JP3252016B2 - Method for producing polyolefin microporous membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various separators used for medical and industrial filtration and separation, separators for batteries, separators for electrolytic capacitors, etc., and especially separators for non-aqueous solvent batteries. The present invention relates to a method for producing a polyolefin microporous porous membrane used in (1).

[0002]

2. Description of the Related Art Microporous polyolefin porous membranes having resistance to organic solvents and alkaline or acidic solutions are used for various separation membranes, separators for batteries, separators for electrolytic capacitors, and the like. Particularly, in a lithium battery which is a non-aqueous solvent battery, a protic electrolyte cannot be used because lithium metal and lithium ions are used, and γ-butyrolactone, polypropylene carbonate, organic solvent such as dimethoxyethane, Li
An electrolyte in which a lithium salt such as BF ₄ or LiClO ₄ is dissolved is used as an electrolyte. Therefore, as a separator provided between the positive electrode and the negative electrode, an olefin-based material such as polyethylene or polypropylene insoluble in an organic solvent as described above is processed into a microporous membrane or nonwoven fabric and used as a separator. In addition, such a microporous porous membrane or nonwoven fabric is made as thin as possible in a range that does not impair reliability, in order to increase the battery capacity. Because of this,
The thickness of the microporous membrane is reduced by stretching or the like, and the thickness of the nonwoven fabric is reduced by hot pressing or the like.

Further, such a separator for a non-aqueous solvent battery such as a lithium battery has high strength, low electric resistance, high permeability, high temperature characteristics and the like from the viewpoint of assembling processability, safety and reliability. Performance is required, and low cost is required. High strength relates to assembly workability, and the higher the strength, the faster the production speed when assembling the battery.

The so-called aprotic electrolyte obtained by dissolving a lithium salt in the above-mentioned organic solvent generally has a high internal resistance. This is required to suppress an increase in resistance. The high temperature property relates to safety and means the following performance. That is, when the temperature inside the battery rises due to the heat generated when the battery is short-circuited externally, the microporous porous membrane shrinks due to the temperature rise, the pore diameter of the microporous membrane decreases, and the electrical resistance increases. However, the lower the temperature at which the material is substantially melted and non-porous (the non-porous temperature), the more it is possible to prevent the permeation of ions at a low temperature, thereby suppressing a sharp rise in the temperature inside the battery. When the temperature further rises, the melt-porous microporous membrane decreases in melt viscosity of the resin and breaks at a specific temperature (film breaking temperature).

Accordingly, it is considered that the lower the non-porous temperature and the larger the difference between the non-porous temperature and the film breaking temperature, the better the high-temperature characteristics and the higher the safety of the battery separator. Can be Conventionally, for example,
JP-A-163938 and JP-B-63-29891 disclose polyethylene or a weight average molecular weight of 200,000 to 200,000.
A plate-like molded product composed of 500,000 polyethylene and a solvent,
After uniaxially stretching in the machine direction by means such as rolling, the technique of extracting a solvent or the like is disclosed, but the membrane obtained in the publications and the like has a small pore size, and has high membrane strength. However, since the membrane has poor permeability and a composition consisting of high-density polyethylene having a low melting point alone, the film has a low film breaking temperature and poor high-temperature characteristics, which is problematic in safety. In addition, because of the means of rolling, control is difficult and continuous productivity is poor. JP-A-46-40119 and JP-A-1-11-11
No. 3442 discloses a microporous porous membrane made of polypropylene, which has a high strength and a high film breaking temperature, but has a high non-porous temperature due to a single composition of a high melting point resin. , High temperature characteristics are poor and there is a problem in safety.

As described above, a simple substance (polyethylene,
For the method for producing a porous membrane (polypropylene only),
For example, U.S. Pat. Nos. 4,247,498 and 4,519.
No. 909 (Castro), which utilizes liquid-liquid phase separation; US Pat. No. 4,539,256 (Shipman);
As disclosed in JP-A-3-314247, there is a method utilizing solid-liquid phase separation, but these techniques do not disclose a method for producing a porous film of a polyolefin resin comprising a mixture of polyethylene and polypropylene.

In order to improve the high temperature characteristics, Japanese Patent Application Laid-Open
In 08866 and JP-A-2-77108,
A method has been disclosed in which a single film made of polyethylene and polypropylene is laminated to obtain a microporous porous film having high strength and excellent high-temperature properties.However, due to lamination, the electrical resistance of the separator increases, and The properties are not sufficient, and it is unsuitable as a high performance battery separator. Further, in Japanese Patent Application Laid-Open No. 2-77108, since the technique of lamination extrusion is employed, the productivity is inferior in terms of the complexity of the manufacturing process and the manufacturing cost.

On the other hand, as a technique for achieving a high film breaking temperature, there is a method using an ultrahigh molecular weight polyolefin.
Japanese Patent Application Laid-Open Nos. 60-242035 and 60-25 to which so-called ultra-high molecular weight polyethylene gel spinning as disclosed in JP-A-58-5228 is applied.
No. 5107 discloses a technique for obtaining a high-strength microporous membrane made of ultrahigh molecular weight polyethylene,
Because the ultra-high molecular weight polyethylene is used, in order to obtain a uniform composition, the ultra-high molecular weight polyethylene is pre-swelled with a solvent and supplied to the kneading machine, or the homogeneous mixture mixed by the kneading machine is not solidified. Since it is supplied to the extruder in a molten state, it takes time, productivity is low, and the non-porous temperature is not sufficiently low, so that the safety remains questionable.

Techniques for obtaining a high-strength film that satisfies both a low pore-free temperature and a high film-breaking temperature are disclosed in JP-A-2-21559 and JP-A-3-64334.
As disclosed in Japanese Unexamined Patent Publication, there is a technique of blending a part of high-density polyethylene with ultra-high-molecular-weight polyethylene. Inferior. There is also a technique of blending ultra-high-molecular-weight polyethylene with high-density polyethylene and polypropylene partially. However, this technique also requires a long time to obtain a uniform composition because of using ultra-high-molecular-weight polyethylene, and is inferior in productivity.

Japanese Patent Laid-Open Publication No. Sho 63-295650 discloses that ultra-high molecular weight polyethylene and an inorganic filler are used.
Although a technique for obtaining a uniform composition is disclosed, since an inorganic filler is used in the manufacturing process, production costs are reduced in terms of maintenance of the molding machine, such as misalignment of the molding machine due to the inorganic filler, and processing of the inorganic filler. Disadvantageous. On the other hand, as a technique for obtaining a high-strength molded article only from polyethylene and polypropylene without using ultra-high molecular weight polyethylene, polyethylene and polypropylene are incompatible in a molecular order (for example, polymer blend <C.
It is known that it is difficult. For example, as described in JP-A-50-111174, a molded article composed of polyethylene and polypropylene is biaxially stretched, or There is a technique for obtaining a porous film by annealing a molded article made of polypropylene after stretching or stretching after annealing, but a microporous porous film having a high porosity has not been obtained. In the case of a material having poor transmission performance and being annealed, it takes time to obtain a molded product due to the annealing, resulting in poor productivity.

Japanese Patent Application Laid-Open Nos. Sho 62-14837 and Sho 57-49629 also disclose techniques for producing a microporous porous film made of polyethylene and polypropylene. Since it is used, it is disadvantageous in terms of production cost in terms of maintenance of the molding machine such as a molding machine using an inorganic filler, slipping of a die and the like, a die and the like, and treatment of an inorganic filler.

[0012]

DISCLOSURE OF THE INVENTION The present invention is free of the above-mentioned drawbacks, namely, a low-cost single-membrane microporous membrane having high performance, high strength, low electric resistance, high permeability and excellent high-temperature characteristics. It is an object of the present invention to provide a manufacturing method that can provide a simple manufacturing process.

[0013]

In order to achieve the above object, the present invention provides (a) a liquid or solid polyolefin resin comprising a mixture of polyethylene and polypropylene having a viscosity average molecular weight of less than 1,000,000 at a weight concentration of 30% or more. (B) extruding the solution obtained in the above step (a) into a sheet, and separating the polyolefin resin and the liquid or solid organic substance into a solid (crystal) -liquid phase; A step of extracting a liquid or solid organic substance from the sheet-like substance obtained in the step (b) and stretching the same from both sides of the membrane without applying pressure, or stretching without applying pressure simultaneously from both sides of the membrane Then, a method for producing a polyolefin microporous membrane comprising a step of extracting a liquid or solid organic substance is provided.

Further, the step (c) is a step of extracting a liquid or solid organic substance from both surfaces of the film without applying pressure at the same time, and extending the film from both surfaces of the film without applying pressure at the same time. And a method for producing a polyolefin microporous porous membrane. According to the present invention, by using an appropriate liquid or solid organic substance and defining the ratio of the organic substance and the polyolefin resin, the mixing property of the mixture of the polyolefin composed of polyethylene and polypropylene is controlled, and the high temperature of the obtained porous membrane is controlled. Good characteristics and strength can be obtained. Further, when the sheet-like material is stretched and then a liquid or solid organic material is extracted and further stretched, stretching before extraction can be performed without increasing porosity. Since the stretching is performed later, the strength of the obtained film is
Further increase.

Further, according to the present invention, when a sheet is formed, the shaping of a forming machine, a die and the like is small, and since the formed sheet-shaped product has few non-uniform points, it is stretched. In this case, the number of defective holes and the like is small, and efficient production can be achieved. The resulting polyolefin microporous membrane has a thickness of 10 to 100 μm and an average pore size of 0.01 to 1 μm.
μm, porosity 30-80%, elastic modulus in machine direction 5000k
gf / cm ² or more, the electric resistance 10 .OMEGA.cm ² or less, more preferably 5Omucm ² or less, air permeability 1000 seconds or less, no Anaka temperature 100 to 145 ° C., film breakage temperature 160 ° C. or more high strength, low electrical resistance, high It is a low-cost single-membrane microporous membrane excellent in permeability and high-temperature properties.

In the present invention, the viscosity average molecular weight is 10
The polyethylene having a molecular weight of less than 100,000 is a low-density polyethylene, a linear low-density polyethylene, and a high-density polyethylene used in ordinary extrusion, injection, inflation or blow molding, and has a viscosity average molecular weight of 1,000,000 or more Does not include molecular weight polyethylene. It is more preferable that the viscosity average molecular weight is 700,000 or less.

The polypropylene in the present invention is a known isotactic, syndiotactic, atactic polypropylene, ethylene propylene random copolymer, and ethylene propylene commonly used for extrusion, injection, inflation or blow molding. It is a propylene block copolymer. In particular, known isotactic polypropylene is desirable from the viewpoint of availability and melt moldability.

In the present invention, the polyolefin resin comprising a mixture of polyethylene and polypropylene includes, among the above polyethylene and polypropylene,
Some of them may be mixed, and polyolefin resins other than polyethylene and polypropylene may be mixed as appropriate. As resins other than polyethylene and polypropylene, for example, polybutene, polymethylpentene,
And ethylene propylene rubber.

It is preferable that the ratio of the polypropylene to the entire polyolefin resin is 5 to 50 wt%, and the ratio of the polymer other than the polypropylene is 95 to 50 wt%. Further, it is preferable that polyethylene accounts for 50 wt% or more of the polymer other than polypropylene. To such a polyolefin resin, if necessary, additives such as an antioxidant, an ultraviolet absorber, a lubricant, an antiblocking agent, a coloring agent, and a flame retardant are added within a range that does not impair the object of the present invention. be able to.

Since polyolefin resins comprising a mixture of such various polymers usually have poor compatibility, it is desirable to use polyolefins used for ordinary extrusion, injection, inflation or blow molding. Such a polyolefin has a viscosity average molecular weight of 700,000 or less, and a fraction of the entire system having a molecular weight of 1,000,000 or less is 80 wt% or more. The fraction having a molecular weight of 1,000,000 or less referred to in the present invention is obtained from an integration curve of GPC (gel permeation chromatography) measurement, and is 80 watts.
When the content is less than t%, the high molecular weight component increases, so that it tends to be difficult to obtain a uniform composition. Further, when high-density polyethylene is included as a polyethylene component, the strength is increased, which is desirable.

The liquid or solid organic substance used in the present invention is kept in a liquid state during heating and dissolving, and is dissolved in a general organic solvent, water and the like, and is easily extracted from the molded article. Further, the solid organic substance refers to an organic substance that is solid at 25 ° C. Among such liquid or solid organic substances, those having a high molecular weight dependency coefficient a of intrinsic viscosity with respect to polyethylene or polypropylene of 0.55 or more are desirable. Such liquid or solid organics are known to be good solvents for polyethylene or polypropylene (eg PGde Genne polymer physics). Such liquid or solid organic substances include, for example, xylene, toluene, decalin, decane,
Examples include dodecane, O-dichlorobenzene, trichlorobenzene, liquid paraffin, paraffin wax, mineral oils such as process oils, and stearyl alcohol. By using such a liquid or solid organic substance, the mixing property between polyethylene and polypropylene is improved, and a space that effectively becomes a pore due to phase separation can be formed.

Particularly, dodecane, decalin, O-dichlorobenzene, trichlorobenzene, mineral oils such as liquid paraffin, paraffin wax, process oil and stearyl alcohol having a flash point of 50 ° C. or more are desirable. Particularly preferred are trichlorobenzene having a temperature of at least 100 ° C., mineral oil such as liquid paraffin, paraffin wax and process oil, and stearyl alcohol. When the flash point is an organic substance having a temperature of 50 ° C. or higher, stretching can be performed before extraction of a liquid or solid organic substance described later, so that the stretching can be performed without largely changing the ratio of the pores, It is desirable because the strength of the obtained film can be increased. Among them, mineral oil such as liquid paraffin, paraffin wax and process oil and stearyl alcohol are particularly preferable from the viewpoint of safety for the human body.

In the present invention, the fact that the polyolefin resin and the liquid or solid organic matter are subjected to solid-liquid phase separation means that the phase separation occurs according to a so-called freezing point depression curve. What dissolved the thermoplastic polymer in organic matter,
It is known that, depending on the composition, a portion that exhibits liquid-liquid phase separation and a portion that exhibits solid-liquid phase separation (see, for example, U.S. Pat. Nos. 4,247,498 and 4,519,909 (Cas
tro), Smolders, vanAsrtsen and Steenbergen K
olloid.ZUZPolymere 243.14-20 (197
1), Polymer Experiments 11, Polymer Solution <Kyoritsu Publishing>
Etc.) In the present invention, in order to perform a solid-liquid phase separation between the polyolefin resin and the liquid or solid organic substance, the above-mentioned appropriate organic substance is used, and the polyolefin resin is dissolved in the organic substance at a weight concentration of 30% or more. is necessary.

If the weight concentration of the polyolefin resin is less than 30%, it is difficult to carry out solid-liquid phase separation between the polyolefin resin and a liquid or solid organic substance. On the other hand, when the weight concentration is more than 80%, the electric resistance increases and the transmission performance deteriorates. Therefore, since the internal resistance increases,
Electric energy cannot be effectively extracted from the battery, resulting in poor performance as a battery separator.

The temperature-composition graph of the polymer and the organic substance can be easily prepared by a known method as shown in the above-mentioned literature and the like. When the liquid-liquid phase separation of the polyolefin resin and the liquid or solid organic substance results in inhomogeneous mixing of polymers such as polyethylene and polypropylene, the solid-liquid phase separation as in the present invention allows the mixing of polymers. Can be kept uniform. Therefore, a film having excellent strength and high-temperature characteristics can be obtained without performing rolling. In addition, since the rolling step can be omitted, control becomes easy and productivity is improved.

In order to heat and dissolve a polyolefin resin comprising a mixture of polyolefins in a liquid or solid organic substance and extrude it into a sheet, it can be extruded by a known means such as a single screw extruder or a twin screw extruder. It is desirable that a gear pump be interposed between the extruder and the die in order to reduce the thickness unevenness of the extruded sheet. More preferably, it is desirable to use a weight feeder or to control the screw rotation speed of the extruder by the pressure before the gear pump.

When a polyolefin resin comprising a mixture of polyolefins and a liquid organic substance are mixed, it is preferable that the polyolefin resin is charged from a hopper, and the liquid organic substance is charged from the middle of the extruder barrel for good workability. When the polyolefin resin and the solid organic substance are mixed, it is preferable that the polyolefin resin and the solid organic substance, which are a mixture of the polyolefin mixed in advance, and the solid organic substance are charged from the hopper. In the present invention, since ultrahigh molecular weight polyethylene is not used as the polyolefin resin, it is not particularly necessary to dissolve the polyolefin resin in a liquid or solid organic substance before putting it in the extruder. A polyolefin resin used in ordinary extrusion, injection, inflation or blow molding can be completely dissolved in a liquid or solid organic substance between the time of charging the hopper and the time of extrusion. For this reason, the required dissolution time is less than 10 minutes, and the production time can be significantly reduced. Further, the heating temperature at the time of dissolution is preferably 150 to 250 ° C. below the boiling point of the solvent.

In the present invention, the extruded resin temperature, the extruding speed and the like are not particularly limited, but the extruded resin temperature is preferably from 180 ° C. to 260 ° C.
It is preferable to extrude at an extrusion speed of m / min to 30 m / min. In the case where the molten mixture is extruded into a film or sheet through a die and cooled, it is preferable to cool with a roll set to a predetermined temperature. Further, a means such as an air knife may be used if desired. The distance from the die discharge section to the cooling section is not limited at all, but is from 5 cm to 1 cm.
m is preferable.

In order to extract a liquid or solid organic substance from the obtained sheet-like molded product, the extraction is carried out in a poor solvent for the resin and a good solvent for the liquid or solid organic substance, preferably at 20 to 90 ° C.
, And liquid or solid organic matter may be removed from the sheet-like molded product. As the extraction solvent, methanol,
Organic solvents such as alcohols such as ethanol, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran, and halogenated hydrocarbons such as 1,1,1-trichloroethane and methylene chloride.

Even when the liquid or solid organic substance is extracted from the sheet-like molded product, the liquid or solid organic substance remains partially. This is because a portion formed by a liquid or solid organic substance has a part in which a liquid or solid organic substance independently exists in addition to a part which becomes a hole. Actually, it is possible to extract the liquid or solid organic substance into carbon tetrachloride from a sheet-like molded product or a product obtained by cutting the obtained membrane into a square of about 5 mm by means such as a Soxhlet extractor. After adjusting the liquid or solid organic substance in carbon tetrachloride to an appropriate concentration, it can be detected and identified by a combination of gas chromatography, liquid chromatography, FT-IR, mass spectrometry and the like.

The contact between the sheet-shaped molded product and the extraction solvent can be carried out by a dipping method in which the sheet is dipped in a solvent at a predetermined temperature for a predetermined time and pulled up. Alternatively, it can be carried out by a method of continuously flowing or jetting the extraction solvent onto the surface of the sheet-like molded product. In order to continuously perform the extraction process, a multi-stage countercurrent method is used in which the extraction solvent flows in a direction opposite to the traveling direction of the sheet while continuously feeding the sheet through a roll through a multi-sectioned tank. Is good.

The drying method in the step of drying the molded article after the extraction treatment includes, for example, a method of blowing air or nitrogen gas, a method of drying under reduced pressure, a method of passing through a hot air or hot nitrogen gas drying chamber, and a method of drying the molded article. A known method such as a method of contacting a metal roll heated to a temperature at which heat shrinkage can be tolerated can be used. The stretching step refers to a means for extending a sheet-like molded product to a desired film thickness. In the present invention, it is not necessary to perform rolling such that pressure is applied simultaneously from both sides of the film. In particular, when using a stretching machine, the sheet is stretched in a machine direction (uniaxial direction) or biaxial direction under a predetermined condition selected from a range of a stretching temperature of 80 to 140 ° C. to adjust to a desired film thickness. The obtained microporous porous membrane is obtained. Here, the order of the extraction and the stretching step is not particularly limited, but the stretching is performed before extracting the liquid or solid organic matter, the liquid or solid organic matter is extracted from the stretched matter, and dried. When the film is further stretched, the permeation performance and strength of the obtained polyolefin microporous membrane become high, which is desirable. The preferred stretching ratio is 2 to 20 in area ratio.
0 times is preferable, and 5 to 100 times is more preferable.

The polyolefin microporous membrane thus obtained has a thickness of 10 to 100 μm and an average pore size of 0.01 to 1 μm.
μm, porosity 30-80%, elastic modulus in machine direction 5000k
gf / cm ² or more, the electric resistance 10 .OMEGA.cm ² or less, more preferably 5Omucm ² or less, air permeability 1000 seconds or less, no Anaka temperature 100 to 145 ° C., film breakage temperature 160 ° C. or more high strength, low electrical resistance, high It is a low-cost single-membrane microporous membrane excellent in permeation performance and safety.

[0034]

EXAMPLES Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not particularly limited to the examples. In addition, the measuring method and evaluation method in an Example are as follows. (1) Film thickness A dial gauge (minimum scale: 1 μm) was used. (2) Porosity porosity was calculated from the following equation.

Porosity = pore volume / membrane total volume × 100 pore volume = water-containing weight-absolute dry weight (3) Modulus of elasticity in machine direction Measured with an Instron type tensile tester in accordance with ASTM-D-882. did. (4) Average Pore Diameter Based on ASTM-F-316-70, evaluation was made by a half dry method. The upper limit of the measurement pressure is 10 kgf / c
It was m ^2. (5) Maximum pore size Calculated from the bubble point in ethanol according to ASTM-E-128-61. (6) Permeability The air permeability was evaluated.

The air permeability conforms to JIS P-8117,
Using a B-type Gurley-type densometer manufactured by Toyo Seiki, the time required for the mark scale from 0 to 100 was measured with a stopwatch. (7) Electric resistance It is 25 by an Ando Electric AG-4311 type LCR meter.
Measured in ° C.

Electrolyte: 50% by volume of propylene carbonate 50% by volume of dimethoxyethane 1 mol / dm ^{3 of} lithium perchlorate ³ Condition: Platinum black electrode Distance between electrode plates 3mm Electrode plate area 0.785cm ² AC 1kHz _Z Assembly: described in FIG. (8) Melt index Unless otherwise specified, it shall conform to ASTM-D-1238. (9) Viscosity average molecular weight (Mv) The intrinsic viscosity [η] at a measurement temperature of 135 ° C. was measured using a solvent (decalin), and calculated by the following equation.

[Η] = 6.2 × 10 ⁻⁴ Mv ^0.7 (Chiang's Formula) (10) High Temperature Properties A 6 cm × 6 cm membrane sample is prepared, and the four corners are fixed so as not to be thermally deformed, and the temperature is adjusted to a predetermined temperature. After being left in the set gear oven for 30 minutes, it was immediately taken out of the gear oven, and the electric resistance of the central portion of the heat-treated sample obtained by air cooling was measured. At a predetermined set temperature, a temperature at which the electrical resistance of the obtained heat-treated sample became 50 times the electrical resistance at 25 ° C. was defined as a nonporous temperature, and a temperature at which film breakage was observed was evaluated as a film breakage temperature. (11) Fraction with a molecular weight of 1,000,000 or less in the whole system It is determined from an integral curve of GPC measurement.

GPC (gel permeation chromatography) measurement Equipment: WATERS 150-GPC Temperature: 140 ° C. Solvent: 1,2,4-trichlorobenzene Concentration: 0.05% (Injection volume: 500 microliter) Column: Shodex GPC AT-807 / S1
This Tosoh TSK-GEL GMH ₆ -HT 2 pieces Dissolution conditions: 160 ° C., 2.5 hours Calibration curve: Measure a polystyrene standard sample, use polyethylene conversion constant (0.48),
(12) Detection of solvent in membrane Approximately 40 g of a sample was cut out into a size of about 2 mm square and extracted with carbon tetrachloride using a Soxhlet extractor at a water bath temperature of 95 ° C. for 10 hours. The extract was concentrated to a 50 ml solution by an evaporator. This solution was detected and identified by gas chromatography, FT-IR, and mass spectrometry.

Gas chromatography equipment: Yanagimoto 3810 Temperature: INJ 300 ° C .; OVEN 230 ° C. (injection amount: 20 microliter) Column: Silicone OV-17 5% 1 m Carrier gas: Helium Detector: FID (13) Polymer / Organic substance temperature-composition graph (determination of solid-liquid phase separation) A polymer / organic substance having several kinds of compositions was melt-kneaded with a plasticizer manufactured by Brabender Co., and the obtained sample was about 5 m.
g by Seiko-Electronic Industries Co., Ltd., differential scanning calorimeter D
Using SC210, under nitrogen stream at 200 ° C for 10
After standing for 10 minutes, the exothermic peak temperatures of polyethylene and polypropylene were measured at a temperature lowering rate of 10 ° C./min, and a graph of the exothermic peak temperature-composition was prepared. Liquid phase separation or liquid-liquid phase separation was determined.

[0041]

Example 1 Melt index (measuring load 5 kg, 1
90 ° C.) 32% by weight of high-density polyethylene of 0.25 g / 10 min, and melt index of 0.5 g / 10
min 8% by weight of a mixture of polypropylene with a viscosity of 7
5.8 cSt (37.8 ° C.) of liquid paraffin (60% by weight) was added, and the mixture was supplied to a film forming apparatus having a 650 m / m width T die attached to a 30 m / m φ twin screw extruder to have a thickness of 290 m.
A sheet-shaped raw film of μm was obtained. The resin temperature was 200 ° C., the extrusion speed was 0.4 m / min, and the distance from the die discharge section to the cooling roll was 10 cm. The film was heated at a temperature of 100 ° C. and a speed of 500 mm with a biaxial stretching tester manufactured by Iwamoto Seisakusho Co., Ltd.
/ Min, twice in the MD direction parallel to the extrusion direction,
After stretching 3 times in the CMD direction perpendicular to the extrusion direction, using 1,1,1-trichloroethane as an extraction solvent for liquid paraffin, immersing in 1,1,1-trichloroethane for 20 minutes to extract and remove liquid paraffin And dried to obtain a stretched film. Further, the film was doubled in the MD direction parallel to the extrusion direction and twice in the CMD direction perpendicular to the extrusion direction at a temperature of 120 ° C. and a speed of 500 mm / min using a biaxial stretching tester manufactured by Iwamoto Seisakusho Co., Ltd. The film was stretched twice to obtain a microporous porous film. The membrane obtained as described above had the performance shown in Table 1, and had high strength, low electric resistance, high permeability, and small pore size.

The viscosity average molecular weight of the used polyethylene having a melt index (measuring load: 5 kg, 190 ° C.) of 0.25 g / 10 min was 200,000. Further, when the molecular weight of the obtained film was measured by GPC measurement, a chart as shown in FIG. 2 was obtained, and the fraction where the molecular weight of the entire system was 1,000,000 or less was 92 wt%.

Further, the content of liquid paraffin in the obtained membrane was 1 ppm. The liquid paraffin used showed a solid-liquid phase separation with respect to polyethylene and polypropylene, and the intrinsic viscosity dependent coefficient of the used liquid paraffin with respect to polyethylene was 0.65, and the intrinsic viscosity of polypropylene with respect to polypropylene was dependent on the high molecular weight. The sex coefficient was 0.6 and the flash point was 250 ° C.

[0044]

Example 2 A microporous porous membrane was obtained in the same manner as in Example 1 except that the film was stretched at a speed of 300 mm / min. As shown in Table 1, the obtained film exhibited lower electric resistance by reducing the stretching speed.

[0045]

Example 3 The polyethylene, polypropylene, and liquid paraffin described in Example 1 (40, 10, and 50% by weight) were applied to a film forming apparatus in which a 650 m / m width T die was attached to a 30 m / m twin screw extruder. The sheet was supplied, and a sheet-shaped raw film having a thickness of 300 μm was obtained in the same manner as in Example 1. In the same manner as in Example 1, a microporous porous membrane was obtained.

The film obtained as described above had the properties shown in Table 1.

[0047]

Example 4 The polyethylene, polypropylene, and liquid paraffin described in Example 1 (48, 12, and 40% by weight) were applied to a film forming apparatus in which a 650 m / m width T die was attached to a 30 m / m twin screw extruder. The sheet was supplied, and a sheet-shaped raw film having a thickness of 400 μm was obtained in the same manner as in Example 1. Using a biaxial stretching tester manufactured by Iwamoto Seisakusho, at a temperature of 100 ° C and a speed of 5
Under the condition of 00 mm / min, after stretching 3 times in the MD direction parallel to the extrusion direction and 3.5 times in the CMD direction perpendicular to the extrusion direction, 1,1,1-trichloroethane was used as an extraction solvent for liquid paraffin. , 1,1,1-trichloroethane for 20 minutes to extract and remove the liquid paraffin, followed by drying to obtain a stretched membrane. Further, the film was subjected to a temperature of 120 ° C. and a speed of 500 m with a biaxial stretching tester manufactured by Iwamoto Seisakusho Co., Ltd.
3 m in the MD direction parallel to the extrusion direction under the condition of m / min.
The film was stretched three times in the CMD direction perpendicular to the extrusion direction to obtain a microporous porous membrane. The film obtained as described above had the performance shown in Table 1.

[0048]

Example 5: Melt index 5.0 g / 10 min
A mixture of 8% by weight of high-density polyethylene, 24% by weight of high-density polyethylene having a melt index of 0.25 g / 10 min, and 8% by weight of polypropylene described in Example 1 has a viscosity of 75.8 cSt (3
7.8 ° C.) of liquid paraffin (60% by weight)
The m / mφ twin screw extruder was supplied to a film forming apparatus equipped with a 650 m / m width T die, extruded into a sheet, and a microporous membrane was obtained in the same manner as in Example 1.

The film obtained as described above had the properties shown in Table 1.

[0050]

Embodiment 6 Melt index: 20.0 g / 10 mi
n, 8% by weight of linear low-density polyethylene, high-density polyethylene 24 having a melt index of 0.25 g / 10 min
Wt. And a mixture of 8% by weight of the polypropylene described in Example 1 with a viscosity of 75.8 cSt used in Example 1.
(37.8 ° C.) liquid paraffin 60% by weight,
It is supplied to a film forming apparatus having a 650 m / m width T die attached to a 30 m / mφ twin screw extruder, and extruded into a sheet.
In the same manner as in Example 1, a microporous porous membrane was obtained.

The film obtained as described above had the properties shown in Table 1.

[0052]

Example 7 Melt index: 0.30 g / 10 mi
n, 8% by weight of low density polyethylene, 24% by weight of high density polyethylene having a melt index of 0.25 g / 10 min, and 8% by weight of polypropylene described in Example 1 were mixed with a viscosity of 75.8 cSt ( 3
7.8 ° C.) of liquid paraffin (60% by weight)
The m / mφ twin screw extruder was supplied to a film forming apparatus equipped with a 650 m / m width T die, extruded in a sheet form, and a microporous porous film was obtained in the same manner as in Example 1.

The film obtained as described above had the properties shown in Table 1.

[0054]

Example 8: Melt index: 0.30 g / 10 mi
n, 8% by weight of linear low-density polyethylene, high-density polyethylene 24 having a melt index of 0.25 g / 10 min
% By weight, 6% by weight of polypropylene described in Example 1 and polymethylpentene TR manufactured by Mitsui Petrochemical Industries, Ltd.
To a mixture of 2% by weight of X (MX002), 60% by weight of liquid paraffin having a viscosity of 75.8 cSt (37.8 ° C.) used in Example 1 was added, and the mixture was fed to a 30 m / mφ twin screw extruder.
The same procedure as in Example 1 was performed except that the mixture was supplied to a film forming apparatus equipped with a 50 m / m width T die, extruded into a sheet, extruded at a resin temperature of 240 ° C., and using methyl ethyl ketone as an extraction solvent. Thus, a microporous porous membrane was obtained.

The membrane obtained as described above had the properties shown in Table 1.

[0056]

Example 9 A microporous porous membrane was obtained in the same manner as in Example 1 except that trichlorobenzene was used as the liquid organic substance. The obtained film had the performance described in Table 1. The used trichlorobenzene exhibited solid-liquid phase separation for polyethylene and polypropylene, and the intrinsic viscosity coefficient of intrinsic viscosity of polyethylene used for polyethylene was 0.70, and the intrinsic viscosity coefficient of polypropylene for polypropylene was high molecular weight dependence. 0.65, flash point 110 ° C
Met. The residual amount of trichlorobenzene is 3 ppm
Met.

[0057]

Comparative Example 1 Melt index (measuring load 5 kg, 1
90 ° C.) 0.25 g / 10 min 16% by weight of high-density polyethylene, and melt index 0.5 g / 10
A microporous membrane was obtained in the same manner as in Example 1 except that 80% by weight of diphenyl ether was used in a mixture of 4% by weight of polypropylene in the same manner as in Example 1. High density polyethylene and polypropylene and diphenyl ether showed liquid-liquid phase separation.

As shown in Table 1, the film obtained as described above had insufficient high-temperature characteristics.

[0059]

Comparative Example 2 Melt index 0.80 g / 10 mi
n of 8% by weight of polyethylene, 24% by weight of ultrahigh molecular weight polyethylene having a viscosity-average molecular weight of 3,000,000, and 8% by weight of polypropylene described in Example 1 were mixed with 75.8 cSt (37.8 cSt) used in Example 1. C)), and the mixture was fed to a film forming apparatus equipped with a 30 m / mφ twin screw extruder equipped with a 650 m / m width T die, and extruded into a sheet. Had a sharkfish-like shape and lacked film-forming properties.

[0060]

Comparative Example 3 Melt Index: 0.25 g / 10 mi
35% by weight of high-density polyethylene with a viscosity of 75.8 cS
t (37.8 ° C.), 65% by weight of liquid paraffin was added, and a 30 m / mφ twin screw extruder was supplied with a film forming apparatus equipped with a 650 m / m width T die, and extruded into a sheet. A sheet-like raw film having a thickness of 290 μm was obtained. next,
After rolling and producing a film having a thickness of 40 μm,
It was immersed in 1,1,1-trichloroethane for 20 minutes to extract and remove liquid paraffin, and dried to obtain a microporous porous membrane.

The film breaking temperature of the obtained film was as low as 145 ° C.

[0062]

[Table 1]

[0063]

According to the method for producing a microporous polyolefin microporous membrane of the present invention, the polyolefin resin and the liquid or solid organic substance are subjected to solid-liquid phase separation, so that even if the resin has poor compatibility, even if the resin has a poor uniformity, It can be formed into a sheet in a short time without the drawback of the above, and it is possible to control the mixing property of a mixture of polyolefins composed of polyethylene and polypropylene, and to obtain a porous film having excellent high-temperature properties and strength without rolling. Can be.

Further, according to the present invention, when shaping into a sheet, the shaving of a forming machine, a die and the like is small, and since the formed sheet-shaped product has few non-uniform points, it is stretched. In this case, the number of defective holes and the like is small, and efficient production can be achieved. Therefore, a low-cost single-membrane microporous membrane excellent in performance, having high strength, low electric resistance, high permeability, and excellent high-temperature characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic view of an assembly for measuring electric resistance of a microporous porous membrane of the present invention.

FIG. 2 is a chart of GPC measurement results of Example 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Electrode 2 Teflon packing 3 Membrane 4 Teflon packing of outer diameter 2cm, inner diameter 1cm, thickness 1mm 5 electrode

Claims (2)

(57) [Claims] 1. A step of heating and dissolving a polyolefin resin comprising a mixture of polyethylene and polypropylene having a viscosity average molecular weight of less than 1,000,000 in a liquid or solid organic substance at a weight concentration of 30% or more. Extruding the solution obtained in the step into a sheet, and separating the polyolefin resin and the liquid or solid organic substance into a solid (crystal) -liquid phase (c) from the sheet obtained in the above step (b) From the step of extracting liquid or solid organic matter and stretching it from both sides of the membrane without applying pressure at the same time, or from the step of stretching from both sides of the membrane without applying pressure at the same time, and extracting the liquid or solid organic matter from A method for producing a polyolefin microporous porous membrane. 2. The step (c) is a step of extracting the liquid or solid organic matter from both sides of the membrane without applying pressure at the same time, and further extending without applying pressure simultaneously from both sides of the membrane. The method for producing a polyolefin microporous porous membrane according to claim 1, comprising a step.