JP6683214B2 - Anti-reflection structure - Google Patents

Description

  The present invention relates to a method for designing an antireflection structure having a moth-eye structure and an antireflection structure obtained by the method.

Observing a so-called moth-eye film having surface irregularities (that is, nanostructures) with a pitch below the visible light wavelength so that external light reflection is reduced and visibility is improved when observing observation objects such as displays and printed matter. It is provided on the surface of an object.
In addition to the observation object, it is also used by being provided on the surface of a light emitting element or the surface of an optical element such as a lens.

  In WO 2012/133394 (Patent Document 1), in order to improve antireflection properties in such a moth-eye film, it is described that the filling rate of the nanostructures is 65% or more, with 100% being the upper limit. ing. Here, the filling rate is the area of the bottom surface of the nanostructure with respect to the area of the unit cell of the array of nanostructures forming the moth-eye film.

  Further, in JP 2012-151012 A (Patent Document 2), in a transparent conductive element including an optical element having a moth-eye structure and a transparent conductive layer provided thereon, wavelength dependency is reduced to improve visibility. It is described that the area ratio of the flat portion is preferably set to 0 to 30% in order to improve. Here, the area ratio of the flat portion is the ratio of the remaining area obtained by subtracting the bottom area of the nanostructure from the unit lattice area of the moth-eye structure to the unit lattice area.

WO2012 / 133943 Publication JP 2012-151012 JP

  In the conventional moth-eye film, the reflectance on the long-wavelength side and the short-wavelength side of the visible light wavelength region increases depending on the shape and arrangement of the individual nanostructures constituting the moth-eye structure. The above-mentioned patent documents describe that the filling rate of the nanostructures or the area ratio of the flat portion influences the tint of the moth-eye film, but detailed studies have not been made.

  On the other hand, when a nanostructure is produced from a master using a resin, the viscosity of the resin strongly affects the reproducibility of the shape of the convex portion of the nanostructure to which the resin is transferred. That is, when the viscosity is high, the filling and the conformability to the irregularities provided on the master are insufficient, and the resulting nanostructure is lower in height than the nanostructure designed on the master. And the tip has a rounder tip than intended.

  Further, when the transfer is continuously performed by the master, there is a concern that the height of the nanostructure becomes small from the start to the end of the transfer due to the resin itself being buried in the recesses of the master. This problem is not limited to one original sheet when the original sheet of the moth-eye film is produced by continuously using the original sheet, and is continued in the other original sheets produced subsequently.

  The original fabric of the moth-eye film produced by transferring the nanostructures from the master is transported in a roll state or in a cut and sheeted state, but even during such handling However, problems such as the loss of nanostructures due to unnecessary friction occur. Similarly, the same kind of problem arises by the work of attaching the moth-eye film to the antireflection object. On the other hand, when the moth-eye film is provided on the surface of the substrate that is frequently contacted and worn, it may be possible to configure the moth-eye film with a resin having a low elastic modulus, but to eliminate the lack of nanostructures. Is not done.

  As described above, there is concern that the height of the nanostructure may vary or may be lost during each process of manufacturing, transporting, attaching, and using the moth-eye film. If the height of the nanostructures varies or is missing, the spectral reflectance changes, causing variations in tint. Therefore, there is a demand for a design method that keeps the variation in color tone within a certain range.

An object of the present invention is to find a design condition for an antireflection structure having a moth-eye structure so that the saturation √ (a ^{* 2} + b ^{* 2} ) of reflected light with respect to a white light source is as close to zero as possible. The object is to suppress or control the change of the tint of the object provided on the surface with respect to the original tint of the object.

In the antireflection structure having a moth-eye structure, the present inventor has found that the saturation of reflected light with respect to a white light source √ (a ^{* 2} ) when the height of each nanostructure constituting the moth-eye structure is within a specific range. The present invention was conceived by finding that + b ^{* 2} ) changes depending on the filling rate of the nanostructure and takes a minimum value at a specific filling rate.

That is, the present invention is a method for designing an antireflection structure in which a plurality of nanostructures formed by convex portions on the substrate surface are provided at intervals of a visible light wavelength or less, and the substrate surface of the nanostructure is flat. The average height from the part is 180 nm or more and 290 nm, preferably the variation in height is within 10%, and the nanostructure is the ratio of the area of the bottom surface of the nanostructure to the area of the substrate surface in plan view of the antireflection structure. The filling rate of the body is ± 5 of the filling rate at which the saturation has a minimum value in the relationship between the filling rate and the saturation √ (a ^{* 2} + b ^{* 2} ) of the reflected light with respect to the white light of the antireflection structure. %, More preferably in the range of 0 to -5%.

  In addition, the present invention is an antireflection structure in which a large number of nanostructures formed by convex portions on the surface of a substrate are provided at intervals of a visible light wavelength or less, and The average height is 180 nm or more and 290 nm or less, and the filling rate of the nanostructure, which is the ratio of the area of the bottom surface of the nanostructure to the area of the substrate surface in plan view of the antireflection structure, is 85% or more and less than 100%. An antireflective structure is provided.

  Here, the average height of the nanostructures is preferably 5 by an atomic force microscope (AFM) along the surface irregularities of the antireflection structure along any same direction in the plane of the antireflection structure. It is measured more than once and calculated from the average. The dispersion of individual measured values is calculated from the ratio of the difference between each measured value and its average to the average [(each measured value-average of each measured value) / average of each measured value] x 100 (%) ). Further, when the antireflection structure is formed into a long film shape by a transfer method using a roll-shaped transfer master, this measurement is preferably performed in the lateral direction. Hereinafter, the “average height of nanostructures” is abbreviated as “height of nanostructures”.

According to the method of designing an antireflection structure of the present invention, the saturation √ (a ^{* 2} + b ^{* 2} ) of the reflected light with respect to the white light source is as close to zero as possible in relation to the filling rate of the nanostructure. Therefore, it is possible to remarkably prevent the adherend of the antireflection structure from being colored unnecessarily.

In addition, according to the antireflection structure of the present invention, the saturation of the reflected light with respect to the white light source is √ (a ^{* 2} + b ^{* 2} ) even if the height of the nanostructure varies due to the manufacturing method. Is suppressed, it is possible to prevent the observed object to which the antireflection structure of the present invention is attached from being colored.

FIG. 1A is a perspective view of an antireflection structure 1A of an example. FIG. 1B is a top view of the antireflection structure 1A of the embodiment. FIG. 1C is a cross-sectional view of the antireflection structure 1A of the example. FIG. 2A is a relationship diagram of the filling factor of the nanostructure (height H180 nm) and the saturation √ (a ^{* 2} + b ^{* 2} ). FIG. 2B is a diagram showing the relationship between the filling factor of the nanostructure (height H200 nm) and the saturation √ (a ^{* 2} + b ^{* 2} ). FIG. 2C is a relationship diagram of the filling factor of the nanostructure (height H230 nm) and the saturation √ (a ^{* 2} + b ^{* 2} ). FIG. 2D is a diagram showing the relationship between the filling factor and the saturation √ (a ^{* 2} + b ^{* 2} ) of the nanostructure (height H290 nm). FIG. 2E is a diagram showing the relationship between the filling factor and the saturation √ (a ^{* 2} + b ^{* 2} ) of the nanostructure (height H150 nm). FIG. 3A is a top view of an antireflection structure 1B in which conical nanostructures are arranged in a four-way lattice. FIG. 3B is a relationship diagram between the filling rate of the nanostructures and the saturation √ (a ^{* 2} + b ^{* 2} ) in the antireflection structure 1B. FIG. 4A is a top view of an antireflection structure 1C in which elliptical cone-shaped nanostructures are arranged in a hexagonal lattice. FIG. 4B is a relationship diagram between the filling rate of the nanostructures and the saturation √ (a ^{* 2} + b ^{* 2} ) in the antireflection structure 1C. FIG. 5A is a top view of an antireflection structure 1D in which elliptical cone-shaped nanostructures are arranged in a four-sided lattice. FIG. 5B is a relationship diagram between the filling rate of the nanostructures in the antireflection structure 1D and the saturation √ (a ^{* 2} + b ^{* 2} ). FIG. 6 is a relationship diagram between the filling factor of the nanostructure and the saturation √ (a ^{* 2} + b ^{* 2} ) when the refractive index is 1.1 in the antireflection structure 1A. FIG. 7 is a relationship diagram between the filling factor of the nanostructure and the saturation √ (a ^{* 2} + b ^{* 2} ) when the refractive index is 3.0 in the antireflection structure 1A.

  Hereinafter, the present invention will be described in detail with reference to the drawings. In each figure, the same reference numerals represent the same or equivalent constituent elements.

  FIG. 1A is a perspective view of an antireflection structure 1A according to an embodiment of the present invention, FIG. 1B is a top view, and FIG. 1C is an xx sectional view thereof.

  This antireflection structure 1A has a moth-eye structure in which a large number of nanostructures 3 formed by convex portions on the surface of a transparent substrate 2 are arranged vertically and horizontally at a pitch of a visible light wavelength or less. More specifically, a large number of tracks T1, T2, T3 in which a large number of nanostructures 3 are arranged at a predetermined arrangement pitch Dp are arranged at a predetermined track pitch Tp, and the center of the nanostructures 3 is a hexagonal lattice. Are arranged in. Here, the arrangement pitch Dp is usually 150 nm or more and 270 nm or less, and the track pitch Tp is usually 130 nm or more and 190 nm or less.

  Further, each nanostructure 3 has a conical shape with a rounded top, and has a shape that can be seen as a bell shape, and its aspect ratio (height H of nanostructure / track pitch Tp) is 0.95. The above is 2.2 or less.

In the present invention, the shape of the nanostructure 3 is not limited to those classes to such conical or bell-shaped, elliptic conical, semi-spherical, semi-ellipsoid shape, columnar, needle-shaped, etc. Various Can take the form of.

Further, the array of the nanostructures can be a tetragonal lattice, a quasi-tetragonal lattice or a quasi-hexagonal lattice that is similar to these, in addition to the hexagonal lattice. Here, the hexagonal lattice is an array in which the center of the nanostructure is located at each corner and center of the regular hexagon. Further, the four-sided lattice is an array in which the center of the nanostructure is located at each corner of the square. The quasi-tetragonal lattice or the quasi-hexagonal lattice is a lattice which is distorted by stretching the tetragonal lattice or the hexagonal lattice in the track direction. It is similar to a 4-way lattice or a 6-way lattice. Further, even when the nanostructures are randomly arranged, the invention is applied by setting the filling rate to be the ratio of the area of the bottom surface of the nanostructure to the area of the substrate surface in plan view of the antireflection structure. You can That is, regardless of the regularity of the filling structure of the nanostructure, in the relationship between the filling rate of the nanostructure and the saturation √ (a ^{* 2} + b ^{* 2} ) of the reflected light with respect to the white light of the antireflection structure, The present invention can be applied as long as the saturation has a minimum value at a specific filling rate.

In this antireflection structure 1A, the height H of the nanostructure from the flat surface of the substrate surface is 180 nm or more and 290 nm or less, and the area of the bottom surface of the nanostructure 3 with respect to the area of the unit lattice of the array of the nanostructure 3 is The filling rate of the nanostructure, which is the ratio, is 85% or more and less than 100%. As a result, the saturation √ (a ^{* 2} + b ^{* 2} ) of the reflected light of the antireflection structure 1A with respect to the white light source is as close to zero as possible in relation to the filling rate of the nanostructure 3, and the antireflection structure When the body 1A is provided on the surface of the adherend and the adherend is observed, the adherend can be prevented from being unnecessarily colored and observed. This means that the refractive index of the substrate 2 is at least 1.1 or more and 3.0 or less, and the height H of the nanostructure 3 from the flat surface of the substrate 2 is 180 nm or more and 290 nm or less. In this case, in the relationship between the filling rate of the nanostructures 3 and the saturation √ (a ^{* 2} + b ^{* 2} ) of the antireflection structure 1A, the filling rate of the nanostructures 3 is 85% or more and less than 100%. This is based on the finding by the present inventor that the saturation √ (a ^{* 2} + b ^{* 2} ) has a minimum value.

That is, FIG. 2 shows that in the antireflection structure 1A in which the conical or bell-shaped nanostructures 3 shown in FIG. 1A are arranged in a 6-direction lattice, the height H of the nanostructures 3 is 180 nm and the refraction of the substrate 2 is small. FIG. 6 is a relationship diagram between the filling rate of the nanostructures 3 and the saturation √ (a ^{* 2} + b ^{* 2} ) when the rate is 1.50.
Here, the filling factor is the ratio of the area of the bottom surface of the nanostructure 3 to the area of the unit lattice, and is the area S2 of the fan shape of the four nanostructures included in this diamond with respect to the area S1 of the diamond shown in FIG. 1B. Can be calculated by the following formula.
Filling rate (%) = (S2 / S1) x 100

Further, the saturation √ (a ^{* 2} + b ^{* 2} ) is calculated and obtained by a method according to JISZ8729. That is, the chromaticities a ^* and b ^* in the L ^* a ^* b ^* color system are calculated and obtained from the reflection spectrum of the wavelength of 380 nm to 780 nm.

FIG. 2B is a relationship diagram when the height H of the nanostructure is 200 nm in the same antireflection structure, and FIG. 2C shows the height H of the nanostructure in the same antireflection structure. FIG. 2D is a relationship diagram when the thickness H is 230 nm, FIG. 2D is a relationship diagram when the height H of the nanostructure 3 is 290 nm in the same antireflection structure, and FIG. 2E is the same antireflection structure. 3 is a relational diagram when the height H of the nanostructure 3 is set to 150 nm. From these relationship diagrams, when the height H of the nanostructure is in the range of 180 nm or more and 290 nm or less, the saturation √ (a ^{* 2} + b ^{* 2} ) takes the minimum value at the filling rate of 95 to 99%. I understand. Therefore, by setting the filling rate and height of the nanostructure exhibiting this minimum value, it becomes possible to obtain an antireflection film exhibiting a stable tint.

When the height H of the nanostructure is 180 to 290 nm, as shown in FIG. 2A, the saturation √ (a ^{* 2} + b ^{* 2} ) does not have a minimum value and is substantially horizontal at the minimum value. In some cases, the inflection point that takes the minimum value (near the end point of the bottom) is regarded as the minimum value for convenience.

On the other hand, in the same antireflection structure 1A, when the height H of the nanostructure 3 is lower than 180 nm, as shown in FIG. 2E, the saturation √ (a ^*) is obtained between the filling rates of 75 to 100% ^{. 2} + b ^{* 2} ) does not have a local minimum, but a local maximum appears.

Even when the height H of the nanostructure is 180 nm or more, the saturation √ (a ^{* 2} + b ^{* 2} ) increases rapidly as the filling rate increases from near 100%. It is speculated that the filling rate exceeds 100% because the lower end portions of the adjacent nanostructures overlap with each other, and the substantial height H of the nanostructures decreases.

  That is, in the present invention, the nanostructures are densely packed within a range in which the nanostructures are not too close to each other and the substantial height H of the nanostructures is not reduced, so that the antireflection structure is colored. Can be said to be suppressing.

  On the other hand, as shown in FIG. 2D, when the height H of the nanostructure 3 is 290 nm, the minimum value becomes a filling rate of 95%, and by improving the filling rate, the antireflection property is improved and the saturation is reduced. A state in which both can be achieved is obtained. However, if the height H of the nanostructures 3 is set higher than 290 nm, the aspect ratio of the nanostructures 3 becomes high. Therefore, when manufacturing the antireflection structure by the transfer method using the master, it is preferable to use the master. It becomes difficult to transfer the shape to.

Further, when the variation in the height H of the nano-structures 3 is large in relation to the filling rate and saturation √ nanostructure described above ^{(a * 2 + b * 2} ), saturation √ (a ^{* 2} + b ^{* It} is difficult to obtain a clear minimum value in ² ). Therefore, it is preferable that the variation of the height H of the nanostructure is within 10%.

As described above, in the method for designing an antireflection structure of the present invention, the height H of the nanostructure 3 is set to 180 nm or more and 290 nm or less, preferably 200 nm or more and 270 or less, and particularly preferably 200 nm or more and 250 nm or less. When the variation of the height H of the body 3 is preferably 10% or less, more preferably 8.7% or less, the height H of the nanostructure 3, the filling rate and the saturation √ (a ^{* 2} + b ^{*). In} relation to ² ), the saturation √ (a ^{* 2} + b ^{* 2} ) is set to a minimum value or a filling rate that is in the vicinity thereof. As a result, the saturation √ (a ^{* 2} + b ^{* 2} ) of the antireflection structure 1A can be made as close to zero as possible, and the adherend of the antireflection structure can be prevented from appearing colored as much as possible. .

In the relationship diagram between the filling rate of the nanostructures 3 and the saturation √ (a ^{* 2} + b ^{* 2} ), the saturation √ (a when the saturation √ (a ^{* 2} + b ^{* 2} ) takes a minimum value The numerical value of ^{* 2} + b ^{* 2} ) and the numerical value of the filling rate at that time vary depending on the arrangement of the nanostructures 3, the shape of the nanostructures 3, the refractive index of the substrate 2 forming the nanostructures 3, and the like. When the refractive index is in the range of 1.1 to 3.3, it can be set to the vicinity of the minimum value of the saturation √ (a ^{* 2} + b ^{* 2} ) regardless of the material.

For example, a conical (bell-shaped) nanostructure (refractive index: 1.5) similar to the nanostructure 3 of the antireflection structure 1A shown in FIG. 1A is converted into a four-way lattice as shown in FIG. 3A. In the case of the arrayed antireflection structures 1B, the relationship between the filling factor and the saturation √ (a ^{* 2} + b ^{* 2} ) when the height H of the nanostructures 3 is 250 nm is as shown in FIG. 3B. A minimum value is shown near 93%.

Further, in the antireflection structure 1A shown in FIG. 1A, the bottom surface shape of the nanostructure 3 is elliptical as shown in FIG. 4A so that the nanostructure 3 has an elliptic cone shape (bell shape). In the case of the antireflection structure 1C in which the pyramidal (bell-shaped) nanostructures 3 are arranged in a hexagonal lattice, the filling factor and the saturation √ (a ^{* 2} + b) when the height H of the nanostructures 3 is 250 nm ^{* 2} ) shows a minimum value near the filling rate of 99% as shown in FIG. 4B. When the ratio (L / S) of the long axis L and the short axis S of the elliptical cone-shaped bottom shape is changed between 1 and 2, the saturation √ (a ^{* 2} + b ^{* 2} ) becomes A minimum value is shown when the filling rate is 85% or more and less than 100%.

In the case of the antireflection structure 1D in which the nanostructures 3 have an elliptical cone shape (bell shape) and are arranged in a hexagonal lattice as shown in FIG. The relationship between the filling factor and the saturation √ (a ^{* 2} + b ^{* 2} ) when the height H of the body 3 is 250 nm shows a minimum value near the filling factor of 95% as shown in FIG. 5B. Also in this case, if the ratio (L / S) of the major axis L and the minor axis S of the elliptical cone-shaped bottom shape is changed between 1 and 2, the saturation becomes √ (a ^{* 2} + b ^{* 2} ) shows a minimum value when the filling rate is 85% or more and less than 100%.

Regarding the relationship between the refractive index and the saturation √ (a ^{* 2} + b ^{* 2} ), in the antireflection structure 1A shown in FIG. 1A, when the height H of the nanostructure 3 is 250 nm, the refractive index is When set to 1.1, as shown in FIG. 6, the slope of the saturation √ (a ^{* 2} + b ^{* 2} ) in the vicinity of the minimum value is not as large as when the refractive index is 1.5, but the saturation √ The value of (a ^{* 2} + b ^{* 2} ) is low. On the other hand, in the antireflection structure 1A shown in FIG. 1A, when the height H of the nanostructure 3 is 250 nm and the refractive index is 3.0, the filling rate is as shown in FIG. The value of saturation √ (a ^{* 2} + b ^{* 2} ) itself at the minimum value around 90% is larger than the minimum value when the refractive index is 1.5, but the slope around the minimum value is large and there is a clear minimum. It becomes a value. Therefore, in the present invention, the refractive index of the substrate is 1.1 or more and 3.0 or less.

By the way, when the antireflection structure is used for a still image display, the saturation √ (a ^{* 2} + b ^{* 2} ) is preferably closer to zero, but if it is 2 or less, the antireflection structure is provided. The surface does not feel unnecessarily colored when observed, and the saturation √ (a ^{* 2} + b ^{* 2} ) may be 2 or less when used for a still image display. From the viewpoint of antireflection performance, it is preferable that a clear minimum value appears in the saturation √ (a ^{* 2} + b ^{* 2} ) in the relationship between the filling rate and the saturation √ (a ^{* 2} + b ^{* 2} ). . From such a point, in the antireflection structure used for the still image display, the refractive index of the nanostructure is 1.5 or more and 3.0 or less, and the filling rate of the nanostructure is 85% or more and less than 99%. It is preferable that The still image display material includes a printed material requiring high resolution.

  Further, when the antireflection structure is a light refractive index material such as an optical lens, it is preferable to approximate the refractive index of the substrate. For example, when provided on a sapphire substrate or the like, the refractive index is preferably 1.7 or more.

  On the other hand, when the antireflection structure is used by being attached to a still image display object or the like, in view of the recent demand for high resolution images, it is uniformly packed with high density as in the manufacturing method of the present invention. It is preferably an antireflection structure. Further, in order to improve the antireflection performance of the antireflection structure, it is preferable that the refractive index of the nanostructure be closer to the refractive index of the surrounding medium (refractive index of air = 1). It is preferable that the refractive index of the structure is less than 1.5 and the filling rate of the nanostructure is 95% or more and 99%.

  As a method for producing the antireflection structure of the present invention, in the case of producing by a transfer method using a roll master, for example, as described in WO2012 / 1333943, first, a roll glass master is irradiated with laser light. It can be obtained by patterning by using a photolithographic method to form a fine concavo-convex pattern on the surface and transferring the concavo-convex pattern to the resin forming the antireflection structure. In this case, the base of the nanostructure 3 of the antireflection structure of the present invention may be provided with a base material formed separately from the nanostructure 3 if necessary.

  The antireflection structure thus obtained is generally formed into a film, and may be a roll body or a sheet-shaped film. The single-wafer film also includes a film that is coded by a method of filling the nanostructures and that can be identified.

  The antireflection structure of the present invention is particularly preferably used for a medium that displays a still image such as a printed matter and a liquid crystal display device, but there is no particular problem even if it is used for various displays used for moving images.

1A, 1B, 1C, 1D Antireflection structure 2 Substrate 3 Nanostructure Dp arrangement pitch H height Tp track pitch T1, T2, T3 track

Claims (6)

The nanostructure formed by the convex portion on the surface of the substrate is an antireflection structure provided in large numbers at intervals of a visible light wavelength or less,
The height from the substrate surface flat portion of the nanostructures, the average of that is less 1 80 nm or more 290nm and variations are within 10%,
The shape of the nanostructure is a cone shape, a bell shape, an elliptical cone shape, a hemispherical shape or a semielliptic shape, and the bottom surface shape is a circular shape or an elliptical shape in a plan view,
The filling rate of the nanostructure, which is the ratio of the area of the bottom surface of the nanostructure to the area of the substrate surface in plan view of the antireflection structure, is 95 to 99% , and the filling rate and the white color of the antireflection structure. An antireflection structure characterized in that, in the relationship of the saturation √ (a ^{* 2} + b ^{* 2} ) of the reflected light with respect to the light, the saturation is within a range of ± 5% of the filling rate at which the saturation has a minimum value.   The antireflection structure according to claim 1, wherein the aspect ratio of the nanostructure is 0.95 or more and 2.2 or less. The antireflection structure according to claim 1 or 2 , wherein the track pitch of the nanostructure is 130 nm or more and 190 nm or less. The arrangement pitch of the nanostructure antireflection structure according to any one of claims 1 to 3, at 150nm or 270nm or less. Refractive index of the substrate, the anti-reflection structure according to any one of claims 1-4 is 1.1 to 3.0. The antireflection structure according to any one of claims 1 to 6 , which is formed into a sheet-shaped film.

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