Single-phase heat-fusible fiber

Abstract

To provide a fusible fiber that exhibits good dispersibility in water when manufacturing a wet-laid nonwoven fabric, has high flexibility, and is capable of obtaining a wet-laid nonwoven fabric suitable for use at high temperatures.SOLUTION: A single-phase heat-fusible fiber applied to a wet-laid nonwoven fabric comprises a quaternary copolymerized polyester of terephthalic acid, ethylene glycol, diethylene glycol, and 1,4-butanediol, wherein the copolymerized polyester exhibits crystallinity with a melting point of 150 to 200°C, and has a fineness of 0.5 to 1.6 dtex and a strength of 3.0 to 6.0 cN / dtex.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a heat-fusible fiber that can be used in a wetlaid nonwoven fabric. [Background technology]

[0002] In recent years, there has been an increasing demand for denser and lighter nonwoven fabrics, which require flexibility and a good texture, from the perspectives of environmental issues and improved handleability, such as in artificial leather for use in miscellaneous goods, furniture, automobile seats, etc., and in nonwoven fabrics for medical and cosmetic applications. Such nonwoven fabrics are mainly produced by impregnating nonwoven fabrics made of synthetic fibers (polyester, nylon, etc.) with small single fiber fineness and fiber diameter with polyurethane resin, or by blending synthetic fibers with small single fiber fineness and fiber diameter with polyurethane fiber.

[0003] However, nonwoven fabrics made from a combination of synthetic fibers and polyurethane resin or polyurethane fibers have problems in that they are difficult to recycle due to the presence of polyurethane, and the manufacturing process places a heavy burden on the environment.

[0004] As a technique for solving the above-mentioned problems associated with polyurethane, the present applicant has proposed a polyester-based elastomer fiber made of a specific copolymer polyester. (Patent Document 1) According to Patent Document 1, the polyester-based elastomer fiber is a fiber made of a copolymer polyester obtained by copolymerizing polyhexamethylene terephthalate and polytetramethylene glycol, and the melting point of the copolymer polyester is 100°C to 150°C, which allows the thermal bonding temperature to be set low, resulting in the effect of being able to produce textile products such as nonwoven fabrics and cushions with excellent flexibility and elastic recovery at low cost.

[0005] However, the melting point of the resin that makes up the fiber is 100°C to 150°C. Because of this low melting point, it is difficult to apply to cases where a drying process is required before the thermal bonding process, such as wet spunlace nonwoven fabrics, or to dyeing processes that involve exposure to high temperatures, and therefore the heat resistance is not good. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6885588 Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a heat-fusible fiber that has sufficient flexibility to be used as an alternative to polyurethane, is preferably applicable to denser wetlaid nonwoven fabrics, and is capable of producing wetlaid nonwoven fabrics that have good dispersibility in water, are highly flexible, and are applicable even at high temperatures. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention.

[0009] That is, the present invention provides a single-phase heat-fusible fiber applicable to wetlaid nonwoven fabrics, the fiber being composed of a thermoplastic polymer, the thermoplastic polymer being a quaternary copolymer polyester of terephthalic acid, ethylene glycol, diethylene glycol, and 1,4-butanediol, the copolymer polyester exhibiting crystallinity with a melting point of 150 to 200°C, the fiber having a fineness of 0.5 to 1.6 dtex, and a strength of 3.0 to 6.0 cN / dtex. [Effects of the Invention]

[0010] The heat-fusible fibers of the present invention have good dispersibility in water and can be used to obtain high-quality wetlaid nonwoven fabrics having high flexibility. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present invention will be described in detail below.

[0012] In the present invention, when functioning as a thermal binder, the fiber is not a core-sheath composite type in which only specific parts have the binder function, but a single-phase type in which all the polymers constituting the fiber melt and function as a binder, and specific constituent components are used as the polymer in order to improve the fiber strength and ensure specific fineness and good dispersibility.

[0013] That is, the thermoplastic polymer constituting the single-phase heat-bondable fiber of the present invention (hereinafter also simply referred to as heat-bondable fiber) is a tetrapolymer polyester of terephthalic acid, ethylene glycol, diethylene glycol, and 1,4-butanediol. Note that the above components constituting the tetrapolymer polyester of the present invention may be components derived from recycled polyester raw materials (such as PET bottle flakes).

[0014] The copolyester constituting the single-phase heat-fusible fiber exhibits crystallinity with a melting point of 150 to 200°C. Since the melting point (melting temperature) showing the melting peak determined by differential scanning calorimetry is 150 to 200°C, the copolyester has high crystallinity and heat resistance, can withstand various heat treatment processes used in producing wetlaid nonwoven fabrics, has excellent dimensional stability during various heat treatments, is highly adaptable to dyeing processes that involve exposure to high temperatures, and the resulting wetlaid nonwoven fabrics undergo little dimensional change even when used at high temperatures. The copolyester's melting point is more preferably 170 to 190°C.

[0015] The copolymerization molar ratio of the copolymer polyester is preferably 100 mol % of terephthalic acid as the acid component, and 40 to 60 mol % of ethylene glycol, 60 to 40 mol % of 1,4 butanediol, and 1.0 to 2.0 mol % of diethylene glycol as the diol component. By using such a molar ratio, the polyester exhibits the above-mentioned specific melting point and high crystallinity, and is excellent in heat resistance and has improved fiber strength despite being a single-phase heat-fusible fiber.

[0016] In order to further improve the crystallinity, the copolymer polyester may contain about 0.01 to 3 mass % of a known crystal nucleating agent, such as inorganic fine particles, an organic compound made of polyolefin, or a sulfate. However, considering that the copolymer polyester itself has excellent crystallinity and recyclability, it is preferable that the copolymer polyester does not contain a crystal nucleating agent.

[0017] The fineness of the heat-fusible fibers of the present invention is 0.5 to 1.6 dtex. In the present invention, the fineness is in the range of 0.5 to 1.6 dtex, which is a relatively small fineness, so that the number of fibers per unit mass is large, and when a wetlaid nonwoven fabric is obtained, such small fineness fibers can be individually and finely dispersed. Furthermore, because the fineness of the heat-fusible fibers is small, the individual bonding points between the heat-fusible fibers and the skeletal fibers that make up the nonwoven fabric (fibers that maintain their fiber shape without thermal melting or softening when the heat-fusible fibers function as a thermal binder, and are also referred to as main fibers) are small, and it is possible to provide many bonding points, which gives the resulting wetlaid nonwoven fabric a good texture and enables the nonwoven fabric strength to be improved by bonding. If the fineness of the heat-fusible fibers exceeds 1.6 dtex, the individual bonded points become large and the number of bonded points becomes small, making it impossible to improve both the texture and strength. On the other hand, if the fineness is less than 0.5 dtex, the small fineness makes it difficult to handle, and, although it depends on the fineness of the main fiber, the main fiber and the heat-fusible fiber tend to be difficult to mix uniformly, making it difficult to obtain a nonwoven fabric with uniform strength. A more preferable fineness is 0.8 to 1.2 dtex.

[0018] The strength of the heat-fusible fiber of the present invention is 3.0 to 6.0 cN / dtex. The heat-fusible fiber of the present invention is a fully fusible, single-phase fiber, yet has a fiber strength of 3.0 to 6.0 cN / dtex. Therefore, the fiber can withstand friction, load, tension, and pressure during the drawing and cutting processes used to produce the fiber, and is less likely to break or fracture, ensuring smooth operation. Because fiber fractures and other issues are less likely to occur during the production process, the resulting fiber is less likely to have defects and is highly homogeneous. When producing a wetlaid nonwoven fabric, the individual fibers disperse well in water and are uniformly mixed with the main fibers, resulting in a nonwoven fabric with homogeneous mechanical properties and favorable texture and feel. If the fiber does not have the above-mentioned strength, the fibers will break during the production process, and the resulting defects will be mixed into the cut short-cut fibers. Therefore, when attempting to produce a wetlaid nonwoven fabric using such fibers, the presence of the defects will result in poor dispersibility in water, making it impossible to obtain a homogeneous wetlaid nonwoven fabric.

[0019] The present invention is a fully meltable single-phase heat-fusible fiber, and therefore, at the heat-bonded portions where the binder component melts or softens to function as a thermal binder, only the binder component is present, thereby providing sufficient flexibility. Heat-fusible fibers generally have high mechanical strength, and sheath-core composite fibers are known. In sheath-core composite fibers, the sheath component melts or softens upon heating to function as a binder, but the core component maintains its fiber shape and exists as a so-called skeleton, making it difficult for the heat-bonded portions to provide sufficient flexibility. In contrast, the present invention is a fully meltable single-phase fiber, and therefore, at the heat-bonded portions where the binder component melts or softens to function as a thermal adhesive, no skeleton is present. When melted or softened, the binder component aggregates at a single point due to surface tension, and functions as a binder in this form, resulting in a wetlaid nonwoven fabric with high flexibility.

[0020] In the present invention, as described above, it is possible to obtain a relatively small fineness of 0.5 to 1.6 dtex and a strength per fineness of 3.0 to 6.0 N / dtex, even though the fiber is a single-phase fiber composed only of a thermal binder component, by selecting the above-mentioned specific crystalline copolymer polyester as the polymer constituting the fiber, controlling the copolymer polyester so that it is not rapidly cooled immediately after discharge in the fiber spinning process, and enabling a high draw ratio to be set in the subsequent drawing process despite the small fineness. That is, by easing the cooling conditions immediately after discharge, crystallization is suppressed and the stress applied to the yarn is reduced, thereby improving the elongation in the undrawn state. Furthermore, by drawing the highly elongated undrawn yarn at a high draw ratio while applying a temperature 5 to 20°C higher than the glass transition temperature of the copolymer polyester, a single-phase heat-bondable fiber having both a small fineness and high strength can be obtained. In the spinning process, methods for gradual cooling immediately after extrusion include, for example, adjusting the nozzle temperature, the temperature and volume of cooling air, the take-up speed, the cooling start position, and the like.

[0021] Since the heat-fusible fibers of the present invention are intended for use in wetlaid nonwoven fabrics, they are preferably short-cut fibers with a fiber length of 3 to 20 mm. A fiber length of 3 mm or more makes the fibers less likely to fuse or stick together due to the heat and pressure applied during cutting, making them easier to handle. Furthermore, a fiber length of 20 mm or less prevents the aspect ratio of the fibers from becoming too large, preventing entanglement of the fibers when dispersed in water and providing good dispersibility in water. A more preferred fiber length is 3 to 10 mm.

[0022] When obtaining a wetlaid nonwoven fabric using the thermal fusion fiber of the present invention as a constituent fiber, it is mixed with other fibers (subject fibers) to obtain the wetlaid nonwoven fabric. The thermal fusion fiber of the present invention has excellent blendability and dispersibility, so when mixed with the subject fiber, it can be densely and uniformly mixed, resulting in a wetlaid nonwoven fabric of excellent quality. In particular, the thermal fusion fiber of the present invention has excellent dispersibility in water despite being a fiber with a relatively small fineness, as described above, so that a wetlaid nonwoven fabric of high quality, with uniform mechanical properties and excellent flexibility can be obtained. Therefore, even if the subject fiber is an ultrafine fiber with a single fiber fineness of 1 dtex or less, the thermal fusion fiber of the present invention can be uniformly mixed with the ultrafine fiber without any unevenness, resulting in a very uniform and dense wetlaid nonwoven fabric.

[0023] The main fiber to be mixed may be any fiber that maintains its fiber shape without being thermally melted or softened when the heat-fusible fiber functions as a thermal binder, and examples thereof include natural fibers, rayon fibers, and thermoplastic fibers made of polyester or polyamide. Among these, polyester fibers made of a polymer having a melting point higher than that of the thermoplastic polymer constituting the single-phase heat-fusible fiber are preferably used, and polyethylene terephthalate fibers are preferably used as the polyester fibers.

[0024] The blend ratio of the heat-fusible fibers of the present invention to the subject fibers may be appropriately selected depending on the required properties of the wetlaid nonwoven fabric. The blend ratio of the heat-fusible fibers of the present invention is preferably about 5 to 80% by mass, more preferably 10 to 50% by mass. To obtain a wetlaid nonwoven fabric, the heat-fusible fibers and subject fibers are agitated and defibrated using a pulp disintegrator, followed by production of a wetlaid web using a papermaking machine. The resulting web is passed through a continuous heat treatment machine that performs hot air treatment and is heat-fusible at a temperature at which the copolymer polyester constituting the heat-fusible fibers of the present invention melts or softens, thereby integrating the constituent fibers with the melted or softened heat-fusible fibers. When the blend ratio of the heat-fusible fibers is high, a dense wetlaid nonwoven fabric is obtained in which the copolymer polyester, which is the molten product of the heat-fusible fibers, is impregnated into the voids between the subject fibers constituting the wetlaid nonwoven fabric. If necessary, a hydroentanglement method using a water jet or the like may be applied to the wet web before the heat treatment, so that the constituent fibers of the wet web are three-dimensionally entangled by the action of the water flow.

[0025] The basis weight of the wetlaid nonwoven fabric obtained by using the heat-fusible fiber of the present invention is not particularly limited and may be appropriately selected depending on the application of the wetlaid nonwoven fabric, for example, 5 to 300 g / m 2 In good condition.

[0026] The wetlaid nonwoven fabric of the present invention is highly flexible and dense, and can be applied to various fields, such as miscellaneous goods such as bags, clothing, interior sheets such as curtains and wallpaper, surface sheets for chairs and vehicle seats, and automobile ceiling materials.

[0027] Next, an example of the method for producing the heat-fusible fiber of the present invention will be described.

[0028] The copolymer polyester having the specific composition described above is melt-spun in a spinning facility equipped with a screw extruder or the like, and the resulting yarn is cooled and solidified, and then taken up at a speed of 700 to 1500 m / min. The yarn discharged from the nozzle by melt spinning is preferably cooled by slow cooling as described above.

[0029] The resulting yarns are collected into a yarn bundle and then stretched between rollers at a stretch ratio equal to or greater than the natural stretch ratio (NDR). The stretch ratio is the speed ratio between the supply roller and the take-up roller (the speed of the take-up roller divided by the speed of the supply roller), and is preferably 1.0 to 4.0. A more preferred stretch ratio is 2.5 to 4.0, and even more preferably 2.5 to 3.8. It is also preferred to use unheated rollers for both the supply roller and the take-up roller. The stretched yarn bundle is then oiled and fed to a rotary cutter, where it is cut to the desired fiber length to obtain short-cut fibers. In this manufacturing method, as described above, by selecting a specific crystalline copolymer polyester and applying a manufacturing method in which the undrawn yarn slowly cooled in the spinning process is drawn at a high drawing ratio in the drawing process, it is possible to obtain a relatively small fineness of 0.5 to 1.6 dtex, and a single-phase type consisting only of a thermal binder component, while still having a strength per fineness of 3.0 to 6.0 N / dtex. [Example]

[0030] The present invention will now be described in detail with reference to examples, in which the various property values ​​and other parameters were measured and evaluated as follows: (1) Melting point, glass transition temperature (Tg) The melting point and Tg of the fiber were measured using a PerkinElmer differential scanning calorimeter in a nitrogen gas flow at a temperature range of -50°C to 280°C, a heating rate of 20°C / min, a cooling rate of 10°C / min, and a sample weight of 8.5 mg (fiber mass). (2) Each copolymer composition amount The fibers were dissolved in a mixed solvent of deuterated trifluoroacetic acid and deuterated chloroform in a volume ratio of 1 / 11, and 1H-NMR was measured using a JEOL ECZ-400R NMR apparatus. The values ​​were calculated from the integrated intensity of the proton peaks of each copolymer component in the resulting chart. (3) Fineness Measurements were carried out in accordance with JIS L1015 8.5.1 Method A, except that 100 fibers obtained in the examples were taken out and the mass was measured and the measurement was carried out four times. (4) Fiber strength A cut length of 15 mm was prepared for measuring fiber strength according to the method of JIS-L-1015 8.7, and measurements were made with a spatial distance of 10 mm, a gripping distance of 10 mm, and a pulling speed of 20 mm / min. (5) Operability If the number of yarn breakages during 24 hours of continuous melt spinning was 3 times / day (spindle) or less and there was no adhesion of the single yarns during the drawing process, the result was marked as "○", and otherwise marked as "×". (6) Dispersibility in water 2000cm 3 1 kg of water at 30°C was weighed into a beaker, 5.0 g of fiber was added, and the mixture was stirred using a DC stirrer (the stirring blade was a three-screw type with a diameter of approximately 50 mm) at a rotation speed of 400 rpm for 2 minutes. After one stirring, the dispersion state was visually evaluated according to the following criteria. A rating of ○ to △ was considered to be acceptable. Rating Number of shives ○: 0 pieces △: 1~5 pieces ×: 5 or more (7) Texture of nonwoven fabric (softness) The texture of the obtained nonwoven fabric was evaluated by touching with the hands on the following three-level scale. ○: It is soft and can be deformed with a light force. △: There is a resilience and the nonwoven fabric does not deform unless it is pressed down slightly. ×: The surface is hard and the nonwoven fabric does not deform unless pressed firmly. (8) Strength of nonwoven fabric The obtained nonwoven fabric was cut into samples of 150 mm in the MD direction and 50 mm in the CD direction, and the MD strength of the nonwoven fabric was measured using an autograph (Shimadzu Corporation AG-50KNI) at a tensile speed of 100 mm / min and a chuck distance of 100 mm. The number of samples was 5, and the average value of the 5 samples was taken as the tensile strength. The tensile strength of the obtained nonwoven fabric was evaluated using the following two-level scale. ○: Tensile strength 170N / 50mm width or more ×: Tensile strength less than 170N / 50mm width

[0031] Example 1 A copolymer polyester (melting point 180° C., Tg 48° C.) consisting of 100 mol % of terephthalic acid as the acid component, and 48.6 mol % of ethylene glycol, 1.4 mol % of diethylene glycol, and 50.0 mol % of 1,4-butanediol as the diol component was prepared.

[0032] The melt spinning conditions were as follows: a spinneret having 1,040 circular spinning holes was used; the melt spinning was performed at a spinning temperature of 250°C, a take-up speed of 850 m / min, and a discharge rate of 287 g / min; and the mixture was gradually cooled by blowing cold air at a set temperature of 27°C at a position 50 mm below the spinning nozzle, to obtain an undrawn yarn.

[0033] The resulting undrawn yarn was collected and drawn at a draw ratio of 3.2 times and a drawing temperature of 62° C. Next, a finishing oil was applied, and the tow was squeezed so that the moisture content was approximately 18% by mass, and then cut to a length of 5 mm with a drum cutter to obtain a single-phase heat-fused fiber having a single fiber fineness of 1.1 dtex and a tenacity of 3.3 cN / dtex.

[0034] Next, the obtained single-phase heat-bonded fiber and polyethylene terephthalate short-cut fiber (manufactured by Unitika Ltd.) with a single fiber fineness of 0.4 dtex and a length of 5 mm were used as the main fiber. <521> The single-phase heat-fusible fiber / subject fiber (mass ratio) was 20 / 80 and dispersed in water, and a paper web was obtained using a cylinder paper machine. After the paper web was obtained, it was subjected to a dry heat treatment (2 minutes) in a Yankee dryer at 200°C, and then excess water was removed, resulting in a basis weight of 50 g / m. 2 A wet-laid nonwoven fabric of this size was obtained.

[0035] Comparative Example 1 Single-phase heat-bondable fibers having a single fiber fineness of 1.7 dtex and a tenacity of 2.6 cN / dtex were obtained in the same manner as in Example 1, except that the take-up speed was 850 m / min, the extrusion rate was 355 g / min, and the draw ratio was 3.7 times. Note that some of the fibers were broken during the cutting step in the production process, and broken fragments were mixed in with the cut fibers.

[0036] A wetlaid nonwoven fabric was obtained in the same manner as in Example 1 using the obtained single-phase heat-fusible fibers.

[0037] Comparative Example 2 Polyethylene terephthalate (melting point 256°C) and the copolymer polyester used in Example 1 were prepared. The melt spinning conditions were as follows: a composite spinneret with 560 core-sheath type composite circular spinning holes was used, with polyethylene terephthalate in the core and the copolymer polyester in the sheath, and the melt spinning was carried out at a spinning temperature of 285°C, a take-up speed of 790 m / min, and a discharge rate of 312 g / min. The set temperature was 20°C, and the air volume was 4.5 m / min., and the melt spinning was carried out at a position 50 mm below the spinning nozzle. 2 The yarn was slowly cooled by blowing cold air at 1 / min. / min to obtain an undrawn yarn.

[0038] The resulting undrawn yarns were collected and drawn at a draw ratio of 3.6 and a drawing temperature of 55°C, and after applying a finishing oil, the yarns were squeezed so that the moisture content of the tow was approximately 18% by mass, and then cut to a length of 5 mm with a drum cutter to obtain core-sheath hybrid heat-fused fibers with a single yarn fineness of 2.2 dtex and a strength of 2.2 cN / dtex. Note that some of the fibers broke during the cutting process in the production process, and broken fragments were mixed in with the cut fibers.

[0039] A wetlaid nonwoven fabric was obtained in the same manner as in Example 1 using the obtained single-phase heat-fusible fibers.

[0040] The evaluation results of the heat-fusible fibers and nonwoven fabrics obtained in Example 1 and Comparative Examples 1 and 2 are shown in Table 1.

[0041] [Table 1]

[0042] As is clear from Table 1, the heat-fusible fiber of Example 1 had good operability, no fiber breakage occurred during the cutting process, excellent dispersibility in water, and good handleability. The obtained wetlaid nonwoven fabric had very good texture and flexibility, and was dense and highly uniform.

[0043] On the other hand, in Comparative Example 1, fiber breakage occurred during the cutting process, dispersibility in water was somewhat poor, and the obtained wetlaid nonwoven fabric had uneven texture and was also poor in strength.

[0044] In Comparative Example 2, fiber breakage occurred during the cutting process, resulting in poor dispersibility in water. Furthermore, the resulting wetlaid nonwoven fabric was less flexible and harder than the nonwoven fabrics of the Examples, which was not the objective of the present invention.

Claims

1. A single-phase heat-fusible fiber suitable for use in wetlaid nonwoven fabrics, the fiber being made of a thermoplastic polymer, the thermoplastic polymer being a quaternary copolymer polyester of terephthalic acid, ethylene glycol, diethylene glycol, and 1,4-butanediol, the copolymer polyester exhibiting crystallinity with a melting point of 150 to 200°C, the fiber having a fineness of 0.5 to 1.6 dtex, and a strength of 3.0 to 6.0 cN / dtex.

2. 2. The single-phase heat-fusible fiber according to claim 1, wherein the molar ratio of ethylene glycol to 1,4-butanediol contained in the glycol component constituting the copolymer polyester is 40 to 60 mol % of ethylene glycol and 60 to 40 mol % of 1,4-butanediol.

3. 3. The single-phase heat-fusible fiber according to claim 2, wherein the molar ratio of diethylene glycol contained in the glycol component constituting the copolymer polyester is 1.0 to 2.0 mol %.

4. 4. A wetlaid nonwoven fabric comprising the single-phase heat-fusible fiber according to claim 1 and polyester fibers made of a polymer having a melting point higher than that of the thermoplastic polymer constituting the single-phase heat-fusible fiber, wherein the polyester fibers are heat-fused together by the thermal melting of the single-phase heat-fusible fiber.

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