Method for forming a pattern using a one-dimensional conductor

Abstract

To provide a pattern forming method by a primary conductor, which can easily form patterns of various shapes including a closed loop shape.SOLUTION: This pattern forming method comprises: treating one or both of a pattern forming region and a non-pattern forming region; setting the surface energy γA of the pattern forming region to be smaller than the surface energy γB of the non-pattern forming region; setting a difference [γB-γA] between the surface energy γA of the pattern forming region and the surface energy γB of the non-pattern forming region to be within the range of 5mJ / m2-25mJ / m2; applying aqueous dispersion containing a primary conductor to the substrate surface; forming a liquid film of the primary conductor aqueous dispersion within the range including the pattern forming region and the non-pattern forming region; and controlling a microflow in the liquid film to self-concentrate nanowires convectively moving in the liquid film in the pattern forming region, thereby forming a prescribed pattern.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for forming a pattern with a one-dimensional conductor. [Background technology]

[0002] In recent years, additive manufacturing, which adds material to replace subtractive manufacturing, a manufacturing method that removes material by cutting or cutting, has been attracting attention. For example, when forming patterns on flexible substrates using conductive ink (functional ink), additive manufacturing can be used to reduce material waste and form patterns with shapes that would be difficult to create using conventional subtractive manufacturing methods.

[0003] Patent Document 1 proposes a method for forming a fine transparent conductive wiring pattern on a transparent substrate using metal nanowires as a conductive material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-181677 Summary of the Invention [Problem to be solved by the invention]

[0005] The method described in Patent Document 1 above involves forming a liquid-repellent layer that is liquid-repellent to a suspension containing metal nanowires on all or part of at least one main surface of a substrate, and then performing a lyophilic treatment on a predetermined wiring pattern formation area on the surface of this liquid-repellent layer to make it liquid-philic to the suspension containing metal nanowires, thereby forming areas on the substrate surface with different wettability (contact angle) of the suspension containing metal nanowires to the substrate, and selectively applying the suspension containing metal nanowires to areas with good wettability (contact angle) of the suspension containing metal nanowires to the substrate, and depositing the metal nanowires by drying and removing the dispersant.

[0006] As in Patent Document 1, various techniques for forming patterns using hydrophilic and hydrophobic regions formed on a substrate have been proposed in the past, but forming a closed-loop pattern has been particularly difficult. In fact, Patent Document 1 lists wiring shapes such as a straight line pattern (FIG. 1(a)), a curved line pattern (FIG. 1(b)), a broken line pattern (having bent portions), a honeycomb pattern, and a ring pattern, but the examples only describe that a linear pattern wiring was obtained using a photomask having openings corresponding to straight line patterns with line widths of 20 μm, 50 μm, 100 μm, and 150 μm.

[0007] In view of the problems with the conventional technology, an object of the present invention is to provide a method for forming a pattern using a one-dimensional conductor, which can easily form patterns of various shapes, including closed loop shapes. [Means for solving the problem]

[0008] To achieve the above object, the inventors focused on the frictional force between the substrate surface and the fluid in contact therewith, and came up with the idea of ​​appropriately adjusting this frictional force to control the minute flows (internal microflows) in the liquid film formed when the substrate surface is coated with a liquid containing one-dimensional conductors such as nanowires or nanotubes, and to guide the one-dimensional conductors contained in the liquid film to a predetermined position. As a result of extensive research by the inventors, the above object can be achieved by a method having the following aspects. [1] Treating either or both of the patterned and non-patterned areas of the substrate surface to reduce the surface energy γ A is the surface energy of the non-patterned area, γ B and the surface energy γ of the patterned region A and the surface energy of the non-patterned region γ B The difference between [γ B -γ A ], 5mJ / m 2 More than 25mJ / m 2 A method for forming a pattern using a one-dimensional conductor, comprising: applying an aqueous dispersion containing a one-dimensional conductor to the surface of a substrate and forming a liquid film of the aqueous dispersion of the one-dimensional conductor in an area including a pattern formation area and a non-pattern formation area; controlling minute flows in the liquid film to cause the one-dimensional conductor, which moves by convection in the liquid film, to self-assemble in the pattern formation area, thereby forming a predetermined pattern. [2] The method of [1], wherein the treatment includes irradiating with vacuum ultraviolet light. [3] The method of [2], in which a photomask having openings corresponding to regions where no pattern is to be formed is placed on the surface of a substrate that is hydrophobic in an untreated state, and the regions where no pattern is to be formed are irradiated with vacuum ultraviolet light. [4] The method of [2] or [3], wherein after the irradiation with vacuum ultraviolet light, either one or both of the patterned region and the non-patterned region are further treated with an alkaline solution. [5] The method according to any one of [1] to [4], further comprising heating the substrate on which the pattern is formed to sinter the one-dimensional conductor. [6] The method according to any one of [1] to [5], wherein the length of the one-dimensional conductor is in the range of 10 μm to 250 μm. [7] The surface tension γ of the aqueous dispersion containing the one-dimensional conductor L is 25mJ / m 2 More than 50mJ / m 2 Any of the following methods: [1] to [6]. [8] The method of any one of [1] to [7], wherein the one-dimensional conductor is selected from the group consisting of metal nanowires, metal oxide nanowires, polymer nanowires, silicon nanowires, carbon nanotubes, and combinations thereof. [9] The method according to any one of [1] to [8], wherein the substrate is selected from the group consisting of cycloolefin polymer (COP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polyethersulfone (PES), polycarbonate (PC), and polydimethylsiloxane (PDMS).

[10] The method according to any one of [1] to [9], wherein the aqueous dispersion containing the one-dimensional conductor is applied to the surface of the substrate using a method selected from the group consisting of dip coating, spin coating, roll coating, and slit coating.

[11] The method according to

[10] , wherein the aqueous dispersion containing the one-dimensional conductor is applied to the surface of the substrate using a slit coating method at a coating speed in the range of 0.5 cm / s to 30 cm / s.

[12] A substrate having a patterned region with low surface energy and a non-patterned region with high surface energy on its surface, in which a pattern made of a one-dimensional conductor is formed in the patterned region.

[13] The substrate of

[12] , wherein the one-dimensional conductor is selected from the group consisting of metal nanowires, metal oxide nanowires, polymer nanowires, silicon nanowires, carbon nanotubes, and combinations thereof, and the substrate is selected from the group consisting of cycloolefin polymer (COP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polyethersulfone (PES), polycarbonate (PC), and polydimethylsiloxane (PDMS).

[14] The substrate of

[13] , wherein the one-dimensional conductor is a metal nanowire selected from the group consisting of silver nanowires, copper nanowires, gold nanowires, and combinations thereof.

[15] The substrate according to

[14] , wherein the metal nanowires are silver nanowires and the substrate is a cycloolefin polymer (COP). [Effects of the Invention]

[0009] According to the present invention, a method for forming a pattern using a one-dimensional conductor is provided, which allows for easy formation of patterns of various shapes, including closed loop shapes. The present invention also provides a substrate having a pattern formed thereon by a one-dimensional conductor. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a flowchart illustrating a method for forming a pattern using a one-dimensional conductor according to an embodiment of the present invention. [Figure 2] 1 is a photographic image (scale bar: 1 cm) showing the appearance of a COP substrate (Example 2) produced in an example, on the surface of which a honeycomb-shaped pattern made of silver nanowires is formed. [Figure 3] SEM images (scale bar: 100 μm) of the substrate of Example 2 prepared in the examples: (a) a portion extending diagonally relative to the coating direction of the aqueous dispersion containing silver nanowires; (b) a portion extending horizontally relative to the coating direction of the aqueous dispersion containing silver nanowires; (c) a branched portion of the pattern. [Figure 4] Optical microscope images (scale bar: 200 μm) of COP substrates prepared in the examples, on whose surfaces a pattern consisting of silver nanowires is formed: (a) substrate of Example 4 (concentration of silver nanowires in the aqueous dispersion containing silver nanowires: 5 wt%); (b) substrate of Example 2 (concentration of silver nanowires in the aqueous dispersion containing silver nanowires: 20 wt%). [Figure 5] FIG. 1 shows the results of measuring (a) sheet resistivity, (b) total light transmittance, and (c) haze value for six types of substrates prepared in the examples by varying the energy applied to the COP substrate by intense pulsed light (IPL). [Figure 6]In the examples, optical microscope images (low magnification and high magnification images) of patterns formed on the surface of substrates prepared using six types of photomasks with different opening ratios are shown: (a) 96.2%; (b) 89.1%; (c) 95.3%; (d) 92.0%; (e) 90.2%; (f) 95.7%. [Figure 7] FIG. 7 is a diagram showing the results of measuring the haze values ​​at a wavelength of 550 nm for the six types of substrates shown in FIG. [Figure 8] (a) Optical microscope image of a geometric pattern made of silver nanowires on a COP substrate prepared in the example; (b) A photographic image showing the application of a constant voltage to both ends of the COP substrate in (a) and a thermographic image measuring the temperature distribution on the surface of the COP substrate; (c) A graph showing the details of the temperature distribution in any two linear regions in the thermographic image in (b). [Figure 9] FIG. 10 is a diagram (scale bar: 2 mm) showing an optical microscope image of an attempt to form a pattern in a hydrophilic region formed by VUV irradiation according to a conventional technique in Comparative Example 1. [Figure 10] 1A to 1C are schematic diagrams showing a procedure of a pattern formation method according to an embodiment of the present invention. [Figure 11A] 1A to 1C are schematic diagrams illustrating the formation of a liquid film of an aqueous dispersion of silver nanowires on a substrate surface in a pattern formation method according to an embodiment of the present invention. [Figure 11B] 1 is a schematic diagram showing fine flows in a liquid film of an aqueous dispersion of silver nanowires formed on the surface of a substrate, and the fixing and placement of silver nanowires, in a pattern formation method according to an embodiment of the present invention. [Figure 11C] FIG. 1 is a schematic diagram showing spontaneous aggregation of silver nanowires moving by convection in a liquid film of an aqueous dispersion of silver nanowires formed on the surface of a substrate in a pattern formation method according to an embodiment of the present invention. [Figure 12] FIG. 10 is a graph showing the relationship between the VUV irradiation time on the substrate surface and the length of silver nanowires, in relation to the formation of a liquid film of a one-dimensional conductor aqueous dispersion on the substrate surface. [Figure 13]1 is a graph showing the results of measuring the contact angle θ of a water droplet on a COP substrate when water (2.0 μL) is dropped onto the COP substrate while changing the VUV irradiation time of the COP substrate. [Figure 14] 1A and 1B are schematic diagrams showing the orientation of a one-dimensional conductor in a pattern formation region on a substrate surface by a pattern formation method according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described.

[0012] FIG. 1 is a flowchart showing a method for forming a pattern using a one-dimensional conductor according to one embodiment of the present invention.

[0013] The method for forming a pattern using a one-dimensional conductor according to this embodiment (hereinafter also simply referred to as a "pattern forming method") includes the following steps S110 and S120. Step S110: Treating either or both of the patterned and non-patterned regions of the substrate surface to reduce the surface energy γ A is the surface energy of the non-patterned area, γ B and the surface energy γ of the patterned region A and the surface energy of the non-patterned region γ B The difference between [γ B -γ A ], 5mJ / m 2 More than 25mJ / m 2 The range is as follows: Step S120: An aqueous dispersion containing a one-dimensional conductor is applied to the surface of the substrate to form a liquid film of the one-dimensional conductor aqueous dispersion in an area including a pattern formation area and a non-pattern formation area.

[0014] In this specification, the term "one-dimensional conductor" refers to a conductive material having a one-dimensional structure such as a fiber, wire, rod, tube, etc. The structure (shape) of the one-dimensional conductor is not limited to the above-mentioned examples, but in the present invention, particle and dot shapes are treated as zero-dimensional structures, and sheet and plate shapes are treated as two-dimensional structures.

[0015] The one-dimensional conductor is preferably a nanostructure. In this specification, the term "nanostructure" refers to a structure in which at least one of the size indicators (length, width, diameter, etc.) commonly used depending on the shape of the structure is on the nano-order (in the range of 1 nm to 1000 nm). Examples of nanostructures include, but are not limited to, nanofibers, nanowires, nanorods, and nanotubes. The shape of the nanostructure may be of one type or of multiple types.

[0016] In a preferred aspect of the pattern formation method according to this embodiment, the one-dimensional conductor is preferably a nanowire, a nanotube, or a combination thereof. In this specification, the term "nanowire" refers to a substance having a diameter in the range of 1 nm to 1000 nm and a wire-like shape. The length of the nanowire is not particularly limited, but typically refers to a substance having a length of 50 times or more the diameter. Preferably, the length of the nanowire is 100 times or more the diameter. In a narrower sense, the term "nanowire" refers to a wire-like substance having a diameter in the range of 1 nm to 500 nm and a length of 100 times or more the diameter. In this aspect, nanotubes having a tubular shape may be used together with or instead of the nanowires.

[0017] In the preferred embodiment described above, specific examples of the one-dimensional conductor include, but are not limited to, metal nanowires (silver nanowires, copper nanowires, gold nanowires, etc.), metal oxide nanowires (e.g., those having photocatalytic functions), polymer nanowires (e.g., polyacetylene nanowires, PEDOT:PSS nanowires), silicon nanowires, carbon nanotubes, etc. In addition, in this embodiment, the one-dimensional conductor may be of one type or a combination of multiple types.

[0018] The substrate used in the pattern formation method according to this embodiment is not particularly limited in type or material, as long as it does not interfere with the function of the pattern formed on its surface. The substrate may be rigid or flexible. The substrate may be transparent, translucent, or opaque (light-shielding). For example, substrates made of resins with excellent heat resistance and transparency, such as cycloolefin polymer (COP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polyethersulfone (PES), polycarbonate (PC), or polydimethylsiloxane (PDMS), can be used as transparent electronics materials, which have seen increasing global demand in recent years. The substrate may be a single material, such as the above-mentioned resins, on whose surface a pattern is intended to be formed, or a composite substrate in which the material is coated on any substrate (base substrate).

[0019] The substrate may be selected depending on the substrate surface treatment means described below. Specifically, in an embodiment in which the substrate surface treatment includes irradiating the surface with vacuum ultraviolet light (VUV), the substrate preferably has a hydrophobic surface. More specifically, in this embodiment, it is preferable to place a photomask having openings corresponding to non-pattern formation regions on the substrate surface, which is hydrophobic in an untreated state, and irradiate the non-pattern formation regions with VUV.

[0020] Generally, when a solid surface has hydrophobic properties, the surface energy γ SIt is known that the contact angle θ of a water droplet on a solid surface is large when the surface energy γ of the COP substrate is small. For example, in a preliminary experiment, the contact angle θ of a water droplet on a cycloolefin polymer (COP) substrate used in the examples described later was measured when water (2.0 μL) was dropped onto the COP substrate in an untreated state, and was found to be approximately 96.7°. Then, when VUV was irradiated onto the surface of this COP substrate for a certain period of time using a vacuum ultraviolet light irradiation device, the contact angle θ of the water droplet dropped onto the COP substrate surface gradually decreased as the VUV irradiation time was increased to 60 seconds, 90 seconds, 150 seconds, 300 seconds, 450 seconds, 15 minutes, and 20 minutes. In other words, the surface energy γ of the portion irradiated with VUV decreased. S It was confirmed that the value of the saturation voltage increases (see FIG. 13 described later).

[0021] The above results indicate that VUV irradiation hydrophilizes the COP substrate surface. Furthermore, XPS analysis of the COP substrate surface revealed oxygen-free C-C and C-H bonds in the untreated COP substrate, whereas oxygen-containing functional groups such as hydroxyl (OH), carboxyl (COOH), and carbonyl (C=O) groups were formed on the surface hydrophilized by VUV irradiation. Furthermore, the longer the VUV irradiation time, the more oxygen-containing functional groups formed. Thus, VUV irradiation of a substrate surface that is hydrophobic in its untreated state can oxidize and hydrophilize the surface. In other words, selective VUV irradiation of a portion of the COP substrate surface can modify the irradiated area to a higher surface energy (activated state), and the degree of modification can be controlled by adjusting the VUV irradiation time.

[0022] By utilizing such a surface modification reaction to treat either or both of the patterned region and the non-patterned region of the substrate surface, the surface energy γ S can be controlled.

[0023] In this specification, when a general explanation is made regarding the surface energy of a substrate, the symbol γ SWhen describing the surface energy of a pattern-formed region (a region where a pattern is intended to be formed by a one-dimensional conductor) separately from the surface energy of a non-pattern-formed region (a region where the pattern is not intended to be formed), the former is represented by the symbol γ A and the latter is represented by the symbol γ B In addition, as a general explanation, when referring to a location of high surface energy and a location of low surface energy on the surface of a substrate, the former will be represented by the symbol γ S + and the latter is represented by the symbol γ S - Furthermore, the surface tension of an aqueous dispersion containing a one-dimensional conductor, which will be described later, is expressed by the symbol γ L It is expressed as:

[0024] As will be described in detail below, in the pattern formation method according to this embodiment, the pattern formation region is a place on the substrate surface where the surface energy is low, and the non-pattern formation region is a place on the substrate surface where the surface energy is high. That is, the surface energy γ A is γ S - and the surface energy of the non-patterned region γ B is γ S + is.

[0025] In the prior art described in Patent Document 1, VUV irradiation creates hydrophilic (lyophilic) regions on the substrate, i.e., regions with relatively high surface energy (γ S + ), and the target material is selectively deposited in this hydrophilic (lyophilic) region. However, in one aspect of the pattern formation method according to this embodiment, unlike such conventional techniques, the target material is selectively deposited in the region not irradiated with VUV, that is, the region with a relatively low surface energy (γ S -In other words, in an embodiment in which the treatment of the substrate surface includes irradiating the surface with VUV, it is common to the prior art in that the substrate surface is irradiated with VUV, but it should be noted that the technical significance is completely different in terms of the purpose and effect.

[0026] In the conventional technology, attention is paid to the hydrophilicity / hydrophobicity of the substrate (solid) surface, and the aim is to move the liquid containing the target material from the hydrophobic area to the hydrophilic area by utilizing the difference (change) in the wettability of the liquid. In contrast, in the pattern formation method according to the present embodiment, the surface energy γ S By controlling the micro-flow (internal micro-flow) that occurs in the liquid film (liquid film) applied there, the dispersoids (one-dimensional conductors) present in the liquid film are directed to a specific region, that is, a region with low surface energy (γ S - ) to spontaneously assemble into the desired pattern.

[0027] As used herein, the term "treatment" as used in reference to a substrate surface refers to the reduction in the surface energy γ S More specifically, the treatment of the substrate surface is intended to change the surface energy γ of the pattern-forming region of the substrate surface. A and the surface energy of the non-patterned region γ B This is done with the aim of changing one or both of the above.

[0028] The substrate surface treatment method is not particularly limited as long as it satisfies the above-mentioned purpose. For example, as described above, VUV irradiation can modify and hydrophilize the surface of a polymer material having a hydrophobic surface, such as a COP substrate, and is therefore suitable for use as a substrate surface treatment method in the pattern formation method according to this embodiment. Furthermore, VUV irradiation is preferable because the degree of surface modification can be relatively easily adjusted by using the irradiation time as a parameter. Additionally, since VUV irradiation parameters include irradiation time, irradiation distance, irradiation atmosphere, and the like, it is possible to more precisely adjust the degree of substrate surface modification by combining these parameters in various ways. Note that, as an indicator of the degree of substrate surface modification, the contact angle θ of a liquid droplet (e.g., water) when a certain amount of the liquid is dropped onto the surface may be used, or the surface energy γ may be calculated using an arbitrary software program or the like. S may be estimated.

[0029] In the pattern formation method according to this embodiment, either one or both of the pattern formation region and the non-pattern formation region of the substrate surface are treated, and the surface energy γ A is the surface energy of the non-patterned area, γ B and the surface energy γ of the patterned region A and the surface energy of the non-patterned region γ B The difference between [γ B -γ A ], 5mJ / m 2 More than 25mJ / m 2 The range is as follows (step S110).

[0030] Specifically, in an embodiment in which the treatment of the substrate surface includes irradiating the surface with VUV, for example, a photomask having openings corresponding to non-pattern formation regions is placed on the substrate surface, which is hydrophobic in an untreated state, and the non-pattern formation regions are irradiated with VUV. As a result, the non-pattern formation regions are hydrophilized by VUV irradiation, and the surface energy γ of the non-pattern formation regions is reduced. B is the surface energy γ of the area not irradiated with VUV (patterned area)A That is, the surface energy γ A is the surface energy of the non-patterned region, γ B At this time, by adjusting the VUV irradiation time, irradiation distance, irradiation atmosphere, etc., the surface energy γ A and the surface energy of the non-patterned region γ B The difference between [γ B -γ A ], 5mJ / m 2 More than 25mJ / m 2 The range is as follows:

[0031] The difference in surface energy [γ B -γ A ] is preferably adjusted taking into account the length of the one-dimensional conductor. B -γ A It is preferable to adjust (select) the length of the one-dimensional conductor to be used depending on the value of [γ B -γ A ] is as follows: The length of the one-dimensional conductor is 10 μm or more and 20 μm or less, and the difference in surface energy [γ B -γ A ] is 5mJ / m 2 More than 10mJ / m 2 The following is the result. The length of the one-dimensional conductor is 20 μm or more and 50 μm or less, and the difference in surface energy [γ B -γ A ] is 10 mJ / m 2 More than 12mJ / m 2 The following is the result. The length of the one-dimensional conductor is 50 μm or more and 100 μm or less, and the difference in surface energy [γ B -γ A] is 12 mJ / m 2 More than 14mJ / m 2 The following is the result. The length of the one-dimensional conductor is 100 μm or more and 150 μm or less, and the difference in surface energy [γ B -γ A ] is 14mJ / m 2 More than 18mJ / m 2 The following is the result. The length of the one-dimensional conductor is 150 μm or more and 200 μm or less, and the difference in surface energy [γ B -γ A ] is 18mJ / m 2 More than 22mJ / m 2 The following is the result. The length of the one-dimensional conductor is 200 μm or more and 250 μm or less, and the difference in surface energy [γ B -γ A ] is 22 mJ / m 2 More than 24mJ / m 2 The following is the result. These conditions are particularly suitable in an embodiment in which the one-dimensional conductor is a metal nanowire selected from the group consisting of silver nanowires, copper nanowires, gold nanowires, and combinations thereof.

[0032] Thus, when the length of a one-dimensional conductor is relatively short, the difference in surface energy [γ B -γ A ] can be a relatively small value, while when the length of the one-dimensional conductor is relatively long, the difference in surface energy [γ B -γ A ] is preferably a relatively large value. This point is also suggested by the results obtained using metal nanowires (silver nanowires) in the examples described later.

[0033] In addition, the difference in surface energy [γ B -γ A] can also be adjusted taking into consideration the type of one-dimensional conductor. For example, in an embodiment in which the one-dimensional conductor is a nanowire, even if the nanowires have the same length, metal nanowires and other types of nanowires (e.g., polymer nanowires) may differ in mass and dispersibility in a solvent. In this regard, the examples described below show cases in which metal nanowires (silver nanowires) are used, and in the case of other types of nanowires, the relationship may differ from that exemplified in the above-mentioned embodiment. However, those skilled in the art will be able to easily determine the relationship between the nanowires to be used and the surface energy difference [γ B -γ A ] may be possible to find a favorable relationship.

[0034] In the pattern formation method according to this embodiment, in an embodiment in which the treatment of the substrate surface includes irradiating the surface with VUV, the substrate surface (either one or both of the pattern formation region and the non-pattern formation region) may be further treated with an alkaline solution after VUV irradiation. By treating with an alkaline solution, hydroxyl groups (OH), carboxyl groups (COOH), carbonyl groups (C=O), etc. formed on the surface that has been hydrophilized by VUV irradiation are ionized, thereby enhancing the interaction with the solution applied (coated) to the surface. Furthermore, by treating with an alkaline solution, residues on the substrate surface after VUV irradiation can be removed, further cleaning the surface.

[0035] Examples of the alkaline solution used in the alkaline solution treatment include aqueous solutions of alkaline compounds such as sodium hydroxide and potassium hydroxide, and aqueous solutions of organic amines.

[0036] In this way, the surface energy γ A and the surface energy of the non-patterned region γ B An aqueous dispersion containing a one-dimensional conductor is applied to the surface of the substrate whose surface has been adjusted, to form a liquid film of the one-dimensional conductor aqueous dispersion in an area including a pattern formation area and a non-pattern formation area (step S120).

[0037] The solvent of the aqueous dispersion containing the one-dimensional conductor is water. To facilitate the dispersion of the one-dimensional conductor, additives such as surfactants may be added to the solvent. Furthermore, the inclusion of components that may be unavoidably mixed during the preparation of the dispersion is permitted.

[0038] The concentration of the aqueous dispersion containing the one-dimensional conductor is not particularly limited and can be adjusted appropriately depending on the size (area) of the pattern formation region, the shape of the target pattern, etc. Small variation in the length of the one-dimensional conductors is preferable because it facilitates uniform dispersion of the one-dimensional conductors in the dispersion. It is also preferable to suppress aggregation of the one-dimensional conductors in the dispersion by using an ultrasonic disperser or the like before applying it to the substrate surface.

[0039] The method for applying the aqueous dispersion containing the one-dimensional conductor to the surface of the substrate is not particularly limited, and for example, a method using a coater device used for coating a liquid material on a predetermined substrate in a photolithography process can be adopted, such as dip coating, spin coating, roll coating, and slit coating.

[0040] In the pattern formation method according to this embodiment, a liquid film of a one-dimensional conductor aqueous dispersion is formed in an area including a pattern formation area and a non-pattern formation area. At this time, a minute flow (internal microflow) in the liquid film is controlled under the application conditions of the dispersion (usually room temperature). More specifically, the surface energy γ of the pattern formation area is controlled. A and the surface energy of the non-patterned region γ B By appropriately adjusting the velocity vector distribution, the internal microflow (hydrodynamic behavior) of the liquid film, which is generated by the difference in friction between the substrate surface and the dispersion, differs between the patterned and non-patterned regions. This change in velocity vector distribution determines the orientation of the one-dimensional conductors in the liquid film, and the one-dimensional conductors self-assemble in the patterned region, forming the desired pattern.

[0041] In other words, in the pattern formation method according to this embodiment, before applying the aqueous dispersion containing the one-dimensional conductor to the surface of the substrate, the surface of the substrate is treated to reduce the surface energy γ A and the surface energy of the non-patterned region γ B By appropriately adjusting the above, the distribution of the velocity vectors (fluid velocity vectors) of the convection occurring in the liquid film of the one-dimensional conductive aqueous dispersion formed in an area including the patterned and non-patterned regions can be controlled.

[0042] In this way, by utilizing the internal microflow generated by friction between the pattern-forming area and non-pattern-forming area and the solvent of the dispersion liquid, the one-dimensional conductors dispersed in the liquid film (moving by convection in the liquid film) do not simply gather along a certain direction (orientate in one direction) relative to the pattern-forming area, but rather are composed of multiple layers of one-dimensional conductors with a certain orientation stacked on top of each other, and a structure can be formed in which the one-dimensional conductors in these layers are connected to each other.

[0043] As a result, the pattern formation method according to this embodiment allows for the accurate formation of a pattern consisting of one-dimensional conductors in the pattern formation region on the substrate surface. The individual one-dimensional conductors constituting the pattern are partially in contact with adjacent one-dimensional conductors, and the pattern consisting of one-dimensional conductors is conductive as a whole. The substrate on which the pattern thus formed may be dried under normal atmospheric conditions, or the substrate may be further heated to sinter the one-dimensional conductors. For example, photosintering using intense pulsed light (IPL) or the like can evaporate the remaining solvent and sinter the one-dimensional conductors together, further solidifying the pattern consisting of one-dimensional conductors, which can then be used as a conductive substrate. Other examples of methods for sintering one-dimensional conductors in this way include heating with a heater or near-infrared laser (NIL). The same purpose can also be achieved by applying pressure.

[0044] In a preferred embodiment of the pattern formation method according to the present embodiment, the surface tension γ of the aqueous dispersion containing the one-dimensional conductor is L is 25mJ / m 2 More than 50mJ / m 2 The surface tension γ of the aqueous dispersion containing the one-dimensional conductor is in the range of L Within this range, when applied to the surface of a substrate, the dispersion liquid easily spreads over an area including the pattern-forming region and the non-pattern-forming region, and a liquid film of the one-dimensional conductor aqueous dispersion liquid is easily formed more efficiently. L tends to be smaller, so the surface tension of the dispersion γ L can be adjusted by the length of the one-dimensional conductor and / or the concentration of the dispersion.

[0045] In another preferred embodiment of the pattern formation method according to this embodiment, an aqueous dispersion containing a one-dimensional conductor is applied to the surface of a substrate using a slit coating method at a coating speed ranging from 0.5 cm / s to 30 cm / s. By using the slit coating method as the dispersion application method and adjusting the coating bar movement speed within the above range, the dispersion easily spreads over an area including pattern formation regions and non-pattern formation regions when applied to the substrate surface, and a liquid film of the one-dimensional conductor aqueous dispersion is easily formed. Specifically, in this embodiment, it is preferable to adjust the coating speed (movement speed of the coating bar) depending on the length of the one-dimensional conductor in the dispersion. Here, examples of preferred relationships between the length of the one-dimensional conductor and the coating speed in this embodiment are as follows: The length of the one-dimensional conductor is between 10 μm and 20 μm, and the coating speed is between 0.5 cm / s and 5 cm / s. The length of the one-dimensional conductor is between 20 μm and 50 μm, and the coating speed is between 5 cm / s and 10 cm / s. The length of the one-dimensional conductor is between 50 μm and 100 μm, and the coating speed is between 10 cm / s and 15 cm / s. The length of the one-dimensional conductor is 100 μm or more and 150 μm or less, and the coating speed is 15 cm / s or more and 20 cm / s or less. The length of the one-dimensional conductor is 150 μm or more and 200 μm or less, and the coating speed is 20 cm / s or more and 25 cm / s or less. The length of the one-dimensional conductor is between 200 μm and 250 μm, and the coating speed is between 25 cm / s and 30 cm / s. These conditions are particularly suitable in an embodiment in which the one-dimensional conductor is a metal nanowire selected from the group consisting of silver nanowires, copper nanowires, gold nanowires, and combinations thereof.

[0046] The pattern thus obtained can have improved electrical properties without impairing the optical properties of the one-dimensional conductor by further sintering the one-dimensional conductor under appropriate conditions.

[0047] Generally, when a pattern formed on a substrate surface undergoes this sintering process, the remaining solvent evaporates and the materials are sintered together, making the pattern more reliable. In addition, sintering also removes the residue of the solvent used to form the pattern, which is useful for improving the conductivity of the pattern.

[0048] The sintering means and conditions that can be applied in the pattern formation method according to this embodiment are not particularly limited, but include, for example, irradiation with intense pulsed light (IPL).

[0049] The conditions for IPL irradiation are the applied voltage (V) and irradiation time (μs), which are used as parameters to determine the energy (J / cm 2) can be adjusted. If the applied energy is appropriate, the one-dimensional conductors can maintain a firmly connected structure after sintering. Conversely, if the applied energy is too low or too high, defects such as insufficient sintering or the loss of the connections of the one-dimensional conductors can occur. Furthermore, even if the applied energy is the same, if the applied voltage is too high, the above-mentioned defects can occur even with a short irradiation time. Therefore, it is preferable to set an appropriate applied voltage and irradiation time taking into account the type and properties of the nanowires used.

[0050] The present invention will be described in more detail below based on examples, but it should be noted that the present invention is not limited to these examples. [Example]

[0051] [Preparation of aqueous dispersion containing metal nanowires] Silver nanowires (Guangzhou Nano Chemical Technology Co.) were dispersed in ultrapure water (purified with PURELAB Chorus manufactured by ELGA) at a concentration of 20 wt % to prepare an aqueous dispersion (conductor ink) containing silver nanowires. The silver nanowires used in this example had an average diameter of 50 nm and average lengths of 20 μm (Example 1), 50 μm (Example 2), and 100 μm (Example 3). The aqueous dispersion containing silver nanowires was gently ultrasonicated for 2 minutes before use to prevent aggregation of the silver nanowires and to uniformly disperse the silver nanowires in the liquid. The surface tension γ of each aqueous dispersion containing silver nanowires L The measurement results are shown in Table 1.

[0052] [Substrate surface treatment] The substrate used was a substrate (thickness: 100 μm) made of cycloolefin polymer (COP). This substrate has a hydrophobic surface, so the surface energy is relatively low in the untreated state. This substrate is 4 x 4 cm 2The specimen was cut to the size of the specimen and placed on the irradiation stage of a mask aligner equipped with a VUV lamp (SUS740, wavelength 150-200 nm) manufactured by Ushio Inc. At this time, a photomask having hexagonal openings was placed on the surface of the substrate to be irradiated with vacuum ultraviolet light. The surface of the substrate was irradiated with vacuum ultraviolet light through a photomask in a nitrogen atmosphere. The irradiation time was set to 120 seconds in Example 1, 150 seconds in Example 2, and 200 seconds in Example 3 to adjust the degree of modification (oxidation) occurring in the area irradiated with vacuum ultraviolet light. The substrate was then removed from the apparatus, the photomask removed from the substrate surface, and the area irradiated with VUV light was cleaned by treating it with an alkaline solution (aqueous organic amine solution), followed by rinsing with deionized water (ELGA water purification system, VWS (UK)). This increased the surface energy of the area irradiated with VUV light (the area corresponding to the hexagonal holes formed in the photomask) above that of the area not irradiated with VUV light (the area protected by the photomask). Next, nitrogen gas was blown onto the substrate to thoroughly dry the surface.

[0053] [Patterning on substrate surface] Five microliters of the aqueous dispersion containing silver nanowires was dropped onto the substrate and swept using a conventional slit coating method. The sweep speed of the coating bar was adjusted depending on the length of the silver nanowires. Specifically, the sweep speeds were 5 cm / s, 10 cm / s, and 15 cm / s for silver nanowire lengths of 20 μm, 50 μm, and 100 μm, respectively. At this time, the coating direction of the aqueous dispersion containing silver nanowires (i.e., the sweep direction of the coating bar) was set to be horizontal (parallel) to the extension direction of two opposing sides of the six sides that make up the honeycomb shape. However, the coating direction of the aqueous dispersion containing silver nanowires is not limited to this, and it may be set to intersect at a right angle with the extension direction of two opposing sides of the six sides that make up the honeycomb shape. It was confirmed that the coated aqueous dispersion of silver nanowires formed a uniform liquid film on the substrate. Furthermore, once a uniform film was formed, the silver nanowires in the liquid film spontaneously accumulated in the patterned areas that were not irradiated with vacuum ultraviolet light. By self-assembly of the silver nanowires on this pattern formation region, a honeycomb-shaped pattern (closed loop-shaped pattern) made of silver nanowires was obtained.

[0054] When the process of pattern formation on the substrate surface was observed over time using an optical microscope, the time when the substrate surface was coated with the aqueous dispersion containing silver nanowires was taken as 0 seconds. Within approximately 2 seconds, silver nanowires were observed to be settling and settled on the pattern formation area. After approximately 6 seconds, another silver nanowire was settling and settled on the settling silver nanowire. After approximately 80 seconds, further silver nanowires accumulated, resulting in stacking of the silver nanowires. After approximately 100 seconds, a pattern formed by the self-assembly of the silver nanowires was confirmed.

[0055] Next, intense pulsed light (IPL) (NovaCentrix, PulseForge® Invent, light-curing device) was irradiated in the wavelength range of 200 nm to 1500 nm to dry the remaining moisture on the substrate surface and sinter the silver nanowires together in the pattern formation area.

[0056] Table 1 below shows the main conditions for producing the pattern made of silver nanowires produced in this example.

[0057] [Table 1]

[0058] In addition, a substrate (Example 4) having a pattern formed on its surface was prepared under the same preparation conditions as in Example 2, except that the concentration of silver nanowires in the aqueous dispersion containing silver nanowires was set to 5 wt %.

[0059] FIG. 2 is a photographic image of the appearance of the substrate obtained in Example 2. The dark areas in Figure 2 are the colors of the gloves worn on the hands holding the COP substrate, which are visible through the transparent COP substrate. As can be seen from this figure, a regular honeycomb-shaped pattern made of silver nanowires was formed on the COP substrate by the pattern forming method according to the present invention.

[0060] Furthermore, when the surface of the substrate of Example 2 was observed using an optical microscope, no deposition of silver nanowires was observed in the non-pattern-forming areas, and it was confirmed that silver nanowires had accumulated on the desired pattern-forming areas, and the boundary between the pattern-forming areas and the non-pattern-forming areas was also clear.

[0061] Furthermore, when the surface of the substrate of Example 2 was observed with a scanning electron microscope (SEM), as shown in Figure 3, it was clearly confirmed that silver nanowires were accumulated in the desired pattern formation area in all of the areas extending diagonally relative to the coating direction of the aqueous dispersion containing silver nanowires (Figure 3(a)), the areas extending horizontally relative to the coating direction of the aqueous dispersion containing silver nanowires (Figure 3(b)), and the branching areas of the pattern (Figure 3(c)). Note that the scale bars in all figures are 100 μm.

[0062] As with Example 2, for the substrates of Examples 1, 3, and 4, it was confirmed by external observation and optical microscope observation that a regular honeycomb-shaped pattern made of silver nanowires had been formed on the COP substrate.

[0063] 4(a) and 4(b) are optical microscope images (scale bar: 200 μm) of the substrates of Examples 4 and 2, respectively. Figures 4(a) and 4(b) are both observation images of the branched portions of the pattern. Comparing these, when the silver nanowire concentration was 5 wt% (Example 4), the density of the silver nanowires accumulated on the pattern formation region was low, while when the silver nanowire concentration was 20 wt% (Example 2), the density of the accumulated silver nanowires was high. However, in both cases, it was clearly observed that the silver nanowires were accumulated only in the pattern formation region. In other words, in the case of the silver nanowires used in Examples 2 and 4, which have an average diameter (50 nm) and an average length (50 μm), the degree of accumulation of the silver nanowires in the optical microscope images shown in Figures 4(a) and (b) reflects the difference in the concentration of the silver nanowires in the aqueous dispersion containing the silver nanowires. In other words, it can be said that the pattern formation method of the present invention can be performed well regardless of the concentration of the one-dimensional conductor in the aqueous dispersion (conductor ink) containing the one-dimensional conductor used.

[0064] [Analysis of a substrate with a pattern of silver nanowires formed on its surface] The sheet resistivity and total light transmittance of the substrates of Examples 1 to 3 were measured, and the sheet resistivities were 30.1, 29.7, and 28.4 Ω / □, respectively, and the transmittance at a wavelength of 550 nm was 98.7, 98.2, and 97.9%, respectively (see Table 2).

[0065] [Table 2]

[0066] Here, to investigate the influence of the difference in the energy imparted to the substrate by IPL irradiation on the characteristics of the substrate on which the pattern was formed, the imparted energy was set to 0.0 J / cm 2 (non-irradiated), 0.6J / cm 2 , 0.8J / cm 2 (Example 2), 1.0 J / cm 2 , 1.2J / cm 2 , and 1.5 J / cm 2 The other production conditions were set to the same as in Example 2, and substrates (six types in total including Example 2) having patterns formed on their surfaces were produced.

[0067] Figures 5(a), 5(b), and 5(c) show the results of measuring the sheet resistivity (Ω / □), total light transmittance (%), and haze value (%) for the six types of substrates mentioned above. The bottom right of Figure 5(b) and the top right of Figure 5(c) show the results of measuring the transmittance and haze value at a wavelength of 550 nm, respectively. In Figures 5(a) to (c), the applied energy was 0.0 J / cm. 2 , 0.6J / cm 2 , 0.8J / cm 2 , 1.0J / cm 2 , 1.2J / cm 2 , and 1.5 J / cm 2 The results for the cases are plotted as squares, circles, upward pointing triangles, downward pointing triangles, diamonds, and left pointing triangles, respectively.

[0068] As shown in FIG. 5(b), under the manufacturing conditions used in this example, the influence of the difference in the energy imparted to the substrate by IPL irradiation on the total light transmittance of the substrate was hardly observed, and the influence of the imparted energy of 1.0 J / cm 2 Above this value, the transmittance at a wavelength of 550 nm tends to decrease slightly (Fig. 5(b) bottom right).

[0069] On the other hand, the measurement results of sheet resistivity (Fig. 5(a)) show that the non-IPL irradiation (irradiation energy 0.0 J / cm 2 It was found that the sheet resistivity of the substrate was reduced to about half or less by irradiating IPL at a constant applied energy compared to the case of 0.8 J / cm. In particular, 2 It was found that the sheet resistivity (29.7 Ω / □) in the case of (Example 2) was reduced by about 85% compared to the value without IPL irradiation (about 200 Ω / □).

[0070] In addition, the haze value (Fig. 5(c)) measurement results show that the applied energy is 1.2 J / cm at a wavelength of 550 nm (upper right of Fig. 5(c)). 2Although the haze value was slightly higher when IPL was not irradiated than when IPL was not irradiated, within the measured wavelength range, there was a tendency for the haze value of the substrate to be smaller when IPL was irradiated at a constant applied energy than when IPL was not irradiated. 2 In the case of (Example 2), it was found that the haze value was smaller not only at a wavelength of 550 nm (haze value 2.8%) but also over the entire measured wavelength range than under other conditions.

[0071] These results demonstrate that, in the pattern formation method according to the present invention, by performing photosintering by IPL irradiation on a substrate on which a one-dimensional conductor pattern has been formed, the electrical properties of the pattern formed on the surface can be improved without impairing the original optical properties of the substrate. Furthermore, it was found that the electrical properties of the pattern can be more effectively exhibited by adjusting the energy imparted to the substrate by IPL irradiation.

[0072] In fact, the patterns formed on the six types of substrates were observed under SEM, and the results showed that the patterns formed on the six types of substrates without IPL irradiation (irradiation energy 0.0 J / cm 2 ), there are some areas where the overlap (contact) between the silver nanowires is insufficient, and the applied energy is 0.6 J / cm 2 In the case of , some areas of the silver nanowires were not sufficiently sintered. 2 , and 1.5 J / cm 2 In the case of 0.8 J / cm, the nanowire connection structure was partially damaged and cracks were observed in the silver nanowires. 2 (Example 2), and 1.0 J / cm 2 In the case of Example 1, the partial defects as described above were hardly observed, and in particular, in the substrate of Example 2, it was confirmed that the pattern made of silver nanowires was more reliably formed by photosintering.

[0073] Next, a bending test was performed according to the following procedure to analyze the mechanical properties of the patterned substrate.

[0074] The six types of substrates were placed on a motorized stage with both ends clamped, and the substrate was repeatedly curved by moving one end toward the other at a speed of 10 r / min. The radius of curvature at the most curved state of the substrate was 7.5 mm. This bending operation was repeated a total of 5,000 times, and the change in resistivity R of the substrate over time was measured and compared with the resistivity R before the test.

[0075] As a result, without IPL irradiation (irradiation energy 0.0 J / cm 2 During the test, the R / R0 value for the substrate (Figure 1) increased to a maximum of approximately 9. This is thought to be due to the high contact resistance between the silver nanowires that make up the pattern.

[0076] On the other hand, the applied energy is 1.5 J / cm 2 In the case of (1), when the number of bending operations exceeded 2000, the R / R0 value tended to exceed 1, and when the number of bending operations exceeded 3000, the R / R0 value rose to a maximum of approximately 5.

[0077] In contrast, the applied energy is 0.8 J / cm 2 In the case of (Example 2), the value of R / R0 remained constant at approximately 1 during the test, and the maximum change in R was less than 0.5.

[0078] These results confirmed the significance of photosintering a substrate with a one-dimensional conductor pattern by IPL irradiation from the viewpoint of mechanical properties as well. Furthermore, it was found that adjusting the energy imparted to the substrate by IPL irradiation not only makes it possible to more effectively demonstrate the electrical properties of the pattern, but also to create a substrate with excellent mechanical properties.

[0079] [Example of pattern formation using a photomask with different opening area ratios] In the production of the substrates of Examples 1, 2, and 3 described above, a photomask with an open area ratio of 92.0% was used. The area of ​​the hexagonal openings was varied to set the ratio of the openings to the photomask area to 89.1%, 90.2%, 92.0% (Example 2), 95.3%, 95.7%, and 96.2%, while maintaining the other production conditions the same as in Example 2. Substrates (six types in total, including Example 2) with patterns formed on their surfaces were produced.

[0080] Figures 6(a) to 6(f) show optical microscope images of patterns formed on the surfaces of the six types of substrates mentioned above. The upper row of each figure shows a low-magnification image (scale bar: 2 mm), and the lower row shows a high-magnification image (scale bar: 200 μm). The ratio of the opening area to the photomask area is indicated in the upper left corner of the upper image of each figure (96.2%, 89.1%, 95.3%, 92.0%, 90.2%, and 95.7%, respectively, for Figures 6(a) to 6(f)). The lower image of each figure shows the numerical value indicating the pattern width (i.e., the width of the pattern-forming region) (200 μm, 200 μm, 100 μm, 100 μm, 100 μm, and 50 μm, respectively, for Figures 6(a) to 6(f)).

[0081] As shown in Figures 6(a) to 6(f), it was confirmed that a honeycomb-shaped pattern made of silver nanowires was formed in the desired pattern formation region regardless of which photomask was used.

[0082] Furthermore, the haze values ​​of the six types of substrates obtained were measured at a wavelength of 550 nm, and the results are shown in Figure 7.

[0083] As shown in Figure 7, the haze value at a wavelength of 550 nm varied depending on the photomask used. This suggests that substrates on which desired patterns are formed by the pattern formation method of the present invention may be suitable for a wide variety of applications, including solar cell and sensor applications requiring high haze values, and display and transparent film heater applications requiring low haze values. For example, a photomask with openings corresponding to a geometric pattern (an arbitrary logo mark) was used instead of a photomask with hexagonal openings to form a pattern of silver nanowires on a COP substrate in the same manner as in the above-described fabrication example. The resulting substrate was then photosintered by IPL irradiation under appropriate conditions. When a constant voltage (2 V) was applied to both ends of the substrate, the patterned region (pattern-formed region) generated heat, and a clear temperature difference between the pattern-formed region and the non-pattern-formed region was observed in thermography images, confirming its ability to function as a transparent film heater.

[0084] Figure 8(a) is an optical microscope image of the geometric pattern made of silver nanowires described above. The upper and lower left of Figure 8(a) are overall images (scale bar: 2 mm) of the two types of geometric patterns (logo marks) formed, respectively, and the upper and lower right of the figure are enlarged images (scale bar: 500 μm) of the areas indicated by the white dotted lines in the images shown on the left. In Figure 8(a), the darker shaded areas are non-patterned areas, and the lighter shaded areas are patterned areas (i.e., areas where silver nanowires are accumulated).

[0085] The upper part of Figure 8(b) is a photographic image (scale bar: 1 cm) showing the application of a constant voltage to both ends of the COP substrate on which the two types of transparent geometric patterns shown in Figure 8(a) were formed, and the lower part of Figure 8(b) is a thermographic image (scale bar: 1 cm) measuring the temperature distribution on the surface of the COP substrate at this time. This thermographic image shows that the patterned region where silver nanowires are accumulated generates heat, making the temperature of the patterned region higher than that of the non-patterned region, and the geometric patterns formed on the COP substrate can be clearly identified.

[0086] Figure 8(c) is a graph showing the details of the temperature distribution in two arbitrary linear regions (Line 1 and Line 2), marked with the numbers "1" and "2" along with dotted lines in the thermographic image at the bottom of Figure 8(b). The horizontal axis represents the measurement position (distance (cm) from the left end of the linear region (length 1 cm)) when the left end is set to zero, and the vertical axis represents the temperature (°C) at that measurement position. The graph in Figure 8(c) also shows a clear temperature difference between the pattern-formed region and the non-pattern-formed region when current is applied, indicating that only the pattern-formed region is uniformly heated.

[0087] (Comparative Example 1) We attempted to form a pattern on the hydrophilic area formed by VUV irradiation using a conventional technique using a zero-dimensional structure. Specifically, a mask with openings and light-shielding areas reversed from the photomask used in the above examples was used, and hexagonal hydrophobic regions and honeycomb-shaped hydrophilic regions were formed on the surface of the COP substrate, with an aqueous dispersion of silver nanoparticles applied by the slit coating method, in an attempt to form a pattern. However, the aqueous dispersion of silver nanoparticles did not spread uniformly over the surface of the substrate, and a liquid film was formed that partially covered the hexagonal hydrophobic regions and the surrounding hydrophilic regions. As a result, silver nanoparticles were deposited in hydrophobic regions where pattern formation was not intended, and it was not possible to successfully form a closed-loop pattern with a honeycomb shape (see Figure 9).

[0088] (Comparative Example 2) An attempt was made to form a honeycomb pattern by following the procedure of the above example, except that ethanol was used as the solvent for the dispersion liquid instead of ultrapure water. However, a closed loop pattern having the desired honeycomb shape was not formed.

[0089] [Analysis of the mechanism of pattern formation] Next, the mechanism of pattern formation according to the above-described embodiment will be described with reference to Figures 10 to 14. This will clarify the mechanism of pattern formation consisting of one-dimensional conductors according to the pattern formation method of the present invention. However, it should be noted that preferred embodiments of the pattern formation method of the present invention are not limited to the substrate, metal nanowires, substrate surface treatment means, etc. used in the examples.

[0090] FIG. 10 is a schematic diagram showing the procedure of the pattern forming method according to the embodiment of the present invention.

[0091] First, in the upper left-hand panel (i) of Figure 10, a photomask having light-shielding portions corresponding to pattern-forming regions and openings corresponding to non-pattern-forming regions is placed on the substrate surface, and vacuum ultraviolet light is irradiated onto the non-pattern-forming regions. The COP substrate used in the examples has a hydrophobic surface and a relatively low surface energy in its untreated state, i.e., it is a low-surface-energy polymer film. The portions of this substrate surface that are not irradiated with VUV become pattern-forming regions, and the portions irradiated with VUV are modified so that the surface energy of the pattern-forming regions becomes smaller than that of the non-pattern-forming regions. Therefore, in the figure, the surface energy of the substrate is represented in parentheses by the symbol γ S -The photomask has light-shielding areas corresponding to the pattern formation areas and hexagonal openings corresponding to the non-pattern formation areas. VUV is irradiated through this photomask (VUV exposure). As a result, hexagonal non-pattern formation areas (hydrophilic pattern) are formed on the surface of the substrate.

[0092] Next, in the center (ii) of the top row of Figure 10, the substrate is treated with an alkaline solution. The figure shows a schematic diagram of the substrate (polymer film) being immersed from left to right in the alkaline solution contained in a container, and the substrate surface being rinsed. This alkaline solution treatment increases (activates) the surface energy of the non-pattern-formed regions formed by VUV irradiation. In other words, the non-pattern-formed regions become regions with higher surface energy than the pattern-formed regions (high-surface-energy regions), and this is indicated by the symbol γ in parentheses. S + It is represented as:

[0093] Next, in (iii) on the upper right side of Figure 10, an aqueous dispersion containing silver nanowires is applied to the substrate surface. The figure shows a schematic diagram of a cross-border overlay, in which a liquid film of the aqueous dispersion containing silver nanowires is formed in an area including both pattern-formed and non-pattern-formed regions by moving a coating bar from left to right using the slit coating method.

[0094] Next, in the lower right-hand side (iv) of Figure 10, the fine flow (internal microflow) in the liquid film of the dispersion is controlled, and the silver nanowires in the liquid film self-assemble in the pattern formation area (AgNW alignment on γ S - regions).

[0095] Next, in the bottom center (v) of Figure 10, the substrate surface is irradiated with intense pulsed light (IPL) to sufficiently dry it, and the silver nanowires that make up the pattern formed in the pattern formation area are selectively sintered together (selective sintering).

[0096] Here, the formation of a liquid film of an aqueous dispersion of silver nanowires on the substrate surface and the spontaneous assembly of silver nanowires in the upper right (iii) and lower right (iv) sections of Figure 10 described above will be explained in three phases, with further reference to Figures 11A, 11B, and 11C.

[0097] [Phase 1] An aqueous dispersion containing silver nanowires is applied to the surface of the substrate and forms a uniform liquid film across patterned and non-patterned areas.

[0098] FIG. 11A is a schematic diagram showing the formation of a liquid film of an aqueous dispersion of silver nanowires on the surface of a substrate in the pattern formation method according to the embodiment of the present invention.

[0099] In the left side (i) of FIG. 11A, the coating bar moves from top to bottom. That is, the application direction (coating direction) of the aqueous dispersion containing silver nanowires to the substrate surface is from top to bottom. In this case, taking into account the wettability of the substrate surface and the surface tension of the dispersion, the pattern formation region (γ S - ) to form hydrophilic non-patterned regions (γ S + ) It is thought that fluid separation occurs in the dispersion liquid.

[0100] On the other hand, in the center (ii) of Figure 11A, silver nanowires are dispersed in the dispersion liquid, and capillary force acts between the dispersed silver nanowires (Dispersed AgNWs), causing fluid coalescence between adjacent non-pattern-formed regions via the pattern-formed region.

[0101] As a result, in (iii) on the right side of Figure 11A, the aqueous dispersion containing silver nanowires applied to the substrate surface spreads almost uniformly over an area including both the pattern-formed and non-pattern-formed regions, forming a liquid film of the aqueous dispersion of silver nanowires (fluid overlay). Furthermore, at this time, a flow that the inventors call instantaneous flow (see (iii) in Figure 11B described below) occurs in the liquid film in the coating direction of the aqueous dispersion, and the silver nanowires in the liquid film are generally aligned in the direction of this flow (aligned AgNWs).

[0102] [Phase 2] The dispersion (distribution) of the flow field causes the settling and placement of silver nanowires.

[0103] Here, in order to analyze the micro-flow (hydrodynamic behavior) in the liquid film of the aqueous dispersion of silver nanowires formed on the surface of the substrate, the inventors performed a simulation using fluid analysis software (ANSYS FLUENT 2021 R1).

[0104] The calculation domain of the fluid simulation (liquid domain) is the pattern formation region (γ S - ) on both sides of the non-patterned region (γ S + A liquid film formed on the surface of a substrate with a liquid surface.

[0105] The mass flow rate was calculated from the measured coating speed and the thickness of the liquid film to be 0.5 g / s. Considering that the liquid flows over the substrate surface whose properties change regularly, this measured value of the mass flow rate was used as a periodic boundary condition with translational symmetry.

[0106] FIG. 11B is a schematic diagram showing the fine flow in the liquid film of the aqueous silver nanowire dispersion formed on the substrate surface, and the fixing and placement of the silver nanowires, in the pattern formation method according to the embodiment of the above example.

[0107] The upper left (i) and upper right (ii) of Figure 11B show the distributions of velocity amplitude and pressure amplitude obtained for the simulation region described above. In each figure, darker shaded areas indicate lower velocity or pressure, and lighter shaded areas indicate higher velocity or pressure.

[0108] Note that (i) and (ii) in Figure 11B show only a portion of the simulation region. Specifically, in the x direction, the center of the pattern-formed region is zero, and the pattern-formed region is a range of 50 μm to the left and right, and the non-pattern-formed region is a range of 150 μm from both ends of this pattern-formed region. In other words, the range of the x axis is a range of 200 μm to the left and right, with the center zero as the reference. Furthermore, the y direction represents the simulation results when the height (thickness) of the liquid film is 250 μm. In addition, please note that in Figure 11B, the flow direction in the liquid film induced in the coating direction is from left to right (different from the coating direction shown in Figure 11A).

[0109] From the diagrams (i) and (ii) of FIG. 11B, the non-patterned region (γ S + The dispersion liquid flowing over the pattern formation region (γ S -), the pressure near the pattern formation area (small value of y) increases, and the flow velocity in the dispersion liquid decreases above the pattern formation area. S - ) and the dispersion liquid flows over the non-patterned area (γ S + ) reaches the non-patterned region (γ S + ) (small value of y), and the flow velocity of the dispersion liquid is high on the non-patterned area.

[0110] The lower panel (iii) of Figure 11B shows a schematic diagram of the behavior of silver nanowires in the dispersion liquid caused by this series of localized flows of the dispersion liquid.

[0111] As shown in this figure, when the dispersion moves along the application direction (coating direction) of the dispersion, the non-patterned area (γ S + In the figure, a velocity-field-induced inertia force, which is greater than the downward gravitational force, acts laterally (to the right in the figure) on the silver nanowires (AgNWs) in the dispersion (referred to as ink in the figure for convenience), causing the silver nanowires to pass through the non-patterned region. On the other hand, in the patterned region (γ S - ), high pressure is applied to the liquid near the surface, which reduces the velocity-field-induced inertial force of the silver nanowires in (or near) that area, and the gravity vector becomes relatively large, leading the silver nanowires to be guided onto the pattern formation area and anchored. This phenomenon is the anchoring of silver nanowires in the pattern formation area. However, among the countless silver nanowires dispersed in the dispersion liquid, some pass through the pattern formation area without changing their position, and they may become anchored when they reach the next or further pattern formation area.

[0112] [Phase 3] Silver nanowires transported by convection caused by evaporation of the solvent in the dispersion liquid are settled and placed on the silver nanowires that have been settled and placed in the pattern formation area.

[0113] In the patterned regions where the silver nanowires have been fixed and positioned as described with reference to (iii) of Figure 11B, and in the adjacent non-patterned regions, the solvent of the dispersion evaporates under the conditions under which the dispersion is applied (usually room temperature).

[0114] Figure 11C is a schematic diagram showing the phenomenon that occurs in the liquid film when the solvent of such a dispersion evaporates, more specifically, the spontaneous aggregation of silver nanowires that move by convection in the liquid film of the aqueous dispersion of silver nanowires formed on the surface of the substrate in the pattern formation method according to the embodiment of the above example.

[0115] As shown on the left side (i) of Figure 11C, when the solvent of the dispersion liquid (ink) applied to the substrate surface evaporates (diffuses into the air), a driving force is generated by the buoyancy force acting from the low density part to the high density part of the liquid film (fluid), and Rayleigh-Benard convection occurs. At this time, the silver nanowires floating in the liquid film (transported by convection) have already reached the pattern formation region (γ S - ) are captured by the silver nanowires that have been fixed and placed on the patterned area. This leads to further accumulation (aggregation) of silver nanowires on the patterned area. Although the figure is shown schematically, the Rayleigh-Bénard convection occurs at a different angle to the already fixed and placed silver nanowires, so the capture of another silver nanowire by a fixed and placed silver nanowire tends to occur in a manner that the other silver nanowire crosses the length of the fixed and placed silver nanowire.

[0116] Next, as shown in (ii) on the right side of Figure 11C, as the solvent in the dispersion liquid (Ink) further evaporates, nonuniform surface tension occurs. A surface tension force due to the difference in surface tension acts from areas with relatively low surface tension to areas with high surface tension, resulting in convection due to the Marangoni effect. At this time, the silver nanowires floating in the liquid film (transported by convection) are further captured by the silver nanowires accumulated on the settled / fixed silver nanowires. This results in further accumulation (aggregation) of silver nanowires on the pattern formation area. Although the figure is shown schematically, the further capture of silver nanowires by the accumulated silver nanowires tends to occur in a manner that causes further accumulation of silver nanowires approximately parallel to the length of the silver nanowires accumulated by Rayleigh-Bénard convection. In addition, when we simulated the process of silver nanowire accumulation, we found that the direction of silver nanowire accumulation due to Rayleigh-Bénard convection and the direction of further silver nanowire accumulation due to Marangoni convection could be opposite to each other. This phenomenon was also confirmed in the actual experiments conducted in the above examples.

[0117] As described above, in the pattern formation method according to the present invention, when an aqueous dispersion containing a one-dimensional conductor is applied to a substrate, the difference in surface energy between the pattern-forming region and the non-pattern-forming region formed on the substrate causes self-assembly of the one-dimensional conductor into the pattern-forming region.

[0118] Here, the inventors performed another simulation using the above-mentioned fluid analysis software, analyzing using a simplified model that does not consider the presence of solutes (dispersoids) in the dispersion. In this model, the dispersion applied to the substrate surface by the slit coating method was assumed to be a laminar flow, and the coating speed (movement speed of the coating bar) was assumed to be constant (10 cm / s). As a result, the surface energy γ of the pattern formation region was A and the surface energy of the non-patterned region γ B The difference between [γ B -γ AIt was suggested that when [ ] is within a certain range, the velocity gradient of the dispersion in the non-patterned region becomes nearly zero, and the velocity becomes the lowest in all patterned regions (data not shown). This means that the sample fabricated in this state produces the cleanest pattern, i.e., a pattern in which one-dimensional conductors are substantially integrated only in the patterned region. Therefore, for convenience, the inventors have decided to refer to the sample fabricated in this state as an onside-patterned film (OPF).

[0119] In addition, in this simplified model, the surface energy of the patterned region, γ A and the surface energy of the non-patterned region γ B The difference between [γ B -γ A If [γ ] is outside the desired range, it is difficult to obtain the lowest flow velocity in the dispersion liquid in the pattern formation region. B -γ A ] is smaller than the desired range, when the dispersion moves with the movement of the coating bar, the local flow velocity in the dispersion becomes the lowest at a position before the pattern formation region, and [γ B -γ AWhen [ ] is higher than the desired range, the flow velocity in the dispersion is lowest at a position beyond the pattern-forming region. This suggests that if samples are fabricated under these conditions, the one-dimensional conductors will settle and settle even in the non-pattern-forming region, making it impossible to draw the desired pattern. Therefore, to describe these conditions, we have named samples fabricated under the conditions below the lower limit and above the upper limit of the OPF condition range as begin-to-pattern films (BPF) and begin-to-overcoat films (BOF), respectively, and samples fabricated under the conditions significantly below the lower limit and significantly above the upper limit as overcoated films (OF).

[0120] On the other hand, as mentioned above, this simplified model does not precisely consider the influence of the presence of dispersoids (one-dimensional conductors) contained in the fluid, and it should be noted that there may be an error in the behavior of an actual aqueous dispersion containing one-dimensional conductors. According to preliminary experiments by the present inventors, the longer the length of the silver nanowires contained in an aqueous dispersion containing silver nanowires, the greater the surface tension γ L It is known that the surface energy γ of the patterned region tends to decrease, and the contact angle θ of the droplet dropped on the surface of any substrate also tends to decrease accordingly. A and the surface energy of the non-patterned region γ B The difference between [γ B -γ A It can be understood that this suggests that by appropriately adjusting [ ], it is possible to set OPF conditions suitable for the aqueous dispersion containing the one-dimensional conductor used.

[0121] For example, in an embodiment in which VUV irradiation is used as a means for treating the substrate surface, as in the embodiment of the above example, assuming that the one-dimensional conductor is a silver nanowire with a length in the range of 20 μm to 100 μm, the relationship between VUV irradiation time and the length of the silver nanowire can be expressed as shown in Figure 12. Here, the horizontal axis of Figure 12 represents the VUV irradiation time (Exposure time, unit: seconds), and the vertical axis represents the length of the silver nanowire (L AgNW , unit: μm).

[0122] As shown in FIG. 12 , for example, when the length of the silver nanowire is 50 μm, the VUV irradiation time that satisfies the OPF condition can be in the range of approximately 100 seconds to approximately 250 seconds. This range can be appropriately adjusted taking into account other conditions, such as the concentration of the aqueous dispersion containing the silver nanowire. Furthermore, when the length of the silver nanowire is 20 μm, the OPF condition can be achieved within a shorter VUV irradiation time range than when the length of the silver nanowire is 50 μm. This is because when the length of the silver nanowire is short, the silver nanowire has a light mass and a small surface area, so even if the difference in surface energy between the pattern-formed region and the non-pattern-formed region is relatively small, a driving force for guiding the silver nanowire to the desired pattern-formed region can be obtained. On the other hand, when the length of the silver nanowire is 100 μm, the OPF condition can be achieved within a longer VUV irradiation time range than when the length of the silver nanowire is 50 μm. In this case, because the mass of the silver nanowire is relatively heavy, it can be said that by extending the VUV irradiation time, a difference in surface energy between the pattern-formed region and the non-pattern-formed region sufficient to guide the silver nanowire to the desired pattern-formed region can be created.

[0123] Figure 13 shows data related to the preliminary experiment described above, which shows the results of measuring the contact angle θ of a water droplet on the COP substrate when water (2.0 μL) was dropped onto the COP substrate while changing the VUV irradiation time on the COP substrate.

[0124] Explaining the OPF conditions using the water contact angle θ shown in Figure 13, it is preferable to set the VUV irradiation time so that the value of θ is in the range of approximately 60° to approximately 70°. On the other hand, if the value of θ exceeds 70° or is below 60°, the OPF conditions are not met, making it difficult for the silver nanowires to be fixed and placed at the intended positions, and forming the desired pattern on the pattern formation area.

[0125] Here, the orientation of the one-dimensional conductor will be described with reference to FIG.

[0126] Here, we consider the case where there is a pattern formation region (whose width is arbitrary) that extends in the same direction as the fluid flow when an aqueous dispersion containing a one-dimensional conductor is applied, i.e., the direction in which the dispersion is applied.

[0127] Interestingly, in the pattern formation method according to the present invention, the settling and placement of the one-dimensional conductor, which corresponds to the above-mentioned Phase 2, occurs in a state where the one-dimensional conductor is oriented in the same direction as the coating direction of the dispersion, i.e., parallel to the direction in which the pattern formation region extends (parallel alignment) (see (i) on the left side of Figure 14). This can be explained by the dispersion (distribution) of the instantaneous flow field generated in the coating direction (see (ii) on the right side of Figure 14, bottom panel).

[0128] Furthermore, regarding the orientation of such one-dimensional conductors, in other words, by analyzing the microstructure of the formed pattern and confirming the orientation state of the one-dimensional conductors near the substrate surface, it is possible to estimate the flow direction of the aqueous dispersion containing the one-dimensional conductors during the manufacturing process.

[0129] Furthermore, the settling of one-dimensional conductors, which corresponds to the above-mentioned phase 3, can be explained by roughly dividing it into two stages.

[0130] In the first stage, the 1D conductor captured by the previously fixed 1D conductor is oriented so as to intersect with the orientation of the fixed 1D conductor (for convenience, in Fig. 14(i), we use the expression "perpendicular alignment" in contrast to the above-mentioned "parallel alignment"). This can be explained by the fact that, as mentioned above, Rayleigh-Benard convection caused by the evaporation of the dispersion solvent occurs at a different angle to the previously fixed silver nanowire, and the direction of the velocity vector generated in the 1D conductor floating in the liquid film (transported by convection) intersects with the orientation of the fixed 1D conductor (see the middle panel of Fig. 14(ii)).

[0131] The second stage, which follows, involves further accumulation of the 1D conductors as the evaporation of the dispersion solvent progresses. This is caused by the flow of 1D conductors due to Marangoni convection, which is approximately 180° opposite to the alignment direction of the 1D conductors captured in the first stage. As a result, although the nanowires appear to have the same perpendicular alignment in the first and second stages, the processes involved are completely different. This can be explained by the reversal of the velocity vectors of the 1D conductors in the liquid film due to the Marangoni convection that replaces the Rayleigh-Bénard convection in the first stage (see Figure 14(ii) top).

[0132] The image inserted at the top of (i) in Figure 14 is an SEM image (scale bar: 2 µm) showing the cross-linked alignment of silver nanowires in the pattern (Example 2) obtained in the above-mentioned example. In the pattern formed by the pattern formation method according to the present invention, the orientation of the one-dimensional conductor is controlled during the process of self-assembly of the one-dimensional conductor on the pattern formation region, and a desired pattern is formed, so that a pattern can be obtained that is likely to fully exhibit the properties of the one-dimensional conductor. [Industrial Applicability]

[0133] The pattern formation method according to the present invention makes it possible to easily form patterns of various shapes, including closed loop shapes, on any substrate, which was difficult to achieve with conventional techniques. For example, when a flexible and transparent substrate is used, the substrate on which a pattern made of one-dimensional conductors is formed according to the present invention can be applied as a high-performance flexible transparent conductor. Furthermore, by appropriately changing the type and properties of the one-dimensional conductor used, applications such as high-efficiency solar cells, touch panels, and smart windows can be realized.

Claims

1. The substrate surface is treated in either or both of the patterned and non-patterned regions, and the surface energy γ Ａ is the surface energy of the non-patterned area, γ Ｂ and the surface energy γ of the patterned region Ａ and the surface energy of the non-patterned region γ Ｂ The difference between [γ Ｂ -γ Ａ ] at 5 mJ / m ２ 25mJ / m or more ２ The following ranges shall be met: applying an aqueous dispersion containing a one-dimensional conductor to the surface of the substrate to form a liquid film of the aqueous dispersion of the one-dimensional conductor in an area including a pattern formation area and a non-pattern formation area; It encompasses a minute flow in the liquid film is controlled to cause one-dimensional conductors moving by convection in the liquid film to self-assemble in the pattern formation region, thereby forming a predetermined pattern; A method for forming a pattern using one-dimensional conductors.

2. The method of claim 1 , wherein the treatment comprises irradiating with vacuum ultraviolet light.

3. 3. The method according to claim 2, wherein a photomask having openings corresponding to non-pattern-forming regions is placed on the surface of the substrate, which is hydrophobic in an untreated state, and the non-pattern-forming regions are irradiated with vacuum ultraviolet light.

4. 4. The method according to claim 2, wherein after the irradiation with vacuum ultraviolet light, either one or both of the patterned region and the non-patterned region are further treated with an alkaline solution.

5. The method of claim 1 , further comprising heating the patterned substrate to sinter the one-dimensional conductor.

6. The method according to claim 1 , wherein the length of the one-dimensional conductor is in the range of 10 μm to 250 μm.

7. The surface tension γ of the aqueous dispersion containing the one-dimensional conductor Ｌ is 25 mJ / m ２ 50mJ / m or more ２ 7. The method of any one of claims 1 to 6, wherein the range is:

8. 8. The method of claim 1, wherein the one-dimensional conductor is selected from the group consisting of metal nanowires, metal oxide nanowires, polymer nanowires, silicon nanowires, carbon nanotubes, and combinations thereof.

9. 9. The method of claim 1, wherein the substrate is selected from the group consisting of cycloolefin polymer (COP), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide (PI), polyethersulfone (PES), polycarbonate (PC), and polydimethylsiloxane (PDMS).

10. 10. The method of claim 1, wherein the aqueous dispersion containing the one-dimensional conductor is applied to the substrate surface using a method selected from the group consisting of dip coating, spin coating, roll coating, and slit coating.

11. The method according to claim 10, wherein the aqueous dispersion containing the one-dimensional conductor is applied to the surface of the substrate using a slit coating method at a coating speed in the range of 0.5 cm / s to 30 cm / s.

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