WO2012017954A1 - Non-woven fabric comprising cellulose fibers and process for production thereof, and separator - Google Patents

Abstract

A non-woven fabric is prepared, which comprises cellulose fibers having an average fiber diameter of 0.1-50 μm and polyolefin fibers having an average fiber diameter of 1.5 μm or less and has a thickness of 20 μm or less. The polyolefin fibers may be polyethylene fibers having an average fiber diameter of 10-1000 nm and an average fiber length of 1-1000 μm. The ratio of the content of the cellulose fibers to that of the polyolefin fibers (the former/the latter) may be 99.9/0.1 to 10/90 (particularly 70/30 to 20/80) (by weight). This non-woven fabric can exhibit both gas permeability and mechanical strength at the same time even when the non-woven fabric has a small thickness, and may be used as a separator for an electrical storage element.

Description

Nonwoven fabric containing cellulose fiber, method for producing the same, and separator

The present invention relates to a nonwoven fabric formed from cellulose fibers and polyolefin fibers, a method for producing the same, and a separator (such as a separator for a storage element) formed from the nonwoven fabric.

Traditionally, non-woven fabrics made of cellulose fibers have been used as printing paper or books as paper by adding sizing agents, paper strength enhancers, etc., but using permeability to gases and liquids, It is also used for filters and separators for energy storage devices. In particular, since cellulose fibers have excellent heat resistance and are electrochemically stable, they are actively used as separators for power storage elements such as batteries, capacitors, and capacitors. Furthermore, in recent years, advanced performance has been demanded for battery and capacitor separators due to miniaturization and long life of electric and electronic devices, and the strength can be maintained even if the internal resistance is reduced even if the thickness is reduced. A separator is needed. Furthermore, among battery separators, for example, lithium secondary battery separators hold electrolytes (ethylene carbonate, propylene carbonate, butyrolactone, dimethyl carbonate, etc.), insulate the electrodes, and melt at a high temperature to form fine particles. A function (shutdown) or the like that closes the hole and blocks ionic conductivity is also required.

For example, Japanese Patent Laid-Open No. 2006-49797 (Patent Document 1) discloses a separator having a maximum fiber thickness of 1000 nm or less and having an air permeability of 5 to 700 seconds / 100 ml. An electrical storage device having an electrical resistance value at 20 ° C. of 1.0 Ωcm ² or less calculated by the AC two-terminal method of a membrane impregnated with 0.8 mol / liter of tetraethylammonium · BF ₄ salt / propylene carbonate solution A separator for use is disclosed. In this document, the thickness of the separator is described as 5 to 50 μm, preferably 10 to 30 μm.

However, since this separator is composed of cellulose fibers alone, it has low strength and does not have a shutdown function.

JP-A-8-171893 (Patent Document 2) discloses a lithium battery composed of a positive electrode, a negative electrode made of lithium or a lithium alloy, a separator, and an electrolyte solution, wherein the separator includes natural pulp 20 to A lithium battery separator is disclosed, which is a sheet made by mixing papermaking at a blending ratio of 70% by weight and fine synthetic fibers of 80 to 30% by weight, and the fine synthetic fibers have a fiber diameter of 5 μm or less. In this document, polyethylene, polypropylene, and aramid fibers are exemplified as fine synthetic fibers, and it is described that the fiber diameter is preferably 2 μm or less. In the examples, polyethylene fine fibers having an average fiber diameter of 2 μm are used. In addition, it is described that the separator makes paper with a basis weight in the range of 15 to 30 g / m ² , and in the examples, a separator with a basis weight of about 30 g / m ² is manufactured. Furthermore, it is described that about 20% of vinylon fiber may be blended as the binder fiber. In the examples, a separator having a thickness of about 50 μm is manufactured by blending 10% vinylon fiber having a heat melting temperature of 70 ° C. and processing at 80 ° C. in addition to natural pulp and fine synthetic fiber.

However, since this separator is small in microfibrillation of natural pulp, the fiber diameter of the synthetic fiber is large, and it is thick, the internal resistance is large. Furthermore, since it contains a hydrophilic binder fiber having a low melting point, it has low heat resistance and is electrochemically unstable.

JP 2006-49797 A (claims, paragraph [0042], examples) JP-A-8-171893 (Claim 1, paragraphs [0007] [0009] [0010], Examples)

Accordingly, an object of the present invention is to provide a non-woven fabric that can achieve both air permeability and mechanical strength, a manufacturing method thereof, and a storage element separator formed of the non-woven fabric even if it is thin.

Another object of the present invention is to provide a non-woven fabric having low internal resistance and electrochemical stability, a method for producing the same, and a separator for a storage element formed from the non-woven fabric.

Still another object of the present invention is to provide a nonwoven fabric having high heat resistance and also having a shutdown function, a method for producing the same, and a storage element separator formed from the nonwoven fabric.

As a result of diligent studies to achieve the above-mentioned problems, the present inventor made a nonwoven fabric having a thickness of 20 μm or less by combining cellulose fibers having an average fiber diameter of 0.1 to 50 μm and polyolefin fibers having an average fiber diameter of 1.5 μm or less. Even if it exists, it discovered that air permeability and mechanical strength were compatible, and completed this invention.

That is, the nonwoven fabric (or papermaking body) of the present invention may contain cellulose fibers having an average fiber diameter of 0.1 to 50 μm and polyolefin fibers having an average fiber diameter of 1.5 μm or less, and may have a thickness of 20 μm or less. The polyolefin fiber may have an average fiber diameter of 10 to 1000 nm. The polyolefin fiber may have an average fiber length of 1 to 1000 μm. The polyolefin fiber may be a polyethylene fiber. The polyolefin fiber is obtained by a production method including a dispersion preparation step of preparing a dispersion by dispersing raw polyolefin fibers in a solvent, and a homogenization step of homogenizing the dispersion with a homogenizer equipped with a crushing type homovalve sheet. It may be a fiber. The average fiber diameter of the cellulose fibers may be 0.2 to 1 μm. The ratio (weight ratio) between the cellulose fibers and the polyolefin fibers is about the former / the latter = 99.9 / 0.1 to 10/90. It is preferable that the nonwoven fabric of this invention does not contain a hydrophilic binder fiber substantially. Moreover, it is preferable that the nonwoven fabric of this invention does not contain the synthetic resin below melting | fusing point less than 100 degreeC substantially. The nonwoven fabric of the present invention can achieve both strength and air permeability, the tensile strength at a basis weight of 10 g / m ² is 12 N / 15 mm or more, and the air permeability at a basis weight of 10 g / m ² is 50 to 100 seconds / 100 ml. is there. The nonwoven fabric of the present invention may have a thickness of 10 to 18 μm.

The present invention also includes a storage element separator formed of the nonwoven fabric. In this separator, the ratio (weight ratio) between cellulose fibers and polyolefin fibers may be the former / the latter = 70/30 to 20/80. The separator of the present invention may be a battery or capacitor separator.

The present invention also includes a method for producing the nonwoven fabric described above, in which cellulose fibers and polyolefin fibers are made. In this method, the ratio (weight ratio) of cellulose fiber to polyolefin fiber is the former / the latter = 70/30 to 20/80, and the treatment may be performed at a temperature lower than the melting point or softening point of the polyolefin fiber. .

In the present invention, by combining a cellulose fiber having an average fiber diameter of 0.1 to 50 μm and a polyolefin fiber having an average fiber diameter of 1.5 μm or less, even a non-woven fabric (or papermaking body) having a thickness of 20 μm or less has air permeability. Both mechanical strength can be achieved. In addition, since it is thin, it has low internal resistance and does not contain a hydrophilic binder fiber or a low-melting synthetic resin, so that it is electrochemically stable. Furthermore, by increasing the proportion of the polyolefin fiber, the heat resistance is high, and a shutdown function in the battery separator can be imparted.

FIG. 1 is a schematic cross-sectional view showing a process of homogenizing a dispersion containing fibers using a homogenizer. FIG. 2 is an enlarged cross-sectional view of a facing portion between the crushing type homovalve seat and the homovalve. FIG. 3 is a perspective view of a crushing type homo valve seat. FIG. 4 is a perspective view of a non-crushing homo valve seat.

The nonwoven fabric of the present invention contains cellulose fibers having an average fiber diameter of 0.1 to 50 μm and polyolefin fibers having an average fiber diameter of 1.5 μm or less.

[Cellulose fiber]
Cellulose fibers are not particularly limited as long as they are polysaccharides having a β-1,4-glucan structure, and cellulose fibers derived from higher plants [eg, wood fibers (wood pulp of conifers, hardwoods, etc.), bamboo fibers, etc. , Natural cellulose fibers such as sugarcane fibers, seed hair fibers (cotton linters, Bombax cotton, kapok, etc.), gin leather fibers (eg, hemp, mulberry, mitsumata, etc.), leaf fibers (eg, Manila hemp, New Zealand hemp) Pulp fibers) etc.], animal-derived cellulose fibers (eg, squirt cellulose), bacteria-derived cellulose fibers, chemically synthesized cellulose fibers [cellulose acetate (cellulose acetate), cellulose propionate, cellulose butyrate, cellulose acetate Propionate, cellulose acetate Organic acid esters such as rate; inorganic acid esters such as cellulose nitrate, cellulose sulfate, and cellulose phosphate; mixed acid esters such as cellulose nitrate acetate; hydroxyalkyl cellulose (eg, hydroxyethyl cellulose (HEC), hydroxypropyl cellulose, etc.); carboxyalkyl Cellulose (carboxymethyl cellulose (CMC), carboxyethyl cellulose, etc.); alkyl cellulose (methyl cellulose, ethyl cellulose, etc.); and cellulose derivatives such as regenerated cellulose (rayon, cellophane, etc.). These cellulose fibers may be used alone or in combination of two or more.

Further, the cellulose fiber is a high-purity cellulose having a high α-cellulose content, for example, an α-cellulose content of 70 to 100% by weight (eg, 95 to 100% by weight), preferably 98 to 100% by weight, depending on the application. % May be sufficient. Furthermore, in the present invention, cellulose fibers having a uniform fiber diameter can be prepared by using high-purity cellulose having a low lignin or hemicellulose content, even if wood fibers or seed hair fibers are used. Cellulose having a low lignin or hemicellulose content is particularly a cellulose having a kappa number (κ value) of 30 or less (eg, 0 to 30), preferably 0 to 20, more preferably 0 to 10 (particularly 0 to 5). There may be. The kappa number can be measured by a method based on “Pulp-Kappa number test method” of JIS P8211.

Among these cellulose fibers, it is easy to adjust to an appropriate fiber diameter by microfibrillation, so plant-derived cellulose, such as wood fibers (wood pulp such as conifers and hardwoods) and seed hair fibers (such as cotton linter pulp) Pulp-derived cellulose such as is preferred. As the pulp, pulp obtained by the same method as the cellulose fiber can be used, but as the cellulose fiber, the entanglement of the raw material fibers is suppressed, and efficient microfibrillation is realized by beating treatment and homogenization treatment. From the viewpoint of obtaining fibers having a uniform fiber diameter, never dry pulp, that is, pulp having no drying history (pulp that has been kept wet without being dried) is particularly preferable.

In addition, when using a pulp as a cellulose fiber, a pulp is obtained by a mechanical method (pulverized wood pulp, refiner ground pulp, thermomechanical pulp, semichemical pulp, chemiground pulp, etc.), or a chemical method. Or the like (craft pulp, sulfite pulp, etc.) obtained in the above, or beating fibers (beating pulp, etc.) subjected to beating (preliminary beating) as described later, if necessary. Further, the cellulose fiber may be a fiber subjected to a conventional purification treatment such as degreasing treatment (for example, absorbent cotton).

In particular, the cellulose fiber may be a fiber derived from never dry pulp which is formed of wood fiber and / or seed hair fiber and has a kappa number of 30 or less (particularly about 0 to 10). Such pulp may be prepared by bleaching wood fibers and / or seed hair fibers with chlorine.

In the present invention, the average fiber diameter of cellulose fibers is less than a micron order. That is, the average fiber diameter is 0.1 to 50 μm, for example, 0.15 to 30 μm, preferably 0.2 to 10 μm, and more preferably 0.25 to 5 μm (particularly 0.25 to 1 μm). In the present invention, since the cellulose fiber has such a fiber diameter, it is easy to make paper and has excellent productivity, and a non-woven fabric suitable for power storage elements such as batteries and capacitors and filters can be prepared.

Furthermore, the standard deviation of the fiber diameter distribution is, for example, 1 μm or less (for example, 5 to 1000 nm), preferably 8 to 500 nm, and more preferably about 10 to 100 nm. In this invention, since the fiber diameter of the cellulose fiber which comprises a nonwoven fabric is uniform, the hole diameter of a nonwoven fabric can be equalized.

The average fiber length of the cellulose fibers is not particularly limited, but is preferably 0.01 mm or more, for example, 0.05 to 10 mm, preferably from the viewpoint that the fibers can be appropriately entangled to ensure the strength of the nonwoven fabric. The thickness is about 0.1 to 5 mm, more preferably about 0.2 to 3 mm (particularly 0.3 to 1 mm). The average fiber length (average aspect ratio) with respect to the average fiber diameter of the cellulose fibers may be, for example, about 100 to 10,000, preferably about 200 to 5,000, more preferably about 300 to 3,000 (particularly 400 to 2,000).

In the present invention, the average fiber diameter and the standard deviation of the fiber diameter distribution are values calculated from the fiber diameter (about n = 20) measured based on an electron micrograph.

The dehydration time of the cellulose fiber is, for example, 1000 seconds or more, preferably 1200 to 10000 seconds, when measured using a fiber slurry having a concentration of 0.5% by weight in accordance with a test method for dewatering amount of API standard. More preferably, it is about 1500 to 8000 seconds (especially 1800 to 7000 seconds). The longer the dehydration time, the higher the average fiber length / average fiber diameter ratio, and the higher the water retention, the better the mechanical properties.

Cellulose fibers are highly dispersible in water and can form a stable dispersion (or suspension). For example, the viscosity of a suspension in which cellulose nanofibers are suspended in water to a concentration of 2% by weight is 2000 mPa · s or more, preferably 3000 to 15000 mPa · s, more preferably about 5000 to 10000 mPa · s. It is. The viscosity was measured using a B-type viscometer using a rotor No. 4 is a value measured as an apparent viscosity at 25 ° C. at a rotation speed of 60 rpm. If the degree of fibrillation is small or the fiber diameter is large, the dispersibility in water decreases, a uniform suspension cannot be obtained, and the viscosity cannot be measured.

[Method for producing cellulose fiber]
Cellulose fibers may be natural pulp or the like, but are usually obtained by microfibrillation of raw material cellulose fibers, and more specifically, dispersion in which raw material cellulose fibers are dispersed in a solvent to prepare a dispersion. You may manufacture through the liquid preparation process and the refiner process which beats a raw material cellulose fiber and makes it microfibril.

(Dispersion preparation process)
The average fiber length of the raw fiber is, for example, 0.01 to 20 mm, preferably 0.05 to 10 mm, more preferably about 0.06 to 8 mm, and usually about 0.1 to 5 mm. The average fiber diameter of the raw fiber is about 0.01 to 500 μm, preferably about 0.05 to 400 μm, more preferably about 0.1 to 300 μm (particularly about 0.2 to 250 μm).

The solvent is not particularly limited as long as it does not cause chemical or physical damage to the raw fiber. For example, water, organic solvents [alcohols (C _1-4 alkanols such as methanol, ethanol, 2-propanol, isopropanol etc.), Ethers (diC _1-4 alkyl ethers such as diethyl ether and diisopropyl ether, cyclic ethers such as tetrahydrofuran (cyclic C _4-6 ethers and the like)), esters (alkanoic esters such as ethyl acetate), ketones (acetone, DiC _1-5 alkyl ketones such as methyl ethyl ketone and methyl butyl ketone, C _4-10 cycloalkanones such as cyclohexanone), aromatic hydrocarbons (toluene, xylene, etc.), halogenated hydrocarbons (methyl chloride, fluorine, etc.) Etc.) That.

These solvents may be used alone or in combination of two or more. Of these solvents, water is preferable from the viewpoint of productivity and cost. If necessary, a mixed solvent of water and an aqueous organic solvent (C _1-4 alkanol, acetone, etc.) may be used.

The raw fiber to be subjected to the refiner treatment may be in a state of coexisting at least in the solvent, and the raw fiber may be dispersed (or suspended) in the solvent prior to the refiner treatment. Dispersion may be performed using, for example, a conventional disperser (such as an ultrasonic disperser, a homodisper, or a three-one motor). The disperser may include mechanical stirring means (such as a stirring bar and a stirring bar).

The concentration of the raw fiber in the solvent is, for example, about 0.01 to 20% by weight, preferably about 0.05 to 10% by weight, more preferably about 0.1 to 5% by weight (particularly about 0.5 to 3% by weight). It may be.

(Refiner process)
In the refiner process, a disk refiner (single disk refiner, double disk refiner, etc.) can be used. The disc refiner has a disc clearance of about 0.1 to 0.3 mm, preferably about 0.12 to 0.28 mm, more preferably about 0.13 to 0.25 mm (eg, 0.14 to 0.23 mm). May be.

The rotational speed of the disk is not particularly limited, and can be selected from a wide range of 1,000 to 10,000 rpm. For example, 1,000 to 8,000 rpm, preferably 1,300 to 6,000 rpm, more preferably 1,000 rpm. It may be about 600 to 4,000 rpm.

In the refiner processing, the number of processing (passing) may be about 1 to 20 times, preferably about 2 to 15 times, more preferably about 3 to 10 times (for example, 4 to 9 times).

The degree of the beating process of the raw fiber may be, for example, such that the Canadian freeness value (CSF) falls within the above range. Note that the degree of the beating process can be adjusted by the disc clearance and the number of refiner processes. If the disk clearance is too narrow or the number of treatments is too high, the raw fiber will receive a large shearing force, fibrillation will proceed, twisting and roughening of the surface will occur, and the fibers will tend to get entangled. The dispersibility of the fibrillated fibers is reduced. On the other hand, if the disk clearance is too wide, the shearing force applied to the raw fiber becomes small, and an undivided portion remains.

Further, when the cellulose fiber is a nanometer-sized fiber, it may be further subjected to a homogenization step using a non-crushing type homovalve sheet after the refiner step, like the polyolefin fiber described later.

[Polyolefin fiber]
In the present invention, the polyolefin fiber has a role as a binder fiber (or paper strength enhancer) and also has a role of providing a shutdown function to the nonwoven fabric by increasing the blending ratio.

The polyolefin constituting the polyolefin fiber may be a polymer containing C _2-6 olefin units such as ethylene and propylene. Examples of polyolefins include C _2-6 olefin homopolymers or copolymers (polyethylene resins such as polyethylene and ethylene-propylene copolymers, polypropylene such as polypropylene, propylene-ethylene copolymers, and propylene-butene copolymers). Resin, poly (methylpentene-1), propylene-methylpentene copolymer, etc.), copolymer of _C2-6 olefin and copolymerizable monomer (ethylene-vinyl acetate copolymer, ethylene-vinyl) Copolymers such as alcohol copolymers, ethylene- (meth) acrylic acid copolymers, ethylene- (meth) acrylic acid copolymers or salts thereof (for example, ionomer resins), ethylene- (meth) acrylic acid ester copolymers, etc. These polyolefins may be used alone or in combination of two or more. You can use.

Of these polyolefins, polyethylene resins are preferable because they have appropriate heat resistance and can provide a shutdown function when used as a battery or capacitor separator.

Examples of polyethylene resins include low, medium or high density polyethylene, linear polyethylene (for example, linear low density polyethylene), branched polyethylene, low molecular weight polyethylene, ionomer, chlorinated polyethylene, ethylene-propylene. Copolymer, ethylene-butene-1 copolymer, ethylene-propylene-butene-1 copolymer, ethylene- (4-methylpentene-1) copolymer, ethylene-vinyl acetate copolymer, ethylene- (meta ) Acrylic acid copolymer or its ionomer, ethylene- (meth) acrylate copolymer such as ethylene-ethyl acrylate copolymer, and the like. These polyethylene resins can be used alone or in combination of two or more. In these polyethylene resins, the ethylene content (ratio of ethylene units in all units of the polymer) is, for example, 85 to 100 mol%, preferably 90 to 100 mol%, more preferably 95 to 100 mol% (particularly 98 to 100 mol%). About 100 mol%). In particular, among these polyethylene resins, low, medium or high density polyethylene, linear low density polyethylene and the like are preferable, and medium or high density polyethylene (particularly high density polyethylene) is particularly preferable.

The melting point or softening point of polyolefin (especially polyethylene resin) may be 100 ° C. or more from the viewpoint of heat resistance, for example, 100 to 150 ° C., preferably 110 to 145 ° C., more preferably 120 to 140 ° C. ( In particular, it is about 130 to 138 ° C. When the melting point or softening point of the polyolefin is within this range, it has moderate heat resistance, is electrochemically stable when used as a battery or capacitor separator, and can exhibit a shutdown function.

The average fiber diameter of the polyolefin fiber is 1.5 μm or less (for example, 10 to 1500 nm), for example, about 10 to 1000 nm, preferably about 100 to 900 nm, more preferably about 300 to 800 nm (particularly 500 to 700 nm). The standard deviation of the fiber diameter distribution is, for example, 1 μm or less (for example, 10 to 1000 nm), preferably 50 to 800 nm, and more preferably about 100 to 500 nm. In this invention, since the fiber diameter of the polyolefin fiber which comprises a nonwoven fabric is uniform, the hole diameter of a nonwoven fabric can be equalize | homogenized.

The ratio of the average fiber diameter of the cellulose fibers to the average fiber diameter of the polyolefin fibers can be selected from the range of the former / the latter = 1000/1 to 1/1000, for example, 100/1 to 1/100, preferably 10 / It may be about 1 to 1/10, more preferably about 5/1 to 1/5 (particularly 1/1 to 1/3). When both fiber diameter ratios are within this range, both fibers are easily mixed and a uniform pore diameter is easily formed.

The average fiber length of the polyolefin fibers can be selected from a range of about 1 to 1000 μm. However, from the viewpoint of improving the mechanical properties of the nonwoven fabric, for example, 10 to 500 μm, preferably 50 to 400 μm, more preferably 100 to 300 μm (particularly 150 to 150 μm). About 200 μm). Further, the ratio of the average fiber length to the average fiber diameter (average fiber length / average fiber diameter) (average aspect ratio) is 10 or more, for example, 10 to 10,000, preferably 50 to 5000, more preferably 100 to 3000 ( In particular, it is about 200 to 1000). In this invention, since it has such fiber length and aspect ratio, since the cellulose fiber and polyolefin fiber or polyolefin fiber are intertwined moderately, the intensity | strength of a nonwoven fabric can be improved.

In the present invention, the average fiber diameter, the standard deviation of the fiber diameter distribution, and the maximum fiber diameter are values calculated from the fiber diameter (about n = 20) measured based on an electron micrograph.

The cross-sectional shape (cross-sectional shape perpendicular to the longitudinal direction of the fiber) of the polyolefin fiber may be an isotropic shape (for example, a substantially circular shape such as a perfect circle shape or a regular polygon shape), or an anisotropic shape (flat shape) Shape, oval shape, etc.). In the case of a substantially isotropic shape, the ratio of the major axis to the minor axis (average aspect ratio) is, for example, 1 to 2, preferably 1 to 1.5, more preferably 1 to 1.3 (particularly 1 to 1.2). It may be a degree.

The Canadian standard freeness (CSF) of the polyolefin fiber may be, for example, about 100 to 600 ml, preferably 150 to 500 ml, and more preferably about 200 to 400 ml.

[Production method of polyolefin fiber]
The polyolefin fiber is usually obtained by microfibrillation of a raw material polyolefin fiber. The average fiber length of the raw material polyolefin fiber is 0.01 to 5 mm, preferably 0.03 to 4 mm, more preferably 0.05 to 3 mm (particularly 0.1 to 2 mm), and usually 0.1 to 5 mm. Degree. The average fiber diameter of the raw polyolefin fibers is about 0.01 to 50 μm, preferably 0.05 to 40 μm, more preferably about 0.1 to 30 μm (for example, 0.2 to 25 μm).

Specifically, the microfibrillation method includes a dispersion preparation step in which a raw material fiber is dispersed in a solvent to prepare a dispersion, and a homogenization step in which the dispersion is homogenized with a homogenizer equipped with a crushing type homovalve sheet. Obtained by the manufacturing method. In the present invention, in particular, polyolefin fibers having an average fiber diameter of 1.5 μm or less can be prepared by microfibrillation of raw material fibers by the production method shown below.

In the dispersion preparation step, a dispersion can be prepared by the same method as the cellulose fiber.

The homogenization process will be described with reference to the drawings. FIG. 1 is a schematic view showing a process of homogenizing the dispersion with a homogenizer equipped with a crushing type homo-valve sheet, and FIG. 2 is an enlarged cross-sectional view of a facing portion between the crushing type homo-valve sheet and the homo-valve. FIG. 3 is a perspective view of a crushing type homo-valve seat. On the other hand, FIG. 4 is a perspective view of a non-crushing homo valve seat.

The homogenizer includes a hollow cylindrical impact ring 6, a hollow cylindrical convex portion 2 b of the homovalve seat 2 that is inserted and disposed on the upstream side of the impact ring 6, and a hollow cylinder on the downstream side of the impact ring 6. A cylindrical homobulb 5 inserted opposite to the cylindrical convex portion 2b is provided, and the hollow cylindrical convex portion 2b and the columnar homobulb 5 have the same outer diameter. In addition, the inner wall on the downstream side of the hollow cylindrical convex portion 2b has a tapered portion (inclined surface) 2d that expands in the downstream direction, and the downstream end of the hollow cylindrical convex portion 2b has an inner diameter d and a thickness t of the end surface. A thin ring-shaped end face 2c having the shape is formed. Further, the ring-shaped end face 2c, the homo valve 5 and the impact ring 6 form a small diameter orifice (gap) 4.

In the present invention, the use of the crushing type homo-valve seat 2 is a great feature. The crushing type homo-valve seat 2 is a hollow member having a cylindrical flow path 3 therein, and extends in a downstream direction from a hollow disc-shaped main body portion 2a having an inflow port 3a and an inner wall of the disc-shaped main body portion 2a. And it is comprised with the hollow cylindrical convex part 2b which has the outflow port 3b. Furthermore, as described above, the crushing type homovalve seat 2 is formed with the tapered portion 2d having an enlarged inner diameter, so that compared to the general (normal) noncrushing type homovalve seat 12 shown in FIG. The ring-shaped end surface 2c that forms the outlet 3b is formed thin.

In such a homogenization process using a homogenizer, as shown in FIG. 1, the dispersion liquid containing the raw fiber 1 flows into the flow path 3 in the homo valve seat from the inlet 3a of the crushing homo valve seat 2, and the flow path After passing through 3, it passes through the small-diameter orifice 4 and becomes a dispersion containing polyolefin fibers 7. Specifically, in the processing by the homogenizer, the raw material fiber 1 that is pumped through the homogenizer at high pressure collides with the wall surface of the small diameter orifice 4 (particularly the wall surface of the impact ring 6) when passing through the small diameter orifice 4 that is a narrow gap. Thus, the polyolefin fiber 7 is divided by receiving a shearing stress or a cutting action and has a uniform fiber diameter. In particular, when the dispersion liquid that has passed through the flow path 3 in the homo valve seat passes through the gap formed by the homo valve seat 2 and the homo valve 5, the flow speed of the dispersion liquid increases rapidly. The pumping pressure of the dispersion rapidly decreases in inverse proportion to the increase in. Therefore, the pressure difference of the dispersion liquid can be increased, the cavitation of the dispersion liquid that has passed through the gap becomes intense, and the uniform microfibril of the raw fiber 1 is increased due to the increase of the collision force with the wall surface in the small diameter orifice 4 and the collapse of the bubbles. It can be inferred that this has been realized.

In order to effectively perform such microfibrillation, it is possible to reduce the thickness of the end surface of the wall portion forming the outlet of the crushing type homovalve seat (the ring-shaped end surface at the downstream end of the hollow cylindrical convex portion). Although it is important, specifically, the ratio between the inner diameter d of the downstream end of the hollow cylindrical convex portion and the thickness t of the ring-shaped end surface of the downstream end in the crush-type homovalve seat is expressed by the former / the latter = 100/1. Adjusted to about 5/1, preferably about 80/1 to 6/1 (for example, 50/1 to 8/1), more preferably about 30/1 to 10/1 (especially 20/1 to 12/1). . When the ratio between the two is within this range, a rapid decrease in the pressure of the dispersion liquid passing through the gap between the homovalve seat and the homovalve can be realized, and the raw fibers can be divided into nanometer-sized uniform fiber diameters. The thickness of the end face of the wall portion forming the outlet can be selected according to the diameter of the outlet, but is usually 0.01 to 2 mm, preferably 0.05 to 1.5 mm, more preferably 0.1 to 1 mm. (Especially 0.2 to 0.8 mm).

The interval or clearance of the small diameter orifice (especially the interval between the end face of the convex portion of the homovalve seat and the homovalve) is, for example, about 5 to 50 μm, preferably 10 to 40 μm, more preferably 15 to 35 μm (particularly 20 to 30 μm). is there.

In such a homogenizer, the pressure for passing through the small-diameter orifice (or the pressure for feeding the dispersion liquid to the homogenizer (or treatment pressure)) can be selected from the range of about 30 to 200 MPa, preferably 35 to 150 MPa, More preferably, it may be about 40 to 140 MPa. In this invention, it can divide | segment into an ultrafine and uniform fiber diameter by pumping a dispersion liquid with such a high pressure with respect to the homogenizer provided with the crushing-type homovalve seat.

Further, by repeatedly passing through the small-diameter orifice and colliding with the wall surface, the degree of microfibrillation of the raw fiber can be appropriately adjusted. The number of treatments (or the number of passes) that pass through the small-diameter orifice can be selected from a range of, for example, about 5 to 100 times, preferably 10 to 80 times, and more preferably about 12 to 60 times.

Further, the treatment pressure may be selected according to the number of treatments. For example, when the treatment pressure is a high-pressure treatment (eg, about 60 to 200 MPa, preferably about 80 to 150 MPa, more preferably about 100 to 130 MPa), The number of times is, for example, about 3 to 50 times, preferably about 5 to 20 times, and more preferably about 7 to 15 times. On the other hand, when the treatment pressure is low-pressure treatment (for example, about 20 to 80 MPa, preferably about 30 to 70 MPa, more preferably about 40 to 60 MPa), the number of treatments is, for example, 5 to 100 times, preferably 10 to 50 times, Preferably about 15 to 30 times.

Generally, in the homogenization treatment, if the treatment pressure is too high or the number of treatments is too high, the fiber is subjected to a large shearing force, causing the fiber to be cut or twisted, resulting in loss of fiber properties or fibrillation. In addition, since strong entanglement between the fibers occurs, the dispersibility of the fibers tends to decrease. On the other hand, in this invention, these problems can be eliminated by using a crushing type homo valve seat.

In the homogenization step, a homogenization process using a homogenizer equipped with a non-crushing type homo valve seat may be combined. In particular, as a pre-process (preliminary process) of a homogenization process (particularly, a high-pressure process of 60 MPa or more) using a homogenizer provided with the crushing type homovalve seat, a homogenization process may be performed using a homogenizer provided with a non-crushing type homogenizer. In the homogenization step, pretreatment with a homogenizer provided with a non-crushing type homovalve sheet can improve the processing efficiency in the homogenizer provided with a crushing type homovalve sheet.

In the non-crushing type homo-valve seat, as shown in FIG. 4, a tapered portion is usually formed on the inner wall of the hollow cylindrical convex portion 12 b extending from the hollow disc-shaped main body portion 12 a of the homo-valve seat 12. First, the ratio of the inner diameter of the downstream end of the hollow cylindrical convex portion of the homovalve seat to the thickness of the ring-shaped end surface of the downstream end is usually the former / the latter = 3/1 to 1/1 (especially 2.5 / 1 to 1.5 / 1).

In the homogenizer provided with the non-crushing type homovalve seat, the pressure for passing through the small-diameter orifice (or the pressure for feeding the dispersion liquid to the homogenizer (or processing pressure)) is, for example, 30 to 100 MPa, preferably 35 to 80 MPa, More preferably, it may be about 40 to 70 MPa. The number of passes may be, for example, about 10 to 40 times, preferably about 12 to 30 times, and more preferably about 15 to 25 times.

Also in the polyolefin fiber manufacturing method, the dispersion may be refined as a pre-process (preliminary process) of the homogenization process. As a refiner process, you may perform the refiner process similar to the manufacturing method of the said cellulose fiber.

When both the cellulose fiber and the polyolefin fiber are microfibrillated, the microfibrillation of both fibers may be either a method of separately processing or a method of simultaneously processing.

[Nonwoven fabric and production method thereof]
In the nonwoven fabric (paper body) of the present invention, the ratio (weight ratio) between cellulose fibers and polyolefin fibers can be selected from the range of the former / the latter = about 99.9 / 0.1 to 10/90. It is about 1-20 / 80, preferably 98 / 2-30 / 70, and more preferably about 97 / 3-40 / 60.

Furthermore, the ratio of the two can be appropriately selected depending on the application, and in the separator for an electricity storage element (especially a battery or capacitor separator) that requires a shutdown function, the ratio (weight ratio) of cellulose fiber to polyolefin fiber is The latter = 70/30 to 20/80, preferably 65/35 to 25/75, more preferably about 60/40 to 30/70 (particularly 55/45 to 40/60). In such a ratio, the shutdown function is manifested by the polyolefin fibers melted at a high temperature closing the pores of the separator.

On the other hand, in applications that require hydrophilicity (for example, aqueous filters), the former / the latter = 99.9 / 0.1 to 50/50, preferably 99.5 / 0.5 to 70/30, more preferably It is about 99/1 to 80/20 (particularly 97/3 to 10/90).

The non-woven fabric of the present invention is a conventional additive such as a sizing agent, wax, inorganic filler, colorant, stabilizer (antioxidant, heat stabilizer, ultraviolet absorber, etc.), plasticizer depending on the application. Further, it may contain an antistatic agent, a flame retardant and the like. In addition, since the nonwoven fabric of the present invention includes polyolefin fibers that also function as binder fibers as described above, other synthetic resins, binder fibers such as vinylon fibers, paper strength enhancers such as polyacrylamide, starch, and natural rubber. May not be included. In particular, since the nonwoven fabric of the present invention does not contain binder fibers having a low melting point such as vinylon fibers, the nonwoven fabric has high heat resistance and is electrochemically stable. That is, it is preferable that the nonwoven fabric of this invention does not contain a hydrophilic binder fiber substantially. Moreover, it is preferable that the nonwoven fabric of this invention does not contain the synthetic resin below melting | fusing point less than 100 degreeC substantially. In addition, since the nonwoven fabric of this invention does not contain polyacrylamide with a possibility of carcinogenicity as a paper strength enhancer, it is also highly safe.

The nonwoven fabric of the present invention is excellent in mechanical properties, has high strength even when thin, and has a tensile strength of 12 N / 15 mm or more at a basis weight of 10 g / m ² , for example, 12 to 30 N / 15 mm, preferably 13 to It is about 25 N / 15 mm, more preferably 14 to 20 N / 15 mm (especially 15 to 18 N / 15 mm).

The nonwoven fabric of the present invention is excellent in air permeability despite having the above tensile strength, and the air permeability at a basis weight of 10 g / m ² is 10 to 500 seconds / 100 ml. It is about 300 seconds / 100 ml, preferably 30 to 200 seconds / 100 ml, more preferably about 50 to 100 seconds / 100 ml (especially 60 to 80 seconds / 100 ml).

The non-woven fabric of the present invention has a thickness of 20 μm or less, for example, 1 to 20 μm, preferably 5 to 19 μm (eg 10 to 18 μm), more preferably 12 to 17 μm (especially 13 to 16 μm). Good. A nonwoven fabric may laminate | stack a some nonwoven fabric according to the objective.

The average pore diameter of the nonwoven fabric of the present invention is 0.1 to 50 μm, for example, 0.15 to 30 μm, preferably 0.2 to 10 μm, more preferably 0.25 to 5 μm (especially 0.25 to 1 μm). is there.

The basis weight of the nonwoven fabric may be, for example, about 0.1 to 50 g / m ² , preferably 1 to 30 g / m ² , more preferably 3 to 20 g / m ² (particularly 5 to 15 g / m ² ). . The porosity of the nonwoven fabric may be 50% or more, preferably 50 to 90%, more preferably about 60 to 80%.

The method for producing the nonwoven fabric of the present invention is not particularly limited, and can be produced by a conventional method, for example, by mixing cellulose fibers and polyolefin fibers and making paper such as wet papermaking or dry papermaking. Further, when cellulose fibers and polyolefin fibers are collectively microfibrillated, they may be produced by papermaking the mixed cotton fibers of both. The wet papermaking can be performed by a conventional method, and for example, the papermaking may be performed using a wet papermaking machine equipped with a manual papermaking machine or a perforated plate. Dry papermaking can also be made using conventional methods such as airlaid and card manufacturing. Further, when used as a separator in an electricity storage device such as a battery, for example, press at a pressure of about 0.1 to 100 MPa, preferably 0.3 to 50 MPa, more preferably 0.5 to 30 MPa (particularly 1 to 10 MPa). It may be processed. The temperature of the press working is not particularly limited, and can be selected, for example, from a range of about 60 to 250 ° C., for example, 80 to 200 ° C., preferably about 100 to 180 ° C. In the case of a separator, the temperature is lower than the melting point (or softening point) of the polyolefin fiber, for example, about 80 to 150 ° C., preferably 90 to 140 ° C., more preferably 100 to 130 ° C. (especially 110 to 130 ° C.). May be.

In the present invention, since cellulose fibers having a moderately large fiber diameter of 100 nm or more include polyolefin fibers having a moderate fiber diameter, paper can be easily made and productivity is high.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. Evaluation of the nonwoven fabric obtained by the Example and the comparative example was measured with the following method.

[Fiber diameter]
About the cellulose fiber or cellulose nanofiber obtained by the Example and the comparative example, the 50000 times scanning electron microscope (SEM) photograph was image | photographed, and two lines are drawn in the arbitrary positions which cross a photograph on the photographed photograph. The average fiber diameter (n = 20 or more) was calculated by counting all fiber diameters intersecting the line. The method of drawing a line is not particularly limited as long as the number of fibers crossing the line is 20 or more. Furthermore, the standard deviation of the fiber diameter distribution and the maximum fiber diameter were determined from the measured values of the fiber diameter. In addition, in the case of the cellulose fiber whose maximum fiber diameter exceeds 1 μm, the calculation was performed using a 5000 times SEM photograph.

[Fiber length]
The fiber length was measured using a fiber length measuring device (“FS-200” manufactured by Kajaani).

[Average pore size]
The nonwoven fabrics obtained in the examples and comparative examples were photographed with a scanning electron microscope (SEM) at a magnification of 5000 times, and only 50 pore diameters on the outermost surface were extracted to obtain an average pore diameter.

[Air permeability]
In accordance with JIS P8117, the time required for 100 ml of air to pass through was measured by the Gurley method.

[Tensile strength]
According to JIS P8113, the obtained non-woven fabric was cut into a strip shape having a width of 15 mm and a length of 250 mm to obtain a sample. The tensile strength was measured at / min. The tensile strength was measured in the length direction (or longitudinal direction).

Example 1
100 liters of slurry containing 1% by weight of raw material polyolefin fiber is prepared using polyolefin fiber ("SWP E400" manufactured by Mitsui Chemicals, average fiber length 0.9 mm, CSF 580 ml) as raw material polyolefin fiber did. This slurry liquid was processed using a homogenizer (manufactured by Gorin, 15M8AT) equipped with a crushing type homovalve sheet (inner diameter of the downstream end of the hollow cylindrical convex portion / thickness of the ring-shaped end face = 16.8 / 1). The treatment was performed 20 times at a pressure of 50 MPa. The average fiber diameter of the obtained polyolefin fiber was 0.6 μm, the standard deviation of the fiber diameter distribution was 253 nm, the average fiber length was 182 μm, and the aspect ratio (average fiber length / average fiber diameter) was 303.

Further, 0.2 weight of slurry obtained by mixing 5 parts by weight of the polyolefin fiber and 95 parts by weight of cellulose fiber (“Cerish KY100G” manufactured by Daicel Chemical Industries, average fiber diameter 0.3 μm, average fiber length 420 μm) is mixed. The paper machine with a decompression device (“Standard Square Machine” manufactured by Toyo Seiki Seisakusho Co., Ltd.) was used. Papermaking was performed using 5C filter paper as a filter cloth. As a blotting paper, no. Stacked 5C filter paper. Next, the paper body was immersed in isopropyl alcohol for 10 minutes with ultrasonic treatment to replace the solvent. Furthermore, the new No. Both surfaces were sandwiched between 5C filter papers and pressed at 180 ° C. and a pressure of 5 MPa for 5 minutes. Then, it was attached to a drum dryer (manufactured by Kumagai Riki Kogyo Co., Ltd.) whose surface temperature was set to 100 ° C. and dried for 120 seconds. Table 1 shows the basis weight, thickness, average pore diameter, air permeability, and tensile strength of the obtained nonwoven fabric.

Example 2
In Example 1, a mixed slurry in which the ratio of polyolefin fiber to cellulose fiber was changed to 50 parts by weight of polyolefin fiber and 50 parts by weight of cellulose was diluted to 0.2% by weight, and a paper machine with a decompression device (Toyo Incorporated) Using a “standard square machine” manufactured by Seiki Seisakusho, Papermaking was performed using 5C filter paper as a filter cloth. As a blotting paper, no. Stacked 5C filter paper. Next, the paper body was immersed in isopropyl alcohol for 10 minutes with ultrasonic treatment to replace the solvent. Furthermore, the new No. Both surfaces were sandwiched between 5C filter papers and pressed at 120 ° C. and a pressure of 1 MPa for 1 minute. Then, it was attached to a drum dryer (manufactured by Kumagai Riki Kogyo Co., Ltd.) whose surface temperature was set to 100 ° C. and dried for 120 seconds. Table 1 shows the basis weight, thickness, average pore diameter, air permeability, and tensile strength of the obtained nonwoven fabric.

Further, the obtained non-woven fabric was sandwiched between stainless steel plates having a thickness of 1 mm, placed in a dryer at 140 ° C., and left for 1 hour. The air permeability of the nonwoven fabric after standing was not measurable (infinite). That is, it was found that this nonwoven fabric is a cellulose-based nonwoven fabric having a shutdown function.

Example 3
Using a normal non-crushing type homo valve seat (inner diameter of the downstream end of the hollow cylindrical convex portion / ring end face thickness = 1.9 / 1) using a homogenizer (manufactured by Gorin, 15M8AT), a processing pressure of 50 MPa The nonwoven fabric was obtained in the same manner as in Example 2 except that a polyolefin fiber having an average fiber diameter of 0.9 μm, a standard deviation of the fiber diameter distribution of 488 nm, an average fiber length of 537 μm, and an aspect ratio of 597 was obtained. Table 1 shows the basis weight, thickness, average pore diameter, air permeability, and tensile strength of the obtained nonwoven fabric.

Comparative Example 1
100 liters of slurry containing 1% by weight of raw material polyolefin fiber is prepared using polyolefin fiber ("SWP E400" manufactured by Mitsui Chemicals, average fiber length 0.9 mm, CSF 580 ml) as raw material polyolefin fiber did. Using this slurry liquid, a homogenizer (manufactured by Gorin, 15M8AT) equipped with a normal non-crushing type homovalve sheet (inner diameter at the downstream end of the hollow cylindrical convex portion / thickness of the ring-shaped end face = 1.9 / 1). Then, it was processed three times at a processing pressure of 50 MPa. The polyolefin fiber obtained had an average fiber diameter of 2.1 μm, a standard deviation of the fiber diameter distribution of 2.5 μm, an average fiber length of 1.2 mm, and an aspect ratio (average fiber length / average fiber diameter) of 571.

Furthermore, a nonwoven fabric was obtained in the same manner as in Example 1 using a slurry in which 5 parts by weight of the obtained polyolefin fiber and 95 parts by weight of cellulose fiber (Cerish KY100G) were mixed. Table 1 shows the basis weight, thickness, average pore diameter, air permeability, and tensile strength of the obtained nonwoven fabric.

Comparative Example 2
A nonwoven fabric was obtained in the same manner as in Comparative Example 1 except that the mixed slurry was used in which the ratio of the polyolefin fiber to the cellulose fiber was changed to 70 parts by weight of the polyolefin fiber and 30 parts by weight of the cellulose. Table 1 shows the basis weight, thickness, average pore diameter, air permeability, and tensile strength of the obtained nonwoven fabric.

As is clear from the results in Table 1, the nonwoven fabrics of the examples have high air permeability and tensile strength. On the other hand, the nonwoven fabric of the comparative example has low tensile strength.

The nonwoven fabric of the present invention can be used for various separators and filters, but because of its high electrochemical stability, the battery (lithium battery, lithium secondary battery, fuel cell, alkaline secondary battery, nickel metal hydride secondary battery, (Nickel-cadmium battery, lead storage battery, etc.), capacitors, capacitors and other storage element separators are useful. In particular, since the shutdown function can be imparted by constituting the nonwoven fabric with a predetermined amount of polyolefin fiber, it is useful for battery and capacitor separators.

DESCRIPTION OF SYMBOLS 1 ... Raw fiber 2 ... Crushing type | mold homo valve seat 3 ... Flow path of crushing type | mold homo valve seat 4 ... Small diameter orifice 5 ... Homo valve 6 ... Impact ring 7 ... Polyolefin fiber 12 ... Non-crushing type homo valve seat

Claims (17)

1. A nonwoven fabric comprising cellulose fibers having an average fiber diameter of 0.1 to 50 μm and polyolefin fibers having an average fiber diameter of 1.5 μm or less and having a thickness of 20 μm or less.
2. The nonwoven fabric according to claim 1, wherein the polyolefin fiber has an average fiber diameter of 10 to 1000 nm.
3. The nonwoven fabric according to claim 1 or 2, wherein the polyolefin fibers have an average fiber length of 1 to 1000 µm.
4. The nonwoven fabric according to any one of claims 1 to 3, wherein the polyolefin fiber is a polyethylene fiber.
5. Claims wherein the polyolefin fiber is obtained by a production method including a dispersion preparation step of preparing a dispersion by dispersing raw polyolefin fibers in a solvent, and a homogenization step of homogenizing the dispersion with a homogenizer equipped with a crushing type homovalve sheet. Item 5. The nonwoven fabric according to any one of Items 1 to 4.
6. The nonwoven fabric according to any one of claims 1 to 5, wherein the average fiber diameter of the cellulose fibers is 0.2 to 1 µm.
7. The nonwoven fabric according to any one of claims 1 to 6, wherein the ratio (weight ratio) of cellulose fiber to polyolefin fiber is the former / the latter = 99.9 / 0.1 to 10/90.
8. The nonwoven fabric according to any one of claims 1 to 7, which is substantially free of hydrophilic binder fibers.
9. The nonwoven fabric according to any one of claims 1 to 8, which is substantially free of a synthetic resin having a melting point of less than 100 ° C.
10. The nonwoven fabric according to any one of claims 1 to 9, having a tensile strength of 12 N / 15 mm or more at a basis weight of 10 g / m ² .
11. The nonwoven fabric according to any one of claims 1 to 10, wherein the air permeability at a basis weight of 10 g / m ² is 50 to 100 seconds / 100 ml.
12. The nonwoven fabric according to any one of claims 1 to 11, having a thickness of 10 to 18 µm.
13. A separator for a storage element formed of the nonwoven fabric according to any one of claims 1 to 12.
14. The separator according to claim 13, wherein the ratio (weight ratio) of cellulose fiber to polyolefin fiber is the former / the latter = 70/30 to 20/80.
15. The separator according to claim 13 or 14, which is a battery or capacitor separator.
16. The method for producing a nonwoven fabric according to claim 1, wherein the cellulose fiber and the polyolefin fiber are made.
17. The nonwoven fabric according to claim 16, wherein the ratio (weight ratio) of cellulose fiber to polyolefin fiber is the former / the latter = 70/30 to 20/80, and the nonwoven fabric is treated at a temperature lower than the melting point or softening point of the polyolefin fiber. Production method.

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