JP2009198626A - Anti-reflective structure and anti-reflective molded body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an anti-reflective structure in which a micro-rugged shape is optimized, thus the anti-reflective performance of electromagnetic waves is improved, and further, the destruction of the micro-shape can be prevented, and which is provided with an anti-reflective function and flaw resistance, and to provide an anti-reflective molded body which is provided with such microstructure, and can cope with a wide wavelength range, e.g., in automotive meter front covers, wind glasses and IR camera lenses. <P>SOLUTION: In the anti-reflective structure, frustum-shaped micro-recessed parts 2 having an opening size D smaller than the wavelength λ of the electromagnetic wave to enter are arranged at a pitch P shorter than the wavelength λ, and, at the bottom part and the circumferential part of the opening of each frustum-shaped micro-recessed part 2, a planar bottom reflective face 2b and a planar opening edge reflective face 2f are respectively formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention includes an antireflection structure excellent in scratch resistance as well as an antireflection function of electromagnetic waves, and such a structure, and as a non-reflective panel for light and radio waves, for example, vehicles and ships including automobiles, The present invention relates to a molded body that can be suitably used for bodies such as aircraft, various meters, display devices, and the like.

In the fields of aircraft, automobiles, ships, etc., it is necessary to prevent reflection of electromagnetic waves in various places such as stealth technology that does not appear in radar, IR measurement cameras such as inter-vehicle measurement, meter covers, and liquid crystal display devices.
For example, a meter front cover is fitted on the front face of a display unit that houses various instruments such as a speedometer and a fuel gauge in a driver's seat of an automobile.
However, when a scene outside the vehicle is reflected on the meter front cover through the front window or the side window, various displays on the display unit may be difficult to see. For this reason, a meter hood is arranged above it so as to block external light from entering the meter display.

As a structure for preventing such reflection of light, a multilayer antireflection film composed of a plurality of thin films having different refractive indexes is known. However, the reflectance can be further reduced as compared with such a multilayer antireflection film. As an example, an antireflection structure using a fine structure has been proposed (for example, see Patent Document 1).
JP 2002-267815 A

In Patent Document 1, the refractive index of light is changed in the thickness direction by forming innumerable fine irregularities made of a transparent material on the surface of the transparent molded article at a pitch equal to or less than the wavelength of light. An antireflection structure is described.
That is, for example, by forming innumerable fine irregularities having a waveform or a triangle on the surface, the proportion of the transparent material existing on the outermost surface of the irregularities is almost as close to 0%, and substantially air It becomes equal to the refractive index. On the other hand, at the bottom of the uneven surface, the air content is almost as close to 0% as the refractive index of the transparent material, and at the intermediate part, the refraction according to the cross-sectional area occupied by the transparent material in the cross section. Become a rate. As a result, the refractive index of light continuously changes between the refractive index of air and the refractive index of the transparent material in the thickness direction of the antireflection structure. Therefore, antireflection performance superior to that of the antireflection film can be achieved based on the same principle as that of a multilayer antireflection film composed of a plurality of thin films having different refractive indexes (in this case, the refractive index changes stepwise). become.

  However, in the structure described in Patent Document 1, although the reflectance of light can be reduced, the surface of the structure is formed when the tip of the fine unevenness is made acute to improve the antireflection effect. When touching or wiping the surface, there is a problem that the tip portion is easily damaged and the antireflection performance is impaired.

The present invention has been made to solve the above-described problems in a conventional antireflection structure comprising a fine concavo-convex structure formed at a pitch and size equal to or smaller than the wavelength of an incident electromagnetic wave.
The object of the present invention is to optimize the fine uneven shape, thereby improving the antireflection performance of electromagnetic waves, and preventing the destruction of the fine shape, and has the antireflection function and scratch resistance. To provide a structure.

  The inventors of the present invention shall be composed of innumerable fine recesses having a hole shape with an antireflective microstructure formed on the surface of the base material, and the shape of the fine recesses is a frustum shape, with the bottom surface of the recess and the periphery of the opening. It has been found that the above object can be achieved by forming two reflecting surfaces, and the present invention has been completed.

  The present invention is based on the above knowledge, and the antireflection structure of the present invention is substantially circular or polygonal, and has a truncated cone shape or a truncated pyramid shape having an opening having a size smaller than the wavelength of the incident electromagnetic wave. The innumerable fine recesses forming the pitch are arranged at a pitch shorter than the wavelength of the incident electromagnetic wave, and each of the frustum-shaped fine recesses has a planar reflecting surface at the bottom and the peripheral edge of the opening. Features.

  According to the present invention, the antireflection structure is composed of innumerable fine recesses, the recess shape is a frustum shape (conical frustum shape or truncated pyramid shape), and the opening shape is a circle having a diameter D or a diameter D. Polygons inscribed in a circle (where D <λ: wavelength of incident electromagnetic wave) are arranged at a pitch P (where P <λ), and reflecting surfaces are provided at the bottom of the frustum-shaped fine recess and the peripheral edge of the opening, respectively. Because it is formed, it is possible to achieve both an antireflection function and scratch resistance.

  Hereinafter, the antireflection structure of the present invention and the antireflection molded body to which the fine structure is applied will be described in more detail along with the production method and embodiments thereof.

  As described above, the antireflection structure of the present invention is composed of innumerable fine recesses having a frustum shape, and includes a reflection surface at the bottom and the peripheral edge of the opening, and the size of the opening of the fine recess is incident. Are arranged at a pitch smaller than the wavelength of the electromagnetic wave and shorter than this wavelength.

  FIG. 1 shows an example of an embodiment of an antireflection structure according to the present invention. The antireflection structure 1 according to the present invention has a truncated cone shape or a truncated pyramid shape with a flat bottom (as a typical example in the figure). An infinite number of fine recesses 2 forming a square frustum are provided with a structure arranged at a pitch P shorter than the wavelength λ of the incident electromagnetic wave. At this time, the opening size of the fine recesses, that is, the diameter of the opening in the case of a truncated cone, the diameter D of a circle circumscribing the polygon forming the opening in the case of a truncated pyramid (in the example of the figure, a diagonal line) Also coincides with the length of the incident electromagnetic wave, as will be described later.

Therefore, the refractive index of the electromagnetic wave in each cross section determined by the abundance ratio of the structural material and air on each step surface in the thickness direction of the antireflection structure is continuous from the refractive index of air to the refractive index of the material in the thickness direction. To change. As a result, the antireflection property of electromagnetic waves is exhibited as in the case of the structure composed of fine irregularities. On the other hand, since the bottom of each fine recess 2 is flattened, the electromagnetic wave reflected from the bottom surface of the fine recess 2 is offset with the electromagnetic wave reflected by the flat portion at the periphery of the opening, thereby enabling further reduction in reflection. .
In addition, the fine recess 2 has a hole shape, and has a reflection surface at the periphery of the opening, and the wall between the openings of the adjacent recesses is connected, so it rubs against or collides with other members. Therefore, it is possible to achieve both the antireflection function of electromagnetic waves and the scratch resistance by minimizing the influence on the antireflection performance.

With respect to the size of the fine recess 2, when the shape is a truncated pyramid shape as shown in FIG. 1B, the diameter of the circle circumscribing the polygon forming the opening of the fine recess 2 is set to D. In this case, it is necessary to set D <λ (wavelength of incident electromagnetic wave). In particular, in order to prevent reflection of visible light, it is desirable that D ≦ 380 nm, more preferably D ≦ 250 nm.
In addition, it is preferable that D ≦ 150 nm for ultraviolet rays and D ≦ 780 nm for near infrared rays.

That is, when the opening dimension D is equal to or greater than the wavelength λ of the incident electromagnetic wave, the pitch P between the adjacent fine recesses 2 cannot be made shorter than the wavelength λ, and the electromagnetic wave is diffracted and the antireflection function is deteriorated. become. In particular, by setting D ≦ 250 nm, the influence of coloring due to diffracted light does not appear even if the incident angle of light changes.
In addition, when the shape of the fine recessed part 2 is a truncated cone shape (circular opening part), let the diameter of an opening part be opening size with D. FIG.

In the present invention, in order to cancel the reflected electromagnetic waves from the bottom surface of the fine recess 2 and the flat portion at the periphery of the opening, the reflection surface occupancy ratios Rb and Rf of the flat portion at the bottom and the periphery of the opening, and the depth of the fine recess 2 are obtained. S is important.
The bottom surface reflecting surface occupancy ratio Rb and the opening edge reflecting surface occupancy ratio Rf are the occupancy ratios of the bottom surface and the reflecting surface of the opening peripheral plane when the repetitive unit of the antireflection structure 1 is extracted.

Specifically, as shown in FIG. 2, when the antireflection structure 1 is viewed from above, first, the flat surface of the bottom of the fine recess 2 is the bottom reflection surface 2 b, and the flat portion at the periphery of the opening of the fine recess 2. Is the opening edge reflecting surface 2f. Then, the area ratio of the bottom reflection surface 2b with respect to the unit area (in the figure, the area of one unit forming a square surrounded by a broken line) is the bottom reflection surface occupancy ratio Rb, and the aperture edge reflection surface 2f with respect to the square unit area. The area ratio is defined as the aperture edge reflecting surface occupation ratio Rf.
In the antireflection structure 1 of the present invention, the antireflection property of electromagnetic waves is improved when the ratio of the reflection surface occupancy between the bottom and the peripheral edge of the opening, Rb / Rf is 0.3 to 2.0. The Rb / Rf ratio is more preferably in the range of 0.8 to 1.2.

The bottom reflection surface 2b and the opening edge reflection surface 2f of the fine recess 2 are not particularly limited as long as they are in a range that satisfies the above occupancy ratio, but are basically flat, Permissible. That is, dents, bulges, and irregularities within a height of 20 nm do not greatly affect the reflectance.
In addition, it is desirable that the bottom reflection surface 2b and the opening edge reflection surface 2f are substantially parallel. However, in this case, the parallelism greatly affects the reflectivity if the angle between both surfaces is within 5 °. There is no.

Next, the depth S of the fine recess 2 is most effective when the phase of the reflected electromagnetic wave from the peripheral edge of the opening and the reflected electromagnetic wave from the bottom surface is shifted by π / 2 in order to cancel the incident electromagnetic wave.
Specifically, the depth S = (incident wavelength λ / (2 × average refractive index n)) × A is expressed by the equation (1), and the value of A is in the range of 0.6 to 1.4. Preferably, it is in the range of 0.8 to 1.2. In addition, the average refractive index said here means the refractive index with respect to incident electromagnetic waves.

  FIG. 3 illustrates the relationship between the value of A in the above equation (1) and the reflectance of visible light. That is, on both surfaces of the polycarbonate substrate, a truncated cone shape having an opening diameter of 100 nm and a bottom surface diameter of 35 nm is formed, and the ridgeline shape is expressed by a second-order nonlinear equation (2) as described later, and has an infinite number of depths. This is a result of making a prototype of an antireflection structure in which fine recesses are arranged at a pitch of 100 nm and measuring the reflectance.

  As described above, when the value of A is smaller than 0.6, the depth S of the fine concave portion 2 becomes shallow, and the reflected electromagnetic waves from the two reflecting surfaces cannot be reduced in the target wavelength range. Further, when the value of A exceeds 1.4, the depth S of the fine concave portion 2 becomes deep and the refractive index change becomes gentle, so that a certain degree of antireflection can be secured, but the value of A increases. It shows a tendency for the reflectance to increase.

In particular, for the purpose of preventing reflection in visible light, it may be designed so that a wavelength near 540 to 560 nm, which is highly sensitive to human eyes, has a minimum reflectance.
About the range of the depth D of the fine recessed part 2 by the kind of electromagnetic wave, what is necessary is just the range derived | led-out by said Formula (1), Especially preferably, it is 80-160 nm in an ultraviolet region, and 160-350 nm in a visible light region. More preferably, the thickness is about 160 to 240 nm, and about 350 nm to 45 μm in the infrared region.

  The average refractive index n is a numerical value obtained by averaging the refractive indexes of materials in the height range from the opening to the bottom of the fine recess 2. In the method of deriving the average refractive index, the fine recesses 2 of the unit unit are divided into 100 in the direction perpendicular to the height direction, the refractive index is derived from the ratio of solid to space in each unit, and the average value is calculated.

The fine concave portion 2 constituting the antireflection structure of the present invention has a “frustum shape” as described above, and FIG. 1 shows a quadrangular frustum shape. However, as the shape of the fine recess 2 in the present invention, not only an accurate truncated pyramid (ridge is straight, side is flat) and a truncated cone (bus is straight), but also a sectional area of the space from the opening toward the bottom side May be a truncated pyramid having a curved side surface, or a truncated cone having a curved generating line.
Furthermore, the straight line connecting the center of the opening of the fine recess 2 and the center point of the bottom surface does not necessarily have to be perpendicular to the opening surface (base material surface), and may be inclined.

  Thus, in the present invention, “frustum shape” means not only an accurate truncated cone and truncated pyramid, but also a flat tip of a deformed pyramid having a bell-shaped or vertebral deformed cone or a curved surface. It shall mean the shape including the ones made and slanted.

The ridgeline shape of the fine recess 2, that is, the line connecting the upper base and the lower base in the trapezoidal cross section perpendicular to the opening surface passing through the center of gravity of the bottom surface of the fine recess 2 is represented by the following equation (2). It is desirable that the shape is represented by the following linear format (where 1.5 <m ≦ 2.5). Thereby, the rate of change in the refractive index from the opening surface to the bottom surface of the fine recess in the antireflection structure becomes uniform, and the antireflection function can be further improved.
That is, the opening side in the vertical cross section passing through the center of the fine recess 2 is on the X axis, the depth to the intersection when the ridge line is extended is s, and when this intersection is on the Z axis, the X coordinate on the ridge line The value can be expressed as shown in FIG. 4 based on the following equation (2). At this time, correction can be made by adding a constant term depending on the position of the intersection.
X = (D / 2) × {1- (Z / s) ^m } (2)

As for the opening shape of the fine concave portion 2, it seems that each side of the substantially circular shape, that is, a circular shape, an elliptical shape, an oval shape, a triangular shape, a quadrangular shape, a pentagonal shape, a hexagonal shape, or a polygonal shape swells outward. It is possible to adopt a shape between a round shape and a polygonal shape. Among these, a circle, a rectangle, and a hexagon are preferable because they are relatively easy to manufacture and can be arranged densely.
In addition, about such a fine recessed part 2, let the diameter D of the circle | rounding circumscribing the shape which forms a bottom face be a bottom face size. That is, the diameter corresponds to D in the case of a circular bottom surface, the major axis diameter in the case of an ellipse or oval, and the diameter of a circle circumscribing the circle in the case of a polygon.

About the arrangement | sequence of the said fine recessed part 2, from a viewpoint of forming the opening edge reflective surface 2f in the peripheral part of the fine recessed part 2, when an opening part is circular, it can arrange finely.
On the other hand, in the case of a regular triangle, a square, a regular hexagon or the like that allows the opening shape of the fine recesses 2 to be spread on the plane without gaps, it is necessary to arrange them with a gap between the fine recesses 2. It becomes.

When the incident light is visible light, the antireflection structure of the present invention can be formed into an antireflection molded body by molding on one side, preferably both sides, of a transparent substrate. And by applying such a molded product to transparent panels such as panels of various display devices, show windows, display cases, etc., reflection of reflected images is effectively reduced by reducing reflection of outside light and indoor lighting. It is possible to improve visibility of images, displays, and internal exhibits.
In addition, by applying various parts such as automobiles, such as glass for windows and roofs, meter front covers, headlamps, rear finishers, and films used for the forefront of display devices such as liquid crystals, the same anti-reflection is applied. An effect can be obtained.

In manufacturing the antireflection molded body of the present invention, a mold having innumerable fine protrusions obtained by inverting the fine recesses 2 as described above is prepared, and one or both of the mold and the substrate are heated. The antireflection structure 1 as described above can be formed on the surface of the base material by relatively pressing the two in the state.
In addition, the active energy ray curable resin is irradiated between the mold and the base material so that the active energy ray is cured, and the resin is cured, so that the surface of the base material is reflected as described above. The prevention structure 1 can be molded into an antireflection molded body.

  As the material for the substrate, typically, a transparent material is desirable. For example, polyethylene, polypropylene, polyvinyl alcohol, polyvinylidene chloride, polyethylene terephthalate, polyvinyl chloride, polystyrene, ABS resin, AS resin, acrylic resin. , Polyamide, polyacetal, polybutylene terephthalate, glass reinforced polyethylene terephthalate, polycarbonate, modified polyphenylene ether, polyphenylene sulfide, polyetheretherketone, liquid crystalline polymer, fluororesin, polyarate, polysulfone, polyethersulfone, polyamideimide, polyetherimide, Thermoplastic resins such as thermoplastic polyimide, phenolic resin, melamine resin, urea resin, epoxy resin, unsaturated polyester resin, Rukido resins, silicone resins, can be used a diallyl phthalate resin, polyamide bismaleimide, poly bisamide thermosetting resin triazole and the like, and two or more of these blended material.

Examples of the active energy ray-curable resin that starts and cures by irradiation with, for example, ultraviolet rays include, for example, an ultraviolet curable acrylic urethane meter resin, an ultraviolet curable polyester acrylate resin, an ultraviolet curable epoxy acrylate resin, and an ultraviolet curable resin. Type polyol acrylate resin, UV curable epoxy resin, etc., and if necessary, a polymerization initiator that generates radicals by irradiating active energy rays can be used. Various curing agents can also be added.
In addition, as an active energy ray used here, although an ultraviolet-ray, an X-ray, other electron beams, electromagnetic waves, etc. are mentioned typically, it is not specifically limited.

  It is also possible to use an inorganic transparent material such as glass. In this case, a method of forming the antireflection structure as described above by cutting the glass surface with an electron beam or the like, or the reflection of the present invention. The antireflection structure can be formed on the surface of the substrate by a method in which a molten inorganic transparent material is poured into a mold having the prevention structure.

  Below, based on an Example, this invention is demonstrated further more concretely. Needless to say, the present invention is not limited to these examples.

Example 1
This mold was heated to 170 ° C. using a mold created by a commercially available electron beam drawing apparatus, and then pressed on both sides of the polycarbonate substrate at a pressure of 10 MPa for 1 hour, and then cooled to 70 ° C. or lower. . As a result, as shown in Table 1, the diameter D of the opening is 1000 nm, the diameter of the bottom surface is 250 nm, the depth S is 750 nm, and the ridge line extending from the outer periphery of the opening to the outer periphery of the bottom is a second-order nonlinear equation. An anti-reflective molded body having anti-reflective structures 1 on both sides of which micro concave portions 2 having a frustum shape represented by (2) are arranged in a hexagonal close-packed state (pitch P = 1000 nm) was produced.

And the infrared rays with a wavelength of 2000 nm were irradiated to the obtained molded object, the reflectance at the incident angle of 0 degree and the measurement angle of 0 degree was measured, and the antireflection performance was evaluated.
In addition, the surface of the molded body was observed by visual observation of the occurrence of scratches after reciprocating and sliding 5000 times at a surface pressure of 392 Pa using a broad cloth, and “x” Scratch resistance was evaluated with “◯” indicating that no occurrence was observed. These results are shown in Table 2.

(Example 2)
As shown in Table 1, the diameter D of the opening is formed on both surfaces of the polymethyl methacrylate base by repeating the same operation as in Example 1 using a mold created by the same electron beam drawing apparatus. 300 nm, bottom diameter of 45 nm, depth S of 220 nm, the ridge line from the outer periphery of the opening to the outer periphery of the bottom is a frustum-shaped fine recess 2 having a frustum shape represented by the second-order nonlinear equation (2) An antireflection molded body provided with the antireflection structure 1 arranged in a state (pitch P = 300 nm) was produced.

  The obtained molded product was irradiated with visible light having a wavelength of 555 nm, the reflectance at an incident angle of 0 degree and a measurement angle of 0 degree was measured, the antireflection performance was evaluated, and the scratch resistance was determined in the same manner as described above. evaluated. The results are also shown in Table 2.

(Examples 3 to 9)
By repeating the same operations as in Example 2, the frustum-shaped fine recesses 2 having the dimensions shown in Table 1 on both sides of the polymethylmethacrylate base material and having the respective ridgeline shapes are in a hexagonal close-packed state. Each of the antireflection molded bodies provided with the arranged antireflection structures 1 was produced.
And about each obtained molded object, the reflectance and scratch resistance were evaluated by the same procedure as Example 2, respectively. These results are also shown in Table 2.

(Comparative Example 1)
Using a mold created by a commercially available electron beam drawing apparatus, an ultraviolet curable acrylic resin was poured into the mold, and the polycarbonate (PC) substrate was pressed and solidified by irradiation with ultraviolet rays. As a result, on both sides of the substrate made of PC, a regular quadrangular pyramid (ridge line is a primary line form) made of polymethyl methacrylate (PPMA), having a diameter D of the bottom circumscribed circle of 200 nm and a height H of 180 nm. An antireflection molded body having a microstructure layer having a thickness of 200 nm in which the fine protrusions formed were arranged without gaps was produced.
And about the obtained molded object, the reflectance and scratch resistance were evaluated by the same procedure as the said Example, respectively. The results are also shown in Table 2.

As a result, in Examples 1 to 9, which are the scope of the present invention, it was confirmed that all had low reflectance with respect to incident electromagnetic waves and excellent scratch resistance.
On the other hand, since the antireflection molded body of Comparative Example 1 is composed of fine convex portions having a quadrangular pyramid shape, the result is particularly poor in scratch resistance.

(A) It is a perspective view which shows an example of the reflection preventing structure of this invention. (B) It is sectional drawing explaining the shape of the fine recessed part which comprises the antireflection structure shown to Fig.1 (a). It is a top view explaining the bottom part reflective surface occupation rate and opening edge reflective surface occupation rate in the reflection preventing structure of this invention. It is a graph which shows the influence of A value (= 2nS / (lambda)) which has on the reflectance of visible light. It is explanatory drawing which represented the ridgeline shape of the fine recessed part in the reflection preventing structure of this invention in the m-th line form.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Antireflection structure 2 Fine recessed part 2b Bottom reflection surface 2f Opening edge reflection surface Rb Bottom reflection surface occupation rate Rf Opening edge reflection surface occupation rate

Claims (8)

  An opening having a substantially circular or polygonal shape, and an innumerable truncated cone-shaped concave portion having a truncated cone shape or a truncated pyramid shape whose diameter of a circle circumscribing the opening shape is D, are arranged at a pitch P, and An antireflection structure characterized by having a planar reflection surface at the bottom of the frustum-shaped fine recess and the peripheral edge of the opening, and wherein the circumscribed circle diameter D and pitch P are smaller than the wavelength λ of the incident electromagnetic wave. The ratio Rb / Rf of the bottom reflecting surface occupancy ratio Rb and the opening edge reflecting surface occupancy ratio Rf of the frustum-shaped fine concave portion is 0.3 to 2.0, and the depth S of the fine concave portion is expressed by the following formula (1). The antireflection structure according to claim 1, wherein the antireflection structure is a value calculated by:
S = A (λ / 2n) (1)
(In the formula, n is the average refractive index of the fine recess forming portion, and A is an arbitrary value in the range of 0.6 to 1.4) The ridgeline shape of the frustum-shaped fine recess is a curve represented by an mth-order nonlinear expression represented by the following formula (2), and the order m is more than 1.5 and not more than 2.5: The antireflection structure according to claim 1 or 2.
X = (D / 2) × {1- (Z / s) ^m } (2)
(S in the formula indicates the depth to the intersection of the extended lines of the frustum-shaped fine recesses)   The circumscribed circle diameter D and the pitch P to the opening shape of the frustum-shaped fine concave portion are 380 nm or less, and the depth S of the fine concave portion is 160 to 240 nm. The antireflection structure according to one item.   The antireflection structure according to claim 4, wherein a circumscribed circle diameter D and a pitch P to the opening shape of the frustum-shaped fine concave portion are 250 nm or less.   An antireflection molded article, comprising the antireflection structure according to any one of claims 1 to 5 on at least one surface of a substrate.   The antireflection molded body according to claim 6, wherein the base material is transparent.   An automobile part, wherein the antireflection molded body according to claim 6 or 7 is used.

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