JP7124972B2 - Laminated nonwovens and sanitary materials - Google Patents

Description

TECHNICAL FIELD The present invention relates to a laminated nonwoven fabric particularly suitable for use in sanitary materials and sanitary materials using the same.

In general, sanitary materials such as disposable diapers, sanitary napkins, and masks are key to comfort by quickly removing moisture such as urine and sweat and keeping the surface of the material dry.

For this reason, members that come into direct contact with the skin are required to have both "water absorption" to quickly absorb moisture and "quick drying" to dry the surface by transferring the absorbed moisture from the outermost layer.

Conventionally, various nonwoven fabrics that have been subjected to hydrophilic treatment have been widely used for this surface member. Although these can induce moisture from the outermost layer to the inner non-woven fabric or absorbent material, moisture tends to remain in the outermost layer, resulting in poor "quick-drying" properties.

In response to this problem, Patent Document 1 proposes a nonwoven fabric in which a fiber layer (skin surface side) made of fine fineness fibers and a fiber layer made of large fineness fibers are laminated and partially entangled at the interface. . In addition, in Patent Document 2, sheets with different average non-fiber-occupied voids are laminated according to the difference in the mixing ratio and fiber diameter of a plurality of fibers, and the average non-fiber-occupied voids of the first layer that touches the skin are more than the layers other than the first layer. A sheet with a larger diameter is also proposed.

JP-A-7-042057 JP-A-7-178133

However, with the technique of Patent Document 1, it was difficult to obtain both "quick drying" and "water absorption".

On the other hand, in the technique of Patent Document 2, by providing a difference in the volume of voids other than fibers between layers, the moisture absorbed in the first layer is transferred to the second layer (the layer opposite to the skin surface) due to the difference in capillary effect. It is described that it is possible to induce However, the technique of Patent Document 2 is insufficient in "quick-drying".

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a laminated nonwoven fabric that has sufficient quick-drying properties to maintain comfort in a member using nonwoven fabrics for sanitary materials and that is excellent in water absorbency.

The present inventors found that in the technique of Patent Document 1, since the fiber layer made of fine fibers on the skin side has a denser structure than the other layers, moisture remains in the fiber layer on the skin side. Furthermore, due to the dense fiber layer on the skin side, the liquid permeability is reduced, and moisture cannot be absorbed quickly, resulting in "water absorption". I found it difficult.

In addition, the inventors of the present invention have found that the average non-fiber-occupied voids disclosed in Patent Document 2 indicate the total volume of spaces occupied by non-fibers, so they are not an index indicating the size of voids between fibers, which is important for capillary force. However, even if there is a difference between layers, it does not mean that there is a difference in capillary force. , the transfer of moisture from the skin surface has a limited effect, and it has been found that the "quick-drying property" is insufficient.

As a result of extensive studies to achieve the above object, the inventors of the present invention have found that in a specific nonwoven fabric layer in a laminated nonwoven fabric, in addition to the basis weight and thickness, the interfiber void size considering the fiber diameter is controlled within a specific range. By doing so, it was found that a laminated nonwoven fabric having sufficient water absorption and quick drying properties to be used as a nonwoven fabric for hygiene products can be obtained.

The present invention has been completed based on these findings, and the following inventions are provided according to the present invention.

The present invention provides a laminated nonwoven fabric in which nonwoven fabric layers made of thermoplastic resin fibers are laminated, and in the nonwoven fabric layer (A) having the smallest average single fiber diameter among the nonwoven fabric layers, It is a laminated nonwoven fabric having an interfiber void size Ra (μm) of 200 μm or less.
Ra=(100×Ta×da)/(Wa×Da)−Da Formula (1)
here,
Ta: thickness (μm) of the nonwoven fabric layer (A)
da: fineness (dtex) of the thermoplastic resin fibers constituting the nonwoven fabric layer (A)
Wa: basis weight of nonwoven fabric layer (A) (g/m ² )
Da: Average single fiber diameter (μm) of the thermoplastic resin fibers constituting the nonwoven fabric layer (A).

The present invention also provides a sanitary material at least partially composed of the laminated nonwoven fabric of the present invention.

ADVANTAGE OF THE INVENTION According to this invention, the laminated nonwoven fabric which has sufficient quick-drying property for use as a nonwoven fabric for sanitary goods, and has the outstanding water absorption rate can be obtained.

The present invention will be described in detail below. However, the present invention is not limited only to the scope described below as long as it does not exceed the gist of the present invention.

[Thermoplastic resin fiber]
First, the laminated nonwoven fabric of the present invention is formed by laminating nonwoven fabric layers made of thermoplastic resin fibers.

The term "thermoplastic resin fiber" as used in the present invention refers to fibers made of thermoplastic resin. Such a thermoplastic resin may be of one kind, or may consist of a plurality of thermoplastic resins.

Examples of thermoplastic resins used for thermoplastic resin fibers in the present invention include:
aromatic polyester polymers such as polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, and polyhexamethylene terephthalate, and copolymers thereof;
Aliphatic polyester polymers such as polylactic acid, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, polyhydroxybutyrate-polyhydroxyvalerate copolymer, polycaprolactone and copolymers thereof,
Aliphatic polyamide polymers such as polyamide 6, polyamide 66, polyamide 610, polyamide 10, polyamide 12, polyamide 6-12 and copolymers thereof,
Polyolefin polymers such as polypropylene, polyethylene, polybutene, polymethylpentene and their copolymers,
a water-insoluble ethylene-vinyl alcohol copolymer-based polymer containing 25 mol% to 70 mol% of ethylene units;
Polystyrene-based, polydiene-based, chlorine-based, polyolefin-based, polyester-based, polyurethane-based, polyamide-based, fluorine-based elastomeric polymers, etc., can be selected and used from among these.

In addition, in thermoplastic resins, various additives such as inorganic substances such as titanium oxide, silica, and barium oxide, carbon black, coloring agents such as dyes and pigments, flame retardants, fluorescent brighteners, antioxidants, and ultraviolet absorbers. agents may be included.

The thermoplastic resins constituting the thermoplastic resin fibers may be the same or different between the nonwoven fabric layers.

The thermoplastic resin fibers in the present invention may be not only monocomponent fibers but also composite fibers obtained by combining two or more kinds of resins. When the above thermoplastic resin fiber is a composite fiber, it is not particularly limited as long as it does not impair the effects of the present invention, and may be appropriately selected from a core-sheath type, a sea-island type, a side-by-side type, an eccentric core-sheath type, and the like. . Alternatively, the fiber may be a split type conjugate fiber in which a single fiber is split into a plurality of fibers in part or in its entirety.

The cross-sectional shape of the thermoplastic resin fiber of the present invention is not particularly limited as long as it does not impair the effects of the present invention. . When the laminated nonwoven fabric of the present invention is used as a sanitary material, a circular cross section is preferred because of its high productivity and excellent flexibility.

[Lamination interface of laminated nonwoven fabric]
The lamination interface for specifying the nonwoven fabric layer in the laminated nonwoven fabric of the present invention will be described. The lamination interface in the laminated nonwoven fabric of the present invention is specified by the following procedure.

(Specification procedure of lamination interface)
Procedure 1: A sample piece of 5 cm x 5 cm is taken from the laminated nonwoven fabric. At this time, avoid the part where the uniformity is bad and the thickness is thin.

Procedure 2: Take a three-dimensional image of the sample piece obtained in Procedure 1 with a high-resolution three-dimensional X-ray microscope. The resolution of the measurement may be within a range in which the fiber diameter of each nonwoven fabric layer can be specified, but is preferably 1.0 μm/voxel or less. Here, when the laminated nonwoven fabric is embossed, the imaging range of the X-ray CT image is captured so as to include the center point between the embossed points, that is, the center of the convex portion left by the embossing.

Procedure 3: A region of 0.5 mm×0.5 mm is extracted as a region to be analyzed from the three-dimensional image captured in Procedure 2. Here, when the laminated nonwoven fabric is embossed, the area to be analyzed is extracted so as to include the center point between the embossed points.

Step 4: For the region to be analyzed extracted in Step 3, slice (cross-sectional) images perpendicular to the thickness direction of the laminated nonwoven fabric and parallel to each other are created at intervals of 1 voxel.

Step 5: Analyze the fiber diameters of all the fibers included in each slice image obtained in Step 4, calculate the average value, and set it as the provisional average fiber diameter.

Step 6: The position in the thickness direction of the laminated nonwoven fabric of each slice image created in Step 4 is on the x-axis (unit: μm), and the provisional average fiber diameter of each slice image obtained in Step 5 is on the y-axis (unit: μm). Plot to get a graph.

Step 7: In the graph obtained in Step 6, the rate of change Δy/Δx of the value of the y-axis with respect to the x-axis is calculated by the least squares method from the data of 15 consecutive voxels, and the x-axis whose absolute value is 0.30 or more The top section is identified as the location of the laminate interface between the nonwoven layers.

[Nonwoven fabric layer (A)]
The nonwoven fabric layer (A) in the laminated nonwoven fabric of the present invention is defined as having the smallest average single fiber diameter among the nonwoven fabric layers constituting the laminated nonwoven fabric.

The average single fiber diameter of each nonwoven fabric layer is determined as follows.

(Measurement procedure for average single fiber diameter of nonwoven fabric layer)
Procedure 1: A cross section in the thickness direction is photographed with a scanning electron microscope (SEM) at a magnification such that the entire thickness direction of the laminated nonwoven fabric is within the photographing range.

Procedure 2: Apply the positional information of the lamination interface obtained by the “procedure for specifying the lamination interface” to the cross-sectional photograph obtained in Procedure 1. Sections on the x-axis where the absolute value of Δy/Δx is 0.30 or more in step 7 of "Procedure for specifying the lamination interface" are defined as the sections of the lamination interface, and the sections divided by the sections of the same lamination interface are each This is the section for analysis of the nonwoven fabric layer.

Procedure 3: For the analysis section of each nonwoven fabric layer specified in Procedure 2, using image analysis software, measure the area Af (μm ² ) formed by the cross-sectional contour of the single fiber, and measure the area Af Calculate the diameter of a perfect circle, which is the area. Twenty single fibers randomly sampled from the same analysis section are measured, the arithmetic mean is obtained, the unit is μm, and the second decimal place is rounded off to obtain the average single fiber diameter.

The average single fiber diameter Da of the thermoplastic resin fibers forming the nonwoven fabric layer (A) is preferably 20.0 μm or less. By setting Da to 20.0 μm or less, more preferably 15.0 μm or less, it is possible to effectively reduce the inter-fiber void size Ra of the nonwoven fabric layer (A), which will be described later, and obtain a suitable capillary force. Moreover, Da is preferably 2.0 μm or more. By setting Da to 2.0 μm or more, it is possible to prevent the void size Ra between fibers of the nonwoven fabric layer (A) from becoming extremely small, and to prevent the liquid permeability from lowering.

In the nonwoven fabric layer (A) of the laminated nonwoven fabric of the present invention, the interfiber void size Ra calculated by the following formula (1) is 200 μm or less.
Ra=(100×Ta×da)/(Wa×Da)−Da Formula (1)
here,
Ta: thickness (μm) of the nonwoven fabric layer (A)
da: fineness (dtex) of the thermoplastic resin fibers constituting the nonwoven fabric layer (A)
Wa: Assumed basis weight of the nonwoven fabric layer (A) (g/m ² )
Da: Average single fiber diameter (μm) of the thermoplastic resin fibers constituting the nonwoven fabric layer (A).

The thickness of each nonwoven fabric layer is determined as follows.

(Procedure for measuring thickness of nonwoven fabric layer)
Procedure 1: Add the average single fiber diameters obtained in the "Procedure for measuring the average single fiber diameter of the nonwoven fabric layer" for each of the nonwoven fabric layer whose thickness is to be measured and the other nonwoven fabric layer laminated thereon, and divide by 2, Calculate the average fiber diameter of the two layers. When another nonwoven fabric layer is laminated on the other side of the nonwoven fabric layer whose thickness is to be measured, similarly between the other nonwoven fabric layers, the average single fiber diameter is added and divided by 2. Two layers Calculate the average fiber diameter of

Procedure 2: In the section of the lamination interface between the nonwoven fabric layer whose thickness is to be measured and the other nonwoven fabric layer laminated thereon on the graph obtained in Procedure 6 of "Procedure for specifying the lamination interface", y is calculated in Procedure 1. Identify the x-coordinate that takes the average of the fiber diameters of the two layers.

Procedure 3: When other nonwoven fabric layers are laminated on both sides of the nonwoven fabric layer whose thickness is to be measured, the distance between the x coordinates that take the average value of the fiber diameters of the two layers laminated in the section of the lamination interface on both sides Calculate the thickness of the nonwoven fabric layer to be measured. When another nonwoven fabric layer is laminated only on one side of the nonwoven fabric layer whose thickness is to be measured, the x coordinate that takes the average value of the fiber diameters of the two layers in the section of the lamination interface, and the other nonwoven fabric layer to be measured. The distance to the x-coordinate of the exposed surface on one side is calculated and taken as the thickness of the nonwoven fabric layer to be measured.

The thickness Tt of the laminated nonwoven fabric can be obtained by calculating the distance between the x-coordinates of the surfaces on both sides of the laminated nonwoven fabric in Procedure 3 of "Procedure for measuring the thickness of the nonwoven fabric layer".

In addition, the fineness of the thermoplastic resin fibers constituting the nonwoven fabric layer is determined by using the average single fiber diameter of the thermoplastic resin fibers and the density of the thermoplastic resin fibers measured in the "Measurement procedure for the average single fiber diameter of the nonwoven fabric layer". The value calculated from the following formula is rounded off to the second decimal place.
d=(π×ρ×D ² )/400
Here,
d: fineness (dtex) of the thermoplastic resin fibers constituting the nonwoven fabric layer
ρ: Density ρ (g/cm ³ ) of thermoplastic resin fibers constituting the nonwoven fabric layer
D: Average single fiber diameter (μm) of thermoplastic resin fibers constituting the nonwoven fabric layer.

The density ρ of the thermoplastic resin fiber is measured based on JIS L1013:2010 "Testing methods for chemical fiber filament yarn", "8.17.2 Density gradient tube method". A density gradient tube with an appropriately adjusted density range is prepared, and the fiber density (g/cm ³ ) is measured to three decimal places for about 0.1 g of a piece of fiber taken from the nonwoven layer. The same operation was randomly taken from the nonwoven fabric layer, and the arithmetic mean of the results of five different samples was obtained, and the value rounded to the third decimal place was calculated as the density ρ of the first thermoplastic fiber (g / cm ³ ).

Further, the assumed basis weight W (g/m ² ) of the nonwoven fabric layer is obtained as follows.

First, the basis weight Wt (g/m ² ) of the laminated nonwoven fabric is measured based on "6.2 Mass per unit area" of JIS L1913:2010 "General nonwoven fabric test methods". Specifically, three test pieces cut out from the laminated nonwoven fabric to a size of 20 cm x 25 cm are collected per 1 m of the width of the sample, and the mass (g) of each is measured in the standard state, and the average value is calculated per 1 m ² . The weight of the laminated nonwoven fabric Wt (g/m ² ) is obtained by rounding off the mass of the second decimal place.

Next, using the thickness T of the target nonwoven fabric layer and the thickness Tt of the laminated nonwoven fabric obtained by the above-described procedure, the value obtained by rounding the value calculated from the following formula to the second decimal place is the nonwoven fabric layer nominal weight W (g/m ² ).
W=W×T/Tt Expression.

The inter-fiber void size represented by the formula (1) is the length of one side of the voids defined by the fibers when assuming a model in which the fibers contained in the nonwoven fabric layer are arranged regularly in a grid pattern. is the value shown. It is thought that the smaller the size of the voids between the fibers, the stronger the capillary force acting on the fiber, and the higher the water absorbing power.

In the laminated nonwoven fabric of the present invention, the interfiber void size Ra of the nonwoven fabric layer (A) having the smallest average single fiber diameter is 200 μm or less, preferably 100 μm or less, and more preferably 80 μm or less. When the liquid is dripped, the capillary force of the nonwoven fabric layer (A) is increased, a large amount of the liquid is transferred to the nonwoven fabric layer (A), and good quick-drying properties can be exhibited.

Further, it is preferable to set the inter-fiber void size Ra to 30 μm or more in order to secure a certain level of liquid permeability and water absorbency.

The inter-fiber void size Ra can be controlled by controlling the average single fiber diameter Da of the thermoplastic resin fibers forming the nonwoven fabric layer.

The thickness of the nonwoven fabric layer (A) is preferably 100 μm or more. By setting the thickness of the nonwoven fabric layer (A) to 100 µm or more, more preferably 120 µm or more, the nonwoven fabric layer (A) retains more of the liquid absorbed by the laminated nonwoven fabric, and the surface of the nonwoven fabric layer (A) side is treated later. It is possible to increase the water distribution ratio.

On the other hand, the thickness of the nonwoven fabric layer (A) is preferably 1000 µm or less. By setting the thickness of the nonwoven fabric layer (A) to 1000 μm or less, it is possible to prevent the liquid from stagnating inside the nonwoven fabric layer (A) and suppressing liquid transfer between the nonwoven fabric layers.

[Nonwoven fabric layer (B)]
The nonwoven fabric layer (B) in the laminated stretchable nonwoven fabric of the present invention is defined as a nonwoven fabric layer laminated in contact with the nonwoven fabric layer (A).

The laminated nonwoven fabric of the present invention includes at least one of the nonwoven fabric layers (B) laminated in contact with the nonwoven fabric layer (A) (when the nonwoven fabric layer (B) is laminated in contact with only one of the nonwoven fabric layers (A), the Regarding the nonwoven fabric layer (B), the ratio Rb/Ra between the inter-fiber void size Rb (μm) calculated by the following formula (2) and the Ra (μm) is 1.1 times or more. Preferably.
Rb=(100×Tb×db)/(Wb×Db)−Db Expression (2)
here,
Tb: Thickness (μm) of nonwoven fabric layer (B)
db: fineness (dtex) of the thermoplastic resin fibers constituting the nonwoven fabric layer (B)
Wb: Assumed basis weight of nonwoven fabric layer (B) (g/m ² )
Db: Average single fiber diameter (μm) of the thermoplastic resin fibers constituting the nonwoven fabric layer (B).

Further, the method for obtaining Tb (μm), db (dtex), Wb (g/m ² ), and Db (μm) according to the formula (2) depends on the thickness T of the nonwoven fabric layer and the thermoplasticity of the nonwoven fabric layer. The fineness d of the resin fiber, the apparent basis weight W of the nonwoven fabric layer, and the average single fiber diameter D of the thermoplastic resin fibers constituting the nonwoven fabric layer are as follows.

By setting Rb/Ra to 1.1 times or more, more preferably 1.2 times or more, and even more preferably 1.5 times or more, there is a large difference in capillary force between the nonwoven fabric layer (A) and the nonwoven fabric layer (B). Thus, moisture can be efficiently transferred to the nonwoven fabric layer (A), and quick drying can be improved.

On the other hand, as the ratio of Rb to Ra increases, the ratio of voids between fibers in the nonwoven fabric layer (B) naturally increases. Rb/Ra is preferably 10.0 times or less from the viewpoint of suppressing unevenness in basis weight that occurs at that time and suppressing a decrease in strength caused by this unevenness in basis weight.

The inter-fiber void size Rb of the nonwoven fabric layer (B) is preferably 100 μm or more. By setting Rb to 100 μm or more, more preferably 120 μm or more, the liquid permeability is improved, so the amount of liquid remaining in the nonwoven fabric layer (B) is reduced, and quick drying can be obtained.

The inter-fiber void size Rb of the nonwoven fabric layer (B) is preferably 500 μm or less. By setting Rb to 500 μm or less, the liquid transferred to the nonwoven fabric layer (A) can be prevented from seeping out when a load is applied to the laminated nonwoven fabric, and a dry surface can be maintained.

In order to control the interfiber void size Rb (μm) in the nonwoven fabric layer (B) within the above range, the average single fiber diameter Db of the thermoplastic resin fibers constituting the nonwoven fabric layer (B) is 15.0 μm to 30.0 μm. is preferably within the range of

The thickness of the nonwoven fabric layer (B) is preferably in the range of 100-1000 μm. By setting the thickness of the nonwoven fabric layer (B) to 100 μm or more, it is possible to suppress an increase in the water distribution rate, which will be described later, due to the seepage of part of the moisture retained in the nonwoven fabric layer (A). Further, by setting the thickness of the nonwoven fabric layer (B) to 1000 μm or less, the liquid absorbed from the nonwoven fabric layer (B) can be rapidly permeated into the nonwoven fabric layer (A).

[Laminated nonwoven fabric]
Of the four surfaces of the laminated nonwoven fabric of the present invention, the absorption surface, which is the surface on which the physiological saline is absorbed, and the surface on the opposite side, when the physiological saline is absorbed by the following procedure on each side of the laminated nonwoven fabric , preferably the water distribution ratio defined by the following formula (3) is 40% or less on at least one surface.

(Measurement procedure for water distribution ratio)
Procedure 1: Cut out a 5 cm x 5 cm sample from the laminated nonwoven fabric.

Procedure 2: Two sheets of 5 cm x 5 cm cut out from JIS P3801 type 2 filter paper are prepared for each measurement, and the mass of each sheet is measured.

Procedure 3: Drop 0.250±0.005 mL of physiological saline onto a polypropylene film. At this time, the mass of the physiological saline to be dripped is measured.

Step 4: Laminated nonwoven fabric is placed on the dripped physiological saline solution with the absorbent surface facing downward, and held for 1 minute.

Step 5: After holding the step 4, remove the laminated nonwoven fabric from the polypropylene film, place it on the first filter paper with the absorption surface facing upward, and quickly place the second filter paper on top of it. put it on

Step 6: Place a weight of 125 g on the second filter paper so that the pressure is 5 g/cm ² and hold for 1 minute.

Step 7: After holding in step 6 above, the weight is removed, the mass of each filter paper is measured, and the increase in mass of each filter paper is calculated.

Step 8: Calculate the water distribution ratio of each surface of the laminated nonwoven fabric from the following formula.
Water distribution ratio (%) = 100 x W1/W0
Here,
W0: Mass (g) of physiological saline dripped in the above procedure 3
W1: Mass increase (g) of the filter paper applied to the surface in step 7 above.

For the water distribution ratio determined by this procedure, the lower the value, the less liquid is retained on the surface. In other words, if the water distribution ratio is low on the surface that comes in contact with the skin, a dry feeling can be felt even after absorbing the liquid.

In the laminated nonwoven fabric of the present invention, at least one of the four surfaces described above has a water distribution ratio of 40% or less, more preferably 30% or less, and still more preferably 20% or less. It has a low moisture content and can effectively maintain a dry surface.

In the laminated nonwoven fabric of the present invention, it is preferable that the nonwoven fabric layer (B) is laminated on at least one of the outermost surfaces in order to achieve the surface water distribution ratio as described above. That is, as described above, the nonwoven fabric layer (B) is defined as a nonwoven fabric layer laminated in contact with the nonwoven fabric layer (A).
Nonwoven fabric layer (B)/Nonwoven fabric layer (A)...
It has a laminated structure of As described above, the nonwoven fabric layer (A) is defined as having the smallest average single fiber diameter among the nonwoven fabric layers constituting the laminated nonwoven fabric. When the liquid is absorbed from the outermost surface, the liquid is quickly transferred to the nonwoven fabric layer (A) in which the inter-fiber void size is controlled to be very small as described above, so The water distribution ratio on the surface is reduced, and quick drying can be obtained.

Further, in the laminated nonwoven fabric of the present invention, it is preferable that the water distribution ratio of the surface opposite to the surface having the water distribution ratio of 40% or less is 50% or more. By setting the water distribution ratio to 50% or more, more preferably 60% or more, the liquid is smoothly transferred from the surface where the liquid is absorbed to the other surface without retaining the absorbed liquid inside the laminated nonwoven fabric. can be made

In the laminated nonwoven fabric of the present invention, a nonwoven fabric layer (A) with high capillary force is arranged on one surface in order to control the water distribution ratio of the surface opposite to the surface on which the liquid is absorbed within the above range. is preferred.

The laminated nonwoven fabric of the present invention preferably has a water absorption rate of 20 seconds or less as measured from at least one surface.

The water absorption rate referred to here is measured based on JIS L1907:2010 "Water absorption test method for textile products", "7.1.1 Dropping method". Drop one drop of water onto the laminated nonwoven fabric, measure the time it takes for the specular reflection on the surface to disappear after being absorbed, and calculate the simple average of the values measured at 10 different points. The value obtained by rounding off to the first place is defined as the water absorption speed referred to in the present invention.

A water absorption rate of 20 seconds or less, more preferably 10 seconds or less indicates good performance in removing moisture adhering to the surface.

The basis weight of the laminated nonwoven fabric of the present invention is preferably 10 to 100 g/m ² .

By setting the basis weight to preferably 10 g/m ² or more, more preferably 13 g/m ² or more, and even more preferably 15 g/m ² or more, it is possible to obtain a laminated nonwoven fabric with mechanical strength suitable for practical use. On the other hand, by setting the basis weight to preferably 100 g/m ² or less, more preferably 50 g/m ² or less, a laminated nonwoven fabric having appropriate softness suitable for use as a nonwoven fabric for sanitary materials can be obtained.

In the laminated nonwoven fabric of the present invention, each nonwoven fabric layer is preferably integrated. The term "integration" as used herein means that the nonwoven fabric layers are joined by entangling fibers, fixing by adhesive or other components, and fusion bonding between thermoplastic resins constituting each layer.

A hydrophilic agent may be added to the laminated nonwoven fabric of the present invention for the purpose of increasing the water absorption.

[Hygiene materials]
The sanitary material of the present invention has excellent water absorbency and quick-drying properties because at least a portion thereof is composed of the laminated nonwoven fabric of the present invention.

The sanitary material of the present invention can be suitably used for health-related purposes such as medical and nursing care. The sanitary material of the present invention can be suitably used mainly for disposable articles such as disposable diapers, sanitary napkins, gauze, bandages, masks, gloves, bandages and the like.

Among them, in paper diapers, it can be used as constituent members in various places such as top sheets, back sheets, and side gathers.

The diaper as a sanitary material of the present invention preferably has a top sheet composed of the laminated nonwoven fabric of the present invention. When the laminated nonwoven fabric of the present invention is used as a top sheet of a diaper, when the nonwoven fabric layer (B) is placed on the skin side of the top sheet, excreted urine is quickly absorbed into the nonwoven fabric layer (A). The rapid transition allows the surface of the topsheet to remain dry.

Moreover, it is also preferable that at least a part of the waist portion of the diaper as a sanitary material of the present invention is composed of the laminated nonwoven fabric of the present invention. When the laminated nonwoven fabric of the present invention is used as part of the waist portion of a diaper, if the nonwoven fabric layer (B) is placed on the skin side of the waist portion of the diaper, it can quickly absorb sweat and the nonwoven fabric layer (A ) to keep the surface of the waist dry.

Moreover, the sanitary material of the present invention can be suitably used as a mask. In the mask as a sanitary material of the present invention, it is preferable that the inner surface layer is composed of the laminated nonwoven fabric of the present invention. The term "inner layer" as used in the present invention refers to the layer of the face piece covering the mouth that is located closest to the mouth. When the laminated nonwoven fabric of the present invention is used so that the nonwoven fabric layer (B) is placed on the skin side, even if moisture adheres to the skin side due to condensation of sweat or exhalation, it is immediately absorbed inside the laminated nonwoven fabric. Since it can keep the skin dry, it can be used without discomfort when worn.

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

The method for producing the nonwoven fabric layer (A) and the nonwoven fabric layer (B) constituting the laminated nonwoven fabric of the present invention can be selected from known production methods such as the spunbond method, the melt blow method, and the staple fiber card method.

Among them, the spunbond method is preferred because of its excellent productivity.

A preferred mode of producing the laminated nonwoven fabric of the present invention based on the spunbond method will be described below, but the present invention is not limited to this.

In the spunbond method, the thermoplastic resin that is the raw material is melted, spun from a spinneret, and then solidified by cooling. It is a nonwoven fabric manufacturing method that requires a step of heat bonding after forming a nonwoven fiber web.

Various shapes such as a round shape and a rectangular shape can be adopted as the shape of the spinneret and the ejector to be used. Among them, it is preferable to use a combination of a rectangular mouthpiece and a rectangular ejector from the viewpoint that the amount of compressed air used is relatively small and the threads are less likely to fuse or rub against each other.

In the present invention, the spinning temperature is preferably (melting temperature of thermoplastic resin as raw material + 10°C) or higher and not higher than (melting temperature of thermoplastic resin as raw material + 100°C). By setting the spinning temperature within the above range, a stable molten state can be obtained and excellent spinning stability can be obtained.

Moreover, when manufacturing the nonwoven fabric layer (A), the average inter-fiber space can be reduced by reducing the fiber diameter. Therefore, in order to stably produce fine fibers, the melt viscosity of the polymer used in the nonwoven fabric layer (A) is preferably 100 Pa·s or less, more preferably 50 Pa·s or less.

The melt viscosity of the polymer referred to here is measured using a chip-shaped polymer with a moisture content of 200 ppm or less in a vacuum dryer, changing the strain rate in stages, and measuring at the same temperature as the spinning temperature. This is the value at a strain rate of 1216s ^-1 .

The spun yarn is then cooled. Methods for cooling the spun yarn include, for example, a method of forcibly blowing cold air onto the yarn, and natural cooling at the ambient temperature around the yarn. and a method of adjusting the distance between the spinneret and the ejector, or a method of combining these methods. Also, the cooling conditions can be appropriately adjusted in consideration of the discharge amount per single hole of the spinneret, the spinning temperature, the ambient temperature, and the like.

Next, the cooled and solidified yarn is pulled and stretched by compressed air jetted from an ejector.

In the laminated nonwoven fabric of the present invention, the average inter-fiber void size of the nonwoven fabric layer (A) and the nonwoven fabric layer (B) can be controlled by the diameter of the constituent fibers.

The diameter of the fiber is determined by the output per hole of the spinneret and the drawing speed, ie spinning speed. Therefore, it is preferable to determine the discharge rate and the spinning speed so that the diameter can be controlled to obtain the desired inter-fiber void size.

The spinning speed is preferably 2000 m/min or higher. By setting the spinning speed to 2000 m/min or more, more preferably 3000 m/min or more, high productivity can be obtained, and the orientation and crystallization of the fibers can be advanced to obtain long fibers with high strength.

The long fiber yarn drawn by pulling in this way is collected by a moving net to be formed into a sheet, and then subjected to a thermal bonding step.

The laminated nonwoven fabric of the present invention is formed by laminating nonwoven fabric layers. As a method for laminating the nonwoven fabric layer, for example, the thermoplastic resin fibers are collected by the spunbond method on the nonwoven fabric layer obtained by collecting the thermoplastic resin fibers on the collection net by the spunbond method as described above. A method in which the next nonwoven fabric layer obtained by collecting is continuously collected inline and integrated by lamination; method etc. can be adopted. Among them, the method of continuously collecting the next nonwoven fabric layer on the nonwoven fabric layer in-line and laminating and integrating them by heat bonding is a preferred mode because it is excellent in productivity.

As a method for forming the laminated nonwoven fabric of the present invention by integrating nonwoven fabric layers by thermal bonding, a thermal embossing roll in which engraving (unevenness) is applied to the surfaces of a pair of upper and lower rolls, and one roll surface is flat (smooth ) and another roll with engraved (unevenness) on the surface, and heat calender rolls that combine a pair of upper and lower flat (smooth) rolls. It is possible to employ a bonding method or a thermocompression bonding method such as ultrasonic bonding in which thermal bonding is performed by ultrasonic vibration of a horn. Moreover, as a method for laminating and integrating the laminated nonwoven fabric of the present invention by thermal bonding, a so-called air-through method, which is a method of blowing hot air, can be mentioned.

Among them, the method of heat-bonding with a pair of upper and lower heat rolls is preferable because the non-woven fabric layer (A) can be densified by bonding while compressing the laminated non-woven fabric layer, and the void size between fibers can be reduced.

When the laminated nonwoven fabric of the present invention is produced by thermocompression using hot rolls, the nonwoven fabric layer (A) can be sufficiently densified by setting the linear pressure that the laminated nonwoven fabric receives between rolls to 100 N/cm or more. Therefore, it is preferable.

Moreover, in the laminated nonwoven fabric, it is preferable to process the surface closer to the nonwoven fabric layer (A) than the nonwoven fabric layer (B) to a flat roll and the opposite surface to a heat-embossed roll with engraving. By adopting such a combination of rolls, the nonwoven fabric layer (B) is less likely to be compressed with respect to the nonwoven fabric layer (A). can be secured to a large extent.

A hydrophilizing agent may be applied to the laminated nonwoven fabric of the present invention before winding. Examples of the method for applying the hydrophilizing agent to the laminated nonwoven fabric include application by a kiss roll or spray, dip coating, etc., but application by a kiss roll is preferred in terms of uniformity and ease of control of the amount of adhesion.

The present invention will now be described in detail based on examples. However, the present invention is not limited only to these examples. In the measurement of each physical property, unless otherwise specified, the measurement was performed according to the method described above.

(1) Identification of Lamination Interface The lamination interface of the laminated nonwoven fabric was identified according to the above-described "Lamination Interface Identification Procedure". In addition, "nano3DX" manufactured by Rigaku Corporation was used as a high-resolution three-dimensional X-ray microscope. Also, the resolution was set to 0.6 μm/voxel.

(2) Average single fiber diameter The average single fiber diameter of each nonwoven fabric layer was measured according to the above-mentioned "Procedure for measuring the average single fiber diameter of the nonwoven fabric layer". "S-5500" manufactured by Hitachi High-Technologies Corporation was used as a scanning electron microscope (SEM), and "WinROOF2015" manufactured by Mitani Shoji Co., Ltd. was used as image analysis software.

(3) Average single fiber diameter in the manufacturing process of laminated nonwoven fabric For each thermoplastic resin fiber, fiber samples were randomly collected from the nonwoven fiber web collected on the net, and the cross section of the fiber was measured by Hitachi High-Technologies Corporation. The image was taken with a scanning electron microscope "S-5500" of No. 1 at a magnification that allows observation of a single fiber. After that, as image analysis software, "WinROOF2015" manufactured by Mitani Shoji Co., Ltd. was used, and the measurement was performed as described above.

When the average single fiber diameter was measured in the manufacturing process of the laminated nonwoven fabric, in the present examples and comparative examples, the average single fiber diameter was obtained with no difference from the measurement by the above-mentioned "Procedure for measuring the average single fiber diameter of the nonwoven fabric layer". I was able to confirm that.

(4) Thickness The thicknesses of the laminated nonwoven fabric and each nonwoven fabric layer were measured according to the "Procedure for measuring the thickness of the nonwoven fabric layer" described above.

(5) Thickness by Simple Method An image of the cross section perpendicular to the machine direction of the laminated nonwoven fabric was taken with a scanning electron microscope ("S-5500" manufactured by Hitachi High-Technologies Corporation) at a magnification that allows observation of the thickness. Based on the photographed images, the thickness of the laminated nonwoven fabric and each nonwoven fabric layer was measured.

When the thickness of the laminated nonwoven fabric and each nonwoven fabric layer was measured by a simple method, in this example and comparative example, it was confirmed that the thickness was obtained with no difference from the measurement by the above "Procedure for measuring the thickness of the nonwoven fabric layer". done.

(6) Interfiber void size The interfiber void size of the nonwoven fabric layer was calculated according to the following formula.
R=(100×T×d)/(W×D)−D
here,
T: Thickness (μm) of the nonwoven fabric layer. Measured by (4) above.
d: Fineness (dtex) of thermoplastic resin fibers constituting the nonwoven fabric layer. Measured by the definition of d above.
W: The nominal basis weight of the nonwoven fabric layer (g/m ² ). Measured by the definition of W above. In addition, in the present examples and comparative examples, it was confirmed that there was no difference from the basis weight of the nonwoven fiber web layer described later.
D: Average single fiber diameter (μm) of thermoplastic resin fibers constituting the nonwoven fabric layer. Measured by (2) above.

(7) Water distribution ratio The water distribution ratio on both sides of the laminated nonwoven fabric was measured according to the above-mentioned "measurement procedure of water distribution ratio". In the present examples and comparative examples, the surface on which the nonwoven fabric layer (B) was placed as the outermost surface was used as the "absorbing surface" in procedure 4 of "procedure for measuring water distribution ratio". The number of samples was set to 5, the arithmetic mean was obtained, and the first decimal place was rounded off.

(8) Water Absorption Rate The water absorption rate was measured according to JIS L1907:2010 "Testing method for water absorption of textile products", "7.1.1 Dropping method". One drop of water was dropped on the laminated nonwoven fabric, and the time it took for the water to be absorbed and the specular reflection on the surface to disappear was measured. A simple average of the values measured at 10 different points was calculated, the unit was seconds, and the first decimal place was rounded off.

(9) Water absorption and quick drying property Regarding the laminated nonwoven fabric after measuring the water distribution ratio in (7) above, healthy general adults (30 people in total, 15 men and 15 men) touched the “absorbent surface” side with their hands, and the dry feeling on the surface was evaluated in the following three stages. The average score of the evaluation results was calculated for each nonwoven fabric, and the feel of the laminated nonwoven fabric was obtained.
5: The surface has a dry feel and does not feel moisture 3: The surface has no moisture but is moist 1: The surface has moisture and is moist [Example 1]
(Nonwoven fibrous web layer (A))
Polypropylene (PP, melt viscosity 30 Pa·s) was melted with an extruder and spun from a rectangular spinneret at a single hole discharge rate of 0.30 g/min. After the spun yarn is cooled and solidified, it is pulled and stretched by compressed air in a rectangular ejector at a pressure of 0.10 MPa at the ejector, collected on a moving net, and spunbonded to form a nonwoven fiber. A web layer (A) was obtained. The fibers constituting the resulting nonwoven fibrous web layer (A) had an average single fiber diameter of 10.6 µm. Also, the basis weight was set to 35.0 g/m ² .

(Nonwoven fibrous web layer (B))
The same polypropylene (PP) as the raw material used for the nonwoven fibrous web layer (A) was melted with an extruder and spun from a rectangular spinneret at a single hole discharge rate of 0.85 g/min. After the spun yarn is cooled and solidified, it is drawn and stretched by compressed air in a rectangular ejector with a pressure of 0.08 MPa at the ejector, and captured on the nonwoven fiber web layer (A) on the moving net. A nonwoven fibrous web layer (B) was obtained by collecting and spunbonding. The fibers constituting the resulting nonwoven fibrous web layer (B) had an average single fiber diameter of 20.4 μm. Also, the basis weight was set to 30.0 g/m ² .

By collecting the nonwoven fibrous web layer (B) on the nonwoven fibrous web layer (A), by in-line lamination, two of the nonwoven fibrous web layer (A)/nonwoven fibrous web layer (B) A laminated fibrous web with a layered structure was obtained.

(Laminated nonwoven fabric)
The obtained laminated fibrous web is placed on top and bottom, with a metal embossing roll having circular projections staggered in both the MD and CD directions at the same pitch as the upper roll and a metal flat roll as the lower roll. Thermal bonding was performed at a linear pressure of 300 N/cm and a thermal bonding temperature of 125° C. using an embossing roll having a pair of heating mechanisms. Then, a hydrophilic treatment was applied to obtain a laminated nonwoven fabric having a basis weight of 65.0 g/m ² .

The obtained laminated nonwoven fabric was evaluated for thickness of each layer, interfiber void size, water distribution ratio, water absorption speed, and water absorption and quick drying property. The nonwoven fabric layer (A) had a thickness of 300 μm and an inter-fiber void size of 54 μm. The nonwoven fabric layer (B) had a thickness of 420 μm and a void size between fibers of 181 μm. Table 1 shows the results.

[Example 2]
Except for setting the single hole discharge rate to 0.80 g/min in the step of obtaining the nonwoven fibrous web layer (A) and setting the single hole discharge rate to 1.20 g/min in the step of obtaining the nonwoven fibrous web layer (B) A laminated nonwoven fabric was obtained in the same manner as in Example 1. Table 1 shows the evaluation results of the obtained laminated nonwoven fabric.

[Example 3]
A laminated nonwoven fabric was obtained in the same manner as in Example 1, except that the discharge rate per hole was changed to 0.35 g/min in the step of obtaining the nonwoven fibrous web layer (B). Table 1 shows the evaluation results of the obtained laminated nonwoven fabric.

[Example 4]
A laminated nonwoven fabric was produced in the same manner as in Example 1, except that the basis weight of the nonwoven fibrous web layer (A) was 15.0 g/m ² and the basis weight of the nonwoven fibrous web layer (B) was 13.0 g/m ² . Obtained. Table 1 shows the evaluation results of the obtained laminated nonwoven fabric.

[Example 5]
A laminated nonwoven fabric was obtained in the same manner as in Example 1, except that the basis weight of the nonwoven fiber web layer (A) was 10.0 g/m ² . Table 1 shows the evaluation results of the obtained laminated nonwoven fabric.

[Example 6]
(Nonwoven fibrous web layer (A))
A nonwoven fibrous web layer (A) was obtained in the same manner as in Example 1.

(Nonwoven fibrous web layer (B))
A nonwoven fibrous web layer (B) was obtained in the same manner as in Example 1, except that the pulled and stretched yarn was directly collected on a moving net.

After obtaining the nonwoven fibrous web layer (A) and the nonwoven fibrous web layer (B), they are laminated offline to obtain a two-layer structure of nonwoven fibrous web layer (A)/nonwoven fibrous web layer (B). of the laminated fibrous web was obtained.

(Laminated nonwoven fabric)
The obtained laminated fiber web was heat-bonded in the same manner as in Example 1 and subjected to hydrophilic treatment to obtain a laminated nonwoven fabric. Table 1 shows the evaluation results of the obtained laminated nonwoven fabric.

[Example 7]
The polymer used for the nonwoven fabric layer (A) and the nonwoven fabric layer (B) was polyethylene glycol-copolymerized polyethylene terephthalate (copolymerized PET, the copolymerization rate of polyethylene glycol of which is 8% by mass of the polymer).

(Nonwoven fibrous web layer (A))
Copolymerized polyethylene terephthalate (copolymerized PET) obtained by copolymerizing 8% by mass of polyethylene glycol was used as a fiber raw material polymer. A nonwoven fibrous web layer (A) was obtained in the same manner as in Example 1, except that copolymer PET was used and the running speed of the net was changed. The fibers constituting the obtained spunbond nonwoven fabric layer (A) had an average single fiber diameter of 8.5 µm. Also, the basis weight was set to 30.0 g/m ² .

(Nonwoven fibrous web layer (B))
A nonwoven fibrous web layer (B) was obtained in the same manner as in Example 1, except that the same copolymerized PET as the raw material used in the nonwoven fibrous web layer (A) was used. The fibers constituting the obtained spunbond nonwoven fabric layer (B) had an average single fiber diameter of 17.5 μm. Also, the basis weight was 30.0 g/m ² and 37.0 g/m ² .

(Laminated nonwoven fabric)
A laminated nonwoven fabric was obtained in the same manner as in Example 1, except that the heat bonding temperature was 200°C. The nonwoven fabric layer (A) had a thickness of 270 μm and an inter-fiber void size of 73 μm. The nonwoven fabric layer (B) had a thickness of 350 μm and a void size between fibers of 158 μm. Table 1 shows the evaluation results of the obtained laminated nonwoven fabric.

[Comparative Example 1]
In the step of obtaining the nonwoven fibrous web layer (A), the single-hole discharge rate was 1.20 g/min, the pressure in the ejector was 0.08 MPa, and the single-hole discharge rate was set in the step of obtaining the nonwoven fibrous web layer (B). A laminated nonwoven fabric was obtained in the same manner as in Example 1, except that the flow rate was 1.20 g/min. The fibers constituting the resulting nonwoven fibrous web layer (A) had an average single fiber diameter of 22.0 μm. The nonwoven fabric layer (A) had a thickness of 430 μm and an inter-fiber void size of 245 μm. Table 1 shows the evaluation results of the obtained laminated nonwoven fabric.

As shown in Table 1, it can be seen that Examples 1 to 7 are excellent in water absorption and quick drying properties. In particular, in Examples 1 and 6, both the water absorption rate and the water absorption and quick drying properties were achieved at high levels. On the other hand, Comparative Example 1 showed low water absorption and quick drying properties.

Claims (10)

In a laminated nonwoven fabric layer (A) having the smallest average single fiber diameter among the nonwoven fabric layers, the gap between fibers is calculated by the following formula (1). A laminated nonwoven fabric having a size Ra (μm) of 200 μm or less.
Ra=(100×Ta×da)/(Wa×Da)−Da Formula (1)
here,
Ta: thickness (μm) of the nonwoven fabric layer (A)
da: fineness (dtex) of the thermoplastic resin fibers constituting the nonwoven fabric layer (A)
Wa: basis weight of nonwoven fabric layer (A) (g/m ² )
Da: Average single fiber diameter (μm) of the thermoplastic resin fibers constituting the nonwoven fabric layer (A). For at least one of the nonwoven fabric layers (B) laminated in contact with the nonwoven fabric layer (A), the ratio Rb/Ra between the interfiber void size Rb (μm) calculated by the following formula (2) and the Ra is 1 .1 or more.
Rb=(100×Tb×db)/(Wb×Db)−Db Expression (2)
here,
Tb: Thickness (μm) of nonwoven fabric layer (B)
db: fineness (dtex) of the thermoplastic resin fibers constituting the nonwoven fabric layer (B)
Wb: basis weight of nonwoven fabric layer (B) (g/m ² )
Db: Average single fiber diameter (μm) of the thermoplastic resin fibers constituting the nonwoven fabric layer (B). At least one of the four surfaces of the absorbent surface, which is the surface on which the physiological saline is absorbed, and the surface on the opposite side when physiological saline is absorbed by the following procedure for each of the surfaces on both sides of the laminated nonwoven fabric 3. The laminated nonwoven fabric according to claim 1 or 2, wherein the surface has a water distribution ratio defined by the following formula (3) of 40% or less.
Procedure 1: Cut out a 5 cm x 5 cm sample from the laminated nonwoven fabric.
Procedure 2: Two sheets of 5 cm x 5 cm cut out from JIS P3801 type 2 filter paper are prepared for each measurement, and the mass of each sheet is measured.
Procedure 3: Drop 0.250±0.005 mL of physiological saline onto a polypropylene film. At this time, the mass of the physiological saline to be dripped is measured.
Step 4: Laminated nonwoven fabric is placed on the dripped physiological saline solution with the absorbent surface facing downward, and held for 1 minute.
Step 5: After holding the step 4, remove the laminated nonwoven fabric from the polypropylene film, place it on the first filter paper with the absorption surface facing upward, and quickly place the second filter paper on top of it. put it on
Step 6: Place a weight of 125 g on the second filter paper so that the pressure is 5 g/cm ² and hold for 1 minute.
Step 7: After holding in step 6 above, the weight is removed, the mass of each filter paper is measured, and the increase in mass of each filter paper is calculated.
Step 8: Calculate the water distribution ratio of each surface of the laminated nonwoven fabric from the following formula.
Water distribution ratio (%) = 100 x W1/W0
Here,
W0: Mass (g) of physiological saline dripped in the above procedure 3
W1: Mass increase (g) of the filter paper applied to the surface in step 7 above. The laminated nonwoven fabric according to claim 3, wherein the water distribution ratio of the surface opposite to the surface having the water distribution ratio of 40% or less is 50% or more. 5. The laminated nonwoven fabric according to any one of claims 1 to 4, wherein at least one surface has a water absorption rate of 20 seconds or less as measured by the dropping method of JIS L1907:2010. A sanitary material at least partially composed of the laminated nonwoven fabric according to any one of claims 1 to 5. 7. The sanitary material according to claim 6, wherein said sanitary material is a diaper. The sanitary material according to claim 7, wherein the top sheet is composed of the laminated nonwoven fabric. The sanitary material according to claim 7, wherein at least part of the waist portion is composed of the laminated nonwoven fabric. 8. The sanitary material according to claim 7, wherein said sanitary material is a mask, and the inner surface layer of said mask is composed of said laminated nonwoven fabric.