JP6713079B2 - Transparent conductive film for electric field drive type light control element, light control film, and electric field drive type light control element - Google Patents

Description

The present invention relates to a transparent conductive film used as an electrode substrate of an electric field drive type light control device. Furthermore, the present invention relates to an electric field drive type light control device using the transparent conductive film as an electrode substrate.

Light control elements are used for window glass and interior materials of buildings and vehicles. Particularly in recent years, from the viewpoints of reducing the heating and cooling load, reducing the lighting load, improving comfort, and the like, demand and expectations for the dimming element have increased.

The electric field drive type light control device is provided with a light control layer between a pair of electrode substrates, and controls the transmission/scattering state of light by the light control layer according to ON/OFF of the electric field. A liquid crystal material, an electrochromic material, or the like is used as the light control material of the electric field drive type light control element.

As the electrode substrate of the electric field drive type light control device, electrode glass having a transparent conductive layer on glass or a transparent conductive film having a transparent conductive layer on a transparent film is used. The transparent conductive film can provide a long electrode having a uniform film thickness and characteristics by forming an electrode layer by roll sputtering or the like, and can easily have a larger area than electrode glass. Further, by continuously forming a light control layer on the electrode, it is possible to provide a long length of the light control film, and since it is easy to bond to a general glass or the like, a transparent conductive film is used. Film is excellent in versatility. Therefore, a transparent conductive film is widely used as an electrode substrate even in a light control element (light control glass) including a light control layer between laminated glasses (for example, Patent Document 1).

The transparent conductive film has a transparent conductive layer made of a conductive metal oxide such as indium tin composite oxide (ITO) on a transparent film substrate. Transparent conductive films are also widely used as electrodes for flexible displays and touch panels. In a display or a touch panel, a transparent conductive film including a transparent conductive layer made of a crystalline metal oxide is generally used from the viewpoint of low resistance and high light transmittance (for example, Patent Document 2). Also in the light control element, it has been proposed to crystallize the conductive layer of the transparent conductive film from the viewpoint of lowering the resistance of the transparent electrode and suppressing resistance change (for example, Patent Document 3).

The transparent conductive layer formed on the film substrate is amorphous immediately after film formation because the substrate temperature during film formation is low. After forming the transparent conductive layer, the transparent conductive layer is crystallized by heating at a high temperature of 100° C. or higher (generally about 150° C.) for 1 hour to several days.

International publication pamphlet of WO2008/075773 JP, 2007-200823, A JP-A-2-32319

As described above, the transparent conductive layer is preferably crystalline from the viewpoint of reducing the resistance. On the other hand, in the electric field drive type light control device, since the light control layer containing the liquid crystal material or the electrochromic material is formed on the electrode, the interaction at the interface between the electrode and the light control layer and the application of the light control layer. The transparent conductive layer may be required to be an amorphous material from the viewpoint of the wettability of the surface when it is formed.

In addition, since the crystalline transparent conductive layer is apt to have scratches or cracks due to bending, it may be required that the transparent conductive layer is amorphous. In particular, a light control element used for windows, interiors, and the like needs to be processed into various sizes and has a larger area than a display or a touch panel, so that it is difficult to automate all steps. Therefore, when the transparent conductive layer is crystalline, due to bending and rubbing during processing such as cutting and bonding of the transparent conductive film, scratches and cracks are likely to occur in the transparent conductive layer, which tends to cause a decrease in yield. is there.

As described above, the transparent conductive layer formed on the film substrate is amorphous immediately after film formation. However, thermodynamically, metal oxides are more stable in crystalline than in amorphous. Therefore, the transparent conductive layer has a natural environmental temperature (for example, about 40° C.) without being actively heated. It tends to be converted to crystalline over time.

When the transparent conductive layer is crystallized, the surface resistance is lowered, and the light transmission/scattering state of the electric field drive type light control device when the voltage is turned on is changed, so that the operation of the device becomes unstable. Further, when crystallization occurs at a low temperature (environmental temperature), the progress of crystallization becomes non-uniform in the plane as compared with the case where crystallization is positively performed by heating. Therefore, there is a problem that the resistance of the transparent conductive layer varies in the plane, the transmission and scattering of light by the light control element becomes non-uniform in the plane, and the designability deteriorates.

Since the amorphous transparent conductive layer has a larger specific resistance than the crystalline transparent conductive layer, it is necessary to increase the film thickness in order to reduce the surface resistance. When the film thickness of the amorphous transparent conductive layer is large, it tends to be crystallized even at a low temperature, and the decrease in surface resistance and the maintenance of the amorphous state are in a contradictory relationship.

In view of the above, the present invention provides a transparent conductive film having a small surface resistance and including an amorphous transparent conductive layer capable of maintaining an amorphous state with time, and applicable to an electric field drive type light control device. With the goal.

As a result of the study by the present inventors, they found that the transparent conductive layer was hard to be crystallized and could maintain an amorphous state when the film thickness and the specific resistance were within a predetermined range, and thus the present invention was completed. The present invention relates to a transparent conductive film used as an electrode substrate of an electric field drive type light control device. The transparent conductive film has an amorphous transparent conductive layer on at least one surface of a transparent plastic film substrate.

The transparent conductive layer has a film thickness of 30 nm to 100 nm and a specific resistance of 6×10 ⁻⁴ Ω·cm or less. The surface resistance of the transparent conductive layer is preferably 170Ω/□ or less.

In the transparent conductive film of the present invention, the absolute value of the resistance change rate of the transparent conductive layer after heating at 80° C. for 240 hours is preferably 55% or less. The total light transmittance of the transparent conductive film is preferably 79% or more. The reflected light of the light emitted from the transparent conductive layer side of the transparent conductive film preferably has a hue b ^* of -10 to 4.

As a material for the transparent conductive layer, indium tin composite oxide (ITO) is preferably used. The indium-tin composite oxide forming the transparent conductive layer preferably has a tin content of 8 to 30 parts by weight based on 100 parts by weight of indium and tin in total.

The transparent conductive layer preferably has a carrier density of 2.90×10 ²⁰ /cm ^{3 to} 4.80×10 ²⁰ /cm ³ . In particular, amorphous ITO having a carrier density in the above range is difficult to crystallize even when the film thickness is large, and therefore there is a tendency to suppress the resistance change after heating at 80° C. for 240 hours.

In one embodiment, in the transparent conductive film, the plastic film substrate and the transparent conductive layer are in direct contact with each other without the other layer interposed between the plastic film substrate and the transparent conductive layer. The arithmetic mean roughness of the transparent plastic film substrate on the transparent conductive layer forming surface side is preferably 0.5 to 5 nm. The arithmetic mean roughness of the transparent conductive layer is preferably 0.8 to 5.5 nm. The water content per unit area of the transparent plastic film substrate is preferably 15 to 200 μg/cm ² .

The present invention also relates to a light control film having a light control layer on the transparent conductive layer of the above transparent conductive film. Further, the present invention relates to an electric field drive type light control device using the transparent conductive film as a conductive substrate. The electric field drive type light control device of the present invention includes a light control layer between a pair of electrode substrates. The light control layer is made of a material capable of controlling the transmission/scattering state of light depending on whether or not an electric field is applied.

Since the transparent conductive layer of the transparent conductive film of the present invention is amorphous, scratches and cracks due to bending and rubbing during processing are unlikely to occur. Further, since the thickness of the transparent conductive layer is large, the surface resistance can be reduced even though the transparent conductive layer is amorphous. Furthermore, since crystallization is less likely to occur in a natural environment, when used as an electrode substrate for an electric field-driven dimming element, a stable dimming element with stable light transmission/scattering control is obtained. To be

It is a typical sectional view showing one embodiment of a transparent conductive film. It is a graph showing the relationship between the amount of oxygen introduced and the specific resistance (A) and the extinction coefficient (B) during the formation of the transparent conductive layer. It is a schematic cross section showing one embodiment of an electric field drive type light control device. It is the graph which plotted the relationship of the carrier density and specific resistance of the transparent conductive film of an Example and a comparative example.

[Transparent conductive film]
FIG. 1 is a schematic cross-sectional view showing an embodiment of a transparent conductive film. The transparent conductive film 1 for an electric field drive type light control device of the present invention includes a transparent conductive layer 21 on a transparent plastic film substrate 11.

<Transparent plastic film substrate>
As the transparent plastic film substrate 11, a plastic material having excellent transparency and heat resistance is preferably used. Examples of such plastic materials include polyester such as polyethylene terephthalate, polyolefin, cyclic polyolefin such as norbornene, polycarbonate, polyether sulfone and polyarylate.

From the viewpoint of enhancing the adhesiveness between the transparent plastic film substrate 11 and the transparent conductive layer 21, before forming the transparent conductive layer, the surface of the substrate is subjected to corona discharge treatment, ultraviolet irradiation treatment, plasma treatment, sputter etching treatment in advance. Appropriate adhesion treatment such as the above may be performed.

The arithmetic mean roughness Ra on the transparent conductive layer 21 formation surface side of the transparent plastic film substrate 11 is preferably 0.5 to 5.0 nm, more preferably 0.6 to 3.5 nm, and 1.0 to 3.0 nm. Is more preferable, and 1.2 to 2.5 nm is particularly preferable. When the Ra of the base material is within the above range, the surface shape of the transparent conductive layer formed thereon can be appropriately adjusted, so that a crystallization hardly occurs and a transparent conductive layer having a low resistance is easily obtained. The arithmetic average roughness Ra is obtained from an AFM observation image of 1 μm square using a scanning probe microscope (AFM).

Moisture content per unit area of the transparent plastic film substrate 11 is preferably 15~200μg / cm ^2, more preferably 30~190μg / cm ^2, more preferably 40~170μg / cm ^2. When the water content of the base material is within the above range, crystallization is less likely to occur and a low-resistance transparent conductive layer is easily obtained. If the water content of the base material is too low, the transparent conductive layer tends to crystallize at ambient temperature, and if the water content of the base material is too high, the specific resistance of the transparent conductive layer tends to increase. The water content (μg/cm ² ) can be calculated as the water content per unit area from the water content obtained by the JIS K 7251-B method (water vaporization method).

Although the thickness of the transparent plastic film substrate 11 is not particularly limited, it is generally about 2 to 500 μm, preferably about 20 to 300 μm. The water content of the transparent plastic film substrate depends on the characteristics of the material and the storage environment (for example, temperature and humidity), and the water content per unit area is approximately proportional to the thickness. Therefore, it is preferable that the material, the storage environment and the thickness of the transparent plastic film substrate are determined so that the water content per unit area falls within the above range.

The transparent plastic film substrate 11 may include an easily adhesive layer, an antistatic layer, or the like. Further, a hard coat layer, an adhesive layer, or the like may be provided on the back side of the transparent plastic film substrate 11 (the side opposite to the surface on which the transparent conductive layer 21 is formed).

An undercoat layer (not shown) may be formed between the transparent plastic film substrate 11 and the transparent conductive layer 21. The undercoat layer is a dielectric layer having transparency and a surface resistance of 1×10 ⁶ Ω/□ or more. Examples of the material of the undercoat layer include an inorganic material, an acrylic resin, a urethane resin, a melamine resin, an alkyd resin, a siloxane polymer, an organic material such as an organic silane condensate, or a mixture of the inorganic material and the above organic material, a vacuum vapor deposition method, It can be formed by a dry coating method such as a sputtering method or an ion plating method, and a wet coating method (application method).

The undercoat layer serves as a base during film formation of the transparent conductive layer, and has an effect of blocking moisture and organic gas generated from the base material and a function of smoothing the surface of the base material. As described above, by setting the water content and the surface roughness of the base material within a predetermined range, both crystallization suppression and low resistance of the transparent conductive layer can be achieved, but when an undercoat layer is present on the base material, These effects may be lost. Therefore, the transparent conductive film of the present invention is provided with an undercoat layer on the surface of the transparent plastic film substrate on which the transparent conductive layer 21 is formed, that is, between the transparent plastic film substrate 11 and the transparent conductive layer 21. Instead, it is preferable that the transparent plastic film substrate 11 and the transparent conductive layer 21 are in direct contact with each other. When the undercoat layer is present between the transparent plastic film substrate 11 and the transparent conductive layer 21, the arithmetic mean roughness Ra of the undercoat layer surface is preferably within the above range. Further, even when the undercoat layer is present, it is preferable to form the undercoat layer by a wet coating method in order not to block moisture and the like generated from the substrate.

<Transparent conductive layer>
A transparent conductive film is obtained by forming the transparent conductive layer 21 on the transparent plastic film substrate 11. The transparent conductive layer 21 is an amorphous metal oxide layer. The film thickness of the transparent conductive layer 21 is 30 to 100 nm. When the film thickness of the transparent conductive layer 21 is within the above range, both high transparency and low surface resistance can be achieved. The thickness of the transparent conductive layer 21 is preferably 40 to 90 nm, more preferably 45 to 85 nm, further preferably 50 to 80 nm.

The constituent material of the transparent conductive layer 21 is not particularly limited, and is selected from the group consisting of, for example, indium, tin, zinc, gallium, antimony, titanium, silicon, zirconium, magnesium, aluminum, gold, silver, copper, palladium and tungsten. An oxide of one kind of metal (or metalloid) is used. From the viewpoint of reducing the resistance, the metal oxide forming the transparent conductive layer is preferably a composite of a plurality of metal oxides, and among them, a composite metal oxide containing indium oxide as a main component is preferable. From the viewpoint of achieving both high transparency and low resistance, indium tin composite oxide (ITO) is particularly preferable.

When the transparent conductive layer is ITO, the content of tin is preferably 8 to 30 parts by weight based on 100 parts by weight of the total of indium and tin. By setting the tin content to 8 parts by weight or more, a transparent conductive layer having a low resistance and easily maintaining an amorphous state can be obtained. When the tin content is 30 parts by weight or less, the light transmittance of the transparent conductive layer tends to increase.

The specific resistance of the transparent conductive layer 21 is 6×10 ⁻⁴ Ω·cm or less, and preferably 5.8×10 ⁻⁴ Ω·cm or less. From the viewpoint of lowering the resistance of the transparent conductive layer, the lower the specific resistance, the more preferable. However, the specific resistance of the amorphous transparent conductive layer is generally 2.8×10 ⁻⁴ Ω·cm or more. In order to maintain the amorphous state of the transparent conductive layer, the specific resistance of the transparent conductive layer is preferably 3.0×10 ⁻⁴ Ω·cm or more, and more preferably 3.5×10 ⁻⁴ Ω·cm or more. preferable. The surface resistance of the transparent conductive layer 21 is preferably 170Ω/□ or less, more preferably 150Ω/□ or less, further preferably 120Ω/□ or less, particularly preferably 100Ω/□ or less, and most preferably 90Ω/□ or less. When the surface resistance of the transparent conductive layer is small, the in-plane potential difference when an electric field is applied becomes small, and the light transmission/scattering state when a voltage is applied to the light control element becomes uniform in the surface. From the viewpoint of increasing the uniformity of the in-plane potential, the smaller the resistance of the transparent conductive layer, the more preferable, but in order to reduce the surface resistance, it is necessary to increase the thickness of the transparent conductive layer, which may impair the transparency. is there. Therefore, the surface resistance of the transparent conductive layer is generally 20Ω/□ or more, preferably 30Ω/□ or more.

When the transparent conductive film 1 is heated at 80° C. for 240 hours, the absolute value of the resistance change rate of the transparent conductive layer 21 before and after heating is preferably 55% or less, more preferably 50% or less, and 40% or less. More preferably, 30% or less is particularly preferable, and 20% or less is most preferable. The rate of resistance change is calculated by the following formula.
Resistance change rate (%)={(surface resistance after heating/surface resistance before heating)-1}×100

If the change in resistance due to heating is small, the change in resistance of the transparent conductive layer 21 with time is small, and a light control element having excellent reliability can be obtained. As described above, the crystallization of the metal oxide tends to be promoted by heating, and the resistivity and the surface resistance of the transparent conductive layer are significantly reduced with the crystallization of the metal oxide. Therefore, it is preferable that the transparent conductive layer 21 maintain an amorphous state even after being heated at 80° C. for 240 hours.

Whether the transparent conductive layer is amorphous or crystalline can be determined by immersing the transparent conductive film in an acid and then measuring the resistance between terminals. As the acid, an acid that dissolves an amorphous metal oxide but does not dissolve a crystalline metal oxide is used. For example, when the metal oxide is ITO, it may be immersed in hydrochloric acid having a concentration of 5 wt% for 15 minutes, washed with water and dried to measure the resistance between terminals. Since amorphous ITO is etched by hydrochloric acid and disappears, immersion in hydrochloric acid increases the resistance. When the metal oxide is ITO, it can be determined that the transparent conductive layer is amorphous when the resistance between terminals for 15 mm exceeds 10 kΩ after immersion in hydrochloric acid, washing with water, and drying.

The arithmetic mean roughness Ra of the transparent conductive layer 21 is preferably 0.8 to 5.5 nm, more preferably 0.9 to 4.0 nm, further preferably 1.0 to 3.5 nm, and 1.1 to 3. 0 nm is particularly preferred. When Ra is in the above range, the transparent conductive layer is less likely to be crystallized and tends to have low resistance. If Ra is too small, crystallization of the transparent conductive layer tends to occur at ambient temperature, and if Ra is too large, the specific resistance of the transparent conductive layer tends to increase. The surface roughness of the transparent conductive layer depends on the film forming conditions of the transparent conductive layer and the surface roughness of the transparent plastic film substrate which is a film forming base. In the sputtering method, a thin film that follows the shape of the base is likely to be formed. Therefore, when the transparent conductive layer is formed by the sputtering method, Ra of the transparent conductive layer particularly depends on Ra of the transparent plastic film substrate. Therefore, in order to set Ra of the transparent conductive layer in the above range, Ra of the transparent plastic film substrate is preferably set in the above range.

The method for forming the transparent conductive layer 21 is not particularly limited, and various film forming methods such as a vacuum vapor deposition method, a sputtering method and an ion plating method can be adopted. Above all, the sputtering method is preferable because it is easy to form a metal oxide thin film having a uniform film thickness. As the sputtering method, not only a standard magnetron sputtering method using a DC power source but also various sputtering methods such as an RF sputtering method, an RF+DC sputtering method, a pulse sputtering method and a dual magnetron sputtering method can be adopted.

As the sputter target, both a metal target (for example, In—Sn target) and a metal oxide target (for example, In ₂ O ₃ —SnO ₂ target) can be used. A metal oxide target is preferably used because it keeps the amount of oxygen in the film constant and easily keeps the film quality uniform.

When the transparent conductive layer is formed by sputtering, it is preferable that the inside of the sputtering apparatus be evacuated to remove the impurities such as water and organic gas generated from the substrate before starting the film formation. The presence of water or organic molecules tends to increase the resistance change rate of the transparent conductive layer and reduce the reliability. On the other hand, since water and organic molecules in the transparent conductive layer have an effect of inhibiting crystallization of the metal oxide, it is preferable to perform sputter film formation in the presence of a trace amount of water and organic molecules. Therefore, the degree of vacuum (achievement degree of vacuum) in the sputtering apparatus before the start of sputtering film formation is preferably 8×10 ⁻² Pa or less, more preferably 3×10 ⁻⁴ Pa to 6×10 ⁻² Pa, and 5× 10< ^-4 >-5*10< ^-3 >Pa is more preferable.

Sputter film formation is performed while introducing an inert gas such as argon and oxygen into the evacuated sputtering apparatus. The substrate temperature during the sputtering film formation is preferably −20° C. to 150° C., more preferably −10° C. to 100° C., and further preferably 0° C. to 70° C. If the substrate temperature is too high, the base material is likely to be deformed by heat or the appearance thereof is poor due to heat wrinkles. On the other hand, if the substrate temperature is too high, the metal oxide is likely to crystallize, which may make it difficult to maintain the amorphous state. On the other hand, when the substrate temperature is too low, the film quality of the transparent conductive layer may be deteriorated.

The amount of oxygen introduced into the inert gas is preferably 0.1% by volume to 10% by volume, more preferably 1% by volume to 6% by volume. The pressure during film formation is preferably 0.08 Pa to 1 Pa, and more preferably 0.2 Pa to 0.8 Pa. If the film formation pressure is too high, the film formation rate tends to decrease, and conversely, if the pressure is too low, the discharge tends to be unstable.

By adjusting the amount of oxygen introduced during sputtering film formation, it is possible to form a transparent conductive layer which has a high light transmittance and is hard to be crystallized at ambient temperature even if the film thickness is large. FIG. 2 is a graph showing the relationship between the amount of oxygen introduced during film formation of the ITO transparent conductive layer, the specific resistance of the transparent conductive layer immediately after film formation, and the extinction coefficient at a wavelength of 380 nm.

When the amount of oxygen introduced is small (region X in FIG. 2A), the amount of oxygen in the metal oxide is smaller than the stoichiometric composition, and a large number of oxygen vacancies are present, which is relatively close to the metallic composition. When the oxygen introduction amount is increased, there is a region where the specific resistance takes a minimum value (region Y in FIG. 2A: bottom region), and when the oxygen introduction amount is further increased, the specific resistance increases again (region Z in FIG. 2A). : Excess oxygen region).

On the other hand, as shown in FIG. 2B, the extinction coefficient of the transparent conductive layer tends to monotonically decrease as the amount of oxygen introduced increases. This is because the metal oxide has a large number of oxygen vacancies in the oxygen-deficient region and has a large number of oxygen vacancies in the region where the oxygen content is low, and the metal oxide approaches a perfect oxide as the oxygen content increases. This is because.

According to the study by the present inventors, it was confirmed that the metal oxide in the transparent conductive layer is less likely to crystallize and the amorphous state tends to be maintained as the amount of introduced oxygen increases. This is because the oxygen deficiency is small and the structure of the metal oxide in an amorphous state is stable, so that it is difficult for the conformational change to occur, and activation for converting the metal oxide from amorphous to crystalline is difficult. It is thought that this is because the energy becomes large.

On the other hand, when the amount of oxygen introduced during film formation is excessively large (region Z in FIG. 2A), the carrier density tends to be low and the specific resistance of the transparent conductive layer tends to be high because oxygen deficiency in the metal oxide is small. is there. If the amount of oxygen introduced is excessive, the rate of resistance change due to heating tends to increase, and reliability tends to decrease.

Therefore, in the present invention, it is preferable to form the transparent conductive layer with the amount of oxygen introduced in the vicinity (bottom region) of the minimum value of the specific resistance of the transparent conductive layer immediately after the film formation. The amount of oxygen introduced into the bottom region varies depending on the composition of the target, the characteristics of the apparatus, the film forming temperature, the film forming pressure, and the like. Therefore, it is difficult to unambiguously specify the range of the oxygen introduction amount, but the conditions other than the oxygen introduction amount are kept constant and the oxygen introduction amount is changed to form a film. As shown in FIG. The optimum amount of oxygen introduced can be found by investigating the relationship between and the specific resistance.

The amorphous transparent conductive layer formed on the base material preferably has a carrier density of 2.90×10 ²⁰ /cm ^{3 to} 4.80×10 ²⁰ /cm ³ , and 3.00×10 ^20. /Cm ^{3 to} 4.60×10 ²⁰ /cm ³ is more preferable, and 3.10×10 ²⁰ /cm ^{3 to} 4.50×10 ²⁰ /cm ³ is more preferable and 3.20×10 3. More preferably, it is ²⁰ /cm ^{3 to} 4.30×10 ²⁰ /cm ³ . If the carrier density is below the above range, the specific resistance tends to be high and the rate of resistance change due to heating tends to be high. On the other hand, when the carrier density exceeds the above range, the amorphous film tends to be converted to crystalline at ambient temperature.

In order to set the carrier density in the above range, the amount of oxygen introduced during film formation of the transparent conductive layer may be adjusted in the above bottom region. Conversely, the amount of oxygen introduced during film formation may be adjusted so that the carrier density of the transparent conductive layer falls within the above range.

<Optical properties of transparent conductive film>
The transparent conductive film preferably has a total light transmittance of 79% or more. When the film thickness of the transparent conductive layer is 100 nm or less and the carrier density is in the above range, light absorption by the transparent conductive layer can be suppressed and the total light transmittance can be increased.

The hue b ^* of the reflected light when the standard light (D65 light source) is irradiated from the transparent conductive layer 21 side of the transparent conductive film is preferably -10 to 4, more preferably -8 to 1, and -7 to 0. More preferable. The sign + of the hue b ^* represents the yellow direction, and the sign − of the hue b ^* represents the blue direction. When b ^* is large, the reflected light becomes yellowish and the design is poor. Therefore, the hue b ^{* of the} reflected light is preferably on the negative side.

The hue of reflected light can be adjusted by the film quality of the transparent conductive layer, but the film thickness has a large effect. This is because the phase difference between the reflected light at the surface of the transparent conductive layer 21 and the reflected light at the interface between the transparent conductive layer 21 and the transparent plastic film substrate 11 depends on the optical film thickness of the transparent conductive layer. This is because the hue of reflected light changes significantly due to the difference in multiple reflection interference that accompanies this.

In order for b ^* of the reflected light to fall within the above range, the optical film thickness (product of the refractive index and the film thickness at a wavelength of 550 nm) of the transparent conductive layer is preferably 110 to 160 nm, and 120 to 155 nm. Is more preferable. When the transparent conductive layer is ITO, the refractive index of amorphous ITO is about 2.0. Therefore, the film thickness is preferably about 55 nm to 75 nm so that b ^* of the reflected light falls within the above range.

[Light control film and light control element]
The transparent conductive film of the present invention is used as an electrode substrate of an electric field drive type light control device. FIG. 3 is a schematic sectional view showing an embodiment of the electric field drive type light control device. The light control element 5 includes a light control layer 50 between the pair of electrode substrates 1 and 2. Each of the electrode substrates 1 and 2 includes transparent conductive layers 21 and 22 on the base materials 11 and 12, and the transparent conductive layers 21 and 22 are arranged so as to face each other, and the light control layer 50 is sandwiched therebetween. There is.

In the form shown in FIG. 3, the light control film 70 in which the light control layer 50 is sandwiched between the pair of transparent conductive films 1 and 2 is arranged between the glass substrates 31 and 32. The electric field drive type light control device includes the transparent conductive film of the present invention as one transparent conductive film 1. The other transparent conductive film may be the transparent conductive film of the present invention or another transparent conductive film. Further, if the transparent conductive film 1 of the present invention is used as one electrode substrate, the other electrode substrate may be electrode glass having an electrode layer on the glass substrate.

The light control film can be produced by forming the light control layer 50 on the transparent conductive layer 21 of the transparent conductive film 1. Further, another transparent conductive film 2 may be disposed on the light control layer 50 to provide the light control film 70 including the light control layer between the transparent conductive layers of the pair of transparent conductive films.

The light control element is formed by connecting the transparent conductive layers of the pair of electrode substrates to the power supply 7. The power field 7 is turned on/off (or a switch (not shown) is turned on/off), and the electric field to the light control layer sandwiched between the transparent conductive layers is turned on/off or the magnitude of the electric field is adjusted. The light transmission state and light scattering state are controlled.

The light control layer 50 is made of a light control material whose light transmission state and/or light scattering state changes depending on whether or not an electric field is applied. As such a light control material, a material whose molecular orientation changes depending on the presence or absence of an electric field (for example, a liquid crystal material) and an electrochromic material whose light absorption changes depending on the presence or absence of an electric field are used.

When a liquid crystal material is used, the material is not particularly limited, but for example, the pores of a transparent resin matrix having a large number of pores are filled with nematic liquid crystal molecules having the ordinary refractive index similar to that of the polymer. A light control layer having a liquid crystal capsule is used. When the electric field is turned off, the nematic liquid crystal molecules are aligned along the inner wall of the capsule in each liquid crystal capsule when the electric field is off. Light is scattered at the interface with and the dimmer becomes opaque.

When an electric field is applied between the transparent conductive layers 21 and 22, the nematic liquid crystal molecules in each liquid crystal capsule are aligned parallel to the direction of the electric field. Since the ordinary refractive index of the nematic liquid crystal molecules and the refractive index of the resin matrix in the light control layer are the same, light is not scattered at the interface between the resin matrix and the liquid crystal capsule, and the light control element becomes transparent.

As the liquid crystal material, liquid crystal that is cholesterically aligned when the electric field is off may be used. Further, the material whose molecular orientation changes depending on the presence or absence of an electric field is not limited to a liquid crystal material, and inorganic fibers such as polyiodide, carbon fiber and carbon nanofiber, and dichroic materials such as carbon nanotube and phthalocyanine may be used. Good.

An electrochromic material is a material that reversibly causes a redox reaction depending on the presence or absence of an electric field, and the light absorption rate or reflectance of the material changes with the redox. As the electrochromic material, both an inorganic electrochromic compound and an organic electrochromic compound can be used. Further, the electrochromic compound can be oxidized/reduced by providing an electrolyte layer or the like adjacent to the electrochromic material layer.

As shown in FIG. 3, when the light control film 70 is used in combination with the glass substrates 31, 32, etc., the light control film may be simply sandwiched between the glass substrates and arranged with an appropriate adhesive. It may be pasted together. From the viewpoint of ease of installation work and prevention of positional deviation, it is preferable that the glass substrate and the light control film are bonded together via an adhesive.

An adhesive is preferably used as the adhesive. By attaching an adhesive to the transparent plastic film substrates 11 and 12 of the transparent conductive films 1 and 12 in advance, the glass substrate and the transparent conductive film are bonded together or the glass substrate and the light control film are bonded together. The bonding can be easily performed. As the pressure-sensitive adhesive, one having excellent transparency such as an acrylic pressure-sensitive adhesive is preferably used.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

[Measuring method used in Examples and Comparative Examples]
<Water content of base material>
Regarding the water content of the film substrate, the water content contained in the film substrate having an area of 10 cm ² was measured according to JIS K 7251-B method (water vaporization method), and the water content per 1 cm ² was calculated. In the case of the substrate having the undercoat layer on the transparent conductive layer formation surface side, the arithmetic mean roughness and the water content of the surface after the undercoat layer formation were measured.

<Calculated average roughness>
The arithmetic mean roughness Ra of the film substrate and the transparent conductive layer was determined by AFM observation (observation area: 1 μm ² ) using a scanning probe microscope (SPI3800 manufactured by Seiko Instruments). In the case of a substrate having an undercoat layer on the transparent conductive layer forming surface side, the arithmetic mean roughness of the surface after the undercoat layer was formed was measured as the roughness of the film substrate.

<Carrier density>
The carrier density was measured using a Hall effect measurement system (HL5500PC manufactured by Bio-Rad).

<Surface resistance and resistivity>
The surface resistance was measured by a four-point probe method using a resistivity meter (Loresta GP MCP-T610 manufactured by Mitsubishi Chemical Analytech), and the specific resistance was calculated from the product of the surface resistance and the film thickness. The film thickness of the transparent conductive layer was measured by observing a cross section with a transmission electron microscope (HF-2000, manufactured by Hitachi High-Tech).

<Total light transmittance and reflected light hue of transparent conductive film>
The total light transmittance was measured according to JIS K7105 using a haze meter (manufactured by Suga Test Instruments). The b ^* of the reflected light is obtained by irradiating the standard light (D65 light source) from the transparent conductive layer side at an incident angle of 2 degrees and measuring the reflected light spectrum of wavelength 380 to 780 nm using a spectrophotometer (U4100 manufactured by Hitachi High-Tech). It was calculated.

<Heating test>
(Rate change rate)
The transparent conductive film was held in an oven at 80° C. for 240 hours and then taken out to measure the surface resistance. The rate of resistance change was determined by the following formula.
Resistance change rate (%)={(surface resistance after heating/surface resistance before heating)-1}×100
The sign + of the resistance change rate means that the resistance has increased after heating, and the sign − means that the resistance has decreased after heating.

(Film quality)
The transparent conductive film after heating was immersed in hydrochloric acid having a concentration of 5 wt% for 15 minutes, washed with water and dried, and the resistance between terminals for 15 mm was measured with a tester. Amorphous ones having an inter-terminal resistance of more than 10 kΩ (that is, most of the transparent conductive layer dissolved in hydrochloric acid) were made amorphous, and ones having an inter-terminal resistance of 10 kΩ or less were made crystalline.

[Example 1]
A roll of polyethylene terephthalate (PET) film (water content: 73 μg/cm ² ) having a thickness of 188 μm was set in the roll sputter device, and the sputter device was evacuated to a water pressure of 2.0×10 ⁻³ Pa. did. After that, argon gas and oxygen gas are introduced, and a sputter deposition is performed under the conditions of a substrate temperature of 40° C. and a pressure of 0.4 Pa, using a mixed sintering target of indium oxide (90% by weight) and tin oxide (10% by weight). Then, an ITO film having a thickness of 65 nm was formed on the PET film. The amount of oxygen introduced during sputtering film formation was adjusted so that the surface resistance of the transparent conductive layer was minimized (see y _{0 in} FIG. 2). The amount of oxygen introduced was 3.1 parts by volume with respect to 100 parts by volume of argon.

[Examples 2 to 4]
A transparent conductive film was produced in the same manner as in Example 1 except that the film thickness of the transparent conductive layer was changed as shown in Table 1 by changing the transport speed of the film substrate during film formation. ..

[Example 5]
The amount of oxygen introduced at the time of film formation was increased by 10% from the amount of oxygen introduced (y _{0 in} FIG. 2) at which the surface resistance of the transparent conductive layer was minimum, and was 3.4 parts by volume with respect to 100 parts by volume of argon. (See y _{1 in} FIG. 2). A transparent conductive film was produced in the same manner as in Example 1 except for the above.

[Comparative Example 1]
The amount of oxygen introduced during film formation was further increased by 10% as compared with Example 5 (see z _{1 in} FIG. 2. Other than that, a transparent conductive film was produced in the same manner as in Example 1.

[Comparative example 2]
A transparent conductive film was produced in the same manner as in Example 1 except that the film thickness of the transparent conductive layer was changed to 29 nm by changing the transport speed of the film substrate during film formation.

[Comparative Example 3]
A thermosetting resin having a weight ratio of 2:2:1 of melamine resin:alkyd resin:organosilane condensate was formed as an undercoat layer on one surface of a PET film having a thickness of 23 μm so as to have a thickness of 30 nm. .. A roll of a PET film (moisture content: 8 μg/cm ² , arithmetic average roughness: 0.5 nm) on which an undercoat layer was formed was set in a roll sputtering device, and the water pressure inside the sputtering device was 2.3×. It was evacuated to 10 ⁻⁴ Pa. After that, argon gas and oxygen gas are introduced, and a sputter deposition is performed under the conditions of a substrate temperature of 140° C. and a pressure of 0.4 Pa using a mixed sintering target of indium oxide (90% by weight) and tin oxide (10% by weight). Then, an ITO film having a thickness of 20 nm was formed on the PET film. The amount of oxygen introduced during sputtering film formation was adjusted to about half of the amount that the surface resistance of the transparent conductive layer was minimum (see y _{0 in} FIG. 2). The amount of oxygen introduced was 1.2 parts by volume with respect to 100 parts by volume of argon.

[Comparative Example 4]
A transparent conductive film was produced in the same manner as in Comparative Example 3 except that the film thickness of the transparent conductive layer was changed to 40 nm by changing the transport speed of the film during film formation.

[Evaluation results]
Characteristics of the substrate of each of the above Examples and Comparative Examples, conditions for forming a transparent conductive film, properties of a transparent conductive layer immediately after film formation, properties after a heating test (heating at 80° C. for 240 hours), and a transparent conductive film. The optical characteristics of are shown in Table 1.

In Comparative Example 1 in which the amount of oxygen introduced during film formation of the transparent conductive layer was excessive, the specific resistance of the transparent conductive layer was higher than that in Example 1, and the resistance increase after the heating test at 80° C. for 240 hours was large. Also in Comparative Examples 3 and 4 in which the amount of oxygen introduced during the formation of the transparent conductive layer was small, the specific resistance of the transparent conductive layer was high. Further, in Comparative Example 2, the transparent conductive layer was formed under the same conditions as in Example 1, but it can be seen that the surface resistance is significantly increased because the film thickness of the transparent conductive layer is small. ..

Comparative Example 3 and Comparative Example 4 have the same film forming conditions for the transparent conductive layer, but in Comparative Example 3 having a film thickness of 20 nm, the transparent conductive layer maintains an amorphous state even after the heating test. In Comparative Example 4 having a film thickness of 40 nm, the transparent conductive layer after the heating test was crystallized. Therefore, in Comparative Example 4, the resistivity after the heating test was significantly reduced. From these comparisons, it can be understood that the surface resistance can be lowered by increasing the film thickness of the transparent conductive layer, but it tends to be difficult to maintain the amorphous state.

On the other hand, in Examples 1 to 5, by setting the amount of oxygen during the formation of the transparent conductive layer in the bottom region (region Y in FIG. 2A), the specific resistance was low and the amorphous state was maintained even after the heating test. It can be seen that a sustainable transparent conductive film is obtained.

Focusing on the carrier densities of the transparent conductive layers of Example 1, Example 5, Comparative Example 1 and Comparative Example 2, the carrier density tends to decrease as the amount of oxygen introduced during film formation increases. It is considered that this is because oxygen vacancies in the film decrease as the amount of oxygen introduced increases.

FIG. 4 is a graph in which the relationship between the carrier density (horizontal axis) and the specific resistance (vertical axis) of the transparent conductive films (immediately after film formation) of Examples and Comparative Examples is plotted. When the amount of oxygen introduced during film formation is near the bottom region, the specific resistance tends to decrease with an increase in carrier density, but when the amount of oxygen introduced is small and the carrier density exceeds a predetermined value, the specific resistance rapidly increases. It turns out to be high

In addition, in Examples 1 to 4 and Comparative Example 2, the film forming conditions of the transparent conductive film are the same and the film thicknesses are different, but there are slight differences in carrier density and specific resistance. This is because the amount of heat received by the base material (heat from the film forming roll and heat from plasma) is different because the film thickness is adjusted by the transport speed of the film base material in the above Examples and Comparative Examples, and the film is released from the base material. It is presumed that this is related to the difference in the amount of water that is stored.

The transparent conductive films of Examples 1 to 5 and Comparative Example 1 had no significant difference in total light transmittance, but a clear difference in b ^{* of} reflected light hue was observed. This is because the multiple interference of reflected light changes as the (optical) film thickness of the transparent conductive layer having a high refractive index changes. From these results, it is possible to obtain a transparent conductive layer having a small specific resistance and capable of maintaining an amorphous state by adjusting the film forming conditions, and by adjusting the film thickness, it is possible to obtain a hue of reflected light. It is understood that a transparent conductive film having excellent transparency can be obtained by adjusting the above.

1, 2 Transparent conductive film 11, 12 Transparent plastic film substrate 21, 22 Transparent conductive layer 31, 32 Glass substrate 5 Light control element 50 Light control layer 70 Light control film 7 Power supply

Claims (12)

A transparent conductive film for an electric field drive type light control device, which is used as an electrode substrate of an electric field drive type light control device having a light control layer between a pair of electrode substrates,
At least one surface of the transparent plastic film substrate is provided with an amorphous transparent conductive layer,
The transparent conductive layer is in direct contact with the transparent plastic film substrate or in contact with a wet coating layer provided on the transparent plastic film substrate, and has a film thickness of 30 nm to 100 nm and a specific resistance. Is 6×10 ⁻⁴ Ω·cm or less, a transparent conductive film for an electric field drive type light control device. The transparent conductive film according to claim 1, wherein the transparent conductive layer is a metal oxide layer containing an indium tin composite oxide as a main component. The transparent conductive film according to claim 2, wherein the transparent conductive layer has a tin content of 8 to 30 parts by weight with respect to a total of 100 parts by weight of indium and tin. The transparent conductive film according to claim 1, wherein the transparent conductive layer has a surface resistance of 170 Ω/□ or less. The transparent conductive film according to claim 1, wherein an absolute value of resistance change rate of the transparent conductive layer after heating at 80° C. for 240 hours is 55% or less. The transparent conductive film according to claim 1, which has a total light transmittance of 79% or more. The transparent conductive film according to any one of claims 1 to 6, wherein a hue b ^* of reflected light of light emitted from the transparent conductive layer side is -10 to 4. The transparent conductive film according to any one of claims 1 to 7, wherein the transparent plastic film substrate has an arithmetic average roughness of 0.5 to 5 nm on the transparent conductive layer formation surface side. The transparent conductive film according to any one of claims 1 to 8, wherein the transparent conductive layer has an arithmetic average roughness of 0.8 to 5.5 nm. The transparent conductive film according to any one of claims 1 to 9, wherein the transparent plastic film substrate has a water content per unit area of 15 to 200 µg/cm ² . A light control film comprising a transparent conductive layer of the transparent conductive film according to any one of claims 1 to 10, comprising a light control layer that controls a light transmission/scattering state depending on whether or not an electric field is applied. Between the pair of electrode substrates, a dimming layer that controls the transmission/scattering state of light depending on whether or not an electric field is applied is provided.
An electric field drive type light control device, wherein at least one of the pair of electrode substrates is the transparent conductive film according to any one of claims 1 to 10.

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