CN109074919B

CN109074919B - Method for forming transparent conductive pattern

Info

Publication number: CN109074919B
Application number: CN201780026692.9A
Authority: CN
Inventors: 若林正一郎; 山木繁
Original assignee: Showa Denko KK
Current assignee: Lishennoco Co ltd; Resonac Holdings Corp
Priority date: 2016-05-31
Filing date: 2017-05-24
Publication date: 2021-04-30
Anticipated expiration: 2037-05-24
Also published as: KR102228232B1; TWI787185B; KR20180121638A; CN109074919A; TW201816000A; WO2017208924A1; JPWO2017208924A1

Abstract

The object is to provide a method for forming a transparent conductive pattern, which can form a transparent conductive pattern by a simple manufacturing process and suppress manufacturing cost and environmental load by reducing damage to a metal nanowire and/or a metal nanotube in screen printing using a transparent conductive ink containing the metal nanowire and/or the metal nanotube as a conductive component. The solution is to screen-print a transparent conductive ink (5) using a squeegee (3) having a curved surface shape at the tip portion in contact with a screen mask (2), the transparent conductive ink (5) containing a dispersion medium and at least one of metal nanowires and metal nanotubes.

Description

Method for forming transparent conductive pattern

Technical Field

The present invention relates to a method for forming a transparent conductive pattern.

Background

Transparent conductive films are used in various fields such as transparent electrodes of Liquid Crystal Displays (LCDs), Plasma Display Panels (PDPs), organic electroluminescent devices (OLEDs), solar cells (PVs), and Touch Panels (TPs), antistatic (ESD) films, and electromagnetic wave shielding (EMI) films, and are required to have (1) low surface resistance, (2) high light transmittance, and (3) high reliability.

For example, for a transparent electrode of an LCD, it is preferable that the surface resistance is in the range of 10 to 300. omega./□ and the light transmittance is 85% or more in the visible light range. More preferably, the surface resistance is 20 to 100. omega./□, and the light transmittance is 90% or more. For the transparent electrode of the OLED, the surface resistance is in the range of 10-100 omega/□, and the light transmittance is preferably more than 80% in the visible light range. More preferably, the surface resistance is 10 to 50. omega./□, and the light transmittance is 85% or more. For the transparent electrode of PV, the surface resistance is in the range of 5-100 omega/□, and the light transmittance is preferably 65% or more in the visible light range. More preferably, the surface resistance is 5 to 20. omega./□, and the light transmittance is 70% or more. For the TP electrode, the surface resistance is in the range of 100-1000 Ω/□, and the light transmittance is preferably 85% or more in the visible light range. More preferably, the surface resistance is in the range of 150 to 500. omega./□, and the light transmittance is 90% or more in the visible light range. For the ESD film, the surface resistance is in the range of 500 to 10000 Ω/□, and the light transmittance is preferably 90% or more in the visible light range. More preferably, the surface resistance is in the range of 1000 to 5000 Ω/□, and the light transmittance is 95% or more in the visible light range.

ITO (indium tin oxide) has been conventionally used as a transparent conductive film used for these transparent electrodes. However, since indium used for ITO is a rare metal, supply and price stabilization have been a problem in recent years. In addition, since a sputtering method, a vapor deposition method, or the like, which requires a high vacuum, is used for forming ITO, a vacuum production apparatus is required, and not only is the production time long, but also the cost increases. Further, ITO is easily broken by cracking due to physical stress such as bending, and thus it is difficult to apply ITO to a substrate to which flexibility is imparted. Therefore, research on alternative ITO materials that eliminate these problems has been advanced, and conductive materials containing a nanostructure conductive component, such as conductive materials containing metal nanowires (see, for example, patent document 1 and non-patent document 1), have been reported as coatable film-forming materials that do not require the use of a vacuum production apparatus.

The conductive material containing the metal nanowires exhibits low surface resistance and high light transmittance, and also has flexibility, and thus is suitable as an "ITO substitute material".

Here, in order to be used as a transparent electrode, the transparent conductive film needs to be patterned according to the application, and as a method for forming a pattern using a conductive material containing metal nanowires, a photolithography method using a resist material is generally applied in the same manner as the patterning of ITO. In both of the methods of patent document 1 and non-patent document 1, a step of forming a photosensitive layer for forming a pattern on a layer containing a metal nanowire is required. Further, since a developing step of the layer having photosensitivity and a removing step of the exposed layer including the metal nanowire are required, the silver nanowire in the removed region is wasted, and waste liquid treatment of the developer is also required. After the development of the photosensitive layer and the removal of the exposed layer including the metal nanowire, a step of removing the photosensitive layer may be necessary.

Therefore, it is desirable to directly pattern silver nanowires by a printing method such as inkjet printing, screen printing, gravure printing, and flexographic printing. However, since a binder resin is required for printing and the amount of silver nanowires used needs to be reduced in order to ensure transparency, the binder resin used has a problem that the surface of the silver nanowires is coated and conductivity is not exhibited. Further, when a binder resin is not used, there is a problem that a pattern cannot be secured at the time of printing, or even if a pattern is barely secured immediately after printing is finished, the pattern is lost when the solvent is dried.

Patent document 2 discloses a transparent conductive ink that can be printed without using a binder resin, the transparent conductive ink comprising at least one of metal nanowires and metal nanotubes, and a dispersion medium containing a shape-retaining agent that contains an organic compound having a molecular weight in the range of 150 to 500 and has a viscosity of 1.0 × 10 at 25 ℃³～2.0×10⁶mPa·s。

In this method, depending on the conditions of screen printing, the metal nanowires and/or metal nanotubes are damaged during repeated printing, and there is a problem that the damage affects the electrical conductivity.

Documents of the prior art

Patent document

Patent document 1: japanese Kokai publication Hei 2009-505358

Patent document 2: international publication No. 2013/161996 handbook

Non-patent document

Non-patent document 1: Shih-HsiangLai, Chun-YaoOu, Chia-HaoTsai, Bor-Chuan Chuang, Ming-YingMa, and Shuo-WeiLiang; SID Symposium Digest of Technical Papers, Vol.39, Issue 1, pp.1200-1202(2008)

Disclosure of Invention

The purpose of the present invention is to provide a method for forming a transparent conductive pattern, which can form a transparent conductive pattern by a simple manufacturing process and suppress manufacturing costs and environmental load by reducing damage to a metal nanowire and/or a metal nanotube in screen printing using a transparent conductive ink containing the metal nanowire and/or the metal nanotube as a conductive component.

In order to achieve the above object, the present invention includes the following embodiments.

[1] A method for forming a transparent conductive pattern is characterized in that a transparent conductive ink containing a dispersion medium and at least one of metal nanowires and metal nanotubes is screen-printed using a squeegee having a curved surface shape at a tip portion in contact with a screen mask.

[2] The method for forming a transparent conductive pattern according to [1], wherein a curvature radius of a curved surface of a tip portion of the squeegee which is in contact with the screen mask is 0.1 to 20 mm.

[3] The method for forming a transparent conductive pattern according to [2], wherein a curvature radius of a curved surface of a tip portion of the squeegee which is in contact with the screen mask is 2 to 10 mm.

[4] The method for forming a transparent conductive pattern according to any one of [1] to [3], wherein the material of the squeegee is any one of synthetic rubber, natural rubber, metal, and plastic.

[5] The method for forming a transparent conductive pattern according to [4], wherein the synthetic rubber is composed of urethane rubber or silicone rubber.

[6] The method for forming a transparent conductive pattern according to any one of [1] to [5], wherein the screen printing is performed at a squeegee speed of 5 to 200 mm/sec.

[7] The method for forming a transparent conductive pattern according to any one of [1] to [6], wherein the total amount of the metal nanowires and the metal nanotubes in the transparent conductive ink is 0.01 to 10 mass% based on the total mass of the transparent conductive ink.

[8] The method for forming a transparent conductive pattern according to any one of [1] to [7], wherein the dispersion medium contains a shape-retaining agent composed of an organic compound having a molecular weight in a range of 150 to 500.

[9] The method for forming a transparent conductive pattern according to [8], wherein the organic compound of the shape-retaining agent is any one of a monosaccharide compound, a polyol compound, and a compound having an alkyl group and a hydroxyl group, the alkyl group having a quaternary carbon atom and/or a bridged ring skeleton.

[10] The method for forming a transparent conductive pattern according to [9], wherein the organic compound of the shape-retaining agent is any one of diglycerin, 2, 4-trimethyl-1, 3-pentanediol monoisobutyrate, xylulose, ribulose, bornyl cyclohexanol, borneol, isobornyl cyclohexanol, and isobornyl.

[11] The method for forming a transparent conductive pattern according to any one of [8] to [10], wherein the dispersion medium further contains a viscosity adjusting solvent for adjusting the viscosity of the shape retaining agent.

[12] The method for forming a transparent conductive pattern according to [11], wherein the viscosity-adjusting solvent is at least one of water, an alcohol, a ketone, an ether, an aliphatic hydrocarbon solvent and an aromatic hydrocarbon solvent.

[13] The method for forming a transparent conductive pattern according to [12], wherein the alcohol of the viscosity adjusting solvent is terpineol.

[14] The method for forming a transparent conductive pattern according to any one of [8] to [13], wherein the content of the shape-retaining agent is 10 to 90% by mass based on the total mass of the dispersion medium.

According to the present invention, it is possible to repeatedly perform screen printing of a transparent conductive ink that uses metal nanowires and/or metal nanotubes as a conductive component and can form a coating film that achieves both conductivity and light transmittance, while reducing damage to the metal nanowires and/or metal nanotubes, and therefore, it is possible to manufacture a stable transparent conductive pattern having a low surface resistance value with high yield.

Drawings

Fig. 1 is a conceptual diagram of screen printing using a circular squeegee.

Fig. 2 is a diagram for explaining the definition of pulsed light.

Fig. 3 is a view showing another example of the circular squeegee.

FIG. 4 is a side view of the flat blade used in comparative example 1.

Detailed Description

Hereinafter, a mode for carrying out the present invention (hereinafter, referred to as an embodiment) will be described.

The method for forming a transparent conductive pattern according to an embodiment is characterized in that a transparent conductive ink containing a dispersion medium and at least one of a metal nanowire and a metal nanotube is screen-printed using a squeegee having a curved surface shape at a tip portion in contact with a screen mask.

A squeegee (hereinafter, sometimes referred to as a "circular squeegee") having a curved surface shape at a distal end portion thereof which contacts the screen mask has a curved surface shape, and a cross-sectional shape of the squeegee at a portion thereof which contacts the squeegee has a curved surface as shown in the text. The curved surface may be an arc shape having a constant curvature or an elliptical shape having a different curvature, but is not limited thereto. Fig. 1 shows a conceptual diagram of screen printing using such a circular squeegee.

In fig. 1, a substrate 1 and a screen mask 2 are arranged with a gap (clearance) therebetween, and a squeegee 3 is pressed against the screen mask 2 to move the substrate 1 and the screen mask 2 in a printing direction 4 while being attached to each other, whereby a transparent conductive ink 5 positioned on the screen mask 2 is pushed out toward the substrate 1 to perform screen printing.

The radius of curvature R of the tip portion of the round scraper 3 (the portion of the screen mask 2 in contact with the round scraper 3) is preferably 0.1 to 20mm, more preferably 1 to 15mm, and still more preferably 2 to 10 mm. If the radius of curvature R is 0.1mm or more, a sufficient printing pressure can be applied to the transparent conductive ink 5 by the squeegee. Further, if the curvature radius R is 20mm or less, the influence of grinding the ink on the screen mask is small, and damage such as bending and cutting of the metal nanowire and the metal nanotube can be reduced.

In the example of fig. 1, the cross-sectional shape of the tip portion of the round squeegee 3 is shown as an arc, but the shape of a portion that does not contact the screen mask 2 is not limited as long as at least a portion that contacts the screen mask 2 has a curved surface shape. That is, the screen printing may be performed by rounding the leading edge of a flat squeegee commonly used for the conventional screen mask 2 and bringing the rounded portion into contact with the screen mask 2.

Fig. 3(a), (b), and (c) show other examples of the circular scraper 3. The example of fig. 3(a) is an example in which both sides of the tip edge of the flat blade are rounded, the example of fig. 3(b) is an example in which one side of the tip edge of the flat blade is rounded, and the example of fig. 3(c) is an example in which the tip of the flat blade is formed in an elliptical shape. In the example of fig. 3(c), the tip shape of the blade is formed into an ellipse, but the shape is not limited to this, and includes all cases where the radius of curvature is not constant but is processed into a curved surface.

The material of the circular squeegee 3 is not particularly limited, and a material similar to a squeegee used in the conventional screen printing can be used. Examples thereof include synthetic rubbers such as urethane rubber and silicone rubber, metals such as natural rubber and stainless steel, and plastics such as polyester.

The hardness of the circular scraper 3 of the rubber material is not particularly limited, and for example, a scraper having an Hs (shore) hardness of 55 to 90 obtained by a durometer in JIS K6031 standard can be used.

As the above-described round blade 3, for example, a round blade manufactured by APOLAN International corporation, a round blade manufactured by sakayodo chemical corporation, a flat blade with rounded corners, a corner blade (with rounded corners), or the like can be used.

The blade speed (moving speed in the printing direction 4) in printing using the circular blade 3 is preferably 5 to 200 mm/sec, more preferably 10 to 150 mm/sec, and still more preferably 20 to 100 mm/sec. If the blade speed is 5 mm/sec or more, productivity is good, and if the blade speed is 200 mm/sec or less, the plate release deterioration due to an excessive ink transfer amount at the time of printing can be suppressed.

The squeegee printing pressure in printing using the circular squeegee 3 is preferably 0.10 to 0.45MPa, and more preferably 0.15 to 0.30 MPa. The uniformity of the film thickness of the ink to be printed can be ensured if the squeegee printing pressure is 0.10MPa or more, and the film thickness of the ink to be printed is not excessively thin if the squeegee printing pressure is 0.45MPa or less, and thus, the formation of the transparent conductive pattern is suitable.

There is no particular limitation other than the restriction of the squeegee angle removing device in printing using the circular squeegee 3. Since the tip of the circular squeegee 3 has a curved surface shape, the metal nanowires and the metal nanotubes in the transparent conductive ink are not greatly affected even if the squeegee angle is finely adjusted, and printing can be performed at a squeegee angle of 60 to 80 ° which is used in general screen printing, and printing can be performed at a smaller squeegee angle if there is no limitation of the device.

In the case of using the screen mask 2 having a general strength and tension, the gap in printing using the circular squeegee 3 is preferably 1/600 to 1/150, more preferably 1/450 to 1/200, of the inner dimension of the screen frame. If the inner size of the screen frame is 1/600 or more, the deterioration of plate separation during printing can be suppressed, and if 1/150 or less, the damage to the screen mask 2 during repeated printing can be suppressed. Further, in the case of using a screen mask having high strength, damage to the screen mask 2 can be suppressed even if the inner size of the screen frame is 1/100 or less.

In the screen printing, the screen mask 2 is inked, and after spreading the ink on the screen mask 2 with a squeegee (squeegee), the base material is printed with a squeegee such as a squeegee 3. If the amount of the transparent conductive ink 5 smeared on the screen mask 2 is large, damage to the metal nanowires and/or metal nanotubes in the transparent conductive ink 5 in the squeegee operation of printing may accumulate. Therefore, in the case of repeating a large number of prints, by limiting the amount of the transparent conductive ink 5 that sticks to the screen mask 2, and repeating an operation of appropriately replenishing the transparent conductive ink 5 that is consumed with the prints onto the screen mask 2, the average length of the metal nanowires and/or metal nanotubes in the transparent conductive ink 5 can be maintained at a desired length.

The transparent conductive ink 5 for screen printing used in the method for forming a transparent conductive pattern according to the present embodiment includes at least one of a metal nanowire and a metal nanotube and a dispersion medium, and may be applied as long as it has an appropriate viscosity capable of retaining the pattern shape by screen printing. The dispersion medium preferably contains the following shape-retaining agent because it can disperse the metal nanowires and/or the metal nanotubes well. By using this transparent conductive ink and performing screen printing using the circular squeegee 3, a pattern obtained by printing can be favorably formed, and by distilling off the dispersion medium, a coating film having both conductivity and light transmittance can be formed.

The shape retaining agent is an organic compound having a molecular weight in the range of 150 to 500, and the viscosity of a dispersion medium containing the shape retaining agent at 25 ℃ is preferably 1.0X 10³～2.0×10⁶mPa · s. Here, when the organic compound is in a liquid state having a viscosity in the above range at 25 ℃, the shape retaining agent may be composed of only the organic compound. On the other hand, when the viscosity at 25 ℃ is higher than the above viscosity range or when the solid is at 25 ℃, the dispersion medium may be formed by mixing (diluting or dissolving) the dispersion medium with an appropriate solvent (a solvent capable of dissolving the organic compound, for example, a viscosity adjusting solvent described later).

If the viscosity of the dispersion medium is lower than the above range, the printed pattern shape cannot be maintained, and if the viscosity is higher than the above range, the adverse effect such as stringiness at the time of printing occurs. The viscosity at 25 ℃ as a dispersion medium is more preferably 5.0X 10⁴～1.0×10⁶mPas range. The viscosity is measured by using a conical plate type rotational viscometer (cone plate type).

Further, if the organic compound used as the shape-retaining agent has a large molecular weight, the shape-retaining agent cannot be removed efficiently during sintering, and the electric resistance does not decrease. Therefore, the molecular weight is 500 or less, preferably 400 or less, and more preferably 300 or less.

Preferred examples of such organic compounds include compounds having hydroxyl groups added thereto, such as monosaccharides, polyols, and compounds having an alkyl group having a quaternary carbon atom and/or a bridged ring skeleton and having hydroxyl groups, and examples thereof include diglycerin, 2, 4-trimethyl-1, 3-pentanediol monoisobutyrate, xylulose, ribulose, bornyl cyclohexanol, borneol, isobornyl cyclohexanol, and isobornyl.

Among the above-listed compounds, compounds having an isobornyl group and a hydroxyl group are particularly preferable. Because, in addition to the complex steric structure possessed by the isoborneol group, appropriate tackiness is imparted to the ink due to hydrogen bonding of the hydroxyl group. Further, since the compound having an isobornyl group and a hydroxyl group has high viscosity although the volatilization temperature is not so high, the viscosity of the ink can be increased. Examples of the compound having an isobornyl group and a hydroxyl group include either one of isobornyl cyclohexanol and isobornyl phenol, or both of them. The compounds listed above have appropriate tackiness and therefore impart appropriate tackiness to the ink. Further, since the ink exhibits an appropriate boiling point as an ink solvent, the residue can be reduced by appropriate heating, photo-sintering, or the like after completion of printing and drying. The content of the shape-retaining agent in the ink is preferably 10 to 90% by mass, and more preferably 30 to 80% by mass, based on the total mass of the dispersion medium. If the content of the shape-retaining agent is 10 to 90 mass% based on the total mass of the dispersion medium, the ink has a viscosity suitable for printing, and printing can be performed without problems such as pattern blur and stringiness in printing.

The shape-retaining agent itself is preferably a viscous liquid within the above-described preferred viscosity range of the dispersion medium, and a dispersion medium having a viscosity within the above-described range may be prepared by mixing another viscosity adjusting solvent so as to satisfy the above-described viscosity range, and the metal nanowires and/or the metal nanotubes may be dispersed as a conductive component in the dispersion medium to form the transparent conductive ink.

Examples of the viscosity adjusting solvent include water, alcohols, ketones, esters, ethers, aliphatic hydrocarbon solvents, and aromatic hydrocarbon solvents. From the viewpoint of well dispersing each component in the ink composition, water, ethanol, isopropanol, 1-methoxy-2-Propanol (PGME), ethylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, diacetone alcohol, ethylene glycol monobutyl ether, propylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, dipropylene glycol monopropyl ether are preferable, diethylene glycol monobutyl ether, tripropylene glycol, triethylene glycol monoethyl ether, terpineol (terpineol), dihydroterpineol monoacetate, methyl ethyl ketone, cyclohexanone, ethyl lactate, propylene glycol monomethyl ether acetate, diethylene glycol monobutyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether acetate, dibutyl ether, octane, toluene, and particularly preferred is terpineol. These solvents may be used alone, or 2 or more kinds thereof may be mixed and used.

The metal nanowires and the metal nanotubes are metal having a diameter of nanometer order, the metal nanowires are linear, and the metal nanotubes are porous or non-porous conductive materials having a tubular shape. In the present specification, "linear" and "tubular" are all linear, but the center of the former is not hollow, and the center of the latter is hollow. The shape may be flexible or rigid. Either one of the metal nanowire and the metal nanotube may be used, or both of them may be mixed and used.

Examples of the metal species include at least 1 selected from gold, silver, platinum, copper, nickel, iron, cobalt, zinc, ruthenium, rhodium, palladium, cadmium, osmium, and iridium, and alloys obtained by combining these metals. In order to obtain a coating film having low surface resistance and high total transmittance, at least 1 kind of any one of gold, silver, and copper is preferably contained. Since these metals have high conductivity, the metal density occupied by the facets can be reduced when a certain surface resistance is obtained, and therefore, a high total transmittance can be achieved.

Among these metals, at least 1 of gold or silver is more preferably contained. The silver nanowires are preferred.

The diameter thickness, length of the long axis, and aspect ratio of the metal nanowires and/or metal nanotubes in the transparent conductive ink preferably have a certain distribution. This distribution is selected so that the coating film obtained from the transparent conductive ink of the present embodiment becomes a coating film having a high total transmittance and a low surface resistance. Specifically, the average diameter of the metal nanowires and the metal nanotubes is preferably 1 to 500nm, more preferably 5 to 200nm, even more preferably 5 to 100nm, and particularly preferably 10 to 100 nm. The average length of the major axis of the metal nanowires and/or metal nanotubes is preferably 1 to 100 μm, more preferably 1 to 50 μm, further preferably 2 to 50 μm, and particularly preferably 5 to 30 μm. The metal nanowires and/or metal nanotubes preferably have an average diameter and thickness and an average length of the major axis that satisfy the above ranges, and an average aspect ratio of more than 5, more preferably 10 or more, still more preferably 100 or more, and particularly preferably 200 or more. Here, when the average diameter of the metal nanowire and/or the metal nanotube is approximated to b and the average length of the major axis is approximated to a, the aspect ratio is a value determined from a/b. The measurement of a and b can be carried out by the method described in examples using a scanning electron microscope. The cross-sectional shape of the metal nanowire and/or the metal nanotube is preferably a circle or an ellipse having no corner, but can be applied even with a corner. Furthermore, the corner portion is preferably obtuse as compared to acute angle. In the case where the cross section has a plurality of corners, the angles of the respective corners may be the same or different.

As a method for producing the metal nanowire and/or the metal nanotube, a known production method can be employed. For example, silver nanowires can be synthesized by reducing silver nitrate in the presence of polyvinylpyrrolidone using a polyol (Poly-ol) method (see chem. mater.,2002,14, 4736). Gold nanowires can also be synthesized by reducing chloroauric acid hydrate in the presence of polyvinylpyrrolidone (see j.am. chem. soc.,2007,129,1733). Techniques for large-scale synthesis and purification of silver nanowires and gold nanowires are described in detail in international publication No. WO2008/073143 and international publication No. 2008/046058. The gold nanotubes having a porous structure can be synthesized by casting silver nanowires and reducing a chloroauric acid solution. Here, the silver nanowires used for the mold are eluted in the solution by the redox reaction with chloroauric acid, and as a result, gold nanotubes having a porous structure are formed (see j.am.chem.soc.,2004,126, 3892-.

The content of the metal nanowires and/or metal nanotubes in the transparent conductive ink according to the present embodiment is preferably 0.01 to 10 mass%, more preferably 0.05 to 5 mass%, and still more preferably 0.1 to 2 mass% of the total mass of the transparent conductive ink, from the viewpoints of good dispersibility thereof, and good pattern formability of a coating film obtained from the transparent conductive ink, high conductivity, and good optical characteristics. If the metal nanowires and/or metal nanotubes are 0.01 mass% or more, the transparent conductive layer does not need to be printed so thick as to ensure desired conductivity, and therefore, it is possible to suppress the increase in difficulty of printing, the occurrence of pattern-shifting during drying, and the like. On the other hand, if the content is 10% by mass or less, printing is not required to be extremely thin in order to secure desired transparency, and printing is easy. The transparent conductive ink may contain other conductive components (metal particles and the like) and inorganic particles (silica and the like) in a range that does not adversely affect optical characteristics, electrical characteristics, and the like. The particles preferably have a small particle diameter, and the average particle diameter is preferably 1 to 30nm, more preferably 5 to 25nm or less, and still more preferably 10 to 20 nm. The amount of these particles is preferably 30 parts by mass or less based on 100 parts by mass of the metal nanowire and/or the metal nanotube.

The transparent conductive ink according to the present embodiment may contain any component other than the above-described components (shape retaining agent, viscosity adjusting solvent, metal nanowire, and metal nanotube), for example, a binder resin, a preservative, a bonding accelerator, a surfactant, and the like, as long as the properties thereof are not impaired.

Examples of the binder resin include polyacrylic compounds such as polymethyl methacrylate, polyacrylate, and polyacrylonitrile; polyvinyl alcohol; polyesters such as polyethylene terephthalate and polyethylene naphthalate; a polycarbonate; highly conjugated polymers such as novolak; imides such as polyimide, polyamideimide, and polyetherimide; a polysulfide; polysulfones; polyphenyl; polyphenylene ether; a polyurethane; an epoxy resin; aromatic polyolefins such as polystyrene, polyvinyltoluene, and polyvinylxylene; aliphatic polyolefins such as polypropylene and polymethylpentene; alicyclic olefins such as polynorbornene, poly-N-vinyl compounds such as poly-N-vinylpyrrolidone, poly-N-vinylcaprolactam and poly-N-vinylacetamide; acrylonitrile-butadiene-styrene copolymer (ABS); celluloses such as hydroxypropyl methylcellulose (HPMC) and nitrocellulose; a silicone resin; a polyacetate; synthesizing rubber; chlorine-containing polymers such as polyvinyl chloride, chlorinated polyethylene, chlorinated polypropylene, etc.; fluoropolymers such as polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoroethylene, and fluorinated olefin-hydrocarbon olefin copolymers.

Further, benzotriazole and the like are given as preservatives, 2-hydroxymethylcellulose and the like are given as adhesion promoters, and F-472SF (manufactured by DIC corporation) and the like are given as surfactants.

The transparent conductive ink can be produced by appropriately selecting the above components by a known method and stirring, mixing, heating, cooling, dissolving, dispersing, or the like.

The transparent conductive ink according to the present embodiment preferably has a viscosity of 100 to 2X 10 at 25 ℃⁵mPas, more preferably 10³～5×10⁴mPa · s. The viscosity is measured by using a conical plate type rotational viscometer (cone plate type).

The transparent conductive ink thus prepared was used to perform pattern printing by screen printing.

The substrate on which the pattern is printed may be hard (rigid) or flexible (flexible). And may be colored. Examples of the substrate include materials such as glass, polyimide, polycarbonate, polyethersulfone, acrylic resin, polyester (polyethylene terephthalate, polyethylene naphthalate, and the like), polyolefin (including cycloolefin polymer), and polyvinyl chloride. They preferably have a high total transmittance and a low haze value. The resin film is preferable in having flexibility. The film thickness is preferably 1mm or less, more preferably 500 μm or less, still more preferably 250 μm or less, and particularly preferably 125 μm or less. From the viewpoint of handling, the thickness is preferably 10 μm or more, more preferably 18 μm or more, still more preferably 25 μm or more, and particularly preferably 38 μm or more. Among the above-mentioned substrates, polyethylene terephthalate and cycloolefin polymer are preferably used from the viewpoint of excellent light transmittance, flexibility, mechanical properties, and the like. As the cycloolefin polymer, a hydrogenated ring-opening metathesis polymerization type cycloolefin polymer of norbornene (ZEONOR (registered trademark, manufactured by japan ZEON corporation), ZEONEX (registered trademark, manufactured by japan ZEON corporation), ARTON (registered trademark, manufactured by JSR corporation) and the like) and/or a norbornene/ethylene addition copolymerization type cycloolefin polymer (APEL (registered trademark, manufactured by mitsui chemical corporation), TOPAS (registered trademark, manufactured by polynosic plastics, LTD.)) can be used. The base material may be a substrate on which a circuit such as a TFT element is further formed, or may be a functional material such as a color filter. In addition, a plurality of substrates may be stacked.

The amount of the transparent conductive ink applied to the substrate is determined in consideration of the film thickness of the transparent conductive pattern required for the application. The film thickness is selected based on the application. The desired film thickness is obtained by adjusting the amount of transparent conductive ink applied and the conditions of the application method. Since the film thickness is preferably as thick as possible from the viewpoint of low surface resistance and as thin as possible from the viewpoint of suppressing display defects due to level differences, a film thickness of 5 to 500nm is preferable, a film thickness of 5 to 200nm is more preferable, and a film thickness of 5 to 100nm is even more preferable, if these factors are considered together.

The printed (coated) transparent conductive ink is dried by heat treatment of the coated material as necessary. The heating temperature varies depending on the liquid component constituting the dispersion medium, but if the drying temperature is too high, the formed pattern may not be maintained. Therefore, the drying temperature is at most 120 ℃ or lower, and more preferably 100 ℃ or lower. In particular, the initial drying temperature is important, and therefore, it is particularly preferable to start drying from about 40 to 80 ℃ and raise the temperature stepwise within a range not exceeding 120 ℃ as necessary. The shape-retaining agent of the viscous liquid has a substantially high boiling point, and when a viscosity-adjusting solvent having a lower boiling point than the shape-retaining agent is present in the dispersion medium, the viscosity-adjusting solvent having a lower boiling point is preferentially distilled off. Therefore, the viscosity of the dispersion medium is increased by drying, and the print pattern can be prevented from being distorted during drying.

The surface resistance and the total transmittance of the obtained transparent conductive pattern can be adjusted to desired values by adjusting the film thickness, that is, the amount of the composition applied and the conditions of the coating method, and by adjusting the concentration of the metal nanowires or the metal nanotubes in the transparent conductive ink according to the present embodiment.

Generally, the thicker the film thickness, the lower the surface resistance and the total transmittance. In addition, the higher the concentration of the metal nanowires or metal nanotubes in the transparent conductive ink, the lower the surface resistance and the total transmittance become.

The coating film obtained as described above preferably has a surface resistance of 5 to 1000 Ω/□ and a total transmittance of 60% or more, more preferably has a surface resistance of 10 to 200 Ω/□ and a total transmittance of 80% or more.

The transparent conductive ink according to the present embodiment has a surface resistance that is lowered to some extent even when dried alone, but is preferably irradiated with pulsed light in order to more effectively reduce the surface resistance.

In this specification, "pulsed light" means light irradiation having a short light irradiation period (irradiation time), and when light irradiation is repeated a plurality of times, as shown in fig. 2, it means light irradiation having a period (irradiation interval (off)) during which light is not irradiated between the first light irradiation period (on) and the second light irradiation period (on). The light intensity of the pulse light is shown as constant in fig. 2, but the light intensity may be changed during 1 light irradiation (on). The pulsed light is irradiated by a light source provided with a flash lamp such as a xenon flash lamp. With such a light source, pulsed light is irradiated to the metal nanowire or the metal nanotube deposited on the substrate. When the irradiation is repeated n times, 1 cycle (on + off) in fig. 2 is repeated n times. In the case of repeated irradiation, it is preferable to cool the substrate from the substrate side so that the substrate can be cooled to near room temperature when the next pulse light irradiation is performed.

In addition, as the pulsed light, electromagnetic waves having a wavelength range of 1pm to 1m, preferably electromagnetic waves having a wavelength range of 10nm to 1000 μm (far ultraviolet to far infrared), and more preferably electromagnetic waves having a wavelength range of 100nm to 2000nm can be used. Examples of such electromagnetic waves include gamma rays, X rays, ultraviolet rays, visible light, infrared rays, microwaves, and radio waves on the long wavelength side of microwaves. When the wavelength is too short in consideration of conversion to thermal energy, it is not preferable because the shape-retaining agent and the resin substrate on which the pattern is printed are damaged greatly. Further, if the wavelength is too long, heat generation cannot be absorbed effectively, which is not preferable. Therefore, the wavelength range is particularly preferably from ultraviolet to infrared among the above-mentioned wavelengths, and more preferably from 100 to 2000 nm.

The 1-time irradiation time (on) of the pulsed light depends on the light intensity, but is preferably in the range of 20 microseconds to 50 milliseconds. If the time is shorter than 20 microseconds, the metal nanowire or the metal nanotube is not sintered, and the performance improvement effect of the conductive film is low. Further, if it is longer than 50 milliseconds, the substrate is adversely affected by light degradation and thermal degradation, and the metal nanowires or the metal nanotubes are easily scattered. More preferably 40 microseconds to 10 milliseconds. For the above reasons, pulsed light is used in the present embodiment instead of continuous light. The pulsed light irradiation is effective even with a single shot, but may be repeated as described above. When the repetition is performed, the irradiation interval (off) is preferably in the range of 20 microseconds to 5 seconds, and more preferably 2 milliseconds to 2 seconds, in consideration of productivity. If the time is shorter than 20 microseconds, the continuous light is irradiated and the substrate is irradiated again after being cooled after one irradiation, and therefore the temperature of the substrate is increased and the substrate may be deteriorated. Further, if it is longer than 5 seconds, the process time becomes long, which is not preferable.

In the case of manufacturing the transparent conductive pattern according to the present embodiment, a pattern of an arbitrary shape (including a shape of the entire surface formed on the entire surface of the substrate) is printed on an appropriate substrate using the transparent conductive ink according to the present embodiment, and after drying by heat treatment, the pattern is irradiated with pulsed light having a pulse width (on) of 20 to 50 milliseconds, more preferably 40 to 10 milliseconds, using a xenon pulsed irradiation lamp or the like, and the metal nanowires or the metal nanotubes are joined at their intersections. Here, the joining is to cause the material (metal) of the metal nanowire or the metal nanotube to absorb the pulsed light at the intersection of the metal nanowire or the metal nanotube, and to cause internal heat generation more effectively at the intersection portion, thereby welding the portion. By this bonding, the connection area between the nanowires or nanotubes at the intersection portion is increased, and the surface resistance can be reduced. In this way, the intersections of the metal nanowires or metal nanotubes are joined by irradiating pulsed light, thereby forming a conductive layer in which the metal nanowires or metal nanotubes are in a mesh shape. Therefore, the conductivity of the transparent conductive pattern can be improved, and the surface resistance value of the transparent conductive pattern is 10-800 omega/□. Further, it is not preferable to form a mesh of metal nanowires or metal nanotubes in a dense state without spaces. Since the transmittance of light decreases if the space is not left. The light irradiation may be performed under an atmospheric atmosphere, but may be performed under an inert atmosphere such as nitrogen and/or under reduced pressure, if necessary.

After the pulse light irradiation, a protective film is preferably attached to the upper portion of the transparent conductive pattern to protect the conductive film.

It is also effective to press (pressurize) the dried coating film instead of irradiating the pulsed light. The pressing referred to herein means applying pressure to the substrate, and various methods are possible as the method, but a method of pressing the substrate while sandwiching the substrate between two flat plates and a method of applying pressure to the substrate using a cylindrical roller are particularly preferable, and particularly the latter method using a roller is preferable because the pressure can be applied uniformly.

When the pressure is applied by the pressure roller, the linear pressure is preferably 0.1kgf/cm (98Pa · m) or more and 1000kgf/cm (980kPa · m) or less, and more preferably 1kgf/cm (980Pa · m) or more and 100kgf/cm (98kPa · m) or less. The conveying speed (linear velocity) of the substrate may be appropriately selected within a practical range, but is generally preferably 10 mm/min or more and 10000 mm/min or less, and more preferably 10 mm/min or more and 100 m/min or less. Because if it is too fast, a sufficient pressing time is not obtained, and it is difficult to uniformly apply the pressure with good accuracy. Further, it is also a useful method to secure the connection of the metal nanowires by increasing the number of the pressing rollers, increasing the number of times of pressing, and increasing the pressing time. In addition, heating may be performed during pressing for more firm attachment.

When the pressing is performed by sandwiching 2 flat plates by a normal pressing apparatus, the pressing cannot be performed uniformly as by a pressing roller, and therefore, the pressing pressure is preferably 0.1 to 200MPa, more preferably 1 to 100 MPa.

In addition, heating may be performed during pressurization for more firm bonding. The volume resistivity is reduced by the pressing, and the mechanical properties such as bending strength can be improved. In addition, the higher the pressure, the more effective the reduction of the volume resistivity and/or the improvement of the mechanical strength, but if the pressure is too high, the cost of the pressurizing device becomes very high, and the obtained effect is not increased on the contrary, so the upper limit value is a desired value.

The light irradiation and the pressing may be performed either one of them or both of them may be used in combination.

Examples

Hereinafter, examples of the present invention will be specifically described. The following embodiments are examples for facilitating understanding of the present invention, and the present invention is not limited to these embodiments.

Example 1

< preparation of silver nanowire >

Polyvinyl pyrrolidone K-90 (manufactured by Nippon catalyst Co., Ltd.) (0.49g) and AgNO were mixed₃(0.52g) and FeCl₃(0.4mg) was dissolved in ethylene glycol (125ml), and the reaction was heated at 150 ℃ for 1 hour. The precipitate thus obtained was separated by centrifugation, and the precipitate was dried to obtain a target silver nanowire (average diameter 36nm, average length 20 μm). The above ethylene glycol and AgNO₃And FeCl₃Manufactured by Nihon Shuichang Kogyo Co., Ltd.

< preparation of transparent conductive ink >

Dibutyl ether was added in an amount of 6 times the volume of the reaction solution of silver nanowires obtained by a heating reaction at 150 ℃ for 1 hour, and the mixture was stirred and then allowed to stand to precipitate nanowires. After precipitation of the nanowires, the supernatant was separated by decantation, thereby performing solvent substitution, resulting in a suspension of silver nanowires dispersed in dibutyl ether (viscosity adjusting solvent) containing about 20 mass% of silver nanowires.

To 0.5g of the silver nanowire suspension, 6g of terpineol (manufactured by Nippon Terpene Chemicals, Inc.) as a viscosity adjusting solvent was added and well dispersed, and then 14g of テルソルブ MTPH (Terusolve MTPH, manufactured by Nippon terpineol chemical corporation) as a shape retaining agent was added and well dispersed using ARV-310 manufactured by seiko corporation to obtain a transparent conductive ink.

The obtained ink was subjected to thermogravimetric analysis, and the residue after heating at 500 ℃ was calculated as silver nanowires in the ink, with the result that the concentration of silver nanowires in the ink was 0.5 mass%. The thermogravimetric analyzer was a differential ultra high temperature thermal scale TG-DTA galaxy (S) manufactured by ブルカー & エイックス K.K. (Bruker AXS).

The obtained ink was measured for viscosity at 25 ℃ using model DV-II + Pro manufactured by BROOKFIELD. The viscosity measured by using the rotor number 52 was 1.5X 10⁴mPa · s. Since the content of the silver nanowires contained in the ink was 0.5 mass% and a small amount, the viscosity of the ink was substantially equal to the viscosity of the dispersion medium itself.

< printing of transparent conductive ink >

A round squeegee (made by APOLAN International Co., Ltd.) was attached to a screen printer MT-320TVZ (made by MICROTECH Co., Ltd.) to make 2.5cm thick by printing with the transparent conductive ink prepared as described above²The full face film (gap: 1.0mm, squeegee angle: 70 degrees, squeegee speed: 100 mm/sec, squeegee movement distance during printing: 15cm, squeegee printing pressure: 0.2MPa, squeegee (pressure) 0.15MPa, back pressure: 0.1 MPa). In addition, polyester films of dongli corporation were used as substrates: lumirror (registered trademark) T60 (thickness 125 μm). After printing, hot air circulation is adoptedThe resultant was dried at 100 ℃ for 1 hour in a dryer to obtain a printed matter of the transparent conductive ink.

< photo-firing of printed Material of transparent conductive ink >

The printed matter of the transparent conductive ink was irradiated with pulsed light of 40 μ s at a single emission of 600V using a Pulse Forge 3300 of a photo-sintering apparatus manufactured by novacenrix corporation.

Comparative example 1

< printing of transparent conductive ink >

Printing was performed in the same manner as in example 1 except that a flat squeegee (micro squeegee made by Microtec, made of polyurethane, having a hardness of 70 and a thickness of 9mm) was attached instead of the round squeegee (round squeegee made by APOLAN International corporation, having a hardness of 70 and a radius of curvature of 4.8 mm). Fig. 4 is a side view of the flat blade used.

< photo-firing of printed Material of transparent conductive ink >

Instead of the 600V and 40 μ s pulsed light irradiation, a Pulse Forge 3300, a photosintering apparatus manufactured by NovaCentrix, inc, was used to perform 600V and 50 μ s pulsed light single shot irradiation.

< measurement of silver nanowire >

The average diameter and average length (average diameter 36nm, average length 20 μm) of the silver nanowires prepared as described above were obtained by subjecting the reaction solution of the silver nanowires after the reaction for 1 hour at 150 ℃ to solvent substitution with dibutyl ether, diluting a part of the suspension of the silver nanowires subjected to solvent substitution with dibutyl ether, spraying the diluted solution onto glass, drying the glass, and measuring the diameter and length of 100 silver nanowires by SEM (S-5000, manufactured by hitachi corporation) to obtain the average value of each of the diameters and lengths.

The length of the silver nanowires before printing (number of printing times 0) was determined by sampling the transparent conductive ink prepared as described above in small amounts, diluting it with methanol, spraying it onto glass, drying it, and measuring the length of 100 silver nanowires with an SEM (S-5000, hitachi, inc.) to obtain an average value.

Further, printing was repeated 200 times by the method of example 1 and comparative example 1, and a small amount of the ink on the screen mask immediately after completion of printing 5, 50, 100, 150, and 200 times and the ink before printing were sampled, diluted with methanol and poured onto glass, and after drying, the lengths of 100 silver nanowires were measured by SEM (S-5000, manufactured by hitachi corporation) to obtain the average values thereof as the lengths of the silver nanowires after printing 5, 50, 100, 150, and 200 times.

Table 1 shows the lengths of silver nanowires before printing (number of prints 0) and after 5, 50, 100, 150, 200 prints.

< measurement of surface resistance >

The surface resistivity and volume resistivity of the deposited layer of silver nanowires after irradiation with pulsed light were measured by using a surface resistivity and volume resistivity measuring device manufactured by mitsubishi chemical corporation of LORESTA-GP MCP-T6104 probe method. The results of measurement are shown in table 1. The number of measurements was 2, and the average value thereof was shown.

< measurement of Total transmittance >

The total transmittance was measured by using a turbidimeter NDH2000 manufactured by Nippon Denshoku industries Co., Ltd. The results of measurement are shown in table 1. The number of measurements was 2, and the average value thereof was shown.

As the length of the comparative line was repeatedly printed, it was found that the surface resistance of example 1 was stably changed while maintaining a state of about 3 times longer than that of comparative example 1 when the number of printing was 50 or more. In example 1 using the circular squeegee, the vertical force applied to the ink is larger and the print film thickness is increased by that much as compared with the case of using the flat squeegee under the same other printing conditions, and as a result, the surface resistance and the total transmittance are lowered.

TABLE 1

Description of the reference numerals

1 substrate, 2 screen mask, 3 circular squeegee, 4 printing direction, 5 transparent conductive ink.

Claims

1. A method for forming a transparent conductive pattern, characterized by screen-printing a transparent conductive ink using a squeegee having a curved surface shape at a tip portion in contact with a screen mask, the transparent conductive ink comprising at least one of metal nanowires and metal nanotubes and a dispersion medium, the average of diameters and thicknesses of the metal nanowires and the metal nanotubes being 1 to 500nm, the average of major axis lengths being 1 to 100 [ mu ] m, and the average of aspect ratios being greater than 5, wherein the transparent conductive ink contains the metal nanowires and the metal nanotubes in a total amount of 0.01 to 10 mass% based on the total mass of the transparent conductive ink.

2. The method for forming a transparent conductive pattern according to claim 1, wherein a curvature radius of a curved surface of a tip portion of the squeegee which is in contact with the screen mask is 0.1 to 20 mm.

3. The method for forming a transparent conductive pattern according to claim 2, wherein a curvature radius of a curved surface of a tip portion of the squeegee that is in contact with the screen mask is 2 to 10 mm.

4. The method of forming a transparent conductive pattern according to any one of claims 1 to 3, wherein the material of the squeegee is any one of synthetic rubber, natural rubber, metal, and plastic.

5. The method for forming a transparent conductive pattern according to claim 4, the synthetic rubber is composed of urethane rubber or silicone rubber.

6. The method for forming a transparent conductive pattern according to any one of claims 1 to 3, wherein the screen printing is performed with a squeegee speed of 5 to 200 mm/sec.

7. The method for forming a transparent conductive pattern according to any one of claims 1 to 3, wherein the dispersion medium contains a shape-retaining agent composed of an organic compound having a molecular weight in the range of 150 to 500.

8. The method for forming a transparent conductive pattern according to claim 7, wherein the organic compound of the shape-retaining agent is any one of a monosaccharide compound, a polyol compound, and a compound having an alkyl group and a hydroxyl group, the alkyl group having a quaternary carbon atom and/or a bridged ring skeleton.

9. The method for forming a transparent conductive pattern according to claim 8, wherein the organic compound of the shape-retaining agent is any one of diglycerin, 2, 4-trimethyl-1, 3-pentanediol monoisobutyrate, xylulose, ribulose, bornyl cyclohexanol, borneol, isobornyl cyclohexanol, and isobornyl.

10. The method for forming a transparent conductive pattern according to claim 7, wherein the dispersion medium further comprises a viscosity adjusting solvent for adjusting the viscosity of the shape retaining agent.

11. The method for forming a transparent conductive pattern according to claim 10, wherein the viscosity adjusting solvent is at least one of water, an alcohol, a ketone, an ether, an aliphatic hydrocarbon solvent, and an aromatic hydrocarbon solvent.

12. The method for forming a transparent conductive pattern according to claim 11, wherein the alcohol of the viscosity adjusting solvent is terpineol.

13. The method for forming a transparent conductive pattern according to claim 7, wherein the content of the shape-retaining agent is 10 to 90% by mass based on the total mass of the dispersion medium.