JP4797813B2 - 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 It is widely used for sanitary materials such as bag 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 polyolefin, is stretched in at least one direction, and filled with a matrix polymer. A method of generating voids (pores) at the interface of the agent (hereinafter referred to as “multi-component stretching method”) is disclosed.
(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) described above, an inorganic filler mixed system and an organic filler mixed system are known. However, in the former case, it is necessary to increase the amount of the inorganic filler added. There were problems such as deterioration of the original physical properties and texture of certain polyolefins and weakness against acids and alkalis. Further, in the latter organic filler mixed system, not only the physical properties and texture of the polyolefin are lowered, but also fine dispersion of the organic filler in the matrix polymer is difficult, and the porous membrane 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 crystalline lamellae, and further, since the highly oriented and highly crystallized sheet is stretched, the obtained porous film is easy to tear. 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.

  On the other hand, as a method for easily obtaining a porous membrane, component A composed of ethylene-propylene block copolymer, component B composed of propylene homopolymer or random copolymer, and component C composed of low molecular weight polypropylene, and component D composed of calcium carbonate as necessary. And a porous film made of a polymer composition to which component E made of beta spherulite 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 therefore is improved by a multi-component system. However, in this component system, pores formed in the porous membrane are improved. Since the diameter is large, it is difficult to reduce the thickness of the porous film, and it is difficult to increase the porosity, and it is difficult to improve the air permeability and moisture permeability. It is difficult to use it for battery separators and microfiltration filters that require high porosity and air permeability.

  The present inventors made it easy to achieve uniform dispersion in the production process by simplifying the resin composition in order to solve the above-mentioned problems associated with conventional polyolefin resin porous membranes. A method (Japanese Patent Application No. 2002-134232, Japanese Patent Application No. 2003-37456) for providing a polyolefin resin porous membrane having a small pore size and a high porosity has been developed.

  However, the polyolefin resin porous membranes of Japanese Patent Application Nos. 2002-134232 and 2003-37456 have good physical properties as a porous property and a battery separator, but have a large pore diameter, a low porosity, As separators for secondary batteries for hybrid vehicles, higher capacity, higher output, and higher strength cannot always be adequately addressed. Further, when the film-like melt was formed into a film-like molded product, sticking / removal to the roll frequently occurred, and the high film-forming stability was not sufficiently satisfactory.

JP-A-4-309546 JP-A-8-208862

  The present invention can realize high capacity and large output when used as a separator, and has excellent stability during film formation, a small pore diameter, a high porosity, and a polyolefin resin porous membrane excellent in strength It is an issue to provide.

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). And a resin composition (F) containing high-density polyethylene (D) having a weight average molecular weight Mw in the range of 3 × 10 ⁴ to 1 × 10 ⁷ to melt and knead to form a film-like melt, and the film-like melt A porous film formed by molding a product into a film-shaped product in the range of a draft ratio of 1 to 10 and then stretching the film-shaped product in at least one direction, and in the copolymer (B) region The inventors have found that this problem can be solved by a polyolefin resin porous membrane having continuous pores, and have completed the present invention based on this finding. 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.

1. Polyolefin resin (C) 60 to 95 wt% comprising 30 to 70 wt% crystalline polypropylene (A) and 30 to 70 wt% propylene-α-olefin copolymer (B) dispersed in crystalline polypropylene (A) % And a resin composition (F) containing 5 to 40% by weight of high-density polyethylene (D) having a weight average molecular weight Mw in the range of 3 × 10 ⁴ to 1 × 10 ⁷ and melted into a film A film formed by forming the film-shaped melt into a film-shaped molded product in a draft ratio of 1 to 10 and then stretching the film-shaped molded product in at least one direction. Polyolefin resin porous membrane having pores.

2. Polyolefin resin (C) 30 to 95 wt% comprising 30 to 70 wt% crystalline polypropylene (A) and 30 to 70 wt% propylene-α-olefin copolymer (B) dispersed in crystalline polypropylene (A) %, A high-density polyethylene (D) having a weight average molecular weight Mw in the range of 3 × 10 ⁴ to 1 × 10 ⁷ , and a melt mass flow rate MFR _(E) of 0.1 g / 10 min to 2 g / min. A resin composition (F) containing 0 to 30% by weight of crystalline polypropylene (E) in a range of less than 10 min is melt-kneaded to form a film-like melt, and the film-like melt has a draft ratio of 1 to 10 A polyolefin resin porous film having a continuous pore, which is a film formed by forming a film-shaped molded article within a range and then stretching the film-shaped molded article in at least one direction.

3. Melt mass flow rate MFR _PP of crystalline polypropylene (A) and melt mass flow rate MFR _RC of propylene-α-olefin copolymer (B) range of MFR _PP / MFR _RC greater than 10 and 1,000 or less 3. The polyolefin resin porous membrane according to 1 or 2 above.

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 5.

5. The polyolefin resin porous membrane according to any one of 1 to 4 above, wherein the propylene content of the propylene-α-olefin copolymer (B) is 30 to 80% by weight.

6). The polyolefin resin porous membrane according to any one of 1 to 4 above, wherein the propylene content of the propylene-α-olefin copolymer (B) is 40 to 70% by weight.

7). 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 1 to 6 above.

8). 8. The air permeability resistance (Gurley) of the porous membrane is in the range of 10 to 20,000 s / 100 ml, and the moisture permeability is in the range of 200 to 10,000 g / m ² · 24 h. Polyolefin polyolefin resin porous membrane.

9. The polyolefin resin porous membrane according to any one of 1 to 8 above, wherein the film-forming method for forming the resin composition (F) into a film-like molded product is a calendar molding method.

10. Polyolefin resin (C) 60 to 95 wt% comprising 30 to 90 wt% crystalline polypropylene (A) and 10 to 70 wt% propylene-α-olefin copolymer (B) dispersed in crystalline polypropylene (A) % And a resin composition (F) containing 5 to 40% by weight of high-density polyethylene (D) having a weight average molecular weight Mw in the range of 3 × 10 ⁴ to 1 × 10 ⁷ and melted into a film A film formed by forming the film-shaped melt into a film-shaped molded product in a draft ratio of 1 to 10 and then stretching the film-shaped molded product in at least one direction. Polyolefin resin porous membrane having pores.

11. The above 10 wherein the melt mass flow rate MFR _PP of the crystalline polypropylene (A) and the melt mass flow rate MFR _RC of the propylene-α-olefin copolymer (B) is 0.1 to 10 in the melt mass flow rate ratio MFR _PP / MFR _RC. The polyolefin resin porous membrane according to Item.

12 12. The polyolefin resin porous membrane according to 10 or 11 above, wherein the draft ratio when the film-shaped melt is formed into a film-shaped molded product is in the range of 1 to 3.

13. The polyolefin resin porous membrane according to any one of the items 10 to 12, wherein the melt mass flow rate ratio MFR _PP / MFR _RC is in the range of 0.2 to 5.

14 14. The polyolefin according to any one of 10 to 13, wherein the polyolefin resin (C) comprises 40 to 70% by weight of crystalline polypropylene (A) and 30 to 60% by weight of the polypropylene-α-olefin copolymer (B). Resin porous membrane.

15. 15. The polyolefin resin porous membrane according to any one of 10 to 14, wherein the propylene content of the propylene-α-olefin copolymer (B) is 30 to 80% by weight.

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

17. 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 10 to 16 above.

18. Any one of the above 10 to 17 items, wherein the air permeability resistance (Gurley) of the porous membrane is in the range of 1 to 2,000 s / 100 ml, and the moisture permeability is in the range of 1,000 to 20,000 g / m ² · 24 h. The polyolefin resin porous membrane described.

19. 19. The polyolefin resin porous membrane according to any one of 10 to 18 above, wherein a film forming method for forming the resin composition (F) into a film-like molded product is a calender molding method.

  The polyolefin resin porous membrane of the present invention is specified in a specific polypropylene resin (C) in which a propylene-α-olefin copolymer (B) is finely dispersed in a crystalline polypropylene (A) under a specific processing method. In combination with the high-density polyethylene (D), the stretchability at low temperatures is improved, and the lamellar crystals in the copolymer (B) region are developed, so that the interlamellar cleavage of the copolymer (B) occurs. Is a porous membrane excellent in porous membrane properties such as porosity, air permeability and pore diameter. Further, 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 requires a separation membrane, a battery separator, and a breathable waterproof material that require continuous fine pores. It can use suitably for uses, such as.

Hereinafter, embodiments of the present invention will be described.
(1) Resin composition (F)
The polyolefin resin porous membrane of the present invention comprises a crystalline polypropylene (A) and a propylene-α-olefin copolymer (B), and the copolymer (B) is used as a domain in the crystalline polypropylene (A) matrix. A resin composition (F) comprising a finely dispersed polyolefin resin (C) and high-density polyethylene (D) is used. Further, in order to reduce the pore diameter of the polyolefin resin porous membrane, crystalline polypropylene having a specific melt mass flow rate instead of a part of the polyolefin resin (C) or high-density polyethylene (D) of the resin composition (F) (E) is used.

(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, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4- Examples thereof include methyl-1-pentene and 3-methyl-1-pentene. 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.

In addition, the melt mass flow rate MFR _PP of crystalline polypropylene (A) is in the range of 0.1 to 50 g / 10 min when crystalline polypropylene (E) is not used in the resin composition (F) because of the stability of film formation. The thing of the range of 2-50 g / 10min is preferable when crystalline polypropylene (E) is used for a resin composition (F).

(ii) Propylene-α-olefin copolymer (B)
The propylene-α-olefin 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 large.

  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 mass flow rate MFR _RC of the propylene-α-olefin copolymer (B) is not particularly limited, but a range of 0.05 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 propylene-α-olefin copolymer (B). Melt mass flow rate MFR _PP of crystalline polypropylene (A) and melt mass flow rate MFR _{RC of} propylene-α-olefin copolymer (B) MFR _PP / MFR _RC (hereinafter referred to as “MFR ratio”) Is not particularly limited, but is preferably 0.1 to 1,000 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.

(Iv) High density polyethylene (D)
The high-density polyethylene (D) is a polymer mainly composed of ethylene polymerized units, preferably polyethylene having 90% by weight or more of ethylene polymerized units. Specifically, it may be a homopolymer of ethylene or a copolymer of 90% by weight or more of ethylene polymer units and 10% by weight or less of α-olefin. Examples of the α-olefin used when “high density polyethylene” (E) is a copolymer include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4 -Methyl-1-pentene, 3-methyl-1-pentene and the like can be mentioned. Of these, it is preferable from the viewpoint of production cost to use an ethylene homopolymer or a propylene-ethylene copolymer having an ethylene polymer unit content of 90% by weight or more.

By using a specific high-density polyethylene (D) in combination, a lamellar crystal in the copolymer (B) region is developed, and cleavage between the lamellae of the copolymer (B) becomes active, and the porosity, air permeability, The porous membrane characteristics such as the pore diameter are improved. The weight average molecular weight Mw of the high density polyethylene (D) is 3 × 10 ⁴ to 1 × 10 ⁷ . Moreover, the addition amount is 5 to 40 weight%. If the weight average molecular weight Mw and the addition amount are in this range, there is no adhesion to the roll during film formation, and the lamellar crystals in the copolymer (B) region are sufficient, the porosity is improved, and the stretchability is improved. There is no problem.

(V) Crystalline polypropylene (E)
The crystalline polypropylene (E) 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 (E) is a copolymer include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4- Examples thereof include methyl-1-pentene and 3-methyl-1-pentene. 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.

The melt mass flow rate MFR _(E) of the crystalline polypropylene (E) is 0.1 g / 10 min or more and less than 2 g / 10 min, preferably 0.1 to 1.5 g / 10 min. Further, the addition amount is 0.1 to 30% by weight, preferably 5 to 30% by weight. Within this range, there is no problem in stretchability when forming the polyolefin resin porous membrane, and the pore diameter is A small porous film is formed.

In the present invention, when the MFR ratio is 0.1 to 10, the air permeability resistance (Gurley) is 1 to 2,000 s (seconds) / 100 ml, and the moisture permeability is 1,000 to 20,000 g / A porous film of m ² · 24 h can be obtained. In the porous film, according to cross-sectional observation with a scanning electron microscope (SEM), a large number of fine pores of 0.1 to 0.5 μm are connected, and the maximum value of the major axis of the pore diameter is 0.5 μm or less. Fine pores are observed.
When the MFR ratio is greater than 10 and less than or equal to 1,000, obtain a porous membrane having a gas permeability resistance (Gurley) of 10 to 20,000 s / 100 ml and a moisture permeability of 200 to 10,000 g / m ² · 24 h. Can do. In the porous film, according to cross-sectional observation by SEM, a large number of pores of about 0.5 μm are connected, and pores having a maximum major axis of pore diameter of 1.0 μm or less are recognized. Such a porous membrane can be suitably used in the field of building materials such as separation membranes, battery separators and breathable waterproofing materials that require high filtration accuracy, and the field of hygiene materials such as breathable sheets for disposable diapers.

In the case of a battery separator, in order to prevent an abnormal temperature rise due to misuse of the battery or the like to cause an accident such as ignition, the separator does not break the membrane when the temperature reaches a certain level. the difference [Delta] T = T occluded have sought the ability to shut down the current (hereinafter referred to as "shutdown function"), the temperature T _b and closing the pores temperature (hereinafter referred to as "shutdown temperature") T _s to film breakage _Although it is desired to increase the _b- T _s and reduce the shutdown temperature in order to stop the abnormal reaction at an earlier stage and suppress the temperature rise, in the present invention, the MFR ratio is larger than 0.1 and 1 , use in the case of 000 or less, since the difference in film breakage temperature T _b and the shutdown temperature T _s can be 20 ° C. or higher, suitably particularly as a battery separator Can be. The excellent shutdown function as the battery separator is that the MFR ratio is greater than 10 and less than or equal to 1,000, so that the pore size is small and the blockage is easy, and the copolymer (B) itself occupies the region. It is presumed that the cause is that the pore formation is large, the copolymer (B) is strongly entangled with the compatible matrix polymer, and the matrix polymer suppresses the thermal shrinkage of the copolymer (B).

  In the polyolefin resin (C), the content of crystalline polypropylene (A) is 30 to 90% by weight, preferably 40 to 70% by weight, and the content of propylene-α-olefin 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). In the case where 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 preferably 30 to 70% by weight, more preferably 40 to 60% by weight. The content of the -α-olefin copolymer (B) is preferably 70 to 30% by weight, more 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) obtained by polymerization separately and the propylene-α-olefin copolymer (B) by melt kneading or the like. . Specifically, commercially available ethylene-propylene rubber and crystalline polypropylene corresponding to propylene-α-olefin copolymer (B) or copolymer (B) polymerized using a Ziegler-Natta catalyst such as a titanium-supported catalyst ( A method of melting and mixing A) can be exemplified.

  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 1,000 or less, more preferably in the range of 0.2 to 800. 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 between the lamella crystals 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 between the lamella crystals in the copolymer (B) region finely dispersed in the crystalline polypropylene (A). Since the propylene-α-olefin copolymer (B) contains a certain amount or more of a propylene component, the propylene-α-olefin copolymer is compatible with crystalline polypropylene, and high-density polyethylene (D) is compatible with the copolymer (B). Since it has compatibility, a lamellar crystal develops in the copolymer (B) region. Therefore, the interlamellar crystal region in the copolymer (B) region compatible with this crystalline polypropylene (A) is crystalline. Since the strength is lower than that of polypropylene (A), it is presumed that cleavage occurred between lamella crystals in the copolymer (B) region due to stretching stress. This mechanism is fundamentally different from the conventional multi-component stretching method in which inorganic fillers or different types of polymers are mixed and stretched. As a result, the resulting porous membrane has a small pore diameter and a high porosity and air permeability. 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 between the lamellar crystals in the copolymer (B) region include pores caused by cleavage between the lamellar crystals and the lamellar crystals in the copolymer (B) region, and crystalline polypropylene (A). And pores due to interfacial peeling that occur in the boundary region between the lamella crystals in the copolymer (B) 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 crystalline polypropylene (A) and MFR _RC of propylene-α-olefin 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)

(2) Resin Composition for Forming Polyolefin Resin Porous Film The resin composition that is a molding material of the film-shaped molded product for forming the polyolefin resin porous film of the present invention is not only a resin composition (F) but also a normal one. 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 fillers A lubricant, an antiblocking agent, an antibacterial agent, an antifungal agent, a pigment 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.

  In addition, the resin composition for forming the polyolefin resin porous membrane of the present invention includes a propylene homopolymer, a monomer 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 of the above and other olefin resins such as polyethylene resin, polybutene resin, and polymethylpentene resin may be used in combination.

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

  The method of blending the resin composition (F) and the additive 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. And a method of pelletizing using a normal single-screw extruder or a twin-screw extruder.

(3) Formation of polyolefin resin porous film The polyolefin resin porous film of the present invention is obtained by melting and kneading the resin composition mainly composed of the resin composition (F) to form a film-shaped melt. After forming into a film-shaped molded product within 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.

(i) Film-forming process In the film-forming process for obtaining a film-shaped molded product from the resin composition, known methods such as an inflation film molding method, a T-die film molding method, and a calendar molding method are used. A calendar molding method in which the ratio can be easily controlled is preferably used.

  In the case of an inflation film molding method and a T-die film molding method, the resin composition can be formed at an extrusion molding temperature of 180 ° C. or higher, but the purpose is to reduce the pressure inside the die and reduce the draft ratio described later. Further, the rigidity of the crystalline polypropylene (A), which is a matrix polymer, is improved so that the lamella crystals in the region of the propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A) are uniformly and finely divided. An extrusion temperature of 220-300 ° C. is preferably used to facilitate the formation of holes.

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 when forming the resin composition is 1 to 10, and the resulting film-like molded product is excellent in stretchability, and fine continuous pores are easily formed by stretching. Become.

  In the case of the calendar molding method, the preliminary kneading of the composition before charging into the calendar is a method using a Banbury mixer, a pre-kneading roll, a method using a monoaxial, biaxial, planetary, etc. A known method is used, but the rigidity of the above-described matrix polymer crystalline polypropylene (A) is improved and the propylene-α-olefin copolymer (B) region dispersed in the crystalline polypropylene (A) is dispersed. In order to easily form uniform and fine pores between lamella crystals, a temperature of 220 to 300 ° C. is preferably used, and in order to put the pre-kneaded material into a stable calendar while maintaining the temperature, A strainer is preferably used.

In the calendering method, a known calender apparatus such as 2 to 6 rolls and L-type, reverse L-type, Z-type, and roll diameters can be used. For thin film formation, four or more rolls are preferably used from the viewpoint of thickness accuracy, and the temperature of the calendar roll is preferably 160 to 220 ° C.
The film from which the final roll has been peeled is taken up by a take-off roll. The ratio (V1 / V0) between the rotation surface speed (V0) of the calendar final roll and the rotation surface speed (V1) of the take-off roll is defined as the draft ratio. In this case as well, in this case, in the present invention, the draft ratio when forming the resin composition is 1 to 10, and the film-like molded product obtained by this has excellent stretchability and is fine by stretching. Communication pores are easily formed.

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.

Further, the rigidity of the crystalline polypropylene (A) which is a matrix polymer is improved, and uniform and fine between lamella crystals in the region of the propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A). In order to facilitate the formation of pores, it is desirable to cool the film-shaped molded product extruded from the die lip slowly, and in the case of inflation molding, an air-cooled cooling method is desirable. In the case of the T-die film molding method It is desirable to cool at a take-off roll of 100 to 150 ° C. and a cooling roll temperature of 70 to 120 ° C.
Moreover, in the case of the calendering method, it is desirable to cool in the range of the take-off roll 100-150 degreeC and the temperature of a cooling roll 70-120 degreeC. When the take-off roll temperature is less than 100 ° C. and the cooling roll temperature is less than 60 ° C., it is difficult to obtain the desired porosity. On the other hand, when the cooling roll temperature exceeds 130 ° C., the molten resin tends to adhere to the roll, resulting in poor productivity. There is a problem.

  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 are composed of 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 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 between the lamellar crystals in the finely dispersed propylene-α-olefin 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 crystalline polyolefin (A), such as complicated extraction and drying steps such as 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 and porosity can be provided with excellent productivity.

  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 A method of performing multi-stage stretching in a uniaxial direction or a method of further stretching after sequential biaxial stretching or simultaneous biaxial stretching may be used, and any method may be used. Since the film-shaped molded product is drafted in the film-forming step, even if the film-shaped molded product is formed at a low draft ratio, ethylene-α- finely dispersed in the crystalline polypropylene (A) is used. The olefin copolymer (B) is oriented along the resin flow direction, that is, the longitudinal (MD) direction, and the first stage stretching is performed by a uniaxial stretching method in the transverse direction or a simultaneous biaxial stretching method in the longitudinal and transverse directions. However, it is possible to use a sequential biaxial stretching method in which stretching in the longitudinal direction is performed in the first stage and stretching in the lateral direction is performed in the second stage.

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 the product (F) a specific composition, it is excellent in low-temperature stretchability in these temperature ranges. The stretching ratio is not particularly limited and is determined from the second stage stretching conditions performed as necessary and the required properties for the use of the porous membrane, but is usually in the range of 1.5 to 7 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 10 ° C. or more lower than the melting point _Tmc of the high-density polyethylene (D). 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 in the second stage is determined by the required characteristics of the porous membrane, but is usually in the range of 1.5 to 7 times.
When the draw ratio is less than 1.5 times, the drawing effect is insufficient, and when it exceeds 7 times, the drawing is frequently broken and the productivity may be lowered.

  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 high-density polyethylene (D). 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 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. In addition, the measurement method and evaluation method used 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) Average pore diameter and maximum pore diameter: In accordance with ASTM F316, the pore diameter of the polyolefin resin porous membrane was measured using a Perm-Porometer manufactured by PMI, and the average flow pore diameter was determined as the average pore diameter and bubble point pore diameter. Was the maximum pore diameter.

(3) Melt mass flow rate: MFR was measured under the conditions of a temperature of 230 ° C. and a nominal load of 2.16 kg according to JIS K 7210. MI was measured according to JIS K 7210 under conditions of a temperature of 190 ° C. and a nominal load of 2.16 kg.

(4) Air permeability resistance (Gurley): According to JIS P 8117, 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.).

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

(6) Film-forming property: The film-forming property was evaluated based on the frequency of adhesion and removal to the calendar roll when the film was formed by the calendar method.
○: No sticking / removal to the calendar roll occurred in 1 hour.
Δ: Adhesion / removal to the calendar roll occurred 1 to 10 times in 1 hour.
X: Adhesion and removal to the calendar roll occurred 10 times or more in 1 hour.

(7) A test piece having a length of 40 mm and a length of 100 mm and having the longitudinal 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.
○: A stretching ratio of 5 times or more is possible. Δ: A stretching ratio of 2 to 5 times or more is possible.

Example 1
1) Creation of Resin Composition for Forming Porous Film To resin composition (F) shown in Example 1 of Table 1, tetrakis [methylene-3- (3 ′, 5′-di-t-) was added as a phenolic antioxidant. 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, and as a neutralizing agent 0.1% by weight of calcium stearate, 0.4% of special fatty acid ester (trade name: Riquester EW-100, Riken Vitamin Co., Ltd.) as a lubricant, mixed with a Henschel mixer (trade name), biaxial extrusion Using a machine (caliber 50 mm), the mixture was melt-kneaded and pelletized to obtain a porous film-forming resin composition. The polyolefin resin (C) used here was obtained by polymerizing crystalline polypropylene (A) in the first stage by a continuous polymerization method, and propylene-α-olefin copolymer (B) (propylene-ethylene in the second stage. Copolymer) was obtained by polymerization.

2) Creation of porous film [Film forming step / Creation of unstretched film-like molded product]
Using a planetary roller extruder, the pellet-shaped resin composition (F) is melted at an extrusion temperature of 230 ° C. and a discharge rate of 15 kg / h, and is placed in a bar shape from the head on four calender rolls arranged in an inverted L shape. And cooled and solidified on a take-off roll and an annealing roll to prepare a film-like molded product having a width of 600 mm and a thickness of 100 μm. The calender roll temperature, take-off roll temperature, and annealing roll temperature were 190 ° C., 140 ° C., and 90 ° C., respectively, and the draft ratio of the surface speed ratio of the final calendar roll and take-off roll was 2. Table 1 shows the evaluation results of the film formability and stretchability of the obtained film-like molded product.

3) [Stretching process / Creation of porous film]
The film-shaped molded product was stretched in the MD direction in a sequential stretching apparatus manufactured by Mitsubishi Heavy Industries, Ltd. under conditions of a stretching temperature of 23 ° C. and a stretching ratio of 3 times, and further stretched at a stretching temperature of 120 ° C. in the TD direction. The polyolefin resin porous membrane was obtained by stretching under the condition of 3 times magnification. The properties of the obtained porous membrane are shown in Table 1.

(Example 2)
A polyolefin resin porous membrane was obtained according to Example 1 except that the resin composition (F) shown in Example 2 of Table 1 was used. Table 1 shows the film formability, stretchability, and characteristics of the porous film of the film-shaped molded product.

(Example 3)
A polyolefin resin porous membrane was obtained according to Example 1 except that the resin composition (F) shown in Example 3 of Table 1 was used. Table 1 shows the film formability, stretchability, and characteristics of the porous film of the film-shaped molded product.

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

(Example 5)
A polyolefin resin porous membrane was obtained according to Example 1 except that the resin composition (F) shown in Example 5 of Table 1 was used. Table 1 shows the film formability, stretchability, and characteristics of the porous film of the film-shaped molded product.

(Comparative Example 1)
A polyolefin resin porous membrane was obtained according to Example 1 using the resin composition (F) shown in Comparative Example 1 of Table 2. Table 2 shows the stretchability of the film-like molded product and the characteristics of the porous film. In Comparative Example 1, adhesion to the calender roll and removal were frequently generated, resulting in difficulty in film formation.

(Comparative Example 2)
A polyolefin resin porous membrane was prepared according to Example 1 using the resin composition (F) shown in Comparative Example 2 of Table 2. The stretchability of the film-like molded product is shown in Table 2. In Comparative Example 2, when stretched in the longitudinal direction, the stretch breakage occurred at a stretch ratio of less than 1.5 times, resulting in poor stretchability. It was not obtained.

(Comparative Example 3)
A polyolefin resin porous membrane was prepared according to Example 1 using the resin composition (F) shown in Comparative Example 3 of Table 2. The stretchability of the film-like molded product is shown in Table 2. In Comparative Example 3, adhesion to the calender roll frequently occurs and film formation is difficult, and when stretching in the longitudinal direction, stretching breakage occurs at a stretching ratio of less than 1.5 times. Therefore, the characteristics as a porous film could not be obtained by a slight stretching at a transverse stretching ratio of about 1.2 times.

(Comparative Example 4)
A polyolefin resin porous membrane was prepared in accordance with Example 1 using the resin composition (F) shown in Comparative Example 4 in Table 2. The stretchability of the film-like molded product is shown in Table 2. In Comparative Example 4, when stretched in the longitudinal direction, the stretch breakage occurred at a stretch ratio of less than 1.5 times, resulting in poor stretchability. It was not obtained.

(Comparative Example 5)
A polyolefin resin porous membrane was prepared in accordance with Example 1 using the resin composition (F) shown in Comparative Example 5 of Table 1. Table 2 shows the stretchability of the film-like molded product and the characteristics of the porous film. In Comparative Example 5, adhesion to the calender roll was frequently generated and the film forming property was difficult, and the average pore diameter was large and the porous property was also difficult.

  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.

2 is a transmission electron micrograph of a TD cross section (End View) of the porous film-forming resin composition obtained in Example 1. FIG. 3 is a transmission electron micrograph of a TD cross section (End View) of a resin composition for forming a porous film obtained in Comparative Example 1. FIG.

Claims (19)

Polyolefin resin (C) 60 to 95 wt% comprising 30 to 70 wt% crystalline polypropylene (A) and 30 to 70 wt% propylene-α-olefin copolymer (B) dispersed in crystalline polypropylene (A) % And a resin composition (F) containing 5 to 40% by weight of high-density polyethylene (D) having a weight average molecular weight Mw in the range of 3 × 10 ⁴ to 1 × 10 ⁷ and melted into a film A film formed by forming the film-shaped melt into a film-shaped molded product in a draft ratio of 1 to 10 and then stretching the film-shaped molded product in at least one direction. Polyolefin resin porous membrane having pores. Polyolefin resin (C) 30 to 95 wt% comprising 30 to 70 wt% crystalline polypropylene (A) and 30 to 70 wt% propylene-α-olefin copolymer (B) dispersed in crystalline polypropylene (A) %, A high-density polyethylene (D) having a weight average molecular weight Mw in the range of 3 × 10 ⁴ to 1 × 10 ⁷ , and a melt mass flow rate MFR _(E) of 0.1 g / 10 min to 2 g / min. A resin composition (F) containing 0 to 30% by weight of crystalline polypropylene (E) in a range of less than 10 min is melt-kneaded to form a film-like melt, and the film-like melt has a draft ratio of 1 to 10 A polyolefin resin porous film having a continuous pore, which is a film formed by forming a film-shaped molded article within a range and then stretching the film-shaped molded article in at least one direction. Melt mass flow rate MFR _PP of crystalline polypropylene (A) and melt mass flow rate MFR _RC of propylene-α-olefin copolymer (B) range of MFR _PP / MFR _RC greater than 10 and 1,000 or less The polyolefin resin porous membrane according to claim 1 or 2.   The polyolefin resin porous membrane according to any one of claims 1 to 3, wherein a draft ratio when the film-shaped melt is formed into a film-shaped molded product is in a range of 1 to 5.   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 4, 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. The air permeability resistance (Gurley) of the porous membrane is in the range of 10 to 20,000 s / 100 ml, and the moisture permeability is in the range of 200 to 10,000 g / m ² · 24 h. Polyolefin resin porous membrane.   The polyolefin resin porous membrane according to any one of claims 1 to 8, wherein a film forming method for forming the resin composition (F) into a film-shaped molded product is a calender molding method. Polyolefin resin (C) 60 to 95 wt% comprising 30 to 90 wt% crystalline polypropylene (A) and 10 to 70 wt% propylene-α-olefin copolymer (B) dispersed in crystalline polypropylene (A) % And a resin composition (F) containing 5 to 40% by weight of high-density polyethylene (D) having a weight average molecular weight Mw in the range of 3 × 10 ⁴ to 1 × 10 ⁷ and melted into a film A film formed by forming the film-shaped melt into a film-shaped molded product in a draft ratio of 1 to 10 and then stretching the film-shaped molded product in at least one direction. Polyolefin resin porous membrane having pores. The melt mass flow rate ratio MFR _PP / MFR _RC of the melt mass flow rate MFR _PP of the crystalline polypropylene (A) and the melt mass flow rate MFR _RC of the propylene-α-olefin copolymer (B) is 0.1-10. The polyolefin resin porous membrane according to 10.   The polyolefin resin porous membrane according to claim 10 or 11, 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 porous membrane according to any one of claims 10 to 12, wherein the melt mass flow rate ratio MFR _PP / MFR _RC is in the range of 0.2 to 5.   The polyolefin according to any one of claims 10 to 13, wherein the polyolefin resin (C) comprises 40 to 70% by weight of crystalline polypropylene (A) and 30 to 60% by weight of a polypropylene-α-olefin copolymer (B). Resin porous membrane.   The polyolefin resin porous membrane according to any one of claims 10 to 14, 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 10 to 14, 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 10 to 16. The air permeability resistance (Gurley) of the porous membrane is in the range of 1 to 2,000 s / 100 ml, and the moisture permeability is in the range of 1,000 to 20,000 g / m ² · 24 h. The polyolefin resin porous membrane described.   The polyolefin resin porous membrane according to any one of claims 10 to 18, wherein a film forming method for forming the resin composition (F) into a film-shaped molded product is a calender molding method.

Images