JP7715224B2 - Method for measuring surface potential of yarn containing potential-generating fiber - Google Patents

Description

The present invention relates to a method for measuring the surface potential of yarns and fabrics containing potential-generating fibers that generate electric charges.

For example, Patent Document 1 discloses yarn and fabric equipped with charge-generating fibers that generate an electric charge when exposed to external energy. The yarn and fabric in Patent Document 1 exhibit antibacterial effects due to the generated electric charge.

Patent No. 2018-90950

However, the charge-generating fibers in Patent Document 1 do not disclose the level of electric potential generated on the surface of the fibers. If the generated electric potential is too low, it may not produce the desired effect.

The object of this invention is to provide a method for measuring the surface potential of yarns and fabrics that achieves the desired effect.

The method for measuring the surface potential of a yarn containing a potential-generating fiber of the present invention is characterized by measuring under the following conditions (a) to (d).
(a) The yarn is stretched in one axial direction by a predetermined amount.
(b) A core material made of conductive fibers is covered with the fibers.
(c) grounding the core material;
(d) Measuring the surface potential of the yarn using an electric force microscope.

Fibers that generate an electric potential on their surface when exposed to external energy include, for example, substances with a piezoelectric effect (e.g., polylactic acid, substances with a photoelectric effect, substances with a pyroelectric effect (e.g., PVDF: Polyvinylidene Difluoride)), or substances that generate an electric charge through chemical changes. The yarn of the present invention exerts an antibacterial effect due to the generated electric potential. Furthermore, the yarn of the present invention can also charge substances by generating an electric potential specified by the above conditions. Alternatively, the yarn of the present invention can adsorb substances by generating an electric potential specified by the above conditions.

According to this invention, by generating a specified potential under predetermined conditions, desired effects such as antibacterial, electrostatic, or adsorption can be achieved.

FIG. 1(A) is a partially exploded view showing the structure of the thread 1, and FIG. 1(B) is a cross-sectional view taken along line AA of FIG. 1(A). FIG. 2 is a partially exploded view showing the configuration of the thread 2. 10 is a simulation result showing the potential when a 2% displacement is applied to yarn 1 in the axial direction. Figure 4(A) shows the simulation results showing the electric field at a cross section of yarn 1, which is a Z-yarn, and Figure 4(B) shows the simulation results showing the electric field at a cross section of yarn 2, which is an S-yarn. A cross-sectional view showing the state of the electric field when threads 1 and 2 are brought close to each other.

An embodiment of the present invention will now be described. Figure 1(A) is a partially exploded view showing the structure of thread 1, and Figure 1(B) is a cross-sectional view taken along line A-A in Figure 1(A).

Yarn 1 is a multifilament yarn made by twisting multiple fibers 10. The fibers 10 have a circular cross section. Yarn 1 is a left-handed twisted yarn (hereinafter referred to as Z-yarn) made by twisting multiple fibers 10 in a left-handed direction.

The fiber 10 is made of, for example, a piezoelectric polymer. The fiber 10 is manufactured, for example, by extruding a piezoelectric polymer to form a fiber. Alternatively, the fiber 10 can be manufactured by melt-spinning a piezoelectric polymer to form a fiber (including, for example, a spinning/drawing method in which the spinning and drawing steps are performed separately, a straight-drawing method in which the spinning and drawing steps are combined, a POY-DTY method in which a false-twisting step can also be performed simultaneously, or an ultra-high-speed spinning method aimed at high speeds), dry- or wet-spinning a piezoelectric polymer (including, for example, a phase separation method or wet-dry spinning method in which a raw polymer is dissolved in a solvent and extruded through a nozzle to form a fiber, a gel spinning method in which a solvent-containing gel is uniformly formed into a fiber, or a liquid crystal spinning method in which a liquid crystal solution or melt is used to form a fiber), or electrostatically spinning a piezoelectric polymer. The cross-sectional shape of the fiber 10 is not limited to a circular shape.

Piezoelectric polymers exist in both pyroelectric and non-pyroelectric forms, but either can be used. For example, PVDF has pyroelectric properties and is polarized by temperature changes, generating an electric potential on the surface of the fiber. Piezoelectric materials with pyroelectric properties, such as PVDF, are also polarized by the thermal energy of the human body. In this case, the thermal energy of the human body is the external energy.

Polylactic acid (PLA) is a piezoelectric polymer that does not exhibit pyroelectric properties. Polylactic acid exhibits piezoelectricity when uniaxially stretched. Depending on the crystalline structure, polylactic acid can be classified as poly-L-lactic acid, which is formed by polymerizing L-lactic acid and L-lactide; poly-D-lactic acid, which is formed by polymerizing D-lactic acid and D-lactide; or stereocomplex polylactic acid, which is a hybrid of these. Any material that exhibits piezoelectricity can be used. From the perspective of high piezoelectricity, poly-L-lactic acid or poly-D-lactic acid is preferable. Poly-L-lactic acid and poly-D-lactic acid each exhibit opposite polarization polarities when subjected to the same deformation.

Polylactic acid exhibits piezoelectricity when it is uniaxially stretched and its molecules are oriented. The piezoelectric constant of polylactic acid can be increased by further heat treatment to increase its crystallinity. Because polylactic acid exhibits piezoelectricity through molecular orientation caused by stretching, there is no need for poling, as there is with other piezoelectric polymers such as PVDF or piezoelectric ceramics.

The piezoelectric constant of uniaxially stretched polylactic acid is approximately 5 to 30 pC/N, which is extremely high among polymers. Furthermore, the piezoelectric constant of polylactic acid does not fluctuate over time and is extremely stable.

When the thickness direction is defined as the first axis, the stretching direction 900 is defined as the third axis, and the direction perpendicular to both the first and third axes is defined as the second axis, the uniaxially stretched fiber 10 containing polylactic acid has tensor components _d14 and _d25 as the piezoelectric strain constants. Therefore, the uniaxially stretched fiber 10 containing polylactic acid generates an electric potential when shear deformation occurs in a direction intersecting the uniaxial stretching direction.

In Figure 1(A), the extension direction 900 of each fiber 10 coincides with the axial direction of the respective fiber 10. By twisting multiple fibers 10, the extension direction 900 of the fibers 10 becomes inclined with respect to the axial direction of the yarn 1.

When tension is applied to such a Z-yarn thread 1 and it is stretched, distortion occurs in the fiber 10 along the axial direction of the thread 1, and shear deformation occurs along the axial direction of the thread 1. Therefore, a positive potential is generated on the surface of the fiber 10, and a negative potential is generated inside. In the case of a right-handed twisted yarn (hereinafter referred to as an S-yarn) in which the fiber 10 is twisted clockwise as shown in Figure 2, a negative potential is generated on the surface of the fiber 10 and a positive potential is generated inside when it is stretched.

Therefore, a positive potential is generated on the surface of thread 1, and a negative potential is generated inside. A negative potential is generated on the surface of thread 2, and a positive potential is generated inside. However, the twist angle of fiber 10 varies depending on the location, and the thickness of thread 1 and thread 2 is not uniform overall. Therefore, fiber 10 does not always generate a uniform surface potential.

Figure 3 shows the simulation results showing the electric potential when a 2% axial displacement is applied to the yarn 1. However, this simulation result assumes that when an axial displacement occurs in the yarn 1, the individual fibers 10 slide relative to each other. In this simulation result, the average twist angle changes from 6.5° to 5.5° when a 2% axial displacement is applied.

As shown in the simulation results in Figure 3, fiber 10 has areas where a positive potential is generated and areas where a negative potential is generated. Yarn 1 generates an electric field between the areas where a positive potential is generated and the areas where a negative potential is generated.

Figure 4(A) shows the simulation results of the electric field at a cross section of Yarn 1, which is a Z-yarn. Figure 4(B) shows the simulation results of the electric field at a cross section of Yarn 2, which is an S-yarn. As these simulation results show, Yarn 1 and Yarn 2 each have areas where an electric field of several MV/m is generated even when used alone.

In this way, the yarn of the present invention comprises multiple fibers 10 that generate an electric potential on their surface when exposed to external energy, and generates an electric field between the multiple fibers 10 when a displacement is applied.

More specifically, the fibers 10 have positive potential portions and negative potential portions (portions with different potentials), and an electric field is generated between the positive and negative portions of the multiple fibers 10.

The stretching direction 900 of the fiber 10 needs to intersect at least with the axial direction of the yarn. Preferably, the average twist angle is 10 to 50°. More preferably, the average twist angle is 20 to 40°.

Of course, an electric field is also generated between thread 1 and another material, between thread 2 and another material, or between thread 1 and thread 2. Figure 5 is a cross-sectional view showing the state of the electric field when thread 1 and thread 2 are brought close together. When axial tension is applied to thread 1 alone, the surface becomes a positive potential and the interior becomes a negative potential. When axial tension is applied to thread 2 alone, the surface becomes a negative potential and the interior becomes a positive potential.

When thread 1 and thread 2 come close to each other, the adjacent parts (surfaces) tend to become the same potential. In this case, the area close to thread 1 and thread 2 becomes 0V, and the negative potential inside thread 1 becomes even lower so as to maintain the original potential difference. Similarly, the positive potential inside thread 2 becomes even higher.

At the cross section of thread 1, an electric field is formed that is mainly directed from the outside to the inside of thread 1, and at the cross section of thread 2, an electric field is formed that is mainly directed from the inside to the outside. When threads 1 and 2 are brought close to each other, these electric fields leak into the air and combine, and an electric field is formed between threads 1 and 2 due to the potential difference between them.

Furthermore, when thread 1 comes close to an object with a predetermined electric potential, such as a human body, an electric field is generated between thread 1 and the nearby object. Furthermore, when thread 2 comes close to an object with a predetermined electric potential, such as a human body, an electric field is generated between thread 2 and the nearby object.

Such electric fields exert antibacterial effects, inhibiting the growth of microorganisms such as viruses, bacteria, fungi, archaea, mites, and fleas.

If moisture containing electrolytes is present in yarn 1 or yarn 2, an electric current will flow through the moisture. Yarn 1 or yarn 2 may also directly exert an antibacterial or bactericidal effect due to this electric current. Alternatively, the antibacterial or bactericidal effect may be indirectly exerted by reactive oxygen species formed when oxygen contained in the moisture is converted by the action of electric current or voltage, or by radical species or other antibacterial chemical species (amine derivatives, etc.) generated by interaction with additives contained in the fiber or catalytic action. Alternatively, oxygen radicals may be generated within bacterial cells due to the stress environment caused by the presence of an electric field or electric current. Possible radicals include superoxide anion radicals (reactive oxygen) and hydroxyl radicals.

Conventional antibacterial materials, such as those containing drugs, do not have long-lasting effects. Furthermore, conventional antibacterial materials can sometimes cause allergic reactions due to drugs, etc. In contrast, the antibacterial effect of the thread of this embodiment lasts longer than the antibacterial effect of drugs, etc. Furthermore, the thread of this embodiment is less likely to cause allergic reactions than drugs. Furthermore, as mentioned above, the piezoelectric constant of polylactic acid does not fluctuate over time and is extremely stable, so the antibacterial effect of the thread is also stable and long-lasting.

In addition, thread 1 or thread 2 can charge other substances due to the generated potential. Alternatively, thread 1 or thread 2 can adsorb substances due to the generated potential. For example, thread 1 can adsorb substances with a negative potential because a positive potential is generated on its surface. Thread 2 can adsorb substances with a positive potential because a negative potential is generated on its surface.

By forming a filter, thread 1 or thread 2 can also efficiently adsorb substances. Such filters are suitable for masks or air purifiers. Furthermore, by using thread 1 or thread 2 as a pre-filter in the front stage to charge substances positively or negatively, and thread 1 or thread 2 that generates a potential of the opposite polarity as a filter in the rear stage, substances can be adsorbed more efficiently. Alternatively, thread 1 or thread 2 can be used as a pre-filter in the front stage to charge substances positively or negatively, and an electret filter with a potential of the opposite polarity can be used as a filter in the rear stage.

Here, if the potential generated on the surface of yarn 1 or yarn 2 is too low, the various desired effects described above may not be achieved. However, the yarn of the present invention is characterized by including fibers that generate a potential on their surface in response to external energy, and by generating a potential of 0.1 V or more on the yarn surface when measured under the following conditions (a) to (d). The yarn of the present invention can achieve the desired effects by generating a potential specified under these conditions.
(a) The yarn is stretched in one axial direction by a predetermined amount.
(b) A core material made of conductive fibers is covered with the fibers.
(c) grounding the core material;
(d) Measuring the surface potential of the yarn using an electric force microscope.

The predetermined amount (a) above is preferably a yarn distortion of 0.1% or more, more preferably 0.5% or more. The surface potential is preferably 0.3 V or more, more preferably 1.0 V or more.

The yarn thickness (single fiber fineness) is preferably 0.005 to 10 dtex. If the single fiber fineness is small, the number of filaments will be too high, making the yarn more susceptible to pilling. On the other hand, if the single fiber fineness is large and the number of filaments is too low, the texture will be impaired. Note that the single fiber fineness referred to here refers to the single fiber fineness of a single twisted yarn. Even if twisted yarns are further combined, this refers to the single fiber fineness of a single twisted yarn before being combined.

Furthermore, the fiber strength of the yarn is preferably 1 to 5 cN/dtex. This allows the yarn to withstand large deformations caused by the generation of a high potential without breaking. The fiber strength is more preferably 2 to 10 cN/dtex, even more preferably 3 to 10 cN/dtex, and most preferably 3.5 to 10 cN/dtex. For the same reason, the elongation of the yarn is preferably 10 to 50%.

In addition, the crystallinity of the polylactic acid is preferably between 15 and 55%. This increases the piezoelectricity derived from the polylactic acid crystals, allowing polarization due to the piezoelectricity of the polylactic acid to occur more effectively.

The following describes the examples. The yarns of Examples 1 to 3 are twisted yarns made from 84 dtex-24 polylactic acid filaments with a crystallinity of 45%, a crystal size of 12 nm, and an orientation of 79%. The yarns of Examples 1 to 3 are made by covering a core material made of conductive fibers with polylactic acid filaments. The core material is also grounded. Therefore, the inside of the yarns of Examples 1 to 3 has a potential of 0 V.

Example 1 has a twist count of 500T/m, Example 2 has a twist count of 1150T/m, and Example 3 has a twist count of 3000T/m. When the twist count is 500T/m, the average twist angle is 10°, when the twist count is 1150T/m, the average twist angle is 28°, and when the twist count is 3000T/m, the average twist angle is 47°.

Table 1 shows the results of measuring the surface potential of the yarn using an electric force microscope after clamping both ends of the yarns of Examples 1 to 3 between rigid jigs, stretching the 40 mm yarn to 40.2 mm, and neutralizing it with an ionizer, then stretching it 0.5% in the axial direction (from 40.2 mm to 40.4 mm). The potential values shown in Table 1 are positive or negative peak values.

As shown in Table 1, the S yarn of Example 1 produces a potential of -0.15V. The Z yarn of Example 1 produces a potential of 0.12V. The S yarn of Example 2 produces a potential of -1.22V. The Z yarn of Example 2 produces a potential of 0.96V. The S yarn of Example 3 produces a potential of -0.35V. The Z yarn of Example 3 produces a potential of 0.40V.

Table 2 shows the results of measuring the surface potential of the yarn using an electric force microscope when it was stretched by 0.25% in the axial direction (stretched between 40.4 mm and 40.5 mm) after measurement under the conditions in Table 1 above. When S yarn is stretched, a negative potential is generated on the surface, and when it is contracted, a positive potential is generated on the surface. When Z yarn is stretched, a positive potential is generated on the surface, and when it is contracted, a negative potential is generated on the surface. Therefore, when the yarn is stretched, positive and negative potentials are generated alternately. The surface potential values shown in Table 2 are the difference between the minimum and maximum values (difference from peak to peak).

As shown in Table 1, the S yarn of Example 1 produces a potential of 0.28 V. The Z yarn of Example 1 produces a potential of 0.33 V. The S yarn of Example 2 produces a potential of 2.83 V. The Z yarn of Example 2 produces a potential of 2.42 V. The S yarn of Example 3 produces a potential of 0.80 V. The Z yarn of Example 3 produces a potential of 0.75 V.

The results in Tables 1 and 2 confirm that when the number of twists is between 500 and 3000 Tm, a potential of approximately 0.1 V or more is generated on the surface of the yarn. All of these examples have been confirmed to produce an antibacterial effect. Therefore, the yarn of the present invention can exert the desired effect by generating a potential (0.1 V or more) specified by the above conditions (a) to (d).

The measurement results of these examples suggest that the average twist angle is preferably 10 to 50 degrees. Furthermore, since the above measurement results show that the highest potential occurs when the twist angle is 30 degrees, it can be said that the average twist angle is more preferably 20 to 40 degrees.

The yarn of the present invention can be used by combining multiple types of twisted yarn as needed. For example, an S-twisted yarn made primarily of poly-L-lactic acid and a Z-twisted yarn made primarily of poly-L-lactic acid can be used. Bringing these yarns close together increases the electric field between the fibers, resulting in increased antibacterial properties.

The same is true when using an S-twisted yarn made primarily of poly-L-lactic acid and an S-twisted yarn made primarily of poly-D-lactic acid, when using a Z-twisted yarn made primarily of poly-L-lactic acid and a Z-twisted yarn made primarily of poly-D-lactic acid, and when using an S-twisted yarn made primarily of poly-D-lactic acid and a Z-twisted yarn made primarily of poly-D-lactic acid.

These twisted yarns may be used as a doubling yarn, or any two of the twisted yarns described above may be used in combination to form a fabric. The fabric of the present invention may be made, for example, of the above-mentioned Yarn 1 or Yarn 2. In this invention, "fabric" refers to textile products such as woven fabrics, knitted fabrics, braided fabrics, nonwoven fabrics, and lace.

Each of the yarns constituting the fabric may generate a potential of 0.1 V or more on its surface under the above-mentioned conditions (a) to (d), but the fabric of the present invention itself may generate a potential of 0.1 V or more on its surface when measured under the following conditions (a) to (d). The fabric of the present invention can also exhibit the desired effects by generating a potential specified under such conditions.
(a) The fabric is stretched in one axial direction by a predetermined amount.
(b) A core material made of conductive fibers is covered with the fibers.
(c) grounding the core material;
(d) measuring the surface potential of the fabric using an electric force microscope;

As with thread, the predetermined amount (a) above is preferably a fabric distortion of 0.1% or more, more preferably 0.5% or more. The surface potential is preferably 0.3 V or more, more preferably 1.0 V or more.

The parameters of the fibers that make up the fabric are the same as those of the yarn described above. That is, the fiber thickness (single fiber fineness) is preferably 0.005 to 10 dtex. Furthermore, the fiber strength is preferably 1 to 5 cN/dtex. The fiber strength is more preferably 2 to 10 cN/dtex, even more preferably 3 to 10 cN/dtex, and most preferably 3.5 to 10 cN/dtex. The fiber elongation is preferably 10 to 50%. The crystallinity of the polylactic acid is preferably 15 to 55%.

When the fibers making up the fabric are twisted yarns, the average twist angle of the twisted yarns is preferably 10 to 50°, and more preferably 20 to 40°.

The fabric preferably has a basis weight of 20 to 200 g/m ² and a porosity of 50 to 95%. When using the fabric as a filter, it is preferable that the filter has a 0.3 μm fine particle collection rate of 40% or more at an air velocity of 5.1 cm/sec or more and a pressure loss of less than 250 Pa in order to improve collection performance and collection stability.

The fabric of the present invention can be used in a variety of products, including clothing and medical devices. For example, the fabric of the present invention can be used in underwear (especially socks), towels, insoles for shoes and boots, sportswear in general, hats, bedding (including futons, mattresses, sheets, pillows, pillowcases, etc.), toothbrushes, floss, various filters (such as filters for water purifiers, air conditioners, or air purifiers), stuffed toys, pet-related products (pet mats, pet clothing, innerwear for pet clothing), various matting products (for feet, hands, or toilet seats, etc.), curtains, kitchen utensils (such as sponges or dishcloths), seats (for cars, trains, or airplanes), cushioning materials and their outer coverings for motorcycle helmets, sofas, bandages, gauze, masks, sutures, doctor's and patient clothing, supports, sanitary products, sports equipment (such as innerwear for apparel and gloves, or gauntlets used in martial arts), or packaging materials.

Socks (or supporters), in particular, are frequently polarized when worn in clothing, as they inevitably stretch along the joints during walking and other movements. Furthermore, socks absorb moisture such as sweat, making them a breeding ground for bacterial growth. However, the fabric of the present invention can inhibit bacterial growth, making it a significant anti-bacterial agent.

The yarn of the present invention may be either a non-twisted yarn or a false-twisted yarn. The yarn that constitutes the fabric of the present invention may also be either a non-twisted yarn or a false-twisted yarn. As long as the yarn has fibers that generate an electric potential on their surface in response to external energy, and generates an electric potential of 0.1 V or higher under the above conditions, it can exhibit various desired effects, such as antibacterial effects.

The description of the present embodiment should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is defined not by the above-described embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications that are equivalent in meaning to and within the scope of the claims.

1, 2... Yarn 10... Fiber 900... Stretching direction

Claims (8)

A method for measuring the surface potential of a yarn containing a potential-generating fiber, characterized by measuring under the following conditions (a) to (d):
(a ) A core material made of conductive fibers is covered with the potential generating fibers.
( b ) grounding the core material;
(c) stretching the yarn in one axial direction by a predetermined amount;
(d) Measuring the surface potential of the yarn using an electric force microscope. The predetermined amount is a distortion of the yarn of 0.1% or more.
The measurement method according to claim 1. 3. The measuring method according to claim 1, wherein the thickness of the potential generating fiber is 0.005 to 10 dtex. The measurement method according to claim 1 , wherein the potential generating fiber contains polylactic acid. The method according to claim 1 , wherein the potential generating fibers are twisted. The measurement method according to claim 5, wherein the average twist angle of the yarn is 10 to 50°. The measurement method according to any one of claims 1 to 6, wherein the potential-generating fiber satisfies the following requirements (A) to (C):
(A) The fiber strength is 1 to 5 cN/dtex.
(B) The elongation is 10 to 50%.
(C) The crystallinity is 15 to 55%. A method for measuring the surface potential of a fabric containing potential-generating fibers, characterized by measuring under the following conditions (a) to (d):
(a ) A core material made of conductive fibers is covered with the potential generating fibers.
( b ) grounding the core material;
(c) stretching the fabric in one axial direction by a predetermined amount;
(d) measuring the surface potential of the fabric using an electric force microscope;