JPH0873643A - Porous film - Google Patents

Abstract

PURPOSE: To provide porous film which is made of a high-molecular weight PE having specific thickness, permeability, porosity and tensile elongation, thus is useful for lithium cells because of its excellency in film breakage resistance, charge and discharge behavior, safety and processability. CONSTITUTION: This porous film comprises a high-molecular weight PE porous film or sheet of 100,000 or higher viscosity-average molecular weight and has 5-100μm thickness, 10-500 seconds/100cc air permeability, 10-90% porosity and more than 150% stretch elongation. This porous film is obtained, for example, by kneading 25 pts.wt. of high-molecular weight PE powder and 75 pts.wt. of paraffin wax of 1mm average particle size and melt-extruding into a film, soaking the film in isopropyl alcohol to remove the paraffin from the film and subjecting the film to heat treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous film having particularly good tensile elongation, and more particularly to a porous film suitable for use as a battery separator and a lithium battery using the same.

[0002]

2. Description of the Related Art Porous films or sheets have been widely used for various purposes. Various methods for producing such a porous resin molded body have been proposed. Porous resin molding for use as a battery separator,
Generally, a film or sheet is once melt-extruded to be produced from a resin composition containing ultra-high molecular weight polyethylene and a plasticizer, and then the plasticizer contained in the film or sheet is treated with an organic solvent such as isopropanol, ethanol or hexane. It is manufactured by dissolving and removing with a solvent.

Some of the inventors of the present invention have previously found that they have excellent characteristics of maintaining the film shape at high temperatures, have a good heat blocking temperature, and
We proposed a porous film or sheet that provides a battery separator with excellent surface strength, especially pin puncture strength (Japanese Patent Application No. 5-276947).

[0004]

When a porous film or sheet is used to form a separator for a lithium battery, for example, the porous film or sheet and the electrodes are usually stacked alternately and then wound. At that time, there is a problem that the porous film or sheet is often torn and the yield is lowered. There are various possible causes of this, and it is necessary to identify these factors and take individual measures. For example, breakage due to electrode roughness can be prevented to a large extent by improving the surface strength of the porous film or sheet.

The present inventors have conducted various studies on other factors causing breakage of the porous film or sheet, and have found that the tensile elongation of the porous film or sheet is one of the main causes. Conventional porous films or sheets generally have a small tensile elongation, and those having a relatively large tensile elongation of about 100% have a low air permeability and cannot be used advantageously as a battery separator.

[0006]

Therefore, the present inventors have further studied to obtain a porous film or sheet having good air permeability and improved tensile elongation. As a result, they knew that the intended purpose could be achieved by kneading a specific granular paraffin wax as a plasticizer into high-molecular-weight polyethylene, molding it into a film or sheet, and cooling it under specific conditions. The present invention has been completed.

That is, the gist of the present invention is a porous film or sheet made of high molecular weight polyethylene having a viscosity average molecular weight of 100,000 or more, and (a) a thickness of 5 to 1
00 μm, (b) Air permeability 10 to 500 seconds / 100 cc,
(C) Porosity 10 to 90%, (d) Porous film having characteristics of tensile elongation of 150% or more, battery separator formed from this film, and stretching treatment or heat treatment of the porous film or sheet. The present invention resides in a battery separator formed from a fixed film and a lithium battery incorporating the battery separator.

The present invention will be described in more detail below. The resin composition forming the film of the present invention usually contains high molecular weight polyethylene and a plasticizer. Examples of the high molecular weight polyethylene used in the present invention include polyethylene having a viscosity average molecular weight (hereinafter simply referred to as “molecular weight”) of 100,000 or more. It is preferably 500,000 to 4,000,000, and particularly preferably 1,000,000 to 3,000,000 linear polyethylene. The high molecular weight polyethylene has a molecular weight distribution index of 4 or more, preferably 8 to 25, and particularly preferably 10 to 20. Here, the molecular weight distribution index means the value of the ratio Mw / Mn between the weight average molecular weight (Mw) and the number average molecular weight (Mn). Mw / M
Since n shows a large value when the molecular weight distribution index covers a wide range, this numerical value serves as a guide for the molecular weight distribution.

Further, in the present invention, the melting temperature of the high molecular weight polyethylene is 110 because it is easily deformed by melting.
An ethylene homopolymer having a temperature of ˜140 ° C. can be preferably used. In the present invention, 1 part of polybutene-1, polypropylene or polyethylene having a viscosity average molecular weight of less than 100,000 is used with respect to 100 parts by weight of high molecular weight polyethylene.
It may be mixed in an amount of not more than 00 parts by weight, preferably 2 to 80 parts by weight.

Examples of such polyethylene include branched or linear low density polyethylene (molecular weight of 5,000 to 10).
10,000), high-density polyethylene (molecular weight 10,000 to 100,000), and polyethylene wax (molecular weight 5,000 or less). Polybutene-1 and polypropylene having a molecular weight of 4,000,000 or less can be used. When low-density or high-density polyethylene, polybutene-1, or polyethylene wax is used in an amount of 100% by weight or less, preferably 30 to 90% by weight, particularly preferably 40 to 80% by weight, based on the high molecular weight polyethylene, the heat blocking temperature is increased. Can be lowered. In addition, polypropylene or polybutene-1 is 100% by weight with respect to high molecular weight polyethylene.
Below, preferably 1 to 50% by weight, particularly preferably 2
When used in an amount of up to 40% by weight, the strength or the elongation at break can be improved.

Paraffin wax is preferably used as the plasticizer. In particular, the average molecular weight is 250 to 700,
Preferably 300 to 600, particularly preferably 350.
~ 500, oil content (JIS K-2235-5, 6) is 0.05 to 2% by weight, preferably 0.1 to 1.5% by weight, particularly preferably 0.15 to 0.5% by weight, Viscosity is 1 to 30 cst / 100 ° C, preferably 2 to 20 cs
t / 100 ° C., particularly preferably 3 to 10 cst / 10
The one at 0 ° C. is preferable. In addition, as the paraffin wax used in the present invention, the penetration at 25 ° C (JIS
K-2235-5, 4) is 5 to 40, preferably 1
0-20, or the density at 25 ℃ is 0.88-0.9
8 g / cm ³ , preferably 0.90 to 0.95 g / c
What is m ³ is preferable.

The proportion of high molecular weight polyethylene and plasticizer used is usually 5 to 60% by weight, preferably 10 to 50% by weight, and 40 to 95% by weight, preferably 90 to 90% by weight, for high molecular weight polyethylene. It is selected from the range of 50% by weight. Various known additives such as antioxidants may be used in the resin composition of the present invention in an amount of about 0.01 to 5% by weight in the resin composition.

The respective components of the above resin composition are uniformly kneaded by a known uniaxial or biaxial extruder and melt-extruded.
A biaxial extruder is preferably used in terms of extrusion rate, extrusion stability, and kneading strength. When kneading, a paraffin wax having an average particle size of 10 mm or less, preferably 0.5 to 5 mm, is preferably introduced into the extruder so that a porous film or sheet having desired characteristics can be easily obtained.
The melt extrusion molding is usually performed at a temperature of 140 to 240 ° C. and extruded into a film or sheet with a thickness of 5 to 50 μ or 50 to 300 μ.

In the present invention, the film or sheet thus extruded is melted and deformed. That is, since the molecular weight is extremely large, the relaxation of the molecular chain orientation due to deformation is unlikely to occur, and the property of high molecular weight polyethylene that it is easily oriented in the direction of deformation is used to melt-deform and finally obtain the porosity. To improve the mechanical strength and elongation of the film or sheet.

The melt deformation is carried out by applying a deformation stress while the resin composition constituting the extruded film or sheet is kept in a molten state. Usually, the temperature of the resin composition is about 130 to 240 ° C., preferably 1
Deformation stress is applied in a state of being kept in the range of 60 to 200 ° C. In that case, the deformation may be applied in not only one direction but also multiple directions. When used as a battery separator, if it is deformed in only one direction, the pores in the film or sheet will be elongated in that deformation direction, the flow path will be slightly narrowed, the air permeability will decrease, and the separator Since the ionic resistivity tends to increase, it is preferable to apply deformation in a balanced manner in multiple directions so as to widen the pores.

Specifically, for example, in the case of applying a deformation in one direction, in the T die or the inflation molding method, preferably, in the inflation molding method, the gap of the die is enlarged to increase the take-up speed and pulling, In other words, by increasing the draft rate, MD (machine)
Add deformation in the direction. In addition, when deformation is applied in multiple directions, MD and TD can be increased by increasing the draft ratio and blow ratio in the inflation molding method.
Melt deformation is applied in the (width) direction. Further, in the case of multi-directional deformation by the T-die molding method, the end of the melted film or sheet in the width direction is fixed to the caterpillar with a pin tenter, and the widths of the two caterpillars are widened in the TD direction. This is performed by deforming in the MD direction and simultaneously deforming in the MD direction by increasing the take-up speed.

The degree of melt deformation is not particularly limited as long as it does not impair the effects of the present invention, but is a melt deformation rate represented by the following formula, and is usually 10 to 1000, preferably 3
It is preferable to apply a deformation stress so as to be in the range of 0 to 800, particularly preferably 50 to 400. For example, when a deformation stress is applied to the vertical and horizontal directions, the aspect ratio of the deformation rate is DR /
BUR ≦ 50, preferably ≦ 20, particularly preferably
It is preferable to do so that ≦ 10.

[0018]

## EQU1 ## Melt deformation rate = (D × ρ ₁ ) / (t × ρ ₂ ) D: Die gap (mm) ρ ₁ : Melt density (g / cm ³ ) of resin composition t: Molded film or sheet Film thickness (mm) ρ ₂ : Solid density (g / cm) of molded film or sheet
³ )

In the inflation molding method, it is known to produce a polyethylene film by melt-deforming using an annular die having a die gap of 0.5 mm (Japanese Patent Laid-Open No. 223245/1987). Conventionally, 10-100μ
When a film or sheet having a thickness of m is formed, the die gap is usually 1 mm or less, and 1.5 mm or less at the maximum. However, the film or sheet obtained by molding in the range of the conventional die gap does not always have sufficient strength, particularly pin puncture strength.

In order to obtain a battery separator having good strength, the range of the die gap is important together with the cooling rate described later. In the present invention, the die gap is preferably 2 to 20 mm, particularly preferably 3 to 10 mm.
It is better to carry out in the range of mm. Thus, by cooling the melt-deformed film or sheet, by removing the plasticizer contained in the film or sheet,
Pores the film or sheet.

At this time, it is important to cool gradually so that the cooling does not become too rapid. For example, cooling rate 5 to 20 ° C / sec, preferably 8 to 15 ° C / sec
It is better to air cool. As a method for removing the plasticizer, for example, the plasticizer in the film or sheet is dissolved in an organic solvent such as isopropanol, ethanol, gasoline, benzene, chloroform, turpentine oil, carbon disulfide, olive oil and the like, and the solvent is replaced to extract and remove. The so-called known organic solvent method can be used.

Thus, (a) the thickness is 5 to 100 μm, preferably 10 to 60 μm, particularly preferably 20 to 40.
μm, (b) air permeability 10-500 seconds / 100 cc, preferably 20-400 seconds / 100 cc, particularly preferably 30-300 seconds / 100 cc, (c) porosity 10-
90%, preferably 20-80%, particularly preferably,
40-70%, (d) tensile elongation 150% or more, preferably 200-600%, particularly preferably 300-50.
An unstretched porous film or sheet can be obtained with 0% properties.

In the porous film of the present invention, when the tensile elongation is less than 100%, the film tends to be broken during winding. Regarding the upper limit, if it is too large, it will be even
Since it becomes difficult to wind at a high speed, it is preferable to set it to about 600% or less. Further, according to the above method, (e) the heat blocking temperature is 100 to 135 ° C., preferably 110 to 1
35 ° C., (f) Thermal rupture temperature is 180 ° C. or higher, preferably 200 ° C. or higher, (g) Pin puncture strength 150 gf / 25
Since it is possible to obtain a non-stretched porous film or sheet having a characteristic of μm or more, preferably 200 gf / 25 μm or more, and particularly preferably 250 gf / 25 μm or more, it can be suitably used as a battery separator.

In the present invention, a battery separator can be formed using such a non-stretched porous film or sheet, and this non-stretched porous film or sheet is uniaxial or in order to improve its mechanical strength. It may be biaxially stretched or heat set at about 100 to 180 ° C. By such a treatment, (a ') the thickness is 5 to 100 m, preferably 10 to 60 m, particularly preferably 20 to 40 m, and (b') the air permeability is 10 to 50.
0 sec / 100 cc, preferably 20 to 400 sec / 10
0 cc, particularly preferably 30 to 300 seconds / 100 c
c, (c ') porosity 10-90%, preferably 20-
80%, particularly preferably 40 to 70%, (d ') tensile elongation 100% or more, preferably 200 to 600%, particularly preferably 300 to 500%, (g') pin puncture strength 200 g / 25 μm. Or more, preferably 250 g / 25
μm or more, particularly preferably 300 g / 25 μm or more,
Furthermore, (e ') heat blocking temperature 100 to 135 ° C, preferably 110 to 135 ° C, (f') thermal film rupture temperature 150 ° C.
As described above, preferably, a porous film or sheet having characteristics of 200 ° C. or higher can be obtained.

For the tensile elongation, a film width of 15 mm and a length of 50 mm or more are cut and used as test pieces. At room temperature of 23 ° C., the distance between chucks is set to 25 mm, a test piece is set, and a tensile test is performed. At this time, a tape or the like may be wrapped around the end of the test piece so as not to break at the chuck portion. The crosshead speed was 300 mm / min. At this time, the tensile cutting load and the distance between the marked lines are measured. The tensile elongation is calculated by the following formula.

[0026]

[Equation 2] The tensile strength is calculated from the tensile breaking load by the following formula.

[0027]

(Equation 3)

For the tensile test, a universal tensile tester was used.
The air permeability was measured according to JIS P8117. The apparatus used was a B-type Gurley type densometer (trade name) manufactured by Toyo Seiki. The porosity is measured by punching 5 places in the width direction of the film into a circle having a diameter of 3 cm, measuring the thickness of the center of the punched film, measuring the weight, and calculating by the following formula.

[0029]

## EQU00004 ## Porosity (%) = (V.rho.-W) / (V.rho.). Times.100 V: Volume of film (5 sheets) W: Weight (5 sheets) ρ: Material density

The thermal blocking temperature and the thermal film rupture temperature were measured by preparing a square Teflon film (TF) with a side of 8 cm and a aluminum plate (Al) having a hole of 4 cm in diameter at the center.
A test piece is prepared by stacking Al / TF / porous film / TF / Al in this order and fixing them with a clip or the like. Test piece at 130 ℃
In an oven at 5 ℃ for 5 minutes while heating at 5 ℃
Samples are taken every minute and the air permeability (JIS P811
7) is measured, and the temperature at which the air permeability becomes 5000 seconds / 100 cc is defined as the heat blocking temperature. Similarly, the temperature at which a hole that can be visually confirmed and recognized is formed in the same manner is defined as the thermal film rupture temperature.

The pin puncture strength is measured in accordance with Japanese Agriculture and Forestry Standards Notification No. 1019 [Measurement equipment: Rheometer (NRM-2002J manufactured by Fudo Kogyo Co., Ltd.), pin diameter 1 mmφ, tip 0.5R, pin puncture speed 200 mm / min. ] The value
In order to ensure safety, the difference between the heat blocking temperature of the separator and the thermal film rupture temperature is 30 ° C or more, preferably 50 ° C or more, and there is a margin in terms of safety against the temperature rise that continues after the heat blocking. It becomes a separator.

The battery separator formed from the above-mentioned porous film or sheet of the present invention can be suitably used in, for example, lithium batteries and lithium ion secondary batteries. The lithium battery (secondary battery) of the present invention is composed of a separator made of the above-mentioned porous film or sheet, an aprotic electrolytic solution, a positive electrode made of a lithium compound (positive electrode during discharge), and a negative electrode.

First, the aprotic electrolytic solution is filled in the pores of the separator, but the filling can be easily performed by dropping, impregnating, coating or spraying. This is because the porous film or sheet has an average through-hole diameter of 0.001 to 0.1 μm, and therefore, an aprotic electrolyte solution having a contact angle of 90 ° or less with respect to the film or sheet is not condensed by capillary condensation. This is because it is easily taken into the holes by the action.

As the aprotic electrolytic solution, propylene carbonate, dimethyl sulfoxide, 3-methyl-
1,3-oxazolidin-2-one, sulfolane, 1,
A single or multi-component organic solvent such as 2-dimethoxyethane or 2-methyltetrahydrofuran may be mixed with LiBF
_A solution in which a lithium salt such as ₄ , LiClO ₄ or the like is dissolved can be used. In particular, propylene carbonate,
A combination of 1,2-dimethoxyethane and LiBF ₄ ,
Dimethyl sulfoxide, 1,2-dimethoxyethane, L
iBF ₆ combination, propylene carbonate, 1,
The combination of 2-dimethoxyethane and LiClO ₄ is
The electrical conductivity at room temperature is known to be 10 ⁻³ to 10 ⁻² s / cm, which is preferable.

By using the separator thus obtained, a lithium battery having excellent reliability and safety can be obtained. The lithium battery of the present invention is a so-called non-aqueous electrolyte type battery using the above-mentioned aprotic electrolytic solution as an electrolyte, and its structure is basically the same as that of a normal lithium battery of the same type. The separator of the present invention, which has been described in detail so far, is installed between the positive and negative electrodes.

When the primary battery is used, the negative electrode is lithiated
Compound, and the positive electrode is silver chromate, fluorocarbon,
Manganese oxide or the like can be used. Also with a secondary battery
When using a lithium compound
Or aluminum or fusible gold (Pb, Cd, In
(Including alloys) and carbon that absorbs lithium
TiS with layered structure as pole₂, MoS₂And NbS
e₃Such as metal chalcogenides and tunnel-shaped holes
Two CoO₂, Cr₂O_FiveAnd V₂O_Five(・ P₂O _Five), M
nO₂(・ LiO₂) Etc. metal oxides, polyacetylene
Using conjugated polymer compounds such as amine and polyaniline
Can be

[0037]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Example 1 25 parts by weight of ultra high molecular weight polyethylene (PE) (Mw / Mn = 8) powder having a melting point of 135 ° C. and a viscosity average molecular weight of 2.3 × 10 ⁶ and paraffin wax 7 having an average particle size of 1 mm
While supplying 5 parts by weight to an extruder having a diameter of 50 mm and kneading at 200 ° C., it was continuously extruded from an inflation die having a die diameter of 50 mm and a die gap of 6.0 mm, and a take-up speed of 5.0 m / min (die temperature: 177). ℃, draft rate:
At 21.7), the film was taken out and melt-deformed at a blow ratio (BUR) of 7.0 to obtain a film having a thickness of 0.034 mm. The melt density of the resin composition used in this example is 0.7.
At 9 g / cm ³ , the extruded film has a solid density of 0.
Since the melt deformation was 917 g / cm ³ , the melt deformation rate applied in this melt deformation was about 152.

The obtained film was dipped in isopropyl alcohol at 60 ° C. to extract and remove paraffin wax from the film, followed by heat treatment with a heating pinch roll at a surface temperature of 122 ° C. for 30 seconds to give a film thickness of 25 μm. A porous film of The physical properties of this film are shown in Table 1. The obtained porous film (width 58 mm, cut into length 1 m) was sandwiched between the positive electrode and the negative electrode of a lithium battery (negative electrode: lithium cobalt oxide, positive electrode: carbon, electrolytic solution: propylene carbonate), and rolled up to 60 mm. The lithium secondary battery was stored in a metal container having a length of 15 mm and a diameter of 15 mm.

The defective rate was tested by the following method. Place the film sample on an iron plate whose surface has a roughness equivalent to No. 120 sandpaper, and apply 0.5 kg /
Place a 30φ terminal on it so that a pressure of cm ² is applied. A voltage of 1.5 kV is applied to this iron plate and terminal for 1 minute,
The voltage was tested to see if current could flow. This was performed 100 times and the number of currents was defined as the defective rate. Equipment used is Kikusui Kogyo Co., Ltd., withstanding voltage tester TOS8
It is 651 type. The roughness equivalent to No. 120 sandpaper is a roughness for imitating an electrode plate. The paraffin wax used in the examples had the following physical properties.

[0040]

[Table 1] Molecular weight: 530 Oil: 0.3% Viscosity: 3.9 mm ² / s / 100 ° C Density: 0.911 g / cm ² Penetration: 13 (25 ° C)

Example 2 In Example 1, paraffin wax having an average particle diameter of 2.5 mm was replaced with a take-up speed of 10 m / min (die temperature: 180 ° C., draft rate (DR): 26.4) and BUR was taken. = 9.0, the film thickness is 0.02
A 2 mm porous film was obtained. Then, the paraffin wax of the porous film was removed in the same manner as in Example 1 and then heat-treated at 115 ° C. to obtain a porous film having a thickness of 18 μm. The physical properties of this film are shown in Table 1. The obtained porous film was used as a separator for a lithium battery in the same manner as in Example 1, and a defective rate test was conducted.

Example 3 In Example 1, the take-up speed was set at 4.5 m / min (die temperature: 170 ° C., DR: 15.4), and BUR =
Melt deformation was applied at 7.0 to obtain a film having a thickness of 0.044 mm. Then, the paraffin wax was removed from this film in the same manner as in Example 1, and the film was heat-treated at 100 ° C. to obtain a porous film having a thickness of 35 μm. The physical properties of this film are shown in Table 1. The obtained porous film was used as a separator for a lithium battery in the same manner as in Example 1, and a defective rate test was conducted.

Example 4 25 parts by weight of ultra high molecular weight polyethylene (PE) (Mw / Mn = 7) powder having a melting point of 136 ° C. and a viscosity average molecular weight of 1.0 × 10 ⁶ and paraffin wax 7 having an average particle diameter of 1 mm
A porous film having a thickness of 35 μm was obtained in the same manner as in Example 1 except that 5 parts by weight was supplied to the extruder. The physical properties of this film are shown in Table 1. The obtained porous film was used as a separator for a lithium battery in the same manner as in Example 1, and a defect rate test was conducted.

Example 5 20 parts by weight of ultrahigh molecular weight polyethylene (Mw / Mn = 6) powder having a melting point of 138 ° C. and a molecular weight (viscosity average) of 3 × 10 ⁶ and 80 parts by weight of paraffin wax having an average particle size of 1.5 mm. 50 mm in diameter and continuously kneaded at 200 ° C with a die diameter of 50 mm and a die gap of 4.5 m.
Extruded from an inflation die of m, with a take-up speed of 6.2 m /
It was taken out at min (die temperature: 180 ° C., DR: 13.8) and melt-deformed at a blow ratio (BUR) of 6.5 to obtain a film having a thickness of 0.043 mm. The melt density of the resin composition used in this example was 0.78 g / cm ³ , and the solid density of the extruded film was 0.913 g / cm ³ , so the melt deformation rate applied in such melt deformation was Was about 89.4.

This film was immersed in isopropyl alcohol at 60 ° C. to extract the paraffin wax, and then heat treated in the same manner as in Example 1 to obtain a porous film having a thickness of 29 μm. The physical properties of this film are shown in Table 1. The obtained porous film was used as a separator for a lithium battery in the same manner as in Example 1. The test results are shown in Table 1.

Example 6 In Example 1, the take-up speed was 2.5 m / min (die temperature: 165 ° C., DR: 10.5), and BUR =
Melt deformation was applied at 6.0 to obtain a film having a thickness of 0.082 mm. After immersing the obtained film in isopropyl alcohol and extracting and removing the paraffin wax,
The film was stretched 3.0 times with a roll stretching machine (stretching temperature: 124 ° C.) to obtain a porous film having a thickness of 25 μm. The physical properties and the like of this molded product are shown in Table 1 as in Example 1.

Example 7 In Example 5, the take-up speed was 2.3 m / min (die temperature: 165 ° C., DR: 9.2), and BUR =
Melt deformation was applied at 6.0 to obtain a film having a thickness of 0.094 mm. After immersing the obtained film in isopropyl alcohol and extracting and removing the paraffin wax,
The film was stretched 2.8 times with a roll stretching machine (stretching temperature 122 ° C.) to obtain a porous film having a thickness of 30 μm. The physical properties and the like of this film are shown in Table 1 as in Example 1.

Comparative Example 1 25 parts by weight of ultra high molecular weight polyethylene powder having a melting point of 135 ° C. and a viscosity average molecular weight of 2 × 10 ⁶ and 75 parts by weight of ceryl alcohol were fed to an extruder having a diameter of 50 mm, and 200
While kneading at ℃, die temperature: 170 ℃ from the inflation die with a die diameter of 40 mm and a die gap of 5.6 mm.
Film formation with DR: 16.8, BUR: 7.0, film thickness 43μ
m sheets were obtained. (Melting density: 0.79 g / cm ³ ,
Solid density: 0.876 g / cm ³ )

This sheet was extracted with ceryl alcohol and heat-treated in the same manner as in Example 1 to obtain a porous sheet having a film thickness of 34 μm. The physical properties of this sheet are shown in Table 1. Then, this sheet was assembled in a battery in the same manner as in Example 1 and a defect rate test was conducted.

Comparative Example 2 20 parts by weight of a powder of ultrahigh molecular weight polyethylene having a melting point of 138 ° C. and a viscosity average molecular weight of 3 × 10 ⁶ and 80 parts by weight of stearyl alcohol were fed to an extruder having a diameter of 50 mm to obtain 200 parts.
Continuously extruding from an inflation die with a die diameter of 50 mm and a die gap of 3 mm while kneading at ℃, die temperature: 17
Melt deformation was applied at 0 ° C, DR: 8.9, BUR: 4.0, and the film was drawn at a take-up speed of 3.1 m / min and a film thickness of 0.0
A 76 mm film was obtained.

This film was immersed in isopropyl alcohol at 60 ° C. to extract stearyl alcohol,
Then, it is stretched 2.7 times with a roll stretching machine (stretching temperature 1
24 ° C.) to obtain a porous film having a thickness of 25 μm.
The physical properties are shown in Table 1.

[0052]

[Table 2]

[0053]

INDUSTRIAL APPLICABILITY The porous film of the present invention is used as a battery separator to supply a lithium secondary battery having excellent charge / discharge characteristics, safety, and processability.

Front page continued (72) Inventor Kyosuke Watanabe 3-10 Shiodori, Kurashiki-shi, Okayama Mitsubishi Kasei Co., Ltd.Mizushima Plant (72) Inventor Yasushi Usami 3-10 10 Shiodo, Kurashiki-shi, Okayama Mitsubishi Kasei Corporation Company Mizushima factory

Claims (11)

[Claims] 1. A porous film or sheet made of high-molecular-weight polyethylene having a viscosity average molecular weight of 100,000 or more, wherein (a) the thickness is 5 to 100 μm, and (b) the air permeability is 10 to 500 seconds / 100 cc. , (C) Porosity 10-9
A porous film having characteristics of 0% and (d) tensile elongation of 150% or more. 2. The porous film according to claim 1, wherein (e) the heat blocking temperature is 100 to 135 ° C. 3. The porous film according to claim 1, wherein (f) the thermal film rupture temperature is 180 ° C. or higher. 4. The porous film according to claim 1, wherein (g) pin puncture strength is 150 gf / 2.
A porous film having a thickness of 5 μm or more. 5. The porous film according to claim 1, which is obtained by stretching treatment or heat setting. 6. The porous film or sheet obtained by the stretching treatment or heat setting according to claim 5, (a ′) has a thickness of 5 to 100 μm, and (b ′) has an air permeability of 10 to 500 seconds / 1.
00cc, (c ') porosity 10 to 90%, (d') tensile elongation 100% or more, (h) tensile strength 400 kg / cm ^2.
A porous film having the above properties. 7. The porous film according to claim 6, wherein (e ′) the heat-sealing temperature is 100 to 135 ° C. 8. The porous film according to claim 6 or 7, wherein (f ') the thermal membrane rupture temperature is 150 ° C or higher. 9. The porous film according to claim 6, which has a (g ′) pin puncture strength of 200 gf /
A porous film having a thickness of 25 μm or more. 10. A porous film, wherein the porous film according to any one of claims 1 to 9 is for a battery separator. 11. A lithium battery incorporating the porous film according to claim 1 as a battery separator.