues in polybutylene adipate terephthalate resin is １H-NMR measurements were performed. The measurement device used was a BRUKER AVANCE-NEO600 NMR device, and the measurements were performed as follows: 10-15 mg of sample was dissolved in deuterated chloroform / trifluoroacetic acid = 85 / 15 (volume ratio), and the solution was then filled into an NMR tube for measurement. Deuterated chloroform was used as the lock solvent, with a waiting time of 1 second, a data acquisition time of 4 seconds, and an accumulation count of 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 terephthalic acid residues to adipic acid residues in polybutylene adipate terephthalate resin can be expressed as molar ratio = ((b / 4) ÷ (a / 4)).

[0076] (4) Melting point (Tm) Resin pellets were collected as samples 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.

[0077] (5) 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 determine the average melting enthalpy (n = 3). The starting point was also designated as the melting onset temperature (° C.).

[0078] (6) Low-Temperature Phase Enthalpy In the DSC curve (5) 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 straight 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 straight line and the curve over the range of 30°C to 70°C to determine the low-temperature phase enthalpy. The point where the curve begins to deviate from the baseline on the low-temperature side (starting point) was defined as the low-temperature phase onset temperature. The above procedure was performed three times, and the average value (n = 3) of the low-temperature phase enthalpy was determined. An example of experimental data is shown in Figure 1.

[0079] (7) 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 measured quickly so as to minimize the amount of moisture in the air. The melt flow was measured using a Melt Indexer F-F01 machine manufactured by Toyo Seiki Seisakusho, Ltd., 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, and the average melt flow rate (n = 3) was calculated.

[0080] (8) 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 (2) above. The sample after thickness measurement was clamped between a jig capable of maintaining 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 calculated. These thicknesses were entered into the following formula to calculate the 40°C compression set. The above operation was performed three times to calculate the average value (n = 3) of the 40°C compression set. 40°C Compression Set (%) = {(c) - (d) / (c)} x 100

[0081] (9) Hardness and Compression Deflection Coefficient at 25%, 40%, and 65% Compression The three-dimensional network structure was cut into a size of 40 cm × 40 cm, and left to stand for 24 hours without load in an environment of 23°C ± 2°C. After that, measurements were made in accordance with ISO2439 (2008) Method E using an Autograph AG-X Plus manufactured by Shimadzu Corporation in an environment of 23°C ± 2°C. Specifically, a pressure plate with a diameter (φ) of 200 mm was placed at the center of the sample, and the thickness when a load reached 5 N was measured and recorded as the initial hardness tester thickness. The position of the pressure plate at this time was set as the zero point, and the specimen was pre-compressed once at a speed of 100 mm / min to 75% of the initial hardness tester thickness. The pressure plate was then returned to the zero point at the same speed and left in that state for 4 minutes. Thereafter, the specimen was immediately compressed at a speed of 100 mm / min to 25%, 40%, and 65% of the initial hardness tester thickness (to 75%, 60%, and 35% of the initial hardness tester thickness). The load (unit: N / φ200) at this time was measured and recorded as the hardness at 25%, 40%, and 65% compression, respectively (average value of n = 3). The hardness at 65% compression divided by the hardness at 25% compression was defined as the compression deflection coefficient. This procedure was repeated three times to calculate the average compression deflection coefficient (n = 3).

[0082] (10) Residual strain after 750N constant load cyclic compression The sample was cut into a size of 40 cm x 40 cm, and the initial hardness meter thickness (e) was measured using the method described in (9) above. The sample whose thickness was measured was then subjected to 750N constant load cyclic compression in accordance with JIS K6400-4 (2004) Method A (constant load method) using an ASKER STM-536 manufactured by Kobunshi Keiki Co., Ltd. The pressure tool used was a circular, flat bottom surface with a diameter of 250±1 mm and a radius of curvature of 25±1 mm at the bottom edge. The load was 750N±20N, the compression frequency was 70±5 times per minute, the number of compressions was 80,000, and the time during which pressure was applied to the maximum 750±20N was 25% or less of the time required for cyclic compression. After the repeated compression, the sample was left unloaded for 10±0.5 minutes, and then, using a Shimadzu Autograph AG-X Plus, a 200 mm diameter (φ) pressure plate was placed at the center of the sample. The thickness was measured at a load of 5 N, and this was taken as the hardness tester thickness (f) after repeated compression. The initial hardness tester thickness (e) and the hardness tester thickness (f) after repeated compression were entered into the following formula to determine the residual strain after repeated compression under a 750 N constant load. The above operation was performed three times, and the residual strain after repeated compression under a 750 N constant load was calculated for each operation. The average value (n = 3) was taken as the residual strain after repeated compression under a 750 N constant load for the sample. Residual strain after repeated compression under a 750 N constant load (unit: %) = {(e) - (f) / (e)} x 100

[0083] (11) Hardness retention at 40% compression after 750N constant load repeated compression The sample was cut into a size of 40 cm x 40 cm, and the initial hardness meter thickness and hardness (g) at 40% compression were measured using the method described in (9) above. The measured sample was then subjected to 750N constant load repeated compression in accordance with JIS K6400-4 (2004) Method A (constant load method) using an ASKER STM-536 manufactured by Kobunshi Keiki Co., Ltd. The pressure tool used was a circular, flat bottom surface with a diameter of 250 ± 1 mm and a radius of curvature of 25 ± 1 mm at the bottom edge, with a load of 750N ± 20N, a compression frequency of 70 ± 5 times per minute, and a compression count of 80,000 times. The time during which pressure was applied to the maximum of 750 ± 20N was 25% or less of the time required for repeated compression. After the repeated compression, the sample was left unloaded for 10 ± 0.5 minutes, using a Shimadzu Corporation autograph AG-X plus, a 200 mm diameter (φ) pressure plate was placed at the center of the sample, and the sample thickness was determined by the initial hardness tester thickness before the 750 N constant load repeated compression, with the initial hardness tester thickness being the zero point. The sample was pre-compressed once to 75% of the initial hardness tester thickness at a speed of 100 mm / min, and the pressure plate was returned to the zero point at the same speed. The sample was then left as is for 4 minutes, and then immediately compressed to 40% of the initial hardness tester thickness at a speed of 100 mm / min. The load at this time was determined as the hardness at 40% compression after the 750 N constant load repeated compression (h). The hardness at 40% compression (h) value after the 750 N constant load repeated compression was divided by the hardness at 40% compression (g) value to determine the hardness retention at 40% compression after the 750 N constant load repeated compression. The above operation was performed three times, and the hardness retention rate at 40% compression after repeated compression under a constant load of 750 N was calculated for each operation. The average value (n = 3) was used as the hardness retention rate at 40% compression after repeated compression under a constant load of 750 N for the sample.

[0084] (12) Hardness retention at 65% compression after 750N constant load repeated compression The sample was cut into a size of 40 cm x 40 cm, and the initial hardness meter thickness and hardness at 65% compression (i) were measured using the method described in (9) above. The measured sample was then subjected to 750N constant load repeated compression in accordance with JIS K6400-4 (2004) Method A (constant load method) using an ASKER STM-536 manufactured by Kobunshi Keiki Co., Ltd. The pressure tool used was a circular, flat bottom surface with a diameter of 250 ± 1 mm and a radius of curvature of 25 ± 1 mm at the bottom edge, with a load of 750N ± 20N, a compression frequency of 70 ± 5 times per minute, and a compression count of 80,000 times. The time during which pressure was applied to the maximum of 750 ± 20N was 25% or less of the time required for repeated compression. After the repeated compression, the sample was left unloaded for 10 ± 0.5 minutes, using a Shimadzu Corporation autograph AG-X plus, a 200 mm diameter (φ) pressure plate was placed at the center of the sample, and the sample thickness was determined by the initial hardness tester thickness before the 750 N constant load repeated compression, with the initial hardness tester thickness being the zero point. The sample was pre-compressed once to 75% of the initial hardness tester thickness at a speed of 100 mm / min, and the pressure plate was returned to the zero point at the same speed. The sample was then left as is for 4 minutes, and then immediately compressed to 65% of the initial hardness tester thickness at a speed of 100 mm / min. The load at that time was determined as the 65% compression hardness (j) after the 750 N constant load repeated compression. The value of the 65% compression hardness (j) after the 750 N constant load repeated compression was divided by the value of the 65% compression hardness (i) to determine the hardness retention rate after the 750 N constant load repeated compression. The above operation was performed three times, and the hardness retention rate at 65% compression after repeated compression under a constant load of 750 N was calculated for each operation. The average value (n = 3) was used as the hardness retention rate at 65% compression after repeated compression under a constant load of 750 N for the sample.

[0085] 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.

[0086] <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.

[0087] <Resin C> Resin C 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 0.50 mol and 0.50 mol, respectively. The obtained Resin C was cooled and then cut with a pellet cutter to produce pellets.

[0088] [Example 1] A nozzle having an effective nozzle surface of 680 mm in the width direction and 64 mm in the thickness direction, in which orifices with a hole diameter of 1.0 mm were arranged in a staggered pattern at a hole pitch of 5 mm, was used to extrude the obtained resin A pellets downward from the nozzle at a spinning temperature of 240°C and a single-hole discharge rate of 1.0 g / min. The ambient temperature was set to 30°C, and cooling air having a temperature of 80°C was blown at a speed of 0.1 m / s from one side of the extruded molten filament in the thickness direction to 10 to 20 cm directly below the nozzle. Cooling water was also blown 30 cm below the nozzle surface. A pair of take-up conveyors was arranged with stainless steel endless nets arranged parallel to each other with openings 48 mm apart so that some of the nets were above the water surface, and the molten discharged filaments were made to meander to form loops and fuse together at the contacting portions to form a network structure, and both sides of the molten network were sandwiched between the take-up conveyors and pulled into cooling water at a speed of 0.75 m per minute to solidify and flatten both sides, after which the network structure was cut to a predetermined size and subjected to a dry heat treatment with hot air at 90°C for 20 minutes to obtain a three-dimensional network structure. The obtained three-dimensional network structure satisfied the requirements of the present invention and had excellent durability against repeated compression.

[0089] Example 2 A three-dimensional network structure was obtained in the same manner as in Example 1, except that the nozzle had an outer diameter of 5.0 mm, an inner diameter of 4.4 mm, and orifices with a triple-bridge hollow-forming cross section, were arranged in a staggered pattern with a hole pitch of 8 mm, the single-hole discharge rate was 3.9 g / min, the mixture passed through a cooling space with an ambient temperature of 40°C, no cooling air was blown, the take-up speed was 2.26 m / min, and the distance between the nozzle surface and the cooling water was 39 cm. The obtained three-dimensional network structure satisfied the requirements of the present invention and was a three-dimensional network structure with excellent repeated compression durability.

[0090] Example 3 A three-dimensional network structure was obtained in the same manner as in Example 2, except that instead of pellets of resin A, a raw material containing 0.06% by mass of water added to 100% by mass of solids of resin A was used, the spinning temperature was 230°C, the ambient temperature was 30°C, the cooling air temperature was 100°C, the cooling air speed was 0.3 m / s, the take-up speed was 2.14 m / min, and the nozzle surface-to-cooling water distance was 34 cm. The obtained three-dimensional network structure satisfied the requirements of the present invention and was a three-dimensional network structure with excellent repeated compression durability.

[0091] Example 4 A three-dimensional network structure was obtained in the same manner as in Example 2, except that the spinning temperature was 230°C, the ambient temperature was 30°C, the cooling air temperature was 100°C, the cooling air speed was 0.3 m / s, the take-up speed was 2.00 m / min, and the nozzle surface-to-cooling water distance was 42 cm. The obtained three-dimensional network structure satisfied the requirements of the present invention and was a three-dimensional network structure with excellent repeated compression durability.

[0092] Example 5 A three-dimensional network structure was obtained in the same manner as in Example 4, except that pellets of Resin C were used instead of pellets of Resin A, the single-hole discharge rate was 3.3 g / min, the cooling air velocity was 0.1 m / s, the take-up speed was 1.70 / min, and the nozzle surface-to-cooling water distance was 37 cm. The obtained three-dimensional network structure satisfied the requirements of the present invention and was a three-dimensional network structure with excellent repeated compression durability.

[0093] Comparative Example 1 A three-dimensional network structure was obtained in the same manner as in Example 2, except that the spinning temperature was 220°C, the ambient temperature was 30°C, cooling air was not blown, the take-up speed was 1.86 m / min, and the distance between the nozzle surface and the cooling water was 44 cm. The obtained three-dimensional network structure did not satisfy the requirements of the present invention and was poor in repeated compression durability.

[0094] Comparative Example 2 A three-dimensional network structure was obtained in the same manner as in Example 2, except that pellets of Resin B were used instead of pellets of Resin A, the spinning temperature was 190° C., the single-hole discharge rate was 2.5 g / min, the ambient temperature was 20° C., no cooling air was blown, the take-up speed was 1.62 / min, the nozzle surface-to-cooling water distance was 35 cm, and the hot air drying temperature was 80° C. The obtained three-dimensional network structure did not satisfy the requirements of the present invention and was poor in repeated compression durability.

[0095] The production conditions and the properties of the resulting three-dimensional network structures in Examples 1 to 5 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.

[0096]

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, and a differential scanning calorimeter is used to measure the differential scanning calorimeter. The differential scanning calorimeter curve of the continuous filaments has a minimum endothermic peak enthalpy of 2.5 J / g or less in the range of 30°C to 70°C, and the continuous filaments have an average fiber diameter of 0.1 mm or more and 3.0 mm or less, and the three-dimensional network structure has an average fiber diameter of a surface layer portion that is 1.05 times or more the average fiber diameter of an inner layer portion, and an apparent density of 0.01 g / cm ３ 0.20g / cm or more ３ The three-dimensional netted structure is characterized in that the residual strain after repeated compression under a constant load of 750N is 15% or less, and the hardness retention rate at 40% compression after repeated compression under a constant load of 750N is 45% or more.

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

3. The three-dimensional network structure according to claim 1 or 2, wherein the polybutylene adipate terephthalate resin has a melting point of 125°C or higher and 180°C or lower.

4. The three-dimensional mesh structure according to claim 1 or 2, which has a hardness retention rate of 60% or more at 65% compression after repeated compression under a constant load of 750N.

5. The three-dimensional mesh structure according to claim 1 or 2, which has a compressive deflection coefficient of 2.5 or more.

6. The three-dimensional mesh structure according to claim 1 or 2, which has a thickness of 10 mm or more and 300 mm or less.

7. The three-dimensional netted structure according to claim 1 or 2, which has a compression set at 40° C. of 25% or less.

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