Meltblown nonwoven fabric

Abstract

We provide meltblown nonwoven fabrics that combine high water retention and water absorption. [Solution] A meltblown nonwoven fabric containing polyamide resin fibers with a water retention rate of 400% or more and a water absorption rate of 10 cm / 20 minutes or more.

Description

[Technical Field]

[0001] This disclosure relates to meltblown nonwoven fabrics. [Background technology]

[0002] Due to its inherent hydrophilicity, polyamide nonwoven fabrics are used in applications requiring good water retention and absorption, such as liquid filters, battery separators, and bacterial testing kits.

[0003] Patent Document 1 discloses a method for producing a polyamide ultrafine fiber nonwoven fabric having an average fiber diameter between 0.5 and 4.0 μm, a CV% of fiber diameter of 35% or less, a packing density between 0.15 and 0.80, and a water absorption height of 5 cm / 30 min or more, which includes melting a polyamide polymer having a relative viscosity between 1.8 and 3.0 in the melt-blown method while containing 0.05% to 1.0% water by mass fraction.

[0004] Patent Document 2 describes a polyamide resin fiber having an average fiber diameter of 0.1 μm or more and less than 0.5 μm, and a CV value of the fiber diameter of 20% or more and less than 65%, with a basis weight of 10 g / m². 2 This disclosure concerns a nonwoven fabric characterized by the above features. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. Hei 8-144166 [Patent Document 2] Japanese Patent Publication No. 2020-190057 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the case of polyamide nonwoven fabrics, a lower filling density increases water retention but slows down the rate of water absorption, while a higher filling density increases the absorption rate but results in insufficient water retention. Thus, there was a trade-off relationship between water retention and absorption rate.

[0007] Patent documents 1 and 2 control the filling rate to maintain a water absorption height above a certain level, but do not improve water retention.

[0008] The problem that this disclosure aims to solve is to provide a meltblown nonwoven fabric that simultaneously satisfies excellent water retention and water absorption. [Means for solving the problem]

[0009] This disclosure includes, for example, the following subjects:

[0010] Section 1. A meltblown nonwoven fabric containing polyamide resin fibers having a water retention rate of 400% or more, a water absorption rate of 10 cm / 20 minutes or more, and a water absorption capacity value of 0.05 or more as shown in formula (1) below. Water suction capacity = (Water suction rate [cm / 20 min]) / (Apparent specific surface area [m²]) 2 / m 3 ]) × 10 3 (1)

[0011] Section 2. The tensile modulus in the MD direction is 4 N / mm when the filling density is 8% or more and 18% or less, and the test specimen is elongated by 2-4%. 2 More than 20N / mm 2 The meltblown nonwoven fabric described in item 1 below.

[0012] Section 3. A meltblown nonwoven fabric according to item 1 or 2, wherein 95% by mass or more of the resin constituting the polyamide resin fibers is nylon 6.

[0013] Section 4. Weight: 50g / m 2A meltblown nonwoven fabric according to item 1 or 2, wherein the burst strength per unit area is 90 kPa or more.

[0014] Section 5. A meltblown nonwoven fabric as described in item 1 or 2, used in fluid filters, battery separators, or bacterial carrying media for bacterial testing kits. [Effects of the Invention]

[0015] According to this disclosure, a meltblown nonwoven fabric having excellent water retention and water absorption properties is provided. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram illustrating an example of the process for manufacturing the meltblown nonwoven fabric of the present invention. [Figure 2] Figure 1 is an exploded perspective view showing the internal structure of collector 4a. [Figure 3] This is an SEM image of the meltblown nonwoven fabric (magnification 500x) from Example 5. [Modes for carrying out the invention]

[0017] In this specification, "contains" is a concept that also includes "substantially consists only of" and "consists only of."

[0018] In the numerical ranges described stepwise in this specification, the upper or lower limit of a numerical range in one step can be arbitrarily combined with the upper or lower limit of a numerical range in another step. Furthermore, in the numerical ranges described in this specification, the upper or lower limit of a numerical range may be replaced with values ​​shown in the examples or values ​​that can be uniquely derived from the examples. Moreover, in this specification, numbers connected by "~" mean a numerical range that includes the numbers before and after "~" as the lower and upper limits.

[0019] The reason why the water retention rate and the water absorption rate (water absorbency) are in a trade-off relationship is that the wider the internal space becomes as the fibers constituting the non-woven fabric are further apart, the higher the water retention rate. However, since the network structure formed by the fusion points and entanglement points of the fibers decreases, the influence of capillary action decreases, and the water absorption rate is considered to slow down.

[0020] Therefore, the inventors optimized the manufacturing conditions of the melt-blown non-woven fabric and developed a melt-blown non-woven fabric that achieves both good water retention and water absorbency by controlling the filling rate and the network structure.

[0021] The present disclosure provides a melt-blown non-woven fabric containing polyamide-based resin fibers having a water retention rate of 400% or more, a water absorption rate of water of 10 cm / 20 minutes or more, and a value of the water absorption capacity of the following formula (1) of 0.05 or more.

[0022] Water absorption capacity = (Water absorption rate [cm / 20 minutes]) / (Apparent specific surface area [m 2 / m 3 ) × 10 3 (1) A melt-blown non-woven fabric having such a configuration satisfies excellent water retention and water absorbency.

[0023] The polyamide-based resin fibers in the melt-blown non-woven fabric are composed of a polyamide-based resin or a resin composition containing a polyamide-based resin. The polyamide-based resin fibers in the melt-blown non-woven fabric are fibers containing a polyamide resin. The melt-blown non-woven fabric preferably contains 50% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, for example, 100% by mass of polyamide-based resin fibers with respect to the total mass of the melt-blown non-woven fabric. The amount of polyamide in the resin composition containing a polyamide-based resin is preferably 50% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more.

[0024] Examples of the polyamide-based resin include polyamide 3 (nylon 3), polyamide 4 (nylon 4), polyamide 6 (nylon 6), polyamide 6,6 (nylon 6,6), and the like.

[0025] It is preferable, in terms of achieving both water retention and water absorption, that 95% or more of the resin constituting the polyamide resin fiber is nylon 6.

[0026] Furthermore, the meltblown nonwoven fabric of this disclosure has a filling density of 8% or more and 18% or less, and a tensile modulus of elasticity in the MD direction of 4 N / mm² when the test specimen is stretched by 2-4%. 2 More than 20N / mm 2 The following is preferable. By designing the meltblown nonwoven fabric to satisfy these conditions, it is possible to provide a meltblown nonwoven fabric that satisfies excellent water retention and water absorption.

[0027] The filling density and tensile modulus of meltblown nonwoven fabrics are indicators that are considered to reflect the internal structure of the nonwoven fabric.

[0028] When the filling density is high, the fibers in the nonwoven fabric are close together and densely packed, resulting in less space to hold moisture and lower water retention. On the other hand, when the filling density is low and the fibers are spaced far apart, there is more space to hold moisture and higher water retention. However, if the fibers are hardly entangled and there are few fusion points, the rate of water absorption will be slow.

[0029] On the other hand, when there are many entanglement and fusion points of fibers, a network structure is formed, and when strain occurs during a tensile test, a large stress acts on the material, which is thought to be reflected in a high modulus of elasticity. In addition, because there are many areas where the fibers are densely packed, the packing density is high and the water retention rate decreases, but the water absorption rate increases.

[0030] Generally, as the average fiber diameter decreases, the number of fibers per unit volume increases, the fibers become more densely packed together, and the fiber surface area also increases, which tends to increase the rate of water absorption. However, even with a relatively thick fiber diameter, in order to improve the rate of water absorption, it is desirable that the fibers do not simply exist densely as fiber bundles, but rather have entanglement points and fusion points at a certain frequency to form a network structure. For these reasons, it is preferable that the packing density and tensile modulus are within a certain range that balances water retention and water absorption. The packing density and tensile modulus can be measured by the measurement methods described in the examples.

[0031] If the filling ratio is less than 8%, the water absorption capacity of the meltblown nonwoven fabric may be insufficient. If the filling ratio exceeds 18%, the water retention capacity of the meltblown nonwoven fabric may decrease.

[0032] The tensile modulus in the MD direction when the test specimen is elongated by 2-4% is 4 N / mm². 2 If it is less than 20 N / mm², the strength of the nonwoven fabric will be weak, and the water absorption of the meltblown nonwoven fabric may decrease. The tensile modulus in the MD direction when the test specimen is stretched by 2-4% is 20 N / mm². 2 If this value is exceeded, the water retention capacity of the meltblown nonwoven fabric may decrease.

[0033] In one preferred embodiment, the meltblown nonwoven fabric of the present disclosure has a filling density of 8% or more and 18% or less, and a tensile modulus of elasticity in the MD direction of 4 N / mm² when the test specimen is stretched by 2-4%. 2 More than 20N / mm 2 The following conditions apply: the water retention rate is 400% or more, and the water suction rate is 10 cm / 20 minutes or more. The upper limit of the water retention rate is not particularly limited, but for example, it is 1000% or less. The upper limit of the water suction rate is not particularly limited, but for example, it is 30 cm / 20 minutes or less.

[0034] The water retention rate and the suction rate can be measured by the measurement methods described in the examples.

[0035] Furthermore, the meltblown nonwoven fabric of the embodiment of the present disclosure satisfies the requirement that the water absorption capacity value of the following formula (1) is 0.05 or greater.

[0036] Water suction capacity = (Water suction rate [cm / 20 min]) / (Apparent specific surface area [m²]) 2 / m 3 ]) × 10 3 (1) The apparent specific surface area in equation (1) was calculated using equation (2), assuming a model meltblown nonwoven fabric described below. Then, the water absorption rate was divided by equation (2) and multiplied by 1000 to obtain equation (1), which was used to evaluate the water absorption capacity of the meltblown nonwoven fabric.

[0037] The value of formula (1) is preferably 0.05 or higher, preferably 0.08 or higher, and more preferably 0.10 or higher. If it is 0.05 or lower, the water absorption capacity is low relative to the fiber diameter, reducing the degree of freedom when designing meltblown nonwoven fabrics for different applications. The upper limit of the water absorption capacity is not particularly limited, but for example, it is 0.5 or lower.

[0038] Meltblown nonwoven fabric has an average fiber diameter R [μm] and a basis weight w [g / m²]. 2 ], thickness t [mm], resin specific gravity a [g / cm] 3 Let's assume π is the value of pi, and 1m 2 Let's assume a meltblown nonwoven fabric model in which only a few cylindrical fibers with radius r [μm] and fiber length 1 m exist. R = 2r. 2 The sum of the lateral surfaces of all cylindrical fibers present in the model nonwoven fabric is (4 × w) / (a ​​× R) [m 2 It can be expressed as ]. In this case, the areas of the top and bottom surfaces of the modeled cylinder are small compared to the area of ​​the sides, so they are not considered. Also, 1 m of this nonwoven fabric 2 The volume per unit area is t × 10, since the thickness is t [mm]. -3 [m 3 ]

[0039] For the meltblown nonwoven fabric assumed above, we introduce the concept of specific surface area as a pseudo-ideal. Normally, if the surface area of ​​an object is S and its volume is V, the specific surface area Sv per unit volume is expressed as Sv = S / V. In this relationship, S is the sum of the lateral surfaces of the cylindrical fibers mentioned above, which is (4 × w) / (a ​​× R) [m 2 ], where V is the volume of the nonwoven fabric, t × 10 -3 [m 3 Substituting ], we get Sv = (4 × w × 10 3 ) / (a×t×R)[m 2 / m 3 This was considered to be the pseudo-apparent specific surface area of ​​the meltblown nonwoven fabric.

[0040] Apparent specific surface area of ​​meltblown nonwoven fabric = (4 × w × 10) 3 ) / (a×t×R)[m 2 / m 3 (2) The basis weight of the meltblown nonwoven fabric disclosed herein can be set appropriately depending on the application, for example, 1 g / m². 2 ~200g / m 2 Preferably 5 g / m 2 ~150g / m 2 It falls within this range. The reading can be adjusted to the desired value, for example, by changing the collector speed.

[0041] The average fiber diameter of the meltblown nonwoven fabric of this disclosure is not particularly limited, but is preferably 0.5 to 50 μm from the viewpoint of filter applications. In some embodiments, the average fiber diameter is 1.0 to 20.0 μm. The average fiber diameter of the meltblown nonwoven fabric can be measured by the measurement method described in the examples.

[0042] The thickness of the meltblown nonwoven fabric of this disclosure is not particularly limited, but is preferably 0.01 to 10 mm, and more preferably 0.1 to 5 mm, in average thickness per sheet of meltblown nonwoven fabric. The average thickness of the meltblown nonwoven fabric can be measured by the measurement method described in the examples.

[0043] The air permeability of the meltblown nonwoven fabrics of this disclosure is not particularly limited, but is between 1 and 700 cm. 3 / cm 2 It is preferable that the value is / second, and is between 5 and 500 cm. 3 / cm 2 / second is more preferable, 5-200cm 3 / cm 2 / second is even more preferable. The air permeability of the meltblown nonwoven fabric can be measured by the measurement method described in the examples.

[0044] The MD strength of the meltblown nonwoven fabric of this disclosure is not particularly limited, but is preferably 1 N / 50 mm or higher. The MD strength of the meltblown nonwoven fabric can be measured by the measurement method described in the examples.

[0045] The meltblown nonwoven fabric disclosed herein has a basis weight of 50 g / m². 2 A bursting strength of 90 kPa or higher per unit area is preferable in terms of maintaining the strength of the nonwoven fabric. Basis weight: 50 g / m 2 There is no particular upper limit to the bursting strength per unit area, but for example, it is 500 kPa or less. (Base weight 50 g / m²) 2 The burst strength per unit can be measured by the measurement method described in the examples.

[0046] This disclosure further provides a laminate comprising multiple melt-blown nonwoven fabrics. Such melt-blown nonwoven fabrics and laminates are useful as filter materials for fluid filters. Fluids include gases and liquids.

[0047] The meltblown nonwoven fabric of this disclosure may be used in combination with other layers, and a fluid filter comprising a laminate including such a combination of meltblown nonwoven fabric and other layers is also included in the fluid filters of this disclosure.

[0048] Other layers include, for example, knitted fabrics, nonwoven fabrics, and films.

[0049] When laminating other layers onto the meltblown nonwoven fabric of this disclosure, various known methods can be employed, including thermal fusion methods such as heat embossing and ultrasonic fusion, mechanical entanglement methods such as needle punching and water jetting, adhesive methods such as hot melt adhesives and urethane-based adhesives, and extrusion lamination.

[0050] Other nonwoven fabrics that can be laminated as layers include spunbond nonwovens, wet-laid nonwovens, dry-laid nonwovens, dry-laid pulp nonwovens, flash-spun nonwovens, and open-fiber nonwovens.

[0051] Next, an example of a method for manufacturing the meltblown nonwoven fabric of the present disclosure will be described with reference to the drawings, but the manufacturing method is not limited to the following. Figure 1 shows an example of a manufacturing apparatus for the meltblown nonwoven fabric of the present disclosure. This manufacturing apparatus consists of a hopper 1a for feeding raw materials, an extruder 1b for melting and kneading the raw materials, a metering pump 2 for sending the molten polymer extruded from the extruder 1b downstream, a die 3a for discharging fibrous material horizontally, a temperature control heater 3b for high-temperature, high-speed air discharged from the die 3a together with the molten polymer, a spinning nozzle 3c attached to the tip of the die, a collector 4a for collecting fibers provided near the die 3a, a suction blower 4b for sucking up the collector 4a (and the fibrous molten polymer 5a collected by the collector 4a), the fibrous molten polymer 5a discharged from the die, a meltblown nonwoven fabric 5b formed when the fibrous molten polymer 5a cools and solidifies on the collector 4a, and a winding machine 6 for winding up the meltblown nonwoven fabric 5b.

[0052] The diameter of the hole 3 in the spinning nozzle 3c in the die 3a is, for example, 0.1 to 2.0 mm.

[0053] As shown in Figure 2, the collector 4a, which continuously collects the polymer fibers discharged and stretched from the spinning nozzle 3c, has a cylindrical member 41 that communicates with the suction blower 4b, a porous cylindrical member 42 provided on the outer circumferential surface of the cylindrical member 41, and a cylindrical mesh member 43 provided on the outer circumferential surface of the porous cylindrical member 42.

[0054] The diameter of collector 4a is preferably 30 to 150 cm, and more preferably 50 to 100 cm.

[0055] The mesh opening of the cylindrical mesh member 43 is not particularly limited as long as a nonwoven fabric can be obtained, but for example, the warp density of the net constituting the mesh member is preferably 10 to 110 threads / inch, and more preferably 10 to 30 threads / inch. Also, the weft density of the net constituting the mesh member is preferably 10 to 50 threads / inch mm, and more preferably 20 to 40 threads / inch. Here, warp threads refer to the threads in the longitudinal direction of the cylindrical mesh member 43, and weft threads refer to the threads that intersect the warp threads. The cylindrical mesh member 43 is preferably made of wire mesh or fibers of a high-melting-point heat-resistant resin (such as nylon).

[0056] The meltblown nonwoven fabric of this disclosure can be manufactured by a method comprising (1) a step of melting and kneading a polymer, (2) a step of extruding the molten polymer from a spinning nozzle and blowing heated air from another nozzle to form polymer fibers, and (3) a step of collecting the obtained fibers with a collector 4a. Referring to the apparatus described above, when manufacturing the meltblown nonwoven fabric, the fibrous molten polymer 5a extruded from the spinning nozzle 3c is stretched by heated air blown from an air nozzle, and the obtained polymer fibers are collected on the collector 4a. The obtained meltblown nonwoven fabric may be subjected to (4) calendering, (5) electrostatic treatment, (6) hydrophilization treatment, etc., as needed.

[0057] (1) Melt-mixing process The melting and kneading temperature of the polymer is preferably between (melting point of the polymer + 30°C) and (melting point of the polymer + 150°C). The melting and kneading temperature of the polyamide is preferably between 250°C and 370°C.

[0058] (2) Fiber formation process Molten polymer is extruded from a number of spinning nozzles 3c, and heated air is ejected from the nozzles to form polymer fibers. The temperature of the die 3a and the heated air is preferably between (the melting point of the polymer) and (the melting point of the polymer + 200°C). This temperature range is preferred from the viewpoint of suppressing rapid solidification of the polymer immediately after extrusion from the spinning nozzles 3c and suppressing fusion of the formed polymer fibers, thereby suppressing variations in fiber diameter.

[0059] The amount of heated compressed air ejected per unit width is 5-50 Nm³. 3 / min / m is preferable.

[0060] (3) Collection process The suction volume of collector 4a per unit width can be appropriately adjusted according to the desired physical properties of the meltblown nonwoven fabric 5b. Most of the heated air is drawn into collector 4a through the suction holes 42a of the porous cylindrical member 42, thereby suppressing turbulence in the fiber flow. Specifically, the suction volume of collector 4a per unit width is 100 to 1000 Nm³. 3 / minutes is preferable.

[0061] The rotational speed of collector 4a is preferably 1 to 20 m / min, and more preferably 3 to 15 m / min. Collector 4a may be at room temperature, but may be heated if necessary.

[0062] The minimum distance (DCD) from nozzle 3c to collector 4a is 50 to 600 mm. If it is less than 50 mm, the time for the molten polymer to fibrousize will be shortened, and it may not solidify completely. If it is more than 600 mm, the suction effect of the collector will decrease, making it difficult to form a stable web. A distance of 100 to 500 mm is preferable.

[0063] (4) Calendar processing process The resulting meltblown nonwoven fabric may be calendered to improve its mechanical strength, reduce its pore size, and for lamination with other substrates.

[0064] (5) Electrostatic treatment process If necessary, the meltblown nonwoven fabric may be subjected to electrostatic treatment such as corona discharge treatment. The electrostatic nonwoven fabric is 10 -11 ~10 -7 It has a charge amount of approximately Coulombs / cm² and can electrostatically capture fine particles.

[0065] (6) Hydrophilization treatment process Meltblown nonwoven fabrics may be subjected to hydrophilic treatment. Hydrophilic treatment can be carried out by monomer grafting, surfactant treatment, plasma treatment, etc. In the case of surfactant treatment, nonionic surfactants are preferred.

[0066] By optimizing the manufacturing conditions of meltblown nonwoven fabric, it is possible to create a meltblown nonwoven fabric with a mesh structure in which fibers are appropriately fused together, while also forming a bulky structure in the thickness direction without compromising the strength of the nonwoven fabric.

[0067] To achieve the above configuration, the polymer melting temperature is set to (polymer melting point + 100°C or higher), and the sum of the die temperature and the heated compressed air temperature (die temperature + heated compressed air temperature) is set to 670°C or higher. This increases the fusion points between fibers, and the tensile modulus in the MD direction when the test specimen is stretched by 2-4% is set to 4 N / mm². 2 More than 20N / mm 2 The following can be achieved. Furthermore, by setting the DCD to 130mm or more, it is possible to prevent excessive thickness and adjust the filling rate to 18% or less.

[0068] Although the meltblown nonwoven fabric and its manufacturing method have been described above with reference to preferred embodiments, the present invention is not limited to the above-described specific embodiments.

[0069] The polyamide nonwoven fabric of this disclosure has a fast water absorption rate, and when used as a liquid filter, it can achieve low pressure drop and good water permeability even without pre-wetting. When used as a battery separator, its high water retention rate leads to stable battery performance, and its fast water absorption rate leads to improved battery production speed. Furthermore, when used as a bacterial testing kit, its high water retention rate leads to stable product quality, and its fast water absorption rate results in good processability and ease of handling during use. Thus, the polyamide nonwoven fabric of this disclosure can be widely used as a fluid filter, battery separator, bacterial carrying medium for bacterial testing kits, clothing, medical bandages, and / or medical implants.

[0070] The following examples are for illustrative purposes only and are not intended to limit the technical scope of the present invention in any way. [Examples]

[0071] 1. Manufacturing of meltblown nonwoven fabrics Example 1 Nylon 6 resin with a relative viscosity of 3.0 was introduced into the raw material hopper of the melt-blown manufacturing apparatus. The melt-mixing temperature was set to 350°C, and the die temperature to 310°C. The distance between the die and collector was 140 mm, and 10 Nm of heated compressed air at 370°C was used. 3 Along with a flow rate of / min / m, resin is discharged into the atmosphere from a nozzle with a diameter of 0.4 mm, and the suction volume is 400 Nm. 3 Fibrous resin is continuously collected on a collector with a rotation speed of / min / m, and the collector's rotation speed is adjusted to achieve a basis weight of 70g / m². 2 Thickness 0.45mm, breathability 11.5cm 3 / cm 2 A melt-blown nonwoven fabric with a fiber diameter of 3.4 μm was obtained.

[0072] Example 2 Nylon 6 resin with a relative viscosity of 3.0 was introduced into the raw material hopper of the melt-blown manufacturing apparatus. The melt-mixing temperature was set to 350°C, and the die temperature to 310°C. The distance between the die and collector was 130 mm, and 10 Nm of heated compressed air at 360°C was used. 3Along with a flow rate of / min / m, resin is discharged into the atmosphere from a nozzle with a diameter of 0.4 mm, and the suction volume is 400 Nm. 3 Fibrous resin is continuously collected on a collector with a rotation speed of / min / m, and the collector's rotation speed is adjusted to achieve a basis weight of 70g / m². 2 Thickness 0.37mm, breathability 11.0cm 3 / cm 2 A melt-blown nonwoven fabric with a fiber diameter of 3.3 μm was obtained.

[0073] Example 3 Nylon 6 resin with a relative viscosity of 3.0 was introduced into the raw material hopper of the melt-blown manufacturing apparatus. The melt-mixing temperature was set to 350°C, and the die temperature to 310°C. The distance between the die and collector was 140 mm, and 10 Nm of heated compressed air at 360°C was used. 3 Along with a flow rate of / min / m, resin is discharged into the atmosphere from a nozzle with a diameter of 0.4 mm, and the suction volume is 400 Nm. 3 Fibrous resin is continuously collected on a collector with a rotation speed of / min / m, and the collector's rotation speed is adjusted to obtain a basis weight of 100g / m². 2 Thickness 0.64mm, breathability 7.8cm 3 / cm 2 A melt-blown nonwoven fabric with a fiber diameter of 3.5 μm was obtained.

[0074] Example 4 Nylon 6 resin with a relative viscosity of 3.0 was introduced into the raw material hopper of the melt-blown manufacturing apparatus. The melt-mixing temperature was set to 350°C, and the die temperature to 310°C. The distance between the die and collector was 300 mm, and 10 Nm of heated compressed air at 360°C was used. 3 Along with a flow rate of / min / m, resin is discharged into the atmosphere from a nozzle with a diameter of 0.4 mm, and the suction volume is 400 Nm. 3 Fibrous resin is continuously collected on a collector with a rotation speed of / min / m, and the collector's rotation speed is adjusted to obtain a basis weight of 100g / m². 2 Thickness 0.98mm, breathability 17.3cm 3 / cm 2 A meltblown nonwoven fabric with a fiber diameter of 4.0 μm was obtained.

[0075] Example 5 Into the raw material hopper of the melt blow production apparatus, nylon 6 resin with a relative viscosity of 3.0 was charged, and the melt kneading temperature was 350 °C and the die temperature was 310 °C. At a distance of 200 mm between the die and the collector, with heated compressed air at 360 °C of 10 Nm 3 / min / m, the resin was discharged into the atmosphere from a nozzle with a nozzle diameter of 0.4 mm, and fibrous resin was continuously collected on a collector with a suction volume of 400 Nm 3 / min / m. By adjusting the rotation speed of the collector, a melt blow nonwoven fabric with a basis weight of 30 g / m 2 , a thickness of 0.30 mm, an air permeability of 44.2 cm 3 / cm 2 / s, and a fiber diameter of 3.5 μm was obtained.

[0076] Comparative Example 1 Into the raw material hopper of the melt blow production apparatus, nylon 6 resin with a relative viscosity of 3.0 was charged, and the melt kneading temperature was 330 °C and the die temperature was 300 °C. At a distance of 110 mm between the die and the collector, with heated compressed air at 330 °C of 12 Nm 3 / min / m, the resin was discharged into the atmosphere from a nozzle with a nozzle diameter of 0.4 mm, and fibrous resin was continuously collected on a collector with a suction volume of 400 Nm 3 / min / m. By adjusting the rotation speed of the collector, a melt blow nonwoven fabric with a basis weight of 70 g / m 2 , a thickness of 0.33 mm, an air permeability of 9.9 cm 3 / cm 2 / s, and a fiber diameter of 3.6 μm was obtained.

[0077] Comparative Example 2 Into the raw material hopper of the melt blow production apparatus, nylon 6 resin with a relative viscosity of 3.0 was charged, and the melt kneading temperature was 330 °C and the die temperature was 300 °C. At a distance of 300 mm between the die and the collector, with heated compressed air at 300 °C of 12 Nm 3 / min / m, the resin was discharged into the atmosphere from a nozzle with a nozzle diameter of 0.4 mm, and fibrous resin was continuously collected on a collector with a suction volume of 400 Nm 3 / min / m. By adjusting the rotation speed of the collector, a melt blow nonwoven fabric with a basis weight of 30 g / m 2 , a thickness of 0.36 mm, an air permeability of 66.2 cm 3 / cm 2 / s, a melt-blown nonwoven fabric with a fiber diameter of 4.0 μm was obtained.

[0078] Comparative Example 3 Nylon 6 resin with a relative viscosity of 3.0 was charged into the raw material hopper of the melt-blow production apparatus, and the melt kneading temperature was 300 °C and the die temperature was 300 °C. At a distance of 170 mm between the die and the collector, 12 Nm of heated compressed air at 330 °C 3 / min / m, and the resin was discharged into the atmosphere from a nozzle with a nozzle diameter of 0.4 mm, and the fibrous resin was continuously collected on a collector with a suction volume of 400 Nm 3 / min / m, and the rotational speed of the collector was adjusted to obtain a basis weight of 30 g / m 2 , a thickness of 0.25 mm, and an air permeability of 43.8 cm 3 / cm 2 / s, a melt-blown nonwoven fabric with a fiber diameter of 4.0 μm was obtained.

[0079] 2. Measurement methods for various physical properties (1) Average fiber diameter The average fiber diameter was determined by measuring the fiber diameters of 10 fibers each at 10 arbitrary locations from an electron micrograph of the melt-blown nonwoven fabric up to an order of 0.1 μm in diameter and averaging them.

[0080] (2) Basis weight For 10 melt-blown nonwoven fabric test pieces of 100 mm × 100 mm, the mass [g] in the moisture equilibrium state at a temperature of 23 °C and a humidity of 50% was measured and averaged.

[0081] (3) Thickness For a melt-blown nonwoven fabric test piece of 100 mm × 100 mm, the thickness of the central portion hitting the center of gravity of the test piece was measured with a linear gauge equipped with a measuring head having a diameter of 2.5 cm and a load of 7 g / cm 2 , and the average of 10 measured values was determined.

[0082] (4) Filling ratio Filling ratio [%] = [basis weight [g / m 2 / (thickness [mm] × resin specific gravity [g / cm 3 × 10)] was determined by the formula.

[0083] (5) Air permeability Measurements were taken on 100mm x 100mm meltblown nonwoven fabric test specimens using a Frazier type testing machine in accordance with JIS L1096.

[0084] (6) Tensile strength and tensile elongation in the MD direction In accordance with JIS L1085 "Test Method for Nonwoven Fabric Cores," the tensile strength and elongation were measured when a 200mm length of nonwoven fabric was cut parallel to the MD direction (Machine Direction) and a 50mm width perpendicular to it. Both ends of the nonwoven fabric were clamped with chucks spaced 100mm apart, and the strength [N] and elongation [%] at the maximum load were measured when the fabric was pulled at a speed of 300mm / min.

[0085] (7) Tensile modulus in the MD direction When measuring the tensile strength and tensile elongation in the MD direction as described above, the tensile modulus was calculated from the slope of the stress-strain curve in the range where the elongation of the test specimen was 2-4%.

[0086] (8) Bursting strength The average value was obtained from three tests conducted using a Muhlen burst strength tester M2-LD manufactured by Toyo Seiki Co., Ltd., in accordance with JIS P8112:2008 "Paper - Bursting strength test method".

[0087] (9) Water retention rate For a 10cm square nonwoven fabric piece, the weight of the test piece before water absorption was measured. A 5g clip was then attached to one side of the test piece as a weight, and the test piece was gently dropped into the water so that the side that had been in contact with the collector during manufacturing (the net side) was in contact with the water surface, allowing it to absorb water for 30 seconds. After removing the test piece, it was suspended from a rod by the clip and left for 1 minute to dehydrate by natural fall, and the weight of the test piece after water absorption was measured. The water retention rate was measured using the following formula. Water retention rate [%] = (Weight after water absorption - Weight before water absorption) / Weight before water absorption × 100%

[0088] (10) Water suction speed The sample was cut into a rectangle 30 cm long in the MD direction and 2 cm wide in the CD direction. The top end was fixed so that the sheet was vertical, and the bottom end was immersed in deionized water to a depth of 5 mm. After 20 minutes, the height to which the water rose within the sample was determined.

[0089] (11) Apparent specific surface area of ​​meltblown nonwoven fabric Meltblown nonwoven fabric has an average fiber diameter R [μm] and a basis weight w [g / m²]. 2 ], thickness t [mm], resin specific gravity a [g / cm] 3 ] was used. Furthermore, pi was set to π, and 1m 2 We assumed a meltblown nonwoven fabric model in which only a few cylindrical fibers with radius r [μm] and fiber length 1 m exist. R = 2r. 2 The sum of the lateral surfaces of all cylindrical fibers present in the model nonwoven fabric is (4 × w) / (a ​​× R) [m 2 It can be expressed as ]. In this case, the areas of the top and bottom surfaces of the modeled cylinder are small compared to the area of ​​the sides, so they are not considered. Also, 1 m of this nonwoven fabric 2 The volume per unit area is t × 10, since the thickness is t [mm]. -3 [m 3 ]

[0090] For the meltblown nonwoven fabric assumed above, we introduced the concept of specific surface area as a pseudo-ideal. Normally, if the surface area of ​​an object is S and its volume is V, the specific surface area Sv per unit volume is expressed as Sv = S / V. In this relationship, S is the sum of the lateral surfaces of the cylindrical fibers mentioned above, which is (4 × w) / (a ​​× R) [m 2 ], where V is the volume of the nonwoven fabric, t × 10 -3 [m 3 Substituting ], we get Sv = (4 × w × 10 3 ) / (a×t×R)[m 2 / m 3 This was considered to be the pseudo-apparent specific surface area of ​​the meltblown nonwoven fabric. Apparent specific surface area of ​​meltblown nonwoven fabric = (4 × w × 10) 3 ) / (a×t×R)[m 2 / m 3 ]

[0091] (12) Water suction capacity (10) The value obtained from the water absorption rate was divided by the apparent specific surface area of ​​the meltblown nonwoven fabric calculated in (11), and multiplied by 1000. This was evaluated as the water absorption capacity. Water suction capacity = (Water suction rate [cm / 20 min]) / (Apparent specific surface area [m²]) 2 / m 3 ]) × 10 3

[0092] 3.Results As shown in Figure 3, in the meltblown nonwoven fabric of Example 5, fiber fusion points (arrows in the figure) and entanglement points are observed at a moderate frequency.

[0093] Table 1 shows that by comparing the polyamide nonwoven fabrics of Examples 1-5 and Comparative Examples 1-3, adjusting the melt-kneading temperature and heated compressed air temperature in the manufacturing conditions to a higher level, the polyamide nonwoven fabrics of Examples 1-5 have a filling density in the range of 8% to 18% and a tensile modulus of 4 N / mm² in the MD direction. 2 More than 20N / mm 2 The structure satisfies the following ranges. In addition, the polyamide nonwoven fabrics of Examples 1 to 5 all had a water retention rate of 400% or more and a water absorption rate of 10 cm / 20 minutes or more.

[0094] In the polyamide nonwoven fabric of Example 2, the packing density was higher than that of the polyamide nonwoven fabric of Example 1. Although the water retention rate was lower compared to the polyamide nonwoven fabric of Example 1, the water absorption rate was faster.

[0095] The polyamide nonwoven fabric of Example 3 had a higher basis weight than that of Example 1, and its water retention rate was slightly lower compared to the polyamide nonwoven fabric of Example 1.

[0096] In the polyamide nonwoven fabric of Example 4, the basis weight was increased and the thickness was increased compared to Example 1. As a result, the water retention rate increased, but the rate of water absorption decreased.

[0097] In the polyamide nonwoven fabric of Example 5, the basis weight was smaller and the thickness was thinner than in Example 1. The retention rate was as high as in Example 1, but the water absorption rate was lower.

[0098] In Comparative Example 1, the polyamide nonwoven fabric had a high filling density and a low water retention rate.

[0099] In Comparative Example 2, the polyamide nonwoven fabric had a low tensile modulus in the MD direction and low nonwoven fabric strength, making it impossible to measure the bursting strength, and the water absorption rate was slow.

[0100] In Comparative Example 3, the polyamide nonwoven fabric had a low tensile modulus in the MD direction, resulting in slow water absorption.

[0101] The results from Comparative Example 3 confirmed that even with an appropriate filling density, a low elastic modulus results in poor water absorption performance, and that simply reducing the thickness does not allow for both water retention and water absorption.

[0102] [Table 1]

Claims

1. A meltblown nonwoven fabric containing polyamide resin fibers having a water retention rate of 400% or more, a water absorption rate of 10 cm / 20 minutes or more, and a water absorption capacity value of 0.05 or more according to the following formula (1). Water suction capacity = (Water suction rate [cm / 20 min]) / (Apparent specific surface area [m²]) ２ / m ３ ]) × 10 ３ (1)

2. The tensile modulus in the MD direction is 4 N / mm when the filling density is 8% or more and 18% or less, and the test specimen is elongated by 2-4%. ２ Above, 20N / mm ２ The meltblown nonwoven fabric according to claim 1, which is as follows:

3. The meltblown nonwoven fabric according to claim 1 or 2, wherein 95% by mass or more of the resin constituting the polyamide resin fibers is nylon 6.

4. Weight: 50g / m ２ A meltblown nonwoven fabric according to claim 1 or 2, wherein the burst strength per unit area is 90 kPa or more.

5. A meltblown nonwoven fabric according to claim 1 or 2, used in fluid filters, battery separators, or as a medium for carrying bacteria in bacterial testing kits.

Images