JP2010195899A - Method for producing porous film, porous film, method for producing laminated porous film, laminated porous film, and separator for battery - Google Patents

Abstract

Disclosed is a method for producing a porous film that does not cause a thin portion in the resulting porous film, a porous film and a laminated porous film obtained by this production method, and the porous film or laminated porous film. A battery separator using the above is provided.
A method for producing a porous film according to the present invention comprises a polyolefin resin (A), a micropore forming agent (B), and 0.5 to 2 weights per 100 parts by weight of the component (B). A sheet molding step for obtaining a sheet (E) by molding a resin kneaded product (D) obtained by kneading a mixture containing a part of sodium stearate and / or sodium laurate (C) into a sheet, A porous film forming step of obtaining a porous film (G) by stretching at least the sheet (E).
[Selection figure] None

Description

  The present invention relates to a method for producing a porous film capable of obtaining a porous film having excellent membrane properties from a polyolefin resin composition, a porous film and a laminated porous film obtained by the method, and these porous films The present invention relates to a battery separator obtained using

  As is well known, porous films are used in a wide variety of products such as sanitary materials, medical materials, and battery separators. Among such porous films used for various applications, those used for battery separators such as lithium ion secondary batteries are thin, uniform, and have fine pores on the order of submicrons. However, it is required to be strong. As a method for producing a porous film excellent in such membrane characteristics, conventionally, for example, as described in Patent Document 1, after kneading a high-molecular polyethylene resin and a large amount of plasticizer of the same weight or more, A method of forming a sheet, removing the plasticizer contained in the sheet, and then stretching the sheet has been used. However, in this method for producing a porous film, a step of immersing the sheet in an organic solvent and extracting a large amount of the plasticizer is essential, so that there is a problem that the steps are many and complicated.

On the other hand, recently, a polyolefin resin sheet is formed by uniformly mixing (kneading) a micropore forming agent such as calcium carbonate fine particles with a polyolefin resin composition to form a sheet. A method of drawing a sheet to obtain a porous film has been used. For example, in Patent Document 2, a high molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more, a thermoplastic resin having a weight average molecular weight of 2 × 10 ⁴ or less, and calcium carbonate are kneaded and molded into a sheet shape. Thereafter, a method of stretching the sheet to obtain a porous film is disclosed. This method for producing a porous film is a very excellent method, and a porous film excellent in shutdown property and heat resistance suitable for use in battery separators can be obtained by a small number of steps.

  In this method for producing a porous film, first, calcium carbonate fine particles, which are micropore forming agents, are uniformly mixed with a polyolefin resin composition. The calcium carbonate fine particles are surface-treated with a surface treatment agent such as a fatty acid in order to improve dispersibility in the resin composition. The use of the surface-treated calcium carbonate fine particles is described in Patent Documents 3 and 4, for example. Next, the surface-treated calcium carbonate fine particles are mixed with the polyolefin resin composition and kneaded to form a uniformly kneaded resin kneaded product into a sheet shape. A porous film having high film strength can be obtained by stretching the molded polyolefin resin sheet. Thereafter, the porous film is brought into contact with a hydrochloric acid ethanol solution to dissolve and remove calcium carbonate fine particles in the film, and then washed with ethanol and dried to obtain a product. In the production method disclosed in Patent Document 2, as described above, the calcium carbonate fine particles in the film are dissolved and removed after stretching. However, it is possible to dissolve and remove the calcium carbonate particles before stretching.

JP 09-157423 A JP 2002-69221 A JP 2001-072890 A JP 2000-336197 A

As described above, the method for producing a porous film described in Patent Document 2 is an excellent method, and a porous film having excellent film characteristics suitable for use in a battery separator can be produced.
In order to further improve the performance of the porous film obtained by using the above-described micropore-forming agent and the performance of the porous film obtained by the method, the present inventors have made various studies. It turns out that there is a point to do.
That is, although not always, a thin-walled portion may occur in the resulting porous film. When a battery is produced using the porous film as a separator, the porous film may be easily broken from this thin portion. If generation | occurrence | production of this thin part can be prevented, the porous film more suitable for manufacture of a battery can be provided.

  Therefore, an object of the present invention is to produce a porous film that does not cause a thin portion in the resulting porous film, a porous film that does not have a thin portion obtained by this production method, and a laminated porous film, An object of the present invention is to provide a battery separator using a porous film or laminated porous film having no thin portion.

  In order to solve the above-mentioned problems, the present inventors diligently conducted experimental studies, and as a result, obtained the following knowledge.

  Conventionally, a mixture containing a plurality of fatty acids such as stearic acid, lauric acid, and oleic acid or a metal salt thereof has been used as the surface treatment agent for the micropore forming agent. As a micropore forming agent used for making a film porous, the most preferable one is calcium carbonate fine particles. In commercially available calcium carbonate, natural fats and oils such as beef tallow are mainly used. Surface treated with fatty acids and their salts.

  The present inventors speculated that the reason why the thin-walled portion is generated in the conventional porous film is that the dispersibility of the calcium carbonate fine particles used as the micropore forming agent is insufficient. . That is, when the calcium carbonate fine particles are uniformly dispersed in the resin, aggregation occurs in a part of the calcium carbonate fine particles, secondary particles are formed, and secondary particles having large diameters are scattered on the film, thereby I guessed that would be thinned.

Therefore, various additives were added when dispersing the calcium carbonate fine particles in the resin, and the relationship with the thinning of the film was examined. As a result, the mechanism of action is unknown, but by using sodium stearate and / or sodium laurate as an additive when dispersing calcium carbonate fine particles in the resin, the thin-walled portion generated in the resulting porous film Was found to decrease dramatically.
It has also been found that the additive amount (sodium stearate and / or sodium laurate) in this case is preferably in the range of 0.5 to 2 parts by weight with respect to 100 parts by weight of the calcium carbonate fine particles.
The effect that the thin-walled portion generated in the porous film is drastically reduced by the addition of sodium stearate and / or sodium laurate is not limited to the case where the micropore-forming agent is calcium carbonate fine particles. The same applies to the case where other water-soluble fine particles such as magnesium sulfate fine particles, calcium oxide fine particles, and calcium hydroxide fine particles are used, and furthermore, the case where general filler fine particles are used.

  The present invention has been made based on the above findings. That is, the manufacturing method of the porous film concerning this invention is 0.5-2 weight part with respect to 100 weight part of polyolefin resin (A), micropore formation agent (B), and the said (B) component. A resin molding (D) obtained by kneading a mixture containing sodium stearate and / or sodium laurate (C) is molded into a sheet to obtain a sheet (E), and the sheet ( A porous film forming step of obtaining a porous film (G) by at least stretching E)

  The said structure WHEREIN: It is preferable that the compounding quantity of the micropore formation agent (B) with respect to 100 weight part of said polyolefin resin (A) is 100-400 weight part. The micropore-forming agent (B) is preferably in the form of fine particles, and the average particle diameter is preferably 0.03 to 0.5 μm.

  In the above configuration, the polyolefin resin (A) comprises 50 to 90 parts by weight of ultra high molecular weight polyethylene (a1) having a weight average molecular weight of 500,000 or more, and an olefin wax (a2) 50 having a weight average molecular weight of 700 to 6000. 10 parts by weight (however, the sum of (a1) and (a2) is 100 parts by weight) is preferable.

  In the above configuration, the porous film forming step includes removing the component (B) from the sheet (E) to obtain the porous sheet (F), and stretching the porous sheet (F). It is preferable that the process comprises a stretching step for obtaining a porous film (G).

  In the above configuration, it is particularly preferable to use calcium carbonate fine particles as the micropore forming agent (B).

  Moreover, the porous film concerning this invention is a thing obtained using the manufacturing method of the said porous film, It is characterized by the above-mentioned.

  Also, the method for producing a laminated porous film according to the present invention comprises applying a coating liquid containing a heat-resistant resin containing nitrogen element and ceramic powder to at least one surface of the porous film of the present invention, and curing the coating liquid. To obtain a laminated porous film in which a heat-resistant resin layer is laminated on the porous film.

  Moreover, the laminated porous film according to the present invention is obtained by using the method for producing a laminated porous film.

  The battery separator according to the present invention is obtained by using the porous film or the laminated porous film.

  According to the method for producing a porous film of the present invention, a porous film having no thin portion can be obtained. Further, the porous film obtained by the method for producing a porous film of the present invention and the laminated porous film obtained by using the porous film do not have a thin portion, and are particularly suitable for use as a battery separator. It is.

It is a schematic diagram of the micropore formation agent removal apparatus in order to remove a micropore formation agent from a sheet | seat in an Example and a comparative example.

  As mentioned above, the manufacturing method of the porous film concerning this invention is 0.5-2 with respect to 100 weight part of polyolefin resin (A), micropore formation agent (B), and the said (B) component. A sheet molding step of obtaining a sheet (E) by molding a resin kneaded product (D) obtained by kneading a mixture containing sodium stearate and / or sodium laurate (C) in parts by weight into a sheet; A porous film forming step of obtaining a porous film (G) by stretching at least the sheet (E).

In such a configuration, as a method of obtaining the porous film (G) from the sheet (E), a porous film can be obtained simply by stretching the sheet (E). In addition, a micropore forming agent (B) is added. It is preferable to remove. The removal of the micropore forming agent (B) may be before stretching or after stretching, but is preferably before stretching. That is, in the present invention, preferably, the porous film forming step comprises removing the component (B) from the sheet (E) to obtain the porous sheet (F), and the porous pore forming agent removing step. The stretching step of stretching the sheet (F) to obtain the porous film (G).
Hereinafter, each component of the present invention will be described in detail.

(Component (A): Polyolefin resin)
The polyolefin resin (A) used in the present invention can be composed of a polyolefin resin (A1) alone or a composition comprising a polyolefin resin (A1) and a polyolefin wax (a2). It is.

(Polyolefin resin (A1))
Examples of the polyolefin-based resin (A1) include homopolymers of olefins such as ethylene, propylene, butene, and hexene, and copolymers of these monomers or these monomers and non-olefin monomers.
Specific examples of the polyolefin resin (A1) include polyethylene resins such as low density polyethylene, linear polyethylene (ethylene-α-olefin copolymer) and high density polyethylene, polypropylene, ethylene-propylene copolymer, and the like. Examples include polypropylene resins, poly (4-methylpentene-1), poly (butene-1), and ethylene-vinyl acetate copolymers.

  When the porous film of the present invention is used as a battery separator, it is preferable to use a polyethylene resin as the polyolefin resin (A1) because the shutdown temperature can be about 120 to 150 ° C. As such a polyethylene resin, in particular, when considering the dispersibility of the micropore forming agent (B) such as calcium carbonate fine particles in the polyolefin resin (A), an ultrahigh molecular weight polyethylene (a1) having a weight average molecular weight of 500,000 or more. ) Is preferably used.

(Ultra high molecular weight polyethylene (a1))
In the polyolefin resin (A), when the ultra high molecular weight polyethylene (a1) having a weight average molecular weight of 500,000 or more is used, the total amount of the ultra high molecular weight polyethylene (a1) and the olefin wax (a2) is 100 parts by weight. In addition, 50 to 90 parts by weight of ultrahigh molecular weight polyethylene (a1) having a weight average molecular weight of 500,000 or more and 50 to 10 parts by weight of olefin wax (a2) having a weight average molecular weight of 700 to 6000 are blended. Is preferred. Such a limited composition is particularly suitable when the porous film of the present invention is applied to a battery separator that requires excellent mechanical properties.

  By using 50 to 90 parts by weight of ultrahigh molecular weight polyethylene (a1) having a weight average molecular weight of 500,000 or more, the dispersibility of the micropore forming agent (B) with respect to the polyolefin resin (A) used in the present invention is further improved. be able to.

(Polyolefin wax (a2))
The polyolefin wax (a2) optionally contained in the polyolefin resin (A) used in the present invention preferably has a weight average molecular weight of 700 to 6000. The olefin wax is usually a solid at 25 ° C. The polyolefin resin (A) containing a wax has improved stretchability, and the resulting porous film has excellent strength.
As described above, the content of the olefin wax (a2) is 50 to 10 parts by weight with respect to 100 parts by weight of the total amount of the ultrahigh molecular weight polyethylene (a1) and the olefin wax (a2), preferably 35 to 25 parts by weight.

  Specific examples of the polyolefin wax (a2) used in the present invention include ethylene homopolymer, ethylene-α-olefin copolymer wax, propylene homopolymer, propylene-ethylene copolymer, poly (4-methyl). Mention may be made of pentene-1), poly (butene-1), and ethylene-vinyl acetate copolymer waxes.

  The weight average molecular weight of the polyolefin resin (A1) is measured by GPC (gel permeation chromatography). When the polyolefin resin (A) is a mixture, the mixing ratio (parts by weight) can be obtained by integration of a molecular weight distribution curve obtained by GPC measurement.

(Component (B): Micropore forming agent)
The micropore-forming agent (B) in the present invention is preferably water-soluble, but is not limited to being water-soluble. If the micropore-forming agent (B) is water-soluble, the micropore-forming agent can be easily obtained from the sheet (E) obtained from the resin kneaded product (D) or the stretched film (H) obtained by stretching the sheet (E). The film thickness uniformity of the porous film (G) obtained by using these sheets can be improved.
Specifically, as the micropore forming agent (B), calcium carbonate fine particles are preferable, but other water-soluble fine particles such as magnesium sulfate fine particles, calcium oxide fine particles, and calcium hydroxide fine particles can be used. Fine particles for general fillers can also be used.

  The content of the micropore forming agent (B) is preferably 100 to 400 parts by weight, and more preferably 150 to 350 parts by weight with respect to 100 parts by weight of the polyolefin resin (A).

  When the amount of the micropore forming agent (B) is 100 parts by weight or more with respect to 100 parts by weight of the polyolefin resin (A), the sheet (E) or the stretched film (H) obtained by stretching the sheet (E) is used. There exists a tendency which becomes easy to remove a micropore formation agent (B) in a short time. On the other hand, when the amount of the micropore forming agent (B) exceeds 400 parts by weight relative to 100 parts by weight of the polyolefin resin (A), the sheet (E) or a stretched film obtained by stretching the sheet (E) (H ), The strength of the porous film (G) obtained using the sheet (E) or the stretched film (H) tends to be weak, and the handling tends to be difficult.

The average particle size of the micropore forming agent (B) used in the present invention is preferably 0.03 to 0.5 μm, more preferably 0.05 to 0.3 μm, and still more preferably 0.05 to 0. 0.2 μm.
By using a micropore forming agent having an average particle size of 0.5 μm or less, a porous film having appropriate ion permeability when used as a separator can be obtained.
On the other hand, the use of a micropore forming agent having an average particle size of 0.03 μm or more makes it difficult for the micropore forming agent to agglomerate and facilitates uniform dispersion, so that a porous film with fewer pinholes and thin portions is formed. Obtainable.

  As the calcium carbonate fine particles used as the micropore forming agent (B) of the present invention, fine fine particles having an average particle size of 0.03 to 0.5 μm are obtained, and therefore precipitated calcium carbonate (synthetic calcium carbonate) fine particles are used. It is preferable that the calcium carbonate fine particles are classified.

The method for classifying the calcium carbonate fine particles is not particularly limited, and a dry classifier such as a known air classifier, mesh classifier, or cyclone classifier can be used. Among them, an air classifier is preferably used. In wind classification, an inorganic filler is put into a classification rotor, the classification rotor is rotated, and centrifugal force and centripetal force due to airflow are applied to the inorganic fine particles. It is a method of dividing into fine powder. The classification point can be easily changed by changing the air volume and the rotation speed. The classification point is preferably 0.5 to 50 μm, and more preferably 1 to 20 μm. The classification point can be determined by the following equation (1).

D = c / ν√ (Q / ρ) (1)

In equation (1), D: classification point (μm), c: constant, ν: rotational speed (rpm), Q: air volume (m ² / h), and constant c is a value determined by the apparatus.
In this case, it is preferable from the viewpoint of dispersibility that the calcium carbonate fine particles added to the extruder are subjected to a known surface treatment.

  In the present invention, the average particle size of the micropore forming agent (B) such as calcium carbonate fine particles is 30000 times using a scanning electron microscope (trade name “S-4200” manufactured by Hitachi, Ltd.). It is the average value of the diameter of the particles found in the size field.

(Component (C): Sodium stearate and / or sodium laurate)
In the present invention, sodium stearate and / or sodium laurate is used as the component (C) together with the polyolefin resin (A) and the micropore forming agent (B). Sodium stearate and / or sodium laurate used in the present invention, when the micropore forming agent (B) is dispersed in the polyolefin resin (A), with respect to 100 parts by weight of the micropore forming agent (B), What is necessary is just to add 0.5-2 weight part as the sum total of a component (C). The amount of component (C) added is preferably 0.5 to 1 part by weight. For example, when sodium stearate and sodium laurate are used in combination as component (C), the total of these may be 0.5 to 2 parts by weight. When the purity of sodium stearate and sodium laurate used is not 100%, the amount of sodium stearate and sodium laurate, excluding the amount of impurities from the amount actually added, should be within the above range. . For example, sodium stearate manufactured by Wako Pure Chemical Industries, Ltd. contains 25 parts by weight of water and 30 parts by weight of palmitic acid (purity 45%). When 4 parts by weight of sodium stearate (manufactured by Wako Pure Chemical Industries, Ltd.) is added to 100 parts by weight of the agent (B), 1.8 parts by weight of sodium stearate is actually added.

  When the addition amount of the component (C) is less than 0.5 parts by weight, it is difficult to obtain a uniform dispersion effect of the micropore-forming agent (B) in the polyolefin resin (A). Not only does the strength of the porous film decrease, but saturated fatty acids bleed out from the film being stretched, and the handling of the tenter guide roll and the like is likely to be contaminated.

(Resin kneaded product (D))
The polyolefin resin (A) in the present invention is mixed with a micropore forming agent (B) and sodium stearate and / or sodium laurate (C), and the mixture is kneaded to obtain a resin kneaded product (D). The kneading method in the case of obtaining is not specifically limited. For example, addition of a polyolefin resin (A), a micropore forming agent (B), sodium stearate and / or sodium laurate (C), and an antioxidant or a nonionic surfactant as necessary An agent is blended, and these are mixed using a mixing device such as a roll, a Banbury mixer, a single screw extruder, a twin screw extruder, etc., to obtain a resin kneaded product (D). By adding sodium stearate and / or sodium laurate (C), the micropore forming agent (B) is uniformly dispersed in the obtained resin kneaded material (D).

(Sheet (E))
The manufacturing method which makes the resin kneaded material (D) used by this invention the sheet | seat (E) is not specifically limited, It manufactures by sheet | seat shaping | molding methods, such as an inflation process, a calendar process, T-die extrusion process, and a Skyf method. be able to.
Especially, since the sheet | seat (E) with a high film thickness precision is obtained, manufacturing with the following method is preferable. The following method is particularly preferably used for producing the sheet (E) when the polyolefin resin (A) contains the ultrahigh molecular weight polyethylene (a1) as the polyolefin resin (A1).

  A preferred method for producing the sheet (E) comprising the resin kneaded product (D) is a pair of rotational molding adjusted to a surface temperature higher than the melting point Tm of the polyolefin resin (A1) contained in the resin kneaded product (D). This is a method of rolling the resin kneaded product (D) using a tool. The surface temperature of the rotary forming tool is preferably {(melting point) +5} ° C. or higher. The upper limit of the surface temperature is preferably {(melting point) +20} ° C. or less, and more preferably {(melting point) +15} ° C. or less. Examples of the pair of rotary forming tools include a roll and a belt. The peripheral speeds of both rotary forming tools do not necessarily have to be exactly the same peripheral speed, and the difference between them may be about ± 5% or less.

  The melting point of the polyolefin resin (A1) can be obtained from the peak temperature in DSC (differential scanning calorimetry). When there are a plurality of peaks, the melting temperature ΔH (J / g) has the highest peak temperature. The melting point. By producing a porous film using the sheet (E) obtained by such a method, a porous film excellent in strength, ion permeability, air permeability and the like can be obtained.

  When the resin kneaded product (D) is roll-formed with a pair of rotary forming tools, the resin kneaded product (D) discharged in a strand form from an extruder may be directly introduced between the pair of rotary forming tools. You may use the pelletized resin kneaded material (D).

(Removal of micropore forming agent (B))
The present invention includes a porous film forming step for obtaining a porous film (G) from the sheet (E) after the sheet forming step for obtaining the sheet (E) from the resin kneaded product (D). The porous film forming step includes the following three types.
(I) A micropore forming agent removing step of removing the component (B) from the sheet (E) to obtain a porous sheet (F), and stretching the porous sheet (F) to form a porous film (G) A step (II) having a stretching step to obtain a stretching step to stretch the sheet (E) to obtain a stretched film (H), and a micropore forming agent removing step to remove the component (B) from the stretched film (H). Step (III) having a step of obtaining a porous film (G) by simply stretching the sheet (E) (for example, in the case of using a water-insoluble micropore-forming agent, To remain.)
From the viewpoint of film thickness uniformity of the obtained porous film (G), the porous film forming step is preferably (I). Hereinafter, although the case of (I) is described in detail, the porous film (G) can be obtained similarly in the case of (II).

As a method for removing the micropore forming agent (B), for example, when water-soluble fine particles such as calcium carbonate fine particles are used, a method in which the aqueous liquid is showered and placed on the sheet (E), a tank containing the aqueous liquid And a method of immersing the sheet (E). The method for removing the water-soluble fine particles by the aqueous liquid may be a batch type or a continuous type, but is preferably a continuous type from the viewpoint of productivity.For example, the aqueous liquid is put into a tank in which a plurality of rolls are placed, and the above-mentioned rotating method is performed. The method of conveying a sheet | seat (E) with a roll and making it pass in an aqueous liquid is mentioned.
The porous sheet (F) from which the water-soluble fine particles have been removed by the aqueous liquid is preferably further washed with water. Although the degree of washing depends on the use of the porous film, it is usually sufficient to carry out washing to such an extent that a dissolved salt or the like does not precipitate.
The porous sheet (F) is usually dried within a time and temperature range in which the physical properties of the porous sheet (F) do not change.
Since the micropore forming agent (B) can be removed at room temperature with an aqueous liquid, it is preferable to use sodium laurate as the surface treatment agent of the micropore forming agent (B).

In the porous sheet (F) washed and dried as described above, when the water-soluble fine particles are calcium carbonate fine particles, in addition to calcium carbonate, alumina and silica previously contained as impurities in the calcium carbonate It is preferable that about 100 to 20000 ppm of inorganic substances such as
The porous sheet (F) in which a small amount of the inorganic substance remains is stretched by a method described later to form a porous film. When this is used as a battery separator, the temperature in the battery rises for some reason, and the porous sheet Even when the temperature reaches the temperature at which the polyolefin resin (A1) constituting the film is melted, the shape of the porous film as a diaphragm can be maintained, and thereby an effect of preventing a short circuit between the electrodes is expected.
It has also been found that the porous film obtained by stretching the porous sheet (F) in which a small amount of the inorganic substance remains has better permeability than the case where the inorganic substance is completely removed. The reason for this is not clear, but it is thought that the film is hardly crushed in the film thickness direction due to the trace amount of inorganic substances remaining in the film.

  The aqueous liquid may be any liquid that can remove water-soluble fine particles such as calcium carbonate fine particles in the sheet (E). Examples of the acidic aqueous liquid include aqueous hydrochloric acid. The aqueous liquid may contain an organic solvent, but if the content of the organic solvent increases, the waste liquid treatment costs. Therefore, the content of the organic solvent is preferably 10 parts by weight or less, and 5 parts by weight. More preferably, it is as follows.

  In order to increase the removal rate, it is preferable to add a small amount of a surfactant or a water-soluble organic solvent such as methanol, ethanol, isopropanol, acetone or N-methylpyrrolidone to the aqueous liquid. It is preferable to add a surfactant without adding.

  Examples of the surfactant include known nonionic surfactants, cationic surfactants, anionic surfactants, and the like, but nonionic surfactants are preferable. Nonionic surfactants have the advantage that they are difficult to hydrolyze even when the aqueous liquid is strongly alkaline (pH 11 or higher) or strongly acidic (pH 3 or lower).

  Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene-polyoxypropylene alkyl ether, polyoxyethylene alkylphenyl ether, polyethylene glycol fatty acid ester, polyoxyethylene alkylamine / fatty acid amide, and the like. It is done. The amount of the nonionic surfactant added to the aqueous liquid increases the removal rate of the micropore forming agent (B) such as calcium carbonate and removes the surfactant from the film after the micropore forming agent (B) is removed. From the balance with the efficiency at the time of carrying out, it is preferable to set it as 0.05-10 weight part.

  The hydrophilic / lipophilic balance (HLB) of the nonionic surfactant used in the present invention is preferably in the range of 3 to 18, more preferably in the range of 5 to 15. The HLB is a value indicating the balance between hydrophilicity and hydrophobicity. If the HLB is too small, the solubility in water tends to be poor. Conversely, if the HLB is too large, the solubility in water is sufficient, but it takes time to penetrate into the sheet due to low hydrophobicity. Tend.

The HLB can be calculated by the following Griffin equation (Equation (2)).

HLB = ((molecular weight of hydrophilic group in surfactant) / (molecular weight of entire surfactant)) × (100/5) (2)

  For the surfactant HLB whose HLB cannot be calculated by the above-mentioned Griffin equation (Equation (2)), this HLB emulsifies oil with an unknown surfactant, and at the same time, a plurality of surfactants with known HLB (HLB The same oil is emulsified and a test is performed to compare their emulsified states. Specifically, the HLB of a surfactant with a known HLB in which the oil emulsified state is the same as that of the surfactant with an unknown HLB is defined as the HLB of the surfactant with an unknown HLB.

(Stretching of porous sheet (F): Production of porous film (G))
By stretching the porous sheet (F) from which the water-soluble micropore-forming agent has been removed from the sheet (E) using the aqueous liquid as described above, by a tenter, a roll, an autograph or the like, a porous film (G ) Can be manufactured.
In order to make the air permeability of the porous film (G) obtained into a suitable range, the draw ratio is preferably 2 to 12 times, and more preferably 4 to 10 times.
The stretching temperature is usually from the softening point to the melting point of the polyolefin resin (A1), preferably in the temperature range of {(melting point) -50 ° C.} to {melting point}. By stretching at a temperature in such a range, a porous film (G) excellent in air permeability and ion permeability can be obtained. For example, when the resin kneaded material (D) to be used is composed of a polyolefin-based resin (A1) mainly composed of polyethylene, the stretching temperature is preferably 80 to 130 ° C, and preferably 90 to 115 ° C. Further preferred. Moreover, it is preferable to heat set after extending | stretching. It is preferable to perform the heat setting temperature at a temperature lower than the melting point of the polyolefin resin (A1).

(Porous film (G))
The porous film (G) of the present invention obtained by the above-described method has no defects such as thin portions and is excellent in film thickness uniformity, and is particularly suitable for a non-aqueous battery separator.

(Laminated porous film (RG))
In the present invention, at least one surface of the porous film (G) obtained by the above-described method is coated with a coating liquid containing ceramic powder and a heat-resistant resin containing a nitrogen element to laminate a heat-resistant resin layer (R). And a laminated porous film (RG). The heat resistant resin layer (R) may be provided on one side of the porous film (G), or may be provided on both sides. Since such a laminated porous film (RG) is excellent in film thickness uniformity, heat resistance, strength, and air permeability (ion permeability), it is used for separators for non-aqueous electrolyte batteries, particularly for lithium ion secondary batteries. It can be suitably used as a separator.

(Heat resistant resin layer (R))
The heat-resistant resin constituting the heat-resistant resin layer (R) is a polymer containing a nitrogen atom in the main chain, and particularly those containing an aromatic ring are preferred from the viewpoint of heat resistance. For example, aromatic polyamide (hereinafter sometimes referred to as “aramid”), aromatic polyimide (hereinafter sometimes referred to as “polyimide”), aromatic polyamideimide and the like can be mentioned.

  Examples of the aramid include meta-oriented aromatic polyamide (hereinafter sometimes referred to as “meta-aramid”) and para-oriented aromatic polyamide (hereinafter sometimes referred to as “para-aramid”). Among these, para-aramid is preferable because it is easy to form a porous heat-resistant resin layer (R) having a uniform film thickness and excellent air permeability.

(Para-aramid)
The para-aramid is obtained by condensation polymerization of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is in the para position of the aromatic ring or an oriented position equivalent thereto (for example, 4, 4 ′ -Biphenylene, 1,5-naphthalene, 2,6-naphthalene and the like, which are substantially composed of repeating units bonded in the opposite direction (orientation positions extending coaxially or in parallel). Specifically, poly (paraphenylene terephthalamide), poly (parabenzamide, poly (4,4′-benzanilide terephthalamide), poly (paraphenylene-4,4′-biphenylenedicarboxylic amide), poly (para Para-oriented or para-oriented, such as phenylene-2,6-naphthalenedicarboxylic acid amide), poly (2-chloro-paraphenylene terephthalamide), paraphenylene terephthalamide / 2,6-dichloroparaphenylene terephthalamide copolymer The para-aramid which has a structure according to is illustrated.

In the present invention, para-aramid is dissolved in a polar organic solvent and used as a coating solution.
Examples of the polar organic solvent include a polar amide solvent or a polar urea solvent, and specifically N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, tetramethylurea. However, it is not limited to these.
From the viewpoint of coating properties, the para-aramid is preferably a para-aramid having an intrinsic viscosity of 1.0 dl / g to 2.8 dl / g, and more preferably an intrinsic viscosity of 1.7 dl / g to 2.5 dl / g. . If the intrinsic viscosity is less than 1.0 dl / g, the strength of the formed heat-resistant resin layer may be insufficient. If the intrinsic viscosity exceeds 2.8 dl / g, it may be difficult to obtain a stable para-aramid-containing coating solution. The intrinsic viscosity here is a value measured by dissolving para-aramid once precipitated and making it into a para-aramid sulfuric acid solution, and is a value serving as a so-called index of molecular weight.
From the viewpoint of coating properties, the para-aramid concentration in the coating solution is preferably 0.5 to 10 parts by weight.

In order to improve the solubility of the resulting para-aramid in a solvent, it is preferable to add an alkali metal or alkaline earth metal chloride during the para-aramid polymerization. Specific examples include, but are not limited to lithium chloride or calcium chloride.
The amount of the chloride added to the polymerization system is preferably in the range of 0.5 to 6.0 mol, more preferably in the range of 1.0 to 4.0 mol, per 1.0 mol of the amide group produced by condensation polymerization. . If the chloride is 0.5 mol or more, the resulting para-aramid is easily dissolved, and if it is 6.0 mol or less, the chloride is easily dissolved in the solvent. Generally, if the alkali metal or alkaline earth metal chloride is less than 2 parts by weight, the solubility of para-aramid may be insufficient. If it exceeds 10 parts by weight, the alkali metal or alkaline earth metal chloride may be insufficient. May not dissolve in polar organic solvents such as polar amide solvents or polar urea solvents.

(Polyimide)
The polyimide used for the heat resistant resin layer (R) of the laminated porous film (RG) of the present invention is preferably a wholly aromatic polyimide produced by condensation polymerization of an aromatic acid dianhydride and a diamine.
Specific examples of the acid dianhydride include pyromellitic dianhydride, 3, 3 ′, 4, 4′-diphenylsulfone tetracarboxylic dianhydride, 3, 3 ′, 4, 4′-benzophenone tetracarboxylic acid. Acid dianhydrides, 2,2′-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and the like can be mentioned.
Specific examples of the diamine include oxydianiline, paraphenylenediamine, benzophenone diamine, 3,3′-methylenedianiline, 3,3′-diaminobenzophenone, 3,3′-diaminodiphenylsulfone, 1,5. '-Naphthalenediamine and the like can be mentioned, but the present invention is not limited to these.

  As said polyimide, the polyimide soluble in a solvent can be used conveniently. An example of such a polyimide is a polycondensate polyimide of 3,3 ', 4,4'-diphenylsulfonetetracarboxylic dianhydride and an aromatic diamine. As a polar organic solvent for dissolving polyimide, dimethyl sulfoxide, cresol, o-chlorophenol, and the like can be suitably used in addition to those exemplified as a solvent for dissolving aramid.

(Ceramic powder (S))
In the present invention, the coating liquid used for forming the heat-resistant resin layer (R) needs to contain ceramic powder (S). By forming a heat resistant resin layer using a coating solution in which ceramic powder (S) is added to a solution having an arbitrary heat resistant resin concentration, a porous heat resistant resin layer (R) having a uniform film thickness and fine pores is formed. ) Can be obtained.

  The air permeability of the porous heat-resistant resin layer (R) can be controlled by the amount of ceramic powder added. The ceramic powder (S) may have an average primary particle diameter of 1.0 μm or less in order to improve the strength of the laminated porous film (RG) and the smoothness of the surface of the heat resistant resin layer (R). Preferably, it is 0.5 μm or less, more preferably 0.1 μm or less. The average particle diameter of the primary particles is measured by a method of analyzing a photograph obtained by an electron microscope using a particle diameter measuring instrument.

The content of the ceramic powder (S) is preferably 1 part by weight or more and 95 parts by weight or less, and more preferably 5 parts by weight or more and 50 parts by weight or less in the laminated porous film (RG). When the content of the ceramic powder (S) in the laminated porous film (RG) is less than the above range, when used as a battery separator, the ion permeability starts to be insufficient, and when it exceeds the above range, the film becomes brittle. Tends to be difficult to handle.
The shape of the ceramic powder (S) to be used is not particularly limited, and can be spherical or random.

  Examples of the ceramic powder (S) include ceramic powder made of an electrically insulating metal oxide, metal nitride, metal carbide and the like. For example, powders such as alumina, silica, titanium dioxide or zirconium oxide are preferably used. The ceramic powders may be used alone, or two or more kinds may be mixed, or the same kind or different kinds of ceramic powders having different particle diameters may be arbitrarily mixed and used.

The average pore diameter of the heat resistant resin layer (R) measured by the mercury intrusion method is preferably 3 μm or less, and more preferably 1 μm or less. When the average pore diameter exceeds 3 μm, when a laminated porous film (RG) is used as a battery separator, a short circuit is likely to occur when carbon powder, which is the main component of the positive electrode or the negative electrode, or a small piece thereof drops off. Problems can arise.
Further, the porosity of the heat resistant resin layer (R) is preferably 30 to 80% by volume, more preferably 40 to 70% by volume. When the porosity is less than 30% by volume, when the laminated porous film (RG) is used as a battery separator, the amount of electrolyte retained may be reduced. When the porosity exceeds 80% by volume, the heat resistant resin layer (R) May be insufficient.
Moreover, 1-15 micrometers is preferable and, as for the thickness of this heat resistant resin layer (R), More preferably, it is 1-10 micrometers. If the thickness is less than 1 μm, the effect on heat resistance may be insufficient. If the thickness exceeds 15 μm, the thickness of the entire battery when the laminated porous film (RG) is used as a non-aqueous battery separator. Becomes too thick, making it difficult to achieve a high electric capacity of the battery. In addition, about the preferable setting range of the thickness of the said heat resistant resin layer (R), when providing a heat resistant resin layer (R) on the single side | surface of a porous film (F), about the thickness of the heat resistant resin layer (R) of the single side | surface side In the case where the heat resistant resin layer (R) is provided on both surfaces of the porous film (F), the total thickness of the heat resistant resin layer (R) on each surface is as follows. )

As a method for forming a heat resistant resin layer (R) by applying a coating liquid containing ceramic powder (S) and a heat resistant resin on at least one surface of the porous film (G), specifically, The method including a process is mentioned.
(A) In a polar organic solvent solution containing 100 parts by weight of a heat resistant resin, a slurry-like coating liquid is prepared by dispersing 1 to 1500 parts by weight of ceramic powder (S) with respect to 100 parts by weight of the heat resistant resin.
(B) The coating liquid is applied to at least one surface of the porous film (G) to form a coating film.
(C) The heat resistant resin is deposited from the coating film by means of humidification, solvent removal, or immersion in a solvent that does not dissolve the heat resistant resin, and then dried as necessary.
The coating solution is preferably applied continuously by, for example, a coating apparatus described in JP-A-2001-316006 and a method described in JP-A-2001-23602.

  The laminated porous film (RG) obtained by the method of the present invention is not only excellent in film thickness uniformity but also excellent in heat resistance, strength, and air permeability (ion permeability). It can be suitably used as a separator for a lithium ion secondary battery.

  As a method of laminating the heat resistant resin layer (R) on the porous film (G), as described above, at least one surface of the porous film (G) is coated with the ceramic powder (S) and the heat resistant resin. The method of forming the heat resistant resin layer (R) by applying a liquid is preferable from the viewpoint of productivity, but a method of separately manufacturing the heat resistant resin layer (R) and then laminating it with the porous film (G) is also possible. is there.

  Examples of the present invention will be described below. The following examples are preferred examples for explaining the present invention, and do not limit the present invention.

  Sheets, porous sheets, and porous films in Examples and Comparative Examples shown below were evaluated by the following characteristic items and measurement methods.

(1) Gurley value (Ventilation resistance)
The Gurley value (second / 100 cc) of the film was measured according to JIS P8117 using a B-type densometer (manufactured by Toyo Seiki Seisakusho Co., Ltd.). The measurement was performed at 10 locations per 1 m ² of film.

(2) Film thickness Based on JISK7130, it measured with the thickness measuring apparatus (The Mitutoyo Corporation make, brand name "VL-50A"). The measurement was performed at 10 locations per 1 m ² of film.

(3) Measurement of weight average molecular weight by GPC As a measuring apparatus, a gel chromatograph (trade name “Alliance GPC2000 type”) manufactured by Japan Waters Co., Ltd. was used. Other conditions are shown below.
(I) Column: manufactured by Tosoh Corporation (trade name “TSKgel GMH HR-H (S) HT” 30 cm × 2, “TSKgel GMH 6-HTL” 30 cm × 2)
(Ii) Mobile phase: o-dichlorobenzene (iii) Detector: differential refractometer (iv) Flow rate: 1.0 mL / min (v) Column temperature: 140 ° C.
(Vi) Injection volume: 500 μL
After completely dissolving 30 mg of the sample in 20 mL of o-dichlorobenzene at 145 ° C., the solution was filtered through a sintered filter having a pore size of 0.45 μm, and the filtrate was used as a feed solution. The calibration curve was prepared using 16 kinds of standard polystyrenes with known molecular weights.

(4) Average particle diameter of micropore-forming agent (B) The particle diameter was measured at 30000 times with a scanning electron microscope (trade name “S-4200”, manufactured by Hitachi, Ltd.), and the diameter of 100 particles was measured. The average was defined as the average particle diameter (μm).

(5) Puncture strength The maximum stress (gf) when the porous film was fixed with a 12 mmφ washer and the pin was punctured at 200 mm / min was defined as the puncture strength of the film. A pin with a pin diameter of 1 mmΦ and a tip of 0.5R was used.

(6) Evaluation of pinholes and thin portions present in porous film About the obtained porous film (G), the number of pinholes and thin portions per 1 m ² of the film was visually measured. Specifically, the light of the fluorescent lamp is applied from one side of the porous film, the film is observed from the other side, and the through hole is a pinhole. The part with much light was judged to be a thin part.

(7) Quantification of surface treatment agent The surface treatment micropore forming agent was determined by the following formula (3) from the weight change before and after baking in a nitrogen stream at 600 ° C. for 4 hours in an oven. In addition, about the identification of the kind of surface treating agent, it identified by comparison with a reference material by IR (infrared analysis) and liquid chromatography, or gas chromatography.

Amount of surface treatment agent (%) = (weight before baking−weight after baking) / weight before baking × 100
(3)

The examples and comparative examples shown below are the main characteristic constitution of the porous film of the present invention “stearin as a component (C) when the micropore forming agent (B) is dispersed in the polyolefin resin (A)”. The polyolefin-based resin (A) used in each example has the following composition, which was carried out to confirm the effect of “adding sodium acid (C ₁ ) or sodium laurate (C ₂ )”. Polyolefin resin (A ₁ ) was commonly used.

(Polyolefin resin _(A 1))
It was composed of ultra high molecular weight polyethylene (a1) and olefinic wax (a2). As the ultra high molecular weight polyethylene (a1), an ultra high molecular weight polyethylene having a weight average molecular weight of 3 million (manufactured by Mitsui Chemical Co., Ltd., trade name “Hi-Zex Million 340M”, melting point 136 ° C.) is used. As the olefin wax (a2), An olefin wax powder having a weight average molecular weight of 1000 (trade name “High Wax 110P”, melting point 110 ° C., manufactured by Mitsui Chemicals, Inc.) was used.
The blending amount is 71 parts by weight of ultrahigh molecular weight polyethylene (a1) with respect to 100 parts by weight of the polyolefin resin (A ₁ ), that is, the total amount of ultrahigh molecular weight polyethylene (a1) and olefinic wax (a2) 29 parts by weight of powdered olefin wax (a2) (41 parts by weight of powdered olefin wax (a2) with respect to 100 parts by weight of ultrahigh molecular weight polyethylene (a1)).

Example 1
(Component (B): Precipitated calcium carbonate (B ₁ ))
Obtain commercially available precipitated calcium carbonate (Vigot-10, manufactured by Shiroishi Calcium Co., Ltd., average particle size of 0.15 μm with 2% surface treatment of 100% by weight of mixed fatty acid based on oleic acid) The precipitated calcium carbonate (B ₁ ) was used as the component (B), that is, the micropore forming agent (B).
(Component (C): Sodium stearate (C ₁ ))
Commercially available sodium stearate (manufactured by Wako Pure Chemical Industries, containing 25 wt% water and 30 wt% palmitic acid) was dried at 150 ° C. for 1 hour to obtain dried sodium stearate (purity 60%). This steering acid sodium (C ₁ ) was used as component (C).

162 parts by weight of precipitated calcium carbonate (B ₁ ), 1.4 parts by weight of antioxidant, 2.4 parts by weight of sodium stearate (C ₁ ) (precipitated carbonate) with respect to 100 parts by weight of the polyolefin resin (A ₁ ) 1.5 parts by weight of calcium (B ₁ ) with respect to 100 parts by weight) was mixed with a Henschel mixer, and then kneaded at 200 ° C. with a biaxial kneader to obtain a resin kneaded product (D ₁ ).

(Preparation of sheet (E ₁ ))
The resin kneaded product (D ₁ ) was rolled with a pair of rolls rotating at the same peripheral speed at a surface temperature of 150 ° C. to produce a single-layer sheet having a thickness of about 33 μm. Next, the obtained single layer sheets were pressure-bonded with a pair of rolls having a surface temperature of 150 ° C. to obtain a multilayer sheet (sheet (E ₁ )). The thickness of the sheet (E ₁ ) was 60 μm.

Next, using a cleaning apparatus shown in FIG. 1, the seat (E ₁₎ microvoided agent in the (B ₁₎ was removed.
The micropore forming agent removing apparatus shown in FIG. 1 includes a bathtub 1, a subsequent dryer 2, a drawer roller 3 that supplies the bathtub 1 with a sheet (E) before removal of the micropore forming agent (B1), A take-up roller 4 for winding the porous sheet (F) after removing the micropore forming agent (B) from the dryer 2 in a roll shape. The bathtub 1 is usually composed of three bathtubs 1a, 1b and 1c, and at least one roller is disposed in the tank in each of the bathtubs 1a, 1b and 1c (in the figure, only the bathtub 1a has two Roller is installed). The bathtub 1a is filled with an aqueous hydrochloric acid solution (hydrochloric acid 2 to 4 mol / L, nonionic surfactant 0.1 to 0.5 parts by weight). The bathtub 1b is filled with an aqueous sodium hydroxide solution (0.1 to 2 mol / L). The bathtub 1c is filled with cleaning water. The dryer 2 is an apparatus having a configuration in which a large-diameter heating roller 2a is installed in a tank 2b. In the micropore forming agent removing apparatus, the roll-shaped sheet (E) continuously passes through the bathtubs 1a, 1b, 1c, and the dryer 2, and is finally wound around the winding roller 4 in a roll shape. . During this time, the conveying speed and load tension of the sheet (E) are adjusted to a suitable range by adjusting the unwinding speed of the unwinding roller 2 and the winding speed of the winding roller 4.

The removal of the micropore forming agent (B ₁ ) from the sheet (E ₁ ) using the micropore forming agent removing apparatus having the above-described configuration was performed as follows using the apparatus shown in FIG.
First, a roll-shaped sheet (E ₁ ) is unwound by the unrolling roller 3 and is immersed in a hydrochloric acid aqueous solution in the bathtub 1 to elute and remove calcium carbonate fine particles from the sheet (E ₁ ), and the porous sheet (F ₁ ) Next, the porous sheet (F ₁ ) containing the hydrochloric acid aqueous solution was neutralized by being immersed in an aqueous sodium hydroxide solution in the bath 1b. Subsequently, the neutralized porous sheet (F ₁ ) was washed by immersing it in water in the bathtub 1c. Subsequently, the porous sheet (F ₁ ) that had been washed with water was brought into contact with the heating roller 2a heated to 50 ° C. and dried. Finally, the dried porous sheet (F ₁ ) was wound up in a roll shape by the winding roller 4.

(Preparation of porous film (G ₁ ))
The micropore forming agent (B ₁ ) was removed as described above, and the washed and dried porous sheet (F ₁ ) was stretched 5.8 times with a tenter (manufactured by Ichikin Kogyo Co., Ltd.) (stretching temperature 105 ° C). The resulting porous film The physical properties of the (G ₁₎ are shown in (Table 1).

(Example 2)
Except that the amount of sodium stearate (C ₁ ) added was 3.2 parts by weight (2 parts by weight with respect to 100 parts by weight of the precipitated calcium carbonate (B ₁ )), the same as in Example 1, A sheet (E ₂ ) of Example 2 was obtained. The thickness of the sheet (E ₂ ) was 60 μm.
The obtained sheet (E ₂ ) was obtained by removing the micropore forming agent (B ₁ ) using the micropore forming agent removing apparatus shown in FIG. The obtained porous sheet (F ₂ ) was wound around a roller 4.

(Preparation of porous film (G ₂ ))
The fine pore forming agent (B ₁ ) was removed as described above, and the washed and dried porous sheet (F ₂ ) was stretched 5.8 times with a tenter (manufactured by Ichikin Kogyo Co., Ltd.) (stretching temperature 105 ° C). The physical properties of the obtained porous film (G ₂ ) are shown in (Table 1).

(Example 3)
(Micropore forming agent (B ₃ ))
Surface treatment with commercially available precipitated calcium carbonate (trade name “MSK-P0” manufactured by Maruo Calcium Co., Ltd., stearic acid as a main component) as a micropore forming agent (B ₃ ) The amount was 3 parts by weight, and the average particle size was 0.17 μm).

(Preparation of resin kneaded material (C ₃ ))
With respect to the polyolefin resin _(A 1) 100 parts by weight, the fine pore forming agent _(B 3) 162 parts by weight of sodium stearate _(C 1) 0.78 parts by weight (microvoided agent _(B 3) 100 0.48 parts by weight with respect to parts by weight) and 1.42 parts by weight of an antioxidant were mixed, mixed with a Henschel mixer, and then kneaded at 200 ° C. using a twin-screw kneader. The resin kneaded material (D ₃ ) of Example 3 was obtained.

(Preparation of sheet (E ₃ ))
A sheet (E ₃ ) of Example 3 was obtained in the same manner as the preparation of the sheet (E ₁ ) of Example 1 except that the resin kneaded product (D ₃ ) was used as the resin kneaded product (D). . The thickness of the sheet (E ₃ ) was 60 μm.
The obtained sheet (E ₃ ) was obtained by removing the micropore forming agent (B ₃ ) using the micropore forming agent removing apparatus shown in FIG. The obtained porous sheet (F ₃ ) was wound around a roller 4.

(Preparation of porous film (G ₃ ))
The fine pore forming agent (B ₃ ) was removed as described above, and the washed and dried porous sheet (F ₃ ) was stretched 5.8 times with a tenter (manufactured by Ichikin Kogyo Co., Ltd.) (stretching temperature 105 ° C). The physical properties of the obtained porous film (G3) are shown in Table 1.

Example 4
(Preparation of resin kneaded material (D ₄ ))
162 parts by weight of the same micropore forming agent (B ₁ ) as used in Example 1, 0.78 parts by weight of sodium stearate (C ₁ ), and 100 parts by weight of the polyolefin resin (A ₁ ), and 1.42 parts by weight of an antioxidant was blended, mixed with a Henschel mixer, and then kneaded at 200 ° C. using a twin-screw kneader to obtain a resin kneaded product (D ₄ ) of Example 4. .

(Preparation of sheet (E ₄ ))
A sheet (E ₄ ) of Example 4 was obtained in the same manner as the preparation of the sheet (E ₁ ) of Example 1, except that the resin kneaded product (D ₄ ) was used as the resin kneaded product (D). . The thickness of the sheet (E ₄ ) was 60 μm.
The obtained sheet (E ₄ ) was obtained by removing the micropore forming agent (B ₁ ) using the micropore forming agent removing apparatus shown in FIG. The obtained porous sheet (F ₄ ) was wound around a roller 4.

(Preparation of porous film (G ₄ ))
The fine pore forming agent (B ₁ ) was removed as described above, and the washed and dried porous sheet (F ₄ ) was stretched 5.8 times with a tenter (manufactured by Ichikin Kogyo Co., Ltd.) (stretching temperature 105 ° C). The physical properties of the obtained porous film (G ₄ ) are shown in (Table 1).

(Example 5)
(Preparation of resin kneaded material (C ₃ ))
With respect to 100 parts by weight of the polyolefin resin (A ₁ ), 162 parts by weight of the same micropore forming agent (B ₃ ) as used in Example 3, and sodium laurate (C ₂ ) 0 as the component (C) .78 parts by weight and 1.42 parts by weight of antioxidant were mixed, mixed with a Henschel mixer, and then kneaded at 200 ° C. using a biaxial kneader to obtain a resin kneaded product (D ₅ ). It was.

(Preparation of sheet (E ₃ ))
A sheet (E ₅ ) was obtained in the same manner as in the preparation of the porous sheet (E ₁ ) of Example 1, except that the resin kneaded product (D ₃ ) was used as the resin kneaded product (D). The thickness of the sheet (E ₅ ) was 60 μm.
The obtained sheet (E ₅ ) was obtained by removing the micropore forming agent (B ₃ ) using the micropore forming agent removing apparatus shown in FIG. The obtained porous sheet (F ₅ ) was wound around a roller 4.

(Preparation of porous film (G ₅ ))
The fine pore forming agent (B ₃ ) was removed as described above, and the washed and dried porous sheet (F ₅ ) was stretched 5.8 times with a tenter (manufactured by Ichikin Kogyo Co., Ltd.) (stretching temperature 105 ° C). The physical properties of the obtained porous film (G ₅ ) are shown in (Table 1).

(Comparative Example 1)
(Component (C) corresponding component)
Calcium stearate (manufactured by Ciba Specialty Chemicals) was dried at 150 ° C. for 1 hour to obtain dried calcium stearate. This calcium stearate (Cc ₁ ) was used as a component corresponding to component (C). As other components, the component (A1), the component (B1), and the antioxidant used in Example 1 were used.

162 parts by weight of precipitated calcium carbonate (B ₁ ), 1.4 parts by weight of antioxidant, 2.4 parts by weight of calcium stearate (Cc ₁ ) (100 parts by weight of precipitated calcium carbonate) with respect to 100 parts by weight of polyolefin resin (A ₁ ) (B ₁ ) was mixed with a Henschel mixer, and then kneaded at 200 ° C. with a biaxial kneader to obtain a resin kneaded product (Dc ₁ ).

(Preparation of sheet (Ec ₁ ))
A sheet (Ec ₁ ) of Comparative Example 1 was obtained in the same manner as the preparation of the sheet (E ₁ ) of Example 1 except that the resin kneaded product (Dc ₁ ) was used as the resin kneaded product (D). . The thickness of the sheet (Ec ₁ ) was 60 μm.
The obtained sheet (Ec ₁ ) was obtained by removing the micropore forming agent (B ₁ ) using the micropore forming agent removing apparatus shown in FIG. The obtained porous sheet (Fc ₁ ) was wound around a roller 4.

(Preparation of porous film (Gc ₁ ))
The micropore forming agent (B ₁ ) was removed as described above, and the washed and dried porous sheet (Fc ₁ ) was stretched 5.8 times with a tenter (manufactured by Ichikin Kogyo Co., Ltd.) (stretching temperature 100). ° C). The physical properties of the obtained porous film (Gc ₁ ) are shown in (Table 2).

(Comparative Example 2)
In the same manner as in Example 3 except that the amount of sodium stearate (C ₁ ) added was 0.81 part by weight (0.5 part by weight with respect to 100 parts by weight of the micropore forming agent (B ₃ )). The resin kneaded product (Dc ₂ ) and the sheet (Ec ₂ ) were sequentially prepared to obtain a porous film (Gc ₂ ). The resulting porous film The physical properties of the (Gc ₂₎ are shown in (Table 2).
In addition, unlike Example 3, when the resin kneaded material (Dc ₂ ) was rolled with a roll to produce a sheet (Ec ₂ ), the sheet was hardly peeled off from the roll. The striped pattern was generated in the stretched porous film (Gc ₂ ) because the striped pattern was caused by the peeling stress from the roll.

(Comparative Example 3)
Except that 0 parts by weight with respect to the addition amount of microporous forming agent (B ₃₎ 100 parts by weight of sodium stearate (C _1), that is, except for not adding sodium stearate (C _1), Example In the same manner as in No. ₃ , a resin kneaded product (Dc ₃ ) and a sheet (Ec ₃ ) were sequentially prepared to obtain a porous film (Gc ₃ ). The physical properties of the obtained porous film (Gc ₃ ) are shown in (Table 2).
In addition, unlike Example 3, when the resin kneaded material (Dc ₃ ) was rolled with a roll to produce a sheet (Ec ₃ ), the sheet was hardly peeled from the roll. A striped pattern was generated in the stretched porous film (Gc ₃ ) because the striped pattern was due to peeling stress from the roll.
In addition, a large number of spots were generated on the T-die that extrudes the resin kneaded material (Dc ₃ ) into a rolling roll.

(Comparative Example 4)
This resin was kneaded in the same manner as in Example 3 except that the amount of sodium stearate (C ₁ ) added was 9.7 parts by weight (6 parts by weight with respect to 100 parts by weight of the micropore forming agent (B ₃ )). An attempt was made to roll the kneaded material with a roll to produce a porous sheet, but air bubbles were mixed between the roll and the resin kneaded material, so that the degree of adhesion between the roll and the resin kneaded material became insufficient, and the sheet Could not get.

As shown in (Table 1), Examples 1 to 4 using “sodium stearate” and “sodium laurate” as additives for dispersing the micropore forming agent in the polyolefin-based resin composition. Example 5 used has a uniform film thickness, high puncture strength, good appearance, no occurrence of pinholes, and almost no occurrence of thin portions.
On the other hand, as shown in Table 2, in Comparative Example 1 using calcium stearate instead of “sodium stearate”, a small number of pinholes occurred and many thin portions were generated. Further, Comparative Example 2 in which the amount of sodium stearate added was 0.5 parts by weight or less with respect to 100 parts by weight of the micropore forming agent, and Comparative Example 3 in which additives such as sodium stearate and calcium stearate were not used. In that case, a small number of pinholes were generated and a thin portion was generated.

(Example 6)
In this example, a heat resistant resin layer (R1) was laminated on one side of the porous film (G ₁ ) prepared in Example 1 to obtain a laminated porous film (RG1).

(Synthesis of para-aramid (poly (paraphenylene terephthalamide))
Poly (paraphenylene terephthalamide) was produced using a 3 liter separable flask having a stirring blade, a thermometer, a nitrogen inlet tube and a powder addition port.
To a well-dried flask, 2200 g of N-methyl-2-pyrrolidone (NMP) was charged, and then 151.07 g of calcium chloride powder vacuum-dried at 200 ° C. for 2 hours was added. This was heated to 100 ° C. to completely dissolve calcium chloride in NMP.
The calcium chloride solution was returned to room temperature, and 68.23 g of paraphenylenediamine was added and completely dissolved. While maintaining this solution at 20 ° C. ± 2 ° C., 124.97 g of terephthalic acid dichloride was added in 10 divided portions every about 5 minutes. Thereafter, with stirring, the solution was aged for 1 hour while maintaining the temperature at 20 ° C. ± 2 ° C. The solution after aging was filtered through a 1500 mesh stainless wire mesh.
The obtained solution showed optical anisotropy in a liquid crystal phase having a para-aramid concentration of 6%. A part of the para-aramid solution was sampled, the para-aramid was reprecipitated with water, and the intrinsic viscosity of the para-aramid was measured and found to be 2.01 dl / g.

(Preparation of coating solution)
100 g of the previously polymerized para-aramid solution was weighed into a flask, 243 g of NMP was added, and finally, an isotropic phase solution having a para-aramid concentration of 1.75 parts by weight was prepared and stirred for 60 minutes.
On the other hand, 6 g of alumina powder (trade name “Alumina C”) manufactured by Nippon Aerosil Co., Ltd. and 6 g of alumina powder (trade name “Advanced Alumina AA-03”) manufactured by Sumitomo Chemical Co., Ltd. (100 parts by weight with respect to para-aramid) was mixed to obtain 12 g of ceramic powder (S1).
12 g of the ceramic powder (S1) was mixed with the solution having the para-aramid concentration of 1.75 parts by weight and stirred for 240 minutes. The coating dope in which the alumina powder was sufficiently dispersed was filtered through a 1000 mesh wire net. Thereafter, 0.73 g of calcium oxide was added to the filtrate, and the mixture was neutralized by stirring for 240 minutes, and defoamed under reduced pressure to obtain a slurry-like coating liquid (M).

(Preparation of laminated porous film (RG1) (continuous method))
The porous film (G1) was rolled while attaching the roll (width 300 mm, length 300 m) of the porous film (G1) prepared in Example 1 above to the unwinder and pulling it at a tension of 2 kg / 300 mm and a line speed of 4 m / min. The said coating liquid (M) was apply | coated to one side of this, and the laminated porous film (RG1) was produced continuously.

Specifically, first, NMP was applied to the lower surface of the drawn porous film (G1) with a micro gravure coater, and the coating liquid (M) was applied to the upper surface with a bar coater to a thickness of 100 μm. Next, the porous film (G1) after coating was passed through a 1.5 m long constant temperature and humidity chamber (temperature 50 ° C., relative humidity 70%) to precipitate para-aramid from the coated film.
Subsequently, the film was washed with a water washing device having a line length of 4 m (ion exchange water was injected at 10 liters / minute, and the ion exchange water filled inside was discharged at the same rate as the injection rate. NMP and calcium chloride were removed from the coated film of the film by passing through a device having a structure in which a guide roll was set in the tank.
Then, while sending hot air with a Yankee dryer to the film having the washed coating film, moisture was dried and removed through a hot roll (diameter 1 m, surface temperature 70 ° C., covered with meta-aramid cloth canvas). Thereby, a laminated porous film (RG1) obtained by laminating the heat resistant resin layer (R1) on one surface of the porous film (G ₁ ) was obtained.

  When the thickness, air permeability, and puncture strength of the laminated porous film (RG1) were measured, the thickness was 16.5 μm (standard deviation 0.32), the air permeability was 270 seconds / 100 cc (standard deviation 10), The puncture strength was 360 gf, and it was confirmed that, for example, it had characteristics suitable for a battery separator.

  As described above, the method for producing a porous film according to the present invention can obtain a porous film having very few thin portions. The porous film obtained by the production method of the present invention is particularly suitable for use as a battery separator.

1, 1a, 1b, 1c Bathtub 2 Dryer 2a Heating roller 2b Tank 3 Drawer roller 4 Winding roller

Claims (11)

A polyolefin resin (A), a micropore forming agent (B), and 0.5 to 2 parts by weight of sodium stearate and / or sodium laurate (C) with respect to 100 parts by weight of the component (B). A sheet molding step for obtaining a sheet (E) by molding a resin kneaded product (D) obtained by kneading a mixture containing
A porous film forming step of obtaining a porous film (G) by stretching at least the sheet (E);
A method for producing a porous film, comprising:   2. The method for producing a porous film according to claim 1, wherein the content of the component (B) in the mixture is 100 to 400 parts by weight per 100 parts by weight of the component (A).   The method for producing a porous film according to claim 1 or 2, wherein the component (B) is in the form of fine particles and has an average particle size of 0.03 to 0.5 µm.   The component (A) comprises 50 to 90 parts by weight of ultrahigh molecular weight polyethylene (a1) having a weight average molecular weight of 500,000 or more, and 50 to 10 parts by weight of an olefin wax (a2) having a weight average molecular weight of 700 to 6000. The method for producing a porous film according to any one of claims 1 to 3, comprising (however, the sum of (a1) and (a2) is 100 parts by weight).   The porous film forming step includes removing the component (B) from the sheet (E) to obtain a porous sheet (F), a micropore forming agent removing step, and stretching the porous sheet (F) to make it porous. The manufacturing method of the porous film of any one of Claims 1-4 which consists of an extending process which obtains a film (G).   The said component (B) is calcium carbonate microparticles | fine-particles, The manufacturing method of the porous film of any one of Claims 1-5 characterized by the above-mentioned.   The porous film obtained using the manufacturing method of any one of Claims 1-6.   A coating solution containing a heat-resistant resin containing nitrogen and ceramic powder is applied to at least one surface of the porous film according to claim 7 and cured to laminate a heat-resistant resin layer on the porous film. A method for producing a laminated porous film, comprising: obtaining a laminated porous film.   A laminated porous film obtained using the method for producing a laminated porous film according to claim 8.   A battery separator using the porous film according to claim 7.   A battery separator using the laminated porous film according to claim 9.

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