Method for producing microporous thin film material

Abstract

To provide a method for manufacturing a microporous thin film material that enables reduction of facility investment costs.SOLUTION: A method for manufacturing a microporous thin film material, which is a dry-stretching thin film technique, does not add oils and fats that are used for forming pores by subsequent removal, or pore-forming fine particles that promote micropore formation, into the polymer of the material. The manufacturing method includes: (1) a non-porous precursor extrusion step 201; (2) an annealing and aging step 202; (3) a longitudinal stretching step 203 with or without transverse relaxation; (4) a transverse stretching step 204 without longitudinal relaxation; (5) a transverse relaxation step 205; and (6) a winding step 206.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for producing a microporous membrane material used for moisture-permeable waterproof microporous membranes or battery separators, and particularly to a method for producing a microporous thin film material that can produce, in a uniaxial stretching machine, the properties of a microporous film produced by a simultaneous biaxial stretching machine and that can provide a microporous thin film with desired material properties and good breathability. [Background technology]

[0002] Studies relating to MD and / or TD stretched and optionally calendered membranes, separators, substrate films, microporous membranes, battery separators comprising said separators, substrate films, or membranes, batteries comprising said separators, and / or methods for making and / or using such membranes, separators, substrate films, microporous membranes, battery separators, and / or batteries are disclosed, for example, in U.S. Patent No. 5,929,999.

[0003] Disclosed is a method used to make new and / or improved microporous membranes and battery separators containing the same, which have a better balance of desired properties compared to microporous membranes and battery separators made by prior art conventional techniques, comprising the steps of: 1) obtaining a non-porous membrane precursor; 2) forming a biaxially stretched porous membrane precursor from the non-porous membrane precursor; and 3) subjecting the biaxially stretched porous membrane precursor to at least one of (a) calendaring, (b) additional machine direction (MD) stretching, (c) additional transverse direction (TD) stretching, and (d) pore filling to form a final microporous membrane.

[0004] The microporous membrane or battery separator described in Patent Document 1 has the following balance of properties when not coated: 2 Over 250kg / cm 2 TD tensile strength of greater than 200gf, greater than 250gf, greater than 300gf, or greater than 400gf, and JIS Gurley of greater than 20s or greater than 50s.

[0005] Furthermore, research into microporous membranes made by a dry stretching process and having substantially round pores and a ratio of tensile strength in the machine direction to the transverse direction within the range of 0.5 to 6.0 is disclosed, for example, in Patent Document 2, in which a method for making the microporous membrane includes the steps of extruding a polymer into a non-porous precursor and biaxially stretching the non-porous precursor, wherein the biaxial stretching includes stretching in the machine direction and the transverse direction, and includes relaxation in the machine direction with simultaneous control of the transverse direction.

[0006] At least selected embodiments of the '591 patent may be directed to biaxially oriented microporous membranes, composites including biaxially oriented microporous membranes, biaxially oriented microporous membranes, biaxially oriented macroporous membranes, battery separators, filtration media, humidity control media, flat sheet membranes, liquid retention media, and the like, related methods, methods of manufacture, methods of use, and the like.

[0007] As shown in the flowchart of the method for manufacturing a microporous membrane material in FIG. 1, the microporous membrane is made by a dry stretching process including step 101 of extruding a polymer into at least a single layer of a non-porous precursor, and step 102 of biaxially stretching the non-porous precursor, the biaxial stretching comprising machine direction stretching and transverse direction stretching, the transverse direction stretching comprising a simultaneously controlled machine direction relaxation, and comprises at least one layer of a microporous polymer thin film having substantially round pores, a porosity of about 40% to 90%, a ratio of machine direction tensile strength to transverse direction tensile strength ranging from about 0.5 to 5.0, a Gurley of less than about 100, a mean flow pore size of at least about 0.04 microns, a water pore size of at least about 0.07 microns, and a hydrohead pressure greater than about 140 psi.

[0008] Furthermore, research on a microporous membrane produced by a dry-stretching method, having pores with approximately round shapes, and having a ratio of longitudinal tensile strength to transverse tensile strength in the range of 0.5 to 5.0 is disclosed, for example, in Patent Document 3. The method for producing the microporous membrane includes extruding a polymer into a non-porous precursor and biaxially stretching the non-porous precursor, the biaxial stretching including longitudinal stretching and transverse stretching, the transverse stretching including simultaneous controlled longitudinal relaxation.

[0009] Further, for example, U.S. Patent No. 6,299,949 discloses a battery separator that includes a coextruded microporous membrane having at least two layers made from an extrudable polymer and having a uniform thickness defined by a standard deviation of <0.80 microns (μm) or an interlayer adhesion defined by a peel strength of >60 grams.

[0010] Prior art includes research on films for packaging fresh foods or fermented foods, and packaging materials and packaging containers using such films. For example, Patent Document 5 discloses that a film for packaging fresh foods or fermented foods has an average pore size of 0.01 to 2 μm and a porosity of 10 to 80%, and is produced from a pure crystalline polymer by a dry stretching method that does not use organic solvents or solvents, without adding any inorganic or organic compounds for forming pores, and is imparted with microporosity. This film effectively prevents the passage of liquids such as water and the escape of odors while allowing food to breathe and release gases through a simple processing process. It is therefore useful as a packaging material for fermented foods such as kimchi or fresh foods such as vegetables, as it can maintain the freshness of food with a simple process.

[0011] Another prior art involves research into a method for producing a microporous laminate sheet having a first membrane layer and a second membrane layer. For example, Patent Document 6 discloses a technique in which a pore-forming initiator is blended into the first membrane layer, the first membrane layer is bonded to the second membrane layer to form a laminate sheet, and then the laminate sheet is stretched using at least one CD intermeshing stretching machine and at least one MDO stretching device. Furthermore, Patent Document 6 above proposes a stretching device for the membrane or laminate, as well as a method for producing a microporous membrane and a microporous membrane laminate. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Taiwan Patent Publication No. TWI762647B Specification [Patent Document 2] People's Republic of China Patent Publication No. CN102892534A Specification [Patent Document 3] U.S. Patent Publication No. US20070196638A1 [Patent Document 4] U.S. Patent Publication No. US20080118827A1 [Patent Document 5] People's Republic of China Patent Publication No. CN101309952A Specification [Patent Document 6] US Patent Publication No. US06811643B2 Summary of the Invention [Problem to be solved by the invention]

[0013] The problem to be solved by the present invention is to provide a method for producing a microporous thin film material that can reduce capital investment costs. [Means for solving the problem]

[0014] The method for producing the microporous thin film material of the present invention is a dry stretch thin film technique, and the material Made of polyolefin Used to create pores in polymers with subsequent removal compound Add No extraction process is performed.The method includes: 1. a non-porous precursor extrusion step of heating a semi-crystalline thermoplastic polymer to extrude a non-porous precursor; 2. an annealing and aging step of applying a temperature lower than the extrusion temperature to cause recrystallization of the non-porous precursor to complete annealing, and then removing the film roll from the extrusion line and storing it to complete aging; and 3. a longitudinal stretching step with or without transverse relaxation of the non-porous precursor to form a longitudinally stretched film at a temperature ranging from room temperature to a temperature equal to or lower than the melting point of the polymer. 4. a transverse stretching step without longitudinal relaxation, in which the longitudinally stretched film is stretched in the transverse direction at least once from above the glass transition temperature to below the melting point temperature of the polymer, without relaxation in the longitudinal direction, i.e., the longitudinal relaxation ratio is 0%, and the speed of the longitudinal production line is increased to form a longitudinally / transversely stretched film; 5. a transverse relaxation step, in which the longitudinally / transversely stretched film is relaxed in the transverse direction at least once from above the glass transition temperature to below the melting point temperature of the polymer, to form a microporous thin film material; and 6. a winding step, in which the microporous thin film material is wound into a roll and stored. In this order Contains fruit , The transverse stretching ratio in the transverse stretching step without longitudinal relaxation is 1.1 to 2.5 times. .

[0017] The aging time in the annealing and aging step is 3 to 7 days or more when stored stationary.

[0018] The longitudinally stretched membrane formed in the longitudinal stretching step with or without transverse relaxation is wound into a roll, and the roll material is removed from the production line and stored stationary to complete secondary aging.

[0019] The secondary aging time is 3 to 7 days or more when stored statically.

[0020] In the longitudinal stretching step with or without transverse relaxation, the longitudinal stretching temperature is cold stretching at an ambient temperature of 0 to 25°C, or hot stretching at a temperature 10 to 100°C below the melting point of the polymer.

[0021] In the transverse stretching step without longitudinal relaxation, the transverse stretching temperature is 10 to 100° C. below the melting point temperature of the polymer.

[0023] The relaxation ratio in the transverse direction relaxation step is 2 to 10%.

[0024] The porosity of the microporous thin film material in the winding step is greater than 50% or less than 90%.

[0025] The gas permeability of the microporous thin film material in the winding step is less than 4 seconds / 10 cc. [Effects of the Invention]

[0026] According to the method for producing a microporous thin film material of the present invention, pore formation in a porous film can be achieved by simultaneous biaxial stretching using uniaxial stretching equipment, and the transverse stretching step without longitudinal relaxation has the advantage of reducing capital investment costs. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a flowchart illustrating a conventional method for manufacturing a microporous thin film material. [Figure 2] 1 is a flowchart showing a method for producing a microporous thin film material according to an embodiment of the present invention. [Figure 3] FIG. 2 is an electron microscope image of a microporous thin film material produced at a transverse stretching ratio of 1.5 times according to an embodiment of the present invention. [Figure 4] FIG. 2 is an electron microscope image of a microporous thin film material produced at a transverse stretching ratio of 1.75 times according to an embodiment of the present invention. [Figure 5] FIG. 2 is an electron microscope image of a microporous thin film material produced at a transverse stretching ratio of 2.0 times according to an embodiment of the present invention. [Figure 6] Electron microscope view of a microporous thin film material produced at a transverse stretching ratio of 2.25 times according to an embodiment of the present invention. [Figure 7] FIG. 2 is an electron microscope image of a microporous thin film material produced at a transverse stretching ratio of 2.5 times according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. It goes without saying that the present invention is not limited to the embodiments.

[0029] The method for producing the microporous thin film material of the present invention is a dry stretch thin film technique that does not add any oils or fats to the polymer of the material that are subsequently removed to form pores, or any pore-forming particulates that promote the formation of micropores.

[0030] In this embodiment, as shown in FIG. 2, the method for producing a microporous thin film material includes: 1. a non-porous precursor extrusion process 201 in which a semi-crystalline thermoplastic polymer is heated to extrude a non-porous precursor; 2. an annealing and aging process 202 in which a temperature lower than the extrusion temperature is applied to cause recrystallization of the non-porous precursor to complete annealing, and the film roll is then removed from the extrusion line and stored to complete aging; 3. a longitudinal stretching process 203 with or without transverse relaxation in which the non-porous precursor is stretched in the longitudinal direction at a temperature from room temperature to below the melting point of the polymer, with or without relaxation in the transverse direction, to form a longitudinally stretched film; and 4. a process from above the glass transition point to the melting point of the polymer to form a longitudinally stretched film. The process then continues with the steps of: 4. transverse stretching without longitudinal relaxation step 204, in which the longitudinally stretched film is stretched at least once in the transverse direction without relaxation in the longitudinal direction, i.e., the relaxation rate in the longitudinal direction is 0%, and the speed of the longitudinal production line is increased to form a longitudinally / transversely stretched film; 5. transverse relaxation step 205, in which the longitudinally / transversely stretched film is relaxed in the transverse direction at least once at a temperature above the glass transition point and below the melting point of the polymer to form a microporous thin film material; and 6. winding step 206, in which the microporous thin film material is wound into a roll and stored. The steps in the dashed block area in Figure 2, i.e., transverse stretching without longitudinal relaxation step 204 and transverse relaxation step 205, can be repeatedly performed (207).

[0031] The semi-crystalline thermoplastic polymer in the non-porous precursor extrusion process 201 is a polyolefin. The semi-crystalline thermoplastic polymer in the non-porous precursor extrusion step 201 can be polyethylene or polypropylene. The maturation time in the annealing and maturation step 202 is 3 to 7 days or more when stored stationary. The longitudinally stretched membrane formed in the longitudinal stretching step 203 with or without transverse relaxation is wound into a roll, and the roll material is removed from the production line and stored statically to complete secondary aging. The secondary aging time is 3 to 7 days or more when stored statically.

[0032] In the longitudinal stretching step 203 with or without transverse relaxation, the longitudinal stretching temperature is cold stretching at an environmental temperature of 0 to 25°C, or hot stretching at a temperature 10 to 100°C below the melting point of the polymer. In the transverse stretching step 204 without longitudinal relaxation, the transverse stretching temperature is 10 to 100° C., which is lower than the melting point temperature of the polymer. In the transverse stretching step 204 without relaxation in the machine direction, the stretching ratio in the transverse direction is 1.1 to 2.5 times. The relaxation ratio in the lateral direction relaxation step 205 is 2 to 10%. The porosity was calculated according to ASTM D2873, and the porosity of the microporous membrane material in the winding process 206 was found to be greater than 50% or less than 90%. According to ASTM D-726, the time required for 100cc of gas to pass through the microporous membrane material was measured using a Gurley 4150 gas permeability analyzer, which gave the gas permeability (Gurley) value (seconds / 10cc) of the microporous membrane material. Five samples of the microporous membrane material were taken and the gas permeability was measured, and the average value was used as the gas permeability of the microporous membrane material. The sample size was 25.4mm x 25.4mm. When the Gurley gas permeability analyzer was used to measure the gas permeability of the microporous membrane material in the winding process 206, the gas permeability was found to be 4 seconds / 10cc.

[0033] Actual finished products produced by the method for producing a microporous thin film material of the present invention are shown in FIGS. The method for producing a microporous thin film material is a dry stretching thin film technology that does not add any oils or fats to the polymer of the material to be removed later to form pores or any pore-forming particles that promote the formation of micropores, and the process comprises: 1. a non-porous precursor extrusion process 201 in which a semi-crystalline thermoplastic polymer is heated to extrude a non-porous precursor; 2. an annealing and aging process 202 in which a temperature lower than the extrusion temperature is applied to cause a recrystallization phenomenon of the non-porous precursor to complete annealing, and then the film roll is removed from the extrusion line and stored to complete aging; and 3. a non-porous precursor is stretched in the longitudinal direction at a temperature between room temperature and the melting point of the polymer, and the non-porous precursor is relaxed in the transverse direction. 3. A transverse stretching step 204 without longitudinal relaxation, in which the longitudinally stretched film is stretched transversely at least once from above the glass transition temperature to below the melting point of the polymer, without longitudinal relaxation, i.e., with a longitudinal relaxation rate of 0%, to form a longitudinally / transversely stretched film; 4. A transverse stretching step 204 without longitudinal relaxation, in which the longitudinally stretched film is stretched transversely at least once from above the glass transition temperature to below the melting point of the polymer, without longitudinal relaxation, i.e., with a longitudinal / transverse stretch rate of 0%, to form a longitudinally / transversely stretched film; 5. A transverse relaxation step 205, in which the longitudinally / transversely stretched film is relaxed transversely at least once from above the glass transition temperature to below the melting point of the polymer, to form a microporous thin film material; and 6. A winding step 206, in which the microporous thin film material is wound into a roll and stored.

[0034] The stretching ratio in the transverse direction without longitudinal relaxation in the transverse stretching step 204 was 1.1 to 2.5 times. The pore morphology of the surface of the microporous thin film material was observed under an electron microscope at a magnification of 10,000 times, the thickness was measured with a thickness gauge, the gas permeability was measured with a Gurley gas permeability analyzer, and the porosity was calculated according to the ASTM D2873 standard.

[0035] Figure 3 shows an electron microscope image of a microporous thin film material produced at a transverse stretching ratio of 1.5x. Figure 3 shows a microporous thin film material produced by a process in which the transverse stretching ratio was 1.5x and no longitudinal relaxation was performed. The light-colored areas are the main surface of the microporous thin film material, and the dark-colored areas are the porous areas, which show uniform micropores with a size of 1 micron or less. The microporous thin film material produced at a transverse stretching ratio of 1.5x had a thickness of 11.8 microns, a gas permeability of 1.5 seconds / 10cc, and a porosity of 60%.

[0036] FIG. 4 shows an electron microscope image of a microporous thin film material produced at a transverse stretching ratio of 1.75 times. Figure 4 shows uniform micropores of less than 1 micron in size. The microporous thin film material produced at a transverse stretching ratio of 1.75 times had a thickness of 11.7 microns, a gas permeability of 1.0 sec / 10 cc, and a porosity of 64%.

[0037] FIG. 5 shows an electron microscope image of a microporous thin film material produced at a transverse stretching ratio of 2.0 times. Figure 5 shows uniform micropores of less than 1 micron in size. The microporous thin film material produced at a transverse stretching ratio of 2.0 times had a thickness of 11.6 microns, a gas permeability of 0.8 seconds / 10 cc, and a porosity of 66%.

[0038] FIG. 6 shows an electron microscope image of a microporous thin film material produced at a transverse stretching ratio of 2.25 times. Figure 6 shows uniform micropores with a size of 1 micron or less. The microporous thin film material produced at a transverse stretch ratio of 2.25 times had a thickness of 11.5 microns, a gas permeability of 0.6 seconds / 10 cc, and a porosity of 69%.

[0039] FIG. 7 shows an electron microscope image of a microporous thin film material produced at a transverse stretching ratio of 2.5 times. Figure 7 shows uniform micropores less than 1 micron in size. The microporous thin film material produced at a transverse stretching ratio of 2.5 times had a thickness of 11.3 microns, a gas permeability of 0.5 seconds / 10 cc, and a porosity of 71%.

[0040] The above describes the best mode for carrying out the present invention, and the scope of the present invention is not limited thereto. All changes and modifications that do not deviate from the scope of the claims are included within the scope of the present invention. [Explanation of symbols]

[0041] 101. Extruding a polymer into at least a single layer of a non-porous precursor. 102 Biaxially stretching the non-porous precursor 201 Non-porous precursor extrusion process 202 Annealing and aging process 203 Machine direction stretching process with or without transverse relaxation 204 Transverse stretching process without longitudinal relaxation 205 Lateral relaxation process 206 Winding process

Claims

1. A method for producing a microporous thin film material, which is a dry stretching thin film technique, and does not add a compound to the polyolefin polymer of the material to be subsequently removed to form pores, and does not involve an extraction step, and the production method comprises:

1. A non-porous precursor extrusion step in which a semi-crystalline thermoplastic polymer is heated to extrude a non-porous precursor; 2. An annealing and aging process in which a temperature lower than the extrusion temperature is applied to cause the non-porous precursor to recrystallize, completing annealing, and then the film roll is removed from the extrusion line and stored to complete aging; 3. A longitudinal stretching step with or without transverse relaxation, in which the non-porous precursor is stretched in the longitudinal direction at a temperature between room temperature and below the melting point of the polymer, with or without transverse relaxation, to form a longitudinally stretched membrane; 4. A transverse stretching process without longitudinal relaxation, in which the longitudinally stretched film is stretched in the transverse direction at least once at a temperature between the glass transition temperature and the melting point temperature of the polymer, without longitudinal relaxation at the same time, i.e., the longitudinal relaxation ratio is 0%, and the speed of the longitudinal production line is increased to form a longitudinal / transversely stretched film; 5. A transverse relaxation step of transversely relaxing the longitudinally / transversely stretched film at least once at a temperature above the glass transition temperature and below the melting point temperature of the polymer to form a microporous thin film material; 6. A winding step of winding the microporous thin film material into a roll and storing it; in this order, the transverse stretching ratio in the transverse stretching step without longitudinal relaxation is 1.1 to 2.5 times; A method for producing a microporous thin film material, comprising:

2. A method for producing a microporous thin film material as described in claim 1, characterized in that the maturation time in the annealing and maturation process is 3 to 7 days or more when stored stationary.

3. A method for producing a microporous thin film material as described in claim 1, characterized in that the roll material, in which the longitudinally stretched film formed in the longitudinal stretching process with or without transverse relaxation is wound into a roll, is removed from the production line and stored stationary to complete secondary aging.

4. A method for producing a microporous thin film material as described in claim 3, characterized in that the secondary aging time is 3 to 7 days or more when stored statically.

5. The method for producing a microporous thin film material according to claim 1, wherein the longitudinal stretching step with or without transverse relaxation is performed at a longitudinal stretching temperature of 0 to 25°C (cold stretch) at an ambient temperature of 0 to 25°C, or at a hot stretching temperature of 10 to 100°C below the melting point temperature of the polymer.

6. A method for producing a microporous thin film material as described in claim 1, characterized in that in the transverse stretching process without longitudinal relaxation, the transverse stretching temperature is 10 to 100°C below the melting point temperature of the polymer.

7. A method for producing a microporous thin film material as described in claim 1, characterized in that the relaxation ratio in the lateral relaxation process is 2 to 10%.

8. A method for producing a microporous thin film material as described in claim 1, characterized in that the porosity of the microporous thin film material in the winding process is more than 50% or less than 90%.

9. A method for producing a microporous thin film material as described in claim 1, characterized in that the gas permeability of the microporous thin film material during the winding process is less than 4 seconds / 10 cc.

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