JP7745273B2 - pillow - Google Patents

Description

Article 30, paragraph 2 of the Patent Act applies 1. March 18, 2020, website 2. April 9, 2020, delivery 3. June 3, 2020, delivery 4. June 25, 2020, delivery

The present invention relates to a pillow made of a woven resin network structure.

BACKGROUND ART A variety of pillows have been proposed for the purpose of improving the quality of sleep.
For example, Patent Document 1 discloses a pillow in which a pair of partition walls are arranged diagonally opposite each other between the pillow fabric on the upper surface side and the pillow fabric on the lower surface side, and a central chamber and both side chambers are separated inside the pillow fabric via the partition walls, and each chamber is filled with stuffing. In this pillow, multiple sheets of pillow fabric are arranged on the upper surface side or the lower surface side, and the inner pillow fabrics arranged in an overlapping manner are sewn to the pillow fabrics arranged on the upper surface side and the lower surface side at a distance above and below the pillow fabrics arranged on the upper surface side and the lower surface side, and the partition walls are formed by the pillow fabrics separated by the two sewn parts.
Furthermore, Patent Document 2 discloses a pillow in which a disposable tea pack, which is made by sealing tea leaves in a breathable bag that does not allow tea powder to pass through, is sandwiched from above and below between soft filler packs, which are made by filling a soft filler in a cloth bag, to form three layers and stored in the bag body.
Furthermore, Patent Document 3 describes the use of a three-dimensional filament bond obtained by partially fusing together a plurality of thermoplastic resin fibers (molten filaments) in a molten state as a pillow.

Japanese Patent Application Laid-Open No. 2015-8757 Registered Utility Model No. 3218275 JP 2017-150100 A

The pillow described in Patent Document 1 is not made of a woven resin network structure. Also, by filling the central chamber with soft stuffing such as feathers and the side chambers with hard, fluid stuffing such as synthetic resin pipes, the firmness of the pillow varies depending on the location in the width direction, but the firmness of the pillow does not vary depending on the location in the height direction.
Furthermore, although the pillow described in Patent Document 2 has a three-layer structure, it does not aim to improve sleep quality by varying the firmness depending on the height, nor does it vary the firmness depending on the width.
Furthermore, Patent Document 3 does not describe any specific configuration when the three-dimensional filament bonded body is used as a pillow.
Therefore, an object of the present invention is to provide a pillow that more effectively improves the quality of sleep.

The pillow 1 of the present invention described in claim 1 is a pillow made of a knitted resin network structure in which a plurality of filamentous molten resins are entangled and partially heat-welded, and in the height direction, it is composed of an upper layer 10 located at the uppermost position when in use, a lower layer 30 located at the lowermost position when in use, and a middle layer 20 located between the upper layer 10 and the lower layer 30, the lower layer 30 is harder than the upper layer 10, and the middle layer 20 is harder than the upper layer 10 and softer than the lower layer 30, at the boundary between the upper layer 10 and the middle layer 20, the knitted resin of the upper layer 10 and the knitted resin of the middle layer 20 are entangled, and at the boundary between the middle layer 20 and the lower layer 30, the knitted resin of the middle layer 20 and the knitted resin of the lower layer 30 are entangled, and in the width direction, it is composed of a central region 40 located at the center, end regions 60 located at both ends, and a middle layer 20 located between the central region 40 and the end region 60. The end region 60 is harder than the central region 40, and the end region 50 is harder than the central region 40 but softer than the end region 60. At the boundary between the central region 40 and the intervening region 50, the woven resin of the central region 40 and the woven resin of the intervening region 50 are intertwined, and at the boundary between the intervening region 50 and the end region 60, the woven resin of the intervening region 50 and the woven resin of the end region 60 are intertwined. The upper surface is inclined from one end to the other in the depth direction. The intervening region 50 is made up of a plurality of small regions 51 having a predetermined width with different hardness in the width direction. Between adjacent small regions 51, the one closer to the central region 40 is softer, and at the boundary between the small regions 51, the woven resin of one small region 51 and the woven resin of the other small region 51 are intertwined.

The present invention described in claim 2 is characterized in that, in the pillow 1 described in claim 1, the lower layer 30 is provided with a protruding portion 31 that protrudes toward the middle layer 20 from one end to the other in the width direction in a portion that supports the user's neck.

The present invention as set forth in claim 3 is characterized in that, in the pillow 1 as set forth in claim 1 or claim 2, the wire diameter of the knitted resin of the upper layer 10 is smaller than the wire diameter of the knitted resin of the middle layer 20, which is smaller than the wire diameter of the knitted resin of the middle layer 20, and when the wire diameter of the knitted resin of the upper layer 10 is taken as 1, the wire diameter of the knitted resin of the middle layer 20 is 1.1 to 1.7, and the wire diameter of the knitted resin of the lower layer 30 is 1.4 to 2.0.

The present invention described in claim 4 is characterized in that, in the pillow 1 described in any one of claims 1 to 3, the bulk density of the central region 40 is smaller than the bulk density of the intermediate region 50, the bulk density of the intermediate region 50 is smaller than the bulk density of the end region 60, and when the bulk density of the central region 40 is 1, the bulk density of the end region 60 is 1.2 to 4.0 .

According to the present invention, a pillow that more effectively improves the quality of sleep can be provided.

A conceptual diagram showing the top surface of a pillow according to one embodiment of the present invention. Conceptual diagram showing the side of the pillow A perspective view of the pillow A conceptual diagram showing each layer of the pillow 1 is a conceptual diagram showing the top surface of a pillow according to another embodiment of the present invention; A diagram showing the manufacturing equipment for the pillow

The pillow according to the first embodiment of the present invention is a pillow made of a knitted resin network structure in which a plurality of filamentous molten resins are entangled and partially heat-welded, and in the height direction, the pillow is made up of an upper layer which is located at the top when in use, a lower layer which is located at the bottom when in use, and a middle layer which is located between the upper and lower layers, the lower layer being harder than the upper layer, the middle layer being harder than the upper layer and softer than the lower layer, and at the boundary between the upper and middle layers, the knitted resin of the upper layer and the knitted resin of the middle layer are entangled, and at the boundary between the middle and lower layers, the middle layer is The knitted resin of the upper layer is intertwined with the knitted resin of the lower layer, and in the width direction it consists of a central region located in the center, end regions located at both ends, and an intermediate region located between the central region and the end region, the end regions being harder than the central region, and the intermediate region being harder than the central region and softer than the end regions, and at the boundary between the central region and the intermediate region, the knitted resin of the central region is intertwined with the knitted resin of the intermediate region, and at the boundary between the intermediate region and the end region, the knitted resin of the intermediate region is intertwined with the knitted resin of the end region.
This embodiment provides a pillow that has adequate cushioning and allows for easy turning over in bed. Also, by making the upper layer the softest, the pillow gradually conforms to the weight and size of the user's head.

In the second embodiment of the present invention, in the pillow according to the first embodiment, the lower layer is provided with a protruding portion that protrudes toward the middle layer from one end to the other in the width direction in the portion that supports the user's neck.
According to this embodiment, the neck of the user can be supported and excessive sinking can be prevented.

A third embodiment of the present invention is a pillow according to the first or second embodiment, wherein the wire diameter of the knitted resin of the upper layer is smaller than the wire diameter of the knitted resin of the middle layer, which is smaller than the wire diameter of the knitted resin of the lower layer, and when the wire diameter of the knitted resin of the upper layer is 1, the wire diameter of the knitted resin of the middle layer is 1.1 to 1.7, and the wire diameter of the knitted resin of the lower layer is 1.4 to 2.0.
According to this embodiment, different hardnesses in the respective layers can be made more appropriate.

A fourth embodiment of the present invention is a pillow according to any one of the first to third embodiments, wherein the bulk density of the central region is smaller than the bulk density of the intermediate region, which is smaller than the bulk density of the end region, and when the bulk density of the central region is 1, the bulk density of the end region is 1.2 to 4.0.
According to this embodiment, different hardness levels are more appropriate in each region, making it easier to turn over in bed.

The fifth embodiment of the present invention is a pillow according to any one of the first to fourth embodiments, in which the intermediate region is made up of a plurality of small regions of different hardness in the width direction, and among adjacent small regions, the one closer to the central region is softer.
According to this embodiment, the hardness can be changed more finely from the central region to the edge region.

A pillow according to one embodiment of the present invention will now be described.
Fig. 1 is a conceptual diagram showing the top surface of a pillow according to this embodiment. Fig. 2 is a conceptual diagram showing the side of the pillow, with Fig. 2(a) showing the small type, which has the smallest height, Fig. 2(c) showing the large type, which has the greatest height, and Fig. 2(b) showing the medium type, which is taller than the small type but shorter than the large type. Fig. 3 is a conceptual diagram showing a perspective view of the pillow, with Fig. 3(a) showing the small type, Fig. 3(b) showing the medium type, and Fig. 3(c) showing the large type.
The pillow 1 is made of a knitted resin network structure in which a plurality of filamentous molten resin threads are entangled and partially heat-welded. Since the shape of the knitted network structure itself forms the shape of the pillow 1, the pillow 1 can be used as is without putting it in a cover.
The knitted resin network structure is formed by melt-kneading a thermoplastic resin at a predetermined temperature, allowing the molten resin to flow down in the form of threads, and then cooling the melted resin. The thermoplastic resin may be, for example, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyvinyl acetate, polytetrafluoroethylene, or acrylonitrile butadiene styrene resin, and these may be used alone or in combination.
The knitted resin network structure manufactured from a thermoplastic resin can be recycled after use and reused as a raw material for knitted resin network structures, etc. Furthermore, the knitted resin network structure can be washed with water, etc., making it easy to keep the pillow 1 clean. Furthermore, the air inside the pillow 1 can easily escape, making it comfortable.

The top surface of pillow 1 slopes from one end to the other in the depth direction, with the heights of one end and the other end varying. This allows the user to use a single pillow 1 at different heights. The dimensions of pillow 1 are, for example, as follows: for the small type, depth L is 350 mm, width W is 600 mm, height H1 at one end is 80 mm, and height H2 at the other end is 60 mm; for the medium type, depth L is 400 mm, width W is 600 mm, height H1 at one end is 110 mm, and height H2 at the other end is 90 mm; and for the large type, depth L is 400 mm, width W is 600 mm, height H1 at one end is 140 mm, and height H2 at the other end is 120 mm.

The pillow 1 has a three-layer structure with different hardness in the height direction. The lower layer 30, which is located at the bottom when in use, is harder than the upper layer 10, which is located at the top when in use, and the middle layer 20, which is located between the upper layer 10 and the lower layer 30, is harder than the upper layer 10 but softer than the lower layer 30. These hardnesses (resilience) are set by varying the wire diameter of the knitted resin in each layer.
The wire diameter of the knitted resin in the upper layer 10 is smaller than that of the knitted resin in the middle layer 20, which is smaller than that of the knitted resin in the lower layer 30. If the wire diameter of the knitted resin in the upper layer 10 is "1", then the wire diameter of the knitted resin in the middle layer 20 is preferably "1.1 to 1.7" and the wire diameter of the knitted resin in the lower layer 30 is preferably "1.4 to 2.0". It is even more preferable that the wire diameter of the knitted resin in the upper layer 10 is 0.3 mm to 0.9 mm, the wire diameter of the knitted resin in the middle layer 20 is 0.5 mm to 1.0 mm, and the wire diameter of the knitted resin in the lower layer 30 is 0.6 mm to 1.5 mm. For example, the wire diameter of the knitted resin in the upper layer 10 is 0.6 mm, the wire diameter of the knitted resin in the middle layer 20 is 0.75 mm, and the wire diameter of the knitted resin in the lower layer 30 is 0.9 mm.

The thickness T4 of the lower layer 30 and the thickness T3 of the middle layer 20 are constant from one end to the other in the depth direction, and the thickness T1 of the upper layer 10 at one end in the depth direction is greater than the thickness T2 at the other end. The middle layer 20 is thicker than the lower layer 30 and thinner than one end of the upper layer 10. If the thickness T1 at one end of the upper layer 10 is "1", it is preferable that the thickness T3 of the middle layer 20 be "0.3 to 0.9" and the thickness T4 of the lower layer 30 be "0.1 to 0.6". For example, in the small type, the thickness T1 of one end of the upper layer 10 is 50 mm, the thickness T2 of the other end of the upper layer 10 is 30 mm, the thickness T3 of the middle layer 20 is 20 mm, and the thickness T4 of the lower layer 30 is 10 mm; in the medium type, the thickness T1 of one end of the upper layer 10 is 50 mm, the thickness T2 of the other end of the upper layer 10 is 30 mm, the thickness T3 of the middle layer 20 is 40 mm, and the thickness T4 of the lower layer 30 is 20 mm; and in the large type, the thickness T1 of one end of the upper layer 10 is 60 mm, the thickness T2 of the other end of the upper layer 10 is 40 mm, the thickness T3 of the middle layer 20 is 50 mm, and the thickness T4 of the lower layer 30 is 30 mm.
At the boundary between the upper layer 10 and the middle layer 20, the knitted resin of the upper layer 10 and the knitted resin of the middle layer 20 are intertwined, and at the boundary between the middle layer 20 and the lower layer 30, the knitted resin of the middle layer 20 and the knitted resin of the lower layer 30 are intertwined. By having knitted resins of different diameters intertwined at the boundary between each layer in this way, the pillow 1 has better shape retention and cushioning properties than when knitted resin network structures formed layer by layer are simply stacked. Also, by making the upper layer 10 the softest, the pillow 1 gradually shapes and fits easily to the weight and size of the user's head.

As shown in FIG. 1, the width direction of the pillow 1 is made up of a central region 40 located in the center, end regions 60 located at both ends, and an intermediate region 50 located between the central region 40 and the end regions 60.
The end regions 60 are harder than the central region 40. The intermediate region 50 is harder than the central region 40 but softer than the end regions 60. In the pillow 1 of this embodiment, the end regions 60 are made about 20% harder than the central region 40, and the intermediate region 50 is made about 10% harder than the central region 40. These hardnesses (resilience) are set by making a difference in bulk density of each region. Bulk density is calculated by weight (g) divided by volume ( ^cm3 ).
The bulk density of the central region 40 is smaller than the bulk density of the intervening region 50, which in turn is smaller than the bulk density of the end region 60. If the bulk density of the central region 40 is "1", the bulk density of the end region 60 is preferably "1.2 to 4.0", and it is more preferable that the bulk density of the central region 40 is 0.005 g/cm ³ to 0.06 g/cm ³ and the bulk density of the end region 60 is 0.002 g/cm ³ to 0.08 g/cm ³ . For example, in the small type, the bulk density in the central region 40 is 0.027 g/cm ³ and the bulk density in the edge region 60 is 0.033 g/cm ³ , and in the medium type, the bulk density in the central region 40 is 0.026 g/cm ³ and the bulk density in the edge region 60 is 0.032 g/cm ³ .
The width W1 of the central region 40 is larger than the width W2 of the intervening region 50 and smaller than the width W3 of the end region 60. For example, the width W1 of the central region 40 is 120 mm, the width W2 of the intervening region 50 is 70 mm, and the width W3 of the end region 60 is 170 mm. By providing the intervening region 50, which has a hardness roughly intermediate between the central region 40 and the end region 60, with an appropriate width, the user can turn over more easily, improving the quality of sleep.
At the boundary between the central region 40 and the intermediate region 50, the woven resin of the central region 40 and the woven resin of the intermediate region 50 are intertwined, and at the boundary between the intermediate region 50 and the end region 60, the woven resin of the intermediate region 50 and the woven resin of the end region 60 are intertwined. By having the woven resins intertwined at the boundary between each region in this way, the pillow 1 has better shape retention and cushioning properties than when the woven resin network structures formed in each region are simply lined up in the width direction.

FIG. 4 is a conceptual diagram showing the layers of the pillow.
It is preferable that the lower layer 30 be provided with protrusions 31 extending from one end to the other in the width direction, protruding toward the middle layer 20, in the portion supporting the user's neck. In this embodiment, protrusions 31 are provided between the center and one end in the depth direction, and between the center and the other end in the depth direction, extending from one end to the other in the width direction. The portions of the lower layer 30 where the protrusions 31 are provided have a thickness T4 that is greater than that of the other portions. However, by reducing the thickness T3 of the portion of the middle layer 20 facing the protrusions 31 by the protrusion height of the protrusions 31, the sum of the thickness T3 of the middle layer 20 and the thickness T4 of the lower layer 30 is the same in the portions where the protrusions 31 are provided and in the portions where the protrusions 31 are not provided.
In this way, by providing a protrusion 31 at the point that supports the user's neck and partially increasing the thickness of the hardest lower layer 30, it is possible to effectively prevent the user's neck from sinking too much.
Furthermore, by providing the protrusion 31 both between the center and one end in the depth direction and between the center and the other end in the depth direction, the protrusion 31 can be positioned in the part that supports the user's neck whether the user uses the device with one end in the depth direction facing forward or the other end in the depth direction facing forward.

Next, a pillow according to another embodiment of the present invention will be described. Figure 5 is a conceptual diagram showing the upper surface of the pillow according to this embodiment. Note that the same functional components as those in the above embodiment are given the same reference numerals and their description will be omitted.
The pillow 1 of this embodiment is the same as the above-mentioned embodiment in that it consists of a central region 40 located in the center, end regions 60 located at both ends, and an intermediate region 50 located between the central region 40 and the end region 60, but differs from the above-mentioned embodiment in that the intermediate region 50 is subdivided and multiple small regions 51 with different hardness are provided in the width direction.

The small regions 51 are composed of first small regions 51A, each of which contacts both sides of the central region 40, and second small regions 51B, each of which contacts the end regions 60. The first small regions 51A are harder than the second small regions 51B. This hardness (resilience) is set by providing a difference in bulk density between the first small regions 51A and the second small regions 51B. At the boundary between the central region 40 and the intermediate region 50, the knitted resin of the central region 40 and the knitted resin of the first small region 51A are intertwined. At the boundary between the intermediate region 50 and the end regions 60, the knitted resin of the second small region 51B and the knitted resin of the end regions 60 are intertwined. At the boundary between the first small region 51A and the second small region 51B, the knitted resin of the first small region 51A and the knitted resin of the second small region 51B are intertwined.
As a result, the pillow 1 of this embodiment can more finely vary the hardness (resilience) from the central region 40 to the end region 60, for example, by making the end region 60 20% harder than the central region 40, making the first small region 51A of the intermediate region 50 5% harder than the central region 40, and making the second small region 51B 10% harder than the central region 40. This makes it easier for the user to turn over in their sleep, further improving the quality of sleep.
The width W1 of the central region 40 is smaller than the width W3 of the edge region 60 and the width W22 of the second small region 51B, but larger than the width W21 of the first small region 51A. The width W3 of the edge region 60 is larger than the width W22 of the second small region 51B. For example, the width W1 of the central region 40 is 60 mm, the width W21 of the first small region 51A is 50 mm, the width W22 of the second small region 51B is 70 mm, and the width W3 of the edge region 60 is 150 mm.
The intermediate region 50 can be further subdivided, for example, by providing a third small region and a fourth small region. In this case, the small region 51 closer to the central region 40 is softer than the small region 51 closer to the end region 60.

FIG. 6 is a diagram showing a pillow manufacturing apparatus according to this embodiment.
The manufacturing apparatus according to this embodiment includes an extruder 110 that melts and kneads thermoplastic resin at a predetermined temperature to form a molten resin and extrudes the molten resin at a predetermined extrusion speed, a resin pool 130 that receives the molten resin extruded from the extruder 110 and causes the molten resin to flow down in threads from multiple holes (nozzles) in the bottom surface 131, a cooling water tank 140 that stores cooling water, and a take-up machine 150 that takes up downward a knitted resin 121 formed by cooling the thread-like molten resin 120 that flows down from the resin pool 130 with the cooling water. The take-up machine 150 has multiple take-up rollers 151 facing each other and is disposed within the cooling water tank 140. A guider 170 is provided between the resin pool 130 and the take-up machine 150.
The filamentous molten resin 120 is formed as it flows down from the holes in the bottom surface 131 of the resin pool 130. The knitted resin 121 obtained by cooling the filamentous molten resin 120 with cooling water is drawn up by a drawer 150 to the bottom plate side of the cooling water tank 140, and after passing through the drawer 150, is drawn up diagonally upward while being cooled in the cooling water by a plurality of conveying rollers 160, which are drawing-up members arranged in the cooling water tank 140, and is conveyed out of the cooling water tank 140. After that, the knitted resin network structure as the pillow 1 is formed by cutting to a predetermined size after cooling. In this embodiment, the direction perpendicular to the extrusion direction is the depth direction of the pillow 1.

The central region 40, the intermediate region 50, and the end region 60 of the pillow 1 are formed by providing variations in density in the direction parallel to the extrusion direction.
The density variation in the direction parallel to the extrusion direction is achieved, for example, by changing the take-up speed of the take-up machine 150 at predetermined time intervals. When the density variation is achieved by changing the take-up speed, the speed at which the take-up machine 150 takes up the knitted resin 121 is set to a first speed, a second speed slower than the first speed, and a third speed slower than the first speed but faster than the second speed. The portion of the knitted resin 121 taken up by the take-up machine 150 at the second speed has a higher bulk density than the portion taken up at the first speed, so the portion taken up at the first speed becomes the central region 40, which is a sparse portion with the lowest bulk density, the portion taken up at the second speed becomes the end region 60, which is a dense portion with the highest bulk density, and the portion taken up at the third speed becomes the intermediate region 50, which is a portion with a bulk density intermediate between the above.
Therefore, by repeating the pattern of the take-up speed of the take-up machine 150 being the second speed → third speed → first speed → third speed → second speed, it becomes possible to manufacture a pillow 1 having an intermediate region 50 between the central region 40 and the end region 60 in the direction parallel to the extrusion direction. Here, by making the take-up time at the second speed the longest, the take-up time at the first speed the next longest, and the take-up time at the third speed the shortest, it is possible to make the widths of each region different. Note that if the intermediate region 50 is subdivided to provide small regions 51, the take-up speed of the take-up machine 150 can be set by changing it even more finely.
The density variation in the direction perpendicular to the extrusion direction is achieved, for example, by varying the diameter of the holes provided in the bottom surface 131 of the resin pool 130 within a predetermined range. When the density variation is achieved by varying the diameter of the holes in the resin pool 130, the diameter of the holes corresponding to the upper layer 10 is set to be the smallest, the diameter of the holes corresponding to the lower layer 30 is set to be the largest, and the diameter of the holes corresponding to the middle layer 20 is set to be an intermediate diameter between them.

1 Pillow 10 Upper layer 20 Middle layer 30 Lower layer 31 Projection part 40 Central region 50 Interval region 51 Small region 51A First small region 51B Second small region 60 End region

Claims (4)

A pillow made of a knitted resin network structure in which a plurality of filamentous molten resins are entangled and partially heat-welded,
The height direction is composed of an upper layer located at the top during use, a lower layer located at the bottom during use, and a middle layer located between the upper layer and the lower layer,
the lower layer being harder than the upper layer;
The middle layer is harder than the upper layer and softer than the lower layer,
At the boundary between the upper layer and the middle layer, the knitted resin of the upper layer and the knitted resin of the middle layer are entangled,
At the boundary between the middle layer and the lower layer, the knitted resin of the middle layer and the knitted resin of the lower layer are entangled,
The width direction is made up of a central region located at the center, end regions located at both ends, and intermediate regions located between the central region and the end regions,
the end regions being harder than the central region;
the intermediate region being harder than the central region and softer than the end regions;
At the boundary between the central region and the intermediate region, the knitted resin of the central region and the knitted resin of the intermediate region are entangled,
At the boundary between the intermediate region and the end region, the knitted resin of the intermediate region and the knitted resin of the end region are entangled,
The top surface is inclined from one end to the other in the depth direction,
The pillow is characterized in that the intermediate region is made up of a plurality of small regions having a predetermined width with different hardness in the width direction, and among adjacent small regions, the one closer to the central region is softer, and at the boundary between the small regions, the woven resin of one small region and the woven resin of the other small region are intertwined. The pillow described in claim 1, characterized in that the lower layer has a protrusion that protrudes toward the middle layer from one end to the other in the width direction in a portion that supports the user's neck. The wire diameter of the knitted resin of the upper layer is smaller than the wire diameter of the knitted resin of the middle layer, and the wire diameter of the knitted resin of the middle layer is smaller than the wire diameter of the knitted resin of the lower layer,
A pillow as described in claim 1 or claim 2, characterized in that when the wire diameter of the knitted resin of the upper layer is 1, the wire diameter of the knitted resin of the middle layer is 1.1 to 1.7, and the wire diameter of the knitted resin of the lower layer is 1.4 to 2.0. the bulk density of the central region is less than the bulk density of the intermediate region, and the bulk density of the intermediate region is less than the bulk density of the end region;
The pillow according to any one of claims 1 to 3, characterized in that when the bulk density of the central region is 1, the bulk density of the end regions is 1.2 to 4.0.