JP2011119142A - Method for manufacturing transparent conductive base material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a transparent conductive base material which has both high conductivity and good transparency and reduces variations in conductivity depending on locations of a film. <P>SOLUTION: In the method for manufacturing the transparent conductive base material having a conductive layer formed by applying a coating liquid including at least metallic nanowires, water soluble polymer, and an aqueous solvent onto a base material and by subsequently drying, a coated film for the conductive layer formed by applying the coating liquid is dried at film surface temperature of 27-42°C and at drying speed (h×ΔT) of 1,000-10,000 (kcal/(m<SP>2</SP>×hr)). Here, h is a heat transfer coefficient (kcal/(m<SP>2</SP>°×C×hr)), and ΔT (°C) is a difference between blast temperature and the film surface temperature of the coated film. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a transparent conductive substrate.

  Transparent conductive substrates are used for liquid crystal displays, plasma displays, electrochromic displays, electroluminescent elements, solar cells, touch panels, transparent electrodes of electronic devices such as electronic paper, and electromagnetic shielding materials.

  In general, for example, a metal oxide is used as the transparent conductive material. Specifically, indium oxide doped with tin or zinc (ITO, IZO), zinc oxide doped with aluminum or gallium (AZO, GZO), Examples thereof include tin oxide (FTO, ATO) doped with fluorine or antimony. In general, the metal oxide transparent conductive layer is produced by vapor deposition such as vacuum deposition, sputtering, or ion plating. However, since these film forming methods require a vacuum environment, the apparatus is large and complicated, and since a large amount of energy is consumed for film forming, it is necessary to develop a technology that can reduce the manufacturing cost and environmental load. It was done. On the other hand, as represented by a liquid crystal display and a touch display, an increase in the area of the transparent conductive material is aimed at, and accordingly, demands for weight reduction and flexibility of the transparent conductive material have increased. Furthermore, since the influence of the voltage drop of a transparent electrode becomes large in a large-area transparent electrode, further reduction in resistance has been demanded.

On the other hand, it has been reported that nanowires of metal elements having a bulk conductivity of 1 × 10 ⁷ S / m or more can be produced by various methods such as a liquid phase method and a gas phase method. For example, Non-Patent Document 1 can be referred to as a method for producing Ag nanowires. Furthermore, as a transparent conductive material technique specifically used for a low-resistance high-transparent conductive film, a method using metal nanowires as a conductor has been proposed (for example, see Patent Document 1). Furthermore, it is described that the surface resistance of the conductive substrate can be controlled by applying the silver nanowire dispersion liquid to the substrate and controlling the environmental humidity until it is dried (see, for example, Patent Document 2). These techniques are preferable because a low-resistance, highly transparent conductive film can be obtained by coating.

  However, it has been found that in a conductive substrate using metal nanowires as a conductor, the conductivity of the film varies depending on the location. The variation depending on the location of the conductivity of the film causes a variation in device performance using the film, and needs to be improved.

US2007 / 0074316A1 Specification US 2009/0166055 A1

Adv. Mater. , 2002, 14, 833-837

  An object of the present invention is to provide a method for producing a transparent conductive substrate having both high conductivity and good transparency, and reduced variation in conductivity depending on the location of the film.

  The above object of the present invention can be achieved by the following configuration.

1. In the method for producing a transparent conductive substrate having a conductive layer formed by applying a coating liquid comprising at least a metal nanowire, a water-soluble polymer, and an aqueous solvent on a substrate and then drying the coating solution, The film surface temperature of the coating film coated with the conductive layer coating liquid is 27 ° C. or higher and 42 ° C. or lower, and the drying rate (h × ΔT) is 1000 to 10,000 (kcal / (m ² · hr)). A method for producing a transparent conductive substrate.

However, h represents a heat transfer coefficient (kcal / (m ² · ° C. · hr)), and ΔT (° C.) represents a difference between the blowing temperature and the film surface temperature of the coating film.

  2. 2. The method for producing a transparent conductive substrate according to 1 above, wherein the drying is performed after the coating solution is applied to the substrate and then passed through a substantially windless region.

  3. 3. The method for producing a transparent conductive substrate according to 2 above, wherein the time passing through the substantially windless region is 2 seconds or more and 20 seconds or less.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the transparent conductive base material which has high electroconductivity and favorable transparency, and reduced the electroconductive dispersion | variation by the location of a film | membrane can be provided.

It is a schematic diagram of the drying apparatus of the transparent conductive base material which concerns on this invention.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

  The present invention relates to a method for producing a transparent conductive substrate having a conductive layer formed by applying and drying a coating liquid comprising at least a metal nanowire, at least one water-soluble polymer, and an aqueous solvent on the substrate. It is an invention that has found that by controlling the drying method, variation in the conductive location of the coating film can be reduced. Although the detailed mechanism is not well understood, in a conductive film using metal nanowires, each metal nanowire is brought into contact with each other to form a continuous path, thereby exhibiting conductivity. For this reason, when the contact frequency of the metal nanowires fluctuates, the conductivity of the coating film changes. In addition, a water-soluble polymer is required as a dispersion aid and a holding material for the coating film, but when this water-soluble polymer enters the contact portion between the metal nanowires, the contact resistance between the metal nanowires increases, The conductivity of the coating film changes. Therefore, in a transparent conductive substrate having a conductive layer formed by applying and drying a coating solution comprising at least a metal nanowire, at least one water-soluble polymer, and an aqueous solvent on the substrate, the drying is a little disturbed. The contact frequency of metal nanowires and the contact resistance between metal nanowires are greatly changed, and it is considered that the conductivity varies depending on the location of the coating film.

In response to these problems, it was considered that the dispersion due to drying can be reduced by setting the drying rate to 1000 (kcal / (m ² · hr)) or more and drying quickly. In addition, even if the drying speed is high, if the film surface temperature at the time of drying is too high, the effect of slight disturbance of drying tends to be large.Therefore, the resistance varies depending on the location, and the film surface temperature is low. In the range where the drying speed of the invention is satisfied, the heat transfer coefficient becomes an extremely large region, and the disturbance of drying is likely to occur. In the scope of the present invention, since it is possible to make it less susceptible to such influence, it is considered that the variation in conductivity depending on the location of the coating film can be suppressed, and further, the coating is performed by passing through a substantially windless region after coating. The leveling of the subtle film thickness unevenness at the time was considered to further reduce the variation, and the present invention was achieved.

[Metal nanowires]
In the present invention, a metal nanowire functions as a main conductor as the transparent conductive material. In the present invention, an element having a bulk conductivity of 1 × 10 ⁶ S / m or more can be used as the metal element of the metal nanowire. Specific examples of metal elements of the metal nanowire that can be preferably used in the present invention include Ag, Cu, Au, Al, Rh, Ir, Co, Zn, Ni, In, Fe, Pd, Pt, Sn, Ti, and the like. Can be mentioned. In the present invention, two or more kinds of metal nanowires can be used in combination, but from the viewpoint of conductivity, it is preferable to use at least an element selected from Ag, Cu, Au, Al, and Co.

  In the present invention, the means for producing the metal nanowire is not particularly limited, and for example, known means such as a liquid phase method and a gas phase method can be used. Moreover, there is no restriction | limiting in particular in a specific manufacturing method, A well-known manufacturing method can be used. For example, as a method for producing Ag nanowires, Adv. Mater. , 2002, 14, 833-837; Chem. Mater. , 2002, 14, 4736-4745, etc. As a method for producing Co nanowires, a method for producing Au nanowires is disclosed in JP 2006-233252A, and a method for producing Cu nanowires is disclosed in JP 2002-266007 A, etc. Reference can be made to Japanese Unexamined Patent Publication No. 2004-149871. In particular, Adv. Mater. And Chem. Mater. The method for producing Ag nanowires reported in 1 can produce silver nanowires easily and in large quantities in an aqueous system, and the conductivity of silver is the largest among metals, so that the production of metal nanowires according to the present invention is possible. It can be preferably applied as a method.

  In the present invention, the metal nanowires come into contact with each other to form a three-dimensional conductive network, exhibiting high conductivity, and allowing light to pass through the window of the conductive network where no metal nanowire exists. Thus, both high conductivity and high transmittance can be achieved.

  In the present invention, the diameter of the metal nanowire is preferably 200 nm or less, and more preferably 100 nm or less, from the viewpoint of transparency. In the present invention, the average length of the metal nanowires is preferably 1 μm or more from the viewpoint of conductivity, and preferably 100 μm or less from the viewpoint of the effect on the transparency due to aggregation. More preferably, it is 1-50 micrometers, and it is still more preferable that it is 3-50 micrometers.

(Aqueous solvent)
In the present application, the “aqueous solvent” refers to a solvent in which 50% by mass or more is water. Of course, pure water that does not contain other solvents may be used, and when considering the dispersion stability of the metal nanowires during drying, it is preferable that the content of other solvents is small. The component other than water in the aqueous solvent is not particularly limited as long as it is a solvent compatible with water, but an alcohol solvent can be preferably used, and among them, isopropyl alcohol having a boiling point relatively close to water can be used. preferable.

(Water-soluble polymer)
In the coating solution used in the present invention, a water-soluble polymer is used in combination to ensure the dispersibility of the metal nanowires and to hold the metal nanowires in the film after coating and drying. Water-soluble means that 0.5 g or more is dissolved in 100 g of water at 20 ° C., and more preferably 1 g or more. In addition, a compound dissolved in hot water and then similarly dissolved at 20 ° C. is also made water-soluble.

  As such a water-soluble polymer, for example, a polyester resin, an acrylic resin, a polyurethane resin, an acrylic urethane resin, a polycarbonate resin, a cellulose resin, a polyvinyl acetal resin, a polyvinyl alcohol resin, etc. may be used alone or in combination. Can be used. Specific compounds of the water-soluble polymer include polyvinyl alcohol PVA-203, PVA-224, PVA-420 (manufactured by Kureha), polyvinyl acetal ESREC BM-1, BM-S, BL-1, BL-10, BL-S, KS-5 (manufactured by Sekisui Chemical Co., Ltd.), hydroxypropyl methylcellulose 60SH-06, 60SH-50, 60SH-4000, 90SH-100 (manufactured by Shin-Etsu Chemical Co., Ltd.), methyl cellulose SM-100 (manufactured by Shin-Etsu Chemical Co., Ltd.) ), Cellulose acetate L-20, L-40, L-70 (manufactured by Daicel Chemical Industries), carboxymethyl cellulose CMC-1160 (manufactured by Daicel Chemical Industries), hydroxyethyl cellulose SP-200, SP-600 (Daicel Chemical Industries, Ltd.) Manufactured), alkyl acrylate copolymer Jurimer AT-210 (Manufactured by Toagosei Co.) AT-510, polyhydroxyethyl acrylate, polyhydroxyethyl methacrylate, and the like.

[Application]
As the coating method, a known coating method can be used, for example, roll coating method, bar coating method, dip coating method, spin coating method, casting method, die coating method, blade coating method, gravure coating method, curtain coating method. A spray coating method, a doctor coating method, or the like can be used. As the printing method, known methods such as letterpress (letter plate) printing, stencil (screen) printing, lithographic (offset) printing, intaglio (gravure) printing, spray printing, and inkjet printing can be used.

〔Base material〕
The base material used in the present invention is not particularly limited as long as it has high light transmittance. For example, a glass substrate, a resin substrate, a resin film, and the like are preferable in terms of excellent hardness as a base material and ease of formation of a conductive layer on the surface. From the viewpoint, it is preferable to use a transparent resin film.

  There is no restriction | limiting in particular in the transparent resin film which can be preferably used as a base material of this invention, About the material, a shape, a structure, thickness, etc., it can select suitably from well-known things. For example, polyester resin films such as polyethylene terephthalate (PET), polyethylene naphthalate, modified polyester, polyethylene (PE) resin films, polypropylene (PP) resin films, polystyrene resin films, polyolefin resin films such as cyclic olefin resins, Vinyl resin films such as polyvinyl chloride and polyvinylidene chloride, polyether ether ketone (PEEK) resin film, polysulfone (PSF) resin film, polyether sulfone (PES) resin film, polycarbonate (PC) resin film, polyamide resin A film, a polyimide resin film, an acrylic resin film, a triacetyl cellulose (TAC) resin film, and the like can be given. If the resin film transmittance of 80% or more in nm), can be preferably applied to a transparent resin film according to the present invention. Among these, from the viewpoint of transparency, heat resistance, ease of handling, strength and cost, it is preferably a biaxially stretched polyethylene terephthalate film, a biaxially stretched polyethylene naphthalate film, a polyethersulfone film, or a polycarbonate film, and biaxially stretched. More preferred are polyethylene terephthalate films and biaxially stretched polyethylene naphthalate films.

  In order to ensure the wettability and adhesiveness of the coating liquid, the substrate used in the present invention can be subjected to a surface treatment or an easy adhesion layer. A conventionally well-known technique can be used about a surface treatment or an easily bonding layer. For example, the surface treatment includes surface activation treatment such as corona discharge treatment, flame treatment, ultraviolet treatment, high frequency treatment, glow discharge treatment, active plasma treatment, and laser treatment.

  Examples of the easy adhesion layer include polyester, polyamide, polyurethane, vinyl copolymer, butadiene copolymer, acrylic copolymer, vinylidene copolymer, and epoxy copolymer. The easy adhesion layer may be a single layer, but may be composed of two or more layers in order to improve adhesion.

(Dry)
As a drying method, the film surface temperature of the coating film is 27 ° C. or higher and 42 ° C. or lower, and the drying speed (h × ΔT) is 1000 to 10,000 (kcal / (m ² · hr)), provided that , H represents a heat transfer coefficient (kcal / (m ² · ° C. · hr)), and ΔT (° C.) represents a difference between the blowing temperature and the film surface temperature of the coating film. Here, the film surface temperature of the coating film is a film surface temperature in a so-called constant rate dry state in which heating by drying air and heat of vaporization of the solvent are in an equilibrium state.

  If this condition can be satisfied, the drying method is not particularly limited, and a conventionally known drying method can be used. For example, a device using air blowing through a slit as disclosed in JP-A-4-226249 and JP-A-5-230549, or a uniform hole as disclosed in JP-B-53-1427 and JP-A-4-2070. An apparatus for drying using a pattern can be used. Moreover, the method of providing a floater on both sides and conveying both surfaces without contact can also be preferably used. A floater is provided on both sides of the support web, and drying is performed by blowing drying air from the floater. For example, JP-B-60-1256, JP-A-60-1257, JP-A-63-27360, and JP-A-2-81852 disclose a contactless floater having a slit-shaped opening. No. -167161 discloses a perforated plate type floater having a large number of circular air blowing holes.

The heat transfer coefficient h (kcal / (m ² · ° C. · hr)) of the present invention can be calculated from the average drying capacity of each drying apparatus.

  As a method for controlling the temperature of the film surface, generally, the dew point of air used for drying can be increased or the drying temperature can be increased, and vice versa. The heat transfer coefficient can be controlled by the wind pressure of the drying air, the distance from the outlet, the diameter of the outlet, and the like.

  In the present invention, it is more preferable that the coating liquid is applied to the substrate and then passes through a substantially windless region before the above-described drying. Here, “substantially windless” means that the drying speed (h × ΔT) is 200 or less, and a state where no wind is blown is more preferable. The time for passing through the substantially windless region is preferably 2 seconds or more in order to obtain more effect. Further, if it is 20 seconds or more, the influence of drying disturbance due to evapotranspiration during this time may occur, and therefore it is preferably 20 seconds or less.

  The drying part of the manufacturing apparatus of the transparent conductive base material concerning this invention is demonstrated using figures.

  In FIG. 1, the coated transparent conductive substrate 1 first enters the windless region 2. The windless area 2 and the dry area 3 are partitioned by a partition plate 6, and the transparent conductive substrate 1 proceeds to the dry area 3 from the lower gap. The web-like transparent conductive substrate 1 is conveyed in the arrow direction by a winder (not shown) and a roller 7. The drying air is blown out from the nozzle 5 toward the transparent conductive substrate 1. The nozzle 5 can be moved, and the distance 9 between the nozzle and the dry surface of the transparent conductive substrate 1 can be adjusted (the moving device is not shown). The nozzle interval and the nozzle diameter can be appropriately determined. For example, the nozzle interval is preferably 10 mm to 500 mm, and the nozzle diameter is preferably 0.5 mm to 5 mm. In the present invention, the transparent conductive substrate 1 is dried by at least three or more nozzles 5.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "%" is used in an Example, unless otherwise indicated, "mass%" is represented.

(Production of AGW-1)
As metal fine particles, Adv. Mater. , 2002, 14, 833 to 837, EG (ethylene glycol; manufactured by Kanto Chemical Co., Inc.) as a reducing agent, and PVP (polyvinylpyrrolidone K30, molecular weight 50,000; ISP) as a shape control agent and protective colloid agent In addition, a nucleation step and a particle growth step were separated to form particles to prepare a silver nanowire dispersion. Each step is described below.

(Nucleation process)
While stirring 100 ml of EG maintained at 160 ° C. in a reaction vessel, 2.0 ml of an EG solution of silver nitrate (silver nitrate concentration: 0.1 mol / L) was added at a constant flow rate over 1 minute, and then 160 ° C. At 10 minutes to reduce silver ions to form silver core particles. The reaction solution had a light yellow color derived from surface plasmon absorption of nano-sized silver fine particles, and it was confirmed that silver ions were reduced to form silver fine particles (nuclear particles). Subsequently, 10.0 ml of PVP EG solution (PVP concentration: 3.24 g / L) was added at a constant flow rate over 10 minutes.

(Particle growth process)
The reaction liquid containing the core particles after completion of the nucleation step is kept at 160 ° C. with stirring, 100 ml of an EG solution of silver nitrate (silver nitrate concentration: 1.0 × 10 ⁻¹ mol / L), and an EG solution of PVP ( 100 ml of PVP concentration: 3.24 g / L) was added over 120 minutes at a constant flow rate using the double jet method. In the particle growth process, the reaction solution was sampled every 30 minutes and confirmed with an electron microscope. As a result, the core particles formed in the nucleation process grew into a wire-like form over time. The formation of new fine particles was not observed. About the silver nanowire finally obtained, the electron micrograph was image | photographed, the particle size of the major axis direction and the minor axis direction of 300 silver nanowire particle images was measured, and the arithmetic average was calculated | required. The average particle size in the minor axis direction was 75 nm, and the average particle size in the major axis direction was 35 μm.

(Demineralized water washing process)
After cooling the reaction liquid which completed the said particle | grain formation process to room temperature, the desalting water washing process was performed using the 0.2 micrometer ultrafiltration membrane. This was further washed with water and dried to obtain silver nanowires.

(Preparation of dispersion)
Thereafter, the silver nanowires are redispersed in a 0.3% by mass aqueous solution of hydroxypropylmethylcellulose 60SH-50 (manufactured by Shin-Etsu Chemical Co., Ltd.) to prepare a silver nanowire dispersion AGW-1 (silver nanowire content 0.4% by mass). did.

(Preparation of transparent conductive substrate)
A 100 μm biaxially stretched PET film cut to a width of 18 cm is subjected to a corona discharge treatment of 12 W · min / m ² , and the silver nanowire dispersion AGW-1 is syringe pumped so that the basis weight of silver is 60 mg / m ^2. The flow rate was adjusted, the solution was fed to an extrusion coater, applied, and dried with the drying apparatus shown in FIG. Each transparent conductive substrate was produced by changing the drying air temperature, the drying air dew point, the drying air pressure, the distance between the slit and the web, and the line speed so as to satisfy the conditions shown in Table 1.

(Evaluation)
Using a resistivity meter (Loresta GP (MCP-T610 type): manufactured by Dia Instruments Co., Ltd.) at a position 15 cm from the top of application, 3 points in the width direction (positions 3 cm, 9 cm, 15 cm from the end), and The surface resistivity was measured at 18 points in total, 5 points every 10 cm in the longitudinal direction and 3 points in the width direction. The variation was evaluated with standard deviation.

  As can be seen from Table 1, the film surface temperature of the coating film coated with the conductive layer coating liquid is 27 ° C. or higher and 42 ° C. or lower, and the drying rate (h × ΔT) is 1000 to 10,000. It can be seen that the variation depending on the location is small. On the other hand, it can be seen that in the sample in which either the film surface temperature or the drying speed deviates from the present invention, the variation in the surface specific resistance depends on the location.

  Further, it can be seen that the sample of the present invention, which is dried after passing through a substantially windless region for 2 to 20 seconds, has a particularly small variation in the surface resistivity depending on the location.

  1 is a drying apparatus for a transparent conductive substrate according to the present invention.

2 Transparent conductive substrate 3 No wind area 4 Dry area 5 Nozzle 6 Dry air 7 Roller 8 Nozzle spacing 9 Nozzle-to-dry surface distance

Claims (3)

In the method for producing a transparent conductive substrate having a conductive layer formed by applying a coating liquid comprising at least a metal nanowire, a water-soluble polymer, and an aqueous solvent on a substrate and then drying the coating solution, The film surface temperature of the coating film coated with the conductive layer coating liquid is 27 ° C. or higher and 42 ° C. or lower, and the drying rate (h × ΔT) is 1000 to 10,000 (kcal / (m ² · hr)). A method for producing a transparent conductive substrate.
However, h represents a heat transfer coefficient (kcal / (m ² · ° C. · hr)), and ΔT (° C.) represents a difference between the blowing temperature and the film surface temperature of the coating film.   The method for producing a transparent conductive substrate according to claim 1, wherein after the coating liquid is applied to the substrate, the drying is performed after passing through a substantially windless region.   3. The method for producing a transparent conductive substrate according to claim 2, wherein the time passing through the substantially windless region is 2 seconds or more and 20 seconds or less.

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