JPS6348362B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a transparent conductive film mainly composed of indium oxide and tin oxide formed on the surface of a plastic substrate. In general, thin films that are transparent in the visible light range and have conductivity are used not only as transparent electrodes in new display systems such as liquid crystal displays, electrochromic displays, and electroluminescent displays, but also as antistatic materials for transparent articles. It is used for purposes such as blocking electromagnetic waves. Hitherto, as such transparent conductive films, films formed by forming a stannic oxide film, an indium oxide film, or the like on glass are known. However, since the base material of this type of membrane is glass, it is inferior in flexibility and workability, and is therefore undesirable for some uses. Therefore, in recent years, transparent conductive films based on plastic have come into the spotlight as they are superior in terms of flexibility, workability, impact resistance, weight, etc. However, since the base material of such a transparent conductive film is plastic, which has poor heat resistance, it has not been possible to use the same manufacturing method as that for a film using glass as a base material. The conventional method using glass as a base material is to spray a hydrochloric acid solution of tin tetrachloride onto glass that has been heated to a high temperature of several hundred degrees, and then perform oxidation treatment at high temperatures to form a thin film made of tin oxide. This is the way to do it. Recently, a method has also become known in which indium oxide is used as an evaporation source and is vacuum evaporated onto glass heated to about 300°C to 350°C under a high vacuum of about 10 ^-4 to ^{10 -5} mmHg. . As is clear, both methods require the glass substrate to be heated to a high temperature. This also applies to other known methods in which water vapor or a gas containing water vapor is introduced into the system during the vacuum deposition described above. Although this method aims to obtain a conductive film with a low resistance, for example, 100 Ω/cm ² or less, it is still necessary to heat the glass substrate to 300°C to 350°C. In this way, all conventional methods using glass as a base material require heating the base material to a high temperature.
Without this, the desired conductive film could not be formed. Therefore, these methods could not be applied to materials based on plastic, which has poor heat resistance. Various improved methods have been proposed to date to overcome this problem. Most of these proposed methods utilize vacuum evaporation methods, and can generally be divided into those using indium oxide as the main evaporation source and those using metallic indium as the main evaporation source. The former method uses indium oxide as the evaporation source,
As seen in Japanese Patent Publication No. 51-35431 and Japanese Patent Publication No. 51-37667, when indium oxide is vapor-deposited onto a plastic substrate, the substrate is not heated at all or the temperature is heated to an acceptable level for the plastic substrate. Vacuum deposition is performed under a high vacuum of 1×10 ^-3 mmHg or less, usually about 1×10 ^-4 to 1×10 ^-5 mmHg, while heating to a temperature of Heat treatment is performed in an atmosphere. However, this proposed method requires considerably harsh conditions for oxidation treatment after vacuum deposition. For example, when heat treatment is performed in air, the optimum temperature for practical use is usually 200°C to 250°C or higher. The purpose of the oxidation treatment is to convert indium oxide into a higher order oxide since it decomposes into lower order oxides during vacuum evaporation, but it cannot be used under the harsh conditions mentioned above. There are natural limitations depending on the material of the plastic base material. Moreover, according to this method, since the evaporation source is an oxide, the heating temperature of the evaporation source is 1300℃ or higher, usually 1500℃ or higher.
The temperature must be around 2100℃. As a result, a specially treated and expensive crucible is required as a container for the evaporation source. Furthermore, at the commonly applied distance between the evaporation source and the plastic substrate, there is a high risk that the plastic substrate will be heated to high temperatures by radiation, which also limits the plastic substrates that can be used. I end up. On the other hand, the latter method, which uses metallic indium as the evaporation source, generally involves introducing an oxidizing gas into the vacuum system to
This method attempts to vacuum-evaporate metallic indium onto a plastic substrate while converting it into its oxide at a relatively low degree of vacuum of about 10 ^-2 to 1×10 ^-4 mmHg. For example, in Japanese Patent Publication No. 40-14304, a plastic base material of 100%
A method is disclosed that aids in the conversion of metallic indium to an oxide by heating to temperatures above 0.degree. C., typically on the order of 110-150.degree. Also, special public service 1977-8137
The publication describes a similar vacuum evaporation process with a deposition rate of 16
While the deposition film thickness is reduced by using a high rate of Å/sec or more, usually 150 Å/sec or more, it is generally
A method is disclosed in which a step of heat treatment at a temperature of around 100° C. for several hours is added. As is clear, in these methods the plastic substrate is not heated at all or only to a relatively low temperature, and since the heating of the evaporation source is also low, only a small amount of heat is received from the evaporation source by radiation. It can be said. Furthermore, even when heat treatment is performed after vacuum deposition, the temperature is sufficiently permissible for various plastic substrates. As described above, the method using metallic indium as an evaporation source has the great advantage of being almost unrestricted by the plastic substrate used, and can be said to be a desirable method as an industrial method for manufacturing transparent conductive films. However, despite these advantages, the conductive film obtained by this method has the disadvantage that its film properties, particularly its transparency, are not fully satisfactory.
For example, when examining the visible light transmittance at 600 nm of a conductive film obtained according to the method described in Japanese Patent Publication No. 40-14304, it was found that even a thin film could only obtain a transmittance of about 30%. Ta. Also, special public service in 1977
- If the method described in Publication No. 8137 is modified by making the oxidation treatment conditions more severe, the transparency can be improved to some extent, but even in this case, if the film thickness is increased to about 1000 Å or more, The highest visible light transmittance is around 80%,
No material showing higher transmittance could be obtained. Therefore, the inventors of the present invention conducted extensive research on a method for greatly improving transparency without sacrificing the above-mentioned advantages of vacuum evaporation using metallic indium as an evaporation source. After vacuum deposition in an oxidizing gas atmosphere,
Furthermore, in the oxidation process, it is better to use a mixed gas of oxygen gas and an inert gas such as nitrogen or argon gas to improve transparency than to use oxygen gas alone as the oxidizing gas. I found that it is more desirable for In addition, when performing vacuum deposition in such an oxidizing gas atmosphere, if an appropriate amount of water vapor is included in the vacuum system, the transparency of the deposited film will be significantly improved when oxidation treatment is performed after vacuum deposition. It turned out that it would be done. The inventors have discovered the surprising fact that, using this method, the oxidation treatment conditions can be made gentler, and high transparency can be obtained even when the film thickness is increased. This is an extremely important fact, and something that could not have been predicted using conventional preconceptions. That is, in general vacuum evaporation methods, the presence of water vapor in the vacuum system is believed to be detrimental to the formation of a uniform, high-quality deposited film, and efforts have been made to eliminate it. Of course, as mentioned above, when forming a vapor deposited film of indium oxide or the like on a glass plate heated to a high temperature, there has been a proposal to introduce water vapor into the vacuum system in order to make the surface resistance of the vapor deposited film extremely low. There is. However, even in this case, it was thought that introducing water vapor would impair the transparency of the membrane. In this way, the inventors used a mixed gas consisting of oxygen gas and an inert gas as the oxidizing gas, and by incorporating water vapor into this oxidizing gas, they were able to greatly improve the transparency. Successful. However, another problem with the above conventional method is that the resulting transparent conductive film has poor resistance stability, and the surface resistance tends to increase significantly when left in air for a long time. This tendency was similarly observed in the above-mentioned improved method by the present inventors. For example, the film thickness obtained by vacuum evaporating a mixed gas containing water vapor and then oxidizing it is 300 Å.
The change over time when the transparent conductive film was left in the air (dark room) is as shown by curve -b in FIG. 3. As is clear, it increases to about 1.7 times the initial value after 240 hours, and to about 2.2 times or more than the initial value after 600 hours, and shows a tendency to increase thereafter. Such materials with poor resistance stability pose a serious problem when applied to applications that require a constant resistance value, such as transparent electrodes and heaters. In the course of subsequent research to improve such resistance stability, the inventors added a specific amount of metallic tin to metallic indium as an evaporation source, and vacuum-deposited and oxidized it in the same manner as described above, thereby converting both metals. When obtaining a transparent conductive film made of oxide,
When a specific vacuum evaporation means is added, a conductive film is formed in which the weight ratio of metal tin to metal indium constituting the oxide changes continuously in the thickness direction, being higher on the outer surface of the film and lower on the inner surface of the film. Being done,
It has been found that this gives significantly better results in resistance stability. Conventionally, it has been known that when a transparent conductive film made of indium oxide contains a very small amount of tin oxide, the surface resistance decreases. However, a transparent conductive film having a structure in which the metal ratio differs in the thickness direction as described above is not known, and the relationship between such a structure and resistance stability has not been elucidated at all. Therefore, an object of the present invention is to provide a transparent conductive film having such a novel structure. That is, the transparent conductive film of the present invention is composed of an oxide of 60 to 95% by weight of metallic indium and 40 to 5% by weight of metallic tin formed on the surface of a plastic substrate, and The weight ratio of metallic tin to metallic indium (hereinafter simply referred to as
By continuously changing the Sn/In ratio (referred to as the Sn/In ratio) in the film thickness direction, the Sn/In ratio on the inner surface of the film is lowered to less than 1/11 times the average ratio (Sn/In ratio) of the entire film. At the same time, the film is characterized in that the Sn/In ratio on the outer surface side of the film is increased to 1.5 times or more the average ratio of the entire film. Figures 1 and 2 show changes in the Sn/In ratio in the film thickness direction for two types of transparent conductive films of the present invention, with the vertical axis representing the Sn/In ratio and the horizontal axis representing the film thickness. It is expressed as The film thickness is 300 in both cases.
Figure 1 shows a transparent conductive film made of an oxide of 90% by weight of metallic indium and 10% by weight of metallic tin obtained by the method of Example 2 described later, and Figure 2 shows the transparent conductive film obtained by the method of Example 4 described later. The transparent conductive films made of oxides of 60% by weight of metallic indium and 40% by weight of metallic tin are respectively shown. Furthermore, the positions of the dotted lines in both figures represent the average Sn/In ratio of the entire film. As can be seen from these figures, there are considerable differences in the degree of Sn/In ratio and the change curve in the thickness direction between the inner surface of the film and the outer surface of the film, depending on the embodiment, but this difference is particularly important in this invention. It's not essential. What is important is that the Sn/In ratio changes continuously in the film thickness direction, and the inner surface of the film is significantly lower than the average ratio of the entire film. As shown in the example, the Sn/In ratio on the inner surface of the film is as low as 1/11 times or normally 1/132 times the average ratio of the entire film, forming a highly concentrated indium oxide layer, while the Sn/In ratio on the outer surface of the film is as low as 1/132 times the average ratio of the entire film. In other words, as shown in both figures above and each example below, the Sn/In ratio on the outer surface of the film is 1.5 times or more than the average ratio of the entire film, usually up to about 113 times. This is due to the high concentration of tin oxide layer forming a high concentration tin oxide layer. FIG. 3 shows the resistance stability of the transparent conductive film of the present invention having such a structure, with Ro (initial resistance value)/Rt (resistance value after aging) as the vertical axis. The horizontal axis represents the time the sample was left in a dark room. Curve a in the figure is composed of an oxide of 80% by weight of metallic indium and 20% by weight of metallic tin obtained by the method of Example 4 described later. 1 shows a transparent conductive film of the present invention having a structure similar to that shown in FIG. 1, and curve -b shows a transparent conductive film made solely of indium oxide obtained in Comparative Example 1 described later. As is clear from this figure, in the transparent conductive film of the present invention, the surface resistance after 240 hours was suppressed to about 1.2 times the initial value, and after that it remained stable and hardly increased. The reason for this is that the Sn/In ratio on the outer surface of the film is the average Sn/In ratio of the entire film.
Since the In ratio is significantly higher than that of In and constitutes a highly concentrated tin oxide layer, this seems to be because this outer layer acts as a barrier layer against resistance changes due to oxidation. As described above, the transparent conductive film of the present invention provides high resistance stability, but other effects include lower chemical resistance and better chemical resistance compared to films that do not contain tin oxide at all or contain tin oxide uniformly in the film. It also has the effect of improving wear resistance. This is also due to the fact that the outer layer is composed of a highly concentrated tin oxide layer. Note that such effects such as resistance stability can be expected even when a complete two-layer structure of an indium oxide layer and a tin oxide layer is used. On the other hand, even if the outer layer is made of a highly concentrated tin oxide layer and the inner layer is made of a highly concentrated indium oxide layer, the Sn/In ratio changes continuously in the film thickness direction. In other words, even if the concentration difference is large, tin oxide is contained throughout the film, so either no tin oxide is included or the film has a complete two-layer structure of indium oxide and tin oxide. It has the advantage that the initial surface resistance of the entire film can be considerably lower than that of a conventional film, and it also has the advantage that it does not suffer from the problem of delamination that occurs with completely two-layer structures. The reason why the weight ratio of metallic indium and metallic tin in the entire film constituting the oxide in the transparent conductive film of the present invention is set to 60 to 95% by weight for the former and 40 to 5% by weight for the latter is as follows. . In other words, the higher the proportion of metallic tin, the better the resistance stability, but on the other hand, there is a tendency for the transparency of the film to decrease and the initial resistance value to increase. This is because if it becomes too much, the effects of improving resistance stability, chemical resistance, and wear resistance will not be sufficiently obtained. The ratio of metallic indium and metallic tin is set within the above range, and particularly preferably 65 to 90% by weight of metallic indium and 35% by weight of metallic tin.
When the content is set at ~10% by weight, good results can be obtained in all of the above-mentioned properties. Next, a method for manufacturing the transparent conductive film of the present invention having such a structure will be explained. As such a method, the inventors used an evaporation source consisting of 60 to 95% by weight of metallic indium and 40 to 5% by weight of metallic tin, and used the evaporation source in an amount necessary to obtain a predetermined film thickness. The deposition rate is increased by setting the container in an oxidizing gas atmosphere consisting of a mixed gas of oxygen gas and an inert gas, and performing an initial heating step to evaporate at least metallic indium, followed by a heating step to raise the temperature. A first production method characterized in that vacuum deposition is performed on a plastic substrate so as to be constant from beginning to end, and further oxidation treatment is performed on the deposited film formed by this vacuum deposition, and in this production method, the above-mentioned mixture It has been found that the second production method, which is characterized by the inclusion of water vapor in the gas, is particularly suitable. In other words, in these methods, metal indium and metal tin are first used as evaporation sources, and these are vacuum evaporated in an oxidizing gas atmosphere, and then further oxidized. This method has advantages such as not being limited by the material of the plastic base material and being able to lower the heating temperature of the evaporation source. Furthermore, according to these methods, Sn/Tin can be deposited in vacuum by simply increasing the temperature gradually from a preset initial heating temperature by utilizing the difference in vapor pressure between the two metals. In
Since it is possible to obtain a transparent conductive film having the above-described structure in which the ratio changes in the thickness direction, industrially difficult vapor deposition techniques are not required. In other words, when heating the evaporation source, first set an initial heating temperature corresponding to a predetermined evaporation rate and heat it for a certain period of time.Since the vapor pressure of metallic indium is considerably higher than that of metallic tin, An oxide mainly consisting of metallic indium is deposited on the surface. If this initial heating temperature is maintained as it is, the deposition rate will decrease as the metal indium evaporates, but if the temperature is gradually raised to keep the deposition rate constant, the metal tin will gradually increase. As the amount of evaporation increases, an oxide mainly consisting of metallic tin is finally deposited. The change in the Sn/In ratio achieved in this way in the thickness direction is typically as shown in FIG. Although FIG. 2 shows the same changes as above, the Sn/In ratio once reaches a peak and then decreases. Depending on the deposition conditions during the heating operation described above, some of the metal indium and metal tin are converted into oxides with low vapor pressure by the oxidizing gas before they are evaporated, and this is evaporated in the later stages of heating. It seems that it is for coming. Next, in the first manufacturing method, a mixed gas of oxygen gas and inert gas is used as the oxidizing gas, which has the effect of lowering the initial surface resistance compared to when oxygen gas is used alone. There is. In other words, according to the transparent conductive film of the present invention in which the Sn/In ratio changes in the thickness direction, as mentioned earlier,
Similar to when tin oxide is evenly included in the entire film, compared to a film made of indium oxide alone,
Although a low surface resistance is obtained, this surface resistance can be further reduced (to about 1/10) by using a mixed gas. Furthermore, when such a mixed gas is used, the transparency of the conductive layer obtained is improved compared to when using oxygen gas alone, and
When making a relatively thin film of about Å or less,
Visible light transmittance at 600 nm can be increased to 80% or more. Further, when water vapor is further included in the above-mentioned mixed gas by the second production method, the initial surface resistance of the resulting transparent conductive film is further reduced, and the transparency is further improved. In particular, regarding transparency, even when the oxidation treatment conditions are made very mild compared to the first manufacturing method, the same or higher transparency can be obtained, and even when the film thickness is increased to about 2000 Å. It has the advantage of providing visible light transmittance of 80% or more. Below, the method for manufacturing the transparent conductive film of the present invention, which is comprised of the first and second manufacturing methods, will be described in detail. The plastic base material used in this invention is hardly limited in terms of its material from a thermal standpoint. As will be described later, the plastic substrate is not heated to a temperature higher than 150℃ during vacuum evaporation, and since the evaporation source is metallic indium and metallic tin, the radiant heat from the evaporation source is small, and oxidation treatment is also possible. This is because relatively hidden conditions are sufficient. Therefore, in the present invention, any of the various conventionally known plastics can be used. Specific examples include polyester, polyamide, polypropylene, polycarbonate, polyimide, polyparabanic acid, polyamideimide, polybenzimidazole, triacetate, polyacrylic, cellulose resin, and fluororesin. When these plastics are used as base materials, they can be appropriately used as sheets, films, and other molded products. In addition, these plastic substrates are cleaned by solvent cleaning, ultrasonic cleaning, etc. to remove dust and
After cleaning, if necessary, an undercoat layer can be formed or a surface treatment can be applied to improve the adhesion and abrasion resistance between the deposited film and the plastic substrate.
Formation of the undercoat layer is also effective for alleviating strain between the base material and the deposited film during the oxidation treatment process. To form an undercoat layer, an organic solvent-based, emulsion-based, or solvent-free resin coating is usually prepared, coated onto the plastic substrate to a predetermined thickness, and then heated, cured at room temperature, or cured at room temperature. It may be dried by an appropriate means such as electron beam or ultraviolet irradiation. Examples of resins used here include epoxy resins, polyester resins, urethane resins, alkyd resins, vinyl chloride-vinyl acetate copolymer resins,
A wide range of known resins such as acrylic resins are included.
As the coating method, methods such as gravure roll coating, Maya bar coating, doctor blade coating, reverse roll coating, dip coating, air knife coating, kiss coating, nip coating, and fountain coating are employed. Examples of methods for surface treatment include corona discharge treatment, fire treatment, sputtering treatment, ultraviolet irradiation treatment, electron beam irradiation treatment, chemical conversion treatment, and oxidizing agent treatment. These surface treatments are particularly effective means for improving the adhesion between the plastic substrate and the deposited film. The evaporation sources used in this invention are metallic indium and metallic tin, and in some cases, the above metals doped with a small amount of other metals such as cadmium or molybdenum may also be used. The proportion of metallic indium and metallic tin is 60 to 95% by weight for the former and 40 to 5% by weight for the latter, particularly preferably the former.
The latter is 65 to 90% by weight, and the latter is 35 to 10% by weight, and the reason for this is as described above. Note that these metals may be made into an alloy from the beginning or may be used as a single metal. Further, the shape is not particularly limited, and any shape such as a rod, a film-like granule, or a powder can be used. In the present invention, when such an evaporation source is vacuum-deposited on the above-mentioned plastic substrate in an atmosphere consisting of an oxidizing gas, a mixed gas consisting of an oxygen gas and an inert gas is used at least as the oxidizing gas. Typical inert gases include nitrogen gas and argon gas. These inert gases may be used alone, both gases may be used together, or other inert gases such as xenon and krypton may be mixed. It has been found that the mixing ratio of such an inert gas and oxygen gas greatly influences the characteristics, particularly the transparency, of the resulting transparent conductive film. Generally applicable and desirable mixing ratio for improving transparency is that the proportion of inert gas in the mixed gas is approximately the proportion of inert gas contained in air (approximately
78-80% by volume). This typical gas mixture is air containing nitrogen gas as the primary inert gas. Using such air can be carried out industrially advantageously. The proportion of inert gas in the gas mixture can be greater than the proportion of inert gas contained in air, but in this case only when water vapor is included in the gas mixture, and at most about 86 It should be below 83% by volume, preferably below 83% by volume. If the number is too large, transparency will be impaired. By increasing the proportion of inert gas in this manner, it is possible to suppress oxidative deterioration of the boat and exhaust system during vacuum evaporation, and the surface resistance can be further reduced. This leads to the benefits of including water vapor. The proportion of inert gas in the gas mixture can also be lower than the proportion of inert gas contained in air, but in this case at least about 5% by volume.
The volume should preferably be 20 or more. If the amount is too small, no improvement in transparency or reduction in surface resistance will be observed in any case. Next, in order to include water vapor in such a mixed gas in the second production method, the mixed gas may be passed through a water tank or a constant humidity atmosphere. Of course, other humidification means can also be used. The amount of water vapor is determined by the relative humidity of the mixed gas being approximately 30% or more, preferably approximately 70%.
% or more. If the relative humidity is too low, little effect of improving transparency or reducing surface resistance can be expected. According to the vacuum evaporation method of this invention, first, the amount of evaporation source necessary to obtain a predetermined film thickness is set in the evaporation source container in a evaporation apparatus such as a bell gear, and the inside of the apparatus is preliminarily adjusted to about 10 ^-5 mmHg. After that, the above-mentioned mixed gas or humidified mixed gas is introduced to adjust the degree of vacuum to an appropriate degree. The degree of vacuum greatly affects the characteristics of the transparent conductive film obtained, and the optimal degree of vacuum also differs depending on whether humidified gas or dry gas is used, so it must be determined appropriately for each case. Good. For example, when using a humidifying gas, the most suitable degree of vacuum is such that the atmospheric pressure within the apparatus is 9 x 10 ^-2 to 5 x 10 ^-3 mmHg. In general, if the degree of vacuum becomes too low, particularly if the degree of vacuum is lower than 1×10 ^-1 mmHg, the evaporation source will be rapidly oxidized, which will easily interfere with the vapor deposition operation, and the vapor deposition efficiency will also deteriorate. Furthermore, the surface of the deposited film becomes uneven, making it impossible to obtain a transparent film even if an oxidation treatment is performed thereafter. On the other hand, it is not preferable if the degree of vacuum becomes too high, and in a high vacuum system, no significant improvement in transparency due to oxidation treatment will be observed. Next, the evaporation source is evaporated onto the plastic substrate by appropriate means such as resistance heating, electron beam, or induction heating under such a moderate degree of vacuum. At this time, a preset evaporation rate is an initial heating step in which an initial heating temperature that allows at least metallic indium to be evaporated is set and heated for a certain period of time, and a temperature increasing heating step in which the temperature is then gradually increased and controlled so that the evaporation rate is constant. will be established. The set vapor velocity is generally in the range of 1 to 16 Å/sec from a transparency perspective, but the optimum rate when using humidifying gas is usually 2 to 10 Å/sec, with a corresponding initial heating rate. Temperature is 600-900
It is about ℃. Further, during this vacuum deposition, it is not necessary to heat the plastic substrate in advance; in fact, non-heating is more effective in improving transparency. However, in general, vacuum evaporation may be carried out under conditions such that the temperature is up to about 150°C, particularly when a humidified gas is used, preferably 125°C or lower, and most preferably 100°C or lower (including non-heating). The vapor-deposited film thus obtained adheres uniformly and firmly to the surface of the plastic substrate, and is mainly composed of lower-order oxides such as indium oxide and tin oxide, and is dark brown in color and has low transparency. The thickness of this deposited film is usually 60~60cm when using a non-humidified gas, that is, a mixed gas that does not contain water vapor.
It is about 500 Å, and when humidified gas is used, it is usually 60 to 2000 Å. Of course, the thickness can be made thinner or thicker than the above thickness depending on the case. However, if the film thickness is too thin, defects are likely to occur locally, whereas if it is too thick, the oxidation treatment must be performed under harsh conditions, such as heat treatment at high temperatures for a long time, which is not preferable. Next, in the present invention, the above deposited film is subjected to an oxidation treatment. Transparency can only be improved by this process. Oxidation treatment is generally performed by heat treatment in an oxidizing atmosphere such as air, oxygen, or ozone. Of course, other oxidation treatments such as anodic oxidation treatment, chemical conversion treatment, glow discharge oxidation treatment, and autograve treatment can also be employed. In this invention, the conditions for the oxidation treatment vary considerably depending on whether water vapor is included in the mixed gas. When water vapor is not included, it is generally better to use somewhat harsher conditions. On the other hand, when water vapor is included, fairly mild conditions can be selected over a relatively wide range of film thicknesses as described above. For example, when heat treatment is performed in air, a temperature of 130 to 150°C is usually sufficient. Of course it is acceptable for plastic base materials.
Processing temperatures up to 200°C may be selected.
A short treatment time of about 30 to 60 minutes is usually sufficient at the above heat treatment temperature. If necessary, the processing time may be longer than this. The transparent conductive film of this invention thus obtained is
The film thickness is generally in the range of 60 to 2000 Å,
The Sn/In ratio changes continuously in the thickness direction, and the Sn/In ratio on the inner surface of the film is less than 1/11 times the average ratio of the entire film and is usually up to about 1/132 times, which is more significant than the above average ratio. It has a structure in which the Sn/In ratio on the outer surface side of the film is significantly higher than the above average ratio, being 1.5 times or more and usually up to about 113 times the average ratio of the entire film. In addition, the surface resistance is generally 0.1KΩ/
^cm2 to about 100KΩ/ ^cm2 , usually 0.1 to 10K
It has a ^low visible light transmittance of 600 nm of 75% or more, usually 80% or more, and particularly preferably 90% or more of transparency. As described above, the transparent conductive film of the present invention can be advantageously manufactured by the first and second manufacturing methods, but it goes without saying that it can also be manufactured by other methods. For example, as a means to continuously change the Sn/In ratio in the thickness direction, instead of using the difference in vapor pressure between metallic indium and metallic tin, two evaporation source containers are used to continuously change the Sn/In ratio between metallic indium and metallic tin. The amount of evaporation may be changed over time by setting tin and tin separately and adjusting the heating temperatures of both metals as appropriate. In addition, in order to enable continuous evaporation, the plastic substrate was run at an appropriate speed, and of the two evaporation source containers lined up in the running direction, metal indium was set in the rear container and metal tin was set in the front container. Even when both are simultaneously heated and evaporated, it is possible to obtain a transparent conductive film having the structure of the invention in which the Sn/In ratio changes continuously in the thickness direction. In addition, in these methods, a mixed gas of oxygen gas and inert gas is used as the oxidizing gas, as in the first and second manufacturing methods,
Further, when using a humidified gas containing water vapor in the mixed gas, good results can be obtained in terms of transparency and initial surface resistance. Of course, if a high degree of transparency or low surface resistance is not required for the transparent conductive film of the present invention, oxygen gas may be used as the oxidizing gas in the first and second manufacturing methods and the other manufacturing methods mentioned above. It is okay to make changes such as using it alone. As detailed above, the transparent conductive film of the present invention has a specific structure in which the Sn/In ratio changes continuously in the thickness direction, and this structure greatly improves resistance stability, chemical resistance, and abrasion resistance. In addition, as seen in the first and second production methods, it is possible to provide a conductive film that is improved in terms of transparency and conductivity compared to conventional ones. Since this conductive film is formed on the surface of a plastic base material, it can take advantage of the base material's advantages in terms of flexibility, processability, impact resistance, weight, etc., so it can be used as a new display. In addition to being used as a transparent electrode in the system, it can be effectively used for various purposes such as preventing static electricity on transparent articles and blocking electromagnetic waves. In this application, in order to further improve the abrasion of the transparent conductive film and to make it moisture resistant, if necessary, a protective coating may be applied to this film by a conventionally known method. Further, in order to impart adhesive properties to the conductive film, this film may be further subjected to appropriate processing, if necessary. The present invention will be described in more detail below based on examples. Note that the present invention is not limited to these examples in any way. Example 1 After evacuating the inside of the bell gear to 1×10 ^-5 mmHg, a dry mixed gas consisting of 20% by volume of oxygen gas and 80% by volume of argon gas was introduced to adjust the degree of vacuum to 20×10 ^-2 mmHg. did. Next, 0.02 g of an evaporation source made of metallic indium and metallic tin (metal tin 10% by weight) loaded on a tungsten board was first heated to about 800°C by resistance heating, and then set at a distance of about 9 cm from the evaporation source. Vacuum deposition was performed on a polyester film with a thickness of 100 μm at a deposition rate of 6 Å/sec.
Thereafter, the temperature was gradually increased to approximately 1100° C. while keeping the above deposition rate constant, thereby depositing the entire amount. The resulting deposited film had a thickness of 300 Å, was dark brown, and was opaque. Also, the surface resistance of this deposited film is
When the visible light transmittance at 600 nm was examined, the surface resistance was 1 KΩ/cm ² and the visible light transmittance was 6%. Note that the visible light transmittance was measured by placing a polyester film on which no vapor-deposited film was formed into the compensation optical path.
All visible light transmittances described in this specification were measured according to the above method. Next, the above deposited film was heat-treated in air at 200°C for 30 minutes to obtain a transparent conductive film of the present invention. The surface resistance of this film is 1.2KΩ/cm ² and the visible light transmittance is 90
It was %. Furthermore, when this film was left in the air (dark room) for 10 days, the surface resistance was 1.4KΩ/ ^cm2 , which was Ro
(Initial value)/Rt (value after days) was 0.83. Furthermore, the film having such characteristics was etched little by little by sputtering, and the contents of metallic indium and metallic tin at each thickness were determined.
Eleotron Spectroscopy for Chemical Analysis
(hereinafter referred to as ESCA)
When the Sn/In ratio was examined, the change in the thickness direction was almost the same as that shown in FIG. On the other hand, in this method, the oxidation treatment conditions were set at 130°C.
When the temperature was changed to 60 minutes at 150°C and 60 minutes at 150°C, the surface resistance was 0.7KΩ/cm ² , and the visible light transmittance was 37% and 60%, respectively. As described above, when water vapor is not included in the vacuum system, high transparency cannot be obtained under relatively mild oxidation conditions. Reference Example 1 A transparent conductive film was obtained in exactly the same manner as in Example 1, except that the metal tin content of the evaporation source consisting of metal indium and metal tin was about 3% by weight. The surface resistance of this film is 3KΩ/cm ² and the visible light transmittance is 92%.
It was hot. Furthermore, after this film was left in the air (dark room) for 10 days, Ro/Rt was 0.65. Reference Example 2 Using the same dry mixed gas as in Example 1 and in a vacuum system adjusted to the same degree of vacuum, metallic indium on a tungsten board was first heated to approximately 800°C at a deposition rate of 6 Å/sec. Vacuum deposition was performed on a polyester film to form a deposited film with a thickness of approximately 250 to 300 Å. Next, the vacuum system was returned to the atmosphere, and metal tin was loaded onto the tungsten board as a new evaporation source, and the same method as in the case of metal indium was used, except that the heating temperature was about 1200°C.
A further vapor-deposited film having a thickness of about 20 to 40 Å was formed on the vapor-deposited film formed on the polyester film. The ratio of the metal indium and the metal tin used as the vapor deposited film is the same as in Example 1.
It is almost the same as in the case of Then, heat treated in air at 200℃ for 30 minutes,
A transparent conductive film having a completely double layered structure of indium oxide and tin oxide was obtained. This film had a surface resistance of 3KΩ/cm ² and a visible light transmittance of about 90%. Furthermore, after this film was left in the air (in a dark room) for 10 days, Ro/Rt was approximately 0.81. On the other hand, when cellophane tape No. 29 manufactured by Nitto Electric Industries Co., Ltd. was attached to the vapor-deposited film of the transparent conductive film described above and then strongly peeled off, a tin oxide film was observed to adhere to the surface of the peeling tape. Ta. After leaving the peeled transparent conductive film in the air (dark room) for 10 days,
Ro/Rt was approximately 0.63 to 0.7, and the resistance stability was significantly reduced. Further, even if an attempt was made to attach the release tape to the vapor-deposited film again, it could not be successfully attached due to the decrease in adhesiveness. Example 2 After evacuating the inside of the bell gear to 1 x 10 ^-5 mmHg, a mixed gas of 20 volume % oxygen gas and 80 volume % argon gas with a relative temperature of about 95% was introduced.
The degree of vacuum was adjusted to 10 ^-2 mmHg. Next, 0.02 g of an evaporation source made of metallic indium and metallic tin (metal tin 10% by weight) loaded onto a tungsten board was first heated to about 800°C by resistance heating, and then set at a distance of about 9 cm from the evaporation source. The film was vacuum deposited onto a 100 μm thick polyester film at an evaporation rate of 6 Å/sec. Thereafter, the temperature was gradually increased to about 1100° C. so as to keep the above-mentioned deposition rate constant, thereby depositing the entire amount. The resulting deposited film had a thickness of 300 Å, was dark brown, and was opaque. Also, the surface resistance of this deposited film is
When the visible light transmittance at 600 nm was examined, the surface resistance was 2.9 KΩ/cm ² and the visible light transmittance was 25%. Next, the above deposited film was heat-treated in air at 150° C. for 60 minutes to obtain a transparent conductive film of the present invention. The surface resistance of this film is 1.5KΩ/cm ² and the visible light transmittance is 97.
It was %. The surface resistance of this film when left in air (dark room) for 10 days was 1.8KΩ/ ^cm2 .
Ro/Rt was 0.83. Furthermore, a membrane having such properties was prepared in the same manner as described in Example 1.
When the Sn/In ratio was examined by ESCA, the changes in the thickness direction were as shown in Figure 1. That is, the thickness from the base material surface is 50 Å or less, 150 Å,
Sn/In at positions 250Å, 270Å and 300Å
The ratios are 1.8×10 ^-3 (range 1×10 ⁻³ to 3×10 ⁻³ ), 3×10 ⁻³ (range 1.6×10 ⁻³ to 6×10 ⁻³ ), and
7×10 ^-2 (range of 3.5×10 ^-2 to 2×10 ^-1 ), 1.1 (4×
10 ^-1 to 2) and 6 (range of 2.5 to 11), and the average Sn/In ratio of each Sn/In ratio above (10/90)
Expressed as a magnification of 1/61 (1/11)
0~1/37x range), 1/37x (1/69~1/19x range), 5/8x (5/16~1.8x range), 9.9x (3.6~
18-fold range) and 55-fold (23- to 100-fold range). Example 3 Oxidation treatment conditions were 130°C for 30 minutes, 130°C for 60 minutes,
Five types of transparent conductive films were obtained in exactly the same manner as in Example 2, except that the heating time was 150°C for 30 minutes, 200°C for 30 minutes, and 200°C for 60 minutes. The surface resistance of these films is 1.3KΩ/cm ² , respectively.
1.3KΩ/cm ² , 1.3KΩ/cm ² , 1.2KΩ/cm ² and
It was 1.2KΩ/ ^cm2 . The visible light transmittances were 87%, 88%, 95%, 99%, and 99%, respectively. We also investigated the change in surface resistance when these films were left in the air (in a dark room) for 10 days.
Almost the same good results as in Example 2 were obtained for Ro/Rt. Example 4 Three types of transparent conductive films were obtained in the same manner as in Example 2, except that the metallic tin content of the evaporation source consisting of metallic indium and metallic tin was changed as shown in Table 1 below. . The surface resistance of these films,
The visible light transmittance and Ro/Rt after being left in the air (dark room) for 10 days were as shown in Table 1.

[Table] We also investigated the relationship between Ro/Rt and standing time for products with a metal tin content of 20% by weight.
This was as shown by curve-a in FIG. Furthermore, for those with a metal tin content of 40% by weight,
When the change in the Sn/In ratio in the thickness direction due to ESCA was investigated, the results were as shown in Figure 2. That is, the thickness from the base material surface is 50 Å or less, 150 Å,
Sn/In at positions 250Å, 270Å and 300Å
The ratios are 3 × 10 ^-2 (range of 1.5 × 10 ^-2 to 6 × 10 ^-2 ), 4.5 × 10 ^-2 (range of 1.5 × 10 ^-2 to 1 × 10 ^-1 ), respectively.
25 (range 12-60), 11 (range 6-20) and 2.5
(range 1 to 5.5), and the average of each Sn/In ratio above
Expressed as a magnification relative to the Sn/In ratio (40/60),
1/22x (1/45-1/11x range), 1/15x (1/44-1/7x range), 37x (18-90x range), respectively.
17 times (range 9-30 times) and 3.7 times (range 1.5-8.2 times). In addition, when the change in the Sn/In ratio in the thickness direction was investigated in the same manner as above for the metal tin content of 5% by weight, it was found that the thickness from the substrate surface was 50 Å or less, 150 Å or less,
The Sn/In ratios at Å, 250 Å and 300 Å positions are 8×10 ^-4 (range 4×10 ^-4 to 2×10 ^-3 ), 1.6×10 ^-3 (range 8×10 ^-4 to 3× 10 ^-3 range), 3.5
×10 ^-2 (range 1.7 × 10 ^-2 to 7 × 10 ^-2 ) and 2.5
(range of 1.1 to 6), and the average of each Sn/In ratio above
Expressed as a magnification relative to the Sn/In ratio (5/95),
1/66x (range of 1/132 to 1/27x), 1/33x (range of 1/66 to 1/17x), 2/3x (range of 1/3 to 1.3x) and 47 times (range 21 to 113 times). Reference Example 3 A transparent conductive film was obtained in exactly the same manner as in Example 2, except that the metallic tin content of the evaporation source consisting of metallic indium and metallic tin was approximately 3% by weight. The surface resistance of this film is 5.5KΩ/cm ² and the visible light transmittance is 98
It was %. Also, put this film in the air (dark room) for 10 minutes.
After being left for one day, the surface resistance increased to 8.6KΩ/cm ² and Ro/Rt was 0.64. Comparative Example 1 A transparent conductive film was obtained in exactly the same manner as in Example 2, except that metallic indium was used alone as an evaporation source. The surface resistance of this film was 6KΩ/cm ² and the visible light transmittance was 98%.When this conductive film was left in the air (dark room) and the change in surface resistance over time was investigated, Ro/Rt was as shown in curve-b in FIG. The surface resistance after standing for 10 days was 9.8KΩ/cm ² , and Ro/Rt was 0.61. Example 5 In Example 2, the gas composition of the mixed gas was changed, and the relationship between the volume ratio of argon gas in the mixed gas and the surface resistance and visible light transmittance of the resulting transparent conductive film was investigated. The results were as shown in Table 2 below. As is clear from the table below,
Particularly good results have been obtained in terms of film transparency in a gas composition range in which the volume proportion of argon gas is approximately the same as the volume proportion of inert gas contained in air (approximately 78 to 80 volume %). In addition, if the volume ratio is higher than the above, it is about 86 volume% or less, and when it is lower than the volume ratio above, it is about 5 volume% or more. It can be seen that a film has been obtained.

[Table] Corresponds to
Example 6 Example 2 except that instead of a mixed gas of oxygen gas and argon gas with a relative humidity of 95%, a mixed gas of 21% by volume of oxygen gas and 79% by volume of nitrogen gas with the same humidity was used. A transparent conductive film was obtained in exactly the same manner. This film had a surface resistance of 1.6 KΩ/cm ² and a visible light transmittance of 98%. The surface resistance of this film after being left in the air (dark room) for 10 days was 1.9KΩ/
cm ² and Ro/Rt at this time was 0.83. Furthermore, when the change in the Sn/In ratio in the thickness direction due to ESCA was examined, it was found to be almost the same as in Example 2. Example 7 Except that the oxidation treatment conditions were 130°C and 60 minutes,
A transparent conductive film was obtained in exactly the same manner as in Example 6.
The surface resistance of this film was 1.2KΩ/cm ² and the visible light transmittance was 88%. Further, the change in surface resistance over time was almost the same as in Example 6. Example 8 In Example 6, the gas composition of the mixed gas was changed and the relationship between the volume ratio of nitrogen gas in the mixed gas and the surface resistance and visible light transmittance of the resulting transparent conductive film was investigated. The results were as shown in Table 3 below.

[Table] As is clear from the table above, especially good results were obtained in terms of film transparency when the gas composition was made so that the volume ratio of nitrogen gas was approximately the same as the volume ratio of inert gas contained in air. ing. In addition, if the volume ratio is higher than the above, it can be set to 86 volume% or less, and if the volume ratio is lower than the volume ratio above, it can be set to about 5 volume% or more, and a conductive film with excellent transparency and low surface resistance can be obtained. It can be seen that Example 9 In Example 2, the degree of vacuum of the vapor deposition atmosphere was changed and the relationship between the degree of vacuum and the surface resistance and visible light transmittance of the resulting transparent conductive film was investigated. The results were as shown in Table 4 below. As is clear from this table, when water vapor is included in the vacuum system in this invention, the atmospheric pressure is 9.
It can be seen that it is particularly desirable to set the value between ×10 ⁻² and 5×10 ⁻³ mmHg.

【table】

[Table] Example 10 In Example 2, the relative humidity of the vapor deposition atmosphere was changed and the relationship between the relative humidity and the surface resistance and visible light transmittance of the resulting transparent conductive film was investigated. The results were as shown in Table 5 below. As is clear from this table, when water vapor is introduced into the vacuum system in the present invention, it is preferable to keep the relative humidity at about 30% or more, preferably about 70% or more.

[Table] Example 11 In Example 2, the polyester film that is the plastic base material was heated during the evaporation of the evaporation source consisting of metallic indium and metallic tin, and the heating temperature of the base material and the surface resistance of the transparent conductive film obtained were determined. The relationship between this and visible light transmittance was investigated. The results were as shown in Table 6 below. The heating means for the substrate was a ceramic heater, and the heating temperature was measured using a thermolabel and a thermocouple. In the table, the substrate temperature in the case of non-heating (corresponding to Example 2) was about 35°C.

【table】

[Table] As is clear from the above table, in the present invention, it is preferable not to heat the plastic base material, and if it is heated, it is preferably at 125°C or lower, particularly preferably at 100°C or lower. I understand. Example 12 In Example 2, the thickness of the deposited film was kept constant (300 Å), and the deposition rate, the initial heating temperature of the deposited film, and the heating temperature at the end of the deposition were changed, and the deposition rate and the resulting transparent conductor were changed. The relationship between the surface resistance of the transparent film and the visible light transmittance was investigated. The results were as shown in Table 7 below. In addition, Sn/
All changes in the thickness direction of In were similar to those in Example 2.

[Table] Example 13 In Example 2, the deposition rate was kept constant (6 Å/sec)
The relationship between the deposited film thickness and the surface resistance and visible light transmittance of the resulting transparent conductive film was investigated by varying the amount of evaporation source charged and the thickness of the deposited film. The results are shown in Table 8 below. It was exactly as shown. Further, the changes in the Sn/In ratio in the thickness direction of the transparent conductive films obtained by these methods by ESCA were similar to those in Example 2. For example, for a film deposited with a thickness of 1500 Å, Sn/
In ratio, the thickness from the base material surface is 50 Å or less, 500 Å,
1.8× at 1000 Å and 1500 Å positions, respectively
10 ^-3 (range of 1 x 10 ^-3 to 3 x 10 ^-3 ), 2.0 x 10 ^-3 (1.4
×10 ^-3 ~5.5×10 ^-3 range), 9×10 ^-3 (4×10 ^-3 ~
2 × 10 ^-2 range) and 6 (range of 2.5 to 11), and the average Sn/In ratio (10/90) for each of the above Sn/In ratios
Expressed as a magnification of 1/61 (1/11)
0~1/37x range), 1/55x (1/79~1/20x range), 1/12x (1/28~1/5x range) and 55x (23~100x range) (range).

[Table] Example 14 The evaporation rate was set to 3 Å/sec, the initial heating temperature of the evaporation source was approximately 700°C, the final heating temperature was approximately 1000°C, and the amount of evaporation source charged was 0.066 g.
Example 2 except that the deposited film thickness was 1000 Å.
A vacuum-deposited film was obtained in exactly the same manner. This film had a surface resistance of 2KΩ/cm ² and a visible light transmittance of 6%. Next, this vapor deposited film was oxidized under the same conditions as in Example 2 to obtain a transparent conductive film of the present invention. The surface resistance of this film is 1KΩ/cm ² and the visible light transmittance is
It was 92%. Also, when we investigated the change in surface resistance when left in the air (dark room) for 10 days, the surface resistance was 1.2KΩ/ ^cm2 , and Ro/Rt at this time was
It was 0.82. Furthermore, the change in the Sn/In ratio in the thickness direction due to ESCA was almost the same as in Example 2. In other words, the Sn/In ratio in the thickness direction is 50 Å or less, 500 Å, and 1000 Å from the base material surface.
1.8×10 ^-3 (range of 1×10 ^-3 to 3×10 ^-3 ), respectively.
3×10 ^-3 (range of 1.6×10 ^-3 to 6×10 ^-3 ) and 6
(range 2.5 to 11), and the average of each Sn/In ratio above
Expressed as a magnification relative to the Sn/In ratio (10/90),
They were 1/61 times (range 1/110 to 1/37 times), 1/37 times (range 1/69 to 1/18 times) and 55 times (range 23 to 100 times), respectively. Example 15 Two types of transparent conductive films of the present invention were obtained in exactly the same manner as in Example 14, except that the oxidation treatment conditions were 130° C. for 60 minutes and 200° C. for 60 minutes. The surface resistance of these films was 1.3KΩ/cm ² and 1KΩ/cm ² , respectively, and the visible light transmittance was 80% and 97%, respectively. When the sample was left in the air (dark room) for 10 days, Ro/Rt was 0.83 to 0.84, respectively. Comparative Example 2 A transparent conductive film was obtained in exactly the same manner as in Example 14, except that metallic indium was used alone as an evaporation source. This film had a surface resistance of 5KΩ/cm ² and a visible light transmittance of 96%. When this conductive film was left in the air (dark room) for 10 days and the change in surface resistance over time was examined, the surface resistance was 8.3KΩ/cm ² and Ro/Rt was 0.6.

[Brief explanation of the drawing]

Figures 1 and 2 are characteristic diagrams showing different examples of changes in the Sn/In ratio in the thickness direction in the transparent conductive film of the present invention, and Figure 3 is a characteristic diagram showing changes over time in the surface resistance of the transparent conductive film. It is a diagram. Curve-a...Transparent conductive film of this invention. curve-
b...Transparent conductive film different from this invention.

Claims (1)

[Scope of Claims] 1. A transparent conductive film formed on the surface of a plastic substrate, comprising an oxide of 60 to 95% by weight of metallic indium and 40 to 5% by weight of metallic tin, and comprising the oxide. By continuously changing the weight ratio of metallic tin to metallic indium in the film thickness direction, the same ratio on the inner surface of the film is lowered to 1/11 times or less of the average ratio of the entire film, and the same ratio on the outer surface of the film is lowered. A transparent conductive film characterized by having a high ratio of 1.5 times or more of the average ratio of the entire film. 2 Film thickness is 60-2000Å, visible light (600nm)
Transmittance is 80% or more, surface resistance is 0.1 to 100kΩ/cm ²
The transparent conductive film according to claim 1.