Laminated nonwoven fabric, method for producing same, and sterilized packaging material

Abstract

The present invention addresses the problem of, for a nonwoven fabric used for a sterilized packaging material, providing a laminated nonwoven fabric having both a virus barrier property capable of maintaining a sterilized state of a sterilized medical device or the like contained in a sterilized packaging material until the time of use and an air permeability for permeating gas during sterilization treatment.　The present invention is a laminated nonwoven fabric obtained by laminating at least one spunbond nonwoven fabric layer and at least one meltblown nonwoven fabric layer, wherein said at least one spunbond nonwoven fabric layer and said at least one meltblown nonwoven fabric layer are both composed of fibers comprising a polypropylene resin composition mainly containing a polypropylene resin, and the laminated nonwoven fabric has a basis weight of 50 g / m2-90 g / m2 inclusive, and satisfies the following formula, wherein y ( / mm2) is the number of fibers having a flatness of 0.80-1.25 inclusive per unit cross-sectional area of the laminated nonwoven fabric, and x (g / m2) is a basis weight of the laminated nonwoven fabric: −600≤a≤0, y≥50, wherein a=y-10.7x

Description

Laminated nonwoven fabric, its manufacturing method, and sterilization packaging material

[0001] The present invention relates to a laminated nonwoven fabric, and more particularly to a laminated nonwoven fabric that is excellent for use as a sterilization packaging material.

[0002] BACKGROUND ART In recent years, nonwoven fabrics have been used in a variety of applications, including industrial materials, civil engineering materials, building materials, daily necessities, agricultural materials, sanitary materials, and medical materials.

[0003] Among these, nonwoven fabrics made from polyolefin resins are attracting attention for use as sterilization packaging materials, taking advantage of the heat resistance that is one of the resin's properties. Nonwoven fabrics used in sterilization packaging materials must have both virus barrier properties that allow sterilized medical devices and other items contained in the packaging to remain sterile until use, and breathability that allows gas to pass through during sterilization processing.

[0004] Laminated nonwoven fabrics have been proposed for use as sterilization packaging materials. For example, Patent Document 1 proposes a nonwoven fabric for sterilization packaging materials, which has a fiber layer (I) with a specific porosity as the outer heat-sealable surface, and a fiber layer (II) with a specific range of fiber specific surface area and number of fibers equivalent to 1 cm per 1 mg as the barrier layer, and in which the fiber layer (I) and the fiber layer (II) are laminated. It is described that this nonwoven fabric for sterilization packaging materials can provide a nonwoven fabric that combines both easy-peel properties and barrier properties.

[0005] International Publication No. 2020 / 196340

[0006] It is believed that a laminated nonwoven fabric of a conventional material, a polypropylene spunbond nonwoven fabric and a meltblown nonwoven fabric, as described in Patent Document 1, exhibits a certain level of barrier property by controlling the specific surface area of ​​the meltblown layer. However, further improvement in virus barrier property is required to maintain the sterilized state of the sterilized packaging material from distribution to use after sterilization.

[0007] Therefore, an object of the present invention has been made in consideration of the above circumstances, and it is an object of the present invention to provide a laminated nonwoven fabric that combines virus barrier properties and breathability, a method for producing the same, and a sterilization packaging material made using the same.

[0008] The present invention and its preferred embodiments have the following configurations: [1] A laminated nonwoven fabric comprising at least one spunbonded nonwoven fabric layer and at least one meltblown nonwoven fabric layer made of fibers composed of a polypropylene-based resin, wherein the at least one spunbonded nonwoven fabric layer and the at least one meltblown nonwoven fabric layer are both made of fibers made of a polypropylene-based resin composition mainly containing a polypropylene-based resin, and the basis weight of the laminated nonwoven fabric is 50 g / m ２ 90g / m or more ２ The number of fibers per unit cross-sectional area of ​​the laminated nonwoven fabric is y (fibers / mm ２ ), the basis weight of the laminated nonwoven fabric is x (g / m ２ ) and satisfying the following relationship: -600≦a≦0 y≧50, where a=y−10.7x [2] The laminated nonwoven fabric according to [1], wherein the arithmetic mean roughness Ra of at least one surface of the laminated nonwoven fabric is 1.0 μm or more and 10.0 μm or less. [3] The apparent density of the laminated nonwoven fabric is 0.30 g / cm ３ 0.60g / cm or more ３ [4] The laminated nonwoven fabric according to [1] or [2], wherein the tensile strength / elongation product per unit area of ​​the laminated nonwoven fabric, as calculated by the following formula, is 0.50 (N / 50 mm) / (g / m ２ ) or more 1.50 (N / 50mm) / (g / m ２ The laminated nonwoven fabric according to any one of [1] to [3], wherein the tensile strength / elongation product per unit area ((N / 50 mm) / (g / m)) or less. ２ )) = [average value of maximum strength (N / 50mm)] x [average value of elongation at maximum strength (-)] / basis weight (g / m ２). [5] The laminated nonwoven fabric according to any one of [1] to [4], wherein the polypropylene resin composition contains a low-crystalline polyolefin resin. [6] The laminated nonwoven fabric according to [5], wherein the content of the low-crystalline polyolefin resin in the polypropylene resin composition is 1% by mass or more and 20% by mass or less. [7] The laminated nonwoven fabric according to [5] or [6], wherein the low-crystalline polyolefin resin is an ethylene-propylene copolymer. [8] A method for producing the laminated nonwoven fabric according to any one of [1] to [7], comprising the steps of forming at least one layer of a first spunbond nonwoven web, forming at least one layer of a meltblown nonwoven web on the at least one first spunbond nonwoven web, forming at least one layer of a second spunbond nonwoven web on the at least one meltblown nonwoven web to form a laminated web, preheating only one surface of the laminated web by contacting the heating surface of a heating device with the heating surface of a heating device to obtain a preheated laminated web, and fusing the preheated laminated web using a thermal calendar roll consisting of a pair of upper and lower flat rolls to form the laminated nonwoven fabric, wherein the preheating temperature in the step of obtaining the preheated laminated web is 40°C or higher and 95°C or lower. [9] A sterilized packaging material using the laminated nonwoven fabric according to any one of [1] to [7].

[0009] According to the present invention, it is possible to obtain a laminated nonwoven fabric that has excellent virus barrier properties and breathability and is suitable for use as a sterilization packaging material, and a sterilization packaging material obtained from the laminated nonwoven fabric.

[0010] The present invention will be described in detail below. However, the present invention is not limited to the embodiments described below as long as the gist of the present invention is not exceeded.

[0011] The laminated nonwoven fabric of the present invention comprises at least one spunbonded nonwoven fabric layer and at least one meltblown nonwoven fabric layer laminated together.

[0012] [Polypropylene-based resin composition] The at least one spunbonded nonwoven fabric layer and the at least one meltblown nonwoven fabric layer are both composed of fibers made of a polypropylene-based resin composition mainly containing a polypropylene-based resin. Herein, the "polypropylene-based resin" in the present invention refers to a resin whose main repeating unit is a propylene unit. Hereinafter, the at least one spunbonded nonwoven fabric layer will be simply referred to as the "spunbonded nonwoven fabric layer," and the at least one meltblown nonwoven fabric layer will be simply referred to as the "meltblown nonwoven fabric layer." In addition, in the present invention, the polypropylene-based resin composition used for the fibers constituting the spunbonded nonwoven fabric layer will be referred to as the polypropylene-based resin composition P. Ｓ The polypropylene resin composition used for the fibers constituting the melt-blown nonwoven fabric layer is referred to as polypropylene resin composition P Ｍ It is sometimes referred to as.

[0013] Examples of the polypropylene resin include a homopolymer of propylene and a copolymer of propylene with various α-olefins.

[0014] The proportion of propylene units in the polypropylene-based resin is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, which can maintain good spinnability and improve the strength of the laminated nonwoven fabric.

[0015] In addition to the polypropylene resin primarily contained, the polypropylene resin composition may also contain other olefin resins such as polyethylene and poly-4-methyl-1-pentene, thermoplastic elastomers, etc. Here, "primarily contained" refers to the fact that they account for the largest mass content in the resin composition. Among the above-mentioned other resins, low-crystalline polyolefin resins are preferred from the viewpoint of imparting flexibility. The low-crystalline polyolefin resin refers to a polyolefin resin in which a copolymerization monomer such as ethylene or 1-butene is incorporated into a regular polypropylene chain; for example, an ethylene-propylene copolymer or a low stereoregular polypropylene is preferably used. Among these, an ethylene-propylene copolymer is more preferred from the viewpoint of flexibility.

[0016] The ethylene content in the ethylene-propylene copolymer is preferably 1% by mass or more and 50% by mass or less. By setting the ethylene content in the ethylene-propylene copolymer to 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, flexibility can be achieved with a low addition amount. By setting the ethylene content in the ethylene-propylene copolymer to 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, the occurrence of partial viscosity unevenness during fiber spinning can be prevented, and good spinnability can be maintained.

[0017] When the fibers constituting the spunbonded nonwoven fabric layer are sheath-core composite fibers, the low-crystalline polyolefin resin may be contained throughout the sheath-core composite fibers, or may be unevenly distributed in the core component.

[0018] The content of the low-crystalline polyolefin resin in the polypropylene resin composition is preferably 1% by mass or more and 20% by mass or less. By setting the content to 1% by mass or more, more preferably 3% by mass or more, and even more preferably 8% by mass or more, flexibility can be more effectively imparted. On the other hand, by setting the content to 20% by mass or less, more preferably 15% by mass or less, the properties of the polypropylene resin can be fully exhibited.

[0019] The content of the other resin in the polypropylene resin can be measured by subjecting the laminated nonwoven fabric to infrared spectroscopy and differential scanning calorimetry.

[0020] Additives such as antioxidants, weathering agents, light stabilizers, anti-fogging agents, blocking agents, lubricants, nucleating agents, and pigments such as titanium oxide may be added to the polypropylene resin composition as needed, provided that the effects of the present invention are not impaired.

[0021] The polypropylene resin composition P Ｓ The polypropylene resin composition P preferably has a melt mass flow rate (sometimes abbreviated as MFR) of 75 g / 10 min or more and 850 g / 10 min or less. Ｓ By setting the MFR to 75 g / 10 min or more, more preferably 120 g / 10 min or more, and even more preferably 155 g / 10 min or more, the stress during drawing can be reduced, and stable spinning becomes possible even when drawn at a high spinning speed. This reduces the fiber diameter of the spunbonded nonwoven fabric layer, making the surface smooth and allowing for a laminated nonwoven fabric that has good lamination properties with films when forming a sterilization packaging material. On the other hand, Ｓ By making the MFR of the polypropylene-based resin (P Ｓ ) has a larger molecular weight and the strength per fiber is increased, so that a laminated nonwoven fabric having sufficient strength for use as a sterilization packaging material can be obtained.

[0022] When the fibers constituting the spunbonded nonwoven fabric layer are sheath-core composite fibers, the MFR of the polypropylene resin composition of the core component is preferably 10 g / 10 min or more and 300 g / 10 min or less. By making the MFR of the core component 10 g / 10 min or more, more preferably 20 g / 10 min or more, and even more preferably 30 g / 10 min or more, the stress during drawing can be reduced, enabling stable spinning even when drawn at a high spinning speed. This reduces the fiber diameter of the spunbonded nonwoven fabric layer, smoothing the surface and allowing for a laminated nonwoven fabric that has good lamination properties with films when forming sterilization packaging. On the other hand, by setting the MFR of the core component to 300 g / 10 min or less, more preferably 250 g / 10 min or less, even more preferably 200 g / 10 min or less, even more preferably 100 g / 10 min or less, even more preferably 80 g / 10 min or less, and even more preferably 60 g / 10 min or less, it is possible to suppress the decrease in single fiber strength and obtain a laminated nonwoven fabric having sufficient strength for use as a sterilization packaging material.

[0023] The MFR of the polypropylene resin composition of the sheath component of the core-sheath composite fiber is preferably 10 g / 10 min or more and 200 g / 10 min or less than the MFR of the polypropylene resin of the core component. That is, the difference obtained by subtracting the MFR of the polypropylene resin of the core component from the MFR of the polypropylene resin composition of the sheath component is preferably 10 g / 10 min or more and 200 g / 10 min or less. By making this difference 10 g / 10 min or more, more preferably 15 g / 10 min or more, and even more preferably 20 g / 10 min or more, spinning stress can be concentrated on the core component during spinning, promoting the orientation of the core component and suppressing the orientation of the sheath component. On the other hand, by making this difference 200 g / 10 min or less, a decrease in the single fiber strength of the core-sheath composite fiber can be suppressed and operational problems such as excessive softening during thermal bonding and sticking to a heated roll can be prevented.

[0024] When measuring and interpreting the MFR of the polypropylene resin composition of the core component or sheath component of an islands-in-sea type composite fiber, the measurement should be carried out after reading "sea component" as "sea component" and "core component" as "island component."

[0025] The polypropylene resin composition P Ｍ The polypropylene resin composition P preferably has an MFR of 200 g / 10 min or more and 2500 g / 10 min or less. Ｍ By setting the MFR of the polypropylene resin composition P to 200 g / 10 min or more, more preferably 400 g / 10 min or more, and even more preferably 600 g / 10 min or more, the stress during stretching is reduced, so that a melt-blown nonwoven fabric layer having a small fiber diameter can be obtained while maintaining productivity. Ｍ By setting the MFR to 2500 g / 10 min or less, more preferably 2000 g / 10 min or less, and even more preferably 1500 g / 10 min or less, the spinneret back pressure increases and fluctuations in the resin discharge rate can be suppressed, resulting in a uniform fiber diameter in the melt-blown nonwoven fabric layer and a laminated nonwoven fabric with a uniform texture.

[0026] In the present invention, the MFR of the polypropylene resin composition is measured by ASTM D1238 (Method A), which stipulates that the MFR of the polypropylene resin is measured under a load of 2.16 kg and at a temperature of 230°C.

[0027] The polypropylene resin composition P Ｓ and / or the polypropylene resin composition P Ｍ The MFR can also be adjusted by blending two or more resins with different MFRs. In this case, the MFR of the resin composition blended with the main polypropylene-based resin (referring to the polypropylene-based resin that accounts for the largest mass % of the polypropylene-based resins) is preferably 10 g / 10 min or more and 1,000 g / 10 min or less. By adjusting the MFR of the blended resin composition to 10 g / 10 min or more, more preferably 20 g / 10 min or more, and even more preferably 30 g / 10 min or more, the stress during stretching can be reduced and deterioration of spinnability can be prevented. On the other hand, by adjusting the MFR of the blended resin composition to 1,000 g / 10 min or less, more preferably 800 g / 10 min or less, and even more preferably 600 g / 10 min, the occurrence of partial viscosity unevenness in the blended polypropylene-based resin composition, resulting in non-uniform fineness, can be prevented.

[0028] Furthermore, when spinning fibers as described below, the molecular weight of the resin composition may be reduced to increase the MFR in order to prevent the occurrence of local viscosity variations, to make the fiber fineness uniform, and to further reduce the fiber diameter as described below. Examples of methods for increasing the MFR include a method in which the resin is heated and thermally decomposed before use, and a method in which a peroxide is added and the resin is heat-treated.

[0029] The melting point of the polypropylene resin composition is preferably 120°C or higher and 200°C or lower. By setting the melting point to preferably 120°C or higher, more preferably 130°C or higher, and even more preferably 140°C or higher, heat resistance can be improved. Furthermore, by setting the melting point to preferably 200°C or lower, more preferably 180°C or lower, it becomes easier to cool the yarn discharged from the spinneret, thereby suppressing fusion between fibers and facilitating stable spinning. Here, the melting point (Tmr) of the polypropylene resin composition refers to the maximum melting peak temperature obtained by measuring the polyolefin resin composition by differential scanning calorimetry (DSC).

[0030] [Fibers] The fibers constituting the spunbonded nonwoven fabric layer may be single-component fibers or core-sheath type composite fibers.

[0031] When the sheath-core composite fibers are used as the fibers constituting the spunbonded nonwoven fabric layer, the composite form may be, for example, a concentric type, an eccentric type, an islands-in-the-sea type, etc. Among these, the concentric sheath-core composite fibers are more preferred because they have excellent spinnability and can be uniformly bonded to each other by thermal bonding.

[0032] In the laminated nonwoven fabric of the present invention, the orientation parameter Os of the sheath component of the sheath-core composite fiber is preferably 1.0 or more and 8.0 or less. By setting the orientation parameter Os to 1.0 or more, more preferably 1.5 or more, and even more preferably 2.0 or more, operational problems such as excessive softening of the fiber surface layer during thermal bonding, resulting in sticking to the heated roll, can be effectively prevented. On the other hand, by setting the orientation parameter Os to 8.0 or less, more preferably 6.0 or less, and even more preferably 5.0 or less, flexibility is improved and the fiber surface layer is more likely to soften during thermal bonding, allowing for strong thermal bonding between the fibers, resulting in a laminated nonwoven fabric with excellent strength. The orientation parameter Os can be controlled by the MFR, melting point, and additives of the polypropylene resin, the mass ratio of the sheath component of the sheath-core composite fiber, and / or the spinning temperature and spinning speed, which will be described later.

[0033] In the laminated nonwoven fabric of the present invention, the orientation parameter Oc of the core component of the sheath-core composite fiber is preferably 8.0 or more and 20.0 or less. By setting the orientation parameter Oc to 8.0 or more, more preferably 9.0 or more, and even more preferably 10.0 or more, the strength of the inner fiber layer can be improved, resulting in a spunbonded nonwoven fabric with excellent strength after thermal bonding. Furthermore, operational problems such as the fiber surface layer becoming excessively softened during thermal bonding and sticking to the heated roll can be prevented. On the other hand, by setting the orientation parameter Oc to 20.0 or less, more preferably 19.0 or less, and even more preferably 18.0 or less, flexibility can be improved and excessive stretching stress concentration on the inner fiber layer during spinning can be suppressed, thereby improving spinning stability. The orientation parameter Oc of the core component of the sheath-core composite fiber in the non-fused portion can be controlled by the MFR, melting point, and additives of the polypropylene resin, the mass ratio of the sheath component of the sheath-core composite fiber, and / or the spinning temperature and spinning speed, which will be described later.

[0034] In the core-sheath composite fiber, the orientation ratio (Os / Oc) of the orientation parameter Os of the sheath component to the orientation parameter Oc of the core component is preferably 0.10 or more and 0.90 or less. The orientation parameter is a unitless index, where a larger value indicates that the molecular chains are more oriented in a specific direction, and a smaller value indicates that the molecular chains are more randomly oriented. The orientation parameter is 1.0 when the molecular chains are completely randomly oriented. By setting Os / Oc to 0.10 or more, more preferably 0.15 or more, and even more preferably 0.20 or more, it is possible to prevent excessive concentration of drawing stress on the inner fiber layer during spinning, which would reduce spinning stability. On the other hand, by setting Os / Oc to 0.90 or less, more preferably 0.70 or less, and even more preferably 0.50 or less, it is possible to soften only the fiber surface layer during thermal bonding. This allows the fibers to be firmly thermally bonded while retaining the molecular orientation of the inner fiber layer, thereby more effectively obtaining a laminated nonwoven fabric with excellent strength and virus barrier properties. Furthermore, a laminated nonwoven fabric having excellent flexibility can be obtained.

[0035] The orientation parameter Os of the sheath component and the orientation parameter Oc of the core component of the sheath-core composite fiber are measured by the following method. In the present invention, islands-in-sea composite fibers are also considered to be sheath-core composite fibers. In the case of islands-in-sea composite fibers, as in the case of the sheath-core composite fiber, when measuring and interpreting the orientation parameters Os and Oc, measurements are performed after replacing the "sheath component" with the "sea component" and the "core component" with the "island component," as in the case of the sheath-core composite fiber. (1) A sample of the laminated nonwoven fabric is embedded in a bisphenol-based epoxy resin. (2) After the resin has hardened, a slice is cut using a microtome so that the cross section of the spunbond nonwoven fabric layer containing the core-sheath composite fiber is the cutting surface. The slice thickness is 2 μm. A location where the cutting angle is within 4° from the fiber axis is selected, and the following measurements are performed. (3) Polarized light is incident on a section of the target sheath-core composite fiber from the surface to the center in the fiber axis direction (parallel direction) and in the direction perpendicular to the fiber axis direction (vertical direction), and the Raman spectrum line measurement is performed using a triple Raman spectrometer. For example, the "T-64000" manufactured by Atago Bussan Co., Ltd. can be used as the triple Raman spectrometer. (4) At the positions of the core component and sheath component of the target sheath-core composite fiber, 810 cm －１ Around 840cm －１ Raman band intensity I near ８１０ and I ８４０ and calculate the intensity ratio I ８１０ / I ８４０ (5) Calculate the orientation parameter based on the following formula (a). If the core component is divided into multiple independent regions, measure the orientation parameter in all regions and use the highest value. Orientation parameter = (I ８１０ / I ８４０ ) par / (I ８１０ / I ８４０ ) per (a) Here, (I ８１０ / I ８４０ ) par : Parallel direction intensity ratio (I ８１０ / I ８４０ ) per: Strength ratio in the perpendicular direction (6) The same measurement is carried out at three different points on the laminated nonwoven fabric, the average value of the orientation parameter is calculated, and the value is rounded off to two decimal places.

[0036] The sheath-core composite fiber preferably has a mass ratio of the sheath component of 20% by mass or more and 80% by mass or less. By setting the mass ratio of the sheath component to 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, the sheath components are firmly fused together during thermal bonding, resulting in a laminated nonwoven fabric with excellent strength. On the other hand, by setting the mass ratio of the sheath component to 80% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less, even more preferably 50% by mass or less, even more preferably 45% by mass or less, and even more preferably 40% by mass or less, the proportion of the highly oriented core component is increased, improving the single fiber strength of the sheath-core composite fiber and resulting in a laminated nonwoven fabric with excellent strength.

[0037] The cross-sectional shape of the fibers constituting the spunbonded nonwoven fabric layer can be round or flat. Of these, round cross-sections are preferred because they can produce a laminated nonwoven fabric with excellent flexibility. Although hollow cross-sections can also be used as the cross-sectional shape, solid cross-sections are preferred because they have excellent spinnability and can stably spin even thin fibers.

[0038] The fibers constituting the spunbonded nonwoven fabric layer preferably have an average single fiber diameter of 8 μm or more and 20 μm or less. By setting the average single fiber diameter to 8 μm or more, more preferably 9 μm or more, and even more preferably 10 μm or more, it is possible to prevent a decrease in spinnability and form a spunbonded nonwoven fabric layer with a stable average single fiber diameter. On the other hand, by setting the average single fiber diameter to 20 μm or less, more preferably 17 μm or less, and even more preferably 14 μm or less, it is possible to obtain a laminated nonwoven fabric with high flexibility and uniformity, and excellent texture uniformity suitable for practical use, even if the content ratio of the melt-blown nonwoven fabric layer in the laminated nonwoven fabric is low. The average single fiber fineness can be controlled by the spinning temperature, single-hole output, spinning speed, etc., as described below.

[0039] The average single fiber diameter (μm) of the fibers constituting the spunbond nonwoven fabric layer is calculated by the following procedure: (1) Ten small sample pieces are randomly collected from the laminated nonwoven fabric. (2) Surface photographs are taken using a scanning electron microscope (SEM) (for example, a VHX-D500 manufactured by Keyence Corporation) at a magnification of 500 to 1000 times, and the widths of 10 polyolefin fibers from each sample, for a total of 100 polyolefin fibers, are measured. If the cross section of the core-sheath composite fiber is irregular, the cross-sectional area is measured and the diameter of a perfect circle having the same cross-sectional area is determined. (3) The average value of the 100 measured values ​​is rounded to two decimal places to calculate the average single fiber diameter (μm).

[0040] The fibers constituting the melt-blown nonwoven fabric layer preferably have an average single fiber diameter of 0.1 μm or more and 8.0 μm or less. By setting the average single fiber diameter to 0.1 μm or more, more preferably 0.4 μm or more, fibers can be easily captured when forming the melt-blown nonwoven fabric layer, preventing scattering to the surroundings and resulting in a more uniform laminated nonwoven fabric. On the other hand, by setting the average fiber diameter to 8.0 μm or less, more preferably 7.0 μm or less, the virus barrier properties of the laminated nonwoven fabric can be improved.

[0041] The average single fiber diameter (μm) of the fibers constituting the meltblown nonwoven fabric layer is calculated by the following procedure. (1) Ten small sample pieces are randomly collected from the laminated nonwoven fabric. (2) The collected test pieces are cut using a freezing microtome, and the resulting cross sections are subjected to a conductive treatment. The cross sections are then photographed at a magnification of 4000 to 10000 times using an SEM (for example, a "VHX-D500" manufactured by Keyence Corporation). (3) The widths of 10 fibers from each meltblown nonwoven fabric layer of each sample, for a total of 100 fibers, are measured. (4) The average single fiber diameter (μm) is calculated from the average of the measured values ​​for the 100 fibers.

[0042] [Laminated Nonwoven Fabric] Specific examples of the laminated nonwoven fabric include an SMS nonwoven fabric formed by laminating, in order from the surface of the spunbond nonwoven fabric layer, a spunbond nonwoven fabric layer, and a spunbond nonwoven fabric layer; an SM nonwoven fabric formed by laminating a spunbond nonwoven fabric layer and a meltblown nonwoven fabric layer; an SMMS nonwoven fabric formed by laminating a spunbond nonwoven fabric layer, a meltblown nonwoven fabric layer, and a spunbond nonwoven fabric layer; and an SSMMS nonwoven fabric formed by laminating (spunbond nonwoven fabric layer) / (spunbond nonwoven fabric layer) / (meltblown nonwoven fabric layer) / (meltblown nonwoven fabric layer) / (spunbond nonwoven fabric layer), or (spunbond nonwoven fabric layer) / (meltblown nonwoven fabric layer) / (meltblown nonwoven fabric layer) / (spunbond nonwoven fabric layer). When there are multiple spunbonded or meltblown nonwoven fabric layers, the respective spunbonded or meltblown nonwoven fabric layers may be different from one another. For example, the first and second spunbonded or meltblown nonwoven fabric layers may be made of different types of fibers, have different melting points, be made of a single component or a composite component, have different cross-sectional shapes, or have different thicknesses, strengths, or pressure losses, or any combination thereof, as long as the object of the present invention is achieved. The different types may be selected appropriately depending on the object.

[0043] The laminated nonwoven fabric of the present invention has a fiber count of y (fibers / mm ２ ), the basis weight of the laminated nonwoven fabric is x (g / m ２ ) the following relational expression is satisfied: -600≦a≦0 y≧50 Where, a=y−10.7x+a By setting the above a to −500 or more, preferably −400 or more, and more preferably −350 or more, a laminated nonwoven fabric with excellent breathability can be obtained. On the other hand, by setting a to 0 or less, preferably −30 or less, more preferably −50 or less, and even more preferably −100 or less, a laminated nonwoven fabric with excellent virus barrier properties can be obtained.

[0044] In the present invention, the number y of fibers per unit cross-sectional area of ​​the laminated nonwoven fabric is 0.80 or more and 1.25 or less (number of fibers / mm ２ ) is measured as follows. (1) Twenty test pieces, each 20 mm wide x 20 mm long, are randomly taken from the laminated nonwoven fabric. (2) The taken test pieces are cut using a freezing microtome, and the cross sections obtained are subjected to a conductive treatment. The cross sections are then photographed at a magnification of 1000 to 1800 times using a scanning electron microscope (SEM) (for example, Keyence Corporation's "VHX-D500"). If the SEM photograph of the cross section contains fused sections due to embossing or the like, the observation field is moved and the photograph is taken again. (3) The thickness of the laminated nonwoven fabric is measured at five points in the SEM photograph of the cross section, and the average value is taken as the thickness (t) (mm) of the laminated nonwoven fabric. (4) The length (l) (mm) of the laminated nonwoven fabric contained in the SEM photograph of the cross section is measured. (5) Of the fibers contained in the SEM photograph of the cross section, any fibers with a cross-sectional area of ​​30 μm are measured. ２ The flattening ratio of the above fibers is measured. The flattening ratio refers to the ratio (A / B or B / A) of the longest line segment (A) to the shortest line segment (B) among any line segments that pass through the center of the fiber cross section and have both end points on the circumference. Note that the flattening ratio of fibers at the edge of the cross-sectional SEM photograph, where the fiber cross section cannot be completely observed, is not measured. (6) Of the fibers included in the cross-sectional SEM photograph, the number h (fibers) with an aspect ratio of 0.80 to 1.25 is calculated. (7) h is divided by t and l to obtain the number of fibers per unit cross-sectional area (h / (t x l)) (fibers / mm ２ (8) The steps (2) to (7) are carried out for 20 test pieces, and the average value of (h / (t×l)) for the 20 test pieces is rounded to one decimal place, and the value is calculated as the number of fibers (h / (t×l)) with an aspect ratio of 0.80 or more and 1.25 or less per unit cross-sectional area (pieces / mm ２ )

[0045] h / (t×l) can be adjusted by adjusting the average single fiber diameter of the spunbonded nonwoven fabric layer, the orientation parameter or orientation ratio of the core-sheath composite fibers, or by appropriately adjusting the preheating conditions (temperature, linear pressure, etc.) and the thermal bonding conditions (shape of the bonded portion, compression ratio, temperature, linear pressure, etc.) described below.

[0046] The basis weight of the laminated nonwoven fabric is 50 g / m ２ 90g / m or more ２ The basis weight is 50 g / m or less. ２ or more, preferably 55 g / m ２ More preferably, 60 g / m ２ By adjusting the weight to 90 g / m or more, it is possible to obtain a laminated nonwoven fabric having practical mechanical strength and more effective virus barrier properties. ２ Preferably 85 g / m or less ２ or less, more preferably 80 g / m ２ By using the following, a laminated nonwoven fabric having excellent processability into sterilization packaging materials and excellent breathability can be obtained.

[0047] In the present invention, the basis weight of the laminated nonwoven fabric is measured in accordance with "6.2 Mass per unit area" of JIS L1913:2010 "Testing methods for general nonwoven fabrics" by the following procedure. (1) Three test pieces of 20 cm x 25 cm are taken per meter of sample width. (2) The mass (g) of each piece is measured under standard conditions. (3) The average value is calculated as the mass per meter. ２ Mass per unit (g / m ２ ) is expressed as

[0048] The apparent density of the laminated nonwoven fabric is 0.30 g / cm ３ 0.70g / cm or more ３ It is preferable that the apparent density is 0.30 g / cm or less. ３ More preferably, 0.35 g / cm ３ More preferably, 0.40 g / cm ３ By setting the apparent density to 0.70 g / cm or more, it is possible to suppress the occurrence of fluffing and delamination, and to provide the laminated nonwoven fabric with strength and ease of handling. ３ or less, more preferably 0.60 g / cm ３ More preferably, 0.55 g / cm ３ More preferably, 0.50 g / cm ３By setting the apparent density to the following value, it is possible to prevent a decrease in the voids inside the laminated nonwoven fabric, which would result in a loss of breathability of the laminated nonwoven fabric. The apparent density can be controlled by appropriately adjusting the average single fiber diameter of the fibers and / or the preheating conditions (temperature, linear pressure, etc.) and thermal bonding conditions (shape of the bonded part, compression rate, temperature, linear pressure, etc.) described below.

[0049] Apparent density of nonwoven fabric (g / cm ３ ) is calculated by the following procedure. (1) The thickness (mm) of the nonwoven fabric is measured in accordance with 6.1.1 "Method A" of JIS L1913:2010 "General Nonwoven Fabric Testing Methods" by the following procedure. (A) Using a pressure probe with a diameter of 10 mm, the thickness is measured at 10 points per 1 m at equal intervals in the width direction of the nonwoven fabric at 0.01 mm increments under a load of 10 kPa. (B) The average value of the 10 points is rounded to two decimal places. (2) The apparent density is calculated from the basis weight and thickness before rounding using the following formula, and the result is rounded to two decimal places. Apparent density (g / cm ３ ) = [basis weight (g / m ２ ) ] / [thickness (mm)] × 10 －３ .

[0050] The laminated nonwoven fabric preferably has an arithmetic mean roughness Ra of at least one surface of 1.0 μm or more and 10.0 μm or less. By setting the Ra to 1.0 μm or more, more preferably 2.0 μm or more, and even more preferably 3.0 μm or more, a laminated nonwoven fabric with excellent breathability can be obtained. On the other hand, by setting the Ra to 10.0 μm or less, more preferably 9.0 μm or less, and even more preferably 8.0 μm or less, the surface is smoothed, resulting in a laminated nonwoven fabric with good adhesion to films when forming sterilization packaging. The arithmetic mean roughness can be controlled by appropriately adjusting the preheating conditions (temperature, linear pressure, etc.) and thermal bonding conditions (shape of the bonded portion, compression rate, temperature, linear pressure, etc.) described below.

[0051] In the present invention, the arithmetic mean roughness Ra of the surface of the laminated nonwoven fabric is determined in accordance with "4.2.1 Arithmetic mean height of the profile curve" of JIS B0601:2013 "Geometric Product Specifications (GPS) - Surface Texture: Profile Curve Method - Terms, Definitions, and Surface Texture Parameters," and is measured as follows: (1) Ten 100 mm wide x 100 mm wide test pieces are taken from the laminated nonwoven fabric at equal intervals across the width of the laminated nonwoven fabric per meter. (2) The test pieces are placed on a sample stage, and the profile curves in the warp direction (the longitudinal direction of the laminated nonwoven fabric, i.e., the MD direction) and the weft direction (the width direction of the laminated nonwoven fabric, i.e., the CD direction) are measured for both sides of the laminated nonwoven fabric using a surface roughness measuring instrument (for example, a small surface roughness measuring instrument such as the "SURFTEST SJ-210" manufactured by Mitutoyo Corporation). The arithmetic mean roughness Ra (μm) is determined as the arithmetic mean roughness Ra. (3) The measured values ​​of all the test pieces on both sides are averaged and rounded to two decimal places to obtain the arithmetic mean roughness Ra (μm).

[0052] The air permeability of the laminated nonwoven fabric is 1.0 cm ３ / (cm ２ It is preferable that the air permeability is 1.0 cm ３ / (cm ２ sec) or more, more preferably 1.5 cm ３ / (cm ２ By setting the airflow rate to 5.0 cm 3 or more, when the material is used as a sterilization packaging material, the sterilization treatment can be carried out efficiently on the object to be sterilized. ３ / (cm ２ The ventilation rate is preferably 5.0 cm ３ / (cm ２ seconds) or less, more preferably 3.5 cm ３ / (cm ２ seconds) or less, more preferably 2.0 cm ３ / (cm ２ By setting the sterilization time to 1 / 2 second or less, the sterilized state of the object to be sterilized after sterilization can be maintained from distribution to use. The amount of air permeation can be adjusted by the basis weight, average single fiber diameter, basis weight of the melt-blown nonwoven fabric layer, preheating conditions (temperature, linear pressure, etc.), thermocompression conditions (compression rate, temperature, and linear pressure), etc.

[0053] In the present invention, the air permeability of a laminated nonwoven fabric is measured in accordance with "6.8.1 Frazier method" of JIS L1913:2010 "General nonwoven fabric testing methods" by the following procedure. (1) A test piece of 80 cm x 100 cm is cut out from the laminated nonwoven fabric. (2) Measurements are taken at 20 random points on the test piece at a barometer pressure of 125 Pa. (3) The average value of the 20 points is calculated as the basis weight (g / m ２ ) and round to three decimal places.

[0054] The tensile strength and elongation product per unit area of ​​the laminated nonwoven fabric is 0.50 (N / 50 mm) / (g / m ２ ) or more 2.00 (N / 50mm) / (g / m ２ It is preferable that the tensile strength / elongation product per unit area is 0.50 (N / 50 mm) / (g / m ２ ) or more, more preferably 0.55 (N / 50 mm) / (g / m ２ ) or more, more preferably 0.60 (N / 50 mm) / (g / m ２ ) or more, more preferably 0.65 (N / 50 mm) / (g / m ２ ) or more, a laminated nonwoven fabric having excellent strength can be obtained even with a low basis weight. ２ ) or less, preferably 1.50 (N / 50 mm) / (g / m ２ ) or less, more preferably 1.30 (N / 50 mm) / (g / m ２ ) or less, it is possible to prevent the flexibility of the laminated nonwoven fabric from decreasing and the texture from being impaired.

[0055] The tensile strength / elongation product per unit area weight can be controlled by appropriately adjusting the MFR of the polypropylene resin, additives, the average single fiber diameter of the sheath / core composite fibers, the ratio (Os / Oc) of the orientation parameter Os of the sheath component of the sheath / core composite fibers to the orientation parameter Oc of the core component of the sheath / core composite fibers in the spunbonded nonwoven fabric layer, the spinning speed, preheating conditions (temperature, linear pressure, etc.), and thermal bonding conditions (shape of the bonded portion, compression rate, temperature, linear pressure, etc.), which will be described later.

[0056] In the present invention, the tensile strength-elongation product per unit area weight of a laminated nonwoven fabric is measured in accordance with "6.3 Tensile strength and elongation (ISO method)" of JIS L1913:2010 "General nonwoven fabric testing methods," using the following procedure. (1) Three 50 mm x 300 mm test pieces are taken per meter of nonwoven fabric width, with the long side facing the warp direction (longitudinal direction of the nonwoven fabric). (2) The test pieces are placed in a tensile tester with a grip spacing of 200 mm. (3) A tensile test is conducted at a pulling speed of 100 mm / min, and the maximum strength and the elongation at maximum strength are measured. Here, the elongation is not converted to a percentage (%) but is expressed as the ratio of the elongation to the initial grip spacing. (4) The maximum strength and the average value of the elongation at maximum strength measured for each test piece are calculated, and the tensile strength / elongation product per unit area is calculated based on the following formula, and rounded to two decimal places. Tensile strength / elongation product per unit area ((N / 50 mm) / (g / m ２ )) = [average value of maximum strength (N / 50mm)] x [average value of elongation at maximum strength (-)] / basis weight (g / m ２ ).

[0057] [Method for producing laminated nonwoven fabric] Next, a preferred embodiment of the method for producing the laminated nonwoven fabric of the present invention will be specifically described.

[0058] The method for producing the laminated nonwoven fabric of the present invention includes the steps of forming at least one first spunbonded nonwoven fabric layer, forming at least one meltblown nonwoven fabric layer on the at least one first spunbonded nonwoven fabric layer, forming at least one second spunbonded nonwoven fabric layer on the at least one meltblown nonwoven fabric layer to form a laminated web (the steps up to this point are referred to as the "laminating step"), preheating by bringing a heating surface into contact with only one surface of the laminated web to obtain a preheated laminated web (preheating step), and fusing the preheated laminated web using a thermal calendar roll consisting of a pair of upper and lower flat rolls to form a laminated nonwoven fabric (thermal fusing step).

[0059] (Laminating Step) In the laminating step, the spunbond nonwoven fabric layer and the meltblown nonwoven fabric layer can be formed by the spunbonding method and the meltblown nonwoven fabric layer, respectively. As a method for laminating these to form a laminate, for example, a method can be preferably adopted in which fibers formed by the meltblown method are deposited directly on the first formed spunbond nonwoven fabric layer to form a meltblown nonwoven fabric layer, and then fibers formed by the spunbonding method are deposited to form a spunbond nonwoven fabric layer, thereby forming a laminate by sequentially depositing additional fibers on the obtained nonwoven fabric layers.

[0060] The spunbond nonwoven web can be formed by spinning a molten polypropylene resin composition into long fibers from a spinneret, cooling and stretching the fibers, and then collecting the fibers on a moving net. The stretching may be performed by suction with compressed air using an ejector or the like.

[0061] The spinneret and ejector may have various shapes such as a round shape, a rectangular shape, etc. Among them, a combination of a rectangular spinneret and a rectangular ejector is preferably used because it uses a relatively small amount of compressed air, is excellent in energy cost, is less likely to cause fusion or friction between the yarns, and facilitates opening of the yarns.

[0062] In the present invention, the polypropylene resin composition is melted in an extruder, metered, and fed to a spinneret to be spun into continuous fibers. The spinning temperature when the polypropylene resin composition is melted and spun is preferably 200° C. or higher and 270° C. or lower, more preferably 210° C. or higher and 260° C. or lower, and even more preferably 220° C. or higher and 250° C. or lower. By setting the spinning temperature within the above range, a stable molten state can be achieved, and excellent spinning stability can be obtained.

[0063] The spun continuous fiber yarn is cooled by, for example, forcibly blowing cold air onto the yarn, naturally cooling at the ambient temperature around the yarn, or adjusting the distance between the spinneret and the ejector, or a combination of these methods can be used. The cooling conditions can be appropriately adjusted in consideration of the output per hole of the spinneret, the spinning temperature, the ambient temperature, etc.

[0064] Next, the cooled and solidified yarn may be drawn by compressed air injected from an ejector. The spinning speed is preferably 3000 m / min to 6500 m / min, more preferably 3500 m / min to 6500 m / min, and even more preferably 4000 m / min to 6500 m / min. By setting the spinning speed to 3000 m / min to 6500 m / min, high productivity is achieved, and the orientation and crystallization of the fibers is promoted, making it possible to obtain high-strength long fibers.

[0065] The meltblown nonwoven fabric layer can be formed by a known manufacturing method. A polypropylene resin composition is melted in an extruder and fed to a nozzle. Hot air is blown onto the extruded filaments to thin them. The meltblown nonwoven fabric layer is then formed on a previously formed spunbonded nonwoven fabric layer or meltblown nonwoven fabric layer placed on a collection net or a moving net. The meltblowing method does not require complicated processes, can easily produce fine fibers of several micrometers, and can exhibit high water resistance.

[0066] The long fibers can be collected on a moving net or on an already formed spunbond or meltblown nonwoven web that is placed on the moving net to further form a nonwoven web.

[0067] (Preheating Step) In the preheating step, the laminated web is preheated by contacting only one surface with the heating surface of a heating device. Preheating is preferably performed by fusing the collected fiber web using a pair of upper and lower flat rolls, or by placing a flat roll or a heating plate above a net conveyor and fusing the web between the net conveyor and the flat roll or heating plate. This method allows for a laminated nonwoven fabric with excellent surface smoothness and virus barrier properties to be obtained while maintaining breathability. The "flat roll" used in these methods refers to a metal roll or elastic roll with a smooth surface. Furthermore, the upper and lower pair of flat rolls refers to a pair of metal rolls or a pair of metal rolls and elastic rolls. Here, an elastic roll refers to a roll made of a material that is more elastic than a metal roll. Examples of elastic rolls include so-called paper rolls made of paper, cotton, aramid paper, etc., as well as resin rolls made of urethane resins, epoxy resins, silicone resins, polyester resins, hard rubber, etc., or mixtures of these.

[0068] In this preheating, when a pair of upper and lower flat rolls are used for fusion bonding, only one of the flat rolls serves as a heated surface. To give an example of an embodiment, only one of the flat rolls has a heating mechanism such as a heater and is a roll (heated roll) heated to a temperature described below, while the other flat roll does not have such a heating mechanism, or has a heating mechanism but the heater is switched off. In this embodiment, the "heated surface" refers to the surface of the heated roll.

[0069] In this preheating, when a flat roll is placed above a net conveyor and preheating is performed between the net conveyor and the flat roll, the flat roll is preferably made of metal, and a heating mechanism such as a heater is provided only on this flat roll, which is heated to a temperature described below. This flat roll is the heated roll, and the surface of this heated roll is the "heated surface" mentioned above.

[0070] Furthermore, in this preheating, when a heating plate is placed above the net conveyor and preheating is performed between the net conveyor and the heating plate, the heating plate is preferably made of metal, and a heating mechanism such as a heater is provided only on this heating plate, and it is heated to a temperature described below. The surface of this heating plate that comes into contact with the fiber web is the "heating surface." The temperature of the heating surface during this preheating is the preheating temperature.

[0071] In the preheating step, the preheating temperature is preferably 40°C or higher and 95°C or lower. By setting the preheating temperature to 40°C or higher, more preferably 45°C or higher, and even more preferably 50°C or higher, thermal crystallization of the fibers before thermocompression bonding can be promoted, preventing a loss of breathability of the nonwoven fabric after thermocompression bonding. Furthermore, deterioration of the texture due to the surface layer of the nonwoven fabric being turned up or blown away during transport on the net can be prevented, and transportability from capturing the yarns to thermocompression bonding can be improved. On the other hand, by setting the preheating temperature to 95°C or lower, more preferably 75°C or lower, and even more preferably 70°C or lower, thermal crystallization of the fibers before thermocompression bonding can be suppressed, resulting in a nonwoven fabric with even better virus barrier properties.

[0072] Furthermore, when a flat roll is used in the preheating step, the linear pressure of the heating surface is preferably 1 N / cm or more and 100 N / cm or less. By setting the lower limit of the linear pressure range to 1 N / cm or more, preferably 5 N / cm or more, the fiber web on the heating surface can be sufficiently preheated. On the other hand, by setting the upper limit of the range to 100 N / cm or less, preferably 50 N / cm or less, heat can be transferred to the interior of the fiber web on the heating surface, thermal crystallization can be suppressed, and sufficient pressure bonding can be achieved during thermal bonding.

[0073] (Heat-sealing step) In the heat-sealing step, the laminated web is fused using a heat calendar roll consisting of a pair of upper and lower flat (smooth) rolls, which allows the thickness of the spunbonded nonwoven fabric to be adjusted to a constant value, and a nonwoven fabric with excellent surface smoothness can be obtained.

[0074] As the surface material of the heat calender roll, it is preferable to use a pair of metal rolls in order to obtain a sufficient heat-pressure bonding effect.

[0075] The surface temperature of the heat calender roll in the heat fusion step is preferably (Tm-50)°C to (Tm-5)°C, where Tm (°C) is the melting point of the polypropylene resin used. By setting the surface temperature of the heat calender roll to (Tm-50)°C or higher, more preferably (Tm-45)°C or higher, it is possible to obtain a laminated nonwoven fabric with adequate fusion and practical strength. Furthermore, by setting the surface temperature of the heat calender roll to (Tm-5)°C or lower, more preferably (Tm-8)°C or lower, excessive fusion is suppressed, and the laminated nonwoven fabric can be obtained with adequate breathability and processability suitable for use in sterilization packaging applications.

[0076] The linear pressure of the hot calendar roll during fusion is preferably 50 N / cm or more and 500 N / cm or less. By setting the linear pressure of the hot embossing roll to 50 N / cm or more, more preferably 100 N / cm or more, and even more preferably 150 N / cm or more, it is possible to obtain a laminated nonwoven fabric with excellent strength through moderate fusion. On the other hand, by setting the linear pressure of the hot calendar roll to 500 N / cm or less, more preferably 400 N / cm or less, and even more preferably 300 N / cm or less, it is possible to more effectively obtain a laminated nonwoven fabric with moderate breathability and processability suitable for use in sterilization packaging applications.

[0077] In the method for producing a laminated nonwoven fabric of the present invention, for the purpose of adjusting the thickness of the laminated nonwoven fabric, thermocompression bonding can be performed using a pair of hot calender rolls consisting of upper and lower flat rolls before and / or after fusion bonding using the above-mentioned hot calender rolls. The pair of hot calender rolls refers to metal rolls or elastic rolls with smooth surfaces, and a pair of metal rolls or a pair of metal rolls and elastic rolls can be used.

[0078] The term "elastic roll" used herein refers to a roll made of a material that has greater elasticity than a metal roll. Examples of elastic rolls include so-called paper rolls made of paper, cotton, aramid paper, etc., and rolls made of resins such as urethane resin, epoxy resin, silicone resin, polyester resin, hard rubber, and mixtures of these.

[0079] [Sterilization Packaging Material] The laminated nonwoven fabric is suitable for sterilization packaging material. That is, the sterilization packaging material of the present invention uses the laminated nonwoven fabric of the present invention.

[0080] The laminated nonwoven fabric and sterilization packaging material of the present invention preferably have a virus barrier property of 2.0 (LRV) or more and 6.0 (LRV) or less. Having a virus barrier property of 2.0 (LRV) or more, more preferably 2.5 (LRV) or more, and even more preferably 3.0 (LRV) or more, enables the laminated nonwoven fabric to maintain a sterile state from the time of distribution to the time of use as a sterilization packaging material after sterilization. On the other hand, having a virus barrier property of 6.0 (LRV) or less, preferably 5.5 (LRV) or less, prevents a decrease in the breathability of the spunbond nonwoven fabric and a loss of gas permeability during sterilization.

[0081] The virus barrier properties of the laminated nonwoven fabric and the sterilization packaging material are determined by the polypropylene resin composition P constituting the melt-blown nonwoven fabric layer. Ｍ The control can be achieved by appropriately adjusting the MFR, the average single fiber diameter of the melt-blown nonwoven fabric layer, the above-mentioned Os / Oc, the spinning speed described below, preheating conditions (temperature, linear pressure, etc.), and thermal bonding conditions (shape of the bonded portion, compression rate, temperature, linear pressure, etc.).

[0082] In the present invention, the virus barrier properties of the laminated nonwoven fabric and the sterilized packaging material are measured by the following procedure in accordance with ASTM F1608. The test bacteria used are Bacillus subtilis spores suspended in sterilized water, and the test bacteria concentration is 10 per port after 15 minutes of treatment. ６(1) Place a membrane filter in the filter unit that will capture the bacteria, and place a test piece on top of it. Six filter units are prepared, one of which will have no sample placed in it and will serve as a control. (2) Place a filter unit in each port. (3) Set the air flow rate inside the device to 2.8 L / min, and while spraying bacteria from the nebulizer, pass the aerosol of the bacterial solution, which has been uniformly dispersed by a fan, through the sample on the membrane filter. This process is carried out for 15 minutes. (4) Count and measure the number of bacteria on the membrane filter. Let N be the number of bacteria in the control, and M be the number of bacteria in the sample. (5) Calculate the virus barrier value of the sample using the following formula, giving it 5 points, and round off the average to three decimal places. Virus barrier value (LRV) = Log(N / M).

[0083] The laminated nonwoven fabric of the present invention will be specifically described based on examples. However, the present invention is not limited to these examples. In measuring each physical property, unless otherwise specified, the measurement was performed according to the above-mentioned method.

[0084] (1) Basis weight of laminated nonwoven fabric (g / m ２ The basis weight of the laminated nonwoven fabric was measured based on the above-mentioned method.

[0085] (2) The number of fibers per unit cross-sectional area with an aspect ratio of 0.80 to 1.25 (number / mm ２ Based on the above-mentioned method, the number of fibers having an aspect ratio of 0.80 or more and 1.25 or less per unit cross-sectional area was measured.

[0086] (3) Average Single Fiber Diameter (μm) of Spunbond Nonwoven Fabric Layer and Meltblown Nonwoven Fabric Layer Measurement was performed using a scanning electron microscope, "VHX-D500" manufactured by Keyence Corporation, according to the method described above.

[0087] (4) Orientation parameter of core-sheath composite fiber of laminated nonwoven fabric The triple Raman spectrometer "T-64000" manufactured by Atago Bussan Co., Ltd. was used and measured by the above-mentioned method. The measurement conditions were as follows: Measurement mode: Microscopic Raman (polarized measurement) Objective lens: ×100 Beam diameter: 1 μm Light source: Ar ＋Laser / 514.5 nm; Laser power: 60 mW; Diffraction grating: Single 1800 gr / mm; Cross slit: 100 μm; Detector resolution: 1024×256.

[0088] (5) Arithmetic mean roughness Ra (μm) of surface The surface roughness was measured by the above-mentioned method using a small surface roughness measuring instrument "SURFTEST SJ-210" manufactured by Mitutoyo Corporation.

[0089] (6) Apparent density (g / cm) of the laminated nonwoven fabric ３ The apparent density of the laminated nonwoven fabric was calculated based on the above-mentioned method.

[0090] (7) Tensile strength and elongation product ((N / 50 mm) / (g / m ２ )) Based on the above-mentioned method, the tensile strength / elongation product of the laminated nonwoven fabric was calculated.

[0091] (8) Air permeability of the laminated nonwoven fabric (cm ３ / (cm ２ The air permeability of the laminated nonwoven fabric was calculated based on the above-mentioned method.

[0092] The breathability was evaluated on a scale of 1 to 3 according to the following criteria. A higher score indicates better performance, and a score of 2 or higher was judged to be "sufficiently breathable." 3: Airflow of 1.5 cm ３ / (cm ２ 2: The ventilation rate is 1.0 cm ３ / (cm ２ ・sec) or more 1.5cm ３ / (cm ２ 1: The airflow rate is less than 1.0 cm ３ / (cm ２ ・seconds).

[0093] (9) Virus Barrier Property (LRV) and Virus Barrier Performance of Laminated Nonwoven Fabric The virus barrier property of the laminated nonwoven fabric was calculated based on the above-mentioned method.

[0094] The virus barrier performance was evaluated from 1 to 3 according to the criteria in the table below. The higher the score, the better the performance, and a score of 2 or higher was judged to have "sufficient virus barrier performance." 3: The virus barrier performance is 3.5 LRV or higher. 2: The virus barrier performance is 2.0 LRV or higher and less than 3.5 LRV. 1: The virus barrier performance is less than 2.0 LRV.

[0095] (10) Overall Evaluation When the total score for breathability and viral barrier performance was 6, the overall evaluation was "A," when the total score for breathability and viral barrier performance was 5, the overall evaluation was "B," and when the scores for breathability and viral barrier performance were each 2, totaling 4, the overall evaluation was "C," with A to C being considered pass. On the other hand, when the score for either breathability or viral barrier performance was 1, the overall evaluation was "F."

[0096] [Example 1] (First spunbond nonwoven fabric web) A polypropylene resin consisting of a homopolymer with a melt flow rate (MFR) of 35 g / 10 min and a melting point of 163°C was used as the core component. A polypropylene resin consisting of a homopolymer with an MFR of 60 g / 10 min and a melting point of 163°C was used as the sheath component. Each component was melted in an extruder, and a concentric sheath-core composite fiber with a sheath component ratio of 30 mass% was spun from a spinneret with a hole diameter of φ0.40 mm and a hole depth of 0.8 mm at a spinning temperature of 235°C and a single-hole throughput of 0.30 g / min. The spun yarn was cooled and solidified, and then pulled and stretched in a rectangular ejector with compressed air at an ejector pressure of 0.35 MPa. The yarn was collected on a moving net and spun into a concentric sheath-core composite fiber with a basis weight of 31.0 g / m2 consisting of polypropylene long fibers. ２ The average single fiber diameter of the fibers constituting the first spunbond nonwoven web was 11.5 μm.

[0097] (Melt-blown nonwoven fabric web) A polypropylene resin consisting of a homopolymer with an MFR of 1,100 g / min was melted in an extruder and spun from a die with a hole diameter of 0.25 mm at a spinning temperature of 260°C and a single-hole throughput of 0.10 g / min. Air was then sprayed onto the yarn at an air temperature of 290°C and an air pressure of 0.10 MPa, and the yarn was collected on the web of the first spunbond nonwoven fabric layer to form a melt-blown nonwoven fabric web. The basis weight of the melt-blown nonwoven fabric web was 13 g / m. ２ The average single fiber diameter was 1.0 μm.

[0098] (Second spunbond nonwoven fabric web) A second spunbond nonwoven fabric web was formed on the meltblown nonwoven fabric web under the same conditions as for the first spunbond nonwoven fabric web, and a total basis weight of 75 g / m ２ A laminated web of 1000 .mu.m was obtained.

[0099] (Laminated Nonwoven Fabric) The laminated web was preheated using a pair of upper and lower flat rolls at a temperature of 60°C and a linear pressure of 30 N / cm. Next, using a thermal calendar roll consisting of a pair of upper and lower flat (smooth) rolls, the laminated web was heat-sealed under conditions of a linear pressure of 300 N / cm and a thermal bonding temperature of 150°C, to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 1.

[0100] Example 2 (First spunbond nonwoven fabric web) The core component was a mixture of a homopolymer polypropylene resin having an MFR of 35 g / 10 min and a melting point of 163°C and a low-crystalline olefin resin, an ethylene-propylene copolymer having an MFR of 20 g / 10 min, kneaded together to provide a 10% by mass blend of ethylene-propylene copolymer with a copolymerization rate of 20% by mass. The sheath component was a mixture of a homopolymer polypropylene resin having an MFR of 60 g / 10 min and a melting point of 163°C and a low-crystalline olefin resin, an ethylene-propylene copolymer having an MFR of 20 g / 10 min, kneaded together to provide a 10% by mass blend of ethylene-propylene copolymer with a copolymerization rate of 20% by mass. A first spunbond nonwoven fabric web was formed in the same manner as in Example 1, except for the above.

[0101] (Meltblown Nonwoven Fabric Web) A meltblown nonwoven fabric web was formed in the same manner as in Example 1 on the first spunbond nonwoven fabric web.

[0102] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0103] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 1.

[0104] Example 3 (First spunbond nonwoven fabric web) A first spunbond nonwoven fabric web was formed in the same manner as in Example 1.

[0105] (Melt-blown nonwoven fabric web) A melt-blown nonwoven fabric web was formed on the first spunbond nonwoven fabric web in the same manner as in Example 1, except that the air pressure was set to 0.05 MPa.

[0106] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0107] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The results are shown in Table 3.

[0108] Example 4 (First spunbond nonwoven fabric web) A first spunbond nonwoven fabric web was formed in the same manner as in Example 1.

[0109] (Meltblown Nonwoven Fabric Web) A meltblown nonwoven fabric web was formed in the same manner as in Example 1 on the first spunbond nonwoven fabric web.

[0110] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0111] (Laminated Nonwoven Fabric) The laminated fiber web was subjected to temporary bonding and heat fusion bonding in the same manner as in Example 1, except that the preheating temperature was set to 95° C., to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 1.

[0112] Example 5 (First spunbond nonwoven fabric web) A first spunbond nonwoven fabric web was formed in the same manner as in Example 1, except that the ejector pressure was set to 0.55 MPa.

[0113] (Meltblown Nonwoven Fabric Web) A meltblown nonwoven fabric web was formed in the same manner as in Example 1 on the first spunbond nonwoven fabric web.

[0114] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0115] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 2.

[0116] Example 6 (First spunbond nonwoven fabric web) A polypropylene resin consisting of a homopolymer with an MFR of 120 g / 10 min and a melting point of 163° C. was used as the core component. A polypropylene resin consisting of a homopolymer with an MFR of 150 g / 10 min and a melting point of 163° C. was used as the sheath component. A first spunbond nonwoven fabric web was formed in the same manner as in Example 1 except for the above.

[0117] (Meltblown Nonwoven Fabric Web) A meltblown nonwoven fabric web was formed in the same manner as in Example 1 on the first spunbond nonwoven fabric web.

[0118] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0119] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 2.

[0120] Example 7 (First spunbond nonwoven web) A first spunbond nonwoven web was formed in the same manner as in Example 6, except that the ratio of the sheath component in the concentric core-sheath composite fibers was 50 mass %.

[0121] (Meltblown Nonwoven Fabric Web) A meltblown nonwoven fabric web was formed in the same manner as in Example 1 on the first spunbond nonwoven fabric web.

[0122] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0123] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 2.

[0124] [Example 8] (First spunbond nonwoven fabric web) Basis weight 37 g / m ２ A first spunbond nonwoven web was formed in the same manner as in Example 7, except that:

[0125] (Melt-blown nonwoven web) The basis weight of the melt-blown nonwoven web is 16 g / m ２ A meltblown nonwoven fabric web was formed on the first spunbonded nonwoven fabric web in the same manner as in Example 1, except that:

[0126] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0127] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 2.

[0128] [Example 9] (First spunbond nonwoven fabric web) Basis weight 21 g / m ２ A first spunbond nonwoven fabric web was formed in the same manner as in Example 7, except that:

[0129] (Melt-blown nonwoven web) The basis weight of the melt-blown nonwoven web is 8 g / m ２ A meltblown nonwoven fabric web was formed on the first spunbonded nonwoven fabric web in the same manner as in Example 1, except that:

[0130] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0131] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 3.

[0132] Example 10 (First spunbond nonwoven fabric web) A first spunbond nonwoven fabric web was formed in the same manner as in Example 6, except that the ratio of the sheath component in the concentric core-sheath composite fibers was 20 mass %.

[0133] (Meltblown Nonwoven Fabric Web) A meltblown nonwoven fabric web was formed in the same manner as in Example 1 on the first spunbond nonwoven fabric web.

[0134] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0135] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 3.

[0136] [Example 11] (First spunbond nonwoven fabric web) Basis weight 37 g / m ２ A first spunbond nonwoven fabric web was formed in the same manner as in Example 10, except that:

[0137] (Melt-blown nonwoven web) The basis weight of the melt-blown nonwoven web is 16 g / m ２ A meltblown nonwoven web was formed in the same manner as in Example 1, except that:

[0138] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0139] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 3.

[0140] [Example 12] (First spunbond nonwoven fabric web) Basis weight 21 g / m ２ A first spunbond nonwoven fabric web was formed in the same manner as in Example 10, except that:

[0141] (Melt-blown nonwoven web) The basis weight of the melt-blown nonwoven web is 8 g / m ２ A meltblown nonwoven web was formed in the same manner as in Example 1, except that:

[0142] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0143] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 3.

[0144] Comparative Example 1 (First spunbond nonwoven fabric web) A first spunbond nonwoven fabric web was formed in the same manner as in Example 1, except that a polypropylene resin consisting of a homopolymer having an MFR of 200 g / 10 min and a melting point of 163°C was used as the core component and the sheath component, i.e., essentially single-component fibers were spun.

[0145] (Meltblown Nonwoven Fabric Web) A meltblown nonwoven fabric web was formed in the same manner as in Example 1 on the first spunbond nonwoven fabric web.

[0146] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0147] (Laminated Nonwoven Fabric) The laminated fiber web was preheated and heat-sealed in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 4.

[0148] Comparative Example 2 (First spunbond nonwoven fabric web) The average single fiber diameter was 14.0 μm and the basis weight was 41 g / m ２ A first spunbond nonwoven fabric web was formed in the same manner as in Example 1, except that:

[0149] (Melt-blown nonwoven web) The average single fiber diameter is 1.0 μm and the basis weight is 18.0 g / m ２ A meltblown nonwoven web was formed on the first spunbonded nonwoven web in the same manner as in Example 1, except that:

[0150] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0151] (Laminated Nonwoven Fabric) The laminated fiber web was subjected to preheating and heat fusion in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 4.

[0152] Comparative Example 3 (First spunbond nonwoven fabric web) A polypropylene resin consisting of a homopolymer with an MFR of 35 g / 10 min and a melting point of 163° C. was used as the core component. A polypropylene resin consisting of a homopolymer with an MFR of 150 g / 10 min and a melting point of 163° C. was used as the sheath component. A first spunbond nonwoven fabric web was formed in the same manner as in Example 1 except for the above.

[0153] (Meltblown Nonwoven Fabric Web) A meltblown nonwoven fabric web was formed in the same manner as in Example 1 on the first spunbond nonwoven fabric web.

[0154] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0155] (Laminated Nonwoven Fabric) The laminated fiber web was subjected to preheating and heat fusion in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 4.

[0156] Comparative Example 4 (First spunbond nonwoven web) A first spunbond nonwoven web was formed in the same manner as in Example 6, except that the ratio of the sheath component in the concentric core-sheath composite fibers was 10 mass %.

[0157] (Meltblown Nonwoven Fabric Web) A meltblown nonwoven fabric web was formed in the same manner as in Example 1 on the first spunbond nonwoven fabric web.

[0158] (Second Spunbond Nonwoven Web) A second spunbond nonwoven web was formed on the meltblown nonwoven web under the same conditions as for the first spunbond nonwoven web, to obtain a laminated fiber web.

[0159] (Laminated Nonwoven Fabric) The laminated fiber web was subjected to preheating and heat fusion in the same manner as in Example 1 to obtain a laminated nonwoven fabric. The evaluation results are shown in Table 4.

[0160] In the table, "S web" means a spunbond web, "M web" means a meltblown web, "S nonwoven fabric layer" means a spunbond nonwoven fabric layer, and "M nonwoven fabric layer" means a meltblown nonwoven fabric layer.

[0161]

[0162]

[0163]

[0164]

[0165] As shown in Tables 1 to 3, the laminated nonwoven fabrics of Examples 1 to 12 were laminated nonwoven fabrics with excellent breathability and virus barrier performance. On the other hand, as shown in Table 4, the laminated nonwoven fabrics of Comparative Examples 1 to 4 were laminated nonwoven fabrics that did not have sufficient breathability or sufficient virus barrier performance.

Claims

1. A laminated nonwoven fabric comprising at least one spunbonded nonwoven fabric layer and at least one meltblown nonwoven fabric layer, wherein the at least one spunbonded nonwoven fabric layer and the at least one meltblown nonwoven fabric layer are both made of fibers made of a polypropylene-based resin composition containing primarily polypropylene-based resin, and the basis weight of the laminated nonwoven fabric is 50 g / m ２ 90g / m or more ２ The number of fibers per unit cross-sectional area of ​​the laminated nonwoven fabric is y (fibers / mm ２ ), and the basis weight of the laminated nonwoven fabric is x, the laminated nonwoven fabric satisfies the following relational expression: -600≦a≦0 y≧50, where a=y−10.7x 2. The laminated nonwoven fabric according to claim 1, wherein the arithmetic mean roughness Ra of at least one surface of said laminated nonwoven fabric is 1.0 μm or more and 10.0 μm or less.

3. The apparent density of the laminated nonwoven fabric is 0.30 g / cm ３ 0.60g / cm or more ３ The laminated nonwoven fabric according to claim 1 or 2, wherein:

4. The tensile strength and elongation product per unit area of ​​the laminated nonwoven fabric, calculated by the following formula, is 0.50 (N / 50 mm) / (g / m ２ ) or more 1.50 (N / 50mm) / (g / m ２ 3. The laminated nonwoven fabric according to claim 1, wherein the tensile strength / elongation product per unit area (N / 50 mm) / (g / m) is equal to or less than 1. ２ )) = [average value of maximum strength (N / 50mm)] x [average value of elongation at maximum strength (-)] / basis weight (g / m ２ ).

5. The laminated nonwoven fabric according to claim 1 or 2, wherein the polypropylene resin composition contains a low-crystalline polyolefin resin.

6. The laminated nonwoven fabric according to claim 5, wherein the content of the low-crystalline polyolefin resin in the polypropylene resin composition is 1% by mass or more and 20% by mass or less.

7. The laminated nonwoven fabric according to claim 5, wherein the low-crystalline polyolefin resin is an ethylene-propylene copolymer.

8. A method for producing a laminated nonwoven fabric as defined in claim 1 or 2, comprising the steps of: forming at least one layer of a first spunbond nonwoven fabric web; forming at least one layer of a meltblown nonwoven fabric web on said at least one layer of first spunbond nonwoven fabric web; forming at least one layer of a second spunbond nonwoven fabric web on said at least one layer of meltblown nonwoven fabric web to form a laminated web; preheating only one surface of said laminated web by bringing the heating surface of a heating device into contact with the laminated web to obtain a preheated laminated web; and fusing said preheated laminated web using a heat calendar roll consisting of a pair of upper and lower flat rolls to form said laminated nonwoven fabric, wherein the preheating temperature in the step of obtaining said preheated laminated web is 40°C or higher and 95°C or lower.

9. A sterilization packaging material comprising the laminated nonwoven fabric according to claim 1 or 2.

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