Non-woven fabric, short-cut heat-adhesive fibers, and filter

Abstract

To provide a nonwoven fabric suitable for filter material, having high collection efficiency, low pressure loss, small distortion under compression, and long life in practical use.SOLUTION: A nonwoven fabric includes a short-cut ultra fine fiber having a fiber diameter of 0.1 to 1 μm and an aspect ratio of 100 to 3000, and a short-cut thermally bondable fiber having a fiber diameter of 0.5 to 4 μm and an aspect ratio of 100 to 3000, and has a compressibility of 30% or less under a compression of 30 kPa.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to nonwoven fabrics, short cut heat - adhesive fibers, and filters using them.

Background Art

[0002] As filters made of nonwoven fabrics, various types have been proposed so far. For example, a filter medium made of an air - laid nonwoven fabric with a multi - layer structure having a gradient of fiber fineness (see, for example, Patent Document 1), and a material obtained by laminating ultrafine fibers obtained by the electrospinning method on the surface layer of a general nonwoven fabric (for example, Patent Documents 2 and 3) have been proposed.

[0003] Among these, in the air - laid multi - layer filter medium with a gradient of fiber fineness, although low pressure loss and high filter life are achieved, there is also a problem that it is insufficient for collecting extremely fine dust. Further, in the filter medium obtained by laminating ultrafine fibers on the surface layer of a general nonwoven fabric, since the ultrafine fibers are in a state of being coated in a planar shape, there are problems such as an easy increase in pressure loss, insufficient adhesiveness with the nonwoven fabric serving as the base material, and easy fiber detachment.

[0004] Patent Document 4 proposes a filter medium made of a wet nonwoven fabric containing short - cut ultrafine fibers with a fiber diameter of 100 to 1000 nm (0.1 to 1 μm) and binder fibers with a single - fiber fineness of 0.1 dtex or more. Although the collection efficiency is better than the conventional ones, since there is a limit to the fineness of the binder fibers, it cannot be said to be sufficient in terms of further improving the collection efficiency for carbon fine particles such as those contained in automobile exhaust gas.

[0005] In addition, Patent Document 5 proposes a filter medium using short-cut ultrafine fibers, which has a multi-layer structure of two or more layers and has no interface between two adjacent layers of the multi-layer structure. Although this is excellent in the balance of high collection efficiency, low pressure loss, and long filter life, similar to the example of Patent Document 4, only the single fiber fineness of the binder fiber is exemplified as 1.1 dtex, and there is room for improvement in improving the collection efficiency for nano-sized fine particles such as carbon in exhaust gas.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0007] According to the studies of the present inventors, it is an important factor for extending the practical filter life that the deformation of the filter medium is small with respect to the external force applied to the filter medium by the medium or particles passing through the filter medium. An object of the present invention is to provide a nonwoven fabric that has a high collection rate and low pressure loss, has little deformation during pressurization, and is suitable as a filter medium with a long life in practical use.

Means for Solving the Problems

[0008] The present invention relates to short-cut It is a nonwoven fabric containing ultra-fine fibers and short-cut thermally adhesive fibers with a fiber diameter of 0.5 to 4 μm and an aspect ratio of 100 to 3000, and characterized in that the compression ratio at 30 kPa pressure is 30% or less. The present invention also relates to short-cut thermally adhesive fibers having a fiber diameter of 0.5 to 4 μm and an aspect ratio of 100 to 3000, and the thermally adhesive component consists only of a polyester with a melting point of 250°C or lower.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a nonwoven fabric that has a high collection rate and low pressure loss, has little deformation under pressure, and is suitable as a filter medium with a long service life in practical applications.

Brief Description of the Drawings

[0010]

Figure 1

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail.

[0012] 〔Short-Cut Ultra-Fine Fibers〕 The short-cut ultra-fine fibers are made of a fiber-forming thermoplastic polymer. The fiber diameter (D) of the short-cut ultra-fine fibers is 0.1 to 1 μm, preferably 0.2 to 0.9 μm, and particularly preferably 0.3 to 0.8 μm. If the fiber diameter (D) exceeds 1 μm, the pore diameter on the surface of the wet nonwoven fabric made by the papermaking method may become non-uniform. On the other hand, if it is less than 0.1 μm, the short-cut ultra-fine fibers may easily fall off from the mesh when the web is lifted by the papermaking method.

[0013] The aspect ratio (the ratio of fiber length (L) to fiber diameter (D)) of the short-cut ultrafine fibers is 100 to 3000, preferably 300 to 2500, and particularly preferably 500 to 2000. When the aspect ratio exceeds 3000, the fibers get entangled in water before the web is formed by the papermaking method, resulting in poor dispersion, and there is a risk that the pore diameters on the surface of the non-woven fabric produced by the papermaking method will become non-uniform. On the other hand, when the aspect ratio is less than 100, the entanglement between fibers becomes extremely weak, making it difficult to transfer from the wire part to the felt after web formation, and there is a risk that the process stability will decrease.

[0014] From the viewpoints of making the structure of the wet non-woven fabric uniform when manufacturing the non-woven fabric by the papermaking method, reducing the occurrence of defects, and improving the yield and manufacturing efficiency when manufacturing the non-woven fabric by the papermaking method, the fiber length of the short-cut ultrafine fibers is preferably 0.05 to 3 mm. As a method for obtaining short-cut ultrafine fibers cut to a predetermined length, examples include a method of cutting ultrafine fibers using a guillotine cutter type fiber bundle cutting device or a rotary cutter such as an Eastman type in which a large number of cutter blades are provided radially outward at equal intervals.

[0015] The fiber cross-section of the short-cut ultrafine fibers may be a round cross-section or an irregular cross-section. As the polymer constituting the short-cut ultrafine fibers, a thermoplastic polymer can be preferably used. For example, polymers such as polyamide-based, polyester-based, polyolefin-based, acrylate-based, and polyphenylene sulfide-based polymers. Since they are relatively easy to be made ultrafine and molded, and are excellent in strength and dimensional stability, polyester-based polymers are preferred.

[0016] In the case of polyester-based polymers, polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, aromatic dicarboxylic acids such as isophthalic acid and metal salts of 5-sulfoisophthalic acid, and aliphatic dicarboxylic acids such as adipic acid, sebacic acid, and succinic acid, and ε-caprolactone, etc., which have these as the main repeating units Hydroxycarboxylic acid condensates, copolymers with glycol components such as diethylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, etc., polylactic acid, polycaprolactone, polyhydroxybutyrate, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate are preferred.

[0017] Among polyamide-based polymers, aliphatic polyamides such as polyamide 6, polyamide 66, and polyamide 610 are preferred.

[0018] Examples of polyolefin-based polymers include high-density polyethylene, medium-density polyethylene, low-density polyethylene by high-pressure method, linear low-density polyethylene, isotactic polypropylene, ethylene-propylene copolymer, ethylene copolymer of vinyl monomers such as maleic anhydride, atactic polystyrene, isotactic polystyrene, and syndiotactic polystyrene. These are preferred because they are difficult to be attacked by acids, alkalis, etc. and can be used as a binder component after being taken out as ultra-fine fibers due to their relatively low melting points.

[0019] Examples of acrylate-based polymers include methyl polyacrylate, ethyl polyacrylate, sodium polyacrylate, methyl polymethacrylate, and acrylamide crosslinked copolymer.

[0020] 〔Method for producing short-cut ultra-fine fibers〕 Short-cut ultra-fine fibers can be produced by a conventionally known method, for example, the method disclosed in International Publication No. 2005 / 095686 pamphlet. In the present invention, it is preferable to use those produced by this method. Hereinafter, a preferable method for producing short-cut ultra-fine fibers will be described.

[0021] From the viewpoint of obtaining a desirable fiber diameter and its uniformity, the short-cut ultrafine fibers are obtained by bundling sea-island composite fibers having an island component composed of a fiber-forming thermoplastic polymer constituting the short-cut ultrafine fibers with an island diameter (D) of 100 to 1000 nm (i.e., 0.1 to 1 μm) and a sea component composed of a polymer more soluble in an aqueous alkali solution than the above fiber-forming thermoplastic polymer (hereinafter sometimes referred to as "aqueous alkali solution-soluble polymer") into a fiber bundle (strand), cutting it, and then subjecting it to alkali weight reduction processing to dissolve and remove the sea component.

[0022] Here, the aqueous alkali solution refers to an aqueous solution of an alkali metal such as potassium hydroxide or sodium hydroxide. The island diameter can be measured by photographing the cross-section of the sea-island composite fiber with a transmission electron microscope. When the shape of the island is a non-circular cross-section other than a circular cross-section, the above island diameter (D) uses the diameter of the circumscribed circle.

[0023] The dissolution rate ratio of the aqueous alkali solution-soluble polymer forming the sea component to the fiber-forming thermoplastic polymer forming the island component is preferably 200 or more, more preferably 300 to 3000. Within this range, the island separability is good, which is preferable. If the dissolution rate is less than 200 times, while dissolving the sea component in the central part of the cross-section of the sea-island composite fiber, the island component in the surface layer part of the cross-section of the separated sea-island composite fiber is dissolved because of its small diameter. Therefore, although a considerable amount of the sea component is reduced in weight, the sea component in the central part of the cross-section of the sea-island composite fiber cannot be completely dissolved and removed, leading to unevenness in the thickness of the island component and solvent erosion of the island component itself, and there is a possibility that short-cut ultrafine fibers with a uniform fiber diameter cannot be obtained, which is not preferable.

[0024] As the aqueous alkali solution-soluble polymer forming the sea component of the sea-island composite fiber, fiber formation From the perspective of properties, among polyester-based polymers, aliphatic polyamides among polyamide-based polymers, and polyethylene or polystyrene among polyolefin-based polymers are preferred, and polyester-based polymers such as polylactic acid, ultra-high molecular weight polyalkylene oxide condensation-based polymers, and copolyester of polyalkylene glycol-based compounds and 5-sodium sulfoisophthalic acid are particularly preferred.

[0025] Among polyester-based polymers, polyethylene terephthalate-based copolyester with an intrinsic viscosity of 0.4 to 0.6, copolymerized with 6 to 12 mol% of 5-sodium sulfoisophthalic acid and 3 to 10 mass% of polyethylene glycol with a molecular weight of 4000 to 12000, is preferred. Here, 5-sodium sulfoisophthalic acid contributes to hydrophilicity and improvement of melt viscosity, and polyethylene glycol (PEG) improves hydrophilicity. Also, the higher the molecular weight of PEG, the more the hydrophilicity increasing effect due to its higher-order structure is considered, but the reactivity deteriorates and it becomes a blend system, so there may be problems in terms of heat resistance and spinning stability. Also, if the copolymerization amount of PEG exceeds 10 mass%, there is an effect of reducing the melt viscosity, which is not preferable.

[0026] In the above-mentioned sea-island composite fiber, it is preferable that the melt viscosity of the sea component during melt spinning is higher than the melt viscosity of the island component polymer. In such a case, even if the composite mass ratio of the sea component is less than 40%, it is less likely that the islands are joined or most of the island components are joined, and it is easy to form a sea-island composite fiber.

[0027] The melt viscosity ratio (sea / island) in the above-mentioned sea-island composite fiber is preferably 1.1 to 2.0, particularly preferably 1.1 to 1.5. If this ratio is less than 1.1 times, the island components are likely to be joined during melt spinning, which is not preferable. On the other hand, if it exceeds 2.0 times, the viscosity difference is too large, so the spinning condition is likely to deteriorate, which is not preferable.

[0028] The short-cut ultra-fine fibers are derived from the island part of the sea-island composite fiber. The number of islands in the cross-section of the sea-island composite fiber is preferably 100 or more, more preferably 300 to 1000. The sea-island composite mass ratio (sea:island), which is the mass ratio of the sea component to the island component, is preferably 5:95 to 95:5. Within this range, the thickness of the sea component between the island component and another adjacent island component can be reduced, facilitating the dissolution and removal of the sea component and the conversion of the island component into ultra-fine fibers, which is preferable. If the proportion of the sea component exceeds 95%, the thickness of the sea component becomes too thick. On the other hand, if it is less than 5%, the amount of the sea component becomes too small and bonding between islands is likely to occur.

[0029] As the spinneret used for melt spinning, any spinneret can be used, such as those having a group of hollow pins or a group of micropores for forming the island component. For example, a spinneret may be used in which the island component extruded from the hollow pins or micropores and the sea component flow designed to fill the space between them merge, and the sea-island cross-section is formed by compressing this. An example of a spinneret having a group of hollow pins is shown in Fig. 1.

[0030] In the spinneret 1 shown in Fig. 1, the molten island component polymer in the polymer reservoir 2 for the island component before distribution is distributed into the polymer introduction passage 3 for the island component formed by a plurality of hollow pins. On the other hand, the molten sea component polymer is introduced into the polymer reservoir 5 for the sea component before distribution through the polymer introduction passage 4 for the sea component. The hollow pins forming the polymer introduction passage 3 for the island component each penetrate the polymer reservoir 5 for the sea component and open downward at the central portion of the entrance of each of the plurality of core-sheath composite flow passages 6 formed thereunder. From the lower end of the polymer introduction passage 3 for the island component, the island component polymer flow is introduced into the central portion of the core-sheath composite flow passage 6, and the sea component polymer flow in the polymer reservoir 5 for the sea component is introduced into the core-sheath composite flow passage 6 so as to surround the island component polymer. A core-sheath composite flow with the island component polymer flow as the core and the sea component polymer flow as the sheath is formed, and a plurality of core-sheath composite flows are introduced into the funnel-shaped merging passage 7. In this merging passage 7, the sheath portions of the plurality of core-sheath composite flows are close to each other, and a sea-island type composite flow is formed. This sea-island type composite flow gradually decreases its horizontal cross-sectional area while flowing down in the funnel-shaped merging passage 7 and is discharged from the discharge port 8 at the lower end of the merging passage 7.

[0031] The discharged sea-island type composite fiber is solidified by cooling air and taken up by a rotating roller or an ejector set at a predetermined take-up speed to obtain an undrawn yarn. This take-up speed is preferably 200 to 5000 m / min. If it is less than 200 m / min, the productivity is poor and it is not preferable. On the other hand, if it exceeds 5000 m / min, the spinning stability is poor and it is not preferable.

[0032] The obtained undrawn yarn may be directly subjected to the cutting process as it is according to the uses and purposes of the superfine fibers obtained after extracting and removing the sea component, or may be subjected to the cutting process after the stretching process or the heat treatment process in order to obtain desired strength, elongation, and heat shrinkage characteristics. The stretching process may be a separate stretching method in which spinning and stretching are performed in separate steps, or a direct stretching method in which stretching is performed immediately after spinning in one step.

[0033] The sea-island composite fiber is cut so that the aspect ratio (the ratio of the fiber length (L) to the island diameter (D): L / D) of the short-cut ultrafine fibers made of the polymer of the island component is within the range of 100 to 3000. This cutting can be performed by cutting the undrawn yarn or drawn yarn as it is, or as a tow bundled in units of dozens to millions of strands, using a guillotine cutter, a rotary cutter, or the like. Also, it may be cut after the sea component extraction and removal process. The sea component extraction and removal process is performed by alkali weight reduction processing.

[0034] In this sea component extraction and removal process, the ratio (bath ratio) of the sea-island composite fiber to the aqueous alkali solution is, for example, 0.1 to 5% by mass, preferably 0.4 to 3% by mass. If it is less than 0.1% by mass, although the contact between the fiber and the alkali solution is large, there is a risk that the processability such as drainage may become difficult. On the other hand, if it exceeds 5% by mass, since the amount of fiber is too large, there is a risk that the fibers may become entangled in the sea component extraction and removal process.

[0035] The bath ratio is defined by the following formula. Bath ratio (% by mass) = [mass of sea-island composite fiber (g) / mass of aqueous alkali solution (g)] × 100

[0036] The treatment time of the alkali weight reduction processing in the sea component extraction and removal process is, for example, 5 to 60 minutes, preferably 10 to 30 minutes. If it is less than 5 minutes, there is a risk that the alkali weight reduction may be insufficient. On the other hand, if it exceeds 60 minutes, there is a risk that even the island component may be weight-reduced. The treatment temperature of the alkali weight reduction processing in the sea component extraction and removal process is, for example, 50 to 90°C, preferably 60 to 80°C.

[0037] In the alkali weight reduction processing of the sea component extraction and removal process, the alkali concentration of the aqueous alkali solution is preferably 2 to 10% by mass. If it is less than 2% by mass, there will be a shortage of alkali, and the weight reduction rate may become extremely slow, which is not preferable. On the other hand, if it exceeds 10% by mass, the alkali weight reduction may progress too much, and there is a risk that even the island part may be weight-reduced, which is not preferable.

[0038] As a method of alkali weight reduction processing in the sea component extraction and removal step, the sea-island composite fiber is put into an alkali solution, treated under predetermined conditions for a predetermined time, then, after passing through a dehydration step once, it is put into water again and neutralized and diluted using organic acids such as acetic acid and oxalic acid, and finally dehydrated. This method can be used.

[0039] Also, after treatment for a predetermined time, a neutralization treatment can be performed, and further water can be injected to proceed with dilution, and then dehydration can be performed. In these cases, in the former case, the treatment is carried out batchwise. Therefore, it is possible to carry out production (processing) in small quantities. On the other hand, since it takes time for the neutralization treatment, the productivity is somewhat poor. In the latter case, semi-continuous production is possible, but a large amount of acid-based aqueous solution and a large amount of water are required for dilution during the neutralization treatment.

[0040] From the viewpoint of preventing fiber shedding during dehydration, the treatment equipment preferably applies a mesh-like material (for example, a non-alkali hydrolyzable bag) with an aperture ratio (the area of the aperture portion per unit area) of 10 to 50% as disclosed in Japanese Patent No. 3678511. In this case, if the aperture ratio is less than 10%, the water drainage is extremely poor and it is not preferable. On the other hand, if it exceeds 50%, there is a risk of shedding of ultra-fine fibers, which is not preferable.

[0041] After the sea component extraction and removal step, in order to enhance the dispersibility of the short-cut ultra-fine fibers, it is preferable to adhere a dispersant (for example, Maker Surf manufactured by Meisei Chemical Industry Co., Ltd.) to the surface of the short-cut ultra-fine fibers in an amount of 0.1 to 5.0% by mass based on the fiber mass.

[0042] By subjecting the sea-island composite fiber cut into a predetermined length to the sea component extraction and removal step described above, the sea-island composite fiber is converted into the short-cut ultra-fine fiber composed of the island component in the present invention. At that time, when the island component is made of a polyester-based polymer, a short-cut ultra-fine fiber made of polyester can be obtained.

[0043] 〔Short-cut thermally adhesive fiber〕 In the present invention, the short-cut thermally adhesive fiber is used as a binder fiber for maintaining the short-cut ultrafine fiber in the form of a nonwoven fabric. By using the short-cut thermally adhesive fiber, the collection efficiency of fine particle size particles when the nonwoven fabric is used as a filter medium can be significantly improved.

[0044] The fiber diameter (D) of the short-cut thermally adhesive fiber is 0.5 to 4 μm, preferably 0.8 to 3 μm, and more preferably 1.0 to 2.8 μm. If the fiber diameter (D) is less than 0.5 μm, the rigidity of the fiber itself becomes low and it may be difficult to maintain the structure of the filter medium, which is not preferable. On the other hand, if it exceeds 4 μm, the number of short-cut thermally adhesive fibers in the filter medium decreases, the adhesion points decrease, the rigidity decreases, the pore diameter of the filter medium increases, and the collection efficiency of fine particle size particles may decrease, which is not preferable.

[0045] The aspect ratio (the ratio of the fiber length (L) to the single fiber diameter (D): L / D) of the short-cut thermally adhesive fiber is 100 to 3000, preferably 300 to 2500, and particularly preferably 500 to 2000. If the aspect ratio is less than 100, the entanglement between fibers becomes extremely weak, and it may be difficult to transfer from the wire part to the felt after web formation, resulting in a decrease in process stability. On the other hand, if the aspect ratio exceeds 3000, the fibers entangle with each other in water before the web is lifted by the papermaking method, resulting in poor dispersion, and the pore diameter of the pores appearing on the surface of the wet nonwoven fabric may become non-uniform (that is, the ratio of the average pore diameter to the maximum pore diameter is large).

[0046] From the viewpoint of the uniformity of the structure of the wet nonwoven fabric, few defects occurring, and problems and yield / manufacturing efficiency in the production of the wet nonwoven fabric, the fiber length of the short-cut thermally adhesive fiber is preferably 0.05 to 10 mm.

[0047] As a method for obtaining short-cut thermally adhesive fibers of a predetermined length, a method using a guillotine cutter type fiber bundle cutting device or a rotary cutter such as an Eastman type in which a large number of cutter blades are provided radially outward at equal intervals can be applied.

[0048] One of the preferred embodiments of the staple heat - adhesive fiber is an embodiment in which the fiber - forming component accounts for 20 - 80% by mass and the heat - adhesive component accounts for 80 - 20% by mass. In this embodiment, the fiber - forming component is a polyester with a melting point of 180°C or higher, and the heat - adhesive component is a polyester with a melting point 20°C or lower than the melting point of the fiber - forming component.

[0049] If the staple heat - adhesive fiber is less than 20% by mass, it is not preferable in that the non - woven fabric cannot maintain its form under a predetermined pressure. On the other hand, if it exceeds 80% by weight, the flowing part of the heat - adhesive component increases, the space volume for capturing the collected matter decreases, leading to a decrease in the collection efficiency and the filter life, which is not preferable.

[0050] The fiber - forming component in the staple heat - adhesive fiber is a polyester having an alkylene terephthalate with a melting point of 180°C or higher, preferably a melting point of 190 - 270°C as the main repeating component. If the melting point of this polyalkylene terephthalate - based polyester is less than 180°C, it is not only difficult to stably produce the composite fiber, but also the dimensional stability during the heat - adhesion treatment decreases, which is not preferable. On the other hand, if the melting point exceeds 270°C, it becomes difficult to make it ultra - fine, which is not preferable.

[0051] As this fiber-forming component's polyalkylene terephthalate-based polyester, polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate are preferable, and polyethylene terephthalate is particularly preferable because it is inexpensive and widely used. In addition, in order to improve the fiber moldability for ultrafine thinning, monomer components such as isophthalic acid, metal salts of 5-sulfoisophthalic acid, organic phosphorus salts of 5-sulfoisophthalic acid, 2,6-dinaphthalic acid, adipic acid, sebacic acid, azelaic acid, dodecanoic acid, ε-caprolactone, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, diethylene glycol, polyalkylene glycol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, triethylene glycol, tetraethylene glycol, etc. may be copolymerized within a range where the melting point is within a predetermined range.

[0052] The heat-adhesive component in the short-cut heat-adhesive fiber is preferably a polyester having a melting point 20°C or more lower than that of the fiber-forming component. In this case, the polyester is preferably a polyalkylene terephthalate-based polyester having a melting point of 250°C or lower. Since the melting point of the heat-adhesive component is 20°C or more lower than that of the fiber-forming component, good adhesion with the short-cut ultrafine fiber can be obtained. And since the heat-adhesive component is a polyalkylene terephthalate-based polyester having a melting point of 250°C or lower, good adhesion and elasticity / rigidity that the space in the nonwoven fabric is not easily crushed even under pressure can be obtained.

[0053] As the polyalkylene terephthalate-based polyester of the heat-adhesive component, it is preferably a polyalkylene-based polyester having ethylene terephthalate, trimethylene terephthalate, butylene terephthalate, or hexamethylene terephthalate as the main repeating unit. In order to adjust the heat adhesion temperature, adjust the crimping temperature and pressure, and improve the fiber formability for ultrafine thinning, isophthalic acid, metal salts of 5-sulfoisophthalic acid, organic phosphorus salts of 5-sulfoisophthalic acid, 2,6-dinaphthalic acid, adipic acid, sebacic acid, azelaic acid, dodecanoic acid, ε-caprolactone, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and other dicarboxylic acids, diethylene glycol, polyalkylene glycol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, triethylene glycol, tetraethylene glycol and other diol components may be copolymerized.

[0054] In order to thermally bond between the above composite fibers, it is necessary that the heat-adhesive component is complexed so as to be exposed on the surface of the composite fiber. As this mode, for example, a composite in which the heat-adhesive component and the fiber-forming component are complexed in a parallel type (side by side type) Examples include coaxial core-sheath composite fibers and eccentric core-sheath composite fibers in which the heat-adhesive component is used as the sheath component and the fiber-forming component is used as the core component. Among them, coaxial core-sheath composite fibers are preferred. Coaxial core-sheath composite fibers can obtain good adhesion points between short-cut ultrafine fibers or between short-cut heat-adhesive fibers, and the fiber spacing that affects the pore diameter, which is important for filter performance, becomes uniform. Also, it is good in terms of dimensional stability under high temperature or high pressure. Even for coaxial core-sheath composite fibers, as long as the center of gravity of the core and the center of gravity of the sheath are offset within an acceptable range, there is no problem, and unless it is a structure intentionally made eccentric, it shall be regarded as a coaxial core-sheath composite fiber.

[0055] As another form of the short-cut thermoadhesive fiber, fibers composed of a single component of polyester with a melting point of 250°C or lower may be used as the thermoadhesive component of the short-cut thermoadhesive fiber. In this case, by thermally fusing or pressure bonding the short-cut thermoadhesive fibers to each other or the short-cut ultrafine fibers, in combination with the fineness of the short-cut thermoadhesive fibers of the present invention, the pore diameter can be made smaller than that of conventionally known thermoadhesive fibers. To do this, it is preferable that the melting point of the short-cut thermoadhesive fiber is 5°C or more lower than the melting point of the short-cut ultrafine fiber. The cross-sectional shape of the short-cut thermoadhesive fiber is arbitrary, and examples thereof include a circular cross-section, a hollow cross-section, a cross-shaped cross-section, a flat cross-section, and a cross-section having fins.

[0056] In the above-mentioned polymer, various stabilizers, ultraviolet absorbers, thickening branching agents, viscosity reducing agents, matting agents, colorants, antibacterial agents, deodorants, carbon black, hydrophilic agents, water repellent agents, metal fine particles, metal oxides, antioxidants, light stabilizers, fluorescent brightening agents, and other various improvers may also be blended as required.

[0057] 〔Method for manufacturing short-cut thermoadhesive fiber〕 The ultrafine short-cut thermoadhesive fiber with a fiber diameter of 0.5 to 4 μm in the present invention can be manufactured, for example, by the following method.

[0058] When the short-cut thermoadhesive fiber is a composite fiber composed of a fiber-forming component and a thermoadhesive component, the polymers constituting the above-mentioned thermoadhesive component and fiber-forming component are formed into chips, and after drying them in a nitrogen or air atmosphere heated or dehumidified, or under vacuum, they are melted and introduced into a composite spinning die, extruded as a molten composite fiber yarn, cooled and solidified at a position 15 to 100 mm below the die, and taken up at a spinning speed of 300 to 1000 m / min to obtain an undrawn yarn. A known composite spinning die can be used.

[0059] When the heat - adhesive component of the short - cut heat - adhesive fiber consists of a single component of a polyalkylene terephthalate - based polyester with a melting point of 250°C or lower, the polymer constituting the heat - adhesive component is made into chip form, dried and melted in the same manner as described above, introduced into a single - component spinning die having a known single - hole nozzle, and then cooled and solidified and drawn to obtain an undrawn yarn.

[0060] As a method for obtaining short - cut heat - adhesive fibers with a desired fiber diameter, the undrawn yarn is subjected to high - magnification drawing of 5 times or more in a state where the orientation of the amorphous part and crystallization in the undrawn yarn are changed as little as possible by flow drawing, and then, if necessary, the draw ratio is further increased by neck drawing until the undrawn part disappears, so that a total high - magnification drawing of 10 times or more can be carried out.

[0061] At this time, it is preferable to apply a polyether - polyester copolymer to the surface of the undrawn yarn. Flow drawing is carried out in warm water 5 - 50°C higher than the higher of the glass transition temperatures of the heat - adhesive component and the fiber - forming component of the undrawn yarn. By applying the polyether - polyester copolymer to the surface of the undrawn yarn, a film is formed on the surface of the undrawn yarn, so that fiber - to - fiber fusion and adhesion are less likely to occur during flow drawing in high - temperature warm water.

[0062] Furthermore, when obtaining a wet non - woven fabric from the obtained fibers by the papermaking method, the polyether - polyester copolymer adheres to the fibers, resulting in good water dispersibility of the fibers. When applying the polyether - polyester copolymer to the undrawn yarn, it is desirable that it be applied by an oiling device immediately after the undrawn yarn is spun, or included in the warm - water bath in the flow - drawing process for application. Subsequently, the undrawn yarn is flow - drawn, and if necessary, neck - drawn or subjected to a restricted heat - shrinkage treatment in a relaxed state, and then, after further applying a fiber treatment agent according to the non - woven fabric forming process and the imparted functions, it is cut with a guillotine cutter, a rotary cutter, etc. to obtain the desired short - cut heat - adhesive fibers.

[0063] Subsequently, the undrawn yarn is flow - drawn, and if necessary, neck - drawn or subjected to a restricted heat - shrinkage treatment in a relaxed state, and then, after further applying a fiber treatment agent according to the non - woven fabric forming process and the imparted functions, it is cut with a guillotine cutter, a rotary cutter, etc. to obtain the desired short - cut heat - adhesive fibers.

[0064] In the case where the nonwoven fabric is a wet nonwoven fabric, when an aqueous emulsion of a polyether-polyester copolymer similar to that applied to the undrawn yarn is applied after stretching or before and after cutting as a fiber treatment agent, the water dispersibility of the fibers in the wet web forming step is further improved. In this case, the polyether-polyester copolymer may be adhered in an amount of 0.03 to 10.0% by mass per 100% by mass of the short cut heat-adhesive fiber. If it is less than 0.03% by mass, the dispersion of the fibers in water in the papermaking process becomes insufficient, which is not preferable. On the other hand, if it exceeds 10.0% by mass, not only the adhesiveness between the fibers tends to be inhibited, but also a large amount of the polyether-polyester copolymer increases the water quality load on the circulating water in the wet web forming process, which is not preferable.

[0065] The above polyether-polyester copolymer is composed of terephthalic acid and / or isophthalic acid, a lower alkylene glycol, and a polyalkylene glycol and / or its monoether. Examples of the preferably used lower alkylene glycol include ethylene glycol, propylene glycol, and tetramethylene glycol. On the other hand, examples of the polyalkylene glycol include polyethylene glycol having an average molecular weight of 600 to 6000, a polyethylene glycol-polypropylene glycol copolymer, and polypropylene glycol. Further, examples of the monoether of the polyalkylene glycol include monomethyl ether, monoethyl ether, monophenyl ether, etc. of polyethylene glycol, polypropylene glycol, etc.

[0066] The above polyether-polyester copolymer preferably has a molar ratio of terephthalate unit to isophthalate unit in the range of 95:5 to 40:60 from the viewpoint of water dispersibility, but a small amount of alkali metal salt sulfoisophthalic acid, adipic acid, sebacic acid, etc. may be copolymerized.

[0067] The average molecular weight of the polyether-polyester copolymer depends on the molecular weight of the polyalkylene glycol used, but is usually 1,000 to 20,000, preferably 3,000 to 15,000. If the average molecular weight is less than 1,000, the effect of improving the water dispersibility is not sufficient. On the other hand, if it exceeds 20,000, it becomes difficult to emulsify and disperse the polymer.

[0068] In order to improve the flow drawability and obtain ultra-fine short-cut thermoadhesive fibers with a fiber diameter of 0.5 to 4 μm, the short-cut thermoadhesive fibers are made of polyester, and the polyester is preferably a copolyester having 60 to 90 mol% of a terephthalic acid component and 10 to 40 mol% of an isophthalic acid component as a dicarboxylic acid component.

[0069] By copolymerizing the isophthalic acid component in the range of 10 to 40 mol% with the polyester, the flow draw ratio can be significantly improved. When not copolymerized, it remains at 10 times or less, whereas in the case of isophthalic acid copolymerization, the ratio can be improved to about 20 to 200 times. The reason for this is not clear, but it is possible to reduce the crystallinity and the molecular orientation of the amorphous phase in the undrawn yarn or the fiber after flow drawing. Also, depending on the copolymerization, even if the molecular weight is increased, the free volume (excluded volume) around the molecules during flow drawing increases, and the molecular chains can move more easily at a temperature higher than the glass transition temperature, and the molecular weight can be increased to such an extent that sufficient entanglement of the molecular chains can be ensured. Therefore, it is estimated that the possible draw ratio is improved.

[0070] If the copolymerization amount of the isophthalic acid component is less than 10 mol%, the flow draw ratio decreases, and it becomes difficult to obtain short-cut thermoadhesive fibers with a fiber diameter of 4 μm or less, which is not preferable. On the other hand, if the copolymerization amount of the isophthalic acid component exceeds 40 mol%, it becomes difficult to suppress the fusion between the fibers during flow drawing, and it also becomes difficult to uniformly and stably produce the desired ultra-fine fibers, which is not preferable. The copolymerization amount of the isophthalic acid component is more preferably 15 to 35 mol%, particularly preferably 20 to 30 mol% based on the total dicarboxylic acid component.

[0071] In the case where the short-cut thermoadhesive fiber is in the form of a composite fiber, it is preferable that the isophthalic acid component is copolymerized with both the fiber-forming component and the thermoadhesive component. The copolymerization amount of the isophthalic acid component may be different between the fiber-forming component and the thermoadhesive component. Even in that case, however, the copolymerization amount of the isophthalic acid component in the weight average of both (i.e., as the whole fiber) is preferably in the range of 10 to 40 mol%.

[0072] The above copolymerized polyester has an alkylene terephthalate as the main repeating component, and this repeating unit is preferably ethylene terephthalate, trimethylene terephthalate, butylene terephthalate, or hexamethylene terephthalate. And as the diol component of the copolymerized polyester, it is preferable to use an aliphatic diol.

[0073] Among the above copolymerized polyesters, an isophthalic acid copolymerized polyalkylene terephthalate-based polyester having ethylene terephthalate as the main repeating unit is most preferable. In addition, for adjusting the flow drawability, the melting point of the thermoadhesive component, and the adhesive strength, bifunctional carboxylic acids such as adipic acid, sebacic acid, and sodium 3-5-dicarboxybenzenesulfonate other than isophthalic acid, and diols such as diethylene glycol, propylene glycol, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, and polyethylene glycol may be copolymerized together.

[0074] 〔Nonwoven fabric〕 The nonwoven fabric of the present invention contains the short-cut ultra-fine fiber and the short-cut thermoadhesive fiber defined above, and may contain other short-cut fibers as necessary, and can be obtained by forming a web and then molding it into the form of a nonwoven fabric by heating or pressurization.

[0075] Examples of web formation methods include the carding method, the airlaid method, and the papermaking method, and it is particularly preferable to use the papermaking method to obtain a wet nonwoven fabric. Examples of web joining methods include the air-through method, the embossing method, the Yankee dryer method, the multi-cylinder dryer method, the calendar method, the resin bonding method, and the water jet method, and the calendar method and the water jet method (sometimes also called the spunlace method, the hydroentanglement method, or the water entanglement method) are particularly suitable.

[0076] In the nonwoven fabric of the present invention, the mass ratio of the short-cut ultrafine fibers to the total mass of the nonwoven fabric is preferably 0.5 to 50% by mass, more preferably 1 to 40% by mass, and particularly preferably 3 to 30% by mass. If the short-cut ultrafine fibers are less than 0.5% by mass, not only can a satisfactory collection efficiency not be obtained, but also there is a possibility of generating ground marks as a wet nonwoven fabric, which is not preferable. On the other hand, if it exceeds 50% by mass, the filter medium (wet nonwoven fabric) becomes too dense, so the water permeability in the papermaking process becomes extremely poor, the productivity deteriorates, or the pressure loss becomes too large, which is not preferable.

[0077] Also, in the nonwoven fabric of the present invention, the mass ratio of the short-cut heat-bondable fibers to the total mass of the nonwoven fabric is preferably 10 to 99.5% by mass, more preferably 10 to 95.5% by mass, still more preferably 15 to 90% by mass, and particularly preferably 20 to 85% by mass. If the short-cut ultrafine fibers are less than 10% by mass, the heat adhesiveness is small, the nonwoven fabric strength and pressure deformation are insufficient, a uniform pore diameter cannot be obtained, the collection efficiency and filter life are inferior, and the quality becomes unstable. In addition, there is a possibility of generating ground marks as a wet nonwoven fabric, which is unsuitable. On the other hand, if it exceeds 95.5% by mass, the effect of the short-cut ultrafine fibers is insufficient, and the filtration performance (collection efficiency) is inferior to that of the prior art using ultrafine fibers.

[0078] The nonwoven fabric of the present invention is characterized in that the number of bonding points of the thermal adhesive component is increased by using short-cut thermal adhesive fibers with a small fiber diameter, and the distance between the fibers is made uniform, thereby maintaining the shape of the filter medium, making it difficult to be crushed by pressure, and providing high collection efficiency, low pressure loss, and long filter life.

[0079] In the nonwoven fabric of the present invention, as fibers other than the above-mentioned short-cut ultrafine fibers and short-cut thermal adhesive fibers, various synthetic fibers (polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, nylon, olefin-based, aramid-based), natural pulp such as wood pulp and linter pulp, synthetic pulp mainly composed of aramid or polyethylene, etc. may be mixed, so long as the amount of the fibers is 50% by mass or less based on the total mass of the nonwoven fabric. In particular, polyethylene terephthalate short fibers made of stretched polyethylene terephthalate having a single fiber fineness of 0.01 to 0.6 dtex and a fiber length of 1 to 10 mm are preferred from the viewpoint of dimensional stability, etc.

[0080] In addition, as long as the nonwoven fabric of the present invention satisfies the requirement of including short-cut ultrafine fibers and short-cut thermally adhesive fibers, depending on the purpose, the short-cut ultrafine fibers and the short-cut thermally adhesive fibers may be in a form in which two or more types of short-cut fibers having different fiber diameters, polymer types, and compositions are mixed. Further, the nonwoven fabric may be a single layer with a uniform mixing ratio throughout, but depending on the purpose, it may be composed of two or more layers. In that case, for use as a filter medium, it is preferable that the mixing ratio and fiber density at the interface between adjacent layers do not exist and have an inclined structure (the mixing ratio and fiber density gradually increase or decrease) in the thickness direction of the nonwoven fabric. Such a form is possible by arranging a plurality of carding machines, airlaid web manufacturing apparatuses, and papermaking machines in the web forming process, laminating layers with different mixing ratios and fiber types, and then fixing the fibers to each other by thermal adhesion or thermocompression bonding. Further, when composed of two or more layers, if the mixing ratio of the short-cut ultrafine fibers is large or the average fiber diameter of the entire fiber composition is small, the density is large and the through pores can be made small. By providing a density difference for each web layer in this way, it is possible to design a filter having high collection efficiency, low pressure loss, and a long filter life. The density of the web layer may be designed to increase in the filtration direction, may be designed to decrease, or may be in a laminated state with a mixture of large and small, and may be freely designed according to the purpose.

[0081] Also, depending on the purpose, for the purpose of improving the tensile strength and firmness of the filter, further improving the filter life of a prefilter for coarse dust, pleat stability, and adhesiveness to other materials, etc., nonwoven fabrics of other materials may be laminated. For example, as other materials, spunbond nonwoven fabric, meltblown nonwoven fabric, heatbond nonwoven fabric, needle-punched nonwoven fabric, spunlace nonwoven fabric, airlaid nonwoven fabric, resinbond nonwoven fabric, stitchbond nonwoven fabric, tow-opened fiber nonwoven fabric, burst fiber nonwoven fabric, composite laminates of these nonwoven fabrics, and other woven and knitted fabrics, etc. may be laminated.

[0082] The basis weight of the nonwoven fabric of the present invention is preferably 1 to 500 g / m 2 , more preferably 3 to 400 g / m 2, particularly preferably 5 to 300 g / m 2 is. When the basis weight is less than 1 g / m 2 , the nonwoven fabric is too thin, resulting in weak strength. Also, it is prone to streaks during papermaking and may have defects such as allowing substances to be filtered through or causing damage when used as a filter. On the other hand, when it exceeds 500 g / m 2 , it becomes difficult for water to drain during papermaking, and problems are likely to occur in terms of manufacturing and cost.

[0083] The thickness of the nonwoven fabric of the present invention is preferably 0.01 to 3.0 mm, more preferably 0.5 to 3.0 mm, and particularly preferably 1.0 to 2.5 mm. When the thickness is less than 0.01 mm, the strength of the filter medium is insufficient, which is not preferable. On the other hand, when it exceeds 3.0 mm, the compactness as a filter medium decreases, and it is particularly difficult to form the pleat processing (zigzag folding structure) performed to increase the filtration area, which is not preferable.

[0084] In the nonwoven fabric of the present invention, the average pore diameter of the through holes is preferably 0.1 to 10.0 μm, more preferably 0.3 to 5.0 μm, and further preferably 0.5 to 2.5 μm. When the average pore diameter is less than 0.1 μm, the pressure loss of the filter medium becomes too high, and the air flow rate after filter filtration decreases, which is not preferable. On the other hand, when it exceeds 10.0 μm, the tightness as a filter medium decreases, and the capture rate of fine particles decreases, which is not preferable.

[0085] Also, in the nonwoven fabric of the present invention, the maximum pore diameter / average pore diameter (the value obtained by dividing the maximum pore diameter by the average pore diameter) of the through holes is preferably 1.0 to 2.5, preferably 1.0 to 2.3. That the maximum pore diameter / average pore diameter is 1.0 indicates that the through-hole diameter of the nonwoven fabric is uniform, which is the most preferable. When the maximum pore diameter / average pore diameter exceeds 2.5, the tightness as a filter medium decreases, and the capture rate of fine particles decreases, which is not preferable. In the case where the pore shape is not a perfect circle, the major axis is used as the pore diameter.

[0086] In the nonwoven fabric of the present invention having the above basis weight and thickness, its air permeability is preferably 0.5 to 10 cm3 / cm 2 / sec, more preferably 0.7 to 5 cm 3 / cm 2 / sec, particularly preferably 1 to 4 cm 3 / cm 2 / sec. When the air permeability is less than 0.5 cm 3 / cm 2 / sec, the pressure loss of the filter becomes too high and the air flow rate after filter filtration decreases, which is not preferable. On the other hand, when the air permeability exceeds 10 cm 3 / cm 2 / sec, the tightness as a filter medium decreases and the collection efficiency decreases, which is not preferable.

[0087] The nonwoven fabric of the present invention has a compression ratio of 30% or less, preferably 26% or less, when pressurized at 30 kPa, which is calculated by the following formula. When the compression ratio at 30 kPa exceeds 30%, the nonwoven fabric as a filter medium is crushed and becomes high density under the pressure when used as a filter, and the life is reduced. Compression ratio during pressurization (%) = Thickness of filter medium during compression (mm) / Thickness of filter medium before compression (mm)

[0088] 〔Method for manufacturing nonwoven fabric〕 The nonwoven fabric of the present invention can be produced by forming a wet nonwoven fabric by papermaking using an ordinary Fourdrinier paper machine, a cylinder paper machine, a cylinder paper machine, or a combination of multiple of these for multi-layer papermaking, and then performing heat treatment.

[0089] The heat treatment step is performed after the web forming step by the papermaking method, and either a Yankee dryer or an air-through dryer can be applied for the heat treatment. The heat treatment temperature is usually 100 to 140 ° C, preferably 110 to 130 ° C, and the heat treatment time is, for example, 30 to 300 seconds, preferably 60 to 180 seconds. The nonwoven fabric may be calendered, embossed, or flat heat pressed as necessary. In the case of calendering, the temperature of the calender roller is, for example, 140 to 250 ° C, and the linear pressure between the rollers is, for example, 1 to 100 kN / m.

[0090] 〔Filter〕 The nonwoven fabric of the present invention is made of short-cut ultrafine fibers, short-cut and thermally adhesive fibers, and very fine fibers. When used as a filter medium, it is possible to obtain a filter that satisfies all of the requirements of high collection efficiency, low pressure loss and long life.

[0091] Filters made using the nonwoven fabric of the present invention can be suitably used as, for example, chemical filters, air filters, liquid filters, and oil filters. The nonwoven fabric of the present invention is homogeneous and has an extremely small pore size, and therefore, in addition to filters, can be suitably used for stencil printing base paper, wipers, battery separators, artificial leather, etc. EXAMPLES

[0092] Next, examples of the present invention and comparative examples will be described in detail. The measurement items in the examples were measured by the following methods.

[0093] (1) Intrinsic viscosity 0.12 g of the polymer sample was dissolved in 10 mL of a mixed solvent of tetrachloroethane / phenol (volume ratio 1 / 1), and the intrinsic viscosity (dL / g) at 35° C. was measured.

[0094] (2) Melting point A DuPont 990 differential thermal analyzer was used to measure at a heating rate of 20°C / min to determine the melting peak. When the melting temperature was not clearly observed, a micro melting point measuring device (Yanagimoto Seisakusho) was used to determine the temperature (softening point) at which the polymer softened and began to flow as the melting point. In either case, five samples were measured, and the average value was calculated.

[0095] (3) Melt Viscosity The test polymer was dried, set in an orifice set at the melting temperature of an extruder for melt spinning, held in a molten state for 5 minutes, and then extruded under a predetermined level of load. At this time, the shear rate and the melt viscosity were plotted. The above operation was repeated under multiple levels of load. Based on the above data, a shear rate - melt viscosity relationship curve was created. On this curve, the melt viscosity when the shear rate was 1000 seconds -1 was estimated.

[0096] (4) Measurement of dissolution rate Each of the polymers for the sea and island components was extruded through a spinneret for producing sea - island composite fibers having 24 discharge holes with a pore diameter of 0.3 mm and a land length of 0.6 mm, wound at a speed of 1000 - 2000 m / min, and the fibers were drawn. The cut elongation rate was controlled within the range of 30 - 60% to produce 75 dtex / 24 - filament multifilaments. These multifilaments were dissolved in a solvent at a predetermined temperature with a bath ratio of 50, and the weight loss rate was calculated from the dissolution time and the dissolved amount at this time.

[0097] (5) Fiber length L Using a Keyence digital microscope (VH - X5000), the single - fiber lengths of 100 fibers were measured, and the average value was taken as the fiber length L (unit: mm).

[0098] (6) Fiber diameter D (in the case of short - cut ultra - fine fibers) Using a transmission electron microscope TEM (with a length - measuring function), a fiber cross - section photograph was taken at a magnification of 30000 times for measurement. The fiber diameter D was the diameter of the circumscribed circle of its single - fiber cross - section (average value of 5 samples).

[0099] (7) Fiber diameter D (in cases other than short - cut ultra - fine fibers) From the single - fiber fineness d (dtex) and the density ρ (g / cm 3 ), it was calculated by the following formula (unit: μm). Here, π is the ratio of the circumference of a circle to its diameter. D (μm)=20×(d / πρ) 1 / 2

[0100] (8) Denier per single filament (d) (in the case of non-short-cut ultra-fine fibers) A 2000-mm fiber bundle after stretching was collected, dried in a hot air dryer at 120 °C for 40 minutes, and then the absolute dry mass measured was multiplied by 5000 to measure the total fineness of the fiber bundle (unit: dtex). The denier per single filament d (unit: dtex) was calculated by dividing the obtained total fineness by the number of single filaments constituting the fiber bundle.

[0101] (9) Fiber density (in the case of non-short-cut ultra-fine fibers) Using the density gradient tube method described in JIS L1015:2010 8.14.2, the fiber density ρ (unit: g / cm 3 ) was measured.

[0102] (10) Aspect ratio (L / D) Using the values of the fiber diameter D (unit: mm) calculated from the denier per single filament and the fiber length L (unit converted from μm to mm), the ratio of the fiber length (L) / fiber diameter (D) was defined as the aspect ratio (L / D).

[0103] (11) Basis weight It was carried out based on JIS P8124:2011 (Paper and board - Method for measuring grammage).

[0104] (12) Thickness It was carried out based on JIS P8118:2014 (Paper and board - Test methods for thickness, density and specific volume).

[0105] (13) Nonwoven fabric density It was carried out based on JIS P8118:2014 (Paper and board - Test methods for thickness, density and specific volume).

[0106] (14) Air permeability It was carried out based on JIS L1913:2010 (General test methods for nonwoven fabrics) 6.8.

[0107] (15) Specific tensile strength Based on JIS P8113:2006 (Paper and Paperboard - Test Methods for Tensile Properties - Part 2: Constant Rate of Elongation Method), measurements were taken in the machine direction (MD) and the direction perpendicular to it (CD) during sample preparation, and converted to specific tensile strength. (Unit: N·m / g)

[0108] (16) 30 kPa Compression Ratio Performed based on JIS L1913:2010 (General Test Methods for Nonwovens) 6.14

[0109] (17) Pore Size Two circular samples with a diameter of 2.5 cm were randomly collected from the nonwoven fabric, and the average pore size, minimum pore size, and maximum pore size (unit: μm) were measured using a palm porometer (pore size distribution measuring instrument manufactured by PMI). Also, the value of maximum pore size / average pore size was calculated.

[0110] (18) Atmospheric Dust Collection Rate Adjusted so that the wind speed was 5.1 cm / sec, and the atmospheric dust before and after the sample was counted using a particle counter (KC-03B manufactured by Rion Co., Ltd.), and the collection rate was calculated based on the ratio. Atmospheric Dust Collection Rate (%) = (1 - (number of atmospheric dust after sample passage / number of atmospheric dust before sample passage)) × 100

[0111] (19) Pressure Loss The pressure before and after the test piece passed during the measurement of the atmospheric dust collection rate (wind speed 5.1 cm / sec) was measured, and the pressure difference was obtained as the pressure loss.

[0112] (20) Filter Life Eight types of JIS Z 8901 were used as test dusts, with a flow rate of 16.7 cm / sec during sample passage and a dust concentration of 1 g / m 3 When it was set as such, the dust collection amount (mass increase) when the pressure loss increased by 2 kPa was measured (g / m 2 )

[0113] [Example 1] The island component is polyethylene terephthalate with a melt viscosity of 120 Pa·sec at 285°C (intrinsic viscosity 0.64 dL / g, melting point 256°C), and the sea component is polyethylene glycol with an average molecular weight of 4000 and a melt viscosity of 135 Pa·sec at 285°C, copolymerized with 4% by mass of 5-sodium sulfoisophthalic acid and 9 mol% of modified polyethylene terephthalate (intrinsic viscosity 0.39 dL / g, melting point 226°C). Using a mass ratio of sea:island = 10:90, spinning was carried out using a spinneret for sea-island composite fibers with 400 islands in the structure shown in Figure 1, and the take-up speed was 1500 m / min. The difference in the alkali weight loss rate between the island component and the sea component was 1000 times.

[0114] After stretching this by 3.9 times, it was cut into fibers with a length of 1 mm using a guillotine cutter to obtain composite fibers for short-cut ultra-fine fiber A. When this was subjected to 10% weight loss at 75°C in an aqueous NaOH solution with a concentration of 4% by mass, ultra-fine short fibers with relatively uniform fiber diameter and fiber length were produced. This was designated as short-cut ultra-fine fiber A. The fiber diameter of the obtained short-cut ultra-fine fiber A was 0.75 μm, the fiber length was 0.8 mm, and the aspect ratio was 1067.

[0115] On the other hand, the fiber-forming component is isophthalic acid 20 mol% copolymerized polyethylene terephthalate (intrinsic viscosity 0.64 dL / g, melting point 202°C), and the thermally adhesive component is isophthalic acid 40 mol% - diethylene glycol 4 mol% copolymerized polyethylene terephthalate (intrinsic viscosity 0.55 dL / g, melting point (softening point) 110°C). A core-sheath type composite fiber (core:sheath = 50:50 mass ratio) was prepared with the fiber-forming component as the core and the thermally adhesive component as the sheath.

[0116] The content of the isophthalic acid component, which is a copolymerized component contained in this core-sheath type composite fiber, was 30 mol% as the sum of 10 mol% (20 mol% × 50%) contained in the fiber-forming component of the core and 20 mol% (40 mol% × 50%) contained in the thermally adhesive component of the sheath.

[0117] To obtain a core-sheath composite fiber, a fiber-forming component and a thermally adhesive component were melted separately using a vented twin-screw extruder. The fiber-forming component was used as the core component, and the thermally adhesive component was used as the sheath component. They were compounded using a known core-sheath composite spinning die having 1336 capillaries with a pore diameter of 0.3 mm so that the mass ratio of the core to the sheath was 50:50, and melt-extruded in a filament form. At this time, the die temperature was 290°C and the discharge rate was 430 g / min.

[0118] Furthermore, the extruded filament was cooled and solidified by cooling air at 25°C at a position 31 mm below the die. While applying a polyester-polyether copolymer aqueous emulsion with a solids adhesion amount of 0.5% by mass at the lower part, it was wound up at 500 m / min to obtain an undrawn yarn.

[0119] This undrawn yarn was drawn 63 times in warm water at 82°C and then drawn 2 times in warm water at 70°C. After applying an aqueous solution of a polyester-polyether copolymer to the fiber surface, it was cut into fibers with a fiber length of 3 mm to obtain short-cut thermally adhesive fibers B with a fineness of 0.051 dtex (fiber diameter 2.3 μm, fiber length 3 mm, aspect ratio 1328).

[0120] In addition, as other fiber C, polyethylene terephthalate short fibers (Tepirus TA04PN SD0.1×3 manufactured by Teijin Frontier Co., Ltd., inherent viscosity 0.47 dL / g, melting point 256°C, fineness 0.1 dtex, fiber diameter 4 μm, fiber length 3 mm, aspect ratio 750) were used.

[0121] Short-cut ultra-fine fibers A, short-cut thermally adhesive fibers B, and other fibers C were mixed and stirred at a predetermined mass ratio (short-cut ultra-fine fibers A / short-cut thermally adhesive fibers B / other fibers C = 15 / 40 / 45), and a basis weight of 100 g / m 2 was formed into a sheet using a TAPPI (square sheet machine manufactured by Kumagai Riki Kogyo Co., Ltd.), and then dried (120°C × 2 minutes) using a Yankee dryer to obtain a wet nonwoven fabric. The physical properties of the obtained nonwoven fabric (filter medium) are shown in Tables 1 and 2.

[0122] [Example 2] In the papermaking of Example 1, the basis weight was 300 g / m 2A wet nonwoven fabric was obtained in the same manner as in Example 1 except for the following. The physical properties of the obtained nonwoven fabric (filter medium) are shown in Tables 1 and 2.

[0123] [Example 3] A wet nonwoven fabric was obtained in the same manner as in Example 1 except that the short-cut thermally adhesive fiber B used was the short-cut fiber of the core-sheath type composite fiber described below and the dryer temperature was changed to 150°C. The physical properties of the obtained nonwoven fabric (filter medium) are shown in Tables 1 and 2.

[0124] The fiber-forming component was isophthalic acid 20 mol% copolymerized polyethylene terephthalate (intrinsic viscosity 0.64 dL / g, melting point 202°C), and the thermally adhesive component was isophthalic acid 20 mol% - 1,4-butanediol 65 mol% copolymerized polyethylene terephthalate (intrinsic viscosity 0.62 dL / g, melting point (softening point) 155°C). Using a core-sheath type composite fiber with the fiber-forming component as the core and the thermally adhesive component as the sheath, short-cut thermally adhesive fiber B was prepared.

[0125] Note that the isophthalic acid component, which is a copolymer contained in the short-cut thermally adhesive fiber B, was 20 mol% as the sum of 10 mol% (50% of 20 mol%) contained in the fiber-forming component and 10 mol% (50% of 20 mol%) contained in the thermally adhesive component.

[0126] To obtain the short-cut thermally adhesive fiber B, the fiber-forming component and the thermally adhesive component were each melted in separate vented twin-screw extruders, with the fiber-forming component as the core component and the thermally adhesive component as the sheath component. Using a known core-sheath type composite spinning die having 1336 holes with a capillary diameter of 0.3 mm, they were compounded and melt-spun in a filament form so that the mass ratio of core:sheath was 50:50. At this time, the die temperature was 290°C and the discharge rate was 430 g / min.

[0127] Furthermore, the discharged filament was cooled and solidified by cooling air at 25°C at a position 42 mm below the die, and while applying a polyether-polyester copolymer aqueous emulsion with a solid content adhesion amount of 0.5 mass%, it was wound up at 500 m / min to obtain an undrawn yarn.

[0128] This undrawn yarn was drawn 28 times in warm water at 82 °C and then drawn 2.9 times in warm water at 70 °C. After applying an aqueous solution of a polyether-polyester copolymer to the fiber surface, it was cut into 3-mm fiber lengths to obtain staple heat-bondable fiber B with a fineness of 0.079 dtex (fiber diameter 2.8 μm, fiber length 3 mm, aspect ratio 1067).

[0129] [Example 4] In the papermaking of Example 3, a wet nonwoven fabric was obtained in the same manner as in Example 3 except that the basis weight was 300 g / m 2 The physical properties of the obtained nonwoven fabric (filter medium) are shown in Tables 1 and 2.

[0130] [Examples 5 and 6] Isophthalic acid 20 mol% copolymerized polyethylene terephthalate (intrinsic viscosity 0.64 dL / g, melting point 202 °C) was melted with a vented twin-screw extruder and melt-spun in a filament form from a known single-component spinneret having 1192 capillaries with a pore diameter of 0.18 mm. At this time, the die temperature was 290 °C and the discharge rate was 200 g / min.

[0131] Furthermore, the extruded yarn was cooled and solidified by cooling air at 25 °C at a position 26 mm below the die, and while applying an aqueous emulsion of a polyether-polyester copolymer at a solid content adhesion amount of 0.5 mass%, it was wound up at 500 m / min to obtain an undrawn yarn. This undrawn yarn was drawn 68 times in warm water at 82 °C and then drawn 2 times in warm water at 70 °C. After applying an aqueous solution of a polyether-polyester copolymer to the fiber surface, it was cut into 3-mm fiber lengths to obtain staple heat-bondable fiber B consisting only of a heat-bondable component with a fineness of 0.025 dtex (fiber diameter 1.6 μm, fiber length 3 mm, aspect ratio 1897). The isophthalic acid component copolymerized in the staple heat-bondable fiber B was 20 mol%.

[0132] In Examples 1 and 2, the short-cut thermally adhesive fiber B was replaced with the aforementioned one, and after papermaking and drying in the same manner as in Examples 1 and 2, a hydraulic clearance embossing machine (manufactured by Yuri Roll Co., Ltd.) was used for thermocompression bonding treatment at 190 °C, 29 kN / m, and a speed of 2 m / min to obtain a wet nonwoven fabric. The physical properties of the obtained nonwoven fabric (filter medium) are shown in Tables 1 and 2 and Tables 3 and 4.

[0133] [Comparative Example 1] A wet nonwoven fabric was obtained in the same manner as in Example 1 except that the core-sheath composite fiber described below was used as the short-cut thermally adhesive fiber B. The physical properties of the obtained nonwoven fabric (filter medium) are shown in Tables 3 and 4.

[0134] The short-cut thermally adhesive fiber B was prepared using a core-sheath composite fiber in which the fiber-forming component was polyethylene terephthalate (intrinsic viscosity 0.64 dL / g, melting point 256 °C) and the thermally adhesive component was 40 mol% isophthalic acid - 4 mol% diethylene glycol copolymerized polyethylene terephthalate (intrinsic viscosity 0.55 dL / g, melting point (softening point) 110 °C), with the fiber-forming component as the core and the thermally adhesive component as the sheath.

[0135] As a method for producing the core-sheath composite fiber, the fiber-forming component and the thermally adhesive component were each melted in separate vented twin-screw extruders, with the fiber-forming component as the core component and the thermally adhesive component as the sheath component, and they were compounded and melt-extruded in a filamentous form using a known core-sheath composite spinning die having 1336 holes with a capillary diameter of 0.3 mm so that the mass ratio of core:sheath was 50:50. At this time, the die temperature was 290 °C and the discharge amount was 600 g / min.

[0136] Furthermore, the extruded filament was cooled and solidified by cooling air at 25°C at a position 56 mm below the die, and a polyether-polyester copolymer aqueous emulsion was applied at a solids adhesion amount of 0.5% by mass below that, followed by winding at 1350 m / min to obtain an undrawn yarn. This undrawn yarn was drawn 2.6 times in warm water at 58°C and then drawn 1.15 times in warm water at 56°C. After applying an aqueous solution of a polyether-polyester copolymer to the fiber surface, it was cut into 5 mm fiber lengths to obtain short-cut thermoadhesive fibers B with a fineness of 1.1 dtex (fiber diameter 10.5 μm, fiber length 5 mm, aspect ratio 477).

[0137] In addition, the isophthalic acid component copolymerized in this short-cut thermoadhesive fiber B was 20 mol% as the sum of 0 mol% (50 parts by mass of 0 mol%) contained in the fiber-forming component and 20 mol% (50 parts by mass of 40 mol%) contained in the thermoadhesive component.

[0138] [Comparative Example 2] In the papermaking of Comparative Example 1, the basis weight was 300 g / m 2 and a wet nonwoven fabric was obtained in the same manner as in Comparative Example 1 except for this. The physical properties of the obtained nonwoven fabric (filter medium) are shown in Tables 3 and 4.

[0139] [Comparative Examples 3 and 4] Using fibers composed of a single thermoadhesive component described below as the short-cut thermoadhesive fiber B, wet nonwoven fabrics were obtained in the same manner as in Examples 5 and 6. The physical properties of the obtained nonwoven fabrics (filter media) are shown in Tables 3 and 4.

[0140] To obtain fibers composed of a single thermoadhesive component, isophthalic acid 20 mol% copolymerized polyethylene terephthalate (intrinsic viscosity 0.64 dL / g, melting point 202°C) was melted using a vented twin-screw extruder and melt-extruded in a filament form from a known single-component spinneret having 1192 holes with a capillary diameter of 0.18 mm. At this time, the die temperature was 285°C and the discharge amount was 180 g / min.

[0141] Furthermore, the extruded filament was cooled and solidified by cooling air at 25°C at a position 25 mm below the die, and a polyether-polyester copolymer aqueous emulsion was applied at a solid content adhesion amount of 0.5% by mass below that, and then wound up at 1350 m / min to obtain an undrawn yarn. After applying an aqueous solution of a polyether-polyester copolymer to the fiber surface without stretching this undrawn yarn, it was cut into a fiber length of 5 mm to obtain a short-cut thermally adhesive fiber B composed of a single thermally adhesive component with a fineness of 1.1 dtex (fiber diameter 10.5 μm, fiber length 5 mm, aspect ratio 477). The amount of the copolymerized isophthalic acid component contained in this short-cut thermally adhesive fiber B was 20 mol%.

[0142]

Table 1

[0143]

Table 2

[0144]

Table 3

[0145]

Table 4

[0146] The numerical value in parentheses in the melting point column represents the softening point. Tables 1 to 4 are summarized as Table 5 and presented below.

[0147]

Table 5

Industrial Applicability

[0148] The non-woven fabric of the present invention can be suitably used as a filter medium. Since this filter has high collection efficiency, low pressure loss, and a long filter life, it can be suitably used as an air filter for an intake internal combustion engine, etc. Of course, it can also be used as an air filter, micro filter, and liquid filter for other applications such as indoor air conditioners, refrigerators, heaters (electric, kerosene, etc.), automotive air conditioners, air purifiers, clean rooms, and indoor humidifiers.

Explanation of Signs

[0149] 1 Spinning nozzle 2 Polymer reservoir for island component 3 Polymer introduction passage for island component 4 Polymer introduction passage for sea component 5 Polymer reservoir for sea component 6 Passage for core-sheath type composite flow 7 Confluence passage 8 Discharge port

Claims

1. Short cut ultra-fine fibers with a fiber diameter of 0.1 to 1 μm and an aspect ratio of 100 to 3000, short cut thermally adhesive fibers with a fiber diameter of 0.5 to 4 μm and an aspect ratio of 100 to 3000, and polyethylene terephthalate staple fibers with a fineness of 0.1 to 0.6 dtex and a fiber length of 1 to 10 mm, wherein the short cut thermally adhesive fibers are composite fibers composed of a fiber-forming component and a thermally adhesive component, in the composite fibers, the fiber-forming component occupies 20 to 80% by mass, the thermally adhesive component occupies 80 to 20% by mass, the fiber-forming component is a polyester with a melting point of 180 °C or higher, the thermally adhesive component is a polyester with a melting point 20 °C or more lower than the melting point of the fiber-forming component, and the compression rate at 30 kPa pressure is 30% or less, a non-woven fabric characterized thereby.

2. The non-woven fabric according to Claim 1, wherein the short cut thermally adhesive fibers are made of polyester, and both the fiber-forming component and the thermally adhesive component copolymerize an isophthalic acid component, and the copolymerization amount of the isophthalic acid component in the weight average of both is in the range of 10 to 40 mol%.

3. The non-woven fabric according to Claim 1, wherein the composite fiber is a core-sheath type composite fiber having a fiber-forming component as a core and a thermally adhesive component as a sheath.

4. The non-woven fabric according to Claim 1 or 2, wherein the thermally adhesive component consists only of a polyester having a melting point of 250 °C or lower.

5. The content of the short cut ultra-fine fibers with a fiber diameter of 0.1 to 1 μm and an aspect ratio of 100 to 3000 is 0.5 to 50% by mass, the content of the short cut thermally adhesive fibers with a fiber diameter of 0.5 to 4 μm and an aspect ratio of 100 to 3000 is 10 to 99.5% by mass, the basis weight is 1 to 500 g / m2, the thickness is 0.01 to 3.0 mm, the average pore diameter is 0.1 to 10.0 μm, and the value of the maximum pore diameter / average pore diameter is 1.0 to 2.5, the non-woven fabric according to Claim 1.

6. A filter made using the non-woven fabric according to any one of Claims 1 to 5.

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