JP2009076449A - Transparent conductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transparent conductor exhibiting a small increase in a resistance value even when used under high-humidity conditions over a long period of time. <P>SOLUTION: The transparent conductor in the preferred embodiment comprises indium tin oxide, an additive component mainly containing zinc oxide, and a resin cured product 12, and the content of the additive component is 0.1 to 50 mass% relative to a total amount of the indium tin oxide and the additive component. The additive component is preferably zinc oxide doped with gallium or aluminum, and is more preferably an insulating particle 13 mainly containing the oxide zinc. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a transparent conductor.

Transparent electrodes are used in display devices such as LCD, PDP, organic EL, and touch panel. This transparent electrode is often composed of a transparent conductor made of indium tin oxide (hereinafter abbreviated as “ITO”) or the like. As such a transparent conductor, for example, one formed from a material containing conductive oxide fine particles including indium oxide, tin oxide, zinc oxide, and the like as shown in Patent Document 1 below is known. .
JP 2006-202738 A

  In recent years, the display device as described above has been used for various purposes, and the exposure to the severe environment such as high temperature and high humidity is increasing. However, when the present inventors have studied, the conventional transparent conductor as described above is initially low resistance and can function as a conductor, but when used in a high humidity environment for a long time, the initial value is obtained. In comparison, it has been found that the resistance value greatly increases, and the function as a conductor cannot often be performed sufficiently.

  Therefore, the present invention has been made in view of such circumstances, and an object thereof is to provide a transparent conductor having a small increase in resistance value even when used for a long time under high humidity conditions.

  In order to achieve the above object, a transparent conductor of the present invention includes indium tin oxide (ITO), an additive component mainly composed of zinc oxide (ZnO), and a cured resin, and indium tin oxide. And 0.1-50 mass% of additional components are contained in the total amount of an additional component, It is characterized by the above-mentioned.

  According to such a transparent conductor of the present invention, ITO contains an additive component containing ZnO as a main component in the above-described specific content ratio, thereby having a low resistance enough to function as a conductor, Moreover, the increase in resistance value can be sufficiently reduced even when exposed to a high humidity environment for a long time. Heretofore, ITO has been excellent in transparency and low resistance, so that it is suitable as a material for a transparent conductor, but it has been extremely likely to cause an increase in resistance due to moisture or the like. On the other hand, ZnO has an extremely high resistance and is more likely to increase in resistance due to moisture than ITO, so that it is usually difficult to function alone as a conductor. In spite of such a conventional tendency, the present invention surprisingly makes it possible to sufficiently reduce both the resistance value and the change in resistance value due to humidity by adding a specific amount of ZnO to the transparent conductor. Has been found to be possible.

  In the transparent conductor of the present invention, the additive component is more preferably ZnO doped with gallium (Ga) or aluminum (Al). In this way, the resistance value of the additive component itself can be reduced, and as a result, the resistance value of the transparent conductor can be further reduced.

  Further, the additive component is preferably an insulating particle containing zinc oxide as a main component. When the additive component has such a shape of insulating particles, the effect of reducing resistance variation while maintaining low resistance by combination with ITO can be more favorably obtained.

  Furthermore, the additive component may be an insulating particle having at least one of alumina, silica, and resin attached to the surface. The stability of the insulating particles as an additive component with respect to temperature and humidity is improved, and it is possible to further suppress an increase in resistance due to moisture or the like of the transparent conductor.

  According to the present invention, it is possible to provide a transparent conductor having a small increase in resistance value even when used under high humidity conditions for a long time and having a low resistance enough for practical use.

  Preferred embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted.

  Drawing 1 is a figure showing typically the section composition of the transparent conductive film using the transparent conductor of a suitable embodiment. As shown in FIG. 1, the transparent conductive film 10 includes a base material 14 and a transparent conductive layer 15 formed on the base material 14. In this transparent conductive film 10, the transparent conductive layer 15 is formed of the transparent conductor according to a preferred embodiment of the present invention.

  First, the base material 14 can be applied without particular limitation as long as it is made of a material transparent to visible light. For example, glass, a transparent resin film such as polyester, polyethylene, polypropylene, polyethylene terephthalate (PET), or various transparent plastic substrates can be applied.

  On the other hand, the transparent conductive layer 15 has a configuration in which a large number of ITO particles 11 and ZnO particles 13 are dispersed in the cured resin 12. That is, the transparent conductive layer 15 is formed from a transparent conductor containing the ITO particles 11, the ZnO particles 13, and the resin. The transparent conductive layer 15 is mostly constituted by the ITO particles 11 and the ZnO particles 13. Therefore, in other words, it can be said that the transparent conductive layer 15 has a configuration in which the ITO particles 11 and the ZnO particles 13 are aggregated, and the resin cured product 12 is arranged in the gap.

  The ITO particles 11 are particles composed of a composite oxide of indium and tin, so-called ITO. The ITO particles 11 preferably have a primary particle diameter of 0.005 to 0.5 μm, and more preferably 0.02 to 0.08 μm. When the primary particle diameter of the ITO particles 11 is smaller than the above range, oxygen defects that are the cause of the conductivity are less likely to be formed than in the range, and the conductivity of the transparent conductive layer 15 is stabilized. Tend not to be obtained. On the other hand, when the primary particle diameter is too large, light scattering is increased and the visibility of the transparent conductive film 10 may be deteriorated as compared with the case where the primary particle diameter is within the above range.

  The ZnO particles 13 are transparent particles composed of an additive component mainly composed of zinc oxide (ZnO). The shape of the ZnO particles 13 may be any shape such as a spherical shape, a needle shape, or a leaf shape. The ZnO particles 13 may be formed of ZnO alone, and may contain other components or may adhere to the surface as long as ZnO is the main component. Here, “having ZnO as a main component” means that at least about 50% by mass or more of ZnO is included among the additive components.

  As a structure of the ZnO particle | grains 13, the following forms are mentioned except the case where it forms only with ZnO. That is, first, ZnO may be doped with aluminum (Al), gallium (Ga), lithium (Li), fluorine (F), nitrogen (N), transition metal, or the like. The component to be doped is preferably selected as appropriate according to the desired properties to be imparted to the transparent conductive layer 15. For example, the resistivity of the transparent conductive layer 15 can be lowered by doping Al or Ga.

  When doping these components into ZnO, the doping amount is preferably 40% by mass or less, more preferably 30% by mass or less, based on the total amount of the additive components described above. When the doping amount is too large, the resistivity of the ZnO particles 13 increases, the light transmittance decreases, and the effect of suppressing the resistance increase due to humidity obtained by the addition of the ZnO particles 13 is insufficient. It tends to be.

  Examples of the form of the ZnO particles 13 include those made of ZnO alone and those having other components attached to the surface of particles made of ZnO alone. Further, as described above, another component may be adhered to the surface of the particle obtained by mixing other component with ZnO. These are all insulating particles containing ZnO as a main component.

  Examples of the ZnO particle 13 having a form in which other components are attached to the surface of the particle made of ZnO include a form in which alumina or silica is attached to the surface of the core made of ZnO. Specifically, alumina or silica may cover the surface of the ZnO nucleus, and these may form a plurality of layers on the surface of the ZnO nucleus. According to the ZnO particles 13 having such a configuration, the stability of the ZnO particles 13 with respect to temperature and humidity is improved, and thereby it is possible to further suppress an increase in resistance due to moisture or the like of the transparent conductive layer 15. The reason is that by coating the surface with alumina or silica, the surface of the ZnO particles 13 is inactivated, the change in resistivity due to redox is suppressed, and it becomes difficult to dissolve in water or acid. The reactivity with a component becomes small, the dispersibility of the ZnO particle | grains 13 becomes favorable, etc. are mentioned. In this case, the amount of alumina or silica covering ZnO is preferably 0.1 to 20% by mass in the total amount of the additive components. If this amount is too small, the effect of coating with alumina or silica cannot be obtained sufficiently, and if it is too large, it becomes difficult to take a conductive path between the ZnO particles 13 by surface coating, resulting in an increase in resistance value, In some cases, the transmittance may decrease.

  Furthermore, the ZnO particles 13 may have a configuration in which the surface of the ZnO core is covered with a resin having transparency. Examples of the resin include polysiloxane. An example of particles in a form in which the surface of the ZnO core is coated with polysiloxane is NANOFINE-50SD (manufactured by Sakai Chemical Industry Co., Ltd.). With such a configuration, there is an effect of improving the adhesive force to the base material 14, increasing the contact surface with the ZnO particles 13 due to resin shrinkage accompanying the curing reaction, and further preventing oxidation / reduction of the surface of the ZnO particles 13. It will be obtained. The amount of this resin is preferably the same as in the case of silica, alumina or the like described above.

  Among the above, if the structure of the ZnO particles 13 is such that ZnO is doped with 40% or less of Ga or Al, the resistance of the transparent conductive layer 15 is sufficiently low, and the resistance increase due to moisture or the like is improved. This is particularly preferable because it can be suppressed.

  The primary particle diameter of the ZnO particles 13 is preferably 0.005 to 0.5 μm, and more preferably 0.01 to 0.08 μm. If the primary particle size is too small, it becomes difficult to control oxygen defects, and environmental resistance and conductivity of the transparent conductive film 10 may be reduced. On the other hand, when too large, the scattering of light will become large and there exists a possibility that the visibility of the transparent conductive film 10 may fall. The size relationship between the ITO particles 11 and the ZnO particles 13 is not particularly limited, but the conductive performance of the transparent conductive film 10 tends to greatly depend on the ITO particles 11. Therefore, when the ITO particles 11 are larger than the ZnO particles 13, it becomes easier to obtain a conductive path, and the probability that the ZnO particles 13 are in contact with the ITO particles 11 is increased, which is advantageous for reducing the resistance. Further, it is more preferable because higher transmittance can be easily obtained.

  In the transparent conductive layer 15, the ITO particles 11 and the ZnO particles 13 are included in the following predetermined mixing ratio. That is, the latter additive component is contained in an amount of 0.1 to 50 mass% in the total amount of the ITO constituting the ITO particles 11 and the additive components constituting the ZnO particles 13. When the content of the additive component is less than 0.1% by mass or more than 50% by mass, the resistance increase due to moisture or the like of the transparent conductive layer 15 becomes larger than in the case where the content is within these ranges. From the viewpoint of more effectively reducing such resistance increase, the content of the additive component described above is more preferably 1 to 30% by mass. It should be noted that if the content of the additive component is 10% by mass or less, the resistance value of the transparent conductive layer 15 can be sufficiently lowered, which is more effective.

  The transparent conductive layer 15 contains the above-described ITO particles 11 and ZnO particles 13, which are desirably separately formed into particles, for example, react with each other to form a composite oxide or the like. Preferably not. However, complex oxides inevitably formed by contact between these particles may be included in part.

  The transparent conductive layer 15 includes a cured resin 12 in addition to the ITO particles 11 and the ZnO particles 13. This cured resin 12 is disposed in the gap between these particles and functions as a binder resin that binds the particles together. The cured resin 12 is not particularly limited as long as it is transparent to visible light, and a known thermosetting resin or a cured product of a photocurable resin can be applied. For example, acrylic resin, epoxy resin, polystyrene, polycarbonate, norbornene resin, fluororesin, urethane resin and the like can be mentioned, and acrylic resin is preferable.

  The transparent conductive film 10 having the above configuration can be manufactured by, for example, the following manufacturing method.

  That is, first, the ITO particles 11 and the ZnO particles 13 described above are respectively prepared and dispersed in a solvent to obtain a dispersion. As the solvent, for example, alcohols such as methanol, ethanol, propanol, butanol, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and the like can be applied. Further, the dispersion can be performed using, for example, a medium stirring type wet pulverizer such as a bead mill, a vibration ball mill, or a planetary ball mill, a container driven medium type wet pulverizer, or a dry pulverizer.

  Next, after applying this dispersion on the base material 14 or the like as described above, the solvent is removed from the dispersion by, for example, volatilizing the solvent. Thereby, the particle layer in which the ITO particles 11 and the ZnO particles 13 are dispersed and adhered on the base material 14 is formed. Application of the dispersion is, for example, reverse roll method, direct roll method, blade method, knife method, extrusion method, nozzle method, curtain method, gravure roll method, bar coat method, dip method, kiss coat method, spin coat method, It can be performed by a squeeze method, a spray method or the like.

  Then, another support substrate such as a PET film is further arranged on the particle layer formed on the substrate 14, and then the whole is pressed in the stacking direction using a pressure roll or the like. Thereby, the ITO particles 11 and the ZnO particles 13 constituting the particle layer are aggregated to obtain an aggregate. By performing such pressurization, the contact area between the particles is increased, and the effect of improving the conductivity is easily obtained. In addition, when the transparent conductive layer 15 having sufficient characteristics can be formed without applying pressure, such pressurization is not necessarily performed.

  After the support substrate is peeled from the obtained aggregate, a resin that forms the cured resin 12 as described above is applied to the aggregate by curing. Thereby, resin permeates between the ITO particles 11 and the ZnO particles 13 constituting the aggregate. As this resin, the monomer and oligomer which can form the resin cured material 12 by hardening are mentioned, for example. For example, the resin may be allowed to permeate into the aggregate in a state where the resin is dissolved in a solvent.

  Thereafter, the resin that has penetrated into the aggregate is cured to form a cured resin 12. The curing of the resin may be appropriately selected according to the type of the resin. For example, when the resin is a thermosetting resin, the laminate in which the aggregate is formed on the substrate 14 is heated to such an extent that the resin is cured. When the resin is a photocurable resin, the aggregate of the laminate is irradiated with a light beam that can cause the resin to cure.

  Thereby, the ITO particles 11 and the ZnO particles 13 constituting the aggregate are bound by the resin cured product 12 to form the transparent conductive layer 15, and as a result, the transparent conductive film 10 having the above-described configuration is obtained. .

  As mentioned above, although the transparent conductive film of preferred embodiment, the transparent conductive layer (transparent conductor) suitable for this, and the manufacturing method of a transparent conductive film were demonstrated, this invention is necessarily limited to embodiment as mentioned above. Is not to be done.

  For example, in the embodiment described above, the transparent conductive layer 15 has a configuration provided on the base material 14, but the transparent conductive film 10 does not necessarily have the base material 14 and is sufficient. When the strength or the like can be maintained, the transparent conductive layer 15 may be used alone.

  Further, the transparent conductive layer 15 further includes other components in addition to the above-described ITO particles 11, the resin cured product 12, and the ZnO particles 13 in accordance with desired characteristics as long as the effects of the present invention are not excessively reduced. You may go out. The transparent conductive film 10 may further include a layer other than the base material 14 and the transparent conductive layer 15. Furthermore, the method for producing the transparent conductive film is not limited to the method of applying the resin for forming the cured resin 12 after forming the aggregate of the ITO particles 11 and the ZnO particles 13 as in the embodiment described above. It can also be formed by a method in which a mixed solution in which the above particles are dispersed in a resin is prepared in advance and this mixed solution is applied to the substrate 14 or the like. In addition to the transparent conductive film 10 shown in FIG. 1, there may be obtained the transparent conductive film 10 shown in FIG.

EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to these Examples.
[Examples 1 to 9, Comparative Examples 1 to 4]

  In Examples 1 to 9 and Comparative Examples 1 to 4, the ITO (ITO particles) and the additive component (ZnO particles) were mixed with ZnO particles as shown in Table 1 (ZnO particles relative to the total of ITO particles and ZnO particles). The transparent conductive film was produced by blending so that the content was expressed as mass%). Comparative Example 1 (ZnO particles 0%) shows a case where only ITO particles are used, and Comparative Example 4 (ZnO particles 100%) shows a case where only ZnO particles are used. The manufacturing method of the transparent conductive film was as shown below.

(Preparation of transparent conductive film)
First, ITO particles having an average particle diameter of 20 nm or more (primary particle average diameter = 0.03 μm) dispersed in 30 g of ethanol are mixed with ZnO particles, Ga-doped ZnO (Ga dope ZnO; HK Tech, GK40, primary particle average) A diameter = 0.03 μm or less and a resistance value (powder specific resistance) = 500 Ω · cm) were added to prepare a dispersion (hereinafter referred to as ITO—ZnO particles). Here, a total of 10 g of ITO particles and ZnO particles were used.

  Next, after apply | coating the obtained dispersion liquid on PET film, ethanol was removed from the dispersion liquid. Subsequently, another PET film was placed on the layer obtained by drying the coating solution, and the whole was pressurized with a pressure roll. Thereby, the aggregate which ITO particle and ZnO particle aggregated was obtained.

  After peeling off one PET film from the aggregate, this aggregate is impregnated with a mixture of uncured acrylic resin, methyl ethyl ketone (manufactured by Kanto Chemical Co., Inc.), and vinyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.). It was. As this uncured acrylic resin, an acrylic polymer (made by Shin-Nakamura Chemical Co., Ltd.), an acrylic monomer (made by Shin-Nakamura Chemical Co., Ltd.) and a photopolymerization initiator was used.

  Thereafter, the mixed liquid impregnated in the aggregate was dried, and then the acrylic resin was cured by irradiating the aggregate with UV, whereby a transparent conductive film was obtained. FIG. 2 is a diagram schematically showing a cross-sectional configuration of the transparent conductive film obtained in each example and comparative example. As shown in FIG. 2, these transparent conductive films are composed of a cured resin 12 between a transparent conductive layer 15 in which ITO particles 11 and ZnO particles 13 are mixed in a cured resin 12 and a base material 14. The intermediate layer 15a is arranged. By having such a structure, the outermost surface of the base material 14 comes into contact only with the cured resin 12, the adhesion between the base material 14 and the transparent conductive layer 15 is improved, and the increase in resistance value is reduced. can do. The intermediate layer 15a is also integrated with the cured resin 12 in the transparent conductive layer 15, so that an increase in resistance value is suppressed.

(Measurement of resistance value and rate of resistance change)
First, about the transparent conductive film obtained by each Example and the comparative example, these resistance value (ohm / square) was measured by the four-terminal method, respectively. Next, an environmental test was performed in which each transparent conductive film was left in an electric furnace for environmental testing (60 ° C., 95% RH) for 650 hours. And the resistance value of each transparent conductive film after this test was measured similarly. And based on the obtained result, the change of the resistance value of each transparent conductive film before and after an environmental test was calculated | required, and this was made into resistance change rate (%).

The obtained results are shown in Table 1 and FIG. FIG. 3 is a graph obtained by plotting resistance change rate values with respect to the content of ZnO particles (Ga dope ZnO) obtained from the results of Examples 1 to 9 and Comparative Examples 1 to 4. In Table 1, “0h” in the resistance value column indicates a resistance value before the environmental test, and “650h” indicates a resistance value after the environmental test. Furthermore, “−” in Comparative Example 4 indicates that the resistance of the transparent conductive film of Comparative Example 4 has increased after the environmental test to such an extent that it cannot be measured by the four-terminal method.

As shown in Table 1 and FIG. 3, according to the transparent conductive films of Examples 1 to 9 in which ZnO particles were added in an amount of 0.1 to 50% by mass in addition to ITO particles, only ITO particles or only ZnO particles were used. In comparison with the case (Comparative Examples 1 and 4) or the case where the ZnO content is outside the range of 0.1 to 50% by mass (Comparative Examples 2 and 3), the resistance change rate can be remarkably reduced. confirmed. Therefore, it was found that the transparent conductive films of Examples 1 to 9 had a small increase in resistance value even when used for a long time under high humidity conditions. Moreover, when the content of ZnO is 1 to 30% by mass, the resistance change rate is particularly low at 1.7% or less, and it has been found that the increase in resistance value can be suppressed even when used for a longer time. In particular, when the ZnO content is 3 to 10% by mass, the resistance value itself is as low as 1000Ω / □ or less, and it was confirmed that the resistance value is particularly preferable for touch panel applications.
[Examples 10 to 16]

(Preparation of transparent conductive film)
The transparent conductive films of Examples 10 to 16 were used in the same manner as described above except that various kinds of ZnO particles shown in Table 2 were used and the content ratio of ZnO particles was changed to the values shown in Table 2. Produced. In Table 2, “Alumina-coated ZnO” is manufactured by Sakai Chemical Industry Co., Ltd., NANOFINE75, and “crosslinking agent added ZnO” is manufactured by Sakai Chemical Industry Co., Ltd., NANOFINE P-1 (average primary particle diameter = 0.02 μm, “Al dope ZnO” is SC-18 (average primary particle size = 0.02 μm, resistance value (powder specific resistance) = 500 Ω · m) manufactured by Sakai Chemical Industry, “Non dope ZnO” indicates additive-free ZnO particles made of only ZnO. Further, for example, “alumina-coated ZnO 10%” in Table 2 indicates that “alumina-coated ZnO” as ZnO particles is contained in an amount of 10% by mass with respect to the total of the ITO particles and the ZnO particles. The other content (%) notations in Table 2 are also the same.

(Measurement of resistance value and rate of resistance change)
About each transparent conductive film obtained in Examples 10-16, the resistance value and the resistance change rate were measured like the above. The obtained results are shown in Table 2 together with the results of Example 5 described above.

  As shown in Table 2, even when various types of ZnO particles are used, by combining ITO particles and ZnO particles at a specific blending ratio, compared to the case of Comparative Examples 1 to 4 described above. It was confirmed that the change in resistivity can be greatly reduced. Therefore, it was found that the transparent conductive films of Examples 10 to 16 had a small increase in resistance value even when used for a long time under high humidity conditions.

It is a figure which shows typically the cross-sectional structure of the transparent conductive film using the transparent conductor of suitable embodiment. It is a figure which shows typically the cross-sectional structure of the transparent conductive film obtained by each Example and the comparative example. It is the graph which plotted the value of the resistance change rate with respect to content of ZnO particle | grains (Gadope ZnO).

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Transparent conductive film, 11 ... ITO particle, 12 ... Resin hardened | cured material, 13 ... ZnO particle, 14 ... Base material, 15 ... Transparent conductive layer, 15a ... Intermediate | middle layer.

Claims (4)

Indium tin oxide, an additive component mainly composed of zinc oxide, and a resin cured product,
A transparent conductor comprising 0.1 to 50% by mass of the additive component in the total amount of indium tin oxide and the additive component.   The transparent conductor according to claim 1, wherein the additive component is zinc oxide doped with gallium or aluminum.   The transparent conductor according to claim 1, wherein the additive component is an insulating particle mainly composed of zinc oxide.   The transparent conductor according to any one of claims 1 to 3, wherein the additive component is an insulating particle having at least one of alumina, silica, and resin attached to a surface thereof.

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