TWI488742B - Laminated porous film, preparation method thereof and separator for secondary cell comprising same - Google Patents

Description

Multilayer porous film, method for producing the same, and separator for secondary battery including the same Field of invention

The present invention relates to a laminated porous film having excellent breaking (SD) and collapse (BD) properties, and high gas permeability, a method for producing the laminated porous film, and a method for containing the porous film. The separator of the secondary battery.

Background of the invention

The separators for batteries (batteries) are widely classified into polypropylene (PP) single-layer separators, polyethylene (PE) single-layer separators, and PE/PP laminated separators. In the case of a PP single-layer separator, the breaking property is inferior, but the collapse property is good. On the contrary, in the case of PE single-layer separators, it has good breaking properties and poor collapse properties.

On the other hand, since the separator having a PE/PP laminate structure has both the collapse property of PP and the disconnection property of PE, in recent years, it has been mainly used to supplement the disadvantages of the above two products. Japanese Patent Publication No. 2010-61973, No. 2010-61974 and No. 2010-120217 disclose one The β-crystal nucleating agent is a laminated porous film mainly composed of a PP resin and a PE resin, and contains at least one group selected from the group consisting of modified polyolefin resin, alicyclic saturated A modified product of a hydrocarbon resin or the like, an ethylene copolymer, and a wax.

However, these conventional films have different properties depending on the thermoplastic gum added to the PE resin layer, and therefore, when these conventional films are applied in the same manner as the conventional methods, they are not sufficiently ensured for the separator. The breathability required, and will limit the method.

Summary of invention

Accordingly, it is an object of the present invention to provide a laminated porous film having excellent breaking and collapse properties and high gas permeability, a method for producing the laminated porous film, and a secondary battery for containing the porous film. Isolation piece.

According to an aspect of the invention, there is provided a laminated porous film having a laminate structure comprising 2 or more layers: 1) a first resin layer containing a polypropylene resin and a β-crystal nucleating agent; and 2) A polyethylene resin and a wax having a melting point of 90 ° C or higher and a crystallinity of 80% or more.

According to another aspect of the present invention, there is provided a method for producing the laminated porous film comprising the steps of: a) adding a polypropylene resin and a β-crystal nucleating agent, and subjecting them to a melt state.揉, thereby forming a first resin; b) adding a polyethylene resin and a wax having a melting point of 90 ° C or higher and a crystallinity of 80% or higher, and kneading the same, thereby making the first a second resin; c) separately extruding the first resin and the second resin, and stratifying the same, thereby forming a laminated first resin layer and a second resin layer a non-drawn sheet; and d) the non-drawn sheet is drawn.

According to another aspect of the present invention, there is provided a separator for a secondary battery comprising the laminated porous film.

According to the present invention, the laminated porous film can have excellent breaking and collapse properties, and high gas permeability, and therefore, can be efficiently applied to a separator for a lithium secondary battery or the like.

Detailed description of the preferred embodiment Multilayer porous membrane

Hereinafter, a laminated porous film according to the present invention will be described.

According to the present invention, the laminated porous film has a laminate structure comprising 2 or more layers: 1) a first resin layer made of a polypropylene resin containing a β-crystal nucleating agent; and 2) A second resin layer made of a polyethylene resin of a wax having a melting point of 90 ° C or higher and a crystallinity of 80% or more.

In the present invention, the β-crystal nucleating agent contained in the first resin layer may be selected from the group consisting of N, N'-dicyclohexyl-2,6-naphthalenedicarbamide, N,N'-dicyclohexyl-p-xylamine, N,N'-dicyclohexanecarbonyl-p-phenylenediamine, N,N'-dibenzoyl-1,5-diamino Naphthalene, N,N'-dicyclohexanecarbonyl-1,4-diaminocyclohexane, N-cyclohexyl-4-benzamide, and mixtures thereof. A preferred useful β-crystal nucleating agent is N,N'-dicyclohexyl-2,6-naphthalenedicarbamide.

The β-crystal nucleating agent is based on 100 parts by weight of the polypropylene resin The amount added is preferably from 0.0001 to 5 parts by weight, and more preferably from 0.001 to 1 part by weight.

The polypropylene resin used in the present invention preferably has a melt index of from 1 to 20 g/10 minutes.

In the present invention, the second resin layer in a porous structure may be provided by adding a wax to the polyethylene resin, the wax having a melting point of 90 ° C or higher, and preferably 95 ° C or higher, and, for example, The wax may have a melting point in the range of from 90 to 150 °C. Moreover, the wax has a crystallinity of 80% or more, and preferably 85% or more, so that it can have a gas permeability suitable for a separator for a lithium secondary battery.

If the melting point of the wax is less than 90 ° C, the wax is melted in the machine direction (MD) during the drawing process, thereby hindering the formation of the porous structure on the surface of the polypropylene resin adjacent to the wax, so that the laminated porous film cannot be ensured to be charged. Part of the breathability. In this case, in order to ensure sufficient gas permeability, although the MD drawing temperature should be set to less than 90 ° C, at a temperature of less than 90 ° C, the collapse performance of the film may increase, which may be undesired. The productivity and film formation stability are deteriorated. Therefore, the melting point of the wax used in the present invention should be 90 ° C or higher.

Moreover, if the crystallinity of the wax is less than 80%, in the drawing method, the wax system is drawn together with the polyethylene layer, making it impossible to form a suitable porous structure of the polyethylene layer, and thus cannot be charged. Part of the breathability. Therefore, the crystallinity of the wax used in the present invention should be 80% or more. The crystallinity can be measured using IR spectroscopy, X-ray diffraction, density measurement, calorimetry, or the like. For example, differential scanning calorimetry (DSC) can be used, and specifically, the melting enthalpy (ΔH _f ) of a sample can be determined and then compared with the melting enthalpy (ΔH _f ) of a completely crystalline material. The crystallinity of the sample was calculated.

The wax having a melting point and crystallinity within the above range may be a polar wax or a non-polar wax, and specific examples thereof may include polypropylene wax, polyethylene wax, castor oil wax, microcrystalline wax, paraffin wax, lignite. A wax, a purely wax, a substituted guanamine wax, or a mixture thereof. Particularly useful waxes are microcrystalline waxes. The microcrystalline wax is a type of wax produced by deoiling a paraffin ester in a petroleum refining process. The microcrystalline wax contains a higher proportion of isoparaffin-dominated branched chain hydrocarbons and naphthenes than the widely known paraffin wax which mainly contains linear paraffins. Unlike paraffin waxes having large crystals, the microcrystalline wax has fine crystals and contains saturated aliphatic hydrocarbons having a high molecular weight. Compared to paraffin wax, the microcrystalline wax exhibits a darker color with higher viscosity, density, adhesion, and elasticity as well as higher molecular weight and melting point. The elasticity and adhesion of the microcrystalline wax are related to the non-linear components contained therein. Since the crystallinity of the microcrystalline wax is small and fine, it is more flexible than paraffin wax.

The wax is preferably added in an amount of from 5 to 30% by weight, and more preferably from 5 to 20% by weight, based on the weight of the second resin layer.

The polyethylene resin used in the present invention preferably has a melt index (MI) of from 1 to 20 g/10 minutes, and may be selected from the group consisting of low density polyethylene, linear low density polyethylene. , linear ultra-low density polyethylene, medium density polyethylene, high density polyethylene, ultra high density polyethylene, copolymer mainly containing ethylene, and resin blends thereof. A preferred useful polyethylene resin is a high density polyethylene resin.

The second resin layer may further comprise an α-crystal nucleating agent. The α-crystal nucleating agent can be used as a crystal once the polyethylene is melted in a molten state. The growing nucleus, so that crystals can be formed quickly, thereby producing many small and uniform crystals. The α-crystal nucleating agent may preferably be added in an amount of 0.0001 to 5 parts by weight, and more preferably 0.001 to 1 part by weight, based on 100 parts by weight of the polyethylene resin. The α-crystal nucleating agent may be selected from the group consisting of dibenzylidene sorbitol; a carboxylic acid comprising an aliphatic carboxylic acid, an alicyclic carboxylic acid, an aromatic carboxylic acid, etc.; an aliphatic guanamine Inorganic particles, including cerium oxide, talc, kaolin, calcium carbide, etc.; glycerin; high carbon fatty acid esters such as monoglycerides; and the like.

The laminated porous film according to the present invention has 2 or more layers, for example, 2 to 5 layers.

Method for making the film

The following is a description of a method for producing the laminated porous film according to one of the present inventions.

The laminated porous film according to the present invention is produced by the following steps: a) adding a polypropylene resin and a β-crystal nucleating agent, and kneading them in a molten state, thereby preparing a first resin; b) adding a polyethylene resin and a wax having a melting point of 90 ° C or higher and a crystallinity of 80% or higher, and kneading the same, thereby preparing a second resin; c) separately extruding the first a resin and a second resin are laminated to form a non-drawn sheet comprising the laminated first resin layer and the second resin layer; and d) the non-drawn sheet is drawn.

Specifically, in the step a), 100 parts by weight of a polypropylene resin having a melt index of 1 to 20 g/10 minutes, and 0.0001 to 5 parts by weight of a β-crystal nucleating agent (for example, N, N) are added. '-Dicyclohexyl-2,6-naphthylcarboxamide), which is then melted and kneaded to thereby form a first resin. because Thus, the melt kneading temperature is preferably set at 250 ° C or lower, for example, 200 to 230 ° C, and the first resin produced is cooled and granulated.

In the step b), a polyethylene resin having a melt index of 1 to 20 g/10 minutes, and a wax having a melting point of 90 ° C or higher and a crystallinity of 80% or higher, and an α- are added. The crystal nucleating agent is then subjected to melt kneading to thereby form a second resin. The melted kneading temperature is preferably set at 230 ° C or lower, for example, 180 to 220 ° C, and the second resin produced is cooled and granulated.

In the step c), the first resin and the second resin produced in the steps a) and b) are respectively melted and kneaded and cooled to be cast using a casting roll, thereby obtaining a first layer containing a layer. And a non-drawn sheet of the second resin layer. The melt extrusion temperature is preferably set to less than 250 ° C, for example, 200 to 230 ° C, and the temperature of the casting roll is preferably set to 100 ° C or lower, for example, 110 to 130 ° C.

In step d), the laminated sheets obtained in step c) are continuously biaxially drawn to form a film. The drawing method can be carried out in a drawing ratio of 2 to 10 times and a direction in the machine direction (MD) and the transverse direction (TD) in a temperature range of 90 ° C or higher. If the drawing temperature is less than 90 ° C, the collapse property is increased, and the film formation stability becomes apparently problematic. Therefore, the drawing temperature in the method according to the present invention is preferably set to a temperature which does not exceed the melting point of the wax contained in the second resin, that is, 90 ° C or higher, for example, 90 ° C or higher. For example, the laminated sheet is drawn at a draw ratio of 2 to 10 times at 95 ° C, and then drawn at 100 ° C and a draw ratio of 2 to 10 times at 100 ° C to form a desired film.

The laminated porous film thus obtained can be subjected to heat treatment at a temperature of 100 ° C or higher, thereby obtaining dimensional stability.

The properties of the film

The laminated porous film according to the present invention may exhibit a 25 ° C Gurley gas permeability of 500 sec/100 ml or less, which means that 100 ml of air is passed through a 645 mm ² at 25 ° C according to ASTM D726. The time required for the film of the area.

Moreover, after heating at 135 ° C for 30 seconds, the laminated porous film according to the present invention can exhibit a Gurley gas permeability of more than 40,000 sec / 100 ml, which means heat treatment in an oven at 135 ° C according to ASTM D726 30 After a second, 100 ml of air was passed through a film having a 645 mm ² area for the time required. Therefore, the film according to the present invention can exhibit excellent breaking properties.

Isolator for secondary battery

The porous polypropylene film according to the present invention can have excellent collapse and breakage properties as well as high gas permeability, and thus can be efficiently applied to a separator of a secondary battery or the like.

Accordingly, the present invention provides a separator for a secondary battery including the laminated porous film. The secondary battery is preferably a lithium secondary battery.

The laminated porous film according to the present invention preferably has a total thickness of 10 to 50 μm, and thus can be used in a separator suitable for a secondary battery.

Example of test sample

In the following, the invention is described in more detail by the following examples, which are intended to illustrate and not to limit the invention.

Example 1: Method for preparing laminated porous film

100 parts by weight of a polypropylene resin (MI: 3.0 g/10 min), and 0.2 part by weight of N,N'-dicyclohexyl-2,6-naphthalenedicarbamide as a β-crystal nucleating agent were added. This was made into a polypropylene resin composition, which was then kneaded by melting at 220 ° C, and cooled and granulated at room temperature to thereby produce a sheet A.

Further, 100 parts by weight of a polyethylene resin (MI 5.5 g/10 min), and 10 parts by weight of a microcrystalline wax having a melting point of 91 ° C and 85% crystallinity, and 0.3 part by weight of an α-crystal nucleating agent are added, whereby A polyethylene resin composition was formed and then at 220. It was kneaded by melting at ° C, and cooled and granulated at room temperature to thereby produce a sheet B.

The sheets A and B were respectively melted into a layer A and a layer B at 220 ° C using a melt extruder, and then the layer layers were made into a three-layer structure using a feeding device (A/). B/A = 3:1:3 thickness ratio), and cooled to be cast at 120 ° C using a casting roll, thereby forming a laminated sheet.

The laminated sheet was drawn at a draw ratio of MD and 4 times at 95 ° C, and then drawn at a drawing ratio of TD and 3 times at 100 ° C to thereby form a laminated porous film.

Example 2: Method for producing laminated porous film

A laminated porous film was produced in the same manner as in Example 1 except that the polyethylene resin composition was made using a microcrystalline wax having a melting point of 101 ° C and a crystallinity of 90%.

Example 3: Method for producing laminated porous film

In addition to using a microcrystalline crystal having a melting point of 116 ° C and 92% crystallinity A laminated porous film was produced in the same manner as in Example 1 except that the wax was made into the polyethylene resin composition.

Example 4: Method for producing laminated porous film

A laminated porous film was produced in the same manner as in Example 1 except that the polyethylene resin composition was made using a microcrystalline wax having a melting point of 128 ° C and 87% crystallinity.

Comparative Example 1: Production of laminated porous film

A laminated porous film was produced in the same manner as in Example 1 except that the polyethylene resin composition was made using a microcrystalline wax having a melting point of 84 ° C and 87% crystallinity.

Comparative Example 2: Production of laminated porous film

A laminated porous film was produced in the same manner as in Example 1 except that the polyethylene resin composition was made using a microcrystalline wax having a melting point of 109 ° C and a crystallinity of 65%.

The properties of the films prepared in Examples 1 to 4 and Comparative Examples 1 and 2 were evaluated as follows. The results are shown in Table 1 below.

Test Example 1: Breathability (at 25 ° C)

The time required to pass 100 ml of air through a film having an area of 645 mm ² was measured at 25 ° C according to ASTM D726 using a Gurley Densitometer (G-B3C Toyoseiki).

Test Example 2: Gas permeability (at 135 ° C)

After heat treatment in an oven for 30 seconds at 135 ° C, the time required to pass 100 ml of air through a film having an area of 645 mm ^{2 was} measured according to ASTM D726 using a G-B3C Toyoseiki. And evaluate the nature of disconnection (SD).

As understood from Table 1, all of the films of the examples and comparative examples showed effective disconnection (SD) performance. However, the films of Examples 1 to 4 using only the wax having a melting point of 90 ° C or higher and a crystallinity of 80% or higher showed suitability for the gas permeability of the separator.

Although the present invention has been described with reference to the specific embodiments thereof, it is to be understood that the various modifications and changes of the present invention as defined by the appended claims.

Claims (10)

A laminated porous film having a laminated structure comprising two or more layers, comprising: 1) a first resin layer comprising a polypropylene resin and a β-crystal nucleating agent, wherein the β-crystal nucleating agent is added , in an amount of 0.0001 to 5 parts by weight based on 100 parts by weight of the polypropylene resin; and 2) a wax containing a polyethylene resin and having a melting point (mp) of 90 ° C or higher and a crystallinity of 80% or more The second resin layer, wherein the wax is added in an amount of from 5 to 30% by weight based on the weight of the second resin layer. The laminated porous film according to claim 1, wherein the β-crystal nucleating agent is selected from the group consisting of N, N'-dicyclohexyl-2,6-naphthalenedicarbamide, N , N'-dicyclohexyl-p-xylamine, N,N'-dicyclohexanecarbonyl-p-phenylenediamine, N,N'-dibenzoyl-1,5-diaminonaphthalene , N,N'-dicyclohexanecarbonyl-1,4-diaminocyclohexane, N-cyclohexyl-4-benzamide, and mixtures thereof. The laminated porous film of claim 1, wherein the polypropylene resin has a melt index (MI) of from 1 to 20 g/10 minutes. The laminated porous film according to claim 1, wherein the wax is selected from the group consisting of polypropylene wax, polyethylene wax, castor oil wax, microcrystalline wax, paraffin wax, montan wax, and pure ground wax. , substituted proguanamine wax and mixtures thereof. The laminated porous film of claim 1, wherein the polyethylene resin has a melt index (MI) of from 1 to 20 g/10 minutes. The laminated porous film according to claim 1, wherein the second resin layer further comprises an α-crystal nucleating agent selected from the group consisting of dibenzylidene sorbitol, aliphatic carboxylic acid, and fat. A mixture of a cyclic carboxylic acid, an aromatic carboxylic acid, an aliphatic decylamine, cerium oxide, talc, kaolin, calcium carbide, glycerin, a high carbon fatty acid ester, and the like. The laminated porous film of claim 1, wherein the film exhibits a gas permeability of less than or equal to 500 sec / 100 cc when measured at 25 ° C according to ASTM D726. A method for producing a laminated porous film according to claim 1, comprising the steps of: a) adding a polypropylene resin and a β-crystal nucleating agent, and melting and kneading the same, thereby producing a first resin; b) a polyethylene resin and a wax having a melting point of 90 ° C or higher and a crystallinity of 80% or higher, and the like is melted and kneaded to thereby produce a second resin; Dissipating the first resin and the second resin separately, and laminating them to form a non-drawn sheet comprising the laminated first resin layer and the second resin layer; and d) drawing the non-drawn sheet Making thin slices. The method of claim 8, wherein the drawing method in the step d) is carried out in a temperature range of 90 ° C or higher, in each of the longitudinal and transverse directions, and a draw ratio of 2 to 10 times. . A separator for a secondary battery comprising the laminated porous film according to any one of claims 1 to 7.