Nanofilm, electronic device including the nanofilm, and method for manufacturing the nanofilm

Abstract

The present invention relates to a nanofilm, a nanofilm module and an electronic device comprising the same, and a method for manufacturing the nanofilm, the nanofilm being formed of polyimide fibers having an average diameter of 0.1 [mu] m to 15 [mu] m and having a porosity of 50% to 90%, the anisotropy of machine direction (MD) strength and transverse direction (TD) strength, namely MD strength / TD strength, is 2 to 11, the ratio of the number of fiber bundles in the machine direction to the number of fiber bundles in the transverse direction, namely MD number of fiber bundles / TD number of fiber bundles, is 1.5 to 10, and the air permeability of the nanofilm is 50 to 200 cm < 3 > / cm < 2 > / sec. The nanofilm has a dust collection efficiency of 95% or more based on the following measurement method. According to the determination method, determination is carried out based on AFT 8130 under the conditions that the dust particle size is 1 [mu] m, the air flow is 32 L / min and the determination area is 100 cm < 2 >.

Description

Technical Field

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

[0002] In recent years, electronic devices such as smartphones and other communication devices are gradually becoming smaller, more integrated, and have low power consumption.

[0003] Communication devices such as smartphones have built-in microelectromechanical systems (MEMS), which contain various electronic components. In order to protect these electronic components from contamination by external pollutants, various research projects are underway on sealing materials.

[0004] However, the dust collection efficiency of the sealing materials that have been successfully commercialized is still insufficient, and due to insufficient durability, the film is damaged by tearing due to tension during the manufacturing process, resulting in quality degradation.

[0005] To solve this problem, attempts have been made to add reinforcing materials to the membrane, such as adding a small amount of inorganic particles or increasing the density of pores, but these attempts have led to problems with decreased air permeability or sound transmission loss.

[0006] Therefore, there is still a need for a nanofilm that improves durability while not reducing air permeability and sound transmission loss. Summary of the Invention

[0007] Technical issues

[0008] The present invention provides a nanofilm having excellent dust collection efficiency and durability, an electronic device including the nanofilm, and a method for manufacturing the nanofilm.

[0009] Technical Solution

[0010] According to one aspect, a nanomembrane is provided, which is formed of polyimide fibers and has a porosity of 50% to 90%, wherein the anisotropy of the machine direction (MD) strength and the transverse direction (TD) strength of the nanomembrane, i.e., the MD strength / TD strength, is 2 to 11, the ratio of the number of fiber bundles in the machine direction of the nanomembrane to the number of fiber bundles in the transverse direction, i.e., the number of MD fiber bundles / the number of TD fiber bundles, is 1.5 to 10, and the air permeability of the nanomembrane is 50 cm 3 / cm 2 / sec to 200cm 3 / cm 2 / sec, the dust collection efficiency of the nanofilm based on the following measurement method is greater than or equal to 95%.

[0011] Determination method:

[0012] The dust particle size is 1 μm, the air flow rate is 32 L / min, and the measurement area is 100 cm 2 Measured based on AFT8130 under the conditions of .

[0013] According to one embodiment, at a 94 dB reference, the sound transmission loss of the nanomembrane may be less than 5 dB / Pa.

[0014] According to one embodiment, the polyimide fiber may include polyethyleneimide, polyamideimide, polyetherimide, or a combination thereof.

[0015] According to one embodiment, the thermal shrinkage rate of the nanofilm at 300° C. may be less than or equal to 1%.

[0016] According to one embodiment, the weight loss rate of the nanofilm at 300° C. may be less than or equal to 1 weight %.

[0017] According to another aspect, a nanofilm assembly is provided, comprising: a substrate; the nanofilm; and an adhesive layer interposed between the substrate and the nanofilm.

[0018] According to another aspect, an electronic device is provided, comprising the nanofilm.

[0019] According to another aspect, a method for manufacturing a nanomembrane is provided, which includes: an electrospinning step of manufacturing a precursor by electrospinning a polyamic acid solution, wherein an anisotropic precursor is manufactured by adjusting the ratio of the machine direction (MD) winding rate to the transverse direction (TD) reciprocating rate, i.e., the MD winding rate / TD reciprocating rate; a processing step of adjusting the density and thickness of the precursor; a conversion step of determining the morphology of the precursor; and a uniaxially oriented imidization step of obtaining a nanomembrane by applying tension to the converted precursor along the machine direction to perform uniaxially oriented imidization, wherein, in the electrospinning step, air is blown in the direction in which the precursor is discharged, the value of the MD winding rate / TD reciprocating rate is 2 to 10, and the dust collection efficiency of the nanomembrane based on the following measurement method is greater than or equal to 95%.

[0020] Determination method:

[0021] The dust particle size is 1 μm, the air flow rate is 32 L / min, and the measurement area is 100 cm 2 Measured based on AFT8130 under the conditions of .

[0022] According to one embodiment, the uniaxially oriented imidization step may be performed while applying a tension of 20N to 100N to the converted precursor along the machine direction.

[0023] Beneficial effects

[0024] According to one aspect, the nanomembrane is inhibited from breaking in a roll-to-roll process by the following process, thereby improving its processability: a polyamic acid solution is electrospun at a specific temperature (e.g., 70°C), and an anisotropic precursor is obtained by adjusting the ratio of the machine direction (MD) winding rate and the transverse direction (TD) reciprocating rate, i.e., MD winding rate / TD reciprocating rate. After the precursor is processed and converted, the fiber bundles are uniaxially oriented by applying tension in the MD direction to perform uniaxial imidization, thereby achieving a ratio of the fiber bundles in the machine direction to the transverse direction of 1.5 to 10, thereby obtaining a unique pore structure, thereby improving the tensile strength in the MD direction, and inhibiting breakage in a roll-to-roll process, thereby improving processability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of a nano-membrane assembly according to one embodiment of the present invention.

[0026] Figure 2 The above diagram shows a nano-membrane assembly prepared according to an embodiment of the present invention.

[0027] Figure 3 This is a graph showing the results of a fiber arrangement experiment on the nanomembranes prepared in Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0028] Hereinafter, terms such as "above" or "above" include not only cases where a component is directly in contact with the component but also cases where the component is not in contact with the component. Singular expressions include plural expressions unless the context clearly indicates otherwise. Furthermore, when a component is described as "including" a certain component, it means that the component also includes the other components, not that the component is excluded, unless otherwise specified.

[0029] The term "said" and similar indicative terms can correspond to both the singular and the plural. The steps constituting the method can be performed in an appropriate order and are not necessarily limited to the order described unless otherwise explicitly stated.

[0030] As used herein, the terms "comprises," "includes," "formed," "having," "having," or any other modifications thereof encompass non-exclusive inclusion. For example, a process, method, article, or machine that comprises a list of elements is not necessarily limited to those elements but may include other elements not expressly listed or inherent to such process, method, article, or machine. Furthermore, unless expressly stated otherwise, "or" is intended to be an inclusive or, not an exclusive or.

[0031] All examples or exemplary terms used are used to describe the technical concept in detail, and these examples or exemplary terms do not limit the scope of the present invention unless otherwise defined in the claims.

[0032] Figure 1 is a schematic diagram of a nanomembrane assembly 10 including a nanomembrane 100, Figure 2 This is a picture showing a group of such nano-membrane modules 10 taken from above.

[0033] See also Figure 1 The nano-membrane assembly 10 includes: a nano-membrane 100; an adhesive layer 110, which is arranged on one side of the nano-membrane along the edge of the nano-membrane; and a substrate 120, which is arranged on the adhesive layer.

[0034] The nano film assembly 10 may be manufactured by disposing an adhesive film having an adhesive layer 110 disposed on a substrate 120 on one side of the nano film 100 along an edge thereof.

[0035] A dustproof part B is arranged on the part of the nano-membrane component 10 where the adhesive film is not arranged. The dustproof part B is breathable, but actually prevents dust of several microns from passing through, and has oleophobicity that substantially blocks water permeability. Therefore, when this nano-membrane component is suitable for micro-electromechanical systems (MEMS), it can prevent the performance of MEMS from being degraded due to the introduction of foreign matter such as saliva and dust.

[0036] The adhesive layer 110 may use a known adhesive that can firmly maintain adhesion between the nanofilm 100 and a subsequently applied MEMS. Examples of such adhesives include epoxy adhesives, polyurethane adhesives, acrylic adhesives, thermosetting adhesives, and petroleum resin adhesives.

[0037] For example, the adhesive layer 110 may include a thermosetting adhesive.

[0038] The substrate 120 may be a release film that serves as a carrier for placing the adhesive film on the nano-membrane 100 , and prevents the adhesive layer from being contaminated before the nano-membrane assembly 10 is subsequently used in an acoustic element such as MEMS.

[0039] The substrate 120 may be selected from known films that can be easily peeled from the adhesive layer 110 .

[0040] The nano-membrane 100 may be a nano-membrane formed of polyimide fibers having an average diameter of 0.1 μm to 15 μm.

[0041] The polyimide fiber refers to a polymer containing imide bonds in the main chain, which may include polyethylene imide, polyamide imide, polyether imide, or a combination thereof.

[0042] According to one embodiment, the polyimide fiber is made by manufacturing a precursor by electrospinning a solution containing a polyimide precursor, processing and converting the precursor, and then heating the precursor to imidize it.

[0043] Polyamic acid may be used as the polyimide precursor.

[0044] The polyamic acid solution may be prepared by dissolving a diamine monomer and a dianhydride monomer in a solvent.

[0045] The diamine monomer can be one or more selected from 4,4'-diaminodiphenyl ether (4,4'-oxydianiline, ODA), 1,3-bis(4-aminophenoxy)benzene (1,3-bis(4-aminophenoxy)benzene, RODA), p-phenylenediamine (p-PDA) and o-phenylene diamine (o-PDA), preferably, 4,4'-diaminodiphenyl ether, p-phenylenediamine, o-phenylene diamine or a mixture thereof.

[0046] The dianhydride monomer may be one or more selected from pyromellitic dianhydride (PMDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-diphenyl ether dianhydride (ODPA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and bis(3,4-dicarboxyphenyl)dimethylsilanedianhydride (SiDA).

[0047] The solvent may be one or more selected from m-cresol, N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, diethyl acetate, tetrahydrofuran (THF), chloroform and γ-butyrolactone.

[0048] The polyamic acid solution may have a solid content of 5% to 30% by weight, and a solution viscosity of 100 to 500 poise. For example, the polyamic acid solution may have a solid content of 10% to 20% by weight, and a solution viscosity of 200 to 300 poise. The solution viscosity can be measured at 23°C according to the KS MISO 2555 method. The solid content and solution viscosity may affect the quality and thickness of the resulting fiber. When the solid content and solution viscosity meet these requirements, polyimide fibers with a thickness of 0.1 μm to 15 μm can be obtained.

[0049] The electrospinning step forms a precursor by electrospinning a polyamic acid solution. To disperse the precursor during the electrospinning step, air may be blown in the direction in which the precursor is discharged. The direction of the air may be adjusted to various angles based on the direction in which the precursor is dispersed to disperse the precursor.

[0050] During the electrospinning process, a polyamic acid solution is spun from a nozzle to form a precursor. The precursor is dispersed by the electrostatic force generated between the spun precursors. At this point, air can be blown toward the precursors at a predetermined angle to disperse the precursors over a wider area. The air pressure causes the precursors to disperse and aggregate over a wider area. During this process, the solvent contained in the precursors is removed.

[0051] In the present invention, the precursor can be dispersed over a wider range by blowing air toward the precursor, so that the nanofilm 100 manufactured thereby has pores with large diameters and high air permeability.

[0052] In addition, high-temperature air can be injected horizontally during the electrospinning step to fully remove the solvent, and the pore size, porosity, physical properties, etc. of the nanomembrane 100 can be finely controlled by adjusting the air and precursors used to disperse the horizontally injected air.

[0053] Furthermore, during the electrospinning step, an anisotropic precursor can be produced by adjusting the ratio of the take-up rate in the machine direction (MD) to the reciprocating rate in the transverse direction (TD) when the spinning solution is discharged from the nozzle, i.e., the MD take-up rate / TD reciprocating rate. Producing an anisotropic precursor can improve the mechanical strength in a specific direction.

[0054] For example, the value of MD wind rate / TD reciprocation rate can be 2 to 10, 3 to 9, 4 to 8, or 5 to 7, but can include any range within the above ranges.

[0055] In the electrospinning step, the discharge rate may be 0.5 mL / min to 8 mL / min, for example, 1 mL / min to 7 mL / min, 2 mL / min to 6 mL / min, or 3 mL / min to 5 mL / min. Since the discharge rate is adjusted to the above range in the electrospinning step, the solvent is fully volatilized and stacked until a sufficient amount of fibers are discharged and accumulated in the collector, thereby forming a film, and ultimately the dust collection efficiency can be improved.

[0056] A constant electric field is applied between the nozzle and the collector to produce a nanofilm with nanofibers of constant thickness. The intensity of the electric field can be 3kV to 80kV. When the intensity of the electric field meets the range, a certain amount of spinning solution can be continuously discharged, and a nanofiber web with uniform thickness can be made. In addition, when the intensity of the electric field is too low, for example, less than 3kV, nozzle clogging may occur because the spinning solution cannot be discharged smoothly. When the intensity of the electric field is too high, for example, greater than 80kV, the solvent of the scattered fibers reaches the collector in an incompletely removed state, making it difficult to obtain nanometer-sized fibers.

[0057] The precursor composed of nanofibers can be formed by combining fibers arranged in a constant direction or randomly arranged on a collector. For example, the precursor can have a structure formed by combining fibers in a non-woven fabric form.

[0058] After the polyamic acid solution is formed into a precursor by electrospinning, a processing step is performed, namely adjusting the density and thickness of the precursor.

[0059] The processing step is a step of adjusting the density and thickness of the precursor gathered in the electrospinning step, which can be performed by a two-stage continuous calender. The processing step can be performed by applying 20 kgf / cm2 at a temperature of 20°C to 100°C. 2 Up to 200kgf / cm 2 For example, the processing step may be performed by applying 30 kgf / cm2 at a temperature of 30°C to 80°C. 2 Up to 150kgf / cm 2 Since the processing step is performed within the above temperature and pressure ranges, excellent durability can be achieved without causing sound transmission loss due to destruction of voids due to excessive density increase.

[0060] After the processing step, which adjusts the density and thickness of the precursor, comes the conversion step, which determines the morphology of the precursor.

[0061] The converting step may include slitting to obtain a product of a desired width and cross-cutting such as guillotining to obtain a product of a desired length, and may include flat-bed or rotary die-cutting to obtain a product of a desired shape.

[0062] After the conversion step, the precursor may be subjected to a uniaxially oriented imidization step in which uniaxially oriented imidization is performed by applying tension to a machine direction (MD), thereby obtaining a nanofilm.

[0063] The converted precursor can be imidized to form strong bonds between fibers.

[0064] The imidization may be performed by thermal imidization, chemical imidization, or a combination thereof.

[0065] For example, the thermal imidization process can be performed 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 performed within the above range, a polyimide nanofilm having desired physical properties can be obtained without causing damage or thermal shrinkage of the polyimide nanofilm.

[0066] For example, the chemical imidization process may be performed by contacting the converted precursor with an acid anhydride such as acetic anhydride or a tertiary amine solvent such as pyridine.

[0067] The polyimide nanofilm subjected to the imidization process may have an imidization rate greater than or equal to 90%. Since the imidization rate reaches 90% or higher, the polyimide nanofilm may have excellent heat resistance and durability capable of withstanding temperatures of 280° C. or higher.

[0068] Furthermore, the imidization process performs uniaxial imidization by applying tension, thereby providing excellent mechanical strength. For example, the uniaxial imidization step can be performed under a tension of 20N to 100N applied to the converted precursor in the machine direction.

[0069] By applying tension in the machine direction, the fibers can be oriented in the machine direction and dense imidized bonds can be formed, and the ratio of fiber bundles in the machine direction to fiber bundles in the transverse direction (i.e., the transverse direction of the machine), that is, the number of MD fiber bundles / the number of TD fiber bundles, can be changed to 1.5 to 10 (e.g., 2 to 9 or 2.5 to 8), thereby improving the strength in the machine direction and preventing breakage in the machine direction.

[0070] In addition, the anisotropy of machine direction (MD) strength and transverse direction (TD) strength, ie, MD strength / TD strength, may be 2 to 11, for example, 2.5 to 9 or 3 to 8.

[0071] Furthermore, through the imidization process, the dust collection efficiency and durability are improved without any loss of sound transmission or decrease in air permeability.

[0072] Furthermore, the polyimide nanofilm subjected to the imidization process may have a porosity of 50% or 90%. For example, the porosity of the polyimide nanofilm may be 60% to 90%, 70% to 90%, or 60% to 80%.

[0073] The dust collection efficiency of the polyimide nanofilm after the imidization process can be greater than or equal to 95% as measured by the following measurement method. For example, the dust collection efficiency of the polyimide nanofilm can be greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, or greater than or equal to 99%.

[0074] Determination method:

[0075] The dust particle size is 1 μm, the air flow rate is 32 L / min, and the measurement area is 100 cm 2 The measurement was performed based on AFT 8130.

[0076] The polyimide nanofilm produced as described above may have the following physical property values.

[0077] The polyimide nanofilm may have a thickness of 0.5 μm to 20 μm.

[0078] The air permeability of the nanofilm can be 50cm 3 / cm 2 / sec to 200cm 3 / cm 2 / sec. For example, the air permeability of the nanofilm can be 100cm 3 / cm 2 / sec to 195cm 3 / cm 2 / sec, or 110cm 3 / cm 2 / sec to 190cm 3 / cm 2 / sec.

[0079] The unit weight of the nanofilm can be 0.1 g / m 2 Up to 10g / m 2 For example, the unit weight of the nanofilm can be 1 g / m 2 Up to 5g / m 2 , or 1g / m 2 Up to 3g / m 2 .

[0080] The thermal shrinkage rate of the nanofilm at 300° C. may be less than or equal to 1%.

[0081] The nanofilm may have a weight loss rate at 300° C. that is less than or equal to 1 weight %.

[0082] At a 94 dB reference, the sound transmission loss of the nano-membrane may be less than 5 dB / Pa. For example, at a 94 dB reference, the sound transmission loss of the nano-membrane may be less than or equal to 4 dB / Pa.

[0083] Figure 3 : is a diagram showing the surface of the nanofilm in Example 1 (left side) and the nanofilm in Comparative Example 2 (right side). Figure 3 The nanomembrane in Example 1 was made by applying tension during the imidization process to perform uniaxial orientation heat treatment. It can be seen that the ratio of the machine direction to the transverse direction of the fiber bundle is larger. The nanomembrane in Comparative Example 2 was made by performing tension-free heat treatment during the imidization process. It can be seen that the orientation ratios of the machine direction to the transverse direction of the fiber bundle are almost the same.

[0084] In the prior art, in the process of imparting anisotropy to a polyimide nanomembrane, there is a problem of the membrane breaking in a specific direction due to tension. However, in a polyimide nanomembrane according to one embodiment of the present invention, the ratio of the MD winding rate to the TD reciprocating rate is adjusted during the electrospinning process of the spinning solution, and the tensile strength in the MD direction is significantly improved by uniaxially oriented imidization in the MD direction. Ultimately, a polyimide nanomembrane with significantly improved tensile strength in the MD direction can be obtained during the process.

[0085] The nano-membrane assembly according to one embodiment of the present invention can be used in various electronic devices including MEMS, such as mobile phones, tablet computers, microphones, speakers, etc.

[0086] Hereinafter, the present invention will be further described in detail through specific examples, but the present invention is not limited thereto.

[0087] Example 1

[0088] 5 L of a polyamic acid solution was prepared, wherein the solid content was 11 wt % and the solution viscosity was 250 poise (KS MISO 2555, 23° C.).

[0089] The prepared polyamic acid solution is transferred to a solution tank, supplied to a spinning chamber with 20 nozzles and a high voltage of 60kV through a quantitative gear pump, and the precursor is made by electrospinning. At this time, the discharge rate is 4mL / min, the ratio of the distance between the nozzle and the collecting plate to the distance at the end of the nozzle is 1.2, and air at 70°C is blown in the direction of discharge of the precursor to disperse the precursor. At this time, as shown in Table 1 below, the manufacturing is carried out while adjusting the winding rate of the precursor in the MD direction and the reciprocating rate in the TD direction. Afterwards, while transferring the precursor in a roll-to-roll manner, a two-stage continuous calender maintained at a temperature of 65°C is used to apply a linear pressure of 100kgf / cm for processing, and a film with a thickness of 5μm and a unit weight of 3g / m is prepared by a conversion process. 2 The converted precursor was then transferred by roll-to-roll method and imidized for 20 minutes in a continuous heat treatment furnace maintained at 400°C while applying a tension of 50N to the precursor in the machine direction. Finally, a film with a thickness of 3 μm and a unit weight of 1.5 g / m was produced. 2 polyimide nanofilm.

[0090] Example 2 to Example 7

[0091] The reaction conditions were modified to those shown in Table 1 below, and an oleophobic nanofilm was prepared by the same method as in Example 1.

[0092] Comparative Example 1

[0093] 5 L of a polyamic acid solution was prepared, wherein the solid content was 11 wt % and the solution viscosity was 250 poise (KS MISO 2555, 23° C.).

[0094] The prepared polyamic acid solution is transferred to a solution tank, and supplied to a spinning chamber with 20 nozzles and a high voltage of 60kV through a quantitative gear pump, and a precursor is made by electrospinning. At this time, the discharge rate is 4mL / min, the ratio of the distance between the nozzle and the collecting plate to the distance at the end of the nozzle is 1.2, and air at 70°C is blown in the direction of discharge of the precursor to disperse the precursor. At this time, as shown in Table 1 below, the manufacturing is carried out while adjusting the ratio of the winding rate of the precursor in the MD direction and the reciprocating rate in the TD direction. Afterwards, while transferring the precursor in a roll-to-roll manner, a two-stage continuous calender with a temperature maintained at 65°C is used to apply a linear pressure of 100kgf / cm for processing, and a film with a thickness of 5μm and a unit weight of 3g / m is prepared by a conversion process. 2 The converted precursor was transferred by roll-to-roll method and imidized for 20 minutes in a continuous heat treatment furnace maintained at 300°C while applying a tension of 10N to the precursor in the machine direction, finally forming a film with a thickness of 3μm and a unit weight of 2g / m 2polyimide nanofilm.

[0095] Comparative Example 2

[0096] 5 L of a polyamic acid solution was prepared, wherein the solid content was 11 wt % and the solution viscosity was 250 poise (KS MISO 2555, 23° C.).

[0097] The prepared polyamic acid solution is transferred to a solution tank, and supplied to a spinning chamber with 20 nozzles and a high voltage of 60kV through a quantitative gear pump, and the precursor is made by electrospinning. At this time, the discharge rate is 3mL / min, the ratio of the distance between the nozzle and the collecting plate to the distance at the end of the nozzle is 1.2, and air at 70°C is blown in the direction of discharge of the precursor to disperse the precursor. At this time, the ratio of the winding rate of the precursor in the MD direction to the reciprocating rate in the TD direction is 3.0. Afterwards, while transferring the precursor in a roll-to-roll manner, a two-stage continuous calender with a temperature maintained at 65°C is used to apply a linear pressure of 100kgf / cm for processing, and a film with a thickness of 4μm and a unit weight of 3g / m is prepared through a conversion process. 2 The converted precursor was then transferred in a roll-to-roll manner without tension and imidized in a continuous heat treatment furnace maintained at 400°C for 20 minutes, ultimately producing a polyimide nanofilm with a thickness of 3μm and a unit weight of 2.5g / m2.

[0098] Comparative Examples 3 to 5

[0099] The reaction conditions were modified to those shown in Table 1 below, and an oleophobic nanofilm was prepared by the same method as in Comparative Example 1.

[0100] Comparative Example 6

[0101] 5 L of electrospinning solution was prepared by dissolving polyvinylidene difluoride (PVDF) in dimethylformamide (DMF). The solid content of the solution was 15 wt % and the solution viscosity was 250 poise (KS MISO 2555, 23° C.).

[0102] The prepared electrospinning solution was transferred to a solution tank and supplied to a spinning chamber with 20 nozzles and a high voltage of 60kV via a quantitative gear pump to produce a PVDF nanomembrane by electrospinning. At this time, the removal rate was 4mL / min, the ratio of the distance between the nozzle and the substrate to the distance from the nozzle end was 1.2, and the ratio of the winding rate in the MD direction to the reciprocating rate in the TD direction was 0.9. Finally, a 4μm thick and 22g / m2 unit weight was produced. 2 Polyvinylidene fluoride nanofilm.

[0103] [Table 1]

[0104]

[0105]

[0106] Evaluation of nanofilms

[0107] The 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, thermal shrinkage, and weight loss rate of the nanofilms in Examples 1 to 7 and Comparative Examples 1 to 6 were measured according to the following methods. The results are shown in Table 2.

[0108] (1) Unit weight: KS K 0514 or ASTM D 3776

[0109] (2) Thickness: KS K 0506 or KS K ISO 9073-2, ISO 4593

[0110] (3) Porosity: The ratio of the air volume to the overall volume of the nanofiber membrane is calculated according to the following mathematical formula 1 (the overall volume is calculated by making a rectangular or circular sample and measuring the width, length and thickness, and the air volume is calculated by subtracting the polymer volume from the overall volume, and the polymer volume is obtained by inverse calculation from the density after measuring the mass of the sample).

[0111] [Mathematical formula 1]

[0112] Porosity (%) = [1-(A / B)] × 100 = {1-[(C / D) / B]} × 100

[0113] In Mathematical Formula 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.

[0114] (4) Air permeability: ASTM D 737, area 38cm 2 , static pressure 125Pa. 3 / cm 2 / sec) to CFM, the conversion factor is 0.508016, the unit is ft 3 / ft 2 / min(CFM).

[0115] (5) Average pore size: The average pore size and pore size distribution are determined by the diameter of the limiting pores (i.e., the pore size in the narrowest area) using a capillary flow porometer (CFP) specified in ASTM F316.

[0116] (6) Strength: The MD value and TD value were measured 10 times in accordance with ASTM D 882, and the average value was calculated after excluding the maximum and minimum values.

[0117] (7) Anisotropy of strength: The ratio of the MD / TD values of the strength was calculated.

[0118] (8) Observation of fiber arrangement: Each sample was prepared, and a SEM image of the sample was measured at a magnification of 2500 in the machine direction using FE-SEM (JSM-7900F, JEOL).

[0119] (9) Fiber bundle ratio: For the SEM image, the ratio of the number of fiber bundles in the MD direction to the number of fiber bundles in the TD direction (MD / TD) was calculated. The MD direction was determined by the fibers within 30° to the left and right of the machine direction as the reference axis, and the TD direction was determined by all fibers outside the MD direction.

[0120] (10) Sound transmission loss: The sensitivity change of the microphone is confirmed within the frequency range of the speaker (100 Hz to 20,000 Hz). The sensitivity is measured when the nanofilm component is attached to the MEMS for identifying the microphone sensitivity and when it is not attached, thereby evaluating the degree of sound transmission loss.

[0121] (11) Dust collection efficiency: When the dust size is 1 μm, the air flow rate is 32 L / min, and the measurement area is 100 cm 2 The measurement was performed using AFT 8130.

[0122] (12) Thermal shrinkage (%): After heat treatment in an oven at 300°C ± 2°C for 30 ± 2 minutes, the length change was measured after placing the specimen at 23°C ± 2°C and 50% ± 5% (relative humidity) for 24 hours.

[0123] (13) Weight loss rate: 0.5 g of each sample was prepared and heated from room temperature to 800°C at a rate of 20°C / min under nitrogen conditions using a Thermoplus EVO II TG8120 (Rigaku Corporation, Japan), and the corresponding weight change was measured.

[0124] [Table 2]

[0125]

[0126]

[0127] As shown in Table 2 above, in the nanofilms of Examples 1 to 7, the ratio of fiber bundles is greater than or equal to 1.5, and has excellent strength that can be free from breakage in the MD or TD directions during a roll-to-roll process, wherein anisotropy is imparted by a uniaxial orientation heat treatment process performed by applying tension during the imidization process.

[0128] In contrast, Comparative Example 1, in which the fiber bundle ratio was 1.1, and Comparative Example 2, in which the fiber bundle ratio was 0.9 and no uniaxial orientation heat treatment process was included, experienced breakage in the MD direction or in both the MD and TD directions during the roll-to-roll process.

[0129] Furthermore, it can be seen that the strength anisotropy of Comparative Example 3, that is, MD strength / TD strength, is 26.1, and that the sample 3 exhibits fracture along the TD direction and has extremely low dust collection efficiency.

[0130] Furthermore, it can be seen that the strength anisotropy of Comparative Example 4, ie, MD strength / TD strength, is 0.1, and the film breaks along the MD direction during the roll-to-roll process.

[0131] Furthermore, it can be seen that Comparative Example 5 has an MD / TD rate ratio of 0.1, and breaks along the TD direction occur during the roll-to-roll process.

[0132] Furthermore, it can be seen that the thermal shrinkage rate and weight loss rate of Comparative Example 6 made of PVDF are extremely high compared to Examples 1 to 7 made of polyamic acid.

[0133] Industrial Applicability

[0134] The present invention improves the tensile strength in the MD direction through a unique pore structure, thereby providing a nanofilm that can suppress breakage in a roll-to-roll process and improve processability.

Claims

1. A nanofilm formed of polyimide fibers and having a porosity of 50% to 90%, wherein: The anisotropy of the machine direction (MD) strength and the transverse direction (TD) strength of the nanomembrane, i.e., the MD strength / TD strength, is 2 to 11, the ratio of the number of fiber bundles in the machine direction of the nanomembrane to the number of fiber bundles in the transverse direction, i.e., the number of MD fiber bundles / the number of TD fiber bundles, is 1.5 to 10, and the air permeability of the nanomembrane is 50 cm 3 / cm 2 / sec to 200cm 3 / cm 2 / sec, the dust collection efficiency of the nanofilm is greater than or equal to 95% based on the following measurement method, Determination method: The dust particle size is 1 μm, the air flow rate is 32 L / min, and the measurement area is 100 cm 2 The measurement was performed based on AFT 8130 under the conditions of .

2. The nanofilm according to claim 1, wherein At a reference of 94 dB, the sound transmission loss of the nano-membrane is less than 5 dB / Pa.

3. The nanofilm according to claim 1, wherein The polyimide fiber includes polyethyleneimide, polyamideimide, polyetherimide, or a combination thereof.

4. The nanofilm according to claim 1, wherein The thermal shrinkage rate of the nanofilm at 300° C. is less than or equal to 1%.

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

6. A nano-membrane assembly comprising: substrate; The nanofilm according to any one of claims 1 to 5; as well as An adhesive layer is sandwiched between the substrate and the nanofilm.

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

8. A method for manufacturing a nanofilm, comprising: an electrospinning step of producing a precursor by electrospinning a polyamic acid solution, wherein an anisotropic precursor is produced by adjusting a ratio of a machine direction (MD) winding rate to a transverse direction (TD) reciprocating rate, i.e., MD winding rate / TD reciprocating rate; a processing step to adjust the density and thickness of the precursor; a conversion step, determining the morphology of the precursor; and a uniaxially oriented imidization step of applying tension to the converted precursor along the machine direction to perform uniaxially oriented imidization, thereby obtaining a nanofilm; wherein, 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 dust collection efficiency of the nanofilm is greater than or equal to 95% based on the following measurement method, Determination method: The dust particle size is 1μm, the air flow rate is 32L / min, and the measurement area is 100cm. 2 The measurement was performed based on AFT 8130 under the conditions of .

9. The method for producing a nanofilm according to claim 8, wherein: The uniaxially oriented imidization step is performed by applying a tension of 20N to 100N to the converted precursor along the machine direction.

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