JP6515801B2 - Thickener for battery separator coating solution, battery separator coating solution and battery separator - Google Patents

Description

  The present invention relates to a thickener for a battery separator coating solution, a battery separator coating solution, and a battery separator.

  Lithium ion secondary batteries have a feature of high energy density, and are widely used as a power source of portable electric devices such as mobile phones, portable music players, and notebook personal computers. A normal lithium ion secondary battery is provided with a separator to prevent contact between positive and negative electrodes.

  Conventionally, as a battery separator, a porous film made of polyethylene or polypropylene is used. However, porous films made of polyethylene or polypropylene have low heat resistance, and when the porous film shrinks and an internal short circuit occurs, local heat generation occurs inside the battery, resulting in safety and fire or rupture etc. I have a problem.

  In response to such problems, battery separators containing inorganic fine particles have been developed. In the battery separator containing the inorganic fine particles, by controlling the pore diameter with the inorganic fine particles, it is possible to suppress internal short circuit and improve the heat resistance.

  In order to make the porous film contain the inorganic fine particles, it is performed to coat the surface of the porous film with a coating liquid containing the inorganic fine particles. However, since the inorganic fine particles have a larger specific gravity than water or an organic solvent, they tend to settle in the inorganic fine particle-containing slurry, and when settling once, the inorganic fine particles may be aggregated, causing a problem. In addition, when the dispersed state of the inorganic fine particles is not good, there is also a problem that application unevenness occurs when applying to the porous film, and improvement in stability of the inorganic fine particles in the coating liquid has been required.

  In order to improve the dispersibility of the inorganic fine particles in the coating solution, it has been studied to add a thickener to the coating solution. For example, Patent Document 1 discloses a battery separator coating liquid to which a thickener such as xanthan gum is added. Patent Document 2 discloses a battery separator coating liquid using a water-soluble polymer such as carboxymethyl cellulose salt as a dispersant and a thickener. Further, Patent Document 3 discloses a battery separator coating liquid containing cellulose fibers. Here, bacterial cellulose fibers and nanocellulose fibers produced by dissociating crystalline cellulose are used.

International Publication WO2009 / 96451 JP, 2013-115031, A JP, 2015-84318, A

  As described above, the dispersibility of the inorganic fine particles can be enhanced to some extent by incorporating a thickener in the battery separator coating liquid. However, when the separator coating liquid for batteries was produced using the thickener used conventionally, it became clear by examination of the present inventors that the dispersibility of microparticles | fine-particles is not enough. Moreover, although strong stirring is often performed at the time of dispersion | distribution of inorganic fine particles, there also existed a problem that the viscosity of the separator coating liquid for batteries will fall by performing strong stirring.

  Moreover, when the battery separator coating liquid containing the thickener used conventionally is coated and a battery separator is produced, a coating liquid may pass a porous film base material and a strike-through may occur. It was a problem.

  Therefore, in order to solve the problems of the prior art as described above, the present inventors have studied for the purpose of providing a separator coating liquid for batteries excellent in fine particle dispersibility and having a small decrease in viscosity even after strong stirring. I proceeded. In addition, the present inventors proceeded with the study for the purpose of providing a battery separator coating solution which does not cause a defect such as strike-through when the battery separator coating solution is coated to prepare a battery separator. The Furthermore, the inventors of the present invention have also studied to provide a thickener for a battery separator coating liquid used for the battery separator coating liquid.

As a result of earnestly examining in order to solve said subject, the present inventors are the fiber width of 1000 nm or less, and the average fiber degree is within the predetermined range for the separator coating liquid for batteries By incorporating the battery separator coating solution as a thickener into the battery separator coating solution, the battery separator coating solution is excellent in fine particle dispersibility, with less decrease in viscosity even after strong stirring, and capable of suppressing occurrence of strike through during coating. I found that I could get it.
Specifically, the present invention has the following configuration.

[1] A thickener for a battery separator coating liquid, which comprises fine fibrous cellulose having a fiber width of 1000 nm or less and an average polymerization degree of 400 or more and 2000 or less.
[2] The thickener for a battery separator coating liquid according to [1], wherein the fine fibrous cellulose is phosphorylated cellulose.
[3] A separator coating solution for a battery comprising fine fibrous cellulose having a fiber width of 1000 nm or less and an average polymerization degree of 400 or more and 2000 or less, fine particles, and a dispersion medium.
[4] The separator coating solution for a battery according to [3], wherein the fine fibrous cellulose is phosphorylated cellulose.
[5] The content of the fine fibrous cellulose is 0.1 to 1.3 parts by mass with respect to 100 parts by mass of the dispersion medium. [3] or [4], liquid.
[6] The fine particles are inorganic fine particles. The battery separator coating liquid according to any one of [3] to [5].
[7] A battery separator having a base material and a coating layer, wherein the coating layer has a fiber width of 1000 nm or less, a fine fibrous cellulose having an average polymerization degree of 400 or more and 2000 or less, and fine particles. Containing battery separator.
[8] The battery separator according to [7], wherein the fine fibrous cellulose is phosphorylated cellulose.
[9] The battery separator according to [7] or [8], wherein the fine particles are inorganic fine particles.
[10] The battery separator according to any one of [7] to [9], wherein the substrate contains a polyolefin resin.

  According to the present invention, it is possible to obtain a battery separator coating liquid which is excellent in fine particle dispersibility and which has a small decrease in viscosity even after strong stirring. Moreover, if the separator coating liquid for batteries of this invention is used, generation | occurrence | production of the strike-through at the time of coating can be suppressed.

FIG. 1 is a graph showing the relationship between the amount of dropped NaOH and the conductivity of a fiber material having a phosphate group. FIG. 2 is a graph showing the relationship between the amount of dropped NaOH and the electrical conductivity for a fiber material having a carboxyl group.

  Hereinafter, the present invention will be described in detail. The description of the configuration requirements described below may be made based on typical embodiments and specific examples, but the present invention is not limited to such embodiments.

(Thickener for battery separator coating solution)
The present invention relates to a thickener for a battery separator coating liquid, which contains fine fibrous cellulose having a fiber width of 1000 nm or less and an average polymerization degree of 400 or more and 2000 or less.

  The thickener for a battery separator coating liquid of the present invention contains the fine fibrous cellulose having the above-described constitution, and therefore, the fine particle dispersibility of the battery separator coating liquid can be enhanced. In addition, the thickener for a battery separator coating liquid according to the present invention can suppress the viscosity decrease of the battery separator coating liquid, and suppress the viscosity decrease even after the battery separator coating liquid is strongly stirred. can do. Furthermore, when the battery separator coating solution containing the thickener for a battery separator coating solution of the present invention is coated on a substrate, the occurrence of the strikethrough is suppressed.

  Since the thickener in the battery separator coating liquid may become an impurity after coating, the amount added is preferably small. The present invention is also characterized in that the addition amount can be suppressed to a small amount by using the above-mentioned thickener for a separator coating solution for a battery. In the present invention, even when the addition amount of the thickener for a battery separator coating liquid is small, the fine particle dispersibility can be enhanced, and the viscosity reduction rate can be suppressed low. Furthermore, in the present invention, the coating property (the ease of coating) can be enhanced by suppressing the addition amount of the thickener for the battery separator coating liquid.

  Furthermore, in the present invention, since the addition amount of the above-mentioned thickener for battery separator coating liquids can be suppressed, it can also control that micropores of a battery separator substrate are blocked. In general, there is a trade-off relationship between the suppression of micropore blocking in the battery separator base and the prevention of the occurrence of strikethrough, but in the present invention, by using the above-mentioned thickener for a battery separator coating liquid, Both the inhibition of the microporous blockage of the substrate and the prevention of the occurrence of the strike-through are achieved.

  The thickener for a battery separator coating liquid of the present invention contains a fine fibrous cellulose having a fiber width of 1000 nm or less and an average polymerization degree of 400 or more and 2000 or less. The thickener for the separator coating solution for a battery preferably contains 60% by mass or more, more preferably 70% by mass or more, and more preferably 80% by mass or more of such fine fibrous cellulose based on the mass of the total solid content. It is more preferable to contain, and it is especially preferable to contain 90 mass% or more. Further, the thickener for a battery separator coating liquid may be made of the above-mentioned fine fibrous cellulose. In addition to the above-mentioned fine fibrous cellulose, a solvent such as water, a water-soluble polymer and the like may be contained in the battery separator coating solution thickener.

  In addition, as a form of a thickener for separator coating liquid for batteries, powder form, gel form, slurry form, solution form, sheet form etc. can be mentioned, for example.

  The average degree of polymerization of the fine fibrous cellulose contained in the thickener for a battery separator coating liquid may be 400 or more, preferably 420 or more, more preferably 430 or more, and 500 or more. Is also possible. The average degree of polymerization of the fine fibrous cellulose may be 2000 or less, preferably 1500 or less, more preferably 1200 or less, still more preferably 1000 or less, and 600 or less. Particularly preferred. By setting the average degree of polymerization of the fine fibrous cellulose in the above range, the fine particle dispersibility of the battery separator coating liquid can be enhanced, and the decrease in viscosity of the battery separator coating liquid can be suppressed. Furthermore, when the battery separator coating solution containing the battery separator coating solution thickener is applied onto the substrate, the occurrence of strikethrough can be suppressed.

The average degree of polymerization of the fine fibrous cellulose contained in the battery separator coating solution thickener is calculated with reference to the following paper.
TAPPI International Standard; ISO / FDIS 5351, 2009.
Smith, DK; Bampton, RF; Alexander, WJ Ind. Eng. Chem., Process Des. Dev. 1963, 2, 57-62.

Specifically, 30 g of a suspension obtained by diluting fine fibrous cellulose with ion-exchanged water to a content of 2 ± 0.3 mass% is collected in a centrifuge tube and allowed to stand in liquid nitrogen for 30 minutes. And freeze it. Furthermore, after drying with a freeze dryer for 5 days or more, heating is carried out for 3 hours or more and 4 hours or less with a constant temperature dryer set at 105 ° C. to obtain fine fibrous cellulose in a state of islet dryness.
In order to measure the reference, 15 ml of pure water and 15 ml of 1 mol / L copper ethylenediamine are added to an empty 50 ml capacity screw tube, and a 0.5 mol / L copper ethylene diamine solution is prepared. 10 ml of the above 0.5 mol / L copper ethylenediamine solution is placed in a Canon Fenceke viscometer, and after 5 minutes, the dropping time is measured to determine the solvent dropping time.

  Next, in order to measure the viscosity of the fine fibrous cellulose, 0.14 g to 0.16 g of fine fibrous cellulose in the as-dried state is weighed into an empty 50 ml screw tube, and 15 ml of pure water is added. Further, 15 ml of 1 mol / L copper ethylenediamine is added, and the mixture is stirred for 10 minutes at 1000 rpm with a rotation-revolution type super mixer to obtain a 0.5 mol / L copper ethylenediamine solution in which fine fibrous cellulose is dissolved. Similar to the measurement of the reference, 10 ml of the prepared 0.5 mol / L copper ethylenediamine solution is put into a Cannon-Fenske viscometer, placed for 5 minutes, and then the drop time is measured. As for evaluation, it is preferable to perform two or more measurements and to use the average value.

The degree of polymerization is calculated using the following equation from the mass of the fibrillated cellulose in the dry state used for the measurement, the solvent dropping time, and the dropping time of the copper ethylenediamine solution in which the fine fibrous cellulose is dissolved. In addition, when the following average degree of polymerization is measured twice or more, it is an average value of each time.
Fine fibrous cellulose mass in the dry state used for measurement: a (g) (where a is 0.14 or more and 0.16 or less)
Cellulose concentration of solution: c = a / 30 (g / mL)
Solvent falling time: t ₀ (sec)
Fall time of fine fibrous cellulose solution: t (sec)
Relative viscosity of solution: _rel = t / t ₀
Specific viscosity of solution: _{sp sp} = _rel- 1
Intrinsic viscosity: [η] = η _{sp /} c (1 + 0.28 _{sp sp} )
Degree of polymerization: DP = [η] /0.57

  In addition, when components other than fine fibrous cellulose are contained in the thickener for separator coating liquid for batteries, after isolating fine fibrous cellulose, the average polymerization degree of fine fibrous cellulose is calculated.

<Observation of thickener solution>
First, a thickener for a battery separator coating solution is diluted and dried, and then observed with a transmission electron microscope to confirm the presence of fine fibrous cellulose. Solid NMR is then used to detect Form I crystals of fine fibrous cellulose.

<Isolation of fine fibrous cellulose in thickener>
When the presence of the fine fibrous cellulose is confirmed in the battery separator coating solution thickener, the fine fibrous cellulose is isolated according to the following procedure.
First, 20 ± 5 g of a thickener for a battery separator coating solution are weighed in a 50 ml aluminum cup. Similarly, a plurality of aluminum cups prepared by weighing out the thickener for battery separator coating liquid are prepared. The battery separator coating liquid thickener is dried by heating at 105 ° C. for 16 hours with a blower constant temperature dryer. A 0.5 mol / L copper ethylenediamine solution is added to 1 g of the dried thickener for a battery separator coating liquid so as to have a ratio of 200 ml, and the mixture is stirred to dissolve fine fibrous cellulose. The obtained solution is filtered to remove the residue, and then dropped into water to obtain regenerated cellulose. This regenerated cellulose is one in which fine fibrous cellulose is dissolved in a copper ethylenediamine solution and regenerated in water. The resulting regenerated cellulose is separated by filtration, thoroughly washed with water and dried.

<Measurement of Fine Fibrous Cellulose Content in Thickener>
The dry weight of the obtained regenerated cellulose is measured. From this weight and the weight of the thickening agent for a battery separator coating liquid used to obtain this weight, the content of the fine fibrous cellulose contained in the thickening agent for a battery separator coating liquid is determined.

<Measurement of Degree of Polymerization of Fine Fibrous Cellulose Isolated from Thickener>
To 0.14 g or more and 0.16 g or less of the obtained dried product of regenerated cellulose, 30 ml of a 0.5 mol / L copper ethylenediamine solution is added and stirred to dissolve the cellulose again. The resulting solution is filtered to remove the residue. After that, 10 ml of the prepared filtrate is put into a Cannonfence viscometer, placed for 5 minutes, and the dropping time is measured. The intrinsic viscosity is determined from the measured fall time according to the method described above, and converted to the degree of polymerization.

<Fine fibrous cellulose>
The fibrous cellulose raw material for obtaining the fine fibrous cellulose is not particularly limited, but it is preferable to use pulp in terms of availability and low cost. The pulp may include wood pulp, non-wood pulp and deinked pulp. As wood pulp, for example, hardwood kraft pulp (LBKP), softwood kraft pulp (NBKP), sulfite pulp (SP), dissolving pulp (DP), soda pulp (AP), unbleached kraft pulp (UKP), oxygen bleached kraft Chemical pulp, such as pulp (OKP), etc. are mentioned. In addition, semichemical pulp such as semichemical pulp (SCP), chemiground wood pulp (CGP), mechanical pulp such as ground pulp (GP), thermomechanical pulp (TMP, BCTMP), etc. may be mentioned, but it is not particularly limited. Non-wood pulps include cotton-based pulps such as cotton linters and cotton lint, non-wood-based pulps such as hemp, wheat straw and bagasse, celluloses isolated from ascidians and seaweeds, chitin, chitosan and the like . Examples of the deinked pulp include, but not particularly limited to, deinked pulp made from waste paper. The pulp of this embodiment may be used singly or in combination of two or more. Among the above-mentioned pulps, wood pulps containing cellulose and deinked pulps are preferable in terms of availability. Among wood pulps, chemical pulp has a large cellulose ratio, so the yield of fine fibrous cellulose is high at the time of fiber refining (fibrillation), and decomposition of cellulose in the pulp is small, and fine fibers of long fibers having a large axial ratio It is preferable at the point from which fibrous cellulose is obtained. Among them, kraft pulp and sulfite pulp are most preferably selected. A high viscosity tends to be obtained when fine fibrous cellulose of long fibers having a large axial ratio is used.

  The average fiber width of the fine fibrous cellulose is 1000 nm or less as observed by an electron microscope. The average fiber width is preferably 2 nm or more and 1000 nm or less, more preferably 2 nm or more and 100 nm or less, more preferably 2 nm or more and 50 nm or less, and still more preferably 2 nm or more and 10 nm or less. If the average fiber width of the fine fibrous cellulose is less than 2 nm, it dissolves in water as cellulose molecules, so the physical properties (strength, rigidity, and dimensional stability) as the fine fibrous cellulose tend to be difficult to express . The fine fibrous cellulose is, for example, monofibrillar cellulose having a fiber width of 1000 nm or less.

  The measurement of the average fiber width by electron microscopic observation of fine fibrous cellulose is performed as follows. Prepare an aqueous suspension of fine fibrous cellulose with a concentration of 0.05% by mass or more and 0.1% by mass or less, cast this suspension on a hydrophilized carbon film-coated grid, and prepare a sample for TEM observation Do. If wide fibers are included, an SEM image of the surface cast on glass may be observed. Observation with an electron microscope image is performed at a magnification of 1000 times, 5000 times, 10000 times or 50000 times depending on the width of the fiber to be constructed. However, the sample, observation conditions and magnification are adjusted to satisfy the following conditions.

(1) One straight line X is drawn at an arbitrary position in the observation image, and 20 or more fibers cross the straight line X.
(2) Draw a straight line Y intersecting perpendicularly with the straight line in the same image, and 20 or more fibers cross the straight line Y.

  With respect to the observation image satisfying the above conditions, the width of the fiber intersecting with the straight line X and the straight line Y is visually read. Thus, three or more sets of images of at least non-overlapping surface portions are observed, and for each image, the width of the fiber intersecting the straight line X and the straight line Y is read. Thus, a fiber width of at least 20 x 2 x 3 = 120 is read. The average fiber width (sometimes simply referred to as "fiber width") of fine fibrous cellulose is the average value of the fiber widths read in this manner.

  The fiber length of the fine fibrous cellulose is not particularly limited, but is preferably 0.1 μm to 1000 μm, more preferably 0.1 μm to 800 μm, and particularly preferably 0.1 μm to 600 μm. By setting the fiber length within the above range, it is possible to suppress the destruction of the crystalline region of the fine fibrous cellulose and to make the slurry viscosity of the fine fibrous cellulose into an appropriate range. In addition, the fiber length of fine fibrous cellulose can be calculated | required from the image analysis by TEM, SEM, and AFM.

The fine fibrous cellulose preferably has a type I crystal structure. Here, the fact that the fine fibrous cellulose has an I-type crystal structure can be identified in a diffraction profile obtained from a wide-angle X-ray diffraction photograph using CuKα (λ = 1.5418 Å) monochromatized with graphite. Specifically, it can be identified from having typical peaks at two positions of 2θ = 14 ° or more and 17 ° or less and 2θ = 22 ° or more and 23 ° or less.
The proportion of crystal form I in fine fibrous cellulose is preferably 30% or more, more preferably 50% or more, and still more preferably 70% or more.

  Although the ratio of the crystal parts contained in the fine fibrous cellulose is not particularly limited in the present invention, it is preferable to use cellulose having a crystallinity of 60% or more as determined by X-ray diffraction. The degree of crystallinity is preferably 65% or more, more preferably 70% or more. In this case, further excellent performance can be expected in terms of heat resistance and low linear thermal expansion. With regard to the degree of crystallinity, the X-ray diffraction profile is measured, and the pattern is determined by a conventional method (Seagal et al., Textile Research Journal, 29: 786, 1959).

  The fine fibrous cellulose is preferably one having a substituent, and the substituent is preferably an anion group. The anionic group is preferably, for example, at least one selected from a phosphoric acid group or a substituent derived from a phosphoric acid group (sometimes simply referred to as a phosphoric acid group), a carboxyl group and a sulfone group. It is more preferable that it is at least one selected from a group and a carboxyl group, and a phosphate group is particularly preferable. That is, the fine fibrous cellulose used in the present invention is preferably phosphated cellulose.

The fine fibrous cellulose is preferably one having a phosphate group or a substituent derived from a phosphate group. The phosphate group is a divalent functional group corresponding to phosphoric acid from which a hydroxyl group has been removed. It is specifically a group represented by -PO ₃ H _2. The substituent derived from the phosphate group includes substituents such as a group obtained by condensation polymerization of a phosphate group, a salt of a phosphate group, and a phosphate ester group, and even if it is an ionic substituent, it is non-ionic substitution It may be a group.

In the present invention, the phosphate group or the substituent derived from the phosphate group may be a substituent represented by the following formula (1).

In formula (1), a, b, m and n each independently represent an integer (where a = b x m); α ⁿ (n = 1 or more and n or less integer) and α 'are each independently Represents R or OR. R represents a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched hydrocarbon group Is an aromatic group, or a derivative group thereof; β is a monovalent or more cation composed of an organic substance or an inorganic substance.

<Phosphoric acid group introduction process>
In the phosphate group introducing step, at least one selected from a compound having a phosphate group and a salt thereof (hereinafter referred to as “phosphorylation reagent” or “compound A”) is reacted with a fiber raw material containing cellulose Can be done by Such a phosphorylation reagent may be mixed with the dry or wet fiber raw material in the form of a powder or an aqueous solution. As another example, a powder or an aqueous solution of a phosphorylation reagent may be added to the slurry of the fiber material.

  The phosphate group introducing step can be performed by reacting a fiber material containing cellulose with at least one selected from a compound having a phosphate group and a salt thereof (phosphorylation reagent or compound A). This reaction may be performed in the presence of at least one selected from urea and derivatives thereof (hereinafter, referred to as “compound B”).

  As an example of the method of allowing compound A to act on the fiber material in the coexistence of compound B, a method of mixing powder or an aqueous solution of compound A and compound B with a dry or wet fiber material can be mentioned. Another example is a method of adding a powder or an aqueous solution of the compound A and the compound B to a slurry of a fiber material. Among them, the method of adding the aqueous solution of compound A and compound B to the fiber material in the dry state or adding the powder or the aqueous solution of compound A and compound B to the fiber material in the wet state because of high uniformity of reaction The method is preferred. Compound A and Compound B may be added simultaneously or separately. Alternatively, the compound A and the compound B to be tested first may be added as an aqueous solution, and excess chemical solution may be removed by pressing. The form of the fiber material is preferably cotton-like or thin sheet, but is not particularly limited.

The compound A used in the present embodiment is at least one selected from a compound having a phosphate group and a salt thereof.
Examples of the compound having a phosphate group include phosphoric acid, lithium salts of phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, ammonium salts of phosphoric acid and the like, but are not particularly limited. Examples of lithium salts of phosphoric acid include lithium dihydrogen phosphate, dilithium hydrogen phosphate, trilithium phosphate, lithium pyrophosphate, lithium polyphosphate and the like. Examples of sodium salts of phosphoric acid include sodium dihydrogenphosphate, disodium hydrogenphosphate, trisodium phosphate, sodium pyrophosphate, sodium polyphosphate and the like. Examples of potassium salts of phosphoric acid include potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, and potassium polyphosphate. Examples of ammonium salts of phosphoric acid include ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium polyphosphate and the like.

  Among these, phosphoric acid and phosphoric acid are preferred from the viewpoint of high efficiency of introduction of a phosphoric acid group, easy improvement of defibrillation efficiency in a fibrillation step described later, low cost, and easy industrial application. Sodium salts or potassium salts of phosphoric acid and ammonium salts of phosphoric acid are preferred. Sodium dihydrogen phosphate or disodium hydrogen phosphate is more preferred.

  In addition, it is preferable to use Compound A as an aqueous solution because the uniformity of the reaction is enhanced and the efficiency of introducing a phosphate group is enhanced. The pH of the aqueous solution of compound A is not particularly limited, but is preferably 7 or less because the efficiency of introduction of the phosphoric acid group is increased, and is preferably 3 or more and 7 or less from the viewpoint of suppressing hydrolysis of pulp fibers. The pH of the aqueous solution of the compound A may be adjusted by, for example, using a compound having a phosphoric acid group in combination of a compound exhibiting acidity and a compound exhibiting alkalinity, and changing its quantitative ratio. The pH of the aqueous solution of the compound A may be adjusted by adding an inorganic alkali or an organic alkali to a compound having an acid group among the compounds having a phosphoric acid group.

  The amount of compound A added to the fiber material is not particularly limited, but when the amount of compound A added is converted to the phosphorus atomic weight, the amount of phosphorus atom added to the fiber material (absolute dry mass) is 0.5% by mass to 100% by mass The following is preferable, 1 to 50 mass% is more preferable, and 2 to 30 mass% is the most preferable. If the addition amount of phosphorus atoms to the fiber raw material is within the above range, the yield of fine fibrous cellulose can be further improved. When the addition amount of phosphorus atoms to the fiber raw material exceeds 100% by mass, the effect of improving the yield becomes flat and the cost of the compound A used is increased. On the other hand, the yield can be increased by setting the addition amount of phosphorus atoms to the fiber raw material to the above lower limit value or more.

  As compound B used in this embodiment, urea, biuret, 1-phenylurea, 1-benzylurea, 1-methylurea, 1-ethylurea and the like can be mentioned.

  The compound B is preferably used as an aqueous solution like the compound A. Further, it is preferable to use an aqueous solution in which both the compound A and the compound B are dissolved, because the uniformity of the reaction is enhanced. It is preferable that the addition amount of the compound B with respect to a fiber raw material (absolute dry mass) is 1 mass% or more and 500 mass% or less, more preferably 10 mass% or more and 400 mass% or less, 100 mass% or more and 350 mass% It is more preferable that it is the following, and it is especially preferable that it is 150 to 300 mass%.

  In addition to the compound A and the compound B, amides or amines may be included in the reaction system. Examples of the amides include formamide, dimethylformamide, acetamide, dimethylacetamide and the like. Examples of amines include methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like. Among these, triethylamine is known to work as a good reaction catalyst.

  It is preferable to heat-process in a phosphoric acid group introduction process. As the heat treatment temperature, it is preferable to select a temperature at which the phosphoric acid group can be efficiently introduced while suppressing the thermal decomposition or hydrolysis reaction of the fiber. Specifically, the temperature is preferably 50 ° C. or more and 300 ° C. or less, more preferably 100 ° C. or more and 250 ° C. or less, and still more preferably 130 ° C. or more and 200 ° C. or less. For heating, a vacuum dryer, an infrared heater, or a microwave heater may be used.

  During the heat treatment, while the fiber material slurry to which Compound A is added contains water, if the time for which the fiber material is allowed to stand becomes long, Compound A, which is dissolved with water molecules, moves to the surface of the fiber material as it dries. Do. Therefore, unevenness may occur in the concentration of the compound A in the fiber raw material, and there is a possibility that the introduction of the phosphate group to the fiber surface may not progress uniformly. In order to suppress the occurrence of uneven concentration of compound A in the fiber raw material due to drying, use a very thin sheet-like fiber raw material or heat dry or vacuum dry while kneading or stirring the fiber raw material and compound A with a kneader etc. You should take the method.

  The heating device used for the heat treatment is preferably a device capable of constantly discharging the water held by the slurry and the water produced by the addition reaction to the hydroxyl groups of the fibers such as phosphoric acid groups, for example, an air-blowing oven. Etc. is preferred. In addition to the fact that hydrolysis of the phosphate ester bond, which is the reverse reaction of phosphorylation, can be suppressed by constantly draining the water in the system, acid hydrolysis of sugar chains in fibers can also be suppressed. And fine fibers with high axial ratio can be obtained.

  The heat treatment time is also affected by the heating temperature, but it is preferably 1 second or more and 300 minutes or less after water is substantially removed from the fiber material slurry, and more preferably 1 second or more and 1000 seconds or less Preferably, it is 10 seconds or more and 800 seconds or less. In the present invention, by setting the heating temperature and the heating time to be in appropriate ranges, the introduction amount of the phosphate group can be made within the preferable range.

  The amount of introduced phosphoric acid group is preferably 0.1 mmol / g or more and 3.5 mmol / g or less per 1 g (mass) of fine fibrous cellulose, more preferably 0.14 mmol / g 2.5 mmol / g or less, 0 2 mmol / g 2.0 mmol / g or less is more preferable, 0.2 mmol / g 1.8 mmol / g or less is more preferable, 0.4 mmol / g 1.8 mmol / g or less is particularly preferable, and most preferably 0.6 mmol / g 1. It is 8 mmol / g or less. By making the introduction amount of the phosphate group within the above range, it is possible to facilitate the miniaturization of the fiber raw material and to enhance the stability of the fine fibrous cellulose. Moreover, when the introduction amount of the phosphoric acid group is in the above range, good characteristics can be exhibited as a thickener for a battery separator coating liquid.

  The amount of phosphate group introduced into the fiber material can be measured by conductivity titration. Specifically, the fineness is carried out by the defibration treatment step, and the obtained fine fibrous cellulose-containing slurry is treated with an ion exchange resin, and then the change in electric conductivity is obtained while adding an aqueous solution of sodium hydroxide, The introduced amount can be measured.

  In conductivity titration, the addition of alkali gives the curve shown in FIG. At the beginning, the electrical conductivity drops sharply (hereinafter referred to as "first region"). Thereafter, the conductivity starts to rise slightly (hereinafter referred to as "the second region"). After that, the increment of conductivity increases (hereinafter, referred to as "third region"). That is, three regions appear. Among them, the amount of alkali required in the first region is equal to the amount of strongly acidic groups in the slurry used for titration, and the amount of alkali required in the second region is the amount of weakly acidic groups in the slurry used for titration Become equal. When the phosphoric acid group causes condensation, the weakly acidic group is apparently lost, and the amount of alkali required for the second region is smaller than the amount of alkali required for the first region. On the other hand, since the amount of strongly acidic groups is the same as the amount of phosphorus atoms regardless of the presence or absence of condensation, the amount of introduction of phosphoric acid groups (or the amount of phosphoric acid groups) or the amount of introduction of substituents (or the amount of substitution groups) When said, it represents the amount of strongly acidic groups. That is, the alkali amount (mmol) required in the first region of the curve shown in FIG. 1 is divided by the solid content (g) in the slurry to be titrated to obtain a substituent introduction amount (mmol / g).

  The phosphate group introduction step may be performed at least once, but can be repeated multiple times. In this case, more phosphate groups are introduced, which is preferable.

<Alkali treatment>
In the case of producing fine fibrous cellulose, an alkali treatment may be performed between the phosphoric acid group introduction step and the defibration treatment step described later. Although it does not specifically limit as the method of an alkali treatment, For example, the method of immersing phosphate group introduction | transduction fiber in an alkali solution is mentioned.
The alkaline compound contained in the alkaline solution is not particularly limited, but may be an inorganic alkaline compound or an organic alkaline compound. The solvent in the alkaline solution may be either water or an organic solvent. The solvent is preferably a polar solvent (water or a polar organic solvent such as alcohol), more preferably an aqueous solvent containing at least water.
Among the alkali solutions, sodium hydroxide aqueous solution or potassium hydroxide aqueous solution is particularly preferable because of high versatility.

The temperature of the alkali solution in the alkali treatment step is not particularly limited, but is preferably 5 ° C. or more and 80 ° C. or less, and more preferably 10 ° C. or more and 60 ° C. or less.
The immersion time in the alkali solution in the alkali treatment step is not particularly limited, but is preferably 5 minutes to 30 minutes, and more preferably 10 minutes to 20 minutes.
The use amount of the alkali solution in the alkali treatment is not particularly limited, but is preferably 100% by mass or more and 100000% by mass or less, and is 1000% by mass or more and 10000% by mass or less based on the absolute dry mass of the phosphate group-introduced fiber Is more preferred.

  In order to reduce the amount of alkali solution used in the alkali treatment step, the phosphate group-introduced fiber may be washed with water or an organic solvent before the alkali treatment step. After the alkali treatment, in order to improve the handleability, it is preferable to wash the alkali-treated phosphate group-introduced fiber with water or an organic solvent before the defibration treatment step.

<Acid treatment>
When producing fine fibrous cellulose, an acid treatment may be performed between the phosphoric acid group introduction step and the defibration treatment step described later. Further, the phosphoric acid group introducing step, the acid treatment, the alkali treatment and the defibration treatment may be performed in this order.

  Although it does not specifically limit as the method of an acid treatment, For example, the method of immersing a phosphate group introduction | transduction fiber in the acidic liquid containing an acid is mentioned. The concentration of the acidic solution to be used is not particularly limited, but 10% by mass or less is preferable, and 5% by mass or less is more preferable. As an acid contained in an acidic liquid, an inorganic acid, sulfonic acid, carboxylic acid etc. can be used, for example. Examples of the inorganic acid include sulfuric acid, nitric acid, hydrochloric acid, hydrobromic acid, hydroiodic acid, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, phosphoric acid, boric acid and the like. Examples of the sulfonic acid include methanesulfonic acid, ethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid and the like. Examples of carboxylic acids include formic acid, acetic acid, citric acid, gluconic acid, lactic acid, oxalic acid, tartaric acid and the like. Among them, it is preferable to use hydrochloric acid as the acid.

The temperature of the acid solution in the acid treatment step is not particularly limited, but is preferably 5 ° C. or more and 80 ° C. or less, and more preferably 10 ° C. or more and 60 ° C. or less.
Although the immersion time to the acid solution in an acid treatment process is not specifically limited, 5 minutes or more and 30 minutes or less are preferable, and 10 minutes or more and 20 minutes or less are more preferable.
The use amount of the acid solution in the acid treatment is not particularly limited, but is preferably 100% by mass or more and 100000% by mass or less, and is 1000% by mass or more and 10000% by mass or less based on the absolute dry mass of the phosphate group-introduced fiber Is more preferred.

<Disintegration processing>
The phosphate group-introduced fiber is subjected to disintegration processing in a disintegration processing step. In the defibration treatment step, fibers are usually defibrated using a defibration treatment device to obtain a fine fibrous cellulose-containing slurry, but the treatment device and treatment method are not particularly limited.
As the defibration processing apparatus, a high-speed fibrillation machine, a grinder (millstone type crusher), a high pressure homogenizer, an ultrahigh pressure homogenizer, a high pressure collision type crusher, a ball mill, a bead mill, etc. can be used. Alternatively, use an apparatus for wet grinding such as a disc refiner, a conical refiner, a twin screw kneader, a vibration mill, a homomixer under high speed rotation, an ultrasonic disperser, or a beater as a defibration treatment apparatus. You can also. The defibration processing apparatus is not limited to the above. As a preferable defibration treatment method, a high-speed fibrillation machine, a high pressure homogenizer, and an ultrahigh pressure homogenizer, which are less affected by the grinding media and less likely to be contaminated, can be mentioned.

  At the time of the defibration treatment, it is preferable to dilute the fiber raw material with water and an organic solvent singly or in combination to form a slurry, but it is not particularly limited. As the dispersion medium, polar organic solvents can be used in addition to water. Preferred polar organic solvents include, but are not particularly limited to, alcohols, ketones, ethers, dimethylsulfoxide (DMSO), dimethylformamide (DMF), and dimethylacetamide (DMAc). As alcohols, methanol, ethanol, n-propanol, isopropanol, n-butanol, or t-butyl alcohol etc. are mentioned. Examples of ketones include acetone or methyl ethyl ketone (MEK). Examples of ethers include diethyl ether or tetrahydrofuran (THF). The dispersion medium may be one type, or two or more types. The dispersion medium may also contain solid components other than the fiber material, such as urea having hydrogen bonding property.

  In the present invention, the fibrillation treatment may be carried out after concentrating and drying the fine fibrous cellulose. In this case, the method of concentration and drying is not particularly limited, and examples thereof include a method of adding a thickener to a slurry containing fine fibrous cellulose, a method of using a generally used dehydrator, a press, and a dryer. Also, known methods can be used, such as the methods described in WO2014 / 024876, WO2012 / 107642, and WO2013 / 121086. Alternatively, concentrated fine fibrous cellulose may be sheeted. The sheet can also be crushed and subjected to disintegration processing.

  As an apparatus used for pulverizing fine fibrous cellulose, a high-speed fibrillation machine, a grinder (stone mill type crusher), a high pressure homogenizer, an ultra high pressure homogenizer, a high pressure collision type crusher, a ball mill, a bead mill, a disc type refiner, a conical An apparatus for wet grinding such as a refiner, a twin screw kneader, a vibration mill, a homomixer under high speed rotation, an ultrasonic dispersion machine, a beater, etc. can also be used, but is not particularly limited. Also, the treatment conditions are not particularly limited as long as a preferable degree of polymerization can be obtained.

  In the present invention, it is possible to control the average degree of polymerization of the fine fibrous cellulose within a preferable range by appropriately selecting the raw material and the production conditions of the fine fibrous cellulose. Such production conditions are not particularly limited, but include, for example, adjusting the pressure conditions and the number of treatments in the defibration treatment process, and selecting the type of production apparatus. For example, when the defibration treatment is performed at a pressure of 245 MPa using a wet atomization device, the average degree of polymerization of the fine fibrous cellulose is controlled within a preferable range by setting the number of treatments one or more and eight or less. It is also good.

  The fine fibrous cellulose having a phosphate group obtained by the above-mentioned method may be in the form of a slurry, or may be used after dilution with water so as to obtain a desired concentration.

(Battery separator coating fluid)
The present invention also relates to a separator coating solution for a battery, which contains fine fibrous cellulose having a fiber width of 1000 nm or less and an average polymerization degree of 400 or more and 2000 or less, fine particles, and a dispersion medium. That is, the battery separator coating liquid contains a thickener for the battery separator coating liquid, contains the above-described fine fibrous cellulose, and preferably contains phosphorylated cellulose.

  The average degree of polymerization of the fine fibrous cellulose may be 400 or more, preferably 420 or more, and more preferably 430 or more. The average degree of polymerization of the fine fibrous cellulose may be 2000 or less, preferably 1500 or less, more preferably 1200 or less, still more preferably 1000 or less, and 600 or less. Particularly preferred.

  When the average degree of polymerization of the fine fibrous cellulose in the battery separator coating solution is calculated, the measurement is performed after the fine fibrous cellulose is isolated from the battery separator coating solution according to the following procedure.

<Observation of battery separator coating solution>
First, the battery separator coating liquid is diluted and dried, and then observed with a transmission electron microscope to confirm the presence of fine fibrous cellulose. Solid-state NMR is then used to detect cellulose Form I crystals.

<Isolation of fine fibrous cellulose in battery separator coating liquid>
When the presence of the fine fibrous cellulose is confirmed in the battery separator coating liquid, the fine fibrous cellulose is isolated according to the following procedure.
First, we measure 20 ± 5 g of the battery separator coating solution in a 50 ml aluminum cup. Similarly, a plurality of aluminum cups from which the battery separator coating liquid is weighed are prepared. The battery separator coating liquid is dried by heating at 105 ° C. for 16 hours with a blower constant temperature dryer. A 0.5 mol / L copper ethylenediamine solution is added to 1 g of the dried battery separator coating liquid so as to have a ratio of 100 ml, and the mixture is stirred to dissolve fine fibrous cellulose. The obtained solution is filtered to remove the residue, and then dropped into water to obtain regenerated cellulose. This regenerated cellulose is one in which fine fibrous cellulose is dissolved in a copper ethylenediamine solution and regenerated in water. The regenerated cellulose obtained is separated by filtration, sufficiently washed with water and dried.

<Measurement of Fine Fibrous Cellulose Content in Separator Coating Liquid for Battery>
The dry weight of the obtained regenerated cellulose is measured. From this weight and the weight of the battery separator coating solution used to obtain this weight, the content of the fine fibrous cellulose contained in the battery separator coating solution is determined.

<Measurement of degree of polymerization of fine fibrous cellulose isolated from battery separator coating liquid>
To 0.14 g or more and 0.16 g or less of the obtained dried product of regenerated cellulose, 30 ml of a 0.5 mol / L copper ethylenediamine solution is added and stirred to dissolve the cellulose again. The resulting solution is filtered to remove the residue. After that, 10 ml of the prepared filtrate is put into a Cannonfence viscometer, placed for 5 minutes, and the dropping time is measured. The intrinsic viscosity is determined from the measured fall time according to the method described above, and converted to the degree of polymerization.

  The content of the fine fibrous cellulose is preferably 0.1 parts by mass or more and 2.0 parts by mass or less with respect to 100 parts by mass of the dispersion medium. The content of the fine fibrous cellulose is more preferably 0.2 parts by mass or more, still more preferably 0.3 parts by mass or more. Further, the content of the fine fibrous cellulose is more preferably 1.3 parts by mass or less, still more preferably 1.1 parts by mass or less, with respect to 100 parts by mass of the dispersion medium. It is particularly preferred that the amount is at most parts by mass.

  The present invention is also characterized in that the content of the fine fibrous cellulose in the battery separator coating liquid is small. In the present invention, even when the amount of fine fibrous cellulose added is small, the fine particle dispersibility can be enhanced, and the viscosity reduction rate after stirring can be suppressed to a low level. If the viscosity reduction rate after stirring is small, the coating liquid can be sufficiently stirred with strong stirring power, and a uniform coating liquid can be obtained. In addition, stable production is realized because there is no change in the coating liquid at the start and end of the coating, even when the battery separator is manufactured. Furthermore, in the present invention, the coating property (the ease of coating) can be enhanced by suppressing the amount of the fine fibrous cellulose added.

  Furthermore, in the present invention, since the amount of fine fibrous cellulose added can be suppressed, clogging of the micropores of the battery separator substrate can also be suppressed. Usually, there is a trade-off relationship between the prevention of micropores blocking of the battery separator substrate and the prevention of the occurrence of the strikethrough, but the battery separator coating liquid of the present invention has a fine fibrous cellulose having a predetermined structure In the above content, it has both the functions of suppressing the blocking of the microporous substrate and preventing the occurrence of strike-through.

The viscosity of the battery separator coating solution is preferably 100 mPa · s or more, more preferably 300 mPa · s or more, and still more preferably 400 mPa · s or more. The viscosity of the battery separator coating solution is preferably 40000 mPa · s or less, more preferably 20000 mPa · s or less, and still more preferably 10000 mPa · s or less. The viscosity of the battery separator coating solution is measured using a B-type viscometer (analog viscometer T-LVT, manufactured by BLOOKFIELD) at a rotational speed of 3 rpm, a measuring time of 3 minutes, and a solution temperature of 25 ° C.
The present invention is characterized in that the viscosity of the battery separator coating liquid is in the above range even after strong stirring. Here, the strong stirring in the present specification means stirring under a condition of 2000 rpm or more with a high-speed stirring device such as a homodisper that generates a suitable shear force. For example, in the present invention, even when stirring is performed at 3000 rpm for 3 hours using a homodisper as a stirrer, the decrease in viscosity of the battery separator coating liquid is small.

The viscosity reduction rate (%) of the battery separator coating liquid is preferably less than 20%, and more preferably less than 10%. Here, the viscosity reduction rate (%) of the battery separator coating liquid can be measured by the following method. First, the viscosity of the prepared battery separator coating solution is measured at 25 ° C. using a B-type viscometer (analog viscometer T-LVT, manufactured by BLOOK FIELD). Then T. K. The mixture is stirred at 3000 rpm for 3 hours with a homodisper (manufactured by Tokushu Kika Kogyo Co., Ltd.), and the viscosity is measured again. The viscosity reduction rate is calculated by the following equation.
Viscosity reduction rate (%) = (viscosity before stirring−viscosity after stirring) / viscosity before stirring × 100

<Particles>
Examples of the fine particles contained in the battery separator coating liquid include organic fine particles and inorganic fine particles. Among them, the fine particles are preferably inorganic fine particles.

  Examples of the resin constituting the organic fine particles include aromatic vinyl compounds such as styrene, α-methylstyrene and p-methylstyrene, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate and the like Resins obtained by polymerizing one or two or more kinds of (meth) acrylic esters, vinyl cyanides such as (meth) acrylonitrile, vinyl halides such as vinyl chloride and vinylidene chloride, and vinyl monomers such as butadiene Can be mentioned.

Examples of the inorganic fine particles include fine particles of oxides such as iron oxide, Al ₂ O ₃ (alumina), SiO ₂ (silica), TiO ₂ , BaTiO ₃ , and ZrO ₂ ; fine particles of nitride such as aluminum nitride and silicon nitride; Calcium chloride, barium fluoride, barium sulfate and other poorly soluble ionic crystal particles; silicon, diamond and other covalently bonded crystalline particles; talc, montmorillonite and other clay particles; boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine Materials derived from mineral resources such as sericite, bentonite, and the like; Further, metal fine particles; oxide fine particles such as SnO ₂ , tin-indium oxide (ITO) and the like; carbon fine particles such as carbon black and graphite; and the like can be mentioned. Among them, at least one fine particle selected from alumina, silica and boehmite is preferable.
Further, it is preferable that the surface of the fine particles be coated with a material having electrical insulation (for example, a material constituting the above-mentioned insulating fine particles) to form fine particles having electrical insulation.

  The form of the fine particles may be any form such as a spherical shape, a polyhedral shape, or a plate shape. Further, the primary average particle diameter of the fine particles is preferably 0.01 μm or more, and more preferably 5 μm or less. In addition, when microparticles | fine-particles are not spherical, it is preferable that the value which calculated the primary average particle diameter supposing that it is spherical of the same volume is in the said range.

The content of the fine particles is preferably 5% by mass or more, and more preferably 10% by mass or more based on the total mass of the battery separator coating liquid. In addition, the content of the fine particles is preferably 90% by mass or less, more preferably 80% by mass or less, and still more preferably 70% by mass or less. By making content of microparticles | fine-particles into the said range, the heat resistance of the battery separator base material mentioned later can be improved more effectively.
In addition, when the content of the fine particles is, for example, 10% by mass or less, the collision probability of the fine particles is reduced, and a tendency to be easily precipitated is observed. However, since the battery separator coating liquid of the present invention contains the fine fibrous cellulose having a predetermined structure, the sedimentation of the fine particles can be suppressed even when the content of the fine particles is small.

<Dispersion medium>
The battery separator coating liquid contains a dispersion medium. As a dispersion medium, water, an organic solvent, and a mixture thereof can be mentioned. Among them, the dispersion medium is preferably water. Examples of the organic solvent include toluene, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, isopropyl alcohol and the like. In the specification of the present application, the dispersion medium refers to the remaining part of the battery separator coating liquid except for the solid content remaining upon drying when forming the coated layer.

  The content of the dispersion medium is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably 30% by mass or more based on the total mass of the battery separator coating liquid. . Further, the content of the dispersion medium is preferably 90% by mass or less, and more preferably 80% by mass or less.

<Other ingredients>
The battery separator coating liquid may further contain a binder component in addition to the above components. Specific examples of the binder component include, for example, ethylene-vinyl acetate copolymer; (meth) acrylic acid copolymer such as ethylene-ethyl acrylate copolymer, ethylene-ethyl methacrylate copolymer, etc .; fluoro rubber; styrene -Butadiene rubber (SBR); Polyvinyl alcohol (PVA); Polyvinyl butyral (PVB); Polyvinyl pyrrolidone (PVP); Poly N-vinyl acetamide; Crosslinked acrylic resin; Polyurethane; Epoxy resin; These binder components may be used alone or in combination of two or more. When the battery separator coating liquid further contains a binder component, the adhesiveness with the battery separator base material mentioned later can be improved. It is preferable that content of the said binder component is 2 mass% or more and 15 mass% or less with respect to the total mass of the microparticles | fine-particles in the separator coating liquid for batteries.

  Moreover, as another component contained in the separator coating liquid for batteries, hydrophilic polymer, an organic ion, etc. are mentioned, for example. Examples of hydrophilic polymers include polyethylene glycol, cellulose derivatives (such as hydroxyethyl cellulose, carboxyethyl cellulose and carboxymethyl cellulose), casein, dextrin, starch, modified starch, polyvinyl alcohol, modified polyvinyl alcohol (such as acetoacetylated polyvinyl alcohol), Examples thereof include polyethylene oxide, polyvinyl pyrrolidone, polyvinyl methyl ether, polyacrylates, polyacrylamide, alkyl acrylate copolymer, urethane copolymer and the like. As an organic ion, a tetraalkyl ammonium ion and a tetraalkyl phosphonium ion can be mentioned. Examples of the tetraalkyl ammonium ion include tetramethyl ammonium ion, tetraethyl ammonium ion, tetrapropyl ammonium ion, tetrabutyl ammonium ion, tetrapentyl ammonium ion, tetrahexyl ammonium ion, tetraheptyl ammonium ion, tributyl methyl ammonium ion, lauryl trimethyl Ammonium ion, cetyl trimethyl ammonium ion, stearyl trimethyl ammonium ion, octyl dimethyl ethyl ammonium ion, lauryl dimethyl ethyl ammonium ion, didecyl dimethyl ammonium ion, lauryl dimethyl benzyl ammonium ion, tributyl benzyl ammonium ion can be mentioned. Examples of the tetraalkyl phosphonium ion include tetramethyl phosphonium ion, tetraethyl phosphonium ion, tetrapropyl phosphonium ion, tetrabutyl phosphonium ion, and lauryl trimethyl phosphonium ion. Moreover, tetra n-propyl onium ion, tetra n-butyl onium ion, etc. can be mentioned as tetrapropyl onium ion and tetrabutyl onium ion, respectively. The content of the hydrophilic polymer and the organic ion is preferably 20% by mass or less based on the total mass of the fine particles in the battery separator coating liquid. The lower limit of the content of the hydrophilic polymer and the organic ion is not particularly limited, but may be, for example, 0.1% by mass, and may not be substantially contained.

(Separator for battery)
The present invention also relates to a battery separator having a substrate and a coating layer. The coating layer contains fine fiber cellulose having a fiber width of 1000 nm or less and an average polymerization degree of 400 or more and 2000 or less.
The battery separator may have a coated layer on at least one surface of the substrate, and may have a coated layer on both sides of the substrate, but the coated layer is on one side of the substrate It is preferable to have In addition, although the battery separator has a coating layer, a part of the battery separator coating liquid which forms a coating layer soaks in the surface layer area | region of a base material.

  The battery separator is formed by coating the above-described battery separator coating liquid on a substrate. The coating layer formed by coating contains the thickener for battery separator coating liquids, and contains the fine fibrous cellulose mentioned above. The fine fibrous cellulose is preferably phosphated cellulose.

  The average degree of polymerization of the fine fibrous cellulose may be 400 or more, preferably 420 or more, and more preferably 430 or more. The average degree of polymerization of the fine fibrous cellulose may be 2000 or less, preferably 1500 or less, more preferably 1200 or less, still more preferably 1000 or less, and 600 or less. Particularly preferred.

  In addition, when calculating the average polymerization degree of the fine fibrous cellulose in the battery separator, the measurement is performed after the fine fibrous cellulose is isolated from the battery separator in the following procedure.

<Surface analysis of battery separator>
First, the surface of the battery separator is observed with a transmission electron microscope to confirm the presence of fine fibrous cellulose. Solid-state NMR is then used to detect cellulose Form I crystals.

<Isolation of fine fibrous cellulose in battery separators>
When the presence of the fine fibrous cellulose is confirmed on the battery separator surface, the fine fibrous cellulose is isolated according to the following procedure.
First, the battery separator is cut into about 1 cm square, and then crushed to about 1 mm square using a cutter mill. Next, a 0.5 mol / L copper ethylenediamine solution is added to 1 g of the pulverized product of the battery separator so as to have a ratio of 100 ml, and stirred to dissolve fine fibrous cellulose. The obtained solution is filtered to remove the residue, and then dropped into water to obtain regenerated cellulose. This regenerated cellulose is one in which fine fibrous cellulose is dissolved in a copper ethylenediamine solution and regenerated in water. The regenerated cellulose obtained is separated by filtration, sufficiently washed with water and dried.

<Fine Fibrous Cellulose Content of Battery Separator>
The dry weight of the obtained regenerated cellulose is measured. From this weight and the weight of the battery separator used to obtain this weight, the content of the fine fibrous cellulose contained in the battery separator is determined.

<Measurement of degree of polymerization of fine fibrous cellulose isolated from battery separator coating liquid>
To 0.14 g or more and 0.16 g or less of the obtained dried product of regenerated cellulose, 30 ml of a 0.5 mol / L copper ethylenediamine solution is added and stirred to dissolve the cellulose again. The resulting solution is filtered to remove the residue. After that, 10 ml of the prepared filtrate is put into a Cannonfence viscometer, placed for 5 minutes, and the dropping time is measured. The intrinsic viscosity is determined from the measured fall time according to the method described above, and converted to the degree of polymerization.

  The coated layer contains fine particles. As microparticles | fine-particles, the microparticles | fine-particles mentioned above can be listed and it is preferable that it is inorganic microparticles. Preferred embodiments are as described above.

  The thickness of the coating layer varies depending on the pore size on the substrate side, but is preferably 0.1 μm or more, more preferably 0.5 m or more, and still more preferably 1 μm or more. Moreover, it is preferable that it is 20 micrometers or less, It is more preferable that it is 15 micrometers or less, It is more preferable that it is 10 micrometers or less.

<Base material>
The battery separator comprises a substrate. The substrate is preferably stable to the electrolyte and is a porous substrate.

Specific examples of the constituent material of the substrate include, for example, cellulose, modified cellulose (such as carboxymethyl cellulose), polyolefin (polypropylene (PP), polyethylene (PE), and copolymerized polyolefin having 85 mol% or more of a structural unit derived from ethylene. Etc.), polyester (polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT) etc.), polyacrylonitrile (PAN), aramid, polyamideimide, polyimide etc. resin; glass, alumina, silica etc. Inorganic materials (inorganic oxides) can be mentioned.
Among them, the constituent material of the base material is preferably a polyolefin resin, and more preferably polypropylene or polyethylene. It is particularly preferable that the substrate is a non-woven fabric or a film made of polypropylene or polyethylene.

  In the case where the base material is a non-woven fabric made of polyethylene, it is preferable to make polyethylene fibers by a wet paper making method to form a non-woven fabric. In the non-woven fabric, polyethylene fibers are preferably randomly oriented.

  When the substrate is a film made of polyethylene, the film is preferably a stretched film, and more preferably a biaxially stretched film.

The battery separator substrate may have an adhesive. When the battery separator base has an adhesive, it is preferable to contain an acrylic resin as the adhesive. Examples of acrylic resins include ethylene- (meth) acrylic acid resins and propylene- (meth) acrylic acid resins. The adhesive is preferably sprayed onto the surface of the substrate, and is preferably present in the surface region of the substrate. Such an adhesive serves to enhance the adhesion between the substrate and the coating layer.
In addition, other resins can be used in combination as needed. As a resin which can be used in combination, vinyl chloride resin, (meth) acrylic acid ester resin, styrene / acrylic acid ester copolymer resin, vinyl acetate resin, vinyl acetate / (meth) acrylic acid ester copolymer resin, urethane resin, Examples thereof include silicone resins, epoxy resins, ethylene / vinyl acetate copolymer resins, polyester resins, polyvinyl alcohol resins, ethylene vinyl alcohol copolymer resins, and rubber emulsions such as SBR and NBR.

The basis weight of the substrate is preferably 10 g / m ² or more, more preferably 20 g / m ² or more. The basis weight of the substrate is preferably 100 g / m ² or less, more preferably 80 g / m ² or less.

The density of the substrate is preferably 0.1 g / cm ³ or more, more preferably 0.2 g / cm ³ or more, and still more preferably 0.3 g / cm ³ or more. The density of the substrate is preferably 3.0 g / cm ³ or less, more preferably 2.0 g / cm ³ or less, and still more preferably 1.0 g / cm ³ or less.

<Method of Manufacturing Battery Separator>
It is preferable that the manufacturing process of the battery separator includes a step of applying a battery separator coating liquid to at least one surface of the substrate, and a step of drying the substrate coated with the battery separator coating liquid. When the battery separator coating liquid is applied to the surface of the substrate, a conventionally known coating machine can be used. As a coating machine, a die coater, a gravure coater, a reverse roll coater, a squeeze roll coater, a curtain coater, a blade coater, a knife coater etc. can be mentioned, for example. In addition, it is preferable that the separator coating liquid for batteries is apply | coated on the single side | surface of a base material.

It is preferable that it is 1 g / m < ² > or more, and, as for the application amount (adhesion amount to a base material) of the separator coating liquid for batteries, it is more preferable that it is ² g / m <2> or more. The coating amount of the battery separator coating solution is preferably 50 g / m ² or less, more preferably 20 g / m ² or less.

(Use)
The battery separator of the present invention is preferably used in an electrochemical device represented by a lithium secondary battery and the like. The electrochemical device can be used in applications such as supercapacitors as well as lithium batteries (primary batteries and secondary batteries) using organic electrolytes.

  The lithium secondary battery may be in the form of a cylinder (square cylinder, cylinder, etc.) using a steel can or aluminum can as an outer case, or a soft package with a laminated film with metal deposited on the outer case. You can also.

The positive electrode is not particularly limited as long as it is a positive electrode used in a conventionally known lithium secondary battery. The positive electrode contains an active material capable of inserting and extracting Li ⁺ ions.
The negative electrode is not particularly limited as long as it is a negative electrode conventionally used in lithium secondary batteries. The negative electrode contains an active material capable of inserting and extracting Li ⁺ ions.

  The positive electrode and the negative electrode can be used in the form of an electrode group of a laminated structure laminated through the battery separator of the present invention, or an electrode group of a wound structure obtained by winding the electrode group.

As the organic electrolytic solution, a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and does not cause side reactions such as decomposition in the voltage range used as a battery. The organic solvent is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in the voltage range used as a battery.

  As mentioned above, lithium secondary batteries are used in addition to power applications for various devices such as mobile phones, portable devices such as laptop personal computers, electric cars, hybrid cars, electric bikes, electrically assisted bicycles, electric tools, electric tools, and shavers. It is used for various conventionally known applications.

  The features of the present invention will be more specifically described below with reference to examples and comparative examples. The materials, amounts used, proportions, treatment contents, treatment procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as limited by the specific examples shown below.

<Production of Fine Fibrous Cellulose 1 (for Example)>
A softwood kraft pulp with a dry mass of 100 parts by mass is impregnated with a mixed aqueous solution of ammonium dihydrogen phosphate and urea, and squeezed so that 49 parts by mass of ammonium dihydrogen phosphate and 130 parts by mass of urea are contained. I got The obtained drug-impregnated pulp was dried by a dryer at 105 ° C., and the water was evaporated to pre-dry. Then, it heated for 10 minutes with the ventilation dryer set to 140 degreeC, the phosphoric acid group was introduce | transduced into the cellulose in pulp, and the phosphated pulp was obtained.

  The phosphated pulp thus obtained was fractionated by 100 g in terms of pulp mass, and 10 L of ion-exchanged water was poured, stirred and uniformly dispersed, and then filtered and dewatered to obtain a dehydrated sheet. This process was repeated twice. Next, the obtained dehydrated sheet was diluted with 10 L of ion-exchanged water, and while stirring, a 1N aqueous solution of sodium hydroxide was added little by little to obtain a pulp slurry having a pH of 12 or more and 13 or less. Thereafter, the pulp slurry was dewatered to obtain a dewatered sheet, and then 10 L of ion exchange water was added. After stirring and dispersing uniformly, the process of filtration dehydration was repeated twice to obtain a dewatered sheet.

With respect to the obtained dehydrated sheet, in the same manner as described above, the step of introducing a phosphoric acid group and the step of filtering and dewatering were repeated to obtain a dehydrated sheet 1 of phosphocellulose twice. The infrared absorption spectrum of the resulting dehydrated sheet 1 was measured by FT-IR. As a result, absorption based on the phosphate group was observed at 1230 cm ⁻¹ or more and 1290 cm ⁻¹ or less, and addition of the phosphate group was confirmed. The obtained dehydrated sheet 1 (twice phosphorylated cellulose) was obtained by substituting part of hydroxyl groups of cellulose with a functional group of the following structural formula (1).

In formula, a, b, m and n each independently represent a natural number (however, a = b × m). α ¹ , α ² ,..., α ⁿ and α ′ each independently represent R or OR. R represents a hydrogen atom, a saturated-linear hydrocarbon group, a saturated-branched hydrocarbon group, a saturated-cyclic hydrocarbon group, an unsaturated-linear hydrocarbon group, an unsaturated-branched hydrocarbon group , Aromatic groups, and any of these derivative groups. β is a monovalent or more cation composed of an organic substance or an inorganic substance.

  Ion-exchanged water was added to the obtained twice-phosphorylated cellulose to prepare a slurry having a solid content concentration of 2% by mass. This slurry was further treated 6 times with a wet atomization device (manufactured by Sugino Machine Ltd., Ultimizer) at a pressure of 245 MPa to obtain fine fibrous cellulose 1. It was confirmed by X-ray diffraction that this fine fibrous cellulose 1 maintained cellulose type I crystals.

<Production of Fine Fibrous Cellulose 2 (for Example)>
A fine fibrous cellulose 2 was obtained in the same manner as in the production of the fine fibrous cellulose 1 except that the number of times of pressure treatment at 245 MPa in the wet atomization device was changed to three. It was confirmed by X-ray diffraction that this fine fibrous cellulose 2 maintained cellulose type I crystals.

<Production of Fine Fibrous Cellulose 3 (for Example)>
After obtaining phosphorylated pulp in the same manner as in the production of the fine fibrous cellulose 1, 5000 parts by mass of ion-exchanged water was added to 100 parts by mass as the bone dry mass of the dehydrated sheet 1 of the phosphorylated pulp to dilute. Then, while stirring, 1 N hydrochloric acid was added little by little to obtain a pulp slurry having a pH of 2 or more and 3 or less. Thereafter, the pulp slurry was dewatered to obtain a dewatered sheet, and then ion-exchanged water was again poured and stirred to disperse uniformly. Then, the procedure of obtaining a dewatered sheet by filtration dewatering was repeated to wash away excess hydrochloric acid sufficiently to obtain a phosphorylated pulp (H type).

5000 parts by mass of ion exchange water was added to 100 parts by mass as the dry weight of the phosphorylated pulp (H type) to dilute. Then, while stirring, a 10% by mass tetrabutylammonium hydroxide aqueous solution was added little by little to obtain a pulp slurry having a pH of 10 or more and 12 or less. Thereafter, the pulp slurry was dewatered to obtain a dewatered sheet, and then ion-exchanged water was again poured and stirred to disperse uniformly. Next, the procedure of filtration dewatering to obtain a dewatered sheet was repeated to sufficiently wash away the excess aqueous solution of tetrabutylammonium hydroxide to obtain phosphorylated pulp (TBA type) (16 carbon atoms of counter ion).
A mixed solvent of isopropanol / water (mass ratio: 70/30) is added to the obtained phosphorylated pulp (TBA type) so that the bone dry solid concentration of the phosphorylated pulp (TBA) becomes 1% by mass. Prepared. Thus, a pre-refining slurry was obtained.
The obtained pre-micronization slurry was treated three times with a wet atomization device (manufactured by Sugino Machine Ltd., Ultimizer) at a pressure of 245 MPa to obtain fine fibrous cellulose 3.

<Production of Fine Fibrous Cellulose A (for Comparative Example)>
Undried softwood bleached kraft pulp equivalent to a dry mass of 100 parts by mass, 1.25 parts by mass of TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl), and 12.5 parts by mass of sodium bromide It was dispersed in 10000 parts by mass of water. Next, a 13% by mass aqueous solution of sodium hypochlorite was added such that the amount of sodium hypochlorite was 8.0 mmol with respect to 1.0 g of pulp to start the reaction. During the reaction, a 0.5 M aqueous solution of sodium hydroxide was added dropwise to keep the pH at 10 or more and 11 or less, and when no change was observed in the pH, the reaction was regarded as complete.

Thereafter, the pulp slurry is dewatered to obtain a dewatered sheet, and then 5000 parts by mass of ion-exchanged water is poured, and after stirring and uniformly dispersing, the step of dewatering by filtration and obtaining the dewatered sheet is repeated twice. The The infrared absorption spectrum of the resulting dehydrated sheet was measured by FT-IR. As a result, absorption based on the carboxyl group was observed at 1730 cm ⁻¹ , and addition of the carboxyl group was confirmed. Using this dehydrated sheet (TEMPO oxidized cellulose), fine fibrous cellulose was prepared.

  Ion-exchanged water was added to the obtained TEMPO oxidized cellulose to prepare a slurry having a solid content concentration of 2% by mass. This slurry was further treated three times with a wet atomization device (manufactured by Sugino Machine Ltd., Ultimizer) at a pressure of 245 MPa to obtain a fine fibrous cellulose A. It was confirmed by X-ray diffraction that this fine fibrous cellulose maintained cellulose type I crystals.

(Physical properties of fine fibrous cellulose)
<Measurement of fiber width>
The fiber width of the fine fibrous cellulose was measured by the following method.
The supernatant liquid of fine fibrous cellulose treated with a wet atomization device was diluted with water so that the concentration of fine fibrous cellulose was 0.01% by mass or more and 0.1% by mass or less, and was hydrophilized. It dripped on the carbon grid film. After drying, it was stained with uranyl acetate and observed with a transmission electron microscope (JEOL-2000EX, manufactured by JEOL Ltd.). Fine fibrous celluloses 1 to 3 and fine fibrous cellulose A were confirmed to be fine fibrous cellulose having a fiber width of about 4 nm.

<Measurement of amount of substituent>
The substituent introduction amount is the introduction amount of phosphoric acid group or carboxylic acid group to the fiber material, and the larger the value is, the more phosphoric acid group or carboxylic acid group is introduced. The amount of introduced substituent was measured by diluting the target fine fibrous cellulose with ion exchange water so that the content would be 0.2% by mass, and then treating with an ion exchange resin and titration using an alkali. In the treatment with ion exchange resin, 1/10 strongly acidic ion exchange resin (Amberjet 1024; Organo Corporation, conditioned) is added to a 0.2% by mass fibrous cellulose-containing slurry and shaken for 1 hour Did. Then, it poured on the mesh of 90 micrometers of openings, and the resin and the slurry were isolate | separated. In the titration using an alkali, a change in the value of electric conductivity exhibited by the slurry was measured while adding a 0.1 N aqueous solution of sodium hydroxide to the fine fibrous cellulose-containing slurry after ion exchange. That is, the amount of alkali (mmol) required in the first region of the curve shown in FIG. 1 (phosphate group) and FIG. 2 (carboxy group) is divided by the solid content (g) in the slurry to be titrated, The amount of introduced substituent (mmol / g). The calculated results are shown in Table 1 below.

<Measurement of polymerization degree>
Evaluation of the average degree of polymerization of the cellulose molecule which comprises fine fibrous cellulose was performed with reference to the following paper.
TAPPI International Standard; ISO / FDIS 5351, 2009.
Smith, DK; Bampton, RF; Alexander, WJ Ind. Eng. Chem., Process Des. Dev. 1963, 2, 57-62.

30 g of a suspension prepared by diluting the target fine fibrous cellulose with ion-exchanged water to a content of 2 ± 0.3 mass% is collected in a centrifuge tube, and allowed to stand overnight in a freezer for freezing The Furthermore, after drying with a lyophilizer for 5 days or more, heating was carried out for 3 hours or more and 4 hours or less with a constant temperature dryer set at 105 ° C. to obtain a fine fibrous cellulose in an asphyxic state.
In order to measure the reference, 15 ml of pure water and 15 ml of 1 mol / L copper ethylenediamine were added to an empty 50 ml screw tube, and a 0.5 mol / L copper ethylene diamine solution was prepared. 10 ml of the above 0.5 mol / L copper ethylenediamine solution was placed in a Cannon-Fenske viscometer, placed for 5 minutes, and then the drop time was measured to determine the solvent drop time.

  Next, in order to measure the viscosity of the fine fibrous cellulose, 0.14 g to 0.16 g of fine fibrous cellulose in an as-dried state was weighed into an empty 50 ml screw tube, and 15 ml of pure water was added. Further, 15 ml of 1 mol / L copper ethylenediamine was added, and the mixture was stirred at 1000 rpm for 10 minutes with a rotation-revolution type super mixer to obtain a 0.5 mol / L copper ethylene diamine solution. Similarly to the measurement of the reference, 10 ml of the prepared 0.5 mol / L copper ethylenediamine solution was put in a Cannon-Fenske viscometer, placed for 5 minutes, and then the fall time was measured. It measured 3 times and used the average value.

The degree of polymerization was calculated using the following equation from the mass of the fibrillated cellulose in the dry state used for the measurement, the solvent dropping time, and the dropping time of the copper ethylenediamine solution in which the fine fibrous cellulose was dissolved. In addition, the following average degree of polymerization is an average value of the value measured 3 times.
Fine fibrous cellulose mass in the dry state used for measurement: a (g) (where a is 0.14 or more and 0.16 or less)
Cellulose concentration of solution: c = a / 30 (g / mL)
Solvent falling time: t ₀ (sec)
Fall time of fine fibrous cellulose solution: t (sec)
Relative viscosity of solution: _rel = t / t ₀
Specific viscosity of solution: _{sp sp} = _rel- 1
Intrinsic viscosity: [η] = η _{sp /} c (1 + 0.28 _{sp sp} )
Degree of polymerization: DP = [η] /0.57

Example 1
Add 51 g of water as a dispersion medium to 100 g of fine silica particles (manufactured by Fuji Silysia Chemical Ltd., Sylysia 310, particle diameter: 1.4 μm), K. The mixture was stirred with a homodisper (manufactured by Tokushu Kika Kogyo) at 3000 rpm for 15 minutes. After that, 50 g of a suspension of fine fibrous cellulose 1 having a solid content concentration of 2% by mass (a suspension of 1 g of solid content of fine fibrous cellulose 1 and 49 g of water) was added, and the mixture was further stirred for 1 hour with a disperser. Thus, a battery separator coating liquid having a solid content concentration of 1 part by mass of fine fibrous cellulose with respect to 50% by mass of the silica fine particles and 100 parts by mass of the dispersion medium (51 g of the above dispersion medium + 49 g of water) was obtained.

Example 2
In Example 1, the amount of water previously added to the silica fine particles was 65.7 g, and the amount of the suspension of the fine fibrous cellulose 1 having a solid content concentration of 2% by mass was 35 g (solid content of the fine fibrous cellulose 1 0 The procedure of Example 1 was repeated, except that 7 g of water and 34.3 g of water were used to prepare a battery separator coating solution.

Example 3
The amount of water previously added to the silica fine particles in Example 1 was 80.4 g, and the amount of the suspension of fine fibrous cellulose 1 having a solid content concentration of 2% by mass was 20 g (solid content of fine fibrous cellulose 1 0 The same procedure as in Example 1 was carried out except that a battery separator coating solution was prepared as .4 g and water 19.6 g).

Example 4
The same procedure as in Example 1 was repeated except that the fine fibrous cellulose 1 was replaced with the fine fibrous cellulose 2 in Example 1.

Example 5
The same procedure as in Example 2 was repeated except that the fine fibrous cellulose 1 was replaced with the fine fibrous cellulose 2 in Example 2.

Example 6
The same procedure as in Example 3 was repeated except that the fine fibrous cellulose 1 was replaced with the fine fibrous cellulose 2 in Example 3.

Example 7
The same procedure as in Example 1 was carried out except that the silica fine particles in Example 1 were replaced with boehmite (manufactured by Kawai Lime Industry Co., Ltd., Seraseule BMB, particle diameter: 1.5 μm to 2 μm).

Example 8
The same procedure as in Example 2 was repeated except that the silica fine particles in Example 2 were replaced with boehmite (manufactured by Kawai Lime Industry Co., Ltd., Seraseule BMB, particle diameter: 1.5 μm to 2 μm).

Example 9
The same procedure as in Example 3 was repeated except that the silica fine particles in Example 3 were replaced with boehmite (manufactured by Kawai Lime Industry Co., Ltd., Seraseule BMB, particle diameter: 1.5 μm to 2 μm).

Example 10
The same procedure as in Example 1 was repeated except that the silica fine particles in Example 1 were replaced with alumina (manufactured by Nippon Light Metal Co., Ltd., fine particle alumina A32, particle diameter: 1 μm).

Example 11
The same procedure as in Example 2 was repeated except that the silica fine particles in Example 2 were replaced with alumina (manufactured by Nippon Light Metal Co., Ltd., fine particle alumina A32, particle diameter: 1 μm).

Example 12
The same procedure as in Example 3 was repeated except that the silica fine particles in Example 3 were replaced with alumina (manufactured by Nippon Light Metal Co., Ltd., fine particle alumina A32, particle diameter: 1 μm).

Example 13
In Example 1, the fine fibrous cellulose 1 is used as the fine fibrous cellulose 3, and the dispersion medium added in advance to the silica fine particles is 60.4 g of a mixed solvent of isopropyl alcohol (IPA) / water = 70/30 (mass ratio), solid content Except that the amount of the suspension of fine fibrous cellulose 3 having a concentration of 1% by mass was 40 g (solid content of the fine fibrous cellulose 3 0.4 g, dispersion medium 39.6 g) and the battery separator coating liquid was prepared All were carried out as in Example 1.

Example 14
The same procedure as in Example 1 was carried out except that the amount of silica fine particles added was 25 g in Example 1.

Example 15
The same procedure as in Example 2 was followed except that the amount of silica fine particles added was 25 g in Example 2.

Example 16
The same procedure as in Example 3 was carried out except that the amount of silica fine particles added was 25 g in Example 3.

Example 17
The amount of water previously added to the silica fine particles in Example 14 is 26.5 g, and the amount of the suspension of the fine fibrous cellulose 1 having a solid content concentration of 2% by mass is 75 g (solid content 1 of the fine fibrous cellulose 1) The procedure of Example 14 was repeated, except that a battery separator coating solution was prepared as .5 g and 73.5 g of water.

Comparative Example 1
The same procedures as in Example 1 were carried out except that the fine fibrous cellulose 1 was replaced with the fine fibrous cellulose A in Example 1.

Comparative Example 2
The same procedure as in Example 1 was repeated except that the fine fibrous cellulose 1 was replaced by carboxymethylcellulose (Telpolymer H, manufactured by Ternite Co., Ltd.) in Example 1.

Comparative Example 3
The same procedure as in Example 1 was repeated except that fine fibrous cellulose 1 was replaced with xanthan gum (manufactured by Tokyo Kasei Kogyo Co., Ltd.).

Comparative Example 4
The same procedure as in Example 14 was repeated except that the fine fibrous cellulose 1 was replaced with the fine fibrous cellulose A in Example 14.

Comparative Example 5
The same procedure as in Example 14 was repeated except that the fine fibrous cellulose 1 was replaced with carboxymethyl cellulose in Example 14.

(Preparation of base material)
A polyethylene fiber (fiber length: 5 mm, fiber strength: 28 cN / dtex, elastic modulus: 900 cN / dtex) is dispersed in water so as to be 0.2% by mass, and a web of randomly oriented is formed by wet papermaking. did. An ethylene- (meth) acrylic acid resin (Hitec S-3148, ethylene / acrylic acid = 80 parts by mass / 20 parts by mass, having a urethane group at the resin end) as an adhesive on this web to polyethylene fibers After spraying so as to have a ratio of 10% by mass, a nonwoven fabric of 30 g / m ² was obtained by drying with a hot air dryer set at 110 ° C. The non-woven fabric was calendered to obtain a non-woven fabric having a density of 0.64 g / cm ³ . This non-woven fabric was used as a non-woven fabric substrate for coating a battery separator coating liquid.

(Production of battery separator)
The battery separator coating liquid was coated on the non-woven fabric substrate such that the amount of the applied battery separator coating liquid after drying was 5 g / m ² to prepare a battery separator.

(Evaluation of battery separator coating solution)
The following evaluations were performed to confirm the stability of the battery separator coating solution. In the battery separator coating liquid, it can be said that the viscosity decrease is small even after stirring, and the one with excellent fine particle dispersibility has high coating liquid stability.

<Viscosity drop evaluation>
The viscosity of the battery separator coating solution after preparation is measured at 25 ° C. using a B-type viscometer (analog viscometer T-LVT manufactured by BLOOK FIELD),
T. K. The mixture was stirred at 3,000 rpm for 3 hours with a homodisper (manufactured by Tokushu Kika Kogyo Co., Ltd.), and the viscosity was measured again. The viscosity reduction rate was calculated by the following equation, and evaluated according to the following criteria.
Viscosity reduction rate (%) = (viscosity before stirring−viscosity after stirring) / viscosity before stirring × 100
○: The viscosity reduction rate is less than 10% Δ: The viscosity reduction rate is 10% or more and less than 20% ×: The viscosity reduction rate is 20% or more

<Fine particle dispersibility>
After the battery separator coating liquid was allowed to stand at 23 ° C. for 1 day, the presence or absence of settling of particles was confirmed and evaluated according to the following criteria.
○: There is no sedimentation of fine particles, and there is no supernatant layer.
X: There is sedimentation of fine particles, and a supernatant layer is present.

(Evaluation of battery separator)
<Coatability>
The battery separator coating liquid is applied to the non-woven fabric substrate so that the amount of the applied battery separator coating liquid after drying is 5 g / m ^2, and the coatability (whether or not the coating can be carried out) is evaluated based on the following criteria. did.
○: There is no unevenness in the entire surface in the appearance observation after coating.
Fair: Some unevenness is observed in the appearance observation after coating.
×: Unevenness is observed on the entire surface in the appearance observation after coating. Or the coating itself can not be done.

<Betrayal>
The battery separator coating solution was applied to the non-woven fabric substrate such that the amount of the applied battery separator coating solution after drying was 5 g / m ^2, and the presence or absence of the battery separator coating solution was checked.
○: There is no adhesion of the coating liquid to the coating base at the time of lab coating.
X: Adhesion of coating liquid to coating base is observed at the time of lab coating.

As can be seen from Tables 2 and 3, the battery separator coating liquid obtained in the examples has a small viscosity reduction rate and is excellent in fine particle dispersibility. Moreover, when coating the battery separator coating liquid obtained in the Example and producing a battery separator, the coating property is good and the penetration of the coating liquid is also suppressed.
On the other hand, the battery separator coating liquid obtained in the comparative example was inferior in fine particle dispersibility. Moreover, the viscosity decreasing rate was also not good. In the battery separator produced by coating the battery separator coating liquid obtained in the comparative example, a strikethrough of the coating liquid occurred.

Claims (8)

A thickener for a battery separator coating solution containing inorganic fine particles, which comprises fine fibrous cellulose having a fiber width of 1000 nm or less and an average polymerization degree of 400 or more and 2000 or less. The thickener for a battery separator coating solution according to claim 1, wherein the fine fibrous cellulose is phosphorylated cellulose. A separator coating solution for a battery, comprising a fine fibrous cellulose having a fiber width of 1000 nm or less and an average polymerization degree of 400 or more and 2000 or less, inorganic fine particles, and a dispersion medium.   The battery separator coating liquid according to claim 3, wherein the fine fibrous cellulose is phosphorylated cellulose.   The battery separator coating liquid according to claim 3 or 4, wherein a content of the fine fibrous cellulose is 0.1 parts by mass or more and 1.3 parts by mass or less with respect to 100 parts by mass of the dispersion medium. A battery separator having a substrate and a coating layer,
The coated layer has a fiber width of 1000 nm or less and a separator for a battery including fine fibrous cellulose having an average polymerization degree of 400 or more and 2000 or less and inorganic fine particles . The battery separator according to claim 6 , wherein the fine fibrous cellulose is phosphorylated cellulose. The battery separator according to claim 6 , wherein the substrate contains a polyolefin resin.

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