JP2009085251A - Plate spring and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plate spring having reduced weight and showing bending behavior suitable for the spring. <P>SOLUTION: A fiber web including wet-heat bondable fiber of 80 mass% or more is heated by high temperature vapor, the wet-heat bondable fiber is fused, and the fiber is fixed, and the plate spring is manufactured. Fiber bonding rates of the plate spring in regions equally divided into three on a thickness direction cross section in a thickness direction are all 30-85%, and a proportion of a minimum value with respect to a maximum value of the fiber bonding rates in the respective regions may be 50% or more. Further, the plate spring has an apparent density of 0.1-0.7 g/cm<SP>3</SP>, a maximum bending stress at least in one direction is 0.5 MPa or more, and bending stress in bending quantity of 1.5 times with respect to the bending quantity showing the maximum bending stress may be half or more with respect to the maximum bending stress. The shape of the plate spring may be a bent plate or a curved plate. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a leaf spring that is widely used in daily necessities, home appliances, bedding, human body aids, vehicles, and the like, and is lightweight and excellent in spring characteristics, and a method for manufacturing the same.

  Conventionally, it has a simple structure and has a rebound and cushioning force as a daily necessities such as stationery, household appliances such as ink ribbons and personal computers, bedding such as pillows and sofas, and human body aids such as artificial legs and short leg orthoses. The leaf spring which has is used. Since the leaf spring is required to have durability that can be used repeatedly in addition to repulsion and cushioning force, a metal has usually been used as the material thereof. However, in applications that need to be carried, such as stationery, and applications that require movement, such as vehicles, the leaf springs are required to be lightweight. Therefore, it has been studied to use a polymer material such as fiber reinforced plastic as a leaf spring instead of metal.

  Japanese Patent Laid-Open No. 2000-18299 (Patent Document 1) discloses a central core made of a first polymer material having predetermined mechanical characteristics and no reinforcing fiber, and a plurality of unidirectional reinforcements covering the central core. A leaf spring for an automobile suspension composed of a cover made of a composite material including a polymer matrix containing a fiber has been proposed. In this leaf spring, excellent mechanical properties and light weight are realized by having a structure in which the central core made of epoxy resin is covered with a cover layer containing fiber reinforced plastic impregnated with glass fiber with epoxy resin. I am letting.

However, even this leaf spring is not light enough and its structure is complicated, so that operability and productivity are low. Further, since the polymer is reinforced with the reinforcing fiber, not only the spring characteristic is small, but also the spring characteristic is lost once the fiber breaks. Furthermore, since the fibers are fixed with a chemical binder such as an epoxy resin, harmful components are easily generated. In addition, although the density of the leaf | plate spring using a fiber reinforced plastic is low compared with a metal, it is about 1 g / cm < ³ > normally and the further lightweight property is calculated | required.
JP 2000-18299 A (Claim 1, paragraphs [0005] [0013] [0014], FIG. 1)

  Accordingly, an object of the present invention is to provide a leaf spring that is lightweight and exhibits a bending behavior suitable for a spring, and a method for manufacturing the same.

  Another object of the present invention is to provide a leaf spring and a method for manufacturing the same which do not deteriorate spring characteristics even when used repeatedly.

  Still another object of the present invention is to provide a leaf spring 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 used a molded body having a non-woven fiber structure in which fibers are appropriately bonded by wet heat adhesive fibers as a leaf spring. The present invention has been completed by finding that it exhibits a bending behavior suitable for a spring.

That is, the leaf spring of the present invention is a leaf spring that contains 80% by mass or more of wet heat adhesive fibers and has a non-woven fiber structure, and the molded body has the fibers fixed by fusion of the wet heat adhesive fibers. It consists of In the cross section in the thickness direction, the leaf spring has a fiber adhesion rate of 20 to 80% in each region divided in three in the thickness direction, and the ratio of the minimum value to the maximum value of the fiber filling rate in each region May be 50% or more. Further, it has an apparent density of 0.1 to 0.7 g / cm ³ , has a maximum bending stress in at least one direction of 0.5 MPa or more, and is 1.5 times the bending amount indicating the maximum bending stress. The bending stress in the amount may be 1/2 or more with respect to the maximum bending stress. The wet heat adhesive fiber is a composite fiber composed of a wet heat adhesive resin and a non-wet heat adhesive resin, and the ratio (mass ratio) of both is wet heat adhesive resin / non-wet heat adhesive resin = 40/60. About 80/20 may be sufficient. The shape of the leaf spring may be, for example, a bent plate shape or a curved plate shape.

  The present invention includes a step of forming a fiber containing wet heat adhesive fibers into a web, and a step of heat-treating the produced fiber web with high-temperature steam to fuse the fibers to obtain a molded body having a non-woven fiber structure. A method for manufacturing the leaf spring is also included.

  The leaf spring of the present invention has a non-woven fiber structure in which the fibers are appropriately bonded by wet heat adhesive fibers, so that even though it is extremely lightweight, it has an appropriate bending stress and bending strength suitable for the spring. Show. Furthermore, since this leaf spring has excellent mechanical properties and high durability, the spring properties do not deteriorate even when used repeatedly. In addition, this leaf spring can be made of only fibers, and it is not necessary to add chemical binders or special chemicals. Therefore, it is easy to manufacture without using components that generate harmful components (such as volatile organic compounds). it can.

[Leaf spring]
The leaf spring of the present invention contains 80% by mass or more of wet heat adhesive fibers and has a non-woven fiber structure. In particular, the leaf spring of the present invention is composed of a molded body in which fibers are fixed by fusion of the wet heat-adhesive fibers, and not only the high lightweight characteristic of the fiber structure but also the fibers constituting the nonwoven fiber structure. By adjusting the alignment and the state of adhesion between these fibers, it is not possible with ordinary nonwoven fabrics. “Bending behavior (has high bending stress and maintains stress even if it is bent beyond the point where maximum bending stress is shown. And the behavior that tries to recover when the stress is released) ”,“ lightness ”and“ surface hardness (characteristics that are difficult to deform even if a load is applied to the surface and a force is applied in the thickness direction) ” In addition, it also has a bending strength suitable for springs, which is more flexible and hard to break.

  Such a leaf spring, as will be described later, causes a high-temperature (superheated or heated) water vapor to act on the web containing the wet heat-adhesive fibers, and exhibits an adhesive action at a temperature below the melting point of the wet heat-adhesive fibers. It can be obtained by partially bonding each other. 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%. Degree. When the degree of saponification 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 the ethylene terephthalate unit, the polyethylene terephthalate resin is not limited to 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 = 30/70 to 90/10, preferably 35/65 to 85/15, more preferably It is about 40/60 to 80/20. 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 leaf spring may further contain non-humid 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 type of leaf spring. When importance is attached to mechanical properties such as hardness, bending stress, and bending strength, it is preferable to use hydrophilic fibers with high hygroscopicity, such as 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 importance is attached to lightness and flexibility (easiness of deflection and size of deflection) rather than hardness and strength, hydrophobic fibers with low hygroscopicity, such as polyolefin fibers, polyester fibers, polyamides, etc. It is preferable to use a polyester fiber (in particular, a polyester fiber (polyethylene terephthalate fiber or the like)) having an excellent balance of various properties. When these hydrophobic fibers are combined with wet heat adhesive fibers containing an ethylene-vinyl alcohol copolymer, a lightweight and highly flexible molded product 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 leaf spring of the present invention contains 80% by mass or more (for example, 80 to 100% by mass) of wet heat adhesive fiber from the viewpoint of expressing the mechanical properties necessary for the spring, for example, 85% by mass or more (for example, 85 to 99.99% by mass), preferably 90% by mass or more (for example, 90 to 99.9% by mass), more preferably 95% by mass or more (for example, 95 to 99.5% by mass). It is out.

  The ratio (mass ratio) of the wet heat adhesive fiber and the non-wet heat adhesive fiber is determined according to the application of the leaf spring, wet heat adhesive fiber / non-wet heat adhesive fiber = 80/20 to 100/0 (for example, 80 / 20 to 99.9 / 0.1), preferably 90/10 to 100/0 (for example, 90/10 to 99.5 / 0.5), more preferably 95/5 to 100/0 (for example, 95 / 5 to 99/1).

  The molded body (or fiber) is further added with conventional additives such as stabilizers (heat stabilizers such as copper compounds, ultraviolet absorbers, light stabilizers, antioxidants, etc.), dispersants, thickeners, fine particles. , Colorant, Antistatic agent, Flame retardant, Plasticizer, Lubricant, Crystallization rate retarding agent, Lubricant, Antibacterial agent, Insect / Anticide agent, Antifungal agent, Matting agent, Animal heat agent, Fragrance, Fluorescent whitening An agent, a wetting agent, a plasticizer 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 leaf spring)
The leaf spring of the present invention has a non-woven fiber structure obtained from the web composed of the fibers, the shape of which can be selected according to the application, and the plate-like molded body is a bent or curved shape. The planar shape of the plate-shaped molded body is not particularly limited, and may be a circle, an ellipse, a polygon, or the like, but is usually a square or a rectangle. The cross-sectional shape in the thickness direction of the leaf spring may be an irregular shape (non-linear shape) that can be deformed by applying pressure, but from the viewpoint of ease of molding, etc. It is U-shaped (or partially circular). The V-shaped or U-shaped angle and radius may be appropriately selected according to the required spring characteristics. For example, in the case of a V shape, the angle is, for example, 5 to 160 °, preferably 10 to 140 °. More preferably, it is about 20 to 120 ° (particularly 30 to 90 °). In addition, although such a bending | flexion and a curve are normally formed in one site | part of a plate-shaped molded object, the wave shape and bellows shape formed in the some site | part may be sufficient. When the bending is formed in one part of the plate-shaped molded body, the bending part is in a state in which the plate-shaped molded body is folded in two from the viewpoint of spring characteristics (for example, when the plate-shaped surface is rectangular, It is preferable that the side is folded in two. In addition, the bending part does not necessarily need to be formed in the central part of one side, and may be appropriately selected according to the application used, the shape of the use part, and the like. Also, in the case of a curved plate shape, the shape and degree of the curve may be appropriately selected according to the application to be used and the shape of the use site.

  Further, in order to have a non-woven fiber structure having a high hardness and mechanical properties, and having a good balance between lightness (low density) and flexibility, the leaf spring has a web structure of non-woven fibers. It is necessary that the arrangement state and adhesion state of the fibers to be adjusted 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). Furthermore, it is preferable that the molded body constituting the leaf spring is fused at the intersection where the fibers intersect. In particular, a molded body that requires high mechanical properties 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 (structure in which fibers are bonded at intersections and entangled like a mesh, or a structure in which fibers bond at intersections and adjacent fibers are constrained to each other) can exhibit the desired bending behavior, hardness, etc. . 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% or more of the thickness of the fiber web. The state is 10% or less (particularly 5% or less) with respect to the total fibers in the cross section.

  Fibers are arranged parallel to the fiber web surface when there are many fibers oriented in the thickness direction (perpendicular to the web surface) and the fiber arrangement is disturbed around the fiber web. This is because an unnecessarily large void is generated in the woven 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, it becomes easy to produce a molded body having high hardness. 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, it is preferable to reduce the degree of fiber entanglement or not to entangle from the viewpoint of arranging the fibers in parallel and easily obtaining a low-density and lightweight molded product.

  In particular, when a load is applied in the thickness direction of the molded body, if a large void portion exists, the void portion is crushed by the load and the surface of the molded body is easily deformed. Furthermore, 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 a resin filling without voids, but the lightness is reduced.

  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 fibers. Rigidity decreases, and conversely bending stress decreases. 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 leaf spring of the present invention has a low density, and the fibers are aligned with each other in parallel along the surface direction of the web and dispersed (or the fiber direction is directed in a random direction) so that the fibers are mutually aligned. By crossing and adhering at the intersection, a small gap is created to ensure lightweight. Furthermore, an appropriate surface hardness is ensured by such a continuous fiber structure. 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 leaf spring of the present invention, the fibers constituting the nonwoven fiber structure reflect the degree of fusion of the wet heat adhesive fibers, and the fibers and bundles in the cross section of the molded body (cross section in the thickness direction) after molding. The area ratio occupied by the cross section formed by the fiber bundle, that is, the fiber filling rate is 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 lightness tends to be lowered.

  Therefore, in the leaf spring of the present invention, it is preferable that the fiber filling rate in each region divided in three 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 with the maximum fiber filling 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, if the fiber filling rate is uniform in the thickness direction, the bending stress, bending strength, folding resistance, toughness, etc. are excellent. The fiber filling rate in this invention is measured by the method as described in the Example mentioned later.

  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.

  On the other hand, in the present invention, the fiber adhesion rate can be used as an index indicating the degree of fiber fusion. In the leaf spring of the present invention, the fibers constituting the non-woven fiber structure have a fiber adhesion rate of 30 to 85% or less, preferably 35 to 80%, more preferably about 40 to 75% by fusion of the wet heat adhesive fibers. It is glued. The fiber adhesion rate in the present invention can be measured based on a photograph taken using a scanning electron microscope (SEM), and the number of cross-sections of two or more fibers bonded with respect to the number of cross-sections of all fibers in the non-woven fiber cross-section. It is shown as a percentage. 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, not only is it difficult to ensure excellent mechanical properties and moldability, but also the shape stability in the portion where the adhesion points are small is lowered.

  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 55 to 99%, more preferably 60 to 98% (especially 70 to 97%). In the present invention, since the fiber adhesion rate has such uniformity in the thickness direction, it is excellent in hardness, bending stress and bending strength, folding resistance and toughness.

  As described above, in the leaf spring 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 several 100 μm), and the network structure is densely stretched. With such a structure, the leaf spring of the present invention has a high followability to strain due to the flexibility of the fiber structure even when an external force is applied, and at each fusion point of finely dispersed fibers. Since the external force is dispersed and reduced, it can be estimated that high folding resistance and toughness are expressed. On the other hand, since the conventional porous molded body and foam form an interface where the periphery of the pores is continuous, the external force is received in a large area compared to the leaf spring of the present invention, It can be presumed that distortion is likely to occur, and folding resistance and toughness are lowered.

In the leaf spring of the present invention, the existence frequency of single fibers (single fiber end faces) 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 / It may be mm ² or more (for example, about 100 to 300 / mm ² ). On the other hand, when mechanical properties are required rather than lightness, the presence frequency of single fibers is, for example, an average of 100 fibers / mm ² or less, preferably 60 fibers / mm ² or less (for example, 1 to 60 fibers / mm ² ). mm ² ), more preferably 25 pieces / mm ² or less (for example, 3 to 25 pieces / mm ² ). When the presence frequency of the single fiber is too high, the fusion of the fibers is small and the strength of the leaf spring 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, it is preferable that the fibers fused in a bundle shape are thin in the thickness direction of the leaf spring 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 leaf springs can suppress the fibers from dropping 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 a point, 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 density and mechanical characteristics of the leaf spring of the present invention are affected by 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 leaf spring 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 leaf spring 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. The fiber adhesion rate can be measured 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.

The leaf spring of the present invention (particularly, 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 recessed by a load even if it is plate-like (board-like). It is desirable to have a surface hardness that is difficult to be deformed. As such an index, the hardness by an E-type durometer hardness test (test using “GS-721N” manufactured by Teclock Co., Ltd.) is, for example, 50 or more, preferably 60 or more (for example, 60 to 100), Preferably it is 70 or more (for example, 70-100). If this hardness is too small, it is likely to be deformed by a load applied to the surface.

  In order to balance bending stress, bending strength, surface hardness, and lightness in a high dimension, the molded body including such a bundle-like fusion fiber has a low frequency of bundle-like fusion fibers 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 filling rate and the fiber adhesion rate are too high, the distances between the bonded points are too close, the flexibility and flexibility are lowered, and it becomes difficult to eliminate distortion due to external stress. Since the fiber filling rate and the fiber adhesion rate are not too high, a passage by fine voids can be secured in the molded body, and the lightness can be improved. Therefore, in order to express a large bending stress, bending strength, and surface hardness with as few contacts as possible, the fiber filling rate and fiber adhesion rate are increased in the thickness direction from the molded body surface to the inside (center) and back surface. It is preferable to distribute uniformly along. When the adhesion points are concentrated on the surface or inside, it becomes difficult to ensure flexibility in addition to the bending stress and bending strength described above.

  One feature of the leaf spring 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.

  In the leaf spring of the present invention, the maximum bending stress in at least one direction (preferably all directions) is 0.5 MPa or more (for example, 0.5 to 100 MPa), preferably 0.7 to 30 MPa, and more preferably 0. It may be about 8 to 20 MPa (1 to 15 MPa). Furthermore, in the case of having a high bending stress, such as a relatively high-density molded body or a molded body including bundled fused fibers (a plurality of fibers fused in a bundled form), the maximum bending stress is 1. It may be 5 MPa or more, preferably 2 to 30 MPa, more preferably about 3 to 20 MPa. If the maximum bending stress is too small, it is easily broken by its own weight or a slight load. 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 leaf spring 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 leaf spring of the present invention may have a so-called “stickiness (or toughness)” without causing a rapid stress drop even when the bending spring exceeds the maximum bending stress (peak of bending stress) and is further bent. 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, in the leaf spring of the present invention, the stress when bending to a displacement of 1.5 times the bending amount indicating the maximum bending stress (hereinafter sometimes referred to as “1.5 times displacement stress”) is the maximum bending stress. It is only necessary to maintain 1/2 or more (for example, 1/2 to 1) of the stress, for example, 5.5 / 10 or more (for example, 5.5 / 10 to 9/10), preferably 6/10. It may be maintained above (for example, 6/10 to 9/10), more preferably 6.5 / 10 or more (for example, 6.5 / 10 to 9/10). The double displacement stress is 1/4 or more (for example, 1/4 to 1) of the maximum bending stress, preferably 5/10 or more (for example, 5/10 to 9/10), and more preferably 6/10. The above (for example, 6/10 to 9/10) may be maintained.

  The leaf spring of the present invention has moderate flexibility and flexibility, and in accordance with JIS K7017 “Fiber-Reinforced Plastics—Method of Obtaining Bending Properties A”, the deflection at the peak in the three-point bending method is For example, in at least one direction (preferably all directions), for example, it is about 0.5 to 20 mm, preferably about 1 to 15 mm, and more preferably about 2 to 10 mm (especially 2.5 to 9 mm).

  The leaf spring of the present invention has high bending strength, and the ratio of 155 ° bending stress to 155 ° bending stress and 155 ° bending stress to 155 ° bending stress is obtained by applying JIS K6400-2 “7.3 Compression Deflection Measurement B Method”. It is preferable to show a predetermined value. The 155 ° bending stress of the leaf spring of the present invention is, for example, 0.1 N / 25 mm or more (for example, 0.1 to 5 N / 25 mm), preferably 0.2 to 3 N / 25 mm, and more preferably 0.3 to 2 N. / 25 mm (particularly 0.5 to 1.5 N / 25 mm). When the 155 ° bending stress is less than 0.1 N / 25 mm, it is difficult to exhibit the performance as a spring.

  On the other hand, when the leaf spring of the present invention is used in a bent state, the leaf spring is bent only up to 180 °. In consideration of the thickness of the leaf spring, if the plate spring is pressurized to bend 180 ° and is bent repeatedly, the durability is reduced due to wear of the leaf spring. Therefore, before reaching this state, it is necessary to prevent bending more than necessary by improving the bending stress. That is, the leaf spring of the present invention needs to have a larger value of 175 ° bending stress than 155 ° bending stress. In the present invention, the ratio of 175 ° bending stress to 155 ° bending stress (175 ° bending stress / 155 ° bending stress) is 1.3 or more, and a relaxation force is obtained, preferably 1.5 or more (for example, 1.. 5 to 10), more preferably 2 or more (for example, 2 to 8).

  The leaf spring of the present invention can ensure high lightness due to the gap generated between the fibers. Moreover, since these voids are not independent voids but are continuous, they have air permeability. Such a structure is a structure that is extremely difficult to manufacture by conventional general hardening techniques, 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 leaf spring of the present invention has a low density. Specifically, the apparent density can be selected from a range of about 0.1 to 0.7 g / cm ³ , and from the point of balance between lightness and mechanical characteristics. For example, 0.12 to 0.6 g / cm ³ , preferably 0.15 to 0.5 g / cm ³ , more preferably 0.18 to 0.45 g / cm ³ (particularly 0.2 to 0.4 g / cm ³ ). cm ³ ). If the apparent density is too low, it is lightweight, but it is difficult to ensure sufficient bending stress, flexural strength and surface hardness. Conversely, if the apparent density is too high, the hardness can be ensured, but the lightness decreases. When the leaf spring is used for an application that requires light weight, it is preferable to adjust the density as low as possible within the above range. 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.

The basis weight of the leaf spring can be selected, for example, from a range of about 50 to 10000 g / m ² , for example, 100 to 5000 g / m ² , preferably 150 to 2000 g / m ² , more preferably 200 to 1500 g / m ² (particularly 300 to 1000 g / m ² ). If the basis weight is too small, it is difficult to ensure hardness and mechanical properties.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. It becomes difficult to obtain a uniform structure.

  The thickness of the leaf spring of the present invention is not particularly limited, but can be selected from a range of about 0.3 to 50 mm, for example, 0.5 to 30 mm, preferably 0.8 to 20 mm, more preferably 1 to 10 mm (particularly 1.5 to 5 mm). If the thickness is too thin, it will be difficult to ensure hardness and mechanical properties. If it is too thick, the mass will be heavy and the shape of the spring will be large, so the application will be limited.

Since the leaf spring of the present invention has a non-woven fiber structure, it has air permeability. Specifically, the air permeability according to the fragile method is, for example, 0.1 cm ³ / (cm ² · sec) or more, preferably 0.1 to 300 cm ³ / (cm ² · sec), more preferably 0.5 to It is about 250 cm ³ / (cm ² · sec).

[Method of manufacturing leaf spring]
In the leaf spring manufacturing method of the present invention, first, the 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.

  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.

  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 processed 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 such that its thickness is impaired by 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 in 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 article having high surface hardness, bending stress and bending strength, when the high-temperature steam is supplied to the web for processing, the web to be processed is placed between the conveyor belt or the rollers. It is important to expose to high-temperature steam in a state compressed to an apparent density (for example, about 0.1 to 0.7 g / cm ³ ). 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 article having desired sound absorption, 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 give a concavo-convex groove, a mark, or the like to a molded product obtained by applying a predetermined concavo-convex pattern or characters to a conveyor belt and transferring them. Moreover, you may laminate | stack with another material in the range which does not reduce the characteristic as a leaf | plate spring, and may form a laminated body.

  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. As for drying, it is necessary that the surface of the molded body 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 does not disappear, and a conventional method can be used as long as 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.

  Further, 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.

  The molded body obtained by such a method is usually plate-shaped or sheet-shaped, and is processed into a square sheet or a rectangular sheet by cutting or the like according to the shape of the target leaf spring. . Further, the obtained plate-like or sheet-like molded body is bent or curved by conventional thermoforming to obtain a leaf spring. Examples of thermoforming methods include compression molding, pressure forming (extrusion pressure forming, hot plate pressure forming, vacuum pressure forming, etc.), free blow molding, vacuum forming, bending, matched mold forming, hot plate forming, wet heat press forming. Etc. are available.

  Since the leaf | plate spring of this invention shows the outstanding spring characteristic, it can be utilized as various spring members, such as daily necessities, household appliances, bedding, a medical instrument, a vehicle, a building. In particular, since it is lightweight, it is suitable for applications such as being carried or reducing the load on the human body or vehicle. Specifically, daily necessities (for example, stationery such as clips, binders, and staples, clothespins, etc.), human body aids (for example, prosthetic legs, short leg braces, etc.), packaging materials (packaging cushioning materials or cushioning materials) , Packing materials, etc.), OA equipment (eg, ink ribbons, magnetic tape cassettes, spring members behind keyboard keys, etc.), bedding (eg, pillows, sofas, bed springs, mattresses, mattresses, etc.), automotive members (eg, , Suspension, bumper, etc.).

  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, “%” is 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 “Test method for general short fiber nonwoven fabric”, 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) Fiber filling rate The photograph which expanded the cross section in the thickness direction of a molded object to 100 time was image | photographed using the scanning electron microscope (SEM). Trace paper was overlaid on this photograph, and the photographed area and fiber (bundle) cross section were traced using transmitted light. Using this image analyzer (manufactured by Toyobo Co., Ltd.), the trace figure was taken into a computer from a CCD camera, binarized, and the percentage of the fiber cross-sectional area in the observed cross-sectional area was determined. It was expressed as This observation is performed by dividing the cross section of the molded body into three equal parts in the thickness direction, and in each of the three divided areas (front surface, inside (center), back surface) corresponding to an area of 1 mm ² . The average value was defined as the fiber filling rate. Further, the fiber cross-section filling rate was determined for each of the three divided regions, and the ratio of the minimum value to the maximum value (minimum value / maximum value) was also determined as the uniformity of the filling rate. However, even when only a part of the fiber cross section was shown in the observation area of each photograph, the portion included in the observation area was measured as the fiber cross-sectional area.

(5) 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.

(6) 1.5 times displacement stress In the measurement of bending stress, the stress when the bending amount (displacement) that shows 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.

(7) Deflection Measured according to JIS K7017 "Fiber-reinforced plastic-Determination of bending properties".

(8) Bending strength (155 ° and 175 ° bending stress)
Applying JIS K6400-2 “7.3 Compression Deflection Measurement B Method”, a 30 mmφ press plate was moved at a speed of 100 mm / min, and the stress at the target position was measured. In other words, in this measurement, a 25 mm wide × 80 mm long sample was folded in half at the center in the length direction, and then a 2 kg weight was placed on the sample and allowed to stand for 24 hours. I attached.

  Open this sample so that the bending angle is about 45 °, place it on the compression tester so that the center of the compressor is in contact with the upper end, and fix the side that is not in contact with the compressor to the surface of the tester with double-sided tape. did. The stress when the sample is pushed down to a bending angle of 25 ° from this state is “155 ° bending stress”, and the stress when the sample is further pushed down to 5 ° is “175 ° bending stress”. It was.

(9) Durometer hardness The durometer was measured using a type E durometer (manufactured by Teclock, "GS-721N").

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 about 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 on 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 (vertically) 0.4 MPa of high-temperature steam from the device in the thickness direction of the card web. 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 3 mm. The nozzles were arranged on the back side of the conveyor belt so as to be almost in contact with the belt. Table 1 shows the evaluation results of the molded body of the obtained molded body.

Example 2
A molded body was manufactured in the same manner as in Example 1 except that five fiber webs were stacked to form a card web having a total basis weight of about 500 g / m ² and the interval between the upper and lower conveyor belts on the nozzle side and suction side was 1 mm. . The evaluation results of the obtained molded body are shown in Table 1.

Example 3
Except using wet heat adhesive fibers in which the mass ratio of polyethylene terephthalate, which is the core component, and the sheath component, ethylene-vinyl alcohol copolymer, as the wet heat adhesive fibers, is the sheath component / core component = 40/60. In the same manner as in Example 1, a molded body was produced. The evaluation results of the obtained molded body are shown in Table 1.

Example 4
Wet heat adhesive fiber (manufactured by Kuraray Co., Ltd., “Sophista”, fineness 3 dtex, fiber length 51 mm, core-sheath mass ratio = 50/50, number of crimps 21/25 mm, crimp rate 13.5%) and polyethylene A card web is produced by blending terephthalate fibers (fineness 1.6 dtex, fiber length 51 mm, mechanical crimp number 15/25 mm) at a ratio of wet heat adhesive fiber / polyethylene terephthalate fiber = 95/5 (mass ratio). A molded body was produced in the same manner as in Example 1 except that. The evaluation results of the obtained molded body are shown in Table 1.

Comparative Example 1
Using a core-sheath composite fiber (2.2 dtex, 51 mm length) whose core component is polyethylene terephthalate and sheath component is low-density polyethylene (MI = 11), a web having a basis weight of about 100 g / m ² is prepared and stacked in five layers A non-woven fiber structure was obtained in the same manner as in Example 1 except that. The evaluation results of this structure are shown in Table 1. Although this structure maintained the shape of the non-woven fabric by fiber bonding, it had a so-called non-woven fabric shape, was very soft and did not form a so-called board shape, and the durometer hardness could not be measured.

Comparative Example 2
Wet heat bonding fiber (manufactured by Kuraray Co., Ltd., “Sophista”), core-sheath type composite staple fiber having a core component of polyethylene terephthalate and a sheath component of low-density polyethylene (MI = 11) (fineness 2.2 dtex, fiber length 51 mm) A non-woven fiber structure was obtained in the same manner as in Example 1 except that the card web was prepared by blending the core / sheath mass ratio = 50/50) at a ratio of the former / the latter = 60/40. Table 1 shows the evaluation results of the obtained structure. Although this structure had a board-like form in appearance, it was very soft and the bending stress after bending once was very low.

Reference Example Table 1 shows the evaluation results of a commercially available polyethylene foam (“Softlon S # 0502” manufactured by Sekisui Chemical Co., Ltd.).

  As is apparent from the results in Table 1, the molded articles of the examples have moderate deflection, high bending stress, and high bending strength despite being lightweight. On the other hand, the nonwoven fabric structure of the comparative example and the commercially available polyethylene foam have low bending stress and bending strength.

Claims (6)

  A leaf spring comprising wet-heat-adhesive fibers of 80% by mass or more and having a non-woven fiber structure, wherein the leaf spring is composed of a molded body to which fibers are fixed by fusion of the wet-heat-adhesive fibers.   In the cross section in the thickness direction, the fiber filling rate in each region divided into three equal parts in the thickness direction is 20 to 80%, and the ratio of the minimum value to the maximum value of the fiber filling rate in each region is 50% or more. The leaf spring according to claim 1. In addition to having an apparent density of 0.1 to 0.7 g / cm ³ , the maximum bending stress in at least one direction is 0.5 MPa or more, and the bending amount is 1.5 times the bending amount indicating the maximum bending stress. The leaf spring according to claim 1 or 2, wherein the bending stress is 1/2 or more with respect to the maximum bending stress.   The wet heat adhesive fiber is a composite fiber composed of a wet heat adhesive resin and a non-wet heat adhesive resin, and the ratio (mass ratio) of both is wet heat adhesive resin / non-wet heat adhesive resin = 40 / 60- The leaf spring according to any one of claims 1 to 3, which is 80/20.   The leaf spring according to any one of claims 1 to 4, which is a bent plate shape or a curved plate shape.   The method comprising the steps of forming a fiber containing a wet heat adhesive fiber into a web, and a step of heat-treating the produced fiber web with high-temperature steam to fuse the fibers to obtain a molded body having a non-woven fiber structure. 6. A method for manufacturing a leaf spring according to any one of 5 above.