JP3003830B2 - Laminated porous film and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated porous film having a high peeling strength, a fine and uniform pore diameter, and a wide temperature range for maintaining nonporosity by heat, and a method for producing the same. More specifically, the present invention relates to a laminated porous film obtained by stretching a three-layer laminated film in which polypropylene and polyethylene are laminated and making the film porous, and relates to the field of electronic devices such as battery separators, electrolytic capacitor separators, and insulators. It can be widely used in medical fields such as artificial lung membranes, plasma purification membranes, respiratory medical clothing, water treatment fields such as bacteria and virus filtration, gas separation fields, and air conditioning fields.

[0002]

2. Description of the Related Art Conventionally, a large number of nonporous laminated films and single-layer porous films have already been known, but there have been few proposals for laminated porous films.
In recent years, with the advancement of technology, the demand for high-precision films according to the purpose of use has been increasing in various fields, and laminated porous films have attracted attention.

[0003] Taking a battery as an example, batteries have both positive and negative
A separator is interposed to prevent short-circuiting of the pole.
Annual energy density, high electromotive force, low self-discharge
Non-aqueous electrolyte batteries such as lithium batteries, especially lithium secondary batteries
Ponds have been developed and put into practical use. Lithium electricity
Positive electrode of the pond, for example, metal lithium, lithium and other
Alloys with metals, lithium ions such as carbon and graphite
ON by the ability to absorb ON or by intercalation
Organic materials with the ability to store lithium ions
Known conductive polymer materials are known, and
For example, (CF_x)_nFluorinated graphite represented by M
nO_Two, V_TwoO_Five, CuO, Ag_TwoCrO_Four, TiO _Two
Metal oxides, sulfides, and chlorides are known.

As a non-aqueous electrolyte, ethylene carbonate
, Propylene carbonate, γ-butyrolactone,
Acetonitrile, 1,2-dimethoxyethane, tetrahi
LiPF for organic solvents such as drofuran₆, LiBF_Four, L
iCLO_Four, LiCF_ThreeSO _ThreeDissolved electrolytes such as
Is used. But lithium is particularly reactive
If an abnormal current flows due to an external short circuit or incorrect connection,
If the battery temperature rises significantly,
There is a concern of causing thermal damage. Such danger
To avoid this, the following types of conventional separators were used.
The use of various porous films has been proposed.

A single-layer porous film of a thermoplastic resin such as polyethylene or polypropylene (Japanese Patent Publication No. 46-401)
No. 19, Japanese Patent Publication No. 55-32531, Japanese Patent Publication No. 5
9-37292, JP-A-60-23954, JP-A-2-75151, U.S. Pat.
No. 538). Porous films made of a mixture of polyethylene having different molecular weights or a mixture of polyethylene and polypropylene (JP-A-2-21559, JP-A-2-33430)
9 and JP-A-5-331306). A porous film using a thermoplastic resin or a non-woven fabric as a support (JP-A-3-245457, JP-A-1-25883)
58 gazette). Laminated porous films in which a plurality of porous films of thermoplastic resins of different materials are laminated (JP-A-62-10857, JP-A-63-308866, Japanese Patent Publication No. 3-65)
776, JP-A-6-20671). In addition, there is known a laminated porous film obtained by bonding or thermocompression bonding two porous films with or without an adhesive.

The basic concept of using such a single-layer or laminated porous film as a separator is to prevent a short circuit between the two electrodes, maintain the battery voltage, etc., and to control the internal temperature of the battery due to an abnormal current or the like. When the temperature rises above the temperature, the porous film is made nonporous, in other words, the pores are closed, the electric resistance is increased so that ions do not flow between the two electrodes, the battery function is stopped, and the temperature rises excessively. The purpose of the present invention is to prevent the danger of fire and the like caused by fire and to ensure safety. The function of preventing danger due to an excessive rise in temperature is a very important function as a battery separator, and is generally called non-porous or shutdown (abbreviated as SD).

In the present specification, the point at which the gas permeation rate (Gurley value: seconds / 100 cc) of the porous film exceeds 6000 is referred to as the nonporous start temperature or the SD start temperature. The gas permeation speed may be referred to as gas permeation rate. In a battery separator, if the non-porous starting temperature is too low, the flow of ions is prevented by a slight rise in temperature, which poses a problem in terms of practicability. There is a problem in terms of safety because there is a risk of causing ignition. Generally, it has been recognized that the nonporous start temperature is preferably 110 to 160 ° C, preferably 120 to 150 ° C. In this specification, the upper limit temperature of the temperature at which the nonporous or SD state is maintained is referred to as the nonporous maintenance upper limit temperature or the heat-resistant temperature, and the temperature range from the nonporous start temperature or the SD start temperature to the heat-resistant temperature or The temperature range is referred to as a nonporous maintenance temperature region or a heat-resistant temperature range. In a battery using a porous film as a separator, if the temperature in the battery rises above the non-porous maintenance upper limit temperature, the film is melted and broken, the non-porous state is lost, and The ions flow out, causing a further rise in temperature. Therefore, a separator for a battery is required to have an appropriate non-poration starting temperature, a high non-poration maintaining upper limit temperature, and a wide non-poration maintaining temperature range. Further, in addition to the characteristics relating to non-porosity, battery separators have low electric resistance, high mechanical strength such as tensile elasticity, and small variations in thickness unevenness and electric resistance. Required.

[0008]

Various types of porous films have been proposed as described above. According to the research of the present inventors, for example, as a separator for batteries,
The single-layer porous film of polypropylene has a drawback that the non-porous onset temperature is about 170 ° C or more, which is close to the melting point of lithium, and the single-layer porous film of polyethylene has a non-porous onset temperature of about 135 ° C. Although the non-porous maintenance upper limit temperature is about 145 ° C., the non-porous maintenance temperature range is too narrow, and the tensile modulus is low, so that elongation is likely to occur in the battery production process and the productivity is high. However, there is room for further improvement in a single layer porous film of a thermoplastic resin in terms of safety and the like.

A porous film obtained by making a polyethylene mixture having a different molecular weight into a porous material has a non-porous maintaining upper limit temperature of about 150 ° C. and a tensile modulus of 3,400 kg / cm ^2.
The degree is slightly higher than that of the single-layer porous film of polyethylene. A sea-island structure porous film obtained by stretching a mixture of polyethylene and polypropylene to make it porous has a nonporous maintenance upper limit temperature of about 180 ° C. and a tensile modulus of elasticity of about 4200 to 6400 kg / cm ² , which is higher than that of the polyethylene mixture. Although the functions and mechanical properties are improved, they cannot be said to be sufficient yet, and the formation of a sea-island structure which is made porous by stretching the mixture is likely to cause variations in quality, and has a problem in its reproducibility.

A porous film using a non-woven fabric or the like as a support not only has a drawback in safety due to the non-woven fabric or the like, but also has a problem in maintaining non-porosity when using a porous film such as the above polyethylene or polypropylene. Similarly, improvement in reliability at high temperatures is required.

Regarding a laminated porous film obtained by laminating a plurality of porous films of a thermoplastic resin of different materials, any of the films is previously made porous by stretching or the like to produce two types of porous films of different materials. After this, they are laminated, stretched, pressed, bonded by an adhesive or the like. The laminated porous film thus obtained should basically have the characteristics as a battery separator, but in actual production, the positions of the holes of the respective films are shifted due to superposition. On the other hand, the laminated porous film, in which micropores often do not communicate from the front surface to the back surface, tends to increase the electric resistance. Also, film curls and wrinkles are particularly likely to occur. Although it is already porous, there is a surface that is difficult to bond itself. However, if pressure bonding or bonding is performed at a high temperature, the holes are crushed and the function as a porous film is lost, and the electric resistance increases. Also, in order to maintain the function as a porous film, if the film is pressure-bonded or adhered lightly, the peel strength is low, so that the film is peeled off, wrinkled, stretched, etc. in the process of incorporating the separator into the battery, and the quality of the battery is reduced. The problem remains. Further, when the porous films are stretched by overlapping, not only basically the number of production steps is increased, but also the above problems are more or less likely to occur, and the Galley value is low, so that it is improved as a battery separator. There is room for

The present inventors have already proposed a single-layer porous film (Japanese Patent Publication No. 11620/1990) and a laminated porous film in which a polyethylene porous film and a polypropylene porous film are laminated (Japanese Patent Laid-Open No. 6-20671). Publication), etc., in view of the above points, in view of the above points, the porous film, particularly having a fine and uniform pore diameter, at an appropriate non-poration start temperature, high non-porous maintenance upper limit temperature, With the task of developing a thermoplastic laminated porous film that has a wide nonporous maintenance temperature range, high peel strength and high tensile elasticity, and that can improve the difficulties of conventional laminated porous films, we have conducted extensive research. As a result, the present invention has been achieved.

[0013]

SUMMARY OF THE INVENTION The present invention provides a laminated porous film comprising a porous polypropylene film and a porous polyethylene film obtained by stretching a three-layer laminated film in which a polypropylene film and a polyethylene film are alternately laminated. And the birefringence of the polypropylene film is 10 × 10 ^{−3 to} 20 × 10 ⁻³ and 1
The elastic recovery at 100% elongation after heat treatment at 50 ° C. for 30 minutes is 80 to 94%, and the birefringence of the polyethylene film is 20 × 10 ⁻³ to 40 × 10 ⁻³ , and at the time of 50% elongation. The elastic recovery rate is 20 to 50%, the maximum porous diameter of the laminated porous film is 0.02 to 2 μm, the porosity is 30 to 80%, and the delamination strength is 3 to 60 g / 15 m.
m, a nonporous starting temperature of 135 to 140 ° C, a nonporous maintaining upper limit temperature of 180 to 190 ° C, and a curl degree of 5 mm or less.

Further, according to the present invention, the polypropylene film and the polyethylene film may be alternately formed in a range of 120 to 1 so that the film is alternately formed.
A three-layer laminated film thermocompressed at a temperature of 40 ° C.
After heat treatment in the temperature range of 0 to 140 ° C, minus 20
5 to 200 while being maintained at a temperature of 50 ° C. to + 50 ° C.
% Stretched, then stretched at 100 to 400% while being maintained at a temperature of 70 to 130 ° C., and then heat-treated at a temperature higher by 5 to 45 ° C. than the temperature of the latter stretching. Related to the production method. Furthermore, the present invention provides a three-layer laminated film thermocompressed at a temperature of 120 to 140 ° C. so that a polypropylene film and a polyethylene film are alternately formed, and then heat-treating the laminated film at a temperature of 110 to 140 ° C. After stretching 10 to 100% while maintaining the temperature of 35 ° C, and then stretching 100 to 400% while maintaining the temperature of 70 to 130 ° C, 5 to 45 ° C higher than the temperature at the time of the latter stretching. Heat treatment at a temperature, the maximum pore size is 0.02 to 2 μm, and the porosity is 30 to 80.
%, Delamination strength of 3 to 60 g / 15 mm, nonporous start temperature of 135 to 140 ° C., nonporous maintenance upper limit temperature of 180
The present invention relates to a method for producing a laminated porous film, characterized in that a laminated porous film having a temperature of up to 190 ° C. is obtained. The present invention also provides
Birefringence is 10 × 10 ^{−3 to} 20 × 10 ⁻³ and ³ at 150 ° C.
The elastic recovery at 100% elongation after heat treatment for 0 minutes is 80 to 9
4% polypropylene film with birefringence of 20 × 10
^-3 to 40 × 10 ^-3 and the elastic recovery rate at 50% elongation is 20
After heat-treating a three-layer laminated film at a temperature of 110 to 140 ° C. in a temperature range of 110 to 140 ° C., a temperature of −20 ° C. to plus 50 ° C. After stretching at 5 to 200% while maintaining the temperature, and then stretching at 100 to 400% while maintaining the temperature at 70 to 130 ° C, heat-treating at a temperature higher by 5 to 45 ° C than the temperature at the time of the latter stretching. The present invention relates to a method for producing a laminated porous film.

In the present invention, the main point is that a three-layer laminated film in which a non-porous polypropylene film and a polyethylene film are alternately laminated is stretched and porous. Polypropylene and polyethylene constituting each layer may have different molecular weights in each layer. Polypropylene is preferably high in stereoregularity, and polyethylene is preferably high density polyethylene, but may be medium density polyethylene. These polypropylene and polyethylene may contain additives such as a surfactant, an antioxidant, a plasticizer, a flame retardant, and a coloring agent. If the three-layer laminated film has the property that the thickness of the film is uniform and has the property of being made porous by stretching, it can be a polyethylene film and a polypropylene film obtained by molding separately, even if they are laminated at once by co-extrusion. They may be stacked. However, considering the equipment such as a molding machine, the ease of the molding operation, and the like, it is advantageous to form the latter separately. As the molding method, melt molding using a T-die is suitable, but an inflation method, a wet solution method, or the like can also be employed. When a film is separately melt-molded by a T-die, the film is generally formed at a draft ratio of 10 to 1000, preferably 200 to 500 at a temperature 20 to 60 ° C. higher than the melting temperature of each resin, and the take-off speed is Although not particularly limited, it is usually 10 to 50 m / min. In particular, the birefringence and elastic recovery of the obtained film affect the pore size, porosity, delamination strength, mechanical strength and the like of the laminated porous film after stretching.

The birefringence of the polypropylene film is 10 × 10 ^{−3 to} 20 × 10 ⁻³ , preferably 11 × 10 ^−3.
~ 14 × 10 ^-3 and after heat treatment at 150 ° C for 30 minutes
The elastic recovery at 0% elongation is 80 to 94%, preferably 8
Preferably, it is in the range of 4-92%. The polyethylene film has a birefringence of 20 × 10 ⁻³ to 40 × 1.
0 ⁻³ , preferably 25 × 10 ^{−3 to} 35 × 10 ⁻³ , and 50
% Elastic recovery at elongation of 20 to 50%, preferably 25%
Preferably it is in the range of ４０40%. If the birefringence of the polypropylene film and the polyethylene film deviates from these ranges, it is not suitable because porosity cannot be sufficiently obtained, and the degree of porosity is not sufficient even if the elastic recovery rate deviates from the above range, which is not preferable. . The thickness of each of these films is related to the thickness, application, and the like of the laminated porous film after stretching and making it porous, but it is usually appropriate that each film has a thickness of 5 to 20 μm, and more preferably 10 to 15 μm.

In the present invention, the birefringence is a value measured using a Bellec compensator under a crossed Nicols using a polarizing microscope. The elastic recovery rate is based on the following equations (1) and (2). Equation (1) is for a polypropylene film, and equation (2) is for a polyethylene film. In addition, the polypropylene film is 3 at 150 ° C.
After heat treatment for 0 minutes, the sample was set in a tensile tester at 25 ° C. and 65% relative humidity with a sample width of 10 mm and a length of 50 mm.
mm / min. After elongating to 100% at the same speed, immediately relax at the same speed, and measure the polyethylene film in a tensile tester at 25 ° C and 65% relative humidity with a sample width of 15 mm and a length of 2 inches. 2 inches / min. After elongating to 50% at the speed, the sample was held in the stretched state for 1 minute and then relaxed at the same speed.

[0018]

(Equation 1)

[0019]

(Equation 2)

The polypropylene film and the polyethylene film are laminated by thermocompression bonding. In the case of laminating three films, they are passed through heated rolls and thermocompressed. Specifically, the film is unwound from three sets of roll roll stands, nip and crimped between heated rolls and laminated. The laminates need to be thermocompression bonded so that the birefringence and elastic recovery of each film do not substantially decrease. Also, the three sheets are laminated so that the front and back are made of polypropylene and the center is made of polyethylene, so there is no film curl, it is hard to be damaged, and the heat resistance, mechanical strength etc. of the laminated porous film are good, It is also suitable for satisfying characteristics such as safety and reliability as a battery separator.

The temperature of the heated roll, in other words, the thermocompression bonding temperature is 120 to 140 ° C., more preferably 125 ° C.
~ 135 ° C is preferred. If the temperature is too low, the peel strength between the films is weak and peeling occurs in the subsequent stretching step,
Conversely, if it is too high, the polyethylene melts, and the birefringence and elastic recovery of the film are greatly reduced, and a laminated porous film satisfying the intended problem cannot be obtained. Nip pressure is 1-3
kg / cm ² , and the unwinding speed is 0.5 to 8 m / min.
Is appropriate. The peel strength of the laminated film is 3-6.
A range of 0 g / 15 mm is preferred. The thickness of the laminated film is not particularly limited, but generally, 20 to 60 μm is appropriate.

The laminated film is heat-treated before stretching. The heat treatment is carried out by a heating air circulation oven or a heating roll under a constant length or under a tension of 3% to 10%.
The heat treatment temperature is 110-140 ° C, preferably 115
The range of ~ 130 ° C is preferred. If the temperature is low, the porous material is not sufficiently made porous. If the temperature is too high, the polyethylene is disadvantageously melted. The heat treatment time may be about 3 seconds to 3 minutes.

The heat-treated laminated film is stretched and made porous to form a laminated porous film. The stretching is preferably performed at a low temperature and then at a high temperature. If only one of the stretchings is performed alone, the polypropylene and the polyethylene are not sufficiently made porous or the delamination strength is lowered, so that the characteristics as a battery separator deteriorate.

The low-temperature stretching is usually performed at a peripheral speed difference of a stretching roll. The temperature of the low-temperature stretching is preferably from -20 ° C to 50 ° C, particularly preferably from 20 to 35 ° C. If the stretching temperature is too low, the film is likely to break during work,
Conversely, if it is too high, porosity becomes insufficient, which is not preferable. The draw ratio at low temperature is 5 to 200%, preferably 10 to 200%.
The range is 100%. If the stretching ratio is too low, only a material having a predetermined porosity is small, and if it is too high, a material having a predetermined porosity and pore size cannot be obtained, so the above range is appropriate. In the present invention, the low-temperature stretching ratio (E ₁ ) complies with the following equation (3). L _{1 in the} formula (3) means the film size after the low temperature stretching, and L ₀ means the film size before the low temperature stretching.

[0025]

(Equation 3)

The laminated film stretched at a low temperature is stretched at a high temperature. High-temperature stretching is usually performed in a heated air circulation oven at a peripheral speed difference of a stretching roll. Although the number of stages is not particularly limited, 7-14 stages are appropriate. The high-temperature stretching temperature is preferably from 70 to 130 ° C, particularly preferably from 80 to 125 ° C.
Outside of this range, it is not suitable because it is not sufficiently porous. In addition, high temperature stretching is 40 to 100 ° below the temperature of low temperature stretching.
C It is preferable to carry out at a high temperature. High-temperature stretching ratio is 1
The range is from 00 to 400%. If the draw ratio is too low,
The above range is preferable since the gas permeability is too low, and if it is too high, the gas permeability becomes too high. In the present invention, the high-temperature stretching ratio (E ₂ ) complies with the following equation (4). In the formula (4), L ₂ means the film size after high-temperature stretching, and L ₁ means the film size after low-temperature stretching.

[0027]

(Equation 4)

In the present invention, after the low-temperature stretching and the high-temperature stretching, heat treatment is performed at a temperature higher by 5 to 45 ° C. than the high-temperature stretching temperature. In order to prevent the film from shrinking in the stretching direction due to the residual stress applied during stretching, a heat-shrinking method is used to reduce the length of the film after stretching by 10 to 50%, and the heat treatment is regulated so that the dimension in the stretching direction does not change. The heat treatment is performed by a method generally called heat setting.
By this heat treatment, a laminated porous film having high delamination strength and satisfying the desired problem of good dimensional stability can be obtained.

In the present invention, the laminated porous film has a porosity of 3 although it varies somewhat depending on the selection of the production conditions.
0 to 80%, preferably 35 to 60%, and the maximum pore size is 0.
It is 02 to 2 μm, preferably 0.08 to 0.5 μm. If the porosity is too low, the function when used as a battery separator is not sufficient, and if it is too high, the mechanical strength deteriorates. If the maximum pore size is too small, the ion mobility is poor when used as a separator for a battery or a separator for an electrolytic capacitor.
It is not suitable for applications such as air-conditioning, because the resistance increases, and if the maximum pore size is too large, ion separation is too large in battery separators and electrolytic capacitor separators, and bacteria and viruses are used in the water treatment field. Etc. are not sufficiently removed, and in the medical field, it becomes insufficient as a plasma purification membrane.

In the present invention, the gas permeation rate of the laminated porous film is 150 to 1500, preferably 300.
８００800. When used as a battery separator, if the gas permeation rate is too slow, the flow of ions is suppressed, and if it is too fast, the flow of ions is too fast and the temperature rise at the time of failure increases, which is not appropriate. . The delamination strength is 3 to 60 g / 15 mm. The degree of curl of the laminated porous film is 5 mm or less, preferably 3 mm or less, and more preferably 2 mm or less. If the delamination strength is low,
For example, film peeling, curling, elongation, etc. are likely to occur in the manufacturing process of a battery separator, which is problematic in terms of product quality. The overall thickness of the laminated porous film is appropriately selected depending on the application and is not particularly limited. However, in the case of a battery separator, the thickness is preferably 20 to 50 μm from the viewpoint of mechanical strength, performance, miniaturization, and the like.

[0031]

Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Using a T-die having a discharge width of 1000 mm and a discharge lip opening of 4 mm, a number average molecular weight of 70,000 and a weight average molecular weight of 48 were used.
000, polypropylene with a melt index of 3 (Ube Polypro F103EA, manufactured by Ube Industries, Ltd.)
Melt extruded at 00 ° C. The discharge film was guided to a cooling roll at 90 ° C. and cooled by blowing cool air at 25 ° C., and then cooled at 32 m / min. Was taken over. The draft ratio at this time was 366. The obtained unstretched polypropylene film has a thickness of 12 μm and a birefringence of 14.
7 × 10 ^-3 , elastic recovery was 88.2% after heat treatment at 150 ° C. for 60 minutes.

Discharge width 1000 mm, discharge lip opening 4 m
Using a T die of m, high-density polyethylene having a density of 0.968 and a melt index of 5.5 (manufactured by Mitsui Petrochemical Co., Ltd., Hyzex 2208J) was melt-extruded at 173 ° C. The discharge film is guided to a cooling roll at 115 ° C. and cooled by blowing cool air at 25 ° C.
40 m / min. Was taken over. The draft ratio at this time was 448. The film thickness of the obtained unstretched polyethylene film is 11 μm, the birefringence is 27.1 × 10 ⁻³ ,
The elastic recovery at 0% elongation was 29.6%.

Using this unstretched polypropylene film and unstretched polyethylene film, a three-layer laminated film having a sandwich construction in which both outer layers were polypropylene and the inner layer was polyethylene was produced as follows. Unrolled polypropylene film and undrawn polyethylene film are wound out of three sets of raw roll rolls at a speed of 5.
4 m / min. And rolled into a heating roll to reach a temperature of 12
Thermocompression bonding was performed at a linear pressure of 1.8 kg / cm at a temperature of 5 ° C., and then guided to a cooling roll of 50 ° C. at the same speed and wound up. The speed at this time is 5.4 m / min. The unwinding tension was 3 kg for the polypropylene film and 0.9 kg for the polyethylene film. The obtained laminated film has a film thickness of 34.
In μm, the peel strength was 16 g / 15 mm.

The three-layer film is introduced into a hot-air circulating oven heated to 125 ° C. and subjected to 1% under 5% tension.
It was heat treated for 13 seconds. Next, the heat-treated laminated film was stretched at a low temperature by 20% between nipples kept at 35 ° C. At this time, the distance between the rolls was 350 mm, and the roll speed on the supply side was 1.6 m / min. Met. It is then led into a hot air circulating oven heated to 110 ° C., and a total stretching amount of 115 between rollers is obtained by utilizing a difference in roll peripheral speed.
%, Stretched at a high temperature to 125 ° C., relaxed by 16.7% with a roll heated to 125 ° C., and heat-fixed for 25 seconds.
A laminated porous film was continuously obtained.

The thickness, porosity, maximum pore size, pore surface area, gas permeation rate, tensile strength, and the like of the obtained laminated porous film
Table 1 shows the measurement results of the tensile modulus, SD start temperature, heat resistance temperature, peel strength, and the like. The laminated porous film has a car
No pinholes were observed. FIG. 1 shows the thermal closing behavior. In FIG. 1, the vertical axis represents gas permeability (sec / 100 cc), and the horizontal axis represents temperature (° C.). The porosity, the maximum pore diameter, and the pore surface area were measured with a mercury porosimeter (manufactured by Yuasa Ionic), and the gas permeation rate (Garay) was measured according to JIS P8117, and the tensile strength and tensile strength were measured. The elastic modulus was measured according to ASTM D-822. The peel strength was 15 mm in width at 25 ° C. and 65% relative humidity. A sample was prepared by peeling off a part of the measured adhesive surface in advance. The sample was set to 75 mm in length and set to T in a tensile tester at 500 mm / min. The delamination strength was measured at the following speed. The heat closing behavior, the SD start temperature, and the heat resistance temperature were measured using a laminated porous film of a sample with a holder of 60 mmφ.
The sample was taken out of the hot air circulation oven and cooled down to room temperature in a constrained condition, and was subjected to each temperature treatment. The transmittance of the sample was measured according to JIS P8117. The degree of curl is 20 mm in width and 10 in length.
Place a 0-mm sample film on a horizontal metal plate, lightly brush it 2-3 times with a neutralization brush, and after 5 minutes, parallel lines connecting both ends of the film curved to the horizontal plane as shown in FIG. Was measured from the center to the horizontal plane (D).

Example 2 Using a T-die having a discharge width of 1000 mm and a discharge lip opening of 4 mm, a number average molecular weight of 70,000 and a weight average molecular weight of 48 were used.
000, polypropylene with a melt index of 3 (Ube Polypro F103EA, manufactured by Ube Industries, Ltd.)
Melt extruded at 00 ° C. The discharge film was guided to a cooling roll at 90 ° C. and cooled by blowing cool air at 25 ° C., and then cooled at 32 m / min. Was taken over. The draft ratio at this time was 366. The obtained unstretched polypropylene film has a thickness of 12 μm and a birefringence of 14.
7 × 10 ^-3 , elastic recovery was 88.2% after heat treatment at 150 ° C. for 60 minutes.

Discharge width 1000 mm, discharge lip opening 2 m
Using a T die of m, high-density polyethylene having a density of 0.964 and a melt index of 0.3 (HIZEX-5202B, manufactured by Mitsui Petrochemical Co., Ltd.) was melt-extruded at 177 ° C. The discharge film is guided to a cooling roll at 120 ° C, and is cooled by blowing cool air at 25 ° C.
35 m / min. Was taken over. The draft ratio at this time was 380. The film thickness of the obtained unstretched polyethylene film is 12 μm, the birefringence is 35.3 × 10 ⁻³ ,
The elastic recovery at 0% elongation was 38.9%.

Using this unstretched polypropylene film and unstretched polyethylene film, a three-layer laminated film having both outer layers of polypropylene and inner layer of polyethylene was produced as follows. Unrolled polypropylene film and undrawn polyethylene film are wound out of three sets of raw roll rolls at a speed of 5.
4 m / min. And rolled to a heating roll to reach a temperature of 13
The thermocompression bonding was carried out at 0 ° C. and a linear pressure of 1.8 kg / cm, and thereafter, it was led to a cooling roll at 50 ° C. at the same speed and wound up. The speed at this time is 5.45 m / min. The unwinding tension was 3 kg for the polypropylene film and 0.9 kg for the polyethylene film. The obtained laminated film has a film thickness of 34.
In μm, the peel strength was 7 g / 15 mm.

The three-layer laminated film was introduced into a hot-air circulating oven heated to 125 ° C., and was placed under a tension of 5%.
It was heat treated for 13 seconds. Next, the heat-treated laminated film was stretched at a low temperature by 20% between nipples kept at 35 ° C. At this time, the distance between the rolls was 350 mm, and the roll speed on the supply side was 1.6 m / min. Met. It is then led into a hot air circulating oven heated to 110 ° C., and a total stretching amount of 115 between rollers is obtained by utilizing a difference in roll peripheral speed.
%, Stretched at a high temperature to 125 ° C., relaxed by 16.7% with a roll heated to 125 ° C., and heat-fixed for 25 seconds.
A laminated porous film was continuously obtained.

The obtained laminated porous film was formed in the same manner as in Example 1 to obtain a film thickness, a porosity, a maximum pore size, a pore surface area, a gas permeation rate, a tensile strength, a tensile elastic modulus, an SD start temperature, a heat resistance temperature, Peel strength and the like were measured. Table 1 shows the measurement results, and FIG. 2 shows the thermal closure behavior. The laminated porous film had almost no curl, and no pinhole was observed.

Comparative Example 1 Using a T-die having a discharge width of 1000 mm and a discharge lip opening of 4 mm, 163 high-density polyethylene having a density of 0.964 and a melt index of 0.3 (manufactured by Mitsui Petrochemical Co., Ltd., Hizex 5202B) was used. Melt extruded at ° C. The discharge film is led to a cooling roll at 125 ° C and 25 ° C.
10m / mi after being cooled by blowing cold air of C
n. Was taken over. The draft ratio at this time was 120. The film thickness of the obtained unstretched polyethylene film was 38 μm, the birefringence was 31.6 × 10 ⁻³ , and the elastic recovery at 50% elongation was 41.3%.

This unstretched polyethylene film is 125
It was introduced into a hot air circulating oven heated to ° C. and heat-treated for 150 seconds under a tension of 10%. Next, the heat-treated film is placed between nipples maintained at 35 ° C. for 5 minutes.
It was stretched by 0% at low temperature. The distance between the rolls at this time is 350 m
m, the roll speed on the supply side is 1.2 m / min. Met. Subsequently, it is led into a hot air circulating oven heated to 80 ° C., and the stretching amount between the rollers is 1 using the difference in roll peripheral speed.
After the film was stretched at a high temperature to 00%, the film was relaxed by a roll heated to 108 ° C. for 16.7% and heat-fixed for 28 seconds to obtain a polyethylene single-layer porous film continuously.

The obtained porous film was measured for film thickness, porosity, maximum pore size, pore surface area, gas permeation rate, tensile strength, tensile modulus, SD start temperature, heat resistance temperature, etc. in the same manner as in Example 1. It was measured. The measurement results are shown in Table 1, and the thermal closing behavior is shown in FIG.

Comparative Example 2 Using a T-die having a discharge width of 1000 mm and a discharge lip opening of 4 mm, a number average molecular weight of 70,000 and a weight average molecular weight of 48 were used.
0000, polypropylene with a melt index of 3 (Ube Polypro F103EA, manufactured by Ube Industries, Ltd.)
It was melt extruded at 90 ° C. The discharge film was guided to a cooling roll at 90 ° C. and cooled by blowing cool air at 25 ° C., and then cooled at 40 m / min. Was taken over. The draft ratio at this time was 156. The film thickness of the obtained unstretched polypropylene film is 29 μm, and the birefringence is 13.
The elastic recovery was 2 × 10 ⁻³ , and the elastic recovery was 92% after heat treatment at 150 ° C. for 60 minutes.

The unstretched polypropylene film has a thickness of 15
10% guided into a hot air circulation oven heated to 0 ° C
Under a tension of 113 seconds. Next, the heat-treated film was stretched at a low temperature by 20% between nipples kept at 130 ° C. The distance between the rolls at this time is 350
mm, and the roll speed on the supply side is 1.6 m / min. Met. Subsequently, it is guided into a hot air circulation oven heated to 130 ° C., stretched at a high temperature to 115% between rolls by using a difference in roll peripheral speed, and then heated to 145 ° C. Roll for 16.7% and heat set for 25 seconds,
Continuously, a polypropylene single-layer porous film was obtained.

The obtained porous film of polypropylene was made in the same manner as in Example 1 for the film thickness, porosity, maximum pore size, pore surface area, gas permeation rate, tensile strength, tensile modulus, SD start temperature, heat resistance temperature. Etc. were measured. The measurement results are shown in Table 1, and the thermal closing behavior is shown in FIG.

Comparative Example 3 According to the method disclosed in Japanese Patent Publication No. 55-32531, the thickness was 8 μm, the porosity was 49%, and the average pore size was 0.1.
A 23 μm polyethylene porous membrane was prepared. Similarly, the thickness is 18 μm, the porosity is 52%, and the average pore size is 0.2 μm.
A 190 μm porous polypropylene membrane was prepared. Then, a polyethylene porous film and a polypropylene porous film were laminated and pressed at 134 ° C. using a roll press to obtain a laminated porous film. Table 1 shows the measurement results of the laminated porous film in the same manner as in Example 1.

[0049]

[Table 1]

[0050]

As described above, the laminated porous film of the present invention has a fine and uniform pore size, a moderate nonporous start temperature, a high nonporous maintaining upper limit temperature, and a high nonporous maintaining temperature range. Wide,
In addition, electronic devices such as separators for batteries, separators for electrolytic capacitors, insulators, etc., which have high peel strength and can improve the difficulties of conventional laminated porous films and require safety, reliability, accuracy, etc. It can be suitably used in medical fields such as fields, artificial lung membranes, plasma purification membranes, respiratory medical clothing, water treatment fields such as bacterial virus filtration, gas separation fields, and air conditioning fields. . Further, according to the present invention, it is possible to continuously and efficiently manufacture the laminated porous film having no quality variation.

[Brief description of the drawings]

FIG. 1 is a graph showing the thermal closure behavior of a laminated porous film of Example 1 of the present invention.

FIG. 2 is a graph showing the thermal clogging behavior of the laminated porous film of Example 2 of the present invention.

FIG. 3 is a graph showing the thermal closure behavior of a polyethylene single-layer porous film of Comparative Example 1.

FIG. 4 is a graph showing a thermal closure behavior of a porous film having a single layer of polypropylene of Comparative Example 2.

FIG. 5 is a diagram illustrating a method of measuring the degree of curl.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-296840 (JP, A) JP-A-5-13062 (JP, A) JP-A-6-20671 (JP, A) JP-A-6-20671 55629 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 H01M 2/16

Claims (4)

(57) [Claims] 1. A polypropylene film and polyethylene-off
The laminated porous film der which the Ilm is composed of a porous polypropylene film and a porous polyethylene film obtained by stretching a laminated film of three-layer laminated alternately
The birefringence of the polypropylene film is 10 × 1
0 ^{-3 to} 20 × 10 ^-3 and 1 after heat treatment at 150 ° C. for 30 minutes.
The elastic recovery rate at the time of 00% elongation is 80 to 94%, and
The birefringence of the polyethylene film is 20 × 10 ⁻³ to 4
0 × 10 ⁻³ , elastic recovery at 50% elongation is 20 to 50
% In the laminated porous film.
0.02 to 2 µm, porosity 30 to 80%, delamination strength
Degree is 3-60g / 15mm, non-porous start temperature is 135-
140 ° C, maximum non-porous maintenance temperature is 180-190 ° C,
A laminated porous film having a degree of penetration of 5 mm or less . 2. A polypropylene film and a polyethylene film.
At a temperature of 120 to 140 ° C so that the
The heat-compressed three-layer laminated film is heated at 110 to 140 ° C.
After heat treatment in the temperature range, minus 20 ° C to plus 50
Stretched 5 to 200% while maintaining the temperature of
100 to 4 with the temperature maintained at 70 to 130 ° C.
After stretching by 00%, the temperature at the time of the latter stretching is 5 to 45 ° C.
Laminated porous film characterized by heat treatment at high temperature
Lum's recipe. 3. A three-layer laminated film thermocompressed at a temperature of 120 to 140 ° C. so that a polypropylene film and a polyethylene film alternately are heat-treated in a temperature range of 110 to 140 ° C. 10 to 100% while maintaining the temperature at 70 ° C.
After stretching 100 to 400% while maintaining the temperature at 0 ° C., heat treatment is performed at a temperature 5 to 45 ° C. higher than the temperature at the time of the stretching , and the maximum pore diameter is 0.02 to 2 μm and the porosity is 30.
~ 80%, delamination strength 3 ~ 60g / 15mm, non-porous
The starting temperature is 135-140 ° C, and the non-porous maintaining upper limit temperature is
A method for producing a laminated porous film, comprising obtaining a laminated porous film at 180 to 190 ° C. 4. The birefringence of a polypropylene film is 10 ×
After heat treatment at 150 ° C. for 30 minutes at 10 ^{−3 to} 20 × 10 ⁻³
The elastic recovery at 100% elongation is 80-94%,
Birefringence of polyethylene film is 20 × 10 ^-3 to 40 × 1
0 ^-3, elastic recovery at 50% elongation is 20-50% der
The laminated porous film according to claim 2 or claim 3
Manufacturing method.