KR20140119019A - Polyolefin microporous film, polyolefin microporous film roll, method for producing polyolefin microporous film or polyolefin microporous film roll, and separator for batteries using polyolefin microporous film or polyolefin microporous film roll - Google Patents

Abstract

The present invention provides a polyolefin microporous film and a polyolefin microporous film roll which are capable of maintaining a good flatness of the film even in a wide and long roll state and are excellent in productivity, and a process for producing them and a battery separator using them The purpose. The present invention relates to a film having a thickness of 1 탆 or more and 50 탆 or less and a durability of 50 seconds / 100 mL or more and 500 seconds / 100 mL or less, a shrinkage in the width direction at 40 캜 and 48 hours of -0.3% A polyolefin microporous film having a shrinkage percentage of not less than 0.0% and not more than 1.5%, a film roll on which the film is wound, a method for producing the same, and a battery separator using the same.

Description

TECHNICAL FIELD [0001] The present invention relates to a polyolefin microporous film, a polyolefin microporous film roll, a method for producing the same, and a battery separator using the same. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyolefin microporous film, a polyolefin microporous film roll, POLYOLEFIN MICROPOROUS FILM ROLL}

The present invention relates to a separator used for separation and selective permeation of a substance, and a microporous film widely used as an insulating material for an alkali, a lithium secondary battery, a fuel cell, a condenser, and the like. And particularly relates to a polyolefin microporous film, a polyolefin microporous film roll, a method for producing the same, and a battery separator using them, which are suitably used as a separator for a lithium ion battery.

Polyolefin microporous films are widely used as separation membranes, separators, and the like, which are used for separation of various materials and selective filtration. They are used, for example, as microfiltration membranes, separators for fuel cells, and separators for capacitors. Among them, the polyolefin microporous film is particularly suitably used as a separator for a lithium ion battery which is widely used in notebook type personal computers, cellular phones, digital cameras, and the like. The reason for this is that the polyolefin microporous film has excellent mechanical strength and shutdown characteristics of the membrane.

As a separator for a lithium ion battery, it is required to maintain the characteristics under high temperature and to exhibit excellent safety at the time of abnormal heat generation, such as exhibiting excellent results in a high temperature cycle test and an oven test in the state of a battery. In recent years, A method of laminating layers for imparting safety and heat resistance as shown in Patent Document 1 may be used. Stabilizing the film thickness of the laminated film is an important item for the performance of the separator, and in order to reduce the manufacturing cost, for example, a film having a thickness of 200 to 200 mm , Further widening to a width of 500 mm or more, or machining with a long roll having a length of 1000 m or more. However, in the case of using a wide and long separator for improvement of productivity, it is difficult to maintain the flatness over the entire width and the entire length due to a minute dimensional change of the separator film, and the film thickness of the laminated film becomes unstable, There has been a problem in that productivity is not increased due to an increase in loss in meandering of the city. In recent years, a large-capacity and high-capacity battery having a large size and a high capacity has been studied. In addition to a large-sized battery, the separator film roll needs to be further reduced in manufacturing cost, .

As an example of improving the dimensional change of the separator film, a method of controlling shrinkage due to heat such as exemplified in Patent Documents 2 to 4 has been studied. In order to improve the battery safety performance under high temperature and the storage capacity of a winding in a prismatic battery or the like, Patent Document 2 discloses a heat shrinkage ratio at 65 占 폚 in the width direction of 1% And a heat shrinkage ratio in the transverse direction is larger than 2. However, it is insufficient to suppress the minute dimensional change of the film in the wide and long roll state, and it is difficult to improve the flatness deterioration.

Patent Document 3 discloses a polyolefin having a heat shrinkage ratio of 2.0% or less in the TD direction (width direction) at 105 ° C and a heat shrinkage ratio of 6% or less in the MD direction (lengthwise direction) A microporous membrane is described. However, as in the case of Patent Document 2, it is insufficient to suppress the minute dimensional change of the film in the wide and long roll state, and it is difficult to improve the deterioration of the flatness.

Patent Document 4 describes a polyolefin microporous membrane having a TD (width direction) heat shrinkage initiation temperature of 80 캜 or higher in order to improve electrolyte impregnability and liquification in a battery production process. However, the TD heat shrinkage starting temperature of Patent Document 4 is defined as a temperature at which the shrinkage load exceeds a predetermined value while raising the film in a short time with a load applied to the film, and a load is applied in the width direction It is insufficient to suppress the minute dimensional change of the film with time in the state of not supporting the film, and it is difficult to suppress deterioration of planarity.

Among these situations, development of a separator film which suppresses a minute dimensional change of the film in a wide and long roll state and has a small sagging and unevenness and a good planarity is an important task for improvement of performance and productivity of the separator .

Japanese Patent Application Laid-Open No. 2004-227972 International Publication No. 2007/069560 Japanese Patent Application Laid-Open No. 11-80078 Japanese Patent Application Laid-Open No. 2008-106237

Accordingly, an object of the present invention is to provide a polyolefin microporous film and a polyolefin microporous film roll which can maintain a good flatness of a film even in a wide-width and long roll state and are excellent in productivity, a method for producing them, .

In order to solve the above problems, the present invention has the following configuration. In other words,

(One). Wherein the polyolefin resin has a thickness of 1 占 퐉 or more and 50 占 퐉 or less and a durability of 50 seconds / 100mL or more and 500 seconds / 100mL or less; and a heat shrinkage ratio in the width direction at 40 占 폚 for 48 hours is -0.3% Or more and 0.3% or less and a longitudinal heat shrinkage ratio of 0.0% or more and 1.5% or less.

(2). A polyolefin microporous film satisfying the following expression (1) when the stiction intensity of the film is P (mN / m) and the porosity is E (%),

≪ Equation (1) >

100 占 P / (100-E)? 400

(3). (1) or (2), wherein the polyolefin comprises 5 to 50 parts by weight of a polyolefin resin having a weight average molecular weight of 1 x 10 ⁶ or more and 100 to 5 parts by weight of a total of polyolefins, and a polyolefin having a weight average molecular weight of less than 1 x 10 ⁶ A polyolefin microporous film made of 50 to 95 parts by weight of a resin,

(4). The polyolefin microporous film according to any one of (1) to (3), wherein the polyolefin is polyethylene,

(5). A polyolefin microporous film roll having a width of 200 mm or more and a length of 500 m or more which is obtained by winding the polyolefin microporous film described in any one of (1) to (4)

(6). (5), a polyolefin microporous film roll having an amount of change of the outer diameter of the film roll within a range of 100 mm in any widthwise position of the film roll of 250 탆 or less,

(7). (5) or (6), a polyolefin microporous film roll in which the amount of change in roll outer diameter in the section from the widthwise end of the film roll toward the central portion of the film roll in the width direction to 50 mm,

(8). A process for producing a polyolefin microporous film for melt-kneading a polyolefin, stretching a sheet formed by extrusion from a die, and subjecting the sheet to a heat fixation treatment, characterized in that after the heat fixation treatment step, 0.5 to 5.0% (1) to (4), wherein the polyolefin microporous film roll and the polyolefin microporous film roll are subjected to relaxation,

(9). (8), a method for producing a polyolefin microporous film having a step of relaxing 0.3 to 3.0% in the longitudinal direction at a temperature of 60 to 100 DEG C after the heat fixation treatment step,

(10). A method for producing a polyolefin microporous film having at least one winding step of winding a film while vibrating the film in the film width direction at an amplitude of 100 mm to 200 mm in the method (8) or (9)

(11). (10), a method of producing a polyolefin microporous film and a polyolefin microporous film roll having a winding tension of 4 to 10 N / m in the winding step of the film,

(12). (8) to (11), wherein the change amount of the outer diameter of the roll of the film roll is measured, and the change in the widthwise direction of the film roll and the change in the widthwise direction of the film measured immediately before winding in the film- A method for producing a polyolefin microporous film in which the film width direction thickness in the film forming step is changed by adjusting the lip gap of the die so as to reduce the variation in the width direction shape of the outer diameter of the film roll,

(13). (8) to (12), a process for producing a polyolefin microporous film having a step of melt-kneading a polyolefin and a film-forming solvent, and a step of removing the film-forming solvent after the stretching of the sheet,

(14). A process for producing a polyolefin film roll according to any one of (5) to (7), wherein the polyolefin microporous film produced by the process for producing a polyolefin microporous film according to any one of (8) Way,

(15). A separator for a battery using the polyolefin microporous film or the polyolefin microporous film roll described in any one of (1) to (7)

to be.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a polyolefin microporous film and a polyolefin microporous film roll which can maintain good planarity even in a wide-width and long roll state, and which are excellent in productivity, and a method for producing them and a battery separator using them.

1 is a schematic sectional view showing a method for measuring the outer diameter of a film roll in the present invention.
2 is a schematic perspective view showing a method of measuring the outer diameter of a film roll in the present invention.
Fig. 3 is a schematic structural view showing a method of measuring deflection at an end portion in the film roll width direction in the present invention. Fig.

The constituent components, characteristics, manufacturing method and the like of the polyolefin microporous film of the present invention will be described in detail below together with the embodiments.

In the polyolefin microporous film of the present invention, a polyolefin and / or a polyolefin composition is used as a main component. The main component referred to here is a component that occupies more than half of the total weight of the film (50 weight parts or more when the whole film is 100 weight parts). The polyolefin used in the present invention is a polyolefin and / or polyolefin composition having a weight average molecular weight of 1 x 10 ⁶ or more and a polyolefin and / or a polyolefin composition having a weight average molecular weight of less than 1 x 10 ⁶ when the total amount of the polyolefin is 100 parts by weight It is preferable that the microporous film is improved in stability and safety when it is made into a battery due to the effects such as improvement in the stiffness of the microporous film and miniaturization of the through-hole diameter. The mixing ratio of polyolefins having different weight average molecular weights can be determined by the integral curve of gel permeation chromatography (GPC) measurement.

As the polyolefin (ultrahigh molecular weight polyolefin) having a weight average molecular weight of 1 x 10 ⁶ or more in the present invention, ultra high molecular weight polyethylene or ultra high molecular weight polypropylene is preferable, and ultra high molecular weight polyethylene is more preferable. Of ultra high molecular weight polyolefin is preferably the weight average molecular weight is more than 1 × 10 ⁶ 1 × 10 ⁷ or less. If the weight average molecular weight exceeds 1 x 10 ⁷ , the uniformity during melt-kneading may deteriorate, or the viscosity may become too high, making melt-extrusion difficult. The mixing ratio of the ultrahigh molecular weight polyolefin having a weight average molecular weight of at least 1 x 10 ⁶ is preferably from 5 to 50 parts by weight, more preferably from 10 to 40 parts by weight, based on 100 parts by weight of the total of the polyolefins. When the amount is less than 5 parts by weight, the strength of the microporous film may be insufficient and the sticking property may be deteriorated or the through hole diameter may become coarse. If the amount is more than 50 parts by weight, the viscosity of the molten resin becomes too high, so that the extrusion stability may deteriorate or the shrinkage ratio of the film may become large and the planarity of the film roll may deteriorate. The molecular weight distribution (weight average molecular weight / number average molecular weight) of the polyolefin is preferably 50 or less, more preferably 1.2 to 50, from the viewpoint of moldability of the microporous film.

As the constitution of the ultra high molecular weight polyethylene having a weight average molecular weight of 1 x 10 ⁶ or more in the present invention, at least 50% of repeating units derived from ethylene are contained, preferably at least 85% of the repeating units are polyethylene, Ethylene homopolymer or an ethylene /? - olefin copolymer, wherein 5.0 mol% or less is a comonomer such as at least one? -Olefin (mol% is a value based on 100 mol% of all monomers of the copolymer). The comonomer is, for example, selected from at least one of propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, vinyl acetate, methyl methacrylate or styrene. Such a polymer or copolymer can be obtained using a Ziegler-Natta catalyst or a single site catalyst. The melting point is preferably 134 占 폚 or higher. Examples of ultrahigh molecular weight polyethylene include Highjax Million (registered trademark) 240M or 340M (manufactured by Mitsui Chemicals, Inc.) polyethylene.

As the polyolefin having a weight average molecular weight of less than 1 x 10 ⁶ in the present invention, straight-chain polyethylene and / or polypropylene are preferable, and linear high-density polyethylene is more preferable. The weight average molecular weight of the polyolefin is preferably 1 10 ⁵ or more and less than 8 10 ⁵ . If the weight average molecular weight is not 1 × 10 ⁵ , the strength of the microporous film may be insufficient and the sticking property may be deteriorated or the heat resistance of the film may be deteriorated. Polyolefin blend ratio of the weight average molecular weight of less than 1 × 10 ⁶ is preferably 50 to 95 parts by weight when the total of the polyolefin is 100 parts by weight, and more preferably from 60 to 90 parts by weight. When the amount is less than 50 parts by weight, the shrinkage ratio of the film becomes large, and the flatness of the film roll may be deteriorated or the thickness of the film may be uneven. When the amount is more than 95 parts by weight, the strength of the microporous film may be insufficient, leading to deterioration of the sticking property, or the diameter of the through-hole may be increased. The molecular weight distribution (weight average molecular weight / number average molecular weight) of the polyolefin is preferably in the range of 2 to 15, more preferably 3.0 to 10.0, from the viewpoint of moldability of the microporous film. The amount of the unsaturated terminal group of the polyolefin is preferably less than 0.20 / 1.0 × 10 ⁴ carbon atoms, more preferably 0.14 / 1.0 × 10 ⁴ carbon atoms or less, particularly preferably 0.05 / 1.0 × 10 ⁴ to 0.14 / 1.0 × 10 ⁴ carbon atoms (measurement limit for lower bound).

The high-density polyethylene having a weight average molecular weight of less than 1 x 10 ⁶ in the present invention preferably contains 50% or more of ethylene-derived repeating units, preferably at least 85% of the repeating units are polyethylene, Ethylene homopolymer or an ethylene /? - olefin copolymer, wherein 5.0 mol% or less is a comonomer such as at least one? -Olefin (mol% is a value of 100 mol% of all monomers of the copolymer). The comonomer is, for example, selected from at least one of propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, vinyl acetate, methyl methacrylate or styrene. Such a polymer or copolymer can be obtained using a Ziegler-Natta catalyst or a single site catalyst. As the high-density polyethylene having a weight average molecular weight less than 1 × 10 ^6, for example, a midwife of (R) SH-800 or SH-810 ((Note) by Asahi Kasei Chemical's Co., Ltd.) and the like.

In the present invention, as the content other than the above-mentioned polyolefin resin, for example, a filler, an antioxidant, a stabilizer and / or a heat-resistant resin may be used within a range not deteriorating the film properties. Examples of the type or kind of the additive preferably used include those described in International Publication No. 2007/132942, International Publication No. 2008/016174, International Publication No. 2008/140835, and the like.

The polyolefin microporous film of the present invention has a heat shrinkage in the transverse direction at 40 DEG C for 48 hours of -0.3% or more and 0.3% or less, preferably -0.2% or more and 0.2% or less. When the heat shrinkage ratio in the width direction at 40 DEG C for 48 hours exceeds 0.3%, the state of deflection at the end portion in the film roll width direction deteriorates. When the heat shrinkage ratio is less than -0.3%, the film- Shrinkage unevenness depending on the location of the film becomes large in the relaxation process, and it tends to be difficult to keep the flatness uniformly on the entire surface of the film, which is not preferable. Shrinkage or elongation of the film in a state close to a room temperature state causes a deterioration in the planarity of the film in the process of keeping the film in a roll form. In the state in which the film is wound in a roll form, the restraining force of the film is weak at the end portion in the width direction of the film roll, and the dimensional change easily occurs due to the residual stress. On the other hand, in the central portion of the film roll, since the film has a strong binding force, the dimensional change is difficult to occur. Therefore, the dimensions of the film at the end portion and the central portion are changed, which leads to deflection of the film at the end portions in the width direction.

In the present invention, the method of setting the shrinkage in the width direction at 40 DEG C for 48 hours in the above-mentioned range can be carried out, for example, at a temperature of 60 DEG C to 100 DEG C, more preferably 80 DEG C to 100 DEG C, To 0.5% to 5.0% in the width direction. In particular, in the case of using an ultrahigh molecular weight polyolefin, the relaxation time of the internal strain of the film is prolonged. Therefore, in order to uniformly reduce the heat shrinkage at 40 캜 near the room temperature region, it is preferably 60 to 100 캜, By carrying out the relaxation treatment at 80 to 100 占 폚, it becomes possible to control the shrinkage amount without deteriorating the uniformity of the plane. Further, by abruptly changing the temperature, deformation may remain in the film to increase the heat shrinkage ratio or to deteriorate the planarity. Therefore, it is preferable that the temperature at the time of the relaxation treatment is gradually lowered from the heat fixation treatment step. When the temperature at relaxation is less than 60 占 폚, all the deformation of the film can not be removed within the time of the film-forming step, the effect of reducing the heat shrinkage rate at 40 占 폚 tends to become smaller, , A large relaxation rate is required to reduce the heat shrinkage rate in the room temperature region, and as a result, the shrinkage is likely to be uneven due to the difference in location in the film, and the planarity of the film tends to deteriorate. In the present invention, the method of loosening the film in the width direction is not particularly limited. For example, there is a method of shortening the distance between opposing clips holding both end portions in the film width direction, And a method in which heat is applied to the film in a state where it is not gripped and relaxed by the contractile force of the film. From the viewpoint of uniformity of the shrinkage characteristics of the film and stabilization of the transportability, a method of shortening the distance between opposing clips holding both ends in the film width direction is preferable. When the melting point of the polyolefin resin having the lowest melting point among the polyolefin resins mixed with 5 parts by weight or more is defined as Tm, it is preferable that the heat setting treatment temperature is set to (Tm-25) DEG C or more and (Tm-5) DEG C or less (Tm-20) DEG C or more and (Tm-5) DEG C or less. When the heat setting treatment temperature is lower than (Tm-25) DEG C, the shrinkage percentage of the film becomes too high or the sticking strength is lowered. When the heat setting temperature is higher than (Tm-5) DEG C, It is undesirable because it deteriorates the productivity.

In the polyolefin microporous film of the present invention, the heat shrinkage in the longitudinal direction at 40 DEG C for 48 hours is 0.0% or more and 1.5% or less, preferably 0.0% or more and 1.0% or less, more preferably 0.0% or more and 0.5 % Or less. When the film is wound in a roll shape, the film is shrunk in the longitudinal direction to increase the force of tightening the film, thereby causing partial shrinkage unevenness and elongation, thereby deteriorating the flatness of the film. When the heat shrinkage in the longitudinal direction at 40 DEG C for 48 hours exceeds 1.5%, the deflection state on the entire surface of the film roll tends to deteriorate. In addition, although the longitudinal heat shrinkage ratio is preferably as small as possible, it is practically difficult to set the film thickness to less than 0.0% from the viewpoint of the production method of the film.

In the present invention, the method of setting the shrinkage in the longitudinal direction at 40 DEG C for 48 hours in the above-mentioned range can be carried out, for example, at a temperature of 60 DEG C to 100 DEG C, more preferably 80 DEG C to 100 DEG C after the heat- And 0.3% to 3.0% relaxation in the longitudinal direction. The temperature at the time of the relaxation treatment is preferably carried out while gradually cooling from the heat fixation treatment step for the same reason as the above-described relaxation in the widthwise direction. The method of relaxing in the longitudinal direction is not particularly limited. For example, a method of shortening the gap between the clips adjacent in the longitudinal direction of the clip holding the both end portions in the film width direction, And a method of relaxation using the peripheral speed difference between rolls. From the viewpoints of stabilizing the shrinkage characteristics and planarity of the film, and stabilizing the transportability, a method of shortening the gap between the clips adjacent in the longitudinal direction of the clip holding both end portions in the film width direction is preferable.

In the present invention, the relaxation process in the width direction and the length direction may be performed simultaneously or separately. From the viewpoint of stabilizing the unevenness of the thermal properties of the film or reducing shrinkage nonuniformity depending on the place, it is preferable to perform the relaxation treatment in the width direction and the longitudinal direction separately. The order of the relaxation process in the width direction and the length direction is not particularly limited.

In the polyolefin microporous film roll of the present invention, the film roll generally has a width of 200 mm or more in most cases, but it is preferable that the change amount of the roll outer diameter within an arbitrary widthwise position 100 mm section of the film roll is 250 탆 or less, Is not more than 150 mu m, and more preferably not more than 100 mu m. Further, in the section from the widthwise end of the film roll in the width direction toward the central portion of the film roll up to 50 mm, the change amount of the roll outer diameter is preferably 150 占 퐉 or less, more preferably 100 占 퐉 or less. When the roll outer diameter change amount in a short section called a section of a film roll in a width direction of 100 mm is larger than 250 탆, the outer diameter changes sharply in a short section and the stress applied to the film largely varies depending on the position in the width direction, As a result, depending on the position, elongation is caused by the amount of shrinkage due to the shrinkage force of the film itself and the difference in the stress applied to the film, so that the planarity tends to deteriorate. As regards the film roll end, it is preferable that the size of the film roll is changed by contraction or elongation of the film because the constraining force against the film is small as described above. If the amount of change in the roll outer diameter in the section from the widthwise end of the film roll in the width direction toward the central portion of the film roll to 50 mm exceeds 150 탆, the deflection of the end portion of the film tends to deteriorate.

A method in which the amount of change in the roll outer diameter within an arbitrary widthwise position of 100 mm of the polyolefin microporous film roll of the present invention is made 250 탆 or less or a method in which the film roll is stretched in the width direction from the end in the width direction to 50 mm In the film production process such as the resin extrusion process, the stretching process, the drying process, the heat-fixing process process, and the relaxation process, the method of making the amount of change of the roll outer diameter in the range of Width direction and longitudinal direction) of the film, and suppressing unevenness of the film transporting and stretching speed, a method of suppressing the thickness unevenness of the film itself, a method of preventing the thickness uneven layer at the time of winding, A method of winding while vibrated, measuring the outer diameter of the rolled film roll, changing the gap of the die so as to offset the unevenness of the outer diameter Method, it is possible to properly set the tension during winding to illustrate a method of reducing the internal stress of the film.

In the film winding of the polyolefin microporous film roll of the present invention, the method of performing appropriate vibration is particularly preferable because the unevenness (change amount) of the outer diameter of the film roll can be easily and surely improved. The amplitude of the vibration at the time of winding the film is preferably 100 to 200 mm. If the amplitude is less than 100 mm, the effect may be inadequate. If the amplitude is more than 200 mm, the width of the ear portions at both ends in the film width direction can not be commercialized, and the productivity may be deteriorated. Further, the speed of vibration is preferably 5 to 100 mm / min, more preferably 10 to 50 mm / min. If the vibration velocity is too high, wrinkles tend to curl up when the film is conveyed and wound, and if it is too late, the film may be partially laminated with a fixed thickness unevenness to deteriorate planarity.

Further, at the time of producing the polyolefin microporous film roll of the present invention, the amount of change in roll outer diameter of the rolled intermediate product roll was measured, and the change in shape in the width direction thereof and the change A film thickness target in the film forming step is set so as to reduce the shape change chart in the width direction of the outer diameter of the intermediate product by comparing changes in the film thickness in the width direction, Is particularly preferable because the thickness irregularity of the film itself can be improved and the outer diameter of the film roll can be made uniform. When the film is wound in a roll form, the film is laminated with a thickness unevenness in a state in which several hundreds and thousands of layers are overlapped. Furthermore, in the case of a porous film, due to uneven distribution of vacancies and vacancies, It is preferable to use a method of directly adjusting the shape change in the width direction of the outer diameter of the film and reflecting it on the thickness target in view of the fact that the characteristics such as the specific gravity of the film roll are not constant depending on the position in the width direction, Which is preferable. In addition, it is particularly preferable to carry out in combination with the above-mentioned appropriate vibration.

The polyolefin microporous film of the present invention preferably satisfies the following expression (1) when the sticking strength of the film is P (mN / 占 퐉) and the porosity is E (%).

≪ Equation (1) >

100 占 P / (100-E)? 400

When the value of the left side of Equation (1) is less than 400, the safety of the battery is deteriorated when it is used as a battery separator. There is a concern. As a method of setting the value of the left side of the formula (1) to 400 or more, for example, when the blending ratio of the ultrahigh molecular weight polyolefin having a weight average molecular weight of 1 x 10 ⁶ or more is 100 parts by weight as the whole polyolefin, 50 to 50 parts by weight, preferably 10 to 50 parts by weight, a method of raising the drawing magnification in the step of drawing an unstretched film, a method of setting the temperature in the heat fixation treatment step of the drawn film at (Tm-25) Tm-5) DEG C or less, and a method of re-stretching the stretched film in the longitudinal direction and / or the width direction. However, by increasing the mixing ratio of the ultrahigh molecular weight polyolefin and raising the stretching magnification including re-stretching, the internal stress in the polyolefin microporous film is increased, and as a result, the heat shrinkage rate in the room temperature region rises and the film flatness deteriorates Therefore, it is possible to set both the stiction intensity and the heat shrinkage ratio in a preferable range by suitably adjusting the value of the heat shrinkage ratio while considering the above-mentioned relaxation treatment.

The thickness of the polyolefin microporous film of the present invention is 1 占 퐉 or more and 50 占 퐉 or less, preferably 5 占 퐉 or more and 30 占 퐉 or less, from the viewpoints of film strength and permeability. When the film thickness is less than 1 탆, the film strength is insufficient and the safety of the battery is impaired, and breakage at the time of production tends to occur, and productivity is lowered. If it exceeds 50 탆, the permeability is deteriorated.

The permeation resistance of the polyolefin microporous film of the present invention is 50 seconds / 100 mL or more and 500 seconds / 100 mL or less, preferably 100 seconds / 100 mL or more and 300 seconds / 100 mL or less. When the specimen resistance exceeds 500 sec / 100 ml, the self-discharge phenomenon can not be suppressed at all when used as a separator for a battery, and the impedance becomes too high and battery characteristics deteriorate. In the case of less than 50 sec / 100 mL, the sticking strength of the film may be lowered, or the dendrite growth may not be suppressed at all, and short-circuiting may easily occur.

In the polyolefin microporous film of the present invention, the heat shrinkage rate at 105 ° C for 8 hours is preferably 10% or less, more preferably 6% or less in both the longitudinal and transverse directions. If it exceeds 10%, the risk of occurrence of a safety problem such as occurrence of a short circuit when the battery becomes hot is increased, which is not preferable.

Next, a method of producing the polyolefin microporous film of the present invention will be described by taking as an example the case where the polyolefin resin is made of polyethylene, but the present invention is not limited thereto.

[Mixing, extrusion]

A mixture containing ultrahigh molecular weight polyethylene and high density polyethylene (containing ultra high molecular weight polyethylene and high density polyethylene in a desired ratio) and a film forming solvent are extruded and cooled and solidified. The film-forming solvent may be any kind of solvent, or a combination thereof, provided that it is generally compatible with the polymer and usable at the melt extrusion temperature. Specific examples of the solvent for film formation include aliphatic hydrocarbons or cyclic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane and liquid paraffin, or mineral oil fractions corresponding to these boiling points. In order to obtain a molten mixture having a stable solvent content, it is preferable to use a nonvolatile solvent such as liquid paraffin. The viscosity of the solvent is preferably 30 to 500 cSt at 25 캜, and further preferably 50 to 200 cSt. If the viscosity at 25 DEG C is less than 30 cSt, kneading with polyolefin becomes difficult, and if it exceeds 500 cSt, solvent removal becomes difficult.

The mixing ratio of the film forming solvent and the polyethylene composition is preferably 50 to 50% by weight to 90% by weight / 10% by weight of the solvent for forming a film / polyethylene composition.

In the present invention, it is preferable to form (mix) or extrude the mixture of the polyethylene and / or polyethylene composition with the solvent for film formation by using a twin screw extruder. Here, the additive such as filler described above may be added by a side feeder.

The mixing energy in the twin-screw extruder is preferably 0.1 to 0.7 KWh / kg. More preferably, 0.66 KWh / kg> mixed energy? 0.12 KWh / kg. When the mixing energy is within this range, the draw ratio can be increased, and (a) a high yield point and (b) high strength can be obtained. When the mixing energy is 0.12 KWh / kg or more, the planarity of the film is improved. When the mixing energy is larger than 0.66 KWh / kg, the biaxial stretchability tends to be insufficient due to the decomposition of the polymer, so that the stretching at a stretching ratio of 3 times 3 times or more in the longitudinal direction x width direction may become difficult.

The above-mentioned mixture is mixed in an extruder at a rotational speed of 450 rpm or less, preferably 430 rpm or less, more preferably 410 rpm or less, further preferably 150 rpm or more, more preferably 250 rpm or more. The mixing temperature of the mixture of the polyethylene composition and the film forming solvent is from 140 캜 to 260 캜, preferably from 210 캜 to 250 캜.

[Production of non-stretched sheet]

The mixture of the polyethylene and / or polyethylene composition and the film forming solvent is subjected to a filtration process to remove foreign matter, and then extruded from the die to form an extrudate. The extrudate is adjusted to a desired thickness for subsequent processing and is adjusted to obtain the desired thickness of the final film after stretching. For example, the thickness of the extrudate is 0.1 mm to 10 mm or 0.5 mm to 5 mm. Extrusion is carried out while the mixture is in a molten state. When a die making a sheet is used, the die is typically heated to 140 to 250 占 폚. Preferred conditions of manufacture may be those described in International Publication No. 2007/132942 and International Publication No. 2008/016174.

The sheet extruded from the die is exposed to a temperature range of 15 to 80 占 폚, for example, by a cooling roll or the like to form an unstretched sheet. The cooling rate is not particularly critical, but it is preferably less than 30 DEG C / min and is cooled to near the gel temperature of the extrudate. As for the manufacturing conditions of cooling, those described in International Publication No. 2007/132942, International Publication No. 2008/016174, International Publication No. 2008/140835 can be applied. When the unstretched sheet is produced, the amount of change in the outer diameter of the roll of the wound intermediate product roll is measured, and the change in shape in the width direction thereof and the film thickness measured in the film- To set the film thickness direction target in the film forming step so as to reduce the profile change chart in the width direction of the outer diameter of the intermediate product and to adjust the thickness of the die It is preferable to carry out a method of adjusting the gap between the ribs.

[Stretching of extrudate (Upstream stretching)]

The cooled unoriented sheet is stretched at least in one axis, preferably in two longitudinal axes (widthwise direction) and widthwise direction (up-directional stretching or wet-stretching). This stretching causes orientation in the polymer in the mixture. The stretching method of the non-stretched sheet is not particularly limited. For example, the stretching method of the non-stretched sheet is not particularly limited. For example, both ends of the film in the transverse direction are gripped by a tenter by means of a tenter and the distance in the width direction of the opposing clip and / , A roll stretching method in which stretching is performed by adjusting the speed difference between a plurality of rolls, an inflation method in which the film is stretched under the pressure of air, or a combination thereof. These methods are described, for example, in International Publication No. 2008/016174. The stretching is preferably biaxial stretching. In biaxial stretching, it is possible to use two simultaneous axes, two axes of rotation, multi-step stretching, and combinations thereof.

The draw ratio of the unstretched sheet (in the case of biaxial stretching, the length direction x width direction) is preferably 4 to 50 times, more preferably 9 to 49 times. The stretching temperature is preferably set to be between the crystallization temperature (Tcd) of the polyethylene and the melting point (Tm) of the polyethylene. Here, Tcd and Tm are values in polyethylene having the lowest melting point among the polyethylene mixed more than 5 parts by weight used in the extrudate. The crystal dispersion temperature is measured as the characteristic temperature of the dynamic viscoelasticity measurement described in ASTM D4065. In the present invention, Tcd is preferably 90 占 폚 to 100 占 폚, and the stretching temperature is preferably 90 占 폚 to 125 占 폚. More preferably from 100 deg. C to 125 deg. C, and from 105 deg. C to 125 deg.

[Removal of solvent for forming film]

Subsequently, the film-forming solvent is cleaned with a volatile cleaning solvent to remove the solvent. As the solvent for clearing the volatility, hydrocarbons such as pentane, hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, fluorinated hydrocarbons such as trifluoromethane, and ethers such as diethyl ether and dioxane can be used. The solvent may be appropriately selected depending on the solvent for forming a film used for dissolving the polyolefin, and may be used alone or in combination. As a specific method of cleaning, for example, the method described in International Publication No. 2008/016174 can be used. Next, the residual volatility-cleansing solvent is removed by, for example, thermal drying, wind drying or the like. As a specific method, for example, the method described in International Publication No. 2008/016174 can be used.

[Re-stretching of the dried film (downstream stretching)]

If necessary, the dried stretched film may be re-stretched (sometimes referred to as downstream stretching or dry stretching). The re-winding may be performed in one direction in the longitudinal direction and / or the width direction, or in both directions. The draw ratio of the re-stretching shrinkage is preferably 1.1 to 1.6 times, more preferably 1.1 to 1.5 times in the longitudinal direction. Further, the width direction is preferably 1.1 to 1.6 times, more preferably 1.2 to 1.4 times. Further, in the case of re-stretching in the biaxial direction, the longitudinal direction and the width direction can be stretched at the same time or separately. Further, in the case of separate drawing, either the longitudinal direction or the width direction may be elongated first. It is preferable that the temperature of the reheat discharge is not more than Tm, for example, in the range of Tcd-30 DEG C to Tm. Here, Tm and Tcd are values in polyethylene having the lowest melting point among the polyethylene mixed in 5 parts by weight or more, which is used in the extrudate. Concretely, the temperature is preferably in the range of 70 占 폚 to 135 占 폚, more preferably 120 占 폚 to 132 占 폚, particularly 128 占 폚 to 132 占 폚. Also, the reheating can be performed simultaneously with the heat fixing process described later.

[Heat fix treatment]

Then, the crystal of the polyethylene is stabilized, a uniform lamellar is formed in the film, and heat relaxation treatment is performed to eliminate stress strain remaining in the film. The temperature in the heat treatment process is preferably between Tcd and Tm, more preferably (Tm-25) C or higher and (Tm-5) Is particularly preferable. Concretely, it is from 105 캜 to 135 캜, more preferably from 120 캜 to 132 캜, and still more preferably from 122 캜 to 130 캜. Generally, the heat treatment is a sufficient time to form a uniform lamellar film in the film and to relieve strain deformation remaining in the film by thermal relaxation, and a processing time in consideration of productivity is in the range of 1 to 300 seconds And more preferably in the range of 1 to 120 seconds.

[Relaxation processing]

In order to reduce the shrinkage at room temperature after the heat setting treatment, it is preferable to perform relaxation treatment in the width direction and / or the length direction at 60 占 폚 to 100 占 폚, more preferably 80 占 폚 to 100 占 폚. The relaxation rate in the relaxation treatment is preferably in the range of 0.5 to 5.0% in the width direction and 0.3 to 3.0% in the lengthwise direction since the heat shrinkage rate at 40 캜 can be lowered uniformly without fluctuation. As the relaxation treatment method, the above-described method can be used.

[Winding]

The polyolefin microporous film that has undergone the relaxation treatment is wound, after cutting and removing both ends of the clip, if necessary, to obtain an intermediate product roll. Further, at the time of winding, it is preferable to take up the roll while vibrating at an amplitude of 100 to 200 mm in the width direction in order to alleviate the influence of the thickness unevenness and make the outer diameter of the intermediate product roll uniform. Further, immediately after the first winding after the film-forming step, the amount of dimensional change due to the internal stress release of the film is large, and in order not to increase the internal stress of the film during winding, the winding tension is preferably set to 4 to 10 N / m, Preferably 5 to 8 N / m. If the winding tension is more than 10 N / m, the flatness of the film may deteriorate. If the winding tension is lower than 4 N / m, a deviation may occur during winding, or wrinkles may occur in the inner layer of the intermediate product roll . The rolled intermediate product roll may be subjected to an annealing process if necessary in order to release deformation inside the film which is further left over. The temperature at the time of annealing is preferably 40 to 80 占 폚, more preferably 50 to 70 占 폚, from the viewpoint of preventing deterioration of the roll shape of the intermediate product. The treatment time is preferably 10 to 50 hours, more preferably 20 to 40 hours.

[Slit]

The obtained intermediate product roll is cut into a desired width in the slit process and wound to be a product roll. Also, in the slit process, vibration may be applied at the time of winding. The width and length of the polyolefin microporous film here are not particularly limited, but when used as a battery separator, the width is 30 to 1000 mm, more preferably 50 to 800 mm, the length is 300 to 3000 m, and more preferably 500 to 2000 m . Particularly, in the case of a separator for use in a large-sized battery or a use in which the heat-resistant layer or the like is directly laminated on the separator, it is preferable that the width and length are increased to improve productivity. However, when the film is generally wide and long, it is difficult to maintain the flatness of the film wound in a roll shape over the entire width and the entire length. However, according to the present invention, it is possible to obtain a wide and long film roll having good flatness . In consideration of the productivity in the case where the functional layer or the like is laminated on the separator, the width of the film roll is preferably 200 mm or more, more preferably 300 mm or more, and the film length is preferably 500 m or more and more preferably 1000 m or more.

[Example]

Hereinafter, specific examples of the present invention will be described using examples, but the present invention is not limited thereto.

[Assessment Methods]

1. Thickness

The film was cut into a square shape of 5 cm x 5 cm from an arbitrary position of the microporous film, and the film thickness of five points of the cut microporous film was measured by a contact thickness meter and averaged. As the film thickness measuring instrument, Lightmatic VL-50A manufactured by Mitutoyo was used.

2. Sting intensity (P)

The maximum load when a microporous film having a thickness T (占 퐉) was stuck at a speed of 2 mm / sec with a needle having a spherical surface (radius of curvature R: 0.5 mm) with a diameter of 1 mm was measured. The measured value L (mN) of the maximum load was converted into the maximum load P (mN / m) per 1 mu m of film thickness by the formula: P = L / T to obtain the stuck strength.

3. Public rate (E)

The porosity of the microporous film was measured by comparing the mass w1 of the microporous film with the weight w2 of the vacancy-free polymer equivalent to that of the same polymer of the same width, length and composition. The porosity was determined by the following equation.

The porosity E (%) = ((w2-w1) / w2) x100

4. Heat shrinkage

The heat shrinkage ratios at 40 占 폚 and 105 占 폚 in the width direction and the longitudinal direction of the microporous film were measured as follows. The surface layer of the microporous film roll was peeled off by 30 m and cut out into a square of 200 mm in the longitudinal direction and 200 mm in the width direction from the center position in the width direction. (i) the dimensions of the microporous film at 23 占 폚 were measured (width direction and length direction), (ii) the sample was exposed to the conditions of 40 占 폚 for 48 hours or 105 占 폚 for 8 hours without weighting, 23 DEG C, and (iii) dimensions in the width direction and the longitudinal direction were measured. The heat shrinkage ratio in the width direction and the longitudinal direction is expressed by a percentage obtained by dividing the dimension of (iii) by the dimension of (i) and subtracting it from 1. [ Similar measurements were made on the three samples, and the average value thereof was defined as a heat shrinkage ratio.

5. Speculation resistance

The durability (sec / 100 mL) was measured in accordance with the organic test method of JIS P8117 (2009) 6.

6. Maximum variation of film roll outer diameter

As shown in Figs. 1 and 2, the film roll 1 wound on the core 2 is hung in the air with a lot 7 inserted through the core 2, And the position of the upper surface measured by the laser beam 5 to the sensor head 3 (the light-emitting-side sensor head 3a and the light-receiving-side sensor head 3b) And the position difference of the lower surface measured by the laser light 5 at the sensor head 4 (the light-emitting side sensor head 4a and the light-receiving side sensor head 4b) was measured to measure the roll outer diameter. The measurement was carried out every 1 mm in width while moving the sensor head fixing frame 6 with the sensor heads 3 and 4 fixed in the film width direction (while moving the frame 6 in the arrow 8 direction) In the chart of the film roll diameter, a value at which the amount of change in an arbitrary section in the width direction of 100 mm was found was obtained. The amount of change in the 50 mm width section from the end of the film roll toward the center of the film roll in the width direction was found in the 50 mm width section from the end of the film in the chart of the obtained film roll diameter.

(Laser measuring machine)

Measuring section: Sensor head LS-3060 manufactured by Keisuke Kabushiki Kaisha

Controller part: controller LS-3000 manufactured by Keisuke Kabushiki Kaisha.

7. Planarity of Film

(1) Deflection in the width direction end portion

In the apparatus shown in Fig. 3, the film roll 1 is wound, and two rolls 9 and 9 arranged in parallel at a distance of 1 m are interposed between the rolls 1, Lt; / RTI > The distance L1 between the reference frame 10 and the film end portion is set to JIS Class 1 at a central position of the two rolls 9 and 9 after 30 seconds from the application of the load to the film 11, . The distance L0 between the reference line 10 measured beforehand and the line connecting the upper surfaces of the two rolls 9 and 9 (the imaginary line 13 connecting the upper surfaces of the rolls 9 and 9) The difference from the obtained measured value (L1), L0-L1, was defined as the deflection amount. The measurement was performed at both ends in the width direction, and the value of the larger deflection amount was defined as the deflection amount at the end portion in the width direction of the film roll. In addition, judgment was made using the following criteria. S is very good, A is good, B is a practical range, B or more is in the acceptable range, and C is in the rejection.

S: Deflection is less than 3mm at both ends.

A: Deflection is more than 3mm and less than 6mm at both ends.

B: Deflection is more than 6mm and less than 10mm at both ends.

C: Deflection exceeds 10mm at both ends.

(2) Deflection at the center in the width direction

The film was taken out from the roll and a measurement sample having a length of 1 m was taken. The collected sample was spread on a glass plane surface using a static elimination brush and adhered to the glass surface, and the maximum width of the excited portion of the film continuously generated in the longitudinal direction after 10 seconds of the measurement was measured using a JIS grade 1 crucible. The determination was made using the following criteria. S is very good, A is good, B is a practical range, B or more is in the acceptable range, and C is in the rejection.

S: There is no continuous section in the longitudinal direction in the center part.

A: The width of the excited portion continuous in the longitudinal direction of the central portion is 100 mm or less.

B: The width of the excited portion continuous in the longitudinal direction of the center portion is more than 100 mm and less than 200 mm.

C: The width of the lifting portion continuous in the longitudinal direction of the central portion exceeds 200 mm.

8. Melting point (Tm), crystal dispersion temperature (Tcd)

(1) Melting point · Crystallization temperature

Measurement is carried out under the following conditions using differential scanning calorimetry.

· Measuring device: PerkinElma manufactured by using 1DSC.

Measurement method: A sample adjusted to 5.5 to 6.5 g is sealed in an aluminum pan, heated from 30 占 폚 to 230 占 폚 at a rate of 10 占 폚 / min, and held at 230 占 폚 for 10 minutes. The sample is then cooled (crystallized) from 230 DEG C to 25 DEG C at a cooling rate of 10 DEG C / min and held at 25 DEG C for 10 minutes. Thereafter, the temperature is raised (second melting) to 230 deg. C at a rate of 10 deg. C / min. Thermal analysis of both the crystallization and the second melting is recorded. The melting point (Tm) is a peak of the second melting curve, and measurement is performed on three samples, and a value obtained by averaging the results is used.

(2) Crystal dispersion temperature

The dynamic viscoelastic behavior is measured under the method and conditions described in ASTM D4065 to determine the relaxation peak of the crystal lattice, and the crystal dispersion temperature is determined.

[Example 1]

(1) Preparation of a mixture of polymer and film forming solvent

20 parts by weight of an ultrahigh molecular weight polyethylene resin A having a weight average molecular weight of 2.5 x 10 < ⁶ > and a melting point of 136 DEG C, and a polypropylene resin having a weight average molecular weight of 3.5 10 ⁵ , a melting point of 135 캜, a weight average molecular weight / number average molecular weight of 4.05, A mixture of 80 parts by weight of a linear high-density polyethylene resin B having a molar ratio of 0.14 / 1.0 × 10 ⁴ carbon atoms was charged into a twin-screw extruder and liquid paraffin (135 cSt / 25 ° C.) was injected from the side feed of the twin- Respectively. The injection amount of the liquid paraffin was adjusted so that the amount of the polyethylene resin mixture became 30% by weight when the total of the polyethylene resin mixture and the liquid paraffin was 100% by weight. The polyethylene resin composition and the concentration of the polyethylene resin in the liquid paraffin mixture are shown in Table 1. The inside of the twin screw extruder was reduced in pressure by a vacuum pump and melt-kneaded at 200 DEG C and 300 rpm to obtain a mixed solution of a polyethylene resin mixture and a liquid paraffin (solvent for film formation).

(2) Production of film

A mixed solution of the obtained polyethylene resin mixture and liquid paraffin (solvent for forming a film) was fed into a single screw extruder and subjected to melt extrusion at a temperature of 210 캜. The stainless steel fibers were sintered and compressed, and filtered through a filter having an average graduation of 20 탆. The sheet was then extruded from a T-shaped die and cooled with a cooling roll at a temperature of 20 캜 to obtain an unstretched gel sheet. The unstretched sheet was subjected to simultaneous biaxial stretching at 114 占 폚 in a first tenter at a stretching magnification of 5 times in both the transverse direction and longitudinal direction and then the stretched gel sheet was immersed in methylene chloride at 25 占 폚 to remove liquid paraffin, And air-dried to obtain a microporous film. The obtained microporous film was guided to the second tenter while holding both ends of the microporous film at a temperature of 125 DEG C for 12 seconds and then the distance in the width direction of the clip was reduced at a temperature of 95 DEG C 1.0% in the widthwise direction by a method of shortening the distance in the width direction of the clip at a temperature of 80 ° C, and furthermore, by a method of shortening the distance in the width direction of the clip at a temperature of 60 ° C 0.5% < / RTI > After removing both ends in the width direction of the film from the second tenter, the film was wound in a width direction at a speed of 20 m / minute while vibrating under the conditions of an amplitude of 150 mm, a vibration speed of 50 mm / min and a winding tension of 7 N / m, An intermediate product of 1800 mm polyolefin microporous film was obtained. The obtained intermediate product (winding roll) was measured for the outer diameter of the intermediate product according to the item 6 described in the above-mentioned measurement method, and the width of the film measured in the portion just before winding The thickness direction of the intermediate product in the width direction of the intermediate product is set so that the shape of the intermediate product becomes straight, The thickness of the film was adjusted by a method of controlling the temperature of the heat bolt for adjusting the gap between the film and the film. Subsequently, in the slit process, the intermediate product was cut into three product rolls having a width of 400 mm and the ear portions at both ends, and the cut films were each wound with an ABS plastic core having an inner diameter of 3 inches to obtain a polyolefin fine A porous film roll was obtained. The conditions for producing this film are summarized in Table 1.

After the obtained film roll was stored at room temperature for one week, various properties were evaluated for three rolls in the width direction. The results are shown in Table 3. It was a film roll excellent in planarity with good end deflection, good center deflection. In addition, the average values of the values measured on three rolls in the width direction are described for the heat shrinkage ratio, the durability, the sticking strength, the porosity, the maximum change amount of the roll outer diameter, and the planarity.

[Examples 2 to 19], [Comparative Examples 1 to 7]

A polyolefin microporous film having a thickness of 9 占 퐉 was obtained in the same manner as in Example 1 except for the conditions shown in Tables 1 and 2, and a polyolefin microporous film roll was obtained. In Example 19, except that the target thickness setting in the width direction of the film was adjusted using the thickness of one film measured at intervals of 50 mm in the width direction by the contact thickness meter described in Measurement Method 1, 1 was used. In Comparative Example 7, the drawing temperature of the unstretched sheet was changed to 118 占 폚, and the heat fixing treatment time was changed to 20 seconds. The width direction re-stretching used in Examples 11, 12 and 13 and Comparative Example 4 is a step of stretching the film in the width direction at the same time as the heat fixing treatment. After heat treatment for 6 seconds at a heat fixing temperature , And the stretching was performed at the specified magnification in the width direction while continuing the heat setting treatment for 6 seconds. As for the longitudinal relaxation of Examples 8, 9, and 10, relaxation in the longitudinal direction by the method of shortening the gap between the clips adjacent in the longitudinal direction holding both end portions in the film width direction in the second tenter, And after the relaxation treatment was completed. In the intermediate transfer hot-rolling process applied in Example 7, a plurality of rolls heated to a predetermined temperature are disposed in the middle of the process of cutting and removing both ends in the width direction of the film from the second tenter and winding the film And the film is relaxed in the longitudinal direction by the difference in rotation speed of the heating roll while heating the film. Further, in this relaxation process, the film is not held in the width direction, and therefore, the film is also relaxed by the contracting force of the film itself in the width direction. The relaxation rate at that time was calculated by measuring the film width before and after the intermediate transfer hot-rolling process. The evaluation results are shown in Tables 3 and 4.

[Review of results]

(Heat shrinkage and planarity)

The amount of deflection at the end in the width direction was deeply related to the heat shrinkage rate in the width direction at 40 DEG C for 48 hours. In Comparative Examples 1 to 6 where the value was out of the range of -0.3% to 0.3%, the end deflection was largely unacceptable. On the other hand, when the value was in the range of -0.2% to 0.2%, the deflection at the end was good, and the closer to 0, the better the deflection amount. It is considered that this indicates that, in the roll state, a minute dimensional change in the state of the end portion at which the film is easy to move at room temperature causes deflection. Further, in Comparative Example 4 in which the heat shrinkage ratio in the longitudinal direction exceeded 1.5%, the planarity of both the end portion and the center portion deteriorated. It is considered that the force of winding by the change in the dimension in the longitudinal direction in the roll state causes the deterioration of the flatness. In Examples 7 to 10 in which the heat shrinkage in the longitudinal direction was in the range of 0 to 0.5%, the planarity was very good at both the center and the end portions. Particularly in Example 10, although the winding length of Example 8 was doubled And maintains a very good planarity, thus being a film excellent in productivity.

(Roll outer diameter variation and planarity)

The smaller the variation in the width of the outer diameter of the film roll of 100 mm, the better the flatness of the film. In Example 17, the vibration amplitude at the time of winding in Example 1 was reduced from 150 mm to 80 mm. The amount of change in the outer diameter in a narrow section called the 100 mm wide section was large, and the flatness of the film deteriorated in the abrupt change portion . This was also the same result in the comparison of Comparative Example 2 and Comparative Example 6. On the other hand, in Examples 14 and 15 in which the vibration amplitude of Example 1 was widened to 200 mm, the change in outer diameter of rolls was 100 mu m or less, which was extremely good, and particularly excellent in planarity. In Example 15, the film was maintained in a very good planarity and was excellent in productivity even though the winding length was doubled. In Example 18 in which the intermediate product of Example 1 had a winding tension of 12 N / m, the amount of strain in the film was increased so that the thickness setting of the film in the width direction was made to be the thickness of one film measured on the contact thickness meter , The film flatness was within the practical range but tended to deteriorate.

(Sting intensity)

(1)) was less than 400 in Examples 4, 5, and 12, which is slightly lower than the stipulated strength (Equation (1)) per a thickness corresponding to a substantial resin component excluding the void portion. The composition ratio of the ultra high molecular weight polyethylene to the entire polyethylene resin is 5 wt% or less, and when the appropriate amount of ultrahigh molecular weight polyethylene is added, the sticking strength is improved. On the other hand, by adding ultra-high molecular weight polyethylene, the heat shrinkage ratio is increased. However, as in Examples 8 to 10 and 14 to 15, by reducing the heat shrinkage rate by the relaxation process, it is possible to achieve very good planarity .

≪ Industrial applicability >

The polyolefin microporous film and the microporous film roll according to the present invention can maintain good planarity even when rolled in a wide and elongated roll shape while maintaining a suitable durability per unit of durability or a dripping strength per resin amount, Separation and selective permeation, and as an insulating material for an alkali, a lithium secondary battery, a fuel cell, a condenser, and the like, and the like. In particular, when used as a separator for a lithium ion battery, it is possible to uniformly coat a functional layer such as a heat resistant layer on a separator with high productivity, thereby making it possible to produce a battery having excellent battery safety, productivity and manufacturing cost.

1 film roll
2 cores
3 Sensor head of Laser Dimension Measuring Instrument for Positioning Film Roll Top Position
3a Sensor head (light emitting side)
3b Sensor head (light receiving side)
4 Sensor head of laser dimension measuring instrument for measurement of side position of film roll
4a Sensor head (light emitting side)
4b Sensor head (light receiving side)
5 Laser light (outline city)
6 Frame for fixing the sensor head
7 loads
Moving direction of 8 frames
9 rolls
10 bases
11 film
12 Weight to apply load to film
13 Virtual line connecting top side of two rolls
L0 Line connecting top side of two rolls and distance from reference bar
L1 Distance between end of film and base

Claims (15)

Wherein the polyolefin resin has a thickness of 1 占 퐉 or more and 50 占 퐉 or less and a durability of 50 seconds / 100mL or more and 500 seconds / 100mL or less; and a heat shrinkage ratio in the width direction at 40 占 폚 for 48 hours is -0.3% Or more and 0.3% or less and a longitudinal heat shrinkage ratio of 0.0% or more and 1.5% or less. A polyolefin microporous film satisfying the following expression (1) when the stiction intensity of the film is P (mN / m) and the porosity is E (%).
≪ Equation (1) >
100 占 P / (100-E)? 400 The method of claim 1 or claim 2, wherein the polyolefin is, by the total of the polyolefin is 100 parts by weight, weight average molecular weight of 1 × 10 ⁶ or more polyolefin resin 5 to 50 parts by weight, and the weight average molecular weight of 1 × 10 ⁶ less than the polyolefin And 50 to 95 parts by weight of a resin is used as the polyolefin microporous film. The polyolefin microporous film according to any one of claims 1 to 3, wherein the polyolefin is polyethylene. A polyolefin microporous film roll obtained by winding the polyolefin microporous film according to any one of claims 1 to 4 and having a width of 200 mm or more and a length of 500 m or more. The polyolefin microporous film roll according to claim 5, wherein the change amount of the outer diameter of the film roll in an arbitrary width direction position of the film roll in a section of 100 mm is 250 탆 or less. The polyolefin microporous film roll according to claim 5 or 6, wherein the change amount of the roll outer diameter in the section from the width direction end portion of the film roll toward the center portion of the film roll in the width direction up to 50 mm is 150 탆 or less. A process for producing a polyolefin microporous film for melt-kneading a polyolefin, stretching a sheet formed by extrusion from a die, and thermally fixing the polyolefin film, characterized in that after the heat fixation treatment step, The method of producing a polyolefin microporous film according to any one of claims 1 to 4, wherein the polyolefin microporous film has a step of relaxation. The method of producing a polyolefin microporous film according to claim 8, wherein after the heat fixation treatment step, a relaxation of 0.3 to 3.0% in the longitudinal direction is performed at a temperature of 60 to 100 캜. The method of producing a polyolefin microporous film according to claim 8 or 9, wherein the film is rolled while being vibrated with an amplitude of 100 mm to 200 mm in the film width direction. The method of producing a polyolefin microporous film according to claim 10, wherein the winding tension of the film is 4 to 10 N / m. The method according to any one of claims 8 to 11, wherein the change amount of the outer diameter of the roll of the film roll is measured, and the change in the widthwise direction of the film roll and the change in the widthwise direction of the film thickness measured immediately before winding in the film- The thickness of the film in the film width direction in the film forming step is changed by adjusting the lip gap of the die so as to reduce the variation in the width direction shape of the outer diameter of the film roll. 13. The method of producing a polyolefin microporous film according to any one of claims 8 to 12, which comprises melt kneading a polyolefin and a film forming solvent, and removing the film forming solvent after stretching the sheet. A process for producing a polyolefin film roll according to any one of claims 5 to 7, wherein the polyolefin microporous film produced by the process for producing a polyolefin microporous film according to any one of claims 8 to 13 is wound Way. A battery separator using the polyolefin microporous film or the polyolefin microporous film roll according to any one of claims 1 to 7.

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