JP2017197634A - Method for deciding drawing condition for polymer microporous film, and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means for deciding drawing conditions for obtaining a crystalline polymer microporous film having desired characteristics.SOLUTION: Polarization Raman spectroscopy is performed to a gelatinous sheet including a crystalline polymer and a solvent for film formation, and, from an orientation distribution function calculated using peak area strength obtained by the polarization Raman spectroscopy, the drawing field ratio of a suitable gelatinous sheet is decided. As the orientation distribution function, the orientation distribution function at least in a direction crossed in the film plane in the drawing direction is preferably used.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for determining stretching conditions for a polymer microporous membrane and a method for producing the same.

  Since the polymer microporous membrane is excellent in chemical resistance, insulation, mechanical strength, etc., it is used in various applications such as filters such as filtration membranes and dialysis membranes, separators for batteries, and separators for capacitors. In particular, a microporous membrane manufactured by a so-called wet manufacturing method in which a gel-like sheet containing a crystalline polymer and a film-forming solvent is stretched and then the film-forming solvent is removed has a dense pore structure and a homogeneous structure. For example, it is widely used as a secondary battery separator.

  In the wet manufacturing method of the polymer microporous membrane, the gel-like sheet is machine direction (film forming direction, also referred to as longitudinal direction, hereinafter referred to as MD direction) or a direction perpendicular to the MD direction in the film plane (width direction, In the so-called sequential stretching method in which the film is stretched in the direction perpendicular to the stretching direction in the film plane after uniaxial stretching in the film plane (hereinafter also referred to as the transverse direction, hereinafter referred to as the TD direction) This affects not only the physical and thermal properties, structure and appearance of the porous membrane, but also the handling workability during secondary processing.

  In recent years, polymer microporous membranes composed of polyethylene having a specific molecular weight, a mixture thereof, a copolymer, and a crystalline polymer other than polyolefin have been studied. In order to determine the optimum stretching conditions therefor. The preliminary film forming apparatus in which the stretching ratio in the MD direction and the stretching ratio in the TD direction were changed for each of various conditions such as temperature and speed, and after measuring the physical properties, the actual film forming apparatus for the possible stretching conditions. There was a problem that required a lot of time, labor and money.

  Patent Document 1 discloses a method for producing a microporous film, but does not disclose a method for finding optimum conditions in a wide range of stretching conditions with a surface magnification of 50 to 400 times.

  It is known to perform crystal orientation measurement by X-ray measurement or Raman spectroscopic measurement (see Patent Document 2 and Patent Document 3). However, in the method of measuring a film obtained after stretching in the MD direction and the TD direction, it is necessary to individually examine all stretching conditions, and there is a problem that a lot of time and labor are required.

JP 2000-272017 A JP 2011-201949 A JP 2013-199545 A

  An object of the present invention is to solve the above problems and to provide a method for quickly determining the stretching conditions of a crystalline polymer microporous membrane by simple prior measurement and a method for producing the same.

  The present invention uses the orientation distribution function in the stretching direction and the orientation distribution function in the direction orthogonal to the stretching direction, calculated by polarization Raman spectroscopy measurement of a gel-like sheet comprising a crystalline polymer and a film-forming solvent. This is a method for determining the draw ratio.

  Moreover, another aspect of the present invention relates to a method for producing a microporous membrane using the stretching conditions determined by the above-described stretching condition determination method. Still another embodiment of the present invention relates to a microporous film produced by the above production method and a roll formed by winding a microporous film.

  The method for determining the draw ratio of the gel-like sheet of the present invention uses a polarized Raman spectroscopic measurement, so that even when a new crystalline polymer is used or a resin composition is changed, it can be easily obtained. Stretching conditions for obtaining a crystalline polymer microporous film having characteristics can be determined.

  Further, in one embodiment of the method for producing a crystalline polymer microporous membrane of the present invention, the crystalline polymer microporous membrane is excellent in winding property, improved yield in secondary processing, and excellent in productivity. Can be produced efficiently.

    In another aspect of the method for producing a crystalline polymer microporous membrane of the present invention, a crystalline polymer microporous membrane having excellent tear strength can be produced efficiently.

FIG. 1 is a diagram showing an example of the shape of a gel-like sheet test piece used for polarized Raman spectroscopy measurement. FIG. 2 is a diagram showing an example in which the orientation distribution function of a gel-like sheet, measured by changing the amount of strain, is plotted against the angle θ when the stretching direction is 0 ° in the film plane. S in the figure represents the amount of strain and corresponds to a numerical value obtained by subtracting 1 from the draw ratio. FIG. 3 is an example in which the orientation parameters <P ₂ > and <P ₄ > calculated from the stretching stress and the polarization Raman spectroscopic measurement result when the gel sheet is stretched are plotted against the gel sheet strain amount. FIG. The amount of strain in the figure corresponds to a value obtained by subtracting 1 from the draw ratio.

  In the uniaxial stretching process of the gel sheet, the present invention acquires a polarization Raman spectroscopy spectrum of a plurality of stretching magnifications in a single measurement, and analyzes the result to thereby intersect the stretching direction in the film plane. The stretching condition is determined by clarifying the molecular state. Specifically, in order to produce a microporous film having desired characteristics by deriving an orientation distribution function from the obtained polarization Raman spectroscopy spectrum and clarifying the molecular state in the direction intersecting the stretching direction in the film plane. Determine the draw ratio.

  Here, the direction intersecting the stretching direction in the film plane includes a direction perpendicular to the stretching direction in the film plane, and 45 ° to 135 °, preferably 60 ° to 120 ° in the stretching direction in the film plane, More preferably, the direction intersects at an angle of 80 ° to 100 °. Typically, the direction orthogonal to the stretching direction can be used in the film plane, but depending on the stretching method and the specifications of the stretching machine, the angle that intersects the stretching direction and the above angle in the film plane can be selected. Good.

  The orientation distribution function used for determining the stretching ratio can be used depending on the purpose.For example, the orientation distribution function in the stretching direction, the orientation distribution function in the direction perpendicular to the stretching direction in the film plane, and the ratio of both. Can be used. Above all, by using the ratio of the orientation distribution function in the stretching direction and the orientation distribution function in the direction perpendicular to the stretching direction in the film plane, the difference in the polarization Raman spectroscopy measurement device can be normalized, and the relative This is preferable because it enables comparison.

  For example, in the gel-like sheet, the orientation distribution function in the stretching direction is 10.0 times or more, preferably 10.5 times or more, more preferably 11.0 times or more of the orientation distribution function in the direction perpendicular to the stretching direction. It is preferable to stretch at a draw ratio. Compared with the molecular orientation in the stretching direction, since the molecular orientation in the direction perpendicular to the stretching direction in the film plane is negligible, from the method for producing a crystalline polymer microporous film including such steps, This is because a crystalline polymer microporous membrane having a homogeneous and fine pore structure can be expected.

  Further, for example, the gel-like sheet has an orientation distribution function in the stretching direction of less than 10.0 times, preferably 5 times or more and less than 10.0 times, more preferably 6. You may extend | stretch by the draw ratio used as 0 times or more and less than 9.5 times. This is because, since the molecular orientation in the direction intersecting the stretching direction remains moderately, improvement in tear strength of the obtained crystalline polymer microporous film can be expected.

[Gel-like sheet]
The gel-like sheet is a sheet-like molded body made of a crystalline polymer and a film-forming solvent. The blending ratio of the crystalline polymer and the film-forming solvent is not particularly limited, but is preferably 50 to 90 parts by mass with respect to 10 to 50 parts by mass of the crystalline polymer.

  The preparation method is not particularly limited, and examples thereof include a method of extruding a molten mixture of a crystalline polymer and a film-forming solvent from a die, cooling the extruded molded body, and molding it into a sheet.

  As a melt-kneading method, for example, a method using a twin-screw extruder described in Japanese Patent No. 2132327 and Japanese Patent No. 3347835 can be used. Since the melt-kneading method is known, the description thereof is omitted.

  The melt-kneaded product can be fed from an extruder to a die and extruded into a sheet. A molten mixture composed of a plurality of crystalline polymers having the same or different composition and a film-forming solvent may be fed from an extruder to one die, laminated there in a layer form, and extruded into a sheet form.

  A gel-like sheet can be shape | molded by cooling the obtained extrusion molding. As a method for forming the gel sheet, for example, methods disclosed in Japanese Patent No. 2132327 and Japanese Patent No. 3347835 can be used.

[Crystalline polymer]
Crystalline polymers include polyolefins such as polyethylene, polypropylene, polymethylpentene, polyamides, polyacetals, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polyether ether ketone, liquid crystal polymers, polytetrafluoroethylene, and mixtures thereof. Can be included. Among these, it is preferable to include a crystalline polyolefin resin such as polyethylene or polypropylene.

  Examples of polyolefins include homopolymers of ethylene and propylene, copolymers of olefin copolymers such as ethylene, propylene, butene, hexene, pentene, methylpentene, octene, vinyl acetate, methyl methacrylate, and styrene, and mixtures thereof. Illustrated.

  The type of polyethylene is not particularly limited, and various polyethylenes can be used. For example, high density polyethylene, medium density polyethylene, ultra high molecular weight polyethylene (UHMwPE), branched low density polyethylene, linear low density polyethylene and Mixtures of these can be used. Among these, high-density polyethylene, ultrahigh molecular weight polyethylene, and mixtures thereof are preferable from the viewpoint of controlling the pore structure of the microporous membrane and the thermal properties and strength of the membrane.

The high density polyethylene has a density of 0.920 g / m ³ or more and 0.970 g / m ³ or less, and a weight average molecular weight (Mw) of, for example, 1 × 10 ⁴ or more and less than 1 × 10 ⁶ , and molecular weight dispersion. (MWD: Mn / Mw) is, for example, 1 to 25, preferably 3 to 10. Examples of the ultra high molecular weight polyethylene include those having a weight average molecular weight (Mw) of 1 × 10 ⁶ or more, preferably 1 × 10 ⁶ or more and 8 × 10 ⁶ or less. The weight average molecular weight is a value measured by gel permeation chromatography (GPC).

The type of polypropylene is not particularly limited, and various types of polypropylene can be used. The weight average molecular weight (Mw) of polypropylene is preferably 1 × 10 ⁵ or more and 1 × 10 ⁸ or less, more preferably 1 × 10 ⁶ or more and 1 × 10 ⁸ or less. The molecular weight dispersion (MWD) of polypropylene is preferably 5 or more and 10 or less, for example.

  The crystalline polymer is within the range not impairing the effects of the present invention, for example, amorphous heat resistant resin, antioxidant, heat stabilizer, antistatic agent, ultraviolet absorber, antiblocking agent or filler, crystal Various additives such as a nucleating agent and a crystallization retarder may be included.

[Film forming solvent]
The solvent for film formation is not particularly limited, and can be appropriately selected according to the type of crystalline polymer to be used and the production process of the microporous film. As the film-forming solvent, a liquid solvent, a solid solvent, and a mixture thereof can be used.

  Liquid solvents include nonane, decane, decalin, para-xylene, undecane, dodecane, liquid paraffin and other aliphatic or cyclic hydrocarbons; phthalates such as dibutyl phthalate and dioctyl phthalate; A mineral oil fraction is exemplified. From the viewpoint of preventing change in the content of the film-forming solvent in the gel sheet, it is preferable to use a non-volatile film-forming solvent such as liquid paraffin. Among these, when the crystalline polymer is a crystalline polyolefin resin, liquid paraffin having a kinematic viscosity at 40 ° C. of 20 to 200 cSt is preferable.

  Examples of the solid solvent include paraffin wax, ceryl alcohol, stearyl alcohol, and dicyclohexyl phthalate. The melting point of the solid solvent is preferably 80 ° C. or less.

[Orientation distribution function]
The orientation distribution function is a function relating to an arbitrary angle θ in the film plane when the stretching direction is 0 ° in the film plane, and can be expressed as N (θ). When θ coincides with the stretching direction, that is, θ = 0 °, and when θ is an angle perpendicular to the stretching direction and the film plane, that is, when θ = 90 °, each orientation distribution function is N (0 °). , N (90 °), and the ratio is expressed by the formula: N (0 °) / N (90 °).

  The orientation distribution function N (θ) is calculated from the orientation parameters <P2> and <P4> calculated from the polarization Raman spectroscopic measurement result of the gel sheet by the method described in Polymer 58 (2015) 88-95, for example. Can lead.

[Calculation of orientation parameters <P ₂ > and <P ₄ >]
The orientation parameters <P ₂ > and <P ₄ > can be calculated, for example, from the peak area intensity of the polarization Raman spectrum of the gel sheet measured by changing the polarization direction of incident light and scattered light with a polarizer. The peak area intensity will be described later.

The peak area intensity (I _xx , I _yy , I _ix ) in each polarization state can be expressed by the following formulas (1) to (3). Here, the subscript x indicates the polarization direction parallel to the stretching direction of the gel-like sheet in the film plane, and the subscript y indicates the polarization in the direction perpendicular to the stretching direction of the gel-like sheet in the film plane. The subscript written earlier indicates the polarization state of the incident light, and the subscript written later indicates the polarization state of the scattered light (detection side).

In the above formula, a is a constant obtained from the following formula (4) using the peak area intensities I _yx and I _xx .

By substituting I _xx , I _yy , I _ix obtained from the polarization Raman spectroscopic measurement result of the gel sheet stretched with the constant a and an arbitrary strain into the above formulas (1) to (4), < P ₂ >, <P ₄ >, a and b can be calculated.

[Derivation of orientation distribution function N (θ)]
The orientation distribution function N (θ) is expressed by, for example, the following formula (5).

In formula (5), <P ₂ >, <P ₄ >, <P ₆ >, <P ₈ >, <P ₁₀ > are orientation parameters of the gel sheet represented by formulas (6) to (10). Yes, derived from 2 to 10 even-order terms of the Legendre polynomial (Polymer 58 (2015) 88-95). Note that <cos θ> means an integral value when θ is 0 ° to 180 °, so <cos θ> is 0. From this fact, all odd-order terms of the Legendre polynomial when x = <cos θ> are set to 0.

  Since the Legendre polynomial can be defined from the 0th order term to the ∞ order term, an even order term of the 12th order or more Legendre polynomial may be used. Since the contribution of higher-order orientation parameters is small, in Equation (5), Legendre polynomial even-order terms from the 0th-order term to the 10th-order term are used for the sake of simplicity.

<Cos ² θ> is obtained from equation (6) and / or equation (7) using the values of <P ₂ > and <P ₄ > calculated from the polarization Raman spectroscopy measurement result of the gel sheet described above. Can do. The calculated values of <P ₆ >, <P ₈ >, and <P ₁₀ > can be calculated by inserting <cos ² θ> into the above formulas (8) to (10).

In formula (5), P ₂ (cos θ), P ₄ (cos θ), P ₆ (cos θ), P ₈ (cos θ), and P ₁₀ (cos θ) are represented by formulas (11) to (15). This is an orientation parameter at an arbitrary θ derived from an even-order term of a Legendre polynomial.

Further, instead of the above formula (5), a maximum orientation distribution function N _mp (θ): formula (16) applying the maximum entropy principle may be used.

In the equation, λ2 and λ4 are constants called Lagrange undetermined multipliers.

[Polarization Raman spectroscopy measurement]
Below, an example of measurement conditions for polarized Raman spectroscopy is shown.

A typical apparatus configuration and measurement conditions are shown below.
・ 180 ° backscattering arrangement ・ Excitation wavelength 639.7 nm (LASOS DPSS laser, output 200 mW)
・ Spot size Diameter 1mm
・ Spherical plano-convex condenser lens (NA = 0.33)
Spectroscope Spectra Pro 2300i manufactured by Nippon Roper
・ Detector PIXIS 100 manufactured by Nippon Roper
・ Exposure time 1000ms
・ Number of integration: 10 times ・ Extension speed: 1 mm / min ・ Dimensions of test piece: Full width: 8 mm, notch depth: 2 mm, notch length: 2 mm

  The laser is polarized using a polarizer disposed on the optical path, and is perpendicularly incident from the normal direction of the film plane (XY plane). It is preferable from the viewpoint of measurement reliability that the laser irradiation position is adjusted to the center of the test piece extension site. Backscattered light is collected by a convex lens and a polarizer is placed on the optical path. By changing the arrangement of the polarizers arranged in the laser beam path and the scattered light beam path, the Raman spectrum of each polarization state can be measured. In order to improve the monochromaticity of the laser, a laser line filter may be disposed in the laser beam path. Further, a line pass filter may be arranged on the scattered light path in order to remove Rayleigh scattered light in the scattered light. The exposure time and the number of integrations can be adjusted according to the detector and the stretching conditions. Typically, for example, the exposure time is 1000 ms and the number of integrations is 10 to 20 times.

[Polarized Raman Spectroscopy Gel-like Sheet Specimen and Drawing Method]
The gel-like sheet test piece for measurement of polarized Raman spectroscopy is preferably a tape-like test piece provided with a rectangular notch at a position symmetrical with respect to the long axis of the test piece. FIG. 1 shows the shape of a typical gel-like sheet test piece. As shown in FIG. 1, it is preferable that the extending | stretching direction of a gel-like sheet | seat test piece corresponds with the major axis direction.

  The major axis of the gel-like sheet test piece is the MD direction (also referred to as film forming direction, machine direction, length direction, longitudinal direction), TD direction (direction perpendicular to the MD direction and the film plane, and the width direction). , Also referred to as a horizontal direction). In addition, it is preferable that the extending | stretching direction of a gel-like sheet test piece needs to correspond with the extending | stretching direction of the 1st gel-like sheet extending process mentioned later. Tests can be performed in a form close to that of actual machines such as MD roll stretching, and the optimum stretching ratio during fibrillation can be easily grasped, and a separator having a dense structure with little variation in physical properties can be rapidly developed.

  The stretching condition of the test piece can be changed according to the polarization Raman spectroscopy measurement method. Typically, the stretching speed is 0.1 mm / min to 10 mm / min in an atmosphere of 0 ° C. to 150 ° C. In order to facilitate the maintenance of the laser irradiation position, both test piece gripping portions may be stretched by moving the displacement amount and the speed in the direction in which they are separated from each other.

[Calculation of peak area intensity]
For the calculation of the orientation parameter, it is preferable to use the peak area intensity attributed to the Ag band in the polarized Raman spectrum. This is because it is sensitive to changes in crystal orientation due to stretching. In general, the Ag band is defined as a band having a depolarization degree of 0.75 or less. When there are a plurality of peaks attributed to the Ag band in the polarization Raman spectrum, from the viewpoint of measurement accuracy, a peak attributed to the Ag band having a small peak overlap and a large peak area intensity may be selected. . This is because the orientation distribution function obtained is the same regardless of the peak attributed to any Ag band. For example, in the case of polyethylene, the peaks attributed to the Ag band are 1418 cm ⁻¹ and 1130 cm ⁻¹ , and the orientation distribution function obtained by using the area intensity of either peak is the same.

  Specific methods of peak fitting include the Gauss method, Lorentz mixing function, Levenberg-Marquardt method, and Forked method. The peak area intensity can be obtained by calculating the area surrounded by the curve and base line obtained by peak fitting.

For example, if the crystalline polymer is polyethylene, the peak area intensity of 1130 cm ^-1 is a curve obtained by peak fitting with Levenberg-Marquardt method, the linear approximation of 1020 cm ^-1 or 1160 cm ^-1 following areas It can obtain | require using the baseline acquired by.

[Production Method of Crystalline Polymer Microporous Film]
The method for producing a crystalline polymer microporous membrane according to the present invention includes a step of stretching a gel-like sheet in at least a uniaxial direction at a draw ratio that satisfies the above-mentioned orientation distribution function. The method for preparing the gel sheet is as described above.

The method for preparing the crystalline polymer microporous membrane from the gel sheet can include, for example, the following steps (1) to (3), and may further include the following steps (4) to (6). . Specifically, for example, the methods described in the specifications of Japanese Patent No. 2132327 and Japanese Patent No. 3347835, International Publication No. 2006/137540, and the like can be used as these steps.
(1) Step of stretching gel sheet (2) Step of removing solvent for film formation from stretched gel sheet (3) Step of drying sheet after removal of solvent for film formation (4) Micropore after drying (5) Step of heat-treating the microporous membrane (6) Step of crosslinking and / or hydrophilizing the microporous membrane

(1) Stretching step of gel-like sheet The gel-like sheet is preferably stretched uniaxially in a direction coinciding with the stretching direction of the gel-like sheet test piece at the time of measurement of polarized Raman spectroscopy. Here, the process of initially uniaxially stretching the gel sheet is referred to as a first gel sheet stretching process. In the first gel-like sheet stretching step, it is preferable to perform uniaxial stretching at a stretching ratio in which the orientation distribution function satisfies the formula: N (0 °) / N (90 °) ≧ 10.0. Specific examples of the stretching means include a roll method and a tenter method. The gel sheet thus stretched is preferably stretched in a direction perpendicular to the stretching direction from the viewpoint of improving the physical and thermal properties of the obtained crystalline polymer microporous film. Here, the stretching step after the first gel-like sheet stretching step is referred to as a second gel-like sheet stretching step. The stretching method in the second gel-like sheet stretching step may be uniaxial stretching or biaxial stretching, or a combination of uniaxial stretching and biaxial stretching.

  The stretching temperature in this step is preferably in the range of the crystal dispersion temperature (Tcd) to Tcd + 30 ° C. of the polyolefin resin, and in the range of crystal dispersion temperature (Tcd) + 5 ° C. to crystal dispersion temperature (Tcd) + 28 ° C. Is more preferable, and the range of Tcd + 10 ° C. to Tcd + 26 ° C. is particularly preferable. When the stretching temperature is within the above range, membrane breakage due to polyolefin resin stretching is suppressed, and stretching at a high magnification is possible.

  The crystal dispersion temperature (Tcd) is determined by measuring the temperature characteristic of dynamic viscoelasticity according to ASTM D4065.

(2) Film-forming solvent removal step The film-forming solvent is removed (washed) using a cleaning solvent. Since the cleaning solvent and the method for removing the film-forming solvent using the same are known, the description thereof is omitted.

(3) Drying process The microporous film from which the film-forming solvent has been removed is dried by a heat drying method or an air drying method. The drying temperature is preferably not higher than the crystal dispersion temperature (Tcd) of the polyolefin resin, and particularly preferably 5 ° C. or more lower than Tcd. Drying is preferably carried out until the residual cleaning solvent is 5% by mass or less, more preferably 3% by mass or less, with the microporous membrane being 100% by mass (dry weight).

(4) Step of stretching microporous membrane after drying The microporous membrane after drying may be stretched in at least a uniaxial direction. The stretching in this step can be performed by a roll method, a tenter method or the like in the same manner as described above while heating. The stretching may be uniaxial stretching or biaxial stretching. In the case of biaxial stretching, either simultaneous biaxial stretching or sequential stretching may be used.

  Although the extending | stretching temperature in this process is not specifically limited, Usually, it is 90-135 degreeC, More preferably, it is 95-130 degreeC.

  The stretching ratio in the uniaxial direction of stretching of the microporous membrane in this step is preferably 1.0 to 2.5. In the case of biaxial stretching, the area stretching ratio is preferably 1.0 to 3.5, and the stretching ratios in the MD direction and the TD direction may be the same or different. In addition, the draw ratio in this process means the draw ratio of the microporous film just before being provided to the next process on the basis of the microporous film immediately before this process.

(5) Heat treatment Moreover, the microporous film after drying can be heat-treated. The crystal is stabilized by heat treatment, and the lamella is made uniform. As the heat treatment method, heat setting treatment and / or heat relaxation treatment can be used. The heat setting treatment is a heat treatment in which heating is performed while keeping the dimensions of the film unchanged. The thermal relaxation treatment is a heat treatment that heat-shrinks the film in the MD direction or the TD direction during heating. The heat setting treatment is preferably performed by a tenter method or a roll method. For example, as a thermal relaxation treatment method, a method disclosed in Japanese Patent Application Laid-Open No. 2002-256099 can be given. The heat treatment temperature is preferably within the range of Tcd to Tm of the polyolefin resin, more preferably within the range of the stretching temperature of the microporous membrane ± 5 ° C, and particularly preferably within the range of the second stretching temperature ± 3 ° C of the microporous membrane.

(6) Crosslinking treatment, hydrophilization treatment The microporous membrane after drying is irradiated with ionizing radiation such as α-ray, β-ray, γ-ray, electron beam, monomer graft, surfactant treatment, cross-linking such as corona discharge. You may perform a process and a hydrophilization process.

[Crystalline polymer microporous film]
Physical properties such as film thickness, porosity, pore diameter, Gurley value (air permeability resistance), etc. of the crystalline polymer microporous membrane obtained by the above-described crystalline polymer microporous membrane production method are not particularly limited. It is preferable to adjust to the following range.

[Film thickness]
The film thickness of the crystalline polymer microporous membrane is preferably 1 to 100 μm, more preferably 1 to 30 μm. A method for measuring the film thickness will be described later.

[Porosity]
The porosity of the crystalline polymer microporous membrane of the present invention is preferably 20% or more and 60% or less, more preferably 30% or more and 50% or less from the viewpoint of ion permeability, membrane strength, and the like. . A method for measuring the porosity will be described later.

[Average pore size]
The upper limit of the average pore diameter of the crystalline polymer microporous membrane of the present invention is 300 nm or less, preferably 100 nm or less, more preferably 50 nm or less, and further preferably, from the viewpoint of improving the film strength and withstand voltage characteristics. Is 38 nm or less. The lower limit of the average pore diameter of the crystalline polymer microporous membrane of the present invention is not particularly limited, but is preferably 1 nm or more, and more preferably 5 nm or more from the relationship of the air resistance described later. When the average pore diameter of the crystalline polymer microporous membrane of the present invention is in the above range, a membrane having a dense structure and a microporous membrane having excellent membrane strength can be obtained.

[Maximum hole diameter]
The upper limit of the maximum pore size of the crystalline polymer microporous membrane of the present invention is 500 nm or less, preferably 300 nm or less, more preferably 80 nm or less, from the viewpoint of improving the film strength and voltage resistance characteristics. The lower limit of the maximum pore size of the crystalline polymer microporous membrane of the present invention is not particularly limited, but is preferably 1 nm or more, and more preferably 5 nm or more from the relationship of air resistance described later. When the maximum pore size of the crystalline polymer microporous membrane of the present invention is in the above range, a membrane having a dense structure and a microporous membrane having excellent membrane strength can be obtained. From such a viewpoint, the maximum pore size is preferably 2.5 times or less of the average pore size, and more preferably 1.8 times or less.

The maximum pore diameter and the average flow pore diameter of the crystalline polymer microporous membrane can be measured in the order of Dry-up and Wet-up using a palm porometer (manufactured by PMI, CFP-1500A). For the wet-up, pressure was applied to a microporous membrane sufficiently immersed in Galwick (trade name) manufactured by PMI with a known surface tension, and the pore diameter converted from the pressure at which air began to penetrate was defined as the maximum pore diameter.
As for the average flow pore size, the pore size was converted from the pressure at the point where the curve showing the 1/2 slope of the pressure and flow curve in the Dry-up measurement and the curve of the Wet-up measurement intersect. The following formula was used for conversion of pressure and pore diameter.
d = C · γ / P
(In the above formula, “d (μm)” is the pore diameter of the microporous membrane, “γ (mN / m)” is the surface tension of the liquid, “P (Pa)” is the pressure, and “C” is a constant.

[Gurley value (air permeability resistance)]
In this embodiment, from the viewpoint of ion permeability, the Gurley value (air permeability resistance) when the film thickness is 20 μm is 100 to 1000 sec / 100 cc, preferably 100 to 800 sec / 100 cc, Particularly preferred is 600 sec / 100 cc. If the Gurley value exceeds 1000 sec / 100 cc, the ion permeability deteriorates and the electrical resistance increases, which is not preferable. On the other hand, when the Gurley value is less than 100 sec / 100 cc, the film structure becomes excessively sparse, and when the temperature inside the battery rises, shutdown before meltdown may not be performed sufficiently, which is not preferable.

  Here, the Gurley value when the film thickness is 20 μm is an expression when the Gurley value measured according to JIS P 8117 (2009) is P1 in a microporous film having a film thickness T1 (μm). : P2 = Gurley value P2 calculated by (P1 × 20) / T1. In the following description, the term “Gurley value” is used to mean “Gurley value when the film thickness is 20 μm” unless otherwise specified.

[Puncture strength]
The puncture strength of the crystalline polymer microporous membrane is preferably 400 gf or more, and more preferably 550 gf or more. By setting it as such a range, even if it makes it thin, it will not break, and safety | security improves.

  Here, the membrane puncture strength is the maximum when a microporous membrane having a thickness of T1 (μm) is pierced at a speed of 2 mm / sec with a needle having a spherical surface (curvature radius R: 0.5 mm) and a diameter of 1 mm. It is a load (gf).

[Heat shrinkage]
The thermal contraction rate at 105 ° C. in each of the MD and TD directions of the crystalline polymer microporous film is, for example, about 0.1% to 10%. When the heat shrinkage rate is in the above range, the heat resistance and durability of the product using the microporous membrane are improved, and the product can be expected to have a long life. The 105 ° C. thermal shrinkage rate of the microporous membrane 1 is determined by the heat treatment of the test piece at a temperature of 105 ° C. for 8 hours. The size (L1) of the test piece in each direction before the heat treatment and the direction of the test piece after the heat treatment The size (L2) is measured, and in each direction, the shrinkage rate of L2 when L1 is 100% is a value calculated by the formula: [100− (L2 / L1) × 100] (%). .

[Laminated microporous membrane]
Moreover, a porous layer may be provided on at least one surface or both surfaces of the crystalline polymer microporous membrane to form a laminated porous membrane. Although it does not specifically limit as a porous layer, For example, you may laminate | stack the inorganic particle layer containing a binder and an inorganic particle. The binder component constituting the inorganic particle layer is not particularly limited, and known components can be used. For example, acrylic resin, polyvinylidene fluoride resin, polyamideimide resin, polyamide resin, aromatic polyamide resin, polyimide resin, etc. Can be used. The inorganic particles constituting the inorganic particle layer are not particularly limited, and known materials can be used. For example, alumina, boehmite, barium sulfate, magnesium oxide, magnesium hydroxide, magnesium carbonate, silicon, or the like can be used. it can. The laminated crystalline polymer microporous membrane may be a laminate of the porous binder resin laminated on at least one surface of the crystalline polymer microporous membrane.

[Battery separator]
The crystalline polymer microporous membrane obtained by the method for producing a crystalline polymer microporous membrane of the present invention can be suitably used for both a battery using an aqueous electrolyte and a battery using a non-aqueous electrolyte. Specifically, it can be preferably used as a separator for secondary batteries such as nickel-hydrogen batteries, nickel-cadmium batteries, nickel-zinc batteries, silver-zinc batteries, lithium secondary batteries, lithium polymer secondary batteries and the like. Especially, it is preferable to use as a separator of a lithium ion secondary battery.

  In a lithium ion secondary battery, a positive electrode and a negative electrode are laminated via a separator, and the separator contains an electrolytic solution (electrolyte). The structure of the electrode is not particularly limited, and a conventionally known structure can be used. For example, an electrode structure (coin type) arranged so that a disc-shaped positive electrode and a negative electrode face each other, a plate-shaped positive electrode and a negative electrode An electrode structure in which layers are stacked alternately (stacked type), an electrode structure in which stacked strip-like positive and negative electrodes are wound (winding type), and the like can be used.

  The current collector, the positive electrode, the positive electrode active material, the negative electrode, the negative electrode active material, and the electrolyte used for the lithium ion secondary battery are not particularly limited, and conventionally known materials can be used in appropriate combination.

  In addition, this invention is not limited to the said embodiment, It can implement in various deformation | transformation within the range of the summary.

  The roll manufacturing method of this embodiment is characterized in that, for example, a crystalline polymer microporous film after stretching is wound around a core material. The roll may be, for example, a raw roll before secondary processing, or may be a roll slit into a predetermined width. The crystalline polymer microporous film is excellent in winding property, and thus has a relatively large area. For example, even when the length is about 1000 mm and the width is about 500 mm, horizontal meandering and vertical vibration are not observed. A roll can be formed. The microporous membrane 1 after being wound on a roll can be unwound again from the roll and subjected to processing such as slitting or surface coating. Since the microporous film 1 is excellent in winding property and coating property, it is very excellent in productivity at the time of processing.

  In another embodiment of the method for producing a crystalline polymer microporous membrane, the crystalline polymer microporous membrane obtained after the film formation is obtained by using the above-described crystalline polymer microporous membrane evaluation method, Selecting a microporous membrane that has been determined to have a good evaluation result. In the manufacturing method of crystalline polymer microporous membrane, by using the above evaluation method, select a microporous membrane with good winding and coating properties before winding or secondary processing on the core material. can do.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[Example 1]
Ultrahigh molecular weight polyethylene (weight average molecular weight (Mw) 3.5 × 10 ⁵ , high density polyethylene (HDPE 1) 24.6 mass% with MWD 5 and weight average molecular weight (Mw) 2.0 × 10 ⁶ ultrahigh molecular weight polyethylene ( (UHMWPE) 5.4% by mass and liquid paraffin 70% by mass were uniformly kneaded at 180 ° C. in a small kneader (Toyo Seiki Laboplast Mill), and the resulting mixture was pressed at 180 ° C. and cooled to 25 ° C. A gel-like sheet having a thickness of 1.2 mm was obtained. In the mixture, 0.375 parts by mass of tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] methane was blended with 100 parts by mass of polyethylene.

  A test piece having a thickness of 1.2 mm having the shape shown in FIG. 1 is prepared from the gel-like sheet thus obtained, and polarized when the draw ratio is 1 to 8 times while being drawn using a small tensile tester manufactured by Abe Seisakusho. Raman spectroscopy measurement was performed. The above-mentioned method was used for the polarization Raman spectroscopy measurement apparatus and measurement conditions. From the obtained polarized Raman spectrum, the peak area intensity of 1130 cm −1 was obtained from the peak fit using the Levenberg-Markt method, and the orientation distribution function was derived from the above formula (5). Table 1 shows the peak area intensity at the draw ratio of 5 to 8 times (strain 4 to 7), the calculated a, b, <P2>, <P4>, N (0 °), and N (90 °).

[Example 2]
Ultrahigh molecular weight polyethylene (weight average molecular weight (Mw) 3.5 × 10 ⁵ , high density polyethylene (HDPE 1) 24.6 mass% with MWD 5 and weight average molecular weight (Mw) 2.0 × 10 ⁶ ultrahigh molecular weight polyethylene ( (UHMWPE) 5.4% by mass and liquid paraffin 70% by mass were charged into a strong kneading type twin screw extruder and melt kneaded at 180 ° C. to prepare a polyethylene solution. In addition, 0.375 parts by mass of tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] methane was blended with 100 parts by mass of polyethylene.

  The obtained polyethylene solution was extruded into a sheet form from a T-die, and cooled while being drawn with a cooling roll to form a gel-like sheet.

  A test piece with a thickness of 1.2 mm having the shape shown in FIG. 1 with the MD direction of the obtained gel-like sheet as the stretching direction was prepared, and in the same manner as in Example 1, the polarization Raman spectroscopic measurement was performed, and the alignment was performed. The distribution function was derived. Table 2 shows the peak area intensity and the calculated parameters when the draw ratio is 5 to 8 times (strain 4 to 7).

[Experiment No. # 1- # 8]
The gel-like sheet obtained in Example 2 was sequentially biaxially stretched in the order of the MD direction and the TD direction under the conditions shown in Table 2 using a roll stretching machine and a tenter stretching machine. Liquid paraffin was removed from the stretched gel-like sheet, dried, and heat-fixed at 126 ° C. by a tenter method to obtain a polyethylene microporous membrane. Tables 4 and 5 show the composition, manufacturing conditions, evaluation results, and the like of the polyethylene microporous membrane.

  In Example # 5, after removing the liquid paraffin and drying, uniaxial stretching was performed in the TD direction at a stretching ratio of Table 2 at 126 ° C. using a tenter stretching machine, and then heat setting was performed.

  In order to obtain a microporous membrane excellent in secondary workability from the value of N (0 °) / N (90 °) obtained in Example 1 and Example 2, stretching of the first gel-like sheet In the process, it was found that the draw ratio should be 7 times or more. On the other hand, in order to obtain a microporous membrane having improved tear strength, it has been found that it is preferable to set the draw ratio to 6 times or less in the drawing step of the first gel-like sheet.

[Example 3]
Ultrahigh molecular weight polyethylene (weight average molecular weight (Mw) 2.8 × 10 ⁵ , high density polyethylene (HDPE 2) 20.0 mass% with MWD 15 and weight average molecular weight (Mw) 2.0 × 10 ⁶ (UHMWPE) A gel-like sheet was prepared in the same manner as in Example 1 except that a mixture composed of 8.5% by mass and 71.5% by mass of liquid paraffin was used.

  In the same manner as in Example 1, an orientation distribution function was derived from the polarized Raman spectrum of the gel sheet. Table 4 shows the peak area intensity and each parameter when the draw ratio is 5 to 8 times (strain 4 to 7).

[Experiment No. # 8- # 11]
Ultrahigh molecular weight polyethylene (weight average molecular weight (Mw) 2.8 × 10 ⁵ , high density polyethylene (HDPE 2) 20.0 mass% with MWD 15 and weight average molecular weight (Mw) 2.0 × 10 ⁶ UHMWPE) A gel sheet was prepared in the same manner as in Example 2 except that 8.5% by mass and 71.5% by mass of liquid paraffin were used.

  The obtained gel-like sheet was sequentially biaxially stretched in the order of the MD direction and the TD direction under the conditions shown in Table 5 using a roll stretching machine and a tenter stretching machine. Liquid paraffin was removed from the stretched gel-like sheet, dried, and heat-fixed at 126 ° C. by a tenter method to obtain a polyethylene microporous membrane. Table 5 shows the composition, production conditions, evaluation results, and the like of the polyethylene microporous membrane.

  In Experiment # 10, after removal of liquid paraffin and drying, uniaxial stretching was performed at a stretching ratio of Table 2 in the TD direction at 126 ° C. using a tenter stretching machine, and then heat setting was performed.

  In order to obtain a microporous film excellent in secondary processability from the value of N (0 °) / N (90 °), the stretching ratio is set to 6 times or more in the stretching process of the first gel-like sheet. It turns out that it should be. On the other hand, in order to obtain a microporous membrane having improved tear strength, it has been found that it is preferable to set the draw ratio to 5 times or less in the first gel-like sheet drawing step.

[Measurement method and evaluation method]
The measurement method and evaluation method for each characteristic are described below.
(1) Film thickness (μm)
The film thickness at 5 points in the range of 95 mm × 95 mm of the microporous membrane was measured with a contact thickness meter (Lightmatic manufactured by Mitutoyo Corporation), and the average value was obtained.

(2) Porosity (%)
The weight w _{1 of the} microporous membrane was compared with the weight w _{2 of the} polymer without pores equivalent to the weight (a polymer having the same width, length and composition), and the measurement was performed by the following equation.
Porosity (%) = (w ₂ −w ₁ ) / w ₂ × 100

(3) Puncture strength Measures the maximum load when a microporous membrane with a film thickness T1 (μm) is pierced at a speed of 2 mm / sec with a needle having a spherical surface (curvature radius R: 0.5 mm) and a diameter of 1 mm. did.

(4) Gurley value (air permeability resistance) (in terms of thickness 20 μm)
Air permeability resistance P ₁ (sec / sec) measured with an air permeability meter (Asahi Seiko Co., Ltd., EGO-1T) in accordance with JIS P-8117 with respect to a microporous film having a film thickness T1 (μm). 100 cm ³ ) was converted into the air resistance P ₂ when the film thickness was 20 μm by the formula: P ₂ = (P ₁ × 20) / T ₁ .

(5) Shutdown temperature The shutdown temperature was measured by the method disclosed in International Publication No. 2007/052663. According to this method, the microporous membrane is exposed to an atmosphere of 30 ° C., and the temperature is raised at 5 ° C./minute, during which the air permeability of the membrane is measured. The temperature at which the Gurley value (after air resistance) of the microporous membrane first exceeded 100,000 seconds / 100 cm ³ was defined as the shutdown temperature of the microporous membrane. The air permeability of the microporous film was measured in accordance with JIS P8117 using an air permeability meter (Asahi Seiko Co., Ltd., EGO-1T).

(6) Heat Shrinkage The test piece was heat treated at a temperature of 105 ° C. for 8 hours, the size of the test piece in each direction before the heat treatment (L ₁ ) and the size of the test piece in each direction after the heat treatment (L ₂ ) were measured, in each direction, when the _{L 1} is 100%, the shrinkage rate of the _{L 2} formula: was calculated by _{[100- (L 2 / L 1} ) × 100] (%).

(7) Maximum pore size and average flow pore size (nm)
Using a palm porometer (PFP, CFP-1500A), the maximum pore size and the average flow pore size were measured in the order of Dry-up and Wet-up. For the wet-up, pressure was applied to a microporous membrane sufficiently immersed in Galwick (trade name) manufactured by PMI with a known surface tension, and the pore diameter converted from the pressure at which air began to penetrate was defined as the maximum pore diameter.
As for the average flow pore size, the pore size was converted from the pressure at the point where the curve showing the 1/2 slope of the pressure and flow curve in the Dry-up measurement and the curve of the Wet-up measurement intersect. The following formula was used for conversion of pressure and pore diameter.
d = C · γ / P
In the above formula, “d (μm)” is the pore diameter of the microporous membrane, “γ (mN / m)” is the surface tension of the liquid, “P (Pa)” is the pressure, and “C” is a constant.

(8) Evaluation of film winding property When the film roll (500 mm wide) (microporous film) before being subjected to secondary processing is unwound at a tension of 30 N and wound again, it is in the form of a transport roll. The running condition of the film in the horizontal running section (length in the transport direction: 1 m) was visually evaluated according to the following criteria.
Good: Neither horizontal meandering nor vertical vibration was observed during film running in the horizontal running section.
Defect: At least one of horizontal meandering and vertical vibration was observed during film running in the horizontal running section.
(9) Evaluation of tear resistance The TD direction of the microporous membrane was made to coincide with the long axis of the test piece, an angled test piece was collected, and the tear strength was measured according to JIS K6252-1. The following indicators were used for evaluation.
◎: 300 kN / m or more ○: 200 kN / m or more, less than 300 kN / m ×: less than 200 kN / m

  The method for determining the draw ratio of the crystalline polymer microporous membrane of the present invention is excellent in the simplicity of the determination method and can be suitably used for the production of crystalline polymer microporous membranes for various applications. The method for producing a crystalline polymer microporous membrane of the present invention efficiently produces a crystalline polymer microporous membrane with excellent winding properties, improved yield during secondary processing, and excellent productivity. be able to. This makes it possible to produce crystalline polymer microporous membranes used in various fields that require secondary processing after film formation, such as filters such as filtration membranes and dialysis membranes, separators for batteries, and separators for electrolytic capacitors. Useful. In particular, it can be suitably used for the production of a secondary battery separator that requires a thin film.

  Further, another crystalline polymer microporous membrane production method of the present invention can efficiently produce a crystalline polymer microporous membrane excellent in tear strength. From this, it is useful for the production of crystalline polymer microporous membranes used in various fields where tear strength is required at the time of parts production, for example, microporous membranes for filters such as filtration membranes and dialysis membranes.

1 …… Test specimen for measurement of polarized Raman spectroscopy 2 …… Test specimen for measurement of polarized Raman spectroscopy 3

Claims (6)

  A gel-like sheet containing a crystalline polymer and a film-forming solvent is stretched and subjected to polarization Raman spectroscopy measurement, and the gel is calculated from the orientation distribution function calculated using the peak area intensity obtained by polarization Raman spectroscopy measurement. A method for determining the stretch ratio of a gel-like sheet comprising a crystalline polymer and a film-forming solvent, wherein the stretch ratio of the sheet-like sheet is determined.   2. The gel-like sheet comprising a crystalline polymer and a film-forming solvent according to claim 1, wherein the orientation distribution function is at least an orientation distribution function in a direction intersecting with the stretching direction in the film plane. A method for determining the draw ratio.   A step of stretching a gel-like sheet comprising a crystalline polymer and a film-forming solvent at a draw ratio at which the orientation distribution function in the drawing direction is 10.0 times or more of the orientation distribution function in the direction perpendicular to the drawing direction. A method for producing a crystalline polymer microporous membrane comprising   A step of stretching a gel-like sheet comprising a crystalline polymer and a film-forming solvent at a draw ratio at which the orientation distribution function in the drawing direction is less than 10.0 times the orientation distribution function in the direction perpendicular to the drawing direction. A method for producing a crystalline polymer microporous membrane comprising   A gel-like sheet comprising a crystalline polymer and a film-forming solvent is stretched at a stretching ratio such that the orientation distribution function in the stretching direction is 10.0 times or more of the orientation distribution function in the direction perpendicular to the stretching direction, Next, a method for producing a film roll, comprising winding a crystalline polymer microporous film formed by removing a film-forming solvent. A crystalline polymer microporous membrane having an average pore diameter measured using a porometer of 38 nm or less and a ratio of the maximum pore diameter measured using the porometer to the average pore diameter of 1.8 or less.