JP2016107229A - Transparent conductive base material manufacturing method, coating liquid for forming transparent conductive layer, and transparent conductive base material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a transparent conductive base material having no anisotropic conductivity, a transparent conductive layer formation coating liquid used for the same, and a transparent conductive base material.SOLUTION: The method for manufacturing a transparent conductive base material includes the coating step of coating a transparent base material with a transparent conductive layer formation coating liquid containing at least a metal fiber, a first solvent, and a second solvent, the boiling point of the first solvent being within the range of 50°C to 95°C, the boiling point of the second solvent being higher than that of the first solvent, the blending ratio of the first solvent and the second solvent being within the range of 20 mass%: 80 mass% to 70 mass: 30 mass%, and a solid concentration being within the range of 0.1 mass% to 2.0 mass% to form a transparent conductive layer forming layer, the first drying step of drying the transparent conductive layer forming layer on the transparent substrate at 40°C to remove the first solvent, and the second drying step of drying the transparent conductive layer forming layer after the first drying step to remove the second solvent, and forming a transparent conductive layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a transparent conductive substrate having a transparent conductive layer containing metal fibers, and the like.

Conventionally, a transparent conductive layer made of a transparent and conductive thin film has been used as a transparent electrode for displays such as LCDs and PDPs, touch panels and solar cells. As the transparent conductive substrate having this transparent conductive layer, a layer obtained by laminating a transparent conductive layer made of indium tin oxide (ITO) or the like (hereinafter simply referred to as an ITO film) on a transparent resin substrate is used. Has been.
However, as a method for forming such an ITO film, there is a problem that a vacuum process such as sputtering is required and the production cost is high, and it is necessary to perform baking at a high temperature in order to make the ITO film have desired conductivity. For this reason, there has been a problem that there are significant restrictions on materials such as transparent resin base materials. Furthermore, there is a problem that the ITO film is easily broken and cannot be used for applications requiring flexibility.

  For such problems, the use of metal nanowires as a conductive material instead of ITO has been studied. For example, Patent Document 1 discloses a transparent conductive substrate in which a transparent conductive layer containing a metal nanowire and a binder resin that fixes the metal nanowire is formed on a transparent resin substrate.

International Publication No. 2010/106899 Pamphlet

  As a method for forming a transparent conductive layer containing metal nanowires on a transparent substrate, for example, an ink in which metal nanowires and a binder resin are dispersed in a solvent (hereinafter, sometimes referred to as metal nanowire ink) is used. A solution coating method is used in which the coating is performed in one direction on the surface of the transparent substrate with a taper or the like. However, when such a coating method is used, the major axis (length direction) of the metal nanowire tends to be oriented along the coating direction, and the distribution of the conductive paths formed in the transparent conductive layer is not dense. Therefore, there is a problem that anisotropy occurs in the conductivity.

That is, as shown in FIG. 5, when the metal nanowire ink 111 is applied using the die coater D while the transparent base material 102 is conveyed, the metal nanowire 112 is easily oriented along the application direction X. That is, it is easy to align along the longitudinal direction (MD direction in FIG. 5) of the transparent substrate 102 corresponding to the coating direction X, and it is difficult to align in the short direction (TD direction in FIG. 5). For this reason, as shown in FIG. 6, the obtained transparent conductive substrate 100 has a transparent conductive layer 101 in which the major axis of the metal nanowire 112 is oriented along the longitudinal direction of the transparent substrate 102 (MD direction in FIG. 6). It will have.
In the transparent conductive layer 101, the metal nanowires 112 are connected to each other with the contact C, and the conductive path P is formed, so that the conductivity is improved. Here, when the metal nanowire 112 has the above-mentioned orientation, the conductive path P is easily formed in the same direction as the orientation direction, but in the direction orthogonal to the orientation direction (TD direction in FIG. 6), the metal nanowire 112 cannot be connected, and the conductive path P is not easily formed. For this reason, the distribution of the conductive paths P in the transparent conductive layer 101 becomes coarse and dense, and the conductivity becomes anisotropic.
FIG. 5 is an explanatory diagram for explaining a general metal nanowire ink application process, and FIG. 6 is a schematic plan view showing an example of a conventional transparent conductive substrate.

  In various devices, the transparent electrode is generally formed in a pattern. However, when forming a transparent electrode by patterning a transparent conductive layer having conductivity anisotropy, there is a difference in conductivity even in the transparent electrode. There is a problem that a problem occurs in conduction.

  The present invention has been made in view of the above problems, and includes a method for producing a transparent conductive base material having no anisotropy in conductivity, a coating liquid for forming a transparent conductive layer used therefor, and a transparent conductive base material. The main purpose is to provide.

  In order to achieve the above object, the present invention includes at least a metal fiber, a first solvent, and a second solvent, wherein the boiling point of the first solvent is in the range of 50 ° C to 95 ° C, The boiling point is higher than the boiling point of the first solvent, the blending ratio of the first solvent and the second solvent is in the range of 20% by mass: 80% by mass to 70% by mass: 30% by mass, and the solid content concentration A transparent conductive layer is formed by applying the transparent conductive layer-forming coating solution on a transparent substrate using a transparent conductive layer-forming coating solution in the range of 0.1% by mass to 2.0% by mass. A coating step for forming a layer, a first drying step for drying the transparent conductive layer forming layer on the transparent substrate at 40 ° C. or less to remove the first solvent, and the transparent after the first drying step. A second drying step of drying the conductive layer forming layer to remove the second solvent and forming a transparent conductive layer; It provides a method for producing a transparent conductive substrate, characterized by.

  According to the present invention, by performing drying at a desired temperature in the first drying step, the metal fibers can flow and diffuse due to spontaneous volatilization of the first solvent, and the metal fibers can be randomly oriented. In addition, by performing drying at a temperature at which the second solvent evaporates in the subsequent second drying step, the random orientation of the metal fibers can be fixed and held. Thereby, the transparent conductive base material without anisotropy in electroconductivity can be manufactured.

  Moreover, this invention contains a metal fiber, a 1st solvent, and a 2nd solvent at least, the boiling point of the said 1st solvent exists in the range of 50 to 95 degreeC, and the boiling point of the said 2nd solvent is the said 1st solvent. It is higher than the boiling point, the blending ratio of the first solvent and the second solvent is in the range of 20% by mass: 80% by mass to 70% by mass: 30% by mass, and the solid content concentration is 0.1% by mass to Provided is a coating liquid for forming a transparent conductive layer, which is within a range of 2.0% by mass.

  According to the present invention, the coating liquid for forming a transparent conductive layer having the above-mentioned composition can randomly orient metal fibers by spontaneously volatilizing or heating and evaporating two kinds of solvents using the difference in boiling points. In addition, since the orientation can be fixed and held, a transparent conductive layer having no conductivity anisotropy can be formed.

  Moreover, this invention has a transparent base material and the transparent conductive layer which is formed on the said transparent base material and contains a metal fiber at least, and the electrical resistivity which one direction on planar view shows the said transparent conductive layer The transparent conductive substrate is characterized in that the ratio of the electrical resistivity indicated by the other direction orthogonal to the one direction is within the range of 0.75 to 1.25.

  According to this invention, it can be set as the transparent conductive base material without electroconductivity.

  In this invention, there exists an effect that the transparent conductive base material without anisotropy in electroconductivity can be manufactured.

It is process drawing which shows an example of the manufacturing method of the transparent conductive base material of this invention. It is a schematic sectional drawing which shows an example of the transparent conductive base material of this invention. It is the schematic sectional drawing and the top view which show the other example of the transparent conductive base material of this invention. It is explanatory drawing explaining the aspect of the transparent conductive layer in this invention. It is explanatory drawing for demonstrating the application | coating process of general metal nanowire ink. It is a schematic plan view which shows an example of the conventional transparent conductive base material.

  Hereinafter, the manufacturing method of the transparent conductive base material of this invention, the coating liquid for transparent conductive layer formation, and a transparent conductive base material are demonstrated in detail.

A. The manufacturing method of a transparent conductive base material The manufacturing method of the transparent conductive base material of this invention contains a metal fiber, the 1st solvent, and the 2nd solvent at least, and the boiling point of the said 1st solvent is in the range of 50 to 95 degreeC. Yes, the boiling point of the second solvent is higher than the boiling point of the first solvent, and the blending ratio of the first solvent and the second solvent ranges from 20% by mass to 80% by mass to 70% by mass to 30% by mass. The transparent conductive layer forming coating solution is formed on a transparent substrate using a transparent conductive layer forming coating solution having a solid content concentration in the range of 0.1% by mass to 2.0% by mass. A coating step of coating to form a transparent conductive layer forming layer; a first drying step of drying the transparent conductive layer forming layer on the transparent substrate at 40 ° C. or less to remove the first solvent; 1) The transparent conductive layer forming layer after the drying step is dried to remove the second solvent, and a transparent conductive layer is formed. And a second drying step.

The manufacturing method of the transparent conductive base material of this invention is demonstrated referring drawings. FIG. 1 is a process diagram showing an example of a method for producing a transparent conductive substrate of the present invention. FIG. 2 is a schematic cross-sectional view of FIG. 1E, that is, a schematic cross-sectional view showing an example of a transparent conductive substrate obtained by the production method of the present invention.
First, a transparent conductive layer forming coating solution containing at least a metal fiber, a first solvent, and a second solvent is prepared. The coating liquid for forming a transparent conductive layer comprises a first solvent having a boiling point in the range of 50 ° C. to 95 ° C. and a second solvent having a boiling point higher than the boiling point of the first solvent, with a blending ratio of 20% by mass: 80%. % To 70% by mass: prepared to be in the range of 30% by mass. Moreover, the coating liquid for transparent conductive layer formation is prepared so that solid content concentration may be in the range of 0.1 mass%-2.0 mass%.
Next, a transparent conductive layer forming coating solution is applied on the transparent substrate 2 using the die coater D to form the transparent conductive layer forming layer 11 (FIG. 1A). At this time, the long axis of the metal fiber 12 in the transparent conductive layer forming layer 11 is oriented along the coating direction X.
Subsequently, the transparent conductive layer forming layer 11 on the transparent substrate 2 is dried at a drying temperature T1 of 40 ° C. or less to remove the first solvent contained in the transparent conductive layer forming layer 11 (FIG. 1B). (C)). At this time, since the drying temperature T1 is lower than the boiling point of the first solvent, spontaneous volatilization of the first solvent occurs. Here, since the coating liquid for forming the transparent conductive layer has a low solid content concentration and viscosity, the metal fiber 12 in the transparent conductive layer forming layer 11 flows and diffuses in the layer in the process of volatilization of the first solvent. The Thereby, the metal fibers 12 can be randomly oriented (FIG. 1C).
Thereafter, the transparent conductive layer forming layer 11 ′ on the transparent substrate 2 after the first drying step is dried at the drying temperature T2 to remove the second solvent contained in the transparent conductive layer forming layer 11 ′ (FIG. 1). (D), (e)). At this time, in the evaporation process of the second solvent, the random orientation of the metal fibers 12 is fixed, so that the transparent conductive layer 1 in which the random orientation is maintained is formed, and the transparent conductive substrate 10 is obtained (see FIG. 1 (e), FIG. 2).
1A corresponds to the coating process, FIGS. 1B and 1C correspond to the first drying process, and FIGS. 1D and 1E correspond to the second drying process.

  According to the present invention, a transparent conductive layer forming layer formed by applying a coating solution for forming a transparent conductive layer having a low solid content concentration is dried at a desired temperature in the first drying step. Due to spontaneous volatilization of one solvent, metal fibers flow and diffusion occurs in the layer, and the metal fibers can be randomly oriented. In addition, by performing drying at a temperature at which the second solvent evaporates in the subsequent second drying step, the random orientation of the metal fibers can be fixed and held. Since the metal fibers are randomly oriented in the transparent conductive layer, the transparent conductive layer can exhibit high conductivity (electrical conductivity) regardless of the in-plane direction. For this reason, the transparent conductive base material without anisotropy in electroconductivity can be manufactured.

  Hereinafter, each process in the manufacturing method of the transparent conductive base material of this invention is demonstrated.

1. Coating step The coating step in the present invention is a step of forming a transparent conductive layer forming layer by applying the transparent conductive layer forming coating solution on a transparent substrate using a desired transparent conductive layer forming coating solution. is there.

(1) Transparent conductive layer forming coating solution The transparent conductive layer forming coating solution used in this step contains at least a metal fiber, a first solvent and a second solvent, and the boiling point of the first solvent is 50 ° C. The boiling point of the second solvent is higher than the boiling point of the first solvent, and the blending ratio of the first solvent and the second solvent is 20% by mass: 80% by mass to 70% by mass. %: It is in the range of 30% by mass, and the solid content concentration is in the range of 0.1% by mass to 2.0% by mass.

In the process of drying the transparent conductive layer forming layer, the coating liquid for forming the transparent conductive layer in the present invention has a solid content concentration in order to randomize the orientation of the metal fibers by flowing and diffusing the metal fibers. It is characterized by containing two types of solvents, a low and low boiling point first solvent and a high boiling point second solvent. This is because the solid content concentration of the coating liquid for forming a transparent conductive layer is low, and by using the difference in boiling point between the two types of solvents, the first solvent having a low boiling point is volatilized first to form a metal fiber. Can exhibit high fluidity and can be diffused and oriented at random, and by evaporating the second solvent with a high boiling point, the random orientation of the metal fibers can be fixed while preventing aggregation of the metal fibers. This is because the orientation can be maintained.
Here, when the solvent contained in the coating liquid for forming a transparent conductive layer is only the first solvent having a low boiling point, the first solvent is spontaneously volatilized quickly, so that the metal fibers are aggregated at the time of diffusion, resulting in variation in conductivity. May occur. On the other hand, when the solvent contained in the coating liquid for forming the transparent conductive layer is only the second solvent having a high boiling point, the metal fibers are aggregated due to the heating temperature for evaporating the second solvent, and there is a variation in conductivity. It may occur or conductivity may be reduced. For this reason, the coating liquid for transparent conductive layer formation in this invention contains two types of solvents from which boiling points differ, and adjusts the removal conditions of each solvent in the 1st drying process and 2nd drying process which are mentioned later. Is required.

  Hereinafter, each component of the coating liquid for forming a transparent conductive layer will be described.

(A) 1st solvent and 2nd solvent The coating liquid for transparent conductive layer formation contains the 1st solvent of a low boiling point, and the 2nd solvent of a high boiling point.

(I) 1st solvent A 1st solvent is a solvent which shows the boiling point within the range of 50 to 95 degreeC, and shows a boiling point within the range of 60 to 90 degreeC especially in the range of 70 to 85 degreeC. A solvent is preferred. If the boiling point of the first solvent is larger than the above range, the first solvent is less likely to volatilize naturally in the first drying step, and the metal fibers are less likely to flow and diffuse. For this reason, metal fibers do not exhibit random orientation, and anisotropy may occur in the conductivity of the obtained transparent conductive substrate. On the other hand, if the boiling point of the first solvent is smaller than the above range, the metal fibers may vigorously flow and diffuse during spontaneous volatilization of the first solvent, and the metal fibers may easily aggregate.

  Although it does not specifically limit as a 1st solvent which has the above-mentioned boiling point, Usually, a polar solvent is used. Specific examples include isopropyl alcohol (IPA), ethanol, methanol, propanol and the like.

(Ii) Second solvent The second solvent is a solvent having a boiling point higher than that of the first solvent. Specifically, the boiling point of the second solvent is preferably in the range of 100 ° C to 200 ° C, more preferably in the range of 120 ° C to 180 ° C, and particularly preferably in the range of 130 ° C to 160 ° C. When the boiling point of the second solvent is larger than the above range, metal fiber aggregates are easily formed due to the drying temperature when the second solvent is evaporated, and the aggregates are contained in the transparent conductive layer. In some cases, the conductivity of the transparent conductive substrate obtained by the production method of the invention varies, and the conductivity may decrease. On the other hand, if the boiling point of the second solvent is smaller than the above range, volatilization of the second solvent also occurs in the first drying step, so that the diffusion time of the metal fiber due to the volatilization of the solvent becomes long and the aggregation of the metal fiber occurs. It may be easier.

  The second solvent having the above boiling point may be any solvent that does not significantly deteriorate the dispersibility of the metal fibers and does not significantly deteriorate the affinity with the first solvent, and a polar solvent is usually used. Examples of such a solvent include water, n-butanol, dioxane, cyclohexanone, ethylene glycol, propylene glycol and the like.

(Iii) Others The blending ratio of the first solvent and the second solvent (first solvent: second solvent) is in the range of 20% by mass: 80% by mass to 70% by mass: 30% by mass, especially 25 The mass% is preferably in the range of 75 mass% to 60 mass%: 40 mass%, particularly preferably in the range of 30 mass%: 70 mass% to 45 mass%: 55 mass%. If the blending ratio of the first solvent and the second solvent is smaller than the above range, the amount of the second solvent becomes excessive, so that the metal fibers are less likely to flow and diffuse in the first drying step. Anisotropy may occur in the conductivity of the transparent conductive substrate obtained without showing random orientation. Also, if the amount of the second solvent is excessive, the metal fibers will flow again and diffuse in the second drying step, so that random orientation cannot be maintained, or the second solvent is dried to evaporate the second solvent. It may be necessary to lengthen the time and the like, and the metal fibers may easily aggregate. On the other hand, if the blending ratio of the first solvent and the second solvent is larger than the above range, the amount of the first solvent becomes excessive, so that the metal fibers excessively flow and diffuse in the first drying step. In some cases, metal fibers tend to aggregate.

(B) Metal fiber Examples of the metal fiber contained in the transparent conductive layer forming coating solution include metal nanowires, metal microwires, metal nanotubes, and metal microtubes. Especially, since it is excellent in transparency and electroconductivity, metal nanowire is preferable.

  Examples of the material constituting the metal fiber include metals, alloys, and metal oxides. Specifically, silver, copper, gold, platinum, nickel, palladium, rhodium, iridium, ruthenium, osmium, iron, cobalt, tin, manganese, molybdenum, tungsten, niobium, tantalum, titanium, bismuth, antimony, lead, or These alloys etc. are mentioned. Moreover, ZnO etc. are mentioned. A metal fiber may be used individually by 1 type, and 2 or more types may be mixed and used for it.

Moreover, the metal nanowire and the metal microwire may have a core-shell structure. For example, it is possible to use silver as a core and gold, platinum, palladium, or copper as a shell. In this case, since silver is covered with any of the metals that become the shell described above, oxidation of silver can be suppressed and good conductivity can be obtained.
Further, although depending on the type of metal constituting the metal fiber, the surface of the metal fiber may be oxidized.

The average diameter of the metal fiber is appropriately adjusted according to the form of the metal fiber, the use of the transparent conductive substrate, and the like, for example, within a range of 0.1 nm to 1 mm, and particularly within a range of 0.1 nm to 100 μm. preferable. In the case of metal nanowires, the average diameter is preferably in the range of 1 nm to 100 nm, more preferably in the range of 10 nm to 80 nm, particularly in the range of 20 nm to 60 nm, and further preferably in the range of 40 nm to 60 nm.
When the diameter of the metal fiber is within the above range, conductivity and transparency can be ensured.

  In addition, the average length of the metal fibers may be sufficiently larger than the average diameter of the metal fibers, and is appropriately adjusted according to the form of the metal fibers, the use of the transparent conductive substrate, and the like. In the case of metal nanowires, the average length is preferably in the range of 50 nm to 1000 μm, and more preferably in the range of 50 nm to 500 μm. If the length of the metal fiber is long, a long conductive path can be formed with one metal fiber.

The metal fiber preferably has a large aspect ratio (length of metal fiber / diameter of metal fiber). This is because by increasing the aspect ratio, it is possible to effectively form a contact point between metal fibers, and the obtained transparent conductive layer can exhibit high transparency and a low haze value.
As a specific aspect ratio, for example, in the case of metal nanowires, a range of 100 to 5000 is preferable. When the aspect ratio of the metal nanowire is smaller than the above range, the contact between the metal nanowires cannot be effectively formed, and the obtained transparent conductive layer exhibits a high surface resistivity. Furthermore, since the light absorption and reflection components of the transparent conductive layer obtained increase, the light transmission tends to decrease. On the other hand, when the aspect ratio of the metal nanowire is larger than the above range, it takes time to refine the metal nanowire, resulting in poor productivity, and clogging is likely to occur at the discharge port of the die head or the like during coating. .

  The diameter and length of the metal fiber and the aspect ratio can be measured using, for example, a transmission electron microscope.

  The method for producing the metal fiber is not particularly limited as long as it is a known method.

The content of the metal fiber in the coating liquid for forming the transparent conductive layer is such that the dispersion stability of the metal fiber is good and the formed transparent conductive layer can exhibit the desired conductivity. Good.
Specifically, in the coating liquid for forming a transparent conductive layer, it is within the range of 0.1% by mass to 1.0% by mass, particularly within the range of 0.15% by mass to 0.8% by mass, particularly preferably 0.1% by mass. It is preferable to be within the range of 18% by mass to 0.5% by mass. If the content of the metal fiber is larger than the above range, coating is difficult, and the transparent conductive layer forming layer may be thin. On the other hand, if the content is less than the above range, the transparent conductive layer forming layer is thick. In some cases, the amount of the solvent is large and the metal fibers tend to aggregate.

(C) Arbitrary material The coating liquid for transparent conductive layer formation may contain arbitrary materials other than the material mentioned above as needed.
Hereinafter, arbitrary materials contained in the coating liquid for forming a transparent conductive layer will be described.

(I) Resin The coating liquid for forming a transparent conductive layer may contain a resin. This is because the metal fibers can be firmly fixed.
The resin is not particularly limited as long as it has insulating properties and functions as a binder. For example, a curable resin such as a thermosetting resin, an ultraviolet curable resin, and an electron beam curable resin, A plastic resin etc. can be mentioned. Specifically, acrylic resin, polyester resin, alkyd resin, urethane resin, silicone resin, fluorine resin, epoxy resin, polycarbonate resin, polyvinyl chloride resin, polyvinyl alcohol resin, acrylic urethane resin, polyester acrylate resin, epoxy acrylate And thermosetting resins such as epoxy resins, polyol acrylate resins, cellulose resins, polyester-melamine resins, epoxy-melamine resins, melamine resins, and phenol resins.

  The resin may contain known additives such as a stabilizer, a dispersant, an antioxidant, and a viscosity modifier.

  The resin content in the transparent conductive layer forming coating solution is preferably less than the metal fiber content. Specifically, the resin content is preferably 100 parts by mass or less, more preferably 50 parts by mass or less, and particularly preferably 30 parts by mass or less with respect to 100 parts by mass of the metal fibers. This is because if the content of the resin relative to the metal fiber is larger than the above range, the resin exhibits insulating properties, so that the electrical resistance is increased and the conductivity of the obtained transparent conductive substrate may be lowered.

(Ii) Arbitrary material As an arbitrary material contained in the coating liquid for transparent conductive layer formation, surfactant, a dispersing agent, a thickener, a electrically conductive agent etc. are mentioned other than that.

(D) Others It is preferable that the solid content concentration of the coating liquid for forming a transparent conductive layer is small. The metal fiber in the coating liquid for forming the transparent conductive layer needs to exhibit high fluidity, and the metal fiber is randomly generated by causing the metal fiber to flow and diffuse by volatilization of the first solvent in the first drying step. This is because it needs to be oriented. In addition, solid content here means the total solid content except the solvent in the coating liquid for transparent conductive layer formation.
The solid content concentration in the coating liquid for forming the transparent conductive layer is in the range of 0.1% by mass to 2.0% by mass, and particularly in the range of 0.15% by mass to 1.5% by mass. It is preferably within the range of 0.18% by mass to 1.0% by mass. When the solid content concentration is larger than the above range, the metal fiber is less likely to flow and diffuse, and in the obtained transparent conductive layer, the electrical resistivity may vary depending on the in-plane direction. This is because if the amount is less than 1, the ratio of the solvent increases, and the aggregation of the metal fibers tends to occur.

  Moreover, the viscosity of the coating liquid for forming a transparent conductive layer is such that the metal fibers can exhibit high fluidity, and the metal fibers are randomly oriented by causing the metal fibers to flow and diffuse in the first drying step. Any size is acceptable as long as it is possible. The viscosity is, for example, preferably in the range of 0.3 mPa · s to 10.0 mPa · s at 25 ° C., and more preferably in the range of 0.5 mPa · s to 5.0 mPa · s. When the viscosity of the coating liquid for forming the transparent conductive layer is larger than the above range, sufficient flow and diffusion of the metal fiber does not occur, and in the obtained transparent conductive layer, the electrical resistivity varies depending on the in-plane direction. On the other hand, if it is smaller than the above range, the metal fibers tend to excessively flow and diffuse, and the metal fibers may easily aggregate. The viscosity is a value measured by “PHYSICA MCR301” manufactured by Anton Paar.

(2) Transparent base material The transparent base material in this invention will not be specifically limited if it has desired transparency and can support a transparent conductive layer, For example, a transparent resin base material, transparent inorganic A base material etc. can be used. Moreover, the transparent base material may have rigidity and may have a softness | flexibility.

  Examples of the resin constituting the transparent resin base material include acetyl cellulose resins such as triacetyl cellulose, polyester resins such as polyethylene terephthalate and polyethylene naphthalate, olefin resins such as polyethylene and polymethylpentene, acrylic resins, Examples thereof include polyurethane resins, polyvinyl resins, polyether sulfone, polycarbonate, polysulfone, polyether, polyether ketone, polyimide, acrylonitrile, methacrylonitrile, cycloolefin polymer, and cycloolefin copolymer.

  In addition, the transparent resin base material may contain additives as necessary. The additive is appropriately selected according to the type of resin constituting the transparent resin base material, for example, when the resin constituting the transparent resin base material is an ultraviolet curable resin, a polymerization initiator is used. Can be mentioned.

  On the other hand, examples of the material when the transparent substrate is a transparent inorganic substrate include glass such as soda glass, potassium glass, and lead glass, ceramics such as PLZT, quartz, and fluorite.

  The transparent substrate may be subjected to a surface treatment in order to ensure wettability of the transparent conductive layer forming coating solution. A general method can be mentioned for the surface treatment.

  The transparent substrate may be a single layer or may be a laminate of two transparent substrates of the same or different materials.

  The thickness of the transparent substrate is appropriately selected according to the use of the transparent conductive substrate obtained by the production method of the present invention. For example, when using a transparent conductive substrate for a touch panel sensor, the thickness of the transparent substrate can be set to about 20 μm to 1500 μm.

  The transparent substrate has transparency. Here, unless otherwise specified, “transparent” or “transparency” means transparency that does not hinder the user of a product using a transparent conductive base material from being viewed from the screen or the operation surface. Say. Therefore, the transparency includes colorless and transparent and colored transparency that does not hinder visibility, is not defined by strict transmittance, and is appropriately determined according to the use of the transparent conductive substrate obtained by the production method of the present invention. can do.

(3) Coating method The coating method of the transparent conductive layer forming coating solution may be any method that can form a transparent conductive layer forming layer on the surface of a transparent substrate, and generally a coating solution containing metal fibers. The method used for coating can be used. Among them, the method of applying along one direction on a transparent substrate in plan view is because the long axis of the metal fiber is easily oriented isotropically along the application direction in the transparent conductive layer forming layer. This is preferable in that the effect of using the manufacturing method is easily exhibited.
Specific examples of the coating method include a die coating method, a knife coating method, a gravure coating method, a micro gravure coating method, a comma coating method, and a blade coating method.

  The coating liquid for forming a transparent conductive layer may be applied to the entire surface of one surface of the transparent substrate, or may be applied in a pattern.

  The coating conditions such as the coating speed of the coating liquid for forming the transparent conductive layer are not particularly limited as long as the transparent conductive layer forming layer having a desired thickness can be formed. It can be set appropriately.

(4) Transparent conductive layer formation layer The transparent conductive layer formation layer formed in this process is a layer which becomes a transparent conductive layer through the 1st drying process and the 2nd drying process which are mentioned below.
The thickness of the transparent conductive layer forming layer formed in this step may be a thickness that allows the obtained transparent conductive layer to have a desired conductivity, and has a thickness required for the transparent conductive layer. It can be designed accordingly.

2. 1st drying process The 1st drying process in this process is a process of drying the said transparent conductive layer formation layer on the said transparent base material at 40 degrees C or less, and removing the said 1st solvent.
In this step, by drying the transparent conductive layer forming layer at a desired temperature, the first solvent contained in the transparent conductive layer forming layer volatilizes spontaneously. Metal fibers can be oriented randomly.

  The drying temperature in this step is a temperature at which the first solvent volatilizes spontaneously and may be 40 ° C. or less, and is preferably within the range of room temperature (25 ° C.) ± 10 ° C. The lower limit of the drying temperature is preferably 15 ° C. or higher although it depends on the type of the first solvent. This is because if the drying temperature is higher than the above range, the volatilization rate of the first solvent increases and the metal fibers may aggregate. On the other hand, if it is lower than the above range, the first solvent is less likely to volatilize spontaneously, and the orientation of the metal fibers in the transparent conductive layer forming layer cannot be made random in this step.

  The drying time under the above temperature may be a time that allows the first solvent in the transparent conductive layer forming layer to be sufficiently removed, and depends on the type of the first solvent and the evaporation rate. It is preferably within minutes, and more preferably within 30 minutes to 2 minutes.

The drying method in this step may be any method that can be dried at a desired temperature and can spontaneously volatilize the first solvent in the transparent conductive layer forming layer. It is preferable that the method not be exposed to warm air. It is because it may become difficult to orient metal fibers randomly by directing hot air directly on the transparent conductive layer forming layer.
Examples of the drying method include room temperature drying, IR heater, dry oven, hot plate, flash heating, vacuum, reduced pressure and the like.

3. Second drying step The second drying step in this step is a step of drying the transparent conductive layer forming layer after the first drying step to remove the second solvent and forming the transparent conductive layer.
In this step, the transparent conductive layer forming layer is dried at a desired temperature, thereby evaporating the second solvent contained in the transparent conductive layer forming layer, fixing the random orientation of the metal fibers, and maintaining the orientation. it can.

  The drying temperature in this step may be any temperature that can suppress thermal damage to the transparent substrate and remove the second solvent, and is appropriately set according to the types of the transparent substrate and the second solvent. However, it may be within the range of 120 ° C. to 150 ° C., for example, and preferably within the range of 130 ° C. to 140 ° C. If the drying temperature is higher than the above range, the transparent substrate may be deformed and the optical properties may be deteriorated. On the other hand, if the drying temperature is lower than the above range, the solvent remains in the obtained transparent conductive layer and the degassing is sufficient. This is because sticking may occur when the transparent conductive substrate obtained by the present invention is wound up into a roll shape. Note that sticking to a roll-shaped transparent conductive substrate means that the wound transparent conductive substrate is solidified in a roll shape. In this case, the transparent conductive substrate cannot be unwound, When taking out, troubles, such as a transparent conductive layer peeling from a transparent base material and a surface being damaged, will arise.

  The drying time under the above temperature is not particularly limited as long as the second solvent can be sufficiently removed and the random orientation of the metal fibers can be fixed, and the type of the second solvent And can be set as appropriate in consideration of productivity and the like. The drying time is preferably, for example, 30 seconds or more and 60 minutes or less, and particularly preferably 30 seconds or more and 30 minutes or less. If the drying time is longer than the above range, the productivity may be reduced, the transparent substrate may be deformed, or the optical properties may be deteriorated. On the other hand, if the drying time is shorter than the above range, the solvent is contained in the transparent conductive layer. This is because there is a case where degassing is not sufficiently performed and the transparent conductive layer is likely to be peeled off from the transparent substrate.

  The drying method in this step is not particularly limited as long as it can be heated at a desired temperature and can evaporate the second solvent. In this step, a method in which the hot air at the temperature described above directly hits the transparent conductive layer forming layer may be used, or a method in which the hot air does not hit may be used. Specifically, in addition to the method described in the section “2. First drying step”, a hot air drying method or the like can be used.

  The details of the transparent conductive layer formed by this step will be described in the section “5. Transparent conductive substrate” described later.

4). Arbitrary process This invention may have arbitrary processes other than each process mentioned above.
Examples of the optional process include a patterning process for forming the transparent conductive layer in a pattern, a baking process for heating and baking the transparent conductive layer, a surface resistance adjusting process for reducing the surface resistance of the transparent conductive layer by pressure bonding and thermocompression bonding, and the like. Can be mentioned.
Hereinafter, a patterning process and a baking process among arbitrary processes are demonstrated.

(1) Patterning step The patterning step is a step of forming the transparent conductive layer in a pattern. The method for forming the transparent conductive layer in a pattern in plan view is not particularly limited, but for example, a method of forming a resist pattern on the transparent conductive layer and etching, a transparent formed on a transparent substrate Examples thereof include a method of partially peeling off the conductive layer and a method of patterning the transparent conductive layer formed on the transparent substrate with a laser. Note that a general method can be used as a resist formation method and an etching method.
Further, as described in “1. Application process”, a method may be used in which the transparent conductive layer forming coating liquid is applied in a pattern. In this case, the patterning step is included in the coating step.

  The width of the pattern when the transparent conductive layer is formed in a pattern is not particularly limited as long as desired conductivity can be obtained and can be formed. For example, the width is several tens μm to several hundreds μm. Can be about.

  The pattern shape of the transparent conductive layer formed by this step is not particularly limited and can be an arbitrary shape. For example, as shown in FIG. 3 (b), a pattern shape orthogonal to the longitudinal direction and the lateral direction of the transparent substrate 1 can be mentioned. FIGS. 3A and 3B are a schematic cross-sectional view and a plan view showing an example of a transparent conductive substrate having a patterned transparent conductive layer.

(2) Firing step The firing step is a step of heating and firing the transparent conductive layer. By this step, the metal fibers can be more firmly fixed.
The firing temperature of the heat firing in this step is not particularly limited as long as it is a temperature at which the random orientation of the metal fibers can be fixed, and can be set within a range of 60 ° C to 250 ° C, for example.
In addition, this process is normally performed after a 2nd drying process.

5. Transparent conductive base material The transparent conductive base material obtained by the manufacturing method of this invention has a transparent base material and the transparent conductive layer which is formed on the said transparent base material and contains a metal fiber at least.

  The transparent conductive substrate in the present invention may be one having a transparent conductive layer on at least one surface of the transparent substrate, and may have a transparent conductive layer on both surfaces of the transparent substrate.

(1) Transparent conductive layer The thickness of the transparent conductive layer may be any size as long as the desired conductivity can be exhibited. For example, the thickness is in the range of 10 nm to 5.0 μm, and in particular, 20 nm to 1.0 μm. It is preferable to be within the range, particularly within the range of 30 nm to 300 nm. If the transparent conductive layer is thinner than the above range, it may be difficult to conduct, and manufacturing may be difficult. On the other hand, if the transparent conductive layer is thicker than the above range, the manufacturing cost may be high.

The surface resistivity of the transparent conductive layer can be appropriately set according to the conductivity required for the transparent conductive substrate, and is preferably in the range of 10Ω / □ to 500Ω / □, for example, 25Ω / □ to 400Ω / □. Within the range of □, particularly within the range of 50Ω / □ to 300Ω / □ is preferable.
The surface resistivity can be measured using, for example, a resistivity meter Loresta “AX MCP-T370” manufactured by Mitsubishi Chemical Analytech Co., Ltd.

Further, the transparent conductive layer preferably has a small variation in electrical resistivity depending on the in-plane direction. That is, in the transparent conductive layer in the transparent conductive substrate, the ratio of the electrical resistivity indicated by the other direction orthogonal to the one direction to the electrical resistivity indicated by the one direction in plan view is 0.75 to 1.25. It is preferable that it is in the range of 0.80 to 1.20, particularly preferably in the range of 0.90 to 1.10. The electrical resistivity is obtained by patterning the transparent conductive layer so that the wiring width is 1 mm and the wiring length is 10 mm, and the resistance between the wirings is measured. The electrical resistivity ratio is determined by measuring electrical resistance values in two directions (one direction and the other direction) in a plane orthogonal to each other between the wirings, and using the electrical resistance value in one direction as the other direction. It is a value obtained by dividing the electrical resistance value.
When the electrical resistivity ratio of the transparent conductive layer is not within the above range, it means that there is a large difference in electrical resistivity between the two directions orthogonal to each other in the plane. That is, the transparent conductive substrate obtained according to the present invention has anisotropy in conductivity, which may cause problems in conduction. Therefore, in the present invention, “the conductivity of the transparent conductive substrate is not anisotropic” means that the two-way electrical resistivity ratio in the orthogonal relationship is within the above range in the plan view of the transparent conductive layer. Say.
The one direction and the other direction in the plan view of the transparent conductive layer are not particularly limited as long as they are two directions orthogonal to each other in the plane. For example, the one direction is a direction corresponding to the application direction of the coating liquid for forming a transparent conductive layer in the production method of the present invention, and the other direction is a coating for forming the transparent conductive layer in the production method of the present invention. The direction can be perpendicular to the application direction of the working liquid. In the present invention, the electrical resistivity ratio can be within the above-mentioned range at any position in the plane of the transparent conductive layer.

The transparent conductive layer may be formed on the entire area of one surface of the transparent substrate, or may be formed in a pattern on one surface.
Further, as illustrated in FIG. 4A, the transparent conductive layer may be a layer formed by forming a contact with the surface of the metal fiber 12 exposed, as illustrated in FIG. 4B. In addition, the metal fiber 12 may be a layer in which contacts are formed in a layer made of the resin 13 which is an arbitrary material. FIG. 4 is an explanatory diagram for explaining an embodiment of the transparent conductive layer in the present invention. Reference numerals not described in FIG. 4 are the same as those in FIG.
Further, the transparent conductive layer may be an embodiment in which metal fibers constituting the transparent conductive layer are included in a protective layer described later.

(2) Others The transparent conductive substrate obtained by the production method of the present invention may have an arbitrary member in addition to the transparent substrate and the transparent conductive layer.
Examples of the optional member include a protective layer for protecting the transparent conductive layer, a primer layer for improving the adhesion between the transparent conductive layer and the transparent substrate, and an undercoat layer.
As a protective layer, the matrix material etc. which are indicated by Japanese translations of PCT publication No. 2009-505358 are mentioned, for example. When the protective layer is formed on the transparent conductive layer, the metal fibers of the transparent conductive layer may be included in the protective layer, and a part of the metal fibers may protrude from the surface of the protective layer. .

  The transparent conductive substrate obtained by the production method of the present invention preferably has high light transmittance. Specifically, the total light transmittance of the transparent conductive substrate obtained by the production method of the present invention is preferably 85% or more. The total light transmittance is a value measured by a method in accordance with JIS K7361 using a haze meter (manufactured by Murakami Color Research Laboratory, HM-150).

  Moreover, it is preferable that the transparent conductive base material obtained by the manufacturing method of this invention has a low haze value. When the transparent conductive substrate has a large haze value, the metal fibers tend to agglomerate in the transparent conductive layer. According to the production method of the present invention, since the occurrence of aggregation of the metal fibers is suppressed, the haze value is low. Because it becomes. The specific haze value is not particularly limited as long as the transparent conductive substrate obtained by the production method of the present invention is within a range in which the above-described total light transmittance can be exhibited.

  Examples of the use of the transparent conductive substrate obtained by the production method of the present invention include various devices such as touch panel sensors, display devices such as liquid crystal display devices and EL display devices, electronic paper, and solar cells.

B. Transparent conductive layer forming coating solution The transparent conductive layer forming coating solution of the present invention contains at least metal fibers, a first solvent and a second solvent, and the boiling point of the first solvent is in the range of 50C to 95C. The boiling point of the second solvent is higher than the boiling point of the first solvent, and the blending ratio of the first solvent and the second solvent is 20% by mass: 80% by mass to 70% by mass: 30% by mass. The solid content concentration is in the range of 0.1% by mass to 2.0% by mass.

  According to the present invention, the coating liquid for forming a transparent conductive layer having the above-described composition allows the metal fibers to flow in the coating layer by volatilizing or heating and evaporating two kinds of solvents using the difference in boiling points. The metal fibers can be randomly oriented by being diffused and the orientation can be maintained by the resin, so that a transparent conductive layer having no conductivity anisotropy can be formed.

  In addition, about the detail regarding the coating liquid for transparent conductive layer formation of this invention, with the content demonstrated by the term of "A. transparent conductive base material 1. application | coating process (1) coating liquid for transparent conductive layer formation" mentioned above. Since it is the same, description here is abbreviate | omitted.

C. Transparent conductive base material The transparent conductive base material of the present invention has a transparent base material and a transparent conductive layer formed on the transparent base material and containing at least metal fibers. The ratio of the electrical resistivity indicated by the other direction orthogonal to the one direction to the electrical resistivity indicated by the one direction is in the range of 0.75 to 1.25.

1 (e) and 2 are a schematic plan view and a sectional view showing an example of the transparent conductive substrate of the present invention, and FIG. 3 is a schematic sectional view showing another example of the transparent conductive substrate of the present invention. It is a top view.
Since FIG.1 (e), FIG.2, and FIG.3 was already demonstrated, description here is abbreviate | omitted.

  According to this invention, it can be set as the transparent conductive base material without electroconductivity.

  The details regarding the transparent conductive substrate of the present invention are the same as the details regarding the transparent conductive substrate described in the above-mentioned section “A. Method for producing transparent conductive substrate”, and thus the description thereof is omitted here.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

  Hereinafter, the present invention will be specifically described with reference to examples.

[Example 1]
A transparent conductive substrate was obtained by the following method.

(Preparation of coating solution for forming transparent conductive layer)
A coating liquid for forming a transparent conductive layer having the following composition was prepared.
<Coating liquid for forming transparent conductive layer>
Metal fiber: Silver nanowire (average diameter 35 ± 15 μm, average length 15 μm, SLV-NW-35 manufactured by Blueno) 0.3 parts by mass Resin: ethyl cellulose 0.06 parts by mass First solvent: isopropyl alcohol ( Boiling point 82 ° C.) 40 parts by mass Second solvent: n-butanol (boiling point 118 ° C.) 60 parts by mass

(Coating process)
As a transparent substrate, a polycarbonate substrate (manufactured by Teijin Chemicals Ltd., product name: Panlite thickness: 100 μm) is used, and a coating solution for forming a transparent conductive layer is applied onto the transparent substrate using a die coater. Then, a transparent conductive layer forming layer was formed. In addition, the application direction of the coating liquid for forming the transparent conductive layer was defined as the MD direction, and the direction orthogonal to the application direction was defined as the TD direction.

(First drying step)
Next, the transparent base material on which the transparent conductive layer forming layer was formed was dried at 25 ° C. for 2 minutes to remove the first solvent in the transparent conductive layer forming layer.

(Second drying step)
Next, the transparent substrate on which the transparent conductive layer forming layer after the first drying step is formed is dried at 130 ° C. for 3 minutes, and the second solvent in the transparent conductive layer forming layer is removed to obtain a transparent conductive layer. It was. This obtained the transparent conductive base material.

[Comparative Example 1]
A transparent conductive substrate was obtained in the same manner as in Example 1 except that the transparent conductive layer forming coating solution having the following composition was used.
<Coating liquid for forming transparent conductive layer>
Metal fiber: Silver nanowire (average diameter 35 ± 15 μm, average length 15 μm, SLV-NW-35 manufactured by Blueno) 0.3 parts by mass Resin: ethyl cellulose 0.06 parts by mass First solvent: isopropyl alcohol ( Boiling point 82 ° C.) 100 parts by mass

[Comparative Example 2]
A transparent conductive substrate was obtained in the same manner as in Example 1 except that the transparent conductive layer forming coating solution having the following composition was used.
<Coating liquid for forming transparent conductive layer>
Metal fiber: Silver nanowire (average diameter 35 ± 15 μm, average length 15 μm, SLV-NW-35 manufactured by Blueno) 0.3 parts by mass Resin: ethyl cellulose 0.06 parts by mass First solvent: isopropyl alcohol ( (Boiling point 82 ° C.) 10 parts by mass, second solvent: n-butanol (boiling point 118 ° C.) 90 parts by mass

[Comparative Example 3]
A transparent conductive substrate was obtained in the same manner as in Example 1 except that the drying temperature in the first drying step was 45 ° C.

[Evaluation 1]
(Electric resistivity ratio)
A test piece (150 mm × 150 mm size) was cut out from the transparent conductive substrate obtained in Example 1 and Comparative Examples 1 to 3, and the transparent conductive layer was patterned so as to have a wiring width of 1 mm and a wiring length of 10 mm. The electrical resistivity in the MD direction and TD direction at the desired five locations (pt1 to pt5) was measured, and the electrical resistivity ratio was calculated from the following formula.
Electrical resistivity ratio = (Electric resistivity in MD direction / Electric resistivity in TD direction)
The case where the electrical resistivity ratio was within the specified range (within the range of 0.75 to 1.25) at all five locations was marked as ◯, and the case where the electrical resistivity ratio at the five locations was not within the specified range was marked as x.

[Evaluation 2]
The total light transmittance and haze value of the transparent conductive substrate obtained in Example 1 and Comparative Examples 1 to 3 were measured. The total light transmittance and haze value were measured by a method based on JIS K7361 using a haze meter (manufactured by Murakami Color Research Laboratory, HM-150).
Each evaluation result is shown in Table 1.

In the transparent conductive base material obtained in the examples, the electrical resistivity ratio is within a specified range (within a range of 0.75 to 1.25) at all measurement locations, and variation in electrical resistivity depending on the in-plane direction. It was suggested that the conductivity anisotropy was small. Moreover, since the haze value was small, it was suggested that generation | occurrence | production of metal fiber aggregation was suppressed.
On the other hand, in Comparative Examples 1 to 3, the electrical resistivity ratio was not within the specified range (within the range of 0.75 to 1.25) at all measurement locations, and the electrical resistivity varied greatly depending on the in-plane direction. This suggests that the conductivity anisotropy is large.
In the transparent conductive base material obtained in Comparative Example 1, the orientation of the metal fibers was not fixed in the second drying step, and further diffusion occurred. Therefore, the electrical resistivity ratio was different depending on the measurement location, and the variation was large. Moreover, haze value became large because aggregation of the metal fiber occurred.
In the transparent conductive base material obtained in Comparative Example 2, the major axis of the metal fiber is fixed in an orientation that becomes the MD direction, and the MD direction has a lower electrical resistivity than the TD direction. For this reason, the electrical resistivity ratio of the transparent conductive layer was not more than the lower limit of the desired range.
In the transparent conductive base material obtained in Comparative Example 3, the diffusion of the metal fibers was greatly caused by the drying process, so that the electrical resistivity ratio was different depending on the measurement location, and the variation was large. Moreover, haze value became large because aggregation of the metal fiber occurred.

DESCRIPTION OF SYMBOLS 1 ... Transparent conductive layer 2 ... Transparent base material 10 ... Transparent conductive base material 11 ... Transparent conductive layer formation layer 12 ... Metal fiber

Claims (3)

Containing at least a metal fiber, a first solvent and a second solvent,
The boiling point of the first solvent is in the range of 50C to 95C;
The boiling point of the second solvent is higher than the boiling point of the first solvent;
The blending ratio of the first solvent and the second solvent is in the range of 20% by mass: 80% by mass to 70% by mass: 30% by mass,
Using a coating liquid for forming a transparent conductive layer having a solid content concentration in the range of 0.1% by mass to 2.0% by mass,
An application step of applying the transparent conductive layer forming coating liquid on a transparent substrate to form a transparent conductive layer forming layer; and
A first drying step of drying the transparent conductive layer forming layer on the transparent substrate at 40 ° C. or less to remove the first solvent;
A method for producing a transparent conductive substrate, comprising: a second drying step of drying the transparent conductive layer forming layer after the first drying step to remove the second solvent and forming a transparent conductive layer. . Containing at least a metal fiber, a first solvent and a second solvent,
The boiling point of the first solvent is in the range of 50C to 95C;
The boiling point of the second solvent is higher than the boiling point of the first solvent;
The blending ratio of the first solvent and the second solvent is in the range of 20% by mass: 80% by mass to 70% by mass: 30% by mass,
A coating liquid for forming a transparent conductive layer, wherein the solid content concentration is in the range of 0.1% by mass to 2.0% by mass. A transparent substrate;
Formed on the transparent substrate, and having a transparent conductive layer containing at least metal fibers,
The ratio of the electrical resistivity indicated by the other direction orthogonal to the one direction to the electrical resistivity indicated by the one direction in plan view of the transparent conductive layer is within a range of 0.75 to 1.25. A transparent conductive substrate characterized by