JP4446848B2 - Conductive nonwoven fabric - Google Patents

Description

  The present invention relates to a conductive nonwoven fabric.

As a conductive nonwoven fabric such as an earth grounding material and a battery electrode material, a material using a carbon material has been proposed. For example, “a sheet made of polyacrylonitrile-based oxidized fiber having a fiber density of 1.36 to 1.44 g / cm ³ , a knot strength of 0.5 to 1.8 g / dtex, a knot elongation of 5% or more, and a core ratio of 33 to 70%. Of the carbon fiber produced by compressing in the thickness direction at a pressure of 10 to 100 MPa at a temperature of 150 to 300 ° C. to obtain an oxidized fiber sheet, and then heat-treating the oxidized fiber sheet in an inert gas atmosphere. "A carbon fiber sheet having an X-ray crystallite size of 1.3 to 3.5 nm" has been proposed, and a manufacturing method using a water jet method or a needle punch method has been disclosed as a method for manufacturing an oxidized fiber sheet (Patent Document 1). .

JP-A-2002-194650 (Claim 5, Examples, etc.)

  However, since the oxidized fiber sheet manufactured by the above-described method is intertwined uniformly and has almost no pores, the carbon fiber sheet manufactured from this oxidized fiber sheet is also uniformly dispersed. There are no pores, and the uniform dispersion state of the carbon fiber may be inconvenient depending on the application. For example, when a carbon fiber sheet is used as an electrode, it is difficult to increase the filling amount of the active material, and it is difficult to increase the battery capacity.

  Accordingly, an object of the present invention is to provide a conductive nonwoven fabric that can be applied to uses that have been impossible in the past by providing the openings.

  The invention according to claim 1 of the present invention is “a conductive nonwoven fabric provided with a large number of aperture groups in which apertures are densely packed, and the amount of fibers gradually increases in the radial direction from each aperture group. The conductive nonwoven fabric is characterized in that the porosity is 2 to 15%, the average pore diameter is 10 to 25 μm, and the pore diameter of 50 μm or more is less than 3%.

The invention according to claim 2 of the present invention is “the conductive nonwoven fabric according to claim 1, wherein the basis weight is 50 to 200 g / m ² ”.

The invention according to claim 3 of the present invention is the conductive nonwoven fabric according to claim 1 or 2, wherein the compression ratio (Cr) defined by the following formula is 30 to 80%. Cr = {(P ₂ −P ₁₅₅ ) / P ₂ } × 100
Here, P2 means the thickness (mm) of the conductive nonwoven fabric at a load of ₂ kPa, and P155 means the thickness (mm) of the conductive nonwoven fabric at a load of ₁₅₅ kPa.

  The invention according to claim 1 of the present invention can be applied to applications in which a conductive nonwoven fabric having a number of aperture groups of 2 to 15% and a porosity of 2 to 15% has been difficult in the past, particularly when the average pore diameter is 10 μm or more. It has been found that it is preferable. For example, it has been found that when a conductive nonwoven fabric is used as an electrode, the amount of active material can be increased, and the battery capacity can be increased. In addition, the conductive nonwoven fabric has a large number of aperture groups, and the above-described effects can be obtained. However, if there are many large apertures, the current collection efficiency decreases and the electrical resistance increases. The upper limit of the hole diameter was 25 μm, and the hole having a hole diameter of 50 μm or more was less than 3%. Further, since the amount of fibers gradually increases in the radial direction from each aperture group, the retention of various substances (for example, active materials) is also excellent.

In the invention according to claim 2 of the present invention, since the basis weight of the conductive nonwoven fabric is 50 to 200 g / m ² , it can be provided with an electric resistance value and mechanical strength that can be satisfied as the conductive nonwoven fabric. Easy to apply to applications. That is, when the basis weight is less than 50 g / m ^2, it tends to be difficult to obtain sufficient mechanical strength and low electrical resistance value that can withstand post-processing, and when the basis weight is larger than 200 g / m ² , It tends to be difficult to efficiently and stably produce a conductive nonwoven fabric having a rate of 2 to 15%, an average pore size of 10 to 25 μm, and a pore size of 50 μm or more of less than 3%.

  In the invention according to claim 3 of the present invention, since the compressibility of the conductive nonwoven fabric is 30 to 80%, the contact area with other materials is wide, and the contact resistance with other materials is low. It can conduct electricity.

  In the conductive nonwoven fabric of the present invention, the fiber amount gradually increases in the radial direction from each aperture group in which the apertures are dense, that is, in the aperture group, there are fibers with a small amount of fibers. In addition, the retention of various substances (for example, active material) is excellent, and since the amount of fibers is small in the aperture group, the permeability and filling properties of various substances (for example, active material) are excellent. In addition, when the fibers are arranged so as to surround each aperture group of the conductive nonwoven fabric of the present invention in a circle or an ellipse, the shape stability of each aperture group is excellent, and the mechanical strength of the conductive nonwoven fabric is Since it is excellent, it is a preferred embodiment. Such a group of holes can be present regularly or irregularly, but a regular one is preferable because it is excellent in filling properties of various substances. The fiber amount gradually increases in the radial direction from each aperture group, but it does not increase infinitely, but may have a region where the fiber amount is constant, or adjacent In some cases, the fiber amount gradually decreases after the fiber amount gradually increases due to the relationship with the opening group.

  Such a conductive nonwoven fabric of the present invention has a porosity of 2 to 15% and an average pore diameter of 10 μm or more, and therefore can be applied to applications that have been difficult in the past. For example, when used as an electrode, the filling amount of the active material can be increased, and the battery capacity can be increased. On the other hand, if there are too many holes having a large hole diameter, the current collection efficiency is lowered, the electrical resistance is increased, or the filling material cannot be held. Therefore, the upper limit of the average hole diameter is set to 25 μm, which is 50 μm or more. The pore size was less than 3%.

  The “open hole” in the present invention means a hole through which light leaks when irradiated with light from behind the conductive nonwoven fabric, that is, a through hole. The porosity of such a conductive nonwoven fabric is 2 to 15% as described above. When the open area ratio is less than 2%, the dispersion state of the conductive nonwoven fabric constituting fibers is relatively uniform, which is not much different from the conventional conductive nonwoven fabric, and may be difficult to apply to various applications. Or more, preferably 2.5% or more, more preferably 3% or more. On the other hand, if the open area ratio exceeds 15%, the electrical resistance of the conductive nonwoven fabric may increase, or in some cases, the diameter of the open hole may become too large to hold the filling material and may not be applicable to various applications. , 15% or less, preferably 14% or less, and more preferably 13.5% or less.

In the present invention, “aperture ratio” refers to a value obtained by the following method.
(1) Light is irradiated from behind the conductive nonwoven fabric, and the area (Sl) of the portion where the light leaks is measured with a stereomicroscope.
(2) Considering the area (Sl) of the light leaking portion as the area of opening (So: unit = cm ² ), the percentage of the total area of all openings per 1 cm ² is calculated, and the opening ratio { = (So / 1) × 100 = 100So}.

  As described above, the average pore diameter of the conductive nonwoven fabric of the present invention is 10 to 25 μm, preferably 12 μm or more, and more preferably 18 μm or more. On the other hand, it is preferably 23 μm or less, and more preferably 21 μm or less. The “average pore diameter” in the present invention refers to the value of “average flow pore diameter” obtained by the method prescribed in ASTM-F316, and is a linear shape other than the above-mentioned “open holes (through holes)”. It also includes holes that are not in a through state. Thus, the “hole” of the present invention is a concept wider than an opening including holes other than the opening (through hole). The average pore diameter can be measured, for example, by a mean flow point method using a porometer (Polometer, manufactured by Coulter).

  Moreover, the conductive nonwoven fabric of the present invention has less than 3% of holes having a diameter of 50 μm or more. If the hole diameter is 50% or more and the hole diameter is 3% or more, the current collection efficiency tends to deteriorate or the electric resistance tends to increase. Therefore, it is preferably 2.8% or less, more preferably 2.4%. It is as follows. The “ratio of pores having a pore diameter of 50 μm or more” refers to the percentage of the total pore diameter of the pores having a diameter of 50 μm or more as a result of measuring the pore size distribution by the method prescribed in ASTM-F316. For example, the pore size distribution can be measured by means of the mean flow point method using a porometer (Polometer, manufactured by Coulter), and the percentage of the total pore size of pores having a pore size of 50 μm or more can be calculated and determined.

The basis weight of the conductive nonwoven fabric of the present invention is preferably 50 to 200 g / m ² . If the basis weight is less than 50 g / m ² , there is a tendency that sufficient mechanical strength and low electrical resistance value that can withstand post-processing cannot be obtained, so that it is more preferably 60 g / m ² or more, and 70 g / m ^2. More preferably, it is m ² or more. On the other hand, if the basis weight exceeds 200 g / m ² , it tends to be difficult to efficiently and stably produce a conductive nonwoven fabric having pore groups, and it is more preferably 180 g / m ² or less. More preferably, it is 150 g / m ² or less. In addition, the “weight per unit area” in the present invention is a value obtained by converting into a mass per 1 m ² based on a mass when the conductive nonwoven fabric is punched into a 20 cm square.

Although the thickness of the conductive nonwoven fabric of this invention is not specifically limited, It is preferable that it is 0.1-2 mm, and it is more preferable that it is 0.1-0.5 mm. Although not limited to particular apparent density of the conductive nonwoven fabric is preferably from 0.1~0.9g / cm ^3, more preferably from 0.3 to 0.7 g / cm ³ . In the present invention, “thickness” means a thickness at a load of 155 kPa, and “apparent density” means a quotient obtained by dividing the basis weight by the thickness.

In addition, the conductive nonwoven fabric of the present invention preferably has a compression rate of 30 to 80%. If the compression ratio is less than 30%, it is difficult to increase the contact area with other materials, and the contact resistance tends to increase with other materials. More preferably, it is more preferably 50% or more. On the other hand, if the compression rate exceeds 80%, the form tends to be unstable, and the yield during processing of the conductive nonwoven fabric may be reduced, or the strength may be reduced due to compression deformation, so the content is 75% or less. More preferably, it is 70% or less. The compression rate is a value defined by the following equation.
Cr = {(P ₂ −P ₁₅₅ ) / P ₂ } × 100
Here, P2 means the thickness (mm) of the conductive nonwoven fabric at a load of ₂ kPa, and P155 means the thickness (mm) of the conductive nonwoven fabric at a load of ₁₅₅ kPa.

Furthermore, the porosity of the conductive nonwoven fabric of the present invention is preferably 50 to 90%, more preferably 65 to 85%. When the porosity is less than 50%, for example, when it is used as an electrode, the space in which the active material can be filled tends to be small, and it tends to be difficult to increase the filling amount of the active material. If it exceeds 90%, the number of contacts between the conductive fibers constituting the conductive nonwoven fabric tends to decrease and the electrical resistance tends to increase, that is, the electrical resistance tends to increase. “Porosity (P)” is a value obtained by the following equation.
Porosity (P) = {1−W / (T × d)} × 100
Here, W means the basis weight (g / m ² ) of the conductive nonwoven fabric, T means the thickness (μm) of the conductive nonwoven fabric, and d means the density of the conductive nonwoven fabric fibers (g / cm ³ ). Means.

  The conductive nonwoven fabric of the present invention only needs to have conductivity suitable for various applications, and its electrical resistance is not particularly limited. For example, when used as a current-carrying material, 10 mΩ so as to be excellent in conductivity. Or less, more preferably 6 mΩ or less. The electrical resistance is a value measured by the following method. First, the conductive nonwoven fabric is left in a standard state (temperature 22 ° C., relative humidity 65%) for 2 hours or more. Next, the conductive non-woven fabric is sandwiched between a pair of brass electrodes (diameter: 4 cm), and a load (155 kPa) is applied to the electrodes by a compression tester (Orientec), and then conductive with an LCR tester (manufactured by Hioki). The electrical resistance of the conductive nonwoven fabric is measured. In the measurement, a constant current of DC 10 mA is applied.

  The conductive nonwoven fabric of the present invention only needs to have conductivity suitable for various applications, and the constituent fibers thereof are not particularly limited. For example, carbon fibers, metal fibers, metal-plated fibers, conductive polymer-coated fibers, etc. Can be single or mixed. In addition, the nonconductive fiber may be included in the range which does not disturb the electroconductivity of an electroconductive nonwoven fabric.

  The tensile strength of the conductive nonwoven fabric of the present invention is preferably 1 N / cm or more, and more preferably 2 N / cm or more so that the workability is excellent. “Tensile strength” refers to a value measured by the following method. A conductive nonwoven fabric cut to 1.5 cm in the direction perpendicular to the longitudinal direction (that is, the width direction) and 7 cm in the longitudinal direction is fixed to a chuck of a tensile strength tester (manufactured by Minebea) (distance between chucks: 3 cm), Tensile speed 3 mm / min. Then, by pulling the conductive nonwoven fabric, the force (tensile strength) required for the conductive nonwoven fabric to break is measured, and the value obtained by converting this measured value per 1 cm width is taken as the tensile strength.

  Thus, the electroconductive nonwoven fabric which has the aperture group of this invention can be used conveniently as a use which was difficult conventionally, for example, a grounding earth material, a battery electrode material, etc. When used in such applications, the amount of active material filled can be increased, battery capacity can be increased, current collection efficiency is high, and electrical resistance is low. In addition, the active material retainability is also excellent.

  Such a conductive nonwoven fabric of the present invention can be produced using, for example, a conductive fiber having conductivity after firing.

  This conductive fiber refers to a fiber that is solid-phase carbonized by firing and exhibits conductivity, and examples thereof include rayon fiber, acrylated fiber, pitch fiber, and phenol fiber. Among these, acrylated fibers having high bending strength and high tensile strength after firing are preferable. This acrylic oxidized fiber is a fiber manufactured by oxidizing acrylic fiber as a raw material, heat-treating it in air at a temperature of 200 to 300 ° C., and oxidizing it. The acrylic fiber used as a raw material for the preferred acrylic oxidized fiber includes 90 to 98% of acrylonitrile monomer units, and 2 to 10% of comonomer units (for example, vinyl monomers such as acrylic acid methyl ester, acrylamide, and itaconic acid). What is contained is preferable.

  The fineness of the conductive fiber is not particularly limited, but is preferably 0.5 dtex or more, and more preferably 1 dtex or more so that the mechanical strength of the conductive nonwoven fabric is excellent. On the other hand, in order to form the aperture group, since it is preferable that the fineness is small, it is preferably 6 dtex or less, and more preferably 3 dtex or less. In addition, the fineness in this invention says the value obtained by JISL1015 (chemical fiber staple test method) B method (simple method).

  The fiber length of the conductive fiber is not particularly limited because it varies depending on the method of forming the fiber web. For example, when the fiber web is formed by a card machine, the cardability of the conductive fiber is improved. In order to be excellent, it is preferably 10 to 110 mm, and more preferably 30 to 80 mm. In addition, even if this fiber length entangles the fiber web with a fluid flow to form a conductive non-woven fabric, it can be sufficiently entangled to produce a conductive non-woven fabric having sufficient mechanical strength. can do. The “fiber length” in the present invention refers to a length obtained by JIS L 1015 (chemical fiber staple test method) B method (corrected staple diagram method).

  Two or more types of conductive fibers that differ in composition, fineness, and / or fiber length can be used.

  Using such a conductive fiber, a conductive nonwoven fabric having apertures is produced. For example, after a fiber web made of conductive fibers is formed by a dry method or a wet method such as a card method or an air array method, the fiber web is entangled by a fluid flow and an aperture group is formed, so that a conductive material having the aperture group is formed. Can be produced. When a conductive nonwoven fabric is produced by entanglement by a fluid flow and forming an aperture group in this way, a conductive nonwoven fabric excellent in strength, and thus a conductive nonwoven fabric excellent in strength can be manufactured. . In addition, by changing the shape of the openings in the support that supports the fiber web and the energy of the fluid flow that is used when the fluid flow is applied, the design of the aperture group of the conductive nonwoven fabric and thus the conductive nonwoven fabric The design of the aperture group is easy, and the entanglement of the conductive fibers and the formation of the aperture group can be carried out in the same process, and the productivity is high.

  Specifically, in a state where the fiber web is supported by a support of 10 to 30 mesh, a high-pressure fluid flow having a fluid pressure of 5 MPa or more is entangled by ejecting the fiber web once or twice. In addition, by manufacturing fibers that exist in the knuckle part of the support incompletely, and having a group of apertures, a conductive non-woven fabric in which the amount of fibers gradually increases in the radial direction from each aperture group is manufactured. Can do. The condition for incompletely pushing the fibers present in the knuckle part of the support can be found by repeating the experiment. In addition, the fluid flow is ejected to the fiber web once or twice or more in a state where the fiber web is supported by a support of 50 to 100 mesh before being entangled and forming the aperture group as described above. When entangled to some extent, a conductive non-woven fabric having excellent mechanical strength, and thus a conductive non-woven fabric can be produced.

  In addition, after forming an aperture group by a fluid flow etc. as mentioned above, it is preferable to implement a compression process using a calendar | calender etc. By carrying out such a compression treatment, it becomes easy to obtain a conductive nonwoven fabric having a desired thickness and density. The pressure of the compression treatment is not particularly limited as long as it is a pressure that can obtain a conductive nonwoven fabric having a desired thickness, but it is preferably performed at a pressure of 50 to 200 kg / cm. In addition, although this compression process can also be implemented under normal temperature, since it can suppress the damage to the fiber by an excessive linear pressure load when implemented under heating, it is preferable to implement under heating. When carried out under heating, it is preferably carried out at a temperature of 160 ° C to 240 ° C.

  The porosity of the conductive non-woven fabric formed in this way (including when compressed) is 0.2 to 12% so that a conductive nonwoven fabric with a porosity of 2 to 15% can be easily produced. Preferably there is. More preferably, the open area ratio is 0.3% or more, further preferably 0.5% or more, more preferably 10% or less, and further preferably 9% or less. preferable.

The basis weight, thickness, and apparent density of the conductive nonwoven fabric are not particularly limited, but the conductive nonwoven fabric having the appropriate basis weight, thickness, and apparent density as described above can be efficiently and stably provided. as can be prepared by, weight of the conductive possible nonwoven fabric is preferably from 80~350g / ^{m 2,} and more preferably 100 to 200 g / ^{m 2.} Moreover, it is preferable that it is 0.1-2 mm in thickness, and it is more preferable that it is 0.2-0.9 mm. Furthermore, the apparent density is preferably 0.2 to 0.8 g / cm ³ , more preferably 0.3 to 0.75 g / cm ³ .

  Next, the conductive non-woven fabric can be fired to produce the conductive non-woven fabric of the present invention. In addition, although the conditions for baking are not specifically limited, For example, it can bak by processing for 0.5 to 30 minutes at the temperature of 1000-2000 degreeC in inert gas atmosphere, such as nitrogen, helium, and argon. .

  In addition, the fineness, basis weight, thickness, and / or support of the constituent fibers of the electrically conductive nonwoven fabric so that the average pore diameter of the conductive nonwoven fabric is 10 to 25 μm and the pores having a pore diameter of 50 μm or more are less than 3%. It can be manufactured by appropriately adjusting the aperture group forming conditions such as the aperture shape, the fluid flow pressure, the knuckle shape and height of the support.

  Moreover, the conductive nonwoven fabric whose compression rate is 30 to 80% can be manufactured by firing after adjusting the basis weight and thickness so that the compression rate of the conductive nonwoven fabric becomes 10 to 80%.

A conductive nonwoven fabric with a porosity of 50 to 90% is manufactured by adjusting the thickness of a conductive nonwoven fabric with a calendar, adjusting the apparent density to 0.3 to 1.0 g / cm ³ , and then firing the conductive nonwoven fabric. can do.

  Furthermore, the conductive nonwoven fabric in which the fibers are arranged so as to surround each aperture group in a circular shape or an elliptical shape can be produced by using a support having a knuckle portion.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

(Examples 1-6, Comparative Examples 1-5)
The raw material is acrylic fiber containing methyl acrylate as a comonomer, the fineness is 2.2 dtex (Examples 1 to 6, Comparative Examples 1 to 4) or 0.8 dtex (Comparative Example 5), the fiber length is 51 mm, The acrylic oxidized fiber having a density of 1.41 g / cm ³ was opened by a card machine to form a fiber web made of the acrylic oxidized fiber.

  Next, a 6MPa water stream is collided while the fiber web is conveyed by a 100 mesh conveyor, the fibers are entangled, and then a 12MPa stream is collided while being conveyed by a conveyor made of plain weave mesh as shown in Table 1. And entangled nonwoven fabrics (Examples 1 to 6, Comparative Example 1) or entangled nonwoven fabrics (Comparative Examples 2 to 5). .

  Subsequently, these open entangled nonwoven fabrics or entangled nonwoven fabrics were supplied between calender rolls heated to a temperature of 200 ° C. (linear pressure: 150 kg / cm) and subjected to compression treatment to produce a conductive non-woven fabric. Table 1 shows the physical properties of these conductive non-woven fabrics. In Example 2 and Comparative Example 5, a compressible treatment was not performed, and a conductive non-woven fabric was used.

  Thereafter, these conductive non-woven fabrics were heated in a nitrogen atmosphere at a maximum temperature of 1500 ° C. for 5 minutes to produce conductive non-woven fabrics. The physical properties of these conductive nonwoven fabrics are as shown in Table 1. In addition, the conductive nonwoven fabrics of Examples 1 to 6 and Comparative Example 1 are in a state where the amount of fibers gradually increases in the radial direction from each aperture group, and each aperture group that exists regularly is elliptical. The fibers were arranged so as to surround them.

  The filling property was evaluated as follows. A conductive nonwoven fabric is impregnated with 80 parts by weight of nickel hydroxide, 0.2 parts by weight of carboxymethyl cellulose as a binder, and 19.8% by weight of water and impregnated with a conductive nonwoven fabric, and then dried and filled. The filling amount per unit area of the active material was determined from the difference in weight before and after. The packing density of the active material was calculated by dividing this by the thickness of the conductive nonwoven fabric.

From Examples 2 and 6 and Comparative Examples 1 and 2, the porosity was 2 to 15%. From Examples 2 and 6 and Comparative Examples 1 and 4, the average pore diameter was 10 to 25 μm. If the hole having a hole diameter of 50 μm or more was 3% or less, it was found that the conductive nonwoven fabric had a high packing density.

Claims (3)

It is a conductive nonwoven fabric provided with a large number of aperture groups in which the apertures are dense, and the amount of fibers gradually increases in the radial direction from each aperture group, and the aperture ratio is 2 to 15%. A conductive nonwoven fabric having a pore diameter of 10 to 25 µm and a pore diameter of 50 µm or more is less than 3%. Wherein the basis weight is 50 to 200 g / ^{m 2,} according to claim 1, wherein the conductive nonwoven fabric. The conductive nonwoven fabric according to claim 1 or 2, wherein the compressibility (Cr) defined by the following formula is 30 to 80%.
Cr = {(P ₂ −P ₁₅₅ ) / P ₂ } × 100
Here, P2 means the thickness (mm) of the conductive nonwoven fabric at ₂ kPa load, and P155 means the thickness (mm) of the conductive nonwoven fabric at ₁₅₅ kPa load.