Transparent electroconductive film and manufacturing method therefor

The present invention relates to a transparent conductive film in which a crystalline ITO film is formed as a transparent conductive layer on a flexible transparent base material. The transparent conductive film of the present invention is particularly preferably used for a transparent electrode in a touch panel or the like.

Conventionally, so-called conductive glass in which an indium oxide thin film is formed on glass is well known as a transparent conductive thin film, but conductive glass is inferior in flexibility and workability because the base material is glass. , It may not be preferable depending on the application. Therefore, in recent years, transparent conductive films based on various plastic films such as polyethylene terephthalate film have been awarded because of their advantages such as excellent impact resistance and light weight in addition to flexibility and workability. Has been used.

When a transparent conductive layer such as an ITO film is formed on a plastic film base material, it cannot be sputtered at a high temperature due to restrictions due to the heat resistance of the base material. Therefore, the ITO immediately after film formation is an amorphous film (some of which may be crystallized). Such an amorphous ITO film has problems such as strong yellowing, poor transparency, and a large change in resistance after a humidification heat test.

Therefore, in general, it is possible to convert an amorphous ITO film into a crystalline ITO film by forming an amorphous ITO film on a film substrate made of a polymer molded product and then heating it in an oxygen atmosphere in the atmosphere. It has been done (see, for example, Patent Document 1). This method has advantages such as improved transparency of the ITO film, a small change in resistance after the humidification heat test, and improvement in the reliability of the humidification heat.

On the other hand, the transparent conductive film using the film base material has a problem that the transparent conductive layer is inferior in scratch resistance and is scratched during use to increase the electric resistance or cause disconnection. In particular, in a transparent conductive film for a touch panel, a pair of thin films facing each other via a spacer are strongly contacted with each other at a pressing point from one of the panel plate sides, so that good durability characteristics that can withstand this, That is, it is desired to have a dot characteristic. However, since the transparent conductive film using the film base material is generally inferior in spotting characteristics to the conductive glass, there is a problem that the life as a touch panel is shortened.

In response to the above problem, a transparent dielectric thin film in which a film base material having a specific film thickness is used and the refractive index of light is smaller than the light refractive index of the film base material on one surface thereof, and further A transparent conductive film has been proposed in which a transparent conductive layer is sequentially formed and another transparent substrate is bonded to the other surface of the film substrate via a transparent adhesive layer (Patent Document 2). According to such a transparent conductive film, the transparency of the transparent conductive layer and the scratch resistance of the conductive layer can be improved, and the dot characteristics for a touch panel are improved. Further, by forming a transparent conductive layer on one surface of a transparent film base material via a plurality of dielectric thin films, the dot characteristics when the touch panel is used in a bent state are improved (Patent Document 3). ).

On the other hand, since the touch panel of a game machine is often hit hard compared to other uses, the transparent conductive film used is required to have hitting characteristics under a heavier load. In addition, with the narrowing of the frame of the touch panel, the striking characteristics and sliding durability at the edge of the screen are also required, but the input operation at the edge of the screen is more than the case of the center of the screen. , The transparent conductive film is in a higher bending state. Therefore, the transparent conductive film is required to have higher bending resistance in addition to the hitting characteristics under a heavy load.

<p num="0008"><patcit num="1"><text>Special Fair 3-15536 Gazette</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 6-222352</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 2002-326301</text></patcit></p>

<p num="0009"> In view of the above circumstances, it is an object of the present invention to provide a transparent conductive film having excellent spotting characteristics under a heavy load and excellent bending resistance.</p>

<p num="0010"> As a result of diligent studies by the present inventors, they have found that when the transparent conductive layer has a predetermined compressive residual stress, the striking characteristics and bending resistance are improved, and the present invention has been made.</p><p num="0011"> The present invention relates to a transparent conductive film having a transparent conductive layer made of a crystalline indium tin oxide composite oxide (crystalline ITO) formed on a flexible transparent substrate. The compressive residual stress of the crystalline ITO film is preferably 0.4 to 2 GPa. The transparent conductive layer is preferably crystallized by heating. Further, it is preferable that the dimensional change of the crystalline ITO film with respect to the amorphous ITO film before crystallization is -0.3% to -1.5% in at least one direction in the plane.</p><p num="0012"> Furthermore, the present invention relates to a method for producing the transparent conductive film. The production method of the present invention is a base material preparation step for preparing a flexible transparent base material, and an amorphous transparent conductive layer made of an amorphous indium-tin composite oxide is formed on the flexible transparent base material. It has a film forming step and a heat treatment step of heating the amorphous transparent conductive layer to convert it into a crystalline indium tin oxide composite oxide (crystalline ITO film). In the heat treatment step, compressive stress is applied to the transparent conductive layer at least in one direction in the plane.</p><p num="0013"> In the heat treatment step, it is preferable that the transparent conductive layer is compressed so that the dimensional change in at least one direction in the plane is -0.3% to -1.5%. Further, it is preferable that the compressive residual stress of the crystalline transparent conductive layer is set to 0.4 to 2 GPa by applying the compressive stress in the heat treatment step.</p><p num="0014"> The heating temperature in the heat treatment step is preferably 150 ° C to 210 ° C, and the heating time is preferably 150 minutes or less.</p>

<p num="0015"> In the transparent conductive film of the present invention, a crystalline ITO film having a predetermined compressive residual stress is formed on a flexible transparent base material. The crystalline ITO film having compressive residual stress has excellent spotting characteristics under heavy load, and also has high bending resistance. Therefore, the transparent conductive film of the present invention is suitably used for a touch panel, and particularly preferably for a game machine that requires hitting characteristics under a heavy load and a touch panel of a flexible display that requires high bending resistance. ..</p>

<figref num="1">It is a schematic cross-sectional view which shows the laminated structure of the transparent conductive film which concerns on one Embodiment.</figref><figref num="2">It is a schematic cross-sectional view which shows the laminated structure of the transparent conductive film which concerns on one Embodiment.</figref><figref num="3A">It is a schematic cross-sectional view which conceptually represents an example of the manufacturing process of a transparent conductive film.</figref><figref num="3B">It is a schematic cross-sectional view which conceptually represents an example of the manufacturing process of a transparent conductive film.</figref><figref num="3C">It is a schematic cross-sectional view which conceptually represents an example of the manufacturing process of a transparent conductive film.</figref><figref num="4">It is a figure for demonstrating the angle θ and Ψ in the measurement by the X-ray scattering method.</figref><figref num="5">It is a schematic cross-sectional view which shows the structure of the touch panel produced for evaluation.</figref><figref num="6">It is explanatory drawing which shows the outline of linearity measurement.</figref><figref num="7">It is a figure which shows the result of having measured the dimensional change behavior of a transparent conductive film by TMA.</figref><figref num="8">It is a figure which shows the result of having measured the dimensional change behavior of a transparent conductive film by TMA.</figref>

The configuration of the transparent conductive film according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing the transparent conductive film 101 according to the first embodiment of the present invention. The transparent conductive film 101 has a structure in which a crystalline indium tin oxide composite oxide (ITO) film 3 is formed on a flexible transparent base material 1 including one transparent base film 11. The flexible transparent substrate 1 may be composed of only the transparent substrate film 11, and as shown in FIG. 1, the undercoat layer 16 and the surface of the transparent substrate film 11 on the side where the ITO film is formed may be formed. The back coat layer 17 may be formed on the surface on the opposite side. Although FIG. 1 shows a form in which one undercoat layer 16 and one back coat layer 17 are formed, these layers may be composed of two or more layers.

FIG. 2 is a cross-sectional view schematically showing the transparent conductive film 102 according to the second embodiment of the present invention. The transparent conductive film 102 includes two or more flexible transparent substrates, and a crystalline indium tin oxide composite oxide (ITO) film 3 is formed on the first flexible transparent substrate 1. Has a structure. The flexible transparent substrates 1 and 2 are preferably bonded via an appropriate pressure-sensitive adhesive layer 5. Although the configuration having two flexible transparent base materials 1 and 2 is shown in FIG. 2, three or more flexible transparent base materials may be laminated. The flexible transparent substrates 1 and 2 may be composed of only the transparent substrate films 11 and 12, respectively. Further, as shown in FIG. 2, a form in which the undercoat layer 16 is formed on the surface of the first transparent substrate film 11 constituting the first flexible transparent substrate 1 on the side where the ITO film is formed. Alternatively, the back coat layer 17 is formed on the surface of the second transparent substrate film 12 constituting the second flexible transparent substrate 2 on the opposite side to the first flexible transparent substrate 1. The form described above can also be preferably adopted. Although FIG. 2 shows a form in which one undercoat layer 16 and one back coat layer 17 are formed, these layers may be composed of two or more layers. Further, it may have a coat layer other than those shown in the figure.

Hereinafter, the structure and manufacturing method of the transparent conductive film will be described mainly with respect to the first embodiment, but the description regarding each structure and manufacturing method will be incorporated as it is with respect to the second embodiment.

&lt;Flexible transparent base material&gt; (Transparent substrate film) The transparent substrate film 11 constituting the flexible transparent substrate 1 is not particularly limited in its material as long as it has flexibility and transparency, and any appropriate material can be used. Specifically, polyester resin, acetate resin, polyether sulfone resin, polycarbonate resin, polyamide resin, polyimide resin, polyolefin resin, acrylic resin, polyvinyl chloride resin, polystyrene resin, polyvinyl Examples thereof include alcohol-based resins, polyarylate-based resins, polyphenylene sulfide-based resins, polyvinylidene chloride-based resins, and (meth) acrylic-based resins. Among these, particularly preferable ones are polyester-based resins, polycarbonate-based resins, polyolefin-based resins and the like.

The thickness of the transparent substrate film 11 is preferably about 2 to 300 μm, more preferably 6 to 200 μm. If the thickness of the film is excessively small, the mechanical strength may be insufficient, and it may be difficult to form the undercoat layer 16 or the transparent conductive layer (ITO film) 3 on the film. On the other hand, if the thickness of the film is excessively large, it may not be possible to improve the scratch resistance of the transparent conductive layer and the spotting characteristics for a touch panel.

(Undercoat layer) An undercoat layer 16 is provided on the surface of the transparent substrate film 11 on the side where the ITO film 3 is formed for the purpose of improving the adhesion between the flexible transparent substrate 1 and the ITO film 3 and controlling the reflection characteristics. It may be provided. The undercoat layer may be one layer, two layers or more. The undercoat layer is formed of an inorganic substance, an organic substance, or a mixture of an inorganic substance and an organic substance. As a material for forming the undercoat layer, for example, as an inorganic substance, SiO₂, MgF₂, A1₂O₃Etc. are preferably used. Examples of the organic substance include an organic substance such as an acrylic resin, a urethane resin, a melamine resin, an alkyd resin, and a siloxane-based polymer. In particular, as the organic substance, it is preferable to use a thermosetting resin composed of a mixture of a melamine resin, an alkyd resin and an organic silane condensate. The undercoat layer can be formed by a vacuum deposition method, a sputtering method, an ion plating method, a coating method, or the like using the above materials.

Before forming the ITO film, the surface of the flexible transparent base material 1 is subjected to appropriate adhesive treatment such as corona discharge treatment, ultraviolet irradiation treatment, plasma treatment, and sputter etching treatment to adhere to the ITO film. Can also be increased.

(Back coat layer) On the surface of the transparent substrate film 11 opposite to the ITO film 3 formed, as the back coat layer 17, for example, an antiglare treatment layer or an antireflection treatment layer for the purpose of improving visibility is provided, or the outside is provided. A hard coat layer can be provided for the purpose of protecting the surface. For the hard coat layer, a cured film made of a curable resin such as a melamine-based resin, a urethane-based resin, an alkyd-based resin, an acrylic-based resin, or a silicone-based resin is preferably used. These back coat layers 17 may be provided on the transparent substrate film 11 before the transparent conductive layer 3 is formed, or may be provided after the transparent conductive layer 3 is formed.

The flexible transparent substrate before the ITO film is formed preferably has heat shrinkage in at least one direction. As will be described later, the crystalline ITO film can be formed by heat-treating the amorphous ITO film, but if the base material has heat shrinkage, the base material shrinks during the heat treatment to cause ITO. Since compressive stress is applied to the film, a crystalline ITO film having a desired compressive residual stress can be easily formed.

The dimensional change rate (heat shrinkage rate) of the flexible transparent substrate 1 during heating is preferably set so that a predetermined compressive stress is applied when the ITO film is crystallized. Therefore, the preferable range of the heat shrinkage rate differs depending on the heating conditions (temperature and time) at the time of crystallization of the ITO film, but the base material before forming the ITO film conforms to, for example, JIS K 7133 (1995). Therefore, the dimensional change rate when heated at 150 ° C. for 1 hour is preferably about -2% to + 1%, and more preferably about -1.5% to 0%. For example, by using a stretched film stretched in at least one direction as the transparent substrate film 11, the flexible transparent substrate 1 can be made to have the above-mentioned heat shrinkage property. The amount of heat shrinkage can be controlled within a predetermined range by the stretch ratio of the film or the like.

When the dimensional change rate (heat shrinkage rate) of the flexible transparent base material differs depending on the direction, it is preferable that the dimensional change rate in any one direction is in the above range. Even if the base material does not have heat shrinkage or the dimensional change rate of the base material is outside the above range, the shrinkage amount is adjusted by adjusting the conditions for thermal crystallization of the ITO film. Can be controlled. Further, at the time of heat crystallization of the ITO film, a shrinkage stress is applied from the outside by a method such as laminating a heat shrink film separately from the base material 1, or a tension is applied from the outside to control the amount of heat shrinkage. A crystalline ITO film having a desired compressive residual stress can also be formed by the above method.

&lt;Transparent conductive layer&gt; The transparent conductive layer 3 contains crystalline ITO as a main component. Hereinafter, the transparent conductive layer may be referred to as "crystalline ITO film" or simply "ITO film". In the present invention, the compressive residual stress of the crystalline ITO film 3 is preferably 0.4 to 2 GPa, more preferably 0.7 to 1.6 GPa, further preferably 0.9 to 1.55 GPa, and even more preferably 1.2 to 1.4 GPa. Is particularly preferable. The fact that the crystalline ITO film has compressive residual stress means that the lattice constant is smaller than that in the case where there is no strain. When the compressive residual stress is 0.4 GPa or more, the crystalline ITO film is excellent in spotting characteristics and bending resistance under heavy load. On the other hand, the compressive residual stress is preferably 2 GPa or less from the viewpoint of suppressing problems such as peeling of the ITO film and curling of the transparent conductive film.

Further, if the compressive residual stress of the ITO film is excessively large, the resistance change due to the heat of humidification becomes large, and the reliability of the heat of humidification of the transparent conductive film may not be sufficient. Therefore, from the viewpoint of obtaining a more reliable transparent conductive film, the compressive residual stress of the crystalline ITO film is preferably 1.6 GPa or less, more preferably 1.55 GPa or less, and 1.4 GPa or less. Is even more preferable. When the compressive residual stress of the ITO film is large, the cause of the large resistance change due to the humidification heat is considered to be that the ITO film having a large compressive residual stress is likely to have strains and cracks at the grain boundaries. That is, when the transparent conductive film is exposed to a high temperature and high humidity environment, the transparent substrate film absorbs moisture and expands, so that tensile stress is applied to the ITO film formed on the transparent substrate film, which causes distortion of grain boundaries and distortion. It is presumed that the film breaks from the crack and the resistance increases.

As will be described in detail in a later example, the compressive residual stress σ of the crystalline ITO film is the lattice strain ε obtained from the diffraction peak of the (622) plane near 2θ = 60 ° in powder X-ray diffraction and the elastic modulus. It can be calculated based on the coefficient (Young's modulus) E and Poisson's ratio ν.

A crystalline ITO film can also be obtained by sputtering ITO on a base material at a high temperature of, for example, 200 ° C. or higher, but considering the heat resistance of the base material, it is once amorphous on the base material. After forming the ITO film, it is preferable to form the amorphous ITO film by heating and crystallizing it together with the base material.

(Formation of amorphous ITO film) Amorphous ITO films are formed by the vapor phase method. Examples of the vapor phase method include an electron beam vapor deposition method, a sputtering method, and an ion plating method. The sputtering method is preferable from the viewpoint of obtaining a uniform thin film, and the DC magnetron sputtering method can be preferably adopted. The "amorphous ITO" is not limited to a completely amorphous one, and may have a small amount of crystal components. To determine whether ITO is amorphous, the laminate with the ITO film formed on the substrate is immersed in hydrochloric acid with a concentration of 5 wt% for 15 minutes, washed with water and dried, and the resistance between terminals between terminals of 15 mm is tested. It is possible to measure with. Since the amorphous ITO film is etched by hydrochloric acid and disappears, the resistance increases when immersed in hydrochloric acid. In the present specification, it is assumed that the ITO film is amorphous when the resistance between terminals between 15 mm exceeds 10 kΩ after immersion in hydrochloric acid, washing with water, and drying.

The amorphous ITO film 3a formed on the substrate is preferably crystallized by heating for a short time. Specifically, it is preferable that crystallization can be completed within 60 minutes, more preferably within 30 minutes, and even more preferably within 20 minutes when heated at 150 ° C. If ITO can be crystallized on such a time scale, the crystallization of ITO proceeds in accordance with the heat shrinkage of the base material, so that compressive stress is applied during crystallization and has compressive residual stress. Crystallized ITO film is easily formed. Whether or not the crystallization of the ITO film is completed can be judged from the resistance between terminals between terminals of 15 mm by immersing in hydrochloric acid, washing with water, and drying in the same manner as in the above-mentioned determination of amorphous ITO. If the resistance between terminals is within 10 kΩ, it is judged that the product has been converted to crystalline ITO.

The amorphous ITO film adjusts the temperature and time required for perfect crystallization by adjusting, for example, the type of target used for sputtering, the ultimate vacuum during sputtering, the flow rate of introduced gas, and the film formation temperature (substrate temperature). be able to.

Sputter targets include metal targets (In-Sn targets) or metal oxide targets (In).₂O₃-SnO₂Target) is preferably used. In₂O₃-SnO₂If a metal oxide target is used, SnO in the metal oxide target₂The amount of In₂O₃And SnO₂It is preferably 0.5% by weight to 15% by weight, more preferably 1 to 10% by weight, still more preferably 2 to 6% by weight, based on the total weight of the above. In the case of reactive sputtering using an In-Sn metal target, the amount of Sn atoms in the metal target may be 0.5% by weight to 15% by weight based on the total weight of In atoms and Sn atoms. It is preferably 1 to 10% by weight, more preferably 2 to 6% by weight. Sn or SnO in the target₂If the amount of is too small, the durability of the ITO film may be inferior. Also, Sn or SnO₂If the amount of is too large, the time required for crystallization tends to be long. That is, during crystallization, Sn is In₂O₃Other than the amount incorporated into the crystal lattice, it acts as an impurity and tends to hinder the crystallization of ITO. Therefore, Sn or SnO in the target₂The amount of is preferably within the above range.

When forming a sputtering film using such a target, first, the degree of vacuum (reaching vacuum degree) in the sputtering apparatus is preferably 1 × 10.^-3Pa or less, more preferably 1 x 10^-4It is preferable to exhaust the air until it becomes Pa or less to create an atmosphere in which impurities such as water in the sputtering apparatus and organic gas generated from the substrate are removed. This is because the presence of water and organic gas terminates the dangling bonds generated during the sputtering film formation and hinders the crystal growth of ITO.

Next, an inert gas such as Ar is introduced into the sputtering apparatus exhausted in this way to perform sputtering film formation. When a metal target (In-Sn target) is used as the sputtering target, oxygen gas, which is a reactive gas, is introduced together with the inert gas to perform sputtering film formation. The amount of oxygen introduced into the inert gas is preferably 0.1% by volume to 15% by volume, more preferably 0.1% by volume to 10% by volume. The pressure during film formation is preferably 0.05 Pa to 1.0 Pa, more preferably 0.1 Pa to 0.7 Pa. If the film forming pressure is too high, the film forming speed tends to decrease, and conversely, if the pressure is too low, the discharge tends to become unstable.

The substrate temperature during sputter film formation is preferably 40 ° C to 190 ° C, more preferably 80 ° C to 180 ° C. If the film forming temperature is too high, the appearance may be poor due to heat wrinkles and the base material may be thermally deteriorated. On the contrary, if the film forming temperature is too low, the film quality such as the transparency of the ITO film may deteriorate.

The film thickness of the ITO film can be appropriately adjusted so that the crystallized ITO film has a desired resistance, but is preferably, for example, 10 to 300 nm, and more preferably 15 to 100 nm. If the film thickness of the ITO film is small, the time required for crystallization tends to be long, and if the film thickness of the ITO film is large, the specific resistance after crystallization becomes too low or the transparency decreases. May be inferior in quality as a transparent conductive film.

(Heat crystallization of ITO film) The laminate of the flexible transparent base material 1 and the amorphous ITO film 3a thus obtained is subjected to heat treatment, and the amorphous ITO film is heated to be converted into a crystalline ITO film. From the viewpoint of obtaining a crystalline ITO film having compressive residual stress, it is preferable that compressive stress is applied to the ITO film in this heat treatment step. Specifically, the dimensional change of the ITO film in one direction is preferably -0.3% to -1.5%, more preferably -0.55% to -1.2%, and -0.7% to-. It is more preferably 1.05%, and particularly preferably -0.7% to -0.9%. The dimensional change (%) is the distance L between two points in one direction of the ITO film before it is subjected to the heat treatment step.₀However, when it changes to L after heat treatment heat, 100 × (L)₁-L₀) / L₀Defined in. By setting the dimensional change within the above range, the crystalline ITO film after the heat treatment can have the predetermined compressive residual stress as described above, so that a transparent conductive film having excellent spotting characteristics and flexibility can be obtained.

The heating temperature and heating time in the heat treatment can be appropriately set so that the ITO film is completely crystallized. For example, the heating temperature is preferably 150 ° C to 210 ° C, more preferably 160 ° C to 200 ° C, and even more preferably 170 ° C to 190 ° C. If the heating temperature is too low, crystallization does not proceed, or crystallization takes a long time and tends to be inferior in productivity. Further, if the heating temperature is low, the amount of heat shrinkage of the base material is small, so that an appropriate compressive stress may not be applied when the ITO film is crystallized. On the other hand, if the heating temperature is too high, the base material may deteriorate or the residual compressive stress of the ITO film may become excessive due to the rapid heat shrinkage of the base material, and the humidification heat reliability of the transparent conductive film may not be ensured.

The heating time is preferably 150 minutes or less. If the heating time is too long, the base material tends to deteriorate or the productivity tends to be poor. On the other hand, if the heating time is too short, crystallization of ITO may not proceed or the heat shrinkage of the base material may be insufficient, so that an appropriate compressive stress may not be applied to the ITO film. From this point of view, the heating time is preferably 5 to 60 minutes, more preferably 5 to 30 minutes. When the ITO film is heated and crystallized on such a time scale, the stress caused by the shrinkage of the base material is transmitted to the ITO, and a crystalline ITO film having compressive residual stress is easily formed. The above heating temperature and heating time are examples, and an appropriate heating temperature and heating time can be selected depending on the characteristics of the amorphous ITO film.

For applying the compressive stress to the ITO film, a method utilizing heat shrinkage of the flexible transparent substrate is preferably adopted. From the viewpoint that the dimensional change rate during heat crystallization of the ITO film is within the preferable range as described above, the laminate in which the amorphous ITO film 3a before crystallization is formed on the flexible transparent substrate 1 is 150. The dimensional change rate when heated at ° C for 1 hour is preferably about -2% to + 1%, more preferably about -1.5% to 0%, and about -1.2% to -0.3%. Is more preferable. In general, the thickness of the amorphous ITO film is much smaller than the thickness of the flexible transparent base material, so that the dimensional change rate of the laminate of the amorphous ITO film and the flexible transparent base material is flexible. It is almost the same as the dimensional change rate of the transparent base material.

In addition to the heat shrinkage force of the substrate as described above, the compressive stress is applied to the ITO film, for example, when the ITO film is thermally crystallized, heat is applied to the surface of the ITO film and the substrate separately from the substrate 1. It can also be realized by applying shrinkage stress from the outside by a method such as laminating shrinkage films. Further, it is also possible to control the shrinkage amount by applying tension from the outside by using a base material having a large shrinkage amount (the dimensional change rate is negative and the absolute value is large).

When the dimensional change rate (heat shrinkage rate) of the flexible transparent base material differs depending on the direction, it is preferable that the dimensional change rate in any one direction is in the above range. Even when the base material does not have heat shrinkage or the dimensional change rate is out of the above range, the shrinkage amount is controlled by adjusting the conditions for heat crystallization of the ITO film. be able to.

The heating conditions during the heat treatment are preferably selected so that the substrate is thermally shrunk according to the crystallization timescale of ITO, in addition to the viewpoint of crystallization of ITO. That is, if the substrate is thermally shrunk as the crystallization of ITO progresses or after the crystallization of ITO, compressive stress is applied to the crystalline ITO film, so that the crystalline ITO film having compressive residual stress becomes can get.

Such heating conditions differ depending on the thermal deformation profile of the base material, but for example, by confirming the thermal deformation profile of the base material or the base material after forming the amorphous ITO film by thermal analysis such as TMA in advance, the ITO can be used. It is possible to select heating conditions such that the substrate is thermally shrunk according to the time scale of the crystal. Figures 7 and 8 show examples of a schematic analysis of the relationship between ITO crystallization and thermal deformation of the substrate using TMA.

In FIGS. 7 and 8, an amorphous ITO film having a thickness of 20 nm is formed on one surface of a PET film having a thickness of 25 μm, and a PET film having a total thickness of 130 μm (hard coat layer) is formed on the other surface via an adhesive layer having a thickness of 25 μm. This is an analysis of the dimensional change behavior of a transparent conductive film laminated with a thickness of 5 μm) during heating by TMA. The horizontal axis represents time, and the vertical axis represents temperature and dimensional change rate. The measurement conditions are sample width: 4 mm, load: 20 mN / 4 mm, initial length: 10 mm, heating rate and temperature decreasing rate: 5 ° C / min, holding time: 60 minutes, and Fig. 7 and Fig. 8 show, respectively. It shows the measurement results of holding temperatures of 190 ° C and 150 ° C.

The progress of crystallization over time when heated with the same temperature profile as in FIGS. 7 and 8 was analyzed by the diffraction peak intensity of the (222) plane in the X-ray diffraction method, and the holding temperature was 190. At ° C (corresponding to Fig. 7), crystallization proceeded from a temperature of about 120 ° C, and crystallization was almost completed when the temperature reached 180 ° C. On the other hand, at a holding temperature of 150 ° C (corresponding to FIG. 8), crystallization was almost completed about 30 minutes after the temperature reached 150 ° C.

In Fig. 7, from the progress of crystallization to the time when crystallization is completed (30 to 40 minutes from the start of temperature rise), a large shrinkage (dimensional change in the negative direction) occurs in the first stage, and when the temperature drops (= crystallization). After the completion of crystallization), the second stage of shrinkage occurs, and it is presumed that compressive stress is applied to the ITO film during these shrinkages. On the other hand, in FIG. 8, shrinkage occurs during the progress of crystallization and when the temperature drops, but it can be seen that the amount of shrinkage in the first stage is smaller than that in FIG. On the other hand, comparing Example 2 and Example 6 described later, in Example 2 in which crystallization was performed at 190 ° C, the residual compressive stress of the ITO film was 1.50 GPa, whereas it was 150 ° C. In Example 6 crystallized in, the residual compressive stress of the ITO film is 0.57 GPa. From this, it is considered that the schematic analysis using TMA reproduces the tendency of the dimensional change behavior when the ITO film is actually crystallized, and the ITO crystal is based on the TMA analysis result. It can be said that the heating conditions that cause the base material to shrink can be selected according to the time scale of.

In the present invention, as described above, a transparent conductive film having excellent durability can be obtained by applying compressive stress to the ITO film during film formation and crystallization. Further, the crystals of the ITO film may have a predetermined particle size distribution from the viewpoint of suppressing crack generation during bending, obtaining a transparent conductive film having better hitting characteristics under heavy load, and pen sliding durability. preferable. That is, on the ITO film surface, the crystal content having a maximum particle size of 300 nm or less is preferably 95 area% or more, and it is more preferable that no crystal having a maximum particle size exceeding 300 nm exists. Further, it is preferable that the crystal content having a maximum particle size of 200 nm or less exceeds 50 area%. Among them, it is preferable that the crystal content having a maximum particle size of 100 nm or less exceeds 5 area%, the maximum particle size of the remaining crystals exceeds 100 nm and exists in a distribution width of 200 nm, and the crystal content of 100 nm or less is 10 areas. It is particularly preferable that it is% or more.

If the crystal grain size of the ITO film becomes too small, there may be a portion similar to the amorphous state in the film, which may reduce reliability and pen durability, so that the crystal grain size becomes extremely small. It is desirable not to overdo it. From this point of view, the maximum particle size of the crystal is preferably 10 nm or more, and more preferably 30 nm or more.

The maximum particle size and distribution of crystals are determined by surface observation of the conductive thin film with a field emission transmission electron microscope (FE-TEM). The maximum grain size of a crystal is the largest diagonal or diameter in each of the observed polygonal or oval regions. Further, the content of the crystal having the maximum particle size is specifically the area ratio occupied by the crystal having each particle size per unit area (1.5 μm × 1.5 μm) in the electron microscope image.

In order to control the crystal grain size and the grain size distribution of the ITO film as described above, the material composition of the conductive thin film and the thin film forming method thereof may be appropriately selected. For example, SnO in ITO₂By increasing the content, the content ratio of crystals having a small particle size can be increased. SnO in ITO₂Content (In₂O₃And SnO₂SnO for weight plus₂Content) is preferably 2% by weight or more, more preferably 3% by weight or more. Further, an inorganic film formed by the vacuum vapor deposition method, particularly preferably SiO formed by the vacuum vapor deposition method.₂By having the thin film as an anchor layer serving as an underlayer for forming the ITO film, that is, as an anchor layer closest to the ITO film, the crystal grain size of the ITO film after crystallization can be reduced. In addition, the crystal grain size tends to be reduced by reducing the ultimate vacuum during ITO film formation (making it closer to vacuum) or by raising the substrate temperature during film formation.

[Second Embodiment] Next, the transparent conductive film 102 according to the second embodiment of the present invention including two or more flexible transparent substrates will be described focusing on the points different from those of the first embodiment.

The transparent conductive film 102 according to the second embodiment includes two or more flexible transparent substrates. The first flexible transparent base material 1 is a base material for forming an ITO film, and an undercoat layer 16 or the like is formed on the first transparent base film 11 as needed. The second flexible transparent base material is attached to the first flexible transparent base material via an appropriate adhesive means such as the pressure-sensitive adhesive layer 5. The second flexible transparent substrate is obtained by forming a back coat layer 17 or the like on the second transparent substrate film 12, if necessary. As the transparent substrate films 11 and 12, the same ones as described above with respect to the first embodiment are preferably used. Although the form having two flexible transparent substrates is shown in FIG. 2, a form having three or more flexible transparent substrates can also be adopted.

Also in the second embodiment, the crystalline ITO film preferably has the same compressive residual stress as described above with respect to the first embodiment. As described above for the first embodiment, such a crystalline ITO film is preferably formed by once forming an amorphous ITO film and then heating and crystallizing the amorphous ITO film together with a substrate.

&lt;Adhesive layer&gt; The plurality of transparent substrate films 11 and 12 are preferably bonded via the pressure-sensitive adhesive layer 5. As the constituent material of the pressure-sensitive adhesive layer 5, any material having transparency can be used without particular limitation. For example, based polymers such as acrylic polymers, silicone polymers, polyesters, polyurethanes, polyamides, polyvinyl ethers, vinyl acetate / vinyl chloride copolymers, modified polyolefins, epoxy-based, fluorine-based, natural rubbers, synthetic rubbers and other rubber-based polymers. Can be appropriately selected and used. In particular, an acrylic pressure-sensitive adhesive is preferably used because it has excellent optical transparency, exhibits appropriate wettability, cohesiveness, adhesiveness, and other adhesive properties, and is also excellent in weather resistance, heat resistance, and the like.

The pressure-sensitive adhesive layer 5 may have, for example, a function of improving the scratch resistance of the transparent conductive layer 3 provided on the transparent substrate film 11 and the spotting characteristics for a touch panel due to its cushioning effect. From the viewpoint of exerting this function more effectively, the elastic modulus of the adhesive layer 5 is set to 1 to 100 N / cm.²It is preferable to set the range and the thickness in the range of 1 μm or more (more preferably 5 to 100 μm). Within this range, the above effects are sufficiently exhibited, and the adhesion between the transparent substrates is also sufficient.

&lt;Manufacturing process of transparent conductive film&gt; 3A to 3C are schematic cross-sectional views conceptually showing the manufacturing process of the transparent conductive film 102. In FIGS. 3A to 3C, the undercoat layer and the back coat layer are not shown. The transparent substrate films 11 and 12 are bonded via the pressure-sensitive adhesive layer 5 before forming the ITO film (Fig. 3A), after forming the amorphous ITO film, before heat crystallization (Fig. 3B), and heating the amorphous ITO film. It can be done either after crystallization (Fig. 3C).

In general, the formation of an amorphous ITO film by a sputtering method or the like is continuously performed by a roll-to-roll method, whereas in the heating crystallization of an ITO film, a film cut into a single leaf is heated in a batch method. Often processed. Therefore, as shown in FIGS. 3A and 3B, in the form in which the base materials are bonded before the crystallization of the ITO film, the bonding can be continuously performed by the roll-to-roll method.

In particular, as shown in FIG. 3B, if the amorphous ITO film 3a is formed on the first flexible transparent base material 1 before the base materials are bonded, a plurality of transparent base films are bonded in advance. Compared to the case (Fig. 3A), the thickness of the base material during sputter film formation is smaller. Therefore, the winding diameter of the roll winding body becomes small, and the film forming length that can be continuously formed by the winding sputtering apparatus becomes long, which is preferable from the viewpoint of productivity.

As shown in FIG. 3A, when the flexible transparent substrates 1 and 2 are bonded before the ITO film formation, the amorphous ITO film 3a is formed on the flexible transparent substrate to which a plurality of substrates are bonded. It is formed (Fig. 3A (c)) and crystallized. Therefore, the thickness, dimensional change rate, etc. of the two (or two or more) flexible transparent base materials after the bonding are regarded as one, within the above-mentioned range with respect to the first embodiment. It is preferable to do so.

As shown in FIG. 3B, when the transparent substrate films 11 and 12 are bonded after the amorphous ITO film is formed and before the heat crystallization, the amorphous ITO film is heated at the time of film formation (FIG. 3B (b)). The first flexible transparent base material and the second flexible transparent base material which is not used for forming an ITO film are bonded together (Fig. 3B (c)) and crystallized). 3B (d)). Also in this case, it is preferable that the thickness, the dimensional change rate, and the like when the flexible transparent base material after bonding is regarded as one body are within the above-mentioned ranges with respect to the first embodiment.

In the manufacturing method as shown in FIGS. 3A and 3B, the ITO film is crystallized in the heat treatment step after two or more flexible transparent substrates are bonded together. At that time, as described above with respect to the first embodiment, it is preferable that compressive stress is applied to the ITO film with the heat shrinkage of the base material, but at the same time, the dimensional change of each flexible transparent base material is changed. Is substantially equivalent. If the dimensional changes of each flexible transparent base material are different, problems such as peeling between the base materials and curling of the transparent conductive film may occur in the heat treatment step. From this point of view, the absolute value of the difference in dimensional change rate when each flexible transparent substrate before being subjected to the heat treatment step is heated at 150 ° C. for 1 hour is preferably 0.5% or less, preferably 0.3. More preferably, it is less than or equal to%.

In particular, in the form shown in FIG. 3B, the first flexible transparent base material 1 is heated when it is subjected to the formation of the ITO film, whereas the second flexible transparent base material 2 is heated. However, if the heat treatment step is performed without undergoing such heating, the difference in dimensional change in the heat treatment step may be large because the heat histories of the two are significantly different. From the viewpoint of reducing the difference in the dimensional change rate between the flexible transparent base materials 1 and 2, for example, the second flexible transparent base material 2 before being bonded to the first flexible transparent base material 1 is used. It is preferable to heat-treat in advance to stabilize the dimensions. The heating conditions for dimensional stabilization are appropriately set so that the difference in the dimensional change rate becomes small, but it is preferable to heat at 130 ° C to 160 ° C for about 0.5 to 3 minutes, for example.

As shown in FIG. 3C, when the transparent substrate films 11 and 12 are bonded after heat crystallization of the ITO film, a flexible transparent substrate containing one transparent substrate film is used as in the first embodiment. A crystalline ITO film 3 is formed on 1 (Fig. 3C (c)). After that, the second transparent substrate film 12 is bonded via the pressure-sensitive adhesive layer 5 (FIG. 3C (d)).

The transparent conductive film of the present invention as described above is suitably used for forming transparent electrodes and touch panels of various devices. In particular, the transparent conductive film of the present invention is suitable for a resistance film type touch panel because the transparent conductive layer is excellent in spotting characteristics under heavy load and bending resistance, and is particularly suitable for a touch panel of a game machine or a flexible display. Suitable for use.

<p num="0069"> Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the following examples.</p><p num="0070">[Evaluation method] The evaluation in the examples was carried out by the following method.</p><p num="0071">&lt;Resistance and surface resistance&gt; The resistance value was measured by the two-terminal method. The surface resistance was measured by the four-probe method according to JIS K 7194 (1994).</p><p num="0072">&lt;Dimensional change rate&gt; Two reference points (scratches) are formed on the ITO film surface of the laminate in which the amorphous ITO film is formed on the base material at intervals of about 80 mm in the transport direction during sputtering film formation (hereinafter, "MD direction"). And the distance between the gauge points before heat crystallization L₀Then, the distance L between the gauge points after heating was measured by a two-dimensional length measuring machine to determine the dimensional change rate (%).</p><p num="0073">&lt;Compressive residual stress of ITO film&gt; The residual stress was indirectly obtained from the crystal lattice strain of the ITO film by the X-ray scattering method. The diffraction intensity was measured every 0.04 ° in the measurement scattering angle of 2θ = 59 to 62 ° with a powder X-ray diffractometer manufactured by Rigaku Co., Ltd. The integrated time (exposure time) at each measurement angle was 100 seconds.</p><p num="0074"> The crystal lattice spacing d of the ITO film was calculated from the peak (peak of the (622) plane of ITO) angle 2θ of the obtained diffraction image and the wavelength λ of the X-ray source, and the lattice strain ε was calculated based on d. .. The following equations (1) and (2) were used in the calculation.</p><p num="0075"><maths num="1"><img id="000002" he="12" wi="47" file="JP6023402B2_D0001.tif" img-format="tif" img-content="drawing" /></maths> Here, λ is the wavelength (= 0.15418 nm) of the X-ray source (Cu Kα ray), and d₀Is the lattice spacing (= 0.15241 nm) of the ITO in the stress-free state. In addition, d₀Is the value obtained from the ICDD (The International Center for Diffraction Data) database.</p><p num="0076"> In the above X-ray diffraction measurement, the angles Ψ between the film surface normal and the ITO crystal plane normal shown in Fig. 4 are 45 °, 50 °, 55 °, 60 °, 65 °, 70 °, 77 °, 90. The lattice strain ε at each Ψ was calculated for each °. The angle Ψ formed by the film normal and the ITO crystal normal was adjusted by rotating the sample around the TD direction (the direction orthogonal to the MD direction). The residual stress σ in the in-plane direction of the ITO film is sin²The relationship between Ψ and lattice strain ε was calculated from the slope of a straight line plotted by Eq. (3) below.</p><p num="0077"><maths num="2"><img id="000003" he="8" wi="54" file="JP6023402B2_D0001.tif" img-format="tif" img-content="drawing" /></maths> In the above equation, E is the Young's modulus of ITO (116 GPa) and ν is the Poisson's ratio (0.35). These values are known measured values described in DG Neerinck and TJ Vink, Depth profiling of thin ITO films by grazing incidence X-ray diffraction, Thin Solid Films, 278 (1996), PP 12-17. Is.</p><p num="0078">&lt;Durability of heavy load pen hitting point&gt; (Making a touch panel) The transparent conductive film was cut into a rectangle of 60 mm × 140 mm having a long side in the MD direction. A silver paste was screen-printed on both short sides with a width of 5 mm and dried at room temperature for 24 hours to form a silver electrode. A transparent conductive film on which a silver electrode is formed and an ITO conductive glass (manufactured by Nippon Soda) on which an ITO film 22 having a surface roughness Ra = 0.9 nm is formed on the glass 21 are placed through an ITO spacer 8 having a thickness of 180 μm. A touch panel as schematically shown in FIG. 5 was produced by arranging the formed surfaces so as to face each other.</p><p num="0079">(Heavy load pen dot test) A polyacetal pen with a pen tip R = 0.8 mm with a load of 1.5 kg was freely dropped from a height of 2 cm above the upper electrode (transparent conductive film) side of the manufactured touch panel. This operation was performed linearly at 1 mm intervals for a total of 10 points. This 10-point drop test was taken as one set, and the linearity after one set of tests and after five sets of tests was measured.</p><p num="0080">(Measurement of linearity) A voltage of 5 V was applied between the silver electrodes formed on the short side of the transparent conductive film, and the output voltage between one electrode (terminal A) and the other electrode (terminal B) was measured. Linearity sets the output voltage at the measurement start position A to E_A, E the output voltage at the measurement end position B_B, L distance between AB_AB, E the output voltage at the measurement point at the distance X from the start position A_X, Theoretical value E_XXThen, it can be obtained from the following calculation. E_XX= {X (E_B-E_A) / L_AB} + E_A Linearity (%) = [(E_XX-E_X) / (E_B-E_A)〕×100 </p><p num="0081"> The outline of the linearity measurement is as shown in FIG. In an image display device using a touch panel, the position of the pen displayed on the screen is determined from the resistance value of the contact portion between the upper panel and the lower panel by being pressed by the pen. The resistance value is determined assuming that the output voltage distribution on the surface of the upper and lower panels is like the theoretical line (ideal line), but if the voltage value deviates from the theoretical line as shown in the measured value in the figure, the actual resistance value is determined. The pen position on the screen, which is determined by the pen position and the resistance value, does not synchronize well. The deviation from the theoretical line is linearity, and the larger the value, the larger the deviation between the actual pen position and the position of the pen on the screen. That is, the smaller the linearity after the durability test, the better the durability.</p><p num="0082">&lt;Pen sliding durability test&gt; (Making a touch panel) A touch panel as schematically shown in FIG. 5 was formed in the same manner as in the case of the heavy load pen striking point durability described above, except that the thickness of the spacer was changed from 180 μm to 100 μm.</p><p num="0083">(Pen sliding test) From the upper electrode (transparent conductive film) side of the manufactured touch panel, a polyacetal pen with a pen tip R = 0.8 mm was slid 50,000 times (25,000 reciprocations) with a load of 250 g. For each sample when sliding at a distance of 1.66 mm from the touch panel end (silver electrode) and when sliding at a distance of 1.39 mm, the above-mentioned heavy load pen dot durability Linearity was measured in the same manner.</p><p num="0084">&lt;Bending resistance&gt; (Preparation of test piece) The transparent conductive film was cut into a rectangle having a long side in the MD direction of 10 mm × 150 mm, a silver paste was screen-printed on both short sides with a width of 5 mm, and dried at room temperature for 24 hours to form a silver electrode. Resistance of this test piece (initial resistance R₀) Was obtained by the two-terminal method.</p><p num="0085">(Tensile flexibility) The test piece was curved along a cork polar with a drilling diameter of 17 mmφ with the ITO forming surface on the outside, and held for 10 seconds under a load of 1.0 kg. After that, sequentially, using a cork polar with a drilling diameter of 15.5 mmφ, 14 mmφ, 12.5 mmφ, 11 mmφ, bend it in the same way and hold it with a load of 1.0 kg for 10 seconds, and then repeat the resistance R._11TR_11T/ R_{o o}Asked. After that, the test piece is further curved along a cork polar with a drilling diameter of 9.5 mmφ, held for 10 seconds with a load of 1.0 kg, and then the resistor R._9.5TR_9.5T/ R_{o o}Asked.</p><p num="0086">(Compressive flexibility) Cork polarers with drilling diameters of 17 mmφ, 15.5 mmφ, 14 mmφ, 12.5 mmφ, 11 mmφ in the same manner as the above tensile flexibility test, except that the test piece was curved along the cork polar with the ITO forming surface inside. Resistance R after bending along_11C, And a resistor R after further drilling and bending along a 9.5 mmφ cork polar_9.5CR_11C/ R_{o o}And R_9.5C/ R_{o o}Asked.</p><p num="0087">&lt;Humidification heat reliability&gt; The transparent conductive film was placed in a constant temperature and humidity chamber at 60 ° C. and 95% humidity for 500 hours, and the surface resistance was measured by the four-probe method to evaluate the resistance fluctuation under humidification heat. The resistance fluctuation under humidification heat is the initial surface resistance R₁Ratio of surface resistance R after humidification heat to R / R₁).</p><p num="0088">[Example 1] In Example 1, after forming an amorphous ITO film on a PET film (first flexible transparent substrate) having a thickness of 25 μm on which two undercoat layers were formed, a hard having a thickness of 5 μm was used as the back coat layer. A 125 μm-thick PET film (second flexible transparent substrate) on which a coat layer was formed was bonded via an adhesive layer having a thickness of 25 μm. Then, the ITO film was heat-crystallized to prepare a transparent conductive film in which a crystalline transparent conductive layer having a thickness of 20 nm was formed on a substrate having a total thickness of 180 μm. This is due to the same process as shown in FIG. 3B, and the details of each process are as follows.</p><p num="0089">(Formation of undercoat layer) As the first transparent substrate, a biaxially stretched polyethylene terephthalate film with a thickness of 25 μm (trade name Diafoil made by Mitsubishi Chemical Polyester, glass transition temperature 80 ° C, refractive index 1.66, 150 ° C dimensions in the MD direction when heated for 1 hour Using a rate of change of -0.80%), two undercoat layers were formed on this PET film.</p><p num="0090"> First, a thermosetting resin composition containing a melamine resin: alkyd resin: organic silane condensate in a solid content ratio of 2: 2: 1 was diluted with methyl ethyl ketone so that the solid content concentration was 8% by weight. .. This solution was applied to one main surface of a PET film and heat-cured at 150 ° C. for 2 minutes to form a first undercoat layer having a film thickness of 150 nm and a refractive index of 1.54. Next, a siloxane-based thermosetting resin (trade name "Colcoat P" manufactured by Corcoat) was diluted with methyl ethyl ketone so that the solid content concentration was 1% by weight, and this solution was applied onto the first undercoat layer. Then, heat-cure at 150 ° C for 1 minute to make a SiO with a thickness of 30 nm and a refractive index of 1.45.₂A thin film (second undercoat layer) was formed. Even after the undercoat layer was formed, the dimensional change rate in the MD direction when the substrate was heated at 150 ° C. for 1 hour was -0.80%, which was unchanged from before the undercoat layer was formed.</p><p num="0091">(Amorphous ITO film formation) A sintered body containing indium oxide and tin oxide in a weight ratio of 97: 3 was mounted as a target material on a parallel plate type retractable magnetron sputtering apparatus. While transporting the PET film base material on which the two undercoat layers are formed, dehydration and degassing are performed, and 5 × 10^-3Exhausted until Pa. In this state, the heating temperature of the base material is set to 120 ° C, and the pressure is 4 × 10.^-1Argon gas and oxygen gas were introduced at a flow rate ratio of 98%: 2% so as to be Pa, and a film was formed by the DC sputtering method to form an amorphous ITO film having a thickness of 20 nm on the substrate. After the laminate after forming the amorphous ITO film was cooled at room temperature to release the residual stress, the dimensional change rate in the MD direction when heated at 150 ° C. for 1 hour was measured and found to be -0.45%.</p><p num="0092">(Making PET film with hard coat layer) As the second transparent substrate film, a biaxially stretched polyethylene terephthalate film (manufactured by Toray Industries, Inc., trade name "Lumirror U43 125 μm") having a thickness of 125 μm is used, and a hard coat layer is formed as follows by a roll-to-roll method. did.</p><p num="0093"> To 100 parts by weight of acrylic / urethane resin (DIC product name "Unidic 17-806"), add 5 parts by weight of hydroxycyclohexylphenyl ketone (Ciba Geigy product name "Irgacure 184") as a photopolymerization initiator. , Diluted with toluene to prepare a hard coat coating solution so that the solid content was 50% by weight. This solution is applied on a second transparent substrate film, heated at 100 ° C for 3 minutes to dry, and then the integrated light intensity is 300 mJ / cm with a high-pressure mercury lamp.²A hard coat layer having a thickness of 5 μm was formed by irradiating with the ultraviolet rays of.</p><p num="0094"> While transporting the PET film on which the hard coat layer was formed by a roll transporter, the PET film was heated at 150 ° C. for 1 minute in a heating furnace to stabilize the dimensions. Then, after cooling at room temperature to release the residual stress, the dimensional change rate in the MD direction when heated at 150 ° C for 1 hour was measured. The dimensional change rate of the PET film with a hard coat layer after dimensional stabilization was-. It was 0.45%.</p><p num="0095">(Formation of adhesive layer) In a polymerization tank equipped with a stirring mixer, thermometer, nitrogen gas introduction pipe, and cooler, 100 parts by weight of butyl acrylate, 5 parts by weight of acrylic acid and 0.075 parts by weight of 2-hydroxyethyl acrylate, 2,2'-as a polymerization initiator. 0.2 parts by weight of azobisisobutyronitrile and 200 parts by weight of ethyl acetate as a polymerization solvent were charged, and after sufficient nitrogen substitution, the temperature in the polymerization tank was maintained at around 55 ° C for 10 hours while stirring under a nitrogen stream. A polymerization reaction was carried out to prepare an acrylic polymer solution. In addition to 100 parts by weight of the solid content of this acrylic polymer solution, 0.2 parts by weight of dibenzoyl peroxide (trade name "Niper BMT" manufactured by Nippon Polyurethane Industry Co., Ltd.) as a peroxide, and trimethylolpropane / tolylene diisocyanate adduct as an isocyanate-based cross-linking agent. 0.5 parts by weight of body (manufactured by Nippon Polyurethane Industry Co., Ltd., trade name "Coronate L") and 0.075 parts by weight of silane coupling agent (manufactured by Shinetsu Chemical Industry Co., Ltd., trade name "KBM403") are uniformly mixed and stirred to form an adhesive solution (adhesive solution). Solid content 10.9% by weight) was prepared.</p><p num="0096"> The acrylic pressure-sensitive adhesive solution was applied to the surface of the PET film with a hard coat layer after dimensional stabilization on the side where the hard coat layer was not formed, and heat-cured at 155 ° C for 1 minute to a thickness of 25 μm. A pressure-sensitive adhesive layer was formed. Next, a separator having a silicone layer attached was bonded to the pressure-sensitive adhesive layer surface by roll bonding. The dimensional change rate in the MD direction of this hard-coated PET film with adhesive when heated at 150 ° C for 1 hour was -0.45%.</p><p num="0097">(Lasting of base materials) By roll bonding, the separator was peeled off from the hard-coated PET film with an adhesive layer, and the surface of the PET film on which the ITO film was formed on the exposed surface was continuously bonded on the side where the ITO film was not formed. The obtained laminate had an amorphous ITO film having a thickness of 20 nm formed on a flexible transparent substrate having a total thickness of 180 μm.</p><p num="0098">(Crystallization of ITO film) A 300 mm square single frond was cut out from the above laminate and heated in a heating tank at 200 ° C. for 1 hour to crystallize the ITO film, and a transparent conductive film having a crystalline ITO film was obtained.</p><p num="0099">[Examples 2 to 6, Comparative Examples 1 and 2] In Examples 2 to 6 and Comparative Examples 1 and 2, the transparent conductivity having a crystalline ITO film was obtained in the same manner as in Example 1 above, except that the heating conditions for crystallization of the ITO film were changed as shown in Table 1. A sex film was made.</p><p num="0100">[Example 7] In Example 7, a transparent conductive film was produced in the same manner as in Example 1, but the transport tension when sputter-forming an amorphous ITO film and when stabilizing the dimensions of a PET film with a hard coat layer. It was different from Example 1 in that the temperature was increased and the heating temperature in the heat treatment step was set to 150 ° C.</p><p num="0101"> Specifically, the transport tension during sputter film formation was set to twice that of Example 1, and an amorphous ITO film was formed in a situation where the PET film was stretched. After the laminate after forming the amorphous ITO film was cooled at room temperature to release the residual stress, the dimensional change rate in the MD direction when heated at 150 ° C. for 1 hour was measured and found to be -0.85%.</p><p num="0102"> In addition, the transport tension when heating the PET film with the hard coat layer in the heating furnace to stabilize the dimensions while transporting it by the roll transporter was set to 8 times that of Example 1. After dimensional stabilization, after cooling at room temperature to release residual stress, the dimensional change rate in the MD direction when heated at 150 ° C for 1 hour was measured. The dimensional change rate of the PET film with a hard coat layer after dimensional stabilization. Was -0.85%.</p><p num="0103">[Example 8] In Example 8, amorphous ITO is formed on the undercoat layer forming surface of the PET film having a total thickness of 180 μm in which two undercoat layers are formed on one surface and a hard coat layer having a thickness of 5 μm is formed on the other surface. After forming the film, it was subjected to heat crystallization to prepare a transparent conductive film in which a crystalline transparent conductive layer having a thickness of 20 nm was formed on a substrate having a total thickness of 180 μm.</p><p num="0104">(Formation of undercoat layer and hardcoat layer) Biaxially stretched polyethylene terephthalate film with a thickness of 175 μm (manufactured by Toray Industries, Inc., trade name Lumilar U43 175 μm, glass transition temperature 80 ° C, refractive index 1.66, 150 ° C dimensional change rate in MD direction when heated for 1 hour-0.9%) Two undercoat layers were formed on one surface in the same manner as in Example 1. Then, a hard coat layer having a thickness of 5 μm was formed on the other surface of the PET film in the same manner as in Example 1. The dimensional change rate in the MD direction when the base material was heated at 150 ° C. for 1 hour after the undercoat layer and the hardcoat layer were formed was -0.65%.</p><p num="0105"> An amorphous ITO film having a thickness of 20 nm was formed on the undercoat layer forming surface of this base material by a sputtering method in the same manner as in Example 1. After the laminate after forming the amorphous ITO film is cooled at room temperature to release the residual stress, a 300 mm square single-wafer is cut out from this laminate and heated in a heating tank at 150 ° C. for 1 hour to release the ITO film. Was crystallized to obtain a transparent conductive film having a crystalline ITO film. The dimensional change rate in the MD direction of the laminate after the formation of the ITO film and before crystallization was -0.59% when heated at 150 ° C for 1 hour.</p><p num="0106">[Example 9] In Example 9, an amorphous ITO film was formed on a 25 μm-thick PET film (first flexible transparent substrate) on which two undercoat layers were formed, and the ITO film was heat-crystallized. After that, a 125 μm-thick PET film (second flexible transparent base material) on which a hard coat layer having a thickness of 5 μm was formed was bonded via an adhesive layer having a thickness of 25 μm. This is due to the same process as shown in Fig. 3C.</p><p num="0107"> Specifically, in the same manner as in Example 1, the amorphous ITO film was formed on the first flexible transparent substrate and the second flexible transparent substrate on which the hard coat layer was formed was formed. The pressure-sensitive adhesive layer was formed. A laminate in which an amorphous ITO film is formed on the first flexible transparent base material without bonding the first flexible transparent base material and the second flexible transparent base material is 300 mm. The four-sided fronds were cut out and heated in a heating tank at 180 ° C. for 1 hour to crystallize the ITO film. Then, the first flexible transparent base material on which the crystalline ITO film was formed was bonded to the second flexible transparent base material having an adhesive layer cut into a 300 mm square frond. A transparent conductive film having a total thickness of 180 μm was obtained.</p><p num="0108">[Example 10] In Example 10, a transparent conductive film having a crystalline ITO film and having a total thickness of 180 μm was produced in the same manner as in Example 9 above, except that the heating temperature for crystallization of the ITO film was changed to 150 ° C. It was.</p><p num="0109"> Table 1 shows the conditions of each example and comparative example, and the evaluation results of the transparent conductive film. The thickness of the base material in Table 1 represents the thickness in the crystallization step. The total thickness of the transparent conductive films of each of the Examples and Comparative Examples used for the evaluation was 180 μm.</p><p num="0110"><tables num="1"><img id="000004" he="224" wi="159" file="JP6023402B2_D0001.tif" img-format="tif" img-content="drawing" /></tables></p><p num="0111"> As is clear from Table 1, the transparent conductive film of each example in which the ITO film has a predetermined residual compressive stress is superior in bending resistance and heavy load spotting characteristics as compared with the transparent conductive film of the comparative example. I understand. On the other hand, as the residual compressive stress of the ITO film increases, the resistance change due to humidification heat tends to increase. Therefore, it can be said that it is more preferable that the residual compressive stress of the ITO film is set in an appropriate range in consideration of the balance between bending resistance, heavy load impact characteristics and humidification heat reliability.</p><p num="0112"> Comparing Examples 3 and 4 and Examples 8 and 9 in which the thickness of the base material at the time of crystallization is different, crystallization shrinkage is caused by increasing the temperature of the heat treatment step regardless of the thickness of the base material at the time of crystallization. It can be seen that a transparent conductive film having excellent bending resistance and heavy load impact characteristics can be obtained because the rate increases (= the dimensional change is negative and the absolute value increases) and the residual compressive stress of the crystalline ITO film increases. ..</p><p num="0113"> In the tensile bending test, when the curvature of bending becomes large, a sudden change in resistance may occur, but in Examples 1 to 4 and 9, R_9.5T/ R₀Is also suppressed to 2 or less. Further, in these examples, in the pen sliding durability test, even when the pen is slid at a position of 1.39 mm from the screen edge, it is compared with the case where the pen is slid at 1.66 mm from the screen edge. It can be seen that the linearity is not significantly increased and the bending resistance is particularly excellent.</p><p num="0114"> In Example 7, a high stress is applied in the MD direction of the base material during sputter formation of the amorphous ITO film, and the stress is released after the film formation. Therefore, the ITO film in an amorphous state as compared with Example 6. It is considered that a high compressive stress is applied to the surface. However, the residual compressive stresses of the crystalline ITO films in the transparent conductive films of Examples 6 and 7 are substantially the same, and their durability is also substantially the same. From this result, it can be said that in order to improve the durability of the ITO film, it is more important to apply the compressive stress during the subsequent thermal crystallization than to apply the compressive stress to the ITO film in the amorphous state. ..</p><p num="0115">&lt;Crystal grain size distribution of ITO film&gt; A 300 μm × 300 μm square test piece was cut out from the transparent conductive films of Examples 3 and 6 and fixed to a sample holder of an ultramicrotome so that the ITO film surface was facing the front. Next, a microtome knife was placed at an extremely acute angle with respect to the ITO film surface, and cutting was performed at a set thickness of 70 nm so that the cut surface was substantially parallel to the ITO film surface to obtain an observation sample. Select an observation field of view of 1.5 μm × 1.5 μm from the ITO film surface side of this observation sample and the part where the thin film is not significantly damaged, and use a transmission electron microscope (Hitachi, model number H-7650) to accelerate the voltage. It was observed at 100 kV. From the observation photograph (magnification: 50,000 times), the maximum particle size of all crystal grains observed in a 1.5 μm square field of view was obtained, and the maximum particle size of crystals with a maximum particle size of 30 to 100 nm, exceeding 100 nm, 200 nm, and exceeding 200 nm and 300 nm or less was obtained. The area ratio was calculated. The area ratio (%) is shown in Table 2.</p><p num="0116"><tables num="2"><img id="000005" he="32" wi="159" file="JP6023402B2_D0001.tif" img-format="tif" img-content="drawing" /></tables></p>

1, 2 Flexible transparent base material 3 Transparent conductive layer (crystalline ITO film) 3a Amorphous ITO film 5 Adhesive layer 11, 12 transparent substrate film 16 Undercoat layer 17 Back coat layer 101 Transparent conductive film 102 Transparent conductive film