KR20140104934A - Preparing method of silver nanowire - Google Patents

Abstract

The present invention relates to a method of preparing a silver nanowire which satisfies the diameter and length required for a flexible transparent electrode material. According to the present invention, the method includes the steps of preparing a first solution containing silver halide and a polyol solvent and a second solution containing a capping reagent, a halogen catalyst, and a polyol solvent; heating the second solution; and mixing the second solution with the first solution to make the silver nanowire. The diameter, length, and aspect ratio of the silver nanowire are controlled through metal reducing power, thus having the diameter of average 30 nm or less, the length of 25 to 35 μm, and high aspect ratio required for a flexible transparent conductive film to improve the yield of the silver nanowire over 90 mol% of the silver halide injected.

Description

PREPARING METHOD OF SILVER NANOWIRE "

The present invention relates to a silver nanowire manufacturing method that satisfies the diameter and length required as a flexible transparent electrode material.

Along with the rapid development of the display field and the solar cell industry, the demand for the transparent conductive film is also surging. Currently, various materials such as ITO (Indium Tin Oxide), CNT, Graphen, ZnO, and PEDOT have been developed as transparent electrode materials, and double ITO is mainly used due to its suitability for mass production technology and applications.

ITO electrode is not easy to use as a transparent electrode for flexible display because of lack of flexibility of electrode layer, and ITO electrode is expensive to manufacture. Indium (In), which is a raw material, is dominant in China and supply amount is sufficient There is a big price increase factor because it does not.

Recently, as the demand for flexible displays increases, the demand for materials for replacing ITO transparent electrodes has increased. As a means for replacing ITO transparent electrodes, transparent electrode materials using silver nanowires having good electrical properties and physical properties of silver have been developed.

As a new transparent electrode material, silver nanoparticles have high chemical stability in metals, high silver and high electrical conductivity, and transparency, which is an optical characteristic due to the very small dimensions of nanowires. Electrode material. These silver nanowires are expected to be used in electric, magnetic and optical devices such as PDP (plasma display panel), optical filter, electromagnetic shielding, organic light emitting diode (OLED), solar cell, liquid crystal display And sensors.

In order to use nanowires in various fields, it is necessary to meet the requirements of diameter, length and shortening ratio required in applied fields, and to control each size deviation to a small amount and to mass-produce them in a relaxed condition Most important.

Transparent film The transparent film is transparent in visible light (380 ~ 780nm wavelength) and has excellent electrical conductivity. Recently, requirements for light transmittance and sheet resistance of transparent film have been strengthened. The light transmittance is required to be 90% or more, and the sheet resistance is required to be 150? /? Or less.

The length, diameter, and long axis ratio of nanowires affect electrical conductivity and light transmission. That is, longer nanowires require less nanowires to achieve the desired conductivity of the transparent conductive film, so nanowires with higher long axis ratios are advantageous. Smaller diameter nanowires can also provide higher light transmittance and lower haze.

A conventional method for producing nanowires on a large scale is a liquid chemical method, which is also referred to as a "polyol process". The precursor solution is mixed with a polyol solvent by a capping reagent, a halogen catalyst, AgNO ₃ , .

The following papers and patents are known for the polyol process.

- Sun, Y. et al., (2002) Science, 298, 2176; Sun, Y. et al., (2002) Nano Lett. 2, 165; Sun, Y. et al, (2002) Adv. Mater. 14, 833; Kim, F. et al., (2004) Angew. Chem. Int. Ed. 1 16, 3759

- U.S. Published Patent Application 2005/0056118

Such a polyol process includes reduction of a silver salt with a polyol such as ethylene glycol, propylene glycol or the like in the presence of polyvinyl pyrrolidone (hereinafter referred to as 'PVP'). Generally, the reduction process is carried out at a temperature of 160 DEG C or lower. At this time, the polyol generally has a dual function as a reducing agent as well as a solvent.

Silver salts are reduced to silver atoms in solution by polyol solvents. In general, silver atoms initially form a seed through a homogeneous nucleation process. This seed is generally a crystal with a diameter of 1-5 nm. Some of these seeds continue to grow in solution to form isotropic nanostructures (nanoparticles). Nanoparticles are the result of the same growth in all directions. In contrast, some seeds grow into anisotropic nanostructures (nanotubes, nanorods, nanobelts, nanowires, etc.), which is the result of preferential growth along the lateral direction.

The diameter and length of the silver nanowires are affected by several variables including the type and relative amount of PVP and silver salt, the concentration of PVP and silver salt, the type and concentration of halogen catalyst, reaction time and reaction temperature.

A common problem with the above-described polyol process is that silver nanoparticles, silver nanobelts, and the like, as well as nanowires, are produced accompanied by a mixture of nanostructures having various shapes. Therefore, pure water requires a purification step to obtain nanowires. In addition, it was difficult to control and control silver nanowires having a long length, a small diameter, and a long short axis ratio.

In the case of the polyol process using AgNO ₃ silver salt, excess silver nuclei are generated at the initial stage of the reaction, and silver nuclei formed in excess are combined with dissolved silver ions to inhibit the silver nanowires from growing in a certain direction, The diameter of the nanowire is large and the length thereof is short, so that there is a problem that the light transmittance, haze, and electric conductivity required for the electrode material of the flexible transparent conductive film can not be satisfied.

The silver nanowire manufacturing method of the present invention for solving the problems of the prior art described above is characterized in that the silver nanowire is substituted with AgNO ₃ to control the growth rate of the silver nanowire by controlling nucleation, And a method of manufacturing the nanowire.

According to another aspect of the present invention, there is provided a silver nanowire manufacturing method for silver nanowire by mixing a silver salt, a polyol solvent, a capping reagent, and a halogen catalyst, ), AgClO _4, characterized in that Ag (pyridine) which is one or a mixture of two or more of the _second.

(A) preparing a first solution including the silver salt and the polyol solvent, and a second solution including the capping reagent, the halogen catalyst, and the polyol solvent; (b) heating the second solution; And (c) preparing silver nanowires from the reaction mixture solution in which the first solution is mixed with the second solution.

Preferably, the polyol solvent is any one or two or more of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, and glycerol.

Preferably, the capping reagent is mixed with one or more of PVP K90 and PVP K30.

Preferably, the halogen catalyst is mixed with any one of AgCl, KBr and SnCl 2 or more.

Preferably, the silver salt is 0.01M to 0.2M, the capping reagent is 0.01M to 1M, and the halogen catalyst is 0.001M to 0.5M, based on the reaction mixture solution.

Preferably, the halogen catalyst has a relative molar ratio of 0.1 to 30% with the silver salt.

Preferably, in the step (b), the second solution is heated to 50 to 200 캜.

Preferably, in step (c), the second solution is added dropwise at 0.1 to 2% by volume / second based on the volume of the first solution.

According to the present invention method for producing nanowires, silver salts as Agx (EDTA), AgClO _4, a via metal reducing power controlled in accordance with the use of the Ag (pyridine) ₂ is flexible by controlling the diameter and length and the major axis Danielle of the nanowire It is possible to improve the yield to 90 mol% or more of the silver salt into silver nanowires having an average diameter of 30 nm or less and a length of 25 to 35 μm and a high long axis ratio required as a transparent conductive film.

1 and 2 are SEM photographs showing the diameter and length of silver nanowires according to Example 1, respectively.
FIGS. 3 and 4 are SEM photographs showing the diameter and length of silver nanowires according to Example 2, respectively.
5 and 6 are SEM photographs showing the diameter and length of the silver nanowires according to Example 3, respectively.
7 and 8 are SEM photographs showing the diameters and lengths of the silver nanowires according to Comparative Example 1, respectively.
9 and 10 are SEM photographs showing the diameters and lengths of silver nanowires according to Comparative Example 2, respectively.

Hereinafter, the present invention will be described in detail.

The silver nanowire manufacturing method of the present invention is a silver nanowire manufacturing method for manufacturing silver nanowires by mixing a silver salt, a polyol solvent, a capping reagent, and a halogen catalyst, wherein the silver nanowire includes Agx (EDTA), AgClO ₄ , Ag ) ₂ or a mixture of two or more thereof.

Select a suitable polyol solvent, silver salt, catalyst, and capping reagent to increase the yield of the nanowire and achieve the desired diameter, length and long axis ratio, and control the reaction concentration, temperature and time.

"Silver salt" refers to a neutral compound having a positively charged silver ion and a negatively charged counter ion. The counter ion can be inorganic or organic. In the present invention, the silver salt includes Ag x (EDTA) or AgClO ₄ or Ag (pyridine) x. Generally, the silver salt is dissolved in a reducing solvent (eg, a polyol) and decomposed into metal ions and counter ions having opposite charges. Reduction of the silver salt in the reaction mixture produces silver, which is crystallized or grows into nanowires.

"Capping reagent" refers to a chemical agent that preferentially interacts with and adheres to the lateral surface of the growing nanowire such that the cross-sectional surface of the nanowire can be crystallized. The capping reagent interacts more strongly with the lateral surface than interacts with the transverse surface. Thus, the side surface is passivated, while the cross-sectional surface is used for further crystallization to produce nanowires. Such a capping reagent may include a mixed reagent of PVP K90, PVP K30, and PVP K90 / PVP K30 as the polyvinylpyrrolidone.

"Polyol solvent" refers to polar solvents in which silver salts, halogen catalysts, and capping reagents are dissolved. In addition, the polyol solvent functions as a reducing agent to transform silver salts into elemental metals. Generally, the reducing solvent is a chemical reagent comprising at least two hydroxyl groups. Such polyol solvents include ethylene glycol, propylene glycol, and glycerol. More specifically, the polyol solvent is, for example, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, glycerol, etc., alone or arbitrarily mixed.

"Halogen catalyst" refers to salt additives including cations and anions. Cations and anions are ionically bound and are ionically separated into polar solvents such as water, alcohols, diols and polyols (including ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, glycerin, glycerol and glucose) . The cation may be organic or inorganic. Anions are generally inorganic and include halogen ions (Cl-, Br-, F-, etc.). Due to the presence of the catalyst, the anisotropic nanostructures are preferentially grown and thus nanowires with relatively high yield and relatively high monodispersity are obtained. Such halogen catalysts include AgCl, KBr, SnCl, and the like and a mixture thereof.

A method of preparing silver nanowires using the components of the above reaction mixture is as follows.

(a) First, a first solution containing a silver salt and a polyol solvent and a second solution containing a capping reagent, a halogen catalyst and a polyol solvent are prepared.

The first solution is formed by mixing a silver salt in a polyol solvent (for example, ethylene glycol or propylene glycol) at 20 to 160 ° C. The second solution is constituted by sequentially mixing PVP and a halogen catalyst in a polyol solvent.

At this time, the concentrations of the constituents of the first and second solutions have a certain influence on the formation of the nanostructures and the yield thereof, and the concentration of the silver salt, the PVP and the halogen catalyst in the reaction mixture is controlled for the optimum yield of the silver nanowire .

Specifically, the silver salt is 0.01M to 0.2M, preferably 0.05M to 0.1M. The concentration of PVP is 0.01M to 1M, preferably 0.1M to 0.7M. When the amount of silver salt is too large, there is a problem that the nanowire grows rapidly and the diameter becomes large and the length becomes long. When the amount is too small, particles are generated rapidly.

And the concentration of the halogen catalyst can be avoided at 0.001M to 0.5M, preferably 0.01M to 0.3M. When the amount of the halogen catalyst is too large, there is a problem that the particles are rapidly increased. When the amount is too small, there is a problem that the diameter and the length of the nanowire are rapidly increased.

In particular, the halogen catalyst has a relative molar ratio with silver salt of 0.1 to 30%, preferably 5 to 20%. When the relative molar ratio is small, there is a problem that the nanowire grows rapidly and the diameter and the length increase. When the relative mole ratio is too large, there is a problem that a large amount of particles are generated.

(b) Next, the second solution is heated to 50 to 200 캜. Preferably 80 to < RTI ID = 0.0 > 140 C. < / RTI > If the temperature is too low, there is a problem of increasing the amount of silver particles, which is an obstacle to the growth of the nanowires. If the temperature is too high, there is a problem that the diameter and the length increase due to rapid growth.

The temperature of the second solution will affect the yield and length of the silver nanowire in the mixing step described below.

(c) Next, the first solution is mixed while maintaining the heating state of the second solution to generate silver nanowires in the reaction mixture solution.

At this time, it is preferable to stir the second solution at a rate of 0.1 to 2% by volume / second based on the volume (V1) of the heated first solution. The reaction time and stirring speed are controlled, Adjust the length. At this time, if the injection rate is too low, a large amount of particles are generated. If the injection rate is too high, particles are generated.

The reaction time is 2 to 8 hours, and the stirring speed is preferably 20 to 300 rpm. If the reaction time is too short, there is a problem in the production yield of the nanowires. If the reaction time is too long, there is a problem in production cost and production amount.

(d) The reaction mixture solution in which the reaction is finally completed is cooled to room temperature, and then purified with acetone and ultrapure water one or more times to obtain silver nanowires.

Through the above steps, the yield of the silver nanowire can be increased by 80% or more, more preferably by 95% or more. Where the yield is the amount of silver nanowires ultimately obtained for silver added to the reaction mixture during silver salt formation.

Hereinafter, specific examples of the silver nanowire manufacturing method of the present invention will be described in comparison with comparative examples.

(Example 1)

 2 g of Agx (EDTA) (x = 1, 2, 3, 4) was dissolved in 70 ml of ethylene glycol at room temperature to prepare a first solution. 150 ml of ethylene glycol was added to the 300 ml reactor and heating was started. 6 g of polyvinylpyrrolidone and 60 mg of NaCl were added, and the mixture was continuously added at 80 to 160 ° C over 1 hour to dissolve and prepare a second solution.

Then, the second solution was heated to 130 DEG C and the first solution was dripped into the heated second solution at a rate of 0.5 mL / sec using a micropipette while stirring at 250 rpm.

After 5 hours from the completion of the addition of the first solution, it was confirmed that the color of the mixed solution changed to the silver gray color, and the reaction was terminated by cooling to room temperature.

Thereafter, an excessive amount of acetone solvent is supplied to the solution in which the reaction has been completed to form a precipitate, and the silver nanowires are settled, the solvent is discarded, and then acetone is supplied again to redisperse the silver nanowires, Was repeated twice to obtain silver nanowires.

Scanning electron microscope photographs showing the diameter and length of the obtained nanowires are shown in FIGS. 1 and 2. FIG.

(Example 2)

The silver halide was tested in the same manner as in Example 1 except that AgClO ₄ was used. SEM photographs showing the diameters and lengths of the obtained nanowires are shown in FIGS. 3 and 4.

(Example 3)

Samples were tested in the same manner as in Example 1, except that silver (pyridine) ₂ was used. The scanning electron microscope photographs showing the diameters and lengths of the obtained nanowires are shown in FIGS. 5 and 6.

(Comparative Example 1)

The first solution was prepared by dissolving 1.7 g of AgNO ₃ in ethylene glycol 70. 150 ml of ethylene glycol was added to the 300 ml reactor and heating was started. 6 g of polyvinylpyrrolidone and 60 mg of NaCl were added to the polyol solvent, At 160 DEG C over 1 hour, and dissolved to prepare a second solution.

Then, the second solution was heated to 130 DEG C and the first solution was dripped into the heated second solution at a rate of 0.5 mL / sec using a micropipette while stirring at 250 rpm.

After 5 hours from the completion of the addition of the first solution, it was confirmed that the color of the mixed solution changed to the silver gray color, and the reaction was terminated by cooling to room temperature.

Thereafter, an excessive amount of acetone solvent is supplied to the solution in which the reaction has been completed to form a precipitate, and the silver nanowires are settled, the solvent is discarded, and then acetone is supplied again to redisperse the silver nanowires, Was repeated twice to obtain silver nanowires.

Scanning electron micrographs showing the diameter and length of the obtained nanowires are shown in FIGS. 7 and 8. FIG.

(Comparative Example 2)

1.7 g of AgNO ₃ was dissolved in ethylene glycol 70 at room temperature to prepare a first solution. 150 ml of ethylene glycol was added to the 300 ml reactor and heating was started. To this polyol solvent were added 6 g of polyvinylpyrrolidone, 60 mg of KBr and 0.35 g of AgCl And then the solution was added sequentially at 80 to 160 ° C over 1 hour to dissolve the solution, thereby preparing a second solution.

Then, the second solution was heated to 130 DEG C and the first solution was dripped into the heated second solution at a rate of 0.5 mL / sec using a micropipette while stirring at 250 rpm.

After 5 hours from the completion of the addition of the first solution, it was confirmed that the color of the mixed solution changed to the silver gray color, and the reaction was terminated by cooling to room temperature.

Thereafter, an excessive amount of acetone solvent is supplied to the solution in which the reaction has been completed to form a precipitate, and the silver nanowires are settled, the solvent is discarded, and then acetone is supplied again to redisperse the silver nanowires, Was repeated twice to obtain silver nanowires.

Scanning electron microscope photographs showing the diameter and length of the obtained nanowires are shown in FIGS.

The average diameter, average length and major axis ratio of silver nanowires according to Examples 1 to 3 and Comparative Examples 1 and 2 according to the present invention are summarized in Table 1 below.

Comparison of properties of Examples and Comparative Examples Average diameter Average length Long shaft ratio Example 1 24nm 30um 1250 Example 2 27 nm 30um 1110 Example 3 28nm 25um 890 Comparative Example 1 60nm 25um 415 Comparative Example 2 45nm 20um 444

Table 1 shows that the long axis ratio is superior in Examples 1, 2 and 3, Comparative Examples 2 and 1 in that order. The haze was about 0.35%, the silver wire of Example 2 was 0.34%, and the silver wire of Example 3 was haze of about 0.43% after the silver nano wire prepared in Example 1 was made of ink and coated on the PET film. The haze values of Comparative Examples 2 and 1 were 0.8% and 1.5%, respectively, and their haze values were smaller as the diameter was smaller and the aspect ratio was larger.

Unsigned

Claims (3)

A silver salt composed of AgClO ₄ ; A polyol solvent composed of any one or a mixture of two or more of ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol and glycerol; A capping reagent composed of any one or a mixture of two or more of PVP K90 and PVP K30; And a halogen catalyst composed of any one of AgCl, KBr and SnCl 2 or a mixture of two or more thereof; Based on the reaction mixture solution,
Wherein the silver salt is 0.01M to 0.2M, the capping reagent is 0.01M to 1M, the halogen catalyst is 0.001M to 0.5M,
Wherein the halogen catalyst has a relative molar ratio of 0.1 to 30% with the silver salt to produce silver nanowires having a diameter of 25.20 to 29.02 nm. The method according to claim 1,
(a) preparing a first solution including the silver salt and the polyol solvent, and a second solution including the capping reagent, the halogen catalyst, and the polyol solvent;
(b) heating the second solution to 50-200 < 0 >C; And
(c) dropping the solution into the second solution at a rate of 0.1 to 2% by volume / second based on the volume of the first solution, thereby preparing silver nanowires;
≪ / RTI > The method according to claim 1,
Wherein the silver salt is further mixed with at least one of Ag x (EDTA) (x = 1, 2, 3, 4) and Ag (pyridine) ₂ .

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