JPH0131601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical element having non-reflective properties.

Optical components of various commonly used optical devices that target visible light (e.g. television receivers, cameras, overhead projectors, etc.), transparent panels such as window windows and display cases, and even instruments and displays. Attempts have been made to improve the optical properties (light transmittance) of so-called optical elements such as front plates, and various antireflection treatments have been proposed. For example, a so-called interference coating is used in glass-based optical elements, but this interference coating is difficult to apply to plastics, and it is difficult to manufacture uniform characteristics over a large area. Furthermore, the fine needle-like structures that have been used in solar cells and the like in recent years tend to cause scattering of transmitted light, are difficult to manufacture, and have drawbacks in the durability of the element surface.

The present invention solves the above-mentioned drawbacks and provides a non-reflective optical element which has an anti-reflection function by providing a novel surface shape and is suitable for application mainly to plastic optical elements.

Hereinafter, a non-reflective optical element according to the present invention will be explained using the drawings.

1 and 2 both show the basic configuration of the present invention. In FIG. 1, a plurality of cylindrical holes 2 having a constant depth D and a substantially constant radius R are formed on the surface of an element body 1 made of transparent plastic, for example, at an average distance A.
The optical element 3A is formed by irregularly arranging and forming the optical element 3A. In the case of FIG. 2, a plurality of cylindrical projections 4 having a constant height D and a substantially constant radius R are irregularly spaced apart from each other by an average distance A on the surface of a similar element body 1. The optical element 3B is formed by forming an array. Hereinafter, for convenience, the optical element 3A in FIG. 1 will be referred to as a porous structure element, and the optical element 3B in FIG. 2 will be referred to as a multi-column structure element.

Respective elements 3A and 3 having such a configuration
When B satisfies specific conditions regarding the holes 2 or protrusions 4, the reflectance for visible light decreases to 1/5 to 1/10 of that of the untreated material. The conditions are shown below.

In the above elements 3A and 3B, let us now assume that the refractive index of air is n _p and the refractive index of the plastic of the element body 1 is n _p . Let the proportion of space occupied by plastic be x(0
x1), the average refractive index n of that part
can be approximately expressed by the following relational expression.

n _p・x＋n _p (1−x)=n ∴ x=n−n _p ／n _p −n _p ………(1) The amplitude condition for complete anti-reflection is n=√ _p・_p ………(2 ) For simplicity, let n _p = 1, n _p = 1.5, then n =
1.225, x=0.4495.

If the ratio of the radius R and the average distance A is r≡R/A, then in the case of the porous structure element 3A, 1-πr ² = x ......(3) In the case of the multi-column structure element 3B, πr ² = x ......( 4) Therefore, R = 0.418A (porous structure element) and R = 0.378A (multi-column structure element) are the values to be obtained.

Also, the phase condition for complete anti-reflection is nD=λ/4 (5) (where λ is the center wavelength of the light to be prevented from reflecting), so if the center wavelength of visible light λ is 5500 Å,
D=1123 Å.

It has been experimentally confirmed that approximately the above value reduces the reflectance to about 0.5% over the entire visible light range.

Thus, in the present invention, the surface of the optical element has a depth or height D of approximately 1/4λ (where λ is the center wavelength of the light to be prevented from reflection) and a predetermined average radius R.
The present invention proposes a non-reflective optical element in which a plurality of holes 2 or protrusions 4 having a shape are irregularly arranged two-dimensionally. Here, as the value of the average distance A increases, it is good for manufacturing and durability, but the scattering of transmitted light increases from the blue side, which has a short wavelength. Therefore, the value of this average distance A should be selected depending on the use of the optical element. For example, in the case of a lens, etc., A = about 600Å to 1000Å, and in the case of a projector screen or character display front panel,
Good results can be obtained with a thickness of about 6000 Å to 1 μm. In the porous structure element 3A, the depth D of the hole 2 is
It is possible to select the ratio R/A of the radius R and the average distance A to be in the range of 0.41 to 0.43, respectively, in the range of 1100 Å to 1150 Å. Moreover, in the multi-column structural element 3B,
The height D of the protrusion 4 is in the range of 1100 Å to 1150 Å,
The ratio R/A of its radius R and average distance A is 0.37 to 0.39.
It is possible to select within the range of . Overall, as a condition for non-reflection of visible light, the average distance A is
It is possible to select the ratio R/A between the radius R and the average distance A to be in the range of 0.3 to 0.5 in the range of 500 Å to 2 μm.

In addition, in the above basic structure, the hole 2 or the protrusion 4
Although it is assumed to have a cylindrical shape, it can also be formed with a conical protrusion 5 or hole (this example is not shown), for example, as shown in FIG. In this case, as the radius R, the average radius R' (position of the chain line) of the protrusion 5 may be considered.

According to the present invention described above, the uneven layer acts as a so-called single interference film due to the large number of holes 2 or protrusions 4 that are integrally formed on the surface of the transparent substrate 1 and satisfies the above conditions, and visible light A non-reflective optical element whose reflectance is significantly reduced over the entire area can be obtained. In this non-reflective optical element, the depth (height) D of each hole 2 or protrusion 4 on the surface is small and the radius R
Since it has a large porous or multi-column structure and is composed of a single piece, it is easy to manufacture with a mold and is scratch resistant (good durability), and has a practically sufficient antireflection effect and wavelength dependence. have sex. Therefore, it is suitable mainly for preventing the surface of transparent plastic from reflecting visible light. It goes without saying that the present invention can also be applied to glass-based optical elements in addition to plastic-based optical elements. Therefore, the present invention is suitable for application to transparent plates or front plates of optical components of various optical devices that use visible light, such as window windows, display cases, meters, display units, and the like.

[Brief explanation of drawings]

FIGS. 1 and 2 are perspective views showing an example of the basic structure of a non-reflective optical element according to the present invention, and FIG. 3 is a perspective view of essential parts showing another example of the present invention. 1 is the element body, 2 is the hole, 3A, 3B are the optical elements,
4 and 5 are protrusions.

Claims (1)

[Claims] 1 A plurality of holes or projections having a depth or height of approximately 1/4λ (where λ is the center wavelength of the light to be prevented from reflection) and a predetermined average radius are two-dimensionally irregular on the surface of the optical element. A non-reflective optical element formed by