JP5337901B1 - Microporous film, method for producing the same, precursor film body, and locally embrittled film body - Google Patents

Abstract

The present invention provides a microporous film that is relatively inexpensive to manufacture and that can easily obtain a desired air flow rate.
A hole formed by causing an external force to act on a highly brittle region made of a second resin interspersed so as to be adjacent to each other in a film body formed of a first resin, thereby collapsing the highly brittle region. It was decided to prepare. The highly brittle region has a net-like structure formed of the second resin, and connects the mesh portion of the highly brittle region formed by the external force to penetrate the front and back of the film body. It is also characterized by the formation of holes.
[Selection] Figure 1

Description

  The present invention relates to a microporous film, a method for producing the microporous film, a precursor film body for producing the microporous film, and a locally embrittled film body for producing the microporous film.

  Conventionally, microporous films having many fine holes are used in various fields such as sanitary goods and batteries.

  For example, it is used as a diaper back sheet as a sanitary product, and is employed to ensure breathability in order to prevent the buttocks from becoming stuffy.

  Moreover, as a battery, it is utilized as a partition (separator) arrange | positioned, for example in a lithium ion battery, hold | maintains electrolyte solution, isolating a positive electrode and a negative electrode, and ion conductivity between a positive electrode and a negative electrode Has been adopted to ensure.

  As described above, microporous films are indispensable in various fields, and in recent years, various methods for efficiently producing microporous films have been proposed.

  For example, the method described in Patent Document 1 is an example in which a film is physically perforated, and a hole is formed by puncturing a needle that moves up and down quickly from the film surface.

  Further, the method described in Patent Document 2 is based on a polycondensate microporous film of bisphenol A and polyalkylene oxide, 3 to 10% by weight of a polycarbonate resin, and a maximum of 15% (1 to 6%) non-solvent. The mixture is cast and treated in a polar solvent / alcohol mixing tank.

  According to these methods, a microporous film having a large number of pores can be provided.

JP 05-031700 A JP-A-57-52461

  However, each of the above conventional microporous films has a high manufacturing cost, and the adjustment of the air flow rate is relatively difficult.

  The present invention has been made in view of such circumstances, and provides a microporous film that is relatively inexpensive to manufacture and that can easily obtain a desired air flow rate. Moreover, in this invention, the manufacturing method of the above microporous films, the precursor film body for microporous film manufacture, and the local embrittlement film body for microporous film manufacture are also provided.

In order to solve the above problems, an external force is applied to a highly brittle region made of the second resin dispersed so as to be adjacent to each other in the film body formed of the first resin, and the highly brittle region is collapsed. The highly brittle region has a network structure formed of the second resin, and the film body is formed by connecting mesh portions of the highly brittle region formed by the external force. The film body is obtained by heating the precursor film body in which the embrittleable regions that change to the highly brittle regions are scattered by heat, and the precursor film body is And formed from a kneaded product of the first resin and the second resin that are incompatible with each other .

The microporous film according to the present invention is also characterized by the following points.
It pre-Symbol first resin is a resin mainly composed of polypropylene, the second resin is a resin mainly composed of ultra low density polyethylene with the addition of peroxide.
Further, in order to solve the above-mentioned problems, an external force is applied to the highly brittle region made of the second resin dispersed so as to be adjacent to each other in the film body formed of the first resin, and the highly brittle region The highly brittle region has a network structure formed of the second resin, and the mesh portion of the highly brittle region formed by the external force is connected by the external force. A hole penetrating the front and back of the film body is formed, the first resin is a resin whose main component is polypropylene, and the second resin is a resin whose main component is ultra-low density polyethylene to which peroxide is added. It was decided that.

  In the method for producing a microporous film according to the present invention, the embrittlement is performed by exposing a resin precursor film body interspersed with an embrittleable region that is changed to a highly brittle region by heat in a temperature atmosphere capable of embrittlement. The possible region is embrittled, and an external force is applied to the film body in which the highly brittle regions generated by the embrittlement are scattered, thereby forming holes in the film body.

The method for producing a microporous film according to the present invention is also characterized by the following points.
(1) The external force is tension on the film body.
(2) The external force is ultrasonic vibration.

  Moreover, in the precursor film body for microporous film manufacture which concerns on this invention, it formed in the resin-made film body so that the embrittleable area | region which changes to a highly brittle area | region with heat might be scattered so that it might mutually adjoin.

  Furthermore, in the locally embrittled film body for producing the microporous film according to the present invention, the resin-made film body is formed by interspersing the embrittleable regions that change into a highly brittle region by heat so as to be adjacent to each other. An embrittleable region of a precursor film body for producing a microporous film was embrittled.

  According to the present invention, it is possible to provide a microporous film that can be obtained at a relatively low manufacturing cost and that can easily obtain a desired air permeability, and a method for manufacturing the microporous film.

  In addition, according to the present invention, there are provided a precursor film body for producing a microporous film and a locally embrittled film body for producing a microporous film, which can be obtained at a relatively low manufacturing cost and can easily obtain a desired air flow rate. can do.

It is the schematic diagram which showed the structure of the local embrittlement film body for microporous film manufacture which concerns on this embodiment. It is the schematic diagram which showed the structure of the microporous film which concerns on this embodiment. It is the schematic diagram which showed a mode that it changed from the precursor film body which concerns on this embodiment to a local embrittlement film body. It is the schematic diagram which showed the low molecular weight area | region formed in a local embrittlement film body and a microporous film. It is the schematic diagram which showed the state by which the hole of the microporous film was obstruct | occluded with the hole part obstruction | occlusion body. It is the flow which showed an example of the manufacturing process. It is the schematic diagram which showed a part of process in a manufacture example. It is explanatory drawing which showed the electron microscope image of the hole of a microporous film.

  The present invention provides a hole formed by applying an external force to a highly brittle region made of a second resin dispersed so as to be adjacent to each other in a film body formed of the first resin, and collapsing the highly brittle region. A microporous film comprising: is provided. The diameter of the hole is not particularly limited, but is a fine hole of about 0.05 to 10 μm.

  The microporous film according to the present embodiment is used in any scene that requires a gas, liquid, particles such as electrons and ions, electromagnetic waves including light, waves, and, in some cases, a solid such as a sieve. be able to. That is, it can be used when the film is moved from one side of the film to the other side or transmitted through the hole.

  If only an example is given about a use, there exist a medical instrument sterilization packaging film, a back sheet of a paper diaper, a battery separator, a filtration membrane etc., for example.

  For example, when the microporous film according to the present embodiment is applied to a medical instrument sterilization packaging film, the sterilization target instrument is placed in an alkaline atmosphere as compared with the case where a conventional film using calcium carbonate as an inorganic filler is applied. Since it is not exposed, microbial contamination after sterilization can be further suppressed.

  For example, when the microporous film according to the present embodiment is applied to a back sheet of a paper diaper, the promotion of microbial contamination due to an alkaline atmosphere can be prevented as described above, and the buttocks and the like can be kept clean. In addition, since air permeability according to the degree of sweating such as for children and adults can be easily realized, it is possible to provide a hygienic article having an extremely excellent anti-steaming effect at low cost.

  For example, when the microporous film according to the present embodiment is applied to a battery separator, a shutdown characteristic can be imparted to the battery, which will be described in detail later.

  For example, when the microporous film according to the present embodiment is applied to a filtration membrane, it can be used in a wide range of fields such as water treatment, solution concentration, and filter sterilization.

  More specifically, by using the microporous film according to this embodiment as a filtration membrane such as a reverse osmosis membrane, an ultrafiltration membrane, a microfiltration membrane, etc., it is possible to efficiently remove solute components and insoluble components and filter sterilization. Can be done well.

  For example, in areas with little fresh water or island countries, it is important to produce fresh water from seawater.However, reverse osmosis membranes, ultrafiltration membranes, microfiltration membranes, etc., have clogged pores due to trapped substances, etc. Filtration efficiency may be significantly reduced.

  Therefore, by generating a fresh water while discarding a predetermined amount of water by a cross flow method or the like, the filter can be prevented from being clogged and the filter can be used for as long as possible.

  On the other hand, the method for producing a microporous film according to the present embodiment can form a microporous film having a desired diameter easily and inexpensively. The filter can be easily replaced, and fresh water can be collected more efficiently.

  In addition, in the event of a disaster or outdoors, there are cases where it is unavoidable to use unsterilized water for drinking, but at this time, by using the filter device to which the microporous film according to this embodiment is applied, drinking In addition, poor physical condition and infection due to microorganisms can be prevented. That is, the microporous film according to this embodiment can be used very suitably in water treatment.

  In addition, these uses are illustrated in order to facilitate understanding of the usefulness of the microporous film according to the present embodiment, and the uses of the microporous film according to the present embodiment are limited to the above-described uses. It does not indicate that. However, this does not prevent the present invention from being limited to these applications.

  Conventionally, the microporous film and its manufacturing method are mechanically perforated as described above, for example, those that are optically perforated, those that add an inorganic filler, those that add stearyl alcohol or the like into a resin, etc. Various proposals have been made, but each of the following has the following problems.

  For example, mechanical perforation includes a method in which a very small needle is pressed against a resin film to perforate. In this case, a hole having a relatively large hole diameter and a large air flow rate is generally used. It is difficult to make a small hole with a small amount of ventilation.

  In addition, as for optically perforating, for example, there is a method of perforating by irradiating a resin film with a laser, but the formed hole is a hole penetrating linearly on the front and back, and water retention power and water vapor It is difficult to balance the passage.

  Moreover, as a method of adding an inorganic filler, for example, a method of adding calcium carbonate is known. However, since calcium carbonate makes the periphery of the particles alkaline, it is unsuitable for uses that dislike microbial contamination.

  In addition, a method of adding stearyl alcohol or the like into a resin, agglomerating the resin in the middle of solidification to form particles, and removing the granular parts with a solvent requires an extraction step, and a large amount of solvent must be used. Large facilities such as solvent regeneration and wastewater treatment are required.

  On the other hand, the microporous film according to the present embodiment is in a highly brittle region (brittle and fragile region) made of the second resin dispersed so as to be adjacent to each other in the film body formed of the first resin. It has a hole formed by applying an external force to collapse the highly brittle region.

  Here, the concept of the microporous film according to the present embodiment will be described with reference to the drawings. FIG. 1 is an explanatory view showing a state during the production of the microporous film according to the present embodiment. Specifically, the surface 15 and the cross section of a film body (hereinafter referred to as a local embrittlement film body 10) in which the highly brittle regions 12 before application of external force are scattered are schematically shown partially enlarged.

  As shown in FIG. 1, the local embrittled film body 10 is substantially spherical and has a high brittleness region 12 made of a large number of (a plurality of) second resins in a film body 11 formed of the first resin. It has a structure and is a film having locally fragile sites.

  The first resin that constitutes the film body 11 is a resin that is incompatible with the second resin that constitutes the highly brittle region 12 described in detail below (has incompatibility), and the melting point temperature of the second resin. The resin can have a higher melting point temperature. Although such resin is not specifically limited, For example, resin which has a polypropylene as a main component can be used suitably. In addition, the resin which has a polypropylene as a main component here is the concept also including the copolymer with another monomer other than the resin in which the additive etc. were added to the polypropylene, and the polypropylene resin itself.

  The second resin that forms the highly brittle region is a resin that is incompatible with the first resin (has incompatibility) and has a melting point temperature lower than the melting point temperature of the first resin. be able to. Such a resin is not particularly limited. For example, a resin mainly composed of ultra-low density polyethylene (VLDPE), more preferably, a metallocene ultra-low density polyethylene synthesized using a metallocene catalyst as a main component. The following resin can be used. Here, the resin mainly composed of ultra-low density polyethylene is a concept including an ultra-low density polyethylene resin itself in addition to a resin obtained by adding an additive to ultra-low density polyethylene.

  In the local embrittled film body 10, the highly brittle region 12 made of the second resin is a region weaker than the film body 11 made of the first resin, and the region collapses due to external force and voids are formed. It has the property of being formed. In other words, the external force is a force that does not break the film body 11 formed of the first resin and breaks the highly brittle region 12 made of the second resin.

  In particular, in the local embrittled film body 10 for forming the microporous film according to the present embodiment, the highly brittle region 12 is constituted by a network structure 40 extending in a three-dimensional direction. For example, the local embrittled film body When an external force such as tension is applied to 10, the net structure 40 collapses and the mesh portions 41 are connected to each other to form a gap.

  Further, the local embrittled film body 10 has a highly brittle region 12 made of the second resin as if the film body 11 made of the first resin is regarded as the sea, as if the islands are scattered in the sea. doing. In addition, the structure comprising the first resin and the second resin in the first resin, in other words, the second resin associates and disperses in the first resin. This structure may be referred to as a “sea-island structure” in this specification for convenience of explanation.

  In the sea-island structure of the local embrittled film body 10, as shown in FIG. 1, the highly brittle region 12 made of the second resin is adjacent to each other and connected in a bead shape (hereinafter referred to as a chain highly brittle region 13). .) Exists.

  In addition, in the chain highly brittle region 13 in the infinite number of sea island structures, the chain is formed transversely from one surface of the film body 11 to the other surface in the thickness direction, that is, FIG. Some of them are formed from the front surface 15 to the back surface 16 (hereinafter referred to as a chain crossing highly brittle region 14).

  In such a chain crossing highly brittle region 14, when the external force as described above is applied, the network structure 40 of each highly brittle region 12 collapses, and as shown in FIG. 2, holes 21 penetrating the front and back of the film body 11. Will be formed, and the microporous film 20 will be formed. That is, it can be said that the microporous film 20 according to the present embodiment includes the holes 21 formed by collapsing the chain crossing highly brittle region 14. However, in the case where the thickness of the film body 11 is smaller than the size of the highly brittle region 12, the film body 11 crosses the front and back of the film body 11 only by the single highly brittle region 12. No formation is necessary. That is, the microporous film 20 according to this embodiment is provided with a hole penetrating the front and back of the film body 11 due to the collapse of the highly brittle region 12 derived from external force application, whether the chain crossing type or the single film. It can be said that it is one of the features.

  The external force can also function as one of means for controlling the air permeability of the microporous film 20 according to this embodiment. For example, when the external force is tension applied to the local embrittled film body 10, the diameter of the hole 21 to be formed can be adjusted by adjusting the magnitude of the tension.

  Specifically, the external force is desirably applied within a range in which the film body 11 is elastically deformed, and is a force that is greater than the start of the breakage of the highly brittle region 12 and is less than the force that breaks the hole 21. It is good to do. Here, the force less than that at which the hole 21 is broken is intended to be a force that does not completely break the hole, and the force that causes a slight crack in the vicinity of the hole 21 is within an allowable range. It is.

  Within such a range, for example, a microporous film 20 with a large external force applied to increase the diameter of the hole 21 to improve the air permeability may be produced, or a small external force applied to provide a high brittleness. The microporous film 20 having a small air permeability may be manufactured by keeping the degree of destruction of the region 12 small.

  However, the external force is not necessarily limited to the range in which the film body 11 can be elastically deformed, and may be applied beyond the range of elastic deformation. It is possible to set the force within a range in which the hole 21 is broken and within the range of plastic deformation. For example, you may form the hole which has a diameter larger than the diameter of the highly brittle area | region 12 of the local embrittlement film body 10 by giving the external force slightly exceeding the range which elastically deforms.

  Thus, the microporous film 20 according to the present embodiment can control the air permeability by changing the diameter of the holes 21.

  2, the microporous film 20 according to the present embodiment has a bottomed hole 21b that opens only on one surface of the film body 11, in addition to the through-hole 21a that penetrates the front and back of the film body 11, A branch hole (not shown) that branches off from the through hole 21a or the bottomed hole 21b but has a dead end and is closed at one end, is not branched from the through hole 21a or the bottomed hole 21b, and either the front or back of the film body 11 In addition, a porous film having various holes 21 such as a sealed hole (not shown) that does not open to the surface is obtained. In other words, it can be regarded as a sponge-like film having an infinite number of various holes.

  Therefore, the microporous film 20 according to the present embodiment has excellent water retention capability while ensuring air permeability. Moreover, as can be seen from FIG. 2, the through hole 21 a penetrates the front and back of the film body 11, but the shape is meandering instead of a straight line, and such a structure also contributes to the improvement of the water retention capacity. .

  In addition, when the microporous film 20 according to the present embodiment is used for a battery separator, the wettability and impregnation with respect to a liquid substance such as an electrolytic solution accommodated in the battery is improved due to the extremely excellent water retention. Therefore, it becomes possible to dramatically improve the productivity of the battery.

  In addition, as shown in FIG. 2, on the inner wall surface of the hole 21 of the microporous film 20 according to the present embodiment, a net-like deposit 23 (residue destroyed by an external force) constituting the highly brittle region 12. ) Exists. For example, when the second resin is a resin mainly composed of a metallocene ultra-low density polyethylene, the deposit 23 has an extremely excellent property of elasticity, and excessive damage to the holes 21 when an external force is applied. Play a role to prevent.

  That is, when an external force such as tension is applied to the local embrittled film body 10, the highly brittle region 12 is stretched in the extending direction to break the network structure and form the holes 21. In order to suppress the propagation of further external force and absorb the stress derived from the external force due to the adhesion of the highly elastic net structure residue (adhesive 23), the hole 21 itself is effectively destroyed by the tension. To prevent. In other words, it can be said that the inner wall of the hole 21 is provided with a stress absorber made of a residue destroyed by an external force.

  Therefore, even if there is a slight error in the tension applied in the manufacturing process of the microporous film 20, the holes 21 themselves can be prevented from being destroyed, which is extremely advantageous in manufacturing.

  Incidentally, as described above, the microporous film 20 according to the present embodiment is obtained by applying an external force to the local embrittled film body 10. The film body 25 is formed by locally embrittlement.

  As shown in FIG. 3A, the precursor film body 25 is embrittled formed by a second resin that changes into a highly brittle region by heat in the film body 11 formed by the first resin. The possible regions 26 are scattered so as to be adjacent to each other to form a film. In addition to the change due to heat shown in the present embodiment, the change from the embrittleable region 26 to the highly brittle region 12 is particularly limited in terms of external stimulating factors such as electromagnetic waves including light, sound waves, and chemical reactions. Is not to be done.

  Such a precursor film body 25 can be obtained by kneading the incompatible first resin and the second resin and forming the film into a film shape. In addition, as a method of kneading | mixing or shape | molding here, it can be based on the well-known method generally used in resin film manufacture.

  By kneading the incompatible first resin and the second resin, the second resin associates with the substantially constant particle size by melt microphase separation in the first resin. By forming the film into a film shape, a precursor film body 25 in which the embrittleable regions 26 are scattered is formed.

  In manufacturing the microporous film 20 having a thickness larger than the particle size with which the second resin is associated, the microporous film 20 is formed in the precursor film body 25 in order to be able to form the through-hole 21a. It is necessary to mix the second resin with the first resin to such an extent that the many embrittleable regions 26 are adjacent to each other with a high probability.

  That is, if the amount of the second resin added to the first resin is small, the aggregate of the second resin forming the embrittleable region 26 becomes sparse, and the sea-island structure becomes rough (the island interval is increased). Therefore, the cross-chain highly brittle region 14 is hardly formed.

  Therefore, the second resin needs to be added in such an amount that the cross-chain highly brittle region 14 is formed when the local embrittled film body 10 is formed with respect to the first resin.

  For example, when the first resin is polypropylene and the second resin is metallocene ultra-low density polyethylene, the volume ratio of the first resin: the second resin = 7: 3 The mixing ratio is 3: 7, more preferably 6: 4 to 4: 6.

  In addition, a modifier that promotes polymerization of the molecular chains of the second resin and promotes fragmentation of the molecular chains may be added to the second resin.

  As such a modifier, for example, when the first resin is polypropylene and the second resin is metallocene ultra-low density polyethylene, for example, peroxide can be used.

  By forming the precursor film body 25 by adding the modifier as described above to the second resin, when the local embrittlement film body 10 is formed from the precursor film body 25, the second is triggered by heat. This resin can be cross-linked to promote embrittlement.

  In particular, in the case of the precursor film body 25 in which the first resin is polypropylene and the second resin is metallocene ultra-low density polyethylene, a high-temperature decomposition type peroxide (one-hour half-temperature is about 120 to 160 ° C.) as a modifier. ) Is exposed to a temperature atmosphere (for example, 105 to 130 ° C.) at a temperature lower than the melting point temperature of the first resin and higher than the melting point temperature of the second resin. By forming (embrittlement), a highly brittle region 12 suitable for manufacturing the microporous film 20 can be formed.

  In addition, the modifier added to the second resin penetrates the first resin in the vicinity of the embrittleable region 26 when the precursor film body 25 is formed. The molecular weight of the molecular chain of 1 resin is reduced.

  Specifically, as shown in FIG. 4A, a low molecular weight region 27 of the first resin by the modifier is formed around the high brittle region 12 of the local embrittled film body 10. The low molecular weight region 27 exists even in a state in which the microporous film 20 is formed, as shown in FIG.

  In particular, when the first resin is a resin composed of continuous tertiary carbon, more specifically, in the case of polypropylene, the molecular weight distribution of the first resin becomes sharp and the average molecular weight decreases. A decrease in the melt tension (melt tension) of the resin occurs.

  Therefore, when the microporous film 20 is in an overheated state (for example, when heated to a temperature close to the melting point temperature of the first resin), as shown in FIG. The first resin constituting the region 27 quickly fluidizes and exudes from the inner wall surface of the hole 21. The first resin having a low molecular weight that has oozed out stays in each hole 21, particularly in the narrowed portion, forms a hole closing body 28, and closes the hole 21.

  This action exhibits an extremely remarkable effect particularly when the microporous film 20 according to the present embodiment is used as a battery separator. That is, when the battery abnormally generates heat for some reason, the hole 21 is blocked, the chemical reaction in the battery is stopped, and a shutdown characteristic that avoids an ignition accident can be provided.

  As described above, according to the manufacturing method of the microporous film 20 and the microporous film, the precursor film body 25, and the local embrittlement film body 10 according to the present embodiment, the application is extremely wide and useful, and it is relatively manufactured. To provide a microporous film 20, a method for producing a microporous film, a precursor film body 25 for producing a microporous film, and a locally embrittled film body 10 that are inexpensive and can easily obtain a desired air permeability. Can do.

  Note that the above description is an example, and the configuration and manufacture of the microporous film 20 may be as follows.

  For example, in the above description, the diameter of the hole 21 is controlled by an external force. However, as another method for controlling the hole diameter, the combination of the first resin and the second resin is changed to change the precursor film. The pore diameter of the microporous film 20 may be adjusted by changing the size of the embrittleable region 26 of the body 25.

  Formation of the embrittleable region 26 in the precursor film body 25 is performed by using the first resin and the second resin that are not compatible with each other, and the second resin associates in the first resin during kneading. At this time, the particle size of the second resin generated by the microphase separation, that is, the diameter of the embrittleable region 26 becomes a substantially constant size determined by the type and molecular weight of the resin.

  In other words, the diameter of the hole 21 formed in the microporous film 20 can be adjusted by changing the diameter of the embrittleable region 26 by changing the type and molecular weight of the resin.

  Moreover, although the example which provides tension | tensile_strength for the local embrittlement film body 10 was shown as an example of the external force for collapsing the highly brittle area | region 12 in the previous description, it is not limited to this. For example, the external force can be ultrasonic vibration.

  This ultrasonic vibration may be propagated to the highly brittle region 12 through an appropriate medium such as gas, liquid, or solid, and has a frequency suitable for collapsing the highly brittle region 12 (for example, resonates with a network structure). To promote destruction).

  Next, an example of a manufacturing process based on the above technique will be described. FIG. 6 is a flow showing the steps of the method for manufacturing the microporous film 20 according to this embodiment.

  In the manufacture of the microporous film 20 according to the present embodiment, first, a measuring step for measuring the resin to be used is performed (step S10). In this measurement step, the blending ratio of the first resin and the second resin is determined and weighed while taking into consideration the thickness and length of the microporous film 20 to be manufactured, the diameter of the holes 21 to be formed, and the like. Note that a modifier such as a high-temperature decomposition type peroxide may be added to the second resin in advance at this time.

  Next, a kneading step for kneading the measured raw materials is performed (step S11). In this kneading step, the first resin and the second resin are kneaded and the above-mentioned sea-island structure is formed in the resin mixture. As the kneader used at this time, a known kneader generally used in resin processing can be used. For example, it may be kneaded with an extruder at a specific energy of about 0.1 (0.08 to 0.12).

  Next, the precursor film body formation process which shape | molds the resin mixture obtained at the kneading | mixing process in the shape of a film, and makes it the precursor film body 25 is performed (step S12). By performing this process, the precursor film body 25 in which innumerable embrittleable regions 26 are scattered in the film body 11 is formed. In addition, you may distribute | circulate as a raw material for microporous film manufacture by winding up the precursor film body 25 formed in this way in roll shape.

  Next, an embrittlement process for embrittlement of the embrittleable region 26 of the precursor film body 25 formed in this way is performed (step S13). In addition, it demonstrates referring FIG. 7 also including the below-mentioned external force provision process and drying process which follow this embrittlement process. FIG. 7 is a schematic explanatory view showing an example of an embrittlement process, an external force application process, and a drying process.

  As shown in FIG. 7, the precursor film body 25 obtained in the precursor film body forming step is fed into a hot tub 30 that houses a heated liquid heat medium 31. A heater 32 that is electrically connected to a control device (not shown) is disposed in the hot tub 30 so that the liquid heat medium 31 accommodated in the hot tub 30 can be held at a predetermined temperature. .

  Specifically, for example, in the case of the precursor film body 25 in which the first resin is polypropylene, the second resin is metallocene ultra-low density polyethylene, and a high temperature decomposition type peroxide is added to the second resin, The temperature of the liquid heat medium 31 in the bath 30 is 95 ° C. <hot bath temperature <135 ° C., more preferably 100 ° C. <hot bath temperature <130 ° C., from the melting point temperature of the ultra-low density polyethylene resin and polypropylene resin. be able to.

  In the precursor film body 25 fed to such a hot tub 30, a high-temperature decomposition type peroxide as a modifier added to the second resin causes a reaction, and the polymerization of the second resin is promoted. Thus, the highly brittle region 12 is formed. That is, an embrittlement process is performed and the local embrittlement film body 10 will be formed. At the same time, the molecular weight of the first resin in the vicinity of the second resin is lowered, and the melt tension is lowered. FIG. 7 shows a process of continuously producing from the precursor film body 25 to the microporous film 20, but is not limited to this, and the formed locally embrittled film body 10 is wound into a roll shape. For example, it may be distributed as a material for producing a microporous film.

  Moreover, in the hot tub 30, the ultrasonic generator 33 which irradiates an ultrasonic wave with respect to the local embrittlement film body 10 in which the highly brittle area | region 12 was formed by being immersed in the hot tub 30 (after the embrittlement process). Is arranged.

  The ultrasonic generator 33 is provided with an ultrasonic transducer (not shown), and an ultrasonic wave having a frequency and intensity capable of collapsing the network structure of the highly brittle region 12 is emitted.

  And in the local embrittlement film body 10 irradiated with the ultrasonic wave, the external force by the ultrasonic wave is applied to the highly brittle region 12, and the collapse of the highly brittle region 12 is caused. That is, an external force application process is performed (step S14).

  When the external force application process is performed in this manner, the microporous film 20 is formed through the drying process (step S15) by the drying apparatus 34 by being pulled up from the hot tub 30. The formed microporous film 20 is taken up by the take-up device 35 and distributed to the market.

  Next, actual production examples and test results will be mentioned.

[Production Example 1]
(Raw material measurement process)
First, in order to prepare a microporous film, the raw materials were weighed as follows.
・ Ultra low density polyethylene resin (Japan Polyethylene Corporation) 400kg
・ Polypropylene resin (Nippon Polypro Co., Ltd.) 600kg
・ High-temperature decomposition type peroxide (Nippon Yushi Co., Ltd .: Perhexa 25B)
8g

  The ultra-low density polyethylene resin used in this step was a density of 0.900 and a melting point temperature of 95 ° C.

  The polypropylene resin used in this step was a resin with a density of 0.85 and a melting point temperature of 135 ° C.

  The high-temperature decomposable peroxide used in this process is an active oxygen generator containing 2,5-Dimethyl-2,5-bis (t-butylperoxy) hexyne-3 as the main component, and is reduced by half for 10 hours. The one having an initial temperature of 128.4 ° C. (1 hour half-life temperature of 149.9 ° C.) was used.

  Further, from the melting point temperatures of the ultra-low density polyethylene resin and the polypropylene resin, the heat treatment temperature for perforation is required to be 95 ° C. <treatment temperature <135 ° C., more preferably 100 ° C. <treatment temperature <130 ° C. It was.

(Kneading process and precursor film body forming process)
Next, each raw material weighed in the raw material measuring step was kneaded.

  Specifically, using a twin-screw extruder TEM65 manufactured by Toshiba Machine, a film having a width of 1 m and a thickness of 25 μm was formed at a temperature of 230 ° C. while kneading with a specific energy of about 0.05 to 0.2 (kneading step) ( Raw material film forming step for producing microporous film).

(Ebrittlement process)
Next, the embrittlement process which embrittles the obtained precursor film body was performed. In the embrittlement step, as shown in FIG. 7, the precursor film body is passed through a warm bath in which the liquid heat medium is 105 to 125 ° C. so that the immersion time is 10 to 100 seconds. A formed film body was formed.

(External force application process and drying process)
Next, an external force is applied to the locally embrittled film body 10 formed through the embrittlement process by applying an ultrasonic vibration of 300 kHz (external force application process), and it is pulled up from the hot tub and dried. A porous film A1 was obtained. The warm bath temperature, immersion time, and frequency of ultrasonic vibration set in the external force application step and the embrittlement step described above are examples, and the film material, the blending ratio of each raw material, the size of the hole to be formed, etc. It is also possible to set as appropriate.

[Production Example 2]
Next, Production Example 2 will be described. In this production example 2, a microporous film is produced through the same steps as in the production example 1 described above. However, in the external force application step, external force is applied to the locally embrittled film body by ultrasonic waves. The external force was applied by applying tension.

  Specifically, in an environment set to 105 to 125 ° C., the external embrittlement film body was subjected to an external force application step by applying tension to the locally embrittled film body in the extending direction and elastically deforming it about 1.05 to 1.5 times. Thereafter, a microporous film A2 which is a microporous film according to the present embodiment was obtained through a drying process.

[Quality confirmation test]
Next, a confirmation test was performed on the quality of the obtained microporous film A1 and microporous film A2.

(Thickness measurement test)
The thickness of the microporous films A1 and A2 was measured using a contact type film thickness measuring device manufactured by Yamabun Electric Co. As a result, both the microporous film A1 and the microporous film A2 were 25 ± 2 μm.

(Air permeability measurement test)
The air permeability (Gurley value) of the microporous films A1 and A2 was measured using a Gurley type automatic air permeability meter manufactured by Matsubo. As a result, the microporous film A1 was 70 seconds / 100 cm ³ and the microporous film A2 was 75 seconds / 100 cm ³ .

(Microscopic observation)
Next, the microporous films A1 and A2 were examined with a scanning electron microscope. FIG. 8 shows a microscopic image of the microporous film A2.

  As can be seen from FIG. 8A, it was confirmed that pores were formed in the microporous film A2. Further, as can be seen from FIG. 8 (b) showing an enlarged image of the part indicated by X in FIG. 8 (a), a net structure was observed at the peripheral part of the hole. From this image, the network structure is formed in all the parts that become holes in the state of the locally embrittled film body, and the mesh structure is broken by external force to form the holes by connecting the eyes. It was shown that. Here, although a microscopic image of the microporous film A1 is not shown, a microscopic image similar to the microporous film A2 was observed.

(Air permeability variable test)
Next, the tension | tensile_strength provided in manufacture example 2 was changed, and the test which adjusts the air permeability of a microporous film was done. Specifically, three types of samples were prepared: a microporous film A2x with an elastic deformation ratio of 1.1 times, a microporous film A2y with an elastic deformation ratio of 1.2 times, and a microporous film A2z with an elastic deformation ratio of 1.4 times. did. The tension was applied within the range of elastic deformation, and after annealing, the stress was released and returned to its original size. The results are shown in Table 1.

As can be seen from Table 1, when tension is applied and the initial tensile magnification is 1.1 times (microporous film A2x), the air permeability is 183 seconds / 100 cm ³ , and the initial tensile magnification is 1.2 times ( The microporous film A2y) had an air permeability of 142 seconds / 100 cm ³ , and when the initial tensile magnification was 1.4 (microporous film A2z), the air permeability was 61 seconds / 100 cm ³ .

  From these results, it is possible to easily change the air permeability of the microporous film by changing the external force applied to the locally embrittled film body, in other words, by controlling the initial pulling ratio when applying tension. It was shown that.

  As described above, in the microporous film according to the present invention, an external force is applied to the highly brittle region made of the second resin dispersed so as to be adjacent to each other in the film body formed of the first resin, Since the hole formed by collapsing the highly brittle region is provided, a microporous film can be obtained that is relatively inexpensive to manufacture and that can easily obtain a desired air flow rate.

  Further, according to the method for producing a microporous film according to the present invention, the resin precursor film body interspersed with a brittle region that is changed to a highly brittle region by heat is exposed to a temperature atmosphere capable of embrittlement, and Since the embrittleable region is embrittled and the external force is applied to the film body in which the highly brittle regions generated by the embrittlement are scattered, holes are formed in the film body, so that the manufacturing cost is relatively low. A microporous film capable of easily obtaining a desired air permeability can be produced.

  In addition, according to the precursor film body according to the present invention, since the embrittleable regions that change into a highly brittle region by heat are scattered in the resin film body so as to be adjacent to each other, the manufacturing cost is relatively high. It is possible to provide a precursor film body that is inexpensive and can easily obtain a desired air permeability.

  Further, according to the locally embrittled film body according to the present invention, since the embrittleable region of the precursor film body is embrittled, the manufacturing cost is relatively low, and a desired air flow rate can be easily obtained. The precursor film body which can be provided can be provided.

  Finally, the description of each embodiment described above is an example of the present invention, and the present invention is not limited to the above-described embodiment. For this reason, it is a matter of course that various modifications can be made in accordance with the design and the like as long as they do not depart from the technical idea according to the present invention other than the embodiments described above.

DESCRIPTION OF SYMBOLS 10 Locally embrittled film body 11 Film body 12 High brittle area 13 Chain high brittle area 14 Chain crossing highly brittle area 20 Microporous film 21 Pore 23 Adhesion 25 Precursor film body 26 Embrittleable area 27 Low molecular weight area 33 Ultrasonic wave Generator

Claims (8)

An external force is applied to the highly brittle region made of the second resin dispersed so as to be adjacent to each other in the film body formed of the first resin, and the holes formed by collapsing the highly brittle region are provided.
The highly brittle region has a network structure formed of the second resin, and has a hole penetrating the front and back of the film body by connecting the mesh portion of the highly brittle region formed by the external force. Forming ,
The film body is obtained by heating a precursor film body interspersed with an embrittleable region that changes to the highly brittle region by heat,
The precursor film body is formed of a kneaded product of the first resin and the second resin that are incompatible with each other, and is a microporous film.   The first resin is a resin whose main component is polypropylene, and the second resin is a resin whose main component is ultra-low density polyethylene to which peroxide is added. Microporous film. An external force is applied to the highly brittle region made of the second resin dispersed so as to be adjacent to each other in the film body formed of the first resin, and the holes formed by collapsing the highly brittle region are provided.
The highly brittle region has a network structure formed of the second resin, and has a hole penetrating the front and back of the film body by connecting the mesh portion of the highly brittle region formed by the external force. Forming ,
The microporous film, wherein the first resin is a resin whose main component is polypropylene, and the second resin is a resin whose main component is ultra-low density polyethylene to which peroxide is added .   The resin-made precursor film body in which the brittle regions that change into high brittle regions due to heat are scattered is exposed to a temperature atmosphere that can be embrittled to embrittle the brittle regions. A method for producing a microporous film, wherein pores are formed in a film body by applying an external force to the film body in which brittle regions are scattered. The method for producing a microporous film according to claim 4 , wherein the external force is a tension applied to the film body. The method for producing a microporous film according to claim 4 , wherein the external force is ultrasonic vibration.   A precursor film body for producing a microporous film, which is formed by dispersing embrittleable regions that change into a highly brittle region by heat in a resin film body so as to be adjacent to each other. The local embrittlement film body for microporous film manufacture formed by embrittlement of the embrittleable area | region of the precursor film body of Claim 7 .