KR102601396B1 - Method Of Manufacturing Inorganic Nano­Fiber Web At Low­Temperature - Google Patents

Abstract

The present invention relates to a method for stably and continuously mass-producing an inorganic nanofiber web at low temperature through electrospinning of a spinning solution containing oxidizing metal salt and nitrocellulose and then low-temperature firing.

Description

Low-temperature manufacturing method of inorganic nanofiber web {Method Of Manufacturing Inorganic NanoFiber Web At LowTemperature}

The present invention relates to a method for stably and continuously mass-producing an inorganic nanofiber web at low temperature through electrospinning of a spinning solution containing oxidizing metal salt and nitrocellulose and then low-temperature firing.

Inorganic nanofibers (oxides, metals) are next-generation functional fiber materials that are in the spotlight as they are widely used in applications such as electronic materials, optical materials, catalyst materials, and environmental materials. In particular, when applied as an electronic material to a flexible plastic or stretchable substrate, it is a promising material for flexible and stretchable electronic wearable devices and can be applied to next-generation electronic devices.

Previous methods of producing inorganic nanofibers containing ceramics and metals were produced by electrospinning polymer binders and sol-gel precursors. However, this conventional technology is limited to oxides of specific metals such as silicon, titanium, and zirconium, and the method is complicated as it requires two reaction steps. The conventional method for synthesizing metal oxide nanofibers using a solution method also uses zinc. , it could only be applied to certain metals such as aluminum.

To solve this problem, Korean Patent Registration No. 10-0803716 discloses the steps of preparing a mixed solution containing a metal hydroxide by mixing a metal ion-containing precursor with a polymer resin solution, electrospinning the mixed solution to produce the metal hydroxide and the polymer resin. A method for producing metal oxide nanofibers comprising the steps of producing a composite fiber containing a metal hydroxide and sintering the composite fiber to convert the metal hydroxide into a metal oxide and remove the polymer resin. It is provided.

However, even in the above prior art, the firing of composite fibers is carried out at 400 to 800°C, requiring a complex process of electrospinning on a support such as metal, silicon wafer, or glass that can be used at high temperatures, then sintering at high temperature, and transferring it to a flexible substrate. This has the problem of limiting the production of application devices. In addition, as a side effect of high-temperature firing, deformation of the shape of the inorganic nanofibers occurred, making it difficult to form a uniform web.

In addition, even when applied as a filter material, it must be directly electrospun on a polymer nonwoven fabric base material that has permeability and can be applied to bending processes, etc., and then goes through a process to convert it into an inorganic material. In this case, too, when sintered at a high temperature, the polymer nonwoven base material There was a problem that stable web formation was impossible due to melting or thermal deformation.

Republic of Korea Patent Registration No. 10-0803716 (announced on February 18, 2008)

Therefore, according to the present invention, it is possible to completely sinter the matrix present in the electrospun inorganic fiber web and convert the inorganic material precursor, while using a support made of paper or polymer, which is a nanofiber web support that can be used only at low temperatures below 300°C. Continuous mass production is possible using the roll-to-roll method, and the inorganic fibers of the manufactured inorganic fiber web are not only able to form the target inorganic material without agglomerating at high temperatures, but also maintain the fiber shape well. The technical task is to provide a stable web.

Therefore, according to the present invention, one or two or more types of oxidizing metal salts are dissolved in a solvent to form a precursor composition,
After adding nitrocellulose to the precursor composition and continuously stirring to prepare a spinning solution for electrospinning,
After supplying the spinning solution to an electrospinning device and spinning it to form a nanoweb,
A low-temperature manufacturing method of an inorganic nanofiber web is provided, which involves annealing at 200 to 300°C to sinter nitrocellulose in the nanoweb, leaving only the inorganic nanofiber web.

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Hereinafter, the present invention will be described in more detail.

The present invention relates to a method for electrospinning a spinning solution containing an oxidizing metal salt and nitrocellulose, forming a stable web through low-temperature firing, and continuously mass-producing an inorganic nanofiber web at low temperature.

The spinning solution for electrospinning of the present invention is prepared as follows. First, one or two or more types of oxidizing metal salts are dissolved in a solvent to form a precursor composition, wherein the oxidizing metal salts are a metal compound selected from nitrate, perchlorate, and perbromate, or a mixture of two or more types.

The oxidizing metal salt is dissolved in a solvent to form a precursor composition to form an inorganic nanofiber web after electrospinning, and the added polymer material acts as a matrix to form a web.

Among the oxidizing metal salts, the nitrate metal compound is indium nitrate hydrate (In(NO ₃ ) ₃ ㆍxH ₂ O(x=3~6)), gallium nitrate hydrate (Ga(NO ₃ ) ₃ ㆍxH ₂ O(x=3) ~6)), aluminum nitrate nonahydrate (Al(NO ₃ ) ₃ ㆍ9H ₂ O), zinc nitrate hexahydrate (Zn(NO ₃ ) ₃ ㆍ6H ₂ O), cadmium nitrate (Cd(NO ₃ ) ₂ ), _Tin nitrate _{( Sn (} NO ₃ ) Earth metal (A(NO ₃ ) ₂ , A=Mg,Ca, Sr, Ba) silver nitrate (AgNO ₃ ), copper nitrate (Cu(NO ₃ ) ₂ ), zirconium oxynitrate hydrate (ZrO(NO ₃ ) ₂ ㆍxH ₂ O), hafnium oxynitrate hydrate (HfO(NO ₃ ) ₂ ㆍxH ₂ O),

Perchlorate metal compounds include indium perchlorate (In(ClO ₄ ) ₃ ), gallium perchlorate (Ga(ClO ₄ ) ₃ ), aluminum perchlorate (Al(ClO ₄ ) ₃ ), zinc perchlorate (Zn(ClO ₄ ) ₂ ), and perchloric acid. Cadmium (Cd(ClO ₄ ) ₂ ), tin perchlorate (Sn(ClO ₄ ) _x , x = 2 or 4), lead perchlorate (Pb(ClO ₄ ) ₂ ), alkali metal perchlorate (AClO ₄ , A = Li, Na , K, Rb, Cs), alkaline earth metal perchlorate (A(ClO ₄ ) ₂ , A = Mg, Ca, Sr, Ba), silver perchlorate (AgClO ₄ ), copper perchlorate (Cu(ClO ₄ ) ₂ ), zirconium perchlorate (Zr(ClO ₄ ) ₄ ), hafnium perchlorate (Hf(ClO ₄ ) ₄ ),

Perbromate metal compounds include indium perbromate (In(BrO ₄ ) ₃ ), gallium perbromate (Ga(BrO ₄ ) ₃ ), aluminum perbromate (Al(BrO ₄ ) ₃ ), and zinc perbromate (Zn). (BrO ₄ ) ₂ ), cadmium perbromate (Cd(BrO ₄ ) ₂ ), tin perbromate (Sn(BrO ₄ ) _x , x = 2 or 4), lead perbromate (Pb(BrO ₄ ) ₂ ) , alkali metal perbromate (ABrO ₄ , A = Li, Na, K, Rb, Cs), alkaline earth metal perbromate (A(BrO ₄ ) ₂ , A = Mg, Ca, Sr, Ba), silver perbromate (AgBrO ₄ ), copper perbromate (Cu(BrO ₄ ) ₂ ), zirconium perbromate (Zr(BrO ₄ ) ₄ ), or hafnium perbromate (Hf(BrO ₄ ) ₄ ) at low temperatures. This is desirable because it allows smooth removal of organic residues through oxygen radicals generated from thermal decomposition of oxidizing metal salts.

In addition, the solvent is any one of 2-methoxylethanol, methanol, ethanol, isopropyl alcohol, propanol, butanol, acetone, acetylacetone, and dimethylformamide. A sole solvent of N-methylformamide, dimethylsulfoxdie, and organic amines (RNH ₂ , R ₂ NH, R ₃ N: R= C _n H _{2n +1} and n=1-9) is preferable for smooth dissolution of metal salts using polar or coordinating solvents.

In particular, the solvent used during electrospinning is a mixed solvent in which any one of 2-methoxylethanol, methanol, ethanol, isopropyl alcohol, propanol, and butanol and acetone are mixed in a weight ratio of 2:8 to 8:2. This is more preferable because solvent removal is smooth and the resulting increase in viscosity facilitates the formation of nanofibers.

The solvent preferably has a molar concentration of 0.02 to 1 mol/l, but at low concentrations of less than 0.02 mol/l, there is a problem in that smooth nanofiber formation is not achieved due to lack of viscosity, and the molar concentration is 1 mol. At high concentrations exceeding /l, problems with electrospinning may occur due to high electrical conductivity and viscosity.

Afterwards, nitrocellulose is added to the precursor composition prepared in this way and continuously stirred to prepare a spinning solution for electrospinning.

The nitrocellulose is a high-energy reactive polymer material that can be decomposed at a temperature of 192 ~ 202 ℃, and is introduced as a matrix of the spinning solution applied to the electrospinning process, and is simultaneously used as a chemical energy source built into the system due to rapid combustion at this temperature. do. Therefore, the polymer material can contribute to lowering the annealing temperature by providing enormous intrinsic energy for chemical transformation.

In addition, it can be converted into a metal nanofiber form by sufficiently firing it at a low temperature of less than 300℃, so it can be electrospun on a polymer belt and fired (annealed) continuously, producing a continuous inorganic fiber web. This is possible.

It is preferable to add 10 to 40 parts by weight of the nitrocellulose to 100 parts by weight of the precursor composition. If it is less than 10 parts by weight, a problem occurs in which the fiber shape cannot be properly formed during electrospinning due to low viscosity. 40 If it exceeds parts by weight, problems may arise where it is difficult to transfer the solution during electrospinning due to the viscosity of the solution being too high.

The spinning solution prepared in this way is supplied to an electrospinning device and spun to form a nanoweb, and then annealed at 80 to 300°C to produce the inorganic nanofiber web of the present invention. Through the annealing process, the matrix portion of the nanoweb spun by the electrospinning device is fired, thereby forming an inorganic nanofiber web.

When the annealing temperature is below 80℃, a problem arises in which the plasticity of the solvent and the matrix portion of the fiber web is insufficient, and when the annealing temperature exceeds 300℃, some of the constituent fibers of the nanoweb made of metal materials such as gold, silver, and copper are partially melted, causing the fiber shape to change. It may be destroyed, and thermal deformation of the polymer support, which is the web support, may occur during electrospinning, which may cause problems in forming a stable web.

As such, in the manufacturing process of the present invention, a continuous mass production process is carried out using a roll-to-roll method using a support made of paper or polymer, which is a nanofiber web support that can be used only at low temperatures below 300°C by annealing at 80 to 300°C. Can be applied to. In addition, the inorganic fibers of the manufactured inorganic fiber web are able to maintain their fiber shape without clumping at high temperatures, making it possible to manufacture a stable web.

In addition, during the annealing, it is preferable to additionally irradiate light with a wavelength between 150 and 400 nm to cause a photoactivation reaction, thereby achieving a smoother conversion of the precursor to an inorganic material and a reduction in the reaction temperature.

Therefore, according to the present invention, nitrocellulose, which is a matrix present in the inorganic fiber web, is completely calcined by annealing below 300°C, and conversion of the precursor metal salt into an inorganic material can be achieved using high chemical energy. As a nanofiber web support that can only be used at low temperatures, a support made of paper or polymer can be used, which has the effect of enabling continuous mass production in a roll-to-roll method. In addition, it is possible to manufacture a stable web by ensuring that the inorganic fibers of the manufactured inorganic fiber web do not agglomerate at high temperatures and maintain their fiber shape well, and the flexibility and elasticity due to nano-level thickness and the high ratio of nanomaterials are achieved. It is possible to provide an inorganic nanofiber web with an advantage in surface area. The inorganic nanofiber web is used in various industrial fields such as electronic materials, optical materials, catalyst materials, and environmental materials as a flexible/stretchable electronic/optical material, a highly reactive catalyst material with a high specific surface area, and a filter for harmful factors in the air or water. application may be possible.

Figure 1 shows the results of thermogravimetric analysis and differential thermal analysis of the In ₂ O ₃ precursor of Example 1;
Figure 2 shows the results of X-ray diffraction analysis of the In ₂ O ₃ oxide nanofibers of Example 1;
Figure 3 is a field emission scanning microscope (FE-SEM) photo of the indium oxide (In ₂ O ₃ ) nanofiber membrane prepared in Example 1, showing before and after heat treatment;
Figure 4 is a field emission micrograph of the ZnO nanofibers of Example 2;
Figure 5a shows the results of X-ray diffraction analysis of the Ag nanofiber web of Example 3;
Figure 5b is the thermal analysis result of the Ag nanofiber web of Example 3,
Figure 6 is a field emission microscope image of Ag nanofibers obtained after heat treatment at 250°C of the Ag nanofiber web of Example 3;
Figure 7 shows the transmittance and sheet resistance results of the Ag nanofiber web of Example 3;
Figure 8 is a field emission micrograph of Al2O3 nanofibers of Example 4;
Figure 9 shows the results of X-ray diffraction analysis of the copper oxide nanofibers of Example 5;
Figure 10 is a field emission micrograph of the copper oxide nanofibers of Example 5;
Figure 11 shows the electrical characteristics results of the In2O3 nanofiber thin film transistor of Example 6;
Figure 12 shows the electrical characteristics results of the In2O3 nanofiber thin film transistor of Example 7.

The following example provides a non-limiting example of manufacturing the inorganic nanofiber web of the present invention.

[Example 1]

Ⅰ. Preparation of spinning solution

1. 0.3 g of oxidizing metal salt (Indium (III) nitrate hydrate ((In(NO ₃ ) ₃ ) indium nitrate hydrate) is completely dissolved in 5 ml of solvent (2-methoxyethanol: acetone = 3: 2) to obtain a precursor composition. was formed.

2. To prepare a spinning solution for electrospinning, 0.66 g of nitrocellulose was added to the precursor composition and stirred continuously at 60°C for 12 hours to prepare a uniform spinning solution.

Ⅱ. Nanofiber manufacturing

1. The prepared spinning solution was placed in an electrospinning machine and loaded into the vertical frame of the electrospinning machine. The electrospinning process was performed at a high voltage of 30 kV and a supply rate of 3 ㎖/hr, and the distance from the tip of the spinneret to the grounded collector was 16 cm.

2. To remove organic components and form metal oxides in the electrospun fiber web, heat treatment was performed at 300°C for 30 minutes to obtain an inorganic nanofiber web.

Ⅲ. Analysis of nanofiber precursors and nanofiber membranes

1. To analyze the thermochemical properties of the electrospinning solution prepared above, thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were performed on the dried precursor in air, and the results shown in Figure 1 were obtained, 190-200 It was confirmed that the conversion reaction of the precursor was completed simultaneously with a strong exothermic reaction at ℃.

2. Through X-ray diffraction analysis of the prepared indium oxide (In ₂ O ₃ ) nanofiber membrane, it was confirmed that weak crystallinity began to form at 300°C, as shown in FIG. 2.

3. The prepared indium oxide (In ₂ O ₃ ) nanofiber film was observed with a field emission scanning microscope (FE-SEM) to reveal a uniform metal salt-nitrocellulose mixture precursor nanofiber spun as shown in FIG. 3 (average diameter 273 nm). The formation of was confirmed, and it was confirmed that conversion into uniform oxide nanofibers (average diameter 120 nm) occurred at low temperature through annealing at 300°C.

[Example 2]

An inorganic nanofiber web was obtained in the same manner as in Example 1, except that Zn(II) nitrate ((Zn(NO ₃ ) ₂ ) zinc nitrate) was used as the oxidizing metal salt. In addition, field emission scanning microscopy analysis was performed on this to confirm the formation of a ZnO nanofiber film, as shown in Figure 4.

[Example 3]

An inorganic nanofiber web was obtained in the same manner as in Example 1, except that silver nitrate ((AgNO ₃ ) silver nitrate) was used as the oxidizing metal salt and the heat treatment was performed at 250°C. X-ray diffraction analysis, thermal analysis, and field emission microscopy analysis were performed similarly to those performed in Example 1, and as shown in FIGS. 5A and 5B, the crystalline phase of Ag was clearly formed above 250°C and at around 200°C. The decomposition reaction of the precursor was confirmed, and the formation of nanofibers was also confirmed, as shown in Figure 6.

In addition, the electrical and optical properties of the nanofiber membrane formed in this way were confirmed, and the transmittance and sheet resistance under visible light with a wavelength of 350 nm to 800 nm were confirmed for application as a transparent electrode, as shown in FIG. 7.

[Example 4]

In Example 1, the same procedure as Example 1 was carried out, except that the oxidizing metal salt was used as Aluminum nitrate nonahydrate ((Al(NO ₃ ) _{3.9H 2} O) Aluminum nitrate nonahydrate), and the inorganic material was deposited on the stainless steel mesh. Got nano fiber web. To measure the air filter efficiency of the Al2O3 nanofiber membrane obtained after heat treatment at 300°C, a filtration efficiency of 44.8% was achieved at a differential pressure of 0.92mmAq using a TSI8130A analyzer. As shown in Figure 8, the formation of nanofibers was also confirmed.

[Example 5]

Inorganic nanofibers were prepared in the same manner as in Example 1, except that copper(II) nitrate ((Cu(NO ₃ ) ₂ ) copper nitrate) was used as the oxidizing metal salt in Example 1 and the heat treatment temperature was performed at 200-300°C. Got the web. By performing _an The formation of nanofibers was also confirmed.

[Example 6]

To implement a metal oxide nanofiber thin film transistor device, a p++ Si wafer topped with 300 nm SiO ₂ grown by high-temperature dry oxidation was used as a substrate, and heat treated at 300°C after electrospinning the In ₂ O ₃ nanofiber as shown in Example 1. were applied together for 30 minutes. A p++ Si wafer with 300 nm SiO ₂ is used as a substrate, gate electrode, and insulator, and a 50 nm thick Al layer is formed on the In ₂ O ₃ nanofibers formed by heat treatment using thermal evaporation that passes through a shadow mask. The electrode was formed with a channel width of 1000 μm and a channel length of 50 μm.

[Example 7]

To implement a metal oxide nanofiber thin film transistor device, a p++ Si wafer topped with 300 nm SiO ₂ grown by high-temperature dry oxidation was used as a substrate, and heat treated at 300°C after electrospinning the In ₂ O ₃ nanofiber as shown in Example 1. /ultraviolet (UV) treatment was applied together for 30 minutes. The p++ Si wafer with 300 nm SiO ₂ is used as a substrate, gate electrode, and insulator, and a 50 nm thick layer is formed using thermal evaporation through an additional shadow mask on the In ₂ O ₃ nanofibers formed by photothermal treatment. An Al electrode was formed with a channel width of 1000 ㎛ and a channel length of 50 ㎛.

As can be seen in FIG. 11 below, crystalline In ₂ O ₃ is formed through heat treatment at 300°C, but TFT device characteristics are barely visible due to insufficient lattice stabilization. However, in the case of heat treatment with light irradiation in FIG. 12, The mobility of the TFT device was improved to 0.52 cm2/Vs, confirming the improvement of the electrical properties of the oxide semiconductor nanofibers through photothermal reaction.

Claims (8)

After dissolving one or two or more types of oxidizing metal salts in a solvent to form a precursor composition,
After adding nitrocellulose to the precursor composition and continuously stirring to prepare a spinning solution for electrospinning,
After supplying the spinning solution to an electrospinning device and spinning it to form a nanoweb,
A low-temperature manufacturing method of an inorganic nanofiber web, characterized in that nitrocellulose in the nanoweb is calcined by annealing at 200 to 300°C, leaving only the inorganic nanofiber web. According to clause 1,
A low-temperature manufacturing method of an inorganic nanofiber web, wherein the oxidizing metal salt is a metal compound selected from nitrate, perchlorate, and perbromate, or a mixture of two or more types. According to clause 2,
The nitrate metal compound is indium nitrate hydrate (In(NO ₃ ) ₃ ㆍxH ₂ O (x=3~6)) and gallium nitrate hydrate (Ga(NO ₃ ) ₃ ㆍxH ₂ O (x=3~6)). , aluminum nitrate hexahydrate (Al(NO ₃ ) ₃ ㆍ9H ₂ O), zinc nitrate hexahydrate (Zn(NO ₃ ) ₃ ㆍ6H ₂ O), cadmium nitrate (Cd(NO ₃ ) ₂ ), tin nitrate (Sn) _{( NO 3 ) _} NO ₃ ) ₂ , A=Mg,Ca,Sr,Ba), silver nitrate (AgNO ₃ ), copper nitrate (Cu(NO ₃ ) ₂ ), zirconium oxynitrate hydrate (ZrO(NO ₃ ) ₂ ㆍxH ₂ O), Any one of hafnium nitrate hydrate (HfO(NO ₃ ) ₂ ㆍxH ₂ O),
Perchlorate metal compounds include indium perchlorate (In(ClO ₄ ) ₃ ), gallium perchlorate (Ga(ClO ₄ ) ₃ ), aluminum perchlorate (Al(ClO ₄ ) ₃ ), zinc perchlorate (Zn(ClO ₄ ) ₂ ), and perchloric acid. Cadmium (Cd(ClO ₄ ) ₂ ), tin perchlorate (Sn(ClO ₄ ) _x , x = 2 or 4), lead perchlorate (Pb(ClO ₄ ) ₂ ), alkali metal perchlorate (AClO ₄ , A = Li, Na , K, Rb, Cs), alkaline earth metal perchlorate (A(ClO ₄ ) ₂ , A = Mg, Ca, Sr, Ba), silver perchlorate (AgClO ₄ ), copper perchlorate (Cu(ClO ₄ ) ₂ ), zirconium perchlorate (Zr(ClO ₄ ) ₄ ), hafnium perchlorate (Hf(ClO ₄ ) ₄ ),
Perbromate metal compounds include indium perbromate (In(BrO ₄ ) ₃ ), gallium perbromate (Ga(BrO ₄ ) ₃ ), aluminum perbromate (Al(BrO ₄ ) ₃ ), and zinc perbromate (Zn). (BrO ₄ ) ₂ ), cadmium perbromate (Cd(BrO ₄ ) ₂ ), tin perbromate (Sn(BrO ₄ ) _x , x = 2 or 4), lead perbromate (Pb(BrO ₄ ) ₂ ) , alkali metal perbromate (ABrO ₄ , A = Li, Na, K, Rb, Cs), alkaline earth metal perbromate (A(BrO ₄ ) ₂ , A = Mg, Ca, Sr, Ba), silver perbromate (AgBrO ₄ ), copper perbromate (Cu(BrO ₄ ) ₂ ), zirconium perbromate (Zr(BrO ₄ ) ₄ ), and hafnium perbromate (Hf(BrO ₄ ) ₄ ). Low-temperature manufacturing method of inorganic nanofiber web. According to clause 1,
The solvent is any one of 2-methoxylethanol, methanol, ethanol, isopropyl alcohol, propanol, butanol, acetone, acetylacetone, and dimethylformamide. N-methylformamide, dimethylsulfoxdie, sole solvent of organic amines (RNH ₂ , R ₂ NH, R ₃ N: R= C _n H _2n+1 and n=1-9) A low-temperature manufacturing method of an inorganic nanofiber web, characterized in that: According to clause 1,
The solvent is an inorganic nanofiber web characterized in that it is a mixed solvent in which acetone and any one of 2-methoxylethanol, methanol, ethanol, isopropyl alcohol, propanol, and butanol are mixed at a weight ratio of 2:8 to 8:2. Low-temperature manufacturing method. According to clause 4,
A low-temperature manufacturing method of an inorganic nanofiber web, characterized in that the solvent has a molar concentration of 0.02 to 1 mol/l. According to clause 1,
A low-temperature manufacturing method of an inorganic nanofiber web, characterized in that 10 to 40 parts by weight of the nitrocellulose is added to 100 parts by weight of the precursor composition. According to clause 1,
A low-temperature manufacturing method of an inorganic nanofiber web, characterized by additionally irradiating light with a wavelength between 150-400 nm during annealing at 200-300°C.