TW201736479A - Polyolefin microporous membrane and method for producing same, method for evaluating laminated polyolefin microporous membrane, roll, and polyolefin microporous membrane - Google Patents

Abstract

Provided is a polyolefin microporous membrane having excellent winding property and coatability. A polyolefin microporous membrane in which the ratio of the orientation parameter corresponding to the 45 DEG direction and the orientation parameter corresponding to the 135 DEG direction, obtained from values measured by Raman spectroscopy in a 45 DEG direction forming an angle of 45 DEG with respect to the lengthwise direction during film production in a plane parallel to the film surface and a 135 DEG direction forming an angle of 135 DEG in the same direction as the 45 DEG direction, is higher than 0.91 and lower than 1.10.

Description

Polyolefin microporous film and preparation method thereof, evaluation method of laminated polyolefin microporous film, roll and polyolefin microporous film

The present invention relates to a polyolefin microporous film, a method for preparing the same, a laminated polyolefin microporous film, a roll, and a method for evaluating a polyolefin microporous film.

The polyolefin microporous membrane is used in various fields such as a filter membrane, a filter such as a dialysis membrane, a separator for a battery, and a separator for a capacitor. Among them, the polyolefin microporous membrane is widely used as a separator for secondary batteries in recent years because it has excellent chemical resistance, insulating properties, mechanical strength, and the like, and has shutdown-down characteristics.

With the development of high energy density and miniaturization of secondary batteries, thin films have been required for separators for secondary batteries. When the roll of the film-formed polyolefin microporous film is taken up by the winding device, when the roll is prepared, problems such as wrinkles and winding deviation are likely to occur. Further, it is possible for the polyolefin microporous film to laminate other layers on at least one surface thereof. In the film-formed, wide-width polyolefin microporous film, when the other layers are applied, the coating property of the entire film surface is required to be uniform.

For example, Patent Document 1 describes a winding offset from a roll rewinding. A polyolefin microporous film winding with less conditions. Patent Document 1 discloses that when the positive and negative friction coefficient is 1.5 or less, the winding property of the microporous film wound is good at the time of rewinding. However, with the further thinning of the polyolefin microporous film, when the polyolefin microporous film is wound up or subjected to secondary processing, it is required to further improve the windability and the coating property.

On the other hand, there has been a report on a polyester film or a polypropylene resin film which is defined by the Raman spectroscopy, and a method for evaluating the film (for example, Patent Document 2 to Patent Document 5). However, the orientation parameters described in Patent Document 2 to Patent Document 5 measure only the orientation parameters in the longitudinal direction (MD direction) of the film surface, the width direction (TD direction) perpendicular to the longitudinal direction, or the film thickness direction. Other directions than others are not disclosed. Further, there is no description about the relationship between the orientation parameter corresponding to a specific direction and the windability and coatability in the polyolefin microporous film.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open Publication No. 2004-099799.

Patent Document 2: Japanese Laid-Open Patent Publication No. 2013-155223.

Patent Document 3: Japanese Laid-Open Patent Publication No. 2012-036286.

Patent Document 4: Japanese Patent Laid-Open Publication No. 2010-060516.

Patent Document 5: Japanese Patent Laid-Open Publication No. 2010-058455.

The present invention has been developed in view of the above problems, and has focused on the orientation parameters in a specific direction of the polyolefin microporous film, and based on this novel idea, provides a polyolefin microporous film excellent in windability and coatability.

The polyolefin microporous film according to the first aspect of the present invention is in the plane parallel to the surface of the film, and has a 45° direction at an angle of 45° with respect to the longitudinal direction of the film formation, and an orientation which is the same as the 45° direction. The 135° direction in which the length direction is an angle of 135° is measured by Raman spectroscopy, and the ratio of the orientation parameter corresponding to the 45° direction and the orientation parameter corresponding to the 135° direction obtained according to the measured value exceeds 0.91. And less than 1.10.

Further, the 0° direction, the 45° direction, the 90° direction, and the 135° direction which are the same toward the 0°, 45°, 90°, and 135° angles in the longitudinal direction correspond to the 0° direction, the 45° direction, and the 90° direction. In the orientation parameters of the ° direction and the 135° direction, the ratio of the maximum value to the minimum value (Rmin/Rmax) may be 0.9 or more and 1 or less. Further, with respect to the 0° direction, the 45° direction, the 90° direction, and the 135° direction which are the same in the longitudinal direction at 0°, 45°, 90°, and 135° in the longitudinal direction, the orientation parameter corresponding to the 45° direction and the corresponding The two values of the orientation parameter in the 135° direction may be 0.5 times or more and 0.95 times or less of the orientation parameter corresponding to the 0° direction and the smaller of the orientation parameter values corresponding to the 90° direction. Further, the orientation parameter corresponding to the 0° direction may be 3 or more and 6 or less, and the orientation parameter corresponding to the 90° direction may be 2 or more. 5 or less. Further, the orientation parameter corresponding to the 45° direction and the 135° direction may be 2 or more and 3.5 or less. Further, the polyolefin microporous film may contain high density polyethylene. Further, the film thickness of the polyolefin microporous film may be 1 μm or more and 20 μm or less.

The laminated polyolefin microporous film according to the second aspect of the present invention is obtained by laminating a porous layer on at least one surface of the polyolefin microporous film.

A roll according to a third aspect of the present invention comprises the above polyolefin microporous film.

A roll of a fourth aspect of the present invention comprises a roll of a polyolefin microporous film comprising a polyolefin microporous film as described below: in a surface of one surface of a polyolefin microporous film, for rolling out in a counterclockwise direction The direction of the 45° direction of the 45° angle and the 135° direction of the angle of 135° in the counterclockwise direction and the unwinding direction are measured by Raman spectroscopy, and the orientation parameter corresponding to the 45° direction obtained from the measured value is obtained. The ratio to the orientation parameter corresponding to the 135° direction exceeds 0.91 and is less than 1.10.

The method for producing a polyolefin microporous film according to a fifth aspect of the present invention comprises: in a plane parallel to the surface of the polyolefin microporous film, a 45° direction at an angle of 45° with respect to the longitudinal direction of the film formation, and an orientation and 45 The direction of 135° which is the same in the direction of the same direction and at an angle of 135° to the longitudinal direction of the film formation, is measured by Raman spectroscopy, and the orientation parameter corresponding to the direction of 45° obtained from the measured value and the direction corresponding to the direction of 135° The ratio of orientation parameters is controlled to exceed 0.9 And less than 1.1.

In addition, the method for preparing the polyolefin microporous film may further include: directions of 0°, 45°, 90°, and 135°, which are the same toward the longitudinal direction, respectively, corresponding to the 0° direction, the 45° direction, and 90°. In the orientation parameters of the ° direction and the 135° direction, the ratio of the maximum value to the minimum value (Rmin/Rmax) is controlled within a range of 0.9 or more and 1 or less. In addition, the orientation parameters corresponding to the 45° direction and the orientation parameters corresponding to the 135° direction may be included with respect to directions that are the same, respectively, at angles of 0°, 45°, 90°, and 135° with the length direction. Each of them is controlled within a range of 0.5 times or more and 0.95 times or less of the orientation parameter corresponding to the 0° direction and the orientation parameter corresponding to any of the orientation parameters of the 90° direction.

In the method for evaluating a polyolefin microporous film according to the sixth aspect of the present invention, the longitudinal direction of the film formation is set to a 0° direction, and the direction orthogonal to the longitudinal direction is set to a 90° direction, and the Raman spectroscopy is calculated. The ratio of the measured orientation parameter in the 45° direction to the orientation parameter in the 135° direction.

Further, the evaluation method of the polyolefin microporous film can be judged whether the ratio of the orientation parameter in the 45° direction to the orientation parameter in the 135° direction is more than 0.9 and less than 1.1. Further, the above ratio can be used to evaluate the coilability or coatability.

The polyolefin microporous film of the present invention is excellent in windability and coatability. Further, the preparation method can efficiently produce a polyolefin microporous film excellent in windability and coatability. Further, the evaluation method of the polyolefin microporous film can easily evaluate the windability and coatability of the polyolefin microporous film before secondary processing.

1‧‧‧Polyolefin microporous membrane (microporous membrane)

Fig. 1 is a view showing an example of each direction in the in-plane direction of the polyolefin microporous film.

Fig. 2 is a view showing an example of an orientation parameter distribution pattern in the in-plane direction of the polyolefin microporous film.

Fig. 3 is a flow chart showing an example of a method for evaluating a polyolefin microporous film.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Hereinafter, the direction in the drawing will be described using an XYZ coordinate system. In the XYZ coordinate system, a surface parallel to the surface (in-plane direction) of the microporous film is referred to as an XY plane. Further, the direction (thickness direction) perpendicular to the XY plane is set to the Z direction. The directions indicated by the arrows in the figure are the + direction, and the opposite directions of the arrow directions are the - directions, and the X direction, the Y direction, and the Z direction are described. In addition, in order to facilitate understanding of each configuration, a part of the drawings may be highlighted or partially omitted, and may be different from the actual structure, shape, reduction ratio, and the like.

FIG. 1 is a view showing a polyolefin microporous membrane 1 (hereinafter also referred to as "microporous membrane 1") according to the present embodiment. As shown in FIG. 1, the direction in the XY plane (in-plane direction) of the microporous film 1 is set to the 0° direction (machine direction: MD direction). Further, a direction at an angle of 45° with respect to the 0° direction is set to a 45° direction, and a direction that is the same as the 45° direction and an angle of 90° with the 0° direction is set to a 90° direction (width direction: TD direction). The direction at an angle of 135° to the 0° direction is set to the 135° direction. In addition, each direction in FIG. 1 is a counterclockwise rotation direction from the 0° direction, and may be a clockwise rotation direction.

The ratio of the orientation parameter (R45°) corresponding to the 45° direction of the microporous membrane 1 to the orientation parameter (R135°) corresponding to the 135° direction (R135°/R45°) exceeds 0.91 and is less than 1.10. R135°/R45°. It is preferably 0.92 or more and 1.09 or less, more preferably 0.94 or more and 1.06 or less. When R135°/R45° is in the above range, the windability and coatability of the microporous film 1 can be further improved. In addition, as described later, the orientation parameter can be brought to the above range by appropriately adjusting the composition of the microporous membrane 1 or the stretching ratio at the time of film formation. Further, the values of R45° and R135° are not particularly limited, and may be, for example, about 1.7 or less.

In the microporous membrane 1, the difference (|R135°-R45°|) of the orientation parameter (R45°) corresponding to the 45° direction and the orientation parameter (R135°) corresponding to the 135° direction is not particularly limited, for example, Less than 0.5, preferably less than 0.3, More preferably less than 0.2. When the difference between R45° and R135° is small, the take-up property and coatability of the microporous film 1 are further improved.

The orientation parameter can be calculated from the peak intensity ratio (I1130/I1060) of 1130 cm ^-1 and 1060 cm ^-1 as determined by polarized Raman spectroscopy. The peaks of 1130 cm ^-1 and 1060 cm ^-1 are derived from the symmetric vibration mode and the antisymmetric vibration mode of the CC telescopic band, respectively, and exhibit strong anisotropy for the polarization angle. The peak intensity ratio (I1130/I1060) is a parameter related to the degree of molecular chain orientation in the incident polarization direction. In addition, there is no orientation when the orientation parameter is 1.7, and molecular orientation is being performed when it is higher than 1.7.

For example, using a Raman microscope, the peak intensity ratio of 1130 cm ^-1 to 1060 cm ^-1 is calculated from the Raman spectrum in a polarized configuration corresponding to the 0° direction, the 45° direction, and the 135° direction (I1130/I1060). ), so that orientation parameters can be obtained. The measurement conditions are shown below.

(device)

. The measurement apparatus used was a micro Raman spectroscopy system inVia (manufactured by Renishaw Co., Ltd.).

. 180° backscatter configuration

. Spectral length 250mm

. Diffraction grating 3000 strips/mm

. Excitation wavelength 532nm (semiconductor laser 2 times wave)

. 50x objective lens (N.A.=0.75)

. Spot size (spatial resolution) 5μm

(polarized condition)

The laser is incident perpendicularly from the normal direction of the film surface (XY plane), and is polarized using a polarizer. The incident light is arranged in parallel with the polarized light polarizer. Further, the sample was rotated on the incident polarizing surface to obtain a Raman spectrum in each direction.

(calculation of peak intensity)

1020cm ^-1 to the above, in the region of 1160 cm ^-1, a baseline is obtained by linear approximation, and by the Gaussian, Lorentzian mixed function approximation, for PeakFit process, were calculated for each peak intensity.

FIG. 2 is a conceptual diagram showing an example of a distribution pattern of orientation parameters of the microporous membrane 1 in each direction. The microporous membrane 1 has, for example, an orientation parameter distribution pattern shown in (A) to (D) of Fig. 2 .

(A) of Fig. 2 shows an example of a distribution pattern (circle) in which the orientation parameter values of the respective directions are relatively uniformly distributed. In this case, for example, the ratio of the maximum value to the minimum value (Rmin/Rmax) of the orientation parameters corresponding to the 0°, 45°, 90°, and 135° directions may be 0.9 or more and 1 or less. Further, the lower limit of Rmin/Rmax is preferably 0.92 or more, more preferably 0.95 or more. The upper limit of Rmin/Rmax is 1.0 or less. When Rmin/Rmax is in the above range, the uniformity of the degree of molecular orientation of the microporous film 1 in each direction is improved, and the windability and coatability are improved. In addition, the uniformity of the heat shrinkage rate of the parties will also increase.

When the circular distribution pattern is provided, the lower limit of the orientation parameter of the microporous membrane 1 corresponding to each of 0°, 45°, 90°, and 135° is, for example, 2.5 or more. Further, the upper limit of the orientation parameter corresponding to each direction is, for example, 4 or less. If the orientation parameter is within the above range, a microporous membrane 1 excellent in more uniform mechanical strength can be obtained.

Fig. 2(B) shows an example of a distribution pattern (elliptical shape) as follows: the orientation parameter values corresponding to the 0° direction and the 90° direction are relatively different, and correspond to the 45° direction and the 135° direction. Each orientation parameter value is an approximation of the median value of the orientation parameter values in the 0° direction and the 90° direction (but not exceeding the median value). In this case, the ratio of the orientation parameter corresponding to the 0° direction to the orientation parameter corresponding to the 90° direction is, for example, less than 0.9 or more than 1.1. Further, for example, the orientation parameter corresponding to the 45° direction and the 135° direction exceeds 0.95 times of any of the orientation parameters corresponding to the 0° direction and the 90° direction.

2(C) and 2(D) show an example of a distribution pattern (cross type) as follows, that is, the orientation parameter values corresponding to the 45° direction and the 135° direction are smaller than the corresponding 0° direction. And any smaller value of the orientation parameter in the 90° direction. In this case, the upper limit of the orientation parameter value corresponding to the 45° direction and the 135° direction is, for example, 0.95 times or less, preferably 0.9 times or less, of any smaller one of the orientation parameters corresponding to the 0° direction and the 90° direction. More preferably, it is 0.85 times or less, and particularly preferably a value of 0.8 times or less. In this case, the lower limit of the orientation parameter corresponding to the 45° direction and the 135° direction is not particularly limited, for example, It is 0.5 times or more of any smaller value of the orientation parameters corresponding to the 0° direction and the 90° direction.

In addition, (C) of FIG. 2 indicates that the orientation parameter (R0°) corresponding to the 0° direction is substantially the same as the orientation parameter (R90°) corresponding to the 90° direction (for example, R90°/R0° is An example of 0.8 or more and 1.25 or less), (D) of FIG. 2 indicates a distribution pattern in which the orientation parameter value corresponding to the 0° direction is larger than the orientation parameter value corresponding to the 90° direction (for example, R90°/R0°). Example less than 0.8). Further, the microporous film 1 may have a distribution pattern in which the orientation parameter value corresponding to the 0° direction is smaller than the orientation parameter value corresponding to the 90° direction (for example, R90°/R0° exceeds 1.25).

When the cross-type distribution pattern is provided, the lower limit of the orientation parameter of the microporous film 1 corresponding to the 0° direction is, for example, 3 or more, preferably 4 or more. Further, the upper limit of the orientation parameter corresponding to the 0° direction is 6 or less, preferably 5 or less. Further, the lower limit of the orientation parameter corresponding to the 90° direction is, for example, 2 or more, preferably 2.5 or more. Further, the upper limit of the orientation parameter in the 90° direction is, for example, 5 or less, preferably 4 or less. If the orientation parameter is within the above range, a microporous membrane 1 excellent in more uniform mechanical strength can be obtained.

When the cross-type distribution pattern is provided, the lower limit of the orientation parameter of the microporous film 1 corresponding to the 45° direction and the 135° direction is, for example, more than 1.7, preferably 2.0 or more. The upper limit of the orientation parameter of the microporous membrane 1 corresponding to the 45° direction and the 135° direction is, for example, 3.5 or less, preferably 3.1 or less. Directional parameter When the number is within the above range, the microporous film 1 having more uniform mechanical strength can be obtained.

Further, if the orientation parameter ratio (R135°/R45°) corresponding to the 45° direction and the 135° direction is within the above range, the microporous membrane 1 may have other than those shown in FIGS. 2(A) to (D). Distribution pattern. For example, the values of the orientation parameters of the microporous membrane 1 corresponding to the 45° direction and the 135° direction may be greater than the orientation parameter values of the 0° direction and the 90° direction. In addition, (B) of FIG. 2 shows an example in which the orientation parameter value corresponding to the 90° direction is larger than the orientation parameter value corresponding to the 0° direction, but conversely, the orientation parameter value corresponding to the 90° direction may also be smaller than the corresponding Orientation parameter value in the 0° direction.

The microporous film 1 uses a polyolefin resin as a resin component. The polyolefin resin may contain, for example, polyethylene, polypropylene, or the like. The polyethylene may be an ethylene homopolymer or a copolymer of ethylene and other alpha-olefins. Examples of the α-olefin include propylene, butene-1, hexene-1, pentene-1, 4-methylpentene-1, octene, vinyl acetate, methyl methacrylate, and styrene.

The type of the polyethylene is not particularly limited, and various polyethylenes can be used. For example, high density polyethylene (HDPE), medium density polyethylene, branched low density polyethylene, linear low density polyethylene, or the like can be used. When the polyethylene-based resin contains, for example, high-density polyethylene (density: 0.920 g/m ³ or more, 0.970 g/m ³ or less), the puncture strength is further improved. The weight-average molecular weight (Mw) of the polyethylene is, for example, 1 × 10 ⁴ or more and less than about 1 × 10 ⁶ .

For example, the content of the high-density polyethylene is 50% by mass or more based on 100% by mass of the entire polyolefin resin component. For example, when the high-density polyethylene is contained in an amount of 90% by mass or more, there is a tendency that the orientation parameter of the microporous film 1 is easily controlled to the above-described circular distribution pattern. The upper limit of the content of the high-density polyethylene is, for example, 100% by mass or less, and when other components are contained, it is, for example, 90% by mass or less. When the polyolefin resin contains high-density polyethylene, it has excellent melt-extrusion characteristics and is excellent in uniform stretch processing properties.

Further, the polyethylene may comprise ultra high molecular weight polyethylene (UHMwPE). The weight average molecular weight (Mw) of the ultrahigh molecular weight polyethylene is 1 × 10 ⁶ or more, preferably 1 × 10 ⁶ or more and 8 × 10 ⁶ or less. When Mw is in the above range, moldability is good. Further, Mw is a value measured by gel permeation chromatography (GPC). The ultrahigh molecular weight polyethylene may be used singly or in combination of two or more kinds, or two or more types of ultrahigh molecular weight polyethylenes having different Mw may be used.

The content of the ultrahigh molecular weight polyethylene may be, for example, more than 0% by mass and 60% by mass or less based on 100% by mass of the entire polyolefin resin. For example, when the content of the ultrahigh molecular weight polyethylene is 10% by mass or more and 40% by mass or less, the orientation parameter of the microporous membrane 1 is easily controlled to the above-described cross-type distribution pattern, and the production efficiency such as extrusion kneading property is excellent. . When the polyolefin resin contains ultra high molecular weight polyethylene, When the microporous film 1 is formed into a film, high mechanical strength and high porosity can be obtained.

The type of the polypropylene is not particularly limited, and may be any of a propylene homopolymer, a copolymer of propylene and another α-olefin and/or a diene (propylene copolymer), or a mixture thereof, but mechanical strength and From the viewpoint of miniaturization of the diameter of the through hole, etc., it is preferred to use a propylene homopolymer. The content of the polypropylene in the polyolefin resin component is, for example, 2.5 mass% or more and 15 mass% or less. When the content of the polypropylene is within the above range, heat resistance is improved.

Further, the polyolefin resin component may contain other resin components other than polyethylene or polypropylene as needed. As another resin component, a heat resistant resin etc. can be used, for example. In addition, the microporous membrane 1 may also contain an antioxidant, a heat stabilizer, an antistatic agent, an ultraviolet absorber, an anti-caking agent and a filler, a nucleating agent, a crystallization retardant, within a range not impairing the efficacy of the present invention. And other additives.

The film thickness of the microporous membrane 1 is not particularly limited, and is, for example, 30 μm or less. The lower limit of the film thickness is preferably 1 μm or more, more preferably 2 μm or more, and particularly preferably 3 μm or more. When used as a separator for a secondary battery, the film thickness of the microporous membrane 1 is preferably 20 μm or less, more preferably 15 μm or less. When the film thickness is within the above range, when the microporous film 1 is used as a battery separator, the battery capacity is improved. When the microporous film 1 is formed into a film, it also has good windability and coating properties.

The porosity of the microporous membrane 1 is not particularly limited and is, for example, 10% or more. When used as a separator for a secondary battery, the lower limit of the porosity of the microporous membrane 1 is preferably 20% or more, more preferably 25% or more, and particularly preferably 30% or more. When the lower limit of the porosity is within the above range, the amount of the electrolytic solution can be increased to ensure high ion permeability. The upper limit of the porosity is not particularly limited, and is, for example, about 70% or less. The porosity can be made into the above range by adjusting the compatibility of the constituent components of the polyolefin resin, the stretching ratio of the stretching process, and the like.

Further, the weight w _{1 of the} microporous membrane and the weight w ₂ (polymer having the same width, length, and composition) of the void-free polymer equivalent thereto are compared, and can be determined according to the following formula (1). Empty porosity.

Porosity (%) = (w ₂ - w ₁ ) / w ₂ × 100‧‧‧(1)

The gas permeability value (Gurley value; also referred to as "Gurley value") of the microporous membrane 1 is not particularly limited. For example, the lower limit of the gas permeability value (gas resistance) in terms of a film thickness of 20 μm is 100 sec/100 cm ³ or more. When used as a separator for a secondary battery, the gas permeability of the microporous membrane 1 is preferably 200 sec/100 cm ³ or more, more preferably 250 sec/100 cm ³ or more. Further, the upper limit of the air permeability is 1000 sec/100 cm ³ or less. When the gas permeability is within the above range, when used as a battery separator, ion permeability is excellent, impedance is lowered, and battery output is improved. The air permeability value can reach the above range by adjusting the gel-like sheet, the stretching conditions of the microporous film after drying, and the like.

For the microporous film having a film thickness T ₁ (μm), the gas permeability value P ₁ (sec/100 cc) was measured with a gas permeability meter (EGO-1T, manufactured by Asahi Seiko Co., Ltd.) in accordance with JIS P-8117, and then according to the formula: P ₂ = (P ₁ × 20) / T ₁ , and the gas permeability value P _{1 is} converted into a gas permeability value P ₂ at a film thickness of 20 μm, and the obtained value (sec/100 cc / 20 μm) is a gas permeability value.

The lower limit of the puncture strength after conversion of the microporous film 1 to a film thickness of 20 μm is, for example, 250 gf/20 μm or more, preferably 280 gf/20 μm or more, more preferably 300 gf/20 μm, and particularly preferably 320 gf/20 μm or more. The upper limit of the puncture strength is not particularly limited and is about 1500 gf/20 μm. When the puncture strength is within the above range, the film strength is excellent in mechanical strength, and when used as a battery separator, it is possible to prevent film breakage and short circuit due to impact, and it is excellent in safety. The puncture strength can be controlled to the above range by adjusting the polypropylene content in the polyolefin resin, the ultrahigh molecular weight polyethylene content, the stretching ratio of the stretching process, and the like.

Department puncture strength according to the _{formula: L 2 = (L 1 ×} 20) / T 1, the measured maximum load value L ₁ (gf) value in terms of the maximum load L ₂ when the film thickness of 20μm. The measured value L ₁ (gf) of the maximum load is a microporous film having a thickness T ₁ (μm) at a speed of 2 mm/sec using a needle having a spherical surface (curvature radius R: 0.5 mm) and a diameter of 1 mm. Maximum load measurement value.

The heat shrinkage rate at 105 ° C in each direction of the microporous film 1 is, for example, about 0.1% or more and 10% or less. If the heat shrinkage rate is within the above range, it is expected to improve the heat resistance and durability of the product using the microporous film and prolong the service life of the product. The test piece (microporous film 1) was heat-treated at a temperature of 105 ° C for 8 hours, and the test piece size (L ₁ ) in each direction before the heat treatment and the size (L ₂ ) in each direction of the test piece after the heat treatment were measured, according to the formula: [100 - (L ₂ / L ₁ ) × 100] (%) The shrinkage ratio of L ₂ when each direction L ₁ is 100% is calculated, and the obtained value is the 105 ° C heat shrinkage ratio of the microporous film 1.

The method for producing the microporous membrane 1 of the present embodiment includes, in a plane parallel to the surface of the microporous membrane, a 45° direction at an angle of 45° with respect to the longitudinal direction of the film formation, and a direction similar to the 45° direction, and The longitudinal direction of the film formation is 135° in an angle of 135°, and is measured by Raman spectroscopy, and the orientation parameter corresponding to the 45° direction obtained from the measured value and the orientation parameter corresponding to the 135° direction are used. The ratio is controlled to be in the range of more than 0.91 and less than 1.10. In the well-known film forming method, the composition of the polyolefin resin, the stretching ratio in the MD direction and the TD direction, and the stretching conditions (magnification, temperature, and tension) in the MD direction and the TD direction during heat setting can be appropriately adjusted. The parameters reach the above range.

The method for preparing the microporous membrane 1 includes: when the orientation parameter is set to the circular distribution pattern, for example, the orientation parameter corresponding to the 0° direction, the 45° direction, the 90° direction, and the 135° direction, the maximum value The ratio of the minimum value to the minimum value (Rmin/Rmax) is controlled to be in the range of 0.9 or more and 1 or less.

The method for preparing the microporous membrane 1 includes: when the orientation parameter is set to the circular distribution pattern, for example, the orientation parameters corresponding to the 45° direction and the 135° direction are controlled to the orientation parameters corresponding to the 0° direction and the 90° direction. Any of the smaller value orientation parameters is in the range of 0.5 times or more and 0.95 times or less.

The method for producing the microporous membrane 1 is not particularly limited as long as a microporous membrane having the above characteristics can be obtained, and a known method for preparing a polyolefin microporous membrane can be used. Examples of the method for producing the microporous membrane 1 include a dry film forming method and a wet film forming method. The dry film forming method is, for example, a method of melting and extruding a polyolefin resin to form a sheet, and stretching it during cooling to form fine pores starting from spherulites, thereby obtaining a microporous film. The wet film forming method is, for example, a method in which a polyolefin solution obtained by melt-kneading a polyolefin resin and a film-forming solvent is melted and extruded to form a sheet, and then a polymer microphase separation and a film forming solvent are used in the cooling process. The micropores are formed by extraction to form microporous membranes. As a method of preparing the microporous membrane 1, from the viewpoint of easiness of membrane structure and physical property control, a wet membrane forming method is preferred.

The wet film forming method can be, for example, a method described in Japanese Patent No. 2132327, Japanese Patent No. 3347835, and International Publication No. 2006/137540. The wet film forming method may include, for example, the following processes (1) to (5), and may further include the following processes (6) to (8).

(1) A process for preparing a polyolefin solution by melt-kneading a polyolefin resin and a solvent for film formation.

(2) A process in which a polyolefin solution is melted and extruded to form a sheet and then cooled to form a gel-like sheet.

(3) A first stretching process for stretching a gel-like sheet.

(4) A process for removing the solvent for film formation from the gel-like sheet after stretching.

(5) A process for drying a sheet obtained by removing a solvent for film formation.

(6) A second stretching process of stretching the dried sheet.

(7) A process for heat-treating the dried sheet.

(8) A process of crosslinking treatment and/or hydrophilization treatment of the sheet after the stretching process.

The stretching method in the above stretching process may be uniaxial stretching or biaxial stretching. When biaxial stretching is used, it is easier to adjust the orientation parameter to the above range. When biaxial stretching is employed, it may be any of simultaneous biaxial stretching, sequential stretching, and multi-stage stretching (for example, a combination of simultaneous biaxial stretching and sequential stretching). For example, when simultaneous biaxial stretching is employed, there is a tendency to easily control the orientation parameter of the microporous membrane 1 to the above circular distribution pattern.

For example, when uniaxial stretching is employed, the final stretching ratio (area stretching ratio) is preferably 2 times or more, more preferably 3 times to 30 times. When biaxial stretching is employed, it is preferably 16 times or more, more preferably 49 times or more. Further, it is preferred to stretch at least three times in either of the longitudinal direction and the width direction (MD and TD directions). In addition, the stretching ratios in the MD direction and the TD direction may be the same or different from each other. The draw ratio of the first process and/or the second process can be appropriately adjusted according to the composition of the resin material to ensure The orientation parameters in each direction reach the above range.

Further, the microporous membrane 1 may be a single layer or a plurality of layers of a polyolefin microporous membrane in which a layer containing at least two polyolefin microporous membranes is laminated. The plurality of layers of the polyolefin microporous film can be formed into two or more layers. In the case of a plurality of layers of the polyolefin microporous film, the composition of the polyolefin resin constituting each layer may be the same or a different composition. Further, when the microporous membrane 1 is a multilayered polyolefin microporous membrane having two or more layers of a polyolefin resin as a resin component, as in the case of a single layer, the coiling property can be obtained by making the orientation parameter reach the above specific range. And a microporous film excellent in coatability.

For example, the stretched microporous film 1 is wound around the core material to form the roll of the present embodiment. The roller may be, for example, a raw material roll before secondary processing, or a roll cut into a predetermined width (also referred to as a "reel" or a "cutting reel"). Since the microporous film 1 is excellent in the coiling property, for example, a film having a relatively large area, for example, a length of 1000 mm and a width of about 500 mm, a roll can be formed, and horizontal ridges, up and down vibrations, and the like are not observed. The microporous film 1 wound up as a roll can be unwound from the roll and processed by cutting or surface coating. Since the microporous membrane 1 is excellent in the windability and the coating property, the production efficiency at the time of processing is extremely excellent.

The roller is, for example, a roller having the microporous membrane 1. The microporous film 1 constituting the roller is formed in a plane of a certain surface in a 45° direction at an angle of 45° in the counterclockwise direction with the unwinding direction, and in a counterclockwise direction and a winding direction. 135° angle of 135°, measured by Raman spectroscopy, the ratio of the orientation parameter (R45°) corresponding to the 45° direction and the orientation parameter (R135°) corresponding to the 135° direction obtained from the measured value ( R135°/R45°) is more than 0.91 and less than 1.10, preferably 0.92 or more and 1.09 or less, more preferably 0.94 or more and 1.06 or less. In addition, the roll provided with the microporous film 1 may be a roll formed by including a core material and a microporous film 1 and the microporous film 1 is wound around the core material, and may have a core material and a laminated polymer as will be described later. An olefin microporous film in which a laminated polyolefin microporous film is wound around a core material, and the laminated polyolefin microporous film is laminated on at least any surface of the microporous film 1 to form a porous layer other than the microporous film 1 Made of layers.

Further, the microporous film 1 can be laminated on another porous layer other than the polyolefin resin to form a laminated polyolefin porous film. The laminated polyolefin porous film is formed by laminating a porous layer other than the microporous membrane 1 on at least one surface of the microporous membrane 1. The other porous layer is not particularly limited, and for example, an inorganic particle layer containing a binder and inorganic particles may be laminated. The binder component constituting the inorganic particle layer is not particularly limited, and a known component can be used. For example, an acrylic resin, a polyvinylidene fluoride resin, a polyamidoximine resin, a polyamide resin, or an aromatic compound can be used. Polyamide resin, polyimine resin, and the like. The inorganic particles constituting the inorganic particle layer are not particularly limited, and a known material can be used. For example, alumina, boehmite, barium sulfate, magnesium oxide, magnesium hydroxide, magnesium carbonate, barium or the like can be used. Further, as the laminated polyolefin porous film, at least the porous binder resin may be laminated on the polyolefin porous film. A surface builder.

3 is a flow chart showing an example of a method for evaluating a polyolefin microporous film of the present embodiment. This evaluation method is first in the plane parallel to the surface of the film, in the 45° direction at an angle of 45° with respect to the longitudinal direction (MD direction) at the time of film formation, and in the same direction as the 45° direction, and in the longitudinal direction at the time of film formation. In the 135° direction of the 135° angle, the orientation parameter (R45°) corresponding to the 45° direction and the orientation parameter (R135°) corresponding to the 135° direction are determined by Raman spectroscopy, and the ratio between the two is calculated (R135°/ R45°) (step S1). The measurement method and measurement conditions of the orientation parameters are as described above. Then, it is judged whether or not the ratio of the orientation parameter (R135°/R45°) exceeds 0.91 and is less than 1.10 (step S2). The ratio (R135°/R45°) is preferably 0.92 or more and 1.09 or less, more preferably 0.94 or more and 1.06 or less.

If the ratio of the orientation parameters (R135°/R45°) is within the above range, for example, it can be judged that the coiling property is good. On the other hand, if the orientation parameter ratio (R135°/R45°) is outside the above range, for example, it is possible to judge that the take-up property is poor.

If the ratio of the orientation parameters (R135°/R45°) is within the above range, for example, it can be judged that the coatability is good. On the other hand, if the orientation parameter ratio (R135°/R45°) is outside the above range, for example, it is possible to judge that the coatability is poor.

The evaluation method calculates the orientation parameters in the 45° direction and the 135° direction in the plane, and judges, so that it is not necessary to actually perform, for example, winding and coating. The windability and/or coatability of the polyolefin microporous film was evaluated. Further, when performing the evaluation, the orientation parameters corresponding to the 45° direction and the 135° direction and the orientation parameters corresponding to the 0° direction (MD direction) and the 90° direction (TD direction) are calculated, and it is determined whether the distribution pattern of the orientation parameter is Any one of the above-described circular, elliptical or cross-shaped distribution patterns can be used to evaluate the polyolefin microporous film.

Further, other embodiments of the method for producing a polyolefin microporous film may include the following process: the polyolefin microporous film obtained after film formation is evaluated by the evaluation method of the above polyolefin microporous film, and the selection evaluation result is judged to be good. Microporous membrane. In the method for producing a polyolefin microporous film, by using the above-described evaluation method, a microporous film having excellent windability and coatability can be selected before being wound up on a core material or before secondary processing.

Example

The invention is further illustrated by the following examples, but the invention is not limited to the examples.

1. Determination method and evaluation method

(1) Film thickness (μm)

The film thickness of the microporous film in the range of 95 mm × 95 mm was measured by a contact thickness meter (Lite Matic manufactured by Mitutoyo Co., Ltd.), and the average value was calculated.

(2) porosity (%)

The weight w _{1 of the} microporous membrane and the weight w ₂ (polymer of the same width, length, and composition) of the nonporous polymer equivalent thereto were compared and measured according to the following formula.

Porosity (%) = (w ₂ - w ₁ ) / w ₂ × 100

(3) Air permeability value (air resistance) (sec/100cm ³ /20μm)

For the microporous film having a film thickness T ₁ (μm), the gas permeability value P ₁ (sec/100 cm ³ ) was measured by a gas permeability meter (EGO-1T, manufactured by Asahi Seiko Co., Ltd.) in accordance with JIS P-8117, and then according to the formula. : P ₂ = (P ₁ × 20) / T ₁ , and the gas permeability value P _{1 is} converted into a gas permeability value P ₂ at a film thickness of 20 μm.

(4) Puncture strength

The maximum load when the microporous membrane having a thickness T ₁ (μm) was pierced at a speed of 2 mm/sec by a needle having a spherical surface (curvature radius R: 0.5 mm) and a diameter of 1 mm at the distal end of the measurement. According to the formula: L ₂ = (L ₁ × 20) / T ₁ , the measured value L ₁ (gf) of the maximum load is converted into the maximum load L ₂ at a film thickness of 20 μm, and is set as the puncture strength.

(5) 105 ° C heat shrinkage rate

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

(6) Evaluation of take-up

The film (microporous film) having a take-up width of 500 mm and the raw material roll before the secondary processing were wound up under a tension of 30 N, and when re-rolling, the film was confirmed by visual inspection. The film was conveyed in a traveling state of a conveyance-shaped horizontal traveling section (length in the conveying direction: 1 m), and evaluated based on the following criteria.

Good: Nothing in the horizontal direction and in the up and down direction were observed when the film traveled in the horizontal travel section.

Poor: At least one of the horizontal direction and the up-and-down vibration is observed when the film travels in the horizontal traveling section.

(7) Evaluation of coating properties

A ceramic powder slurry was coated on one surface of a microporous film having a take-up tension of 30 N and a width of 500 mm by a gravure coater and dried to obtain a ceramic layer having a coating film thickness of 3 μm (reference value). Microporous membrane. The entire film thickness (coating layer + material thickness) including the coating layer of the obtained laminated microporous film was measured by a distance of 50 mm in the TD direction, and the thickness of the raw material was subtracted, and the coating thickness of each measurement site was calculated. When the film thickness of 3 μm was 100%, the film thickness L ₃ variation range (100×L ₃ (μm)/3 (μm)) (%) of each measurement site was calculated, and the coatability was evaluated according to the following criteria.

Good: The film thickness variation range is -3% or more and +3% or less with respect to the reference value, and the coating film thickness is uniform.

Poor: The film thickness variation range is less than -3% and more than +3% with respect to the reference value, and the coating film thickness fluctuates.

(Preparation of coating liquid)

60.8 parts by mass of a solvent was added to 0.8 parts by mass of CMC (carboxymethylcellulose: Daicel FineChem Co., Ltd., product number 2200), and the mixture was stirred for 2 hours. Then, 38.4 parts by mass of spherical alumina fine particles having an average particle diameter of 0.5 μm were added, and the mixture was stirred for 2 hours to sufficiently disperse the alumina fine particles, and then made of FELT-type polypropylene having a filter particle size (initial filtration efficiency: 95%) of 10 μm. The filter is precisely filtered to prepare a coating liquid. At this time, the volume ratio of the resin component to the fine particles was 5:95. (calculated according to the specific gravity of CMC being 1.6 g/cm ³ and the specific gravity of alumina being 4.0 g/cm ³ ).

(Examples 1 to 4)

According to the composition shown in Table 1, the polyolefin resin and the liquid paraffin were melt-kneaded by a biaxial extruder to prepare a polyolefin solution. The polyolefin solution was supplied from a biaxial extruder to a T die and extruded. The extruded molded body was pulled and cooled by a cooling roll to form a gel-like sheet. The gel-like sheet is simultaneously biaxially stretched or sequentially biaxially stretched (first stretched) by 5 times or more and 9 times in the MD direction and the TD direction by a tenter stretching machine at 110 ° C to 125 ° C. the following. The stretched gel-like sheet was fixed in a 20 cm × 20 cm aluminum frame plate, immersed in a dichloromethane bath adjusted to a temperature of 25 ° C, and shaken at 100 rpm for 3 minutes while removing the liquid paraffin and air-dried at room temperature. A dry film was obtained. The dried film was stretched by 1.0 times or more and 1.8 times or less (second stretch) in the TD direction at 126 ° C using a batch stretching machine. Next, the film was heat-set at 126 ° C by a tenter method. The compatibility ratio, preparation conditions, evaluation results, and the like of each component of the produced polyolefin microporous membrane are described in Table 1. In addition, in Table 1, HDPE means high density polyethylene, and UHMwPE means ultra high molecular weight polyethylene.

(Comparative Example 1 and Comparative Example 2)

As a comparative example, the preparation conditions, evaluation results, and the like of two kinds of commercially available products (Comparative Example 1 and Comparative Example 2) containing a microporous film using a polyethylene resin are shown in Table 1.

[Industrial availability]

Since the polyolefin microporous film of the present invention is excellent in windability and coating property, the yield at the time of secondary processing is improved, and the production efficiency is excellent. Therefore, it is suitable for polyolefin microporous membranes used in various fields in which secondary processing is required after film formation, for example, a filter such as a filtration membrane or a dialysis membrane, a separator for a battery, and a separator for an electrolytic capacitor. Among them, it is suitably used as a separator for a secondary battery which is required to be thinned. Further, the evaluation method of the polyolefin microporous film of the present invention can evaluate the coilability and coatability before secondary processing.

Further, the technical scope of the present invention is not limited to the embodiments described in the above embodiments and the like. One or more of the requirements described in the above embodiments and the like may be omitted. Further, the elements described in the above embodiments and the like may be combined as appropriate. Further, as long as the law permits, the disclosure of all the documents cited in the above embodiments and the like can be referred to as a part of this document. In addition, as long as the law permits, the contents of Japanese Patent Application No. 2015-256942 can be cited as a part of this document.

1‧‧‧Polyolefin microporous membrane (microporous membrane)

Claims (16)

A polyolefin microporous film having a 45° direction at an angle of 45° with respect to a longitudinal direction at the time of film formation and an orientation of the same as the 45° direction and an angle of 135° with the longitudinal direction in a plane parallel to the surface of the film. The 135° direction was measured by Raman spectroscopy, and the ratio of the orientation parameter corresponding to the aforementioned 45° direction and the orientation parameter corresponding to the aforementioned 135° direction obtained based on the measured value exceeded 0.91 and was less than 1.10. The polyolefin microporous film according to claim 1, wherein the 0° direction, the 45° direction, the 90° direction, and the 135° are the same as the angles of 0°, 45°, 90°, and 135° with respect to the longitudinal direction. The direction, the ratio of the maximum value to the minimum value (Rmin/Rmax) in the orientation parameters corresponding to the 0° direction, the 45° direction, the 90° direction, and the 135° direction is 0.9 or more and 1 or less. The polyolefin microporous film according to claim 1, wherein the 0° direction, the 45° direction, the 90° direction, and the 135° are the same as the angles of 0°, 45°, 90°, and 135° with respect to the longitudinal direction. The direction, the orientation parameter corresponding to the aforementioned 45° direction and the orientation parameter corresponding to the aforementioned 135° direction are both the orientation parameter corresponding to the aforementioned 0° direction and the orientation parameter value corresponding to the aforementioned 90° direction. The smaller value is 0.5 times or more and 0.95 times or less. The polyolefin microporous film according to claim 3, wherein the orientation parameter corresponding to the 0° direction is 3 or more and 6 or less, and the orientation parameter corresponding to the 90° direction is 2 or more and 5 or less. The polyolefin microporous film according to claim 3, wherein the orientation parameter corresponding to the 45° direction and the 135° direction is 2 or more and 3.5 or less. The polyolefin microporous film according to any one of claims 1 to 5, wherein the polyolefin microporous film comprises a high density polyethylene. The polyolefin microporous film according to any one of claims 1 to 6, wherein the polyolefin microporous film has a film thickness of 1 μm or more and 20 μm or less. A laminated polyolefin microporous film obtained by laminating a porous layer on at least one surface of the polyolefin microporous film according to any one of claims 1 to 7. A roll comprising the polyolefin microporous film according to any one of claims 1 to 7 or the laminated polyolefin microporous film according to claim 8. A roll comprising a polyolefin microporous film having a polyolefin microporous film as described below: in a surface of one surface of the polyolefin microporous film, in a counterclockwise direction and a roll-out direction The 45° direction of the 45° angle and the 135° direction at an angle of 135° in the counterclockwise direction and the unwinding direction are measured by Raman spectroscopy, and the orientation parameters corresponding to the 45° direction obtained from the measured values are The ratio of the orientation parameters corresponding to the aforementioned 135° direction exceeds 0.91 and is less than 1.10. A method for preparing a polyolefin microporous membrane comprising: in a plane parallel to the surface of the polyolefin microporous membrane, for the length of the film The direction of 45° which is an angle of 45° and the direction of 135° which is the same as the 45° direction and which is 135° with respect to the longitudinal direction are measured by Raman spectroscopy, and the obtained according to the measured value corresponds to the aforementioned The ratio of the orientation parameter in the 45° direction to the orientation parameter corresponding to the aforementioned 135° direction is controlled to be in the range of more than 0.91 and less than 1.10. The method for producing a polyolefin microporous film according to claim 11, further comprising: a 0° direction and a 45° direction in which the directions are the same, and the angles are 0°, 45°, 90°, and 135° with respect to the longitudinal direction, In the 90° direction and the 135° direction, the ratio of the maximum value to the minimum value (Rmin/Rmax) is controlled to be 0.9 or more in the orientation parameters corresponding to the aforementioned 0° direction, 45° direction, 90° direction, and 135° direction. Within the scope below. The method for producing a polyolefin microporous film according to claim 11, further comprising: a 0° direction and a 45° direction in which the directions are the same, and the angles are 0°, 45°, 90°, and 135° with respect to the longitudinal direction, In the 90° direction and the 135° direction, both the orientation parameter corresponding to the aforementioned 45° direction and the orientation parameter corresponding to the aforementioned 135° direction are controlled in the orientation parameter corresponding to the aforementioned 0° direction and corresponding to the aforementioned 90° direction. The orientation parameter of any of the orientation parameters is in the range of 0.5 times or more and 0.95 times or less. A method for evaluating a polyolefin microporous film, which is in a plane parallel to the surface of the film, has a 45° direction at an angle of 45° with respect to the longitudinal direction of the film formation, and has the same orientation and a length direction as the 45° direction. 135° direction at an angle of 135°, determined by Raman spectroscopy The ratio between the orientation parameter in the 45° direction and the orientation parameter corresponding to the 135° direction is calculated. The method for evaluating a polyolefin microporous film according to claim 14, which further determines whether a ratio of the orientation parameter in the 45° direction to the orientation parameter in the 135° direction exceeds 0.91 and is less than 1.10. The method for evaluating a polyolefin microporous film according to claim 14 or 15, wherein the above ratio is used to evaluate the coilability or coatability.