JP4466039B2 - Polyolefin resin porous membrane - Google Patents

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, electrolytic capacitor separators, and paper diapers Widely used in sanitary materials such as backsheets, 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, which is incompatible with the polyolefin resin, is stretched in at least one direction, and the polyolefin resin And a method of generating voids (pores) at the interface between the filler and the filler (hereinafter referred to as “multi-component stretching method”).
(b) A method of obtaining a porous film by heating a crystalline polypropylene sheet formed at a high draft ratio as needed and stretching it in at least one direction to fibrillate between crystal lamellae (hereinafter referred to as “single component stretching”). Law ") is disclosed.
(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. There were problems such as deterioration in physical properties and texture, and weakness to acids and alkalis. Further, in the latter organic filler mixed system, not only the physical properties and texture of polyolefin are deteriorated, but also fine dispersion of the organic filler in the polyolefin resin is difficult, and a porous film having a small pore diameter or a large porosity. There are problems such as difficult to obtain.

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.

As a method for easily obtaining a porous film, component A composed of an ethylene-propylene block copolymer, component B composed of a propylene homopolymer or random copolymer, and component C composed of low molecular weight polypropylene, and optionally component D or β composed of calcium carbonate. A porous film made of a polymeric composition to which component E made of a spherulitic nucleating agent is added and a method for producing the same are disclosed (for example, see Patent Document 1). In addition, a porous sheet is disclosed in which an ethylene-propylene block copolymer alone or, if necessary, a crystalline polyolefin resin in which a polypropylene resin or a polyethylene resin is used in combination contains a mineral oil or an ester compound having a melting point of 100 ° C. or less (for example, , See Patent Document 2).

In these technologies, the ethylene-propylene block copolymer alone does not exhibit sufficient porosity and air permeability, and thus is improved by a multi-component system. However, since these components are multi-component, they are not uniformly dispersed. It is difficult to obtain a uniform porous film, and because the pores formed in the porous film have a large pore diameter, it is difficult to reduce the thickness of the porous film, or it is difficult to increase the porosity, and the air permeability and moisture permeability Therefore, it is difficult to use it for a battery separator that requires a small pore size and a microfiltration filter that requires a high porosity and air permeability.

In addition, a method for producing a porous film by blending a nucleating agent with polypropylene is also known (see, for example, Patent Document 3 and Patent Document 4). These are methods for obtaining a porous film by stretching a film-like material using an α-crystal nucleating agent such as a benzylidene sorbitol compound or a film-like material produced under film-forming conditions such that α-crystals grow. . According to such a method, the porosity of the membrane is improved to some extent, but it is desired that the membrane be made more highly porous. On the other hand, a method for producing a porous film using β-crystals peculiar to polypropylene is also known, but it is difficult to produce a sufficient amount of β-crystals under realistic conditions, which is satisfactory. At present, a porous film having a porosity cannot be obtained.

As a method for producing β crystals in polypropylene, a method of crystallizing molten polypropylene under a temperature gradient, a method of adding and mixing a small amount of β crystal nucleating agent (γ-quinacridone), and the like have been proposed. However, the former requires a long time and has a drawback that only a small amount of sample can be obtained. Further, the latter method of adding a β-crystal nucleating agent exhibiting β-transformation (β-crystal) to polypropylene has low thermal stability and is likely to be already converted to α-transformation at the melting stage. When trying to obtain a porous film by adding a β crystal nucleating agent to polypropylene, the β crystal nucleating agent to be used, the molding conditions of the raw fabric sheet, and the stretching conditions are problematic. However, it is disclosed that uniaxial or biaxial stretching is performed at the same temperature, and it is not practical because it is uniaxial or biaxially stretched at the same temperature. Further, there is a problem that the product is colored red. .

JP-A-4-309546 JP-A-8-208862 JP-A 63-199742 JP-A 64-54042

The present invention has been made to solve the above-mentioned problems related to conventional polyolefin resin porous membranes, facilitates the realization of uniform dispersion in the production process, and has a small pore diameter and a low porosity in spite of a simple resin composition. It is an object to provide a high polyolefin resin porous membrane.

As a result of intensive studies, the present inventors have determined that a specific polyolefin resin (C) comprising crystalline polypropylene (A) and a propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A). On the other hand, the resin composition (E) containing 0.01 to 5% by weight of the α crystal nucleating agent (D) based on the weight of the resin composition (E) is melted and kneaded to form a film-like melt, A porous film formed by forming a film-form melt into a film-form product under specific conditions and then stretching the film-form product in at least one direction, and communicates with the copolymer (B) region. The present invention has been completed based on the finding that this problem can be solved by the polyolefin resin porous membrane having pores. 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. An α crystal nucleating agent (D) is added to a polyolefin resin (C) composed of crystalline polypropylene (A) and a propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A). The resin composition (E) blended in an amount of 0.01 to 5% by weight based on the weight of the composition (E) is melted and kneaded to form a film-like melt, and the film-like melt has a lip clearance of 0.2 to 1. A porous film formed by extruding into a film shape from a T die adjusted to 2 mm and then forming the film shape in at least one direction, and the polyolefin resin (C) is It consists crystalline polypropylene (a) 30 to 90 wt% of propylene-.alpha.-olefin copolymer (B) and 10 to 70 wt%, propylene with a melt flow rate _{MFR PP} of the crystalline polypropylene (a)-.alpha.- Olefin copolymer (B) is a melt flow rate _{MFR RC} melt flow rate ratio _MFR PP / _{MFR RC} is 0.1 to 10 of a polyolefin resin porous membrane having pores communicating with the copolymer (B) region .

2. 2. The polyolefin resin porous membrane according to 1 above, wherein the melt flow rate ratio MFR _PP / MFR _RC is 0.2 to 5.

3. 3. The polyolefin resin porous membrane according to the above item 1 or 2, 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.

4). 3. The polyolefin resin porous membrane according to the above item 1 or 2, wherein a draft ratio when the film-shaped melt is formed into a film-shaped molded product is in the range of 1 to 3.

5. Any one of said 1-4 characterized by polyolefin resin (C) consisting of crystalline polypropylene (A) 40 to 70 weight% and polypropylene-alpha-olefin copolymer (B) 30 to 60 weight%. 2. A polyolefin resin porous membrane according to item 1.

6). 6. The polyolefin resin porous membrane according to any one of 1 to 5 above, wherein the propylene content of the propylene-α-olefin copolymer (B) is 30 to 80% by weight.

7). 6. The polyolefin resin porous membrane according to any one of 1 to 5 above, wherein the propylene content of the propylene-α-olefin copolymer (B) is 40 to 70% by weight.

8). The polyolefin resin (C) is obtained by a multistage polymerization method including the steps of producing a crystalline polypropylene (A) in the first stage and continuously producing a propylene-α-olefin copolymer (B) in the second stage. 8. The polyolefin resin porous membrane according to any one of 1 to 7 above, wherein the porous membrane is a polyolefin resin porous membrane.

9. 9. The polyolefin according to any one of 1 to 8 above, wherein the porous membrane has a gas permeability resistance (Gurley) of 1 to 1,000 seconds / 100 ml and a moisture permeability of 2,000 to 20,000 g / m ² · 24 h. Resin porous membrane.

10. An α crystal nucleating agent (D) is added to a polyolefin resin (C) composed of crystalline polypropylene (A) and a propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A). The resin composition (E) blended in an amount of 0.01 to 5% by weight based on the weight of the composition (E) is melted and kneaded to form a film-like melt, and the film-like melt has a lip clearance of 0.2 to 1. A porous film formed by extruding a T-die adjusted to 2 mm into a film shape and forming it into a film-shaped molded product, and then stretching the film-shaped molded product in at least one direction, which is a polyolefin resin (C) There melt flow rate _{MFR PP} and propylene -α crystalline polypropylene (a) 30 to 70 wt% propylene -α- olefin copolymer (B) consists of a 30 to 70% by weight, crystalline polypropylene (a) Olefin copolymer melt flow rate _{MFR RC} melt flow rate ratio _MFR PP / _{MFR RC} of (B) is at greater than 10 1,000, the polyolefin resin having pores communicating with the copolymer (B) region Porous membrane.

11. 11. The polyolefin resin porous membrane according to the above item 10, 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.

12 11. The polyolefin resin porous membrane according to the above item 10, wherein the draft ratio when the film-shaped melt is formed into a film-shaped molded product is in the range of 1 to 5.

13. 13. The polyolefin resin porous membrane according to any one of 10 to 12, wherein the propylene content of the propylene-α-olefin copolymer (B) is 30 to 80% by weight.

14 13. The polyolefin resin porous membrane according to any one of 10 to 12 above, wherein the propylene content of the propylene-α-olefin copolymer (B) is 40 to 70% by weight.

15. The polyolefin resin (C) is obtained by a multistage polymerization method including the steps of producing a crystalline polypropylene (A) in the first stage and continuously producing a propylene-α-olefin copolymer (B) in the second stage. 15. The polyolefin resin porous membrane according to any one of items 10 to 14, wherein the porous membrane is a polyolefin resin porous membrane.

16. The air permeability resistance (Gurley) of the porous membrane is 10 to 10,000 seconds / 100 ml, and the moisture permeability is 1,000 to 15,000 g / m ² · 24 h. Polyolefin resin porous membrane.

The polyolefin resin porous membrane of the present invention is obtained by using a specific polyolefin resin (C) in which a propylene-α-olefin copolymer (B) is finely dispersed in crystalline polypropylene (A) under a specific processing method. A porous film obtained by adding a crystal nucleating agent (D) to improve stretchability at low temperatures and forming pores by cleavage of the copolymer (B) in the copolymer (B) region. Yes, it is a porous membrane excellent in porous membrane properties in which the pores become finer than the porous membrane containing no α crystal nucleating agent (D) and the porosity and air permeability are improved. The polyolefin resin porous membrane of the present invention is an economical porous membrane that can be obtained without using a complicated manufacturing process as in the prior art, and requires a separation membrane, a battery separator, and a breathable waterproof material that require continuous micropores. It can use suitably for uses, such as.

Hereinafter, embodiments of the present invention will be described.
(1) Polyolefin resin In the polyolefin resin porous membrane of the present invention, crystalline polypropylene (A) and propylene-α-olefin copolymer (B) (hereinafter, simply referred to as “copolymer (B)” may be used. And a polyolefin resin (C) in which the copolymer (B) is finely dispersed as a region in the matrix of the crystalline polypropylene (A).

(I) Crystalline polypropylene (A)
The crystalline polypropylene (A) is a crystalline polymer mainly composed of propylene polymerized units, preferably polypropylene having 90% by weight or more of propylene polymerized units. Specifically, it may be a propylene homopolymer, or may be a random or block copolymer of 90% by weight or more of propylene polymer units and 10% by weight or less of α-olefin. Examples of the α-olefin used when the crystalline polypropylene (A) is a copolymer include ethylene (included in the α-olefin in the present invention), 1-butene, 1-pentene, 1-hexene and 1-octene. 1-decene, 1-dodecene, 4-methyl-1-pentene, 3-methyl-1-pentene and the like. Among these, it is preferable from the viewpoint of production cost to use a propylene homopolymer or a propylene-ethylene copolymer having a propylene polymer unit content of 90% by weight or more.

Further, the melt flow rate MFR _PP of the crystalline polypropylene (A) is preferably in the range of 0.1 to 50 g / 10 min from the stability of film formation.

(ii) Propylene-α-olefin copolymer (B)
The copolymer (B) is a random copolymer of propylene and an α-olefin other than propylene. The content of propylene polymerized units is preferably in the range of 30 to 80% by weight, more preferably 35 to 75% by weight, still more preferably 40 to 70% by weight, based on the weight of the entire copolymer (B). is there. When the content of the propylene polymerized unit is more than the above range, pores are hardly formed in the copolymer (B) region present in the matrix of the crystalline polypropylene (A), and the content of the propylene polymerized unit is When the amount is less than the above range, interfacial peeling between the crystalline polypropylene (A) and the copolymer (B) is likely to occur, so that the low-temperature stretchability is lowered and the pore diameter is likely to be increased.

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

The melt flow rate MFR _RC 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) is composed of crystalline polypropylene (A) and a copolymer (B). The melt flow rate ratio MFR _PP / MFR _RC (hereinafter referred to as “MFR ratio”) between the melt flow rate MFR _PP of the crystalline polypropylene (A) and the melt flow rate MFR _RC of the copolymer (B) is not particularly limited. However, 0.1 to 1,000 is preferable from the viewpoint of moldability.

In particular, when the MFR ratio is 0.1 to 10, particularly 0.2 to 5, the copolymer (B) is finely dispersed in the crystalline polypropylene (A), so fine and continuous pores are present. It is easy to obtain, the contact point between fine pores increases, the air permeability resistance (Gurley) specified in JIS P8117 is small, and a porous membrane 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.

When the MFR ratio is greater than 10 and less than or equal to 1,000, the pore diameter of the pores formed by stretching is larger than that when the MFR ratio is 0.1 to 10, and the proportion of connected pores decreases. Although there is a tendency, since the resin composition is not easily affected by fluctuations in film forming conditions and stretching conditions, a porous film having stable characteristics is easily obtained.

In the present invention, when the MFR ratio is 0.1 to 10, the air permeability resistance (Gurley) is 1 to 1,000 seconds / 100 ml, and the moisture permeability is 2,000 to 20,000 g / m ² · 24 h. Can be obtained. According to the cross-sectional observation with a scanning electron microscope (SEM), the porous film has a large number of fine pores of 1 to 2 μm, and fine pores having a maximum major axis of the pore diameter of 5 μm or less. Is recognized. Such a porous membrane can be suitably used for separation membranes, battery separators, and the like that require high filtration accuracy.

When the MFR ratio is greater than 10 and less than or equal to 1,000, the porous film has an air permeability resistance (Gurley) of 10 to 10,000 seconds / 100 ml and a moisture permeability of 1,000 to 15,000 g / m ² · 24 h. Can be obtained. In the porous film, according to cross-sectional observation by SEM, a large number of pores of about 5 μm are connected, and pores having a maximum major axis of pore diameter of 10 μm or less are recognized. Such porous membranes are relatively low cost with little variation in quality characteristics due to manufacturing conditions, and can be suitably used in the field of building materials such as breathable waterproofing materials, the field of hygiene materials such as breathable sheets for disposable diapers, etc. is there.

The content of the crystalline polypropylene (A) in the polyolefin resin (C) is 30 to 90% by weight, preferably 40 to 70% by weight when the MFR ratio is 0.1 to 10, and the copolymer (B ) Is 10 to 70% by weight, preferably 30 to 60% by weight. When the content of the copolymer (B) is less than 10% by weight, it is difficult to obtain the continuous pores of the present invention because the continuous pores formed in the copolymer (B) region is reduced. When it exceeds 70% by weight, it becomes difficult to obtain a finely dispersed structure of the copolymer (B) present in the crystalline polypropylene (A).

When the MFR ratio is greater than 10 and 1,000 or less, the content of the crystalline polypropylene (A) in the polyolefin resin (C) is 30 to 70% by weight, preferably 40 to 60% by weight. The content of the union (B) is 70 to 30% by weight, preferably 60 to 40% by weight. If the content of the crystalline polypropylene (A) and the copolymer (B) is in the above range, continuous pores are obtained and the dispersibility of the copolymer (B) is good.

The production method of the polyolefin resin (C) is not particularly limited, and any production method may be used as long as the above conditions are satisfied. For example, the polyolefin resin (C) may be produced by mixing the crystalline polypropylene (A) and the copolymer (B) obtained by separately polymerizing by melt kneading or the like. Specifically, a copolymer (B) polymerized using a Ziegler-Natta catalyst such as a titanium-supported catalyst or a commercially available ethylene-propylene rubber corresponding to the copolymer (B) and crystalline polypropylene (A) are melted. The method of mixing can be illustrated.

Alternatively, the polyolefin resin (C) may be produced by continuously polymerizing the crystalline polypropylene (A) and the copolymer (B) by multistage polymerization. For example, by using a plurality of polymerization vessels, a crystalline polypropylene (A) is produced in the first stage, and then a copolymer (B) is produced in the presence of the crystalline polypropylene (A) in the second stage. A method for continuously producing the resin (C) can be exemplified. This continuous polymerization method is lower in production cost than the melt mixing method described above, and a polyolefin resin (C) in which the copolymer (B) is uniformly dispersed in the crystalline polypropylene (A) can be stably obtained. Therefore, it is preferable.

In the present invention, a particularly preferred polyolefin resin (C) is produced by the above continuous polymerization method and adjusted so that the MFR ratio is 10 or less, more preferably in the range of 0.2 to 5. By setting the MFR ratio within this range, the copolymer (B) is uniformly and finely dispersed in the crystalline polypropylene (A). Therefore, when the polyolefin resin (C) is stretched, the crystalline polypropylene is used. Uniform and fine pores are generated in the copolymer (B) region dispersed in (A), and as a result, a porous membrane having a small pore diameter and a high porosity is obtained.

In the polyolefin resin porous membrane of the present invention, many fine cleavages are observed in the copolymer (B) region finely dispersed in the crystalline polypropylene (A). Since the copolymer (B) contains a certain amount or more of a propylene component, the copolymer (B) is compatible with crystalline polypropylene, and the copolymer (B) having compatibility with the crystalline polypropylene (A) is crystallized. Since the strength is lower than that of the conductive polypropylene (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 multi-component stretching method in which inorganic fillers and different polymers are mixed and stretched. It has become.

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. Therefore, 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 crystalline polypropylene (A) and the copolymer (B). And pores due to interfacial delamination that occur in the boundary region.

Specifically, the polyolefin resin (C) having the MFR ratio as described above can be produced by a method described in International Publication No. 97/19135, JP-A-8-27238, and the like.
In addition, the polyolefin resin (C) can be produced by the above-described method, and one having a desired specification may be selected from commercially available products.

The MFR ratio is usually determined by measuring MFR _PP of the crystalline polypropylene (A) and MFR _RC of the copolymer (B). However, when the polypropylene resin is continuously produced by multistage polymerization (when the crystalline polypropylene (A) is first polymerized and then the copolymer (B) is polymerized), the MFR _{RC of the} copolymer (B) is used. Of MFR _PP of crystalline polypropylene (A) that can be directly measured, melt flow rate MFR _{WHOLE of} the resulting polyolefin resin (C), and content of copolymer (B) in polyolefin resin (C) The MFR ratio can be obtained by calculating MFR _RC from W _RC (weight%) by the following formula.
log (MFR _RC ) = {log (MFR _WHOLE ) − (1−W _RC / 100) log (MFR _PP )} / (W _RC / 100)

(Iv) α crystal nucleating agent (D)
In the present invention, the α crystal nucleating agent (D) is blended with the polyolefin resin (C). Porous membranes containing the α crystal nucleating agent (D) exhibit superior porous membrane properties with finer pore diameters and improved porosity and air permeability than porous membranes not containing the α crystal nucleating agent (D). it can. As the α crystal nucleating agent (D), known ones can be used without particular limitation, but preferably 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-tert-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- And bis (4,6-di-t-butylphenyl) phosphate. These may be used alone or in combination of two or more.

In the present invention, the blending amount of the α crystal nucleating agent (D) is 0.01 to 5% by weight, preferably 0.03 to 3% by weight, based on the weight of the polyolefin resin porous membrane forming resin composition (E). %. Here, when the blending amount of the α crystal nucleating agent (D) is smaller than 0.01 parts by weight, it is difficult to obtain the effect of the characteristics due to the addition of the α crystal nucleating agent (D). When the blending amount is larger than 5 parts by weight, the α crystal nucleating agent (D) tends to cause poor dispersion in the polyolefin resin (C), the effect is lowered, and it is economically disadvantageous. The method of blending the α crystal nucleating agent (D) with the polyolefin resin (C) is not particularly limited. For example, a usual mixer such as a Henschel mixer (trade name) with a high-speed stirrer, a ribbon blender, a tumbler mixer, etc. The method (dry blend) which mix | blends by the compounding apparatus of this can be illustrated, and also the method of pelletizing using a normal single screw extruder or a twin screw extruder etc. can be illustrated.

(2) Resin composition for forming a polyolefin resin porous film The resin composition (E), which is a molding material of a film-shaped molded product for forming the polyolefin resin porous film of the present invention, comprises a polyolefin resin (C) and an α crystal structure. In addition to the nucleating agent (D), surfactants such as antioxidants, neutralizing agents, β crystal nucleating agents, hindered amine weathering agents, ultraviolet absorbers, antifogging agents and antistatic agents used in ordinary polyolefins. Agents, inorganic fillers, 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.

Although the compounding quantity of these additives can be suitably selected according to the purpose of use of the polyolefin resin porous membrane, it is usually preferably about 0.001 to 5% by weight with respect to the total amount of the resin composition (E).

In addition, the resin composition (E) for forming the polyolefin resin porous membrane of the present invention has a propylene homopolymer and a single amount other than propylene containing propylene as a main component, as long as the effects of the present invention are not impaired. Two or more random polymers with the body and other olefin resins such as polyethylene resin, polybutene resin, and polymethylpentene resin may be used in combination.

Further, an ethylene-diene elastic copolymer or ethylene-propylene elastic copolymer polymerized with a single site catalyst or a known multi-site catalyst in order to lower the softening temperature of the resin composition (E) or improve the flexibility. Further, an elastic copolymer such as a styrene-butadiene elastic copolymer may be added.

The method of blending the above-mentioned additives into the resin composition (E) is not particularly limited. For example, the blending is performed by a usual blending apparatus such as a mixer with a high-speed stirrer such as a Henschel mixer (trade name), a ribbon blender, and a tumbler mixer. A method (dry blending) can be exemplified, and further a pelletizing method using a normal single screw extruder or twin screw extruder can be exemplified.

(3) Formation of polyolefin resin porous film The polyolefin resin porous film of the present invention is obtained by melting and kneading a resin composition (E) containing a polyolefin resin (C) as a main component to form a film-like melt. Can be formed by stretching the film-shaped molded product 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 (E), 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 film thickness accuracy and easy multilayering is preferably used.

The resin composition (E) can be formed at an extrusion molding temperature of 180 ° C. or higher. The purpose is to reduce the pressure inside the die and the draft ratio described later, and the crystalline polypropylene (A) which is a matrix polymer. In order to improve the rigidity of the copolymer and facilitate the formation of uniform and fine pores in the copolymer (B) region dispersed in the crystalline polypropylene (A), an extrusion temperature of 220 to 300 ° C. is preferably used. .

The melted and kneaded resin composition (E) is extruded from the die lip. At this time, the linear velocity V _{CL in} the flow direction (MD) of the resin composition (E) passing through the die lip and the flow of the film-like molded product The draft ratio (V _CL / V _f ) defined by the ratio of the linear velocity V _{f in} the direction (MD) 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 (E) is 1 to 10, and the resulting film-like molded product is excellent in stretchability, and fine communicating pores are formed by stretching. It becomes easy to be done.

When the MFR ratio is 0.1 to 10, the draft ratio is preferably 1 to 5, and more preferably 1 to 3. When the MFR ratio is greater than 10 and 1,000 or less, the draft ratio of 1 to 5 is more preferable.
According to the above method, it is possible to form continuous pores even in the polyolefin resin (C) having an MFR ratio of more than 10 and 1,000 or less, which makes it difficult to obtain continuous pores at a general draft ratio. The resulting porous membrane has sufficient air permeability for use in sanitary materials and building materials.

In addition, in order to improve the rigidity of the crystalline polypropylene (A) which is a matrix polymer and to easily generate uniform and fine pores in the copolymer (B) region dispersed in the crystalline polypropylene (A), The cooling of the film-like molded product to be extruded is desirably slow cooling, and the cooling roll temperature is desirably 60 to 120 ° C, more preferably 70 to 110 ° C. When the roll temperature is less than 60 ° C., it is difficult to obtain the desired porosity, and when it exceeds 120 ° C., the molten resin tends to adhere to the roll, resulting in poor productivity.

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 μm 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.

Furthermore, the polyolefin resin porous film of the present invention is obtained by coextruding a resin composition containing a known inorganic filler, organic filler, etc. with the resin composition for forming a polyolefin resin porous film of the present invention as a film-shaped molded product. It doesn't matter. In this case, the polymer constituting the resin composition containing a filler or the like is preferably a polyolefin resin such as a polypropylene resin or a polyethylene resin from the viewpoint of compatibility.

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 80 to 150 ° C. for about 1 to 30 minutes with a heated air circulation oven or a heating roll.

(ii) Stretching process The film-shaped molded product formed in the film-forming process is then stretched in at least one of the machine direction (MD) direction or the transverse (TD) direction, and into the crystalline polypropylene (A). Fine pores communicating with the finely dispersed 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. Thus, the production method of the present invention is a single component stretching method in which pores are expressed by fibrillation between lamellar crystals of a crystalline polyolefin (A), such as complicated extraction and drying steps such as a mixed extraction method. In addition to eliminating the need for a crystallization step by heat treatment after film formation as seen in Fig. 1, the stretchability is poor and the average pore size is large in the case of the multicomponent stretching method that creates voids at the interface between the matrix polymer and the filler. The problems such as easy and low porosity are greatly improved, and a porous film having an arbitrary average pore diameter or porosity can be provided with excellent productivity.

In addition to the uniaxial stretching method for stretching in one direction, the stretching method includes a sequential biaxial stretching method for stretching in one direction and then stretching in the other direction, a simultaneous biaxial stretching method for simultaneously stretching in the longitudinal and transverse directions, and uniaxial There are a method of performing multistage stretching in the 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 process, even a film-shaped molded product formed at a low draft ratio is a finely dispersed copolymer (in the crystalline polypropylene (A)). B) 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. A sequential biaxial stretching method in which stretching in the longitudinal direction in the first stage 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 T _mα of the propylene-α-olefin copolymer (B), and a temperature range of 10 to 100 ° C. is preferably used. It has been found that by making (C) a specific composition, the stretchability in these low temperature regions is excellent. In addition, the draw ratio is not particularly limited and is determined based on the second-stage drawing conditions performed as necessary and the required characteristics of the use of the porous membrane. When the MFR ratio is 1 to 10, the MFR ratio is 10 or more. Since the stretchability is excellent as compared with the case of 1,000 or less, it is usually in the range of 1.5 to 7 times. When the MFR ratio is greater than 10 and 1,000 or less, the draw ratio is usually in the range 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 50 times, and more preferably 4 to 40 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 necessary. The second-stage stretching temperature is preferably lower by 10 ° C. or more than the melting point _Tmc of the crystalline polypropylene (A). Moreover, when this _{extending | stretching} temperature is higher than melting _| fusing point Tm (alpha) of a propylene-alpha-olefin copolymer (B), there exists a tendency for the porosity not to increase so much and to reduce the thickness of the porous film obtained. Furthermore, when the _stretching temperature is lower than T _mα , the porosity increases, but the thickness tends not to decrease much.

The draw ratio of the second stage is determined by the required characteristics of the use of the porous membrane. When the MFR ratio is 1 to 10, the drawability is higher than when the MFR ratio is greater than 10 and 1,000 or less. Since it is excellent, it is usually in the range of 1.5 to 7 times. When the MFR ratio is greater than 10 and 1,000 or less, the draw ratio is usually in the range of 1.5 to 4 times.
When the draw ratio is within the above range, the drawing effect is sufficient, and there is no possibility that productivity is lowered due to the drawing being cut.

It is preferable that the membrane-shaped molded product that has been formed into pores by the above stretching step and then becomes porous is then heat-treated. This heat treatment is mainly intended for heat fixation for maintaining the formed pores, and is usually carried out on heating rolls, between heating rolls or through a hot air circulating furnace.

In this heat treatment (heat setting), the film-like molded product that has become porous while maintaining the stretched state is heated to a temperature 5 to 60 ° C. lower than the melting point T _mc of the crystalline polypropylene (A). It is carried out by setting it to 50%. When the heating temperature is higher than the above upper limit temperature, the formed pores may be clogged, and when the temperature is lower than the lower limit temperature, heat fixation tends to be insufficient, and the pores are closed later, In addition, when used as a polyolefin resin porous membrane, thermal shrinkage easily occurs due to temperature change.

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%, and more preferably 50 to 80%. If the porosity is in 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. A coating film can be formed.

The polyolefin resin porous membrane obtained by the above method is a moisture permeable waterproof material such as a filtration membrane or separation membrane for air purification or water treatment, a separator for batteries or electrolysis, a building material or clothing, as in the case of conventional porous membranes. It can be used in various fields such as applications.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention concretely, this invention is not limited by these.
The polyolefin resin (C) used in Examples and Comparative Examples polymerizes crystalline polypropylene (A) at the first stage by a continuous polymerization method, and propylene-α-olefin copolymer (B) at the second stage. It was obtained by polymerizing (propylene-ethylene copolymer).
In addition, the measuring method and evaluation method used by the Example and the comparative example are as follows.

(1) Porosity: The bulk specific gravity is obtained from a stretched porous membrane sample 100 × 100 mm, and from the non-porous sample 100 × 100 mm before stretching, an automatic hydrometer DENSIMTER, D manufactured by Toyo Seiki Seisakusho Co., Ltd. The true specific gravity was determined at -S, and the porosity was determined from the following formula.
Porosity (%) = (1-bulk specific gravity / true specific gravity) × 100

(2) 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.

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

(4) Melt flow rate (MFR): Measured in accordance with JIS K 7210 under conditions of a temperature of 230 ° C. and a load of 21.18N.

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

(6) Stretchability: A test piece having a dimension of 40 mm in width and 100 mm in length and having the length direction as the longitudinal direction (MD) or the 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.

1) Preparation of porous film-forming resin composition (E) Using polyolefin resin (C) shown in Example 1 of Table 1 as the α-crystal nucleating agent (D) based on the weight of resin composition (E) Sodium-2,2′-methylene-bis (4,6-di-t-butylphenyl) phosphate is 0.3% by weight, tetrakis [methylene-3- (3 ′, 5′-) as a phenolic antioxidant. Di-t-butyl-4′-hydroxyphenyl) propionate] 0.1% by weight of methane, 0.1% by weight of tris (2,4-di-t-butylphenyl) phosphite as a phosphorus antioxidant, 0.1% by weight of calcium stearate as a neutralizing agent is mixed, mixed with a Henschel mixer (trade name), melted and kneaded using a twin screw extruder (caliber 50 mm), pelletized, and resin composition (E) Got.

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 resin composition was melted at an extrusion temperature of 280 ° C. and a discharge rate of 4 kg / h, and the lip clearance was adjusted to 0.20 mm. The film was further extruded into a film shape and cooled and solidified on a cooling roll at 80 ° C. 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 is stretched in the transverse direction (TD direction) under the conditions of a stretching temperature of 23 ° C., a deformation rate of 200% / second, and a stretching ratio of 3 times while constraining the machine direction (MD direction). The polyolefin resin porous membrane was obtained by stretching in the machine direction (MD direction) under the conditions of a stretching temperature of 100 ° C., a deformation rate of 1,000% / second, and a stretching ratio of 3 times. 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 polyolefin resin (C) shown in Example 2 of Table 1 was used. Table 1 shows the stretchability of the film-like molded product and the characteristics of the porous film.

A polyolefin resin porous membrane was obtained in the same manner as in Example 1 except that the polyolefin resin (C) shown in Example 3 of Table 1 was used. Table 1 shows the stretchability of the film-like molded product and the characteristics of the porous film.

A polyolefin resin porous membrane was obtained according to Example 1 except that the polyolefin resin (C) shown in Example 4 of Table 1 was used. Table 1 shows the stretchability of the film-like molded product and the characteristics of the porous film.

( Comparative Example 1 )
A polyolefin resin porous membrane was obtained according to Example 1 using the polyolefin resin (C) shown in Comparative Example 1 of Table 1. In Comparative Example 1 , when the film was stretched in the transverse direction, there were many breaks in the stretching under the condition of a stretching ratio of 3 times, so that the polyolefin resin porous film was stretched at a stretching ratio of 2.5 times.
Table 1 shows the stretchability of the film-like molded product and the characteristics of the porous film.

( Comparative Example 2 )
Instead of the polyolefin resin (C), the polyolefin resin shown in Comparative Example 2 in Table 1 was used to obtain a polyolefin resin porous membrane according to Example 1. Table 1 shows the stretchability of the film-like molded product and the characteristics of the porous film.

( Comparative Example 3 )
A polyolefin resin porous membrane was prepared in accordance with Example 1 using the polyolefin resin (C) shown in Comparative Example 3 of Table 1. In Comparative Example 3 , when stretched in the transverse direction, stretching breakage occurred at a stretch ratio of less than 1.5 times, resulting in poor stretchability. It was not obtained.

( Comparative Example 4 )
Instead of the polyolefin resin (C), a propylene homopolymer (MFR of 2.5 g / 10)
50% by weight of crystalline polypropylene of min) and ethylene homopolymer (MFR of 0.75 g)
/ Min (HDPE at a temperature of 190 ° C. and a load of 21.18 N)) of 50% by weight,
A polyolefin resin porous membrane was prepared according to Example 1. However, when the film was stretched in the transverse direction, the film was inferior in stretchability due to breakage of stretching at a stretch ratio of less than 1.5 times . The characteristics as a porous film could not be obtained by slight stretching at a transverse stretching ratio of about 1.2 times.

The same process as in Example 4 was performed except that the lip clearance of the die was adjusted to 0.6 mm in the film forming process. Table 2 shows the stretchability of the film-like molded product and the characteristics of the porous film.

The same process as in Example 4 was performed except that the lip clearance of the die was adjusted to 1.2 mm in the film forming process. Table 2 shows the stretchability of the film-like molded product and the characteristics of the porous film.

( Comparative Example 5 )
The same process as in Example 4 was performed except that the lip clearance of the die was adjusted to 2.0 mm in the film forming process. Table 2 shows the stretchability of the film-like molded product and the characteristics of the porous film.

The same operation as in Example 4 was carried out except that the transverse stretching ratio was 5 times and the longitudinal stretching ratio was 6 times. Table 2 shows the stretchability of the film-like molded product and the characteristics of the porous film.

The same operation as in Example 4 was performed except that the transverse stretching temperature was 80 ° C. Table 2 shows the stretchability of the film-like molded product and the characteristics of the porous film.

( Comparative Example 6 )
The same operation as in Example 4 was performed except that the transverse stretching temperature was 120 ° C. Table 2 shows the stretchability of the film-like molded product and the characteristics of the porous film.

Except that we did not stretch in the machine direction, only in the transverse direction,
The same operation as in Example 4 was performed. Table 2 shows the stretchability of the film-like molded product and the characteristics of the porous film.

The same operation as in Example 4 was carried out except that the addition amount of the α crystal nucleating agent (D) was 0.05% by weight. Table 3 shows the stretchability of the film-shaped molded product and the characteristics of the porous film.

The same operation as in Example 4 was carried out except that the addition amount of the α crystal nucleating agent (D) was 2 wt%. Table 3 shows the stretchability of the film-shaped molded product and the characteristics of the porous film.

( Comparative Example 7 )
The same operation as in Example 4 was carried out except that the α crystal nucleating agent (D) was not added. Table 3 shows the stretchability of the film-shaped molded product and the characteristics of the porous film.

( Comparative Example 8 )
The same operation as in Example 4 was carried out except that the addition amount of the α crystal nucleating agent (D) was 0.001% by weight. Table 3 shows the stretchability of the film-shaped molded product and the characteristics of the porous film. The effect of adding the α crystal nucleating agent (D) was not observed.

( Comparative Example 9 )
The same operation as in Example 4 was carried out except that the addition amount of the α crystal nucleating agent (D) was 8 wt%. Table 3 shows the stretchability of the film-shaped molded product and the characteristics of the porous film. The effect due to the addition of the α crystal nucleating agent (D) reaches its peak and no advantage is recognized, which is economically disadvantageous.

The same procedure as in Example 1 was performed except that the polyolefin resin (C) shown in Example 12 of Table 4 was used and the lip clearance of the T die was adjusted to 0.4 mm and the transverse stretching temperature was set to 80 ° C. did. In Example 12 , when the film was stretched in the transverse direction, there were many breaks in the stretching under the condition of a stretching ratio of 3 times, so that the polyolefin resin porous film was stretched at a stretching ratio of 2.5 times. Table 4 shows the stretchability of the film-like molded product and the characteristics of the porous film.

A polyolefin resin porous membrane was obtained according to Example 12 except that the polyolefin resin (C) shown in Example 13 of Table 4 was used. Table 4 shows the stretchability of the film-like molded product and the characteristics of the porous film.

A polyolefin resin porous membrane was obtained according to Example 12 except that the polyolefin resin (C) shown in Example 14 of Table 4 was used. Table 4 shows the stretchability of the film-like molded product and the characteristics of the porous film.

A polyolefin resin porous membrane was obtained according to Example 12 except that the polyolefin resin (C) shown in Example 15 of Table 4 was used. Table 4 shows the stretchability of the film-like molded product and the characteristics of the porous film.

Example 13 except that the lip clearance of the T die was 0.2 mm in the film forming process.
According to the above, a polyolefin resin porous membrane was obtained. Table 5 shows the stretchability of the film-like molded product and the characteristics of the porous film.

Example 13 except that the lip clearance of the T die was set to 1.2 mm in the film forming process.
According to the above, a polyolefin resin porous membrane was obtained. Table 5 shows the stretchability of the film-like molded product and the characteristics of the porous film.

A polyolefin resin porous membrane was obtained in the same manner as in Example 13 except that the stretching in the longitudinal direction was not carried out and only the stretching in the transverse direction was carried out . Table 5 shows the stretchability of the film-like molded product and the characteristics of the porous film.

According to Example 13 , except that in the stretching step, the first stage stretching was stretched 3 times in the longitudinal direction at a stretching temperature of 23 ° C., and the second stage stretching was stretched 3 times in the transverse direction at a stretching temperature of 80 ° C. Thus, a polyolefin resin porous membrane was obtained. Table 5 shows the stretchability of the film-like molded product and the characteristics of the porous film.

( Comparative Example 10 )
Example 13 except that the lip clearance of the T die was set to 2.0 mm in the film forming process.
According to the above, a polyolefin resin porous membrane was obtained. Table 5 shows the stretchability of the film-like molded product and the characteristics of the porous film.

( Comparative Example 11 )
A polyolefin resin porous membrane was obtained in the same manner as in Example 13 except that the temperature of the cooling roll was set to 30 ° C. in the film forming step. Table 5 shows the stretchability of the film-like molded product and the characteristics of the porous film.

The same operation as in Example 13 was carried out except that the addition amount of the α crystal nucleating agent (D) was 0.05% by weight. Table 6 shows the stretchability of the film-like molded product and the characteristics of the porous film.

The same operation as in Example 13 was carried out except that the addition amount of the α crystal nucleating agent (D) was 2 wt%. Table 6 shows the stretchability of the film-like molded product and the characteristics of the porous film.

( Comparative Example 12 )
The same operation as in Example 13 was carried out except that the α crystal nucleating agent (D) was not added. Table 6 shows the stretchability of the film-like molded product and the characteristics of the porous film.

( Comparative Example 13 )
The same operation as in Example 13 was carried out except that the addition amount of the α crystal nucleating agent (D) was 0.001% by weight. The properties of the film-like molded product are shown in Table 6. The effect of adding the α crystal nucleating agent (D) was not observed.

( Comparative Example 14 )
The same operation as in Example 13 was carried out except that the addition amount of the α crystal nucleating agent (D) was 8 wt%. The properties of the film-like molded product are shown in Table 6. The effect due to the addition of the α crystal nucleating agent (D) reaches its peak and no advantage is recognized, which is economically disadvantageous.

(Table 1)

(Table 2)

(Table 3)

(Table 4)

(Table 5)

(Table 6)

The polyolefin resin porous membrane of the present invention is suitably used in the field of building materials such as battery separators, separation membranes and breathable waterproof materials, and the field of hygiene materials such as breathable sheets for disposable diapers.

Claims (14)

An α crystal nucleating agent (D) is added to a polyolefin resin (C) composed of crystalline polypropylene (A) and a propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A). The resin composition (E) blended in an amount of 0.01 to 5% by weight based on the weight of the composition (E) is melted and kneaded to form a film-like melt, and the film-like melt has a lip clearance of 0.2 to 1. A porous film formed by extruding into a film shape from a T die adjusted to 2 mm and then forming the film shape in at least one direction, and the polyolefin resin (C) is It consists crystalline polypropylene (a) 30 to 90 wt% of propylene-.alpha.-olefin copolymer (B) and 10 to 70 wt%, propylene with a melt flow rate _{MFR PP} of the crystalline polypropylene (a)-.alpha.- The melt flow rate _{MFR RC} melt flow rate ratio _MFR PP / _{MFR RC} of olefin copolymer (B) is 0.1 to 10, the draft ratio at the time of forming the film-like melt film-shaped molded product is 1 A polyolefin resin porous membrane having a pore that communicates with the copolymer (B) region, having a temperature range of 10 to 100 ° C in a first-stage stretching temperature when stretching in at least one direction. The polyolefin resin porous membrane according to claim 1, wherein the melt flow rate ratio MFR _PP / MFR _RC is 0.2 to 5. The polyolefin resin porous membrane according to claim 1 or 2, wherein a draft ratio when the film-shaped melt is formed into a film-shaped molded product is in a range of 1 to 3 . The polyolefin resin (C) is composed of 40 to 70% by weight of a crystalline polypropylene (A) and 30 to 60% by weight of a polypropylene-α-olefin copolymer (B). 2. A polyolefin resin porous membrane according to item 1. The polyolefin resin porous membrane according to any one of claims 1 to 4, wherein the propylene content of the propylene-α-olefin copolymer (B) is 30 to 80% by weight. The polyolefin resin porous membrane according to any one of claims 1 to 5, wherein the propylene content of the propylene-α-olefin copolymer (B) is 40 to 70% by weight. The polyolefin resin (C) is obtained by a multistage polymerization method including the steps of producing a crystalline polypropylene (A) in the first stage and continuously producing a propylene-α-olefin copolymer (B) in the second stage. The polyolefin resin porous membrane according to any one of claims 1 to 6, wherein the porous membrane is a polyolefin resin porous membrane. The air permeability resistance (Gurley) of the porous membrane is 1 to 1,000 seconds / 100 ml, and the moisture permeability is 2,000 to 20,000 g / m. ² The polyolefin resin porous membrane according to any one of claims 1 to 7, which is 24h. An α crystal nucleating agent (D) is added to a polyolefin resin (C) composed of crystalline polypropylene (A) and a propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A). After melting and kneading the resin composition (E) blended in an amount of 0.01 to 5% by weight based on the weight of the composition (E) to form a film-like melt, and forming the film-like melt into a film-like molded product , A porous film formed by stretching the film-shaped product in at least one direction, wherein the polyolefin resin (C) is 30 to 70% by weight of crystalline polypropylene (A) and a propylene-α-olefin copolymer. (B) Melt flow rate of 30 to 70% by weight of melt flow rate MFR _PP of crystalline polypropylene (A) and melt flow rate MFR _RC of propylene-α-olefin copolymer (B) The film ratio MFR _PP / MFR _RC is greater than 10 and 1,000 or less, and the film-like melt is extruded into a film shape from a T-die having a lip clearance adjusted to 0.2 to 1.2 mm to form a film-like molded article. The draft ratio at the time of molding is in the range of 1 to 10, the stretching temperature at the first stage when stretching in at least one direction is in the temperature range of 10 to 100 ° C., and the fine ratio communicated with the copolymer (B) region. Polyolefin resin porous membrane having pores. The polyolefin resin porous membrane according to claim 9, wherein a draft ratio when the film-shaped melt is formed into a film-shaped molded product is in the range of 1 to 5. The polyolefin resin porous membrane according to claim 9 or 10, wherein the propylene content of the propylene-α-olefin copolymer (B) is 30 to 80% by weight. The polyolefin resin porous membrane according to any one of claims 9 to 11, wherein the propylene content of the propylene-α-olefin copolymer (B) is 40 to 70 wt%. The polyolefin resin (C) is obtained by a multistage polymerization method including the steps of producing a crystalline polypropylene (A) in the first stage and continuously producing a propylene-α-olefin copolymer (B) in the second stage. The polyolefin resin porous membrane according to any one of claims 9 to 12, wherein the porous membrane is a polyolefin resin porous membrane. The air permeability resistance (Gurley) of the porous membrane is 10 to 10,000 seconds / 100 ml, and the moisture permeability is 1,000 to 15,000 g / m. ² The polyolefin resin porous membrane according to any one of claims 9 to 13, which is 24h.