JP2009294341A - Water-repellent antireflection structure and water-repellent antireflection molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent breakage of a minute projection part top end without damaging an antireflection function of electromagnetic waves and a water-repellent function and to make the antireflection function, the water-repellent function and scratch resistance of minute structure compatible in water-repellent antireflection structure using the minute structure. <P>SOLUTION: Frustum-shaped minute projection parts 2, each of which has a bottom surface that is about circular or polygonal and has size D smaller than a wavelength λ of an incident electromagnetic wave, are arranged with a pitch P shorter than the wavelength λ. A high refractive index material layer 3 consisting of a material of higher refractive index than that of a material constituting the minute projection part 2 is provided at a top end surface of the frustum-shaped minute projection part 2. Further two reflection surfaces, that are a top end reflection surface 3t and a root reflection surface 2b, are formed respectively at a surface of the high refractive index material layer 3 and a root part of the minute projection part 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a water-repellent antireflection structure excellent in water repellency in addition to an electromagnetic wave antireflection function and scratch resistance. Furthermore, with such a water-repellent antireflection structure, as a non-reflective panel with water repellency, for example, vehicles such as automobiles, bodies such as ships, aircraft, and various meters, display devices, glass, mirrors, The present invention relates to a molded body that can be suitably used for a lamp unit or 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.
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 a thing, the antireflection structure using a fine structure is proposed (for example, refer to patent documents 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.

As a result, antireflection performance superior to that of the antireflection film can be exhibited by the same principle as a multilayer antireflection film consisting of a plurality of thin films having different refractive indexes (in this case, the refractive index changes stepwise). Can do.
It should be noted that by making the tip of the fine irregularities as described above thin, air is retained between the water and water droplets are prevented from adhering, and a water repellent function can be provided.

However, in the structure described in Patent Document 1, although the light reflectance can be reduced, the tip of the fine unevenness is easily damaged, and by touching the surface of the structure or wiping the surface, There was a problem that the structure was damaged, and the antireflection performance and the water repellent function were impaired.
In particular, when used outdoors, the fine concavo-convex structure is buried due to adhesion of water droplets, which may reduce the antireflection effect. In addition, when water droplets adhere, the light diffuses, making it difficult to see the field of view in front of the panel and the reflected image from the mirror.

  The present invention has been made to solve the above-mentioned problems in a conventional antireflection structure comprising a fine concavo-convex structure formed at a pitch and size equal to or less than the wavelength of light (incident electromagnetic waves). An object of the invention is to provide a water-repellent antireflection structure capable of preventing the breakage of the tips of the fine convex portions without impairing the antireflection function and the water repellent function of electromagnetic waves.

  As a result of intensive studies to achieve the above object, the inventors of the present invention dare to flatten the tip portions of the individual convex portions constituting the fine concavo-convex structure so that the fine convex portions have a truncated cone shape or a truncated pyramid shape. It has been found that the reflectance can be reduced by forming two reflecting surfaces on the plane portion between the adjacent fine convex portions and the tip portion of the fine convex portion. Further, it has been found that by increasing the refractive index of the tip portion of the fine convex portion, the tip portion can be made thinner, thereby improving the water repellency of the surface of the fine concavo-convex structure, thereby completing the present invention. It was.

  The present invention is based on the above knowledge, and the water-repellent antireflection structure of the present invention has a substantially circular or polygonal shape and has a truncated cone shape or a truncated pyramid shape having a bottom surface having a size smaller than the wavelength of incident electromagnetic waves. The innumerable fine convex portions having a shape are arranged at a pitch shorter than the wavelength of the incident electromagnetic wave. Further, a high refractive index material layer made of a material having a refractive index higher than that of the material constituting the fine convex portion is provided on the tip surface of the frustum-shaped fine convex portion, and the surface between the high refractive index material layer surface and the fine convex portion is provided. It has the reflective surface in the base part of each, It is characterized by the above-mentioned.

  According to the present invention, the shape of each fine convex portion constituting the antireflection structure is a truncated cone shape or a truncated pyramid shape, and the bottom surface shape is a circle having a diameter D or a plurality of inscribed in the circle having the diameter D. The prisms (where D <λ is the wavelength of the incident electromagnetic wave) are arranged at a pitch P (where P <λ), and a high refractive index material layer is provided on the tip surface of the frustum-shaped fine concave portion. The flat part between the surface of the rate material layer and the fine convex part was made to be a reflection surface. Therefore, the height of the fine convex portion can be lowered without impairing the antireflection performance and the water repellency, and both of these functions and scratch resistance can be achieved.

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

  As described above, the antireflection structure of the present invention is composed of innumerable fine convex portions having a truncated cone shape or a truncated pyramid shape, and a high refractive index material layer is provided on a tip surface thereof. Each of the surface and the root portion between the fine convex portions is provided with a reflecting surface, and the bottom surface size of the fine convex portion and the pitch between the convex portions are made smaller than the wavelength of the incident electromagnetic wave.

FIG. 1 shows an example of an embodiment of the water-repellent antireflection structure of the present invention. The water-repellent antireflective structure 1 of the present invention has a truncated cone shape or a truncated pyramid shape (in this example) Innumerable fine convex portions 2 forming a truncated cone are arranged at a pitch P shorter than the wavelength λ of the incident electromagnetic wave.
At this time, the bottom surface size of the fine projection, that is, the bottom surface diameter in the case of the truncated cone and the diameter of the circle circumscribing the bottom polygon in the case of the truncated pyramid are also smaller than the wavelength λ of the incident electromagnetic wave. become. Moreover, the surface of the fine convex part 2 is provided with a high refractive index material layer 3 made of a material having a higher refractive index than the material constituting the fine convex part.

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 water-repellent antireflection structure is continuous from the refractive index of air to the refractive index of the material in the thickness direction. Therefore, the antireflection characteristic of electromagnetic waves is exhibited.
On the other hand, each fine convex portion 2 has a truncated cone shape, and its tip portion is flattened. Therefore, the electromagnetic wave reflected from the root plane portion between the fine convex portions 2 is reflected by the high refractive index material layer 3. This cancels out the electromagnetic waves reflected on the surface of the film and enables further reduction in reflection. At this time, with respect to water repellency, since the tip portion is flat, the water repellency tends to decrease. However, since the tip surface is provided with the layer 3 made of a high refractive index material, the area of the tip plane is reduced. The contact angle with water can be increased, and the water repellency can be increased.

  And since the tip part of the fine convex part 2 is smooth, it is hard to be damaged even if it rubs against or collides with other members, and the influence on the antireflection performance and water repellency is minimized. The antireflection function and water repellent function can be made compatible with scratch resistance.

As for the size of the fine convex portion 2, as shown in FIG. 2A, when the shape is a truncated cone, D <λ (wavelength of incident electromagnetic wave), where D is the diameter of the bottom surface In order to prevent reflection of visible light, it is necessary to satisfy D ≦ 380 nm. Further, from the viewpoint of preventing coloring of reflected light due to diffraction, it is desirable that 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 bottom surface dimension D is equal to or greater than the wavelength λ of the incident electromagnetic wave, the pitch P between the adjacent fine protrusions 2 cannot be made shorter than the wavelength λ, and the electromagnetic wave is diffracted and does not prevent reflection.

  On the other hand, when the shape of the fine convex portion 2 is a truncated pyramid shape as shown in FIG. 2 (b) (in the figure, a quadrangular frustum is shown as a typical example), it circumscribes the polygon that forms the bottom surface. Let the diameter D of the circle to be the bottom size.

In the present invention, the surface of the high refractive index material layer 3 formed on the front end surface of the frustum-shaped fine convex portion 2 and the surface of the high refractive index material layer can be offset to cancel the reflected electromagnetic waves from the flat portion between the roots. The reflection surface occupancy ratios Rt and Rb at the root portion between the fine convex portions 2, the height H of the fine convex portions 2, and the thickness t of the high refractive index material layer 3 are important.
The tip reflecting surface occupancy rate Rt and the base reflecting surface occupancy rate Rb are the root portion between the tip portion (high refractive index material layer 3) and the fine convex portion 2 when one repetitive unit of the antireflection structure 1 is extracted. Is the occupancy of the reflecting surface.

Specifically, as shown in FIG. 3, when the water repellent antireflection structure 1 is viewed from above, first, the surface of the high refractive index material layer 3 formed on the tip surface of the fine convex portion 2 is reflected at the tip. A plane portion between the fine projections formed at the root portion between the surface 3t and the fine projections 2 is defined as a root reflection surface 2b. The area ratio of the tip reflecting surface (the surface of the high refractive index material layer 3) 3t relative to the unit area (in the drawing, one unit area forming a hexagon) is the tip reflecting surface occupancy ratio Rt, which is also a hexagonal unit area. The area ratio of the base reflection surface 2b with respect to is defined as a root reflection surface occupation ratio Rb.
In the water-repellent antireflection structure 1 of the present invention, when the high refractive index material layer 3 is present at the tip portion, the ratio Rt / Rb of the reflection surface occupancy ratio between the tip portion and the root portion is 0.1 to 2. In addition, the antireflection property of electromagnetic waves is improved. Furthermore, it is preferable that this Rt / Rb ratio is 0.2 to 1.4.

Further, the tip reflection surface occupation ratio Rt on the surface of the high refractive index material layer is preferably in the range of 0.015 to 0.1.
That is, if the tip reflection surface occupation ratio Rt per unit area is less than 0.015, the reflected light intensity from the tip surface becomes small, and the reflected light from the root cannot be canceled. On the other hand, if it exceeds 0.1, the intensity of the reflected light from the tip surface increases, and the reflected light from the tip cannot be canceled out by the reflected light from the root.

  The shape of the tip of the fine convex portion 2 is not particularly limited as long as it is within a range that satisfies the above occupancy ratio, and may not necessarily be a perfect plane. That is, dents, bulges, and irregularities within a height of 20 nm do not greatly affect the reflectance.

Next, with respect to the height H of the fine convex portion 2, the total height H + t including the thickness t of the high refractive index material layer 3 is used to cancel the incident electromagnetic wave (the surface of the high refractive index material layer surface). The effect is greatest when the phase of the reflected electromagnetic wave of) and the reflected electromagnetic wave at the base is shifted by π / 2.
Specifically, H + t = (incident wavelength λ / (2 × average refractive index n)) × A is expressed by the formula (1), and the value of A is in the range of 0.6 to 1.4. More preferably, it is the range of A = 0.8-1.2.

  When the value of A is smaller than 0.6, the height H + t of the entire fine convex portion including the high refractive index material layer 3 is reduced, and the reflected electromagnetic waves from the two reflecting surfaces are within the target wavelength range. It becomes impossible to make low reflection. Further, when the value of A exceeds 1.4, the height H + t of the entire fine convex portion becomes high and the refractive index change becomes gradual, so that a certain degree of antireflection can be secured, but the scratch resistance is deteriorated. Tend to.

In particular, for the purpose of preventing reflection in visible light, it may be designed so that the minimum reflectance is in the vicinity of 540 to 560 nm, which is highly sensitive to human eyes.
The range of the height H + t of the entire fine convex portion depending on the type of electromagnetic wave may be a range derived from the above formula, but is particularly preferably 80 to 160 nm in the ultraviolet region, 160 to 350 nm in the visible light region, Preferably, it is about 160 to 240 nm, and about 350 nm to 45 μm in the infrared region.

  The average refractive index at this time is a numerical value obtained by averaging the refractive indexes from the tip to the base including the high refractive index material layer 3 of the fine convex portion 2. The method for deriving the average refractive index is to divide the fine convex part 2 of the unit unit into 100 in the direction perpendicular to the height direction, derive the refractive index from the ratio of solid to space in each unit, and calculate the average value. . In addition, it cannot be overemphasized that the average refractive index said here is a refractive index with respect to the wavelength of incident electromagnetic waves.

In the present invention, the thickness t of the high refractive index material layer 3 applied to the tip of the fine convex portion 2 is preferably 30 nm or less. That is, FIG. 4 is made of polymethyl methacrylate (PMMA), has a frustum shape (bottom diameter D: 100 nm, tip surface diameter: 30 nm, height H: 200 nm), and is arranged in a hexagonal close-packed state at a pitch of 100 nm. 5 is a graph showing the relationship between the thickness and the reflectance of a titanium oxide layer (high refractive index material layer 3) formed on the tip surface of the fine convex portion 2;
As is apparent from the figure, the reflectance increases when the thickness of the high refractive index material layer 3 exceeds 30 nm, whereas it is less than 0.2% when the thickness of the high refractive index material layer 3 is 5 to 25 nm. It can be seen that a low reflectance can be obtained.

And about the material which comprises this high refractive index material layer 3, the area of a front-end | tip can be made small, so that it is high refractive index, and it becomes a structure advantageous to water repellency.
Such a material is preferably a material having a refractive index difference of 0.2 or more with respect to the material constituting the fine convex portion 2. Specifically, inorganic oxides such as titanium oxide, zinc oxide, niobium oxide, and aluminum oxide are good, and there is no particular limitation in order to selectively apply to the vicinity of the tip, but when performed by a dry process such as sputtering. The adjustment becomes easy.

The fine convex portion 2 constituting the water-repellent antireflection structure of the present invention has a “frustum shape” as described above, and FIG. 1 shows a truncated cone shape. However, as the shape of the fine convex portion 2 in the present invention, not only an accurate truncated cone (the bus line is a straight line) and a truncated pyramid (a ridge is a straight line, a side surface is a plane), but the cross-sectional area is sequentially from the bottom to the tip side As long as the shape is small, there may be a truncated cone having a curved generating line, or a truncated pyramid having a curved side surface.
Furthermore, the straight line connecting the center of the bottom surface of the fine protrusion 2 and the center point of the top surface is not necessarily perpendicular to the bottom 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 end of a deformed pyramid having a side surface formed of a bell-shaped or vertebral deformed cone or curved surface. Various shapes including those formed and inclined are meant.

The ridge line shape of the cone-shaped fine convex portion 2, that is, the line connecting the upper base and the lower base in the trapezoidal cross section perpendicular to the bottom surface passing through the center of gravity of the tip surface of the fine protrusion 2 is expressed by the following equation (2). It is desirable to have a shape represented by a linear form (where 1 <m ≦ 1.5). As a result, the rate of change in the refractive index from the surface of the fine convex portion to the bottom surface in the water-repellent antireflection structure becomes uniform, and the antireflection function can be further improved.
That is, if the bottom of a vertical cross section passing through the center of the cone-shaped fine convex portion 2 is on the X axis, the height to the vertex appearing as an intersection when the ridge line is extended is h, and this vertex is taken on the Z axis. The X coordinate value on the ridge line can be expressed as shown in FIG. 5 based on the following equation (2). At this time, correction can also be made by adding a constant term depending on the position of the vertex.
X = (D / 2) × {1- (Z / h) ^m } (2)

Further, the bottom shape of the cone-shaped fine convex portion 2 is substantially circular, that is, a circle, an ellipse, an egg, a polygon, a triangle, a quadrangle, a pentagon, a hexagon, and each side of the polygon is outside. It is possible to adopt a shape that is in the middle of a circular shape and a polygonal shape that swells like a circle. 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 convex part 2, let the diameter D of the circle | rounding circumscribing the shape which forms a bottom face be 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.

Regarding the arrangement of the cone-shaped fine convex portions 2, from the viewpoint of forming the root reflection surface 2 b on the root side of the fine convex portions 2 (see FIG. 3), the arrangement may be finely arranged when the bottom surface is circular. it can.
On the other hand, in the case of regular triangles, squares, regular hexagons, etc. in which the bottom surface shape of the fine protrusions 2 can be spread on the plane without gaps, in order to secure a root reflection surface between the fine protrusions 2 It is necessary to arrange with a gap.

Furthermore, in the water-repellent antireflection structure of the present invention, as shown in FIG. 6, from the viewpoint of further improving the water repellency, the infinite number of cone-shaped fine convex portions 2 each having the high refractive index material layer 3 on the tip surface. It is desirable to further provide a water repellent coating 4 made of a material having a contact angle with water of 90 ° or more on the surface of the fine concavo-convex structure made of At this time, the water-repellent coating 4 only needs to cover at least the surface of the high refractive index material layer 3, but as shown in the drawing, the entire fine structure including the high refractive index material layer 3 is uniformly formed as a monomolecular film or It is desirable to coat in a state of covering with a thickness of about 1 to 20 nm.
As a result, air is easily held between the fine convex portions 2, and even when the tip shape of the fine convex portion 2 is made thick with an emphasis on scratch resistance, the contact area with water does not increase and the water repellency is increased. It is possible to ensure both water repellency and scratch resistance at a higher level.

Such a material is not particularly limited as long as the contact angle with water is 90 ° or more, but preferably the contact angle with water is 100 ° or more, more preferably 110 ° or more. Specifically, a silicone compound or a fluorine compound can be used. In particular, a water repellent having a functional group capable of reacting with a hydroxyl group such as a silanol group is preferable for immobilization on the inorganic oxide surface.
As a method for applying such a water repellent coating 4, a generally known coating method such as dip coating, gravure coating, or screen coating, or a known dry process such as vacuum deposition, sputtering, or gas phase polymerization can be used.

When the water-repellent antireflection structure of the present invention is a substrate or visible light, a water-repellent antireflection molded body can be obtained by molding on one side, preferably both sides, of a transparent substrate. By applying such molded products to transparent panels such as panels of various display devices, show windows, and display cases, reflection of external light and room lighting is reduced, and reflection of reflected images is effectively prevented. However, it is possible to prevent the attachment of raindrops and improve the 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 and a water repellent effect can be obtained.

In producing the water-repellent antireflection molded article of the present invention, a mold having a fine concave portion obtained by inverting the innumerable fine convex portions 2 as described above is prepared. Or countless fine convex part 2 can be shape | molded on the surface of the said base material by pressing both relatively in the state which heated both. In addition, the active energy ray is irradiated between the mold and the base material in a state where the active energy ray curable resin is interposed, and the resin is cured, so that the surface of the base material is fine as described above. The convex part 2 can be shape | molded.
Then, a high refractive index material layer 3 made of titanium oxide, zinc oxide, aluminum oxide or the like is formed on the tip surfaces of these fine projections 2 by, for example, a dry process, and a water repellent coating 4 is further applied as necessary. The water-repellent antireflection molded body having the water repellent antireflection structure 1 as described above can be obtained.

  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 water-repellent antireflection structure as described above by cutting the glass surface with an electron beam or the like, or pouring a molten inorganic transparent material into a mold having the antireflection structure of the present invention. The water-repellent antireflection structure can be formed on the substrate surface by a method.

  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 against both sides of a polycarbonate substrate (refractive index: 1.59) at a pressure of 10 MPa for 1 hour. Then, it cooled to 70 degrees C or less. As a result, as shown in Tables 1 and 2, the fine convex portions 2 having a frustum shape having a bottom surface diameter D of 1000 nm, a tip surface diameter of 200 nm, and a height H of 750 nm are in a hexagonal close-packed state (pitch: 1000 nm). ) Were prepared.
The tip surface of the frustum-shaped fine convex part 2 obtained in this way was coated with titanium oxide (refractive index: 2.52) to a thickness of 10 nm by sputtering to obtain a high refractive index material layer 3. Then, a 0.1% solution of 2-perfluorooctylethyltrimethoxysilane is applied on the surface of such a fine structure, and dried at 100 ° C. to thereby form a water repellent coating 4 (with the water of the coating material itself). The water-repellent antireflection molded body of this example provided with the water-repellent antireflection structure 1 was obtained.

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.
For the contact angle, a contact angle meter (manufactured by Kyowa Interface Chemical Co., Ltd .: CA-X) was used to measure the contact angle when 10 μL of water was left on the sample surface with a syringe five times, and the average value thereof. Was the contact angle.

In addition, when the surface of the molded body was wiped back and forth 5000 times at a surface pressure of 392 Pa, the occurrence of scratches was observed with the naked eye. Was evaluated as scratch resistance.
These evaluation results are shown in Table 3.

(Example 2)
By using a mold created by the same electron beam drawing apparatus and repeating the same operation as in Example 1, the bottom surface diameter D as shown in Tables 1 and 2 on both surfaces of the polymethyl methacrylate substrate. A structure in which fine convex portions 2 having a truncated cone shape having a diameter of 300 nm, a tip surface diameter of 35 nm, and a height H of 220 nm are arranged in a hexagonal close-packed state (pitch: 300 nm) was produced.
Next, the same operation as in Example 1 was repeated except that titanium oxide was formed to a thickness of 20 nm on the tip surface of the obtained frustum-shaped fine convex portion 2, and the high refractive index material layer 4 and A water-repellent coating 4 was formed to obtain a water-repellent antireflection molded body of this example.

  The obtained molded body was irradiated with visible light having a wavelength of 555 nm, the reflectance at an incident angle of 0 ° and a measurement angle of 0 ° was measured, the antireflection performance was evaluated, and the scratch resistance and the contact angle were the same as described above. It was evaluated according to the procedure. The results are also shown in Table 3.

(Examples 3-5, 8, 9)
By repeating the same operation as in Example 2, the fine convex portions 2 having a trapezoidal shape having the dimensions shown in Tables 1 and 2 were arranged on both sides of the polymethylmethacrylate base material in a hexagonal close-packed state. Each structure was produced.
Next, the tip surface of the frustum-shaped fine convex portion 2 in each of the obtained structures is coated with titanium oxide or zinc oxide (refractive index: 2.0) to a thickness shown in Table 2 by sputtering. After the refractive index material layer 3 was formed, the water-repellent coating 4 was formed by the same operation as in the above-described example, and the water-repellent antireflection molded body of each example was obtained.

  And about each obtained molded object, the reflectance, scratch resistance, and the contact angle were evaluated by the same procedure as Example 2, respectively. These results are also shown in Table 3.

(Examples 6 and 7)
By repeating the same operation as in Example 2, the polymethylmethacrylate base material has the dimensions shown in Tables 1 and 2, respectively, and the ridge line extending from the outer peripheral portion of the tip surface to the outer peripheral portion of the bottom surface is of order m = 1. Structures in which the truncated cone-shaped fine protrusions 2 represented by the line formats (1) of 2 and 1.5 were arranged in a hexagonal close-packed state were produced.
Next, the tip surface of the frustum-shaped fine convex portion 2 of each structure obtained is coated with titanium oxide and niobium oxide (refractive index: 2.33) to a thickness of 10 nm by sputtering, respectively, so that a high refractive index material is obtained. After the layer 3 was formed, a water-repellent coating 4 was formed by the same operation as in the above examples, and water-repellent antireflection molded articles of respective examples were obtained.

  And about each obtained molded object, the reflectance, scratch resistance, and the contact angle were evaluated by the same procedure as Example 2, respectively. These results are also shown in Table 3.

(Comparative Example 1)
Using a mold created with the same electron beam drawing apparatus, the same operation as in Example 2 was repeated, and the bottom surface diameter D was as shown in Tables 1 and 2 on both sides of the polymethyl methacrylate base. A structure in which fine convex portions having a conical shape with a height of 200 nm and a height H of 195 nm are arranged in a hexagonal close-packed state (pitch: 200 nm) was produced.
Next, silicon oxide (refractive index: 1.45) is uniformly deposited to a thickness of 5 nm on the surface of the conical fine convex portion of the obtained structure, and the surface is repelled by the same operation as in the example. A water film was formed to obtain a water-repellent antireflection molded article of this comparative example.

  And about the obtained molded object, the reflectance, scratch resistance, and the contact angle were evaluated by the same procedure as Example 2, respectively. These results are also shown in Table 3.

As a result, in Examples 1 to 9 according to the present invention, it is confirmed that the reflectivity with respect to the incident electromagnetic wave is low, and the contact angle with water is 140 ° or more, and water adhesion hardly occurs. It was confirmed that the film was excellent in scratch resistance.
On the other hand, in the water-repellent antireflection molded body of Comparative Example 1, the fine convex portion has a conical shape and does not have a reflection surface for incident electromagnetic waves at the tip portion, so that the antireflection function is inferior and scratch resistance The result was also inferior in adherence.

It is a perspective view which shows the water-repellent antireflection structure of this invention. (A) It is explanatory drawing which shows the measurement position in case the fine convex part which comprises a water-repellent antireflection structure makes a truncated cone shape. (B) It is explanatory drawing which shows the measurement position in case the fine convex part which comprises a water-repellent antireflection structure makes a pyramid shape. It is a top view of the water-repellent antireflection structure for explaining the tip reflecting surface occupancy and the root reflecting surface occupancy in the present invention. It is a graph which shows the relationship between the thickness of a high refractive index material layer and the reflectance in the water-repellent antireflection structure of the present invention. It is explanatory drawing which represented the ridgeline shape of the fine convex part in the water-repellent antireflection structure of this invention in the m-th line form. (A) And (b) is explanatory drawing which shows the form example which gave the water-repellent film to the surface of a cone-shaped fine convex part and the high refractive index material layer as a suitable form of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water-repellent antireflection structure 2 Fine convex part 3 High refractive index material layer 4 Water-repellent coating Rt Tip reflective surface occupation rate Rb Root reflective surface occupation rate

Claims (12)

  An innumerable fine convex portion having a substantially circular or polygonal bottom surface and having a circular truncated cone shape or a truncated pyramid shape whose diameter of a circle circumscribing the bottom surface shape is D is arranged at a predetermined pitch P. A high refractive index material layer made of a material having a higher refractive index than the material constituting the fine convex portion is provided on the tip surface of the trapezoidal fine convex portion, A water-repellent antireflection structure having a reflective surface at a base portion between fine convex portions, wherein a circumscribed circle diameter D and a pitch P of the bottom surface are smaller than a wavelength λ of an incident electromagnetic wave. The ratio Rt / Rb of the tip reflecting surface occupancy ratio Rt and the base reflecting surface occupancy ratio Rb on the surface of the high refractive index material layer is 0.1 to 2, and the height H of the fine convex portion and the high refractive index material layer 2. The water-repellent antireflection structure according to claim 1, wherein a distance H + t between the reflecting surfaces obtained by summing the thicknesses t is a value calculated by the following equation (1):
H + t = A (λ / 2n) (1)
(In the formula, n is the average refractive index of the fine convex portion forming portion including the high refractive index material layer, and A is an arbitrary value in the range of 0.6 to 1.4)   The water repellent antireflection structure according to claim 2, wherein the ratio Rt / Rb is 0.2 to 1.4.   The water repellent antireflection structure according to any one of claims 1 to 3, wherein a front-end reflecting surface occupation ratio Rt of the surface of the high refractive index material layer is 0.015 to 0.1.   The water repellent antireflection structure according to any one of claims 1 to 4, wherein a thickness t of the high refractive index material layer is 30 nm or less. The ridgeline shape of the frustum-shaped fine convex portion is a curve represented by the following formula (2), and the order m is more than 1 and 1.5 or less. The water-repellent antireflection structure according to one item.
X = (D / 2) × {1- (Z / h) ^m } (2)
(H in the formula indicates the height to the apex that appears as the intersection of the extended lines of the frustum-shaped fine convex portions)   The circumscribed circle diameter D and the pitch P of the bottom surface of the frustum-shaped fine convex portion are 380 nm or less, and the height H of the fine convex portion is 160 to 350 nm. The water-repellent antireflection structure according to one item.   8. The water-repellent antireflection structure according to claim 7, wherein a circumscribed circle diameter D and a pitch P of the bottom surface of the frustum-shaped fine convex portion are 250 nm or less.   9. The water repellent film made of a material having a contact angle with water of 90 ° or more is provided on the surface of the high refractive index material layer on the tip surface of the frustum-shaped fine convex portion. The water-repellent antireflection structure according to any one item.   A water repellent antireflective molded article comprising the water repellent antireflective structure according to any one of claims 1 to 9 on at least one surface of a substrate.   The water-repellent antireflection molded article according to claim 10, wherein the substrate is transparent.   An automobile part using the water-repellent antireflection molded article according to claim 10 or 11.

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