Three-dimensional network structure

Abstract

Provided is a biodegradable three-dimensional network structure which has excellent compression recoverability after compression at a use ambient temperature, has excellent compression durability on both sides, and has a small difference in compression durability on both sides. A three-dimensional network structure having a three-dimensional random ring-bonded structure, said three-dimensional network structure being characterized in that: the continuous lines are formed from a thermoplastic resin composition containing 70 mass% or more of a poly (butylene terephthalate)-adipate resin; the apparent density of one surface of the three-dimensional network structure is higher than the apparent density of the other surface of the three-dimensional network structure, and both the residual strain (R1) after 13,000 times of compression at a load of 750 N from the one surface side and the residual strain (R2) after 13,000 times of compression at a load of 750 N from the other surface side are 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 DEG C is 15% or less.

Description

Technical Field

[0001] This invention relates to three-dimensional mesh structures. Background Technology

[0002] To date, three-dimensional mesh structures have been widely used as cushioning materials in furniture, bedding such as beds, and vehicle seats such as trams, cars, and motorcycles, due to their excellent breathability and recyclability. With the recent acceleration of responses to environmental issues, research on these three-dimensional mesh structures has also progressed towards biodegradable polymers that degrade in a shorter time than previous polymers, and various technologies for biodegradable three-dimensional mesh structures have been disclosed to date.

[0003] Patent Document 1 discloses a technique for improving the plant retention properties of a mesh structure that enhances biodegradability. Patent Document 2 discloses a technique for locally bonding fibrous materials in a mesh structure that enhances biodegradability. Patent Document 3 discloses a technique that, by forming coil-spring-like or ring-shaped portions within a biodegradable three-dimensional structure, allows these portions to deform appropriately under compressive stress, thereby dispersing stress.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2001-032236

[0007] Patent Document 2: Japanese Patent Application Publication No. 2020-128608

[0008] Patent Document 3: Japanese Patent Application Publication No. 2000-328422 Summary of the Invention

[0009] The problem the invention aims to solve

[0010] Various attempts have been made to date to improve the functionality of biodegradable mesh structures, but biodegradable mesh structures with excellent recovery and cushioning properties under compression at the ambient temperature when used as cushioning materials are still unknown. In particular, among three-dimensional mesh structures with different cushioning properties on both sides, three-dimensional mesh structures with excellent compression durability on both sides are still unknown.

[0011] The present invention was made in view of the above circumstances, and its object is to provide a biodegradable three-dimensional mesh structure with excellent compression recovery after compression at the operating ambient temperature, excellent compression durability on both sides, and a small difference in compression durability between the two sides.

[0012] Solution for solving the problem

[0013] That is, the present invention includes the following inventions.

[0014] [1] A three-dimensional mesh structure, characterized in that it is a three-dimensional mesh structure composed of continuous lines and having a three-dimensional random ring joint structure, wherein the continuous lines are composed of a thermoplastic resin composition, wherein the thermoplastic resin composition contains more than 70% by mass of polybutylene terephthalate-adipate resin, wherein the apparent density of one surface of the three-dimensional mesh structure is higher than the apparent density of the other surface, wherein the residual strain R1 after repeated compression 13,000 times under a load of 750N from the one surface side and the residual strain R2 after repeated compression 13,000 times under a load of 750N from the other surface side are both less than 20%, wherein the absolute value of the difference between the value of R1 and the value of R2 is less than 10%, and the residual strain of the three-dimensional mesh structure under compression at 40°C is less than 15%.

[0015] [2] According to the three-dimensional network structure described in [1] above, the aforementioned polybutylene terephthalate resin comprises adipic acid units and terephthalic acid units, wherein the molar ratio of the aforementioned terephthalic acid units to the aforementioned adipic acid units is 1.0 or more and 3.0 or less.

[0016] [3] According to the three-dimensional network structure described in [1] or [2] above, wherein the melting point of the aforementioned polybutylene terephthalate resin is above 125°C and below 180°C.

[0017] [4] The apparent density of the three-dimensional network structure described in [1] to [3] above is 0.005 g / cm³. 3 Above and 0.20 g / cm 3 the following.

[0018] [5] According to any one of [1] to [4] above, the three-dimensional mesh structure wherein, when the larger of the 25% compression hardness when pressure is applied from one of the aforementioned surface sides and the 25% compression hardness when pressure is applied from the other of the aforementioned surface sides is set as H1 and the smaller of the two values ​​is set as H2, H1 / H2 is 1.03 or more.

[0019] [6] According to any one of [1] to [5] above, the three-dimensional mesh structure wherein, when the larger of the hardness when compressed at 40% when pressure is applied from one of the aforementioned surface sides and the hardness when compressed at 40% when pressure is applied from the other of the aforementioned surface sides is set as H3 and the smaller of the two values ​​is set as H4, H3 / H4 is 1.05 or more.

[0020] [7] The three-dimensional mesh structure according to any one of [1] to [6] above, wherein the absolute value of the difference between the compression deflection coefficient when pressure is applied from one of the aforementioned surface sides and the compression deflection coefficient when pressure is applied from the other of the aforementioned surface sides is 5.0 or less.

[0021] [8] The three-dimensional network structure according to any one of [1] to [7] above, wherein the enthalpy of the endothermic peak with the minimum value in the range of 30°C to 70°C is 2.5 J / g or less in the differential scanning calorimetry curve of the aforementioned continuous lines measured by a differential scanning calorimeter.

[0022] [9] The three-dimensional mesh structure according to any one of [1] to [8] above, wherein the absolute value of the difference between the apparent density of the aforementioned one surface and the apparent density of the aforementioned other surface is 0.015 g / cm³. 3 above.

[0023]

[10] A cushioning material comprising any one of the above [1] to [9] three-dimensional mesh structure and reversible.

[0024] The effects of the invention

[0025] The three-dimensional mesh structure of the present invention, by being configured as described above, exhibits excellent compression recovery after compression at the operating ambient temperature, as well as excellent compression durability on both sides and a smaller difference in compression durability between the two sides. Attached Figure Description

[0026] Figure 1 This is an example of a differential scanning calorimetry curve used to determine the enthalpy of the endothermic peak with a minimum value in the range of 30°C to 70°C for continuous lines constituting a three-dimensional network structure. Detailed Implementation

[0027] The three-dimensional mesh structure of the present invention is composed of continuous lines and has a three-dimensional random ring bonding structure, wherein the continuous lines are composed of a thermoplastic resin composition. The aforementioned thermoplastic resin composition comprises 70% by weight or more of polybutylene terephthalate-adipate resin. Furthermore, the apparent density of one surface of the three-dimensional mesh structure of the present invention is higher than the apparent density of the other surface.

[0028] By configuring it as described above, a three-dimensional mesh structure with excellent compression recovery after compression at the operating ambient temperature, excellent compression durability on both sides, and a small difference in compression durability between the two sides can be manufactured. The aforementioned operating ambient temperature refers to the temperature at which the three-dimensional mesh structure of the present invention is used as a cushioning material or similar product. In this specification, the operating ambient temperature is set to 40°C, and the residual strain after compression at 40°C is used as an indicator of the compression recovery after compression at the operating ambient temperature. Hereinafter, the compression recovery after compression at the operating ambient temperature will sometimes be simply referred to as "compression recovery." Furthermore, the residual strain after repeated compression is used as an indicator of compression durability; the smaller the residual strain after repeated compression, the better the compression durability. The methods for measuring these properties will be described later.

[0029] The following is a detailed explanation of each component.

[0030] <Thermoplastic Resin Composition>

[0031] The thermoplastic resin composition constituting the continuous lines contains 70% by mass or more of polybutylene terephthalate (PET) resin. By selecting PET resin from biodegradable resins and using a thermoplastic resin composition containing 70% by mass or more of PET resin, a three-dimensional network structure with excellent cushioning and biodegradability can be obtained. The content of PET resin relative to the aforementioned thermoplastic resin composition is preferably 75% by mass or more, more preferably 80% by mass or more, further 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 lines can be 100% by mass of PET resin.

[0032] Polybutylene terephthalate (PET) resin is a biodegradable thermoplastic resin, a copolymer of adipic acid, terephthalic acid, and butanediol. Its biodegradability makes it a promising solution for waste and microplastic problems. Furthermore, it allows for copolymerization of adipic acid, terephthalic acid, and butanediol in multiple stages, without the need for simultaneous copolymerization.

[0033] In polybutylene terephthalate (PET) resin, the molar ratio of the terephthalic acid unit to the adipic acid unit 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. By setting the aforementioned molar ratio to 1.0 or more, the compression durability of both sides of the three-dimensional network structure and the compression recovery after compression at the operating temperature are easily improved. On the other hand, by setting the aforementioned molar ratio to 3.0 or less, the flexibility is improved, and the difference in compression durability between the two sides is reduced. Therefore, it is suitable for cushioning materials, etc.

[0034] The melting point of the polybutylene terephthalate (PET) 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. By setting the melting point to 125°C or higher, the compression recovery of the three-dimensional mesh structure after compression at the ambient temperature can be easily improved. On the other hand, by setting the melting point to 180°C or lower, the softness is improved, making it suitable for use in cushioning materials, etc.

[0035] The melt flow rate (MFR) of the polybutylene terephthalate (PET) resin is preferably 3 g / 10 min to 60 g / 10 min. An MFR of 3 g / 10 min or higher readily improves compression recovery and compression durability on both sides. Conversely, an MFR of 60 g / 10 min or lower increases melt viscosity, allowing for a larger fiber diameter in the continuous line. A more preferred MFR is 4 g / 10 min to 50 g / 10 min, further 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. Furthermore, it is also preferable that the MFR of the thermoplastic resin composition constituting the continuous line falls within this range. The MFR of the resin can be measured using the method described in the examples below.

[0036] When using commercially available resins as polybutylene terephthalate (PET) resins, if the resin has a low melt flow rate (MFR), the MFR can be increased by adding water to the resin and hydrolyzing it during melt extrusion. Conversely, if the resin has a high MFR, the MFR can be decreased by drying the resin before melt extrusion.

[0037] The thermoplastic resin composition constituting the continuous line may also include other biodegradable resins besides polybutylene terephthalate (PET) resin. Preferred other biodegradable resins include polylactic acid, polylactic acid / polycaprolactone copolymer, polylactic acid / polyether copolymer, polyethylene succinate, polybutylene succinate, polybutylene adipate, polyglycolic acid, polycaprolactone, polyvinyl alcohol, and cellulose acetate. These can be used alone or in combination of two or more. For details, please refer to the positive list of classification number A-1 for green plastics (biodegradable plastics) of the Japan Bioplastics Association. The thermoplastic resin composition constituting the continuous line may also include resins other than biodegradable resins. Examples of such resins include thermoplastic resins such as polyolefins, polyurethanes, and polyesters.

[0038] In addition to polybutylene terephthalate-adipate resin, the thermoplastic resin composition constituting the continuous lines may also include resins containing other copolymer components other than adipic acid, terephthalic acid, and butylene glycol in the unit. Examples of other copolymer components include dicarboxylic acids other than terephthalic acid and adipic acid, glycols other than butylene glycol, polyalkylene glycols, and modifiers for chain extension and / or end-capping purposes. These can be used alone or in combination of two or more.

[0039] Other dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, pimelic acid, and octanoic acid. They can be used alone or in combination of two or more.

[0040] Examples of other glycols include methane glycol, ethylene glycol, propylene glycol, pentane glycol, and hexane glycol. Examples of polyalkylene glycols include polymethyl methacrylate (PMMA), polyethylene glycol, polypropylene glycol, and polybutylene glycol (polytetramethylene glycol). They can be used alone or in combination of two or more.

[0041] Examples of such modifiers include polyisocyanate compounds and diol compounds. Examples of polyisocyanate compounds include diisocyanate compounds.

[0042] Examples of diisocyanate compounds include hexamethylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, phenylenediethylene diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, tetramethylxylene diisocyanate, carbodiimide-modified MDI, and polymethylene phenyl polyisocyanate. These compounds can be used alone or in combination of two or more.

[0043] As monomers used to synthesize thermoplastic resin compositions constituting continuous lines, petroleum-derived monomers can be used. However, from the viewpoint of reducing environmental burden, it is preferable to use biomass-derived monomers. Regarding 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.

[0044] The total content of dicarboxylic acid units, adipic acid units, and terephthalic acid units in the thermoplastic resin composition constituting the continuous lines is preferably 70 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, more preferably 95 mol% or more, and particularly preferably 99 mol% or more, relative to 100 mol% of diol units in the thermoplastic resin composition constituting the continuous lines. Furthermore, the content of butanediol units is preferably 70 mol% or more, more preferably 80 mol% or more, further preferably 90 mol% or more, more preferably 95 mol% or more, and particularly preferably 99 mol% or more, relative to 100 mol% of diol units in the thermoplastic resin composition constituting the continuous lines.

[0045] To impart the specified function, the thermoplastic resin composition constituting the continuous lines may contain additives. Examples of additives include deodorizers, antibacterial agents, antifungal agents, anti-mite agents, odor removers, antifungal agents, fragrances, flame retardants, moisture absorbers, antioxidants, and lubricants. They may be used alone or in combination of two or more.

[0046] As antioxidants, well-known examples include phenolic antioxidants, phosphite antioxidants, thioether antioxidants, benzotriazole UV absorbers, triazine UV absorbers, benzophenone UV absorbers, NH-type hindered amine light stabilizers, and N-CH3-type hindered amine light stabilizers.

[0047] 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'-butidene bis(6-tert-butyl-m-cresol), and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid. Esters, pentaerythritol tetra[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)propionate], 2,4,6-tris(3',5'-di-tert-butyl-4'-hydroxybenzyl)trimethylbenzene, etc.

[0048] Examples of phosphite-based antioxidants include 3,9-bis(octadecoxy)-2,4,8,10-tetraoxa-3,9-diphosspiro[5.5]undecane, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosspiro[5.5]undecane, and 2,4,8,10-tetra(1,1-dimethylethyl)-6-[(2 [-ethylhexyl)oxy]-12H-dibenzo[d,g][1,3,2]dioxaphosphata-octacyclic, tris(2,4-di-tert-butylphenyl) phosphite, tris(4-nonylphenyl) phosphite, tetraalkyl(C12-15)-4,4'-isopropylidene diphenyl diphosphite, diphenyl(2-ethylhexyl) phosphite, diphenyl isodecanyl phosphite, triisodecyl phosphite, triphenyl phosphite, etc.

[0049] Examples of thioether-based antioxidants include bis[3-(dodecylthio)propionic acid]2,2-bis[[3-(dodecylthio)-1-oxopropoxy]methyl]-1,3-propanediyl ester and 3,3'-thiodipropionic acid ditridecyl ester.

[0050] To prevent the thermal degradation of thermoplastic resins, phenolic antioxidants and phosphite antioxidants can be used in combination.

[0051] Lubricants can be categorized into hydrocarbon waxes, higher alcohol waxes, amide waxes, ester waxes, and metal soaps.

[0052] <Continuous lines>

[0053] The three-dimensional mesh structure of the present invention is composed of continuous lines and has a three-dimensional random ring joint structure, wherein the continuous lines are composed of a thermoplastic resin composition. A continuous line refers to a filament having a continuous portion of at least 5 mm. The three-dimensional mesh structure is easily formed by bonding the intersections of the continuous lines. Therefore, the three-dimensional mesh structure preferably has adhesive portions where the intersections of the continuous lines are bonded together.

[0054] If the continuous lines constituting the three-dimensional mesh structure of the present invention have the same fineness, the moment of inertia of the hollow fiber section is higher than that of the solid fiber section. Therefore, the compressive resistance increases when using hollow fibers. Therefore, to obtain different cushioning properties on both sides, it is preferable to use both hollow and solid fibers. It should be noted that hollow fiber refers to a fiber with a hollow cross-section, and solid fiber refers to a fiber with a solid cross-section.

[0055] The hollow fiber has a hollowness ratio preferably of 1-30%, more preferably 2-30%, and particularly preferably 5-25% or more. The hollowness ratio can be measured by the method described in the examples below. It should be noted that the hollowness ratio of solid fiber is less than 1%.

[0056] Furthermore, to obtain different cushioning properties on both sides, it is preferable that the average fiber diameter of the hollow fibers is greater than that of the solid fibers. When the average fiber diameter of the hollow fibers is greater than that of the solid fibers, the difference between the average fiber diameters of the hollow fibers and 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 diameters of the hollow fibers and the solid fibers is 0.12 mm or more, it is easy to fabricate a three-dimensional mesh structure with different cushioning properties on both sides.

[0057] The average fiber diameter of the hollow fibers is preferably 0.1 mm or more and 3.0 mm or less, more preferably 0.3 mm or more and 2.0 mm or less, even more preferably 0.5 mm or more and 1.5 mm or less, and even more preferably 0.6 mm or more and 1.0 mm or less. The average fiber diameter of the solid fibers is preferably 0.1 mm or more and 3.0 mm or less, more preferably 0.2 mm or more and 2.0 mm or less, even more preferably 0.3 mm or more and 1.5 mm or less, and even more preferably 0.4 mm or more and less than 0.6 mm.

[0058] Solid fibers and hollow fibers are preferably approximately circular in shape, but there are also cases where compression resistance and tactile properties can be imparted by forming irregular cross-sections. Furthermore, without prejudice to the purpose of this invention, the continuous lines constituting the three-dimensional mesh structure of this invention can also be composite lines formed by combining continuous lines made of other thermoplastic resins. Examples of composite forms, where the lines themselves are composite, include sheath-core type, side-by-side type, and eccentric sheath-core type.

[0059] The enthalpy of fusion for the continuous lines is preferably 16 to 30 J / g. By setting the enthalpy of fusion to 16 J / g or higher, the compression durability and compression recovery of the three-dimensional mesh structure can be improved. Furthermore, by setting it to 30 J / g or lower, the flexibility of the three-dimensional mesh structure is improved, reducing noise generation during compression and recovery. The enthalpy of fusion is more preferably 17 J / g or higher, even more preferably 18 J / g or higher, even more preferably 19 J / g or higher, even more preferably 20 J / g or higher, and particularly preferably 21 J / g or higher. Furthermore, the enthalpy of fusion is more preferably 28 J / g or lower.

[0060] The enthalpy (J / g) of the endothermic peak of the continuous curve can be obtained from the DSC curve and from the integral value of the endothermic peak (melting peak). This DSC curve was obtained using a differential scanning calorimeter at a heating rate of 20°C / min under a nitrogen atmosphere with a sample mass of 2.0 mg ± 0.1 mg. The integral value can be obtained as follows: taking the point where the curve involving 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 ending point, a straight line connecting the starting and ending points is drawn. The integral value is then obtained by integrating the portion enclosed by the straight line and the curve. An example of a DSC curve is shown below. Figure 1 . Figure 1 The dashed line in the figure is a straight line connecting the start and end points of the endothermic peak (melting peak). The part enclosed by the dashed line and the curve is the integration region to be integrated.

[0061] In the DSC curve of the continuous lines constituting the three-dimensional network structure, measured using a differential scanning calorimeter, the enthalpy of the endothermic peak with a minimum value in the range of 30°C to 70°C is preferably 2.5 J / g or less. It should be noted that in this invention, the aforementioned "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. By making the low-temperature phase enthalpy 2.5 J / g or less, the compressive residual strain at 40°C is easily reduced. As a result, the collapse sensation 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.

[0062] <Composition of Three-Dimensional Network Structures>

[0063] Before describing the structure of the three-dimensional mesh structure of the present invention, a typical mesh structure comprising hollow fibers and solid fibers will first be described.

[0064] For example, by creating a laminated mesh structure formed by overlapping a mesh structure made of hollow fibers and a mesh structure made of solid fibers, different cushioning properties can be imparted on both sides. While such a laminated mesh structure can impart different cushioning properties on both sides, if pressure is gradually applied from the side of the mesh structure with lower compressibility, initially only the mesh structure with lower compressibility undergoes compressive deformation, and only the mesh structure with lower compressibility flexes independently of the mesh structure with higher compressibility. Then, in the stage where the mesh structure with lower compressibility cannot withstand the compressive load alone, the compressive stress is finally transferred to the mesh structure with higher compressibility, which begins to deform and flex. Therefore, if compression is repeated, fatigue accumulates in the mesh structure with lower compressibility, causing its thickness to decrease or its compressibility to reduce. That is, the above-mentioned layered mesh structure can impart different buffering properties on both sides, but when repeatedly pressurized, the residual strain of the mesh structure with low compression hardness increases, resulting in a layered mesh structure with significantly different compression durability on both sides.

[0065] As a type of laminated mesh structure other than the aforementioned laminated mesh structure, an integrated laminated mesh structure can be obtained by bonding a mesh structure formed of hollow fibers with a mesh structure formed of solid fibers using an adhesive. While such a laminated mesh structure can impart different cushioning properties on both sides, during periods of low compression, the two mesh structures deform and flex as a single unit relative to the applied compressive load. However, with repeated compression, stress concentrates at the bonding surface, leading to a decrease in adhesive strength and eventual peeling. Therefore, the difference in compressive durability between the two sides of the laminated mesh structure formed by bonding the structures together is also significant.

[0066] Furthermore, by layering solid fiber mesh structures by extruding solid fibers onto a mesh structure formed of hollow fibers, and then fusing them together to form a single unit, a laminated mesh structure with a three-dimensional mesh structure can be obtained. While such a laminated mesh structure can impart different cushioning properties on both sides, the low bonding strength at the interface between the hollow fiber layers and the solid fiber layers is due to the temporary solidification of the hollow fibers before the solid fibers are fused. If repeatedly subjected to compressive loads, stress concentrates at the interface, leading to interfacial delamination and consequently, reduced durability.

[0067] The inventors have discovered that by having a hybrid region (hereinafter referred to as "hybrid region") consisting of a hollow fiber-dominated region on one surface and a solid fiber-dominated region on the other surface, the difference in residual strain after repeated compression of the two surfaces can be reduced (which can reduce the difference in compression durability between the two surfaces).

[0068] The three layered mesh structures described above have virtually no or no mixed regions. However, if a three-dimensional mesh structure is fabricated by sequentially layering a region dominated by hollow fibers, a mixed region, and a region dominated by solid fibers from one surface to the other, a mixed region exists near the midpoint between the two surfaces. Therefore, the regions dominated by hollow fibers, the mixed region, and the region dominated by solid fibers do not separate, forming an integrated three-dimensional mesh structure. Consequently, even when compression is applied from the side with lower compression hardness, stress is transferred through the mixed region from the moment of few compression cycles to the side with higher compression hardness. The stress is efficiently dispersed along the thickness direction, and the mesh structure deforms and flexes as a whole relative to the compression load. This reduces the difference in compression durability between the side with lower compression hardness and the side with higher compression hardness. It should be noted that, in the case of a three-dimensional mesh structure formed by sequentially stacking regions mainly composed of hollow fibers, mixed regions, and regions mainly composed of solid fibers, from the viewpoint of making the apparent density of one surface higher than that of another surface, it is preferable that one surface (the surface of the high-density surface) has a region mainly composed of hollow fibers, and another surface (the surface of the low-density surface) has a region mainly composed of solid fibers.

[0069] <Physical Properties of Three-Dimensional Reticulated Structures>

[0070] The three-dimensional mesh structure of the present invention is characterized by small residual strain after repeated compression when pressure is applied from one surface (the surface of the high-density surface) and small residual strain after repeated compression when pressure is applied from the other surface (the surface of the low-density surface), resulting in excellent compressibility on both surfaces. Specifically, the residual strain R1 after repeated compressions of 13,000 times under a load of 750N from one surface (the surface of the high-density surface) and the residual strain R2 after repeated compressions of 13,000 times under a load of 750N from the other surface (the surface of the low-density surface) are both 20% or less. R1 and R2 are preferably 15% or less, more preferably 13% or less, further preferably 10.5% or less, and particularly preferably 9.5% or less.

[0071] A further feature of the three-dimensional mesh structure of the present invention is that the difference in compressive durability between the two sides is small, that is, the difference in residual strain after repeated compression when pressure is applied from one surface (the surface of the high-density surface) and from the other surface (the surface of the low-density surface) is small. Specifically, the absolute value of the difference between the values ​​of R1 and R2 is 10% or less. When the absolute value of the difference between the values ​​of R1 and R2 exceeds 10%, the difference in residual strain after repeated compression between the two surfaces becomes too large. When both sides of the three-dimensional mesh structure of the present invention are used, the side with a larger residual strain after repeated compression is more prone to collapse compared to the side with a smaller residual strain after repeated compression. The absolute value of the difference between the values ​​of R1 and R2 is preferably 9% or less, more preferably 8% or less, further preferably 6% or less, and particularly preferably 1.5% or less. The lower limit of the absolute value of the difference between the values ​​of R1 and R2 is not particularly limited, for example, it is 0% or more, preferably 0.1% or more.

[0072] The residual compressive strain at 40°C of the three-dimensional mesh structure is 15% or less, preferably 14.5% or less. By keeping the residual compressive strain at 40°C below 15%, compression recovery can be improved. There is no lower limit to the residual compressive strain at 40°C; for example, it is 1% or more, preferably 5% or more. The residual compressive strain at 40°C can be measured using the method described in the examples below.

[0073] When applying pressure to a high-density three-dimensional mesh structure, the compression hardness (hereinafter referred to as "25% compression hardness") during 25% compression in the thickness direction (compressed to 75% thickness) 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, further 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 setting the 25% compression hardness to 5.0 N / φ50 mm or more, the bottoming sensation when using the three-dimensional mesh structure as a cushioning material can be reduced. On the other hand, by setting the 25% compression hardness to 100 N / φ50 mm or less, the cushioning performance can be improved. The hardness at 25% compression can be determined by the method described in the examples below.

[0074] When applying pressure to a three-dimensional mesh structure from a low-density surface, 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, further 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 making the hardness at 25% compression 5.0 N / φ50 mm or more, the bottoming sensation when using the three-dimensional mesh structure as a cushioning material can be reduced. On the other hand, by making the hardness at 25% compression 100 N / φ50 mm or less, the cushioning performance can be improved.

[0075] If the larger of the hardness at 25% compression when pressure is applied to the high-density side and the harderness at 25% compression when pressure is applied to the low-density side is defined as H1, and the smaller value as H2, then H1 / H2 is preferably 1.03 or higher, more preferably 1.05 or higher, even more preferably 1.07 or higher, particularly preferably 1.10 or higher, and most preferably 1.13 or higher. When the ratio of hardness at 25% compression is less than 1.03, the difference in cushioning performance between the two sides may become smaller. There is no particular upper limit to H1 / H2, for example, it is 1.50 or lower, preferably 1.40 or lower.

[0076] When a high-density surface is compressed onto a three-dimensional mesh structure, the compression hardness (hereinafter referred to as "40% compression hardness") when 40% compression is applied in the thickness direction (compressed to 60% thickness) 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, further 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 setting the 40% compression hardness to 10 N / φ50 mm or more, the bottoming sensation when using the three-dimensional mesh structure as a cushioning material can be reduced. On the other hand, by setting the 40% compression hardness to 500 N / φ50 mm or less, the cushioning performance can be improved. The 40% compression hardness can be measured by the method described in the examples described later.

[0077] When applying pressure to a three-dimensional mesh structure from a low-density surface, the stiffness 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, further 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 ensuring a stiffness of 10 N / φ50 mm or more at 40% compression, the bottoming sensation when using the three-dimensional mesh structure as a cushioning material can be reduced. On the other hand, by ensuring a stiffness of 500 N / φ50 mm or less at 40% compression, the cushioning performance can be improved.

[0078] If 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 H3 and the smaller of the smaller value as H4, then H3 / H4 is preferably 1.05 or higher, more preferably 1.07 or higher, and even more preferably 1.09 or higher. When the ratio of hardness at 40% compression is less than 1.05, the difference in cushioning performance between the two sides may become smaller. There is no particular upper limit to H3 / H4, for example, it is 1.50 or lower, preferably 1.40 or lower.

[0079] The compressive flexural coefficient when pressure is applied from the high-density surface and the compressive flexural coefficient when pressure is applied from the low-density surface are both preferably 2.5 or higher and 10.0 or lower. When the compressive flexural coefficient is less than 2.5, the difference in cushioning performance relative to the change in compression ratio is sometimes small, resulting in poorer sleeping and riding comfort. Conversely, if it exceeds 10.0, the difference in cushioning performance due to the change in compression ratio becomes too large, which may sometimes cause a feeling of bottoming out and discomfort.

[0080] The compressive flexural coefficient when pressure is applied from a high-density surface 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 compressive flexural coefficient when pressure is applied from a low-density surface 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.

[0081] The absolute value of the difference between the compressive flexural coefficient when pressure is applied from the high-density surface and the compressive flexural coefficient when pressure is applied from the low-density surface is preferably 5.0 or less, more preferably 3.0 or less, further 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 compressive flexural coefficients exceeds 5.0, a bottoming sensation or discomfort may sometimes occur when using the surface with the high compressive flexural coefficient. The lower limit of the absolute value of the difference in compressive flexural coefficients is not particularly limited, for example, it is 0 or more, preferably 0.1 or more. In addition, it is preferable that the compressive flexural coefficient when pressure is applied from the low-density surface is greater than the compressive flexural coefficient when pressure is applied from the high-density surface.

[0082] The apparent density of the three-dimensional network structure is preferably 0.005 g / cm³. 3 ~0.20g / cm 3 More preferably, it is 0.010 g / cm³. 3 ~0.17g / cm 3 Further preferred value is 0.020 g / cm³. 3 ~0.15g / cm 3 The preferred value is 0.030 g / cm³. 3 ~0.12g / cm 3 The optimal value is 0.045 g / cm³. 3 ~0.10g / cm 3 By making the apparent density 0.005 g / cm³ 3 The above demonstrates an increase in the stiffness of the three-dimensional mesh structure. As a result, when using the three-dimensional mesh structure in cushioning materials, the tactile feedback can be reduced. Furthermore, the apparent density is 0.30 g / cm³. 3 The following results in improved softness, making it suitable for use in cushioning materials, etc. The apparent density of the three-dimensional mesh structure can be determined using the method described in the examples below.

[0083] The three-dimensional mesh structure of the present invention has different cushioning properties on its two sides; therefore, the apparent density of one surface is higher than that of the other surface. The absolute value of the difference between the apparent density of one surface (the high-density surface) and the apparent density of the other surface (the low-density surface) is preferably 0.015 g / cm³. 3 More preferably, it is 0.020~0.100 g / cm³. 3 More preferably, it is 0.030~0.080 g / cm³. 3 The apparent density of one surface and the other surface of the three-dimensional mesh structure can be determined by the method described in the embodiments described later.

[0084] The thickness of the three-dimensional mesh structure is preferably 10 mm to 120 mm. By having a thickness of 10 mm or more, the three-dimensional mesh structure can easily be used as a cushioning material, etc. Therefore, the lower limit of the aforementioned thickness is more preferably 15 mm or more, further preferably 20 mm or more, and particularly preferably 22 mm or more. On the other hand, considering the size of the manufacturing apparatus, the upper limit of the aforementioned thickness is more preferably 100 mm or less, further preferably 80 mm or less, and particularly preferably 50 mm or less. The thickness of the three-dimensional mesh structure can be measured using the method described in the embodiments described later.

[0085] The three-dimensional network structure preferably does not contain a bonding accelerator. This makes it easy to prevent over-hardening caused by excessive bonding within the three-dimensional network structure based on the bonding accelerator. Furthermore, it becomes easier to prevent a decrease in the density of the three-dimensional network structure associated with an excessive increase in the bonding range at each joint. Examples of the aforementioned bonding accelerators include polycaprolactone, polybutylene succinate, polybutylene sebacate, and polybutylene azelaate.

[0086] Three-dimensional network structures can be colored. Pigments, dyes, and other colorants can be used in the coloring process. The colorant can be contained in the resin before melt spinning, or it can be applied to the continuous lines after the three-dimensional network structure is formed by impregnation or coating.

[0087] There are no particular limitations on the shape of the three-dimensional mesh structure. Examples include plate-shaped, triangular prisms, square prisms and other polygons, cylinders, spheres, and combinations thereof. When molding into a three-dimensional mesh structure, it can be formed by using a limiting plate during the melt extrusion of the resin, or by cutting, hot pressing, etc.

[0088] The present invention also includes a cushioning material comprising the aforementioned three-dimensional mesh structure that can be used on both sides. "Usable on both sides" means that both the high-density and low-density sides can be used as cushioning material; the use of only one side as cushioning material is also included in the cushioning material of the present invention.

[0089] Examples of cushioning materials include cushioning materials used in office chairs, furniture, sofas, beds and other bedding, vehicle seats such as trams, cars, two-wheeled vehicles, child seats, and strollers, as well as cushioning materials used in floor mats, anti-collision components, anti-pinch components and other impact-absorbing pads.

[0090] <Manufacturing Method of Three-Dimensional Mesh Structures>

[0091] The following describes the manufacturing method of a three-dimensional mesh structure in which regions mainly composed of hollow fibers, mixed regions, and regions mainly composed of solid fibers are sequentially stacked from one surface side to the other.

[0092] A preferred method for manufacturing the aforementioned three-dimensional mesh structure includes the following steps: an extrusion step, in which molten thermoplastic resin composition is discharged from a nozzle; a molding step, in which a molded body formed into a three-dimensional mesh structure is obtained using a continuous line composed of the aforementioned thermoplastic resin composition extruded from the nozzle; and a heat treatment step, in which the molded body is heat-treated. It should be noted that, to avoid confusion with the finished three-dimensional mesh structure (the three-dimensional mesh structure after the heat treatment step), the three-dimensional mesh structure before the heat treatment step is completed is referred to as the molded body. The extrusion step and the molding step are not particularly limited as long as they are known manufacturing methods; specific manufacturing methods include, for example, the following methods.

[0093] First, regarding a multi-row nozzle with multiple orifices and multiple different orifice diameters, a thermoplastic resin composition containing polybutylene terephthalate (PET) resin is dispensed into the nozzle orifice, and discharged downwards from the nozzle at a spinning temperature above (melting point + 20°C) and below (melting point + 180°C) of the resin. Specific examples of the aforementioned multi-row nozzle will be described later. Next, in the molten state, continuous lines are brought into contact with each other and fused to form a three-dimensional network structure, while being held by a traction conveyor and cooled with cooling water in a water bath. Then, the solidified molded body is drawn out and subjected to water control or drying to obtain a molded body that is smoothed on both sides or one side. For these spinning and cooling processes, for example, refer to the description in Japanese Patent Application Publication No. 7-68061. In the case of smoothing only one side, continuous lines are discharged onto an inclined traction net, and in the molten state, the continuous lines are brought into contact with each other and fused. At this time, a three-dimensional network structure is formed, and only the shape of the traction net surface is softened, while cooling is performed. The resulting molded body is then subjected to heat treatment. It should be noted that drying the molded body can also be considered a form of heat treatment.

[0094] As a means of adjusting flexibility, water can 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 relative to the thermoplastic resin composition.

[0095] There are no particular limitations on the method of adding water to the thermoplastic resin composition. For example, the thermoplastic resin composition can be absolutely dried by vacuum drying at 100°C for more than 12 hours before the resin is discharged from the nozzle. Then, a predetermined amount of pure water can be added relative to 100% by mass of the absolutely dried thermoplastic resin composition.

[0096] Cooling of polybutylene terephthalate (PET) resin after melt molding is preferably performed using cooling water. PET resin sometimes experiences molding shrinkage before it solidifies. Therefore, it is desirable to form a three-dimensional mesh structure that takes into account the width and thickness of the molding shrinkage. For example, molding shrinkage can be reduced by lowering the melt curing temperature. Therefore, the temperature of the cooling water in the water bath is preferably below 20°C, more preferably below 15°C. Furthermore, the cooling time based on the cooling water is preferably 30 seconds or more. The aforementioned cooling and curing is preferably performed in a water bath.

[0097] The heat treatment can be performed using a commercially available hot air drying oven or in a hot water bath. The heat treatment temperature is preferably 50°C or higher. This increases the enthalpy of fusion. More preferably, the heat treatment temperature is 60°C or higher, and even more preferably 70°C or higher. The heat treatment can be performed multiple times at different temperatures.

[0098] When performing the aforementioned heat treatment, the melting point of the thermoplastic resin composition constituting the continuous lines is preferably 125°C or higher and 180°C or lower. The lower limit of the aforementioned melting point is more preferably 130°C or higher, further preferably 135°C or higher, even more preferably 140°C or higher, and particularly preferably 145°C or higher. On the other hand, the upper limit of the aforementioned melting point is more preferably 170°C or lower, and further preferably 160°C or lower. By setting the melting point to 125°C or higher, heat treatment can be performed within a suitable temperature range. On the other hand, by setting the melting point to 180°C or lower, the softness is improved, making it suitable for use in cushioning materials, etc.

[0099] The heat treatment time in each heat treatment step is preferably 1 minute or more. This increases the enthalpy of fusion. More preferably, the heat treatment time is 5 minutes or more, further 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 reduces yellowing, odor, and molecular weight reduction of polybutylene terephthalate resin associated with polymer decomposition and degradation during heat treatment. Furthermore, it improves productivity.

[0100] The molded body, after being cooled and solidified in a water bath, is preferably held at a temperature of 20°C to 50°C for at least 1 minute (preferably 10 minutes or more, more preferably 30 minutes or more) before heat treatment. During heat treatment, the thickness of the molded body can change due to its own weight. However, by holding it at a temperature of 20°C to 50°C after cooling and solidification, the thickness change of the molded body caused by heat treatment can be reduced. For example, after cooling and solidification in a water bath, a continuous dryer can be used to lower and maintain the temperature of the first half of the hot air oven, and then raise the temperature of the second half of the hot air oven for heat treatment.

[0101] To impart the specified function, the three-dimensional mesh structure may contain the various additives mentioned above. Additives may be included at any stage, from the manufacturing process of the thermoplastic resin to the molding process of the three-dimensional mesh structure, or a pre-contained polybutylene terephthalate (PET) resin may be used. Preferably, the content of the additives is adjusted by mixing the various additives with the resin during melt extrusion, according to the color and quality of the melted resin.

[0102] It should be noted that the manufacturing method of the three-dimensional mesh structure of the present invention is not limited to the above-described manufacturing method. For example, the three-dimensional mesh structure of the present invention can also be manufactured by sequentially stacking a mesh structure formed of hollow fibers, a mesh structure formed of a mixture of solid fibers and hollow fibers, and a mesh structure formed of solid fibers and integrating them by bonding.

[0103] <nozzle>

[0104] The following is a detailed description of a multi-row nozzle with multiple orifices and multiple different orifice diameters.

[0105] To obtain the three-dimensional mesh structure of the present invention, the nozzle shape, nozzle cross-section, and nozzle orifice arrangement are preferably optimized. Regarding the nozzle shape, the orifice diameter for forming fine fibers is preferably 1.5 mm or less, and the orifice diameter for forming coarse fibers is preferably 2.0 mm or more. Furthermore, the orifice shape for forming coarse fibers is preferably hollow; examples include C-shaped nozzles and triple-bridge shaped nozzles. From a pressure resistance perspective, triple-bridge shaped nozzles are preferred. Regarding the orifice spacing, both the orifices for forming fine fibers and coarse fibers are preferably 4 mm or more and 12 mm or less, more preferably 5 mm or more and 11 mm or less. Examples of nozzle orifice arrangements include grid arrangements, circular arrangements, and staggered arrangements. From the viewpoint of the quality of the mesh structure, grid arrangements or staggered arrangements are preferred. Here, the orifice spacing refers to the distance between the centers of the nozzle orifices. There are orifice spacing in the width direction of the obtained three-dimensional mesh structure (hereinafter referred to as "width direction orifice spacing") and orifice spacing in the thickness direction of the obtained three-dimensional mesh structure (hereinafter referred to as "thickness direction orifice spacing"). Preferably, the spacing between holes in the width direction and the spacing between holes in the thickness direction are both within the above range.

[0106] As a nozzle for obtaining a three-dimensional mesh structure with a mixed region, a nozzle consisting of the following three groups (group a, mixed group ab, and group b) can be listed. Preferably, group b, mixed group ab, and group a are arranged sequentially from top to bottom in the thickness direction (height direction) of the nozzle arrangement area.

[0107] Group A: A group of perforations for solid fibers, consisting of multiple rows of perforations arranged along the thickness direction.

[0108] AB hybrid group: A group of holes consisting of multiple rows arranged along the thickness direction, with a mixture of holes for solid fibers and holes for hollow fibers.

[0109] Group b: Hollow fiber pore group consisting of multiple rows of pores arranged along the thickness direction.

[0110] Other nozzles used to obtain a three-dimensional mesh structure with mixed regions include nozzles consisting of the following two groups (group α and group β).

[0111] Group α: A group of perforations for solid fibers, consisting of multiple rows of perforations arranged along the thickness direction.

[0112] β group: Hollow fiber pore group consisting of multiple rows of pores arranged along the thickness direction.

[0113] From the viewpoint of simplifying the nozzle structure, a nozzle composed of the aforementioned α group and β group is preferred. Preferably, the upper half of the nozzle configuration area in the thickness direction (height direction) is the β group and the lower half is the α group. There are two orifice groups for the nozzle, but the fibers spun near the boundary between the α group and the β group form a mixed region of solid and hollow fibers. Therefore, the mesh structure of the present invention, composed of three regions in the thickness direction, can be obtained.

[0114] To obtain a three-dimensional mesh structure with a small difference in compressive durability between the two sides, it is preferable to reduce the difference between the width-direction spacing of the orifices of the solid fibers and the width-direction spacing of the hollow fibers. Specifically, it is preferably 2 mm or less, more preferably 1 mm or less, and even more preferably 0 mm, i.e., the width-direction spacing is the same. The detailed reason why a smaller difference in width-direction spacing between the solid fiber orifices and the hollow fiber orifices results in a smaller difference in compressive durability between the two sides is not yet clear, but it is speculated as follows. It should be noted that, hereinafter, the difference between the width-direction spacing of the solid fiber orifices and the hollow fiber orifices will be simply referred to as the "width-direction spacing difference".

[0115] In a hybrid region composed of solid and hollow fibers, a small difference in the spacing between holes in the width direction indicates that the number of solid and hollow fibers in the hybrid region is similar. If the number of solid and hollow fibers is similar, each solid fiber has multiple contact points with a hollow fiber, and each hollow fiber has multiple contact points with a solid fiber. Therefore, stress is easily transmitted when pressure is applied from either side, thus the difference in compressive durability between the two sides can be considered smaller.

[0116] In contrast, when a mesh structure is formed from nozzles with a large difference in the spacing between holes in the width direction, in the mixed region composed of solid and hollow fibers—for example, when the number of solid fibers is greater than the number of hollow fibers—a portion of the solid fibers in the mixed region has almost no contact points with the hollow fibers. Therefore, it can be considered that when pressure is applied from the side dominated by solid fibers, the solid fibers, which have almost no contact points with the hollow fibers, cannot adequately transfer stress to the hollow fibers. Furthermore, it can be considered that when pressure is applied from the side dominated by hollow fibers, the hollow fibers cannot adequately transfer stress to the solid fibers, which have almost no contact points with the hollow fibers.

[0117] That is, when a three-dimensional mesh structure is formed by nozzles with a large difference in the spacing between holes in the width direction, in the mixed region composed of solid and hollow fibers, the stress transmission direction is dispersed to the thickness direction and the direction orthogonal to the thickness direction, thus reducing the stress transmission efficiency. As a result, it can be considered that the difference in compression durability increases when pressure is applied from the solid fiber side versus the hollow fiber side.

[0118] This application claims a benefit based on priority of Japanese Patent Application No. 2023-168862, filed on September 28, 2023. The entire contents of the description of Japanese Patent Application No. 2023-168862, filed on September 28, 2023, are incorporated herein by reference.

[0119] Example

[0120] The present invention will be described in more detail below with examples. It should be noted that the present invention is not limited to the examples described below. Furthermore, modifications may be made within the scope of the foregoing / hereafter described, and all such modifications are included within the scope of protection of the present invention.

[0121] The characteristic values ​​of the three-dimensional mesh structures in Examples 1-4 and Comparative Examples 1 and 2 were determined based on the following method. It should be noted that the size of the sample described below is the standard, but in the case of insufficient sample size, a sample of an achievable size was used for measurement.

[0122] (1) Average fiber diameter

[0123] The three-dimensional mesh structure was cut into 10cm × 10cm pieces along both longitudinal and transverse directions. Continuous lines, approximately 5mm long, were collected from 10 locations to form hollow cross-sections. Next, an optical microscope was used to focus on the location where the fiber diameter of the collected continuous lines was to be measured, and the diameter was determined. The average fiber diameter of the hollow cross-sections at the 10 locations was calculated (n=10). The average fiber diameter of the solid cross-sections was calculated in the same manner as the average fiber diameter of the hollow cross-sections.

[0124] (2) Hollowness ratio

[0125] Ten continuous lines were randomly selected from a three-dimensional mesh structure. These lines were then cut into circular slices and placed vertically along the fiber axis on a glass slide. The fiber cross-section along the cutting direction of the slices was observed using an optical microscope. Only continuous lines with hollow fiber cross-sections were selected. The area within the outer perimeter of the fiber (a) and the area of ​​the hollow portion (b) were calculated. The hollow ratio was calculated based on the following formula, and the average hollow ratio of the selected continuous lines with hollow cross-sections was obtained (n=10).

[0126] Hollow rate (%) = (b) / (a) × 100

[0127] (3) Thickness and apparent density

[0128] The three-dimensional mesh structure was cut into 10cm × 10cm pieces along both the longitudinal and transverse directions, and the resulting samples were placed under no-load conditions for 24 hours. Then, using a test piece thickness gauge (KOBUNSHI KEIKI CO.,LTD., FD-80N type), the height at the center point was measured, and this height was taken as the thickness of the three-dimensional mesh structure. Next, the sample was placed on an electronic balance, and its weight was measured. The height of the sample was then compared with the area (100cm²) of the cross-section. 2 The volume of the sample is obtained by multiplying the weight of the sample by the volume, and the apparent density is obtained by dividing the weight of the sample by the volume. The above operation is performed three times to obtain the average value of the thickness and apparent density of the three-dimensional network structure (n=3).

[0129] (4) Apparent density of one surface and another surface

[0130] The three-dimensional mesh structure was cut into 5cm×5cm pieces along the longitudinal and transverse directions. The thickness (t1) and weight (w1) of the obtained samples were measured in the same manner as in (3). Then, the samples were cut with the cutting surface perpendicular to the thickness direction and bisected in the thickness direction. The thickness (t2) and weight (w2) of the hollow fiber-based samples were measured, and the weight (w2 (g)) was divided by the volume (5×5×t2 (cm)). 3 From this, the apparent density (g / cm³) of the sample mainly composed of hollow fibers was calculated. 3 The apparent density of a surface is then calculated by subtracting the weight (w2(g)) from the weight (w1(g)) and dividing the volume (5 × 5 × (t1 - t2) (cm³)). 3 From this, the apparent density (g / cm³) of the sample, which is mainly composed of solid fibers, can be calculated. 3 ), which serves as the apparent density of another surface. It should be noted that these apparent densities are set as the average value of n=3.

[0131] (5) The molar ratio of the aforementioned terephthalic acid units to adipic acid units in the polybutylene terephthalate-adipate resin

[0132] The molar ratio of terephthalic acid units to adipic acid units in the polybutylene terephthalate-adipate resin is determined by a resonance frequency of 600 MHz. 1 The measurements were performed using 1H-NMR. The measuring apparatus used was a Bruner AVANCE-NEO600 NMR system, and the measurements were conducted as follows.

[0133] Dissolve 10-15 mg of the sample in deuterated chloroform / trifluoroacetic acid (85 / 15, volume ratio), then fill the NMR tube with the solution for analysis. Use deuterated chloroform as the blocking solvent, set the standby time to 1 second, the data acquisition time to 4 seconds, and the cumulative number of measurements to 64.

[0134] When the peak value of chloroform was set to 7.28 ppm, the peak value of adipic acid was detected at 2.45 ppm, and the peak value of terephthalic acid was detected at 8.15 ppm.

[0135] When the peak integral value of adipic acid is set as A and the peak integral value of terephthalic acid is set as B, the molar ratio of the aforementioned terephthalic acid unit to the adipic acid unit in the poly(butylene terephthalate-adipate) resin can be expressed by the following formula.

[0136] Mole ratio = ((B / 4) ÷ (A / 4))

[0137] (6) Melting point (Tm)

[0138] Samples were collected from a three-dimensional mesh structure and weighed to a mass of 2.0 mg ± 0.1 mg. Then, the endothermic peak (melting peak) temperature was determined based on the DSC curve obtained using a differential scanning calorimeter (TA Instruments, Discovery DSC25) under a nitrogen atmosphere at a heating rate of 20 °C / min. This process was repeated three times, and the average melting point was calculated (n=3).

[0139] (7) Enthalpy of fusion

[0140] Samples were collected from a three-dimensional network structure and weighed to a mass of 2.0 mg ± 0.1 mg. Then, the enthalpy of fusion (J / g) was determined from the integral value of the endothermic peak (melting peak) based on the DSC curve obtained using a differential scanning calorimeter (TA Instruments Discovery DSC25) under a nitrogen atmosphere at a heating rate of 20 °C / min.

[0141] It should be noted that, regarding the integral value of the endothermic peak (melting peak), the starting point is the point where the curve involving the endothermic peak (melting peak) begins to deviate from the low-temperature baseline, and the ending point is the point where it begins to contact the high-temperature baseline. A straight line connecting the starting and ending points is drawn, and the portion enclosed by the straight line and the curve is integrated to obtain the enthalpy of fusion. This process is repeated three times to obtain the average enthalpy of fusion (n=3). Furthermore, the starting point is taken as the melting initiation temperature (°C).

[0142] (8) Low-temperature phase enthalpy

[0143] In the DSC curve mentioned above (7), the enthalpy of the endothermic peak with the minimum value in the range of 30℃ to 70℃ is obtained and defined as the low-temperature phase enthalpy. Regarding the integral value of the endothermic peak in the aforementioned low-temperature phase region, the point where the curve involving the aforementioned endothermic peak begins to leave the low-temperature side baseline is taken as the starting point, and the point where it begins to contact the high-temperature side baseline is taken as the ending point. A straight line connecting the aforementioned starting point and ending point is drawn, and the range of 30℃ to 70℃ within the part enclosed by the aforementioned straight line and curve is integrated to obtain the low-temperature phase enthalpy. The aforementioned operation is performed 3 times to obtain the average value of the low-temperature phase enthalpy (n=3). In addition, the aforementioned starting point is set as the low-temperature phase initiation temperature (℃). An example of experimental data is shown in Figure 1 .

[0144] (9) Melt Flow Rate (MFR)

[0145] After vacuum drying the polybutylene terephthalate (PET) resin at 80°C for at least 2 hours, the melt flow rate (MFR) was rapidly measured to minimize the amount of moisture in the air. The melt flow rate was measured using a Toyo Seiki F-F01 melt indexer according to ISO 1133. The measurement temperature was set to 190°C, and the load was set to 2.16 kg. The above procedure was performed three times, and the average melt flow rate was calculated (n=3).

[0146] (10) Residual strain under compression at 40℃

[0147] The three-dimensional mesh structure was cut into 10cm × 10cm pieces. Next, the thickness (c) of the obtained sample before treatment was measured using the method described in (3) above. The sample with the measured thickness was clamped in a fixture capable of maintaining 50% compression and placed in a dryer controlled at 40°C for 22 hours. Afterward, the sample was removed, cooled, and the thickness (d) after removing the compressive strain and standing for 30 minutes was measured using the method described in (3) above. The thicknesses were substituted into the following formula to calculate the residual compressive strain at 40°C. The above operation was performed three times, and the average value of the residual compressive strain at 40°C was calculated (n=3).

[0148] Residual compressive strain at 40℃ (%) = ((c) - (d)) / (c) × 100

[0149] (11) Residual strain after repeated compression

[0150] The three-dimensional mesh structure was cut into 10cm × 10cm pieces. Next, the thickness (e) before compression was measured using the method described in (3) above. Then, the sample with the measured thickness was repeatedly compressed from one surface (high-density surface) under the following conditions using a constant-load repeated compression tester (STM-536, Polymer Instruments Co., Ltd.). The compression head used was a circular head with a radius of curvature of 25 ± 1 mm at the edge of the bottom surface, a diameter of 250 ± 1 mm, a thickness of 3 mm, and a flat lower surface. The load was set to 750 N ± 20 N, the compression frequency to 70 ± 5 times per minute, and the number of repeated compressions to 13,000. After repeated compression, 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 substituted into the following formula to calculate the residual strain after repeated compression. The aforementioned operation was performed three times, and the average residual strain after repeated compression from one surface side was calculated (n = 3).

[0151] Residual strain after repeated compression (%) = ((e) - (f)) / (e) × 100

[0152] In addition, another specimen was prepared and repeatedly compressed from the other surface (low-density side) of the specimen. Otherwise, the residual strain after repeated compression from the other surface side was determined using the same method as described above.

[0153] Finally, the residual strain after repeated compression from one surface side is set as R1, and the residual strain after repeated compression from the other surface side is set as R2. The absolute value of the difference between the values ​​of R1 and R2 is then calculated.

[0154] (12) Hardness at 25% compression

[0155] The three-dimensional mesh structure was cut into 10cm × 10cm pieces, and the resulting samples were placed under no-load conditions at 23℃ ± 2℃ for 24 hours. Then, measurements were performed at 23℃ ± 2℃ using an Autograph AG-X plus (Shimadzu Corporation) according to ISO 2439 (2008) E method. Specifically, a pressure plate with a diameter (φ) of 50mm was placed at the center of one surface (high-density surface) of the sample, and the thickness was measured when the load reached 0.5N, which was taken as the initial thickness. Using this position of the pressure plate as the zero point, a pre-compression was performed at a speed of 100mm / min until 75% of the initial thickness was reached. The pressure plate was then returned to the zero point at the same speed and left in this state for 4 minutes. Immediately afterwards, the sample was compressed at a speed of 100mm / min to 75% of the initial thickness, and the load at this point was measured. This load was taken as the hardness (N / φ50mm) at 25% compression when pressure was applied from one surface side. Perform the above operation three times to obtain the average hardness at 25% compression when pressure is applied from one surface side (n=3).

[0156] In addition, a pressure plate with a diameter (φ) of 50 mm is placed at the center of the other surface (low-density surface) of the specimen. Otherwise, the 25% compression hardness when pressure is applied from the other surface side is determined using the same method as described above. It should be noted that different specimens are prepared for the determination of compression hardness when pressure is applied from one surface side and compression hardness when pressure is applied from the other surface side, as will be the case below (13) and thereafter.

[0157] Finally, the larger of the 25% compression hardness when pressure is applied from one surface side and the 25% compression hardness when pressure is applied from the other surface side is set as H1, and the smaller value is set as H2, and the value of H1 / H2 is calculated.

[0158] (13) Hardness at 40% compression

[0159] After 4 minutes of placement, the material is immediately compressed to 60% of its initial thickness at a speed of 100 mm / min. The load at this time is measured and taken as the 40% compression hardness (N / φ50mm) when pressure is applied from one surface side. Otherwise, the 40% compression hardness when pressure is applied from one surface side is determined by the method described in (12) above.

[0160] In addition, a pressure plate with a diameter (φ) of 50 mm was placed at the center of the other surface (low density surface) of the sample. In addition, the 40% compression hardness when pressure was applied from the other surface was determined using the same method as when pressure was applied from one surface side.

[0161] Finally, the larger of the 40% compression hardness when pressure is applied from one surface side and the 40% compression hardness when pressure is applied from the other surface side is set as H3, and the smaller value is set as H4, and the value of H3 / H4 is calculated.

[0162] (14) Compression deflection coefficient

[0163] After 4 minutes of placement, the material is immediately compressed to 35% of its initial thickness at a speed of 100 mm / min. The load at this time is measured and taken as the 65% compression hardness (N / φ50mm) when pressure is applied from one surface side. Otherwise, the 65% compression hardness when pressure is applied from one surface side is determined by the method described in (12) above.

[0164] In addition, a pressure plate with a diameter (φ) of 50 mm was placed at the center of the other surface (low density surface) of the sample. In addition, the 65% compression hardness when pressure was applied from the other surface was determined using the same method as when pressure was applied from one surface side.

[0165] The compressive flexural coefficient when pressure is applied from one surface side is obtained by dividing the hardness at 65% compression by the hardness at 25% compression. This value is then used as the compressive flexural coefficient when pressure is applied from one surface side. This process is repeated three times to obtain the average compressive flexural coefficient when pressure is applied from one surface side (n=3). The compressive flexural coefficient when pressure is applied from the other surface side is obtained using the same method.

[0166] Finally, the absolute value of the difference between the compressive deflection coefficient when pressure is applied from one surface side and the compressive deflection coefficient when pressure is applied from the other surface side is obtained.

[0167] Polybutylene terephthalate (PET) resin is synthesized by the following method.

[0168] <Resin A>

[0169] In a reactor equipped with a stirrer, thermometer, and distillation condenser, 1.5 mol of 1,4-butanediol, 0.4 mol of adipic acid, and 0.6 mol of dimethyl terephthalate were mixed. Then, 300 ppm of tetrabutyl titanate (manufactured by Aldrich) as a titanium-based catalyst was added to the mixture. Subsequently, transesterification and esterification reactions were carried out at 220°C for 2 hours under normal pressure to prepare a prepolymer. The prepolymer was then heated to 240°C and subjected to polycondensation at 0.1 mmHg for 2 hours. After cooling, the resulting resin A was cut into granules using a granulator.

[0170] <Resin B>

[0171] In the manufacture of resin A, adipic acid was changed to 0.53 mol and dimethyl terephthalate was changed to 0.47 mol. Otherwise, resin B was manufactured using the same method. After cooling, the obtained resin B was cut into granules using a granulator.

[0172] [Example 1]

[0173] Using resin A as raw material, molten resin is discharged downwards from the nozzle at a spinning temperature of 240℃, 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. It should be noted that in the effective surface of the nozzle, which is 96 mm in width and 31 mm in thickness, the upper half in the thickness direction (height direction) is equipped with an object consisting of orifices with a hollow cross-section of 3.0 mm outer diameter and 2.6 mm inner diameter, arranged in a staggered pattern with a hole spacing of 6 mm in width and 5.2 mm in thickness. The lower half in the thickness direction is equipped with an object consisting of orifices with a solid cross-section of 1.0 mm outer diameter, arranged in a staggered pattern with a hole spacing of 6 mm in width and 5.2 mm in thickness.

[0174] For molten resin, a water tank is configured such that the surface of the cooling water is 30 cm below the nozzle face of the discharge nozzle, and the water temperature is set to 12°C. A pair of traction conveyor belts are arranged in the water tank with a portion protruding above the water surface. The traction conveyor belts have a 20 cm wide stainless steel ring mesh, which is arranged parallel to the width direction of the nozzle face. The opening width of the ring mesh is set to 30 mm. To form the side face, an aluminum plate is arranged at a 90-degree angle relative to the mesh direction, and water is flowed at a rate of 1.0 L / min to form the side face.

[0175] Molten resin is discharged in a linear fashion through the openings of the conveyor belt mesh, the conveyor belt mesh, and the aluminum plates on the side surfaces. This causes the continuous lines to fall and bend, forming loops, and the contact parts to fuse and form a three-dimensional mesh structure. The molten three-dimensional mesh structure is then held on both sides by a traction conveyor belt and simultaneously introduced into cooling water at a speed of 0.86 m / min to solidify. This flattens both sides in the thickness and side directions. Next, it is cut to a specified size and left to stand at 25°C for 1 hour. Then, it is heat-treated with 90°C hot air for 20 minutes to obtain a three-dimensional mesh structure with a width of 100 mm.

[0176] [Example 2]

[0177] The single-hole discharge rate of the hollow hole was set to 1.8 g / min, the single-hole discharge rate of the solid hole was set to 1.20 g / min, and the traction speed was set to 1.43 m / min. Otherwise, a three-dimensional mesh structure was obtained in the same manner as in Example 1.

[0178] [Example 3]

[0179] The single-hole discharge rate of the hollow hole was set to 1.8 g / min, the single-hole discharge rate of the solid hole was set to 1.20 g / min, the distance from the nozzle surface to the surface of the cooling water in the water tank was set to 40 cm, and the traction speed was set to 1.43 m / min. Otherwise, a three-dimensional mesh structure was obtained in the same manner as in Example 1.

[0180] [Example 4]

[0181] Instead of resin A, a substance containing 0.1% water at 100% by mass of the solid component of resin A as a raw material was used. The distance from the nozzle surface to the surface of the cooling water in the water tank was set to 18 cm, and the traction speed was set to 0.95 m / min. Otherwise, a three-dimensional mesh structure was obtained in the same manner as in Example 1.

[0182] [Comparative Example 1]

[0183] The nozzle, with a width of 96 mm and a thickness of 31 mm, is formed by alternating arrangements of orifices with a hollow cross-section (outer diameter 3.0 mm, inner diameter 2.6 mm) and a thickness of 7.5 mm, with holes spaced 10 mm apart in the width direction and 7.5 mm apart in the thickness direction, and orifices with a solid cross-section (outer diameter 0.7 mm) and a thickness of 3.7 mm apart in the width direction. The nozzle is constructed by setting the single-hole discharge rate of the hollow orifices to 2.0 g / min, the single-hole discharge rate of the solid orifices to 0.50 g / min, the distance from the nozzle surface to the surface of the cooling water in the tank to 18 cm, and the traction speed to 1.14 m / min. Otherwise, a three-dimensional mesh structure is obtained in the same manner as in Example 1.

[0184] [Comparative Example 2]

[0185] Resin B was used as the raw material, the spinning temperature was set to 190°C, the distance from the nozzle surface to the surface of the cooling water in the water tank was set to 28cm, and the traction speed was set to 0.95m / min. Otherwise, a three-dimensional mesh structure was obtained in the same manner as in Example 1.

[0186] Table 1 shows the manufacturing conditions and characteristics of the obtained three-dimensional mesh structures in Examples 1-4 and Comparative Examples 1 and 2. It should be noted that the values ​​for characteristics evaluated multiple times in Table 1 are average values.

[0187] [Table 1]

[0188]

[0189] The three-dimensional mesh structures in Examples 1-4 exhibit excellent compression recovery after compression at ambient temperature, as well as excellent compression durability on both sides with a small difference in compression durability between the two sides.

Claims

1. A three-dimensional mesh structure, characterized in that, It is a three-dimensional mesh structure composed of continuous lines and having a three-dimensional random ring joint structure, wherein the continuous lines are composed of a thermoplastic resin composition. The thermoplastic resin composition comprises more than 70% by weight of polybutylene terephthalate-adipate resin. The apparent density of one surface of the three-dimensional mesh structure is higher than the apparent density of the other surface. The residual strain R1 after repeated compressions with a load of 750 N for 13,000 cycles from one surface and the residual strain R2 after repeated compressions with a load of 750 N for 13,000 cycles from the other surface are both less than 20%. The absolute value of the difference between the values ​​of R1 and R2 is less than 10%. The residual compressive strain of the three-dimensional mesh structure at 40°C is less than 15%.

2. The three-dimensional mesh structure according to claim 1, wherein, The polybutylene terephthalate-adipate resin comprises adipic acid units and terephthalic acid units, wherein 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 mesh structure according to claim 1, wherein, The melting point of the polybutylene terephthalate-adipate resin is above 125°C and below 180°C.

4. The three-dimensional mesh structure according to claim 1, has an apparent density of 0.005 g / cm³. 3 Above and 0.20 g / cm 3 the following.

5. The three-dimensional mesh structure according to claim 1, wherein, When 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 set as H1 and the smaller of the smaller value is set as H2, H1 / H2 is 1.03 or higher.

6. The three-dimensional mesh structure according to claim 1, wherein, When 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 set as H3 and the smaller of the smaller value is set as H4, the ratio of H3 to H4 is 1.05 or higher.

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

8. The three-dimensional mesh structure according to claim 1, wherein, In the differential scanning calorimetry curve of the continuous lines obtained using a differential scanning calorimeter, the enthalpy of the endothermic peak with the minimum value in the range of 30°C to 70°C is less than 2.5 J / g.

9. The three-dimensional mesh structure according to claim 1, wherein, 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 / cm³. 3 above.

10. A cushioning material comprising a three-dimensional mesh structure as described in any one of claims 1 to 9, and usable on both sides.

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