JP5724329B2 - Porous polypropylene film roll - Google Patents

Description

  The present invention relates to a porous polypropylene film roll that is excellent in productivity, exhibits excellent battery characteristics when used in a separator of an electricity storage device, and has improved processability in a battery manufacturing process.

  Polypropylene films are used in various applications such as industrial materials, packaging materials, optical materials, and electrical materials due to their excellent mechanical, thermal, electrical, and optical properties. Since this porous polypropylene film is porous and porous, it has excellent properties such as permeability and low specific gravity in addition to the properties of a polypropylene film. Development into a wide range of applications such as separation membranes, clothing, moisture-permeable waterproof membranes in medical applications, reflectors for flat panel displays, and thermal transfer recording sheets has been studied. In particular, when a porous film is used as a separator, it is important to improve the running stability of the film in the assembling process of the electricity storage device as well as to reduce the cost by improving productivity.

  Various proposals have been made as methods for making a polypropylene film porous. Porous methods can be broadly classified into wet methods and dry methods. In the wet method, polypropylene is used as the matrix resin, the extractables to be extracted after sheeting are added and mixed, and only the additives are extracted using the good solvent of the extractables, creating voids in the matrix resin. Various methods have been proposed (for example, see Patent Document 1). The wet method is excellent in quality because it can reduce the viscosity of the resin composition and can be filtered with high precision, and it can be cast at a low temperature to reduce deterioration of the resin composition, but the extraction process is complicated. And the need for a solvent treatment step, it was difficult to reduce the cost.

  On the other hand, as a dry method, for example, by adopting low-temperature extrusion and a high draft ratio at the time of melt extrusion, the lamella structure in the film before stretching formed into a sheet is controlled, and this is uniaxially stretched so that at the lamella interface There has been proposed a method (so-called lamellar stretching method) in which cleavage occurs to form voids (see, for example, Patent Document 2). When this method is used, the film is uniaxially stretched and the stretch ratio is low, so that the flatness of the film is hardly deteriorated and the running stability during the assembly process is excellent, but the stretch area ratio is low and the stretch speed is slow. Therefore, it is difficult to improve productivity, and it is difficult to obtain a high porosity, and when used as a separator for an electricity storage device, particularly a lithium ion secondary battery, the battery performance may be lowered.

  As a method of achieving high productivity and achieving a higher porosity, a large amount of incompatible resin is added as inorganic particles or polypropylene as a matrix resin by a dry method, and a sheet is formed and stretched. A method has also been proposed in which cleavage is generated at the interface between the particles and the polypropylene resin to form voids (see, for example, Patent Document 3). Furthermore, there is a so-called β crystal method in which voids are formed in the film by utilizing the crystal density difference and crystal transition between α type crystal (α crystal) and β type crystal (β crystal), which are polymorphs of polypropylene. Many proposals of the called method are also made (for example, refer patent documents 4-6).

  When the porous polypropylene film produced by the various methods described above is used as a separator for an electricity storage device, particularly a lithium ion secondary battery, the β crystal method usually forms voids by biaxial stretching, so it is compared with other methods. Thus, a high porosity can be achieved. Therefore, the internal resistance of the battery can be lowered, and it is particularly suitable for a separator for a high-output power storage device that requires a large current (see, for example, Patent Document 7). However, the porous film produced by the biaxial stretching of the dry method is liable to deteriorate in flatness, and further improvement in the running stability of the film in the assembly process is necessary.

  For improving the flatness of the film, for example, a method for controlling the orientation angle by increasing the tension after the tenter is described for a polypropylene film for print lamination (Patent Document 8). However, when producing a porous film by the dry method, if the tension after the tenter is increased, the pores may be deformed and the porosity and air permeability may be lowered, so it is difficult to use the same method. .

  In addition, as a method for improving the flatness of a film made of an organic polymer for a magnetic recording medium, a method for controlling humidity when storing a film roll is described (Patent Document 9). However, in the porous film, the influence of the atmospheric humidity on the flatness is small, and it has been difficult to improve the flatness by the same method.

Japanese Patent Laid-Open No. 55-131028 Japanese Patent Publication No.55-32531 JP-A-57-203520 JP-A 63-199742 JP-A-6-100720 Japanese Patent Laid-Open No. 9-255804 International Publication No. 05/103127 Pamphlet Japanese Patent Laid-Open No. 11-240067 JP-A-9-71669

  The present invention has been achieved as a result of studying the solution of the problems in the prior art described above as an issue. That is, an object of the present invention is to provide a porous polypropylene film roll that is excellent in productivity, exhibits excellent battery characteristics when used in a power storage device separator, and has improved processing suitability in a battery manufacturing process. It is in.

  The present invention for achieving the above object is a porous polypropylene film roll obtained by winding a porous polypropylene film by a dry method on a core, and the film is placed at any place in the longitudinal direction in the porous polypropylene film roll. This is achieved by a porous polypropylene film roll in which the amount of bending and the amount of sag at a film length of 1 m are both 3 mm or less when measured by unwinding.

  The porous polypropylene film roll of the present invention is excellent in productivity, exhibits excellent battery characteristics when used as a separator for an electricity storage device, and is excellent in processability in the battery manufacturing process, and is therefore suitable as a separator for an electricity storage device. Can be applied to.

It is the schematic which showed the measurement site | part of the curvature amount when the porous polypropylene film which concerns on this invention is seen from the top. It is the schematic which shows the measurement site | part of the amount of sagging in the porous polypropylene film of FIG.

  The porous polypropylene film constituting the porous polypropylene film roll of the present invention is a porous polypropylene film obtained by a dry method, and is preferably biaxially oriented. Moreover, this porous polypropylene film has a through-hole. Here, a through-hole means the hole which penetrates both surfaces of a film and has air permeability. As a specific method for obtaining the through hole, for example, a β crystal method can be mentioned as described later. Thereby, uniform physical properties and thinning can be achieved.

  In order to form a through-hole in a film using the β crystal method, the polypropylene resin used preferably has a β crystal forming ability of 40 to 90%. If the β-crystal forming ability is less than 40%, the amount of β-crystals is small at the time of film production, so the number of voids formed in the film is reduced by utilizing the transition to α-crystal, and as a result, only films with low permeability are obtained. It may not be possible. On the other hand, in order to make the β crystal forming ability exceed 90%, it is necessary to add a large amount of a β crystal nucleating agent described later, or to make the stereoregularity of the polypropylene resin to be used extremely high. Industrial practical value is low, such as deterioration of stability. Industrially, β-crystal forming ability is preferably 60 to 85%, particularly preferably 65 to 80%.

  In order to control the β crystal formation ability to 40 to 90%, a polypropylene resin having a high isotactic index is used, or a β crystal is selectively added by adding it to a polypropylene resin called a β crystal nucleating agent. The crystallization nucleating agent to be formed is preferably used as an additive. Examples of the β crystal nucleating agent include various pigment compounds and amide compounds. In particular, amide compounds disclosed in JP-A-5-310665 can be preferably used. The addition amount of the β crystal nucleating agent is preferably 0.05 to 0.5% by mass when the porous polypropylene film is 100% by mass, and is 0.1 to 0.3% by mass. More preferred.

  The polypropylene resin used in the present invention preferably has a melt flow rate (hereinafter referred to as MFR, the measurement conditions are 230 ° C., 2.16 kg) in the range of 2 to 30 g / 10 min, and is further an isotactic polypropylene resin. It is preferable that When the MFR is less than 2 g / 10 minutes, the melt viscosity of the resin becomes high and high-precision filtration becomes difficult, and the quality of the film may be lowered. When the MFR exceeds 30 g / 10 min, the molecular weight becomes too low, so that the film is easily broken during stretching, and the productivity may be lowered. More preferably, the MFR is 3 to 20 g / 10 minutes.

  Moreover, when using an isotactic polypropylene resin, it is preferable that an isotactic index is 90 to 99.9%. If the isotactic index is less than 90%, the crystallinity of the resin is low, and it may be difficult to achieve high air permeability.

  As the polypropylene resin used in the present invention, it is possible to use a homopolypropylene resin, as well as from the viewpoint of stability in the film-forming process, film-forming properties, and uniformity of physical properties, polypropylene with an ethylene component or butene, Resins obtained by copolymerizing α-olefin components such as hexene and octene in the range of 5% by mass or less can also be used. The form of introduction of the comonomer (copolymerization component) into polypropylene may be either random copolymerization or block copolymerization.

  Moreover, it is preferable that the above-mentioned polypropylene resin contains a high melt tension polypropylene in the range of 0.5 to 5% by mass in terms of improving the film forming property. High melt tension polypropylene is a polypropylene resin whose tension in the molten state is increased by mixing a high molecular weight component or a component having a branched structure into the polypropylene resin or by copolymerizing a long-chain branched component with polypropylene. However, among these, it is preferable to use a polypropylene resin copolymerized with a long chain branching component. This high melt tension polypropylene is commercially available, and for example, polypropylene resins PF814, PF633, and PF611 manufactured by Basel, polypropylene resin WB130HMS manufactured by Borealis, and polypropylene resins D114 and D206 manufactured by Dow can be used.

  Polypropylene resin used in the present invention is 80 to 99 parts by mass of polypropylene and ethylene / α-olefin copolymer 20 to 20% from the viewpoint of improving void formation efficiency during biaxial stretching and improving air permeability by increasing the pore diameter. It is preferable to use a mixture having a mass ratio of 1 part by mass. Here, examples of the ethylene / α-olefin copolymer include linear low-density polyethylene and ultra-low-density polyethylene, and among them, copolymerized octene-1 copolymerized polyethylene having a melting point of 60 to 90 ° C. A resin (copolymerized PE resin) can be preferably used. Examples of the copolymerized polyethylene include commercially available resins such as “Engage (registered trademark)” (type names: 8411, 8452, 8100, etc.) manufactured by Dow Chemical.

  When the porous polyethylene film of the present invention is 100% by mass, the copolymerized polyethylene resin contains 1 to 10% by mass to control the porosity and average through-hole diameter described below within a preferable range. Since it becomes easy, it is preferable. From the viewpoint of the mechanical properties of the film, it is more preferably 1 to 7% by mass.

  When the porous polypropylene film in the present invention is measured by unwinding the film at an arbitrary position in the longitudinal direction in the porous polypropylene film roll, the amount of curvature at a film length of 1 m is 3 mm or less. More preferably, it is 2 mm or less, More preferably, it is 1 mm or less. When the amount of bending exceeds 3 mm, the traveling property of the porous polypropylene film becomes unstable in the assembly process of the electricity storage device, and the yield may be reduced.

  As shown in FIG. 1, the amount of bending described above is such that 1 m of the porous polypropylene film is unwound from the porous polypropylene film roll after slitting and closely adhered on a horizontal plane, and the two points on one side in the film width direction are straight lines. And the deviation (mm) of the film side at the intermediate point in the longitudinal direction with respect to this straight line.

  Moreover, when the porous polypropylene film in this invention unwinds and measures the film in the arbitrary places of the longitudinal direction in a porous polypropylene film roll, the amount of sagging in 1 m of film length is 3 mm or less. More preferably, it is 2 mm or less, More preferably, it is 1 mm or less. If the amount of sag exceeds 3 mm, the runnability of the porous polypropylene film becomes unstable in the assembly process of the electricity storage device, and the yield may be reduced.

  Here, the amount of sag is as follows: when the porous polypropylene film is unrolled 1 m from the porous polypropylene film roll after slitting and placed on a horizontal plane along a straight line, as shown in FIG. Represents the maximum value when the amount of lifting (mm) from the film is measured for a total of 2 m at both ends of the film.

  In order to obtain a film excellent in quality in which the amount of bending and the amount of sag are in the above ranges, it is first important to reduce the thickness unevenness in the width direction of the porous polypropylene film, and the thickness unevenness is ± 10% or less. It is preferable that If the thickness unevenness in the width direction is large, when the porous polypropylene film is used as a take-up roll, the circumference of the thick portion may increase and rise. Since a porous film is weaker than a general film and easily deforms, the raised portion of the film stretches, and when the film is unwound, the flatness may be deteriorated. In particular, since a film having a high porosity is more easily deformed, the thickness unevenness in the width direction is more preferably + 5% or less, and further preferably ± 3% or less.

  In addition, the porous polypropylene film roll of the present invention is wound up as an intermediate roll by removing the edge portion with a slit in the film forming process, and then adjusted to a required width with a slitter to obtain a wound porous polypropylene film roll. It is preferable. Here, it is effective to hold the intermediate roll at a predetermined temperature and time from the viewpoint of improving dimensional stability.

  The porous polypropylene film in the present invention is preferably a biaxially oriented film, but in this case, the residual stress of the film immediately after film formation is large, and since the porous film is a porous film, there is a dimensional change due to the residual stress. Prone to occur. In particular, in a film having a high porosity, the strength of the film may be reduced, and the dimensional change may be increased. When a dimensional change occurs after winding on a roll, stress concentrates on the tightened portion, which may lead to deterioration of flatness when the film is unwound. In order to prevent such deterioration of flatness, the intermediate roll is wound at a low tension and maintained at a predetermined temperature and time to relieve the residual stress in the film, and then adjusted to the required width with a slitter. A wound porous polypropylene film roll is preferred.

  As temperature which hold | maintains an intermediate | middle roll, it is preferable that it is 0-90 degreeC, and if it is 0-60 degreeC, it is more preferable. When the temperature is lower than 0 ° C., it takes a long time to relieve the residual stress, and the productivity may be lowered. When the temperature exceeds 90 ° C., the dimensional change of the porous film occurs abruptly, resulting in local tightening and deterioration of flatness.

  The time for holding the intermediate roll is preferably 1 to 1,000 hours. If the heat treatment time is less than 1 hour, the effect of residual stress relaxation may be insufficient. Also, if the amount of film deformation in the intermediate roll is large, if the holding time is long, wrinkles will enter on the intermediate roll, and the flatness may deteriorate when slitting into a porous polypropylene film roll, The holding time of the intermediate roll is preferably 1,000 hours or less. More preferably, it is 1-200 hours, More preferably, it is 1-50 hours.

  The winding tension when winding the intermediate roll is preferably 1 to 150 N / m, more preferably 1 to 50 N / m, and further preferably 1 to 10 N / m. When the winding tension is less than 1 N / m, the film roll may be displaced. On the other hand, when the winding tension exceeds 150 N / m, the porous polypropylene film roll may be tightened and the flatness may be deteriorated.

  In the present invention, the core for winding the intermediate roll and the porous polypropylene film roll is a cylindrical one, and the material is not particularly limited, and paper, resin, metal, and a combination thereof may be used. it can. Furthermore, what wound the cushioning molded object which consists of foams around the outer periphery of these cores can be used preferably. The length of the core is not particularly limited as long as it is not less than the film width.

  The porous polypropylene film roll of the present invention is preferably one obtained by continuously winding (winding) a film on the core at least 100 m or more in the longitudinal direction. The film length in the longitudinal direction is more preferably 200 to 10,000 m. In the case of a porous film, if it is wound too long, the film will be crushed by its own weight, so it is more preferably 300 to 5,000 m, even more preferably 500 to 3,000 m, and more preferably 500 to 2,000 m is particularly preferable. In addition, the film width is not particularly limited, but an intermediate roll can be manufactured with a width of 0.005 to 10 m if it is a normal film forming apparatus, and then slit to a width of 0.005 to 2 m. The porous polypropylene film roll of the present invention is preferably wound. The width after the slit is preferably slit to an appropriate width in accordance with the size of the use and power storage device to be used, preferably 0.005 to 1 m, more preferably 0.01 to 0.5 m. It is preferable.

  The porous polypropylene film in the present invention preferably has a porosity of 60 to 85% from the viewpoint of ion conductivity when used as a separator. When the porosity is less than 60%, the electric resistance increases when used as a separator, and when used for a high output, heat may be generated and energy may be lost. On the other hand, when the porosity exceeds 85%, the strength of the film becomes too low, and the handleability may be inferior, for example, the film may be broken when wound together with the electrode to be stored inside the battery. From the viewpoint of achieving both excellent battery characteristics and strength, the porosity of the film is more preferably 65 to 80%, and particularly preferably 65 to 75%.

  As a method for controlling the porosity of the film to such a preferable range, when the polypropylene film is made porous by the β crystal method, as described above, a resin in which a polypropylene resin and a copolymer polyethylene resin are mixed at a specific ratio is used. This can be easily achieved, and can be effectively achieved by adopting specific biaxial stretching conditions described later. In a wet method or a uniaxially stretched film, it is difficult to obtain a porous film having such a high porosity and strength that can be put into practical use.

Porous polypropylene film of the present invention is preferably break strength E _M in the longitudinal direction is not less than 65 MPa. When the pressure is less than 65 MPa, the film may be stretched, wrinkled, or broken in the processing step for the electricity storage device using the separator. From the viewpoint of workability at the time of winding the battery, it is more preferably 70 MPa or more. The upper limit of the breaking strength is not particularly limited, but is practically about 150 MPa or less.

The porous polypropylene film of the present invention preferably has a breaking strength E _{T in the} width direction of 45 MPa or more. If it is less than 45 MPa, the difference from the breaking strength in the longitudinal direction becomes large, and the porous polypropylene film may be easily torn in the longitudinal direction.

  The breaking strength can be controlled by the crystallinity of polypropylene, the porosity of the resulting porous film, the orientation state (orientation state in the film plane), and the like. It becomes stronger by decreasing the porosity within 60 to 85%, and weaker by increasing it. Here, even with the same porosity, the higher the plane orientation, the higher the strength, so the control of the orientation state is important. For example, when the film is produced by stretching in at least one direction in the film-forming process, the planar orientation of the porous film can be increased as the stretching condition is higher or low temperature. In particular, in order to improve the breaking strength in the longitudinal direction and the width direction in a well-balanced manner, it is effective to use a longitudinal-transverse sequential biaxial stretching method and increase the longitudinal direction and the width direction by 3 to 10 times.

  Since the porous polypropylene film in the present invention is suitably used for a separator for an electricity storage device, the air resistance is preferably 10 to 1,000 seconds / 100 ml. Here, the air permeation resistance is the air permeation resistance (Gurley) defined in JIS P8117 (1998), and is a value evaluated using the JIS B-type tester in the present invention. If the air permeability resistance is less than 10 seconds / 100 ml, the film strength is low, and pinholes are easily generated when used as a separator, causing a short circuit or tearing when wound for storage inside the battery. May be inferior in handleability. On the contrary, if the air permeation resistance exceeds 1,000 seconds / 100 ml, the ion conductivity is poor. From the viewpoint of exhibiting excellent ionic conductivity as a separator, the air permeability resistance is more preferably 30 to 300 seconds / 100 ml, and particularly preferably 50 to 200 seconds / 100 ml.

  As a method for controlling the air permeability resistance to such a preferable range, it is easy to achieve by using a resin in which a polypropylene resin and a copolymerized polyethylene resin are mixed at a specific ratio, similar to the above-described porosity, and further described later. It can be effectively achieved by adopting specific biaxial stretching conditions.

  The porous polypropylene film in the present invention preferably has a total film thickness of 10 to 50 μm. If the total thickness is less than 10 μm, the film may break during use. If the total thickness exceeds 50 μm, the volume ratio of the porous film in the electricity storage device becomes too high, and a high energy density cannot be obtained. The total film thickness is more preferably 12 to 30 μm, and still more preferably 14 to 25 μm.

  In the porous polypropylene film of the present invention, an antioxidant, a heat stabilizer, an antistatic agent, a lubricant composed of inorganic or organic particles, an anti-blocking agent, a filler, Various additives such as a compatible polymer may be contained. In particular, it is preferable to add 0.01 to 0.5 parts by mass of an antioxidant with respect to 100 parts by mass of the polypropylene resin in order to suppress oxidative degradation due to the thermal history of the polypropylene resin.

  Below, the manufacturing method of the porous polypropylene film roll of this invention is demonstrated concretely. In addition, the manufacturing method of this invention is not limited to this.

  First, as a polypropylene resin, 94 parts by mass of a commercially available homopolypropylene resin having an MFR of 8 g / 10 minutes, 1 part by mass of a commercially available MFR of 2.5 g / 10 minutes and a high melt tension polypropylene resin, and an ultra low density polyethylene having a melt index of 18 g / 10 minutes. A raw material is prepared by mixing 5 parts by mass of resin with 0.2 part by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide and using a twin screw extruder in advance at a predetermined ratio. At this time, the melting temperature is preferably 270 to 300 ° C. It is preferable to remove foreign matters by providing a high-accuracy filter that can remove foreign matters of, for example, 20 μm or more on the downstream side of the twin-screw extruder.

  Next, the above-mentioned mixed raw material is supplied to a single screw melt extruder, and melt extrusion is performed at 200 to 230 ° C. And after removing a foreign material, a modified polymer, etc. with the filter installed in the middle of the polymer pipe | tube, it discharges on a cast drum from T-die, and an unstretched sheet is obtained. At this time, for example, it is preferable to remove the foreign matter by providing a high-accuracy filter that can remove the foreign matter of 20 μm or more.

  Moreover, it is preferable from the viewpoint of controlling the β crystal fraction in the unstretched sheet that the cast drum for obtaining the unstretched sheet has a surface temperature of 105 to 130 ° C. At this time, in particular, since the forming of the end portion of the sheet affects the subsequent stretchability, it is preferable that the end portion is sprayed with spot air to be in close contact with the drum. Further, air may be blown over the entire surface using an air knife as necessary based on the state of close contact of the entire sheet on the drum.

  Next, the obtained unstretched sheet is biaxially stretched to form pores (through holes) in the film. As a biaxial stretching method, the film is stretched in the longitudinal direction of the film and then stretched in the width direction, or the sequential biaxial stretching method of stretching in the longitudinal direction after stretching in the width direction, or the longitudinal direction and the width direction of the film are stretched almost simultaneously. The simultaneous biaxial stretching method can be used, but it is preferable to adopt the sequential biaxial stretching method in that it is easy to obtain a highly air-permeable film, and in particular, it is possible to stretch in the width direction after stretching in the longitudinal direction. preferable.

  As specific stretching conditions, first, the unstretched sheet is controlled to a temperature at which it can be stretched in the longitudinal direction. As a temperature control method, a method using a temperature-controlled rotating roll, a method using a hot air oven, or the like can be adopted. As the stretching temperature in the longitudinal direction, it is preferable to employ a temperature of 110 to 140 ° C., more preferably 120 to 135 ° C., from the viewpoint of film characteristics and uniformity. The draw ratio is preferably 3 to 10 times, more preferably 4 to 6 times, still more preferably 4.5 to 5.8 times. When the draw ratio is less than 3 times, the porosity may be lowered to deteriorate the battery characteristics, and the productivity may be lowered. As the stretching ratio is increased, the porosity is increased. However, if the stretching ratio exceeds 10 times, the film may be easily broken in the next transverse stretching step. Here, the stretching temperature in the longitudinal direction that can particularly obtain a high porosity film is 120 to 125 ° C.

  Next, the uniaxially stretched polypropylene film obtained above is introduced by gripping the end of the film with a tenter stretcher, and stretched in the width direction to obtain a biaxially stretched (biaxially oriented) film. The stretching temperature is preferably 130 to 155 ° C, and more preferably 145 to 150 ° C because a high porosity is obtained. The stretching ratio in the width direction is preferably 3 to 10 times, more preferably 4 to 8 times. When the draw ratio is less than 3 times, the porosity may be lowered to deteriorate the battery characteristics, and the productivity may be lowered. Moreover, the higher the stretching ratio, the higher the porosity. However, if the stretching ratio exceeds 10 times, the film may be easily broken. The transverse stretching speed at this time is preferably 500 to 6,000% / min, more preferably 1,000 to 5,000% / min.

  Subsequently, heat setting is performed in the tenter as it is, and the temperature is preferably from the transverse stretching temperature to 160 ° C., and the heat setting time is preferably 1 to 30 seconds. Further, the heat setting may be performed while relaxing in the longitudinal direction and / or the width direction of the film. In particular, the relaxation rate in the width direction is preferably 7 to 20% from the viewpoint of thermal dimensional stability.

  Next, the biaxially stretched porous polypropylene film in the winding process is slit to a predetermined width, and a constant winding tension is applied within the above-described range to obtain a winding intermediate roll on the core. Further, the obtained intermediate roll is stored at a predetermined temperature and time within the above-mentioned range, and then slitted to a predetermined product width with a slitter and wound around a core to obtain the porous polypropylene film roll of the present invention.

  As a method for storing the intermediate roll, a method in which the film roll is placed horizontally in an oven or a temperature-controlled room under a predetermined temperature and humidity while holding both ends of the film roll, stored for a predetermined time, and then taken out. Is preferred. The humidity during storage is preferably 65% RH or less, and more preferably 30% RH or less. When the humidity exceeds 65% RH, the water content of the porous polypropylene film increases, and the battery characteristics may deteriorate when used as a separator for an electricity storage device.

  Next, in the slitting step, the intermediate roll is unwound and slit to the required product width, and then the porous polypropylene film roll of the present invention is wound around the core. The winding tension at this time is preferably 10 to 150 N / m, and more preferably 10 to 50 N / m. If it is less than 10 N / m, the winding tension may be too weak to cause a winding slip during conveyance of the product, and if it exceeds 150 N / m, the porous polypropylene film may be crushed and the thickness of the product may change. Note that the width of the slit process may be adjusted stepwise by dividing it into two or more times.

  The porous polypropylene film roll of the present invention is excellent in productivity and not only exhibits excellent battery characteristics when used as a separator for an electricity storage device, but also has excellent processability in the battery manufacturing process. It can preferably be used as a separator for non-aqueous electrolyte secondary batteries.

  Hereinafter, the present invention will be described in detail by way of examples. The characteristics were measured and evaluated by the following methods.

(1) β-crystal forming ability 5 mg of resin or film was sampled in an aluminum pan and measured using a differential scanning calorimeter (Seiko Denshi Kogyo RDC220). First, the temperature is raised from room temperature to 260 ° C. at a rate of 10 ° C./minute (first run) in a nitrogen atmosphere, held for 10 minutes, and then cooled to 20 ° C. at a rate of 10 ° C./minute. After holding for 5 minutes, the melting peak observed when the temperature is raised again at 10 ° C./min (second run) is the melting peak of the β crystal at 145 ° C. to 157 ° C., 158 ° C. The melting at which the peak is observed is defined as the melting peak of the α crystal, and the melting heat amount of the α crystal is obtained from the baseline and the area of the region surrounded by the peak drawn from the flat portion on the high temperature side. Is the ΔHα, and the heat of fusion of the β crystal is ΔHβ, the value calculated by the following formula is the β crystal forming ability. The heat of fusion was calibrated using indium.

β crystal forming ability (%) = [ΔHβ / (ΔHα + ΔHβ)] × 100
In addition, the β crystal fraction in the state of the sample can be calculated by calculating the abundance ratio of the β crystal in the same manner from the melting peak observed in the first run.

(2) Melt flow rate (MFR)
The MFR of the polypropylene resin is measured according to the condition M (230 ° C., 2.16 kg) of JIS K 7210 (1995). The polyethylene resin is measured in accordance with the condition D (190 ° C., 2.16 kg) of JIS K 7210 (1995).

(3) Porosity The film was cut into a size of 30 mm × 40 mm and used as a sample. Using an electronic hydrometer (SD-120L manufactured by Mirage Trading Co., Ltd.), the specific gravity was measured in an atmosphere at a room temperature of 23 ° C. and a relative humidity of 65%. The measurement was performed three times, and the average value was defined as the specific gravity ρ of the film.

  Next, the measured film was hot-pressed at 280 ° C. and 5 MPa, and then rapidly cooled with water at 25 ° C. to prepare a sheet in which pores were completely erased. The specific gravity of this sheet was measured in the same manner as described above, and the average value was defined as the specific gravity (d) of the resin. In the examples described later, the specific gravity d of the resin was 0.91 in any case. From the specific gravity of the film and the specific gravity of the resin, the porosity was calculated by the following formula.

Porosity (%) = [(d−ρ) / d] × 100
(4) Curvature amount As shown in FIG. 1, 1 m of the porous polypropylene film is unwound from the porous polypropylene film roll after slitting and closely adhered on a horizontal plane, and the two points on one side in the film width direction are connected by a straight line, The displacement (mm) of the film side at the midpoint in the longitudinal direction with respect to this straight line was measured using a caliper.

(5) Slack amount When 1 m of a porous polypropylene film is unwound from a porous polypropylene film roll after slitting and placed along a straight line on a horizontal plane, the film is lifted from the plane as shown in FIG. The maximum value when the amount (mm) is measured using a caliper for 2 m in total on both ends of the film.

(6) Breaking strength According to JIS K 7127 (1999, test piece type 2), using an orientec film strength measuring device (AMF / RTA-100) at 25 ° C. and 65% RH. The breaking strength was measured. Specifically, the porous polypropylene film was cut into a size of 15 cm in the longitudinal direction and 1 cm in the width direction, stretched at an original length of 50 mm, and a tensile speed of 300 mm / min, and the breaking strength (unit: MPa) was measured. The same measurement was performed 5 times for the same sample, and the average value of the obtained breaking strengths was taken as the breaking strength in the longitudinal direction of the sample. Further, the longitudinal direction and the width direction of the sample were interchanged, and the breaking strength in the width direction was measured in the same manner.

(7) Air permeability resistance (Gurley air permeability)
Based on B method of JIS P 8117 (1998), measurement was performed at 23 ° C. and 65% RH (unit: second / 100 ml). The same measurement was performed for the same sample five times at different locations, and the average value of the obtained Gurley air permeability was taken as the air resistance of the sample. At this time, those having an average value of Gurley air permeability exceeding 7,200 seconds / 100 ml were regarded as substantially having no air resistance, and were set to infinity (∞) seconds / 100 ml.

(8) Battery characteristic evaluation Using a positive electrode with a lithium cobalt oxide (LiCoO ₂ ) thickness of 40 μm manufactured by Hosen Co., Ltd., punched into a circle with a diameter of 15.9 mm, and the thickness of graphite manufactured by Hosen Co., Ltd. Is punched into a circular shape with a diameter of 16.2 mm, and then the separator film of each example and comparative example is punched into a diameter of 24.0 mm so that the positive electrode active material faces the negative electrode active material surface. From the bottom, the negative electrode, the separator, and the positive electrode were stacked in this order and stored in a small stainless steel container with a lid. The container and the lid are insulated, the container is in contact with the negative electrode copper foil, and the lid is in contact with the positive electrode aluminum foil. Into this container, an electrolytic solution in which LiPF ₆ was dissolved as a solute in a mixed solvent of ethylene carbonate: dimethyl carbonate = 3: 7 (mass ratio) to a concentration of 1 M / L was injected and sealed. A battery was produced for each example and comparative example.

  Each of the fabricated secondary batteries was subjected to a charge / discharge operation in a 25 ° C. atmosphere at a charge of 3 mA to 4.2 V for 1.5 hours and a discharge of 3 mA to 2.7 V, and the discharge capacity was examined. Further, a charging / discharging operation was performed in which charging was performed at 3 mA up to 4.2 V for 1.5 hours, and discharging was performed at 30 mA up to 2.7 V, and the discharge capacity was examined.

  The value obtained by the formula of [(30 mA discharge capacity) / (3 mA discharge capacity)] × 100 was evaluated according to the following criteria. In addition, 20 test pieces were measured, and the average value was evaluated.

○: 80% or more Δ: 75% or more and less than 80% ×: less than 75% (9) Evaluation of workability As a runnability evaluation of a porous polypropylene film roll, meandering during winding was evaluated using a small slitter. A porous polypropylene film roll was set on a slitter unwinder, and the film was run at a speed of 20 m / min and wound without slitting. The unwinding tension, winding tension and conveying tension at this time were 30 N / m. Evaluation was made according to the following criteria based on the displacement of the end face when rolled up by 100 m.

○: Less than 1 mm Δ: 1 mm or more and less than 3 mm ×: 3 mm or more (Example 1)
As a raw material resin for a porous polypropylene film, 94 parts by mass of homopolypropylene FLX80E4 (hereinafter referred to as PP-1; MFR = 8) manufactured by Sumitomo Chemical Co., Ltd., Basel polypropylene PF-814 (which is a high melt tension polypropylene resin) Hereinafter, HMS-PP, MFR = 2.5) 1 part by mass, ethylene-octene-1 copolymer Dow Chemical Engage 8411 (melt index: 18 g / 10 min, hereinafter simply referred to as PE) Is added to 5 parts by mass of N, N′-dicyclohexyl-2,6-naphthalenedicarboxamide (Nippon Rika Co., Ltd., Nu-100, hereinafter referred to as “β crystal nucleating agent”). 0.2 parts by mass), IRGANOX1010 manufactured by Ciba Specialty Chemicals, which is an antioxidant, and IRG The raw material is supplied from the weighing hopper to the twin screw extruder so that 0.15 and 0.1 parts by mass of FOS 168 are mixed at this ratio, melt kneaded at 300 ° C., and discharged from the die in a strand shape. Then, it was cooled and solidified in a water bath at 25 ° C. and cut into chips to obtain chip raw materials.

  This chip is supplied to a single screw extruder and melt extruded at 210 ° C. After removing foreign matter with a 25 μm cut sintered filter, it is discharged from a T die to a cast drum whose surface temperature is controlled at 120 ° C. An unstretched sheet was obtained by casting for 15 seconds. The β-crystal forming ability of the unstretched film was 65%. Next, preheating was performed using a ceramic roll heated to 125 ° C., and the film was stretched 5 times in the longitudinal direction of the film. Next, the end portion was introduced into a tenter-type stretching machine by grasping with a clip, and stretched in the width direction at 150 ° C. five times at a stretching speed of 1,800% / min. As it is, heat fixing treatment is performed for 3 seconds at 155 ° C. while relaxing 10% in the width direction, and then the edge part is cut off by 200 mm at both ends, slit to 500 mm in width, and the intermediate roll is wound with a tension of 3 N / m. Obtained. Thereafter, the core of the intermediate roll was held horizontally in a storage room at 30 ° C. for 100 hours. Then, it slit to 200 mm in width | variety with the slitter, and it wound up with the tension | tensile_strength of 30 N / m, and obtained the porous polypropylene film roll. The thickness of the porous polypropylene film was 25 μm. Table 1 shows the physical properties of the obtained film.

(Example 2)
A porous polypropylene film roll was obtained with the raw material composition and film forming conditions described in Example 1 except that the holding time after winding the intermediate roll in Example 1 was 48 hours.

(Example 3)
A porous polypropylene film roll was obtained with the raw material composition and film forming conditions described in Example 1 except that the draw ratio in the width direction was changed to 2.5 times and the draw speed was changed to 900% / min in Example 1. .

Example 4
A porous polypropylene film roll was obtained with the raw material composition and film forming conditions described in Example 1, except that the draw ratio in the longitudinal direction was changed to 2.5 in Example 1.

(Example 5)
A porous polypropylene film roll was obtained with the raw material composition and film forming conditions described in Example 1, except that the tension when winding the intermediate roll in Example 1 was 30 N / m.

(Example 6)
A porous polypropylene film roll was obtained with the raw material composition and film forming conditions described in Example 1 except that the tension when winding the intermediate roll in Example 1 was 100 N / m.

(Example 7)
As a raw material resin for the porous polypropylene film, a homopolypropylene FLX80E4 manufactured by Sumitomo Chemical Co., Ltd. is supplied to a uniaxial melt extruder as a raw material for the surface layer A, and a material for the intermediate layer B layer is Sumitomo Chemical Co., Ltd. ) Homopolypropylene D101 (MFR = 0.5) made by a single-screw melt extruder, melt extruded at 230 ° C., and after removing foreign matter with a 25 μm cut sintered filter, three layers in a feed block Laminated (A / B / A laminated), discharged from a T-die (slit gap 1.8 mm) onto a cast drum whose surface temperature was controlled at 115 ° C., and wound an unstretched film having a thickness of 150 μm at 60 m / min. . Subsequently, the obtained unstretched film was stretched 1.5 times in the longitudinal direction at 50 ° C. and further 1.7 times in the longitudinal direction at 150 ° C., and subjected to heat setting treatment at 140 ° C. for 3 seconds. The edge portion was cut off and slit to a width of 300 mm to obtain a winding intermediate roll with a tension of 3 N / m. Thereafter, the core of the intermediate roll was held horizontally in a storage room at 30 ° C. for 100 hours. Then, it slit to 200 mm in width | variety with the slitter, and it wound up with the tension | tensile_strength of 30 N / m, and obtained the porous polypropylene film roll. The thickness of the porous polypropylene film was 55 μm. Table 1 shows the physical properties of the obtained film.

(Comparative Example 1)
A porous polypropylene film roll was obtained with the raw material composition and film forming conditions described in Example 1, except that the tension when winding the intermediate roll in Example 1 was 200 N / m.

(Comparative Example 2)
A porous polypropylene film roll was obtained with the raw material composition and film forming conditions described in Example 1 except that the tension when winding the intermediate roll in Example 1 was 300 N / m.

(Comparative Example 3)
A porous polypropylene film roll was obtained with the raw material composition and film forming conditions described in Example 1 except that the holding time after winding the intermediate roll in Example 1 was 10 minutes.

(Comparative Example 4)
A porous polypropylene film roll was obtained with the raw material composition and film forming conditions described in Example 1, except that the holding time after winding the intermediate roll in Example 1 was 1,500 hours.

  In Examples satisfying the requirements of the present invention, in addition to high porosity and excellent productivity, the film quality and flatness are excellent, and therefore it can be suitably used as a separator for an electricity storage device. On the other hand, in the comparative example, since the flatness that causes the battery assembly failure is deteriorated, it is difficult to use as a separator for the electricity storage device.

  The porous polypropylene film roll of the present invention is excellent in productivity, exhibits excellent battery characteristics when used as a separator of an electricity storage device, and is suitable as a separator for a lithium ion battery because of excellent processing suitability in a battery manufacturing process. Can be used for

11: Porous polypropylene film 12: Distance from the porous polypropylene film to the bending amount measurement site (500 mm)
13: bending amount measurement site 14: distance from the porous polypropylene film to the bending amount measurement site (500 mm)
21: Porous polypropylene film 22: Stand having a horizontal plane 23: Sag amount measurement site

Claims (4)

A porous polypropylene film roll obtained by winding a porous polypropylene film by a dry method on a core, and the film length when measured by unwinding the film at an arbitrary position in the longitudinal direction in the porous polypropylene film roll A porous polypropylene film roll having a bending amount and a sagging amount of 1 mm or less at 1 m. The porous polypropylene film roll according to claim 1, wherein the porous polypropylene film is formed by winding a porous polypropylene film having a porosity of 60 to 85%. Longitudinal breaking strength E _M is at least 65 MPa, the breaking strength E _T in the width direction is by winding a porous polypropylene film is not less than 45 MPa, the porous polypropylene film roll according to claim 1 or 2. The porous polypropylene film roll in any one of Claims 1-3 formed by winding the porous polypropylene film containing the polypropylene resin whose (beta) crystal formation ability is 40 to 90%.

Images