Melt-blown non-woven fabric

Abstract

This meltblown nonwoven fabric is a nonwoven fabric with an average fiber diameter of 4. Micrometers or less and with a linear fiber rate of 35% or higher in each. The first direction follows the plane of the meltblown nonwoven fabric and has a rate of straight-line fiber orientation. The highest point and the second direction perpendicular to the first direction;

Description

Meltblown nonwoven fabric

[0001] This invention relates to a meltblown nonwoven fabric produced by the meltblown method.

[0002] Meltblown nonwoven fabrics are nonwoven fabrics manufactured by the meltblown method, and are known to have high water resistance because the distance between fibers is small due to the dense overlapping of fine fibers (Patent Document 1).

[0003] The melt-blown method is a method that comprises a spinning step in which a molten thermoplastic resin composition is blown out of a die having multiple nozzles with a high-temperature, high-speed airflow to be stretched into fibers, and a deposition step in which the obtained fibers are deposited on a collection surface and fused together, and is suitable for producing fine fibers.

[0004] (Patent Document 1) International Publication No. 2012 / 102398

[0005] The present invention provides a meltblown nonwoven fabric having an average fiber diameter of 4 μm or less, wherein the meltblown nonwoven fabric has a first direction along the plane of the meltblown nonwoven fabric in which the straightness of the fibers is highest, and a second direction perpendicular to the first direction. In the embodiment, the straightness of the fibers in both the first direction and the second direction is 35% or more.

[0006] In the embodiment, the meltblown nonwoven fabric satisfies one or more conditions selected from (I), (II), and (III) below: (I) The straightness rate of the fibers in the first direction and the second direction is 35% or more. (II) The ratio of the straightness rate of the fibers in the first direction to the straightness rate of the fibers in the second direction (straightness rate of the fibers in the first direction / straightness rate of the fibers in the second direction) is 1 or more and 2.5 or less. (III) The water pressure resistance of the meltblown nonwoven fabric is 100 mmH2O or more and 10000 mmH2O or less, and optionally, the water pressure resistance retention rate when the meltblown nonwoven fabric is deformed in the second direction is 85% or more. In the embodiment, the meltblown nonwoven fabric of (I) has a ratio of the straightness rate of the fibers in the first direction to the straightness rate of the fibers in the second direction (straightness rate of the fibers in the first direction / straightness rate of the fibers in the second direction) of 1 or more and 2.5 or less. In the embodiment, the meltblown nonwoven fabric of (I) or (II) has a water pressure resistance of 100 mmH2O or more and 10,000 mmH2O or less. In the embodiment, the meltblown nonwoven fabric of (I) or (II) has a water pressure resistance retention rate of 85% or more when the meltblown nonwoven fabric is deformed in the second direction. In the embodiment, the meltblown nonwoven fabric has a filling rate of 3% or more and / or 30% or less. In the embodiment, the heat of fusion of the fibers is greater than 5 mJ / mg and / or less than 94 mJ / mg.

[0007] Furthermore, the present invention provides a meltblown nonwoven fabric having an average fiber diameter of 0.1 μm or more and 4 μm or less, wherein the straightness of the fibers in a first direction along the plane of the meltblown nonwoven fabric and the straightness of the fibers being highest, and in a second direction perpendicular to the first direction, are both 35% or more, the ratio of the straightness of the fibers in the first direction to the straightness of the fibers in the second direction (straightness of the fibers in the first direction / straightness of the fibers in the second direction) is 1 or more and 2.5 or less, the filling density is 3% or more and 30% or less, and the heat of fusion of the fibers is greater than 5 mJ / mg and less than 94 mJ / mg.

[0008] In the embodiment, the meltblown nonwoven fabric has a ratio of the straightness of fibers in the first direction to the straightness of fibers in the second direction (straightness of fibers in the first direction / straightness of fibers in the second direction) of 1 or more and 1.9 or less. In the embodiment, the first direction, the second direction, and the straightness of fibers in the meltblown nonwoven fabric are determined by the following procedure (a) to (g). (a) Using a desktop scanning electron microscope (JCM-6000Plus, manufactured by JEOL Ltd.), acquire an SEM image with an observation magnification of 3000 / average fiber diameter (μm), with the central part of the meltblown nonwoven fabric as the observation position, and set the direction of the long side of the SEM image to 0°. However, if the nonwoven fabric to be measured is approximately rectangular in shape, set the direction of the long side of the nonwoven fabric to 0° and acquire the SEM image so that the direction of the long side of the SEM image is parallel to 0°. (b) Acquire an SEM image by rotating the field of view by θ°, and then further rotate the field of view by θ° increments to acquire X SEM images from 0° to (180-θ)°, where the number of images X = (180° / θ°) - 1. (c) Perform the operations of procedures (a) and (b) at seven observation points different from the observation position in procedure (a) above, and acquire X sheets × 8 points of SEM images, provided that the eight observation points are within a 40 mm × 20 mm area in the center of the meltblown nonwoven fabric and are separated by at least 10 mm from each other. (d) For each of the SEM images obtained in procedures (a) to (c) above, calculate the straightness of the fibers at each angle from 0° to (180-θ)° using the following formula (1), round to the nearest whole number, and take the average value of the eight points as the straightness of the fibers at each angle. (e) Of the straightness of the fibers at each angle calculated in procedure (d) above, the angle with the largest straightness of the fibers is designated as the first direction, and the straightness of the fibers with the largest value is designated as the straightness of the fibers in the first direction. (f) The direction perpendicular to the first direction is designated as the second direction. (g) At each of the eight observation points, acquire an SEM image in which the direction of the long side of the SEM image is parallel to the second direction, calculate the straightness of the fiber in the second direction using the following formula (1), obtain the average value of the eight points, and round to the nearest whole number. Here, N(0), N(1), and N(2) represent the following, respectively: N(0) is the number of fibers extending continuously from one end to the other in the long-side direction of the SEM image; N(1) is the number of fibers intersecting one end in the long-side direction; and N(2) is the number of fibers intersecting the other end in the long-side direction. In the embodiment, the meltblown nonwoven fabric has a filling density of 6% or more and / or 15% or less. In the embodiment, the meltblown nonwoven fabric has a fabricity index of 30 or more and / or 300 or less, and is arbitrarily 200 or less. In the embodiment, the heat of fusion of the fibers is 20 mJ / mg or more and / or 80 mJ / mg or less.

[0009] The present invention also provides a leak-proof sheet having the melt-blown nonwoven fabric. The present invention also provides an absorbent article comprising a liquid-permeable surface sheet disposed on the skin-facing side, a liquid-leak-proof back sheet disposed on the non-skin-facing side, and an absorbent disposed between these sheets, wherein the back sheet is the leak-proof sheet.

[0010] Furthermore, the present invention provides a method for producing a meltblown nonwoven fabric, comprising a spinning step in which a molten thermoplastic resin composition is extruded from a nozzle and formed into fibers by an airflow. In the embodiment, the production method produces a meltblown nonwoven fabric having an average fiber diameter of 4 μm or less. In the embodiment, the temperature of the airflow is set to be above the melting point of the thermoplastic resin composition. In the embodiment, the heat of fusion of the thermoplastic resin composition is greater than 5 mJ / mg and / or less than 94 mJ / mg.

[0011] In the embodiment, the temperature of the airflow is set to 260°C or lower, optionally 250°C or lower, optionally 240°C or lower. In the embodiment, the manufacturing method includes in the thermoplastic resin composition two or more polyolefins with different heats of fusion. In the embodiment, the thermoplastic resin composition contains a polyolefin comprising a first polyolefin having a heat of fusion of 94 mJ / mg or more, and / or a second polyolefin having a heat of fusion of less than 94 mJ / mg. In the embodiment, the second polyolefin includes one or more selected from low-crystalline polypropylene with an MFR of 400 g / 10 min or more, low-crystalline polypropylene with an MFR of less than 400 g / 10 min, and polypropylene-based elastomers with an MFR of less than 400 g / 10 min. In the embodiment, the polyolefin includes one or more selected from α-olefin homopolymers and copolymers of two or more α-olefins. In the embodiment, the α-olefin homopolymer comprises one or more selected from highly crystalline polyolefins and low-crystalline polyolefins. In the embodiment, the copolymer of two or more α-olefins comprises one or more selected from low-crystalline olefin elastomers and amorphous olefin elastomers. In the embodiment, the first polyolefin comprises a highly crystalline polyolefin, and the melt flow rate of the highly crystalline polyolefin is 100 g / 10 min or more and / or 2000 g / 10 min or less. In the embodiment, the first polyolefin comprises a highly crystalline polyolefin, and the melt flow rate of the highly crystalline polyolefin is 300 g / 10 min or more and / or 1800 g / 10 min or less. In the embodiment, the content of the second polyolefin relative to the total amount of the first polyolefin and the second polyolefin is 50% by mass or more and / or 70% by mass or less when the second polyolefin is a low-crystalline polypropylene with an MFR of 400 g / 10 min or more, and 10% by mass or more and / or 15% by mass or less when the second polyolefin is a low-crystalline polypropylene with an MFR of less than 400 g / 10 min or a polypropylene-based elastomer with an MFR of less than 400 g / 10 min.In the embodiment, the manufacturing method further comprises a deposition step of depositing the fibers obtained in the spinning step onto a collection surface. In the embodiment, the manufacturing method sets the distance between the nozzle and the collection surface to 400 mm or less, optionally 300 mm or less, optionally 150 mm or less, and / or 50 mm or more. In the embodiment, the manufacturing method includes a heating step of heating the fibers obtained in the spinning step before they are deposited onto the collection surface.

[0012] Furthermore, the present invention provides a meltblown nonwoven fabric manufactured by the above manufacturing method.

[0013] Figure 1 is a schematic diagram showing an example of an SEM image of a meltblown nonwoven fabric according to the present invention. Detailed description of the invention

[0014] Generally, the direction in which the nonwoven fabric is transported during the manufacturing of meltblown nonwoven fabric is called the MD direction (Machine Direction), and the direction perpendicular to the MD direction is called the CD direction (Cross Direction).

[0015] The inventors have found that while meltblown nonwoven fabrics have sufficient strength in the MD direction, their strength in the CD direction is low. Therefore, when a tensile load is applied to a meltblown nonwoven fabric, for example, in the CD direction, deformation occurs, causing the distance between fibers to widen, creating gaps and potentially significantly reducing water resistance. Generally, when meltblown nonwoven fabrics are used in areas where deformation due to load is likely, they are typically laminated with a high-strength spunbond nonwoven fabric or air-through nonwoven fabric to cover the meltblown nonwoven fabric.

[0016] This invention relates to a meltblown nonwoven fabric that suppresses the reduction in water pressure resistance due to deformation.

[0017] The meltblown nonwoven fabric according to the present invention can suppress the decrease in water pressure resistance due to deformation.

[0018] The meltblown nonwoven fabric according to the present invention has an average fiber diameter of 4 μm or less. The smaller the average fiber diameter, the better the water pressure resistance in the low packing density region. The average fiber diameter is preferably 3.6 μm or less, more preferably 3.2 μm or less, even more preferably 3 μm or less, particularly preferably 2.5 μm or less, and especially preferably 2 μm or less. Furthermore, the average fiber diameter is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. Specifically, the average fiber diameter is preferably 0.1 μm or more and 4 μm or less, more preferably 0.2 μm or more and 3.6 μm, even more preferably 0.3 μm or more and 3.2 μm or less, even more preferably 0.3 μm or more and 3 μm or less, particularly preferably 0.3 μm or more and 2.5 μm or less, and especially preferably 0.3 μm or more and 2 μm or less.

[0019] It is believed that a meltblown nonwoven fabric with superior strength is obtained when the average fiber diameter is above this lower limit, and superior water pressure resistance is obtained when it is below this upper limit. The average fiber diameter of the meltblown nonwoven fabric according to the present invention is calculated as follows. First, a scanning electron microscope (SEM) image is taken in a field of view in which 20 to 60 fibers are visible. The fiber diameter of each fiber in the field of view is measured once, and the average value is calculated. The average value is rounded to the nearest 10 nm to obtain the average fiber diameter. The unit of the average fiber diameter is μm.

[0020] The meltblown nonwoven fabric according to the present invention has a first direction along the plane of the meltblown nonwoven fabric in which the straightness of the fibers is highest, and a second direction perpendicular to the first direction. The straightness of the fibers in the first direction and the straightness of the fibers in the second direction are preferably 35% or more, more preferably 38% or more, even more preferably 40% or more, and also preferably 90% or less, more preferably 85% or less, and even more preferably 80% or less. Specifically, they are preferably 35% to 90%, more preferably 38% to 85%, and even more preferably 40% to 80%. The first direction is preferably the MD direction during manufacturing. The second direction is preferably the CD direction during manufacturing. By having the straightness of the fibers in the first direction and the straightness of the fibers in the second direction both be above this lower limit, gaps are less likely to form between the fibers when deformed in either the first or second direction, and the decrease in water pressure resistance is suppressed.

[0021] The meltblown nonwoven fabric according to the present invention has a first direction which is along the plane of the meltblown nonwoven fabric and has the highest straightness of fiber propagation, and a second direction which is perpendicular to the first direction. The ratio (A / B) of the straightness of fiber propagation in the first direction (A) to the straightness of fiber propagation in the second direction (B) is preferably 1 or more, preferably 2.5 or less, more preferably 2.1 or less, and even more preferably 1.9 or less. Specifically, the ratio (A / B) is preferably 1 or more and 2.5 or less, more preferably 1 or more and 2.1 or less, and even more preferably 1 or more and 1.9 or less. By keeping the ratio (A / B) below this upper limit, gaps are less likely to form between fibers when deformed in either the first or second direction, and the decrease in water pressure resistance is suppressed.

[0022] The meltblown nonwoven fabric according to the present invention preferably has a water pressure resistance of 100 mmH2O or more, and more preferably 10,000 mmH2O or less. When the meltblown nonwoven fabric is deformed in a second direction perpendicular to the first direction which is along the plane of the meltblown nonwoven fabric and has the highest fiber straightness, the water pressure resistance retention rate is preferably 85% or more, more preferably 88% or more, even more preferably 90% or more, and practically 100% or less. The meltblown nonwoven fabric according to the present invention has a water pressure resistance retention rate above this lower limit when deformed in the second direction, so that gaps are less likely to form between fibers regardless of whether it is deformed in the first or second direction. For this reason, even if deformation occurs when used without lamination with spunbond nonwoven fabric or air-through nonwoven fabric, the decrease in water pressure resistance is suppressed.

[0023] The first direction in which the straightness of the fibers of the meltblown nonwoven fabric according to the present invention is highest, the second direction perpendicular to the first direction, and the straightness of the fibers in the first direction (A) and the straightness of the fibers in the second direction (B) can be determined by the following procedure (a) to (g). Note that the "first direction in which the straightness of the fibers is highest" of the meltblown nonwoven fabric according to the present invention means the direction determined by the following procedure (a) to (g), and may differ from the direction in which the straightness of the fibers is actually highest. (a) Using a desktop scanning electron microscope (JCM-6000Plus, manufactured by JEOL Ltd.), the observation magnification is set to 3000 / average fiber diameter (μm), and an SEM image is acquired with the central part of the meltblown nonwoven fabric as the observation position, with the direction of the long side of the SEM image set to 0°. If the nonwoven fabric to be measured is approximately rectangular in shape, the long side of the nonwoven fabric is set to 0°, and an SEM image is acquired so that the direction of the long side of the SEM image is parallel to 0°. (b) Rotate the field of view by θ° and acquire an SEM image. Similarly, rotate the field of view by θ° increments to acquire X SEM images from 0° to (180-θ)°. The number of images X = (180° / θ°) - 1. (c) At seven observation points different from the observation position in procedure (a) above, perform the operations in procedures (a) and (b) above, respectively, to acquire X images × 8 points of SEM images. The eight observation points are within a 40 mm × 20 mm area in the center of the meltblown nonwoven fabric, and are separated by at least 10 mm from each other. (d) For each of the SEM images obtained in procedures (a) to (c) above, calculate the straightness of the fibers at each angle from 0° to (180-θ)° using the following formula (1), and round to the nearest whole number. Find the average value of the eight points and use it as the straightness of the fibers at each angle. (e) Of the straightness rates of each angle calculated in the above procedure (d), the angle with the largest straightness rate is designated as the first direction, and the straightness rate of the fiber in the first direction with the largest value is designated as the straightness rate (A) of the fiber in the first direction. (f) The direction perpendicular to the first direction is designated as the second direction. (g) At the eight observation points, an SEM image is obtained in which the direction of the long side of the SEM image is parallel to the second direction, and the straightness rate (B) of the fiber in the second direction is calculated for each point using the following formula (1), and the average value of the eight points is obtained and rounded to the nearest whole number. Here, N(0), N(1), and N(2) represent the following, respectively: N(0) is the number of fibers that extend continuously from one end to the other in the long-side direction of the SEM image; N(1) is the number of fibers that intersect at one end in the long-side direction; and N(2) is the number of fibers that intersect at the other end in the long-side direction. Fibers that reach one end in the long-side direction of the SEM image are defined as "fibers that intersect at one end in the long-side direction." The same applies to the other end.

[0024] The method for calculating the straightness rate of the fibers in the above procedure (d) will be explained in detail with reference to Figure 1. Figure 1 is a schematic diagram showing an example of an SEM image where the long side direction is parallel to the first direction. Note that in Figure 1, the fibers are shown as straight lines for the sake of illustration, but actual fibers are not necessarily straight. Also, the number of fibers shown in the SEM image may differ from the actual number. In the SEM image shown in Figure 1, the number of fibers intersecting at the left end of the long side direction is 6 (intersections a to f), and the number of fibers intersecting at the right end of the long side direction is 6 (intersections g to l). In addition, there are a total of 5 fibers that extend continuously from the left end to the right end of the long side direction: straight lines ah, ci, dg, el, and fk. Therefore, the straightness rate (A) (%) in the first direction = [5 × 2 / (6 + 6)] × 100 = 83%.

[0025] In the above procedure (b), the angle θ° when changing the field of view can be any value, but it is preferably 15° or less, more preferably 10° or less, and even more preferably 5° or less. Furthermore, if the above measurement is performed multiple times, the "direction with the highest straightness rate" determined may differ due to differences in observation position, angle θ, and other conditions. In that case, the direction with the highest straightness rate among the multiple measurement results can be adopted as the first direction.

[0026] The meltblown nonwoven fabric according to the present invention has a fiber straightness rate of 35% or more in both the first direction, where the fiber straightness rate is highest, and the second direction perpendicular thereto. As a result, gaps are less likely to form between fibers even when deformed, and a decrease in water pressure resistance can be suppressed. Furthermore, even when the meltblown nonwoven fabric according to the present invention is used without lamination with spunbond nonwoven fabric or air-through nonwoven fabric and deformation occurs, the decrease in water pressure resistance is suppressed.

[0027] The decrease in water pressure resistance due to deformation of the meltblown nonwoven fabric according to the present invention can be evaluated by the ratio of the water pressure resistance after deformation to the water pressure resistance before deformation (water pressure retention rate). The water pressure resistance and water pressure retention rate are measured by the method described later. The meltblown nonwoven fabric may be integrated with a base material such as a spunbond nonwoven fabric or an air-through nonwoven fabric by thermal embossing. The integrated meltblown nonwoven fabric is stretched in its integrated state, and then the water pressure resistance is measured. If the meltblown nonwoven fabric is integrated with a resin film by thermal embossing, only the film in the area that has not been embossed is removed and used as the measurement target.

[0028] The meltblown nonwoven fabric according to the present invention can be obtained by adjusting the heat of fusion of the thermoplastic resin composition constituting the fibers, adjusting the airflow temperature during the spinning process, or heating the fibers after the spinning process but before the deposition process. The airflow temperature during the spinning process and the heating of the fibers will be described later. The thermoplastic resin composition is a mixture containing one or more thermoplastic resins and, if necessary, other components as appropriate.

[0029] From the viewpoint of spinnability, the heat of fusion of the thermoplastic resin composition is preferably greater than 5 mJ / mg, more preferably 10 mJ / mg or more, and particularly preferably 20 mJ / mg or more. Furthermore, from the viewpoint of obtaining soft fibers and thinning the fibers in a low-temperature hot air range, it is preferably less than 94 mJ / mg, more preferably 90 mJ / mg or less, even more preferably 80 mJ / mg or less, even more preferably 75 mJ / mg or less, especially preferably 45 mJ / mg or less, and particularly preferably 35 mJ / mg or less.

[0030] Specifically, the heat of fusion is preferably greater than 5 mJ / mg and less than 94 mJ / mg, more preferably 10 mJ / mg or more and 90 mJ / mg or less, still more preferably 20 mJ / mg or more and 80 mJ / mg or less, still more preferably 20 mJ / mg or more and 75 mJ / mg or less, particularly preferably 20 mJ / mg or more and 45 mJ / mg or less, and most preferably 20 mJ / mg or more and 35 mJ / mg or less.

[0031] The heat of fusion is an index indicating the amount of crystalline regions in the thermoplastic resin composition, that is, flexibility. The heat of fusion of the thermoplastic resin composition can be made within a desired range by adjusting the thermoplastic resin used and its content. The heat of fusion of the thermoplastic resin composition can be determined by collecting a 1 mg measurement piece from the central part of the melt-blown nonwoven fabric and using the method described below.

[0032] If the heat of fusion is less than the above upper limit, the proportion of amorphous regions present in the fibers increases. As a result, the fibers become softer and the orientation that occurs during the spinning process is suppressed. The orientation of the fibers will be described later. If the heat of fusion is greater than the above lower limit, the fibers become softer and orientation is less likely to occur. On the other hand, if it is less than the above upper limit, there are sufficiently many crystalline regions present in the fibers, the fusion between the fibers is suppressed, the distance between the fibers is narrowed, and the water pressure resistance can be improved.

[0033] The thermoplastic resin composition may contain a thermoplastic resin having a heat of fusion within a desired range alone. Also, two or more thermoplastic resins having different heats of fusion can be mixed so that the heat of fusion is within a desired range. When using a plurality of thermoplastic resins, a thermoplastic resin having a heat of fusion greater than or equal to the upper limit of the desired range and a thermoplastic resin having a heat of fusion less than or equal to the lower limit of the desired range may be mixed so that the heat of fusion is within the desired range, or a plurality of thermoplastic resins each having a heat of fusion within the desired range may be mixed.

[0034] As the thermoplastic resin, for example, polyolefin, polyester, polyether ether ketone, polyphenylene sulfide, polyamide, etc. can be used. Among them, polyolefin or polyester is preferable, and polyolefin is particularly preferable. As long as the heat of fusion is within the desired range, one of these thermoplastic resins may be used alone, or two or more of them may be used in combination.

[0035] It is preferable that 70% by mass or more of the thermoplastic resin composition is polyolefin. More preferably, polyolefin occupies 80% by mass or more of the thermoplastic resin composition, and still more preferably, it occupies 90% by mass or more.

[0036] As the polyolefin, a homopolymer of α-olefin or a copolymer of two or more α-olefins can be used. These may be used alone or in combination of two or more. As the polyolefin, those obtained by copolymerizing α-olefin with any one of unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, esters of these unsaturated carboxylic acids, and acid anhydrides can also be used.

[0037] The α-olefin preferably has 2 to 20 carbon atoms, and more preferably 2 to 10 carbon atoms. As the α-olefin, propylene, ethylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, etc. are preferable, propylene or ethylene is more preferable, and propylene is most preferable.

[0038] As the homopolymer of α-olefin, highly crystalline polyolefin or lowly crystalline polyolefin can be used. The highly crystalline polyolefin is a polyolefin having a high stereoregularity of α-olefin. Specific examples of the highly crystalline polyolefin include highly crystalline polypropylene such as isotactic polypropylene and syndiotactic polypropylene; highly crystalline polyethylene such as high-density polyethylene and medium-density polyethylene, etc.

[0039] Highly crystalline polypropylene, commonly used in meltblown nonwovens, has a heat of fusion value exceeding 94 mJ / mg and is a hard resin with many crystalline regions. During the spinning process, shear flow is generated on the spinning line, and rigid fibers with many crystalline regions tend to orient themselves in the direction of this airflow. Since this airflow is blown onto a collection surface driven in the MD direction, it is thought that the fibers accumulate on the collection surface with their orientation direction aligned with the MD direction. Therefore, by making the heat of fusion value of the thermoplastic resin composition constituting the fibers less than 94 mJ / mg, many flexible amorphous regions are present in the fibers, making it less likely for fibers to orient themselves according to the shear direction. As a result, it is thought that the nonwoven fabric accumulated on the collection surface will have less fiber orientation in the MD direction and a higher straightness in the CD direction.

[0040] The heat of fusion of highly crystalline polyolefin is preferably greater than 94 mJ / mg, more preferably 96 mJ / mg or more, even more preferably 98 mJ / mg or more, and also preferably less than 120 mJ / mg, more preferably 115 mJ / mg or less, and even more preferably 110 mJ / mg or less. Specifically, it is preferably greater than 94 mJ / mg and less than 120 mJ / mg, more preferably 96 mJ / mg or more and 115 mJ / mg or less, and even more preferably 98 mJ / mg or more and 110 mJ / mg or less.

[0041] The highly crystalline polyolefin preferably has a melt flow rate (MFR) (230°C) of 100 g / 10 min or more, more preferably 300 g / 10 min or more, more preferably 2000 g / 10 min or less, and more preferably 1800 g / 10 min or less. Specifically, it is preferably 100 g / 10 min or more and 2000 g / 10 min or less, and more preferably 300 g / 10 min or more and 1800 g / 10 min or less. The MFR is measured at a load of 2.16 kg and a temperature of 230°C according to JIS K7210. When the MFR is below this upper limit, the fluidity of the resin during the spinning process is not too high, suppressing yarn breakage and making it easier to realize fine fibers. On the other hand, when the MFR is above this lower limit, the resin has fluidity, the fibers can be sufficiently stretched during the spinning process, and the fiber diameter can be made fine.

[0042] The highly crystalline polyolefin preferably has a weight-average molecular weight (Mw) of 5,000 or more, more preferably 10,000 or more, even more preferably 15,000 or more, and also preferably 500,000 or less, more preferably 200,000 or less, and even more preferably 150,000 or less. Specifically, it is preferably 5,000 to 500,000, more preferably 10,000 to 200,000, and even more preferably 15,000 to 150,000. When the weight-average molecular weight is above this lower limit, the polymer chains intertwine strongly during the spinning process, preventing yarn breakage and enabling the creation of fine fibers. On the other hand, when the weight-average molecular weight is below this upper limit, the polymer chains do not intertwine too strongly, allowing the fibers to be sufficiently stretched during the spinning process and enabling the creation of finer fibers.

[0043] The highly crystalline polyolefin preferably has a molecular weight distribution (average molecular weight (Mw) / number-average molecular weight (Mn)) of 1.1 or higher, more preferably 1.5 or higher, even more preferably 2 or higher, and also preferably 5 or lower, more preferably 4 or lower, and even more preferably 3.5 or lower. Specifically, it is preferably 1.1 to 5, more preferably 1.5 to 4, and even more preferably 2 to 3.5.

[0044] Low-crystallinity polyolefins are polyolefins with low stereoregularity of the α-olefin group. Specific examples of low-crystallinity polyolefins include low-crystallinity polypropylenes such as atactic polypropylene and low-stereoregularity polypropylene; and low-crystallinity polyethylenes such as low-density polyethylene and linear low-density polyethylene. Low-stereoregularity polypropylene can be obtained by polymerizing propylene using a known metaceron catalyst.

[0045] The heat of fusion of the low-crystalline polyolefin is preferably greater than 0 mJ / mg, more preferably 3 mJ / mg or more, even more preferably 5 mJ / mg or more, and also preferably less than 94 mJ / mg, more preferably 85 mJ / mg or less, and even more preferably 70 mJ / mg or less. Specifically, it is preferably greater than 0 mJ / mg and less than 94 mJ / mg, more preferably 3 mJ / mg or more and 85 mJ / mg or less, and even more preferably 5 mJ / mg or more and 70 mJ / mg or less.

[0046] The low-crystalline polyolefin preferably has an MFR (at 230°C) of 100 g / 10 min or more, more preferably 1000 g / 10 min or more, even more preferably 1800 g / 10 min or more, and also preferably 2500 g / 10 min or less, more preferably 2300 g / 10 min or less, and even more preferably 2100 g / 10 min or less. Specifically, it is preferably 100 g / 10 min or more and 2500 g / 10 min or less, more preferably 1000 g / 10 min or more and 2300 g / 10 min or less, and even more preferably 1800 g / 10 min or more and 2100 g / 10 min or less. The MFR is measured at a load of 2.16 kg and a temperature of 230°C according to JIS K7210.

[0047] The low-crystalline polyolefin preferably has a weight-average molecular weight (Mw) of 5,000 or more, more preferably 20,000 or more, even more preferably 30,000 or more, and also preferably 150,000 or less, more preferably 70,000 or less, and even more preferably 50,000 or less. Specifically, it is preferably 5,000 to 150,000, more preferably 20,000 to 70,000, and even more preferably 30,000 to 50,000.

[0048] Copolymers of two or more α-olefins are low-crystallinity or amorphous olefin-based elastomers. Random copolymers, block copolymers, graft copolymers, or alternating copolymers can be used as α-olefin copolymers. In the case of block copolymers, it is preferable that the α-olefins are bonded in an atactic structure. Hereinafter, copolymers of two or more α-olefins will be referred to as olefin-based elastomers.

[0049] The olefin-based elastomer has a heat of fusion greater than 0 mJ / mg and less than 94 mJ / mg, preferably 3 mJ / mg or more, more preferably 5 mJ / mg or more, preferably 90 mJ / mg or less, and more preferably 85 mJ / mg or less.

[0050] In addition to α-olefins, olefin-based elastomers may optionally contain at least one monomer selected from the group consisting of polyene compound units such as butadiene, isoprene, ethylidene norbornene, and dicyclopentadiene, cyclic olefin units, and vinyl aromatic compound units.

[0051] Specific examples of olefin-based elastomers include, for example, propylene-ethylene copolymer, propylene-ethylene-1-butene copolymer, propylene-1-butene copolymer, propylene-ethylene-cyclic olefin copolymer, propylene-ethylene-butadiene copolymer, and propylene-1-butene-styrene copolymer. Among these copolymers, propylene-ethylene copolymer or propylene-ethylene-1-butene copolymer is the most preferred. One of these can be used alone, or two or more can be used in combination.

[0052] The olefin-based elastomer preferably has an MFR (at 230°C) of 10 g / 10 min or more, more preferably 300 g / 10 min or more, preferably 2000 g / 10 min or less, and more preferably 1800 g / 10 min or less. The MFR is measured at a load of 2.16 kg and a temperature of 230°C according to JIS K7210.

[0053] The olefin-based elastomer preferably has a molecular weight distribution (weight-average molecular weight (Mw) / number-average molecular weight (Mn)) of 1.1 or higher, more preferably 1.3 or higher, even more preferably 1.5 or higher, and also preferably 5 or lower, more preferably 4 or lower, and even more preferably 3.5 or lower.

[0054] Olefin elastomers can be produced using polymerization catalysts such as known Ziegler-Natta type catalysts or single-site catalysts (e.g., metallocene catalysts).

[0055] The thermoplastic resin composition preferably contains a highly crystalline polyolefin and a low-crystalline polyolefin or polyolefin-based elastomer.

[0056] The thermoplastic resin composition preferably contains a mixture of a first polyolefin having a heat of fusion of 94 mJ / mg or more and a second polyolefin having a heat of fusion of less than 94 mJ / mg.

[0057] In melt-blown spinning, fibers are formed by stretching the molten resin. Considering stringability and suppression of yarn breakage, it is particularly preferable that the thermoplastic resin composition contains a mixture of highly crystalline polypropylene, which is commonly used in melt-blown spinning and has a heat of fusion of 94 mJ / mg or more, and low-crystalline polypropylene or polypropylene-based elastomer, which has a heat of fusion of less than 94 mJ / mg.

[0058] Preferred specific examples of the second polyolefin include highly fluid low-crystalline polypropylene with an MFR of 400 g / 10 min or more, low-crystalline polypropylene with an MFR of less than 400 g / 10 min, and low-flow polypropylene-based elastomers with an MFR of less than 400 g / 10 min.

[0059] The content of highly fluid, low-crystalline polypropylene with an MFR of 400 g / 10 min or more is preferably 90% by mass or less of the total thermoplastic resin composition, more preferably 80% by mass or less, and even more preferably 70% by mass or less. The content of highly fluid, low-crystalline polypropylene is preferably 3% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, and especially preferably 50% by mass or more. Specifically, it is preferably 3% by mass or more and 90% by mass or less, more preferably 10% by mass or more and 80% by mass or less, even more preferably 20% by mass or more and 70% by mass or less, and especially preferably 50% by mass or more and 70% by mass or less.

[0060] If the content of highly fluid, low-crystalline polypropylene is below this upper limit, the amorphous regions within the fibers will not become too numerous, suppressing fusion between fibers, reducing the distance between fibers, and improving water pressure resistance. On the other hand, if the content of highly fluid, low-crystalline polypropylene is above this lower limit, there will be sufficient amorphous regions within the fibers, making them softer and less prone to orientation during the spinning process.

[0061] The content of low-crystalline polypropylene or polypropylene-based elastomer with an MFR of less than 400 g / 10 min is preferably 30% by mass or less, more preferably less than 30% by mass, even more preferably 20% by mass or less, and especially preferably 15% by mass or less of the total thermoplastic resin composition. The content of polypropylene-based elastomer is preferably 3% by mass or more, more preferably 5% by mass or more, especially preferably 10% by mass or more, particularly preferably 20% by mass or more, more specifically preferably 3% by mass or more and 30% by mass or less, more preferably 3% by mass or more and less than 30% by mass, even more preferably 5% by mass or more and 20% by mass or less, particularly preferably 10% by mass or more and 20% by mass or less, especially preferably 20% by mass or more and 15% by mass or less, and most preferably 10% by mass or more and 15% by mass or less.

[0062] Generally, low-crystallinity polypropylene with an MFR of less than 400 g / 10 min and polypropylene-based elastomers with an MFR of less than 400 g / 10 min have lower fluidity compared to polypropylene resins for melt-blown polypropylene. Keeping their content below this upper limit increases the overall fluidity of the resin, allowing for sufficient fiber stretching during the spinning process and resulting in finer fiber diameters. To achieve fine fibers during the spinning process while increasing the amorphous region within the fibers, it is preferable that the content of low-crystallinity polypropylene with an MFR of less than 400 g / 10 min and polypropylene-based elastomers with an MFR of less than 400 g / 10 min be within the above range.

[0063] A specific example of the first polyolefin is highly crystalline polypropylene. The mass-based blending ratio (first polypropylene / second polypropylene) of the first polyolefin and the second polypropylene is selected according to the type.

[0064] For example, when using Mopen® HP461Y (manufactured by Lyondellbasell) as the first polypropylene (highly crystalline polypropylene) and L-MODU® S400 (manufactured by Idemitsu Kosan Co., Ltd.) at MFR 2600 g / 10 as the second polypropylene (highly fluid, low-crystalline polypropylene), the blending ratio of these materials is preferably greater than 5 / 95, more preferably 10 / 90 or greater, even more preferably 20 / 80 or greater, particularly preferably 30 / 70 or greater, and also preferably 97 / 3 or less, more preferably 90 / 10 or less, even more preferably 80 / 20 or less, and particularly preferably 50 / 50 or less. Specifically, it is preferably greater than 5 / 95 and 97 / 3 or less, more preferably 10 / 90 or more and 90 / 10 or less, even more preferably 20 / 80 or more and 80 / 20 or less, and particularly preferably 30 / 70 or more and 50 / 50 or less.

[0065] Specific examples of low-flow, low-crystallinity polypropylenes that can be used as a second polypropylene include, for example, L-MODU® S600 with an MFR of 350 g / 10 min and L-MODU® S901 with an MFR of 50 g / 10 min (both manufactured by Idemitsu Kosan Co., Ltd.). An example of a propylene-based elastomer that can be used as a second polypropylene is Toughlesene® H5002 with an MFR of 10 g / 10 min (manufactured by Sumitomo Chemical Co., Ltd.).

[0066] When such a second polypropylene is used together with Moplen® HP461Y (manufactured by Lyondellbasell) as the first polypropylene, the blending ratio (first polypropylene / second polypropylene) is preferably 70 / 30 or more, more preferably 75 / 25 or more, even more preferably 80 / 20 or more, particularly preferably 85 / 15 or more, and also preferably 97 / 3 or less, more preferably 95 / 5 or less, and even more preferably 90 / 10 or less. Specifically, it is preferably 70 / 30 or more and 95 / 5 or less, more preferably 75 / 25 or more and 95 / 5 or less, even more preferably 80 / 20 or more and 90 / 10 or less, and particularly preferably 85 / 15 or more and 90 / 10 or less.

[0067] Examples of polyesters that can be used include polyethylene terephthalate, polybutylene terephthalate, and polytrimethylene terephthalate. Among these, polyethylene terephthalate or polybutylene terephthalate are preferred. When using a mixture of multiple types of polyester, it is preferable that one of the polyesters makes up 50% by mass or more of the total polyester, more preferably 70% by mass or more, and even more preferably 90% by mass or more.

[0068] Examples of polyamides that can be used include polyamide 3, polyamide 4, polyamide 6, polyamide 66, polyamide 12, and the like.

[0069] The thermoplastic resin composition may contain additives such as nucleating agents, matting agents, pigments, dyes, antifungal agents, antibacterial agents, flame retardants, hydrophilic agents, light stabilizers, antioxidants, anti-aging agents, synthetic oils, waxes, color inhibitors, and viscosity modifiers, to an extent that does not impair the effects of the present invention.

[0070] The meltblown nonwoven fabric according to the present invention preferably has a filling rate of 3% or more, more preferably 5% or more, and even more preferably 6% or more. The higher the filling rate, the denser the fibers are, and therefore the greater the water pressure resistance of the meltblown nonwoven fabric. The higher the filling rate, the harder the meltblown nonwoven fabric becomes, and the lower the filling rate, the softer it becomes. When using meltblown nonwoven fabric as a wearable item, a softer fabric is preferred, so the filling rate is preferably 30% or less, more preferably 20% or less, and even more preferably 15% or less. Specifically, the meltblown nonwoven fabric according to the present invention preferably has a filling rate of 3% or more and 30% or less, more preferably 5% or more and 20% or less, and even more preferably 6% or more and 15% or less.

[0071] The filling density can be increased above the lower limit by reducing the distance from the nozzle to the collection surface of the nonwoven fabric manufacturing apparatus (described later) to 400 mm or less, thereby compacting the fibers with air pressure. Alternatively, the filling density can be adjusted above the lower limit by compressing the meltblown nonwoven fabric using a calender roll or similar device during manufacturing.

[0072] To calculate the filling density, first, the thickness of the nonwoven fabric obtained using the method described later is measured using a laser displacement meter manufactured by Omron Corporation, while a load of 4 kPa is applied to the meltblown nonwoven fabric. The filling density is then calculated using the formula (2) described below, according to the method described later.

[0073] The meltblown nonwoven fabric according to the present invention preferably has a fabricity index of 300 or less, more preferably 280 or less, even more preferably 260 or less, particularly preferably 250 or less, and especially preferably 200 or less. By setting the distance from the nozzle to the collection surface of the nonwoven fabric manufacturing apparatus described later to 400 mm or less, and suppressing unevenness in fiber deposition, the fabricity index can be kept below the above upper limit.

[0074] In practice, the fabric density index is at least around 30 when manufacturing nonwoven fabrics by the melt-blown method. A smaller fabric density index indicates a more uniform distribution of fibers, resulting in a higher water pressure resistance for the melt-blown nonwoven fabric. The fabric density index is measured at the center of the short-side of the melt-blown nonwoven fabric and at any position in the long-side using the method described later.

[0075] Furthermore, meltblown nonwovens, which are integrated with substrates such as spunbond nonwovens and air-through nonwovens by thermal embossing, may develop holes when peeled off to obtain a sample. For perforated samples, the texture index is calculated using the standard deviation and mean value of the absorbance after subtracting the absorbance E originating from the hole.

[0076] The meltblown nonwoven fabric according to the present invention has a basis weight of 20 g / m², from the viewpoint of keeping the filling rate and fabricity index within the above range. 2 Preferably, it is 15 g / m 2 It is more preferable that the following is the case: 10 g / m 2 It is even more preferable that the basis weight is below this upper limit, as this reduces the volume of fibers relative to the airflow pressure, making compaction easier and resulting in a sufficient filling rate. Furthermore, when the basis weight is below this upper limit, the material is deposited uniformly during the deposition process, resulting in a sufficient form index.

[0077] The basis weight is 1 g / m² for the meltblown nonwoven fabric to exhibit water pressure resistance. 2 The above is preferable, 2 g / m 2 The above is more preferable. Specifically, the basis weight of the meltblown nonwoven fabric according to the present invention is 1 g / m². 2 20g / m or more 2It is preferably the following, 1 g / m 2 or more and 15 g / m 2 or less, more preferably 2 g / m 2 to 10 g / m 2 or less, and even more preferably.

[0078] In the case of the melt-blown nonwoven fabric alone, the basis weight can be measured from the weight per area of 0.05 m². When the melt-blown nonwoven fabric is adhered to a substrate such as a resin film, paper, spunbond nonwoven fabric, or air-through nonwoven fabric with hot melt or the like to form a composite, first, heat it with a cold spray or a dryer to reduce the adhesive strength of the hot melt and peel off the melt-blown nonwoven fabric from the substrate. The hot melt adhering to the melt-blown nonwoven fabric is dissolved by immersing the melt-blown nonwoven fabric in a large excess of an organic solvent such as toluene in which the hot melt is soluble for 24 hours. The melt-blown nonwoven fabric taken out from the organic solvent is dried, and the basis weight of the melt-blown nonwoven fabric is measured by the above method.

[0079] Note that the method of taking out this melt-blown nonwoven fabric from the composite is also applicable to other measurements in this specification. When the melt-blown nonwoven fabric is integrated with a substrate such as a resin film, spunbond nonwoven fabric, or air-through nonwoven fabric by thermal embossing, first, peel off the melt-blown nonwoven fabric so as to remove the embossed part. Next, the area of the melt-blown nonwoven fabric with holes in the embossed part is obtained from image processing such as binarization, and the basis weight can be measured from the weight at that time.

[0080] The 0.05 m² area of melt-blown nonwoven fabric used for measuring the basis weight is preferably obtained from a continuous melt-blown nonwoven fabric. When the area of a single melt-blown nonwoven fabric obtained from a product is small, it can be the sum of the areas of a plurality of melt-blown nonwoven fabrics obtained from the same product.

[0081] When the melt-blown nonwoven fabric is integrated with a substrate such as a resin film, spunbond nonwoven fabric, or air-through nonwoven fabric by thermal embossing, except for the measurement of water pressure resistance and the measurement of water pressure resistance after deformation described later, the melt-blown nonwoven fabric is appropriately peeled off so as not to include the embossed part and used as the measurement object.

[0082] As described above, the meltblown nonwoven fabric according to the present invention has an average fiber diameter of 4 μm or less, and the straightness of the fibers in both the first direction, which is aligned with the plane and has the highest straightness of the fibers, and the second direction perpendicular to the first direction, is 35% or more. Therefore, it has excellent water pressure resistance, and even if deformation occurs, gaps are less likely to form between the fibers, thus suppressing a decrease in water pressure resistance.

[0083] The water pressure resistance of meltblown nonwoven fabric can be obtained and measured using the same methods as described above. However, if the meltblown nonwoven fabric is integrated with a base material such as spunbond nonwoven fabric or air-through nonwoven fabric by thermal embossing, the water pressure resistance should be measured in that form and that value should be taken as the water pressure resistance of the meltblown nonwoven fabric. In the case of such laminated nonwoven fabrics, the fine-mesh meltblown nonwoven fabric is the layer that determines the water pressure resistance, so the water pressure resistance of the entire laminated nonwoven fabric can be considered as the water pressure resistance of the meltblown nonwoven fabric.

[0084] The meltblown nonwoven fabric according to the present invention is not particularly limited in its applications and can be used in a variety of applications by taking advantage of its properties. The meltblown nonwoven fabric according to the present invention can be used as a single layer or in a laminated form. Multiple meltblown nonwoven fabrics according to the present invention may be laminated, or they may be laminated together with other known nonwoven fabrics such as spunbond nonwoven fabrics or air-through nonwoven fabrics. Furthermore, the meltblown nonwoven fabric according to the present invention may be embossed as needed.

[0085] Specifically, the spunbond layer and the meltblown layer may be spun separately, then laminated and integrated by heat embossing. Alternatively, the spunbond nonwoven fabric may be spun, then laminated with a separately prepared meltblown nonwoven fabric and embossed. Furthermore, the meltblown nonwoven fabric and the spunbond nonwoven fabric may be manufactured separately and integrated by heat embossing. In any case, the basis weight can be measured by appropriately peeling off the meltblown nonwoven fabric without including the embossed portion, as described above.

[0086] The meltblown nonwoven fabric according to the present invention can be used, for example, as a component of absorbent articles such as disposable diapers, sanitary napkins, and incontinence pads. Because the reduction in water pressure resistance due to deformation is suppressed, it is particularly suitable as a leak-proof sheet where water resistance is required. Such absorbent articles can be manufactured by laminating a leak-proof sheet, an absorbent body, and a surface sheet made of the meltblown nonwoven fabric according to the present invention. Furthermore, the meltblown nonwoven fabric according to the present invention can also be used in sanitary masks, liquid filters, air filters, battery separators, gloves, and the like.

[0087] Next, a method for producing meltblown nonwoven fabric according to the present invention will be described. The meltblown nonwoven fabric according to the present invention can be produced by the meltblown method using a known nonwoven fabric manufacturing apparatus conventionally used for the production of meltblown nonwoven fabrics.

[0088] A nonwoven fabric manufacturing apparatus comprises, for example, an extruder equipped with a barrel containing a screw and a raw material input section, a die connected directly to the extruder or via a gear pump or the like, and a collection surface for depositing the fibrous molten material. The die has multiple nozzles arranged in series for discharging the molten material, with outlets on both sides of each nozzle. A high-temperature, high-pressure airflow (hot air) is injected from the outlets to stretch the molten material discharged from the nozzles into a fibrous form. The multiple nozzles are preferably arranged in series at regular intervals. The diameter of the nozzles is preferably several hundred micrometers. The high-temperature, high-pressure airflow is preferably an airflow, but it may also be an airflow of other gases. As the collection surface, known materials such as net conveyors and collection screens can be used.

[0089] The present invention relates to a method for producing a meltblown nonwoven fabric having an average fiber diameter of 4 μm or less, and comprises a spinning step in which a thermoplastic resin composition is supplied to an extruder from a raw material input section, for example in the form of pellets, heated and melted in the extruder, the molten material is supplied to a die and discharged from a nozzle, and the discharged molten material is stretched into fibers by a high-temperature, high-pressure airflow (hot air). The fibrous molten material is deposited on a collection surface in a deposition step, and the fibers fuse with each other to form a meltblown nonwoven fabric.

[0090] The thermoplastic resin composition used in the method for producing meltblown nonwoven fabric according to the present invention may be the thermoplastic resin composition described above. The thermoplastic resin composition may also be prepared by directly feeding the thermoplastic resin and optionally blended components into an extruder instead of pellets.

[0091] In the method for producing meltblown nonwoven fabric according to the present invention, the temperature of the airflow (hot air temperature) in the spinning process is preferably 260°C or lower, more preferably 250°C or lower, and more preferably 240°C or lower. It is believed that by keeping the airflow temperature below this upper limit, the time during which the fibers are sticky is shortened, making it less likely for the fibers to entangle with each other, suppressing the air resistance of the fibers, making it less likely for them to orient in the MD direction during the spinning process, and increasing the straightness of the fibers in the CD direction. Furthermore, the lower limit of the airflow temperature must be above the melting point of the thermoplastic resin composition. The melting point is measured by differential scanning calorimetry (DSC), and a DSC curve is obtained while increasing the temperature from 30°C at 20°C / min, with the temperature at the highest endothermic peak point appearing between 30 and 240°C being defined as the melting point.

[0092] The thermoplastic resin composition preferably contains highly crystalline polypropylene. The hot air temperature is preferably 160°C or higher, more preferably 180°C or higher, and even more preferably 200°C or higher, which is the melting point of highly crystalline polypropylene. Specifically, the hot air temperature is preferably 160°C to 260°C, more preferably 180°C to 250°C, and even more preferably 200°C to 240°C.

[0093] From the viewpoint of ensuring that the average fiber diameter of the meltblown nonwoven fabric according to the present invention is less than 4 μm, the airflow rate in the spinning process is set to 500 Nm per meter of the width through which the airflow is blown. 3 It is preferable to set it to 700 Nm / hr or more. 3 It is more preferable to set the flow rate to 1700 Nm / hr or higher. In addition, in order to suppress yarn breakage during the fiber stretching process and as a result reduce the fiber diameter, the airflow rate should be 1700 Nm per meter of the width through which the airflow is blown. 3 It is preferable to set it to less than / hr, and 1300 Nm 3 It is even more preferable to set it to / hr or less.

[0094] In the method for producing meltblown nonwoven fabric according to the present invention, the distance from the nozzle of the nonwoven fabric manufacturing apparatus to the collection surface is preferably 400 mm or less, more preferably 300 mm or less, and even more preferably 150 mm or less. It is believed that by keeping the distance from the nozzle to the collection surface below this upper limit, the fibers can be densely deposited, improving water pressure resistance. In the meltblown method, by cooling and depositing the molten fibers, coalescence between the molten fibers can be prevented, thereby improving water pressure resistance. For this reason, it is preferable that the fibers are cooled when they are deposited, and the distance from the nozzle to the collection surface is preferably 50 mm or more, more preferably 50 mm or more, more preferably 80 mm or more, and even more preferably 100 mm or more.

[0095] The method for producing meltblown nonwoven fabric according to the present invention preferably includes a heating step in which the fibers are heated after the spinning step and before the deposition step in which the fibers are deposited on the collection surface. In the heating step, it is preferable to use an IR heater instead of hot air, from the viewpoint that it is preferable to apply only heat to the fibers without applying external disturbances such as wind. Furthermore, from the viewpoint of preventing the fibers discharged from the nozzle from cooling and solidifying in the spinning space, the position in which the fibers are heated is preferably 100 mm or more below the nozzle, and preferably 200 mm or less. Thus, it is preferable to heat the spinning space rather than applying heat to the fibers immediately after spinning, as described in Japanese Patent Publication No. 2015-59294 and International Publication No. 2012 / 014501. Furthermore, the position in which the fibers are heated is preferably 80 mm or more, more preferably 100 mm or more, more preferably 200 mm or less, and more preferably 180 mm or less, in the direction perpendicular to the spinning line.

[0096] As described above, the method for producing meltblown nonwoven fabric according to the present invention sets the temperature of the airflow in the spinning process to 260°C or lower, and the heat of fusion of the thermoplastic resin composition constituting the fibers to be greater than 5 mJ / mg and less than 94 mJ / mg, thereby making it possible to obtain a meltblown nonwoven fabric in which the straightness of the fibers in the CD direction is 35% or more.

[0097] Next, embodiments of the present invention will be described, but this will not limit the present invention.

[0098] [Thermoplastic Resin Compositions] In Examples 1 to 11 and Comparative Examples 1 to 4, the resins used as raw materials for the thermoplastic resin compositions are as follows: Resin 1: Polypropylene (Moplen® HP461Y, manufactured by Lyondellbasell), with a heat of fusion of 98 mJ / mg, an MFR of 1300 g / 10 min, and a melting point of 160°C. Resin 2: Low-crystallinity polypropylene (L-MODU® S400, manufactured by Idemitsu Kosan Co., Ltd.), with a heat of fusion of 0.3 mJ / mg, an MFR of 2600 g / 10 min, Mw = 45000, Mw / Mn = 2, and low stereoregularity polypropylene. Resin 3: Polypropylene elastomer (Toughselenium® H5002 manufactured by Sumitomo Chemical Co., Ltd.), heat of fusion 6 mJ / mg, MFR 10 g / 10 min, melting point 135°C, Mw = 230000, Mw / Mn = 1.8, amorphous propylene-(1-butene) copolymer.

[0099] Furthermore, the meltblown nonwoven fabrics used in Comparative Examples 5 and 6 are as follows: Nonwoven fabric 1: Meltblown nonwoven fabric (PC0009) manufactured by Kuraray Kuraflex Co., Ltd. Nonwoven fabric 2: Meltblown nonwoven fabric (P010SW-00X) manufactured by Tapirus Co., Ltd.

[0100] [Evaluation] Next, the methods for measuring various physical properties of the meltblown nonwoven fabrics in the examples and comparative examples are shown below. The measurement results for the various physical properties are shown in Table 2.

[0101] (1) Heat of fusion of thermoplastic resin composition The heat of fusion of the thermoplastic resin composition was measured by differential scanning calorimetry (DSC). A DSC curve was obtained while increasing the temperature from 30°C at 20°C / min, and the amount of heat at the endothermic peak that appeared between 100 and 200°C was defined as the heat of fusion.

[0102] (2) Basis weight The basis weight of the meltblown nonwoven fabric is determined by cutting out three 50 mm square measuring pieces from the center of the meltblown nonwoven fabric, measuring the mass (g) of each measuring piece, and using this as the area (m²) of the measuring piece. 2 Divide by ( ) and the arithmetic mean of the three sheets was used as the basis weight.

[0103] (3) Filling Ratio The filling ratio of the meltblown nonwoven fabric can be calculated using the following formula (2). The thickness of the meltblown nonwoven fabric was measured using an Omron Corporation laser displacement meter with a load applied to create a pressure of 4 kPa. Each thickness measurement was performed five times, and the average value was calculated to determine the thickness of the meltblown nonwoven fabric. The fiber density was measured using the method described in JIS K 7112, specifically the pycnometer method.

[0104] (4) Fabric Condition Index The fabric condition index of meltblown nonwoven fabric was calculated using a fabric condition measuring instrument (FMT-MIII) manufactured by Nomura Trading Co., Ltd. Specifically, a sample of meltblown nonwoven fabric was placed on a sample stand, and the transmission image was captured by the CCD camera when light was shone from one side of the sample, with the height of the CCD camera set to 26 cm, the effective size to 10 cm × 10 cm, and the moving average pixel to 1. The effective size of 10 cm × 10 cm was decomposed into 320 × 230 pixels, the intensity of light received by each pixel was measured, and the transmittance T for each pixel was calculated using the following formula (3). However, V T This is the amount of transmitted light when lit (sample available), V R This is the amount of transmitted light when the lights are off (with sample), V 100 V0 is the transmitted light amount when the light is on (no sample), and V0 is the transmitted light amount when the light is off (no sample). From the obtained transmittance T, the absorbance E was calculated using the following formula (4). The market condition index was calculated from the obtained absorbance E using the following formula (5). Measurements were taken on three test pieces, and the average value was used as the texture index for the sample. If the sample size is small and a usable area of ​​10 cm x 10 cm cannot be obtained, the texture index for that sample can be determined by placing the sample in the center of the test stand and adjusting the usable area to be less than the sample size but as large as possible.

[0105] (5) Average Fiber Diameter To measure the average fiber diameter, first, five small sample pieces were randomly taken from the meltblown nonwoven fabric. Next, using a JEOL Ltd. desktop scanning electron microscope (JCM-6000Plus), magnified SEM images were taken so that 20 to 60 fibers were visible in the field of view. For all fibers in the field of view, the fiber diameter was measured once for each fiber, and the average value was calculated. The fiber diameter of the small sample was then rounded to the nearest 10 nm. The fiber diameter was measured similarly for the five small sample pieces, and the average value of the five samples was taken as the average fiber diameter of the meltblown nonwoven fabric.

[0106] (6) Straightness of fibers The straightness of fibers in the first and second directions was calculated for the meltblown nonwoven fabrics of the examples and comparative examples according to the means described above. Here, since the MD direction and CD direction are known for the nonwoven fabrics of the examples and comparative examples, the MD direction was designated as the first direction and the CD direction as the second direction.

[0107] (7) Water pressure resistance The water pressure resistance was measured in accordance with the water resistance test (hydrostatic pressure method) Method A (low water pressure method) of JIS L1092-1998. During the water resistance test, a nylon mesh sheet (pore size: 133 μm, thickness: 121 μm, manufactured by Kurabo Industries Ltd., DO-ML-20) was placed on top of the test piece for measurement. If the size of the test piece does not meet the specifications, a device can be assembled to reduce the measurement area so that water comes into contact with the test piece of a size that can be sampled, and the water pressure resistance can be measured in the same manner. Measurements were taken for 10 test pieces, and the average value was calculated to be the water pressure resistance of the meltblown nonwoven fabrics related to the examples and comparative examples.

[0108] (8) Water pressure resistance after deformation First, the meltblown nonwoven fabric according to the example and comparative example was cut to a size of 130 mm or more in length and 150 mm in width, with the CD direction being the length direction and the MD direction being the width direction during manufacturing. Next, it was fixed with a chuck (tensile testing machine AG-IS manufactured by Shimadzu Corporation) so that the distance between the chucks in the length direction was 130 mm. Next, the meltblown nonwoven fabric was stretched (tensile speed 1 cm / 5 seconds) so that the distance between the chucks in the length direction was 150 mm, and held for 5 seconds to deform the meltblown nonwoven fabric in the CD direction. After that, the chuck was released, and the water pressure resistance after deformation was measured on the central part of the deformed meltblown nonwoven fabric in the same manner as the water pressure resistance measurement in (7) above.

[0109] (9) Water pressure resistance The water pressure resistance was calculated using the following formula (6).

[0110] [Example 1] A thermoplastic resin composition was prepared by mixing resin 1 and resin 2 in a ratio of resin 1 / resin 2 = 97 / 3. A meltblown nonwoven fabric according to Example 1 was manufactured using this thermoplastic resin composition. The manufacturing conditions for the meltblown nonwoven fabric according to Example 1 were as follows. The manufacturing conditions are shown in Table 1. Resin temperature (temperature when discharged from the nozzle): 270°C Single-hole discharge volume: 0.20 g / min / hole Hot air flow rate: 300 Nm 3 The hot air outlet width was 400 mm, the hot air temperature (temperature of the airflow in the spinning process) was 200°C, the nozzle diameter was 0.15 mm, the nozzle length was 3 mm, and the nozzle pitch was 0.85 mm. The distance from the nozzle to the collection surface was 300 mm. In addition, various physical properties of the meltblown nonwoven fabric according to Example 1 were measured using the methods described in (1) to (9) above, and the results are shown in Table 2.

[0111] [Examples 2-11, Comparative Examples 1-4] Meltblown nonwoven fabrics were prepared in the same manner as in Example 1, except that the type of resin, mixing ratio, and manufacturing conditions were changed as shown in Table 1. The manufacturing conditions not listed in Table 1 were the same as in Example 1. In addition, various physical properties of the meltblown nonwoven fabrics of Examples 2-11 and Comparative Examples 1-4 were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0112] [Example 12] Using resin 1, a Heraeus short-wavelength infrared heater (model IRMA900 / 160) was installed so that its center was located 150 mm below the nozzle and 120 mm perpendicular to the spinning wire, and heating was performed at 100% output (total output 9000 W). The meltblown nonwoven fabric according to Example 12 was produced under the same manufacturing conditions as in Example 1. In addition, various physical properties of the obtained meltblown nonwoven fabric were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0113] [Comparative Examples 5 and 6] Various physical properties of the meltblown nonwoven fabrics of Comparative Examples 5 and 6 were measured in the same manner as in Example 1, and the results are shown in Table 2.

[0114]

[0115]

[0116] As shown in Table 2, the meltblown nonwoven fabrics according to Examples 1 to 12 have an average fiber diameter of 4 μm or less, and the straightness of the fibers in the first direction where the straightness of the fibers is highest and in the second direction perpendicular to the first direction is 35% or more, or the average fiber diameter is 4 μm or less, and the ratio of the straightness of the fibers in the first direction to the straightness of the fibers in the second direction on the plane of the meltblown nonwoven fabric is 2.5 or less, resulting in a high water pressure retention rate and suppression of the decrease in water pressure resistance due to deformation.

Claims

DEPCT641. A meltblown nonwoven fabric with an average fiber diameter of 0.1 micrometers to 4 micrometers, composed of a first direction along the plane of the meltblown nonwoven fabric with the highest rate of linear fibers and a second direction perpendicular to the first direction, the meltblown nonwoven fabric meets one or more of the following selected conditions from (I), (II), and (III): (l) has a rate of linear fibers of 35% or higher in each of the first and second directions; (II) has a ratio of the rate of linear fibers of 35% or higher; (III) The meltblown nonwoven fabric has a water resistance of 100mmH2O to 10000mmH2O and a water resistance retention rate of 85% or higher when the meltblown nonwoven fabric is deformed in the second direction.

2. Meltblown nonwoven fabric with an average fiber diameter of 0.1 micrometers to 4 micrometers,Composed of a linear fiber rate of 35% or higher in each of the first directions lying in the plane of the meltblown nonwoven fabric, with the highest linear fiber rate and the second direction perpendicular to the first direction.

3. Meltblown nonwoven fabric according to claim 1 or 2, where the ratio of the linear fiber rate in the first direction to the linear fiber rate in the second direction (linear fiber rate in the first direction / linear fiber rate in the second direction) is from 1 to 2.

5.

4. Meltblown nonwoven fabric with an average fiber diameter of from 0.1 micrometers to 4 micrometers, composed of a first direction lying in the plane of the meltblown nonwoven fabric with the highest linear fiber rate and the second direction perpendicular to the first direction.Meltblown nonwoven fabrics with a ratio of the rate of straight fibers in the first direction to the rate of straight fibers in the second direction (rate of straight fibers in the first direction / rate of straight fibers in the second direction) from 1 to 2.

55. Meltblown nonwoven fabrics according to any one of the claims 1 to 4, where the ratio of the rate of straight fibers in the first direction to the rate of straight fibers in the second direction (rate of straight fibers in the first direction / rate of straight fibers in the second direction) The linearity rate of the fibers in the second direction) is from 1 to 1.

96. Meltblown nonwoven fabrics according to one of the claims 11 to 15, where the first and second directions and linearity rate are determined by following steps (a) to (g): (a) SEM image capture of the meltblown nonwoven fabric at the observation position at its center using a desktop scanning electron microscope (JCM-6000Plus, manufactured by JEOL Ltd.) at magnification = 3000 / average fiber diameter (µm), and longitudinal orientation of the SEM image is adjusted to 0 degrees,(a) SEM image capture when the measured non-woven fabric is significantly rectangular, the resulting SEM image has the longitudinal direction of the non-woven fabric adjusted to 0 degrees and the longitudinal direction of the SEM image parallel to the 0-degree direction; (b) SEM image capture when the field of view is rotated by 1 theta degrees and capture of X-slices of the SEM image from 0 degrees to (180-theta) degrees when the field of view is rotated by another 1 theta degree, where the number of X-slices = (180 degrees / theta degrees)-1; (c) Perform steps (a) and (b) at 7 observation positions. (d) Calculation, using the following equation (1), the rate of linear fibers at each angle from 0 degrees to (180-theta) degrees relative to the corresponding SEM images obtained through steps (a) to (c), and rounding the rate to the nearest integer.and averaging the rate values ​​at 8 positions to obtain the linearity rate at each angle; (e) arranging the angle with the greatest linearity rate among the linearity rates calculated in step (d) for each angle as the first direction and arranging the greatest linearity rate as the rate of the linearity fiber in the first direction; (f) arranging the direction perpendicular to the first direction as the second direction; and (g) capturing the SEM, the longitudinal direction which is parallel to the second direction, at 8 observation positions, calculating the rate of the linearity fiber in the second direction using the following equation (1), averaging the rate at 8 positions and rounding to the nearest integer: [Expression 1] Linearity rate (%) = (N(0)X2 / (N(1)+N(2)))x100....(1) where N(0), N(1), and N(2) are substituted for the following,where N(0) is the number of fibers continuously stretched from one end to the other of each SEM image in the longitudinal direction; N(1) is the number of fibers that cut through one end in the longitudinal direction; and N(2) is the number of fibers that cut through the other end in the longitudinal direction.

7. Meltblown nonwoven fabric according to any of claims 1 to 6, where the water pressure resistance is from 100 mmH2O to 10000 mmH2O.

8. Meltblown nonwoven fabric according to any of claims 2 to 7, where the water pressure resistance retention rate when the meltblown nonwoven fabric is made 9. Meltblown nonwoven fabric with an average fiber diameter of 0.1 micrometers to 4 micrometers, comprising: water pressure resistance of 100 mmH2O to 10000 mmH2O; and a water pressure resistance retention rate of 85% or higher when the meltblown nonwoven fabric is deformed in a second direction perpendicular to the first direction in the plane of the meltblown nonwoven fabric and has the highest rate of linear fiber orientation.

10. Meltblown nonwoven fabric according to any one of the claims 1 to 9,Where its filling factor is from 3% to 30%11. Meltblown nonwoven fabrics with an average fiber diameter of from 0.1 micrometers to 4 micrometers, consisting of: a fiber orientation rate of 35% or higher in each of the first directions in the plane of the meltblown nonwoven fabric and having the highest fiber orientation rate and the second direction perpendicular to the first direction; the ratio of the fiber orientation rate in the first direction to the fiber orientation rate in the second direction (the fiber orientation rate in the second direction).

11. Meltblown nonwoven fabrics according to one of the claims 1 to 11, where the average fiber diameter is from 0.3 micrometers to 2 micrometers; 13. Meltblown nonwoven fabrics according to one of the claims 1 to 12, where its filling factor is from 6% to 15%; and 14. Meltblown nonwoven fabrics according to one of the claims 1 to 13,15. Melt-blown non-woven fabrics according to any one of the claims 1 to 14, where their formation index is from 30 to 300.

16. Melt-blown non-woven fabrics according to any one of the claims 1 to 15, where the heat of fiber melting is greater than 5 mJ / mg but less than 94 mJ / mg.

17. Melt-blown non-woven fabrics according to any one of the claims 1 to 16, where the heat of fiber melting is from 20 mJ / mg to 80 mJ / mg.

18. Leak-proof sheets composed of... The absorbent product is composed of: a permeable surface layer placed on the skin-contact side; another leak-proof surface layer placed on the non-skin-contact side; and an absorbent material interspersed between the layers, where the other surface layer is the leak-proof layer as per claim 1820. The method of manufacturing melt-blown non-woven fabric with an average fiber diameter of 4 micrometers or less.It comprises a spinning process in which a molten thermoplastic resin mixture is released from a nozzle to produce fibers using an air flow, the air flow temperature is at or above the melting point of the thermoplastic resin mixture, and the thermoplastic resin mixture has a heat of melt greater than 5 mJ / mg but less than 94 mJ / mg.

21. The melt-blown non-woven fabric manufacturing method according to claim20, where the air flow temperature is adjusted to 260 degrees Celsius or lower.

22. The melt-blown non-woven fabric manufacturing method.

21. The melt-blown non-woven fabric manufacturing method under claim 21, where the air flow temperature is adjusted to 250°C or lower.

23. The melt-blown non-woven fabric manufacturing method under claim 22, where the air flow temperature is adjusted to 240°C or lower.

24. The melt-blown non-woven fabric manufacturing method under any of claims 20 through 23, where a thermoplastic resin mixture consists of two or more different polyolefins with different melt heats.

25. The melt-blown non-woven fabric manufacturing method under claim 24,Where the thermoplastic resin mixture comprises a polyolefin compound consisting of a primary polyolefin with a heat of melt of 94 mJ / mg or higher and a secondary polyolefin with a heat of melt of less than 94 mJ / mg, and the secondary polyolefin is combined with at least one compound selected from low-crystalline polypropylene with an MFR of 400 g / 10 min or higher, low-crystalline polypropylene with an MFR of less than 400 g / 10 min, and a polypropylene-based elastomer.

25. Melt-blown non-woven fabric ...Where a copolymer of at least two different alpha-olefins is incorporated with at least one elastomer based on a low crystallinity olefin or an amorphous olefin-based elastomer.

29. Any melt-blown non-woven fabric ... In any of the claims 24 through 29, where the first polyolefin consists of a highly crystalline polyolefin, the highly crystalline polyolefin has a melt flow rate of from 300 g / 10 min to 1800 g / 10 min.

31. The melt-blown non-woven fabric production method according to claim 30, where the amount of the second polyolefin relative to the total amount of the first and second polyolefins is from 50% mass% to 70% mass%, when the second polyolefin is a low-crystalline polyolefin with an MFR of 400 g / 10 min or more.and from 10% mass to 15% mass when the secondary polyolefin is a low crystallinity polyolefin with an MFR of less than 400 g / 10 min or a polyolefin-based elastomer with an MFR of less than 400 g / 10 min.

32. Any of the meltblown nonwoven fabric fabric production methods of claims 20 to 31, incorporating a deposition step which involves the deposition of fibers obtained in the spinning step on a collecting surface, where the distance from the nozzle to the collecting surface is 400 mm or shorter.

33. Any of the meltblown nonwoven fabric fabric production methods of claims 20 to 31. 20 to 22, also includes an accumulation process which is the accumulation of fibers obtained in the spinning stage on a collecting surface, where the distance from the nozzle to the collecting surface is from 50 mm to 300 mm.

34. Any of the meltblown nonwoven fabric manufacturing methods under claims 20 to 33, also includes an accumulation process which is the accumulation of fibers obtained in the spinning stage on a collecting surface, where the distance from the nozzle to the collecting surface is from 50 mm to 150 mm.

35. Any of the meltblown nonwoven fabric manufacturing methods under claims 20 to 34,It also includes an accumulation step, which involves the accumulation of the spinning fibers on the collecting surface, and a heating step, which involves heating the spinning fibers before they are accumulated on the collecting surface.

36. Meltblown nonwoven fabrics produced by any of the manufacturing methods of claims 20 to 35.