JP4980837B2 - Electromagnetic wave absorber and manufacturing method thereof - Google Patents

Description

  The present invention relates to an electromagnetic wave absorber used as an electromagnetic wave shielding material for constituting an electromagnetic wave receiver in microwave communication or the like, a housing inner / outer wall of an electronic device that generates electromagnetic waves, a structure such as a house or a vehicle, and an interior material, and the like It relates to a manufacturing method.

  In a broad sense, an electromagnetic wave means a wave that collectively refers to radiation, radio waves, and light, but in a narrow sense, it means a radio wave such as a microwave and is generated by the flow of electricity. In addition, electromagnetic waves have the property that they naturally resonate with magnetism or conductive compounds and are converted into thermal energy by conductive loss. Utilizing such properties of electromagnetic waves, combining with magnetic or conductive compounds (conductive agents or electromagnetic wave absorbers) that can be absorbed by resonating with electromagnetic waves, communication systems such as laser communication and microwave communication, and parking lots And automatic toll collection (ETC) systems such as toll roads have been developed. In such a system, an electromagnetic wave receiver such as an antenna is composed of the above electromagnetic wave absorber, but may be combined with other materials in order to improve lightness, moldability, economic efficiency, environmental conservation, and the like. It is being considered.

  For example, as an electromagnetic wave absorbing plate using industrial waste, JP 2006-351893 (Patent Document 1) discloses an electromagnetic wave absorbing plate in which waste ferrite powder and waste resin material are molded into a desired shape. Yes. This electromagnetic wave absorbing plate is manufactured by heating and melting a waste ferrite resin pellet and a waste synthetic resin. However, since this electromagnetic wave absorbing plate does not have air permeability, it cannot be used for applications that require air permeability.

  On the other hand, there are concerns about adverse effects on human bodies due to electromagnetic waves (particularly microwaves and low frequencies) generated from electronic devices such as home appliances and OA devices, high-voltage power transmission lines, wireless LANs, and mobile phones. It is also known that such leaked electromagnetic waves act on other electronic devices such as heart pacemakers and precision medical devices, adversely affect electronic control of these devices, and cause malfunctions. . Therefore, an electromagnetic wave shielding material has been developed for shielding or absorbing electromagnetic waves using an electromagnetic wave absorber and suppressing harmful effects caused by the electromagnetic waves.

  For example, in Japanese Patent Application Laid-Open No. 2002-164690 (Patent Document 2), an air layer (3) is provided between a surface layer (1) and a reflective substrate (2). It has the property of transmitting part of electromagnetic waves and sound and reflecting part of it, and the reflective substrate (2) has the characteristic of reflecting both electromagnetic waves and sound, and has a surface layer (1) and an air layer ( An electromagnetic wave absorbing sound absorbing plate that has a layer structure having 3) and a reflective base material (2) and absorbs and attenuates both electromagnetic waves and sound is disclosed. This document describes a breathable electromagnetic wave absorbing sheet containing a conductive material, for example, an electromagnetic wave absorbing sheet composed of pulp, a binder, and carbon fibers. However, this electromagnetic wave absorbing plate does not have sufficient moldability and mechanical properties, and uses a harmful chemical binder, and therefore has low environmental conservation.

Furthermore, JP-A-2002-178313 (Patent Document 3) includes a pair of front and back board bodies formed from a thin wood fiber base material, and an electromagnetic shielding sheet provided between the pair of front and back board bodies. The electromagnetic shielding sheet is formed by braiding metal fine wires into a net shape, and an odor adsorption and electromagnetic shielding board in which an odor adsorbent is inserted between the pair of front and back board bodies is disclosed. In this document, a wood board made of wood fibers such as wood chips and a binder is described as the wood fiber base material. However, this electromagnetic shielding board has low electromagnetic wave absorbability, and has low moldability and environmental conservation.
JP 2006-351893 A (Claim 1, paragraph [0011], Example) JP 2002-164690 A (claim 1, paragraph [0014] [0015] embodiment) JP 2002-178313 A (Claim 1, paragraph [0018])

  Accordingly, an object of the present invention is to provide an electromagnetic wave absorbing material having a high absorbability with respect to electromagnetic waves in a wide range of incident angles and frequencies, and excellent in air permeability and moldability, and a method for producing the same.

  Another object of the present invention is to provide an electromagnetic wave absorbing material having a heat insulating property and excellent in mechanical properties such as bending stress and toughness, and a method for producing the same.

  Still another object of the present invention is to provide an electromagnetic wave absorbing material that can be easily manufactured without using harmful components and a method for manufacturing the same.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have incorporated a conductive agent (electromagnetic wave absorber) into a molded article having a non-woven fiber structure in which fibers are appropriately bonded by wet heat adhesive fibers. The present invention has been completed by finding that it can exhibit high absorptivity with respect to electromagnetic waves having a wide range of incident angles and frequencies, and can improve air permeability and moldability.

That is, the electromagnetic wave absorbing material of the present invention is an electromagnetic wave absorbing material containing a wet heat adhesive fiber and a conductive agent (electromagnetic wave absorber), has a non-woven fiber structure, and is bonded to the wet heat adhesive fiber. Is formed of a fixed molded body. This electromagnetic wave absorbing material has a fiber adhesion rate of 85% or less in each region divided in three in the thickness direction in the cross section in the thickness direction, and the ratio of the minimum value to the maximum value of the fiber adhesion rate in each region Is 50% or more. Further, it has an apparent density of 0.1 to 1 g / cm ³ and has a maximum bending stress in at least one direction of 0.05 MPa or more, and a bending amount 1.5 times the bending amount indicating the maximum bending stress. The bending stress may be 1/5 or more with respect to the maximum bending stress. Furthermore, the air permeability according to the fragile method is about 0.1 to 300 cm ³ / (cm ² · sec). The wet heat adhesive fiber may contain an ethylene-vinyl alcohol copolymer. The ratio of the conductive agent is about 0.1 to 100 parts by mass with respect to 100 parts by mass of the wet heat adhesive fiber. Furthermore, in the electromagnetic wave absorbing material, the conductive agent is incorporated in the non-woven structure. For example, the conductive agent may be granular and may be dispersed and incorporated in the inter-fiber voids in the nonwoven fiber structure.

  The present invention relates to a method for producing an electromagnetic wave absorbing material containing wet heat adhesive fibers and a conductive agent, wherein a nonwoven fiber web containing wet heat adhesive fibers is heat-treated with high-temperature steam to form a nonwoven fiber structure. The manufacturing method of the said electromagnetic wave absorber containing the process of obtaining a body is also included. This manufacturing method may include a step of immersing a molded body having a non-woven structure in a slurry containing a conductive agent.

  In the present invention, since the molded article having a non-woven fiber structure in which fibers are appropriately bonded by wet heat adhesive fibers contains a conductive agent (electromagnetic wave absorber), it absorbs high electromagnetic waves with a wide incident angle and frequency. And has excellent breathability and moldability. Moreover, since it is a non-woven fiber structure, heat insulation is high.

  Furthermore, since the wet heat adhesive fibers are uniformly fused inside the nonwoven fiber structure, the mechanical properties are also excellent. For example, it has a high bending stress even if it is lightweight and has a low density. Moreover, although it has high hardness, it is excellent also in bending resistance and toughness. In other words, this electromagnetic wave absorbing material is molded into a plate shape and hardly undergoes local deformation even when a load is applied to the surface, and because it absorbs the stress by bending and deforming against the applied stress, It has high impact resistance and does not easily break or break even if a strong impact is applied.

  Furthermore, this electromagnetic wave absorbing material can be substantially composed only of fibers, and it is not necessary to add chemical binders or special chemicals, so there is no need to use components that generate harmful components (such as volatile organic compounds such as formaldehyde). Can be easily manufactured.

[Electromagnetic wave absorber]
The electromagnetic wave absorber of the present invention includes a wet heat adhesive fiber and a conductive agent (electromagnetic wave absorber), and has a non-woven fiber structure. In particular, the electromagnetic wave absorbing material of the present invention is composed of a molded body in which fibers are fixed by fusion of the wet heat-adhesive fibers, and has an electromagnetic wave absorbability, as well as an array of fibers constituting a non-woven fiber structure. By setting the bonding state between the fibers within a predetermined range, it cannot be obtained by a normal nonwoven fabric. “Bending behavior (having a high bending stress, and even if bending further past the point showing the maximum bending stress, "Restoring behavior when the stress is released" and "Lightness" and "Surface hardness (characteristics that do not easily deform even when a load is applied to the surface and a force is applied in the thickness direction)" In addition, it is hard to break, and at the same time, it retains shape retention and breathability.

  Such an electromagnetic wave absorbing material, as will be described later, causes high-temperature (superheated or heated) water vapor to act on the web containing the wet heat-adhesive fiber, and exhibits an adhesive action at a temperature below the melting point of the wet heat adhesive fiber, It is obtained by partially bonding the fibers together and focusing them. That is, it is obtained by point-bonding or partial-bonding single fibers and bundle-like bundled fibers so as to form a “scrum” while holding moderately small voids under wet heat.

(Wet heat adhesive fiber)
The wet heat adhesive fiber is composed of at least a wet heat adhesive resin. The wet heat adhesive resin only needs to be able to flow or easily deform at a temperature that can be easily realized by high-temperature steam and to exhibit an adhesive function. Specifically, a thermoplastic resin that is softened with hot water (for example, about 80 to 120 ° C., particularly about 95 to 100 ° C.) and can be self-adhered or bonded to other fibers, for example, a cellulose-based resin (C such as methylcellulose) _1-3 alkylcelluloses, hydroxyalkyl C _1-3 alkyl celluloses such as hydroxypropyl cellulose, carboxy C _1-3 alkyl cellulose or a salt thereof, such as carboxymethyl cellulose), polyalkylene glycol resin (polyethylene oxide, poly C ₂ such as polypropylene oxide _-4 alkylene oxide), polyvinyl resins (polyvinyl pyrrolidone, polyvinyl ether, vinyl alcohol polymers, polyvinyl acetals, etc.), acrylic copolymers and alkali metal salts thereof [(meth) acrylic acid, (meth) acrylamide, etc. Copolymers containing units composed of any acrylic monomers or their salts], modified vinyl copolymers (such as vinyl monomers such as isobutylene, styrene, ethylene, vinyl ether, and maleic anhydride) Copolymer with unsaturated carboxylic acid or its anhydride or salt thereof), polymer with hydrophilic substituent introduced (polyester, polyamide, polystyrene or salt with introduced sulfonic acid group, carboxyl group, hydroxyl group, etc.) Etc.), aliphatic polyester resins (polylactic acid resins, etc.). Furthermore, among polyolefin resins, polyester resins, polyamide resins, polyurethane resins, thermoplastic elastomers or rubbers (such as styrene elastomers), it can be softened at the temperature of hot water (high-temperature steam) to exhibit an adhesive function. Other resins are also included.

These wet heat adhesive resins can be used alone or in combination of two or more. The wet heat adhesive resin is usually composed of a hydrophilic or water-soluble polymer. Among these wet heat adhesive resins, vinyl alcohol polymers such as ethylene-vinyl alcohol copolymers, polylactic acid resins such as polylactic acid, (meth) acrylic copolymers containing (meth) acrylamide units, A vinyl alcohol polymer containing an α-C _2-10 olefin unit such as ethylene or propylene, particularly an ethylene-vinyl alcohol copolymer is preferred.

  In the ethylene-vinyl alcohol copolymer, the ethylene unit content (copolymerization ratio) is, for example, about 10 to 60 mol%, preferably about 20 to 55 mol%, and more preferably about 30 to 50 mol%. When the ethylene unit is in this range, a unique property of having wet heat adhesiveness but not hot water solubility is obtained. If the proportion of the ethylene units is too small, the ethylene-vinyl alcohol copolymer easily swells or gels with low-temperature steam (water), and its form is likely to change only once wetted with water. On the other hand, when the ratio of the ethylene unit is too large, the hygroscopicity is lowered, and fiber fusion due to wet heat is difficult to be exhibited, so that it is difficult to ensure practical strength. When the ratio of the ethylene unit is particularly in the range of 30 to 50 mol%, the processability into a sheet or plate is particularly excellent.

  The saponification degree of the vinyl alcohol unit in the ethylene-vinyl alcohol copolymer is, for example, about 90 to 99.99 mol%, preferably 95 to 99.98 mol%, more preferably 96 to 99.97 mol. %. When the saponification degree is too small, the thermal stability is lowered, and the stability is lowered by thermal decomposition or gelation. On the other hand, if the degree of saponification is too large, it is difficult to produce the fiber itself.

  Although the viscosity average degree of polymerization of an ethylene-vinyl alcohol-type copolymer can be selected as needed, it is 200-2500, for example, Preferably it is 300-2000, More preferably, it is about 400-1500. When the degree of polymerization is within this range, the balance between spinnability and wet heat adhesion is excellent.

  The cross-sectional shape (cross-sectional shape perpendicular to the fiber length direction) of the wet heat-adhesive fiber is a general solid cross-sectional shape, such as a round cross-section or an irregular cross-section [flat, elliptical, polygonal, 3-14 Leaf shape, T-shape, H-shape, V-shape, dogbone (I-shape, etc.)], and may be a hollow cross-section. The wet heat adhesive fiber may be a composite fiber composed of a plurality of resins including at least a wet heat adhesive resin. The composite fiber only needs to have the wet heat adhesive resin on at least a part of the fiber surface, but from the viewpoint of adhesiveness, the wet heat adhesive resin continuously occupies at least a part of the surface in the length direction. Is preferred.

  Examples of the cross-sectional structure of the composite fiber in which the wet heat adhesive fiber occupies the surface include a core-sheath type, a sea-island type, a side-by-side type, a multilayer bonding type, a radial bonding type, and a random composite type. Among these cross-sectional structures, the core-sheath structure (that is, the sheath part is wet-heat-adhesive, which is a structure in which the wet-heat adhesive resin occupies the entire surface continuously in the length direction because it is a highly adhesive structure. A core-sheath structure made of resin is preferred.

  In the case of a composite fiber, wet heat adhesive resins may be combined with each other, but may be combined with non-wet heat adhesive resins. Non-wet heat adhesive resins include water-insoluble or hydrophobic resins such as polyolefin resins, (meth) acrylic resins, vinyl chloride resins, styrene resins, polyester resins, polyamide resins, polycarbonate resins, Examples include polyurethane resins and thermoplastic elastomers. These non-wet heat adhesive resins can be used alone or in combination of two or more.

  Among these non-wet heat adhesive resins, from the viewpoint of heat resistance and dimensional stability, resins having a melting point higher than that of wet heat adhesive resins (particularly ethylene-vinyl alcohol copolymers), such as polypropylene resins and polyester resins. Resins and polyamide resins, particularly polyester resins and polyamide resins are preferred from the standpoint of excellent balance between heat resistance and fiber-forming properties.

Polyester resins include aromatic polyester resins such as poly C _2-4 alkylene arylate resins (polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.), especially polyethylene such as PET. A terephthalate resin is preferred. In addition to ethylene terephthalate units, the polyethylene terephthalate-based resin is composed of other dicarboxylic acids (for example, isophthalic acid, naphthalene-2,6-dicarboxylic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, bis (carboxyphenyl) ethane. , 5-sodium sulfoisophthalic acid, etc.) and diols (for example, diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, cyclohexane-1,4-dimethanol, Units composed of polyethylene glycol, polytetramethylene glycol, etc.) may be included at a ratio of about 20 mol% or less.

  Polyamide resins include polyamides 6, polyamides 66, polyamides 610, polyamides 10, polyamides 12, polyamides 6-12 and other aliphatic polyamides and copolymers thereof, half-synthesized from aromatic dicarboxylic acids and aliphatic diamines. Aromatic polyamide is preferred. These polyamide-based resins may also contain other copolymerizable units.

  In the case of a composite fiber composed of a wet heat adhesive resin and a non-wet heat adhesive resin (fiber-forming polymer), the ratio (mass ratio) of both can be selected according to the structure (for example, core-sheath structure). The wet heat adhesive resin is not particularly limited as long as it exists on the surface. For example, wet heat adhesive resin / non-wet heat adhesive resin = 90/10 to 10/90, preferably 80/20 to 15/85, more preferably 60 / 40 to about 20/80. If the proportion of wet heat adhesive resin is too large, it will be difficult to ensure the strength of the fiber, and if the proportion of wet heat adhesive resin is too small, it will be difficult to have the wet heat adhesive resin continuously in the length direction of the fiber surface. Thus, the wet heat adhesiveness is lowered. This tendency is the same when the wet heat adhesive resin is coated on the surface of the non-wet heat adhesive fiber.

  The average fineness of the wet heat adhesive fiber can be selected, for example, from the range of about 0.01 to 100 dtex, preferably 0.1 to 50 dtex, more preferably 0.5 to 30 dtex (particularly 1 to 10 dtex) depending on the application. Degree. When the average fineness is in this range, the balance between the strength of the fiber and the expression of wet heat adhesion is excellent.

  The average fiber length of the wet heat adhesive fibers can be selected, for example, from a range of about 10 to 100 mm, preferably 20 to 80 mm, more preferably about 25 to 75 mm (particularly 35 to 55 mm). When the average fiber length is within this range, the fibers are sufficiently entangled, so that the mechanical strength of the molded body is improved.

  The crimp rate of the wet heat adhesive fiber is, for example, about 1 to 50%, preferably 3 to 40%, more preferably about 5 to 30% (particularly 10 to 20%). The number of crimps is, for example, about 1 to 100 pieces / 25 mm, preferably about 5 to 50 pieces / 25 mm, and more preferably about 10 to 30 pieces / 25 mm.

(Other fibers)
The electromagnetic wave absorbing material may further contain non-wet heat adhesive fibers. Non-wet heat adhesive fibers include polyester fibers (polyethylene terephthalate fibers, polytrimethylene terephthalate fibers, polybutylene terephthalate fibers, aromatic polyester fibers such as polyethylene naphthalate fibers), polyamide fibers (polyamide 6, polyamide 66, Aliphatic polyamide fibers such as polyamide 11, polyamide 12, polyamide 610, polyamide 612, semi-aromatic polyamide fibers, aromatic polyamide fibers such as polyphenylene isophthalamide, polyhexamethylene terephthalamide, poly p-phenylene terephthalamide, etc. ), Polyolefin fibers (poly C _2-4 olefin fibers such as polyethylene and polypropylene), acrylic fibers (acrylonitrile-vinyl chloride copolymer, etc.) Acrylonitrile fibers having rilonitrile units), polyvinyl fibers (polyvinyl acetal fibers, etc.), polyvinyl chloride fibers (polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, vinyl chloride-acrylonitrile copolymer fibers, etc.) ), Polyvinylidene chloride fiber (fiber such as vinylidene chloride-vinyl chloride copolymer, vinylidene chloride-vinyl acetate copolymer), polyparaphenylene benzobisoxazole fiber, polyphenylene sulfide fiber, cellulosic fiber (for example, rayon fiber) And acetate fibers). These non-wet heat adhesive fibers can be used alone or in combination of two or more.

  These non-wet heat adhesive fibers can be appropriately selected and used according to the application. In the case where mechanical properties such as hardness and bending strength are more important than lightness, it is preferable to use hydrophilic fibers having high hygroscopicity, for example, polyvinyl fibers and cellulose fibers, particularly cellulose fibers. Cellulosic fibers include natural fibers (cotton, wool, silk, hemp, etc.), semi-synthetic fibers (acetate fibers such as triacetate fiber), regenerated fibers (rayon, polynosic, cupra, lyocell (for example, registered trademark name: “ Tencel "etc.)). Among these cellulosic fibers, for example, semi-synthetic fibers such as rayon can be suitably used, and when combined with wet heat adhesive fibers containing an ethylene-vinyl alcohol copolymer, the affinity with wet heat adhesive fibers is high. As the shrinkage progresses, the adhesiveness also improves, and in the present invention, a molded body having a relatively high density and high mechanical properties can be obtained.

  On the other hand, when weight is important, hydrophobic fibers with low hygroscopicity, for example, polyolefin fibers, polyester fibers, polyamide fibers, especially polyester fibers (polyethylene terephthalate fibers, etc.) with an excellent balance of properties. Is preferably used. When these hydrophobic fibers are combined with wet heat adhesive fibers containing an ethylene-vinyl alcohol copolymer, a molded article excellent in light weight can be obtained.

  The average fineness and average fiber length of the non-wet heat adhesive fibers are the same as those of the wet heat adhesive fibers.

  The ratio (mass ratio) between the wet heat adhesive fiber and the non-wet heat adhesive fiber is also determined according to the use of the molded body. The wet heat adhesive fiber / non-wet heat adhesive fiber = 10/90 to 100/0 (for example, 20 / 80 to 100/0). When manufacturing a hard molded object, the one where the ratio of wet heat adhesive fiber is large is preferable, and the ratio (mass ratio) of both is wet heat adhesive fiber / non-wet heat adhesive fiber = 80/20 to 100/0. , Preferably 90/10 to 100/0, more preferably about 95/5 to 100/0. When the ratio of the wet heat adhesive fibers is within this range, a molded product that can ensure high surface hardness and bending behavior can be obtained. In the case of producing a molded body utilizing the characteristics of non-wet heat adhesive fibers, the ratio (mass ratio) of both is wet heat adhesive fibers / non-wet heat adhesive fibers = 20/80 to 99/1, preferably 30. / 70 to 90/10, more preferably about 40/60 to 80/20.

(Conductive agent)
The electromagnetic wave absorber includes a conductive agent (electromagnetic wave absorber) that can resonate with the electromagnetic wave in order to absorb the electromagnetic wave. The conductive agent includes an inorganic conductive agent and an organic conductive agent.

  Examples of the inorganic conductive agent include carbons (for example, carbon black such as furnace black, acetylene black, ketjen black, graphite, etc.), simple metals or alloys (for example, iron, copper, magnesium, aluminum, gold, platinum). , Zinc, manganese, stainless steel, etc.], ceramics [for example, composite metal oxides containing ferrite (mainly iron oxide and metal oxides such as copper, nickel, manganese, zinc, cobalt, barium, magnesium etc.) ), Tourmaline (ionic crystal ore composed of calcium, potassium, sodium, aluminum, chromium, iron, lithium, magnesium, manganese silicon, etc., also referred to as “tourite”), diatomaceous earth, etc.] Is mentioned. Further, it may be a compound containing these inorganic conductive agents, for example, an organic or inorganic compound obtained by plating or vapor-depositing the metal simple substance, or a ceramic carrying carbon black or graphite. These inorganic conductive agents can be used alone or in combination of two or more.

  Examples of the organic conductive agent include polyacetylene resins (eg, polyacetylene), polythiophene polymers (eg, polythiophene), polypyrrole polymers (eg, polypyrrole), and polyaniline polymers (eg, polyaniline). ), A polyester resin modified with an acrylic polymer (for example, a polyester resin with a high degree of polymerization modified with a copolymer of isobutyl methacrylate and butyl acrylate described in JP-A-10-7867, etc.) ) And the like.

  Examples of the shape of these conductive agents include particles (powder), plates (or scales), fibers, and the like. Among these shapes, in the present invention, a particulate shape is preferable because it easily enters and disperses the inter-fiber voids in the nonwoven fiber structure.

  The average particle diameter of the granular conductive agent can be selected according to the fiber diameter of the wet heat adhesive fiber, and can be selected from the range of, for example, about 0.1 to 100 μm, but is usually 0.3 to 50 μm, preferably 0.5. It may be about ˜30 μm, more preferably about 1 to 10 μm (particularly 2 to 5 μm).

  Among these conductive agents, a conductive agent containing at least an inorganic conductive agent [for example, a combination of conductive inorganic particles and a conductive polymer (for example, a polyester-based resin modified with an acrylic polymer)] is preferable. In particular, conductive inorganic particles (for example, metal powder such as magnesium, aluminum and silver, ceramic powder such as ferrite and tourmaline, carbon powder such as carbon black and the like) are preferable. Among the conductive inorganic particles, ceramic powders such as ferrite and carbon powders such as carbon black are preferable from the viewpoint of electromagnetic wave absorption and versatility, and both may be combined. The ratio (mass ratio) between the ceramic powder and the carbon powder is, for example, ceramic powder / carbon powder = 99/1 to 10/90, preferably 90/10 to 30/70, and more preferably 80/20 to 50/50. Degree.

  The proportion of the conductive agent may be appropriately selected according to the type and shape of the conductive agent. For example, 0.1 to 100 parts by mass, preferably 5 to 80 parts by mass with respect to 100 parts by mass of the wet heat adhesive fiber. More preferably, it is about 10-60 mass parts (especially 20-50 mass parts).

  The presence form in the molded body of the conductive agent is not particularly limited, and can be selected according to the shape and type. For example, in the case of a fibrous form, it may be mixed with wet heat adhesive fibers, and may be granular or plate-like. In the case of such a shape, it may be contained in a fiber having a non-woven fiber structure or may be supported on the surface of the molded body (or the fiber surface). In particular, in the present invention, the granular conductive agent is accommodated in the nonwoven fiber structure (in particular, dispersed in the voids between the fibers) because it can exhibit high electromagnetic wave absorption over a wide incident angle and can be easily manufactured. Is particularly preferred.

  The molded body (or fiber) further contains conventional additives such as stabilizers (heat stabilizers such as copper compounds, ultraviolet absorbers, light stabilizers, antioxidants, etc.), dispersants, fine particles, colorants, An antistatic agent, a flame retardant, a plasticizer, a lubricant, a crystallization rate retarder, and the like may be contained. These additives can be used alone or in combination of two or more. These additives may be carried on the surface of the molded body or may be contained in the fiber.

(Characteristics of electromagnetic wave absorber)
The electromagnetic wave absorbing material of the present invention contains a conductive agent (electromagnetic wave absorbing agent) and has a non-woven fiber structure obtained from a web composed of the fibers, and its shape can be selected according to the use, Usually, it is a sheet shape or a plate shape.

  Further, in the electromagnetic wave absorbing material, in order to have a non-woven fiber structure having high surface hardness and bending hardness, and having a good balance between lightness and air permeability, the fibers constituting the non-woven fiber web It is necessary that the arrangement state and the adhesion state of these are appropriately adjusted. That is, it is desirable that the fibers constituting the fiber web are arranged so as to intersect each other while being arranged substantially parallel to the surface of the fiber web (non-woven fiber). Further, the molded body constituting the electromagnetic wave absorbing material is preferably fused at the intersection where the fibers intersect. In particular, a molded body that requires high hardness and strength forms bundled fused fibers that are fused in a bundle of several to several tens at a portion where fibers other than the intersections are arranged substantially in parallel. It may be. These fibers form a “scrum” by partially forming a fused structure at the intersection of single fibers, the intersection of bundle fibers, or the intersection of single fibers and bundle fibers A structure (a structure in which fibers are bonded at an intersection and entangled like a mesh, or a structure in which fibers are bonded at an intersection to constrain adjacent fibers to each other) to achieve the desired bending behavior, surface hardness, etc. it can. In the present invention, it is desirable that such a structure is distributed substantially uniformly along the surface direction and the thickness direction of the fiber web.

  The phrase “arranged approximately parallel to the fiber web surface” as used herein indicates a state where there are no repeated portions where a large number of fibers are locally arranged along the thickness direction. More specifically, when an arbitrary cross section of the fiber web of the formed body is observed with a microscope, the existence ratio (number ratio) of fibers continuously extending in the thickness direction over 30% of the thickness of the fiber web. Is 10% or less (especially 5% or less) with respect to all the fibers in the cross section.

  The fibers are arranged in parallel to the fiber web surface because if there are many fibers oriented along the thickness direction (perpendicular to the web surface), the fiber arrangement is disturbed in the surrounding area and is not woven. This is because an unnecessarily large void is formed in the fiber, and the bending strength and surface hardness of the molded body are reduced. Therefore, it is preferable to reduce this gap as much as possible. For this purpose, it is desirable to arrange the fibers as parallel to the fiber web surface as possible.

  In addition, when the web is entangled by means such as a needle punch, a high-density molded body can be easily manufactured. Furthermore, when the fibers are entangled before being wet-heat bonded, the shape of the fibers before bonding is maintained, so that it becomes easy to produce a molded product having a large thickness, which is advantageous in terms of production efficiency. However, the entanglement of the fibers by the needle punch or the like is disadvantageous in that the fibers are arranged in parallel to the fiber web surface. Furthermore, since the density of the molded body is increased by the entanglement, it is difficult to manufacture a low-density and lightweight molded body. Therefore, from the viewpoint of arranging the fibers in parallel and light weight, it is preferable to reduce the degree of fiber entanglement or not to entangle.

  In particular, when a load is applied in the thickness direction of the molded body when the molded body is in the form of a sheet or plate, if there is a large void, the void is crushed by the load and the surface of the molded body is easily deformed. . Further, when this load is applied to the entire surface of the molded body, the thickness tends to be reduced as a whole. Such a problem can be avoided if the molded body itself is made of a resin filling without voids. However, this reduces the air permeability and makes it difficult to bend (bend resistance) and light weight when bent. It becomes difficult.

  On the other hand, in order to reduce the deformation in the thickness direction due to the load, it is conceivable to make the fibers thinner and more densely filled with the fibers, but when trying to ensure lightweight and breathability with only thin fibers, The rigidity of each fiber is lowered, and conversely, the bending stress is lowered. In order to secure bending stress, it is necessary to increase the fiber diameter to some extent. However, if thick fibers are simply mixed, large voids are easily formed near the intersections of the thick fibers and deformed in the thickness direction. It becomes easy to do.

  Therefore, the electromagnetic wave absorbing material of the present invention is arranged such that the directions of the fibers are arranged in parallel along the surface direction of the web and dispersed (or the fiber directions are directed in a random direction), so that the fibers intersect each other, and the intersections thereof. By adhering with, a small gap is generated to ensure light weight. Furthermore, since such a fiber structure is continuous, an appropriate air permeability and surface hardness are secured. In particular, when a bundle of fibers fused in parallel in the fiber length direction is formed in a place where the fibers are aligned in parallel without intersecting with other fibers, compared to the case where the fibers are composed of only single fibers. High bending strength can be secured mainly. When a molded body having high hardness and strength is desired, several bundles are formed at the portion where each fiber is arranged in a bundle between the intersections while adhering at the intersections where the fibers intersect each other. It is preferable to form a fiber. Such a structure can be confirmed from the existence state of the single fiber when the cross section of the compact is observed.

  Furthermore, in the electromagnetic wave absorbing material of the present invention, the fiber constituting the nonwoven fiber structure has a fiber adhesion rate of, for example, 85% or less (for example, 1 to 85%), preferably 3 by fusing the wet heat adhesive fibers. It is bonded at about 70%, more preferably 5-60% (especially 10-35%). Although the fiber adhesion rate in this invention can be measured by the method as described in the Example mentioned later, the ratio of the cross section number of the fiber which adhered 2 or more with respect to the cross section number of all the fibers in a non-woven fiber cross section is shown. Therefore, a low fiber adhesion rate means that a ratio of a plurality of fibers fused to each other (a ratio of fibers fused by fusing) is small.

  In the present invention, the fibers constituting the non-woven fiber structure are bonded at the contact points of the respective fibers. In order to express a large bending stress with as few contacts as possible, this bonding point is the thickness direction. In addition, it is preferably distributed uniformly from the surface of the molded body to the inside (center) and the back surface. When the adhesion points are concentrated on the surface or inside, it is not only difficult to secure a sufficient bending stress, but also the form stability in a portion where the adhesion points are small.

  Therefore, in the cross section in the thickness direction of the molded body, it is preferable that the fiber adhesion rate in each region divided in three in the thickness direction is in the above range. Furthermore, the ratio of the minimum value to the maximum value of the fiber adhesion rate in each region (minimum value / maximum value) (the ratio of the minimum region to the region with the maximum fiber adhesion rate) is, for example, 50% or more (for example, 50 to 100%), preferably 60 to 99%, more preferably 70 to 98% (especially 80 to 97%). In the present invention, since the fiber adhesion rate has such uniformity in the thickness direction, it is excellent in hardness, bending strength, folding resistance and toughness.

  In the present invention, the “region divided into three in the thickness direction” means each region divided into three equal parts by slicing in a direction orthogonal to the thickness direction of the plate-like molded body.

  Thus, in the electromagnetic wave absorbing material of the present invention, not only fusion by wet heat adhesive fibers is uniformly dispersed and point-bonded, but also the point adhesion of these points is short (for example, several tens to The network structure is stretched densely at several hundred μm). Due to such a structure, the electromagnetic wave absorbing material of the present invention has high followability to strain due to the flexibility of the fiber structure even when an external force acts, and each fusion point of finely dispersed fibers. Therefore, it can be estimated that high folding resistance and toughness are expressed. In contrast, conventional porous molded bodies and foams form a continuous interface around the pores, so that external forces are received in a larger area than the electromagnetic wave absorbing material of the present invention. It can be presumed that distortion is likely to occur and folding resistance and toughness are lowered.

In the electromagnetic wave absorbing material of the present invention, the existence frequency of the single fiber (single fiber end face) in the cross section in the thickness direction is not particularly limited. For example, the average frequency of single fibers existing in any 1 mm ^{2 of the} cross section is 100 pieces. / Mm ² or more (for example, about 100 to 300 pieces / mm ² ), but particularly when mechanical properties are required rather than lightness, the presence frequency of single fibers is, for example, an average. 100 pieces / mm ² or less, preferably 60 pieces / mm ² or less (eg, 1-60 pieces / mm ² ), more preferably 25 pieces / mm ² or less (eg, 3-25 pieces / mm ² ), Also good. When the presence frequency of the single fiber is too high, the fusion of the fibers is small and the strength of the molded body is lowered. If the frequency of single fibers exceeds 100 fibers / mm ² , bundle fusion of fibers decreases, making it difficult to ensure high bending strength. Furthermore, in the case of a plate-shaped molded body, it is preferable that the fibers fused in a bundle shape are thin in the thickness direction of the molded body and have a wide shape in the surface direction (length direction or width direction).

In the present invention, the existence frequency of the single fiber is measured as follows. That is, the range corresponding to 1 mm ² selected from the scanning electron microscope (SEM) photograph of the cross section of the compact is observed, and the number of single fiber cross sections is counted. Arbitrary several places (for example, 10 places selected at random) are observed in the same manner, and the average value per unit area of the single fiber end face is defined as the existence frequency of single fibers. At this time, all the number of fibers in a single fiber state are counted in the cross section. That is, in addition to fibers that are completely in a single fiber state, even if a plurality of fibers are fused, a fiber that is separated from the fused portion in the cross section and is in a single fiber state is counted as a single fiber.

  The wet heat-adhesive fibers in the molded body can prevent the fibers from dropping off from the molded body due to fiber slipping or the like because the fibers do not penetrate the molded body in the thickness direction. The production method for arranging the wet heat adhesive fibers in this way is not particularly limited, but a means for laminating a plurality of shaped bodies in which the wet heat adhesive fibers are entangled and performing wet heat adhesion is simple and reliable. Moreover, the fiber which penetrates in the thickness direction of a molded object can be reduced significantly by adjusting the relationship between fiber length and the thickness of a molded object. From such points, the thickness of the molded body is 10% or more (for example, 10 to 1000%), preferably 40% or more (for example, 40 to 800%), more preferably 60% or more with respect to the fiber length. (For example, 60 to 700%), particularly 100% or more (for example, 100 to 600%). By such adjustment, the dropout of fibers from the molded body can be suppressed without lowering the mechanical strength such as bending stress of the molded body.

  As described above, the electromagnetic wave absorbing material of the present invention is affected by the density and mechanical properties depending on the ratio and the presence state of the bundle-like fused fibers. The fiber adhesion rate indicating the degree of fusion can be easily measured based on the number of bonded fiber cross sections in a predetermined region by taking a photograph of an enlarged cross section of the electromagnetic wave absorber using SEM. However, when fibers are fused in a bundle, each fiber is fused in a bundle or at an intersection, making it difficult to observe as a single fiber, especially when the density is high. easy. In this case, for example, when the electromagnetic wave absorbing material of the present invention is bonded with a core-sheath type composite fiber formed of a sheath part made of wet heat adhesive fiber and a core part made of a fiber-forming polymer. For example, it is possible to measure the fiber adhesion rate by releasing the adhesion of the bonded portion by means such as melting or washing and comparing it with the cut surface before the release. On the other hand, in the present invention, as an index reflecting the degree of fiber fusion, the area ratio occupied by the cross section formed by the fiber and the bundle of fiber bundles in the cross section (thickness direction cross section) of the molded body after molding, that is, fiber filling Rate can also be used. The fiber filling rate in the cross section in the thickness direction is, for example, 20 to 80%, preferably 20 to 60%, and more preferably about 30 to 50%. If the fiber filling rate is too small, there are too many voids in the molded body, making it difficult to ensure the desired surface hardness and bending stress. On the other hand, if it is too large, the surface hardness and bending stress can be sufficiently secured, but it becomes very heavy and the air permeability tends to decrease.

The electromagnetic wave absorbing material of the present invention (in particular, a molded product in which fibers are fused in a bundle and the frequency of single fibers is 100 pieces / mm ² or less) is plate-like (board-like), depending on the load. It is desirable to have a surface hardness that is not recessed or difficult to deform. As such an index, the hardness by an A-type durometer hardness test (a test based on JIS K6253 “hardness test method for vulcanized rubber and thermoplastic rubber”) is, for example, 50 or more, preferably 60 or more. More preferably, it is 70 or more (for example, 70 to 100). If this hardness is too small, it is likely to be deformed by a load applied to the surface.

  In order to balance the bending strength, surface hardness, lightness, and air permeability in a high dimension, the molded body including such a bundle-like fused fiber has a low frequency of the bundle-like fused fiber and each fiber ( It is preferable to adhere at a high frequency at the intersection of bundle fibers and / or single fibers). However, if the fiber adhesion rate is too high, the distances between the bonded points are too close to each other, the flexibility is lowered, and it becomes difficult to eliminate distortion due to external stress. For this reason, the molded body needs to have a fiber adhesion rate of 85% or less. Since the fiber adhesion rate is not too high, a passage with fine voids can be secured in the molded body, and the lightness and air permeability can be improved. Therefore, in order to develop a large bending stress, surface hardness and air permeability with as few contacts as possible, the fiber adhesion rate is uniform along the thickness direction from the molded body surface to the inside (center) and back side. It is preferable that they are distributed. If the adhesion points are concentrated on the surface or inside, it becomes difficult to ensure the air permeability in addition to the bending stress and the form stability described above.

  Therefore, in the electromagnetic wave absorbing material of the present invention, it is preferable that the fiber filling rate in each region divided into three equal parts in the thickness direction is in the above range in the cross section in the thickness direction. Furthermore, the ratio of the minimum value to the maximum value of the fiber filling rate in each region (minimum value / maximum value) (the ratio of the minimum region to the region having the maximum fiber emphasis ratio) is, for example, 50% or more (for example, 50 to 100%), preferably 60 to 99%, more preferably 70 to 98% (especially 80 to 97%). In the present invention, if the fiber filling rate is uniform in the thickness direction, the bending strength, folding resistance, toughness and the like are excellent. The fiber filling rate in the present invention can be measured from a SEM photograph by a method using an image analyzer.

  One feature of the electromagnetic wave absorbing material of the present invention is that it has high toughness and bending stress and exhibits excellent bending behavior. In the present invention, in order to express this bending behavior, the repulsive force of the sample generated when the sample is gradually bent is measured according to JIS K7017 “Fiber-Reinforced Plastics—How to Obtain Bending Properties”, and the maximum stress (peak stress) is measured. ) As a bending stress and used as an index of bending behavior. That is, the larger the bending stress, the harder the molded body, and the more the bending amount (displacement) until the measurement object breaks, the better the curved body.

  The electromagnetic wave absorbing material of the present invention has a maximum bending stress in at least one direction (preferably in all directions) of 0.05 MPa or more (for example, 0.05 to 100 MPa), preferably 0.1 to 30 MPa, more preferably It may be about 0.2 to 20 MPa. Furthermore, in the case of having a high bending stress, such as a molded body containing bundled fused fibers (a plurality of fibers fused in a bundled form), the maximum bending stress is 2 MPa or more, preferably 5 to 100 MPa, Preferably, it may be about 10-60 MPa. If the maximum bending stress is too small, it is easily broken by its own weight or a slight load when used in a plate shape. Further, if the maximum bending stress is too high, it becomes too hard, and if it is bent beyond the peak of the stress, it is easily broken and broken. In addition, in order to obtain the hardness exceeding 100 MPa, it is necessary to increase the density of the molded body, and it is difficult to ensure light weight.

  Looking at the correlation between the bending amount (displacement) and the bending stress caused by the bending amount, the stress increases as the bending amount increases. For example, the bending amount increases approximately linearly. In the electromagnetic wave absorbing material of the present invention, when the measurement sample reaches a specific bending amount, the stress gradually decreases thereafter. That is, when the amount of bending and the stress are graphed, a correlation is shown in which an upward convex parabola is drawn. The electromagnetic wave absorbing material of the present invention has a so-called “stickiness (or toughness)” without causing a rapid stress drop even when attempting to bend beyond the maximum bending stress (peak of bending stress). Is also one of the features. In the present invention, as an index representing such “stickiness”, the bending stress remaining in a state exceeding the bending amount (displacement) at the peak of the bending stress can be used. That is, the electromagnetic wave absorbing material of the present invention has a maximum stress (hereinafter sometimes referred to as “1.5 times displacement stress”) when bent to a displacement of 1.5 times the bending amount indicating the maximum bending stress. It is only necessary to maintain 1/5 or more of the bending stress (for example, 1/5 to 1), for example, 1/3 or more (for example, 1/3 to 9/10), preferably 2/5 or more (for example, 2/5 to 9/10), more preferably 3/5 or more (for example, 3/5 to 9/10). The double displacement stress is 1/10 or more (for example, 1/10 to 1) of the maximum bending stress, preferably 3/10 or more (for example, 3/10 to 9/10), more preferably 5/10. You may maintain above (for example, 5 / 10-9 / 10).

  The electromagnetic wave absorbing material of the present invention can ensure excellent lightness due to the voids generated between the fibers. In addition, unlike the resin foam such as sponge, these voids are continuous rather than independent voids. Therefore, when the conductive agent is granular, the granular conductive agent is sufficiently contained inside. Can be dispersed and held. Such a structure is a structure that is extremely difficult to produce by conventional hardening methods such as a method of impregnating a resin and a method of forming a film-like structure by closely adhering surface portions. .

That is, the apparent density of the electromagnetic wave absorbing material of the present invention can be selected depending on the application, for example, 0.1 to 1 g / cm ³ , preferably 0.15 to 0.9 g / cm ³ , and more preferably 0.2. It is about -0.8 g / cm < ³ > (especially 0.3-0.6 g / cm < ³ >). If the apparent density is too low, it is lightweight, but it is difficult to ensure sufficient bending hardness and surface hardness. Conversely, if it is too high, the hardness can be ensured, but the lightness is reduced. On the other hand, if the density is too high, it becomes difficult to allow the particulate conductive agent to enter and hold the fiber. When the density decreases, the fibers become entangled and become close to a general non-woven fiber structure in which the fibers are fused at the intersections. On the other hand, when the density is increased, the fibers are fused in a bundle, and the porous molded body. It becomes a structure close to.

Basis weight of the electromagnetic wave absorbing material, for example, be selected from 100~10000g / m ² approximately in the range of preferably 200~8000g / m ^2, more preferably 300~6000g / m ² approximately. In applications where hardness than light weight is required and a basis weight, for example, 1000~10000g / m ^2, preferably 1500~8000g / m ^2, more preferably about 2000~6000g / m ^2. If the basis weight is too small, it is difficult to ensure the hardness. If the basis weight is too large, the web is too thick and high-temperature steam cannot sufficiently enter the inside of the web in wet heat processing, and the structure is uniform in the thickness direction. It becomes difficult to make a body.

  When the electromagnetic wave absorbing material of the present invention is in the form of a plate or a sheet, the thickness is not particularly limited, but can be selected from a range of about 1 to 500 mm, for example, 2 to 300 mm, preferably 3 to 200 mm, more preferably Is about 5 to 150 mm (especially 10 to 100 mm). If the thickness is too thin, it will be difficult to ensure the hardness, and if it is too thick, the mass will also become heavy, so the handling properties as a sheet will be reduced.

Since the electromagnetic wave absorber of the present invention has a non-woven fiber structure, the air permeability is high. Specifically, the air permeability according to the fragile 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 to 250 cm ^3. / (Cm ² · sec) [for example, 1 to 250 cm ³ / (cm ² · sec)], more preferably about 5 to ²⁰⁰ cm ³ / (cm ² · sec), and usually 1 to 100 cm ³ / (cm ² · s). If the air permeability is too small, it is necessary to apply pressure from the outside in order to allow air to pass through the molded body, making it difficult for natural air to enter and exit. On the other hand, if the air permeability is too high, the air permeability increases, but the fiber voids in the molded body become too large and the bending stress decreases.

  Since the electromagnetic wave absorbing material of the present invention has a non-woven fiber structure, the heat insulating property is also high, and the thermal conductivity is as low as 0.1 W / m · K or less, for example, 0.03 to 0.1 W / m. · K, preferably about 0.05 to 0.08 W / m · K.

[Method of manufacturing electromagnetic wave absorbing material]
In the method for producing an electromagnetic wave absorbing material of the present invention, first, a fiber containing the wet heat adhesive fiber is formed into a web. As a method for forming the web, a conventional method, for example, a direct method such as a spunbond method or a meltblowing method, a card method using meltblown fibers or staple fibers, a dry method such as an airlay method, or the like can be used. When a conductive agent is contained in the fiber, the conductive agent may be mixed into the spinning dope.

  Among these methods, a card method using melt blown fibers or staple fibers, particularly a card method using staple fibers is widely used. Examples of the web obtained using staple fibers include a random web, a semi-random web, a parallel web, and a cross-wrap web. Of these webs, a semi-random web and a parallel web are preferred when the proportion of bundled fused fibers is increased.

  In addition, when using a non-wet heat adhesive fiber and a fibrous electrically conductive agent, you may mix these fibers with a wet heat adhesive fiber. Moreover, when using a granular or plate-like conductive agent, these conductive agents may be added to and supported on the fiber web. In order to support the granular or plate-like conductive agent on the fiber web, for example, hot-melt adhesive resin such as olefin resin or polyamide resin, water-soluble polymer such as polyvinyl alcohol or vinyl acetate resin, and the like as a binder component It may be used.

  Next, the obtained fiber web is sent to the next step by a belt conveyor, and then exposed to superheated or high-temperature steam (high-pressure steam) flow to obtain a shaped body having a non-woven fiber structure. That is, when the fiber web transported by the belt conveyor passes through the high-speed high-temperature steam flow ejected from the nozzle of the steam spraying device, the wet-heat adhesive fibers are fused by the sprayed high-temperature steam, and the fiber Each other (wet heat adhesive fibers or wet heat adhesive fibers and other fibers) are three-dimensionally bonded. In particular, since the fiber web in the present invention has air permeability, high-temperature water vapor penetrates into the inside, and a molded body having a substantially uniform fusion state can be obtained.

  The belt conveyor to be used is not particularly limited as long as it can be subjected to high-temperature steam treatment while basically compressing the fiber web used for processing to a desired density, and an endless conveyor is preferably used. In addition, it may be a general single belt conveyor, or may be transported by combining two belt conveyors as necessary and sandwiching the web between both belts. By carrying in this way, when processing a fiber web, it can suppress that the form of the fiber web conveyed by external forces, such as water used for processing, high temperature steam, and vibration of a conveyor, changes. It is also possible to control the density and thickness of the treated non-woven fibers by adjusting the distance between the belts.

  In order to supply water vapor to the fiber web, a conventional water vapor jet apparatus is used. As this steam spraying device, a device capable of spraying steam substantially uniformly over the entire width of the web at a desired pressure and amount is preferable. When two belt conveyors are combined, water vapor is supplied to the web through a water-permeable conveyor belt or a conveyor net placed on the conveyor. A suction box may be attached to the other conveyor. Excess water vapor that has passed through the fiber web can be sucked and discharged by the suction box. Further, in order to perform steam treatment on both sides of the front and back of the fiber web at a time, in a conveyor opposite to the conveyor on which the steam spraying device is mounted, more than the portion on which the steam spraying device is mounted. You may install another water vapor | steam injection apparatus in the conveyor of a downstream part. If there is no downstream steam injection device and suction box, and if you want to steam-treat the front and back of the fiber web, you can reverse the front and back of the fiber web that has been treated once and pass it through the processing device again. Good.

  The endless belt used for the conveyor is not particularly limited as long as it does not hinder the conveyance of the fiber web or the high-temperature steam treatment. However, when high-temperature steam treatment is performed, the surface shape of the belt may be transferred to the surface of the fiber web depending on the conditions. In particular, when it is desired to obtain a molded body having a flat surface, a net with a fine mesh may be used. The upper limit is about 90 mesh, and a net that is roughly coarser than 90 mesh (for example, a net of about 10 to 50 mesh) is preferable. A finer mesh net than this has low air permeability and makes it difficult for water vapor to pass through. The mesh belt is made of metal, heat-treated polyester resin, polyphenylene sulfide resin, polyarylate resin (fully aromatic polyester resin), aromatic polyamide resin, etc. The heat resistant resin is preferable.

  Since the high-temperature steam sprayed from the steam spraying device is an air stream, unlike the hydroentanglement process or the needle punch process, the fibers in the fiber web that is the object to be processed enter the inside of the fiber web without largely moving. . It is considered that due to the invasion action and wet heat action of the water vapor flow into the fiber web, the water vapor flow efficiently covers the surface of each fiber existing in the fiber web in a wet heat state, and uniform heat bonding becomes possible. In addition, since this treatment is performed in a very short time under a high-speed air flow, the heat conduction of the water vapor to the fiber surface is sufficient, but the treatment is completed before the heat conduction to the inside of the fiber is sufficiently achieved. For this reason, the entire fiber web to be processed is not easily crushed or deformed so as to lose its thickness due to the pressure or heat of high-temperature steam. As a result, the wet heat bonding is completed so that the degree of bonding in the surface and the thickness direction is substantially uniform without causing large deformation of the fiber web. Moreover, since heat can be sufficiently transmitted to the inside of the nonwoven structure as compared with the dry heat treatment, the degree of fusion in the surface and thickness direction becomes substantially uniform.

Furthermore, when obtaining a molded body having a high surface hardness and bending strength, when the high-temperature steam is supplied to the web for processing, the web to be processed is placed between a conveyor belt or rollers with a desired apparent density (for example, , About 0.3 to 1 g / cm ³ ), and exposure to high temperature water vapor is important. In particular, when trying to obtain a relatively high-density molded body, it is necessary to compress the fiber web with sufficient pressure when processing with high-temperature steam. Furthermore, it is also possible to adjust to a target thickness and density by securing an appropriate clearance between rollers or between conveyors. In the case of a conveyor, since it is difficult to compress the web at a stretch, it is preferable to set the belt tension as high as possible and gradually narrow the clearance from the upstream of the steam treatment point. Furthermore, it is processed into a molded body having desired bending hardness, surface hardness, lightness, and air permeability by adjusting the steam pressure and the processing speed.

  At this time, if it is desired to increase the hardness, the back side of the endless belt on the opposite side of the nozzle across the web is made of a stainless steel plate or the like so that the steam cannot pass through. Since it reflects here, it adhere | attaches more firmly by the heat retention effect of vapor | steam. Conversely, when light adhesion is required, a suction box may be provided to discharge excess water vapor to the outside.

  The nozzle for injecting the high-temperature steam may be a plate or a die in which predetermined orifices are continuously arranged in the width direction, and may be arranged so that the orifices are arranged in the width direction of the fiber web to be supplied. There may be one or more orifice rows, and a plurality of rows may be arranged in parallel. A plurality of nozzle dies having a single orifice array may be installed in parallel.

  When using a type of nozzle having an orifice in the plate, the thickness of the plate may be about 0.5 to 1 mm. The orifice diameter and pitch are not particularly limited as long as the target fiber fixation is possible, but the orifice diameter is usually 0.05 to 2 mm, preferably 0.1 to 1 mm, more preferably. It is about 0.2 to 0.5 mm. The pitch of the orifices is usually about 0.5 to 3 mm, preferably about 1 to 2.5 mm, and more preferably about 1 to 1.5 mm. If the orifice diameter is too small, the processing accuracy of the nozzle becomes low and the processing becomes difficult, and the operational problem that clogging is likely to occur easily occurs. On the other hand, if it is too large, the water vapor jetting power is reduced. On the other hand, if the pitch is too small, the nozzle holes become too dense and the strength of the nozzle itself is reduced. On the other hand, when the pitch is too large, there is a case where high-temperature water vapor does not sufficiently hit the web, so that the web strength is lowered.

  The high-temperature steam is not particularly limited as long as the target fiber can be fixed, and may be set according to the material and form of the fiber used. The pressure is, for example, 0.1 to 2 MPa, preferably 0.2 to The pressure is about 1.5 MPa, more preferably about 0.3 to 1 MPa. If the water vapor pressure is too high or too strong, the fibers that make up the web may move more than necessary, causing turbulence, or the fibers may melt too much to partially retain the fiber shape. There is. On the other hand, if the pressure is too weak, it may not be possible to give the web the amount of heat necessary for fiber fusion, or water vapor may not penetrate the web, resulting in fiber fusion spots in the thickness direction. In addition, it may be difficult to control the uniform ejection of water vapor from the nozzle.

  The temperature of the high-temperature steam is, for example, about 70 to 150 ° C, preferably about 80 to 120 ° C, and more preferably about 90 to 110 ° C. The processing speed of the high temperature steam is, for example, 200 m / min or less, preferably 0.1 to 100 m / min, and more preferably about 1 to 50 m / min.

  If necessary, it is also possible to impart designability to a molded body obtained by applying predetermined uneven patterns, characters, pictures, etc. to the conveyor belt and transferring them. Further, it may be laminated with other materials to form a laminated body, or may be processed into a desired form (various shapes such as a columnar shape, a quadrangular prism shape, a spherical shape, an ellipsoidal shape) by molding.

  After the fibers of the fiber web are partially wet-heat bonded in this way, moisture may remain in the resulting molded body having the nonwoven fiber structure, and the web may be dried as necessary. Regarding drying, it is necessary that the surface of the molded body that is in contact with the heating body for drying does not lose the fiber form due to the heat of drying, so that the fiber form can be maintained. . For example, a large dryer such as a cylinder dryer or tenter used for drying nonwoven fabrics may be used, but the remaining moisture is very small and can be dried by a relatively light drying means. Therefore, a non-contact method such as far-infrared irradiation, microwave irradiation, electron beam irradiation, or a method of blowing or passing hot air is preferable.

  Furthermore, as described above, the molded body is obtained by adhering wet heat adhesive fibers with high-temperature steam, but partially (such as bonding between molded bodies obtained by wet heat bonding), other conventional methods, For example, you may adhere | attach by processing methods, such as partial hot-pressure melt | fusion (hot embossing etc.) and mechanical compression (needle punch etc.).

  The wet heat adhesive fibers can also be fused by dipping the fiber web in hot water. However, it is difficult to control the fiber adhesion rate by such a method, and a molded product with high uniformity of the fiber adhesion rate is obtained. Is difficult. The reason for this is that the wet heat adhesiveness differs depending on the position due to the air contained in the fiber web, the influence on the structure caused by this air being pushed out of the fiber web, the wet heat bonded fiber web It can be presumed that the deformation of the fine structure inside the fiber by the take-off roller when taking out from the hot water or the difference in the deformation of the fine structure in the vertical direction due to the weight of the hot water contained in the taken-out fiber web.

  As described above, as a method for applying a conductive agent, a method for applying a conductive agent in a manufacturing process of a molded body, for example, a method for spinning fibers containing a conductive agent, a method for blending a fibrous conductive agent into a fiber web, Although a method of adding a conductive agent to the fiber web may be used, a method of applying a conductive agent after obtaining a molded body having a non-woven structure is preferable from the viewpoint of simplicity and electromagnetic wave absorption.

  Furthermore, among the methods of applying a conductive agent to a molded body, the molded body is placed in a slurry containing a conductive agent (particularly a granular conductive agent) because it is easy to uniformly disperse the conductive agent inside the nonwoven structure. A dipping method is preferred.

  The solvent used in the slurry is not particularly limited, but water is usually used from the viewpoint of operability. Furthermore, in order to disperse the conductive agent in water, a water-soluble polymer may be used as a dispersant (viscosity modifier). The water-soluble polymer is preferably a water-soluble polymer of the same type as the wet heat adhesive resin from the viewpoint of affinity with the molded body (particularly, adhesion between the conductive agent and the fiber). Is an ethylene-vinyl alcohol polymer, a vinyl alcohol polymer such as polyvinyl alcohol can be preferably used as a dispersant.

  The density | concentration (ratio) of the electrically conductive agent in a slurry is 1-50 mass% with respect to the whole slurry, for example, Preferably it is 3-40 mass%, More preferably, it is 5-30 mass% (especially 10-25 mass%). Degree. The density | concentration (ratio) of a dispersing agent is 1-30 mass% with respect to the whole slurry, for example, Preferably it is 3-25 mass%, More preferably, it is about 5-20 mass%.

  Such a slurry can be prepared by adding a conductive agent and a dispersant to water and stirring so as to obtain the above concentration. Furthermore, the electromagnetic wave absorbing material of the present invention can be produced by immersing the molded body in the prepared slurry, and then removing the molded body from the slurry and drying it. The immersion time of the molded body in the slurry is, for example, about 0.1 minute to 1 hour, preferably 1 to 30 minutes, and more preferably about 5 to 10 minutes. The drying method is not particularly limited and may be heated (for example, about 40 to 80 ° C.), but is usually natural drying. The electromagnetic wave absorbing material obtained by such a method exhibits electromagnetic wave absorptivity over a wide angle range since the conductive agent is uniformly distributed inside the non-woven structure.

  The electromagnetic wave absorbing material of the present invention can be widely used as various base materials for absorbing electromagnetic waves. For example, it can be used as an electromagnetic wave receiver or an electromagnetic wave shield. Specifically, examples of the electromagnetic wave receiver include a communication system such as laser communication and microwave communication, and an antenna such as an automatic toll collection (ETC) system such as a parking lot and a toll road. Examples of the electromagnetic shielding (shielding) body include inner and outer walls of a housing in an electronic device that generates electromagnetic waves, structures such as houses and vehicles, and interior materials.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. Each physical property value in the examples was measured by the following method. In the examples, “parts” and “%” are based on mass unless otherwise specified.

(1) Weight per unit (g / m ² )
Measured according to JIS L1913 “Testing method for general short fiber nonwoven fabric”.

(2) Thickness (mm), apparent density (g / cm ³ )
The thickness was measured according to JIS L1913 “General Short Fiber Nonwoven Fabric Testing Method”, and the apparent density was calculated from this value and the basis weight value.

(3) Number of crimps Evaluation was made according to JIS L1015 “Testing method for chemical fiber staples” (8.12.1).

(4) Air permeability Measured by the fragile method according to JIS L1096.

(5) Fiber Adhesion Rate Using a scanning electron microscope (SEM), a photograph was taken with the cross section of the molded body magnified 100 times. The photograph of the cross section in the thickness direction of the photographed molded product is divided into three equal parts in the thickness direction, and the number of fiber cut surfaces (fiber end faces) that can be found in each of the three divided regions (front surface, inside (center), back surface) On the other hand, the ratio of the number of cut surfaces where the fibers are bonded to each other was determined. Of the total number of fiber cross sections that can be found in each region, the ratio of the number of cross sections in a state where two or more fibers are bonded is expressed as a percentage based on the following formula. In addition, in the part which fibers contact, there exists a part which is simply contacting, without melt | fusion, and a part which has adhere | attached by melt | fusion. However, by cutting the molded body for microscopic photography, the fibers in contact with each other are separated from each other by the stress of each fiber on the cut surface of the molded body. Therefore, in the cross-sectional photograph, it can be determined that the contacting fibers are bonded to each other.

Fiber adhesion rate (%) = (number of cross sections of fibers bonded two or more) / (total number of cross sections of fibers) × 100
However, for each photograph, all the fibers with visible cross sections were counted, and when the number of fiber cross sections was 100 or less, a photograph to be observed was added so that the total fiber cross section number exceeded 100. In addition, the fiber adhesion rate was calculated | required about each area | region divided into three equally, and the ratio (minimum value / maximum value) of the minimum value with respect to the maximum value was calculated | required collectively.

(6) Bending stress It measured according to A method (three-point bending method) among the methods as described in JIS K7017. At this time, the measurement sample was a 25 mm wide × 80 mm long sample, the distance between fulcrums was 50 mm, and the test speed was 2 mm / min. In the present invention, the maximum stress (peak stress) in this measurement result chart is defined as the maximum bending stress. The bending stress was measured in the MD direction and the CD direction. Here, the MD direction refers to a state in which the measurement sample is collected so that the web flow direction (MD) is parallel to the long side of the measurement sample, while the CD direction refers to the long side of the measurement sample. A state in which a measurement sample is collected so that the web width direction (CD) is parallel.

(7) 1.5 times displacement stress In the measurement of bending stress, the stress when the bending amount (displacement) exceeding the maximum bending stress (peak stress) is exceeded and further bent to 1.5 times the displacement is continued. 1.5 times the displacement stress.

(8) Electromagnetic wave absorptivity Using a vector network analyzer, the surface of the measurement sample is irradiated with circularly polarized waves in the range of 4.9 to 7.05 GHz at an incident angle of 15 °, 5 GHz, 5.5 GHz, The reflection coefficient S11 was measured for 6 GHz, 6.5 GHz, and 7 GHz. A metal plate having the same area as the sample was placed behind the sample.

Example 1
As a wet heat adhesive fiber, a core-sheath type composite staple fiber having a core component of polyethylene terephthalate and a sheath component of ethylene-vinyl alcohol copolymer (ethylene content 44 mol%, saponification degree 98.4 mol%) ) "Sophista", fineness 3dtex, fiber length 51mm, core-sheath mass ratio = 50/50, number of crimps 21 / 25mm, crimp rate 13.5%) was prepared.

Using this core-sheath type composite staple fiber, a card web having a basis weight of about 100 g / m ² was prepared by a card method, and seven sheets of this web were stacked to obtain a card web having a total basis weight of 700 g / m ² . The card web was transferred to a belt conveyor equipped with a 50 mesh, 500 mm wide stainless steel endless net. In addition, the belt conveyor which has the same metal mesh is equipped in the upper part of the metal mesh of this belt conveyor, and it rotated in the same direction at the same speed, respectively, and used the belt conveyor which can adjust the space | interval of these metal meshes arbitrarily. .

  Next, the steam web is introduced into the steam jetting device provided in the lower conveyor, and steam treatment is performed by ejecting 0.4 MPa high-temperature steam from the device in the thickness direction of the card web (perpendicularly). As a result, a molded body having a non-woven fiber structure was obtained. In this steam spraying device, a nozzle is installed in the lower conveyor so as to spray high-temperature steam toward the web via a conveyor net, and a suction device is installed in the upper conveyor. Further, another jetting device, which is a combination of the arrangement of the nozzle and the suction device reversed, is installed on the downstream side in the web traveling direction of the jetting device, and steam treatment is performed on both the front and back sides of the web. did.

  In addition, the hole diameter of the water vapor | steam injection nozzle was 0.3 mm, and the vapor | steam injection apparatus with which the nozzle was arranged in 1 row at 1 mm pitch along the width direction of the conveyor was used. The processing speed was 3 m / min, and the interval (distance) between the upper and lower conveyor belts on the nozzle side and the suction side was 10 mm. The nozzles were arranged on the back side of the conveyor belt so as to be almost in contact with the belt.

  The obtained molded body had a board-like form and had such a hardness that it became self-supporting only by lightly supporting it.

  Next, 100 parts by mass of a mixed powder of 75 parts by mass of Mn—Zn ferrite powder (average particle diameter 3.1 μm) and 25 parts by mass of carbon powder (average particle diameter 3.1 μm), 15 parts by mass of polyvinyl alcohol 385 masses of water. And a slurry having a mixed powder solid content concentration (conducting agent concentration) of 20% by mass was prepared. The molded body was immersed in a container containing the slurry for 30 minutes, impregnated with a granular conductive agent in a non-woven structure, and then naturally dried to obtain an electromagnetic wave absorber.

Example 2
In the preparation of the slurry, an electromagnetic wave absorber was produced in the same manner as in Example 1 except that the amount of polyvinyl alcohol was 25 parts by mass, the amount of water was 875 parts by mass, and the solid content concentration of the slurry was 10% by mass. . Table 1 shows the evaluation results of the obtained electromagnetic wave absorbing material.

Example 3
In the preparation of the slurry, an electromagnetic wave absorber was produced in the same manner as in Example 1 except that the amount of polyvinyl alcohol was 10 parts by mass, the amount of water was 290 parts by mass, and the solid content concentration of the slurry was 25% by mass. . Table 1 shows the evaluation results of the obtained electromagnetic wave absorbing material.

Comparative Example 1
Table 1 shows the results of evaluation without immersing the board-like molded body obtained in Example 1 in the slurry.

  As is clear from the results in Table 1, the electromagnetic wave absorbers of the examples have high electromagnetic wave absorbability at a wide incident angle, and high air permeability and mechanical properties. On the other hand, the molded body of the comparative example has low electromagnetic wave absorptivity.

Claims (7)

An electromagnetic wave absorber comprising a wet heat adhesive fiber and a conductive agent,
Nonwoven having a fiber structure, and the wet heat fibers by fusion of the adhesive fiber is constituted by a fixed molded body Rutotomoni,
In the cross section in the thickness direction, the fiber adhesion rate in each region divided into three equal parts in the thickness direction is 85% or less, and the ratio of the minimum value to the maximum value of the fiber adhesion rate in each region is 50% or more. Electromagnetic wave absorber. Bending stress at a bending amount of 1.5 times the bending amount showing a maximum bending stress, having an apparent density of 0.1 to 1 g / cm ³ and having a maximum bending stress of at least 0.05 MPa in at least one direction. but the maximum bending wave absorbing material according to claim 1 Symbol placement is 1/5 or more with respect to stress. The electromagnetic wave absorbing material according to claim 1 or 2, wherein the air permeability according to the fragile method is 0.1 to 300 cm ³ / (cm ² · sec). Thermal adhesive fiber under moisture ethylene - containing vinyl alcohol copolymer, and the ratio of the conductive agent with respect to the thermal adhesive fiber under moisture 100 parts by weight of claims 1 to 3 is 0.1 parts by weight The electromagnetic wave absorber in any one. The electromagnetic wave absorber according to any one of claims 1 to 4 , wherein the conductive agent is in a granular form and dispersed and incorporated in inter-fiber voids in the nonwoven fiber structure. A method for producing an electromagnetic wave absorbing material comprising a wet heat adhesive fiber and a conductive agent, wherein the nonwoven fiber web containing the wet heat adhesive fiber is heated with high-temperature steam to obtain a molded article having a nonwoven fiber structure. The manufacturing method of the electromagnetic wave absorber in any one of Claims 1-5 containing. The manufacturing method of Claim 6 including the process of immersing the molded object which has a nonwoven structure in the slurry containing a electrically conductive agent.