|
(11) | EP 3 547 332 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
| published in accordance with Art. 153(4) EPC |
|
|
|
|
|||||||||||||||||||||||||||
| (54) | FLEXIBLE TRANSPARENT CONDUCTIVE ELECTRODE |
[0001] The present invention discloses a flexible transparent conductive electrode. The flexible transparent conductive electrode is made of transparent flexible base materials and a transparent flexible substrate coated with a silver nanowire coating. The process of fabricating the flexible transparent conductive electrode comprises a few steps as followings: adding silver nanowire aqueous dispersion, waterborn acrylic resin, triethylenetetramine, 1-2 parts of p-methylsulfonyl toluene, 0.1-0.3 pars of hydrogenated castor oil and a mixture solvent into a vacuum mixer where evenly mixed, vacuum defoamed, and thus the coating is prepared. The concentration of the silver nanowire in the coating is 2-10mg/mL and the mixture solvents used are the mixture of alcohol and ketone. The film is coated with above coating and moved into a vacuum dryer to be dried at 150°C for 3-10min so that the solvents in the coating are completely volatilized and the flexible transparent conductive electrode is obtained. The flexible transparent conductive electrode of the invention has characteristics of the lower conductive resistivity, less stacks of silver nanowires, higher uniformity of conductivity and better optical transmittance comparison with the existing products.
FLEXIBLE TRANSPARENT CONDUCTIVE ELECTRODE
FIELD OF THE INVENTION
[0002] The present invention relates to a technology of silver nanowires, particularly relates to a flexible transparent conductive electrode.
BACKGROUND OF THE INVENTION
[0003] Metal oxides, especially ITO, has the characteristics of good optical transmittance in visible region and low resistivity which have been hot spots in researches and applications of transparent conductive electrodes in the past 5 decades. However, metal oxides have the disadvantages as limited conductivity, brittle and hard to deform. Concurrently, scarce resources and risen prices are unable to meet the requirements for developing the modern optoelectronic devices. Two dimensional micro-nano new materials and structured thin film electrodes are new fields of transparent conductive electrodes with the development of micro nanotechnology in recent years, such as conductive thin film of polymers, carbon nanotube film, graphene film and metal nanowire film. Unique morphology contributes great flexibility and electron mobility to graphene film, but large scale of production is not mature; uniform dispersion and resistance between carbon tubes limit the inner surface conductivity of carbon tubes film which need a little bit large aspect ratio. Transparent conductive film has advantages of not only great conductivity but also good optical transmission while nanometallic silver wire electrode's are excellent. Micro-nano silver wires can be used as electrode materials with less energy consumption (compared with electrode of oxide thin film) since silver is an electric conductor with great electrical conductivity. At the same time, micro nano structure of metal with plasma effect increases transmittance while diameters of micro silver nanowires' particles are smaller than the incident wavelength of visible light, and perfect photoelectric properties are achieved for electrodes. Simultaneously, micro silver nanowire electrode is benefit for flexible industries and large scale productions with lower cost. Therefore, the micro silver nanowire electrode will be a favorable alternative to ITO transparent conductive electrode. The additives for preparing coating fluid of micro silver nanowires determines performances of the electrode. Therefore, various additives are used to prepare different coating fluid for different properties in order to get better performances. Properties as conductivity and flexural endurance are still to be improved by using current formula. To overcome the problems and go on improving in the prior art are directions for those skilled in this field.
SUMMARY OF THE INVENTION
[0004] The object of the present invention is to provide a flexible transparent conductive electrode, in which silver nanowire coating is used. It can not only reduce the content of silver nanowires, effectively disperse silver nanowires, reduce the conductive resistivity, but also improve the bending resistance to be more than 5000 bending times .
[0005] To achieve the above purpose, the technical scheme adopted by the present invention is a flexible transparent conductive electrode consisting of a transparent flexible substrate and a silver nanowire coating, which the coating is coated on the surface of the transparent flexible substrate and the thickness of the silver nanowire coating is 20-100 microns after dried. The silver nanowire coating comprises following compounds by weight: 100 parts of silver nanowire aqueous dispersion, 5-8 parts of waterborn acrylic resin, 2-5 parts of triethylenetetramine, 1-2 parts of p-methylsulfonyl toluene, 0.2-0.5 parts of polyvinyl alcohol aqueous solution, 0.2-0.4 parts of alkanolamide, 0.3-0.5 parts of isopropoxyethanol, 0.1-0.3 parts of hydrogenated castor oil, 30-40 parts of mixture solvents.
[0006] The process of fabricating the flexible transparent conductive electrode comprises a few steps as followings:
The first step: 100 parts of silver nanowire aqueous dispersion, 5-8 parts of waterborn acrylic resin, 2-5 parts of triethylenetetramine, 0.1-0.3 parts of hydrogenated castor oil and 30-40 parts of mixture slovents are all added into a vacuum mixer where evenly mixed, vacuum defoamed, and then the mixture solution is prepared, in which the concentration of the silver nanowire in the aqueous dispersion is 2-10mg/mL and the mixture solvent is a mixture of alcohol solvents and ketone solvents;
The second step: 1-2 parts of p-methylsulfonyl toluene and 0.2-0.5 parts of polyvinyl alcohol aqueous solution are added into the mixture solution during the process of stirring. The waterborn resin fluid is waterborn polyester resin fluid after evenly mixed for 10min stirring;
The third step: 0.2-0.4 parts of alkanolamide and 0.3-0.5 parts of isopropoxyethanol are added into a vacuum mixer to be continually stirred and evenly mixed. The coating based on the silver nanowires is prepared ;
The fourth step: Transparent flexible substrate is PET film which uniformly coated with the silver nanowire coating by using miceo gravure. The distances between the bars are 15µm and the rolling speed for coating is 80cm/min, a uniform wet film is formed on the surface of the transparent flexible substrate;
The fifth step: The wet film coated with above coating is completely volatilized after dried in a vacuum dryer at 150 °C for 3-10min,and the flexible transparent conductive electrode is obtained.
[0007] Further improvements of the invention are as follows:
- 1. In according with the invention, the silver nanowires in the silver nanowire aqueous dispersion has the diameters of 20-150nm and lengths of 50-500mm.
- 2. In according with the invention, the alcohols is one of methanol, ethanol and isopropanol.
- 3. In according with the invention, the ketones solvent is one of acetone, butanone, cyclohexanone and isophorone.
- 4. In according with the invention, the mixture solution is a mixture of alcohols and ketones with 10:(2-4) by weight.
[0008] The invention has the following advantages and characteristics in comparison with the prior art:
The flexible transparent conductive electrode of the invention contains 100 parts of silver nanowire aqueous dispersion, 5-8 parts of water-borne acrylic resin, 0.2-0.5 parts of polyvinyl alcohol aqueous solution, 0.2-0.4 parts of alkyholamide, 0.3-0.5 parts of isopropoxyethylanol as a primary formula, and further adds with 2-5 parts of triethylenetetramine and 1-2 parts of p-methylsulfonyl toluene which reduces the content of silver nanowires, effectively disperses the silver nanowires, reduces the resistivity and improve the bending resistance to be more than 5000 bending times. Furthermore, the formula added with 0.3-0.5 parts of isopropoxyethanol and a mixture solvent of alcohols and ketones with 10: (2-4) by weight, which has advantages of effectively adjusting viscosity and drying rate of the coating further avoiding stacks of silver nanowires, ensuring uniformity of conductivity and improving transmittance.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0009] The following is detailed description of certain embodiments of the present invention.
formulations 1-4: a flexible transparent conductive electrode is comprised of a transparent flexible substrate coated with a silver nanowires coating at a thickness of 20-100µm after the silver nanowire coating is dried. The silver nanowire coating is consist of the following ingredients by weight as shown in Table 1:
| Ingredients | formulation 1 (parts) | formulation 2 (parts) | formulation 3 (parts) | formulation 4 (parts) |
| Silver Nanowire Aqueous Dispersion | 100 | 100 | 100 | 100 |
| waterborn Acrylic Resin | 6 | 5 | 6.2 | 7 |
| Triethylenetetramine | 3 | 2.2 | 5 | 4 |
| p-methylsulfonyl toluene | 1.8 | 1 | 1.5 | 1.2 |
| PVA Aqueous Solution | 0.24 | 0.4 | 0.3 | 0.45 |
| Alkanolamide | 0.3 | 0.35 | 0.4 | 0.26 |
| Isopropoxyethanol | 0.4 | 0.5 | 0.35 | 0.42 |
| Hydrogenated Castor Oil | 0. 15 | 0.25 | 0. 1 | 0.2 |
| Mixture Solvents | 35 | 32 | 38 | 35 |
[0010] In the formulation 1, wherein the mixture solution is a mixture of methanol and cyclohexanone of 10:2 by weight; In the formulation 2, wherein the mixture solution a mixture of isopropanol and butanone of 10:2.5 by weight; In the formulation 3, wherein the mixture solution is a mixture of ethanol and cyclohexanone of 10:3 by weight in; In the formulation 4, wherein the mixture solution is a mixture of methanol and isophorone of 10:3.8 by weight.
[0011] The process of fabricating the flexible transparent conductive electrode comprises a few steps as followings:
The first step: 100 parts of silver nanowire aqueous dispersion, 5-8 parts of waterborn acrylic resin, 2-5 parts of triethylenetetramine, 0.1-0.3 parts of hydrogenated castor oil and 30-40 parts of mixture slovents are all added into a vacuum mixer where evenly mixed, vacuum defoamed, and then the mixture solution is prepared, in which the concentration of the silver nanowire in the aqueous dispersion is 2-10mg/mL and the mixture solvent is a mixture of alcohol solvent and ketone solvent.
The second step: 1-2 parts of p-methylsulfonyl toluene and 0.2-0.5 parts of polyvinyl alcohol aqueous solution are added into the mixture solution during the process of stirring. The waterborn resin fluid is waterborn polyester resin fluid after evenly mixed for 10min stirring;
The third step: 0.2-0.4 parts of alkanolamide and 0.3-0.5 parts of isopropoxyethanol are added into a vacuum mixer to be continually stirred and evenly mixed. The coating based on the silver nanowires is prepared ;
The fourth step: Transparent flexible substrate is PET film which uniformly coated with the silver nanowire coating by using miceo gravure. The distances between the bars are 15µm and the rolling speed for coating is 80cm/min, a uniform wet film is formed on the surface of the transparent flexible substrate;
The fifth step: The wet film coated with above coating is completely volatilized after dried in a vacuum dryer at 150 °C for 3-10min,and the flexible transparent conductive electrode is obtained.
[0012] The silver nanowires in the above coating have the diameters of 20-150nm and lengths of 50-500mm:
The tested results of the flexible transparent conductive electrode in the Embodiment 1-4 are shown in Table 2:
| Embodiment 1 | Embodiment 2 | Embodiment 3 | Embodiment 4 | |
| Resistance(Ω/square) (Four-probe Resistance Tester) | 31 | 30 | 30 | 32 |
| Adhesion(Vertical Pulled with 3M600) | No shedding | No shedding | No shedding | No shedding |
| Transmittance(%)(WGW Optical Haze Meter) | 92 | 92 | 91 | 92 |
| Haze(WGW Optical Haze Meter) | 1.2 | 1.3 | 1.2 | 1.3 |
| Flexural Endurance(time) | >5000 | >5000 | >5000 | >5000 |
[0013] The characteristics of the flexible transparent electrode which is provided in the present invention have thus been shown in Table 2 to be achieved in reducing the content of silver nanowires, effectively dispersing the silver nanowires, reducing resistivity and improve the bending resistance to be more than 5000 bending times; and effectively adjusting the viscosity and drying rate of coating fluid, further avoiding stacks of the silver nanowires, ensuring uniformity of the conductivity and improving transmittance.
[0014] The embodiments are only to illustrate the technical conception and characteristics of the present invention, the purpose of which is to enable people familiar with the technology to understand the contents of the present invention and to implement it, and not to limit the scope of protection of the present invention. Any equivalent substitution made with the same idea of the present invention is in the scope of protection of the present invention.
The process of fabricating the flexible transparent conductive electrode comprises following steps:
step 1, 100 parts of silver nanowire aqueous dispersion, 5-8 parts of waterborn acrylic resin, 2-5 parts of triethylenetetramine, 0.1-0.3 parts of hydrogenated castor oil and 30-40 parts of mixture slovents are all added into a vacuum mixer where evenly mixed, vacuum defoamed, and then the mixture solution is prepared, in which the concentration of the silver nanowire in the aqueous dispersion is 2-10mg/mL and the mixture solvent is a mixture of alcohol solvent and ketone solvent;
step 2, 1-2 parts of p-methylsulfonyl toluene and 0.2-0.5 parts of polyvinyl alcohol aqueous solution are added into the mixture solution during the process of stirring. The waterborn resin fluid is waterborn polyester resin fluid after evenly mixed for 10min stirring;
step 3, 0.2-0.4 parts of alkanolamide and 0.3-0.5 parts of isopropoxyethanol are added into a vacuum mixer to be continually stirred and evenly mixed. The coating based on the silver nanowires is prepared ;
step 4,Transparent flexible substrate is PET film which uniformly coated with the silver nanowire coating by using miceo gravure. The distances between the bars are 15µm and the rolling speed for coating is 80cm/min, a uniform wet film is formed on the surface of the transparent flexible substrate;
step 5,The wet film coated with above coating is completely volatilized after dried in a vacuum dryer at 150°C for 3-10min,and the flexible transparent conductive electrode is obtained.