JP4362465B2 - Cushion structure - Google Patents

Description

  The present invention relates to a cushion structure made of a three-dimensional multi-woven structure substantially composed of fibers. More specifically, a cushion structure that can be used in fields requiring breathability, cushioning, washability, etc., such as bedding, vehicle seats, chair seats, cushion seats, reception seats, or sports materials. About.

  Conventionally, a cushion structure having a three-dimensional structure has been used in a wide range of fields, but a three-dimensional structure composed of a resin foam represented by a urethane mat and a fiber material has been put into practical use. The resin foam is easy to mold, but it is inferior in air permeability because the foamed space is not communicated. Moreover, it is easy to deform | transform with respect to compression for a long time, and compression recovery power falls.

  As a three-dimensional structure made of a fiber material, for example, there is one that forms a three-dimensional structure with a woven structure described in Patent Document 1. In Patent Document 1, a three-dimensional multi-woven structure in which the woven structure of filament fibers is three-dimensional, the surface void layer portion is formed with convex portions of a certain size and shape, and the intermediate void layer portion is unidirectional. 1 or 2 or more layers having a plurality of communicating cavities parallel to each other are formed. As described in Patent Document 2, such a three-dimensional multi-woven structure is formed by weaving a multi-woven structure using high-shrinkage yarns for warps and then shrinking the high-shrinkage yarns to form a three-dimensional structure. As a similar multilayer fabric structure, for example, there is a corrugated cardboard structure fabric described in Patent Document 3.

Further, as described in Patent Document 4, there is a three-dimensional knitted fabric composed of two layers of front and back knitted fabrics and connecting yarns connecting these two layers of knitted fabrics. Patent Document 5 describes a three-dimensional woven fabric in which two layers of front and back are woven and these two layers are connected by a connecting yarn.
Japanese Patent No. 2883288 JP-A-6-128837 Registered Utility Model No. 3010467 Japanese Patent No. 3394183 JP 2003-13337 A

  When a three-dimensional structure made of the above-described fiber material is used as a cushioning material, a lateral shift that occurs in a portion compressed by a load is applied. For example, FIG. 11 is a partially enlarged perspective view of a conventional three-dimensional multi-woven structure. In this conventional example, the ground texture 100 woven in plain weave is vertically woven in multiple layers, and a number of high shrinkage yarns 101 are woven in the warp direction. Are entangled with each other and bent into a wave shape. Since the ground structure 100 is curved in a wave shape, a layer structure L in which a large number of communicating void portions 102 are arranged along the weft direction is formed.

  In such a layer structure, the warp yarns 100a constituting the ground structure 100 are entangled with the upper and lower high-shrinkage yarns 101 so as to maintain a space so that the communication gap 102 is maintained. It is responsible for 102 skeleton formation. And the weft thread 100b which comprises the ground structure 100 is woven in the warp thread 100a, The whole warp thread 100a is integrated and functions.

  When a load is applied to such a conventional layer structure, the warp 100a responsible for forming the skeleton is deflected by receiving the load, and the communication gap portion 102 is crushed. As a result of the elastic recovery, the communication gap 102 returns to its original state. Therefore, since the elastic force which always repels it with respect to a load generate | occur | produces, it comes to have cushioning properties.

  FIG. 12 is a schematic view of the conventional three-dimensional multi-woven structure before the load is applied (FIG. 12 (a)) and after the load is applied (FIG. 12 (b)) as viewed from the warp direction of the layer structure. It is. When the warp 100a is compressed in the vertical direction by a load, it is once compressed and bent, but as shown in FIG. 12B, the warp 100a is inclined so as to fall in the weft direction. When the warp 100a is tilted so as to fall down, the upper part of the warp 100a moves in the weft direction, so that the surface of the three-dimensional structure is felt as if it is laterally displaced. Such lateral displacement becomes more prominent as the interval between the communication gaps becomes larger. Therefore, when the cushioning property is increased, the lateral displacement becomes larger and the usability becomes worse.

  Further, when the warp yarn 100a is deformed so as to fall, twisting occurs at the root portion entangled with the lower high-shrinkage yarn, so that a large load is applied to the root portion of the warp yarn 100a. Therefore, when a load is repeatedly applied to the same position, the torsional deformation is repeatedly applied to the root portion of the same warp 100a, the elastic recovery force is lowered, and the function as a cushion material is lost early. .

  Such a problem of lateral displacement is a problem that occurs also in the connecting yarns described in Patent Documents 4 and 5.

  Therefore, an object of the present invention is to provide a cushion structure that has excellent cushioning properties that do not cause lateral slip in a three-dimensional multi-woven structure substantially composed of fibers and that has stable compression recovery properties. Is.

The cushion structure according to the present invention is composed of a three-dimensional multi-woven structure substantially composed of fibers, and warps constituting the ground structure are entangled with upper and lower high-shrinkage yarns to maintain a distance along one direction. A cushion structure having at least one layer structure in which a large number of communicating voids are arranged, wherein the communicating voids are formed by using flat monofilaments satisfying the following conditions (1) and (2) for the warp: A cushion structure characterized by being substantially skeleton-formed.
(1) Fineness is 100 dtex or more and 10,000 dtex or less (2) Flatness (H) of fiber cross section is 2 or more and 4.5 or less H = b / a
However, b is the maximum length in the longitudinal direction of the fiber cross section, and a is a value obtained from the following formula from b and the fiber cross-sectional area S.
a = 4S / b
Further, the flat monofilament is made of polyester. Further, the flat monofilament is composed of polytrimethylene terephthalate, or a copolymer or blend polymer of polytrimethylene terephthalate and polybutylene terephthalate.

  By having the structure as described above, the skeletal structure of the communication gap is formed by a flat monofilament that satisfies the above conditions (1) and (2). It can have resilience.

  In other words, the use of flat monofilaments can suppress the occurrence of side-falling that has occurred in the past, so that the load can be supported by the rigidity of the filament itself, and the rigidity of the flat monofilament can be used in the design of the cushion structure. It is possible to save. For example, the cushion rigidity can be finely adjusted by changing the rigidity of the filament for each layer of the multilayer structure. In addition, since it is difficult to fall down even if a force in the lateral displacement direction is applied, the same cushioning property can be given to loads from various directions, and an unprecedented superior cushioning property can be realized. .

  Hereinafter, embodiments according to the present invention will be described in detail. The embodiments described below are preferable specific examples for carrying out the present invention, and thus various technical limitations are made. However, the present invention is particularly limited in the following description. Unless otherwise specified, the present invention is not limited to these forms.

  FIG. 1 schematically shows a cross-sectional view of an embodiment according to the present invention. A ground structure 10 woven in plain weave is vertically woven in multiple layers, and a large number of high shrink yarns 11 are woven in the warp direction, and the ground structure 10 is alternately entangled with the upper and lower high shrink yarns 11 in a wavy shape. It is configured in a curved state. Since the ground structure 10 is curved in a wave shape, a layer structure M in which a large number of communication gaps 12 are arranged along the weft direction is formed.

  In the layer structure M, the warp yarns 10a constituting the ground structure 10 are entangled with the upper and lower high-shrinkage yarns 11 so as to maintain the interval so that the communication gap 12 is maintained. It is responsible for 12 skeleton formation. And the weft yarn 10b which comprises the ground structure 10 is woven in the warp yarn 10a, The whole warp yarn 10a is integrated and functions. A flat monofilament is used for the warp 10a constituting the ground structure 10.

  FIG. 2 is a schematic view showing a state of deformation of the warp yarn 10a when the cushion structure according to the present embodiment is compressed. As shown in FIG. 2, the warp 10a is curved and deformed in a wave shape before compression to form a large number of communicating voids (see FIG. 2 (a)), but when a compressive force is applied from above, the warp 10a Although it is bent from the top and is compressed and deformed (see FIG. 2 (b)), it is made of a flat monofilament so that it is compressed and deformed so as to be crushed in the vertical direction without falling down. Accordingly, the lateral displacement does not occur as a whole of the cushion structure, and the load is supported by the rigidity of the warp 10a itself, so that a natural cushioning property without a sense of incongruity is exhibited. In addition, since the root portion is not twisted due to the lateral fall, the elastic recovery force of the warp yarn 10a is not impaired, and good cushioning properties can be stably maintained.

  In this example, a flat monofilament is used for the warp, but any other cushion structure having a layer structure having such a communication gap portion may be used as the yarn forming the skeleton. A flat monofilament may be used. In this case, the number of layer structures is not particularly limited, and at least one layer may be provided. Preferably, 1-5 layers are good, More preferably, it is 1-3 layers. Further, the present invention can also be applied to a case where such a layer structure is provided in a part of the cushion structure. Further, the shape of the communication gap can be applied to shapes other than the trapezoid as in the above-described example, and is not particularly limited.

  In this embodiment, the communication gap portion does not have to be completely communicated from one end portion to the other end portion, and if the cushioning property is maintained even if it is partially closed by sewing or other means, there is a problem. Absent. In general, the communication gap may be set to a length of 5 cm or more, preferably 10 cm or more. If the thickness of the entire structure is 10 to 50 mm, preferably 15 to 40 mm, a practically sufficient cushioning property can be obtained.

  In the cushion structure according to the present embodiment, another woven structure may be combined on the surface according to the use.

  The flat monofilament used in the embodiment according to the present invention has a fineness of 100 dtex or more and 10,000 dtex or less. If the fineness is less than 100 dtex, the rigidity due to compression is low and soft, so it is not suitable as a cushioning material. On the other hand, if the fineness exceeds 10,000 dtex, the rigidity becomes high and hard, which is also unsuitable as a cushioning material. More preferably, it is 300 dtex or more and 1,000 dtex or less.

For flat monofilaments, the flatness (H) is defined by the ratio of b and a as shown in the following equation.
H = b / a
a and b can be obtained by the following method. First, a cross-sectional photograph of a flat monofilament is taken, and the maximum length (b) in the longitudinal direction of the cross-section and its cross-sectional area (S) are obtained. FIG. 2 shows cross sections of various flat monofilaments, and illustrates b and S in each case. After b and S are obtained, a is obtained by the following equation.
a = 4S / πb
When the cross section is an ellipse, b is the length of the major axis and a is the length of the minor axis.

  And the flatness (H) of the flat monofilament used for this invention is 2 or more and 4.5 or less. When H is less than 2, like a warp described in the above-described conventional example, when a load is applied, the roll falls down and a twist occurs at the root portion. When H exceeds 4.5, the monofilament breaks or breaks during processing such as weaving. More preferably, it is 2 or more and 4 or less.

  In addition, the cross-sectional shape of the flat monofilament may be a quadrangular shape other than that illustrated in FIG. 3 and is not particularly limited as long as the fineness and flatness conditions are satisfied.

  Examples of the polymer constituting the flat monofilament include polyester, polyamide, aromatic polyamide, polyvinyl alcohol, and polyolefin. Preferably, polyester or polyamide having excellent deformation resilience is used. More preferred are polytrimethyl terephthalate (PTT) and polybutylene terephthalate (PBT), and in particular, a blend polymer or copolymer polymer of PTT and PBT. A preferable blend ratio or copolymerization ratio of PTT and PBT is such that the ratio of PBT (PBT%) is 12 wt% or more and 45 wt% or less. By adding PBT in this range, the stretchability is improved as compared with the PTT single polymer, and the resulting fiber has high strength, high initial elastic modulus, and good elastic recovery. If the PBT% is less than 12% by weight, there is not much difference from the properties of the PTT homopolymer, and if it exceeds 45% by weight, the elastic recovery rate is lowered.

  Examples of the fibers constituting the weft of the ground texture include polyester, polyamide, aromatic polyamide, polyvinyl alcohol, and polyolefin. Preferably, polyester or polyamide having excellent deformation resilience is used.

  Examples of the polymer constituting the high shrinkage yarn include polyester, polyamide, and polyolefin. Preferably, it is a polyester copolymerized with 5 to 15 mol% of other components. However, in the present invention, the high shrinkage yarn is not indispensable. In short, any material other than the high shrinkage yarn may be used as long as it has a layer structure in which the communication gap is formed.

  Examples of the fibers constituting the weft of the ground texture include polyester, polyamide, aromatic polyamide, polyvinyl alcohol, and polyolefin. Preferably, polyester or polyamide having excellent deformation resilience is used.

<Manufacture of flat monofilament>
The following parameters were used as characteristics of the flat monofilament used in the examples.
(1) Intrinsic viscosity [η] is a value determined based on the following defining formula.

Η _r in the definition is a value obtained by dividing the viscosity at a temperature of 35 ° C. of a solution in which a polymer is dissolved in a solvent of 0-chlorophenol having a purity of 98% or more by the viscosity of the solvent measured at the same temperature. It is defined as viscosity. C is the weight concentration of the polymer (g / 100 ml).
(2) The breaking strength and elongation were measured by performing a tensile test under the conditions of a yarn length of 20 cm and a tensile speed of 20 cm / min in accordance with JIS-L-1013.
(3) The elongation elastic modulus was deweighted after 20% elongation in accordance with the method A shown in JIS-L-1013, and the instantaneous recovery rate (R00) and the recovery rate after 2 minutes (R20) were measured.
(4) The maximum draw ratio (HDmax) was determined by increasing the draw ratio in a water bath at a temperature of 60 ° C., and obtaining the ratio when the monofilament was cut.

(In case of PTT 100%; TT type)
Using a PTT tip with [η] = 0.85 dl / g, melt spinning was performed at a temperature of 260 ° C. from a nozzle having the shape shown in FIG. The HDmax of the spun yarn was 5.3. The spun yarn was continuously stretched by 3.7 times in a water bath at a temperature of 60 ° C., and subsequently stretched by 1.25 times (a total of 4.6 times) in a hot air oven at a temperature of 130 ° C. Subsequently, the film was wound after being subjected to a shrinkage treatment of 3% in a hot air oven at a temperature of 180 ° C. Through the above manufacturing process, a flat monofilament having a fineness of 600 dtex and a flatness (H) of 2.5 was obtained. The produced flat monofilament had a breaking strength of 2.8 cN / dtex, an elongation of 38%, and an elongation elastic modulus of ROO = 82% and R20 = 97%.

  As a comparative example in which the flat monofilament described above is type TT-1 and the shape of the nozzle is changed to change the flatness (H) to 1.0, 1.5 and 4.7, types TT-2 and TT- 3 and TT-4 were produced in the same manner as TT-1.

(In case of PTT + PBT; TB type)
Using a PTT tip with [η] = 0.85 dl / g and a PBT tip with [η] = 0.83 dl / g, blending at a ratio of 80% PTT tip and 20% PBT tip, the nozzle shown in FIG. And melt spinning at a temperature of 260 ° C. The HDmax of the spun yarn was 6.8. The spun yarn was continuously stretched 4.2 times in a water bath at a temperature of 60 ° C., and subsequently stretched 1.26 times (totally 5.3 times) in a 130 ° C. hot air oven. Subsequently, the film was wound after being subjected to a shrinkage treatment of 3% in a hot air oven at 180 ° C. Through the above manufacturing process, a flat monofilament having a fineness of 600 dtex and a flatness (H) of 2.5 was obtained. The produced flat monofilament had a breaking strength of 3.9 cN / dtex, an elongation of 35%, and an elongation modulus of R00 = 90% and R20 = 99%.

  The flat monofilament described above was made into type TB-2, and types TB-1 and TB-3 in which the ratio of the PBT chip was changed to 8% and 50% were also produced in the same manner as TB-2.

Table 1 summarizes the characteristics of each type manufactured.

<Weaving cushion structure>
Three types of warp are used. Three layers of high shrinkage yarn (total fineness 1100 dtex; Teijin Soku Latex) (36 layers / inch each), four layers of flat monofilaments (36 layers / inch each), polyethylene terephthalate wool yarn SD475 / 144 filaments Polyethylene terephthalate wool yarn SD475 / 144 filament is used for the weft exterior when it is arranged in the outermost layer (13 layers / inch for each layer), and a triple beam warped product wound on 3 beams each to make a modified 5 layer weave on a rapier loom Then, a polyethylene terephthalate monofilament (330 dtex) is used in the intermediate space, and a low melting point polyethylene terephthalate spun yarn 20/1 / twist yarn is used at the intersection with the intermediate high shrinkage yarn to prevent misalignment. A highly breathable cushion structure in which a woven fabric is heat-set at 150 ° C. for 2 minutes and contracted by 40% with a high shrinkage yarn in the warp direction of the fabric to form a skeleton as shown in FIG. Got.

  Regarding type TT-4, the fibers themselves were cracked during weaving and could not be weaved. As for Type TT-2, when the manufactured cushion structure was compressed in the vertical direction as in the conventional example, the warp yarn collapsed in the layer structure and a lateral shift occurred in the entire structure. For type TT-3 as well, when compressed in the vertical direction, the warp in the layer structure fell down and a lateral shift occurred as in the conventional example. When the remaining types of flat monofilaments are used to form the skeleton of the communication gap, the warp yarn is compressed without falling down while being bent in the vertical direction, and no lateral slippage is observed. Had sex. Therefore, when the flatness exceeds 4.5, troubles occur when weaving the cushion structure.

  In addition, the low-melting spun yarn melted during the heat setting, and the high shrinkage yarn and the flat monofilament were joined, and the deformation of the flat monofilament during compression could be completely prevented. It was confirmed that the flat monofilament was able to suppress the lateral collapse, and the cushioning performance was almost equal to the compression from all directions as well as the vertical direction.

<Manufacture of flat monofilament>
(In case of PTT 100%; TT type)
Using the same PTT tip as in Example 1, melt spinning was performed at a temperature of 240 ° C. from an elliptical nozzle shown in FIG. The spun yarn was continuously stretched to 0.7 times of HDmax in a water bath at a temperature of 60 ° C., and further stretched by 1.2 times in a hot air oven at a temperature of 130 ° C. The whole was subjected to 8% shrinkage treatment in a hot air oven at a temperature of 180 ° C. and then wound up. Through the above manufacturing process, a flat monofilament having a fineness of 515 dtex and a flatness (H) of 2.6 was obtained. The produced flat monofilament had a breaking strength of 2.75 cN / dtex, an elongation of 57%, and an elongation elastic modulus of ROO = 93%. The flat monofilament described above is designated as type TT-10. As comparative examples, the shape of the nozzle is changed to the type TT-11 changed to the circular shape shown in FIG. 5B, the type TT-12 changed to the shape shown in FIG. 5C, and the shape shown in FIG. 5D. Modified type TT-13 was produced in the same manner as TT-10.

(In case of PTT + PBT; TB type)
The same PTT tip and PBT tip as in Example 1 were used, blended at a ratio of 85% PTT tip and 15% PBT tip, and melt-spun at a temperature of 250 ° C. from a nozzle having the shape shown in FIG. The spun yarn was continuously stretched 4.2 times in a water bath at a temperature of 60 ° C., and subsequently stretched to 6.0 times in a 130 ° C. hot air oven. The whole was subjected to shrinkage treatment in a hot air oven at 180 ° C. until it became 5.6 times and then wound up. Through the above manufacturing process, a flat monofilament having a fineness of 525 dtex and a flatness (H) of 2.6 was obtained. The produced flat monofilament had a breaking strength of 3.6 cN / dtex, an elongation of 34%, and an elongation modulus of R00 = 99%. The flat monofilament described above is designated as type TT-10.

Table 2 summarizes the characteristics of each type produced.

(Comparison between TT type and TB type)
FIG. 6 is a graph showing the correlation between elongation and breaking strength for TT-10 and TB-10. For comparison, nylon fiber (480 dtex) is also described. As can be seen from FIG. 6, the TB type has characteristics similar to nylon fibers in terms of elongation and breaking strength, and the TB type has higher strength at the same elongation. Therefore, when the TB type is used for the cushion structure, the stability of the cushioning property is increased and the durability is improved.

  From the above results, since the TB type has a larger Hdmax than the TT type, it is easy to be stretched, the tensile strength is increased, and the tensile elastic modulus is increased. Therefore, as a flat monofilament used for the cushion structure, it is considered that the TB type is more preferable than the TT type.

(Compression characteristics of flat monofilament)
A monofilament of TT-10 to 13 is cut into a predetermined length, and as shown in FIG. 7A, it is curved so that the height is 7 mm and the width is 16 mm, so that it is almost perpendicular to the mounting table. Both sides were fixed with tape. This shape is similar to the wavy shape of the warp in the layer structure in the cushion structure shown in FIG. Then, three monofilaments were arranged at intervals of 1 mm, a constant load was applied in the vertical direction from above, and compression deformation was performed as shown in FIG. 7B, and the amount of deformation was measured. The compression tester is manufactured by Kato Tech Co., Ltd. (KES-G5). The compression force is increased from 0 at a constant pace to 10 cN / cm ² and then reduced at the same pace to release the compression force. I made it.

FIG. 8 is a graph showing the measurement results. The deformation amount (height (mm)) of the compressed monofilament is taken on the horizontal axis, and the repulsive force (cN / cm ² ) against compression is taken on the vertical axis. Referring to FIG. 7, in TT-10 and TT-12, the repulsion force increases as the height decreases and the compression force is released and returns to the original state as the compression force is released. When the height falls below 5 mm, a lateral fall occurs and the repulsive force decreases rapidly. As for TT-13, when it is compressed and the height is less than 5 mm, twisting occurs and no increase in the repulsive force is observed, and when it is smaller than 3 mm, a lateral collapse occurs and the repulsive force decreases rapidly. ing.

  As seen from the above results, when the flatness (H) is less than 2, it cannot sufficiently withstand the compression in the vertical direction, and a lateral fall or the like occurs. Will be adversely affected.

<Weaving cushion structure>
A cushion structure was woven by the same weaving method as in Example 1, using a flat monofilament of TB-10 as a warp for forming a skeleton with a continuous void portion having a layer structure. The photograph which image | photographed the compression process of the woven cushion structure is shown in FIG.9 and FIG.10. FIG. 9 is a photograph of the cushion structure in an uncompressed state from the warp direction, and the warp yarns of four layer structures are arranged in the vertical direction. FIG. 10 is a photograph of the cushion structure compressed by 60%, the middle two layers are not seen compressed, and the upper and lower two layers are also greatly compressed and deformed. The arrangement direction of the warps is still maintained in the up-down direction, and no side-falling has occurred. In addition, it is difficult to cause a lateral fall, so even if a force in the lateral displacement direction is applied, it is difficult to deform in that direction, and the same repulsive force is generated with respect to the force from various directions, and the cushioning is directed. Excellent cushioning can be achieved.

  As described above, the warp forming the communication gap portion of the layer structure is deformed so as to be crushed in the vertical direction in accordance with the compression, but the lateral displacement does not occur without causing the lateral collapse. Further, the repulsive force increases by being crushed in the vertical direction, and an excellent cushioning property is realized. In addition, since the warp is deformed so as to be crushed in the vertical direction, variation occurs in the deformation of each warp. Therefore, the warp yarns are connected to each other using a low-melting-point fusion yarn, and the variation in deformation is reduced. It is good to prevent.

  The cushion structure according to the present invention has an excellent cushioning property without lateral slip, and is excellent in air permeability, uniformity of pressure distribution, durability and washability, and bedding, a vehicle seat, a chair seat, and a cushion. Suitable for seats for seats, seats for reception sets, sports equipment and the like.

It is sectional drawing regarding the embodiment which concerns on this invention. It is a schematic diagram which shows the mode of deformation | transformation of the warp when this embodiment is compressed. It is a schematic diagram which shows the cross-sectional shape of a flat monofilament. It is a schematic diagram which shows the shape of a nozzle. It is a schematic diagram which shows the shape of a nozzle. It is a graph which shows the correlation of elongation and breaking strength regarding TT-10 and TB-10. It is a schematic diagram which shows the setting state of the filament which performs a compression test. It is a graph regarding the measurement result of a compression test. It is the photograph which image | photographed the state before compression of a cushion structure. It is the photograph which image | photographed the compression state of the cushion structure. It is a partial expansion perspective view of the conventional three-dimensional multi-woven structure. It is a schematic diagram explaining the case where a load is added to the conventional three-dimensional multi-woven structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Ground organization 10a Warp yarn 10b Weft 11 High shrinkage yarn 12 Communication space part

Claims (3)

It consists of a three-dimensional multi-woven structure substantially composed of fibers, and warps constituting the ground structure are entangled with the upper and lower high-shrinkage yarns to maintain a distance so that a large number of communicating voids are arranged along one direction. A cushion structure having at least one layer structure, wherein the communication gap is substantially formed by using a flat monofilament satisfying the following conditions (1) and (2) for the warp: Cushion structure characterized by.
(1) Fineness is 100 dtex or more and 10,000 dtex or less (2) Flatness (H) of fiber cross section is 2 or more and 4.5 or less H = b / a
However, b is the maximum length in the longitudinal direction of the fiber cross section, and a is a value obtained from the following formula from b and the fiber cross-sectional area S.
a = 4S / b   The cushion structure according to claim 1, wherein the flat monofilament is made of polyester.   The cushion structure according to claim 2, wherein the flat monofilament is made of polytrimethylene terephthalate or a copolymer or blend polymer of polytrimethylene terephthalate and polybutylene terephthalate.