CN104861776A - Anti-settling and self-leveling silver nanowire conductive printing ink and method for preparing transparent conducting thin film by using same - Google Patents

Abstract

The invention discloses a nano-silver wire conductive ink with anti-settling and self-leveling properties, which is composed of nano-silver wire, water-based resin, conductive polymer, organic solvent and deionized water, and its weight composition is: nano-silver wire 0.1 %~5%; water-based resin 1%~10%; conductive polymer 0.1%~5%; organic solvent 10%~45%; deionized water 35%~88.5%. The invention also discloses a method for preparing a transparent conductive film by using the nano-silver wire conductive ink. The method includes coating the nano-silver wire conductive ink on a PET transparent substrate through a coating method, drying and curing to obtain a transparent conductive film. The surface resistivity of the transparent conductive film prepared by the method is 50-100Ω/sq, the light transmittance is 88.5%-90.1%, and the haze is 1.1%-1.5%. At the same time, the ink formula has simple components and low cost, and is suitable for large-scale production.

Description

A kind of anti-sedimentation, self-leveling nano-silver wire conductive ink and method for preparing transparent conductive film therefrom

technical field

The invention belongs to the technical field of preparation of conductive ink and conductive film.

Background technique

Current touch display electronic products are mainly designed based on indium tin oxide semiconductor material (ITO), but this technology faces problems such as scarcity of indium resources, complicated processing, high energy consumption, difficult storage, and easy yellowing. , especially as an oxide, ITO has high brittleness and poor flexibility, and it is difficult to meet the needs of the new generation of touch display technology for product flexibility and bendability. The new transparent conductive film based on nano-silver wire conductive ink has shown superior performance as a class of alternative technology, especially it has good conductivity, flexibility, and light transmission, and the reserves of silver on the earth are relatively low compared to Indium should be abundant, with low processing cost, low energy consumption, and less pollution. Therefore, it is the trend of the times to replace the ITO film with nano-silver wire transparent conductive film, which has the advantages of extremely high light transmittance, strong conductivity and bendability.

At present, there are many patent applications for transparent conductive films based on silver nanowires and their inks, but the usual processing technology is relatively complicated, and it takes several steps of transfer printing or repeated coating processes to finally achieve the desired results. Or introduce a large amount of additives such as polymer resin, surfactant, leveling agent, anti-sedimentation agent and dispersant in the ink preparation process. The introduction of these various additives not only complicates the ink formulation, but also greatly increases the ink formulation cost. The present invention selects the optimized formula and only adds a small number of components to the nano-silver wire stock solution, so that the transparent conductive film can be prepared conveniently and the obtained film can reach or even exceed the existing data index.

Contents of the invention

The first aspect of the present invention provides a nano-silver wire conductive ink with anti-settling and self-leveling properties, which is composed of nano-silver wire, water-based resin, conductive polymer, organic solvent and deionized water, and its weight is composed of:

Nano silver wire 0.1%~5%;

Water-based resin 1% to 10%;

Conductive polymer 0.1% to 5%;

Organic solvent 10% ~ 45%;

Deionized water 35% to 88.5%.

The weight of the silver nanowires refers to the weight of the silver nanowires itself, excluding the weight of the solvent or suspension medium in the silver nanowire suspension.

In a preferred embodiment, the silver nanowires have a length of 5-60 μm and a diameter of 20-60 nm.

In a preferred embodiment, the water-based resin is a water-based polyurethane resin.

In a preferred embodiment, the conductive polymer is poly-3,4-ethylenedioxythiophene: polystyrene sulfonate (abbreviated as PEDOT:PSS).

In a preferred embodiment, the organic solvent is selected from one or more of methanol, ethanol, isopropanol, dimethyl sulfoxide, tetrahydrofuran, and N,N-dimethylacetamide.

The second aspect of the present invention provides a kind of preparation method of transparent conductive film, it comprises the following steps:

A. prepare the nano-silver wire conductive ink with anti-settling and self-leveling properties as shown in the first aspect of the present invention;

b. coating the nano-silver wire conductive ink on the PET transparent substrate by a wire bar roll coating method, drying and curing to obtain a transparent conductive film.

In a preferred embodiment, the drying and curing temperature is 110-130° C., and the drying time is 1-5 minutes.

The specific steps of the method of the present invention are as follows: first, add the corresponding amount of nano-silver wire, water-based resin, organic solvent, conductive polymer and deionized water into the beaker at room temperature, and stir to make it completely mixed. The prepared ink is dropped onto the PET substrate, and then rolled at a certain speed by a wire rod to obtain a conductive ink wet film. Put the wet film in a vacuum oven, wait until the deionized water and organic solvent in the wet film are completely volatilized, take out the PET to obtain a dry film, that is, the above-mentioned transparent conductive film.

Since the surface of the silver nanowires is coated with polyvinylpyrrolidone (PVP), a large amount of contact resistance will be generated between the silver nanowires during the overlapping process. Therefore, in order to reduce the contact resistance, the conductive polymer poly-3,4-ethylene is introduced into the ink Dioxythiophene: polystyrene sulfonate (PEDOT:PSS). Among them, the sulfur on the thiophene ring in poly-3,4-ethylenedioxythiophene (PEDOT) can be chemically bonded to the silver on the nano-silver wire, and the π-π of poly-3,4-ethylenedioxythiophene (PEDOT) The conjugated structure can conduct electrons, thereby greatly reducing the contact resistance and improving the conductivity of the diaphragm. The combination of polystyrene sulfonate (PSS) and poly-3,4-ethylenedioxythiophene (PEDOT) improves its water solubility.

The role of the water-based polyurethane resin is to improve the adhesion between the silver nanowires and the substrate PET, prevent the silver nanowires from falling off, and obtain a reliable silver nanowire film.

The thickness and flatness of the nano-silver wire conductive layer can be effectively controlled by the coating method of wire bar roll coating.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

Conductive ink is water-based ink, no harmful substances volatilize, no irritating smell, non-toxic and environmentally friendly.

The composition of conductive ink is simple, and it still has self-leveling and anti-sedimentation properties without adding complex additives, such as leveling agents, anti-settling agents, surfactants and other additives, and can still obtain excellent conductivity and Translucency.

Due to the addition of conductive polymers, the amount of silver wires is greatly reduced. For example, a transparent conductive film with a surface resistance of 100 ohm/sq can be obtained with only 0.17 wt% silver content.

The water-based polyurethane resin can make the nano-silver wire firmly adhere to the PET substrate, and the nano-silver wire will not fall off.

The transparent conductive film is based on PET, which can be bent and twisted at will, fully meeting the requirements of future flexible screens.

In order to make the above and other objects, features, and advantages of the present invention more comprehensible, preferred embodiments are listed below and described in detail in conjunction with the accompanying drawings.

Description of drawings

FIG. 1 is a scanning electron microscope (SEM) photo of a transparent conductive film prepared by a silver wire with a diameter of 40 nm in Example 1 of the present invention.

Fig. 2 is a scanning electron microscope (SEM) photograph of a silver wire with a diameter of 40 nm in Example 1 of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with examples, but the embodiments of the present invention are not limited thereto.

Example 1

(1) Preparation of nano-silver wire conductive ink:

In a 1000mL three-necked flask with a stirrer, add 500g of deionized water, then add 10g of water-based polyurethane resin, PEDOT:PSS solution 200g (wherein PEDOT:PSS mass fraction is 1wt%, solvent is water: isopropanol 1:1 ), 150 g of nano-silver wire isopropanol solution (the concentration of nano-silver wire solution is 10 mg/ml), the average diameter of nano-silver wire is 40 nm, the average length is 40 μm, and the aspect ratio is about 1000. After stirring for 30 minutes, the nano-silver wire conductive ink was prepared after uniform mixing, and the concentration of the nano-silver wire in the prepared nano-silver wire conductive ink was 0.17wt%.

(2) Preparation of transparent conductive film and performance test:

Using PET as a transparent flexible substrate, its own light transmittance is 92.1%, and its thickness is 100 μm. The nano-silver wire conductive ink prepared above was evenly coated on PET by wire bar roller coating, wherein the distance between the wire rods was 15 μm, and the roller coating speed was 80 cm/min. A uniform wet film was formed on the surface of the substrate. Dry in a vacuum oven at 130°C for 3 minutes. After the deionized water and organic solvent in the wet film are completely volatilized, take out the PET dry film with nano-silver wire network, that is, the transparent conductive film. The sheet resistance of the obtained film was measured by a four-probe tester, and the light transmittance and haze of the prepared film were tested by a photoelectric haze meter. The light transmittance of the prepared transparent conductive film is 89.9±0.1%, the sheet resistance is 100±10Ω/□, and the haze is 1.3%.

Fig. 1 is a scanning electron microscope (SEM) photograph of a transparent conductive film prepared by a silver wire with a diameter of 40nm in Example 1 of the present invention, showing that the nano silver wire is coated with a conductive polymer.

Fig. 2 is a scanning electron microscope (SEM) photograph of a silver wire with a diameter of 40 nm in Example 1 of the present invention, showing that the diameter is 20-60 nm and the length is 5-60 μm.

Table 1 is the content of each component and each performance index.

Example 2

(1) Preparation of nano-silver wire conductive ink:

In a 1000mL three-necked flask with a stirrer, add 350g of deionized water, then add 20g of water-based polyurethane resin, PEDOT:PSS solution 200g (wherein PEDOT:PSS mass fraction is 2wt%, solvent is water: isopropanol 1:1 ), 300g of nano-silver wire isopropanol solution (the concentration of nano-silver wire solution is 10mg/ml), the average diameter of nano-silver wire is 40nm, the average length is 40 μm, and the aspect ratio is about 1000. Stir for 30 minutes, and after mixing evenly, the nano-silver wire conductive ink is prepared. In the prepared nano-silver wire conductive ink, the concentration of the nano-silver wire is 0.34wt%.

(2) Preparation of transparent conductive film and performance test:

Using PET as a transparent flexible substrate, its own light transmittance is 92.1%, and its thickness is 100 μm. The nano-silver wire conductive ink prepared above was evenly coated on PET by wire bar roller coating, wherein the distance between the wire rods was 15 μm, and the roller coating speed was 80 cm/min. A uniform wet film was formed on the surface of the substrate. Dry in a vacuum oven at 130°C for 3 minutes. After the deionized water and organic solvent in the wet film are completely volatilized, take out the PET dry film with nano-silver wire network, that is, the transparent conductive film. The sheet resistance of the obtained film was measured by a four-probe tester, and the light transmittance and haze of the prepared film were tested by a photoelectric haze meter. The light transmittance of the prepared transparent conductive film is 88.1±0.1%, the sheet resistance is 50±5Ω/□, and the haze is 1.5%. Table 1 is the content of each component and each performance index.

Comparative Example 1

(1) Preparation of nano-silver wire conductive ink:

In a 1000mL three-necked flask with a stirrer, add 500g of deionized water, PEDOT:PSS solution 200g (wherein PEDOT:PSS mass fraction is 1wt%, solvent is water:isopropanol 1:1), nano silver wire isopropanol The solution is 150g (the concentration of the nano-silver wire solution is 10mg/ml), the average diameter of the nano-silver wire is 40nm, the average length is 40μm, and the aspect ratio is about 1000. After stirring for 30 minutes, the silver nano wire conductive ink was prepared after uniform mixing, and the silver nano wire concentration in the prepared silver nano wire conductive ink was 0.18wt%.

(2) Preparation of transparent conductive film and performance test:

Using PET as a transparent flexible substrate, its own light transmittance is 92.1%, and its thickness is 100 μm. The nano-silver wire conductive ink prepared above was evenly coated on PET by wire bar roller coating, wherein the distance between the wire rods was 15 μm, and the roller coating speed was 80 cm/min. A uniform wet film was formed on the surface of the substrate. Dry in a vacuum oven at 130°C for 3 minutes. After the deionized water and organic solvent in the wet film are completely volatilized, take out the PET dry film with nano-silver wire network, that is, the transparent conductive film. The sheet resistance of the obtained film was measured by a four-probe tester, and the light transmittance and haze of the prepared film were tested by a photoelectric haze meter. The light transmittance of the prepared transparent conductive film is 89.9±0.1%, the sheet resistance is 100±10Ω/□, and the haze is 1.3%. Table 1 is the content of each component and each performance index.

Comparative Example 2

(1) Preparation of nano-silver wire conductive ink:

Add 500g of deionized water and 100g of isopropanol into a 1000mL three-necked flask with a stirrer, then add 10g of water-based polyurethane, 150g of nano-silver wire isopropanol solution (the concentration of nano-silver wire solution is 10mg/ml), nano-silver The average diameter of the wire is 40nm, the average length is 40μm, and the aspect ratio is about 1000. After stirring for 30 minutes, the nano-silver wire conductive ink was prepared after uniform mixing, and the concentration of the nano-silver wire in the prepared nano-silver wire conductive ink was 0.17wt%.

(2) Preparation of transparent conductive film and performance test:

Using PET as a transparent flexible substrate, its own light transmittance is 92.1%, and its thickness is 100 μm. The nano-silver wire conductive ink prepared above was evenly coated on PET by wire bar roller coating, wherein the distance between the wire rods was 15 μm, and the roller coating speed was 80 cm/min. A uniform wet film was formed on the surface of the substrate. Dry in a vacuum oven at 130°C for 3 minutes. After the deionized water and organic solvent in the wet film are completely volatilized, take out the PET dry film with nano-silver wire network, that is, the transparent conductive film. The sheet resistance of the obtained film was measured by a four-probe tester, and the light transmittance and haze of the prepared film were tested by a photoelectric haze meter. The light transmittance of the prepared transparent conductive film is 89.9±0.1%, the sheet resistance is greater than 3000Ω/□, and the haze is 1.4%. Table 1 is the content of each component and each performance index.

Comparative Example 3

(1) Preparation of nano-silver wire conductive ink:

In a 1000mL three-necked flask with a stirrer, add 600g of deionized water, 100g of isopropanol, 150g of nano-silver wire isopropanol solution (the concentration of nano-silver wire solution is 10mg/ml), the average diameter of nano-silver wire is 40nm, and the average length 40μm, the aspect ratio is around 1000. After stirring for 30 minutes, the nano-silver wire conductive ink was prepared after uniform mixing, and the concentration of the nano-silver wire in the prepared nano-silver wire conductive ink was 0.17wt%.

(2) Preparation of transparent conductive film and performance test:

Using PET as a transparent flexible substrate, its own light transmittance is 92.1%, and its thickness is 100 μm. The nano-silver wire conductive ink prepared above was evenly coated on PET by wire bar roller coating, wherein the distance between the wire rods was 15 μm, and the roller coating speed was 80 cm/min. A uniform wet film was formed on the surface of the substrate. Dry in a vacuum oven at 130°C for 3 minutes. After the deionized water and organic solvent in the wet film are completely volatilized, take out the PET dry film with nano-silver wire network, that is, the transparent conductive film. The sheet resistance of the obtained film was measured by a four-probe tester, and the light transmittance and haze of the prepared film were tested by a photoelectric haze meter. The light transmittance of the prepared transparent conductive film is 89.8±0.1%, the sheet resistance is greater than 3000Ω/□, and the haze is 1.3%. Table 1 is the content of each component and each performance index.

Table 1:

It can be seen from Table 1 that the addition of water-based polyurethane resin can greatly improve the adhesion of ink on PET, and the addition of poly-3,4-ethylenedioxythiophene: polystyrene sulfonate (PEDOT:PSS) can improve the conductivity of PET film .

Uniformity test:

Comparative Example 4

According to the method of Example 1 in Application Publication No. CN 103627255 A "A Nano-Silver Conductive Ink and a Conductive Film Prepared by Using the Ink", a transparent conductive film with a size of 10cm*10cm was prepared, and 140 samples were randomly drawn on the transparent conductive film. points, test the sheet resistance of these 140 points, and calculate the mean and variance. At the same time, under the same environment, a transparent conductive film with a size of 10cm*10cm was prepared according to the method in Example 1 of the present invention, and the above operations were carried out. The results are shown in Table 2:

Table 2:

Example number average value variance maximum value minimum value Comparative Example 4 99.25ohm/sq 7.07ohm/sq 108.5ohm/sq 93.1ohm/sq Example 1 99.79ohm/sq 3.77ohm/sq 105.1ohm/sq 93.5ohm/sq

It can be seen from Table 2 that the sheet resistance distribution is uniform, that is, the content of silver wires per unit surface is uniform. This is unexpected, because the silver nano wire conductive ink of the present invention does not use dispersants and leveling agents, and can also achieve the uniform resistance distribution in Comparative Example 4, which is commendable.

Comparative Example 5

According to the method of embodiment 1 in the application publication number CN 103627255 A "a kind of nano-silver conductive ink and the conductive film prepared by using the ink", the nano-silver wire conductive ink is prepared, and it is placed statically for 10 days, 15 days, 20 days, 25 days and 30 days, observe its settlement situation. At the same time, the conductive ink was prepared according to the preparation method of the nano-silver wire conductive ink in Example 1 of the present invention, and its sedimentation was observed under the same conditions. The results obtained are shown in Table 3:

table 3:

project 10 days 15 days 20 days 25 days 30 days 60 days Comparative Example 5 uniform uniform uniform Subsidence occurs fallout increased severe stratification Example 1 uniform uniform uniform Subsidence occurs fallout increased slightly layered

It can be seen from Table 3 that the present invention can still achieve and exceed the anti-settling effect of adding an anti-settling agent (dibutyl phthalate) in Comparative Example 5 without adding any anti-settling agent. This also illustrates the superiority of the silver nano wire conductive ink of the present invention in formulation.

Claims (7)

1. A nano silver wire conductive ink with anti-sedimentation and self-leveling properties, it is made up of nano silver wire, water-based resin, conductive macromolecule, organic solvent and deionized water, and its weight consists of: Nano silver wire 0.1%~5%; Water-based resin 1% to 10%; Conductive polymer 0.1% to 5%; Organic solvent 10% ~ 45%; Deionized water 35% ~ 88.5%. 2. The method according to claim 1, wherein the nano-silver wire has a length of 5-60 μm and a diameter of 20-60 nm. 3. The method according to claim 1, wherein the water-based resin is a water-based polyurethane resin. 4. The method according to claim 1, wherein said conductive polymer is poly(3,4-ethylenedioxythiophene: polystyrene sulfonate), which is abbreviated as PEDOT:PSS. 5. The method according to claim 1, wherein the organic solvent is selected from one or more of methanol, ethanol, isopropanol, dimethylsulfoxide, tetrahydrofuran, and N,N-dimethylacetamide. 6. A preparation method for a transparent conductive film, comprising the following steps: A. prepare the nano-silver wire conductive ink with anti-settling and self-leveling properties as claimed in claim 1; b. coating the nano-silver wire conductive ink on the PET transparent substrate by a wire bar roll coating method, drying and curing to obtain a transparent conductive film. 7. The method according to claim 6, wherein the drying and curing temperature is 110-130° C. and the drying time is 1-5 minutes.