JP6294176B2 - Method for producing microporous film - Google Patents

Description

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

  Microporous films, particularly polyolefin microporous films, are used in microfiltration membranes, battery separators, capacitor separators, fuel cell materials, and the like, and in particular, lithium ion battery separators. In recent years, lithium-ion batteries have been used for small electronic devices such as mobile phones and laptop computers, and are also being applied to electric vehicles and hybrid vehicles.

  Here, a lithium ion battery used for an electric vehicle or a hybrid vehicle is required to have higher output characteristics for taking out a lot of energy in a short time. Further, since lithium ion batteries used for hybrid electric vehicle applications are generally large and have high energy capacity, it is required to ensure higher safety and to be low in cost. As a separator having such a role, a microporous film by a dry method as shown in Patent Document 1 has been proposed.

  On the other hand, in the example of Patent Document 2, a method of stretching and stacking four microporous films is exemplified. In this method, when the film thickness is 20 μm or more, it is possible to obtain a microporous film excellent in permeability with less generation of wrinkles in the heat treatment process and the stretching process.

Special table 2003-519723 gazette JP 2005-56851 A

  However, in the conventional manufacturing method, it is difficult to obtain a microporous film having a good permeability because it tends to cause a thin film having a thickness of 16 μm or less.

  In recent years, a lithium ion battery has been required to have a high capacity, and a thinner (specifically, 16 μm or less) separator is required to accommodate more electrode active materials. Therefore, a method for producing a microporous film of 16 μm or less with excellent productivity is desired.

  The present invention has been made in view of the above problems, and even a microporous film having a thickness of 16 μm or less can be heat-treated and stretched without being wrinkled, and has good permeability. A production method capable of obtaining a microporous film is provided.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have formed a laminate by thermocompression bonding 2 to 6 original film containing a specific polypropylene resin in advance, It has been found that a microporous film that suppresses the generation of wrinkles in the stretching process and has good permeability can be obtained.

That is, the present invention is as follows.
[1]
A single resin comprising at least one polypropylene resin selected from the group consisting of a polypropylene resin (A) having a pentad fraction of 90 to 96% and a polypropylene resin (B) having a propylene content of 98 to 99.5 mol%. A film forming step of obtaining a layer original film, or a laminated original film having an outermost layer including one or more kinds of polypropylene resins selected from the group consisting of the polypropylene resin (A) and the polypropylene resin (B); ,
A thermocompression bonding step in which the single layer original film or the laminated original film 2-6 obtained in the film formation step is laminated and thermocompression bonded to obtain a laminate;
A heat treatment step of heat-treating one or two to six of the laminates obtained in the thermocompression step; and
In the state where the laminate after the heat treatment obtained in the heat treatment step is maintained at 90 ° C. to 160 ° C., a stretching step of stretching 1.05 times to 5.0 times in at least one direction;
A peeling step of peeling the layer of the laminate after drawing obtained in the drawing step to obtain a microporous film;
A method for producing a microporous film having a thickness of 16 μm or less.
[2]
The method for producing a microporous film according to [1] above, wherein the film thickness of the microporous film obtained in the peeling step is 10 to 14 μm.

  According to the present invention, even a microporous film having a thickness of 16 μm or less can be heat-treated and stretched without being wrinkled, and a microporous film having excellent permeability can be obtained. A method can be provided.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiment, and can be implemented with various modifications within the scope of the gist.

[Method for producing microporous film]
The manufacturing method of the microporous film whose film thickness of this embodiment is 16 micrometers or less,
A single resin comprising at least one polypropylene resin selected from the group consisting of a polypropylene resin (A) having a pentad fraction of 90 to 96% and a polypropylene resin (B) having a propylene content of 98 to 99.5 mol%. A film forming step of obtaining a layer original film, or a laminated original film having an outermost layer including one or more kinds of polypropylene resins selected from the group consisting of the polypropylene resin (A) and the polypropylene resin (B); ,
A thermocompression bonding step in which the single layer original film or the laminated original film 2-6 obtained in the film formation step is laminated and thermocompression bonded to obtain a laminate;
A heat treatment step of heat-treating one or two to six of the laminates obtained in the thermocompression step; and
In the state where the laminate after the heat treatment obtained in the heat treatment step is maintained at 90 ° C. to 160 ° C., a stretching step of stretching 1.05 times to 5.0 times in at least one direction;
A peeling step of peeling the layer of the laminate after drawing obtained in the drawing step to obtain a microporous film;
In this order.

[Film formation process]
The film forming step includes at least one selected from the group consisting of a polypropylene resin (A) having a pentad fraction of 90 to 96% and a polypropylene resin (B) having a propylene content of 98 to 99.5 mol%. The process of obtaining the lamination | stacking original film which has the layer which contains 1 or more types of polypropylene resin chosen from the group which consists of a polypropylene resin (A) and a polypropylene resin (B) in the outermost layer including the single layer original film containing a polypropylene resin It is.

  Although it does not specifically limit as a manufacturing method of the single layer original film or laminated | stacked original film in a film-forming process, For example, sheet | seat shaping | molding methods, such as T-die extrusion molding, inflation shaping | molding, calendar shaping | molding, and Skyf method, are mentioned. Of these, T-die extrusion is preferred from the viewpoints of physical properties and applications required for the microporous film of the present embodiment.

  The draw ratio after extrusion in the film forming step, that is, the film winding speed (unit: m / min) is the resin extrusion speed (linear velocity in the flow direction of the molten resin passing through the die lip. Unit: m / min). The divided value is preferably 10 to 500, more preferably 50 to 300, and further preferably 100 to 250. Moreover, the winding speed of the film when winding the raw film is preferably about 2 to 400 m / min, more preferably 10 to 200 m / min, and further preferably 15 to 30 m / min. When the draw ratio is in the above range, it is preferable from the viewpoint of improving the permeability of the obtained microporous film.

[Polypropylene resin (A)]
The polypropylene resin (A) is a polypropylene having a pentad fraction of 90 to 96%. “Pentad fraction” refers to the proportion of isotactic chains existing in pentad units in the molecular chain. The proportion of propylene monomer units at the center of a chain in which five propylene monomer units are continuously meso-bonded. Rate.

  As the Pendat fraction approaches 100%, the stereoregularity becomes higher and the polypropylene resin has higher crystallinity. As illustrated in the examples of Patent Document 1, a microporous film having good permeability can be obtained by using a polypropylene resin exceeding 98%.

  On the other hand, in this embodiment, by using a polypropylene resin having a pentad fraction of 90 to 96%, which has a slightly low crystallinity, it is possible to achieve both the press-bonding property and the permeability in the thermo-compression bonding step described later. The pentad fraction is 90 to 96%, preferably 92 to 95%, more preferably 94 to 95%. When the pentad fraction is 90% or more, the opening property at the time of stretching is improved, and good permeability can be obtained. On the other hand, when the pentad fraction is 96% or less, an original film that can be bonded at an appropriate temperature in the pressure-bonding step can be obtained. The pentad fraction can be measured by the method described in the examples.

  The polypropylene resin (A) is preferably homopolypropylene. When the polypropylene resin (A) is homopolypropylene, the permeability of the microporous film tends to be further improved.

[Polypropylene resin (B)]
The polypropylene resin (B) is propylene having a propylene content of 98 to 99.5 mol%. The polypropylene resin (B) is preferably a propylene-based copolymer obtained by copolymerizing ethylene and / or α-olefin. When the polypropylene resin (B) is a propylene-based copolymer, the α-olefin serves as a tie molecule that connects the polypropylene crystals, and the destruction that occurs between the crystals tends to be further suppressed. The α-olefin is not particularly limited, and examples thereof include butene-1, pentene-1, 4-methyl-pentene-1, hexene-1, and octene-1.

  In a conventional method for producing a microporous film, a propylene homopolymer is used as in Patent Document 1 in order to increase crystallinity and improve permeability. On the other hand, in this embodiment, 0.5 to 2.0 mol% of ethylene and / or α-olefin is copolymerized, thereby making it possible to achieve both pressability and permeability in the thermocompression bonding step. Propylene content is 98-99.5 mol%, Preferably it is 98.5-99.5 mol%, More preferably, it is 99-99.5 mol%. The propylene content can be measured by the method described in the examples.

  In addition, ethylene and α-olefin play a role of tie molecules that connect between polypropylene crystals, and tend to suppress destruction that occurs between the crystals. From this point of view, ethylene and α-olefin are preferably present dispersed in the molecular chain, and the propylene-based copolymer is preferably a random copolymer.

  The pentad fraction of the polypropylene resin (B) is preferably 95 to 99.9%, more preferably 97 to 99.9%, and further preferably 98 to 99.9%. When the pentad fraction is 95% or more, the openability during stretching is improved and the permeability tends to be further improved.

  Further, the melt flow rate (MFR) of the polypropylene resin (A) and the polypropylene resin (B) is preferably 0.1 to 1.0 g / 10 minutes, more preferably 0.3 to 0.8 g / 10 minutes. And more preferably 0.5 to 0.7 g / 10 min. When the MFR is 0.1 g / 10 min or more, there is a tendency that breakage in the film forming process hardly occurs. Moreover, it exists in the tendency for the puncture strength of the microporous film obtained to become favorable because MFR is 1.0 g / 10min or less. MFR can be measured by the method described in the Examples.

[Polyethylene resin]
In the present embodiment, when a laminated microporous film having a layer containing a polyethylene resin is produced, a polyethylene resin can also be used. The MFR of the polyethylene resin is preferably 0.01 to 10 g / 10 minutes, more preferably 0.1 to 1.0 g / 10 minutes, and further preferably 0.1 to 0.5 g / 10 minutes. . When MFR is 0.01 g / 10 min or more, it tends to be difficult to generate fish eyes. Moreover, when MFR is 10 g / 10 min or less, the permeability tends to be further improved. MFR can be measured by the method described in the Examples.

The density of the polyethylene resin is preferably 955 to 970 kg / m ³ , more preferably 955 to 967 kg / m ³ , and further preferably 958 to 965 kg / m ³ . When the density is 955 kg / m ³ or more, a microporous film with better air permeability tends to be obtained. Moreover, when it is 970 kg / m ³ or less, it tends to be difficult for the membrane to break during stretching. The density can be measured by the method described in the examples.

  The polypropylene resin (A), the polypropylene resin (B), and the polyethylene resin used as necessary in the present embodiment may contain other additional components as necessary in addition to the above components. Although it does not specifically limit as an additional component, For example, an olefin type elastomer, antioxidant, a metal deactivator, a heat stabilizer, a flame retardant (an organic phosphate ester type compound, an ammonium polyphosphate type compound, an aromatic halogen) Flame retardants, silicone flame retardants, etc.), fluoropolymers, plasticizers (low molecular weight polyethylene, epoxidized soybean oil, polyethylene glycol, fatty acid esters, etc.), flame retardant aids such as antimony trioxide, weather resistance (light) Property improver, polyolefin nucleating agent, slip agent, inorganic or organic filler or reinforcing material (polyacrylonitrile fiber, carbon black, titanium oxide, calcium carbonate, conductive metal fiber, conductive carbon black, etc.), various colors Agents, release agents and the like. The total content of these additional components is preferably 20 parts by mass or less, more preferably 100 parts by mass of the polypropylene resin (A), the polypropylene resin (B), or the polyethylene resin used as necessary. Is 10 parts by mass or less, more preferably 5 parts by mass or less.

  The configuration of the laminated raw film is not particularly limited as long as it has a layer containing one or more polypropylene resins selected from the group consisting of polypropylene resin (A) and polypropylene resin (B) in the outermost layer. , Polypropylene resin layer / polypropylene resin layer, polypropylene resin layer / polyethylene resin layer, polypropylene resin layer / polyethylene resin layer / polypropylene resin layer, and the like.

[Thermo-compression process]
In the thermocompression bonding process, 2 to 6 single layer original film or laminated original film (hereinafter collectively referred to as “original film”) obtained in the film forming process are stacked and thermocompression bonded to obtain a laminate. It is a process. Specifically, 2 to 6 single layer original films or laminated original films obtained in the film forming step are unwound, nipped between heated rolls, and bonded to obtain a laminate. However, it is not particularly limited.

  The temperature of the heated roll (hereinafter also referred to as “thermocompression bonding temperature”) is preferably 110 to 160 ° C., more preferably 120 to 150 ° C. in the case of a single-layer raw film. When the thermocompression bonding temperature is 110 ° C. or higher, the adhesive strength of each original fabric film becomes good, and there is a tendency that peeling in the stretching step described below can be prevented. Moreover, when the thermocompression bonding temperature is 160 ° C. or lower, a microporous film having good permeability tends to be obtained.

  In the case of a laminated original film having no layer containing a polyethylene resin, the thermocompression bonding temperature is preferably 110 to 130 ° C, more preferably 115 to 125 ° C. When the thermocompression bonding temperature is 110 ° C. or higher, the adhesive strength of each original fabric film becomes good, and there is a tendency that peeling in the stretching step described below can be prevented. Moreover, when the thermocompression bonding temperature is 130 ° C. or lower, a microporous film having good permeability tends to be obtained.

  In the case of a laminated original film having a layer containing a polyethylene resin, the thermocompression bonding temperature is preferably 110 to 130 ° C, more preferably 115 to 125 ° C. When the thermocompression bonding temperature is 110 ° C. or higher, the adhesive strength of each original fabric film becomes good, and there is a tendency that peeling in the stretching step described below can be prevented. Moreover, when the thermocompression bonding temperature is 130 ° C. or lower, a microporous film having good permeability tends to be obtained.

  Moreover, the linear pressure at the time of roll pressing is preferably 1.0 to 10.0 kg / cm, more preferably 5.0 to 7.0 kg / cm. When the linear pressure at the time of roll pressing is within the above range, the adhesive strength of each raw film becomes good, and it tends to prevent peeling in the stretching step described below.

[Heat treatment process]
A heat treatment process is a process heat-processed in the state which piled up the said laminated body obtained by the thermocompression-bonding process, or 2-6 sheets. Although it does not specifically limit as the method of heat processing, For example, the method of contacting a laminated body on a heating roll, the method of exposing a laminated body in a heating gas phase, and the method of combining these are mentioned.

  The temperature of the heating roll and / or the temperature in the heated gas phase (hereinafter also referred to as “heat treatment temperature”) is preferably 120 ° C. to 160 ° C., more preferably, in the case of a laminate composed of a single-layer raw film. It is 130-150 degreeC, More preferably, it is 130-140 degreeC. When the heat treatment temperature is 120 ° C. or higher, the permeability tends to be further improved. Moreover, when the heat treatment temperature is 160 ° C. or lower, the puncture strength tends to be further improved.

  In the case of a laminate comprising a laminated raw film having a layer containing a polyethylene resin, the heat treatment temperature is preferably 110 to 130 ° C, more preferably 120 to 128 ° C, still more preferably 125 to 128 ° C. is there. When the heat treatment temperature is 110 ° C. or higher, the permeability tends to be further improved. Moreover, when the heat treatment temperature is 130 ° C. or lower, the puncture strength tends to be further improved.

  The time for performing heat treatment (hereinafter also referred to as “heat treatment time”) is preferably 10 seconds or longer, more preferably 10 to 30 minutes, and further preferably 10 to 20 minutes. When the heat treatment time is 10 seconds or longer, the permeability tends to be further improved. Moreover, it exists in the tendency for puncture strength to improve more because heat processing time is 30 minutes or less.

  The laminate tends to expand due to thermal expansion in the heat treatment step. Therefore, it is preferable to stretch the laminate at a magnification of 1.01 to 1.05 times in at least one direction before or during the heat treatment step. When the draw ratio is 1.01 or more, the laminate tends to be heat-treated without wrinkling. Moreover, it exists in the tendency which can obtain a microporous film with favorable permeability | transmittance by the peeling process mentioned later because a draw ratio is 1.05 times or less.

  If the film thickness of the microporous film to be obtained as exemplified in Patent Document 2 is 20 μm or more, it is possible to obtain a microporous film with less wrinkles and good permeability in the heat treatment step. Is possible. However, when the film thickness of the microporous film is 16 μm or less, if heat treatment is performed in a state where two or more sheets are stacked without prior thermocompression bonding as in Patent Document 2, wrinkles are likely to occur, and the microporous film It becomes difficult to obtain a conductive film. In such a case, the wrinkle is eliminated by increasing the draw ratio before or during the heat treatment step from 1.05 times, but the microporosity finally obtained without the thermocompression bonding step. The permeability of the film deteriorates.

[Stretching process]
The stretching step is a step of stretching the laminated body after the heat treatment obtained in the heat treatment step at a rate of 1.05 times to 5.0 times in at least one direction while being maintained at 90 ° C to 160 ° C. By this stretching, the layer constituting the laminate is made porous.

  Although it does not specifically limit as an extending | stretching method, For example, the method of extending | stretching to a uniaxial direction and / or a biaxial direction with a roll, a tenter, an autograph, etc. is mentioned. In particular, from the viewpoint of physical properties and applications required for the microporous film of the present embodiment, two or more stages of uniaxial stretching with a roll are preferable.

  The stretching step preferably includes the following cold stretching step and thermal stretching step in this order. In the cold stretching step, the laminate obtained in the heat treatment step is preferably stretched at a temperature of −20 ° C. to 80 ° C. in at least one direction 1.03 times to 2.0 times.

  The stretching temperature for cold stretching in the cold stretching step is preferably −20 ° C. or higher and lower than 80 ° C., more preferably 0 ° C. or higher and 50 ° C. or lower, and further preferably 10 ° C. or higher and 30 ° C. or lower. When the stretching temperature is −20 ° C. or higher, the microporous film tends to be difficult to break. Moreover, it exists in the tendency for the permeability | transmittance of the microporous film obtained to become favorable because extending | stretching temperature is less than 80 degreeC. Here, the drawing temperature of cold drawing shows the surface temperature of the film in the cold drawing process. The surface temperature of the film can be measured by providing a non-contact type thermocouple in the stretching roll machine.

  The draw ratio of cold drawing in the cold drawing step is preferably 1.03 to 1.5 times, more preferably 1.05 to 1.3 times, and even more preferably 1.1 times or more. 1.3 times or less. When the draw ratio is 1.03 times or more, the permeability tends to be good. Moreover, it exists in the tendency for a film to become difficult to fracture | rupture because a draw ratio is 1.5 times or less. The cold stretch of the raw film may be performed in at least one direction and may be performed in two directions. Preferably, the original film is uniaxially stretched only in the film extrusion direction (hereinafter also referred to as “MD direction”).

  In the hot stretching step, it is preferable to perform hot stretching at least 1.05 times to 5.0 times in the state where the temperature is kept at 90 ° C. to 160 ° C. after cold drawing as described above.

  In the case of a laminate composed of a single-layer raw film, the stretching temperature for hot stretching is 90 ° C. to 160 ° C., preferably 120 ° C. to 150 ° C., more preferably 120 to 140 ° C. By heat-stretching at 90 ° C. or higher, the film is hardly broken. Moreover, the permeability | transmittance of the microporous film obtained becomes favorable by heat-stretching below 160 degreeC. Here, the stretching temperature of the heat stretching indicates the surface temperature of the film in the heat stretching process.

  In the case of a laminate composed of a laminated raw film having no layer containing a polyethylene resin, the stretching temperature of the hot stretching is 90 ° C to 160 ° C, preferably 90 ° C to 130 ° C, more preferably 110 ° C. ~ 125 ° C. By heat-stretching at 90 ° C. or higher, the film is hardly broken. Moreover, it exists in the tendency for the permeability | transmittance of the microporous film obtained to become favorable by heat-stretching at 130 degrees C or less.

  On the other hand, in the case of a laminate composed of a laminated raw film having a layer containing a polyethylene resin, the stretching temperature for hot stretching is 90 ° C to 160 ° C, preferably 90 ° C to 130 ° C, more preferably 110 ° C. C. to 125.degree. By heat-stretching at 90 ° C. or higher, the film is hardly broken. Moreover, it exists in the tendency for the permeability | transmittance of the microporous film obtained to become favorable by heat-stretching at 130 degrees C or less.

[Heat setting process]
The manufacturing method of the microporous film of the present embodiment preferably includes a heat setting step in which heat treatment is performed on the laminate obtained through the stretching step at a temperature higher by 0 ° C to 30 ° C than the heat stretching temperature. preferable. As this heat setting method, a method of heat shrinking to the extent that the length of the laminate after heat setting is reduced by 3 to 50% with respect to the length of the microporous film before heat setting (hereinafter referred to as this method). "Relaxation"), and a method of heat setting so that the dimension in the stretching direction does not change. By this heat setting, a microporous film having much better dimensional stability, that is, having a small heat shrinkage rate can be obtained.

  In the case of a laminate composed of a single-layer raw film, the heat setting temperature is preferably 120 ° C to 160 ° C, more preferably 140 ° C to 160 ° C or less, and further preferably 145 to 155 ° C. When the heat setting temperature is within the above range, the permeability tends to be further improved. Here, the heat setting temperature indicates the surface temperature of the microporous film in the heat setting process.

  In the case of a laminate comprising a laminated raw film having a layer containing a polyethylene resin, the heat setting temperature is preferably 120 ° C. to 130 ° C., more preferably 120 ° C. to 125 ° C., and still more preferably 122 to 125 ° C. When the heat setting temperature is within the above range, the permeability tends to be further improved.

[Peeling process]
A peeling process is a process of peeling the layer of the said laminated body obtained by the extending process, and obtaining a microporous film. Specifically, in the peeling step, each microporous film is peeled off from the laminate obtained in the stretching step or the heat setting step and wound up. At the same time, all the microporous films may be peeled off and wound up, or only one sheet may be peeled off, and the peeled microporous film and the remaining laminate may be wound up respectively. When only one sheet is peeled off, the remaining laminate is unwound again and only one sheet is repeatedly peeled to obtain a predetermined number of microporous films.

[Microporous film]
The microporous film of the present embodiment is not particularly limited as long as the film thickness is 16 μm or less. For example, a monolayer microporous film containing a polypropylene resin or a laminated microporous film having a polypropylene resin layer as an outermost layer is used. A porous film is mentioned.

  The film thickness of the microporous film is 16 μm or less, preferably 10 to 14 μm, and more preferably 12 to 14 μm. When the film thickness of the microporous film is 16 μm or less, the permeability tends to be further improved. Moreover, when the film thickness of the microporous film is 10 μm or more, the puncture strength tends to be further improved. The film thickness can be measured by the method described in the examples.

  Examples of the laminated microporous film of the present embodiment include a single-layer laminated microporous film comprising a layer containing a polypropylene resin and a laminated laminated microporous film having a layer containing a polypropylene resin. Among these, a laminated laminated microporous film having a layer containing a polypropylene resin as the outermost layer is preferable. As a specific example of the embodiment, a three-layer laminated microporous film having a layer containing a polyethylene resin as an intermediate layer and layers containing a polypropylene resin on both sides thereof can be mentioned.

  As a manufacturing method of the lamination | stacking microporous film of this embodiment, said method is mentioned, for example. Specifically, using a T-die or a circular die, a method of forming a laminated film in which each resin film is laminated by a coextrusion method, and then stretching the laminated film to make it porous; extruding each resin film separately The laminated film which laminated | stacked each resin film by the laminating method bonded after doing is formed, Then, the method of extending | stretching and making the laminated film porous is mentioned.

  Next, although an example and a comparative example are given and explained more concretely, the present invention is not limited to the following examples.

  In addition, about the raw material used in the Example and the comparative example, and the evaluation method of various characteristics are as follows. In each example and comparative example, the number of microporous films shown in “Number of sheets obtained in peeling process” in Table 1 is obtained. All the obtained microporous films were evaluated, and the average value is shown in Table 1 as an evaluation result.

(1) MFR of polypropylene resin
Based on JIS K7210, it is a value measured under conditions of a temperature of 210 ° C. and a load of 2.16 kg, and its unit is g / 10 minutes.

(2) MFR of polyethylene resin
Based on JIS K7210, it is a value measured under conditions of a temperature of 190 ° C. and a load of 2.16 kg, and its unit is g / 10 minutes.

(3) Pentad fraction (%)
The pentad fraction of the polypropylene resin was calculated by the peak height method from the 13C-NMR spectrum assigned based on the description in the Polymer Analysis Handbook (edited by the Japan Analytical Chemical Society). The 13C-NMR spectrum was measured using ECS-400 manufactured by JEOL Ltd., and the microporous film was dissolved in o-dichlorobenzene-d under the conditions of a measurement temperature of 130 ° C. and a cumulative number of 10,000 times. It was.

(4) Propylene content (mol%), ethylene content (mol%)
The propylene content and the ethylene content of the polypropylene resin were calculated by the peak height method from the 13C-NMR spectrum assigned based on the description in the Polymer Analysis Handbook (edited by the Analytical Society of Japan). The 13C-NMR spectrum was measured using ECS-400 manufactured by JEOL Ltd., and the microporous film was dissolved in o-dichlorobenzene-d under the conditions of a measurement temperature of 130 ° C. and a cumulative number of 10,000 times. It was.

(5) Density Based on JIS K7112, it is a value measured under the condition of 25 ° C., and its unit is kg / m ³ .

(6) Molecular weight distribution (Mw / Mn)
The molecular weight distribution of the resin in the polyethylene resin is a value of the ratio Mw / Mn of the weight average molecular weight (Mw) and the number average molecular weight (Mn) obtained from gel permeation chromatography (GPC). The GPC measurement was performed using a GPS device (trade name “HLC-8121GPC / HT”) manufactured by Tosoh Corporation. Using the trade name “TSKgel GMHHR-H (20)” (two) manufactured by Tosoh Corporation as the column, mobile phase o-dichlorobenzene (o-DCB), column temperature 155 ° C., flow rate 1.0 mL / min, sample concentration The measurement was performed under the conditions of 0.5 mg / mL (o-DCB), an injection amount of 500 μL, a sample dissolution temperature of 160 ° C., and a sample dissolution time of 3 hours. The molecular weight was calibrated with polystyrene, and Mw and Mn were obtained from the polystyrene-equivalent molecular weight to derive the molecular weight distribution.

(7) Film thickness (μm)
The film thickness of the microporous film was measured using a dial gauge (manufactured by Ozaki Seisakusho, trade name “PEACOCK No. 25”).

(8) Air permeability (sec / 100cc)
The air permeability of the microporous film was measured with a Gurley type air permeability meter based on JIS P-8117.

(9) Porosity (%)
The porosity of the microporous film was determined by cutting out a 10 cm × 10 cm square sample from the microporous film, the volume V (cm ³ ) and mass M (g) of the sample, and the density ρ (g of the resin constituting the film / Cm ³ ) and using the following formula. In the case of the microporous film composed only of a polypropylene resin, ρ = 0.91g / cm ^3, when the laminated microporous film having a layer comprising polyethylene resin, ρ = 0.93g / cm ³ Calculated as
Porosity (%) = {(VM−ρ / V} × 100

(10) Puncture strength (g)
Using a “KES-G5 Handy Compression Tester” (trademark) manufactured by Kato Tech, a piercing test was performed under the conditions of a radius of curvature of the needle tip of 0.5 mm and a piercing speed of 2 mm / sec, and the maximum piercing load (g) was measured. .

In addition, the used polypropylene resin and polyethylene resin are as follows.
Polypropylene (A): propylene homopolymer, MFR = 3, pentad fraction = 96%
Polypropylene (B): propylene homopolymer, MFR = 3, pentad fraction = 90%
Polypropylene (C): propylene copolymer, MFR = 3, pentad fraction = 98%, propylene content = 99.5 mol%, ethylene content = 0.5 mol%
Polypropylene (D): propylene copolymer, MFR = 3, pentad fraction = 98%, propylene content = 98 mol%, ethylene content = 2 mol%
Polypropylene (E): propylene homopolymer, MFR = 3, pentad fraction = 98%
Polyethylene (A): MFR = 0.7, density = 963 kg / m ³ , Mw / Mn = 12.

[Example 1]
Polypropylene (A) 20 mm in diameter, L / D = 30 (L: distance from raw material supply port to discharge port (m) of single screw extruder, D: inner diameter of single screw extruder (m)), cylinder temperature 200 The polyethylene (A) was charged into a single screw extruder having a diameter of 20 mm, L / D = 30, and a cylinder temperature of 200 ° C. via a feeder. A film having polypropylene (A) as a surface layer and polyethylene (A) as an intermediate layer was extruded from a two-type three-layer coextrusion T die having a lip thickness of 3.0 mm installed at the tip of the single screw extruder. The ratio of the extrusion weight of the surface layer to the intermediate layer was 2: 1, and the T die temperature (also referred to as “film formation temperature”) was 190 ° C. Immediately apply cold air of 25 ° C to the molten resin after extrusion, and then wind it on a core with a cast roll cooled to 95 ° C at a draw ratio of 200 and a winding speed of 15 m / min. Obtained (film formation step).

  Three laminated original films wound up on a core are prepared, each unwound at an unwinding speed of 10 m / min, led to a heating roll in a state where the three sheets are overlapped, and there is a thermocompression bonding temperature of 125. Thermocompression bonding was performed at a temperature of 0 ° C. and a linear pressure of 6.0 kg / cm (thermocompression bonding process). Thereafter, the film was guided to a cooling roll at 25 ° C. at the same speed and wound to obtain a laminate.

  The obtained laminate was unwound and passed through a furnace heated to 128 ° C. over 30 minutes (heat treatment step), and then led to a 25 ° C. cooling roll and wound up to obtain a laminate. The laminate was stretched 1.03 times in the MD direction (also referred to as “heat treatment stretch ratio”) in a furnace so that wrinkles were not generated in the laminate.

  The obtained laminate was uniaxially stretched 1.3 times in the MD direction at a temperature of 25 ° C., and then uniaxially stretched 2.5 times in the MD direction at a temperature of 110 ° C. (stretching step). It was relaxed by a factor of 0.9 at a temperature of 125 ° C. and heat-fixed, and three laminated microporous films forming the laminate were separated (peeling step) and wound on three cores. About the obtained microporous film, the film thickness, the air permeability, the porosity, and the puncture strength were measured. The results are shown in Table 1.

[Comparative Example 1]
After obtaining a laminated raw film in the same manner as in Example 1, heat treatment was attempted without performing thermocompression bonding. When three sheets of the laminated raw film were unwound and heat treated under the same conditions as in Example 1 with the three laminated, the laminated raw film was wrinkled in the furnace and the heat treated laminated original An anti-film could not be obtained.

[Comparative Example 2]
After obtaining the laminated raw film in the same manner as in Example 1, the three laminated raw films were unwound without performing thermocompression bonding, respectively, and the inside of the furnace heated to 128 ° C. in a state where the three laminated films were superposed on each other. It was allowed to pass for 30 minutes (heat treatment step), and then led to a 25 ° C. cooling roll and wound up to obtain a laminate. In addition, it was able to heat-process without generating a wrinkle by extending | stretching three laminated | multilayer raw fabric films 1.1 times in MD direction in a furnace.

  In the state where the obtained three laminated original films were laminated, the film was uniaxially stretched 1.3 times in the MD direction at a temperature of 25 ° C., and then 2.5 times in the MD direction at a temperature of 110 ° C. The film was uniaxially stretched (stretching process), further relaxed by a factor of 0.9 at a temperature of 125 ° C. and heat-set, and three laminated microporous films were wound on three cores, respectively. About the obtained microporous film, the film thickness, the air permeability, the porosity, and the puncture strength were measured. The results are shown in Table 1. Compared with Example 1, the air permeability was extremely high, and the permeability was inferior.

[Example 2]
The process up to the thermocompression bonding process was performed in the same manner as in Example 1, and the obtained four laminates were unwound and passed through a furnace heated to 128 ° C. over 30 minutes (heat treatment process), and then cooled to 25 ° C. It was led to a roll and wound up to obtain a laminate. In addition, the laminated body was extended | stretched 1.03 times in MD direction within the furnace so that a wrinkle might not generate | occur | produce in a laminated body.

  The obtained laminate was uniaxially stretched 1.3 times in the MD direction at a temperature of 25 ° C., and then uniaxially stretched 2.5 times in the MD direction at a temperature of 110 ° C. (stretching step). Heat-fixing was performed by relaxing 0.9 times at a temperature of 125 ° C., 12 laminated microporous films forming the laminate were separated (peeling step), and wound on 12 cores. About the obtained microporous film, the film thickness, the air permeability, the porosity, and the puncture strength were measured. The results are shown in Table 1.

Example 3
A laminated microporous film was obtained in the same manner as in Example 2 except that the number of raw film in the thermocompression bonding process was changed to 6 and the number of the laminated bodies in the heat treatment process was changed to 6.

Example 4
A laminated microporous film was obtained in the same manner as in Example 1 except that the lip thickness in the film forming step was changed to 4 mm.

Example 5
Polypropylene (A) 20 mm in diameter, L / D = 30 (L: distance from raw material supply port to discharge port (m) of single screw extruder, D: inner diameter of single screw extruder (m)), cylinder temperature 200 It injected | thrown-in to the single screw extruder of ° C through the feeder. The film was extruded from a single-layer T-die installed at the tip of this single-screw extruder. The T die temperature was 190 ° C. The extruded molten resin is immediately applied with cold air at 25 ° C., and then wound on a core with a cast roll cooled to 95 ° C. under a draw ratio of 200 and a winding speed of 15 m / min. (Film formation step).

  Three raw films wound up on the core are prepared, each unwound at an unwinding speed of 10 m / min, and led to a heating roll in a state where the three sheets are superposed, where the thermocompression bonding temperature is 125 ° C. Then, thermocompression bonding was performed at a linear pressure of 6.0 kg / cm (thermocompression bonding process), and then the film was guided to a 25 ° C. cooling roll at the same speed and wound to obtain a laminate.

  The obtained laminate was unwound and passed through a furnace heated to 128 ° C. over 30 minutes (heat treatment step), and then led to a 25 ° C. cooling roll and wound up to obtain a laminate. The laminate was stretched 1.03 times in the MD direction (also referred to as “heat treatment stretch ratio”) in a furnace so that wrinkles were not generated in the laminate.

  The obtained laminate was uniaxially stretched 1.3 times in the MD direction at a temperature of 25 ° C., and then uniaxially stretched 2.5 times in the MD direction at a temperature of 130 ° C. (stretching step). The film was heat-set by relaxing it by a factor of 0.9 at a temperature of 145 ° C., and three microporous films forming the laminate were separated (peeling step) and wound on three cores. About the obtained microporous film, the film thickness, the air permeability, the porosity, and the puncture strength were measured. The results are shown in Table 1.

[Examples 6 to 8]
A laminated microporous film was obtained in the same manner as in Example 1 except that the polypropylene used in the film forming step was changed to the polypropylene shown in Table 1.

[Comparative Example 3]
After obtaining a laminated raw film in the same manner as in Example 4, heat treatment was attempted without performing thermocompression bonding. When three sheets of the laminated raw film were unwound and heat treated under the same conditions as in Example 1 with the three laminated, the laminated raw film was wrinkled in the furnace and the heat treated laminated original An anti-film could not be obtained.

[Comparative Example 4]
After obtaining the laminated raw film in the same manner as in Example 4, the three laminated raw films were unwound respectively without performing thermocompression bonding, and the inside of the furnace heated to 128 ° C. in a state where the three laminated sheets were superposed on each other. It was allowed to pass for 30 minutes (heat treatment step), and then led to a 25 ° C. cooling roll and wound up to obtain a laminate. In addition, it was able to heat-process without generating a wrinkle by extending | stretching three laminated | multilayer raw fabric films 1.07 times in MD direction in a furnace.

  In the state where the obtained three laminated original films were laminated, the film was uniaxially stretched 1.3 times in the MD direction at a temperature of 25 ° C., and then 2.5 times in the MD direction at a temperature of 110 ° C. The film was uniaxially stretched (stretching process), further relaxed by a factor of 0.9 at a temperature of 125 ° C. and heat-set, and three laminated microporous films were wound on three cores, respectively. About the obtained microporous film, the film thickness, the air permeability, the porosity, and the puncture strength were measured. The results are shown in Table 1. Compared to Example 4, the air permeability was high and the permeability was inferior.

[Comparative Example 5]
After obtaining a raw film in the same manner as in Example 5, heat treatment was attempted without performing thermocompression bonding. When three raw films were unwound and heat-treated under the same conditions as in Example 1 with the three sheets being superposed, wrinkles were generated in the original film in the furnace, and the heat-treated laminated original film Could not get.

[Comparative Example 6]
After obtaining the raw film in the same manner as in Example 5, the three original films were unwound without performing thermocompression bonding, and the inside of the furnace heated to 128 ° C. in a state where the three films were stacked for 30 minutes. Then, it was passed through (heat treatment step), and then led to a cooling roll at 25 ° C. and wound up to obtain a laminate. In addition, it was able to heat-process without generating a wrinkle by extending | stretching three laminated | multilayer raw fabric films 1.1 times in MD direction in a furnace.

  In a state where the obtained three original films were laminated, the film was uniaxially stretched 1.3 times in the MD direction at a temperature of 25 ° C., and then uniaxially stretched 2.5 times in the MD direction at a temperature of 130 ° C. The film was stretched (stretching step), further relaxed by a factor of 0.9 at a temperature of 145 ° C., heat-fixed, and three microporous films were wound on three cores, respectively. About the obtained microporous film, the film thickness, the air permeability, the porosity, and the puncture strength were measured. The results are shown in Table 1. Compared to Example 5, the air permeability was high and the permeability was inferior.

[Comparative Example 7]
After obtaining a laminated raw film in the same manner as in Example 6, heat treatment was attempted without performing thermocompression bonding. When three sheets of the laminated raw film were unwound and heat treated under the same conditions as in Example 1 with the three laminated, the laminated raw film was wrinkled in the furnace and the heat treated laminated original An anti-film could not be obtained.

[Comparative Example 8]
After obtaining the laminated raw film in the same manner as in Example 6, the three laminated raw films were unwound without performing thermocompression bonding, respectively, and the inside of the furnace heated to 128 ° C. in a state where the three laminated films were superposed on each other. It was allowed to pass for 30 minutes (heat treatment step), and then led to a 25 ° C. cooling roll and wound up to obtain a laminate. In addition, it was able to heat-process without generating a wrinkle by extending | stretching three laminated | multilayer raw fabric films 1.07 times in MD direction in a furnace.

  In the state where the obtained three laminated original films were laminated, the film was uniaxially stretched 1.3 times in the MD direction at a temperature of 25 ° C., and then 2.5 times in the MD direction at a temperature of 110 ° C. The film was uniaxially stretched (stretching process), further relaxed by a factor of 0.9 at a temperature of 125 ° C. and heat-set, and three laminated microporous films were wound on three cores, respectively. About the obtained microporous film, the film thickness, the air permeability, the porosity, and the puncture strength were measured. The results are shown in Table 1. Compared to Example 6, the air permeability was extremely high and the permeability was inferior.

[Comparative Example 9]
A laminated raw film was obtained in the same manner as in Example 1 except that the polypropylene (A) used in the film forming step was changed to polypropylene (E). Although thermocompression bonding was attempted in the same manner as in Example 1, the laminated microporous film could not be crimped and a laminate could not be obtained.

  The microporous film of the present invention has industrial applicability as a battery separator, more specifically as a lithium secondary battery separator.

Claims (2)

A single resin comprising at least one polypropylene resin selected from the group consisting of a polypropylene resin (A) having a pentad fraction of 90 to 96% and a polypropylene resin (B) having a propylene content of 98 to 99.5 mol%. A film forming step of obtaining a layer original film, or a laminated original film having an outermost layer including one or more kinds of polypropylene resins selected from the group consisting of the polypropylene resin (A) and the polypropylene resin (B); ,
A thermocompression bonding step in which the single layer original film or the laminated original film 2-6 obtained in the film formation step is laminated and thermocompression bonded to obtain a laminate;
A heat treatment step of heat-treating one or two to six of the laminates obtained in the thermocompression step; and
In the state where the laminate after the heat treatment obtained in the heat treatment step is maintained at 90 ° C. to 160 ° C., a stretching step of stretching 1.05 times to 5.0 times in at least one direction;
A peeling step of peeling the layer of the laminate after drawing obtained in the drawing step to obtain a microporous film;
A method for producing a microporous film having a thickness of 16 μm or less.   The manufacturing method of the microporous film of Claim 1 whose film thickness of the said microporous film obtained at the said peeling process is 10-14 micrometers.