Spunbond nonwovens and hygiene materials

Abstract

The present invention provides a spun-bonded nonwoven fabric which has water absorption and quick-drying properties that are sufficient to maintain comfort when worn, and which has a texture that feels soft. This spun-bonded nonwoven fabric is suitable for use in a sanitary material.　A spun-bonded nonwoven fabric which has a fused part and a non-fused part, wherein: the ratio of the average single fiber diameter (Da) of the fibers in one surface (A) to the average single fiber diameter (Db) of the fibers in the other surface (B), namely Da / Db is 1.1 or more; the contact angles with water of the surface (A) and the surface (B) are both 30° or less; and the tortuosity of the fibers in the surface (A) is 1.1 or more.

Description

[Technical Field]

[0001] The present invention relates to a spunbond nonwoven fabric that combines excellent moisture absorption and quick-drying properties with a soft feel and is particularly suitable for use as a sanitary material, and to a sanitary material using the same. [Background technology]

[0002] In recent years, various studies have been conducted to further improve the wearing comfort of nonwoven fabrics used in hygiene materials such as disposable diapers, sanitary napkins, and masks. In particular, surface materials that come into direct contact with the skin must be both highly absorbent (rapidly absorbing moisture) and quick-drying (transferring absorbed moisture from the outermost layer to a dry, non-wet surface). At the same time, they must also be soft to the touch.

[0003] Effective means of imparting water absorbency to nonwoven fabrics include using nonwoven fabrics made of hydrophilic fibers and subjecting nonwoven fabrics to hydrophilic treatment, but these techniques do not have the function of transferring absorbed moisture from the outermost layer, and therefore do not provide sufficient quick-drying properties.

[0004] Against this background, a spunbond nonwoven fabric has been proposed that has a laminated structure of fiber layers containing long fibers, with the aim of imparting moisture-absorbing and quick-drying properties to the nonwoven fabric. The spunbond nonwoven fabric is composed of a hydrophobic layer containing hydrophobic fibers and a hydrophilic layer containing hydrophilic fibers with interfiber distances and flattening ratios within specific ranges, with the hydrophobic layer disposed on the surface of the nonwoven fabric (see Patent Document 1).

[0005] Another proposed technique for laminating nonwoven fabrics is an absorbent article comprising a spunbond nonwoven fabric in which first and third nonwoven fabric constituent layers containing fibers having an average single fiber diameter within a specific range and a second nonwoven fabric constituent layer containing fibers with an even smaller average single fiber diameter are disposed between the first and third nonwoven fabric layers (see Patent Document 2). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2018 / 167881 [Patent Document 2] Special Publication No. 2013-518698 Summary of the Invention [Problem to be solved by the invention]

[0007] The technology of Patent Document 1 creates a hydrophilic gradient in the thickness direction of the nonwoven fabric, thereby achieving a certain level of water absorption performance even on a surface with a hydrophobic layer on the outermost surface. However, because the outermost surface is a hydrophobic layer, the performance is insufficient for absorbing large amounts of water such as urine, and the quick-drying properties are insufficient due to the tendency for liquid to remain. Furthermore, the surface that comes into contact with the skin is not soft enough.

[0008] On the other hand, the technology of Patent Document 2 relates to a spunbond nonwoven fabric having a structure in which nonwoven fabric layers composed of fibers with different average single fiber diameters are laminated. However, this nonwoven fabric is used in barrier cuffs and has a structure that prevents fluids from seeping through to the back, i.e., it is moisture-impermeable, and liquid tends to remain on the surface of the nonwoven fabric, resulting in insufficient water absorption and quick-drying properties. In addition, the surface that comes into contact with the skin is not soft enough.

[0009] Therefore, an object of the present invention, which has been made in consideration of the above circumstances, is to provide a spunbond nonwoven fabric which has sufficient water absorbency and quick-drying properties to maintain comfort when worn, and which has a soft feel, and which is suitable for use as a sanitary material. [Means for solving the problem]

[0010] As a result of further investigations, the inventors of the present invention have confirmed that, although increasing the hydrophilicity of the nonwoven fabric itself is effective in increasing the water absorbency of the nonwoven fabric, when a nonwoven fabric with only increased hydrophilicity is used, the surface remains wet and does not dry, resulting in problems such as poor comfort when worn. On the other hand, when hydrophobic fibers are used in part of the nonwoven fabric or a hydrophilicity gradient is imparted in the thickness direction in order to increase quick-drying properties, the water absorbency of the nonwoven fabric surface is ultimately reduced, resulting in problems such as residual liquid.

[0011] Therefore, the present inventors conducted further intensive research in order to achieve the above-mentioned object, and found that by providing a spunbonded nonwoven fabric with fused portions and non-fused portions, by setting the ratio of the average single fiber diameter of the fibers constituting one surface (A) to the fibers constituting the other surface (B) and by setting the contact angle with water between surface (A) and surface (B) within specific ranges, and by setting the degree of curvature of the fibers constituting surface (A) within specific ranges, it is possible to obtain a nonwoven fabric that has sufficient water absorbency and quick-drying properties to maintain comfort when worn and that has a soft feel.

[0012] The present invention has been completed based on these findings, and provides the following inventions.

[0013] The spunbond nonwoven fabric of the present invention has fused portions and non-fused portions, and has a ratio (Da / Db) of the average single fiber diameter (Da) of fibers on one surface (A) to the average single fiber diameter (Db) of fibers on the other surface (B) of 1.1 or more, and the contact angles with water of both surfaces (A) and (B) are 30° or less, and the degree of tortuosity of the fibers on surface (A) is 1.1 or more.

[0014] According to a preferred embodiment of the spunbonded nonwoven fabric of the present invention, the diameter of the maximum inscribed circle of the non-fused portion is 2.0 mm or more.

[0015] According to a preferred embodiment of the spunbonded nonwoven fabric of the present invention, the thickness (Tu) of the spunbonded nonwoven fabric in the non-fused portion is 0.5 mm or more.

[0016] According to a preferred embodiment of the spunbonded nonwoven fabric of the present invention, the ratio (Tu / Tm) of the thickness (Tu) of the spunbonded nonwoven fabric in the non-fused portions to the thickness (Tm) of the spunbonded nonwoven fabric in the fused portions is 2.0 or more.

[0017] According to a preferred embodiment of the spunbond nonwoven fabric of the present invention, the degree of bending of the fibers on the surface (B) is 1.1 or less.

[0018] The sanitary material of the present invention is at least partially composed of the above-mentioned spunbond nonwoven fabric.

[0019] According to a preferred embodiment of the sanitary material of the present invention, the surface (A) is arranged facing the skin of the wearer. [Effects of the Invention]

[0020] According to the present invention, it is possible to obtain a spunbond nonwoven fabric that is excellent in water absorption, quick drying properties, and soft to the touch, and is particularly suitable for use as a sanitary material, and a sanitary material using the same. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a top view conceptual diagram illustrating a method for determining the maximum inscribed circle of the unfused portion in one embodiment of the spunbonded nonwoven fabric of the present invention. [Figure 2] FIG. 2 is a top view conceptual diagram illustrating a method for determining the maximum inscribed circle of the unfused portion in another embodiment of the spunbonded nonwoven fabric of the present invention. [Figure 3] FIG. 3 is a conceptual top view illustrating a method for determining the maximum inscribed circle of the unfused portion in yet another embodiment of the spunbonded nonwoven fabric of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The spunbond nonwoven fabric of the present invention has fused portions and non-fused portions, and has a ratio (Da / Db) of the average single fiber diameter (Da) of fibers on one surface (A) to the average single fiber diameter (Db) of fibers on the other surface (B) of 1.1 or more, and both surfaces (A) and (B) have contact angles with water of 30° or less, and the degree of tortuosity of the fibers on surface (A) is 1.1 or more. The components thereof are described in detail below, but the present invention is not limited in any way to the scope described below as long as it does not depart from the gist of the invention.

[0023] [fiber] The spunbond nonwoven fabric of the present invention is preferably made of a thermoplastic resin, which may be one type of thermoplastic resin or a plurality of thermoplastic resins.

[0024] Examples of thermoplastic resins that can be used in the fibers according to the present invention include aromatic polyester polymers and copolymers thereof, such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyhexamethylene terephthalate; aliphatic polyester polymers and copolymers thereof, such as polylactic acid, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, polyhydroxybutyrate-polyhydroxyvalerate copolymer, and polycaprolactone; aliphatic polyamide polymers and copolymers thereof, such as polyamide 6, polyamide 66, polyamide 610, polyamide 10, polyamide 12, and polyamide 6-12; polyolefin polymers and copolymers thereof, such as polypropylene, polyethylene, polybutene, and polymethylpentene; a water-insoluble ethylene-vinyl alcohol copolymer polymer containing 25 mol % to 70 mol % of ethylene units; The polymers may be selected from polystyrene-based, polydiene-based, chlorine-based, polyolefin-based, polyester-based, polyurethane-based, polyamide-based, fluorine-based elastomer polymers, etc. The polymers may contain various additives such as inorganic substances such as titanium oxide, silica, barium oxide, etc., colorants such as carbon black, dyes, and pigments, flame retardants, fluorescent brighteners, antioxidants, and ultraviolet absorbers.

[0025] The fibers in the present invention may be monocomponent fibers or conjugated fibers made by conjugating two or more types of resins. When the above-mentioned fibers are conjugated fibers, there are no particular limitations on the type as long as the effects of the present invention are not impaired, and they may be appropriately selected from sheath-core, sea-island, side-by-side, eccentric sheath-core, etc. Furthermore, they may be split conjugated fibers in which a portion or the entire fiber is split into multiple fibers from a single fiber.

[0026] The cross-sectional shape of the fibers in the present invention is not particularly limited as long as it does not impair the effects of the present invention, and may be a circular cross-section as well as an irregular cross-section such as a triangular, flat, hexagonal, hollow, or the like.

[0027] It is preferable that all fibers in the present invention have a contact angle with water of 90° or less. The contact angle with water on a fiber is an index different from the contact angle with water on the surface of a nonwoven fabric, which will be described later; a contact angle of more than 90° is hydrophobic, and a contact angle of 90° or less is hydrophilic. By using fibers with a contact angle with water of 90° or less, the contact angle with water on the surface of the nonwoven fabric can easily be made 30° or less.

[0028] The contact angle of the fiber with water in the present invention can be determined by, for example, measuring the angle between the air interface of the droplet and the fiber when a very small amount of water (15 pL) of water droplet is applied to the surface of the fiber using an automatic contact angle meter equipped with an inkjet type water droplet ejection unit, after the fiber is taken out of a nonwoven fabric that has been left in a room at room temperature of 20°C and a relative humidity of 65% for 24 hours or more.

[0029] The fibers on the surface (A) and the fibers on the surface (B) may be made of the same or different thermoplastic resins and have the same fiber cross sections.

[0030] [Surface (A)] The surface (A) of the spunbonded nonwoven fabric of the present invention is composed of fibers made of the above-mentioned thermoplastic resin.

[0031] The spunbond nonwoven fabric of the present invention is preferably made of long fibers, and the constituent fibers of the surface (A) are preferably long fibers, because the long fibers make it easier to achieve both high productivity and excellent mechanical properties.

[0032] The average single fiber diameter of the fibers constituting the surface (A) of the spunbonded nonwoven fabric of the present invention is preferably 3.0 to 30.0 μm. The average single fiber diameter of the fibers constituting the surface (A) is preferably 3.0 μm or more, more preferably 5.0 μm or more, and even more preferably 10.0 μm or more. By making the average single fiber diameter of the fibers constituting the surface (A) 3.0 μm or more, moisture can be easily transferred to the adjacent water absorbent body when used as a sanitary material. Furthermore, the average single fiber diameter of the fibers constituting the surface (A) is preferably 30.0 μm or less, more preferably 28.0 μm or less, and even more preferably 25.0 μm or less. By making the average single fiber diameter of the fibers constituting the surface (A) 30.0 μm or less, a soft texture can be easily obtained.

[0033] The average single fiber diameter is determined as follows.

[0034] First, an image of the cross section of the fiber that constitutes one surface is taken with a scanning electron microscope at a magnification that allows observation of a single fiber. Next, the area Af (μm) formed by the cross-sectional contour of the single fiber is calculated using the taken image and image analysis software (for example, "WinROOF2015" manufactured by Mitani Corporation). 2) is measured, and the diameter of a perfect circle having the same area as this area Af is calculated. This is measured for 20 randomly selected fibers constituting the same surface, and a simple number average is calculated. The value, in units of μm, is rounded to one decimal place and is the average single fiber diameter of that surface as referred to in the present invention.

[0035] In the spunbond nonwoven fabric of the present invention, the degree of curvature of the fibers on the surface (A) is 1.1 or more. The degree of curvature of the fibers on the surface (A) is preferably 1.2 or more, more preferably 1.3 or more. This is because a high water absorption rate can be obtained by having the degree of curvature of the fibers on the surface (A) be 1.1 or more. The mechanism by which a high water absorption rate is obtained is not clear, but it is presumed to be the effect of the formation of various inter-fiber voids. Furthermore, a degree of curvature of the fibers on the surface (A) of 1.1 or more makes it easier to obtain a soft feel. There is no particular upper limit to the degree of curvature of the fibers on the surface (A), but from the viewpoints of process stability and productivity, it is preferably 10.0 or less.

[0036] The degree of bending of the fiber referred to here is determined as follows.

[0037] First, an image of one surface is taken with a scanning electron microscope at a magnification that allows observation of a single fiber over a linear distance of 500 μm or more. Next, using the captured image and image analysis software (e.g., the National Institutes of Health's "ImageJ"), the apparent length of the fiber between two points on the fiber that are 500 μm apart in a linear direction is measured, and this apparent length is divided by 500 μm to calculate the apparent length / linear length. This is measured for 20 randomly selected fibers that make up the same surface, and a simple number average is calculated. The value, rounded to one decimal place, is the degree of curvature of the fiber on that surface as referred to in this invention.

[0038] [Surface (B)] The surface (B) of the spunbonded nonwoven fabric of the present invention is composed of fibers made of the above-mentioned thermoplastic resin, similar to the surface (A).

[0039] The spunbond nonwoven fabric of the present invention is preferably made of long fibers, and the constituent fibers of surface (B) are preferably long fibers, similar to those of surface (A). This is because the long fibers make it easier to achieve both high productivity and excellent mechanical properties.

[0040] The average single fiber diameter of the fibers constituting the surface (B) of the spunbonded nonwoven fabric of the present invention is preferably 1.0 to 25.0 μm. The average single fiber diameter of the fibers constituting the surface (B) is preferably 1.0 μm or more, more preferably 3.0 μm or more, and even more preferably 5.0 μm or more. By making the average single fiber diameter 1.0 μm or more, the fiber arrangement does not become too dense, and when used as a material for disposable diapers, moisture easily transfers to the adjacent water absorbent body. Furthermore, the average single fiber diameter of the fibers constituting the surface (B) is preferably 25.0 μm or less, more preferably 20.0 μm or less, and even more preferably 16.0 μm or less. By making the average single fiber diameter 25.0 μm or less, high capillary force is easily obtained, resulting in excellent water absorption.

[0041] The degree of curvature of the fibers on the surface (B) of the spunbonded nonwoven fabric of the present invention is preferably 1.1 or less, and more preferably 1.0. This is because a degree of curvature of the fibers on the surface (B) of 1.1 or less facilitates the formation of small interfiber gaps and the attainment of high capillary force. The lower limit of the degree of curvature of the fibers on the surface (B) is 1.0, which is included when the apparent length and the straight length are the same, and this is a preferred embodiment.

[0042] [Average single fiber diameter on surface (A) and surface (B)] The spunbond nonwoven fabric of the present invention has a ratio of the average single fiber diameter (Da) of the fibers on one surface (A) to the average single fiber diameter (Db) of the fibers on the other surface (B) (Da / Db, hereinafter sometimes simply referred to as "average single fiber diameter ratio") of 1.1 or more.

[0043] The average single fiber diameter ratio referred to here is the value obtained by measuring the average single fiber diameter (Da) of the fibers constituting surface (A) and the average single fiber diameter (Db) of the fibers constituting surface (B) using the method described above, calculating the ratio (Da / Db), and rounding it to one decimal place.

[0044] In general, in a nonwoven fabric, the size of the voids between the fibers varies depending on the average single fiber diameter of the constituent fibers. Therefore, when layers with different average single fiber diameters are formed, layers with different inter-fiber void sizes are formed. When moisture adheres to the layers, the moisture absorbed in the layer made of thick fibers can be transferred to the layer made of thin fibers due to the difference in capillary force. Furthermore, as a result of extensive research, the inventors have found that by setting this average single fiber diameter ratio within a specific range, not only is the water absorbency improved due to the difference in capillary effect, but also quick-drying properties are imparted to the surface of the nonwoven fabric layer made of thick fibers.

[0045] The average single fiber diameter ratio (Da / Db) in the present invention is preferably 1.2 or more, more preferably 1.3 or more, and even more preferably 1.4 or more. By making the average single fiber diameter ratio (Da / Db) 1.1 or more, the above-mentioned capillary effect can be exerted, resulting in good water absorption and quick drying properties on the surface (A). There is no particular upper limit to the average single fiber diameter ratio in the present invention, but from the viewpoints of process stability and productivity, it is preferably 10.0 or less.

[0046] [Spunbond nonwoven fabric] As described above, the spunbonded nonwoven fabric of the present invention has fused portions and non-fused portions. The fused portions are the areas where the fibers on surface (A) and the fibers on surface (B) are fused together, and the non-fused portions are the remaining areas on the spunbonded nonwoven fabric that are surrounded by the fused portions. Because the fibers on surface (A) and the fibers on surface (B) are fused together in the fused portions, the surrounding area tends to be dense. The presence of high-density fused portions and relatively low-density non-fused portions within the plane of the spunbonded nonwoven fabric facilitates the movement of water within the plane, making it easier to achieve more efficient water absorption and quick-drying performance than simply moving water in the thickness direction.

[0047] In the present invention, whether or not a certain portion of a spunbonded nonwoven fabric is a fused portion, i.e., whether or not the fiber of surface (A) is fused to the fiber of surface (B), is determined by observing an image of a cross section of the portion of the spunbonded nonwoven fabric under a scanning electron microscope at a magnification that brings the thickness direction of the spunbonded nonwoven fabric into the field of view, and in an arbitrarily selected portion where surface (A) is fused, if surface (B) is fused at the same position in the plane direction, then the portion is determined to be a fused portion.

[0048] Furthermore, in the spunbonded nonwoven fabric of the present invention, the diameter of the maximum inscribed circle of the non-fused portion is preferably 2.0 mm or more. The diameter of the maximum inscribed circle is more preferably 3.0 mm or more, and even more preferably 4.0 mm or more. When the diameter of the maximum inscribed circle is 2.0 mm or more, it is easy to form a low-density portion sufficiently separated from the fused portion, making it easy to obtain a high water absorption rate. It is also preferable in that it is easy to obtain a soft feel. The diameter of the maximum inscribed circle is preferably 10.0 mm or less, more preferably 9.0 mm or less, and even more preferably 8.0 mm or less. When the diameter of the maximum inscribed circle is 10.0 mm or less, it is easy to suppress fuzzing due to friction, etc.

[0049] As shown in Figures 1 to 3, the diameter of the maximum inscribed circle in the present invention is determined by observing the surface of a spunbonded nonwoven fabric (1) from above with a microscope, capturing a field of view of 10 mm x 10 mm or more in which the non-fused portions surrounded by the fused portions (11) can be observed. The captured image is then used to measure the diameter of the maximum inscribed circle (13) that can be placed on the non-fused portions (12) using image analysis software (e.g., WinROOF2015 manufactured by Mitani Shoji Co., Ltd.). This measurement is performed at 20 randomly selected locations on the same surface, and a simple number average is calculated. The value, rounded to one decimal place in mm, is the diameter of the maximum inscribed circle of that surface in the present invention.

[0050] The spunbond nonwoven fabric of the present invention has one surface (A) whose fibers have an average single fiber diameter of Da and the other surface (B) whose fibers have an average single fiber diameter of Db, and as described above, the average single fiber diameter ratio (Da / Db) is 1.1 or more. By doing so, surface (A), which has a large average single fiber diameter and is likely to have large interfiber voids within the nonwoven fabric layer, becomes the outermost layer, and when moisture is absorbed on the surface (A) side, the moisture is quickly transferred to the surface (B) side, thereby achieving quick-drying properties at the outermost surface on the surface (A) side.

[0051] Furthermore, the spunbond nonwoven fabric of the present invention has a water contact angle of 30° or less on both surfaces (A) and (B). Having both the front and back surfaces of the spunbond nonwoven fabric have a water contact angle of 30° or less, preferably 20° or less, and more preferably 10° or less is preferred because water that comes into contact with the surface of the spunbond nonwoven fabric is easily absorbed by the nonwoven fabric. The lower limit of the water contact angle in the present invention is 0°, and a water contact angle of 0° refers to a state in which all water has been absorbed by the nonwoven fabric, as measured by the method described below.

[0052] The contact angle of the surface of a spunbonded nonwoven fabric with water can be controlled by the hydrophilicity of the thermoplastic resin used in the fibers constituting the spunbonded nonwoven fabric and the application of a hydrophilic oil agent in a post-process. For example, the higher the hydrophilicity of the thermoplastic resin and the greater the amount of hydrophilic oil agent applied, the smaller the contact angle with water tends to be.

[0053] The contact angle of the surface of the spunbonded nonwoven fabric of the present invention with water refers to a value measured and calculated by the following method. (1) Leave the spunbond nonwoven fabric in a room at a room temperature of 20°C and a relative humidity of 65% for at least 24 hours. (2) The spunbond nonwoven fabric that has been subjected to the above treatment is placed on the stage of a contact angle meter installed in the same room so that surface (A) becomes the measurement surface. (3) A 2 μL droplet of ion-exchanged water is created on the tip of the needle and applied to the nonwoven fabric. (4) The contact angle with the droplet is determined from the image taken 2 seconds after the droplet hits the nonwoven fabric. If all the water is absorbed by the nonwoven fabric within 2 seconds, the interface between the droplet and the air is determined to be on the same plane as the surface of the nonwoven fabric layer, and the contact angle with water is defined as 0°. (5) For each level, measure five times by changing the measurement position, and the arithmetic mean value is the contact angle between surface (A) and water. (6) A spunbond nonwoven fabric that has been treated in the same manner as in (1) is set so that the surface (A) faces the back, and the above operations (2) to (5) are repeated, and the arithmetic average value is taken as the contact angle between the surface (B) and water.

[0054] The spunbonded nonwoven fabric of the present invention has a minimum breaking strength σ among the breaking strengths measured by rotating the spunbonded nonwoven fabric in the plane from an arbitrary direction of 0° to 180° in 22.5° increments. min Maximum breaking strength σ max The ratio (σ max / σ min(hereinafter sometimes simply referred to as breaking strength ratio) is preferably 1.2 to 4.0. By setting the breaking strength ratio to preferably 1.2 or more, more preferably 1.3 or more, the fibers are more likely to be oriented in the plane of the nonwoven fabric, and a high capillary force is more likely to be exhibited, which leads to in-plane fiber movement and makes it possible to obtain higher water absorption and quick-drying properties. Furthermore, by setting the breaking strength ratio to preferably 4.0 or less, more preferably 3.5 or less, there are no angles with extremely low breaking strength, which makes it possible to suppress tearing of the nonwoven fabric during processing or product processing.

[0055] The breaking strength ratio of the spunbond nonwoven fabric of the present invention refers to a value measured and calculated by the following method based on "6.3 Tensile strength and elongation (ISO method)" of JIS L1913:2010 "Testing methods for general nonwoven fabrics." (1) Any one direction of the spunbond nonwoven fabric is set to 0°, and a test piece measuring 300 mm long x 25 mm wide is cut out so that the longitudinal direction coincides with the above direction, and three test pieces are taken from different locations. (2) Set the test piece in the tensile testing machine with a gripping distance of 200 mm. (3) Conduct a tensile test at a tensile speed of 100 m / min, measure the strength at break [N] for three test pieces, and use the arithmetic mean value as the breaking strength σ. (4) Using the direction rotated 22.5° clockwise within the plane of the spunbond nonwoven fabric relative to any direction set at 0° as the axis, cut out a test piece measuring 300 mm in length and 25 mm in width so that the longitudinal direction coincides with the above-mentioned axial direction, and take three test pieces at different locations. Then, repeat the above steps (2) to (3) to calculate the breaking strength σ. (5) The above operation (4) is repeated until the in-plane rotation angle of the spunbond nonwoven fabric reaches 180°, and the breaking strength σ at each angle is calculated. (6) The minimum breaking strength σ among the breaking strength σ calculated by the above method min Maximum breaking strength σ max The ratio (σ max / σ min ) is calculated and used as the breaking strength ratio of the spunbond nonwoven fabric.

[0056] The spunbond nonwoven fabric of the present invention can be configured with a layer (S) of spunbond nonwoven fabric and a layer (M) of meltblown nonwoven fabric, depending on the purpose, as long as the effects of the present invention are not impaired. Examples of such configurations include SMS, SMMS, SSMMS, and SMSMS. In these cases, one surface of the laminated nonwoven fabric is considered to be the surface (A) of the spunbond nonwoven fabric, and the other surface is considered to be the surface (B) of the spunbond nonwoven fabric.

[0057] The spunbond nonwoven fabric of the present invention preferably has a water absorption rate measured on the surface (A) of 20 seconds or less. By setting the water absorption rate to preferably 20 seconds or less, more preferably 15 seconds or less, and even more preferably 10 seconds or less, the nonwoven fabric has good performance in removing moisture adhering to the surface, i.e., excellent water absorption.

[0058] The water absorption rate referred to here is measured based on "7.1.1 Drop Method" in JIS L1907:2010 "Testing Method for Water Absorption of Textile Products." A single drop of water is dropped onto a spunbond nonwoven fabric, and the time it takes for the fabric to be absorbed and for the specular reflection on the surface to disappear is measured. This time is measured at 10 different points, and the simple average is calculated. The value is expressed in seconds and rounded to one decimal place, and this value is the water absorption rate referred to in the present invention.

[0059] The basis weight of the spunbond nonwoven fabric of the present invention is 10 to 100 g / m 2 The basis weight is preferably 10 g / m 2 More preferably, 13 g / m 2 More preferably, 15 g / m 2 By adjusting the weight to the above, a spunbond nonwoven fabric having a mechanical strength sufficient for practical use can be obtained. 2 Less than 50 g / m 2 By using the following, it is possible to obtain a spunbond nonwoven fabric having appropriate flexibility suitable for use as a nonwoven fabric for sanitary materials.

[0060] The basis weight (g / m 2) is based on "6.2 Mass per unit area" of JIS L1913:2010 "General nonwoven fabric test method", 20cm x 25cm test pieces are taken, three pieces per 1m width of the sample, and the mass (g) of each is measured under standard conditions, and the mass per 1m is calculated from the average value. 2 This refers to the mass per unit mass.

[0061] The spunbond nonwoven fabric of the present invention may be treated with a hydrophilizing agent to enhance its water absorption. Examples of the hydrophilizing agent include surfactants, and among these, nonionic surfactants are preferred.

[0062] The spunbonded nonwoven fabric of the present invention preferably has a thickness (Tu) of 0.5 mm or more of the unfused portion. By setting Tu to 0.5 mm or more, more preferably 0.7 mm or more, and even more preferably 0.9 mm or more, the spunbonded nonwoven fabric will have appropriate cushioning properties. On the other hand, by setting Tu to 1.50 mm or less, more preferably 1.40 mm or less, and even more preferably 1.30 mm or less, the spunbonded nonwoven fabric will have excellent bending flexibility.

[0063] The thickness (Tu) of the unfused portion of the spunbonded nonwoven fabric of the present invention is not particularly limited, but refers to the thickness under no load measured, for example, with a shape measuring machine (for example, "VR3050" manufactured by Keyence Corporation).

[0064] In the spunbond nonwoven fabric of the present invention, the ratio (Tu / Tm) of the thickness of the non-fused portions (Tu) to the thickness of the fused portions (Tm) is preferably 2.0 or more, more preferably 5.0 or more, and even more preferably 10.0 or more. A Tu / Tm of 2.0 or more increases the difference in density between the areas around the fused portions and areas away from the fused portions, making it easier to achieve both high water absorbency in the high-density areas around the fused portions and excellent softness in the low-density areas away from the fused portions. There is no particular upper limit, but it is usually 50 or less.

[0065] The thickness (Tm) of the fused portion of the spunbonded nonwoven fabric of the present invention is not particularly limited, but for example, a field of view in which the cross section can be observed is photographed with a microscope. The photographed image is then used to measure the thickness using image analysis software (e.g., "WinROOF2015" manufactured by Mitani Shoji Co., Ltd.). This measurement is performed at 10 randomly selected locations, and a simple number average is calculated. The value, in mm, is rounded to two decimal places to obtain the thickness (Tm) of the fused portion of the spunbonded nonwoven fabric referred to in the present invention.

[0066] The ratio (Tu / Tm) of the thickness of the non-fused portion (Tu) to the thickness of the fused portion (Tm) is calculated by dividing Tu (mm) measured and calculated as above by Tm (mm) and rounding off to one decimal place.

[0067] [Hygiene materials] The sanitary material of the present invention is at least partially composed of the spunbond nonwoven fabric. This results in a sanitary material with excellent water absorbency and quick-drying properties. The sanitary material of the present invention is primarily a disposable product used for health-related purposes such as medical care and nursing, including disposable diapers, sanitary napkins, gauze, bandages, masks, gloves, and adhesive bandages, as well as their constituent parts, such as top sheets, back sheets, and side gathers of disposable diapers.

[0068] Among these, a sanitary material in which the surface (A) of the spunbonded nonwoven fabric is arranged facing the skin side of the wearer is more preferred because moisture adhering to the skin side can be immediately absorbed into the interior of the spunbonded nonwoven fabric, thereby reducing discomfort to the wearer.

[0069] For example, when the sanitary material is a disposable diaper and the spunbond nonwoven fabric is placed inside the disposable diaper, and the surface (A) is arranged facing the wearer's skin, sweat produced during wear and urine excreted are quickly absorbed and the liquid is quickly transferred to the surface (B), thereby keeping the surface dry and free from excessive moisture.

[0070] Furthermore, when the sanitary material is a mask and the spunbond nonwoven fabric is used on the inside of the mask, and the surface (A) is arranged facing the wearer's skin, even if sweat or breath condenses and moisture adheres to the skin side, it is quickly absorbed into the spunbond nonwoven fabric and then the liquid is quickly transferred to the surface (B), so that the skin side can be kept dry and free from excessive moisture.

[0071] [Manufacturing method of spunbond nonwoven fabric] Next, a preferred embodiment for producing the spunbonded nonwoven fabric of the present invention will be specifically described.

[0072] The spunbond nonwoven fabric of the present invention is produced by a spunbonding method, which involves melting a thermoplastic resin as a raw material, spinning it through a spinneret, cooling it to solidify it, pulling and stretching the resulting yarn with an ejector, collecting it on a moving net to form a nonwoven fiber web, and then heat-sealing the web.

[0073] The spinneret and ejector to be used may have various shapes such as round, rectangular, etc. Among them, a preferred embodiment is to use a combination of a rectangular spinneret and a rectangular ejector, from the viewpoints that the amount of compressed air used is relatively small and fusion and abrasion between the yarns are unlikely to occur.

[0074] In the present invention, the spinning temperature is preferably set to (the melting temperature of the thermoplastic resin as the raw material + 10°C) or higher (the melting temperature of the thermoplastic resin as the raw material + 100°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.

[0075] The spun yarn is then cooled, and examples of methods for cooling the spun yarn include a method of forcibly blowing cold air onto the yarn, a method of naturally cooling the yarn at the ambient temperature around the yarn, and a method of 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 taking into consideration the output per hole of the spinneret, the spinning temperature, the ambient temperature, etc.

[0076] Next, the cooled and solidified yarn is drawn and stretched by compressed air jetted from an ejector.

[0077] In the spunbond nonwoven fabric of the present invention, it is essential to control the average single fiber diameter of the fibers constituting the surface (A) and the surface (B).

[0078] The average single fiber diameter of the fiber is determined by the output rate per nozzle hole of the spinneret and the drawing speed, i.e., the spinning speed. Therefore, it is preferable to determine the output rate and the spinning speed according to the desired average single fiber diameter.

[0079] The spinning speed is preferably 2000 m / min or more, more preferably 3000 m / min or more. By setting the spinning speed to 2000 m / min or more, high productivity is achieved, and the orientation and crystallization of the fibers is promoted, allowing long fibers with high strength to be obtained.

[0080] The filament yarn thus drawn by pulling is collected on a moving net to be formed into a sheet, which is then subjected to a heat fusion step.

[0081] To obtain fibers with a bending degree of 1.1 or more on the surface (A) of the spunbond nonwoven fabric of the present invention, conjugated spun fibers made from thermoplastic resins with different properties can be used, or the degree of cooling can be varied to form regions with different stresses in the fiber cross section, thereby controlling the bending degree. When producing conjugated spun fibers, a bending degree of 1.1 or more can be achieved by using thermoplastic resins with a large difference in melting point or a large difference in viscosity. Furthermore, a bending degree of 1.1 or more can be achieved by increasing the difference in cooling conditions between one side of the fiber and the opposite side.

[0082] To obtain fibers with a bending degree of 1.1 or less, which is a preferred embodiment of the surface (B) of the spunbond nonwoven fabric of the present invention, it is important to equalize the stress borne by the fiber cross section by adjusting the degree of cooling, even when using conjugated spun fibers made from thermoplastic resins with different properties or when using single or blended monocomponent spun fibers. Therefore, when producing conjugated spun fibers, the bending degree can be made 1.1 or less by using thermoplastic resins with a small difference in melting point or a small difference in viscosity. Furthermore, uniform cooling of the fibers is also important for achieving a bending degree of 1.1 or less.

[0083] The spunbond nonwoven fabric of the present invention has a surface (A) and a surface (B) with different fiber diameters. The tortuosity of the fibers constituting surface (A) is 1.1 or more. For example, a method for obtaining such a spunbond nonwoven fabric can be used in which a fiber web is deposited on a collection net from a spinneret for surface (B), which is disposed downstream of the collection net, onto the fiber web obtained by collecting the fibers from the spinneret for surface (A) as described above, and the two are then heat-sealed and fixed all at once.

[0084] The spunbond nonwoven fabric of the present invention can be heat-sealed using a variety of rolls, including a heat embossing roll consisting of a pair of upper and lower rolls, one of which is a heat embossing roll with an engraved (concave or recessed) surface and the other of which is a flat (smooth) roll with no engraved surface, and a heat calender roll consisting of a pair of upper and lower flat (smooth) rolls, as well as ultrasonic fusion, which uses ultrasonic vibrations from a horn to fuse the fabric.

[0085] When the spunbonded nonwoven fabric of the present invention is produced by heat-sealing with an embossing roll, it is preferable because the fibers on both surfaces (A) and (B) can be easily fused at positions corresponding to the convex portions of the embossing roll. This is also a preferred embodiment because the maximum inscribed circle of the unfused portion can be controlled by designing the positions of the convex portions of the embossing roll.

[0086] A hydrophilizing agent may be applied to the spunbonded nonwoven fabric obtained in this manner before winding. Methods for applying a hydrophilizing agent to the spunbonded nonwoven fabric include application with a kiss roll or spray, and dip coating, but application with a kiss roll is preferred from the viewpoint of uniformity and ease of control of the amount of application. [Example]

[0087] Next, the present invention will be described in detail based on examples. However, the present invention is not limited to these examples. In addition, in measuring each physical property, unless otherwise specified, the measurement was performed according to the above-mentioned method.

[0088] (1) Thickness Measurements were carried out as previously described.

[0089] (2) Metsuke Measurements were carried out as previously described.

[0090] (3) Ratio of the average single fiber diameter (Db) on surface (B) to the average single fiber diameter (Da) on surface (A) (Da / Db) For each fiber, a fiber sample was randomly taken from the nonwoven fiber web collected on a net, and the cross section of the fiber was imaged using a scanning electron microscope "S-5500" manufactured by Hitachi High-Technologies Corporation at a magnification that allowed individual fibers to be observed. Then, measurements were carried out as described above using image analysis software "WinROOF2015" manufactured by Mitani Shoji Co., Ltd.

[0091] The average single fiber diameter (Da) of the fibers that make up surface (A) and the average single fiber diameter (Db) of the fibers that make up surface (B) are measured, and the ratio (Da / Db) is calculated and rounded to one decimal place.

[0092] (4) Flexibility Measurements were carried out as previously described.

[0093] (5) Water contact angle of spunbond nonwoven fabric The measurement was carried out as described above using a contact angle meter "DMo-501" manufactured by Kyowa Interface Science Co., Ltd.

[0094] (6) Presence or absence of fused parts Observations and measurements were carried out as described above.

[0095] (7) Water absorption and quick drying properties A drop of water was placed on the surface (A) of a spunbond nonwoven fabric, and after one minute, healthy adults (15 men and 15 women, a total of 30 people) touched the surface with their hands and evaluated it using the following three-point scale. The average score of the evaluation results for each nonwoven fabric was calculated and used as the feel of the spunbond nonwoven fabric. 5: The surface is smooth and doesn't feel wet. 3: No moisture on the surface, but moist 1: The surface is moist and moist (8) Softness Healthy adults (15 men and 15 women, a total of 30 people) touched the spunbond nonwoven fabrics with their hands and evaluated the surface feel using the following three-point scale. The average score of the evaluation results for each nonwoven fabric was calculated and used as the softness of that nonwoven fabric.

[0096] 5: Very soft (the surface feels smooth to the touch and has a moderate elasticity in the thickness direction) 3: Not quite soft 1: Not feeling soft (the surface feels rough when stroked, and feels a strong rebound when pressed, or becomes worn out) [Example 1] (Fiber web forming surface (A)) Polypropylene (PP) and ethylene copolymer polypropylene (co-PP) were melted in separate extruders and spun into side-by-side composite fibers (mass ratio 1:1) from a rectangular spinneret with round holes of 0.4 mm diameter at a single-hole throughput rate of 0.9 g / min. The spun yarn was cooled and solidified, then pulled and stretched in a rectangular ejector using compressed air at an ejector pressure of 0.08 MPa, and collected on a moving net to obtain a nonwoven fiber web. The average single fiber diameter of the fibers constituting the resulting surface (A) was 18.4 μm.

[0097] (Fiber web forming surface (B)) Polypropylene was melted in an extruder and spun from a rectangular spinneret with 0.4 mm diameter round holes at a single-hole output rate of 0.3 g / min. The spun yarn was cooled and solidified with cold air, then pulled and stretched in a rectangular ejector using compressed air at an ejector pressure of 0.08 MPa, and collected on a moving net onto a fiber web that formed surface (A). The average single fiber diameter of the fibers that made up the resulting surface (B) was 10.6 μm.

[0098] (spunbond nonwoven fabric) The laminated fiber web thus obtained was heat-sealed at a line pressure of 300 N / cm and a heat-sealing temperature of 125°C using a metal embossing roll on the upper roll, which was arranged in a quilted pattern, a grid pattern in which straight lines formed by circular convex portions intersected at right angles, and a metal flat roll on the lower roll, which had a pair of upper and lower heating mechanisms. 2A spunbond nonwoven fabric was obtained. After that, a nonionic surfactant was applied to the nonwoven fabric using a kiss roll so that the active ingredient was 0.5 wt % relative to the weight of the spunbond nonwoven fabric, to give a hydrophilic finish.

[0099] The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 1.

[0100] [Example 2] A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that a metal embossing roll with circular convex portions arranged in a staggered pattern at the same pitch in both the MD and CD directions was used as the upper roll.

[0101] The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 1.

[0102] [Example 3] A spunbond nonwoven fabric was obtained in the same manner as in Example 2, except that the single-hole discharge rate of the fiber web forming the surface (A) was 0.53 g / min.

[0103] The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 1.

[0104] [Example 4] A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that heat fusion was performed using an embossing roll at a linear pressure of 10 N / cm.

[0105] The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 1.

[0106] [Example 5] A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that the fiber web forming surface (B) was prepared by melting polypropylene and ethylene copolymer polypropylene in separate extruders and spinning them into side-by-side composite fibers (mass ratio 1:1).

[0107] The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 1.

[0108] [Comparative Example 1] A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that the fiber web constituting surface (A) and the fibers and fiber web constituting surface (B) were both melted and spun in separate extruders at a single-hole output rate of 0.6 g / min using ethylene copolymer polypropylene and the same ethylene copolymer polypropylene.

[0109] The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 2.

[0110] Comparative Example 2 A spunbonded nonwoven fabric was obtained in the same manner as in Example 1, except that the obtained fiber web was heat-fused by heating with hot air at 150°C instead of heat-fusion using an embossing roll. Although fusion with hot air fuses adjacent fibers together, it does not form a "fused part" where the fibers on surface (A) and the fibers on surface (B) are fused together.

[0111] The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 2.

[0112] Comparative Example 3 A spunbond nonwoven fabric was obtained in the same manner as in Example 1, except that the fiber web forming the surface (A) was prepared by melting an ethylene copolymerized polypropylene and the same ethylene copolymerized polypropylene in separate extruders, and spinning them into side-by-side composite fibers (mass ratio 1:1).

[0113] The evaluation results of the obtained spunbond nonwoven fabric are shown in Table 2.

[0114] [Table 1]

[0115] [Table 2]

[0116] Examples 1 to 5 have a large average single fiber diameter ratio (Da / Db), a large degree of curvature on surface (A), and have areas where the fibers on surface (A) and the fibers on surface (B) are fused together, which indicates that they have excellent moisture absorption and quick-drying properties and an excellent soft feel.

[0117] On the other hand, in Comparative Example 1, the average single fiber diameter ratio was small, so moisture did not migrate to the surface (B) side within the nonwoven fabric, resulting in poor water absorption and quick-drying properties. In Comparative Example 2, the fibers on the surface (A) and the fibers on the surface (B) did not have any fusion bonding locations, so water did not easily migrate in-plane, resulting in poor water absorption and quick-drying properties. In Comparative Example 3, the degree of bending of the surface (A) was small, so it was difficult to obtain a high water absorption rate, the water absorption and quick-drying properties were insufficient, and the softness was also poor. [Explanation of symbols]

[0118] 1: Spunbond nonwoven fabric 11: Fusion part 12: Non-fused part 13: Maximum inscribed circle of unfused part

Claims

1. A spunbond nonwoven fabric having fused portions and non-fused portions, wherein the ratio (Da / Db) of the average single fiber diameter (Da) of the fibers on one surface (A) to the average single fiber diameter (Db) of the fibers on the other surface (B) is 1.1 or more and 10.0 or less, the contact angles with water of both surfaces (A) and (B) are 30° or less, and the degree of bending of the fibers on surface (A) is 1.1 or more and the degree of bending of the fibers on surface (B) is 1.1 or less.

2. 2. The spunbond nonwoven fabric according to claim 1, wherein the diameter of the maximum inscribed circle of the unfused portion is 2.0 mm or more.

3. 3. The spunbonded nonwoven fabric according to claim 1, wherein the thickness (Tu) of the spunbonded nonwoven fabric in the non-fused portion is 0.5 mm or more.

4. The spunbonded nonwoven fabric according to any one of claims 1 to 3, wherein the ratio (Tu / Tm) of the thickness (Tu) of the spunbonded nonwoven fabric in the non-fused portions to the thickness (Tm) of the spunbonded nonwoven fabric in the fused portions is 2.0 or more.

5. A sanitary material, at least a part of which is composed of the spunbond nonwoven fabric according to any one of claims 1 to 4.

6. The hygienic material according to claim 5, wherein the surface (A) faces the skin of the wearer.

Images