JP2026000294A - Optical element, roll master, and method for manufacturing optical element - Google Patents

Abstract

The present invention provides an anti-reflection film that ensures anti-reflection properties against incident light in a wide wavelength range from the visible light region to the near-infrared region, as well as against obliquely incident light at a high angle.
[Solution] The optical element comprises a substrate 11 and a plurality of convex structures 3 arranged on at least one surface of the substrate 11 at a pitch equal to or less than the wavelength band of visible light, the structures 3 having a composite structure consisting of a first tapered portion 31 formed on the surface of the substrate 11 and a second tapered portion 32 formed on the first tapered portion 31, the taper ratio _C2 of the second tapered portion 32 being smaller than the taper ratio _C1 of the first tapered portion 31, the second tapered portion 32 having a needle-like tapered shape thinner than the first tapered portion 31, and the height h of the structures 3 being 400 nm or more.
[Selected Figure] Figure 2

Description

The present invention relates to an optical element, a roll master, and a method for manufacturing an optical element.

In recent years, the applications of film-like optical elements with anti-reflection properties (anti-reflection films) have expanded. Anti-reflection films are used in a variety of devices, such as display devices installed in smartphones or personal computers, in-vehicle cameras for autonomous driving technology, and cameras in devices that use virtual reality (VR) or augmented reality (AR).

In addition, one type of microfabrication technology being developed is imprinting, in which a roll master with a fine uneven structure formed on its outer peripheral surface is pressed against a film substrate, and the fine uneven structure of the roll master is transferred to the resin layer of the film substrate. Using this imprinting technology, it is possible to transfer, for example, a fine uneven structure (a so-called moth-eye structure) arranged at a period (pitch) equal to or smaller than the wavelength of visible light to the resin layer of a transparent film substrate. This provides anti-reflective properties to the film substrate, enabling efficient mass production of anti-reflective films.

The micro-relief structure on the surface of such anti-reflection films causes the refractive index to change gradually with respect to incident light, making it less likely that abrupt changes in refractive index that cause reflection will occur. Therefore, by providing anti-reflection films in the necessary locations on the various devices listed above, it is possible to suppress reflection of incident light.

As an example of such an anti-reflection film, Patent Document 1 discloses an optical element having a plurality of structures each having an elliptical cone or frustum of an elliptical cone shape. Furthermore, Patent Document 2 discloses an optical element having a plurality of structures each having a cone shape, in which the effective refractive index of the structures in the depth direction gradually increases toward the substrate of the optical element, forming an S-shaped curve.

Patent No. 4404161 Patent No. 5257066

As the applications of devices to which anti-reflection films are applied expand, some applications of the devices require the ability to detect light in a wide wavelength band (e.g., 380-950 nm) from the visible light range to the near-infrared range. For example, a camera mounted on the windshield of a vehicle must be able to properly detect and capture images of the surrounding environment in dark places, such as when driving at night. Furthermore, in wearable devices such as VR or AR, an eye-tracking camera is installed in a dark, light-blocking area within the device's housing. Therefore, the eye-tracking camera must be able to detect a person's eye movements and facial expressions even in dark places within the housing. Therefore, when an anti-reflection film is installed on an anti-reflection-treated area of the windshield where the in-vehicle camera is installed, or on the cover glass of the eye-tracking camera, the anti-reflection film must be able to exhibit anti-reflection properties for light in a wide wavelength band from the visible light range to the near-infrared range.

However, due to the structure of automobiles, windshields are positioned at an extreme incline, and an on-board camera is installed behind this inclined windshield. Therefore, when applying an anti-reflection film to an inclined windshield to prevent reflection, the angle of incidence of light on the anti-reflection film can be very high, for example, around 45° to 70°. In such cases, the anti-reflection film must be able to exhibit anti-reflection properties against light that is obliquely incident at such a high angle. Furthermore, since lightweight and compactness are essential for wearable devices such as VR, the camera must be installed close to the face and be able to detect a wide area of the face. Therefore, even in this case, the anti-reflection film used in such cameras must be able to exhibit anti-reflection properties against light that is obliquely incident at a high angle, for example, around 45° to 70°.

However, the conventional anti-reflection films described in Patent Documents 1 and 2 above were unable to adequately handle light in a wide wavelength range from the visible light region to the near-infrared region, and had the problem of reduced anti-reflection properties in some wavelength ranges. Furthermore, these conventional anti-reflection films also had the problem of reduced anti-reflection properties for light incident obliquely at high angles of approximately 45° to 70°.

For example, in the anti-reflection film described in Patent Document 1, the multiple structures that make up the micro-relief structure have a simple elliptical cone or elliptical truncated cone shape. This prevents reflection of incident light in only a specific wavelength band, while a sub-reflection peak occurs for incident light in other wavelength bands, resulting in increased reflection. Furthermore, the anti-reflection film described in Patent Document 2 suppresses the sub-reflection peak and broadens the anti-reflection range in the visible light range compared to the simple elliptical cone shape of Patent Document 1, but it is difficult to prevent reflection of incident light in the near-infrared range. Furthermore, it is difficult to accommodate oblique incident light at high angles, for example, around 45° to 70°.

The present invention has been made in consideration of the above problems, and its object is to provide an optical element, a roll master, and a method for manufacturing an optical element that can ensure anti-reflection properties for incident light in a wide wavelength range from the visible light region to the near-infrared region, as well as for oblique incident light at high angles.

In order to solve the above problem, according to one aspect of the present invention,
A substrate;
a plurality of convex structures arranged on at least one surface of the substrate at a pitch equal to or smaller than the wavelength band of visible light;
Equipped with
the structure has a composite structure including a first tapered portion formed on a surface of the base material and a second tapered portion formed on the first tapered portion,
a taper ratio _C2 of the second tapered portion is smaller than a taper ratio _C1 of the first tapered portion;
the second tapered portion has a needle-like tapered shape that is thinner than the first tapered portion,
The height h of the structure is 400 nm or more.
An optical element is provided.

The structure may have a transition point where the taper ratio of the side surface of the structure changes at the junction between the top of the first tapered section and the bottom of the second tapered section.

the first tapered portion and the second tapered portion have a linearly tapered approximation shape;
The vertical cross-sectional shapes of the tapered surfaces of the first tapered portion and the second tapered portion may be substantially straight lines.

The height h of the structure may be 490 nm or more.

The height _h2 of the second tapered portion is 160 to 300 nm,
The height _h1 of the first tapered portion may be 150 to 500 nm.

In order to solve the above problems, according to another aspect of the present invention,
A roll master for manufacturing the optical element,
a cylindrical or columnar master substrate;
a first microrelief structure formed on the outer peripheral surface of the master substrate;
Equipped with
the first microrelief structure includes a plurality of recesses having an inverted shape of the structures of the optical element,
The recessed portion is
A roll master is provided, which has a composite structure consisting of a first tapered recess having an inverted shape of the first tapered portion, and a second tapered recess formed inside the first tapered recess and having an inverted shape of the second tapered portion.

In order to solve the above problems, according to another aspect of the present invention,
The method for manufacturing an optical element,
a step of manufacturing a roll master on which a first microrelief structure is formed;
a step of applying a resin layer made of a curable resin to a surface of the substrate of the optical element;
forming a second microrelief structure including the structures of the optical element on the resin layer by transferring the first microrelief structure of the roll master onto the resin layer;
Including,
the first microrelief structure includes a plurality of recesses having an inverted shape of the structures of the optical element,
The recessed portion is
A method for manufacturing an optical element is provided, which has a composite structure consisting of a first tapered recess having an inverted shape of the first tapered portion, and a second tapered recess formed inside the first tapered recess and having an inverted shape of the second tapered portion.

The step of manufacturing the roll master includes:
a film-forming step of forming a resist layer on an outer peripheral surface of a master substrate of the roll master;
an exposure step of irradiating the resist layer with laser light to form a latent image;
a developing step of developing the resist layer on which the latent image is formed to form a pattern in the resist layer;
an etching step of etching the master substrate using the resist layer on which the pattern has been formed as a mask to form a concave-convex pattern of the first fine concave-convex structure on the outer peripheral surface of the master substrate;
Including,
In the etching step, etching conditions may be changed during etching of the master substrate to form the recess having a composite structure consisting of the first tapered recess and the second tapered recess.

The present invention provides an optical element that can ensure anti-reflection properties for incident light in a wide wavelength range from the visible light region to the near-infrared region, as well as for obliquely incident light at high angles.

FIG. 1 is a partially enlarged cross-sectional view showing an optical film according to one embodiment of the present invention. FIG. 2 is a partially enlarged cross-sectional view showing the structure according to the embodiment. FIG. 3 is a plan view showing the fine concave-convex structure of the optical film according to the embodiment. FIG. 4 is a perspective view schematically illustrating the roll master according to the embodiment. FIG. 5 is a block diagram showing the configuration of an exposure device used in manufacturing the roll master according to the embodiment. FIG. 6 is a schematic view illustrating an exposure method for a roll master according to the embodiment. FIG. 7 is an explanatory diagram showing the correspondence between the exposure signal and the exposure pattern according to the embodiment. FIG. 8 is a process diagram showing the method for manufacturing a roll master according to the embodiment. FIG. 9 is a process diagram showing the method for manufacturing a roll master according to the embodiment. FIG. 10 is a process diagram showing a method for producing an optical film according to the embodiment. FIG. 11 is a process diagram showing a method for producing an optical film according to the embodiment. FIG. 12 is a schematic diagram showing the configuration of the transfer device according to the same embodiment. FIG. 13 is a schematic diagram showing a convex structure according to a comparative example. FIG. 14 is a schematic diagram showing a convex structure according to an example. FIG. 15 is a graph showing the relationship between the height h of the convex structures according to the example and the average reflectance Re _θ=70° in the wavelength band of 400 to 950 nm. FIG. 16 is a graph showing the relationship between the wavelength λ of incident light and the reflectance Re when the light is obliquely incident at a low angle of about 10°. FIG. 17 is a graph showing the relationship between the wavelength λ of incident light and the reflectance Re when the light is obliquely incident at a high angle of about 70°.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Dimensions, materials, and other specific values shown in these embodiments are merely examples to facilitate understanding of the invention and, unless otherwise specified, do not limit the present invention. Furthermore, in this specification and drawings, elements having substantially the same function and configuration are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present invention are not shown.

[1. Optical film configuration]
[1.1. Schematic configuration of optical film]
First, the schematic configuration of an optical film 1, which is an optical element according to one embodiment of the present invention, will be described with reference to Fig. 1. Fig. 1 is a partially enlarged cross-sectional view showing the optical film 1 according to this embodiment.

As shown in FIG. 1, the optical film 1 according to this embodiment is an example of an optical element and is a film-like optical element. The optical film 1 is a transparent optical film (anti-reflection film) with anti-reflection properties and is transparent to visible light. For example, the optical film 1 is a moth-eye film on whose surface a micro-relief structure 2 with anti-reflection properties is formed. Note that this embodiment mainly describes an example of an optical film 1 in which the micro-relief structure 2 is formed on one surface of the optical film 1, but the micro-relief structure 2 may also be formed on both surfaces (front and back) of the optical film 1.

Generally, when a periodic uneven structure is provided on the surface of a transparent film, diffraction occurs when light passes through the uneven structure, significantly reducing the linear component of the transmitted light. However, if the pitch of the uneven structure is shorter than the wavelength of the incident light (e.g., visible light or near-infrared light) that is being transmitted, diffraction does not occur, and effective anti-reflection properties can be obtained for incident light with a wavelength corresponding to the pitch and depth of the uneven structure. In this way, among uneven structures, a fine uneven structure 2 having a pitch equal to or shorter than the wavelength of visible light is also called a moth-eye structure.

By forming a microrelief structure 2 on the surface of optical film 1, reflection at the interface between optical film 1 and air can be effectively suppressed. For example, when optical film 1 is used in the windshield of the aforementioned automobile or in an eye-tracking camera for a wearable device such as a VR, it is necessary to appropriately suppress the reflection of visible light or near-infrared light incident at a high incident angle θ to maintain a good field of view for the camera. From this perspective, the refractive index n of optical film 1 is preferably 1.40 or more and 2.00 or less, and more preferably 1.43 or more and 2.00 or less. Furthermore, in optical film 1, the transmittance of light with a wavelength of 550 nm is preferably 94.0% or more, more preferably 98.0% or more, and particularly preferably 98.5% or more.

The surface region of the optical film 1 includes a concave-convex pattern region in which a fine concave-convex structure 2 is formed. The concave-convex pattern region is a transparent region (anti-reflection region) that is endowed with anti-reflection properties by the fine concave-convex structure 2. The fine concave-convex structure 2 consists of a plurality of convex structures 3 (convex portions) and concave portions 4 arranged at a pitch P that is equal to or less than the wavelength of visible light (e.g., 350 nm or less). Due to this fine concave-convex structure 2, the concave-convex pattern region of the optical film 1 has very low reflectance of incident light and high light transmittance.

The optical film 1 according to this embodiment can be used as an anti-reflection film in the various devices described above. The wavelength λ of light incident on the optical film 1 (incident light) is a wide wavelength band ranging from the visible light region to the near-infrared region. The wavelength λ of the incident light is, for example, 380 nm to 780 nm, preferably 380 nm to 950 nm, and more preferably 380 nm to 2000 nm.

Furthermore, the optical film 1 according to this embodiment is applicable not only to incident light (normal incident light: incident angle θ = 0°) incident from a direction perpendicular to the surface (XY plane) of the optical film 1 (Z direction), but also to oblique incident light (incident angle θ > 0°) incident from a direction inclined relative to the perpendicular direction. In particular, the optical film 1 according to this embodiment is applicable not only to oblique incident light incident at a high incident angle θ of, for example, 45° or more, but also to oblique incident light incident at an ultra-high incident angle θ of, for example, about 70°.

As such, the optical film 1 according to this embodiment exhibits anti-reflection properties for incident light over a wide wavelength range, from the visible light region to the near-infrared region, while also maintaining anti-reflection properties for obliquely incident light at high angles. The configuration that realizes the excellent anti-reflection properties of the optical film 1 is described in detail below.

[1.2. Layer structure of optical film]
Next, the layer structure of the optical film 1 according to this embodiment will be described in more detail with reference to FIG.

As shown in FIG. 1 , the optical film 1 includes, for example, a flexible, transparent substrate 11 and a transparent resin layer 12 laminated on at least one surface of the substrate 11. Thus, the optical film 1 according to this embodiment has, for example, a two-layer structure including the substrate 11 and the resin layer 12. However, the present invention is not limited to this example. A laminated structure of three or more layers may be formed by providing another intermediate layer, such as an adhesion layer (not shown) to enhance adhesion, between the substrate 11 and the resin layer 12. Alternatively, a laminated structure of three or more layers may be formed by providing resin layers 12, 12 on both the front and back surfaces of the substrate 11. A coating layer or the like may also be added to the surface of the resin layer 12. Alternatively, instead of separating the substrate 11 and the resin layer 12, the optical film may be integrally formed from the same material (e.g., glass or resin) to form a single-layer optical film.

The substrate 11 is a flexible, transparent film substrate. The substrate 11 may be composed of a single sheet-like transparent material, or may be composed of multiple sheet-like transparent materials laminated together. The thickness of the substrate 11 is selected appropriately depending on the application of the optical film 1, and it is preferable to impart flexibility, rigidity, thickness, etc. according to the application.

Examples of materials for the substrate 11 include transparent plastic materials and glass materials. More specifically, examples of plastic materials for the substrate 11 include polyethylene terephthalate (PET), methyl methacrylate (co)polymer, polycarbonate, styrene (co)polymer, methyl methacrylate-styrene copolymer, cellulose diacetate, cellulose triacetate, cellulose acetate butyrate, polyester, polyamide, polyimide, polyethersulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal, polyether ketone, and polyurethane. Examples of glass materials for the substrate 11 include soda-lime glass, lead glass, hard glass, quartz glass, and liquid crystal glass. However, the material for the substrate 11 is not particularly limited to the materials listed above.

When a plastic material is used as the substrate 11, a primer layer (not shown) may be provided by surface treatment to further improve the surface energy, coatability, slipperiness, flatness, etc. of the plastic material's surface. Examples of such a primer layer include organoalkoxymetal compounds, polyester, acrylic-modified polyester, and polyurethane. Furthermore, to achieve the same effect as providing a primer layer, the surface of the substrate 11 may be subjected to corona discharge treatment, UV irradiation treatment, etc.

The substrate 11 can be formed, for example, by stretching the above-mentioned resin or diluting it in a solvent, forming it into a film, and then drying it. The thickness of the substrate 11 is preferably selected appropriately depending on the application of the optical film 1, and is, for example, approximately 10 μm to 500 μm, preferably 50 μm to 500 μm, and more preferably 50 μm to 300 μm. When the thickness of the substrate 11 is 10 μm or more, the protective performance and durability of the optical film 1 are improved. On the other hand, when the thickness of the substrate 11 is 500 μm or less, the optical film 1 can be made lighter. Furthermore, the flexibility of the substrate 11 allows it to be curved and deformed. Therefore, the optical film 1 can be suitably attached to curved surfaces, and the durability of the optical film 1 can also be improved.

The resin layer 12 is a transparent resin layer laminated on the surface of the substrate 11. To suppress reflection within the optical film 1 and improve contrast, the refractive index of the resin layer 12 is preferably the same as that of the substrate 11. The resin layer 12 also preferably has the same transparency as the substrate 11. A concavo-convex pattern such as the micro-convex structure 2 is formed in the resin layer 12. In this embodiment, the micro-convex structure 2 is formed, for example, by transfer processing using a roll master, as described below.

The resin layer 12 is a layer formed from a curable resin. The resin layer 12 is formed, for example, from a cured product of a curable resin composition (transfer material) such as an energy ray-curable resin composition. In the process of forming the resin layer 12, first, an uncured energy ray-curable resin composition is applied as a transfer material to the surface of the substrate 11, and the concave-convex pattern of the microrelief structure 2 is transferred to the energy ray-curable resin composition. The curable resin composition is then cured by irradiation with energy rays. As a result, a resin layer 12 to which the concave-convex pattern of the microrelief structure 2 has been transferred is formed on the surface of the substrate 11.

An energy ray-curable resin composition is a resin that has the property of being cured by irradiation with energy rays. Here, the energy rays may be, for example, ultraviolet rays, electron beams, infrared rays, laser beams, visible light, ionizing radiation (X-rays, alpha rays, beta rays, gamma rays, etc.), microwaves, or high-frequency waves. From the standpoint of ease of handling, it is preferable to use, for example, an ultraviolet-curable resin composition as the energy ray-curable resin composition. An ultraviolet-curable resin composition is a resin that has the property of being cured by irradiation with ultraviolet rays.

The energy ray-curable resin composition may also contain fillers or functional additives, as needed. For example, the ultraviolet ray-curable resin composition may contain an acrylate or an initiator, and may also contain a monofunctional monomer, a bifunctional monomer, a polyfunctional monomer, etc.

In addition, the cured product of the energy ray-curable resin composition may have hydrophilic properties. For this reason, the energy ray-curable resin composition preferably contains one or more functional groups that have hydrophilic properties. Examples of such functional groups that have hydrophilic properties include a hydroxyl group, a carboxyl group, and a carbonyl group.

[1.3. Characteristics of the fine uneven structure]
Next, the characteristics of the microrelief structure 2 of the optical film 1 according to this embodiment will be described in more detail with reference to FIGS. 1 to 3. FIG. 2 is a partially enlarged cross-sectional view showing the microrelief structure 2 of the optical film 1 according to this embodiment. FIG. 3 is a plan view showing the microrelief structure 2 of the optical film 1 according to this embodiment. For ease of explanation, in the thickness direction (Z direction) of the optical film 1, the direction toward the substrate 11 (-Z direction) will be referred to as the downward direction or lower side, and the direction opposite the substrate 11 (+Z direction) will be referred to as the upward direction or upper side.

As shown in Figures 1 to 3, the microrelief structure 2 (moth-eye structure) according to this embodiment is composed of a plurality of convex structures 3 (convex portions) and a plurality of concave portions 4. The plurality of convex structures 3 and the plurality of concave portions 4 are formed in a resin layer 12 laminated on the surface of a substrate 11 of an optical film 1. By providing the microrelief structure 2 in the resin layer 12 in the concave-convex pattern region of the entire surface of the optical film 1, the surface of the concave-convex pattern region (XY plane) becomes the concave-convex surface of a moth-eye structure.

The convex structures 3 (convex portions) protrude in a direction (Z direction) perpendicular to the surface (XY plane) of the optical film 1. Multiple structures 3 are arranged on the surface (XY plane) of the substrate 11 at a pitch P that is equal to or less than the wavelength of visible light (e.g., 350 nm or less).

The recesses 4 are recessed portions formed between adjacent structures 3, 3. The recesses 4 are also arranged on the surface (XY plane) of the substrate 11 at a pitch P that is equal to or less than the wavelength of visible light (e.g., 350 nm or less).

The microrelief structure 2 according to this embodiment is characterized by the shape of the convex structures 3 (convex portions). The structures 3 according to this embodiment have a composite structure in which at least two tapered portions (a first tapered portion 31 and a second tapered portion 32) are stacked in the thickness direction (Z direction) of the optical film 1.

In detail, the structure 3 has a composite structure consisting of a first tapered portion 31 (lower tapered portion) and a second tapered portion 32 (upper tapered portion). The first tapered portion 31 and the second tapered portion 32 are structures having a tapered shape that becomes thinner with increasing distance from the substrate 11. The first tapered portion 31 is formed on the surface of the substrate 11 and forms the base of the bottom side of the structure 3. The second tapered portion 32 is formed on the first tapered portion 31 and forms the apex of the tip side of the structure 3.

The first tapered portion 31 has a tapered shape, such as a truncated cone shape, that narrows toward the upper side in the Z direction (the side opposite the substrate 11). The first tapered portion 31 in the example shown in Figures 1 and 2 is a truncated cone shape, but other truncated cone shapes are also acceptable. For example, the first tapered portion 31 may be an elliptical truncated cone shape, or any other truncated cone shape, such as a triangular truncated cone, a square truncated cone, a hexagonal truncated cone, or an octagonal truncated cone. Furthermore, the first tapered portion 31 is preferably a truncated cone shape that is symmetrical with respect to the central axis in the Z direction, but may also be a truncated cone shape that is asymmetrical with respect to the central axis.

The second tapered portion 32 has a tapered shape, such as a cone shape or a frustum shape, that narrows toward the upper side in the Z direction (the side opposite the substrate 11). While the shape of the second tapered portion 32 in the example shown in Figures 1 and 2 is a truncated cone shape, other truncated cone shapes are also acceptable. For example, the second tapered portion 32 may be an elliptical truncated cone shape, or any other truncated cone shape, such as a triangular truncated cone, a square truncated cone, a hexagonal truncated cone, or an octagonal truncated cone. Examples of truncated cone shapes include a flat-topped truncated cone shape, or a truncated cone shape with a convex or concave curved surface at the top. The shape of the second tapered portion 32 may also be a pyramid shape with a pointed apex, such as a cone shape or an elliptical cone shape, or any other pyramid shape, such as a triangular pyramid, a square pyramid, a hexagonal pyramid, or an octagonal pyramid. Furthermore, the second tapered section 32 preferably has a frustum or pyramid shape that is symmetrical with respect to the central axis in the Z direction, but may also have a frustum or pyramid shape that is asymmetrical with respect to the central axis.

A single structure 3 is formed by stacking the above-mentioned first tapered portion 31 and second tapered portion 32 one above the other. The bottom of the lower first tapered portion 31 is positioned on the surface of the substrate 11 or adjacent to that surface. The top of the lower first tapered portion 31 and the bottom of the upper second tapered portion 32 are joined.

2, when the diameter _φ1 of the bottom of the first tapered portion 31 is compared with the diameter _φ2 of the top of the first tapered portion 31 and the diameter _φ3 of the top of the second tapered portion 32, the relationship _φ1 > _φ2 > _φ3 holds. The diameter _φ2 of the top of the first tapered portion 31 is equal to the diameter of the bottom of the second tapered portion 32, and both are _φ2 .

In this embodiment, since the second tapered portion 32 has a frustum shape, the top of the second tapered portion 32 is a substantially flat surface, and the diameter _φ3 of the top (substantially flat top surface) of the second tapered portion 32 is greater than 0 ( _φ3 > 0). However, this is not limited to this example, and the top (curve surface) of the second tapered portion 32 may not be a flat surface, but may be a convex or concave curved surface. Furthermore, when the second tapered portion 32 has a cone shape, the tip of the second tapered portion 32 has a pointed shape, so the diameter _φ3 of the top of the second tapered portion 32 may be substantially zero ( _φ3 ≒ 0).

1 to 3 , in this embodiment, for example, a plurality of structures 3 are arranged without gaps on the surface (XY plane) of the substrate 11, and the bottoms of the first tapered portions 31 of adjacent structures 3 are in contact with each other. In this case, the arrangement pitch P of the structures 3 is substantially equal to the diameter _φ1 of the bottoms of the first tapered portions 31 (P≒ _φ1 ). By arranging a plurality of structures 3 without gaps in this manner, the packing rate of the structures 3 on the surface (XY plane) of the optical film 1 is increased, and the area of the flat surface where no structures 3 are present is reduced, thereby improving the antireflection properties. However, this is not limited to such an example. A plurality of structures 3 may be arranged on the surface (XY plane) of the substrate 11 with some gaps between them. In this case, the arrangement pitch P of the structures 3 is greater than the diameter _φ1 of the bottoms of the first tapered portions 31 (P> _φ1 ). The packing rate is the proportion of the area occupied by a plurality of structures 3 on the surface (XY plane) of the optical film 1 when the surface is viewed in plan.

[1.4. Characteristics of tapered shape and taper ratio]
Next, the tapered shapes and taper ratios of the first tapered portion 31 and the second tapered portion 32 according to this embodiment will be described in more detail.

As shown in Figures 1 and 2, the tapered shape of the first tapered section 31 is preferably an approximation of a linear taper, and the vertical cross-sectional shape of the tapered surface (side surface) of the first tapered section 31 is preferably a substantially straight line. Similarly, the tapered shape of the second tapered section 32 is preferably an approximation of a linear taper, and the vertical cross-sectional shape of the tapered surface (side surface) of the second tapered section 32 is preferably a substantially straight line.

Here, a linearly tapered approximate shape includes a linear tapered shape and a shape that is considered to be substantially a linear tapered shape. A linear tapered shape is a tapered shape in which the diameter of the tapered portion changes linearly. In a linear tapered shape, the vertical cross-sectional shape of the tapered surface consists of straight lines and does not include curves. A shape that is considered to be substantially a linear tapered shape is a shape that can be considered to be a linear tapered shape if the error range is allowed, even though there is a slight deviation within the error range from a perfect linear tapered shape due to molding errors when molding the tapered portion, etc.

The tapered shapes of the first tapered section 31 and the second tapered section 32 according to this embodiment are preferably linear tapered shapes, but they may be approximations of linear tapered shapes and do not have to be completely linear tapered shapes. In other words, as long as the vertical cross-sectional shape of the tapered surfaces of the first tapered section 31 and the second tapered section 32 is a tapered shape consisting essentially of straight lines, the vertical cross-sectional shape may be a tapered shape that includes partial curves or minute irregularities.

In this manner, the first tapered section 31 and the second tapered section 32 according to this embodiment have linearly tapered approximation shapes with different taper ratios C ₁ and C _2. By combining two different linearly tapered approximation shapes, it is possible to improve the anti-reflection properties for incident light in different wavelength bands, such as the visible light region and the near-infrared region.

Next, the taper ratios of the first tapered portion 31 and the second tapered portion 32 will be described. As shown in FIGS. 1 and 2, the taper ratio _C2 of the side surface of the upper second tapered portion 32 is smaller than the taper ratio _C1 of the side surface of the first tapered portion 31 ( _C2 < _C1 ). In other words, the second tapered portion 32 has a thinner tapered shape than the first tapered portion 31, and has a tapered, needle-like shape. From this perspective, the second tapered portion 32 can be said to have an elongated, needle-like structure. On the other hand, the first tapered portion 31 has a thicker tapered shape than the second tapered portion 32, and has a stable tapered shape that becomes thicker toward the substrate 11. From this perspective, the first tapered portion 31 can be said to have a relatively thick, base-like structure.

Here, the taper ratio _C1 of the first tapered portion 31 is calculated by the following formula (1), and the taper ratio _C2 of the second tapered portion 32 is calculated by the following formula (2). Here, _h1 is the height of the first tapered portion 31 in the Z direction, and _h2 is the height of the second tapered portion 32 in the Z direction.
C ₁ = (φ ₁ - _{φ 2} )/h ₁ ...(1)
C ₂ = (φ ₂ - _{φ 3} )/h ₂ ...(2)

The taper ratio _C1 of the first tapered portion 31 is preferably, for example, 0.30 to 0.75, and more preferably 0.30 to 0.65. This has the effect of improving the anti-reflection characteristics against obliquely incident light at high angles. The taper ratio _C2 of the second tapered portion 32 is preferably, for example, 0.10 to 0.18, and more preferably 0.12 to 0.18. This has the effect of improving the anti-reflection characteristics against obliquely incident light at high angles.

Furthermore, the ratio ( _C2 / _C1 ) of the taper ratio _C2 of the second taper section 32 to the taper ratio _C1 of the first taper section 31 is preferably 0.2 to 0.5, and more preferably about 0.5, which has the effect of improving the anti-reflection characteristics against obliquely incident light at a high angle.

As described above, the taper ratio _C1 of the first taper portion 31 is different from the taper ratio _C2 of the second taper portion 32, and _C2 is smaller than _C1 ( _C2 < _C1 ). In other words, the taper angle of the first taper portion 31 is larger than the taper angle of the second taper portion 32. Therefore, the inclination angle of the side surface (tapered surface) of the second taper portion 32 with respect to the XY plane is larger than the inclination angle of the side surface (tapered surface) of the first taper portion 31 with respect to the XY plane. As a result, the side surface (tapered surface) of the entire structure 3, which is the combination of the first taper portion 31 and the second taper portion 32, has a shape that is recessed near the center in the Z direction (the position of the change point 33).

The structure 3 has a change point 33 at which the taper ratio of the side surface (tapered surface) of the entire structure 3 changes discontinuously at the junction between the top of the first tapered portion 31 and the bottom of the second tapered portion 32. Below the change point 33 (junction position), the side surface of the structure 3 is the side surface of the first tapered portion 31 having a shape that approximates a linear taper, and has a constant taper ratio _C1 . On the other hand, above the change point 33 (junction position), the side surface of the structure 3 is the side surface of the second tapered portion 32 having a shape that approximates a linear taper, and has a constant taper ratio _C2 that is smaller than the taper ratio _C1 .

As described above, the structure 3 according to this embodiment has a composite structure made up of a first tapered section 31 and a second tapered section 32 having different taper ratios _C1 and _C2 , and a change point 33 where the taper ratios _C1 and _C2 clearly switch is provided on the side of the entire structure 3. This has the effect that the action of the two types of tapered structures, the first tapered section 31 and the second tapered section 32, can exhibit anti-reflection properties against incident light in a wide wavelength band including the visible light region and the near-infrared region, and against oblique incident light at a wide range of incident angles.

1.5. Height Characteristics of Structure
Next, the height h of the structure 3 according to this embodiment, the height h ₁ of the first tapered portion 31, and the height h ₂ of the second tapered portion 32 will be described in more detail.

2 , the height h of the structures 3 is the height of the structures 3 in the Z direction (thickness direction of the optical film 1). The height h of the structures 3 is the sum of the height _h1 of the first tapered portion 31 and the height _h2 of the second tapered portion 32 (h = _h1 + _h2 ). It is preferable that the heights h of the multiple structures 3 constituting the microrelief structure 2 are approximately the same, but there may be some error in the height h among the multiple structures 3.

The height h of such structures 3 is preferably 400 nm or greater. This ensures that the multiple structures 3 constituting the microrelief structure 2 have a height h suitable for anti-reflection, ensuring anti-reflection properties not only for incident light in the short-wavelength visible light range, but also for incident light in the long-wavelength near-infrared range, and for oblique incident light at a wide range of angles of incidence.

Furthermore, the height h of the structures 3 is preferably 490 nm or greater, and even more preferably 560 nm or greater. This ensures anti-reflection properties for incident light in an even wider wavelength range, from the visible light region to the near-infrared region.

The height h of the structures 3 is preferably 1500 nm or less, for example, at the visible range level, and more preferably 1000 nm or less. This has the effect of suppressing transfer defects.

The height _h2 of the second tapered portion is preferably 160 to 300 nm, and more preferably 190 to 230 nm, which has the effect of improving the anti-reflection characteristics at wide angles of incidence.

The height _h1 of the first tapered portion is preferably 150 to 500 nm, and more preferably 220 to 340 nm, which has the effect of improving anti-reflection properties while improving transfer defects.

The height h of the structures 3 may be the arithmetic mean value (average height) of the heights of the multiple structures 3 that make up the fine concave-convex structure 2. For example, the heights of the multiple structures 3 that make up the fine concave-convex structure 2 can be measured, and the arithmetic mean value (average height) of these measured values can be calculated as the height h. Similarly, the height _h1 of the first tapered portion 31 and the height _h2 of the second tapered portion 32 can also be calculated using the arithmetic mean value.

[1.6. Characteristics of structure placement]
Next, the arrangement of the plurality of structures 3 on the surface of the optical film 1 according to this embodiment will be described in more detail.

As shown in Figure 3, the planar shape (dot shape) of the structure 3 when projected onto the surface (XY plane) of the optical film 1 is, for example, circular, but is not limited to this example and may be any shape, such as an ellipse, an oval, or a polygon.

In the examples shown in Figures 1 to 3, the multiple structures 3 in the microrelief structure 2 have the same size, shape, and height h. However, the configuration of the structures 3 is not limited to this, and two or more types of structures 3 having different sizes, shapes, and heights may be formed on the surface of the resin layer 12.

The structures 3 and recesses 4 of the microrelief structure 2 (hereinafter sometimes referred to as the "reliefs of the microrelief structure 2") are periodically arranged on the surface (XY plane) of the substrate 11 at a predetermined pitch P. In this way, the microrelief structure 2 has a periodic structure in which multiple structures 3 and recesses 4 are periodically arranged on the XY plane. Here, the pitch P is the center-to-center distance (vertex-to-vertex distance) between adjacent structures 3, 3, as shown in Figures 2 and 3. In this way, the pitch P of the recesses and protrusions of the microrelief structure 2 refers to the period of the periodic structure of the microrelief structure 2.

The pitch P of the concave-convex structure 2 may be the arithmetic mean value (average pitch, average period) of the center-to-center distance between adjacent structures 3, 3 in the fine concave-convex structure 2. For example, several combinations of adjacent structures 3, 3 in the fine concave-convex structure 2 can be selected, the center-to-center distance between the structures 3, 3 in each combination can be measured, and the arithmetic mean value (average pitch, average period) of these measurements can be calculated as the pitch P. The concave-convex pattern of the fine concave-convex structure 2 can be observed using, for example, a scanning electron microscope (SEM) or a cross-sectional transmission electron microscope (cross-sectional TEM).

In this embodiment, to impart anti-reflection properties to visible light, the pitch P of the concave-convex structure 2 is equal to or less than the wavelength of visible light. The wavelength band of visible light is 360 nm to 830 nm, and the concave-convex structure 2 of this embodiment has a regular arrangement with a pitch P less than the wavelength band of visible light. From this perspective, the pitch P of the concave-convex structure 2 is, for example, 350 nm or less, preferably 250 nm or less, and may be, for example, approximately 200 nm. Furthermore, the pitch P of the concave-convex structure 2 is, for example, 100 nm or more, preferably 120 nm or more, and more preferably 130 nm or more. A pitch P of less than 100 nm is undesirable because it may be difficult to form the concave-convex structure 2. On the other hand, a pitch P of more than 350 nm is undesirable because the intensity of diffracted light may increase, causing external light to be diffracted on the surface on which the concave-convex structure 2 is formed, thereby reducing the anti-reflection effect. If the pitch P is 350 nm or less, the anti-reflection properties of the micro-relief structure 2 can be improved, and the desired anti-reflection effect can be achieved.

The aspect ratio (height h/pitch P) of the structures 3 of the microrelief structure 2 is preferably 0.66 or more and 1.96 or less, and more preferably 0.76 or more and 1.96 or less. An aspect ratio of 0.66 or more can improve low reflectivity characteristics. On the other hand, an aspect ratio of 1.96 or less can improve releasability when peeling the microrelief structure 2 from the roll master.

3, the size D of the structures 3 of the microrelief structure 2 is the size (dot size) of the planar shape of the structures 3 when the structures 3 of the microrelief structure 2 are projected onto the surface (XY plane) of the optical film 1. The size D of the structures 3 according to this embodiment is the same as the diameter _φ1 of the bottom of the first tapered section 31 described above (D= _φ1 ). For example, when the planar shape of the structures 3 is a circle, the size D of the structures 3 is the diameter of the circle, and when the planar shape of the structures 3 is an ellipse, the size D of the irregularities is the major axis of the ellipse.

The size D of the structures 3 is determined according to the exposure resolution when exposing the concave-convex pattern of the fine concave-convex structure to the outer peripheral surface of the roll master in the roll master manufacturing method described below. The size D of the structures 3 is equal to or less than the pitch P (e.g., 350 nm or less) (D≦P), and is preferably equal to the pitch P (D≒φ ₁ ≒P), for example, about 200 nm. For example, as shown in FIG. 3 , by making the size D of the structures 3 equal to the pitch P, multiple structures 3 can be densely arranged on the XY plane, thereby reducing the area of the gap between adjacent structures 3. The size D of the structures 3 may be the arithmetic average (average size) of the planar shapes of the multiple structures 3 constituting the fine concave-convex structure 2. For example, the planar shapes of the multiple structures 3 constituting the fine concave-convex structure 2 can be measured individually, and the arithmetic average (average size) of these measured values can be calculated as the size D.

Now, with reference to Figure 3, the arrangement of the concave-convex pattern of the micro-convex structure 2 on the surface (XY plane) of the optical film 1 according to this embodiment will be described in more detail. Note that in Figure 3, the X direction corresponds to the longitudinal direction of the optical film 1, the Y direction corresponds to the width direction of the optical film 1, and the Z direction corresponds to the thickness direction of the optical film 1.

As shown in Figure 3, on the surface of the optical film 1 according to this embodiment, multiple structures 3 of the microrelief structure 2 are arranged in a hexagonal lattice pattern. In the hexagonal lattice arrangement, multiple structures 3 are arranged at the vertices of a hexagonal lattice on the XY plane. In the example of Figure 3, the planar shape of the structures 3 is circular, but they may also be other shapes such as oval or polygonal.

Here, the multiple structures 3 are arranged along multiple tracks T that are parallel to one another. In other words, the multiple structures 3 are arranged along multiple rows of tracks T on the surface of the optical film 1.

The tracks T are virtual straight lines extending in a predetermined first direction (X direction) on the XY plane of the optical film 1 and indicate the arrangement direction of the concavo-convex pattern of the micro concavo-convex structure 2. A plurality of tracks T are arranged at predetermined intervals (track pitch P _T ) in a second direction (Y direction) perpendicular to the first direction (X direction). Here, the first direction is the direction in which the tracks T extend (hereinafter referred to as the "track extension direction"). The second direction is the direction in which the plurality of tracks T are arranged (hereinafter referred to as the "track pitch direction") and is perpendicular to the first direction. For example, as shown in FIG. 3 , the first direction (track extension direction) may be the longitudinal direction (X direction) of the optical film 1, and the second direction (track pitch direction) may be, for example, the width direction (Y direction) of the optical film 1. However, the present invention is not limited to this example, and the track extension direction may be any direction other than the longitudinal direction (X direction) of the optical film 1.

3, the dot pitch P _D is the pitch P (period) of a plurality of structures 3 arranged in the track extension direction (X direction) along the track T. The track pitch P _T is the mutual interval between a plurality of tracks T, T adjacent to each other in the track pitch direction (Y direction).

The dot pitch _PD and the track pitch _PT , like the pitch P described above, are equal to or less than the wavelength of visible light, for example, 350 nm or less, preferably 250 nm or less, and may be, for example, about 200 nm. Furthermore, _PD and _PT are, for example, 100 nm or more, preferably 120 nm or more, and more preferably 130 nm or more. This allows the fine uneven structure 2 to function as a so-called moth-eye structure that suppresses reflection of incident light in a wide wavelength range.

The dot pitch _PD and the track pitch _PT may be the same or different as long as they are within the above range. In the example of Fig. 3, the dot pitch _PD is larger than the track pitch _PT ( _PD > _PT ). For example, _PD = 230 nm and _PT = 150 nm.

Furthermore, in the hexagonal lattice arrangement of the microrelief structure 2 shown in Figure 3, the structures 3 are arranged at positions shifted by half a pitch (1/2P _D ) in the X direction between tracks T, T adjacent to each other in the Y direction. That is, the phases of the structures 3 arranged in the X direction between tracks T, T adjacent to each other in the Y direction are shifted by half a period (180°). Specifically, between two adjacent tracks T, T, the structures 3 arranged in one track T are arranged at the middle position (position shifted by half a pitch) in the X direction of the structures 3 arranged in the other track T. As a result, as shown in Figure 3, a plurality of structures 3 are arranged in a hexagonal lattice pattern in three adjacent rows of tracks T.

In this way, by shifting the arrangement of the structures 3 by half the pitch (½P _D ) for each track T, it is possible to arrange the plurality of structures 3 in a close-packed hexagonal lattice pattern on the XY plane. Therefore, it is possible to maximize the proportion of the area occupied by the plurality of structures 3 on the XY plane (the filling rate of the structures 3), thereby improving the anti-reflection function per unit area.

The arrangement of the projections and recesses of the micro-relief structure 2 is not limited to the hexagonal lattice example described above, and may be other arrangements. For example, the arrangement of the projections and recesses of the micro-relief structure 2 may be a square lattice arrangement in which the structures 3 are arranged at the vertices of a square lattice, or a rectangular lattice or other lattice arrangement. However, in order to pack the structures 3 most densely on the XY plane, a hexagonal lattice arrangement is preferable.

Furthermore, the shape of the track T is not limited to the linear track T example described above; for example, curved tracks such as arc-shaped tracks may be arranged concentrically. Tracks T of these shapes may also be made to wobble (meander). By making the track T wobble in this way, it is possible to suppress the occurrence of unevenness in appearance.

[1.7. Principle of anti-reflection properties]
Next, the principle by which the optical film 1 according to this embodiment has excellent anti-reflection properties against incident light in a wide wavelength range and obliquely incident light at a high angle will be described.

As described above, the optical film 1 according to this embodiment exhibits anti-reflection properties for incident light in a wide wavelength range from the visible light region to the near-infrared region, while also ensuring anti-reflection properties for obliquely incident light at a high angle, for example, approximately 45 to 70°. To achieve such excellent anti-reflection properties, each structure 3 in the microrelief structure 2 of the optical film 1 according to this embodiment has a composite structure (two-stage tapered structure) consisting of the first tapered portion 31 and the second tapered portion 32 described above. The second tapered portion 32 is needle-shaped and more elongated than the first tapered portion 31, and the taper ratio _C2 of the second tapered portion 32 is smaller than the taper ratio _C1 of the first tapered portion 31. Additionally, the height h of the structures 3 is 400 nm or greater, preferably 490 nm or greater.

To improve the anti-reflection properties for incident light in the short wavelength range, such as the visible light range, thin, needle-shaped convex structures (equivalent to the second tapered portion 32 described above) with a height of approximately 200 nm can be used, and these convex structures can be arranged at a pitch equal to or less than the wavelength of visible light (e.g., 380 nm). The fine uneven structure formed by such convex structures reduces the effective spatial refractive index on the surface of the optical film. Therefore, the interference effect of light waves in the visible light range weakens reflected light, improving the anti-reflection properties. However, using a fine uneven structure formed by convex structures with a height of approximately 200 nm described above will conversely deteriorate the anti-reflection properties for incident light in the near-infrared range (e.g., 800 nm to 950 nm).

Therefore, in order to achieve an anti-reflection structure that utilizes interference effects in response to each wavelength band of incident light, it is necessary to set the height of the convex structures in proportion to the wavelength λ of the incident light. Therefore, if the total height of the convex structures is around 200 nm, anti-reflection properties can only be achieved for incident light in the visible light range, and not for incident light in the near-infrared range.

Furthermore, the anti-reflection properties change depending on the angle of incidence θ of obliquely incident light (incident angle dependency), with oblique incidence at an extremely high angle of around 70°, causing the wavelength band in which the anti-reflection properties are effective to shift toward shorter wavelengths. Therefore, in order to accommodate both oblique incidence and long wavelength bands, it is necessary to ensure that the total height of the convex structures is sufficiently high.

Therefore, to prevent reflection of incident light with long wavelengths such as the near-infrared range, the total height of the convex structures should be 400 nm or more. This makes it possible to prevent reflection of light with long wavelengths of approximately 950 nm due to the interference effect between the waves of the incident light when the light is incident obliquely at an extremely high angle of approximately 70°. However, if the convex shape of the convex structures is a simple elliptical cone shape as described in Patent Document 1, the wave interference effect can only prevent reflection of incident light with long wavelengths, and the wave interference effect is weaker for incident light with short wavelengths such as the visible light range, resulting in a problem of poor anti-reflection properties.

Therefore, in the optical film 1 according to this embodiment, the height h of the convex structures 3 is set to 400 nm or more as described above, and a thin, needle-like second tapered portion 32 (needle-like structure) is provided at the tip side of the structures 3, and a composite structure consisting of the second tapered portion 32 and the first tapered portion 31 is adopted. In this case, a transition point 33 where the taper ratios _C1 and _C2 clearly change is formed at the junction between the first tapered portion 31 and the second tapered portion 32. The composite structure 3 produces two interference effects between light waves of different wavelength bands, making it possible to prevent reflection of incident light in the visible light range while also preventing reflection of incident light in the near-infrared range. Therefore, excellent anti-reflection properties can be exhibited for incident light in a wide wavelength band, from the visible light range to the near-infrared range.

In contrast, in the conventional technology described in Patent Document 2, the side shape of the structure changes smoothly, drawing an S-shaped curve, and there is no clear change point 33 like the side of the structure 3 according to this embodiment. With the conventional technology described in Patent Document 2, the change point of the wave interference effect is not clear, which poses the problem of weakening the anti-reflection properties due to the interference effect of waves in two different wavelength bands.

In this regard, the structure 3 according to this embodiment has a composite structure of two tapered portions 31, 32 with different taper ratios C ₁ and C ₂ , and there is a clear change point 33 where the taper ratios C ₁ and C ₂ change. Therefore, according to the structure 3 of this embodiment, it is possible to prevent reflection of incident light in a wide wavelength band from the visible light region to the near-infrared region, and also to prevent reflection of obliquely incident light at an ultra-high angle of about 70°.

[1.8. Uses of Optical Films]
The optical film 1 according to this embodiment can be applied to various devices, such as the above-described on-board camera for the autonomous driving technology of automobiles, a highly inclined windshield arranged adjacent to the on-board camera, an eye-tracking camera for a wearable device that uses VR or AR, a display device provided in a smartphone or personal computer, or the like, a cover glass thereof, or an optical component. However, without being limited to such examples, the optical film 1 may also be used as, for example, a shielding member such as a face shield or an eye shield, or an anti-reflection film for other applications. The optical film 1 may also be used as, for example, a surface plasmon filter, a light-emitting device, or any other optical component.

By applying the optical film 1 having the structure 3 according to this embodiment as an anti-reflection film to the various devices described above, the sensitivity of the image sensor of the camera installed in the device can be improved. This can improve the accuracy of autonomous driving using the camera and the operating accuracy of VR devices, etc., while also enabling the various devices to be made smaller and lighter.

[2. Structure of the roll master]
[2.1. Overall structure of roll master]
Next, the configuration of the roll master 100 used to produce the optical film 1 according to this embodiment will be described with reference to Fig. 4. Fig. 4 is a perspective view schematically showing the roll master 100 according to this embodiment.

As shown in FIG. 4, the roll master 100 according to this embodiment comprises a cylindrical or columnar master substrate 110 and a fine concave-convex structure 120 (convex-convex pattern) formed on the outer peripheral surface of the master substrate 110.

The roll master 100 according to this embodiment is a master used, for example, in roll-to-roll imprinting technology. In roll-to-roll imprinting technology, the outer peripheral surface of the roll master 100 is pressed against a strip-shaped optical film while the roll master 100 is rotating, thereby transferring the concave-convex pattern formed on the outer peripheral surface of the roll master 100 to the surface of the optical film. By using this type of imprinting technology, it is possible to efficiently manufacture a large-area optical film 1 to which the concave-convex pattern formed on the outer peripheral surface of the roll master 100 has been transferred.

The roll master 100 according to this embodiment is a roll-shaped master having a cylindrical or columnar shape. The outer peripheral surface of the roll master 100 serves as a molding surface for molding a concave-convex structure on the surface of the optical film 1. A concave-convex pattern that serves as a transfer pattern is arranged two-dimensionally on the outer peripheral surface of this roll master 100. The concave-convex pattern (first fine concave-convex structure) arranged on the outer peripheral surface of the roll master 100 and the concave-convex pattern (second fine concave-convex structure) arranged on the surface of the optical film 1 described above have an inverted concave-convex relationship. In other words, the shape, arrangement, arrangement pitch, etc. of the concave-convex pattern of the roll master 100 are the same as those of the concave-convex pattern of the optical film 1.

The master substrate 110 is, for example, a cylindrical or columnar member as shown in Fig. 4. The concave-convex pattern to be transferred (fine concave-convex structure 120) is formed on the outer peripheral surface of the master substrate 110. The master substrate 110 may be made of a glass material such as fused silica glass or synthetic silica glass, or may be made of a metal such as stainless steel, or a metal whose outer peripheral surface is coated with _SiO2 or the like.

However, it is preferable that at least the outer peripheral surface of the master substrate 110 is formed of a glass material such as quartz glass. Furthermore, it is even more preferable that the entire master substrate 110 is formed of a glass material such as quartz glass. The reason for this is that by forming the master substrate 110 from a glass material primarily composed of SiO ₂ , a fine concave-convex pattern can be easily formed on the outer peripheral surface of the master substrate 110 by etching with a fluorine compound. Specifically, a concave-convex pattern is formed on a resist layer provided on the outer peripheral surface of the master substrate 110 using laser lithography. Then, the outer peripheral surface of the master substrate 110 is dry-etched using the concave-convex pattern of the resist layer as a mask, thereby easily forming a concave-convex pattern on the outer peripheral surface of the master substrate 110. The master substrate 110 formed of a glass material is, for example, a transparent roll type.

The size of the master substrate 110 is not particularly limited, but the axial length (roll width) of the master substrate 110 may be, for example, 100 mm or more, and the outer diameter of the master substrate 110 may be, for example, 50 mm or more and 300 mm or less. Furthermore, if the master substrate 110 is cylindrical, the thickness of the cylinder may be, for example, 2 mm or more and 50 mm or less.

As shown in FIG. 4, a concave-convex pattern region 102 is provided on the outer peripheral surface of the master substrate 110 according to this embodiment. The concave-convex pattern region 102 is a cylindrical curved region provided around the entire circumference of the roll master 100 in the circumferential direction (hereinafter sometimes referred to as the "roll circumferential direction"), and occupies most of the outer peripheral surface of the master substrate 110. For example, the width of the concave-convex pattern region 102 in the roll width direction may be several hundred mm (e.g., 500 mm). The concave-convex pattern region 102 of such a roll master 100 corresponds to the concave-convex pattern region (the region where the fine concave-convex structure 2 is formed) of the optical film 1 described above.

[2.2. Configuration of the fine concave-convex structure of the concave-convex pattern region]
Next, with reference to FIG. 4, the fine concave-convex structure 120 formed in the concave-convex pattern region 102 on the outer peripheral surface of the roll master 100 according to this embodiment will be described in detail.

A microrelief structure 120 (first microrelief structure) is formed as a transfer pattern in the concave-convex pattern region 102 of the roll master 100. This microrelief structure 120 (first microrelief structure) of the roll master 100 has an inverted shape of the microrelief structure 2 (second microrelief structure) of the optical film 1. In other words, the recesses 130 of the microrelief structure 120 of the roll master 100 have an inverted shape corresponding to the convex structures 3 (convex portions) of the microrelief structure 2 of the optical film 1. Furthermore, the convex portions 140 of the microrelief structure 120 of the roll master 100 have an inverted shape corresponding to the recesses 4 of the microrelief structure 2 of the optical film 1.

In the example of the micro-relief structure 120 shown in Figure 4, a plurality of recesses 130 with circular planar shapes are formed in the recessed/relief pattern region 102 of the roll master 100. These recesses 130 are arranged in a hexagonal lattice pattern on the outer peripheral surface of the master substrate 110. The protrusions 140 are protruding portions provided between adjacent recesses 130, 130.

Each recess 130 has a composite structure consisting of an outer first tapered recess 131 and an inner second tapered recess 132. The second tapered recess 132 is formed in the center of the first tapered recess 131. The inner diameter of the second tapered recess 132 is smaller than the inner diameter of the first tapered recess 131. The second tapered recess 132 is positioned deeper than the first tapered recess 131.

The first tapered recess 131 is a relatively thick tapered recess, and has an inverted shape of the first tapered portion 31 of the structure 3 of the optical film 1 described above (see FIGS. 9 and 10 ). The second tapered recess 132 is a relatively thin tapered recess, and has an inverted shape of the second tapered portion 32 of the structure 3 of the optical film 1 described above (see FIGS. 9 and 10 ). The taper ratio and depth of the first tapered recess 131 are substantially the same as the taper ratio _C1 and height _h1 of the first tapered portion 31, respectively. Similarly, the taper ratio and depth of the second tapered recess 132 are substantially the same as the taper ratio _C2 and height _h2 of the second tapered portion 32, respectively.

In this way, the recesses 130 of the microrelief structure 120 of the roll master 100 have a composite structure consisting of first tapered recesses 131 and second tapered recesses 132, and have a shape corresponding to the composite structure of the structures 3 of the optical film 1. Therefore, by transferring the microrelief structure 120 consisting of multiple recesses 130 to the optical film 1, it is possible to appropriately form the microrelief structure 2 consisting of multiple structures 3 shown in FIG. 1 on the surface of the optical film 1. Details of the transfer of such a microrelief structure 120 will be described later.

Next, the arrangement of the multiple recesses 130 that make up the microrelief structure 120 will be described in detail. On the outer peripheral surface of the roll master 100 according to this embodiment, the multiple recesses 130 of the microrelief structure 120 are arranged in a hexagonal lattice pattern at a pitch P' that is equal to or less than the wavelength of visible light. The pitch P' of the recesses 130 of the microrelief structure 120 is the same as the pitch P of the structures 3 of the microrelief structure 2 of the optical film 1 described above. The pitch P' is equal to or less than the wavelength of visible light, and may be, for example, 350 nm or less, preferably 250 nm or less, and may be, for example, approximately 200 nm.

Here, similar to the hexagonal lattice arrangement of the structures 3 of the microrelief structure 2 described above (see FIG. 3), the recesses 130 of the microrelief structure 120 of the roll master 100 are also arranged along a plurality of tracks T' that are parallel to one another, as shown in the enlarged view of FIG. 4. The plurality of tracks T' are arranged at predetermined intervals (track pitch P _T ') in a second direction (track pitch direction) perpendicular to the first direction (track extension direction). For example, as shown in FIG. 4, the first direction (track extension direction) may be the roll circumferential direction, and the second direction may be the roll width direction.

Here, the dot pitch P _D ' is the pitch (period) of the multiple recesses 130 arranged along the track T' in a first direction (e.g., the roll circumferential direction). The track pitch P _T ' is the distance between the multiple tracks T' arranged adjacent to each other in a second direction (e.g., the roll width direction). The dot pitch P _D ' and track pitch P _T ' of the recesses 130 in the microrelief structure 120 are the same as the dot pitch P _D and track pitch P _T of the structures 3 in the microrelief structure 2 of the optical film 1 described above, respectively. For example, the dot pitch P _D ' may be 230 nm, and the track pitch P _T ' may be 150 nm.

In the hexagonal lattice arrangement of the microrelief structure 120 shown in Fig. 4, the recesses 130 are arranged at positions shifted by half a pitch (½P _D ') in the roll circumferential direction between tracks T', T' adjacent to each other in the roll width direction. In other words, the phases of the recesses 130 arranged in the roll circumferential direction are shifted by half a period (180°) between tracks T', T' adjacent to each other in the roll width direction.

By shifting the arrangement of the recesses 130 by half the pitch (½P _D ′) for each track T′ (i.e., for each rotation of the roll), the recesses 130 can be arranged in a close-packed hexagonal lattice pattern on the outer peripheral surface of the roll master 100. This makes it possible to maximize the proportion of the area occupied by the recesses 130 of the fine concave-convex structure 120 on the outer peripheral surface (the filling rate of the recesses 130). This improves the anti-reflection function per unit area of the optical film 1 to which the fine concave-convex structure 120 has been transferred.

Note that the various dimensions of the recesses 130 in the microrelief structure 120, such as the depth H', size D' (dot size), and aspect ratio (depth H'/arrangement pitch P'), are the same as the height h, size D (dot size), and aspect ratio (height h/arrangement pitch P) of the structures 3 in the microrelief structure 2 of the optical film 1 described above. Therefore, a detailed description of these dimensions will be omitted.

The above describes the fine concave-convex structure 120 formed in the concave-convex pattern region 102 of the roll master 100. By transferring the fine concave-convex structure 120 of this roll master 100 to the optical film 1, the above-mentioned fine concave-convex structure 2 (see Figures 1 to 3) can be suitably formed in the concave-convex pattern region of the optical film 1.

[3. Configuration of exposure equipment]
Next, the configuration of the exposure device 200 used in manufacturing the roll master 100 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a block diagram showing the configuration of the exposure device 200 used in manufacturing the roll master 100 according to this embodiment.

As shown in FIG. 5, the exposure device 200 includes a laser light source 201, a first mirror 203, a photodiode (PD) 205, a condenser lens 207, an electro-optic deflector (EOD) 209, a collimator lens 211, a second mirror 213, a movable optical table 220, a spindle motor 225, a turntable 227, and a control device 230.

The laser light source 201 is a light source that emits laser light 202 for exposing the roll master 100. The laser light source 201 may be, for example, a semiconductor laser light source that emits laser light with a wavelength in the blue light band of 400 nm to 500 nm. The laser light source 201 is controlled by the control device 230.

Laser light 202 emitted from laser light source 201 travels straight as a parallel beam and is reflected by first mirror 203. First mirror 203 is composed of a polarizing beam splitter, and has the function of reflecting one polarized component and transmitting the other polarized component. The polarized component that passes through first mirror 203 is photoelectrically converted by photodiode 205. The photoelectrically converted received light signal is input to laser light source 201. This allows laser light source 201 to adjust the output of laser light 202 based on feedback from the input received light signal.

The laser light 202 reflected by the first mirror 203 is guided to the deflection optical system. The deflection optical system includes a condenser lens 207, an electro-optical deflection element 209, and a collimator lens 211.

In the deflection optical system, the laser beam 202 is focused onto an electro-optical deflection element 209 by a focusing lens 207. The electro-optical deflection element 209 is an element that can control the irradiation position of the laser beam 202 at a distance of about nanometers. The electro-optical deflection element 209 makes it possible to finely adjust the irradiation position of the laser beam 202 on the master substrate 110 of the roll master 100. After the irradiation position of the laser beam 202 is adjusted by the electro-optical deflection element 209, the laser beam 202 is collimated again by a collimator lens 211. The collimated laser beam 202 is reflected by a second mirror 213 and directed horizontally onto the movable optical table 220.

The moving optical table 220 includes a beam expander (BEX) 221 and an objective lens 223. The roll master 100 is placed on a turntable 227. The turntable 227 supports the roll master 100 and can be rotated by a spindle motor 225.

The beam expander 221 shapes the laser light 202 guided by the second mirror 213 into the desired beam shape. The shaped laser light 202 passes through the objective lens 223 and is irradiated onto a resist layer formed on the outer peripheral surface of the master substrate 110 of the roll master 100.

When the master substrate 110 of the roll master 100 is irradiated with the laser beam 202, the spindle motor 225 rotates the turntable 227 and the master substrate 110 around the roll axis 110a, while the movable optical table 220 moves the irradiation position of the laser beam 202 in the axial direction of the roll master 100 (roll width direction). For example, with each rotation of the master substrate 110, the movable optical table 220 moves the irradiation position of the laser beam 202 by one feed pitch (track pitch) in the direction of arrow R (feed pitch direction). This allows the laser beam 202 to be irradiated spirally onto the outer peripheral surface of the master substrate 110, exposing the resist layer on the outer peripheral surface of the master substrate 110 along a spiral scanning trajectory. The irradiation position of the laser beam 202 may also be moved by moving either the laser head including the laser light source 201 or the turntable 227 supporting the roll master 100 along a slider.

The control device 230 also controls the emission of the laser beam 202 from the laser light source 201, thereby controlling the irradiation time and irradiation position of the laser beam 202. The control device 230 generates an exposure signal that controls the emission of the laser beam 202. The control device 230 may include, for example, a function generator that includes a signal generation circuit capable of generating a signal of any waveform. The control device 230 includes a formatter 231 and a driver 233.

The formatter 231 generates an exposure signal from the reference clock signal to control the emission of the laser beam 202. The exposure signal represents the concave-convex pattern to be formed on the outer peripheral surface of the roll master 100. The driver 233 controls the emission of the laser beam 202 from the laser beam source 201 based on the exposure signal generated by the formatter 231. For example, the driver 233 may control the laser beam source 201 so that the laser beam 202 is emitted when the exposure signal consisting of a rectangular pulse wave is at a high level. The spindle motor 225 also rotates the turntable 227 based on a rotation control signal generated from the reference clock signal. For example, the spindle motor 225 may control the rotation of the turntable 227 so that the turntable 227 rotates once during the period in which a predetermined number of pulses of the rotation control signal are input.

As described above, the laser light source 201 is controlled by an exposure signal generated by the control device 230, and the laser light 202 emitted from the laser light source 201 is irradiated onto the roll master 100 placed on the turntable 227. Furthermore, the spindle motor 225 rotates the turntable 227 on which the roll master 100 is placed based on the rotation control signal. Here, the exposure signal and the rotation control signal may be generated from a common reference clock signal and may be synchronized with each other.

The above describes an example configuration of the exposure device 200 according to this embodiment. The exposure device 200 according to this embodiment can expose the outer peripheral surface of the master substrate 110 of the roll master 100 to light, thereby precisely forming an exposure pattern (concave-convex pattern) of the desired shape.

[4. Exposure Method]
Next, an exposure method for exposing the outer peripheral surface of the master substrate 110 of the roll master 100 using the exposure device 200 will be described with reference to Fig. 6. Fig. 6 is a schematic diagram illustrating the exposure method for the roll master 100 according to this embodiment.

As shown in FIG. 6 , in the exposure method for the roll master 100 according to this embodiment, the exposure device 200 described above is used to irradiate the outer peripheral surface of the master substrate 110 with laser light 202 to form an exposure pattern. As described above, the exposure device 200 includes a laser light source 201 that emits laser light 202 and a control device 230 that controls the emission of the laser light 202.

In the exposure process, the master substrate 110 of the roll master 100 is rotated around the roll axis 110a, and the laser light source 201 of the exposure device 200 is moved in the roll width direction (the direction of arrow R in Figure 6) while irradiating the outer peripheral surface of the master substrate 110 with laser light 202. As a result, the laser light 202 is irradiated spirally onto the outer peripheral surface of the master substrate 110, and an exposure pattern of the desired shape can be formed in the desired area of the outer peripheral surface of the master substrate 110.

An exposure pattern corresponding to the fine uneven structure 120 is formed in the uneven pattern region 102 on the outer peripheral surface of the master substrate 110. The example in Figure 6 shows how the exposure pattern corresponding to the fine uneven structure 120 is formed by irradiating the uneven pattern region 102 with laser light 202 along a spiral irradiation trajectory.

Now, with reference to Figure 7, we will specifically explain the correspondence between the exposure signal used by the exposure device 200 according to this embodiment and the exposure pattern formed on the outer peripheral surface of the master substrate 110. Figure 7 is an explanatory diagram showing the correspondence between the exposure signal and the exposure pattern according to this embodiment.

As shown in Fig. 7 , in this embodiment, an exposure pattern in which circular dot patterns are arranged in a hexagonal lattice pattern is formed on the outer peripheral surface of the master substrate 110 by irradiating the laser beam 202 along a spiral irradiation locus. In this exposure pattern, circular dot patterns corresponding to the recesses 130 of the microrelief structure 120 are arranged in a hexagonal lattice pattern. These circular dot patterns are arranged along a plurality of rows of tracks T' arranged at a predetermined track pitch P _T '. Note that the planar shape of the dot pattern is not limited to the circular example shown in Fig. 7 , and may be, for example, an ellipse or an oval having a major axis direction in the extension direction of the tracks T'.

The exposure device 200 according to this embodiment uses, as the exposure signal, for example, a pulse wave signal that alternates between high and low levels at a predetermined cycle to form an exposure pattern consisting of multiple dot patterns arranged along the track T'. The cycle of the pulse wave signal is t. The exposure device 200 controls the irradiation of the laser light 202 so that a circular dot pattern is formed on the outer peripheral surface of the master substrate 110 when the exposure signal is at a high level.

Furthermore, in order to form an exposure pattern in which the dot pattern is arranged in a hexagonal lattice pattern as shown in FIG. 7 , the frequency of the exposure signal is set so that the exposure signal is shifted by ½ pulse (t/2) between tracks T′, T′ adjacent to each other in the roll width direction of the master substrate 110. In other words, while maintaining the continuity of the exposure signal, the phase of the exposure signal is inverted by 180° for each revolution of the spiral laser irradiation locus (i.e., for each track T′). As a result, the position of the dot pattern is shifted by 0.5 pitches (= (½) × P _D′ ) in the roll circumferential direction for each revolution of the dot pattern arranged spirally in the roll circumferential direction (i.e., for each track T′). In this way, an exposure pattern in which the dot pattern is precisely arranged in a hexagonal lattice pattern can be formed on the outer peripheral surface of the master substrate 110 using the spiral laser irradiation locus.

When the laser beam 202 is irradiated along a spiral irradiation path as described above, the length of one circumference of the master substrate 110 can vary from circumference to circumference due to processing errors in the master substrate 110. For this reason, if the exposure signal and the rotation control signal are not synchronized, the arrangement of the exposure pattern will be disrupted as the exposure progresses. Furthermore, the spindle motor 225 of the turntable 227 that rotates the master substrate 110 has fluctuations in rotation speed, and these fluctuations in rotation speed will disrupt the arrangement of the exposure pattern.

In this embodiment, the exposure signal and the rotation control signal are synchronized by sharing a reference clock on which they are based. This means that the frequency of the exposure signal is no longer limited to dividing or multiplying the rotation control signal, and can be set to any value. This makes it possible to continuously form the desired exposure pattern on the outer peripheral surface of the master substrate 110 while maintaining the continuity of the exposure signal. This prevents interruptions and disruptions to the exposure pattern in the exposure pattern of the micro-relief structure 120, in which multiple dot patterns are arranged in a hexagonal lattice pattern, and enables the exposure pattern to be continuously formed with high precision.

An example of forming a hexagonal lattice-shaped exposure pattern corresponding to the fine uneven structure 120 in the uneven pattern region 102 on the outer peripheral surface of the master substrate 110 has been described above with reference to Figure 7. As described above, according to this embodiment, an exposure pattern corresponding to the fine uneven structure 120 in the uneven pattern region 102 can be formed on the outer peripheral surface of the roll master 100 using the exposure device 200. Therefore, the exposure pattern can be formed easily and quickly, thereby reducing the manufacturing cost and manufacturing time of the roll master 100.

[5. Manufacturing method of roll master]
Next, a method for manufacturing the roll master 100 according to this embodiment will be described with reference to Fig. 8 and Fig. 9. Fig. 8 and Fig. 9 are process diagrams showing the method for manufacturing the roll master 100 according to this embodiment.

In this embodiment, the roll master 100 according to this embodiment is manufactured by forming a concave-convex pattern of the fine concave-convex structure 120 on the outer peripheral surface of the master substrate 110 using laser light lithography, which allows for highly accurate control of the irradiation position. By using such laser light lithography, it is possible to precisely control the arrangement of the concave-convex pattern of the fine concave-convex structure 120.

The method for manufacturing the roll master 100 according to this embodiment includes a film-forming step (S10), an exposure step (S12), a development step (S14), and an etching step (S16). First, in the film-forming step (S10), a resist layer 111 is formed on the outer peripheral surface of the master substrate 110. Next, in the exposure step (S12), a latent image 112 is formed by irradiating the resist layer 111 with laser light. Furthermore, in the development step (S14), the resist layer 111 on which the latent image 112 has been formed is developed to form a pattern in the resist layer 111. Thereafter, in the etching step (S16), the master substrate 110 is etched using the patterned resist layer 111 as a mask, thereby forming a concavo-convex pattern of the micro-convex structure 120 on the outer peripheral surface of the master substrate 110. Each step in the method for manufacturing the roll master 100 according to this embodiment is described below.

(S10) Film Forming Process In the film forming process, first, as shown in A of FIG. 8, a master substrate 110 of the roll master 100 is prepared. The master substrate 110 is, for example, a cylindrical or columnar glass master. Next, as shown in B of FIG. 8, a resist layer 111 is formed on the outer peripheral surface of the master substrate 110. The resist layer 111 contains an inorganic or organic material capable of forming a latent image 112 by laser light. As the inorganic material, for example, a metal oxide containing one or more transition metals such as tungsten or molybdenum can be used. Furthermore, a resist layer containing an inorganic material can be formed by, for example, a sputtering method. On the other hand, as the organic material, for example, a novolac resist or a chemically amplified resist can be used. Furthermore, a resist layer containing an organic material can be formed by, for example, a spin coating method.

(S12) Exposure Step Next, in the exposure step, as shown in C of Fig. 8 , a laser beam 202 is irradiated onto the resist layer 111 formed on the outer peripheral surface of the master substrate 110. Specifically, the roll master 100 is placed on the turntable 227 of the exposure device 200 shown in Fig. 5 , and the roll master 100 is rotated while the laser beam 202 (exposure beam) is irradiated onto the resist layer 111. At this time, the laser beam 202 is irradiated onto the resist layer 111 while moving in the axial direction (roll width direction) of the roll master 100, thereby exposing the resist layer 111 along a spiral irradiation locus. As a result, a latent image 112 corresponding to the irradiation spot of the laser beam 202 is formed on the resist layer 111.

In this embodiment, laser light 202 is intermittently irradiated along a spiral irradiation trajectory onto the concave-convex pattern region 102 in the center of the roll width direction on the outer circumferential surface of the roll master 100. This exposes the entire surface of the resist layer 111 in the concave-convex pattern region 102 with an exposure pattern corresponding to the fine concave-convex structure 120 (for example, a pattern in which the circular dot pattern shown in Figure 7 is arranged in a hexagonal lattice pattern). As a result, a latent image 112 of the exposure pattern corresponding to the fine concave-convex structure 120 is formed in the resist layer 111 in the concave-convex pattern region 102.

(S14) Development Step Next, in the development step, as shown in A of FIG. 9 , the resist layer 111 on which the latent image 112 is formed is developed using a developer. As a result, a pattern of openings 113 corresponding to the latent image 112 is formed in the resist layer 111. For example, if the resist layer 111 contains the inorganic material described above, an alkaline solution such as a TMAH (Tetramethylammonium Hydroxide) aqueous solution can be used to develop the resist layer 111. Furthermore, if the resist layer 111 contains the organic material described above, various organic solvents such as esters or alcohols can be used to develop the resist layer 111.

In the development process, for example, a developer is dropped onto the resist layer 111 while the roll master 100 is rotating, and the resist layer 111 is developed. As a result, multiple openings 113 are formed in the resist layer 111, as shown in Figure 9A. If the resist layer 111 is formed from a positive resist, the latent image 112 (exposed area) exposed to the laser light 202 dissolves faster in the developer than the non-exposed area, and a pattern of openings 113 corresponding to the latent image 112 (exposed area) is formed in the resist layer 111.

In this embodiment, openings 113 are formed in the concave-convex pattern region 102 in an opening pattern corresponding to the fine concave-convex structure 120 (for example, a pattern in which the circular dot pattern shown in Figure 7 is arranged in a hexagonal lattice pattern).

(S16) Etching Step Next, in the etching step, the outer peripheral surface of the master substrate 110 is etched using the pattern of the resist layer 111 in which the openings 113 have been formed as a mask. As a result, as shown in FIG. 9B, a concavo-convex pattern (fine concavo-convex structure 120) corresponding to the exposure pattern and the pattern of the openings 113 is formed on the outer peripheral surface of the master substrate 110. Etching of the master substrate 110 may be performed by either dry etching or wet etching. When the master substrate 110 is made of a glass material mainly containing SiO ₂ (for example, quartz glass), etching of the master substrate 110 may be dry etching using a fluorocarbon gas or wet etching using hydrofluoric acid or the like.

According to the etching process of this embodiment, a fine concave-convex structure 120 corresponding to the openings 113 is formed as a concave-convex pattern in the concave-convex pattern region 102 on the outer peripheral surface of the master substrate 110. The fine concave-convex structure 120 is, for example, a moth-eye structure in which a plurality of concave portions 130 and convex portions 140 are arranged in a hexagonal lattice pattern at a pitch P' on the nano-order (e.g., 350 nm or less) that is equal to or less than the wavelength of visible light.

As described above, the recess 130 has a composite structure consisting of a first tapered recess 131 and a second tapered recess 132. The first tapered recess 131 is a tapered recess formed on the outer periphery of the master substrate 110. The first tapered recess 131 is a tapered hole having a truncated cone shape that is thicker than the second tapered recess 132. The second tapered recess 132 is a needle-like tapered hole that is longer and thinner than the first tapered recess 131. The second tapered recess 132 is a tapered recess formed at the bottom of the first tapered recess 131. The taper ratio _C2 of the second tapered recess 132 is smaller than the taper ratio _C1 of the first tapered recess 131.

The microrelief structure 120 of the roll master 100 (see B in Figure 9) has an inverted shape of the microrelief structure 2 of the optical film 1 described above (see Figure 1). Therefore, the recesses 130 of the microrelief structure 120 have an inverted shape of the convex structures 3 (convex portions) of the microrelief structure 2, and the convex portions 140 of the microrelief structure 120 have an inverted shape of the recesses 4 of the microrelief structure 2. Of the recesses 130 of the microrelief structure 120 of the roll master 100, the first tapered recesses 131 have an inverted shape of the first tapered portions 31 of the structures 3 of the microrelief structure 2 of the optical film 1, and the second tapered recesses 132 have an inverted shape of the second tapered portions 32 of the structures 3.

To form recesses 130 having a composite structure consisting of first tapered recesses 131 and second tapered recesses 132 in the master substrate 110, the etching process (S16) according to this embodiment involves changing the etching conditions during etching when etching the outer peripheral surface of the master substrate 110 using an etching gas. For example, the etching rate in the depth direction of the recesses 130 can be changed by switching the etching gas during etching, for example, to CF4 gas, which has strong isotropic etching properties, or by changing the input power output or pressure. It is also effective to reform resist during etching and etch again. This allows the first tapered recesses 131 and second tapered recesses 132, which have different taper ratios, to be formed in the master substrate 110 in a single etching process.

As described above, in the etching process according to this embodiment, the resist layer 111, on which an opening pattern consisting of multiple openings 113 is formed, is used as a mask to simultaneously etch the entire outer peripheral surface of the master substrate 110. This allows a fine concave-convex structure 120 (an anti-reflection concave-convex pattern) including multiple recesses 130 with a composite structure to be processed on the outer peripheral surface of the master substrate 110.

[6. Manufacturing method of optical film]
Next, a method for producing the optical film 1 according to this embodiment will be described with reference to Fig. 10 and Fig. 11. Fig. 10 and Fig. 11 are process diagrams showing the method for producing the optical film 1 according to this embodiment.

The method for manufacturing optical film 1 according to this embodiment includes a step (S20) of preparing roll master 100, a coating step (S22) of coating a resin layer 12A made of a curable resin on the surface of substrate 11 of optical film 1, a first transfer step (S24) of transferring a transfer pattern formed on the outer peripheral surface of roll master 100 to resin layer 12A of optical film 1, and a molding step (S28) of molding optical film 1 into a predetermined shape. Furthermore, when a concave-convex pattern is provided on both sides of optical film 1 (see FIG. 11), the method for manufacturing optical film 1 according to this embodiment may include a second coating and transfer step (S26) in addition to the above steps.

(S20) Roll master preparation step The roll master 100 preparation step may be, for example, each step (film formation step (S10), exposure step (S12), development step (S14), and etching step (S16)) of the method for manufacturing the roll master 100 according to this embodiment described with reference to Figures 8 and 9. By the method for manufacturing the roll master 100, a roll master 100 having a fine relief structure 120 formed on the outer peripheral surface is suitably prepared.

Coating step (S22)
In the coating step, an uncured resin layer 12A made of a curable resin (transfer material) is coated on the surface of the substrate 11 of the optical film 1. The curable resin (transfer material) is a resin material that has fluidity before curing, and is, for example, an energy ray-curable resin such as an ultraviolet-curable resin or a photocurable resin. In this embodiment, the transfer pattern of the roll master 100 is continuously transferred to the resin layer 12A of the optical film 1 by a roll-to-roll system, so the coating step (S22) and the subsequent transfer step (S24) are performed simultaneously in parallel.

(S24) Transfer Step In the transfer step (S24), the transfer pattern on the outer peripheral surface of the roll master 100 is transferred to one surface of the optical film 1. In detail, as shown in A of FIG. 10 , an uncured resin layer 12A (transfer material) applied to the substrate 11 of the optical film 1 is brought into close contact with the outer peripheral surface of the roll master 100. Thereafter, energy rays such as ultraviolet rays are irradiated onto the resin layer 12A from the light source 58 to cure the resin layer 12A. Thereafter, the substrate 11 integrated with the cured resin layer 12A (corresponding to the resin layer 12) is peeled off from the roll master 100.

This results in the optical film 1 shown in Figure 10B. In the optical film 1, a resin layer 12 is laminated on the surface of the substrate 11, and a microrelief structure 2 is formed on the surface of the resin layer 12. If necessary, an intermediate layer (not shown), such as an adhesion layer, adhesive layer, or base layer, may be further provided between the resin layer 12 and the substrate 11 of the optical film 1.

According to the transfer process of this embodiment, the transfer pattern (fine relief structure 120) on the outer peripheral surface of the roll master 100 is transferred to the resin layer 12 of the optical film 1, and a fine relief structure 2 is formed on the surface of the resin layer 12. In detail, the fine relief structure 120 of the relief pattern region 102 of the roll master 100 is transferred to the resin layer 12 of the optical film 1, and a fine relief structure 2 having anti-reflection properties is formed on the surface of the optical film 1.

The microrelief structure 120 of the roll master 100 and the microrelief structure 2 of the optical film 1 have mutually inverted recessed and recessed shapes. In the transfer process, the recesses 130 of the microrelief structure 120 of the roll master 100 form the convex structures 3 (convex portions) of the microrelief structure 2 of the optical film 1, and the convex portions 140 of the microrelief structure 120 of the roll master 100 form the recesses 4 of the microrelief structure 2 of the optical film 1.

Here, the recesses 130 of the microrelief structure 120 of the roll master 100 according to this embodiment have a composite structure (two-step tapered recess structure) consisting of a first tapered recess 131 and a second tapered recess 132, as shown in FIG. 10A. By transferring the recesses 130 to this two-step tapered recess structure, the structures 3 of the microrelief structure 2 of the optical film 1 have a composite structure (two-step tapered convex structure) consisting of a first tapered portion 31 and a second tapered portion 32, as shown in FIG. 10B.

By the above coating step (S22) and transfer step (S24), a fine relief structure 2 is formed in the resin layer 12 on one surface of the optical film 1, as shown in FIG. 10B. The resin layer 12 having the fine relief structure 2 may be provided on only one surface (one side) of the optical film 1, as shown in FIG. 10B, or may be provided on both surfaces (front and back) of the optical film 1, as shown in the following FIG. 11B. In the latter case, the second coating and transfer step (S26), which will be described next, may be carried out.

11A, after the first transfer step (S24), a resin layer 12A made of a curable resin is also applied to the other surface (rear surface) of the substrate 11 of the optical film 1. Next, the transfer pattern (fine relief structure 120) formed on the outer peripheral surface of the roll master 100 is transferred to the resin layer 12A on the other surface (rear surface) of the optical film 1.

Specifically, as shown in Figure 11A, an uncured resin layer 12A coated on the other surface of the film substrate 11 is brought into close contact with the outer peripheral surface of the roll master 100. Next, energy rays such as ultraviolet light are irradiated onto the resin layer 12A from the light source 58 to cure the resin layer 12A. Thereafter, the substrate 11 integrated with the cured resin layer 12A (corresponding to the resin layer 12) is peeled off from the roll master 100. This results in an optical film 1 in which resin layers 12 are laminated on both the front and back surfaces of the substrate 11 and a microrelief structure 2 is formed on the surface of the resin layer 12, as shown in Figure 11B.

(S28) Molding Step Next, in the molding step, the optical film 1 obtained in the transfer step (S24 or S26) is molded into a predetermined size and shape. For example, the optical film 1 is cut to a predetermined size, cut out into a desired shape, or punched into a desired shape using a mold. This allows the optical film 1 to be molded into a product (sheet product) suitable for the intended use. A cutting machine, a laser processing device, a punching press, or the like can be used for this molding process.

Next, with reference to Figure 12, we will explain the method for continuously transferring a transfer pattern from a roll master 100 to the optical film 1 using a roll-to-roll system in the manufacturing method of the optical film 1 according to this embodiment. Figure 12 is a schematic diagram showing the configuration of a transfer device 5 according to this embodiment.

As shown in FIG. 12, the transfer device 5 includes a roll master 100, a substrate supply roll 51, a take-up roll 52, guide rolls 53 and 54, a nip roll 55, a peeling roll 56, an application device 57, and a light source 58. In other words, the transfer device 5 shown in FIG. 12 is a roll-to-roll imprint transfer device.

The substrate supply roll 51 is, for example, a roll on which the substrate 11 of the optical film 1 is wound into a roll. The take-up roll 52 is a roll for winding up the optical film 1 having the microrelief structure 2 formed in the resin layer 12. The guide rolls 53 and 54 are rolls for transporting the substrate 11 before and after transfer. The nip roll 55 is a roll for pressing the substrate 11 coated with the uncured resin layer 12A against the outer peripheral surface of the roll master 100. The peeling roll 56 is a roll for peeling the substrate 11, on which the resin layer 12 to which the microrelief structure 120 has been transferred, from the roll master 100.

The coating device 57 applies a transfer material, for example, an uncured curable resin composition, to the substrate 11 to form an uncured resin layer 12A on the substrate 11. The coating device 57 may be, for example, a gravure coater, a wire bar coater, or a die coater. The light source 58 is a light source that emits light of a wavelength capable of curing the photocurable resin composition, such as an ultraviolet lamp.

The curable resin composition may be, for example, a photocurable resin that cures when irradiated with light of a specific wavelength. Specifically, the photocurable resin composition may be an ultraviolet-curable resin such as an acrylic resin acrylate or an epoxy acrylate. The photocurable resin composition may also contain initiators, fillers, functional additives, solvents, inorganic materials, pigments, antistatic agents, or sensitizing dyes, as needed.

The uncured resin layer 12A may be formed from a thermosetting resin composition. In this case, the transfer device 5 may be provided with a heat source (e.g., a heater) instead of the light source 58, and the resin layer 12A may be heated by the heat source to cure the resin layer 12A. The thermosetting resin composition may be, for example, a phenolic resin, an epoxy resin, a melamine resin, or a urea resin.

Next, we will explain the roll-to-roll transfer method using the transfer device 5 configured as described above.

First, the strip-shaped substrate 11 wound around the substrate supply roll 51 is unwound from the substrate supply roll 51 and continuously fed out via the guide roll 53. Next, a photocurable resin composition (transfer material) is continuously applied onto the surface of the substrate 11 by the coating device 57, and an uncured resin layer 12A is laminated on the substrate 11. Furthermore, the resin layer 12A laminated on the substrate 11 is pressed against the outer peripheral surface of the roll master 100 by the nip roll 55. As a result, the microrelief structure 120 formed on the outer peripheral surface of the roll master 100 is continuously transferred to the resin layer 12A.

The resin layer 12A onto which the microrelief structure 120 has been transferred is then cured by irradiation with light from the light source 58. As a result, an inverted structure of the microrelief structure 120 (for example, the microrelief structure 2 described above) is formed in the resin layer 12. The optical film 1, consisting of the resin layer 12 on which the microrelief structure 2 has been formed and the substrate 11, is then peeled from the roll master 100 by the peeling roll 56. The optical film 1 is then fed via the guide roll 54 to the take-up roll 52, where it is wound into a roll.

As described above, the transfer device 5 according to this embodiment can continuously transfer the microrelief structure 120 formed on the outer peripheral surface of the roll master 100 using a roll-to-roll method to produce the optical film 1. This allows for efficient mass production of the optical film 1.

Next, we will explain optical elements according to examples of the present invention. Please note that the following examples are merely examples intended to demonstrate the effects and feasibility of the optical elements according to the present invention, and the present invention is not limited to the following examples.

[1. Design and manufacturing conditions]
Optical films according to examples of the present invention and optical films according to comparative examples were designed and manufactured under the conditions described below, while changing the shape and dimensions of the convex structures of the fine uneven structure formed on the surface of the optical film.

Table 1 and Figures 13 and 14 show the design conditions for the convex structures of the microrelief structure (corresponding to the convex structures 3 of the optical film 1 according to the above embodiment) in the optical films of Examples 1 to 3, Comparative Examples 1 to 4, and the Reference Example. Table 1 also shows the results of measuring the average reflectance of the optical films of Examples 1 to 3, Comparative Examples 1 to 4, and the Reference Example when light in the visible to near-infrared range was obliquely incident. Furthermore, Figures 13 and 14 show images of the cross-sections of the microrelief structures that were actually manufactured, observed with a scanning electron microscope (SEM).

(1) Conditions common to Examples and Comparative Examples As shown in Table 1 and Figures 13 to 14, in all of Examples 1 to 3 and Comparative Examples 1 to 4, a fine uneven structure (moth-eye structure) was formed by regularly arranging a plurality of convex structures on the surface (XY plane) of the substrate of the optical film at a predetermined pitch P. However, in Examples 1 to 3 and Comparative Examples 1 to 4, the shapes and dimensions of the plurality of convex structures constituting the fine uneven structure were different from one another.

To manufacture the optical films according to Examples 1 to 3 and Comparative Examples 1 to 4, roll masters 100 (see Figure 4) according to Examples 1 to 3 and Comparative Examples 1 to 4 were first manufactured.

Specifically, as shown in Figure 8 above, first, in the film formation process (S10), a resist layer 111 was formed on the outer peripheral surface of the master substrate 110. Next, in the exposure process (S12), a latent image 112 was formed by irradiating the resist layer 111 with laser light. Furthermore, in the development process (S14), the resist layer 111 with the latent image 112 formed thereon was developed to form a pattern in the resist layer 111. Thereafter, in the etching process (S16), the master substrate 110 was etched using the patterned resist layer 111 as a mask, thereby forming a concavo-convex pattern of the fine concavo-convex structure 120 on the outer peripheral surface of the master substrate 110.

By changing the etching conditions in this etching step (S16), a microrelief structure 120 corresponding to various convex structures as shown in Figures 13 and 14 was formed on the outer surface of the master substrate 110. In this way, roll masters 100 corresponding to the optical films of Examples 1 to 3 and Comparative Examples 1 to 4 were manufactured.

Next, using the various roll masters 100 according to Examples 1 to 3 and Comparative Examples 1 to 4, roll-to-roll nanoimprinting was performed to transfer the fine relief structure to the surface of the optical film.

Specifically, as shown in FIG. 9 above, first, in the coating step (S22), a resin layer 12A made of a curable resin was coated on the surface of the substrate 11 of the optical film 1. Next, in the transfer step (S24), the fine concave-convex structure 120 formed on the outer peripheral surface of the roll master 100 was transferred to the resin layer 12A of the optical film 1, while the resin layer 12A was cured by irradiation with ultraviolet light. Thereafter, the optical film 1 was peeled from the roll master 100 to obtain an optical film 1 having a fine concave-convex structure 2 formed in the resin layer 12.

Here, a 125 μm-thick PET film (manufactured by Toyobo Co., Ltd., product name "A4360") was used as the substrate 11 of the optical film 1. Furthermore, a UV resin (manufactured by Dexerials Corporation, product name "SK1120"), a UV-curable acrylic resin composition, was used as the transfer material for forming the resin layer 12A of the optical film 1. Furthermore, a UV-LED device that irradiates ultraviolet light with a wavelength of 365 nm was used to cure the resin layer 12A.

In this manner, optical films according to Examples 1 to 3 and Comparative Examples 1 to 4 were produced. As shown in Table 1 and Figures 13 and 14, the shapes and dimensions of the convex structures differed from one another in Examples 1 to 3 and Comparative Examples 1 to 4, but the arrangement pitch P of the convex structures was all the same, 200 μm, and the size of the bottom of the convex structures (for example, the diameter φ ₁ of the bottom of the first tapered portion 31 of the structure 3 according to Examples 1 to 3) was also the same, 200 μm.

In the reference example shown in Table 1, an optical film consisting of only a substrate was used, and no convex structures were formed on the surface of the optical film. The substrate used in this reference example was a 125 μm thick PET film (manufactured by Toyobo Co., Ltd., product name "A4360").

(2) Conditions of the comparative example
<Comparative Example 1>
In Comparative Example 1, the convex structures of the microrelief structure of the optical film have a simple structure consisting of bell-shaped elliptical cones, as shown in Fig. 13. The convex structures of Comparative Example 1 correspond to the convex structures described in the above-mentioned Patent Document 1 (Japanese Patent No. 4404161). The overall height h of the convex structures of Comparative Example 1 is approximately 310 nm.

<Comparative Example 2>
In Comparative Example 2, the convex structures of the microrelief structure of the optical film are non-tapered composite structures, and the side surfaces of the convex structures have inflection points at the midpoints of the slopes, as shown in Fig. 13. The convex structures of Comparative Example 2 are convex structures in which bell-shaped structures are stacked in two tiers, one above the other. The overall height h of the convex structures of Comparative Example 2 is approximately 620 nm.

In order to manufacture an optical film having a two-tiered bell-shaped convex structure according to Comparative Example 2, a roll master according to Comparative Example 2 was manufactured. In the etching step (S16) for manufacturing the roll master of Comparative Example 2, the etching conditions were changed during etching of the master substrate 110, and a two-tiered bell-shaped concave structure having the above-mentioned inflection point was formed on the outer peripheral surface of the master substrate 110.

Specifically, in the etching step (S16) of Comparative Example 2, CHF3 gas was used as the etching gas to perform anisotropic etching. Then, during this etching, the gas was switched and etching was performed with CF4 gas. Next, etching was performed by switching to CHF3 gas. By switching the gas during etching, a recessed structure having a composite structure in which two bell-shaped recessed structures with different curved shapes and thicknesses were stacked one on top of the other was formed on the outer surface of the roll master. Then, the recessed structure with a two-tiered bell-shaped structure having an inflection point of the roll master was transferred to the resin layer of the optical film, thereby forming a convex structure with a two-tiered bell-shaped structure having an inflection point according to Comparative Example 2.

<Comparative Example 3>
In Comparative Example 3, the convex structure of the microrelief structure of the optical film has a composite structure in which two tapered structures (first tapered portion, second tapered portion) are stacked one above the other, as shown in Figure 13. As such, the convex structure of Comparative Example 3 has a composite structure (two-stage tapered structure) in which two tapered portions with different taper ratios are stacked one above the other, similar to the convex structure 3 according to the present embodiment (see Figure 1, etc.) and the convex structures of Examples 1 to 3 (see Figure 14). However, the overall height h of the convex structure of Comparative Example 3 is approximately 300 nm, which is shorter than the height h (400 nm or more) of the convex structures of Examples 1 to 3.

In order to manufacture an optical film having convex structures according to Comparative Example 3, a roll master according to Comparative Example 3 was manufactured. In the etching step (S16) for manufacturing the roll master of Comparative Example 3, the etching conditions were changed during etching of the master substrate 110, and concave structures having the above-mentioned two-step tapered structure were formed on the outer peripheral surface of the master substrate 110.

In detail, in the etching process (S16) of Comparative Example 3, CHF3 gas was used as the etching gas to perform anisotropic etching in the first step. Then, in the second step, the gas was switched during the etching process to CF4 gas for etching. By switching the gas during the etching process, a two-stage tapered concave structure having a composite structure in which two tapered sections with different taper ratios and thicknesses are stacked one on top of the other was formed on the outer surface of the roll master. The two-stage tapered concave structure of the roll master had a change point on its side where the taper ratio changed. The second tapered section of the two-stage tapered structure was formed in the first step, and the first tapered section was formed in the second step. The two-stage tapered concave structure of the roll master was then transferred to the resin layer of the optical film to form the two-stage tapered convex structure with a change point according to Comparative Example 3.

<Comparative Example 4>
In Comparative Example 4, similar to Comparative Example 3, the convex structures of the microrelief structure of the optical film have a composite structure in which two tapered structures (tapered portions) are stacked one above the other, as shown in Fig. 13. In this way, the convex structure of Comparative Example 4 also has a composite structure (two-stage tapered structure) in which two tapered portions with different taper ratios are stacked one above the other. However, the overall height h of the convex structure of Comparative Example 4 is approximately 353 nm, which is shorter than the height h (400 nm or more) of the convex structures of Examples 1 to 3.

In Comparative Example 4, as in Comparative Example 3, in the etching step (S16) for manufacturing the roll master of Comparative Example 4, the etching conditions were changed during etching of the master substrate 110, and a recessed structure having the above-mentioned two-stage tapered structure was formed on the outer peripheral surface of the master substrate 110.

Specifically, in the etching step (S16) of Comparative Example 4, CHF gas was used as the etching gas to perform anisotropic etching as the first step. Then, as the second step, the gas was switched during the etching process to perform etching with CF gas. By switching the gas during the etching process, a two-stage tapered concave structure having a composite structure in which two tapered portions with different taper ratios and thicknesses were stacked one on top of the other was formed on the outer circumferential surface of the roll master. The two-stage tapered concave structure having a change point on the roll master was then transferred to the resin layer of the optical film, thereby forming the two-stage tapered convex structure having a change point according to Comparative Example 4. The second tapered portion of the two-stage tapered structure was formed in the first step, and the first tapered portion was formed in the second step.
Thereafter, the concave structures of the roll master were transferred to the resin layer of the optical film, thereby forming convex structures having a two-step tapered structure according to Comparative Example 4.

(3) Conditions of the Example
Example 1
In Example 1, the convex structure of the fine concave-convex structure of the optical film is a composite structure in which two tapered structures (the first tapered portion 31 and the second tapered portion 32 shown in FIG. 2) are stacked one above the other, as shown in FIG. 14. In this way, the convex structure according to Example 1 has a composite structure (two-stage tapered structure) in which two tapered portions with different taper ratios are stacked one above the other. The overall height h of the convex structure according to Example 1 is approximately 413 nm.

In order to manufacture an optical film having the convex structures according to Example 1, a roll master according to Example 1 was manufactured. In the etching step (S16) for manufacturing the roll master of Example 1, the etching conditions were changed during etching of the master substrate 110, and the concave structures having the above-mentioned two-step tapered structure were formed on the outer peripheral surface of the master substrate 110.

In detail, in the etching process (S16) of Example 1, a mixture of CHF3 and CF4 gases was used as the etching gas in the first step to perform slightly isotropic anisotropic etching. Then, in the second step, the gas was switched during the etching process to perform etching with CF4 gas. By switching the gas during the etching process, a two-stage tapered concave structure was formed on the outer circumferential surface of the roll master. The two-stage tapered concave structure of the roll master had a transition point on its side where the taper ratio changed. The second tapered portion of the two-stage tapered structure was formed in the first step, and the first tapered portion was formed in the second step. The two-stage tapered concave structure of the roll master was then transferred to the resin layer of the optical film to form the two-stage tapered convex structure with a transition point according to Example 1.

Example 2
In Example 2, as in Example 1, the convex structures of the microrelief structure of the optical film are a composite structure in which two tapered structures (first tapered portion 31 and second tapered portion 32 shown in FIG. 2) are stacked one above the other, as shown in Figure 14. In this way, the convex structure of Example 2 has a composite structure (two-stage tapered structure) in which two tapered portions with different taper ratios are stacked one above the other. The overall height h of the convex structure of Example 2 is approximately 493 nm.

In Example 2, as in Example 1, in the etching step (S16) for manufacturing the roll master of Example 2, the etching conditions were changed during etching of the master substrate 110, and a recessed structure having the above-mentioned two-stage tapered structure was formed on the outer peripheral surface of the master substrate 110.

In detail, in the etching process (S16) of Example 2, a mixture of CHF3 and CF4 gases was used as the etching gas to perform slightly isotropic anisotropic etching in the first step. Then, in the second step, the gas was switched during the etching process to CF4 gas. By switching the gas during the etching process, a two-stage tapered recessed structure was formed on the outer surface of the roll master, with a composite structure in which two tapered sections with different taper ratios and thicknesses were stacked one on top of the other. The two-stage tapered recessed structure of the roll master had a transition point on its side where the taper ratio changed. The second tapered section with a two-stage tapered structure was formed in the first step, and the first tapered section was formed in the second step. In Example 2, the etching time in the second step was 30% longer than in Example 1, thereby increasing the height of the first tapered section. The two-step tapered concave structure of the roll master was then transferred to the resin layer of the optical film, thereby forming the two-step tapered convex structure having the change point according to Example 2.

As shown in the SEM image in Figure 14, the height of the convex structure produced in Example 2 is approximately 493 nm. It can be seen that the lower portion of the convex structure in Example 2 is a thick truncated cone-shaped tapered structure (first tapered portion 31), and above that, a thin, elongated cone-shaped tapered structure (second tapered portion 32) has grown in a needle-like shape.

Example 3
In Example 3, as in Example 1, the convex structure of the microrelief structure of the optical film is a composite structure in which two tapered structures (first tapered portion 31 and second tapered portion 32 shown in FIG. 2) are stacked one above the other, as shown in Figure 14. In this way, the convex structure of Example 3 has a composite structure (two-stage tapered structure) in which two tapered portions with different taper ratios are stacked one above the other. The overall height h of the convex structure of Example 3 is approximately 567 nm.

In Example 3, as in Example 1, in the etching step (S16) for manufacturing the roll master of Example 3, the etching conditions were changed during etching of the master substrate 110, and a recessed structure having the above-mentioned two-stage tapered structure was formed on the outer peripheral surface of the master substrate 110.

In detail, in the etching process (S16) of Example 3, a mixture of CHF3 and CF4 gases was used as the etching gas to perform slightly isotropic anisotropic etching in the first step. Then, in the second step, the gas was switched during the etching process to CF4 gas. By switching the gas during the etching process, a two-stage tapered recessed structure was formed on the outer surface of the roll master, with a composite structure in which two tapered sections with different taper ratios and thicknesses were stacked one on top of the other. The two-stage tapered recessed structure of the roll master had a transition point on its side where the taper ratio changed. The second tapered section with a two-stage tapered structure was formed in the first step, and the first tapered section was formed in the second step. In Example 3, the etching time in the second step was 50% longer than in Example 1, thereby increasing the height of the first tapered section. The two-step tapered concave structure of the roll master was then transferred to the resin layer of the optical film, thereby forming the two-step tapered convex structure having the change point according to Example 3.

As shown in the SEM image in Figure 14, the height of the convex structure produced in Example 3 is approximately 567 nm. It can be seen that the lower portion of the convex structure in Example 3 is a thick truncated cone-shaped tapered structure (first tapered portion 31), and above that, a slender conical tapered structure (second tapered portion 32) has grown in a needle-like shape.

2. Evaluation of anti-reflection properties
The optical film samples according to Examples 1 to 3 and Comparative Examples 1 to 4 produced as described above were subjected to a test to evaluate the antireflection properties.

In this evaluation test, the wavelength λ of the incident light was changed in 1 nm increments within the range of 400 to 950 nm, and the incident light of each wavelength λ was incident on the surface of each optical film sample (the finely textured surface on which the finely textured structure was formed) at an incident angle θ of 10° or 70°. The reflectance Re [%] of the incident light on the surface of the optical film at this time was measured using a spectroscopic reflectometer (manufactured by JASCO Corporation, product name "V770"). At this time, black tape was attached to the back of each optical film sample, and only the reflectance on the surface (finely textured surface) of each sample was measured.

The reflectance was determined as the average reflectance Re [%] of incident light with a wavelength λ of 400 to 950 nm. That is, the wavelength λ of the incident light was changed in 1 nm increments within the range of 400 to 950 nm, and the reflectance Re [%] for each wavelength λ was measured. The average of these 550 reflectances Re was calculated and used as the average reflectance Re. The incident angle θ of the incident light with respect to the surface of the optical film was set to 10° or 70°, and the average reflectance Re _θ=10° [%] when θ=10° and the average reflectance Re _θ=70° [%] when θ=70° were calculated. Furthermore, the average value Re_ave [%] for Re _θ=10° and Re _θ=70° was also calculated.

The thus determined Re _θ=10° , Re _θ=70° and Re_ave are shown in Table 1. Fig. 15 is a graph showing the relationship between the height h of the convex structure and the average reflectance Re _θ=70° in the wavelength band of 400 to 950 nm.

As shown in Table 1, the average reflectance Re _{θ=10° when} θ=10° is about 1%, which is similar in both Comparative Examples 1 to 4 and Examples 1 to 3. Therefore, it can be seen that in the case of oblique incidence at a low angle of incidence θ of about 10°, there is not much difference in antireflection properties between Comparative Examples 1 to 4 and Examples 1 to 3.

On the other hand, with regard to the average reflectance Re _θ=70° when θ=70°, as shown in Table 1 and FIG. 15, Re _θ=70° in Comparative Examples 1 to 4 was around 10%, which was poor. In contrast, Re _θ=70° in Examples 1 to 3 was 6.5% or less, which was a significant improvement compared to Comparative Examples 1 to 4. In particular, Re _θ=70° in Examples 2 and 3 was 5% or less, which was a significant improvement compared to Comparative Examples 1 to 4. If _{Re θ=70°} is 6.5% or less, there is an effect that the prevention of reflection from extremely oblique angles is superior to that of conventional technology. Furthermore, if Re _θ=70° is 5% or less, there is an effect that the anti-reflection properties are even better than those of a typical moth-eye lens.

As such, in Examples 1 to 3, excellent anti-reflection properties were achieved for obliquely incident light over a wide wavelength range of 400 to 950 nm, even in the case of high-angle oblique incidence of approximately 70°. The reasons for this are thought to be as follows:

In other words, in Examples 1 to 3, the height h of the convex structures having a two-step tapered structure is high, at 400 nm or more, and in Examples 2 and 3 in particular, the height h is even higher, at 490 nm or more. On the other hand, in Comparative Examples 3 and 4, although the convex structures have a two-step tapered structure similar to Examples 1 to 3, the height h of the convex structures is low, at approximately 350 nm or less. Therefore, in Comparative Examples 3 and 4, the anti-reflection properties for incident light in the long-wavelength near-infrared region deteriorate when the light is incident obliquely at a high angle of approximately 70°. In contrast, Examples 1 to 3 are equipped with convex structures with a high two-step tapered structure, which allows them to accommodate both long-wavelength near-infrared light and short-wavelength visible light. Therefore, compared to Comparative Examples 3 and 4, they are considered to have superior anti-reflection properties for incident light at a high angle of approximately 70° over a wide wavelength band.

In addition, in Comparative Example 2, the height h of the convex structures is 620 nm, which is higher than the height h of the convex structures in Examples 1 to 3, and therefore is capable of accommodating light in the long-wavelength near-infrared range. However, the shape of the convex structures in Comparative Example 2 is not a two-step tapered structure. Therefore, in Comparative Example 2, when light is incident obliquely at a high angle, it is unable to accommodate both the long-wavelength near-infrared range and the short-wavelength visible light range, and the anti-reflection properties are reduced. In Comparative Example 1, the height h of the convex structures is low and the shape of the convex structures is not a two-step tapered structure, so it is thought that the anti-reflection properties for light incident obliquely at a high angle are poor.

Next, referring to Figures 16 and 17, we will evaluate the relationship between the wavelength band of incident light (350-1000 nm) and anti-reflection properties. Figure 16 is a graph showing the relationship between the wavelength λ of incident light and the reflectance Re when the light is obliquely incident at a low angle of approximately 10°. Figure 17 is a graph showing the relationship between the wavelength λ of incident light and the reflectance Re when the light is obliquely incident at a high angle of approximately 70°.

As shown in Figure 16, at low-angle oblique incidence where the incident angle θ is approximately 10°, the reflectance Re of Comparative Examples 1 to 3 and Examples 2 and 3 is approximately 0 to 3%, across a wide wavelength band (350 to 1000 nm) from the visible light region to the near-infrared region, which is lower than the reflectance Re of the Reference Example (approximately 5 to 6%). This demonstrates that by providing a fine concave-convex structure having convex structures of various shapes, as in Comparative Examples 1 to 3 and Examples 2 and 3, it is possible to improve anti-reflection properties at low-angle oblique incidence. The reflectance Re of Comparative Example 4 is approximately 0 to 4%, which is lower than the reflectance Re of the Reference Example (approximately 5 to 6%), but higher than Examples 2 and 3.

On the other hand, as shown in Figure 17, when light is incident obliquely at a high angle, where the incident angle θ is approximately 70°, there was a difference in the anti-reflection properties between Comparative Examples 1 to 4 and Examples 2 and 3 over a wide wavelength range (350 to 1000 nm) from the visible light region to the near-infrared region.

Specifically, in the short-wavelength visible light range of 550 nm or less, Examples 2 and 3 have a very low reflectance Re of around 2%, while Comparative Examples 1 to 4 have a high reflectance Re of around 4 to 12%. Therefore, when incident light in the short-wavelength visible light range (350 to 550 nm) is obliquely incident at a high angle of around 70°, Examples 2 and 3 can exhibit better anti-reflection properties than Comparative Examples 1 to 3.

Furthermore, even in the near-infrared region of approximately 950 nm, the reflectance Re of Examples 2 and 3 is suppressed to 10% or less, which is less than half the reflectance Re of the Reference Example (approximately 18%). In contrast, the reflectance Re of Comparative Examples 1 to 4 is high, at approximately 12 to 15%. Therefore, it can be seen that Examples 2 and 3 can exhibit significantly better anti-reflection properties than Comparative Examples 1 to 4, even when incident light in the near-infrared region of approximately 950 nm is obliquely incident at a high angle of approximately 70°.

These results confirm that Examples 1 to 3 can exhibit excellent anti-reflection properties against incident light in a wide wavelength range from the visible light range (380-750 nm) to the near-infrared range (approximately 950 nm), and can ensure anti-reflection properties even when the incident light is obliquely incident at a high angle of approximately 70°. The convex structures of Examples 1 to 3 have a composite structure (two-stage tapered structure) in which the two tapered sections described above are stacked, and the height h of the convex structure is 400 nm or more, preferably 490 nm or more. Therefore, it is believed that anti-reflection properties can be ensured against incident light in a wide wavelength range from the visible light range to the near-infrared range, as well as against obliquely incident light at a high angle of approximately 70°.

Although the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such embodiments. It is clear that a person skilled in the art could conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

REFERENCE SIGNS LIST 1 Optical film 2 Fine concave-convex structure 3 Structure 4 Recess 5 Transfer device 11 Substrate 12 Resin layer 12A Uncured resin layer 31 First tapered portion 32 Second tapered portion 33 Change point 100 Roll master 102 Concave-convex pattern area 110 Master substrate 111 Resist layer 112 Latent image 113 Opening 120 Fine concave-convex structure 130 Recess 131 First tapered recess 132 Second tapered recess 140 Convex portion 200 Exposure device 201 Laser light source 202 Laser light

Claims (8)

A substrate;
a plurality of convex structures arranged on at least one surface of the substrate at a pitch equal to or smaller than the wavelength band of visible light;
Equipped with
the structure has a composite structure including a first tapered portion formed on a surface of the base material and a second tapered portion formed on the first tapered portion,
a taper ratio _C2 of the second tapered portion is smaller than a taper ratio _C1 of the first tapered portion;
the second tapered portion has a needle-like tapered shape that is thinner than the first tapered portion,
The height h of the structure is 400 nm or more.
Optical elements. The optical element described in claim 1, wherein the structure has a transition point where the taper ratio of the side surface of the structure changes at the junction between the top of the first tapered section and the bottom of the second tapered section. the first tapered portion and the second tapered portion have a linearly tapered approximation shape;
The optical element according to claim 1 , wherein the vertical cross-sectional shapes of the tapered surfaces of the first tapered portion and the second tapered portion are substantially straight lines. The optical element described in claim 1 or 2, wherein the height h of the structure is 490 nm or greater. The height _h2 of the second tapered portion is 160 to 300 nm,
3. The optical element according to claim 1, wherein the height _h1 of the first tapered portion is 150 to 500 nm. A roll master for producing the optical element according to claim 1 or 2, comprising:
a cylindrical or columnar master substrate;
a first microrelief structure formed on the outer peripheral surface of the master substrate;
Equipped with
the first microrelief structure includes a plurality of recesses having an inverted shape of the structures of the optical element,
The recess has a composite structure including a first tapered recess having an inverted shape of the first tapered portion, and a second tapered recess formed inside the first tapered recess and having an inverted shape of the second tapered portion. 3. A method for manufacturing an optical element according to claim 1 or 2, comprising:
a step of manufacturing a roll master on which a first microrelief structure is formed;
a step of applying a resin layer made of a curable resin to a surface of the substrate of the optical element;
forming a second microrelief structure including the structures of the optical element on the resin layer by transferring the first microrelief structure of the roll master onto the resin layer;
Including,
the first microrelief structure includes a plurality of recesses having an inverted shape of the structures of the optical element,
A method for manufacturing an optical element, wherein the recess has a composite structure consisting of a first tapered recess having an inverted shape of the first tapered portion, and a second tapered recess formed inside the first tapered recess and having an inverted shape of the second tapered portion. The step of manufacturing the roll master includes:
a film-forming step of forming a resist layer on an outer peripheral surface of a master substrate of the roll master;
an exposure step of irradiating the resist layer with laser light to form a latent image;
a developing step of developing the resist layer on which the latent image is formed to form a pattern in the resist layer;
an etching step of etching the master substrate using the resist layer on which the pattern has been formed as a mask to form a concave-convex pattern of the first fine concave-convex structure on the outer peripheral surface of the master substrate;
Including,
8. The method for manufacturing an optical element according to claim 7, wherein in the etching step, the recess having a composite structure consisting of the first tapered recess and the second tapered recess is formed by changing the etching conditions during etching of the master substrate.