KR101479758B1 - Polyimide nanofiber filter with excellent heat-resisting property and its method - Google Patents

Abstract

A polyimide nanofiber filter with enhanced heat resistance is manufactured by using meta-aramid as a filter base material and heat resistant polyimide as a nanofiber material. Therefore, the polyimide nanofiber filter has excellent thermal stability and is highly functional. A method for manufacturing the functional filter with excellent thermal stability includes the steps of: producing a polyamic acid solution by dissolving polyamic acid in an organic solvent; stacking polyamic acid nanofiber nonwoven fabric by electrospinning the polyamic acid solution on the meta-aramid base material; and imidizing the polyamic acid nanofiber nonwoven fabric by treating the laminated polyamic acid nanofiber nonwoven fabric with heat.

Description

TECHNICAL FIELD [0001] The present invention relates to a polyimide nanofiber filter having improved heat resistance and a method for manufacturing the same,

The present invention relates to a polyimide nanofiber filter having improved heat resistance and a method of manufacturing the same. More particularly, the present invention relates to a polyimide nanofiber filter fabricated by laminating a polyamic acid nanofiber nonwoven fabric by electrospinning a polyamic acid on a heat- The present invention relates to a polyimide nanofiber filter having improved heat resistance and imidizing a nanofiber nonwoven fabric and a method for producing the same.

In recent years, as the industry has become more sensitive to environmental pollution due to the development of the industry, the development of filters for filtering various harmful substances and air has been actively progressed. Generally, as a filtration device for filtering foreign matters in a fluid, the filter performs functions such as refining of industrial products, purification treatment facilities, adsorption and removal of harmful exhaust gases, and the like.

Among them, an air filter for filtering harmful substances of air forms a microporous porous layer on the surface of the filter filter material, thereby performing a function of preventing the dust from penetrating into the filter material and performing filtration. However, conventional filters have difficulties in filtering nano-sized fine fibers due to the limit of the fiber diameter. Therefore, large particles are formed by a filter cake deposited on the filter media surface, and fine particles pass through the primary surface layer and gradually accumulate in the filter media, thereby blocking the pores of the filter. As a result, large particles and fine particles that trap the pores of the filter increase the pressure loss of the filter, deteriorate the life of the filter, and decrease the efficiency. In addition, the efficiency of the conventional air filter is measured by the principle that the static electricity is given to the fibrous aggregate constituting the filter medium and the particles are collected by the electrostatic force. However, recent European air filter classification standard EN779 has been found to reduce the actual efficiency of existing filters by more than 20%, as it is decided to exclude the efficiency of the filter due to the electrostatic effect in 2012.

In addition, since the glass fiber used as the material of the conventional heat-resistant filter breaks the minute glass fragments with time, and workers can inhale the glass fragments, the regulation of the use of glass fiber for environmental stability in Europe and the United States to be.

In order to solve the above-mentioned problems, various methods of applying nano-sized fibers to cellulose or synthetic fiber substrates by electrospinning and applying them to filters have been developed. When nanofibers are implemented in a filter, they have a large specific surface area compared to conventional filter media having a large diameter, good flexibility for surface functional groups, and nanoparticle pore size, so that harmful fine particles and gas can be efficiently removed It was.

However, the implementation of the filter using the nanofibers causes a large production cost, and it is not easy to control various conditions for production, and since it is difficult to mass-produce the filter, the filter using the nanofiber is produced at a relatively low unit price I can not.

In addition, a filter used in a gas turbine, a furnace, and the like requires a filter having a higher heat resistance than that of a conventional filter in order to satisfy heat resistance. Accordingly, there is a need for a filter having heat resistance in both existing substrates and nano- Was raised.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method for producing a heat resistant material, which uses a heat resistant material such as meta-aramid and simultaneously uses polyamic acid as a heat- And an object of the present invention is to provide an improved polyimide nanofiber filter and a method for manufacturing the same.

According to a preferred embodiment of the present invention, there is provided a process for preparing a filter for electrospinning a polymer on a meta-aramid substrate, comprising the steps of: preparing a polyamic acid solution by dissolving polyamic acid in an organic solvent; And a step of heat-treating the laminated polyamic acid nanofiber nonwoven fabric to imidize the polyamic acid nanofiber nonwoven fabric. The method for manufacturing a polyimide nanofiber filter having improved heat resistance, comprising the steps of: .

According to another preferred embodiment of the present invention, the imidization step is performed by calcining at a temperature of 150 to 350 ° C.

According to another preferred embodiment of the present invention, in the step of forming the polyamic acid nanofiber nonwoven fabric layer by electrospinning the polyamic acid solution onto the meta-aramid base material, in the front end block of the electrospinning device, the polyamic acid nanofiber layer The polyamideimide nanofiber layer is electrospun on the meta-aramid substrate to form a laminate, and in the rear end block, a thin polyamic acid nanofiber layer having a small fiber thickness is electrospun on the polyamic acid nanofiber layer having a large fiber thickness to form a laminate .

According to another preferred embodiment of the present invention, the step of electrospinning the polyamic acid solution onto the meta-aramid substrate to form the laminate of the polyamic acid nanofiber nonwoven fabric is characterized in that the electrospinning uses a bottom-up electrospinning method.

According to another preferred embodiment of the present invention, there is provided a polyimide nanofiber filter having improved heat resistance produced by the above manufacturing method.

According to the configuration of the present invention, the objects of the present invention described above can be achieved. Specific effects according to the configuration of the present invention are as follows.

First, the heat resistance is excellent by using a meta-aramid base material having heat resistance as a filter base material.

Further, the nanofiber laminated on the filter substrate is further improved in heat resistance by using heat-resistant polyimide.

Further, by forming the nanofiber nonwoven fabric on the substrate, the filtration efficiency of the filter is excellent.

In addition, the electrospinning device for spinning nanofibers has a plurality of blocks, and mass production of nanofibers is possible.

1 is a schematic view of a filter manufactured by the present invention.
2 is a schematic view of a polyimide nanofiber filter having different fiber thicknesses produced by the present invention.
3 is a view showing an electrospinning apparatus used in the present invention.
4 is a block diagram of an electrospinning device used in the present invention.
5 is a view showing a nozzle block and a nozzle of the electrospinning device used in the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the scope of the present invention, but is merely an example, and various modifications can be made without departing from the technical spirit of the present invention.

First, an electrospinning device used in the present invention will be described with reference to the drawings.

FIG. 1 is a schematic view of a filter manufactured by the present invention, FIG. 2 is a schematic view of a polyimide nanofiber filter manufactured by the present invention having different fiber thicknesses, FIG. 3 is an illustration of an electrospinning device Fig. 4 is a block diagram of the electrospinning device used in the present invention, and Fig. 5 is a diagram of a nozzle block and a nozzle of the electrospinning device used in the present invention.

As shown in the drawing, the electrospinning apparatus 10 of the present invention is a device for supplying a spinning solution main tank (not shown) in which a spinning solution is filled and a polymer spinning solution filled in the spinning solution main tank (3) in which a plurality of nozzles (2) in the form of a pin are arranged and a polymer spraying liquid in the spinning liquid main tank (1) is discharged from a metering pump (not shown) A block 20 for accommodating therein a collector 4 spaced apart from the nozzle 2 in order to integrate the spinning solution and a voltage generating device 1 for generating a voltage to the collector, And a case 8 made of a negative conductor.

In the present invention, one spinning liquid main tank (not shown) is provided. However, in the case where the spinning liquid is composed of two or more spinning liquids, two or more main spinning liquid main tanks may be provided, or one spinning liquid main tanks It is also possible to divide into two or more spaces and supply two or more polymer spinning solution filled in each divided space.

Further, in the present invention, the electrospinning device 10 uses a bottom-up electrospinning device for spraying the spinning liquid in the upward direction.

Meanwhile, in one embodiment of the present invention, a bottom-up electrospinning device for spraying the spinning solution upward by the electrospinning device may be used, but a top-down electrospinning device for spraying the spinning solution in the downward direction may be used. A composite electrospinning device in which a spinning device is used together may also be used.

With the above structure, the electrospinning apparatus 10 is configured such that the spinning liquid filled in the spinning liquid main tank in the block 20 continuously flows into the plurality of nozzles 2 to which a high voltage is applied through the metering pump And the spinning liquid of the polymer supplied to the nozzle 2 is radiated and focused on the collector 13 with a high voltage applied thereto through the nozzle 2 to form a nanofiber nonwoven fabric (not shown) The nanofiber nonwoven fabric is laminated to produce a filter.

A feeding roller 11 for feeding a long sheet in which nanofibers are laminated by spraying the polymer spinning solution in each block 20 is provided at the front end of the electrospinning device 10 and nanofibers are laminated on the rear end Up rollers 12 for winding up a long sheet.

The elongated sheet is provided for preventing and transporting the nanofibers. One end and the other end of the elongated sheet are wound around a feeding roller 11 provided at the front end of the electrospinning device 10 and a winding roller 12 provided at the rear end.

On the other hand, the electrospinning device 10 of each block 20 is installed in the advancing direction (a) of the long sheet with respect to the collector 4. An auxiliary belt 6 is provided between the collector 4 and the long sheet and a long sheet in which nanofibers are stacked and formed on the respective collectors 4 through the auxiliary belts 6 is formed in a horizontal direction Lt; / RTI > That is, the auxiliary belt 6 rotates in synchronization with the conveyance speed of the long sheet, and has the auxiliary belt roller 7 for driving the auxiliary belt 6. The auxiliary belt roller 7 is an automatic roller having at least two frictional forces. Since the auxiliary belt 6 is provided between the collector 4 and the long sheet, the long sheet is smoothly conveyed without being attracted to the collector 4 to which the high voltage is applied.

With the structure as described above, the spinning solution filled in the spinning liquid main tank in the block 20 of the electrospinning device 10 is sprayed onto the elongate sheet placed on the collector 4 through the nozzle 2 , The spinning liquid sprayed on the long sheet is accumulated, and the nanofiber nonwoven fabric is laminated. The auxiliary belt 6 is driven by the rotation of the auxiliary belt roller 7 provided on both sides of the collector 4 so that the elongated sheet is conveyed and positioned within the block 20 at the rear end of the electrospinning device 10 And the above-described process is repeatedly performed.

5, the nozzle block 3 includes a plurality of nozzles 2 arranged upward from the discharge port, a tube 43 formed of a row of nozzles 2, a spinning solution storage tank 44, And a spinning liquid circulating pipe (45).

First, the spinning liquid storage tank 44 connected to the spinning liquid main tank to receive and store the spinning solution is connected to the nozzle 2 through the spinning liquid circulating pipe 45 by the metering pump (not shown) And the spinning solution is supplied to the spinning solution. Here, the tube 43 having a plurality of nozzles 2 in a row is supplied with the same spinning solution from the spinning solution storage tank 44, but a plurality of spinning solution main tanks are provided, It is also possible to supply a spinning liquid of different kinds to each of the tubes 43 and radiate them.

When radiated from the discharge port of the plurality of nozzles 2, the overflowed solution is moved to the overflow solution storage tank 41. The overflow solution storage tank 41 is connected to the spinning solution main tank so that the overflow solution can be reused for spinning.

The main controller 30 of the present invention controls the amount of spinning solution supplied to the nozzle block 3 and controls the amount of spinning solution supplied to the voltage generator 1, and controls the conveying speed of each block 20 according to the thickness of the nanofiber nonwoven fabric and the long sheet measured by the thickness measuring device 9.

The thickness measuring device 9 is disposed at a front end and a rear end of the block 20 and faces the long sheets with the nano fiber nonwoven fabric laminated therebetween. The thickness measuring device 9 is connected to the main controller 30 for controlling the radiation conditions of the electrospinning device 10 so that the thickness measuring device 9 measures the thickness of the non- The main controller 30 controls the conveying speed of each block 20 based on the received signal. For example, in the case of electrospinning, when the thickness of the nanofibers discharged to the block 20 located at the front end portion is measured thinly, the conveying speed of the block 20 located at the rear end portion is reduced, The thickness of the film is controlled to be constant. In addition, the main controller 30 increases the discharge amount of the nozzle block 3 and adjusts the voltage intensity of the voltage generator 1 to increase the discharge amount of the nanofibers per unit area, thereby uniformizing the thickness of the nanofiber nonwoven fabric It is possible to adjust.

The thickness measuring device 9 includes a thickness measurement unit configured to measure a distance between the nanofiber nonwoven fabric in which the nanofiber nonwoven fabric is laminated and the elongated sheet by ultrasonic measurement, and a pair of ultrasonic longitudinal waves and a transverse wave, And the thickness of the nanofiber nonwoven fabric and the long sheet is calculated on the basis of the distance measured by the pair of ultrasonic measuring devices. More particularly, the present invention relates to a method and a device for measuring the propagation time of longitudinal waves and transverse waves of longitudinal waves and transverse waves, respectively, by projecting ultrasound waves and transverse waves to longitudinal sheets laminated with nanofibers, Measuring the time, measuring a propagation time of the longitudinal wave and the transverse wave and a temperature coefficient of propagation velocity and propagation velocity of the longitudinal wave and the transverse wave at a reference temperature of the long sheet in which the nanofibers are stacked, Is a thickness measuring apparatus for calculating a thickness

The electrospinning apparatus 10 used in the present invention does not change the conveying speed from the initial value when the thickness deviation amount of the nanofiber nonwoven fabric is less than the predetermined value and sets the conveying speed to the initial value It is possible to simplify the control of the conveyance speed by the conveyance speed control apparatus. Further, in addition to the control of the conveying speed, the discharge amount and the voltage intensity of the nozzle block 3 can be adjusted. When the thickness deviation amount is less than the predetermined value, the discharge amount of the nozzle block 3 and the voltage intensity are not changed from the initial value , It is possible to control the amount of discharge of the nozzle block 3 and the intensity of the voltage to be changed from the initial value when the amount of deviation of the nozzle block 3 is equal to or larger than the predetermined value. .

The block 20 of the electrospinning apparatus 10 is divided into a front end block 20 located at the front end portion and a rear end block 20 located at the rear end portion according to the radiation position. In the embodiment of the present invention, the number of blocks is limited to two, but it is also possible to have two or more blocks.

In addition, in the present invention, the polymer solution for the same kind is radiated in each block 20, but it is also possible that two or more different polymer solutions are radiated in any one block. In each block 20, It is also possible to emit the polymer spinning solution separately.

When the same polymer of the same type is electrospun in each block 20, the nanofiber nonwoven fabric discharged from the block 20 located at the front end portion and the block 20 located at the rear end of the non- It is possible to spin the nano-fiber non-woven fabric discharged from the nano-fiber nonwoven fabric with different fiber thicknesses. For example, in order to make a difference in the thickness of the fibers, it is possible to form the nanofiber nonwoven fabric having different thicknesses by varying the intensity of the voltage applied to each block 20 or adjusting the distance between the nozzle 2 and the collector 4 If the spinning liquid is the same and the supply voltage is the same, the diameter of the fiber becomes thicker as the spinning distance becomes closer, and the nanofiber nonwoven fabric having a different fiber diameter is formed according to the principle that the fiber diameter becomes narrower as the spinning distance becomes longer It is possible. The difference in fiber thickness can be determined by adjusting the concentration of the spinning liquid or by adjusting the feeding speed of the long sheet.

On the other hand, a laminating device 19 is provided at the rear end of the electrospinning device 10 of the present invention. The laminating device 19 applies heat and pressure through which the elongated sheet and the nanofiber nonwoven fabric are adhered to each other, and then wound on the winding roller 12 to produce a filter.

The electrospinning device 10 can increase the collecting area to uniform the density of the nanofibers and effectively prevent the droplet phenomenon, thereby improving the quality of the nanofibers, The nanofibers and nanofibers thereof can be mass-produced. In addition, since the material and the electrospinning condition can be controlled in the electrospinning in the block 20 having the nozzle 2 having a plurality of pins, the width and thickness of the nonwoven fabric and the filament can be freely changed and adjusted.

In addition, when the polymer is spun as described above, it differs depending on the polymer material, but it is most preferable to spin the polymer under the environmental conditions of a temperature range of 30 to 40 DEG C and a humidity of 40 to 70%.

In the present invention, the diameter of the nanofiber is preferably 30 to 1000 nm, more preferably 50 to 500 nm.

Hereinafter, the meta-aramid base used in the present invention will be described.

First, meta-aramid is one kind of polyamide and is a kind of aromatic polyamide. A polyamide is a polymer having an amide bond (-CONH) and is divided into an aliphatic polyamide and an aromatic polyamide. Among these aromatic polyamides, amide bonds bond aromatic rings such as a benzene ring to form a polymer polyamide. Aromatic polyamides, also known as aramids, have enough strength to lift a 2-tonne car with a thin thread about 5mm thick.

Such polyamides are generally divided into para-aramid and meta-aramid having heat-resistant properties. The para-aramid is bound to the meta-position of the benzene ring of the meta-aramid, while the benzene ring is bonded to the para-system.

(Structure 1) Structure of meta and para-aramid

The meta-aramid fibers are available from Wilmington, Delaware, USA. children. Nomex < (R) > aramid fibers available from EI du Pont de Nemours and Company, but meta-aramid fibers are available from Teijin Ltd., Tokyo, Japan Tejinconex (registered trademark); New Star (TM) meta-aramid available from Yantai Spandex Co. Ltd, Shandong, China; And Chinfunex (registered trademark) Aramid 1313, available from Guangdong Charming Chemical Co., Ltd., Shinduo, Guangdong, China.

The organic solvent may be at least one selected from the group consisting of propylene carbonate, butylene carbonate, 1,4-butyrolactone, diethyl carbonate, dimethyl carbonate, 1,2-dimethoxyethane, 1,3- N, N-dimethylacetamide, N-methyl-2-pyrrolidone, polyethylene sulfolane, tetraethylene glycol dimethyl ether, acetone, alcohol or a mixture thereof. (DMF) or dimethylacetamide (DMAc) is preferably used as the solvent, and more preferably, at least one selected from the group consisting of dimethylformamide (DMF) and dimethylacetamide (DMAc).

Meta-aramid does not burn or melt even in the fire, it is carbonized black only at 500 ℃, has excellent heat resistance, and has excellent tensile strength that does not stretch even when applied with any force. Most of all, unlike other fibers that are flame retarded or refractory treated, they are also used as eco-friendly fibers because they do not emit toxic gases or harmful substances even when carbonized.

A meta-aramid has a very strong molecular structure of the fiber itself, so it is not only strong in its original strength but also easily oriented in the fiber axis direction in the spinning stage to improve the crystallinity and increase the strength of the fiber .

In general, the specific gravity of the meta-aramid is 1.3 to 1.4, and the weight average molecular weight is preferably 300,000 to 1,000,000. The most preferred weight average molecular weight is 300,000 to 500,000.

The above-mentioned meta-aramid is used as a substrate in the present invention. Due to the characteristics of the meta-aramid as described above, it can be suitably used as a base material to secure the heat-resistant stability of the filter.

Hereinafter, the polyimide used in the present invention will be described.

First, polyimide is a polymer containing an imide group in the repeating unit. The polyimide is characterized in that its physical properties do not change even in a temperature range from -273 DEG C to 400 DEG C, and has excellent mechanical strength and heat resistance. However, most of the polyimides are insoluble and have poor physical properties and are difficult to process by conventional techniques, so it is common to process them in the form of its precursor poly (amic acid) (PAA). Therefore, the polyimide is prepared by first polymerizing a polyamic acid and then carrying out an imidation process.

Generally, polyimides are prepared by a two-step reaction.

The first step is a step of synthesizing polyamic acid. The polyamic acid is polymerized by adding a dianhydride to a reaction solution in which diamine is dissolved. In order to increase the degree of polymerization, the reaction temperature, the water content of the solvent, Purity control is required. Organic polar solvents such as dimethylacetamide (DMAc), dimethylformamide (DMF) and en-methyl-2-pyrrolidone (NMP) are mainly used as the solvent used in this step. Examples of the diamine include 4,4'-oxydianiline (ODA), para-phenylene diamine (p-PDA), and o-phenylene diamine diamine, o-PDA) may be used. Examples of the anhydride include pyromellitic dianhydride (PMDA), benzophenonetetracarboxylic dianhydride (BTDA), 4-4'-oxydiphthalic anhydride (4-4 ' bisdiphthalic anhydride (ODPA), biphenyl-tetracarboxylic acid dianhydride (BPDA), and bis (3,4'-dicarboxyphenyl) dimethylsilanediamine hydride (bis (3,4-dicarboxyphenyl) dimethylsilane dianhydride, SIDA).

(Scheme 1) Preparation of polyamic acid

The weight average molecular weight (Mw) of the polyamic acid prepared by the above method is preferably 10,000 to 500,000. If the molecular weight of the polyamic acid is less than 10,000, sufficient physical properties for forming the nanofiber nonwoven fabric can not be obtained. If the molecular weight exceeds 500,000, the handling of the solution is not easy and the processability is degraded.

The second step is the dehydration and ring-closing reaction step of producing the polyimide from polyamic acid as the following four methods.

In the re-impregnation method, a polyamic acid solution is added to an excess amount of a poor solvent to obtain a solid polyamic acid. As the re-precipitation solvent, water is mainly used, but toluene or ether is used as a co-solvent.

The chemical imidization method is a method in which a imidization reaction is chemically performed using a dehydration catalyst such as acetic anhydride / pyridine, and is useful for producing a polyimide film.

The thermal imidization method is a method in which the polyamic acid solution is heated to 150 to 350 ° C to thermally imidize it. In the simplest process and the crystallization degree is high, the amine exchange reaction occurs when the amine type solvent is used. have.

Finally, in the isocyanate method, diisocyanate is used instead of diamine as a monomer, and a monomer mixture is heated to a temperature of 120 ° C or higher to produce polyimide while CO ₂ gas is generated.

(Scheme 2) Preparation of polyimide

Hereinafter, a method for producing a polyimide nanofiber filter having improved heat resistance, which is produced by electrospinning a polyamic acid on a meta-aramid substrate prepared using the electrospinning device 10, will be described.

First, in the present invention, a polyamic acid is used as a polymer for a spinning solution, and a meta-aramid base material 100 is used as a long sheet.

A polyamic acid solution obtained by dissolving polyamic acid in an organic solvent is supplied to the spinning liquid main tank of the electrospinning device 10 and the polyamic acid solution supplied to the spinning liquid main tank is supplied through a metering pump to a nozzle block (3) in a plurality of nozzles (2). The polyamic acid solution supplied from each of the nozzles 2 is radiated and focused on the collector 4 with a high voltage applied thereto through the nozzle 2 and is electrospinned to the meta-aramid substrate 100 to form a polyamic acid nanofiber nonwoven fabric .

In the present invention, a polyamic acid solution is used as the spinning solution.

In one embodiment of the present invention, a polyamic acid solution is used as a spinning solution, but the present invention is not limited thereto.

The meta-aramid base 100 of the electrospinning apparatus 10 includes a feed roller 11 driven by a motor (not shown) and an auxiliary belt 6 driven by the rotation of the feed roller 11 The polyamic acid nanofiber nonwoven fabric is formed on the meta-aramid base material 100 and transferred while repeating the above-described process.

Hereinafter, the meta-aramid substrate 100 will be described.

The meta-aramid has a strength and elongation similar to that of ordinary nylon, but has excellent stability against heat, and is light and absorbable compared to other heat-resistant materials, because the benzene ring is bonded to the amide group at the meta position. This can be suitably used as a filter substrate since the filter stability can be ensured at higher operating conditions.

In an embodiment of the present invention, the meta-aramid substrate 100 is used instead of the long sheet, but the present invention is not limited thereto.

Thus, a nanofiber filter in which a polyamic acid nanofiber nonwoven fabric is laminated on the meta-aramid substrate 100 is produced.

On the other hand, a polyamic acid nanofiber nonwoven fabric is laminated on the meta-aramid base material by the electrospinning as described above to form a polyamic acid nanofiber filter.

As described above, the laminated polyamic acid nanofiber filter is manufactured as a polyimide nanofiber filter through thermal imidization while passing through the laminating device 19. [ Imidization in the laminating apparatus 19 is carried out at 150 to 350 ° C, and the polyamic acid nanofiber nonwoven fabric is dehydrated to prepare a polyimide nanofiber nonwoven fabric 200.

After the imidization process described above, the production of the filter of the present invention in which polyimide nanofibers are laminated on a meta-aramid substrate is completed.

Meanwhile, it is possible to change the fiber diameters of the nanofibers by changing the radiation voltages of the front end block and the rear end block 20 of the electrospinning device 10, that is, the same polyamic acid nanofiber nonwoven fabric, If the radiation voltage of the sub-block is lowered and the radiation voltage of the rear end block is increased, the nanofibers having a larger fiber diameter and the polyamic acid nanofibers having a smaller fiber diameter can be successively laminated on the meta-aramid substrate 100 . For example, a polyamic acid nanofiber nonwoven fabric having a thick fiber layer is formed at a lower end of the front end block by applying a lower voltage to the front end block, and a polyimic acid nanofiber nonwoven fabric having a higher fiber thickness is provided at a rear end block When each of the polyamic acid nanofiber nonwoven fabrics is imaged after the electrospinning process, the polyamic acid nano- The woven nonwoven fabric may be a polyimide nanofiber nonwoven fabric 300 having a large fiber thickness and a polyimide nanofiber nonwoven fabric 400 having a small fiber thickness may be laminated on the polyimide nanofiber nonwoven fabric 300 having a large fiber thickness have.

In an embodiment of the present invention, a filter may be fabricated by sequentially laminating polyamic acid nanofiber nonwoven fabrics having different fiber thicknesses by radiating a voltage difference between the block at the front end and the block at the rear end.

In order to impart a difference in fiber thickness of the polyamic acid nanofiber nonwoven fabric to the polyimic acid nanofiber nonwoven fabric, a method of imparting a different voltage intensity to each block 20 of the electrospinning device 10 is used as one embodiment. However, A method of adjusting the distance between the nozzle 2 and the collector 4 or adjusting the feeding speed of the long sheet may be used.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the invention are provided to more fully describe the present invention to those skilled in the art.

Example 1

A polyamic acid having a weight average molecular weight of 100,000 was dissolved in dimethylacetamide (DMAc) to prepare a spinning solution. The spinning solution was applied on a meta-aramid substrate having a basis weight of 30 gs, and the distance between the electrodes and the collector was 40 cm, A polyimic acid nanofiber nonwoven fabric having a thickness of 5 탆 was laminated by electrospinning under the conditions of a use liquid flow rate of 0.1 mL / h, a temperature of 22 캜 and a humidity of 20%. Then, the polyimide nanofiber filter was prepared by imidizing polyamic acid by heat treatment at 150 ° C in a laminating apparatus.

Example 2

A filter was prepared under the same conditions as in Example 1, except that the laminate was heat-treated at 250 ° C in the laminating apparatus of Example 1.

Example 3

A filter was prepared under the same conditions as in Example 1, except that the heat treatment was performed at 350 ° C in the laminating apparatus of Example 1.

Example 4

A polyamic acid solution was prepared by dissolving polyamic acid having a weight average molecular weight of 100,000 in dimethylacetamide (DMAc), and the poreamic acid solution was added to a spinning liquid main tank for supplying a spinning solution to each block of the electrospinning device . The front end block located at the front end portion was applied with an applied voltage of 15 kV, and then the polyamic acid solution was electrospun on a meta-aramid base having a basis weight of 30 gsm to laminate a polyamic acid nanofiber nonwoven fabric having a thickness of 2.5 m and a fiber diameter of 350 nm, A polyamic acid solution was applied to the polyamic acid nanofiber nonwoven fabric by electrospinning to form a laminate of a polyamic acid nanofiber nonwoven fabric having a thickness of 2.5 m and a fiber diameter of 150 nm. At this time, electrospinning was performed under the conditions of a distance between the electrode and the collector of 40 cm, a spinning solution flow rate of 0.1 mL / h, a temperature of 22 ° C, and a humidity of 20%. Thereafter, the polyimide nanofiber nonwoven fabric was imidized by heat treatment at 150 ° C in a laminating apparatus to prepare a polyimide nanofiber filter.

Comparative Example 1

A meta-aramid base was used as filter media.

Comparative Example 2

A filter was prepared in the same manner as in Example 1, except that the PET substrate was used instead of the meta-aramid substrate in Example 1.

- Evaluation of heat shrinkage

The nanofiber filter having a size of 5 cm x 2.5 cm was placed between two slide glasses, and the tube was clamped with a clip. The tube was allowed to stand at 150 ° C for 30 minutes, and the shrinkage was measured.

- Filtration efficiency measurement

The DOP test method was used to measure the efficiency of the fabricated nanofiber filter. The DOP test method is to measure the dioctyl phthalate (DOP) efficiency with an automated filter analyzer (AFT) of TSI 3160 from TSI Incorporated, which can measure the filter efficiency of the filter media material.

The automation analyzer is a device that automatically measures the velocity of air, DOP filtration efficiency, air permeability (permeability), etc. by passing DOP through the filter sheet by making particles of desired size and is a very important device for high efficiency filter.

The DOP% efficiency is defined as:

DOP% efficiency = 1 - 100 (DOP concentration downstream / DOP concentration upstream)

Here, the filtration efficiencies of Examples and Comparative Examples were measured using DOP having a particle size of 0.35 mu m.

Examples 1 to 3 Example 4 Comparative Example 1 Comparative Example 2 Heat shrinkage (%) <3 3 6 15 Filtration efficiency (%) > 84 88 60 83

Comparing the example with the comparative example 1, it can be confirmed that the filtration efficiency of the filter in which the nanofibers are laminated is superior to the filter using only the meta-aramid filter.

Comparing Examples 1 to 4 and Comparative Example 2, it was confirmed that the filter having polyimide nanofiber nonwoven fabric had a similar filtration efficiency, but the heat shrinkage was much better in Example 1 using the meta-aramid base.

Thus, those skilled in the art will appreciate that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the embodiments described above are to be considered in all respects only as illustrative and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description and all changes or modifications derived from the meaning and scope of the claims and their equivalents are to be construed as being included within the scope of the present invention do.

1: voltage generating device, 2: nozzle,
3: nozzle block, 4: collector,
6: auxiliary belt, 7: auxiliary belt roller,
8: case, 9: thickness measuring device,
10: electrospinning device, 11: feed roller,
12: take-up roller, 19: laminating apparatus,
20: block, 30: main controller,
41: Overflow solution storage tank, 43: Tubular body,
44: spinning liquid storage tank, 45: spinning liquid circulation pipe,
100: a meta-aramid substrate,
200: polyimide nanofiber nonwoven fabric,
300: polyimide nanofiber nonwoven fabric having a large fiber thickness,
400: Polyimide nanofiber nonwoven fabric having a small fiber thickness.

Claims (5)

Dissolving polyamic acid in an organic solvent to prepare a polyamic acid solution;
Electrospinning the polyamic acid solution onto a meta-aramid base to form a polyamic acid nanofiber nonwoven fabric layer; And
Heat-treating the laminated polyamic acid nanofiber nonwoven fabric to imidize the polyamic acid nanofiber nonwoven fabric;
Wherein the imidization step is carried out by plastic working at a temperature of 150 to 350 ° C.
delete The method according to claim 1,
In the step of forming the polyamic acid nanofiber nonwoven fabric layer by electrospinning the polyamic acid solution onto the meta-aramid base material, the polyamic acid nanofiber nonwoven fabric having a large fiber thickness in the front end block of the electrospinning device is subjected to electrospinning And a polyamic acid nanofiber nonwoven fabric having a small fiber thickness is electrospun on the polyamic acid nanofiber layer having a large fiber thickness to form a laminate in the rear end block;
Wherein the polyimide nanofiber filter further comprises a polyimide resin.
The method according to claim 1,
Wherein the polyimic acid solution is electrospun onto a meta-aramid base to form a layer of a polyamic acid nanofiber nonwoven fabric, wherein electrospinning employs a bottom-up electrospinning method.
A polyimide nanofiber filter having improved heat resistance, which is produced by the production method according to any one of claims 1 to 3.

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