JP6394346B2 - Method for producing alumina slurry - Google Patents

Description

  The present invention relates to an alumina slurry and a method for producing the same. More specifically, the present invention relates to an alumina slurry suitable for forming a coating layer that is excellent in gas permeability, heat resistance, and the like, which constitutes a laminated porous film that can be used as a battery separator and the like, and a method for producing the same.

  The polymer porous body with many fine communication holes is made of ultra-pure water, purification of chemicals, separation membranes used for water treatment, waterproof and moisture-permeable films used for clothing, sanitary materials, etc., or secondary batteries, etc. It is used in various fields such as battery separators.

  Secondary batteries are widely used as power sources for portable devices such as OA, FA, household electric appliances or communication devices. In particular, portable devices using lithium ion secondary batteries are increasing because they have a high volumetric efficiency and are reduced in size and weight when installed in devices. On the other hand, large-scale secondary batteries are being researched and developed in many fields related to energy / environmental issues, including road leveling, uninterruptible power supply (UPS), and electric vehicles. Since it is excellent in voltage and long-term storage properties, the use of lithium ion secondary batteries, which are one type of non-aqueous electrolyte secondary batteries, is expanding.

  The working voltage of a lithium ion secondary battery is usually designed with an upper limit of 4.1V to 4.2V. At such a high voltage, the aqueous solution causes electrolysis and cannot be used as an electrolyte. Therefore, so-called non-aqueous electrolytes using organic solvents are used as electrolytes that can withstand high voltages. As the solvent for the non-aqueous electrolyte, a high dielectric constant organic solvent capable of allowing more lithium ions to be present is used, and organic carbonate compounds such as propylene carbonate and ethylene carbonate are mainly used as the high dielectric constant organic solvent. It is used. As a supporting electrolyte that becomes a lithium ion source in the solvent, a highly reactive electrolyte such as lithium hexafluorophosphate is dissolved in the solvent and used.

  In the lithium ion secondary battery, a separator is interposed between the positive electrode and the negative electrode from the viewpoint of preventing an internal short circuit. Of course, the separator is required to have insulating properties due to its role. Moreover, it is necessary to have a microporous structure in order to provide air permeability as a lithium ion passage, and a function of diffusing and holding the electrolyte. In order to satisfy these requirements, a porous film is used as a separator.

  Also, with the recent increase in capacity of batteries, the importance of battery safety has increased. A characteristic that contributes to the safety of the battery separator is a shutdown characteristic (hereinafter referred to as “SD characteristic”). This SD characteristic has a function of preventing the subsequent increase in temperature inside the battery because the pores of the porous film are blocked when the temperature is about 100 to 150 ° C., and as a result, ion conduction inside the battery is blocked. It is. At this time, the lowest temperature among the temperatures at which the micropores of the porous film are blocked is referred to as a shutdown temperature (hereinafter referred to as “SD temperature”). When used as a battery separator, it is necessary to have this SD characteristic.

  However, with the recent increase in energy density and capacity of lithium ion secondary batteries, normal SD characteristics do not function sufficiently, and the temperature inside the battery is the melting point of polyethylene used as a material for battery separators. The temperature further rises above about 130 ° C., and there is a possibility that an accident may occur in which both the electrodes are short-circuited due to the film breakage accompanying the thermal contraction of the separator, resulting in ignition. Therefore, in order to ensure safety, the separator is required to have higher heat resistance than the current SD characteristics.

  As the porous film used as the separator as described above, for example, a multilayer porous film having a porous coating layer containing a metal oxide such as alumina and a resin binder on at least one surface of a polyolefin resin porous film. It has been proposed (Patent Documents 1 to 5). The coating layer is formed, for example, by coating and drying a slurry prepared by blending alumina, a resin binder, and other components.

Various methods for producing alumina are known. Of these, alumina produced by firing aluminum hydroxide contains an oxide of a metal belonging to Group 2 of the periodic table such as magnesium and calcium as impurities. When alumina containing such impurities is dispersed in a water-based dispersion medium to form a slurry, the impurities are eluted in the slurry, so that alumina tends to aggregate, resulting in high viscosity and unstable productivity.
Thus, for example, a method of re-dissolving alumina and purifying alumina using a recrystallization method, an alkoxide method, or the like has been studied, but this method requires a lot of energy and resources and is not economical.

On the other hand, there is known a method of removing the impurities from the slurry by acid cleaning the alumina slurry or treating it with an ion exchange resin.
For example, Patent Document 6 discloses a high-purity α-alumina manufacturing method in which aluminum hydroxide having a predetermined composition and average particle size is fired under predetermined conditions and the resulting α-alumina is subjected to a cleaning process. Further, it is disclosed that after further pulverizing and re-slurry, an impurity metal is removed using an ion exchange resin.

JP 2004-227972 A JP 2008-186721 A International Publication No. 2008/149986 JP 2008-305783 A International Publication No. 2012/023199 JP 2008-150238 A

  In the method described in Patent Document 6, a strong cation exchange resin is used to remove impurity metals. However, the alumina slurry treated under such strong acid conditions is dispersed in the state of single particles of alumina particles and has a very low viscosity, so when stored for a long period of time, excessively dispersed alumina will settle. It has been found that there is a problem that a solidified product (hard cake) is formed.

  An object of the present invention is to provide an alumina slurry in which alumina is dispersed in an aqueous solvent, in which aggregation of alumina is reduced, and generation of the hard cake is suppressed, and a method for producing the same.

The present inventors have found that the manufacturing method of a particular condition is satisfied alumina slurry over can solve the above problems, and have completed the present invention.
That is, the present invention relates to the following.
[1] having lower Symbol step (1) to (3) in this order, a viscosity of 10 mPa · s or more at a temperature 25 ° C., the manufacturing method of the alumina slurry is below 3000 mPa · s.
Step (1): Alumina having a primary average particle size of 0.1 μm or more and 1.0 μm or less and a dispersion medium having a water content of 50% by mass or more are mixed, and the content of the alumina is 30% by mass. Process step (2) for obtaining liquid mixture 1 of not less than 70% by mass and not more than 70% by mass: After acid-treating liquid mixture 1 obtained in step (1) using an acidic cation exchange resin , an alkali metal hydroxide is added. Step of adding and adjusting pH to 6 or more and 8 or less to obtain liquid mixture 2 (3): Step of dispersing liquid mixture 2 obtained in step (2) to obtain an alumina slurry [ 2 ] The method for producing an alumina slurry according to the above [ 1 ], wherein the alumina is obtained by firing aluminum hydroxide.
[ 3 ] The alumina slurry according to the above [ 1 ] or [ 2], wherein the addition amount of the alkali metal hydroxide in the step (2) is 50 mass ppm or more and 1000 mass ppm or less with respect to the mixed solution 1. Production method.
[ 4 ] The production of the alumina slurry according to any one of [1] to [ 3 ] , wherein the dispersion medium contains a lower alcohol having 1 to 4 carbon atoms in a range of 1% by mass to 20% by mass. Way .

  According to the alumina slurry and the production method thereof of the present invention, there is little aggregation of alumina, and the formation of the hard cake is also suppressed. For example, in the production of laminated porous films suitably used for separators for non-aqueous electrolyte secondary batteries, etc., when a porous coating layer is formed using a dispersion containing the slurry, a uniform layer is stabilized by a coating method. Therefore, the productivity of the film can be stabilized.

It is a schematic sectional drawing of the battery which accommodates the lamination | stacking porous film of this invention.

Hereinafter, embodiments of the alumina slurry and the production method thereof of the present invention will be described in detail.
In the present invention, the expression “main component” includes the intention to allow other components to be contained within a range that does not interfere with the function of the main component, unless otherwise specified. The content includes 50% by mass or more, preferably 70% by mass or more, and particularly preferably 90% by mass or more (including 100% by mass).
In addition, when described as “X to Y” (X and Y are arbitrary numbers), “X is preferably greater than X” and “preferably smaller than Y” together with the meaning of “X to Y” unless otherwise specified. Is included.

[Alumina slurry]
The alumina slurry of the present invention is an alumina slurry obtained by dispersing alumina in a dispersion medium, and the alumina has a primary average particle size of 0.1 μm or more and 1.0 μm or less, and the content of the alumina in the slurry Is 30% by mass or more and 70% by mass or less, the content of water in the dispersion medium is 50% by mass or more, and the viscosity of the slurry at 25 ° C. is 10 mPa · s or more and 3000 mPa · s or less. And the pH is 6 or more and 8 or less.
Since the alumina slurry of the present invention has the above-described configuration, the agglomeration of alumina is reduced, and generation of a solidified product (hereinafter also simply referred to as “hard cake”) in which excessively dispersed alumina settles and solidifies. It is suppressed.

The reason why the above effect is obtained in the present invention is not clear, but is presumed as follows.
Alumina produced by firing aluminum hydroxide contains an oxide of a metal belonging to Group 2 of the periodic table such as magnesium or calcium as an impurity. When the alumina containing the impurities is dispersed in an aqueous dispersion medium to form a slurry, the impurities are eluted into the slurry, so that the alumina tends to aggregate.
In order to solve the above problem, for example, the impurities can be removed by the method described in Patent Document 6 described above. However, when the alumina slurry is treated under strongly acidic conditions, alumina agglomeration is suppressed, while alumina may be excessively dispersed. When the excessively dispersed alumina settles in the slurry and solidifies to form a hard cake, it is very difficult to crush the hard cake, so the slurry and various products such as a laminated porous film using the slurry. This is a factor that reduces productivity.
Therefore, in the present invention, in an alumina slurry obtained by dispersing alumina in a dispersion medium, in particular, the viscosity and pH of the slurry are set within a predetermined range, and further, a specific method is used in the production of the alumina slurry. The present inventors have found that the above problems can be solved.
Below, each component which comprises the alumina slurry of this invention is demonstrated.

<Alumina>
Examples of the alumina used in the alumina slurry of the present invention include α alumina, γ alumina, θ alumina, κ alumina, and pseudo boehmite. Especially, when using the alumina slurry of this invention for the lamination | stacking porous film for separators for non-aqueous-electrolyte secondary batteries, alpha alumina is preferable from a viewpoint that it is chemically inactive when incorporating in a battery.

The alumina used in the present invention has a primary average particle size of 0.1 μm or more and 1.0 μm or less. The primary average particle diameter of the alumina is preferably 0.2 μm or more, more preferably 0.3 μm or more. On the other hand, the primary average particle diameter of the alumina is preferably 0.8 μm or less, more preferably 0.7 μm or less. By setting the primary average particle diameter of alumina to be used to 0.1 μm or more, sufficient heat resistance can be exhibited when used for a laminated porous film for a separator for a non-aqueous electrolyte secondary battery. Moreover, the dispersibility of an alumina improves because this primary average particle diameter shall be 1.0 micrometer or less.
In the present invention, “primary average particle diameter of alumina” is measured and calculated by the method described in Examples.

The specific surface area of the alumina used in the present invention is preferably 5 m ² / g or more and 15 m ² / g or less. If a specific surface area is 5 m < ² > / g or more, the viscosity of an alumina slurry will be hold | maintained and viscosity stability will improve. Further, when the laminated porous film obtained using the alumina slurry of the present invention is incorporated as a separator in a non-aqueous electrolyte secondary battery, the penetration of the electrolyte solution becomes faster, and the productivity of the non-aqueous electrolyte secondary battery is good. Become. Moreover, if a specific surface area is 15 m < ² > / g or less, when incorporating the laminated porous film obtained using an alumina slurry as a separator in a nonaqueous electrolyte secondary battery, adsorption | suction of electrolyte component will be suppressed.
From the above viewpoint, the specific surface area of alumina is more preferably 5.5 m ² / g or more, further preferably 6 m ² / g or more, more preferably 14 m ² / g or less, and further preferably 13 m ² / g or less. .
In the present invention, the “specific surface area of alumina” is a value measured by a constant volume gas adsorption method, and can be specifically measured by the method described in Examples.

The method for producing alumina used in the present invention is not particularly limited. For example, a method of firing aluminum hydroxide produced by an aluminum alkoxide method, a method of using organic aluminum as a raw material, and transition alumina or And a method of firing in a gas atmosphere containing hydrogen chloride.
Among these, from the viewpoint of the effect of the present invention that suppresses the formation of hard cake while reducing the aggregation of alumina derived from impurity metals, the alumina used in the present invention is obtained by firing aluminum hydroxide. Is preferred.

As the aluminum alkoxide method, for example, aluminum alkoxide is hydrolyzed with water to obtain slurry, sol, or gel aluminum hydroxide, and dried to obtain dry powdered aluminum hydroxide. The method of obtaining is mentioned.
Alumina is obtained by calcining dry powdered aluminum hydroxide obtained by the above-described aluminum alkoxide method or the like. The calcining temperature of aluminum hydroxide, the heating rate up to the calcining temperature, and the calcining time can be appropriately selected so as to obtain alumina having desired physical properties. Firing of aluminum hydroxide can be performed, for example, within a firing temperature range of 1100 to 1500 ° C. and a firing time of 0.5 to 24 hours.
Aluminum hydroxide may be baked in an air atmosphere or in an inert gas atmosphere such as nitrogen gas or argon gas, and the partial pressure of water vapor is reduced as in a gas furnace baked by combustion of propane gas or the like. You may bake in a high atmosphere.

  When the primary average particle diameter of alumina obtained by the above method is agglomerated in a state exceeding 1.0 μm, it is preferable to perform a pulverization process in advance to make the primary average particle diameter 1.0 μm or less. The pulverization of alumina can be performed using a known apparatus such as a vibration mill, a ball mill, or a jet mill, and any of a dry pulverization method and a wet pulverization method can be used.

<Dispersion medium>
The alumina slurry of the present invention is obtained by dispersing the alumina in a dispersion medium. The dispersion medium is not particularly limited as long as it can disperse alumina in a moderately uniform and stable manner. However, the cost and environmental load, the viewpoint of suppressing the aggregation of alumina, and the lamination of alumina slurry are described later. When used for forming the coating layer in the porous film, the content of water in the dispersion medium is preferably 50% by mass or more from the viewpoint of coating properties when the coating layer is formed by a coating method. More preferably, it is more preferably 80% by weight or more, and still more preferably 85% by weight or more. Further, the content of water in the dispersion medium is 100% by mass or less, preferably 99% by mass or less, more preferably 95% by mass or less.
Examples of the dispersion medium that can be used in addition to water include N-methylpyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, water, dioxane, acetonitrile, lower alcohol, glycols, glycerin, and lactic acid ester. Is mentioned. Especially, it is preferable that a dispersion medium contains a C1-C4 lower alcohol. The lower alcohol is preferably a monohydric alcohol having 1 to 4 carbon atoms, more preferably at least one selected from methanol, ethanol and isopropyl alcohol. These can be used alone or in combination of two or more.
Among these, the dispersion medium is preferably a mixed dispersion medium of water and a lower alcohol having 1 to 4 carbon atoms, more preferably a mixed dispersion medium of water and a monovalent alcohol having 1 to 4 carbon atoms, and water and isopropyl alcohol. A mixed dispersion medium is more preferable.
The content of the lower alcohol having 1 to 4 carbon atoms in the dispersion medium is preferably 1% by mass or more, more preferably 5% by mass or more, preferably 20% by mass or less, more preferably 15% by mass or less. It is.

  The content of the alumina in the alumina slurry of the present invention is 30% by mass or more, preferably 40% by mass or more, more preferably 45% by mass, from the viewpoint of ensuring the viscosity for suppressing the formation of hard cake. % Or more. Further, from the viewpoint of suppressing the aggregation of alumina and the handling property, the content of alumina in the alumina slurry is 70% by mass or less, preferably 65% by mass or less, more preferably 60% by mass or less.

The alumina slurry of the present invention has a viscosity at a temperature of 25 ° C. of 10 mPa · s or more and 3000 mPa · s or less. When the viscosity is in the above range, the aggregation of alumina is reduced, and the productivity is stabilized when the slurry is used for forming a coating layer of a laminated porous film. Moreover, the coating property at the time of forming the coating layer is also improved. The viscosity is preferably 50 mPa · s or more, and more preferably 100 mPa · s or more. Moreover, 2000 mPa * s or less is preferable, 1000 mPa * s or less is more preferable, and 800 mPa * s or less is more preferable.
The viscosity of the alumina slurry is, for example, a value measured using a B-type viscometer (“TVB10H” manufactured by Toki Sangyo Co., Ltd.) at a temperature of 25 ° C. and a peripheral speed of 100 rpm. It can be measured by the method described in the examples.

The alumina slurry of the present invention has a pH of 6 or more and 8 or less. If the pH of the slurry is less than 6, the formation of a hard cake due to sedimentation and solidification of excessively dispersed alumina cannot be suppressed. On the other hand, when the pH of the slurry exceeds 8, agglomeration of alumina cannot be suppressed, and coatability when the slurry is used for forming a coating layer of a laminated porous film is lowered.
From the above viewpoint, the pH of the alumina slurry is preferably 6.2 or more, more preferably 6.5 or more, preferably 7.8 or less, more preferably 7.5 or less. The pH is a value measured with a pH meter at a temperature of 25 ° C.

[Production method of alumina slurry]
Although there is no restriction | limiting in particular in the manufacturing method of the alumina slurry of this invention, From a viewpoint which acquires the effect of this invention, the manufacturing method (henceforth "the manufacturing method of this invention") which has the following process (1)-(3) in order. ) Is preferably used.
Step (1): Alumina having a primary average particle size of 0.1 μm or more and 1.0 μm or less and a dispersion medium having a water content of 50% by mass or more are mixed, and the content of the alumina is 30% by mass. Process step (2) for obtaining a mixed solution 1 of not less than 70% by mass and not more than 70% by mass: After acid treatment of the mixed solution 1 obtained in step (1), the pH is adjusted to 6 or more by adding an alkali metal hydroxide. Step of adjusting to 8 or less to obtain the mixed solution 2 (3): Step of dispersing the mixed solution 2 obtained in the step (2) to obtain an alumina slurry Hereinafter, the production method of the present invention will be described in detail. To do.

<Step (1)>
In the step (1), an alumina having a primary average particle size of 0.1 μm or more and 1.0 μm or less and a dispersion medium having a water content of 50% by mass or more are mixed, and the content of the alumina is 30. The liquid mixture 1 of mass% or more and 70 mass% or less is obtained. The alumina and the dispersion medium are the same as described above.
The method for mixing the predetermined amount of alumina and the dispersion medium is not particularly limited.For example, a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, a high-speed impeller dispersion, a disperser, A mechanical stirring method using a homogenizer, a high-speed impact mill, ultrasonic dispersion, a stirring blade, or the like can be used.

<Step (2)>
In the step (2), after the mixed solution 1 obtained in the step (1) is subjected to an acid treatment, an alkali metal hydroxide is added to adjust the pH to 6 or more and 8 or less to obtain the mixed solution 2. Aggregation of alumina in the slurry can be suppressed by acid-treating the mixed solution 1 in the step (2). Furthermore, by adding an alkali metal hydroxide after the acid treatment and adjusting the pH of the slurry to a predetermined range, it is possible to suppress excessive dispersion of alumina, thereby suppressing generation of a hard cake. Can do.

The acid component used for the acid treatment can be used without particular limitation as long as it can reduce the aggregation of alumina.
When the alumina used for the slurry is obtained by firing aluminum hydroxide, an acidic cation exchange resin should be used for the acid treatment from the viewpoint of removing impurities contained in the alumina and suppressing aggregation of the alumina. Is preferred. A preferable acidic cation exchange resin includes, for example, polystyrene sulfonic acid.
Examples of acid components that can be used for acid treatment other than acidic cation exchange resins include lower primary carboxylic acids such as formic acid, acetic acid, propionic acid, and acrylic acid; nitro acids such as nitric acid and nitrous acid; perchloric acid And halogen oxoacids such as hypochlorous acid; halide ions such as hydrochloric acid, hydrofluoric acid, and hydrobromic acid; phosphoric acid, salicylic acid, glycolic acid, lactic acid, ascorbic acid, erythorbic acid, and the like. Among these, at least one selected from formic acid, acetic acid, nitric acid, hydrochloric acid, and phosphoric acid is preferable from the viewpoint that pH can be lowered by addition in a small amount, availability, and acid stability are high.
The pH of the mixed solution after the acid treatment is preferably less than 6, more preferably 5 or less. When the pH is less than 6, aggregation of alumina in the slurry can be suppressed.

In the step (2), after performing the acid treatment, an alkali metal hydroxide is added to adjust the pH to 6 or more and 8 or less to obtain a mixed solution 2. Thereby, the viscosity of the alumina slurry that has been reduced in viscosity by the acid treatment is moderately increased, and it can be suppressed that the alumina is precipitated and solidified to form a hard cake.
Preferred alkali metal hydroxides include lithium hydroxide, potassium hydroxide, and sodium hydroxide, and these can be used alone or in combination of two or more. Among these, at least one selected from lithium hydroxide and potassium hydroxide is more preferable. The alkali metal hydroxide may be added in a solid state, or an aqueous solution of an alkali metal hydroxide may be prepared and added.
The addition amount of the alkali metal hydroxide in the step (2) is not particularly limited as long as the pH can be adjusted to 6 or more and 8 or less, but is 50 mass ppm or more and 1000 mass ppm or less with respect to the mixed solution 1. Preferably there is. If it is the said range, aggregation of an alumina can be suppressed and the production | generation of a hard cake can also be suppressed. The addition amount of the alkali metal hydroxide is more preferably 60 mass ppm or more, and further preferably 70 mass ppm or more. Moreover, this addition amount becomes like this. More preferably, it is 900 mass ppm or less, More preferably, it is 800 mass ppm or less.

<Step (3)>
In step (3), the mixed liquid 2 obtained in step (2) is subjected to dispersion treatment to obtain an alumina slurry.
There are no particular restrictions on the method for dispersing the mixed liquid 2, but for example, ball mill, bead mill, planetary ball mill, vibrating ball mill, sand mill, colloid mill, attritor, roll mill, high-speed impeller dispersion, disperser, homogenizer, high-speed impact mill And a mechanical stirring method using ultrasonic dispersion, stirring blades, and the like. Among these, it is preferable to carry out a dispersion treatment using a bead mill from the viewpoint of preventing mixing of the ground product.
Examples of types of beads used in the bead mill include glass beads and ceramic beads. From the viewpoint of the hardness of the beads, ceramic beads are preferable, and one or more ceramic beads selected from alumina, zirconia, and zircon are more preferable. The bead diameter is preferably 0.1 mm or more and 3 mm or less, more preferably 1.5 mm or less, and still more preferably 0.8 mm or less from the viewpoint of the dispersibility of alumina.
Moreover, from the viewpoint of dispersion efficiency, the filling rate of beads in the bead mill is preferably 30% or more, more preferably 50% or more, still more preferably 70% or more, and preferably 90% or less.
There are no particular restrictions on the temperature and average residence time during the dispersion treatment. For example, when the dispersion is continuously performed using a bead mill, the dispersion is usually performed at a temperature of 10 to 50 ° C. and an average residence time of 0.1 to 60 minutes. Processing can be performed.

<Uses of alumina slurry>
The alumina slurry of the present invention can be used for forming a polishing agent, a ceramic molded body, forming an electrode or separator coating layer of a nonaqueous electrolyte secondary battery, forming a reflective layer of a light reflecting material, and the like. In particular, it is suitably used for forming a coating layer of a laminated porous film that can be used as a battery separator or the like.

(Laminated porous film)
The alumina slurry of the present invention can be used for forming a coating layer of a laminated porous film that can be used as a battery separator or the like. The laminated porous film has, for example, a coating layer on at least one surface of a polyolefin resin porous film, and the coating layer is formed using a dispersion containing the alumina slurry of the present invention and a resin binder described later. is there.
Below, each component which comprises the said laminated porous film is demonstrated.

[Polyolefin resin porous film]
The laminated porous film has a polyolefin-based resin porous film from the viewpoint of chemical stability inside the battery.
Examples of the polyolefin resin used for the polyolefin resin porous film include homopolymers or copolymers obtained by polymerizing α-olefins such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and 1-hexene. . Two or more of these homopolymers or copolymers can also be mixed. Among these, it is preferable to use a polypropylene-based resin or a polyethylene-based resin, and it is particularly preferable to use a polypropylene-based resin from the viewpoint of maintaining the mechanical strength, heat resistance, and the like of the laminated porous film.

≪Polypropylene resin≫
Polypropylene resins that can be used for polyolefin resin porous films include homopolypropylene (propylene homopolymer), or propylene and ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-heptene, Examples thereof include a random copolymer or a block copolymer with an α-olefin such as octene, 1-nonene or 1-decene. Among these, homopolypropylene is more preferably used from the viewpoint of maintaining the mechanical strength and heat resistance of the laminated porous film.

Moreover, as a polypropylene resin, it is preferable that the isotactic pentad fraction (mmmm fraction) which shows stereoregularity is 80 to 99%. More preferably, it is 83-98%, More preferably, it is 85-97%. If the isotactic pentad fraction is 80% or more, the mechanical strength of the film is good. On the other hand, the upper limit of the isotactic pentad fraction is defined by the upper limit obtained industrially at the present time, but this is not the case when a more regular resin is developed in the industrial level in the future. is not.
The isotactic pentad fraction (mmmm fraction) is the same direction for all five methyl groups that are side chains with respect to the main chain of carbon-carbon bonds composed of arbitrary five consecutive propylene units. Means the three-dimensional structure located at or its proportion. Signal assignment of the methyl group region is as follows. It conforms to Zambelli et al ("Macromolecules", 8,687, (1975)).

Moreover, it is preferable that Mw / Mn which is a parameter which shows the molecular weight distribution of polypropylene resin is 2.0-10.0. More preferably, 2.0 to 8.0, more preferably 2.0 to 6.0 is used. The smaller the M _w / M _n is, the narrower the molecular weight distribution is. However, when M _w / M _n is less than 2.0, there are problems such as deterioration of extrusion moldability, and industrial production. It is also difficult. On the other hand, when M _w / M _n exceeds 10.0, the low molecular weight component increases, and the mechanical strength of the laminated porous film tends to decrease.
M _w / M _n of the polypropylene resin is measured by a GPC (gel permeation chromatography) method.

The density of the polypropylene resin is preferably 0.890~0.970g / cm ^3, more preferably ^{0.895~0.970g / cm 3, 0.900~0.970g / cm} 3 More preferably. A density of 0.890 g / cm ³ or more is preferable because an appropriate SD characteristic can be exhibited when the laminated porous film is used for a separator for a non-aqueous electrolyte secondary battery. On the other hand, 0.970 g / cm ³ or less is preferable in that appropriate SD characteristics can be expressed and stretchability is maintained.
The density of the polypropylene resin is measured according to JIS K7112 (1999) using a density gradient tube method.

Further, the melt flow rate (MFR) of the polypropylene-based resin is not particularly limited, but usually the MFR is preferably 0.5 to 15 g / 10 minutes, and 1.0 to 10 g / 10 minutes. It is more preferable. When the MFR is 0.5 g / 10 min or more, the resin has a high melt viscosity at the time of molding, and sufficient productivity can be ensured. On the other hand, the mechanical strength of the obtained laminated porous film can be sufficiently maintained by setting it to 15 g / 10 min or less.
The MFR of the polypropylene resin is measured under conditions of a temperature of 230 ° C. and a load of 2.16 kg according to JIS K7210 (1999).

  The method for producing the polypropylene resin is not particularly limited, and a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst or a metallocene catalyst represented by a Ziegler-Natta type catalyst. And suspension polymerization method, melt polymerization method, bulk polymerization method, gas phase polymerization method, and bulk polymerization method using a radical initiator.

  Examples of the polypropylene resin include trade names “Novatech PP”, “WINTEC” (manufactured by Nippon Polypro Co., Ltd.), “Notio”, “Toughmer XR” (manufactured by Mitsui Chemicals, Inc.), “Zeras”. ", Thermorun" (Mitsubishi Chemical Corporation), "Sumitomo Noblen", "Tough Selenium" (Sumitomo Chemical Co., Ltd.), "Prime Polypro", "Prime TPO" (Mitsubishi Corporation) Prime polymer), “Adflex”, “Adsyl”, “HMS-PP (PF814)” (manufactured by Sun Allomer Co., Ltd.), “Versify”, “Inspire” (manufactured by Dow Chemical Co., Ltd.), etc. Commercially available products can be used.

≪Polyethylene resin≫
Polyethylene resins that can be used for polyolefin resin porous films include low-density polyethylene, linear low-density polyethylene, linear ultra-low-density polyethylene, medium-density polyethylene, high-density polyethylene, and copolymers based on ethylene. That is, α-olefin having 3 to 10 carbon atoms such as ethylene and propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene; vinyl esters such as vinyl acetate and vinyl propionate; acrylic Copolymerization with one or more comonomers selected from unsaturated carboxylic acid esters such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, and unsaturated compounds such as conjugated dienes and non-conjugated dienes. Polymer or multi-component copolymer or a mixed composition thereof. . The ethylene unit content of the ethylene polymer is usually more than 50% by mass.

  Among these polyethylene resins, at least one polyethylene resin selected from low density polyethylene, linear low density polyethylene, and high density polyethylene is preferable, and high density polyethylene is more preferable.

Density of the polyethylene resin is preferably 0.910~0.970g / cm ^3, more preferably 0.930~0.970g / cm ^3, 0.940~0.970g / cm ³ is more preferable. A density of 0.910 g / cm ³ or more is preferable because an appropriate SD characteristic can be exhibited when the laminated porous film is used for a separator for a non-aqueous electrolyte secondary battery. On the other hand, 0.970 g / cm ³ or less is preferable in that appropriate SD characteristics can be expressed and stretchability is maintained.
The density of the polyethylene resin is measured according to JIS K7112 (1999) using a density gradient tube method.

Further, the melt flow rate (MFR) of the polyethylene resin is not particularly limited, but usually the MFR is preferably 0.03 to 30 g / 10 minutes, and preferably 0.3 to 10 g / 10 minutes. It is more preferable. When the MFR is 0.03 g / 10 min or more, the melt viscosity of the resin during the molding process is sufficiently low, so that productivity is excellent. On the other hand, if it is 30 g / 10 minutes or less, sufficient mechanical strength can be obtained.
The MFR of the polyethylene resin is measured under conditions of a temperature of 190 ° C. and a load of 2.16 kg according to JIS K7210 (1999).

  The production method of the polyethylene resin is not particularly limited, and is a known polymerization method using a known olefin polymerization catalyst, for example, a multisite catalyst represented by a Ziegler-Natta type catalyst or a metallocene catalyst. A polymerization method using a single site catalyst may be mentioned. As a polymerization method of the polyethylene resin, there are a one-stage polymerization, a two-stage polymerization, or a multistage polymerization more than that, and any method of the polyethylene resin can be used.

≪Other ingredients≫
In addition to the above-described resins, additives that are generally blended into the resin can be appropriately added to the polyolefin resin porous film within a range that does not significantly impair the intended effect.
As the above additive, for the purpose of improving and adjusting the moldability, productivity and various physical properties of the polyolefin resin porous film, recycled resin generated from trimming loss such as ears, silica, talc, kaolin, Inorganic particles such as calcium carbonate, pigments such as carbon black, flame retardants, weathering stabilizers, heat stabilizers, antistatic agents, melt viscosity modifiers, crosslinking agents, lubricants, nucleating agents, plasticizers, anti-aging agents, oxidation Examples thereof include additives such as an inhibitor, a light stabilizer, an ultraviolet absorber, a neutralizer, an antifogging agent, an antiblocking agent, a slip agent, and a colorant.
In addition, various resins and low molecular weight compounds such as waxes may be added in order to promote the opening of the polyolefin-based resin porous film and to impart moldability, so long as the intended effect is not significantly impaired. Good.

≪Layer structure of polyolefin resin porous film≫
The polyolefin resin porous film may be a single layer or a laminate. Among them, a single layer of the polyolefin resin-containing layer (hereinafter sometimes referred to as “A layer”), within a range that does not interfere with the function of the A layer, the A layer and other layers (hereinafter referred to as “B layer”) Is sometimes preferred). The B layer may be a layer containing a polyolefin resin different from the A layer.
Specifically, a two-layer structure in which A layer / B layer is laminated, a three-layer structure in which A layer / B layer / A layer, or B layer / A layer / B layer are laminated can be exemplified. In addition, it is possible to adopt a form of three types and three layers in combination with layers having other functions. In this case, the order of stacking with layers having other functions is not particularly limited. As the number of layers, four layers, five layers, six layers, and seven layers may be increased as necessary.

≪Method for producing polyolefin resin porous film≫
The method for producing a polyolefin-based resin porous film can be suitably used a conventionally known method for producing a porous film, and is not particularly limited, but is usually a precursor for forming a polyolefin-based resin porous film. A method of forming a polyolefin-based resin porous film by producing a non-porous film-like material and making the same porous is preferable.

  There is no particular limitation on the method for producing the non-porous membrane that is a precursor for forming the polyolefin resin porous film, and a known method can be used. For example, a method may be used in which an extruder is used to melt a polyolefin resin or a mixture of a polyolefin resin as a raw material for a porous film and various additives, extrude from a T-die, and cool and solidify with a cast roll. Further, a method of cutting a film-like material manufactured by a tubular method into a flat shape can be applied.

  There are no particular limitations on the method for making the nonporous membrane-like material, and known methods such as wet uniaxial or higher uniaxial stretching and dry uniaxial or higher uniaxial stretching can be used. Regarding the stretching method in stretching and stretching, there are methods such as a roll stretching method, a rolling method, a tenter stretching method, and a simultaneous biaxial stretching method, and these methods are used alone or in combination of two or more to perform uniaxial stretching or biaxial stretching. Do. Among these, sequential biaxial stretching is preferable from the viewpoint of controlling the porous structure. Moreover, the method of extracting and drying the plasticizer contained in the resin composition before and after extending | stretching with a solvent as needed is also applied. Furthermore, for the purpose of improving dimensional stability, heat treatment or relaxation treatment can be performed after stretching.

Here, when a polypropylene resin is used for the polyolefin resin porous film, it is preferable to generate a so-called β crystal in the nonporous film-like material. If β-crystals are generated in the non-porous film-like material, even if no filler or other additive is used, fine pores can be easily formed by stretching, so it has excellent air permeability. A polyolefin resin porous film can be obtained.
As a method of generating β crystals in a non-porous film of a polypropylene resin, a method in which a substance that promotes the formation of α crystals of the polypropylene resin is not added, or as described in Japanese Patent No. 3739481 The method of adding the polypropylene which performed the process which generate | occur | produces a peroxide radical in this, the method of adding a (beta) crystal nucleating agent to a composition, etc. are mentioned.

≪β crystal nucleating agent≫
Examples of the β crystal nucleating agent that can be used in the present invention include the following, but are not particularly limited as long as they increase the generation and growth of β crystals of the polypropylene resin. Further, β crystal nucleating agents may be used in combination of two or more.
Examples of the β crystal nucleating agent include amide compounds; tetraoxaspiro compounds; quinacridones; iron oxides having a nanoscale size; potassium 1,2-hydroxystearate, magnesium benzoate or magnesium succinate, magnesium phthalate, etc. Alkali or alkaline earth metal salts of carboxylic acids represented by: aromatic sulfonic acid compounds represented by sodium benzenesulfonate or sodium naphthalenesulfonate; di- or triesters of dibasic or tribasic carboxylic acids; phthalocyanine blue Phthalocyanine pigments typified by, for example; a two-component compound comprising component A which is an organic dibasic acid and a component B which is an oxide, hydroxide or salt of a Group 2 metal in the periodic table; a cyclic phosphorus compound; Composition composed of magnesium compounds And the like. In addition, specific types of nucleating agents are described in JP-A No. 2003-306585, JP-A No. 08-144122, and JP-A No. 09-194650.

  As a commercial product of β crystal nucleating agent, β crystal nucleating agent “NJESTER NU-100” manufactured by Shin Nippon Rika Co., Ltd. may be mentioned. In addition, as a commercial product of a polypropylene resin to which a β crystal nucleating agent is added, a polypropylene resin “Bepol B-022SP” manufactured by Aristech, a polypropylene resin “Beta (β) -PP BE60-7032” manufactured by Borealis, Inc. ", A polypropylene resin" BNX BETAPP-LN "manufactured by Mayzo.

The blending ratio of the β crystal nucleating agent to be added to the polypropylene resin constituting the polyolefin resin porous film needs to be appropriately adjusted depending on the type of the β crystal nucleating agent or the composition of the polypropylene resin. It is preferable that it is 0.0001-5 mass parts with respect to 100 mass parts of resin. Moreover, 0.001-3 mass parts is more preferable, and 0.01-1 mass part is further more preferable.
If the blending ratio of the β crystal nucleating agent is 0.0001 parts by mass or more with respect to 100 parts by mass of the polypropylene resin, the β crystal of the polypropylene resin can be generated and grown sufficiently at the time of production. Even when the laminated porous film is used as a separator for a non-aqueous electrolyte secondary battery, sufficient β crystal activity is expressed, and a desired air permeability is obtained. In addition, if the blending ratio of the β crystal nucleating agent is 5 parts by mass or less with respect to 100 parts by mass of the polypropylene resin, the cost is advantageous, and the β crystal nucleating agent bleeds onto the polyolefin resin porous film surface. There is no such thing and it is preferable.

Moreover, when the polyolefin resin porous film has a laminated structure, its production method is roughly divided into the following three types depending on the order of the porous formation and lamination.
(I) A method in which each layer is made porous, and then the layers made porous are laminated or bonded with an adhesive or the like.
(Ii) A method of laminating each layer to produce a laminated nonporous film-like material, and then making the nonporous film-like material porous.
(Iii) A method in which one of the layers is made porous and then laminated with another layer of non-porous film to make it porous.
Among the above, it is preferable to use the method (ii) from the viewpoint of simplicity of the process and productivity, and in particular, in order to ensure the interlayer adhesion of the two layers, the laminated nonporous film-like material is formed by coextrusion. A method of making it porous after production is particularly preferred.

  The thickness of the polyolefin resin porous film is preferably 5 to 100 μm, more preferably 8 to 50 μm, and still more preferably 10 to 30 μm. When the thickness of the polyolefin-based resin porous film is 5 μm or more, when the laminated porous film is used as a separator for a non-aqueous electrolyte secondary battery, substantially necessary electrical insulation can be obtained. Even when a large force is applied to the part, it is hard to break through the separator and is excellent in safety. Also, if the thickness of the polyolefin resin porous film is 100 μm or less, the electrical resistance can be reduced when the laminated porous film is used as a separator for a non-aqueous electrolyte secondary battery, so that sufficient battery performance is ensured. can do.

(Coating layer)
The laminated porous film has a coating layer on at least one surface of the polyolefin resin porous film. The coating layer is formed by using the alumina slurry of the present invention and a dispersion containing a resin binder (hereinafter also referred to as “dispersion for forming a coating layer”), and includes at least alumina and a resin binder. The alumina slurry used for the dispersion is as described above.

≪Resin binder≫
The resin binder acts as a binder for alumina in the coating layer, and is used to improve the adhesion between the coating layer containing a large amount of alumina and the polyolefin resin porous film.
As the resin binder used for the coating layer, the coating layer containing a large amount of alumina and the polyolefin resin porous film can be bonded well, and is electrochemically stable, and the laminated porous film can be used for non-aqueous electrolyte secondary batteries. As long as it is stable with respect to an organic electrolyte when used as a separator, it can be used without particular limitation.
Specifically, polyether, polyamide, polyimide, polyamideimide, polyaramid, polyoxyethylene, ethylene-vinyl acetate copolymer (with a vinyl acetate-derived structural unit of 0 to 20 mol%), ethylene-ethyl acrylate copolymer Ethylene-acrylic acid copolymers such as polymers, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polytetrafluoroethylene, fluorine-based rubber, styrene-butadiene rubber, nitrile butadiene rubber, polybutadiene rubber , Polyacrylonitrile, polyacrylic acid and its derivatives, polymethacrylic acid and its derivatives, carboxymethyl cellulose, hydroxyethyl cellulose, cyanoethyl cellulose, polyvinyl alcohol, Roh ethyl polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, N- vinyl acetamide, crosslinked acrylic resin, polyurethane, epoxy resins, maleic acid-modified polyolefin. These resin binders may be used alone or in combination of two or more.
Among these, polyoxyethylene, polyvinyl alcohol, polyvinylidene fluoride are used because they are relatively stable in a dispersion medium mainly composed of water used in the dispersion for forming a coating layer and in an electrolytic solution inside the battery. , Polyvinyl pyrrolidone, polyacrylonitrile resin, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid and derivatives thereof, and maleic acid-modified polyolefin are preferable, from polyvinyl alcohol, polyvinylidene fluoride, carboxymethyl cellulose, polyacrylic acid, and polyacrylic acid derivatives. At least one selected is more preferable.

In the coating layer, the content of alumina with respect to the total amount of alumina and resin binder is preferably in the range of 80% by mass or more and 99.9% by mass or less. The content of the alumina is more preferably 92% by mass or more, further preferably 95% by mass or more, and particularly preferably 98% by mass or more. When the content of alumina with respect to the total amount of alumina and the resin binder is within the above range, the coating layer exhibits excellent air permeability, and the binding property of alumina can also be maintained.
Therefore, it is preferable to mix the alumina slurry and the resin binder in the coating layer forming dispersion so that the content ratio of the alumina and the resin binder falls within the above range.

  Further, the dispersion for forming a coating layer may contain a dispersion aid, a stabilizer, a thickener and the like in order to improve dispersion stability and optimize the viscosity suitable for forming the coating layer. Further, a dispersion medium may be further added. It is preferable to use a dispersion medium in which alumina, a resin binder, and other components can be dissolved or dispersed in a reasonably uniform and stable manner, and the same dispersion medium as exemplified in the alumina slurry can be used.

  The dispersion for forming a coating layer can be prepared by mixing the alumina slurry of the present invention, the resin binder, and other components used as necessary, and further dispersing as necessary. As a method for mixing and dispersing each component contained in the coating layer forming dispersion, the same method as exemplified in the method for producing the alumina slurry can be used.

[Method of forming coating layer]
The coating layer is formed using the above-described dispersion for forming a coating layer. Examples of the method for forming the coating layer include a co-extrusion method, a laminating method, and a coating method. From the viewpoint of continuous productivity, the coating layer is preferably formed by a coating method. That is, it is preferable to form a coating layer by applying a coating layer-forming dispersion on at least one side of the polyolefin resin porous film.
The dispersion for forming a coating layer may be applied only to one side of the polyolefin resin porous film or may be applied to both sides depending on the application. That is, in the laminated porous film of the present invention, the coating layer may be formed only on one side of the polyolefin-based resin porous film, or may be formed on both sides.

  The coating method for the coating layer forming dispersion is not particularly limited as long as it can realize a required layer thickness and coating area. For example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast Examples include a coater method, a die coater method, a screen printing method, and a spray coating method.

  In addition, you may perform the process of apply | coating the dispersion liquid for coating layer coating on the surface of a polyolefin resin porous film in the middle of the manufacturing process of the polyolefin resin porous film to be used. For example, it may be performed after extrusion molding of the polyolefin resin film and before the stretching step, may be performed after the longitudinal stretching step, or may be performed after the lateral stretching step.

It is preferable to perform a step of further removing the dispersion medium after the coating layer forming dispersion is applied. Thereby, the coating layer containing an alumina and a resin binder can be formed on the polyolefin resin porous film. The method for removing the dispersion medium is not particularly limited as long as it does not adversely affect the polyolefin resin porous film. For example, a method of drying at a temperature below the melting point while fixing a polyolefin resin porous film, a method of drying under reduced pressure at a low temperature, and dipping in a poor solvent for the resin binder to solidify the resin binder and simultaneously extract the solvent The method etc. are mentioned.
Preferably, by using the above method, a coating layer can be formed on the polyolefin resin porous film to produce a laminated porous film.

[Shape and physical properties of laminated porous film]
The total thickness of the laminated porous film can be appropriately selected depending on the application. When the laminated porous film is used as a separator for a nonaqueous electrolyte secondary battery, the total thickness of the laminated porous film is preferably 5 to 100 μm, more preferably 8 to 50 μm, and still more preferably 10 to 30 μm. When the total thickness is 5 μm or more, it is possible to obtain substantially the necessary electrical insulation as a separator for a non-aqueous electrolyte secondary battery. For example, even when a large force is applied to the protruding portion of the electrode, non-aqueous electrolysis It breaks through the separator for a liquid secondary battery and is not easily short-circuited. Moreover, since the electrical resistance of a laminated porous film can be made small if the total thickness of a laminated porous film is 100 micrometers or less, the performance of a battery can fully be ensured.

  Moreover, the thickness of the coating layer in the laminated porous film is preferably 0.5 μm or more, more preferably 1 μm or more, further preferably 2 μm or more, and particularly preferably 3 μm or more from the viewpoint of heat resistance. On the other hand, the thickness of the coating layer is preferably 90 μm or less, more preferably 50 μm or less, still more preferably 30 μm or less, and particularly preferably 10 μm or less from the viewpoint of ensuring communication and providing excellent air permeability. In addition, when it has two or more coating layers, the thickness of the said coating layer means the thickness per layer.

In the laminated porous film, the porosity is preferably 30% or more, more preferably 35% or more, and further preferably 40% or more. If the porosity is 30% or more, it is possible to obtain a laminated porous film that ensures communication and has excellent air permeability.
On the other hand, the porosity of the laminated porous film is preferably 70% or less, more preferably 65% or less, and further preferably 60% or less. If the porosity is 70% or less, the strength of the laminated porous film can be sufficiently maintained, which is preferable from the viewpoint of handling.

The air permeability of the laminated porous film is preferably 1000 sec / 100 mL or less, more preferably 10 to 800 sec / 100 mL, and further preferably 50 to 500 sec / 100 mL. If the air permeability is 1000 seconds / 100 mL or less, it is preferable that the laminated porous film has a communication property and can exhibit excellent air permeability characteristics.
The air permeability represents the difficulty of air passage in the film thickness direction, and is specifically expressed as the time required for 100 mL of air to pass through the film. Therefore, it means that the smaller the numerical value is, the easier it is to pass through, and the higher numerical value is, the more difficult it is to pass. That is, a smaller value means that the film thickness direction is better, and a larger value means that the film thickness direction is worse. Communication is the degree of connection of holes in the film thickness direction. If the air permeability of the laminated porous film is low, it can be used for various applications. For example, when used as a separator for a non-aqueous electrolyte secondary battery, a low air permeability means that lithium ions can be easily transferred, which is preferable because battery performance is excellent.
The air permeability (Gurley value) of the laminated porous film is measured by a method based on JIS P8117 (2009).

  The laminated porous film preferably has SD characteristics when used as a battery separator. Specifically, the air permeability after heating at 135 ° C. for 5 seconds is preferably 10,000 seconds / 100 mL or more, more preferably 25000 seconds / 100 mL or more, and further preferably 50000 seconds / 100 mL or more. By setting the air permeability after heating at 135 ° C for 5 seconds to 10000 seconds / 100 mL or more, the holes are quickly closed and the current is interrupted during abnormal heat generation, thus avoiding problems such as battery rupture. be able to.

In the laminated porous film, since the coating layer is formed using the dispersion containing the alumina slurry of the present invention, a uniform coating layer can be obtained, and the surface smoothness of the coating layer is also improved. For surface smoothness, for example, using a fine shape measuring instrument ("ET4000A" manufactured by Kosaka Laboratory Co., Ltd.), a viewing angle of 300 μm × 400 μm was observed on the surface of the coating layer side of the laminated porous film, and more than the surroundings. It can be evaluated by counting the number of protrusions protruding from 5 μm or more (amount of roughness), and the smaller the amount of roughness, the better the surface smoothness.
The amount of roughness is preferably less than 100 pieces / mm ² , and more preferably less than 80 pieces / mm ² , since film conveyance troubles and appearance defects can be reduced. The lower limit is not particularly limited and is ideally 0 piece / mm ^2, but it is preferably 10 ⁻¹⁰ piece / mm ² or more in practice.

(Non-aqueous electrolyte secondary battery)
Next, a nonaqueous electrolyte secondary battery containing the laminated porous film as a battery separator will be described with reference to FIG.
Both electrodes of the positive electrode plate 21 and the negative electrode plate 22 are wound in a spiral shape so as to overlap each other via the battery separator 10, and the outside is stopped with a winding tape to form a wound body.
The winding process will be described in detail. One end of the battery separator is passed between the slit portions of the pin, and the pin is slightly rotated to wind one end of the battery separator around the pin. At this time, the surface of the pin is in contact with the coating layer of the battery separator. Thereafter, the positive electrode and the negative electrode are arranged so as to sandwich the battery separator, and the pins are rotated by a winding machine to wind the positive and negative electrodes and the battery separator. After winding, the pin is pulled out of the wound object.

  A wound body in which the positive electrode plate 21, the battery separator 10 and the negative electrode plate 22 are integrally wound is housed in a bottomed cylindrical battery case and welded to the positive and negative electrode lead bodies 24 and 25. Next, the electrolyte is injected into the battery can, and after the electrolyte has sufficiently penetrated into the battery separator 10 or the like, the positive electrode lid 27 is sealed around the opening periphery of the battery can via the gasket 26, and precharging and aging are performed. A cylindrical non-aqueous electrolyte secondary battery is produced.

As the electrolytic solution, an electrolytic solution in which a lithium salt is used as an electrolytic solution and is dissolved in an organic solvent is used.
The organic solvent is not particularly limited. For example, propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, γ-valerolactone, esters such as dimethyl carbonate, methyl propionate or butyl acetate, nitriles such as acetonitrile, Examples include 2-dimethoxyethane, 1,2-dimethoxymethane, dimethoxypropane, 1,3-dioxolane, ethers such as tetrahydrofuran, 2-methyltetrahydrofuran or 4-methyl-1,3-dioxolane, or sulfolane. Can be used alone or in admixture of two or more.
Among them, an electrolyte obtained by dissolving lithium hexafluorophosphate (LiPF ₆₎ at a rate of 1.0 mol / L in a solvent obtained by mixing 2 parts by mass of methyl ethyl carbonate relative to ethylene carbonate 1 part by weight is preferred.

  As the negative electrode, an alkali metal or a compound containing an alkali metal integrated with a current collecting material such as a stainless steel net is used. Examples of the alkali metal include lithium, sodium, and potassium. Examples of the compound containing an alkali metal include an alloy of an alkali metal and aluminum, lead, indium, potassium, cadmium, tin or magnesium, a compound of an alkali metal and a carbon material, a low potential alkali metal and a metal oxide, and the like. Or a compound with a sulfide or the like. When a carbon material is used for the negative electrode, the carbon material may be any material that can be doped and dedoped with lithium ions, such as graphite, pyrolytic carbons, cokes, glassy carbons, a fired body of an organic polymer compound, Mesocarbon microbeads, carbon fibers, activated carbon and the like can be used.

  As the positive electrode, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, manganese dioxide, metal oxide such as vanadium pentoxide or chromium oxide, metal sulfide such as molybdenum disulfide, etc. are used as active materials. , These positive electrode active materials are combined with conductive additives and binders such as polytetrafluoroethylene as appropriate, and finished with a current collector material such as a stainless steel mesh as a core material. It is done.

  Although an Example and a comparative example are shown below and it demonstrates in detail about the alumina slurry of this invention, this invention is not limited to these.

<Evaluation method>
(1) Primary average particle diameter of alumina The primary average particle diameter of alumina was determined by a laser diffraction method using “Microtrack 9320HRA” manufactured by Nikkiso Co., Ltd.

(2) Specific surface area of alumina The specific surface area of alumina was measured by a constant volume gas adsorption method.

(3) pH
The alumina slurry was centrifuged and the pH of the supernatant obtained was measured using a simple pH tester (pHep: manufactured by Hanna Instruments Japan Co., Ltd.).

(4) Viscosity of alumina slurry Using a B-type viscometer (“TVB10H” manufactured by Toki Sangyo Co., Ltd.), the viscosity was measured at a temperature of 25 ° C. and a peripheral speed of 100 rpm.

(5) Presence or absence of hard cake 100 g of alumina slurry was put in a 100 mL polyethylene bottle and left and allowed to stand for 1 week. The sediment was reciprocated in the horizontal direction for 5 minutes with a stroke width of 20 cm and a period of 100 Hz. The presence or absence of a hard cake was confirmed according to the following criteria.
○: The sediment layer on the bottom of the bottle is redispersed by the reciprocating motion and almost disappears.
X: The sediment layer on the bottom of the bottle remains after the reciprocating motion.

(6) Coating property The coating property of the coating layer forming dispersion was evaluated by the amount of roughness. For the amount of roughness, use a fine shape measuring instrument ("ET4000A" manufactured by Kosaka Laboratory Ltd.) to observe a viewing angle of 300 µm x 400 µm on the coating layer side surface of the laminated porous film and protrude 5 µm or more from the surroundings. The number of convex parts was counted. The coatability was evaluated according to the following criteria based on the roughness value.
○: The amount of roughness is less than 100 pieces / mm ² ×: The amount of roughness is 100 pieces / mm ² or more

(7) Total Thickness of Laminated Porous Film The total thickness of the laminated porous film was calculated as an average value of five in-plane measurements of the laminated porous film with a 1/1000 mm dial gauge.

(8) Thickness of coating layer The thickness of the coating layer was calculated as the difference between the total thickness of the laminated porous film after the formation of the coating layer and the thickness of the polyolefin resin porous film.

(9) Air permeability (Gurley value)
The air permeability was measured according to JIS P8117 (2009).

(Preparation of polyolefin resin porous film)
Polypropylene resin (“Novatec PP FY6HA” manufactured by Nippon Polypro Co., Ltd., density: 0.90 g / cm ³ , MFR: 2.4 g / 10 min) and 3,9-bis [4- ( N-cyclohexylcarbamoyl) phenyl] -2,4,8,10-tetraoxaspiro [5.5] undecane was prepared. Each raw material is blended at a ratio of 0.2 part by mass of β-crystal nucleating agent with respect to 100 parts by mass of this polypropylene resin, and the same direction twin screw extruder manufactured by Toshiba Machine Co., Ltd. (caliber: 40 mmφ, L / D : 32), melted and mixed at a set temperature of 300 ° C., cooled and solidified the strands in a water tank, cut the strands with a pelletizer, and produced raw material pellets.

The raw material pellets were again put into an extruder, melted, extruded from a T die (die), and cooled and solidified with a casting roll at 124 ° C. to produce a film-like material.
The film-like material was stretched 4.6 times in the longitudinal direction at 100 ° C. using a longitudinal stretching machine, then stretched 2.1 times in the transverse direction at 150 ° C. with a transverse stretching machine, and then heat-set at 153 ° C. Went. Subsequently, relaxation treatment was performed, and a corona surface treatment was performed at a power of 0.4 kW and a speed of 10 m / min using a generator CP1 manufactured by VETAPHONE to obtain a polyolefin resin porous film (thickness 20 μm).

[Example 1]
52.6 parts by mass of alumina (“LS-235C” manufactured by Nippon Light Metal Co., Ltd., primary average particle size 0.5 μm, specific surface area 6.4 m ² / g), 5.3 parts by mass of isopropyl alcohol, 42. 1 part by mass was put into a container and mixed, and stirred using a stirring blade of polytetrafluoroethylene at a rotational speed of 1000 rpm for 15 minutes to obtain a mixed solution 1 [step (1)].
Next, with respect to 100 parts by mass of polystyrene sulfonic acid (“Amberlite: IR124” manufactured by Organo Corporation) which is an acidic ion exchange resin, washing is performed 3 times with 1000 parts by mass of 10% by weight hydrochloric acid, and then dried. Crude ion exchange resin (EX-A) was prepared.
5 parts by mass of the crude ion exchange resin (EX-A) was added to the mixed solution 1, and the mixture was stirred for 30 minutes for acid treatment. The pH of the mixed solution after the acid treatment was 3.5. Subsequently, the ion exchange resin floating on the liquid surface is removed, and the remaining mixed solution is added with lithium hydroxide as an alkali metal hydroxide so as to be 500 ppm by mass with respect to the total amount of the mixed solution and mixed. A liquid 2 was obtained [Step (2)]. Thereafter, the mixed solution 2 was continuously dispersed by a bead mill at a temperature of 25 ° C. to obtain an alumina slurry having a pH of 7.0 [step (3)]. Detailed conditions of the bead mill were as follows.
Apparatus: “NVM-1.5” manufactured by Imex
Beads: φ0.5mm zirconia beads (filling rate 85%)
Peripheral speed: 10 m / sec Discharge rate: 350 mL / min Average residence time: 0.6 min

The obtained alumina slurry was allowed to stand for 1 week, and then 61.8 parts by mass of the alumina slurry, 9.9 parts by mass of an aqueous solution of 5% by mass polyvinyl alcohol (“PVA-124” manufactured by Kuraray Co., Ltd.), ion exchange 28.3 parts by mass of water was mixed to obtain a dispersion for forming a coating layer having a solid concentration of 33% by mass.
The obtained dispersion for forming a coating layer was applied to the polyolefin resin porous film using a gravure roll (lattice type, number of lines: 25 L / inch, depth 290 μm, cell capacity 145 mL / m ² ), and then 45 ° C. Were dried in a drying oven to form a coating layer, and a laminated porous film having a total thickness of 24 μm was obtained.
The said evaluation was performed about the obtained alumina slurry and laminated porous film. The results are shown in Table 1.

[Example 2]
First, 100 parts by mass of the crude ion exchange resin (EX-A) produced in Example 1 was washed with 1000 parts by mass of ion exchange water three times and dried to obtain a purified ion exchange resin (EX-B). It was.
In Example 1, except that the crude ion exchange resin (EX-A) was changed to a purified ion exchange resin (EX-B), and 100 mass ppm of potassium hydroxide as an alkali metal hydroxide was added to the total amount. Obtained an alumina slurry having a pH of 7.5 in the same manner as in Example 1.
The obtained slurry was allowed to stand for 1 week, then shaken for 5 minutes, redispersed, and 61.8 parts by mass of the slurry, 5 mass% polyvinyl alcohol (“PVA-124” manufactured by Kuraray Co., Ltd.) aqueous solution 9 .9 parts by mass and 28.3 parts by mass of ion-exchanged water were mixed to obtain a dispersion for forming a coating layer having a solid concentration of 33% by mass.
The obtained dispersion for forming a coating layer was applied to the polyolefin resin porous film using a gravure roll (lattice type, number of lines: 25 L / inch, depth 290 μm, cell capacity 145 mL / m ² ), and then 45 ° C. Were dried in a drying oven to form a coating layer, and a laminated porous film having a total thickness of 24 μm was obtained.
The said evaluation was performed about the obtained alumina slurry and laminated porous film. The results are shown in Table 1.

[Comparative Example 1]
In Example 1, an alumina slurry was prepared in the same manner as in Example 1 except that lithium hydroxide was not added. However, the alumina slurry after standing for 1 week produced a hard cake at the bottom, and it was difficult to redisperse even after shaking for 5 minutes.
Moreover, using the supernatant of the obtained slurry, a laminated porous film having a total thickness of 22 μm was produced in the same manner as in Example 1, and the evaluation was performed. The results are shown in Table 1.

[Comparative Example 2]
In Example 1, an alumina slurry was prepared in the same manner as in Example 1 except that acid treatment with an ion exchange resin was not performed and lithium hydroxide was not added. Since the alumina slurry was not subjected to an acid treatment with an ion exchange resin, it contained 350 mass ppm of sodium hydroxide derived from the raw material alumina, and its pH was 9.0.
Moreover, the obtained slurry was used to produce a laminated porous film having a total thickness of 33 μm by the same method as in Example 1, and the evaluation was performed. The results are shown in Table 1.

From Table 1, since the alumina slurry obtained in the Examples has suppressed the formation of hard cake and the aggregation of alumina is also reduced, the coating layer-forming dispersion using the alumina slurry is coated. And the formed coating layer is excellent in surface smoothness. Moreover, the air permeability of the obtained laminated porous film was also good.
On the other hand, the alumina slurry of Comparative Example 1 could not suppress the formation of hard cake as described above. Moreover, although the production | generation of the hard cake was not seen by the alumina slurry of the comparative example 2, since the aggregation of an alumina cannot be suppressed, the obtained lamination | stacking porous film is remarkable in a rough surface over unwinding, and is inferior to productivity. It was a thing.

  According to the alumina slurry and the production method thereof of the present invention, there is little aggregation of alumina, and the formation of the hard cake is also suppressed. For example, in the production of laminated porous films suitably used for separators for non-aqueous electrolyte secondary batteries, etc., when a porous coating layer is formed using a dispersion containing the slurry, a uniform layer is stabilized by a coating method. Therefore, the productivity of the film can be stabilized.

DESCRIPTION OF SYMBOLS 10 Separator for nonaqueous electrolyte secondary battery 20 Secondary battery 21 Positive electrode plate 22 Negative electrode plate 24 Positive electrode lead body 25 Negative electrode lead body 26 Gasket 27 Positive electrode lid

Claims (4)

The manufacturing method of the alumina slurry which has the following process (1)-(3) in order and whose viscosity in the temperature of 25 degreeC is 10 mPa * s or more and 3000 mPa * s or less .
Step (1): Alumina having a primary average particle size of 0.1 μm or more and 1.0 μm or less and a dispersion medium having a water content of 50% by mass or more are mixed, and the content of the alumina is 30% by mass. Process step (2) for obtaining liquid mixture 1 of not less than 70% by mass and not more than 70% by mass: After acid-treating liquid mixture 1 obtained in step (1) using an acidic cation exchange resin , an alkali metal hydroxide is added. Step of adding and adjusting the pH to 6 or more and 8 or less to obtain a mixed solution 2 (3): A step of dispersing the mixed solution 2 obtained in the step (2) to obtain an alumina slurry The method for producing an alumina slurry according to claim 1 , wherein the alumina is obtained by firing aluminum hydroxide. The manufacturing method of the alumina slurry of Claim 1 or 2 whose addition amount of the alkali metal hydroxide in the said process (2) is 50 mass ppm or more with respect to the liquid mixture 1 and 1000 mass ppm or less. The method for producing an alumina slurry according to any one of claims 1 to 3, wherein the dispersion medium contains a lower alcohol having 1 to 4 carbon atoms in a range of 1% by mass to 20% by mass.