JP2008150628A - Polyolefin resin porous film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyolefin resin porous film which has a function suitable for cell separators, separating films, air-permeable waterproofing materials and the like having an excellent function as a porous film and, simultaneously, is at a low cost. <P>SOLUTION: The polyolefin resin porous film is prepared by melt-extruding a resin composition comprising a polyolefin resin (C), as a main component, comprising 30-90 wt.% of a crystalline polypropylene (A) and 10-70 wt.% of a propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A) in which the ratio MFR<SB>PP</SB>/MFR<SB>RC</SB>between the melt flow rate of the crystalline polypropylene (A) MFR<SB>PP</SB>, and the melt flow rate of the propylene-α-olefin copolymer (B) MFR<SB>RC</SB>, is ≤10, and obtained by a multi-stage polymerization method including a first stage of producing the crystalline polypropylene (A) and continuously a second stage of producing the propylene-α-olefin copolymer (B); molding the melt-extruded resin composition into a film-like formed product at a draft ratio of 1-10; and stretching the film-like formed product at least in one direction at a temperature of ≤100°C, whereby open cell pores are formed by cleavage generated in a region occupied by the copolymer (B) per se. <P>COPYRIGHT: (C)2008,JPO&INPIT

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 “multicomponent stretching method”) is disclosed (for example, see Patent Documents 1, 2, and 3).
(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”). (Refer to Patent Documents 4, 5 and 6).
(c) From a sheet formed by mixing an organic liquid or an inorganic filler with a polyolefin resin,
A method of extracting the organic liquid or the inorganic filler and performing stretching before and after the extraction as necessary (hereinafter referred to as “mixed extraction method”) is disclosed (for example, Patent Documents 7, 8, 9 and 10). reference).

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 average pore diameter and the porosity are not good. There were problems such as difficulty in obtaining a large 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. Had.

  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 was a problem in productivity.

JP 52-69476 A Japanese Patent No. 1638935 JP 58-198536 A JP 56-106928 A Japanese Patent No. 1945346 Japanese Patent No. 25009030 Japanese Patent No. 1290422 Japanese Patent No. 1882898 Specification Japanese Patent No. 1699207 Japanese Patent No. 2513768

  The present invention has been made in order to solve the above-mentioned problems related to conventional polyolefin resin porous membranes, and has a function suitable for battery separators, separation membranes, breathable waterproofing materials and the like excellent in functions as porous membranes, and It is an object to provide an inexpensive polyolefin resin porous membrane.

As a result of intensive studies, the present inventors have found that 30 to 90% by weight of the crystalline polypropylene (A) and 10 to 70% by weight of the propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A). When the melt flow rate of the crystalline polypropylene (A) is MFR _PP and the melt flow rate of the propylene-α-olefin copolymer (B) is MFR _RC , the ratio of the melt flow rate MFR _PP / MFR _RC is 10 or less, obtained by a multi-stage polymerization method including a step of producing a crystalline polypropylene (A) in the first stage and continuously producing a propylene-α-olefin copolymer (B) in the second stage. The resin composition comprising the polyolefin resin (C) as a main component is melt-extruded and molded into a film-shaped molded product within a draft ratio of 1 to 10, and then the film-shaped molded product is By a polyolefin resin porous membrane characterized by having continuous pores formed by cleavage occurring in a region occupied by the copolymer (B) by stretching in at least one direction at a temperature of 00 ° C. or less Based on this finding, the present invention has been completed. In the present invention, the pores communicating with each other are pores that are continuously formed by cleavage occurring in the region occupied by the copolymer (B) itself, resulting in a path connecting both surfaces of the porous membrane. .

The present invention is constituted by the following.
1. The crystalline polypropylene (A) comprises 30 to 90% by weight and the propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A) in an amount of 10 to 70% by weight. When the melt flow rate is MFR _PP and the melt flow rate of the propylene-α-olefin copolymer (B) is MFR _RC , the ratio MFR _PP / MFR _{RC of} the melt flow rate is 10 or less. The main component is a polyolefin resin (C) obtained by a multistage polymerization method including a step of producing a crystalline polypropylene (A) and continuously producing a propylene-α-olefin copolymer (B) in the second stage. After the melted resin composition is melt extruded and formed into a film-shaped molded product in the range of a draft ratio of 1 to 10, the film-shaped molded product is at least at a temperature of 100 ° C. or less. By stretching in direction, the copolymer (B) a polyolefin resin porous membrane which is characterized by having pores communicating formed by cleavage occurring in the region itself occupied.

2. 2. The polyolefin resin porous membrane according to 1 above, wherein the average pore diameter of the pores is 0.01 to 10 μm, and the porosity of the porous membrane is 20 to 90%.

3. 3. The polyolefin resin porous membrane according to item 1 or 2, wherein the direction in which the film-shaped molded product is stretched is a transverse (TD) direction.

The polyolefin resin porous membrane of the present invention uses a specific polypropylene resin in which the propylene-α-olefin copolymer (B) is finely dispersed in the crystalline polypropylene (A), thereby improving the stretchability at low temperatures. It is a porous membrane excellent in porous membrane properties such as porosity and air permeability, obtained by forming pores by cleavage of the copolymer (B) in the polymer (B) region. The polyolefin resin porous membrane of the present invention is an economical porous membrane obtained without using a complicated manufacturing process as in the past, and is suitably used for applications such as separation membranes, battery separators, and breathable waterproof materials. can do.

  Hereinafter, embodiments of the present invention will be described.

(1) Polyolefin resin The polyolefin resin porous membrane of the present invention comprises crystalline polypropylene (A) and a propylene-α-olefin copolymer (B), and is co-polymerized in the matrix of crystalline polypropylene (A). A polyolefin resin (C) in which the coalescence (B) is finely dispersed as a domain 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.

The melt flow rate MFR _PP of 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 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 20 to 80% by weight, more preferably 20 to 75% by weight, still more preferably 20 to 70% by weight, based on the weight of the entire copolymer (B). is there. When the content of the propylene polymer unit exceeds 80% by weight or less than 20% by weight, pores are hardly formed in the copolymer (B) domain existing in the matrix of the crystalline polypropylene (A), and the present invention. It is difficult to obtain the desired porous membrane characteristics.

  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 propylene-α-olefin copolymer (B) is not particularly limited, but a range of 0.1 to 20 g / 10 min is preferable because the molding process is easy. In order to finely disperse the copolymer (B) in the matrix of the crystalline polypropylene (A), the ratio of MFR between the crystalline polypropylene (A) and the copolymer (B) is MFR _PP / MFR _RC (hereinafter referred to as “FR”). The MFR _RC of the copolymer (B) is selected so that the “MFR ratio” is 10 or less, more preferably in the range of 0.2-5. When the MFR ratio is in the above range, the stretchability at a low temperature in the stretching process described later is improved.

(iii) Polyolefin resin (C)
The content of the crystalline polypropylene (A) in the polyolefin resin (C) of the present invention is 30 to 90% by weight, preferably 40 to 80% by weight, based on the total amount of the polyolefin resin (C). The content of the polymer (B) is 10 to 70% by weight, preferably 20 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).

  The method for producing the polyolefin resin (C) is a method for producing the polyolefin resin (C) 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. This is a method for continuously producing the resin (C). This continuous polymerization method is preferable because the production cost is low and the polyolefin resin (C) in which the copolymer (B) is uniformly dispersed in the crystalline polypropylene (A) can be stably obtained.

  In the present invention, the polyolefin resin (C) is produced by the continuous polymerization method, and the MFR ratio is adjusted to 10 or less, preferably 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 average pore diameter and a high porosity can be 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) having compatibility with the crystalline polypropylene (A) has a lower strength than the crystalline polypropylene (A), it is assumed that cleavage occurred in the copolymer (B) region due to stretching stress. The This mechanism is fundamentally different from the conventional multicomponent stretching method in which inorganic fillers and different polymers are mixed and stretched. As a result, the obtained porous membrane has a small average pore diameter and a large porosity and air permeability. It has become a thing.

  In the present invention, the copolymer (B) region means a region occupied by the copolymer (B) itself. Therefore, the pore generated in the copolymer (B) region is a pore due to cleavage generated in the region occupied by the copolymer (B) itself.

Specifically, the polyolefin resin (C) having the MFR ratio as described above can be produced by a method described in International Publication WO 97/19135, Japanese Patent Laid-Open No. 8-27238, or 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 determined 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 copolymer ( Since the MFR _RC of B) cannot be measured directly, the MFR _PP of the crystalline polypropylene (A) that can be directly measured, the melt flow rate MFR _{WHOLE of} the resulting polyolefin resin (C), and the copolymer (C) in the polyolefin resin (C) ( The MFR ratio can be obtained by calculating MFR _RC from the content W _RC (% by weight) of B) 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 a polyolefin resin porous film The resin composition, which is a molding material for a film-shaped molded product for forming the polyolefin resin porous film of the present invention, contains a polyolefin resin (C) as a main component. In addition, surfactants such as antioxidants, neutralizers, hindered amine-based weathering agents, UV absorbers, antifogging agents and antistatic agents used in ordinary polyolefins, lubricants, antibacterial agents, antifungal agents, pigments, etc. It can mix | blend as needed. In the present invention, the main component means the most abundant component.

  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 the neutralizing agent include higher fatty acid salts such as calcium stearate, examples of the lubricant include higher fatty acid amides such as stearic acid amide, and examples of the antistatic agent include fatty acid esters such as glycerin monostearate.

  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 polyolefin resin (C) and the additive is not particularly limited, and is blended by a usual blending device such as a mixer with a high-speed stirrer such as a Henschel mixer (trade name), a ribbon blender, and a tumbler mixer. 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 membrane The polyolefin resin porous membrane of the present invention is obtained by melt-extruding the resin composition containing the polyolefin resin (C) as a main component and molding it into a film-shaped molded product with a low draft ratio. 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, methods such as a known inflation film molding method, T-die film molding method, and calendar molding method are used. A T-die film forming method with high thickness accuracy and easy multilayering is preferably used.

  The resin composition can be formed at an extrusion temperature of 180 ° C. or higher. The purpose is to reduce the pressure inside the die and reduce the draft ratio described later, and the rigidity of the crystalline polypropylene (A) as the matrix polymer. The extrusion molding temperature of 220 to 300 ° C. is preferable in order to improve the viscosity and facilitate the formation of uniform and fine pores in the propylene-α-olefin copolymer (B) region dispersed in the crystalline polypropylene (A). Used for.

  The melt-kneaded resin composition is extruded from a die lip. At this time, the clearance of the die lip is a draft ratio (CL / d0) defined by the ratio of the die lip clearance CL and the film thickness d0 of the film-shaped molded product. ) Is preferably 1 to 10, more preferably 1 to 5. If the draft ratio is within this range, a porous film having the desired average pore diameter and porosity can be obtained.

  Further, the rigidity of the crystalline polypropylene (A) which is the matrix polymer is improved, and uniform and fine pores are generated in the propylene-α-olefin copolymer (B) region dispersed in the crystalline polypropylene (A). In order to facilitate the cooling of the film-like molded product extruded from the die lip, it is desirable to gradually cool it. In the case of inflation molding, the air volume during cooling is reduced. In the T-die film molding method, the temperature of the cooling roll is reduced. It is desirable to cool in the range of 60 to 120 ° C, more preferably 70 to 110 ° C. When the roll temperature is less than 60 ° C., the desired porosity is difficult to obtain, 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. Film-shaped molded articles having these thicknesses are obtained by various film forming apparatuses composed of a combination of the cooling roll and an air knife having an air outlet, the cooling roll and a pair of metal rolls, the cooling roll and a stainless belt, and the like. .

  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 of about 0.01 to 10 μm communicating with 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 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 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, the 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. It is desirable.

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 low-temperature stretchability in these temperature regions is excellent. Further, the stretching ratio is not particularly limited and is determined from the second stage stretching conditions performed as necessary and the required characteristics of the use of the porous membrane, but in the case of longitudinal stretching, it is usually 1.5 to 7 times. . If the draw ratio is in this range, a porous film having excellent characteristics can be obtained, and there is no risk 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 stretching ratio of the second stage is determined by the required characteristics of the use of the porous membrane, but is generally 1.5 to 7 times, and when the stretching ratio is less than 1.5 times, the stretching effect becomes insufficient, If it exceeds 7 times, stretching breakage occurs frequently 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 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 thickness of the polyolefin resin porous membrane of the present invention is not particularly limited, but is preferably about 10 to 100 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 and evaluation in an Example and a comparative example were implemented with the following method.

(1) Porosity: A 100 × 100 mm sample was cut out from the film porous membrane before stretching, the weight and thickness of the sample were measured, and obtained from the following formula.
Porosity (%) = (1-bulk specific gravity / true specific gravity) × 100
Bulk specific gravity = sample weight (mg) ÷ {10 × sample thickness (μm)}
In addition, true specific gravity was measured by the automatic specific gravity meter DENSIMTER, DS made from Toyo Seiki Seisakusyo Co., Ltd. about the sample 100x100mm which is not made porous before extending | stretching.

(2) Average pore diameter and maximum pore diameter: Based on ASTM F316-86 and ASTM E128, measured by Perm-Poromometer (manufactured by PORUS MATERIALS INC.).

(3) Moisture permeability: Measured according to JIS Z 0208.

(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.

Examples 1 to 4 and Comparative Examples 1 and 2
1) Preparation of porous film-forming resin composition Tetrakis [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) as a phenolic antioxidant was added to the polyolefin resin shown in Table 1. Propionate] 0.1% by weight of methane, 0.1% by weight of tris (2,4-di-t-butylphenyl) phosphite as a phosphorus antioxidant, and 0.1% by weight of calcium stearate as a neutralizing agent After blending and mixing with a Henschel mixer (trade name), the mixture was melt-kneaded and pelletized using a twin screw extruder (caliber 50 mm) 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. It is obtained by polymerizing a copolymer.

2) Film-forming process / Preparation of unstretched film-shaped molded product The obtained pellet-shaped resin composition was extruded using a 20 mm extruder equipped with a T-die having a lip width of 120 mm, an extrusion temperature of 280 ° C., and a discharge rate of 4 kg / hr. The lip clearance of a T-die having a lip width of 120 mm is adjusted to 0.20 mm while being melted and extruded at 0.20 mm, extruded from the lip into a film shape, cooled and solidified on a cooling roll at 80 ° C., width 100 mm, thickness A 200 μm film-shaped molded product was prepared. 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.

3) Stretching Step The film-shaped molded product was 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 restraining the longitudinal direction (MD direction). Thereafter, the film was further stretched in the machine direction (MD direction) under conditions of a stretching temperature of 100 ° C., a deformation rate of 1,000% / second, and a stretching ratio of 3 times to obtain a polyolefin resin porous film. Incidentally, in Comparative Example 2, during stretching in the transverse direction, stretching breakage occurs at a stretching ratio of less than 1.5 times and the stretchability is inferior, and the porous film is slightly stretched at a lateral stretching ratio of about 1.2 times. As a result, no characteristics were obtained.

Comparative Example 3
The polyolefin resin was carried out in the same manner as in Example 1 except that the propylene homopolymer crystalline polypropylene was 50% by weight and the ethylene homopolymer was 50% by weight. If it was less than the range, stretching breakage occurred and the stretchability was poor. Moreover, the characteristic as a porous film was not acquired by the slight extending | stretching of about 1.2 times of lateral stretch ratio.

Examples 5 and 6, Comparative Example 4
The same procedure as in Example 4 was performed except that the lip clearance of the die was adjusted to 0.6 mm, 1.2 mm, and 2.0 mm in the film forming step.

Example 7
The same operation as in Example 4 was performed except that the transverse draw ratio was 5 times and the longitudinal draw ratio was 6 times.

Example 8, Comparative Example 5
The same procedure as in Example 4 was performed except that the transverse stretching temperature was 80 ° C. and 120 ° C.

Example 9
The stretching was performed in the same manner as in Example 4 except that the stretching in the longitudinal direction was not performed and only the stretching in the lateral direction was performed.

It is a conceptual diagram which shows the observation surface of the polyolefin resin porous film of this invention. It is an electron micrograph (magnification: 5000 times) of MD cross section of the polyolefin resin porous membrane obtained in Example 4. 4 is an electron micrograph (magnification: 5000 times) of a TD cross section of the polyolefin resin porous film obtained in Example 4. FIG. 4 is a transmission electron micrograph of a TD cross section in the vicinity of a polypropylene-α-olefin copolymer region of a polyolefin resin porous membrane obtained in Example 4. FIG. The conceptual diagram explaining FIG.

Explanation of symbols

A: Crystalline polyolefin (A)
B: Propylene-α-olefin copolymer (B)
D: pores formed in the copolymer (B) region

Claims (3)

The crystalline polypropylene (A) comprises 30 to 90% by weight and the propylene-α-olefin copolymer (B) dispersed in the crystalline polypropylene (A) in an amount of 10 to 70% by weight. When the melt flow rate is MFR _PP and the melt flow rate of the propylene-α-olefin copolymer (B) is MFR _RC , the ratio MFR _PP / MFR _{RC of} the melt flow rate is 10 or less. The main component is a polyolefin resin (C) obtained by a multistage polymerization method including a step of producing a crystalline polypropylene (A) and continuously producing a propylene-α-olefin copolymer (B) in the second stage. After the melted resin composition is melt extruded and formed into a film-shaped molded product in the range of a draft ratio of 1 to 10, the film-shaped molded product is at least at a temperature of 100 ° C. or less. By stretching in direction, the copolymer (B) a polyolefin resin porous membrane which is characterized by having pores communicating formed by cleavage occurring in the region itself occupied. 2. The polyolefin resin porous membrane according to claim 1, wherein the average pore diameter is 0.01 to 10 [mu] m, and the porosity of the porous membrane is 20 to 90%. The polyolefin resin porous membrane according to claim 1 or 2, wherein a direction in which the film-shaped molded product is stretched is a transverse (TD) direction.

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