WO2012017953A1

WO2012017953A1 - Non-woven fabric comprising cellulose fibers, and separator for electrical storage element

Info

Publication number: WO2012017953A1
Application number: PCT/JP2011/067486
Authority: WO
Inventors: 大村　雅也
Original assignee: ダイセル化学工業株式会社
Priority date: 2010-08-04
Filing date: 2011-07-29
Publication date: 2012-02-09
Also published as: TW201215715A; JP2012036517A

Abstract

Cellulose fibers having an average fiber diameter of 0.1-20 μm and cellulose nanofibers having an average fiber diameter of less than 100 nm are made into a sheet form, thereby preparing a non-woven fabric. The non-woven fabric may have a thickness of 20 μm or less. The content ratio of the cellulose nanofibers may be about 0.01-15 parts by weight relative to 100 parts by weight of the cellulose fibers. This non-woven fabric may contain substantially no synthetic resin, and can have excellent mechanical strength even when the non-woven fabric does not contain any sheet force increasing agent such as a polyacrylamide or has a small thickness. Further, this non-woven fabric has excellent gas permeability, and therefore can be used as a separator or a filter for an electrical storage element.

Description

Nonwoven fabric and storage element separator formed of cellulose fiber

The present invention relates to a nonwoven fabric that is substantially free of a paper strength enhancer formed of a synthetic resin and that is formed of cellulose fibers having a fine fiber diameter of a micron order or less, and a power storage device that is formed of the nonwoven fabric. It relates to a separator.

Conventionally, nonwoven fabrics formed of cellulose fibers have been used as printing paper and books as paper with the addition of sizing agents and paper strength enhancing agents, etc., but using permeability to gases and liquids, It is also used for filters and separators for energy storage devices. In particular, in recent years, with the development of power storage elements such as batteries and capacitors in hybrid vehicles and mobile devices, non-woven fabrics made of cellulose fibers with excellent thermal stability and electrochemical stability are used as separators. The technology to use as is proposed.

For example, in Japanese Patent Laid-Open No. 10-223196 (Patent Document 1), in a nonaqueous battery in which a positive electrode active material and a negative electrode active material are electronically separated by a separator, the separator is made of cellulose as a raw material and wet paper is used. A non-aqueous battery that is manufactured and dried while retaining the void structure present in the wet paper is disclosed. In this document, microfibrillated cellulose and bacterial cellulose having a fiber diameter of 1 μm or less defibrated by shearing force under high pressure are described as cellulose fibers constituting the separator, and the fiber diameter of the microfibrillated cellulose beaten is 0.4 μm. It has been suggested that In addition, as a method of drying while maintaining a void structure on a wet paper, a method of replacing water with an organic solvent and drying is described. Furthermore, it is described that the thickness of the separator is preferably 15 to 100 μm, and in the examples, a separator of about 50 μm is prepared.

Japanese Patent Laid-Open No. 2006-49797 (Patent Document 2) discloses a separator having a maximum fiber thickness of 1000 nm or less and having an air permeability of 5 to 700 sec / 100 cc. A separator for an electricity storage device having an electrical resistance value at 20 ° C. of 1.0 Ωcm ² or less calculated by an alternating current two-terminal method of a membrane impregnated with an 8 mol / L tetraethylammonium · BF ₄ salt / propylene carbonate solution Is disclosed. In this document, the maximum fiber diameter of cellulose fibers is preferably 400 nm or less, more preferably 150 nm or less, and fibrillated cellulose and bacterial cellulose are described as cellulose fibers. Furthermore, the thickness of the separator is described as 5 to 50 μm, preferably 10 to 30 μm.

However, among these separators, the separator composed of microfibrillated cellulose alone has low strength. In general, in order to improve the strength of the cellulose fiber nonwoven fabric, polyacrylamide is generally blended as a paper strength enhancer. However, when polyacrylamide is blended, it is electrochemically unstable and polyacrylamide is a carcinogenic substance, which is not preferable from the viewpoint of safety. On the other hand, a separator composed of bacterial cellulose alone is difficult to make paper and has low productivity, and has a small pore size, which is unsuitable for a separator such as a capacitor, for example, and has limited applications.

Further, JP-A-8-171893 (Patent Document 3) 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 are used as synthetic fibers that do not hydrogen bond with natural pulp when the sheet is dried in order to reduce the pore diameter of the nonwoven fabric. Furthermore, in the examples, a separator having a thickness of about 50 μm is manufactured by blending 10% of vinylon fiber having a heat melting temperature of 70 ° C. in addition to natural pulp and fine synthetic fiber and treating at 80 ° C.

However, even this separator is electrochemically unstable because it contains fibers made of synthetic resin such as vinylon fibers. Furthermore, since a thick natural pulp is included, it is difficult to reduce the thickness of the separator.

JP-A-10-223196 (Claims, paragraphs [0032] [0043] [0057], Examples) JP 2006-49797 A (claims, paragraphs [0019] [0020] [0042], Examples) JP-A-8-171893 (Claim 1, paragraph [0009], Example)

Accordingly, an object of the present invention is to provide a cellulose fiber nonwoven fabric formed of cellulose fibers having a fine fiber diameter of micron order or less and having high mechanical strength and heat resistance, and a storage element separator formed of the nonwoven fabric. There is.

Another object of the present invention is to provide a cellulose fiber nonwoven fabric that can achieve both air permeability and mechanical strength, even if it is thin, and a separator for an electricity storage element formed from this nonwoven fabric.

Still another object of the present invention is to provide a cellulose fiber nonwoven fabric that is electrochemically stable and has high productivity and safety, and a storage element separator formed of the nonwoven fabric.

Another object of the present invention is to provide a cellulose fiber nonwoven fabric having a relatively large pore diameter and suitable for capacitors and the like and a storage element separator formed of this nonwoven fabric.

As a result of diligent studies to achieve the above-mentioned problems, the present inventor made a paper having a cellulose fiber having an average fiber diameter of 0.1 to 20 μm and a cellulose nanofiber having an average fiber diameter of less than 100 nm, thereby obtaining a micron order or less. The present inventors have found that the heat resistance and mechanical strength of a nonwoven fabric formed of cellulose fibers having a fiber diameter can be improved, and the present invention has been completed.

That is, the non-woven fabric of the present invention is a non-woven fabric (paper body) obtained by making a paper with cellulose fibers having an average fiber diameter of 0.1 to 20 μm and cellulose nanofibers with an average fiber diameter of less than 100 nm. The nonwoven fabric of the present invention may have a thickness of 20 μm or less. The cellulose nanofibers may be derived from plants, and the ratio of the average fiber length to the average fiber diameter may be 2000 or more. The cellulose nanofibers may have an average fiber diameter of 15 to 80 nm and a standard deviation of fiber diameter distribution of 80 nm or less. The cellulose nanofibers are obtained by a production method including a dispersion preparation step in which a raw material cellulose fiber is dispersed in a solvent to prepare a dispersion, and a homogenization step in which the dispersion is homogenized with a homogenizer having a crushing type homovalve sheet. It may be a nanofiber. The raw material cellulose fiber may be a cellulose fiber derived from never dry pulp formed of wood fibers and / or seed hair fibers, and the kappa number may be 30 or less. The average fiber diameter of the cellulose fibers may be 0.1 to 10 μm. The ratio of the average fiber diameter of the cellulose fibers to the average fiber diameter of the cellulose nanofibers may be about the former / the latter = 10/1 to 100/1. The ratio of the cellulose nanofiber may be about 0.01 to 15 parts by weight with respect to 100 parts by weight of the cellulose fiber. The nonwoven fabric of the present invention preferably contains substantially no synthetic resin. For example, even if it does not contain a paper strength enhancer such as polyacrylamide, it is thin and excellent in mechanical strength. That is, the nonwoven fabric of the present invention may have a tensile strength of 10 N / 15 mm or more at a basis weight of 10 g / m ² . Furthermore, the nonwoven fabric of the present invention may have excellent air permeability while maintaining mechanical strength, and the air permeability at a basis weight of 10 g / m ² may be 10 to 500 seconds / 100 ml.

The present invention also includes a storage element separator formed of the nonwoven fabric.

In the present invention, a non-woven fabric formed of cellulose fibers having a fine fiber diameter of micron order or less because paper is made of cellulose fibers having an average fiber diameter of 0.1 to 20 μm and cellulose nanofibers having an average fiber diameter of less than 100 nm. The mechanical strength and heat resistance of can be improved. Furthermore, even if it is thin, it can be used for a filter, a separator of a power storage element, and the like because it can achieve both air permeability and mechanical strength. In particular, since it is electrochemically stable, it is particularly useful for a separator of an electricity storage device and has excellent productivity. Furthermore, since it does not contain harmful paper strength enhancers such as polyacrylamide, it is highly safe. In addition, since the hole diameter is relatively large, it is particularly suitable for a capacitor or the like among power storage elements.

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 is a nonwoven fabric obtained by papermaking cellulose fibers having an average fiber diameter of 0.1 to 20 μm and cellulose nanofibers having an average fiber diameter of less than 100 nm.

[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.

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). Furthermore, the cellulose fiber may be a fiber derived from never dry pulp having a kappa number of 30 or less (particularly about 0 to 10), as in the case of the cellulose nanofiber described later.

In the present invention, the average fiber diameter of the cellulose fibers is a fine fiber diameter of the order of microns or less. That is, the average fiber diameter is 0.1 to 20 μm, for example, 0.1 to 10 μm, preferably 0.15 to 3 μm (for example, 0.2 to 2 μm), and more preferably 0.2 to 1 μm (particularly 0.2 μm). 25 to 0.5 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 short circuit is also suppressed, and a nonwoven fabric suitable for a power storage element such as a capacitor or a filter that requires thinning can be prepared. .

Furthermore, the standard deviation of the fiber diameter distribution is, for example, 1 μm or less (for example, 5 to 100 nm), preferably 8 to 500 nm, and more preferably about 10 to 100 nm. Further, the minimum fiber diameter of the cellulose fiber may be about 0.1 μm or more (for example, 0.1 to 0.3 μm). 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 0.3 to 4 mm (particularly 0.4 to 3 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, the standard deviation of the fiber diameter distribution, and the minimum fiber diameter are values calculated from the fiber diameter (about n = 20) measured based on an electron micrograph.

[Method for producing cellulose fiber]
Cellulose fibers are usually obtained by microfibrillation, and more specifically, a dispersion preparation step for preparing a dispersion by dispersing raw cellulose fibers in a solvent, a refiner for refining microfibrils by beating raw cellulose fibers You may manufacture through a process.

(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 beating treatment of the raw fiber may be, for example, such that the Canadian freeness value (Canadian standard freeness) is about 100 to 300 ml, preferably about 120 to 280 ml, more preferably about 150 to 250 ml. The Canadian Freeness Value (CSF) is a value measured using a 0.1% by weight fiber slurry in accordance with JIS P8121 “Pulp Freeness Test Method; Canadian Standard Type”.

The degree of beating 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.

[Cellulose nanofibers]
In the present invention, the cellulose nanofiber is a fiber having a nanometer-size fiber diameter finer than that of the cellulose fiber, and has a function as a paper strength enhancer for the cellulose fiber in the nonwoven fabric.

The cellulose constituting the cellulose nanofiber may be formed of the same cellulose as the cellulose constituting the cellulose fiber. Among the celluloses, nanofibers are highly productive and have an appropriate fiber diameter and fiber length, so that plant-derived celluloses such as wood fibers (wood pulp such as conifers and hardwoods) and seed hair fibers (cotton) are used. Cellulose derived from pulp such as linter pulp is preferred. As the pulp, pulp obtained by the same method as the cellulose fiber can be used, but as the cellulose nanofiber, the entanglement between the raw material fibers is suppressed, and efficient microfibril formation by homogenization treatment is realized and uniform. From the viewpoint of obtaining a nanometer-sized fiber, never dry pulp, that is, pulp having no drying history (pulp that has been kept wet without being dried) is particularly preferable.

Furthermore, the cellulose nanofibers have a high purity cellulose having a high α-cellulose content, for example, an α-cellulose content of 70 to 100% by weight (for example, 95 to 100% by weight), preferably 98 to 100, depending on applications. It may be about wt%. Furthermore, in the present invention, by using high-purity cellulose having a low lignin or hemicellulose content, cellulose nanofibers having a uniform fiber diameter can be prepared even with wood fibers and seed hair fibers. . 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. These raw celluloses may be used alone or in combination of two or more.

In particular, the cellulose nanofiber may be a fiber derived from never dry pulp which is formed of wood fibers and / or seed hair fibers 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.

The cellulose nanofiber is thinner than the cellulose fiber and has an average fiber diameter of less than 100 nm. The average fiber diameter is, for example, about 10 to 90 nm, preferably 15 to 80 nm, and more preferably 20 to 60 nm (particularly 25 to 50 nm). Further, the standard deviation of the fiber diameter distribution is, for example, about 80 nm or less (for example, 1 to 80 nm), preferably 3 to 50 nm, and more preferably 5 to 40 nm (particularly 10 to 30 nm). In this invention, since it is uniform by nanometer size, while being able to reinforce a cellulose fiber uniformly, the hole diameter of a nonwoven fabric can also be equalized. Furthermore, the cellulose nanofibers have a uniform nanometer size, and the maximum fiber diameter is also less than 100 nm, for example, about 30 to 90 nm, preferably about 40 to 80 nm, and more preferably about 50 to 70 nm.

The ratio of the average fiber diameter of cellulose fibers to the average fiber diameter of cellulose nanofibers can be selected from the range of the former / the latter = 2/1 to 1000/1, for example, 5/1 to 500/1, preferably 10 / 1 to 100/1, more preferably about 20/1 to 80/1 (especially 25/1 to 70/1). If the fiber diameter ratio between the two is in this range, it is possible to reinforce the cellulose nanofibers without closing the holes formed by the cellulose fibers, or to achieve both air permeability and strength.

The average fiber length of cellulose nanofibers can be selected from the range of about 10 to 1000 μm. From the viewpoint of improving the mechanical properties of the nonwoven fabric, for example, 100 to 500 μm, preferably 110 to 400 μm, more preferably 120 to 300 μm (particularly, 130 to 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 2000 or more, for example, 2000 to 15000, preferably 3000 to 10,000, more preferably 4000 to 8000 ( In particular, it is about 5000 to 7000). In the present invention, cellulose fibers and nanofibers or nanofibers are appropriately entangled by using nanofibers having a relatively long fiber length and aspect ratio in spite of having an average diameter of nanometer size. Therefore, the strength of the 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 of the cellulose nanofiber (cross-sectional shape perpendicular to the longitudinal direction of the fiber) may be an anisotropic shape (flat shape) such as bacterial cellulose. Isotropic shape. Examples of the substantially isotropic shape include a substantially circular shape such as a perfect circle shape, a regular polygonal shape, and the like. In the case of a substantially circular shape, the ratio of the major axis to the minor axis (average aspect ratio) is, for example, 1 to 2, It is preferably about 1 to 1.5, more preferably about 1 to 1.3 (particularly 1 to 1.2).

The dehydration time of the cellulose nanofiber is, for example, 1000 seconds or more 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, and preferably 1200 to 10000. Second, more preferably 1500 to 8000 seconds (particularly 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 nanofibers 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 3000 mPa · s or more, preferably 4000 to 15000 mPa · s, more preferably about 5000 to 10,000 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 nanofiber]
As cellulose nanofibers, nanometer-sized fibers such as bacterial cellulose may be used as they are or divided, but when plant-derived cellulose fibers are used, natural plant-derived cellulose fibers are on the order of microns, Usually, it is obtained by microfibrillating (dividing) the raw material cellulose fiber into nanometer size.

The average fiber length of the raw material cellulose fibers is 0.01 to 5 mm (eg, 0.01 to 3 mm), preferably 0.03 to 4 mm (eg, 0.05 to 2.5 mm), more preferably 0.06 to It is about 3 mm (particularly 0.1 to 2 mm), and usually about 0.1 to 5 mm. The average fiber diameter of the raw cellulose fibers is 0.01 to 500 μm (for example, 0.03 to 400 μm), preferably 0.05 to 450 μm (for example, 0.06 to 400 μm), more preferably 0.1 to 500 μm. It is about 300 μm (for example, 0.2 to 250 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, cellulose nanofibers having an average fiber diameter of less than 100 nm can be prepared by microfibrillation of raw material cellulose fibers by the production method described 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 cellulose nanofibers 7. Specifically, in the processing by the homogenizer, the raw material fiber 1 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 which is a narrow gap. As a result, the cellulose nanofibers 7 are divided by receiving a shearing stress or a cutting action to be uniform nanometer-sized cellulose nanofibers 7. 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 nanometer size of the raw fiber 1 is increased due to an increase in the collision force with the wall surface in the small diameter orifice 4 and the collapse of the bubbles. It can be inferred that microfibrillation is 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 a nanometer size fiber diameter by pumping a dispersion liquid with such a high pressure with respect to the homogenizer provided with the crushing type | mold homo valve 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 5 to 50 times, preferably about 10 to 40 times, more preferably about 12 to 30 times (particularly about 15 to 25 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, 10 to 100 times, preferably 20 to 80 times, Preferably, it is about 30 to 70 times (particularly 40 to 60 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 particular, it is effective to use never dry pulp as the raw fiber.

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.

In addition, also in the manufacturing method of a cellulose nanofiber, you may refiner process a dispersion liquid as a pre-process (preliminary process) of the said homogenization process. As a refiner process, you may perform the refiner process similar to the manufacturing method of the said cellulose fiber.

[Nonwoven fabric and production method thereof]
In the nonwoven fabric (or paper body) of the present invention, the ratio of cellulose nanofibers is, for example, 0.01 to 15 parts by weight, preferably 0.1 to 10 parts by weight (for example, 0 to 100 parts by weight of cellulose fibers). 0.5 to 8 parts by weight), more preferably about 1 to 8 parts by weight (particularly 3 to 7 parts by weight). In the present invention, the nonwoven fabric can be thinned and the strength can be improved without reducing the air permeability of the nonwoven fabric by simply adding a small amount of cellulose nanofiber to the cellulose fiber. Furthermore, since the cellulose nanofibers are nanometer-sized and in a small amount, the air permeability is also high because they are entangled without filling the pores (mesh) of the nonwoven fabric composed of cellulose fibers. On the other hand, when the ratio of cellulose nanofiber is too large, the air permeability is too high (for example, more than 200 seconds / ml) and it is not suitable for a separator.

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 this invention can improve the intensity | strength of a nonwoven fabric by the mixing | blending of cellulose nanofiber as mentioned above, it does not need to contain paper strength enhancers, such as a synthetic resin, starch, and natural rubber. In particular, since it does not substantially contain a synthetic resin such as polyacrylamide, it has excellent heat resistance and electrochemical stability, and also has high safety.

The nonwoven fabric of the present invention is excellent in mechanical properties, has high strength even if it is thin, and has a tensile strength of 10 N / 15 mm or more at a basis weight of 10 g / m ² , for example, 6 to 20 N / 15 mm, preferably 6. It is about 5 to 15 N / 15 mm, more preferably about 7 to 10 N / 15 mm (especially 7.2 to 8 N / 15 mm).

The nonwoven fabric of the present invention is excellent in air permeability despite having the above tensile strength, and has an air permeability of 10 to 500 seconds / 100 ml at a basis weight of 10 g / m ² . It is about -200 seconds / 100 ml, preferably about 30-150 seconds / 100 ml, more preferably about 50-100 seconds / 100 ml (especially 60-80 seconds / 100 ml).

The average pore diameter of the nonwoven fabric of the present invention is 0.1 μm or more (for example, 0.1 to 20 μm), for example, 0.1 to 10 μm, preferably 0.15 to 3 μm (for example, 0.2 to 2 μm), and more preferably. Is about 0.2 to 1 μm (especially 0.25 to 0.5 μm). The nonwoven fabric having such a hole diameter is suitable as a capacitor separator, for example.

The thickness of the nonwoven fabric of the present invention may be thick, but even if it is thin, it is characterized in that the strength can be maintained, and is preferably thin. That is, the nonwoven fabric of the present invention may have a thickness of 20 μm or less, for example, 1 to 20 μm, preferably 5 to 19 μm, and more preferably 10 to 18 μm (particularly 12 to 17 μm). A nonwoven fabric may laminate | stack a some nonwoven fabric according to the objective.

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 cellulose nanofibers and making paper such as wet papermaking or dry papermaking. 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. Furthermore, when used as a separator in an electricity storage device such as a battery, for example, it may be pressed at a pressure of about 0.1 to 100 MPa, preferably 1 to 50 MPa, more preferably 5 to 30 MPa (particularly 8 to 20 MPa). Good. In the present invention, since a small amount of cellulose nanofibers are contained with respect to cellulose fibers having a reasonably large fiber diameter of 100 nm or more, paper can be easily produced 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
Using NBKP pulp (manufactured by Marusumi Paper Co., Ltd., solid content of about 50% by weight, copper number of about 0.3), 100 liters of a slurry liquid containing 2% by weight of pulp was prepared. Subsequently, using a disc refiner (SUPERFIBRATER 400-TFS, manufactured by Hasegawa Tekko Co., Ltd.), a refiner-treated product having a CSF of 200 ml was obtained by beating 10 times with a clearance of 0.15 mm and a disc rotational speed of 1750 rpm. This refiner-treated product (cellulose fiber) had an average fiber diameter of 1.6 μm and an average fiber length of 2.1 mm.

This refiner-treated product was converted into a first homogenizer (manufactured by Gorin, 15M8AT) equipped with a normal non-crushing type homovalve seat (inner diameter at the downstream end of the hollow cylindrical projection / thickness of the ring-shaped end surface = 1.9 / 1). ) Was used 20 times at a processing pressure of 50 MPa. Furthermore, using a second homogenizer (manufactured by Nirosoavi, PANDA2K) equipped with a crushing type homovalve seat (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 120 MPa. Furthermore, the average fiber diameter of the obtained cellulose nanofibers is 29 nm, the standard deviation of the fiber diameter distribution is 14.1 nm, the maximum fiber diameter is 64.3 nm, the average fiber length is 153 μm, the aspect ratio (average fiber length / average fiber diameter) ) Was 5276.

Further, a slurry obtained by mixing 95 parts by weight of cellulose fibers and 5 parts by weight of cellulose nanofibers was diluted to 0.2% by weight, and a paper machine with a decompression device (“Standard Square Machine” manufactured by Toyo Seiki Seisakusho Co., Ltd.). ), No. 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 a pressure of 10 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.

Example 2
A nonwoven fabric was obtained in the same manner as in Example 1 except that 99 parts by weight of cellulose fibers and 1 part by weight of cellulose nanofibers were mixed. The evaluation results are shown in Table 1.

Example 3
A nonwoven fabric was obtained in the same manner as in Example 1 except that a commercially available cellulose fiber (“Serish KY100G” manufactured by Daicel Chemical Industries, Ltd., average fiber diameter 0.3 μm, average fiber length 420 μm) was used as the cellulose fiber. The evaluation results are shown in Table 1.

Example 4
A nonwoven fabric was obtained in the same manner as in Example 1 except that 5 parts by weight of cellulose fibers and 95 parts by weight of cellulose nanofibers were mixed. The evaluation results are shown in Table 1.

Example 5
A nonwoven fabric was obtained in the same manner as in Example 1 except that 92 parts by weight of commercially available cellulose fiber (Cerish KY100G) and 8 parts by weight of cellulose nanofiber were mixed. The evaluation results are shown in Table 1.

Example 6
A nonwoven fabric was obtained in the same manner as in Example 1 except that 92 parts by weight of commercially available cellulose fiber (Cerish KY100G) and 8 parts by weight of cellulose nanofiber were mixed. The evaluation results are shown in Table 1.

Comparative Example 1
A nonwoven fabric was obtained in the same manner as in Example 1 except that the cellulose fiber (Serish KY100G) was made alone. The evaluation results are shown in Table 1.

Comparative Example 2
A nonwoven fabric was obtained in the same manner as in Example 1 except that cellulose fibers (Serish KY100G) were used instead of cellulose nanofibers. The evaluation results are shown in Table 1.

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-acid battery, etc.), capacitors, capacitors and other storage element separators are useful. In particular, even though it is thin, its air permeability and strength are high, and its pore size is relatively large. Therefore, it is suitable for electronic devices, electrical devices, automobiles (hybrid automobiles, large automobiles, etc.), power storage capacitors and auxiliary power supply capacitors. .

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 ... Cellulose nanofiber 12 ... Non-crushing type homo valve seat

Claims

Nonwoven fabric made of paper made of cellulose fibers having an average fiber diameter of 0.1 to 20 μm and cellulose nanofibers having an average fiber diameter of less than 100 nm.
The nonwoven fabric according to claim 1, wherein the thickness is 20 μm or less.
The nonwoven fabric according to claim 1 or 2, wherein the cellulose nanofiber is derived from a plant and the ratio of the average fiber length to the average fiber diameter is 2000 or more.
The nonwoven fabric according to any one of claims 1 to 3, wherein the cellulose nanofibers have an average fiber diameter of 15 to 80 nm and a standard deviation of the fiber diameter distribution of 80 nm or less.
Cellulose nanofibers can be obtained by a production method including a dispersion preparation step of preparing a dispersion by dispersing raw cellulose fibers in a solvent, and a homogenization step of homogenizing the dispersion with a homogenizer equipped with a crushing type homovalve sheet. The nonwoven fabric according to any one of claims 1 to 4.
The nonwoven fabric according to claim 5, wherein the raw material cellulose fibers are cellulose fibers derived from never dry pulp formed of wood fibers and / or seed hair fibers, and have a kappa number of 30 or less.
The nonwoven fabric according to any one of claims 1 to 6, wherein the average fiber diameter of the cellulose fibers is 0.1 to 10 µm.
The nonwoven fabric according to any one of claims 1 to 7, wherein the ratio of the average fiber diameter of the cellulose fibers to the average fiber diameter of the cellulose nanofibers is the former / the latter = 10/1 to 100/1.
The nonwoven fabric according to any one of claims 1 to 8, wherein the ratio of cellulose nanofibers is 0.01 to 15 parts by weight with respect to 100 parts by weight of cellulose fibers.
The nonwoven fabric according to any one of claims 1 to 9, which is substantially free of synthetic resin.
The nonwoven fabric according to any one of claims 1 to 10, which has a tensile strength of 6 N / 15 mm or more at a basis weight of 10 g / m 2 .
The nonwoven fabric according to any one of claims 1 to 11, wherein the air permeability at a basis weight of 10 g / m 2 is 10 to 500 seconds / 100 ml.
A separator for a storage element formed of the nonwoven fabric according to any one of claims 1 to 12.