JP7680241B2 - Thermally adhesive splittable composite short fiber, wet-laid nonwoven fabric and its manufacturing method - Google Patents

Description

The present invention relates to a heat-adhesive splittable composite staple fiber suitable for wetlaid nonwoven fabrics, and a method for producing a wetlaid nonwoven fabric made of the same .

Conventionally, copolymer polyester composite fibers have been widely used as thermally adhesive staple fibers suitable for the manufacture of nonwoven fabrics. For example, Patent Documents 1 and 2 provide thermally 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 thermally adhesive component, is present in the sheath as the thermally adhesive component, and polyalkylene terephthalate, which has a melting point 20°C higher than that of the thermally adhesive component, is present in the core as the fiber-formable component, and the two components are composited so that the thermally adhesive component is exposed on the surface.

Patent Document 3 also proposes a composite fiber with a single yarn fineness of 0.01 to 1.5 dtex, in which the fiber-forming component that forms the core is made of polyalkylene terephthalate with a melting point of 220°C or higher and an intrinsic viscosity of 0.30 to 0.55 dL/g, and the thermal adhesive component that forms the sheath is made of polyolefin and is composited so that it is exposed on the surface.

The above-mentioned thermally adhesive composite fibers have a problem in that the exposed area of the thermally adhesive component is large, and when multiple fibers are heated and stretched simultaneously, the thermally adhesive components of adjacent fibers fuse together, resulting in a significant decrease in the dispersibility and openability of the resulting fibers. In particular, when fine thermally adhesive fibers are produced, the heating and stretching temperature is higher, making fusion more likely to occur. For example, when producing a wet nonwoven fabric using fine thermally adhesive fibers, the fused fibers do not disperse sufficiently in the pulper that dissociates the fibers, resulting in a wet nonwoven fabric with an uneven texture and numerous undispersed defects. The same problem exists in dry nonwoven fabrics with low basis weight and density.

JP 2011-74506 A JP 2011-195978 A JP 2014-201855 A

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 conjugate staple fiber which has little fusion between fibers, excellent dispersibility, and excellent collection of fine particles, and a method for producing a wetlaid nonwoven fabric made thereof .

The thermally adhesive splittable conjugate staple fiber of the present invention is a thermally adhesive splittable conjugate staple fiber composed of component A made of a polyester resin and component B made of a copolymerized polyester resin having a melting point 20° C. or more lower than that of component A, and is characterized in that components A and B are arranged in a total of 8 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.

It is further preferred that the melting point of the copolymerized polyester resin component B is 220° C. or lower, that the melting point of the polyester resin component A is 180° C. or higher, that the intrinsic viscosity is in the range of 0.35 to 0.70 dL/g, and that the proportion of the copolymerized polyester resin component B on the fiber surface is 80% or lower. It is also preferred that the polyester resin component A and the copolymerized polyester resin component B are alternately arranged radially from the center of the fiber, and that the center of the fiber has a solid or hollow structure .

Furthermore , a method for producing a wetlaid nonwoven fabric made of the above-mentioned heat-adhesive splittable conjugate staple fibers is characterized in that the heat-adhesive splittable conjugate staple fibers of the present invention are wetlaid into paper and then calendered.

According to the present invention, there are provided a thermally bondable splittable conjugate staple fiber which has little fusion between fibers, excellent dispersibility, and excellent collection of fine particles, and a method for producing a wetlaid nonwoven fabric using the thermally bondable splittable conjugate staple fiber.

FIG. 1 is a schematic diagram illustrating an example of a cross-sectional structure (hollow type) of a thermally adhesive splittable conjugate short fiber of the present invention. 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 (a solid type having component B in the center). 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. 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.

The present invention will be described in more detail below.

The thermally adhesive splittable conjugate staple fiber of the present invention is a thermally adhesive splittable conjugate staple fiber composed of component A made of a polyester resin and component B, a copolymerized polyester resin having a melting point 20° C. or more lower than that of component A. Furthermore, components A and B are arranged in a total of 8 or more segments, and the fiber has a fineness in the range of 0.01 dtex to 0.6 dtex and an aspect ratio in the range of 100 to 3,000.

Component A constituting the thermal adhesive splittable composite short fiber of the present invention is a polyester- based component, and more specifically, is arbitrarily selected from polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, polylactic acid, polybutylene succinate, and copolymers thereof .

Examples 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 the following may be copolymerized as acid components: 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; and one or more of the following diol components: diethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, polyalkylene glycol, etc.; 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 provide 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.

Moreover, component A made of a polyester resin preferably has a melting point of 180°C or higher, particularly preferably 205 to 275°C. Furthermore, the intrinsic viscosity is preferably in the range of 0.35 to 0.70 dl/g, particularly preferably 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 discharge in the manufacturing process, which is not preferable. Conversely, if the intrinsic viscosity is too high, the molecules will be strongly entangled and tend to be oriented, which is not preferable as it will make it impossible to perform high-magnification stretching.

The copolymerized polyester resin component B constituting the heat-adhesive splittable composite staple fiber of the present invention must have a melting point at least 20°C lower than that of the above-mentioned component A, and preferably has a melting point 30 to 130°C lower than that of component A. The melting point of component B is preferably 220 °C or lower, and particularly preferably 120 to 220°C. If the melting point difference between components A and B is less than 20°C, component A, which is the main component of fiber formability, also softens and deforms during heat adhesion, which is not preferable for composite fibers. Furthermore, the entire fiber tends to become a film during nonwoven fabric production, and the breathability of the nonwoven fabric tends to decrease. Furthermore, by using a component with a low melting point, such as 220 °C or lower, the binder performance is improved, the strength of the nonwoven fabric is increased, and it is easy to obtain a splittable composite fiber of 1 dtex or less that can be stretched at a high ratio.

Examples of such component B include polyethylene terephthalate , which is a polyester component copolymerized with a dicarboxylic acid or a diol as a third component, polytrimethylene terephthalate and its copolymers, polybutylene terephthalate and its copolymers, polyhexamethylene terephthalate and its copolymers, polylactic acid, etc. Among the above-mentioned thermal 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.

Furthermore, in the heat-adhesive splittable composite staple fiber of the present invention, it is essential that the components A and B in the composite staple fiber are arranged in a total of 8 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 3000. Furthermore, it is preferable that the ratio of component B occupying the fiber surface is in the range of 80% or less, and preferably in the range of 0 to 80%, and particularly preferably in the range of 20 to 70%. If the ratio of component B occupying the fiber surface is too large, not only will the short fibers before splitting be fused to each other, 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 to the surface is too large, single yarns will be fused to each other during hot water drawing, which is not preferable. Also, in the case of 0%, for example, it is preferable that component A is in the form of a thin outer skin, and in such a case, it is preferable that the thin skin made of component A is broken and the internal binder component B is exposed during the subsequent nonwoven fabric production process, particularly during heat compression bonding in the calendaring process.

In the present invention, it is sufficient that component B, which serves as the binder, and component A, which serves as the main fiber, are arranged in a total of eight or more segments, and preferably in an alternating arrangement. The fiber shape is preferably a flat type, a cross-shaped type, or a thin-skinned outer periphery shape. Furthermore, in the splittable composite short fiber of the present invention, as shown in Figures 1 and 2, it is preferable that components A and B are arranged radially and alternatingly in the fiber cross-sectional direction.

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 thermally adhesive component B exposed on the fiber surface is limited, and the fusing of the single filaments 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 12 or more segments, and more preferably 16 to 48 segments. By increasing the number of segments, the surface exposed area of the thermally 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 Figure 1, or that a core composed of component B exists in the center as shown in Figure 2. The resulting splittable composite staple fiber is easy to split and can be easily made into a nonwoven fabric made 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.

When the splittable composite short fibers of the present invention are heat-pressed in the subsequent nonwoven fabric manufacturing 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-pressing, and a nonwoven fabric with higher breathability can be obtained. In addition, as shown in Figure 4, the surface of the obtained nonwoven fabric is deformed into a flat shape with surface irregularities in which the main component A forms convex portions as the binder component melts during heat-pressing, making it possible to obtain a nonwoven fabric that is thinner and more uniform than nonwoven fabrics using conventional core-sheath composite binder fibers.

Furthermore, the fineness of the entire fiber of the thermally adhesive splittable composite staple fiber of the present invention before splitting is in the range of 0.01 dtex to 0.6 dtex . If the fineness is too small, when the obtained staple fiber is processed into a nonwoven fabric, spun yarn, etc., it is difficult to sufficiently open the fibers, and the fibers tend to become non-uniform. Conversely, if the fineness is too large, the surface area of each component B of the thermal adhesiveness on the fiber surface becomes large, and the fibers tend to be easily fused to each other during hot water drawing.

The fiber length of the splittable composite 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 the wet 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 also tends to reduce water dispersibility.

The aspect ratio of the entire fiber before splitting is in the range of 100 to 3000, but it is more preferable that the aspect ratio before splitting is in the range of 200 to 1000. By having such a thin 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, making it possible to obtain a uniform nonwoven fabric without excessive fusion.

Furthermore, by splitting such thermally adhesive splittable composite short fibers of the present invention in the subsequent processing, 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. If the 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 the excellent texture and high mechanical properties that can be obtained when the composite fiber of the present invention is used.

The heat-adhesive splittable composite short fibers of the present invention are particularly preferably used for nonwoven fabric applications, and can be used for nonwoven fabrics manufactured by conventional methods, such as wet-laid nonwoven fabrics and dry-laid nonwoven fabrics. However, they are particularly preferably used for wet-laid nonwoven fabrics, as described below, and are even more preferably used to make thinner nonwoven fabrics by heat compression bonding.

The thermally adhesive splittable composite short fibers of the present invention can be obtained, for example, by the following manufacturing method.

Specifically, for example, splittable composite fibers as shown in Figures 1 and 2 can be obtained by forming the polymers of the main component A and the binder component B into chips, drying each of them, melting them, and introducing them into a known composite spinneret to extrude them into a thread shape, 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 thread. At this time, it is preferable to add a polyether-polyester copolymer to the undrawn thread. Furthermore, it is preferable to stretch the obtained undrawn thread 5.0 to 120.0 times in warm water at Tg to Tg + 30°C, where Tg is the glass transition temperature of the 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 composite fiber. Here, known methods can be used to produce fibers in which components A and B are arranged alternately. For example, it is possible to obtain the fibers in accordance with the composite fiber manufacturing methods described in JP-A-52-88620 and JP-A-5-239717.

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 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 adding the polyether-polyester copolymer to the undrawn yarn, it is preferable to add it by using an oiling device immediately after the undrawn yarn is spun, or to add it by immersing it in a warm water bath in the flow drawing process.

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, increasing the strength of the nonwoven fabric, and it is possible to obtain a splittable composite fiber of 1 dtex or less by allowing high-magnification stretching. For example, isophthalic acid copolymer, polytrimethylene glycolic acid copolymer, etc. are also preferable.

Among the components of the splittable composite short fiber, component A is preferably a copolymer polyester resin having an intrinsic viscosity of 0.35 to 0.70 dL/g. If the intrinsic viscosity is less than 0.35 dL/g, the melting point is low, the melt viscosity is too low, and stable extrusion tends to be difficult. On the other hand, if the intrinsic viscosity exceeds 0.70 dL/g, the molecules tend to be strongly entangled and oriented, making high-magnification drawing difficult and making it difficult to obtain thin fibers .

The wetlaid nonwoven fabric of the present invention 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 wetlaid 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.).

The weight ratio of the thermally adhesive composite fiber in the wet nonwoven fabric is preferably 25% or more. Furthermore, the weight ratio of component B, which is the binder component in the wet nonwoven fabric, among the thermally adhesive composite fibers 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 binder component B is too small, adhesion becomes insufficient and the strength of the wet nonwoven fabric tends to decrease. Conversely, if the ratio of component B is too large, the binder component is likely to form a film within the nonwoven fabric, and breathability tends to decrease.

Furthermore, the wet 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 wet nonwoven fabric will be poor. Also, if the fiber diameter is too large, the density of the nonwoven fabric will decrease and the thickness will tend to decrease.

For the drying process after papermaking, it is preferable to use a Yankee dryer, an air-through dryer, or the like, in accordance with conventional methods. 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 will be insufficient, and the strength of the wet nonwoven fabric may ultimately be insufficient. Conversely, if the drying temperature is too high, the binder component B will flow too much and will fuse to the metal surfaces of the dryer or air-through dryer during the process, which will deteriorate the process passability, deteriorate the texture of the nonwoven fabric, increase the film-formed area in the nonwoven fabric, and reduce the breathability of the nonwoven fabric.

In the method for producing a wet-laid nonwoven fabric of the present invention, it is essential to carry out a calendering process after papermaking by a conventional method. The nonwoven fabric is heat-pressed by the calendering process, and the paper strength is improved. As the calender roll used for the calendering process, a metal/metal roll, a metal/paper roll, a metal/elastic roll, 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. On the other hand, if the calendering temperature is too high, problems such as the thermal adhesive component being fused to the roll surface, the process passability being deteriorated, and the texture of the nonwoven fabric being deteriorated 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 .

In the wetlaid nonwoven fabric manufacturing method of the present 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 composed 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.

The basis weight of the wetlaid nonwoven fabric of the present invention is preferably within the range of 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 difficulty in production. The basis weight is further preferably 10 to 200 g/m ² , more preferably 15 to 150 g/m ² .

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 the wetlaid nonwoven fabric is preferably within the range of 100 to 600 kg/ ^m3 , and more preferably within the range of 300 to 500 kg/ ^m3 .

The air permeability of the nonwoven fabric of the present invention is preferably 15 to 100 cm ³ /cm ² /sec, more preferably 20 to 80 cm ³ /cm ² /sec, and even more preferably 30 to 70 cm ³ /cm ² /sec. If the air permeability is too low, it reflects the fact that the thermal adhesive component in the nonwoven fabric turns into a film and the porosity is reduced, which 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.

The average pore size of the through-holes in the nonwoven fabric of the present invention is preferably 0.1 to 10 μm, and 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.

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 small, the practical strength of the nonwoven fabric tends to be insufficient.

The nonwoven fabric obtained using the thermally adhesive splittable composite short fibers of the present invention is a wet nonwoven fabric with little fusion between fibers, excellent dispersibility, and excellent collection of fine particles.

The following examples are provided to illustrate the configuration and effects of the present invention, but the present invention is not limited to these examples. The values in the examples were determined according to the following methods.

(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.

(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).

(3) Single Yarn Fineness After drawing, 1,800 mm of the fiber bundle was sampled and dried for 40 minutes in a hot air dryer at 120° C., and 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 filaments constituting the fiber bundle to obtain the single filament fineness (unit: denier), which was then multiplied by 1.111 to calculate the single filament fineness (unit: dtex).

(4) Strength and Elongation From the fiber bundle after drawing, a fiber bundle of about 2,000 de was taken, and a piece of 1,800 mm 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.
The same fiber bundle was used to measure the strength (g) and elongation (%) 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).

(5) Dry Heat Shrinkage Ratio This was carried out at 180° C. in accordance with JIS L 1015 7.15(2).

(6) Fiber Length The side of the short fiber was magnified under a microscope, and its length was measured for N=10 samples, and the average value was calculated.

(7) Dispersibility in Water 500 mL of tap water was placed in a 1000 mL measuring cylinder, and 0.1 g net of short fibers was placed in the measuring cylinder. When the fibers reached the bottom of the measuring cylinder, the opening of the measuring cylinder was covered, the top and bottom were held with both hands, and the measuring cylinder was inverted once to disperse the fibers. The dispersibility in water was evaluated according to the following criteria.
Good: There are no undispersed fiber bundles, and each single fiber is neatly spread out in the water. Bad: There are several or more undispersed fiber bundles, and the single fibers are often entangled with each other.

(8) Weight per unit area Measurement was carried out in accordance with the weight per unit area test method of JIS L1906 to determine the weight per unit area (g/m ² ).

(9) Thickness Using a Digital Linear Gauge DG-925 (diameter of the measurement terminal part is 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).
From the obtained basis weight (g/m ² ) and thickness (μm), the density (basis weight/thickness) was calculated (kg/m ³ ).

(10) Air permeability: Measurement was carried out according to the JIS L 1913 Frazier method.

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

(12) Pore size Two circular samples having a diameter of 2.5 cm were randomly taken from the nonwoven fabric, and the average pore size was measured using a Palm Porometer (manufactured by PMI).

(13) Division number 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 "division number of ultrafine fibers on the surface of the nonwoven fabric." The fiber diameter was determined 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 the density.

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

(15) Pressure Loss The pressure before and after the test piece passed when measuring the air dust collection rate (wind speed 5.1 cm/sec) was measured, and the pressure difference was calculated as the pressure loss.

[Example 1]
Polyester A (component A; polyethylene terephthalate) having 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) having 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. At this time, eight discharge holes for component B having 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 having 20 holes was used for the number of spinning holes (11) in which components A and B were mixed. The spinning temperature was 280°C, the winding speed was 900 m/min, and an aqueous polyether-polyester copolymer emulsion was applied to the lower part in an amount of 0.5 mass% in terms of solid content adhesion to obtain an undrawn yarn. The undrawn yarn was drawn 20 times in 83°C warm water, and further drawn 2 times in 70°C warm water, and then 0.3% by mass of a polyether-polyester copolymer aqueous emulsion was applied to the fiber surface in terms of solid content adhesion, and the fiber was 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.

The above-mentioned heat-adhesive splittable composite fiber was weighed out so that the basis weight was 100 g/m ² , dispersed in water, and strongly stirred with a mixer to form a slurry. The slurry was then transferred to a hand-made paper machine, and a dispersant (DT-100) was added to 0.1% by mass, and thoroughly stirred. The water was removed, and the sheet was formed on a mesh, and dried with a rotary dryer at 110°C to form a base paper. The basis weight, thickness, and density of the base paper were 100 g/m ² , 530 μm, and 189 kg/m ³ , respectively. The obtained base paper was heat-pressed using a calendar 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 wet-laid nonwoven fabric. The manufacturing conditions of the wet-laid nonwoven fabric are shown in Table 3, and the physical properties of the obtained wet-laid nonwoven fabric are shown in Table 4.

[Example 2]
The same components A and B as those 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), and the components were melted and discharged by an extruder to obtain a composite fiber. 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 portion with a diameter of 0.15 mm so that a core made of component B was formed, while a spinneret having 20 spinning holes (11) for mixing components A and B was used. The spinning temperature was 275°C, the winding speed was 900 m/min, and an aqueous polyether-polyester copolymer emulsion was applied to the lower part of the spinneret in an amount of 0.5% by mass in terms of solid content adhesion to obtain an undrawn yarn. The undrawn yarn was stretched 17 times in warm water at 82°C, and then further stretched 2 times in warm water at 70°C, 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 adhesion, and the fiber was cut to a fiber length of 3 mm to obtain a thermally adhesive splittable composite short fiber having a fineness of 0.49 dtex. The composition and physical properties of the obtained fiber are shown in Tables 1 and 2.

A wetlaid 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 100 g/m ² , 550 μm and 182 kg/m 2 , respectively. The production conditions of the wetlaid nonwoven fabric are shown in Table 3, and the physical properties of the final wetlaid nonwoven fabric obtained after the press treatment are shown in Table 4.

[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) having 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 take-up speed was 500 m/min, and an aqueous polyether-polyester copolymer emulsion was applied to the lower part of the extruder in an amount of 0.5% by mass in terms of solid content adhesion, to obtain an undrawn yarn. The fiber was stretched 40 times in 82°C warm water, and then further stretched 2 times in 70°C 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 fiber length of 3 mm to obtain a thermally adhesive splittable composite short fiber having a fineness of 0.23 dtex. The composition and physical properties of the obtained fiber are shown in Tables 1 and 2.

A wetlaid 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 pressing were 100 g/m ² , 550 μm, and 182 kg/m ³ , respectively. The production conditions of the wetlaid nonwoven fabric are shown in Table 3, and the physical properties of the final wetlaid nonwoven fabric obtained after pressing are shown in Table 4.

[Example 4]
A wetlaid nonwoven fabric was obtained in the same manner as in Example 1, except that the splittable composite staple fiber described in Example 3 and "Tepyrus (TA04PN SD 0.06x3, 0.08dtexx3mm)" manufactured by Teijin Frontier Corporation were mixed in a mass ratio of 40:60, weighed out to give a basis weight of 100g/ ^m2 , and the rotary dryer temperature was set to 110°C and the calendar temperature to 210°C. After drying, the basis weight, thickness and density of the base paper before press treatment were 100g/ ^m2 , 546μm and 174kg/ ^m3 , respectively. The composition and physical properties of the obtained fiber 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 obtained after press treatment are shown in Table 4.

[Example 5]
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 40 mol% isophthalic acid and 4 mol% diethylene glycol, melting point 110°C) having an intrinsic viscosity of 0.55 dL/g was used, and 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 in an amount of 0.5% by mass in terms of solid content adhesion, to obtain an undrawn yarn. The undrawn yarn was drawn 17 times in warm water at 82°C, and then further drawn 2 times in warm water at 70°C, 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 adhesion, and the fiber was cut to a fiber length of 3 mm to obtain a thermally adhesive splittable composite short fiber having a fineness of 0.23 dtex. The composition and physical properties of the obtained fiber are shown in Tables 1 and 2.

A wetlaid 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 100 g/m ² , 550 μm and 182 kg/m ³ , respectively. The production conditions of the wetlaid nonwoven fabric are shown in Table 3, and the physical properties of the final wetlaid nonwoven fabric obtained after the press treatment are shown in Table 4.

[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, the winding speed was 500 m/min, and 0.5% by mass of a polyether-polyester copolymer aqueous emulsion was applied to the lower part of the die in terms of solid content adhesion, to obtain an undrawn yarn made of a single component. The undrawn yarn was stretched 62 times in 83°C warm water, and further stretched twice in 70°C warm water, and 0.3% by mass of a polyether-polyester copolymer aqueous emulsion was applied to the fiber surface in terms of solid content adhesion, and the fiber was cut to a fiber length of 3 mm to obtain a heat-adhesive staple fiber with a fineness of 0.03 dtex. The composition and physical properties of the obtained fibers are shown in Tables 1 and 2.

The above-mentioned heat-bonding staple fiber and "Tepirus (TA04PN SD)" manufactured by Teijin Frontier Co., Ltd.
A wetlaid nonwoven fabric was obtained in the same manner as in Example 1, except that the base paper (0.06 dtex x 3, 0.08 dtex x 3 mm) and the base paper (0.06 dtex x 3 mm) were mixed in a mass ratio of 40:60, weighed out to give a basis weight of 100 g/m2, and the rotary dryer temperature was set to 120°C and the calendar temperature to 190°C. The basis weight, thickness and density of the base paper were 100 g/ ^m2 , 290 μm and 340 kg/ ^m3 , respectively. 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.

[Comparative Example 2]
The fiber-forming component forming the central part of the core-sheath fiber was a polyester (polyethylene terephthalate) with an intrinsic viscosity of 0.47 dL/g and a melting point of 255°C, and the thermal adhesive component forming the sheath was a 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 1336 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 filament. The spinning temperature was 285°C, and the mixture was cooled and solidified with 25°C cooling air below the spinneret, and below that, 0.5% by mass of polyether-polyester copolymer aqueous emulsion was applied in terms of solid content adhesion, and 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, and 0.3% by mass of polyether-polyester copolymer aqueous emulsion was applied to the fiber surface in terms of solid content adhesion, and the fiber was cut to a fiber length of 3 mm to obtain a heat-adhesive core-sheath type 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.

The above-mentioned heat-adhesive core-sheath type staple fiber and "Tepyrus (TA04PN)" manufactured by Teijin Frontier Co., Ltd.
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.

A Component A
B Component B
C Hollow portion 1 Pack case 2 Upper nozzle plate 3 Lower nozzle plate 4 Knock pin 5 Partition plate 6 Discharge small hole for component B 7 Distribution hole for component B 8 Distribution hole for component A 9 Passage for component A 10 Circumferential discharge hole having discontinuities 11 Spinning hole

Claims (7)

The present invention relates to a heat-adhesive splittable composite staple fiber that is composed of a component A made of a polyester resin and a copolymerized polyester resin component B having a melting point 20°C or more lower than that of the component A, the component A and the component B being arranged in a total of 8 or more segments, the fiber having a fineness in the range of 0.01 dtex to 0.6 dtex as a whole, and an aspect ratio in the range of 100 to 3000 as a whole. 2. The thermal adhesive splittable conjugate staple fiber according to claim 1, wherein the copolymer polyester resin component B has a melting point of 220° C. or lower. 3. The heat-adhesive splittable composite staple fiber according to claim 1, wherein component A made of a polyester resin has a melting point of 180° C. or higher and an intrinsic viscosity in the range of 0.35 to 0.70 dL/g. 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. The heat-adhesive splittable composite staple fiber according to claim 1, wherein component A made of a polyester resin and component B made of a copolymerized polyester resin are alternately arranged radially from the center of the fiber. The thermally adhesive splittable composite short fiber according to claim 5, wherein the center of the fiber has a solid or hollow structure. A method for producing a wetlaid nonwoven fabric, comprising wetlaid papermaking of the thermally adhesive splittable composite staple fiber according to any one of claims 1 to 6, followed by calendering.