TW201736659A - Heat resistant fiber structure - Google Patents

Abstract

The heat-resistant fiber structure contains heat-resistant fibers having a glass transition temperature of 100 ° C or higher, and is formed by adhering heat-resistant fibers to each other.

Description

Heat resistant fiber structure

The present invention relates to a heat-resistant fiber structure made of heat-resistant fibers and used as a heat insulating material or a sound absorbing material, and a method for producing the same.

Heretofore, fibrous materials made of heat-resistant fibers have been used as heat insulating materials or sound absorbing materials in fields such as vehicles, airplanes, and construction.

From the viewpoint of lightweightness, there is a demand for a fiber material in a fiber structure or the like having the above-described use to have a low density. Further, the fiber material is required to have strength such as bending stress and tensile strength, and it is particularly important to have strength under high temperature conditions. For example, when the above-mentioned fibrous material is used as a sound absorbing and insulating material mounted on the wall surface of an aircraft or used as a filter or the like installed in an engine portion of an automobile, the strength at a high temperature is extremely required in the above applications.

It has been proposed to use the following steps to produce an adiabatic sound absorbing material, that is, the adhesive is added to two or more kinds of cotton to make cotton, and then the cotton material is matted to manufacture the above-mentioned heat insulating and absorbing material. . More specifically, for example, a heat-insulating sound absorbing material produced by the following steps is disclosed, that is, a heat-resistant resin adhesive is added to a cotton material and the cotton material is used. The heat treatment is performed, and the heat insulating sound absorbing material is obtained by padding the whole. Among them, the cotton material is obtained by uniformly mixing the high heat resistant inorganic fiber with the flame retardant organic fiber having a heat melting temperature or a thermal decomposition temperature of 350 ° C or higher. Further, it is also described that by using such a heat insulating sound absorbing material, it is possible to provide a highly safe heat insulating sound absorbing material which is provided by high heat insulating property and high sound absorbing property.

Patent Document 1: Japanese Patent No. 4951507

According to the above-described Patent Document 1, it is possible to obtain a heat-insulating sound absorbing material which has high heat insulating property and high sound absorbing property and can be bent. However, the heat insulating sound absorbing material at this time is formed by adhering fibers to each other with an adhesive. Therefore, it cannot be said that the strength is large enough. In particular, since the adhesive dissolves under high temperature conditions, there is a problem that the strength is lowered.

In the case where the fiber structure system is formed by adhering fibers to each other via an adhesive, it is necessary to increase the amount of the adhesive in order to increase the strength. However, if the content of the adhesive is increased, the content of the heat-resistant fiber is lowered, so that heat resistance is not obtained. As a result, there is a problem that it is difficult to obtain both strength and heat resistance at the same time.

Accordingly, the present invention has been made to solve the above problems. It is an object of the invention to provide a heat-resistant fiber structure which is excellent in heat resistance, bending stress, tensile strength and the like.

In order to achieve the above object, the heat-resistant fiber structure of the present invention is a fiber structure containing heat-resistant fibers having a glass transition temperature of 100 ° C or higher, and the heat-resistant fibers are adhered to each other.

According to the present invention, it is possible to provide a heat-resistant fibrous structure having excellent heat resistance, bending stress, tensile strength, and the like.

The heat-resistant fiber structure of the present invention (hereinafter, simply referred to as "fiber structure") is made of a plurality of heat-resistant fibers that are adhered to each other. The fiber structure of the present invention is different from the fiber structure of the above-described prior art. The fiber structure of the present invention does not use a low-melting adhesive fiber, but directly bonds the heat-resistant fibers to each other, and thus has the following characteristics: excellent heat resistance and excellent strength.

In addition, the term "adhesive" as used herein means a state in which the fibers are softened by heating, and the fibers are deformed by the overlapping force at the intersection thereof to be bitten together or the fibers are melted and integrated.

<heat-resistant fiber>

A fiber having a glass transition temperature T _g of 100 ° C or more is used as a heat-resistant fiber for forming a fiber structure.

Here, the heat resistance index generally uses the glass transition temperature (polymer open The temperature at which micromolecular motion begins. However, the resin having a glass transition temperature of 100 ° C or higher is called an engineering plastic, and is very suitable for use in applications requiring heat resistance. Further, the fiber used as the raw material of the resin is referred to as a heat resistant fiber.

The heat-resistant fiber is a fiber which is softened by high-temperature superheated steam (150 ° C to 600 ° C) and is self-adhesive. The heat resistant fibers are, for example, polyamine fibers, meta-aramid fibers, para-aramid fibers, melamine fibers, polybenzoxazole fibers, Polybenzimidazole fiber, polybenzoxazole fiber, polyarylate fiber, polyether fluorene fiber, liquid crystal polyester fiber, polyamidamine fiber, polyether amide fiber, polyetheretherketone fiber, polyether ketone Fiber, polyetherketoneketone fiber, polyamidamine fiber, and the like. The above fibers may be used singly or in combination of two or more.

In the above-mentioned fibers, polyamine fibers are preferably used from the viewpoint of low water absorbability and chemical resistance, and from the viewpoint of flame retardancy and low smoke generation, polyether ya is preferably used. Amidamide fiber.

The polyamide fiber is, for example, a fiber formed of a semi-aromatic polyamine, which is obtained from a dicarboxylic acid mainly composed of an aliphatic diamine and an aromatic component. The aliphatic diamine is represented by the following general formula (1), preferably n = 4 to 12, more preferably n = 6 and n = 9, and particularly preferably n = 9.

[Formula 1] N ₂ -(CH ₂ ) _n -NH ₂ (1)

The dicarboxylic acid mainly composed of an aromatic component is a dicarboxylic acid having an aromatic component of at least 60 mol% or more. Preferred examples are terephthalic acid and isophthalic acid. Formic acid, naphthalene dicarboxylic acid, and the like. The combination of the aliphatic diamine and the aromatic dicarboxylic acid is preferably a combination of an aliphatic diamine (n=9 in the above general formula (1)) and a phthalic acid.

The polyether phthalimide fiber uses a non-melting point amorphous polyether quinone fiber, and the glass transition temperature T _g can be 200 ° C or higher, preferably: even a small fineness, at a high temperature of 200 ° C or the like Maintain heat resistance. Such heat resistance can be judged by a dry heat shrinkage rate at 200 ° C, and the amorphous polyether fluorene-based fiber used as the heat-resistant fiber of the present invention has a dry heat shrinkage at 200 ° C. The rate can be below 5.0%. Specifically, the dry heat shrinkage ratio is preferably -1.0 to 5.0%.

The amorphous polyether quinone-based fiber is derived from a polymer and is excellent in flame retardancy. For example, the limiting oxygen index value (LOI value) may be 25 or more, preferably 28 or more, and more preferably 30 or more.

The single-fiber fineness of the amorphous polyether quinone-based fiber may be 15.0 dtex or less. The single fiber fineness is preferably from 0.1 to 12.0 dtex, more preferably from 0.5 to 10.0 dtex, from the viewpoint of production cost and ease of handling.

The fiber strength of the amorphous polyether fluorene-based fiber at room temperature is preferably 2.0 cN/dtex or more. When the fiber strength is less than 2.0 cN/dtex, when the paper is made of the amorphous polyether fluorene-imine fiber, paper, non-woven fabric, all fabrics, and the like, there is a case where the process gas permeability is poor. Moreover, the use is limited, so it is not preferred. More preferably, it is 2.3 to 4.0 cN/dtex, and particularly preferably 2.5 to 4.0 cN/dtex.

Cross-sectional shape of the heat-resistant fiber (perpendicular to the longitudinal direction of the fiber) The cross-sectional shape is not limited to the ordinary cross-sectional shape, that is, a circular cross section or a profiled cross section (flat, elliptical, polygonal, three to fourteen-leaf, T-shaped, H-shaped, V-shaped) The dog bone shape (I shape), etc., may also be a hollow cross-sectional shape or the like.

The average fineness of the heat-resistant fibers can be selected, for example, from 0.01 to 100 dtex, preferably from 0.1 to 50 dtex, more preferably from 0.5 to 30 dtex (especially from 1 to 10 dtex), depending on the application. If the average fineness is within this range, the fiber strength and adhesion are in good balance.

The average fiber length of the heat-resistant fibers can be selected, for example, from 10 to 100 mm, preferably from 20 to 80 mm, more preferably from 25 to 75 mm (especially from 35 to 55 mm). If the average fiber length is within this range, the fibers are sufficiently complexed together, so that the mechanical strength of the fiber structure is improved.

For example, the heat-resistant fiber has a crimp ratio of 1 to 50%, preferably 3 to 40%, more preferably 5 to 30% (particularly 10 to 20%). The number of crimps per unit of inch is, for example, 1 to 100/inch, preferably 5 to 50/inch, more preferably 10 to 30/inch.

<Fibrous structure>

The fiber structure of the present invention contains the above heat-resistant fibers and has a structure in which heat-resistant fibers are adhered to each other, and the shape thereof can be selected according to the use, but is usually in the form of a sheet or a plate.

Since the fiber structure of the present invention has a non-woven fiber structure, it is necessary to appropriately adjust the arrangement state and adhesion of the fibers constituting the nonwoven web. status. Among them, the non-woven fiber structure has a high surface hardness and a high bending hardness, and a good balance between lightness and gas permeability. That is to say, it is desirable that the fibers constituting the fiber web are arranged substantially parallel to the faces of the fiber web (non-woven fibers) and are arranged to cross each other.

Preferably, the fiber structure of the present invention is such that the fibers are adhered together at the intersection of the intersections. In particular, a fiber structure (molded body) having high hardness and high strength is required to form a bundle-shaped adhesive fiber, which is a plurality of tens of tens of pieces in a state in which fibers other than the intersection point are arranged approximately in parallel. The left and right fibers are glued together. The fiber structure of the present invention is twisted into a group by locally forming a structure in which the fibers are adhered to each other at the intersection of the single fibers, the intersection of the bundle fibers, or the intersection of the single fibers and the bundle fibers. The structure (the structure in which the fibers are adhered at the intersection, the structure in which the mesh is entangled or the fibers are adhered at the intersection and the adjacent fibers are bound to each other), and the required bending strength, surface hardness, etc. can be exhibited. . In the present invention, it is preferable that the above structure has a form in which the structure is substantially uniformly distributed along the fiber web surface direction and the thickness direction.

In addition, the term "arranged substantially parallel to the fiber web surface" as used herein means a state in which a portion in which a plurality of fibers are partially arranged in the thickness direction is repeated. More specifically, it refers to a state in which the ratio of the number of fibers extending over 30% of the thickness of the fiber web and continuously extending in the thickness direction is observed when the fiber structure of the fiber structure is observed with a microscope. It is 10% or less (especially 5% or less) of all the fibers on the cross section.

The reasons for arranging the fibers parallel to the fiber web are as follows: if there is If the fibers are oriented in the thickness direction (the direction perpendicular to the mesh surface), then the arrangement of the fibers at the peripheral position will be confused, and a large non-essential void will be generated in the non-woven fibers, and the fiber structure is resistant. The bending strength and surface hardness are lowered. Therefore, it is preferable to minimize the gap. Because of this, the ideal situation is to have the fibers aligned as parallel as possible to the fiber web.

In particular, when the fiber structure of the present invention is a sheet-like or plate-shaped formed body, if a load is applied along the thickness direction of the fiber structure, a large void portion is present, and the void portion is subjected to the The surface of the formed body is easily deformed by the destruction of the load. If the load is applied to the entire formed body, the overall thickness is liable to become small. Therefore, if the fiber structure itself is a resin filler having no voids, the above problem can be avoided, but this causes a decrease in gas permeability, and it is difficult to ensure difficulty in bending (folding resistance) and light weight when bending. Sex.

On the other hand, in order to reduce the deformation of the fiber structure in the thickness direction due to the load, it is conceivable to make the fibers finer and to fill the fibers more densely. However, if it is desired to ensure lightweightness and gas permeability by only fine fibers, the rigidity of each fiber is lowered, and the bending stress is rather lowered. In order to ensure the bending stress, it is necessary to increase the fiber diameter to some extent, but if the coarser fibers are simply added to the fine fibers, the larger voids are likely to appear near the intersection of the coarser fibers, and the fiber structure The body is easily deformed in the thickness direction.

Therefore, the fiber structure of the present invention is formed by arranging and dispersing the fibers in parallel with the mesh surface direction (or making the fiber direction in any direction) so that the fibers cross each other and adhere together at the intersection, thereby forming a small The gaps to ensure lightweight. By the above-mentioned fiber structure, it is also integrated Proper air permeability and surface hardness are guaranteed. In particular, in the case where bundle fibers which are adhered in parallel to the longitudinal direction of the fiber are formed at positions which are not substantially intersected with other fibers but are arranged substantially in parallel, compared with the case where the fiber structure is made only of a single fiber. Mainly to ensure high bending strength. In the case where it is desired to obtain a fiber structure having a high hardness and strength, it is preferred that the fibers are adhered one by one at the intersection of the intersections, and the fibers are arranged in a bundle at the intersection and the intersection. A plurality of bundles of fibers are formed. The above structure can be confirmed by observing the existence state of the single fiber in the cross section of the molded body.

In the fiber structure of the present invention, the fiber adhesion rate of the heat-resistant fiber is preferably from 10 to 85%, more preferably from 25 to 75%, still more preferably from 40 to 65%.

The reason is as follows: in the case where the fiber adhesion rate is less than 10%, the hardness, the bending stress, and the tensile strength are sometimes lowered; in the case where the fiber adhesion ratio is more than 85%, the voids between the fibers are changed. Small, so there are occasions that the apparent density is too large, and the lightweight is impaired. In other words, by setting the fiber adhesion ratio to 10 to 85%, it is possible to further increase the strength such as bending stress and tensile strength without deteriorating the lightweight property.

It should be noted that the fiber adhesion ratio indicates the ratio of the number of cross-sections of two or more fibers bonded together to the number of cross-sections of all the fibers in the non-woven fiber cross-section, and the fiber adhesion ratio can be described in Examples described later. The method is measured. Therefore, the low fiber adhesion rate means that the ratio of the plurality of fibers sticking to each other (the ratio of the fibers that are collectively bonded together) is small.

The heat-resistant fibers constituting the nonwoven fabric structure are adhered to each other at the joint of the fibers, but in order to exhibit a large bending stress with as few joints as possible, it is preferable that the adhesion point is in the thickness direction. The surface of the fibrous structure is evenly distributed to the inside (central portion) up to the back. If the adhesion point is concentrated on the surface or the inside, it is not only difficult to ensure sufficient bending stress, but also the morphological stability of a portion having a small adhesion point is lowered. Therefore, from the viewpoint of further improving the bending stress without lowering the morphological stability, it is preferably in the three regions formed by the cross section in the thickness direction of the fiber structure and three equal parts in the thickness direction. The fiber adhesion rate of the portion (center portion) is within the above range (10 to 85%).

The uniformity of the fiber adhesion ratio in each region (that is, the difference between the maximum value and the minimum value of the fiber adhesion ratio) is preferably 20% or less (for example, 0.1 to 20%), more preferably 15% or less (for example, 0.5 to 15). %), especially preferably less than 10% (for example, 1 to 10%).

Since the fiber structure of the present invention has the above-described uniformity in the thickness direction of the fiber structure, the fiber structure is excellent in hardness, bending strength, folding resistance, and toughness.

In the present invention, the "region formed by three equal divisions in the thickness direction" means that each region is divided into three equal portions by cutting in a direction orthogonal to the thickness direction of the sheet-like fiber structure.

Therefore, in the fiber structure of the present invention, not only the adhesion of the heat-resistant fibers is uniformly dispersed and adhered, but also the dots are densely woven in a short adhesion point distance (for example, several tens to several hundreds of μm). A network structure. With the above configuration, the fiber of the present invention can be The dimensional structure has the following assumptions: the fiber structure can improve the followability to deformation by the flexibility of the fiber structure even if it has an external force, and the external force dispersion is applied to the adhesion points of the finely dispersed fibers. It becomes smaller and higher, so it exhibits higher bending stress and higher tensile strength. On the other hand, in the prior art, the fiber structure in which the heat-resistant fibers are adhered to each other via the adhesive fibers can be presumed to be: in order to secure heat resistance, the amount of the adhesive fibers is limited, and the number of the adhesive spots is reduced; Even if the amount of the adhesive fiber is increased and the adhesion point is increased, heat resistance cannot be obtained. It is difficult to uniformly disperse the adhesion point in the thickness direction of the fiber structure, so that deformation is likely to occur, and bending stress and tensile strength are lowered.

In the fiber structure of the present invention, the frequency of occurrence of the single fiber (single fiber end face) in the cross section in the thickness direction is not particularly limited. For example, the frequency of occurrence of the single fibers present in an area of any 1 mm ² of the cross section may be 100/mm ² or more (for example, 100 to 300). In particular, in the case where mechanical properties are more required than lightness, the frequency of occurrence of the single fibers may be, for example, 100 pieces/mm ² or less, preferably 60 pieces/mm ² or less (for example, 1 to 60 pieces/mm ^{2 ).} More preferably, it is 25 / mm ² or less (for example, 3 to 25 / mm ² ). If the frequency of occurrence of the single fibers is too high, the adhesion point of the fibers is reduced, and the strength of the formed body formed of the fiber structure is lowered. It should be noted that if the frequency of occurrence of the single fibers exceeds 100/mm ² , the bundle-like adhesion point of the fibers is reduced. Since the adhesion point of the bundled adhesive fiber is reduced, it is difficult to ensure a high bending strength. In the case where the molded body has a plate shape, it is preferable that the shape of the fibers bundled in a bundle shape is thin in the thickness direction of the molded body and wide in the surface direction (longitudinal direction or width direction).

In the present invention, the frequency of occurrence of the single fibers is measured as follows. In other words, the range corresponding to 1 mm ² selected from the scanning electron microscope (SEM) photograph of the cross section of the molded body was observed, and the number of single fiber cross sections was counted. Several places are arbitrarily selected from the photographs (for example, 10 places are randomly selected) and the same observation is made, and the average value per unit area of the single fiber cross section is determined as the frequency of occurrence of the single fibers. At this time, all the fibers in the single fiber state in the cross section were counted. That is to say, in addition to the fibers completely in the single fiber state, even if a plurality of fibers are adhered together, as long as they are kept at a certain distance from the adhesive portion in the cross section and are in a single fiber state, these fibers are also used as the fibers. Single fiber counts out.

The heat-resistant fiber in the fiber structure suppresses the decrease in the yield of the fiber structure due to the fiber drop or the like by not restraining both ends in the thickness direction (the fiber does not penetrate the fiber structure in the thickness direction). The method for producing the heat-resistant fibers is not particularly limited. However, the fiber molded body obtained by entanglement of the heat-resistant fibers is laminated, and the number of layers to be laminated is a plurality of layers, and the means for adhering by the superheated vapor is used. Simple and reliable. Further, by adjusting the relationship between the fiber length and the thickness of the fiber structure, the fibers at both ends in the thickness direction of the fiber structure can be greatly reduced. From the above viewpoint, the thickness of the fiber structure is 10% or more (for example, 10 to 1000%), preferably 40% or more (for example, 40 to 800%), and more preferably 60% or more (for example, 60%) with respect to the fiber length. 700%), especially preferably 100% or more (for example, 100 to 600%). If the thickness of the fiber structure When the degree of the fiber and the fiber length are within this range, the mechanical strength of the fiber structure is not reduced, and the yield of the fiber structure can be suppressed from being lowered by the fiber falling off or the like.

As described above, the density and mechanical properties of the fiber structure of the present invention are affected by the ratio of the bundled binder fibers and the state of existence. The photograph obtained by magnifying the cross section of the fiber structure by SEM can easily measure the fiber adhesion rate indicating the degree of adhesion based on the number of fiber cross-sections adhered in a predetermined region. However, in the case where the fibers are bundled, since the fibers are bundled or the fibers are adhered at the intersection, it is easy to become a fiber sheet especially at a high density. Body observation.

In the present invention, the area occupied by the cross section of the fiber structure and the bundle fiber bundle in the cross section (section in the thickness direction) of the fiber structure, that is, the fiber filling ratio can be used as an index reflecting the degree of adhesion of the fiber. . The fiber filling ratio in the cross section in the thickness direction is, for example, 20 to 80%, preferably 20 to 60%, more preferably 30 to 50%. If the fiber filling ratio is too small, the voids in the fiber structure are excessive, and it is difficult to secure the required surface hardness and bending stress. On the other hand, if the voids in the fiber structure are excessively large, although the surface hardness and the bending stress can be sufficiently ensured, there is a tendency that it is very heavy and the air permeability is lowered.

Even if the fiber structure of the present invention (especially, the fiber structure is bundled, the fiber structure having a single fiber having a frequency of 100/mm ² or less) has a plate shape, and preferably, the fiber structure has difficulty in deformation. The surface hardness is, for example, a concave shape or the like by a load. As the above-mentioned index, the hardness of the A-type rubber hardness tester (test according to the "Test method for hardness of vulcanized rubber and thermoplastic rubber" according to Japanese Industrial Standard JIS K6253) is, for example, A50 or more, preferably A60 or more, and more preferably A70. the above. If the hardness is too small, it is easily deformed by the load applied to the surface.

In order to balance the flexural strength and the surface hardness at a high level with lightness and gas permeability, the fiber structure containing such a bundled adhesive fiber preferably has a low frequency of occurrence of the bundled adhesive fiber and The intersection of the fibers (bundle fibers and/or single fibers) is adhered at a relatively high frequency. However, if the fiber adhesion rate is too high, the distance between the adhesion points is too short, the flexibility is lowered, and it is difficult to eliminate the deformation caused by the external stress. Therefore, as described above, the fiber structure of the present invention preferably has a fiber adhesion ratio of 85% or less. Since the fiber adhesion rate is not too high, the passage formed by the small voids can be secured in the fiber structure, and the lightness and the air permeability can be improved. Therefore, in order to exhibit a large bending stress, surface hardness, and air permeability with as few joints as possible, it is preferred that the fiber adhesion ratio is uniformly distributed from the surface of the fiber structure to the inside along the thickness direction ( Central part) up to the back.

If the adhesion point is concentrated on the surface or the inside, it is difficult to ensure the above-mentioned bending stress and shape stability, and it is difficult to ensure the air permeability. Therefore, in the fiber structure of the present invention, the fiber adhesion rate in the central portion in the region (surface, central portion, and back surface) formed by halving in the thickness direction in the thickness direction cross section is preferably In the above range, it is more preferable that the fiber adhesion rate of any of the surface, the central portion, and the back surface is above Within the scope. The difference between the maximum value and the minimum value of the fiber adhesion ratio in each region may be 20% or less (for example, 0.1 to 20%), preferably 15% or less (for example, 0.5 to 15%), and more preferably 10% or less (for example, 1). ~10%). In the present invention, if the fiber adhesion ratio is uniform in the thickness direction, the bending stress, the tensile strength, the folding endurance, the toughness, and the like are excellent. The fiber adhesion rate in the present invention is measured by the method described in the examples below.

The fiber structure of the present invention exhibits the bending strength which is not obtained by the fiber structure formed by the heat-resistant fibers adhered together by the adhesive fibers in the prior art, which is also a characteristic of the fiber structure of the present invention. One. In the present invention, in order to exhibit the bending strength, according to Japanese Industrial Standard JIS K7171 "Method for Calculating Plastic Bending Properties", the bending stress is measured by the reaction force and the bending amount of the sample which is caused when the sample is gradually bent. The bending stress is used as an indicator of the bending behavior. That is, the greater the bending stress, the harder the fiber structure. Moreover, the larger the amount of bending (displacement) until the object to be measured is damaged, the better the molded body is bent.

The fiber structure of the present invention has a bending stress in at least one direction (preferably all directions) of 0.05 MPa or more (for example, 0.05 to 100 MPa), preferably 0.1 to 30 MPa, and more preferably 0.2 to 10 MPa. . If the bending stress is too small, the fiber structure can be easily bent by its own weight or a small load when it is used as a sheet material. If the bending stress is too large, the fiber structure will be too hard. If the stress peak is exceeded and the fiber structure is bent, the fiber structure is bent and is easily broken. In addition, in order to obtain hardness exceeding 100 MPa, it is necessary to increase the density of a fiber structure, and it is difficult to ensure lightweight.

In the fiber structure of the present invention, excellent lightness can be ensured by the voids generated between the fibers. The voids are different from the sponge-like resin foam, and the respective pores are not independent but integrated, and the fiber structure of the present invention has gas permeability. The above construction is extremely difficult to manufacture by ordinary hardening techniques in the prior art. The conventional hardening method includes, for example, a method of impregnating a resin, a method of forming a film-like structure by adhering the surface portions densely together.

That is, the fiber structure of the present invention has a low density. Specifically, the apparent density is, for example, 0.03 to 0.7 g/cm ³ . In particular, in applications requiring light weight, the apparent density may be, for example, 0.05 to 0.5 g/cm ³ , preferably 0.08 to 0.4 g/cm ³ , and more preferably 0.1 to 0.35 g/cm ³ . In applications where hardness is required more than lightness, the apparent density is, for example, 0.2 to 0.7 g/cm ³ , preferably 0.25 to 0.65 g/cm ³ , more preferably 0.3 to 0.6 g/cm ³ . If the apparent density is too low, although it is lightweight, it is difficult to ensure sufficient bending hardness and surface hardness. On the contrary, if the apparent density is too high, although the hardness is ensured, the lightness is lowered. It should be noted that if the apparent density is lowered, the fibers will entangle and approach the common non-woven fibrous structure that is adhered together at the intersection. On the other hand, if the density is increased, the fibers adhere to a bundle and become a structure close to the porous formed body.

It should be noted that the "apparent density" herein refers to a density calculated based on the thickness and the mass per unit area measured according to the standard of Japanese Industrial Standard JIS L1913 (general non-woven test method).

The mass per unit area of the fiber structure of the present invention can be selected, for example, from about 50 to 10,000 g/m ² , preferably from 150 to 8,000 g/m ² , more preferably from about 300 to 6000 g/m ² . In a more lightweight as compared with the use of which hardness is required, for example, mass per unit area of 1000 ~ 10000g / m ^2, preferably 1500 ~ 8000g / m ^2, more preferably 2000 ~ 6000g / approximately m ^2. If the mass per unit area is too small, it is difficult to ensure hardness. If the mass per unit area is too large, the mesh may be too thick, and during the processing by the superheated steam, the superheated steam does not sufficiently enter the inside of the mesh, and it is difficult to make it a fiber structure having a uniform thickness direction.

When the fiber structure of the present invention has a plate shape or a sheet shape, the thickness thereof is not particularly limited, and can be selected from the range of about 1 to 100 mm. For example, it is 2 to 50 mm, preferably 3 to 20 mm, more preferably 5 to 150 mm. If the thickness is too thin, it is difficult to ensure hardness. If the thickness is too thick, the quality becomes heavy, and the handleability as a sheet is lowered.

The gas permeability of the fiber structure of the present invention is high because it has a nonwoven fabric structure. With respect to the gas permeability of the fiber structure of the present invention, the gas permeability measured by the Frazier method is 0.1 cm ³ /cm ² /sec or more (for example, 0.1 to 300 cm ³ /cm ² /sec), preferably 0.5. ~250 cm ³ /cm ² /sec (for example, 1 to 250 cm ³ /cm ² /sec), more preferably 5 to 200 cm ³ /cm ² /sec. Usually, the air permeability is 1 to 100 cm ³ /cm ² /sec. If the air permeability is too small, it is necessary to apply pressure from the outside so that the air passes through the fiber structure, and it is difficult for the air to naturally enter and exit. On the other hand, if the air permeability is too large, the gas permeability is improved, but if the fiber voids in the fiber structure are excessively large, the bending stress is lowered.

The heat insulating property of the fiber structure of the present invention is also due to its non-woven fiber structure It is made higher and has a lower thermal conductivity of 0.1 W/m ‧ or less. For example, it is 0.03 to 0.1 W/m‧K, preferably 0.05 to 0.08 W/m‧K.

Next, a method of producing the fiber structure of the present invention will be described.

In the method for producing a fiber structure of the present invention, first, the heat resistant fiber is first formed into a mesh. The forming method of the net can adopt a conventional method, such as a direct method, such as a spunbonding method, a meltblowing method, etc.; a dry method, such as a card method using a meltblown fiber, a fixed length fiber, or the like, and an air drying method. (airlaid) law and so on. In the above method, the carding method using meltblown fibers and fixed length fibers is common, and in particular, the carding method using fixed length fibers is common. The mesh made of fixed length fibers is, for example, a random mesh, a semi-random mesh, a parallel mesh, a crossover mesh, or the like. In the case where the ratio of the bundle-shaped adhesive fibers is high, the mesh is preferably a semi-random mesh or a parallel mesh.

In the process of adhering the fibers of the prepared web to each other, the means for adhering the fibers to each other can be adhered to each other by hot air treatment, hot pressing treatment in the prior art, or by overheating. The vapor causes the fibers to stick to each other. In the case of using superheated steam, the web produced in the above process is sent to the next process by a belt conveyor and exposed to a superheated vapor (high pressure vapor) stream, thereby preparing the present invention without A fibrous structure of a woven fiber structure. That is, the web fed by the belt conveyor passes through the superheated vapor stream ejected from the nozzle of the vapor ejecting apparatus, and the heat-resistant fibers are three-dimensionally adhered (heat-adhered) to each other due to the superheated vapor that is blown. together.

Heat treatment with the above superheated steam (150 ° C ~ 600 ° C), heat-resistant fibers will stick to each other and can be made into a fiber network (network). Therefore, it is possible to perform uniform and large-volume processing up to the inside of the thickness direction of the fiber structure.

In addition, the temperature of the superheated vapor sprayed on the heat resistant fiber is preferably in the range of 150 to 600 °C. The reason why it is preferably in the range of 150 to 600 ° C is as follows: if the temperature is lower than 150 ° C, sometimes the energy applied to the heat resistant fiber is insufficient, and the adhesion of the fibers to each other is insufficient; if it is more than 600 ° C Then, sometimes, the energy transmitted to the fibers near the ejection device becomes too large, and the uniformity of the fiber adhesion rate is lowered.

The belt conveyor to be used is basically not particularly limited as long as it can be processed by superheated steam while compressing the web used for processing to a desired density. An endless belt conveyor is most suitable. It should be noted that a conventional independent belt conveyor can be used, and two belt conveyors can be used in combination as needed to sandwich the fiber web between the two belts and transport the web. By transporting in this manner, it is possible to suppress the occurrence of the following problem when the fiber web is processed: the transported web is deformed by an external force such as superheated steam for processing or conveyor vibration. It is also possible to control the density or thickness of the treated nonwoven fabric by adjusting the interval of the tape.

In the case where two belt conveyors are used in combination, a steam injection device for supplying superheated steam to the fiber web is installed in a conveyor, and a superheated vapor is used by a net on the conveyor. Supply to the fiber web. It is also possible to mount the suction box on the conveyor on the opposite side. Excess superheated vapor passing through the web can be sucked in and discharged through the suction box. for At the same time, the both sides of the surface side and the back side of the fiber web are treated with superheated steam, and the suction box can be further installed at the downstream portion of the conveyor on the side where one of the superheated steam injection devices is installed, and the heat is overheated. The steam injection device is disposed in a conveyor opposite to the side on which one of the suction boxes has been mounted. In the case of the superheated steam injection device and the suction tank without the downstream portion, if the surface and the back surface of the fiber web are treated with steam, the following alternative method may be employed: the surface and the back surface of the treated web are turned over, And let it pass through the internal space of the processing device again.

The endless belt used for the conveyor is not particularly limited as long as it does not interfere with the transportation of the web and the superheated steam treatment. However, in the case of treatment with superheated steam, sometimes the surface shape of the belt is transferred to the surface of the web under such conditions, and therefore it is preferred to appropriately select the belt depending on the use. In particular, in the case where the surface of the fiber structure is relatively flat, a mesh having a fine mesh is used. It should be noted that 90 meshes are the upper limit, and the fine mesh mesh with more than 90 meshes has low gas permeability and is difficult to pass through the vapor. From the viewpoint of heat resistance against hot steam treatment, etc., the material of the mesh belt is preferably metal, heat-treated polyester resin, polyphenylene sulfide resin, or polyarylate resin. (all-aromatic polyester-based resin), heat-resistant resin such as aromatic polyamine-based resin, and the like.

The superheated steam ejected from the steam injection device is a gas flow, so unlike the water flow complex treatment and the needling treatment, the superheated vapor enters the fiber without moving the fiber in the fiber web, which is the object to be treated, at a long distance. The interior of the net. It can generally be understood that the superheated vapor stream is efficiently activated in the superheated state by its superheating action and its entry into the fiber web. Covering the surface of each heat-resistant fiber present in the fiber web, the heat adhesion can be uniform. Since the treatment is carried out under a high-speed air stream and the time is extremely short, the superheated vapor can sufficiently conduct heat to the surface of the fiber. However, the treatment is terminated before the heat conduction to the inside of the fiber is sufficiently performed, so that it is difficult to cause the following problem: the entire treated web is damaged due to the pressure of superheated steam, heat, etc.; Such deformation. As a result, the thermal adhesion ends without greatly deforming the fiber web, and the degree of adhesion between the surface and the thickness direction is substantially uniform.

In the case of a fiber structure having a high surface hardness and high flexural strength, when superheated steam is supplied to the fiber web and the fiber web is treated, it is important that the fiber web to be treated is exposed to superheated steam. . At this time, the web to be treated is in a state of being compressed to a desired apparent density (for example, 0.03 to 0.7 g/cm ³ ) between the belts used for the conveyor or between the rolls. In particular, in the case where a fiber structure having a relatively high density is desired, it is necessary to compress the fiber web with a sufficiently large pressure when it is treated with superheated steam. The web can also be adjusted to the desired thickness or density by ensuring a suitable gap between the rolls or between the belts for the conveyor. In the case of using a conveyor, it is difficult to compress the web at once, so it is preferable to set the tension of the belt as high as possible, and then gradually narrow the gap from the upstream of the steam treatment place. Moreover, the fiber structure having the required bending hardness, surface hardness, lightness, and air permeability is processed by adjusting the vapor pressure and the processing speed.

At this time, if you want to increase the hardness, if you sandwich the fiber web and spray The back side of the endless belt on the opposite side of the mouth is a stainless steel plate or the like, and the endless belt is made into a structure in which the vapor cannot pass therethrough, and the vapor passing through the web of the object to be treated is reflected therein. With the thermal insulation effect of the vapor, the adhesion will be stronger. On the contrary, in the case where it is required to be slightly adhered, a suction box can be provided to discharge excess steam to the outside.

The nozzle for jetting the superheated steam may be arranged as follows, and a flat plate or a prescribed orifice having a predetermined orifice in the width direction is continuously arranged using a prescribed orifice, and the flow is allowed to flow. The holes are arranged in the width direction of the web receiving the superheated vapor. As long as there are more than one row of orifices, there may be a plurality of orifices. A plurality of nozzle molds having a row of orifices may be arranged in an array.

In the case of using a nozzle having a flow hole in the flat plate, the thickness of the flat plate may be 0.5 to 1 mm. The diameter and the pitch of the orifice are not particularly limited as long as the conditions for fixing the desired fiber are satisfied. However, the diameter of the orifice is usually 0.05 to 2 mm, preferably 0.1 to 1 mm, more preferably 0.2 to 0.5 mm. The spacing of the orifices is usually from 0.5 to 3 mm, preferably from 1 to 2.5 mm, more preferably from 1 to 1.5 mm. If the diameter of the orifice is too small, problems such as low processing accuracy of the nozzle, difficulty in processing, and the like are likely to occur, and problems such as easy clogging of the mesh are likely to occur. On the contrary, if the diameter of the orifice is too large, the vapor ejection force is lowered. On the other hand, if the pitch is too small, the nozzle holes are too dense, so the strength of the nozzle itself is lowered. On the other hand, if the pitch is too large, there is a case where high-temperature steam does not sufficiently contact the fiber web, and the strength of the fiber web is lowered.

As long as the superheated steam can be fixed to the heat resistant fiber, and It is not particularly limited, and the pressure of the superheated vapor may be set depending on the material and form of the fiber to be used. The pressure is, for example, 0.1 to 2 MPa, preferably 0.2 to 1.5 MPa, more preferably 0.3 to 1 MPa. In the case where the pressure of the vapor is too high or too strong, the fibers forming the fiber web will move, the uniformity of the mass distribution of the cloth will be damaged, or the fibers will be excessively melted, which may result in failure to maintain in some places. The shape of the fiber. If the pressure is too weak, there is a case where the heat required for the adhesive fiber cannot be supplied to the fiber web, and there is a case where the superheated vapor cannot pass through the fiber web and the fiber adhesion is uneven in the thickness direction. Therefore, if the pressure is too strong or too weak, there will be a case where it is difficult to control the vapor ejected from the nozzle to be relatively uniform.

The fiber structure having the nonwoven fabric structure obtained as described above has a density substantially equal to that of the ordinary nonwoven fabric and has a high bending stress and surface hardness. Further, the fiber structure not only has gas permeability, sound absorbing property, heat insulating property but also heat resistance. Therefore, with the above properties, the fiber structure can be applied to applications requiring heat resistance such as an interior material of an automobile, an inner wall of an airplane, a building board, and the like.

[Examples]

Hereinafter, the present invention will be described based on examples. It is to be noted that the present invention is not limited to the embodiments described below, and variations or modifications may be made to the embodiments without departing from the scope of the invention.

The values of the respective physical properties in the examples were measured by the methods shown below. It should be noted that “parts” in the examples mean parts by mass, "%" means % by mass.

(Example 1) <Production of fiber structure>

The following heat-resistant fibers (denier: 1.7 dtex, fiber length: 51 mm) were prepared as the heat-resistant fibers of Example 1. The heat-resistant fiber prepared is a semi-aromatic polyamide resin formed from a carbon number of 9 diamine and phthalic acid (manufactured by Kuraray Co., Ltd., trade name: genestar, melting point: 265 ° C, glass conversion) It was made at a temperature of 125 ° C and a thermal decomposition temperature of 400 ° C. Next, a card web having a mass per unit area of 50 g/m ² was produced by the carding method using the heat-resistant fibers, and 12 such carded webs were twisted to form a carded web having a total mass per unit area of 600 g/m ² . The card web was conveyed to a conveyor equipped with a stainless steel endless net having a mesh of 50 and a width of 500 mm.

It should be noted that the belt conveyor is constituted by a pair of conveyors of a lower conveyor and an upper conveyor, and a steam injection nozzle is provided on a belt back side of at least one conveyor. The superheated vapor can be sprayed by the belt to the passing card web. Further, on the upstream side of the nozzle, a metal roller for adjusting the mesh thickness is provided on each of the conveyors (hereinafter, simply referred to as "roller for adjusting the mesh thickness"). The upper surface of the lower conveyor (that is, the surface through which the net passes) is a flat surface, and the lower surface of the upper conveyor is a curved surface curved along the wire thickness adjusting roller, and the upper thickness adjusting roller of the upper conveyor is The web thickness adjusting rollers of the lower conveyor are arranged in pairs.

The upper conveyor can be moved up and down, whereby the interval between the belts for the two conveyors and the roller for adjusting the thickness can be adjusted to a predetermined value. The upstream side of the upper conveyor is inclined at an angle of 30 degrees with respect to the downstream portion as a base point of the wire thickness adjusting roller (relative to the lower surface of the downstream side of the upper conveyor), and the downstream portion is bent so as to be parallel with the lower conveyor . It should be noted that when the upper conveyor moves up and down, the system moves while maintaining the parallel relationship.

The belt conveyors are respectively rotated in the same direction at the same speed, and the belt conveyor has the following structure: the belt and the belt for adjusting the thickness of the belt between the belts of the two conveyors can be maintained The adjustment rollers have a predetermined gap and are pressurized. This is a configuration that works as a so-called calendering process to adjust the web thickness before steam treatment. That is, the card web fed from the upstream side moves on the lower conveyor, but the interval between the card web and the upper conveyor is gradually narrowed during the period in which the card web reaches the web thickness adjusting roller. . Further, when the interval becomes narrower than the mesh thickness, the net is caught between the belts of the upper and lower conveyors, and moves while being gradually compressed. The web is compressed until it reaches a thickness substantially equal to the gap set for the net thickness adjusting roller, and the superheated steam treatment is performed in the thickness state, and then the thickness is maintained while maintaining the thickness at the downstream portion of the conveyor. Here, the wire thickness adjusting roller was adjusted to have a linear load of 50 kg/cm.

Next, a card web is introduced toward the vapor ejecting apparatus provided on the lower conveyor, and 300° C of superheated steam is ejected from the apparatus toward the thickness direction (vertical) of the card web, and the superheated steam is passed through the thickness direction to be steamed. By gas treatment, a fiber structure having the nonwoven fabric structure of the present example was obtained. The nozzle of the vapor injection device is placed in the lower conveyor to ensure that superheated vapor is blown to the carding web via the web on the conveyor, and a suction device is provided on the upper conveyor. On the downstream side of the net forward direction of the spraying device, an injection device in which the arrangement position of the nozzle and the suction device has been exchanged is additionally provided, and the surface and the back surface of the card web are subjected to superheated steam treatment.

It is to be noted that a steam injection device having a diameter of 0.3 mm and a nozzle arranged in a row at a pitch of 1 mm along the width direction of the conveyor was used. The processing speed was set to 3 m/min, and the interval (distance) between the nozzle side and the suction side upper and lower conveyor belts was set to 5 mm. The nozzle is set in a state in which it is in contact with the belt on the back side of the belt used for the conveyor, and sometimes it is not in contact.

<Measurement of mass per unit area>

The mass per unit area (g/m ² ) of the produced fiber structure was measured in accordance with Japanese Industrial Standard JIS L1913. The above results are shown in Table 1.

<Measurement of apparent density>

The thickness (mm) of the produced fiber structure was measured in accordance with Japanese Industrial Standard JIS L1913, and the apparent density (g/cm ³ ) was calculated based on the thickness value and the mass per unit area. The above results are shown in Table 1.

<Measurement of fiber adhesion rate>

A photograph of the cross section of the fiber structure was expanded to 100 times by a scanning electron microscope (SEM). Next, the photograph of the cross section in the thickness direction is divided into three in the thickness direction of the photographed fiber structure, and the number of the cut faces in which the fibers are adhered to each other is determined with respect to the three-divided portion. The ratio of the number of fiber-cut surfaces (fiber end faces) that can be identified in each of the regions (the front side region, the inner portion (central portion) region, and the back surface region).

More specifically, based on the following formula (1), the number of cross-sections in which the fibers in which two or more fibers are adhered together is expressed as a percentage of the number of all the cross-sections of the fibers that can be recognized in each region. The proportion.

[Math 1] Fiber adhesion ratio (%) = (number of cross-sections of two or more fibers bonded together) / (number of all cross-sections of fibers) × 100 (1)

It should be noted that the portions where the fibers are in contact with each other are divided into: a portion that does not adhere to only the simple contact and a portion that is adhered by adhesion. The fiber structure was cut in order to perform photography with a microscope. In the cut surface of the fiber structure, the fibers that are simply contacted are separated from each other by the stress of the respective fibers. Therefore, in the photograph of the section, it is assumed that the contacting fibers are adhered to each other.

In the case where the number of the fiber cross-sections is 100 or less in each of the photographs, the photograph to be observed is added so that the number of the cross-sections of all the fibers exceeds 100. Calculate the fiber adhesion rate for each region formed after three equal divisions, and find the difference between the maximum value and the minimum value (ie, both Uniformity). The above results are shown in Table 1.

<Measurement of bending stress>

A test piece (width: 10 mm, length: 100 mm) was prepared from the prepared fiber structure according to the standard of Japanese Industrial Standard JIS K7171 (Purification of Plastic Bending), and the distance between the fulcrums was set to 80 mm, and the test speed was set to 10 mm. /min, the bending stress (MPa) was measured. The above results are shown in Table 1.

<Measurement of tensile strength>

A test piece (having a width of 30 mm and a length of 150 mm) was prepared from the prepared fiber structure according to the standard of Japanese Industrial Standard JIS L1913 (Testing method for general non-woven fabric), and the clamping interval was set to 100 mm, and the test speed was set to 10 mm. /min, tensile strength (N/30mm) was measured. The above results are shown in Table 1.

(Example 2) <Production of fiber structure>

Amorphous polyether phthalamide fiber (manufactured by Kuraray Co., Ltd., trade name: KURAKISSS, glass transition temperature: 125 ° C, thermal decomposition temperature: 540 ° C, fineness: 8.9 dtex, fiber length: 51 mm) was prepared as the fiber of Example 2. Used for structures. Next, a card web having a mass per unit area of 100 g/m ² was produced by the heat-resistant fiber and carding method, and the card web was sheet-formed by a water flow method.

Next, ten sheets of the sheet were laminated, and the laminate was conveyed to a belt conveyor equipped with a stainless steel ring net having a mesh size of 500 and a width of 500 mm.

Next, in accordance with the above-described Embodiment 1, a card web is introduced toward a vapor ejecting apparatus provided on the lower conveyor, and 300 ° C of superheated steam is ejected from the apparatus toward the thickness direction of the card web (vertical) and the superheated steam is allowed. The vapor treatment was carried out through the thickness direction to obtain a fiber structure having the nonwoven fabric structure of the present example.

Next, according to the above-described Embodiment 1, the mass per unit area, the apparent density, the fiber adhesion rate, the bending stress, the bending load, and the tensile strength were measured. The above results are shown in Table 1.

(Example 3) <Production of fiber structure>

Nine sheets of the card web used in Example 1 were laminated, and the laminated nine carded webs were subjected to hot press treatment at 260 ° C for 1 minute in a hot press apparatus to obtain a fiber structure.

Next, according to the above-described Embodiment 1, the mass per unit area, the apparent density, the fiber adhesion rate, the bending stress, the bending load, and the tensile strength were measured. The above results are shown in Table 1.

(Comparative Example 1) <Production of fiber structure>

The semi-aromatic polyamide fiber prepared in Example 1 and the polypropylene/polyethylene core sheath type composite fiber for the adhesive fiber (manufactured by UBE EXSYMO Co., LTD., HR-NTW, core) were prepared. The glass transition temperature is: -20 ° C, the glass transition temperature of the sheath: -120 ° C, the thermal decomposition temperature of the core: 240 ° C, the thermal decomposition temperature of the sheath: 270 ° C, the fineness: 1.7 dtex, the fiber length: 51 mm) And mixed together in a mass ratio of 80/20. Next, a carding web having a mass per unit area of 50 g/m ^{2 was} produced by the blending fiber and carding method, and six carding webs were laminated to form a carding web having a total mass per unit area of 300 g/m ² . The card web was heat-treated at 150 ° C for 1 minute in a hot air dryer to obtain a fiber structure of the comparative example.

Next, according to the above-described Embodiment 1, the mass per unit area, the apparent density, the fiber adhesion rate, the bending stress, the bending load, and the tensile strength were measured. The above results are shown in Table 1.

As shown in Table 1, the heat-resistant fibers having the glass transition temperatures of 100 ° C or higher in Examples 1 to 3 were compared with the fiber structures in which the heat-resistant fibers of Comparative Example 1 were adhered to each other by the adhesive. Heat stuck in The fiber structure together is excellent in bending stress and tensile strength. In particular, it can be said that the fiber structures having higher uniformity of fiber adhesion in Examples 1 and 2 have significantly higher values of bending stress and tensile strength than those of Comparative Example 1, and the strength is very excellent. .

It can be said that the fiber structure in Examples 1 to 2 has a tensile strength retention ratio (tensile strength at 180 ° C / tensile strength at normal temperature) which is very large compared with Comparative Example 1, and the heat resistance is very high. excellent.

As shown in Table 1, the fiber structure of Comparative Example 1 had a bending stress of 0, and such a fiber structure was soft to be bent by its own weight, and the bending stress was below the measurement limit. For example, when such a fiber structure is used as a heat insulating material for construction, it does not adhere to a wall surface, a ceiling surface, or the like, and it hangs down, so that handling property is poor. On the other hand, the bending stress in Example 3 was 0.4 MPa, which was superior to Comparative Example 1. If it has a bending stress of about 0.4 MPa, it will not hang down from the wall during construction. Therefore, it can be said that the operability of the third embodiment is greatly improved from the viewpoint of ease of handling and the like.

It can be said that the fiber structure of Example 3 has a tensile strength retention ratio (tensile strength at 180 ° C / tensile strength at normal temperature) which is extremely large compared with Comparative Example 1, and the heat resistance is extremely excellent.

On the other hand, in Comparative Example 1, the structure in which the fibers were adhered to each other with an adhesive was used, and as shown in Table 1, the fiber adhesion rate was remarkably lowered. As a result, it can be said that the bending stress and the tensile strength are remarkably lowered as compared with Examples 1 to 2.

- Industrial availability -

As described above, the present invention is applicable to a heat-resistant fiber structure made of heat-resistant fibers and used as a heat insulating material or a sound absorbing material.

Claims (5)

A heat-resistant fiber structure characterized by comprising a fiber structure having heat-resistant fibers having a glass transition temperature of 100 ° C or higher, and the heat-resistant fibers are adhered to each other. The fiber structure according to claim 1, wherein the heat resistant fiber has a fiber adhesion ratio of 10 to 85%. The fiber structure according to claim 1 or 2, wherein in the three regions obtained by halving the thickness in the thickness direction of the fiber structure, the fiber adhesion rate at the central portion is 10~85%. The fiber structure according to claim 2, wherein the uniformity of the fiber adhesion is 20% or less. The fiber structure according to any one of claims 1 to 4, wherein the apparent density is 0.03 to 0.7 g/cm ³ .