JPH01153769A - Composition for forming transparent electrically conductive film of zinc oxide - Google Patents

Abstract

PURPOSE:To obtain the title composition widely usable for automobiles and electronic devices, imparting inexpensive and transparent electrically conductive films, containing fine powder of electrically conductive zinc oxide as an electrical conductivity imparting component in a specific ratio. CONSTITUTION:(A) A film forming composition is blended with (B) 20-70wt.% (calculated as solid content) fine powder of electrically conductive zinc oxide having <=0.1mum specific surface area diameter by BET method and <=10<4>OMEGAcm volume specific resistance in 100kg/cm<2> pressure state to give the titled composition suitable as an ultraviolet cutting material in glass of show window and in transparent plastic material or surface protecting agent for molded article of resin by using ultraviolet light screening effects.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a composition containing conductive zinc oxide as a conductivity-imparting component and capable of forming an inexpensive and transparent conductive film. The conductive film-forming composition can be used in clean rooms or windows of automobiles and vehicles, antistatic films on cathode ray tubes, various touch panels such as CRT displays, EL panels, and liquid crystal cells in various electronic devices such as computers. It is widely used as an antistatic film formed on the surface of materials such as transparent electrostatic recording paper, conductive film forming material for various information industry recording papers such as magnetic tape, etc., and as a constituent material for conductive paints and inks. can do.

[Prior Art] As means for forming a transparent conductive film applied to the above-mentioned uses, various methods as shown below are known.

■A method in which a thin metal film such as gold, palladium, or chromium-based alloy is deposited on the surface of a transparent resin sheet or film such as polyester, or glass.

(2) A method of making the entire film-forming substrate transparent and conductive, such as a transparent conductive polymer.

■On the surface of a transparent substrate heated to about 300-600℃,
A method of spraying a solution of a metal salt such as InC14 or S n C14 in an organic solvent and thermally decomposing it to form a conductive metal oxide thin film.

(2) A method in which a transparent metal oxide film with conductivity is formed by applying a metal alkoxide such as In or Sn or an acetylacetone solution to the surface of a transparent substrate and then heat-treating it.

(2) A method in which conductive fine powder, such as conductive tin oxide fine powder, is dispersed in a binder such as a polymer solution and applied to a transparent substrate.

These methods are appropriately used depending on the use and required characteristics of the transparent conductive film as described above.

The present invention relates to the improvement of a transparent conductive film-forming composition of a conductive fine powder dispersion type that is particularly applicable to the method shown in (1) above. Antimony-containing tin oxide and tin-containing indium oxide are known as conductive fine powders that can be applied to these methods, and these provide conductivity and antistatic properties by utilizing the conductive properties of the fine powder itself. Moreover, since the above-mentioned antimony-containing tin oxide and the like have a particle size smaller than the local wavelength of visible light, the coating becomes transparent. This method of forming a conductive film has good workability and productivity because it simply combines dispersion of conductive fine powder, coating, and drying, and the conductivity can be adjusted freely by changing the blending amount of conductive fine powder. It has various features such as being adjustable.

By the way, the current widely used conductive fine powder is conductive zinc oxide activated by aluminum, tin, titanium, etc., but the particle size of this conductive zinc oxide powder is at least 1 μm. Since it is only a small amount, it cannot be called a fine powder in relation to its purpose, and it cannot provide transparency to the coating.

Therefore, as a fine powder for forming a transparent conductive film, a tin oxide-based or indium oxide-based fine powder, which can be obtained as a fine powder of about 0.1 μm or less, is used. However, these fine powders are 10 to 50 times more expensive than conductive zinc oxide powder. Moreover, in tin oxide-based conductive fine powder, a large amount of antimony is added to obtain a high level of conductivity, which gives it a bluish color. ■This blue color is further colored by ultraviolet rays. (2) The electrical conductivity may change due to changes in humidity, and problems such as a lack of suitability as a conductive material for electronic devices have been pointed out.

Under these circumstances, the present applicant has been conducting research for some time in order to develop conductive zinc oxide fine powder that satisfies the required characteristics for use in transparent conductive films. The method described in Japanese Patent No. 58-161923 was developed. This method consists of (A) zinc oxide, (B) an aluminum salt acting as an activator, and (C)
The mixture is stirred in an aqueous dispersion system with ammonium carbonate, ammonium bicarbonate, ammonium nitrate, or urea, which acts as an erosion agent (disintegrant), filtered, dehydrated, dried, and fired at 600 to 1000°C in a reducing atmosphere to form a conductive oxidizer. According to this method, zinc oxide can be made fine by the action of a disintegrant, so activation is promoted and the fineness of the sintered powder is also promoted.

[Problems to be solved by the invention] However, even with the method described in the above publication, the particle size of conductive zinc oxide is 0.2 μm in terms of specific surface area diameter (value determined by the 13ET method; the same applies hereinafter). The extent of this change is limited, and it cannot be said that it completely satisfies the required characteristics as a transparent conductive film.

In other words, as a means to obtain a transparent film with a pigment-filled system,
Make the particle size of the pigment smaller than the % wavelength of visible light, or
Alternatively, in paints, etc., it is considered effective to reduce the refractive index of the vehicle component resin as much as possible, and considering the properties of the pigment itself, the purpose of imparting transparency can be achieved by reducing the particle size to 0.1 μm or less. However, at present, conductive zinc oxide fine powder with such a fine particle size structure has not been obtained.

The present invention was made in view of these circumstances, and its purpose is to use zinc oxide as the main raw material, which can be industrially produced manually at low cost, to form a fine, stable, and highly conductive film with a transparent coating. The purpose of the present invention is to develop a conductive zinc oxide fine powder that can provide the following properties, and to provide a transparent conductive film-forming composition that is inexpensive and has excellent performance by using such a fine zinc oxide powder.

[Means for Solving the Problems] The transparent conductive film-forming composition according to the present invention that can achieve the above-mentioned object is a transparent conductive film-forming composition that can be measured by the BET method of conductive zinc oxide fine powder, which is a conductivity imparting component. The specific surface area diameter is 0
．． The volume resistivity measured under a pressure of 1 μm or less and 100 kg/cm2 is determined to be 10'Ωcm or less, and the electrically conductive zinc oxide fine powder is added to the film-forming composition in an amount of 20 to 70% in terms of the solid content of the dry film. The gist of this is that it is blended in such a manner that the weight percentage is as follows.

[Function] As mentioned above, the film-forming composition according to the present invention has a specific surface area diameter of 0.1 μm or less and a volume resistivity (100 kg/c
The value measured under pressure of 104Ω (same below) is 104Ω.
This product contains conductive zinc oxide fine powder having a size of less than cm as a conductivity-imparting component.

Conductive zinc oxide powder with a specific surface area diameter exceeding 0.1 μm causes significant scattering of visible light when blended as a coating component, and if a sufficient amount of the powder is blended in an attempt to provide excellent conductivity, the conductivity will decrease. The film becomes opaque. Further, if the volume resistivity of the zinc oxide fine powder exceeds 104 Ωcm, satisfactory conductivity cannot be provided even if a sufficient amount of zinc oxide fine powder is blended into the coating component. On the other hand, if conductive zinc oxide fine powder with a specific surface area diameter of 0.1 μm or less and a volume resistivity of 104 Ωcm or less is blended so that the solid content of the dry film is 20 to 70% by weight. The dried film is transparent and exhibits excellent conductivity (and antistatic properties). If the content of the conductive zinc oxide fine powder is less than 20% by weight, the absolute amount of the conductivity-imparting component in the dry film will be insufficient, and sufficient conductivity will not be obtained; If it exceeds 70% by weight, the amount of binder or film-forming component will be insufficient, resulting in poor film properties, poor adhesion to the substrate, and easy peeling, and furthermore, the transparency of the film will deteriorate. It's going to decline.

By the way, the known conductive zinc oxide powder is conductive SnO2.
As explained above, the particles are coarser than the Inks-based fine powder and the Inks-based fine powder, and are not suitable for use in transparent conductive films. Excellent zinc oxide powder can be obtained, for example, by the following method developed by the present inventors (separate patent application method: application number undetermined).

That is, the method is as follows: [I] Non-conductive zinc oxide = 100 parts by weight [n] Activator selected from formates, acetates, halides, hydroxides, sulfates, nitrates, etc. of aluminum oxide: aluminum oxide 0.1 to 10 parts by weight in terms of [m] Erosion agent (disintegrant) selected from ammonium carbonate, ammonium bicarbonate, ammonium nitrate, urea, etc.
; 5 to 100 parts by weight of the three components are stirred in an aqueous dispersion system in the presence of [TV] inorganic fine powder (colloidal silica, alumina gel, titania gel, silicate, etc.) with a specific surface area diameter of 0.10 μm or less. After dehydration, heat treatment is performed at a temperature of about 200 to 600° C. in a non-oxidizing atmosphere.

With this method, after the non-conductive zinc oxide [Il is disintegrated into a fine powder of 0.05 μm or less by stirring treatment in the coexistence with the corrosive agent [IV], the It is uniformly mixed with the aluminum hydroxide precipitate to give conductivity in the next heat treatment process, and furthermore, inorganic fine powder [IV
] is present between the zinc oxide fine powders,
The particle growth of the fine zinc oxide powder during drying or heat treatment is also suppressed, and combined with the effect of suppressing fusion by keeping the heat treatment temperature below 600°C, extremely fine conductive particles with a specific surface area diameter of 0.10 μm or less can be achieved. Zinc oxide fine powder can be easily obtained. In addition, this fine powder is
Zinc oxide, which has been finely broken down during the stirring process, and aluminum hydroxide produced from the activator are mixed evenly and uniformly, and then activated by heating in a non-oxidizing atmosphere, resulting in a volume resistivity. The ratio is 104 Ωcm or less, which indicates excellent conductivity.

The conductive zinc oxide fine powder that meets the purpose of the present invention is produced, for example, by the method described above, but the present invention is not characterized by the manufacturing method itself of the conductive zinc oxide fine powder, but is limited to the specific surface area and diameter. It is characterized by containing conductive zinc oxide fine powder, which has the required characteristics of 0.10 μm or less and a volume resistivity of 104 ΩcI11 or less, as one quarter of the transparent conductive film composition. It is of course possible to use conductive zinc oxide fine powder produced by other methods as long as it satisfies the above requirements, and it is also possible to use conductive zinc oxide fine powder using a compound containing Sn or Ti as an activator. You can also do it.

Next, vehicle components that act as binders or film-forming components for the conductive zinc oxide fine powder include acrylic, vinyl, carbonate, polyester, urethane, epoxy, polypropylene, silicone,
Various polymers capable of forming a transparent film, such as fluorine-based, styrene-based, and cellulose-based polymers, or various modified products thereof can be used. Water-soluble vehicle components include polyvinyl alcohol, methylcellulose, carboxymethylcellulose, starch, gum arabic, styrene-maleic acid copolymer, etc. Emulsions or latexes include vinyl acetate-acrylic emulsion and acrylic ester emulsion. , styrene-butadiene latex, etc. For these vehicle components, it is most common to use an aqueous dispersion medium in consideration of cost, safety (including fires, health injuries, etc.), painting workability, etc., but if necessary, aliphatic dispersion media may be used. , alicyclic or aromatic hydrocarbon, alcohol, ester,
Of course, it is also possible to use organic solvents such as Kent-based solvents or mixed solvents thereof.

The essential components of the conductive film-forming composition according to the present invention are as described above, but in addition, auxiliary agents for improving paintability and film performance include dispersants, surfactants, anti-settling agents, wetting agents, and anti-sagging agents. Depending on the application, one or more of one or more of agents, leveling agents, antifoaming agents, coupling agents, antioxidants, etc. can be added in appropriate amounts, and graphite, carbon black, metal powder, etc. , metal fibers, metal flakes, conductive metal oxide fine powder other than zinc oxide, ion conductive agents, etc. can be used in combination to further increase the conductivity, and furthermore, the transparency and conductivity of the film can be inhibited. Extender pigments within the range not
It is also effective to add color pigments, dyes, etc.

Formation of a conductive film using the composition of the present invention does not require any particularly special technique, but can be applied to the surface of a substrate by impregnation coating, brush coating, roll coating, spray coating, etc., and then dried. Alternatively, it may be applied to the surface of a base material that has been subjected to mold release treatment, dried, and then peeled off from the base material to form a transparent conductive film in the form of a film or sheet. In addition, in the composition of the present invention, since the conductive zinc oxide is extremely fine as described above, sufficient transparency can be obtained even with a one-coat method, but if a two-coat method is adopted, for example, When a clear lacquer or the like is overcoated on the coated surface of the material, the fine irregularities caused by the fine zinc oxide powder on the surface of the composition of the present invention are filled with the clear lacquer, etc., and diffused reflection is further suppressed, as shown in the examples below. With one coat, what used to be semi-transparent with a transmittance of about 50% becomes transparent with a transmittance of about 70%. The increase in surface resistance due to the application of the clear lacquer is about one digit at most, and it does not have much of an adverse effect on the performance as a conductive film or antistatic film, so the two-coat method is a very advantageous film forming method. Recommended.

Regarding the known transparent conductive film, (A) a polyethylene film mixed with a polymer electrolyte (manufactured by Richmond, USA) with a transmittance of 80 to 85% and a surface resistance of 108 to 1010.
Ωcm, (B) Polyester film coated with gold or palladium (manufactured by Sealasin, USA) with transmittance of 80
~90%, surface resistance 10'~103Ωcm, (C) Polyester film with indium oxide vapor deposited (domestic,
Transmittance 80-90%, surface resistance 10
Various types are known depending on the usage and purpose, such as 2 to 105 Ωcm, but the transmittance is about 70% or more, and the surface resistance is about 102 to 10 I0 Ωcm (for antistatic coatings on cathode ray tubes, etc., it is 10 to 10 I0 ΩcI11). It is considered that the transparent conductive film according to the present invention satisfies these required characteristics to a certain extent and can be obtained at a very low cost, as shown in the following examples.

[Example] Reference example (manufacture of conductive zinc oxide fine powder) 20 to 40 g of corrosive agent (ammonium carbonate or ammonium bicarbonate)
Dissolve in 500cc of water. - Add and dissolve 5 g of an activating material (aluminum sulfate or aluminum nitrate) in terms of aluminum oxide into 50 cc of power water, and add and mix the above-mentioned erosion-splitting water solution. The mixed solution was mixed with separately prepared French method zinc white (average specific surface area diameter 0.3 μm) 10
After adding 0g of water to 200cc of dispersion and raising the temperature to 60 to 90°C, colloidal silica (trade name "Aerosil 200J, manufactured by Nippon Aerosil Co., Ltd., specific surface area diameter 0.03 μm) I
g and stirred for 1 hour while maintaining the same temperature. Thereafter, insoluble matter is filtered and washed with water, and the resulting cake-like product is dried and heat-treated at 350 to 600° C. for 60 minutes in a hydrogen atmosphere to produce conductive zinc oxide fine powder.

In accordance with the above method, several types of conductive zinc oxide fine powders with different specific surface area diameters and volume resistivities were produced by variously changing the types and amounts of corrosive agents and activators, stirring treatment conditions, and heat treatment conditions. .

Each of the conductive zinc oxide fine powders obtained above, a film-forming resin (urethane resin, polyvinyl alcohol, or acrylic resin), and a predetermined amount of solvent (dimethylformamide) were blended according to the content ratios shown in Table 1, and then mixed with a homogenizer for 30 minutes.
The mixture was mixed for 0 minutes to produce a conductive film forming composition.

For comparison, commercially available conductive zinc oxide powder (manufactured by Hakusui Kagaku Kogyo Co., Ltd., specific surface area diameter 0.20 μm, volume resistivity 100
A conductive film forming composition was produced in the same manner as above except that Ωcm) was used. Each of the obtained compositions had a dry film thickness of 10 to
Coat it on a polyester film (trade name, "Lumirror TJ type" manufactured by Toshisha Co., Ltd.) using a bar coater so that the film has a thickness of 15 μm.
A conductive film was formed.

Table 1 shows the surface resistance and transparency of each dried film obtained.

The details of the blended pigments shown in Table 1 and the performance test method of the obtained conductive film are as follows.

(Film-forming resin) Urethane resin: Manufactured by Kasei Trading Co., Ltd., product name, rEX-4513
-MJ Acrylic resin: Mitsubishi Rayon Co., Ltd., product name rLR-472
J (solid content 40%) Polyvinyl alcohol: Denka Poval B-20J (partially saponified product) (volume resistivity) Polyvinyl alcohol: manufactured by Denki Kagaku Co., Ltd. (partially saponified product) (volume resistivity) 100 kg when charged into a 25 mm cylinder
/cm2 (filling rate: 20%), and the volume resistivity (0 cm) was measured using a "R3223 type" tester manufactured by Yokotsutsu Denki Seisakusho.

(Specific surface area diameter) Rapid surface area measuring device rSA-100 manufactured by Shibata Kagaku Kikai Co., Ltd.
The specific surface area (S
g: m2/g) was measured, and the specific surface area diameter (d: μm) was determined using the measuring device and the true specific gravity of the sample powder (ρ: 5.6 for ZnO) using the following formula.

(Surface Resistance) The surface resistance of the conductive film was measured by applying a conductive paste to the test surface on which the conductive film was formed and applying electricity.

(Surface potential) For each conductive film, electrostatic copying paper tester r manufactured by Kawaguchi Electric Co., Ltd.
Dynamic using SP-428J.

The charging position (volt) was measured under the condition of -6 KV.

(Transparency) The transmittance of 500 nm light was measured using a transmittance measuring device manufactured by Bokuji Seisakusho, and each measured value was evaluated according to the following criteria.

Transmittance of 50% or more: Transparent) 13Q% or more and less than 50%: Translucent Less than 30%: Opaque As is clear from Table 1, Examples (No. 2 to 4. 7~12°15~17.2
0-22.27-29.32-37.40-42.45
~47. The coating obtained by 50~57) has an appropriate surface resistance depending on the amount of conductive zinc oxide fine powder, and the coating is transparent to semitransparent (even if it is semitransparent, a clear lacquer may be applied on it). (It has been confirmed that the composition becomes transparent by coating it on the film), making it an excellent composition for forming a transparent conductive film.

On the other hand, experiment No. 1.6.14, 19°26.31
, 39, and 44.51 are comparative examples in which the content of conductive zinc oxide fine powder is insufficient, and although the transparency is good, the surface resistance is very high due to the lack of conductivity-imparting components, and the conductivity is poor. It cannot be used as a membrane. Also, experiment No. 5
．． 13゜18.23, 30.3B, 43, and 48.58 are all comparative examples in which the content of conductive zinc oxide fine powder exceeds the specified range, and the dried films are all opaque and transparent conductive films. can't get it. Furthermore, experiment No. 24.
Nos. 25, 49, 50, and 59.60 are conventional examples in which the specific surface area diameter of the conductive zinc oxide powder exceeds 0.1 μm, and it is impossible to obtain a transparent film because the diffused reflection of light within the film is significant.

[Effects of the Invention] The present invention is constructed as described above, and uses conductive zinc oxide fine powder that can be produced at low cost, instead of conventional tin oxide-based or indium oxide-based conductive fine powder. It is possible to obtain a conductive film with a transparency equal to or higher than that of 2000 at a very low cost, and it can be widely used as a composition for forming a transparent conductive film or an antistatic film in a variety of applications as listed at the beginning. can do.

1. Indication of the case Patent Application No. 314779 filed in 1988 2. Name of the invention Zinc oxide-based transparent conductive film forming composition 3. Person making the amendment Relationship to the case Patent applicant 4. Address of agent Kita-ku, Osaka City Dojima 2-3-7 Shishiko j1%
4075, subject of amendment, ``Detailed Description of the Invention'' column of Book W, ``Brief Explanation of Drawings'' column of the specification, Errors Table Experiment Nos. 24.25, 49, 50, 59.60 are This is a conventional example in which the specific surface area diameter of the conductive zinc oxide powder exceeds 0.1 μm, and it is impossible to obtain a transparent film because the diffused reflection of light within the film is significant.

FIG. 1 shows the light transmission curve of the fine zinc oxide powder obtained in Experiment No. 9, and absorption peculiar to zinc oxide is observed in the ultraviolet region.

[Effects of the Invention] The present invention is constructed as described above, and uses conductive zinc oxide fine powder that can be produced at low cost7, and replaces conventional tin oxide-based or indium oxide-based conductive fine powder. It is possible to obtain a conductive film at a very low cost with transparency equal to or higher than that of a conventional conductive film, and it can be widely used as a composition for forming a transparent conductive film or an antistatic film in a variety of applications as listed at the beginning. In addition, by utilizing its ultraviolet shielding effect, it can be mixed into glass and transparent plastic materials for show windows, etc. as an ultraviolet blocking material,
Alternatively, it can be used as a surface coating agent for various resin moldings to suppress deterioration of the resin itself.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a light transmission curve of fine zinc oxide powder obtained in an example.

Claims (1)

[Claims] In the film-forming composition containing conductive zinc oxide fine powder as a conductivity imparting component, the conductive zinc oxide fine powder is B
The conductive zinc oxide fine powder has a specific surface area diameter of 0.1 μm or less as measured by the ET method and a volume resistivity of 10^4 Ωcm or less as measured under a pressure of 100 kg/cm^2. 1. A zinc oxide-based transparent conductive film-forming composition, characterized in that the zinc oxide-based transparent conductive film-forming composition is blended in an amount of 20 to 70% by weight in terms of dry film solids.