WO2012133097A1

WO2012133097A1 - Process for producing roll of microporous plastic film

Info

Publication number: WO2012133097A1
Application number: PCT/JP2012/057311
Authority: WO
Inventors: 一ノ宮崇; 松本忠
Original assignee: 東レ株式会社
Priority date: 2011-03-30
Filing date: 2012-03-22
Publication date: 2012-10-04
Also published as: CN103459283A; CN103459283B; KR101883191B1; KR20130143104A; US20140014762A1; JPWO2012133097A1; JP5853951B2; TW201302895A

Abstract

A process for producing a roll (12) of a microporous plastic film which includes conveying a microporous plastic film (1) by means of a plurality of conveyor rollers (21-24) and winding the film on a core (6). At least one of the conveyor rollers (21-24) has a surface constituted of a fluororesin or a silicone rubber or of a composite material (9) containing either. The composite material (9) comprises a hard chromium layer (7) formed by plating and a fluororesin (8). The at least one roller has a surface roughness RzJIS of 0.3-30 µm. The film (1) has a plurality of through-holes (17) therein and is for use as the separators (16) of a lithium-ion secondary battery (10) or as the separators of capacitors. The film (1) can be prevented from creasing or breaking, because the coefficient of friction between the film (1) and the conveyor rollers (21-24) is low.

Description

Method for producing microporous plastic film roll

The present invention relates to a method for producing a microporous plastic film roll.

Conventionally, when a microporous plastic film used for a secondary battery separator or the like is transported and wound into a roll, it has been extremely difficult to avoid wrinkles and tears that may be caused by microporosity.

Non-Patent Document 1 theoretically obtains a wrinkle generation limit value of a general film, and proposes a countermeasure under a method of preventing a crease. According to this document, the wrinkle generation limit value is expressed by the tension and the alignment angle. In particular, the limit value regarding the tension is determined by the thickness, Young's modulus, width, and friction coefficient of the film. Further, as a countermeasure, it has been proposed to adjust the film tension while predicting the slip limit value which is a trade-off so as to straddle the wrinkle limit value determined by the above parameters. However, according to the knowledge of the present inventors, it is difficult to adjust the tension freely with a film that has a low strength against tearing and is easily crushed in the thickness direction, such as a microporous plastic film. It was difficult to carry the sheet so as to achieve both wrinkles and tears.

On the other hand, Patent Document 1 proposes to control the roughness and friction coefficient by arranging particles on the film surface in order to solve the handling problems such as blisters and wrinkles of the polyester film for high-density magnetic recording media. is doing. However, according to the knowledge of the present inventors, in the microporous plastic film, the friction coefficient is not increased due to the smoothness of the film surface. It was difficult to do. Also, particles are no solution for breaking.

Non-Patent Document 2 describes the coefficient of static friction and the characteristics of substances. The coefficient of static friction is proportional to the ratio of the shear strength τ due to intermolecular force and the hardness H of the substance, and it is said that friction can be reduced by selecting a material with a large H and a small τ (silver, fluororesin, lead, etc.). . However, the main purpose of this document is to clarify the friction mechanism and to clarify the actual friction phenomenon under air lubrication, and to take concrete measures against coexistence of wrinkling and tearing of microporous plastic film. It has not yet been revealed.

Further, Non-Patent Document 3 describes an example in which the theory described in Non-Patent Document 1 is applied to an actual production process. Although there is a consideration that reduction of the friction coefficient is effective for reducing wrinkles in conveyance, according to the knowledge of the present inventors, it is necessary to take measures against a unique friction generation mechanism, such as a microporous plastic film, Non-Patent Document 3 does not clearly indicate a countermeasure for coexistence of wrinkles and tears.

In Patent Document 2, diamond-like carbon (hereinafter referred to as DLC) is used in order to reduce the friction coefficient of a rubber layer on the surface of a pressing roller or a conveying roller that is pressed against a film roll while removing air. Proposals have been made on techniques for forming on the surface. However, according to the knowledge of the present inventors, the effect of reducing the friction coefficient by the DLC layer is realized by preventing the micro deformation of the surface by the high hardness of the thin DLC layer and reducing the true contact area. It is less effective against the phenomenon that the coefficient of friction increases due to the flexibility of the film itself.

On the other hand, Patent Document 3 proposes a means for preventing scratches generated on the film by forming the surface of the transport roller with metal, smoothing the surface roughness, and reducing the coefficient of friction. However, according to the knowledge of the present inventors, in a synthetic resin film having a smooth surface as described in Patent Document 3, the phenomenon is considered to be air lubrication by reducing the protrusions by smoothing the roughness of the roller. It can be expected that the friction coefficient will be reduced by using the film.However, in the case of a film in which air escapes from the micropore, such as a microporous plastic film, air lubrication cannot be expected, and the reverse will occur due to contact with a smooth metal surface. In this case, the coefficient of friction increases, and the wrinkles and tears as described above cannot be prevented.

Thus, conventionally, there has been no suitable technique for transporting a microporous plastic film without wrinkles or tearing and winding it into a roll.

JP 11-314333 A JP 2004-251373 A JP 2001-63884 A

An object of the present invention is to provide a method for producing a microporous plastic film, which has been difficult to handle due to wrinkles or tears due to the presence of micropores.

In order to achieve the above object, the present invention provides a surface roughness RzJIS (μm) of 0.3 ≦ RzJIS ≦ 30 and a surface material of fluororesin or silicone as at least one of the plurality of transport rollers. Provided is a method for producing a microporous plastic film roll, characterized by using a rubber or a composite material containing these, transporting a microporous plastic film having a through-hole inside and winding it into a roll. .

Further, according to a further preferred aspect of the present invention, there is provided the method for producing a plastic film roll according to the feature, wherein the material of the surface of the transport roller is polytetrafluoroethylene.

Also, according to a preferred embodiment of the present invention, there is provided a method for producing a microporous plastic film roll, wherein the Gurley gas resistance of the microporous plastic film is 10 to 1000 seconds / 100 ml.

Further, according to a preferred embodiment of the present invention, there is provided the method for producing a microporous plastic film roll according to the above, wherein the porosity of the microporous plastic film is 30% or more.

Further, according to a preferred embodiment of the present invention, there is provided a method for producing a microporous plastic film roll, wherein the microporous plastic film has a microporous average pore diameter of 50 to 200 nm.

Further, according to a preferred embodiment of the present invention, there is provided a method for producing a microporous plastic film roll, wherein the cushion ratio of the microporous plastic film is 15% or more and less than 50%.

Also, according to a preferred embodiment of the present invention, there is provided a method for producing a microporous plastic film roll, wherein the thickness of the microporous plastic film is 50 μm or less.

Also, according to a preferred embodiment of the present invention, there is provided a method for producing a microporous plastic film roll, wherein the microporous plastic film has a width of 100 mm or more.

Further, according to a preferred embodiment of the present invention, there is provided a method for producing a microporous plastic film roll having a static friction coefficient of 0.6 or less between the microporous plastic film and the transport roller.

Also provided is a method for producing a microporous plastic film roll, wherein the microporous plastic film is a separator for a secondary battery or a capacitor.

In the present invention, the “conveying roller” is a means for conveying a microporous plastic film continuous in the length direction from the upstream to the downstream of the manufacturing process, and means a cylindrical body that is rotatably supported.

In the present invention, “RzJIS” means ten-point average roughness.

In the present invention, “fluororesin” refers to a generic name for synthetic resins containing a part of fluorine element such as ethylene hydrocarbon.

In the present invention, “silicone rubber” refers to a silicone resin exhibiting rubber-like elasticity, and the silicone resin refers to a generic name for synthetic resins having a siloxy acid bond composed of silicon (silicon) and oxygen.

In the present invention, the “composite material” means a material mixed to such an extent that the properties of the fluororesin or silicone resin can effectively contribute. For example, the fluororesin or silicone resin is interposed between a rubber material and a metal plating material. This includes things that are coated or filled.

In the present invention, the “microporous plastic film” refers to a polymer thin film having a large number of micropores inside the film, and a part or all of the micropores are composed of through-holes.

In the present invention, “polytetrafluoroethylene” is a kind of fluororesin called abbreviated PTFE, which is also called “tetrafluoroethylene”. In the present invention, the “thickness” is a volume obtained by dividing the volume constituting the microporous plastic film roll by the width and the length, and means the thickness including the air layer constituting the microporous.

In the present invention, “Gurley air resistance” is an index of air permeability of a film or sheet obtained by a test method shown in Japanese Industrial Standard JIS P8117 (2009).
The higher the air permeability, the shorter the time for passing through the micropores, and the Gurley air resistance shows a small value.

In the present invention, “porosity” refers to the area ratio of the micropores in the cross-sectional area of the film.

In the present invention, the “microporous average pore diameter” indicates the average value of the microporous diameter composed of a large number of pores having different diameters.

In the present invention, the “cushion rate” is a rate of change in thickness when a surface pressure is applied in the thickness direction of the sheet represented by the following formula.

Cushion rate (%) = (1−T1 / T2) × 100
T1: When a probe with a diameter of 10 mm is attached to a dial gauge manufactured by Mitoyo Seisakusho and a load of 50 g is applied in the film thickness direction from the probe side, the value before sandwiching the film is set to zero when the film is sandwiched. Film thickness after 2 seconds T2: When a probe of φ10 mm is attached to a dial gauge manufactured by Mitoyo Seisakusho, and a load of 500 g is applied in the film thickness direction from the probe, the value before sandwiching the film is zero. Film thickness 30 seconds after sandwiching the film In the present invention, the “secondary battery” refers to a battery that can be charged and discharged, and also referred to as a storage battery.

In the present invention, the “separator” refers to a functional film that prevents the electrodes from being short-circuited, and those that are permeable to the ionic electrolyte due to the presence of micropores are those that can be used in batteries. Say.

In the present invention, a “capacitor” refers to a passive element that can store or discharge electrical energy by electrostatic capacitance.

According to the present invention, as described below, it is possible to obtain a microporous plastic film roll manufacturing method capable of manufacturing a microporous plastic film excellent in quality by preventing wrinkles and tearing with high productivity. it can.

1 is a schematic side view of an embodiment of the present invention. It is a schematic enlarged view of the conveyance roller surface of one Embodiment of this invention. It is the example which applied the microporous plastic film manufactured by one Embodiment of this invention to the separator for secondary batteries. It is an enlarged plan view of the microporous plastic film manufactured by one Embodiment of this invention. It is the schematic side view which showed the measuring method of the coefficient of static friction between the part which contacts a film of a conveyance roller, and a film.

Hereinafter, an example of the best embodiment of the present invention will be described with reference to the drawings, taking as an example the case of applying to a method for producing a microporous plastic film used for a separator film for a secondary battery.

FIG. 1 is a schematic side view of a conveyance / winding unit which is a manufacturing process of a microporous plastic film roll according to an embodiment of the present invention.

The microporous plastic film 1 may be formed by any method. As a preferred example, after melted polyolefin resin is kneaded with a highly volatile solvent in an extruder, it is discharged from a die onto a cooling drum to form a gel sheet, and after appropriately stretching and orientation, the solvent is washed and dried. It is obtained by. Alternatively, a polyolefin resin kneaded with a crystal nucleating agent may be obtained by discharging the resin from a die onto a cooling drum and forming micropores by controlling the crystal structure without using a solvent. Alternatively, a microporous film 1 may be obtained by combining a solvent having a different compatibility with a heat-resistant polymer such as polyamide or polyimide to form micropores and discharging or coating. In addition, heat-resistant coating or the like may be performed on one or both surfaces of the polyolefin microporous film as long as the microporous air permeability is maintained. Alternatively, a microporous film may be formed as an aggregate of synthetic fibers, such as paper or nonwoven fabric.

The microporous plastic film 1 obtained in this way is preferably uniaxially or biaxially stretched as appropriate in order to achieve control of the pore structure and strength.

FIG. 4 is an enlarged plan view of an example of the microporous plastic film 1. As shown in the figure, the microporosity of the plastic film 1 may be formed by any means. When the resin layer portion constituting the periphery of the hole is formed by stretching orientation, it becomes a fibrous column as shown in the figure, and this may be called a fibril 18. A part or all of the micropores function as the through holes 17.

FIG. 3 is an explanatory diagram schematically showing a part of a cylindrical lithium ion secondary battery. Inside the case 11, a separator 16 is disposed between the positive electrode 14 and the negative electrode 15 as an insulating material that prevents a short circuit between the electrodes. The inside of the case is filled with a lithium ion electrolytic solution, and the separator 16 is required to have an ion permeation performance in the electrolytic solution as well as an insulating performance. For this reason, the microporous plastic film 1 which has a through-hole in the one part or the whole surface manufactured by the manufacturing method of this invention is suitable.

The microporous plastic film 1 is conveyed at a predetermined speed by the conveying roller group 2 as shown in FIG. 1, and is wound up as a film roll 12 on the core 6 with a predetermined tension. In FIG. 1, the transport roller group 2 is driven by a drive source 32 such as a motor via a drive transmission means 4 such as a belt or a chain. The drive transmission means 4 is supported by a necessary tension given by a pulley 5. Here, the transport roller group 2 does not necessarily have to be driven by the drive source 32 in all cases, and can support the transport of the film 1 as an idler as long as the transport roller group 2 is rotatably supported by a bearing. In this case, when the scratches and abrasion powder of the film 1 are disliked, the film 1 may be driven indirectly through a bearing, or the inertia of the roller and the friction loss of the bearing may be reduced as much as possible.

Here, the microporous plastic film 1 suitable for a battery separator or the like generally causes a hysteresis loss and an increase in a real contact area due to the collapse of the microporous, and increases a coefficient of static friction with a contacting object. In particular, when the film 1 is transported by the transport roller group 2 as shown in FIG. 1, the static friction coefficient due to the above factors increases at the portion where the roller and the film are in contact with each other, and the air that can be expected when transporting a film without a normal hole Lubrication is not performed due to air escape through the micropores, resulting in a high coefficient of friction. As described above, the increase in the friction coefficient causes problems of wrinkles and tears on the transport rollers and between the transport rollers. To avoid this problem, in the present invention, at least of the plurality of transport roller groups 2. By reducing the static friction coefficient on the surface of one transport roller, the stress caused by the speed difference was reduced and the microporous plastic film was successfully prevented from being torn.

In order to reduce the static friction coefficient of the conveying roller 2, the ten-point average surface roughness of the surface is set to 0.3 ≦ RzJIS (μm) ≦ 30. When RzJIS is set to 0.3 μm or more, the true contact area, which is increased by crushing the micropores in the microporous plastic film 1, can be kept small, and the static friction coefficient is reduced. Further, the microporous plastic film 1 tends to have a large contact area because air escapes from the microporous due to the air permeability, but the static friction coefficient can be reduced by appropriately roughening the surface of the conveying roller 2. . On the other hand, if the roughness of the surface of the conveying roller 2 becomes too large, processing becomes difficult, and if RzJIS exceeds 30 μm, the roller surface becomes expensive and low in accuracy. If the roughness is too large, the contact area between each surface protrusion and the film increases, so that the coefficient of static friction increases conversely. More preferably, RzJIS is in the range of 2 ≦ RzJIS (μm) ≦ 10.

In addition, as a result of intensive studies by the inventor of the present application, in order to achieve a low coefficient of friction for a film such as a microporous plastic in which air permeability and hole collapse occur, The present inventors have found that it is necessary to realize low friction by intermolecular force rather than a surface that aims at low friction due to the hardness of the contact surface such as DLC (diamond-like carbon). This is because no matter how hard the surface material of the roller 2 is, the surface of the microporous plastic film 1 is crushed and the real contact area is not reduced.

Therefore, as the surface material of the transport roller group 2 that comes into contact with the microporous plastic film 1, rubber is generally used, whereas in the present invention, the material having a small intermolecular force is a fluororesin or silicone rubber, or A composite material containing these is applied. The thickness of the fluororesin is several tens of μm, preferably about 10 to 100 μm, from the viewpoint of improving durability and processing spots. In general, the fluororesin is preferably fired at 300 to 400 ° C. When coating on resin or rubber, it is preferable to mold at 100 ° C. or lower. In this case, in order to obtain the accuracy of the roller surface, it is effective to use polishing together. Moreover, the method of forming the fluororesin on the roller is preferably formed by coating, spraying, or fitting. For example, it may be formed by coating a roller with a tape-like or tube-like fluororesin. When a roller is coated with a tape-shaped or tube-shaped fluororesin, a thickness of about several mm is preferable because it is easy to form.

In the case of silicone rubber, the thickness is preferably several mm, and it is preferable to provide a thickness of about 1 to 10 mm.

It is preferable to use steel, stainless steel, aluminum alloy, CFRP, or the like as the transport roller base material 2A.

Here, the composite material refers to a material mixed to such an extent that the property of contributing to low friction of the fluororesin or silicone rubber acts effectively. For example, it includes a material coated or filled between a rubber material and a metal plating material. FIG. 2 shows an example of such a composite material 9 in which a fluororesin 8 is impregnated between the roughness of the hard chrome plating layer 7 applied on the conveying roller base material 2A. At this time, the portion in contact with the microporous plastic film 1 is configured such that the metal plating layer 7 and the fluororesin 8 are randomly scattered, and the function of reducing the friction coefficient of the fluororesin and the wear resistance of the metal plating layer. Each merit can function effectively.

When such a fluororesin is combined with the plating layer, the processing method is preferably fired at a high temperature as described above to obtain the strength of the surface treatment, and the conveying roller base material 2A is distorted at a high temperature. Steel that has been heat-treated in advance so as not to occur can be used.

For the purpose of satisfying the above functions, it is not necessary to be a composite material with metal plating, and it may be a composite material with ceramics, rubber, or other resin, for example. The roller surface may be covered with the fluororesin or silicone rubber or both.

Here again, the composite material has a function of controlling wear resistance and roughness by interspersing a hard material such as ceramic with respect to fluororesin or silicone rubber.

By selecting such a material, the coefficient of static friction with the microporous plastic film 1 can be reduced.

By using these roughness and material together, the coefficient of static friction with the microporous plastic film 1 can be reduced to a value necessary for preventing tearing and wrinkling. In other words, the friction coefficient is effectively reduced only when the material is selected within the above range so that the material with small intermolecular force is selected and the contact area is effectively reduced even when the surface of the microporous plastic film is crushed. Can be made.

In particular, in the case of a composite material, the above-mentioned roughness is not obtained only by the plating layer 7, but the roughening after a fluororesin or silicone rubber is formed on a base material such as a plating layer and subjected to final finishing such as polishing as necessary. However, it is necessary to satisfy the range of RzJIS.

A preferable value of the static friction coefficient can be 0.6 or less. Furthermore, if the value of the ten-point average roughness is increased within the above range, or a combination with the material is performed, the static friction coefficient can be further reduced to 0.5 or less.

For example, as the material of the conveying roller 2, polytetrafluoroethylene is more preferable among the fluororesins. The fluororesin is characterized by its composition such as heat resistance and releasability, but the resin is particularly effective in reducing the friction coefficient due to intermolecular force. Depending on the combination of roughness and material, it is possible to express a value of 0.3 or less as a more preferable value of the static friction coefficient.

As described above, the microporous plastic film 1 is required to have a performance of allowing gas or liquid to pass through the microporous according to the application. In particular, in the above-described separator for a lithium ion secondary battery, a method of indirectly measuring the electrolyte permeation performance by the air permeation performance is generally performed.

The air permeability of the microporous plastic film can be measured by the Gurley air resistance described in JIS P8117 (2009). The preferred range is 10 to 1000 seconds / 100 ml, so that it can be used as a battery or capacitor separator. Useful electrolyte permeability can be exhibited. When the Gurley air resistance is 10 seconds / 100 ml or more, the insulating property is maintained moderately, and the risk of short circuit in the case of using a separator is reduced. In addition, the strength can be secured, so in combination with the transport roller of the present invention It becomes easier to avoid tearing during film conveyance. On the other hand, if the Gurley air resistance is 1000 seconds / 100 ml or less, the through-hole property can be ensured, so that the required gas or liquid permeability is not hindered. In particular, when used as a separator for a lithium ion secondary battery, the electrolyte permeability is maintained and the battery can be charged and discharged quickly. By adopting the above-described transport roller group 2 as a method for producing such a microporous plastic film 1, even the microporous plastic film 1 having a high function effective as a separator for a battery or the like can reduce the coefficient of static friction and can be wrinkled or broken. Can be avoided.

Also, the microporous plastic film 1 is pressed against the conveying roller by the tension T. The surface pressure at this time is expressed as tension × winding angle. With this surface pressure, in the microporous plastic film, air escapes from the micropore, and high friction is generated between the microporous plastic film and the conveying roller due to the collapse of the micropore. The microporous plastic film 1 that has the effect of preventing wrinkles and tears by using the transport roller of the present invention is a film that is crushed by this surface pressure. The cushion rate is the rate of change in thickness when a load of 50 g and 500 g is applied in the thickness direction of the film through a gauge gauge.

The load for measuring the cushion rate may be any method such as a spring or weight, but it is better to place the weight on the probe or indicator so that the moment is not applied to the probe as much as possible.

The microporous plastic film suitable for the present invention has a cushion rate of 15% or more and less than 50%. If the cushion rate is 15% or more, the microporous plastic film 1 is maintained with a certain degree of microporous penetration while preventing an increase in friction with the transport roller of the present invention, and obstructs permeation of necessary gases and liquids. do not do. In particular, when used as a separator for a lithium ion secondary battery, electrolyte permeability can be ensured and the battery can be charged and discharged quickly. On the other hand, if the cushion rate is less than 50%, the air permeability resistance is appropriately maintained, the risk of a short circuit in the case of using a separator can be prevented, and it is difficult to break during film conveyance. By adopting the above-described transport roller group 2 as a method for producing such a microporous plastic film 1 having a cushion ratio of 15% or more and less than 50%, the microporous plastic film 1 having a high function effective as a separator for a battery or the like. However, the coefficient of static friction that increases with the cushion rate can be reduced, and wrinkles and tears can be avoided.

In addition, the porosity of the microporous plastic film 1 is preferably 50% or less, and particularly preferably 30% or less in order not to increase the friction coefficient significantly with the cushion rate. When the microporous plastic film is used as a separator for a secondary battery, in order to obtain a high output or to shorten the charge / discharge time, a high porosity microporous having excellent ion permeability is preferable. . It is preferably 30% or more, more preferably about 50 to 80%. Further, it can be said that the porosity is 80% or less from the viewpoint of tearing.

Here, the porosity of the microporous plastic film 1 can be considered by several measuring means. As a measuring method of the present invention, a predetermined amount of the film 1 is sampled, and the film of the weight and the resin is constituted. The volume Va of the resin part is calculated from the density of the resin to be measured, and the volume Vb calculated from the measured film thickness, film width, and length is obtained from Equation 1. Regarding the thickness of the film, a method of preferably obtaining the film continuously by a light projecting / receiving type or a reflection type laser sensor on the conveying roller can be applied. In addition, means using a radiation or infrared sensor, a method of sampling the wound film 1 and measuring it with a dial gauge at a low load can be used.

The average pore diameter of the microporous plastic film 1 of the present invention is 50 to 200 nm. When the average pore diameter is 50 nm or more, when used as a battery separator, electrolyte permeability is ensured to some extent, and the battery can be quickly charged and discharged. On the other hand, when the average pore diameter is less than 200 nm, it is possible to prevent a short circuit when using a separator, and to easily avoid tearing during film conveyance to some extent.

When the thickness is 50 μm or less, which is suitable for a secondary battery or a capacitor separator, wrinkles and tears are particularly likely to occur when the friction coefficient is high as described above, so that the transport roller 2 of the present invention can be suitably applied.

Also, wrinkles are prominent when the width of the microporous plastic film 1 exceeds 100 mm. One reason for this is that the microporous plastic film 1 receives a moment because there is a poor parallelism (alignment error) between the conveying rollers. The moment for inducing this wrinkle is proportional to α × the width of the film 1 where α is the angle formed by the rotation axes of the two transport rollers. α is an angle that becomes 0 when the conveyance rollers are completely parallel, and represents an alignment error. Therefore, when the alignment error is only α, reducing the width of the microporous plastic film 1 reduces the moment that induces wrinkles. As a result of intensive studies by the inventor of the present application, it has been found that the frequency of occurrence of wrinkles with a width of 100 mm as a boundary varies greatly.

In addition, since the microporous plastic film 1 is distorted by film formation and each processing step, the planarity is often not completely uniform. In addition to the geometrical moment of roller parallelism described above, there are wrinkles created by the flatness of the film. Therefore, there is a peak other than alignment where wrinkles are likely to occur, and particularly when the width exceeds 500 mm, wrinkles are more likely to occur. In this way, the inventors of the present application are very difficult to handle when the width of the microporous plastic film 1 exceeds 100 mm, particularly when it exceeds 500 mm, but by reducing the static friction coefficient with the transport roller, In the conveyance of the microporous plastic film 1 having poor parallelism and poor flatness as described above, it was possible to prevent wrinkling and to find a balance with tearing.

More preferably, the coefficient of static friction between the microporous plastic film 1 and the conveying roller group 2 is reduced by the above-mentioned means as described above, and further used in combination with the wrinkle-stretching means to further reduce the fineness in the conveying unit. Wrinkles generated in the porous plastic film 1 can be prevented.

In FIG. 1, it is said that reducing the static friction coefficient on the surface as described above is effective in preventing wrinkles and tearing among at least one of the plurality of transport rollers 2. In this case, all of the conveying rollers 2 may have the static friction coefficient, but may be applied to, for example, a location where tearing is likely to occur or a location where wrinkles are likely to occur. Further, in a portion where it is desired to avoid the slippage between the transport roller 2 and the film 1, it is effective to use the wrinkle-stretching means 19 instead without reducing the friction coefficient of the transport roller 2. That is, as a preferable example, the conveyance roller 2 having a friction coefficient of 0.7 or less, more preferably 0.5 or less, disposed on the whole or a part of the conveyance roller 2 is arranged. It is effective to appropriately arrange wrinkle-stretching means in places where the friction coefficient cannot be reduced, or places where wrinkles are likely to occur even if the friction coefficient is reduced, for example, places where parallelism is difficult to adjust.

Here, the static friction coefficient between the conveyance roller 2 and the plastic film 1 is measured by the following measuring method. As shown in FIG. 5, the tension T (N (N) at the start of sliding when the film 1 is wound around a roller 2 fixed so as not to rotate at a predetermined angle θ (rad) and a weight with a weight W (N) is suspended. ) Can be obtained from Equation 2 by reading only the spring 31. At this time, the weight W of the weight is preferably determined from the preferable tension conditions described later, and the width of the film 1 to be measured may be any, but for example, if it is easy to handle 0.1 m, W = 1 N / m × 0.1 m to 30N / m × 0.1m = 0.1N to 3N is preferable. This is because, when the static friction coefficient greatly deviates from the above load range, the aspect of hole collapse changes and the value changes.
In another method, the film 1 is attached to a contact of a portable friction measuring device “Muse” manufactured by Shinto Kagaku Co., Ltd., and the contact is brought into contact with a roller 2 for measurement. When the above tension range is converted to the surface pressure against the roller surface, the surface pressure is p [Pa], the tension is T [N / m], and the roller diameter is D [m], and the relationship is p = 2 T / D. For example, when the roller diameter D = 0.1 m, the range of the surface pressure p in the preferable tension range is 20 to 600 Pa. Since the weight in “Muse” has a mass of 0.4 N and a diameter of 0.03 m, the surface pressure is p = 570 Pa, which is the same value as the above preferred range.

In FIG. 1, the tension of the film 1 may be applied by the torque of the motor 31 of FIG. 1, and when a film that is easy to break such as a microporous plastic film is transported, the tension is applied by indentation pressure. A dancer roller that can be controlled even at low tension may be used. In this case, the motor 31 and the motor 32 are preferably controlled for speed and rotation speed.

As the tension value, the effect of the present invention can be obtained if a necessary value is selected as appropriate, but from the viewpoint of easily avoiding tearing and crushing, it is more effective if it is preferably set lower than a general resin film. Is. For example, 1 N / m to 30 N / m is preferable.

More preferably, by setting the tension in the range of 5 N / m to 20 N / m, it becomes easier to prevent the occurrence of tears and wrinkles while performing the tension control of the machine with appropriate accuracy.

Here, the cause of the tear between the transport roller groups 2 is mainly due to a slight speed difference between the transport rollers. This is because the speed control error is not zero when driven by a plurality of motors or the like, and in the example of FIG. 1, slippage of the drive adjusting means 4 and the pulley that drives the conveying roller group 2 and the outer diameter error of the pulley. Depending on this, a speed difference will occur. In such a case, the microporous plastic film is easily broken due to the stress due to the speed difference concentrated on the pores due to the presence of the micropores described above.

Explaining the mechanism by which tearing occurs due to the speed difference. When the slip is zero, for example, the rotational peripheral speed of the transport roller 21 in FIG. 1 is V2, the rotational peripheral speed of the transport roller 23 is V1, and V2> V1. Then, the strain ε when the microporous plastic film 1 is pulled due to the speed difference may be roughly considered as Equation 3. The stress σ1 generated by this strain is expressed by Equation 4 according to Hooke's law, where E is the Young's modulus in the length direction of the microporous plastic film 1.

On the other hand, when the process tension per unit width given to the microporous plastic film 1 by a winding core is T, the stress σ2 is expressed by Equation 5 when the thickness of the microporous plastic film 1 is t.

The tear occurs when the rupture stress σb of the microporous plastic film 1 is satisfied and the inequality of Expression 6 is satisfied. Here, σb can be known by performing a rupture test of the microporous plastic film 1 with a tensile tester or the like. In particular, in the case of a film having microporosity, the edge of the film 1 is caused by a continuous cutting portion by a blade during the manufacturing process. In many cases, scratches enter the part, the cut part causes further stress concentration, and tearing occurs at a value smaller than the breaking stress obtained in the tensile test. Therefore, the inventor of the present application has found that σ1 is made as small as possible to prevent the tearing. By reducing the coefficient of static friction between the portion of the transport roller group 2 that contacts the film and the film, the strain ε caused by the speed difference is prevented, and the stress does not exceed σb. This succeeded in preventing tearing.

The result of manufacturing a microporous plastic film roll for a secondary battery separator using the above microporous plastic film manufacturing will be described.

[Example 1]
A polypropylene microporous plastic film 1 in which a through-hole as shown in FIG. 4 is formed in a biaxial stretching process by controlling the crystal structure of polypropylene is conveyed by a conveying roller 2 as shown in FIG. Was wound up to produce a microporous plastic film roll 12. The Gurley permeability resistance of the polypropylene microporous film is 500 seconds / 100 ml, the porosity is 70%, the average pore diameter is 100 nm, and the cushion rate is 17%. The width of the film 1 is 600 mm and the thickness is 60 μm. The thickness was measured by a light emitting / receiving laser sensor, and the porosity was determined by Equation 6 based on the measured thickness.

Here, the air permeation performance can be represented by the Gurley air permeation resistance (seconds / 100 ml) based on JISP 8117 (2001). The Gurley air resistance is the passage time of the microporous membrane when 100 ml of air is pressed at a constant pressure. The higher the air permeability, the smaller the time for the air to escape, the smaller the value of the Gurley air resistance.

Here, the average pore diameter of the microporous plastic film 1 may be measured by any method, but can be measured by the following measuring device and conditions.

Measuring instrument: POROUS MATERIALS, Inc. Automatic pore size distribution measuring instrument “PERM-POROMETER”
Test solution: 3M “Fluorinert” FC-40
Test temperature: 25 ° C
Test gas: Air Analysis software: Capwin
Measurement conditions: Capillary Flow Porometry-Wet up, Automatic measurement under default conditions of Dry down Conversion formula: d = Cγ / P × 10 ^ 3
d: pore diameter (nm), C: constant, γ: surface tension of fluorinate (16 mN / m), P: pressure (Pa)
As shown in FIG. 1, the conveying roller 21, the conveying roller 23, and the conveying roller 24 immediately before winding are driven by a motor 32 by a belt and controlled so as to have a constant speed. Here, a load measuring device is installed in the bearing for measuring the tension of the transport roller 22. The conveyance roller 22 is driven by the film 1 without being driven by the motor 32 so that the resultant direction of tension is not changed by the frictional force of the roller.

The winding core 6 is rotatably supported by a winding shaft and is driven by a motor 31 so as to have a constant tension. In this embodiment, the conveyance roller 21, the conveyance roller 22, the conveyance roller 23, and the conveyance roller 24 are set so that the static friction coefficient of the conveyance roller 21 to the conveyance roller 24 in contact with the four films 1 is 0.7 or less. A composite material of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), which is a fluororesin, and a metal was formed on the surface as shown in FIG. The surface roughness of the roller at this time was measured using a contact type surface roughness measuring instrument manufactured by Mitutoyo Corporation, with a stylus material diamond, a stylus tip radius of 2 μm, and a measuring force of 0.75 mN. Based on (2001), ten-point average roughness RzJIS was determined.

As a result, the coefficient of static friction with the film 1 measured by the Shinto Kagaku Muse was 0.55. The contact pressure p at this time is about 570 Pa.

The production conditions of the microporous plastic film roll 1 were a conveyance speed of 10 m / min, a tension of 20 N / m, and a film roll was taken out by an automatic rewinder every winding length of 1000 m.

The above combination conditions are summarized in Table 1.

[Example 2]
A film having a thickness of 20 μm was wound up under the same conditions as in Example 1 to produce a microporous plastic film roll 12. The porosity of this film was the same as in the Examples, and the Gurley air resistance was 100 seconds / 100 ml because the thickness was reduced.

[Example 3]
Compared to Example 2, polytetrafluoroethylene (PTFE) and metal were placed on the surfaces of these rollers so that the friction coefficient of the portions of the conveying rollers 21 to 24 contacting the four films 1 was 0.5 or less. The composite membrane was formed in the form as shown in FIG. As the surface roughness of the roller surface, ten-point average roughness was measured under the same conditions as in Example 1.

[Example 4]
In contrast to Example 3, the film 1 having a Gurley air resistance of 400 seconds / 100 ml and a porosity of 40% was wound up to produce a microporous plastic film roll 12.

[Example 5]
A microporous plastic having a small surface roughness satisfying a friction coefficient of 0.5 or less of the roller in the portion of the conveyance roller 21 to the conveyance roller 24 that contacts the four films 1 is applied to the third embodiment. A film roll 12 was produced.

[Example 6]
The film 1 having a Gurley air permeability resistance of 900 seconds / 100 ml and a porosity of 30% was wound up on Example 3 to produce a microporous plastic film roll 12.

[Comparative Example 1]
The same Gurley permeability resistance as in Examples 2 and 3 is 100 sec / 100 ml, the porosity is 70%, and the thickness is 20 μm. The microporous plastic film 12 was manufactured by carrying and winding with a hard chromium plating (Hcr) having a thickness of RzJIS = 0.1 μm.

[Comparative Example 2]
The same Gurley permeability resistance as in Examples 2 and 3 is 100 sec / 100 ml, the porosity is 70%, and the thickness is 20 μm. The microporous plastic film 12 was manufactured by conveying and winding the diamond-like carbon (DLC) coated with a thickness of RzJIS = 3 μm.

[Comparative Example 3]
A biaxially stretched polypropylene film roll was manufactured by transporting and winding the film 1 having no porosity, which is effective as a secondary battery separator, with the same transporting roller as in Example 3, and being effective as a secondary battery separator. .

[Comparative Example 4]
The surface roughness of the film 1 having the same Gurley gas permeability of 100 seconds / 100 ml, porosity of 70%, and thickness of 20 μm as in Example 2 is in contact with the four films 1 of the transport rollers 21 to 24. The microporous plastic film 12 was manufactured by conveying and winding in a state of a composite film of TFE and metal of RzJIS = 0.1 μm.

Table 1 shows the results of manufacturing the microporous plastic film roll 1 for the secondary separator in Examples and Comparative Examples.

Here, as a determination method of “wrinkle”, the wrinkle generated in the conveyance part reaches the film roll 1 and “x” indicates that the wrinkle was observed as a rolled-up roll. The rolls that could not be observed as rolls were judged as “Δ”, and the others as “◯”.

Regarding the method of determining “break”, “X” is indicated when a break occurs during conveyance within a winding length of 1000 m, “△” is indicated when break occurs even during conveyance within 90,000 m, and “ “Yes”.

The Gurley permeability resistance is used as the performance of the secondary battery separator. As a separator for a secondary battery, it is preferable to allow ions to pass through as little as possible through a minute through hole that does not cause dielectric breakdown. As performance, it is preferable that the Gurley air resistance is higher. Accordingly, the Gurley gas permeability resistance was set to “X” when the gas resistance was 1000 sec / 100 ml or more, “Δ” when 200 to 1000 sec / 100 ml was set, and “◯” when 10 to 200 sec / 100 ml or less.

As shown in Table 1, in Example 1, a secondary battery is obtained by using a PFA composite material for a portion of the transport roller 2 that contacts the microporous plastic film 1 and having a coefficient of friction with the film 1 of 0.6 or less. The microporous plastic film roll was able to be manufactured in a state where wrinkles were completely prevented and the frequency of tearing was very low while realizing the porosity and the Gurley gas permeability resistance necessary for the separator for use.

In Example 2, the air permeability improves as the film thickness decreases, but the risk of tearing and wrinkles increases. However, by using the PFA composite film as in Example 1, the static friction coefficient is set to 0.6 or less. , Minimizing wrinkles and tears.

In Example 3, wrinkles and tears can be prevented by reducing the static friction coefficient to 0.6 or less with a PTFE composite film, which is the same thin film as in Example 2 and difficult to handle. It was.

In Example 4, although the air permeability performance is slightly inferior due to the decrease in the porosity, the friction coefficient is further lowered by the same PTFE composite film as in Example 3, so that wrinkles and tears are equally good results. became.

In Example 5, since the roughness of the composite film was smaller than in Examples 1 to 4, the static friction coefficient slightly increased and wrinkles were observed, but PTFE was able to realize a static friction coefficient of 0.6 or less, Wrinkles were not observed from the rolled up film, which was good.

In Example 6, since the air permeability performance of the film is lowered (Gurley air resistance is increased) and the cushion rate is also low, the coefficient of static friction is the lowest, and the composite film equivalent to Example 4 and the like is equivalent to a normal film. Good transportability was shown.

On the other hand, in Comparative Example 1, the surface of the conveying roller is Hcr plated with a small roughness, the contact area is large and the friction is large due to the air permeability and cushioning property of the microporous plastic film, and the coefficient of static friction is increased to 0.6. Exceeded. As a result, wrinkles that deteriorate the separator performance were observed in the rolled up film roll, and tearing occurred frequently, resulting in a low productivity state.

In Comparative Example 2, the friction coefficient was improved compared to Comparative Example 1 by coating DLC on the surface of the transport roller, but the static friction coefficient was still higher than 0.6, and the speed difference between the transport rollers could not be absorbed. I couldn't avoid the tears.

In Comparative Example 3, it is a transparent polypropylene film that does not have micropores that are effective as separators, and there are no problems with the above-described transport caused by microporosity, but it does not show air permeability as a battery separator. .

In Comparative Example 4, the surface of the transport roller is made of a PTFE composite material. However, since the roughness is too smooth, the desired friction coefficient cannot be reduced, the speed difference between the transport rollers cannot be absorbed, and tearing can be avoided. could not.

Thus, according to the present invention, a microporous plastic film roll having air permeability suitable for a secondary battery separator can be produced by being transported and wound without wrinkle tearing or tearing.

The present invention is not limited to secondary battery separators, but can be widely applied to fields where microporous plastic films such as capacitor separators and other separation membranes, filtration membranes, optical reflective substrates, and printed membranes can be used. The application range is not limited to these.

DESCRIPTION OF SYMBOLS 1 Microporous plastic film 12 Microporous plastic film roll 2 Conveyance roller group 21 Conveyance roller A
22 Transport roller B
23 Transport roller C
2A Transport roller base material 3 Drive source 4 Drive transmission means 5 Pulley 6 Winding core 7 Metal plating layer 8 Fluorine resin layer 9 Composite material 10 Disassembled schematic diagram of lithium ion secondary battery 11 Case 13 Electrode tab 14 Positive electrode 15 Negative electrode 16 Microporous Separator made of plastic film 17 Through hole 18 Fibril 19 Wrinkle stretching means 30 Weight 31 Spring measurement
A Transport direction W Weight of weight

Claims

Among the plurality of transport rollers, as at least one transport roller, the surface roughness RzJIS (μm) is 0.3 ≦ RzJIS ≦ 30, the surface material is fluororesin or silicone rubber, or a composite material containing these A method for producing a microporous plastic film roll, comprising transporting a microporous plastic film having a through-hole inside and winding it into a roll.
The method for producing a plastic film roll according to claim 1, wherein the material of the surface of the conveying roller is polytetrafluoroethylene.
The method for producing a microporous plastic film roll according to claim 1 or 2, wherein the microporous plastic film has a Gurley gas resistance of 10 to 1000 seconds / 100 ml.
The method for producing a microporous plastic film roll according to any one of claims 1 to 3, wherein the porosity of the microporous plastic film is 30% or more.
The method for producing a microporous plastic film roll according to any one of claims 1 to 4, wherein the microporous plastic film has a microporous average pore diameter of 50 to 200 nm.
6. The method for producing a microporous plastic film roll according to claim 1, wherein the cushion ratio of the microporous plastic film is 15% or more and less than 50%.
7. The method for producing a microporous plastic film roll according to claim 1, wherein the thickness of the microporous plastic film is 50 μm or less.
The method for producing a microporous plastic film roll according to any one of claims 1 to 7, wherein the width of the microporous plastic film is 100 mm or more.
The method for producing a microporous plastic film roll according to any one of claims 1 to 8, wherein a coefficient of static friction between the microporous plastic film and the conveying roller is 0.6 or less.
The method for producing a microporous plastic film roll according to any one of claims 1 to 9, wherein the microporous plastic film is used as a separator for a secondary battery or a capacitor.