Nanomembrane, electronic device including same, and method for manufacturing said nanomembrane

Abstract

The present invention provides a nanomembrane formed of polyimide fibers having an average diameter of 0.1 to 15 μm and a porosity of 50 to 90%, wherein the nanomembrane has an anisotropy between the strength in the machine direction (MD) and the strength in the transverse direction (TD) (MD strength / TD strength) of 2 to 11, a ratio of the number of fiber strands in the machine direction to the number of fiber strands in the transverse direction (MD fiber strands / TD fiber strands) of 1.5 to 10, and an air permeability of the nanomembrane of 50 to 200 cm 3 / cm 2 The nanomembrane has a dust collection efficiency of 95% or more as measured by the following method, a nanomembrane assembly and an electronic device including the same, and a method for manufacturing the nanomembrane. [Measurement method] Dust size: 1 μm; Air flow rate: 32 L / min; Measurement area: 100 cm 2 Measure according to AFT8130.

Description

[Technical Field]

[0001] The present invention relates to a nanomembrane having excellent dust collection efficiency and durability, an electronic device including the same, and a method for manufacturing the nanomembrane. [Background technology]

[0002] Recently, electronic devices have become communication devices such as smartphones. They are becoming smaller, more integrated, and less power-consuming.

[0003] Communication devices such as smartphones contain built-in microelectromechanical systems (MEMS), which contain a variety of electronic components. To prevent these electronic components from being contaminated by external contaminants, extensive research has been conducted on sealing materials.

[0004] However, the sealing materials that have been successfully commercialized to date not only lack dust collection efficiency but also durability, resulting in damage such as membrane tearing due to tension during the nanomembrane manufacturing process, resulting in a decline in quality.

[0005] To solve these problems, attempts have been made to add small amounts of reinforcing materials, such as inorganic particles, to the membrane or to increase the pore density, but these attempts have a limit where they cause air permeability or sound transmission loss.

[0006] Therefore, there is still a demand for nanomembranes with improved durability without reducing air permeability and sound transmission loss. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a nanomembrane having excellent dust collection efficiency and durability, an electronic device including the same, and a method for manufacturing the nanomembrane. [Means for solving the problem]

[0008] According to one aspect, a nanomembrane is formed from polyimide fibers and has a porosity of 50 to 90%, wherein the nanomembrane has an anisotropy between machine direction (MD) strength and transverse direction (TD) strength (MD strength / TD strength) of 2 to 11, a ratio of the number of fiber strands in the machine direction to the number of fiber strands in the transverse direction (MD fiber strands / TD fiber strands) of 1.5 to 10, and an air permeability of the nanomembrane of 50 to 200 cm 3 / sec, and the nanomembrane has a dust collection efficiency of 95% or more as measured by the following method.

[0009] [Measurement method] Dust size: 1 μm; Air flow: 32 l / min; Measurement area: 100 cm 2 Measured by AFT8130 at

[0010] According to one embodiment, the sound transmission loss of the nanomembrane may be less than 5 dB / pa at 94 dB.

[0011] According to an embodiment, the polyimide fiber may include polyimide, polyamideimide, polyetherimide, or a combination thereof.

[0012] According to one embodiment, the nanomembrane may have a thermal shrinkage rate of 1% or less at 300°C.

[0013] According to one embodiment, the weight loss rate of the nanomembrane at 300°C may be 1 wt% or less.

[0014] According to another aspect, a nanomembrane assembly is provided that includes a substrate; the nanomembrane; and an adhesive layer interposed between the substrate and the nanomembrane.

[0015] Another aspect provides an electronic device comprising the nanomembrane.

[0016] In another aspect, there is provided a method for producing a nanomembrane, the method comprising: an electrospinning step of electrospinning a polyamic acid solution to produce a precursor, wherein the ratio of the take-up speed in the machine direction (MD) to the reciprocating speed in the transverse direction (TD) in the electrospinning step (MD take-up speed / TD reciprocating speed) is adjusted to produce an anisotropic precursor; a processing step of adjusting the density and thickness of the precursor; a converting step of determining the shape of the precursor; and a step of applying tension in the MD direction to the converted precursor to imidize it in a uniaxial orientation to obtain a nanomembrane; wherein air is blown in the direction in which the precursor is discharged, and the value of the MD take-up speed / TD reciprocating speed is 2 to 10, and the nanomembrane has a dust collection efficiency of 95% or more as measured by the following method.

[0017] [Measurement method] Dust size: 1 μm; Air flow: 32 l / min; Measurement area: 100 cm 2 Measured by AFT8130 at

[0018] According to one embodiment, the uniaxially oriented imidization step may be performed by applying a tension of 20N to 100N to the converted precursor in the machine direction. [Effects of the Invention]

[0019] In one aspect, nanomembranes are made by electrospinning a polyamic acid solution at a specific temperature, e.g., 70°C. The ratio of the take-up speed in the machine direction (MD) to the reciprocating speed in the transverse direction (TD) (MD take-up speed / TD reciprocating speed) is adjusted to obtain an anisotropic precursor. This precursor is then processed and converted, and tension is applied in the MD direction to imidize it into a uniaxially oriented membrane. This results in a ratio of the number of fiber strands in the machine direction to the number of fiber strands in the transverse direction of 1.5 to 10. The resulting unique pore structure improves tensile strength in the MD direction, suppresses breakage during roll-to-roll processing, and improves processability. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram of a nanomembrane assembly according to an embodiment of the present invention. [Figure 2] 1 is a photograph taken from above of a nanomembrane assembly manufactured according to an embodiment of the present invention. [Figure 3] 1 is a photograph showing the experimental results of fiber arrangement for the nanomembranes prepared in Example 1 and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, the terms "top" and "above" may refer not only to something directly on top in contact with the object, but also to something on top without contact. The singular expression includes the plural expression unless the context clearly indicates otherwise. Furthermore, when a part is described as "comprising" a certain element, this does not mean that it excludes other elements, but that it may further include other elements, unless otherwise specified.

[0022] The use of the term "said" and similar directives can refer to both the singular and the plural. Unless a clear order is stated for method steps or a statement to the contrary, these steps can be performed in any suitable order and are not necessarily limited to the order stated.

[0023] As used herein, the terms "comprise," "comprising," "formed," "has," "having," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that includes a list of elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent in such process, method, article, or apparatus. Furthermore, unless clearly stated to the contrary, "or" refers to an inclusive or and not an exclusive or.

[0024] The use of any examples or exemplary terms is merely to illustrate the technical concepts in detail, and such examples or exemplary terms are not intended to limit the scope unless otherwise limited by the claims.

[0025] FIG. 1 is a schematic diagram of a nanomembrane assembly (10) containing a nanomembrane (100), and FIG. 2 is a photograph taken from above of a group of such nanomembrane assemblies (10).

[0026] Referring to Figure 1, the nanomembrane assembly (10) includes a nanomembrane (100), an adhesive layer (110) arranged on one side of the nanomembrane along the frame of the nanomembrane; and a substrate (120) arranged on the adhesive layer.

[0027] The nanomembrane assembly (10) can be manufactured by placing an adhesive film having an adhesive layer (110) disposed on a substrate (120) all over the periphery of the nanomembrane (100).

[0028] A dustproof section (B) is formed in the part of the nanomembrane assembly (10) where the adhesive film is not placed, and the dustproof section (B) allows air to pass through but not substantially allows dust particles of a few microns to pass through, and has oil-proof properties that substantially prevent the passage of moisture. Therefore, when such a nanomembrane assembly is applied to a microelectromechanical system (MEMS), it can prevent the performance of the MEMS from being degraded by the inflow of foreign substances such as saliva and dust.

[0029] The adhesive layer (110) can be made of a known adhesive that can firmly maintain adhesion between the nanomembrane (100) and the MEMS that will be applied later, and examples of such adhesives include epoxy adhesives, urethane adhesives, acrylic adhesives, thermosetting adhesives, petroleum resin adhesives, etc.

[0030] For example, the adhesive layer (110) may include a thermosetting adhesive.

[0031] The substrate (120) can be a release film that acts as a carrier for placing an adhesive film on the nanomembrane (100) and prevents contamination of the adhesive layer prior to subsequent application of the nanomembrane assembly (10) to an acoustic device such as a MEMS.

[0032] The substrate (120) can be selected from known films that are easily peeled from the adhesive layer (110).

[0033] The nanomembrane 100 may be a nanomembrane formed of polyimide fibers having an average diameter of 0.1 to 15 μm.

[0034] The polyimide fiber refers to a polymer containing an imide bond in the main chain, and may include polyimide, polyamideimide, polyetherimide, or a combination thereof.

[0035] According to one embodiment, the polyimide fiber may be prepared by electrospinning a solution containing a polyimide precursor to prepare a precursor, processing and converting the precursor, and then heating the precursor to imidize it.

[0036] The polyimide precursor may be a polyamic acid.

[0037] The syngid polyamic acid solution can be prepared by dissolving a diamine monomer and a dianhydride monomer in a solvent.

[0038] The diamine monomer may be at least one selected from the group consisting of 4,4'-oxydianiline (ODA), 1,3-bis(4-aminophenoxy)benzene (RODA), p-phenylene diamine (p-PDA), and o-phenylene diamine (o-PDA), and preferably 4,4'-oxydianiline (ODA), p-phenylene diamine (p-PDA), o-phenylene diamine (o-PDA), or a mixture thereof.

[0039] The dianhydride monomer may be at least one selected from the group consisting of pyromellitic dianhydride (PMDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 4,4'-oxydiphthalic anhydride (ODPA), 3,4,3',4'-biphenyltetracarboxylic dianhydride (BPDA), and bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride (SiDA).

[0040] The solvent may be one or more selected from the group consisting of m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), acetone, diethyl acetate, tetrahydrofuran (THF), chloroform, and γ-butyrolactone.

[0041] The polyamic acid solution may have a solids content of 5 to 30 wt % and a solution viscosity of 100 to 500 poise. For example, the polyamic acid solution may have a solids content of 10 to 20 wt % and a solution viscosity of 200 to 300 poise. The solution viscosity can be measured at 23°C using the KSMISO 2555 method. The solids content and solution viscosity can affect the quality and thickness of the resulting fiber, but when the solids content and solution viscosity are satisfied, polyimide fibers of 0.1 to 15 μm can be obtained.

[0042] The electrospinning step is a step of electrospinning a polyamic acid solution to produce a precursor. To disperse the precursor during the electrospinning step, air can be blown in the direction of the precursor being extruded. The direction of the air can be adjusted at various angles based on the direction of the precursor being extruded to disperse the precursor.

[0043] During electrospinning, a polyamic acid solution is spun from a nozzle to produce a precursor, which is dispersed by electrostatic forces generated between the spun precursors. To disperse the precursor over a wider area, air can be blown toward the precursor at a specific angle. The pressure of the air disperses the precursor over a wider area, causing it to accumulate. During this process, the solvent contained in the precursor is removed.

[0044] In the present invention, by blowing air toward the precursor, the precursor can be dispersed over a wider area, and the nanomembrane (100) thus produced has pores with large diameters and high air permeability.

[0045] In addition, in order to thoroughly remove the solvent during the electrospinning step, high-temperature air can be injected horizontally, and the temperature and amount of the horizontally injected air and the air for dispersing the precursor can be adjusted to finely adjust the pore size, porosity, and physical properties of the nanomembrane (100).

[0046] In addition, in the electrospinning step, when the spinning solution is discharged through a nozzle, an anisotropic precursor can be produced by adjusting the ratio of the machine direction (MD) winding speed and the transverse direction (TD) reciprocating speed (MD winding speed / TD reciprocating speed). By producing an anisotropic precursor, improved mechanical strength in a specific direction can be expected.

[0047] For example, the MD winding speed / TD reciprocating speed value can be 2 to 10 days, 3 to 9, 4 to 8, or 5 to 7 days, including any range within the above ranges.

[0048] The discharge rate in the electrospinning step may be 0.5 to 8 ml / min, for example, 1 to 7 ml / min, 2 to 6 ml / min, or 3 to 5 ml / min. By adjusting the discharge rate in the electrospinning step within this range, a sufficient amount of fibers can be discharged and collected from the collector, and the solvent can be sufficiently evaporated and layered to form a membrane, thereby increasing the dust collection efficiency.

[0049] A certain electric field can be applied between the nozzle and the collector to produce a nanomembrane with nanofibers of a certain thickness. The strength of the electric field can be 3 to 80 kV. When the electric field strength is within this range, a certain amount of spinning solution can be continuously discharged, making it possible to produce a nanofiber web of uniform thickness. On the other hand, if the electric field strength is too low, for example, less than 3 kV, the spinning solution cannot be discharged smoothly, which can lead to nozzle clogging. If the electric field strength is too high, for example, more than 80 kV, the solvent in the scattered fibers reaches the collector without being completely removed, making it difficult to obtain nano-sized fibers.

[0050] The nanofiber precursor may be formed by bonding fibers that are aligned in a specific direction or randomly aligned in a collector, for example, the precursor may have a structure formed by bonding in the form of a nonwoven fabric.

[0051] A polyamic acid solution is electrospun to form a precursor, followed by a processing step to control the density and thickness of the precursor.

[0052] The processing step is a step of adjusting the density and thickness of the precursor accumulated in the electrospinning step, and can be carried out through a two-stage continuous calender. The processing step is carried out at a temperature of 20 to 100°C and a pressure of 20 to 200 kgf / cm. 2 For example, the processing step can be carried out at a temperature of 30 to 80°C and a pressure of 30 to 150 kgf / cm. 2 By carrying out the processing step within the above temperature and pressure ranges, there is no sound transmission loss due to void destruction caused by excessive density increase, and excellent durability can be achieved.

[0053] The processing step, which adjusts the density and thickness of the precursor, is followed by a converting step, which determines the shape of the precursor.

[0054] The converting step can include cross-cutting, such as slitting to obtain articles of the desired width and guillotining to obtain articles of the desired length, and can include, for example, flat or rotary die cutting to obtain articles of the desired shape.

[0055] The precursor that has undergone the converting step can be subjected to a step of imidizing it in a uniaxial orientation by applying tension in the machine direction (MD) to obtain a nanomembrane.

[0056] The converted precursor can be imidized to form strong bonds between fibers.

[0057] The imidization can be carried out by thermal imidization, chemical imidization, or a combination thereof.

[0058] For example, the thermal imidization process can be carried out by heating the converted precursor at a temperature of 200°C to 500°C for 10 to 30 minutes. When the thermal imidization process is carried out within the above range, a polyimide nanomembrane with desired physical properties can be obtained without destruction or thermal shrinkage of the polyimide nanomembrane.

[0059] For example, the chemical imidization step can be carried out by contacting the converted precursor with a solvent such as an acid anhydride, such as acetic anhydride, or a tertiary amine, such as pyridine.

[0060] The polyimide nanomembrane that has undergone the imidization process can have an imidization rate of 90% or more, which allows it to have excellent heat resistance and durability, even at temperatures above 280°C.

[0061] In addition, the imidization process can provide excellent mechanical strength by applying tension in the machine direction to imidize the converted precursor in a uniaxial orientation. For example, the uniaxial imidization process can be performed by applying a tension of 20N to 100N in the machine direction to the converted precursor.

[0062] By applying tension in the machine direction, the fibers are oriented in the machine direction and imidization bonds are formed densely, and the ratio of the number of fiber strands in the machine direction to the number of fiber strands in the width direction (i.e., cross machine direction) (number of MD fiber strands / number of TD fiber strands) is changed to 1.5 to 10, for example, 2 to 9 or 2.5 to 8, thereby improving the strength in the machine direction and suppressing breakage in the machine direction.

[0063] The anisotropy between the strength in the machine direction (MD) and the strength in the transverse direction (TD) (MD strength / TD strength) may be 2 to 11, for example, 2.5 to 9 or 3 to 8.

[0064] Furthermore, the imidization process has the effect of improving dust collection efficiency and durability without reducing sound transmission loss and air permeability.

[0065] Furthermore, the polyimide nanomembrane obtained through the imidization process may have a porosity of 50 to 90%. For example, the porosity of the polyimide nanomembrane may be 60 to 90%, 70 to 90%, or 60 to 80%.

[0066] The polyimide nanomembrane that has undergone the imidization process may have a dust collection efficiency of 95% or more, as measured by the following method. For example, the dust collection efficiency of the polyimide nanomembrane may be 96% or more, 97% or more, 98% or more, or 99% or more.

[0067] [Measurement method] Dust size: 1 μm; Air flow: 32 l / min; Measurement area: 100 cm 2 Measured by AFT8130 at

[0068] The polyimide nanomembrane manufactured as described above can have the following physical properties:

[0069] The polyimide nanomembrane may have a thickness of 0.5 to 20 μm.

[0070] The air permeability of the nanomembrane is 50 to 200 cm 3 / cm 2 For example, the air permeability of the nanomembrane may be 100 to 195 cm 3 / cm 2 / sec, or 110 to 190 cm 3 / cm 2 / sec.

[0071] The nanomembrane has a unit weight of 0.1 to 10 g / m 2For example, the nanomembrane may have a unit weight of 1 to 5 g / m 2 , or 1 to 3 g / m 2 It is possible.

[0072] The nanomembrane may have a thermal shrinkage of 1% or less at 300°C.

[0073] The weight loss rate of the nanomembrane at 300°C may be 1% by weight or less.

[0074] The nanomembrane may have a sound transmission loss of less than 5 dB / pa at 94 dB, for example, a sound transmission loss of 4 dB / pa or less at 94 dB.

[0075] Figure 3 is a photograph showing the surfaces of the nanomembrane of Example 1 (left side) and the nanomembrane of Comparative Example 2 (right side). Referring to Figure 3, it can be seen that the nanomembrane of Example 1 was produced through uniaxially oriented heat treatment by applying tension during the imidization process, and therefore the ratio of the fiber streaks in the machine direction to the width direction is higher. On the other hand, the nanomembrane of Comparative Example 2 was produced through non-tensioned heat treatment during the imidization process, and therefore the ratio of the fiber streaks in the machine direction to the width direction is almost the same.

[0076] In the past, when imparting anisotropy to polyimide nanomembranes, there was a problem of membrane breakage due to tension in a specific direction. However, in the polyimide nanomembrane according to one embodiment of the present invention, the ratio of the MD take-up speed to the TD reciprocating speed was adjusted during the electrospinning process of the spinning solution, and uniaxially oriented imidization was promoted in the MD direction, thereby significantly improving the tensile strength in the MD direction. As a result, a polyimide nanomembrane with significantly improved tensile strength in the MD direction could be obtained during the process.

[0077] The nanomembrane assembly according to an embodiment of the present invention can be used in a variety of electronic devices including MEMS, such as mobile phones, electronic pads, microphones, and speakers. [Example]

[0078] The present invention will be described in more detail below through specific examples, but the present invention is not limited to the following examples.

[0079] Example 1 5 L of polyamic acid solution was prepared with a solids content of 11 wt % and a solution viscosity of 250 poise (KSMISO2555, 23° C.).

[0080] The prepared polyamic acid solution was transferred to a solution tank and then supplied to a spinning chamber equipped with 20 nozzles and a high voltage of 60 kV via a metering gear pump. The precursor was electrospun at a discharge rate of 4 ml / min, with a ratio of the distance between the nozzle and the accumulating plate to the distance at the nozzle tip of 1.2. Air at 70°C was blown in the direction of the precursor discharge to disperse the precursor. The precursor was then manufactured while controlling the winding speed in the MD and the reciprocating speed in the TD as shown in Table 1 below. The precursor was then transferred in a roll-to-roll fashion and processed using a two-stage continuous calender maintained at 65°C, applying a linear pressure of 100 kgf / cm. The resulting precursor was then converted into a 5 μm thick film with a unit weight of 3 g / m. 2 Then, the converted precursor was transferred in a roll-to-roll manner, and imidized in a continuous heat treatment furnace maintained at a temperature of 400°C for 20 minutes while applying a tension of 50 N in the machine direction, resulting in a final thickness of 3 μm and a unit weight of 1.5 g / m. 2 A polyimide nanomembrane was fabricated.

[0081] <Examples 2 to 7> The reaction conditions were modified as shown in Table 1 below, and an oil-repellent nanomembrane was prepared in the same manner as in Example 1.

[0082] <Comparative Example 1> 5 L of polyamic acid solution was prepared with a solids content of 11 wt % and a solution viscosity of 250 poise (KSMISO2555, 23° C.).

[0083] The prepared polyamic acid solution was transferred to a solution tank and then supplied to a spinning chamber equipped with 20 nozzles and a high voltage of 60 kV via a metering gear pump. The precursor was electrospun at a discharge rate of 4 ml / min, with a nozzle-to-plate distance ratio of 1.2 to the nozzle tip distance. Air at 70°C was blown in the precursor discharge direction to disperse the precursor. The ratio of the precursor winding speed in the MD direction to the reciprocating speed in the TD direction was controlled as shown in Table 1. The precursor was then transferred in a roll-to-roll fashion and processed using a two-stage continuous calender maintained at 65°C under a linear pressure of 100 kgf / cm. The resulting precursor was converted into a 5 μm thick film with a unit weight of 3 g / m. 2 The converted precursor was transferred in a roll-to-roll manner, and the precursor was imidized for 20 minutes in a continuous heat treatment furnace maintained at a temperature of 300°C while applying a tension of 10 N in the machine direction, resulting in a final thickness of 3 μm and a unit weight of 2 g / m. 2 A polyimide nanomembrane was fabricated.

[0084] <Comparative Example 2> 5 L of polyamic acid solution was prepared with a solids content of 11 wt % and a solution viscosity of 250 poise (KSMISO2555, 23° C.).

[0085] The prepared polyamic acid solution was transferred to a solution tank and then supplied to a spinning chamber equipped with 20 nozzles and a high voltage of 60 kV via a metering gear pump. The precursor was electrospun. The discharge rate was 3 ml / min, the ratio of the distance between the nozzle and the accumulating plate to the distance at the nozzle tip was 1.2, and air at 70°C was blown in the direction of the precursor discharge to disperse the precursor. The ratio of the precursor's winding speed in the MD to its reciprocating speed in the TD was 3.0. The precursor was then transferred in a roll-to-roll fashion and processed using a two-stage continuous calender maintained at 65°C, applying a linear pressure of 100 kgf / cm. After the converting process, the precursor was processed to a thickness of 4 μm and a unit weight of 3 g / m. 2 The converted precursor was then imidized for 20 minutes in a continuous heat treatment furnace maintained at a temperature of 400°C while being transported in a roll-to-roll manner without tension, resulting in a final thickness of 3 μm and a unit weight of 2.5 g / m. 2 A polyimide nanomembrane was fabricated.

[0086] <Comparative Examples 3 to 5> The reaction conditions were modified as shown in Table 1 below, and an oil-repellent nanomembrane was produced in the same manner as in Comparative Example 1.

[0087] <Comparative Example 6> Polyvinylidene difluoride (PVDF) was dissolved in dimethylformamide (DMF) solvent to prepare 5 L of electrospinning solution with a solid content of 15 wt % and a solution viscosity of 250 poise (KS MISO 2555, 23°C).

[0088] The electrospinning solution was transferred to a solution tank and then supplied to a spinning chamber consisting of 20 nozzles and a high voltage of 60 kV via a metering gear pump. PVDF nanomembranes were then electrospun. The discharge rate was 4 ml / min, the ratio of the distance between the nozzle and the accumulating plate to the distance at the nozzle tip was 1.2, and the ratio of the winding speed in the MD direction to the reciprocating speed in the TD direction was 0.9. Finally, a membrane with a thickness of 4 μm and a unit weight of 2 g / m was obtained. 2 Polyvinylidene fluoride nanomembranes were fabricated.

[0089] [Table 1]

[0090] <Nanomembrane evaluation> The nanomembranes of Examples 1 to 7 and Comparative Examples 1 to 6 were measured for unit weight, thickness, porosity, air permeability, average pore size, tensile strength (MD), tensile strength (TD), roll-to-roll stability, sound transmission loss, dust collection efficiency, heat shrinkage, and weight loss using the following methods, and the results are shown in Table 2.

[0091] (1) Unit weight: KSK0514 or ASTM D3776 (2) Thickness: KSK0506 or KSK ISO 9073-2, ISO 4593

[0092] (3) Porosity: Calculated as the ratio of air volume to the total volume of the nanofiber membrane based on the following equation 1 (total volume was calculated by manufacturing a rectangular or circular sample and measuring its width, length, and thickness, and air volume was calculated by measuring the mass of the sample and subtracting the polymer volume, calculated from the density, from the total volume).

[0093] [Formula 1] Porosity (%) = [1-(A / B)] x 100 = {1-[(C / D) / B]} x 100

[0094] In Equation 1, A is the density of the nanomembrane, B is the density of the nanomembrane polymer, C is the weight of the nanomembrane, and D is the volume of the nanomembrane.

[0095] (4) Air permeability: ASTM D737, area 38 cm 2 , measured under a constant pressure of 125 Pa (cm 3 / cm 2 / sec) can be converted to CFM (Cubic Feet per Minute), with a conversion factor of 0.508016, and the unit is ft 3 / ft 2 / min (CFM).

[0096] (5) Average pore diameter: Using a capillary flow porometer (CFP) specified in ASTM F316, the average pore size and pore size distribution were measured from the diameter of the limiting pore, which is the pore size at the narrowest section.

[0097] (6) Strength: According to ASTM D882, MD (machine direction) and TD (transverse direction) were measured 10 times each, and the average value was calculated by excluding the maximum and minimum values.

[0098] (7) Strength anisotropy: Calculate the ratio of the MD / TD values ​​of the strength.

[0099] (8) Fiber arrangement observation: Each sample was prepared, and an FE-SEM (JSM-7900F, JEOL) was used to measure the sample at a magnification of 2500 times with the machine direction as the reference, to obtain SEM photographs.

[0100] (9) Ratio of fiber streaks: In the SEM photograph, the ratio of the number of fiber streaks in the MD direction to the number of fiber streaks in the TD direction (MD / TD) was calculated. The criterion for determining the MD direction is the fibers within a range of 30° to the left and right of the machine direction as the reference axis. TD is all fibers other than those in the MD direction.

[0101] (10) Sound transmission loss: The change in microphone sensitivity was confirmed within the speaker frequency range (100 to 20,000 Hz), and the sensitivity was measured when a nanomembrane assembly was attached to the MEMS that detects the microphone sensitivity, and when it was not attached, to evaluate the degree of sound loss.

[0102] (11) Dust collection efficiency: Dust size 1 μm, air flow rate 32 l / min, and measurement area 100 cm 2 Measured using AFT8130.

[0103] (12) Heat shrinkage rate (%): After heat treatment in an oven at a temperature of 300°C ± 2°C for 30 ± 2 minutes, the sample is left at a temperature of 23°C ± 2°C and a humidity (relative humidity) of 50% ± 5% for 24 hours, and then the change in length is measured.

[0104] (13) Weight loss rate: 0.5 g of each sample was prepared, and the samples were heated under nitrogen conditions at a rate of 20°C / min from room temperature to 800°C using a TGA analyzer (Thermoplus EVOII TG8120, Rigaku Co., Ltd.), and the resulting weight change was measured.

[0105] [Table 2]

[0106] As shown in Table 2, the nanomembranes of Examples 1 to 7 have a fiber ratio of 1.5 or more, and by applying tension during the imidization process and undergoing a uniaxially oriented heat treatment process, they are anisotropic, and have excellent strength that does not break in the MD or TD direction during the roll-to-roll process.

[0107] On the other hand, in Comparative Example 1, in which the ratio of fiber strands is 1.1, and Comparative Example 2, in which the ratio of fiber strands is 0.9 and does not include a uniaxial orientation heat treatment process, it can be confirmed that fractures occur in the MD or MD and TD directions during the roll-to-roll process.

[0108] Furthermore, in Comparative Example 3, in which the strength anisotropy (MD strength / TD strength) was 26.1, fracture occurred in the TD direction, and it was confirmed that the dust collection efficiency was very low.

[0109] Furthermore, it can be confirmed that Comparative Example 4, in which the strength anisotropy (MD strength / TD strength) is 0.1, breakage occurs in the MD direction during the roll-to-roll process.

[0110] Furthermore, it can be confirmed that in Comparative Example 5, where the MD / TD speed ratio is 15, fracture occurs in the TD direction during the roll-to-roll process.

[0111] On the other hand, it can be seen that Comparative Example 6 made of PVDF has significantly higher sound transmission loss, heat shrinkage rate and weight loss rate than Examples 1 to 7 made of polyamic acid. [Industrial Applicability]

[0112] The present invention can provide a nanomembrane with improved tensile strength in the MD direction due to its unique pore structure, and with reduced breakage during roll-to-roll processing, improving processability.

Claims

1. A nanomembrane formed of polyimide fibers and having a porosity of 50 to 90%, The nanomembrane has an anisotropy between machine direction (MD) strength and transverse direction (TD) strength (MD strength / TD strength) of 2 to 11; The nanomembrane has a ratio of the number of fiber strands in the machine direction to the number of fiber strands in the width direction (MD fiber strands / TD fiber strands) of 1.5 to 10; The air permeability of the nanomembrane is 50 to 200 cm ３ / cm ２ / sec, The nanomembrane has a dust collection efficiency of 95% or more as measured by the following method: [Measurement method] Dust size: 1 μm; Air flow rate: 32 l / min; Measurement area: 100 cm ２ Measured by AFT8130 at .

2. 10. The nanomembrane of claim 1, wherein the nanomembrane has a sound transmission loss of less than 5 dB / pa at a 94 dB standard.

3. 10. The nanomembrane of claim 1, wherein the polyimide fibers comprise polyimide, polyamideimide, polyetherimide, or a combination thereof.

4. The nanomembrane according to claim 1, wherein the nanomembrane has a thermal shrinkage rate of 1% or less at 300°C.

5. The nanomembrane according to claim 1, wherein the weight loss rate of the nanomembrane at 300°C is 1% by weight or less.

6. Base material; The nanomembrane of any one of claims 1 to 5; and an adhesive layer interposed between the substrate and the nanomembrane; A nanomembrane assembly comprising:

7. An electronic device comprising the nanomembrane of any one of claims 1 to 5.

8. an electrospinning step of electrospinning a polyamic acid solution to produce a precursor, wherein the ratio of a machine direction (MD) take-up speed to a transverse direction (TD) reciprocating speed (MD take-up speed / TD reciprocating speed) in the electrospinning step is adjusted to produce an anisotropic precursor; a processing step for adjusting the density and thickness of the precursor; a converting step to determine the shape of the precursor; and The converted precursor is imidized in a uniaxial orientation by applying tension in the MD direction to obtain a nanomembrane; In the electrospinning step, air is blown in the direction in which the precursor is discharged, the value of the MD winding speed / TD reciprocating speed is 2 to 10; The nanomembrane manufacturing method is characterized in that the nanomembrane has a dust collection efficiency of 95% or more as measured by the following method. [Measurement method] Dust size: 1 μm; Air flow rate: 32 l / min; Measurement area: 100 cm ２ Measured by AFT8130 at .

9. The method of claim 8, wherein the imidization step is performed by applying a tension of 20N to 100N in the converted machine direction.

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