JP2020204665A - Optical filter and optical device - Google Patents

Abstract

To provide an optical filter enhanced in durability against an external force such as contact with the outside while maintaining a reflection reducing effect, and also to provide an optical device with improved durability by using such an optical filter.SOLUTION: An optical filter of the present invention includes a microstructure A (11) which is arranged at a pitch shorter than a visible wavelength at the outermost layer part on one side of a transparent substrate 10 having the opportunity of contact with the outside, and also includes a microstructure B (12) which is arranged at the pitch shorter than the visible wavelength at the outermost layer part on the other side of the substrate 10 having no opportunity for contact with the outside. The aspect ratio of the microstructure A (11) is smaller than that of the microstructure B (12).SELECTED DRAWING: Figure 2

Description

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

Optical filters used in a variety of applications often have problems due to the reflection of the filter itself. For example, in an optical filter used in an imaging optical system or the like, a phenomenon occurs in which a part of the light transmitted through the filter is reflected by another member and is incident on the optical filter again from the light emitting surface of the optical filter. There is. In such a case, if the optical filter has a reflectance in the wavelength region of the incident light, the light is reflected again, which may cause a problem. Therefore, further enhancement of the reflection reduction function in the optical filter is strongly desired.

Furthermore, even in filters such as display panels and touch panels used as displays, reflection is reduced as much as possible for the purpose of improving problems such as deterioration of visibility due to external light and efficiency of light extraction from the light source in the device. It is desired to do.

When light is incident on a substance, a reflection called Fresnel reflection occurs on the surface of the substance due to the difference in the refractive index of the substance before and after the incident. Such reflection can be reduced by reducing the difference in refractive index between the substances. As one of the methods for reducing the difference in refractive index, various methods using the structure shape of the substance have been proposed. Microstructures have come to be manufactured with the improvement of microfabrication technology in recent years, and these microstructures represented by Moss Eye continuously change the structure shape between two substances. By making the substance continuously change the refractive index between substances, the reflection is reduced.

Patent Document 1 discloses a method of reducing the reflectance by using such a fine structure in an optical filter. Further, Patent Documents 2 and 3 disclose a method for improving the rigidity of a microstructure that exhibits such a reflection reducing effect.

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

A microstructure having a reflection reducing effect as shown in Patent Document 1 has lower reflection than an antireflection film produced by laminating a single layer or a plurality of thin films by a vacuum film forming method or the like. The rate can be easily realized, and it is relatively easy to expand the antireflection wavelength range, and it has various merits such as a small difference in the spectral reflectance depending on the incident angle, and the change in the refractive index can be changed. By making it gentle, it is possible to further reduce reflection. However, since the pitch between each structure is limited by the required wavelength region of light, it is necessary to have a high structure shape, that is, a large aspect ratio in order to obtain a higher reflectance reduction effect. With such a shape, the rigidity is remarkably lowered, and there is a problem that the durability against an external force is lowered.

In order to solve this, for example, in Patent Document 2, the above-mentioned above-mentioned in a microstructure that exhibits a reflection reducing effect by filling the gap between the convex portions forming the microstructure with a low refractive index material. A method has been proposed to reduce the problem of rigidity of the. However, the method of filling the gaps between the microstructures or covering the entire microstructures with a protective film or hard coat material improves the rigidity, but changes the refractive index required to reduce the reflection. There is a problem that it is difficult to obtain the effect and the effect of reducing reflection is impaired.

Further, in Patent Document 3, in a structure having a water-repellent layer via an adhesive layer on the surface of a substrate having a fine concavo-convex structure, a buffer layer is formed between the substrate and the adhesive layer. , A method of improving rigidity has been proposed. By providing such a buffer layer, it is possible to reduce the destruction of the fine concavo-convex structure due to cracks in the adhesion layer caused by an external force and propagated to the fine concavo-convex structure. With such a configuration, it is difficult to improve the rigidity against direct destruction of the microstructure by an external force.

From the above, an object of the present invention is to provide an optical filter having improved durability against external forces such as contact with the outside while maintaining the reflection reducing effect. Another object of the present invention is to provide an optical device having improved durability by using such an optical filter.

A fine structure A arranged at a pitch shorter than the visible wavelength is provided on the outermost surface layer on one side of a transparent substrate having an opportunity to contact the outside, and the other surface of the substrate having no opportunity to contact the outside is provided. A microstructure B arranged at a pitch shorter than the visible wavelength is provided on the outermost surface layer portion on the side, and the aspect ratio of the microstructure A is smaller than the aspect ratio of the microstructure B.

According to the present invention, an optical filter with reduced reflection can be obtained by arranging a microstructure having a pitch equal to or smaller than the wavelength size of visible light and exhibiting a reflection reducing effect on the outermost layer of each of both sides of a transparent substrate. be able to. With such an optical filter, 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 driving the filter, and the other side has some contact with the outside. By using it as an optical filter such as a touch panel that has no contact with the outside, a fine structure with a high structure height and a high reflection reduction effect is placed on the surface without contact with the outside, and contact with the outside can be achieved. By arranging a microstructure having a smaller aspect ratio than the previous microstructure on a certain surface, an optical filter and an optical device having improved durability against external force while reducing reflection as a whole are provided. can do.

Explanatory drawing of pillar array-like fine periodic structure Cross-sectional view of the optical filter produced in Example 1 Spectral reflectance characteristics of the optical filter produced in Example 1 Cross-sectional view of the optical filter produced in Example 2 Spectral reflectance characteristics of the optical filter produced in Example 2 Schematic diagram of the touch panel cross section in the fourth embodiment

The microstructure according to the present invention is composed of innumerable microstructures formed on a substrate and arranged at a pitch shorter than the wavelength size of light, as shown in FIG. 1, for example. Further, the optical filter according to the present invention may have an optical film exhibiting predetermined optical characteristics in addition to the above-mentioned substrate and microstructure.

The substrate for forming the microstructure or the optical filter may be any substrate having the strength and optical characteristics of the substrate of the microstructure or the optical filter, and the substrate for forming the microstructure or various optics. Those capable of functioning as a substrate for the membrane are used. Examples of such a substrate include a substrate made of a glass-based material such as BK7 and SFL-6, or PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PES (polyethersulfon), PC (polycarbonate), PO ( A substrate made of a resin material selected from (polyolefin), PI (polyimide), PMMA (polymethylmethacrylate), TAC (triacetylcellulose) and the like can be used. Further, a substrate made of a composite material of a glass substrate and a resin layer, an organic-inorganic hybrid substrate in which an organic material and an inorganic material are mixed, and the like can also be used.

A fine structure is formed on the substrate as described above. The microstructures produced in this example have a reflection reduction function, which is required to obtain the optical characteristics of a desired optical filter, and are arranged at a pitch shorter than the wavelength of visible light. It has an uneven shape. As one type of such a structure, the protrusions or recesses of a randomly formed needle-like body, a columnar body, or the like, and the protrusions or recesses of a concave-convex structure finely formed in a stepped shape are used to refract with the atmosphere or an adjacent medium. Those having a reduced rate difference may be included, and those arbitrarily selected from known microstructures according to the purpose can be used.

Further, these microstructures are arranged on the outermost surface layer of each surface on both sides of the substrate, so that the required reflection reducing effect can be exhibited.
In the case of such a fine structure composed of a large number of protrusions and uneven structures arranged at a cycle shorter than the wavelength of the light transmitted through the substrate, reproducibility can be obtained by using a method such as a thermal nanoimprint method or an optical nanoimprint method. Can be made well.

Further, in the case of the configuration according to the present invention, an interface is always formed between the microstructure and the substrate, but when the microstructure having a reflection reducing effect is formed, the reflection of the entire optical filter is reduced. It is also necessary to reduce the interfacial reflection between these different substances. Therefore, it is desirable that the difference in refractive index between the two substances forming the interface be as small as possible.
Hereinafter, the microstructure, the optical filter, and the optical device of the present invention will be specifically described based on examples.

(Example 1)
Examples in which microstructures having different aspect ratios are formed on each surface of the transparent substrate will be described in detail below.

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

Microstructures have come to be manufactured with the improvement of microfabrication technology in recent years. A microstructure having an antireflection effect, which is one of such structures, is generally called a moss-eye structure, and the shape of the structure is a shape in which changes in the refractive index are continuous. By doing so, the reflection caused by the difference in the refractive index between the substances is reduced.

The microstructure A11 in the first embodiment has a pillar array shape in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure has a bell-shaped moss eye shape, a height of 300 nm, and a period of 250 nm. Furthermore, regarding the arrangement of the protrusion structures, a square arrangement or a three-way (hexagonal) arrangement can be considered, but the three-way arrangement is said to have a higher reflection reduction effect because the exposed surface of the substrate material is smaller. For this reason, a three-way arrangement was used in this example.

Further, the microstructure B12 has a pillar array shape in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure has a bell-shaped moss eye shape, a height of 500 nm, and a period of 250 nm. Furthermore, the protruding structure has a three-way arrangement, which is said to have a high reflection reducing effect.

As described above, the microstructure A11 has an aspect ratio close to 1 obtained by dividing the structural height by the structural period, and has higher rigidity as a structure than the microstructure B12. On the other hand, the fine structure B12 has a large aspect ratio of 2 and a large reflection reducing effect. Therefore, by combining these, the surface side of the microstructure A11 is arranged with respect to the surface having some contact with the external force while maintaining the reflection reduction effect as the optical filter 14 total. Rigidity can be increased.

Here, when it is desired to further reduce the reflectance of the optical filter or to remove the influence of reflection at each interface constituting the microstructure, the substrate 10 and the microstructure A11 or the substrate 10 and the microstructure B12 It is desirable that the difference in refractive index at all the interfaces that affect the interface is 0.1 or less. Also in the first embodiment, the values were adjusted to be such values. 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 microstructure B12 is about 1.51, and the refractive index of the substrate 10 and the microstructure A11 is about 1.51. , And the difference in refractive index at the interface between the substrate 10 and the microstructure B12 is 0.01. In this way, by reducing the difference in refractive index between adjacent and different substances to 0.1 or less, it is possible to significantly reduce the reflection at this interface, and more preferably as in the first embodiment. It is configured to be 0.05 or less.

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 fine structure A11 is smaller than that of the substrate 10. Based on the above, it is most preferable that the fine structure A11 has a smaller refractive index than the substrate and the difference in refractive index is 0.05 or less in combination with the above-mentioned refractive index.

Various production methods have been proposed for the production method of such a fine structure, but in this example, the optical nanoimprint method using a UV (ultraviolet) curable resin was selected.

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 UV curable resin so as to have a predetermined film thickness by a spin coating method. .. After that, a quartz mold that has been subjected to a mold release treatment to the hole array shape designed by reversing the above-mentioned shape is pressed against this substrate in consideration of the curing shrinkage of the resin, and after holding this state for a short time, it remains as it is. The resin was cured by irradiating with UV light in this state to prepare a fine structure A11. Various various materials can be used for such a UV curable resin. In this example, an acrylic UV curable resin was used, but a fluorine resin, a resin obtained by adding a fluorine component to an acrylic resin, and others. A material containing the above resin as a main component may be used, or an inorganic material such as SOG or an organic-inorganic hybrid type material may be used depending on the imprinting process.

After that, the front and back sides of the substrate are reversed, an appropriate amount of UV curable resin is dropped onto the other surface of the substrate through a 0.2 μm PTFE filter, and then the entire surface of the substrate is subjected to a spin coating method so as to have a predetermined thickness. After coating, taking into account the curing shrinkage of the resin, pressing the quartz mold that has been subjected to the mold release treatment to the hole array shape designed by reversing the above shape, and holding this state for a short time, it remains as it is. The resin was cured by irradiating with UV light to prepare a fine structure B12.
Here, when 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. 2B, the substrate 10 and the microstructure are subjected to primer treatment. It is also possible to provide the adhesion layer 13 at the interface between the A11 and the substrate 10 and the microstructure B12, or it is possible to provide the adhesion layer 13 only at one of the interfaces. As an example of such a primer solution, a silane coupling agent based on an appropriate amount of IPA, nitric acid or the like, and TEOS added for the purpose of further strengthening the adhesion can be used. This is dropped onto a substrate through a 0.2 μm PTFE filter, coated to form an ultrathin film by spin coating, and then dried under predetermined conditions to form an adhesion layer 13. Further, in order to apply the primer solution more uniformly as long as it does not adversely affect the substrate 10 as a base, a hydrophilic treatment such as UV ozone may be performed before the application of the primer solution. Further, when coating by such a process, it is possible to limit the coating area by applying masking or changing the process to an inkjet method, a gravure method, a microcontact printing method, or the like. At this time, as described above, when reflection reduction is required, the difference in refractive index at the adjacent interface is preferably adjusted to 0.1 or less, more preferably 0.05 or less.

FIG. 3 shows the results of measuring the spectral reflectance characteristics of the optical filter 14 produced as described above using a spectrophotometer U4100 manufactured by Hitachi High-Technologies Corporation. The spectral reflectance in the visible wavelength region of 400 nm to 700 nm was 0.7% or less, and the optical filter produced in Example 1 was able to realize a very low reflectance.

The surface side of the microstructure A11 is arranged with respect to a surface that has an opportunity to come into contact with the outside, such as contact with a finger or a pen or rubbing against an adjacent member that occurs when the filter is driven, and has an opportunity to contact. By arranging the microstructure B12 on the non-surface side, it is possible to increase the rigidity against an external force while maintaining the low reflection characteristics as the entire optical filter 14.
Further, in the first embodiment, the nanoimprint process was repeated twice to form microstructures on both sides of the substrate. However, after the resin was applied to the front and back surfaces of the substrate by spin coating or dip coating, both sides were simultaneously coated. A similar microstructure can be formed by UV nanoimprinting.

(Example 2)
An example in which a UV cut filter is prepared by providing a microstructure that exhibits a reflection reduction effect on a UV cut film, which is an optical film that blocks ultraviolet rays and is composed of a multilayer thin film, will be described in detail below.

Optical filters used in optical systems such as photographic equipment have become more sensitive and finer in recent years, and the reflection of the filter itself causes ghosts, flares, and other captured images. The possibility of problems is increasing, and reducing the spectral reflectance in a predetermined wavelength region such as the visible wavelength region is one of the major issues.

Regarding such a filter, as shown in FIG. 4, a UV cut film 21 is formed on a transparent substrate, a microstructure A22 is arranged on the UV cut film 21 which is the outermost layer portion of the substrate, and further, the substrate The microstructure B23 was arranged on the outermost surface layer of the other surface to form an optical filter 25. In the configuration shown in FIG. 4, a 1.0 mm-thick PMMA resin was used as the substrate 20, a UV cut film 21 was formed on the substrate 20, and a microstructure A22 was formed on the UV cut film 21. As the optical characteristics of the substrate used for the optical filter 25 as in this embodiment, the total light transmittance in the visible light wavelength region is preferably 89% or more, and more preferably 91% or more.

First, a UV cut film 21 in which a plurality of thin films were laminated was formed on one side of the substrate 20 by a vacuum vapor deposition method. The vacuum vapor deposition method has the advantages that the film thickness can be controlled relatively easily, the scattering is very small in the visible light wavelength region, and the wavelength dependence of the spectral transmittance can be controlled to a small value. There is. However, the film formation is not limited to the vacuum vapor deposition method, and the film formation method such as the sputtering method, the IAD method, the IBS method, the ion plating method, and the cluster vapor deposition method can also be used, and the most important consideration is given to the purpose and conditions. An appropriate film forming method may be selected.

Examples of the thin film material constituting the UV cut film 21 include SiO2, TiO2, Al2O3, Ti, Nb, Ta, Zr, Ni, Cr, W, Mo, Au, Ag, Cu, Mg, Al, or alloys thereof. In addition to the layer composed of a metal compound, MgF2 or the like having a relatively low refractive index and excellent environmental friendliness can be used for the purpose of reducing reflection of the outermost layer. However, in this embodiment, SiO2 and TiO2 films are used. The alternating layers of the above were laminated so as to form a 9-layer film directly above the substrate and having the outermost surface layer of SiO2. As described above, in the second embodiment, the outermost layer of the UV cut film 21 is the SiO2 layer, but the present invention is not limited to these, and for example, Al2O3, SiO and the like having different acid values, SiN and the like, Si, Al and Mg. It is possible to appropriately select a metal compound, a layer in which these are mixed, and the like. Similarly, it may be a metal compound such as Ti, Nb, Ta, Zr, Ni, Cr, W, Mo, Au, Ag, Cu.

Here, in such a film configuration of the UV cut film 21, in this embodiment, reflection at the interface between the SiO2 layer, which is the outermost layer of the UV cut film 21, and the microstructure A22 is ignored, and the other interfaces are ignored. By canceling the reflection in the visible wavelength region in the above by the light interference effect, the film configuration is made so that the overall reflection at the other interfaces is as small as possible. This is for the following reasons. The details will be described later, but by reducing the difference in refractive index between the outermost layer of the optical film and the microstructure, the reflection at this interface is reduced as much as possible, and the reflection reduction effect of the microstructure is utilized. Ideally, the reflection from the medium (air) to the outermost layer of the optical film is reduced. Next, after the outermost layer of the optical film toward the substrate side, reflection is reduced by the optical interference effect at an interface other than the interface between the outermost layer and the microstructure. Then, by combining these two reflection reduction configurations, the reflection of the entire optical filter is reduced. In this type of optical filter, the authors use the reflection at the interface between the outermost layer and an incident medium such as air, which has a large difference in refractive index between the outermost layer and the outermost layer, as an optical filter. It has the greatest effect on the reflection of the light, and if the reflection of this part is sufficiently reduced and the reflection of all other interfaces is offset to reduce the reflection formed by the optical interference effect, the optical The overall reflection as a filter can be made smaller. Therefore, with the configuration of the first embodiment, it is possible to remarkably reduce the reflection of the entire optical filter.

Here, from the viewpoint of reducing reflection, the difference in refractive index 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, respectively. Taking the refractive index at a wavelength of 540 nm as an example, the refractive index of the microstructure A22 is 1.51, the refractive index of the SiO2 layer which is the outermost layer of the UV cut film 21 is 1.46, and the UV cut film 21 The difference in refractive index between the fine structure A22 and the interface is 0.05. In this way, by setting the difference in refractive index between adjacent and different substances to 0.1 or less, it is possible to significantly reduce the reflection at this interface, and more preferably 0 as in this example. It is configured to be 0.05 or less. Further, the refractive indexes of the substrate 20 and the microstructure B23 at 540 nm are 1.52 and 1.51, respectively, and the difference in refractive index between the two is set to 0.01 for the same reason as described above.

The microstructure A22 was formed on the UV cut film 21 produced as described above. For the production of the microstructure, the optical nanoimprint method using a UV curable resin was selected in this example.

Here, the microstructure A22 in the second embodiment has a pillar array shape in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure has a bell-shaped moss eye shape, a height of 300 nm, and a period of 250 nm. And said. Furthermore, the protruding structure has a three-way arrangement, which is said to have a high reflection reducing effect.

Further, the microstructure B23 has a pillar array shape in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure has a bell-shaped moss eye shape, a height of 500 nm, and a period of 250 nm. Furthermore, the protruding structure has a three-way arrangement, which is said to have a high reflection reducing effect.

As described above, the microstructure A22 has an aspect ratio close to 1 obtained by dividing the structural height by the structural period, and has higher rigidity as a structure than the microstructure B23. On the other hand, the fine structure B23 has a large aspect ratio of 2 and a large reflection reducing effect. Therefore, by combining these, the surface side of the microstructure A22 is arranged with respect to the surface having some contact with the external force while maintaining the reflection reduction effect as the optical filter 25 total. The rigidity of the filter can be increased.

First, an appropriate amount of the 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 a spin coating method so as to have a predetermined film thickness. After that, a quartz mold that has been subjected to a mold release treatment to the hole array shape designed by reversing the above-mentioned shape is pressed against this substrate in consideration of the curing shrinkage of the resin, and after holding this state for a short time, it remains as it is. The resin was cured by irradiating with UV light in this state to prepare a fine structure A22. Various materials can be used for such a UV curable resin, and in this example, an acrylic UV curable resin was used.

After that, the front and back sides of the substrate are reversed, an appropriate amount of UV curable resin is dropped onto the other surface of the substrate through a 0.2 μm PTFE filter, and then the entire surface of the substrate is subjected to a spin coating method so as to have a predetermined thickness. After coating, taking into account the curing shrinkage of the resin, pressing the quartz mold that has been subjected to the mold release treatment to the hole array shape designed by reversing the above shape, and holding this state for a short time, it remains as it is. The resin was cured by irradiating with UV light to prepare a fine structure B23.
Here, when it is necessary to improve the adhesion of each layer such as the substrate 20 and the UV cut film 24, the substrate 20 and the microstructure B23, and the UV cut film and the microstructure A22, primer treatment is performed to each interface. It is also possible to provide an adhesion layer on the surface. Further, in order to apply the primer solution more uniformly as long as it does not adversely affect the underlying layer, a hydrophilization treatment with UV ozone or the like may be performed before the application of the primer solution. Further, when coating by such a process, it is possible to limit the coating area by applying masking or changing the process to an inkjet method, a gravure method, a microcontact printing method, or the like. At this time, as described above, when reflection reduction is required, the difference in refractive index at the adjacent interface is preferably adjusted to 0.1 or less, more preferably 0.05 or less.

Further, in the case of a filter having absorption or reflection in a part of the ultraviolet wavelength region such as a UV cut filter, depending on the wavelength of the UV light used, when light is irradiated from the substrate side of the filter, the filter is at least the light. Part of it may be absorbed or reflected, and sufficient light may not reach the resin. Therefore, in such a case, it is necessary to irradiate UV light from the mold side, and it is necessary to select a mold made of a material that sufficiently transmits the required wavelength of UV light.

FIG. 6 shows the results of measuring the spectral reflectance characteristics of the optical filter 23 produced as described above using a spectrophotometer U4100 manufactured by Hitachi High-Technologies Corporation. In the ultraviolet wavelength region, the spectral reflectance in the visible wavelength region of 450 nm to 700 nm, which is the transmission blocking wavelength region, is 0.8% or less in consideration of providing the UV cut function while maintaining a good UV cut function. , The optical filter produced in Example 2 was able to realize a very low reflectance.

The surface side of the microstructure A22 is arranged on the surface that has an opportunity to come into contact with the outside, such as contact with a finger or a pen or rubbing against an adjacent member that occurs when the filter is driven, and has an opportunity to contact. By arranging the microstructure B23 on the non-surface side, it is possible to increase the rigidity against an external force while maintaining the low reflection characteristics as the entire optical filter 25.

Further, in the second embodiment, the nanoimprint process was repeated twice to form microstructures on both sides of the substrate. However, after the resin was applied to the front and back surfaces of the substrate by spin coating or dip coating, both sides were simultaneously coated. A similar microstructure can be formed by UV nanoimprinting. Further, in the second embodiment, the UV cut film is formed only on one surface of the substrate, but the present invention is not limited to this, and it is also possible to separately arrange the UV cut film on both sides of the substrate. Further, it is also possible to divide into a plurality of UV cut films having different transmission blocking wavelength ranges and arrange them separately on both surfaces of the substrate.

(Example 3)
In the second embodiment described above, an optical filter with a UV cut function having a microstructure having 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 an AR film, an IR (infrared) cut film, a UVIR cut film, a color filter film, a fluorescent filter film, an ND (Neutral Density) film, and other bandpass filter films and edge filter films. Furthermore, it is also possible to apply a barrier film such as water vapor.

A microstructure that exhibits a reflection reduction effect is formed on these optical films, which are the outermost layers on one side of the substrate. Here, the difference in refractive index between the microstructure and the outermost layer of the optical film forming the interface is made small, and each optical film ignores reflection at the interface between the outermost layer of the optical film and the microstructure. The laminated structure is such that the reflection formed by the optical interference effect from other interfaces is minimized.

Further, the front and back surfaces of the substrate are changed, and a microstructure that exhibits a reflection reduction effect is formed on the outermost layer portion of the other surface on the substrate. At this time, if the microstructure is arranged on the outermost layer portion on the substrate, it is possible to exhibit a sufficient reflection reduction effect, and an optical film is formed on the same concept as the first surface. It is possible to form a microstructure, and it is also possible to form a microstructure directly on the substrate. Further, if necessary, the adhesion layer may be inserted at any position of each of these interfaces. As a result, it is possible to obtain an optical filter with reduced reflection as a whole.

The one with the smaller aspect ratio, which is the structural height divided by the structural period, with respect to the surface that has an opportunity to come into contact with the outside, such as contact with a finger or pen or rubbing with an adjacent member that occurs when driving the filter. By arranging the surface side on which the microstructure is formed and the surface side on which the other microstructure is formed on the surface side where there is no contact opportunity, the low reflection characteristics of the entire optical filter are maintained. At the same time, it is possible to increase the rigidity against external force. Here, from the two viewpoints of the reflection reduction effect and the durability against external force, the aspect ratio of the microstructure arranged on the surface having an opportunity to come into contact with the outside is preferably a value close to 1, and is approximately 0.8. It is particularly preferably in the range of ~ 1.2. Further, since it is preferable that the aspect ratio of the microstructure arranged on the surface having no contact with the outside has a high reflection reducing effect, it is desirable that the aspect ratio of the microstructure is 1 or more. It is particularly desirable that it is 2 or more.

In such an optical film, it is also possible to divide and arrange a plurality of optical films having different functions, such as an IR cut film and a UV cut film, on both sides of the substrate. Further, for example, in the case of an IR cut film, it is possible to divide the IR cut film into a plurality of IR cut films having different transmission blocking wavelength ranges and arrange them separately on both surfaces of the substrate.

(Example 4)
Next, an example in which the touch panel is regarded as one substrate and microstructures having different aspect ratios are formed on both surfaces of the substrate will be described below with reference to FIG. 7.

FIG. 7 is a schematic cross-sectional view of an example of a touch panel. Two conductive films in which ITO or the like is formed are formed on a base substrate 40 made of resin, glass, or the like via a spacer. The substrate 40 in FIG. 7 also serves as a protective plate for a light source (not shown) arranged below the substrate 40. Further, since the lower surface of the substrate 40 has a sealed structure, it basically does not have contact with the outside. On the contrary, the upper surface of the upper conductive film 43 in FIG. 7 is a surface that a human finger, a stylus, or the like touches. In the fourth embodiment, the substrate 40 uses a PET resin having a thickness of 2.0 mm, but it may be a PC resin or other resin, a glass-based material, or an inorganic / organic hybrid material, and the substrate may be used. Any material that can function as a touch panel substrate, including the thickness of the above, can be appropriately selected.

Here, the entire touch panel is regarded as one substrate, and as shown in FIG. 7, the microstructure A41 and the microstructure B42 are placed on the outermost surface layer of each surface which is the input / output surface of light with respect to the substrate. Formed. The microstructure A41 in Example 4 has a pillar array shape in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure has a bell-shaped moss eye shape, a height of 300 nm, and a period of 250 nm. Furthermore, the protruding structure has a three-way arrangement, which is said to have a high reflection reducing effect.
Further, the microstructure B42 has a pillar array shape in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure has a bell-shaped moss eye shape, a height of 500 nm, and a period of 250 nm. Furthermore, the protruding structure has a three-way arrangement, which is said to have a high reflection reducing effect.

As described above, the fine structure A41 has an aspect ratio close to 1 obtained by dividing the structural height by the structural period, and has higher rigidity as a structure than the fine structure B42. On the other hand, the fine structure B42 has a large aspect ratio of 2 and a large reflection reducing effect. Therefore, by combining these, the surface side of the microstructure A41 is arranged with respect to the surface having some contact with the external force while maintaining the reflection reduction effect as the optical filter 46 as a whole. Rigidity can be increased.

For the production of such microstructures A41 and B42, the optical nanoimprint method using a UV curable resin was selected in this example.

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 coated by a spin coating method so as to have a predetermined film thickness. After that, the curing shrinkage of the resin is added to this, and the quartz mold that has been subjected to the mold release treatment is pressed against the hole array shape designed by inverting the above-mentioned shape, and after holding this state for a short time, it remains as it is. The resin was cured by irradiating with UV light to prepare a fine structure A41. Various various materials can be used for such a UV curable resin, and in this example, an acrylic UV curable resin to which a fluorine component having a low refractive index is added is used from the viewpoint of reducing reflection.

Then, the front and back sides of the substrate are inverted, and an appropriate amount of UV curable resin is dropped onto the lower surface of the substrate 40 in FIG. 7 through a 0.2 μm PTFE filter, and then the substrate is subjected to a spin coating method so as to have a predetermined thickness. The entire surface is coated, the curing shrinkage of the resin is taken into consideration, and the above-mentioned shape is inverted and the hole array shape designed is pressed against the quartz mold, which has been subjected to the mold release treatment, and after holding this state for a short time, it remains as it is. The resin was cured by irradiating with UV light in this state to prepare a fine structure B42.

Here, as described above, the difference in refractive index at each interface of the substrate 40 and the microstructure B42, the upper conductive film 43 and the microstructure A41, etc. is preferably adjusted to 0.1 or less. 05 or less is more desirable.

Further, when it is necessary to improve the adhesion of each layer, it is also possible to perform primer treatment and provide an adhesion layer at each interface. Further, in order to apply the primer solution more uniformly as long as it does not adversely affect the underlying layer, a hydrophilization treatment with UV ozone or the like may be performed before the application of the primer solution. Further, when coating by such a process, it is possible to limit the coating 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 well, as described above, the difference in refractive index at each adjacent interface is preferably adjusted to 0.1 or less, more preferably 0.05 or less.

Similarly, by forming a UV cut film as produced in Example 2 on, for example, a substrate 40, it is possible to obtain a panel to which a UV cut function is added, which is described in Example 3. It is also possible to apply the various optical films to these panels.

Further, not limited to these, other optical devices and optical devices are also arranged at a pitch shorter than the visible wavelength, which has different aspect ratios on both sides of the substrate as described in Examples 1 to 3. By using an optical filter having a fine structure having a reflected reflection reducing effect, it is possible to increase the rigidity against an external force while maintaining a sufficient reflection reducing effect.

For example, if the optical filter has a scene in which the filter changes its relative position with the surroundings, such as when the filter is taken in and out depending on the conditions, it may come into contact with some member during driving. By appropriately arranging the optical filters 1 to 3 as appropriate, it is possible to realize an optical device having improved durability against contact with the outside while maintaining very small 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 (6)

A microstructure A arranged at a pitch shorter than the visible wavelength is provided on the outermost surface layer on one side of the transparent substrate having an opportunity to contact the outside.
A microstructure B arranged at a pitch shorter than the visible wavelength is provided on the outermost surface layer on the other surface side of the substrate, which has no opportunity to contact the outside.
An optical filter characterized in that the aspect ratio of the microstructure A is smaller than the aspect ratio of the microstructure B. Between the substrate and the microstructure A,
Alternatively, between the substrate and the microstructure B,
The optical filter according to claim 1, wherein an optical film is formed. The optical film is characterized by having one or more functions of an AR film, an IR cut film, a UV cut film, an ND film, a color filter film, a fluorescent filter film, and a water vapor barrier film.
The optical filter according to claim 2. The fine structure is characterized in that the refractive index is lower than that of the substrate.
The optical filter according to any one of claims 1 to 3. A close contact layer is provided at a part of the interface of each layer constituting the optical filter.
The optical filter according to any one of claims 1 to 4. An optical device comprising the optical filter according to any one of claims 1 to 5.

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