JP6202782B2 - Transparent conductive coating composition, transparent conductive sheet and method for producing the same - Google Patents

Description

  The present invention relates to a transparent conductive coating composition, a transparent conductive sheet, and a method for producing the same.

  In recent years, thiophene-based and aniline-based polymers have excellent stability and conductivity, and thus are expected to be used as organic conductive materials. An organic solvent dispersion in which a conductive polymer in which a dopant is added to such a polymer is dispersed in an organic solvent is used as a general aqueous colloidal dispersion or an organic solvent dispersion. However, when the conductive polymer is used as a coating composition and a thin film is formed on a substrate using this coating composition, the hardness of the thin film and the adhesion of the thin film to the substrate are not sufficient. In particular, when the base material is a transparent plastic substrate, it is difficult to form a thin film having sufficient hardness without impairing the transparency of the base material. For example, Patent Document 1 proposes a binder that can improve the hardness of the thin film and the adhesion of the thin film to the substrate.

JP 2007-324143 A

  Patent Document 1 describes that by using a resin such as polyvinyl alcohol (PVA) as a binder, the hardness of the thin film and the adhesion to the substrate can be improved. However, the transparency, conductivity, and strength of the obtained thin film are not sufficient, and there is still room for improvement.

  The present invention has been made to solve the above problems, and provides a transparent conductive coating composition capable of forming a transparent conductive thin film excellent in transparency, conductivity, and strength. Furthermore, the transparent conductive sheet which has a transparent conductive thin film excellent in transparency, electroconductivity, and intensity | strength, and its manufacturing method are provided.

  In order to solve the above-mentioned problems, the transparent conductive coating composition of the present invention is characterized by containing a conductive polymer, polyethylene glycol, and alkoxysilane.

  The transparent conductive sheet of the present invention comprises a transparent substrate, and a transparent conductive thin film formed by applying the transparent conductive coating composition of the present invention to at least one main surface of the substrate. It is characterized by having.

  The method for producing a transparent conductive sheet of the present invention comprises a step of applying the transparent conductive coating composition of the present invention to at least one main surface of a transparent substrate, and heating the transparent conductive coating composition. And a step of forming a transparent conductive thin film.

  According to the transparent conductive coating composition of the present invention, a transparent conductive thin film excellent in transparency, conductivity and strength can be formed.

  Moreover, according to the transparent conductive sheet of this invention, the transparent conductive sheet which has a transparent conductive thin film excellent in transparency, electroconductivity, and intensity | strength can be provided.

  Moreover, according to the manufacturing method of the transparent conductive sheet of this invention, the transparent conductive sheet which has a transparent conductive thin film excellent in transparency, electroconductivity, and intensity | strength can be manufactured.

(Transparent conductive coating composition)
The transparent conductive coating composition of the present invention comprises a conductive polymer, polyethylene glycol (hereinafter referred to as PEG), and alkoxysilane. Thereby, the transparent conductive thin film excellent in transparency, electroconductivity, and intensity | strength can be formed.

<Conductive polymer>
The conductive polymer is a polymer called Conductive Polymers (CPs), and it exhibits conductivity in a state where a polyradical cationic salt or a polyradical anionic salt is formed by doping with a dopant. It refers to the polymer obtained.

  In the present invention, the conductive polymer containing a polythiophene compound and a dopant is used. As the conductive polymer in the present invention, a mixture (also referred to as PEDOT / PSS) containing poly (3,4-ethylenedioxythiophene) as a polythiophene compound and polystyrene sulfonic acid as a dopant can be used.

<Polyethylene glycol>
PEG constituting the transparent conductive coating composition of the present invention serves as a binder. Since PEG is water-soluble and has a very good affinity, it will be dispersed at the molecular level in the transparent conductive thin film formed using the transparent conductive coating composition of the present invention. Therefore, even if the addition amount of PEG is small, it is possible to exert a great effect. Moreover, since PEG itself is extremely high in transparency, the transparency of the transparent conductive thin film is not impaired. Furthermore, the presence of PEG in the transparent conductive thin film can improve the adhesion to the substrate.

Since the water solubility of the PEG decreases with increasing molecular weight, the upper limit of the molecular weight is preferably 1 × 10 ⁷ , more preferably 1 × 10 ⁶ . On the other hand, when the molecular weight is decreased, the water solubility is further increased. However, when the molecular weight is too small, the hardness of the transparent conductive thin film tends to decrease. Therefore, the lower limit of the molecular weight is preferably 1 × 10 ³ .

  The content of the PEG is 30 to 95% by weight, preferably 50 to 85% by weight, based on the conductive polymer. When the content of PEG is too small, the adhesiveness of the transparent conductive thin film to the substrate is lowered, and cracks tend to occur in the transparent conductive thin film. If the content of PEG is too large, the electrical characteristics tend to deteriorate.

  The weight ratio of the conductive polymer to the PEG is preferably 5:95 to 30:70.

<Alkoxysilane>
The alkoxysilane constituting the transparent conductive coating composition of the present invention is a compound in which 3 to 4 alkoxy groups are bonded to silicon. When dissolved in water, the alkoxysilane is polymerized and connected with -OSiO-. It becomes a molecular weight SiO ₂ body.

  The alkoxysilane preferably contains at least one polyfunctional alkoxysilane selected from the group consisting of tetraalkoxysilane, trialkoxysilane, dialkoxysilane and alkoxy oligomer.

  Examples of the tetraalkoxysilane include silane tetrasubstituted with an alkoxy group having 1 to 4 carbon atoms such as tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraiso-propoxysilane, and tetra-t-butoxysilane. It is done.

  Examples of the trialkoxysilane include trimethoxysilane, triethoxysilane, tripropoxysilane, tributoxysilane, triiso-propoxysilane, tri-L-butoxysilane, and the like. Silane.

  Examples of the dialkoxysilane include dimethyldimethoxysilane, diphenyldimethoxysilane, dimethyldiethoxysilane, and diphenyldiethoxysilane.

  As an example of the alkoxy oligomer, the alkoxy oligomer is a relatively low-molecular resin having both an organic group and an alkoxysilyl group. Specific examples include “X-40-2308”, “X-40-9238”, “X-40-9247”, “KR-401N”, “KR-510”, “KR-9218” manufactured by Shin-Etsu Chemical Co., Ltd. ".

  Among the specific examples of the alkoxysilane, tetraalkoxylane is preferable for forming a transparent conductive thin film having higher hardness. In order to form a high-quality film in a more stable state with good reproducibility, tetraalkoxylane is preferable. It is preferable to use together alkoxysilane and trialkoxysilane.

  When tetraalkoxysilane and trialkoxysilane are used in combination as the alkoxysilane, the molar ratio of tetraalkoxysilane to trialkoxysilane is preferably 9: 1 to 5: 5, more preferably 8: 2. ~ 6: 4. The reason why this molar ratio relationship is preferable is that the decrease in hardness of the transparent conductive thin film is prevented, the risk of cracking in the transparent conductive thin film due to aging is further reduced, and the adhesion to the substrate is further increased. Because it can. It is considered that the tetraalkoxysilane acts on the expression of high film hardness, and the trialkoxysilane acts on prevention of film cracking and adhesion to the substrate.

  The content of the alkoxysilane is 60 to 95% by weight, preferably 80 to 90% by weight, based on the total amount of the conductive polymer and PEG. When the content of alkoxysilane is too small, it is difficult to obtain sufficient hardness for the transparent conductive thin film. If the alkoxysilane content is too high, the generated silicon dioxide aggregates to cause the film to become cloudy and optical properties tend to deteriorate.

<Others>
In addition to the above, a mixed solvent of alcohol (ethanol, methanol, isopropyl alcohol, etc.) and water is added to the transparent conductive coating composition of the present invention. By the addition of a mixed solvent of alcohol and water, the alkoxysilane is slightly hydrolyzed, but a hydrosol solution is obtained without substantially proceeding to the gel. The content of water is preferably 1 to 4.5 mol, more preferably 2 to 4 mol, with respect to 1 mol of alkoxysilane, and the content of alcohol is 5 to 40 mol with respect to 1 mol of alkoxysilane. Is more preferable, and more preferably 10 to 30 mol. The reason why the water content is preferably within the above numerical range is as follows. Water not only affects the reaction rate of the hydrolysis reaction but also affects the quality of the transparent conductive thin film. That is, when there is too much content of water, there exists a tendency for adhesiveness with a base material to fall, and it may become impossible to obtain the transparent conductive thin film of uniform film thickness. On the other hand, if the water content is too small, there may be a case where a transparent conductive thin film having sufficient hardness cannot be obtained, for example, the reaction rate of the hydrolysis reaction becomes slow or unreacted substances are likely to remain. On the other hand, since alcohol is not directly related to the hydrolysis reaction, the alcohol content is not so severely limited. However, if the alcohol content is too high, the reaction rate of the hydrolysis reaction is slow. Or the thickness of the transparent conductive thin film is reduced. Therefore, it is necessary to adjust appropriately.

  Moreover, generally used acid catalysts (hydrochloric acid, sulfuric acid, acetic acid, etc.) can be further added to the transparent conductive coating composition of the present invention. In this case, it is possible to form a high-quality transparent conductive thin film with more reproducibility with more stable performance. The amount of the acid catalyst is about 0.01 mol with respect to 1 mol of alkoxysilane.

  The preparation method of the transparent conductive coating composition of this invention is not specifically limited, What is necessary is just to mix suitably by a well-known method.

(Transparent conductive sheet)
The transparent conductive sheet of this invention has a transparent base material and the transparent conductive thin film formed in the at least one main surface of the base material using the said transparent conductive coating composition of this invention. Thereby, the transparent conductive sheet which has a transparent conductive thin film excellent in transparency, electroconductivity, and intensity | strength can be provided.

  As the base material, various materials such as plastic, rubber, glass, metal, ceramics, and paper can be used.

  The surface resistivity of the transparent conductive thin film of the present invention is preferably 500Ω / square or less. The smaller the surface resistivity, the better the electrical characteristics. The surface resistivity can be measured by a surface resistivity measuring device, for example, “Loresta EP” manufactured by Dia Instruments.

  The total light transmittance in the wavelength range of 380 to 780 nm of the transparent conductive thin film is preferably 85% or more, more preferably 88% or more. The higher the total light transmittance, the better the optical properties. The total light transmittance can be measured with an ultraviolet-visible near-infrared spectrophotometer, for example, “V-570” manufactured by JASCO Corporation.

  The surface hardness of the transparent conductive thin film is determined by the pencil hardness measurement method specified in Japanese Industrial Standard (JIS) K5400, and is preferably H or higher, more preferably 2H or higher. The higher the pencil hardness, the better the hardness.

  Although the film thickness of the transparent conductive thin film of this invention is suitably set according to a use, it is about 0.01-10 micrometers normally. If the film thickness is too thin or too thick, it becomes difficult to form a uniform transparent conductive thin film. Depending on the proportion of the conductive polymer contained in the transparent conductive coating composition, if the film thickness is thin, the surface resistivity tends to increase. If the film thickness is too thick, the total light transmittance decreases. Tend to.

(Transparent conductive sheet manufacturing method)
The method for producing a transparent conductive sheet of the present invention includes a step of applying the transparent conductive coating composition of the present invention to at least one main surface of a transparent substrate, and heating the transparent conductive coating composition. And a step of forming a transparent conductive film. Thereby, the transparent conductive sheet which has the transparent conductive thin film excellent in transparency, electroconductivity, and intensity | strength can be manufactured.

  Examples of the method for applying the transparent conductive coating composition include a known coating method such as a bar coating method, a reverse method, a gravure printing method, a micro gravure printing method, a dipping method, a spin coating method, and a spray method. Can do.

  The heating may be performed under the condition that the solvent component in the transparent conductive coating composition evaporates, and is preferably performed at 100 to 150 ° C. for 30 to 90 minutes. If the solvent remains in the transparent conductive film, the strength tends to be inferior. Examples of the heating method include hot air drying.

  Hereinafter, the present invention will be described in detail using examples. However, the present invention is not limited to the following examples. Unless otherwise indicated, in the following, “part” means “part by weight”.

Example 1
First, the following composition was added and mixed to prepare a hydrosol solution.
(1) Tetraethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “KBE-04”) 10.0 parts (2) ethanol 4.2 parts (3) distilled water 1.3 parts (4) nitric acid aqueous solution (concentration: 1 (% By weight) 4.5 parts

Next, the following composition was added and mixed to obtain a transparent conductive coating composition.
(5) PEDOT-PSS (manufactured by Heraeus, trade name “PH-1000”, solid content concentration: 1.5%) 20.0 parts (6) PEG (average molecular weight: 3000, concentration: 1% by weight) aqueous solution 18 0.0 part (7) ethylene glycol 8.57 parts (8) hydrosol solution 3.04 parts

  Next, alkali-free glass (total light transmittance: 91.2%) having a thickness of 0.7 mm was used as a substrate, and the transparent conductive coating composition was applied to one main surface of the substrate by a spin coating method at a rotational speed of 1000 rpm. For 30 seconds and then heated at 120 ° C. for 1 hour. This produced the transparent conductive sheet of Example 1 in which the transparent conductive thin film was formed on one main surface. The film thickness of the transparent conductive thin film was 0.5 μm. And each evaluation shown below was performed about the obtained transparent conductive sheet.

<Electrical characteristics>
First, the electrical characteristics of the transparent conductive sheet were evaluated by measuring the surface resistivity using a surface resistivity measuring device “Loresta EP” (MCP-360T type) manufactured by Dia Instruments and an LSP probe. As a result of the evaluation, when the surface resistivity was 500 Ω / square or less, it was determined that the electrical characteristics were good, and when the surface resistivity was greater than 500 Ω / square, it was determined that the electrical characteristics were not good. Since the surface resistivity of the transparent conductive sheet of Example 1 was 400Ω / square, it was judged that the electrical characteristics were good.

<Optical characteristics>
Next, the optical characteristics of the transparent conductive sheet were evaluated using the total light transmittance.

  The total light transmittance of the transparent conductive sheet was determined using an ultraviolet-visible near-infrared spectrophotometer “V-570” manufactured by JASCO Corporation. Specifically, in combination with integrating sphere ILN-472, in the haze value calculation mode, the response is Fast, the bandwidth is 2.0 nm, the near infrared bandwidth is 8.0 nm, and the scanning speed is 400 nm / min. The light transmission spectrum in the range of 380 to 780 nm was measured, and the total light transmittance was calculated under the conditions of the C light source and the visual field of 2 degrees using the measurement result of the light transmission spectrum. The higher the value of total light transmittance, the better the optical characteristics. In this example, it was judged that the optical characteristics were excellent if the value of the total light transmittance was larger than 88.0%.

  Since the transparent conductive sheet of Example 1 had a total light transmittance of 91.2%, it was judged to be excellent in optical characteristics.

<Surface hardness>
Next, the surface hardness of the transparent conductive sheet was evaluated by measuring the pencil hardness based on the provisions of JIS K5400. Since the transparent conductive sheet of Example 1 had a pencil hardness of 2H, it was judged that the surface hardness was high and the strength was excellent.

(Example 2)
Except for changing the tetraethoxysilane of the composition component (1) to a mixture of tetraethoxysilane and trimethylmethoxysilane (weight ratio 4: 1) (trade name “KBM-13”, manufactured by Shin-Etsu Chemical Co., Ltd.) A transparent conductive sheet of Example 2 was produced in the same manner as Example 1. The film thickness of the transparent conductive thin film was 0.5 μm.

  And about the transparent conductive sheet of Example 2, when each evaluation similar to the said Example 1 was performed, surface resistivity is 450 ohms / square, total light transmittance is 91.6%, and pencil hardness is 2H. The transparent conductive sheet of Example 2 was excellent in all of electric characteristics, optical characteristics, and strength.

(Comparative Example 1)
Composition component (1) A transparent conductive sheet of Comparative Example 1 was produced in the same manner as in Example 1 except that tetraethoxysilane was not used. The film thickness of the transparent conductive thin film was 0.5 μm.

  And about the transparent conductive sheet of the comparative example 1, when each evaluation similar to the said Example 1 was performed, surface resistivity is 450 ohms / square, total light transmittance is 92.4%, pencil hardness is B rather than B. It was low. That is, the transparent conductive sheet of Comparative Example 1 had good electrical characteristics and optical characteristics, but was inferior in strength to Examples 1 and 2. This shows that alkoxysilane affects the strength of the coating film.

(Comparative Example 2)
A transparent conductive sheet of Comparative Example 2 was produced in the same manner as in Example 1 except that the aqueous PEG (average molecular weight: 3000, concentration: 1% by weight) aqueous solution of the composition component (6) was not used. When the thin film of this transparent conductive sheet was visually observed, it was clear that the roughened white turbidity and sufficient transparency was not obtained. Therefore, in Comparative Example 2, each evaluation described in Example 1 was not performed. From this, it can be seen that the binder is involved in the film formability.

(Comparative Example 3)
The aqueous PEG (average molecular weight: 3000, concentration: 1% by weight) aqueous solution of the composition component (6) was changed to an aqueous solution of polyvinyl alcohol (degree of polymerization: 1700, degree of saponification: 87-89%, concentration: 1% by weight). A transparent conductive sheet of Comparative Example 3 was produced in the same manner as Example 1 except that. The film thickness of the transparent conductive thin film was 0.5 μm.

  The transparent conductive sheet of Comparative Example 3 was evaluated in the same manner as in Example 1. The surface resistivity was 450Ω / square, the total light transmittance was 86.4%, and the pencil hardness was 3H. It was. That is, the transparent conductive sheet of Comparative Example 3 was excellent in strength, but was inferior to Examples 1 and 2 in electrical characteristics and optical characteristics. From this, it can be seen that PEG can improve electrical characteristics and optical characteristics when used in combination with alkoxysilane.

  The present invention is a transparent conductive material that can be used for various applications such as transparent electrode materials, transparent antistatic agents, ultraviolet absorbers, heat ray absorbers, electromagnetic wave absorbers, sensors, electrolytes for electrolytic capacitors, and secondary battery electrodes. Can provide a sheet.

Claims (8)

A step of preparing a transparent conductive coating composition by mixing a conductive polymer, polyethylene glycol, and alkoxysilane;
Applying the transparent conductive coating composition to at least one main surface of the glass substrate;
Said transparent conductive coating composition by heating at 100 to 150 ° C. 30 to 90 minutes, look including a step of forming a transparent conductive film,
The step of preparing the transparent conductive coating composition includes the step of preparing a hydrosol solution by mixing alkoxysilane, alcohol, and water, the hydrosol solution, a conductive polymer, and polyethylene glycol. And preparing a transparent conductive coating composition . A method for producing a transparent conductive sheet, comprising:   The method for producing a transparent conductive sheet according to claim 1, wherein the alkoxysilane includes at least one polyfunctional alkoxysilane selected from the group consisting of tetraalkoxysilane, trialkoxysilane, dialkoxysilane, and alkoxy oligomer.   The method for producing a transparent conductive sheet according to claim 1, wherein the conductive polymer includes a polythiophene compound and polystyrene sulfonic acid. The method for producing a transparent conductive sheet according to claim 1, wherein the polyethylene glycol has a molecular weight of 1 × 10 ³ to 1 × 10 ⁷ .   The method for producing a transparent conductive sheet according to claim 1, wherein the weight ratio of the conductive polymer to the polyethylene glycol is 5:95 to 30:70.   2. The method for producing a transparent conductive sheet according to claim 1, wherein the content of the alkoxysilane is 60 to 95% by weight based on the total amount of the conductive polymer and the polyethylene glycol. The thickness of the said transparent conductive film is 0.01-10 micrometers, The manufacturing method of the transparent conductive sheet of any one of Claims 1-6 . The pencil hardness of the transparent conductive film is 2H or more, the surface resistivity of the transparent conductive film is 500Ω / square or less, and the total light transmittance of the transparent conductive film is 85% or more. The manufacturing method of the transparent conductive sheet of any one of Claims 1-6 .