Thermally adhesive splittable composite short fiber, wet-laid nonwoven fabric and its manufacturing method

Abstract

To provide a hot-bonding split-type composite staple fiber which has less fiber-fiber fusion and has excellent dispersibility and excellent collection of fine grains, a wet-type nonwoven fabric, and a manufacturing method thereof.SOLUTION: A hot-bonding split-type composite staple fiber is composed of a component A comprising a fiber-forming synthetic resin and a component B having a melting point lower than 20°C, wherein the component is arranged in segments of eight or over, a fiber fineness is 0.01-1 dtex, and an aspect ratio is 100-3000. Moreover, preferably, each component is arranged alternately radially, and a central part has a solid or a hollow structure. Also provided is a wet-laid nonwoven fabric in which: a thickness of a portion where ultrafine fibers A are exposed to a nonwoven fabric surface is 5 μm or under; and the ultrafine fibers A existing in a fiber bundle shape forms a protrusion and the hot-bonding component B forms a recess. Further provided is a manufacturing method of the wet-laid nonwoven fabric, including a wet-type paper-making and a calender treatment.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a heat-adhesive splittable composite staple fiber suitable for wet-laid nonwoven fabrics. maintenance, and Beauty A wet nonwoven fabric made of the same The present invention relates to a method for producing the above-mentioned product. [Background technology]

[0002] Conventionally, copolymer polyester composite fibers have been widely used as thermal adhesive staple fibers suitable for manufacturing nonwoven fabrics. For example, Patent Document 1 and Patent Document 2 provide thermal adhesive composite fibers in which polyester, which has a melting point in the range of 130 to 230°C and contains 0.5 to 15% by weight of polyolefin based on the weight of the thermal adhesive component, is present in the sheath as a thermal adhesive component, and polyalkylene terephthalate, which has a melting point 20°C higher than that of the thermal adhesive component, is present in the core as a fiber-formable component, and both components are composited so that the thermal adhesive component is exposed on the surface.

[0003] Patent Document 3 proposes a composite fiber having a single fiber fineness of 0.01 to 1.5 dtex, in which a fiber-formable component forming the core is made of a polyalkylene terephthalate having a melting point of 220°C or higher and an intrinsic viscosity of 0.30 to 0.55 dL / g, and a thermal adhesive component formed from a polyolefin forming the sheath is composited so as to be exposed on the surface.

[0004] The above-mentioned heat-adhesive composite fibers have a problem that the exposed area of ​​the heat-adhesive component is large, and when multiple fibers are heated and drawn at the same time, the heat-adhesive components of adjacent fibers fuse together, resulting in a significant decrease in the dispersibility and spreadability of the resulting fibers. In particular, when producing fine heat-adhesive fibers, the heating and drawing temperature is higher, so fusion is more likely to occur. For example, when producing a wet-laid nonwoven fabric using fine heat-adhesive fibers, the fused fibers do not disperse sufficiently in the pulper that dissociates the fibers, resulting in a wet-laid nonwoven fabric with an uneven texture and many undispersed defects. This problem is also present in dry-laid nonwoven fabrics with low basis weight and density. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2011-74506 A [Patent Document 2] JP 2011-195978 A [Patent Document 3] JP 2014-201855 A Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the problems in the background art described above, and an object of the present invention is to provide a heat-adhesive splittable composite staple fiber having less fusion between fibers, excellent dispersibility, and excellent collection of fine particles. maintenance, and Beauty A wet nonwoven fabric made of the same The object of the present invention is to provide a method for producing the above-mentioned [Means for solving the problem]

[0007] The thermal adhesive splittable conjugate short fiber of the present invention is Polyester Resin Component A consists of the above, and a compound having a melting point 20°C or more lower than that of component A. Copolymer polyester resin A thermally adhesive splittable composite staple fiber composed of component A and component B, in which components A and B are arranged in a total of 8 or more segments, and the fineness of the entire fiber is 0.01 dtex to 0.6 It is characterized by having a dtex range and an aspect ratio of the entire fiber in the range of 100 to 3000.

[0008] Furthermore, Copolymer polyester resin The melting point of component B is 220°C or less, Made of polyester resin The melting point of component A is 180°C or higher, the intrinsic viscosity is in the range of 0.35 to 0.70 dL / g, and the surface area of ​​the fiber is Copolymer polyester resin It is preferable that the ratio of component B is 80% or less. Made of polyester resin Ingredient A and Copolymer polyester resin It is preferable that component B is arranged radially and alternately from the center of the fiber, and that the center of the fiber has a solid or hollow structure. 。

[0009] difference Among others, The thermal adhesive splittable composite short fiber The method for producing a wetlaid nonwoven fabric is characterized in that the heat-adhesive splittable composite short fibers of the present invention are wetlaid into paper and then calendered. Effect of the Invention

[0010] According to the present invention, a heat-adhesive splittable composite short fiber is obtained, which has little fusion between fibers, is excellent in dispersibility, and is excellent in capturing fine particles. Maintenance, The present invention also provides a method for producing a wet-laid nonwoven fabric using the thermally adhesive splittable composite short fibers. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of the cross-sectional structure (hollow type) of a thermally adhesive splittable conjugate short fiber of the present invention. [Diagram 2] FIG. 1 is a schematic diagram illustrating an example of the cross-sectional structure of a thermally adhesive splittable conjugate short fiber of the present invention (solid type with component B in the center). [Diagram 3] FIG. 1 is a cross-sectional view showing an example of a spinneret device used in producing the thermally adhesive splittable conjugate short fibers of the present invention. [Figure 4] 1 is a SEM photograph of the surface of a wetlaid nonwoven fabric using the thermal adhesive splittable conjugate short fiber of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The present invention will now be described in further detail.

[0013] The thermal adhesive splittable conjugate short fiber of the present invention is Polyester Resin Component A consists of the above, and a compound having a melting point 20°C or more lower than that of component A. Copolymer polyester resin It is a thermally adhesive splittable composite short fiber composed of component A and component B. Furthermore, components A and B are arranged in a total of 8 or more segments, and the fineness of the entire fiber is 0.01 dtex to 0.6 It is characterized by having a dtex range and an aspect ratio of the entire fiber in the range of 100 to 3000.

[0014] Component A constituting the heat-adhesive splittable composite short fiber of the present invention Is, Po The component is polyester. do. More specifically, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, polybutylene succinate, and copolymers thereof are preferred. Fat etc. is selected arbitrarily from 。

[0015] goodExamples of polyesters preferably used in the present invention include polyesters of aromatic dicarboxylic acids and aliphatic diols, such as polyalkylene terephthalates such as polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate, and polyalkylene naphthalates such as polyethylene naphthalate; polyesters of alicyclic carboxylic acids and aliphatic diols, such as polyalkylene cyclohexane dicarboxylate; polyesters of aromatic carboxylic acids and alicyclic diols, such as polycyclohexane dimethanol terephthalate; polyesters of aliphatic carboxylic acids and aliphatic diols, such as polyethylene succinate, polybutylene succinate, and polyethylene adipate; and polyhydroxycarboxylic acids, such as polylactic acid and polyhydroxybenzoic acid. Depending on the purpose, one or more of isophthalic acid, adipic acid, sebacic acid, α,β-(4-carboxyphenoxy)ethane, 4,4-dicarboxyphenyl, 5-sodium sulfoisophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid or esters thereof may be copolymerized as an acid component, and one or more of diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyalkylene glycol, etc. may be copolymerized as a diol component, and three or more carboxylic acid components or components having hydroxyl groups such as pentaerythritol, trimethylolpropane, trimellitic acid, trimesic acid, etc. may be copolymerized to give branching. Also, a mixture of polyesters having different compositions as exemplified above is preferably used. These polyesters may contain known additives such as pigments, dyes, matting agents, antifouling agents, antibacterial agents, deodorants, fluorescent whitening agents, flame retardants, stabilizers, ultraviolet absorbing agents, and lubricants.

[0016] Also, Made of polyester resinThe melting point of component A is preferably 180°C or higher, and particularly preferably 205 to 275°C. The intrinsic viscosity is also preferably in the range of 0.35 to 0.70 dl / g, and particularly preferably in the range of 0.40 to 0.65 dl / g. If the intrinsic viscosity is too low, the melting point will also be a low value such as less than 180°C, and the melt viscosity will be too low to allow stable extrusion in the manufacturing process, which is not preferred. Conversely, if the intrinsic viscosity is too high, the molecules will be strongly entangled and tend to be oriented, which is not preferred as it will make it impossible to perform high-magnification stretching.

[0017] The thermally adhesive splittable composite short fiber of the present invention is Copolymer polyester resin Component B must have a melting point at least 20° C. lower than that of component A, and preferably has a melting point 30 to 130° C. lower than that of component A. 220 °C or less, and particularly preferably 120 to 220 °C. If the difference in melting points between components A and B is less than 20 °C, component A, which is the main component responsible for fiber formability, also softens and deforms during thermal bonding, which is undesirable for composite fibers. Furthermore, the entire fiber tends to turn into a film during nonwoven fabric production, which reduces the breathability of the nonwoven fabric. Furthermore, if the melting points are 220 By using components with low viscosity such as 0.4 ° C. or less, the binder performance is improved and the strength of the nonwoven fabric is increased, and it is also possible to draw at a high ratio, making it easier to obtain splittable conjugate fibers of 1 dtex or less.

[0018] As such component B Is, Po Examples of the heat-adhesive components include polyethylene terephthalate, polytrimethylene terephthalate and its copolymers, polybutylene terephthalate and its copolymers, polyhexamethylene terephthalate and its copolymers, polylactic acid, etc., in which a dicarboxylic acid or a diol is copolymerized with a polyester component. Among the above heat-adhesive components, polyethylene terephthalate copolymerized with a dicarboxylic acid or a diol, and polybutylene terephthalate copolymerized with a dicarboxylic acid or a diol are preferable.

[0019] Furthermore, in the thermally adhesive splittable composite staple fiber of the present invention, component A and component B in the composite staple fiber are arranged in a total of 8 or more segments, and the fineness of the entire fiber is 0.01 dtex to 0.6 It is essential that the fiber has a dtex range and an aspect ratio of the entire fiber is in the range of 100 to 3000. Furthermore, it is preferable that the ratio of component B on the fiber surface is in the range of 80% or less, and is preferably in the range of 0 to 80%, particularly 20 to 70%. If the ratio of component B on the fiber surface is too large, not only will the short fibers before splitting fuse together, but when the fiber is made into a nonwoven fabric, it will be difficult for ultrafine fibers made of component A to exist on the surface. Furthermore, if the surface area of ​​binder component B exposed on the surface is too large, the single yarns will fuse together during hot water drawing, which is not preferable. In addition, in the case of 0%, it is preferable that component A has a thin outer skin shape, and in such a case, it is preferable that the thin skin made of component A is broken and the binder component B inside is exposed during the subsequent nonwoven fabric production process, particularly during heat compression bonding in the calendar process.

[0020] In the present invention, it is sufficient that component B, which serves as a binder, and component A, which serves as a main fiber, are arranged in a total of eight or more segments, and preferably arranged alternately. The fiber shape is preferably a flat type, a cross irregular type, a thin outer skin type, or the like. Furthermore, in the splittable composite short fiber of the present invention, it is preferable that component A and component B are arranged alternately radially in the fiber cross-sectional direction, as shown in Figures 1 and 2.

[0021] In the splittable composite staple fiber of the present invention, the fiber is arranged in 8 or more segments, so that the surface area of ​​the thermal adhesive component B exposed on the fiber surface is limited, and the fusion of the single filaments occurring during drawing in hot water can be more effectively prevented. Furthermore, when the components A and B are arranged alternately or radially, the short fibers have better spinnability and processability. The segments are preferably divided into 8 or more segments, more preferably into 12 or more segments, and more preferably into 16 to 48 segments. By increasing the number of segments, the surface exposed area of ​​the thermal adhesive component B becomes smaller, and the short fibers have better spinnability and processability. It is also preferable that the center is hollow as shown in FIG. 1, or that a core composed of component B exists in the center as shown in FIG. 2. The obtained splittable composite staple fiber is easy to split and is easy to be made into a nonwoven fabric composed of ultrafine fibers. Conversely, when the solid fiber has a core composed of component A in the center, or when the central part also has a split structure of components A and B, the short fibers tend to be more difficult to split than when the main component A is other than the solid fiber.

[0022] Furthermore, when the splittable conjugate staple fiber of the present invention is heat-pressed in the subsequent nonwoven fabric production process, if the binder component B and the main fiber component A are arranged alternately, the binder component B is restricted from melting and spreading into the space within the nonwoven fabric during heat-pressure bonding, thereby making it possible to obtain a nonwoven fabric with higher breathability. Furthermore, as shown in Figure 4, the surface of the obtained nonwoven fabric is transformed into a flat shape having surface irregularities with main component A forming convex portions as the binder component melts during heat-pressure bonding, making it possible to obtain a nonwoven fabric that is thinner and more uniform than nonwoven fabrics using conventional core-sheath conjugate binder fibers.

[0023] Furthermore, the overall fiber fineness of the thermally adhesive splittable composite short fiber of the present invention before splitting is 0.01 dtex to 0.6 In the range of dtex do.If the fineness is too small, the fibers tend to be difficult to open sufficiently and to be non-uniform when the resulting short fibers are processed into nonwoven fabrics, spun yarns, etc. Conversely, if the fineness is too large, the surface area of ​​each component B of the thermal adhesive properties on the fiber surface becomes large, and the fibers tend to be easily fused to each other during hot water drawing.

[0024] The fiber length of the splittable conjugate fiber of the present invention is preferably in the range of 0.1 to 30 mm. More preferably, it is in the range of 0.5 to 5 mm. If the fiber length is too short and the aspect ratio (fiber length / fiber diameter) is too small, the fibers tend to fall off the papermaking mesh when a wetlaid nonwoven fabric is subsequently produced, which tends to cause fluctuations in the fiber weight and abnormalities in the drainage process. Conversely, if the fiber length is too long, the aspect ratio (fiber length / fiber diameter) of the fibers tends to be high, which tends to cause the fibers to become entangled in the subsequent nonwoven fabric production process and the like, and also tends to reduce water dispersibility.

[0025] The aspect ratio of the entire fiber before splitting is in the range of 100 to 3000, and more preferably, the aspect ratio before splitting is in the range of 200 to 1000. By having such a thin fiber and high aspect ratio, component A, the fiber-formable component, is made into ultrafine fibers after splitting, and component B, the thermal adhesive component, is also finely divided, which prevents excessive fusion and makes it possible to obtain a uniform nonwoven fabric.

[0026] Furthermore, by splitting such thermally adhesive splittable conjugate staple fibers of the present invention in the subsequent treatment, the aspect ratio of component A, which becomes ultrafine fibers after splitting, is further improved, and the strength of the final paper, nonwoven fabric, etc. is improved. When a fiber has a high aspect ratio from the beginning, it is difficult to obtain a uniform fiber during the process, and it tends to be difficult to obtain excellent texture and high mechanical properties as with the conjugate fibers of the present invention.

[0027] The thermally adhesive splittable conjugate staple fiber of the present invention is particularly preferably used for nonwoven fabrics, and can be used for nonwoven fabrics produced by conventionally known methods such as wet-laid nonwoven fabrics, dry-laid nonwoven fabrics, etc. However, it is particularly preferably used for wet-laid nonwoven fabrics, which will be described later, and more preferably used to produce thinner nonwoven fabrics by thermal compression bonding.

[0028] Such a thermally adhesive splittable conjugate short fiber of the present invention can be obtained, for example, by the following production method.

[0029] Specifically, for example, splittable conjugate fibers as shown in FIG. 1 and FIG. 2 can be obtained by forming the above-mentioned main component A and binder component B polymers into chips, drying each of them, melting them, introducing them into a known conjugate spinneret, extruding them into a filament, cooling and solidifying them at a position 10 to 100 mm below the spinneret, and winding them up at a spinning speed of 300 to 1500 m / min to obtain an undrawn yarn. At this time, it is preferable to add a polyether-polyester copolymer to the undrawn yarn. Furthermore, it is preferable to stretch the obtained undrawn yarn 5.0 to 120.0 times in warm water at Tg to Tg+30°C, where Tg is the glass transition temperature of binder component B, and then subjecting it to a fixed length heat treatment, overfeed heat treatment, or relaxation heat treatment at 25 to 130°C, and then cutting it to a predetermined fiber length to obtain a thermally adhesive splittable conjugate fiber. Here, in order to obtain fibers in which components A and B are arranged alternately, known methods can be used, and for example, it is possible to obtain them in accordance with the manufacturing methods for composite fibers described in JP-A-52-88620 and JP-A-5-239717.

[0030] Furthermore, it is preferable to attach a polyether-polyester copolymer to the fiber surface. By attaching such a component, when the obtained fiber is used to obtain a wet-laid nonwoven fabric by a papermaking method, the fiber has good dispersibility in water, making it possible to obtain a uniform nonwoven fabric. As a method for attaching the polyether-polyester copolymer to the undrawn yarn, it is preferable to apply it by using an oiling device immediately after the undrawn yarn is spun, or to apply it by immersing it in a warm water bath in the flow drawing process.

[0031] The components A and B constituting the fiber are as described above, but it is particularly preferable that component B is a polyester with a melting point of 220°C or less. By using a component B with a low melting point, the binder performance is improved, the strength of the nonwoven fabric is increased, and it is possible to obtain a splittable composite fiber of 1 dtex or less by drawing at a high ratio. For example, isophthalic acid copolymer, polytrimethylene glycolic acid copolymer, etc. are also preferable.

[0032] Among the components of the splittable composite short fiber, component A has an intrinsic viscosity of 0.35 to 0.70 dL / g. Copolymer polyester resin If the intrinsic viscosity is less than 0.35 dL / g, the melting point will be low, the melt viscosity will be too low, and stable extrusion will tend to be difficult. Conversely, if it exceeds 0.70 dL / g, the molecules will tend to be strongly entangled and oriented, making it difficult to draw at a high ratio, and thin fibers will tend to be difficult to obtain. 。

[0033] Books Wet-laid nonwoven fabric of the invention Manufacturing method can be obtained by a method for producing a wetlaid nonwoven fabric, which comprises wet-laid papermaking of the thermally adhesive splittable composite short fibers of the present invention, followed by calendaring. The wet-laid papermaking process for producing a wetlaid nonwoven fabric is not particularly limited and follows conventional methods. For example, it is preferable to disperse the fibers in a pulper, and then use a fourdrinier papermaking method, a cylinder papermaking method, a short wire papermaking method, or a combination of a plurality of these methods to produce a multi-layered nonwoven fabric. In order to obtain a more uniform wetlaid nonwoven fabric, it is also preferable to add a dispersant or an antifoaming agent to the pulper. An example of a dispersant is "DT-100" (manufactured by Takamatsu Yushi Co., Ltd.).

[0034] The weight ratio of the thermally adhesive composite fiber in the wetlaid nonwoven fabric is preferably 25% or more. Furthermore, the weight ratio of component B, which is the binder component in the wetlaid nonwoven fabric, in the thermally adhesive composite fiber is preferably 20% to 80%. More preferably, the ratio of component B in the thermally adhesive composite fiber is 10 to 80%, and even more preferably 30 to 50%. If the ratio of the binder component B is too small, the adhesion becomes insufficient and the strength of the wetlaid nonwoven fabric tends to decrease. Conversely, if the ratio of component B is too large, the binder component is likely to form a film in the nonwoven fabric, and the breathability tends to decrease.

[0035] Furthermore, the wetlaid nonwoven fabric of the present invention may contain other main fibers in addition to the component A consisting of the fiber-formable synthetic resin derived from the above-mentioned thermally adhesive composite fiber. The main fiber used preferably has a fiber diameter of 0.1 to 10 μm. Furthermore, polyester fibers, especially polyethylene terephthalate fibers, are preferable. More specifically, for example, "Tepyrus" manufactured by Teijin Frontier Co., Ltd. (more specifically, TA04PN SD 0.06×3 (fineness 0.08 dtex, fiber diameter 2.8 μm, fiber length 3 mm), TA04PN SD 0.1×3 (fineness 0.17 dtex, fiber diameter 4.1 μm, fiber length 3 mm)) can be mentioned. If the fiber diameter is too small, it is not preferable because the drainage during the production of the wetlaid nonwoven fabric becomes poor. Also, if the fiber diameter is too large, the denseness of the nonwoven fabric decreases and the thickness also tends to decrease.

[0036] For the drying process after papermaking, it is preferable to use a Yankee dryer, an air-through dryer, or the like according to a conventional method. The drying temperature is preferably in the range of 70 to 200°C, more preferably 80 to 170°C, and particularly preferably 100 to 160°C. If the drying temperature is too low, the drying may be insufficient, and the strength of the wet nonwoven fabric may ultimately be insufficient. On the other hand, if the drying temperature is too high, the binder component B flows too much and is fused to the metal surface of the dryer or air-through dryer during the process, which deteriorates the process passability, deteriorates the texture of the nonwoven fabric, increases the film-formed region in the nonwoven fabric, and reduces the breathability of the nonwoven fabric. These problems are likely to occur.

[0037] The wetlaid nonwoven fabric of the present invention Manufacturing method In the case of nonwoven fabric, it is essential to carry out a calendering treatment after papermaking in a conventional manner. The calendering process heat-presses the nonwoven fabric, improving the paper strength. As the calendering rolls used in the calendering, metal / metal rolls, metal / paper rolls, metal / elastic rolls, etc. are used. The press temperature during calendering is preferably in the range of 100 to 250°C, more preferably in the range of 130 to 220°C, and more preferably in the range of 150 to 210°C. If the temperature is too low, the strength of the nonwoven fabric tends to be insufficient due to poor adhesion. Conversely, if the calendering temperature is too high, problems such as the thermal adhesive component fusing to the roll surface, deterioration of processability, and deterioration of the texture of the nonwoven fabric tend to occur. The press pressure during calendering is preferably in the range of 5 to 250 kgf / cm, more preferably in the range of 10 to 220 kgf / cm, and particularly preferably in the range of 40 to 200 kgf / cm. 。

[0038] Books In the wetlaid nonwoven fabric manufacturing method of the invention, by performing the calendaring process as described above, component B (thermal adhesive component) in the splittable composite fiber is softened and deformed, and ultrafine fibers made of component A are exposed on the surface of the nonwoven fabric. A nonwoven fabric can then be obtained having ultrafine fibers obtained by splitting the composite fiber on the surface. By thinning the fibers constituting the surface and interior of the nonwoven fabric in this way, the pore size in the nonwoven fabric becomes smaller, making it possible to capture finer particles.

[0039] The basis weight of the wetlaid nonwoven fabric of the present invention is 1 to 300 g / m 2 If the basis weight is too large, the number of fibers in the nonwoven fabric increases, which tends to result in poor drainage and make production difficult. 2 , more preferably 15 to 150 g / m 2 It is preferable that:

[0040] The thickness of the wetlaid nonwoven fabric is preferably 1000 μm or less. If the fabric is too thick, compactness tends to decrease when the fabric is processed into a thin wetlaid nonwoven fabric such as a separator or filter. The thickness is more preferably in the range of 1 to 500 μm, and even more preferably in the range of 30 to 300 μm. The density of wet nonwoven fabric is 100 to 600 kg / m 3 and more preferably within the range of 300 to 500 kg / m 3 It is preferable that the range is 100%.

[0041] The air permeability of the nonwoven fabric of the present invention is 15 to 100 cm 3 / cm 2 / sec, and more preferably 20 to 80 cm 3 / cm 2 / sec, more preferably 30-70cm 3 / cm 2 / sec is preferable. If the air permeability is too low, it reflects the fact that the thermal adhesive component in the nonwoven fabric turns into a film, reducing the porosity, and this is undesirable because it reduces the permeability of air and liquid required for filters and separators. Conversely, if the air permeability is too high, there tends to be problems such as poor texture due to the number of fibers constituting the fabric being too small, and reduced strength.

[0042] The average pore size of the through-holes of the nonwoven fabric of the present invention is preferably 0.1 to 10 μm, more preferably in the range of 3 to 9 μm. If this average pore size is too large, the texture of the nonwoven fabric tends to deteriorate and the uniformity tends to be lost. Conversely, if it is too small, the through-holes in the nonwoven fabric tend to be too small, and the permeability in filters and separators tends to decrease.

[0043] The tensile strength index in the longitudinal direction of the nonwoven fabric of the present invention is preferably 10 N m / g or more, more preferably 15 to 50 N m / g, and even more preferably 20 to 40 N m / g. If the tensile strength index is too low, the practical strength of the nonwoven fabric tends to be insufficient.

[0044] A nonwoven fabric obtained by using such heat-adhesive splittable conjugate staple fibers of the present invention is a wet-laid nonwoven fabric having little fusion between fibers, excellent dispersibility, and excellent collection of fine particles. EXAMPLES

[0045] In order to specifically illustrate the configuration and effects of the present invention, examples are given below, but the present invention is not limited to these examples. Each value in the examples was determined according to the following method.

[0046] (1) Intrinsic viscosity [η] 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.

[0047] (2) Melting point A "Thermal Analyst-2200 Differential Scanning Calorimeter DSC" manufactured by TA Instruments Japan was used. The measurement was performed by heating 10 mg of a sample in a nitrogen atmosphere from room temperature to 300°C at a heating rate of 20°C / min, according to the method described in JIS K7121 (1987).

[0048] (3) Single yarn size After drawing, 1,800 mm of the fiber bundle was sampled and dried in a hot air dryer at 120°C for 40 minutes, and then the measured bone dry mass was multiplied by 5,000 to measure the total fineness (unit: denier) of the fiber bundle. The total fineness obtained was divided by the number of single fibers constituting the bundle to obtain the single yarn fineness (unit: denier), and this was further multiplied by 1.111 to calculate the single yarn fineness (unit: dtex).

[0049] (4) Strength and elongation From the fiber bundle after drawing, a fiber bundle of approximately 2,000 de was taken, and a 1,800 mm piece was taken and dried in a hot air dryer at 120°C for 40 minutes. The measured bone dry mass was then multiplied by 5,000 to measure the total fineness (unit: denier) of the fiber bundle. Using the same fiber bundle, the strength (g) and elongation (%) were measured at a gripping distance of 20 cm and a pulling speed of 20 cm / min according to JIS L 1013 8.5.1. The strength obtained was divided by the total fineness of the fiber bundle and then multiplied by 0.826 to obtain the strength (cN / dtex).

[0050] (5) Dry heat shrinkage rate The test was carried out at 180°C in accordance with JIS L 1015 7.15(2).

[0051] (6) Fiber length The side of the short fiber was magnified under a microscope, and its length was measured in N=10 cases, and the average value was calculated.

[0052] (7) Dispersibility in water Put 500mL of tap water into a 1000mL measuring cylinder and add 0.1g of short fibers. When the fibers reach the bottom of the measuring cylinder, cover the opening of the measuring cylinder, hold the top and bottom with both hands, and invert the measuring cylinder once to disperse the fibers. The dispersibility in water was judged according to the following criteria. Good: There are no undispersed fiber bundles, and each individual fiber is neatly spread out in the water. Poor: There are several or more undispersed fiber bundles and many individual fibers that are entangled with each other.

[0053] (8) Metsuke The measurements were taken according to the weight per unit area test method of JIS L1906, and the basis weight (g / m 2 ) was sought.

[0054] (9) Thickness Using a Digital Linear Gauge DG-925 (measurement terminal diameter 1 cm) manufactured by Ono Sokki Co., Ltd., the thickness was measured at 20 arbitrarily selected points, and the average value was calculated to obtain the thickness (μm). The resulting weight (g / m 2 The density (weight / thickness) was calculated from the thickness (μm) and the density (kg / m 3 ).

[0055] (10) Breathability The measurements were carried out according to the JIS L 1913 Frazier method.

[0056] (11) Tensile strength The tensile strength was measured based on JIS P8113 (Testing method for tensile properties of paper and paperboard).

[0057] (12) Pore diameter Two circular samples with a diameter of 2.5 cm were randomly taken from the nonwoven fabric, and the average pore size was measured using a Perm Porometer (PMI).

[0058] (13) Number of divisions and fiber diameter of ultrafine fibers on the surface of nonwoven fabric The surface of the obtained nonwoven fabric was magnified 1500 times with a scanning electron microscope (SEM), and the number of ultrafine fibers observed from the surface in one fiber bundle derived from one composite fiber was defined as the "number of divisions of ultrafine fibers on the surface of the nonwoven fabric." The fiber diameter was calculated by both the fiber diameter measured directly from a surface photograph (directly observed fiber diameter) and the circular equivalent fiber diameter calculated from the fineness and its density.

[0059] (14) Collection efficiency of atmospheric particles The wind speed was adjusted to 5.1 cm / sec, and the dust particles in the air before and after the sample were counted using a particle counter (KC-03B, manufactured by Rion Co., Ltd.). The ratio of these counts was used to calculate the collection efficiency. Ta. Airborne dust collection rate (%) = (1-(airborne dust number after passing the sample / airborne dust number before passing the sample)) x 100

[0060] (15) Pressure loss When measuring the atmospheric dust collection rate (wind speed 5.1 cm / sec), the pressure before and after the test piece passed was measured, and the pressure difference was calculated as the pressure loss.

[0061] [Example 1] Polyester A (component A; polyethylene terephthalate) with an intrinsic viscosity of 0.47 dL / g and a melting point of 255°C and polyester B (component B; ethylene terephthalate copolymerized with 20 mol% isophthalic acid and 65 mol% butanediol) with an intrinsic viscosity of 0.63 dL / g and a melting point of 157°C were melted in an extruder, and polyester A was extruded at a rate of 16.5 g / min and polyester B at a rate of 13.5 g / min. In this case, eight discharge holes for component B with a diameter of 0.3 mm were drilled per distribution hole (7) so that the number of component B per composite fiber cross section was eight, while a spinneret with 20 holes (11) for mixing components A and B was used. The spinning temperature was 280°C and the winding speed was 900 m / min. An aqueous emulsion of polyether-polyester copolymer was applied to the lower part of the extruder in an amount of 0.5 mass% in terms of solid content adhesion to obtain an undrawn yarn. The undrawn yarn was stretched 20 times in 83℃ warm water, and further stretched twice in 70℃ warm water, and then 0.3% by mass of a polyether-polyester copolymer aqueous emulsion was applied to the fiber surface and cut to a fiber length of 3 mm to obtain a thermally adhesive splittable composite short fiber consisting of a total of 16 segments with a fineness of 0.40 dtex. The composition and physical properties of the obtained fiber are shown in Tables 1 and 2.

[0062] The above heat-adhesive splittable composite fiber is applied with a basis weight of 100 g / m 2 The mixture was weighed out so that the weight was 100 g / m2, dispersed in water, and strongly stirred in a mixer to make a slurry. The slurry was then transferred to a manual paper machine, and a dispersant (DT-100) was added to make 0.1% by mass, followed by thorough stirring. The water was removed, and the mixture was formed into a sheet on a mesh, which was then dried in a rotary dryer at 110°C to produce base paper. The weight, thickness, and density of the base paper were each 100 g / m2. 2 , 530μm, 189kg / m 3 The obtained base paper was heat-pressed using a calendaring device combining a heated metal roll and an elastic roll under conditions of a temperature of 160°C, a linear pressure of 29 kN / m, and a speed of 2 m / min to obtain a wetlaid nonwoven fabric. The manufacturing conditions of the wetlaid nonwoven fabric are shown in Table 3, and the physical properties of the obtained wetlaid nonwoven fabric are shown in Table 4.

[0063] [Example 2] The same components A and B as in Example 1 were used, but the discharge rates were changed to 15.0 g / min for component A (polyester A) and 15.0 g / min for component B (polyester B). The components were melted and extruded in an extruder to obtain composite fibers. The number of components B per composite fiber cross section was 8, and the distribution holes (7) were provided with 8 discharge holes for component B with a diameter of 0.3 mm and one discharge hole for a solid part with a diameter of 0.15 mm so that a core made of component B was formed. Meanwhile, a spinneret with 20 spinning holes (11) where components A and B were mixed was used. The spinning temperature was 275°C, the winding speed was 900 m / min, and an aqueous emulsion of polyether-polyester copolymer was applied to the lower part of the spinneret in an amount of 0.5 mass% in terms of solid content adhesion to obtain undrawn yarn. The undrawn yarn was stretched 17 times in 82℃ warm water, and then further stretched 2 times in 70℃ warm water, and a polyether-polyester copolymer aqueous emulsion was applied to the fiber surface in an amount of 0.3 mass% in terms of solid content, and the fiber was cut to a length of 3 mm to obtain a thermally adhesive splittable composite staple fiber with a fineness of 0.49 dtex. The composition and physical properties of the obtained fiber are shown in Tables 1 and 2.

[0064] A wet-laid nonwoven fabric was obtained in the same manner as in Example 1, except that the temperature of the rotary dryer was changed from 110° C. to 140° C. After drying, the basis weight, thickness and density of the base paper before the press treatment were each 100 g / m 2 The production conditions of the wet-laid nonwoven fabric are shown in Table 3, and the physical properties of the final wet-laid nonwoven fabric obtained after the press treatment are shown in Table 4.

[0065] [Example 3] The same component A (polyester A) as in Example 1 was used, except that as component B, polyester B (component B; ethylene terephthalate copolymerized with 20 mol% isophthalic acid) with an intrinsic viscosity of 0.64 dL / g and a melting point of 202°C (small endothermic peak at the melting point in DSC) was used, and the components were melted and extruded by an extruder at extrusion rates of 7.0 g / min for component A (polyester A) and 11.0 g / min for component B (polyester B). The same die as in Example 2 was used, which made component B solid, and the spinning temperature was 275°C, the winding speed was 500 m / min, and an aqueous polyether-polyester copolymer emulsion was applied to the lower part of the extruder at a solid content of 0.5% by mass to obtain an undrawn yarn. The fiber was stretched 40 times in 82℃ warm water, and then further stretched 2 times in 70℃ warm water, and a polyether-polyester copolymer aqueous emulsion was applied to the fiber surface in an amount of 0.3% by mass in terms of solid content, and the fiber was cut to a length of 3 mm to obtain a thermally adhesive splittable composite staple fiber with a fineness of 0.23 dtex. The composition and physical properties of the obtained fiber are shown in Tables 1 and 2.

[0066] A wet-laid nonwoven fabric was obtained in the same manner as in Example 2, except that the rotary dryer temperature was 140° C., the calendar temperature was 190° C., and the calendar line pressure was 98 kN / m. After drying, the basis weight, thickness, and density of the base paper before the press treatment were each 100 g / m 2 , 550μm, 182kg / m 3 The manufacturing conditions of the wet-laid nonwoven fabric are shown in Table 3, and the physical properties of the final wet-laid nonwoven fabric obtained after the press treatment are shown in Table 4.

[0067] [Example 4] The splittable composite short fiber described in Example 3 and "Tepyrus (TA04PN SD 0.06x3, 0.08dtexx3mm)" manufactured by Teijin Frontier Co., Ltd. were mixed in a mass ratio of 40:60, and a fabric weight of 100g / m was prepared. 2 A wet-laid nonwoven fabric was obtained in the same manner as in Example 1, except that the rotary dryer temperature was 110° C. and the calendar temperature was 210° C. After drying, the basis weight, thickness and density of the base paper before the press treatment were each 100 g / m 2 , 546μm, 174kg / m 3The composition and physical properties of the obtained fibers are shown in Tables 1 and 2, the production conditions of the wetlaid nonwoven fabric are shown in Table 3, and the physical properties of the final wetlaid nonwoven fabric after the press treatment are shown in Table 4.

[0068] [Example 5] The same component A (polyester A) as in Example 1 was used, except that component B was polyester B (component B; ethylene terephthalate copolymerized with 40 mol% isophthalic acid and 4 mol% diethylene glycol, melting point 110°C) with an intrinsic viscosity of 0.55 dL / g. Component A (polyester A) was melted and extruded at a discharge rate of 7.0 g / min and component B (polyester B) at a discharge rate of 11.0 g / min using an extruder. The same spinneret as in Example 2, in which component B was the solid part, was used, the spinning temperature was 275°C, and the winding speed was 500 m / min. An aqueous polyether-polyester copolymer emulsion was applied to the lower part of the spinneret at a solid adhesion amount of 0.5 mass% to obtain an undrawn yarn. The undrawn yarn was stretched 17 times in 82℃ warm water, and then further stretched 2 times in 70℃ warm water, and a polyether-polyester copolymer aqueous emulsion was applied to the fiber surface in an amount of 0.3 mass% solids, and the fiber was cut to a length of 3 mm to obtain a thermally adhesive splittable composite staple fiber with a fineness of 0.23 dtex. The composition and physical properties of the obtained fiber are shown in Tables 1 and 2.

[0069] A wet-laid nonwoven fabric was obtained in the same manner as in Example 1, except that the calender temperature was 190° C. and the calender line pressure was 98 kN / m. After drying, the basis weight, thickness and density of the base paper before the press treatment were each 100 g / m 2 , 550μm, 182kg / m 3 The manufacturing conditions of the wet-laid nonwoven fabric are shown in Table 3, and the physical properties of the final wet-laid nonwoven fabric obtained after the press treatment are shown in Table 4.

[0070] [Comparative Example 1] The polyester (polyethylene terephthalate copolymerized with 20 mol% isophthalic acid) used as component B in Example 3, with an intrinsic viscosity of 0.64 dL / g and a melting point of 202°C (small endothermic peak at the melting point in DSC), was melted in an extruder and discharged from a die having 2504 holes with a diameter of 0.18 mm, the spinning temperature was 260°C, and the winding speed was 500 m / min. At the bottom of the die, a polyether-polyester copolymer aqueous emulsion was applied in an amount of 0.5 mass% in terms of solid content adhesion, to obtain an undrawn yarn made of a single component. The undrawn yarn was stretched 62 times in hot water at 83°C, and further stretched twice in hot water at 70°C, and a polyether-polyester copolymer aqueous emulsion was applied in an amount of 0.3 mass% in terms of solid content adhesion to the fiber surface, and the fiber was cut to a fiber length of 3 mm, to obtain a thermally adhesive staple fiber with a fineness of 0.03 dtex. The composition and physical properties of the obtained fiber are shown in Tables 1 and 2.

[0071] The above-mentioned heat-bonding staple fiber and "Tepirus (TA04PN SD)" manufactured by Teijin Frontier Co., Ltd. A wet-laid nonwoven fabric was obtained in the same manner as in Example 1, except that the temperature of the rotary dryer was 120° C. and the calender temperature was 190° C. The basis weight, thickness and density of the base paper were each 100 g / m2. 2 , 290μm, 340kg / m 3 The production conditions of the wetlaid nonwoven fabric are shown in Table 3, and the physical properties of the obtained wetlaid nonwoven fabric are shown in Table 4.

[0072] [Comparative Example 2] The fiber-forming component that forms the center of the core-sheath fiber was polyester (polyethylene terephthalate) with an intrinsic viscosity of 0.47 dL / g and a melting point of 255°C, and the thermal adhesive component that forms the sheath was polyester (polyethylene terephthalate) with an intrinsic viscosity of 0.55 dL / g and a melting point of 110°C (small endothermic peak at the melting point in DSC) of 40 mol% isophthalic acid copolymerized with 4 mol% diethylene glycol copolymerized with ethylene terephthalate, and each was melted in a separate vent-type twin-screw extruder. The fiber-forming component was the core, and the thermal adhesive component was the sheath. They were combined in a core-sheath type composite spinneret with 1,336 capillaries with a hole diameter of 0.3 mm so that the mass ratio of core:sheath was 60:40, and melted and extruded into a thread. The spinning temperature was 285°C, and the mixture was cooled and solidified by cooling air at 25°C below the spinneret. Below the spinneret, a polyether-polyester copolymer aqueous emulsion was applied at 0.5% by mass in terms of solid content. The winding speed was 500 m / min to obtain an undrawn yarn. The undrawn yarn was drawn 62 times in 83°C warm water, and further drawn 2 times in 70°C warm water. A polyether-polyester copolymer aqueous emulsion was applied to the fiber surface at 0.3% by mass in terms of solid content, and the fiber was cut to a fiber length of 3 mm to obtain a heat-bondable core-sheath staple fiber with a fineness of 0.05 dtex. The composition and physical properties of the obtained fiber are shown in Tables 1 and 2.

[0073] The above-mentioned heat-adhesive core-sheath type staple fiber and "Tepirus (TA04PN SD 0.06×3, 0.08dtex×3mm)" in a mass ratio of 40:60, and the basis weight is 100g / m 2 A wetlaid nonwoven fabric was obtained in the same manner as in Example 1, except that the temperature of the rotary dryer was set to 120° C. and calendaring was not performed. The production conditions of the wetlaid nonwoven fabric are shown in Table 3, and the physical properties of the obtained wetlaid nonwoven fabric are shown in Table 4.

[0074] [Table 1]

[0075] [Table 2]

[0076] [Table 3]

[0077] [Table 4] [Explanation of symbols]

[0078] A Component A B Component B C Hollow part 1 Pack Case 2 Upper metal plate 3 Bottom metal plate 4 Knock pins 5 Partition plate 6. Component B outlet hole 7 Component B distribution hole 8. Distribution hole for component A 9 Component A passage 10 Circumferential discharge hole with discontinuities 11 Spinner hole

Claims

1. A thermally adhesive splittable composite staple fiber composed of component A made of polyester resin and component B of a copolymerized polyester resin having a melting point at least 20°C lower than that of component A, wherein components A and B are arranged in a total of eight or more segments, the fineness of the entire fiber is in the range of 0.01 dtex to 0.6 dtex, and the aspect ratio of the entire fiber is in the range of 100 to 3,000.

2. A heat-adhesive splittable composite short fiber as described in claim 1, wherein the melting point of the copolymer polyester resin component B is 220°C or lower.

3. A heat-adhesive splittable composite short fiber as described in claim 1 or 2, wherein the melting point of component A consisting of a polyester resin is 180°C or higher and the intrinsic viscosity is in the range of 0.35 to 0.70 dL / g.

4. 4. The heat-adhesive splittable conjugate staple fiber according to claim 1, wherein the proportion of the copolymerized polyester resin component B on the fiber surface is in the range of 80% or less.

5. A heat-adhesive splittable composite short fiber described in any one of claims 1 to 4, in which component A consisting of a polyester resin and component B consisting of a copolymerized polyester resin are alternately arranged radially from the center of the fiber.

6. 6. The thermal adhesive splittable composite short fiber according to claim 5, wherein the center of the fiber has a solid or hollow structure.

7. A method for producing a wet-laid nonwoven fabric, comprising wet-laid papermaking of the thermally adhesive splittable composite short fibers according to any one of claims 1 to 6, followed by calendaring.

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