JP5162941B2 - Transparent conductive film and method for producing the same - Google Patents

Description

  The present invention relates to a transparent conductive film excellent in conductivity, transparency and coating film strength, and having a small decrease in conductivity even when stored for a long time in a high humidity environment, and a method for producing the same.

  Transparent conductive films are used for liquid crystal displays, electroluminescence displays, plasma displays, electrochromic displays, solar cells, transparent electrodes such as touch panels, and electromagnetic shielding materials.

  As a transparent conductive film widely applied, indium-tin composite oxide (ITO) is deposited on at least one surface of a transparent film such as polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) by vacuum deposition or Although it is a method of forming a film by a dry process such as a sputtering method, there is a problem that a high temperature is required for the film formation and the film formation cost is high. In addition, an inorganic oxide film such as an ITO film on a film base material is liable to crack due to the bending of the film base material.

On the other hand, a transparent conductive film in which a conductive polymer layer that can be formed at low temperature and low cost by a wet process is formed on a transparent film has been proposed. The transparent conductive layer formed of a conductive polymer has flexibility in the film itself, so that problems such as cracks hardly occur, but it has been difficult to obtain the same conductivity as that of the ITO film. For example, adding a polar solvent to an oxidized polymer of poly (3,4-dialkoxythiophene) with good water dispersibility and a polyanion (see Patent Document 1) and more recently to a dispersion of a conductive polymer However, a material (see Patent Document 2) whose conductivity is greatly improved has been disclosed, but sufficient conductivity has not been obtained yet. As a cause of this, it is known that when a conductive polymer is applied and dried, a polyanion having low conductivity is likely to move to the vicinity of the surface layer (see Non-Patent Document 1). In order to solve this problem, there is a method in which a conductive polymer coating solution is applied in two or more times, or a polyanion component is removed by corona discharge treatment or plasma discharge treatment after forming a coating film (see Patent Document 3). It is disclosed. However, these methods are not only insufficient in electrical conductivity, but also need to add a binder, a silane compound, etc. in order to improve coating strength and film attachment to the film support. There was a problem that caused a drop in
Japanese Patent Laid-Open No. 7-90060 JP 2005-529474 A JP 2006-291032 A J. et al. Electr. spectr. Rel. Phenom. , 121, 1 (2001)

  An object of the present invention is to provide a transparent conductive film excellent in conductivity, transparency and coating film strength, and having a small decrease in conductivity even when stored for a long time in a high humidity environment, and a method for producing the same. .

  The above object of the present invention is achieved by the following configurations.

  1. A transparent conductive film in which a transparent conductive coating film containing a polyanion and a π-conjugated polymer is provided on at least one surface of a transparent substrate film, wherein the transparent conductive film has an upper layer with respect to the polyanion. A transparent conductive film, wherein the ratio of the π-conjugated polymer is higher than the average value of the entire transparent conductive coating film.

  2. A method for producing a transparent conductive film, comprising applying a polyanion solution to at least one surface of a transparent substrate film, and then applying a π-conjugated polymer solution.

  3. 3. The method for producing a transparent conductive film as described in 2 above, wherein the π-conjugated polymer solution contains a polar organic solvent.

  4). 4. The coating composition according to 2 or 3, wherein the polyanion in the polyanion solution and the π-conjugated polymer solution in the π-conjugated polymer solution are applied so that a mass ratio thereof is from 0.5: 1 to 10: 1. A method for producing a transparent conductive film.

  According to the present invention, it is possible to provide a transparent conductive film which is excellent in conductivity, transparency and coating film strength, and has a small decrease in conductivity even when stored for a long time in a high humidity environment. This transparent conductive film can be preferably used as a transparent electrode for liquid crystal displays, electroluminescence displays, plasma displays, electrochromic displays, solar cells and the like.

  As a result of intensive studies to solve the above problems, the present inventors have found that the ratio of the π-conjugated polymer to the polyanion of the transparent conductive film upper layer in the transparent conductive film provided on the transparent substrate film Is higher than the average value of the entire transparent conductive coating film, so that the effect of the present invention, that is, excellent conductivity, transparency and coating film strength, and conductivity even when stored for a long time in a high humidity environment. Succeeded in obtaining a transparent conductive film with a small decrease in the thickness.

  In general, the conductive polymer is colored, and if the conductive coating film is thickened to obtain high conductivity, the transparency is deteriorated. In the present invention, it is considered that the conductivity can be increased while maintaining high transparency by containing a large amount of π-conjugated polymer having high conductivity in the upper layer (layer close to the surface). Here, the upper layer means a side closer to the surface than half the film thickness of the transparent conductive coating film after drying. Furthermore, it is preferable that the ratio of the π-conjugated polymer to polyaniline on the side closer to the surface than 1/3 of the film thickness of the transparent conductive coating film is higher than the average value of the entire transparent conductive coating film.

  The ratio of the π-conjugated polymer to the polyanion is higher than the average value of the total thickness of the transparent conductive coating film in the upper layer. The section cut into an ultrathin film using a microtome or the like using ESCA (Electron Spectroscopy for Chemical Analysis) or the like. It is obtained by measuring several places in the thickness direction of the film or by measuring the depth profile.

  In addition, according to the method for producing a transparent conductive film in which a π-conjugated polymer is laminated and applied after applying a polyanion to a base film, the effect of the present invention, that is, conductivity, transparency and coating strength are excellent. We have succeeded in obtaining a method for producing a transparent conductive film in which the decrease in conductivity is small even when stored for a long time in a high humidity environment.

  The present invention will be described in detail below.

(Π-conjugated polymer)
The π-conjugated polymer used in the present invention may be an organic polymer whose main chain is composed of a π-conjugated system. For example, polypyrroles, polythiophenes, polyacetylenes, polyphenylenes, polyphenylene vinylenes, polyanilines , Polyacenes, polythiophene vinylenes, and copolymers thereof. Among these, polypyrroles, polythiophenes, and polyanilines are preferable.

  The π-conjugated polymer used in the present invention may be unsubstituted or substituted with a functional group such as an alkyl group, a carboxy group, a sulfo group, an alkoxy group, a hydroxy group, or a cyano group.

  Specific examples of such π-conjugated polymers include polypyrrole, poly (N-methylpyrrole), poly (3-methylpyrrole), poly (3-ethylpyrrole), poly (3-n-propylpyrrole), poly (3-butylpyrrole), poly (3-octylpyrrole), poly (3-decylpyrrole), poly (3-dodecylpyrrole), poly (3,4-dimethylpyrrole), poly (3,4-dibutylpyrrole) , Poly (3-carboxypyrrole), poly (3-methyl-4-carboxypyrrole), poly (3-methyl-4-carboxyethylpyrrole), poly (3-methyl-4-carboxybutylpyrrole), poly (3 -Hydroxypyrrole), poly (3-methoxypyrrole), poly (3-ethoxypyrrole), poly (3-butoxypyrrole), poly (3- Siloxypyrrole), poly (3-methyl-4-hexyloxypyrrole), poly (3-methyl-4-hexyloxypyrrole), poly (thiophene), poly (3-methylthiophene), poly (3-ethylthiophene) ), Poly (3-propylthiophene), poly (3-butylthiophene), poly (3-hexylthiophene), poly (3-heptylthiophene), poly (3-octylthiophene), poly (3-decylthiophene), Poly (3-dodecylthiophene), poly (3-octadecylthiophene), poly (3-bromothiophene), poly (3-chlorothiophene), poly (3-iodothiophene), poly (3-cyanothiophene), poly ( 3-phenylthiophene), poly (3,4-dimethylthiophene), poly (3,4-dibutylthio) Offene), poly (3-hydroxythiophene), poly (3-methoxythiophene), poly (3-ethoxythiophene), poly (3-butoxythiophene), poly (3-hexyloxythiophene), poly (3-heptyloxy) Thiophene), poly (3-octyloxythiophene), poly (3-decyloxythiophene), poly (3-dodecyloxythiophene), poly (3-octadecyloxythiophene), poly (3,4-dihydroxythiophene), poly (3,4-dimethoxythiophene), poly (3,4-diethoxythiophene), poly (3,4-dipropoxythiophene), poly (3,4-dibutoxythiophene), poly (3,4-dihexyloxy) Thiophene), poly (3,4-diheptyloxythiophene), poly (3,4 Dioctyloxythiophene), poly (3,4-didecyloxythiophene), poly (3,4-didodecyloxythiophene), poly (3,4-ethylenedioxythiophene), poly (3,4-propylenedioxy) Thiophene), poly (3,4-butenedioxythiophene), poly (3-methyl-4-methoxythiophene), poly (3-methyl-4-ethoxythiophene), poly (3-carboxythiophene), poly (3 -Methyl-4-carboxythiophene), poly (3-methyl-4-carboxyethylthiophene), poly (3-methyl-4-carboxybutylthiophene), polyaniline, poly (2-methylaniline), poly (3-isobutyl Aniline), poly (2-aniline sulfonic acid), poly (3-aniline sulfonic acid), etc. It is.

  Among these, polymers or copolymers selected from polypyrrole, polythiophene, poly (N-methylpyrrole), poly (3-methylthiophene), poly (3-methoxythiophene), poly (3,4-ethylenedioxythiophene). A polymer is preferably used from the viewpoint of resistance and reactivity. In particular, polythiophene represented by the following general formula (1) is preferable.

(In the formula, R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, or an alkylene group having 1 to 12 carbon atoms which may be bonded and substituted.)
(Polyanion)
Examples of the polyanion used in the present invention include polymeric carboxylates and polymeric sulfonic acids.

  Examples of the polymeric carboxylic acid include polyacrylic acid, polymethacrylic acid, and polymaleic acid. Examples of the polymeric sulfonic acid include restyrene sulfonic acid and polyvinyl sulfonic acid. These polymeric carboxylic acids and sulfonic acids may be copolymers of vinyl carboxylic acids and vinyl sulfonic acids with other polymerizable low molecular compounds such as acrylates and styrene.

  Specific examples of the polyanion used in the present invention include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacryl sulfonic acid, polymethacryl sulfonic acid, poly-2-acrylamido-2-methylpropane sulfonic acid, polyisoprene. Examples include sulfonic acid, polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacryl carboxylic acid, polymethacryl carboxylic acid, poly-2-acrylamido-2-methylpropane carboxylic acid, polyisoprene carboxylic acid, polyacrylic acid and the like. It is done. These homopolymers may be sufficient and 2 or more types of copolymers may be sufficient. Among these polyanions, polyacryl sulfonic acid, polymethacryl sulfonic acid, polystyrene sulfonic acid, and all or part of which are metal salts are preferably used. In particular, polystyrene sulfonic acid is most preferable. The number average molecular weight of such a polyanion is suitably in the range of 1,000 to 2,000,000, and preferably in the range of 2,000 to 500,000.

  In the present invention, the ratio of the polyanion to the π-conjugated polymer is preferably in the range of 0.5 to 10 g and more preferably in the range of 1 to 5 g with respect to 1 g of the π-conjugated polymer. When the polyanion content is less than 0.5 g, the coating film strength is weak, and when it is more than 10 g, sufficient conductivity cannot be obtained.

  The π-conjugated polymer used in the present invention may contain other dopants in addition to the polyanion. Other dopants may be donor or acceptor as long as the π-conjugated polymer can be oxidized and reduced. Examples of the donor dopant include alkali metals such as sodium and potassium, alkaline earth metals such as calcium and magnesium, tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, dimethyldiethylammonium, and the like. A quaternary amine compound etc. are mentioned. Examples of the acceptor dopant include halogen compounds, Lewis acids, proton acids, organic cyano compounds, organometallic compounds, fullerenes, hydrogenated fullerenes, hydroxylated fullerenes, carboxylated fullerenes, and sulfonated fullerenes.

(Method for producing transparent conductive film)
The transparent conductive film of the present invention is obtained by applying a polyanion solution to a film substrate and then applying and laminating a π-conjugated polymer solution to form a transparent conductive coating film. The polyanion solution and the π-conjugated polymer solution may be applied alternately and repeatedly. However, in that case, it is important that the application of the π-conjugated polymer solution is the uppermost layer (last application).

  Examples of the application method include a lip direct method, a comma coater method, a slit reverse method, a die coater method, a gravure roll coater method, a blade coater method, a spray coater method, an air knife coat method, a dip coat method, and a bar coater method. Conventionally known methods can be employed.

  Prior to coating, the surface of the film substrate is preferably subjected to cation modification (cation charge imparting). The reason for this is that when the charge density on the substrate surface is higher, a polyanion layer can be uniformly formed on the substrate, while the polymer electrolyte membrane is formed on the substrate to increase the charge density. be able to. Therefore, a polymer electrolyte membrane can be formed on a substrate, and a layer in which the polyanion is uniformly attached can be formed by electrostatic interaction between the polymer electrolyte membrane and the polyanion.

  Examples of a method for imparting a cationic charge to the substrate surface include application of a cationic polymer electrolyte, formation of a polymer electrolyte multilayer film, and the like.

  As the cationic polymer electrolyte, polyallylamine hydrochloride, polyethyleneimine, polydiallyldimethylammonium chloride and the like are preferable.

  Since the substrate surface is often hydrophobic, the polymer surface is subjected to at least one of corona discharge treatment, glow discharge treatment, plasma treatment, hydrolysis treatment, and silane coupling treatment, and then polymer It is also possible to perform electrolyte coating or polymer electrolyte multilayer film formation, which is a preferred method.

  The thickness of the transparent conductive coating film after drying is 50 to 500 nm, preferably 70 to 200 nm. If it is less than 50 nm, sufficient conductivity cannot be obtained, and if it is thicker than 500 nm, the transparency is deteriorated.

  Examples of the solvent for the polyanion solution and the π-conjugated polymer solution include water, alcohols such as methanol and ethanol, ketones such as acetone, hydrocarbons such as hexane and toluene, carboxylic acids such as acetic acid, and the like. These solvents may be used alone or as a mixture of two or more.

  Furthermore, a small amount of a polar organic solvent such as diethylene glycol, triethylene glycol, tetraethylene glycol, dimethylformamide, dimethyl sulfoxide or the like is added to the π-conjugated polymer solution within a range that does not adversely affect the durability of the transparent conductive layer. It is preferable. The addition amount of the polar organic solvent is 0.5 to 50% by mass, preferably 1 to 10% by mass with respect to the 1% by mass aqueous solution of the π-conjugated polymer. When it is more than 50% by mass, not only the durability of the film is deteriorated, but also haze is increased and transparency is also deteriorated. If it is less than 0.5 mass%, the effect of adding a polar organic solvent cannot be obtained.

(Base film)
As the base film used in the present invention, any film can be used depending on the application, for example, polyester, polystyrene, polyimide, polyamide, polysulfone, polycarbonate, polyvinyl chloride, polyethylene, polypropylene, and mixtures thereof. Examples thereof include a film made of a copolymer, and further a phenol resin, an epoxy resin, an ABS resin, or the like. Among these, a biaxially oriented polyester film is preferable because it has excellent properties such as dimensional stability, mechanical properties, heat resistance, and electrical properties, and particularly polyethylene terephthalate film or polyethylene-2,6-naphthalate. A film is preferable because it is excellent in mechanical properties such as a high Young's modulus and excellent in heat-resistant dimensional stability. The thickness of the polyester film is preferably 500 μm or less, and if it exceeds this, the rigidity becomes too strong and the handleability tends to be lowered.

  As the transparency of the transparent conductive film of the present invention, the total light transmittance is 70% or more, preferably 80% or more. When the total light transmittance is less than 70%, the transparency is insufficient and it is not preferable for use in a liquid crystal display or the like.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these. In addition, although the display of "%" is used in an Example, unless otherwise indicated, "mass%" is represented.

Example [Production of transparent conductive film]
(Preparation of sample 101)
After corona discharge treatment was applied to one side of a 100 μm PET film, a 10% aqueous solution of polystyrenesulfonic acid (molecular weight 4000) was applied to the corona discharge-treated surface side using a wire bar so that the film thickness after drying was 107 nm. And dried at 120 ° C. Furthermore, a coating solution in which 5% of dimethyl sulfoxide was added to an aqueous solution in which 1% of poly (3,4-ethylenedioxythiophene) was dispersed thereon was applied so that the film thickness after drying was 150 nm. It dried at ° C and produced sample 101 (transparent conductive film).

(Production of samples 102 to 107)
In the preparation of Sample 101, the content ratio after drying of polystyrene sulfonic acid and poly (3,4-ethylenedioxythiophene) was changed as shown in Table 1 so that the dry film thickness was 150 nm. Samples 102 to 107 were produced.

(Production of samples 108 to 110)
Sample 108 was prepared in the same manner except that the amount of dimethyl sulfoxide added to an aqueous solution in which 1% poly (3,4-ethylenedioxythiophene) was dispersed was changed to 9% and not added. 109 were produced. A sample 110 was prepared in the same manner except that dimethyl sulfoxide added to an aqueous solution in which 1% poly (3,4-ethylenedioxythiophene) was dispersed was changed to 5% diethylene glycol.

(Preparation of samples 111 and 112)
In the preparation of Sample 101, a 10% aqueous solution of polystyrene sulfonic acid was applied, the film thickness after drying was 50 nm, and 5% dimethyl sulfoxide was added to an aqueous solution in which 1% of poly (3,4-ethylenedioxythiophene) was dispersed. Sample 111 having a total film thickness of 70 nm after application of the liquid was coated with a 10% aqueous solution of polystyrene sulfonic acid, the film thickness after drying was 200 nm, and poly (3,4-ethylenedioxythiophene) was dispersed 1%. Sample 112 was prepared by adding a coating solution obtained by adding 5% of dimethyl sulfoxide to an aqueous solution so that the total film thickness after coating was 280 nm.

(Preparation of sample 113)
Using a wire bar, a 10% aqueous solution of polystyrene sulfonic acid (molecular weight 4000) was applied to a PET film that had been subjected to the same corona discharge treatment as that for the preparation of Sample 101 so that the film thickness after drying would be 72 nm, at 120 ° C. Dried. Furthermore, a coating solution in which 5% of dimethyl sulfoxide was added to an aqueous solution in which 1% of poly (3,4-ethylenedioxythiophene) was dispersed thereon was applied so that the film thickness after drying was 85 nm. Dried at ℃. Furthermore, 5% of dimethyl sulfoxide was added to an aqueous solution in which the same polystyrene sulfonic acid aqueous solution was dried once again on this coating film with a thickness of 120 nm and poly (3,4-ethylenedioxythiophene) was dispersed by 1%. The coating solution was applied in this order so that the film thickness after drying was 150 nm, and sample 113 was produced.

(Preparation of sample 114)
Sample 114 was prepared in the same manner as in the preparation of Sample 101 except that polydiallyldimethylammonium chloride was previously applied onto a PET film.

(Preparation of samples 115 and 116)
The same PET film as sample 101 using poly (3,4-ethylenedioxythiophene) polymerized in the presence of polystyrene sulfonic acid (BaytronP, solid content concentration of about 1.3%: manufactured by HC Starck) A sample 115 was prepared by coating the film so that the film thickness after drying was 150 nm, and drying at 120 ° C.

  Furthermore, after applying and drying a solution obtained by adding 2.5% of diethylene glycol to BaytronP so that the film thickness after drying is 100 nm, the same liquid is again deposited thereon so that the total film thickness after drying is 150 nm. The sample 116 was produced by coating and drying.

[Measurement and evaluation of transparent conductive film]
With respect to the transparent conductive film samples 101 to 116 obtained as described above, the ratio of poly (3,4-ethylenedioxythiophene) to polystyrenesulfonic acid in the upper layer of the transparent conductive coating film is measured by the following method. The total light transmittance, surface resistivity, coating film strength, and surface resistivity after high humidity storage were evaluated.

(Ratio of poly (3,4-ethylenedioxythiophene) to polystyrenesulfonic acid in the upper layer)
The transparent conductive film was cut out in a direction perpendicular to the surface with a microtome and calculated from the peak intensity due to thiophene using ESCALAB-200R manufactured by VG Scientific.

(Total light transmittance)
According to JIS K7150, the total light transmittance was measured with a haze meter HCM-2B manufactured by Suga Test Instruments Co., Ltd.

(Surface resistivity)
In accordance with JIS K7194, the surface resistivity was measured using a Lorester GP (MCP-T610 type) manufactured by Mitsubishi Chemical Corporation. The measurement was performed by sampling 50 arbitrary points in a rectangular (17.43 cm × 30.99 cm) size having a diagonal size of 35.56 cm (14 inches), and the average value was obtained as the surface resistance value.

(Coating strength)
The transparent conductive film of the uppermost layer of the transparent conductive film was rubbed with the thumb three times at the same place, the state of the coating film was visually observed, and evaluated according to the following criteria.

◎: No trace of rubbing on the coating film is observed ○: Trace of rubbing on the coating film is slightly seen, but there is no problem in performance △: Some trace of rubbing on the coating film is seen X: A trace of rubbing on the coating film is clearly seen (surface resistivity after high humidity storage)
The transparent conductive film was left in an environment of 60 ° C. and 90% RH for 30 days, and then the surface resistivity was measured in the same manner as the measurement of the surface resistivity at room temperature.

  The results of measurement and evaluation are shown in Table 2.

  As can be seen from Table 2, it can be seen that the sample of the present invention is excellent in conductivity, transparency and coating film strength, and hardly deteriorates in conductivity even when stored for a long time in a high humidity environment.

Claims (4)

A transparent conductive film in which a transparent conductive coating film containing a polyanion and a π-conjugated polymer is provided on at least one surface of a transparent substrate film, wherein the transparent conductive film has an upper layer with respect to the polyanion. A transparent conductive film, wherein the ratio of the π-conjugated polymer is higher than the average value of the entire transparent conductive coating film. A method for producing a transparent conductive film, comprising applying a polyanion solution to at least one surface of a transparent substrate film, and then applying a π-conjugated polymer solution. The method for producing a transparent conductive film according to claim 2, wherein the π-conjugated polymer solution contains a polar organic solvent. The coating is performed such that the mass ratio of the polyanion in the polyanion solution to the π-conjugated height in the π-conjugated polymer solution is 0.5: 1 to 10: 1. Manufacturing method of transparent conductive film.