JP2005145999A - Porous film made of polyolefin resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous film which is made of a polyolefin resin and has a high porosity and high heat resistance in spite of the simple manufacturing process. <P>SOLUTION: The porous film made of the polyolefin resin is formed by melt-kneading a resin composition containing a polyolefin resin (C) comprising a specific poly(4-methyl-1-pentene) polymer (A) and a specific α-olefin copolymer (B) into a film-like melt, forming the film-like melt into a film-like molded product under a specific condition and subsequently stretching the film-like molded product at least in one direction, and has communicated pores in the α-olefin copolymer (B) region. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a polyolefin resin porous membrane. Specifically, the present invention relates to a polyolefin resin porous membrane suitable for a separation membrane, a battery separator, and the like.

  Plastic porous membranes with continuous pores are used in a variety of applications. Separation membranes used for medical and industrial filtration and separation, separators for battery separators, separators for electrolytic capacitors, and bags for paper diapers. It is widely used for sanitary materials such as sheets, building materials such as house wraps and roof base materials. In particular, since the polyolefin resin porous membrane has resistance to an organic solvent or an alkaline or acidic solution, it is widely used for these applications.

The following is known as a method for producing a polyolefin resin porous membrane.
(a) A sheet formed by mixing a polyolefin resin with an inorganic filler such as silica or talc, or an organic filler such as nylon or polyethylene terephthalate that is incompatible with the polyolefin resin, is stretched at least in one direction, and the polyolefin resin A method of generating voids (pores) at the filler interface (hereinafter referred to as “multi-component stretching method”).
(b) A method of obtaining a porous film by heating a high-density polyethylene sheet formed at a high draft ratio as necessary and stretching it in at least one direction to fibrillate between crystal lamellae (hereinafter referred to as “single component stretching”). Law ").
(c) A method in which the organic liquid or inorganic filler is extracted from a sheet formed by mixing an organic liquid or inorganic filler in a polyolefin resin, and stretched before and after the extraction as necessary (hereinafter referred to as “ "Mixed extraction method").

  In the multi-component stretching method (a) above, an inorganic filler mixed system and an organic filler mixed system are known, but in the former case, it is necessary to increase the amount of the inorganic filler added, resulting in a matrix. There were problems such as degradation of the original physical properties and texture of the polyolefin resin and weakness against acids and alkalis. Further, in the latter organic filler mixed system, not only the physical properties and texture of the polyolefin resin are deteriorated, but also the organic filler is difficult to disperse in the polyolefin resin, and the porous film having a small pore diameter and a large porosity are obtained. There are problems such as difficulty in obtaining a porous film.

  The single component stretching method (b) above is a method in which a film-shaped molded product formed at a high draft ratio is heat-treated in a separate process for a long time and then subjected to multistage stretching under special conditions. In addition to this, there is a problem that the production takes a long time and the productivity is low. In addition, it is difficult to obtain a porous film having a large porosity because of fibrillation between the crystal lamellae, and further, the stretched sheet is highly oriented and highly crystallized. Have.

  The mixed extraction method of (c) above comprises a step of extracting an organic liquid in a sheet with an organic solvent and an inorganic filler with an alkaline solvent, and a step of washing and drying the extracted sheet. The process was complicated. Moreover, when using an organic liquid, since the content rate of the organic liquid in the sheet reaches 40 to 60% by weight, in addition to the problems in high-speed film-forming properties and stretchability, rolls and the like in each step As a result, there is a problem in productivity.

  The poly-4-methyl-1-pentene polymer is a polyolefin resin and has a melting point of 220 to 240 ° C. and excellent heat resistance. Therefore, the poly-methyl-1-pentene polymer is obtained by the single-component stretching method, the multi-component stretching method or the mixed extraction method. Application development to the porous membrane field has been studied for a long time. However, since the poly-4-methyl-1-pentene polymer itself is greatly inferior in stretchability compared with polypropylene and polyethylene, a porous film having a large porosity is obtained by the single component stretching method or the multicomponent stretching method. That is even more difficult.

In addition, in the case of a battery separator, in order to prevent an abnormal temperature rise due to misuse of the battery and an accident such as ignition to occur, the separator does not break the membrane when the temperature reaches a certain level. A function to shut down and shut down current (hereinafter referred to as “shutdown function”) is required. Therefore, to increase the difference ΔT = T _b -T _s temperature T _{b (hereinafter,} "film break temperature") and temperatures for closing the pores (hereinafter referred to as "pore closing temperature") T _s to film breakage, and, It is desired to reduce the hole closing temperature in order to stop the abnormal reaction at an earlier stage and suppress the temperature rise. Although only the poly-4-methyl-1-pentene polymer single component can increase the film breaking temperature, the pore blocking temperature cannot be lowered. , Polyethylene wax, low density polyethylene, linear low density polyethylene, polyethylene resin such as high density polyethylene and ultra-high molecular weight polyethylene and liquid or solid organic matter such as liquid paraffin are mixed, and the organic matter is extracted after film formation / stretching, Or the technique of the mixed extraction method which extracts and extends | stretches this organic substance after film forming is disclosed (for example, patent document 1).

  However, in these methods, the production process is complicated and the stretchability is not sufficient, and it is difficult to obtain a porous film having a high porosity. Further, since the liquid or solid organic matter is likely to remain at the interface between the poly-4-methyl-1-pentene polymer and polyethylene, the pores of the porous film after extraction of the organic matter are difficult to close by heating, There is a need for an improved shutdown function in battery separators.

Japanese Patent Laid-Open No. 7-60084

  The present invention has been made to solve the above-mentioned problems associated with conventional polyolefin resin porous membranes, and provides a polyolefin resin porous membrane having excellent air permeability and high heat resistance in spite of a simple manufacturing process. The task is to do.

  As a result of intensive studies, the present inventors have determined that an α-olefin copolymer (A) containing a poly-4-methyl-1-pentene polymer (A) and a main component α-olefin of 40 to 80% by weight ( A resin composition containing the polyolefin resin (C) comprising B) is melt-kneaded to form a film-like melt, and the film-like melt is formed into a film-like molded article. It is a porous film formed by extending in the direction, and the polyolefin resin (C) is 30 to 80% by weight of the poly-4-methyl-1-pentene polymer (A) and the α-olefin copolymer (B). The present invention was completed based on the finding that this problem is solved by a polyolefin resin porous membrane comprising 20 to 70% by weight and having pores communicating with the α-olefin copolymer (B) region. did. In the present invention, the continuous pores refer to pores that are continuously formed in the copolymer (B) region and consequently become a path connecting both surfaces of the porous membrane.

The present invention is constituted by the following.
1. A polyolefin resin (C) comprising a poly-4-methyl-1-pentene polymer (A) and an α-olefin copolymer (B) having a main component α-olefin content of 40 to 80% by weight. A porous film formed by melting and kneading a resin composition contained therein to form a film-like melt, forming the film-like melt into a film-like molding, and then stretching the film-like molding in at least one direction The polyolefin resin (C) comprises 30 to 80% by weight of the poly-4-methyl-1-pentene polymer (A) and 20 to 70% by weight of the α-olefin copolymer (B). A polyolefin resin porous membrane having pores communicating with the olefin copolymer (B) region.

Tensile strength ratio of the tensile strength _{S B} of the poly-4-methyl-1-tensile strength _{S A} and α- olefin copolymer pentene polymer (A) (B) at 2.23 ° C. _S A / S _2. The polyolefin resin porous membrane as described in 1 above, wherein _B is 2 to 50.

3. The polyolefin resin porous membrane according to the item 2, wherein the tensile strength ratio S _A / S _B at 23 ° C. is 2 to 20.

4). 4. The polyolefin resin porous membrane according to any one of 1 to 3 above, wherein a draft ratio when the film-shaped melt is formed into a film-shaped molded product is in the range of 1 to 10.

5). 5. The polyolefin resin porous membrane as described in 4 above, wherein the draft ratio when the film-shaped melt is formed into a film-shaped molding is in the range of 1 to 3.

6). The air resistance (Gurley) is 1 to 2,000 seconds / 100 ml, an in film breakage temperature _{T b} is 200 ° C. or higher, the difference between the film tear temperature _{T b} and pore closing temperature _{T s ΔT} (= _{T b} - T _s) is a polyolefin resin porous membrane according to any one of the 1-5, wherein, characterized in that at 30 ° C. or higher.

  The polyolefin resin porous membrane of the present invention comprises a polyolefin resin (C) excellent in low-temperature stretchability in which an α-olefin copolymer (B) is dispersed in a poly-4-methyl-1-pentene polymer (A). Used to form pores by cleavage of the copolymer (B) in the α-olefin copolymer (B) region by a specific processing method, and was excellent in porous membrane characteristics such as porosity and air permeability It is a porous membrane. The polyolefin resin porous membrane of the present invention is an economical porous membrane obtained without using a complicated manufacturing process as in the prior art, and includes a separation membrane, a battery separator, and a ventilation waterproofing that require continuous micropores. It can be suitably used for applications such as materials.

Hereinafter, embodiments of the present invention will be described.
(1) Polyolefin resin The polyolefin resin porous membrane of the present invention includes a poly-4-methyl-1-pentene polymer (A) (hereinafter sometimes simply referred to as “polymer (A)”) and an α-olefin copolymer. A polyolefin resin (C) comprising a polymer (B) (hereinafter sometimes simply referred to as “copolymer (B)”) is used.

(I) Poly-4-methyl-1-pentene polymer (A)
The polymer (A) is a polymer mainly composed of 4-methyl-1-pentene. For example, a homopolymer of 4-methyl-1-pentene, 4-methyl-1-pentene, Examples include copolymers with α-olefins other than methyl-1-pentene. Examples of the α-olefin other than 4-methyl-1-pentene include ethylene (included in the α-olefin in the present invention), propylene, 1-butene, 1-heptene, 1-hexene, 1-octene and 1-decene. , 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicocene and the like, such as α-olefins having 2 to 20 carbon atoms, and the like, which are used as a copolymer of 4-methyl-1-pentene. The α-olefin may be one type or two or more types. When the 4-methyl-1-pentene polymer is a copolymer with an α-olefin, the content of the α-olefin polymerization unit is 10% by weight or less, preferably 1 to 10% by weight.

The melt flow rate MFR _A (temperature 260 ° C., load 21.18 N) of the polymer (A) is not limited, but is preferably in the range of 1 to 50 g / 10 min from the stability of film formation.

(ii) α-olefin copolymer (B)
The copolymer (B) is a random copolymer of two or more kinds of α-olefins, and the content of α-olefin polymerization units as a main component in the entire copolymer (B) is 40 to 80 weights. %, Preferably in the range of 40 to 75% by weight. When the content of the α-olefin as the main component exceeds 80% by weight, the tensile strength described later becomes too large, and the copolymer (B) is hardly cleaved, and the desired porous film Is difficult to obtain. Here, the “main component” refers to an α-olefin component having the highest content among two or more α-olefins.

  Examples of the α-olefin used in the α-olefin copolymer include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1- Examples include pentene and 3-methyl-1-pentene. Examples of the α-olefin copolymer (B) include an ethylene-propylene copolymer, an ethylene-butene copolymer, and an ethylene-propylene-butene copolymer. Among these, an ethylene-propylene copolymer is preferably used from the viewpoint of production cost.

  The tensile strength of the copolymer (B) needs to be lower than the tensile strength of the poly-4-methyl-1-pentene polymer (A), preferably 1 to 10 MPa, more preferably about 1 to 6 MPa. .

The melt flow rate MFR _B of the copolymer (B) is not particularly limited, but a range of 0.1 to 20 g / 10 min is preferable because of excellent molding processability.

(iii) Polyolefin resin (C)
The polyolefin resin (C) consists of a polymer (A) and a copolymer (B).

Tensile strength _S tensile strength ratio _S A / _{S B} of the _B polymer tensile strength _{S A} and a copolymer of (A) (B) is preferably from 2 to 50 at 23 ° C., 2 to 20 Gayori preferable. When the tensile strength ratio S _A / S _B is within the above range, the copolymer (B) dispersed in the polymer (A) is easily cleaved.

Polymer (A) a melt flow rate MFR _A and copolymer (B) has a melt flow rate MFR _B and the melt flow rate ratio _MFR A / MFR _B of (hereinafter referred to as "MFR ratio") is not particularly limited From the viewpoint of moldability, 0.1 to 1,000 is preferable.

  In particular, when the MFR ratio is 0.1 to 10, particularly 0.2 to 5, the copolymer (B) is finely dispersed in the polymer (A), so fine and continuous pores are obtained. Since the contact point between fine pores increases, the air resistance (Gurley) specified in JIS P8117 is small, and a porous film with high air permeability is easily obtained. Moreover, since it is excellent in stretchability, it is easy to obtain a porous film having a high porosity, and air permeability is further increased.

In the case of the battery separator, increasing the difference [Delta] T = T _b -T _s of film breakage temperature T _b and pore closing temperature T _s as previously described, and to suppress the stopping temperature increase abnormality reaction at an earlier stage Although since it is desired to reduce the pore closing temperature, in the present invention, film breakage temperature T _b of 200 ° C. or higher, and 30 ° C. to 100 ° C. the difference ΔT of film breakage temperature T _b and pore closing temperature T _s In particular, it can be suitably used as a battery separator.

  In the polyolefin resin (C), the content of the polymer (A) is 30 to 80% by weight, preferably 40 to 70% by weight, and the content of the copolymer (B) is 20 to 70% by weight, preferably 30 to 30% by weight. 60% by weight. When the content of the copolymer (B) is less than 20% by weight, it is difficult to obtain the continuous pores of the present invention because the continuous pores formed in the copolymer (B) region are reduced. When it exceeds 70% by weight, it is difficult to obtain a dispersion structure of the copolymer (B) present in the polymer (A).

  In the polyolefin resin porous membrane of the present invention, many fine cleavages are observed in the copolymer (B) region dispersed in the polymer (A). The copolymer (B) has compatibility with the polymer (A) because it contains a certain amount or more of the ethylene component, and the copolymer (B) having compatibility with the polymer (A), Since the strength is lower than that of the polymer (A), it is presumed that cleavage occurred in the copolymer (B) region due to the stretching stress. This mechanism is fundamentally different from the conventional multicomponent stretching method in which inorganic fillers or different types of polymers are mixed and stretched. As a result, the obtained porous membrane has a small pore diameter and a high porosity and air permeability. .

  In the present invention, the copolymer (B) region means a region occupied by the copolymer (B) itself and a boundary region between the copolymer (B) and a substance adjacent thereto. Accordingly, the pores generated in the copolymer (B) region include pores due to cleavage generated in the region occupied by the copolymer (B) itself, and the polymer (A) and the copolymer (B). Pores due to interfacial delamination that occur in the boundary region.

(2) Polyolefin resin-made porous film-forming resin composition The resin composition, which is a molding material for the film-like molded product for forming the polyolefin resin-made porous film of the present invention, is usually in addition to the polyolefin resin (C). Antioxidants, neutralizers, α crystal nucleating agents, β crystal nucleating agents, hindered amine weathering agents, UV absorbers, antifogging agents, antistatic agents and other surfactants used in polyolefins, inorganic filling Agents, lubricants, antiblocking agents, antibacterial agents, antifungal agents, pigments and the like can be blended as necessary.

  Antioxidants include tetrakis [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane, 2,6-di-t-butyl-4-methylphenol, Phenolic compounds such as n-octadecyl-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate and tris (3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate Antioxidant, or tris (2,4-di-t-butylphenyl) phosphite, tris (nonylphenyl) phosphite, distearyl pentaerythritol diphosphite, tetrakis (2,4-di-t-butylphenyl) Examples thereof include phosphorus-based antioxidants such as -4,4'-biphenylene-diphosphonite.

  Examples of neutralizing agents include higher fatty acid salts such as calcium stearate. Examples of inorganic fillers and anti-blocking agents include calcium carbonate, silica, hydrotalcite, zeolite, aluminum silicate, magnesium silicate, and the like. Can be exemplified by higher fatty acid amides such as stearic acid amide, and the antistatic agent can be exemplified by fatty acid esters such as glycerol monostearate.

  Alpha crystal nucleating agents include talc, aluminum hydroxy-bis (4-t-butylbenzoate), 1,3,2,4-dibenzylidene sorbitol, 1,3,2,4-bis (p-methylbenzylidene) Sorbitol, 1,3,2,4-bis (p-ethylbenzylidene) sorbitol, 1,3,2,4-bis (2 ′, 4′-dimethylbenzylidene) sorbitol, 1,3,2,4-bis ( 3 ', 4'-dimethylbenzylidene) sorbitol, 1,3-p-chlorobenzylidene-2,4-p-methylbenzylidenesorbitol, 1,3,2,4-bis (p-chlorobenzylidene) sorbitol, sodium-bis (4-t-Butylphenyl) phosphate, sodium-2,2′-methylene-bis (4,6-di-t-butylphenyl) phosphate Calcium-2,2′-methylene-bis (4,6-di-t-butylphenyl) phosphate, aluminum dihydroxy-2,2′-methylene-bis (4,6-di-t-butylphenyl) Known α-crystal nucleating agents such as phosphate can be used. These may be used alone or in combination of two or more.

  The blending amount of these additives can be appropriately selected depending on the purpose of use of the polyolefin resin porous membrane, but is usually preferably about 0.001 to 5% by weight based on the total amount of the resin composition.

  The resin composition for forming the polyolefin resin porous membrane of the present invention includes polyethylene resins such as low density polyethylene, linear low density polyethylene, and high density polyethylene as long as the effects of the present invention are not impaired. One or more of other olefin resins such as polypropylene resin and polybutene resin may be used in combination.

  Furthermore, the resin composition includes olefin-based thermoplastic elastomers other than the copolymer (B), styrene-based thermoplastic elastomers, urethane-based thermoplastic elastomers, and polyester-based thermoplastic elastomers as long as the effects of the present invention are not impaired. Various thermoplastic elastomers such as polyamide thermoplastic elastomers and vinyl chloride thermoplastic elastomers may be used in combination.

  The method for blending the polyolefin resin (C) and the above additives is not particularly limited, and is blended by a usual blending device such as a mixer with a high-speed stirrer such as a Henschel mixer (trade name), a ribbon blender, and a tumbler mixer. The method (dry blend) is mentioned, Furthermore, the method of pelletizing using a normal single screw extruder or a twin screw extruder etc. is mentioned.

(3) Formation of polyolefin resin porous membrane The polyolefin resin porous membrane of the present invention is obtained by melting and kneading the resin composition containing the polyolefin resin (C) as a main component to form a film-like melt. After forming into a film-shaped molded product in the range of a draft ratio of 1 to 10, the film-shaped molded product can be formed by stretching in at least one direction at a temperature of 100 ° C. or lower. The process consists of a film forming process and a stretching process. The main component is the most abundant component.

(i) Film-forming process In the film-forming process for obtaining a film-shaped molded product from the resin composition, methods such as a known inflation film molding method, T-die film molding method, and calendar molding method are used. A T-die film forming method with high thickness accuracy and easy multilayering is preferably used.

  The resin composition can be formed at an extrusion temperature equal to or higher than the melting point of the polymer (A), but the purpose is to reduce the pressure inside the die and the draft ratio described later, and the polymer (A ), The extrusion temperature of 280 to 300 ° C. is preferably used in order to facilitate formation of uniform and fine pores in the copolymer (B) region dispersed in the polymer (A). .

The melt-kneaded resin composition is extruded from the die lip. At this time, the linear velocity V _{CL in} the flow direction (MD) of the resin composition passing through the die lip and the flow direction (MD) line of the film-shaped molded product The draft ratio (V _CL / V _f ) defined by the ratio of the speed V _f is an important factor for achieving the present invention. Generally, the draft ratio is about 10 to 50 when a thermoplastic resin film is formed. In the present invention, the draft ratio at the time of forming the resin composition is 1 to 10, preferably 1 to 5, more preferably 1 to 3, and the film-shaped product obtained thereby has excellent stretchability. By stretching, fine communicating pores are easily formed.

In the case of an inflation film molding method, in addition to the draft ratio, an olefin resin obtained by a blow ratio L _f / L _m represented by a ratio of a circumferential length L _f of the inflation film and a circumferential length L _m of the circular lip. Although the characteristics of the porous membrane are also changed, a blow ratio in the range of about 1 to 10 is suitably used if the draft ratio is within the above range. If the blow ratio is within the above range, stable production of the film-shaped molded product is possible, and the resulting film-shaped molded product can be easily made porous.

  In order to improve the rigidity of the polymer (A) as a matrix and make it easier to form uniform and fine pores in the copolymer (B) region dispersed in the polymer (A), it is extruded from a die lip. The film-shaped molded product is preferably cooled gradually, and the temperature of the cooling roll is preferably 40 to 160 ° C, more preferably 80 to 120 ° C. If it is lower than this temperature range, it tends to be difficult to make it porous. If it is higher than this temperature range, stickiness to the roll occurs due to the influence of the copolymer (B), and the workability tends to decrease. is there.

  The thickness of the film-like molded product obtained in the film forming process is not particularly limited, but is determined by the stretching and heat treatment conditions in the next stretching process and the required characteristics of the use of the porous film, and is preferably 20 μm to 2 mm. Is about 50 to 500 μm, and the film forming speed is preferably in the range of 1 to 100 m / min. The film-shaped moldings having these thicknesses include a combination of an inflation molding apparatus, an air knife having the cooling roll and an air outlet, the cooling roll and a pair of metal rolls, the cooling roll and a stainless steel belt, and the like. It can be obtained by various film forming apparatuses such as a T-die film forming apparatus and a calendar forming apparatus.

  In addition, you may heat-process in order to further improve a crystallinity degree before using for the obtained film-form molding to the next extending process. The heat treatment is performed, for example, by heating at a temperature of about 100 to 160 ° C. for about 1 to 30 minutes with a heated air circulation oven or a heating roll.

(ii) Stretching step The film-like molded product formed in the film-forming step is then stretched in at least one of the longitudinal (MD) direction and the transverse (TD) direction and dispersed in the polymer (A). Thus, pores communicating with the copolymer (B) region are formed. In this respect, the production method of the present invention is fundamentally different from the conventional single-component stretching method, multi-component stretching method, mixed extraction method and the like. As a result, the production method of the present invention can be found in complicated extraction and drying processes such as the mixed extraction method, and single component stretching methods in which pores are expressed by fibrillation between lamellar crystals of crystalline polyolefin. Not only the crystallization process by heat treatment after film formation is unnecessary, but also poor stretchability and large average pore diameter in the case of the multi-component stretching method that creates voids at the interface between the crystalline polyolefin and the filler. It is possible to provide a porous film having an arbitrary average pore diameter and porosity with excellent productivity by greatly improving problems such as easily becoming low and low porosity.

  In addition to the uniaxial stretching method of stretching in one direction, the stretching method includes a sequential biaxial stretching method of stretching in the other direction after stretching in one direction, a simultaneous biaxial stretching method of stretching simultaneously in the longitudinal and transverse directions, and There are a method of performing multistage stretching in a uniaxial direction, a method of further stretching after sequential biaxial stretching and simultaneous biaxial stretching, and any method may be used. Incidentally, since the film-shaped molded product is drafted in the film-forming step, even if it is a film-shaped molded product formed at a low draft ratio, the copolymer (B) dispersed in the polymer (A) Is oriented along the resin flow direction, that is, the longitudinal (MD) direction, and the first stage of stretching is preferably performed by a uniaxial stretching method in the transverse direction or a simultaneous biaxial stretching method in the longitudinal and transverse directions. Alternatively, a sequential biaxial stretching method in which stretching in the longitudinal direction and stretching in the lateral direction in the second stage may be performed.

  The first stage stretching temperature is preferably lower than the melting point or softening point of the copolymer (B), and a temperature range of 10 to 100 ° C, more preferably a temperature range of 10 to 60 ° C is preferably used. Furthermore, in this invention, it discovered that it was excellent in the drawability in these temperature ranges by making polyolefin resin (C) into a specific composition. The draw ratio is not particularly limited and is determined from the required conditions for the second-stage drawing conditions and the intended use of the porous membrane as required, but the polymer (A) alone is inferior in low-temperature drawability. Although it is about double, the presence of the copolymer (B) enables low-temperature stretching at a stretching ratio of 1.5 to 4 times.

If the draw ratio is in the above range, a porous film having excellent characteristics can be obtained, and there is no fear of a decrease in productivity due to frequent draw breaks. In the case of simultaneous biaxial stretching, the area ratio (= longitudinal stretching ratio × lateral stretching ratio) is preferably 2 to 20 times, and more preferably 4 to 10 times. If the area magnification is within this range, a porous film having excellent characteristics can be obtained, and there is no risk of a decrease in productivity due to frequent stretching.

  The porous film of the present invention is subjected to a second stage stretching as required, and the second stage stretching temperature is preferably 10 to 120 ° C, more preferably 10 to 80 ° C. Within this range, it is possible to achieve porosity while maintaining good productivity without blocking the pores cleaved in the first stage.

  Although the draw ratio of the second stage is determined by the required characteristics of the use of the porous membrane, it is usually 1.5 to 4 times because the low-temperature drawability is excellent as compared with the case of the polymer (A) alone. When the draw ratio is within the above range, the drawing effect is sufficient, and there is no fear that productivity is lowered due to the drawing being cut.

  The porosity of the polyolefin resin porous membrane of the present invention is not particularly limited, but is preferably 20 to 90%, more preferably 30 to 80%. If the porosity is within the above range, a function as a porous film can be obtained, and there is no fear that the strength is lowered.

  The thickness of the polyolefin resin porous membrane of the present invention is not particularly limited, but is preferably about 10 to 200 μm from the viewpoint of productivity.

  The olefin resin porous membrane of the present invention can be subjected to hydrophilic treatment such as surfactant treatment, corona discharge treatment, low temperature plasma treatment, sulfonation treatment, ultraviolet treatment, radiation graft treatment, etc., if necessary. It can be laminated with other types of porous membranes or various coating films can be formed.

  The polyolefin resin porous membrane obtained by the above-mentioned method is similar to conventional porous membranes, such as filtration membranes or separation membranes for air purification and water treatment, separators for batteries and electrolysis, moisture permeability such as building materials and clothing. It can be used in various fields such as waterproofing applications.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these. In addition, the measurement method and evaluation method used are as follows.

(1) Tensile strength at 23 ° C .: The tensile strength at 23 ° C. was measured according to JIS K 6758.

(2) Melt flow rate (MFR) :: In accordance with JIS K 7210, poly-4-methyl-1-pentene polymer (A) has a temperature of 260 ° C., a load of 21.18 N, an α-olefin copolymer (B ) Was measured under conditions of a temperature of 230 ° C. and a load of 21.18N.

(3) Porosity: Bulk specific gravity is obtained from 100 × 100 mm of stretched porous membrane sample, and automatic specific gravity manufactured by Toyo Seiki Seisakusho Co., Ltd. from 100 × 100 mm of a non-porous membrane-like molded product before stretching. The true specific gravity was determined by the total DENSIMTER, DS, and the porosity was determined from the following formula.
Porosity (%) = (1-bulk specific gravity / true specific gravity) × 100

(4) Maximum pore size: The maximum value of the length in the major axis direction of the pore was determined as the maximum pore size by observation with a scanning electron microscope (SEM) of the longitudinal (MD) and lateral (TD) cross sections.

(5) Moisture permeability: Measured according to JIS L 1099.

(6) Air permeability resistance (Gurley): According to JIS P8117, a time required for 100 ml of air to pass through was measured with a B-type Gurley densometer (manufactured by Tester Sangyo Co., Ltd.).

(7) Hole closing temperature T _s and film breaking temperature T _b : A sample fixed to a 3-inch circular holder is left in a constant temperature bath at a temperature range of 100 ° C. to 200 ° C. for 10 hours and heat-treated, the air resistance of the (Gurley) was measured to the temperature at which 10,000 sec / 100 cc or more and pore blocking temperature _{T s.} Further, the temperature was equally heat treated film tearing occurs with the membrane broken temperature T _b.

(8) Stretchability: A test piece having a width of 40 mm and a length of 100 mm and having a length direction of the longitudinal direction (MD) or a transverse direction (TD) was prepared from a film-shaped molded article. The test piece was stretched uniaxially every 0.5 times in the length direction under the conditions of a stretching temperature of 23 ° C. and a deformation rate of 200% / second, and the stretch ratio not to stretch and break was defined as the stretchable ratio, and the stretchability was evaluated. . The higher the stretchable ratio, the better the stretchability, and the easier it is to form a film-like molded product, the higher the porosity is.

The poly-4-methyl-1-pentene polymer (A), the α-olefin copolymer (B), an ethylene-propylene copolymer, and a polypropylene resin used in Examples and Comparative Examples are shown below. .
Poly-4-methyl-1-pentene polymer (A); manufactured by Mitsui Chemicals, trade name MX002 (
MFR (260 ° C.) 25 g / 10 min, tensile strength 15 MPa)
α-olefin copolymer (B); ethylene-propylene copolymer, JSR
Product name EP07P (propylene content 27% by weight, MFR (230 ° C.))
7g / 10min, tensile strength 2MPa)
Polypropylene resin; propylene homopolymer (MFR 1.8 g / 10 min, tensile strength 35 MPa)

1) Preparation of porous film-forming resin composition After polymer (A) and copolymer (B) shown in Example 1 of Table 1 were mixed, they were melt-kneaded using a twin screw extruder (50 mm diameter). The resin composition for forming a porous film was obtained by pelletizing.

2) Creation of porous film [Film forming step / Creation of unstretched film-like molded product]
Using a 20 mm extruder equipped with a T die with a lip width of 120 mm, the pellet-shaped thermoplastic resin composition (C) was melted at an extrusion temperature of 300 ° C. and a discharge rate of 4 kg / h, and a lip clearance of 0.20 mm. The film was extruded from a T-die adjusted to a film shape and cooled and solidified on a 90 ° C. cooling roll to prepare a film-shaped molded product having a width of 100 mm and a thickness of 200 μm. When the film-like molded product in a molten state was cooled and solidified, the non-contact surface with the cooling roll was air-cooled with an air knife.
Table 1 shows the evaluation results of the stretchability of the obtained film-like molded product.

3) [Stretching process / Creation of porous film]
The film-shaped molded product was stretched in the machine direction (MD direction) under the conditions of a stretching temperature of 23 ° C., a deformation rate of 1,000% / second, and a draw ratio of 2.5 times while restraining the transverse direction (TD direction). Thereafter, the polyolefin resin porous membrane is stretched in the transverse direction (TD direction) under the conditions of a stretching temperature of 100 ° C., a deformation rate of 200% / second, and a stretching ratio of 2.5 times while restraining the longitudinal direction (MD direction). Got. The properties of the obtained porous membrane are shown in Table 1.

  A polyolefin resin porous membrane was obtained according to Example 1 except that the polymer (A) and copolymer (B) shown in Example 2 of Table 1 were used. Table 1 shows the properties of the obtained polyolefin resin porous membrane and the evaluation results of the stretchability of the membrane-shaped molded product.

  A polyolefin resin porous membrane was obtained in the same manner as in Example 1 except that the polymer (A) and copolymer (B) shown in Example 3 of Table 1 were used. Table 1 shows the properties of the obtained polyolefin resin porous membrane and the evaluation results of the stretchability of the membrane-shaped molded product.

  A polyolefin resin porous membrane was obtained in the same manner as in Example 2 except that the lip clearance was 1.2 mm, the draft ratio was 3.6, and the thickness of the membrane-like molded product was 400 μm. Table 1 shows the properties of the obtained polyolefin resin porous membrane and the evaluation results of the stretchability of the membrane-shaped molded product.

  A polyolefin resin porous membrane was obtained in the same manner as in Example 2 except that the lip clearance was 1.2 mm, the draft ratio was 7.2, and the thickness of the membrane-shaped molded product was 200 μm. Table 1 shows the properties of the obtained polyolefin resin porous membrane and the evaluation results of the stretchability of the membrane-shaped molded product.

(Comparative Example 1)
The same operation as in Example 1 was carried out except that only the polymer (A) shown in Comparative Example 1 of Table 1 was used. In Comparative Example 1, when stretching in the longitudinal direction, the stretching breakage occurred at a stretching ratio of less than 2 times and the stretchability was inferior, so the longitudinal stretching ratio was 1.5 times and the transverse stretching ratio was 1.5 times. However, the moisture permeability and air permeability resistance were out of the measurement range, and the characteristics as a porous film having air permeability were not obtained. Table 1 shows the properties of the obtained polyolefin resin porous membrane and the evaluation results of the stretchability of the membrane-shaped molded product.

(Comparative Example 2)
It implemented like Example 1 except using a polymer (A) and a polypropylene resin for the comparative example 2 of Table 1. FIG. In Comparative Example 2, when stretching in the longitudinal direction, the stretching breakage occurred when the stretching ratio was less than 2 times, and the stretchability was poor. Therefore, the longitudinal stretching ratio was 1.5 times, and the transverse stretching ratio was 1.5 times. However, the moisture permeability and air permeability resistance were out of the measurement range, and the characteristics as a porous film having air permeability were not obtained. Table 1 shows the properties of the obtained polyolefin resin porous membrane and the evaluation results of the stretchability of the membrane-shaped molded product.

For the polyolefin resin porous membrane obtained in Example 2, the results of measuring the film tearing temperature _{T b} and the pore closing temperature _{T s,} respectively _T b 200 ° C. or _higher, was T s 120 ° C.. ΔT was 80 ° C. or higher, and the hole closing temperature T _s itself was low, which had an excellent shutdown function and safety as a battery separator.

(Comparative Example 3)
With respect to a commercially available battery separator (trade name Celgard 2400, manufactured by Celgard Co., Ltd., thickness 27 μm, porosity 38%, air permeability 600 sec / 100 ml), the film breaking temperature T _b and the pore closing temperature T _s were measured. As a result, _Tb was 165 ° C., but even at 160 ° C., the air permeability resistance was 710 seconds / 100 ml, which did not exceed 10,000 seconds / 100 ml, and the pore closing temperature T _s could not be measured. No shutdown function was observed as a battery separator.

(Table 1)

  The polyolefin resin porous membrane of the present invention is suitably used for battery separators, separation membranes, breathable waterproof materials and the like.

Claims (6)

A polyolefin resin (C) comprising a poly-4-methyl-1-pentene polymer (A) and an α-olefin copolymer (B) having a main component α-olefin content of 40 to 80% by weight. A porous film formed by melting and kneading a resin composition contained therein to form a film-like melt, forming the film-like melt into a film-like molding, and then stretching the film-like molding in at least one direction The polyolefin resin (C) comprises 30 to 80% by weight of the poly-4-methyl-1-pentene polymer (A) and 20 to 70% by weight of the α-olefin copolymer (B). A polyolefin resin porous membrane having pores communicating with the olefin copolymer (B) region. Poly-4-methyl-1-pentene polymer at 23 ° C. tensile strength ratio _S A / _{S B} of the tensile strength _{S B} of the tensile strength _{S A} and α- olefin copolymer (A) (B) The polyolefin resin porous membrane according to claim 1, wherein the porous membrane is 2 to 50. 3. The polyolefin resin porous membrane according to claim 2, wherein the tensile strength ratio S _A / S _B at 23 ° C. is 2 to 20. The polyolefin resin porous membrane according to any one of claims 1 to 3, wherein a draft ratio when the film-like melt is formed into a film-like molding is in the range of 1 to 10. 5. The polyolefin resin porous membrane according to claim 4, wherein a draft ratio when the film-shaped melt is formed into a film-shaped molding is in the range of 1 to 3. The air resistance (Gurley) is 1 to 2,000 seconds / 100 ml, an in film breakage temperature _{T b} is 200 ° C. or higher, the difference between the film tear temperature _{T b} and pore closing temperature _{T s ΔT} (= _{T b} - T _s) is a polyolefin resin porous membrane of any one of claims 1 to 5, wherein the at 30 ° C. or higher.