TWI861376B - Spunbond nonwoven fabric - Google Patents

Abstract

The object of the present invention is to provide a spunbond nonwoven fabric with good printability, excellent gloss, and softness. In order to achieve the above object, the present invention has the following structure. That is, a spunbond nonwoven fabric, which is a spunbond nonwoven fabric containing a polyolefin resin, and the average fiber orientation is 0 to 30 degrees, the proportion of fibers with a fiber orientation of 0 to 30 degrees is 50% to 80%, and the tensile strength in the reference direction is 3 to 6 times the tensile strength in the direction orthogonal to the reference direction.

Description

Spunbond nonwoven fabric

The present invention relates to a spunbond nonwoven fabric.

Generally, in nonwoven fabrics for sanitary materials such as diapers and sanitary napkins, nonwoven fabrics containing polyolefins are often used for reasons such as lightness, low cost, and softness.

In particular, the back sheet of disposable diapers has a lot of opportunities to come into contact with hands and is used over a wide range, which greatly affects the appearance of the diapers. Therefore, in addition to skin touch and softness, the requirements for design are also increasing. Regarding the appearance of disposable diapers, as an appearance that is popular with babies, characters are expected on the surface, and the printability of the non-woven surface is one of the important functions. In addition, in terms of design, those with a silky appearance and high gloss are particularly popular.

As a means of improving the skin touch or softness of nonwoven fabrics, it has been known that a method of controlling the fiber diameter of the fibers constituting the nonwoven fabric is effective. For example, a spunbonded nonwoven fabric has been proposed that improves the bending softness of the fiber itself by setting the fiber density and adsorption force of the fiber to a specific range (see Patent Document 1).

[Prior art literature]

[Patent Literature]

[Patent document 1] Japanese Patent Publication No. 2013-159884

However, in the method disclosed in Patent Document 1, the surface of the nonwoven fabric has large unevenness, resulting in uneven printing, making it difficult to obtain a good appearance.

In order to make the surface smooth, a method of contacting using a heat calender or the like is considered, but in this method, the surface of the nonwoven fabric is film-coated, so the hand feels hard.

As such, nonwoven fabrics with reduced surface irregularities are required, but currently, there is no nonwoven fabric that has both printability and tactile properties that can withstand practical use.

Therefore, the purpose of the present invention is to provide a spunbond nonwoven fabric with good printability, excellent gloss and softness in view of the above-mentioned subject.

The spunbonded nonwoven fabric of the present invention is a spunbonded nonwoven fabric containing a polyolefin resin, and the average fiber orientation is 0 to 30 degrees, the proportion of fibers with a fiber orientation of 0 to 30 degrees is 50% to 80%, and the tensile strength in the reference direction is 3 to 6 times the tensile strength in the direction orthogonal to the reference direction.

According to the preferred embodiment of the spunbonded nonwoven fabric of the present invention, the average single fiber diameter of the fibers constituting the spunbonded nonwoven fabric is 6.5 μm to 11.9 μm.

According to the preferred embodiment of the spunbond nonwoven fabric of the present invention, the ratio of the surface roughness SMD measured by the Kawabata Evaluation System (KES) method between the reference direction and the direction orthogonal to the reference direction on at least one side is 0.30 to 0.85.

According to a preferred embodiment of the spunbond nonwoven fabric of the present invention, the polyolefin resin contains a fatty acid amide compound having a carbon number of 23 to 50.

According to the preferred embodiment of the spunbond nonwoven fabric of the present invention, the content of the fatty acid amide compound in the polyolefin resin is 0.01 mass % to 5.0 mass %.

According to a preferred embodiment of the spunbond nonwoven fabric of the present invention, the fatty acid amide contains ethyl distearate amide.

According to the preferred embodiment of the spunbond nonwoven fabric of the present invention, the stiffness in the reference direction measured by the cantilever method is 10mm~80mm.

According to a preferred embodiment of the spunbond nonwoven fabric of the present invention, the spunbond nonwoven fabric further satisfies the following formula (1).

GL/100≧95...(1)

Here, G is the maximum value of glossiness and L is the average brightness.

According to the present invention, a spunbonded nonwoven fabric with good printability, excellent gloss and softness can be obtained.

The spunbonded nonwoven fabric of the present invention is a spunbonded nonwoven fabric containing a polyolefin resin, and the average fiber orientation is 0 to 30 degrees, the proportion of fibers with a fiber orientation of 0 to 30 degrees is 50% to 80%, and the tensile strength in the reference direction is 3 to 6 times the tensile strength in the direction orthogonal to the reference direction.

By doing this, a spunbond nonwoven fabric with good printability, excellent gloss, and softness can be produced.

The following is a description of these details.

[Polyolefin resin]

Examples of the polyolefin resin used in the present invention include polypropylene resin, polyethylene resin, etc.

Examples of polypropylene resins include homopolymers of propylene and copolymers of propylene and various α-olefins.

As polyethylene resins, there can be listed homopolymers of ethylene or copolymers of ethylene and various α-olefins, etc.

Among these, polypropylene resins are particularly preferred in terms of spinnability and strength.

The polyolefin resin used in the present invention may be a mixture of two or more types, or may be a resin composition containing other olefin resins or thermoplastic elastomers.

The polyolefin resin used in the present invention may be a composite fiber formed by combining a plurality of polyolefin resins. As composite forms of composite fibers, for example, concentric core-sheath type, eccentric core-sheath type, and island type composite forms can be listed. Among them, in terms of excellent spinnability and the ability to evenly bond fibers to each other by thermal bonding, the preferred form is a concentric core-sheath type composite form.

As long as the effects of the present invention are not impaired, antioxidants, weather stabilizers, light stabilizers, antistatic agents, antifogging agents, anti-adhesion agents, lubricants, nucleating agents, pigments and other additives, other polymers, etc. may be added to the polyolefin resin used in the present invention as needed.

The melting point of the polyolefin resin used in the present invention is preferably 80°C to 200°C, more preferably 100°C to 180°C, and further preferably 120°C to 180°C. By setting the melting point preferably to 80°C or more, more preferably to 100°C or more, and further preferably to 120°C or more, high heat resistance can be easily obtained. In addition, by setting the melting point preferably to 200°C or less, and more preferably to 180°C or less, the filament ejected from the die can be easily cooled, and the fusion of the fibers can be suppressed, so that stable spinning can be easily performed.

The melt flow rate (hereinafter, sometimes described as MFR) of the spunbond nonwoven fabric of the present invention is preferably 155 g/10 min to 850 g/10 min. By setting the MFR to 155 g/10 min to 850 g/10 min, preferably 155 g/10 min to 600 g/10 min, and more preferably 155 g/10 min to 400 g/10 min, even if the fabric is stretched at a high spinning speed to improve productivity, it can easily follow the deformation due to the low viscosity, and stable spinning is easy. In addition, by stretching at a high spinning speed, the orientation crystallization of the fiber is promoted, and it is easy to obtain a fiber with high mechanical strength.

The melt flow rate (MFR) of spunbond nonwoven fabric is measured by the method described below.

For the same reason as the MFR of spunbond nonwoven fabric, the MFR of the polyolefin resin used as the raw material of the spunbond nonwoven fabric of the present invention is preferably 155 g/10 min to 850 g/10 min, more preferably 155 g/10 min to 600 g/10 min, and even more preferably 155 g/10 min to 400 g/10 min.

In the spunbonded nonwoven fabric of the present invention, two or more resins with different MFRs can be blended in any proportion to adjust the MFR of the polyolefin resin. In this case, the MFR of the resin blended with the polyolefin resin is preferably 10g/10min to 1000g/10min, more preferably 20g/10min to 800g/10min, and further preferably 30g/10min to 600g/10min. By doing so, it is possible to prevent the polyolefin resin from having uneven viscosity locally and uneven fiber density or deterioration of spinnability after blending.

In addition, when spinning the fibers described below, in order to prevent the occurrence of local viscosity unevenness, make the fiber uniform, and further make the fiber diameter thinner as described below, it is also considered to adjust the MFR by decomposing the resin used. However, it is preferred not to add free radical agents such as peroxides, especially dialkyl peroxides. When using this method, in addition to the local occurrence of viscosity unevenness and fiber unevenness, it is difficult to make the fiber diameter sufficiently thinner, and there is also a situation where the spinnability deteriorates due to viscosity unevenness or bubbles generated by decomposed gas.

In the spunbonded nonwoven fabric of the present invention, it is preferred that the polyolefin resin contains a fatty acid amide compound having 23 to 50 carbon atoms. By containing a fatty acid amide compound having 23 to 50 carbon atoms, the orientation of the fiber or the softness of the nonwoven fabric can be easily improved.

By setting the carbon number of the fatty acid amide compound to 23 or more, preferably 30 or more, the fatty acid amide compound can be prevented from being excessively exposed to the fiber surface, making the spinning property and processing stability excellent and maintaining high productivity. On the other hand, by setting the carbon number of the fatty acid amide compound to 50 or less, preferably 42 or less, the fatty acid amide compound can easily move to the fiber surface, and the fiber orientation can easily become the same, which can further improve the softness of the spunbond nonwoven fabric.

As fatty acid amide compounds having carbon numbers of 23 to 50, there can be listed: saturated fatty acid monoamide compounds, saturated fatty acid diamide compounds, unsaturated fatty acid monoamide compounds, and unsaturated fatty acid diamide compounds, etc.

Specifically, the fatty acid amide compounds having 23 to 50 carbon atoms include: tetracosylamide, hexacosylamide, octacosylamide, ceramide, tetracosopentaenoic acid amide, ceramide, ethyldilaurate amide, methylenedilaurate amide, ethyldistearylamide, ethyldihydroxystearate amide, Amine, ethyl bisbehenylamide, hexamethylenebisstearamide, hexamethylenebisbehenylamide, hexamethylenehydroxystearamide, distearyl adipamide, distearyl sebacic acid amide, ethyl dioleic acid amide, ethyl dierucic acid amide, and hexamethylene dioleic acid amide, etc. These can also be used in combination.

Among these fatty acid amide compounds, ethyl distearate amide, which is a saturated fatty acid diamide compound, can be particularly preferably used. Ethyl distearate amide can be suitably used for melt spinning due to its excellent thermal stability. Therefore, by using a fiber containing a polyolefin resin containing ethyl distearate amide, a spunbonded nonwoven fabric having excellent lubricity or softness while maintaining high productivity can be easily obtained.

In the spunbonded nonwoven fabric of the present invention, the content of the fatty acid amide compound in the polyolefin resin is preferably 0.01 mass% to 5.0 mass%. By setting the content of the fatty acid amide compound preferably to 0.01 mass% to 5.0 mass%, more preferably to 0.1 mass% to 3.0 mass%, and further preferably to 0.1 mass% to 1.5 mass%, it is possible to impart appropriate lubricity and higher softness while maintaining spinnability.

The content mentioned here refers to the mass percentage of the fatty acid amide compound contained in the entire polyolefin resin constituting the spunbonded nonwoven fabric of the present invention. For example, even if the fatty acid amide compound is contained only in the sheath component constituting the core-sheath type composite fiber, the content ratio relative to the total amount of the core-sheath component is calculated.

As a method for measuring the content of fatty acid amide compounds in polyolefin resins, for example, the following method can be cited: extracting additives from the fibers of polyolefin resins with a solvent, and performing quantitative analysis using liquid chromatography/mass spectrometry (LC/MS). At this time, the extraction solvent is appropriately selected according to the type of fatty acid amide compound. For example, in the case of ethyl distearate amide, a method using a chloroform-methanol mixed solution can be cited as an example.

[Fibers containing polyolefin resins]

In the spunbonded nonwoven fabric of the present invention, the average single fiber diameter of the fibers constituting the spunbonded nonwoven fabric is preferably 6.5μm~11.9μm. By setting the average single fiber diameter to 6.5μm~11.9μm, preferably 7.5μm~11.9μm, and more preferably 8.4μm~11.9μm, a softer and more uniform nonwoven fabric can be obtained.

Furthermore, in the present invention, the average single fiber diameter (μm) of the fibers constituting the spunbonded nonwoven fabric is measured by the method described below.

The fiber constituting the spunbonded nonwoven fabric of the present invention preferably has a coefficient of variation (CV value) of single fiber diameter of 7% or less. Here, the CV value of single fiber diameter is calculated by the following formula.

． CV value of single fiber diameter = (standard deviation of single fiber diameter)/(average single fiber diameter)×100

By setting the CV value of the single fiber diameter preferably to 7% or less, more preferably to 6% or less, and further preferably to 5% or less, the surface roughness is prevented and a spunbond nonwoven with high uniformity is easily obtained. For the CV value of the single fiber diameter, the back pressure of the spinning die or the uniformity of the yarn cooling conditions and the stretching conditions play a dominant role, and can be controlled by, for example, appropriately adjusting these.

[Spunbond nonwoven fabric]

The important thing about the spunbond nonwoven fabric of the present invention is that the average fiber orientation is 0 to 30 degrees. By setting the average fiber orientation to 0 to 30 degrees, preferably 5 to 30 degrees, and more preferably 8 to 30 degrees, the fiber orientation becomes uniform, the uniformity or smoothness of the nonwoven fabric surface is improved, and the printing and coating properties become better.

In addition, the important thing about the spunbonded nonwoven fabric of the present invention is that the proportion of fibers with a fiber orientation of 0 to 30 degrees is 50% to 80%. The proportion of fibers with a fiber orientation of 0 to 30 degrees is preferably 60% to 80%. By setting the proportion of fibers with a fiber orientation of 0 to 30 degrees to 50% to 80%, preferably 60% to 80%, the fibers are arranged in the same manner, the texture becomes uniform, and good printability can be imparted to the spunbonded nonwoven fabric.

Furthermore, the fiber orientation in the present invention refers to the angle between the reference direction of the nonwoven fabric and an arbitrarily selected fiber. In addition, the average fiber orientation in the present invention refers to the average value of the fiber orientation measured for a specified number of fibers. The method for determining the reference direction, the fiber orientation, and the method for calculating the average fiber orientation are described below.

The average fiber orientation and the proportion of fibers with a fiber orientation of 0 to 30 degrees can be controlled by, for example, adjusting the fiber opening method or spinning speed, collection conditions, etc., or by adding a lubricant to the polyolefin resin.

The spunbonded nonwoven fabric of the present invention preferably has a surface roughness SMD ratio of 0.30 to 0.85 between the reference direction and the direction perpendicular to the reference direction on at least one side thereof obtained by the KES method. By setting the ratio of the surface roughness SMD obtained by the KES method measured in the reference direction and the direction perpendicular to the reference direction to 0.30 or more, preferably 0.35 or more, and more preferably 0.40 or more, it is possible to prevent excessive reduction in transverse tensile strength. On the other hand, by setting the ratio of the surface roughness SMD obtained by the KES method measured in the reference direction and the direction perpendicular to the reference direction to 0.85 or less, a high gloss can be exhibited. The ratio of the surface roughness SMD obtained by the KES method measured in the reference direction and the direction perpendicular to the reference direction can be controlled by appropriately adjusting the fiber orientation, etc.

Furthermore, in the present invention, the ratio of the surface roughness SMD obtained by the KES method in the reference direction and the direction orthogonal to the reference direction is measured by the method described below.

It is important that the tensile strength of the spunbonded nonwoven fabric of the present invention in the reference direction is 3 to 6 times, preferably 3 to 4 times, the tensile strength in the direction perpendicular to the reference direction. If the ratio of the tensile strength is less than 3 times, there is a concern that the nonwoven fabric will shrink in the transverse direction during the molding process. On the other hand, if the ratio of the tensile strength is greater than 6 times, the tensile strength in the direction perpendicular to the reference direction is not suitable for practical use. The ratio of tensile strength can be adjusted, for example, by the unit area weight, the average single fiber diameter and the embossing roll (crimping rate, temperature and linear pressure), or by adjusting the MFR of the polyolefin resin used.

The spunbonded nonwoven fabric of the present invention preferably has a stiffness of 10 mm to 80 mm in the reference direction measured by the cantilever method. By setting the stiffness preferably below 80 mm, more preferably below 70 mm, further preferably below 67 mm, and particularly preferably below 64 mm, sufficient softness can be obtained when used as a nonwoven fabric for sanitary materials. In addition, regarding the lower limit of the stiffness, if the stiffness is set too low, the operability of the nonwoven fabric may be poor, so it is preferably above 10 mm, and more preferably above 20 mm. The stiffness can be adjusted by the unit area weight, the average single fiber diameter, and the embossing roller (crimping rate, temperature, and line pressure).

The spunbonded nonwoven fabric of the present invention preferably further satisfies the following formula (1).

GL/100≧95...(1)

Here, G is the maximum value of glossiness, and L is the average brightness. As described later, all values are unitless. Methods for setting GL/100 to the above range include, for example, increasing the amount of lubricant added, reducing the average single fiber diameter, reducing the average fiber orientation, and increasing the proportion of fibers with a fiber orientation of 0 to 30 degrees.

The value obtained by dividing the product of G and L in the above formula (1) by 100 (hereinafter, simply recorded as "appearance gloss intensity") is an index that quantitatively indicates that the spunbond nonwoven fabric is not transparent and has gloss. When the appearance gloss intensity is 95 or more, preferably 100 or more, a silk-like nonwoven fabric with high-grade feeling and excellent design, white and excellent gloss is obtained. On the other hand, regarding the appearance gloss intensity, the present invention does not particularly set an upper limit, but from the viewpoint that the gloss is too strong and glaring and loses the sense of luxury, it is preferably 200 or less.

Furthermore, in the present invention, G (maximum value of glossiness) and L (average brightness) used in calculating the glossiness intensity of the appearance are values measured and calculated by the following methods.

(1) G (maximum gloss)

In the present invention, the so-called G (maximum value of gloss) of the spunbond nonwoven fabric refers to the maximum value (unitless) of the values measured by rotating the sample by 0°~360° using a goniophotometer. For example, a three-dimensional goniophotometer (goniophotometer (GONIOPHOTOMETER) GP-200) can be used for the measurement, a 12V 50W halogen lamp can be used as the light source, and a photomultiplier tube can be used as the light receiver.

(2) L (average brightness)

In the present invention, the L (average brightness) of the spunbond nonwoven fabric is a value measured by the following procedure. Furthermore, when scanning an image, for example, a color multifunction machine "DocuCentre-VI C4471 PFS" (FUJI XEROX Co., Ltd.) can be used.

(1) Glue the spunbond nonwoven fabric onto the black backing paper (AC card black #350).

(2) Use a color multi-function machine to scan in full color at 200 dpi to create a color scanned image of the spunbond nonwoven fabric and save it in JPG format.

(3) Cut out a 6-inch x 6-inch (1200 pixels x 1200 pixels) image from the color scanned image.

(4) Divide into grid cells of 0.1 inch × 0.1 inch (20 pixels × 20 pixels).

(5) In each grid, the average value of the brightness (unitless) defined by the YUV color space for each pixel is set as the average brightness using the following formula.

(Brightness of each pixel) = 0.29891×R+0.58661×G+0.11448×B

Here, R, G, and B represent the brightness of red, green, and blue in the RGB color model, respectively (without units).

The spunbonded nonwoven fabric of the present invention preferably has a water pressure resistance per unit area weight of 7 mmH ₂ O/(g/m ² ) to 20 mmH ₂ O/(g/m ² ). By setting the water pressure resistance per unit area weight to the above range, the smoothness of the surface, which is important for printability, can be further improved. The water pressure resistance can be adjusted by, for example, the fiber opening method, the unit area weight, the average single fiber diameter, and the embossing roll (crimping rate, temperature, and linear pressure).

The unit area weight of the spunbonded nonwoven fabric of the present invention is preferably 10 g/m ² to 100 g/m ² . By setting the unit area weight preferably to 10 g/m ² or more, more preferably to 13 g/m ² or more, it is easy to obtain a spunbonded nonwoven fabric with good mechanical strength. On the other hand, when the nonwoven fabric is used for sanitary materials, by setting the unit area weight preferably to 100 g/m ² or less, more preferably to 50 g/m ² or less, and further preferably to 30 g/m ² or less, it is easy to obtain a spunbonded nonwoven fabric with appropriate softness suitable for sanitary materials.

[Manufacturing method of spunbond nonwoven fabric]

Next, the preferred method for manufacturing the spunbonded nonwoven fabric of the present invention is specifically described.

The spunbond nonwoven fabric of the present invention is a long-fiber nonwoven fabric manufactured by the spunbond method. As a manufacturing method for nonwoven fabrics, generally, there are: spunbond method, flash-spinning method, wet method, carding method and air-laid method. Among these, the spunbond method is excellent in productivity and mechanical strength, and can also suppress the fuzzing or fiber shedding that is easy to occur in short-fiber nonwoven fabrics. In addition, by laminating the captured spunbond nonwoven fiber sheet or the spunbond nonwoven fabric after heat pressing (all expressed as S) into multiple layers of SS, SSS and SSSS, the productivity or texture uniformity is improved.

In the spunbond method, first, the molten thermoplastic resin is spun out from the spinning die in the form of long fibers, which are then drawn out by a jet and compressed air, and then captured on a moving net to obtain a nonwoven fiber sheet. The obtained nonwoven fiber sheet is then subjected to a heat-bonding treatment to obtain a spunbond nonwoven fabric.

The spinning die or ejector can be in various shapes such as circular or rectangular. Among them, a combination of a rectangular die and a rectangular ejector is preferred because it uses less compressed air and has excellent energy cost, is less likely to cause welding or abrasion between filaments, and is easy to open the filaments.

In the present invention, the polyolefin resin is melted in an extruder, and then supplied to a spinning die after being measured to be spun out in the form of long fibers. The spinning temperature when the polyolefin resin is melt-spinned is preferably 200°C to 270°C, more preferably 210°C to 260°C, and further preferably 220°C to 250°C. By setting the spinning temperature within the above range, a stable melt state can be produced, and excellent spinning stability can be obtained.

The back pressure of the spinning die is preferably set to 0.1MPa~6.0MPa. By setting the back pressure preferably to 0.1MPa~6.0MPa, more preferably to 0.3MPa~6.0MPa, and further preferably to 0.5MPa~6.0MPa, it is possible to prevent the deterioration of ejection uniformity and the occurrence of fiber diameter deviation, or to prevent the die from being enlarged to improve pressure resistance. The back pressure of the spinning die can be adjusted by the ejection hole diameter or ejection hole depth of the die, the spinning temperature, etc., among which the ejection hole diameter makes the greatest contribution.

The spun filaments are then cooled. Methods for cooling the spun filaments include forcibly blowing cold air onto the filaments, naturally cooling the filaments at the ambient temperature around the filaments, and adjusting the distance between the spinning die and the ejector, or a combination of these methods. In addition, the cooling conditions can be appropriately adjusted and adopted in consideration of the ejection amount per single hole of the spinning die, the spinning temperature, and the ambient temperature.

Then, the cooled and solidified filament is pulled and extended by the compressed air ejected from the ejector.

The spinning speed is preferably 3500m/min to 6500m/min, more preferably 4000m/min to 6500m/min, and even more preferably 4500m/min to 6500m/min. By setting the spinning speed to 3500m/min to 6500m/min, high productivity is achieved, and the fiber orientation crystallization is promoted, so that high-strength long fibers can be obtained.

Generally, if the spinning speed is increased, the spinning properties deteriorate and it becomes difficult to stably produce the fibers in a filament shape. As described above, by using a polyolefin resin having an MFR within a specific range, the desired polyolefin fibers can be easily and stably spun.

Then, the obtained long fibers are captured on a moving net to obtain a nonwoven fiber sheet. Here, if the fiber is stretched at a high spinning speed, the fibers from the ejector are captured on the net under the control of the high-speed airflow, and it is easy to obtain a nonwoven fabric with less fiber entanglement and high uniformity.

At this time, it is preferable to set the ratio of spinning speed/line speed to 18 or more. By setting the ratio of spinning speed/line speed to preferably 18 or more, more preferably 20 or more, the fibers can be captured on the moving web in a longitudinally oriented state.

As methods for aligning the directions of the fibers of the filaments ejected from the ejector in the same manner, there are the following methods: a method of inducing the filaments by providing an angled plate between the ejector and the net; a method of separating the filaments into filaments falling along the plate and filaments falling along the grooves by providing a plurality of grooves at different angles on the plate, thereby dispersing and opening the filaments in the flow direction of the nonwoven fiber sheet; and a method of dispersing and opening the filaments in the flow direction of the nonwoven fiber sheet by arranging a plurality of plates at different angles in a comb shape at the ejector outlet and causing the filaments to fall along each plate, etc.

Among them, the method of arranging multiple flat plates with different angles into a comb shape at the ejector outlet and allowing the filaments to fall along each flat plate to open the fibers can efficiently disperse the filaments of fine fiber diameter in the flow direction of the non-woven fiber sheet, and open the fibers in a controlled state without extreme deceleration, so it is a better state for making the orientation direction of the fibers consistent.

In addition, it is also better to temporarily connect the nonwoven fiber sheet by contacting the hot flat roller from one side on the web. By doing so, the surface of the nonwoven fiber sheet can be prevented from rolling up or blowing away and deteriorating in quality during the conveyance on the web, and the conveyance performance from the capture of the filaments to the heat pressing can be improved.

Then, the obtained nonwoven fiber sheet is integrated by heat bonding, thereby obtaining the desired spunbonded nonwoven fabric.

As methods for heat-welding nonwoven fiber sheets, there are: methods for heat-welding using various rollers, such as a pair of upper and lower roller surfaces each having engravings (concave and convex portions), a combination of a roller having a flat (smooth) surface and another roller having engravings (concave and convex portions) on the roller surface, and a combination of a pair of upper and lower flat (smooth) rollers; or ultrasonic welding methods such as heat-melting by ultrasonic vibration of an ultrasonic horn. Among them, in terms of excellent productivity, imparting strength to some heat-bonded areas, and easily maintaining the unique feel or skin touch of non-woven fabrics in non-bonded areas, the best embodiment is to use a heat embossing roller with engravings (concave and convex parts) on the upper and lower roller surfaces, or a heat embossing roller that includes a roller with a flat (smooth) surface and another roller with engravings (concave and convex parts) on the roller surface.

As the surface material of the embossing roller, in order to obtain a sufficient heat-pressing effect and prevent the engraving (convex and concave parts) of one embossing roller from being transferred to the surface of another roller, it is better to set the metal roller and the metal roller as a pair.

The bonding area ratio based on the heat embossing roller is preferably 5% to 30%. By setting the bonding area ratio preferably to 5% or more, more preferably to 8% or more, and further preferably to 10% or more, it is easy to obtain sufficient strength as a spunbond nonwoven fabric. On the other hand, by setting the bonding area ratio preferably to 30% or less, more preferably to 25% or less, and further preferably to 20% or less, it is easy to obtain appropriate softness suitable for use in diapers as a spunbond nonwoven fabric for sanitary materials. Even in the case of ultrasonic bonding, the bonding area ratio is preferably in the same range.

The bonding area ratio mentioned here refers to the area ratio of the bonding part in the whole spunbonded nonwoven fabric. Specifically, in the case of using a pair of rollers with uneven surfaces for heat bonding, it refers to the area ratio of the part where the convex part of the upper roller overlaps with the convex part of the lower roller and abuts against the nonwoven fiber sheet (bonding part) in the whole spunbonded nonwoven fabric. In addition, in the case of using a roller with uneven surfaces and a flat roller for heat bonding, it refers to the area ratio of the part where the convex part of the roller with uneven surfaces abuts against the nonwoven fiber sheet (bonding part) in the whole spunbonded nonwoven fabric. In addition, in the case of ultrasonic bonding, it refers to the area ratio of the portion (bonded portion) thermally fused by ultrasonic processing to the entire spunbond nonwoven fabric.

As the shape of the bonding part formed by heat embossing roller or ultrasonic bonding, a circle, an ellipse, a square, a rectangle, a parallelogram, a rhombus, a regular hexagon, a regular octagon, etc. can be used. In addition, the bonding part is preferably evenly present at a certain interval in the long side direction (conveying direction) and the width direction of the spunbond nonwoven fabric. By doing so, the strength deviation of the spunbond nonwoven fabric can be reduced.

The surface temperature of the heat embossing roller during heat bonding is preferably set to -50°C to -15°C relative to the melting point of the polyolefin resin used. By setting the surface temperature of the heat embossing roller preferably to -50°C or above, more preferably to -45°C or above relative to the melting point of the polyolefin resin, a spunbond nonwoven fabric having appropriate heat bonding and strength for practical use can be obtained. In addition, by setting the surface temperature of the heat embossing roller to preferably below -15°C, more preferably below -20°C relative to the melting point of the polyolefin resin, excessive heat bonding can be suppressed, and the spunbond nonwoven fabric used as a sanitary material can obtain appropriate softness, especially suitable for use in disposable diapers.

The linear pressure of the heat embossing roller during heat bonding is preferably 50N/cm~500N/cm. By making the linear pressure of the roller preferably 50N/cm or more, more preferably 100N/cm or more, and further preferably 150N/cm or more, it is easy to obtain a spunbond nonwoven fabric with appropriate heat bonding and sufficient strength. On the other hand, by making the linear pressure of the heat embossing roller preferably 500N/cm or less, more preferably 400N/cm or less, and further preferably 300N/cm or less, the spunbond nonwoven fabric used as a sanitary material is easy to obtain appropriate softness, especially suitable for use in diapers.

In addition, for the purpose of adjusting the thickness of the spunbond nonwoven fabric, heat pressing can be performed using a heat pressing roller including a pair of upper and lower flat rollers before and/or after heat pressing using the heat pressing pattern roller. The so-called upper and lower pair of flat rollers refers to a metal roller or elastic roller with no unevenness on the surface of the roller. The metal roller and the metal roller can be used as a pair, or the metal roller and the elastic roller can be used as a pair. In addition, the so-called elastic roller here refers to a roller including a material that is more elastic than the metal roller. Examples of the elastic roller include so-called paper rollers such as paper, cotton, and aramid paper, and rollers made of urethane resins, epoxy resins, silicone resins, polyester resins, and hard rubber, as well as resins containing a mixture thereof.

[Implementation example]

Next, the present invention is specifically described based on the embodiments. However, the present invention is not limited to these embodiments.

[1] Melt flow rate (MFR) of polyolefin resin:

The melt flow rate of polyolefin resin is measured by American Society for Testing Material (ASTM) D-1238 under the conditions of load of 2160g and temperature of 230℃.

[2]Average single fiber diameter (μm):

After being pulled and stretched by the ejector, 10 small pieces of samples are randomly taken from the nonwoven fiber sheet captured on the net, and surface photos are taken at 500x to 1000x magnification using a microscope. The width of 10 fibers in each sample, totaling 100 fibers, is measured, and the average value is set as the average single fiber diameter (μm).

[3] Spinning speed (m/min):

Based on the average single fiber diameter and the solid density of the resin used, the mass per 10,000 m length is set as the single fiber density, and the value is rounded to the second decimal place for calculation. Based on the single fiber density (dtex) and the amount of resin ejected from a single hole of the spinning die set under each condition (hereinafter referred to as the single hole ejection amount), the spinning speed is calculated based on the following formula.

． Spinning speed = (10000 × single hole spray volume) / single fiber density.

[4]Weight per unit area:

Based on 6.2 "Mass per unit area" of Japanese Industrial Standards (JIS) L1913:2010 "General nonwoven fabric test methods", three 20cm×25cm test pieces are taken for every 1m of sample width, and the mass (g) of each piece under the standard state is measured. The average value is expressed as mass per ^1m2 (g/ ^m2 ).

[5] Average fiber orientation and the proportion of fibers with fiber orientation between 0 and 30 degrees:

The values measured as follows were used. In the measurement, a scanning electron microscope "VHX-D500" manufactured by Keyence Corporation was used.

(1) For spunbond nonwoven fabric, take 10 test pieces with a width of 20 mm × 20 mm at equal intervals along the width direction (transverse direction) of the spunbond nonwoven fabric.

(2) Using a scanning electron microscope, for each sample, set the longitudinal direction to 0 degrees and measure the fiber inclination relative to 0 degrees for 20 fibers.

(3) The average value of the tilt angles of a total of 200 fibers is set as the average fiber orientation.

(4) The number of fibers with a fiber orientation of 0 to 30 degrees among a total of 200 fibers is set as the ratio of fibers with a fiber orientation of 0 to 30 degrees.

Furthermore, when the longitudinal direction of a cut sample is unclear, it is determined as follows.

(1) Take 10 non-woven fabric samples with their orientation aligned in a certain direction.

(2) For each sample, the certain direction is set as 0 degrees, and the inclination of the fibers relative to 0 degrees is measured for 20 fibers, and the average value is rounded to the first decimal place to obtain the result.

(3) Relative to 0 degrees in (2), measure the fiber inclination in the directions of 30 degrees, 60 degrees, and 90 degrees in the same manner, and round off the average value to the first decimal place.

(4) The direction with the smallest average value of the tilt angles obtained for the four directions is set as the reference direction.

[6] Surface roughness SMD of spunbond nonwoven fabric obtained by KES method:

The values measured using the following method are used. In addition, the automatic surface testing machine "KES-FB4-AUTO-A" manufactured by Katotech was used for the measurement.

(1) For spunbond nonwoven fabric, take three test pieces with a width of 200 mm × 200 mm at equal intervals along the width direction of the spunbond nonwoven fabric.

(2) Place the test piece on the test bench.

(3) Use a surface roughness measurement contact piece (raw material: Φ0.5mm piano wire, contact length: 5mm) with a load of 10gf to scan the surface of the test piece and measure the average deviation of the surface concave and convex shape.

(4) The above measurement is performed at 3 points in the reference direction (determined by the above method) and in the direction perpendicular to the reference direction of all test pieces. The average deviations of the 9 points in the reference direction and the 9 points in the direction perpendicular to the reference direction are averaged and rounded to the second decimal place, and the values obtained in this way are set as the surface roughness SMD (μm) in the reference direction and the surface roughness SMD (μm) in the direction perpendicular to the reference direction, and the value of the surface roughness SMD (μm) in the reference direction/the surface roughness SMD (μm) in the direction perpendicular to the reference direction is set as the surface roughness SMD ratio.

[7]Tensile strength:

According to 6.3 "Tensile strength and elongation" 6.3.1 "Standard time" of JIS L1913:2010 "General nonwoven fabric test methods", the tensile strength is measured by the following method. Take 10 test pieces of 200mm long × 25mm wide in the longitudinal and transverse directions of the nonwoven fabric. Use a constant speed elongation type tensile testing machine to perform a tensile test on the test piece with a grip interval of 100mm and a tensile speed of 100±10mm/min. The strength (N) at the maximum load until fracture is determined to 0.1N and set as the tensile strength (N/2.5cm).

[8] Stiffness:

According to JIS L1913:2010 "General nonwoven fabric test method" (6.7.3), take 5 test pieces with a width of 25mm×150mm and place them on a horizontal platform with a 45° slope with the short side of the test piece along the scale baseline. Manually slide the test piece in the direction of the slope, and when the center point of one end of the test piece touches the slope, read the moving length of the other end with the scale. Measure the front and back of the 5 test pieces and calculate the average value.

[9] Maximum gloss value (G):

The measurement was performed according to the method described above. In addition, a three-dimensional goniophotometer (GONIOPHOTOMETER GP-200) was used for the measurement. A halogen lamp 12V 50W was used as the light source, a photomultiplier tube was used as the light receiver, and the measurement was performed at an incident angle and a reflection angle of 60°.

[10] Average brightness (L):

The measurement was performed according to the above method. In addition, the color multifunction machine "DocuCentre-VI C4471 PFS" (FUJI XEROX Co., Ltd.) was used for image scanning.

[11] Water pressure resistance per unit area weight:

According to JIS-L1092:2009 "Test Method for Waterproofness of Fiber Products", "7.1.1A Method (Low Water Pressure Method)", the water pressure resistance per unit area weight of nonwoven fabrics is measured. Five test pieces with a width of 150mm×150mm are taken at equal intervals along the width direction of the nonwoven fabric. The test piece is placed in a fixture (the part of the test piece in contact with water is ^100cm2 ) using the FX-3000-IV water pressure tester "Hydro Tester" of Swiss TEXTEST. The water level of the water-filled level device is raised at a speed of 600mm/min±30mm/min, and the water level when water comes out from three places on the inner side of the test piece is measured in mm. This measurement was performed using 5 test pieces, and the average value was calculated as the water pressure resistance per unit area weight.

[12] Printability

Apply oil-based ink pad ink to the entire surface of a 10cm×10cm rubber sheet, press the ink-coated surface of the rubber sheet against the spunbond nonwoven fabric, and hold for 10 seconds. Remove the rubber sheet and judge the printability with the naked eye. In the judgment of printability, the case where there is no uneven printing or white spots is set as A, and the case where there is uneven printing or white spots is set as B.

(Implementation Example 1)

A polypropylene resin having an MFR of 200 g/10 min to which 5.0 mass % of ethylene bisstearamide was added as a fatty acid amide compound was melted using an extruder for the sheath component. On the other hand, a polypropylene resin having an MFR of 200 g/10 min to which ethylene bisstearamide was not added was melted using an extruder for the sheath component. The core component and the sheath component were weighed in a mass ratio of 50:50 and the amount of ethylenediamine in the entire fiber was 2.5%. At a spinning temperature of 235°C, filaments were spun from a rectangular core-sheath die with a hole diameter of 0.40 mm at a single hole ejection rate of 0.30 g/min. After the filaments were cooled and solidified, they were pulled and stretched by a rectangular ejector with compressed air set at a pressure of 0.55 MPa. Then, they were captured on a moving net to obtain a nonwoven fiber sheet containing polypropylene long fibers. The obtained polypropylene long fiber has a fiber density of 0.71 dtex, which translates to a spinning speed of 4225 m/min. The spinnability was good, with no yarn breakage during one hour of spinning.

Next, the upper roller was made of metal and had a water drop pattern-like engraving with a bonding area rate of 11%, and the lower roller was made of a pair of upper and lower heat embossing rollers composed of metal flat rollers. The obtained nonwoven fiber sheet was heat-bonded at a linear pressure of 300N/cm and a heat bonding temperature of 145°C to obtain a spunbond nonwoven fabric with a unit area weight of 25g/ ^m2 . The obtained spunbond nonwoven fabric was evaluated. The results are shown in Table 1.

(Example 2)

A spunbonded nonwoven fabric was obtained by the same method as in Example 1 except that the weight per unit area was 15 g/m ² and the line speed was 160 m/min. The obtained spunbonded nonwoven fabric was evaluated. The results are shown in Table 1.

(Implementation Example 3)

The addition amount of ethylenebis(stearic acid)amide as the sheath component was set to 3.0 mass %, and a spunbond nonwoven fabric was obtained by the same method as in Example 1. The obtained polypropylene long fiber has a characteristic of a fiber fineness of 0.73 dtex, and the spinning speed converted therefrom is 4109 m/min. Regarding the spinnability, the yarn breakage was 0 times in 1 hour of spinning, which is good. The obtained spunbond nonwoven fabric was evaluated. The results are shown in Table 1.

(Implementation Example 4)

A spunbonded nonwoven fabric was obtained by the same method as Example 1 except that ethylenediamine was not added to the sheath component. The characteristics of the obtained polypropylene long fiber are that the fiber density is 0.74 dtex, and the spinning speed converted from this is 4054 m/min. Regarding the spinnability, the yarn breakage in 1 hour of spinning was 0 times and was good. The obtained spunbonded nonwoven fabric was evaluated. The results are shown in Table 1.

(Example 5)

A spunbonded nonwoven fabric was obtained by the same method as in Example 1 except that the addition amount of ethylenediamine as the sheath component was set to 0.5 mass %, the single hole ejection amount was set to 0.40 g/min, the unit area weight was set to 15 g/m ² , and the line speed was set to 200 m/min. The obtained polypropylene long fiber has a characteristic of a fiber fineness of 0.85 dtex, and the spinning speed converted therefrom is 4705 m/min. Regarding the spinnability, the yarn breakage was 0 times in 1 hour of spinning, which is good. The obtained spunbonded nonwoven fabric was evaluated. The results are shown in Table 1.

(Comparison Example 1)

A spunbonded nonwoven fabric was obtained by the same method as in Example 4 except that the single hole ejection amount was set to 0.40 g/min, the unit area weight was set to 10 g/m ² , and the line speed was set to 300 m/min. The obtained polypropylene long fiber had a characteristic of a fiber fineness of 0.91 dtex, and the spinning speed converted therefrom was 3823 m/min. Regarding the spinnability, the yarn breakage was 0 times in 1 hour of spinning, which was good. The obtained spunbonded nonwoven fabric was evaluated. The results are shown in Table 1.

(Comparison Example 2)

The core component and the sheath component both used a polypropylene resin with an MFR of 40g/10min, and the pressure of the ejector was set to 0.30MPa. A spunbond nonwoven fabric was obtained by the same method as in Example 5. The obtained polypropylene long fiber has a fiber density of 1.30dtex, and the spinning speed converted from this is 3076m/min. Regarding the spinnability, there were no breaks in the spinning for 1 hour, which was good. The obtained spunbond nonwoven fabric was evaluated. The results are shown in Table 1.

Examples 1 to 5 show excellent surface smoothness and good printability. In addition, the average single fiber diameter of the fiber is 9.97 μm to 10.9 μm, and the ratio of the surface roughness measured by the KES method in the reference direction and the direction orthogonal to the reference direction is 0.53 to 0.66, so the nonwoven fabric has excellent softness and gloss. On the other hand, as shown in Comparative Examples 1 and 2, when the average fiber orientation value is relatively high, the average single fiber diameter exceeds 11.9 μm, and the surface roughness ratio is greater than 0.85, the surface of the nonwoven fabric becomes larger, resulting in poor printability and gloss.

Claims (7)

A spunbond nonwoven fabric comprising a polyolefin resin, wherein the average fiber orientation is 0 to 30 degrees, the proportion of fibers with a fiber orientation of 0 to 30 degrees is 50% to 80%, and the tensile strength in the reference direction is 3 to 6 times the tensile strength in the direction orthogonal to the reference direction, and the ratio of the surface roughness SMD measured by the Kawabata evaluation system method in the reference direction and the direction orthogonal to the reference direction on at least one side is 0.30 to 0.85. The spunbonded nonwoven fabric as described in claim 1, wherein the average single fiber diameter of the fibers constituting the spunbonded nonwoven fabric is 6.5 μm to 11.9 μm. The spunbonded nonwoven fabric as described in claim 1 or claim 2, wherein the polyolefin resin contains a fatty acid amide compound having 23 to 50 carbon atoms. The spunbonded nonwoven fabric as described in claim 3, wherein the content of the fatty acid amide compound in the polyolefin resin is 0.01 mass % to 5.0 mass %. The spunbonded nonwoven fabric as described in claim 4, wherein the fatty acid amide comprises ethylene bis(stearic acid) amide. The spunbonded nonwoven fabric as described in claim 1 or claim 2, wherein the stiffness in the reference direction measured by the cantilever method is 10 mm to 80 mm. The spunbonded nonwoven fabric as described in claim 1 or claim 2 further satisfies the following formula (1): GL/100≧95...(1) Here, G is the maximum value of glossiness and L is the average brightness.