Propylene-based resin microporous film, separator for battery, battery, and method for producing propylene-based resin microporous film

Abstract

The present invention provides a propylene-based resin microporous film which has excellent lithium ion permeability, can constitute a high-performance lithium ion battery, and can prevent a short circuit between a positive electrode and a negative electrode due to dendrites. The propylene-based resin microporous film of the present invention is a propylene-based resin microporous film containing micropores, wherein the degree of gas permeability is 100 to 400 s/100 mL, the standard deviation of the degree of gas permeability is 7 s/100 mL or less, the thermal shrinkage ratio during heating at 105 C. for 2 hours is 6% or less, and the standard deviation of the thermal shrinkage ratio is 1% or less.

Claims

1. A propylene-based resin microporous film containing micropores, having a degree of gas permeability of 100 to 400 s/100 mL, a standard deviation of the degree of gas permeability of 7 s/100 mL or less, a thermal shrinkage ratio of 6% or less after heating at 105 C. for 2 hours, and a standard deviation of the thermal shrinkage ratio of 1% or less, wherein the micropores are formed by uniaxially stretching a propylene-based resin film containing a propylene-based resin having a melting point of 160 to 165 C.

2. The propylene-based resin microporous film according to claim 1, having a surface aperture ratio of 25 to 55%.

3. The propylene-based resin microporous film according to claim 1, wherein aperture edges of the micropores have a longest diameter of 1 m or smaller and an average longer diameter of 500 nm or smaller.

4. The propylene-based resin microporous film according to claim 1, having a pore density of 15 pores/m.sup.2 or more.

5. A separator for a battery, comprising the propylene-based resin microporous film according to claim 1.

6. A battery comprising the separator for a battery according to claim 5.

7. A propylene-based resin microporous film containing micropores, having a degree of gas permeability of 100 to 400 s/100 mL, a standard deviation of the degree of gas permeability of 7 s/100 mL or less, a thermal shrinkage ratio of 6% or less after heating at 105 C. for 2 hours, and a standard deviation of the thermal shrinkage ratio of 1% or less, wherein the propylene-based resin microporous film is produced by a method comprising: an extrusion step of supplying a propylene-based resin to an extruder, melt-kneading the resin, and extruding the resin through a T die attached to a tip of the extruder to obtain a propylene-based resin film; an aging step of aging the propylene-based resin film obtained in the extrusion step under an atmosphere where a temperature is equal to or higher than a temperature lower than the melting point of the propylene-based resin by 30 C. and equal to or lower than a temperature lower than the melting point of the propylene-based resin by 1 C. for 1 hour or longer; a stretching step of uniaxially stretching the propylene-based resin film after the aging step; and an annealing step of annealing the propylene-based resin film after the stretching step, wherein a melting point of the propylene-based resin is 160 to 165 C.

8. A propylene-based resin microporous film containing micropores, having a degree of gas permeability of 100 to 400 s/100 mL, a standard deviation of the degree of gas permeability of 7 s/100 mL or less, a thermal shrinkage ratio of 6% or less after heating at 105 C. for 2 hours, and a standard deviation of the thermal shrinkage ratio of 1% or less, wherein the propylene-based resin microporous film is produced by a method comprising: an extrusion step of supplying a propylene-based resin to an extruder, melt-kneading the resin, and extruding the resin through a T die attached to a tip of the extruder to obtain a propylene-based resin film; an aging step of winding the propylene-based resin film obtained in the extrusion step into a roll to obtain a propylene-based resin film roll, and aging the propylene-based resin film roll under an atmosphere where a temperature is equal to or higher than a temperature lower than the melting point of the propylene-based resin by 30 C. and equal to or lower than a temperature lower than the melting point of the propylene-based resin by 1 C. for 1 hour or longer while the propylene-based resin film roll is rotated in a circumferential direction; a stretching step of unwinding the propylene-based resin film from the propylene-based resin film roll after the aging step, and uniaxially stretching the propylene-based resin film; and an annealing step of annealing the propylene-based resin film after the stretching step, wherein a melting point of the propylene-based resin is 160 to 165 C.

Description

DESCRIPTION OF EMBODIMENTS

(1) Hereinafter, Examples of the present invention will be described. The present invention is not limited to the Examples.

EXAMPLES 1 to 13, and COMPARATIVE EXAMPLE 6

(2) (Extrusion Step)

(3) A homopolypropylene having the weight average molecular weight, the number average molecular weight, and the melting point, which are shown in Tables 1 and 2, was supplied to an extruder, melt-kneaded at the resin temperature shown in Tables 1 and 2, extruded through a T die attached to the tip of the extruder into a film, and cooled to a surface temperature of 30 C. to obtain an elongated homopolypropylene film having a thickness of 30 m and a width of 200 mm. The extruded rate was 12 kg/hr., the film-forming rate was 22 m/min., and the draw ratio was 70.

(4) (Aging Step)

(5) Next, a cylindrical core body with an outer diameter of 97 mm was prepared. The elongated homopolypropylene film (length: 400 m) was wound into a roll around the core body by rotating the core body in the circumferential direction with the axis core as a center. Thus, a homopolypropylene film roll was obtained. The homopolypropylene film roll was allowed to stand in a hot blast furnace at the atmospheric temperature, shown in Tables 1 and 2, of a place where the homopolypropylene film roll was placed over 24 hours while being rotated at a rotation speed shown in Tables 1 and 2 in the circumferential direction with the axis core of the core body as a center and with the axis core direction maintained horizontal. Thus, the homopolypropylene film roll was aged. At this time, the temperature of the homopolypropylene film from the surface to the inside of the homopolypropylene film roll was entirely the same as the temperature in the hot blast furnace. The atmospheric temperature of the place where the homopolypropylene film roll was placed in the hot blast furnace is described in the column of Aging temperature in Tables 1 and 2.

(6) (First Stretching Step)

(7) Then, the homopolypropylene film was continuously unwound from the aged homopolypropylene film roll at an unwinding rate of 0.5 m/min. The homopolypropylene film was uniaxially stretched using a uniaxial stretching device at a surface temperature of 23 C., a stretching rate of 50%/min and a stretching ratio shown in Tables 1 and 2 only in an extrusion direction.

(8) (Second Stretching Step)

(9) Subsequently, the homopolypropylene film was uniaxially stretched at a surface temperature of 120 C., a stretching rate of 42%/min and a stretching ratio shown in Tables 1 and 2 only in the extrusion direction using a uniaxial stretching device so that the surface temperature was 120 C.

(10) (Annealing Step)

(11) After that, the homopolypropylene film was supplied to a hot blast furnace. The homopolypropylene film was allowed to travel over 1 minute so that the surface temperature thereof was 130 C. and a tension was not applied to the homopolypropylene film, and thus annealed to obtain an elongated homopropylene microporous film having a thickness of 25 m. The shrinkage ratios of the homopolypropylene film in the annealing step were set to the values shown in Tables 1 and 2.

COMPARATIVE EXAMPLE 1

(12) A homopropylene microporous film was obtained in the same manner as in Example 1 except that the homopolypropylene film roll was aged without rotation in the aging step.

COMPARATIVE EXAMPLES 2 to 5

(13) A homopropylene microporous film was obtained in the same manner as in Example 1 except that the resin temperature during melt-kneading the homopolypropylene by the extruder in the extrusion step, the aging temperature in the aging step, the stretching ratios in the first and second stretching steps, and the shrinkage ratio of the homopolypropylene film in the annealing step were each changed as shown in Table 2 and the homopolypropylene film roll was aged without rotation in the aging step.

(14) [Evaluation]

(15) The degree of gas permeability, the standard deviation thereof, the thermal shrinkage ratio, the standard deviation thereof, the longest diameter and the average longer diameter of the aperture edges of the micropores, the pore density, and the surface aperture ratio of the obtained homopolypropylene microporous films were measured as described above. The results are shown in Tables 1 and 2.

(16) TABLE-US-00001 TABLE 1 EXAMPLE EXAMPLE EXAMPLE EXAMPLE EXAMPLE 1 2 3 4 5 HOMOPOLYPROPYLENE WEIGHT AVERAGE MOLECULAR 413000 413000 413000 413000 413000 WEIGHT Mw NUMBER AVERAGE MOLECULAR 44300 44300 44300 44300 44300 WEIGHT Mn MOLECULAR WEIGHT DISTRIBUTION 9.3 93 9.3 9.3 9.3 (Mw/Mn) MELTING POINT ( C.) 163 163 163 163 163 EXTRUSION STEP RESIN TEMPERATURE ( C.) 200 200 190 200 200 AGING STEP AGING TEMPERATURE ( C.) 155 155 158 146 146 AGING TIME (HOUR) 24 24 24 24 24 ROTATION SPEED (rpm) 0.1 50 0.1 0.1 0.1 FIRST STRETCHING STEP STRETCHING RATIO (TIME) 1.2 1.2 1.2 1.2 1.2 SECOND STRETCHING STRETCHING RATIO (TIME) 2.0 2.0 2.0 2.0 2.2 STEP ANNEALING STEP SHRINKAGE RATIO (%) 5 5 5 5 5 HOMOPOLYPROPYLENE DEGREE OF GAS PERMEABILITY 180 185 102 316 387 (s/100 ml) MICROPOROUS FILM STANDARD DEVIATION OF DEGREE OF 2.8 1.0 2.3 4.1 4.6 GAS PERMEABILITY (s/100 ml) THERMAL SHRINKAGE RATIO (%) 3.5 3.3 5.6 2.1 2.5 STANDARD DEVIATION 0.12 0.05 0.30 0.20 0.30 OF THERMAL SHRINKAGE RATIO (%) LONGEST DIAMETER (nm) 620 550 800 460 490 AVERAGE LONGER DIAMETER (nm) 360 320 460 270 280 PORE DENSITY (PORE/m.sup.2) 25 30 32 19 20 SURFACE APERTURE RATIO (%) 36 34 51 30 31 EXAMPLE EXAMPLE EXAMPLE EXAMPLE EXAMPLE 6 7 8 9 10 HOMOPOLYPROPYLENE WEIGHT AVERAGE MOLECULAR 413000 413000 413000 413000 413000 WEIGHT Mw NUMBER AVERAGE MOLECULAR 44300 44300 44300 44300 44300 WEIGHT Mn MOLECULAR WEIGHT DISTRIBUTION 9.3 9.3 9.3 9.3 9.3 (Mw/Mn) MELTING POINT ( C.) 163 163 163 163 163 EXTRUSION STEP RESIN TEMPERATURE ( C.) 200 200 200 200 190 AGING STEP AGING TEMPERATURE ( C.) 155 155 155 139 158 AGING TIME (HOUR) 4 24 4 24 24 ROTATION SPEED (rpm) 0.1 0.1 0.1 0.1 0.1 FIRST STRETCHING STEP STRETCHING RATIO (TIME) 1.2 1.2 1.2 1.2 1.4 SECOND STRETCHING STRETCHING RATIO (TIME) 2.0 2.0 2.0 2.0 2.2 STEP ANNEALING STEP SHRINKAGE RATIO (%) 5 3 3 5 5 HOMOPOLYPROPYLENE DEGREE OF GAS PERMEABILITY 205 170 174 399 101 (s/100 ml) MICROPOROUS FILM STANDARD DEVIATION OF DEGREE OF 6.8 4.6 6.8 6.4 1.8 GAS PERMEABILITY (s/100 ml) THERMAL SHRINKAGE RATIO (%) 2.9 6.0 5.5 1.9 5.7 STANDARD DEVIATION 0.50 0.50 0.90 0.25 029 OF THERMAL SHRINKAGE RATIO (%) LONGEST DIAMETER (nm) 630 760 750 420 900 AVERAGE LONGER DIAMETER (nm) 340 390 370 220 490 PORE DENSITY (PORE/m.sup.2) 24 25 26 20 32 SURFACE APERTURE RATIO (%) 33 39 37 25 55 EXAMPLE EXAMPLE EXAMPLE 11 12 13 HOMOPOLYPROPYLENE WEIGHT AVERAGE MOLECULAR WEIGHT Mw 413000 281000 480000 NUMBER AVERAGE MOLECULAR WEIGHT Mn 44300 33000 42000 MOLECULAR WEIGHT DISTRIBUTION (Mw/Mn) 9.3 8.5 11.4 MELTING POINT ( C.) 163 165 162 EXTRUSION STEP RESIN TEMPERATURE ( C.) 200 200 200 AGING STEP AGING TEMPERATURE ( C.) 133 155 155 AGING TIME (HOUR) 24 24 24 ROTATION SPEED (rpm) 0.1 0.1 0.1 FIRST STRETCHING STEP STRETCHING RATIO (TIME) 1.4 1.2 1.2 SECOND STRETCHING STEP STRETCHING RATIO (TIME) 2.2 2.0 2.0 ANNEALING STEP SHRINKAGE RATIO (%) 5 5 5 HOMOPOLYPROPYLENE DEGREE OF GAS PERMEABILITY (s/100 ml) 395 217 164 MICROPOROUS FILM STANDARD DEVIATION OF DEGREE 6.7 6.4 3.4 OF GAS PERMEABILITY (s/100 ml) THERMAL SHRINKAGE RATIO (%) 1.4 3.0 3.5 STANDARD DEVIATION 0.21 0.30 0.30 OF THERMAL SHRINKAGE RATIO (%) LONGEST DIAMETER (nm) 500 620 640 AVERAGE LONGER DIAMETER (nm) 250 355 380 PORE DENSITY (PORE/m.sup.2) 17 26 29 SURFACE APERTURE RATIO (%) 31 31 39

(17) TABLE-US-00002 TABLE 2 COMPARATIVE COMPARATIVE COMPARATIVE EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 HOMOPOLYPROPYLENE WEIGHT AVERAGE MOLECULAR 413000 413000 413000 WEIGHT Mw NUMBER AVERAGE MOLECULAR 44300 44300 44300 WEIGHT Mn MOLECULAR WEIGHT DISTRIBUTION 9.3 9.3 9.3 (Mw/Mn) MELTING POINT ( C.) 163 163 163 EXTRUSION STEP EXTRUSION RESIN TEMPERATURE ( C.) 200 200 200 AGING STEP AGING TEMPERATURE ( C.) 155 155 155 AGING TIME (HOUR) 24 24 24 ROTATION SPEED (rpm) 0 0 0 FIRST STRETCHING STEP STRETCHING RATIO (TIME) 1.2 1.2 1.2 SECOND STRETCHING STEP STRETCHING RATIO (TIME) 2.0 3.1 2.0 ANNEALING STEP SHRINKAGE RATIO (%) 5 5 0 HOMOPOLYPROPYLENE DEGREE OF GAS PERMEABILITY 182 511 184 (s/100 ml) MICROPOROUS FILM STANDARD DEVIATION OF DEGREE OF 10.6 50.3 44.0 GAS PERMEABILITY (s/100 ml) THERMAL SHRINKAGE RATIO (%) 4.2 6.5 10.8 STANDARD DEVIATION 1.22 1.10 3.80 OF THERMAL SHRINKAGE RATIO (%) LONGEST DIAMETER (nm) 990 500 990 AVERAGE LONGER DIAMETER (nm) 400 240 390 PORE DENSITY (PORE/m.sup.2) 14 13 13 SURFACE APERTURE RATIO (%) 36 24 35 COMPARATIVE COMPARATIVE COMPARATIVE EXAMPLE 4 EXAMPLE 5 EXAMPLE 6 HOMOPOLYPROPYLENE WEIGHT AVERAGE MOLECULAR 413000 413000 413000 WEIGHT Mw NUMBER AVERAGE MOLECULAR 44300 44300 44300 WEIGHT Mn MOLECULAR WEIGHT DISTRIBUTION 9.3 9.3 9.3 (Mw/Mn) MELTING POINT ( C.) 163 163 163 EXTRUSION STEP EXTRUSION RESIN TEMPERATURE ( C.) 200 190 200 AGING STEP AGING TEMPERATURE ( C.) 155 158 129 AGING TIME (HOUR) 24 24 24 ROTATION SPEED (rpm) 0 0 0.1 FIRST STRETCHING STEP STRETCHING RATIO (TIME) 1.4 1.4 1.2 SECOND STRETCHING STEP STRETCHING RATIO (TIME) 3.1 3.1 2.0 ANNEALING STEP SHRINKAGE RATIO (%) 0 0 5 HOMOPOLYPROPYLENE DEGREE OF GAS PERMEABILITY 844 683 1042 (s/100 ml) MICROPOROUS FILM STANDARD DEVIATION OF DEGREE OF 196.0 120.4 33.2 GAS PERMEABILITY (s/100 ml) THERMAL SHRINKAGE RATIO (%) 14.0 22.2 1.1 STANDARD DEVIATION 7.30 6.20 0.20 OF THERMAL SHRINKAGE RATIO (%) LONGEST DIAMETER (nm) 1010 1015 370 AVERAGE LONGER DIAMETER (nm) 490 520 210 PORE DENSITY (PORE/m.sup.2) 7 11 10 SURFACE APERTURE RATIO (%) 41 48 19

INDUSTRIAL APPLICABILITY

(18) The propylene-based resin microporous film of the present invention can allow ions such as lithium ions, sodium ions, calcium ions, and magnesium ions to smoothly and uniformly permeate therethrough. Accordingly, the propylene-based resin microporous film is suitably used as a separator for a battery.