DE102008042694A1 - UV irradiation of indium tin oxide layers - Google Patents

Abstract

The present invention relates to a method for producing transparent conductive layers, comprising the steps of (1) providing a dispersion of TCO nanoparticles, then (2) applying the dispersion obtained according to step (1) to a substrate, and at least partially removing the solution or dispersing agent, then (3) irradiating the UV light obtained after step (2), and a layer obtained by the method of the present invention, and an electronic component having such a layer.

Description

The The present invention relates to a process for producing transparent conductive layers based on transparent, conductive oxide (TCO) nanoparticles, in particular indium tin oxide (ITO) nanoparticles by irradiation with UV light, and the layers obtained by this method.

• – Widerstandsfähigkeit gegen Beanspruchung durch kratzende, scharfkantige Gegenstände oder Materialien, charakterisiert z. B. durch die Stifthärte nach Wolff-Wilborn oder durch die Bleistifthärte nach DIN EN 13523-4: 2001 ;
• – Haftung auf dem Substrat, ermittelt z. B. durch den Kreuzschnitt- oder Tape-Test nach DIN EN ISO 2409 ;
• – Zunahme des Flächenwiderstandes unter wiederholter, in einer definierten Anzahl Biegezyklen und einem definiertem Biegeradius ausgedrückten Biegebeanspruchung der Schicht, um einen begrenzten Faktor.

An electrically-mechanically stable layer is understood in the following to mean a layer which has the following properties:

• - Resistance to stress from scratching, sharp-edged objects or materials, characterized z. B. by the pencil hardness to Wolff-Wilborn or by the pencil hardness after DIN EN 13523-4: 2001 ;
• - adhesion to the substrate, determined z. B. by the cross-cut or tape test after DIN EN ISO 2409 ;
• Increasing the sheet resistance under repeated bending stress of the layer expressed in a defined number of bending cycles and a defined bending radius by a limited factor.

This increase is with a device after Königer et al. and is described by Königer and Münsted in Measurement Science and Technology. The increase in surface resistance decreases with increasing bending radius.

Under Sheet resistance is discussed here and below the ohmic resistance is understood, the on a coating with a uniform layer thickness is obtained if a square area of any size contacted on two opposite edges and the current is measured as a function of the (DC) voltage. The sheet resistance is measured in Ω and marked Ω / ☐. The determination of sheet resistance can also be different Method, such. B. the four-point measurement.

Under resistivity is hereinafter the ohmic resistance understood by multiplying the sheet resistance with the layer thickness [in cm] is obtained and a measure of the ohmic properties of the conductive material itself represents. The resistivity is in Ω · cm specified.

Under Transmission is hereafter the permeability of a transparent body for light of wavelength 550 nm understood.

The Transmission of a coated substrate is in proportion to the transmission in air in percentages.

transparent High ohmic conductivity layers have specific ones Resistances of at most 50 Ω · cm and a transmission of at least 40% on and in all modern displays, eg. B. in LCD (liquid crystal display), plasma displays, OLEDs, and z. B. also needed in organic solar cells, around the electrical stimulated by the photovoltaic effect To be able to use currents with low loss.

in the The state of the art becomes conductive layers, for example produced by flame spraying or in a vacuum by sputtering techniques. A Structuring is not possible or only very expensive. It is generally made by applying various etching techniques receive.

conductive Layers are also produced on the basis of nanoparticles, wherein These must be thermally treated, according to the state the technology, for example, in a furnace process to the desired To achieve conductivity. The thermal aftertreatment of coatings of metallic nanoparticles, for example from silver particles, can also be done by laser irradiation.

For conductive layers that are transparent in the visible range, ITO has proven to be the most suitable material for applications in modern electronics. ITO layers on flexible polyethylene terephthalate (PET) substrates are produced in the prior art in sputtering or vapor deposition processes, the z. B. at DC Paine, H.-Y. Yeom and B. Yaglioglu in "Flexible Flat Panel Displys", pp. 79-98 , and S. Ray, R. Banerjee et al. in J. Appl. Phys. 54 (1983), 3497-3501 , are described in detail.

For continuous production processes are these coating techniques however, expensive, since they are carried out in a vacuum have to. There is also a textured coating of substrates only by a masking or by lithography process possible where ITO is wasted. The coating using printable ITO nanoparticle dispersions although a direct structuring by means of printing process under waiver on a litigation under vacuum, but it resulted the demand for an improvement of the specific resistance.

To achieve economically viable conductivities, coatings of ITO nanoparticles without a binder are thermally treated such that the nanoparticles are fused or sintered. However, this treatment of ITO nanoparticle coatings on flexible polymer substrates is a difficult problem to solve because of the limited thermal stability of the substrate. For example, surface resistances below 1000 Ω / ☐ of ITO nanoparticles To obtain coatings on PET substrates and transmissions of at least 80% in the visible range, the coatings of ITO nanoparticles must be brought to temperatures above 500 ° C. In continuous production processes, for example roll-to-roll production processes, for the coating of flexible transparent polymer substrates, however, the temperatures are limited to values around 200 ° C, otherwise the polymer substrates and / or the coatings show cracks or flake even at low bending stresses Substrate off.

on the other hand are in the art are investigations to improve the Conductivity of ITO nanoparticle coatings on flexible polymer substrates known by UV treatment in which the ITO nanoparticle dispersions modified with UV-curing binders. Such binders affect However, the dispersion of nanoparticles and increase the specific resistance.

A Irradiation with UV light at the same time more transparent and conductive Coatings made of non-metallic nanoparticles know the state but not the technology.

all A common prior art method is that the nanoparticles with each other and with other components and / or the substrate be sintered or fused. So there in the nanoparticulate Layer heat energy is generated, so far always on it to pay attention to the heat transfer into the substrate does not become so large that in the substrate transformations of chemical (eg decomposition) or physical type (eg melting) in Gear set. Especially for sensitive substrates like Most plastic films have the temperature at which such unwanted processes occur in the substrate, generally so low that not enough heat energy in the nanoparticular layer can be generated that sinter the nanoparticles to an optimal extent or merge. On the other hand, one knows that the specific Resistance of conductive layers becomes lower, depending more comprehensively sintering and / or fusing the nanoparticles together.

task The present invention was therefore to provide a method which reduces the thermal load of the substrate and thus overcomes the disadvantages of the prior art.

task It was as well a layer with improved electro-mechanical To provide properties.

These Task is solved by a process for producing transparent conductive Layers with the characterizing features of claim 1 solved.

• (1) Bereitstellung einer Dispersion aus TCO Nanopartikeln, anschließend
• (2) Aufbringen der nach Schritt (1) erhaltenen Dispersion auf ein Substrat, und zumindest teilweises Entfernen des Lösungsmittels oder Dispersionsmittels, anschließend
• (3) Bestrahlen der nach Schritt (2) erhaltenen Beschichtung mit UV-Licht

umfasst.The subject matter of the present invention is therefore a process for producing transparent conductive layers, which comprises the steps

• (1) providing a dispersion of TCO nanoparticles, subsequently
• (2) applying the dispersion obtained after step (1) to a substrate, and at least partially removing the solvent or dispersant, subsequently
• (3) Irradiating the coating obtained after step (2) with UV light

includes.

The inventive method has the advantage that short interaction times are achieved and thus the thermal Loading of the substrate compared to methods in the state of Technology is greatly reduced. The invention Procedure is also inline-capable, synonymous So that this in a continuous production process for substrates with transparent conductive layers can be used, for example in a roll-to-roll process.

Therefore is also the subject of the present invention, a transparent conductive layer associated with the invention Procedure is obtained. Likewise, the subject of the present Invention, an electronic component, the inventive Layer has, as well as the use of the inventive electronic component in an OLED (Organic Light Emitting Diodes), electroluminescent module, display, photovoltaic element, touch-sensitive screen, so-called touch panel, Resistance heating element, infrared protection film, antistatic housing, chemical sensor, electromagnetic sensor, FKD (liquid crystal display), so-called LCD, electrophoretic display.

The Invention will be explained in more detail below.

It may be advantageous to use in step (1) of the process according to the invention a dispersion which contains indium tin oxide nanoparticles. The preparation of such a dispersion is for example in the patent applications DE 102006005019.3 . DE 102006005025.8 , and DE 102006005026.6 , the publication DE 198 40 527 A1 , as well as the European patent application EP 06018493.4 disclosed. ITO nanoparticle dispersions, including ITO-based nanocomposites with, for example, polyvinylpyrrolidone, have the advantage that in step (3) of the process according to the invention most of the energy of the ultraviolet radiation is emitted by the ITO Nanoparticles is absorbed or reflected, thus the energy input into the substrate is further reduced and therefore also sensitive and / or less expensive, less heat-resistant substrates can be used. Preferably, the solvent or dispersion medium used is an alcohol, preferably with a weight fraction of from 10 to 80% by weight, more preferably from 50 to 80% by weight, very particularly preferably with a weight fraction of 75% by weight.

Preferably For example, in step (1), a dispersion can be used which has a contains thermally curable binder. As a binder Generally inorganic and organic binders can be used become. Suitable binders are, for example, polyvinyl resins, polyolefins, PVC, polyvinyl alcohol, polyvinyl esters, polystyrene, acrylic resins, acrylic esters, Alkyd resins, polyurethane paints, urea resins, melamine resins, phenolic resin paints. Preference may be given to cellulose, methylcellulose, hydroxypropylcellulose, Nitrocellulose and cellulose esters are used.

Furthermore Thermoplastics can also be used as binders. Such binders may be selected from the group consisting of polyvinyl acetals, polyvinyl alcohols, acetalated polyvinyl alcohols, Polymethyl methacrylates, polyvinyl chlorides, polyacrylates, cellulose derivatives, Latex binders, polyvinylpyrrolidones, polyurethanes, polyethylenes, Polypropylenes, polyisobutenes, polybutenes, polyamides, polyimides, Polytetrafluoroethylene, polycarbonates, polyethers and polyepoxides. Particularly preferred may polyvinyl acetals and from this Group polyvinyl butyrals are used. Still special Polyvinyl butyrals having a molecular weight may be preferred from 1000 to 120000 g / mol, particularly preferably from 40,000 to 70000 g / mol can be used. Furthermore, the polyvinyl butyral have a hydroxyl content of about 2 to 20 wt .-%.

Prefers can in step (2) of the method according to the invention dispersion by inkjet printing, flexo printing, pad printing, spin coating, spraying, dipping, knife coating, offset printing, screen printing, Thermal transfer printing, gravure printing, flood, Aerosil Jet Deposition process the company optomec, (optomec inc., Albuquerque, New Mexico) or Pour it onto the substrate.

By This printing process is structuring, at least in part Structuring possible on the substrate. Preferably the dispersion once or several times and / or continuously or batchwise be applied. The environmental conditions are of the requirements depending on the application and may how the dispersion is applied may be different.

Advantageously, in step (2) of the method according to the invention a substrate can be used which contains or is glass or plastic. Preference is given to using transparent materials, particularly preferably quartz glass, borosilicate display glass, alkali-free borosilicate display glass, white glass, window glass, float glass, polyester, polyamide, polyimide, polyacrylate, polycarbonate (PC), polyethersulfone (PES), polyetheretherketone (PEEK), polyvinyl chloride (PVC ), Polyethylene (PE), polypropylene (PP), polyacetal (POM), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), polyhydroxybutyrate (PHB), polyamide 6, polyamide 6.6, polyamide 11, polyamide 12, Kapton ^® polymethyl methacrylate (PMMA) or a combination of these materials. It may also be advantageous to use these materials or a combination of these materials in the form of films and / or laminates, particularly preferably PET films, which are particularly inexpensive and combine excellent transparency with flexibility. Since the absorption of UV light by the substrate depends on the wavelength of the UV light, it is advantageously possible to select a substrate which has the lowest possible absorption at a given wavelength, thus also minimizing the heat energy in the substrate by the irradiation with UV light. Light is generated.

Farther Preferably, in step (2) of the invention Process a substrate used for the Wavelengths of the UV light used in step (3) transparent or nearly transparent

It may also be advantageous before step (3) of the invention Process the solvent or dispersant the coating obtained after step (2) by increasing the Temperature in the coating, synonymous with tempering, too remove.

It may be advantageous, the solvent or dispersant at a temperature of 20 ° C to 200 ° C, preferably from 150 ° C to 200 ° C, more preferably from 180 ° C to 200 ° C for a period of 1 s to 120 min by annealing remove. With such an approach is a layer according to the invention with an improved Adhesion on the substrate obtained.

More preferably, the solvent or dispersant may be removed from the dispersion or solution for a period of 20 minutes at a temperature of 200 ° C. The solvent or dispersing agent may be, for example, by introducing electromagnetic energy or by contacting the substrate with a heating plate, in a roll-to-roll process, preferably by contact with at least one heated roll or calender to be removed. The solvent or dispersion medium may furthermore preferably be obtained by irradiation with IR, VIS or UV light, for example by means of halogen lamps or lasers emitting in the IR range, in a tempering oven, or by purging with air or inert gas, preferably with inert gas or Air should be removed at ambient temperature. Most preferably, the solvent or dispersant can be removed by at least one process that can be integrated in a roll-to-roll process. Up to 99% of the solvent or dispersant may preferably be removed from the coating obtained after step (2). The proportion of solvent or dispersant removed by the tempering can be determined by measuring methods known to the person skilled in the art, for example by gravimetric methods. After annealing, a layer thickness of 0.05 to 100 .mu.m, preferably from 0.05 to 75 .mu.m, more preferably from 0.05 to 50 .mu.m, particularly preferably from 0.05 to 30 .mu.m, most preferably from 1 to 3 μm are obtained.

In the method according to the invention, it may be advantageous if in step (3) the coating is irradiated with UV light at a wavelength of 200 to 450 nm, preferably from 200 to 320 nm, and / or with a power related to the irradiated surface from 100 W · cm ^-1 to 200 W · cm ^{-1 ,} preferably 120 W · cm ^{-1 is} irradiated, and / or coating at a flow rate of 1 to 50 m · min ^-1 , preferably from 2 to 20 m · min ^{-1 is passed} through the surface irradiated with UV light.

The Moving the coating through the UV light irradiated area through it is equivalent to having the duration set can be while the same successive each other Surfaces of the coating are irradiated with UV light. This is referred to below as the exposure time. In the method according to the invention can exposure times from 1 to 7 s, preferably from 1 be set to 4 s.

There in the coating in step (3) of the invention Procedure registered energy over the exposure time proportional to the power related to the irradiated area is, thus, the registered energy can be adjusted. Therefore, another advantage of the invention Method that, depending on the UV light wavelength just as much energy can be added to the coating that the substrate does not suffer. Therefore, in the inventive In turn, the maximum amount of ener- gised energy contributes the substrate is undamaged after step (3), be set. For a given UV light wavelength the maximum amount of energy entered in turn corresponds to one maximum value of the exposure time.

The Energy entered into the coating will be energy input in the following called. The energy input can also be done with a UV radiometer Model Power Puck S / N 2437 from EIT. The maximum Energy input in which the substrate is undamaged after step (3), So it can be both set and measured.

The Steps (1), (2), and (3) of the invention Processes can be repeated as often as desired, preferably once become.

object The present invention is also a transparent conductive Layer using the method according to the invention is obtained.

Because the maximum energy input can be set or measured and the resistivity with that used in step (3) Exposure time decreases, given substrate and selection the TCO nanoparticles thus the invention Layer preferably with minimum or a desired higher resistivity, especially preferred with minimum resistivity.

The Layer according to the invention can have a specific Resistance of 0.1 to 2 Ω · cm, preferably 0.5 up to 1.5 Ω · cm.

Preferably the layer according to the invention can increase the sheet resistance under bending stress, if in step (2), a flexible substrate is inserted around a Factor from 1.0 to 10 times after 50 bending cycles at a bending radius of 5 mm and an amplitude of 30 mm, measured according to Königer, preferably by a factor of 1 to 5 times, especially preferably from 1 to 3 times.

The According to the invention, as already stated, have different layer thicknesses after annealing in the step (2), preferably from 0.05 to 50 μm. Therefore can the sheet resistance depending on the use of the invention electronic component, the inventive Layer, advantageously selected.

Becomes the electronic component according to the invention, the the layer according to the invention, in one OLED or FKD may use this sheet resistance from 10 to 100 Ω / □ when used in one Electroluminescence module from 50 to 250 Ω / □, at the use in a touch panel from 250 to 1500 Ω / ☐, or in a sensor from 1500 to 10,000 Ω / □.

Furthermore the layer according to the invention may have a transmission of at least 40%, preferably of at least 80%, more preferably of at least 90%. Most preferably, the inventive Layer have a transmission of at least 95%.

The layer according to the invention can according to a tape test according to DIN EN ISO 2409 measured adhesion preferably from 0% to 65%, equivalent to Gt 0 to Gt 4, preferably from 0% to 35%, equivalent to Gt 0 to Gt 3, more preferably from 0% to 15%, equivalent to Gt 0 to Gt 2 , very particularly preferably from 0% to 5%, meaning Gt 0 to Gt 1.

The layer according to the invention may preferably be made by means of a Scratch Hardness Tester from Erichsen, Model 291, according to test methods DIN 13523-4 measured pencil hardness of 8 B to 6 H, preferably from F to 6 H, more preferably from 3 H to 6 H.

The inventive method and the invention Layer are explained in more detail below by way of example.

1 shows the energy input, measured with the UV-Radiometer Power Puck S / N 2437 from EIT, for different wavelengths depending on the exposure time used in step (3) of the method according to the invention.

Example 1.

• – 35 Gew.-% ITO Nanopartikel mit Primärpartikeln einer Größe unter 20 nm, und
• – 65 Gew.-% Ethanol als Lösungs- oder Dispersionsmittel,

durch Rakeln mittels Erichsen Coatmaster Model 509 C jeweils in einer Dicke von etwa 50 μm aufgebracht, und anschließend an Luft getrocknet.On several PET films were dispersions, each containing

• 35% by weight of ITO nanoparticles with primary particles smaller than 20 nm, and
• 65% by weight of ethanol as solvent or dispersing agent,

applied by knife coating using Erichsen Coatmaster Model 509 C, each in a thickness of about 50 microns, and then dried in air.

The coatings thus obtained were then each exposed to ultraviolet light in a UV continuous-flow type Eltosch UV-Lab 200 in the Science-to-Business Center of Evonik Degussa GmbH. A mercury vapor lamp with an intensity maximum in the wavelength range from 200 to 320 nm was used to generate the UV radiation. The power of the mercury vapor lamp was 120 W · cm ^-1 with a lamp length of 20 cm. The flow rate was adjusted to a value of 2 to 20 m.min ^-1 during the irradiation of each coated PET film. This was synonymous with an exposure time of 1 s to 7 s.

2 shows the resistivity of the layer according to the invention as a function of the exposure time. The dashed line at the abscissa of 4 s marks the maximum exposure time above which the PET film was damaged by the irradiation with UV light.

Example 2.

On several PET films were, as in Example 1, each a dispersion made from ITO nanoparticles. In contrast to Example 1 The layers thus obtained were then placed on a heatable glass plate fixed and by means of this device during a period of 20 minutes at a temperature of 200 ° C each annealed, so that the solvent or dispersant each was at least partially expelled.

The coatings thus obtained were then each exposed to ultraviolet light in a UV continuous-flow type Eltosch UV-Lab 200 in the Science-to-Business Center of Evonik Degussa GmbH. A mercury vapor lamp with an intensity maximum in the wavelength range from 200 to 320 nm was used to generate the UV radiation. The power of the mercury vapor lamp was 120 W · cm ^-1 with a lamp length of 20 cm. The flow rate was adjusted to a value of 2 to 20 m.min ^-1 during the irradiation of each coated PET film. This was synonymous with an exposure time of 1 s to 7 s.

3 shows the resistivity of the layer according to the invention as a function of the exposure time. The dashed line at the abscissa of 4 s marks the maximum exposure time above which the PET film was damaged by the irradiation with UV light.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 102006005019 A [0024]
• - DE 102006005025 A [0024]
• - DE 102006005026 A [0024]
• - DE 19840527 A1 [0024]
• - EP 06018493 [0024]

Cited non-patent literature

• - DIN EN 13523-4: 2001 [0002]
• - DIN EN ISO 2409 [0002]
• - Königer et al. [0003]
• - DC Paine, H.-Y. Yeom and B. Yaglioglu in Flexible Flat Panel Displys, pp. 79-98 [0011]
• - S. Ray, R. Banerjee et al. in J. Appl. Phys. 54 (1983), 3497-3501 [0011]
• - DIN EN ISO 2409 [0046]
• - DIN 13523-4 [0047]

Claims (15)

Process for producing transparent conductive Layers comprising the steps (1) Provision of a Dispersion of TCO nanoparticles, subsequently (2) Applying the dispersion obtained after step (1) to a substrate, and at least partially removing the solvent or Dispersant, then (3) irradiate the after step (2) obtained coating with UV light. Method according to claim 1, characterized in that that in step (1) a dispersion is used, the indium tin oxide Contains nanoparticles. Method according to claim 1 or 2, characterized that in step (1) a dispersion is used, which is a thermal contains curable binder. Method according to claim 1, characterized in that that in step (2) the dispersion by inkjet printing, flexographic printing, Pad printing, spin coating, spraying, dipping, knife coating, offset printing, screen printing, thermal transfer printing, gravure printing, Flooding, Aerosil jet deposition process, or pouring on the substrate is applied. Method according to claim 1, characterized in that that in step (2) the substrate is selected, the glass or plastic contains or is. Method according to claim 1, characterized in that in that before step (3) the solvent or dispersant from the coating obtained after step (2) at a temperature from 20 ° C to 200 ° C for a period of time from 1 s to 120 min is removed by annealing. A method according to claim 1, characterized in that in step (3) the coating is irradiated with UV light at a wavelength of 200 to 450 nm, and / or with a related to the irradiated surface power of 100 W · cm ^-1 to 200 W · cm ^{-1 is} irradiated, and / or coating is moved at a throughput speed of 1 to 50 m · min ^-1 through the surface irradiated with UV light. Transparent conductive layer with a method according to at least one of claims 1-7 becomes. A layer according to claim 8 having a resistivity from 0.1 to 2 Ω · cm. Layer according to claim 8 or 9 with a transmission of at least 40%. Layer according to at least one of the claims 8-10 with a tape test according to DIN EN ISO 2409 measured adhesion coefficients from Gt 0 to Gt 4. Layer according to at least one of the claims 8-11 with one according to test method DIN 13523-4 measured pencil hardness from 8 B to 6 H. Layer according to at least one of the claims 8-12 with an increase in sheet resistance under bending stress, if in step (2) a flexible substrate is used by a factor of 1.0 to 10 times after 50 bending cycles at a bending radius of 5 mm and an amplitude of 30 mm, measured according to King, at an amplitude of 30 mm. Electronic component, one layer after at least one of claims 8-13. Use of the electronic component according to claim 14 in an OLED, electroluminescent module, photovoltaic element, touch-sensitive screen, resistance heating element, Infrared protection film, antistatic housing, chemical Sensor, electromagnetic sensor, FKD, LCD, electrophoretic Display.