JP7521884B2 - Optical filter and optical device - Google Patents

Description

The present invention relates to an optical filter having a microstructure with a pitch shorter than the visible wavelength of light, which exhibits a reflection reducing effect, and further relates to an optical device having such an optical filter.

Optical filters used for a wide variety of applications often have problems caused by reflections from the filters themselves. For example, in optical filters used in imaging optical systems, a phenomenon may occur in which part of the light that passes through the filter is reflected by other components and enters the optical filter again from the light exit surface of the optical filter. In such a case, if the optical filter has a reflectance in the wavelength range of this incident light, the light will be reflected again, which may cause problems. Therefore, there is a strong demand for further strengthening the reflection reduction function of optical filters.

Furthermore, in filters for display panels, touch panels, and other devices used as displays, it is desirable to minimize reflection in order to improve problems such as reduced visibility due to external light and the efficiency of light extraction from the light source inside the device.

When light enters a material, a reflection called Fresnel reflection occurs on the material's surface due to the difference in refractive index between the materials before and after the light enters. This type of reflection can be reduced by reducing the difference in refractive index between the materials. As one method for reducing this difference in refractive index, various methods have been proposed that utilize the structural shape of the material. Microstructures have been produced in recent years with improvements in microfabrication technology, and these microstructures, typified by the moth eye, continuously change the structural shape between two materials, thereby continuously changing the refractive index between the materials and reducing reflection.

Patent Document 1 discloses a method for reducing reflectance by using such microstructures in optical filters. In addition, Patent Documents 2 and 3 disclose methods for improving the rigidity of microstructures that exhibit such a reflection-reducing effect.

JP 2009-122216 A JP 2007-241177 A JP 2010-188584 A

Compared with anti-reflection films prepared by laminating a single or multiple thin layers using a vacuum deposition method or the like, microstructures with a reflection reduction effect as shown in Patent Document 1 have various advantages, such as being able to easily achieve low reflectance, being relatively easy to expand the anti-reflection wavelength range, and having small differences in spectral reflectance depending on the angle of incidence. By making the change in refractive index gentler, it is possible to further reduce reflection. However, since the pitch between each structure is limited by the required wavelength range of light, in order to achieve a higher reflectance reduction effect, it is necessary to make the structure shape tall, that is, to have a large aspect ratio, but such a shape significantly reduces rigidity, resulting in a problem of low durability against external forces.

To solve this problem, for example, Patent Document 2 proposes a method of filling the gaps between the convex portions forming the microstructure with a low refractive index material, thereby reducing the aforementioned rigidity problem in the microstructure that exhibits the reflection reduction effect. However, with methods that fill the gaps between the microstructures or cover the entire microstructure with a protective film or hard coat material, although rigidity is improved, it is difficult to obtain the refractive index change required to reduce reflection, and there is a problem that the reflection reduction effect is impaired.

Patent Document 3 also proposes a method of improving the rigidity of a structure having a water-repellent layer on the surface of a substrate having a fine uneven structure, with an adhesive layer disposed therebetween, by forming a buffer layer between the substrate and the adhesive layer. By providing such a buffer layer, it is possible to reduce the destruction of the fine uneven structure caused by cracks occurring in the adhesive layer due to external forces and propagating to the fine uneven structure, but with this configuration it is difficult to improve the rigidity against direct destruction of the fine structure due to external forces.

In view of the above, an object of the present invention is to provide an optical filter that maintains its reflection-reducing effect while improving durability against external forces, such as contact with the outside. It is also an object of the present invention to provide an optical device that uses such an optical filter and thus improves durability.

The device includes microstructures A arranged at a pitch shorter than a visible wavelength on a top surface layer of one surface of a transparent substrate that has an opportunity for contact with the outside,
a microstructure B arranged at a pitch shorter than a visible wavelength on the outermost layer portion of the other surface side of the substrate, which does not have an opportunity for contact with the outside;
The microstructure A and the microstructure B each have only periodic microprotrusion structures of the same shape arranged on the same surface,
The aspect ratio of the microstructure A is smaller than the aspect ratio of the microstructure B,
A UV-cut film is formed between the substrate and the microstructure A ,
the difference in refractive index between the outermost layer of the UV-cut film and the material of the microstructure A is 0.1 or less;
The outermost layer of the UV-cut film is SiO2,
The material of the microstructure A is a resin.
The present invention is characterized in that it is an optical device equipped with an optical filter having the above-mentioned features.

According to the present invention, an optical filter with reduced reflection can be obtained by disposing microstructures with a pitch equal to or smaller than the wavelength of visible light on the outermost layer of each of both sides of a transparent substrate. By using such an optical filter as an optical filter for a touch panel or the like, where one side of the substrate has some contact with the outside, such as contact with a finger or pen, or rubbing with an adjacent member that occurs when the filter is driven, and the other side has no contact with the outside, a microstructure with a high structure height and a high reflection reduction effect is disposed on the side that has no contact with the outside, and a microstructure with a smaller aspect ratio than the previous microstructure is disposed on the side that has contact with the outside, an optical filter and optical device that, overall, reduces reflection while increasing durability against external forces can be provided.

Illustration of a pillar array-shaped fine periodic structure Cross-sectional view of the optical filter produced in this Example 1. Spectral reflectance characteristics of the optical filter produced in this Example 1 Cross-sectional view of the optical filter produced in this Example 2 Spectral reflectance characteristics of the optical filter produced in this Example 2 1 is a schematic diagram of a cross section of a touch panel according to a fourth embodiment of the present invention;

The microstructure according to the present invention is composed of countless microstructures formed on a substrate and arranged at a pitch shorter than the wavelength of light, as shown in FIG. 1. The optical filter according to the present invention may also have an optical film that exhibits predetermined optical properties in addition to the substrate and microstructures described above.

The substrate for forming the microstructure or optical filter may be any substrate having the strength and optical properties required for the microstructure or optical filter, and may function as a base for forming the microstructure or as a base for various optical films. Such substrates may be made of glass-based materials such as BK7 or SFL-6, or made of a resin material selected from PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PES (polyethersulfone), PC (polycarbonate), PO (polyolefin), PI (polyimide), PMMA (polymethyl methacrylate), and TAC (triacetyl cellulose). Substrates made of a composite material of a glass substrate and a resin layer, or an organic-inorganic hybrid substrate made by mixing organic and inorganic materials, may also be used.

A microstructure is formed on the substrate as described above. The microstructure produced in this embodiment has a reflection reducing function, which is necessary to obtain the optical characteristics of the desired optical filter, and has a concave-convex shape arranged at a pitch shorter than the wavelength of visible light. One type of such structure may include randomly formed needle-shaped and columnar protrusions, or protrusions or recesses of a concave-convex structure finely formed in a staircase shape, which reduce the refractive index difference with the atmosphere or adjacent media, and any microstructure selected from known microstructures according to the purpose can be used.

Furthermore, by arranging these fine structures on the outermost layer of each of the two surfaces of the substrate, it is possible to achieve the necessary reflection reducing effect.
Such microstructures consisting of numerous protrusions or uneven structures arranged at a period shorter than the wavelength of light passing through the substrate can be fabricated with good reproducibility using methods such as thermal nanoimprinting and photo nanoimprinting.

Furthermore, in the case of the configuration according to the present invention, an interface is necessarily formed between the microstructure and the substrate, etc., and when forming a microstructure having a reflection reducing effect, in order to reduce the reflection of the optical filter as a whole, it is necessary to reduce the interface reflection between these different materials as well. Therefore, it is desirable to make the refractive index difference between the two materials forming the interface as small as possible.
The microstructure, optical filter, and optical device of the present invention will be specifically described below with reference to examples.

Example 1
An embodiment in which fine structures with different aspect ratios are formed on each surface of a transparent substrate will be described in detail below.

In the configuration shown in FIG. 2(a), 1.0 mm thick BK-7 glass was used as the substrate 10, and microstructure A11 was formed on the outermost layer on one side of the substrate 10, and microstructure B12 was formed on the outermost layer on the other side.

Microstructures have come to be produced in recent years with improvements in microfabrication technology. One such structure, a microstructure with an anti-reflective effect, is generally called a moth-eye structure, and aims to reduce reflections caused by differences in refractive index between materials by giving the structure a shape that simulates a continuous change in refractive index.

The microstructure A11 in this Example 1 is a pillar array in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structures have a bell-shaped moth-eye shape with a height of 300 nm and a period of 250 nm. Furthermore, while a square array or a trigonal (hexagonal) array can be considered for the arrangement of the protrusion structures, a trigonal array is considered to have a greater effect in reducing reflections, as the exposed surface area of the substrate material is smaller, and for this reason a trigonal array was used in this Example.

The microstructure B12 is a pillar array in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure has a bell-shaped moth-eye shape with a height of 500 nm and a period of 250 nm. Furthermore, the protrusion structure is arranged in a three-sided arrangement, which is considered to have a high reflection reduction effect.

In this way, the aspect ratio of microstructure A11, calculated by dividing the structural height by the structural period, is close to 1, and the structure has greater rigidity than microstructure B12. On the other hand, microstructure B12 has a large aspect ratio of 2, and is structured to have a greater reflection reduction effect. Therefore, by combining these, the reflection reduction effect of the optical filter 14 as a whole can be maintained, while the rigidity of the optical filter 14 as a whole can be increased by placing the surface side of microstructure A11 against a surface that is in some kind of contact with an external force.

Here, if it is desired to further reduce the reflectance of the optical filter or to eliminate the influence of reflection at each interface constituting the microstructure, it is desirable to set the refractive index difference at all influential interfaces, such as the interface between the substrate 10 and the microstructure A11, or the interface between the substrate 10 and the microstructure B12, to 0.1 or less. In this embodiment 1, the refractive index was adjusted to such a value. Taking the refractive index at a wavelength of 540 nm as an example, the refractive index of the substrate 10 is 1.52, the refractive index of the microstructure A11, and the refractive index of the microstructure B12 are about 1.51, and the refractive index difference at the interfaces between the substrate 10 and the microstructure A11, and the substrate 10 and the microstructure B12 is 0.01, respectively. In this way, by setting the refractive index difference at the interface between adjacent different substances to 0.1 or less, it is possible to significantly reduce the reflection at this interface, and more preferably, it is set to 0.05 or less as in this embodiment 1.

On the other hand, when used in a general environment such as an air medium, the smaller the refractive index of the microstructure A11, the greater the reduction effect. Therefore, it is preferable that the refractive index of the microstructure A11 is smaller than that of the substrate 10. In view of the above, in addition to the refractive index difference described above, it is most preferable that the refractive index of the microstructure A11 is smaller than that of the substrate, and further the refractive index difference is 0.05 or less.

Various methods have been proposed for producing such microstructures, but in this example, we selected the photo-nanoimprint method using UV (ultraviolet) curable resin.

First, an appropriate amount of UV-curable resin was dropped onto the substrate through a 0.2 μm PTFE (polytetrafluoroethylene) filter, and then the entire surface of the substrate was coated with the UV-curable resin by spin coating to a predetermined thickness. After that, a quartz mold that had been subjected to a release treatment to be designed as a hole array shape by inverting the above-mentioned shape and taking into account the cure shrinkage of the resin, was pressed against the substrate, and after maintaining this state for a short time, the resin was cured by irradiating it with UV light in this state, to produce the microstructure A11. Various types of materials can be used for such UV-curable resin. In this embodiment, an acrylic UV-curable resin was used, but fluorine-based resins, resins with fluorine components added to acrylic resins, and materials mainly composed of other resins may also be used, and depending on the imprint process, inorganic materials such as SOG and organic-inorganic hybrid materials can also be used.

The substrate was then turned over, and an appropriate amount of UV-curable resin was dropped onto the other side of the substrate through a 0.2 μm PTFE filter, and then the resin was applied to the entire surface of the substrate by spin coating to a specified film thickness. Taking into account the cure shrinkage of the resin, the above-mentioned shape was inverted and a quartz mold that had been treated with a release agent was pressed against the designed hole array shape. This state was maintained for a short time, and then the resin was cured by irradiating it with UV light in that state, producing microstructure B12.
Here, if it is necessary to improve the adhesion between the substrate 10 and the microstructure A11 or the microstructure B12, a primer treatment is performed, and as shown in FIG. 2(b), an adhesion layer 13 can be provided at the interface between the substrate 10 and the microstructure A11 or between the substrate 10 and the microstructure B12, or an adhesion layer 13 can be provided only at one of the interfaces. Examples of such primer solutions include a silane coupling agent-based solution to which an appropriate amount of IPA or nitric acid is added, and TEOS is added for the purpose of further enhancing adhesion. This is dropped onto the substrate through a 0.2 μm PTFE filter, and applied by spin coating to form an extremely thin film, and then dried under specified conditions to form the adhesion layer 13. Furthermore, in order to apply the primer liquid more uniformly, a hydrophilization treatment using UV ozone or the like may be performed before applying the primer liquid, as long as it does not have any adverse effect on the substrate 10 that is the base. Furthermore, when coating by such a process, it is also possible to limit the coating area by applying a mask or by changing the process to an inkjet method, a gravure method, a microcontact printing method, etc. In this case, as described above, if reflection reduction is required, the refractive index difference at the adjacent interfaces is preferably adjusted to 0.1 or less, more preferably 0.05 or less.

The spectral reflectance characteristics of the optical filter 14 produced as described above were measured using a spectrophotometer U4100 manufactured by Hitachi High-Technologies Corporation, and the results are shown in Figure 3. The spectral reflectance in the visible wavelength range of 400 nm to 700 nm was 0.7% or less, and the optical filter produced in this Example 1 was able to achieve a very low reflectance.

By placing the microstructure A11 on the surface that has the opportunity for contact with the outside, such as through contact with a finger or pen, or rubbing against adjacent parts when the filter is operated, and placing the microstructure B12 on the surface that does not have the opportunity for contact, it is possible to increase the rigidity against external forces while maintaining the low reflection characteristics of the optical filter 14 as a whole.
In addition, in this Example 1, the nanoimprint process was repeated twice to form a microstructure on both sides of the substrate, but a similar microstructure can also be formed by applying resin to the front and back of the substrate by spin coating, dip coating, or the like, and then performing UV nanoimprinting on both sides simultaneously.

Example 2
An embodiment of a UV cut filter in which a microstructure that exhibits a reflection reducing effect is provided on a UV cut film, which is an optical film that cuts ultraviolet rays and is composed of a multi-layer thin film, is fabricated will be described in detail below.

In optical filters used in the optical systems of imaging devices and the like, the sensitivity and definition of solid-state imaging elements in recent years have led to an increased likelihood of defects in captured images, such as ghosts and flares, caused by reflections from the filters themselves. One major challenge is to reduce the spectral reflectance in a specific wavelength range, such as the visible wavelength range, more than ever before.

For such a filter, as shown in Figure 4, a UV cut film 21 is formed on a transparent substrate, a microstructure A22 is placed on the UV cut film 21 which is the outermost layer of the substrate, and a microstructure B23 is placed on the outermost layer of the other side of the substrate to form an optical filter 25. In the configuration shown in Figure 4, a 1.0 mm thick PMMA resin is used as the substrate 20, a UV cut film 21 is formed on this substrate 20, and a microstructure A22 is formed on this. As optical characteristics of the substrate used for the optical filter 25 of this embodiment, a total light transmittance of 89% or more in the visible light wavelength range is preferable, and 91% or more is even more preferable.

First, a UV-cut film 21 was formed by laminating multiple thin films by vacuum deposition on one side of a substrate 20. The vacuum deposition method has the advantages that the film thickness can be controlled relatively easily, scattering is very small in the visible light wavelength range, and the wavelength dependency of the spectral transmittance can be controlled to a small value. However, the method is not limited to vacuum deposition, and film formation can also be performed by sputtering, IAD, IBS, ion plating, cluster deposition, and other deposition methods, and the most appropriate deposition method can be selected taking into consideration the purpose, conditions, etc.

As the thin film material constituting the UV cut film 21, in addition to layers composed of metal compounds such as SiO2, TiO2, Al2O3, Ti, Nb, Ta, Zr, Ni, Cr, W, Mo, Au, Ag, Cu, Mg, Al, or alloys thereof, it is possible to use MgF2, which has a relatively low refractive index and is environmentally friendly, for the purpose of reducing the reflection of the outermost layer, but in this embodiment, a layered structure is used in which the alternating layers of SiO2 and TiO2 films are layered directly on the substrate and the outermost layer is a SiO2 layer, resulting in a nine-layer film. Thus, in this embodiment 2, the outermost layer of the UV cut film 21 is a SiO2 layer, but it is not limited to these, and it is possible to appropriately select layers such as Al2O3, SiO, etc. with different acid values, SiN, metal compounds of Si, Al, Mg, and layers in which these are mixed. Similarly, it may be a metal compound such as Ti, Nb, Ta, Zr, Ni, Cr, W, Mo, Au, Ag, or Cu.

Here, in the film configuration of the UV cut film 21, in this embodiment, the reflection at the interface between the SiO2 layer, which is the outermost layer of the UV cut film 21, and the fine structure A22 is ignored, and the reflection in the visible wavelength region at other interfaces is offset by the light interference effect, so that the overall reflection at other interfaces is as small as possible. This is for the following reasons. Although the details will be described later, by reducing the refractive index difference between the outermost layer of the optical film and the fine structure, the reflection at this interface is reduced as much as possible, and by utilizing the reflection reduction effect of the fine structure, the reflection from the medium (air) to the outermost layer of the optical film is ideally reduced. Next, after the outermost layer toward the substrate side of the optical film, the reflection is reduced by the light interference effect of the interfaces other than the interface between the outermost layer and the fine structure. Then, by combining these two reflection reduction configurations, the reflection of the optical filter as a whole is reduced. The authors have found that in this type of optical filter, among all the interfaces, the reflection at the interface between the outermost layer and the incident medium such as air, which has a large refractive index difference from the outermost layer, has the greatest effect on the reflection as an optical filter, and by sufficiently reducing the reflection at this portion and offsetting the reflection at all other interfaces, the reflection formed by the optical interference effect can be reduced, thereby making it possible to further reduce the overall reflection as an optical filter. Therefore, with the configuration of this embodiment 2 , it is possible to significantly reduce the reflection as an optical filter as a whole.

Here, from the viewpoint of reducing reflection, the refractive index difference between the SiO2 layer, which is the outermost layer of the UV cut film 21, and the microstructure A22 is set to 0.1 or less. Taking the refractive index at a wavelength of 540 nm as an example, the refractive index of the microstructure A22 is 1.51, and the refractive index of the SiO2 layer, which is the outermost layer of the UV cut film 21, is 1.46, and the refractive index difference at the interface between the UV cut film 21 and the microstructure A22 is set to 0.05. In this way, by setting the refractive index difference at the interface between adjacent different substances to 0.1 or less, it is possible to significantly reduce the reflection at this interface, and more preferably, it is set to 0.05 or less as in this example. In addition, the refractive indexes of the substrate 20 and the microstructure B23 at 540 nm are 1.52 and 1.51, respectively, and for the same reason as above, the refractive index difference between the two is set to 0.01.

A microstructure A22 was formed on the UV-cutting film 21 prepared as described above. In this example, the photo-nanoimprint method using a UV-curable resin was selected to fabricate the microstructure.

Here, the microstructure A22 in this Example 2 is a pillar array in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure has a bell-shaped moth-eye shape with a height of 300 nm and a period of 250 nm. Furthermore, the protrusion structure is arranged in a three-sided arrangement, which is considered to have a high reflection reduction effect.

The microstructure B23 is a pillar array in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure has a bell-shaped moth-eye shape with a height of 500 nm and a period of 250 nm. Furthermore, the protrusion structures are arranged in a three-sided arrangement, which is considered to have a high reflection reduction effect.

In this way, the aspect ratio of microstructure A22, calculated by dividing the structural height by the structural period, is close to 1, and the structure has greater rigidity than microstructure B23. On the other hand, microstructure B23 has a large aspect ratio of 2, and is structured to have a greater reflection reduction effect. Therefore, by combining these, the reflection reduction effect of the optical filter 25 as a whole can be maintained, while the surface side of microstructure A22 is placed against a surface that is in some kind of contact with an external force, thereby increasing the rigidity of the optical filter 25 as a whole.

First, an appropriate amount of UV-curable resin was dropped onto the substrate through a 0.2 μm PTFE filter, and then the entire surface of the substrate was coated with the UV-curable resin by spin coating to a specified film thickness. After that, taking into account the cure shrinkage of the resin, a quartz mold that had been subjected to a release treatment to create a hole array shape designed by inverting the above-mentioned shape was pressed against this substrate, and after maintaining this state for a short time, the resin was cured by irradiating it with UV light in this state, producing the microstructure A22. A variety of materials can be used for such UV-curable resin, and in this example, an acrylic UV-curable resin was used.

The substrate was then turned over, and an appropriate amount of UV-curable resin was dropped onto the other side of the substrate through a 0.2 μm PTFE filter, and then the resin was applied to the entire surface of the substrate by spin coating to a specified film thickness. Taking into account the cure shrinkage of the resin, the above-mentioned shape was inverted and a quartz mold that had been treated with a release agent was pressed against the designed hole array shape. This state was maintained for a short time, and then the resin was cured by irradiating it with UV light in that state, producing microstructure B23.
Here, when it is necessary to improve the adhesion of each layer, such as between the substrate 20 and the UV cut film 24, between the substrate 20 and the microstructure B23, or between the UV cut film and the microstructure A22, a primer treatment can be performed to provide an adhesion layer at each interface. Furthermore, in order to apply the primer liquid more uniformly, a hydrophilization treatment using UV ozone or the like may be performed before applying the primer liquid, as long as it does not have any adverse effect on the undercoat layer. In addition, when applying the primer liquid by such a process, it is also possible to limit the application area by applying masking or changing the process to an inkjet method, a gravure method, a microcontact printing method, or the like. In this case, as described above, when reflection reduction is required, the refractive index difference at the adjacent interfaces is preferably adjusted to 0.1 or less, and more preferably 0.05 or less.

In addition, in the case of filters that have absorption or reflection in a certain range of ultraviolet wavelengths, such as UV cut filters, depending on the wavelength of UV light used, when light is irradiated from the substrate side of the filter, the filter may absorb or reflect at least a portion of the light, and sufficient light may not reach the resin. Therefore, in such cases, it is necessary to irradiate UV light from the mold side, and to select a mold made of a material that sufficiently transmits the required wavelengths of UV light.

The spectral reflectance characteristics of the optical filter 23 produced as described above were measured using a spectrophotometer U4100 manufactured by Hitachi High-Technologies Corporation, and the results are shown in Figure 6. While maintaining good UV blocking function in the ultraviolet wavelength region, the spectral reflectance in the visible wavelength region of 450 nm to 700 nm, which is set as the transmission blocking wavelength region in consideration of providing UV blocking function, is 0.8% or less, and the optical filter produced in this Example 2 was able to achieve a very low reflectance.

By placing the microstructure A22 on the surface that is likely to come into contact with the outside, such as through contact with a finger or pen, or rubbing against adjacent parts when the filter is operated, and by placing the microstructure B23 on the surface that is not likely to come into contact with the outside, it is possible to increase the rigidity against external forces while maintaining the low reflection characteristics of the optical filter 25 as a whole.

In addition, in this Example 2, the nanoimprint process was repeated twice to form microstructures on both sides of the substrate, but similar microstructures can also be formed by applying resin to the front and back of the substrate by spin coating or dip coating, and then performing UV nanoimprinting on both sides simultaneously. In addition, in this Example 2, the UV-cut film was formed on only one side of the substrate, but this is not limited to this, and it is also possible to divide and place the film on both sides of the substrate. Furthermore, it is also possible to divide the UV-cut film into multiple films with different transmission blocking wavelength ranges and divide and place these on both sides of the substrate.

Example 3
In the above-mentioned second embodiment, an optical filter with a UV cut function having a microstructure with a reflection reducing effect has been described, but the same effect can be obtained with other optical films.

For example, it can be applied to AR films, IR (infrared) cut films, UVIR cut films, color filter films, fluorescent filter films, ND (neutral density) films, other bandpass filter films, edge filter films, etc. Furthermore, it can also be applied to barrier films against water vapor, etc.

Microstructures that exhibit a reflection-reducing effect are formed on these optical films, which form the outermost layer on one side of the substrate. Here, the refractive index difference between the microstructures and the outermost layer of the optical film that forms the interface is small, and each optical film has a layered structure that ignores reflections at the interface between the outermost layer of the optical film and the microstructures and minimizes reflections caused by optical interference effects from other interfaces.

Furthermore, the substrate is turned over, and a microstructure that exhibits a reflection-reducing effect is also formed on the outermost layer of the other surface of the substrate. In this case, if the microstructure is placed on the outermost layer of the substrate, it is possible to exhibit a sufficient reflection-reducing effect. It is also possible to form an optical film with the same concept as the first surface and then form the microstructure on top of it, or to form the microstructure directly on the substrate. Furthermore, if necessary, an adhesive layer may be inserted at any position on each of these interfaces. This makes it possible to obtain an optical filter that reduces reflection as a whole.

By arranging the surface on which the microstructures with the smaller aspect ratio (the structural height divided by the structural period) are formed on a surface that has an opportunity for contact with the outside, such as contact with a finger or pen, or rubbing against adjacent members that occurs when the filter is driven, and arranging the surface on which the other microstructures are formed on a surface that has no opportunity for contact, it is possible to increase the rigidity against external forces while maintaining the low reflection characteristics of the optical filter as a whole. Here, from the two viewpoints of reflection reduction effect and durability against external forces, it is preferable that the aspect ratio of the microstructures arranged on the surface that has an opportunity for contact with the outside be close to 1, and it is particularly preferable that it is in the range of approximately 0.8 to 1.2. Furthermore, since the aspect ratio of the microstructures arranged on the surface that has no opportunity for contact with the outside is better for a high reflection reduction effect, it is preferable that the aspect ratio of the microstructures be 1 or more, and it is particularly preferable that it be 1.2 or more.

Such optical films can be divided into multiple optical films with different functions, such as an IR cut film and a UV cut film, and placed on both sides of the substrate. Furthermore, for example, an IR cut film can be divided into multiple IR cut films with different transmission blocking wavelength ranges, and these can be divided and placed on both sides of the substrate.

Example 4
Next, an embodiment in which a touch panel is regarded as a single substrate and microstructures with different aspect ratios are formed on both sides of the substrate will be described below with reference to FIG.

Figure 7 is a schematic diagram of a cross section of an example of a touch panel. Two conductive films on which ITO or the like is formed are configured via spacers on a base substrate 40 made of resin, glass, or the like. The substrate 40 in Figure 7 also serves as a protective plate for a light source (not shown) located below it. In addition, since the lower surface of the substrate 40 is sealed, it basically does not have contact with the outside. Conversely, the upper surface of the upper conductive film 43 in Figure 7 is the surface that is touched by a human finger or a touch pen. In this Example 4, the substrate 40 is made of PET resin with a thickness of 2.0 mm, but it may be PC resin or other resins, glass-based materials, or inorganic and organic hybrid materials. Any material that can function as a substrate for a touch panel, including the thickness of the substrate, can be appropriately selected.

Here, the entire touch panel was regarded as a single substrate, and as shown in Fig. 7, a microstructure A41 and a microstructure B42 were formed on the outermost layer of each surface that serves as the light input/output surface for the substrate. The microstructure A41 in this Example 4 was a pillar array in which protrusion structures as shown in Fig. 1 were periodically arranged, and the structures had a bell-shaped moth-eye shape with a height of 300 nm and a period of 250 nm. Furthermore, the protrusion structures were arranged in a three-sided arrangement, which is considered to have a high reflection reduction effect.
The microstructure B42 was a pillar array in which the protrusion structures shown in Fig. 1 were periodically arranged, and the structure had a bell-shaped moth-eye shape with a height of 500 nm and a period of 250 nm. Furthermore, the protrusion structures were arranged in a three-sided arrangement, which is considered to have a high reflection reducing effect.

In this way, the aspect ratio of microstructure A41, calculated by dividing the structural height by the structural period, is close to 1, and the rigidity of the structure is stronger than that of microstructure B42. On the other hand, microstructure B42 has a large aspect ratio of 2, and is a structure with a large reflection reduction effect. Therefore, by combining these, the reflection reduction effect of the optical filter 46 as a whole can be maintained, while the rigidity of the optical filter 46 as a whole can be increased by placing the surface side of microstructure A41 against a surface that is in some kind of contact with an external force.

In this embodiment, the photo-nanoimprint method using a UV-curable resin was selected to fabricate the microstructures A41 and B42.

First, an appropriate amount of UV-curable resin was dropped onto the upper conductive film 43, which is the upper part of the substrate, through a 0.2 μm PTFE filter, and then the UV-curable resin was applied to a specified film thickness by spin coating. After that, taking into account the cure shrinkage of the resin, the above-mentioned shape was inverted and a quartz mold that had been subjected to a release treatment was pressed against the designed hole array shape, and after maintaining this state for a short time, the resin was cured by irradiating it with UV light in this state, producing the microstructure A41. Various types of materials can be used for such UV-curable resin, and in this example, an acrylic UV-curable resin with a fluorine component added to it, which has a low refractive index, was used to reduce reflection.

Then, the substrate was turned over, and an appropriate amount of UV-curable resin was dropped through a 0.2 μm PTFE filter onto the surface that would become the lower part of substrate 40 in FIG. 7, and then the entire substrate was coated with a predetermined film thickness by spin coating. Taking into account the cure shrinkage of the resin, the above-mentioned shape was inverted and a quartz mold that had been subjected to a release treatment was pressed against the designed hole array shape. This state was maintained for a short time, and then UV light was irradiated in this state to cure the resin, producing microstructure B42.

As mentioned above, the refractive index difference at each interface, such as between the substrate 40 and the microstructure B42, or between the upper conductive film 43 and the microstructure A41, is preferably adjusted to 0.1 or less, and more preferably 0.05 or less.

Furthermore, if it is necessary to improve the adhesion of each layer, a primer treatment can be performed to provide an adhesion layer at each interface. Furthermore, to ensure a more uniform application of the primer liquid, a hydrophilic treatment using UV ozone or the like can be performed before the primer liquid is applied, so long as it does not adversely affect the undercoat layer. When applying the primer liquid using such a process, it is also possible to limit the application area by applying masking or changing the process to an inkjet method, gravure method, microcontact printing method, or the like. In this case, as mentioned above, it is preferable that the refractive index difference at each adjacent interface is adjusted to 0.1 or less, and more preferably 0.05 or less.

Similarly, it is possible to form a UV-cut film such as that produced in this Example 2 on, for example, the substrate 40, to provide a panel with UV-cut functionality, and it is also possible to apply the various optical films described in this Example 3 to these panels.

Furthermore, not limited to these, even in other optical devices or optical equipment, by using an optical filter equipped with microstructures having a reflection reduction effect arranged at a pitch shorter than the visible wavelength and having different aspect ratios on both sides of the substrate as described in the first to third embodiments, it is possible to increase the rigidity against external forces while maintaining a sufficient reflection reduction effect.

For example, if the optical filter is one in which the relative position to the surroundings changes, such as when the filter is inserted or removed depending on the conditions, there is a possibility that the filter may come into contact with some component when driven. However, by appropriately arranging the optical filters of Examples 1 to 3 in such a mechanism, an optical device with improved durability against contact with the outside world can be realized while maintaining very low reflection.

10.20.40. Substrate 11.22.41. Microstructure A
12.23.42. Microstructure B
13. 24. Adhesion layer 14. 25. 46. Optical filter 21. UV cut film 41. Upper conductive film 42. Lower conductive film 43. Spacer

Claims (3)

The device includes microstructures A arranged at a pitch shorter than a visible wavelength on a top surface layer of one surface of a transparent substrate that has an opportunity for contact with the outside,
a microstructure B arranged at a pitch shorter than a visible wavelength on the outermost layer portion of the other surface side of the substrate, which does not have an opportunity for contact with the outside;
The microstructure A and the microstructure B each have only periodic microprotrusion structures of the same shape arranged on the same surface,
The aspect ratio of the microstructure A is smaller than the aspect ratio of the microstructure B,
A UV-cut film is formed between the substrate and the microstructure A ,
the difference in refractive index between the outermost layer of the UV-cut film and the material of the microstructure A is 0.1 or less;
The outermost layer of the UV-cut film is SiO2,
The material of the microstructure A is a resin.
An optical device equipped with an optical filter. The refractive index of the material of the microstructure is lower than the refractive index of the substrate.
The optical device of claim 1 . An adhesive layer is provided at a part of the interface between each layer constituting the optical filter.
3. An optical device according to claim 1 or 2 .

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