JP4901080B2 - Conductive coating composition and transparent conductive film using the same - Google Patents

Description

  The present invention relates to a coating composition formed into a film by a sol-gel method, and the coated film when formed is a coating composition having excellent antistatic properties and transparency, and a transparent formed from the coating composition The present invention relates to a conductive film.

  In recent years, a coating technique using a sol-gel method has been implemented, and for example, an antireflection film, a surface protective film, and the like have been produced.

  In the sol-gel method, a metal alkoxide as a starting material is first hydrolyzed to prepare a sol, and then the obtained sol is applied and dried to form a coating (gelation), thereby obtaining a coating film. A catalyst is used when hydrolyzing the metal alkoxide, and hydrochloric acid is widely used as the catalyst.

  On the other hand, an antistatic property may be required for a coating film obtained by a sol-gel method such as an antireflection film. In such a case, for example, a means for separately providing a conductive coating (see Patent Document 1) or adding an antistatic agent in advance to the coating composition is performed.

JP 2004-118145 A (Claim 1, paragraph number 0051)

  However, there is a problem that workability is lowered by means of separately providing a conductive coating film. In addition, the means for adding an antistatic agent to the coating composition increases the components other than the component obtained from the metal alkoxide in the coating film, thereby improving the coating properties such as optical properties such as transparency and scratch resistance. There was a problem that would decrease.

As a result of diligent research to solve the above-mentioned problems, the present inventors provided a conductive coating film separately by using a heteropolyacid containing H ⁺ as a partner cation as a catalyst for hydrolyzing a metal alkoxide. In addition, the inventors have found that an antistatic property can be imparted to a coating film obtained by a sol-gel method without adding an antistatic agent, and have come to solve this problem.

That is, the coating composition of the present invention contains a sol obtained by hydrolyzing a metal alkoxide by the action of a catalyst, and is characterized by using a heteropolyacid containing H ⁺ as a partner cation as the catalyst. It is what.

  The transparent conductive film of the present invention is formed from the coating composition.

In the coating composition of the present invention, the heteropolyacid containing H ⁺ as a partner cation functions as a catalyst when hydrolyzing the metal alkoxide and functions as an ion conductive antistatic agent. Antistatic properties can be imparted to the resulting coating film without providing a coating film or adding an antistatic agent. Therefore, the workability at the time of obtaining a coating film is made favorable, and the obtained coating film does not impair the optical properties and physical properties of the coating film.

Moreover, since the heteropolyacid used in the present invention takes a solid form at room temperature and can release H ⁺ , it can continue to exist without volatilization from the coating film formed from the coating composition. The antistatic property described above can be permanently imparted to the coating film.

  The transparent conductive film of the present invention formed with such a coating composition has excellent antistatic properties while being excellent in transparency.

First, the coating composition of the present invention will be described. The coating composition of the present invention contains a sol obtained by hydrolyzing a metal alkoxide by the action of a catalyst, and as the catalyst, a heteropolyacid (hereinafter referred to as “heteropolyacid” as appropriate) containing H ⁺ as a partner cation. .) Is used. Hereinafter, embodiments of each component will be described.

  The metal alkoxide is used as a starting material for obtaining a coating film by a sol-gel method. A coating film obtained by a sol-gel method using a metal alkoxide has transparency.

  Examples of the metal alkoxide include tetraethoxysilane, methyltrimethoxysilane, zirconia propoxide, aluminum isopropoxide, titanium butoxide, titanium isopropoxide, and the like. These metal alkoxides can be appropriately selected and used depending on the application. For example, when it is desired to obtain a highly transparent coating film, alkoxysilane such as tetraethoxysilane or methyltrimethoxysilane is preferably used.

Such metal alkoxide is hydrolyzed into a sol. In the hydrolysis, hydrochloric acid is mainly used as a catalyst. In the present invention, a heteropolyacid containing H ⁺ as a partner cation is used.

The heteropolyacid used in the present invention can function as a catalyst for preparing a sol by hydrolyzing a metal alkoxide due to the presence of the partner cation H ⁺ , and also functions as an ion conductive antistatic agent, Antistatic properties can be imparted to the coating film formed from the coating composition. Moreover, since the heteropolyacid used in the present invention takes a solid form at room temperature and can release H ⁺ , it can continue to exist without volatilization from the coating film formed from the coating composition. The antistatic property described above can be permanently imparted to the coating film.

Examples of the heteropolyacid containing H ⁺ in the partner cation include phosphotungstic acid (H ₃ [PW ₁₂ O ₄₀ ], H ₆ [P ₂ W ₁₈ O ₆₂ ]) and silicotungstic acid (H ₄ [SiW ₁₂ O _40]. ]), Silicomolybdic acid (H ₄ [SiMo ₁₂ O ₄₀ ]) (hereinafter these are referred to as “free acid type heteropolyacid”), and a part of H ⁺ of the free acid type heteropolyacid is an alkali metal cation. And an acid salt of a heteropolyacid exchanged in step (b). Examples of the alkali metal cation used for obtaining the acid salt of the heteropolyacid include a lithium metal cation, a sodium metal cation, a potassium metal cation, and a cesium metal cation.

Among these heteropolyacids, free acid type heteropolyacids having excellent catalytic activity and antistatic properties are preferably used because of excellent H ⁺ release properties. Among free acid heteropolyacids, H ₃ [PW ₁₂ O ₄₀ ] having excellent H ⁺ release properties is preferably used.

The amount of heteropolyacid used varies depending on the type of heteropolyacid used and the like, and thus cannot be generally stated. However, the H ⁺ of the heteropolyacid is 3.0 × 10 ^{−2 to} 3.0 × 10 ^{−1 with} respect to the metal alkoxide. The molar ratio is preferably used. By setting the molar ratio to 3.0 × 10 ⁻² or more, sufficient antistatic properties can be imparted to the coating film, and by setting the molar ratio to 3.0 × 10 ⁻¹ or less, the coating composition It can prevent that the coating film formed from becomes brittle. Moreover, if the content rate of heteropoly acid is such a range, it can fully function also as a catalyst which hydrolyzes a metal alkoxide.

  In order to hydrolyze the metal alkoxide with the action of the heteropolyacid, it may be carried out under the same conditions as in the hydrolysis with the action of hydrochloric acid. For example, by stirring a composition obtained by adding water and alcohol to a metal alkoxide and a heteropolyacid at room temperature for 24 hours, the metal alkoxide is hydrolyzed to prepare a sol.

  Although the form of a coating composition is not specifically limited, The thing diluted with the solvent and liquid-ized is preferable. Examples of the solvent include methanol, ethanol, isopropanol, n-butanol, acetone, 1,4-dioxane, water and the like.

In the coating composition of the present invention as described above, the heteropolyacid containing H ⁺ as a partner cation functions as a catalyst when hydrolyzing the metal alkoxide, and also functions as an ion conductive antistatic agent. Antistatic properties can be imparted to the obtained coating film. Moreover, since the heteropolyacid used in the present invention takes a solid form at room temperature and can release H ⁺ , it can continue to exist without volatilization from the coating film formed from the coating composition. The antistatic property described above can be permanently imparted to the coating film.

  On the other hand, even if a conductive thin film is separately provided or an antistatic agent is added to the coating composition in advance, it is possible to impart antistatic properties to the coating film obtained from the coating composition. However, workability is lowered by means of providing a separate conductive thin film. In addition, the means for adding an antistatic agent to the coating composition increases the components other than the component obtained from the metal alkoxide in the coating film, thereby improving the coating properties such as optical properties such as transparency and scratch resistance. Will be damaged.

  Next, the transparent conductive film of the present invention will be described.

  The transparent conductive film of the present invention is formed from the above-described coating composition of the present invention (a coating composition containing a sol obtained by hydrolyzing a metal alkoxide by the action of a heteropolyacid). Specifically, it can be obtained by coating the coating composition of the present invention described above on a substrate and drying, and dehydrating and condensing components in the sol to form a coating (gelation).

  The base material is not particularly limited because it is selected depending on the application, but for example, polyester film, acrylic film, polyvinyl chloride film, polystyrene film, polycarbonate film, polypropylene film, triacetyl cellulose film, various fluorine resins. In addition to plastic films such as films, plastic plates and glass plates can be used. Although the thickness of a base material is not specifically limited, The thing of 5-300 micrometers is used suitably from viewpoints, such as handleability.

  Examples of means for applying the coating composition to the substrate include known application methods such as a bar coater method, a roll coater method, and a curtain flow method.

  The drying condition of the coating composition is usually about 80 to 150 ° C. for about 1 to 5 minutes.

Since the thickness of a transparent conductive film changes with uses, it cannot be said unconditionally. For example, when used as an antireflection film, the thickness of the transparent conductive film preferably satisfies the following formula (1) from the antireflection theory of light.
d = (a + 1) λ / 4n (1)
Here, d is the thickness of the transparent conductive film (unit: “nm”), a is 0 or a positive even number, λ is a specific wavelength (unit: “nm”), and n is the refractive index of the transparent conductive film.

  In order to improve the adhesion between the base material and the transparent conductive film, an undercoat layer may be provided or a corona discharge treatment may be performed between the base material and the transparent conductive film. The undercoat layer is formed of, for example, a polyester resin, an acrylic resin, a urethane resin, or the like.

  Moreover, you may have the adhesive bond layer and separator for sticking to a to-be-adhered body in the surface on the opposite side to the surface which has a transparent conductive film on a base material.

  The transparent conductive film of the present invention as described above is excellent in transparency and has antistatic properties, and can be used as, for example, an antireflection film or a surface protective film.

  The following examples further illustrate the present invention.

1. Preparation of coating composition (1) Preparation of mother liquor The mixed solution comprising the composition of Table 1 was stirred at 25 ° C. for 24 hours to hydrolyze the metal alkoxide, and coatings of Examples 1 to 4 and Comparative Examples 1 to 2 A mother liquor of the composition was obtained. The unit in the table is “part by weight”. The molar ratios of H ⁺ of the heteropolyacid to the metal alkoxides of Examples 1 to 4 are 4.5 × 10 ⁻² , 9.0 × 10 ⁻² , 1.4 × 10 ⁻¹ , 9.0 × 10 respectively. ^-2 .

(2) Dilution of mother liquor 10 parts by weight of isopropyl alcohol and n-butanol were added to 10 parts by weight of the mother liquors of the coating compositions of Examples 1 to 4 and Comparative Example 1, respectively. The coating composition of Comparative Example 1 was obtained.
For Comparative Example 2, 8.5 parts by weight of ATO dispersion (40% by weight) was added to 10 parts by weight of the mother liquor of the coating composition of Comparative Example 1, and 5.7% each of isopropyl alcohol and n-butanol were added. The coating composition of Comparative Example 2 was obtained by diluting by adding parts by weight. The ATO dispersion is a dispersion in which antimony-doped tin oxide (conductive powder T-1: Mitsubishi Materials Corporation) is dispersed with propylene glycol monomethyl ether so that the ATO component is 40% by weight.

2. Formation of Transparent Conductive Film On the polyester film having a thickness of 100 μm, the coating compositions of Examples 1 to 4 and Comparative Examples 1 and 2 were each applied by the bar coater method and dried at 100 ° C. for 3 minutes. 4 and the conductive sheet in which the transparent conductive film of Comparative Examples 1-2 was formed was obtained.

3. Evaluation The following items were evaluated using the conductive sheet. The results are shown in Table 2.
(1) Transparency It was visually evaluated whether or not the conductive sheet was colored. As a result, the uncolored one was “◯”, and the one that was colored was “x”.
(2) Surface resistivity Based on JIS K6911: 1995, the surface resistivity of the transparent conductive sheet was measured.

As is clear from the above results, since the coating compositions of Examples 1 to 4 use a heteropolyacid containing H ⁺ as a partner cation as a catalyst, the coating film formed from the composition is It had excellent transparency, low surface resistivity, and excellent antistatic properties. In particular, in Examples 1 to 3, since H ₃ [PW ₁₂ O ₄₀ ] having excellent H ⁺ release properties is used as the heteropolyacid, the surface resistivity is lower than that of Example 4, and charging is performed. It was excellent in prevention.

On the other hand, since the coating composition of Comparative Example 1 does not use a heteropolyacid containing H ⁺ as a partner cation as a catalyst and does not contain an antistatic agent separately, a coating film formed from the composition Had high surface resistivity and poor antistatic properties.

Further, the coating composition of Comparative Example 2 does not use a heteropolyacid containing H ⁺ as a partner cation as a catalyst, but also contains an antistatic agent separately, so that a coating film formed from the composition Although the surface resistivity was low and the antistatic property was excellent, the coating film was colored and the transparency was poor.

Claims (2)

A coating composition comprising a sol obtained by hydrolyzing a metal alkoxide by the action of a catalyst, wherein the free-acid heteropolyacid and / or its acidity substantially containing H ⁺ as a counter cation as the catalyst and antistatic agent Using only a salt, and using H ⁺ of a free acid type heteropolyacid and / or its acid salt with respect to a metal alkoxide in a molar ratio of 3.0 × 10 ^{−2 to} 3.0 × 10 ^−1. A conductive coating composition.   A transparent conductive film formed from the conductive coating composition according to claim 1.