JP7167302B2 - Nonwoven fabric manufacturing method - Google Patents

Description

The present invention relates to a nonwoven fabric manufacturing method.

The following Patent Documents 1 to 4 are known as nonwoven fabrics formed of fibers. Nonwoven fabrics are actively being developed for use in various fields. Expected applications include, for example, heat insulating materials, sound absorbing materials, and filters, and are also expected to be used for medical purposes and as scaffolding materials for cells. Nonwoven fabrics are produced, for example, by electrospinning. The electrospinning method is also called an electrospinning method, in which a solution in which a fiber material is dissolved in a solvent is ejected toward a collector to form fibers, and the ejected fibers are collected to form a nonwoven fabric. It is a thing.

JP 2018-026343 A JP 2017-196597 A Japanese Patent Publication No. 2010-501738 JP 2005-097753 A

In nonwoven fabrics, by improving the degree of orientation of fibers, it may be possible to exhibit good performance such as improvement in porosity. However, conventionally, there has been a problem that the degree of orientation of the fiber is low because the straightness of the fiber is low.

The present invention has been made in view of the above background, and an object of the present invention is to provide a nonwoven fabric with an improved degree of orientation of fibers, and a method for producing such a nonwoven fabric.

In order to achieve the above object, the nonwoven fabric of the present invention comprises fibers having an average fiber diameter within the range of 0.10 μm or more and 5.00 μm or less, and a fiber orientation degree of 1.1 or more and 1.3 or less. is.

A porosity of at least 90% is preferred.

A first line segment that connects two adjacent points of contact between a first fiber and another fiber, and two adjacent points of contact between a second fiber that is different from the first fiber and another fiber. Regarding the line-to-line angle, which is the angle with the connecting second line segment, the average line-to-line angle is preferably in the range of 178 degrees or more and 182 degrees or less.

Preferably, the fibers are made of a cellulosic polymer.

Preferably, the average pore size is at least 5 μm and the average line diameter is at least 1 μm.

Further, in order to achieve the above object, the nonwoven fabric manufacturing method of the present invention forms fibers by ejecting a solution in which a fiber material is dissolved in a solvent toward a collector, and collects the fibers to form the nonwoven fabric. The nonwoven fabric manufacturing method includes a heating step of heating the fiber assembly formed by collecting the fibers, and in the heating step, the fiber reaches 90% of the melting temperature and then reaches the melting temperature. The time required for heating is at least 15 seconds.

In the heating step, cooling is performed after reaching the melting temperature,
The cooling preferably takes at least 15 seconds from the melting temperature to reach 90% of the melting temperature.

In the heating step, the thickness of the fiber assembly after heating is preferably maintained at least 50% of the thickness of the fiber assembly before heating.

In the heating step, it is preferable that one side edge and the other side edge of the fiber assembly facing each other in the direction perpendicular to the thickness direction of the fiber assembly are separated from each other by at least a certain distance and held.

In the heating step, it is preferable to widen the distance between one side edge and the other side edge before heating.

Preferably, a voltage is applied between the solution and the collector to eject the fiber.

According to the present invention, a nonwoven fabric with improved fiber orientation can be obtained.

1 is a schematic perspective view of a portion of a nonwoven fabric; FIG. 1 is a schematic diagram of a nonwoven fabric manufacturing facility; FIG.

The nonwoven fabric 10 of this embodiment shown in FIG. 1 is formed of fibers 11 . The fibers 11 are entangled with each other, and there are portions (contact points) that overlap in the thickness direction and/or contact in the surface direction (in the XY plane) of the nonwoven fabric 10 . There are contact points in which the fibers 11 are bonded together and those in which the fibers 11 are not bonded. The nonwoven fabric 10 only needs to contain the fibers 11, and in addition to the fibers 11, may be provided with other fibers made of different materials.

In addition, in FIG. 1, in order to avoid complication of the drawing, only a part of one surface (hereinafter referred to as the first surface) 10A side in the thickness direction of the nonwoven fabric 10 is illustrated. Therefore, the nonwoven fabric 10 has a structure in which a large number of fibers 11 are stacked on the lower side in the thickness direction. In addition, in FIG. 1, the first surface 10A is drawn along the XY plane, and the Z-axis orthogonal to the XY plane is the thickness direction of the nonwoven fabric 10. As shown in FIG.

The fiber 11 is formed to have a substantially constant wire diameter D1. The average of the wire diameters D1 (hereinafter referred to as the average wire diameter) DF (unit: μm) is preferably in the range of 0.10 μm or more and 5.00 μm or less. When the average wire diameter DF is 0.10 μm or more, detachment of the fiber piece is suppressed as compared with the case of less than 0.10 μm. Suppression of detachment of the fiber pieces means that detachment of the fiber pieces from the nonwoven fabric 10 is suppressed, and suppression of detachment of the fiber pieces leads to excellent durability of the nonwoven fabric 10. . When the average wire diameter DF is 5.00 μm or less, the nonwoven fabric 10 has the same volume ratio of air (hereinafter referred to as porosity) as compared to the case where it is larger than 5.00 μm. , become softer. In addition, when the average wire diameter DF is 5.00 μm or less, the nonwoven fabric 10 has a higher porosity than when it is larger than 5.00 μm, even if the softness is about the same. When used as a sound-absorbing material or heat-insulating material, the sound-absorbing performance and heat-insulating performance are improved, and when used as a filter, the filtration throughput is increased. The average wire diameter DF is more preferably within the range of 0.15 μm or more and 4.00 μm or less, and further preferably within the range of 0.20 μm or more and 3.00 μm or less. The average wire diameter DF can be obtained by measuring the wire diameters of 100 fibers 11 from an image taken with a scanning electron microscope and calculating the average value.

The nonwoven fabric 10 is formed through a heating step 22 (see FIG. 2) for heating a fiber assembly 60 (see FIG. 2) in which the fibers 11 are collected to the melting temperature Tm of the fibers 11, as will be described later. Through the heating step 22, the residual stress (the force accumulated in the fibers 11 at the time of collection and bending the fibers 11) is removed from the fiber assembly 60, and the fibers 11 are straightened. (From a curved state, it approaches a straight line (increases the degree of straightness)). The orientation degree of the fibers 11 of the nonwoven fabric 10 is 1.1 or more and 1.3 or less due to the linearization by this heating.

The degree of orientation of the fibers 11 functions as an index indicating the orientation of the fibers 11 (how aligned in the longitudinal direction). weaker), and the greater the degree of orientation, the more aligned the orientation of the fibers 11 (the stronger the orientation). Specifically, when the degree of orientation is 1.0, there is almost no orientation, when the degree of orientation is 1.1 or more, there is orientation, and when the degree of orientation is 1.2 or more, there is strong orientation. indicates that there is In the present invention, the effect is exhibited when the degree of orientation is 1.1 or more and 1.3 or less, preferably 1.15 or more and 1.25 or less, more preferably 1.2 or more and 1.25 or less. The degree of orientation can be calculated using commonly known image analysis software (see “http://psl.fp.a.u-tokyo.ac.jp/research02_04.html”).

As described above, the fibers 11 of the nonwoven fabric 10 have a high degree of orientation, so that the average interline angle of the fibers 11 is close to 180 degrees. Here, the average line-to-line angle is preferably 178 degrees or more and 182 degrees or less.

The line-to-line angle is defined as a line segment that connects two adjacent points of contact 12a and 12b of the points of contact where the first fiber 11A, which is one of the fibers 11 included in the nonwoven fabric 10, contacts the other fiber 11 as the first line. 12, and a line segment connecting two adjacent contact points 13a and 13b among the contact points at which the second fiber 11B, which is one of the fibers 11 included in the nonwoven fabric 10, contacts the other fiber 11 is the second line segment. 13, the angle between the first line segment 12 and the second line segment 13 (the angle of the second line segment 13 with respect to the first line segment 12) is shown. The nonwoven fabric 10 has many line segments corresponding to the first line segment 12 and many line segments corresponding to the second line segment 13. Naturally, the line segments corresponding to the first line segment 12 and the second line segment 13 are present. There are also many combinations with line segments corresponding to the two line segments 13 . The average of the line-to-line angles is obtained by obtaining the line-to-line angles for each combination of the line segment corresponding to the first line segment 12 and the line segment corresponding to the second line segment 13, and obtaining the line-to-line angle It is obtained by calculating the average of the angles.

In the nonwoven fabric 10, a plurality of voids 14, which are spatial regions defined by the fibers 11, are formed as portions where air exists. When the plurality of voids 14 communicate with each other in the thickness direction Z of the nonwoven fabric 10 , they form voids penetrating in the thickness direction Z of the nonwoven fabric 10 . When the nonwoven fabric 10 is used as a filter, for example, the pores function as pores of the filter. Moreover, some of the voids 14 do not form voids and exist as spatial regions that are not penetrated in the thickness direction, for example, are closed by the fibers 11 .

Since the nonwoven fabric 10 has a high degree of orientation of the fibers 11 as described above, the porosity is also high accordingly. Here, the porosity is preferably 90% or more (that is, at least 90%). Moreover, since the porosity can be increased up to 99%, the porosity is more preferably 90 to 99%, particularly preferably 90 to 95%. By increasing the porosity in this way, that is, by containing a large amount of air inside, it is possible to expand the range of applications. For example, it can be used as a sound absorbing material and a heat insulating material because it exhibits superior sound absorbing performance and heat insulating performance compared to a case with a porosity of less than 90%. In addition, compared with the case where the porosity is less than 90%, when it is made into a filter, it exhibits a large filtering performance. Filtration processing performance means throughput per unit time and/or persistence of a state in which clogging is suppressed.

The porosity (unit: %) is defined by setting W (unit: g/m ² ) as the weight of the nonwoven fabric 10 , H (unit: mm) as the thickness, and ρ1 (unit: kg/m ³ ) as the specific gravity of the fiber 11 . can be obtained by [1−{(W/1000)/(H/1000)}/ρ1]×100. The weight W is obtained by cutting the nonwoven fabric 10 into a piece of 5 cm×5 cm, measuring the mass with an electronic balance (manufactured by Mettler Toledo, Inc.), and converting the measured value into 1 m ² . The thickness H is measured by a non-contact laser displacement meter (LK-H025 manufactured by Keyence Corporation) in this example.

The average pore diameter of the voids 14 (hereinafter referred to as average pore diameter DA) is preferably 5.0 μm or more (that is, at least 5.0 μm). Incidentally, the average pore diameter DA can be obtained by the following method. First, a 5 cm square (5 cm×5 cm) is cut from the fiber sheet 10 to obtain a sample. After immersing this sample in GALWICK (manufactured by POROUS MATERIAL) having a surface tension of 15.3 mN/m, the average pore diameter DA was measured by the bubble point method using a perm porometer (manufactured by POROUS MATERIAL). can get.

The nonwoven fabric 10 preferably has an average pore diameter DA of 5.0 μm or more and an average wire diameter DF of 1.0 μm or more (that is, at least 1.0 μm). Thus, when the average pore diameter DA is 5.0 μm or more and the average wire diameter DF is 1.0 μm or more, compared to the case where the average wire diameter is less than 1.0 μm, the case of making a filter In particular, the nonwoven fabric 10 is suitable for use as a biofilter because it suppresses deformation against fluid pressure and exhibits stable filtration performance.

The fiber 11 is made of resin (polymer) (the material (fiber material) of the fiber 11 is polymer). Specifically, cellulosic polymer, cycloolefin polymer (COP), polymethyl methacrylate, polyester, polyurethane, polyethylene (PE), elastomer, polypropylene polylactic acid, polystyrene, polycarbonate, acrylic resin, polyvinyl alcohol (PVA), gelatin, Examples include polyimide, PEEK, liquid crystalline polymer (LCP), and fluororesin. When using a cellulose-based polymer as a raw material, it is preferably cellulose acylate. Cellulose acylate is a cellulose ester in which some or all of the hydrogen atoms constituting the hydroxy groups of cellulose are substituted with acyl groups. Cellulose acylate is preferably cellulose acetate propionate (CAP) or cellulose triacetate (TAC). It should be noted that the polymer that is the material of the fiber 11 is preferably a polymer that can be dissolved in a solvent to form a solution, and more preferably a polymer that can be dissolved in an organic solvent to form a solution.

As described above, in the nonwoven fabric 10, the fibers 11 are linearized by heating the fiber assembly 60, so that the fibers 11 have a high degree of orientation (1.1 or more and 1.3 or less), and the line-to-line angles are uniform. (close to 180 degrees). In addition, as the degree of orientation of the fibers 11 is high, the porosity is also high. As a result, suitable performance can be exhibited in various applications.

The nonwoven fabric 10 can be manufactured by the nonwoven fabric manufacturing equipment 20 shown in FIG. 2, for example. The nonwoven fabric manufacturing facility 20 is composed of a fiber assembly manufacturing process 21 and a heating process 22 . The fiber assembly manufacturing process 21 is for forming the fibers 11 and manufacturing the fiber assembly 60 using the electrospinning method.

The fiber assembly manufacturing process 21 includes a solution preparing section 23 and a fiber assembly manufacturing section 24 . The solution preparing section 23 prepares a solution 23a for forming the fiber 11. FIG. The solution preparation unit 23 prepares a solution 23a by dissolving the raw material (fiber material) of the fiber 11 in a solvent.

The fiber assembly manufacturing section 24 includes a nozzle unit 25 , a stacking section 26 and a power source 27 . The nozzle unit 25 is formed long in the width direction (perpendicular to the drawing) of a support 30, which will be described later, and a plurality of nozzles 25a are arranged side by side along the longitudinal direction (that is, the width direction of the support 30). ing. A solution 23a prepared by the solution preparation unit 23 is supplied to each nozzle 25a, and the solution 23a is discharged from each nozzle 25a toward the stacking unit 26. FIG.

The stacking section 26 has a collector 52 , a support supply section 57 , and a support winding section 58 . The collector 52 is for attracting the solution 23a discharged from the nozzle 27 and collecting the formed fibers 11 to obtain a fiber assembly 60. collect on top. The collector 52 is composed of an endless belt made of a metal belt-like material, stretched over the rollers 61 and 62, and circulated as the rollers 61 and 62 rotate.

A voltage is applied by a power supply 27 between the collector 52 and the nozzle unit 25 (nozzle 25a). As a result, one of the collector 52 and the nozzle 25a is positively (+) charged, and the other is negatively (-) charged. By doing so, the solution 23a is attracted to the collector 52 side and jetted from the nozzle 25a toward the collector 52. As shown in FIG. Note that the collector 52 may be made of a material that is electrified when a voltage is applied by the power supply 27, and is made of stainless steel, for example.

The support supply unit 57 supplies the support 30 made of, for example, a strip-shaped aluminum sheet to the collector 52 . The support 30 moves along with the movement of the collector 52 and passes below the nozzle unit 25 . During this time, the fibers 11 ejected from the nozzle 25a are successively collected on the support 30 to form a band-like fiber assembly 60. As shown in FIG. After that, the support 30 is peeled off from the fiber assembly 60 and wound on the support winding section 58 . On the other hand, fiber assembly 60 is conveyed to heating step 22 . A configuration in which the fibers 11 are collected without the support 30 (a configuration in which the fiber assembly 60 is formed directly on the collector 52 without the support 30) may be employed. Further, in this example, an example in which the fibers 11 (fiber assembly 60) are formed by the electrospinning method was described, but the solution spinning method (the solution 23a from the nozzle 25a drips onto the collector 52 due to its own weight, for example, regardless of the potential difference). Alternatively, the fiber 11 (fiber assembly 60) may be formed by a method for forming the fiber 11.

The heating process 22 includes a tenter 70 and a heating chamber 71 . The tenter 70 includes supporting members 70a that support both sides of the fiber assembly 60 in the width direction. The support member 70a may be of a type that grips the fiber assembly 60 with a clip that can be freely opened and closed, or of a type that supports the fiber assembly 60 by inserting a needle-like member into the fiber assembly 60. .

The heating chamber 71 has a heater 72 which heats the fiber assembly 60 to reach the melting temperature Tm. Since the method of heating the fiber assembly 60 can be freely set, for example, the fiber assembly 60 may be heated by applying the heat from the heater 72 directly to the fiber assembly 60, or the heat from the heater 72 may be applied to the fiber assembly 60 directly. may be blown toward the fiber assembly 60 by a blower, that is, hot air may be applied to heat the fiber assembly 60 . This heating softens and shrinks the fiber assembly 60 to form the nonwoven fabric 10 (the nonwoven fabric 10 is manufactured). This heating also removes residual stress from the fiber assembly 60 and straightens the fibers 11 . As the fibers 11 are linearized, the degree of orientation of the fibers 11 is improved.

However, depending on the temperature history (relationship between temperature and time) in the heating step 22, it may not be possible to produce a good nonwoven fabric. For example, if the melting temperature Tm is reached in a short time, the residual stress cannot be completely removed and the degree of orientation cannot be sufficiently improved. Therefore, in the heating step 22, the required heating time (hereinafter referred to as , sometimes referred to as heating time) is 15 seconds or more (that is, at least 15 seconds) and 500 seconds or less. The required heating time is preferably 15 seconds to 180 seconds. In this way, film formation (a phenomenon in which the fibers 11 are melted and the holes (gaps) are closed) is suppressed, and the residual stress is reliably removed to sufficiently improve the degree of orientation. It becomes possible to set the degree of orientation to 1.1 or more and 1.3 or less.

In the heating step 22, after the fiber assembly 60 reaches the melting temperature Tm of the fibers 11, it is preferable to cool (either natural cooling or forced cooling). In cooling, the time required for cooling from the melting temperature Tm of the fiber 11 to 90% of the melting temperature Tm (hereinafter sometimes referred to as cooling time) is 15 seconds or more (that is, at least 15 seconds)500 Seconds or less is preferred. The required cooling time is more preferably 15 to 180 seconds, more preferably 15 to 60 seconds. By doing so, residual stress can be reliably removed while maintaining productivity.

On the other hand, if the heating time and/or the cooling time is too long as described above, that is, if the time at 90% or more of the melting temperature Tm is too long, there is a problem that the fiber assembly 60 will become a film. Therefore, in the heating step 22, the thickness of the fiber assembly 60 (nonwoven fabric 10) after heating should be maintained at 50% or more (that is, at least 50%) of the thickness of the fiber assembly 60 before heating. , more preferably maintained at a thickness of 80% or more. In other words, it is preferable to limit the heating to such an extent that the thickness of 50% or more, more preferably 80% or more can be maintained. By doing so, it is possible to prevent the fiber assembly 60 from becoming a film.

Here, in the heating step 22 of this example, the distance between the support member 70a that supports one side of the fiber assembly 60 and the support member 70a that supports the other side of the fiber assembly 60 is kept constant. , the fiber assembly 60 is prevented from shrinking in the width direction. In addition, in the heating step 22 of this example, the fiber assembly 60 is prevented from shrinking in the transport direction by controlling the transport tension of the fiber assembly 60 (the force that pulls the fiber assembly 60 in the transport direction). . That is, in the heating step 22 of this example, the width and length of the fiber assembly 60 remain unchanged, and only the thickness changes (thinner). As described above, film formation progresses as the thickness decreases, so the smaller the decrease in thickness, the better. Specifically, as described above, the thickness of the fiber assembly 60 (nonwoven fabric 10) after heating is preferably 50% or more, more preferably 80% or more, of the thickness of the fiber assembly 60 before heating. more preferred. Furthermore, the thickness of the fiber assembly 60 (nonwoven fabric 10) after heating is preferably 80 to 95%, more preferably 90 to 95%, of the thickness of the fiber assembly 60 before heating.

During heating in the heating step 22, the distance between the support member 70a supporting one side of the fiber assembly 60 and the support member 70a supporting the other side of the fiber assembly 60 is expanded, The fiber assembly 60 may be widened. By widening the fiber assembly 60 while heating it in this manner, the linearity of the fibers 11 in the width direction can be more reliably improved. It is also possible to adjust the pore diameter (to increase the pore diameter to a desired pore diameter). In this way, when the width is widened, it is preferable that the width is widened in a range of 50% or less of the width of the fiber assembly 60 before widening. By doing so, the tearing of the nonwoven fabric can be suppressed.

Verification results of verifying the effects of the present invention will be described below. In the verification, 14 types of nonwoven fabrics were manufactured using the nonwoven fabric manufacturing equipment 20 shown in FIG. Then, in the process of production, heating with a temperature history that satisfies the requirements of the present invention, that is, the heating time from 90% of the melting temperature Tm to reaching the melting temperature Tm was set to 15 seconds or more. 12), and a comparative example (comparative example 1) was obtained by heating with a temperature history other than this (see Tables 1 and 2).

Table 1 shows the manufacturing conditions of nonwoven fabrics in Examples 1 to 12 and Comparative Example 1. In addition, in Table 1, "thickness change" describes the ratio of the thickness after heating to the thickness before heating. In addition, the “reaching temperature” is “Tm” when reaching the melting temperature Tm, “Tm or more” when reaching a temperature exceeding the melting temperature Tm, and “Tm less than ”. Furthermore, "heating time" indicates the time required for heating from 90% of the melting temperature Tm to reaching the melting temperature Tm. "Cooling time" indicates the time required for cooling from the melting temperature Tm to reach 90% of the melting temperature Tm. Further, "stretching" is indicated as "yes" when the width of the fiber assembly 60 is widened by the tenter 70, and as "no" when the width is not widened.

Table 2 shows the verification results of the nonwoven fabrics of Examples 1 to 12 and Comparative Example 1 manufactured under the manufacturing conditions in Table 1. In Table 2, for "average wire diameter", "average pore diameter", "degree of orientation", and "angle between wires", values obtained by calculating actual values from the manufactured nonwoven fabric are shown. ing. Regarding "uniformity of pore size distribution", "separation performance of filter", "biocompatibility", "strength", and "suitability for processing", "A" is given when the product is good, and generally good. "B" if there is a problem, "C" if there is no problem, "D" if there is a problem but a minor problem, and "E" if there is a major problem.

As shown in Table 2, by verification, in the heating step 22, by increasing the time at which the melting temperature Tm is 90% or more (both the heating time and the cooling time are 15 seconds or more), the degree of orientation is high, In addition, it was found that the line-to-line angles were uniform (approaching 180 degrees). In addition, it was found that heating at the melting temperature Tm or higher in the heating step 22 results in a high degree of orientation and uniform line-to-line angles. Furthermore, it was found that the average pore diameter DA can be increased (film formation can be prevented) by setting the thickness change to 50% or more. Further, it was found that the average hole diameter DA can be increased by drawing (widening the fiber assembly 60).

REFERENCE SIGNS LIST 10 nonwoven fabric 10A first surface 11 fiber 11A first fiber 11B second fiber 12 first line segment 12a, 12b contact point 13 second line segment 13a, 13b contact point 14 gap 20 nonwoven fabric manufacturing facility 21 fiber assembly manufacturing process 22 heating process 23 Solution preparation section 23a Solution 24 Fiber assembly production section 25 Nozzle unit 25a Nozzle 26 Stacking section 27 Power source 30 Support 52 Collector 57 Support supply section 58 Support winding section 60 Fiber assembly 61, 62 Roller 70 Tenter 70a Support member 71 heating chamber 72 heater D1 wire diameter DF average wire diameter DA average pore diameter Tm melting temperature

Claims (6)

In a method for manufacturing a nonwoven fabric, the nonwoven fabric is formed by ejecting a solution in which a fiber material is dissolved in a solvent toward a collector to form fibers, and collecting the fibers,
A heating step of heating the fiber assembly formed by collecting the fibers,
In the heating step, the time required for heating from reaching 90% of the melting temperature of the fiber to reaching the melting temperature is at least 15 seconds. In the heating step, cooling is performed after reaching the melting temperature,
2. The method of manufacturing a nonwoven fabric according to claim 1 , wherein the cooling takes at least 15 seconds from the melting temperature to 90% of the melting temperature. 3. The method of manufacturing a nonwoven fabric according to claim 1 , wherein in said heating step, the thickness of said fiber assembly after heating is maintained at least 50% of the thickness of said fiber assembly before heating. 2. In the heating step, one side edge portion and the other side edge portion of the fiber assembly facing each other in a direction perpendicular to the thickness direction of the fiber assembly are held apart from each other at least by a predetermined distance. The method for producing a nonwoven fabric according to any one of 3 to 5. The method of manufacturing a nonwoven fabric according to claim 4 , wherein in the heating step, the gap between the one side edge and the other side edge is expanded more than before the heating. 6. The method for producing a nonwoven fabric according to any one of claims 1 to 5 , wherein a voltage is applied between the solution and the collector to eject the fibers.

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